JP2009147200A - Reflective photomask and reflective photomask manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflective photomask excellent in the contrast of a transfer pattern by suppressing a projection effect due to the incidence of exposure light with an angle. <P>SOLUTION: The reflective photomask has an absorption part pattern having a forward tapered shape. By the configuration, since the absorption part pattern has the forward tapered shape, the interruption of the exposure light by the absorption part pattern at the edge part of the absorption part pattern is suppressed, and the influence of the projection effect by the incident angle of the exposure light is suppressed. Thus, the transfer pattern of the excellent contrast can be formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reflective photomask and a method for manufacturing the reflective photomask.

  With the recent high integration in semiconductor elements, the miniaturization of patterns transferred by photolithography is accelerating. Since the resolution limit of the pattern is almost proportional to the exposure wavelength, an exposure apparatus using a short wavelength source such as a mercury lamp (wavelength 365 nm) or an excimer laser (wavelength 248 nm, 193 nm) has been developed so far. It was.

  However, in order to form a pattern of 100 nm or less that is smaller than the wavelength, it is necessary to make full use of techniques such as a phase shift method and proximity effect correction. It has become an issue.

  As a countermeasure for this, a fine pattern such as 45 nm and 32 nm using an existing light source is developed by developing an immersion exposure technique in which exposure is performed by filling a liquid between a wafer to which a pattern is transferred in an exposure apparatus and a reduction lens. It is being considered to form.

  On the other hand, as next-generation lithography technology with an eye toward further miniaturization, lithography technology using EUV light (Extreme Ultra Violet) having a wavelength of 10 to 15 nm as a light source has been developed. From the characteristics of the plasma light source, a wavelength near 13.5 nm is the most promising candidate.

  In the EUV wavelength region, the refractive index of most substances is slightly smaller than 1, and the light absorption is very high. For this reason, in EUV lithography, the refractive optical system conventionally used cannot be used, but becomes a reflection optical system. Similarly, since a conventional transmission type mask cannot be used for the photomask, it is necessary to use a reflection type mask. Thus, in EUV lithography, the optical system and mask used for exposure are significantly different from those of conventional exposure techniques.

  The basic structure of a reflective photomask for EUV lithography is to provide a mirror (reflector) having a high reflectivity at the EUV wavelength on a flat substrate made of a material having a very low coefficient of thermal expansion. In addition, a light absorption layer made of a material having high absorbability with respect to EUV light is formed by pattern processing according to a desired exposure pattern.

  Since a reflective optical system is used, an exposure apparatus for EUV lithography is designed such that exposure light is incident at an angle of 6 ° or the like with respect to the vertical direction of the reflective photomask. (See Patent Document 1)

Thus, in general, in the case of photolithography using a reflective photomask, exposure light is incident at an angle with respect to the vertical direction of the photomask.
JP 2003-45782 A

In general, in the case of photolithography using a reflective photomask, exposure light is incident at an angle with respect to the vertical direction of the photomask.
For this reason, a projection effect is produced according to the incident angle with respect to the absorption portion pattern formed in parallel to the projection axis direction of the traveling direction of the exposure light to the substrate plane. This affects the contrast of the edge portion (FIG. 2).

  Therefore, the present invention has been made to solve the above-described problems, and suppresses the projection effect caused by exposure light incident at an angle, and is a reflective photomask excellent in transfer pattern contrast. The purpose is to provide.

  The present invention according to claim 1 is a reflective photomask characterized in that the absorbing portion pattern is an absorbing portion pattern having a forward tapered shape.

  The present invention according to claim 2 is the reflective photomask according to claim 1, wherein the substrate, the reflection portion for the exposure light wavelength provided on the substrate, and the reflection portion are provided. It comprises at least an absorption part for the exposure light wavelength and an absorption part pattern provided in the absorption part, and the absorption part pattern is an absorption part pattern having a forward taper shape in the incident angle direction of the exposure light. It is a reflection type photomask characterized.

