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Lawrence Berkeley National Laboratory C. Tindall, P. Denes, S. E. Holland, N. Palaio, D. Contarato, D. Doering Thin Contact Development for Silicon Detectors.

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Presentation on theme: "Lawrence Berkeley National Laboratory C. Tindall, P. Denes, S. E. Holland, N. Palaio, D. Contarato, D. Doering Thin Contact Development for Silicon Detectors."— Presentation transcript:

1 Lawrence Berkeley National Laboratory C. Tindall, P. Denes, S. E. Holland, N. Palaio, D. Contarato, D. Doering Thin Contact Development for Silicon Detectors Lawrence Berkeley National Laboratory, Berkeley, CA D.E. Larson, D.W. Curtis, S.E. McBride, R.P. Lin 1 Space Sciences Laboratory, University of California Berkeley, Berkeley, CA Also Physics Department, University of California, Berkeley, CA

2 Lawrence Berkeley National Laboratory 2 Thermco/Expertech 150mm furnaces 150 mm Lithography tool LBNL Microsystems Laboratory LBNL Microsystems Laboratory – Class 10 Cleanroom

3 Lawrence Berkeley National Laboratory Silicon Semiconductor Detectors High purity - Si (n-type) 200 to 300  m SiO 2 n + contact p + B - implant Al Electrode 3 e-e- h+h+ h  (high energy) -Absorbed in the active volume. h (low energy) - Absorbed in the contact.

4 Lawrence Berkeley National Laboratory CCD Project 4 LBNL Engineering Group – 200 fps CCDs for direct detection of low-energy x-rays Amplifiers every 10 columns, metal strapping of poly, and custom IC readout

5 Lawrence Berkeley National Laboratory MSL Processed Silicon Detector Wafer 5

6 Lawrence Berkeley National Laboratory Instrument Size WIND 3-D Plasma and Energetic Particle Experiment Suprathermal Electron Telescope Element (STEREO-IMPACT) (UC Berkeley Space Sciences Lab) 6

7 Lawrence Berkeley National Laboratory In-Situ Doped Polysilicon 7 W127 A3 Detector Area =0.09 cm 2 Baseline Process – In-situ phosphorus doped polysilicon (ISDP). It yields a thin (≤200Å), low leakage (~300 pA/cm ambient temp) contact. Deposition temperature is >600°C so it can not be used on devices with metal. In LBNL’s PIN diode and CCD processes it is deposited before the metal. /cm 2 )

8 Lawrence Berkeley National Laboratory Thin backside n + ohmic contact development The thin backside n + contact technology developed at the MSL is an enabling technology for a)Photodiodes for medical applications b)CCDs c)Charged-particle detectors in space SIMS depth profile ISDP – in-situ doped polysilicon 8

9 Lawrence Berkeley National Laboratory In-Situ Doped Polysilicon Contact 9 Energy lost by the protons in the contact is about 2.3 keV. Data taken by R. Campbell at UC Berkeley’s Space Sciences Laboratory

10 Lawrence Berkeley National Laboratory In-Situ Doped Polysilicon Contact 10 Energy lost by electrons in the 200Å doped polysilicon window is about 353 eV. Data taken by D. Larson at UC Berkeley’s Space Sciences Laboratory

11 Lawrence Berkeley National Laboratory In-Situ Doped Polysilicon Contact 11 Spectrum obtained by illuminating a PIN diode to a mixed 55 Fe and 109 Cd source. The detector has a 200Å in-situ doped polysilicon entrance contact. Data taken by D. Curtis at UC Berkeley’s Space Sciences Laboratory.

12 Lawrence Berkeley National Laboratory MSL detectors on NASA space missions Mars Atmosphere and Volatile Evolution (MAVEN) - MAVEN will make definitive scientific measurements of present-day atmospheric loss that will offer clues about the planet's history. - To date, the MSL has provided 36 thin window detectors for MAVEN. 16 detectors have been selected for flight as part of the Solar Energetic Particle (SEP) Instrument. - Launch: late Mock up of the SEP Instrument Prototype Detector Stack

13 Lawrence Berkeley National Laboratory MSL detectors on space missions Charged particle detectors fabricated in the MSL by Craig Tindall –CINEMA – Understanding space weather –Solid State Telescopes (two for ions, two for electrons per spacecraft) –104 detectors delivered, 80 used in flight THEMIS PIN Diode Fabricated in the MSL

14 Lawrence Berkeley National Laboratory MSL detectors on NASA space missions THEMIS Update –Launched in 2007, all major science goals were achieved by 2009 –MSL detectors on all five spacecraft are still returning science data. –ARTEMIS – extended mission to study the interaction of the moon with the solar wind. Two THEMIS spacecraft diverted to the moon. –These two “ARTEMIS” spacecraft are now in lunar orbit.

