Unconventional Nanotechnology & Nanopatterning (~2 lectures) Scanning Probe Lithography, Soft-Lithography & Nanoimprint Lecture 8

Draw a conceptual picture of an Electric Scanning Probe Lithographic Instrument. Describe how it works? What instrument would you modify? Name one major limitation. Homework/Test questions Name:

Understand the basic function of an electric scanning probe lithography ESPL instruments and draw a picture of an ESPL showing the basic elements (label at least 6 elements that are essential to pattern a surface). Can and Atomic Force Microscope be converted? and if yes what is needed for the conversion to work? Can an STM Microscope be converted to expose and electron beam sensitive resist? and if yes what is needed for the conversion to work? What is the difference in the feedback to operate an AFM when compared to an STM? What does this mean for the samples?

H+H+ OH - H+H+ water meniscus you have modified an atomic force microscope by connecting an electrical lead to apply a voltage bias to the semiconducting AFM tip. The sample is titanium and you would like to form titanium oxide underneath the tip. Do you need to apply a positive or negative potential to the tip with respect to the sample to oxidize the sample? Do you expect that all metals can be oxidized? Are the voltages going to be different what is a minimal voltage that you expect using a first order estimate and looking at:

Exposure of Electron Sensitive Resists. You have modified and AFM to expose "e-beam" sensitive resists. What is the price of such an instrument? $ AFMs cost ~300k, SEMs cost > 1M. What resolution (line widths) do you expect based on previous results (see results)? What is the throughput in time per cm2 sized area? Hint: Maximum line speeds today are ~ 100 um/s. Assume that you were to try to expose the entire surface of a cm2 sized area with a single tip/beam. How does the throughput compare with traditional single cell e-beam lithographic systems?

Explain how KFM can measure the local surface potential by filling in appropriate words: KFM detects localized forces between the tip and the sample to measure the surface potential of the sample. A feedback is used to adjust the DC tip until the force is zero. At this point the DC tip is equal to the local surface

Name two physical effects that will cause a variation in the surface potential? How do you record charge patterns and surface potentials without touching the sample? KFM Kelvin Probe Force Microscopy --- A quick excurse to a special AFM to map electrical charges and potentials

You have IC circuit structure that contains a number of different materials with different electron affinities. The structure has a Al, Au, and Si regions as illustrated. Al AuAu top view Au side view Au Element Work Function(eV) Aluminu m 4.08 Beryllium5.0 Cadmiu m 4.07 Calcium2.9 Carbon4.81 Cesium2.1 Cobalt5.0 Copper4.7 Gold5.1 Iron4.5 Lead4.14 Magnesi um 3.68 Mercury4.5 Nickel5.01 Niobium4.3 Potassiu m 2.3 Platinum6.35 Selenium5.11 Silver4.73 Sodium2.28 Uranium3.6 Zinc4.3 Si 4.52eV Si Homework/Test questions Name: Questions: Is there a electrostatic potential difference between the different regions even if you do not apply an external bias to the films?YES/NO If YES which material is most positive? (Au, Al, Si) which film is most negative? (Au, Al, Si) which is in the center? (Au, Al, Si) What is the potential difference between the Au and the Al? I indicated a 1 um in diameter half circle. Would you expect an electrostatic field along this line? YES/NO If YES how big would this field be? E=... V / m

Surface Charge Double Layer Relationship. Given is the picture with an insulating charged layer that is 100 nm thick and charged to 100 elementary charges per 100 nm x 100 nm area. The layer extends in x-y direction. The charge sits on an insulator with  r = 15. Underneath the insulator is a gold film. Questions: Is the picture missing image charges in the gold substrate? (YES/NO) The field above the surface at location 1 and 2 is constant/not-constant? The field above the surface at location 1 and 2 is zero/non-zero? The field inside the insulator at location 3 is zero/non-zero? The field inside the conductor at location 4 is zero/non-zero? Calculate the potential drop that is caused by the surface charge? delta V = Volts Imagine an AFM tip above the surface. What potential do you need to apply to the tip to null out the attractive force? Volts. You now replace the substrate with a semiconductor. Do you expect a larger or smaller voltage for the same amount of charge?

