JP2007103457A - Polishing slurry, surface treatment method of group iii nitride crystal, group iii nitride crystal substrate, group iii nitride crystal substrate with epitaxial layer, semiconductor device and its fabrication process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide polishing slurry which can form a smooth surface with little potential flaw efficiently on a group III nitride crystal, and to provide a surface treatment method of the group III nitride crystal employing polishing slurry. <P>SOLUTION: Polishing slurry performing the chemical mechanical polishing of the surface of a group III nitride crystal contains abrasive grains having hardness not higher than that of the group III nitride crystal wherein the abrasive grains are secondary particles associated with primary particles, and the ratio d<SB>2</SB>/d<SB>1</SB>of mean particle diameter d<SB>2</SB>of the secondary particles to mean particle diameter d<SB>1</SB>of the primary particles is 1.6 or larger. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention uses a polishing slurry used for mechanically and chemically polishing a surface of a group III nitride crystal used for a substrate of a semiconductor device such as a light emitting element, an electronic element, or a semiconductor sensor, and such a polishing slurry. The present invention relates to a surface treatment method for a group III nitride crystal, a group III nitride crystal substrate obtained by the surface treatment method, a semiconductor device including the group III nitride crystal substrate, and a method for manufacturing the semiconductor device.

Group III nitride crystals such as GaN crystals and AlN crystals are very useful as materials for forming substrates of semiconductor devices such as light emitting elements, electronic elements, and semiconductor sensors. Here, the III-nitride crystal, crystal formed of a group III element and nitrogen, _{e.g., Ga x Al y In 1-} xy N crystal (0 ≦ x, 0 ≦ y , x + y ≦ 1) , such as Say.

  A group III nitride crystal substrate used as a substrate of a semiconductor device is subjected to shape forming processing on the outer periphery of the group III nitride crystal, sliced to a predetermined thickness, and then ground (grinding, the same applies hereinafter) or lapping. However, by such slicing, grinding, or lapping, a process-affected layer is formed in the surface side region of the group III nitride crystal (a layer in which the crystal lattice formed in the surface side region of the crystal is disturbed by processing of the crystal surface). The same applies hereinafter) or the surface roughness of the group III nitride crystal is increased. The higher the density of scratches (referring to linear recesses, hereinafter the same) and latent scratches (referring to work-affected layers on straight lines) on the surface of the group III nitride crystal substrate, the more the surface roughness becomes. The larger the surface quality, the lower the quality of the substrate surface, and the surface of the group III nitride crystal layer epitaxially grown on the surface of the group III nitride crystal becomes uneven and the crystallinity decreases. Therefore, a high-quality semiconductor device cannot be formed.

  Therefore, as a method of forming a group III nitride crystal substrate from a group III nitride crystal, the group III nitride crystal is sliced to a predetermined thickness, and after grinding or lapping the surface, the surface is further dry etched ( For example, the surface treatment by chemical mechanical polishing (hereinafter also referred to as CMP) (see, for example, Patent Documents 2 to 4) is performed by performing surface treatment by using Chemical Mechanical Polishing (refer to Patent Documents 2 to 4). It has been widely practiced to remove scratches and latent scratches on the surface and further reduce the surface roughness.

  However, in the method of dry etching the surface of the group III nitride crystal, it is easy to remove the work-affected layer, but it is difficult to reduce the surface roughness.

  Further, in conventional CMP, a group III nitride crystal is pushed onto the polishing pad while a polishing slurry containing spherical abrasive grains having a hardness lower than the hardness of the group III nitride crystal that is the object to be polished is supplied to the polishing pad. Polishing of the surface of the group III nitride crystal was performed by applying, but since the group III nitride crystal was hard and poor in reactivity, the polishing rate was very low and inefficient. Therefore, in order to improve the polishing speed, a polishing agent comprising a stable sol of silica having a distorted shape having a major axis and a minor axis as the shape of the abrasive grains, and a polishing method using the polishing agent (for example, Patent Documents) Although 4) has been proposed, the polishing rate is not sufficiently high even by such a polishing agent and polishing method, and it has been difficult to remove the work-affected layer produced in the previous process.

In recent years, a polishing slurry containing hard abrasive grains formed of diamond, alumina (Al ₂ O ₃ ), and soft abrasive grains formed of colloidal silica (SiO ₂ ), fumed titania (TiO ₂ ), etc. And a method of polishing the surface of a group III nitride crystal using such a polishing slurry (see, for example, Patent Document 5), which makes it possible to increase the surface smoothness together with the polishing rate of the group III nitride crystal. did. However, in CMP disclosed in Patent Document 5, since hard abrasive grains are included, it is difficult to remove latent scratches that are the above-mentioned work-affected layer and to further increase the surface smoothness. Therefore, there has been a demand for a surface treatment method that can remove not only scratches but also the work-affected layer to obtain a good surface.
JP 2001-322899 A US Pat. No. 6,596,079 US Pat. No. 6,488,767 JP 07-221059 A Japanese Patent Laid-Open No. 2004-311575

  The present invention provides a polishing slurry capable of efficiently forming a smooth surface with few latent scratches on a group III nitride crystal, a surface treatment method for a group III nitride crystal using such a polishing slurry, and such a surface treatment method. It is an object of the present invention to provide a group III nitride crystal substrate, a semiconductor device having such a quality and characteristics, and a method of manufacturing the same including the group III nitride crystal substrate.

The present invention is a polishing slurry for chemically and mechanically polishing the surface of a group III nitride crystal, the polishing slurry including abrasive grains having a hardness equal to or lower than the hardness of the group III nitride crystals, The primary particles are associated secondary particles, and the ratio d ₂ / d ₁ of the average particle diameter d ₂ of the secondary particles to the average particle diameter d ₁ of the primary particles is 1.6 or more. Polishing slurry.

In the polishing slurry according to the present invention, the average particle diameter d ₂ of secondary particles of the abrasive grains can be 200 nm or more. The shape of the abrasive grains can be at least one of a saddle shape, a block shape, and a chain shape. Further, the pH value x of the polishing slurry and the value y (mV) of the oxidation-reduction potential (hereinafter referred to as ORP) are expressed by the following equations (1) and (2).
y ≧ −50x + 1000 (1)
y ≦ −50x + 1900 (2)
Any of these relationships can be satisfied. Moreover, pH of polishing slurry can be 5 or less or 9 or more. Moreover, the polishing slurry can contain the abrasive grains, an organic acid and / or a salt thereof, and an oxidizing agent.

  Further, the present invention is a surface treatment method of a group III nitride crystal using the above polishing slurry, and this surface treatment method prepares a polishing slurry and uses the polishing slurry to form a group III nitride crystal. A surface treatment method for a group III nitride crystal including a step of chemically and mechanically polishing a surface.

