JP5900079B2 - Polishing slurry, manufacturing method thereof, and manufacturing method of group 13 nitride substrate - Google Patents

Description

  The present invention relates to a polishing slurry having excellent chemical mechanical polishing properties and a method for producing a Group 13 nitride substrate using the polishing slurry.

  Nitride semiconductors such as GaN (gallium nitride) and AlN (aluminum nitride) have a large band gap, and the transition between bands is a direct transition type. It is useful as a material for relatively short wavelength light emitting devices such as high frequency and high power electronic devices such as high electron mobility transistors (HEMT) and heterojunction bipolar transistors (HBT). In these optical or electronic applications, a nitride semiconductor substrate having excellent crystallinity and a flat surface is required.

An ingot of a nitride semiconductor crystal that is a raw material for a nitride semiconductor substrate is usually sliced to a predetermined thickness, ground to a desired shape, and then subjected to a polishing process. The polishing step here is a step of reducing distortion of the crystal surface caused by slicing or grinding.
The polishing step is usually performed by dividing into rough polishing (lapping) and precision polishing (polishing). In precision polishing, which is the final stage of the polishing process, chemical mechanical polishing (hereinafter sometimes referred to as CMP) is generally performed. In CMP, a polishing agent and a polishing pad are usually used, and due to a synergistic effect of the chemical polishing effect and the mechanical polishing effect, a nano-order step on the crystal surface caused by rough polishing is removed, and the crystal surface is flattened. be able to.

  For example, the following techniques are known for abrasives used in CMP. Patent Document 1 describes a technique related to CMP on a GaN wafer or the like using an acidic CMP slurry composition (claim 108, etc.). Paragraph [0082] of the specification of the document states that the CMP process is performed in a slurry having a pH of more than 8 or an acidic liquid having a pH of less than 6, and the slurry contains an oxidant to increase the CMP rate. It is described that colloidal silica or alumina is used for the addition and CMP of the GaN wafer.

Patent Document 2 discloses a CMP technique for polishing the −c surface of a GaN layer using a polishing liquid containing potassium hydroxide (KOH) (Claim 4). In paragraph [0040] of the specification of the document, abrasive particles such as SiO ₂ (colloidal silica), CeO ₂ , Al ₂ O ₃ , MnO ₂ , potassium hydroxide (KOH) and the like are included as a CMP slurry. It describes that a dispersion obtained by dispersing in water is used.

  On the other hand, a technique that focuses on the state and shape of abrasive grains in an abrasive as described below is also known. Patent Document 3 discloses a polishing slurry for chemically mechanically polishing the surface of a group III nitride crystal, which includes secondary particles associated with primary particles as abrasive grains (claims). 1). Further, Patent Document 4 discloses a polishing abrasive grain characterized by mainly comprising particles having a roundness of 0.50 to 0.75 (Claim 1).

JP 2012-17259 A JP 2011-211097 A JP 2007-103457 A JP 2005-264057 A

CMP, which is the final polishing step in the surface processing of a nitride crystal substrate, has conventionally required a long time. In particular, in a nitride crystal substrate whose main surface is a Ga polar surface such as (0001) or (10-1-1) which is a chemically stable surface, there is a problem that a significantly long time is spent on CMP. It was. On the other hand, in today's nitride crystal substrate manufacturing process, it is required to reduce the time required for CMP and reduce the cost.
As a result of studying a polishing slurry used for CMP of a nitride crystal substrate, the present inventors have found that an acidic polishing slurry in which two or more kinds of abrasive grains having different average particle diameters are combined contains only one kind of abrasive grains. The present inventors have found that the polishing rate is extremely high as compared with the conventional method and that the time required for CMP can be shortened compared to the conventional method. As a result, for an alkaline polishing slurry, the polishing rate when two or more kinds of abrasive grains having different average particle diameters are combined is substantially the average value of each polishing rate when only one kind of abrasive grains is used. Considering this, it is a very unique phenomenon.
In addition, in the said patent document 1, there is no detailed description regarding the average particle diameter of an abrasive grain, and there is no description or suggestion regarding a polish rate at all. In the above-mentioned Patent Document 2, there is no detailed description regarding the average particle diameter of the abrasive grains. Patent Document 3 and Patent Document 4 disclose only the effect when secondary particles are used as abrasive grains, and there is no description regarding the effect of polishing slurry containing primary particles as abrasive grains.

  As a result of diligent efforts, the present inventors have found that the above problems can be solved by using an acidic polishing slurry containing two or more kinds of abrasive grains having different average particle diameters and water, and completed the present invention shown below. I let you.

