JP2014009115A - Substrate manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a SiC crystal substrate at a good yield.SOLUTION: A method includes an ingot manufacturing step of manufacturing an SiC crystal ingot having an exfoliation layer sandwiched between substrate layers. Also, the method includes a radiation step of radiating laser beam to inside of the ingot and separating the substrate layers from each other with the exfoliation layer as a boundary. In the ingot manufacturing step, the ingot is housed in a chamber, and the substrate layers and the exfoliation layer are sequentially grown from a lower layer by epitaxial growth. During growing the exfoliation layer, a gas containing nitrogen for narrowing a band gap of an SiC crystal is supplied into the chamber. During growing the substrate layers, a gas not containing nitrogen is supplied into the chamber. A wavelength of the laser beam used in the radiation step is longer than an upper limit of an absorption wavelength defined according to the band gap of the substrate layers, and shorter than an upper limit of an absorption wavelength defined according to the band gap of the exfoliation layer.

Description

  In this specification, the technique regarding the manufacturing method of a silicon carbide (SiC) crystal substrate is disclosed.

  In the technique disclosed in Patent Document 1, the condensing point of the laser light is adjusted to the inside of the ingot with a condensing lens. Further, the XY stage on which the ingot is placed is moved in the X and Y directions. Thereby, the surface processing area | region by multiphoton absorption is formed inside Si ingot by scanning an ingot relatively with a laser beam. And by making a planar processing area into a peeling surface, a part of ingot is peeled and the board | substrate is created.

JP 2005-294325 A

  In the technique of Patent Document 1, the position of the condensing point of the laser light changes due to the influence of the undulation of the surface of the ingot and the inclination of the XY stage. Then, since it is difficult to make a planar processing region flat, warping and undulation may occur in the substrate after peeling.

  The present specification discloses a substrate manufacturing method. The substrate manufacturing method includes an ingot manufacturing process for manufacturing an SiC crystal ingot including a second layer sandwiched between first layers. Also, an irradiation step of irradiating the inside of the ingot with laser light from a direction substantially perpendicular to the first layer and the second layer, and separating the first layer from each other with the second layer in the ingot as a boundary. Prepare. In the ingot manufacturing process, the ingot is stored in a storage container, and the first layer and the second layer are grown in order from the lower layer by epitaxial growth. During the period during which the second layer is grown, a gas containing a predetermined element that narrows the band gap of the SiC crystal is supplied into the storage container. During the period during which the first layer is grown, a gas not containing a predetermined element is supplied into the storage container. The wavelength of the laser beam used in the irradiation step is longer than the upper limit of the absorption wavelength determined by the band gap of the first layer and shorter than the upper limit of the absorption wavelength determined by the band gap of the second layer.

  In the above method, the laser irradiated inside the ingot can be transmitted through the first layer and absorbed by the second layer. That is, the second layer can function as a laser condensing layer. Thereby, the second layer can be selectively heated without condensing the laser. Therefore, by generating a thermal stress in the second layer and generating a crack, the first layer can be separated from each other with the second layer as a boundary. As described above, even when there is a undulation of the surface of the ingot or an inclination of the stage on which the ingot is placed, the depth of the layer heated by the laser can be prevented from varying. Therefore, it is possible to prevent a situation in which warpage or undulation occurs in the first layer after peeling. The SiC crystal formed in the ingot manufacturing process may be various polytype crystals.

  According to the technique disclosed in this specification, it is possible to provide a substrate manufacturing method for forming a SiC crystal substrate with high yield.

It is a schematic diagram of a SiC crystal manufacturing apparatus. It is a schematic diagram of a laser irradiation apparatus. It is a schematic diagram of an ingot. It is a flowchart of an ingot manufacturing process. It is a flowchart of an irradiation process. It is explanatory drawing of an irradiation process.

  Hereinafter, some technical features of the embodiments disclosed in this specification will be described. The items described below have technical usefulness independently.

(Feature 1) In the above substrate manufacturing method, the thickness of the second layer may be smaller than the thickness of the first layer. Thereby, the second layer can be used as a separation layer for separating the first layer from each other. Moreover, since the margin at the time of cutting out a board | substrate from the ingot of a SiC crystal can be reduced, the yield of a board | substrate can be raised.

