JP2012129295A - Method for cleaning silicon carbide semiconductor - Google Patents

Abstract

A method for cleaning a SiC semiconductor capable of improving the surface characteristics of the SiC semiconductor is provided.
A method for cleaning an SiC semiconductor includes the following steps. Ions are implanted into the surface of the SiC semiconductor. An oxide film is formed on the surface. The oxide film is removed. In the forming step, an oxide film is formed using ozone water having a concentration of 150 ppm or more. The step of forming preferably includes a step of heating at least one of the surface of the SiC semiconductor and ozone water.
[Selection] Figure 1

Description

  The present invention relates to a method for cleaning a silicon carbide (SiC) semiconductor, and more particularly to a method for cleaning an SiC semiconductor used for a semiconductor device having an oxide film.

  In manufacturing a semiconductor device, the surface of the semiconductor is cleaned. Examples of such cleaning of the surface of the semiconductor include techniques disclosed in Japanese Patent No. 3733792 (Patent Document 1) and Japanese Patent Laid-Open No. 6-314679 (Patent Document 2).

  In Patent Document 1, after annealing for activating impurities ion-implanted into a SiC substrate for the purpose of removing the influence of abnormal deposition, composition change, surface shape change, etc. on the SiC surface after annealing. As a pretreatment method for surface cleaning, it is disclosed to perform surface etching with plasma after performing RCA cleaning.

  Patent Document 2 discloses that the surface of a semiconductor is cleaned as follows for the purpose of removing particles and metal impurities adhering to the surface of the semiconductor. That is, a silicon (Si) substrate is washed with ultrapure water containing ozone to form a Si oxide film, and particles and metal impurities are taken into the inside and the surface of the Si oxide film. Next, the Si substrate is washed with a dilute hydrofluoric acid aqueous solution to remove the Si oxide film by etching, and at the same time, particles and metal impurities are removed.

Japanese Patent No. 3733792 JP-A-6-314679

  The cleaning method disclosed in Patent Document 1 performs surface etching with plasma after performing RCA cleaning. However, the present inventor has found that the surface characteristics cannot be sufficiently improved even by performing surface etching with plasma.

  The cleaning method disclosed in Patent Document 2 relates to a Si semiconductor. When the cleaning method of Patent Document 2 is applied to a SiC semiconductor, the present inventor has found that the surface of the SiC semiconductor is hardly oxidized because SiC is a thermally stable compound than Si. That is, the cleaning method of Patent Document 2 can oxidize the surface of Si, but cannot sufficiently oxidize the surface of SiC. For this reason, since the surface of SiC cannot be washed sufficiently, the surface characteristics of the SiC semiconductor cannot be improved.

  Accordingly, an object of the present invention is to provide a method of cleaning a SiC semiconductor that can improve the surface characteristics of the SiC semiconductor.

  The inventor paid attention to the fact that the crystallinity of the SiC semiconductor ion-implanted on the surface is broken, and has intensively studied a cleaning method for removing the crystal. In addition, the present inventor has intensively studied conditions for expressing a cleaning effect on a SiC semiconductor which is a stable compound. As a result, the present invention has been completed.

  That is, the SiC semiconductor cleaning method includes the following steps. Ions are implanted into the surface of the SiC semiconductor. An oxide film is formed on the surface. The oxide film is removed. In the forming step, an oxide film is formed using ozone water having a concentration of 150 ppm or more.

  The present inventor has found that ozone water having high oxidizing power is used as an oxidizing agent for oxidizing the surface of the SiC semiconductor which is a stable compound. As a result of intensive studies on the conditions for oxidizing the crystal broken by the ion implantation, the present inventors have found that the crystal deteriorated by the ion implantation can be oxidized by setting the concentration of ozone water to 150 ppm or more.

  Therefore, according to the cleaning method of the SiC semiconductor of the present invention, the reaction between the surface of the SiC semiconductor and the ozone water can be enhanced by using ozone water having a concentration of 150 ppm or more. An oxide film can be formed deeply on the surface of a certain SiC semiconductor. Therefore, an oxide film obtained by oxidizing the crystal broken by ion implantation can be formed, and by removing this oxide film, the crystal broken by ion implantation on the surface of the SiC semiconductor can be removed. Therefore, the surface characteristics of the SiC semiconductor can be improved.

  Preferably, in the SiC semiconductor cleaning method, the forming step includes a step of heating at least one of the surface and ozone water.

  As a result of intensive research conducted by the present inventors to oxidize the surface of a SiC semiconductor, which is a stable compound, it is possible to further promote the oxidation of the surface of the SiC semiconductor by heating the wetted surface between ozone water and the surface of the SiC semiconductor. I found. For this reason, an oxide film can be easily formed by heating at least one of the surface of the SiC semiconductor and ozone water. Therefore, the surface characteristics of the SiC semiconductor can be further improved.

