Quantrainx50 Module 3.1 Electron Optics

Quantrainx50 Module 3.1 Electron Optics
place photo here Quantrainx50 Module 3.1 Electron Optics 1-2011 Confidential

SEM Main Components Electron Gun Demagnification system Scan Unit
Wehnelt cylinder or FEG unit Electron Gun Condenser lenses Demagnification system Scan generator Scan Unit Scan generator The SEM is divided into several components: -The electron gun -The Demagnification ( condenser) system -The Scan ( magnification) Unit -The focusing ( objective lens and stigmation correction) -The detecting Unit-- this can be an SED, BSED, GSED, SC, etc.…. Focus Unit Objective and Stigmation lenses Electron detector Detecting Unit

SEM Main Components Wehnelt cylinder FEG Electron Gun Electron Gun

Electron Gun Emitters Tungsten filament (W)
Lanthanum Hexaboride filament (LaB6)(obsolete) Cerium Hexaboride (CeB6) Field emission filament (FEG) This section will discuss the principles of thermionic emission, give a basic description of conventional electron gun assemblies, followed by some definitions of basic electron gun properties and their derivatives. Finally, the three basic types of electron source will be described: Tungsten thermionic emitters (W) Lanthanum Hexaboride thermionic emitters (LaB6) Field emitters (FEG) The ultimate purpose of an electron gun is to provide a large, stable current in the smallest possible electron beam. Those two parameters define the resolution and signal-to- background ratio in the images taken with an SEM. Several gun types are available, and vary in: -the amount of current produced -the size of the electron source -the stability of the source -the lifetime of the gun -design of electron gun assembly -ease of operation -cost The choice of electron gun is determined by the importance of each of the above parameters in the field of application in which the SEM will be operated.

Electron Gun Animation *
* Video courtesy of Oxford Instruments

Electron Source Properties
Current density (brightness) Emission current Stability of source Lifetime of filament Design of electron source assembly Ease of operation Costs involved ą ip do specimen How well the emitted electrons are focused and distributed in cross-over determines the brightness of the electron source. Brightness is defined as current density per solid angle and is given by: ß = current /(area)(solid angle) = 4ib\(pi2d2aperture angle2) in units of A/cm2sr where ib is the beam current at cross-over, d is the diameter of cross-over, and  is the beam convergence at cross-over. Brightness is the most important performance indicator for electron guns. Most of the electrons passing through the cross-over are captured by the anode when traveling further down the microscope column. These electrons flow back to the high voltage supply and can be measured as emission current. This value is indicated in the Settings control area, in or next to the Beam On button. The electrons that leave the gun area through the anode hole constitute the beam current. This current is further reduced in the microscope column at each lens and aperture, and the fraction of the beam current that actually reaches the specimen surface is referred to as the probe current. Typical emission current values for tungsten electron gun assembles are A, whereas the maximum probe current is 1 A, i.e. only a few percent of the emitted electrons can be used in imaging or analytical applications.

Emission Area For Tungsten (W)
Filament heating supply Filament Wehnelt cap Cross-over plane 70 A This course covers mostly tungsten emitters because this electron gun needs users interaction. The emitter or filament needs changing every hours. Anode High voltage supply (200 v- 30 kV)

Bias on Wehnelt Cap Optimum bias voltage Low bias voltage
High bias voltage Equipotential lines of the Voltage Field + + + Negatively charged electrons are repelled by negative equipotentials, thus electrons leave the filament only towards positive equipotentials. Note that the negative equipotentials around the edges of the hole of the Wehnelt cylinder force the electrons to focus in the so-called cross- over, which lies in-between the Wehnelt cylinder and the anode. It is this cross-over which forms the object for the later electromagnetic lenses (see section Column Optics) rather than the filament itself. Two important microscope parameters are defined at this point: virtual source size (which is the diameter of the cross-over), and initial convergence angle . The bias on the Wehnelt cylinder needs to be adjusted according to the emitted current in order to focus the emitted electrons in the smallest possible cross-over. In practice, the bias needs to be changed when changing acceleration voltage. This can be done manually in the Beam expanded page in the Settings control area, or set to automatic. Typical bias settings for Quantax50-SEM's in the voltage range 1-30 kV can be found in the Quantax50 Series Operating Instructions provided with the instrument. The effects of low biasing, optimum biasing, and high biasing of the Wehnelt cylinder are illustrated in (previous page). No emission High emission large spot Sufficient emission small spot

Autobias keeps emission between 90-110 µA for all kV
Emission : Autobias control Bias 255 ……………………………….. Bias 1 µA 90 µA 1 kV kV When the filament has the normal distance to the Wehnelt cap, the instrument can be used at all kVs from 30 kV to 200V. Due to the autobias control using 255 bias steps, the emission will always be between 90 and 110 µA. Autobias keeps emission between µA for all kV 9

W Filament Saturation Saturation point emission current
False peak / Misalignment Thermionic emission occurs when an emitter material is heated to a temperature sufficiently high for electrons to overcome the energy barrier Ew of the material and escape from the surface of the material. The resulting emitted current density is a function of the temperature (T) and work function (Ew) of the emitting material (the filament). The ideal emission material has the lowest possible work function value, emits electrons at the lowest possible homologous temperatures (T/Tmelt) to prevent evaporation of the material, and produces the highest possible current density. Typical values for Tungsten electron sources are: Ew = 4.5 eV, T = 2700 K (T/Tmelt = 0.74) and current density is 3.4 A/cm2. In practice, small variations in temperature of the emitter material cannot be avoided and this results in variations in emitted current density. This represents a major problem because nearly all information gathered with an SEM is collected over time, and thus a stable electron source is needed. The effects of small temperature variations can be reduced by saturating the filament. As the filament current increases, the emitted current reaches a point where there is no further increase despite further increases in filament current. This condition is referred to as saturation. As the filament current is increased, a false peak may be observed where the beam current rises, reaches an apparent stable value, but then proceeds to drop before true saturation is established. At filament currents equal to or higher than the current needed for saturation, small variations in filament temperature will not effect the emitted current. The higher the filament current, the shorter the life-time of the filament, so that the preferred filament current is the lowest possible value at which saturation occurs. The correct filament current can be found by the operator or, optionally, automatically. This graph shows gun saturation as filament current plotted against emitted current. At the saturation point, small temperature variations will not effect the emitted current, and optimum lifetime is guaranteed. filament current

Tungsten Filament Tungsten (W) Filament
Although the brightness of tungsten filaments is less than that of the filaments discussed later in this section, the tungsten filament remains the preferred choice in many application areas. The benefits of a SEM equipped with a tungsten filament are its reliability, well understood properties, and low costs of operation. It provides an electron source with high, stable currents, and may be used without loss of performance, relative to the other filament types, at low to intermediate magnifications (<10.000x). A tungsten filament consists of a wire mounted on an insulator base plate that bends to a V-shape in a radius of about 100 m. Thermionic emission is achieved at 2700K, resulting in an emission area of about 100 x 150 m. The virtual source size at cross-over is in the order of m. The life-time of a tungsten filament in the Quantax50-SEM of the Applications Laboratory is one to several weeks of nearly continuous daily operation.

