Group iii element nitride substrate, substrate with epitaxial layer, processes for producing these, and process for producing semiconductor element

Group III nitride substrates, substrates with epitaxial layers, methods for manufacturing these, and methods for manufacturing semiconductor devices

The present invention relates to a group III nitride substrate, a substrate with an epitaxial layer, a method for manufacturing these and a method for manufacturing a semiconductor device, and more specifically, the present invention relates to an epitaxial layer that can form a good film quality Group III nitride substrates, substrates with epitaxial layers, manufacturing methods for these, and manufacturing methods for semiconductor devices.

Previously, the surface of a compound semiconductor substrate including a group III nitride substrate such as a GaN substrate was mirror-polished, and an epitaxial growth layer was formed on the surface using an epitaxial growth method, and the compound semiconductor substrate was used for light-emitting devices or power Various semiconductor components such as components. As a result, the following problem arises: when the surface is mirror-polished as described above, if stains are generated on the polished surface, defects such as cracks will occur on the formed epitaxial growth layer, which will damage the quality of the epitaxial growth layer. . Therefore, various polishing methods for suppressing the occurrence of stains (reducing haze) as described above have previously been proposed (for example, regarding GaAs, refer to Patent Document 1 (Japanese Patent Laid-Open No. 11-347920)).

Patent Document 1: Japanese Patent Laid-Open No. 11-347920

<p>However, as a result of research conducted by the inventor, it is known that if only the haze on the surface of a group III nitride substrate such as GaN is reduced, defects such as cracks may sometimes occur in the epitaxial growth layer formed on the surface of the substrate. At this time, even if the above-mentioned previous polishing method is applied, it is difficult to sufficiently reduce the occurrence probability of defects on the epitaxial growth layer.</p><p>The present invention was completed in order to solve the above-mentioned problems. The object of the present invention is to provide a Group III nitride substrate capable of forming a good-quality epitaxial growth layer and a manufacturing method thereof.</p><p>In addition, another object of the present invention is to provide a substrate with an epitaxial layer and a manufacturing method thereof, and to provide a method for manufacturing a semiconductor device using the substrate with an epitaxial layer. The above-mentioned substrate with an epitaxial layer is Use the above-mentioned group III nitride substrate to have a good quality epitaxial growth layer.</p>

