Method for forming an attenuated phase-shifting mask

Details Method for forming an attenuated phase-shifting mask Method for forming an attenuated phase-shifting mask

2000-03-24

2002-12-10

Young, Christopher G. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Radiation mask

C430S322000, C430S323000, C430S324000

Reexamination Certificate

active

06492069

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a method of forming a mask for photolithography, and more particularly to a method for forming an attenuated phase-shifting mask (PSM).
BACKGROUND OF THE INVENTION
An attenuated phase-shifting mask (PSM), a widely used mask in photolithography, is mainly fabricated by coating a phase-shifting layer upon on a transparent plate, thus to interfere the phase of light incident through the transparent plate for providing a better exposure accuracy during the photolithography. As a result of the better exposure accuracy, patterns of attenuated phase-shifting mask would be transformed onto chips more accurate than those of conventional mask do. Typically, a stepper, a machine for projecting rays through masks onto chips during photolithography, identifies and locates a mask by detecting reflected ray form bar codes and position marks at edges of the mask. However, the stepper doesn't always successfully identify and locate attenuated phase-shifting masks, since a great amount of incident light would pass through the phase-shifting layer so as provide insufficient amount of reflected ray for identifying and locating them. Moreover, patterns of chips transformed form edges of the phase-shifting layer might be exposed in overlap after the use of several attenuated phase-shifting masks. The photoresist layer of those patterns will undesirably lose due to the overlapped exposures, thereby damaging the accuracy of patterns of chips.
For overcoming the above mentioned problems of applying attenuated phase-shifting mask, many semiconductor manufacturers coat an opaque layer around its edges for facilitating steppers to identify and locate the attenuated phase-shifting mask by the reflected ray from the opaque layer at the edges. Referring to
FIG. 1
, an attenuated phase-shifting mask
34
is coated with a opaque layer
38
around the central image field
36
, which includes patterns formed by a phase-shifting layer coated on a transparent plate. Due to the opaque layer
38
, a stepper is able to detect the reflected ray from the bar code
40
and position marks
42
to identify and locate the attenuated phase-shifting mask
34
.
Through
FIG. 2
to
FIG. 8
, a conventional process for fabricating an attenuated phase-shifting mask with the opaque layer in semiconductor manufacturer's plant is shown.
FIG. 2
shows a cross-sectional view of an attenuated phase-shifting mask
44
provided by mask vendors. The attenuated phase-shifting layer
44
is formed by successively coating a phase-shifting layer
48
, opaque layer
50
, and first photoresist layer
52
on a transparent plate
46
. In order to form patterns on the attenuated phase-shifting mask
44
, the first photoresist layer is defined as shown in
FIG. 3
by exposure and development. Referring to
FIG. 3
, parts of the opaque layer
50
are then stripped through a conventional etching process by employing the photoresist layer
52
as an etching mask. Then the photoresist layer
52
is totally stripped thus to shape the cross-sectional view of FIG.
4
. Using the opaque layer
50
as an etching mask, parts of the phase-shifting layer
48
are removed until exposing the surface of transparent plate
46
, as shown in FIG.
5
.
Referring to
FIG. 6
, a second photoresist layer
54
is blanketed over the transparent plate
46
. Through steps of exposure and development, the second photoresist layer
54
is partially removed as the cross-sectional view shown in FIG.
7
. Parts of the opaque layer
50
exposed out of the second photoresist layer
54
are stripped through an etching process by employing the second photoresist layer
54
as an etching mask, then removing the second photoresist layer
54
to complete the attenuated phase-shifting mask
44
, as shown in FIG.
8
. As a result of the opaque layer
50
around upon the phase-shifting layer
48
and transparent layer
46
, the stepper may correctly identify and located the attenuated phase-shifting mask
44
by detecting reflected rays from the opaque layer
50
.
Although this conventional process enables semiconductor manufacturers to fabricate an attenuated phase-shifting mask with an opaque layer, it exists some shortcomings. This conventional process is much complicated, since it needs to an extra photoresist layer, namely the aforementioned second photoresist layer. For forming the extra photoresist layer, the semiconductor manufacturers need to coat second photoresist layer on a original mask, which already has a first photoresist layer provided by mask vendors. Because of the square shape of mask, it's hard to coat the second photoresist layer uniformly as its corners by semiconductor manufacturers themselves. Therefore, under this conventional process, the semiconductor manufacturers suffer low yield rates and high costs from it.
In brief, for forming an opaque layer around an attenuated phase-shifting mask as well as avoiding the low yield and cost due to the conventional process, there is huge need to improve the conventional process to overcome the above problems.
SUMMARY OF THE INVENTION
An objective of this invention is to provide semiconductor manufacturers a simplified method to from an attenuated phase-shifting mask.
This invention discloses a method for forming an attenuated phase-shifting mask, including following steps. A transparent plate is provided, on which a phase-shifting layer, opaque layer, and undeveloped photoresist layer being stacked on the transparent plate successively. A first part of the photoresist layer is removed until exposing a first region of the opaque layer through exposure and development processes. The first region of the opaque layer is removed for exposing parts of the phase-shifting layer. A solidified thin surface of the photoresist layer is stripped by low-energy plasma treatment. A second part of the photoresist layer is removed for exposing a second region of the opaque layer through exposure and development processes. The exposed phase-shifting layer is then etched by employing the opaque layer as an etching mask. Then the exposed opaque layer and photoresist layer are successively remove, thus forming a complete attenuated phase-shifting mask.


REFERENCES:
patent: 5589303 (1996-12-01), DeMarco

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