High Resolution, High Brightness FEG source…
Tungsten LaB6 FEG Normalized Brightness (-) 1 10 1000 Maximum probe current (nA) 2000 500 100 Life time (hrs) 60-200 > 10000 Beam current stability (10 hrs) <1% <0.4% Resolution 30kV (nm) 3.0 2.0 1.2 Resolution 1kV (nm) 25 15 Cost source (USD) 20 900 26000

Electron sources (comparison)
The quality of a scanning image depends in part on the size of the primary scanning electron beam (which determines the smallest detail which can be seen in the image) and its brightness (which affects the signal -to-noise ratio of the image). It also depends on the interaction volume caused by spreading of the primary electron beam within the sample. Electron scattering within the sample can be reduced by lowering the accelerating voltage of the primary beam to improve the image resolution, but can also reduce the overall signal level (brightness). The beam which scans the specimen surface is a demagnified image of the electron source (conventionally a heated tungsten filament or lanthanum hexaboride crystal). Due to aberrations, the aperture angle has to be limited and this restricts the total current in the probe size. To overcome this, sources of high brightness are a necessity. With the traditional thermionic source, the electrons are emitted from a heated filament or crystal into vacuum and accelerated towards an anode with an aperture through which they merge as an electron beam. The field emission source is different by the way that the electrons are extracted directly from a finely pointed tip by a strong electric field. The size of the tip compared with that of the cloud of electrons surrounding a thermionic filament means that the electron source is several orders of magnitude (typically 103) smaller. Consequently less demagnification is needed in the microscope column. Furthermore, the source brightness is several orders of magnitude (typically 103) greater, and therefore the beam current into the smaller spots is much larger. This allows the use of smaller spots and also lower accelerating voltages with improved resolution and signal level.

XL Schottky FEG Theory o A B C o The Boersch Effect
o o o The Boersch Effect A) Perfect beam: no interactions B) Random beam: one dimension C) Random beam: two dimensions It is actually three dimensional o The Boersch Effect The first applications of the FEG source can be found as far back as the 1960’s when Albert Crewe fitted his FEG source to a scanning transmission electron microscope.As a result many electron microscope designers, to be competative, added FEG sources of similar design without questioning it. This has resulted in a variety of performances and a lack of understanding as to why the results have not been as good as expected. Statistical coulomb interations in high density electron beams were only known as the Boersch effect. This is the longditudinal effect and can be understood by refering to the above figure. Beam A on the left has a purely theoretical distribution of electrons, equally spaced as they travel down the column. All the electrons experience the same force from electrons in their vicinity. This is not the case for Beam B on the right where electrons are randomly distributed along the beam path. Electron 1 is retarded as it travels along the beam path and electron 2 is accelerated which leads to them having different velocities and being focused differently by the lens system. A B C

XL Schottky FEG Theory The Lateral Effect
lateral trajectory displacement This effect results in a larger final spot The diameter of the circle of confusion due to this effect. o o o o o oo In additional to vertical forces as shown on the previous figure, lateral forces also affect the SEM beam. These push the electrons further away from each other. If this sketch could be should three dimensionally, the electrons would also be coming out of the page.

Lens Defects optical axis Aperture Spherical aberration Chromatic
image plane Unfortunately, the force acting on the electrons inside the electromagnetic lens is not uniformly distributed over the entire air gap volume. Electrons passing along the optical axis of the lens experience a force with a slightly different magnitude to those passing at a distance from the optical axis. More important still, the electron beam is not entirely parallel, but has a convergence angle . The change in pathway for separate electrons will thus be different in magnitude and direction. The above complications cause some electrons to be brought to focus away from the correct location. This problem is known as lens aberration. These effects are as listed as follows: spherical aberration chromatic aberration diffraction Spherical aberration Chromatic aberration Diffraction

Spherical Aberrations
Disc of Least Confusion Spherical aberration arises from the non-uniformity of the magnetic field in the air gap. Electrons further away from the optical axis will be more strongly deflected than electrons passing through the optical axis (Fig. 2a). Rather than focusing to a point at the focal length, the electrons are focused in the so-called spherical aberration disk of least confusion. Small apertures can be used to reduce the effects of spherical aberration at the cost of reducing the beam current. The magnitude of spherical aberration is expressed in the spherical aberration coefficient Cs. Electrons entering into a lens at different points get focused at different points

Chromatic Aberrations
Disc of Least Confusion Chromatic aberration arises from the energy spread in the electron beam, causing electrons with slightly lower energy (E0) to be deflected more than electrons with slightly higher energy (E1). Again, rather than focusing to a point at the focal length, the beam is focused in the chromatic aberration disk of least confusion. Such an energy spread is introduced by instabilities in the power supplies for both the filament and the lenses, and an initial energy spread of the electrons leaving the filament. The magnitude of chromatic aberration is expressed in the chromatic aberration coefficient Cc. Electrons of differing energies will be focused at different places

Diffraction The wave nature of electrons cause diffraction limitations
Diffraction occurs when electrons pass through very small apertures. In this condition, the wave-nature of electrons give rise to diffraction, such that instead of a point, a diffraction patterns occurs at the focal length of the lens. The wave nature of electrons cause diffraction limitations

XL Schottky FEG Theory Design Limitations
Longer electron-electron interaction times and smaller electron-electron distances lead to higher statistical aberrations at low KV Chromatic aberration is more dominant at low voltages. Limitations in the design of the Sirion were influenced by the previous points, these can be summarized here as: 1.The longer electron-electron interaction times and the smaller electron-electron distances lead to higher statistical aberrations at low KV. 2.The effect of chromatic aberrations is more dominant at low KV; therefore it is essential to have lenses with a low CC. 3.Transverse chromatic aberrations due to beam deflection are greater at lower KV. The XL design incorporates innovative solutions to this limitation by keeping the beam energy high in the region where these aberrations and interaction have the greatest effect and by removing as early as possible those electrons, which do not contribute to the probe. The former is achieved by using a coulomb tube and the latter by effective aperturing.

