Vibhor Jain , Evan Lobisser, Ashish Baraskar, Brian J Thibeault, Mark Rodwell

1. High performance 110 nm InGaAs/InP DHBTs in dry-etched in-situ refractory emitter contact technology Vibhor Jain, Evan Lobisser, Ashish Baraskar, Brian J Thibeault, Mark Rodwell ECE Department, University of California, Santa Barbara, CA 93106-9560 Zach Griffith, Miguel Urteaga Teledyne Scientific & Imaging, Thousand Oaks, CA 91360 Sebastian T Bartsch Nanoelectronics Device Laboratory, EPFL, Switzerland D Loubychev, A Snyder, Y Wu, J M Fastenau, W K Liu IQE Inc., 119 Technology Drive, Bethlehem, PA 18015 vibhor@ece.ucsb.edu, 805-893-3273

2. Outline • HBT Scaling Laws • Fabrication • Challenges • Process Development • DHBT Epitaxial Design • Results • DC & RF Measurements • Summary 2

3. We Wbc Tb Tc (emitter length Le) Bipolar transistor scaling laws To double cutoff frequencies of a mesa HBT, must: Keep constant all resistances and currents Reduce all capacitances and transit delays by 2 Epitaxial scaling Lateral scaling Ohmic contacts 3

4. InP Bipolar transistor scaling roadmap Design Performance Evan Lobisser et al, IPRM 2009 4

5. Sub-200 nm HBT node: Fabrication Challenges - I Emitter yield drops during base contact, subsequent lift-off steps Fallen emitters High stress in emitter metal stack Poor metal adhesion to InGaAs Need for low stress, high yield emitters 5

6. Sub-200 nm HBT node: Fabrication Challenges - II Undercut in emitter semiconductor Helps in Self Aligned Base Liftoff InP Wet Etch Slow etch plane Fast etch plane • Narrow emitters need controlled semiconductor undercut • Thin semiconductor To prevent short, base metal needs to be thinned • Higher base metal resistance Solution: Undercut in the emitter metal to act as a shadow mask 6

7. Composite Emitter Metal Stack W emitter TiW W Erik Lind Evan Lobisser TiW emitter • W/Ti0.1W0.9 metal stack • Low stress • Refractory metal emitters • Vertical dry etch profile 7

8. M1 BCB TiW 100 nm SiNx 110 nm W 200 nm BC Junction Width via SEM, TEM 100 nm emitter metal-semiconductor junction 110 nm emitter-base junction 8

9. In-situ Emitter Contact In-situ Mo contacts* rc ~ 1.1 W.mm2 • Highly doped n-InGaAs regrown on IQE InGaAs and in-situ Mo deposited • Active carriers ~ 5×1019 cm-3 • In-situ Mo deposition on n-InGaAs - rc ~ 1.1 W.mm2 * • In-situ deposition repeatable contact resistivity * A. Baraskar et al., J. Vac. Sci. Tech. B, 27, 4, 2009 9

10. Process flow Regrown InGaAs emitter cap In-situ Mo dep W/TiW/SiO2/Cr dep SF6/Ar etch SiNx Sidewall SiO2/Cr removal InGaAs Wet Etch Second SiNx Sidewall InP Wet Etch Base Contact Lift-off W/TiW interface acts as shadow mask for base lift off Base and collector formed via lift off and wet etch BCB used to passivate and planarize devices Self-aligned process flow for 110 nm DHBT 10

11. Epitaxial Design Vbe = 1 V, Vcb = 0.7 V, Je = 0, 30 mA/m2 Thin emitter semiconductor  Enables wet etching High collector doping  High Kirk threshold 11

12. Results - DC Measurements Common emitter I-V @Peak ft,fmax Je = 23.1 mA/mm2 P = 41 mW/mm2 Peak ft,fmax BVceo = 2.5 V @ Je = 1 kA/cm2 β = 18 Base ρsheet = 730Ω/□, ρc < 4Ω·µm2 Collector ρsheet = 12 Ω/□, ρc = 9Ω·µm2 Gummel plot 12

13. S G G DUT Open Short Results - RF Measurements using Off-Wafer LRRM * Koolen et al., IEEE BCTM 1991 Standard Off Wafer LRRM Open & Short Pad Cap Extraction 13

14. 1-67 GHz RF Data and Extrapolated Cutoff Frequencies Ic = 8.9 mA Vce = 1.74 V Je = 23.1 mA/mm2 Vcb = 0.7 V Single-pole fitto obtain cut-off frequencies 14

15. Parameter Extraction Jkirk = 32 mA/mm2 (@Vcb = 0.7V) Ccb/Ic = 0.43 psec/V 15

16. Equivalent Circuit Rex ≈ 3.6 Wmm2 Hybrid-p equivalent circuit from measured RF data 16

17. w ~ 1.7 mm t ~ 1 mm h ~ 1 mm BCB Microstrip Style TRL Calibration Ref Plane for TRL Ref Plane for TRL A A’ A – A’ Ref Plane set at device edge No further de-embedding required Metal 1 Collector Metal 17

18. 140-180GHz RF data Ic = 9.1 mA Vce = 1.75 V Je = 23.6 mA/mm2 Vcb = 0.7 V -20dB/decade fitto obtain cut-off frequencies 18

19. Conclusion • Demonstrated smallest junction width for a III-V DHBT (110 nm) • Peak ft/fmax = 465/660 GHz • Je = 23.6 mA/mm2 • Power Density (P) = 41 mW/mm2 • High current and power density operation (P > 50 mW/mm2) 19

20. Thank You Questions? This work was supported by the DARPA THETA program under HR0011-09-C-0060 and DARPA TFAST under N66001-02-C-8080. A portion of this work was done in the UCSB nanofabrication facility, part of NSF funded NNIN network and MRL Central Facilities supported by the MRSEC Program of the NSF under award No. MR05-20415