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WO1992001827A1 - Cristaux de diamant orientes - Google Patents

Cristaux de diamant orientes Download PDF

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Publication number
WO1992001827A1
WO1992001827A1 PCT/US1991/005099 US9105099W WO9201827A1 WO 1992001827 A1 WO1992001827 A1 WO 1992001827A1 US 9105099 W US9105099 W US 9105099W WO 9201827 A1 WO9201827 A1 WO 9201827A1
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WIPO (PCT)
Prior art keywords
substrate
crystals
seed crystals
planes
diamond
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PCT/US1991/005099
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English (en)
Inventor
Michael W. Geis
Nikolay Efremow
Henry I. Smith
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Massachusetts Institute Of Technology
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Publication of WO1992001827A1 publication Critical patent/WO1992001827A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/26—Deposition of carbon only
    • C23C16/27—Diamond only
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/02—Pretreatment of the material to be coated
    • C23C16/0272—Deposition of sub-layers, e.g. to promote the adhesion of the main coating
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
    • C30B25/02—Epitaxial-layer growth
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
    • C30B25/02—Epitaxial-layer growth
    • C30B25/18—Epitaxial-layer growth characterised by the substrate
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/04—Diamond

Definitions

  • This invention relates to the fabrication of semiconductor material for use in electronic devices, and more particularly, to the fabrication of diamond semiconductor films.
  • Diamond is a material with semiconductor properties that are superior to Silicon (Si) , Germanium (Ge) or Gallium Arsenide (GaAs) , which are now commonly used.
  • Si Silicon
  • Ge Germanium
  • GaAs Gallium Arsenide
  • diamond provides a higher band gap, a higher breakdown voltage and a greater saturation velocity which produces a substantial increase in its projected cutoff frequency and maximum operating voltage compared to devices fabricated from Si, Ge, or GaAs.
  • diamond has the highest thermal conductivity of any solid at room temperature and excellent conductivity over a temperature range up to and beyond 500°k. Diamond therefore holds the potential for efficient semiconductor operation at high frequency and power.
  • diamond by virtue of its small molecular size compared to other materials, provides a smaller neutron cross section which reduced its degradation rate in radioactive environments. Unfortunately, however, the advantages of diamond as a semiconductor have not been exploited for various reasons.
  • natural diamonds may be of device quality, they are of limited supply and size. Furthermore, most natural diamonds are insulators, and thus introduction, or doping, of electrically active impurities such as boron by ion implantation is required to render them useful as semiconductors. Doping via ion implantation has proven to be problematic in diamond. A review of this method may be found in Vavilov et al. "Electronic and Optical Processes in Diamond” copyright 1975, Nauka, Moscow.
  • a more practical approach is to synthesize device quality diamonds on a- desirable substrate by chemical vapor deposition (CVD) .
  • CVD chemical vapor deposition
  • a gaseous mixture including a carbon supply usually provided by methane and hydrogen, is pyrolized, or injected into a high frequency plasma, above a substrate surface. Radicals containing carbon react to produce diamond crystals on the substrate, while the hydrogen present is converted to atomic hydrogen which preferentially etches away graphite and thereby leaves a film which is predominately diamond.
  • This method also allows for the possibility of doping by introducing electrically active impurities into the environment above the substrate which are then trapped in the diamond lattices so synthesized.
  • the advantage to this approach is that the seeds may be small, and may take advantage of more readily available natural or synthetic diamond grits. Furthermore, the rate of diamond growth by CVD is enhanced by employing seeds.
  • Another method involves polishing silicon substrates with diamond powder and growing diamond films by CVD about the crystal residue which remains. In both techniques, the seed crystals are completely unoriented and the resulting films are polycrystalline and inhomogeneous.
  • the invention features a method for forming an electrical device having a diamond-like film with a substantially uniform crystalline orientation.
  • the method includes orienting seed crystals on a substrate surface.
  • a slurry fluid is applied to the substrate surface and incorporated in the slurry fluid are seed crystals to substantially separate the seed crystals.
  • Each of the seed crystals has at least one common crystalline plane.
  • the slur*. / fluid is gently removed to enable preferential orien ! ation of seed crystals on the substrate such that t ⁇ ⁇ - common crystalline planes of the crystals are oriented similarly with respect to the substrate.
  • a film about the seed crystals The film is formed of crystalline regions having the common crystalline planes oriented similarly with respect to the substrate.
