METHOD FOR GROWING CRYSTALS

Abstract: A method of producing crystal growth on a substrate, par­ ticularly diamond, includes the steps of depositing the ions, atoms or molecules necessary for formation of the desired crystalline material on or in the surface of the substrate and simultaneously irradiating the deposited material by a laser beam which may be a continuous wave or pulsed laser, having a wavelength so chosen as to obtain resonance absorption by excitation of characteristic lattice vibrations in the deposited material. The method has particular applications to the growth of diamond on a diamond substrate.

Description: Method tor Growing Crystals This invention relates to crystal growth and more particularly to diamond growth. Various methods are known for synthesising diamond in its thermodynamically metastable region. These methods include diamond synthesis from the gas phase in microwave plasma and chemical vapour deposition of diamond in RF glow discharge as well as physical deposition methods such as sputtering and ion beam deposition. A review of these various methods can be found in the paper by D.V. Fedoseev et al which appears in the publication Russian Chemical Reviews, 53 (5), 194 at pages 4o5 to 444. Another method of producing diamond growth on a crystal substrate is described in the complete specification of South African Patent No. 2/1177. This method includes the steps of depositing a layer of a suitable amorphous or partially crystalline material on the surface of the substrate and subjecting the coated surface to irradiation bv a suitable laser beam. According to the present invention, there is provided a method of producing crystal growth on a substrate including the steps of depositing the ions, atoms or molecules necessary for formation of the desired crystalline material on or in the surface of the substrate and simultaneously irradiating the deposited material b a laser beam having a wavelength so chosen as to obtain resonance absorption by excitation of characteristic lattice vibrations in the deposited material. The irradiating laser beam will generally be caused to scan the surface as the deposition is occurring. Essential to the invention is that the ions, atoms or molecules are irradiated by a laser beam as they are deposited on or in the surface of the substrate. This may be achieved, for example, by focussing the beam on the area of the substrate being subjected to the deposition. The ions, atoms or molecules may be deposited on or in the substrate surface by any technique known in the art such as physical vapour deposition, chemical vapour deposition, sputtering, cracking ion implantation and plasma induced chemical vapour deposition. The laser beam may be a continuous wave or pulsed laser suitable for the resonance absorption or surface heating. Such beams have been described in the literature. For example, tunable radiation in the Scun (for diamond) and in the 9Wm and Olun (for silicon and germanium respectively) wavelength reGion may be used. Factors which should be observed in carrrin out the method of the invention are: I. Resonance absorption can be maximised by (a) tuning or sweeping the laser over optimum wave lengths, or (b) using a linearly polarised photon beam oriented in relation to the substrate crystal axes. II. The energy density in the crystal growth region can be controlled by (a) laser intensity, (b) laser pulse duration and time structure, (c) scanning of a continuous wave laser beam over the surface, or (d) adjustment of substrate thermal conductivity through a factor of about 10 by temperature control. Activation energy can be supplied to the atoms in the deposited layer. This activation energy can be supplied by (a) electronic excitation of atoms by W photons of suitably tuned wave length, or (b) deposition of ions, atoms or molecules having a high free energy. For example, in the case of carbon the condensation and subsequent cracking of acetylene on a substrate surface of diamond achieves this. Suitable impurities or dopants may be introduced into the deposited layer in controlled amounts to promote crystal growth. In the case of diamond growth this can be achieved. for example. by providing C=N radicals. The presence of nitrogen. both in the substrate (e.. tyc Ia diamond) as well as in the deposited layer, also allows for the possibility of resonant energy transfer in the Z m wavelength region. Growth of large area thin crystal films may be facilitated by an initial depth-profiled deposition of a suitable impurity into the substrate surface. In the case of diamond. implantation of a small concentration of nitrogen into the substrate surface (which would not substantially alter lattice parameters and would thus not interfere with subsequent crystal growth on this surface) would provide localised resonance absorption of photons of 7.rum wavelength. Cleavage over a large area may then be induced by an intense pulse of 7.8pm radiation, releasing the thin layer of epitaxially grown diamond. The substrate on which the crystal growth occurs may be crystalline or non-crystalline. The substrate is preferably crystalline. Examples of suitable crystal substrates are germanium, silicon, gallium arsenide, indium antimonide, and molybdenum. A particularly suitable example of the crystalline substrate is diamond. Independent or simultaneous illumination of the deposited material by other radiations including particle beams and discharges may be used to enhance growth. The method of the invention has particular application to diamond growth on or in a substrate. The carbon layer may be deposited on the substrate surface by any of the methods described above. Examples of particularly suitable methods are: 1. Plasma induced chemical vapour deposition. In this method it may be advantageous to enhance dissociation of the molecular hydrown into atomic hydrogen and this may be achieved using a laser beam which may be the same or different to that used to induce the resonance absorption in the deposited material. The same laser beam can be used to activate the chemical decomposition of the carbon source material (normally a hydrocarbon such as methane). 2. Carbon can be sublimed from a suitable solid carbon source. e.g. graphite. The sublimation may be achieved using a laser beam. High energy carbon ions can be implanted in the surface of a diamond and the laser beam focussed on the implanted ions below the surface of the substrate. The diamond growth on the substrate may be epitaxial, polycrystalline or single crystal. The nature of the growth will depend on factors such as the nature of the substrate, the temperature of the substrate and the carbon flux rate and the chemical activity of the carbon atoms deposited on or in the surface. It is also possible by the method of the invention to introduce dopant atoms such as boron into the diamond crystal grown on the substrate. by the method of the invention it is possible to enhance the tendency for the dopant atom to find its way more readily into a substitutional position than other doping methods known in the art. This is particularly advantageous as dopant atoms are electrically active only when in lattice positions.

Claims: CLAIMS 1. A method of producing crystal growth on a substrate including the steps of depositing ions, atoms or molecules necessary for formation of the desired crystalline material on or in the surface of the substrate and simultaneously irradiating the deposited material by a laser beam having a wavelength so chosen as to obtain resonance absorption by excitation of characteristic lattice vibrations in the deposited material. 2. A method according to claim 1 wherein the laser beam is a continuous wave or pulsed laser suitable for resonance absorption or surface heating. 3. A method according to claim 1 or claim 2 wherein the ions, atoms or molecules are deposited on or in the substrate surface by a method selected from physical vapour deposition, chemical vapour deposition. sputtering, cracking, ion implantation and plasma-induced chemical vapour deposition. 4. A method according to any one of claims 1 to 3 wherein the substrate is a crystalline substrate. A method accordin to claim 1 herein the crystalline substrate is selected from germanium, silicon, gallium arsenide. indium antimonide and molybdenum. 6. A method according to claim 1 wherein the crystalline substrate is diamond. 7 A method according to claim 6 wherein carbon atoms or ions are deposited on or in the surface of the diamond and the crystal growth is epitexial, polycrystalline or single crystal. 8. A method according to claim 7 wherein a dopant atom is introduced into the grown diamond crystalline material.

Inventors: SELLSCHOP, JACQUES P.F.
Applicants: MORRISON PUMPS S.A. (PTY) LTD.
Application year: 1986
Main classification: C23C16
IPC codes: C30B29, C23C16, C30B25, C30B23