<p>The inventors have studied the mechanism of quality degradation in the epitaxial growth layer formed on the surface of the III-nitride substrate. Specifically, a detailed inspection of the surface of the III nitride substrate before the formation of the epitaxial growth layer (measurement of the type or quantity of attached substances, etc.) is performed, and the correlation between the inspection results and the quality of the formed epitaxial growth layer is investigated . As a result, it was found that the number of acidic substances and the number of silicon atoms present on the surface of the group III nitride substrate when the epitaxial growth layer is formed has a greater impact on the quality of the epitaxial growth layer formed. Furthermore, the so-called group III nitride substrate refers to, for example, a substrate formed of GaN or a substrate formed of AlN, and its mixed crystal substrate (Ga_xAl_yN). In addition, the so-called acidic substances refer to halogens such as chlorine, fluorine, bromine, and iodine, and nitrogen oxides (NO_x), sulfur oxide (SO_x), hydrogen chloride and other substances that react with or dissolve in water and show acidity.</p><p>In addition, the inventors have studied the reason why the above-mentioned acidic substance adheres to the surface of the Group III nitride substrate, and it is estimated that it is caused by the following phenomenon. That is, in the step of manufacturing a group III nitride substrate (such as a GaN substrate, etc.), in addition to using volatile acidic substances such as hydrochloric acid and nitric acid, when polishing the substrate, a polishing liquid containing abrasive grains is used. A chlorine-based substance is often used as an oxidizing agent in the polishing liquid, and the polishing liquid contains a large amount of chlorine as an acidic substance. The grinding step using these acidic substances is usually performed by exhausting the environment in the grinding device through an exhaust device. When the exhaust device does not completely discharge the acidic substance, there is a part of the acidic substance in the environment in the grinding device. It is considered that at this time, the acidic substance is adsorbed on the surface of the group III nitride substrate. It is also believed that such an acidic substance reacts with the elements forming the III-nitride substrate, thereby forming a precipitate on the surface of the substrate. When such a deposit is formed, the surface roughness and haze value of the substrate surface increase.</p><p>The Group III nitride substrate is polished and cleaned, and then surface inspection is performed. If there are many acidic substances on the surface of the III-nitride substrate in the above-mentioned polishing step, it is difficult to fully remove it in the subsequent steps. Therefore, the surface roughness and haze value of the substrate surface in the final state increase. In addition, the surface inspection is performed in a clean room, and the inspection period is at least about 1 hour, and the Group III nitride substrate is placed in the environment of the clean room. At this time, it is also considered that a small amount of acidic substance flowing from the above-mentioned polishing step and the like is adsorbed on the surface of the group III nitride substrate.</p><p>Also, use SiO₂When polishing a Group III nitride substrate such as a GaN substrate with a substance containing Si atoms as a polishing liquid for abrasive grains, even if a cleaning step is performed after polishing, a substance containing Si may remain on the surface of the substrate. Moreover, the inventors have found that when the above-mentioned acidic substances (and/or precipitates) or Si-containing substances are excessively present on the surface of the III-nitride substrate, the quality of the epitaxial growth layer formed on the surface of the substrate deterioration. That is, in order to form a high-quality epitaxial growth layer on the surface of the III-nitride substrate, it is effective to reduce the concentration of the above-mentioned acidic substance or Si-containing substance on the surface of the substrate. Furthermore, the inventors found that in order to reduce the concentration of acidic substances on the surface of the substrate as described above, it is effective to reduce the concentration of acidic substances in the ambient gas in contact with the surface of the substrate in the polishing apparatus as much as possible. In addition, the inventors have discovered that in order to reduce the concentration of Si-containing substances (or silicon atoms) attached to the surface of the substrate, it is effective to include an acid and a surfactant in the polishing liquid used in the polishing step. Furthermore, when the concentration of the acidic substance in the environment of the manufacturing step is high, the problem of increased concentration of the acidic substance on the surface of the substrate occurs. This problem is also present in the polishing step, the inspection step, or other steps.</p><p>The Group III nitride substrate of the present invention completed based on the above findings is characterized in that every 1 cm of the surface of the Group III nitride substrate²The number of atoms of the acidic substance is 2×10¹⁴Below, and every 1 cm of the surface²The number of silicon (Si) atoms is 3×10¹³the following.</p><p>In this way, a good-quality epitaxial growth layer can be formed on the surface of the III-nitride substrate. Furthermore, the group III nitride substrate surface every 1 cm²The number of atoms of the acidic substance is set to 2×10¹⁴The following reason is that if the number of atoms of the acidic substance is suppressed below the above level, the roughness and haze of the substrate surface can be sufficiently reduced (the degree of cracking on the substrate surface can be sufficiently reduced). In addition, every 1 cm of the surface of the group III nitride substrate²The number of silicon (Si) atoms is set to 3×10¹³The following reason is that if this is the case, the quality of the epitaxial growth layer formed (such as the surface roughness or film quality of the epitaxial growth layer) can be maintained sufficiently well (for example, when the epitaxial growth layer is used as a light-emitting device) When the light-emitting layer, a specific luminous intensity can be obtained). Furthermore, the so-called number of atoms of an acidic substance, for example, when halogens such as fluorine, chlorine, bromine, and iodine exist as monomers, it refers to the number of halogen atoms; when nitrogen oxide (NO_x), sulfur oxide (SO_xWhen a compound such as) exists, it refers to the number of molecules of the compound. In addition, the so-called number of silicon atoms refers to the number of silicon atoms when silicon exists as a single substance; when it is expressed as SiO₂When the general compound form exists, it refers to the number of molecules of the compound.</p><p>On the above-mentioned Group III nitride substrate, the surface haze can be less than 5 ppm. The reason is that the surface of the III-nitride substrate can be changed every 1 cm²The number of atoms of the acidic substance (density of the acidic substance) is set below the above-mentioned value to sufficiently reduce the surface roughness of the substrate, and therefore, the degree of staining (haze) can be sufficiently reduced. In this way, by reducing the haze of the substrate surface, the quality of the epitaxial growth layer formed on the substrate surface can be prevented from deteriorating. Furthermore, the reason for setting the upper limit of the haze to 5 ppm is that when the haze exceeds 5 ppm, the quality of the epitaxial growth layer formed decreases. For example, when the epitaxial growth layer is used for the light-emitting layer of a light-emitting device At the same time, sufficient luminous intensity cannot be obtained.</p><p>The III-nitride substrate of the present invention is characterized in that every 1 cm of the surface of the III-nitride substrate²The number of silicon atoms is 3×10¹³Below, and the haze of the surface is 5 ppm or less. In addition, the group III nitride substrate of the present invention is characterized in that every 1 cm of the surface of the group III nitride substrate²The number of atoms of the acidic substance is 2×10¹⁴Below, and the haze of the surface is 5 ppm or less.</p><p>In this way, a good-quality epitaxial growth layer can be formed on the surface of the III-nitride substrate.</p><p>On the above-mentioned group III nitride substrate, every 1 cm of surface²The number of atoms of the acidic substance is preferably 9×10¹³the following. In addition, in the aforementioned Group III nitride substrate, the haze on the surface is preferably 3 ppm or less. Also, on the above-mentioned group III nitride substrate, every 1 cm of the surface²The number of silicon atoms is preferably 1×10¹³the following.</p><p>At this time, the film quality of the epitaxial growth layer formed on the surface of the III nitride substrate can be further improved. For example, when the substrate is used to form a light-emitting element and an epitaxial growth layer is used to form the light-emitting layer, the light-emitting intensity of the light-emitting layer can be further improved.</p><p>The substrate with an epitaxial layer of the present invention includes a base substrate formed of a group III nitride and an epitaxial growth layer formed on the surface of the base substrate. Every 1 cm at the interface between the base substrate and the epitaxial growth layer³The number of silicon (Si) atoms is 1×10²⁰the following.