  Preferably, in the SiC semiconductor cleaning method, the heating step includes a step of heating ozone water to 25 ° C. or higher and 90 ° C. or lower. Preferably, in the SiC semiconductor cleaning method, the heating step includes a step of heating the surface of the SiC semiconductor to 25 ° C. or more and 90 ° C. or less.

  As a result of intensive studies on the conditions for promoting the oxidation of the surface of the SiC semiconductor, the present inventors have found the above conditions. When it is 25 ° C. or higher, the oxidation reaction can be promoted, and when it is 90 ° C. or lower, decomposition of ozone can be suppressed.

  Preferably, in the SiC semiconductor cleaning method, in the removing step, the oxide film is removed using hydrogen fluoride (HF).

  Thereby, since the oxide film can be easily removed, the oxide film remaining on the surface can be reduced.

  Preferably, in the SiC semiconductor cleaning method, the surface has an off angle of 50 ° or more and 65 ° or less with respect to the {0001} plane.

  The present inventor has found that when the surface has an off angle in the above range, a crystal broken by ion implantation is easily oxidized. For this reason, the cleaning effect of the SiC semiconductor which has the said surface can be expressed more effectively.

  In the SiC semiconductor cleaning method, preferably, the forming step and the removing step are performed simultaneously.

  Thereby, the crystal broken by the ion implantation can be oxidized and the oxide film can be removed, so that the time for cleaning the SiC semiconductor can be shortened.

  As described above, according to the SiC semiconductor cleaning method of the present invention, an oxide film is formed on the surface of the SiC semiconductor using ozone water having a concentration of 150 ppm or more, thereby removing crystals broken by ion implantation. Therefore, the surface characteristics of the SiC semiconductor can be improved.

It is a flowchart which shows the cleaning method of the SiC semiconductor in embodiment of this invention. It is sectional drawing which shows schematically the SiC substrate in embodiment of this invention. It is sectional drawing which shows roughly the state in which the epitaxial layer was formed in embodiment of this invention. It is sectional drawing which shows schematically the epitaxial wafer into which the ion implantation was carried out in embodiment of this invention. It is a schematic diagram which shows schematically the washing | cleaning apparatus of the SiC semiconductor in embodiment of this invention. It is a schematic diagram which shows schematically the washing | cleaning apparatus of the SiC semiconductor in the modification of embodiment of this invention. It is sectional drawing which shows roughly the epitaxial wafer wash | cleaned by this invention example 1 and the comparative examples 1 and 2. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated. In the present specification, the set direction is indicated by <>, the individual plane is indicated by (), and the set plane is indicated by {}. As for the negative index, “−” (bar) is attached on the number in crystallography, but in this specification, a negative sign is attached before the number.

  With reference to FIGS. 1-6, the cleaning method of the SiC semiconductor of one embodiment of this invention is demonstrated.

  First, as shown in FIGS. 1 and 2, an SiC substrate 2 having a surface 2a is prepared (step S1). SiC substrate 2 is not particularly limited, but can be prepared, for example, by the following method.

  Specifically, for example, HVPE (Hydride Vapor Phase Epitaxy) method, MBE (Molecular Beam Epitaxy) method, OMVPE (Organo Metallic Vapor Phase Epitaxy) method, sublimation method. A SiC ingot grown by a vapor phase growth method such as a CVD (Chemical Vapor Deposition) method, a liquid phase growth method such as a flux method or a high nitrogen pressure solution method is prepared. Thereafter, a SiC substrate having a surface is cut out from the SiC ingot. The cutting method is not particularly limited, and the SiC substrate is cut from the SiC ingot by slicing or the like. Next, the cut surface of the SiC substrate is polished. The surface to be polished may be only the front surface, or the back surface opposite to the front surface may be further polished. The method of polishing is not particularly limited, but CMP (Chemical Mechanical Polishing) is performed, for example, in order to flatten the surface and reduce damage such as scratches. In CMP, colloidal silica is used as an abrasive, diamond, chromium oxide is used as abrasive grains, an adhesive, wax, or the like is used as a fixing agent. In addition to or in place of CMP, other polishing such as an electric field polishing method, a chemical polishing method, and a mechanical polishing method may be further performed. Polishing may be omitted. Thereby, SiC substrate 2 having surface 2a shown in FIG. 2 can be prepared. As such SiC substrate 2, for example, a substrate having an n-type conductivity and a resistance of 0.02 Ωcm is used.

  Surface 2a of SiC substrate 2 preferably has an off angle of 50 ° to 65 ° with respect to the {0001} plane, and has an off angle of 5 ° or less with respect to the <1-100> direction. Is more preferable. In particular, surface 2a of SiC substrate 2 preferably has an off angle with respect to the {03-38} plane in the <1-100> direction of −3 ° to + 5 °, and (0− It is more preferable that the off angle with respect to the 33-8) plane is -3 ° or more and + 5 ° or less. By making the surface 2a of the SiC substrate 2 into such a surface, the surface 120a (see FIG. 3) of the epitaxial layer formed thereon can be formed in the same surface.