(Feature 2) In the above substrate manufacturing method, the crystal structure of the SiC crystal forming the first layer may be a hexagonal crystal. The range of the concentration of the predetermined element contained in the SiC crystal forming the second layer may be a range in which the crystal structure of the second layer is a hexagonal crystal. Depending on the concentration of the predetermined element contained in the SiC crystal forming the second layer, the crystal structure of SiC that is epitaxially grown may change. When the crystal structure of SiC is different between the first layer and the second layer, stacking faults occur and the crystallinity of SiC deteriorates. In the above substrate manufacturing method, the SiC crystal structure can be made the same between the first layer and the second layer, so that a SiC substrate with good crystallinity can be produced.

(Feature 3) In the substrate manufacturing method described above, the first layer may be a 6H—SiC crystal. The range of the concentration of the predetermined element contained in the SiC crystal forming the second layer may be a range in which the second layer becomes a 3C—SiC crystal. A 6H—SiC crystal is grown as the first layer and a 3C—SiC crystal is grown as the second layer by adjusting the concentration of the predetermined element contained in the SiC crystal forming the second layer. Can do. Accordingly, since the thermal expansion coefficients of the first layer and the second layer can be made different from each other, the thermal stress generated in the second layer when the second layer is heated is changed to the first layer. And the crystal structure of the second layer can be made larger than the case where they are the same. In addition, since a stacking fault can be formed at the interface between the first layer and the second layer, the second layer can be formed more than the case where the crystal structures of the first layer and the second layer are the same. It is possible to easily generate cracks in the layer. Thereby, the band gap of the second layer can be narrowed as compared with the case where the second layer is formed of 6H—SiC crystal. Therefore, since the difference in absorption wavelength between the first layer and the second layer can be increased, the second layer can be easily heated selectively. As described above, the first layers can be separated from each other with the second layer as a boundary.

(Feature 4) In the above substrate manufacturing method, the predetermined element may be nitrogen. Nitrogen is an element that is unlikely to be an acceptor and a donor with respect to the SiC crystal. Therefore, the conductivity type of the SiC crystal can be brought close to neutrality.

(Feature 5) In the substrate manufacturing method described above, in the ingot manufacturing process, the growth surface of the first layer and the second layer may be controlled so that the temperature of the outer peripheral portion is lower than the temperature of the central portion. . In the first layer and the second layer, the growth rate of epitaxial growth tends to be higher at the outer peripheral portion of the growth surface than at the central portion. In epitaxial growth, the growth rate tends to increase as the substrate temperature increases. In the above substrate manufacturing method, the difference in growth rate between the outer peripheral portion and the central portion of the growth surface can be reduced by controlling the temperature of the outer peripheral portion lower than the temperature of the central portion. Therefore, the first layer and the second layer can be epitaxially grown while the growth surface is kept flat.

<Structure of crystal manufacturing equipment>
FIG. 1 shows an SiC crystal manufacturing apparatus (hereinafter abbreviated as a crystal manufacturing apparatus) 1. The crystal manufacturing apparatus 1 is a horizontal CVD (Chemical Vapor Deposition) apparatus. The crystal manufacturing apparatus 1 includes a chamber 10, a substrate holding unit 11, a heating unit 12, a coil 13, an argon gas supply unit 21, a silane gas supply unit 22, a propane gas supply unit 23, a nitrogen gas supply unit 24, a gas supply line 25, and an exhaust. Line 26 and MFC (mass flow controller) 31-34 are provided.

  The chamber 10 may be composed of a quartz tube. The substrate holding unit 11 is a susceptor that holds the SiC base substrate 100. The substrate holding unit 11 is provided with a heating unit 12 at a portion in contact with the central portion of the SiC base substrate 100. The heating unit 12 may be made of graphite. The coil 13 is disposed outside the chamber 10 so as to surround the chamber 10. The gas supply line 25 is a line for introducing various gases supplied from the argon gas supply unit 21 to the nitrogen gas supply unit 24 into the chamber 10. The MFCs 31 to 34 are controllers that control the amount of gas supplied from each of the argon gas supply unit 21 to the nitrogen gas supply unit 24. The exhaust line 26 is a line for exhausting various gases introduced into the chamber 10.

