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Features of hydrogenated amorphous silicon films developed under an unexplored region of parameter space of radio-frequency plasma-enhanced chemical vapor deposition Plasma-enhanced chemical vapor deposition of intrinsic microcrystalline silicon from chlorine-containing source gas J. Vac. Sci. Technol. A 16, 3218 (1998); 10.1116/1.581525 Dominant monohydride bonding in hydrogenated amorphous silicon thin films formed by plasma enhanced chemical vapor deposition at room temperature

A multichannel spectroscopic ellipsometer based on the rotating-compensator principle was developed and applied to measure the time evolution of spectra (1.5–4.0 eV) in the normalized Stokes vector of the light beam reflected from the surface of a growing film. With this instrument, a time resolution of 32 ms for full spectra is possible. Several advantages of the rotating-compensator multichannel ellipsometer design over the simpler rotating-polarizer design are demonstrated here. These include the ability to: (i) determine the sign of the p-s wave phase-shift difference Δ, (ii) obtain accurate Δ values for low ellipticity polarization states, and (iii) deduce spectra in the degree of polarization of the light beam reflected from the sample. We have demonstrated the use of the latter spectra to characterize instrument errors such as stray light inside the spectrograph attached to the multichannel detector. The degree of polarization of the reflected beam has also been applied to characterize the time evolution of light scattering during the nucleation of thin film diamond by plasma-enhanced chemical vapor deposition, as well as the time evolution of thickness nonuniformities over the probed area of the growing diamond film. In this article, a detailed description of calibration and data reduction for the new instrument is provided. Future applications of this instrument are expected for real time characterization of film growth and etching on patterned surfaces for microelectronics and on thick transparent substrates for large area displays and photovoltaics.

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A rotating-compensator multichannel ellipsometer has been applied to measure the unnormalized Stokes vector that describes the polarization state of light reflected from specular and textured SnO2:F transparent conducting films on glass substrates. This four parameter spectroscopy yields the ellipsometric angles (ψ, Δ), the reflectance R, and the degree of polarization p, with a potential repetition time of 32 ms for all four 100 point spectra from 1.5 to 3.75 eV. The rotating-compensator design permits high accuracy evaluation of Δ over its full range (−180°<Δ⩽180°), even in the presence of random depolarization. This allows accurate analyses of the microscopic structure and optical properties of the SnO2:F films, based on fits to (ψ, Δ) using an ideal (specular) multilayer model. Differences between the reflectance spectrum predicted from the ideal model and that from experiment can be understood by including light scattering at the film surface due to texture (i.e., macroscopic roughness on the scale of the wavelength) in the model. The macroscopic roughness layer distribution can be extracted based on fits to R. The information obtained optically from {(ψ, Δ), R} is corroborated by direct structural measurements. Finally, we find that the spectra in p for both the specular and textured SnO2:F films exhibit oscillations that are attributed to sample nonuniformities over the beam area, with possible contributions from other sources. The similarity of p for both samples, along with the consistency of the (ψ, Δ) analysis results for the textured SnO2:F film, suggest that the scattering generated by the texture does not distort the information accessible through the polarized component of the reflected beam.

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In studies of hydrogenated amorphous silicon (a-Si:H) n-i-p solar cells fabricated by rf plasma-enhanced chemical vapor deposition ͑PECVD͒, we have found that the maximum open circuit voltage (V oc) is obtained by incorporating p-type doped Si:H layers that are protocrystalline in nature. Specifically, these optimum p layers are prepared by PECVD in the a-Si:H growth regime using the maximum hydrogen-to-silane flow ratio possible without crossing the thickness-dependent transition into the mixed-phase (amorphousϩmicrocrystalline) growth regime for the ϳ200 Å player thickness. The strong dependence of the player phase and solar cell V oc on the underlying i-layer phase also confirms the protocrystalline nature of the optimum Si:H p layer.

Biplate compensators made from MgF2 are being used increasingly in rotating-element single-channel and multichannel ellipsometers. For the measurement of accurate ellipsometric spectra, the compensator must be carefully (i) aligned internally to ensure that the fast axes of the two plates are perpendicular and (ii) calibrated to determine the phase retardance delta versus photon energy E. We present alignment and calibration procedures for multichannel ellipsometer configurations with special attention directed to the precision, accuracy, and reproducibility in the determination of delta (E). Run-to-run variations in external compensator alignment, i.e., alignment with respect to the incident beam, can lead to irreproducibilities in delta of approximately 0.2 degrees . Errors in the ellipsometric measurement of a sample can be minimized by calibrating with an external compensator alignment that matches as closely as possible that used in the measurement.