Method for manufacturing structure, device for manufacturing structure, and intermediate structure

Abstract

The method for manufacturing a structure has the following steps: a step of preparing an etching object whose surface at least consists of a group III nitride; and a step of irradiating the surface of the etching object with light through the etching solution while the etching object is immersed in an etching solution containing peroxydisulfate ions, thereby generating sulfate ion radicals from the peroxydisulfate ions and generating holes in the group III nitride, thereby etching the group III nitride. In the step of etching the group III nitride, the etching solution is made acidic at the start time of etching the group III nitride, thereby maintaining the etching solution in an acidic state during the period when the group III nitride is etched, and etching is performed in a state where a resist mask is formed on the surface.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a structure, an apparatus for manufacturing a structure, and an intermediate 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 on 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 that causes less damage than general dry etching, and is preferred in terms of simplicity of apparatus compared to special dry etching that causes less damage, such as neutral particle beam etching (see, for example, non-patent document 2) and atomic layer etching (see, for example, non-patent document 3).

[0004] Prior art literature

[0005] Non-patent literature

[0006] 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

[0007] Non-patent document 2: S. Samukawa, JJAP, 45 (2006) 2395.

[0008] Non-patent document 3: T. Faraz, ECS J. Solid Stat. Scie. & Technol., 4, N5023 (2015). Summary of the invention

[0009] Problem that the invention aims to solve

[0010] An object of the present invention is to provide a technique capable of suppressing temporal variation in etching conditions in PEC etching of group III nitrides.

[0011] Solutions for solving problems

[0012] According to one embodiment of the present invention, there is provided a method for manufacturing a structure, which comprises the following steps:

[0013] A step of preparing an etching object having at least a surface composed of a group III nitride; and

[0014] a step of irradiating the surface of the etching object with light through the etching solution while the etching object is immersed in an etching solution containing peroxydisulfate ions, thereby generating sulfate ion radicals from the peroxydisulfate ions and generating holes in the group III nitride, thereby etching the group III nitride;

[0015] In the step of etching the group III nitride, the etching solution is acidic at the start time of etching the group III nitride, thereby maintaining the acidic state of the etching solution during the period when the group III nitride is etched.

[0016] The etching is performed in a state where a resist mask is formed on the surface.

[0017] According to another aspect of the present invention, there is provided an intermediate structure having:

[0018] An etching object having at least a surface composed of a group III nitride; and

[0019] A resist mask is formed on the aforementioned surface,

[0020] The intermediate structure is immersed in an acidic etching solution containing peroxodisulfate ions in a state where the resist mask is formed on the surface.

[0021] Effects of the Invention

[0022] Provided is a technique capable of suppressing temporal variation in etching conditions in PEC etching of group III nitrides. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 (a) is a schematic cross-sectional view illustrating an etching object according to one embodiment of the present invention, Figure 1 (b) is a schematic diagram of a PEC etching apparatus illustrating a PEC etching process according to one embodiment.

[0024] Figure 2 (a) is a graph showing the results of the first experimental example, Figure 2 (b) is a graph showing the results of the second experimental example.

[0025] Figure 3 (a) and Figure 3 (b) is a graph showing the results of the third experimental example.

[0026] Figure 4 (a) is a laser microscope image showing the results of the fourth experimental example, Figure 4(b) is a SEM image showing the results of the fourth experimental example.

[0027] Figure 5 (a) shows various data of AFM measurement showing the results of the fourth experimental example, Figure 5 (b) is an AFM image showing the results of the fourth experimental example.

[0028] Figure 6 This is a schematic diagram of a PEC etching apparatus for illustrating a pre-treatment step of a modified example. DETAILED DESCRIPTION

[0029] <One embodiment of the present invention>

[0030] A method for manufacturing a structure according to an embodiment of the present invention is described. The manufacturing method of this embodiment includes an etching step (hereinafter also referred to as a PEC etching step) using photoelectrochemical (PEC) etching of an etching object 10 (hereinafter also referred to as a wafer 10) that is a material of the structure. Hereinafter, PEC etching is referred to as etching.

[0031] Figure 1 (a) is a schematic cross-sectional view of a wafer 10 that is subjected to PEC etching. Figure 1 As shown in (a) of FIG. 1 , a wafer 10 is prepared. At least a surface 20 (an etched surface 20 to be etched) of the wafer 10 is composed of a group III nitride.