XL Schottky FEG Theory Innovative solutions to reduce design limitations A Coulomb tube designed into the column to reduce aberrations and interactions by keeping a high beam energy in the tube Effective aperturing of the beam to remove those electrons not contributing to the probe The demand for a system that will deliver a wide variation in accelerating voltage comes from the differing application fields of X-ray analysis and electron beam lithography for high KV’s (15-30), and the semiconductor and biological fields for low voltage (200V to 5kV). High resolution is needed not only at high KV but also at the lower voltages; therefore a controlled continuous range of accelerating voltages is essential. For the Sirion it is 200V to 30kV. The zirconiated tungsten Schottky emitter is used in the Sirion microscopes, This has low energy spread (approx eV) and high brightness (> 1000 A/cm2srV) with a source size of 20nm. Because of the larger source size than that of a cold field emitter (2nm), a higher total beam current can be obtained with the Schottky emitter. This is particularly useful for X-ray analysis and lithography. No flashing is necessary as the extraction voltage is not changed for KV changes and therefore the beam current is held stable, again unlike the cold field emitter.

FEG Column Principle Diagram
10KV Drift Space (Coulomb Tube) Gun Alignment Coils C2 Objective Aperture The first electrostatic lens has extraction, focusing and accelerating functions. The beam limiting apertures in this area are as small as possible to prevent high beam currents in the beam and thus minimizing coulomb interactions. For beam energies below 10keV, the drift tube acts as an intermediate drift space (between 10 and 30keV), the so-called “coulomb tube”. The electromagnetic deflectors around the coulomb tube can serve as precision alignment coils to ensure that the crossover is always precisely centered and thus prevent image shifts when changing beam current, accelerating voltage or spotsize. With good mechanical pre-alignment the transverse chromatic aberration can be ignored because the beam energy is always above 10kV. The magnetic condenser lens C2 is also around the coulomb tube. The C1/C2 excitation provides the two necessary degrees of freedom to vary the size of the crossover with magnification without changing its position in the principle plane of the deceleration zone. By placing a fixed aperture in the C2 lens, the beam current in the low voltage range is automatically limited at smaller spot sizes to reduce the effect of coulomb interactions in the rest of the column. Scan Coils Objective Lens

FEG gun (electron source)
Emitter type Schottky Cold Source size 20nm 2nm Beam current stability <1%/hour decreases steadily 10-50%/hour Flashing not required always needed (daily) depends on vacuum quality Furthermore the larger size has an engineering advantage: it is 10x less sensitive to magnetic stray fields and mechanical vibrations.

Emission Area for FEG Filament heating supply Extractor system
C1 static lens 150 A This is a schematic drawing the the Field Emission Gun (FEG). The filament is heated to a point where some thermal emission is noted. The strong localized electrostatic fields of the extractor draw the electrons off the fine filament tip. The electron become accelerated toward the anode. A unique part of the module is the fact that the first condenser lens is located within the firing unit. The use and application of C1 will be addressed soon. Anode High voltage supply (200 v- 30 KV)

Schottky Gun Design E Fil = Filament current input (2.4 Ampere)
S = Suppressor (-500V) E = Extractor (+5000V) C1 = Electrostatic Condenser lens Fil S Filament current The running value of the filament current (when the instrument is in the Operate mode) is roughly 2.4 A, but its actual value is defined for each individual tip. This is done by a factory procedure. At this current the temperature of the tip is around °K, which in combination with the good vacuum will result in sufficient emission. Extraction Voltage The extraction voltage is the voltage `seen' by the electrons when they leave the tip and, of course, it plays a major role in obtaining emission. The extraction voltage is set to a pre-defined value of 5.0 KV. Again this value is factory adjusted and is related to the initial conditioning of the tip. The extraction voltage should not be changed because the tip is conditioned at a corresponding value or, in other words, the tip is conditioned in such a way that its use is optimal at the extraction voltage of 5.0 KV. Suppresser voltage The suppresser has an influence on the formation of the actual source (its position and size). In fact both the extractor voltage and the suppresser voltages determine this virtual source of electrons. The suppresser "suppresses" emission from other areas than the tip and therefore its voltage is negative with respect to the tip voltage. Its value is set to -500V and it cannot be changed by the user. E E C1

Schottky Tip design M = Tip module W = Welded tungsten Tip
Fil = Tungsten wire filament T = Sharpened Tip Zr = Zirconium reservoir M T W Gun status and parameters The parameters of the gun determine the emission and stability of the tip The heating of the tip is strongly coupled to the vacuum condition: a bad vacuum may destroy the tip when it is hot. For this reason the tip is automatically switched off if the pressure of the upper IGP is worse than 5x10-7 mbar. However, this should be considered as an emergency stop, rather than a poor operating condition. For this reason it is recommended to regularly check the pressure of the upper IGP. The normal working pressure for the tip is about 5x10-9 mbar or better. Fil Zr

FEG Startup Steps Warmstart / Coldstart Gun conditioning
This is a menu that is different from the other XL SEM products. This is the beam control menu. By and large, it should remain untouched. However, if there is a power outage, then the operator may have to go through a warm start or a cold start. If the power has been off for a few minutes then the filament is still hot, so a “warm start” can be used. If the gun has been off for over 30 minutes than a “cold start” should be used. The XL’s automated controls will take over and do what is necessary to turn on the beam and get you up and running!

Beam Menu Final operation status
This menu may be used to facilitate aperture alignment. Occasionally the image may “swing” during focus. The operator has two choices, electronically bring the beam to the aperture, using the “Gun Shift (Lens Adjust)” control. The user may also manually adjust the aperture while doing a lens modulation to prevent the image swing. In principle, this should seldom be used if the column is well aligned.

