Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-12-13
2002-07-16
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S022000, C430S269000, C430S311000, C430S396000
Reexamination Certificate
active
06420075
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a mask for use in photolithography and its manufacturing technique, and particularly to a technique effectively applicable to a mask for use of manufacturing semiconductor integrated circuit device.
In recent years, very fine elements constituting a circuit, very fine wirings and very narrow spaces between the elements and wirings have been developed in semiconductor integrated circuit devices.
However, along with such development of the elements and wirings and of the spaces between elements and wirings, there arises a problem in that the accuracy of mask pattern transfer is lowered when an integrated circuit pattern is transferred onto a wafer by coherent light.
This problem will subsequently be described with reference to FIGS.
24
(
a
)-(
d
).
When a given integrated circuit pattern formed on a mask
50
shown in FIG.
24
(
a
) is transferred onto a wafer by a method of projection exposure or the like, the phases of lights each transmitted through each of a pair of transmission regions P
1
, P
2
having light shield region N therebetween are identical to each other as shown in FIG.
24
(
b
). Consequently, these interferential lights increase their intensities in light shield region N located between the above-mentioned pair of transmission regions P
1
, P
2
as shown in FIG.
24
(
c
). As a result, as shown in FIG.
24
(
d
) the contrast of a projected image on a wafer is not only lowered, but also the depth of focus becomes shallow, causing the transfer accuracy of the mask pattern to be considerably lowered.
As a means to counteract these problems, a technique of phase shifting lithography has been developed, whereby the phase of light transmitted through the mask is controlled so as to improve the resolution and contrast of the projected image. The phase shifting lithography technique is disclosed, for example, in Japanese Laid-Open Patent No. 173744/1983 and Japanese Laid-Open Patent No. 67514/1987.
In the above-mentioned Japanese Laid-Open Patent No. 173744/1983 there is described the structure of a-mask having a light shield region and a pair of transmission regions, wherein a transparent material is arranged at least in either one of the transmission regions sandwiching the light shield region therebetween, allowing a phase difference to be generated between the lights each transmitted through each of transmission regions at the time of exposure and thus these lights being interfered with each other to weaken themselves in the region on a wafer which should primarily be a light shield region.
The function of the light transmitted through such a mask as above will subsequently be described with reference to FIGS.
25
(
a
)-(
d
).
When a given integrated circuit pattern formed on a mask
51
shown in FIG.
25
(
a
) is transferred onto a wafer by the method of projection exposure or the like, a phase difference of 180° is generated between the phase of light transmitted through a transmission region P
2
having transparent material
52
of a pair of transmission regions P
1
, P
2
which have light shield region N sandwiched therebetween and the phase of light transmitted through the normal transmission region P
1
, as shown in FIGS.
25
(
b
) and (
c
). Therefore, the lights transmitted through the pair of transmission regions P
1
, P
2
interfere with each other to offset them in light shield region N located between these transmission regions P
1
, P
2
. Consequently, as shown in FIG.
25
(
d
), the contrast of a projected image on a wafer is improved. Thus, the resolution and depth of focus is improved, resulting in a higher accuracy of pattern transfer of the mask
51
.
Also, in the above-mentioned Japanese Laid-Open Patent No. 67514/1987, there is described the structure of a mask having a light shield region formed by light shielding film and a transmission region formed by removing the light shielding film, wherein a fine aperture pattern is formed by removing a part of shielding film and at the same time, a phase shifting layer is provided on either one of the transmission region or the aperture pattern, and thus a phase difference is generated between the lights transmitted through the transmission region and the aperture pattern, preventing the distribution of amplitude of light transmitted through the transmission region from being spread in the horizontal direction.
SUMMARY OF THE INVENTION
Nevertheless, the present inventor has found that the conventional technique disclosed in the above-mentioned Japanese Laid-Open Patent No. 173744/1983 has the following problem:
The above-mentioned conventional technique in which a phase difference is generated between the lights transmitted through the pair of transmission regions does not has any problem as far as a pattern is simply and unidimensionally arranged in a repetitive manner. However, in the case that the pattern is complicated as in an actual integrated circuit pattern, the arrangement of the transparent material may be impossible, and a problem arises in that sufficient resolution is not obtained at some sections.
For example, in the case of an integrated circuit pattern
53
shown in FIG.
26
. If transparent material is arranged in a transmission region P
2
, the resolutions in light shield regions N
1
and N
2
are certainly improved. However, if transparent material is arranged in transmission region P
1
, in order to improve the resolution in light shield region N
3
, the lights transmitted through transmission regions P
1
, P
2
will have an identical phase, causing the resolution in light shield region N
2
to be lowered. Also, in order to improve the resolution in the light shield region N
3
, a transparent material should be provided in such a transmission region as the transmission region P
3
. Then, the transparent material can be arranged in a part of transmission region P
3
. In such a case, however, there appears the reversing of phases in the lights transmitted through the same transmission region P
3
, and an unwanted pattern is formed on a wafer. Consequently, it becomes impossible to improve the resolution in light shield region N
3
.
Furthermore, if the pattern is complicated like an actual integrated circuit one, the arrangement of transparent material is restricted as mentioned above. This makes it difficult to prepare the pattern data of the transparent material. Conventionally, therefore, the pattern of the transparent material should be produced specially while taking into consideration the above-mentioned restriction on the arrangement when a mask having means for shifting phase of light is manufactured.
On the other hand, the known technique disclosed in Japanese Laid-Open Patent No. 67514/1987, whereby an aperture pattern is formed in a light shield region so as to generate a phase contrast between the light transmitted through the aperture pattern and the one transmitted through the transmission region, makes it difficult to arrange the aperture pattern, the same as in the case of the above-mentioned publication, if a pattern is as complicated and extremely fine as an actual integrated circuit pattern. For example, should the width of pattern of light shield region become narrower, there arises a problem in that the arrangement of an aperture pattern is difficult.
Furthermore, in this conventional technique, no consideration is given as to the lowering of light intensity at the corners of transmission region which takes place along with a further miniaturization of transmission region required, resulting in a problem posed in that the corners of a projected image are rounded.
The present invention is to solve the above-mentioned problems, and the object thereof is to provide a technique whereby the transfer accuracy of a pattern formed on a mask can be improved.
Another object of the present invention is to provide a technique whereby the manufacturing time of a mask having means for shifting phase of light can be reduced.
Still another object of the present invention is to provide a technique whereby the resolution
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