Method for manufacturing structure and structure

Abstract

The manufacturing method of the structure has the following steps: a step of forming a recess by performing a first etching on the surface of a component composed of a group III nitride; and a step of flattening the bottom by performing a second etching on the bottom of the recess. In the step of forming the recess, a flat portion and a convex portion are formed at the bottom of the recess. The convex portion is difficult to be etched by the first etching compared with the flat portion, and thus is raised relative to the flat portion. In the step of flattening the bottom, the convex portion is etched by using the second etching to make the convex portion lower.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a structure and the structure. Background Art

[0002] Group III nitrides such as gallium nitride (GaN) are used as materials for manufacturing semiconductor devices such as light-emitting elements and transistors.

[0003] As an etching technique for forming various structures of group III nitrides such as GaN, photoelectrochemical (PEC) etching has been proposed (see, for example, non-patent document 1). PEC etching is a wet etching method that causes less damage than general dry etching, and is preferred in terms of simplicity of apparatus compared to special dry etching methods such as neutral particle beam etching (see, for example, non-patent document 2) and atomic layer etching (see, for example, non-patent document 3) that causes less damage.

[0004] When a semiconductor device made of a group III nitride is manufactured using PEC etching, the flatness of the bottom of a recessed portion formed by PEC etching affects the characteristics of the semiconductor device.

[0005] Prior art literature

[0006] Non-patent literature

[0007] Non-patent document 1: J.Murata et al., "Photo-electrochemical etching of free-standing GaN wafer surfaces grown by hydride vapor phase epitaxy", Electrochimica Acta 171 (2015) 89-95

[0008] Non-patent document 2: S. Samukawa, JJAP, 45 (2006) 2395.

[0009] Non-patent document 3: T. Faraz, ECS J. Solid Stat. Scie. & Technol., 4, N5023 (2015). Summary of the invention

[0010] Problem that the invention aims to solve

[0011] An object of the present invention is to provide a technique for improving the flatness of the bottom of a recessed portion formed by PEC etching.

[0012] Solutions for solving problems

[0013] According to one embodiment of the present invention, there is provided a method for manufacturing a structure, which comprises the following steps:

[0014] a step of forming a recess by performing a first etching on the surface of the member made of group III nitride; and

[0015] A step of flattening the bottom of the concave portion by performing a second etching on the bottom of the concave portion,

[0016] In the step of forming the concave portion, a flat portion and a convex portion are formed at the bottom of the concave portion, and the convex portion is difficult to be etched by the first etching process compared with the flat portion, and thus rises relative to the flat portion.

[0017] In the step of flattening the bottom portion, the convex portion is etched by the second etching to make the convex portion lower.

[0018] According to another aspect of the present invention, there is provided a structure,

[0019] The device has a member made of a group III nitride and having a recessed portion.

[0020] The maximum height of the position corresponding to the dislocation of the group III nitride constituting the member measured by observing a 1000 nm square area at the bottom of the recess by AFM is 2 nm or less,

[0021] The arithmetic mean roughness (Ra) of the bottom portion measured by observation with the AFM is 0.4 nm or less.

[0022] Effects of the Invention

[0023] Provided is a technique for improving the flatness of the bottom of a recessed portion formed by PEC etching. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 (a) is a schematic cross-sectional view illustrating a HEMT according to one embodiment of the present invention, Figure 1 (b) is a schematic cross-sectional view illustrating a wafer used as a material for HEMT according to one embodiment.

[0025] Figure 2 (a) is a schematic cross-sectional view of a PEC object illustrating an embodiment, Figure 2 (b) is a schematic cross-sectional view of a PEC etching apparatus illustrating a recess forming step.

[0026] Figure 3 (a) is a schematic cross-sectional view of a flattened object illustrating an embodiment, Figure 3(b) is a schematic cross-sectional view of a planarization etching device illustrating a planarization step.

[0027] Figure 4 (a) is a graph showing the relationship between the etching time and the etching depth of PEC etching in the experimental example, Figure 4 (b) is an AFM image of the epitaxial layer surface in the experimental example.

[0028] Figure 5 (a) is an AFM image of the unplanarized bottom in the experimental example. Figure 5 (b) is an AFM image of the flattened bottom in the experimental example.

[0029] Figure 6 (a) is a schematic cross-sectional view of a flattened object illustrating a second modification example, Figure 6 (b) is a schematic cross-sectional view of a planarization etching device illustrating a planarization step.

[0030] Figure 7 It is a schematic cross-sectional view of a planarization etching device according to a third variation.

[0031] Figure 8 It is a schematic cross-sectional view illustrating a PEC object according to another embodiment. DETAILED DESCRIPTION

[0032] <Implementation Method>

[0033] A method for manufacturing the structure 150 according to one embodiment of the present invention will be described. A high electron mobility transistor (HEMT) can be exemplified as the structure 150. Hereinafter, the structure 150 is also referred to as HEMT150.

[0034] First, the structures of the HEMT 150 and the wafer 10 used as a material of the HEMT 150 will be described. Figure 1 (a) is a schematic cross-sectional view illustrating a HEMT 150. Figure 1 (b) is a schematic cross-sectional view illustrating the wafer 10 .

[0035] The wafer 10 includes a substrate 11 and a group III nitride layer 12 (hereinafter also referred to as epitaxial layer 12) formed (epitaxially grown) on the substrate 11. As the substrate 11, for example, a semi-insulating silicon carbide (SiC) substrate can be used. Here, "semi-insulating" means, for example, a resistivity of 10 5 In contrast, for example, a state where the resistivity is less than 10 5The state of Ωcm is called “conductivity.” It should be noted that a substrate having a thick semi-insulating epitaxial layer formed on a conductive substrate (for example, a substrate having a 10 μm thick carbon (C)-doped semi-insulating GaN layer formed on an n-type conductive gallium nitride (GaN) substrate) may be used as the substrate 11.

[0036] When a SiC substrate is used as the substrate 11, the epitaxial layer 12 has a stacked structure of, for example, a nucleation layer 12a made of aluminum nitride (AlN), a thick channel layer 12b made of gallium nitride (GaN), a barrier layer 12c made of aluminum gallium nitride (AlGaN), and a cap layer 12d made of GaN. In the stacking of the channel layer 12b and the barrier layer 12c, a two-dimensional electron gas (2DEG) that becomes a channel of the HEMT 150 is generated near the upper surface of the channel layer 12b.

[0037] The substrate 11 is not limited to a SiC substrate, and other substrates (sapphire substrate, silicon (Si) substrate, (semi-insulating) GaN substrate, etc.) can be used. The stacking structure of the epitaxial layer 12 can be appropriately selected according to the type of substrate 11, the characteristics of the HEMT 150 to be obtained, etc.

[0038] The surface 20 of the epitaxial layer 12 is composed of the c-plane of the group III nitride constituting the epitaxial layer 12. Here, "composed of the c-plane" means that the low-index crystal plane closest to the surface 20 is the c-plane of the group III nitride crystal constituting the epitaxial layer 12. The group III nitride constituting the epitaxial layer 12 has dislocations (threading dislocations), and the dislocations are distributed in the surface 20 at a predetermined density.