<Structure of laser irradiation device>
In FIG. 2, the schematic of the laser irradiation apparatus 50 is shown. The laser irradiation apparatus 50 includes a laser light generation unit 51, a stage 52, and a stage drive unit 53. The laser beam generator 51 is a part that outputs a laser beam 60. The stage 52 is a part on which the ingot 110 is placed. The stage driving unit 53 is a part that moves the stage 52 in the X and Y directions (direction in a plane perpendicular to the laser beam 60) and the Z direction (direction parallel to the laser beam 60). The relative position of the ingot 110 with respect to the laser beam generator 51 can be changed by the stage drive unit 53.

<Substrate manufacturing method>
A substrate manufacturing method according to this embodiment will be described. The substrate manufacturing method includes an ingot manufacturing process and an irradiation process. The ingot manufacturing process is a process of manufacturing the ingot 110 using the crystal manufacturing apparatus 1. The irradiation step is a step of separating the substrate layer from the ingot 110 by using the laser irradiation device 50 to irradiate the ingot 110 with the laser beam 60, with the release layer as a boundary.

  An example of the ingot formed by the ingot manufacturing process will be described with reference to the schematic diagram of FIG. FIG. 3 shows a top view and a side view of the ingot 110. The ingot 110 has a substantially cylindrical shape. The ingot 110 has a configuration in which a release layer 101, a substrate layer 102, a release layer 103, a substrate layer 104, a release layer 105, and a substrate layer 106 are sequentially stacked on a SiC base substrate 100. The SiC base substrate 100 and the substrate layers 102, 104, 106 are 6H—SiC crystals. The peeling layers 101, 103, and 105 are 6H—SiC crystals doped with nitrogen. The thickness T1 of the release layers 101, 103, and 105 is thinner than the thickness T2 of the substrate layers 102, 104, and 106. For example, the ingot 110 may have a diameter of 1 to 8 inches and a height of about 100 μm. The thickness T2 of the substrate layers 102, 104, 106 may be, for example, in the range of 0.1 μm to 1000 μm. The thickness T1 of the release layers 101, 103, 105 may be, for example, in the range of 0.1 μm to 1000 μm.

<Ingot manufacturing process>
The contents of the ingot manufacturing process will be described with reference to the flow of FIG. In step S <b> 1, the SiC base substrate 100 of 6H—SiC crystal is held on the substrate holding part 11 in the chamber 10. The plane orientation of the main surface of SiC base substrate 100 is preferably a (0001) plane. Then, argon (Ar) gas is purged from the argon gas supply unit 21 into the chamber 10.

In step S <b> 2, a 6H—SiC crystal peeling layer 101 is epitaxially grown on the SiC base substrate 100. A thermal CVD method is used for epitaxial growth of the release layer. Specifically, an induction current is generated on the surface of the heating unit 12 by flowing a high-frequency current through the coil 13, and the heating unit 12 is heated by the induction current. Thereby, the central part of SiC base substrate 100 is heated. Further, the heating unit 12 is not in contact with the outer peripheral portion of the SiC base substrate 100. Thereby, in the growth surface of the peeling layer 101, the temperature of the peripheral portion is controlled to be lower than that of the central portion. Then, silane (SiH ₄ ) gas and propane (C ₃ H ₈ ) gas, which are source gases, are supplied from the silane gas supply unit 22 and the propane gas supply unit 23 into the chamber 10 through the gas supply line 25. Further, nitrogen (N ₂ ) gas is supplied from the nitrogen gas supply unit 24 into the chamber 10 through the gas supply line 25.

  In step S <b> 2 for growing the release layer, nitrogen gas is supplied into the chamber 10. Therefore, 6H-SiC crystal containing nitrogen can be epitaxially grown. Specifically, in the atomic arrangement of the 6H—SiC crystal, some carbon atoms can be replaced with nitrogen atoms. Nitrogen is an element that narrows the band gap of the SiC crystal. Therefore, the band gap of the 6H—SiC crystal in the release layer can be narrower than the band gap of the 6H—SiC crystal in the substrate layer. As the band gap of the 6H—SiC crystal is narrowed, the absorption wavelength can be increased. Thereby, since the absorbed light can be changed, the color of the 6H—SiC crystal changes. Specifically, if the wavelength of the incident light is shorter than the wavelength corresponding to the band gap (the wavelength at the optical absorption edge), the light is not transmitted, and the semiconductor is colored to the complementary color of the absorbed color.