  In the III-nitride crystal surface treatment method according to the present invention, after the chemical-mechanical polishing step, a step of cleaning the surface of the chemically-mechanically polished group-III nitride crystal with pure water. Can be included. In addition, after the chemical mechanical polishing step, the method may include a step of polishing the surface of the chemically mechanically polished group III nitride crystal using a polishing solution formed of an acidic aqueous solution or a basic aqueous solution. it can. Further, after the step of polishing using the polishing solution, a step of washing the surface of the group III nitride crystal polished using the polishing solution with pure water can be included.

Further, the present invention is a group III nitride crystal substrate obtained by the above surface treatment method, wherein the density of latent scratches by ultraviolet fluorescence observation or cathodoluminescence observation is 1 × 10 ³ pieces / mm or less. It is a nitride crystal substrate.

  In the group III nitride crystal substrate according to the present invention, the surface roughness Ry can be 30 nm or less, and the surface roughness Ra can be 3 nm or less. Further, the off angle, which is an angle formed between the main surface of the group III nitride crystal substrate and any one of the C, A, R, and S surfaces in the wurtzite structure, may be 15 ° or less. it can.

  The present invention is also a group III nitride crystal substrate with an epitaxial layer including one or more group III nitride layers formed by epitaxial growth on at least one main surface side of the group III nitride crystal substrate.

  The present invention also relates to a semiconductor device comprising the above group III nitride crystal substrate and one or more group III nitride layers formed on at least one main surface side of the group III nitride crystal substrate. is there.

  According to the present invention, the group III nitride crystal substrate is selected as a substrate for a semiconductor device, and at least one group III nitride layer is grown on at least one main surface of the group III nitride crystal substrate. This is a method for manufacturing a semiconductor device.

  According to the present invention, a polishing slurry capable of efficiently forming a smooth surface with few latent scratches on a group III nitride crystal, a surface treatment method for a group III nitride crystal using such a polishing slurry, and such a surface treatment method The group III nitride crystal substrate obtained by the above, a semiconductor device having good quality and characteristics including the group III nitride crystal substrate, and a method for manufacturing the same can be provided.

(Embodiment 1)
One embodiment of the polishing slurry according to the present invention is a polishing slurry for chemically and mechanically polishing the surface of a group III nitride crystal, and the polishing slurry has a hardness equal to or lower than the hardness of the group III nitride crystal. includes abrasive grains having this abrasive is secondary particles in which the primary particles are associated, the average particle size d ₂ of the ratio of the secondary particles to the average particle size d ₁ of the primary particles (hereinafter, d ₂ / d ₍ Also referred to as ₁ ratio) is 1.6 or more.

  Here, the term “chemical mechanical polishing” means that the surface of an object to be polished is chemically and mechanically smoothed by using the polishing slurry 17. For example, referring to FIG. While rotating the fixed polishing pad 18 around the rotation shaft 15c, the polishing slurry 17 is supplied from the polishing slurry supply port 19 onto the polishing pad 18, and the group III nitride crystal 1 is fixed on the crystal holder 11. The surface of the group III nitride crystal 1 is chemically and mechanically polished by pressing the group III nitride crystal 1 against the polishing pad 18 while placing the weight 14 on the rotating shaft 11c and rotating it around the rotation axis 11c. be able to.

The polishing slurry 17 of the present embodiment includes abrasive grains 16 having a hardness equal to or lower than the hardness of the group III nitride crystal 1, so that when scratching the surface of the group III nitride crystal 1, new scratches and latent scratches are generated. It is possible to reduce scratches and latent scratches that have been generated in the pre-processing step without causing the occurrence of. Abrasive grains 16 is not particularly limited as long as it has a hardness of less hardness of the Group III nitride crystal _{1, SiO 2, CeO 2,} TiO 2, MgO, MnO 2, Fe 2 O 3, Fe 3 O ₄ , abrasive grains containing at least one material selected from the group consisting of NiO, ZnO, CoO ₂ , Co ₃ O ₄ , CuO, Cu ₂ O, GeO ₂ , CaO, Ga ₂ O ₃ , and In ₂ O _3. It is preferable.

  Further, since the abrasive grains 16 are secondary particles in which primary particles are associated with each other, the polishing rate is increased and the surface treatment of the group III nitride crystal 1 can be performed efficiently. As the primary particles associate to become secondary particles, abrasive grains having irregular shapes with no edges on the surface are formed, and the polishing rate is increased without generating new scratches and latent scratches. Use of abrasive grains having edges on the surface increases the occurrence of scratches and / or latent scratches during polishing. Further, from the viewpoint of forming an uneven shape without edges, the primary particles are preferably spherical or elliptical rotator.

Here, from the viewpoint that the hardness is lower than that of the group III nitride crystal and the primary particles are spherical or elliptical rotator shape, and secondary particles having uneven shapes without edges on the surface are easy to form. Is preferably made of SiO ₂ such as fumed silica or colloidal silica, particularly colloidal silica. Colloidal silica includes a synthesis method using water glass (such as sodium silicate) as a raw material and a synthesis method (sol-gel method) using alkoxysilane as a raw material. The former is low-cost and easy to mass-produce, and the latter provides high-purity abrasive grains. By adjusting the synthesis conditions, the particle size of the primary particles, the degree of association of the primary particles, and the particle size of the secondary particles can be freely controlled.

The degree of association of the abrasive grains 16 is not particularly limited, from the viewpoint of forming an edge-free irregularities on the surface, of the secondary particles to the average particle size d ₁ of the primary particles having an average particle diameter d ₂ The ratio (d ₂ / d ₁ ratio) is 1.6 or more. Furthermore, the d ₂ / d ₁ ratio is preferably 2.0 or more. Here, the average particle diameter d ₁ of the primary particles of the abrasive grains 16 is determined by the following equation (4) from the measurement of the adsorption specific surface area (hereinafter referred to as the BET specific surface area) by the gas adsorption method.
d ₁ = 6 / (ρ × S) (4)
Is calculated by In the formula (4), ρ represents the density of the particles, and S represents the BET specific surface area. The average particle size d ₂ of the abrasive grains of the secondary particles is the measurement of the diffusion coefficient in the Brownian movement of the particles by dynamic light scattering method, the following equation (5)
d ₂ = (k × T) / (3 × π × η ₀ × D) (5)
Is calculated by In equation (5), k is the Boltzmann constant, T is the absolute temperature, π is the circumference, η ₀ is the viscosity of the solvent, and D is the diffusion coefficient.

