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在CMOS中,有n—MOS和P—MOS两种晶体管。为了简化制造工艺,在制作多晶硅栅时,最好先都制成n~+多晶硅,然后再对P—MOS管栅的n~+多晶硅注入B~+,使其变成p~+型多晶硅。可是,随着集成度的提高,最小线宽越变越窄,也要求多晶硅膜更薄,即使用很低能量的B~+来注入,B~+也会穿透多晶硅层进入基片中。为避免穿透,已发展了采用BF_2~+注入来形成P~+型多晶硅栅的办法。它确实能有效地降低B的注入深度,但也带来了另外的问题,这就是BF_2~+注入多晶硅中的F元素,在氧化膜中扩散,在随后的热处理中,会使氧化膜中B加速扩散到基片中,引起V_(TH)的变化,而成为一个麻烦问题。
In CMOS, there are n-MOS and P-MOS two transistors. In order to simplify the manufacturing process, it is better to make n ~ + polycrystalline silicon before making the polycrystalline silicon gate, then injecting B ~ + into the n ~ + polycrystalline silicon of the P-MOS gate to make it into p ~ + polycrystalline silicon. However, as the integration increases, the narrower the minimum width, the thinner polysilicon film is required. Even with very low energy B ~ +, B + penetrates the polysilicon layer into the substrate. In order to avoid penetration, BF2 ~ + implantation has been developed to form P ~ + type polysilicon gate approach. It can effectively reduce the depth of B implantation, but also brought another problem, which is BF2 ~ + F polycrystalline silicon in the diffusion, diffusion in the oxide film, in the subsequent heat treatment, the oxide film will B Accelerated diffusion into the substrate, causing V_ (TH) changes, and become a troublesome problem.