Effects of nitrogen pulsing on sputter-deposited beryllium films
- University of California, Lawrence Livermore National Laboratory, Livermore, CA (USA)
Beryllium films have been used as a heat sink'' layer between the reflective coating of a mirror and its glass substrate to improve the mirror's radiation resistance to prompt deposition of x rays. Under x-ray irradiation, the beryllium heat sink layer is subjected to tensile stresses caused by differences in thermal expansion coefficients. Test results indicated that the predominant failure mode was the film's crazing under tensile stress. The inherent columnar structure of the beryllium films deposited under normal conditions is detrimental to the tensile strength of the films and may be responsible for this type of failure. We successfully suppressed the inherent columnar growth in beryllium films by incorporating periodic N{sub 2} pulses during sputter deposition. The traditional substrate biasing approach did not seem to be as effective in modifying the grain structure. The results showed that higher N{sub 2} pulse rates during deposition were more effective in suppressing the columnar growth. However, we noticed that films deposited with nitrogen pulsing show higher secondary-electron emission in SEM micrographs, which indicates a significant incorporation of contaminants into the beryllium films. Quantitative analyses were conducted for nitrogen and oxygen contamination in the beryllium films using standards prepared by ion implantation. Secondary ion mass spectroscopy (SIMS) depth profiles were obtained for oxygen and nitrogen using mass isotopes {sup 16}O and 23({sup 9}Be+{sup 14}N). More than 2% of contaminants was observed in beryllium films at the higher pulse rates that were used. Thus, a minimum pulsing frequency and duration should be selected that provides grain refinement with a minimum amount of contamination.
- OSTI ID:
- 6901794
- Journal Information:
- Journal of Vacuum Science and Technology, A (Vacuum, Surfaces and Films); (USA), Vol. 8:3; ISSN 0734-2101
- Country of Publication:
- United States
- Language:
- English
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