</p><p>In the substrate with an epitaxial layer constructed in this way, the epitaxial growth layer is formed while keeping the number of silicon atoms on the surface of the base substrate small, so that the epitaxial growth layer with good film quality can be formed. Therefore, it is possible to suppress the problem that when a semiconductor element (such as a light-emitting element) is formed using the above-mentioned substrate with an epitaxial layer, the semiconductor element does not fully exhibit its performance due to poor quality of the epitaxial growth layer (defective product). In addition, the so-called substrate with an epitaxial layer refers to a substrate on which at least one layer formed by the epitaxial growth method (epitaxial growth layer) is formed on the surface of a base substrate. In addition, in the above-mentioned substrate with an epitaxial layer, the interface between the base substrate and the epitaxial growth layer is every 1 cm³The number of silicon (Si) atoms can be 1×10¹⁹the following. At this time, the film quality of the epitaxial growth layer can be made better. Furthermore, every 1 cm of the above interface³The number of silicon atoms is preferably 1×10¹⁸Below, better is 1×10¹⁷the following.</p><p>In addition, the surface roughness Ra of the above-mentioned group III nitride substrate may be 1 nm or less. In addition, the surface roughness Ra of the epitaxial growth layer of the substrate with the epitaxial layer may be 1 nm or less. Furthermore, the thickness of the processed modified layer formed on the surface of the above-mentioned group III nitride substrate may be 50 nm or less. In addition, the thickness of the processed modified layer formed on the surface of the base substrate of the above-mentioned substrate with an epitaxial layer may be 50 nm or less. Here, the thickness of the above-mentioned modified layer can be evaluated by the following way, that is, by observing the substrate with a transmission electron microscope (TEM, transmission electron microscope), and taking the observed area with lattice deformation as The above-mentioned processed modified layer was measured for the thickness of the portion where the deformation occurred (processed modified layer).</p><p>The manufacturing method of the group III nitride substrate of the present invention includes: a polishing step, which polishes the surface of the group III nitride substrate; and a cleaning step, which cleans the surface of the group III nitride substrate after the polishing step. After the cleaning step, every 1 cm on the surface of the III nitride substrate²The number of atoms of the acidic substance is maintained at 2×10¹⁴The following methods are used to control the ambient gas in contact with the Group III nitride substrate during the polishing step and after the cleaning step. In the polishing step, the surface of the group III nitride substrate is polished by a chemical mechanical polishing method. The polishing liquid used in the chemical mechanical polishing method contains a surfactant and an acid.</p><p>In this way, the exhaust mechanism can be operated by controlling the above-mentioned ambient gas (for example, the ambient gas containing acidic substances can be quickly removed from around the group III nitride substrate; or the acidic substance contained in the ambient gas can be activated. The way that the concentration of the substance is lower than a specific value is to arrange an adsorbent for removing acidic substances in the flow path of the ambient gas, so as to reduce the adhesion of the acidic substances in the ambient gas to the group III nitrogen during the polishing step and after the cleaning step Possibility of compounding on the surface of the substrate. In addition, by using the above-mentioned polishing liquid in the polishing step, the SiO2 content in the polishing liquid can be reduced.₂The possibility of foreign matter (Si-containing matter) like the formed abrasive grains (particulate matter) attached to the surface of the Group III nitride substrate after the polishing step. Therefore, the density of Si-containing substances, that is, silicon atoms, on the surface of the group III nitride substrate can be reduced.</p><p>In the manufacturing method of the above-mentioned group III nitride substrate, the polishing liquid may further contain an oxidizing agent. At this time, the polishing rate in the polishing step can be increased. As a result, the manufacturing efficiency of the group III nitride substrate can be improved.</p><p>In the above-mentioned manufacturing method of Group III nitride substrate, the acid contained in the polishing liquid is not particularly limited. For example, in addition to hydrochloric acid, hydrofluoric acid, bromic acid, iodic acid, nitric acid, sulfuric acid, phosphoric acid, carbonic acid, In addition to such inorganic acids, organic acids such as formic acid, acetic acid, citric acid, malic acid, tartaric acid, succinic acid, dicarboxylic acid, fumaric acid, and oxalic acid can also be used. In addition, in the manufacturing method of the above-mentioned group III nitride substrate, the organic acid may be a carboxylic acid having a valence of two or more. At this time, the polishing rate in the polishing step can be increased, and the possibility of foreign matter adhering to the surface of the substrate due to the acid contained in the polishing liquid can be reduced. Furthermore, the so-called organic acid here is an organic compound exhibiting acidity. In addition, the surfactant contained in the polishing liquid is not particularly limited, and any one of cationic, anionic, and nonionic surfactants can be used.</p><p>The manufacturing method of the group III nitride substrate may further include the following steps: after the grinding step and before the cleaning step, an acid solution or an alkaline solution is used to polish the surface of the group III nitride substrate. In addition, in this polishing step, both the step of polishing the surface of the group III nitride substrate with an acidic solution and the step of polishing the surface of the group III nitride substrate with an alkaline solution can be carried out in sequence, and the acidic solution can be repeated multiple times. Solution polishing step and/or polishing step using alkaline solution. There is no special restriction on alkaline solution, KOH, NaOH, NH can be used₄Alkali such as OH and amine. At this time, the foreign matter can be removed from the surface of the III nitride substrate by polishing before the cleaning step. Therefore, the probability of the problem that foreign matter (such as Si-containing material) remains on the substrate surface after the cleaning step can be reduced.</p><p>Furthermore, in addition to chemical mechanical polishing, the surface of the substrate can also be removed and processed by dry etching. The so-called dry etching refers to the general term of the following methods, that is, the use of gas, plasma, ions or light, etc., chemical or physical reaction at the gas-solid interface to remove the group III nitrides as solids The surface of the substrate.</p><p>Chlorine-based gas is often used in dry etching of group III nitride substrates, and sometimes chlorine, which is an acid substance, remains on the surface of the substrate. Chlorine gas has Cl₂, BCl₃, SiCl₄Wait. It is also possible to set the gas used for dry etching to these chlorine-based gases and Ar and N as inert gases₂The mixed gas. The acidic substance on the surface of the substrate can be reduced by adjusting the dilution, pressure, flow and other conditions of the inert gas. In addition, the presence of Si in the plasma is effective for smoothing the surface of the group III nitride substrate by dry etching. Si can be used by SiCl₄It can be added to the plasma with other gases, and the Si compound may be placed around the substrate while etching the substrate and the Si compound to be present in the plasma. Furthermore, sometimes Si remains on the surface of the substrate after dry etching due to the presence of Si in the etching environment. At this time, the silicon on the surface of the substrate can be reduced by controlling the Si concentration in the plasma.</p><p>In addition, the method for manufacturing a group III nitride substrate of the present invention is characterized in that a chlorine-based gas is used to dry-etch the surface of the group III nitride substrate in a Si-containing environment, thereby making the surface per 1 cm²The number of atoms of the acid substance becomes 2×10¹⁴Below, and make the surface every 1 cm²The number of silicon atoms becomes 3×10¹³the following. Here, the term "chlorine-based gas system" refers to a gas containing chlorine in its component composition, and may be, for example, chlorine gas or a gas containing chlorine in its composition, or a mixed gas containing at least one of these gases.</p><p>The method for manufacturing a substrate with an epitaxial layer of the present invention includes: a substrate preparation step for implementing the method for manufacturing the above-mentioned group III nitride substrate; and on the surface of the group III nitride substrate obtained by the substrate preparation step The step of forming an epitaxial growth layer. In this way, a good-quality epitaxial growth layer can be formed on the surface of the III-nitride substrate.</p><p>The method for manufacturing a substrate with an epitaxial layer of the present invention includes: a substrate preparation step of preparing the above-mentioned group III nitride substrate; and forming an epitaxial crystal on the surface of the group III nitride substrate prepared by the substrate preparation step Steps in the growth layer. In this way, a good-quality epitaxial growth layer can be formed on the surface of the III-nitride substrate.</p><p>The method for manufacturing a semiconductor device of the present invention includes: a substrate preparation step with an epitaxial layer, which implements the above-mentioned method for manufacturing a substrate with an epitaxial layer; and the step of preparing a substrate with an epitaxial layer The substrate with the epitaxial layer is subjected to electrode forming steps and processing steps, thereby forming semiconductor devices. In this way, a semiconductor device can be formed using a substrate with an epitaxial growth layer with good quality epitaxial growth layer. Therefore, the probability of defective semiconductor devices due to poor quality of the epitaxial growth layer can be reduced. Therefore, it is possible to suppress the decrease in the yield of the semiconductor device.</p>

