JP2014036195A - Group iii nitride semiconductor wafer manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a group III nitride semiconductor wafer manufacturing method which can efficiently separate a base substrate by accelerating etching of the base substrate.SOLUTION: A group III nitride semiconductor wafer manufacturing method of the present embodiment comprises: a process S1 of preparing a composite substrate including a base substrate containing first oxide which reacts with hydrofluoric acid to create fluoride substantially insoluble in hydrofluoric acid, a bonding oxide film soluble in hydrofluoric acid and a group III nitride semiconductor film; an acid contact set sub-process S60 of performing one and more sub-process sets each including an HF contact sub-process S61 of bringing the composite substrate into contact with hydrofluoric acid and an FSA contact sub-process F63 of bringing the composite substrate into contact with acid which dissolves fluoride created from the first oxide; a last HF contact sub-process S65 of bringing the composite substrate into contact with hydrofluoric acid; and a process S6 of separating the base substrate from the group III nitride semiconductor film of the composite substrate.

Description

  The present invention relates to a method for manufacturing a group III nitride semiconductor wafer using a composite substrate including a base substrate, a bonding oxide film, and a group III nitride semiconductor film.

  In order to efficiently manufacture a group III nitride semiconductor wafer suitably used for a semiconductor device such as a light emitting device or an electronic device, a composite substrate in which a base substrate and a group III nitride semiconductor film are bonded is used.

  For example, Japanese Patent Laying-Open No. 2006-210660 (Patent Document 1) discloses a method for manufacturing a semiconductor substrate in which a surface layer of a first nitride semiconductor substrate is superimposed on a second substrate which is a base substrate.

  Japanese Patent Laying-Open No. 2010-232625 (Patent Document 2) discloses a method for manufacturing a bonded substrate by bonding a group III nitride semiconductor layer to a first support substrate that is a base substrate via a first buffer film. Disclose. Furthermore, in the method for manufacturing a bonded substrate, forming any one convex portion among the bonded surface of the first support substrate, the bonded surface of the group III nitride semiconductor layer, and the surface of the first buffer film. Disclose.

JP 2006-210660 A JP 2010-232625 A

  In the manufacture of a group III nitride semiconductor wafer using the above bonded substrate, a group III nitride epitaxial layer is grown on the group III nitride layer of the bonded substrate, and then the group III nitride of the bonded substrate is used. It may be necessary to separate the underlying substrate from the layer. In such a case, in the method for manufacturing a semiconductor substrate disclosed in Japanese Patent Application Laid-Open No. 2006-210660 (Patent Document 1), the surface layer of the first nitride semiconductor substrate and the second substrate as the base substrate are directly bonded. Therefore, it is difficult to separate the second substrate from the surface layer of the first nitride semiconductor substrate.

  In the method for manufacturing a bonded substrate disclosed in Japanese Patent Application Laid-Open No. 2010-232625 (Patent Document 2), the group III nitride semiconductor layer and the first support substrate that is the base substrate are interposed via the first buffer film. Since they are bonded, it is possible to separate the first support substrate from the group III nitride semiconductor layer by removing the first buffer film by etching or the like. However, since the thickness of the exposed side surface of the first buffer film is thin, there is a problem that the etching time becomes long and the manufacturing cost becomes high.

  In order to solve the above-described problem, in the method for manufacturing a bonded substrate disclosed in Japanese Patent Application Laid-Open No. 2010-232625 (Patent Document 2), a bonded surface of a first support substrate that is a base substrate, a group III nitride semiconductor layer Any one of the bonding surface and the surface of the first buffer film was formed. However, since a complicated process is required to form the recess as described above, there is a problem in that the manufacturing efficiency is lowered and the manufacturing cost is increased.

  In addition, if the entire base substrate is etched with an etching solution, the etching time is long and the manufacturing efficiency is low and the manufacturing cost is high. In some cases, the etching solution penetrates to a portion where etching is to be avoided, and the yield is significantly reduced. There was a problem.

  Therefore, in order to solve the above-described problems, a base substrate that is partially etched porous by the etchant, a bonding film that is etched by the etchant disposed on the base substrate, and a III that is disposed on the bonding film Developed a method for manufacturing a group III nitride semiconductor wafer, comprising: preparing a composite substrate including a group nitride semiconductor film; and removing a part of the base substrate and the bonding film by etching with an etchant To do.

In the above-described III nitride semiconductor wafer manufacturing method, an Al ₂ O ₃ —SiO ₂ sintered body such as a mullite (3Al ₂ O ₃ .2SiO _{2 to} 2Al ₂ O ₃ .SiO ₂ ) sintered body substrate as a base substrate. Hydrofluoric acid or the like is used as an etchant for Al ₂ O ₃ —SiO ₂ —ZrO ₂ —Y ₂ O ₃ sintered substrates such as substrates and mullite-yttria stabilized zirconia sintered substrates. Here, when mullite-yttria stabilized zirconia sintered body substrate is used as the base substrate and hydrofluoric acid is used as the etchant, yttria in the mullite-yttria stabilized zirconia sintered body substrate is fluorinated by hydrofluoric acid. To produce fluoride such as yttrium fluoride. Since such yttrium fluoride is substantially insoluble in hydrofluoric acid, it inhibits further penetration of hydrofluoric acid into the base substrate. For this reason, there was a problem of suppressing etching of the base substrate.

  An object of the present invention is to solve the above-mentioned problems and to provide a method for producing a group III nitride semiconductor wafer capable of efficiently separating a base substrate by promoting etching of the base substrate. To do.

  The present invention relates to a base substrate including a first oxide that reacts with hydrofluoric acid to generate a fluoride that is substantially insoluble in hydrofluoric acid, and hydrofluoric acid disposed on the base substrate. Preparing a composite substrate including a soluble junction oxide film and a group III nitride semiconductor film disposed on the junction oxide film; and an HF contact sub-step of contacting the composite substrate with hydrofluoric acid And an acid contact set sub-process for performing one or more sub-process sets including an FSA contact sub-process for bringing the composite substrate into contact with an acid dissolving fluoride generated from the first oxide, and the composite substrate after the acid contact set sub-process And a final HF contact sub-step for contacting the hydrofluoric acid, and in the acid contact set sub-step and the final HF contact sub-step, by etching a part of the base substrate and the bonding oxide film, the composite substrate And separating the base substrate from the group III nitride semiconductor film, a manufacturing method of a group III nitride semiconductor wafer comprising.

  In the method for manufacturing a group III nitride semiconductor wafer according to the present invention, the step of separating the base substrate is performed by lift-off of the base substrate from the group III nitride semiconductor film by etching the bonding oxide film with hydrofluoric acid. obtain. Further, in the step of separating the base substrate, hydrofluoric acid for etching the bonding oxide film is obtained by dissolving the fluoride formed from the first oxide in the HF contact sub-step in the FSA contact sub-step, The junction oxide film can be supplied via an etched region formed in a part of the base substrate. Here, after each of the HF contact sub-step, the FSA contact sub-step, and the final HF contact sub-step, it may further include a water-washing and drying sub-step of washing the composite substrate and then drying.

  In the method for manufacturing a group III nitride semiconductor wafer according to the present invention, the step of separating the base substrate may be performed by bringing the composite substrate into contact with an acid that dissolves the fluoride of the first oxide after the final HF contact sub-step. A final FSA contact sub-step can further be included. Here, after the final FSA contact sub-step, the composite substrate may further include a water-washing and drying sub-step of washing and drying the composite substrate.

  In the method for producing a group III nitride semiconductor wafer according to the present invention, the acid dissolving the fluoride generated from the first oxide may contain at least one acid selected from the group consisting of nitric acid and hydrochloric acid. it can. Moreover, the acid which dissolves the fluoride produced | generated from a 1st oxide can be made into 10 mass% or more and 50 mass% or less nitric acid aqueous solution.

