Dry Etching of Copper at High Rates
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DRY ETCHING OF COPPER AT HIGH RATES JANOS FARKAS *, FRANCOIS ROUSSEAU*, KAI-MING CHI**, TOIVO T. KODAS#* and MARK J. HAMPDEN-SMITH#** *Chemical Engineering Department, University of New Mexico, Albuquerque, NM 87131 "**Chemistry Department, University of New Mexico, Albuquerque, NM 87131 #Authors to whom correspondence should be addressed ABSTRACT Three new methods for dry etching of copper at temperatures below 200'C have been developed. The first relies on the formation of volatile CICu(PR 3 )2 species via reaction of PR 3 with CuCI where R = ethyl, and butyl. The second relies on the reaction of Cu(hfac)2 and neutral ligands L such as butyne, pentyne or bistrimethylsilylacetylene to form (hfac)CuL. The last approach involves reaction of CuO with hexafluoroacetylacetone (hfacH) to form Cu(hfac)2 and water. These approaches have provided etch rates as high as 1 gam/min at 150'C. INTRODUCTION The microelectronics industry is currently evaluating the use of copper as an interconnect material in integrated circuits [1]. Most applications require patterned copper films which can be produced by selective Chemical Vapor Deposition (CVD) [2] or by etching of blanket copper films. However, although selective copper CVD has been demonstrated [3], industrial applications have yet to be demonstrated. Thus, it is important to develop a method for copper etching. Most attempts at copper dry etching have relied on the formation of copper chloride. The rate of reaction of molecular and atomic chlorine with copper surfaces is rapid [4-6]. However, the low vapor pressure of copper chloride limits the etch rate to values that are too low for industrial applications [7]. This problem can be partially overcome by using elevated temperatures [8-11], but this approach prohibits use of standard polymeric mask materials. Since the etch rate is limited by evaporation of CuCI, it is logical to explore new routes that rely on formation of more volatile copper-containing reaction by-products. Only a few attempts have been made in this direction. The reaction of copper with species produced by dissociation of methyl iodide has been investigated [12]. Etch rates were only 6 nm/min, too low for most applications. Formation of CuCI2-AI2CI6 has been investigated as a method for generating higher vapor pressure species [13]. Although etch rates up to 500 nm/min were obtained, this method has not been adopted by industry. Here we describe three new approaches for copper etching that rely on the generation of high vapor pressure copper species which desorb at high rates and low temperatures, typically below 2000 C. One approach involves generation of volatile Lewis base adducts of CuCl. This approach prevents oligomerization of the halide through reaction of the copper halide with a neutral ligand L such as a tertiary phosphine according to Eqs. 1 and 2. Cl 2 + 2Cu ---> 2CuCI
(1)
CuCI + nL --- > LnCuCI
(2)
The second approach (Eq. 3) involves the reverse of the CVD disproportionation reaction used for deposition of copper where L is a neutral li
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