<p>In this way, according to the present invention, a substrate with an epitaxial layer with an epitaxial growth layer of good quality formed on the surface of a III nitride substrate can be obtained, and thus a semiconductor device can be formed by using the substrate with an epitaxial layer , Can reduce the probability of defective semiconductor components.</p>

Hereinafter, embodiments and examples of the present invention will be described using drawings. Furthermore, in the following drawings, the same or equivalent parts are attached with the same reference numbers, and the description is not repeated.

Fig. 1 is a schematic perspective view showing a GaN substrate as an example of the Group III nitride substrate of the present invention. FIG. 2 is a flowchart for explaining a method of manufacturing a semiconductor device using the GaN substrate shown in FIG. 1. Fig. 3 is a flow chart for explaining the content of the processing steps shown in Fig. 2. 4 is a schematic perspective view showing a substrate with an epitaxial layer using the GaN substrate shown in FIG. 1. 1 to 4, the embodiment of the method for manufacturing a GaN substrate, a substrate with an epitaxial layer, and a semiconductor device of the present invention will be described.

As shown in FIG. 1, the GaN substrate 1 of the present invention is placed on the surface (for example, after polishing and cleaning) by performing the following processing steps, every 1 cm²The number of atoms of the acidic substance (such as chlorine atoms) is 2×10¹⁴Below, and every 1 cm on the surface²The number of silicon atoms is 3×10¹³the following. In addition, on the GaN substrate 1, the haze on the surface is 5 ppm or less. In this way, a good-quality epitaxial growth layer can be formed on the surface of the III-nitride substrate.

In the above GaN substrate 1, every 1 cm on the surface 3²The number of atoms of the acidic substance is preferably 9×10¹³the following. In addition, in the GaN substrate 1 described above, the haze of the surface 3 is preferably 3 ppm or less. Moreover, in the above-mentioned GaN substrate 1, every 1 cm on the surface 3²The number of silicon atoms is preferably 1×10¹³the following.

At this time, the film quality of the epitaxial growth layer 5 (refer to FIG. 4) formed on the surface 3 of the GaN substrate 1 can be further improved. For example, as described below, when the GaN substrate 1 is used to form a light-emitting element and the light-emitting layer is formed by an epitaxial growth layer, the light-emitting intensity on the light-emitting layer can be further increased.

Furthermore, TXRF (Total X-ray Reflection Fluorescence: total reflection X-ray fluorescence analysis) was used to measure the number of atoms of the acidic substance and the number of silicon atoms. In addition, the haze was measured using SURFSCAN4500 manufactured by Tencor.

Next, referring to FIGS. 2 and 3, a method of manufacturing a semiconductor device including the steps of manufacturing the GaN substrate shown in FIG. 1 will be described.

As shown in FIG. 2, first, the preparation step (S100), that is, the step of preparing a GaN substrate is performed. In this preparation step (S100), the GaN substrate can be prepared according to any previously known method.

Next, a processing step such as polishing the GaN substrate is performed (S200). With reference to FIG. 3, the processing content in the processing step (S200) will be described. In the processing step (S200), as shown in FIG. 3, a CMP (chemical mechanical polishing) step (S210) as a polishing step is first performed. In the CMP step (S210), a chemical mechanical polishing method CMP is used to polish the surface of the GaN substrate prepared in the preparation step (S100). As a result, the surface of the GaN substrate is processed into a mirror surface.