(1) A polishing slurry for chemically mechanically polishing the surface of a Group 13 nitride crystal, comprising N types of abrasive grains having different average particle sizes (where N is an integer of 2 or more ) and water, The N kinds of abrasive grains have the same hardness, and in the N kinds of abrasive grains, the average grain diameter of the abrasive grains of the smallest average grain diameter is 10 to 50 nm, and the average grain diameter The average grain size of the abrasive grains having the largest particle size is 40 to 100 nm and more than twice the average grain diameter of the abrasive grains having the smallest average grain size. The total mass of the N kinds of abrasive grains is 100 A polishing slurry, characterized in that the ratio of the total mass of abrasive grains of the smallest average particle diameter when it is defined as mass% is 35 to 65 mass% and is acidic.
(2) A polishing slurry for chemical mechanical polishing the surface of a Group 13 nitride crystal, comprising N types of abrasive grains having different average grain sizes (where N is an integer of 2 or more) and water, The materials of the N types of abrasive grains are the same, and in the N types of abrasive grains, the average particle diameter of the type of abrasive grains having the smallest average particle diameter is 10 to 50 nm, and the average particle diameter The average grain size of the abrasive grains having the largest particle size is 40 to 100 nm and more than twice the average grain diameter of the abrasive grains having the smallest average grain size. The total mass of the N kinds of abrasive grains is 100 A polishing slurry, characterized in that the ratio of the total mass of abrasive grains of the smallest average particle diameter when it is defined as mass% is 35 to 65 mass% and is acidic.
(3) When the total mass of the N types of abrasive grains is 100 mass%, the ratio of the total mass of the abrasive grains of the smallest average particle diameter is 53 to 65 mass%, (1) or ( Polishing slurry as described in 2).
(4) The polishing slurry according to any one of (1) to (3), wherein each of the N types of abrasive grains contains an inorganic oxide as a main component.
(5) The polishing slurry according to any one of (1) to (4), wherein all of the N types of abrasive grains are colloidal silica.
(6) The polishing slurry according to any one of (1) to (5), wherein the N is 2.

  (7) A method for producing a polishing slurry according to any one of (1) to (6), wherein each N contains any one kind of abrasive grains selected from the N kinds of abrasive grains and water. Preparing a slurry of more than seeds;
  And a step of obtaining a mixture obtained by mixing the N or more kinds of slurries.
  (8) preparing a group 13 nitride crystal; and using the polishing slurry according to any one of (1) to (6), at least one of the group 13 nitride crystals prepared And a step of chemically mechanically polishing the surface. A method for producing a Group 13 nitride substrate.
  (9) A step of preparing a Group 13 nitride crystal, and a step of chemically mechanically polishing at least one surface of the prepared Group 13 nitride crystal using the polishing slurry of (A) below. A method for producing a Group 13 nitride substrate comprising: (A) N types of abrasive grains having different average particle diameters (where N is an integer of 2 or more) and water, and the N types of abrasives The hardness of each of the grains is equal to or less than the hardness of the Group 13 nitride crystal, and in the N kinds of abrasive grains, the average grain diameter of the abrasive grains having the smallest average grain diameter is 10 to 50 nm. The average grain size of the abrasive grains having the largest average grain size is 40 to 100 nm and at least twice the average grain diameter of the abrasive grains having the smallest average grain size. Kind with the smallest average particle diameter when the total mass of the grains is 100% by mass Ratio of the total mass of the abrasive grains is 35 to 65 wt%, and an acidic, polishing slurry.

  According to the present invention, by including two or more kinds of abrasive grains having different average particle diameters, the interaction between different kinds of abrasive grains as compared with a conventional polishing slurry containing only one kind of abrasive grains having an average particle diameter. Can exhibit excellent chemical mechanical polishing properties.

It is the bar graph which compared the polishing rate of the polishing slurry of Example 1-Example 3, Comparative Example 1-Comparative Example 3, and Reference Example 1-Reference Example 2.

1. Polishing slurry The polishing slurry of the present invention is a polishing slurry for chemically mechanically polishing the surface of a Group 13 nitride crystal, and contains two or more kinds of abrasive grains having different average particle diameters and water, and is acidic. It is characterized by being. Specifically, it is preferably a polishing slurry prepared by mixing two or more kinds of slurries that are abrasive slurries and water and that have different average particle diameters. Usually, a slurry containing abrasive grains used for polishing is prepared so that the abrasive grains have a predetermined particle size distribution and an average particle diameter. Here, the average particle size of the abrasive grains is calculated by the average particle size obtained by the BET method or the mode diameter or the median diameter when the distribution is obtained by a method such as the dynamic light scattering method. It is preferable to employ the average particle size determined by

In the present invention, the group 13 nitride crystal is represented by, for example, a Ga _x Al _y In _1-xy N crystal (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), specifically, gallium nitride, Aluminum nitride, indium nitride, or a mixed crystal thereof such as aluminum gallium nitride and indium gallium nitride can be given. The plane index of the main surface of the group 13 nitride crystal is not particularly limited, and examples thereof include a polar surface such as a C surface; a nonpolar surface such as an A surface and an M surface; a semipolar surface;
In the present invention, a crystal having a surface on which an epitaxial layer is formed in order to form a semiconductor element is referred to as a substrate. In general, morphological processing such as slicing and grinding is performed from an as-grown crystal to obtain a substrate, but in the present invention, a substrate in the middle of processing is not called a substrate but called a crystal.

