Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-09-08
2001-10-02
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06296974
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming a photo mask, and more particularly, to a method of forming a multi-layer photo mask.
2. Description of the Prior Art
In semiconductor processing, a designed pattern is initially formed on a photo mask and then the pattern of the photo mask is transferred onto the surface of a semiconductor wafer by a photolithography process so as to define the pattern of integrated circuits. The photo mask with poor quality is not in favor of the pattern transfer which may result in the poor electrical performance of semiconductor products and the high cost of processing. Therefore, how to form a photo mask with good quality becomes a very important issue.
Please refer to
FIG. 1
to FIG.
4
.
FIG. 1
to
FIG. 4
are schematic diagrams of a method of forming a phase-shift photo mask
26
according to the prior art. A method of forming a phase-shift photo mask is performed on a photo mask substrate
10
made of quartz. The photo mask substrate
10
is defined by a plurality of predetermined regions
20
according to a designed pattern required by a semiconductor process. During the method of forming the phase-shift photo mask
26
, an anti-reflective layer
12
, a phase shifter
14
, a first opaque layer
16
made of chromium (Cr), and a first photoresist layer
18
are formed in sequence, as shown in FIG.
1
. The anti-reflective layer
12
is used for enhancing the light transmission rate of the photo mask substrate
10
. The phase-shift layer
14
is used for driving the transmitting light to generate a phase-shift angle for about 180°.
Next, an exposure process is performed by using laser beam or electronical beam (E-beam) to expose the first photoresist layer
18
. Then a development process is performed to form a second photoresist layer
19
on the predetermined region
20
of the photo mask substrate
10
, as shown in FIG.
2
. Afterward, an etching process is performed to vertically remove the first opaque layer
16
outside the predetermined region
20
so as to form a second opaque layer
17
where the designed pattern is defined, as shown in FIG.
3
. Finally, a resist stripping process is performed to completely remove the second photoresist layer
19
so that the phase-shift photo mask
26
is completed, as shown in
FIG. 4
According to the prior art method of forming the phase-shift photo mask
26
, the designed pattern is defined on the second opaque layer
17
wherein a line width W and a line space S form a minimum pitch
25
. The minimum line width and the minimum line space of the pattern on the phase-shift photo mask
26
are both limited, because of a certain resolution of laser beam or E-beam. Therefore, there will be a limitation in the minimum pitch
25
of the phase-shift photo mask
26
. Since the line width of the pattern is related to the pitch
25
of the phase-shift photo mask
26
, the phase-shift photo mask
26
with the minimum pitch
25
may not be applied to a semiconductor process with a narrower width. Although the minimum pitch
25
could be further reduced by changing the light source used in the exposure process and the material of the first photoresist layer
18
, this will greatly increase the process cost and hence not meet the economic efficiency.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present invention to provide a method of forming a multi-layer photo mask, which can not only form a pattern of narrower width but also define various minimum pitches to be employed in a semiconductor process with a narrower width.
In a preferred embodiment, the present invention provides a method of forming a multi-layer photo mask on a photo mask substrate comprising:
forming a first transparent layer on at least one predetermined area of the photo mask substrate, the first transparent layer comprising at least one vertical side wall;
forming a first opaque spacer around the vertical side wall of the first transparent layer, the top side of the first spacer being approximately leveled off with the upper surface of the first transparent layer;
forming an external transparent layer on the photo mask substrate and outside the predetermined area, the upper surface of the external transparent layer being leveled off with that of the first transparent layer and the first transparent layer and the external transparent layer forming a first photo mask layer;
forming a second transparent layer on at least one predetermined area of the first photo mask layer the second transparent layer comprising at least one vertical side wall; and
forming a second opaque spacer around the vertical side wall of the second transparent layer, the top side of the second spacer approximately being leveled off with the upper surface of the second transparent layer.
It is an advantage of the present invention that the method of forming the multi-layer photo mask can define narrower pitches by adjusting the space between the first opaque spacer and the second opaque spacer. So the method can be employed in a semiconductor process with a narrower width.
This and other objective of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.
REFERENCES:
patent: 5536606 (1996-07-01), Doan
patent: 5698349 (1997-12-01), Yang
patent: 6071653 (2000-06-01), Lin
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