  • the common crystalline planes are the (111) planes.
  • the common crystalline planes of the crystals are substantially parallel to the surface of the substrate on which each of the crystals is supported.
  • the common crystalline planes of the crystals are substantially parallel to the complementary crystalline planes of the substrate.
  • the crystals have a cubic crystalline structure.
  • the crystals are selected from the group consisting of diamond and boron nitride.
  • the crystals have the (111) planes exposed, and/or the crystals have the (100) planes exposed.
  • the substrate is non-diamond.
  • the substrate is a metal, silicon or quartz.
  • the method includes the step of cleaning the seed crystals before the step of incorporating the seed crystals in a slurry.
  • the cleaning includes etching the diamond crystals.
  • the cleaning includes cleaning the crystals in NaN0 3 .
  • the NaNo 3 is at about 300°C.
  • the seed crystals are greater than about 1.0 and less than about 100 ⁇ m.
  • the slurry fluid is a mixture of water and soap.
  • the slurry fluid is a mixture of hydrocarbon oil and trichloroethylene.
  • the slurry fluid is sulfuric acid.
  • the slurry fluid includes an etchant for diamond.
  • the substrate is a smooth*single plar ⁇ e.
  • the surface of the substrate is patterned to all w preferential orientation of the seed crystals with respect to rotation about an axis perpendicular to the common planes.
  • the substrate includes pits distributed over the surface.
  • the substrate includes gratings.
  • the seed crystals are substantially symmetric faceted crystals.
  • the seed crystals are about the size of the textured features.
  • the film approaches single crystal diamond.
  • crystals not similarly oriented are removed by applying to the substrate and seed crystals, glue-type material, drying the glue-type material and washing the substrate.
  • the steps of orienting the seed crystals and removing crystals not similarly oriented may be repeated to provide a desired density of crystals on the substrate.
  • the invention features a method for forming a diamond-like film with a substantially uniform crystalline orientation.
  • the method includes selecting cubic seed crystals having a preformed shape and size and preparing a substrate by patterning the substrate to form surfaces complementary to the shape and size of the cubic seed crystals.
  • the seed crystals are oriented on the substrate surface by applying a slurry fluid to the substrate surface and incorporating in the slurry fluid seed crystals to substantially separate the seed crystals.
  • Each of the seed crystals has at least one common crystalline plane.
  • the slurry fluid is gently removed to enable preferential orientation of seed crystals on the substrate such that the common crystalline planes of the crystals are oriented similarly with respect to the substrate and the rotational orientation of the seed crystals is defined by the patterned surfaces.
  • a film is grown about the seed crystals.
  • the film is formed of crystalline regions having the common crystalline planes oriented similarly with respect to the substrate.
  • the common crystalline planes of the crystals are substantially parallel to the surface of the substrate on which each of the crystals is supported.
  • the common crystalline planes of the crystals are substantially parallel to the complementary crystalline planes of the substrate.
  • the substrate is silicon.
  • the common crystalline planes are the (ill) planes.
  • the patterned features are pits having exposed the (111) planes of the substrate.
  • the seed crystals are faceted diamond seed crystals, having substantially symmetric shape.
  • the film approaches single crystal diamond.
  • Fig. 2 is a perspective view of a diamond crystal seeded onto a flat substrate in practice of process steps 1-3 of Fig. 1, showing a preferred crystal orientation on the substrate;
  • Fig. 3 is a graphic representation of an X-ray diffraction intensity pattern obtained from diamond crystals oriented on a fused silica substrate according to the present invention, where X-ray intensity is plotted on the Y-axis against the " Bragg angle 20;
  • Fig. 3a is the x-ray diffraction signal from randomly oriented seed crystals, suspended in a paste.
  • Fig. 4 is a graphic representation of the distribution of the orientations of the crystals' (111) p .anes relative to the substrate planes, before (dotted ine) and after (solid line) step 3 of Fig. 1, where diffraction intensity is plotted on the Y-axis in arbitrary units and degree of tilt of crystals* (111) planes relative to the substrate planes is plotted along the X-axis;
  • Fig. 4a is an illustration of a diamond seed crystal with its (111) axis displaced by ⁇ from the substrate normal;
  • Fig. 5a is a schematic view of seed crystals on a substrate surface before step 4 of the present invention;
  • Fig. 5b is a schematic view showing growth of the seed crystals during the early stage of step 4 of the present invention;
  • Fig. 5c is a schematic view showing formation of a crystal film after step 4 of the present invention;
  • Figs. 6-6a are schematic views, respectively, of a random crystalline film and an oriented film.