  Next, as shown in FIGS. 1 and 3, epitaxial layer 120 is formed on surface 2a of SiC substrate 2 by vapor phase growth, liquid phase growth, or the like (step S2). In the present embodiment, epitaxial layer 120 is formed as follows, for example.

Specifically, as shown in FIG. 3, buffer layer 121 is formed on surface 2 a of SiC substrate 2. Buffer layer 121 is an epitaxial layer made of, for example, n-type SiC and having a thickness of 0.5 μm, for example. The concentration of conductive impurities in the buffer layer 121 is, for example, 5 × 10 ¹⁷ cm ⁻³ .

Thereafter, as shown in FIG. 3, a breakdown voltage holding layer 122 is formed on the buffer layer 121. As the breakdown voltage holding layer 122, a layer made of SiC of n-type conductivity is formed by a vapor phase growth method, a liquid phase growth method, or the like. The thickness of the breakdown voltage holding layer 122 is, for example, 15 μm. The concentration of the n-type conductive impurity in the breakdown voltage holding layer 122 is, for example, 5 × 10 ¹⁵ cm ⁻³ .

Next, as shown in FIGS. 1 and 4, ions are implanted into the surface 120a of the epitaxial layer 120 (step S3). In the present embodiment, as shown in FIG. 4, a p-type well region 123, an n ⁺ source region 124, and a p ⁺ contact region 125 are formed as follows. First, a well region 123 is formed by selectively injecting p-type impurities into a part of the breakdown voltage holding layer 122. Thereafter, a source region 124 is formed by selectively injecting an n-type conductive impurity into a predetermined region, and a contact is formed by selectively injecting a p-type conductive impurity into the predetermined region. Region 125 is formed. The impurity is selectively implanted using a mask made of an oxide film, for example.

  After such an ion implantation step (step S3), an activation annealing process may be performed. For example, annealing is performed in an argon atmosphere at a heating temperature of 1700 ° C. for 30 minutes.

  By these steps, epitaxial wafer 100 including SiC substrate 2 and epitaxial layer 120 formed on SiC substrate 2 can be prepared. In the epitaxial wafer 100, the crystallinity of the ion-implanted surface 120a is broken. In other words, the surface 120a is damaged by the ion implantation.

  Surface 120a of epitaxial wafer 100 preferably has an off angle of 50 ° to 65 ° with respect to the {0001} plane, and has an off angle of 5 ° or less with respect to the <1-100> direction. Is more preferable. In particular, the surface 120a of the epitaxial wafer 100 preferably has an off angle with respect to the {03-38} plane in the <1-100> direction of -3 ° or more and + 5 ° or less, and (0− It is more preferable that the off angle with respect to the 33-8) plane is -3 ° or more and + 5 ° or less. When the surface 120a has an off angle in such a range, the crystal broken by the ion implantation (step S3) has a characteristic of being easily oxidized. For this reason, the cleaning effect of the epitaxial wafer 100 having the surface 120a can be expressed more effectively by the step S4 for forming an oxide film, which will be described later, and the step S5 for removing the oxide film.

  When the surface 120a has an off angle in the above range, it is advantageous to clean the surface 120a to manufacture a semiconductor device in the following points. Since the off-angle increases and the carrier mobility increases significantly from the (01-14) plane having an off angle of 43.3 ° to the (01-13) plane having an off angle of 51.5 °, the surface 120a is The angle is preferably 50 ° or more with respect to the {0001} plane. Since the off-angle increases from the (01-12) plane having an off-angle of 62.1 ° to the (01-10) plane having an off-angle of 90 °, a significant decrease in the carrier concentration is observed as the off-angle increases. The angle is preferably 65 ° or less with respect to the 0001} plane. The <1-100> direction is a typical off orientation in SiC. By setting the angle formed by the off angle to the <1-100> direction to 5 ° or less, processing variations in the manufacturing process can be reduced. When the off angle of the surface 2a of the SiC substrate 2 with respect to the {03-38} plane in the <1-100> direction is not less than −3 ° and not more than + 5 °, particularly high channel mobility can be obtained. By adopting a structure in which an insulating film is formed on the (0-33-8) plane which is the C (carbon) plane side among the {03-38} plane, the carrier mobility is greatly improved.

  Here, the state that “the off angle is −3 ° or more and + 5 ° or less with respect to the plane orientation {03-38}” means that the <0001> direction and the <01-10> direction as a reference for the off orientation are stretched. It means a state in which the angle formed between the normal projection of the surface normal to the plane and the normal of the {03-38} plane is -3 ° or more and + 5 ° or less. The case where it approaches parallel to the 01-10> direction is positive, and the case where the orthographic projection approaches parallel to the <0001> direction is negative.