FEG Column Double condenser lens
Extraction voltage changes not necessary, beam current is set by condenser lenses C1 is electrostatic C2 is electromagnetic Variable lens strengths: A = high beam current mode B = low beam current mode Final beam energy 30keV down to 200eV C1 Double condenser lens Instead of using a method of changing the extraction voltage to change the beam current a double condenser lens is employed which is able to focus the source at the same position but at different magnifications. By varying the intermediate source magnification, the beam current can be adapted very quickly. Computer control allows the adjustment to be made while the SEM image remains in focus by keeping the crossover at a fixed height relative to the objective lens. This drawing shows that the range over which the C1 lens operates is quite large. It is essential that C1 has very small aberration constants whilst being a strong lens. For engineering reason, the best solution is an electrostatic lens. Although it would be possible to incorporate this lens into the beam accelerator, the following three criteria are extremely demanding for an electrostatic design: 1.Variable lens strength from strong lenses to almost zero. 2.Low axial aberrations in the strong lens mode. 3.Final beam energy from 30keV down to 200eV. If the third criterion could be limited to 30 KV down to 10kV, the design becomes feasible because the dynamic ratio would be 3:1 instead of 150:1. This is achieved in practice by having a deceleration area for lower beam voltages below the lens. C2 A B

FEG Column Double Condenser Lens
Extraction voltage changes not necessary, beam current is set by condenser lenses C1 is electrostatic C2 is electromagnetic Variable lens strengths: A = high beam current mode B = low beam current mode Final beam energy 30keV down to 200eV C1 Internal Spray Aperture Double condenser lens Instead of using a method of changing the extraction voltage to change the beam current a double condenser lens is employed which is able to focus the source at the same position but at different magnifications. By varying the intermediate source magnification, the beam current can be adapted very quickly. Computer control allows the adjustment to be made while the SEM image remains in focus by keeping the crossover at a fixed height relative to the objective lens. This drawing shows that the range over which the C1 lens operates is quite large. It is essential that C1 has very small aberration constants whilst being a strong lens. For engineering reason, the best solution is an electrostatic lens. Although it would be possible to incorporate this lens into the beam accelerator, the following three criteria are extremely demanding for an electrostatic design: 1.Variable lens strength from strong lenses to almost zero. 2.Low axial aberrations in the strong lens mode. 3.Final beam energy from 30keV down to 200eV. If the third criterion could be limited to 30 kV down to 10kV, the design becomes feasible because the dynamic ratio would be 3:1 instead of 150:1. This is achieved in practice by having a deceleration area for lower beam voltages below the lens. C2 A B

FEG Column Different paths for low and high beam current
conditions through the coulomb tube, but common path to objective C1 C2 Condenser Lens One is part of the Electron Gun Module. It is an electrostatic lens. Is it relaxed at small spot sizes, while C2 is stronger. This means that there is more spray of the electron beam on the aperture and less probe current to strike the beam. In a Large spot size mode, C1 is strengthened and C2 is relaxed a bit. Note that it is a non linear relationship between the two condenser lenses. The Deceleration lens is part of the Coloumb Assembly that “slows down” the beam to its original energy. These are the top three lenses of the “Hexalens” column Deceleration Lens Aperture Small Spot Large Spot

Comparison of Columns(20KV)

Probe Current for FEG Beam Current:
Spotsize 30kV 20kV 10kV 5kV 2kV 1kV 500V 1 21 p 13 p 8 p 5 p 2.5 p 1.4 p 0.7 p 2 44 p 40 p 33 p 25 p 13 p 7 p 4 p 3 154 p 148 p 130 p 98 p 53 p 30 p 16 p 4 625 p 617 p 538 p 398 p 211 p 116 p 62 p n 2.39 n 2.11 n 1.57 n 840 p 464 p 249 p n 9.45 n 8.37 n 6.27 n 3.37 n 1.86 n 1.00 n n 36.5 n 32.4 n 24.3 n 13.1 n 7.24 n 3.89 n

FEG Spot Size (nM) Spotsize: Spotsize 30kV 20kV 10kV 5kV 2kV 1kV 500V

SEM Main Components Electron Gun Demagnification system
Wehnelt cylinder Electron Gun Condenser lenses Demagnification system Demagnification system Scan Unit Scan generator The Condenser lens and scan coils are closely linked. As one changes scan condition ( magnification) the probe diameter needs to be changed by adjusting the condenser lens.

Magnification L M=L/l L l ***-important
Magnification is the ratio of the viewed area to the actual area being scanned by the electron beam on the sample. Since the viewed area remains fixed, the smaller the scan area, the higher the magnification. Magnification can be different for different viewing areas, so the Quantax50 user is prompted to select the desired output device. Regardless of the selected magnification, the read out will be corrected for the area being viewed ( I.s. Fast monitor, video printer, Polaroid or digital print). l ***-important

Scan Size Vs. Magnification
Low Mag. Med Mag. Hi Mag. This drawing shows that as the area scanned on the sample decreases, magnification increases.

Magnifying Your Sample on Quantax50
This is your sample and a blank monitor. Our goal is to get an image of your sample onto this monitor. Once the image is one the monitor your goal will be to interpret the image. L _ M= l

Low Magnification Scan Here Display Here
At low magnification the electron beam is scanned across the sample. The reflecting electrons are amplified and displaying nearly simultaneously on the CRT of the SEM Scan Here Display Here

Intermediate Magnification
As the scan area on the specimen is decreased, the resulting image on the CRT appears magnified Scan Here Display Here

Higher Magnification Scan Here Display Here
The image on the CRT shows apparent high magnification as the electron beam is scanned over a smaller area on the specimen. Scan Here Display Here

The viewed area (L) is fixed The smaller the area scanned on the sample results in higher viewed magnification

A Focused Vs. An Unfocused Beam
The beam path drawing on the left shows a focused beam on the sample surface. The unfocused beam on the right is not a desired form of operation.

The Crossover point on the Beam is of a Finite Size
I = Beam Current D= Spot Size We tend to think the cross over size of the beam is infinitely small, but in reality it is of a finite size. This size is measured in square centimeters and call the spot size. Also included in this beam description of the angle of the cone and the number of electrons in the beam. ą = Measurement of the ‘cone’

Current Density β a 4 X I Amps = 2 ( ) Cm Steradians X d o X
π 2 a ( ) Cm Steradians X d o X Current density is the measurement of the amount of electrons in a given area. This density is also called ‘brightness’. But it is not to be confused with the brightness of the image ( as in contrast and brightness). Current density is measured in Amps ( number of electrons) per spot size ( d in squared centimeters) and the angle of the beam (steradians), To make a long story short- spot size and beam current are very closely related…. As spot size goes up, so does beam current - and vica versa. Current Density remains constant through the optical path of the electron beam

Current Density (remove constants)
I Amps β = 2 ( ) Cm d o Current density is the measurement of the amount of electrons in a given area. This density is also called ‘brightness’. But it is not to be confused with the brightness of the image ( as in contrast and brightness). Current density is measured in Amps ( number of electrons) per spot size ( d in squared centimeters) and the angle of the beam (steradians), To make a long story short- spot size and beam current are very closely related…. As spot size goes up, so does beam current - and vica versa. Current and Spot size are directly proportional

Resolution resolved unresolved The resolution of the microscope
is a measure of the smallest separation that can be distinguished in the image

The Diameter of the Electron Beam Must Be Smaller Than the Feature to Be Resolved
The spot size of the focused beam must be smaller than the feature being resolved. Since desired resolution is a function of magnification, this spot size will have to change at different magnifications. An analogy is if you need to sign your name in a small area, a sharp pen is needed. A Magic Marker can’t be used on a small line in a small area. Yet a Magic Marker can be used for a poster. This example shows two different “magnifications” required for two different needs.

