JP2012209404A - Reflective mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective mask used for extreme-ultraviolet (EUV) lithography, which will not be damaged or will not vary in optical characteristics by processing of an absorption layer and a multi-layered reflective layer, and has high light-shield properties.SOLUTION: In an outer periphery portion of a circuit pattern region of a reflective mask, a light-shield region, formed of a separate member, is provided. Thereby, a reflective mask including a light-shield frame with high light-shield properties can be provided through a simple process, without involving complex processing or handling.

Description

  The present invention relates to a reflective mask, and more particularly to a reflective mask used in a semiconductor manufacturing apparatus using EUV lithography that uses extreme ultraviolet light (hereinafter referred to as EUV: Extreme Ultra Violet) as a light source. .

(Description of EUV lithography)
With recent miniaturization of semiconductor devices, EUV lithography using EUV having a wavelength of around 13.5 nm as a light source has been proposed. Since EUV lithography has a short light source wavelength and very high light absorption, it needs to be performed in a vacuum. In the EUV wavelength range, the refractive index of most substances is slightly smaller than 1. For this reason, the EUV lithography cannot use a transmission type refractive optical system which has been used conventionally, and becomes a reflection optical system. Therefore, a photomask (hereinafter referred to as a mask) as an original plate must be a reflection type mask because a conventional transmission type mask cannot be used.

(Description of EUV mask and blank structure)
Such a reflective mask is produced based on a substrate called a mask blank. On the surface of the substrate, a multilayer reflective layer showing a high reflectance with respect to the exposure light source wavelength and an absorption layer having the exposure light source wavelength are sequentially formed on the low thermal expansion substrate. On the back surface of the substrate, a back surface conductive film for an electrostatic chuck in the exposure machine is formed. Some have a structure having a buffer layer between the multilayer reflective layer described above and the absorption layer.

  When processing from a mask blank to a reflective mask, the absorber layer is partially removed by electron beam (EB) lithography and etching technology, and in the case of a structure having a buffer layer, this is also removed, and the absorber and reflector are reflected. A circuit pattern consisting of parts is formed. The light image reflected by the reflection type mask thus created is transferred onto the semiconductor substrate via the reflection optical system.

(Explanation of the film thickness and reflectance of the absorption layer of the EUV mask)
In the exposure method using the reflective optical system, irradiation is performed at an incident angle (usually 6 ° as an example) inclined by a predetermined angle from the vertical direction with respect to the mask surface. Occurs. Since the reflection intensity in the shadowed portion is smaller than that in the non-shadowed portion, the contrast is lowered, and the edge portion of the transfer pattern may be blurred or deviated from the design dimension. Such a phenomenon is called shadowing and is one of the fundamental problems of the reflective mask.

  In order to prevent such blurring of the pattern edge portion and deviation from the design dimension, it is effective to reduce the thickness of the absorption layer and reduce the height of the pattern. However, when the thickness of the absorbing layer is reduced, the light shielding property in the absorbing layer is lowered, the transfer contrast is lowered, and the accuracy of the transfer pattern is lowered. That is, if the absorption layer is made too thin, the contrast necessary for maintaining the accuracy of the transfer pattern cannot be obtained.

  As described above, since the thickness of the absorption layer is too thick or too thin, it is currently in the range of about 50 to 90 nm, and the reflectance of the EUV light at the absorption layer is 0. It is about 5 to 2%.

(Explanation of multiple exposure of adjacent chips)
On the other hand, when a transfer circuit pattern is formed on a semiconductor substrate such as a silicon wafer using a reflective mask, chips having a plurality of circuit patterns are formed on one semiconductor substrate. There may be a region where the outer periphery of the chip overlaps between the adjacent chips. This is because the chips are arranged at a high density in order to improve productivity to increase the number of chips that can be taken per wafer.

  In this case, the region where the chip outer peripheral portions overlap is exposed (multiple exposure) a plurality of times (up to four times). The chip outer peripheral portion of this transfer pattern is also the outer peripheral portion on the mask, and is usually the absorption layer portion. However, as described above, since the reflectance of EUV light on the absorption layer is about 0.5 to 2%, there is a problem that the outer periphery of the chip is exposed by multiple exposure. Therefore, the outer periphery of the chip on the mask needs to be a low-reflectance region (hereinafter referred to as a light-shielding frame) that has a higher light-shielding property for EUV light than a normal absorbing layer and has a reflectance of 0.3% or less Sex came out.

