Presentation on theme: "Thin Contact Development for"— Presentation transcript:
1 Thin Contact Development for Silicon DetectorsC. Tindall, P. Denes, S. E. Holland, N. Palaio,D. Contarato, D. DoeringLawrence Berkeley National Laboratory, Berkeley, CA 94720D.E. Larson, D.W. Curtis, S.E. McBride, R.P. Lin1Space Sciences Laboratory, University of California Berkeley, Berkeley, CA1Also Physics Department, University of California, Berkeley, CA
2 LBNL Microsystems Laboratory Thermco/Expertech 150mm furnaces150 mm Lithography toolLBNL Microsystems Laboratory – Class 10 Cleanroom
3 Silicon Semiconductor Detectors Al ElectrodeSiO2p+ B - implant200 to 300 mmHigh purity - Si(n-type)h+e-n+ contacthn (high energy)Absorbed in theactive volume.hn (low energy)-Absorbed in thecontact.
4 CCD ProjectLBNL Engineering Group – 200 fps CCDs for direct detection of low-energy x-raysAmplifiers every 10 columns, metal strapping of poly, and custom IC readout
6 Instrument Size WIND 3-D Plasma and Energetic Particle Experiment Suprathermal Electron TelescopeElement (STEREO-IMPACT)(UC Berkeley Space Sciences Lab)
7 In-Situ Doped Polysilicon Baseline Process – In-situ phosphorus doped polysilicon (ISDP).It yields a thin (≤200Å), low leakage (~300 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.W127 A3Detector Area =0.09 cm2/cm2)
8 Thin backside n+ ohmic contact development SIMS depth profileISDP – in-situ dopedpolysiliconThe thin backside n+ contact technologydeveloped at the MSL is an enablingtechnology forPhotodiodes for medical applicationsCCDsCharged-particle detectors in space
9 In-Situ Doped Polysilicon Contact Energy lost by the protons in the contact is about 2.3 keV.Data taken by R. Campbell atUC Berkeley’s Space Sciences Laboratory
10 Data taken by D. Larson at UC Berkeley’s Space Sciences Laboratory In-Situ Doped Polysilicon ContactEnergy 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 Data taken by D. Curtis at UC Berkeley’s Space Sciences Laboratory. In-Situ Doped Polysilicon ContactData taken by D. Curtis at UC Berkeley’s Space Sciences Laboratory.Spectrum obtained by illuminating a PIN diode to a mixed 55Fe and 109Cd source. The detector has a 200Å in-situ doped polysilicon entrance contact.
12 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 EnergeticParticle (SEP) Instrument.- Launch: late 2013.Prototype Detector StackMock up of the SEP Instrument
13 MSL detectors on space missions Charged particle detectors fabricated in the MSL by Craig TindallCINEMA – Understanding space weatherSolid State Telescopes (two for ions, two for electrons per spacecraft)104 detectors delivered, 80 used in flightTHEMIS PIN DiodeFabricated in the MSL
14 MSL detectors on NASA space missions THEMIS UpdateLaunched in 2007, all major science goals were achieved by 2009MSL detectors on all five spacecraft are still returning science data.ARTEMIS – extended mission to study the interaction of the moonwith the solar wind. Two THEMIS spacecraft diverted to the moon.These two “ARTEMIS” spacecraft are now in lunar orbit.
15 STEIN Detector (First Design) Low Energy Threshold (1-2 keV)~1 keV Energy ResolutionSensitive to Electrons, Ions, and Neutrals (But Can’t Separate)4 x 1 Pixel ArrayFlight Heritage: STEREO Mission STE Instrument(SupraThermal Electrons)(STE)Silicon Semiconductor Detector
16 STEIN Instrument Collimator ± 2000 V Field Separates Electrons, Ions, and Neutrals to ~20 keVParticle Attenuator(Blocks 99% of Particles)Initial Version of the Instrument – Designed by Space Sciences Laboratory
17 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 2012.Cubesat Mock-upSTEIN Detectors and Readout ASIC
18 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 instrumentare being fabricated in the MSL.- Detectors with active volumes that are 10mm and 25mm thick are required.- Launch – 2015.675 mmSiO2p+ B - implantAl ElectrodeHandle WaferBack ContactActive Layer – 10 mmn+ P - Implant
20 Other Thin Contact Techniques Commercial silicon detectors (PIN diodes) are available withcontacts that are ≥500Å thick. (ion implantation)Reported leakage currents are roughly 20nA/cm2.A 500Å contact transmits only about 65% of 280eV photons intothe active volume of the detector.A thinner contact is needed to get high efficiencyat 280eV (C - K edge).