The Electron Beam Scans From Left to Right
There can be from 512 to 4096 scan lines, at all magnifications Regardless of the area scanned ( magnification) the will be the same number of actual scan lines. This number is determined by the user.

The Electron Beam Spot Size Must Be Smaller Than the Features Being Resolved
The ideal spot size The diameter of the focused beam on the sample is referred to as spot size. The idea diameter of the beam should be such that it fills a scan line but has no over lap into the next scanned beam

Too Large of Spot Size Looks Out of Focus
Too big of spot size creates an out of focus image If the focused spot size is too big, the image will appear out of focus

Spot size for low mag is not acceptable for higher mag The spot size needed for lower magnifications ( large scanned areas) is different than the spot size needed for larger magnification images. ***-important

Spot size for medium mag is not acceptable for highest mag This further demonstrates that one must decrease the spot size of the focused beam as one increases magnification. ***-important

The SEM operator needs to do two things:
Obtaining an Image The SEM operator needs to do two things: 1- find the correct focus 2- determine the correct spot size

Obtaining an Image Focusing moves the crossover point of the beam up and down, trying to place the focal point onto the sample Spot size controls the lateral size of the focused beam on the sample

Electro-magnetic Condenser Lens
metal jacket copper windings Air gap The electron beam is rather large when it leaves the electron gun. To get the diameter of this beam down to usable sizes one must use a series of lenses called condenser lenses. The condenser lens does what is says… it condenses the beam… it selects the final beam diameter on the sample. The condenser lens acts on an electron beam virtually identical to the way a glass lens operates on a light beam…. The strength of the lens creates a a focal point. Refer to the above illustration. An electromagnetic lens consists of an iron cylinder with a central bore through which the electron beam moves down the column. Within this cylinder, and surrounding the electron beam, are many copper windings, subjected to a current when in operation. A hole is present inside the lens, separating the upper and lower pole piece. This hole is referred to as the air gap. The magnetic field inside the gap can be resolved into two components: one along the direction of the optical axis, and one perpendicular to it. An electron entering the lens interacts with both components. The component perpendicular to the optical axis produces a rotational force. This rotational force then interacts with the magnetic component parallel to the optical axis, producing an overall radial force. This radial force causes the electron to curve towards the optical axis and to cross it providing the lens with focusing capabilities. Cross-over Optic axis

Electro-magnetic Condenser Lens
metal jacket copper windings Air gap All electrons cross the optical lens in about the same position, which is referred to as the focal point of the lens. The distance from the air gap to the focal point is defined as the focal length of the lens. The actual path of the electron beam resembles that of a spiral. Any change in lens current would thus cause image rotation. The Quantax50 series of microscopes correct for this image rotation, so that image rotation no longer occurs when magnification, acceleration voltage, or spot size are changed. The degree of deflection of the electron beam at a given lens current is a function of the initial energy of the electron beam. The higher the energy of the beam, the smaller the deflection of the beam at a given lens current. Therefore, to prevent image rotation and/or shift when changing from low to high acceleration voltage or vice versa, the lens current has to be changed to new values. These values are determined in the adjustment procedures necessary to align the microscope. Cross-over Optic axis

Condenser Lens Action on Beam
Electron beam In Condenser lens Electron spray The beam is focused by the lens to a cross over point. The beam then “sprays” on an aperture. The aperture placement and size permits just part of the beam to continue through. The placement of the column apertures determines how much beam current passes through the condenser lens system, It is obvious that the placement and size of the aperture is critical. Aperture Electron beam Out

Decreased lens current creates more beam current Decreasing the current through the magnetic lens causes the beam to be focused lower in the condenser lens unit. This means less “spray” on the aperture and more beam current. More beam current will also mean a larger spot size.

Increased lens current creates less beam current My focusing the beam higher in the lens area, there is more spray and less beam current. Therefore, changing spot size is merely changing the current in the condenser lens. In actuality, the electron beam and the lens system is much more complex than this example, But for the sake of this course, this basic simplified summary is sufficient.

Spot Size Summary Smaller spot sizes for higher magnification
Larger spot size for x-ray analysis Too large of spot may result in a de-focused image Too small of spot may result in poor S/N

How to get High Resolution (100.000 - 150.000x) (Tungsten)
Use kV Use spot 1 Use WD 5 mm Tilt stage 10° Take BSE detector out Lock stage Use image definition of 1024x884 or 2048x1768 Take 1 Frame, frametime min. 60 seconds Move to new area after focusing/stigmation Factors affecting resolution In the SEM the resolution is mainly limited by the diameter of the beam (spotsize). A narrow beam passing over the two particles will collect information at more points than a broad beam, making it easier to distinguish individual particles. There can be, however, a trade off if the signal-to-noise is poor, as smaller spotsizes produce less signal in the image. Chromatic aberration (which limits resolution) is reduced at higher accelerating voltages so in theory a high kV beam will give the best resolution. This is complicated by the fact that higher energy beams penetrate further into the specimen (especially low atomic number materials) and therefore the image information comes from a greater volume of the specimen which can degrade the image resolution. It is also true that specimen charging and damage is more likely at higher accelerating voltages. Slower scan speeds improve the signal-to-noise ratio of images, often giving a clearer and more detailed image where it becomes easier to distinguish individual particles. Using shorter working distances will improve resolution but at the same time limit depth of focus. It is advisable to remove the solid state backscatter detector (if present) at short working distances, particularly when using tilt. Tilting the specimen towards the SE detector can increase the number of electrons detected and therefore improve signal-to-noise.