The abrasive used in the present invention is not particularly limited as long as it contains a material usually used for CMP of a group 13 nitride crystal. Two or more kinds of abrasive grains are used in the present invention, but each abrasive grain may contain a material having the same hardness, or may contain a material having a different hardness. From the viewpoint of efficient CMP and less wear between abrasive grains during CMP, the abrasive grains used in the present invention preferably contain materials of the same hardness, and more preferably contain the same materials.
Only two types of abrasive grains used in the present invention may be used, or three or more types may be combined. The number of abrasive grains is preferably 10 or less, more preferably 5 or less.

Each of the abrasive grains used in the present invention preferably has a hardness equal to or lower than the hardness of the group 13 nitride crystal. This is because, when polishing the surface of the group 13 nitride crystal, scratches and latent scratches generated by grinding and rough polishing can be reduced without generating new scratches and latent scratches.
In the present invention, hardness refers to mechanical strength. Therefore, in addition to what is generally known as hardness (so-called scratch strength) such as so-called Mohs hardness and Vickers hardness, fracture strength (fracture energy), shear stress, yield stress, etc. are also included in the hardness in the present invention. .

Each abrasive grain used in the present invention is not particularly limited as long as it preferably has a hardness equal to or lower than that of the group 13 nitride crystal, but it is relatively easy to obtain and easy to handle. It is preferable that inorganic fine particles are the main component. Examples of inorganic fine particles include SiO ₂ , Al ₂ O ₃ , CeO ₂ , TiO ₂ , MgO, MnO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , NiO, ZnO, CoO ₂ , Co ₃ O ₄ , CuO, Examples thereof include fine particles containing at least one material selected from the group consisting of Cu ₂ O, GeO ₂ , CaO, Ga ₂ O ₃ , and In ₂ O ₃ . Among these materials, it is preferable to include at least one material selected from the group consisting of SiO ₂ , Al ₂ O ₃ , and TiO ₂ , and it is more preferable to include colloidal silica.

In the polishing slurry according to the present invention, excellent chemical mechanical polishing characteristics are exhibited by the interaction between two or more kinds of abrasive grains having different average grain diameters as compared with the case of using each kind of abrasive grains one by one. be able to.
The average particle diameter of the abrasive grains used in the present invention is calculated by a conventional method before mixing. Examples of the method for calculating the average particle diameter of the particles include a method using a BET method, a dynamic light scattering method, TEM observation, or SEM observation.
An example of a method for calculating the average particle diameter by the BET method is as follows. First, as described in JIS H7008 6026, from the relationship between the pressure of an adsorbed gas such as nitrogen gas and the adsorbed amount, the monomolecular adsorbed amount is measured using the BET equation to determine the specific surface area. Next, from the determined specific surface area and the specific gravity (true specific gravity) of the abrasive grains, it is possible to determine the average particle diameter when the abrasive grains are assumed to be spherical.
Dynamic light scattering is a technique for determining the particle size and particle size distribution from the intensity of the Brownian motion of colloidal particles. Specifically, the fluctuation of the light scattering generated by applying laser light to the particles. The particle size distribution is measured by a commercially available particle size distribution measuring device, and the average particle size is calculated by the mode diameter or the median diameter.
The example of the method of calculating an average particle diameter by TEM observation or SEM observation is as follows. First, in a TEM (transmission electron microscope) image or SEM (scanning electron microscope) image at an appropriate magnification (for example, 1,000 to 1,000,000 times), for a certain particle, the particle is spherical. Calculate the particle size when considered. The calculation of the particle size by such TEM observation or SEM observation is performed for a predetermined number of particles of the same type (for example, 100 to 10,000 particles), and the average of each particle is defined as the average particle size.

  The grain size of the abrasive grains usually has a predetermined grain size distribution, and the histogram of the grain size distribution of abrasive grains having only one type of average grain size shows one peak. The polishing slurry according to the present invention may have, for example, two or more peaks (frequency) in the histogram of the particle size distribution for all abrasive grains contained in the polishing slurry. By having at least two frequency peaks in the histogram in this way, it can be estimated that the polishing slurry contains two types of abrasive grains having different average particle diameters. In addition, the interval of the horizontal axis (particle diameter) in the histogram is, for example, 1 to 10 nm. In addition, the particle diameter corresponding to the frequency peak is not necessarily the average particle diameter itself.

Of the two or more types of abrasive grains used in the present invention, the average grain size of the abrasive grains having the largest average grain diameter (hereinafter sometimes referred to as large abrasive grains) is preferably 40 to 100 nm. . When the average grain size of the large abrasive grains exceeds 100 nm, the abrasive grains tend to settle and the role as a polishing liquid may not be fulfilled. When the average grain size of the large abrasive grains is less than 40 nm, the difference in average grain size with the small abrasive grains becomes too small, so that the excellent chemical mechanical polishing effect due to the interaction between the different abrasive grains is sufficient. There is a possibility that you cannot enjoy.
The average particle size of the large abrasive grains is more preferably 50 to 95 nm, and further preferably 60 to 90 nm.