  Next, an oxide film is formed on the surface 120a of the epitaxial layer 120 in the epitaxial wafer 100 using ozone water having a concentration of 150 ppm or more (step S4). In this step S4, since the surface 120a of the epitaxial layer 120 can be oxidized, the surface whose crystallinity is broken by ion implantation in step S3 can be oxidized. Further, particles, metal impurities, etc. adhering to the surface 120a of the epitaxial wafer 100 can be taken into the surface or inside of the oxide film. The oxide film is, for example, silicon oxide.

  In this step S2, an oxide film is formed using ozone water having a concentration of 150 ppm or more. In the case of 150 ppm or more, the reaction rate between the surface 120a and ozone can be increased, so that an oxide film can be substantially formed on the surface 120a. Since SiC is a chemically stable compound, the higher the dissolved ozone concentration of ozone water, the better the oxidation reaction is promoted. However, for manufacturing reasons, the upper limit is, for example, 300 ppm. From such a viewpoint, the concentration of ozone water is preferably 150 ppm or more and 300 ppm or less.

  The ozone water is not particularly limited as long as it contains 150 ppm or more of ozone, but is preferably ultrapure water containing 150 ppm or more of ozone. The concentration of the ozone water is a concentration when supplied to the ion-implanted surface 120a.

  In this step S4, it is preferable to heat at least one of the surface 120a and ozone water. Thereby, the wetted surface of the surface 120a and ozone water is heated. When the temperature of the liquid contact surface is high, the oxidation reaction can be promoted. From this point of view, it is preferable to heat the liquid contact surface to 25 ° C. or higher and 90 ° C. or lower. That is, it is preferable to heat at least one of the surface 120a and the ozone water so as to be 25 ° C. or higher and 90 ° C. or lower. When it is 25 ° C. or higher, the oxidation reaction can be promoted, and when it is 90 ° C. or lower, decomposition of ozone can be suppressed.

  The method for heating epitaxial wafer 100 is not particularly limited. For example, a heater may be disposed on the back side of SiC substrate 2 to heat it from the back side. Although the heating method of ozone water is not specifically limited, For example, the supply part which supplies ozone water can be heated.

  The oxidation-reduction potential of ozone water is preferably 500 mV or more, and more preferably 1 V or more. Thereby, since the oxidizing power of ozone water increases more, the oxidation reaction in the surface 120a can be promoted more.

  In this step S4, carbon dioxide gas may be mixed in ozone water. By mixing the carbon dioxide gas, the pH of the ozone water can be lowered, the decomposition of ozone can be suppressed, and the metal adhering to the surface 120a can be effectively removed. For this reason, it is preferable to adjust the pH of the ozone water by adjusting the pH of the ozone water using carbon dioxide gas so that the carbon dioxide gas is mixed so as to promote the oxidation reaction of the surface 120a.

  Further, in this step S4, ozone water is applied to the surface 120a of the epitaxial wafer 100 by using, for example, a cleaning device for cleaning the wafer, and a surface of the surface 120a of the epitaxial wafer 100 using a swinging ozone water supply nozzle or the like for 30 seconds. Supply for 3 minutes or less. In the case of 30 seconds or longer, the oxide film can be reliably formed on the surface 120a of the epitaxial wafer 100. In the case of 3 minutes or less, the cleaning throughput of the surface 120a of the epitaxial wafer 100 can be increased. Actually, it depends on the supply functionality in the cleaning system, such as the outer diameter size of the surface 120a of the epitaxial wafer 100, the flow rate of ozone water supply, the number of nozzles, etc., but in practice it takes about 3 minutes. It is possible.

  In this step S4, for example, an oxide film having a thickness of 10 nm to 100 nm is formed. By forming an oxide film having a thickness of 10 nm or more, crystals broken by ion implantation (step S3) can be oxidized. By forming an oxide film having a thickness of 100 nm or less, it is possible to suppress oxidation of a region where there is no change in crystallinity in ion implantation (step S3).

  Here, with reference to FIG. 5, the main structure of the SiC semiconductor cleaning apparatus that can be used to form the oxide film in step S4 will be described.

  As shown in FIG. 5, the SiC semiconductor cleaning apparatus mainly includes an ozone water supply unit 205 and a reaction vessel 251 connected to the ozone water supply unit 205. The ozone water supply unit 205 holds the ozone water 215 described above and supplies it to the reaction vessel 251. The reaction vessel 251 accommodates ozone water 215 and the epitaxial wafer 100 inside. The reaction vessel 251 has an opening 251a for flowing ozone water 215 from the ozone water supply unit 205 and an opening 251b for discharging ozone water 215 to the outside.

  Note that the SiC semiconductor cleaning apparatus may include various elements other than those described above, but the illustration and description of these elements are omitted for convenience of description.