The average particle size d ₂ of the secondary particles of the abrasive grains 16 is not particularly limited, from the viewpoint of enhancing the polishing rate is preferably 200nm or more. Further, the shape of the abrasive grains 16 is not particularly limited, but referring to FIG. 2, from the viewpoint of forming an uneven shape without edges, the shape as shown in FIG. At least one of a block shape as shown in (b-1) and (b-2) of b) and a chain shape as shown in (c-1) and (c-2) of FIG. 2 (c) It is preferable that Furthermore, from the viewpoint of increasing the polishing speed, the shape of the abrasive grains 16 is more preferably a block shape or a chain shape than a bowl shape. Since the polishing slurry of this embodiment has an uneven shape with no edges as described above on the surface, the mechanical polishing effect is increased, and the polishing speed can be increased without increasing the thickness of the work-affected layer 1a. It becomes. Here, the shape of the abrasive grains 16 can be observed with an SEM (scanning electron microscope) or the like.

  Specifically, the polishing slurry 17 of the present embodiment is a slurry in which abrasive grains 16 having a hardness equal to or lower than the hardness of the group IIIIII nitride crystal 1 are dispersed in water as a dispersion medium. The content of the abrasive grains in the polishing slurry 17 is not particularly limited, but is preferably 3% by mass or more and 40% by mass or less from the viewpoint of efficiently polishing the surface of the group III nitride crystal. More preferably, it is 30 mass% or less.

Further, the pH value x and the ORP value y (mV) of the polishing slurry of the present embodiment are expressed by the following equations (1) and (2).
y ≧ −50x + 1000 (1)
y ≦ −50x + 1900 (2)
It is preferable to satisfy any of these relationships. Here, ORP means an energy level (potential) determined by an equilibrium state between an oxidant and a reductant coexisting in a solution. The ORP obtained by the measurement is a value with respect to the reference electrode. If the type of the reference electrode is different, the measured value of the same solution is apparently different. In general academic papers, a standard hydrogen electrode (NHE) is often used as a reference electrode. The ORP in the present application is shown as a value using a standard hydrogen electrode (NHE) as a reference electrode.

  When the polishing slurry 17 of the present embodiment has a pH value x and an ORP value y (mV) of y <−50x + 1000, the polishing slurry 17 has low oxidizing power, and polishing of the surface of the group III nitride crystal 1 is performed. Reduces speed. On the other hand, when y> −50x + 1900, the oxidizing power of the polishing slurry 17 becomes too strong, and the corrosive action on polishing equipment such as a polishing pad and a surface plate becomes strong, and stable CMP becomes difficult.

Further, from the viewpoint of further increasing the polishing speed, it is further preferable that y ≧ −50x + 1300. That is, the pH value x of the polishing slurry 17 and the ORP value y (mV) are expressed by the following equations (2) and (3).
y ≦ −50x + 1900 (2)
y ≧ −50x + 1300 (3)
It is preferable to satisfy any of these relationships.

  Acids such as hydrochloric acid and sulfuric acid, and bases such as KOH and NaOH contained in normal polishing slurries have a weak ability to oxidize the surface of chemically stable group III nitride crystals. For this reason, it is preferable that the polishing slurry of this embodiment is added with an oxidizing agent to increase the ORP, that is, to increase the oxidizing power. The amount of the oxidizing agent added is such that the pH value x of the polishing slurry 17 and the ORP value y (mV) are either y ≧ −50x + 1000 (formula (1)) or y ≦ −50x + 1900 (formula (2)). Adjusted to meet the relationship.

  Here, the oxidizing agent added to the polishing slurry is not particularly limited, but from the viewpoint of increasing the polishing rate, chlorinated isocyanuric acid such as hypochlorous acid and trichloroisocyanuric acid, and chlorinated isocyanuric such as sodium dichloroisocyanurate. Permanganates such as acid salts, potassium permanganate, dichromates such as potassium dichromate, bromates such as potassium bromate, thiosulfates such as sodium thiosulfate, ammonium persulfate and potassium persulfate. Sulfate, nitric acid, hydrogen peroxide solution, ozone and the like are preferably used. In addition, these oxidizing agents may be used independently or may use 2 or more together.

  Moreover, it is preferable that the pH of the polishing slurry 17 of this embodiment is 5 or less or 9 or more. The polishing rate is increased by bringing an acidic polishing slurry having a pH of 5 or less or a basic polishing slurry having a pH of 9 or more into contact with the group III nitride crystal and etching away the work-affected layer 1a of the group III nitride crystal. be able to. From this viewpoint, the pH of the polishing slurry 17 is more preferably 4 or less, and further preferably 3 or less. Further, the pH of the polishing slurry 17 is more preferably 10 or more.

Here, the acid and base used for adjusting the pH are not particularly limited, and examples thereof include inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and carbonic acid, formic acid, acetic acid, citric acid, malic acid, tartaric acid, and succinic acid. In addition to organic acids such as phthalic acid and fumaric acid, bases such as KOH, NaOH, NH ₄ OH and amines, salts containing these acids or bases can be used. Moreover, pH can also be adjusted by addition of the said oxidizing agent.

  In particular, the use of the organic acid and / or salt thereof for pH adjustment increases the polishing rate for the group III nitride crystal compared with the case where the inorganic acid and / or salt is used to achieve the same pH. Become. From the viewpoint of increasing the polishing rate, the organic acid and / or salt thereof is preferably a carboxylic acid and / or salt thereof containing two or more carboxyl groups in each molecule. Preferred examples of the dicarboxylic acid include malic acid, succinic acid, phthalic acid, and tartaric acid. Preferred examples of the tricarboxylic acid include citric acid. Therefore, the polishing slurry preferably contains the abrasive grains, the oxidizing agent, and the organic acid and / or salt thereof.

(Embodiment 2)
One embodiment of the surface treatment method for a group III nitride crystal according to the present invention is a method for surface treatment of a group III nitride crystal 1 using the polishing slurry 17 of the first embodiment with reference to FIG. A surface treatment method for a group III nitride crystal including the steps of preparing the polishing slurry 17 and polishing the surface of the group III nitride crystal 1 chemically and mechanically using the polishing slurry 17. Here, the chemical mechanical polishing is as described in the first embodiment. By using the polishing slurry of Embodiment 1, it is possible to efficiently chemically and mechanically polish the surface of the group III nitride crystal without generating scratches and reducing the occurrence of latent scratches.

  In the surface treatment method for a group III nitride crystal of the present embodiment, a step of cleaning the surface of the chemically and mechanically polished group III nitride crystal with pure water after the step of chemical mechanical polishing. It is preferable to include. By washing the surface of the group III nitride crystal with pure water, impurities such as polishing slurry (abrasive grains and polishing liquid) adhering to the surface of the group III nitride crystal during the chemical mechanical polishing step are removed. Can be removed. The method for cleaning the group III nitride crystal is not particularly limited, but an ultrasonic cleaning method, a scrub cleaning method, and the like are preferably used from the viewpoint of effectively removing impurities by mechanical action.

