Polishing method, method for manufacturing a semiconductor substrate

Abstract

The present disclosure relates to a method for manufacturing a semiconductor substrate. A catalyst metal film composed of a transition metal is formed on a main surface to be polished of a workpiece substrate made of any one of diamond, silicon carbide, gallium nitride, and sapphire. The workpiece substrate on which the catalyst metal film is formed is moved relative to a polishing table in an oxidant liquid medicine to remove a compound generated by a chemical reaction between active radicals and surface atoms of the main surface of the workpiece substrate, thereby polishing the workpiece substrate, wherein the active radicals are generated by a reaction between the catalyst metal film and the oxidant liquid medicine. An epitaxial substrate having a nitride semiconductor layer formed on a main surface of a growth substrate and a support substrate are prepared. The nitride semiconductor layer of the epitaxial substrate and the support substrate are bonded via a resin bonding layer, the growth substrate is removed, and the nitride semiconductor layer is exposed. The polished workpiece substrate is bonded onto the nitride semiconductor layer by a room-temperature bonding method, and the support substrate and the resin bonding layer are removed.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a semiconductor substrate, and more particularly to a method for manufacturing a semiconductor substrate having a nitride semiconductor layer formed thereon. Background Art

[0002] As a high-output semiconductor device, a field effect transistor using a nitride semiconductor, such as a high-electron mobility transistor (HEMT), is known. When such a semiconductor device operates at high output, the operating characteristics and reliability are significantly reduced due to temperature rise. Therefore, in order to suppress the temperature rise of the semiconductor device, a structure in which a material having high heat dissipation is provided near the heat generating portion to dissipate heat is mostly adopted. In particular, diamond is a material having the highest thermal conductivity among solid substances and has properties suitable as a heat dissipation material. Therefore, a technique for improving the heat dissipation of a semiconductor device by forming a nitride semiconductor layer on diamond has been disclosed.

[0003] As a technique for manufacturing a nitride semiconductor layer, a technique for forming a nitride semiconductor layer by heteroepitaxial growth on a substrate made of silicon (Si), silicon carbide (SiC), sapphire (Al2O3), etc. has been established and is widely used as a part of the manufacturing technique for nitride semiconductor devices.

[0004] On the other hand, a technique for directly forming a nitride semiconductor layer on a diamond substrate by heteroepitaxial growth is still under research, and its manufacturing method has not been established. Therefore, as an example of a technique for manufacturing a composite substrate having a semiconductor layer formed on a high heat dissipation substrate such as diamond, a method of bonding and integrating a semiconductor layer and a diamond substrate is known.

[0005] In such a method, in order to bond a semiconductor layer and a substrate such as diamond, a metal solder or an adhesive may sometimes be used. In particular, in the case where heat dissipation performance is emphasized, it is required to directly bond the objects to be bonded to each other.

[0006] In order to achieve such direct bonding of dissimilar materials, it is necessary to smooth the surfaces of the materials to be bonded at the atomic layer level.

[0007] As a method for precisely smoothing a semiconductor or a metal material, a method such as chemical mechanical polishing in which a mixture of a chemical solution and abrasive particles is used to polish the material surface is known. However, it is difficult to perform smoothing at the atomic layer level on a difficult-to-process material such as diamond having high chemical stability by chemical mechanical polishing.

[0008] As a method for planarizing a material with low processability at the atomic layer level in this way, for example, a technique using highly reactive active radicals generated in a catalytic reaction in a polishing liquid is disclosed in Patent Document 1. In such a manner, a metal platform composed of a catalyst is immersed in the polishing liquid, and the radicals generated by the reaction in the polishing liquid act on the contact point between the metal platform and the workpiece to dissolve the compound on the surface of the workpiece, thereby removing it by polishing.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-114632 Summary of the Invention

[0012] Problems to be Solved by the Invention

[0013] In a processing method using a catalytic reaction, the active radicals generated in the reaction between the catalyst metal and the polishing liquid have high reactivity and short lifetimes, so their effects are only effective near the generation point. Generally, polishing is performed by relatively moving while bringing the workpiece into contact with the polishing platform. The polishing action in this method is locally manifested as an oxidation action and a planarization action through the action of active radicals generated mainly around the contact points between the convex regions of the μm-level unevenness on the surface of the metal platform and the convex regions of the μm-level unevenness on the surface of the workpiece at a certain time, and the entire surface of the workpiece is gradually processed through its repetition. Therefore, in order to make the polishing action act on the entire surface of the workpiece, long-term polishing is required, and the problem is that high polishing efficiency cannot be obtained.