Summary of Spot Size Affecting SEM Image
The electron column is designed to produce smallest spot containing highest possible probe current Spot size limits minimum size of objects that can be separated Higher probe current improves the signal to background ratio

Wehnelt cylinder Electron Gun Condenser lenses Demagnification system Scan Unit Scan generator The SEM is divided into several components: The electron gun The Demagnification ( condenser) system The Scan ( magnification) Unit The focusing ( objective lens and stigmation correction) The detecting Unit-- this can be an SED, BSED, GSED, SC, etc.…. Focus Unit Objective and Stigmation lenses

Focusing the Beam Onto the Sample Uses the Objective Lens
final lens aperture objective lens pole piece Objective Lenses The final lens in the column is the objective lens. The function of this lens is to focus the cross-over below the lens onto the specimen surface. The most common objective lens is the so-called conical lens. Design of this lens is such that most of the magnetic fields are kept within the lens. As a consequence, the specimen may be brought close to the lens and the image remains undisturbed by the magnetic field. The objective lens is the strongest lens and needs water cooling. Associated with the final lens are the stigmator, scanning coils, and the final lens aperture. The objective lens in the Quantax50-SEM is operated by focusing, i.e. moving the mouse from left to right while keeping the right button pressed. sample

Focusing the Beam Onto the Sample
final lens aperture objective lens pole piece One simply changes the current in the objective lens to move the crossover point up or down. When the cross over point is at the sample surface, the image is in focus, The objective lens acts very similar to the condenser sample

final lens aperture objective lens pole piece If the current in the objective lens is too low, the apparent crossover will be below the sample, resulting in an out-of-focus image, This image will be out of focus regardless of the spot size selected. sample

final lens aperture objective lens pole piece It is said to be in focus when the objective lens is set to have the crossover of the beam on the sample surface, The operator has to use the condenser lens system to control the actual diameter of the beam at this focus point. sample

Working Distance (WD) objective lens final lens aperture pole piece
OWD Just below the final lens the electron beam passes another aperture before reaching the specimen surface. This aperture is referred to as the final lens aperture and plays an important role in determining the final probe current and the depth of focus. The Quantax50-SEMs are supplied with an aperture of 200 m diameter, but this can be replaced by other apertures of different size. Alignment of the optical axis to the center of the aperture is extremely important to prevent image shift during focusing and scanning. The distance from the final lens aperture to the cross-over below the aperture is referred to as the optical working distance (OWD); and the distance from the lower surface of the final pole piece to the specimen surface is referred to as free working distance (FWD). There are two notations for WD- fixed WD (FWD) and Objective WD (OWD). Most people use the FWD connotation. Working distance(WD) is the measurement of the path of the beam from the column to the sample. This also corresponds to gas path length (GPL). This measurement is calculated from the current in the objective lens and will be an accurate reading of the distance from the final lens area to the crossover point. FWD specimen

Synchronizing Stage Height With WD
Sample have different heights in relationship to the final lens, therefore ,as the operator changes focus, will have different FWD readings. The FEI Quantax50 series of SEMS has a feature where the operator can tell the stage what the present working distance is. This will change the stage height (“Z”) scale to correspond directly to the FWD of the particular sample. If the stage and FWD are linked and the stage is moved- then the focus of the beam will change FWD to the new “Z”.Note that changing the FWD will not change the “Z” of the stage motion. specimen specimen

WD Vs. Gas Path Length(GPL)
Hi-Vac Final Lens Pole Piece EDS Working Distance is defined as the measurement from the final lens pole piece to the focal cross-over point of the electron beam. Gas Path Length (GPL) is the total distance that the electron beam is exposed to a gas. If the final lens aperture is above the final lens pole piece end plane, then the GPL is longer than WD. GPL is used on low vacuum and ESEM mode and is not applicable to high vacuum SEMs. GPL WD

WD Vs. Gas Path Length(GPL)
Intermediate Vacuum Hi-Vac Final Lens Pole Piece EDS Cone(8mm) EDS The further the electron beam travels in a gas, the more beam spread ( or skirt) occurs. FEI has a special EDS cone that minimizes the GPL to 2 mm. The SEM still reads out 10mm WD, which is accurate. However, the 8mm cone is kept at an intermediate vacuum level and the beam is actually in a gaseous area for only two millimeters of travel. This makes for a far superior X-ray analysis, as the X-rays will emanate from a point closer to the actual probe location. WD= 10 mm GPL= 2MM

in Low-vacuum with use of
Using the EDS Cone.. Low noise EDS Mapping in Low-vacuum with use of EDS Cone

Focus and Stigmation Focusing brings the beam crossover up or down
Stigmation controls the ovalness of the beam The term ‘astigmation’ refers to an out of round beam. Stigmation is contributed to the electron beam through many ways. The biggest contributor to astigmation, however, is the final aperture.

Astigmation Is an Un-oval Beam
There is a set of coils in the object lens area called the stigmation coils. These coils push and/or pull the electron beam into a round beam.

Astigmatism disc of least confusion magnified point source
An astigmatic image will look slightly out of focus and have a slight stretching in one direction or another. Feature of direction might be in or out of focus. It depends on which direction the stigmation coils are set. Astigmatism is caused when the lens system does not have perfect rotational symmetry. This may be caused by machining errors, heterogeneities in the iron of the lens, asymmetry in the copper windings, and dirty apertures. When the lens has a slightly elliptical shape, the electrons will come to focus at the specimen as two separate foci at right angles to each other (instead of a point). disc of least confusion magnified point source

Astigmatism...Continued
You have to see it to believe it… Correcting for stigmation is probably the most difficult thing for an SEM operator to perform. The method of correction varies with each operator but it is strongly suggested to only adjust one direction (x or y) at a time, while observing the image. Refocusing will be necessary between each stigmation correction. This process may take several iterations before a final image is perfected.

Wehnelt cylinder Electron Gun Condenser lenses Demagnification system Scan Unit Scan generator The SEM is divided into several components: The electron gun The Demagnification ( condenser) system The Scan ( magnification) Unit The focusing ( objective lens and stigmation correction) The detecting Unit-- this can be an SED, BSED, GSED, SC, etc.…. Objective and Stigmation lenses Detector Specimen + detector Detecting Unit

Different Types of Electron Detectors
A detector is a detector to the SEM SEM Quantax50 Electron Detector : The SEM display just shows the operator what they have selected as an image to “see”. There are, as discussed earlier, many different detectors to select. To the Quantax50, a detector is a detector.. It just displays what the operator wants to see!