  In the method for producing a group III nitride semiconductor wafer according to the present invention, the base substrate may further include a second oxide that is substantially insoluble in hydrofluoric acid. In addition, the base substrate can further include a third oxide soluble in hydrofluoric acid.

  Further, in the method for producing a group III nitride semiconductor wafer according to the present invention, after the step of preparing the composite substrate, before the step of separating the base substrate from the group III nitride semiconductor film of the composite substrate, the group III nitride The method may further include growing at least one group III nitride semiconductor layer on the semiconductor film.

  In the method for manufacturing a group III nitride semiconductor wafer according to the present invention, the contact time between the base substrate and hydrofluoric acid in the HF contact sub-process is generated from the base substrate and the first oxide in the FSA contact sub-process. The contact time with the acid dissolving the fluoride to be used can be 0.5 times or more and 20 times or less.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the group III nitride semiconductor wafer which can isolate | separate a base substrate efficiently can be provided by promoting the etching of a base substrate.

It is a flowchart which shows each process of the manufacturing method of the group III nitride semiconductor wafer concerning this invention. It is a schematic sectional drawing which shows each process of the manufacturing method of the group III nitride semiconductor wafer concerning this invention. It is a schematic sectional drawing which shows the state of the composite substrate in the HF contact subprocess in the process of isolate | separating a base substrate from the composite substrate of the manufacturing method of the group III nitride semiconductor wafer concerning this invention. It is a schematic sectional drawing which shows the state of the composite substrate in the FSA contact subprocess in the process of isolate | separating a base substrate from the composite substrate of the manufacturing method of the group III nitride semiconductor wafer concerning this invention. It is a schematic sectional drawing which shows the state of the composite substrate in the last HF contact subprocess in the process of isolate | separating a base substrate from the composite substrate of the manufacturing method of the group III nitride semiconductor wafer concerning this invention. 4 is a graph showing a correlation between etching mass and etching depth in the method for producing a group III nitride semiconductor wafer according to the present invention.

  Referring to FIGS. 1 and 2, the method of manufacturing a group III nitride semiconductor wafer according to one embodiment of the present invention generates a fluoride that is substantially insoluble in hydrofluoric acid by reacting with hydrofluoric acid. A base substrate 11 including a first oxide, a hydrofluoric acid-soluble junction oxide film 12 disposed on the base substrate 11, and a group III nitride disposed on the junction oxide film 12 Step S1 for preparing the composite substrate 1 including the semiconductor film 13, the HF contact substep S61 for bringing the composite substrate 1 into contact with hydrofluoric acid, and the composite substrate 1 for dissolving the fluoride generated from the first oxide are dissolved. An acid contact set sub-step S60 for performing one or more sub-process sets including an FSA contact sub-step S63 for contacting with an acid, and a final HF contact sub for contacting the composite substrate 1 after the acid contact set sub-step S60 with hydrofluoric acid Process S In the acid contact setting sub-step S60 and the final HF contact sub-step S65, the group III nitride semiconductor film 13 of the composite substrate 1 is etched by etching a part of the base substrate 11 and the bonding oxide film 12. And a step S6 of separating the base substrate 11 from the substrate.

  In the manufacturing method of the group III nitride semiconductor wafer of the present embodiment, the HF contact in which the composite substrate 1 is brought into contact with hydrofluoric acid in the step S6 of separating the base substrate 11 from the group III nitride semiconductor film 13 of the composite substrate 1. By the acid contact set sub-step S60 in which one or more sub-step sets including the sub-step S61 and the FSA contact sub-step S63 in which the composite substrate 1 is brought into contact with the acid dissolving the fluoride generated from the first oxide are performed, the base substrate 11 By promoting the etching, the base substrate 11 can be efficiently separated.

(Preparation process of composite substrate)
Referring to FIGS. 1 and 2 (A), in the method for producing a group III nitride semiconductor wafer of this embodiment, first, a fluoride that is substantially insoluble in hydrofluoric acid is reacted with hydrofluoric acid. A base substrate 11 containing the first oxide to be generated, a hydrofluoric acid-soluble junction oxide film 12 disposed on the base substrate 11, and a group III nitride disposed on the joint oxide film 12 Step S1 of preparing the composite substrate 1 including the physical semiconductor film 13 is included.

  The composite substrate 1 prepared in this step includes a first oxide that generates a fluoride that is substantially insoluble in hydrofluoric acid when the base substrate 11 included in the composite substrate 1 reacts with hydrofluoric acid. Therefore, etching by hydrofluoric acid of the base substrate 11 is inhibited by the generated fluoride. For this reason, it is necessary to promote the etching of the base substrate 11 by removing the fluoride by bringing it into contact with an acid that dissolves the fluoride.

  In the present invention, that a substance is substantially insoluble in hydrofluoric acid means that a sufficiently large amount (1000 times the mass of the substance to be etched) that is being stirred by a magnetic stirrer at a rotation speed of 200 rpm (rotation / min). When the substance is immersed in a 49 mass% hydrofluoric acid aqueous solution of the above mass) for 1 hour, the etching depth of the substance is less than 1 μm.

Here, the first oxide that reacts with hydrogen fluoride to generate a fluoride that is substantially insoluble in hydrofluoric acid is not particularly limited, but is not limited to the group III nitride semiconductor film 13 of the composite substrate 1. From the viewpoint of forming a base substrate 11 suitable for growing at least one group III nitride semiconductor layer 20 on the substrate, yttria (Y ₂ O ₃ ), magnesia (MgO), calcia (CaO), scandia (Sc ₂ ). O ₃ ) and at least one oxide selected from the group consisting of ceria (CeO) is preferably included.

  The base substrate 11 can further include a second oxide that is substantially insoluble in hydrofluoric acid. Even if the base substrate 11 includes the second oxide, the base substrate 11 may be fluoride that is substantially insoluble in hydrofluoric acid by contacting with hydrofluoric acid as long as the first substrate includes the first oxide. Even if it produces | generates, it is possible to accelerate | stimulate the etching of the base substrate 11 by making it contact with the acid which melt | dissolves this fluoride.

Here, the second oxide substantially insoluble in hydrofluoric acid is not particularly limited, but at least one group III nitride semiconductor layer 20 is provided on the group III nitride semiconductor film 13 of the composite substrate 1. From the viewpoint of forming the base substrate 11 suitable for growing the substrate, it is preferable to include at least one oxide selected from the group consisting of alumina (Al ₂ O ₃ ) and zircon (ZrSiO ₄ ).

  Moreover, it is preferable that the base substrate 11 further includes a third oxide soluble in hydrofluoric acid from the viewpoint of promoting etching of the base substrate 11 with hydrofluoric acid. In the present invention, that a certain substance is soluble in hydrofluoric acid means that a sufficiently large amount (more than 1000 times the mass of the substance to be etched) that is being stirred by a magnetic stirrer at a rotation speed of 200 rpm (rotation / minute). When the substance is immersed in a 49 mass% hydrofluoric acid aqueous solution for 1 hour, the etching depth of the substance is 1 μm or more.

Here, the third oxide soluble in hydrofluoric acid is not particularly limited, but at least one group III nitride semiconductor layer 20 is grown on the group III nitride semiconductor film 13 of the composite substrate 1. From the viewpoint of forming a base substrate 11 suitable for the production, at least one oxide selected from the group consisting of silica (SiO ₂ ), titania (TiO ₂ ), zirconia (ZrO ₂ ) and hafnia (HfO ₂ ) is used. It is preferable to include.

