Optical mask correction method

Details Optical mask correction method Optical mask correction method

2001-09-18

2003-10-28

Duda, Kathleen (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Radiation mask

C430S327000

Reexamination Certificate

active

06638664

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial No. 90112993, filed May 30, 2001.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a photolithographic process. More particularly, the present invention relates to a method of correcting an optical mask pattern.
2. Description of Related Art
As the level of integration of integrated circuit continues to increase, size of all semiconductor devices shrinks correspondingly. Photolithography is an important process in semiconductor fabrication. Any processes related to the fabrication of metaloxide-semiconductor (MOS) device such as the patterning of various film layers and the doping of substrate demand photolithography. To produce devices having ever-decreasing dimensions, an optical mask of ever-increasing resolution have been developed. Methods capable of increasing mask resolution include optical proximity correction (OPC) and phase shifting.
Optical proximity correction is a method for eliminating deviations in the critical dimensions of a device due to a proximity effect. The proximity effect occurs when a light beam is projected onto a photomask having a pattern thereon. Due to a diffraction of the light beam, the light beam diverges and spreads a little. In addition, a portion of the light beam passing through the photoresist layer on a silicon chip may be reflected back by the semiconductor substrate causing some light interference. Hence, multiple exposure of photoresist may occur, leading to over-exposure of photoresist in part of the pattern.
FIGS. 1A through 1D
are schematic top views showing the progression of steps for correcting a mask pattern according to a conventional method. As shown in
FIGS. 1A and 1B
, a T-shaped original pattern
106
that includes a first strip-like pattern
102
and a second strip-like pattern
104
is provided. A gate-shrinking step is conducted such that a portion of the first strip-like pattern
102
is reduced to form a first modified pattern
110
. The reduced portion of the first strip-like pattern
102
is used for patterning the gate portion in an active region. Hence, the reduced dimension of the first strip-like pattern
102
is a critical dimension (CD) of the gate pattern.
As shown in
FIG. 1C
, a pair of assistant patterns
108
and
109
is added to the respective sides of the first strip-like pattern
102
to form a second modified pattern
112
.
As shown in
FIG. 1D
, an optical proximity correction method is applied to correct the second modified pattern
112
into a third modified pattern
114
.
In a conventional mask correction method, the assistant patterns are added after the gate pattern is reduced. Since file size of the third modified pattern
114
is relatively large, considerable time is wasted in writing and inspecting the mask pattern data.
FIG. 2
is a top view showing a photoresist pattern on a photoresist layer after photo-exposure employing a conventional mask correction method. The third modified pattern
114
in
FIG. 1D
is used to perform a photo-exposure so that the pattern on the photomask is reproduced as a photoresist pattern
202
in the photoresist layer
200
. As shown in
FIG. 2
, the exposed pattern
202
has a pair of necking points
204
. The pair of necking points exist due to a discontinuity between the assistant patterns
108
and
109
.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a method of correcting an optical mask pattern so that size of file for holding mask pattern data and time for writing and inspecting the file data are reduced.
A second object of this invention is to provide a method of correcting an optical mask pattern so that necking points in exposed pattern resulting from conventional assistant patterns are removed.
A third object of this invention is to provide a method of correcting an optical mask pattern such that resolution of photolithographic process is increased and non-uniformity of post-exposure critical dimensions of devices is improved.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of correcting an optical mask pattern. First, a T-shaped original pattern having a first strip-like pattern and a second strip-like pattern is provided. The first strip-like pattern is attached to the mid-section of the second strip-like pattern. A first modification step is conducted. A pair of assistant patterns is added to the respective sides of the first strip-like pattern to form a first modified pattern. Thereafter, a second modification step is conducted to shrink a portion of the first strip-like pattern to form a second modified pattern. Dimension in the reduced portion of the first strip-like pattern is a critical dimension of a main pattern. A third modification step is conducted using an optical proximity correction method. The second modified pattern is modified to a third modified pattern.
In this invention, a pair of assistant patterns is added to the respective sides of the device pattern before shrinking the main pattern. Because only a set of assistant patterns is used instead of two sets for a conventional method, size of file for holding mask pattern data is reduced by half. Hence, time for writing and inspecting file data is reduced considerably. In addition, the method of first adding assistant patterns to the sides of the device pattern before shrinking the main pattern prevents the formation of necking points in the subsequently developed exposed pattern. Furthermore, the optical mask correction method is capable of increasing the resolution of photolithographic process and improving uniformity of critical dimensions in the pattern.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanations of the invention as claimed.


REFERENCES:
patent: 6165693 (2000-12-01), Lin
patent: 6413683 (2002-07-01), Liebman
patent: 6482559 (2002-11-01), Lin

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