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Laser deposition of crystalline boron nitride films

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Information

  • Patent Grant
  • 5139591
  • Patent Number
    5,139,591
  • Date Filed
    Wednesday, June 26, 1991
    33 years ago
  • Date Issued
    Tuesday, August 18, 1992
    32 years ago
Information
Abstract
Thin films of boron nitride are grown on single crystal silicon substrates using laser deposition techniques. The films are characterized by essentially a single crystal throughout and having a cubic structure which is in epitaxial registry with the underlying silicon substrate.
Description
Claims
  • 1. A method of forming thin films of cubic boron nitride comprising the following steps:
  • providing a a single-crystal silicon substrate orientated throughout along its (100) crystallographic axis;
  • providing a hexagonally orientated boron nitride target, said target being disposed in proximity with said appropriate substrate material;
  • inducing vaporization of said target using a pulsed excimer laser to disassociate and vaporize said target, such that the vaporized material deposits onto a surface of said substrate to form a thin film layer of cubic boron nitride on said surface, said thin film layer of cubic boron nitride being crystallographically aligned with said substrate.
  • 2. A method of forming thin films of cubic boron nitride comprising the following steps:
  • providing a silicon substrate oriented along the (100) cyrstallographic axis;
  • providing a hexagonally orientated boron nitride target, said boron nitride target being disposed in proximity with said silicon substrate;
  • inducing vaporization of said boron nitride target using wave energy sufficient to disassociate and vaporize said target, such that the vaporized material deposits onto a surface of said substrate to form a thin film layer of cubic boron nitride on said surface, said thin film layer of cubic boron nitride being crystallographically aligned with said silicon substrate.
  • 3. A method for forming thin films of boron nitride on a silicon substrate comprising the steps of:
  • vaporizing a hexagonally oriented pyrolitic boron nitride target to deposit a thin film of cubic boron nitride on a silicon substrate oriented along the (100) cystallographic axis of the substrate.
  • 4. A process of forming thin films of boron nitride on a silicon substrate comprising the steps of:
  • directing a laser beam onto a hexagonally oriented pyrolitic boron nitride target to vaporize portions of said target and to deposit a thin film of cubic boron nitride on a silicon substrate oriented along its (100) crystallographic axis.
BACKGROUND OF THE INVENTION

This is a division of application Ser. No. 07/663781 filed on Mar. 4, 1991. now U.S. Pat. No. 5,080,753, which application is a file-wrapper-continuation of U.S. application Ser. No. 07/446,758, filed on Dec. 6, 1989, now abandoned. This invention relates to the formation of thin films of boron nitride. In particular, this invention relates to a method for forming thin films of single crystal, cubic phase boron nitride epitaxially oriented upon a silicon substrate using laser ablation techniques. Boron nitride (BN) is a most interesting III-IV compound from both the practical and scientific viewpoints. Boron nitride is characterized by three different crystal structures: hexagonal (hBN), wurtzite (wBN) and cubic zincblende (zBN). It is interesting that the physical properties of the boron nitride phase characterized by the cubic zincblende crystal structure are comparable to diamond in that the cubic zincblende boron nitride and diamond have low densities, extremely high thermal conductivities, and large resistivities. In addition, the cubic zincblende boron nitride and diamond have similar tribological properties and are relatively inert chemically. There has been much research directed toward the growth of diamond thin films for various purposes. Therefore significant effort has also been directed to growing these cubic zincblende boron nitride films for the same purposes. This is not only because of the similarities between the two materials in their electrical, thermal and tribological properties, but because the cubic zincblende boron nitride may also prove to be an attractive substrate for subsequent diamond growth due to the small mismatch in crystal lattice constants. As with the diamond films, previous attempts at depositing cubic boron nitride films have failed to produce the desired homogeneous, single-crystal, and epitaxially oriented films. Pulsed laser deposition of thin films has recently been demonstrated to be a useful technique for preparation of thin films of a wide variety of materials including polymers, semiconductors, superconductors, and nonlinear dielectrics. Typically, when utilizing laser deposition techniques, a substrate of appropriate material is maintained at an elevated temperature opposite to a target having a composition the same or similar to the desired thin film. A focused pulsed laser beam, usually from an excimer laser source, is incident on the target at an angle of approximately 45.degree.. The deposition is generally performed in a vacuum or other appropriate atmosphere such as flowing oxygen in the case of the copper oxide superconductors. Advantages of the laser deposition method over other deposition techniques, such as evaporation, include a faster deposition rate, the requirement for only a single target, and the ability to deposit materials possessing high boiling point temperatures, such as refractory materials. Advantages over sputtering deposition methods also include the requirement of only a single target, as well as the preservation of material composition from the target to the film. It is therefore advantageous to use laser deposition techniques for the formation of thin films of materials. In particular it would appear to be advantageous to use these laser deposition methods for the formation of thin films of materials such as boron nitride. In summary, it is desirable to provide cubic boron nitride thin films, and particularly, to provide a method for forming these thin films, wherein the resulting thin films of cubic boron nitride are essentially single-crystal, homogeneous and epitaxially oriented with the underlying substrate. It is an object of the present invention to provide thin films of boron nitride. It is a further object of this invention to provide a method for forming these thin films of boron nitride using laser deposition techniques. Lastly, it is still a further object of this invention that these thin films of boron nitride be characterized by a homogeneous single crystal, cubic structure, which is epitaxially aligned with an underlying substrate. In accordance with a preferred embodiment of this invention, these and other objects and advantages are accomplished as follows. We are the first to grow thin films of boron nitride on single-crystal silicon substrates using laser deposition techniques, wherein the films are characterized by being essentially single-crystal and having a cubic structure which is in registry with the underlying silicon substrate. This was accomplished by first providing a single-crystal silicon substrate oriented throughout along its [100] crystallographic axis. A boron nitride target containing polycrystalline, hexagonally oriented, pyrolitic boron nitride was located opposite from the single-crystal silicon substrate within a stainless steel 6-way cross chamber which was evacuated to a pressure of about about 3.times.10.sup.-4 Torr. The n-type single crystal silicon substrate was heated to approximately 400.degree. C. and maintained there during deposition. A KrF excimer laser operating at approximately 248 nanometers and approximately 10 pulses per second was used as the ablating beam. The laser ablation of the boron nitride target was conducted in ultra high purity nitrogen gas, and at various laser fluences ranging from about 1.5 to 5.2 J/cm.sup.2. The deposited, boron nitride films were examined using characterization probes of transmission electron microscopy, scanning electron miscroscopy, optical microscopy, and electron probe microanalysis. The boron nitride films were determined to be essentially characterized by a single-crystal, cubic structure which is in registry with the underlying silicon substrate. Other objects and advantages of this invention will be better appreciated from the detailed description thereof, which follows.

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Divisions (1)
Number Date Country
Parent 663781 Mar 1991
Continuations (1)
Number Date Country
Parent 446758 Dec 1989