High Resolution Patterning Using Scanning Probes. Scanning probe lithography (SPL) is an area of research in which the scanning tunneling microscope (STM) or the atomic force microscope (AFM) is used to pattern nanometer-scale features. Patterning methods include mechanical patterning such as scratching or nanoindentation, or local heating with the sharp tip. When a voltage bias is applied between a sharp probe tip and a sample, an intense electric field is generated in the vicinity of the tip. This concentrated field is the enabling element for three other SPL methods: field enhanced oxidation (of silicon or metals) and electron exposure of resist materials or the injection of charge in thin dielectric fields.field enhanced oxidationelectron exposure of resist materials Characteristics ultimately scanning probe microscopes (SPM) can manipulate structures atom-by-atom at a resolution < 1 nm writing process is very slow, µm/s for a single ultranarrow line SPM lithography is inexpensive and very useful in research labs

Remember Patterning in the Context of IC Substrate Example IC (today nano) materials need to be deposited (film thickness control ~1 nm) Materials need to be patterned Substrate lithography --- advanced lithography

Throughput vs. Resolution traditional $$$ "cheap" < $200k unconventional (inexpensive, $0-$100k) traditional (available at most top 20 research universities $2000k) traditional (>$2000k) unconventional (inexpensive, $0-$100k)

Throughput vs. Resolution traditional $$$ "cheap" < $200k unconventional (inexpensive, $0-$100k) traditional (available at most top 20 research universities $2000k) traditional (>$2000k) unconventional (inexpensive, $0-$100k)

traditional $$$ Mask Making and Pattern Generation: Remember Every Mask Needs to be Generated

Scanning Probe Based Methods Scanning probe devices have been used as novel tools to create patterned materials of all kinds with sub 100 nm resolution. Here the most well established examples: An STM can manipulate atoms (IBM example given before) An atomic force microscope (AFM) can physically move nanoparticles on surfaces. Conducting AFM probes can Pattern Charge Conducting AFM probes can Perform Local Electrochemistry Conducting AFM probes can expose electron beam sensitive resists. Scanning Near Field optical probes can expose photosensitive resists beyond the diffraction limit AFM probes can be used as a pen to transfer liquids (chemicals, molecules, and polymer melts) -- Dip Pen Lithography

Ok, how is it possible to manipulate atoms with an STM?

Electric Scanning Probe Lithography

Remember

The Principle of Electric Scanning Probe Lithography

Electric Scanning Probe Lithography The Principle of Electric Scanning Probe Lithography

Draw a conceptual picture of an Electric Scanning Probe Lithographic Instrument. Describe how it works? What instrument would you modify? Name one major limitation. Homework/Test questions Name:

Understand the basic function of an electric scanning probe lithography ESPL instruments and draw a picture of an ESPL showing the basic elements (label at least 6 elements that are essential to pattern a surface). Can and Atomic Force Microscope be converted? and if yes what is needed for the conversion to work? Can an STM Microscope be converted to expose and electron beam sensitive resist? and if yes what is needed for the conversion to work? What is the difference in the feedback to operate an AFM when compared to an STM? What does this mean for the samples?

M + 2OH electrons => MO 2 + H 2 H+H+ OH - H+H+ Localized Electrochemistry due to water meniscus water meniscus

Electric Scanning Probe Lithography Field Enhanced Oxidation A voltage bias between a sharp probe tip and a sample generates an intense electric field at the tip. The high field can be used to locally oxidize silicon in a process known as electric-field-enhanced oxidation. The high field desorbes the hydrogen passivation on the silicon surface, allowing the exposed silicon to oxidize in air. Both single-crystal silicon and amorphous silicon may be locally oxidized in such a way. This local oxidation process is powerful because of its fine resolution (sub-50-nm) and the resistant oxide etch mask that is created.