Here, in the polishing liquid used in the CMP step (S210), in addition to the abrasive grains, a surfactant and an acid are also added. Furthermore, as the abrasive particles contained in the polishing liquid, for example, SiO can be used₂Or Al₂O₃, ZrO₂, CeO₂, Fe₂O₃, Cr₂O₃Wait. Here, in order to improve the cleaning properties, it is preferable to use a metal element having a higher ionization tendency as the metal element constituting the abrasive grains. For example, when abrasive grains containing a metal element with a higher ionization tendency than hydrogen (H) are used, the removal efficiency of abrasive grains and the like in the following cleaning step is improved. In addition, as the acid, hydrochloric acid or the like can be used, but organic acids such as malic acid or citric acid can also be used. As the organic acid, it is preferable to use a carboxylic acid having a valence of two or more. In addition, an oxidizing agent may be further added to the polishing liquid. As the oxidizing agent, it is preferable to use chlorinated isocyanuric acid such as hypochlorous acid and hypochlorite, trichloroisocyanuric acid (TCIA), and chlorinated isocyanuric acid such as sodium dichloroisocyanuric acid. Permanganate such as urate, potassium permanganate, dichromate such as potassium dichromate, bromate such as potassium bromate, thiosulfate such as sodium thiosulfate, persulfate such as ammonium persulfate, potassium persulfate, etc. , Nitric acid, hydrogen peroxide water, ozone, etc.

Next, a polishing step (S220) is implemented. In this polishing step, an acidic or alkaline polishing liquid is used. As the acidic polishing liquid, for example, hydrochloric acid, nitric acid, phosphoric acid, citric acid, malic acid, etc. can be used. Moreover, as an alkaline polishing liquid, potassium hydroxide, sodium hydroxide, sodium carbonate, etc. can be used, for example.

Next, a cleaning step (S230) is implemented. In this cleaning step (S230), any cleaning method can be used. For example, as the washing step (S230), pure water washing using pure water may be implemented. Moreover, at least in the CMP step (S210), the polishing step (S220), and the cleaning step (S230) and subsequent steps, the ambient gas that the GaN substrate is exposed to (the ambient gas in the clean room where the GaN substrate is processed) is In a way to keep the concentration of acidic substances, especially chlorine atoms, low, the ambient gas is discharged from the surroundings of the GaN substrate, and an adsorbent for adsorbing acidic substances is arranged in the circulation system of the ambient gas. As the adsorbent, for example, activated carbon is used. In this way, the concentration of acidic substances in the ambient gas, especially chlorine atoms, can be kept below a specific value (for example, 0.02 ppm or less). As a result, it is possible to reduce the amount of acidic substances that are chlorine atoms adhering to the surface of the polished and cleaned GaN substrate. Furthermore, in the polishing step (S220), for the ambient gas in contact with the GaN substrate, the ambient gas can also be discharged from the GaN substrate as described above, and an adsorbent for adsorbing acidic substances is arranged in the circulation system of the ambient gas .

The GaN substrate 1 with a very low density of acidic substances and silicon atoms on the surface as shown in FIG. 1 can be obtained by performing the above-mentioned steps. Furthermore, in the processing step (S200), in addition to the CMP step, the surface of the GaN substrate can also be processed by a dry etching step. It is also possible to perform a dry etching step in addition to the CMP step.

Next, as shown in FIG. 2, a post-processing step (S300) is performed on the GaN substrate processed into a mirror surface by the processing step (S200). In the post-processing step (S300), for example, a step of forming a specific epitaxial growth layer on the surface of the GaN substrate (film forming step) is performed. As a result of this film forming step, as shown in FIG. 4, a substrate 10 with an epitaxial layer 5 having an epitaxial growth layer 5 formed on the surface of the GaN substrate 1 can be obtained. Furthermore, in the post-processing step (S300), the following steps are performed, that is, the step of forming an electrode on the surface of the substrate 10 with the epitaxial layer (electrode forming step), and separating the epitaxial substrate 10 into individual elements The separation step, and the step of connecting the formed element to the frame (processing step), thereby implementing the assembly step of assembling the light-emitting device and other elements.

There are also parts that overlap with the above-mentioned embodiments, and the embodiments of the present invention are listed and explained. The manufacturing method of the Group III nitride substrate (GaN substrate 1) of the present invention includes: a polishing step (CMP step (S210)), polishing the surface of the GaN substrate 1; and a cleaning step (S230), after the CMP step (S210), The surface of the GaN substrate 1 is cleaned. After the cleaning step (S230), every 1 cm of the surface of the GaN substrate 1²The number of atoms of the acidic substance is maintained at 2×10¹⁴In the following manner, the ambient gas in contact with the GaN substrate 1 is controlled during the polishing step (CMP step (S210)) and after the cleaning step (S230). Specifically, in order to maintain the concentration of the acidic substance in the ambient gas below a specific value, an adsorption member such as activated carbon that adsorbs the acidic substance is arranged in the ambient gas. In addition, in the CMP step (S210) and after the cleaning step (S230), an exhaust mechanism may be provided to maintain the concentration of acidic substances in the ambient gas below a specific value. In the CMP step (S210), the surface of the GaN substrate 1 is polished by a chemical mechanical polishing method. The polishing liquid used in the chemical mechanical polishing method contains a surfactant and an acid.

In this way, the environmental gas is controlled by removing acidic substances from the above-mentioned environmental gas, thereby reducing the possibility of the acidic substances in the environmental gas adhering to the surface of the GaN substrate 1 during the CMP step or after the cleaning step. In addition, by using the above-mentioned polishing liquid in the CMP step (S210), the possibility that the Si-containing material in the polishing liquid adheres to the surface of the GaN substrate 1 after the CMP step (S210) can be reduced. Therefore, the density of the Si-containing material on the surface of the GaN substrate 1, that is, the silicon atom can be reduced.

In the above-mentioned CMP step (S210), the polishing liquid may further contain an oxidizing agent. At this time, the polishing rate in the polishing step can be increased.

In addition, the acid contained in the polishing liquid may be an organic acid. In addition, the organic acid may be a carboxylic acid having a valence of two or more. At this time, the polishing rate in the polishing step can be increased, and the possibility of foreign matter adhering to the surface of the substrate due to the acid contained in the polishing liquid can be reduced.

