Effect of Ion Bombardment on the Structure and Properties of Pecvd SiO 2
- PDF / 334,896 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 26 Downloads / 203 Views
Department of Chemical Engineering, Drexel University, Philadelphia PA 19104
ABSTRACT Si0 2 films were deposited on silicon wafers at 25°C by plasma enhanced decomposition of tetraethoxysilane (TEOS) in a mixture of argon and oxygen. The deposition was performed in a rf-powered (13.56 MIHz) asymmetric plasma reactor. The effect of ion bombardment was evaluated by varying the ion energy flux (IEF) at the substrate surface from 0.93 to 9.94 W/cm2 . On-line optical emission spectra (OES) revealed CO, CH, and H peaks whose absorption intensities increased with increasing applied power. On-line mass spectrometer data showed that the peak intensities of OC2H5, SiOH (m/e=45), and HSiOH (m/e=46) fragments decreased with increasing applied power indicating the decomposition of these species. FTIR spectra of the deposited films showed that the concentrations of Si-OH and trapped CO gases in the film decreased with increasing IEF. Also, the FTIR results and the refractive index measurements indicated that the film density increased as a function of IEF. The stoichiometry of the film did not change when IEF was below 2, but for IEF greater than 4.91 W/cm 2, the film became Si-rich.
1. INTRODUCTION Silicon dioxide deposited by plasma-enhanced chemical vapor deposition (PECVD) is used widely in fabricating integrated circuits. The application areas include interlayers, gate oxides, passivation layers in VLSI devices, flat panel displays, high power ICs, and others. The PECVD method is attractive because the film can be deposited at temperatures much lower than those used in thermal CVD. Ion bombardmentlA on the substrate during film deposition can lower the substrate temperature significantly. In this method, the surface of a growing film is bombarded by positive ions attracted by the negative bias on the substrate. As a result, the average energy of the surface atoms is increased due to the transfer of momentum carried by positive ions. The energetic ions can drive off surface gases and sputter off the loosely bonded surface atoms. 5 Thus, the ion bombardment is an effective way to enhance the purity and quality of the deposited films in addition to lowering the deposition temperature. There have been limited studies on the gas phase kinetics and the effect of ion bombardment on film properties of Si0 2 prepared by PECVD. The purpose of this study is to assess the effects of the ion bombardment on film properties of PECVD SiO 2. The species in the plasma and the reaction products are analyzed by using an in-situ mass spectrometer (MS) and an optical emission spectroscope (OES). The deposited films are characterized by Fourier-tansform infrared spectroscopy (FTIR) and an ellipsometer.
107
Mat. Res. Soc. Symp. Proc. Vol. 363 01995 Materials Research Society
2. EXPERIMENTAL The details of the experimental set-up are described elsewhere. 6 Tetraethoxysilane was obtained from Aldrich (Milwaukee, WIS). Film depositions are carried out in a capacitively coupled, asymmetric plasma reactor driven by a 13.56 MHz rf power supply. Th
Data Loading...
