JP2005033186A - Manufacturing method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformly control residual stress or residual distortion in a wafer surface where the crystal of a semiconductor layer is grown while preventing the misregistration of the semiconductor layer in a semiconductor manufacturing process and its contamination, deterioration, deformation, etc. in a thermal treatment step. <P>SOLUTION: On a GaN layer 12 formed on the main surface of a sapphire substrate 11, light is irradiated from the back of the substrate, and thereby part of an area on the GaN layer 12 contacting the substrate is thermally decomposed to form a thermally decomposed layer 14. After that, while keeping the state of the sapphire substrate 11 and the GaN layer 12 being bonded, the thermally decomposed layer 14 is removed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a semiconductor device such as a field effect transistor, a bipolar transistor, or a light emitting element using a group III nitride, and more particularly to a technique for extracting a semiconductor element by dividing a substrate.

  Group III nitride semiconductors (hereinafter simply referred to as nitride semiconductors) made of GaN, AlN, InN or mixed crystals thereof are not only applied to light-emitting devices because of their wide band gaps, but also their breakdown voltage, electron Because of its high saturation speed and high electron mobility, it is also used for the development of high-frequency and high-power electronic devices such as field effect transistors or bipolar transistors.

In the manufacture of semiconductor devices using these nitride semiconductors, it is difficult to manufacture single crystal wafers. As a result, a base substrate made of a material having a lattice constant or a thermal expansion coefficient different from these nitride semiconductors, for example, sapphire A nitride semiconductor crystal layer has been grown on a substrate or a SiC substrate. However, when a crystal is grown on a sapphire substrate or SiC substrate, there is a residual stress due to lattice mismatch between the substrate and the nitride semiconductor crystal layer and a residual strain associated therewith, thereby warping the substrate. Such problems arise. On the other hand, as one method for removing this residual strain, the crystal layer is thermally decomposed at the interface between the substrate and the nitride semiconductor crystal layer by irradiating light from the back surface side of the base material substrate. A technique for forming a pyrolysis layer has been developed (see Patent Documents 1 and 2).
JP 2003-37286 A US Pat. No. 6,071,795

  However, in the prior art in which light is simply irradiated from the back surface of the base material substrate and the thermal decomposition layer is formed at the interface between the substrate and the nitride semiconductor crystal layer, the following problems occur. That is, since the pyrolysis layer is mainly composed of a group III metal, it has a low melting point and easily undergoes a chemical reaction. For this reason, when a normal semiconductor manufacturing process such as a process of heating the wafer or a process of exposing the wafer to a reactive gas atmosphere is performed after the process of forming the pyrolysis layer, the group III metal is removed from the pyrolysis layer. There arises a problem that evaporation causes contamination, or a problem that the thermal decomposition layer itself is altered or deformed by a chemical reaction to deteriorate the uniformity of the wafer.

  Further, in the prior art, since the entire region on the back surface of the wafer is irradiated with light, the above-described pyrolysis layer is formed in the entire region at the interface between the nitride semiconductor layer and the base material substrate. Since the layer cannot be completely fixed to the base material substrate, there is a problem that the semiconductor layer is displaced in the semiconductor device manufacturing process. In such a case, even if the pyrolysis layer is solidified again in the process of lowering the temperature of the substrate performed later, the pyrolysis layer has a low melting point because it is mainly composed of a group III metal such as Ga, Al, or In. When the substrate temperature is raised to room temperature or higher in the process of forming the semiconductor element on the substrate, the pyrolysis layer is melted again, resulting in a problem that the semiconductor element is displaced from the substrate. .

  In view of the above, the present invention provides a residual stress or residual strain within a wafer surface on which a semiconductor layer is crystal-grown while preventing misalignment of the semiconductor layer in the semiconductor device manufacturing process and contamination, alteration or deformation in the heat treatment step. The purpose is to be able to alleviate uniformly.

  In order to achieve the above object, a semiconductor device manufacturing method according to the present invention irradiates a semiconductor layer formed on one surface of a substrate with light from the other surface side of the substrate, thereby forming a substrate in the semiconductor layer. And a step of partially pyrolyzing the contact region with the substrate to form a pyrolysis layer, and a step of removing the pyrolysis layer while maintaining a state where the substrate and the semiconductor layer are bonded to each other.

  According to the method for manufacturing a semiconductor device of the present invention, the semiconductor layer formed on one surface (front surface) of the substrate is irradiated with light from the other surface (back surface) side of the substrate to form the thermal decomposition layer. Residual strain in the substrate surface can be relaxed by the elasticity of the decomposition layer, so that problems such as warpage of the substrate can be prevented. In addition, in order to form a thermal decomposition layer by partially thermally decomposing the semiconductor layer, in other words, to form a thermal decomposition layer by irradiating only a part of the back surface of the substrate, the semiconductor layer (precisely, A thermal decomposition layer is not formed in a portion of the semiconductor layer that is not irradiated with light in a contact region with the substrate. In other words, since the direct bonding between the non-pyrolyzed region of the semiconductor layer and the substrate is maintained, the semiconductor layer can be kept completely fixed to the base material substrate, thereby shifting the position of the semiconductor layer. Can be prevented.

  In addition, according to the method for manufacturing a semiconductor device of the present invention, even if a step of heating the substrate to a temperature equal to or higher than the melting point of the pyrolysis layer is performed to remove the pyrolysis layer itself, contamination and alteration caused by the heat treatment are performed. Alternatively, deformation can be prevented. That is, the step of raising the temperature of the substrate above the melting point of the pyrolysis layer can be performed while preventing contamination, alteration or deformation due to heat treatment.

  In the method for manufacturing a semiconductor device of the present invention, the semiconductor layer is preferably a semiconductor layer made of a group III nitride. If it does in this way, formation of a thermal decomposition layer can be performed reliably.

  In the method of manufacturing a semiconductor device of the present invention, in the step of forming the pyrolysis layer, the pyrolysis layer is preferably formed in a symmetrical shape with respect to the center of the one surface on one surface of the substrate.

  In this way, the initial residual strain generated in the substrate surface during the formation of the semiconductor layer can be released uniformly and isotropically in the substrate surface.

  In the step of forming the thermal decomposition layer in the method for manufacturing a semiconductor device of the present invention, the thermal decomposition layer may be formed only on the peripheral edge portion of the substrate surface, or other part other than the central portion on the substrate surface. It may be formed on the top.

  In the method for manufacturing a semiconductor device of the present invention, in the step of forming the pyrolysis layer, the pyrolysis layer is preferably formed concentrically, radially or spirally on one surface of the substrate.

  In this way, strain existing in the substrate surface can be relaxed substantially symmetrically and uniformly with respect to the center of the substrate surface.

  In the method for manufacturing a semiconductor device of the present invention, in the step of forming the pyrolysis layer, the pyrolysis layer is formed to have a portion exposed at the end of the semiconductor layer, and in the step of removing the pyrolysis layer, heat is The decomposition layer is preferably etched from the exposed portion with an acidic solution.

  In this way, the entire pyrolysis layer can be reliably removed by etching.

  The semiconductor device manufacturing method of the present invention may further include a step of heating the substrate to a temperature equal to or higher than the melting point of the pyrolysis layer after the step of removing the pyrolysis layer.

  The method for manufacturing a semiconductor device of the present invention may further include a step of forming a plurality of semiconductor elements using the semiconductor layer as an active layer after the step of removing the thermal decomposition layer.

  In this case, the method further includes the step of dividing the plurality of semiconductor elements by dividing the substrate after the step of forming the plurality of semiconductor elements, and the step of forming the thermal decomposition layer is performed along the dividing line of the substrate. Including the step of forming the thermal decomposition layer in a line shape by irradiating the semiconductor layer with light, and the step of dividing the plurality of semiconductor elements into the linear region from which the thermal decomposition layer has been removed. Preferably, the method includes a step of dividing the substrate along the substrate. Thus, each semiconductor element can be formed while relaxing the residual strain in the substrate surface, and each semiconductor element can be cut out as a chip.

  In this case, the method further includes the step of dividing the plurality of semiconductor elements into pieces by dividing the substrate after the step of forming the plurality of semiconductor elements, and the step of forming the thermal decomposition layer includes a dividing line of the substrate. The step of irradiating the semiconductor layer with light so that the region not irradiated with light exists along the line, and the step of dividing the plurality of semiconductor elements into pieces is not irradiated with the light existing in the line shape It is preferable to include a step of dividing the substrate along the region. In this way, each semiconductor element can be formed while relaxing the residual strain in the substrate surface, and each semiconductor element can be cut out from the substrate in a thin film state that can be bonded to another substrate.