[0032] The structure of the wafer 10 is not particularly limited. As an example of the structure of the wafer 10 (the structure used in the experimental examples described later), there can be cited a stacked structure of an n-type gallium nitride (GaN) substrate 11 and an n-type GaN layer 12 epitaxially grown on the GaN substrate 11. The n-type GaN layer 12 has an n-type impurity concentration of, for example, 5×10 16 / cm 3 , thickness is 3μm.

[0033] The object to be processed by PEC etching, in other words, the object immersed in (contacting) the etching liquid 201 is called the processing object 100. The processing object 100 has at least a wafer 10, and further, as a component required for the PEC etching process, it can have a mask 50, for example. The mask 50 is formed in the form of a pattern with an opening in the etched area 21 on the etched surface 20 of the wafer 10. The material of the mask 50 is not particularly limited as long as it is a material that can withstand the etching liquid 201 and function as a mask. For example, it can be a resist, and further, for example, it can be silicon oxide, and further, for example, it can be silicon nitride, and further, for example, it can be a metal such as titanium. The shape, width, and etching depth of the etched area 21 can be appropriately selected as needed. The processing object 100 can be regarded as a structure (intermediate structure) at an intermediate stage for obtaining a final structure.

[0034] Figure 1 (b) is a schematic cross-sectional view of a PEC etching apparatus 200 showing a PEC etching process. The PEC etching apparatus 200 includes a container 210 containing an etching solution 201 and a light source 220 emitting ultraviolet (UV) light 221. The PEC etching apparatus 200 may include a support table 240 for placing the wafer 10 at a predetermined height.

[0035] In the PEC etching process, while the object 100 (in other words, the wafer 10) is immersed in the etching solution 201, the UV light 221 is irradiated to the etched surface 20 through the etching solution 201, thereby etching the group III nitride constituting the etched surface 20. The mechanism of the etching solution 201, the UV light 221 and the PEC etching will be described in detail later.

[0036] The PEC etching apparatus 200 preferably further includes a pH meter 230. The PEC etching process is preferably performed while measuring whether the pH of the etching solution 201 is within an appropriate range using the pH meter 230. At this time, the probe 231 of the pH meter 230 is preferably arranged at a position where the shadow of the probe 231 caused by the UV light 221 is not projected on the etched surface 20.

[0037] In addition, the method for producing the structured body of the present embodiment may include steps such as electrode formation and protective film formation as other steps as necessary.

[0038] Next, the details of the etching solution 201, the UV light 221, and the mechanism of PEC etching are described. GaN is exemplified as the group III nitride to be etched.

[0039] As the etching solution 201, it is possible to use an etchant containing oxygen for generating an oxide of a group III element contained in the group III nitride constituting the etched surface 20, and also containing persulfate ions (S2O8) as an oxidant that accepts electrons. 2-) etching solution 201. In addition, as the etching solution 201 in this embodiment, an etching solution 201 that is acidic at the start time of etching of the group III nitride constituting the etched surface 20 can be used.

[0040] As a first example of the etching solution 201, an etching solution obtained by mixing a potassium hydroxide (KOH) aqueous solution with a potassium persulfate (K2S2O8) aqueous solution can be cited. Such an etching solution 201 is prepared, for example, by mixing a 0.001M KOH aqueous solution with a 0.05M K2S2O8 aqueous solution in a ratio of 1:1. It should be noted that 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.

[0041] A single KOH aqueous solution is alkaline, and a single K2S2O8 aqueous solution is acidic. Therefore, if the concentration of the KOH aqueous solution is too high (for example, set to 0.01M), the etching solution 201, which is a mixture of the KOH aqueous solution and the K2S2O8 aqueous solution, will become alkaline (hereinafter, this alkaline etching solution 201 is referred to as the etching solution 201 of the reference example). The etching solution 201 of the first example is made acidic by appropriately reducing the concentration of the KOH aqueous solution.

[0042] The PEC etching mechanism when the etching solution 201 of the first example is used is described. By irradiating the wafer 10 with UV light 221 having a wavelength of less than 365 nm, holes and electrons are generated in pairs in the GaN constituting the etched surface 20. The generated holes decompose the GaN into Ga 3+ and N2 (chemical formula 1), and further, Ga 3+ The hydroxide ion (OH - ) is oxidized to generate gallium oxide (Ga2O3) (chemical formula 2). The generated Ga2O3 is dissolved in an acid (or alkali). 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).