  Also, if the nitrogen concentration contained in the SiC crystal forming the release layer is too high, the crystal structure of the growing SiC crystal changes from 6H—SiC (hexagonal) to 3C—SiC (cubic). There is. In this case, since a stacking fault occurs with a change in the crystal structure, the crystallinity of the SiC crystal is deteriorated. Therefore, the nitrogen concentration contained in the SiC crystal forming the release layer is preferably within a range in which the crystal structure of the release layer is maintained in a hexagonal crystal.

  In step S2, when the release layer 101 grows to a predetermined thickness T1, the supply of nitrogen gas from the nitrogen gas supply unit 24 is stopped, and the process proceeds to step S3. Note that the transition to step S3 may be performed in response to the processing time in step S2 reaching the growth time necessary for the peeling layer 101 to grow to the thickness T1.

  In step S <b> 3, a 6H—SiC crystal substrate layer 102 is epitaxially grown on the release layer 101. A thermal CVD method is used for epitaxial growth of the substrate layer 102. Specifically, as described above, silane gas and propane gas, which are source gases, are supplied into the chamber 10 while the heating unit 12 is heated. Note that nitrogen gas is not supplied into the chamber 10. Thereby, a 6H—SiC crystal containing no nitrogen can be epitaxially grown as the substrate layer 102.

  In step S3, when the substrate layer 102 grows to a predetermined thickness T2, supply of nitrogen gas from the nitrogen gas supply unit 24 is started, and the process proceeds to step S4. Note that the transition to step S4 may be performed according to the processing time in step S3 reaching the growth time necessary for the substrate layer 102 to grow to the thickness T2.

  In step S4, a 6H—SiC crystal release layer is epitaxially grown on the substrate layer. Note that the detailed contents of step S4 are the same as the contents of step S2 described above, and thus the description thereof is omitted here. In step S5, a 6H—SiC crystal substrate layer is epitaxially grown on the release layer. Note that the detailed content of step S5 is the same as the content of step S3 described above, and thus the description thereof is omitted here.

  In step S6, it is determined whether or not the number of substrate layers has reached a predetermined number. In the present embodiment, as an example, a case where the number of substrate layers is three will be described. If the number of substrate layers is less than 3, return to step S4. Then, one release layer (step S4) and one substrate layer (step S5) are further grown. On the other hand, when the number of substrate layers reaches three, the flow ends. Thereby, the ingot 110 shown in FIG. 3 can be formed.

<Irradiation process>
The contents of the irradiation process will be described with reference to the flowchart of FIG. 5 and the explanatory diagram of FIG. In step S <b> 10, the ingot 110 is fixed to the stage 52 of the laser irradiation apparatus 50. In step S11, the height of the stage 52 in the Z direction is adjusted so that the distance H from the surface of the ingot 110 to the laser output portion of the laser light generator 51 is a predetermined distance.

  In step S <b> 12, the laser beam 60 is output from the laser beam generator 51. The laser beam 60 is applied to the inside of the ingot 110 from the upper surface side of the ingot 110. The wavelength of the laser beam 60 is longer than the upper limit of the absorption wavelength (wavelength of the optical absorption edge) determined by the band gap of the substrate layer, and shorter than the upper limit of the absorption wavelength (wavelength of the optical absorption edge) determined by the band gap of the release layer. Is the wavelength. By using the laser light 60 having such a wavelength, as shown in FIG. 2, the laser light 60 irradiated inside the ingot 110 is transmitted through the substrate layer 106, and the peeling layer is a lower layer of the substrate layer 106. 105 can be absorbed. That is, the peeling layer 105 can function as a light condensing layer for the laser beam 60. Accordingly, the peeling layer 105 can be selectively heated without performing the process of condensing the laser beam 60 using a lens or the like. Therefore, thermal stress can be generated in the release layer 105 to generate a crack.

  The kind of the laser beam 60 may be a solid laser, a liquid laser, a semiconductor laser, a gas laser, a free electron laser, a metal vapor laser, or a chemical laser. The wavelength of the laser beam 60 may be 400 nm or more, for example. A more preferable wavelength range is 500 nm or more.

