Foundation substrate for producing diamond film and method for producing diamond substrate using same

Abstract

It is an object to provide a method for producing a diamond substrate effective for reducing various defects including dislocation defects and a foundation substrate used for the same. This object is achieved by a foundation substrate for forming a diamond film by a chemical vapor deposition method, wherein an off angle is provided to the surface of the foundation substrate with respect to a predetermined crystal plane orientation.

Claims

1. A foundation substrate for forming a diamond film by a chemical vapor deposition method, wherein an off angle is provided to a surface of the foundation substrate toward a crystal axis of [−1−1 2] direction or its three-fold symmetric direction with respect to a crystal plane orientation of (111); wherein the off angle is in the range of 2 to 15°; and wherein a deviation of the direction of the off angle is within ±15°.

2. The foundation substrate for forming a diamond film according to claim 1, wherein the surface of the foundation substrate is any one of diamond, iridium, rhodium, palladium and platinum.

3. The foundation substrate for forming a diamond film according to claim 1, wherein the foundation substrate has a multilayer structure in which a surface film forming the surface is laminated.

4. The foundation substrate for forming a diamond film according to claim 3, wherein the multilayer structure comprises a MgO substrate and a surface film formed thereon.

5. The foundation substrate for forming a diamond film according to claim 3, wherein the multilayer structure comprises a silicon substrate, an intermediate film comprising a single layer or multiple layers formed thereon, and a surface film formed on the intermediate film.

6. A method for producing a diamond substrate which comprises homoepitaxially growing or heteroepitaxially growing diamond on the foundation substrate for forming a diamond film according to claim 3, wherein the off angle is formed on the surface film by providing the off angle to any of the layers in a course of forming the multilayer structure.

7. A method for producing a diamond substrate which comprises homoepitaxially growing or heteroepitaxially growing diamond on the foundation substrate for forming a diamond film according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows a structural example (1) of a foundation substrate;

(2) FIG. 2 shows a structural example (2) of a foundation substrate;

(3) FIG. 3 shows an explanatory drawing of the off angle;

(4) FIG. 4A to 4C show photographs of the surfaces of diamond;

(5) FIG. 5 shows evaluation results of etch pits; and

(6) FIG. 6A to 6C show SEM images of etch pits.

DESCRIPTION OF EMBODIMENTS

(7) A cross section of the foundation substrate is shown in FIG. 1. As shown in FIG. 1, double-side-polished single crystal silicon (Si) substrates 3 having a diameter of 10.0 mm, a thickness of 1.0 mm and a surface of a (100) plane with an off angle of 0°, 4° and 8° toward the crystal axis of [011] direction were prepared.

(8) An intermediate film 2 consisting of single crystal MgO was formed on one side of each of the prepared single crystal silicon substrates 3 by electron beam evaporation.

(9) At this time, the conditions were made under vacuum at a substrate temperature of 900° C., and the single crystal MgO (intermediate film) was epitaxially grown until it reaches to 1 μm.

(10) Further, a surface film 1 consisting of Ir was formed on each of the intermediate films consisting of the single crystal MgO.

(11) For the formation of the Ir surface film 1, a high frequency (RF) magnetron sputtering method (13.56 MHz) targeting Ir having a diameter of 6 inches (150 mm), a thickness of 5.0 mm and a purity of 99.9% or more was used.

(12) Each of the substrates on which the single crystal MgO layer has been formed was heated to 800° C., and after the base pressure was confirmed to be 6×10.sup.−7 Torr (about 8.0×10.sup.−5 Pa) or less, an Ar gas was introduced with 10 sccm.

(13) After making the pressure 5×10.sup.−2 Torr (about 6.7 Pa) by adjusting the aperture of the valve communicating to the exhaust system, an RF power of 1,000 W was input to carry out film formation for 15 minutes.

(14) The resulting Ir layer had a thickness of 0.7 μm.

(15) Each of the layered products in which the single crystal MgO layer and the Ir layer had been laminated onto the single crystal silicon substrate thus obtained was heteroepitaxially grown in accordance with the off angle provided to the single crystal silicon substrate. Therefore, each of the layered products including the silicon substrate with an off angle has a surface of which is a (100) plane with an off angle of 4° and 8° toward a crystal axis of [011] direction.

(16) It should be noted that the off angle may be formed at any stage such as the initial silicon substrate and the intermediate film formed thereon.