  When an oxide film is formed on surface 120a of epitaxial wafer 100 using this SiC semiconductor cleaning apparatus, for example, the following is performed. That is, the above-described ozone water is supplied from the opening 251a of the ozone water supply unit 205 into the reaction vessel 251 at a flow rate of several L / m as indicated by the arrow in FIG. And ozone water is made to overflow from the opening part 251b of the reaction container 251 as the arrow of FIG. Thereby, the ozone water 215 can be stored inside the reaction vessel 251. In addition, the epitaxial wafer 100 is accommodated in the reaction vessel 251. The number of epitaxial wafers 100 to be accommodated is not particularly limited, but a plurality of epitaxial wafers 100 are preferable from the viewpoint of improving throughput. Thereby, since the surface 120a of the epitaxial wafer 100 immersed in ozone water and ozone water can be made to react, an oxide film can be formed on the surface 120a of the epitaxial wafer 100.

  Next, the surface 120a of the epitaxial wafer 100 is washed with pure water (pure water rinsing step). The pure water is preferably ultrapure water. You may wash by applying an ultrasonic wave to pure water. This pure water rinsing step may be omitted.

  Next, the surface 120a of the epitaxial wafer 100 is dried (drying process). Although the method of drying is not specifically limited, For example, it dries with a spin dryer etc. This drying step may be omitted.

  Next, the oxide film is removed (step S5). In this step S5, the oxide film obtained by oxidizing the crystal broken by the ion implantation is removed, so that the crystal broken by the ion implantation (step S3) can be removed. At the same time, since the oxide film that has taken in impurities, particles, and the like is removed, the impurities, particles, and the like can be removed.

  The method for removing the oxide film is not particularly limited. For example, wet etching, dry etching, thermal decomposition, halogen plasma, H plasma, or the like can be used.

In the wet etching, the oxide film is removed using a solution such as HF or NH ₄ F (ammonium fluoride). In wet etching, HF is preferably used, and dilute HF (DHF) of 1% to 10% is more preferable. In the case of removing using HF, for example, the oxide film can be removed by storing HF in a reaction vessel and immersing the epitaxial wafer 100 in HF.

  When performing wet cleaning using a liquid phase such as wet etching, the surface of the epitaxial wafer 100 may be cleaned with pure water after the wet cleaning. The pure water is preferably ultrapure water. You may wash by applying an ultrasonic wave to pure water. Note that this step may be omitted.

  When wet cleaning is performed, the surface of the epitaxial wafer 100 may be dried. Although the method of drying is not specifically limited, For example, it dries with a spin dryer etc. Note that this step may be omitted.

In dry etching, for example, the oxide film is removed using at least one of hydrogen (H ₂ ) gas and hydrogen chloride (HCl) gas at a temperature of 1000 ° C. or higher and lower than the sublimation temperature of SiC. Hydrogen gas and hydrogen chloride gas at 1000 ° C. or higher have a high effect of reducing the oxide film. When the oxide film is SiO _x , hydrogen gas decomposes SiO _x into H ₂ O and SiH _y, and hydrogen chloride gas decomposes SiO _x into H ₂ O and SiCl _z . Degradation of the epitaxial wafer 100 can be suppressed by setting the temperature to a sublimation temperature of SiC or lower. Also, dry etching is preferably performed under reduced pressure from the viewpoint of promoting the reaction.

  The thermal decomposition is preferably performed by thermally decomposing the oxide film in an atmosphere containing no O and at a temperature of 1200 ° C. or higher and a SiC sublimation temperature or lower. When the oxide film is heated in an atmosphere not containing O at 1200 ° C. or higher, the oxide film can be easily pyrolyzed. Degradation of the epitaxial wafer 100 can be suppressed by setting the temperature to a sublimation temperature of SiC or lower. Moreover, it is preferable to perform a thermal decomposition under reduced pressure from a viewpoint which can accelerate | stimulate reaction.

  Halogen plasma means plasma generated from a gas containing a halogen element. The halogen element is fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). “Removing the oxide film using halogen plasma” means that the oxide film is etched by plasma using a gas containing a halogen element. In other words, it means that the oxide film is removed by processing with plasma generated from a gas containing a halogen element.

As the halogen plasma, it is preferable to use F plasma. F plasma means plasma generated from a gas containing F element. For example, carbon tetrafluoride (CF ₄ ), trifluoromethane (CHF ₃ ), chlorofluorocarbon (C ₂ F ₆ ), sulfur hexafluoride. Supply single or mixed gas of (SF ₆ ), nitrogen trifluoride (NF ₃ ), xenon difluoride (XeF ₂ ), fluorine (F ₂ ), and chlorine trifluoride (ClF ₃ ) to the plasma generator Can be generated. “Removing the oxide film using F plasma” means removing the oxide film by plasma using a gas containing an F element. In other words, it means that the oxide film is removed by processing with plasma generated from a gas containing F element.

H plasma means plasma generated from a gas containing H element, and can be generated, for example, by supplying H ₂ gas to a plasma generator. “Removing the oxide film using H plasma” means that the oxide film is etched by plasma using a gas containing H element. In other words, it means that the oxide film is removed by processing with plasma generated from a gas containing H element.