  In step S12, the laser beam 60 is scanned relative to the ingot 110 by moving the stage 52 in the X and Y directions. Thus, a crack can be generated on the entire surface of the release layer 105 by generating thermal stress on the entire surface of the release layer 105. When the process of scanning the release layer 105 with the laser beam 60 is completed, the process proceeds to step S13.

  In step S13, as shown in FIG. 6, the uppermost substrate layer is separated from the ingot 110 with the release layer 105 as a boundary. For example, by holding the substrate layer 106 with a vacuum chuck or the like and applying a force in a peeling direction (for example, a force above the ingot 110), the peeling layer 105 starts from a crack generated on the entire surface of the peeling layer 105. When broken, the substrate layer 106 can be separated from the ingot 110.

  In step S14, it is determined whether or not there is a substrate layer not yet separated in the ingot 110. If the substrate layer does not exist, the flow ends. On the other hand, if there is a substrate layer, the process returns to step S11, and the step of irradiating the laser beam 60 (step S12) and the step of separating the uppermost substrate layer from the ingot 110 (step S13) are repeated. Thereby, a plurality of substrates can be obtained from one ingot 110.

  In the ingot 110 shown in FIG. 6, since the substrate layers 104 and 102 are not yet separated from the ingot (step S14: YES), the process returns to step S11. Then, the laser beam 60 is irradiated from the upper surface side of the substrate layer 104 to the peeling layer 103 inside the ingot 110. At this time, part of the peeling layer 105 may remain on the surface of the substrate layer 104. However, since the thickness of the remaining peeling layer 105 is sufficiently thinner than the thickness T1 of the peeling layer 105 before peeling, most of the laser beam 60 can be absorbed by the peeling layer 103. Therefore, a thermal stress can be generated in the release layer 103 to generate a crack.

<Effect>
In the above substrate manufacturing method, the band gap of the SiC crystal forming the release layer can be narrower than the band gap of the SiC crystal forming the substrate layer. And by making a peeling layer function as a condensing layer of the laser beam 60, a board | substrate layer can be mutually isolate | separated by a peeling layer as a boundary. Thereby, it is possible to selectively heat the release layer without performing control such as condensing the laser. Therefore, even when there is a wave of the surface of the ingot 110 or an inclination of the stage 52 on which the ingot is placed, it is possible to prevent the depth of the layer heated by the laser light 60 from varying. Therefore, it is possible to prevent a situation in which warpage or undulation occurs in the substrate layer after peeling.

  In the substrate manufacturing method described above, the nitrogen concentration contained in the SiC crystal forming the release layer is in a range where the crystal structure of the release layer is a hexagonal crystal. Thereby, since the crystal structure of SiC can be made the same between the substrate layer and the release layer, an SiC substrate with good crystallinity can be produced.

  In the above substrate manufacturing method, the element included in the 6H—SiC crystal forming the release layer is nitrogen. Nitrogen is an element that is unlikely to be an acceptor and a donor with respect to the SiC crystal. Therefore, the conductivity type of the SiC crystal can be brought close to neutrality.

  When an SiC crystal is epitaxially grown in the ingot manufacturing process, the growth rate tends to be higher at the outer peripheral portion of the growth surface than at the central portion. One of the factors that cause this tendency is the so-called Berg effect. In the epitaxial growth of SiC crystal, the growth rate tends to increase as the temperature of the growth surface increases. Therefore, in the above-described substrate manufacturing method, when the ingot is grown, the heating unit 12 performs control so that the temperature at the periphery of the growth surface is lower than that at the center of the growth surface. Thereby, the difference in growth rate between the outer peripheral portion of the growth surface and the central portion of the growth surface can be reduced. Therefore, it is possible to epitaxially grow the SiC crystal while maintaining a flat growth surface.

  When an SiC substrate is produced using a so-called smart cut method, a hydrogen high-concentration layer is formed by implanting hydrogen ions from the main surface of the SiC crystal substrate, and then the main surface is attached to the base substrate. Thereafter, the SiC crystal thin film is peeled from the SiC crystal substrate with the hydrogen high concentration layer. In the smart cut method, as the thickness of the SiC crystal thin film is increased, it is necessary to increase the hydrogen ion implantation energy, and the damage to the substrate increases. Therefore, the SiC crystal having a thickness of several tens of μm or more is required. A thin film cannot be created. Therefore, in order to produce a SiC crystal layer having a thickness of several tens of μm, it is necessary to further epitaxially grow a SiC crystal on the SiC crystal layer after the smart cut. On the other hand, in the substrate manufacturing method of the present specification, a SiC crystal thin film having a thickness of several tens of μm can be produced with a higher yield than when a wire saw is used. Further, in the substrate manufacturing method of the present specification, it is not necessary to perform a hydrogen ion implantation step, a two-step SiC crystal epitaxial growth step, or the like. As described above, in the substrate manufacturing method of this specification, it is possible to easily manufacture a SiC crystal thin film having a thickness of several tens of μm as compared with the smart cut method.