  The base substrate 11 is not particularly limited, but is formed of a polycrystalline material from the viewpoint of easy partial etching by contact with hydrofluoric acid and contact with an acid that dissolves fluoride. And is preferably formed of a composite oxide composed of a plurality of oxides. The polycrystalline body is preferentially etched at grain boundaries between the grains of the polycrystalline body, so it is easily etched partially in a porous state, and the composite oxide is easily dissolved in hydrofluoric acid and an acid that dissolves fluoride. Since the object is preferentially etched, it is likely to be etched partially in a porous shape. Furthermore, from the above viewpoint, the base substrate 11 is obtained by sintering the first oxide and at least one oxide selected from the group consisting of the second oxide and the third oxide. It is more preferable that the sintered body is formed.

Specifically, as the base substrate 11, Y ₂ O ₃ —ZrO ₂ based sintered body such as YSZ (yttria stabilized zirconia) sintered body, YSZ (yttria stabilized zirconia) -mullite (3Al ₂ O ₃ .2SiO). _{2 ~2Al 2 O 3 · SiO 2} ) Y 2 O 3 -ZrO 2 -Al 2 O 3 -SiO 2 based sintered body such as a sintered body, magnesia - mullite _{(3Al 2 O 3 · 2SiO 2} ~2Al 2 O _A suitable example is a MgO—Al ₂ O ₃ —SiO ₂ sintered body such as a ₃ · SiO ₂ ) sintered body.

The composite substrate 1 includes a bonding oxide film 12 soluble in hydrofluoric acid and disposed on the base substrate 11. The bonding oxide film 12 is for bonding the base substrate 11 and the group III nitride semiconductor film 13 and is not particularly limited as long as it is soluble in hydrofluoric acid, but its bonding strength is increased. And at least one oxide selected from the group consisting of silica (SiO ₂ ), titania (TiO ₂ ), zirconia (ZrO ₂ ) and hafnia (HfO ₂ ) from the viewpoint of being easily dissolved in hydrofluoric acid. A membrane is preferred.

Composite substrate 1 includes a group III nitride semiconductor film 13 disposed on bonding oxide film 12. The group III nitride semiconductor film 13 is not particularly limited, but from the viewpoint of epitaxially growing at least one group III nitride semiconductor layer 20 having a high crystal quality on the group III nitride semiconductor film 20 and the group III nitride semiconductor layer 20 and atoms to be epitaxially grown. The arrangement and the interatomic distance (lattice constant) are preferably the same or approximate. Further, the temperature during epitaxial growth (the GaN, Al _x Ga _1-x N layer (0 <x <1), and / or the In _y Ga _1-y N layer (0 <y <1 as the group III nitride semiconductor layer 20). ), It is preferable that the temperature at the time of epitaxial growth reaches 1100 ° C.). Furthermore, since epitaxial growth is greatly influenced by information such as defects on the growth start surface (here, the main surface of the group III nitride semiconductor film 13), the main surface of the group III nitride semiconductor film 13 has as few defects as possible. It is preferably made of a material. For example, a GaN thin film cut out from a bulk GaN substrate manufactured by HVPE or the like is suitable.

  The method for preparing composite substrate 1 is not particularly limited. For example, an ion implantation region is formed at a predetermined depth from one main surface of a group III nitride semiconductor substrate, and junction oxidation is performed on one main surface of base substrate 11. After bonding one main surface of the group III nitride semiconductor substrate on the side of the ion implantation region with the material film 12 interposed, the group III nitride semiconductor substrate is separated in the ion implantation region, thereby providing a base substrate For example, a method of forming a group III nitride semiconductor film 13 disposed on the junction oxide film 12 disposed on 11 is preferably used.

(Growth process of at least one group III nitride semiconductor layer)
Referring to FIGS. 1 and 2B, the method for manufacturing a group III nitride semiconductor wafer according to the present embodiment is the same as the method for manufacturing a group III nitride semiconductor wafer according to the present embodiment. A step S2 of growing at least one group III nitride semiconductor layer 20 on the group nitride semiconductor film 13 may be included.

  In this step, the method for growing at least one group III nitride semiconductor layer 20 is not particularly limited. However, from the viewpoint of epitaxially growing group III nitride semiconductor layer 20 with few crystal defects and high crystal quality, MOCVD ( Suitable are metal organic chemical vapor deposition), MBE (molecular beam growth), HVPE (hydride vapor deposition), gas phase methods such as sublimation, liquid phase methods such as flux method, high nitrogen pressure dissolution method, etc. It is.

  Through this step, at least one group III nitride semiconductor layer 20 including a functional layer that exhibits a function as a semiconductor device is formed on the group III nitride semiconductor film 13 of the composite substrate 1. Is obtained.

(First electrode forming step)
Referring to FIGS. 1 and 2 (C), in the manufacturing method of the group III nitride semiconductor wafer of the present embodiment, next, on at least one group III nitride semiconductor layer 20 of the composite substrate 2 with a semiconductor layer. A step S3 of forming the first electrode 30 can be included.

  In this step, the method for forming the first electrode 30 is not particularly limited, but from the viewpoint of efficiently forming a high-quality electrode, an EB (electron beam) deposition method, a sputtering method, a resistance heating method, or the like is preferable. It is.

  By this step, the composite substrate 3 with an electrode semiconductor layer in which the first electrode 30 is formed on the group III nitride semiconductor layer 20 of the composite substrate 2 with a semiconductor layer is obtained.

(Support substrate bonding process)
Referring to FIGS. 1, 2 (D) and (E), in the manufacturing method of the group III nitride semiconductor wafer of this embodiment, next, on the first electrode 30 of the composite substrate 3 with an electrode semiconductor layer. The process S4 which bonds the support substrate 40 together can be included.

  This step is not particularly limited, but the support substrate 40 is bonded to the first electrode 30 in the following manner from the viewpoint of ensuring the conductivity of the composite substrate 3 with electrode semiconductor layer 3 and increasing the bonding strength. be able to. First, the bonding pad metal layer 31 is formed on the first electrode 30 of the composite substrate 3 with electrode semiconductor layer. The method for forming the bonding pad metal layer 31 is not particularly limited, but from the viewpoint of efficiently forming a high-quality metal layer, an EB vapor deposition method, a sputtering method, a resistance heating method, a plating method, or the like is preferable. In addition, ohmic junction metal layers 41 are formed on both main surfaces of the support substrate 40. The method for forming the ohmic junction metal layer 41 is not particularly limited, but from the viewpoint of efficiently forming a high-quality metal layer, an EB vapor deposition method, a sputtering method, a resistance heating method, a plating method, or the like is preferable. Next, a bonding metal layer 42 is formed on one ohmic bonding metal layer 41 of the support substrate 40. The method for forming the bonding metal layer 42 is not particularly limited, but from the viewpoint of efficiently forming a metal layer having high bonding strength, a resistance heating method, an EB vapor deposition method, a sputtering method, or the like is preferable.

  By this step, a bonded substrate 4 in which the support substrate 40 is bonded to the composite substrate 3 with an electrode-attached semiconductor layer is obtained.

(Substrate thickness reduction process by partially removing the support substrate)
Referring to FIGS. 1 and 2E, in the manufacturing process of the group III nitride semiconductor wafer of this embodiment, the base substrate 11 is then removed by removing a part of the base substrate 11 of the bonded substrate 4. Step S5 for reducing the thickness of the substrate can be included.

  In this step, the method for removing a part of the base substrate 11 is not particularly limited, and methods such as grinding and cutting can be used as necessary. In this step, the bonded substrate 4 can shorten the time for separating the base substrate 11 by etching by reducing the thickness of the base substrate 11.