  When halogen plasma or H plasma is used in step S5, it is preferable to remove the oxide film at a temperature of 20 ° C. or higher and 400 ° C. or lower. In this case, damage to the epitaxial wafer 100 can be reduced.

  Further, when halogen plasma or H plasma is used in step S5, it is preferable to remove the oxide film at a pressure of 0.1 Pa to 20 Pa. In this case, since the reactivity between the halogen plasma or H plasma and the oxide film can be increased, the oxide film can be easily removed.

  Further, step S4 for forming the oxide film and step S5 for removing the oxide film may be performed simultaneously. Here, at the same time, at least a part of the steps may be duplicated. That is, at least one of the start and end may be the same timing, and the start and end timings may be different.

  When step S4 for forming the oxide film and step S5 for removing the oxide film are simultaneously performed, for example, ozone water and HF are simultaneously supplied. Thereby, the oxide film can be removed while forming the oxide film on the surface 120a of the epitaxial wafer 100.

  By carrying out the above steps (steps S1 to S5), crystals broken by ion implantation (step S3) can be removed. In addition, impurities, particles, and the like attached to the surface 120a can be removed.

  Here, it is preferable to confirm the crystallinity of the surface 120a after step S5 by using an XPS (X-ray Photoelectron Spectroscopy) method or the like. In this confirmation process, if the broken crystal is removed by the ion implantation (step S3), the cleaning is completed. On the other hand, in this confirmation step, if crystals broken by ion implantation (step S3) remain, step S4 for forming the oxide film and step S5 for removing the oxide film are repeated.

  In addition, after preparing a SiC substrate (step S1), you may implement by adding the washing | cleaning process with the same chemical | medical solution or another chemical | medical solution, a pure water rinse process, a drying process etc. as needed. Examples of the other chemical liquid include SPM containing sulfuric acid and hydrogen peroxide solution. In the case of cleaning with SPM, organic substances can also be removed. Further, RCA cleaning or the like may be performed.

(Modification)
With reference to FIG. 6, the cleaning method of the SiC semiconductor of a modification is demonstrated. The SiC semiconductor cleaning method in the modification is different in that the SiC semiconductor cleaning apparatus shown in FIG. 6 is used instead of the SiC semiconductor cleaning apparatus shown in FIG.

  The SiC semiconductor cleaning apparatus shown in FIG. 6 mainly includes a chamber 201, a wafer holding unit 202, a support base 203, a drive unit 204, an ozone water supply unit 205, and an HF supply unit 206. The SiC semiconductor cleaning apparatus shown in FIG. 6 is also an apparatus for removing an oxide film formed on the surface 120 a of the epitaxial wafer 100.

  The chamber 201 includes a wafer holding unit 202, a support base 203, and a driving unit 204 inside. Wafer holding unit 202 holds epitaxial wafer 100. The number of epitaxial wafers 100 to be held is not particularly limited, but is one, for example, from the viewpoint of forming an oxide film with improved in-plane uniformity. The support table 203 is connected to the wafer holding unit 202 and holds the wafer holding unit 202. The driving unit 204 is connected to the support table 203 and rotates the wafer holding unit 202 via the support table 203. That is, the driving unit 204 can rotate the epitaxial wafer 100 placed on the wafer holding unit 202 as shown by the arrows in FIG. The drive unit 204 is, for example, a motor.

  The ozone water supply unit 205 holds the ozone water 215 described above inside, and supplies ozone water to the surface 120 a of the epitaxial wafer 100 placed on the wafer holding unit 202. The ozone water supply unit 205 has a nozzle 205 a for discharging the ozone water 215. The distance L between the tip of the nozzle 205a and the surface 120a of the epitaxial wafer 100 is preferably 3 cm or less, for example. In this case, since ozone decomposition due to the difference between the pressure when ozone water is discharged from the nozzle and the pressure when supplying the epitaxial wafer 100 can be reduced, ozone decomposes before the reaction with the surface 120a of the epitaxial wafer 100. This can be suppressed, and the oxidation reaction on the surface 120a can be performed efficiently.

  The HF supply unit 206 holds the above-described HF 216 inside, and supplies HF to the surface 120 a of the epitaxial wafer 100 placed on the wafer holding unit 202. The HF supply unit 206 includes a nozzle 206 a for discharging the HF 216.

  The SiC semiconductor cleaning apparatus shown in FIG. 6 may include various elements other than those described above, but illustration and description of these elements are omitted for convenience of description. The SiC semiconductor cleaning apparatus shown in FIG. 6 is not particularly limited to a single wafer type.

