PRECISE STRESS-CONTROL OF TA ABSORBER USING LOW-STRESS ALUMINA ETCHING MASK FOR X-RAY MASK FABRICATION

In the stress control of an X-ray mask absorber, the repeatability of control and stability are important. We found that the change in the s tress in a Ta film resulting from annealing depends on the oxygen conc entration in the film; the magnitude of the stress change is determine d by the annealing temperature and time. Using this characteristic of Ta film, we have successfully controlled the stress in the Ta absorber to less than 5 MPa with good repeatability. In our mask fabrication p rocess, Al2O3 film was used as an etching mask. We found that the Al2O 3 film prevented the Ta absorber stress from changing in high-temperat ure atmospheres because the Al2O3 film prevented oxygen diffusion into the Ta film. Utilizing Al2O3 films, we succeeded in preventing change s in Ta absorber stress in the thermal processes after Ta stress contr ol, such as frame bonding and resist baking. Consequently, we were abl e to precisely control the Ta absorber stress in X-ray masks with good repeatability and stability in a realistic X-ray mask fabrication pro cess.