High Temperature Ohmic Contact Technology to N-Type Gaas James Eun Purdue University School of Electrical Engineering

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High Temperature Ohmic Contact Technology to N-Type Gaas James Eun Purdue University School of Electrical Engineering Purdue University Purdue e-Pubs ECE Technical Reports Electrical and Computer Engineering 1-1-1993 High Temperature Ohmic Contact Technology to N-Type GaAs James Eun Purdue University School of Electrical Engineering James A. Cooper Jr. Purdue University School of Electrical Engineering Follow this and additional works at: http://docs.lib.purdue.edu/ecetr Eun, James and Cooper, James A. Jr., "High Temperature Ohmic Contact Technology to N-Type GaAs" (1993). ECE Technical Reports. Paper 218. http://docs.lib.purdue.edu/ecetr/218 This document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact [email protected] for additional information. TR-EE 93-7 JANUARY 1993 High Temperature Ohmic Contact Technology to N-Type GaAs Submitted as a Final Technical Report to Allied Signal Aerospace Corp. 717 N. Bendix Dr. South Bend, IN 46620 James Eun James A. Cooper, Jr. School of Electrical Engineering Purdue University West Lafayette, IN 47907 January, 1993 TABLE OF CONTENTS page LIST OF FIGURES ............................................................................................. iv ABSTRACT ........................................................................................................... vii CHAPTER 1.1 Characteristics of GaAs ................................................................... 1 1.2 High Temperature Electronics .......................................................... 3 1. 3 High Temperature Ohmic Contact Technology ............................... 4 1.4 Thesis Overview ............................................................................... 5 CHAFI'ER 2 . BACKGROUND ............................................................................. 6 2.1 Ohmic Contacts ............................................................................ 6 2.1.1 Specific Contact Resistance ................................................ 6 2.1.2 Metal-Semiconductur Interface .............................................9 2.1.3 Conduction Mechanisms...................................................... 12 2.2 Au/Ge/Nirri Ohmic Contacts to N-type GaAs ................................ 14 2.3 High... Temperature Ni/AUiio/GeJIn Ohmic Contact. ....................19 2.4 Rehabhty Prediction......................................................................... 19 2.4.1 Arrhenius Equation................................................................ 21 2.4.2 Assumptions......................................................................... 22 CHAPER 3. HIGH TEMPERATURE OHMIC CONTACT FABRICATION TECHNOLOGY ............................................................................. 24 3.1 Overview of High Temperature Ohmic Contact Fabrication ........... 24 3.2 Evaporation/Sputterin@tching Systems ......................................... 26 3.2.1 Varian E-beam Evaporation System.................................... 26 3.2.2 Airco E-beam System. ......................................................... 27 Page 3.2.3 NRC Thermal Evaporation System. ..................................... 28 3.2.4 MRC 8620 Sputter System................................................... 29 3.2.5. Technics. Plasma Etch System. ............................................. 29 3.3 Fabnca~onTechnology ................................................................. 35 3.3.1 Lift-off .................................................................................. 35 3.3.2 Etch....................................................................................... 37 3.3.3 Metal Evaporation................................................................ 38 3.3.4 Rapid Thermal Annealing..................................................... 39 3.3.5 SputttredSiliconNitrideChaacterhtion.......................... 41 CHAP'IER 4 . MEASUREMENT TECHNIQUES................................................. 54 4.1 Transfer Length Model..................................................................... 54 4.2 N-i-P-i-N Storage Capacitor............................................................. 62 4.3 Mask Design .....................................................................................66 5.1 Ni/Al/ri/MoK;& High Temperature Ohmic Contact ................... 69 5.1.1 Effect of RTA on I-V CharactMistics................................... 69 5.1.2 Thermal Stability of High Temperature Ohmic Contacts.... 71 5.1.3 Spiking Effect .....................................................................77 5.1.4 Modification of Contact Structure ....................................... 77 5.2 Au/Ge/Ni/Ti Non-High Temperature Ohmic Contact..................... 81 5.3 Morns Non-Alloying Ohmic Contact ......................................... 87 CHAFER 6 . SUMMARY AND RECOMMENDATION mR FUTURE WORK ..............................................................................................89 REFERENCES .........................................................................................................92 APPENDIX............................................................................................................. 97 LIST OF FIGURES Figure Page 1.1 Drift velocity of electrons in GaAs and Si................................................... 2 2.1 A slab of semiconductor with ohmic contacts at the two ends .................... 8 2.2 Planar contact structure with the imaginary plane ....................................... 8 2.3 Accumulated type contact ............................................................................ 10 Depleted type contact ................................................................................. 10 Fermi level pinning due to the surface states ................................................ 11 Conduction mechanisms ............................................................................... 13 Band diagram of an abrupt InAsIGaAs heterojunction................................ 15 Au/Ge/Ni/Ti ohmic contact system at Purdue University ............................ 18 Ni/AWio/Ge/In ohmic contact system at Purdue University.................. 20 MTBF vs l/r plot ..................................................................................... 23 MTBF vs l/r plot due to failure mechanisms obeying the Arrhenius equation with activation energies of 0.5. 1.0. 1.5. and 2.0 eV ..................... 23 Ni/AlEi/Mo/Ge/In high temperature ohmic contact process 0vervie.w....... 25 Varian E-beam evaporation system .............................................................30 3.3 Airco E-beam evaporation system ............................................................... 31 3.4 NRC thermal evaporation system ..................................................................32 3.5 Tungsten filament for A1 evaporation ......................................................... 32 Figure Page A1 layer after thermally stressing at 400 'C for 1 hour................................ 33 MRC 8620 sputter sysm............................................................................ 34 (a) Four Merent areas with different dissolution rate. and (b) photoresist profile after the development...................................................................... 36 Ni/Wi/MoKielIn high temperature ohmic contact after 850 'C. 5 seconds RTA ................................................................................................ 40 Auger plot of Ni/AUTi/Mo/Ge/In contact after RTA ................................... 42 Sputtered silicon nitride layer (a) with argon gas only. and (b) with 1: 1 argon:nitrogen gas mixture ........................................................................... 43 Characterization of silicon nitride sputtering process.................................. 46 Sputtered silicon nitride layer (a) before and (b) after RTA ........................ 49 Sputtered silicon nitride after RTA .............................................................. Sputtered silicon nitride after RTA with surface treatment ........................ 53 4.1 (a) Ohmic contact model. and (b) transmission line equivalent circuit ....... 55 4.2 TLM test structure........................................................................................ 60 4.3 Total resistance between two TLM pads with variable spacing.................. 60 4.4 End resistance measurement ........................................................................ 61 4.5 Film structure used for non-alloying Mo/InAs contact............................... 63 4.6 Film structure used for Ni/Al/I'i/Mo/Ge/ln high temperature contact........ 64 4.7 N-P-N capacitor and charge storage band diagrant ..................................... 65 4.8 High temperature ohmic contact test mask design .................................. 67 4.9 TLM co guration....................................................................................... 68 5.1 I-V curves for Ni/A]/ri/Mo/G& TLM structures ..................................... 70 5.2 Change in spedlc contact resistance without the surface passivation ........ 72 5.3 Change in Wiccontact resistance with the surface passivation ............. 72 nfi Figure Page 5.4 MTBF vs l/r for high temperature ohmic contacts ..................................... 74 5.5 High temperature contacts after thermal stress ............................................. 75 5.6 Capacitance vs time for high temperature contacts before RTA .................. 78 . 5.7 Capacitance vs time for high temperature contacts after RTA .................... 78 5.8 High temperature ohmic contact structure
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