  • Fig. 7 is a perspective view of a flat surface, seeded with diamond crystals in practice of the present invention wherein the orientation of the (111) planes is depicted;
  • Fig. 8 is a perspective view of a grated surface, seeded with diamond crystals in practice of the present invention wherein certain planes and directions are depicted;
  • Fig. 9 is an x-ray diffraction pattern from a substrate as in Fig. 8 seeded with faceted crystals.
  • Fig. 10 is a perspective view of a pitted substrate, included faceted diamond seed crystals, while Fig. 10a is an enlarged view of the boxed region "a" of Fig. 10 and
  • Fig. 11 is a side cross-sectional view of a vertical semiconductor device having an oriented polycrystalline film grown in practice of the present invention on a conductive substrate.
  • FIG. 1 there is provided a flow diagram of the preferred method for oriented diamond crystal growth, including suspending seed crystals in a slurry applied to the surface of a prepared substrate, gently removing the slurry fluid, for example, by heating the substrate to evaporate the fluid, and growing a film of diamond crystals on the treated substrate, by CVD.
  • a diamond crystal film can be grown on a substrate.
  • steps 1-3 of this procedure produce oriented seed crystals, i.e., a desired crystalline orientation of seed crystals on the substrate is effected such that a common planes of the crystals is oriented similarly with respect to the substrate.
  • the seed crystals may be oriented such that particular crystalline planes of the seed crystals, the (111) planes, are substantially parallel to the plane or planes of the substrate surface on which the crystals are supported.
  • These seed crystals may be, for example, diamond or boron nitride or any other crystal whose crystal structure and behavior is similar to diamond.
  • Step 4 a single crystal film is grown around these oriented seeds preferably by CVD.
  • the crystalline orientation of the film with respect to the substrate is the same as the seed crystals from which the film is grown since the crystal planes exposed to the reaction chamber are the same for all seeds.
  • a plurality of oriented seed crystals, having common planes oriented similarly with respect to the substrate results in a film formed of grown crystalline regions all having the same crystalline orientation.
  • the resultant film is typically smoother than films grown from seeds having random orientations since the rate of crystal growth is dependent on the crystal planes.
  • films formed from oriented seed crystals produce a more uniform doping concentration throughout the film, since dopant incorporation is also dependent on the particular crystalline planes which is grown.
  • synthetic or natural diamond grit is prepared for use, preferably by immersion in a bath of boiling sulfuric acid and ammonium persulfate at approximately 300°C for 10 minutes. Thereafter, after the wash solution is decanted from the grit, the grit is next rinsed with deionized water, concentrated hydrofluoric acid and again with deionized water. The grit is thus made ready for use in the first step of the present invention.
  • Grit sizes from less than 2 ⁇ m up to lOO ⁇ have proven to yield satisfactory results in laboratory tests of the present invention.
  • the crystals be faceted, i.e., have substantially symmetric shapes such as cubic, square, pyramidal or triangular shapes.
  • the seeds are of fairly uniform size and spacial distribution on the substrate.
  • the first step of the present method is directed to separating or declumping, the seed crystals.
  • the washed seeds are suspended in a slurry, preferably by mixture of 0.1 grams of grit per 10 ml of a 40,000:1 solution of water in soap, such as common microelectronics cleaning soap.
  • Alternate slurry solutions include silicone base diffusion pump oil in trichloroethylene.
  • Still other slurry solutions include hydrocarbon oil or sulfuric acid.
  • the slurry mixture is then subjected to an ultrasonic vibratory mixer to suspend the grit.
  • the substrate which may be, for example, a standard Si wafer, is preferably prepared by cleaning in an oxygen plasma asher. Other substrates having metal or quartz surfaces also may be used.
  • the substrate surface may be etched to form a complementary shape to that of the seed crystals to effect rotational orientation.
  • the substrate is wetted across " its surface by application of the slurry (step 2) in any conventional manner, such as by use of a dropper or the like.
  • the slurry is carried out gently to avoid substantially modifying the substrate by, for example, scratching the substrate with the diamond grit acting as an abrasive.
  • the slurry fluid may also be applied to the substrate and the seed crystals lightly sprinkled onto the fluid.