High Vacuum Everhardt-Thornley Secondary Electron Detector
Faraday cage ( V) Light guide Phosphorous screen (Al-coated) ( +10 kV) The Everhardt-Thornley Detector Secondary Electron Detector ( E.T. SED) is the most used SEM detector. The Faraday cage can be biased to attract or repel electrons of varying energies. Note that all SE images with the E.T. SED will have a BSE component. The electrons are then accelerated to a higher potential and strike a phosphorous detector at the end of the light pipe. This causes a pulse of light to be given off and amplified. This pulse of light is directly proportional to the bundle of electrons that entered the detector. This pulse will be displayed on the SEM monitor as the beam rasters across the sample. By putting a negative bias on the Faraday cage, the operator can repulse the low voltage SEs and only detect the high energy BSEs. This later form of imaging is called reflected BSE or “poor man’s backscatter”. glass target Scintillator Photomultiplier

Solid State Backscattered Detector
Semiconductor Base plate Silicon dead layer Surface electrode The solid state BSD (SSBSD) is the most common BSE detector on the market. It is basically a diode that amplifies the high energy BSE that strike it. The SSBSD is usually divided into two detection areas. This will allow for either topographical or elemental imaging of BSE. Backscattered electrons

The Solid State BSD

The Gaseous Analytical Detector (GAD)
The Gad is the BSD with a cone added to it… this allows a short GPL (gas path length) and BSE imaging. This is frequently used for X-ray analysis and mapping,as the beam skirt is minimized.

Low voltage high Contrast Detector (vCD)
Semiconductor Base plate Silicon dead layer Surface electrode The solid state BSD (SSBSD) is the most common BSE detector on the market. It is basically a diode that amplifies the high energy BSE that strike it. The SSBSD is usually divided into two detection areas. This will allow for either topographical or elemental imaging of BSE. Backscattered electrons

The best imaging conditions at LV Low KeV: flat cone short beam gas path length, low pressures and long amplification path Electron beam Detected electron signal EDX Detector Optimum Low KeV or X-ray Conditions Can Be Obtained With the LF & x-ray Cone 5 mm WD Sample

LF (Large Field) Detector
Large field of view SE detector for LV based on gas amplification Excellent signal yield at low pressures Works from 0.5 to 1 Torr (2-3T with PLA) Detects primarily: SE1, SE2, SE3 Not too sensitive to light or temperature Can be used with x-ray cone for low KeV or x-ray analysis LF (Large Field) Detector Latest SE detector for ESEM based on gas amplification Excellent signal yield at low pressures Works from 0.5 to 1 Torr (2-3T with PLA) Detects primarily: SE1, SE2, SE3 Not sensitive to light or temperature Less sensitive to working distance Can be used with x-ray cone for low KeV or x-ray analysis

The Large Field (LF) Detector

Gaseous Secondary Electron Detector
Primary beam Detected electron signal GSED Collection area at high positive voltage Signal amplification by gas ionisation non-conductive specimen

GSED (Gaseous Secondary Electron Detector)
Second generation SE detector for ESEM based on gas amplification Works from 0.5 to 20 Torr Not too sensitive to light or temperature

GSED (Gaseous Secondary Electron Detector)
Second generation SE detector for ESEM based on gas amplification Good signal yield, discriminates against SE3 and BSE signals Works from 0.5 to 20 Torr Detects: SE1 and SE2 (some SE3) Not sensitive to light or temperature

Available SE Gas Amplification Detectors & Cones
LFD Low KV Cap X-Ray Cone GSED GBSD Quantax50 is using the third generation ESEM detectors which use a single insert (no bullet swapping), which are recognized by the software and which have an improved amplifier for lower noise.

HighVac / LowVac: LF-GSE + SS-BSE
LFD Low vac mode: Pa Large Field (LF) and solid state back-scattered detector both mounted The LF detector works simultaneously with the back-scattered detector. Not sensitive to light or temperature. Detects primarily: SE1, SE2, SE3 Changing from high vac to low vac is done by software control only. There is no hardware change, the detectors are not changed. This is the ideal setup for high vac and low vac mode, as one can use the ET and BSD in hi vac and the LF and BSD in Low vacuum. Changing modes without detector change

Low kV imaging with Low KV Cap
LFD The Low KV cap reduces the Beam Gas Path Length. Therefore, the signal to noise ratio at low kV is improved. With the Low KV Cap imaging at 1-4 kV is possible. LF-Detector + Low KV Cap

X-Ray Cone X-Ray Cone LFD LF-Detector + X-Ray cone: no BSE detection
LF Detector with X-Ray Cone: - Good EDX quantification - No BSE detection possible Minimum magnification 250x This cone ( also called the witch’s hat) allows a very short GPL (gas path length) and yet a long cascade path for the SE to be amplified by the LF detector. LF-Detector + X-Ray cone: no BSE detection

Gaseous Analytical Detector
GAD LFD The GAD is a SS-BSED + X-Ray cone Optimised low vacuum microanalysis and imaging (SE and BSE) at the analytical WD Minimum Magnification 250 x With the GAD, good EDX quantification is possible and the BSE detector can still be used. Note that the minimum magnification is 250x.

GBSD (Gaseous Backscattered Electron) Detector
The GBSED work art higher pressures ( 4 torr and greater) as well as allowing Se imaging. Note the size and resulting GPL and WD restrictions.

The GBSD BSE Converter Plate Buried Signal Track PLA SE 3
+ + + - - - Buried Signal Track PLA SE 3 BSE Generated by Primary Beam SE Collection Grid

GBSD (Gaseous Backscattered Electron) Detector
Specialized detector allows BSE imaging at higher pressures >4T SE & BSE detector for ESEM based on gas amplification Works from 4-10 Torr Detects SE or BSE Signal in a gas Not sensitive to light or temperature GBSD (Gaseous Backscattered Electron) Detector Specialized detector allows BSE imaging at higher pressures >4T SE & BSE detector for ESEM based on gas amplification Works from 4-10 Torr Detects SE or BSE Signal in a gas Not sensitive to light or temperature

GBSD Optimized for High Pressures
Signal vs Pressure 1.2 B C 1 0.8 0.6 Signal (Arbitrary) 0.4 0.2 2 4 6 8 10 Pressure

Oil in Water Secondary Mode Backscattered Mode

When to use what detector…
BSE Pressure Lowest kV X-ray Area GSED YES NO 1.0-20T 3kV up BULK LF/SS BSE .1-1.0T( FEG) 5kV up LF/GAD 0.1-4T POINT GBSD 4-10T 10KV up ET SE/ SSBE Hi-VAC 1KV up ICD Hi-VAC no insert 1 KV with BD When to use what… GSED ultimate SE resolution may see more charging LF More signal (lower pressures) GBSD BSE at high pressures SE/BSE High vacuum compatible specimens