The manufacturing method of the GaN substrate described above may further include the following steps (polishing step (S220)), that is, after the CMP step (S210) and before the cleaning step (S230), the surface of the GaN substrate 1 is polished using an acidic solution or an alkaline solution. In addition, in the polishing step (S220), both the step of polishing the surface of the GaN substrate 1 with an acidic solution and the step of polishing the surface of the GaN substrate 1 with an alkaline solution can be performed sequentially, and the polishing with the acid solution can be repeated multiple times. Steps and/or polishing steps using alkaline solutions. At this time, the foreign matter on the surface of the GaN substrate 1 can be removed by polishing before the cleaning step, thereby reducing the probability of the problem of foreign matter remaining on the surface of the GaN substrate after the cleaning step (S230). In addition, the polishing step can also reduce acidic substances before the cleaning step, thereby reducing the amount of acidic substances after the cleaning step.

In addition to the CMP step, dry etching can be performed. Examples of the dry etching include RIE (Reactive Ion Ethcing), ICP (Inductively Coupled Plasma)-RIE, ECR (Electron Cyclotron). Resonance, electron cyclotron resonance-RIE, CAIBE (chemically assisted ion beam etching), RIBE (reactive ion beam etching), etc.

The method of manufacturing a substrate with an epitaxial layer of the present invention includes: a substrate preparation step (processing step (S200) in FIG. 2), implementing the method of manufacturing the above-mentioned GaN substrate (or preparing the GaN substrate as the above-mentioned group III nitride substrate) 1); and the step of forming an epitaxial growth layer on the surface of the III nitride substrate obtained by the processing step (S200) (the film forming step included in the post-processing step (S300)). In this way, a good-quality epitaxial growth layer 5 can be formed on the surface 3 of the GaN substrate 1.

The method of manufacturing a semiconductor device of the present invention includes: preparing a substrate with an epitaxial layer (processing step (S200) and a film forming step), implementing the above-mentioned method for manufacturing a substrate with an epitaxial layer; and The substrate 10 with the epitaxial layer obtained by the substrate preparation step of the epitaxial layer implements the electrode formation step and the processing step (included in the post-processing step (S300)), thereby forming the step of forming a semiconductor device (post-processing step ( Steps after the film forming step in S300)). In this way, semiconductor devices can be formed using the epitaxial layer-attached substrate 10 with the epitaxial growth layer 5 of good quality, thereby reducing the probability of semiconductor device defects due to poor quality of the epitaxial growth layer 5.

In addition, the substrate 10 with an epitaxial layer of the present invention, as shown in FIG. 4, includes: a GaN substrate 1 formed of a group III nitride as a base substrate; and epitaxial growth formed on the surface 3 of the GaN substrate 1 Layer 5. Every 1 cm at the interface between the GaN substrate 1 and the epitaxial growth layer 5³The number of silicon (Si) atoms is 1×10²⁰the following. In addition, the substrate 10 with an epitaxial layer of the present invention includes: a GaN substrate 1 as the Group III nitride substrate of the present invention; and an epitaxial growth layer formed on the surface of the GaN substrate 1.

In the substrate 10 with an epitaxial layer constructed in the above-mentioned manner, the epitaxial growth layer 5 is formed in a state in which the number of silicon atoms on the surface of the GaN substrate 1 is kept small, so that the epitaxial growth layer 5 can be Good quality. Therefore, when the above-mentioned substrate 10 with an epitaxial layer is used to form, for example, a light-emitting element, it is possible to suppress the occurrence of the problem that the quality of the epitaxial growth layer 5 is poor and the element becomes defective.

Moreover, in the above-mentioned substrate with an epitaxial layer, every 1 cm of the interface between the GaN substrate 1 and the epitaxial growth layer 5³The number of silicon (Si) atoms can also be 1×10¹⁹the following. At this time, the quality of the epitaxial growth layer 5 can be made better. Furthermore, SIMS (Secondary Ion Mass Spectroscopy) can be used to measure every 1 cm of the interface between the GaN substrate 1 and the epitaxial growth layer 5³The number of silicon (Si) atoms (the density of Si atoms). For example, the measurement device can be a sector magnetic field SIMS device manufactured by CAMECA, and as a measurement condition, Cs can be used^＋It is measured as the original ion.

Example 1

In order to confirm the effect of the present invention, the following experiment was performed.

(Preparation of samples) As samples of the examples of the present invention, samples of Examples 1 to 13 were prepared, and as comparative examples, samples of Comparative Examples 1 to 4 were prepared. Specifically, GaN substrates that should be samples of Examples 1 to 13 and Comparative Examples 1 to 4 were prepared. The GaN substrates are all disc-shaped, with a size of 50 mm in diameter and 0.5 mm in thickness. For these GaN substrates, diamond abrasive grains are used to grind the surface of the substrate in advance. As the abrasive grains used in this grinding, prepare those with an average diameter of 6 μm, 2 μm, and 0.5 μm. The abrasive grains are reduced step by step from a larger abrasive grain to a smaller abrasive grain. Grind the diameter side. Furthermore, after this grinding, polishing is performed using alumina abrasive grains. As alumina abrasive grains, those having an average diameter of 0.5 μm were used. In this way, the pre-treatment of the surface condition of the GaN substrate sample is performed.

