Diagnostic Techniques for Polycrystalline Thin Film Growth
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The depositions of polycrystalline Si on SiO 2 and SiC on Si were investigated. Conventionally, the structure of polycrystalline Si on SiO 2 and glass has been obtained by hightemperature, long-time annealing of the amorphous Si grown by plasma enhanced chemical vapor deposition (PECVD). In this work, similar polycrystalline Si was grown on Si0 2 and Coming 7059 glass directly at temperatures lower than 300°C by ECR-CVD, without any other thermal treatments. Polycrystalline (Poly) Si deposited on glass and SiO 2 at very low temperatures can be used to fabricate thin film transistors (TFTs), especially for flat-panel displays as active matrices, because of the higher carrier mobility and lower threshold voltage than amorphous TFTs.[1] The structure of SiC deposited on Si has been widely used because Si substrates are much less expensive and SiC has the potential applications in photoelectronics, high temperature semiconductor devices, anti-radiation devices, and hard wear resistant coatings, and protective barriers for corrosion or thermal oxidation. Conventionally, crystalline SiC has been grown at temperatures higher than 1000°C by chemical vapor deposition (CVD).[2] In this work, the SiC growth on Si were carried out at 178-500'C by ECR-CVD. EXPERIMENTAL PROCEDURES
157 Mat. Res. Soc. Symp. Proc. Vol. 406 01996 Materials Research Society
Thermal oxide-patterned wafers, Corning 7059 glass, and Si(100) substrates were used as substrates for polycrystalline Si and SiC depositions. The electron cyclotron resonance chemical vapor deposition (ECR-CVD) reactor used for deposition is a commercial Plasma Quest model357. The ECR-CVD reactor contains an Astex microwave power supply, an ENI rf bias generator, and upper and lower electromagnets to produce plasma and confine the plasma zone, respectively. The carrier gas such as H 2 was introduced through the upstream gas inlet for plasma generation. Reaction gases such as SiH 4 and SiH 4 /CH 4 were introduced through the downstream gas inlet for deposition. A Leybold transpect residual gas analyzer, with differential pumping system and pressure converter installed, was connected to the growth chamber to in-situ monitor the gas species in the chamber prior to and during deposition processes. The reaction gases for poly-Si and poly-SiC depositions are SiH4 /H2 and SiH 4/CH 4/H2, respectively. The deposition temperature was 165-300'C, with the chamber pressure of 10-60 mTorr.
RESULTS AND DISCUSSIONS In addition to hydrogen etching effect, the maximum grain size of the poly-Si was found to depend on the SiH 3/SiH and SiH 2/SiH ratios measured by quadruple mass spectrum. Figure l(a) shows the maximum grain size of poly-Si grown on Si0 2 versus microwave power for the deposition at 250 C , 20 mTorr, and 98% SiH 4 in H 2 . Figure l(b) shows the SiH 3/SiH and SiH 2/SiH ratios versus microwave power. Comparing Fig. ](a) and Fig. l(b), it can be seen that the maximum grain size, SiH 3/SiH ratios, and SiH 2/SiH ratios all have similar trends with respect to microwave power.
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