Oxygen Atom Induced Deposition of Silicon Dioxide
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OXYGEN ATOM INDUCED DEPOSITION OF SILICON DIOXIDE DIMITRI A. LEVEDAKIS AND GREGORY B.RAUPP Department of Chemical, Bio & Materials Engineering and Center for Solid State Electronics Research Arizona State University Tempe, AZ 85287-6006 ABSTRACT Silicon dioxide was deposited from tetraethylorthosilicate (TEOS) and remote microwave oxygen plasma on a heated silicon substrate in a cold-wall reactor. The deposition rate and film quality were examined as functions of substrate temperature, total pressure, absorbed plasma power and 0 2 :TEOS flow ratio. The deposition reaction exhibited an activation energy of approximately 10 kJ/mol for substrate temperatures in the range of 323623 K. The deposition rate reached a maximum with increasing total pressure. The rate was found to be a near-linear function of the absorbed microwave power. At fixed absorbed power the rate reached a maximum with increasing O2 :TEOS flow ratio. A one-dimensional mathematical model was developed to predict the oxygen radical concentration at the exit of the afterglow region of the oxygen discharge. Comparisons of the predicted oxygen radical concentrations with the deposition rates at corresponding deposition conditions supports the view that the overall SiO 2 deposition reaction is largely controlled by the concentration of oxygen radicals. The average refractive index of the deposited films was 1.466 + 0.011. Fourier transform infra-red (FTIR) transmission spectra showed significant concentrations of hydroxyls in the deposited films. INTRODUCTION Silicon dioxide is used as an interlevel dielecric in silicon very-large scale integrated (VLSI) circuit fabrication. If there are aluminum contacts in the substrate, the deposition temperature must be lower than 450"C [1]. This temperature limitation makes plasma enhanced CVD (PECVD) of SiO 2 from TEOS a potentially attractive process, since plasma is used to activate the deposition reactions instead of thermal energy. The majority of articles published in this area are concerned with deposition of SiO2 from TEOS in direct, capacitively-coupled radio-frequency (RF) plasmas [2-6]. In such systems the substrate is located inside the electric field which creates the plasma and is therefore bombarded by both neutral and ionic species. In our remote PECVD system, the substrate is located downstream of the plasma where virtually no charged species exist to contribute to the reactions leading to deposition. This characteristic feature of the remote system enables us to isolate and study the effect of the oxygen radicals generated by the microwave plasma on the chemistry of SiO 2 deposition from TEOS. EXPERIMENT A simplified flow diagram of the remote PECVD system is shown in Figure 1. The oxygen-plasma was generated in a quartz-wall cavity, 1.0 in-diameter and 1.625 in-long coupled to a microwave guide (Sairem GMP03) powered by a 300 W, 2.44 GHz power supply (Sairem GMP03KEJD). The plasma effluent passed through a 6 in-long and 1.0 indiameter afterglow region before it entered the deposition reactor. TEOS v
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