Of the two or more types of abrasive grains used in the present invention, the average grain size of the abrasive grains having the smallest average grain size (hereinafter sometimes referred to as small abrasive grains) is preferably 10 to 50 nm. . When the average grain size of the small abrasive grains exceeds 50 nm, the difference in average grain size from the large abrasive grains becomes too small, so that the excellent chemical mechanical polishing effect due to the interaction between different abrasive grains is sufficient. There is a possibility that you cannot enjoy. Even when the average grain size of the small abrasive grains is less than 10 nm, the abrasive grains themselves become too small and the polishing action may be reduced.
The average particle size of the small abrasive grains is more preferably 12 to 40 nm, and further preferably 15 to 30 nm.

The average grain size of the large abrasive grains is preferably at least twice that of the small abrasive grains. When the average grain size of the large abrasive grains is less than twice the average grain size of the small abrasive grains, the overlap between the grain size distribution of the large abrasive grains and the grain size distribution of the small abrasive grains becomes too large. There is a possibility that the excellent chemical mechanical polishing effect due to the interaction between them cannot be fully enjoyed.
The average particle size of the large abrasive grains is more preferably 2.5 times or more, and more preferably 3 to 5 times the average particle size of the small abrasive grains.

  When three or more types of abrasive grains are used, the average grain size of abrasive grains other than large abrasive grains and small abrasive grains (hereinafter sometimes referred to as medium abrasive grains) is less than the average grain diameter of large abrasive grains. And there is no restriction | limiting in particular except exceeding the average particle diameter of a small abrasive grain. However, either the relationship between the size of large abrasive grains and the size of medium abrasive grains, or the relationship between the size of large abrasive grains and small abrasive grains, or the relationship between the sizes of medium abrasive grains and small abrasive grains, It is preferable to be under the above-mentioned suitable conditions.

The content rate of each abrasive grain is not specifically limited, What is necessary is just to adjust suitably with CMP conditions. In this invention, it is preferable that the ratio of the total mass of a small abrasive grain is 35-65 mass% when the total mass of 2 or more types of abrasive grains contained in a slurry is 100 mass%. When the ratio of the total mass of the small abrasive grains is less than 35 mass% or exceeds 65 mass%, the ratio of the small particle diameter is too small or too large, so that excellent chemistry due to the interaction between different kinds of abrasive grains There is a possibility that the effect of mechanical polishing cannot be fully enjoyed.
In the present invention, when the total mass of two or more kinds of abrasive grains contained in the slurry is 100 mass%, the ratio of the total mass of the small abrasive grains is more preferably 37 to 64 mass%, More preferably, it is -63 mass%.

Since the polishing slurry according to the present invention is acidic, the interaction between two or more kinds of abrasive grains having different average particle diameters is extremely effectively exhibited as compared with an alkaline slurry or a neutral slurry.
The acidic polishing slurry according to the present invention is preferably obtained by dispersing the above-described two or more kinds of abrasive grains in an aqueous dispersant. The acidic polishing slurry according to the present invention may contain an additive that can be normally used for CMP. There are no particular limitations on the concentration of the abrasive grains and additives, and the concentration may be adjusted as appropriate according to the CMP conditions.
The polishing slurry according to the present invention has a pH of less than 7, preferably 6 or less, more preferably 4 or less. As the polishing slurry according to the present invention, it is preferable to use a slurry having good dispersion stability in an acidic aqueous solution.

When an inorganic oxide is used as the abrasive grains, the properties as an acidic polishing slurry can be kept good by subjecting the abrasive grains to a surface treatment so that they are acidic when dispersed in water. The property as an acidic polishing slurry here is, for example, excellent dispersibility in an acidic aqueous medium. For example, when colloidal silica produced by a water glass method is used as abrasive grains, it contains a base such as an alkali metal and exhibits alkalinity, but it can be made acidic by applying a cation exchange treatment.
Here, as long as it has a dispersibility in the acidic aqueous medium as described above, it may be an acidic polishing slurry or may contain alkaline impurities. Specifically, the concentration is 0.1% or less. May be included. The term “alkaline impurities” as used herein refers to substances or ions that exhibit alkalinity by reacting with water, such as alkali metals, alkaline earth metals, or ions thereof.

The polishing slurry according to the present invention is preferably one that can be confirmed to be acidic by the following test method, for example.
First, a polishing slurry is added to an acidic (less than pH 7) aqueous solution and dispersed by appropriately stirring. Next, the acidic aqueous solution is allowed to stand at room temperature (15 to 30 ° C.) for 1 week. One week later, an acidic aqueous solution is visually confirmed, and if the abrasive grains maintain the original dispersed state, they are included in the present invention as an acidic polishing slurry. If a neutral or alkaline polishing slurry is put into an acidic aqueous solution, it is considered that the slurry is agglomerated after being left for one week and the original dispersibility cannot be maintained.
As a method for confirming the dispersion state, in addition to visual confirmation, for example, a dynamic light scattering method, measurement of particle size distribution with a particle size distribution meter, and the like can be mentioned.
In addition, as another method for confirming whether or not the polishing slurry is acidic, for example, the polishing slurry is appropriately diluted with water and dispersed, and the dispersion liquid can be dispersed with litmus paper, pH test paper, pH indicator, pH meter, or the like. The method of measuring pH is mentioned.