[0039] In the HEMT 150 of the present embodiment, the gate electrode 152 is formed on the bottom 120 of the recess (recess) 110 formed on the surface (upper surface) 20 of the epitaxial layer 12. The bottom 120 of the recess 110 is arranged within the thickness range of the barrier layer 12c, and the thickness of the barrier layer 12c below the recess 110 (the thickness from the upper surface of the channel layer 12b to the bottom 12 of the recess 110) can be set to a predetermined thickness so that the threshold gate voltage of the HEMT 150 becomes a predetermined value. The source electrode 151 and the drain electrode 153 are formed on the surface 20 of the epitaxial layer 12. A protective film 154 is formed so as to have openings on the upper surfaces of the source electrode 151, the gate electrode 152, and the drain electrode 153.

[0040] The gate electrode 152 is formed of, for example, a Ni / Au layer in which a gold (Au) layer is stacked on a nickel (Ni) layer. The source electrode 151 and the drain electrode 153 are formed of, for example, a Ti / Al / Au layer in which an Al layer is stacked on a titanium (Ti) layer, and an Au layer is stacked on the Al layer.

[0041] The HEMT 150 has an element isolation trench 160 for isolating adjacent elements. The element isolation trench 160 is provided so that its bottom is located deeper than the upper surface of the channel layer 12 b , that is, the 2DEG between adjacent elements is blocked by the element isolation trench 160 .

[0042] Next, a method for manufacturing the HEMT 150 is described. The method for manufacturing the HEMT 150 according to the present embodiment includes the following steps: a step of forming the recess 110 by first etching the surface 20 of the epitaxial layer 12 (a member made of group III nitride) (hereinafter also referred to as a recess forming step); and a step of flattening the bottom 120 of the recess 110 by second etching (hereinafter also referred to as a flattening step).

[0043] First, the recess forming step is described. In the recess forming step, photoelectrochemical (PEC) etching is performed as the first etching to form the recess 110 in the epitaxial layer 12. Here, the "recess 110" refers to the region in the epitaxial layer 12 (a member composed of group III nitride) where PEC etching is performed. Figure 2 (a) is a schematic cross-sectional view illustrating an object to be subjected to PEC etching treatment, in other words, an object 100 (hereinafter also referred to as PEC object 100) to be immersed in (to be in contact with) the etching solution 201 for PEC etching.

[0044] The PEC object 100 has a structure in which a mask 50 and a cathode pad 30 are provided on the epitaxial layer 12 of the wafer 10. The PEC object 100 of this example is a method in which the cathode pad 30 is used as (at least one of) the source electrode 151 and the drain electrode 153 of the HEMT. Specifically, for example, the PEC object 100 has a structure in which a mask 50 for PEC etching is formed on a member at a stage in which the source electrode 151 and the drain electrode 153 are formed on the surface 20 of the wafer 10.

[0045] The mask 50 is formed on the surface 20 of the epitaxial layer 12, has an opening in the region 21 (hereinafter also referred to as the etched region 21) where the recess 110 is to be formed, and has an opening that exposes the upper surface of the cathode pad 30 (source electrode 151 and drain electrode 153). The mask 50 is formed of a non-conductive material such as a resist, silicon oxide, or the like.

[0046] The cathode pad 30 is a conductive member formed of a conductive material and is provided in contact with at least a portion of the surface of a conductive region of the wafer 10 (epitaxial layer 12 ) that is electrically connected to the etched region 21 .

[0047] Figure 2(b) is a schematic cross-sectional view of a PEC etching apparatus 200 showing a recessed portion forming step (in other words, a PEC etching step). The PEC etching apparatus 200 includes a container 210 storing an etching solution 201 and a light source 220 emitting ultraviolet (UV) light 221 .

[0048] In the recess forming step, the PEC object 100 is immersed in an etching solution 201, and the surface 20 of the epitaxial layer 12 is irradiated with UV light 221 through the etching solution 201 in a state where the etched region 21 and the cathode pad 30 (at least a portion of the cathode pad 30, such as the upper surface) are in contact with the etching solution 201. In this way, the recess 110 is formed by etching the group III nitride constituting the etched region 21.

[0049] Here, the mechanism of PEC etching is described, and the etching solution 201, the cathode pad 30, etc. are described in more detail. As an example of the group III nitride to be etched, GaN is cited for description.

[0050] As the etching solution 201 for PEC etching, an alkaline or acidic etching solution 201 can be used, which contains oxygen for generating an oxide of a group III element contained in the group III nitride constituting the etched area 21 (the bottom 120 after the recess 110 begins to be formed), and also contains an electron-accepting oxidant.

[0051] As the oxidizing agent, there can be exemplified peroxydisulfate ions (S2O8 2- ). The following is an example of supplying S2O8 from potassium persulfate (K2S2O8). 2- But S2O8 2- It can be supplied by other substances, such as sodium peroxodisulfate (Na2S2O8), ammonium peroxodisulfate (ammonium persulfate, (NH4)2S2O8), etc.

[0052] As a first example of the etching solution 201, there can be cited an etching solution obtained by mixing a potassium hydroxide (KOH) aqueous solution with a potassium persulfate (K2S2O8) aqueous solution, which is alkaline at the start of PEC etching. This etching solution 201 is prepared, for example, by mixing a 0.01M KOH aqueous solution with a 0.05M K2S2O8 aqueous solution in a ratio of 1:1. The concentration of the KOH aqueous solution, the concentration of the K2S2O8 aqueous solution, and the mixing ratio of these aqueous solutions can be appropriately adjusted as needed. It should be noted that the etching solution 201 obtained by mixing the KOH aqueous solution and the K2S2O8 aqueous solution can also be made acidic at the start of PEC etching, for example, by reducing the concentration of the KOH aqueous solution.

[0053] The PEC etching mechanism when the etching solution 201 of the first example is used is described. By irradiating the surface 20 to be PEC-etched with UV light 221 having a wavelength of 365 nm or less, holes and electrons are generated in pairs in the GaN constituting the etched area 21. The generated holes decompose the GaN into Ga 3+ and N2 (chemical formula 1), and further, Ga 3+ The hydroxide ion (OH - ) is oxidized, thereby generating gallium oxide (Ga2O3) (chemical formula 2). And the generated Ga2O3 dissolves in alkali (or acid). In this way, PEC etching of GaN is performed. It should be noted that the generated holes react with water, and the water is decomposed, thereby generating oxygen (chemical formula 3).

[0054] [Chemical formula 1]

[0055]

[0056] [Chemical formula 2]

[0057]

[0058] [Chemical formula 3]

[0059]

[0060] In addition, K2S2O8 dissolves in water to generate persulfate ions (S2O8 2- )(chemical formula 4), by S2O8 2- UV light 221 is irradiated to generate sulfate ion radicals (SO4 -* Free radicals) (chemical formula 5). The electrons that are paired with holes are the same as SO4 -* The free radicals react with water, and the water is decomposed, thereby generating hydrogen (chemical formula 6). -* Free radicals can consume electrons that are paired with holes in GaN, so PEC etching can be performed well. It should be noted that as shown in (chemical formula 6), as PEC etching proceeds, sulfate ions (SO4 2- ) will increase, and therefore, the acidity of the etching solution 201 gradually becomes stronger (the pH gradually decreases).

