JP2014068044A - Substrate and light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate capable of quick polishing, and a light emitting element.SOLUTION: A substrate 10 comprises a surface whose arithmetic mean roughness Ra is 0.1 nm≤Ra≤3.0 nm and whose depth D of a deepest scratch is 2 nm≤D≤90 nm. Also, a roll-off amount dx in a direction parallel to the substrate surface is 10 μm≤dx≤500 μm, and a roll-off amount dz in a direction vertical to the substrate surface is 5 nm≤dz≤2,500 μm.

Description

  The present invention relates to a substrate and a light-emitting element, and more particularly to a substrate made of a group III nitride material and a light-emitting element formed using the substrate.

  Since gallium nitride (GaN) has a band gap in the ultraviolet region, it is used in semiconductor lasers that oscillate light of short wavelengths such as blue and ultraviolet light. In recent years, as a method for producing a GaN crystal, a method of homoepitaxially growing GaN on a GaN substrate is becoming mainstream. Therefore, the GaN substrate is expected to play an important role in various semiconductor devices using GaN crystals such as light emitting elements.

  A GaN substrate is usually manufactured by grinding an outer periphery of an ingot into a predetermined shape and then cutting a wafer from the ingot with a desired thickness. Further, after cutting out, the surface of the GaN substrate is planarized by grinding or polishing so that it can be epitaxially grown (epi-ready state). When flattening the surface of the GaN substrate, first, coarse polishing is performed using abrasive grains having a relatively large particle diameter (particle diameter r> 1 μm), and then small abrasive grains (particle diameter r ≦ 1 μm) are used. And finish polishing. Rough polishing is aimed mainly at cutting, whereas final polishing is aimed at flattening the surface.

  Here, chemical mechanical polishing (CMP) and mechanical polishing are mainly known as finish polishing methods. CMP is a method of polishing a wafer by both the action of chemical components contained in the polishing liquid and the action of mechanical polishing with abrasive grains. When CMP is performed, the wafer is pressed against the rotating polishing pad while supplying a polishing liquid in which the dispersoid abrasive grains are dispersed in a dispersion medium such as water and an oxidizing agent and a pH adjusting agent are added. On the other hand, mechanical polishing is a method of mechanically polishing a wafer by pressing the wafer against a metal surface plate or the like.

Note that conventional GaN substrate polishing methods include, for example, Japanese Patent Application Laid-Open No. 2004-311575 (Patent Document 1), International Patent Publication No. 2005/1099481 (Patent Document 2), and Japanese Patent Application Laid-Open No. 2006-310362 (Patent Document 1). Document 3) and Japanese Patent Application Laid-Open No. 2008-42157 (Patent Document 4). Patent Document 1 uses a soft abrasive grains hardness in Vickers hardness test is 400~1000kg / mm ^2, a polishing composition and a hard abrasive grains are 1300~6000kg / mm ² was dispersed in water, It discloses that a GaN-based semiconductor substrate is polished. Patent Document 2 discloses that a GaN-based semiconductor substrate is polished with a predetermined polishing composition. As the polishing composition, soft abrasive grains and hard abrasive grains dispersed in water and having a pH value adjusted to a range of 1.5 to 5.0 are used. Patent Document 3 discloses that the surface of a GaN crystal is mechanically polished and further polished. At the time of polishing, a polishing liquid adjusted so that the pH value x and the oxidation-reduction potential y satisfy a predetermined relationship is used. Patent Document 4 discloses a method for polishing a GaN substrate by subjecting the substrate to three types of processes: grinding, lapping, and polishing. A polishing liquid is used in polishing, and the abrasive grains contained in the polishing liquid are sequentially switched from coarse abrasive grains to fine abrasive grains. As a result, a GaN substrate having a surface roughness Rms of 1.2 nm to 1.5 nm, a horizontal sag of 140 μm, and a vertical sag of 43 μm is obtained.

Japanese Patent Laid-Open No. 2004-311575 International Patent Publication No. 2005/1099481 Pamphlet JP 2006-310362 A JP 2008-42157 A

  However, the conventional GaN substrate polishing method has a problem that polishing with high flatness cannot be performed quickly.

  In CMP, it is necessary to finely adjust the components of the polishing liquid in order to ensure the mechanical action and chemical action of the polishing liquid. For this reason, it took time to prepare the polishing liquid, and quick polishing could not be performed.

In mechanical polishing, there was no polishing tool (abrasive grain) having a hardness suitable for polishing GaN, and high-precision polishing could not be performed quickly. For example, when abrasive grains having a high hardness (Vickers hardness Hv ≧ 1300) such as diamond are used, diamond is too hard compared to GaN, resulting in surface roughness of the GaN substrate and deterioration of the flatness of the GaN substrate surface. . On the other hand, when low hardness abrasive grains such as SiO ₂ were used, the polishing rate of GaN deteriorated and rapid polishing could not be performed.

  Furthermore, when the abrasive grains are sequentially switched from coarse to fine as in Patent Document 4, the value of the arithmetic average roughness Ra of the GaN substrate surface is improved, but the value of the maximum height Ry is deteriorated. It was. This is because, when fine abrasive grains are used, the overall flatness of the GaN substrate surface is improved, but the abrasive grains aggregate in the polishing liquid or on the surface plate (on the polishing tool) and partially on the GaN substrate surface. Deep scratches and local flatness deteriorated.

  The above-described problem does not occur only in the polishing of the GaN substrate, but occurs in the entire substrate made of a group III nitride material.

  Therefore, an object of the present invention is to provide a substrate polishing method and a substrate that can improve the flatness of the substrate.

  Another object of the present invention is to provide a substrate polishing method and a substrate capable of performing rapid polishing.

  The method for polishing a substrate in the present invention is a method for polishing a substrate made of a group III nitride material, and includes the following steps. A soft material having a Vickers hardness Hv in the range of 50 ≦ Hv ≦ 2800 is prepared. The substrate is polished together with the soft material using a polishing tool.

