Origin of stress distribution in sputtered x-ray absorber film

To eliminate distortion in x-ray masks, not only lower average stress but also uniformity of the stress distribution in the x-ray absorber film are very important. We investigated the cause of stress distribution in sputtered x-ray absorber films both theoretically and experimentally. Our investigation clarified that stress distribution is determined by the distribution of the average velocity of sputtered and working gas atoms and/or the arrival frequency of incident working gas atoms when arriving at the wafer in sputtering systems. These determinants are strongly influenced by the geometry of the sputtering apparatus, i.e., the shape of the erosion area of the target and the substrate-to-target distance. We obtained a good uniformity of stress by optimizing the sputtering equipment configuration taking the erosion area of the target into consideration. Two ways to accomplish this are by adjusting the gap between the target and the substrate and by achieving uniformity of the erosion area.