  When the surface 120a of the epitaxial wafer 100 is cleaned using the SiC semiconductor cleaning apparatus of FIG. 6, for example, the following is performed. That is, the epitaxial wafer 100 is mounted on the wafer holding unit 202 so that the surface 120a ion-implanted in step S3 faces the ozone water supply unit 205 and the HF supply unit 206. Next, the above-described ozone water 215 is supplied from the nozzle 205 a of the ozone water supply unit 205 to the surface 120 a of the epitaxial wafer 100. The epitaxial wafer 100 placed on the wafer holding unit 202 is rotated at, for example, 200 rpm by the drive unit 204. The nozzles may be supplied while swinging left and right. Thereby, ozone water having a concentration of 150 ppm or more can be uniformly supplied to the surface 120 a of the epitaxial wafer 100. As a result, the supplied ozone water can react with the surface 120a of the epitaxial wafer 100, so that an oxide film can be formed on the surface 120a of the epitaxial wafer 100. When the formation of the oxide film is completed, the supply of ozone water from the ozone water supply unit 205 is stopped.

  Next, in step S <b> 5 for removing the oxide film, the HF described above is supplied from the HF supply unit 206 to the surface 120 a of the epitaxial wafer 100. The epitaxial wafer 100 is similarly rotated by the drive unit 204. As a result, HF can be uniformly supplied to the surface 120 a of the epitaxial wafer 100. As a result, the supplied HF can be reacted with the oxide film formed on the surface 120a of the epitaxial wafer 100, so that the oxide film formed on the surface 120a can be removed.

  If the apparatus of FIG. 6 includes a pure water supply unit (not shown), pure water may be supplied to the surface 120a of the epitaxial wafer 100 after step S4 or step S5. In this case, a pure water rinse process can be performed.

  In the case where the step S4 for forming the oxide film and the step S5 for removing the oxide film are performed at the same time, the ozone water discharged from the ozone water supply unit 205 and the HF discharged from the HF supply unit 206 simultaneously 100. Thereby, the reaction for forming the oxide film and the reaction for removing the formed oxide film can be simultaneously generated.

As described above, according to the method for cleaning epitaxial wafer 100 in the present embodiment, even if the epitaxial wafer 100 is a SiC semiconductor that is not easily oxidized, ion implantation is performed by using ozone water having a concentration of 150 ppm or more. C deposited on the surface 120a by (step S3) can be oxidized and removed as CO or CO ₂ . Further, the Si droplets generated on the surface 120a and the SiC surface 120a can be oxidized. That is, the crystal deteriorated by the ion implantation (step S3) can be oxidized. Therefore, by removing this oxide film, it is possible to remove crystals broken by ion implantation on the surface 120a of the epitaxial wafer 100. It can also be formed on a surface close to the stoichiometric composition. Furthermore, since impurities, particles, and the like existing on the surface 120a can be taken into the oxide film, the surface can be cleaned by removing the oxide film. Therefore, the surface characteristics of the epitaxial wafer 100 can be improved.

  By performing step S4 for forming the oxide film and step S5 for removing the oxide film, the surface characteristics are improved compared to the case of performing the step of directly removing the surface 120a by etching or the like without forming the oxide film. The present inventor has obtained the knowledge that it becomes higher.

  As described above, since the characteristics of the ion-implanted surface 120a of the epitaxial wafer 100 can be improved, an insulating film that forms a semiconductor device such as a gate oxide film is formed on the surface after cleaning to produce a semiconductor device. The characteristics of the film can be improved, and the interface between the cleaned surface and the insulating film, and impurities, particles, etc. existing in the insulating film can be reduced. Therefore, it is possible to improve the breakdown voltage when applying the reverse voltage to the semiconductor device, and to improve the stability and long-term reliability of the operation when applying the forward voltage. Therefore, the SiC semiconductor cleaning method of the present invention is particularly preferably used for the surface 120a of the epitaxial wafer 100 before the gate oxide film is formed.

  Note that the epitaxial wafer 100 cleaned in this embodiment can be suitably used for a semiconductor device having an insulating film because the insulating film can be improved by forming the insulating film on the cleaned surface 100a. Therefore, the epitaxial wafer 100 cleaned in the present embodiment has an insulated gate field effect portion such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor). It can be suitably used for a semiconductor device having JFET (Junction Field-Effect Transistor).

  In this example, the effect of forming an oxide film on the surface of the SiC semiconductor using ozone water having a concentration of 150 ppm or more was examined.

(Invention Example 1)
As the SiC semiconductor of Example 1 of the present invention, the epitaxial wafer 130 shown in FIG. 7 was cleaned.

  Specifically, first, a 4H—SiC substrate having a (0-33-8) plane as a surface was prepared as the SiC substrate 2 (step S1).

Next, a p-type SiC layer 131 having a thickness of 10 μm and an impurity concentration of 1 × 10 ¹⁶ cm ⁻³ was grown by CVD as a layer constituting the epitaxial layer 120 (step S2).

Next, using SiO ₂ as a mask, source region 124 and drain region 129 having an impurity concentration of 1 × 10 ¹⁹ cm ⁻³ using phosphorus (P) as an n-type impurity were formed by ion implantation (step S3). Further, a contact region 125 having an impurity concentration of 1 × 10 ¹⁹ cm ⁻³ is formed by ion implantation using aluminum (Al) as a p-type impurity (step S3). Note that the mask was removed after each ion implantation.