  As mentioned above, although the Example of this invention was described in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

<Modification>
In this embodiment, the case where the substrate layer and the release layer are formed of 6H—SiC crystals has been described, but the present invention is not limited to this. Any polytype SiC crystal may be used as long as it is a polytype that can be controlled so as not to cause a polymorphic change in the substrate layer in the ingot manufacturing process. For example, 4H—SiC crystal or 3C—SiC crystal may be used. In the case where the substrate layer or the release layer is formed using 4H—SiC crystals, 4H—SiC crystals may be used for the SiC base substrate 100. In this case, the plane orientation of the main surface of SiC base substrate 100 is preferably a (0001) plane. In the case where the substrate layer and the release layer are formed using 3C—SiC crystals, 3C—SiC crystals may be used for the SiC base substrate 100. In this case, the plane orientation of the main surface of SiC base substrate 100 is preferably (111) plane or (001) plane.

  Further, when the crystal structure of the SiC crystal forming the substrate layer is cubic (eg, 3C-SiC), the nitrogen concentration contained in the SiC crystal forming the release layer is the cubic structure of the release layer. It is good to set it as the range which becomes. Thereby, since the crystal structure of SiC can be made the same between the substrate layer and the release layer, an SiC substrate with good crystallinity can be produced.

  The concentration of nitrogen contained in the SiC crystal forming the release layer may be in a range where the release layer becomes a 3C-SiC crystal. When the concentration of nitrogen contained in the SiC crystal forming the release layer is increased, the crystal structure of the growing SiC crystal can be changed from 6H—SiC (hexagonal) to 3C—SiC (cubic). Specifically, when the release layer is grown in the ingot manufacturing process, the partial pressure ratio of the nitrogen gas supplied into the chamber 10 to the source gas is set as compared with the case where the release layer is formed of 6H—SiC crystals. You only have to increase it. Thereby, a peeling layer can be formed with 3C-SiC crystal. Further, when the substrate layer is grown on the release layer, the supply of nitrogen gas into the chamber 10 may be stopped. Thereby, the substrate layer can be formed of 6H—SiC crystal.

  By forming the release layer with 3C—SiC crystal and forming the substrate layer with 6H—SiC crystal, as a first effect, the thermal expansion coefficients of the substrate layer and the release layer can be made different. Therefore, the thermal stress generated in the release layer when the release layer is heated by irradiation with the laser beam 60 can be made larger than when the crystal structure of the substrate layer and the release layer is the same. As a second effect, since a stacking fault can be formed at the interface between the substrate layer and the release layer, it is easier to generate cracks in the release layer than when the crystal structure of the substrate layer and the release layer is the same. can do. As a third effect, the band gap of the release layer can be narrowed compared to the case where the release layer is formed of 6H—SiC crystals. Therefore, since the difference in absorption wavelength between the substrate layer and the release layer can be further increased, the release layer can easily be selectively heated. With the above effects, it is possible to more reliably perform the process of separating the substrate layer with the release layer as a boundary.

  Although the element contained in the release layer is nitrogen, it is not limited to this form. Any element may be used as long as the band gap of the release layer can be narrower than the band gap of the substrate layer. For example, elements such as N, P, As, B, Sb, Tl, Bi, B, Al, Ga, In, Mg, Zn, Cd, O, S, Se, Te, H, and F may be used.

