Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
2001-02-09
2003-04-15
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S326000, C430S396000
Reexamination Certificate
active
06548226
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a semiconductor process. More particularly, the present invention relates to a photolithographic process.
2. Description of Related Art
To improve the resolution and process window of photolithographic process, an ArF excimer laser light source and a corresponding ArF photoresist material are used. The ArF photoresist contains a photoacid generator that catalyzes the dissociation or association reaction of photoresist molecules so that a pattern is formed after development. However, the diffusion of photoacid in ArF positive photoresist after photo-exposure together with the need for producing lines with a narrow line width frequently aggravate the proximity effect. This often leads to considerably more reduction of line width for an isolated line pattern than for a densely packed line pattern.
FIG. 1
is a schematic cross-sectional view showing the variation of line width between a conventional dense photoresist pattern and a conventional isolated photoresist pattern due to a variation of duty ratio.
FIG. 1A
is a schematic cross-sectional view of a photomask for producing the photoresist pattern shown in FIG.
1
. The photomask
10
includes a dense pattern
12
and an isolated pattern
14
. The dense pattern
12
and the isolated pattern
14
are used to produce a dense pattern
110
a
and an isolated pattern
110
b
on the substrate
100
.
As shown in
FIGS. 1 and 1A
, the dense pattern
12
and the isolated pattern
14
on the photomask
10
both have a line width x. However, the dense pattern
12
has a duty ratio w:x of 1:1 while the isolated pattern
14
has a duty ratio y:x of 8:1. The dense photoresist pattern
110
a
on the substrate
100
has a line with of about 150 nm when the dense pattern
12
on the photomask is used. On the contrary, the isolated photoresist pattern
110
b
on the substrate
100
possibly has a line width of only about 60 nm when the isolated pattern
14
on the photomask is used. Because the difference in line width between the isolated photoresist pattern
110
b
and the dense photoresist pattern
110
a
is so big, simply employing an optical proximity correction (OPC) can hardly make any obvious improvement.
According to the results of an investigation, the large drop in line width in the isolated photoresist pattern relative to the dense photoresist pattern is due to the presence of a large background region surrounding the isolated photoresist pattern.
FIG. 2
is a graph showing the variation of photoacid concentration in an ArF positive photoresist layer versus position, wherein a dense pattern is formed on the left, an isolated pattern is formed on the right and the direction of diffusion is indicated by arrows. According to the position versus photoacid concentration relationship in
FIG. 2
, the isolated pattern on the right is surrounded by a large quantity of photoacid. Ultimately, the diffusion of the photoacid leads to a great reduction of line width. Conversely, the dense pattern on the left is surrounded by only a small quantity of photoacid because the dense pattern already occupies a large portion of the region. Thus, line width is less affected by the diffusion of photoacid.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a photolithographic process that utilizes the addition of photobase generator into a positive photoresist to counteract the photoacid generator in the photoresist, distributed according to the duty ratio of a pattern. The reaction threshold of the photobase generator to light is greater in a dense pattern region (having a smaller duty ratio) while the reaction threshold of the photobase generator to light is smaller in an isolated region (having a greater duty ratio). Hence, the amount of photobase generator produced in the isolated pattern region is much greater than that produced in the dense pattern region. The presence of photobase generator in the photoresist blocks some of the diffusion of photoacid generator and hence prevents severe reduction of line width in an isolated pattern region without affecting the development of positive photoresist in the dense pattern region.
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: 5206117 (1993-04-01), Labadie et al.
patent: 5650261 (1997-07-01), Winkle
patent: 6294295 (2001-09-01), Lin et al.
patent: 6338934 (2002-01-01), Chen et al.
patent: 6395451 (2002-05-01), Jung et al.
Barreca Nicole
Huff Mark F.
United Microelectronics Corp.
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