Growth of MgO by Metal-Organic Molecular Beam Epitaxy
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pressure is low ( 10-5 Torr); 2) A single metalcontaining volatile species in the molecular beam; 3) A high sticking coefficient; 4) High long-term stability at the sublimation temperature (No decomposition or oxidation of the source materials). In the present work, we describe the growth of MgO thin films by MOMBE using Mg (acac)2 ( acac= acetylacetonate) as the Mg precursor and a RF 0 plasma as the oxidant. The growth conditions, structure, compositions and surface morphology of the deposited films characterized by transmission electron microscopy (TEM), Auger spectrometry and atomic force microscopy (AFM). Further more, in order to optimize the growth conditions, the effects of the growth temperature on growth rate and surface morphology have been systematically investigated. EXPERIMENTAL The films were deposited in a SVT Associates SN35 MBE system equipped with low temperature effusion cells and oxygen plasma as shown in Figure 1. The solid metal-organic precursor was contained in an effusion cells. The cell temperature can be precisely controlled to within 0.2 'C. Mg
45 Mat. Res. Soc. Symp. Proc. Vol. 606 © 2000 Materials Research Society
precursor was contained in an effusion cell. The cell temperature can be precisely controlled to within 0.2 'C. Mg (acac)2 was used as the precursor. The source pressure was controlled by a flux monitor. An oxygen plasma from an SVT RF Plasma 02 gun with output energy of 300400 W was used as an oxidant. The substrate temperature was measured by a thermocouple Turbo-molecular-pump station
Plasma Oxygen Gun 0. Effusion cells LN2 shroud ,
\Stage
Shutter
jt
Manipulator
Y Gate Value Load Lock Door
Flux MonitorRHEED Gun a Turbo-molecular-pump
calibrated by an infrared optical pyrometer. N-type Si (100) wafers with resistivities of 1-10 f1cm were used as substrates. Prior to growth, the Si surface was chemically etched in a HNO3 :HF:H 20 (5:3:92 by volume
percentage)
Figure 1 Schematic of a SVT Associate MBE system
solution for several seconds to remove the surface oxide layer. It was then was subsequently cleaned in methanol and acetone for 15 minutes. The chemically etched Si wafer was immediately placed in the system load lock and then transferred to the growth chamber pre-pumped down to a base pressure of 10-9 to 10'10 Torr. The Si was subsequently degassed for 30 minutes at 200'C and desorped for 30 minutes at 850'C. The Si surface cleaned by this simple procedure showed a clear and streaky RHEED pattern with Kikuchi lines indicating the Si surface was atomically clean. The film thickness was measured by a Tencor P-10 surface profiler. The film composition was measured by Auger electron spectroscopy (AES). The microstructure was determined by a Hitachi HF-2000, cold field emission TEM operated at 200kV. TEM samples were prepared by mechanical grinding and polishing followed by further mechanical dimpling to a thickness of less than 10 pm and final thinning in a Gatan Model 691 precision ion polishing system. Surface morphology and roughness of the MgO thin films w
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