(Grinding the sample) In a clean room, the GaN substrate prepared in the above manner was processed as follows. Furthermore, for the ambient gas installed in the polishing device in the clean room, the concentration of acidic substances, especially chlorine atoms, is very low, so the ambient gas can be discharged from the inside of the processing chamber where the GaN substrate is disposed. Set the exhaust air velocity to 0.6 m/s. In addition, in this polishing device, the surface of the GaN substrate, which should be the samples of Examples 1 to 8, and 11 to 13, was polished by the CMP method. As shown in Table 1, the polishing liquid used in the polishing of Examples 1-8 contains SiO₂As abrasive grains. In addition, the polishing liquid used in the polishing of Examples 11-13 contained ZrO in each of the examples.₂, Cr₂O₃, Fe₂O₃As abrasive grains. In addition, the acid used for pH adjustment in the polishing liquid includes hydrochloric acid, malic acid, or citric acid. By adding these acids, the pH of the polishing liquid can reach a level of 2 or more and 4 or less. In addition, in the polishing liquid, 0.05% by weight of sodium polyacrylate was added as a surfactant. In addition, in Examples 2, 5, 6, and 10 to 13, 0.1% by weight of trichloroisocyanuric acid (TCIA) was added as an oxidizing agent to the polishing liquid used. In Examples 1 and 7, hypochlorous acid was added. In Example 3, sodium dichloroisocyanurate (Na-DCIA) was added. In addition, in Examples 4 and 8, the polishing liquid to which no oxidizing agent was added was used. Furthermore, by performing pure water cleaning after the polishing step, a GaN substrate with a mirror-finished surface is obtained. As described below, the Si concentration, chlorine concentration, surface roughness, haze, and the thickness of the modified layer on the surface of the GaN substrate were measured.

Furthermore, in Example 9, the GaN substrate was processed by dry etching (DE, Dry Etching) to prepare a GaN substrate as a sample for measuring the surface Si concentration and the like. The process of dry etching uses a parallel flat plate RIE device. As the process condition, the etching gas uses Cl₂Gas and BCl₃Gas, Cl₂The gas flow rate is 25 sccm (sccm: refers to the standard gas flow through 1 cm within 1 minute³The flow unit is the same as below), BCl₃The gas flow rate is 235 sccm, the pressure is 2.66 Pa, and the RF (Radio Frequency, radio frequency) power is 200 W.

In addition, in Example 10, after polishing by the same CMP method as in Example 1, polishing (cleaning polishing) was performed. In this polishing, a solution containing 0.3% by weight of citric acid and 0.1% by weight of TCIA was used as a polishing liquid. Thereafter, in the same manner as in Examples 1 to 9, a cleaning step was performed, thereby preparing a GaN substrate as a sample for measuring the surface Si concentration and the like.

In addition, in Comparative Examples 1 to 4, the surface of the GaN substrate was polished by the CMP method, respectively. Among them, in Comparative Example 1, as a polishing liquid, containing SiO₂Formed abrasive particles and hydrochloric acid used to adjust pH. In addition, in Comparative Example 2, it was used as a polishing liquid containing SiO₂Formed abrasive grains, malic acid used to adjust pH, surfactant (sodium polyacrylate) and oxidant (TCIA). In addition, in Comparative Example 3, a polishing liquid containing diamond abrasive grains, malic acid for pH adjustment, a surfactant (sodium polyacrylate), and an oxidizing agent (TCIA) was used. In addition, in Comparative Example 4, as the polishing liquid, one containing abrasive grains made of SiC, malic acid for pH adjustment, a surfactant (sodium polyacrylate), and an oxidizing agent (TCIA) was used. In addition, the content rates of the surfactant and the oxidizing agent were 0.3% by weight and 0.1% by weight, respectively.

Furthermore, in Comparative Examples 1 to 4, as in Examples 1 to 8, and 11 to 13, pure water washing was performed after the polishing step to prepare a GaN substrate as a sample for measuring the surface Si concentration and the like.

Furthermore, during the period from the above-mentioned processing steps to the following measurement, in Examples 1-13 and Comparative Examples 1, 3, and 4, the ambient gas in the device was exhausted, but in Comparative Example 2, exhaust was not performed.

(Measurement of substrate surface) The substrate characteristics of the samples (GaN substrates) of Examples 1 to 13 and Comparative Examples 1 to 4 prepared in the above manner were measured. Specifically, the silicon (Si) concentration, chlorine (Cl) concentration, surface roughness, haze, and the thickness of the processed modified layer on the mirror-finished surface are measured. Table 1 shows the results.

<tables><img file="TW200831723A_D0001.tif" /></tables>

Furthermore, for the Si concentration and Cl concentration, the total reflection x-ray fluorescence analysis (TXRF) was used to investigate every 1 cm in the center of the substrate surface²The number of atoms is shown in Table 1. In addition, the surface roughness was measured at 5 places on the surface of the substrate, and Table 1 shows the average value. In addition, the haze was measured using SURFSCAN4500 manufactured by Tencor. In addition, the thickness of the processed modified layer was evaluated by observing the lattice deformation of the GaN substrate using TEM.

As can be seen from Table 1, the Si concentration of Examples 1 to 8 in which the polishing liquid used in the CMP method contains acids such as hydrochloric acid or citric acid and a surfactant, is compared with the comparative example where the polishing liquid does not contain a surfactant The Si concentration of 1 is extremely low. In addition, it can be seen that in Examples 1 to 8, especially Examples 5 to 8, which use malic acid or citric acid as the acid in the polishing liquid, the Si concentration is particularly low. Furthermore, use in addition to SiO₂In Examples 11-13 and Comparative Example 3 in which abrasive grains other than SiC (abrasive grains containing no Si element) were used as the abrasive grains of the polishing liquid used in the CMP method, Si was not detected from the substrate surface.