[0014] The present disclosure has been completed to solve the above problems, and its object is to provide a manufacturing method of a semiconductor substrate having a semiconductor layer formed on a substrate of a difficult-to-process material such as diamond with high chemical stability at high quality and low cost.

[0015] Means for Solving the Problems

[0016] The grinding method related to the present disclosure is a grinding method for grinding a workpiece substrate composed of any one of diamond, silicon carbide, gallium nitride, and sapphire, and includes: (a) a step of forming a catalyst metal film composed of a transition metal on the main surface of the workpiece substrate to be ground; and (b) a step of bringing the workpiece substrate formed with the catalyst metal film into contact with a grinding table in an oxidant liquid medicine, reacting the catalyst metal film with the oxidant liquid medicine to generate active radicals, and removing the compound generated by the chemical reaction between the active radicals and the surface atoms of the main surface of the workpiece substrate by moving the workpiece substrate relative to the grinding table, thereby grinding the workpiece substrate.

[0017] Advantages of the Invention

[0018] According to the grinding method related to the present disclosure, since a catalyst transition metal film is pre-formed on the main surface of the workpiece substrate, active radicals generated in the reaction between the oxidant liquid medicine and the transition metal are generated on the entire surface of the main surface of the workpiece substrate having unevenness on the μm level, and an oxidation effect is produced. Therefore, the area where the grinding effect effectively acts increases, and the grinding efficiency is greatly improved. Description of the Drawings

[0019] Figure 1 It is a cross-sectional view illustrating the grinding method of Embodiment 1.

[0020] Figure 2 It is a cross-sectional view illustrating the grinding method of Embodiment 1.

[0021] Figure 3 It is a diagram schematically showing the configuration of a grinding apparatus used in grinding a workpiece substrate by the grinding method of Embodiment 1.

[0022] Figure 4 It is a cross-sectional view showing the workpiece substrate after grinding by the grinding method of Embodiment 1.

[0023] Figure 5 It is a cross-sectional view showing a semiconductor substrate manufactured by the manufacturing method of the semiconductor substrate of Embodiment 2.

[0024] Figure 6 It is a cross-sectional view illustrating the manufacturing method of the semiconductor substrate of Embodiment 2.

[0025] Figure 7 It is a cross-sectional view illustrating the manufacturing method of the semiconductor substrate of Embodiment 2.

[0026] Figure 8 It is a cross-sectional view illustrating the manufacturing method of the semiconductor substrate of Embodiment 2.

[0027] Figure 9 It is a cross-sectional view showing a method for manufacturing a semiconductor substrate according to Embodiment 2.

[0028] Figure 10 It is a cross-sectional view showing a method for manufacturing a semiconductor substrate according to Embodiment 2.

[0029] Figure 11 It is a diagram showing polishing conditions of the polishing method according to Embodiment 1. Detailed implementation manners

[0030] Hereinafter, the polishing method and the method for manufacturing a semiconductor substrate according to the present disclosure will be described with reference to the drawings. Note that the drawings are schematic, and the mutual relationships of the sizes and positions of the images shown in different drawings are not necessarily accurately described. The relationships and ratios of the sizes in the length direction, the depth direction, and the height direction are different from the actual ones. In addition, in the following description, the same reference numerals are given to the same constituent elements in the drawings, and their names and functions are also the same. Therefore, detailed descriptions thereof may sometimes be omitted.