[0061] [Chemical formula 4]

[0062]

[0063] [Chemical formula 5]

[0064]

[0065] [Chemical formula 6]

[0066]

[0067] As a second example of the etching solution 201, an etching solution that is obtained by mixing a phosphoric acid (H3PO4) aqueous solution with a potassium persulfate (K2S2O8) aqueous solution and is acidic at the beginning of PEC etching can be cited. This etching solution 201 is prepared, for example, by mixing a 0.01M H3PO4 aqueous solution with a 0.05M K2S2O8 aqueous solution in a ratio of 1:1. The concentration of the H3PO4 aqueous solution, the concentration of the K2S2O8 aqueous solution, and the mixing ratio of these aqueous solutions can be appropriately adjusted as needed. Both the H3PO4 aqueous solution and the K2S2O8 aqueous solution are acidic, so the etching solution 201 formed by mixing the H3PO4 aqueous solution and the K2S2O8 aqueous solution is acidic at any mixing ratio. It should be noted that since the K2S2O8 aqueous solution itself is acidic, as the etching solution 201 that is acidic at the beginning of etching, only the K2S2O8 aqueous solution can be used. At this time, the concentration of the K2S2O8 aqueous solution, for example, only needs to be set to 0.025M.

[0068] From the viewpoint of making it easy to use the resist as the mask 50, it is preferred that the etching solution 201 is acidic from the moment the PEC etching starts. This is because if the etching solution 201 is alkaline, the resist mask is easily peeled off. It should be noted that when silicon oxide is used as the mask 50, there is no particular problem whether the etching solution 201 is acidic or alkaline.

[0069] It can be inferred that the PEC etching mechanism when the etching solution 201 of the second example is to replace (chemical formula 1) to (chemical formula 3) described for the etching solution 201 of the first example with (chemical formula 7). In other words, GaN, holes generated by irradiation with UV light 221 and water react to generate Ga2O3 and hydrogen ions (H + ) and N2 (chemical formula 7). And the generated Ga2O3 is dissolved in acid. In this way, PEC etching of GaN is performed. It should be noted that the electrons generated in pairs with holes as shown in (chemical formula 4) to (chemical formula 6) are oxidized by S2O8 2- The mechanism of consumption is the same as that in the case of using the etching solution 201 of the first example.

[0070] [Chemical formula 7]

[0071]

[0072] According to (Chemical Formula 1) and (Chemical Formula 2) or (Chemical Formula 7), it can be understood that the etched region 21 (bottom 120 of recess 110) where PEC etching occurs functions as an anode that consumes holes. In addition, according to (Chemical Formula 6), it can be understood that the surface of the cathode pad 30, which is a conductive member electrically connected to the etched region 21 and in contact with the etching solution 201, functions as a cathode that consumes (releases) electrons.

[0073] (In particular, when the substrate 11 is semi-insulating (non-conductive)), if the cathode pad 30 is not provided, it is difficult to ensure the area that functions as the cathode, and it is difficult to perform PEC etching. In the present embodiment, by providing the cathode pad 30, PEC etching can be performed well. In addition, by making the mask 50 have an opening on the upper surface of the cathode pad 30, in other words, by making the wide area on the upper surface of the cathode pad 30 function as the cathode, PEC etching can be performed more well.

[0074] As shown in (chemical formula 5), ​​as S2O8 2- Generate SO4 -* The free radical method may use at least one of irradiation with UV light 221 and heating. When irradiation with UV light 221 is used, in order to increase the S2O8 2- The light absorption can efficiently generate SO4 -* The wavelength of the UV light 221 is preferably 200 nm or more and less than 310 nm. In other words, holes are efficiently generated in the III-nitride in the epitaxial layer 12 by irradiation with the UV light 221, and S2O8 is efficiently generated in the etching solution 201. 2- Generate SO4 -* From the perspective of free radicals, it is preferred that the wavelength of UV light 221 be greater than 200 nm and less than 310 nm. 2- Generate SO4 -* In the case of free radicals, the wavelength of the UV light 221 can be set to (365 nm or less and) 310 nm or more.

[0075] By irradiation of UV light 221, S2O8 2- Generate SO4 -* When the free radical is generated, the distance L (wafer configuration depth) from the surface 20 of the wafer 10 to the upper surface of the etching solution 201 (refer to Figure 2 (b)) is preferably set to be greater than 1 mm and less than 100 mm. If the distance L is too short, for example, less than 1 mm, the SO4 generated in the etching solution 201 above the wafer 10 -*The amount of free radicals may become unstable due to the change of the distance L. It should be noted that if the distance L is short, it is difficult to control the height of the liquid level. Therefore, the distance L is preferably 1 mm or more, more preferably 3 mm or more, and further preferably 5 mm or more. In addition, if the distance L is too long, for example, exceeding 100 mm, an excessive amount of SO4 that does not participate in PEC etching is generated in the etching solution 201 above the wafer 10. -* The free radicals are generated, and therefore, the utilization efficiency of the etching solution 201 is reduced.

[0076] The inventors of the present invention have obtained the following knowledge: if the edge of the mask used in PEC etching is made of a conductive material, the shape of the edge of the recess formed by PEC etching is likely to become a disordered shape that does not follow the edge of the mask. By making the edge of the mask of a non-conductive material, it is easy to control the shape of the edge of the recess formed by PEC etching to a shape that follows the edge of the mask. Therefore, it is preferred to use a mask 50 made of a non-conductive material to define the end of the mask that defines the etched area 21 (in other words, the edge of the recess 110). The cathode pad 30 is preferably arranged at a position (when viewed from above) that is at a distance from the edge of the recess 110 (a position that does not define the edge of the recess 110). From the viewpoint of well controlling the edge shape of the recess 110, the distance D between the edge of the mask 50 (when viewed from above) and the edge of the cathode pad 30 is OFF (Refer to Figure 2 The thickness (a)) is preferably 5 μm or more, more preferably 10 μm or more.

[0077] PEC etching can also be performed on group III nitrides other than the exemplified GaN. The group III element contained in the group III nitride can be at least one of aluminum (Al), gallium (Ga) and indium (In). The concept of PEC etching of the Al component or the In component in the group III nitride is the same as the concept described for the Ga component with reference to (chemical formula 1) and (chemical formula 2) or (chemical formula 7). That is, holes are generated by irradiating UV light 221 to generate Al oxides or In oxides, and these oxides are dissolved in alkali or acid, so that PEC etching can be performed. The wavelength of UV light 221 can be appropriately changed according to the composition of the group III nitride to be etched. Taking the PEC etching of GaN as a benchmark, when Al is contained, shorter wavelength light can be used, and when In is contained, longer wavelength light can also be used. In other words, light of a wavelength at which the group III nitride can be PEC-etched can be appropriately selected and used according to the composition of the group III nitride to be processed.