  According to the present invention, since the residual stress or residual strain can be uniformly relaxed by forming the thermal decomposition layer on the wafer surface on which the semiconductor layer is crystal-grown, it is possible to prevent problems such as substrate warpage from occurring. . Also, by removing the thermal decomposition layer while maintaining the state where the substrate and the semiconductor layer are bonded, the semiconductor layer is displaced in the subsequent semiconductor device manufacturing process, and contamination, alteration or deformation of the heat treatment process occurs. You can also prevent the situation. That is, it is possible to manufacture a semiconductor device using a semiconductor layer capable of withstanding a heat treatment process without causing a positional shift in a semiconductor device manufacturing process while relaxing a residual stress or a residual strain and preventing a warp of the substrate. it can.

(First embodiment)
A method for manufacturing a semiconductor device according to the first embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1A and FIGS. 1C to 1G are cross-sectional views showing respective steps of the semiconductor device manufacturing method according to the first embodiment, and FIG. 1B shows the first embodiment. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns on a form.

First, as shown in FIG. 1A, for example, nitridation is performed on the main surface of a sapphire substrate 11 having a C surface as a main surface and a thickness of about 400 μm, for example, by metal organic vapor phase epitaxy (MOVPE method). A first semiconductor layer 12 made of gallium (GaN) and having a thickness of about 2 to 3 μm is formed. Thereafter, on the first semiconductor layer 12, for example, a second layer having a thickness of about 25 nm made of a nitride mixed crystal (Al _x Ga _1-x N (where 0 <x <1)) containing aluminum and gallium is used. The semiconductor layer 13 is formed. At this time, there is a residual stress due to lattice mismatch between the sapphire substrate 11 and the first semiconductor layer 12 and a residual strain associated therewith. As a result, as shown in FIG. Is warped.

Subsequently, from the back surface (opposite surface of the main surface) of the sapphire substrate 11 in which the semiconductor layers 12 and 13 are stacked on the main surface, for example, a third harmonic of an Nd: YAG laser is applied, for example, with an irradiation energy of 0. Irradiation is performed under irradiation conditions of 3 J / cm ² , a pulse width of 5 ns, and a beam diameter of 1.00 μm. Specifically, in the present embodiment, as shown in FIG. 1B, the peripheral portion on the back surface of the sapphire substrate 11 is defined as a light irradiation unit 11a. Since the sapphire substrate 11 is transparent to the laser light, the laser light irradiated from the back side of the sapphire substrate 11 is absorbed near the interface with the sapphire substrate 11 in the first semiconductor layer (GaN layer) 12. Only the GaN layer 12 in the vicinity of the interface is thermally decomposed. As a result, as shown in FIG. 1C, a thin pyrolysis layer 14 mainly composed of Ga is formed in the vicinity of the interface with the sapphire substrate 11 at the peripheral part of the GaN layer 12 corresponding to the light irradiation part 11a. The By forming the thermal decomposition layer 14 in this way, the strain existing in the peripheral portion of the sapphire substrate 11 can be relaxed substantially symmetrically and uniformly with respect to the center of the substrate surface.

  By the way, since the melting point of the pyrolysis layer 14 is generally low, the pyrolysis layer 14 is formed in the manufacturing process of the semiconductor device using the first semiconductor layer (GaN layer) 12 and the second semiconductor layer (AlGaN layer) 13. If the process of raising the temperature of the sapphire substrate 11 is performed as it is, the following problems will occur. That is, contamination due to evaporation or diffusion of Ga in the pyrolysis layer 14 or oxidation of the Ga causes unevenness in the thickness of the pyrolysis layer 14 or the surface shape of the AlGaN layer 13 becomes non-uniform. As a result, in-plane performance variation also occurs in the finally fabricated semiconductor device.

  Therefore, in this embodiment, the sapphire substrate 11 having the thermal decomposition layer 14 formed by laser light irradiation is immersed in hydrochloric acid, for example, to remove the thermal decomposition layer 14 as shown in FIG. . At this time, as shown in FIG. 1 (d), the GaN layer 12 is kept in a state of being coupled to the sapphire substrate 11 in an unirradiated portion of the laser light (a region where the thermal decomposition layer 14 is not formed).

  Next, as shown in FIG. 1E, after a mask 15 made of, for example, Si is deposited on the region used as the device active region in the GaN layer 12 and the AlGaN layer 13, an oxygen atmosphere of, eg, about 900 ° C. Annealing is performed for about 9 hours. As a result, a region of the AlGaN layer 13 that is not covered by the mask 15 is selectively oxidized, whereby the element isolation layer 16 is formed. Here, the sapphire substrate 11 can be exposed to an oxygen atmosphere at a temperature higher than the melting point of the pyrolysis layer 14 of about 900 ° C. because the pyrolysis layer 14 has already been removed in the step shown in FIG. Because.

  Next, as shown in FIG. 1 (f), after removing the mask 15, on the exposed portion of the AlGaN layer 13, for example, a pair of source / layers mainly composed of a laminated structure of a Ti layer and an Al layer are formed. The drain electrode 17 is formed and then annealed in a hydrogen atmosphere at, for example, about 600 ° C., thereby realizing ohmic contact between each source / drain electrode 17 and the AlGaN layer 13. Here, since the pyrolysis layer 14 is removed in the step shown in FIG. 1D, even if the sapphire substrate 11 is processed at a temperature higher than the melting point of the pyrolysis layer 14 of about 600 ° C., the pyrolysis layer 14 It is possible to prevent adverse effects caused by evaporation or chemical reaction.

  Next, as shown in FIG. 1G, after the gate electrode 18 is formed on the region between the pair of source / drain electrodes 17 in the AlGaN layer 13 by, for example, the lift-off method, the remaining portions of the AlGaN layer 13 are formed. A surface passivation film 19 is formed on the exposed portion. Thereafter, although not shown, the semiconductor device is completed through a wiring process and the like.

  As described above, according to the first embodiment, the back surface of the sapphire substrate 11 (opposite of the main surface on which the GaN layer 12 is formed) with respect to the GaN layer 12 formed on the main surface of the sapphire substrate 11. Since the thermal decomposition layer 14 is formed by irradiating light from the surface), the residual strain in the main surface of the substrate can be relaxed by the elasticity of the thermal decomposition layer 14, so that problems such as warpage of the sapphire substrate 11 occur. Can be prevented. Further, in the first embodiment, when warping or the like occurs, distortion of the peripheral edge of the substrate, which generally has a large amount of deformation, can be alleviated by adjusting the way of light irradiation (laser light irradiation).

  Further, according to the first embodiment, the GaN layer 12 is partially pyrolyzed to form the pyrolysis layer 14, in other words, only a part of the back surface of the substrate is irradiated with light so as to form the pyrolysis layer 14. Therefore, the pyrolysis layer 14 is not formed on the portion of the GaN layer 12 (more precisely, the contact region with the sapphire substrate 11 in the GaN layer 12) that is not irradiated with light. That is, even after the pyrolysis layer 14 is removed, the direct bonding between the non-formation region of the pyrolysis layer 14 in the GaN layer 12 and the sapphire substrate 11 is maintained. The completely fixed state of the layer 12 can be maintained, thereby preventing the misalignment of the GaN layer 12. Thereby, it is possible to improve accuracy in a later lithography process or the like.

  Further, according to the first embodiment, in order to remove the pyrolysis layer 14 itself, even if the step of heating the sapphire substrate 11 to a temperature equal to or higher than the melting point of the pyrolysis layer 14 is performed, contamination caused by heat treatment, Alteration or deformation can be prevented. That is, the step of raising the temperature of the sapphire substrate 11 above the melting point of the thermal decomposition layer 14 can be performed while preventing contamination, alteration or deformation due to heat treatment.

  In the first embodiment, the type of light irradiated from the back side of the substrate is not particularly limited as long as it is light that can thermally decompose the first semiconductor layer 12.

  In the first embodiment, the GaN layer is used as the first semiconductor layer 12. However, the present invention is not limited to this, and the formation of the thermal decomposition layer 14 is ensured by using a group III nitride layer. Can do. However, it goes without saying that a semiconductor layer other than the group III nitride layer, such as a GaAs layer or a Si layer, may be used.

  In the first embodiment, the sapphire substrate 11 is used. However, instead of this, a SiC substrate or a glass substrate may be used.

  In the first embodiment, hydrochloric acid is used for removing the thermal decomposition layer 14 by etching, but other acidic solutions may be used instead. Moreover, you may remove the thermal decomposition layer 14 by methods other than the etching using an acidic solution.

(Second Embodiment)
A method for manufacturing a semiconductor device according to the second embodiment of the present invention will be described below with reference to the drawings.

  2A and 2C to 2G are cross-sectional views showing respective steps of the semiconductor device manufacturing method according to the second embodiment, and FIG. 2B is a second embodiment. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns on a form.