[0031] <Embodiment 1>

[0032] Use Figures 1 to 4 to describe the polishing method according to Embodiment 1 of the present disclosure. First, in the process shown in Figure 1 , a workpiece substrate 100 to be polished is prepared. The material of the workpiece substrate 100 can be any one of diamond, SiC (silicon carbide), and GaN (gallium nitride). Considering the formation of a nitride semiconductor layer, diamond with high thermal conductivity is particularly preferably used. In addition, in Figure 1 etc., the μm-level unevenness AS on the surface of the workpiece substrate 100 is emphasized.

[0033] Next, in the process shown in Figure 2 , a catalyst metal film MF made of a transition metal element is formed on the main surface to be polished among the two main surfaces of the workpiece substrate 100. The main surface on which the catalyst metal film MF is formed is the main surface on the side where the nitride semiconductor layer is to be formed later.

[0034] The catalyst metal film MF can be formed by a known forming method such as vacuum evaporation, sputtering, or plating. From the viewpoint of improving the adhesion between the workpiece substrate 100 and the catalyst metal film MF, sputtering is particularly preferably used.

[0035] The type of the catalyst metal film MF is not limited as long as it reacts with an oxidizing agent solution used as a polishing solution to generate chemically active free radicals (active free radicals). When nickel or iron is used, active free radicals can be efficiently generated, so it is particularly preferred.

[0036] From the viewpoint of improving the efficiency of substrate grinding, it is preferable that the film thickness of the catalyst metal film MF is larger than the value of the maximum height difference of the minute unevenness AS present on the main surface of the workpiece substrate 100 measured by a scanning white interferometer. Further, it is preferable that the maximum value of the film thickness of the catalyst metal film MF is less than 10 times the maximum height difference of the minute unevenness AS.

[0037] It should be noted that when hydrogen peroxide water is used as the oxidizing agent liquid medicine and iron is used for the catalyst metal film MF composed of transition metal elements, the free radical is an active free radical called a hydroxyl radical (OH · ), and its generation reaction is well-known as the Fenton reaction shown by the following chemical formula (1).

[0038] Fe 2+ +H2O2→Fe 3+ +OH - +OH . ···(1)

[0039] Next, the workpiece substrate 100 formed with the catalyst metal film MF is ground using the grinding device PM shown in Figure 3 . Figure 3 The configuration of the grinding device PM is schematically shown. As shown in Figure 3 , the grinding device PM includes: a liquid medicine tank CB that stores the oxidizing agent liquid medicine OS; a grinding table PD that is coupled to a table rotation mechanism RD and mounts the workpiece substrate 100 so as to face the catalyst metal film MF in the liquid medicine tank CB; a substrate holding disk HB that holds the workpiece substrate 100 on the grinding table PD; and a substrate rotation mechanism RB that presses the workpiece substrate 100 via the substrate holding disk HB and rotates it while pressing it against the grinding table PD.

[0040] The grinding table PD of the grinding device PM becomes the reference surface for grinding, and any metal, ceramic, inorganic oxide, etc. can be used as the material. It is preferably a material that reacts with an oxidizing agent liquid medicine OS such as hydrogen peroxide water to generate active free radicals. When iron or nickel is used, active free radicals can be efficiently generated, so it is particularly preferred.

[0041] The oxidizing agent liquid medicine OS stored in the liquid medicine tank CB of the grinding device PM is preferably a liquid medicine that generates active free radicals by reacting with a transition metal, and hydrogen peroxide water is particularly preferably used.

[0042] In the grinding device PM having such a configuration, the catalyst metal film MF is formed ([[]] Figure 2The work piece substrate 100 is subjected to a polishing process, thereby smoothing the μm-level unevenness AS on the main surface of the side of the work piece substrate 100 where the catalyst metal film MF is formed. In Figure 4 The work piece substrate 100 is shown in which the unevenness AS on the main surface to be polished is removed to form a smooth main surface MS.

[0043] Regarding the polishing conditions, any conditions can be used within the range of smoothing the main surface of the work piece substrate 100. For example, 1 wt% hydrogen peroxide water can be used as the oxidizing agent solution OS, and the conditions of the rotational speed of the work piece substrate 100 being 50 rpm, the rotational speed of the polishing table PD being 50 rpm, and the pressing pressure of the work piece substrate 100 being 0.5 MPa can be used.

