An Investigation of Local Nanomorphology and Doping at the Metal-semiconductor Interface

Open Access
Author:
Lin, Joyce Chia-i
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
January 11, 2013
Committee Members:
  • Suzanne E Mohney, Committee Chair
  • Douglas Edward Wolfe, Dissertation Advisor
  • Suman Datta, Committee Member
  • Joan Marie Redwing, Committee Member
Keywords:
  • ohmic contacts
  • compound semiconductors
  • transmission electron microscopy
  • InGaAs
  • GaAs
  • III-V compounds
  • transistors
Abstract:
The fabrication and characterization of ohmic contacts to n-InGaAs epilayers and methods of engineering the metal/InGaAs interface to reduce contact resistance are addressed in this thesis. InGaAs is an important material for the continued development of high speed, aggressively scaled transistors, and a fundamental understanding of the formation and behavior of low-resistance ohmic contacts to InGaAs is vital to address issues such as reducing parasitic resistance and improving processing reliability. Cross-sectional transmission electron microscopy (XTEM) characterization and Schottky barrier height fitting was used to better understand the origins of low contact resistance and properties after thermal annealing for non-alloyed contacts to n+- and n-In_0.53Ga_0.47As, given constant surface preparation of UV-ozone and buffered oxide etch (BOE). Two methods of engineering the metal/InGaAs interface were also explored in order to address complexities in ex situ surface preparation and the need for heavily-doped material. Enhanced topography was introduced in ohmic contacts of Ti/Pt/Au via selective etching through refractory thin film etch masks fabricated by glancing angle deposition (GLAD). Specific contact resistance was reduced up to 85%, and features with dimensions 30-50 nm wide and 2-3 nm deep were obtained. This method shows potential as a method for introducing controlled nanomorphology at a substrate surface. A Pd/Si/Pd solid-phase regrowth (SPR) contact was fabricated using a low-temperature, two-step annealing process that resulted in the formation of shallow, ultra-low resistance ohmic contacts with little lateral diffusion. An optimum Pd/Si atomic ratio of 1.5 was needed for the SPR process to result in extremely low specific contact resistances on the order of 9x10^-8 and 1.8x10^-8 Ω-cm^2, respectively, for both lightly and heavily-doped n-InGaAs. I-V-T measurements and Schottky barrier height modeling was used to calculate the addition of increased Si dopant concentration of about 1.0x10^19 cm^-3 at the InGaAs interface from the SPR process. XTEM analysis was used to corroborate the SPR mechanism with the electrical measurements at each step of the annealing process.