  Next, activation annealing treatment was performed. As this activation annealing treatment, Ar gas was used as the atmosphere gas, and the heating temperature was 1700 to 1800 ° C. and the heating time was 30 minutes.

  As a result, an epitaxial wafer 130 having an ion-implanted surface 130a was prepared.

  Next, ultrapure water containing ozone having a concentration of 150 ppm is heated to 25 ° C., and a single wafer SiC semiconductor cleaning device shown in FIG. 6 is used to flow onto the surface 130a of the epitaxial wafer 130 at a flow rate of 1 slm. Supplied. At this time, the rotational speed of the epitaxial wafer 100 was 200 rpm. This confirmed that an oxide film could be formed on the surface 130a of the epitaxial wafer 130 (step S4).

  Next, the surface 130a of the epitaxial wafer 130 was washed with ultrapure water for 1 minute (pure water rinsing step).

  Next, dilute HF having a concentration of 5% or more and 10% or less was supplied to the surface 130 a of the epitaxial wafer 130. Thus, it was confirmed that the oxide film formed in step S4 can be removed (step S5).

  Next, the surface 130a of the epitaxial wafer 130 was washed with ultrapure water for 1 minute (pure water rinsing step).

  The surface 130a of the epitaxial wafer 130 was cleaned by the above processes (Steps S1 to S5). The cleaned surface 130a was confirmed to be free of impurities and particles while the crystals broken by ion implantation (step S3) were removed by the XPS method.

(Comparative Example 1)
Comparative Example 1 was basically the same as Example 1 of the present invention, but differed in that 20 ppm of ozone water was supplied to the surface 130a of the epitaxial wafer 130 in Step S4. In this case, it was confirmed that no oxide film was formed on the surface 130a. For this reason, the surface 130a after the cleaning of Comparative Example 1 cannot remove crystals broken by ion implantation (step S3), and impurities and particles are hardly reduced.

(Comparative Example 2)
Comparative Example 2 was basically the same as Inventive Example 1, but differed in that 30 ppm of ozone water was supplied to the surface 130a of the epitaxial wafer 130 in Step S4. In this case, although the oxide film was formed on the surface 130a, the thickness was very thin. For this reason, although the surface 130a after the cleaning of Comparative Example 2 had reduced impurities and particles, it was not possible to remove crystals broken by ion implantation (step S3).

  Further, although ozone water having a concentration of 30 ppm was supplied a plurality of times, the formed oxide film was very thin, so that crystals broken by ion implantation (step S3) were removed using ozone water having a concentration of 30 ppm. It turned out to be difficult industrially.

  From the above, according to this example, it was found that a thick oxide film can be formed on the surface of the SiC semiconductor by using ozone water of 150 ppm or more. For this reason, it has been found that the crystal broken by the ion implantation can be removed by forming an oxide film on the surface of the SiC semiconductor and removing the oxide film.

  Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the features of the embodiments and examples. The embodiments and examples disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the embodiments and examples described above but by the scope of claims for patent, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims for patent.

  2 SiC substrate, 2a, 100a, 130a surface, 100, 130 epitaxial wafer, 100a, 130a surface, 120 epitaxial layer, 121 buffer layer, 122 breakdown voltage holding layer, 123 well region, 124 source region, 125 contact region, 129 drain region 131 p-type SiC layer, 201 chamber, 202 wafer holder, 203 support base, 204 drive unit, 205 ozone water supply unit, 205a, 206a nozzle, 206 HF supply unit, 215 ozone water, 251 reaction vessel, 251a, 251b Aperture.

Claims (7)

Ion implantation into the surface of the silicon carbide semiconductor;
Forming an oxide film on the surface;
A step of removing the oxide film,
The silicon carbide semiconductor cleaning method, wherein, in the forming step, the oxide film is formed using ozone water having a concentration of 150 ppm or more.   The silicon carbide semiconductor cleaning method according to claim 1, wherein the forming step includes a step of heating at least one of the surface and the ozone water.   The silicon carbide semiconductor cleaning method according to claim 2, wherein the heating step includes a step of heating the ozone water to 25 ° C. or more and 90 ° C. or less.   The method for cleaning a silicon carbide semiconductor according to claim 2, wherein the heating step includes a step of heating the surface to 25 ° C. or higher and 90 ° C. or lower.   The silicon carbide semiconductor cleaning method according to claim 1, wherein, in the removing step, the oxide film is removed using hydrogen fluoride.   6. The method for cleaning a silicon carbide semiconductor according to claim 1, wherein said surface has an off angle of 50 ° to 65 ° with respect to the {0001} plane.   The method for cleaning a silicon carbide semiconductor according to claim 1, wherein the forming step and the removing step are performed simultaneously.

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