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MOCVD Emitter Regrowth Technology for Scaling InGaAs/InP HBTs to Sub-100nm Emitter Width

Choudhary, Prateek
Degree Grantor:
University of California, Santa Barbara. Electrical & Computer Engineering
Degree Supervisor:
Mark JW Rodwell
Place of Publication:
[Santa Barbara, Calif.]
University of California, Santa Barbara
Creation Date:
Issued Date:
Electrical engineering
Dissertations, Academic and Online resources
Ph.D.--University of California, Santa Barbara, 2015

By scaling semiconductor thicknesses, lithographic dimensions, and contact resistivities, the bandwidth of InGaAs/InP Hetero-junction Bipolar Transistors (HBTs) has reached 550/1100 GHz ft/f max at 128 nm emitter width (wE). Primary challenges faced in scaling the emitter width are: developing high aspect ratio emitter metal process for wE < 100nm, reducing base contact resistivity rhob,c, and maintaining high DC current gain beta.

The existing W/TiW emitter process for RF HBTs cannot scale below 100 nm. Process modules for scaling the emitter width to 60 nm are demonstrated. High aspect ratio trenches are etched into a sacrificial Si layer and then filled with metal via Atomic Layer Deposition (ALD). Metals with high melting points are chosen to withstand high emitter current densities (J E) at elevated junction temperatures without suffering from electromigration or thermal decomposition and is thus manufacturable. ALD deposition of TiN, Pt, and Ru are explored.

Novel base epi designs are proposed for reducing Auger recombination current (IB,Auger). A dual doping layer in the base is proposed with a higher doping in the upper 5 nm of the base for lower rho b,c and a lower doping in the remainder of the base for reducing IB,Auger. Presence of a quasi-electric field (DeltaEC) in the upper doping grade accelerates electrons away from the region towards the collector, thus further reducing IB,Auger.

Selective regrowth of the emitter semiconductor via Metal-Organic Chemical Vapour Deposition (MOCVD) is proposed for decoupling the extrinsic base region under the base metal from the intrinsic region under the emitter-base junction, for increasing beta,ft, and improving rho b,c. Carbon p-dopants in the InGaAs base are passivated by H+ during regrowth. Annealing to reactivate carbon induces surface damage and increases base sheet resistance (Rb,sh) and rhob,c. Process techniques for minimizing Rb,sh and rhob,c in an emitter regrowth process are demonstrated and compared. rhob,c of 5.5 .mum2 on p-InGaAs is demonstrated on Transmission Line Measurement (TLM) structures after regrowth and anneal, by protecting the semiconductor surface with tungsten. This is comparable to 2.9 O.mum2 measured on TLM structures that do not undergo regrowth and anneal.

Feasibility of emitter regrowth is demonstrated on Large Area Devices (LADs) with SiO2 as regrowth mask, and W cap during anneal. Emitter-regrowth and non-regrowth devices of identical dimensions and epi design are compared. Emitterregrown HBTs yield higher beta of 28 as compared to 13 for non-regrowth devices. Benefits of emitter regrowth cannot be ascertained on LADs due to high series resistance and large gap spacings between base metal and emitter-base junction.

A process flow is proposed for scaling regrown HBTs to 60 nm emitter widths. The process incorporates ALD emitter metal technology that is demonstrated in the first half of the dissertation. New epi designs for regrown-emitter HBTs are optimized for maximizing beta, ft. Scaling regrown-emitter HBTs is essential for realizing their benefit over non-regrowth HBTs.

Physical Description:
1 online resource (130 pages)
UCSB electronic theses and dissertations
Catalog System Number:
Inc.icon only.dark In Copyright
Copyright Holder:
Prateek Choudhary
File Description
Access: Public access
Choudhary_ucsb_0035D_12885.pdf pdf (Portable Document Format)