  • slurry solvent is gently removed.
  • the wafer is gently heated (step 3) until the solvent is removed and the surface is visually dry.
  • the heating is accomplished slowly to effect gradual evaporation but avoid boiling or rapid evaporation that may disturb the seed crystals and disturb the preferential orientation.
  • Such heating has been achieved by use of an ordinary laboratory hot plate, where the substrate is placed on the hot plate surface and is raised to approximately 200°C for approximately two minutes.
  • the slurry solvent may be air dried, or evaporated gradually under vacuum.
  • the diamond growth CVD process involves heating the substrate to 900°C and passing a gaseous mixture of, for example, 99% hydrogen and 1% methane, through a 2.75 GHz discharge above the substrate surface to create a plasma. Since pure diamond is an insulator, it may be necessary to introduce or dope electrically active impurities to render the diamond useful as a semiconductor.
  • B 2 H 6 may be added to the gas during CVD at chosen concentrations in the parts per million range.
  • PH 3 may be added to the gas during CVD at chosen concentrations in the parts per million range. As a result, diamond films may be produced with a chosen level of doping.
  • Another CVD method of growing diamond is to flow a mixture of hydrogen and a hydrocarbon gas, such as methane, past a hot tungsten filament located in close proximity to the substrate surface.
  • This method of diamond CVD growth was described originally by S. Matsumoto et al. in the Japan Journal of Applied Physics, vol. 21, page L183, (1982), with recent elaborations by Hirose and Terasawa, in Japan. J. Appl. Phys. vol, 25, p. L519 (1986) . Referring now to the perspective view of Fig.
  • step 2 a diamond crystal seeded onto a flat substrate in practice of process steps 1-3, and prior to step 4, is conceptually presented, 'lere, the desired orientation of the (111) planes of the seed crystal is shown with respect to the substrate surface.
  • seeded crystals after the heating of step 3 and prior to the CVD of step 4 are oriented such that the (111) planes of the crystals (using the Miller indices referencing method) will lie parallel to the substrate planes on which the crystals are supported.
  • FIG. 3 a graphic representation of an X-ray diffraction pattern obtained from diamond crystals applied to a silicon substrate by the present method, and substantially as oriented in Fig. 2 , is shown, where X-ray intensity is plotted in arbitrary units on the Y-axis and diffraction angle 2 ⁇ is plotted on the X-axis, where 2 ⁇ represents the Bragg angle.
  • X-ray intensity is plotted in arbitrary units on the Y-axis
  • diffraction angle 2 ⁇ is plotted on the X-axis, where 2 ⁇ represents the Bragg angle.
  • the distribution of crystals with (111) crystal planes oriented relative to the substrate planes is presented before and after the heating of step 3.
  • X-ray diffraction intensity is plotted along the Y-axis in arbitrary units, while the degree of tilt of the crystals' (111) planes relative to the substrata planes is plotted along the X-axis.
  • the graph Represents the variation of the (111) planes (from-* 4- tor8- ⁇ m-diam > diamond seeds as a function of the angle ⁇ measured from the substrate normal.
  • the schematic Fig. 4a is of a diamond seed with its (111) axis displaced (tilted) by ⁇ from the substrate normal.
  • the schematic mildly curvilinear dotted line in Fig. 4 represents diffraction intensity after the step 2 application of the seed crystals to a substrate but before the heating of step 3, and shows some amount of (111) planes orientation.
  • the sharply parabolic curve (in solid line) represents vastly improved diffraction intensity after the fluid removal annealing of step 3, suggestive of vastly improved crystal orientation. It will thus be appreciated that the heating process of step 3 substantially improves the conformity of the seed crystal orientation on the substrate surface.
  • the film growth process of the invention (step 4) is shown in detail in Figs. 5a-c.
  • Fig. 5a is a schematic view of seed crystals on a substrate surface in practice of the invention, after step 3 but before step 4. These crystals, as seeded, obtain the preferred orientation shown in Fig. 2.
  • the preferred orientation of the seed crystals is indicated by the horizontal hash marks drawn across the cross-section of the crystals.
  • Fig. 5b is a schematic representation of the early stage of the CVD process of step 4, where it will be seen that the seeded crystals become enlarged as new diamond material is deposited on the seed surface.
  • the new diamond material is also favorably oriented in coincidence with the orientation of the seed crystals, as indicated by the horizontal hash marks of Fig. 5b, coincident wit the hash marks of 5a.