  A third aspect of the present invention is the reflective photomask according to the first or second aspect, wherein the absorbing portion pattern further includes a projection axis direction on a substrate plane in a traveling direction of exposure light. It is a reflection type photomask characterized by being an absorption part pattern having a vertical cross-sectional shape in the vertical direction.

A fourth aspect of the present invention is the reflective photomask according to any one of the first to third aspects, wherein the projection axis direction of the exposure light traveling direction onto the substrate plane is the X axis, In a three-dimensional orthogonal space system in which the axis direction orthogonal and parallel to the substrate plane is the Y axis, and the direction perpendicular to the substrate plane is the Z axis, when exposure light is incident at an incident angle θ1, The taper angle θ2 of the cross-sectional side wall of the cut-out absorption part pattern is
θ2 = 90 ° −θ1
A reflective photomask characterized by satisfying the relationship shown in FIG.

The present invention according to claim 5 is the reflective photomask according to any one of claims 1 to 4, wherein the projection axis direction on the substrate plane in the traveling direction of the exposure light is an X axis, In a three-dimensional orthogonal space system in which the axis direction orthogonal and parallel to the substrate plane is the Y axis, and the direction perpendicular to the substrate plane is the Z axis, exposure light is incident at an incident angle θ1, and the thickness of the absorber In the case where an absorbing portion pattern is formed on the XY plane and inclined by an angle θ3 with respect to the X axis, the line width b of the portion in the forward tapered shape of the absorbing portion pattern is
b = h × sin θ3 / tan θ1
A reflective photomask characterized by satisfying the relationship shown in FIG.

  The present invention according to claim 6 is a reflection type comprising a substrate, a reflection part for the exposure light wavelength provided on the substrate, and an absorption part for the exposure light wavelength provided on the reflection part. A step of preparing a photomask blank; a step of forming a pattern on the absorption portion; and a step of forming a forward taper shape on a sidewall of the pattern formed on the absorption portion to form an absorption portion pattern. A reflection type photomask manufacturing method characterized by the above.

The reflective photomask of the present invention is characterized by having an absorbing portion pattern having a forward tapered shape.
According to the configuration of the present invention, since the absorption portion pattern has a forward tapered shape, it is possible to suppress exposure light from being blocked by the absorption portion pattern at the edge portion of the absorption portion pattern, and to perform projection by the incident angle of the exposure light. The influence of the effect can be suppressed.
Therefore, it is possible to form a transfer pattern with excellent contrast.

Hereinafter, a conventional reflective photomask will be exemplified.
In this specification, the spatial coordinate system indicated by the X axis, the Y axis, and the Z axis is “the projection axis direction of the exposure light traveling direction onto the substrate plane is the X axis, and the substrate plane is orthogonal to the X axis. It is assumed that it is a “three-dimensional orthogonal space system” in which the parallel axis direction is the Y axis and the direction perpendicular to the substrate plane is the Z axis. Further, the incident angle of the exposure light is assumed to be θ1.

  In general, a reflective photomask is a photomask blank having a reflecting portion 2 on a substrate 1 and an absorbing portion 3 on the reflecting portion 2 as shown in FIG. Is manufactured by a fine processing method.

  FIG. 2 shows an example of a conventional reflective photomask. 2a is a schematic perspective view, FIG. 2b is a schematic cross-sectional view in the XZ plane, FIG. 2c is a plan view in the XY plane, and FIG. 2d is a transfer pattern plan view in the XY plane.

  In the conventional reflection type photomask, since the exposure light is incident at a certain angle with respect to the vertical direction of the photomask, the exposure light is formed in parallel to the projection axis direction to the substrate plane in the traveling direction. With respect to the absorbing portion pattern, a projection effect is generated according to the incident angle (FIGS. 2a and 2b). This affects the contrast of the transfer pattern edge (FIG. 2d).

