Growth of diamond particles in chemical vapor deposition
- PDF / 9,534,559 Bytes
- 7 Pages / 612 x 828 pts Page_size
- 58 Downloads / 246 Views
An early stage of diamond growth in hot-filament chemical vapor deposition on silicon substrates was examined by the high resolution electron microscope. "Pretreatment" of the substrate surfaces by diamond powder abrading was found to plant diamond seed crystals with a density of as high as 10 n /cm 2 . These crystals provide sites for subsequent growth of diamond films. The CVD grown diamond particles tend to be cuboctahedra. Smaller particles in nanometer size are faultless, but larger ones of several tens of nanometers develop crystal faults. Some of them may originate from the seed crystals. Degradation of the diamond seed crystals due to the electron beam irradiation is discussed in terms of fabrication of diamond film.
I. INTRODUCTION Diamond, one of the important minerals, has been studied extensively in terms of the terrestrial and planetary science of carbon. The study of diamond growth is based on examination of crystal morphologies and growth features such as surface steps, crystalline defects, foreign atom inclusions, and dislocations, which occur commonly in natural diamond.1 The spiral growth mechanism in natural diamond was suggested by mineralogists.2 Synthetic bulk diamond grown under high pressure and high temperature environment has been studied,3 and their growth features were compared with those of natural diamond to elucidate a mechanism for diamond crystal growth.4 Diamond films grown in chemical vapor deposition (CVD) of carbon5'6 has provided another approach to be compared with the natural diamond. The CVD grown diamond is formed under a metastable condition involving chemical reaction. Its growth history is quite different from that of natural diamond, which is formed under a thermodynamically stable condition. A metastable nucleation of diamond film grown by CVD, therefore, is of extreme interest, requiring microscopic observation. One of the mysteries in growing diamond thin films by the CVD technique was the role of pretreatment of substrate materials, commonly silicon wafers.7 That is, abrading the substrate by diamond powder increases the number of nucleation sites for crystallization by almost five orders of magnitude. A high density nucleation brings about a smooth surface film of polycrystalline diamond, which is essential for the thin film technology. It has been suspected, though without convincing evidence, that some diamond powder was left on the substrate surfaces during the pretreatment, since enhancement of the growth nucleation doesn't seem to occur when other kinds of polishing powder such as SiC and alumina are used.8 The seeding effect, however, was reported recently by the present authors.9 They found J. Mater. Res., Vol. 6, No. 7, Jul 1991
http://journals.cambridge.org
Downloaded: 20 May 2014
through transmission electron microscope studies that the Si wafer surfaces after abrading with diamond powder were planted with a number of tiny diamond particles of less than several tens of nanometers. These diamond particles act as nucleation sites for the film growth. Th