  • the film thickness is preferably greater than the average separation between adjacent seeds.
  • This oriented film is characterized by a multiplicity of crystallites A, B, C grown from individual seeds a, b, c, all of whose (111) planes are similarly oriented.
  • crystal defects may occur due to the differing rotational orientation of the seeds about their (111) axis.
  • a randomly oriented crystal film formed, for example, from seed crystals having random orientations is compared to an oriented film formed from seed crystals having uniform crystal planes orientation according to the invention are shown, respectively.
  • the oriented films according to the invention have advantages over randomly oriented polycrystalline films.
  • dopant incorporation during crystal growth is a strong function of orientation.
  • incorporation of boron, a p- type dopant is 100 times higher on (111) planes than on (100) planes during low pressure diamond growth (Buin et al. J. Cryst. Growth 31, 44 (1975)). Similar results have been reported for phosphorus n-type dopant. As illustrated in Fig.
  • the resultant film grown from randomly oriented crystals includes regions 20 having higher dopant (illustrated by dots) concentrations and regions 22 having lower dopant concentrations.
  • oriented films formed according to the invention ha-sre a substa: tially more uniform dopant concentration?throughout _he film.
  • crystallites of a .andomly oriented film grow at different rates resulting in an uneven surface, again as illustrated in Figs. 6-6a.
  • the film is oriented, formed from oriented seed crystals, the seed crystals grow at substantially the same rate, forming a smoother film surface.
  • Oriented films of high quality will have electrical properties approaching those of single crystal diamond films, i.e., the grain boundaries are reduced or absent and the defects between adjacent crystallites (crystal portions grown from adjacent seeds) are not electrically active, i.e., they don't create an insulating barrier.
  • EXAMPLE 1 The following technique has been used to grow (111) oriented diamond films on smooth substrates using oriented diamond seeds.
  • the degree of orientation of the film is defined by the initial orientation of the seeds.
  • the initial orientation was effected by the seed size and the cleaning procedure.
  • Over 90% of the seeds exhibit a (111) orientation with a tip angle of less than 0.25°. Further growth of diamond on these seeds does not affect the orientation, and diamond films obtained by such growth allow smoother surfaces and more controlled doping.
  • the seed crystals are diamond grit obtained by pulverizing either natural (Micronized natural diamond with sizes ranging from 0.25 to 100 ⁇ m in diameter was obtained from Dubbledee Corp, 100 Stierli Court, Mount Arlington, NJ 07856) or synthetic (Micronized synthetic diamond was obtained from Specialty Materials Dept. General Electric, Worthington, OH 43085) single-crystal diamonds. Seeds were cleaned in either molten NaN0 3
  • the slurry was spread across a silicon substrate and the fluid evaporated.
  • the loosely adherent seeds were then removed by light ultrasonic cleaning in water or isopropyl alcohol.
  • Diamond films were then grown on the attached seeds by either the plasma (D.D. Rathman et al. in Diamond and Diamond-Like Materials Synthesis, Ed. H. Johnson, A.R. Badzian, and M.W. Geis (Materials Research, Pittsburgh, PA, 1988, p. 115.) or the hot filament method (S Matsumoto, Y. Sato, N. Ka o, and N. Setaka, Jpn.J.Appl.Phys.21, L183 (1982).)
  • the orientation of films grown from attached seeds were characterized as a function of deposition and growth parameters.
  • a lone (111) peak, as shown in Fig. 3 indicated that the diamond seeds have a (111) orientation.
  • the angular distribution of the (111) crystal axes of the seeds about the substrate normal can be used as a measure of the quality of the orientation. This distribution can be characterized by measuring the x-ray diffraction intensity from the (111) planes as a function of the angle measured from the substrate normal.
  • Figure 4a schematically shows a single seed with its (111) axis ⁇ degrees from the substrate normal.
  • the half-width angle at half the maximum x-ray peak intensity, HWHM is defined as the tip angl..
  • the tip angle was found to increase with a d v rease in seed size.
  • the tip angle varied from ⁇ 3.5° for 0- to 0.25- ⁇ m-diam seeds to less than ⁇ 0.25° for seeds larger than 20 ⁇ m.
  • Seeds cleaned in NaN0 3 have tip angles about half of those cleaned with H 2 S0 4 and (NH 4 ) 2 S 2 O g .
