Polycrystalline Silicon-c-Si Interface

Semi-insulating polycrystalline silicon (SIPOS) is found in many applications, including the electrical passivation of high-voltage planar devices, emitters in heterojunction transistors, and thin-film silicon solar cells on cheap foreign substrates. SIPOS is usually deposited by CVD onto a Si substrate. The composition of the SIPOS SiOx Aim varies from x = 0 (polycrystalline or amorphous Si) to X = 2 (Si02). The untreated film consists of a nonrandom mixture of Si and Si02 and relatively small amounts of an intermediate oxide of SiOi A (A = 0.14) [75, 76]. 

The interface layer formed in the CVD process between the silicon substrate and the SIPOS film can lead to unstable I-V characteristics or to an electric breakdown in high-voltage planar devices. The modified ATR method was applied to study this interfacial layer between a Si substrate and polycrystalline Si [77], IR reflectance spectra were recorded in p- and 5-polarized radiation at 80°. The normalized reflectance spectra R = Rp/Rs were compared to the spectra of a test (reference) structure with a known thickness of Si02 and were calcnlated by the three-phase model, with an absorbing layer characterized by a complex dielectric constant and two transparent silicon layers with real dielectric constants. The analysis of the vlo band at 1210 cm revealed that the interface layer is comprised of silicon oxides, mainly Si02, with a thickness of 0.7 nm [77]. 

IR transmission of the Si-bonded wafers at a grazing angle of is a highly sensitive technique and does not require multiple internal reflections (which would necessitate a beveled Si substrate). The resulting spectra are the best for 

Hydrophobic and hydrophilic bonded silicon wafers were studied by the methods of multiple internal reflection spectroscopy (MIR) and multiple internal transmission spectroscopy (MIT) [79, 81, 83, 84]. The sensitivity of the MIT configmation is 20-40 times higher than that of the traditional MIR configuration [81]. However, both of these techniques require beveled Si wafers. 

The modes of all three hydrides SiH, S1H2, and SiHs are observed simultaneously in the 2100-cm range however, the absorption intensities differ for hydrophobic and hydrophilic wafers. For a hydrophobic surface, the ratio AR/R is approximately 100 times higher than for a bonded hydrophilic sample [79]. In addition to Si—H, O2—Si—H (2200 cm ) and O3—Si—H (2250 cm ) vibration modes and O—H stretch modes (3725 cm ) are also observed (Fig. 6.18 [84]). 

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