Reactor Issues Important for the Deposition of Selective Tungsten by Chemical Vapor Deposition Using the SiH 4 Reduction
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REACTOR ISSUES IMPORTANT FOR TI IE DEPOSITION OF SELECTIVETUNGSTEN BY CIIEMICAL VAPOR DEPOSITION USING TI ILi Sill 4 REI)UCTION OF WIF 6 David E. Kotecki*, Evan Co.Colgan', and Alan Rose** *IBM, Scmiconductor Research and Development Ccntcr, I lopewcll Junction, NY 12533 'Tcxas Instruments Corporation, Dallas, TX 75265 ABSTRACT Wc have analyzed a singlc-wafer chcmical vapor deposition (CVI)) reactor used for the selective deposition of tungsten (W) by the silanc (Sil1 4) reduction of tungsten hcxafluoridc (Wl6). Results from a reactor model, which incorporates simplified heterogeneous reaction chemistry, are compared to experimental data obtained from the same reactor to provide insight and understanding into reactor performance and define some of the tradc-offs in the design of the reactor. A reactor for this process must provide: a cold-wall temperature to suppress homogeneous reactions, a uniform wafer temperature to ensure uniform stress and resistivity in deposited films, and a uniform flux of Sil14 to the wafer surface to ensure uniform thickness of films. Maintaining a small internal volume in the reaction chamber was found to be beneficial for reducing both the quantity of reactant gas at elevated temperatures and the residence time of the gas in the reactor, both of which lead to improved selectivity. INTROI)UCTION The selective deposition of tungsten (W) films continues to be of interest for metallization, including the filling of high aspect ratio vias and studs, and the replacement of silicides in Very-Large Scale Integrated (VLSI) circuit technology. The use of a selective, rather than blanket, deposition process offers the potential for reducing cost, process time, and complexity in process integration. Published results on the selective deposition of W by CVI) vary significantly[1]. Recently, a wide process window has recently been reported[2,3] for the chemical vapor deposition (CVD) of selective W by the silane (Sill,4) reduction of tungsten hcxafluoride (WI' 6) in the reactor described here. Films with low resistivity and stress were obtained at substrate temperatures -400'C. The rate of deposition was shown to be linearly dependent upon the concentration of Sil 14 in the reactor, and only slightly dependent on the wafer temperature and WI76 concentration. The film resistivity and stress were shown to be influenccd strongly by the wafer temperature, decreasing as the temperature of the wafer was increased. I lence, a uniform Sil 14 concentration is required at the wafer surface to ensure films with a uniform thickness, while a uniform wafer temperature is required to maintain uniform film properties. In addition, the degree of selectivity was reported to degrade with increasing wafer temperature, deposition rate, and residence time. For the deposition of W by the Sil14 reduction of WF 6, the detailed heterogeneous chemistry, the possibility of homogeneous chemistry, and the composition of gas phase products are still being debated in the literature[4,5], as is the relative importance of gas phase
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