[0044] In this way, by pre-forming the catalyst metal film MF on the main surface of the work piece substrate 100 and then polishing, active radicals generated by the reaction of the oxidizing agent solution and the transition metal are generated on the entire main surface of the work piece substrate. The active radicals oxidize the main surface of the work piece substrate 100, and a compound is generated through a chemical reaction with the surface atoms of the main surface of the work piece substrate. This compound is removed by the relative movement of the work piece substrate 100 and the polishing table PD, thereby polishing the main surface of the work piece substrate 100. Therefore, compared with the case of polishing without forming the catalyst metal film MF on the work piece substrate 100, the polishing is promoted, and the time required to complete the polishing until the surface arithmetic roughness (Ra) becomes less than 0.5 nm on the entire main surface of the work piece substrate 100 to be polished is significantly shortened. As a result, the work piece substrate 100 with a high-quality smooth surface can be manufactured at low cost.

[0045] <Embodiment 2>

[0046] Next, use Figures 5 to 10 The manufacturing method of the semiconductor substrate according to Embodiment 2 of the present disclosure will be described.

[0047] Figure 6 is a cross-sectional view showing the structure of the semiconductor substrate 300 manufactured by the manufacturing method of the present Embodiment 2. As Figure 6 shown, the semiconductor substrate 300 has, for example, a semiconductor layer 2 made of a semiconductor material such as a nitride semiconductor formed on a support substrate 10 with a high thermal conductivity such as a diamond substrate.

[0048] In the first step of the present Embodiment 2, the polishing method described in Embodiment 1 is used to polish the main surface to be polished among the two main surfaces of the support substrate 10. As Figure 5 shown, the support substrate 10 with a surface arithmetic mean roughness of the main surface MS less than 0.5 nm is obtained.

[0049] In the second process, as Figure 7 shown, on the growth substrate 1, the support substrate BS is bonded to a semiconductor layer 2 (nitride semiconductor layer) made of, for example, a nitride semiconductor by heteroepitaxial growth using a resin adhesive layer.

[0050] In the second process, first, an epitaxial substrate ES on which a semiconductor layer 2 made of a nitride semiconductor or the like is formed by heteroepitaxial growth on the main surface of a growth substrate 1 such as a Si substrate is prepared. In the semiconductor layer 2, electronic components such as diodes, transistors, and resistors can be formed in advance.

[0051] After that, a support substrate BS selected from a glass substrate, a sapphire substrate, a Si substrate, a SiC substrate, etc. is prepared, and the epitaxial substrate ES and the support substrate BS are bonded using a resin adhesive such that the main surface (first main surface) on the side where the semiconductor layer 2 is formed of the epitaxial substrate ES faces the main surface for bonding with the support substrate BS, thereby forming a state in which the epitaxial substrate ES and the support substrate BS are bonded by a resin adhesive layer AH.

[0052] As the resin adhesive, known resin adhesives such as acrylic resins, epoxy resins, silicone resins, modified silicone resins, and alumina adhesives can be used. Preferably, a non-solvent-diluted adhesive that cures by a chemical reaction is used. For example, acrylic resins, epoxy resins, and silicone resins are suitable.

[0053] After bonding, a curing treatment is performed for the purpose of improving the mechanical strength of the resin adhesive layer AH. Regarding the curing conditions, any conditions can be used according to the resin adhesive layer AH used. For example, a heat treatment is performed for 6 hours in a hot air drying oven at 70 degrees.

[0054] The role of the support substrate BS is to support the semiconductor layer 2 in subsequent processes. Therefore, from the viewpoints of heat resistance, mechanical strength, and resistance to the chemical solutions used in the manufacturing process, any material can be used as long as it can withstand the processes, and it is not limited to the above substrates.

