Paper EM-ThP13
Self-Limiting Growth of Semiconductor Grade Zinc Oxide at Low Temperature by Pulsed Pecvd and Plasma-Enhanced Atomic Layer Deposition

Thursday, October 23, 2008, 6:00 pm, Room Hall D

Self-limiting growth of ZnO was accomplished using both pulsed plasma-enhanced chemical vapor deposition (PECVD) and plasma-enhanced atomic layer deposition (PE-ALD) at temperatures ranging from 25–155 ºC. This work explored the suitability of dimethyl zinc (DMZ, Zn(CH3)2) as an alternative to the commonly used diethyl zinc (DEZ, Zn(C2H5)2) precursor. Mass spectrometry shows that DMZ is less reactive than DEZ, which may be advantageous for self-limiting growth of semiconductor grade ZnO. In pulsed PECVD DMZ and O2 were both supplied continuously, while in PE-ALD the DMZ was delivered in pulses separated by purge steps. Films were characterized using spectroscopic ellipsometry, Fourier transform infrared (FTIR) spectroscopy, photoluminescence (PL), Hall measurements, energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), atomic force microscopy (AFM), and field emission scanning electron microcopy (FE-SEM). Deposition rates scaled with DMZ exposure during pulsed PECVD films, and could be tuned over a large range (1.5 – 6.0 Å/pulse). The PE-ALD growth rate saturated at 2.9 Å/cycle for DMZ exposures >50 mTorr*s. Deposition rates increased exponentially for pulsed PECVD films as a function of substrate temperature, while PE-ALD displayed a constant rate within a temperature window of 85 to 120 ºC. With the substrate temperatures elevated above 70 ºC, impurities related to carbon and hydroxyl groups were attenuated below the detection limit of FTIR for both deposition modes. EDS analysis showed that all films were stoichiometric. At low temperatures pulsed PECVD films were amorphous, and became polycrystalline at higher temperatures with a preferred orientation in the (100) direction. PE-ALD produced polycrystalline films with a (100) texture at room temperature, with the preferred orientation switching to the (002) direction as the substrate temperature was increased. Changes in orientation were accompanied by alterations in surface morphology. The as-deposited films were semiconductor grade, with resistivity values ranging from of 1 – 20 W-cm. The high quality of the films was confirmed by strong band edge emission in room temperature PL experiments. Films deposited at room temperature also showed strong emission from oxygen vacancies, however emission from these defects was attenuated for substrate temperatures ? 120 ºC.