Method of improving astigmatism of a photoresist layer

Details Method of improving astigmatism of a photoresist layer Method of improving astigmatism of a photoresist layer

2001-04-25

2003-06-10

Huff, Mark F. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Forming nonplanar surface

C430S290000, C430S311000, C430S313000, C430S396000

Reexamination Certificate

active

06576407

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method of adjusting the polarization intensity for high numerical apertures (NA), and more particularly, to a method of adjusting the intensity ratio of an S wave polarization to a P wave polarization after penetrating a photoresist layer to a predetermined depth.
DESCRIPTION OF THE PRIOR ART
The photolithography process is very important in the field of semiconductor manufacturing. The definition of each thin film, the interconnects, the doped areas, etc. are controlled by the photolithography process. The photolithography process is very complicated, including the coating of a photoresist layer, an exposure process, a development process, etc. Since the patterns of the mask must be transferred to the semiconductor wafer, the quality of the photolithography process is decisive to the product yield.
FIG. 1
is a schematic diagram of an exposure light source emitting light. During a photolithography process, an incident linearly polarized light
10
penetrates a photoresist layer
12
through a reduction lens (not shown) of high numerical aperture (NA), and has an incident angle &thgr;. The incident linearly polarized light
10
is divided into an S wave polarization
14
and a P wave polarization
16
, which are orthogonal. The S wave polarization
14
has an electric field
18
and a magnetic field
20
, and the P wave polarization has an electric field
22
and a magnetic field
24
wherein the electric field
18
is perpendicular to the electric field
22
.
FIG. 2
shows the transmission coefficients of the S wave polarization and the P wave polarization for the photoresist layer according to the prior art. As shown in
FIG. 2
, using NA=sin &thgr; (where &thgr; is the incident angle), when the NA of the reduction lens is more than 0.7, the incident angle &thgr; is more than sin
−1
0.7, and the S wave polarization
14
has a transmission coefficient for the photoresist layer
12
that is different from the P wave polarization.
Since the S wave polarization
14
and the P wave polarization
16
have different transmission coefficients for the photoresist layer
12
, the intensity ratio of the S wave polarization
14
to the P wave polarization after penetrating the photoresist layer
12
is not 1:1. Following this, due to the intensity ratio not being 1:1, the exposure effect along the perpendicular direction and the parallel direction of the patterns is not equal. This then causes astigmatism.
Astigmatism affects the fidelity of the parallel direction and the perpendicular direction of the patterns, and affects the exposure process greatly. Moreover, all the photolithography processes for high NA have similar problems.
SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide a method of improving astigmatism of the photoresist layer.
It is another objective of the present invention to provide a method of adjusting the intensity of the polarization for high NA.
The preferred embodiment of the present invention provides an exposure system comprising a light source to provide light, a mask comprising a mask pattern, the light capable of passing through the mask pattern, a photoresist layer comprising an optically active component, a reduction lens system adapted to accept light passing through the mask to form an image in the photoresist layer, and a linear polarizer positioned between the light source and the photoresist layer to linearly polarize the light from the light source. The optically active component divides linearly polarized light into an intensity-adjusted S wave polarization and an intensity-adjusted P wave polarization. The proportion of the intensity of the S wave polarization to the P wave polarization is effectively 1:1 after penetrating the photoresist layer to a predetermined depth.
It is an advantage of the present invention that it can improve astigmatism of all exposure processes having high NA.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.


REFERENCES:
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patent: 5153773 (1992-10-01), Muraki et al.
patent: 5648857 (1997-07-01), Ando et al.
patent: 5668590 (1997-09-01), Maruo et al.
patent: 5786911 (1998-07-01), Tawa et al.
patent: 2002/0160314 (2002-10-01), Lin et al.
patent: 61-267946 (1986-11-01), None

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