Field Enhanced Oxidation using 50 tips in parallel. Electric Scanning Probe Lithography Field Enhanced Oxidation

Field enhanced oxidation (STM can be used as well) Electric Scanning Probe Lithography

Field enhanced oxidation (STM can be used as well) Electric Scanning Probe Lithography

H+H+ OH - H+H+ water meniscus you have modified an atomic force microscope by connecting an electrical lead to apply a voltage bias to the semiconducting AFM tip. The sample is titanium and you would like to form titanium oxide underneath the tip. Do you need to apply a positive or negative potential to the tip with respect to the sample to oxidize the sample? Do you expect that all metals can be oxidized? Are the voltages going to be different what is a minimal voltage that you expect using a first order estimate and looking at:

Electric Scanning Probe Lithography Exposure of Electron Sensitive Resists. Electron Exposure of Resist. One scheme for performing lithography with scanning probes involves the electron exposure of a resist material, such as an organic polymer or a monolayer resist. When a conducting tip is biased negatively with respect to a sample, electrons are field- emitted from the tip. If a sample is coated with a thin resist, the emitted electrons traverse the resist. The resist absorbs energy from the electron radiation, which induces chemical changes in the resist. For organic polymer resists, the radiation: scissions bonds (positive resist) or crosslinks molecules (negative resist). As a result, when the resist is submersed in a special solvent (the developer), only the irradiated areas dissolve (for positive resists; opposite for negative resists).The resist pattern can then be transferred to the substrate using selective chemical etching or dry etching or through lift-off. from Quate Group

Cross-sectional SEM images of etched silicon features patterned by scanning probe lithography. (a) 50-nm-wide line written in SAL601 and etched 300 nm into the silicon using an HBr+O2 high density plasma (6:1 aspect ratio). (b) 26-nm-wide line written in PMMA and transferred through lift-off and anisotropic etching (NF3) into the silicon substrate. The etch depth is 260 nm, giving the line an aspect ratio of 10:1. Electric Scanning Probe Lithography Exposure of Electron Sensitive Resists.

You have modified and AFM to expose "e-beam" sensitive resists. What is the price of such an instrument? $ AFMs cost ~300k, SEMs cost > 1M. What resolution (line widths) do you expect based on previous results (see results)? What is the throughput in time per cm2 sized area? Hint: Maximum line speeds today are ~ 100 um/s. Assume that you were to try to expose the entire surface of a cm2 sized area with a single tip/beam. How does the throughput compare with traditional single cell e-beam lithographic systems?

Electric Scanning Probe Lithography Patterning of Charge Electret: SiO2 PMMA, PS Teflon

Electric Scanning Probe Lithography

A quick excurse A special AFM to map electrical charges and potentials

How do you record charge patterns and surface potentials without touching the sample? How do you record charge patterns and surface potentials without touching the sample?

How do you record charge patterns and surface potentials without touching the sample? How do you record charge patterns and surface potentials without touching the sample?

Explain how KFM can measure the local surface potential by filling in appropriate words: KFM detects localized forces between the tip and the sample to measure the surface potential of the sample. A feedback is used to adjust the DC tip until the force is zero. At this point the DC tip is equal to the local surface

How do you record charge patterns and surface potentials without touching the sample? KFM Kelvin Probe Force Microscopy --- A quick excurse to a special AFM to map electrical charges and potentials

Name two physical effects that will cause a variation in the surface potential? How do you record charge patterns and surface potentials without touching the sample? KFM Kelvin Probe Force Microscopy --- A quick excurse to a special AFM to map electrical charges and potentials

How do you record charge patterns and surface potentials without touching the sample? KFM Kelvin Probe Force Microscopy --- A quick excurse to a special AFM to map electrical charges and potentials

You have IC circuit structure that contains a number of different materials with different electron affinities. The structure has a Al, Au, and Si regions as illustrated. Al AuAu top view Au side view Au Element Work Function(eV) Aluminu m 4.08 Beryllium5.0 Cadmiu m 4.07 Calcium2.9 Carbon4.81 Cesium2.1 Cobalt5.0 Copper4.7 Gold5.1 Iron4.5 Lead4.14 Magnesi um 3.68 Mercury4.5 Nickel5.01 Niobium4.3 Potassiu m 2.3 Platinum6.35 Selenium5.11 Silver4.73 Sodium2.28 Uranium3.6 Zinc4.3 Si 4.52eV Si Homework/Test questions Name: Questions: Is there a electrostatic potential difference between the different regions even if you do not apply an external bias to the films?YES/NO If YES which material is most positive? (Au, Al, Si) which film is most negative? (Au, Al, Si) which is in the center? (Au, Al, Si) What is the potential difference between the Au and the Al? I indicated a 1 um in diameter half circle. Would you expect an electrostatic field along this line? YES/NO If YES how big would this field be? E=... V / m

