Method for forming semiconductor device

Abstract

The invention discloses a method for forming a semiconductor device. The method includes that a substrate is provided, the substrate includes a first area and a second area, two gate structures which are located in the first area and the second area respectively are formed on the substrate, a first side wall and a second side wall are formed, the first side wall covers the substrate surface and two sides and surface of the gate structure in the first area, the second side wall covers the substrate surface and two sides and surface of the gate structure in the second area, the second side wall and the substrate are subjected to patterning etching, an opening is formed in the substrate which is located on two sides of the second side wall, an epitaxial layer is formed in the opening, before the epitaxial layer is formed, the first side wall is subjected to an ion implantation or an ion doping process, and thereby the density of the first side wall is improved. According to the method, the density of the first side wall is improved by the ion implantation or the ion doping process, and thereby the process selection ratio of the n-channel metal oxide semiconductor (NMOS) and the p-channel metal oxide semiconductor (PMOS) is improved when the epitaxial layer is formed on the same substrate.

Description

technical field [0001] The invention relates to the technical field of semiconductors, in particular to a method for forming a semiconductor device. Background technique [0002] It is well known that mechanical stress can change the energy gap and carrier mobility of silicon materials, and recently, mechanical stress has played an increasingly important role in affecting the performance of MOSFETs. If the stress can be properly controlled to increase the mobility of the carriers (electrons in n-channel transistors, holes in p-channel transistors) and drive current, stress can greatly improve the performance of transistors. [0003] Taking the PMOS transistor as an example, an epitaxial layer, such as a silicon germanium epitaxial layer, is first formed in the area where the source and drain regions need to be formed, and then doped to form the source and drain regions of the PMOS transistor. The silicon germanium epitaxial layer is formed to introduce The compressive stres...

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Problems solved by technology

[0006] However, after the actual epitaxial layer process, not only an epitaxial layer is formed in the PMOS area, but also an epitaxial layer of the same material as the epitaxial layer in the PMOS area may also be formed in the NMOS area, which reduces the reliability of the semiconductor device.

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