First, as shown in FIG. 2A, for example, on the main surface of the sapphire substrate 21 having a thickness of about 400 μm with the C surface as the main surface, a thickness of about 2 to 3 μm made of GaN, for example, by the MOVPE method. The first semiconductor layer 22 is formed. After that, a second layer having a thickness of about 25 nm made of a nitride mixed crystal (Al _x Ga _1-x N (where 0 <x <1)) containing, for example, aluminum and gallium is formed on the first semiconductor layer 22. A semiconductor layer 23 is formed. At this time, there is a residual stress due to lattice mismatch between the sapphire substrate 21 and the first semiconductor layer 22 and a residual strain associated therewith. As a result, as shown in FIG. Is warped.

Subsequently, from the back surface (opposite surface of the main surface) of the sapphire substrate 21 in which the semiconductor layers 22 and 23 are stacked on the main surface, for example, the third harmonic of an Nd: YAG laser is applied, for example, with an irradiation energy of 0. Irradiation is performed under irradiation conditions of 3 J / cm ² , a pulse width of 5 ns, and a beam diameter of 1.00 μm. Specifically, in the present embodiment, as shown in FIG. 2B, almost the entire area of the back surface of the sapphire substrate 21 excluding the vicinity of the center is set as the light irradiation unit 21a. Since the sapphire substrate 21 is transparent to the laser light, the laser light irradiated from the back side of the sapphire substrate 21 is absorbed near the interface with the sapphire substrate 21 in the first semiconductor layer (GaN layer) 22. Only the GaN layer 22 near the interface is thermally decomposed. As a result, as shown in FIG. 2C, a thin film containing Ga as a main component is present in the vicinity of the interface with the sapphire substrate 21 in almost the entire area of the GaN layer 22 corresponding to the light irradiation part 21a (excluding the part near the center). A pyrolysis layer 24 is formed. By forming the thermal decomposition layer 24 in this manner, the residual stress of the sapphire substrate 21 that existed before the light irradiation is in a wide range excluding the vicinity of the center of the substrate with respect to the center of the substrate. Relaxed almost symmetrically and uniformly.

  By the way, since the melting point of the pyrolysis layer 24 is generally low, the pyrolysis layer 24 is formed in the manufacturing process of the semiconductor device using the first semiconductor layer (GaN layer) 22 and the second semiconductor layer (AlGaN layer) 23. If the step of raising the temperature of the sapphire substrate 21 is carried out as it is, the following problem occurs. That is, due to contamination caused by evaporation or diffusion of Ga in the pyrolysis layer 24 or oxidation of the Ga, the pyrolysis layer 24 is uneven in thickness, or the surface shape of the AlGaN layer 23 is not uniform. As a result, in-plane performance variation also occurs in the finally fabricated semiconductor device.

  Therefore, in this embodiment, the sapphire substrate 21 having the thermal decomposition layer 24 formed by laser light irradiation is immersed in hydrochloric acid, for example, to remove the thermal decomposition layer 24 as shown in FIG. . At this time, as shown in FIG. 2D, the GaN layer 22 is kept in a state where it is coupled to the sapphire substrate 21 at a laser light non-irradiated portion (non-formed region of the thermal decomposition layer 24), that is, at the central portion. It is.

  Next, as shown in FIG. 2E, after a mask 25 made of, for example, Si is deposited on the region used as the device active region in the GaN layer 22 and the AlGaN layer 23, an oxygen atmosphere of, eg, about 900 ° C. Annealing is performed for about 9 hours. As a result, a region of the AlGaN layer 23 that is not covered by the mask 25 is selectively oxidized, whereby an element isolation layer 26 is formed. Here, the reason why the sapphire substrate 21 can be exposed to the oxygen atmosphere for a long time at a temperature higher than the melting point of the pyrolysis layer 24 of about 900 ° C. is that the pyrolysis layer 24 has already been removed in the step shown in FIG. Because it is.

  Next, as shown in FIG. 2 (f), after removing the mask 25, a pair of source / layers mainly composed of a laminated structure of, for example, a Ti layer and an Al layer are formed on the exposed portion of the AlGaN layer 23. The drain electrode 27 is formed and then annealed in a hydrogen atmosphere at, for example, about 600 ° C., thereby realizing ohmic contact between each source / drain electrode 27 and the AlGaN layer 23. Here, since the pyrolysis layer 24 is removed in advance in the step shown in FIG. 2D, the pyrolysis layer of about 600 ° C. is prevented while preventing adverse effects due to evaporation or chemical reaction of the pyrolysis layer 24. The sapphire substrate 21 can be processed at a high temperature equal to or higher than the melting point of 24.

  Next, as shown in FIG. 2G, after the gate electrode 28 is formed on the region between the pair of source / drain electrodes 27 in the AlGaN layer 23 by, for example, a lift-off method, the remaining portions of the AlGaN layer 23 are formed. A surface passivation film 29 is formed on the exposed portion. Thereafter, although not shown, the semiconductor device is completed through a wiring process and the like.

  As described above, according to the second embodiment, the back surface of the sapphire substrate 21 (opposite of the main surface on which the GaN layer 22 is formed) with respect to the GaN layer 22 formed on the main surface of the sapphire substrate 21. Since the thermal decomposition layer 24 is formed by irradiating light from the surface), the residual strain in the main surface of the substrate can be relaxed by the elasticity of the thermal decomposition layer 24, and thus problems such as warpage of the sapphire substrate 21 occur. Can be prevented. In the second embodiment, when warpage or the like occurs, the distortion of all portions other than the central portion of the substrate where the deformation amount is the smallest is alleviated by adjusting the method of light irradiation (laser light irradiation). be able to.

  In addition, according to the second embodiment, since the thermal decomposition layer 24 is formed by thermally decomposing portions other than the central portion of the GaN layer 22, in other words, the thermal decomposition is performed by irradiating light other than the central portion of the back surface of the substrate. Since the layer 24 is formed, the thermal decomposition layer 24 is not formed in the central portion where the light is not irradiated in the GaN layer 22 (exactly, the contact region of the GaN layer 22 with the sapphire substrate 21). For this reason, even after the pyrolysis layer 14 is removed, direct bonding between the non-formation region of the pyrolysis layer 24 in the GaN layer 22 and the sapphire substrate 21 is maintained. In other words, even after the pyrolysis layer 24 is removed, the GaN layer 22 can be supported by the sapphire substrate 21 at the center thereof. Accordingly, it is possible to maintain the GaN layer 22 in a completely fixed state with respect to the sapphire substrate 21 which is the base material substrate, thereby preventing the GaN layer 22 from being displaced. Thereby, it is possible to improve accuracy in a later lithography process or the like.

  In addition, according to the second embodiment, in order to remove the pyrolysis layer 24 itself, even if a step of heating the sapphire substrate 21 to a temperature equal to or higher than the melting point of the pyrolysis layer 24 is performed, contamination caused by heat treatment, Alteration or deformation can be prevented. That is, the step of raising the temperature of the sapphire substrate 21 above the melting point of the thermal decomposition layer 24 can be performed while preventing contamination, alteration or deformation due to heat treatment.

  In the second embodiment, the type of light irradiated from the back side of the substrate is not particularly limited as long as it is light that can thermally decompose the first semiconductor layer 22.

  In the second embodiment, the GaN layer is used as the first semiconductor layer 22. However, the present invention is not limited to this, and the formation of the thermal decomposition layer 24 is ensured by using a group III nitride layer. Can do. However, it goes without saying that a semiconductor layer other than the group III nitride layer, such as a GaAs layer or a Si layer, may be used.

  In the second embodiment, the sapphire substrate 21 is used. However, instead of this, a SiC substrate or a glass substrate may be used.

  In the second embodiment, hydrochloric acid is used for removing the thermal decomposition layer 24 by etching, but other acidic solutions may be used instead. Moreover, you may remove the thermal decomposition layer 24 by methods other than the etching using an acidic solution.

(Third embodiment)
Hereinafter, a method for manufacturing a semiconductor device according to the third embodiment of the present invention will be described with reference to the drawings.

  3A, 3C, and 3D are cross-sectional views showing respective steps of the method of manufacturing a semiconductor device according to the third embodiment, and FIG. 3B shows the third embodiment. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns.

First, as shown in FIG. 3A, on the main surface of a sapphire substrate 31 having a thickness of about 400 μm with a C-plane as a main surface, for example, a thickness of about 2 to 3 μm made of GaN, for example, by MOVPE. The first semiconductor layer 32 is formed. Thereafter, on the first semiconductor layer 32, a second layer having a thickness of about 25 nm made of, for example, a nitride mixed crystal containing aluminum and gallium (Al _x Ga _1-x N (where 0 <x <1)) is formed. A semiconductor layer 33 is formed. At this time, there is a residual stress due to lattice mismatch between the sapphire substrate 31 and the first semiconductor layer 32 and a residual strain associated therewith, and as a result, as shown in FIG. Is warped.

