Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-02-10
2001-12-04
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S322000
Reexamination Certificate
active
06326107
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is related to Japanese Patent Application No. HEI 11(1999)-075435 filed on Mar. 19, 1999, whose priority is claimed under 35 USC §119, the disclosure of which is incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a phase-shifting mask and a process for manufacturing the same. More particularly, the invention relates to the structure of a phase-shifting mask which allows image formation of a pattern on a wafer at high resolution in manufacture of semiconductor devices and a manufacturing process of the same.
2. Description of Related Art
A conventional technique of phase-shifting masks is now explained in detail.
FIGS.
3
(
a
) to
3
(
h
) are schematic sectional views illustrating a process for producing a conventional-Levenson type phase-shifting mask (a mask having a section for shifting the phase of light emitted for exposure, referred to as “Levenson mask” hereinafter).
Referring to FIGS.
3
(
a
) to
3
(
h
), a blank mask
2
(a mask only of chromium without a pattern) used for producing a Levenson mask has a two-layered structure of a transparent substrate
1
and a light-tight film
3
formed thereon. Quartz is mainly used as a material for the transparent substrate
1
of the blank mask and chromium is mainly used as a material for the light-tight film
3
. The chromium film used for the blank mask
2
is usually about 110 nm thick and is formed by a vacuum deposition method or by a sputtering method.
An electron-beam (EB) resist is mainly used as a material for a protective film required in processing from the blank mask
2
to the Levenson mask. The resist
4
is usually applied onto the blank mask
2
to a thickness of about 500 nm by a spin-on method (FIG.
3
(
a
)). The resist film
4
is patterned by EB writing and development, thereby to form a resist mask. The light-tight film
3
is patterned by dry etching (FIG.
3
(
b
)) using this resist mask.
After the light-tight film
3
is etched, the resist film
4
is removed (FIG.
3
(
c
)).
After the removal of the resist film
4
, the resulting blank mask is washed. The resist
4
d
is applied again to a thickness of about 500 nm. A conductive film
5
is then formed by application to a thickness of about 20 nm (FIG.
3
(
d
)) and EB writing for alignment is conducted (FIG.
3
(
e
)).
The resist film
4
d
in a recess region of the transparent substrate
1
is selectively removed by washing the conductive film
5
away with water and by development (FIG.
3
(
f
)).
A recess
6
is formed in the transparent substrate
1
by etching to have such depth that the phase of exposure light passing through the recess
6
can be controlled to be inverted by 180 degrees with respect to the phase of exposure light passing through an adjacent transparent section of a pattern. (FIG.
3
(
g
)).
The remaining resist film
4
d
is removed (FIG.
3
(
h
)).
Through the above-mentioned process, completed is a phase-shifting mask wherein the recess
6
is formed in one of a pair of transparent sections of the pattern adjacent to a light-tight section
7
, that is, a Levenson mask.
Next, the principle of the Levenson mask is explained.
FIGS.
4
(
a
) to
4
(
c
) illustrate the principle of the Levenson mask.
As shown in FIG.
4
(
a
), the Levenson mask is provided with a shifter (a section which changes the phase of exposure light by 180 degrees) in one of a pair of regions where exposure light passes. In the case of FIG.
4
(
a
), the shifter is the recess
6
in the transparent substrate
1
. Light having passed a region c without a shifter and light having passed a region d with the shifter have the same intensity but their phases are shifted by 180 degrees. Waveforms of light from the light-passing regions have amplitudes in opposite directions at the feet of the waveforms where they overlap each other, and offset each other (FIG.
4
(
b
)). As a result, there is a portion where the intensity of light becomes zero, and accordingly the resolution can be improved. Japanese Unexamined Patent Publication No. HEI 2(1990)-211450 discloses a Levenson type phase-shifting mask of a recess-in-transparent-substrate type having the above-described structure.
Fine patterning by photolithography is limited depending on wavelength of exposure light. However, a stepper (light-exposure device) providing a smaller wavelength of exposure light is far more expensive and requires troublesome preparation. Accordingly, the Levenson mask is used as inexpensive means for overcoming the limit of fine patterning with the wavelength of exposure light unchanged.
However, for performing further finer patterning with the wavelength of exposure light unchanged, the Levenson mask described here is not sufficient, and it is necessary to apply a novel photo mask allowing further enhancement of resolution.
SUMMARY OF THE INVENTION
The present invention provides a phase-shifting mask comprising a transparent substrate and a pattern formed of a translucent film on the transparent substrate, wherein one of two regions of the substrate along both sidewalls of a trace of the pattern has a recess such that phases of exposure light passing through the two regions are 180° inverse to each other, and the trace has different thicknesses on its sides adjacent to the two regions of the substrate so that phases of exposure light passing through said one region of the substrate and one side of the trace adjacent thereto are 180° inverse to each other and phases of exposure light passing through the other of the two regions of the substrate and the other side of the trace adjacent thereto are 180° inverse to each other.
To put that another way, the phase-shifting mask of the invention has a pattern of a translucent film on a transparent substrate. One of two substrate regions along both sidewalls of a trace of the pattern has a recess so that the phases of exposure light passing through the two substrate regions are 180° inverse to each other. The trace of the pattern has different thicknesses on its sides to the two substrate regions so that the phases of exposure light passing through said sides and the corresponding substrate regions are 180° inverse to each other between the corresponding substrate region and side of the trace. Accordingly, the phases of exposure light passing through both the sides different in thickness are shifted 180° to those of light passing through the substrate regions adjacent thereto, and the amplitudes of passing exposure light are inverse to each other and offset at feet of amplitude curves where they overlap each other (see FIG.
1
(
b
)). As a result, the resolution is further improved.
In the phase-shifting mask of the invention, the pattern of the translucent film is formed on the transparent substrate. The two substrate (transparent substrate) regions along both sidewalls of the trace of the pattern in a sectional view perpendicular to a longitudinal direction of the trace of the pattern are traces of a transparent pattern.
One of the two substrate regions is dug to form a recess as a so-called “shifter” for inverting the phase of exposure light by 180°.
The depth C of the recess satisfies the following equation so that the phase of exposure light is 180° inverted:
C=&lgr;/
2(n
1
−1)
wherein &lgr; is wavelength of exposure light and n
1
is refractive index of the translucent film.
On the other hand, one side of the trace of the pattern of the translucent film adjacent to said one substrate region where the recess is formed is constructed to have a thickness such that the phases of exposure light passing through said side of the translucent trace and said one substrate region are 180° inverse to each other. The other side of the translucent trace is constructed to have thickness such that the phases of exposure light passing through said other side of the translucent trace and the other one of the two substrate regions are 180° inverse to each other.
That is, the thickness a of said other side of th
Nixon & Vanderhye P.C.
Rosasco S.
Sharp Kabushiki Kaisha
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