The polishing slurry according to the present invention can be produced by a known method. As an example of the manufacturing method of the polishing slurry used in the present invention, two or more kinds of acidic slurries containing only one kind of abrasive grains and having different average grain diameters of abrasive grains are prepared, The method of preparing by mixing so that it may become a ratio and dispersing suitably is mentioned. That is, it is preferably a polishing slurry prepared by mixing two or more kinds of slurries that are abrasive slurries and water and that have different average particle diameters. In this case, each slurry is preferably an acidic slurry. The acidity here can be confirmed in the same manner as in the case of the acidic polishing slurry described above. The pH of each slurry is less than 7, preferably 6 or less, more preferably 4 or less.
In two or more kinds of slurries having different average particle diameters of abrasive grains, the grain diameter of the abrasive grains contained in each slurry usually has a width of the grain diameter. The width of the particle size of each slurry is preferably ± 30 nm of the average particle size, more preferably ± 20 nm, and particularly preferably ± 10 nm.
The polishing slurry according to the present invention may be used for CMP as it is, or may be used by appropriately adjusting the concentration, pH, etc. of the abrasive grains by appropriately adding a predetermined amount of additives according to the CMP conditions. Good. The additive will be described later.

2. A method for producing a Group 13 nitride substrate of the present invention includes a step of preparing a Group 13 nitride crystal, two or more kinds of abrasive grains having different average grain sizes, and water, And a step of preparing an acidic polishing slurry, and a step of chemically mechanically polishing at least one surface of the Group 13 nitride crystal using the polishing slurry to obtain a Group 13 nitride substrate. It is characterized by having.

  The present invention includes (1) a step of preparing a group 13 nitride crystal, (2) a step of preparing a polishing slurry, and (3) a chemical mechanical polishing step. The present invention is not necessarily limited to only the above three steps, and may include, for example, a slicing step, a grinding step, a cleaning step and the like as described later in addition to the above three steps.

The Group 13 nitride crystal can be prepared by a known method. As the group 13 nitride crystal, a crystal grown in advance may be used, or a commercially available one may be used.
The polishing slurry used in the present invention is the same as the above-described acidic polishing slurry according to the present invention. As described above, the polishing slurry used in the present invention may be used for CMP as it is, or may be used for CMP after adjusting the concentration and dispersibility of abrasive grains by appropriately adding additives.
The additive is not particularly limited as long as it does not excessively damage the crystal to be polished while improving the efficiency of chemical mechanical polishing in cooperation with the polishing slurry. For example, phosphoric acid, nitric acid, peroxide Examples thereof include acids such as hydrogen water, hydrochloric acid, and sulfuric acid, and mixtures of these acids.
The additive may be added to the polishing slurry, or may be added directly to the polishing portion together with the polishing slurry.

  In general, the group 13 nitride substrate is obtained by processing, such as slicing, grinding, and polishing, using as-grown crystal as a raw material. The chemical mechanical polishing step in the present invention is usually performed after the as-grown crystal is sliced, the side surfaces are beveled, and the back surface and the surface are subjected to processing such as grinding, etching, and rough polishing (lapping) as necessary. This is performed for a group 13 nitride crystal. A known method may be employed for the processing from slicing to rough polishing, and the processing method and order are not particularly limited. Further, the above-described processing from slicing to rough polishing is merely an example, and the chemical mechanical polishing step of the present invention is not necessarily applied to crystals that have been subjected to all of these processing.

CMP can be performed using a known method. For example, a polishing slurry is added between the surface of the group 13 nitride crystal to be polished and the polishing pad attached to the polishing surface plate. Then, a method of polishing the surface while holding the crystal at a predetermined pressure can be mentioned. The material of the polishing pad may be a known material, and examples thereof include polyurethane.
The polishing speed is not particularly limited, and in the case of polishing by rotation, the rotation speed is usually 50 to 200 rpm.
The pressure at the time of disposing the crystal so as to face the polishing platen is not particularly limited, but is preferably 300 to 1,500 g / cm ² . When the pressure is less than 300 g / cm ² , sufficient polishing does not proceed and the polish rate may not be improved. On the other hand, when the pressure exceeds 1,500 g / cm ² , the pressure is too high, which may cause extreme wear on the polishing pad. The plate surface to which the crystal is attached is preferably flat in order to obtain a substrate having a uniform thickness after polishing.
More preferably, the pressure in the chemical mechanical polishing process is 500~1,400g / cm ^2, further preferably 700~1,300g / cm ^2.

When the polishing platen is used, the relative speed between the group 13 nitride crystal and the polishing platen in the chemical mechanical polishing step is preferably 1 to 3 m / s. When the relative speed is less than 1 m / s, sufficient polishing does not proceed and the polish rate may not be improved. On the other hand, when the relative speed exceeds 3 m / s, the polishing speed is too high, and there is a possibility that extreme wear occurs on the polishing pad.
The relative speed between the group 13 nitride crystal and the polishing platen in the chemical mechanical polishing step is more preferably 1.3 to 2.8 m / s, and more preferably 1.5 to 2.5 m / s. Is more preferable.