Subsequently, from the back surface (opposite surface of the main surface) of the sapphire substrate 31 in which the semiconductor layers 32 and 33 are stacked on the main surface, for example, a third harmonic of an Nd: YAG laser is applied, for example, with an irradiation energy of 0. Irradiation is performed under irradiation conditions of 3 J / cm ² , a pulse width of 5 ns, and a beam diameter of 1.00 μm. Specifically, in this embodiment, as shown in FIG. 3B, the light irradiation unit 35 having a concentric pattern on the back surface of the sapphire substrate 31 is set. Since the sapphire substrate 31 is transparent to the laser light, the laser light irradiated from the back side of the sapphire substrate 31 is absorbed near the interface with the sapphire substrate 31 in the first semiconductor layer (GaN layer) 32. Only the GaN layer 32 in the vicinity of the interface is thermally decomposed. As a result, as shown in FIG. 3C, in the vicinity of the interface with the sapphire substrate 31 in the portion corresponding to the light irradiation portion 35 of the GaN layer 32 (portion concentrically on the substrate main surface), A thin pyrolysis layer 34 mainly composed of Ga is formed. In this way, by forming the pyrolysis layer 34 on the main surface of the sapphire substrate 31 in a symmetric shape with respect to the center of the substrate, the residual stress of the sapphire substrate 31 existing before the light irradiation is reduced over the entire surface of the substrate. In the meantime, it is relaxed substantially symmetrically and uniformly with respect to the center of the substrate.

  By the way, since the melting point of the pyrolysis layer 34 is generally low, the pyrolysis layer 34 is formed in the manufacturing process of the semiconductor device using the first semiconductor layer (GaN layer) 32 and the second semiconductor layer (AlGaN layer) 33. If the step of raising the temperature of the sapphire substrate 31 is performed as it is, the following problems will occur. That is, contamination due to evaporation or diffusion of Ga in the pyrolysis layer 34 or oxidation of the Ga causes unevenness in the thickness of the pyrolysis layer 34, or the surface shape of the AlGaN layer 33 becomes non-uniform. As a result, in-plane performance variation also occurs in the finally fabricated semiconductor device.

  Therefore, in this embodiment, the sapphire substrate 31 having the thermal decomposition layer 34 formed by laser light irradiation is immersed in hydrochloric acid, for example, to remove the thermal decomposition layer 34 as shown in FIG. . Here, regarding the pyrolysis layer 34 having a concentric pattern corresponding to the light irradiation part 35 shown in FIG. 3C, the sapphire substrate 31 is simply immersed in hydrochloric acid so that the inner side of the pyrolysis layer 34 can be obtained. As a result of the fact that hydrochloric acid is not supplied up to the annular zone, the inner annular zone is not removed by etching. Therefore, in the present embodiment, on the back surface of the sapphire substrate 31, a light irradiation unit 36 that connects the annular portions of the light irradiation unit 35 together with the light irradiation unit 35 having a concentric pattern is provided. As a result, the pyrolysis layer 34 is also formed in the portion of the GaN layer 32 corresponding to the light irradiation portion 36, so that the portion exposed to the end of the GaN layer 32 in the pyrolysis layer 34 (the outermost annular zone) The thermal decomposition layer 34 is sequentially removed from the portion) toward the center of the substrate. As a result, hydrochloric acid is also supplied to the inner annular zone in the pyrolysis layer 34, so that all the pyrolysis layer 34 is etched away by hydrochloric acid.

  Also in this embodiment, the GaN layer 32 after the removal of the pyrolysis layer 34 is not irradiated with a laser beam (a concentric circle that is a region where the pyrolysis layer 34 is not formed) as shown in FIG. The state of being coupled to the sapphire substrate 31 at the shape portion) is maintained.

  Thereafter, although not shown, the semiconductor device is obtained by performing the same steps as those in the first or second embodiment shown in FIGS. 1 (e) to (g) or FIGS. 2 (e) to (g). Can be completed.

  As described above, according to the third embodiment, the back surface of the sapphire substrate 31 (opposite of the main surface on which the GaN layer 32 is formed) with respect to the GaN layer 32 formed on the main surface of the sapphire substrate 31. Since the thermal decomposition layer 34 is formed by irradiating light from the surface), the residual distortion in the main surface of the substrate can be relaxed by the elasticity of the thermal decomposition layer 34, and thus problems such as warpage of the sapphire substrate 31 occur. Can be prevented. That is, it is possible to alleviate the strain generated concentrically on the main surface of the substrate by the method of light irradiation (laser light irradiation) described in the present embodiment.

  Further, according to the third embodiment, since the GaN layer 32 is partially thermally decomposed to form the thermally decomposed layer 34, in other words, the back surface of the substrate is partially irradiated with light to thermally decompose the layer 34. Therefore, the thermal decomposition layer 34 is not formed on the portion of the GaN layer 32 (more precisely, the contact region with the sapphire substrate 31 in the GaN layer 32) that is not irradiated with light. That is, even after removal of the pyrolysis layer 34, the direct bonding between the non-formation region of the pyrolysis layer 34 in the GaN layer 32 and the sapphire substrate 31 is maintained. The completely fixed state of the layer 32 can be maintained, thereby preventing the misalignment of the GaN layer 32. Thereby, it is possible to improve accuracy in a later lithography process or the like.

  In addition, according to the third embodiment, in order to remove the pyrolysis layer 34 itself, even if the step of heating the sapphire substrate 31 to a temperature equal to or higher than the melting point of the pyrolysis layer 34 is performed, contamination caused by heat treatment, Alteration or deformation can be prevented. That is, the step of raising the temperature of the sapphire substrate 31 above the melting point of the thermal decomposition layer 34 can be performed while preventing contamination, alteration, or deformation due to heat treatment.

  In the third embodiment, the type of light irradiated from the back side of the substrate is not particularly limited as long as it is light that can thermally decompose the first semiconductor layer 32.

  In the third embodiment, a GaN layer is used as the first semiconductor layer 32. However, the present invention is not limited to this. By using a group III nitride layer, the pyrolysis layer 34 can be reliably formed. Can do. However, it goes without saying that a semiconductor layer other than the group III nitride layer, such as a GaAs layer or a Si layer, may be used.

  In the third embodiment, the sapphire substrate 31 is used. However, instead of this, a SiC substrate or a glass substrate may be used.

  In the third embodiment, hydrochloric acid is used for removing the thermal decomposition layer 34 by etching, but other acidic solutions may be used instead. Moreover, you may remove the thermal decomposition layer 34 by methods other than the etching using an acidic solution.

(Fourth embodiment)
Hereinafter, a method for fabricating a semiconductor device according to the fourth embodiment of the present invention will be described with reference to the drawings.

  FIGS. 4A, 4C, and 4D are cross-sectional views showing respective steps of the semiconductor device manufacturing method according to the fourth embodiment, and FIG. 4B shows the fourth embodiment. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns.

First, as shown in FIG. 4A, on the main surface of a sapphire substrate 41 having a thickness of about 400 μm with the C surface as the main surface, for example, a thickness of about 2 to 3 μm made of GaN, for example, by the MOVPE method. The first semiconductor layer 42 is formed. Thereafter, on the first semiconductor layer 42, for example, a second layer having a thickness of about 25 nm made of a nitride mixed crystal (Al _x Ga _1-x N (where 0 <x <1)) containing aluminum and gallium is used. A semiconductor layer 43 is formed. At this time, there is a residual stress due to lattice mismatch between the sapphire substrate 41 and the first semiconductor layer 42 and a residual strain associated therewith. As a result, as shown in FIG. Is warped.

Subsequently, from the back surface (opposite surface of the main surface) of the sapphire substrate 41 in which the semiconductor layers 42 and 43 are stacked on the main surface, for example, the third harmonic of an Nd: YAG laser is applied, for example, with an irradiation energy of 0. Irradiation is performed under irradiation conditions of 3 J / cm ² , a pulse width of 5 ns, and a beam diameter of 1.00 μm. Specifically, in this embodiment, as shown in FIG. 4B, a light irradiation unit 41a having a radial pattern on the back surface of the sapphire substrate 41 is set. Since the sapphire substrate 41 is transparent to the laser light, the laser light irradiated from the back side of the sapphire substrate 41 is absorbed in the vicinity of the interface with the sapphire substrate 41 in the first semiconductor layer (GaN layer) 42. Only the GaN layer 42 in the vicinity of the interface is thermally decomposed. As a result, as shown in FIG. 4C, in the vicinity of the interface with the sapphire substrate 41 in the portion corresponding to the light irradiation portion 41a in the GaN layer 42 (portion existing radially on the substrate main surface), Ga A thin pyrolysis layer 44 containing as a main component is formed. Thus, by forming the pyrolysis layer 44 in a symmetric shape with respect to the center of the substrate on the main surface of the sapphire substrate 41, the residual stress of the sapphire substrate 41 existing before the light irradiation is reduced over the entire surface of the substrate. In the meantime, it is relaxed almost symmetrically and uniformly with respect to the center of the substrate. FIG. 4C is a cross-sectional view taken along line IV-IV in FIG.