(Step of separating base substrate from group III nitride semiconductor film of composite substrate)
Referring to FIGS. 1 and 2 (F), in the manufacturing process of the group III nitride semiconductor wafer of this embodiment, the composite substrate 1 of the bonded substrate 4 is then brought into contact with hydrofluoric acid. One or more sets of sub-steps including a hydro-acid) contact sub-step S61 and an FSA (fluoride-dissolving acid) contact sub-step S63 in which the composite substrate 1 is brought into contact with an acid that dissolves fluoride generated from the first oxide. An acid contact set sub-step S60, and a final HF contact sub-step S65 in which the composite substrate 11 after the acid contact set sub-step S60 is brought into contact with hydrofluoric acid. The acid contact set sub-step S60 and the final HF contact sub-step In S65, the base substrate 11 is removed from the group III nitride semiconductor film 13 of the composite substrate 1 by etching a part of the base substrate 11 and the bonding oxide film 12. Comprising the step S6 to be away.

  In this step, the base substrate 11 is made efficient by promoting the etching of the base substrate 11 by the acid contact set sub-step S60 in which one or more sub-step sets including the HF contact sub-step S61 and the FSA contact sub-step S63 are performed. Can be separated.

  Referring to FIGS. 1 and 3, in HF (hydrofluoric acid) contact sub-step S61 in which composite substrate 1 is brought into contact with hydrofluoric acid A1, fluorination in contact with the main surface of base substrate 11 of composite substrate 1 is performed. Etching proceeds with the hydrofluoric acid permeation region 11f formed by preferentially penetrating the hydronic acid A1 into the grain boundary region 11b between the polycrystalline grains forming the base substrate 11. Here, since the base substrate 11 of this embodiment contains the 1st oxide which reacts with hydrofluoric acid A1 and produces | generates a fluoride substantially insoluble in hydrofluoric acid, it is fluorinated. Since the insoluble fluoride is accumulated in the hydrofluoric acid A1 generated from the first oxide in the hydroacid penetrating region 11f, etching by the hydrofluoric acid A1 is suppressed. For this reason, it is necessary to accelerate the etching of the base substrate 11 by removing the fluoride accumulated in the hydrofluoric acid permeation region 11f by the following sub-process.

  Next, referring to FIGS. 1 and 4, the composite substrate in which the fluoride generated from the first oxide is accumulated in the hydrofluoric acid permeation region 11 f formed in the base substrate 11 by the HF contact sub-process shown in FIG. 3. In FSA (fluoride-dissolving acid) contact sub-step S63 in which 1 is brought into contact with the acid A2 that dissolves fluoride, the fluoride accumulated in the hydrofluoric acid permeation region 11f is dissolved and removed by the acid that dissolves fluoride. As a result, a region to be etched 11e is formed.

  In this way, hydrofluoric acid from the grain boundary region 11b in the HF contact sub-step S61 is obtained by the acid contact set sub-step S60 in which one or more sub-step sets including the HF contact sub-step S61 and the FSA contact sub-step S63 are performed. By alternately repeating the formation of the permeation region 11f and the formation of the etched region 11e from the hydrofluoric acid permeation region 11f in the FSA contact sub-step S63, predetermined grains are sequentially formed from the main surface side to the inside of the base substrate 11. The boundary region 11b becomes the etched region 11e through the hydrofluoric acid permeation region 11f, and the base substrate 11 is partially etched efficiently and sequentially from the main surface side to the inside, so that the etching of the base substrate 11 is promoted. The

  By the acid contact setting sub-step S60, the etched region 11e penetrating the base substrate 11 is formed from the exposed main surface side of the base substrate 11 to the main surface side bonded to the bonding oxide film 12. .

  Referring to FIGS. 2F and 5, in the final HF contact sub-process, a base substrate in which etched region 11e penetrating base substrate 11 in the thickness direction is formed in a part of base substrate 11 described above. 11, when hydrofluoric acid A1 is brought into contact with the exposed main surface, the hydrofluoric acid reaches the junction oxide film 12 via the etched region 11e, and the junction oxide film In order to remove 12 by etching, the base substrate 11 is separated from the group III nitride semiconductor film 13 of the composite substrate 1 by lift-off.

  That is, referring to FIGS. 1 to 5, in step S <b> 6 for separating base substrate 11, base layer from group III nitride semiconductor film 13 is etched by etching of junction oxide film 12 with hydrofluoric acid A <b> 1 as described above. This is performed by lifting off the substrate 11. Further, in the step S6 of separating the base substrate 11, the hydrofluoric acid that etches the bonding oxide film 12 is the fluoride formed from the first oxide in the HF contact sub-step S61, in the FSA contact sub-step S63. By being melted, it is supplied to the bonding oxide film 12 via the etched region 11 e formed in a part of the base substrate 11.

  Referring to FIG. 1, in the method for manufacturing a group III nitride semiconductor wafer of this embodiment, composite substrate 1 is formed after each of HF contact sub-step S61, FSA contact sub-step S63, and final HF contact sub-step S65. It is preferable to further include water washing and drying sub-steps S62, S64, and S66 after washing with water and drying. By including the water washing and drying sub-steps S62, S64, and S66, hydrofluoric acid used in the HF contact sub-step S61 is mixed into an acid that dissolves the fluoride used in the subsequent FSA contact sub-step S63. The acid used to dissolve the fluoride used in the FSA contact sub-step S63 is mixed into the hydrofluoric acid used in the subsequent HF contact sub-step S61 or the final HF contact sub-step S65, and the final HF If the hydrofluoric acid used in the contact sub-step S65 remains in the subsequent step or if the final FSA contact sub-step S67 is included in the subsequent step, the fluoride used in the final FSA contact sub-step S67 The etching of the base substrate 11 is further promoted by preventing it from being mixed into the acid that dissolves the base. Can be further efficiently separate the plate 11.

  Referring to FIG. 1, in the group III nitride semiconductor wafer manufacturing method of this embodiment, step S6 for separating base substrate 11 from group III nitride semiconductor film 13 of composite substrate 1 is a final HF contact sub-step S65. Thereafter, it is preferable to further include a final FSA contact sub-step S67 in which the composite substrate 1 is contacted with an acid that dissolves the fluoride of the first oxide. By this final FSA contact sub-step S67, the fluoride remaining on the composite substrate 1 can be reliably removed.

  Referring to FIG. 1, in the group III nitride semiconductor wafer manufacturing method of this embodiment, step S6 for separating base substrate 11 from group III nitride semiconductor film 13 of composite substrate 1 is a final FSA contact sub-step S67. After that, it is preferable to further include a water washing and drying sub-step S68 in which the composite substrate 1 is washed with water and then dried. By the water washing and drying sub-step S68, the acid that dissolves the fluoride remaining on the composite substrate 1 can be reliably removed.

  In the group III nitride semiconductor wafer manufacturing method of the present embodiment, the acid that dissolves the fluoride generated from the first oxide is at least selected from the group consisting of nitric acid and hydrochloric acid from the viewpoint of high solubility of the fluoride. It preferably contains one kind of acid. Here, the at least one acid selected from the group consisting of nitric acid and hydrochloric acid is not particularly limited, and nitric acid, hydrochloric acid, and aqua regia (concentrated hydrochloric acid (30% by mass) aqueous solution and concentrated nitric acid (70% by mass) aqueous solution) And the like in a volume ratio of 3: 1). Moreover, it is preferable that the acid which dissolves the fluoride produced | generated from a 1st oxide is nitric acid aqueous solution of 10 mass% or more and 50 mass% or less from a viewpoint with the high solubility of fluoride.

