JP6694102B1 - Structure manufacturing method, manufacturing apparatus, and intermediate structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of suppressing temporal variation of etching conditions in PEC etching for group III nitrides. A method for manufacturing a structure includes a step of preparing an etching object having at least a surface composed of a group III nitride, and a step of immersing the etching object in an etching solution containing peroxodisulfate ions. , Etching the group III nitride by irradiating the surface of the object to be etched with light through an etching solution to generate a sulfate ion radical from peroxodisulfate ion and to generate a hole in the group III nitride. In the step of etching the group III nitride, the etching solution is made acidic at the start of the etching of the group III nitride, so that the etching solution during the etching of the group III nitride is performed. Keeps it acidic. [Selection diagram] Figure 2

Description

  The present invention relates to a method for manufacturing a structure and an intermediate structure.

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

  Photoelectrochemical (PEC) etching has been proposed as an etching technique for forming various structures in group III nitrides such as GaN (see Non-Patent Document 1, for example). PEC etching is wet etching that causes less damage than general dry etching, and damage such as neutral particle beam etching (for example, see Non-Patent Document 2) and atomic layer etching (for example, see Non-Patent Document 3). It is preferable in that the apparatus is simpler than special dry etching with less energy consumption.

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. S. Samukawa, JJAP, 45 (2006) 2395. T. Faraz, ECS J. Solid Stat. Scie. & Technol., 4, N5023 (2015).

  An object of the present invention is to provide a technique capable of suppressing temporal fluctuation of etching conditions in PEC etching for group III nitrides.

According to one aspect of the invention,
Providing an etching object having at least a surface composed of a group III nitride,
The object to be etched is immersed in an etching solution containing peroxodisulfate ions, and the surface of the object to be etched is irradiated with ultraviolet light through the etching solution to convert the peroxodisulfate ions to sulfate ions. Etching radicals in the group III-nitride by generating radicals and holes in the group III-nitride,
Have
In the step of etching the group III-nitride, the etching solution is made acidic during the period when the group III-nitride is etched by making the etching solution acidic at the start of etching the group III-nitride. A method of manufacturing a structure is provided that maintains a state.

According to another aspect of the invention,
An etching object having at least a surface composed of a group III nitride;
A mask formed on the surface,
Have
An intermediate structure is provided that is immersed in an acidic etchant containing peroxodisulfate ions.

  Provided is a technique capable of suppressing temporal variation in etching conditions in PEC etching for group III nitrides.

1A is a schematic cross-sectional view illustrating an etching target according to an embodiment of the present invention, and FIG. 1B is a schematic view of a PEC etching apparatus illustrating a PEC etching process according to an embodiment. Is. FIG. 2A is a graph showing the results of the first experimental example, and FIG. 2B is a graph showing the results of the second experimental example. FIG. 3A and FIG. 3B are graphs showing the results of the third experimental example. FIG. 4A is a laser microscope image showing the result of the fourth experimental example, and FIG. 4B is an SEM image showing the result of the fourth experimental example. FIG. 5A is various data of AFM measurement showing the result of the fourth experimental example, and FIG. 5B is an AFM image showing the result of the fourth experimental example. FIG. 6 is a schematic diagram of a PEC etching apparatus illustrating a pretreatment process according to a modification.

<One Embodiment of the Present Invention>
A method of manufacturing a structure according to an embodiment of the present invention will be described. In the manufacturing method according to the present embodiment, an etching process using photoelectrochemical (PEC) etching for an etching target 10 (hereinafter, also referred to as a wafer 10) that is a material of the structure (hereinafter, also referred to as a PEC etching process). Have. Hereinafter, the PEC etching is also simply referred to as etching.

  FIG. 1A is a schematic sectional view illustrating a wafer 10 to be PEC-etched. First, as shown in FIG. 1A, a wafer 10 is prepared. At least the surface 20 (the surface to be etched 20 to be etched) of the wafer 10 is composed of a group III nitride.

The structure of the wafer 10 is not particularly limited. As an example of the structure of the wafer 10 (the one used in the experimental example described later), there is a laminated 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, for example, an n-type impurity concentration of 5 × 10 ¹⁶ / cm ³ and a thickness of 3 μm.

