Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-11-16
2004-05-18
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06737201
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention broadly relates to a substrate with a multilayer film, a reflection type mask blank, and a reflection type mask for use in a semiconductor production to control a light ray, and a production method thereof as well as a method for manufacturing a semiconductor device.
Herein, it should be noted that an EUV (Extreme Ultra Violet) light ray, which will be described later, represents a light ray with wavelength band of a soft X-ray region or a vacuum ultraviolet region, more specifically a light ray with wavelength of about 0.2-100 nm.
Conventionally, use has been made of a photolithography method using a visible light ray or an ultraviolet light ray as a transfer technique of a fine pattern required for forming an integrated circuit with fine patterns on a Si substrate or the like in a semiconductor industry.
However, a semiconductor device has been rapidly reduced in size in recent years. Consequently, shortening wavelength has been largely restricted because of an exposure limit in conventional optical exposure.
Under such a circumstance, a resolution limit of a pattern will be a half of exposure wavelength in case of the optical exposure. It is predicted that the resolution limit is equal to approximately 70 nm even if an F
2
laser ray (157 nm) is used.
Therefore, a great attention has been paid for an EUV lithography (hereinafter, it will be abbreviated as “EUVL”) as an exposure technique, in which an EUV light ray (13 nm) having wavelength shorter than the F
2
laser ray is used, as a next generation exposure technique with 70 nm or shorter.
In general, an image forming principle of EUVL is the same as the photolithography. However, absorption rate for all substances with respect to the EUV light ray is high, and further, index of refraction is substantially equal to 1.
In consequence, a refraction optical system can not be used different from the optical exposure, and alternatively, a reflection optical system must be used.
In this event, suggestion has been made about a transmission type mask using a membrane as a mask used in the above-mentioned case. However, the absorption rate of the membrane for the EUV light ray becomes high. Thereby, exposure duration becomes long, and a desired throughput can not be maintained. For this reason, the reflection type mask for exposure is generally used in the recent years.
For example, a reflection type mask for exposure is disclosed in Japanese Examined patent publication No. 7-27198 and Japanese Unexamined Patent Publication No. 8-213303. In such a reflection type mask, a reflection layer with a multilayer structure is formed on a substrate and an absorber for absorbing a soft X-ray or a vacuum ultraviolet ray is formed to a pattern shape on the reflection layer.
FIGS. 1A and 1B
are schematic views showing an example of the conventional reflection type mask blank for exposure and the conventional reflection type mask for exposure.
As illustrated in
FIG. 1A
, a reflection film
22
with a multilayer structure is deposited on a substrate
21
, an etching stopper layer
23
is deposited on the reflection film
22
, and an absorber layer
24
is deposited on the etching stopper layer
23
.
With such a structure, a pattern is formed for the absorber layer
24
of the reflection type mask blank for exposure, and an unnecessary etching stopper layer
23
on the multilayer film is removed, thus manufacturing the reflection type mask for exposure illustrated in FIG.
1
B.
Under this circumstance, the soft X-rays entered to the reflection type mask for exposure is reflected by the reflection film
22
, and is absorbed at a portion, in which the pattern of the absorber
24
is formed, without reflection. As a result, the pattern can be formed with high contrast between a reflection portion and an absorption portion.
However, it is necessary to increase film density of each layer of the multilayer film
22
to obtain high index of reflection in the reflection type mask for exposure in which the multilayer film
22
is deposited on the above-mentioned substrate
21
. Consequently, the multilayer film
22
inevitably has high compression stress.
In the cause of such high compression stress, the substrate
21
is largely warped or deformed through a convex surface, as illustrated in FIG.
2
. As a result, warping also occurs for the surface of the multilayer film
22
serving as a reflection surface of the EUV light ray.
For example, when the compression stress of about 200 MPa is applied for the multilayer film
22
with a 0.3 &mgr;m thickness on a quartz substrate having a 6 inch square and a 6.35 mm thickness, warping (deformation) on the order of 500 nm inevitably takes place for an area of 140×140 mm.
As discussed above, transfer accuracy is lowered or image placement error occurs in the cause of the warping of the surface of the multilayer film
22
during transferring a pattern onto a wafer according to the conventional technique. Thereby, transfer can not be carried out with high accuracy. To solve such a problem, the stress of the multilayer film
22
may be reduced. However, this method is not preferable from a practical viewpoint because the film density and the reflectivity of the EUV light ray are lowered.
Further, the warping of the multilayer film
22
is affected by the warping inherent to the substrate
21
in addition to the deformation of the substrate
21
due to the compression stress of the above-mentioned multilayer film
22
.
Accordingly, it is difficult to effectively correct the warping of the surface of the multilayer film
22
by merely reducing the stress of the multilayer film
22
.
SUMMARY OF THE INVENTION
This invention is made under the above-discussed background. It is therefore an object of this invention to provide a substrate with a multilayer film, a reflection type mask blank for exposure, and a reflection type mask for exposure which has a surface of a multilayer film with high flatness by correcting warping (deformation) of the surface of the multilayer film formed by stress of the multilayer film and the warping (deformation) of the substrate itself.
According to a first aspect of this invention, a reflection type mask blank for EUV exposure has a substrate.
Further, a multilayer film is formed on the substrate so as to reflect an EUV light ray. An absorber layer is formed on the multilayer film so as to absorb the EUV light ray. Under this circumstance, the multilayer film has flatness with respect to a surface thereof, and the flatness is 100 nm or less.
Herein, the flatness described in the instance specification indicates the warping (deformation quantity) of the surface represented by TIR (Total Indicated Reading), and will be defined as follows.
Namely, a plane surface defined by a least square method based upon a substrate surface
31
is defined as a focal plane in FIG.
3
. Subsequently, an absolute value of a difference between a highest position A of the substrate surface
31
over the focal plane
32
based upon the focal plane
32
and a lowest position B of the substrate surface
31
under the focal plane
32
is defined as the flatness. Therefore, the flatness is always a positive number.
In this event, a measured value within a area of 140×140 mm is defined as the flatness according to this invention. For example, it is a measured value within the area of 140 ×140 mm with respect to a center of a 6 inch substrate.
According to a second aspect of this invention, a reflection type mask blank for EUV exposure has a substrate.
Further, a multilayer film is formed on the substrate so as to reflect an EUV light ray. A light absorber layer is formed on the multilayer film so as to absorb the EUV light ray. A stress correction film corrects warping of a surface of the multilayer film. In this event, the warping is formed by warping of the substrate and stress of the multilayer film.
According to a third aspect of this invention, the stress correction film has tensile stress, and is placed between the substrate and the multilayer film
Hosoya Morio
Shoki Tsutomu
Hoya Corporation
Rosasco S.
Sughrue & Mion, PLLC
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