  In the method for manufacturing a group III nitride semiconductor wafer of the present embodiment, a suitable contact time (etching time) between the composite substrate 1 and hydrofluoric acid in the HF contact substep S61 in the acid contact set substep S60, the FSA contact sub Suitable contact time (etching time) between the composite substrate 1 in step S63 and the acid dissolving the fluoride generated from the first oxide, a suitable ratio of these contact times, and preferred acid contact setting sub-step S60 The number of sets depends on the rate at which fluoride is generated by the reaction between the first oxide and hydrofluoric acid, and the rate at which fluoride is dissolved by the acid dissolving the fluoride, that is, the chemical composition of the base substrate 11 and hydrogen fluoride. It fluctuates depending on the respective concentrations of acids that dissolve acids and fluorides. However, from the viewpoint of promoting etching of the base substrate 11, the contact time between the base substrate 11 and hydrofluoric acid in the HF contact sub-step S61 is generated from the base substrate 11 and the first oxide in the FSA contact sub-step S63. It is preferable that the contact time is 0.5 to 20 times the contact time with the acid that dissolves the fluoride to be dissolved.

  Further, a suitable contact time (etching time) between the composite substrate 1 and hydrofluoric acid in the final HF contact sub-step S65, and fluoride generated from the composite substrate 1 and the first oxide in the final FSA contact sub-step S67. The preferred contact time (etching time) with the acid to be dissolved and the preferred ratio of the contact times are the same as described above.

  By this step (step S6 of separating the base substrate 11 from the group III nitride semiconductor film 13 of the composite substrate 1), a part of the base substrate 11 and the bonding oxide film 12 in the composite substrate 1 portion of the bonded substrate 4 are formed. By removing the base substrate 11 from the group III nitride semiconductor film 13 of the composite substrate 1 by etching, the group III nitride semiconductor wafer 5 is obtained.

(Second electrode formation step)
With reference to FIGS. 1 and 2 (G), in the method for manufacturing a group III nitride semiconductor wafer of the present embodiment, next, step S7 of forming the second electrode 50 on the group III nitride semiconductor film 13 is performed. Can be included.

  In this step, the method for forming the second electrode 50 is not particularly limited, but from the viewpoint of efficiently forming a high-quality electrode, an EB (electron beam) deposition method, a sputtering method, a resistance heating method, or the like is preferable. It is.

  Through this step, the group III nitride semiconductor wafer 6 having a function as a semiconductor device in which the second electrode 50 is formed on the group III nitride semiconductor film 13 of the group III nitride semiconductor wafer 5 is obtained.

(Process for forming semiconductor devices by chip fabrication)
Referring to FIG. 1, the method for manufacturing a group III nitride semiconductor wafer according to the present embodiment may further include a step S8 of forming a semiconductor device by forming the group III nitride semiconductor wafer 6 into chips. In this step, the method for forming the group III nitride semiconductor wafer 6 into a chip is not particularly limited, and examples thereof include a dicing method, a laser scribing method, and a cleavage method. By this step, a semiconductor device having high characteristics can be obtained with good yield and efficiency.

(Reference Example A)
In this reference example, a YSZ (yttria-stabilized zirconia) -mullite sintered body substrate as a base substrate is brought into contact with hydrofluoric acid (Example AR1), and mixed acid of hydrofluoric acid and nitric acid (Example AR2). ), And etching mass and etching depth when alternately contacting with hydrofluoric acid and nitric acid (Examples A1 to A4). In this reference example, nitric acid was used as an acid for dissolving a fluoride substantially insoluble in hydrofluoric acid.

1. Preparation of Base Substrate As a base substrate, a plurality of 12 mm × 12 mm × 450 μm thick YSZ-mullite sintered substrates were prepared. Such a YSZ-mullite substrate is sintered at a ratio of 30% by mass of YSZ and 70% by mass of mullite, and the chemical composition of YSZ is 90% by mole of ZrO _{2 and} 10% by mole of Y ₂ O _3. The chemical composition of mullite was 60 mol% Al ₂ O _{3 and} 40 mol% SiO ₂ .

2. Preparation of etching solution As an etching solution for bringing the base substrate into contact with hydrofluoric acid, 500 ml of a 49 mass% hydrofluoric acid aqueous solution was prepared. As an etching solution for bringing nitric acid into contact with the base substrate, 250 ml of 70% by mass nitric acid aqueous solution was diluted with 250 ml of pure water to prepare 500 ml of 35% by mass nitric acid aqueous solution. As an etching solution for bringing the mixed acid of hydrofluoric acid and nitric acid into contact with the base substrate, 500 ml of a mixed aqueous solution prepared by mixing 450 ml of a 49% by mass hydrofluoric acid aqueous solution and 50 ml of a 70% by mass nitric acid aqueous solution was prepared.

3. Etching Etching was performed by immersing the base substrate in the at least one etching solution stirred at 200 rpm with a magnetic stirrer at room temperature (23 ° C.) for 2 hours.

  Specifically, in Example AR1, a 49% by mass hydrofluoric acid aqueous solution is used as an etchant, the base substrate is immersed in a 49% by mass hydrofluoric acid aqueous solution for 120 minutes, and then washed with running water and nitrogen gas blow for 30 seconds. Dried. In Example AR2, a mixed aqueous solution in which a 49% by mass hydrofluoric acid aqueous solution and a 70% by mass nitric acid aqueous solution are uniformly mixed at a volume ratio of 9: 1 is used as an etching solution, and the base substrate is placed in the mixed aqueous solution. After soaking for 30 minutes, running water was washed for 30 seconds and blown with nitrogen gas. Note that the etching solution used in Example AR2 had a mixing volume ratio that gave the highest etching rate when a 49% by mass hydrofluoric acid aqueous solution and a 70% by mass nitric acid aqueous solution were mixed.

  About Example A1-A4, 49 mass% hydrofluoric acid aqueous solution and 35 mass% nitric acid aqueous solution were used alternately as etching liquid, and it etched with the following immersion patterns.

  In Example A1, the base substrate was immersed in a 49% by mass hydrofluoric acid aqueous solution for 55 minutes, then washed with running water for 30 seconds and blown with nitrogen gas, and then in a 35% by mass nitric acid aqueous solution for 5 minutes. One set consists of washing with running water for 30 seconds and dipping with nitrogen gas blow after immersion, and two sets were performed. That is, the contact time between the base substrate and hydrofluoric acid was 11 times the contact time between the base substrate and nitric acid.

  In Example A2, the base substrate was immersed in a 49 mass% hydrofluoric acid aqueous solution for 25 minutes, washed with running water for 30 seconds and blown with nitrogen gas, and then immersed in a 35 mass% nitric acid aqueous solution for 5 minutes. One set consists of washing with running water for 30 seconds after immersion and nitrogen gas blow drying, and four sets were performed. That is, the contact time between the base substrate and hydrofluoric acid was five times the contact time between the base substrate and nitric acid.

  In Example A3, the base substrate was immersed in an aqueous 49% by mass hydrofluoric acid solution for 10 minutes, washed with running water for 30 seconds and blown with nitrogen gas, and then in an aqueous 35% by mass nitric acid solution for 5 minutes. Eight sets were performed with one set of washing with running water for 30 seconds and nitrogen gas blow drying after immersion. That is, the contact time between the base substrate and hydrofluoric acid was twice the contact time between the base substrate and nitric acid.

  In Example A4, the base substrate was immersed in an aqueous 49% by mass hydrofluoric acid solution for 5 minutes, washed with running water for 30 seconds and blown with nitrogen gas, and then immersed in an aqueous 35% by mass nitric acid solution for 5 minutes. 12 sets were performed by setting running water washing and nitrogen gas blow drying for 30 seconds after immersion as one set. That is, the contact time between the base substrate and hydrofluoric acid was one time the contact time between the base substrate and nitric acid.

4). Evaluation of Etching Mass For each of the above examples, the mass etched in 2 hours per 1 mm ^{2 of the} base substrate (hereinafter referred to as etching mass) from the difference between the dry weight of the base substrate before etching and the dry weight of the base substrate after etching. Calculated).