  According to the substrate polishing method of the present invention, the soft material is scraped by the abrasive grains, and the scrap of the soft material is generated. And this shaving residue adheres to an abrasive grain and functions as a cushioning material between a board | substrate and an abrasive grain. When the soft material has a Vickers hardness Hv of 50 or more, the soft material functions as a cushioning material between the substrate and the blade. When the soft material has a Vickers hardness Hv of 2800 or less, damage to the substrate due to the soft material can be suppressed. As a result, the surface roughness of the substrate due to the abrasive grains is suppressed, and the flatness of the substrate can be improved. In addition, in order to improve the flatness of the substrate, it is not necessary to use low hardness abrasive grains, finely adjust the components of the polishing liquid, or use a polishing liquid containing fine abrasive grains. Can be performed.

  Preferably, in the polishing method, in the step of preparing the soft material, a soft material having a Vickers hardness Hv in the range of 100 ≦ Hv ≦ 1300 is prepared. Thereby, the function of the soft material as a cushioning material between the substrate and the abrasive grains is enhanced, and damage to the substrate by the soft material can be further suppressed.

  Preferably, in the manufacturing method, a load is applied from a soft material to the polishing tool in the step of polishing the substrate. Thereby, the soft material is easily scraped by the abrasive grains of the polishing tool, and the scrap of the soft material is easily generated.

  Preferably, in the above manufacturing method, a platen made of metal is used as a polishing tool in the step of polishing the substrate.

  Preferably in the manufacturing method, a polishing pad made of a resin is used as a polishing tool in the step of polishing the substrate.

  Thus, if a surface plate made of metal or a polishing pad with a low compression rate (hard) is used, the substrate to be polished is less likely to be deformed. For this reason, since it becomes difficult to produce big edge roll-off to the said board | substrate, the flatness of a board | substrate can be improved.

  Preferably, in the manufacturing method, the position of the substrate is fixed using a soft material in the step of polishing the substrate. This eliminates the need for a jig for fixing the substrate during polishing.

  Preferably in the manufacturing method, in the step of polishing the substrate, a polishing liquid containing soft abrasive grains having a Vickers hardness Hv in the range of 50 ≦ Hv ≦ 2800 is supplied to the polishing tool. Thereby, the grinding | polishing conditions of a board | substrate can be freely changed with the supply amount of a soft abrasive grain.

  The substrate in the present invention is a substrate made of a group III nitride material, the arithmetic average roughness Ra is 0.1 nm ≦ Ra ≦ 3.0 nm, and the deepest scratch depth D is 2 nm ≦ D ≦ 90 nm. It has a surface that is The roll-off amount dx in the direction parallel to the substrate surface is 10 μm ≦ dx ≦ 500 μm, and the roll-off amount dz in the direction perpendicular to the substrate surface is 5 nm ≦ dz ≦ 2500 nm. Here, it is more preferable to have a surface where the arithmetic average roughness Ra is 0.5 nm ≦ Ra ≦ 2.0 nm and the depth D of the scratch is 5 nm ≦ D ≦ 70 nm. Alternatively, the roll-off amount dx in the direction parallel to the substrate surface is preferably 10 μm ≦ dx ≦ 50 μm, and the roll-off amount dz in the direction perpendicular to the substrate surface is preferably 5 nm ≦ dz ≦ 200 nm.

  The substrate of the present invention can improve flatness. Moreover, rapid polishing can be performed.

  A light-emitting element formed using the above-described substrate according to the present invention has a large light output and can reduce a drivable voltage value. Accordingly, a light-emitting element having low energy and high output and excellent electrical characteristics and optical characteristics can be provided.

  According to the substrate polishing method of the present invention, the flatness of the substrate can be improved. Moreover, rapid polishing can be performed. The substrate of the present invention has a high quality with improved flatness. Furthermore, electrical characteristics and optical characteristics of a light-emitting element formed using the substrate can be improved.

It is a side view which shows typically the polish device used in Embodiment 1 of this invention. It is a side view which shows typically the polish device used in Embodiment 2 of this invention. It is a bottom view which shows typically the inside of the guide ring of a rotation surface plate part in the grinding | polishing apparatus used in Embodiment 2 of this invention. It is a top view which shows typically the board | substrate after grinding | polishing in Embodiment 3 of this invention. It is sectional drawing which follows the VV line of FIG. (A) It is a figure which shows the shape of the surface near the edge part of the GaN board | substrate grind | polished using the surface plate which consists of a tin alloy measured in Example 1 of this invention. (B) It is a figure which shows the shape of the surface near the edge part of the GaN board | substrate grind | polished using the polishing pad which consists of a polyurethane measured in Example 1 of this invention. It is sectional drawing which shows typically the structure which laminated | stacked the thin film on the board | substrate concerning this invention. It is sectional drawing which shows typically the aspect of the light emitting element formed using the structure of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a side view schematically showing a polishing apparatus used in Embodiment 1 of the present invention. Referring to FIG. 1, the polishing apparatus used in the present embodiment is for polishing a substrate 10 made of a group III nitride material having a diameter of 50 mm, for example. The polishing apparatus includes a substrate holding unit 1, a rotation mechanism unit 2, a polishing tool 3, a polishing liquid supply unit 4, a soft material 5, and a soft material holding unit 6. The substrate holding unit 1, the polishing liquid supply unit 4, and the soft material holding unit 6 are disposed on the rotation mechanism unit 2.

  The substrate holding unit 1 can hold a plurality of substrates 10 (only two substrates are shown in FIG. 1), and includes a pressure head 1a and a shaft 1b. The pressure head 1 a can fix the position of the substrate 10 by applying a load from the substrate 10 to the rotation mechanism unit 2. The shaft 1b is connected to the center of the upper surface of the annular pressure head 1a, and can rotate the pressure head 1a.

  The rotation mechanism unit 2 includes a fixed platen 2a and a shaft 2b. The fixed platen 2 a is a rotatable member used as a base for placing the polishing tool 3 used for polishing the substrate 10. The stationary platen 2a is made of a metal such as stainless steel, for example. The shaft 2b is connected to the center of the bottom surface of the fixed platen 2a, and can rotate the fixed platen 2a.

