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 $(a-{\mathrm{Si}}_{1-x}{\mathrm{C}}_x:\mathrm{H})$ are described. In the RFS carbides with $x<~19\hspace{0.5em}\mathrm{at}.\mathrm{}\%,$ 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 $\sim 1.1\hspace{0.5em}\mathrm{nm}$ in diameter, of total content $0.5<~C_{\mathrm{nV}}<~1.0\hspace{0.5em}\mathrm{vol}.\mathrm{}\%.\mathrm{}$ $C_{\mathrm{nV}}$ increased by $\sim 100\%$ after isochronal 1-h annealing at 300, 350, and $375°\mathrm{C},$ followed by further annealing for 2–15 hours at $375°\mathrm{C}.$ The growth of $C_{\mathrm{nV}}$ was apparently due largely to a $\sim 20\%$ increase in the average void diameter. This growth was noticeably weaker than in similarly fabricated $a-\mathrm{S}\mathrm{i}:\mathrm{H}.$ In RFS carbides with $x<~3$ at. %, the DSIMS yielded power-law time dependent H diffusion constants ${D\left(t\right)=D}_{00}(\omega {t)}^{-\alpha },$ where the dispersion parameter $\alpha$ varied from 0 to $\sim 0.5\pm 0.1$ among the samples, but was temperature independent at $350°<~T<~475°\mathrm{C}.$ The moderate values of $\alpha$ are consistent with the moderate initial nanovoid contents $C_{\mathrm{nV}}<~1.0$ 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 $a-\mathrm{S}\mathrm{i}:\mathrm{H}.$ The values of activation energy $E_a\left(1000\mathrm{}\hspace{0.5em}\mathrm{\AA }\mathrm{}\right)$ for a diffusion length $L=1000\mathrm{}\hspace{0.5em}\mathrm{\AA }\mathrm{}$ among the different films were $\sim 1.7,$ $\sim 1.4,$ and $\sim 0.65\hspace{0.5em}\mathrm{eV}.$ While the first two values are similar to those found in $a-\mathrm{S}\mathrm{i}:\mathrm{H},$ the nature of the anomalously low value of $\sim 0.65\hspace{0.5em}\mathrm{eV}\mathrm{}$ is not clear. In undoped ECR $a-{\mathrm{Si}}_{0.86}{\mathrm{C}}_{0.14}:\mathrm{H},$ $D\left(t\right)\mathrm{}$ exhibited a similar power-law time dependence, but $\alpha$ decreased from $\sim 0.3$ at $350°\mathrm{C}$ and 400$°\mathrm{C}$ to $\sim 0.1$ at $450°\mathrm{C},$ also consistent with a low $C_{\mathrm{nV}}.$ Thus, in spite of the high-C content, the behavior of $\alpha$ was similar to that of typical $a-\mathrm{S}\mathrm{i}:\mathrm{H}$ at lower temperatures, where it decreases at $T<~350°\mathrm{C}.$ However, $E_a\left(1000\mathrm{}\hspace{0.5em}\mathrm{\AA }\mathrm{}\right)$ was an anomalously low $\sim 1.0\hspace{0.5em}\mathrm{eV}.$ 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 $2000-{\mathrm{cm}}^{-1}$ band characteristic of bulk-like Si-H group was much greater than the reduction of the $2100-{\mathrm{cm}}^{-1}$ 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 $a-\mathrm{S}\mathrm{i}:\mathrm{H}.$

• Received 16 March 1999

DOI:https://doi.org/10.1103/PhysRevB.60.15875