  • Optical and scanning electron microscope examination determined that for the films grown from seeds larger than 10 ⁇ m, over 90% of the seeded crystals on the substrate have a (111) orientation.
  • Fig. 7 a flat substrate surface, seeded with diamond crystals, is shown in perspective view. These crystals are indicated to have dissimilar orientations with respect to rotation about an axis perpendicular to the (111) planes. It will be appreciated that these crystals may have irregular shapes. However, regular tetrahedral crystal shapes are drawn in Fig. 7 for ease of indicating the orientations of the (111) planes.
  • the seed crystals are faceted as shown, i.e., they have regular, symmetric shapes. Growth of diamond films by CVD from such crystals may lead to crystal defects at the point at which film growth from adjacent crystals meet.
  • An alternative embodiment of the present invention is to apply the method of steps 1-4 to a surface which has been previously patterned, for example, in the form of a grating, as disclosed in the perspective view of Figure 8 to allow preferential orientation of the seed crystals with respect to rotation about an axis perpendicular to the common planes of the crystals similarly oriented with respect to the substrate.
  • the shape or morphology of the substrate grating is formed complementary to the shape of the seed crystals by exposing the crystalline planes of the substrate that is complementary to the exposed planes of faceted seed crystals.
  • a silicon substrate may be formed with a grating having exposed on the walls of the grating, the (111) crystal planes and the seed crystals are faceted preferably to form symmetric seeds having exposed the (111) crystal planes.
  • the shape of the grating is inherently complementary to the shape of the crystals.
  • the perimeter of the gratings formed run along the crystalline planes of the wafer to provide a smooth grating, the walls of which are formed from the (111) planes of the silicon.
  • the perimeter of the gratings are oriented with respect to the 110 axis of the silicon wafer.
  • the gratings may be formed by lithographic techniques (as discussed below with respect to etched pits) .
  • the crystals are of a size that approximates that of the grating.
  • Seed crystals applied in a slurry, and after evaporation, are oriented such that the (111) crystal face of the crystal and the substrate are in face-wise arrangement.
  • the (111) planes of the seed crystal is thus being parallel to the planes of the (111) substrate surface, i.e., the wall of the grating that supports the seed crystals.
  • the crystalline orientation of the crystals, i.e., the (111) planes being parallel to the substrate surface supporting the crystals is achieved by the phenomenon discussed above and obtained by the process of Fig. 1, while the rotational orientation of the seeds is achieved by the complementary shape of the seeds and the textured substrate.
  • an x-ray diffraction pattern is shown as a function of substrate rotation, from the (311) diamond planes of diamond seed crystals (about 100 microns) oriented on a silicon surface that was etched with a grating such that the (111) planes is exposed.
  • the grating was approximately lOO ⁇ m in width at the surface of the substrate with adjacent gratings separated by 100-200 microns.
  • the diffraction maxima from the (311) planes is detected predominantly only at regular orientations of the substrate as the substrate is rotated, indicating that the majority of the crystals are similarly oriented in the gratings.
  • the substrate in another embodiment employing a substrate with a patterned film, may be patterned with a series of preformed pits and faceted seed crystals applied to the substrate such that they are positioned within the pits.
  • the pits Preferably have a shape complementary to the shape of preformed crystals.
  • the seed crystals may be faceted diamond crystals faceted along the (111) and/or (100) planes and have a substantially symmetric crystalline shape, such as square, triangular or cubic-trapezoidal .shapes.
  • the pits are then formed with complementary shapes.
  • the substrate is a silicon substrate having cubic-form pits, the walls of which are exposed (111) planes.
  • the seed crystals may be oriented within the pits such that the (111) planes of the crystals mates in face-wise manner with the (111) planes exposed in the substrate pit.
  • Fig. 10a illustrates the use of symmetric crystals having a cubic-trapezoidal shape with the (111) and (100) planes exposed. In this manner, the seed crystal is oriented such that the (111) planes is parallel to the contacting planes of the substrate and the rotational orientation of the various crystals seeded on the substrate are defined.
  • This embodiment has the advantage of enabling selecting the density of oriented seed crystals on the substrate and the proximity of adjacent seed crystals to enable fine tuning of the final grown film.
  • the seed crystals are either tetrahedral or triangular diamond seed crystals of about 10 to 100 micron.
  • the pits are dimensioned to have a size that approximates that of the seed crystals.