  In order to solve such problems, a groove is formed by digging from the absorption layer of the reflective mask to the multilayer reflective layer, or the reflection of the multilayer reflective layer is performed by laser irradiation or ion implantation on the reflective mask. A reflective mask provided with a light-shielding frame having a high light-shielding property with respect to the exposure light source wavelength by reducing the rate has been proposed. (For example, see Patent Document 1)

JP 2009-212220 A

  However, in the technique described in the above-mentioned Patent Document 1, it is necessary to process a total of 80 layers of Si and Mo for the dug of the multilayer reflective layer after creating the mask pattern. In the technique of forming a groove that has been dug up to the reflective layer, the multilayer reflective layer is dug after the mask pattern is created, and particle generation is unavoidable, leading to a decrease in mask quality. It was. In addition, since the multilayer reflective layer is removed after removing the upper absorption layer, there is a disadvantage that the reflectance is increased when only a few multilayer reflective layers remain.

  In addition, in the technique of forming a light-shielding frame with low reflectivity on a reflective mask by laser irradiation or ion implantation, there is a loss of laser light or ions due to other than the multilayer reflective layer. It must be irradiated with light or ions. Then, the film other than the multilayer reflective layer is damaged by the irradiation of laser light or ions, and there is a disadvantage that the absorption rate of the exposure light source wavelength of the absorption layer is lowered.

  In any case, the conventional method has a disadvantage that it is necessary to perform complicated processing and processing on a portion near the circuit pattern already formed on the reflective mask.

  An object of the present invention is to provide a reflective mask provided with a light shielding frame having a high light shielding property, which is mounted by a simple process without complicated processing and processing.

  The present invention employs the following configuration in order to solve the above problems.

The present invention relates to a reflective mask used in extreme ultraviolet (EUV) lithography.
Then, a substrate, a circuit pattern portion formed on the circuit pattern forming surface of the substrate, and a light-shielding portion provided on the outer periphery of the circuit pattern portion and having a lower reflectivity with respect to extreme ultraviolet light than the extreme ultraviolet absorption region of the circuit pattern portion. The light shielding portion is formed by mounting a light shielding member separate from the substrate on the substrate.

  Further, the light shielding member is formed in a frame shape.

  In addition, the light shielding member includes at least an absorption layer that absorbs extreme ultraviolet rays and an adhesive layer that adheres to the substrate.

  And the reflectance with respect to the extreme ultraviolet rays of the absorption layer of the light shielding member is 0.3% or less.

  According to the present invention, since it has the above-described features, the following can be achieved.

  That is, in a reflective mask used in extreme ultraviolet (EUV) lithography, the circuit pattern portion formed on the substrate, the circuit pattern formation surface of the substrate, and the outer periphery of the circuit pattern portion are absorbed by the circuit pattern portion. It has a light-shielding part that has a lower reflectivity for extreme ultraviolet rays than the area, and the light-shielding part is formed by mounting a light-shielding member that is separate from the substrate on the substrate, so it is easy without complicated processing and processing With this process, it is possible to obtain a reflective mask having a light shielding frame with high light shielding properties.

  Further, since the light shielding member is formed in a frame shape, it is possible to prevent the outer periphery of the chip on the semiconductor substrate from being exposed even when multiple exposure is performed.

  In addition, since the light shielding member includes at least an absorption layer that absorbs extreme ultraviolet rays and an adhesive layer that adheres to the substrate, the light shielding member can be attached to the substrate.

  And since the reflectance with respect to the extreme ultraviolet rays of the absorption layer of a light shielding member is 0.3% or less, it can have sufficient light-shielding property.

Schematic which shows an example of the reflective mask used for one Embodiment of this invention. Schematic which shows the principal part of the reflective mask which is one Embodiment of this invention. Schematic which shows the reflective mask which is one Embodiment of this invention. Schematic showing the EUV reflectivity in an embodiment of the present invention

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(Description of the reflective mask 100 before the shading frame is attached)
First, a reflective mask 100 according to an embodiment of the present invention, which is a reflective mask 100 before a light shielding frame is attached, will be described with reference to FIG. FIG. 1 is a schematic view of a circuit pattern forming surface of a reflective mask 100 patterned by electron beam lithography. The surfaces of the outer peripheral region 21 and the light shielding region 31 of the circuit pattern region 11 are formed of an absorption film or a multilayer reflection film.

(Description of light shielding frame plate (light shielding member) 200)
Next, a light shielding frame plate 200 used for light shielding of the reflective mask 100 according to an embodiment of the present invention will be described with reference to FIG. FIG. 2A shows the surface of the light shielding frame plate 200. The light shielding frame plate 200 has a rectangular frame shape that is the size of the light shielding region 31 of the reflective mask 100. FIG. 2B shows a cross-sectional view of the light shielding frame plate in the direction of arrows AA. The light shielding frame plate 200 includes an absorption layer 41 and an adhesive layer 51 made of a material that exhibits a low reflectance with respect to EUV light.