  The polishing tool 3 may be attached to the upper surface of the fixed platen 2a. The polishing tool 3 is a surface plate made of a metal material such as a tin alloy. Alternatively, the polishing tool 3 may be a polishing pad made of a resin such as polyurethane. The polishing tool 3 may include diamond as an abrasive having an average particle diameter of 1 μm or less regardless of whether it is made of the above-described metal material (surface plate) or resin (polishing pad). Good. Alternatively, the surface of the polishing tool 3 may include a material as abrasive grains other than diamond. Here, the average particle size of the abrasive grains means that the volume of the abrasive grains is integrated from the small particle size side to the large particle size side when measured using a particle size distribution measuring method by a laser diffraction / scattering method. This means the value of the diameter of the cross section at the location where the cumulative volume becomes 50%. Specifically, the measurement method described above is a method of measuring the particle diameter by analyzing the scattering intensity distribution of the scattered light of the laser light irradiated on the abrasive grains.

  For example, when the polishing tool 3 is made of a resin polishing pad, the polishing tool 3 may be attached so as to contact the upper surface of the fixed platen 2a as shown in FIG. However, for example, when the polishing tool 3 is a surface plate made of a metal material, a grooved region is formed at a certain depth (vertical direction in FIG. 1) from the upper surface of the fixed platen 2a, and the grooved region is formed inside the grooved region. You may arrange | position so that the polishing tool 3 may be fitted.

  Further, the polishing tool 3 as a surface plate disposed so as to be fitted in the groove-shaped region formed in the fixed platen 2a is not limited to the above-described metal material, but other types of high-hardness materials such as glass and plastic materials. It may be.

  When the surface plate or the polishing pad functions as the polishing tool 3, the soft material 5 and the substrate 10 can be polished by the abrasive grains included in the polishing tool 3. As described above, when the substrate 10 is polished using the surface plate made of a metal material or glass material having a high hardness or the polishing pad made of a hard resin material having a low compressibility as the polishing tool 3, the edge roll-off is less likely to occur. . For this reason, the flatness of the substrate 10 can be improved.

  Further, the polishing liquid supply unit 4 can supply the polishing liquid from the tip part to the upper surface of the polishing tool 3 including a surface plate and a polishing pad. The polishing liquid supplied from the polishing liquid supply unit 4 preferably contains, for example, diamond abrasive grains. In this way, the surface of the substrate 10 is polished by the polishing liquid. That is, the polishing liquid has a role of polishing the substrate 10 in the same manner as the polishing tool 3 described above.

  The soft material holding part 6 can hold the soft material 5 and is soft by applying a load from the soft material 5 so as to press the soft material 5 against the polishing tool 3 (a surface plate or a polishing pad). It is possible to fix the position of the material 5.

The substrate 10 is made of a group III nitride material such as Al _x Ga _1-x N (0 ≦ x ≦ 1), and is particularly preferably made of GaN.

Subsequently, a method for polishing a substrate in the present embodiment will be described.
First, the soft material 5 is prepared. The soft material 5 has a Vickers hardness Hv in the range of 50 ≦ Hv ≦ 2800, and preferably has a Vickers hardness Hv in the range of 100 ≦ Hv ≦ 1300. When the soft material has a Vickers hardness Hv of 50 or more, preferably 100 or more, the soft material functions as a cushioning material between the substrate and the blade. When the soft material has a Vickers hardness Hv of 2800 or less, preferably 1300 or less, damage to the substrate by the soft material can be suppressed. The Vickers hardness Hv of diamond exceeds 2800, and the Vickers hardness Hv of the substrate 10 made of GaN is 1300. Therefore, as described above, if the soft material 5 having an Hv of 2800 or less, more preferably an Hv of 1300 or less is used, damage to the substrate 10 can be more reliably suppressed. Also, a sufficient amount of soft material can be obtained without excessively pressing the soft material 5 against the polishing tool 3 (that is, the load applied from the polishing tool 3 to the soft material 5) or the surface area of the soft material 5 contacting the polishing tool 3. The scraps of the material 5 are generated.

  Subsequently, the substrate 10 is attached to the substrate holding unit 1, and the substrate 10 is disposed so that the surface 12 (polishing surface) of the substrate 10 faces the upper surface of the polishing tool 3. Then, the pressure head 1 a is lowered to fix the position of the substrate 10.

  Similarly to the substrate 10, the soft material 5 is attached to the soft material holding unit 6, and the soft material 5 is disposed so that the surface 13 of the soft material 5 faces the upper surface of the polishing tool 3. Then, the position of the soft material 5 is fixed by lowering the soft material holding portion 6. In order to fix the soft material 5 and scrape the soft material 5, it is preferable to apply a pressure P of 0.2 kPa or more, more preferably 0.5 kPa or more from the soft material 5 to the polishing tool 3. The pressure P includes the pressure due to the weight of the soft material 5. That is, depending on the material of the soft material 5, there may be a case where only the pressure due to the weight of the soft material 5 is sufficient (the pressure from the soft material 5 to the polishing tool 3 may not be applied again). On the other hand, in order to prevent excessive scraping of the soft material 5, it is preferable to apply a pressure P of 50 kPa or less, more preferably 20 kPa or less, from the soft material 5 to the polishing tool 3. The position of the soft material holding part 6 and the density of the soft material 5 are appropriately selected so that the pressure P falls within the above range. By applying pressure from the soft material 5 to the polishing tool 3, the soft material 5 is pressed against the polishing tool 3, and the soft material 5 is easily scraped by the abrasive grains of the polishing tool 3. Become.

  After fixing the substrate 10 and the soft material 5, the fixing plate 2 a, the pressure head 1 a, and the soft material holding unit 6 are rotated while supplying the polishing liquid from the polishing liquid supply unit 4 to the polishing tool 3. Thereby, the surface 12 of the substrate 10 is polished together with the soft material 5. The soft material 5 is scraped by the abrasive grains supplied on the surface of the polishing tool 3, and the scrap of the soft material 5 is generated (that is, the soft material 5 changes from bulk to a plurality of particles). The scraps adhere to the abrasive grains of the polishing tool 3 and function as a cushion material between the substrate and the abrasive grains.

  When the substrate 10 is polished, the pressure head 1a, the soft material holding unit 6, and the stationary platen 2a may be rotated in opposite directions or in the same direction. Furthermore, you may fix one side among the pressurization head 1a and the soft material holding | maintenance part 6, and the stationary platen 2a, and you may rotate the other.