  • the opening of the substrate pits are typically about 100 microns for crystals about 75 microns.
  • the pits are separated, for example, between 100 to 200 microns. Good results have been obtained with the seed crystals and pits sized such that the top of the crystal, when seated in the pit is approximately even with the planes of the unpitted substrate surface. Using smaller crystals has the advantage that less crystal growth is needed to form a film with a uniform surface.
  • a silicon wafer may be provided having on its exposed outer surface the (100) planes. Onto the wafer surface is deposited a 1,000 angstrom thick silicon dioxide film and thereafter evaporated a metal layer such as a 500 angstrom chromium or aluminum layer, for example by electron beam evaporation techniques.
  • a photoresist is applied to the metal layer and the photoresist exposed through a mask having a desired pattern to form a desired pattern of pits (as in Figs. 9-9a or a grating as in Fig. 8). After exposure, the photoresist is developed and the underlying metal layer etched.
  • the silicon dioxide layer is removed by employing an etchant aqueous solution of HF or reactive ion etching in a fluorine containing gas.
  • the silicon is etched with an etchant that selectively removes silicon along the (100) planes leaving exposed the (111) planes.
  • etchants include sodium hydroxide, tetramethyl ammonium hydroxide, ethyl diamine/pyrocatechol or hydrazine. It will be understood that pits of complementary shape and size may be formed by other methods and on other substrates, including non- crystalline substrates.
  • the crystals Prior to applying the seed crystals, it is preferable to clean the crystals in a NaN0 3 at less than 600°C (to avoid pitting the surface of the crystals) , preferably about 300°C to finish the surface of the faceted diamond crystals and remove irregularities and dissolve rogue crystals.
  • the substrate surface is gently wetted with concentrated sulfuric acid such that it forms a thin film over the substrate.
  • the seed crystals are then applied by gently sprinkling onto the sulfuric acid film.
  • the sulfuric acid is evaporated, gently and without boiling, by heating to about 300°C. It has been observed by microscopy that as the sulfuric acid evaporates, the crystals are drawn into the pits. Crystallographic analyses have indicated that the crystals are oriented such that the (111) planes is oriented in face-wise manner with respect to the (111) planes exposed in the silicon substrate pits.
  • a small amount of tetramethyl ammonium hydroxide may be added to the sulfuric acid to slightly etch the silicon substrate as the seed crystals are oriented, and thus accommodate burrs or irregularities on the surface of the faceted crystals.
  • An etchant for diamond such as NaN0 3 may also ' be included in the slurry fluid.
  • Seed crystals applied to pitted substrates show an improvement in orientation by about a factor of two (measured by the half-width at half maximum of the x-ray diffraction peaks as in Fig. 3) over crystals applied to grated surfaces (as in Fig. 8) .
  • the seeding process may be carried out iteratively.
  • a glue in the form of a photoresist (Selusol AZ thinner and Novolak photoresist polymer) preferably in dilute solution (0.1% by weight) is gently applied, for example, with an eye dropper to a substrate surface and allowed to spread thereover and dry.
  • a light cleaning is carried out by gentle agitation with an ultrasonic cleaner and rinsing with water. It has been found that this process particularly removes crystals that are poorly oriented in pits or gratings etched into the substrate surface while not substantially removing those crystals which are properly oriented.
  • the glue which forms a thin film (believed to be less than 2 to 4,000 angstroms) on the substrate, fixes the oriented crystals more firmly since a greater surface area between the crystals and the substrate exist when the faces of the (111) planes are parallel and face-wise, compared to randomly oriented crystals.
  • the substrate may be reseeded and the gluing procedure discussed above, repeated to increase the density of oriented crystals on the substrate to a desired level.
  • the present invention may be favorably employed in the growth of vertical semiconductor devices. These devices are characterized by vertical current flow through the device.
  • Fig. 11 there is shown a side cross-sectional view of a vertical semiconductor device having an oriented polycrystalline film grown on an ungrated conductive substrate (such as of nickel or carbon) , created by the present method of crystal film growth.
  • a grating pattern has been etched into the surface of the prepared polycrystalline film, and where the device is provided with an emitter, base, and collector.
  • the vertical axes of the crystals of the textured film are within a few degrees of the substrate normal, where rotational orientations about the normal axis have not been controlled.
  • the film has been doped with boron sufficient to render it a suitable semiconductor.
  • Ohmic contacts may be created by conventional means.