  Further, in the surface treatment method of a group III nitride crystal of the present embodiment, referring to FIG. 3, the surface of the group III nitride crystal chemically polished after the above-mentioned chemical mechanical polishing step is performed. It is preferable to include a step of polishing using a polishing solution formed of an acidic aqueous solution or a basic aqueous solution.

  Here, the step of polishing using the polishing liquid refers to the impurities adhering to the surface of the object to be polished using a polishing liquid that does not contain solid substances such as abrasive grains, such as an acidic aqueous solution or a basic aqueous solution. For example, referring to FIG. 3, the polishing pad 38 fixed on the surface plate 35 is rotated from the polishing liquid supply port 39 while rotating around the rotation shaft 35c. The polishing liquid 37 is supplied onto the pad 38, and the group III nitride crystal 1 is placed on the crystal holder 31 on which the group III nitride crystal 1 is fixed while the weight 34 is placed and rotated around the rotation axis 31c. By pressing against the polishing pad 38, impurities on the surface of the group III nitride crystal 1 can be removed.

By polishing the surface of the group III nitride crystal 1 using the polishing liquid 37 of the present embodiment formed of an acidic aqueous solution or a basic aqueous solution, the group III nitride is polished during the chemical mechanical polishing step. Impurities such as polishing slurry (abrasive grains and polishing liquid) adhering to the crystal surface can be efficiently removed. From the viewpoint of removing impurities adhering to the group III nitride crystal surface, the polishing solution is preferably an acidic aqueous solution having a pH of 5 or less or a basic aqueous solution having a pH of 9 or more. Here, the acidic aqueous solution is not particularly limited, but an aqueous solution of inorganic acid such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, citric acid, malic acid, tartaric acid, succinic acid, phthalic acid, fumaric acid, etc. An aqueous solution of an organic acid or an aqueous solution containing two or more acids from the above-mentioned inorganic acid and organic acid is preferably used. The basic aqueous solution is not particularly limited, but an aqueous solution of a base such as KOH, NaOH, NH ₄ OH or amine is preferably used.

  Furthermore, in the surface treatment method of a group III nitride crystal of the present embodiment, after the step of polishing using the polishing liquid, the surface of the group III nitride crystal polished using the polishing liquid is washed with pure water. It is preferable that the process to include is included. By washing the surface of the group III nitride crystal with pure water, the polishing liquid adhering to the surface of the group III nitride crystal during the polishing step using the polishing liquid can be efficiently removed. The method for cleaning the group III nitride crystal is not particularly limited, but from the viewpoint of efficiently removing metal ions and ions containing light elements having an atomic number of 1 to 18 in an acidic aqueous solution and a basic aqueous solution, an ultrasonic wave is used. A cleaning method is preferably used.

(Embodiment 3)
One embodiment of a group III nitride substrate according to the present invention is a group III nitride crystal substrate obtained by the surface treatment method of embodiment 2, and is for ultraviolet fluorescence observation or cathodoluminescence (hereinafter referred to as CL) observation. The density of latent scratches is 1 × 10 ³ / mm or less. According to the surface treatment method of the second embodiment, a group III nitride crystal substrate having a density of latent flaws that is a work-affected layer resulting from a work flaw in the previous step is 1 × 10 ³ pieces / mm or less is obtained. An epitaxial layer with good morphology and crystallinity can be formed on the main surface of the group III nitride crystal substrate having a density of latent scratches of 1 × 10 ³ pieces / mm or less, so that a semiconductor device with good characteristics can be obtained. . From this point of view, the density of group III nitride crystals is more preferably 1 × 10 ² / mm or less. Here, the latent scratch can be observed by ultraviolet fluorescence observation or CL observation.

  Ultraviolet fluorescence observation refers to the observation of fluorescence with energy (wavelength) corresponding to the band gap of group III nitride crystals by making excitation light of energy (low wavelength) sufficiently higher than the band gap of group III nitride crystals incident. To do. For example, the fluorescence of a GaN crystal (wavelength: 365 nm) is observed using mercury emission lines (wavelength: 337 nm) or He—Cd laser (wavelength: 325 nm) as excitation light. When the group III nitride crystal is observed with ultraviolet fluorescence, the fluorescence is observed in the crystal region having a good surface state, the fluorescence is not observed in the region of the work-affected layer where the crystal is disordered, and the latent flaw is a black linear shape. It is observed as a shadow of.

  In ultraviolet fluorescence observation, since it is possible to observe even when the group III nitride crystal is fixed to the crystal holder, it is possible to observe the surface state of the group III nitride crystal at each step in the surface treatment of the group III nitride crystal. It is possible, and it becomes easy to grasp the problems in each process. In addition, ultraviolet fluorescence observation can be performed by using a combination of an ultraviolet fluorescence microscope and an optical microscope (especially, a differential interference microscope is preferred), so that the same field of view can be observed in comparison. It is possible to contrast and observe information on the processed surface layer such as latent scratches.

  CL observation refers to observing visible light or light having a wavelength close to the visible wavelength region that is emitted when an electron beam is incident on the III nitride crystal as excitation light. When cathodoluminescence observation of group III nitride crystal is performed, light is observed in the crystal region where the surface condition is good, light is not observed in the region of the work-affected layer where the crystal is disordered, and the latent flaw is a black linear shape It is observed as a shadow of.

  The CL observation apparatus can be observed at a high magnification in combination with an SEM (scanning electron microscope), and can observe delicate latent scratches. By comparing the CL image with the SEM image, it is possible to compare and observe surface irregularity information such as scratches and information on the processed surface layer such as latent flaws.

Further, the surface roughness Ry of the group III nitride crystal substrate of the present embodiment is preferably 30 nm or less. Here, the surface roughness Ry is a 10 μm square (10 μm × 10 μm = 100 μm ² , the same applies hereinafter) as a reference area in the direction of the average surface from the roughness curved surface, and the highest peak from the average surface of this extracted portion The sum of the height to the bottom and the depth to the lowest valley. By setting the surface roughness Ry of the group III nitride crystal substrate to 30 nm or less, an epitaxial layer having good morphology and crystallinity can be formed on the main surface of the group III nitride crystal substrate. From this point of view, the surface roughness Ry of the group III nitride crystal substrate is more preferably 10 nm or less. The surface roughness Ry can be measured using an AFM (atomic force microscope, hereinafter the same).