[0043] [Chemical formula 1]

[0044]

[0045] [Chemical formula 2]

[0046]

[0047] [Chemical formula 3]

[0048]

[0049] In addition, peroxydisulfate ions (S2O8) are generated by dissolving K2S2O8 in water. 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 and holes that are generated in pairs The free radicals react with water, decomposing the water to generate hydrogen (chemical formula 6). 2- ), the acidity of the etching solution 201 becomes stronger. Radicals can consume electrons generated in GaN and paired with holes, so PEC etching can be performed well. In addition, as PEC etching proceeds, the acidity of the etching solution 201 gradually increases (the pH gradually decreases).

[0050] [Chemical formula 4]

[0051]

[0052] [Chemical formula 5]

[0053]

[0054] [Chemical formula 6]

[0055]

[0056] As a second example of the etching solution 201, an etching solution obtained by mixing a phosphoric acid (H3PO4) aqueous solution with a potassium persulfate (K2S2O8) aqueous solution 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. It should be noted that 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.

[0057] Both the H3PO4 aqueous solution and the K2S2O8 aqueous solution are acidic. Therefore, the etching solution obtained by mixing the H3PO4 aqueous solution and the K2S2O8 aqueous solution listed as the second example is acidic at any mixing ratio.

[0058] The PEC etching mechanism when the etching solution 201 of the second example is used can be presumed to be that (Chemical Formula 1) to (Chemical Formula 3) described for the case of using the etching solution 201 of the first example are replaced by (Chemical Formula 7). In other words, GaN, holes generated by irradiation with UV light 221, and water react to generate Ga2O3, 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 removed 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.

[0059] [Chemical formula 7]

[0060]

[0061] As shown in (chemical formula 5), ​​as S2O8 2- generate 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 is efficiently generated The wavelength of the UV light 221 is preferably 200 nm or more and less than 310 nm. In other words, the UV light 221 is irradiated to efficiently generate holes in the III-nitride in the wafer 10 and to generate S2O8 in the etching solution 201. 2- generate 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 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.

[0062] By irradiation of UV light 221, S2O8 2- generate When the free radicals are generated, the distance L from the etched surface 20 of the wafer 10 to the upper surface 202 of the etching liquid 201 is preferably set to 5 mm or more and 100 mm or less. If the distance L is too short, for example, less than 5 mm, the free radicals generated in the etching liquid 201 above the wafer 10 The amount of free radicals may become unstable due to the change in the distance L. In addition, if the distance L is too long, for example, more than 100 mm, the etching liquid 201 above the wafer 10 generates free radicals that do not participate in the PEC etching and increase uselessly. Free radicals are generated, and therefore, the utilization efficiency of the etching solution 201 is reduced.

[0063] Next, an experimental example of PEC etching according to the present embodiment will be described. Figure 2 (a) and Figure 2 (b) are graphs showing the results of the first experimental example and the second experimental example, respectively. Figure 2(a) and Figure 2 (b) also shows the results of the reference experimental example.

[0064] In the first experimental example, the etching solution 201 described as the etching solution 201 of the first example, which was obtained by mixing a 0.001M KOH aqueous solution and a 0.05M K2S2O8 aqueous solution at a ratio of 1:1, was used. In the second experimental example, the etching solution 201 described as the etching solution 201 of the second example, which was obtained by mixing a 0.01M H3PO4 aqueous solution and a 0.05M K2S2O8 aqueous solution at a ratio of 1:1, was used. In the reference experimental example, the etching solution 201 described as the etching solution 201 of the reference example, which was obtained by mixing a 0.01M KOH aqueous solution and a 0.05M K2S2O8 aqueous solution at a ratio of 1:1, was used.

[0065] In this experimental example, it is measured how the pH of the etching solution changes over time by irradiating the etching solution 201 with UV light 221. The UV light 221 with a peak wavelength of 260 nm is irradiated. It should be noted that in this experimental example, the wafer 10 is not immersed in the etching solution for PEC etching, but only the pH change of the etching solution is measured. However, it can be considered that even in the case of PEC etching, the pH change of the etching solution is roughly the same.

[0066] Figure 2 (a) and Figure 2 In (b), the horizontal axis represents the time from the start of irradiation of UV light 221, and the vertical axis represents the pH of etching solution 201. The time on the horizontal axis can be regarded as the time from the start of PEC etching.

[0067] like Figure 2 As shown in (a) of the reference experimental example, the pH of the etching solution 201 of the reference example at the start time of etching is about 12, which is alkaline. As described above, by irradiation with UV light 221, SO4 in the etching solution 201 2- Therefore, the longer the etching time is, the lower the pH of the etching solution 201 will be. The etching solution 201 of the reference example has a neutral pH of 7 when the etching time is 40 minutes, and then becomes acidic.