  By the way, since the melting point of the pyrolysis layer 44 is generally low, the pyrolysis layer 44 is formed in the manufacturing process of the semiconductor device using the first semiconductor layer (GaN layer) 42 and the second semiconductor layer (AlGaN layer) 43. If the process of raising the temperature of the sapphire substrate 41 is performed as it is, the following problem occurs. That is, due to contamination caused by evaporation or diffusion of Ga in the pyrolysis layer 44 or oxidation of the Ga, the pyrolysis layer 44 is uneven in thickness, or the surface shape of the AlGaN layer 43 is not uniform. As a result, in-plane performance variation also occurs in the finally fabricated semiconductor device.

  Therefore, in this embodiment, the sapphire substrate 41 having the thermal decomposition layer 44 formed by laser light irradiation is immersed in, for example, hydrochloric acid, thereby removing the thermal decomposition layer 44 as shown in FIG. . At this time, the pyrolysis layer 44 is sequentially removed from the portion of the pyrolysis layer 44 exposed at the end of the GaN layer 42 toward the center of the substrate. As a result, hydrochloric acid is also supplied to the portion of the thermal decomposition layer 44 formed near the center of the substrate, so that all the thermal decomposition layer 44 is etched away by hydrochloric acid.

  In the present embodiment as well, the GaN layer 42 after the removal of the pyrolysis layer 44 has a non-irradiated portion of the laser light (radial area that is a non-formation region of the pyrolysis layer 44), as shown in FIG. The state of being coupled to the sapphire substrate 41 is maintained at (part).

  Thereafter, although not shown, the semiconductor device is obtained by performing the same steps as those in the first or second embodiment shown in FIGS. 1 (e) to (g) or FIGS. 2 (e) to (g). Can be completed.

  As described above, according to the fourth embodiment, the back surface of the sapphire substrate 41 (opposite of the main surface on which the GaN layer 42 is formed) with respect to the GaN layer 42 formed on the main surface of the sapphire substrate 41. Since the thermal decomposition layer 44 is formed by irradiating light from the surface), the residual distortion in the main surface of the substrate can be relaxed by the elasticity of the thermal decomposition layer 44, and thus problems such as warping of the sapphire substrate 41 occur. Can be prevented. That is, the strain existing on the main surface of the substrate can be relaxed symmetrically and uniformly with respect to the center of the substrate by the method of light irradiation (laser light irradiation) described in the present embodiment.

  According to the fourth embodiment, the GaN layer 42 is partially pyrolyzed to form the pyrolysis layer 44. In other words, the rear surface of the substrate is partially irradiated with light to thermally decompose the layer 44. Therefore, the thermal decomposition layer 44 is not formed in a portion of the GaN layer 42 (exactly, the contact region with the sapphire substrate 41 in the GaN layer 42) that is not irradiated with light. That is, even after removal of the pyrolysis layer 44, direct bonding between the non-formation region of the pyrolysis layer 44 in the GaN layer 42 and the sapphire substrate 41 is maintained, so that the GaN with respect to the sapphire substrate 41 which is the base material substrate is maintained. The completely fixed state of the layer 42 can be maintained, thereby preventing the misalignment of the GaN layer 42. Thereby, it is possible to improve accuracy in a later lithography process or the like.

  In addition, according to the fourth embodiment, in order to remove the pyrolysis layer 44 itself, even if a step of heating the sapphire substrate 41 to a temperature equal to or higher than the melting point of the pyrolysis layer 44 is performed, contamination caused by heat treatment, Alteration or deformation can be prevented. That is, the step of raising the temperature of the sapphire substrate 41 above the melting point of the thermal decomposition layer 44 can be performed while preventing contamination, alteration or deformation due to heat treatment.

  In the fourth embodiment, the type of light irradiated from the back side of the substrate is not particularly limited as long as it is light that can thermally decompose the first semiconductor layer 42.

  In the fourth embodiment, the GaN layer is used as the first semiconductor layer 42. However, the present invention is not limited to this, and the formation of the thermal decomposition layer 44 is ensured by using a group III nitride layer. Can do. However, it goes without saying that a semiconductor layer other than the group III nitride layer, such as a GaAs layer or a Si layer, may be used.

  In the fourth embodiment, the sapphire substrate 41 is used. However, instead of this, a SiC substrate or a glass substrate may be used.

  In the fourth embodiment, hydrochloric acid is used for removing the thermal decomposition layer 44 by etching, but other acidic solutions may be used instead. Further, the thermal decomposition layer 44 may be removed by a method other than etching using an acidic solution.

(Fifth embodiment)
A semiconductor device manufacturing method according to the fifth embodiment of the present invention will be described below with reference to the drawings.

  FIGS. 5A, 5C, and 5D are cross-sectional views showing the respective steps of the semiconductor device manufacturing method according to the fifth embodiment, and FIG. 5B shows the fifth embodiment. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns.

First, as shown in FIG. 5A, for example, on the main surface of a sapphire substrate 51 having a thickness of about 400 μm with the C surface as the main surface, a thickness of about 2 to 3 μm made of GaN, for example, by the MOVPE method. The first semiconductor layer 52 is formed. Thereafter, on the first semiconductor layer 52, for example, a second layer having a thickness of about 25 nm made of a nitride mixed crystal (Al _x Ga _1-x N (where 0 <x <1)) containing aluminum and gallium is used. A semiconductor layer 53 is formed. At this time, there is a residual stress due to lattice mismatch between the sapphire substrate 51 and the first semiconductor layer 52 and a residual strain associated therewith. As a result, as shown in FIG. Is warped.

Subsequently, from the back surface (opposite surface of the main surface) side of the sapphire substrate 51 in which the semiconductor layers 52 and 53 are stacked on the main surface, for example, a third harmonic of an Nd: YAG laser is applied, for example, with an irradiation energy of 0. Irradiation is performed under irradiation conditions of 3 J / cm ² , a pulse width of 5 ns, and a beam diameter of 1.00 μm. Specifically, in the present embodiment, as shown in FIG. 5B, a light irradiation unit 51 a having a spiral pattern is set on the back surface of the sapphire substrate 51. Since the sapphire substrate 51 is transparent to the laser light, the laser light irradiated from the back side of the sapphire substrate 51 is absorbed near the interface with the sapphire substrate 51 in the first semiconductor layer (GaN layer) 52. Only the GaN layer 52 in the vicinity of the interface is thermally decomposed. As a result, as shown in FIG. 5C, in the vicinity of the interface with the sapphire substrate 51 in the portion corresponding to the light irradiation portion 51a in the GaN layer 52 (portion that exists in a spiral shape on the substrate main surface), A thin pyrolysis layer 54 mainly composed of Ga is formed. As described above, by forming the pyrolysis layer 54 on the main surface of the sapphire substrate 51 in a symmetric shape with respect to the center of the substrate, the residual stress of the sapphire substrate 51 existing before the light irradiation is reduced over the entire surface of the substrate. Are alleviated evenly.

  By the way, since the melting point of the pyrolysis layer 54 is generally low, the pyrolysis layer 54 is formed in the manufacturing process of the semiconductor device using the first semiconductor layer (GaN layer) 52 and the second semiconductor layer (AlGaN layer) 53. If the step of raising the temperature of the sapphire substrate 51 is carried out as it is, the following problem occurs. That is, contamination due to evaporation or diffusion of Ga in the pyrolysis layer 54 or oxidation of the Ga causes unevenness in the thickness of the pyrolysis layer 54, or the surface shape of the AlGaN layer 53 becomes nonuniform. As a result, in-plane performance variation also occurs in the finally fabricated semiconductor device.

  Therefore, in this embodiment, the sapphire substrate 51 having the thermal decomposition layer 54 formed by laser light irradiation is immersed in hydrochloric acid, for example, to remove the thermal decomposition layer 54 as shown in FIG. . At this time, the pyrolysis layer 54 is sequentially removed from the portion of the pyrolysis layer 54 exposed at the end of the GaN layer 52 toward the center of the substrate. As a result, hydrochloric acid is also supplied to the portion of the thermal decomposition layer 54 formed near the center of the substrate, so that all the thermal decomposition layer 54 is removed by etching with hydrochloric acid.

  Also in the present embodiment, the GaN layer 52 after the removal of the pyrolysis layer 54 is an unirradiated portion of the laser beam (a non-formation region of the pyrolysis layer 54, as shown in FIG. 5D). The state of being coupled to the sapphire substrate 51 at the spiral portion) is maintained.

  Thereafter, although not shown, the semiconductor device is obtained by performing the same steps as those in the first or second embodiment shown in FIGS. 1 (e) to (g) or FIGS. 2 (e) to (g). Can be completed.