The execution time of CMP can be appropriately adjusted depending on the CMP conditions, but it is preferable to carry out until the polishing scratches due to rough polishing are eliminated. Elimination of polishing scratches can be confirmed by observation with a fluorescent microscope or CL (cathode luminescence method). Considering productivity, the CMP time is preferably 10 hours or less, and more preferably 5 hours or less.
The surface roughness Rms of the Group 13 nitride substrate after the CMP is preferably less than 3 nm, more preferably 1 nm or less, and further preferably 0.1 nm or less.

  The Group 13 nitride substrate obtained by the production method of the present invention is a product through a cleaning process usually performed after polishing.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited only to these examples.

1. Production of GaN substrate [Example 1]
First, the Ga face of an as-grown GaN crystal having a diameter of 2 inches was attached to a plate with wax, and the N face of the GaN crystal was ground until it became flat. Next, the GaN crystal was peeled from the plate, and the N surface was etched with a 120 ° C. aqueous KOH solution to remove grinding damage. Subsequently, the N face of the GaN crystal was attached to the plate with wax, and the Ga face of the GaN crystal was ground until it became flat. The outer periphery of the GaN crystal was ground to adjust the shape to a circle.
Next, four types of diamond slurries having different average particle diameters were used, and lapping of the GaN crystals was performed in four steps using the diamond slurries having a large average particle diameter in order. The average particle diameter of the diamond slurry was 3 μm, 1 μm, 1/2 μm, and 1/4 μm for each stage.

Using polishing slurry A, CMP of GaN crystals was performed. Polishing slurry A includes abrasive grains having an average particle size of 80 nm determined by the BET method (acidic colloidal silica, particle size width: 70 to 100 nm) and abrasive particles having an average particle size of 20 nm determined by the BET method ( Acidic colloidal silica, particle size width: 20-25 nm) (abrasive grains having an average particle diameter of 80 nm): (abrasive grains having an average particle diameter of 20 nm) = 47% by mass: 53% by mass, Moreover, it is an acidic colloidal silica slurry using water as a dispersion medium. The pH of the polishing slurry A is 2.
Polishing slurry A, nitric acid, phosphoric acid, and hydrogen peroxide water were added in predetermined amounts to a polishing platen (plate diameter: φ500 mm). The content ratio of SiO _{2 in} the polishing slurry on the polishing platen was 32.8% by mass. The urethane pad affixed to the polishing platen and the C surface of the GaN crystal face each other, and CMP is performed under the conditions of a pressure of 1,000 g / cm ² and a pad / plate relative speed of 1.6 m / s. A substrate was manufactured. The polishing rate was 0.41 μm / h. Moreover, when Rms was measured in the range of 10 μm × 10 μm by AFM, it was 0.09 nm, and an atomic step could be confirmed.

[Example 2]
As in Example 1, the GaN crystal was ground and lapped.
Using polishing slurry B, GaN crystals were subjected to CMP. Polishing slurry B includes abrasive grains having an average particle size of 80 nm determined by the BET method (acidic colloidal silica, particle size width: 70 to 100 nm) and abrasive particles having an average particle size of 20 nm determined by the BET method ( Acidic colloidal silica, particle size width: 20 to 25 nm) (abrasive grains having an average particle diameter of 80 nm): (abrasive grains having an average particle diameter of 20 nm) = 37% by mass: 63% by mass, Moreover, it is an acidic colloidal silica slurry using water as a dispersion medium. The pH of the polishing slurry B is 2.
Polishing slurry B and nitric acid, phosphoric acid, and hydrogen peroxide water were added in predetermined amounts to a polishing platen (platen diameter: φ500 mm). The content ratio of SiO _{2 in} the polishing slurry on the polishing platen was 33.2% by mass. The urethane pad affixed to the polishing surface plate and the C surface of the GaN crystal face each other, and CMP was performed under the same pressure and pad / plate relative speed conditions as in Example 1 to manufacture the GaN substrate of Example 2. . The polishing rate was 0.28 μm / h.

[Example 3]
As in Example 1, the GaN crystal was ground and lapped.
Using polishing slurry C, GaN crystals were subjected to CMP. Polishing slurry C includes abrasive grains having an average particle size determined by the BET method of 80 nm (acidic colloidal silica, particle size width: 70 to 100 nm) and abrasive grains having an average particle size of 20 nm determined by the BET method ( Acidic colloidal silica, particle size width: 20 to 25 nm) (abrasive grains having an average particle diameter of 80 nm): (abrasive grains having an average particle diameter of 20 nm) = 57% by mass: 43% by mass, Moreover, it is an acidic colloidal silica slurry using water as a dispersion medium. The pH of the polishing slurry C is 2.
A predetermined amount of polishing slurry C, nitric acid, phosphoric acid, and hydrogen peroxide water were added to a polishing platen (platen diameter: φ500 mm). The content ratio of SiO _{2 in} the polishing slurry on the polishing platen was 32.4% by mass. The urethane pad affixed to the polishing surface plate and the C surface of the GaN crystal were made to face each other, and CMP was performed under the same pressure and pad / plate relative speed conditions as in Example 1 to manufacture the GaN substrate of Example 3. . The polishing rate was 0.27 μm / h.

