Microstructure and hydrogen dynamics in hydrogenated amorphous silicon carbides


PHYSICAL REVIEW B, vol.60, no.23, pp.15875-15889, 1999 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 60 Issue: 23
  • Publication Date: 1999
  • Doi Number: 10.1103/physrevb.60.15875
  • Title of Journal : PHYSICAL REVIEW B
  • Page Numbers: pp.15875-15889


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-Sil-xCx:H) are described. In the RFS carbides with x less than or equal to 9 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 similar to 1.1 nm in diameter, of total content 0.5 less than or equal to C(nv)less than or equal to 1.0 vol. %. C-nV increased by similar to 100% after isochronal 1-h annealing at 300, 350, and 375 degrees C, followed by further annealing for 2-15 hours at 375 degrees C. The growth of C-nV was apparently due largely to a similar to 20% increase in the average void diameter. This growth was noticeably weaker than in similarly fabricated a-Si:H. In RFS carbides with x less than or equal to 3 at. %, the DSIMS yielded power-law time dependent H diffusion constants D(t)= D-00(omega t)(-alpha), where the dispersion parameter ct varied from 0 to similar to 0.5+/-0.1 among the samples, but was temperature independent at 350 degrees less than or equal to T less than or equal to 475 degrees C. The moderate values of a are consistent with the moderate initial nanovoid contents C(nV)less than or equal to 1.0 vol. % determined by SAXS. The weak dependence of cu on Tis consistent with the weaker growth of the SAXS with annealing as compared to a-Si:H. The values of activation energy E-a(1000 Angstrom) for a diffusion length L=1000 Angstrom among the different films were similar to 1.7, similar to 1.4, and similar to 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 -0.65 eV is not clear. In undoped ECR a-Si0.86C0.14:H, D(t) exhibited a similar power-law time dependence, but alpha decreased from similar to 0.3 at 350 degrees C and 400 degrees C to similar to 0.1 at 450 degrees C, also consistent with a low C-nV. Thus, in spite of the high-C content, the behavior of Lu was similar to that of typical a-Si:H at lower temperatures, where it decreases at T less than or equal to 350 degrees C. However, E-a(1000 Angstrom)was an anomalously low similar to 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(-1) band characteristic of bulk-like Si-H group was much greater than the reduction of the 2100-cm(-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. [S0163-1829(99)07247-1].