[0068] PEC etching is performed by dissolving the generated Ga2O3 in an alkali or acid. Therefore, in the reference experimental example, etching is no longer performed during the period when the etching solution 201 is near neutral. In addition, in the reference experimental example, the pH of the etching solution 201 varies greatly over time, so the dissolution conditions of Ga2O3 vary greatly over time. Therefore, it is difficult to ensure the uniformity of PEC etching over time.

[0069] like Figure 2As shown in (a), in the first experimental example, the pH of the etching solution 201 of the first example at the etching start time is 4.4, which is acidic. Therefore, the etching solution 201 of the first example has been acidic since the etching start time. Therefore, it is possible to prevent the situation where the PEC etching does not proceed due to the etching solution 201 becoming neutral by using the etching solution 201 of the first example. In addition, compared with the case of using the etching solution 201 of the reference example, the fluctuation range of the pH during the etching period can be reduced.

[0070] like Figure 2 As shown in (b), in the second experimental example, the pH of the etching solution 201 of the second example at the etching start time is 2.3, which is acidic. Therefore, the etching solution 201 of the second example is acidic from the etching start time, similarly to the etching solution 201 of the first example. Therefore, by using the etching solution 201 of the second example, the situation where the PEC etching stops due to the etching solution 201 being neutral can be avoided, similarly to the etching solution 201 of the first example, and the pH fluctuation range during the etching period can be reduced compared to the case of using the etching solution 201 of the reference example.

[0071] As described above, in this embodiment, by using the acidic etching solution 201 at the etching start time point as in the first and second examples, the etching solution 201 is maintained in an acidic state throughout the etching period. As a result, it is possible to suppress the situation where the PEC etching does not proceed due to the etching solution 201 being neutral. In addition, compared with the case where the etching solution 201 of the reference example changes from alkaline to acidic during the etching period, the pH fluctuation range during the etching period can be reduced.

[0072] Furthermore, from the viewpoint of easily using the resist mask as the mask 50, it is also preferable to maintain the etching solution 201 in an acidic state. On the other hand, if the etching solution 201 is alkaline, the resist is easily peeled off, so it is difficult to use the resist mask as the mask 50. It should be noted that when using the acidic etching solution 201, a mask material other than the resist (silicon oxide, silicon nitride, etc.) may be used as needed.

[0073] It should be noted that a method of continuously replacing the etching solution 201 until it reaches neutrality to maintain the etching solution 201 of the reference example in an alkaline state, thereby suppressing the PEC etching from no longer proceeding, is also considered. However, in this method, the operation of replacing the etching solution 201 is complicated. By using the etching solution 201 of the first example and the second example, even if the etching solution 201 is not replaced, it is not necessary to replace the etching solution 201. In other words, the same etching solution 201 can be used to easily perform PEC etching for a long time (for example, preferably 30 minutes, more preferably 60 minutes, more preferably 90 minutes or more, and more preferably 120 minutes or more).

[0074] In addition, by not replacing the etching liquid 201, it is also possible to suppress the etching liquid 201 from being stirred. By not stirring the etching liquid 201, it is possible to increase the supply of S2O8 to the etched surface 20. 2- , The supply state of free radicals, etc. is uniform over time, so it is easy to improve the flatness of the etched surface (improve the uniformity within the surface). This also becomes an advantage when etching for a long time. It should be noted that in this embodiment, there is no need to make the etching liquid 201 still, and PEC etching can be performed while circulating (acidic) etching liquid 201 as needed. In the case of circulating etching liquid 201, it can be a method of circulating the same etching liquid 201 (without replacing the etching liquid 201) or a method of continuously supplying new etching liquid 201 (replacing the etching liquid 201).

[0075] By using the etching solution 201 of the second example, the following effects can be further obtained. In the etching solution 201 of the second example, as an acid having a dissociation constant pK greater than 0 and less than 7 a An example of a weak acid includes H3PO4. By using the etching solution 201 of the second example, the buffering effect of the weak acid can be utilized in the acidic region where the pH is greater than 0 and less than 7, so it is easy to reduce the decrease in pH during the etching period. In other words, it is easy to make the pH during the etching period nearly constant. The first acid dissociation constant pK of H3PO4 is a1 is 2.12.

[0076] Therefore, by using the etching solution 201 of the second example, the pH variation of the etching solution 201 over time can be further reduced compared to the method of using the etching solution 201 of the first example, and thus the variation of the dissolution conditions of Ga2O3 over time can be reduced. Therefore, it is easier to maintain the uniformity of PEC etching over time.

