Arsine Ambient Rapid Thermal Annealing

Abstract

ABSTRACTWe have constructed a multiple wafer arsine ambient rapid thermal anneal (RTA) system and have applied it to the fabrication of high-performance refractory-gate self-aligned GaAs MESFETs. This has allowed us to take advantage of some of the features of rapid thermal annealing for these devices (reduced dopant movement and gate-channel interaction) without the difficulties of capped RTA (decapping problems, cap thermal mismatch stress driven dopant movement and gate-channel interaction) or the uncertain As loss characteristics of uncapped or proximity RTA. The anneal system uses a cylindrical furnace with a graphite boat heated by tungsten lamps with a 60 KW maximum power input. This allows heating rates in excess of 100°C/sec for up to four, two-inch wafers per run with a controlled arsine ambient of 0–20 Torr in an inert gas carrier. Closed loop temperature control is accomplished using a 5 μm wavelength optical pyrometer. The system has been designed to collect the As cracked from AsH, in a downstream trap and essentially no As is deposited in the wafer load area.Using arsine ambient RTA to anneal 15 KV 20Si+ self-aligning implants for GaAs MESFETs with MOCVD grown channels (30 nm, 1.7 × 1018/cm3), we have been able to fabricate enhancementmode self-aligned MESFETs with gm/gd > 20 and extrinsic k-factor as large as 765 mS/V-mm for 0.15 μm gate length.