Calculated etched mass is 31.6μg / mm ² Example AR1 is 36.2μg / mm ² Example AR2 is 41.7μg / mm ² In Example A1, Example A2 64.7μg / a mm ^2, an example A3 in 84.1μg / mm ^2, was example A4 in 107μg / mm ^2. The results are summarized in Table 1.

5. Evaluation of Etching Depth For each of the above examples, the underlying substrate after etching was cleaved at the center, and the cross section was observed by SEM (scanning electron microscope) -EDX (energy dispersive X-ray spectroscopy). Since ZrO ₂ and Y ₂ O _3, that is, YSZ, exist in granular form independent of mullite, when the elemental composition distribution of the cross section is mapped and photographed by EDX, the place where YSZ exists is scattered like a floating island. In the hydrofluoric acid permeation region and the region to be etched formed by the progress of etching, Zr is significantly decreased and F and Y are significantly increased at locations where ZrO ₂ and Y ₂ O ₃ should be present. Was observed. Further, the end surface (surface farther from the exposed main surface of the base substrate in the depth direction) of the Zr decrease and F and Y increase regions is a distance from the exposed main surface of the base substrate at an arbitrary position of the end surface. Was found to be the same. Here, the distance from the end surface of the region where F is not detected to the exposed main surface of the base substrate is defined as the etching depth.

  The calculated etching depth was 15 μm in Example AR1, 17 μm in Example AR2, 20 μm in Example A1, 27 μm in Example A2, 45 μm in Example A3, and 45 μm in Example A4. The results are summarized in Table 1. Moreover, the correlation with the etching mass and etching depth about Example AR1, AR2, and A1-A4 was shown in FIG.

  In each example, the etching rate (unit: nm / min) per minute was calculated from the etching depth (unit: μm) when etching was performed for 2 hours.

  The calculated average etching rate is 130 nm / min in the average example AR1, 140 nm / min in the example AR2, 170 nm / min in the example A1, 230 nm / min in the example A2, and 380 nm / min in the example A3. min, which was 380 nm / min in Example A4. The results are summarized in Table 1.

  Referring to Table 1, with reference to Examples AR1 to AR2 and A1 to A4, as compared with the case of etching using only an aqueous hydrofluoric acid solution or an aqueous solution of hydrofluoric acid and nitric acid as an etching solution, When etching was alternately performed using an aqueous hydrofluoric acid solution and an aqueous nitric acid solution as the etching solution, the etching mass and the etching depth of the base substrate were both increased. Specifically, the etching mass was increased by 2.7 times in Example A3 and 3.4 times in Example A4 compared to Example AR1. Also, the etching depth was increased by 3.0 times in the case of Example A3 and 3.0 times in the case of Example A4, compared with the case of Example AR1. Further, referring to FIG. 6, the correlation coefficient r between the etching mass and the etching depth was 0.95, and had a strong positive correlation.

(Reference Example B)
In this reference example, a YSZ (yttria-stabilized zirconia) -mullite sintered body substrate as a base substrate is treated with nitric acid (example) as an acid that dissolves hydrofluoric acid and a fluoride substantially insoluble in hydrofluoric acid. B1 and Example B4), hydrochloric acid (Example B2), or aqua regia (Example B3) were evaluated for etching mass and etching depth when contacted alternately.

1. Preparation of Base Substrate A plurality of base substrates similar to Reference Example A were prepared.

2. Preparation of etching solution As an etching solution for bringing the base substrate into contact with hydrofluoric acid, 500 ml of a 49 mass% hydrofluoric acid aqueous solution was prepared. As etching solutions for bringing nitric acid into contact with the base substrate, 500 ml of a 35 mass% nitric acid aqueous solution and 500 ml of a 70 mass% nitric acid aqueous solution were prepared. As an etching solution for bringing hydrochloric acid into contact with the base substrate, 500 ml of a 30% by mass hydrochloric acid aqueous solution was prepared. As an etching solution for bringing aqua regia into contact with the base substrate, 500 ml of aqua regia in which a 30% by mass hydrochloric acid aqueous solution and a 70% by mass nitric acid aqueous solution were mixed at a volume ratio of 3: 1 was prepared.

3. Etching Etching was performed by immersing the base substrate for 2 hours in the etching solution stirred at 200 rpm with a magnetic stirrer at room temperature (23 ° C.).

  Specifically, in Example B1, the base substrate was immersed in a 49 mass% hydrofluoric acid aqueous solution for 10 minutes, then washed with running water for 30 seconds and blown with nitrogen gas, and then 35 mass% nitric acid. Eight sets were performed by immersing in an aqueous solution for 5 minutes and then washing with running water for 30 seconds and drying with nitrogen gas blow as one set. In Example B2, the base substrate was immersed in an aqueous 49% by mass hydrofluoric acid solution for 10 minutes, washed with running water for 30 seconds and blown with nitrogen gas, and then in an aqueous 30% by mass hydrochloric acid solution for 5 minutes. Eight sets were performed with one set of washing with running water for 30 seconds and nitrogen gas blow drying after immersion. In Example B3, the base substrate was immersed in a 49% by mass hydrofluoric acid aqueous solution for 10 minutes, washed with running water for 30 seconds and then blown with nitrogen gas, and then immersed in aqua regia for 5 minutes. One set consists of washing with running water for 2 seconds and nitrogen gas blow drying, and 8 sets were performed. In Example B4, the base substrate was immersed in a 49% by mass hydrofluoric acid aqueous solution for 10 minutes, washed with running water for 30 seconds and then blown with nitrogen gas, and then in a 70% by mass nitric acid aqueous solution for 5 minutes. Eight sets were performed with one set of washing with running water for 30 seconds and nitrogen gas blow drying after immersion.

4). Evaluation of etching mass The etching mass was calculated in the same manner as in Reference Example A for each of the above examples. The calculated etching mass is 82.6 μg / mm ² when a 35% by mass nitric acid aqueous solution is used as in Example B1 as an acid for dissolving fluoride, and a 30% by mass hydrochloric acid aqueous solution is used as in Example B2. in the case where had a 73.7μg / mm ^2, in the case of using aqua regia as in example B3 was 66.9μg / mm ^2, 52 in the case of using a 70 wt% nitric acid aqueous solution as in example B4. It was 0 μg / mm ² . The results are summarized in Table 2.

  Referring to Table 2, the acid that dissolves the fluoride substantially insoluble in hydrofluoric acid is preferably at least one acid selected from the group consisting of nitric acid such as nitric acid, hydrochloric acid, aqua regia and hydrochloric acid, Of these, 35% by mass of nitric acid was more preferred.

Example 1
1. Preparation of Composite Substrate As the base substrate 11, a YSZ-mullite sintered substrate having a diameter of 2 inches (50.8 mm) and a thickness of 450 μm was prepared. Such a YSZ-mullite substrate is sintered at a ratio of 30% by mass of YSZ and 70% by mass of mullite, and the chemical composition of YSZ is 90% by mole of ZrO _{2 and} 10% by mole of Y ₂ O _3. The chemical composition of mullite was 60 mol% Al ₂ O _{3 and} 40 mol% SiO ₂ . The main surface of the base substrate 11 was mirror-polished so that the arithmetic average roughness Ra specified in JIS B0601: 2001 was 10 nm or less.

  Referring to FIG. 2A, a group III nitride semiconductor substrate having a thickness of 350 μm made of GaN having a main surface of base substrate 11 and a hydrogen ion implantation region formed at a depth of 150 nm from the main surface. The main surface on the side where the hydrogen ion implantation region is formed is bonded with a 400 nm thick junction oxide film interposed therebetween, and then the group III nitride semiconductor substrate is separated by the hydrogen ion implantation region By doing so, the base substrate 11, the 400-nm-thick junction oxide film 12 disposed on the base substrate 11, and the 150-nm-thick group III nitride semiconductor film 13 disposed on the junction oxide film 12 are provided. The composite substrate 1 comprised by these was prepared.

