Chemical Vapor Deposition of Chromium Carbide from Organometallic Precursors
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CHEMICAL VAPOR DEPOSITION OF CHROMIUM CARBIDE FROM ORGANOMETALLIC PRECURSORS N.M. RUTHERFORD, C.E. LARSON, AND R.L. JACKSON IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120
ABSTRACT Chemical vapor deposition from CpCr(CO)3H, Cr(CH2CMe3)4, and Cr(NPri2)3 at low pressures yields chromium carbide films at temperatures as low as 330 *C. The films are mirror-bright and extremely smooth with no significant features observable by SEM. In general, films prepared at higher temperatures had lower resistivities, and were more likely to be crystalline than those prepared at lower temperatures. However, amorphous films deposited at 330 'C were much harder than the crystalline films. Chemical vapor deposition from 1 Cr(NPr 2)3 resulted in carbide films with the most desirable properties. INTRODUCTION Interest in metal-organic chemical vapor deposition (MOCVD) of thin films has seen a resurgence during recent years, in areas from micoelectronics to tribology [1-3]. Much of the reason behind the renewed interest in the area of microelectronics has been in response to the need for lower processing temperatures. Much success has been found with the use of organometallic compounds for deposition of semiconductors such as GaAs from GaMe3 and AsH3 [4], InP from InEt3 and PH3 [5], and ZnSe from ZnMe2 and MeSeH or Me2Se [6]. In addition, many main group and late transition metals have been deposited in pure form from metal alkyls, carbonyl complexes, and arene complexes [7-9]. The early transition metals have not yet been deposited in pure form, undoubtably due to their extreme reactivity. Nevertheless, there have been many cases where useful compounds such as early transition metal silicides [10], carbides [11], borides [12] and oxides [13] have been deposited at low temperatures where previously they had been deposited only at temperatures in excess of 1000 *C. In the present paper, we explore organometallic precursors to chromium carbide, Cr3C2, with an interest in observing how the metal ligands (arene, carbonyl, amide, or alkyl) affect the properties of the final solid state product. EXPERIMENTAL The low pressure MOCVD system is described below. The stainless steel chamber was pumped by a Balzers 50 I/s turbgmolecular pump (TMP). The base pressure of the system was approximately 10 torr. During deposition, the TMP was isolated from the system by a vacuum gate valve, and the chamber was pumped by a liquid N2-trapped mechanical pump. Helium, argon, and hydrogen carrier gases passed through 02 and water filters before being introduced into the precursor chamber using mass flow controllers. Typical flow rates for the inert carrier gas and hydrogen gas were 17-20 and 3 sccm, respectively. The total pressure in the chamber, usually maintained at 300 mtorr, was controlled by throttling the mechanical pump. The silicon substrates were placed on a copper block (2" dia. x 1/4") heated by a tungsten filament situated directly beneath it. The temperature of the block was monitored using a thermocouple attached to the surface, wh
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