  The target of the PEC etching process, that is, the target immersed (contacted) in the etching solution 201 is referred to as a target 100. The processing object 100 includes at least the wafer 10 and may further include, for example, a mask 50 as a member required for the PEC etching process. The mask 50 is formed on the surface 20 to be etched of the wafer 10 in a pattern in which a region 21 to be etched is opened. The material of the mask 50 is not particularly limited as long as it is a material that withstands the etching liquid 201 and functions as a mask, and may be, for example, a resist, silicon oxide, or silicon nitride, It may also be a metal such as titanium. The shape, width, depth of etching, etc. of the region 21 to be etched may be appropriately selected as necessary. The processing object 100 can be regarded as an intermediate stage structure (intermediate structure) for obtaining a final structure.

  FIG. 1B is a schematic sectional view of the PEC etching apparatus 200 showing the PEC etching step. The PEC etching apparatus 200 includes a container 210 that stores the etching solution 201 and a light source 220 that emits ultraviolet (UV) light 221. The PEC etching apparatus 200 may include a support 240 on which the wafer 10 is placed at a predetermined height.

  In the PEC etching step, by irradiating the surface 20 to be etched with the UV light 221 through the etching liquid 201 in a state where the processing object 100 (that is, the wafer 10) is immersed in the etching liquid 201, The group III nitride forming the etching surface 20 is etched. Details of the etching solution 201, the UV light 221, and the mechanism of PEC etching will be described later.

  The PEC etching apparatus 200 preferably further includes a pH meter 230. It is preferable to perform the PEC etching step while measuring whether or not the pH of the etching solution 201 is within a proper range with the pH meter 230. At this time, it is preferable to dispose the probe 231 at a position where the shadow of the UV light 221 of the probe 231 of the pH meter 230 is not reflected on the surface 20 to be etched.

  The method for manufacturing the structure according to the present embodiment may include other steps, such as electrode formation and protective film formation, as necessary.

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

The etching solution 201 contains oxygen used for producing an oxide of a group III element contained in the group III nitride constituting the surface to be etched 20, and further contains peroxodisulfate ion (S ₂ as an oxidizing agent for receiving electrons). An etching solution 201 containing O ₈ ²⁻ ) is used. In addition, as the etching solution 201 in the present embodiment, the etching solution 201 that is acidic at the time of starting the etching of the group III nitride forming the surface to be etched 20 is used.

A first example of the etching solution 201 is a mixture of an aqueous potassium hydroxide (KOH) solution and an aqueous potassium peroxodisulfate (K ₂ S ₂ O ₈ ) solution. Such an etching solution 201 is prepared, for example, by mixing a 0.001 M KOH aqueous solution and a 0.05 M K ₂ S ₂ O ₈ aqueous solution at a ratio of 1: 1. The concentration of the KOH aqueous solution, the concentration of the K ₂ S ₂ O ₈ aqueous solution, and the mixing ratio of these aqueous solutions may be appropriately adjusted as necessary.

A simple KOH aqueous solution is alkaline, and a simple K ₂ S ₂ O ₈ aqueous solution is acidic. Therefore, if the concentration of the KOH aqueous solution is excessively high (for example, 0.01 M), the etching solution 201 in which the KOH aqueous solution and the K ₂ S ₂ O ₈ aqueous solution are mixed becomes alkaline (such a case). Hereinafter, the alkaline etching solution 201 is also referred to as the etching solution 201 of the reference example). The etching solution 201 of the first example makes the concentration of the KOH aqueous solution appropriately low to make the etching solution 201 in which the KOH aqueous solution and the K ₂ S ₂ O ₈ aqueous solution are mixed, acidic.

The PEC etching mechanism when using the etching liquid 201 of the first example will be described. By irradiating the wafer 10 with the UV light 221 having a wavelength of 365 nm or less, a pair of holes and electrons is generated in the GaN forming the surface 20 to be etched. The generated holes decompose GaN into Ga ³⁺ and N ₂ (chemical ^formula 1), and Ga ³⁺ is further oxidized by hydroxide ions (OH ⁻ ) to generate gallium oxide (Ga ₂ O ₃ ). Yes (chemical formula 2). Then, the generated Ga ₂ O ₃ is dissolved in acid (or alkali). In this way, PEC etching of GaN is performed. The generated holes react with water to decompose the water, and oxygen is generated (Chemical Formula 3).