Hot Stage “Hook” (ESD) ESD (Environmental Secondary Detector)
First SE detector for ESEM based on gas amplification Good signal yield Works from 0.5 to 20 Torr Detects primarily: SE1, SE2, SE3 Not sensitive to light or temperature, therefore used with the hotstage

Hot Stage ‘Hook” and Detector

Through The Lens Detector (TLD)
PMT The electron detector used in the Sirion is quite unique. It is a photomultiplier tube(PMT) with two detectors on it. One detector is the standard Everdhardt-Thornley S.E.D. as described earlier. Inside the lower lens is another detector.. The “Through the Lens Detector” (TLD). This detector has a scintillator similar to the E-T SED with a +10KV bias in it. Electrons are drawn up into the column to this detector and amplified by the PMT. The electron imaged by the TLD are trapped inside the final lens’ magnetic field and drawn up the column. This detector, in combination with the external objective lens, gives the ultimate in imaging resolution and low voltage performance. E.T. SED Specimen

Scintillator-type Backscattered Detector (Robinson & Centaurus)
P-scintillator through light guide to Photomultiplier tube specimen The Robinson BSD is considered the most efficient of in chamber BSDs on the market. It is basically a glass tube with a phosphor coating. As the electron strike the phosphorus, the phosphorus gives off light that is amplified and converted to a signal that is sent to the SEM display. Scintillator backscattered detectors operate on the same principle as the secondary electron detector, except that no bias voltage is applied to the scintillator because the backscattered electrons already carry sufficient energy. Without such a bias voltage, secondary electrons have very little influence on the performance of the detector. In addition the primary beam is not influenced by the detector, due to a grounded ring in the primary tube, so the detector may be placed above the specimen. The most commonly applied scintillator backscatter detector is the Robinson detector; this is shown in . The above detector is a Phosphor scintillator with a coating of Aluminum. The size and shape of this detector is such that it may be placed just above the specimen, and backscattered electrons traveling in all directions are captured. A small hole is drilled through the detector to allow the primary electron beam access to the specimen surface. The efficiency of the detector allows imaging at Fast scan-rates and results in high image quality. The size and shape of the detector, however, strongly limits the mobility of the specimen, in particular when tilting. Also, no other detectors except the Specimen Current detector may be used simultaneously although the Robinson detector is retractable from outside the chamber. The Robinson is the highest resolving BSE detector on the market with a mean atomic number resolving power of at 30kV. Aluminium

Cathodoluminescence Detector
Polished Aluminium Light guide The retractable Cathodoluminescence detector (CLD) for the Quantax50 microscopes is mounted on the side port of the chamber, opposite the SED. The light emitted by the specimen is focused onto the photomultiplier by a high purity aluminum reflector. The photocathode is a Bi-Alkali type and is sensitive for wavelengths in the range of nM. An option is available to extend the sensitivity towards larger wavelengths. During operation of the microscope the detector can be inserted to just below the final lens. The geometrical detection efficiency is optimized for the eucentric working distance. The 8 X 8 mm active area of the reflector ensures a spatial collection of close to 2 pi if the specimen is at the eucentric position. In addition, the CLD can be mounted slightly lower to accommodate the use of the BSD. This detector operates at all scan rates, although (as with all detectors) will give the best S/N at slower scan rates. specimen Photomultiplier

Electron Backscatter Pattern (EBSD) Detector
Primary Beam Final Lens BSE The electron backscatter pattern (EBSP) detector is used to observe electron diffraction patterns within a sample. The detector consists of a phosphor screen that is on a light pipe. The diffraction pattern (while in ‘spot’ mode) is projected onto the screen and amplified by the PMT. The resulting diffraction pattern image is displayed on the SEM screen. EBSD

EBSD Applications OIM from 1000 Å PVD Copper Damascene lines

Specimen Current Detector
iPC iBSE iSE iSC The Specimen Current(SC) detector actually allows an operator to do two things: Image the specimen current Measure the current flow The straight SC image is basically an inverted BSE image. When used in semiconductor inspection and properly hooked up the SC amp can give Electron Beam Induced Current(EBIC) information . This gives information on P-N junctions such as depletion layer size, location, etc.. When in measure mode the current can be measured at a particular location in the scanned area if used in conjunction with the "Spot" mode in the SEM. The specimen current detector measures the current that flows through the specimen to or from Earth, depending on beam energy and specimen composition. From the initial current input to the specimen by the electron probe, part is lost by excitation of backscattered electrons and secondary electrons. A balance can thus be written as: ISC = IPC - IBSE - ISE where ISC is the specimen current, IPC is the probe current, IBSE is the current lost by emission of backscattered electrons, and ISE is the current lost by emission of secondary electrons. See The specimen current can be measured by wiring the specimen to ground. Since the specimen current signal does not contain any directional information, useful information is often obtained in conjunction with the BSE or SE signal. The Quantax50-SEM specimen current detector may be used in the imaging mode, to display the specimen current (useful for WDX and EBSP applications explained below), or can be used as touch alarm. The efficiency of the detector is insufficient to allow imaging at Fast scan-rates. specimen

Electron Beam Induced Current (EBIC)
PE Another affect that can be used in specimen current affect is electron beam induced current(EBIC). A special type of signal is important for the examination of junctions (depletion layers) in semiconductors. If the electron beam penetrates into this depletion layer then electron-hole pairs are locally produced. Since for the production of electron-hole pairs only a few eV is required, one energetic electron from the beam is capable of producing about 2000 electron-hole pairs. So there is a good internal multiplication of the number of charge carriers: they are separated by the internal electric field of the semiconductor resulting in a current that can be used to form an electron beam induced current (EBIC) image. In the case of a vertical p-n junction the EBIC picture shows the position and the width of the depletion layer. If there are any dislocations or local cracks in the depletion layer they will act as recombination centers and thus produce a contrast on the image. This EBIC technique which is only used for the investigation of semiconductors produces an image of the specimen as well, but here the information is strongly restricted to that part of the specimen where the actual interaction takes place, i.e. the depletion layer of the semiconductor. So for EBIC it is very important to be aware of the actual penetration depth of the beam since overlap of depletion layer and interaction volume is required to obtain the EBIC signal. P N P SCA

CCD Camera - Quantax50 View
E.T. SED LFD BSD Sample As viewed from under the EDS detector The Charge Coupled Device (CCD) is basically a Fast camera. This gives the SEM user a live, low magnification image of the interior of the SEM. This is a tremendous aide for navigation, as well as making sure that samples are mounted below the SEM pole piece,

The end QUANTRAINx50 3.2PPT- Optics

Quantrainx50 Module 3.1 Electron Optics

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