15 Lawrence Berkeley National Laboratory STEIN Detector (First Design) 15 Low Energy Threshold (1-2 keV) ~1 keV Energy Resolution Sensitive to Electrons, Ions, and Neutrals (But Can’t Separate) 4 x 1 Pixel Array Flight Heritage: STEREO Mission STE Instrument (SupraThermal Electrons) (STE) Silicon Semiconductor Detector

16 Lawrence Berkeley National Laboratory STEIN Instrument Collimator ± 2000 V Field Separates Electrons, Ions, and Neutrals to ~20 keV Particle Attenuator (Blocks 99% of Particles) Initial Version of the Instrument – Designed by Space Sciences Laboratory

17 Lawrence Berkeley National Laboratory MSL detectors on an NSF space mission Cubesat for Ions, Neutrals and Magnetic Fields (CINEMA) –Mission consists of four “triple” cubesats, small satellites (10cm x 10cm x 30cm) Two will be made by UC Berkeley’s Space Sciences Laboratory and two by Kyung Hee University in South Korea. –Each cubesat contains a magnetometer and a Suprathermal Electrons, Ions and Neutrals (STEIN) instrument. STEIN contains a 30 pixel array of detectors with a thin entrance window. –First spacecraft has been delivered. Launched: September Cubesat Mock-up STEIN Detectors and Readout ASIC

18 Lawrence Berkeley National Laboratory MSL detectors on NASA space missions Solar Probe Plus (SPP) – Prototyping Phase - Mission to study the sun close-up. The closest approach – 9.5 solar radii. - Prototype detectors for the Low Energy Telescope in the EPI-HI instrument are being fabricated in the MSL. - Detectors with active volumes that are 10  m and 25  m thick are required. - Launch –  m SiO 2 p + B - implant Al Electrode Handle Wafer Back Contact Active Layer – 10  m n + P - Implant

19 Lawrence Berkeley National Laboratory Thin Silicon Alpha Spectrum 19

20 Lawrence Berkeley National Laboratory Other Thin Contact Techniques - Commercial silicon detectors (PIN diodes) are available with contacts that are ≥500Å thick. (ion implantation) - Reported leakage currents are roughly 20nA/cm 2. - A 500Å contact transmits only about 65% of 280eV photons into the active volume of the detector. -A thinner contact is needed to get high efficiency at 280eV (C - K edge). 20

21 Lawrence Berkeley National Laboratory Silicon x-ray Transmission 21

22 Lawrence Berkeley National Laboratory Thin Contact Fabrication Techniques 22 TechniqueThickness (Å) Compatible with metal? %Transmission at 280eV Amorphous Si≥300Yes≤77 In-situ doped poly200No84 Implant/Anneal~1000Yes42 Implant/Laser~700Yes54 MBE≤100Yes≥92

23 Lawrence Berkeley National Laboratory Implant/Low Temperature Anneal 23 - ISDP is a very useful process for making thin contacts. However: a.) The deposition temperature ≥600°C so it can’t be used ondevices with metal. b.) Integration with the CCD process is complex. c.) Integration with CMOS processes used to make active pixel sensors is impossible. - For applications that do not require the thinnest contact we developed a much simpler alternative – ion implantation and low temperature annealing – that does not damage the metal. - Informally referred to as our “pizza process”.

24 Lawrence Berkeley National Laboratory Implant/Low Temperature Anneal 24 - Leakage current ranges from about 600 pA/cm 2 to several nA/cm 2 at 100V bias and ambient temperature with this method. - The window thickness is about 1000Å of silicon. - Good uniformity. Used successfully with our largest CCD – cm 2. Our CCDs that utilize “pizza process” contacts for soft x-ray detection.