In such a composite substrate 1, the base substrate 11 exhibits the same thermal expansion coefficient as that of the GaN crystal from room temperature (23 ° C.) to 1200 ° C., and the crystal defect density of the group III nitride semiconductor film 13 is as low as 10 ⁵ cm ⁻² order. It is possible to epitaxially grow a group III nitride semiconductor layer having high crystal quality on the group III nitride semiconductor film 13.

2. Growth of Group III Nitride Semiconductor Layer Referring to FIG. 2B, a thickness of at least one group III nitride semiconductor layer 20 is formed on group III nitride semiconductor film 13 of composite substrate 1 by MOCVD. 3 cycles of an n-GaN layer 21 having a thickness of 5 μm, an n-In _0.05 Ga _0.95 N layer 22 having a thickness of 50 nm, an In _0.14 Ga _0.86 N well layer having a thickness of 3 nm, and a GaN barrier layer having a thickness of 15 nm. An active layer 23 having a multiple quantum well structure, a p-Al _0.08 Ga _0.92 N layer 24 having a thickness of 20 nm, and a p ⁺ -GaN layer 25 having a thickness of 50 nm are epitaxially grown in this order to obtain the composite substrate 2 with a semiconductor layer. It was. During this time, the growth temperature of the group III nitride semiconductor layer 20 reached 1050 ° C. at the maximum, but no crack was found in the group III nitride semiconductor layer 20 of the composite substrate with a semiconductor layer 2. When the crystal defect density of the group III nitride semiconductor layer 20 was measured by CL (cathode luminescence) method, it was on the order of 10 ⁵ cm ⁻² . The emission center wavelength of the composite substrate 2 with a semiconductor layer was 460 nm as measured by a PL (photoluminescence) mapper.

Furthermore, the RTA apparatus (rapid thermal annealing apparatus, which is an apparatus that rapidly heats with infrared rays) is used to anneal the composite substrate 2 with a semiconductor layer at 800 ° C. for 3 minutes in a nitrogen gas atmosphere, and p-Al _0.08 Ga _0.92. The N layer 24 and the p ⁺ -GaN layer 25 were activated.

3. Formation of First Electrode Referring to FIG. 2C, a thickness of EB deposition apparatus is used to form a thickness on p-GaN layer 25 that is the uppermost layer of group III nitride semiconductor layer 20 of composite substrate 2 with a semiconductor layer. A 7 nm thick Ni layer and a 300 nm thick Au layer are sequentially formed, and then alloyed by annealing at 500 ° C. for 1 minute in a nitrogen gas atmosphere with an RTA apparatus to form the first electrode 30. Thus, a composite substrate 3 with an electrode-attached semiconductor layer was obtained.

4). Bonding of Support Substrate With reference to FIGS. 2 (D) and (E), a Ti layer having a thickness of 10 nm is formed on the first electrode 30 of the composite substrate 3 with an electrode-attached semiconductor layer using an EB vapor deposition apparatus. The bonding pad metal layer 31 was formed by sequentially forming a Pt layer having a thickness of 80 nm and an Au layer having a thickness of 300 nm.

  Also prepared is a support substrate 40 made of Si and having two main surfaces with a diameter of 2 inches (50.8 mm) × thickness of 300 μm and a mirror surface with an arithmetic average roughness Ra defined by JIS B0601: 2001 of 10 nm or less. did. Here, the support substrate 40 formed of Si was doped p-type, and the resistivity was 0.01 Ωcm or less.

  On one main surface of the support substrate 40, a Ti layer having a thickness of 10 nm and a Pt layer having a thickness of 80 nm are sequentially formed using an EB vapor deposition apparatus, and an Au layer having a thickness of 300 nm is sequentially formed using a resistance heating apparatus. The ohmic junction metal layer 41 was formed by forming. An ohmic junction metal layer 41 is formed on the other main surface of the support substrate 40 in the same manner as described above, and then AuSn (mass ratio) having a thickness of 1.5 μm is formed on the ohmic junction metal layer 41 using a resistance heating device. The bonding metal layer 42 was formed by forming an Au: Sn 8: 2) layer.

  A bonding pad metal layer 31 formed on the composite substrate with electrode semiconductor layer 30; a bonding metal layer formed on the ohmic bonding metal layer 41 formed on one main surface of the support substrate; Are bonded and bonded using a wafer bonder to obtain a bonded substrate 4. Such joining was performed by applying a pressure of 3 MPa between both layers at 300 ° C. in a vacuum of 1 Pa or less for 10 minutes. After joining, it was confirmed that there was no joining failure such as a void in the joining surface using an ultrasonic microscope.

5. Step of Reducing Substrate Thickness by Partially Removing Substrate Referring to FIG. 2 (E), wax (alco wax 819 manufactured by Nikka Seiko Co., Ltd.) and wafer bonder are used on the support substrate 40 side of bonded substrate 4. Then, after being attached to a grinding jig in vacuum (less than 10 Pa) at 120 ° C. and a pressure of 3 MPa, using a surface grinder, the base substrate 11 of the bonded substrate 4 is made to have a thickness of 450 μm to 50 μm. Grinded.

6). Separation of base substrate As an etching solution for bringing the base substrate 11 into contact with hydrofluoric acid, 500 ml of a 49 mass% hydrofluoric acid aqueous solution was prepared. As an etching solution for bringing nitric acid into contact with the base substrate 11, 500 ml of a 35 mass% nitric acid aqueous solution was prepared.

  Referring to FIG. 2 (F), after the ground bonded substrate 4 is removed from the grinding jig on a hot plate at 120 ° C., a sapphire substrate having a diameter of 3 inches and a thickness of 500 μm is formed in the same manner as described above. Pasted. Thereafter, the bonded substrate 4 was etched by being immersed in any one of the above-described etching solutions stirred at 200 rpm with a magnetic stirrer in a room temperature (23 ° C.) environment according to the following procedure. .

  The bonded substrate 4 was immersed in a 49% by mass hydrofluoric acid aqueous solution for 10 minutes, then washed with running water for 30 seconds and blown with nitrogen gas, and then immersed in a 35% by mass nitric acid aqueous solution for 5 minutes and then for 30 seconds. Washing with running water and nitrogen gas blow drying as one set, this set was repeated, and after performing this set 8 sets, when immersed in a 49% by weight hydrofluoric acid aqueous solution for 10 minutes, The base substrate 11 was separated from the bonded substrate 4. The bonded substrate 4 was removed by etching up to the bonding oxide film 12.

  In this manner, the base substrate 11 is separated from the bonded substrate 4 and the bonding oxide film 12 is removed, so that the group III nitride semiconductor wafer 5 in which the group III nitride semiconductor film 13 is exposed on the main surface is obtained. It was.

  In the obtained group III nitride semiconductor wafer 5, no change was observed in the metal junction surface seen through the group III nitride semiconductor film 13 and the group III nitride semiconductor layer 20 that are transparent to visible light.

7). Formation of Second Electrode Referring to FIG. 2G, the obtained group III nitride semiconductor wafer 5 is removed from the sapphire substrate on a hot plate at 120 ° C., and then the group III nitride semiconductor wafer 5 is formed. A second electrode 50 that is an n-electrode was formed on group nitride semiconductor film 13. The second electrode 50 is formed on a resist mask (not shown) formed on the group III nitride semiconductor film 13 by a photolithography method, using a EB vapor deposition method to form a 20 nm thick Ti layer, a 200 nm thick Al layer, A Ti layer having a thickness of 20 nm and an Au layer having a thickness of 300 nm were formed, lifted off to form a pattern, and then annealed at 250 ° C. for 3 minutes in a nitrogen gas atmosphere using an RTA apparatus. Thereby, the group III nitride semiconductor wafer 6 which expresses the semiconductor device function as LED was obtained.