[0078] In the PEC object 100 of the present embodiment, the etched region 21 (bottom 120 of the recess 110) as the anode and the cathode pad 30 as the cathode are connected by 2DEG. Therefore, as the PEC etching proceeds, the barrier layer 12c becomes thinner, and when the 2DEG below the recess 110 decreases, the PEC etching becomes difficult to proceed, and soon, the PEC etching can be automatically stopped in a state where a barrier layer 12c of a predetermined thickness remains below the recess 110. The predetermined thickness can be adjusted, for example, by the intensity of the UV light 221. In this way, in the recess forming step, the formation of the recess 110 can be ended by automatically stopping the PEC etching.

[0079] Next, the planarization process will be described. Figure 3 (a) is a schematic cross-sectional view of the PEC object 100 showing a state where the recessed portion forming step is completed. The PEC object 100 in which the recessed portion 110 is formed in the recessed portion forming step becomes an object 140 to be planarized in the planarizing step (hereinafter also referred to as a planarized object 140).

[0080] As described above, dislocations are distributed at a predetermined density in the surface 20 of the epitaxial layer 12. In dislocations, the lifetime of holes is short, so PEC etching is difficult to occur. Therefore, at the position corresponding to the dislocation at the bottom 120 of the recess 110, a convex portion 122 is easily formed as a dissolved residual portion of PEC etching. In other words, in the recess forming step, a flat portion 121 (a portion without dislocations and subjected to PEC etching) and a convex portion 122 that is raised relative to the flat portion 121 because it is difficult to be PEC-etched compared to the flat portion 121 are formed at the bottom 120 of the recess 110. The convex portion 122 is a dissolved residual portion of PEC etching, and therefore its maximum height is also less than the depth of the recess 110.

[0081] In the planarization step, as described above, the bottom 120 of the concave portion 110 is planarized by performing second etching (hereinafter also referred to as planarization etching). Specifically, the convex portion 122 is etched (selectively with respect to the flat portion 121) by the planarization etching, so that the convex portion 122 is lowered.

[0082] As the planarization etching, for example, wet etching using an acidic or alkaline etching solution (non-PEC etching) can be used. As the etching solution for the planarization etching, for example, a hydrochloric acid (HCl) aqueous solution, a mixed aqueous solution of hydrochloric acid (HCl) and hydrogen peroxide (H2O2) (hydrochloric acid perhydrate), a mixed aqueous solution of sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) (piranha solution), a tetramethylammonium hydroxide (TMAH) aqueous solution, a hydrogen fluoride aqueous solution (hydrofluoric acid), a potassium hydroxide (KOH) aqueous solution, etc. can be used.

[0083] The epitaxial layer 12 heteroepitaxially grown on a substrate 11 which is a heterogeneous substrate such as a SiC substrate, a sapphire substrate, or a Si substrate has, for example, a 1×10 8 / cm 2 Therefore, when the substrate 11 which is a different type of substrate is used, the protrusions 122 are easily formed by PEC etching in the recess forming step, and therefore, the planarization of the bottom 120 by the planarization step becomes particularly effective.

[0084] Figure 3 (b) is a schematic cross-sectional view of a planarization etching apparatus 300 showing a planarization process (in other words, a planarization etching process). The planarization etching apparatus 300 has a container 310 for storing an etching solution 301. In the planarization process, the convex portion 122 is etched by immersing the flattened object 140 in the etching solution 301 so that the concave portion 110 contacts the etching solution 301. As a result, the bottom 120 of the concave portion 110 is planarized. Planarization etching is not PEC etching. Therefore, in the planarization process, UV light is not irradiated to the surface 20 of the epitaxial layer 12. Here, "no UV light irradiation" means: no (strong) UV light that would cause useless PEC etching is irradiated.

[0085] It is known that it is difficult to etch the c-plane of group III nitrides such as GaN, but PEC etching can etch group III nitrides regardless of their crystal orientation, so even the c-plane can be etched. By performing the PEC etching process of forming a recess while irradiating UV light 221 from above the surface 20 of the epitaxial layer 12, which is the c-plane, the group III nitride constituting the epitaxial layer 12 is etched from a direction perpendicular to the surface 20 (in other words, along the thickness direction of the epitaxial layer 12).

[0086] In contrast, the planarization etching is performed in the form of a conventional wet etching using an etching solution such as hydrochloric acid permeate and not PEC etching. In conventional wet etching, the c-plane of the group III nitride is difficult to etch, and therefore, in the bottom 120 of the recess 110, the flat portion 121 formed by the c-plane is not etched. However, the convex portion 122 of the bottom 120 is formed by including a crystal plane other than the c-plane, and therefore, can be etched using conventional etching. Therefore, by planarization etching, the convex portion 122 can be selectively etched relative to the flat portion 121. The planarization etching etches the crystal plane other than the c-plane, that is, the crystal plane intersecting the c-plane, and etches the convex portion 122 from a direction that is non-perpendicular to the c-plane (in other words, along a direction intersecting the thickness direction of the epitaxial layer 12 (lateral direction)).

[0087] By etching the convex portion 122 by planarization etching, the convex portion 122 can be lowered and the bottom 120 can be made close to the flatness, in other words, the convex portion 122 can be made close to the c-plane constituting the flat portion 121. If the convex portion 122 is etched and close to the c-plane, etching is difficult to perform. Therefore, in the planarization process of this embodiment, it is possible to suppress the convex portion 122 from being over-etched, and it is easy to end the planarization etching with the bottom 120 being substantially flat.

[0088] After the planarization etching is performed until the bottom portion 122 having a predetermined planarity is obtained, the planarization step is terminated. The appropriate planarity of the bottom portion 122 will be described later with reference to an experimental example.

[0089] It should be noted that the mask 50 used in the recessed portion forming step may be removed in the planarizing step, or may be removed by separately providing a mask removing step for removing the mask 50 .

[0090] After the planarization step is completed, other steps for completing the HEMT 150 are performed (see Figure 1 As other steps, a step of forming the element isolation groove 160, a step of forming the gate electrode 152 on the bottom 120 of the recess 110, a step of forming the protective film 154, etc. are performed. In this way, the HEMT 150 is manufactured.

[0091] It should be noted that the PEC object 100 (see Figure 2 In the method (a)), that is, the element separation groove 160 is formed after the recess forming step, the PEC object 100 in a state where the element separation groove 160 is formed by forming the element separation groove 160 before the recess forming step can also be used.

[0092] The method for forming the element separation groove 160 is not particularly limited, and the element separation groove 160 can be formed, for example, by dry etching, or by PEC etching. When PEC etching is used, for example, the intensity of the irradiated UV light is sufficiently increased to set the etching depth to a depth that reaches the middle of the channel layer 12b.

[0093] As described above, according to the present embodiment, the bottom 120 of the recess 110 formed by the PEC etching (first etching) in the recess forming step can be flattened by the flattening etching (second etching) in the flattening step. Thus, when the recess 110 is used as a groove for arranging the gate electrode 152 of the HEMT 150, the characteristics of the HEMT 150 can be improved (for example, the leakage current can be reduced) compared to the case where the recess 110 is not flattened and the convex portion 122 is present at the bottom 120.

