Reflective mask blank and process for producing the reflective mask blank
A reflective mask blank, which includes a substrate, a reflective multilayer film for reflecting exposure light, and an absorber layer for absorbing the exposure light in this order; the reflective multilayer film having at least three fiducial marks formed in a concave shape in an area outside an exposure area for patterning the reflective multilayer film on a front side thereof, each of the fiducial marks including a concave portion having an inclination angle α, the absorber layer having a film thickness of from 40 to 90 nm; the absorber layer having transferred marks formed in a concave shape on a front side thereof, the transferred marks being transferred from the at least three fiducial marks, each of the transferred marks including a concave portion having an inclination angle of from 35 to 80°; and a difference between the inclination angle β and the inclination angle α (inclination angle β−inclination angle α) being at least 10°.
1. A reflective mask blank, which includes a substrate, a reflective multilayer film for reflecting exposure light, and an absorber layer for absorbing the exposure light in this order;
the reflective multilayer film having at least three fiducial marks formed in a concave shape in an area outside an exposure area for patterning the reflective multilayer film on a front side thereof, each of the fiducial marks including a concave portion having an inclination angle α, the absorber layer having a film thickness of from 40 to 90 nm;
the absorber layer having transferred marks formed in a concave shape on a front side thereof, the transferred marks being transferred from the at least three fiducial marks, each of the transferred marks including a concave portion having an inclination angle β of from 35 to 80°; and
a difference between the inclination angle β and the inclination angle α (inclination angle β−inclination angle α) being at least 10°.
2. The reflective mask blank according to claim 1 , wherein the concave portion of each of the transferred marks has a depth of at least 50 nm.
3. The reflective mask blank according to claim 1 , wherein the inclination angle α is from 25 to 45°.
4. The reflective mask blank according to claim 2 , wherein the inclination angle α is from 25 to 45°.
5. The reflective mask blank according to claim 1 , wherein the at least three fiducial marks are not present on a single imaginary linear line on the front side of the reflective multilayer film.
6. The reflective mask blank according to claim 2 , wherein the at least three fiducial marks are not present on a single imaginary linear line on the front side of the reflective multilayer film.
7. The reflective mask blank according to claim 3 , wherein the at least three fiducial marks are not present on a single imaginary linear line on the front side of the reflective multilayer film.
8. The reflective mask blank according to claim 4 , wherein the at least three fiducial marks are not present on a single imaginary linear line on the front side of the reflective multilayer film.
9. A process for producing the reflective mask blank defined in claim 1 , comprising using a FIB (Forced Ion Beam) method or a dry etching process to form at least three concave fiducial marks on a reflective multilayer film in an area outside an exposure area for patterning the reflective multilayer film on a front side of the reflective multilayer film; and forming an absorber layer on the reflective multilayer film by sputtering after formation of the at least three fiducial marks such that the at least three fiducial marks are transferred onto the absorber layer.
10. The process according to claim 9 , wherein the forming of the absorber layer by sputtering is carried out under a pressure of at most 0.3 Pa.