JP2012002908A - Photo mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photo mask with which the defect such as foreign body or pattern deformation can be detected with high accuracy in the defect inspection using a reflection image.SOLUTION: A photo mask in which a pattern is formed in a pattern region includes a glass substrate, a reflective film provided on the entire surface of the pattern region on the glass substrate and having higher reflectance with respect to light than that of the glass substrate, and a light shielding film forming patterns on the reflective film and having higher reflectance with respect to light than that of the reflective film.

Description

  The present invention relates to a photomask that can detect defects with high sensitivity.

  In recent years, the miniaturization of semiconductor patterns has advanced remarkably. A semiconductor is generally manufactured by reducing and projecting a pattern drawn on a photomask. Therefore, miniaturization of a photomask pattern is indispensable for miniaturization of a semiconductor. Photomasks corresponding to fine patterns include binary masks and phase shift masks.

  In these conventional photomasks, the reflectance of a thin film on glass (hereinafter referred to as a light shielding film) on which a pattern is drawn is extremely low at the exposure wavelength. For example, the reflectivity of the phase shift mask is 19.4%, and the recently proposed OMOG (Opaque MoSi on Glass) mask has only 11.7% (see Non-Patent Document 1, for example). ).

  With the miniaturization of photomasks, the mask inspection wavelength has recently become thinner than the exposure wavelength. For this reason, the low reflectance of the light shielding film hinders mask inspection using a reflected image of the photomask.

Kojima, et al. “Alternating phase-shift mask and binary mask for 45-nm node and beyond: the impact on the mask error control”. Proc. SPIE Vol. 6607, 66070C (2007).

  In view of the above circumstances, an object of the present invention is to provide a photomask capable of detecting a defect such as a foreign matter or pattern deformation with high accuracy in defect inspection using a reflected image.

  The photomask of one embodiment of the present invention is a photomask in which a pattern is formed in a pattern region, and is provided on the entire surface of the pattern region on the glass substrate and the glass substrate, and has a reflectance with respect to light from the glass substrate. And a light-shielding film that is provided on the reflective film, forms the pattern, and has a higher reflectance with respect to the light than the reflective film.

  In the photomask of the above aspect, it is desirable that the light transmittance of the reflective film is 80% or more.

  In the photomask of the above aspect, it is preferable that the wavelength of the light is 180 nm or more and 200 nm or less.

  In the photomask of the above aspect, the reflective film is preferably ruthenium.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the photomask which can detect a defect, such as a foreign material and a pattern deformation, in the defect inspection by a reflected image with high precision.

It is a schematic diagram of the photomask of embodiment. It is a figure which shows the reflected light intensity distribution of the inspection light of the photomask of a prior art. It is a figure which shows the reflected light intensity distribution of the inspection light of the photomask of a highly reflective light shielding film. It is a figure which shows the reflected light intensity distribution of the inspection light of the photomask of this Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  A photomask according to an embodiment of the present invention is a photomask in which a pattern is formed in a pattern region, and is provided on the entire surface of the pattern region on the glass substrate and the glass substrate, and has a higher reflectance to light than the glass substrate. A reflective film; and a light-shielding film that is provided on the reflective film, forms a pattern, and has a higher reflectance with respect to light than the reflective film.

  FIG. 1 is a schematic diagram of a photomask according to the present embodiment. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the line AA in FIG.

  In the photomask 10 of the present embodiment, for example, a first pattern 14a and a second pattern 14b are formed as a plurality of patterns in the pattern region 12 on one surface thereof. The photomask 10 is provided on the entire surface of the glass substrate 16 and the pattern region 12 on the glass substrate 16. The photomask 10 is provided on the reflective film 18 having a higher light reflectance than the glass substrate 16 and on the reflective film 18. Pattern 14a and second pattern 14b are formed, and a light shielding film 20 having a higher reflectance with respect to light than the reflective film 18 is provided.

  Here, the light at the time of comparing the reflectance of the glass substrate 16, the reflective film 18, and the light shielding film 20 is the wavelength of the inspection light at the time of defect inspection of the photomask, and is, for example, 180 nm to 200 nm.

  Here, the case where the first pattern 14a and the second pattern 14b are formed as the remaining pattern of the light shielding film 20 is described as an example. However, the first pattern 14 a and the second pattern 14 b may be formed as a blank pattern of the light shielding film 20.

  The glass substrate 16 is, for example, transparent quartz glass. Other materials that are transparent to light may be used.

  The reflective film 18 is made of ruthenium, which is a metal, for example. It is desirable that the light transmittance of the reflective film 18 is 80% or more, more preferably 95% or more. This is because if it falls below this range, the influence on the pattern formation in the lithography process using the photomask increases.

  When the reflective film 18 is ruthenium, the film thickness is preferably 1 nm or more and 3 nm or less. This is because if it falls below this range, sufficient reflectance may not be obtained. Further, if it exceeds this range, the light transmittance may be deteriorated.

  The light shielding film 20 is made of, for example, metal or metal silicide such as MoSi (molybdenum silicide).

  Next, problems of the prior art and actions / effects of the photomask of the present embodiment will be described with reference to FIGS. FIG. 2 is a diagram showing a reflected light intensity distribution of inspection light of a conventional photomask. FIG. 3 is a diagram showing a reflected light intensity distribution of inspection light of a photomask having a high reflection light shielding film. FIG. 4 is a diagram showing the reflected light intensity distribution of the inspection light of the photomask according to the present embodiment. 2 (a), 3 (a), and 4 (a) are wide line and space patterns, and FIGS. 2 (b), 3 (b), and 4 (b) are wavelengths of inspection light. The case of a line-and-space pattern with a narrow width that is smaller than 1 mm is shown.