  FIG. 2 b shows the XZ plane of the reflective photomask 100. When transfer exposure is performed using the reflective photomask 100, the side wall angle of the mask pattern formed on the absorbing portion 3 is 90 °, so that exposure light is completely projected by the orthogonal projection with respect to the x-axis at the pattern side wall portion. It cannot be absorbed.

  Considering the XY plane of the reflective photomask 100 shown in FIG. 2c, even if the mask pattern including the absorber 3 and the reflector 2 is accurately formed on the reflective photomask, When a reflection type photomask is installed and transferred, in the pattern formed on the wafer shown in FIG. 2d, the pattern formed in parallel to the Y axis, the photosensitive portion 5 and the non-photosensitive portion 6 The transfer contrast lowering portion 7 occurs at the boundary between the two.

Hereinafter, the reflective photomask of the present invention will be described.
FIG. 3 shows an example of the reflective photomask of the present invention. 3a is a schematic perspective view, FIG. 3b is a schematic cross-sectional view in the XZ plane, FIG. 3c is a plan view in the XY plane, and FIG. 3d is a transfer pattern plan view in the XY plane.

  The reflective photomask shown in FIG. 3 has an absorption portion pattern having a forward taper shape in the incident angle direction of exposure light. Since the absorption part pattern has a forward taper shape in the incident angle direction of the exposure light, it is possible to suppress exposure light from being blocked by the absorption part pattern at the edge part of the absorption part pattern, and the projection effect by the incident angle of the exposure light The influence of can be suppressed. Therefore, it is possible to form a transfer pattern with excellent contrast.

In the reflection type photomask of the present invention, it is preferable that the absorption part pattern further has an absorption part pattern having a vertical cross-sectional shape in the direction perpendicular to the projection axis direction on the substrate plane in the traveling direction of the exposure light.
By making the absorption portion pattern a pattern having a vertical cross-sectional shape in the direction perpendicular to the projection axis direction on the substrate plane in the traveling direction of exposure light, the contrast of the transfer pattern in the direction perpendicular to the incident angle direction can be improved.

  FIG. 4 shows an absorption part pattern in which the absorption part pattern has a forward taper shape in the incident angle direction of the exposure light, and a vertical cross-sectional shape perpendicular to the projection axis direction to the substrate plane in the traveling direction of the exposure light. An example of the implementation of the reflective photomask of the present invention in the case of the provided absorption part pattern is shown. 4a is a schematic perspective view, FIG. 4b is a schematic cross-sectional view in the XZ plane, FIG. 4c is a plan view in the XY plane, and FIG. 4d is a transfer pattern plan view in the XY plane.

At this time, when the transfer patterns are compared (compare FIG. 3d with FIG. 4d), in the case of FIG. 3d, among the transfer patterns formed on the wafer, the transfer pattern formed parallel to the X axis. The forward taper portion cannot absorb the exposure light sufficiently because the thickness of the absorbing portion is small, and the transfer contrast lowering portion 7 is generated at the boundary between the photosensitive portion 5 and the non-photosensitive portion 6. However, in FIG. 4d, even a transfer pattern formed parallel to the X axis can sufficiently absorb the exposure light, and therefore can be transferred with good contrast.
For this reason, the absorption part pattern of the present invention is an absorption part pattern having a forward taper shape in the incident angle direction of the exposure light, and is perpendicular to the projection axis direction on the substrate plane in the traveling direction of the exposure light. By using the absorption portion pattern having a cross-sectional shape, exposure light in the direction perpendicular to the incident angle direction can be sufficiently absorbed, and the contrast of the transfer pattern in the direction perpendicular to the incident angle direction can be improved.

The reflective photomask of the present invention is a three-dimensional orthogonal space system in which the projection axis in the traveling direction of the exposure light is the X axis, the substrate plane is the XY plane, and the direction perpendicular to the substrate plane is the Z axis. When the exposure light is incident at an incident angle θ1, the taper angle θ2 of the cross-sectional side wall of the absorber pattern cut out in the XZ plane is
θ2 = 90 ° −θ1
It is preferable to satisfy the relationship shown in FIG.
By setting the taper angle to θ2 that satisfies the above formula, the taper angle suitable for the incident angle can be obtained.