[0094] Next, an experimental example of PEC etching and planarization etching is described. In this experimental example, a wafer having the following substrate and epitaxial layer is used. The substrate is a semi-insulating SiC substrate. The epitaxial layer is a stacked structure of a nucleation layer composed of AlN, a channel layer composed of GaN and having a thickness of 0.75 μm, a barrier layer composed of AlGaN (Al composition is 0.22) and having a thickness of 24 nm, and a cap layer composed of GaN and having a thickness of 5 nm.

[0095] The PEC etching was performed as follows: a 0.025 M aqueous solution of K2S2O8 was used as an etching solution while the etching was performed at 3.8 mW / cm 2 The wafer was irradiated with UV light of 260 nm in wavelength for 120 minutes. The wafer configuration depth L was set to 5 mm. The mask was formed of silicon oxide and the cathode pad was formed of titanium. A recess with a depth of 23.2 nm was formed. Since the thickness of the cover layer was 5 nm and the thickness of the barrier layer was 24 nm, the thickness of the barrier layer remaining under the recess was 5.8 nm.

[0096] After the PEC etching, the bottom of the recess is flattened by planarization etching. The planarization etching is performed for 10 minutes using hydrochloric acid water (for example, a solution obtained by mixing 30% HCl and 30% H2O2 in a ratio of 1:1) as an etching solution.

[0097] Figure 4 (a) is a graph showing the relationship between the etching time and the etching depth of PEC etching. The horizontal axis represents the etching time, and the vertical axis represents the etching depth. From the start of etching to about 40 minutes, the etching depth deepens in proportion to the etching time. About 40 minutes after the start of etching, the etching depth reaches 23.2nm, and thereafter, the etching depth reaches a constant. That is, PEC etching is performed in a manner that automatically stops etching about 40 minutes after the start of etching.

[0098] An atomic force microscope (AFM) was used to observe a 1000 nm square area for the surface of the epitaxial layer before PEC etching (hereinafter referred to as the epitaxial layer surface), the bottom of the recessed portion formed by PEC etching but not subjected to planarization etching (hereinafter referred to as the unplanarized bottom), and the bottom of the recessed portion subjected to planarization etching after PEC etching (hereinafter referred to as the planarized bottom).

[0099] Figure 4 (b) is an AFM image of the epitaxial layer surface. The arithmetic mean roughness (Ra) of the epitaxial layer surface measured by AFM is 0.14nm. From the perspective of the desired epitaxial layer having high crystallinity, the Ra of the epitaxial layer surface is preferably less than 0.4nm, more preferably less than 0.3nm, and further preferably less than 0.2nm.

[0100] Figure 5 (a) is an AFM image of an unplanarized bottom. In the unplanarized bottom, convex portions are observed at positions corresponding to dislocations. It can be observed that the heights of the multiple convex portions distributed in the unplanarized bottom tend to be non-constant. The height of the largest convex portion exceeds 10 nm.

[0101] The Ra of the unplanarized bottom measured by AFM is 0.22nm. The Ra of the epitaxial layer surface is, for example, 0.14nm, while the Ra of the unplanarized bottom is, for example, 0.22nm. Although the unplanarized bottom has a convex portion, its Ra is, for example, less than 2 times the Ra of the epitaxial layer surface, and has not increased that much. It can be said that the reason is that PEC etching is performed in a manner in which the flat portion occupying most of the area of ​​the unplanarized bottom has high flatness, that is, the high flatness of the epitaxial layer surface is almost not damaged in the flat portion. The Ra of the unplanarized bottom is preferably less than 0.4nm, and more preferably less than 0.3nm.

[0102] Figure 5 (b) is an AFM image of the flattened bottom. It can be seen that: at the flattened bottom, the convex part observed at the unflattened bottom is not clearly observed, and the bottom of the concave part has been flattened. At the flattened bottom, the position where the convex part is presumed to have been formed, that is, the position corresponding to the dislocation, is observed in the form of a bright area, which is distinguished from the flat part. This bright area is not observed at a clear convex shape, but is observed at a roughly flat shape (almost the same height as the flat part). In the following, for the sake of convenience, this bright area is sometimes referred to as a convex part.

[0103] The Ra of the flattened bottom measured by AFM is 0.24nm. The Ra of the unflattened bottom is, for example, 0.22nm. In contrast, the Ra of the flattened bottom is, for example, 0.24nm, which is slightly larger. It can be considered that the difference is an error caused by the difference between the measurement area of ​​the unflattened bottom and the measurement area of ​​the flattened bottom. It can be considered that the Ra of the unflattened bottom is the same as the Ra of the flattened bottom. It can be said that it is difficult to clearly distinguish the unflattened bottom from the flattened bottom only by Ra. From the AFM image of the flattened bottom, it can be seen that by flattening etching, the convex portion can be selectively etched without reducing the flatness of the flat portion.

[0104] The suitable flatness of the flattened bottom can be expressed as follows. For example, among the multiple convex portions distributed on the flattened bottom, the height of the largest convex portion is less than 1 / 10 of the depth of the concave portion. In addition, for example, among the multiple convex portions distributed on the flattened bottom, the height of the largest convex portion is preferably less than 2nm, more preferably less than 1nm (the maximum height of the position corresponding to the dislocation is preferably less than 2nm, more preferably less than 1nm). In addition, for example, the Ra of the flattened bottom is preferably less than 0.4nm, more preferably less than 0.3nm.

[0105] The features related to the epitaxial layer surface described above can be said to be features observed on the surface 20 of the epitaxial layer 12 before the recess forming step in the above embodiment (or features observed on the surface 20 of the epitaxial layer 12 of the portion outside the recess 110 that is not subjected to PEC etching after the recess forming step or the flattening step). In addition, the features related to the unflattened bottom described above can be said to be features observed on the bottom 120 of the recess 110 after the recess forming step and before the flattening step in the above embodiment. In addition, the features related to the flattened bottom described above can be said to be features observed on the bottom 120 of the recess 110 after the flattening step in the above embodiment. The features observed on the bottom 120 of the recess 110 after the flattening step can be said to be features possessed by the HEMT 150 described in the embodiment.

[0106] It should be noted that, in the bottom 120 of the recess 110 formed by PEC etching, damage to the group III nitride crystal caused by etching for forming the recess 110 is small (for example, compared with dry etching).

[0107] In addition, less halogen elements remain in the bottom 120 of the recess 110 formed by PEC etching than in the case where the recess 110 is formed by dry etching. When the recess 110 is to be formed by dry etching, an etching gas containing a halogen element is made to impact the bottom 120, or a reaction for halogenating the bottom 120 is used, so that halogen elements remain in the bottom 120 of the recess 110 (in the surface portion of the specified thickness). Compared with such dry etching, the PEC etching and planarization etching in the present embodiment can be performed in the form of wet etching that does not leave halogen elements in the bottom 120 of the recess 110 (in the surface portion of the specified thickness). The concentration of halogen elements (e.g., chlorine (Cl)) in the bottom 120 of the recess 110 is preferably less than 1×10 15 / cm 3 , more preferably less than 5×10 14 / cm 3 , and more preferably less than 2×10 14 / cm 3 .