(17) For example, after finishing the surface of the foundation substrate without an off angle, a material in which the off angle of 4° or 8° is finally provided in the crystal axis of [011] direction may be formed by polishing as schematically shown in FIG. 3.

(18) Next, a pretreatment (bias treatment) was performed for nucleation of diamond.

(19) The foundation substrate was set on a flat plate type electrode with a diameter of 15 mm with the Ir layer side up.

(20) After the base pressure was confirmed to be 1×10.sup.−6 Torr (about 1.3×10.sup.−4 Pa) or less, hydrogen-diluted methane (CH.sub.4/(CH.sub.4+H.sub.2)=5.0 vol. %) was introduced with 500 sccm.

(21) After the pressure was made 100 Torr (about 1.3×10.sup.4 Pa) by adjusting the aperture of the valve communicating to the exhaust system, a negative voltage was applied to the electrode at the substrate side to expose it to plasma for 90 seconds whereby the foundation surface was subjected to the bias treatment.

(22) Diamond 10 was heteroepitaxially grown on the respective foundation substrates of off-angles of 0°, 4° and 8° produced by the above by the DC plasma CVD method.

(23) The foundation substrate subjected to the bias treatment was set in a chamber of a DC plasma CVD apparatus, and after evacuating it to a base pressure of 10.sup.−3 Torr (about 1.3×10.sup.−1 Pa) or less by a rotary pump, hydrogen-diluted methane (CH.sub.4/(CH.sub.4+H.sub.2)=5.0 vol. %) which is a raw material gas was introduced with 1,000 sccm.

(24) After making the pressure of the chamber 110 Torr (about 1.5×10.sup.4 Pa) by adjusting the aperture of the valve communicating to the exhaust system, and then, a direct current of 2.0 A was passed therethrough to carry out film formation.

(25) When the temperature of the foundation substrate during the film formation was measured by a pyrometer, it was 950° C.

(26) When the resulting diamond film was subjected to X-ray diffraction measurement (incident X-ray wavelength: 1.54 Å), the half value width of the rocking curve of the diffraction intensity peak at 2θ=119.5° belonging to the diamond (004) was 720 arcsec (about 0.2°).

(27) An observation photograph of the resulting diamond film by the optical microscope is shown in FIG. 4.

(28) FIG. 4A in which the off angle of 0° shows many hillocks being generated, while those in which the off angle of 4° and the off angle of 8° show step bunching forms in which the steps are flown in one direction and no hillocks or abnormal growth particles were observed as shown in FIGS. 4B and 4C.

(29) Next, the etch pit density was evaluated.

(30) The surfaces of the diamond film were subjected to plasma treatment by using a microwave plasma CVD apparatus (Astex Model AX6350) under conditions of 2,200 W, a hydrogen gas with 500 sccm, at 110 Torr for 1 hour.

(31) The results of SEM observation of the surfaces treated above are shown in FIG. 6.

(32) FIG. 6A in which the off angle is 0° showed an etch pit density (EPD) of 1×10.sup.8 cm.sup.−2, FIG. 6B in which the off angle is 4° showed the EPD of 5×10.sup.7 cm.sup.−2, and FIG. 6C in which the off angle is 8° showed the EPD of 3×10.sup.7 cm.sup.−2.

(33) A graph of the results in which the relation between the film thickness of the diamond film and the EPD is investigated is shown in FIG. 5.

(34) It could be clarified that generation of hillocks and abnormally grown particles could be suppressed and dislocation defects (EPD) could be reduced by forming an off angle on the surface of the foundation substrate.

(35) In particular, whereas at the off angle of 0°, hillocks and abnormally grown particles occurred more frequently so that it could not be made a thick film, at the off angle of 8°, EPD could be reduced by about two orders of magnitude with a thick film of a film thickness of about 1 mm.

(36) As shown in FIG. 2, an off angle is provided to the surface of the substrate 3a consisting of a single crystal MgO, YSZ, SrTiO.sub.3 or α-alumina (Al.sub.2O.sub.3), and a surface film 1 consisting of Rh, Pd, Ir or Pt may be formed as a surface film.

(37) When a surface film consisting of an Ir layer is formed on a MgO substrate to which an off angle is provided in the same manner as in the above-described example and a diamond film is formed thereon, it can be confirmed that dislocation defects are reduced by providing the off angle.