22 Thin Contact Fabrication Techniques Thickness (Å)Compatible with metal?%Transmission at 280eVAmorphous Si≥300Yes≤77In-situ doped poly200No84Implant/Anneal~100042Implant/Laser~70054MBE≤100≥92
23 Implant/Low Temperature Anneal - ISDP is a very useful process for making thin contacts.However: a.) The deposition temperature ≥600°C so itcan’t be used on devices with metal.b.) Integration with the CCD process is complex.c.) Integration with CMOS processes used to makeactive pixel sensors is impossible.For applications that do not require the thinnest contact wedeveloped a much simpler alternative – ion implantation andlow temperature annealing – that does not damage the metal.- Informally referred to as our “pizza process”.
24 Implant/Low Temperature Anneal Our CCDs that utilize “pizza process” contacts for soft x-ray detection.Leakage current ranges from about 600 pA/cm2 to several nA/cm2at 100V bias and ambient temperature with this method.The window thickness is about 1000Å of silicon.Good uniformity. Used successfully with our largest CCD – cm2.
25 Implant/Low Temperature Anneal Guibilato, et. al. NIM A 650(2011) 184SOI Imager (Active Pixel Sensor)
26 Implant/Low Temperature Anneal After ThinningBefore ThinningAfter the“Pizza”ProcessSOI Imager-2 (Active Pixel Sensor)Battaglia, et. Al. NIM A 676 (2012) 50
27 Implant/Laser AnnealGives only a nominal decrease in the window thickness from 1000Åto an estimated 700Å.Requires a significant amount of stitching. Stitching only in one directionworks at some level. The yield is about 80%.X-Y stitching doesn’t seem to give low enough leakage current, but ourtesting of this is limited.Bottom line – further testing needed to optimize the process. Most likely alaser with a larger spot size would improve the result significantly.
28 Chemical Etching/a-Si Surface is chemically etched, then a 300Å thick layer of a-Siis sputtered onto the surface. It is essentially a roomtemperature process.The defects on the surface form the contact. One obtains thesame contact properties with or without the a-Si.The contact thickness has not been measured.
29 Molecular Beam Epitaxy (MBE) Contact ConfigurationIdeally a single monolayer of electrically active dopant atoms is desired.The silicon capping layer is required to form a stable contact.Incoming x-raysSilicon cap layerd-doping layerSilicon deviceThe Key:This is a deposited contact, sothe beginning surface defectdensity must be low in orderto obtain low leakage current.Front side pattern/electronicsPioneering work on d-doped contacts was done by Nikzad’s group at JPL.IEEE TED, 55, Dec. 2008
32 Thin Contact Fabrication Techniques AdvantagesDisadvantagesAmorphous 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 UVProcess temperature too high, expensive equipment.
33 Silicon x-ray Transmission MBEImplant/Low Temperature Anneal“Pizza Process”
34 Fine Pitch Germanium Strip Detector 1024 strips, 50 mm pitch, 5 mm length1 mm thick detector~ 30 pA / Vb = 55 V, T >100 KDeveloped for time-resolved x-ray absorption spectroscopyJ. Headspith, et al., Daresbury Lab
35 Detector Group at LBNLHistorical accomplishments with significant impacton radiation detector technology: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 passivationInvented shaped-field point-contact Ge detector (1989)Invented coplanar-grid technique for CdZnTe-based detectors (1994)
36 Summary Thin contacts are needed for imaging soft x-rays. The techniques of most interest appear to be:1.) implant/low temperature anneal or “pizza” process2.) Molecular Beam Epitaxy (MBE)Germanium may be useful for higher energies. We have producedstrip detectors with 50mm pitch for use at light sources.Thin contacts also have application in other fields of science,for example - space science.