[0077] From the viewpoint of reducing the temporal variation of the pH of the etching solution 201, as a reference, the following can be set: the pH of the etching solution 201 at the time of etching completion is preferably reduced by 4 or less, more preferably 3 or less, further preferably 2 or less, further preferably 1.5 or less, further preferably 1 or less, for example.

[0078] In addition, from this point of view, as another standard, it can be set as follows. 2- All converted into SO4 2-The decrease in pH of the etching solution 201 at the time of etching is preferably, for example, 4 or less, more preferably 3 or less, further preferably 2 or less, further preferably 1.5 or less, and further preferably 1 or less.

[0079] In the etching solution 201 of the first and second examples, S2O8 2- All converted into SO4 2- The pH of the etching solution 201 at this time (in other words, the limiting pH when the etching time is extended) is about 1.5.

[0080] When the etching solution 201 of the second example contains a weak acid, it is more preferable to select the following conditions. The pH of the etching solution 201 at the start of etching is relative to the acid dissociation constant pK of the weak acid. a The difference is preferably less than ±1, more preferably less than ±0.5. The buffering effect of a weak acid is determined by the acid dissociation constant pK of the weak acid. a Therefore, by reducing the pH of the etching solution 201 at the time of etching start, the acid dissociation constant pK of the weak acid is reduced. a The difference between the two groups can easily utilize the buffering effect of the weak acid.

[0081] In addition, the pH of the etching solution 201 at the start time of etching is preferably higher than the acid dissociation constant pK of the weak acid. a As a result, as the PEC etching progresses, the pH of the etching solution 201 gradually decreases and gradually approaches the acid dissociation constant pK of the weak acid. a , therefore, it is easy to utilize the buffering effect of the weak acid for a longer period of time.

[0082] In addition, the acid dissociation constant pK of the weak acid contained in the etching solution 201 is a It is preferred that the S2O8 content in the etching solution 201 is higher than 2- All converted into SO4 2- Thus, the buffering effect of the weak acid can be utilized in the process in which the pH of the etching solution 201 gradually approaches the limiting pH.

[0083] Figure 3 (a) and Figure 3 (b) is a graph showing the results of the third experimental example, showing the relationship between etching time and etching depth in PEC etching under various conditions. The slope of the graph represents the etching rate.

[0084] Figure 3(a) shows the results of etching the object 100 formed with a mask 50 based on silicon oxide (SiO2) using the etching solution 201 of the reference example (square marks), the results of etching the object 100 formed with a mask 50 based on silicon oxide using the etching solution 201 of the second example (triangular marks), and the results of etching the object 100 formed with a mask 50 based on a resist using the etching solution 201 of the second example (circular marks). The wavelength (λ UVC ) was set to 260nm, and the irradiation intensity (I) was set to 4mW / cm 2 The distance L (d electrolyte ) is set to 5mm.

[0085] It can be seen that PEC etching can be performed at substantially the same etching rate when the etching solution 201 of the reference example is used and when the etching solution 201 of the second example is used. In addition, when the etching solution 201 of the second example is used, PEC etching can be performed at substantially the same etching rate regardless of whether the mask 50 is formed of silicon oxide or resist. It should be noted that the etching solution 201 of the reference example is alkaline, so it is difficult to use the mask 50 based on the resist.

[0086] Figure 3 (b) shows another result of etching the object 100 formed with the mask 50 made of the resist using the etching solution 201 of the second example. Figure 3 Similarly to the result shown in (a), it can be seen that PEC etching using a resist mask can be performed well by using the etching solution 201 of the second example.

[0087] Next, the fourth experimental example will be described. Figure 4 (a) is a laser microscope image showing the result of PEC etching performed using the etching solution 201 (using phosphoric acid) of the second example after forming a resist mask with a line and space pattern of 10 μm in width. The dark area in the laser microscope image indicates the etched area.

[0088] Figure 4 (b) is Figure 4 (a) shows a scanning electron microscope (SEM) image of the etched region of the sample. The root mean square (RMS) surface roughness of the etched region in a 5 μm square area is 2.76 nm.

[0089] Figure 5 (a) is Figure 4 (a) shows various data of the sample measured by atomic force microscopy (AFM). Figure 5(b) is an AFM image of another sample in which a resist mask is formed and etching is performed using the etching solution 201 (using phosphoric acid) of the second example.