  FIG. 3 b shows the XZ plane of the reflective photomask 200. When transfer exposure is performed using the reflective photomask 200, the pattern side wall angle θ2 of the absorbing portion is 90 ° −θ1, so that the exposure light at the incident angle θ1 is parallel to the side wall of the absorbing portion pattern. Incidence and reflection occur, and the transfer contrast lowering portion 7 shown in FIG. 2d is eliminated.

The reflective photomask of the present invention is a three-dimensional orthogonal space system in which the projection axis in the traveling direction of the exposure light is the X axis, the substrate plane is the XY plane, and the direction perpendicular to the substrate plane is the Z axis. In the case where the thickness of the absorbing portion is h and an absorbing portion pattern is formed on the XY plane and inclined by an angle θ3 with respect to the X axis, the line width b of the portion in the forward tapered shape of the absorbing portion pattern is:
b = h × sin θ3 / tan θ1
It is preferable to satisfy the relationship shown in FIG.

  In the case of forming an absorption portion pattern that is on the XY plane and is inclined by an angle θ3 with respect to the X axis, the film thickness h of the absorption portion, the incident angle θ1 of the exposure light, and the angle θ3 of the absorption portion pattern with respect to the X axis, By deriving the forward tapered shape of the absorbing portion pattern from the above, the forward tapered shape suitable for the incident angle of the exposure light can be determined.

  FIG. 5 shows an example of the reflective photomask of the present invention in the case of forming an absorption portion pattern that is on the XY plane and is inclined by an angle θ3 with respect to the X axis. 5a is a schematic perspective view, FIG. 5b is a schematic cross-sectional view in the XZ plane, and FIG. 26 is a plan view in the XY plane.

  In FIG. 5a, the film thickness of the absorber 3 is h, the inclination is θ3 with respect to the x axis of the pattern to be formed, the projection axis in the traveling direction of the exposure light is the x axis, and the incident angle is θ1. Think about the case.

Even when the absorber pattern is inclined by θ3 with respect to the x-axis on the XY plane, the side wall angle θ2 of the pattern of the absorber 3 formed on the xz plane is 90 ° −θ1 as shown in FIG. 5B. preferable.
For this reason, with respect to the pattern of the absorbing portion 3 in the XZ plane, the line width a of the portion forming the side wall taper angle is
Line width a = h / tan θ1 (Equation 1)
It can be expressed by the thickness h of the absorbing portion 3 and the incident angle θ1 of the exposure light.

Further, as shown in FIG. 5c, when the absorber pattern is inclined by θ3 with respect to the X axis on the XY plane, the line width b on the perpendicular drawn with respect to the inclination θ3 is
Line width b = Line width a × sin θ3 (Expression 2)
It can be expressed as.

By substituting (Equation 1) into (Equation 2) above,
Line width b = h × sin θ3 / tan θ1 (Equation 3)
Is derived.
Therefore, when satisfying (Equation 3), it is possible to obtain an absorbing portion pattern having a particularly suitable tapered shape suitable for the incident angle of the exposure light.

  In this case, in the XY plane, θ3 = 0 for the pattern parallel to the X axis, so the line width b = 0, and as a result, it is preferable not to give a taper angle to the pattern of θ3 = 0. Also shown.

  Thus, by determining the line width b of the portion whose side wall is tapered, forming a resist pattern corresponding to this, and performing dry etching, a pattern inclined at an arbitrary angle with respect to the X axis can be obtained. A reflective photomask 400 that does not lower the transfer contrast can be produced.

Hereinafter, the reflective photomask manufacturing method of the present invention will be described.
In order to manufacture the reflective photomask of the present invention, after forming a pattern, a <step of forming a forward tapered shape on the side wall of the pattern> may be performed. The step of forming the forward taper shape may use a known fine processing technique, for example, electron beam lithography.
Hereinafter, as an example, the reflective photomask manufacturing method of the present invention when electron beam lithography is used will be described.