  • metal is evaporated on all horizontal grating surfaces without metallizing the vertical walls of the grating, thus creating a Schottk base and contacts on the tops of the grating.
  • This vertical device is only one of several devices which may be created in practice of the present invention.
  • the preferred process is as follows:

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Abstract

Procédé destiné à produire des pellicules de diamant orientées sur un substrat. Des germes cristallins de diamant sont tenus en suspension dans une pâte et appliqués à la surface d'un substrat. En enlevant le fluide de la pâte, on obtient des germes cristallins (111) dont les facettes ont une orientation pratiquement semblable à celle du substrat. Une pellicule de diamant polycristalline et orientée peut être produite autour des germes cristallins par procédé de dépôt chimique en phase gazeuse.
PCT/US1991/005099 1988-06-03 1991-07-19 Cristaux de diamant orientes WO1992001827A1 (fr)

Applications Claiming Priority (3)

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US20287788A 1988-06-03 1988-06-03
US55674690A 1990-07-23 1990-07-23
US556,746 1990-07-23

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WO1992001827A1 true WO1992001827A1 (fr) 1992-02-06

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0630994A1 (fr) * 1993-01-14 1994-12-28 Sumitomo Electric Industries, Ltd. Procede de synthese de diamant en phase vapeur
US5453106A (en) * 1993-10-27 1995-09-26 Roberts; Ellis E. Oriented particles in hard surfaces
WO1996006732A1 (fr) * 1994-08-31 1996-03-07 Roberts Ellis E Ensembles de cristaux orientes
US6158952A (en) * 1994-08-31 2000-12-12 Roberts; Ellis Earl Oriented synthetic crystal assemblies
WO2011035848A3 (fr) * 2009-09-24 2011-07-21 Schott Ag Procédé de fabrication d'une cellule solaire ou d'un transistor doté d'une couche mince de silicium cristallin

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3714334A (en) * 1971-05-03 1973-01-30 Diamond Squared Ind Inc Process for epitaxial growth of diamonds
US4434188A (en) * 1981-12-17 1984-02-28 National Institute For Researches In Inorganic Materials Method for synthesizing diamond
JPS60195094A (ja) * 1984-03-15 1985-10-03 Agency Of Ind Science & Technol ダイヤモンド薄膜の製造方法
JPS6168395A (ja) * 1984-09-13 1986-04-08 Showa Denko Kk ダイヤモンド結晶の成長法
US4638553A (en) * 1982-12-08 1987-01-27 International Rectifier Corporation Method of manufacture of semiconductor device

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3714334A (en) * 1971-05-03 1973-01-30 Diamond Squared Ind Inc Process for epitaxial growth of diamonds
US4434188A (en) * 1981-12-17 1984-02-28 National Institute For Researches In Inorganic Materials Method for synthesizing diamond
US4638553A (en) * 1982-12-08 1987-01-27 International Rectifier Corporation Method of manufacture of semiconductor device
JPS60195094A (ja) * 1984-03-15 1985-10-03 Agency Of Ind Science & Technol ダイヤモンド薄膜の製造方法
JPS6168395A (ja) * 1984-09-13 1986-04-08 Showa Denko Kk ダイヤモンド結晶の成長法

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0630994A1 (fr) * 1993-01-14 1994-12-28 Sumitomo Electric Industries, Ltd. Procede de synthese de diamant en phase vapeur
EP0630994A4 (fr) * 1993-01-14 1995-08-02 Sumitomo Electric Industries Procede de synthese de diamant en phase vapeur.
US5499601A (en) * 1993-01-14 1996-03-19 Sumitomo Electric Industries, Ltd. Method for vapor phase synthesis of diamond
US5453106A (en) * 1993-10-27 1995-09-26 Roberts; Ellis E. Oriented particles in hard surfaces
US5560745A (en) * 1993-10-27 1996-10-01 Roberts; Ellis E. Oriented particles in hard surfaces
WO1996006732A1 (fr) * 1994-08-31 1996-03-07 Roberts Ellis E Ensembles de cristaux orientes
US6158952A (en) * 1994-08-31 2000-12-12 Roberts; Ellis Earl Oriented synthetic crystal assemblies
WO2011035848A3 (fr) * 2009-09-24 2011-07-21 Schott Ag Procédé de fabrication d'une cellule solaire ou d'un transistor doté d'une couche mince de silicium cristallin

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