  The surface roughness Ra of the group III nitride crystal substrate of the present embodiment is preferably 3 nm or less. Here, the surface roughness Ra is extracted from the roughness curved surface by a 10 μm square as a reference area in the direction of the average surface, and the absolute value of the deviation from the average surface of the extracted portion to the measurement curved surface is summed up. The value averaged with the reference area. By setting the surface roughness Ra of the group III nitride crystal substrate to 3 nm or less, an epitaxial layer having good morphology and crystallinity can be formed on the group III nitride crystal. From such a viewpoint, the surface roughness Ra of the group III nitride crystal substrate is more preferably 1 nm or less. The surface roughness Ra can be measured using AFM.

  In addition, the main surface of the group III nitride crystal substrate of the present embodiment is parallel to any one of the C, A, R, and S surfaces in the wurtzite structure, or the group III nitride It is preferable that an off angle, which is an angle formed between the main surface of the crystal substrate and any one of the C, A, R, and S surfaces in the wurtzite structure, is 15 ° or less. Here, the C plane is the {0001} plane and the {000-1} plane, the A plane is the {11-20} plane and its equivalent plane, and the R plane is the {01-12} plane and its equivalent plane. , M plane means {10-10} plane and its equivalent plane, and S plane means {10-11} plane and its equivalent plane.

  By setting the off angle, which is the angle formed between the main surface of the group III nitride crystal substrate and each of the above surfaces in the wurtzite structure, to 15 ° or less, the morphology and crystallinity on the group III nitride crystal substrate are excellent. It becomes easy to form an epitaxial layer. If the off-angle exceeds 15 °, a stepped step is easily formed in the epitaxial layer. The Oz angle is preferably 0.1 ° or more and 10 ° or less. By providing an off angle of 0.1 ° or more, defects in the epitaxial layer formed on the group III nitride crystal substrate can be reduced. If the off-angle exceeds 10 °, step flow growth is difficult to proceed. By forming an epitaxial layer with good morphology and crystallinity on the group III nitride crystal substrate as described above, a semiconductor device with high characteristics and long life can be obtained. In addition, the polishing rate can be increased by providing the above-described off angle. In addition, it is possible to suppress the occurrence of dents due to preferential removal in the latent scratch portion and / or dislocation concentration portion during CMP, and to obtain a flat surface.

(Embodiment 4)
One embodiment of the III-nitride crystal substrate with an epitaxial layer according to the present invention includes at least one group III-nitride formed by epitaxial growth on at least one main surface side of the group III nitride crystal substrate of the third embodiment. Includes material layers. The one or more III-nitride layers are epitaxial layers having good morphology and crystal, and an epitaxial layer having good morphology and crystal is further formed on the epitaxial layer so as to have high characteristics and long life. It becomes easy to manufacture a semiconductor device.

Here, the group III nitride layer is not particularly limited, for example, _{Ga x Al y In 1-xy} N layer (0 ≦ x, 0 ≦ y , x + y ≦ 1) , and the like. Also, the method for epitaxial growth of the group III nitride layer is not particularly limited, and includes HVPE (hydride vapor phase growth, the same applies hereinafter) method, MBE (molecular beam epitaxy, the same applies hereinafter) method, MOCVD (organometallic chemical vapor phase). The deposition method is the same).

(Embodiment 5)
One embodiment of a semiconductor device according to the present invention is formed on the main surface side of at least one of group III nitride crystal substrate 410 and group III nitride crystal substrate 410 of embodiment 3 with reference to FIG. The semiconductor device 400 includes one or more III-nitride layers 450. In the semiconductor device of this embodiment, the group III nitride crystal substrate 410 of the second embodiment has a density of latent scratches of 1 × 10 ³ pieces / mm or less, and at least one main surface of the group III nitride crystal substrate 410 Since one or more Group III nitride layers, which are epitaxial layers having good morphology and crystal, are formed on the side, a semiconductor device having high characteristics and a long lifetime can be obtained.

  Such semiconductor devices include light emitting elements such as light emitting diodes and laser diodes, rectifiers, bipolar transistors, field effect transistors, electronic elements such as HEMTs (High Electron Mobility Transistors), temperature sensors, pressure sensors, and radiation. Examples include sensors, semiconductor sensors such as a visible-ultraviolet light detector, and SAW devices (Surface Acoustic Wave Devices).

(Embodiment 6)
In one embodiment of the method for manufacturing a semiconductor device according to the present invention, referring to FIG. 4, group III nitride crystal substrate 410 of embodiment 3 is selected as a substrate for a semiconductor device, and group III nitride crystal substrate 410 is selected. One or more III-nitride layers 450 are grown on at least one main surface side. According to such a manufacturing method, an epitaxial layer with good morphology and crystal is formed on at least one main surface side of the group III nitride crystal substrate 410 of Embodiment 3 in which the density of latent scratches is 1 × 10 ³ pieces / mm or less. Since one or more group III nitride layers are formed, a semiconductor device having high characteristics and a long lifetime can be obtained.

  Based on the following examples and comparative examples, a polishing slurry according to the present invention, a surface treatment method of a group III nitride crystal using the polishing slurry, a group III nitride crystal substrate obtained by the surface treatment method, and A semiconductor device including such a group III nitride crystal substrate will be described more specifically.

Example 1
(1-1) Lapping of n-type GaN crystal An n-type GaN crystal (dopant: Si) grown by the HVPE method is sliced in a plane parallel to the (0001) plane, and has a diameter of 50 mm and a thickness of 0.5 mm. An n-type GaN crystal substrate was obtained. The C plane ((0001) plane) on the Ga atom plane side of this n-type GaN crystal substrate was lapped as follows. A 300mm surface plate is placed in the lapping machine, and the (000 1) plane of the n-type GaN crystal substrate fixed to the crystal holder is pressed against the surface plate while supplying lapping slurry in which diamond abrasive grains are dispersed. However, the surface plate and the n-type GaN crystal substrate were rotated relative to each other with the rotation axis shifted. Here, a copper surface plate or a tin surface plate was used as the surface plate. Three types of diamond abrasive grains having an abrasive grain size of 6 μm, 3 μm, and 1 μm were prepared, and the abrasive grain size was gradually reduced with the progress of mechanical polishing. The lapping pressure was 19.6 kPa (200 g / cm ² ) to 49 kPa (500 g / cm ² ), and the rotation speeds of the n-type GaN crystal substrate and the surface plate were both 30 times / min to 100 times / min. By such lapping, the surface of the GaN crystal substrate became a mirror surface. The latent scratch density of the n-type GaN crystal substrate after this lapping was 8500 / mm, Ry was 9.0 nm, and Ra was 0.87 nm. The lapping time was 120 min. The average wrapping speed was 1 μm / hr.