  Although the form using the CVD method has been described in the ingot manufacturing process, the form is not limited to this form. It is also possible to use a sublimation recrystallization method or a liquid phase growth method. In the case of using the sublimation recrystallization method, control may be performed so that nitrogen is supplied into the crucible in the step of growing the release layer and nitrogen is not supplied into the crucible in the step of growing the substrate layer. The supply of nitrogen into the crucible may be performed, for example, by supplying nitrogen gas or by supplying a solid containing nitrogen. When the liquid phase growth method is used, in the step of growing the release layer, the seed crystal substrate may be immersed in a solution containing an element that narrows the band gap of the SiC crystal. In the step of growing the substrate layer, the seed crystal substrate may be immersed in a solution that does not contain an element that narrows the band gap of the SiC crystal. The method of adding an element that narrows the band gap to the solution may be, for example, a method of replacing the atmosphere in the crystal manufacturing apparatus with a gas containing an element that narrows the band gap.

  When a part of the peeling layer remains on the surface of the substrate layer, the remaining peeling layer is removed by a process such as CMP (Chemical Mechanical Polishing) and then irradiated with the laser beam 60. Also good. Thereby, the laser beam 60 can be reliably absorbed by the peeling layer located under the uppermost substrate layer.

  In the laser irradiation apparatus 50, a condensing lens may be used. In this case, the condensing point of the laser beam 60 may be set in the vicinity of the release layer located below the uppermost substrate layer. Thereby, even when a part of the peeling layer remains on the surface of the substrate layer, the laser beam 60 can be made difficult to be absorbed by the remaining peeling layer. Further, since the release layer functions as a condensing layer for the laser beam 60, high accuracy can be eliminated in controlling the position of the condensing point.

  The gas used for purging the chamber 10 is not limited to argon gas. Any gas may be used as long as it is a stable gas that is not taken into the SiC crystal. For example, helium gas can be used.

  In the ingot manufacturing process, various methods can be used as a method of performing control so that the temperature in the peripheral portion of the growth surface is lower than that in the central portion of the growth surface. For example, in the substrate holding unit 11, a cooling pipe may be provided in a portion where the outer peripheral portion of the SiC base substrate 100 contacts.

  In the ingot 110 illustrated in FIG. 3, the case where the number of stacked substrate layers is three has been described, but the present invention is not limited to this configuration. Two or less layers or four or more substrate layers may be laminated.

  In step S12, various methods can be used as the method of scanning the laser beam 60 relative to the ingot 110. For example, the stage 52 may be fixed and the laser light generator 51 may be scanned.

  The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

  1: Crystal manufacturing apparatus, 10: Chamber, 50: Laser irradiation apparatus, 60: Laser light, 100: SiC base substrate, 101 and 103 and 105: Release layer, 102 and 104 and 106: Substrate layer, 110: Ingot

Claims (6)

An ingot production process for producing an SiC crystal ingot comprising a second layer sandwiched between first layers;
The inside of the ingot is irradiated with laser light from a direction substantially perpendicular to the first layer and the second layer, and the first layer is separated from each other with the second layer in the ingot as a boundary. An irradiation process to perform,
With
The ingot manufacturing process includes:
The ingot is stored in a storage container, and the first layer and the second layer are grown in order from the lower layer by epitaxial growth,
During the period during which the second layer is grown, a gas containing a predetermined element that narrows the band gap of the SiC crystal is supplied into the storage container,
During the period during which the first layer is grown, a gas not containing the predetermined element is supplied into the storage container,
The wavelength of the laser beam used in the irradiation step is longer than the upper limit of the absorption wavelength determined by the band gap of the first layer and shorter than the upper limit of the absorption wavelength determined by the band gap of the second layer. There is provided a substrate manufacturing method.   The substrate manufacturing method according to claim 1, wherein a thickness of the second layer is smaller than a thickness of the first layer. The crystal structure of the SiC crystal forming the first layer is a hexagonal crystal,
The concentration range of the predetermined element contained in the SiC crystal forming the second layer is a range in which the crystal structure of the second layer is a hexagonal crystal. The board | substrate manufacturing method of description. The first layer is 6H-SiC crystal;
The range of the concentration of the predetermined element contained in the SiC crystal forming the second layer is a range in which the second layer becomes a 3C-SiC crystal. The manufacturing method of a board | substrate of description.   The substrate manufacturing method according to claim 1, wherein the predetermined element is nitrogen.   In the ingot manufacturing process, the growth surface of the first layer and the second layer is controlled so that the temperature of the outer peripheral portion is lower than the temperature of the central portion. The substrate manufacturing method according to any one of the above.

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