[0055] Next, in the third process, as Figure 8 shown, the growth substrate 1 is removed. Regarding the method for removing the growth substrate 1, for example, mechanical polishing, dry etching, or wet etching using a solution can be used to remove it from the main surface on the opposite side (back surface) of the main surface on which the semiconductor layer 2 is formed. From the viewpoint of the removal speed, mechanical polishing is preferably used.

[0056] Next, in the fourth process, the surface (back surface) of the semiconductor layer 2 on the side where the growth substrate 1 has been removed is polished to make it smooth. As the smoothing method, known methods such as mechanical polishing, chemical mechanical polishing (CMP), dry etching, and wet etching using a solution can be used. In order to improve the bonding quality in the subsequent bonding process, high smoothing quality is required. Therefore, the chemical mechanical polishing method is preferably used.

[0057] In the fifth process, as Figure 9 shown, the support substrate 10 obtained in the first process is bonded to the back surface of the semiconductor layer 2. Considering the operating characteristics and reliability improvement of the nitride semiconductor element formed in the semiconductor layer 2, the support substrate 10 is made of a diamond substrate with high thermal conductivity.

[0058] As a method of bonding the support substrate 10 to the semiconductor layer 2, any direct bonding method for dissimilar materials can be used. However, in order to improve the performance and reliability of the nitride semiconductor element, it is preferable to reduce the interfacial thermal resistance between the semiconductor layer 2 and the support substrate 10 as much as possible. In addition, in order to prevent warping of the substrate after bonding, it is preferable to bond the semiconductor layer 2 and the support substrate 10 without heating. Therefore, it is most preferable to use a room temperature bonding method for bonding. As an example of the room temperature bonding method, surface activated room temperature bonding can be cited. It is a method of bonding by making the atoms on the surface into an active state that is easily chemically bonded by surface treatment of the bonding surface in a vacuum.

[0059] It should be noted that as the room temperature bonding method, atomic diffusion bonding and hydrophilic group pressure bonding can also be used. Atomic diffusion bonding is a method of forming a metal film on the surface of the bonding object by sputtering or the like and bonding the metal films to each other in a vacuum.

[0060] Hydrophilic group pressure bonding is a method as follows: the surface of the bonding object is slightly oxidized to form a thin oxide film, and after performing a hydrophilization treatment to attach a plurality of hydroxyl groups to the surface, the hydrophilized surfaces are overlapped and pressed to bond.

[0061] Finally, in the sixth process, the support substrate BS and the resin adhesive layer AH on the side opposite to the support substrate 10 are removed. As Figure 10 shown, a semiconductor substrate 300 having the semiconductor layer 2 formed on the support substrate 10 is obtained.

[0062] The removal method can use well-known methods: a method of mechanically peeling the resin adhesive layer AH together with the support substrate BS from the support substrate 10; a method of immersing the resin adhesive layer AH in a solvent to embrittle its physical properties and then mechanically peeling it from the support substrate 10; a method of heat-treating the resin adhesive layer AH to burn it and remove the support substrate BS; a method of treating the resin adhesive layer AH with sulfuric peroxide to burn it and remove the support substrate BS, etc.

[0063] The semiconductor substrate 300 manufactured by the manufacturing method of the semiconductor substrate according to the above-described Embodiment 2 has a semiconductor layer 2 made of a nitride semiconductor or the like on a support substrate 10 having a high thermal conductivity such as a diamond substrate on which planarization polishing processing at the atomic layer level has been efficiently performed. The semiconductor layer 2 is a semiconductor layer formed by heteroepitaxial growth on a growth substrate different from the support substrate 10 and is transferred onto the support substrate 10 while maintaining the crystal plane during heteroepitaxial growth unchanged. Therefore, a high-quality nitride semiconductor element can be formed on the semiconductor layer 2. In addition, the diamond substrate can be efficiently polished and planarized by using the polishing method of Embodiment 1, so that the semiconductor substrate 300 can be manufactured at low cost.

[0064] <Modification Example>

[0065] Furthermore, in the above-described Embodiment 1 and Embodiment 2, the case where the semiconductor layer 2 is formed by heteroepitaxial growth on the main surface of the growth substrate 1 has been described, but the semiconductor layer 2 is not limited to a semiconductor layer formed by heteroepitaxial growth and may be composed of a semiconductor film formed by homoepitaxial growth.