[0090] Through these experimental examples, the inventors of the present application have obtained the following findings: 2- The etching solution 201, which is an oxidant that accepts electrons and is acidic from the start time of etching, can perform PEC etching. In addition, the following knowledge is obtained: in order to prepare such an etching solution 201, for example, phosphoric acid, which is a weak acid, can be preferably used. Furthermore, the inventors of the present application have also obtained the following knowledge: by using such an etching solution 201, PEC etching using a resist mask can be performed well. The use of such an etching solution 201 for PEC etching and the use of a resist mask in the PEC etching have not been proposed so far, and this is a solution first proposed by the inventors of the present application.

[0091] In summary, according to the present embodiment, by performing PEC etching using the etching solution 201 that is acidic from the start time of etching, PEC etching can be performed in which the change of etching conditions over time is suppressed, compared with the case where PEC etching is performed using the etching solution 201 that is alkaline from the start time of etching. In addition, by using such an acidic etching solution 201, it is easy to use a resist mask as the mask 50.

[0092] <Modification>

[0093] Next, a modification of the above embodiment will be described. In the above embodiment, the etching solution 201 ( Figure 2 (a)), thus comparing with the case where the etching solution 201 of the second example is used ( Figure 2 In this modification, a method in which the pH at the start time of etching is higher than that at the start time of etching, in other words, a method in which the pH fluctuation range during etching is larger. In this modification, a method in which the pH at the start time of etching can be lowered even when the etching solution 201 of the first example is used, in other words, a method in which the pH fluctuation range during etching can be reduced is exemplified.

[0094] Figure 6 2 is a schematic diagram of a PEC etching apparatus 200 illustrating a pre-processing step added in this modification. The pre-processing step is a step of etching the wafer 10 ( Figure 1 Before (b), when the wafer 10 is not immersed in the etching solution 201, the etching solution 201 is irradiated with UV light 221 to make S2O8 2- Part of it is converted into SO4 2- , thereby lowering the pH of the etching solution 201.

[0095] Specifically, for example, Figure 2(a) When the etching solution 201 of the first example is used, the pH of the etching solution 201 is reduced to 2.5 by irradiating the UV light 221 for 20 minutes before the etching starts. Thereafter, the wafer 10 is immersed in the etching solution 201 to start etching, whereby the pH at the time of the etching start is, for example, 2.5.

[0096] In this modification, the etching is started after the pH of the etching solution 201 is reduced to a predetermined pH by the pretreatment step. Thus, compared with the case where the pretreatment step is not performed, the pH reduction range from the etching start time point to the etching end time point can be reduced, thereby suppressing the change of the etching conditions.

[0097] <Other Implementation Methods>

[0098] The embodiments and modifications of the present invention have been specifically described above. However, the present invention is not limited to the above-described embodiments and modifications, and various changes, improvements, combinations, etc. can be made within the scope of the gist thereof.

[0099] For example, containing S2O8 2- The etching solution 201 that is acidic at the start of etching is not limited to the etching solutions of the first and second examples. For example, only a K2S2O8 aqueous solution may be used as such an etching solution 201. In this case, the concentration of the K2S2O8 aqueous solution may be set to 0.025M, for example.

[0100] In the above description, potassium persulfate (K2S2O8) is used as an example to supply S2O8. 2- But S2O8 2- It can also be supplied by other substances such as sodium peroxodisulfate (Na2S2O8), ammonium peroxodisulfate (ammonium persulfate, (NH4)2S2O8), etc.

[0101] It should be noted that 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 is 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). In other words, holes are generated by irradiating UV light 221, thereby generating Al oxides or In oxides, and these oxides are dissolved in acid (or alkali), thereby enabling PEC etching. The peak wavelength (below 365nm) of the 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, UV light with a shorter wavelength can be used, and when In is contained, UV light with a longer wavelength can also be used. It should be noted that the group III nitride to be PEC-etched can be added with impurities such as conductivity-determining impurities as needed.

[0102] <Preferred Mode of the Invention>

[0103] Hereinafter, preferred embodiments of the present invention will be described.

[0104] (Note 1)

[0105] A method for manufacturing a structure, comprising the following steps:

[0106] A step of preparing an etching object having at least a surface composed of a group III nitride; and

[0107] The step of irradiating the surface of the etching object with ultraviolet light through the etching solution while the etching object is immersed in an etching solution containing peroxydisulfate ions, thereby generating sulfate ion radicals from the peroxydisulfate ions and generating holes in the group III nitride, thereby etching the group III nitride.

[0108] In the step of etching the group III nitride, the etching solution is acidic at the start time of etching the group III nitride, thereby maintaining the etching solution in an acidic state while the group III nitride is being etched.

[0109] (Note 2)

[0110] According to the method for manufacturing a structure described in Appendix 1, the decrease in the pH of the etching solution at the end time of the etching relative to the pH of the etching solution at the start time is preferably 4 or less, more preferably 3 or less, further preferably 2 or less, further preferably 1.5 or less, and further preferably 1 or less.

[0111] (Note 3)

[0112] The method for producing a structure according to Appendix 1 or 2, wherein the decrease in the pH of the etching solution when all the peroxodisulfate ions contained in the etching solution are converted into sulfate ions relative to the pH of the etching solution at the starting time is preferably 4 or less, more preferably 3 or less, further preferably 2 or less, further preferably 1.5 or less, and further preferably 1 or less.

[0113] (Note 4)

[0114] The method for producing a structure according to any one of Supplementary Notes 1 to 3, wherein the etching solution contains an acid having a dissociation constant pK greater than 0 and less than 7. a of weak acid.

[0115] (Note 5)

[0116] The method for producing a structure according to Supplementary Note 4, wherein the weak acid is phosphoric acid.

[0117] (Note 6)

[0118] The method for manufacturing a structure according to Supplement 4 or 5, wherein the pH of the etching solution at the start time is relative to the acid dissociation constant pK of the weak acid. a The difference is preferably ±1 or less, more preferably ±0.5 or less.

[0119] (Note 7)

[0120] The method for producing a structure according to any one of Supplementary Notes 4 to 6, wherein the pH of the etching solution at the start time is higher than the acid dissociation constant pK of the weak acid. a .

[0121] (Note 8)

[0122] The method for producing a structure according to any one of Appendixes 4 to 7, wherein the acid dissociation constant pK of the weak acid is a The pH of the etching solution is higher than the pH of the etching solution when all the peroxodisulfate ions contained in the etching solution are converted into sulfate ions.

[0123] (Note 9)

[0124] The method for producing a structure according to any one of Supplementary Notes 1 to 8, wherein the etching solution is not replaced while the group III nitride is being etched.

[0125] (Note 10)

[0126] The method for producing a structure according to any one of Supplementary Notes 1 to 9, wherein the etching solution is not stirred while the group III nitride is being etched.

[0127] (Note 11)

[0128] The method for producing a structure according to any one of Appendixes 1 to 10, wherein the period for etching the group III nitride is preferably 30 minutes, more preferably 60 minutes, further preferably 90 minutes or longer, further preferably 120 minutes or longer.

[0129] (Note 12)

[0130] The method for producing a structured body according to any one of Supplementary Notes 1 to 11, wherein the pH of the etching solution is measured while the Group III nitride is being etched.

[0131] (Note 13)

[0132] The method for manufacturing a structure according to Supplementary Note 12, wherein, when measuring the pH of the etching solution, the probe is arranged at a position where a shadow of the probe of the pH meter caused by the ultraviolet light is not cast on the surface of the etching object.

[0133] (Note 14)

[0134] The method for manufacturing a structure according to any one of Appendixes 1 to 13 further comprises the step of, before the step of etching the group III nitride, converting a portion of the peroxydisulfate ions into sulfate ions by irradiating the etching solution with ultraviolet light while the etching object is not immersed in the etching solution, thereby lowering the pH of the etching solution.

[0135] (Note 15)

[0136] The method for producing a structure according to any one of Supplementary Notes 1 to 14, wherein in the step of etching the group III nitride, the etching is performed with a mask formed on the surface (on a part of the surface).

[0137] (Note 16)

[0138] The method for manufacturing a structure according to Supplementary Note 15, wherein the mask is a resist mask.

[0139] (Note 17)

[0140] An intermediate structure having:

[0141] An etching object having at least a surface composed of a group III nitride; and

[0142] a mask formed on the aforementioned surface (on a portion of the aforementioned surface),

[0143] The intermediate structure is immersed in an acidic etching solution containing peroxydisulfate ions.

[0144] (Note 18)

[0145] The intermediate structure according to Supplementary Note 17, wherein the mask is a resist mask.

[0146] (Note 19)

[0147] The intermediate structure according to Supplementary Note 17 or 18, wherein the surface is irradiated with ultraviolet light via the etching solution.

[0148] Description of Reference Numerals

[0149] 10 ... etching object, 20 ... etching surface, 20, 21 ... etching region, 50 ... mask, 100 ... processing object, 200 ... PEC etching device, 201 ... etching solution, 202 ... upper surface of etching solution, 210 ... container, 220 ... light source, 221 ... UV light, 230 ... pH meter, 231 ... probe, 240 ... support table

Claims

1. A method for manufacturing a structure, comprising the following steps: A step of preparing an etching object having at least a surface composed of a group III nitride; and The step of irradiating the surface of the etching object with light through the etching solution while the etching object is immersed in an etching solution containing peroxydisulfate ions, thereby generating sulfate ion radicals from the peroxydisulfate ions and generating holes in the group III nitride, thereby etching the group III nitride. In the step of etching the group III nitride, the etching solution is acidic at the start time of etching the group III nitride, thereby maintaining the etching solution in an acidic state during the period when the group III nitride is etched. The etching is performed with a resist mask formed on the surface. in, The decrease in pH of the etching solution at the end time of the etching relative to the pH of the etching solution at the start time is 4 or less.

2. The method for manufacturing a structure according to claim 1, in, The etching is performed so that the root mean square surface roughness in a 5 μm square region of the surface etched by the irradiation of the light is 2.76 nm or less.

3. The method for manufacturing a structure according to claim 2, wherein: The decrease in pH of the etching solution at the end time of the etching relative to the pH of the etching solution at the start time is 3 or less.

4. The method for producing a structure according to any one of claims 1 to 3, wherein: When all the peroxodisulfate ions contained in the etching solution are converted into sulfate ions, the pH of the etching solution decreases by 4 or less relative to the pH of the etching solution at the start time.

5. The method for producing a structure according to any one of claims 1 to 3, wherein: The etching solution contains a weak acid having an acid dissociation constant pKa greater than 0 and less than 7.

6. The method for manufacturing a structure according to claim 5, wherein: The weak acid is phosphoric acid.

7. The method for manufacturing a structure according to claim 5, wherein: The difference between the pH of the etching solution at the start time and the acid dissociation constant pKa of the weak acid is ±1 or less.

8. The method for manufacturing a structure according to claim 5, wherein: The pH of the etching solution at the starting time point is higher than the acid dissociation constant pKa of the weak acid.

9. The method for manufacturing a structure according to claim 5, wherein: The acid dissociation constant pKa of the weak acid is higher than the pH of the etching solution when all the peroxodisulfate ions contained in the etching solution are converted into sulfate ions.

10. The method for producing a structure according to any one of claims 1 to 3, wherein: During the period in which the group III nitride is etched, the etching solution is not replaced.

11. The method for producing a structure according to any one of claims 1 to 3, wherein: During the period in which the group III nitride is etched, the etching solution is not stirred.

12. The method for producing a structure according to any one of claims 1 to 3, wherein: The period during which the group III nitride is etched is 30 minutes or more.

13. The method for producing a structure according to any one of claims 1 to 3, wherein: The pH of the etching solution is measured while the group III nitride is being etched.

14. The method for manufacturing a structure according to claim 13, wherein: When measuring the pH of the etching solution, the probe of the pH meter is arranged at a position where a shadow of the probe due to the light is not projected on the surface of the etching object.

15. The method for manufacturing a structure according to any one of claims 1 to 3, further comprising the step of converting a portion of the peroxydisulfate ions into sulfate ions by irradiating the etching solution with light while the etching object is not immersed in the etching solution, thereby lowering the pH of the etching solution.

16. A device for manufacturing a structure, comprising: A container configured to accommodate an object to be etched in a state where the object is immersed in an acidic etching solution containing peroxodisulfate ions, wherein at least a surface of the object to be etched is composed of a group III nitride and a resist mask is formed on the surface; and a light source configured to start irradiating light to the surface of the etching object through the etching liquid when the etching liquid is acidic; in, The decrease in pH of the etching solution at the end of etching is 4 or less relative to the decrease in pH of the etching solution at the start of etching.

17. The manufacturing device of the structure according to claim 16, wherein: The manufacturing device is configured as follows: in the container, while the etching object is immersed in the etching solution, the light is irradiated on the surface of the etching object, and the surface of the etching object is etched so that the root mean square surface roughness within a 5 μm square area of ​​the surface is less than 2.76 nm.

18. The manufacturing device of a structure according to claim 16, wherein: The manufacturing apparatus includes a pH meter for measuring the pH of the etching solution. The probe of the pH meter is disposed at a position where a shadow of the probe caused by the light is not projected on the surface of the etching object.

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