  When polishing the substrate 10, the polishing liquid may be supplied to the upper surface of the polishing tool 3 through the polishing liquid supply unit 4. This polishing liquid may not be supplied at the start of polishing, but may be started in the middle of polishing.

  The polishing liquid contains abrasive grains for polishing the substrate 10. As the abrasive grains, for example, so-called hard abrasive grains such as diamond are used. However, the polishing liquid may contain so-called soft abrasive grains having a lower hardness than the hard abrasive grains in addition to the hard abrasive grains. Here, abrasive grains made of a material having a high hardness such as diamond are called hard abrasive grains, and abrasive grains made of a material having a relatively lower hardness than diamond are called soft abrasive grains.

That is, for example, soft abrasive grains having Vickers hardness Hv in the range of 50 ≦ Hv ≦ 2800 may be included as in the soft material 5 described above. The soft abrasive grains preferably have a Vickers hardness Hv of 100 ≦ Hv ≦ 1300. This is based on the fact that the Vickers hardness Hv of diamond exceeds 2800 and the Vickers hardness Hv of the substrate made of GaN is 1300, as in the soft material 5 described above. Specifically, as soft abrasive _{grains, SiO 2, CeO 2, TiO} 2, MgO, MnO 2, Fe 2 O 3, Fe 3 O 4, NiO, ZnO, CoO 2, Co 3 O 4, CuO, Cu 2 Abrasive grains made of O, GeO ₂ , CaO, Ga ₂ O ₃ , Al ₂ O ₃ and hydrates of all the materials described above or In ₂ O ₃ (and hydrates described above) may be included. . The polishing liquid may contain abrasive grains having a hardness higher than that of the group III nitride crystal, for example, in addition to the soft abrasive grains or instead of the soft abrasive grains. Specifically, abrasive grains made of diamond, SiC, Si ₃ N ₄ , BN, Cr ₂ O ₃ , ZrO ₂ , or the like may be included.

  That is, the above-described soft material having Vickers hardness Hv in the range of 50 ≦ Hv ≦ 2800 is supplied as a scraped material between the substrate 10 and the polishing tool 3 by cutting the soft material 5 in FIG. Alternatively, the soft material may be contained in the polishing liquid supplied from the polishing liquid supply unit 4.

  It should be noted that the abrasive grains present on the surface of the polishing tool 3 and the abrasive grains contained in the polishing liquid, regardless of whether or not they are specifically abrasive grains made of diamond. The average particle size of is preferably 1 μm or less. Thereby, the flatness of the substrate 10 can be improved. Further, the polishing liquid may contain a chemical component that promotes polishing of the substrate 10 by a chemical action.

  Here, as a measuring method of the average particle diameter of the abrasive grains, for example, as described above, a method of measuring the particle diameter by analyzing the scattering intensity distribution of the scattered light of the laser light irradiated on the particles may be used. preferable.

  Through the above steps, polishing of the substrate is completed. Note that the surface 12 of the substrate 10 may be dry-etched after the above polishing method is performed. When the above polishing method is performed by mechanical polishing, a work-affected layer may be formed on the surface 12 in some cases. This work-affected layer can be removed by dry etching the surface 12.

  The method for polishing a substrate in the present embodiment is a method for polishing a substrate 10 made of a group III nitride material, and includes the following steps. A soft material 5 having a Vickers hardness Hv in a range of 50 ≦ Hv ≦ 2800 is prepared. The substrate 10 is polished together with the soft material 5 using the polishing tool 3.

  According to the substrate polishing method in the present embodiment, the soft material 5 is scraped by the abrasive grains on the polishing tool 3, and scraping of the soft material 5 is generated. Then, this shaving residue adheres to the abrasive grains and functions as a cushion material between the substrate 10 and the abrasive grains. When the soft material 5 has a Vickers hardness Hv of 50 or more, the soft material 5 functions as a cushioning material between the substrate 10 and the abrasive grains. When the soft material 5 has a Vickers hardness Hv of 2800 or less, damage to the substrate 10 by the soft material 5 can be suppressed. As a result, the surface roughness of the substrate 10 due to the abrasive grains on the polishing tool 3 is suppressed, and the flatness of the substrate 10 can be improved.

According to the substrate polishing method in the present embodiment, the surface roughness of the substrate due to the abrasive grains can be suppressed and the flatness of the substrate can be improved, particularly as compared with conventional mechanical polishing. Moreover, since it is not necessary to use low-hardness abrasive grains such as SiO ₂ , rapid polishing can be performed. Further, compared with the conventional CMP, it is not necessary to finely adjust the components of the polishing liquid, and quick polishing can be performed. Furthermore, compared with the case where a polishing liquid containing fine abrasive grains is used, it is possible to suppress the agglomeration of the abrasive grains and cause partial deep scratches on the substrate surface, thereby improving the flatness of the substrate.

(Embodiment 2)
2 and 3 are diagrams schematically showing a polishing apparatus used in the second embodiment of the present invention. 2 is a side view, and FIG. 3 is a bottom view inside the guide ring of the rotation mechanism. Referring to FIGS. 2 and 3, the polishing method in the present embodiment is different from the polishing method in Embodiment 1 in that the position of the substrate is fixed using a soft material.

  A plurality of guide rings 14 (only two guide rings are shown in FIG. 2) are provided below the substrate holding unit 1. Each of the guide rings 14 has a hollow cylindrical shape and has a circumferential lower surface. A plurality of slits 7 are formed on the lower surface of each guide ring 14. As the guide ring 14 rotates during polishing, the polishing liquid flowing into the guide ring 14 is blocked by the slit 7, and the amount of polishing liquid supplied into the guide ring 14 is controlled.

  A disc-shaped soft material 5 and a substrate 10 are arranged inside each guide ring 14. The soft material 5 has a cylindrical shape, and a groove 15 is formed on the circular surface 13 of the soft material 5. Inside the groove 15, the substrate 10 attached to the plate is arranged. Thereby, the soft material 5 becomes a jig for the substrate 10, and the position of the substrate 10 is fixed using the soft material 5 at the time of polishing.

