Investigation of CF 3 I as an Environmentally Benign Dielectric Etchant
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Investigation of CF3 I as an environmentally benign dielectric etchant R. A. Levy, V. B. Zaitsev, K. Aryusook, C. Ravindranath, and V. Sigal New Jersey Institute of Technology, University Heights, Newark, New Jersey 07102
A. Misra Air Liquide Electronics Chemicals & Services, Dallas, Texas 75243
S. Kesari and D. Rufin Air Liquide Electronics, Walnut Creek, California 94596
J. Sees and L. Hall Texas Instruments, M/S 301, Dallas, Texas 75243 (Received 7 August 1997; accepted 22 December 1997)
In this study, trifluoroiodomethane (CF3 I), a non-global-warming gas, has been investigated as a substitute for typical PFC’s currently used in wafer patterning and CVD chamber cleaning processes. Dielectric films consisting of plasma enhanced chemically vapor deposited silicon dioxide and silicon nitride were comparatively etched in CF3 I and C2 F6 /O2 plasma environments. The etch rate of these films was ascertained as a function of applied rf power, etchant gas flow rate, reaction chamber pressure, and CF3 I : O2 ratio. Destruction efficiencies of CF3 I at different processing parameters were evaluated. Depending on the flow rate, rf power, and chamber pressure, utilization efficiency of CF3 I varied from as low as 10% to as high as 68%. CF4 , C2 F6 , COF2 , and CO2 were the predominant by-products found in the exhaust stream; however, their concentrations were very low compared to the traditional process employing C2 F6 /O2 mixtures.
I. INTRODUCTION
Perfluorinated compounds (PFC’s) are widely used in the microelectronics industry for wafer patterning and CVD chamber cleaning applications. However, there are rising concerns regarding the environmental hazards associated with these compounds,1 prompting both chemical suppliers and chip manufacturers to examine alternate etchants. Since PFC’s have extremely long atmospheric lifetimes2 and absorb infrared radiation, they contribute to the greenhouse effect which accounts for the global warming phenomenon.3 Recently, research efforts have been directed toward the investigation of novel etchants such as the hydrofluorocarbons,4 C3 F8 (octafluoropropane),5 and (CF3 CO)2 O (trifluoroacetic anhydride)6 in plasma processes. These efforts have yet to yield a suitable replacement candidate for conventional PFC’s. In this study, we examine the use of CF3 I, the first member in the family of iodofluorocarbons, as a potential non-global-warming alternative to PFC’s. Iodofluorocarbons have become the subject of recent studies as promising replacements for halons in fire extinguishing applications.7 The weak C –I bond in iodofluorocarbons makes these compounds chemically and photochemically active, and as a result, they possess very short atmospheric lifetimes. In the case of CF3 I, for instance, the lifetime in a sunlit atmosphere is calculated J. Mater. Res., Vol. 13, No. 9, Sep 1998
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to be less than one day and the steady state ozone depletion potential (ODP) for surface releases is
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