Reflective photomask, method for manufacturing same and program for making mask pattern
A reflective photomask includes a substrate and a reflective layer on the substrate. The reflective layer has a top surface opposite to the substrate and a reflectivity distribution on the top surface. The reflective layer includes mask patterns, the mask patterns having sizes depending on the reflectivity distribution. The mask patterns include a first pattern and a second pattern, the first pattern having a first space size smaller than a second space size of the second pattern. The first pattern is provided in a first region of the top surface, and the second pattern is provided in a second region of the top surface, wherein a reflectivity in the first region is lower than a reflectivity in the second region.
1. A reflective photomask to be provided between a light source and an object to project mask patterns of the reflective photomask on the object using exposure light emitted from a light source, the exposure light propagating through an irradiation part and a projection part via the reflective photomask, the irradiation part being provided between the light source and the reflective photomask to introduce the exposure light to the reflective photomask, and the projection part being provided between the reflective photomask and the object to focus the exposure light onto the object, the reflective photomask comprising:
a substrate; and
a reflective layer on the substrate, the reflective layer having a top surface opposite to the substrate and including the mask patterns,
the mask patterns including a first pattern provided in a first region comprising first plural patterns apart from each other with a first space size and a second pattern provided in a second region comprising second plural patterns apart from each other with a second space size larger than the first space size,
the difference of the first space size and the second space size being determined based on an overall reflectivity, the overall reflectivity representing a ratio of an intensity of the exposure light on the object to an intensity of the exposure light at the light source, and the overall reflectivity having a first value at the first region and a second value at the second region, the second value being larger than the first value.
2. The reflective photomask according to claim 1 , wherein the second region has a maximum reflectivity on the top surface; and the second space size is a minimum size among space sizes included in the mask patterns.
3. The reflective photomask according to claim 1 , wherein each of the mask patterns is an opening shape of a recessed portion provided in the reflective layer.
4. The reflective photomask according to claim 3 , wherein the recessed portion extends through the reflective layer from the top surface to the substrate.
5. The reflective photomask according to claim 1 , wherein the reflective layer has a structure in which a first film and a second film are stacked, and the second film is different in a refractive index from the first film.
6. The reflective photomask according to claim 1 , wherein the substrate is a transparent glass substrate.
7. The reflective photomask according to claim 1 , further comprising a cap layer provided on the reflective layer.
8. A method for manufacturing a reflective photomask to be provided between a light source and an object to project mask patterns of the reflective photomask on the object using exposure light emitted from a light source, the exposure light propagating through an irradiation part and a projection part via the reflective photomask, the irradiation part being provided between the light source and the reflective photomask to introduce the exposure light to the reflective photomask, and the projection part being provided between the reflective photomask and the object to focus the exposure light onto the object, the method comprising:
measuring a reflectance spectrum in a wavelength range of the exposure light respectively in a plurality of regions on a surface of a reflective layer of the reflective photomask;
determining an overall reflectivity in each of the plurality of regions based on the reflectance spectrum, the overall reflectivity representing a ratio of an intensity of the exposure light on the object to an intensity of the exposure light at the light source, and the overall reflectivity having a first value at the first region and a second value at the second region, the second value being larger than the first value; and
adjusting a size of a mask pattern in each of the plurality of regions based on a distribution of the overall reflectivity.
9. The method according to claim 8 , further comprising:
determining an MEEF value for the mask pattern in each of the plurality of regions; and
adjusting a size of the mask pattern using the MEEF value.
10. The method according to claim 8 , wherein the overall reflectivity is a value obtained by integrating an overall reflectance spectrum over wavelength, the overall reflectance spectrum being obtained by multiplying the reflectance spectrum in each of the plurality of regions by the reflectance spectrum of the irradiation part and the projection part.
11. The method according to claim 8 , wherein
the irradiation part and the projection part include a plurality of mirrors; and
the reflectance spectrum of the irradiation part and the projection part is an overall reflectance spectrum of the plurality of mirrors.
12. The method according to claim 8 , wherein the exposure light is light in a EUV wavelength region.
13. The method according to claim 8 , wherein the reflective layer has a first region and a second region, the first region having first plural patterns apart from each other with a first space size, and the second region having second plural patterns apart from each other with a second space size larger than the first space size.