[0066] <Examples>

[0067] Hereinafter, Examples 1 to 4 of the polishing method of Embodiment 1 and the manufacturing method of the semiconductor substrate of Embodiment 2 will be described in more detail, but the implementation conditions are not limited thereto.

[0068] Figure 11 is a diagram showing at a glance the polishing conditions of the polishing method of Embodiment 1 for Examples 1 to 4 and Comparative Examples. In Figure 11 it shows, for Examples 1 to 4 and Comparative Examples, the material of the workpiece substrate and the catalyst metal film used, the polishing completion time, the ratio (%) of the bonding surface area, the type of oxidizing agent liquid medicine, and the material of the polishing table.

[0069] <Type of workpiece substrate>

[0070] In Examples 1 and 2 and the Comparative Example, diamond was used as the work substrate. In Example 3, a 6H-SiC substrate was used as the work substrate. In Example 4, a GaN substrate was used as the work substrate. Each work substrate was cut into a size of 10 mm square and used.

[0071] <Type of catalyst metal film>

[0072] In Examples 1, 3, and 4, a nickel film formed by sputtering was used as the catalyst metal film. The thickness of the nickel film was 10 μm.

[0073] In Example 2, an iron film formed by sputtering was used as the catalyst metal film. The thickness of the iron film was 10 μm. It should be noted that in the Comparative Example, polishing was carried out without forming a catalyst metal film on the work substrate.

[0074] <Polishing platen>

[0075] In Examples 1, 3 to 4, and the Comparative Example, nickel was used as the material of the polishing platen used in the polishing apparatus. In Example 2, cast iron was used as the material of the polishing platen used in the polishing apparatus.

[0076] <Oxidizing agent solution>

[0077] In the polishing of each work substrate in Examples 1 to 4 and the Comparative Example, hydrogen peroxide water diluted to 1 weight percentage (wt%) was used as the oxidizing agent solution.

[0078] <Evaluation of the shape of the main surface of the substrate>

[0079] The change in the shape of the main surface before and after polishing of each work substrate in Examples 1 to 4 and the Comparative Example was evaluated for surface shape by an optical shape evaluation method using a scanning white interferometer.

[0080] The evaluation was carried out in a field of view of 90 μm square, and a total of 5 points were measured, including 1 point at the in-plane center and 4 points at the corners of the 10 mm square substrate.

[0081] <Polishing conditions>

[0082] As the polishing conditions for each workpiece substrate in Examples 1 to 4 and the Comparative Example, the polishing pressure was set to 0.5 MPa, the rotational speed of the workpiece substrate was 50 rpm, and the rotational speed of the polishing table was 50 rpm. During polishing, the workpiece substrate was taken out of the polishing apparatus every 5 hours and the main surface shape was evaluated. The state where all the points at the shape measurement points on the main surface of the workpiece substrate had a surface arithmetic roughness (Ra) of less than 0.5 nm was regarded as the completion of polishing. Polishing was carried out up to a maximum of 50 hours while repeating polishing and evaluation of the main surface shape of the substrate.

[0083] <Manufacture of Semiconductor Substrate with Semiconductor Layer>

[0084] In Examples 1 to 4 and the Comparative Example, a gallium nitride film was formed as a nitride semiconductor layer on a Si substrate by heteroepitaxial growth, bonded to a support substrate made of a glass substrate using an acrylic adhesive, the Si substrate was removed by mechanical grinding, and the removed surface was precisely polished by chemical mechanical polishing. Then, the gallium nitride film bonded to the glass substrate and each workpiece substrate formed in Examples 1 to 4 and the Comparative Example were bonded by surface-activated room-temperature bonding to manufacture a semiconductor substrate in which the nitride semiconductor layer was integrated with each workpiece substrate.

