Diffusion and electrical properties of boron and arsenic doped poly-Si and poly-Ge_xSi_1-x (x ∼ 0.3) as gate material for Sub-0.25 μm complementary metal oxide Semiconductor applications

In this paper the texture, morphology, diffusion and electrical (de-) activation of dopants in polycrystalline Ge_xSi_1-x and Si have been studied in detail. For gate doping B⁺, BF⁺₂, and As⁺ were used and thermal budgets were chosen to be compatible with deep submicron CMOS processes. Diffusion of dopants is different for GeSi alloys, B diffuses significantly more slowly and As has a much faster diffusion in GeSi. For B doped samples both electrical activation and mobility are higher compared to poly-Si. Also for the first time, data of BF⁺₂ doped layers are presented, these show the same trend as the B doped samples but with an overall higher sheet resistance. For arsenic doping, activation and mobility are lower compared to poly-Si, resulting in a higher sheet resistance. The dopant deactivation due to long low temperature steps after the final activation anneal is also found to be quite different. Boron-doped GeSi samples show considerable reduced deactivation whereas arsenic shows a higher deactivation rate. The electrical properties are interpreted in terms of different grain size, quality and properties of the grain boundaries, defects, dopant clustering, and segregation, and the solid solubility of the dopants.