Sumitomo Electric Industries, Limited

Sony Corporation

Masahiro Nakayama

Masato Irikura

Naoki Matsumoto

Masao Ikeda

Koshi Tamamura

Yasushi Mochida

Masaki Ueno

Katsushi Akita

Takashi Kyono

Takayuki Nishiura

Eiryo Takasuka

Kouhei Miura

Yoshio Mezaki

Tetsuya Hirano

Technology of making freestanding gallium nitride (GaN) wafers has been matured at length. Gallium nitride is rigid but fragile. Chamfering of a periphery of a GaN wafer is difficult. At present edges are chamfered by a rotary whetstone of gross granules with weak pressure. Minimum roughness of the chamfered edges is still about Ra 10 &#x3bc;m to Ra 6 &#x3bc;m. The large edge roughness causes scratches, cracks, splits or breaks in transferring process or wafer process. A wafer of the present invention is bevelled by fixing the wafer to a chuck of a rotor, bringing an edge of the wafer into contact with an elastic whetting material having a soft matrix and granules implanted on the soft matrix, rotating the wafer and feeding the whetting material. Favorably, several times of chamfering edges by changing the whetting materials of smaller granules are given to the wafer. The chamfering can realize small roughness of Ra10 nm and Ra5 &#x3bc;m at edges of wafers.

Chamfered freestanding nitride semiconductor wafer and method of chamfering nitride semiconductor wafer

Technology of making freestanding gallium nitride (GaN) wafers has been matured at length. Gallium nitride is rigid but fragile. Chamfering of a periphery of a GaN wafer is difficult. At present edges are chamfered by a rotary whetstone of gross granules with weak pressure. Minimum roughness of the chamfered edges is still about Ra 10 &#x3bc;m to Ra 6 &#x3bc;m. The large edge roughness causes scratches, cracks, splits or breaks in transferring process or wafer process. A wafer of the present invention is bevelled by fixing the wafer to a chuck of a rotor, bringing an edge of the wafer into contact with an elastic whetting material having a soft matrix and granules implanted on the soft matrix, rotating the wafer and feeding the whetting material. Favorably, several times of chamfering edges by changing the whetting materials of smaller granules are given to the wafer. The chamfering can realize small roughness of Ra 10 nm and Ra 5 &#x3bc;m at edges of wafers.

Compound-semiconductor-substrate polishing methods, compound semiconductor substrates, compound-semiconductor-epitaxial-substrate manufacturing methods, and compound semiconductor epitaxial substrates whereby oxygen superficially present on the substrates reduced. A compound semiconductor-substrate polishing method includes a preparation step (S), a first polishing step (S), and a second polishing step (S). In the preparation step (S), a compound semiconductor substrate is prepared. In the first polishing step (S), the compound semiconductor substrate is polished with a chloric polishing agent. In the second polishing step (S), subsequent to the first polishing step (S), a polishing operation utilizing an alkaline aqueous solution containing an inorganic builder and having pH of 8.5 to 13.0 inclusive is performed.

Method of polishing compound semiconductor substrate, compound semiconductor substrate, method of manufacturing compound semiconductor epitaxial substrate, and compound semiconductor epitaxial substrate

Nitride semiconductor wafers which are produced by epitaxially grown nitride films on a foreign undersubstrate in vapor phase have strong inner stress due to misfit between the nitride and the undersubstrate material. A GaN wafer which has made by piling GaN films upon a GaAs undersubstrate in vapor phase and eliminating the GaAs undersubstrate bends upward due to the inner stress owing to the misfit of lattice constants between GaN and GaAs.

Nitride semiconductor wafer and method of processing nitride semiconductor wafer

A method of producing a separated GaN crystal body grown by vapor phase epitaxy on a substrate made of material different from GaN is provided. In this method, a nitride deposit is formed during the growth on a periphery of the substrate and GaN crystal body. The present method comprises the steps of: processing the periphery of the substrate to remove the nitride deposit; and, after the peripheral processing, separating the substrate from the GaN crystal body to make the substrate and the GaN crystal body independent of each other.

Method of producing gallium nitride (GaN) independent substrate, method of producing GaN crystal body, and method of producing GaN substrate

Nitride semiconductor wafers which are produced by epitaxially grown nitride films on a foreign undersubstrate in vapor phase have strong inner stress due to misfit between the nitride and the undersubstrate material. A GaN wafer which has made by piling GaN films upon a GaAs undersubstrate in vapor phase and eliminating the GaAs undersubstrate bends upward due to the inner stress owing to the misfit of lattice constants between GaN and GaAs. Ordinary one-surface polishing having the steps of gluing a wafer with a surface on a flat disc, bringing another surface in contact with a lower turntable, pressing the disc, rotating the disc, revolving the turntable and whetting the lower surface, cannot remedy the inherent distortion. The Distortion worsens morphology of epitaxial wafers, lowers yield of via-mask exposure and invites cracks on surfaces. Nitride crystals are rigid but fragile. Chemical/mechanical polishing has been requested in vain. Current GaN wafers have roughened bottom surfaces, which induce contamination of particles and fluctuation of thickness.