[Comparative Example 1]
As in Example 1, the GaN crystal was ground and lapped.
Using the polishing slurry a, CMP of the GaN crystal was performed. The polishing slurry a is an acidic colloidal silica slurry containing abrasive grains (acidic colloidal silica, particle size width: 70 to 100 nm) having an average particle diameter of 80 nm determined by the BET method and water. The polishing slurry a has a pH of 2.
A predetermined amount of polishing slurry a, nitric acid, phosphoric acid, and aqueous hydrogen peroxide were added to a polishing platen (platen diameter: φ500 mm). The content ratio of SiO _{2 in} the polishing slurry on the polishing platen was 30.7% by mass. The urethane pad affixed to the polishing platen and the C surface of the GaN crystal were made to face each other, and CMP was performed under the same pressure and pad / plate relative speed conditions as in Example 1 to produce a GaN substrate of Comparative Example 1. . The polishing rate was 0.15 μm / h.

[Comparative Example 2]
As in Example 1, the GaN crystal was ground and lapped.
Using the polishing slurry b, CMP of GaN crystals was performed. The polishing slurry b is an acidic colloidal silica slurry containing abrasive grains (acid colloidal silica, particle size width: 20 to 25 nm) having an average particle diameter determined by the BET method of 20 nm and water. The pH of the polishing slurry b is 2.
A predetermined amount of the polishing slurry b, nitric acid, phosphoric acid, and aqueous hydrogen peroxide was added to a polishing surface plate (surface plate diameter: φ500 mm). The content ratio of SiO _{2 in} the polishing slurry on the polishing platen was 34.9% by mass. The urethane pad affixed to the polishing platen and the C surface of the GaN crystal were made to face each other, and CMP was performed under the same pressure and pad / plate relative speed conditions as in Example 1 to produce a GaN substrate of Comparative Example 2. . The polishing rate was 0.12 μm / h.

[Comparative Example 3]
As in Example 1, the GaN crystal was ground and lapped.
Using polishing slurry c, GaN crystals were subjected to CMP. The polishing slurry c comprises abrasive grains (alkaline colloidal silica) having an average particle diameter determined by the BET method of 80 nm and abrasive grains (alkaline colloidal silica) having an average particle diameter determined by the BET method of 40 nm (average). Abrasive grains having a particle diameter of 80 nm): (Abrasive grains having an average particle diameter of 40 nm) = 50% by mass: An alkaline colloidal silica slurry containing 50% by mass and containing water as a dispersion medium. The pH of the polishing slurry c is 10.
A predetermined amount of polishing slurry c, nitric acid, phosphoric acid, and aqueous hydrogen peroxide were added to a polishing platen (platen diameter: φ500 mm). The content ratio of SiO _{2 in} the polishing slurry on the polishing platen was 30.0% by mass. The urethane pad affixed to the polishing platen and the C surface of the GaN crystal face each other, and CMP was performed under the same pressure and pad / plate relative speed conditions as in Example 1 to produce a GaN substrate of Comparative Example 3. . The polishing rate was 0.22 μm / h.

[Reference Example 1]
As in Example 1, the GaN crystal was ground and lapped.
Using the polishing slurry d, CMP of GaN crystals was performed. The polishing slurry d is an alkaline colloidal silica slurry containing abrasive grains (alkaline colloidal silica) having an average particle diameter of 80 nm determined by the BET method and water. The pH of the polishing slurry d is 10.
A predetermined amount of polishing slurry d, nitric acid, phosphoric acid, and aqueous hydrogen peroxide were added to a polishing platen (platen diameter: φ500 mm). The content ratio of SiO _{2 in} the polishing slurry on the polishing platen was 30.0% by mass. The urethane pad affixed to the polishing platen and the C surface of the GaN crystal face each other, and CMP was performed under the same pressure and pad / plate relative speed conditions as in Example 1 to manufacture the GaN substrate of Reference Example 1. . The polishing rate was 0.15 μm / h.

[Reference Example 2]
As in Example 1, the GaN crystal was ground and lapped.
Using the polishing slurry e, CMP of the GaN crystal was performed. The polishing slurry e is an alkaline colloidal silica slurry containing abrasive grains (alkaline colloidal silica) having an average particle diameter determined by the BET method of 40 nm and water. The pH of the polishing slurry d is 10.
A predetermined amount of polishing slurry e, nitric acid, phosphoric acid, and aqueous hydrogen peroxide were added to a polishing platen (platen diameter: φ500 mm). The content ratio of SiO _{2 in} the polishing slurry on the polishing platen was 30.0% by mass. The urethane pad affixed to the polishing platen and the C surface of the GaN crystal face each other, and CMP was performed under the same pressure and pad / plate relative speed conditions as in Example 1 to manufacture the GaN substrate of Reference Example 2. . The polishing rate was 0.38 μm / h.