  Since the configuration of the polishing apparatus and the polishing method other than those described above are the same as those of the polishing apparatus and the polishing method in the first embodiment, the same members are denoted by the same reference numerals, and description thereof will not be repeated.

  According to the substrate polishing method in the present embodiment, the same effects as those of the substrate polishing method in Embodiment 1 can be obtained. In addition, a jig for fixing the substrate 10 during polishing becomes unnecessary.

(Embodiment 3)
In this embodiment, a substrate polished by the method described in Embodiment 1 or 2 will be described.

  4 and 5 are diagrams schematically showing the substrate after polishing in the third embodiment of the present invention. 4 is a plan view, and FIG. 5 is a cross-sectional view taken along the line VV in FIG. 4 and 5, surface 12 of substrate 10 polished by the method described in the first or second embodiment is excellent in both arithmetic average roughness Ra and maximum height Ry. The value of the arithmetic average roughness Ra of the surface 12 of the substrate 10 affects the crystallinity of the epitaxial layer formed on the surface 12, and the value of the maximum height Ry of the surface 12 of the substrate 10 is determined on the surface 12. Affects the yield of devices formed.

  Specifically, the surface 12 of the substrate 10 has an arithmetic average roughness Ra in a 86 μm square surface of 0.1 nm ≦ Ra ≦ 3.0 nm, and the entire surface excluding the outer peripheral portion of the substrate 10 (inside the substrate 10 ) Is 2 nm ≦ D ≦ 90 nm (the value of the maximum height Ry depends on the value of the scratch depth D). Here, the outer peripheral portion of the substrate 10 refers to a region corresponding to a length within 10% of the diameter in the radial direction from the end surface of the outer edge portion to the center of the surface of the substrate having a disk shape. Further, the roll-off amount at the end of the substrate 10 is small. Specifically, the roll-off amount dx in the direction parallel to the surface 12 is 10 μm ≦ dx ≦ 500 μm, and preferably 10 μm ≦ dx ≦ 50 μm. The roll-off amount dz in the direction perpendicular to the surface 12 is 5 nm ≦ dz ≦ 2500 nm, preferably 5 nm ≦ dz ≦ 200 nm.

  Here, the arithmetic average roughness Ra, the scratch depth D, and the roll-off amounts dx, dz are calculated by the following method.

  First, using a two-beam interference optical system, light is irradiated onto the edge portion (about 500 μm from the outer edge portion) of the surface 12 of the substrate 10 and the resulting interference image of the light is photographed with a CCD (Charge Coupled Device) camera. By doing so, the shape of the surface 12 is measured. Next, after correcting the inclination of the surface 12, the arithmetic average roughness Ra and the scratch depth D of the surface 12 are measured based on the shape of the surface 12 obtained. The scratch depth D is the deepest depth of the scratch 111 on the entire surface 12 excluding the outer peripheral portion of the substrate 10. Next, based on the measured arithmetic average roughness Ra, a region where the arithmetic average roughness Ra is Ra ≦ 5 nm is identified as the substrate surface, and a region where Ra> 5 nm is excluded from the substrate surface (in the present invention). In the case of a substrate, since Ra ≦ 5 nm over the entire region of the surface 12, the measured entire region is specified as the substrate surface). Next, based on the shape of the obtained surface 12, the roll-off amounts dx and dz in the region specified as the substrate surface are measured.

  When mechanical polishing is employed in the method described in the first or second embodiment, the surface 12 of the substrate 10 immediately after polishing has an arithmetic average roughness Ra of 0.1 nm ≦ Ra ≦ 1.5 nm and a scratch. The depth D of 111 is 1 nm ≦ D ≦ 30 nm. However, when mechanical polishing is performed, a work-affected layer is formed on the surface 12 of the substrate 10. For this reason, it is necessary to remove this work-affected layer by dry etching after mechanical polishing. Usually, the scratch portion is more easily etched than the other portions, so that the scratch depth is often increased by dry etching. As a result, the surface 12 of the substrate 10 after dry etching has an arithmetic average roughness Ra of 0.1 nm ≦ Ra ≦ 3.0 nm and a scratch depth D of 2 nm ≦ D ≦ 90 nm as described above.

  On the other hand, conventional mechanical polishing cannot obtain both the range of the arithmetic average roughness Ra and the range of the scratch depth D as in the present embodiment. When abrasive grains of high hardness (Vickers hardness Hv> 2800) such as diamond are used in conventional mechanical polishing, surface roughness of the substrate due to the abrasive grains occurs, and the value of the arithmetic average roughness Ra deteriorates. In addition, when trying to improve flatness (reducing the value of arithmetic average roughness Ra) using a polishing liquid containing fine abrasive grains in conventional mechanical polishing, the abrasive grains aggregate and are partially deep on the substrate surface. A scratch is caused, and the value of the scratch depth D is deteriorated.

  Further, the conventional CMP cannot obtain the range of the roll-off amounts dx and dz as in the present embodiment. In conventional CMP, a substrate is polished using a polishing pad having a high compression rate (soft). When a polishing pad having a high compression ratio is used, the pad contacts not only the substrate surface but also the substrate side surface during polishing, and the substrate side surface is polished. As a result, a large edge roll-off portion 112 is generated, and the roll-off amounts dx and dz are deteriorated.

  Further, by specifying the substrate surface based on the arithmetic average roughness Ra and calculating the roll-off amount as described above, even if the substrate is chamfered at the end after polishing, the substrate of the present embodiment It can be determined whether or not. That is, when the end portion of the substrate is chamfered, the arithmetic average roughness Ra of the chamfered portion is 10 nm or more and never 5 nm or less. Therefore, the chamfered portion is excluded from the substrate surface, and the roll-off amount can be calculated in the region excluding the chamfered portion. In addition, when chamfering is performed, a smooth curved surface in which the chamfered portion and the substrate surface are continuous is not obtained.

  In this example, GaN substrate samples were prepared by changing the polishing conditions in various ways. The arithmetic average roughness Ra, scratch depth D, and roll-off amounts dx, dz of the formed GaN substrate were calculated using the method described in the third embodiment.