You have IC circuit structure that contains a number of different materials with different electron affinities. The structure has a Al, Au, and Si regions as illustrated. Al AuAu top view Au side view Au Element Work Function(eV) Aluminu m 4.08 Beryllium5.0 Cadmiu m 4.07 Calcium2.9 Carbon4.81 Cesium2.1 Cobalt5.0 Copper4.7 Gold5.1 Iron4.5 Lead4.14 Magnesi um 3.68 Mercury4.5 Nickel5.01 Niobium4.3 Potassiu m 2.3 Platinum6.35 Selenium5.11 Silver4.73 Sodium2.28 Uranium3.6 Zinc4.3 Si 4.52eV Si Homework/Test questions Name: Questions: Is there a electrostatic potential difference between the different regions even if you do not apply an external bias to the films?YES/NO If YES which material is most positive? (Au, Al, Si) which film is most negative? (Au, Al, Si) which is in the center? (Au, Al, Si) What is the potential difference between the Au and the Al? I indicated a 1 um in diameter half circle. Would you expect an electrostatic field along this line? YES/NO If YES how big would this field be? E=... V / m

You have IC circuit structure that contains a number of different materials with different electron affinities. The structure has a Al, Au, and Si regions as illustrated. Al AuAu top view Au side view Au Element Work Function(eV) Aluminu m 4.08 Beryllium5.0 Cadmiu m 4.07 Calcium2.9 Carbon4.81 Cesium2.1 Cobalt5.0 Copper4.7 Gold5.1 Iron4.5 Lead4.14 Magnesi um 3.68 Mercury4.5 Nickel5.01 Niobium4.3 Potassiu m 2.3 Platinum6.35 Selenium5.11 Silver4.73 Sodium2.28 Uranium3.6 Zinc4.3 Si 4.52eV Si Homework/Test questions Name: Questions: Is there a electrostatic potential difference between the different regions even if you do not apply an external bias to the films?YES/NO If YES which material is most positive? (Au, Al, Si) which film is most negative? (Au, Al, Si) which is in the center? (Au, Al, Si) What is the potential difference between the Au and the Al? I indicated a 1 um in diameter half circle. Would you expect an electrostatic field along this line? YES/NO If YES how big would this field be? E=... V / m

You have IC circuit structure that contains a number of different materials with different electron affinities. The structure has a Al, Au, and Si regions as illustrated. Al AuAu top view Au side view Au Element Work Function(eV) Aluminu m 4.08 Beryllium5.0 Cadmiu m 4.07 Calcium2.9 Carbon4.81 Cesium2.1 Cobalt5.0 Copper4.7 Gold5.1 Iron4.5 Lead4.14 Magnesi um 3.68 Mercury4.5 Nickel5.01 Niobium4.3 Potassiu m 2.3 Platinum6.35 Selenium5.11 Silver4.73 Sodium2.28 Uranium3.6 Zinc4.3 Si 4.52eV Si Homework/Test questions Name: Questions: Is there a electrostatic potential difference between the different regions even if you do not apply an external bias to the films?YES/NO If YES which material is most positive? (Au, Al, Si) which film is most negative? (Au, Al, Si) which is in the center? (Au, Al, Si) What is the potential difference between the Au and the Al? I indicated a 1 um in diameter half circle. Would you expect an electrostatic field along this line? YES/NO If YES how big would this field be? E=... V / m

How do you record charge patterns and surface potentials without touching the sample? KFM Kelvin Probe Force Microscopy --- A quick excurse to a special AFM to map electrical charges and potentials

Surface Charge Double Layer Relationship. Given is the picture with an insulating charged layer that is 100 nm thick and charged to 100 elementary charges per 100 nm x 100 nm area. The layer extends in x-y direction. The charge sits on an insulator with  r = 15. Underneath the insulator is a gold film. Questions: Is the picture missing image charges in the gold substrate? (YES/NO) The field above the surface at location 1 and 2 is constant/not-constant? The field above the surface at location 1 and 2 is zero/non-zero? The field inside the insulator at location 3 is zero/non-zero? The field inside the conductor at location 4 is zero/non-zero? Calculate the potential drop that is caused by the surface charge? delta V = Volts Imagine an AFM tip above the surface. What potential do you need to apply to the tip to null out the attractive force? Volts. You now replace the substrate with a semiconductor. Do you expect a larger or smaller voltage for the same amount of charge?

