Synthesis and Oxidation Kinetics of Sol-Gel and Sputtered Tantalum Nitride Thin Films
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Mat. Res. Soc. Symp. Proc. Vol. 410 01996 Materials Research Society
2000 rpm onto (1102) sapphire. Nitridation was performed by rapid thermal annealing at 1223 K for 5 minutes. The heating rate was approximately 50 K/s, while the cooling rate was approximately 50 K/min. Reduction was performed under flowing H2 in a tube furnace at 1523 K for 30 minutes. Sputtered tantalum nitride thin films were deposited in a CVC AST-601 sputtering system on 500 nm of plasma-enhanced chemical vapor deposited (PECVD) Si0 2 on (100) Si wafers. A low-energy nitrogen ion beam was employed to incorporate nitrogen into a DC magnetron sputtered tantalum film [3]. Substrates were alternately rotated under a Kaufman type ion source and a tantalum target. Direct control of nitrogen incorporation into the film is possible since the ion beam is the only source of nitrogen. Deposition occurred at a pressure of 2 mTorr (8 sccm Ar, 3 sccm N 2) with a cathode power of 0.45 kW and a substrate bias of 450 V. Ion source voltage and current were 400 V and 3 A, respectively. The tantalum nitride films were cut into specimens one cm square. In the center of these samples van der Pauw geometries, 4 mm on a side, were defined in the tantalum nitride films using a CF 4 reactive ion etch and standard lithography techniques. Platinum contacts, 250 nm thick and 3 mm on a side, were deposited at the sample corners and overlapped the van der Pauw structure by 10 ýtm at each corner. X-ray diffraction spectra were acquired on a Scintag PADX 0-0 diffractometer using Cu KcL radiation. Transmission electron microscopy (TEM) samples were prepared by standard dimpling and ion milling procedures and imaged in a JOEL 1200EX (at 120keV). Rutherford backscattering spectrometry (RBS) measurements were performed using a 2.8 MeV He2+beam. An Auger spectrometer equipped with an Ar+ source was used for depth profiling. Sheet resistance measurement were made using a Keithley 181 voltmeter and a Keithley 220 current source. Contact from the electrical measurement equipment to the sample in the furnace was made with platinum wires. The sample to be oxidized was placed in a quartz furnace tube 28 mm in diameter and heated to a temperature between 550 and 720 K in flowing argon to prevent oxidation during warm-up. Once the temperature stabilized, the argon flow was stopped. Oxidation experiments were performed in air with a flow rate of 700 sccm. An alumel-chromel thermocouple monitored the temperature of the sample throughout the measurements. RESULTS After nitridation, X-ray diffraction indicated the sol-gel thin films were single phase Ta 3N5. The Ta 3N 5 films were dark orange, transparent, and insulating. After the hydrogen anneal X-ray diffraction showed the films were reduced to Ta 2N. RBS and Auger measurements showed the film had an atomic composition of 65% Ta, 29% N, and 6% 0, and that the composition was uniform throughout the thickness of the film.. Reduced films were golden in color and 80 nm thick with a resistivity of 1740 lýtf-cm at 300 K. Sputtered films were e
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