(1-2) Chemical mechanical polishing (CMP) of n-type GaN crystal
The (0001) plane of the n-type GaN crystal substrate after lapping was chemically and mechanically polished as follows. That is, referring to FIG. 1, the C plane ((000-1) plane) on the N atom plane side of the l-type GaN crystal substrate (Group III nitride crystal 1) after the lapping is placed in a ceramic crystal holder 11. Pasted with wax. A polishing pad 18 is installed on a surface plate 15 having a diameter of 380 mm installed in a polishing apparatus (not shown), and a polishing slurry 17 in which abrasive grains 16 are dispersed is supplied to the polishing pad 18 from a polishing slurry supply port 19. The GaN crystal is rotated while the polishing pad 18 is rotated about the rotating shaft 15c and the weight 14 is placed on the crystal holder 11 to press the n-type GaN crystal substrate (Group III nitride crystal 1) against the polishing pad 18. By rotating the substrate (group III nitride crystal 1) about the rotation axis 11c of the crystal holder 11, the surface of the n-type GaN crystal (the C plane ((0001) plane) on the Ga atom plane side) is changed to a chemical machine. Policed.

Here, the polishing slurry 17 is colloidal silica (SiO ₂ ) having an average primary particle size of 90 nm and an average secondary particle size of 220 nm as the abrasive grains 16 (Quatron PL-10H manufactured by Fuso Chemical Industry Co., Ltd.). (SiO ₂ solid content 24% by mass) is dispersed and diluted in water to make SiO ₂ solid content 15% by mass, citric acid, sodium citrate, trichloroisocyanuric acid (TCIA) as an oxidizing agent is added as appropriate, It was prepared by adjusting the pH to 4.0 and the ORP to 1200 mV. The polishing pad 18 was a polyurethane suede pad (Supreme RN-R manufactured by Nitta Haas Co., Ltd.), and the surface plate 15 was a stainless steel surface plate. The polishing pressure is 19.6 kPa (200 g / cm ² ) to 98 kPa (1000 g / cm ² ), and the n-type GaN crystal substrate (group III nitride crystal 1) and the polishing pad 18 are both rotated 30 times / min. 120 times / min, and the polishing time was 60 min.

The polishing rate in this CMP was 1.2 μm / hr. The latent scratch density of the n-type GaN crystal substrate after CMP was 0 / mm, the surface roughness Ry was 6.5 nm, and Ra was 0.69 nm. The results are summarized in Table 1,
(1-3) Fabrication of Semiconductor Device Including n-type GaN Crystal Substrate Referring to FIG. 4, the n-type GaN crystal substrate after CMP is placed in an MOCVD apparatus, and this n-type GaN crystal substrate (III N-type GaN layer 421 (dopant: Si) having a thickness of 1 μm as n-type semiconductor layer 420 is formed on one main surface (group (0001) surface subjected to CMP) side of group nitride crystal substrate 410) by MOCVD. and a thickness of 150 nm n-type Al _0.1 Ga _0.9 n layer 422 (dopant: Si), the light-emitting layer 440, p-type thickness 20nm as a p-type semiconductor layer 430 Al _0.2 Ga _0.8 n layer 431 (dopant: Mg) and A p-type GaN layer 432 (dopant: Mg) having a thickness of 150 nm was sequentially formed to obtain an LED (light emitting diode, hereinafter the same) as a semiconductor device. Here, the light emitting layer 440 includes four barrier layers formed of GaN layers having a thickness of 10 nm and three layers of well layers formed of Ga _0.85 In _0.15 N layers having a thickness of 3 nm. A multi-quantum well structure was adopted.

  Next, as the first electrode 461 on the other main surface ((000-1) plane) side of the n-type GaN crystal substrate, a Ti layer with a thickness of 200 nm, an Al layer with a thickness of 1000 nm, and a Ti layer with a thickness of 200 nm are formed. A layered structure formed of an Au layer having a thickness of 2000 nm was formed, and heated in a nitrogen atmosphere to form an n-side electrode having a diameter of 100 μm. On the other hand, as a second electrode 462 on the p-type GaN layer 432, a stacked structure formed of a 4 nm thick Ni layer and a 4 nm thick Au layer is formed and heated in an inert gas atmosphere, A p-side electrode was formed. After the laminated body was chipped into a 400 μm square, the p-side electrode was bonded to a conductor 482 with a solder layer 470 formed of AuSn. Further, the n-side electrode and the conductor 481 were bonded with a wire 490 to obtain a semiconductor device 400 having a configuration as an LED.

  The light output of the obtained LED (semiconductor device 400) was measured under the condition of an injection current of 20 mA using an integrating sphere. The relative intensity of the light output of the LED in this example when the intensity of the light output of the LED in Example 4 described later is 1.0 was 2.2. The results are summarized in Table 1.

(Examples 2-5, Comparative Examples 1-3)
In the above (1-2), colloidal silica (SiO ₂ ) abrasive having average particle diameter d ₁ of primary particles and average particle diameter d ₂ of secondary particles and d ₂ / d ₁ ratio shown in Table 1 as abrasive grains The n-type GaN crystal substrate is lapped and subjected to CMP in the same manner as in Example 1 except that a polishing slurry containing grains is used, and a semiconductor device is manufactured using the n-type GaN crystal substrate after CMP. The optical output of the obtained semiconductor device was measured. The intensity of the light output of the LED in Example 4 was set to 1.0, and the relative intensity of the light output of the LED in each Example and each Comparative Example was obtained. The results are summarized in Table 1.

In addition, the polishing slurry of each Example and each Comparative Example is a colloidal silica abrasive material in Example 2, Quatron PL-7H (SiO ₂ solid content 20 mass%) manufactured by Fuso Chemical Co., Ltd., and in Example 3, Fuso Chemical Quatron PL-7 manufactured by Kogyo Co., Ltd. (SiO ₂ solid content 20% by mass), Example 4 Quatron PL-3H manufactured by Fuso Chemical Industries, Ltd. (SiO ₂ solid content 20% by mass), and Example 5 Nissan Chemical Industries Ltd. using company Ltd. SNOWTEX PS-MO (SiO ₂ solid content 18 to 19 wt%), in Comparative examples 1 to 3, using a colloidal silica unassociated (SiO _2), both diluted in water The SiO ₂ solid content was 15% by mass. The pH and ORP of the polishing slurries of each Example and each Comparative Example were adjusted in the same manner as Example 1.

  As shown in Comparative Examples 1 to 3, the latent scratch density, surface roughness Ry, and surface roughness Ra of the n-type GaN crystal substrate subjected to CMP using a polishing slurry containing non-associated colloidal silica abrasive grains The LED fabricated using this n-type GaN crystal substrate did not emit light.