The absorption layer 41 of the light shielding frame plate 200 may have a single layer structure or a multilayer structure. For example, the absorption layer 41 is composed of two layers, a strong plastic or aluminum is used as a lower layer, and a tantalum (Ta) nitrogen compound (TaN) having a low reflectivity with respect to EUV light is used as an upper layer. It is good also as a structure formed by film-forming. As another material of the absorption layer 41, tantalum boron nitride (TaBN), tantalum silicon (TaSi), tantalum (Ta), or oxides thereof (TaBON, TaSiO, TaO) may be used. The absorbing layer 41 may be formed by sputtering, plating, chemical vapor deposition (CVD), or the like.
Further, as the lower layer, a material having the same expansion coefficient as that of the semiconductor substrate such as a silicon thin plate may be used.

The adhesive force of the adhesive used for the adhesive layer 51 provided on the back surface of the light shielding frame plate 200 may be more than that which does not peel from the original reflective mask 100. The material of the adhesive layer 51 is made of, for example, an adhesive such as silicone, acrylic, styrene, vinyl, or rubber.

  Thus, by configuring the light shielding frame plate 200 separately from the reflective mask 100, the light shielding frame plate 200 having sufficient performance such as reflectance without affecting the reflective mask 100 due to processing or processing. Can be obtained.

(Description of the reflective mask 300 with a light shielding frame)
Finally, a reflective mask 300 with a light shielding frame, which is an embodiment of the present invention, will be described with reference to FIG. FIG. 3 is a view of the created reflective mask 300 with a light shielding frame as viewed from the surface. The reflective mask 300 with the light shielding frame was prepared by attaching the light shielding frame plate 200 to the light shielding region 31 outside the circuit pattern region 11 of the original reflective mask 100 by bonding with the adhesive layer 51.

  With the above configuration, the reflective mask can have a high light-shielding property by a simple process without damage due to processing of the absorption layer and the multilayer reflective layer and changes in optical properties. Further, by using this reflective mask for semiconductor manufacture, even when multiple exposure is performed, it is possible to prevent the peripheral portion of the chip from being exposed to light and to manufacture a high-quality semiconductor.

  Examples of the method for manufacturing a reflective mask according to the present invention will be described below. First, a reflective mask shown in FIG. 1 was prepared. The surface of the outer peripheral portion 21 of the circuit pattern region 11 was formed of an absorption film. Next, in the light shielding frame plate 200, an absorption layer 41 made of tantalum nitride (TaN) was formed on the surface of a substrate made of aluminum having the same size as the light shielding region 31, by a sputtering apparatus. The film thickness of the absorption layer 41 at this time was 100 nm. In addition, an adhesive made of silicone was formed on the adhesive layer 51 and attached to the light shielding region 31 on the circuit pattern formation surface of the original patterned reflective mask 100 with an adhesive. From the above, a reflective mask 300 with a light-shielding frame having a sufficiently low reflectivity for EUV light was completed outside the circuit pattern region 11.

  The reflectance with respect to EUV light (wavelength: 13.5 nm) of the reflective mask with a light shielding frame 300 thus manufactured was measured. As shown in FIG. 4, the reflectance of the absorption film on the outer periphery of the circuit pattern region 11 is 1.24%, whereas the reflectance of the light shielding frame plate 200 mounted on the surface of the light shielding region 31 is 0. 11%.

  Then, using this reflective mask 300, exposure using 13.5 nm EUV as a light source was performed, and four adjacent chips were transferred onto the semiconductor substrate. In the adjacent chip, although a part of the region corresponding to the light shielding frame on the manufactured reflective mask was overlapped, the resist exposure in the region on the semiconductor substrate was not confirmed.

DESCRIPTION OF SYMBOLS 11 Circuit pattern area | region 21 Peripheral area | region 31 Light-shielding area 41 Absorbing layer 51 Adhesive layer 100 Reflective mask 200 Light-shielding frame board 300 Reflective mask with light-shielding frame

Claims (4)

A reflective mask used in extreme ultraviolet (EUV) lithography,
A substrate,
A circuit pattern portion formed on the circuit pattern forming surface of the substrate;
Provided on the outer periphery of the circuit pattern part, comprising a light shielding part having a lower reflectivity for extreme ultraviolet light than the extreme ultraviolet absorption region of the circuit pattern part,
The light-shielding part is formed by attaching a light-shielding member separate from the substrate to the substrate. The reflective mask according to claim 1, wherein the light shielding member is formed in a frame shape. The reflective mask according to claim 2, wherein the light shielding member includes at least an absorption layer that absorbs extreme ultraviolet rays and an adhesive layer that adheres to the substrate. 4. The reflective mask according to claim 3, wherein a reflectance of the light-shielding member to the extreme ultraviolet rays of the absorbing layer is 0.3% or less.

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