As shown in FIG. 2, the reflectance of the light shielding film 20a is low in the conventional mask. For this reason, there is a problem that the amplitude W _N1 of the reflected light intensity distribution in the narrow portion with respect to the inspection light is not large enough to make the inspection highly accurate.

On the other hand, a method of increasing the amplitude by using the light shielding film 20b having a high reflectance with respect to the inspection light can be considered. In this case, as shown in FIG. 3, the amplitude W _N2 of the narrow portion can be increased. At the same time, the amplitude _WW2 of the wide portion also increases.

  However, as a result of the reflection intensity simulation by the inventors, as shown in FIG. 3, in the finer and narrower part, the reflection intensity of the glass part becomes brighter than the light shielding film 20 b having a high reflectance. As a result, it has been found that there is a tendency for a difference from the reflection intensity of the wide glass portion.

  When inspecting a photomask with a mask inspection apparatus, the reflected light intensity is acquired using an image pickup device such as a CCD, and the reflected light intensity is converted into a gradation value (or the number of gray scale bits) for each pixel. At this time, the maximum gradation value that a pixel can take from the image sensor, the image processing method, and the like is fixed to a predetermined value, for example, 256 gradations of 8 bits.

The maximum gradation value is assigned to the maximum amplitude obtained from the pattern area to be inspected, for example, the amplitudes W _W1 to 3 in FIGS. 2 to 4 or the intensity obtained by adding a certain margin to these maximum amplitudes. It is done.

  When the reflected light intensity distribution has the same amplitude, the gradation resolution of the reflected image obtained by the inspection is improved and the highly accurate defect inspection is realized if the amplitude can be divided by more gradation values. .

In the case of FIG. 3, for example, when the amplitude _WW2 is set as the maximum gradation value, the gradation value is also assigned to the difference portion of the glass portion, resulting in waste. For this reason, the gradation value width cannot be used effectively, and the amplitude W _N2 of the narrow portion with the increased width cannot be utilized to the maximum extent for the high accuracy of the inspection.

In the present embodiment, since the reflection film 18 exists in the glass portion, the reflected light intensity of the glass portion increases in a wide portion as shown in FIG. On the other hand, the reflected light intensity of the glass portion in the narrow portion is so narrow that the space is lower than the wavelength of the inspection light, so that the reflected light intensity does not increase and the reflection film 18 has little influence. For this reason, the amplitude W _N3 is kept at the same level as the amplitude W _N2 .

Therefore, the difference in the reflection intensity between the glass portion at the wide portion and the narrow portion as generated in FIG. 3 disappears. Therefore, by setting the amplitude W _W3 smaller than W _W2 as the maximum gradation value, more gradation values can be assigned to the amplitude W _N3 of the narrower portion than in the case of FIG. Therefore, the amplitude W _N3 spread by the light shielding film 20b having a high reflectance can be utilized to the maximum. In other words, the number of gray scale bits of the image can be used more effectively than in the case of FIG.

  As a result, the gradation resolution of the reflected image can be improved, and the inspection performance can be improved. Therefore, according to the present embodiment, it is possible to provide a photomask that can detect defects such as foreign matter and pattern deformation with high accuracy in defect inspection using a reflected image.

  Reflection of glass part for multiple spatial frequency components by simulation for inspection light wavelength of 199 nm, quartz glass substrate, ruthenium reflection film of about 2 nm thickness, and light-shielding film whose reflectivity is significantly larger than conventional photomask It has been confirmed that the light intensities are equal and a profile as shown in FIG. 4 is obtained. At this time, the reflectance of quartz glass is about 4.7%, and the reflectance of the ruthenium reflective film is 9.0%. Further, the transmittance of the ruthenium reflective film is 80% or more.

  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. Although the description of the portions that are not directly necessary for the description of the present invention is omitted, the required configuration of the photomask can be appropriately selected and used. In addition, all photomasks that include the elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention.

  For example, in the embodiment, the case where the pattern is formed by a single light shielding film has been described as an example, but the pattern is formed by a multilayer film, and the uppermost layer is a light shielding film having a higher reflectance to light than the reflective film. You may be the structure to do.

  For example, in the embodiment, the case where the reflective film is formed on the entire surface of the glass substrate has been described as an example. However, the reflective film may be formed only in the pattern region.

DESCRIPTION OF SYMBOLS 10 Photomask 12 Pattern area | region 14a, b Pattern 16 Glass substrate 18 Reflective film 20 Light-shielding film

Claims (4)

A photomask in which a pattern is formed in a pattern region,
A glass substrate;
A reflective film that is provided on the entire surface of the pattern region on the glass substrate, and has a higher reflectance with respect to light than the glass substrate;
A light-shielding film provided on the reflective film, forming the pattern, and having a higher reflectance with respect to the light than the reflective film;
A photomask comprising:   2. The photomask according to claim 1, wherein the light transmittance of the reflective film is 80% or more.   3. The photomask according to claim 1, wherein a wavelength of the light is 180 nm or more and 200 nm or less. 4. The photomask according to claim 1, wherein the reflective film is ruthenium.

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