  As described above, according to the fifth embodiment, the back surface of the sapphire substrate 51 (opposite of the main surface on which the GaN layer 52 is formed) with respect to the GaN layer 52 formed on the main surface of the sapphire substrate 51. Since the thermal decomposition layer 54 is formed by irradiating light from the front surface), the residual strain in the main surface of the substrate can be relaxed by the elasticity of the thermal decomposition layer 54, and thus problems such as warpage of the sapphire substrate 51 occur. Can be prevented. That is, the residual stress existing in the main surface of the substrate can be relaxed substantially symmetrically and substantially uniformly with respect to the center of the substrate by the method of light irradiation (laser light irradiation) described in the present embodiment.

  Further, according to the fifth embodiment, the GaN layer 52 is partially thermally decomposed to form the thermally decomposed layer 54. In other words, the rear surface of the substrate is partially irradiated with light to thermally decompose the layer 54. Therefore, the pyrolysis layer 54 is not formed in the portion of the GaN layer 52 (exactly the contact area with the sapphire substrate 51 in the GaN layer 52) that is not irradiated with light. That is, even after the pyrolysis layer 54 is removed, the direct bonding between the non-formation region of the pyrolysis layer 54 in the GaN layer 52 and the sapphire substrate 51 is maintained. The completely fixed state of the layer 52 can be maintained, and thereby the misalignment of the GaN layer 52 can be prevented. Thereby, it is possible to improve accuracy in a later lithography process or the like.

  In addition, according to the fifth embodiment, in order to remove the pyrolysis layer 54 itself, even if a step of heating the sapphire substrate 51 to a temperature equal to or higher than the melting point of the pyrolysis layer 54 is performed, contamination caused by heat treatment, Alteration or deformation can be prevented. That is, the process of raising the temperature of the sapphire substrate 51 to a temperature equal to or higher than the melting point of the thermal decomposition layer 54 can be performed while preventing contamination, alteration, or deformation due to heat treatment.

  In the fifth embodiment, the type of light irradiated from the back side of the substrate is not particularly limited as long as it is light that can thermally decompose the first semiconductor layer 52.

  In the fifth embodiment, the GaN layer is used as the first semiconductor layer 52. However, the present invention is not limited to this, and the formation of the thermal decomposition layer 54 is ensured by using a group III nitride layer. Can do. However, it goes without saying that a semiconductor layer other than the group III nitride layer, such as a GaAs layer or a Si layer, may be used.

  In the fifth embodiment, the sapphire substrate 51 is used. However, instead of this, a SiC substrate or a glass substrate may be used.

  Further, in the fifth embodiment, hydrochloric acid is used for etching removal of the thermal decomposition layer 54, but another acidic solution may be used instead. Further, the thermal decomposition layer 54 may be removed by a method other than etching using an acidic solution.

(Sixth embodiment)
A semiconductor device manufacturing method according to the sixth embodiment of the present invention will be described below with reference to the drawings.

  FIGS. 6A and 6C to 6E are cross-sectional views showing respective steps of the semiconductor device manufacturing method according to the sixth embodiment, and FIG. 6B shows the sixth embodiment. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns on a form.

First, as shown in FIG. 6A, for example, on the main surface of a sapphire substrate 61 having a thickness of about 400 μm with the C surface as the main surface, a thickness of about 2 to 3 μm made of GaN, for example, by the MOVPE method. The first semiconductor layer 62 is formed. Thereafter, on the first semiconductor layer 62, for example, a second layer having a thickness of about 25 nm made of a nitride mixed crystal containing aluminum and gallium (Al _x Ga _1-x N (where 0 <x <1)) is formed. A semiconductor layer 63 is formed. At this time, there is a residual stress due to lattice mismatch between the sapphire substrate 61 and the first semiconductor layer 62 and a residual strain associated therewith, and as a result, as shown in FIG. Is warped.

Subsequently, from the back surface (opposite surface of the main surface) of the sapphire substrate 61 in which the semiconductor layers 62 and 63 are stacked on the main surface, for example, the third harmonic of an Nd: YAG laser is applied, for example, with an irradiation energy of 0. Irradiation is performed under irradiation conditions of 3 J / cm ² , a pulse width of 5 ns, and a beam diameter of 1.00 μm. Specifically, in the present embodiment, as shown in FIG. 6B, a dividing line for taking out chips from the sapphire substrate 61 on the back surface of the sapphire substrate 61 (refer to the alternate long and short dash line in FIG. 6D). The light irradiation part 65 with the pattern along is set. That is, in the present embodiment, a region partitioned by the light irradiation unit 65 (that is, a light non-irradiation unit) becomes the chip formation region 66. Since the sapphire substrate 61 is transparent to the laser light, the laser light irradiated from the back side of the sapphire substrate 61 is absorbed near the interface with the sapphire substrate 61 in the first semiconductor layer (GaN layer) 62. Only the GaN layer 62 in the vicinity of the interface is thermally decomposed. As a result, as shown in FIG. 6C, the vicinity of the interface with the sapphire substrate 61 in the portion corresponding to the light irradiation portion 65 of the GaN layer 62 (the portion existing along the dividing line on the substrate main surface). In addition, a thin pyrolysis layer 64 containing Ga as a main component is formed. That is, the linear pyrolysis layer 64 is formed along the dividing line of the sapphire substrate 61. Note that the thermal decomposition layer 64 of the present embodiment is formed over the entire surface of the wafer in a sufficiently small size compared to the overall size of the substrate (wafer), so that it remains in the wafer surface that existed before the light irradiation. The stress is alleviated uniformly in the plane.

  By the way, since the melting point of the pyrolysis layer 64 is generally low, the pyrolysis layer 64 is formed in the manufacturing process of the semiconductor device using the first semiconductor layer (GaN layer) 62 and the second semiconductor layer (AlGaN layer) 63. If the step of raising the temperature of the sapphire substrate 61 is performed as it is, the following problem occurs. That is, contamination due to evaporation or diffusion of Ga in the pyrolysis layer 64 or oxidation of the Ga causes unevenness in the thickness of the pyrolysis layer 64, or the surface shape of the AlGaN layer 63 becomes non-uniform. As a result, in-plane performance variation also occurs in the finally fabricated semiconductor device.

  Therefore, in this embodiment, the sapphire substrate 61 having the thermal decomposition layer 64 formed by laser light irradiation is immersed in, for example, hydrochloric acid, thereby removing the thermal decomposition layer 64 as shown in FIG. . At this time, the pyrolysis layer 64 is sequentially removed from the portion of the pyrolysis layer 64 exposed at the end of the GaN layer 62 toward the center of the substrate. As a result, hydrochloric acid is also supplied to the portion of the thermal decomposition layer 64 formed near the center of the substrate, so that all of the thermal decomposition layer 64 is removed by etching with hydrochloric acid.

  Also in this embodiment, the GaN layer 62 after the removal of the pyrolysis layer 64 is made of sapphire in the unirradiated portion of the laser beam (the non-formation region of the pyrolysis layer 64) as shown in FIG. The state of being coupled with the substrate 61 is maintained.

  Thereafter, although not shown in the drawings, each chip is obtained by performing the same steps as those in the first or second embodiment shown in FIG. 1 (e) to (g) or FIG. 2 (e) to (g). A semiconductor element using the GaN layer 62 and the AlGaN layer 63 as active layers is formed in the formation region 66 (see FIG. 6B).

  Subsequently, after manufacturing the semiconductor device shown in FIG. 6D, dicing is performed on the sapphire substrate 61 along the dividing line of the sapphire substrate 61 as shown in FIG. That is, the sapphire substrate 61 is divided along the region where the thermal decomposition layer 64 formed in a line shape is removed. At this time, the GaN layer 62 (hereinafter referred to as the upper GaN layer 62) and the AlGaN layer 63 on the upper side of the region from which the thermal decomposition layer 64 has been removed are very thin and can be easily cut. Further, the sapphire substrate 61 can be cut and individual semiconductor elements can be taken out without causing any damage to the GaN layer 62 and the AlGaN layer 63 in the chip formation region 66.

  As described above, according to the sixth embodiment, the back surface of the sapphire substrate 61 (opposite of the main surface on which the GaN layer 62 is formed) with respect to the GaN layer 62 formed on the main surface of the sapphire substrate 61. Since the thermal decomposition layer 64 is formed by irradiating light from the surface), the residual strain in the main surface of the substrate can be relaxed by the elasticity of the thermal decomposition layer 64, and thus problems such as warpage of the sapphire substrate 61 occur. Can be prevented.

  Further, according to the sixth embodiment, the GaN layer 62 is partially thermally decomposed to form the thermally decomposed layer 64. In other words, the back surface of the substrate is partially irradiated with light to thermally decompose the layer 64. Therefore, the pyrolysis layer 64 is not formed in the portion of the GaN layer 62 (exactly the contact region with the sapphire substrate 61 in the GaN layer 62) that is not irradiated with light. That is, even after the pyrolysis layer 64 is removed, the direct bonding between the non-formation region of the pyrolysis layer 64 in the GaN layer 62 and the sapphire substrate 61 is maintained. The completely fixed state of the layer 62 can be maintained, and thereby the misalignment of the GaN layer 62 can be prevented. Thereby, it is possible to improve accuracy in a lithography process or the like for forming a semiconductor element later.

