Microstructure and hydrogen dynamics in hydrogenated amorphous silicon carbides

Small angle x-ray scattering (SAXS) and deuterium secondary-ion-mass spectr ometry (DSIMS) studies of the microstructure and hydrogen dynamics in undop ed rf-sputter-deposited (RFS) and undoped and boron-doped electron-cyclotro n-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 columnarl ike growth of the films. In addition, the SAXS also included a clear nanost ructural 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 tha n or equal to 1.0 vol. %. C-nV increased by similar to 100% after isochrona l 1-h annealing at 300, 350, and 375 degrees C, followed by further anneali ng for 2-15 hours at 375 degrees C. The growth of C-nV was apparently due l argely to a similar to 20% increase in the average void diameter. This grow th was noticeably weaker than in similarly fabricated a-Si:H. In RFS carbid es with x less than or equal to 3 at. %, the DSIMS yielded power-law time d ependent H diffusion constants D(t)= D-00(omega t)(-alpha), where the dispe rsion 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 les s than or equal to 475 degrees C. The moderate values of a are consistent w ith the moderate initial nanovoid contents C(nV)less than or equal to 1.0 v ol. % 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 val ues of activation energy E-a(1000 Angstrom) for a diffusion length L=1000 A ngstrom 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 i n 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 de pendence, 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 anomalou sly low similar to 1.0 eV. The evolution of the infrared (IR) spectra of bo th the RFS and ECR films showed that during annealing the Si-bonded H conte nt 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 re duction 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 s urface Si-H, O-Si-H, and C-Si-H groups. Boron doping of the ECR carbides al so reduced the bulklike Si-bonded H content, suggesting that it induces nan ovoids, consistent with the observed suppression of long-range motion of mo st 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-S i:H. [S0163-1829(99)07247-1].