John E Tyler

Chemical states study of Si in SiOx films grown by PECVD

Abstract Thin films of SiO x have been grown by low temperature (350°C) plasma enhanced chemical vapor deposition (PECVD), and the local chemical bond of Si and O has been investigated by infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Comparisons between the IR spectra of Si-rich oxides (SiO x , x 2 and low oxygen content a-Si:H:O alloys demonstrates a continuous variation in the character of the Si-O stretching, bending and rocking vibrations as a function of the oxygen concentration. In particular, the frequency of the dominant stretching vibration displays a linear frequency shift with the relative oxygen concentration. A similar behavior prevails in the XPS spectra where the position of the Si2p core states shifts monotonically with increasing oxygen concentration from a value of about 98.8 eV in a-Si to 103.1 eV in a-SiO 2 . The IR and XPS then reflect the average chemical bonding in these films. In contrast, the AES spectra of suboxides display two strong features in the SiL 23 VV spectrum. We show that one of these features at approximately 78 to 80 eV is associated with ejection of electrons from Si-O valence bonding states, and a second at about 90 eV is associated with ejection of electrons from Si-Si bonding states. Therefore, the AES spectra reflects the details of the local bonding, i.e., the relative numbers of Si-O and Si-Si bonds, while the IR and XPS spectra reflect the average chemical bonding. In this context, the combination of the three techniques confirms that the suboxide fims produced by this low temperature PECVD process are homogeneous, in contrast to being two phases with regions of a-Si and a-SiO 2 .

Thermal Stability of W/C Multilayer Films

W(10A)/C(40A), W(15A)/C(15A) and W(40A)/C(10A) periodic multilayer films were prepared by magnetron sputtering and subsequently annealed at 730°C. The resulting change of the layered and crystal structures was studied by X-ray diffraction. The resulting structures largely depended on the thickness ratio of W to C. For example, in the W(15Å)/C(15Å) sample a-W as formed without any peaks of carbon crystals; in W(40Å) C(10Å)only W2C (orthorhombic) peaks appeared.