Claims
- 1. A photo-mask blank for use in a lithography technique, comprising a transparent substrate member having a principal surface and a shading layer of chromium having a first surface in contact with said principal surface and a second surface opposite said first surface, said shading layer comprising:
- a first portion which is adjacent said principal surface and which provides said first surface, said first portion having a first etch rate; and
- a second portion which is farther from said first surface than said first portion and which provides said second surface, said second portion having a second etch rate lower than first etch rate to provide in combination therewith a means for rapidly reducing undesired spots of the chromium layer remaining on the substrate to a number which is not greater than 0.1/cm.sup.2 wherein the difference in etch time between the first and second portions is sufficiently great to effect reduction in a time period which is not more than 1.4 times greater than the time period for producing etching without undercutting.
- 2. A photo-mask blank as claimed in claim 1 wherein said difference in etch time between the first and second portions is so great that the ratio of the increase in the time period of etching approaches unity.
- 3. A photo-mask blank as claimed in claim 1 wherein the ratio of etch time of the seond layer to that of the first layer is at least 4.
- 4. A photo-mask for use in lithography technique, comprising a transparent substrate member having a principal surface and a patterned shading layer of chromium having a first surface in contact with said principal surface and a second surface opposite said first surface, said patterned shading layer comprising:
- a first portion which is adjacent said principal surface and which provides said first surface, said first portion having a first etch rate; and
- a second portion which is farther from said first surface than said first portion and which provides said second surface, said second portion having a second etch rate lower than said first etch rate to provide in combination therewith a means for rapidly reducing undesired spots of the chromium layer remaining on the substrate to a number which is not greater than 0.1/cm.sup.2 wherein the difference in etch time between the first and second portions is sufficiently great to effect reduction in a time period which is not more than 1.4 time greater than the time period for producing etching without undercutting.
- 5. A photo-mask as claimed in claim 4 wherein said difference in etch time between the first and second portions is so great that the ratio of the increase in the time period of etching approaches unity.
- 6. A photo-mask as claimed in claim 2 wherein the ratio of etch time of the second layer to that of the first layer is at least 4.
Priority Claims (2)
Number |
Date |
Country |
Kind |
57-199786 |
Nov 1982 |
JPX |
|
57-199787 |
Nov 1982 |
JPX |
|
Parent Case Info
This is a division of application Ser. No. 552,156 filed 11/15/83, now U.S. Pat. No. 4,563,407.
US Referenced Citations (2)
Number |
Name |
Date |
Kind |
4497878 |
Hatano et al. |
Feb 1985 |
|
4530891 |
Nagarekawa et al. |
Jul 1985 |
|
Divisions (1)
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Number |
Date |
Country |
Parent |
552156 |
Nov 1983 |
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