Half-tone phase shift mask for fabrication of poly line

Details Half-tone phase shift mask for fabrication of poly line Half-tone phase shift mask for fabrication of poly line

1999-12-07

2001-11-06

Rosasco, S. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Radiation mask

Reexamination Certificate

active

06312856

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to phase shift mask (PSM). More particularly, the present invention relates to half-tone phase shift mask.
2. Description of Related Art
Currently, photolithography plays an essential role in semiconductor fabrication. For example, processes for patterning a structure or doping a region in a wafer always require several photolithography processes. In a photolithography process, exposure resolution and depth of focus (DOF) are two important parameters that determine photolithography quality.
A binary mask, which is made of quartz having chrome pattern coated thereon and is used for design rule above 0.18 &mgr;m in semiconductor fabrication, can obtain a pattern with high quality on the photoresist layer. However, when the semiconductor structure is required to be under 0.18 &mgr;m in size, diffraction of light causes serious problems due to the reduced size of the hole and line on the mask. In the photolithography process, especially, for forming a poly gate in the logic circuitry region of dynamic random access memory (DRAM), a desired pattern such as sole poly line is hard to obtain on the wafer because of the diffraction of light. As a result, the incorrect pattern causes a failure of a subsequent etching process of poly line and yield of the product is thus reduced.
SUMMARY OF THE INVENTION
The invention provides a half-tone phase shift mask applicable to the photolithography process of a poly gate with a size under 0.18 &mgr;m.
As embodied and broadly described herein, the invention provides a half-tone phase shift mask which includes a mask substrate and a half-tone phase shifting layer formed thereon, wherein light passing through the half-tone phase shifting layer portion of the mask has a 180° phase shift. The half tone phase shifting layer further includes a main pattern having a first width and a first length, and an assist feature having a second width and a second length, in which the assist feature is parallel to the main pattern and disposed at a distance on both sides of the main pattern. Using deep ultraviolet light (DUB) as exposing source, a wafer scale of the first width is about 0.1-0.15 &mgr;m, a wafer scale of the second width is about 0.055-0.09 &mgr;m and the distance between the main pattern and the assist feature is about 0.22-&mgr;m.
This invention further provides a method of fabricating a poly line formed on a logic circuitry region of DRAM. A polysilicon layer is formed on a semiconductor substrate and a photoresist layer is formed on the polysilicon layer. A half-tone PSM is employed to pattern the photoresist layer and then the patterned photoresist layer patterns the polysilicon layer to form a poly line. The half-tone PSM has a mask substrate and a half-tone phase shifting layer formed thereon. The half-tone phase shifting layer includes a main pattern and an assist feature. The main pattern and the assist feature are used to form a poly line pattern on a wafer when the light penetrates through the half-tone PSM.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.


REFERENCES:
patent: 6114071 (2000-09-01), Chen et al.

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