[0108] <First Modification>

[0109] Next, a first variation of the above embodiment is described. In the above embodiment, as the planarization etching, a method of wet etching (non-PEC etching) using an acidic or alkaline etching solution is exemplified, that is, a method of chemically etching the protrusion 122. The planarization etching mechanism is not particularly limited as long as the protrusion 122 is etched in a manner that the bottom 120 is planarized. Therefore, the planarization etching can be performed by etching based on other mechanisms other than chemical etching. By combining etching based on multiple mechanisms, the planarization etching can be performed more effectively.

[0110] The planarization etching can be performed, for example, by mechanically removing the protrusion 122. As a mechanical planarization etching, for example, bubbling cleaning can be used, and in addition, for example, brushing can be used. As an etching liquid (cleaning liquid) for bubbling cleaning, for example, hydrochloric acid water as illustrated in the above embodiment can be listed. When the protrusion 122 is etched by hydrochloric acid water, bubbles are violently generated. Therefore, the protrusion 122 can be destroyed and removed by the impact generated by the bubbles. It can be said that hydrochloric acid water is an etching liquid for chemically etching and mechanically etching the protrusion 122.

[0111] <Second Modification>

[0112] Next, a second modification of the above embodiment will be described. In the above embodiment, a method is exemplified in which, after the PEC etching for forming the recess 110 is completed, the planarization etching for planarizing the bottom 120 of the recess 110 is performed.

[0113] In this modification, the following method is illustrated: before the PEC etching for forming the recess 110 is completed, that is, at the stage where the recess 110 is formed to a mid-depth, the planarization etching is performed, and then the PEC etching is performed again to further deepen the recess 110. That is, in this modification, a method of alternately repeating the recess forming step and the planarization step is illustrated. The planarization step can be performed multiple times as needed. As in the above embodiment, the planarization step can be performed after the formation of the recess 110 is completed.

[0114] Figure 6 (a) is a schematic cross-sectional view illustrating a flattened object 140 in this modification. Figure 6 (b) is a schematic cross-sectional view of a planarization etching apparatus 300 showing a planarization step of this modification. The planarization etching apparatus 300 is the same as that of the above-described embodiment.

[0115] Figure 6The concave portion 110 shown in (a) is formed to the middle depth. The convex portion 122 is the dissolved residual portion of the PEC etching. Therefore, the convex portion 122 formed in this modification example where the concave portion 110 is shallower is different from the convex portion 122 formed in the above embodiment where the concave portion 110 is deeper (see Figure 3 The entire structure is lower than that of (a) and the height difference between the protrusions 122 is small.

[0116] Therefore, in the planarization process (each time) of this modification, the etching of the protrusion 122 becomes easy, and it is easy to make the height of the etched protrusion 122 uniform. In addition, by repeating the planarization process multiple times, the protrusion 122 can be etched more reliably. Therefore, in this modification, the flatness of the bottom 120 of the recess 110 can be further improved.

[0117] <Third Modification>

[0118] Next, a third modification of the above embodiment will be described. This modification is different from the planarization etching apparatus 300 in the above embodiment. Figure 7 Schematic cross-sectional view of a planarization etching apparatus 300 according to a third modification example.

[0119] The planarization etching device 300 of this modification has a structure in which a liquid flow generating mechanism 320 and a vibration generating mechanism 330 are added to the planarization etching device 300 described in the above embodiment. The liquid flow generating mechanism 320 generates a liquid flow (flow) of the etching liquid 301. The vibration generating mechanism 330 is, for example, an ultrasonic generator, and applies vibration to the etching liquid 301. In this modification, by performing at least one of generating a liquid flow (flow) of the etching liquid 301 and applying vibration to the etching liquid 301, the effect of mechanically etching the protrusion 122 can be enhanced.

[0120] <Other Implementation Methods>

[0121] The embodiments of the present invention have been specifically described above. However, the present invention is not limited to the above-described embodiments, and various changes, improvements, combinations, etc. can be made without departing from the spirit and scope of the present invention.

[0122] For example, in the above embodiment, the cathode pad 30 is used as at least one of the source electrode 151 and the drain electrode 153 of the HEMT 150 , but the cathode pad 30 may be a conductive member different from the source electrode 151 or the drain electrode 153 of the HEMT 150 .

[0123] Figure 81 is a schematic cross-sectional view of a PEC object 100 illustrating such another embodiment. In this embodiment, a conductive member having a configuration and shape different from that of the source electrode 151 or the drain electrode 153 can be used as the cathode pad 30. The cathode pad 30 is, for example, arranged in a ring shape along the outer circumference of the wafer 10. It should be noted that the configuration, shape, size, number, etc. of the cathode pad 30 can be variously adjusted as needed. The mask 50 has an opening in the etched region 21 where the recess (groove for configuring the gate electrode 152) 110 of each HEMT element is to be formed, and has an opening for exposing the upper surface of the cathode pad 30.

[0124] In this embodiment, the cathode pad 30 may not be provided for each HEMT element, and the cathode pad 30 disposed outside a certain HEMT element (outside the element separation groove 160 surrounding the HEMT element in a plan view) may be used to form the recess 110 of the HEMT element. As described above, during PEC etching, it is preferred that the etched region 21 (the bottom 120 of the recess 110) is electrically connected to the cathode pad 30 via 2DEG. Therefore, in this method, it is preferred to provide the element separation groove 160 that separates the 2DEG of each HEMT element from each other after the PEC etching is completed.

[0125] After the PEC etching is completed, that is, after the recess forming step is completed, the cathode pad 30 is removed. The cathode pad 30 may be removed after the recess forming step is completed and before the planarizing step, or after the planarizing step, or during the planarizing step. In this embodiment, after the recess forming step is completed, the source electrode 151 and the drain electrode 153 of each HEMT element are formed as conductive members different from the cathode pad 30 (see Figure 1 (a)).

[0126] It should be noted that in the above description, the completed HEMT is referred to as the structure 150 , and the structure 150 may be a member having at least the epitaxial layer 12 having the recess 110 formed by the recess forming step and the planarizing step.

[0127] <Preferred Mode of the Invention>

[0128] Hereinafter, preferred embodiments of the present invention will be described.

[0129] (Note 1)

[0130] A method for manufacturing a structure, comprising the following steps:

[0131] a step of forming a recess by performing a first etching on the surface of the member made of group III nitride; and

[0132] A step of flattening the bottom of the concave portion by performing a second etching on the bottom of the concave portion,

[0133] In the step of forming the concave portion, a flat portion and a convex portion are formed at the bottom of the concave portion, and the convex portion is difficult to be etched by the first etching process compared with the flat portion, and thus rises relative to the flat portion.

[0134] In the step of flattening the bottom portion, the protruding portion is etched (selectively with respect to the flat portion) by the second etching, thereby making the protruding portion lower.

[0135] (Note 2)

[0136] The method for manufacturing a structure according to Supplementary Note 1, wherein the protrusion is formed at a position corresponding to a dislocation of the group III nitride constituting the member.

[0137] (Note 3)

[0138] The method for producing a structure according to Appendix 1 or 2, wherein the surface is composed of a c-plane of a group III nitride,

[0139] The first etching etches the group III nitride in a direction perpendicular to the surface.

