Refractory Suicide Schottky Contacts to GaAs
- PDF / 1,390,143 Bytes
- 8 Pages / 417.6 x 639 pts Page_size
- 108 Downloads / 277 Views
N. YOKOYAMA, T. OHNISHI, T. NAKAMURA, AND H. NISHI Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi 243-01, Japan
ABSTRACT Refractory silicides form high temperature stable Schottky contacts to GaAs. This finding enabled us to develop self-aligned GaAs MESFETs, thereby enabling the development of today's GaAs ICs. This paper reviews electrical and metallurgical studies on refractory-metal/GaAs and refractory-metalsilicide/GaAs interfaces. We emphasize the fact that W5 Si 3 /GaAs contacts have extremely stable electrical properties even after annealing at 0 temperatures up to 850 C. Crystallographical properties of the W5 Si 3 film on GaAs, investigated by x-ray and TEM measurement techiques, are also covered. We found that the Schottky electrical characteristics are not affected by whether the film is amorphous or crystalline. INTRODUCTION Tremendous reduction in computer size and increased speed spur an ongoing effort in search of faster logic and memory. The superior electronic properties of GaAs, as compared with Si, have made it of great interest for ultrahigh-speed logic and memory applications. However, there was a critical problem that had to be tackled in the development of GaAs integrated circuits. In conventional MESFETs, surface depletion layers are formed due to a high density of surface states. The width of the surface depletion layer is considered to be comparable to the width of depletion layer extending from the Schottky gate electrode. Clearly, the surface depletion layer causes a considerable increase in source series resistance, and deteriorates FET transconductance. The effect of the surface depletion layer is particularly serious in enhancement GaAs MESFETs using a very thin channel layer. Thus, it appears that it is impossible to develop GaAs integrated circuits using the conventional GaAs MESFETs. This problem has been solved by the development of self-aligned technology [I). Figure 1 shows the major steps in self-aligned GaAs MESFET fabrication. First, Schottky gates are formed on n-type GaAs. Next, a high dosage Si+ implantation is made with the gate acting as an implantation mask. Then, annealing is carried out to activate dopants and to form the self-aligned n+-regions. Fabrication is completed by ohmic metallization. In this structure, high-density n+ regions are self-aligned with the gate. The self-aligned n+ regions are expected to prevent extension of the surface depletion layer, so that the undepleted n+-layer considerably reduces source series resistance. The key of this process is that the Schottky gates have to be stable during the post-implantation annealing. Thus, high-temperature-stable Schottky gates for GaAs are required, to develop GaAs MESFET integrated circuits. This paper reviews efforts made in this direction, and describes crystallographical properties of tungsten-silicide films on GaAs, based on a recent analysis by x-ray and transmission electron microscope techniques.
Mat. Res. Soc. Symp. Proc. Vol. 54. t1986 Materials Research Society
402
Si+
Gate n
Data Loading...