25 Lawrence Berkeley National Laboratory Implant/Low Temperature Anneal 25 SOI Imager (Active Pixel Sensor) Guibilato, et. al. NIM A 650(2011) 184

26 Lawrence Berkeley National Laboratory Implant/Low Temperature Anneal 26 After Thinning Before Thinning After the “Pizza” Process SOI Imager-2 (Active Pixel Sensor) Battaglia, et. Al. NIM A 676 (2012) 50

27 Lawrence Berkeley National Laboratory Implant/Laser Anneal 27 - Gives only a nominal decrease in the window thickness from 1000Å to an estimated 700Å. - Requires a significant amount of stitching. Stitching only in one direction works at some level. The yield is about 80%. - X-Y stitching doesn’t seem to give low enough leakage current, but our testing of this is limited. - Bottom line – further testing needed to optimize the process. Most likely a laser with a larger spot size would improve the result significantly.

28 Lawrence Berkeley National Laboratory Chemical Etching/a-Si 28 - Surface is chemically etched, then a 300Å thick layer of a-Si is sputtered onto the surface. It is essentially a room temperature process. - The defects on the surface form the contact. One obtains the same contact properties with or without the a-Si. - The contact thickness has not been measured.

29 Lawrence Berkeley National Laboratory - Ideally a single monolayer of electrically active dopant atoms is desired. - The silicon capping layer is required to form a stable contact. Molecular Beam Epitaxy (MBE) 29 Contact Configuration Incoming x-rays Silicon cap layer  -doping layer Silicon device Front side pattern/electronics The Key: - This is a deposited contact, so the beginning surface defect density must be low in order to obtain low leakage current. Pioneering work on  -doped contacts was done by Nikzad’s group at JPL. IEEE TED, 55, Dec. 2008

30 Lawrence Berkeley National Laboratory Molecular Beam Epitaxy (MBE) 30 Load Lock Buffer Chamber MBE Chamber Base Pressure ~5x torr e-beam gun (silicon) Sb or B Knudsen Cell Substrate

31 Lawrence Berkeley National Laboratory Molecular Beam Epitaxy (MBE) 31 Deposition Chamber Load-Lock Substrate Preparation Chamber Typical SVT Associates Silicon MBE System

32 Lawrence Berkeley National Laboratory Thin Contact Fabrication Techniques 32 TechniqueAdvantagesDisadvantages Amorphous SiliconRoom Temperature ProcessLeakage current varies significantly from run to run, n-type only. Implant/Low Temp AnnealLow temperature, low leakage, simple process, high yield. Relatively thick contact. Implant/Laser AnnealPatterned side of the wafer is at room temperature. Leakage current is somewhat variable, thicker than optimal. MBELow temperature, low leakage, ultimately thin contact. Complex equipment and process. In-situ doped poly.Thin contact, low leakage.Process temperature too high for metalized devices. Implant/Flash UVThin contact, low leakage.Process temperature too high, expensive equipment.

33 Lawrence Berkeley National Laboratory Silicon x-ray Transmission 33 Implant/Low Temperature Anneal “Pizza Process” MBE

34 Lawrence Berkeley National Laboratory Fine Pitch Germanium Strip Detector 34 Developed for time-resolved x-ray absorption spectroscopy J. Headspith, et al., Daresbury Lab 1024 strips, 50  m pitch, 5 mm length 1 mm thick detector ~ 30 pA / V b = 55 V, T >100 K

35 Lawrence Berkeley National Laboratory Detector Group at LBNL 35 One of the first groups to develop lithium-drifted Si detectors (early 1960’s) One of two groups that originally developed high-purity Ge crystal growth (early 1970’s) Fabrication technologies developed include: amorphous semiconductor contact, implanted contact, and surface passivation Invented shaped-field point-contact Ge detector (1989) Invented coplanar-grid technique for CdZnTe-based detectors (1994) Historical accomplishments with significant impact on radiation detector technology:

36 Lawrence Berkeley National Laboratory Summary 36 - Thin contacts are needed for imaging soft x-rays. - The techniques of most interest appear to be: 1.) implant/low temperature anneal or “pizza” process 2.) Molecular Beam Epitaxy (MBE) - Germanium may be useful for higher energies. We have produced strip detectors with 50  m pitch for use at light sources. - Thin contacts also have application in other fields of science, for example - space science.


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