Surface Charge Double Layer Relationship. Given is the picture with an insulating charged layer that is 100 nm thick and charged to 100 elementary charges per 100 nm x 100 nm area. The layer extends in x-y direction. The charge sits on an insulator with  r = 15. Underneath the insulator is a gold film. Questions: Is the picture missing image charges in the gold substrate? (YES/NO) The field above the surface at location 1 and 2 is constant/not-constant? The field above the surface at location 1 and 2 is zero/non-zero? The field inside the insulator at location 3 is zero/non-zero? The field inside the conductor at location 4 is zero/non-zero? Calculate the potential drop that is caused by the surface charge? delta V = Volts Imagine an AFM tip above the surface. What potential do you need to apply to the tip to null out the attractive force? Volts. You now replace the substrate with a semiconductor. Do you expect a larger or smaller voltage for the same amount of charge?

Surface Charge Double Layer Relationship. Given is the picture with an insulating charged layer that is 100 nm thick and charged to 100 elementary charges per 100 nm x 100 nm area. The layer extends in x-y direction. The charge sits on an insulator with  r = 15. Underneath the insulator is a gold film. Questions: Is the picture missing image charges in the gold substrate? (YES/NO) The field above the surface at location 1 and 2 is constant/not-constant? The field above the surface at location 1 and 2 is zero/non-zero? The field inside the insulator at location 3 is zero/non-zero? The field inside the conductor at location 4 is zero/non-zero? Calculate the potential drop that is caused by the surface charge? delta V = Volts Imagine an AFM tip above the surface. What potential do you need to apply to the tip to null out the attractive force? Volts. You now replace the substrate with a semiconductor. Do you expect a larger or smaller voltage for the same amount of charge?

Surface Charge Double Layer Relationship. Given is the picture with an insulating charged layer that is 100 nm thick and charged to 100 elementary charges per 100 nm x 100 nm area. The layer extends in x-y direction. The charge sits on an insulator with  r = 15. Underneath the insulator is a gold film. Questions: Is the picture missing image charges in the gold substrate? (YES/NO) The field above the surface at location 1 and 2 is constant/not-constant? The field above the surface at location 1 and 2 is zero/non-zero? The field inside the insulator at location 3 is zero/non-zero? The field inside the conductor at location 4 is zero/non-zero? Calculate the potential drop that is caused by the surface charge? delta V = Volts Imagine an AFM tip above the surface. What potential do you need to apply to the tip to null out the attractive force? Volts. You now replace the substrate with a semiconductor. Do you expect a larger or smaller voltage for the same amount of charge?

One More Scanning Probe Lithographic Technique that does not require electrical voltages: Dip Pen Lithography

Dip-pen lithography Coat tip of AFM with molecules that react with a gold surface. Drop of water condenses between gold surface and AFM tip. As the tip moves across the surface, the drop of water acts as a bridge for molecules to migrate from AFM tip to gold surface Slow, but can be used for many different types of molecules as inks. May be used for precise modification of circuit designs. molecules are written to the substrate high resolution, but very slow

Potential Future – Tip Arrays..

1.2 cm

Parallel Techniques: Patterning with micro and nanocontacts... outlook next lecture....

Electric Scanning Probe Lithography

Proc. Nanostructured Materials 2004 Science 291, 1763 (2001). Exposure times 10 seconds Electric Nanocontact Lithography

Hot Embossing, Injection Molding, Casting on a nanoscale... Old concepts with new names?

Emerging nanopattering methods (replication) pioneer (Whitesides)pioneer (Steven Choi) IBM Early adaptors (IBM and HP)