[0085] <Evaluation of Semiconductor Substrate>

[0086] In Examples 1 to 4 and the Comparative Example, ultrasonic flaw detection was used to evaluate the bonding quality of the manufactured semiconductor substrate. Here, it was the ratio of the area of the region where bonding defects (interface voids) remained with respect to the area of the main surface of the workpiece substrate, and the ratio of the area of the region where no interface voids remained was used as the bonding surface region ratio.

[0087] <Evaluation Results of Workpiece Surface after Polishing and Composite Substrate>

[0088] In Examples 1 to 4, a catalyst metal film composed of a transition metal element was formed on the surface of the workpiece substrate in advance and polishing was carried out. Therefore, the polishing action was more effectively exerted over the entire surface of the substrate. As Figure 11 shown, the time until the completion of polishing of the main surface of the substrate (polishing completion time) was within 20 hours in Examples 1 to 4, and ended in a short time compared to more than 50 hours in the Comparative Example.

[0089] In addition, in the evaluation results of the bonding quality of the semiconductor substrates manufactured in each Example, as Figure 11 shown, the ratio of the bonding surface region in Examples 1 to 4 was approximately 100%, and bonding was formed over the entire main surface of the workpiece substrate.

[0090] On the other hand, in the comparative example, polishing was performed without forming a catalyst metal film on the surface of the workpiece substrate. Therefore, the region where the polishing action effectively functions is limited, and even after polishing for 50 hours, polishing was not completed on the entire main surface of the workpiece substrate. In addition, the bonding quality of the semiconductor substrate was evaluated by ultrasonic flaw detection method, and as a result, bonding defects occurred in 35% of the area region.

[0091] As described above, according to the polishing method and the semiconductor substrate manufacturing method according to the present disclosure, the diamond substrate can be polished and smoothed with high efficiency. Therefore, a semiconductor substrate having a nitride semiconductor layer formed on a diamond substrate with high heat dissipation can be manufactured with high quality and low cost.

[0092] The present disclosure has been described in detail, but the above description is illustrative in all aspects, and the present disclosure is not limited thereto. It should be understood that countless variations that are not illustrated can be conceived without departing from the scope of the present disclosure.

[0093] Furthermore, the present disclosure can freely combine the respective embodiments within the scope of its disclosure, or appropriately modify or omit the respective embodiments.

Claims

1. A method for manufacturing a semiconductor substrate, comprising: (a) a step of forming a catalyst metal film made of a transition metal on a main surface to be polished of a workpiece substrate made of any one of diamond, silicon carbide, gallium nitride, and sapphire; (b) A step of polishing the substrate to be processed having the catalyst metal film formed thereon by relatively moving the substrate to be processed and a polishing table in an oxidizing agent liquid to remove a compound generated by a chemical reaction between active radicals and surface atoms of the main surface of the substrate to be processed, wherein, The active radicals are generated by the reaction of the catalyst metal film with the oxidant liquid medicine. (c) a step of preparing an epitaxial substrate and a support substrate in which a nitride semiconductor layer is epitaxially grown on a main surface of a growth substrate as the semiconductor substrate, forming a resin bonding layer between the nitride semiconductor layer of the growth substrate and the main surface of the support substrate, and bonding the epitaxial substrate and the support substrate; (d) a step of removing the growth substrate after the step (c) to expose the nitride semiconductor layer; (e) a step of bonding the workpiece substrate polished by the step (b) to the nitride semiconductor layer by a room temperature bonding method after the step (d); and (f) a step of removing the support substrate and the resin bonding layer after the step (e).

2. The manufacturing method of the semiconductor substrate according to claim 1, wherein, The step (a) includes the step of forming the catalyst metal film using iron or nickel. The step (b) uses hydrogen peroxide water as the oxidant liquid medicine.

3. The manufacturing method of the semiconductor substrate according to claim 1, wherein, The step (a) includes the step of forming the film thickness of the catalyst metal film to be greater than the maximum height difference of the unevenness existing on the main surface of the workpiece substrate and less than 10 times the maximum height difference.

4. The manufacturing method of the semiconductor substrate according to claim 2, wherein, The polishing table is made of iron or nickel.

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