Regarding the environment at the time of treatment, it is known that the Cl concentration, surface roughness and haze values of the sample subjected to exhaust gas are all small. In contrast, in Comparative Example 2 without exhaust gas, the Cl concentration and surface roughness The values of degree and haze are relatively large. In addition, the thicknesses of the processed modified layers in Examples 1 to 13 are all thinner than the thickness of the processed modified layers in Comparative Examples 3 and 4. Especially, use SiO₂Or Fe₂O₃In Examples 1 to 10 and 13, which are abrasive grains, no processed modified layer was detected. Furthermore, in Examples 11 and 12, the processed modified layer was detected, but its thickness was very thin compared to the thickness of the processed modified layer in Comparative Examples 3 and 4.

In addition, it can be seen that the removal rate in the polishing step is faster in Examples 1 to 3, 5 to 7, and 11 to 13 in which the polishing liquid contains an oxidizing agent, compared to Examples 4 and 8 in which the polishing liquid does not contain an oxidizing agent.

(Production of light-emitting element) A plurality of epitaxial growth layers are formed on the surface of the samples (GaN substrates) of Examples 1 to 13 and Comparative Examples 1 to 4 processed in the above manner, and then electrodes are formed and divided into individual wafers And mount the chip to a lead frame or the like to produce a light-emitting element (LED, Light Emitting Diode, light-emitting diode). Furthermore, specifically, the structure of the epitaxial growth layer formed on the surface of the GaN substrate is: an n-type GaN layer (dopant: Si) with a thickness of 1 μm as an n-type semiconductor layer and a layer with a thickness of 150 nm n-type Al_0.1Ga_0.9N layer (dopant: Si); light-emitting layer; p-type Al with a thickness of 20 nm as a p-type semiconductor layer_0.2Ga_0.8N layer (dopant: Mg) and a p-type GaN layer (dopant: Mg) with a thickness of 150 nm. Here, the light-emitting layer has the following multiple quantum well structure, that is, four barrier layers composed of a GaN layer with a thickness of 10 nm, and three layers composed of a Ga with a thickness of 3 nm._0.85In_0.15The well layers formed by the N layer are alternately stacked.

In addition, the following multilayer structure is formed as the first electrode on the back side of the substrate. The multilayer structure consists of a Ti layer with a thickness of 200 nm, an Al layer with a thickness of 1000 nm, a Ti layer with a thickness of 200 nm, and an Au layer with a thickness of 2000 nm. The layer is formed and heated in a nitrogen atmosphere, thereby forming an n-side electrode with a diameter of 100 μm. On the other hand, on the above-mentioned p-type GaN layer, the following laminated structure is formed as the second electrode. The laminated structure is formed of a Ni layer with a thickness of 4 nm and an Au layer with a thickness of 4 nm, and is heated in an inert gas atmosphere , Thereby forming a p-side electrode. After wafering the above-mentioned laminate (the above-mentioned epitaxial growth layer, n-side electrode, and p-side electrode formed on a GaN substrate) into a 400 μm square, the p The side electrode is welded to the conductor. Furthermore, the n-side electrode and the conductor were welded with a wire to obtain a semiconductor element having a structure as a light-emitting element.

(Measurement of the epitaxial growth layer) Using the same method as the measurement of the surface roughness of the above GaN substrate, the epitaxy formed on the surface of the GaN substrate of Examples 1 to 13 and Comparative Examples 1 to 4 prepared in the above manner was measured The surface roughness of the growth layer. Table 1 also shows the results. According to Table 1, it can be seen that the surface roughness of the epitaxial growth layer of Examples 1 to 13 is smaller than that of Comparative Examples 1 to 4.

The Si concentration at the interface between the substrate and the epitaxial layer was measured by SIMS. In Example 1, Example 5, Example 10, Example 13, and Comparative Example 1, the Si concentration at the interface between the substrate and the epitaxial layer was 1×10, respectively²⁰/cm³、1×10¹⁹/cm³、1×10¹⁸/cm³、1×10¹⁷/cm³、5×10²⁰/cm³. Compared with Comparative Example 1, Examples 1, 5, 10, and 13 have lower silicon concentration at the interface.

(Measurement of Luminous Intensity) The luminous intensity of the light-emitting elements of Examples 1 to 13 and Comparative Examples 1 to 4 prepared in the same manner as described above was measured. Table 1 also shows the results. According to Table 1, it can be seen that the light-emitting elements of Comparative Examples 1 to 4 did not emit light per se. On the other hand, the light-emitting elements of Examples 1 to 13 were confirmed to emit light in the light-emitting layer of the epitaxial growth layer. Furthermore, as a method of measuring the luminous intensity, after mounting the light-emitting element as each sample in the integrating sphere, apply a specific current (20 mA) to the light-emitting element to measure the light output from the condensing detector value.

The embodiments and embodiments of the present invention have been described above, but the embodiments and embodiments of the present invention disclosed above are only examples, and the scope of the present invention is not limited to the embodiments of these inventions. The scope of the present invention is indicated by the disclosure of the scope of the patent application, and further includes the meaning and all changes within the scope equivalent to the disclosure of the scope of the patent application.

[Industrial availability]

The present invention is particularly effective for group III nitride substrates used in light-emitting devices, power devices, etc., substrates with epitaxial layers using the group III nitride substrates, and manufacturing methods thereof.

<p>1. . . Substrate</p><p>3. . . surface</p><p>5. . . Epitaxial growth layer</p><p>10. . . Substrate with epitaxial layer</p>

Fig. 1 is a schematic perspective view showing a GaN substrate as an example of the Group III nitride substrate of the present invention.

FIG. 2 is a flowchart for explaining a method of manufacturing a semiconductor device using the GaN substrate shown in FIG. 1.

Fig. 3 is a flow chart for explaining the content of the processing steps shown in Fig. 2.

FIG. 4 is a schematic perspective view of a substrate with an epitaxial layer using the GaN substrate shown in FIG. 1.