Microstructure and hydrogen dynamics in hydrogenated amorphous silicon carbides
- Ames Laboratory-USDOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States)
- Microelectronics Research Center, Iowa State University, Ames, Iowa 50011 (United States)
- Department of Physics, Colorado School of Mines, Golden, Colorado 80401 (United States)
- Department of Engineering Physics, University of Tulsa, Tulsa, Oklahoma 74104 (United States)
Small angle x-ray scattering (SAXS) and deuterium secondary-ion-mass spectrometry (DSIMS) studies of the microstructure and hydrogen dynamics in undoped rf-sputter-deposited (RFS) and undoped and boron-doped electron-cyclotron-resonance-deposited (ECR) hydrogenated amorphous silicon carbides (a-Si{sub 1-x}C{sub x}:H) are described. In the RFS carbides with x{<=}19 at. %, the SAXS indicated that the films contained elongated features larger than 20 nm with preferred orientation, consistent with a residual columnarlike growth of the films. In addition, the SAXS also included a clear nanostructural component consistent with roughly spherical nanovoids {approx}1.1 nm in diameter, of total content 0.5{<=}C{sub nV}{<=}1.0 vol. %. C{sub nV} increased by {approx}100% after isochronal 1-h annealing at 300, 350, and 375 degree sign C, followed by further annealing for 2-15 hours at 375 degree sign C. The growth of C{sub nV} was apparently due largely to a {approx}20% increase in the average void diameter. This growth was noticeably weaker than in similarly fabricated a-Si:H. In RFS carbides with x{<=}3 at. %, the DSIMS yielded power-law time dependent H diffusion constants D(t)=D{sub 00}({omega}t){sup -{alpha}}, where the dispersion parameter {alpha} varied from 0 to {approx}0.5{+-}0.1 among the samples, but was temperature independent at 350 degree sign {<=}T{<=}475 degree sign C. The moderate values of {alpha} are consistent with the moderate initial nanovoid contents C{sub nV}{<=}1.0 vol. % determined by SAXS. The weak dependence of {alpha} on T is consistent with the weaker growth of the SAXS with annealing as compared to a-Si:H. The values of activation energy E{sub a}(1000 Aa ) for a diffusion length L=1000 Aa among the different films were {approx}1.7, {approx}1.4, and {approx}0.65 eV. While the first two values are similar to those found in a-Si:H, the nature of the anomalously low value of {approx}0.65 eV is not clear. In undoped ECR a-Si{sub 0.86}C{sub 0.14}:H, D(t) exhibited a similar power-law time dependence, but {alpha} decreased from {approx}0.3 at 350 degree sign C and 400 degree sign C to {approx}0.1 at 450 degree sign C, also consistent with a low C{sub nV}. Thus, in spite of the high-C content, the behavior of {alpha} was similar to that of typical a-Si:H at lower temperatures, where it decreases at T{<=}350 degree sign C. However, E{sub a}(1000 Aa ) was an anomalously low {approx}1.0 eV. The evolution of the infrared (IR) spectra of both the RFS and ECR films showed that during annealing the Si-bonded H content decreases relative to the C-bonded H content, consistent with a transfer of H from Si- to C-bonded sites or hydrogen evolution. In addition, the reduction in the 2000-cm{sup -1} band characteristic of bulk-like Si-H group was much greater than the reduction of the 2100-cm{sup -1} band characteristic of surface Si-H, O-Si-H, and C-Si-H groups. Boron doping of the ECR carbides also reduced the bulklike Si-bonded H content, suggesting that it induces nanovoids, consistent with the observed suppression of long-range motion of most of the H and D atoms. However, a small fraction of the H atoms appeared to undergo fast diffusion, reminiscent of the fast diffusion in B-doped a-Si:H. (c) 1999 The American Physical Society.
- OSTI ID:
- 20217822
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 60, Issue 23; Other Information: PBD: 15 Dec 1999; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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