8). Formation of Semiconductor Device by Chip Formation Group III nitride semiconductor wafer 6 was formed into a semiconductor device by dicing to form a semiconductor device, and then mounted on the stem. The yield at the time of such chip formation and mounting was 100%. Further, uniform light emission within the surface was obtained for the mounted semiconductor device.

(Comparative Example 1)
The bonded substrate 4 produced in the same manner as in Example 1 was ground in the same manner as in Example 1 so that the base substrate 11 had a thickness of 450 μm to 50 μm. 49 masses of which the ground bonded substrate 4 was affixed on a sapphire substrate having a diameter of 3 inches and a thickness of 500 μm in the same manner as in Example 1, and then stirred at 200 rpm by a magnetic stirrer at room temperature (23 ° C.). It was immersed in 500 ml of a 100% aqueous hydrofluoric acid solution. 10 hours after the start of immersion, the base substrate 11 is separated from the bonded substrate 4 and the bonding oxide film 12 is removed, so that the group III nitride semiconductor wafer 5 with the group III nitride semiconductor film 13 exposed on the main surface is obtained. Obtained.

  In the obtained group III nitride semiconductor wafer 5, the metal of the metal junction surface that is visible through the group III nitride semiconductor film 13 and the group III nitride semiconductor layer 20 that is transparent to visible light is discolored. The first electrode 30 (particularly the Ti layer and Ni layer) was affected. Further, a part of the group III nitride semiconductor film 13 and the group III nitride semiconductor layer 20 have been removed along with the erosion of the first electrode 30. Although depending on the sample, the area of the remaining group III nitride semiconductor film 13 and group III nitride semiconductor layer 20 (hereinafter referred to as the remaining area) was 18% before etching.

  The group III nitride semiconductor wafer 5 (residual area 18%) is formed into a group III nitride semiconductor wafer 6 by forming the second electrode 50 in the same manner as in the first embodiment, and is formed into chips by dicing. And then mounted on the stem. The yield at the time of such chip formation and mounting was 5%. In such a group III nitride semiconductor wafer 6, the first electrode 30 and the group III nitride semiconductor layer 20 are peeled off during dancing, or the second electrode 50 and the bonding wire are separated when mounted on the stem. There was a problem of peeling. In addition, in-plane uniform light emission was not obtained for the mounted semiconductor device. As a result of the failure analysis, it was found that these were caused by corrosion caused by hydrofluoric acid exerted on the first electrode 30 and the second electrode 50 because the bonded substrate 4 was immersed in hydrofluoric acid for a long time.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Composite board | substrate, 2 Composite board | substrate with a semiconductor layer, 3 Composite board | substrate with a semiconductor layer with an electrode, 4 Bonding board | substrates, 5, 6 Group III nitride semiconductor wafer, 11 Ground substrate, 11b Grain boundary area | region, 11e Etched area | region, 11f Hydrofluoric acid permeation region, 12 junction oxide film, 13 group III nitride semiconductor film, 20 group III nitride semiconductor layer, 21 n-GaN layer, 22 n-In _0.05 Ga _0.95 N layer, 23 active layer, 24 p-Al _0.08 Ga _0.92 N layer, 25 p ⁺ -GaN layer, 30 first electrode, 31 bonding pad metal layer, 40 support substrate, 41 ohmic bonding metal layer, 42 bonding metal layer, 50 second electrode, A1 Hydrofluoric acid, A2 Acid for dissolving fluoride, S1 Step for preparing composite substrate, S2 Step for growing at least one group III nitride semiconductor layer, S3 Process for forming first electrode The step of attaching the S4 support substrate, the step of reducing the thickness of the base substrate, the step of separating the base substrate, the step of forming the second electrode, the step of forming the second electrode, the step of forming a device by forming a chip, S60 Acid contact set sub-step, S61 HF contact sub-step, S62, S64, S66, S68 Washing and drying sub-step, S63 FSA contact sub-step, S65 Final HF contact sub-step, S67 Final FSA contact sub-step.

Claims (12)

A base substrate including a first oxide that reacts with hydrofluoric acid to produce a fluoride substantially insoluble in hydrofluoric acid, and is soluble in hydrofluoric acid disposed on the base substrate Preparing a composite substrate including a junction oxide film and a group III nitride semiconductor film disposed on the junction oxide film;
One set of sub-processes including an HF contact sub-process for contacting the composite substrate with hydrofluoric acid and an FSA contact sub-process for contacting the composite substrate with an acid dissolving the fluoride generated from the first oxide. An acid contact setting sub-step, and a final HF contact sub-step for contacting the composite substrate after the acid contact setting sub-step with hydrofluoric acid, the acid contact setting sub-step and the final HF contact sub-step A step of separating the base substrate from the group III nitride semiconductor film of the composite substrate by etching a part of the base substrate and the bonding oxide film; and a group III nitride semiconductor wafer including: Production method.   2. The group III nitride semiconductor according to claim 1, wherein the step of separating the base substrate is performed by lift-off of the base substrate from the group III nitride semiconductor film by etching the bonding oxide film with hydrofluoric acid. 3. Wafer manufacturing method.   In the step of separating the base substrate, the hydrofluoric acid for etching the bonding oxide film is obtained by dissolving the fluoride formed from the first oxide in the HF contact sub-step in the FSA contact sub-step. 3. The method for manufacturing a group III nitride semiconductor wafer according to claim 1, wherein the first oxide film is supplied to the junction oxide film via an etching void region formed in a part of the base substrate.   4. The water washing and drying sub-step of further drying the composite substrate after washing the composite substrate after each of the HF contact sub-step, the FSA contact sub-step, and the final HF contact step. 5. A method for producing a group III nitride semiconductor wafer of   The step of separating the base substrate further includes a final FSA contact sub-step of contacting the composite substrate with an acid that dissolves the fluoride of the first oxide after the final HF contact sub-step. 5. A method for producing a group III nitride semiconductor wafer according to any one of 4 above.   6. The method of manufacturing a group III nitride semiconductor wafer according to claim 5, wherein the step of separating the base substrate further includes a water washing and drying sub-step of washing the composite substrate and then drying the composite substrate after the final FSA contact sub-step. .   The group III nitride semiconductor wafer according to any one of claims 1 to 6, wherein the acid that dissolves the fluoride generated from the first oxide includes at least one acid selected from the group consisting of nitric acid and hydrochloric acid. Manufacturing method.   The method for producing a group III nitride semiconductor wafer according to any one of claims 1 to 6, wherein the acid that dissolves the fluoride produced from the first oxide is a nitric acid aqueous solution of 10 mass% or more and 50 mass% or less. .   9. The method for producing a group III nitride semiconductor wafer according to claim 1, wherein the base substrate further includes a second oxide that is substantially insoluble in hydrofluoric acid.   The method for producing a group III nitride semiconductor wafer according to claim 1, wherein the base substrate further includes a third oxide soluble in hydrofluoric acid. After the step of preparing the composite substrate, before the step of separating the base substrate from the group III nitride semiconductor film of the composite substrate,
The method for producing a group III nitride semiconductor wafer according to claim 1, further comprising a step of growing at least one group III nitride semiconductor layer on the group III nitride semiconductor film.   The contact time between the base substrate and hydrofluoric acid in the HF contact sub-step is the contact time between the base substrate and the acid dissolving the fluoride generated from the first oxide in the FSA contact sub-step. The method for producing a group III nitride semiconductor wafer according to any one of claims 1 to 11, wherein the method is 0.5 to 20 times.

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