2. Discussion FIG. 1 is a bar graph comparing the polishing rates of the polishing slurries of Example 1 to Example 3, Comparative Example 1 to Comparative Example 3, and Reference Example 1 to Reference Example 2.
As can be seen from FIG. 1, in Comparative Examples 1 and 2 using only one type of acidic colloidal silica abrasive, the polish rate remains at 0.15 μm / h or less. On the other hand, in Example 1 to Example 3 using two types of acidic colloidal silica abrasive grains having different average particle diameters, the polish rate is 0.27 μm / h or more. From these results, CMP with a combination of two types of acidic colloidal silica abrasive grains has a polishing rate difference of 0.12 μm / h or more as compared with CMP using only one type of acidic colloidal silica abrasive grains. I understand.

On the other hand, as can be seen from FIG. 1, the polishing rate of Comparative Example 3 using two kinds of alkaline colloidal silica abrasive grains having different average particle diameters in a mass ratio of 1: 1 is the abrasive grains of alkaline colloidal silica. The polishing rate of Reference Example 1 and Reference Example 2 using only one type was almost the average value.
From the above results, even when two or more kinds of alkaline colloidal silica abrasive grains are used in combination, the polishing rate of conventional CMP using only one kind of alkaline colloidal silica abrasive grains cannot be exceeded. It can be seen that when the acidic colloidal silica abrasive grains are used in combination, the chemical mechanical polishing property is dramatically improved as compared with the conventional CMP using only one kind of acidic colloidal silica abrasive grains. Although the details of this excellent chemical mechanical polishing property are unknown, it is presumed to be due to the interaction between different kinds of abrasive grains in the acidic polishing slurry.

Claims (9)

A polishing slurry for chemical mechanical polishing the surface of a Group 13 nitride crystal,
N types of abrasive grains having different average particle diameters (where N is an integer of 2 or more ) and water,
The N types of abrasive grains have the same hardness,
In the N kinds of abrasive grains, the average grain diameter of the abrasive grains of the smallest average grain diameter is 10 to 50 nm, and the average grain diameter of the abrasive grains of the largest average grain diameter is 40 to 100 nm. And the average particle size is at least twice the average particle size of the smallest type of abrasive grains,
When the total mass of the N types of abrasive grains is 100 mass%, the ratio of the total mass of the abrasive grains of the smallest average particle size is 35 to 65 mass%, and
It is characterized by being acidic,
Polishing slurry.   A polishing slurry for chemical mechanical polishing the surface of a Group 13 nitride crystal,
  N types of abrasive grains having different average particle diameters (where N is an integer of 2 or more) and water,
  The materials of the N types of abrasive grains are the same,
  In the N kinds of abrasive grains, the average grain diameter of the abrasive grains of the smallest average grain diameter is 10 to 50 nm, and the average grain diameter of the abrasive grains of the largest average grain diameter is 40 to 100 nm. And the average particle size is at least twice the average particle size of the smallest type of abrasive grains,
  When the total mass of the N types of abrasive grains is 100 mass%, the ratio of the total mass of the abrasive grains of the smallest average particle size is 35 to 65 mass%, and
  It is characterized by being acidic,
  Polishing slurry.   The ratio of the total mass of the abrasive grains having the smallest average particle diameter when the total mass of the N types of abrasive grains is 100 mass% is 53 to 65 mass%. Or the polishing slurry according to 2. The polishing slurry according to any one of claims 1 to 3, wherein each of the N types of abrasive grains contains an inorganic oxide as a main component.   The polishing slurry according to any one of claims 1 to 4, wherein all of the N types of abrasive grains are colloidal silica.   The polishing slurry according to any one of claims 1 to 5, wherein N is 2.   A method for producing a polishing slurry according to any one of claims 1 to 6,
  Preparing N or more types of slurry each containing any one kind of abrasive grains selected from the N types of abrasive grains and water;
  And a step of obtaining a mixture obtained by mixing the N or more kinds of slurries. A step of preparing a Group 13 nitride crystal,
Using polishing slurry according to any one of claims 1 to 6, characterized in that it and a step of chemical mechanical polishing at least one surface of the prepared Group 13 nitride crystal The manufacturing method of the group 13 nitride substrate.   Preparing a Group 13 nitride crystal;
  Chemical mechanical polishing of at least one surface of the prepared group 13 nitride crystal using the polishing slurry of (A) below;
  A method for producing a group 13 nitride substrate, comprising:
  (A) N types (where N is an integer of 2 or more) abrasive grains and water having different average particle diameters,
  The hardness of the N types of abrasive grains is less than or equal to the hardness of the group 13 nitride crystal,
  In the N kinds of abrasive grains, the average grain diameter of the abrasive grains of the smallest average grain diameter is 10 to 50 nm, and the average grain diameter of the abrasive grains of the largest average grain diameter is 40 to 100 nm. And the average particle size is at least twice the average particle size of the smallest type of abrasive grains,
  When the total mass of the N types of abrasive grains is 100 mass%, the ratio of the total mass of the abrasive grains of the smallest average particle size is 35 to 65 mass%, and
  Polishing slurry that is acidic.

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