Improved ohmic contact to the n-type 4H-SiC semiconductor using cobalt silicides

Abstract

Multilayer structures of cobalt and silicon have been deposited as an ohmic contact on n-type 4H-SiC substrates in order to obtain lower contact resistance and higher thermal stability. The metal structures were prepared by using electron beam evaporation on top of the silicon face of the 4H-SiC substrates, and were annealed in an atmosphere of argon with 10% hydrogen. The metal film thickness was monitored during the film deposition, and the ratio of the cobalt and silicon was fixed at 0.5 for the formation of the silicon-rich silicide structure (CoSi 2 ). The electrical property of the ohmic contact has been significantly improved by the reduction of the oxide content in the metal contact layer. A two-step annealing process was employed to reduce oxidation problems that may occur in the heat treatment at high temperatures. The specific contact resistance of the contact structure prepared by the two-step annealing process was measured to decrease by more than one order of magnitude compared to that prepared by one-step annealing. The best result has been obtained as 1.8 × 10 −6 cm 2 for Co/Si/Co/Si/Co metal structures after two-step annealing, at 500 • C for 600 s and 800 • C for 120 s. In the field emission scanning electron microscopy, the interface of the contact structure and SiC substrate was observed to have smooth surface morphology with CoSi 2 grains.

Sputtered Ohmic Cobalt Silicide Contacts to 4H-SiC

“…For temperatures above ambient temperature, ρ c drastically dropped to 7.5•10 -6 Ωcm 2 at 200 °C, whereafter a further increase in temperature did not drastically change the resistance as seen in Fig 7 and Table 2. I-V measurements of the contacts to p-type SiC on sample B did not show ohmic behavior at any temperature, probably related to the low grade of doping in the epitaxial layer of the sample compared to earlier reported CoSi 2 contacts to p-SiC (doped to 2•10 19 cm -3 [2]). Sheet resistance, R sh .…”

Investigation of a Self-Aligned Cobalt Silicide Process for Ohmic Contacts to Silicon Carbide

“…As such, the CoSi x /4H-SiC system could instead give low resistance ohmic contacts to n-type 4H-SiC, just like the Ni 2 Si/4H-SiC system. CoSi 2 /4H-SiC, formed by multilayer deposition of silicon and cobalt, has been previously studied and been shown to provide low resistance ohmic contact to n-type 4H-SiC, [21][22][23] and the result to p-type 4H-SiC is unclear. 24 We investigated the CoSi x /4H-SiC system to answer the following two research questions 25 :…”

“…The difference from previous contact studies to 4H-SiC is that only cobalt is deposited instead of the silicon/cobalt multilayer stacks. [21][22][23] Moreover, interface reactions between cobalt and 4H-SiC are studied using rapid thermal processing (RTP) to anneal cobalt/4H-SiC instead of furnace annealing cobalt/6H-SiC. 26,27 The annealing temperature range was limited in this study up to 1000 C. It was considered that any contact process requiring higher annealing temperatures than 1000 C would not be competitive with already established contact processes.…”

Interface metallization and electrical characterization of Ta–Pt multilayers on n-type SiC

“…A number of different metals and metal combinations such as Ni, Cr, Ti, Mo, TiW, TiN, Ti-Al, Ti/Ni/Ti, and Co/Si/Co have been tried to obtain these contacts [4][5][6][7]. However, most metals start to react with SiC at elevated temperatures resulting in a modification of the electrical properties of the metal/SiC junctions.…”