  First, as a sample formation method, the substrate 10 is polished under different conditions using the polishing apparatus shown in FIG. Specifically, as shown in the “condition system” column of Tables 1 and 2 below, the material of the polishing tool 3 (see FIG. 1) made of a surface plate (metal material) or a polishing pad (resin material) is used. Each sample consists of metal (tin alloy, copper), polyurethane (hard polishing pad) with small foam, and suede resin (soft polishing pad; “Suede” in the table) 3 Prepare a modified type. In the column of “Material of polishing tool 3” in Table 1, the upper row indicates whether it is a surface plate or a polishing pad, and the lower row indicates the specific material of each polishing tool 3.

  Further, the compressibility of the material when polyurethane or suede is used as the polishing tool 3 described above is changed for each sample. As shown in Tables 1 and 2, all samples prepared in Example 1 were set with the polishing tool 3 on the stationary platen 2a shown in FIG. 1 (the surface plate was placed in the groove formed on the stationary platen 2a). It is polished using a material that is inserted or affixed with a polishing pad.

  As shown in Tables 1 and 2, the polishing liquid supplied from the polishing liquid supply unit 4 contains abrasive grains made of diamond. The grain size of the abrasive grains is changed to 0.5 μm, 0.25 μm, and 0.125 μm for each sample. These particle sizes are all average values. Further, the Hv of the soft material 5 and the pressure P to the soft material 5 are changed for each sample as shown in Tables 1 and 2. Note that the soft material 5 is not used for the sample 11, the sample 12, the sample 13, and the sample 18.

  As described above, dry etching is performed on the surface of the sample of the GaN substrate polished by changing the condition (condition system) for each sample to remove the work-affected layer, and then the arithmetic average roughness Ra of each substrate is determined. The scratch depth D and roll-off amounts dx and dz were calculated. Specifically, a non-contact three-dimensional level difference meter “Micromap” (manufactured by Ryoka System) was used as a two-beam interference optical system, and an interference image of light obtained from the GaN substrate surface was taken with a CCD camera. At the time of photographing, the magnification of the two-beam objective lens was set to 50 times. Then, the shape of the GaN substrate surface was measured based on the photographed image. The shape of the measured GaN substrate surface is shown in FIG. 6A shows the surface of the GaN substrate polished using a metal surface plate as the polishing tool 3, and FIG. 6B shows the GaN substrate polished using a polyurethane polishing pad as the polishing tool 3. FIG. The surface.

  Subsequently, based on the corrected shape of the GaN substrate surface, the arithmetic average roughness Ra and scratch depth D of the GaN substrate surface were measured. Then, the substrate surface was specified based on the measured arithmetic average roughness Ra. In Example 1, the entire measured area was specified as the substrate surface. Next, roll-off amounts dx and dz were measured in a region specified as the substrate surface.

  Furthermore, it was also observed whether or not chipping occurred at the edge portion (outer peripheral portion of the surface) of the polished GaN substrate. In Tables 1 and 2, “◯” indicates that no chipping has occurred at the location, and “X” indicates that chipping has occurred at the location. More specifically, “X” indicates a sample in which chipping occurred at a rate of 10% or more among samples of each condition. “◯” indicates a sample in which the chipping ratio is less than 10%. “Chipping” indicates that the size of a region where an appearance defect such as chipping is formed is 0.3 mm or more from the outer edge which should be originally. In addition, since the numbers of samples shown in Tables 1 and 2 are all different, each data in the above tables shows an average value of measured values in each sample.

  In the column of “Result System (Substrate)” in Tables 1 and 2, the average value of the measured values of each item of each sample is shown. Table 1 shows the results of the substrate (sample) polished using the preferable conditions according to the present invention described above in each item of “conditional system”. On the other hand, Table 2 shows the results of the substrate (sample) obtained by polishing using at least one of the items in the “conditional system” using conditions other than the preferred conditions according to the present invention. Yes.

  As for Table 1, in any of the samples 01 to 09, the polishing is performed using the soft material 5 whose Hv is in the range of 50 ≦ Hv ≦ 2800. In this case, the arithmetic average roughness Ra of each formed substrate is 0.1 nm ≦ Ra ≦ 3.0 nm, and the scratch depth D is 2 nm ≦ D ≦ 90 nm. Further, the horizontal roll-off amount (indicating a direction parallel to the substrate 10) dx of each formed substrate is 10 μm ≦ dx ≦ 500 μm, and the vertical roll-off amount dz is 5 nm ≦ dz ≦ 2500 nm. In addition, regarding the chipping of the edge portion, all the samples were “◯”.

  From the above data, the substrate (sample) polished using the preferred conditions according to the present invention described above in each item of “conditional system” shown in Table 1 has a flat surface and good quality. I know that there is.

  Moreover, the yield (device overall yield) of devices (light emitting elements) formed on each of these substrates and shown in Example 2 (see FIG. 8), which will be described later, is 70% or more in Table 1. In Table 2, it was less than 70% in all cases. This is shown in the column “Result System (Device)” in Tables 1 and 2. Therefore, it can be said that the yield of light-emitting elements formed using a substrate having a flat and favorable surface shown in Table 1 is increased. Here, the criteria for judging the yield of devices formed in each sample are as follows. For example, if the light output intensity is 20 mW or more, the device is determined to be a non-defective product, and if the light output intensity is less than 20 mW, the device is determined to be a defective product.

  The above-described total device yield is the total yield of “device yield (inside substrate) (%)” and “device yield (outer peripheral portion of substrate) (%)” shown in Tables 1 and 2. Specifically, as described above, the device yield at the outer peripheral portion of the substrate is a portion within 10% of the diameter in the radial direction from the end surface of the outer edge portion to the center of the surface of the disk-shaped substrate. This shows the yield of devices formed on the outer periphery of the substrate, which is the area of. On the other hand, the device yield inside the substrate indicates the yield of devices formed in a region (on the center side) other than the outer peripheral portion of the substrate. For example, if the substrate has a diameter of 50 mm, the region on the center side having a diameter of 40 mm is “inside the substrate”, and the region within 5 mm from the end surface of the outer edge is “substrate outer peripheral portion”.