[0140] The second etching is performed by etching the protrusion from a direction that is not perpendicular to the c-plane.

[0141] (Note 4)

[0142] The method for manufacturing a structure according to Supplementary Note 3, wherein the first etching is photoelectrochemical etching.

[0143] (Note 5)

[0144] The method for manufacturing a structure according to Supplement 3 or 4, wherein the second etching is wet etching using an acidic or alkaline etching solution (not photoelectrochemical etching).

[0145] (Note 6)

[0146] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 5, wherein the first etching etches the group III nitride in a direction perpendicular to the surface,

[0147] The second etching mechanically removes the protrusion.

[0148] (Note 7)

[0149] The method for manufacturing a structure according to Supplementary Note 6, wherein the first etching is photoelectrochemical etching.

[0150] (Note 8)

[0151] The method for manufacturing a structure according to Supplementary Note 6 or 7, wherein the second etching is bubble cleaning.

[0152] (Note 9)

[0153] The method for manufacturing a structure according to any one of Supplementary Notes 6 to 8, wherein the second etching is brush cleaning.

[0154] (Note 10)

[0155] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 9, wherein the first etching is photoelectrochemical etching, and the group III nitride is etched in a direction perpendicular to the surface by irradiating the surface with ultraviolet light from above.

[0156] (Note 11)

[0157] The method for producing a structure according to any one of Supplementary Notes 1 to 10, wherein in the second etching, ultraviolet light (which causes photoelectrochemical etching) is not irradiated on the surface.

[0158] (Note 12)

[0159] A method for manufacturing a structure according to any one of Appendixes 1 to 11, wherein after the step of flattening the bottom, the maximum height of the protrusion measured by observing a 1000 nm square area of ​​the bottom with AFM is less than 1 / 10 of the depth of the concave portion.

[0160] (Note 13)

[0161] The method for manufacturing a structure according to any one of Appendixes 1 to 12, wherein after the step of flattening the bottom, the maximum height of the protrusion measured by observing a 1000 nm square area of ​​the bottom with an AFM is preferably 2 nm or less, more preferably 1 nm or less.

[0162] (Note 14)

[0163] A method for manufacturing a structure according to any one of Appendixes 1 to 13, wherein after the step of flattening the bottom, the arithmetic mean roughness (Ra) of the bottom measured by observing a 1000 nm square area of ​​the bottom with an AFM is preferably 0.4 nm or less, more preferably 0.3 nm or less.

[0164] (Note 15)

[0165] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 14, wherein in the step of flattening the bottom portion, the second etching selectively etches the convex portion with respect to the flat portion.

[0166] (Note 16)

[0167] A method for manufacturing a structure according to any one of Notes 1 to 15, wherein, after the step of forming the recess and before the step of flattening the bottom, the arithmetic mean roughness (Ra) of the bottom measured by observing a 1000 nm square area of ​​the bottom with an AFM is preferably less than 0.4 nm, more preferably less than 0.3 nm.

[0168] (Note 17)

[0169] A method for manufacturing a structure according to any one of Appendixes 1 to 16, wherein, before the step of forming the recessed portion, the arithmetic mean roughness (Ra) of the surface measured by observing the surface with an AFM is preferably 0.4 nm or less, more preferably 0.3 nm or less, and further preferably 0.2 nm or less.

[0170] (Note 18)

[0171] The method for manufacturing a structure according to any one of Supplements 1 to 17, wherein the structure is used as a high electron mobility transistor, wherein:

[0172] After the step of planarizing the bottom portion, there is a step of forming a gate electrode of the high electron mobility transistor on the bottom portion.

[0173] (Note 19)

[0174] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 18, wherein the first etching is photoelectrochemical etching,

[0175] The etching solution for the photoelectrochemical etching is an alkaline or acidic etching solution containing an electron-accepting oxidant.

[0176] (Note 20)

[0177] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 19, wherein the first etching is photoelectrochemical etching,

[0178] In the step of forming the recessed portion, the photoelectrochemical etching is performed with a mask disposed on the surface.

[0179] The etching solution of the aforementioned photoelectrochemical etching (from the moment when the first etching starts) is an acidic etching solution,

[0180] The aforementioned mask is a resist mask.

[0181] (Note 21)

[0182] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 20, wherein the first etching is photoelectrochemical etching,

[0183] In the step of forming the recessed portion, the photoelectrochemical etching is performed with a mask and a conductive member disposed on the surface.

[0184] The mask is made of a non-conductive material and defines the edge of the concave portion.

[0185] The conductive member is disposed at a position offset from the edge of the recess (a position not defining the edge of the recess), and is disposed so that at least a portion (upper surface) of the conductive member contacts the etching solution of the photoelectrochemical etching.

[0186] (Note 22)

[0187] A method for manufacturing a structure according to Note 21, wherein the structure is used as a high electron mobility transistor, the recess is used as a groove for configuring a gate electrode of the high electron mobility transistor, and the conductive component is used as at least one of a source electrode and a drain electrode of the high electron mobility transistor.

[0188] (Note 23)

[0189] The method for manufacturing a structure according to Supplementary Note 21, wherein the structure is used as a high electron mobility transistor, and the recess is used as a groove for configuring a gate electrode of the high electron mobility transistor,

[0190] After the step of forming the recessed portion, a source electrode and a drain electrode of the high electron mobility transistor are formed as a conductive member different from the conductive member.

[0191] (Note 24)

[0192] The method for manufacturing a structure according to Supplementary Note 23, wherein after the step of forming the recessed portion, an element isolation trench of the high electron mobility transistor is formed.

[0193] (Note 25)

[0194] The method for producing a structure according to any one of Supplementary Notes 1 to 24, wherein the step of forming the recessed portion and the step of flattening the bottom are repeated alternately.

[0195] (Note 26)

[0196] The method for producing a structure according to any one of Supplementary Notes 1 to 25, wherein the second etching is performed while causing an etching solution used in the second etching to generate a liquid flow (flow).

[0197] (Note 27)

[0198] The method for producing a structure according to any one of Supplementary Notes 1 to 26, wherein the second etching is performed while applying vibration to an etching liquid used in the second etching.

[0199] (Note 28)

[0200] A structure having a member composed of a group III nitride and having a recessed portion formed therein,

[0201] The maximum height of the position corresponding to the dislocation of the group III nitride constituting the member measured by observing a 1000 nm square area at the bottom of the recess with an AFM is preferably 2 nm or less, more preferably 1 nm or less.

[0202] The arithmetic mean roughness (Ra) of the bottom portion measured by observation with the AFM is preferably 0.4 nm or less, more preferably 0.3 nm or less.

[0203] (Note 29)

[0204] The structure according to Supplementary Note 28, wherein the member has a surface consisting of a c-plane of a group III nitride, and the recessed portion is formed on the surface.

[0205] (Note 30)

[0206] The structure according to Supplementary Note 28 or 29, comprising a substrate, wherein the member is composed of a Group III nitride heteroepitaxially grown on the substrate.

[0207] (Note 31)

[0208] The structure according to any one of Supplementary Notes 28 to 30, wherein the concentration of the halogen element (e.g., chlorine) at the bottom of the concave portion is preferably less than 1×10 15 / cm 3 , more preferably less than 5×10 14 / cm 3 , and more preferably less than 3×10 14 / cm 3 .

[0209] (Note 32)

[0210] The structure according to any one of Supplementary Notes 28 to 31, wherein the structure is used as a high electron mobility transistor, and the recessed portion is used as a groove for arranging a gate electrode of the high electron mobility transistor.

[0211] (Note 33)

[0212] A method for manufacturing a structure, comprising the following steps:

[0213] A step of performing photoelectrochemical etching on an etched region composed of a group III nitride and serving as a component of a high electron mobility transistor; and

[0214] forming a device isolation region of the high electron mobility transistor on the member;

[0215] In the process of implementing the photoelectrochemical etching, the photoelectrochemical etching is performed using a conductive member, which is arranged outside the region where the element isolation region is to be formed relative to the etched region and is connected to the etched region via a two-dimensional electron gas.

[0216] The step of forming the device isolation region is performed after the step of performing the photoelectrochemical etching.

[0217] (Note 34)

[0218] The method for manufacturing a structure according to Supplementary Note 33, wherein the etched region is a region where a recessed portion in which a gate electrode of the high electron mobility transistor is arranged is formed.

[0219] (Note 35)

[0220] A method for manufacturing a structure according to Note 33 or 34, wherein, in the process of implementing the aforementioned photoelectrochemical etching, the aforementioned photoelectrochemical etching is performed using a mask made of a non-conductive material, the mask having an opening in the aforementioned etched area and having an opening for exposing the aforementioned conductive component.

[0221] (Note 36)

[0222] The method for manufacturing a structure according to any one of Supplementary Notes 33 to 35, wherein after the photoelectrochemical etching step is performed, the conductive member is removed to form a source electrode and a drain electrode of the high electron mobility transistor.

[0223] Description of Reference Numerals

[0224] 10…wafer, 11…substrate, 12…epitaxial layer, 20…surface (of epitaxial layer), 21…etched region, 30…cathode pad, 50…mask, 100…PEC object, 110…recess, 120…bottom, 121…flat portion, 122…convex portion, 140…flattening object, 150…structure, 151…source electrode, 152…gate electrode, 153…drain electrode, 160…element separation groove, 200…PEC etching device, 201…etching liquid, 210…container, 220…light source, 221…UV light, 300…flattening etching device, 301…etching liquid, 310…container, 320…liquid flow generating mechanism, 330…vibration generating mechanism.

Claims

1. A method for manufacturing a structure, comprising the following steps: a step of forming a recess by performing a first etching on the surface of the member made of group III nitride; and A step of flattening the bottom of the recess by performing a second etching on the bottom of the recess, In the step of forming the concave portion, a flat portion and a convex portion are formed at the bottom of the concave portion, and the convex portion is difficult to be etched by the first etching process compared with the flat portion, and thus rises relative to the flat portion. In the step of flattening the bottom, the convex portion is etched by the second etching so as to be lowered. The first etching is photoelectrochemical etching, The second etching is not photoelectrochemical etching, and in the second etching, ultraviolet light is not irradiated to the surface.

2. The method for manufacturing a structure according to claim 1, wherein: The protrusions are formed at positions corresponding to dislocations of the group III nitride constituting the member.

3. The method for manufacturing a structure according to claim 1 or 2, wherein: The surface is composed of a c-plane of a group III nitride, The first etching etches the group III nitride from a direction perpendicular to the surface, The second etching is performed by etching the protrusion in a direction that is non-perpendicular to the c-plane.

4. The method for manufacturing a structure according to claim 3, wherein: The second etching is wet etching using an acidic or alkaline etching solution.

5. The method for manufacturing a structure according to claim 1 or 2, wherein: The first etching etches the group III nitride from a direction perpendicular to the surface, The second etching mechanically removes the protrusion.

6. The method for manufacturing a structure according to claim 5, wherein: The second etching is bubble cleaning.

7. The method for manufacturing a structure according to claim 5, wherein: The second etching is brushing.

8. The method for manufacturing a structure according to claim 1 or 2, wherein: After the step of flattening the bottom, the maximum height of the convex portion measured by observing a 1000 nm square region of the bottom with an AFM is 1 / 10 or less of the depth of the concave portion.

9. The method for manufacturing a structure according to claim 1 or 2, wherein: After the step of flattening the bottom, the maximum height of the protrusion measured by observing a 1000 nm square region of the bottom with an AFM is 2 nm or less.

10. The method for manufacturing a structure according to claim 1 or 2, wherein: After the step of flattening the bottom, the arithmetic mean roughness (Ra) of the bottom measured by observing a 1000 nm square region of the bottom with an AFM is 0.4 nm or less.

11. The method for manufacturing a structure according to claim 1 or 2, wherein: In the step of planarizing the bottom portion, the second etching selectively etches the convex portion with respect to the flat portion.

12. The method for manufacturing a structure according to claim 1 or 2, wherein: After the step of forming the recessed portion and before the step of flattening the bottom portion, an arithmetic mean roughness (Ra) of the bottom portion measured by observing a 1000 nm square region of the bottom portion with an AFM is 0.4 nm or less.

13. The method for manufacturing a structure according to claim 1 or 2, wherein: The structure is used as a high electron mobility transistor, and in the manufacturing method, After the step of planarizing the bottom portion, there is a step of forming a gate electrode of the high electron mobility transistor on the bottom portion.

14. The method for manufacturing a structure according to claim 1 or 2, wherein: In the step of forming the recessed portion, the photoelectrochemical etching is performed with a mask disposed on the surface. The etching solution for the photoelectrochemical etching is an acidic etching solution. The mask is a resist mask.

15. The method for manufacturing a structure according to claim 1 or 2, wherein: In the step of forming the recessed portion, the photoelectrochemical etching is performed with a mask and a conductive member disposed on the surface. The mask is made of a non-conductive material and defines the edge of the recess. The conductive member is disposed at a position offset from an edge of the recessed portion, and is disposed so that at least a portion of the conductive member is in contact with an etching solution of the photoelectrochemical etching.

16. The method for manufacturing a structure according to claim 15, wherein: The structure is used as a high electron mobility transistor, the recess is used as a groove for configuring a gate electrode of the high electron mobility transistor, and the conductive member is used as at least one of a source electrode and a drain electrode of the high electron mobility transistor.

17. The method for manufacturing a structure according to claim 1 or 2, wherein: The step of forming the concave portion and the step of flattening the bottom portion are repeated alternately.

18. A method for manufacturing a structure according to claim 1 or 2, wherein: The structure has a member made of a group III nitride and having a recessed portion. The maximum height of the position corresponding to the dislocation of the group III nitride constituting the member measured by observing a 1000 nm square area at the bottom of the recess by AFM is 2 nm or less, The arithmetic mean roughness (Ra) of the bottom portion measured by observation with the AFM is 0.4 nm or less. 19 . The method for manufacturing a structure according to claim 18 , wherein the structure is used as a high electron mobility transistor, and the concave portion is used as a groove for configuring a gate electrode of the high electron mobility transistor.

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