RAPID THERMAL ANNEALING FOR REDUCING STRESS IN TUNGSTEN X-RAY MASK ABSORBER

X-ray masks are one of the key issues of x-ray lithography. In order to eliminate distortions, a good mask necessitates a low stress x-ray absorber layer. Tungsten is one of the most promising materials for use as an x-ray absorber, but the stress strongly depends on deposition conditions. Therefore, it is very difficult to control precisely the stress during the deposition process. A new approach is proposed, which consists of ''fine tuning'' the stress in the deposited layer with an annealing treatment. In this article, a process is presented which controls the stress in tungsten deposited thin films using rapid annealing. Stresses of less than 2 X 10(8) dyn/cm2 can be routinely obtained in annealed films for which initial compressive stresses after deposition were up to 3 X 10(9) dyn/cm2. This allows better film deposition process latitude for the sputtering gas pressure and substrate temperature. The evolution of stress with annealing temperature and time is studied and x-ray diffraction and scanning electron microscopy measurements are discussed.