Method for forming shallow trench isolation (STI) structure used for flash memory

Abstract

The invention provides a method for forming a shallow trench isolation (STI) structure used for improving the 'smiling face' effect of a flash memory. The method comprises the following steps: providing a semiconductor substrate, wherein a tunneling oxidization layer and a floating gate polycrystalline silicon layer are sequentially formed on the surface of the semiconductor substrate; forming a hard mask layer on the surface of the floating gate polycrystalline silicon layer, sequentially etching the hard mask layer, the floating gate polycrystalline silicon layer, the tunneling oxidization layer and the semiconductor substrate, and forming a shallow trench in the semiconductor substrate; adopting in-situ steam generation process to form a liner oxidization layer covering the surface of the shallow trench; and adopting chemical vapor deposition to form an isolation medium layer filling the shallow trench. Through the STI structure forming method for the flash memory, the smiling face problem of the floating gate tunneling oxide caused by the traditional process can be effectively solved, the programming and erasure efficiency of the flash memory can be improved, and the read current of the flash memory in an erasure state can be increased, thus achieving the purpose of increasing a memory window.

Description

technical field [0001] The invention relates to a method for forming a shallow trench isolation structure, in particular to a method for forming a shallow trench isolation structure for a flash memory. Background technique [0002] In the current semiconductor industry, integrated circuit products can be mainly divided into three types: logic, memory and analog circuits, among which memory devices account for a considerable proportion of integrated circuit products. Among storage devices, the development of flash memory (flash memory) is particularly rapid in recent years. Its main feature is that it can keep stored information for a long time without power on, and has many advantages such as high integration, fast access speed, easy erasure and rewriting, etc. The field has been widely used. [0003] The standard physical structure of flash memory is called a flash cell (bit). The structure of the flash memory cell is different from that of conventional MOS transistors. ...

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Problems solved by technology

However, the thickness of the polysilicon layer formed by the above method is not uniform

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