Plasma Enhanced Chemical Vapor Deposition of Zirconium Nitride Thin Films
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ABSTRACT Depositions of high quality zirconium nitride, (Zr 3 N4 ), films using the metal-organic precursor Zr(NEt 2 )4 were carried out in a microwave argon/ammonia plasma (2.45 GHz). The films were deposited on crystalline silicon wafers and quartz substrates at temperatures of 200400 'C. The transparent yellow films have resistivity values greater than ML2 cm. The stoichiometry is N/Zr = 1.3, with less than 5 atom % carbon and little of no oxygen. The hydrogen content is less than 9 atom %, and it does not vary with deposition temperature. The growth rates range from 600 to 1200 A/min, depending on the flow rates and precursor bubbler temperature. X-ray diffraction studies show a Zr 3N 4 film deposited at 400 'C is polycrystalline with some (220) orientation. The crystallite size is approximately 30 A. The band gap, as estimated from transmission spectra, is 3.1 eV. INTRODUCTION The mononitrides of titanium, zirconium and hafnium (MN) are all refractory metals [1]. In contrast, the metastable nitrogen-rich phase of zirconium and hafnium nitrides with stoichiometries close to M3 N4 are reported to be transparent insulators or semiconductors [2-9]. There has been considerable research on the preparation and characterization of group IV mononitride thin films because of their desirable physical properties and attendant potential for applications. By comparison, films of the nitrogen-rich materials have not been studied in great detail; for example, it is only recently that a chemical vapor deposition route to the films has been reported [9]. In this paper we report the chemical vapor deposition of high quality Zr 3N 4 thin films using the metal-organic precursor Zr(NEt 2 )4 [Et = CH 3 CH 2 ] in a microwave argon/ammonia plasma at temperatures of 200-400 'C. EXPERIMENTAL The metal-organic precursor Zr(NEt 2)4 (b.p. 120, 0.1 torr) was prepared as described in the literature [10]. The purity (> 98%) was checked by using 1H NMR. Depositions were carried out in a six-way cross stainless steel reactor using an argon/ammonia RF microwave 289
Mat. Res. Soc. Symp. Proc. Vol. 410 0 1996 Materials Research Society
plasma (2.45 GHz) at 0.3 torr. Ultra-high purity argon and semiconductor grade ammonia were passed through purifiers before introduction into the system. The precursor was placed in a stainless steel bubbler that was heated with heating tape. Precursor temperature (115 'C) was measured using a thermocouple inserted directly into the liquid in the bubbler. Gas flow rates were controlled using mass flow controllers. The typical argon carrier gas flow rate through the bubbler was 10 sccm; the ammonia flow rate was varied from 50 to 70 sccm. The lines leading into the chamber were heated to 120 0 C using heating tape. The stainless steel stage was heated from below using a lamp. The films were deposited on crystalline silicon wafers with a (100) orientation and p-type 1 Q cm resistivity, and on quartz substrates. The substrates were degreased with methanol and affixed to the stage using silver paste to insure good th
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