Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-03-15
2004-02-10
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C204S298110
Reexamination Certificate
active
06689515
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for preparing a thin film and more particularly to a phase-shifting photomask blank which permits the improvement of transferred patterns in their resolution by making a difference in phase between exposed light rays passing through a mask and a phase-shifting photomask prepared from the phase-shifting photomask blank as well as a method for producing the photomask blank and the photomask and an apparatus for manufacturing the phase-shifting photomask blank. In other words, the present invention relates to a so-called half-tone type phase-shifting photomask blank, a phase-shifting photomask as well as a method for producing them and an apparatus for manufacturing the phase-shifting photomask blank.
2. Disclosure of the Related Art
In case of a phase-shifting photomask
208
as shown in FIG.
21
(B), a circuit pattern
230
to be transferred onto a semiconductor substrate has in general been formed by making use of a phase-shifting photomask which is produced by etching the surface of a phase-shifting photomask blank
200
which consists of a quartz substrate
201
and a phase-shifting film
204
, as shown in FIG.
21
(A), to remove a desired portion of the film
204
and to thus form openings
210
through which the surface of the quartz substrate
201
is exposed and phase-shifting portions
205
, i.e., the unetched portions of the film
204
remaining on the substrate.
The phase-shifting portion
205
has light-transmission properties to the exposed light rays and the thickness thereof is designed in such a manner that a phase of the exposed light rays transmitting through the opening
210
has a phase difference, by 180 degrees, from that of the light rays transmitting through the phase-shifting portion
205
. Therefore, when exposing a wafer as shown in FIG.
21
(C) to light rays, the light intensity observed on the wafer at the boundary between the opening
210
and the phase-shifting portion
205
becomes zero. For this reason, the circuit pattern transferred using the phase-shifting photomask
208
would have a high resolution.
As the phase-shifting film
204
, there have in general been used a monolayer or multi-layer film and it has been desired for the phase-shifting portion
205
to have a light-transmittance to the exposed light rays in the range of from 4% to 40% in order to obtain an appropriate quantity of exposed light rays during lithography operations and to control the thickness, as determined after development, of a resist film applied onto the wafer.
Up to now, when forming a monolayer phase-shifting film
204
having a desired thickness on a substrate on which a film is deposited (hereinafter simply referred to as “film-forming substrate”) in order to form a phase-shifting photomask blank as shown in FIG.
21
(A) using a film-forming device wherein a reactive gas is supplied to a film-forming chamber and a thin film is formed on the film-forming substrate according to the reactive sputtering technique while passing the substrate over a sputtering target, a film is formed by passing the substrate over the target only one time by controlling the deposition rate of the film on the substrate and the conveying speed of the substrate in such a manner that a desired film thickness can be obtained by a single pass (see, for instance, Japanese Un-Examined Patent Publication (hereinafter referred to as “J.P. KOKAI”) No. Hei 9-17928). The disclosure of the above publication is hereby incorporated by reference herein.
Such a conventional technique will hereinafter be described with reference to the attached FIG.
1
.
FIG. 1
shows a part of a film-forming chamber
11
of a film-forming device. A mixed gas comprising a sputtering gas and a reactive gas is supplied to the film-forming chamber through a gas-supply port
14
after vacuum exhaustion through an exhaust port
15
. A DC voltage which is negative with respect to the grounding voltage is applied to a sputtering target
12
(MoSi) to thus form a discharge zone in the proximity to the sputtering target and as a result, the target
12
begins to discharge sputter materials. If a film-forming quartz substrate
101
is continuously conveyed along a conveying path
18
positioned at a predetermined distance from the target
12
, a desired film is formed on the substrate.
As has been discussed above, when forming the monolayer film having a desired thickness on the film-forming substrate using the film-forming device wherein the reactive gas is supplied to the film-forming chamber and the film is formed on the film-forming substrate according to the reactive sputtering technique while passing the substrate over the sputtering target, the thin film has conventionally been formed by passing the substrate over the target only one time by controlling the deposition rate of the film on the substrate and the conveying speed of the substrate in such a manner that a desired film thickness can be obtained by a single pass. In this case, however, the thickness distribution of the monolayer film has a tendency as shown in FIG.
1
. More specifically,
FIG. 1
shows the deposition rate distribution of the target component
19
-
1
(or the thickness distribution of the target component formed on a static substrate). The distribution of the target component along a conveying path
18
is not uniform and therefore, the higher the deposition rate of the target component along the conveying path
18
, the larger the amount of the unreacted target component if it is assumed that the frequency of the reactive gas incident upon the substrate
101
is approximately constant along the conveying path
18
as shown in
FIG. 1
(see line
19
-
2
). Accordingly, the content of the reaction product in the resulting film is low and a non-uniform film is formed on the conveyed substrate. If an opening
17
-
1
positioned between shielding plates
17
is divided into regions A, B and C arranged along the conveying path
18
, a non-uniform film
31
shown in
FIG. 2
is formed on the substrate
101
by a single forward movement of the substrate
101
, in a horizontal direction, over a target
12
. The non-uniform film is thus formed on the substrate and this accordingly results in various drawbacks. For instance, the resulting film shows optical characteristics which are widely different from those expected for a uniform monolayer film and exhibits resistance to chemicals considerably inferior to that of a uniform film. Moreover, this film cannot optically be handled as a monolayer film and this in turn results in such disadvantages that this makes the calculation of the optical constants quite difficult and that the design and the quality control of films become difficult. In order to eliminate such drawbacks, it has been devised to reduce the lengths of the opening
17
-
1
of the shielding plate and that of a chimney
13
along the substrate-conveying direction (this is referred to as “opening length”) so that only the region B (for instance, the region whose deposition rate is not less than 90% of the maximum level thereof) in which the deposition rate of the target component is approximately constant contributes to the film-formation, or so that even a part of the region A contributes to the film-formation. However, the former suffers from a problem of reduction of the utilization efficiency of the target
12
(the ratio of the amount of the target capable of being used in the film-formation to the total consumed amount thereof) and productivity, while the latter suffers from a problem of, for instance, the reduction in the utilization efficiency of the target according to the reduction in the opening length, the deterioration of the resistance to chemicals due to the non-uniformity of the film composition and complication of optical characteristics.
SUMMARY OF THE INVENTION
Accordingly, it is generally an object of the present invention to solve the foregoing problems associated with the conventional sputtering techniques and specifically to pro
Amano Jun
Isao Akihiko
Kawada Susumu
Kobayashi Ryoichi
Yamamoto Tsuneo
Arent Fox Kintner Plotkin & Kahn
Rosasco S.
Ulvac Coating Corporation
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