  Further, according to the sixth embodiment, in order to remove the pyrolysis layer 64 itself, even if a step of heating the sapphire substrate 61 to a temperature equal to or higher than the melting point of the pyrolysis layer 64 is performed, contamination caused by heat treatment, Alteration or deformation can be prevented. That is, the step of raising the temperature of the sapphire substrate 61 above the melting point of the thermal decomposition layer 64 can be performed while preventing contamination, alteration, or deformation due to heat treatment.

  Further, according to the sixth embodiment, the pyrolysis layer 64 is formed in a line by irradiating the GaN layer 62 with light along the dividing line of the sapphire substrate 61, and then the pyrolysis layer 64 is removed. Thereafter, the sapphire substrate 61 is divided along the dividing line, that is, along the line-shaped region from which the thermal decomposition layer 64 is removed. Thereby, the plurality of semiconductor elements formed on the sapphire substrate 61 are separated into pieces. That is, according to the sixth embodiment, each of the semiconductor elements can be formed while relaxing the residual strain in the surface of the sapphire substrate 61 by using the thermal decomposition layer 64, and the linear shape from which the thermal decomposition layer 64 has been removed. By dicing the sapphire substrate 61 using the regions as division lines, each semiconductor element can be cut out as a chip without damaging the chip formation region 66 in which each semiconductor element is formed.

  In the sixth embodiment, the type of light irradiated from the back side of the substrate is not particularly limited as long as it is light that can thermally decompose the first semiconductor layer 62.

  In the sixth embodiment, the GaN layer is used as the first semiconductor layer 62. However, the present invention is not limited to this, and the formation of the thermal decomposition layer 64 is ensured by using a group III nitride layer. Can do. However, it goes without saying that a semiconductor layer other than the group III nitride layer, such as a GaAs layer or a Si layer, may be used.

  In the sixth embodiment, the sapphire substrate 61 is used. However, instead of this, a SiC substrate or a glass substrate may be used.

  Further, in the sixth embodiment, hydrochloric acid is used for etching removal of the thermal decomposition layer 64, but other acidic solutions may be used instead. Moreover, you may remove the thermal decomposition layer 64 by methods other than the etching using an acidic solution.

  In the sixth embodiment, the thickness of the sapphire substrate 61 may be reduced to about 70 μm before dicing the sapphire substrate 61.

(Seventh embodiment)
Hereinafter, a method for fabricating a semiconductor device according to a seventh embodiment of the present invention will be described with reference to the drawings.

  FIG. 7A and FIGS. 7C to 7E are cross-sectional views showing respective steps of the semiconductor device manufacturing method according to the seventh embodiment, and FIG. 7B shows the seventh embodiment. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns on a form.

First, as shown in FIG. 7A, on the main surface of a sapphire substrate 71 having a thickness of about 400 μm with the C surface as the main surface, for example, a thickness of about 2 to 3 μm made of GaN, for example, by the MOVPE method. The first semiconductor layer 72 is formed. Thereafter, on the first semiconductor layer 72, for example, a second layer having a thickness of about 25 nm made of a nitride mixed crystal (Al _x Ga _1-x N (where 0 <x <1)) containing aluminum and gallium is used. A semiconductor layer 73 is formed. At this time, there is a residual stress caused by lattice mismatch between the sapphire substrate 71 and the first semiconductor layer 72 and a residual strain associated therewith. As a result, as shown in FIG. Is warped.

Subsequently, from the back surface (opposite surface of the main surface) of the sapphire substrate 71 on which the semiconductor layers 72 and 73 are laminated on the main surface, for example, a third harmonic of an Nd: YAG laser is applied, for example, with an irradiation energy of 0. Irradiation is performed under irradiation conditions of 3 J / cm ² , a pulse width of 5 ns, and a beam diameter of 1.00 μm. Specifically, in the present embodiment, as shown in FIG. 7B, the light irradiation unit 76 having a pattern corresponding to the chip formation region is set on the back surface of the sapphire substrate 71. In other words, in this embodiment, the region (that is, the light non-irradiation unit) 75 that partitions the light irradiation unit 76 is a dividing line for taking out the chip from the sapphire substrate 71 (see the one-dot chain line in FIG. 7D). Exist along. Since the sapphire substrate 71 is transparent to the laser light, the laser light irradiated from the back side of the sapphire substrate 71 is absorbed in the vicinity of the interface with the sapphire substrate 71 in the first semiconductor layer (GaN layer) 72. Only the GaN layer 72 in the vicinity of the interface is thermally decomposed. As a result, as shown in FIG. 7C, in the vicinity of the interface with the sapphire substrate 71 in the portion corresponding to the light irradiation portion 76 of the GaN layer 72 (portion existing in the chip formation region on the substrate main surface). A thin pyrolysis layer 74 containing Ga as a main component is formed. That is, the pyrolysis layer 74 is formed so as to be surrounded by the dividing lines of the sapphire substrate 71. Note that the thermal decomposition layer 74 of the present embodiment is formed over the entire surface of the wafer in a sufficiently small size compared to the size of the entire substrate (wafer), so that the residual in the wafer surface that existed before the light irradiation was present. The stress is alleviated uniformly in the plane.

  By the way, since the melting point of the pyrolysis layer 74 is generally low, the pyrolysis layer 74 is formed in the manufacturing process of the semiconductor device using the first semiconductor layer (GaN layer) 72 and the second semiconductor layer (AlGaN layer) 73. If the process of raising the temperature of the sapphire substrate 71 is performed as it is, the following problem occurs. That is, contamination due to evaporation or diffusion of Ga in the pyrolysis layer 74 or oxidation of the Ga causes unevenness in the thickness of the pyrolysis layer 74, or the surface shape of the AlGaN layer 73 becomes non-uniform. As a result, in-plane performance variation also occurs in the finally fabricated semiconductor device.

  Therefore, in this embodiment, the sapphire substrate 71 having the thermal decomposition layer 74 formed by laser light irradiation is immersed in hydrochloric acid, for example, to remove the thermal decomposition layer 74 as shown in FIG. . At this time, in order to remove the pyrolysis layer 74 sequentially from the portion of the pyrolysis layer 74 exposed at the end of the GaN layer 72 toward the center of the substrate, the pyrolysis layer 74 shown in FIG. It is preferable to provide a bridge pattern that connects the thermal decomposition layers 74 corresponding to the chip formation regions and serves as the thermal decomposition layer. That is, it is preferable to previously provide a bridge pattern that connects the light irradiation portions 76 corresponding to each chip formation region and serves as the light irradiation portion when setting the light irradiation portions 76 shown in FIG. In this way, hydrochloric acid is also supplied to the portion of the thermal decomposition layer 74 formed near the center of the substrate, so that all the thermal decomposition layer 74 is removed by etching with hydrochloric acid.

  In the present embodiment as well, the GaN layer 72 after the removal of the pyrolysis layer 74 is made of sapphire in an unirradiated portion of the laser beam (a region where the pyrolysis layer 74 is not formed) as shown in FIG. The state of being coupled with the substrate 71 is maintained.

  Thereafter, although not shown in the drawings, each chip is obtained by performing the same steps as those in the first or second embodiment shown in FIG. 1 (e) to (g) or FIG. 2 (e) to (g). A semiconductor element using the GaN layer 72 and the AlGaN layer 73 as active layers is formed in the formation region (the region corresponding to the light irradiation unit 76 in FIG. 6B).

  Subsequently, after manufacturing the semiconductor device shown in FIG. 7D, dicing is performed on the sapphire substrate 71 along the dividing line of the sapphire substrate 71 as shown in FIG. That is, the sapphire substrate 71 is divided along a line-shaped light non-irradiation part 75 (see FIG. 7B) corresponding to the division line. In this way, each semiconductor element having the GaN layer 72 (hereinafter referred to as the upper GaN layer 72) on the upper side of the region where the thermal decomposition layer 74 has been removed and the AlGaN layer 73 as the active layer is attached to another substrate. It can be cut out from the sapphire substrate 71 in a thin film state that can be matched.

  As described above, according to the seventh embodiment, the back surface of the sapphire substrate 71 (opposite of the main surface on which the GaN layer 72 is formed) with respect to the GaN layer 72 formed on the main surface of the sapphire substrate 71. Since the thermal decomposition layer 74 is formed by irradiating light from the surface), the residual distortion in the main surface of the substrate can be relaxed by the elasticity of the thermal decomposition layer 74, and thus problems such as warpage of the sapphire substrate 71 occur. Can be prevented.