  Even if polyurethane is used as the polishing tool 3 (polishing pad) as in sample 08, the overall device yield is not greatly affected. However, for example, the values of dx and dz are larger than those of other samples, and as a result, the device yield at the outer periphery of the substrate is lower than that of other samples. For this reason, it is more preferable to use a tin alloy as the polishing tool 3 (metal surface plate). It is more preferable that dx is 10 μm ≦ dx ≦ 50 μm and dz is 5 nm ≦ dz ≦ 200 nm from the data of other samples in Table 1 excluding dx and dz data in sample 08.

  In addition, the sample 02 in which the soft material Hv is 50 and the sample 07 in which the Hv is 2800 have a device overall yield of 70% or more and less than 80%. On the other hand, with respect to each sample except for the above-described sample 08, sample 02, and sample 07, the overall yield of the formed device is 80% or more. From this, it can be said that the value of Hv is more preferably 100 ≦ Hv ≦ 1300. Sample 02 and sample 07 have a large scratch depth D. For this reason, excluding these, it can be said that it is more preferable to have a surface having a scratch depth D of 5 nm ≦ D ≦ 70 nm.

  Sample 09 has a smaller diameter of diamond abrasive grains in the polishing liquid compared to other samples. In this way, the arithmetic average roughness Ra and scratch depth D are smaller than those of the other samples. Thus, when the value of Ra becomes small, it takes a long time to process the surface so as to have the roughness. That is, the productivity of processing deteriorates. Specifically, for example, when the surface of the GaN substrate is polished using the sample 01, the average polishing rate was 1.5 μm / h, whereas when the surface of the GaN substrate was polished using the sample 09, The average polishing rate was 0.2 μm / h. Therefore, as described above, 0.1 nm ≦ Ra is preferable, but 0.5 nm ≦ Ra is more preferable. However, if processing productivity is not taken into consideration, it is more preferable that Ra is small, that is, the surface is flatter. Therefore, as described above, Ra ≦ 3.0 nm is preferable, but Ra ≦ 2.0 nm is more preferable. From this, it can be said that a flatter and higher quality substrate surface can be obtained by reducing the diameter of the diamond abrasive grains in the polishing liquid.

  Next, Table 2 as comparison data will be described. First, samples 11, 12, 13, and 18 are polished without using the soft material 5. Among these samples, the scratch depth D of the sample 11 is 180 nm, which is twice the preferable range of D ≦ 90 nm. When a device (light emitting element) is formed using a substrate having such a deep scratch formed on the surface, the scratch is also removed even if the substrate is subjected to heat treatment (thermal annealing) before film formation. Is difficult. That is, the device is formed with the scratch remaining. From this, it is considered that the overall device yield has decreased.

  Next, in Sample 12, the diamond abrasive grain size in the polishing liquid is reduced (to 0.25 μm). In this case, the arithmetic average depth Ra is smaller than that of the sample 11, but the scratch depth D is not significantly changed as compared with the sample 11. Sample 13 has a diamond abrasive grain size in the polishing liquid smaller than that of sample 12 (0.125 μm). In this case, the arithmetic average depth Ra is smaller than that of the sample 12, but the scratch depth D is larger than those of the samples 11 and 12. This is because the abrasive grains aggregate on the surface of the polishing tool 3 if the abrasive grain size of the diamond in the polishing liquid is reduced without using the soft material 5. The scratch depth D of the sample 18 using a polishing pad made of polyurethane as the polishing tool 3 is also large as in the case of the sample 13. As a result, the overall device yield is low.

  Samples 14 and 15 were obtained by polishing each sample shown in Table 1 using a soft material 5 having a Hv outside the preferable range. Also in this case, the scratch depth D is particularly large. For example, if the Hv of the soft material 5 is too small like the sample 14, the cut soft material 5 does not function sufficiently as a cushion. If the Hv of the soft material 5 is too large as in the sample 15, the shaved soft material 5 may damage the surface of the substrate 10. For this reason, it is considered that the value of the scratch depth D is outside the preferable range.

  Sample 16 and sample 19 use a resin (soft polishing pad) that is suede processed instead of tin alloy as the material of the polishing tool 3. In this case, particularly in the sample 16, the roll-off amounts dx and dz are very large. For this reason, the device yield is particularly low at the outer periphery of the substrate. For this reason, it is not preferable to use the suede type polishing tool 3.

  For sample 19 in which the abrasive grain diameter of the polishing liquid diamond is made as small as 0.125 μm using the suede processed resin, the scratch depth D is small, but the roll-off amounts dx and dz are large as in sample 16. . For this reason, like the sample 16, the device yield is particularly low particularly at the outer peripheral portion of the substrate.

  In the sample 17 using copper which is harder than the tin alloy instead of the tin alloy as the material of the polishing tool 3, chipping occurred at the edge portion of the substrate. For this reason, the device yield especially in the outer peripheral portion of the substrate is very low. This is because copper is harder than a tin alloy, and the roll-off of the polished substrate is much smaller than usual (eg, dx <10 μm, dz <5 nm). For this reason, since the edge part of a board | substrate will be in the state near a right angle, it is because edge chipping will occur easily.

  As described above, the substrate (sample) polished using the preferable conditions according to the present invention can have a flat and high quality surface. For this reason, it can be said that the yield of devices (light-emitting elements) formed over the substrate can be improved.

  The devices (light-emitting elements) shown in the “Result System (Device)” column of Tables 1 and 2 described above were formed using a GaN substrate polished under the conditions shown in Example 1. Details will be described below.

  In order to form a light emitting element (light emitting diode), first, a laminated structure shown in FIG. 7 was formed. Specifically, for example, a substrate 10 shown in FIG. 1 (corresponding to each sample in Example 1) was prepared. The surface of these substrates 10 is polished using the polishing apparatus shown in FIG. Thereafter, dry etching was performed to remove the work-affected layer present on the surface of the substrate 10.

  Next, these substrates were subjected to thermal cleaning (thermal cleaning). Specifically, the pressure in the furnace is controlled to be 101 kPa while the substrate 10 is installed in the metal organic chemical vapor deposition furnace. In this state, the temperature in the furnace is set to 1050 ° C. and held for 10 minutes, whereby cleaning such as removal of scratches formed on the surface of the substrate 10 is performed.