  First, a reflection type photomask blank comprising a substrate 1, a reflection part 2, and an absorption part 3 is prepared, and a resist 8 for electron beam lithography is applied to this, electron beam drawing and development are performed, and an electron is formed on the photomask blank. A resist pattern A for line lithography is formed (FIG. 6a).

Next, a pattern is formed in the absorber 3 by dry etching. At this time, the dry etching conditions are set so that the side wall angle of the absorbing portion pattern is 90 °.
Next, the resist 8 for electron beam lithography is peeled off to obtain a reflective photomask having an absorption portion pattern with a side wall angle of 90 ° (FIG. 6b).

  Next, the resist 8 for electron beam lithography is applied again, and a resist pattern for electron beam lithography for forming a taper angle on the side wall of the pattern is formed by electron beam drawing and development.

At this time, as an example of a resist pattern for electron beam lithography,
(1) Resist pattern B1 (FIG. 6c) in which the line width α of the portion that gives the taper angle is added to the line width of the absorbing portion pattern formed in the previous step;
(2) Resist pattern B2 formed so that the resist on the portion where the taper angle is added has a forward taper shape in addition to the line width of the absorbing portion pattern formed in the previous step. (FIG. 6d) may be used.

  Next, using the formed resist pattern for electron beam lithography as a mask, dry etching is performed under such a condition that the side wall of the absorbing portion 3 has a forward taper shape to form an absorbing portion pattern having a forward taper shape (FIG. 6e). .

  From the above, the reflective photomask of the present invention can be manufactured.

  Hereinafter, an example of the implementation of the reflective photomask manufacturing method of the present invention will be shown.

  First, a CrN layer 9 is provided on the back surface of the low thermal expansion glass substrate 10 for holding against an electrostatic chuck during exposure, and a multilayer reflective layer 11 in which 40 pairs of Mo and Si are alternately laminated on the surface of the low thermal expansion glass substrate 10. A protective layer 12 made of 11 nm Si, a buffer layer 13 made of 10 nm Cr, a light-absorbing layer lower layer 14 made of a material containing Si of 75 nm and containing Si, and a material containing Si containing Si of 14 nm as a main ingredient. A photomask blank in which the light absorption layer upper layer 15 made of an oxide was sequentially provided was prepared (FIG. 7a).

  Next, a resist 16 for electron beam lithography (FEP171: manufactured by Fuji Film Electronics Co., Ltd.) having a film thickness of 300 nm is applied to the outermost surface of the prepared photomask blank, and these are electron beam drawn and developed to form a resist pattern C. (FIG. 7b).

Next, the light absorption layer upper layer 15 made of a material containing Ta as a main component and containing Si, and the light absorption layer lower layer 14 made of an oxide of a material containing Ta as a main component and containing Si are dry-etched by F-based gas plasma, The pattern of the light absorption part was formed.
At this time, the dry etching conditions were controlled so that the side wall angle of the formed pattern was 90 °.

  Next, the resist for electron beam lithography was peeled off to form a light absorption layer pattern having a side wall angle of 90 ° (FIG. 7c).

  Next, resist 16 for electron beam lithography (FEP171: manufactured by Fuji Film Electronics Co., Ltd.) is applied again to a resist film thickness of 300 nm, this is drawn and developed, and the line width of the portion where the taper angle is added to the resist pattern C A resist pattern D designed with the above added was formed (FIG. 7d).

Next, the exposed light absorption layer lower layer 15 made of a material containing Ta as a main component and containing Si, and the light absorption layer upper layer 14 made of an oxide of a material containing Ta as a main component and containing Si by F-based gas plasma. Dry etching was performed to form a light absorption layer pattern.
At this time, the etching conditions were set so that the exposed light absorbing layer had a right-angled triangular forward taper shape with the line width as the base and the combined thickness of the upper and lower layers of the light absorbing layer as the height.

