Scanning Atomic Force Microscopy and Scanning Electron Microscopy Study of Diamond Thin Films Grown by Microwave Plasma
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SCANNING ATOMIC FORCE MICROSCOPY AND SCANNING ELECTRON MICROSCOPY STUDY OF DIAMOND THIN FILMS GROWN BY MICROWAVE PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION JAESHIN AHN, F.H. TAN, H.S. TAN AND W. ZHU School of Electrical and Electronic Engineering,
Nanyang Technological
University, Singapore 2263, Republic of Singapore
ABSTRACT The early stages of diamond thin film growth under various growth conditions have been investigated using Scanning Atomic Force Microscopy and Scanning Electron Microscopy . A series of experiment with various source gas combinations, substrate surface preparation methods and different substrates have been carried out to determine the effect on the diamond nucleation. The highest early nucleation density was obtained with CH It is 4 (1%)/H2 process among other gas combinations used. suggested that the atomic oxygen content should be kept minimum during the initial nucleation period of CVD diamond. It has been observed that diamond nucleation does not necessarily require diamond seeding dust. The silicon substrate polished with alumina powder showed diamond nucleation along the alumina scratched lines. In the process of diamond crystal growth, screw dislocations and stacking faults have been observed. 1)INTRODUCTION Diamond is considered an excellent material for various applications because of its unique physical, mechanical and chemical properties such as high thermal conductivity, extreme hardness and chemical inertness, etc. [1]. Polycrystalline diamond films have been successfully grown by various chemical vapour deposition (CVD) methods; and characterisation of these films has been discussed in several review articles[2-4]. One of the areas that has to be understood concerns the mechanism of nucleation and growth of diamond on substrates such as BN and Si. In this paper, we report the growth of polycrystalline diamond films using microwave plasma enhanced CVD , and the results of crystal growth of such films at early stages using Scanning Atomic Force Microscopy (SFM) and Scanning Electron Microscopy (SEM). 2)EXPERIMENTAL A high pressure microwave plasma enhanced CVD system is used in our experiments to grow polycrystalline diamond films. Substrate mounted on a graphite substrate holder is heated by a RF heater. The substrate temperature is measured by a thermocouple which is embedded in the substrate holder. Initially the reaction chamber is evacuated to the base pressure (1 X 104- torr) and backfilled with hydrogen and methane until the chamber pressure reaches the deposition pressure. Once the chamber pressure stabilizes, the microwave power supply is turned on to enable the formation of plasma. Diamond for these studies are grown on* N-type Si wafers which are pretreated by scratching with 1/4 micron diamond powder. Three series of experiments are carried out and these are classified accordingly to Expt. A, Expt. B and Expt. C. The first experiment determines the optimum process conditions in synthesizing diamond using various gas source systems. Gas combinations like CH4 (1%)/H 2
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