When the heat treatment was completed, the laminated structure shown in FIG. 7 was formed by epitaxial growth. First, an n-type AlGaN film 97 shown in FIG. 7 was deposited. Specifically, TMGa (trimethylgallium), TMAl (trimethylaluminum), NH ₃ , SiH ₄ gas is supplied into the furnace, and the furnace is heated to 1050 ° C., whereby n-type AlGaN is formed on the substrate 10. A film 97 was grown. The film thickness of the n-type AlGaN film 97 is 50 nm. If the n-type AlGaN film 97 is formed, the microscopic roughness present on the surface of the substrate 10 can be removed and the surface can be made flatter.

Next, the temperature in the furnace was raised to 1100 ° C., and an n-type GaN film 95 was deposited to 2000 nm on the n-type AlGaN film 97 as shown in FIG. Here, the n-type GaN film 95 was formed by supplying gases of TMGa, NH ₃ and SiH ₄ into the furnace. The film formation rate was 4 μm / hour. The n-type GaN film 95 is a region that functions as a cladding layer or a buffer layer when a light emitting element is formed. During the formation of the n-type GaN film 95, the supply of TMGa and SiH ₄ into the furnace was stopped, and the furnace temperature was lowered to 800 ° C. Then, by supplying TMGa and TMIn again, an In _0.05 Ga _0.95 N buffer layer (InGaN layer 93) having a thickness of 50 nm was formed.

Next, a quantum well structure 91 in which a plurality of thin film layers shown in FIG. 7 was laminated was formed. The quantum well structure 91 has a configuration in which InGaN films (InGaN well layers) and GaN films (GaN barrier layers) are alternately stacked. Here, in order to form the quantum well structure 91, first, gas of TMGa, TMIn, and NH ₃ is supplied into the furnace, and the temperature in the furnace is set to 800 ° C., so that the thickness is 3 nm and the composition is In _0.14. An InGaN well layer of Ga _0.86 N was formed. Next, TMGa, NH ₃ , and SiH ₄ gases were supplied into the furnace, and the temperature in the furnace was set to 1100 ° C. to form a GaN barrier layer having a thickness of 15 nm. A quantum well structure 91 was formed by alternately forming three layers of the InGaN well layer and the GaN barrier layer.

Next, a p-type AlGaN film 89 shown in FIG. 7 was formed. Specifically, a gas of TMGa, TMAl, NH ₃ , Cp ₂ Mg (biscyclopentadienyl magnesium) is supplied into the furnace, and the inside of the furnace is heated to 1000 ° C., whereby the p-type AlGaN film 89 is formed. Formed. The p-type AlGaN film 89 is doped with Mg (magnesium). The p-type AlGaN film 89 can function as a cladding layer or an electron block layer.

Finally, a p-type GaN film 87 was formed. Specifically, by supplying TMGa, NH ₃ , and Cp ₂ Mg gases into the furnace, the p-type GaN film 87 was formed to have a thickness of 50 nm. The film formation temperature at this time was 1000 ° C. The p-type GaN film 87 is doped with Mg and functions as a contact layer.

  The laminated structure shown in FIG. 7 is formed by the above procedure. On the other hand, as shown in FIG. 8, a part (outer peripheral side) region in the direction along the surface of the substrate 10 (left and right direction in FIG. 8) is removed by RIE (reactive ion etching). Specifically, a part of the n-type GaN film 95 in the depth direction of the laminated structure (vertical direction in FIG. 8), the InGaN layer 93, the quantum well structure 91, the p-type AlGaN film 89, and the p-type GaN film 87 are formed. Remove. In this way, the mesa structure shown in the sectional view of FIG. 8 is formed. The depth of the mesa structure was set to 500 nm. Thereafter, the p-type transparent electrode 70 made of NiAu (gold nickel), the p-type pad electrode 60 made of Au (gold) on the p-type GaN film 87, and TiAl on the back surface of the substrate 10 (lower side in FIG. 8). An n-type electrode 80 made of (titanium aluminum) was formed. In forming each electrode, photolithography technique (photosensitive agent application, exposure, development), ultrasonic cleaning, and the like were performed. The size of the p-type pad electrode 60 is 400 μm × 400 μm.

  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.

  The present invention is suitable as a substrate polishing method and substrate made of a group III nitride material such as a GaN substrate.

  DESCRIPTION OF SYMBOLS 1 Board | substrate holding | maintenance part, 1a Pressurization head, 1b, 2b shaft, 2 Rotation mechanism part, 2a Fixing board, 3 Polishing tool, 4 Polishing liquid supply part, 5 Soft material, 6 Soft material holding part, 7 Slit, 10 Substrate, 12 substrate surface, 13 soft material surface, 14 guide ring, 15 groove, 60 p-type pad electrode, 70 p-type transparent electrode, 80 n-type electrode, 87 p-type GaN film, 89 p-type AlGaN film, 91 quantum well structure, 93 InGaN layer, 95 n-type GaN film, 97 n-type AlGaN film, 111 scratch, 112 edge roll-off portion.

Claims (4)

A substrate made of a group III nitride material,
Arithmetic average roughness Ra has a surface where 0.1 nm ≦ Ra ≦ 3.0 nm and deepest scratch depth D is 2 nm ≦ D ≦ 90 nm,
A substrate in which a roll-off amount dx in a direction parallel to the surface is 10 μm ≦ dx ≦ 500 μm, and a roll-off amount dz in a direction perpendicular to the surface is 5 nm ≦ dz ≦ 2500 nm.   2. The substrate according to claim 1, wherein the substrate has a surface where the arithmetic average roughness Ra is 0.5 nm ≦ Ra ≦ 2.0 nm, and the depth D of the scratch is 5 nm ≦ D ≦ 70 nm.   The roll-off amount dx in the direction parallel to the surface is 10 μm ≦ dx ≦ 50 μm, and the roll-off amount dz in the direction perpendicular to the surface is 5 nm ≦ dz ≦ 200 nm. substrate.   The light emitting element formed using the board | substrate of any one of Claims 1-3.

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