Properties of Plasma‐Enhanced CVD Silicon Films: II . Films Doped During Deposition

Abstract

Doped polycrystalline silicon films were deposited by plasma‐enhanced CVD from a mixture of dichlorosilane and phosphine in argon at 628°C and a pressure of approximately 2 Torr. The films were annealed at temperatures varying from 450° to 1050°C, and their properties were compared to those of conventional LPCVD polysilicon films deposited from silane at 0.2 Torr. The doped PECVD films are polycrystalline as deposited, with a less well‐developed structure than that of undoped LPCVD films. The phosphorus concentration in the PECVD films is approximately . The chlorine concentration of about seen after deposition decreases near the film surface after annealing at high temperatures. The films have a fine‐grain, polycrystalline structure after deposition; the grain size increases from about 10 nm to about 500 nm on annealing. A small amount of {111} preferred orientation is observed after deposition, but strong {100} texture develops after annealing above 750°C. The other properties of the films also improve when the films are annealed above 750°C. The optical properties become more like those of crystalline silicon, and the compressive stress decreases from its initial value of about 1010 dynes/cm2. The sheet resistance decreases from about 1500 to about 13 Ω/sq on annealing, although more phosphorus is needed in the PECVD films to obtain this sheet resistance than is needed in LPCVD films. The flatband voltage of MOS capacitors fabricated using PECVD silicon films for the gate electrodes decreases in magnitude on annealing above 750°C, approaching that of capacitors with LPCVD polysilicon. The fixed charge density also decreases on annealing. The properties of the PECVD films are suitable for use in MOS integrated circuits after annealing at temperatures above 750°C.