  Next, the resist for electron beam lithography was peeled off to form a light absorption layer pattern having a forward tapered shape (FIG. 7e).

Next, the buffer layer 13 was dry-etched with a mixed gas plasma of Cl-based gas and O-based gas to expose the protective layer.
At this time, the etching conditions were set so that the buffer layer pattern formed a tapered shape having the same angle as the light absorption layer pattern (FIG. 7f).

  From the above, the reflective photomask of the present invention could be manufactured.

It is a cross-sectional schematic diagram of a general reflective photomask blank. It is the schematic which shows the transfer pattern using the conventional reflective photomask and this reflective photomask. It is the schematic which shows the transfer pattern using the reflective photomask of this invention, and this reflective photomask. It is the schematic which shows the transfer pattern using the reflective photomask of this invention, and this reflective photomask. It is a figure which shows the reflection type photomask of this invention. It is a figure which shows an example of implementation of the reflection type photomask manufacturing method of this invention. It is a figure which shows an example of implementation of the reflection type photomask manufacturing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate 2 ... Reflection part 3 ... Absorption part 4 ... Absorption part pattern side wall angle order taper formation part 5 ... Photosensitive part 6 ... Non-photosensitive part 7 ... Transfer contrast fall Part 8 ... Resist 9 ... CrN layer 10 ... Low thermal expansion glass substrate 11 ... Multi-layer reflective layer 12 ... Protective layer 13 ... Buffer layer 14 ... Light absorption layer lower layer 15 ... .Light absorbing layer upper layer 16... Resist for electron beam lithography

Claims (6)

A reflective photomask, wherein the absorbing portion pattern is an absorbing portion pattern having a forward tapered shape. The reflective photomask according to claim 1,
A substrate,
A reflection portion for the exposure light wavelength provided on the substrate;
An absorption part for the exposure light wavelength provided on the reflection part;
An absorption part pattern provided in the absorption part, at least,
The reflective photomask according to claim 1, wherein the absorbing portion pattern is an absorbing portion pattern having a forward tapered shape in an incident angle direction of exposure light. The reflective photomask according to claim 1, wherein
The reflection type photomask according to claim 1, wherein the absorption portion pattern is an absorption portion pattern having a vertical cross-sectional shape in a direction perpendicular to a projection axis direction of the traveling direction of exposure light onto the substrate plane. The reflective photomask according to any one of claims 1 to 3,
Three-dimensional with the projection axis direction of the exposure light traveling direction on the substrate plane as the X axis, the axis direction orthogonal to the X axis and parallel to the substrate plane as the Y axis, and the direction perpendicular to the substrate plane as the Z axis In an orthogonal space system,
When exposure light is incident at an incident angle θ1,
The taper angle θ2 of the cross-sectional side wall of the absorber pattern cut out in the XZ plane is
θ2 = 90 ° −θ1
A reflective photomask characterized by satisfying the relationship shown in FIG. The reflective photomask according to any one of claims 1 to 4,
Three-dimensional with the projection axis direction of the exposure light traveling direction on the substrate plane as the X axis, the axis direction orthogonal to the X axis and parallel to the substrate plane as the Y axis, and the direction perpendicular to the substrate plane as the Z axis In an orthogonal space system,
When exposure light is incident at an incident angle θ1, the thickness of the absorber is h, and an absorber pattern is formed on the XY plane and inclined by an angle θ3 with respect to the X axis,
The line width b of the site in the forward tapered shape of the absorber pattern is
b = h × sin θ3 / tan θ1
A reflective photomask characterized by satisfying the relationship shown in FIG. Preparing a reflective photomask blank comprising a substrate, a reflection portion for the exposure light wavelength provided on the substrate, and an absorption portion for the exposure light wavelength provided on the reflection portion;
Forming a pattern on the absorbing portion;
Forming a forward taper shape on the side wall of the pattern formed in the absorber, and forming the absorber pattern;
A method for producing a reflective photomask, comprising: