Ki-Su Keum

Annealing effect of low-temperature (<150°C) Cat-CVD gate dielectric silicon nitride films diluted with atomic hydrogen

— The effect of in-situ hydrogen pretreatment on dielectric properties of silicon nitride (SiNx) thin films for a gate dielectric layer has been studied. SiNxthin films were grown at a low temperature (150°C) by Catalytic CVD followed by conventional furnace annealing at 150°C for 2 hours. The in-situ hydrogen pretreatment was performed without vacuum break before the sample was transferred to the furnace for thermal annealing. Capacitance—voltage (C-V) and current-density—voltage (J-V) measurement showed that the hydrogen pretreatment was effective in reducing the hysteresis in the C-V curve and in increasing the breakdown voltage. Without the treatment, the 150°C annealing failed to produce reliable C-V and I-V characteristics. The C-V hysteresis and the threshold voltage shift of SiNx were improved by furnace annealing as the hydrogen dilution ratio increased. Also, addition of hydrogen to the deposition gas mixture helped to improve the dielectric properties of the SiNx films after thermal annealing. The combination of hydrogen dilution of the source gas and the in-situ hydrogen treatment was successful in producing low-temperature SiNx films applicable to a-Si TFTs. The TFT fabricated by using these films showed a field-effect mobility of 0.23 cm2/V-sec and a Vth of 3.1 V.

Influence of filament geometry on film uniformity in a catalytic CVD system for low-temperature processing

The influence of the filament configuration in a low-temperature catalytic chemical vapor deposition system on the substrate temperature and thickness uniformity was investigated for application to the silicon-based thin-film transistor backplane on flexible substrates. Serial and parallel arrangements of the filament were attempted. In the serial connection, the self-heating of the substrate was suppressed as the total length of the filament decreased for a given filament temperature. The areal distribution of the film thickness was affected more by the shape of the reactor than by the filament arrangement, whereas the variation of the breakdown field strength and resistivity showed little correlation with the filament of the chamber geometry. On the contrary, in the parallel connection, the thickness distribution was influenced more by the location of the filaments than by the reactor shape. The 56 mm interfilament spacing resulted in the highest deposition rate, and the film thickness decreased radially from the center. When the interfilament spacing was 88 mm, both the average and the standard deviations of the thickness decreased, and the distribution changed, assuming an elliptical symmetry.

High‐rate, low‐temperature deposition of multifunctional nano‐crystalline silicon nitride films

Abstract The solid phase compositions and dielectric properties of silicon nitride (SiNx) films prepared using the plasma enhanced chemical vapor deposition (PECVD) technique at a low temperature (200°C) were studied. Controlling the source gas mixing ratio, R = [N2]/[SiH4], and the plasma power successfully produced both silicon‐rich and nitrogen‐rich compositions in the final films. The composition parameter, X, varied from 0.83 to 1.62. Depending on the film composition, the dielectric properties of the SiNx films also varied substantially. Silicon‐rich silicon nitride (SRSN) films were obtained at a low plasma power and a low R. The photoluminescence (PL) spectra of these films revealed the existence of nano‐sized silicon particles even in the absence of a post‐annealing process. Nitrogen‐rich silicon nitride (NRSN) films were obtained at a high plasma power and a high R. These films showed a fairly high dielectric constant (κ = 7.1) and a suppressed hysteresis window in their capacitance‐voltage (C‐V) characteristics.