Method for forming NMOS (N-channel Metal Oxide Semiconductor) transistor

Abstract

The invention provides a method for forming an NMOS (N-channel Metal Oxide Semiconductor) transistor. The method comprises the following steps of: providing a substrate and a grid structure located on the substrate; taking the grid structure as a mask to carry out ion implantation on the substrate, and forming a source area and a drain area in the substrate at the both sides of the grid structure; forming a stopping layer on the exposed surfaces of the substrate and the grid structure; forming a stress layer on the stopping layer, wherein the stopping layer is used for preventing hydrogen elements used in the forming environment of the stress layer from entering the source area and the drain area; carrying out heat treatment on the source area and the drain area; and removing the stopping layer and the strain layer. According to the method disclosed by the invention, the compact stopping layer is formed on the surfaces of the substrate and the grid structure before the stress layer is formed, so as to prevent the hydrogen elements used in the forming environment of the stress layer from entering the source area / drain area in the substrate. Therefore, the problem of descending of threshold voltage, caused when the diffusion of doped ions in the source area / drain area is enhanced by the hydrogen elements, is solved, the reliability of the threshold voltage is improved, and the property reliability of the NMOS transistor is further improved.

Description

technical field [0001] The invention relates to the field of semiconductor manufacturing, in particular to a method for forming an NMOS transistor. 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, the mobility of carriers (electrons in n-channel transistors, holes in p-channel transistors) is increased, and the drive current is increased, so stress can greatly improve the performance of transistors. [0003] The prior art uses stress liner technology to improve the mechanical stress performance of transistors. For example, a tensile stress liner (tensile stress liner) is formed on the NMOS transistor, and a compressive stress liner (compressive stress liner) is formed on the PMOS transistor, thereby increasing the driving current o...

AI Technical Summary

Problems solved by technology

[0011] The problem solved by the present invention is to provide a method for forming an NMOS transistor to solve the problem of the threshold voltage drop of the NMOS transistor formed by the stress memory process

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