Hybridization of a sigma-delta-based CMOS hybrid detector Kolb, K.E. a ; Stoffel, N.C. c, Douglas, B. c ; Maloney, C.W. a ; Raisanen, A.D. b ; Ashe, B. a ; Figer, D.F. a ; Tamagawa, T. d ; Halpern, B. d a Rochester Imaging Detector Lab, 54 Lomb Memorial Dr., 76-A230, Rochester, USA; b Rochester Institute of Technology IT Collaboratory, 74 Lomb Memorial Dr., Rochester, USA; c Infotonics Technology Center, 5450 Campus Dr., Canandaigua, USA d Jet Process Corporation, 57B Dodge Avenue, North Haven, USA

22 Outline Introduction Process development Initial results Future work

3 Introduction: Detector Back-illuminated Silicon PIN diode, 250 μm thick 15 μm pixels, 256x128 array 50 V reverse bias during integration 0.1 pA/cm 2 at 200 K (1 e - per second per pixel) dark current expected by design Multi-temperature operation

4 Introduction: ReadOut Integrated Circuit (ROIC) CMOS readout circuitry (3T) Sigma-delta sampling (very low read noise) For more information, see Zeljko Ignjatovic’s talk Tuesday at 4:10pm –“Fully digital image sensor employing sigma-delta indirect feedback ADC with high-sensitivity to low-light illuminations for astronomical imaging applications”

55 Introduction: Hybridization 100% fill factor of illuminated surface Individual pixel addressing hνhν

66 Introduction: Roadmap for Hybridization Process Design Structure for Metal Bump Formation Develop Process for Polymer Structure Fabrication Evaluate Polymer Structure Efficacy Test Sacrificial Structure (LOR) Removal Test Metal Deposition Process Test Reflow of Bump Metal Evaluate Alignment Process and Tolerance Evaluate Bond Integrity Polymer Structure Development Metal Deposition Bump Bonding Process

77 Process Development: Design Structure for Metal Bump Formation Bump Metal Aluminum Contact LOR Silicon Substrate ROIC / Detector LOR Bump Metal Photosensitive Resist LOR Bump Metal

88 Process Development: Polymer Structure Fabrication Key Dimensions: Opening in the photosensitive resist over the contact pads (7μm). Base opening of the LOR layer around the contact pads (8-9μm). Height of the LOR layer in the polymer structure (4μm). All points received a bake at 170 °C for 5 minutes. 170 °C was chosen based on etch rate of the LOR (a separate experiment) and the bake time of 5 minutes is based on the manufacturer’s recommendation. 7 μm 8-9 μm 4 μm A spin speed of 2000 rpm for 45 seconds gives a thickness of 4 μm to the LOR layer.

9 LOR Height 9 Process Development: Polymer Structure Fabrication Before fabricating the sacrificial polymer structure on working die, the structure was first built on bare silicon wafers to prove the viability of the fabrication process. 7 μm 8-9 μm 4 μm 7 μm 9 μm 4.1 μm

10 Process Development: Metal Deposition Process Collimated jet of gas (Argon/Helium) Inert Gas Into the System Vapor Source Collimated Jet V=10 3 cm / s Substrate Localized Deposition Choked Flow Bump metal is vaporized and enters gas jet Evaporated metal atoms bond together into nanoclusters Highly perpendicular trajectory at impact Vaporization Chamber

11 Process Development: Evaluate Alignment Process Mirrors show alignment marks on both die and an operator can align them using the tool’s relative positioning Verification of alignment after hybridization is accomplished with a real-time infrared optical system. Alignment Mark

12 Initial Results: Polymer Structure Fabrication Polymer structure before metal deposition. Photosensitive Resist Opening is 7.0 μm in diameter, the LOR Base Opening is 8 μm, and the LOR Height is 4.0 μm. LOR Base Opening LOR Height

13 Initial Results: Sacrificial Polymer Structure Efficacy AuSn deposited on top of the sacrificial polymer structure Indium deposited on top of the sacrificial polymer structure Missing Overhangs in Photosensitive Resist Layer

14 Initial Results: Polymer Structure Removal and Reflow AuSn before reflow Indium after deposition AuSn after reflow

15 Initial Results: Bond Integrity Image with focus set at bump plane to highlight the material left after pull test (demonstrating that failure occurred inside the bumps rather than at the interface between the bumps and the bonding pads). 5 kg bond force was used to bond and 2.2 kg pull (separation) force was required to separate the die.

16 Initial Results: Bond Integrity Evaluation Examples of “taffy pull” failures Pull test gives strength of bond between die Best failure mode is ductile –“taffy pull”

17 Future Work: Planned Increase strength of photosensitive resist overhangs to withstand JVD metal deposition –change thickness / material for photosensitive resist Once bump size is correct, hybridize and test bond integrity Electrical testing / characterization of the hybridized device

18 Future Work: Alternative Materials for Polymer Structure Photosensitive Resist Opening LOR Base Opening LOR Height 2.2 μm 5 μm 4.5 μm Sacrificial polymer structure (new photosensitive resist on top of LOR) on a bare Silicon wafer. All dimensions are small, but this can be addressed in future process development.

19 References (1) Gorski, Mike; Halpern, Bret. "Jet Vapor Deposition for AuSn Solder Applications". Advanced Packaging, February, (2) Komarenko, Paul et. al. "Jet Vapor Deposition". Chapter 18 in Handbook of Deposition Technologies for Films and Coatings, 3rd Edition, edited by Peter Martin, Elsevier, (3) Ingjatovic, Zeljko et. al. “Fully digital image sensor employing sigma-delta indirect feedback ADC with high-sensitivity to low-light illuminations for astronomical imaging applications”. SPIE Conference Proceedings, Astronomical Telescopes and Instrumentation. June, 2010.

20 Acknowledgements The author would also like to thank: BAE Systems, Inc. Dr. Karl Hirschman (Rochester Institute of Technology) Christopher Shea (Rochester Institute of Technology) Almon Fisher (Infotonics Technology Center) This material is based upon work supported by the National Aeronautics and Space Administration under Grant NNX07AG99G, issued through the Astronomy and Physics Research and Analysis Program of the Science Mission Directorate. Part of this research was performed in the Rochester Imaging Detector Laboratory and was supported by a NYSTAR Faculty Development Program grant for D. Figer.