As shown in Examples 1 to 5, colloidal silica in which primary particles (average particle diameter d ₁ ) associate to form secondary particles (average particle diameter d ₂ ) and the ratio d ₂ / d ₁ is 1.6 or more. By carrying out CMP using a polishing slurry that contains abrasive grains, the pH value x and the ORP value y (mV) satisfy the relationship of −50x + 1000 ≦ y ≦ −50x + 1900, and the pH is 5 or less, the latent scratch density There 1 × 10 ³ lines / mm or less, the surface roughness Ry of 30nm or less and the surface roughness Ra was obtained following the n-type GaN crystal substrate 3 nm. In addition to the above conditions, in Example 1 using a polishing slurry containing colloidal silica abrasive grains having an average secondary particle size of 200 nm or more, an n-type crystal having a latent scratch density of 0 / mm A substrate was obtained. About Examples 1-5, all the LED produced using each n-type GaN crystal substrate light-emitted. In particular, the intensity of the light output of the LED increased as the latent scratch density of the n-type GaN substrate decreased.

(Examples 6 to 9)
Except that the polishing slurry having pH and ORP shown in Table 2 was used, mechanical polishing and CMP of the n-type GaN crystal substrate were performed in the same manner as in Example 1, and the semiconductor was formed using the n-type GaN crystal substrate after CMP. An LED as a device was produced, and the light output of the obtained LED was measured. The intensity of the light output of the LED in Example 4 was set to 1.0, and the relative intensity of the light output of the LED in each Example and each Comparative Example was obtained. The results are summarized in Table 2 together with Example 1.

The polishing slurry of each example uses the same colloidal silica abrasive as in Example 1, hydrochloric acid and trichloroisocyanuric acid (TCIA) as an oxidizing agent in Example 6, malic acid in Example 7 and Using trichloroisocyanuric acid (TCIA) which is an oxidizing agent, sodium carbonate (Na ₂ CO ₃ ) and oxidizing agent sodium dichloroisocyanurate (Na-DCIA) are used in Example 8, respectively. Adjusted to pH and ORP. In Example 9, no oxidizing agent, acid, base, or salt was added.

As shown in Examples 1 and 6 to 8, primary particles (average particle diameter d ₁ ) are associated to form secondary particles (average particle diameter d ₂ ), and the ratio d ₂ / d ₁ is 1.6 or more. Polishing slurry containing colloidal silica abrasive grains having d ₂ of 200 nm or more, pH value x and ORP value y (mV) satisfying a relationship of −50x + 1000 ≦ y ≦ −50x + 1900, and pH of 5 or less or 9 or more The n-type GaN crystal having a high polishing rate, efficiently having a latent flaw density of 1 × 10 ² / mm or less, a surface roughness Ry of 30 nm or less, and a surface roughness Ra of 3 nm or less A substrate was obtained. Moreover, the LED produced using each n-type GaN crystal substrate in Examples 1 and 6 to 8 provided high light output.

  In Examples 1 and 7, n-type GaN crystal substrates having a high polishing rate in CMP and a latent scratch density of 0 / mm were obtained. This is considered to be because the polishing effect is further enhanced because the polishing slurry contains an organic acid and / or a salt thereof and an oxidizing agent. Here, in the polishing slurry, citric acid which is a tricarboxylic acid and its sodium salt are included in the polishing slurry as organic acids and / or salts thereof for pH adjustment, and apple which is a dicarboxylic acid in Example 7. It turns out that it is preferable to use the carboxylic acid and / or its salt which contain two or more carboxyl groups as an organic acid and / or its salt since an acid is contained. Further, as apparent from comparison between Examples 1 and 6 to 8, the light output intensity of the LED increased as the latent scratch density, surface roughness Ry, and surface roughness Ra of the n-type GaN crystal substrate decreased.

  In Example 9, the relationship between the pH value x and the ORP value y (mV) was y ≦ −50x + 1000, and the polishing slurry having a pH of 7 was used. Therefore, the polishing rate was low, and the latent scar density was reduced less. Thus, an n-type GaN crystal substrate having a high surface roughness Ry and a high surface roughness Ra was obtained. The light output intensity of the LED using this n-type GaN crystal substrate was low.

(Examples 10 to 14)
The n-type GaN crystal (dopant: Si) grown by the HVPE method is sliced so as to form a main surface having the off angle of Table 2 with respect to the surface having the surface orientation shown in Table 3. Except for obtaining an n-type GaN crystal substrate having a diameter of 50 mm and a thickness of 0.5 mm, mechanical polishing and CMP of the n-type GaN crystal substrate were performed in the same manner as in Example 1. The results are summarized in Table 3 together with Example 1.

  As shown in Examples 1, 10, and 11, the off angle, which is the angle formed between the main surface of the n-type GaN substrate and the C-plane ((0001) plane) on the Ga atom plane side, is 0 °, 2 °, 5 °. As the thickness increases, the polishing speed increases, the latent scratch density becomes 0 / mm, and the surface roughness Ry and the surface roughness Ra can be further reduced. In addition, the M surface and the A surface, which have lower chemical durability than the C surface on the Ga atom surface side, have a high polishing speed and zero latent scratch density even when CMP is performed under the same conditions as in Example 1. / Mm, the surface roughness Ry and the surface roughness Ra can be further reduced. Furthermore, even if a polishing slurry having a higher pH and a lower ORP than that of Example 1 is used for the C surface on the N atom surface side with the lowest chemical durability, the polishing speed is large and the latent scratch density is 0. A surface having a low thickness / mm, surface roughness Ry, and surface roughness Ra is obtained.

(Examples 15 to 18)
In Example 1, as shown in Table 4, the n-type GaN crystal substrate after the CMP step was used as an acidic aqueous solution having a concentration of 0.5 N (hereinafter referred to as 0.5 N, the same applies) H ₂ SO ₄ aqueous solution or basic solution. Polishing with a 2N concentration (2N, hereinafter the same) KOH aqueous solution as an aqueous solution and / or washing with 1 MHz (1 × 10 ⁶ Hz) ultrasonic waves using pure water It was.

In the polishing step, referring to FIG. 3, the C-plane ((000-1) plane) on the N-atom plane side of the n-type GaN crystal substrate (Group III nitride crystal 1) after the CMP is applied. The ceramic crystal holder 31 was pasted with wax. A polishing pad 38 is installed on a surface plate 35 having a diameter of 380 mm installed in a polishing apparatus (not shown), and the polishing liquid 37 is supplied from the polishing liquid supply port 39 to the polishing pad 38, with the rotating shaft 35c as the center. The polishing pad 38 is rotated, and the n-type GaN crystal substrate (Group III nitride crystal 1) is pressed against the polishing pad 38 by placing a weight 34 on the crystal holder 31, while the GaN crystal substrate (Group III nitride crystal) is pressed. By rotating 1) around the rotation axis 31c of the crystal holder 11, the surface of the n-type GaN crystal (the C plane ((0001) plane) on the Ga atom plane side) was chemically mechanically polished. Here, a polyurethane suede pad (Supreme RN-R manufactured by Nitta Haas Co., Ltd.) was used as the polishing pad 38, and a stainless steel surface plate was used as the surface plate 35. The polishing pressure is 19.6 kPa (200 g / cm ² ) to 49 kPa (500 g / cm ² ), and the n-type GaN crystal substrate (Group III nitride crystal 1) and the polishing pad 38 are both rotated 30 times / min. 100 times / min, polishing time was 20 min.

