Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-05-17
2003-09-30
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S323000
Reexamination Certificate
active
06627359
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a photomask and a photomask manufactured thereby, and more particularly, relates to a method of manufacturing a phase-shift (phase-shifting) photomask and a substrate etching-type phase-shift (phase-shifting) photomask manufactured thereby.
In these days, there has been remarkably developed an optical lithography technology for forming more fine resist pattern on a wafer. Such technology includes a phase-shift method, as one means for improving resolution of a projection/exposure device, in which phases of lights passing through two transparent portions adjacent to each other on a photomask are changed respectively.
This method is performed to carry out projection and exposure on the wafer by using a photomask formed so as to satisfy a relationship of d=&lgr;/2(n−1) (in which d: film thickness; n: refraction factor; &lgr;: exposure wave length) as a shifter for inverting a phase on one of adjacent two light transmitting portions (in this meaning, the photomask may be called “phase-shift photomask, hereinlater”), and the light passing the shifter has a phase reverse to that (180° shift) of the transmitting light of the other on of the transmitting portions, so that light intensity at a pattern boundary portion becomes zero (0) and, thereby, the pattern is separated and the resolution is improved.
Examples of photomasks having shapes realizing the high resolution through the phase-shift method of the characters mentioned above are shown in FIG.
4
.
FIG. 4A
shows a shifter-formation type phase photomask in which a transparent medium
330
, which may be called phase shift film or shifter, having a refraction factor different from that of air is provided for one of adjacent two openings
321
(light transmission sections) formed to a substrate
310
. In such photomask, it is difficult to pile, with high performance, the phase-shift photomask having the same refraction factor as that of the substrate, and there is a possibility of occurrence of a further problem of multipath refraction at the phase shift film
330
.
FIGS. 4B and 4C
show other examples, to solve the above mentioned problem, of a phase shift photomask in which the transparent substrate is subjected to an etching working, which maybe called etching-type or etching-type phase-shift photomask.
With reference to
FIG. 4B
showing the example of etching type phase-shift photomask, an etched portion is formed through an aeolotropic etching process. In such photomask, an amount of light transmitting through the etched portion is reduced in comparison with that transmitting through a non-etched portion, and resist patterns of projection images corresponding to the etched portion and the non-etched portion have dimensions different from each other. This matter is known from the paper 1 (J.Vac.Sci.Technol. B 10(6) (1992) p.3055), R. L. Kostelak, [Exposure characteristics of alternate aperture phase-shifting photomasks fabricated using a subtractive process]).
Furthermore, with reference to
FIG. 4C
showing a phase-shift photomask, in which an etched portion is formed through an isotropic etching process. In such photomask, resist dimension difference is reduced in comparison with the photomask of
FIG. 4B
, which is also known from the above paper 1. This reduction is not, however, remarkable. The phase-shift photomask of
FIG. 4C
may be also called a single-etching type phase-shift photomask, and symbol Wa in
FIG. 4C
shows a side-etching amount (length).
Further, in the etching-type phase-shift photomask of
FIG. 4B
, the amount of light transmitting through the etched portion is reduced in comparison with the non-etched portion because of the existence of side walls of the etched portion, thus generating a difference in dimension to the corresponding resist patterns. Particularly, in the case of hole-arrangement-layer, the transmitting light intensities do not become equal and the dimension difference occurs in the resist patterns on the wafer. This phenomenon is remarkably observed for the hole pattern arranged obliquely less than 1.0 &mgr;m.
Further, in general, the etching through the aeolotropic etching process is performed with dry-etching, and on the other hand, the isotropic etching is performed with wet-etching by using heat alkaline (sodium hydroxide) or hydrofluoric acid.
Furthermore, the prior art reference of the paper 2 (SPIE. Vol. 1927 (1933) p.28, Christophe Pierrat and others, [Phase-shifting Photomask Topography Effects on Lithographic Image Quality]) is known. In this paper 2, as a method of correcting or adjusting difference in dimension of a resist of the example shown in
FIG. 4B
, after etching vertically by an amount corresponding to 180° phase difference through the aeolotropic etching process, which is a state shown in
FIG. 4B
, the isotropic etching process is effected to all the light transmitting section to thereby form an etching-type phase shift photomask represented by the example of FIG.
4
D.
Further, the phase shift photomask shown in
FIG. 4D
may be called double-surface etching-type phase-shift photomask or double-surface etching-type substrate etching phase-shift photomask.
However, when the phase-shift photomask shown in
FIG. 4D
is used to obtain effect of correction by the isotropic etching, the side etching amounts Wb1 and Wb2 are made large and a projecting portion having a hood-like shape (hood-like portions, hereinlater)
325
formed to the light-blocking (light-shielding) material (film)
320
are made fragile in structure. The portions of the light-blocking material to which such hood-like portions
325
are formed to be liable to be peeled during a photomask washing process or like and hence become a cause of occurrence of a defective material or product, which will be called “peeled defective” hereinlater, and moreover, the sum of the Wb1 and Wb2 becomes large, so that the entire structure of the light-blocking films
320
, whose both sides are subjected to the side etching process, becomes easily peelable.
In these days, the single-surface etching-type phase-shift photomask shown in FIG.
4
C and the double-surface etching-type phase-shift photomask shown in
FIG. 4D
have been used as the etching-type phase-shift photomask as shown in FIG.
4
B. However, the single-surface etching-type phase-shift photomask shown in
FIG. 4C
does not provide the structure for sufficiently solving the problem of the difference in dimension of the resists on the wafer corresponding respectively to the etched portion and non-etched portion. On the other hand, in the double-surface etching-type phase-shift photomask shown in
FIG. 4D
, the sum of Wb1 and Wb2 becomes large to obtain sufficient dimension correction effect, and the portions corresponding to the portions of Wb1 and Wb2 are liable to be peeled during a photomask washing process or like and hence become a cause of the “peeled defective”. Moreover, the entire structure of the light-blocking films
320
becomes easily peelable as mentioned above, thus also providing a problem.
SUMMARY OF THE INVENTION
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a method of manufacturing a phase-shift photomask, particularly of an etching-type phase-shift photomask manufacturing method, capable of solving the problem of the difference in dimension of resists on a wafer corresponding to etched portion and non-etched portion and also provide a phase-shift photomask manufactured by such method having a structure having strength suitable for a practical use.
This and other objects can be achieved according to the present invention by providing, in one aspect, a method of manufacturing a phase-shift photomask comprising the steps of:
preparing a substrate transparent to an exposure light having a wavelength &lgr; and having a refraction factor n;
forming, on the substrate, a pattern including light-blocking portion blocking the lig
Dai Nippon Printing Co. Ltd.
Ladas & Parry
Rosasco S.
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