  According to the seventh embodiment, the GaN layer 72 is partially thermally decomposed to form the thermally decomposed layer 74. In other words, the rear surface of the substrate is partially irradiated with light to thermally decompose the layer 74. Therefore, the pyrolysis layer 74 is not formed in the portion of the GaN layer 72 (exactly, the contact region with the sapphire substrate 71 in the GaN layer 72) that is not irradiated with light. That is, even after removal of the pyrolysis layer 74, the direct bonding between the non-formation region of the pyrolysis layer 74 in the GaN layer 72 and the sapphire substrate 71 is maintained. The completely fixed state of the layer 72 can be maintained, and thereby the misalignment of the GaN layer 72 can be prevented. Thereby, it is possible to improve accuracy in a lithography process or the like for forming a semiconductor element later.

  In addition, according to the seventh embodiment, in order to remove the pyrolysis layer 74 itself, even if the step of heating the sapphire substrate 71 to a temperature equal to or higher than the melting point of the pyrolysis layer 74 is performed, contamination caused by heat treatment, Alteration or deformation can be prevented. That is, the step of raising the temperature of the sapphire substrate 71 above the melting point of the thermal decomposition layer 74 can be performed while preventing contamination, alteration or deformation due to heat treatment.

  In addition, according to the seventh embodiment, the pyrolysis layer 74 is formed by irradiating the GaN layer 72 with light so that the light non-irradiation portions 75 exist in a line along the dividing lines of the sapphire substrate 71. Thereafter, the thermal decomposition layer 74 is removed, and then the sapphire substrate 71 is divided along the dividing lines, that is, along the light non-irradiation portions 75 existing in a line shape. Thereby, a some semiconductor element can be isolate | separated from the sapphire substrate 71, and each semiconductor element can be separated into pieces. That is, according to the seventh embodiment, each of the semiconductor elements can be formed while relaxing the residual strain in the surface of the sapphire substrate 71 using the thermal decomposition layer 74, and each semiconductor element can be transferred from the sapphire substrate 71 substrate to the other. It can be cut out in a thin film state that can be bonded to the substrate.

  In the seventh embodiment, the type of light irradiated from the back side of the substrate is not particularly limited as long as it is light that can thermally decompose the first semiconductor layer 72.

  In the seventh embodiment, the GaN layer is used as the first semiconductor layer 72. However, the present invention is not limited to this, and the formation of the thermal decomposition layer 74 is ensured by using a group III nitride layer. Can do. However, it goes without saying that a semiconductor layer other than the group III nitride layer, such as a GaAs layer or a Si layer, may be used.

  In the seventh embodiment, the sapphire substrate 71 is used. However, instead of this, a SiC substrate or a glass substrate may be used.

  In the seventh embodiment, hydrochloric acid is used for removing the thermal decomposition layer 74 by etching, but other acidic solutions may be used instead. Moreover, you may remove the thermal decomposition layer 74 by methods other than the etching using an acidic solution.

  In the seventh embodiment, the thickness of the sapphire substrate 71 may be reduced to about 70 μm before dicing the sapphire substrate 71.

  The present invention relates to a method for manufacturing a semiconductor device, and, when applied to crystal growth of a semiconductor layer on a wafer, prevents misalignment of the semiconductor layer in the semiconductor device manufacturing process and contamination, alteration or deformation in a heat treatment step. The effect that the residual stress or the residual strain can be uniformly relieved in the wafer surface where the semiconductor layer is crystal-grown is obtained and useful.

1A and 1C to 1G are cross-sectional views showing respective steps of the method for manufacturing a semiconductor device according to the first embodiment of the present invention, and FIG. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns on the 1st Embodiment of invention. 2 (a) and 2 (c) to 2 (g) are cross-sectional views showing respective steps of the method of manufacturing a semiconductor device according to the second embodiment of the present invention, and FIG. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns on the 2nd Embodiment of invention. 3A, 3C, and 3D are cross-sectional views showing respective steps of a method of manufacturing a semiconductor device according to the third embodiment of the present invention, and FIG. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns on 3rd Embodiment. 4A, 4C, and 4D are cross-sectional views showing respective steps of a method for manufacturing a semiconductor device according to the fourth embodiment of the present invention, and FIG. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns on 4th Embodiment. FIGS. 5A, 5C, and 5D are cross-sectional views showing respective steps of a semiconductor device manufacturing method according to the fifth embodiment of the present invention, and FIG. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns on 5th Embodiment. 6 (a) and 6 (c) to 6 (e) are cross-sectional views showing the respective steps of the method of manufacturing a semiconductor device according to the sixth embodiment of the present invention, and FIG. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns on the 6th Embodiment of invention. FIGS. 7A and 7C to 7E are cross-sectional views showing respective steps of the method for manufacturing a semiconductor device according to the seventh embodiment of the present invention, and FIG. It is a top view which shows 1 process of the manufacturing method of the semiconductor device which concerns on the 7th Embodiment of invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Sapphire substrate 11a Light irradiation part 12 1st semiconductor layer 13 2nd semiconductor layer 14 Pyrolysis layer 15 Mask 16 Element isolation layer 17 Source / drain electrode 18 Gate electrode 19 Passivation film 21 Sapphire substrate 21a Light irradiation part 22 1st Semiconductor layer 23 Second semiconductor layer 24 Thermal decomposition layer 25 Mask 26 Element isolation layer 27 Source / drain electrode 28 Gate electrode 29 Passivation film 31 Sapphire substrate 32 First semiconductor layer 33 Second semiconductor layer 34 Thermal decomposition layer 35 Light irradiation unit 36 Light irradiation unit 41 Sapphire substrate 41a Light irradiation unit 42 First semiconductor layer 43 Second semiconductor layer 44 Thermal decomposition layer 51 Sapphire substrate 51a Light irradiation unit 52 First semiconductor layer 53 Second semiconductor layer 54 Thermal decomposition layer 61 Sapphire substrate 62 First semiconductor layer 6 3 Second Semiconductor Layer 64 Thermal Decomposition Layer 65 Light Irradiation Unit 66 Chip Formation Area 71 Sapphire Substrate 72 First Semiconductor Layer 73 Second Semiconductor Layer 74 Thermal Decomposition Layer 75 Light Non-irradiation Unit 76 Light Irradiation Unit

Claims (11)

A semiconductor layer formed on one surface of the substrate is irradiated with light from the other surface side of the substrate, thereby partially thermally decomposing a contact region of the semiconductor layer with the substrate to form a pyrolysis layer. And a process of
And a step of removing the thermal decomposition layer while maintaining a state in which the substrate and the semiconductor layer are bonded to each other.   The method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor layer is made of a group III nitride.   2. The semiconductor device according to claim 1, wherein in the step of forming the thermal decomposition layer, the thermal decomposition layer is formed in a shape symmetrical to the center of the one surface on the one surface of the substrate. Manufacturing method.   2. The method of manufacturing a semiconductor device according to claim 1, wherein in the step of forming the thermal decomposition layer, the thermal decomposition layer is formed only on a peripheral portion of the one surface of the substrate.   2. The manufacturing method of a semiconductor device according to claim 1, wherein in the step of forming the thermal decomposition layer, the thermal decomposition layer is formed on a portion other than a central portion on the one surface of the substrate. Method.   2. The method of manufacturing a semiconductor device according to claim 1, wherein, in the step of forming the thermal decomposition layer, the thermal decomposition layer is formed concentrically, radially, or spirally on the one surface of the substrate. . In the step of forming the pyrolysis layer, the pyrolysis layer is formed to have a portion exposed at an end of the semiconductor layer,
2. The method of manufacturing a semiconductor device according to claim 1, wherein, in the step of removing the thermal decomposition layer, the thermal decomposition layer is etched from the exposed portion with an acidic solution.   The semiconductor according to any one of claims 1 to 7, further comprising a step of heating the substrate to a temperature equal to or higher than a melting point of the pyrolysis layer after the step of removing the pyrolysis layer. Device manufacturing method.   9. The method according to claim 1, further comprising a step of forming a plurality of semiconductor elements using the semiconductor layer as an active layer after the step of removing the thermal decomposition layer. The manufacturing method of the semiconductor device of description. A step of dividing the plurality of semiconductor elements into pieces by dividing the substrate after the step of forming the plurality of semiconductor elements;
The step of forming the pyrolysis layer includes the step of forming the pyrolysis layer in a line by irradiating the light to the semiconductor layer along a division line of the substrate,
10. The semiconductor device according to claim 9, wherein the step of dividing the plurality of semiconductor elements includes a step of dividing the substrate along a line-shaped region from which the thermal decomposition layer has been removed. Production method. A step of dividing the plurality of semiconductor elements into pieces by dividing the substrate after the step of forming the plurality of semiconductor elements;
The step of forming the pyrolysis layer includes a step of irradiating the semiconductor layer with the light so that regions where the light is not irradiated along the dividing lines of the substrate exist in a line shape,
10. The semiconductor device according to claim 9, wherein the step of dividing the plurality of semiconductor elements includes a step of dividing the substrate along a region where the light existing in the line shape is not irradiated. Production method.

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