  The ultrasonic cleaning step with pure water was performed by immersing the n-type GaN crystal substrate after the CMP step or after the polishing step in pure water and applying ultrasonic waves of 1 MHz to the pure water. The cleaning time was 20 min.

  Elemental analysis of impurities remaining on the surface of the n-type GaN crystal substrate after the polishing step or the pure water cleaning step was performed using TXRF (total reflection X-ray fluorescence analysis). The results are summarized in Table 4.

  As shown in Examples 1 and 17, impurities on the surface of the n-type GaN crystal substrate could be reduced by providing a pure water cleaning step after the CMP step. Further, as shown in Examples 1, 15, and 16, by providing the polishing step after the CMP step, impurities on the surface of the n-type GaN crystal substrate, particularly Si atom-containing material derived from colloidal silica abrasive grains during CMP Can be significantly reduced. Furthermore, as shown in Example 18, by providing a pure water cleaning step after the polishing step, impurities on the surface of the n-type GaN crystal substrate, in particular, K atom-containing materials derived from the polishing liquid during the polishing step are significantly reduced. We were able to.

  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.

It is a cross-sectional schematic diagram which shows the method of carrying out the chemical mechanical polishing of the surface of a group III nitride crystal in this invention. It is a schematic diagram which shows the shape of the abrasive grain in the polishing slurry concerning this invention. Here, (a) is a bowl-shaped abrasive grain, (b) is a block-shaped abrasive grain, and (c) is a chain-shaped abrasive grain. It is a cross-sectional schematic diagram which shows the method of polishing the surface of a group III nitride crystal using a polishing liquid in this invention. It is a cross-sectional schematic diagram which shows one Embodiment of the semiconductor device concerning this invention.

Explanation of symbols

1 Group III nitride crystal, 1a Work-affected layer, 11, 31 Crystal holder, 11c, 15c, 31c, 35c Rotating shaft, 14, 34 Weight, 15, 35 Surface plate, 16 Abrasive grain, 17 Polishing slurry, 18, 38 Polishing pad, 19 Polishing slurry supply port, 37 Polishing solution, 39 Polishing solution supply port, 400 Semiconductor device, 410 Group III nitride crystal substrate, 420 n-type semiconductor layer, 421 n-type GaN layer, 422 n-type Al _0.1 Ga _0.9 N layer, 430 p-type semiconductor layer, 431 p-type Al _0.2 Ga _0.8 N layer, 432 p-type GaN layer, 440 light-emitting layer, 450 III-nitride layer, 461 a first electrode, 462 a second electrode, 470 a solder Layer, 481, 482 conductor, 490 wire.

Claims (17)

A polishing slurry for chemically and mechanically polishing the surface of a group III nitride crystal,
The polishing slurry includes abrasive grains having a hardness equal to or lower than the hardness of the group III nitride crystal,
The abrasive grains are secondary particles associated with primary particles,
A polishing slurry, wherein a ratio d ₂ / d ₁ of the average particle diameter d ₂ of the secondary particles to the average particle diameter d ₁ of the primary particles is 1.6 or more. Policing slurry according to claim 1, wherein the average particle size d ₂ of the abrasive grains of the secondary particles is equal to or is 200nm or more.   The polishing slurry according to claim 1 or 2, wherein the shape of the abrasive grains is at least one of a bowl shape, a block shape, and a chain shape. The pH value x and the redox potential value y (mV) of the polishing slurry are expressed by the following equations (1) and (2).
y ≧ −50x + 1000 (1)
y ≦ −50x + 1900 (2)
The polishing slurry according to any one of claims 1 to 3, wherein any one of the above relationships is satisfied.   The polishing slurry according to any one of claims 1 to 4, wherein the polishing slurry has a pH of 5 or less or 9 or more.   The polishing slurry according to any one of claims 1 to 5, comprising the abrasive grains, an organic acid and / or a salt thereof, and an oxidizing agent. A surface treatment method for a group III nitride crystal using the polishing slurry according to any one of claims 1 to 6,
The surface treatment method is a group III nitride crystal surface treatment method including the step of preparing the polishing slurry and polishing the surface of the group III nitride crystal chemically and mechanically using the polishing slurry.   8. The surface treatment method for a group III nitride crystal according to claim 7, further comprising a step of cleaning the surface of the group III nitride crystal subjected to chemical mechanical polishing with pure water after the step of chemical mechanical polishing.   9. The method according to claim 8, further comprising: polishing the surface of the chemically mechanically polished group III nitride crystal using a polishing solution formed of an acidic aqueous solution or a basic aqueous solution after the chemical mechanical polishing step. The surface treatment method of the group III nitride crystal of description.   The surface of the group III nitride crystal according to claim 9, further comprising a step of washing the surface of the group III nitride crystal polished with the polishing liquid with pure water after the step of polishing with the polishing liquid. Processing method. A group III nitride crystal substrate obtained by the surface treatment method according to any one of claims 7 to 10,
A group III nitride crystal substrate in which the density of latent scratches by ultraviolet fluorescence observation or cathodoluminescence observation is 1 × 10 ³ pieces / mm or less.   The group III nitride crystal substrate according to claim 11, wherein the surface roughness Ry is 30 nm or less.   The group III nitride crystal substrate according to claim 11, wherein the surface roughness Ra is 3 nm or less.   The off-angle, which is an angle formed between the principal surface of the group III nitride crystal substrate and any one of the C, A, R, and S surfaces in the wurtzite structure, is 15 ° or less. The group III nitride crystal substrate according to any one of claims 11 to 13.   An III-nitride crystal with an epitaxial layer comprising one or more III-nitride layers formed by epitaxial growth on at least one main surface side of the III-nitride crystal substrate according to any one of claims 11 to 14. substrate.   A group III nitride crystal substrate according to any one of claims 11 to 14, and at least one group III nitride layer formed on at least one main surface side of the group III nitride crystal substrate. Including semiconductor devices.   A group III nitride crystal substrate according to any one of claims 11 to 14 is selected as a substrate for a semiconductor device, and one or more group III nitrides are formed on at least one main surface side of the group III nitride crystal substrate. A method of manufacturing a semiconductor device, comprising growing a layer.

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