A nitride semiconductor substrate having a rugged surface being lapped by whetting granules to roughness between Rms5 nm and Rms200 nm, which has a function of reducing dislocations of a GaN, InGaN or AlGaN layer epitaxially grown on the lapped substrate by gathering dislocations in the epi-layer to boundaries of holes, pulling the dislocations to bottoms of the holes. Higher roughness of the nitride substrate degrades morphology of an epitaxially-grown layer thereon but reduces dislocation density to a lower level. Morphology of the epi-layer contradicts the dislocation density of the epi-layer. The nitride semiconductor substrate can reduce dislocation density and can be low cost and useful substrates.

Nitride semiconductor substrate and method of producing same

A GaN substrate comprises a GaN single crystal substrate, an AlGaN intermediate layer (0&#x3c;x&#x2266;1) epitaxially grown on the substrate, and an GaN epitaxial layer grown on the intermediate layer. The intermediate layer is made of AlGaN and this AlGaN grows over the entire surface of the substrate with contaminants thereon and high dislocation regions therein. Thus, the intermediate layer is normally grown on the substrate, and a growth surface of the intermediate layer can be made flat. Since the growth surface is flat, a growth surface of the GaN epitaxial layer epitaxially grown on the intermediate layer is also flat.

GaN substrate and method of fabricating the same, nitride semiconductor device and method of fabricating the same

A mirror-polished obverse surface and a roughened reverse surface of the conventional GaN wafers have been discriminated by difference of roughness on the surfaces with human eyesight. The difference of the surfaces is rather ambiguous. Cracks/breaks and distortion of the wafers have been likely to occur because the roughness of the reverse surface is apt to bring fine particles. To discern an obverse from a reverse without making use of the difference of the surface roughness, the present invention provides an obverse/reverse discriminative rectangular nitride semiconductor wafer having a longer slanting edge and a shorter slanting edge at obversely-clockwise neighboring corners, or having an asymmetric slanting edge at a corner, or having asymmetrically bevelled parts or having discriminating characters marked by laser. The present invention can make the reverse surface mirror-polished and smooth, so that particles on the reverse surface and distortion, cracks or breaks of the wafer decrease.

Obverse/reverse discriminative rectangular nitride semiconductor wafer

Nitride semiconductor wafers which are produced by epitaxially grown nitride films on a foreign undersubstrate in vapor phase have strong inner stress due to misfit between the nitride and the undersubstrate material. A GaN wafer which has made by piling GaN films upon a GaAs undersubstrate in vapor phase and eliminating the GaAs undersubstrate bends upward due to the inner stress owing to the misfit of lattice constants between GaN and GaAs. Ordinary one-surface polishing having the steps of gluing a wafer with a surface on a flat disc, bringing another surface in contact with a lower turntable, pressing the disc, rotating the disc, revolving the turntable and whetting the lower surface, cannot remedy the inherent distortion. The Distortion worsens morphology of epitaxial wafers, lowers yield of via-mask exposure and invites cracks on surfaces. Nitride crystals are rigid but fragile. Chemical/mechanical polishing has been requested in vain. Current GaN wafers have roughened bottom surfaces, which induce contamination of particles and fluctuation of thickness. Circular nitride wafers having a diameter larger than 45 mm are made and polished. Gross-polishing polishes the nitride wafers in a pressureless state with pressure less than 60 g/cmby lifting up the upper turntable for remedying distortion. Distortion height H at a center is reduced to H&#x2266;12 &#x3bc;m. Minute-polishing is a newly-contrived CMP which polishes the nitride wafers with a liquid including potassium hydroxide, potassium peroxodisulfate and powder, irradiates the potassium peroxodisulfate with ultraviolet rays. The CMP-polished top surface has roughness RMS of 0.1 nm&#x2266;RMS&#x2266;5 nm or more favorably 0.1 nm&#x2266;RMS&#x2266;0.5 nm. The CMP-polished bottom surface has roughness RMS of 0.1 nm&#x2266;RMS&#x2266;5000 nm or more favorably 0.1 nm&#x2266;RMS&#x2266;2 nm. TTV is less than 10 &#x3bc;m.

Growing community of inventors

Hyogo, Japan

Masahiro Nakayama