Photomask having a transparency-adjusting layer, method of manufacturing the photomask, and exposure method using the photomask

A method of manufacturing a photomask, the method comprising:

• providing a photomask that includes a substrate having a front side and a rear side, and a main pattern located at said front side of the substrate;
• and
• providing substrate transparency-adjusting pattern features, capable of changing the intensity of illumination directed through the rear side of the photomask and onto the main pattern, in respective sections at the rear side of the substrate, the transparency-adjusting pattern features having a density in each of the sections that is a function of the size and spacing of the features and is proportional to the change that the features will make in the intensity of the illumination when the illumination is directed through the rear side of the substrate, and
• wherein the transparency-adjusting pattern features are provided in sets in said sections at the rear side of the substrate, respectively, such that the density of the set of the features in one of said sections differs from that of the set of features in another of said sections, whereby when the illumination is directed through the substrate from the rear side thereof with a uniform intensity, the intensity of the illumination incident on the main pattern has variations corresponding to the different densities, in each of the sections, of the respective sets of transparency-adjusting pattern features.

A method of manufacturing a photomask, the method comprising:

• providing a photomask that includes a substrate having a front side and a rear side, and a main pattern located at said front side of the substrate;
• dividing a region at the rear side of the substrate into a plurality of sections including a first section and a second section;
• and
• providing a transparency-adjusting pattern layer, capable of changing the intensity of illumination directed through the rear side of the photomask and onto the main pattern, in said sections at the rear side of the substrate such that a first part of said transparency-adjusting pattern layer resides in said first section and a second part of said transparency-adjusting pattern layer resides in said second section, and
• wherein said first part of the transparency-adjusting pattern layer is formed at said first section with uniform characteristics with respect to its ability to change the intensity of that portion of the illumination passing through the first section, said second part of the transparency-adjusting pattern layer is formed at said second section with uniform characteristics with respect to its ability to change the intensity of that portion of the illumination passing through the second section, and the characteristics of said first part of the transparency-adjusting pattern layer in said first section are different from the characteristics of said second part of the transparency-adjusting pattern layer in said second section, whereby when illumination is directed through the rear side of the substrate and onto the main pattern, the intensity of the illumination passing through the first section and incident on the main pattern differs from the intensity of the illumination passing through the second section and incident on the main pattern.

A method of manufacturing a photomask, the method comprising:

• providing a photomask that includes a substrate having a front side and a rear side, and a main pattern located at said front side of the substrate;
• transferring an image of the main pattern to a wafer by directing illumination onto the wafer through said photomask in an exposure process, and using the image to produce a pattern on the wafer formed of elements having critical dimensions;
• quantifying the critical dimensions to obtain a distribution of values of the critical dimensions on the wafer;
• comparing the critical dimension values to a reference critical dimension value in order to ascertain the differences therebetween;
• determining, in relation to localities on the photomask, degrees to which the intensity of the illumination used in the exposure process would need to be decreased in order to reduce the differences, respectively, between the critical dimension values and the reference critical dimension value, thereby obtaining a distribution of said degrees in relation to said localities;
• and
• providing a light-shielding layer, having a light-absorbing characteristic, on a rear side of the photomask substrate so that the intensity of the illumination directed through the rear side of the substrate and onto the main pattern will be reduced by the light-shielding layer, and
• wherein the light-absorbing characteristic is varied across said light-shielding layer in correspondence with said distribution of the degrees to which the intensity of illumination needs to be decreased.

A photomask comprising:

• a photomask substrate having a front side and a rear side;
• a main mask pattern disposed on the front side of said substrate;
• and
• a transparency-adjusting pattern layer disposed on a rear side of said substrate,
• said transparency-adjusting pattern layer including sets of transparency-adjusting pattern features, capable of changing the intensity of illumination directed through the rear side of the photomask and onto the main pattern, in respective sections at the rear side of the substrate,
• each set of the transparency-adjusting pattern features having a density in that is a function of the size and spacing of the features and is proportional to the change that the features will make in the intensity of the illumination when the illumination is directed through the respective section at the rear side of the substrate, and
• the density of the set of said transparency-adjusting pattern features in one of said sections being different from that of the set of transparency-adjusting pattern features in another of said sections, whereby when the illumination is directed through the photomask substrate from the rear side thereof with a uniform intensity, the intensity of the illumination incident on the main pattern has variations corresponding to the different densities, in each of the sections, of the respective sets of said transparency-adjusting pattern features.

A photomask comprising:

• a photomask substrate having a front side and a rear side;
• a main mask pattern disposed on the front side of said substrate;
• and
• a transparency-adjusting pattern layer disposed on a rear side of said substrate,
• said transparency-adjusting pattern layer being capable of changing the intensity of illumination directed through the rear side of the photomask and onto the main pattern, a first part of said transparency-adjusting pattern layer residing in a first section of a region at the rear side of said mask substrate, and a second part of said transparency-adjusting pattern layer residing in a second section of said region,
• said first part of the transparency-adjusting pattern layer in said first section having uniform characteristics with respect to its ability to change the intensity of that portion of the illumination passing through the first section, said second part of the transparency-adjusting pattern layer having uniform characteristics with respect to its ability to change the intensity of that portion of the illumination passing through the second section, and the characteristics of said first part of the transparency-adjusting pattern layer in said first section being different from the characteristics of said second part of the transparency-adjusting pattern layer in said second section, whereby when illumination is directed through the rear side of said photomask substrate and onto the main pattern, the intensity-of the illumination passing through the first section and incident on the main pattern will differ from the intensity of the illumination passing through the second section and incident on the main pattern.

An exposure method for use in photolithography, the method comprising:

• providing a photomask that includes a substrate having a front side and a rear side, and a main pattern located at said front side of the substrate;
• transferring an image of the main pattern to a wafer by directing illumination onto the wafer through said photomask in a first exposure process, and using the image to produce a pattern on the wafer formed of elements having critical dimensions;
• quantifying the critical dimensions to obtain a distribution of values of the critical dimensions on the wafer;
• comparing the critical dimension values to a reference critical dimension value in order to ascertain the differences therebetween;
• determining, in relation to localities on the photomask, degrees to which the intensity of the illumination used in the exposure process would need to be decreased in order to reduce the differences, respectively, between the critical dimension values and the reference critical dimension value, thereby obtaining a distribution of said degrees in relation to said localities;
• providing a transparency-adjusting layer on the rear side of the photomask substrate, the transparency-adjusting layer being capable of changing the intensity of illumination directed through the rear side of the photomask and onto the main pattern, and
• wherein the characteristics of the transparency-adjusting layer with respect to its ability to change the intensity of the illumination are varied in accordance with said distribution of the degrees to which the intensity of the illumination used in the exposure process needs to be decreased;
• and
• subsequently transferring the image of the main pattern onto a wafer by performing a second exposure process using the photomask substrate having the transparency-adjusting layer at the rear side thereof.