Further, K ₂ S ₂ O ₈ is dissolved in water to generate peroxodisulfate ion (S ₂ O ₈ ²⁻ ) (Chemical formula 4), and S ₂ O ₈ ²⁻ is irradiated with UV light 221. Sulfate ion radicals (SO ₄ ^{− *} radicals) are generated at (Chemical formula 5). The electrons generated in pairs with the holes react with water together with the SO ₄ ^{− *} radicals to decompose water, thereby generating hydrogen (chemical formula 6). At this time, sulfuric acid ions (SO ₄ ²⁻ ) are generated, so that the acidity of the etching liquid 201 becomes strong. As described above, in the PEC etching of the present embodiment, by using SO ₄ ^{− *} radicals, electrons generated in pairs with holes in GaN can be consumed, so that PEC etching can be favorably advanced. it can. Then, as the PEC etching progresses, the acidity of the etching solution 201 becomes stronger (the pH decreases).

A second example of the etching solution 201 is a mixture of a phosphoric acid (H ₃ PO ₄ ) aqueous solution and a potassium peroxodisulfate (K ₂ S ₂ O ₈ ) aqueous solution. Such an etching solution 201 is prepared, for example, by mixing 0.01M H ₃ PO ₄ aqueous solution and 0.05M K ₂ S ₂ O ₈ aqueous solution at a ratio of 1: 1. The concentration of the H ₃ PO ₄ aqueous solution, the concentration of the K ₂ S ₂ O ₈ aqueous solution, and the mixing ratio of these aqueous solutions may be appropriately adjusted as necessary.

Both the H ₃ PO ₄ aqueous solution and the K ₂ S ₂ O ₈ aqueous solution are acidic. Therefore, the etching solution in which the H ₃ PO ₄ aqueous solution and the K ₂ S ₂ O ₈ aqueous solution, which are given as the second example, are mixed is acidic at an arbitrary mixing ratio.

Regarding the PEC etching mechanism when the etching solution 201 of the second example is used, it is assumed that (Chemical formula 1) to (Chemical formula 3) described in the case of using the etching liquid 201 of the first example are replaced by (Chemical formula 7). To be done. That is, by reacting GaN, the hole generated by irradiation with the UV light 221, and water, Ga ₂ O ₃ , hydrogen ions (H ⁺ ), and N ₂ are generated (Chemical Formula 7). ). Then, the generated Ga ₂ O ₃ is dissolved in the acid. In this way, PEC etching of GaN is performed. Note that, as shown in (Chemical Formula 4) to (Chemical Formula 6), the mechanism in which electrons generated in pairs with holes are consumed by S ₂ O ₈ ²⁻ is different from the case where the etching liquid 201 of the first example is used. It is the same.

As shown in Chemical formula 5, at least one of irradiation with UV light 221 and heating can be used as a method for generating SO ₄ ^{− *} radicals from S ₂ O ₈ ²⁻ . When the irradiation with the UV light 221 is used, the wavelength of the UV light 221 is set to be 200 nm or more and less than 310 nm in order to increase the light absorption by S ₂ O ₈ ²⁻ and efficiently generate SO ₄ ^{− *} radicals. Is preferred. That is, by irradiation with the UV light 221, holes are efficiently generated in the group III nitride on the wafer 10 and SO ₄ ^{− *} radicals are efficiently generated from S ₂ O ₈ ²⁻ in the etching solution 201. From the viewpoint, the wavelength of the UV light 221 is preferably 200 nm or more and less than 310 nm. When generating SO ₄ ^{− *} radicals from S ₂ O ₈ ²⁻ by heating, the wavelength of the UV light 221 may be 310 nm or more (at 365 nm or less).

When S ₂ O ₈ ²⁻ produces SO ₄ ^{− *} radicals by irradiation with UV light 221, the distance L from the surface 20 to be etched of the wafer 10 to the upper surface 202 of the etching solution 201 is, for example, 5 mm or more and 100 mm or less. Preferably. If the distance L is too short, for example, less than 5 mm, the amount of SO ₄ ^{− *} radicals generated in the etching liquid 201 above the wafer 10 may become unstable due to the fluctuation of the distance L. Further, if the distance L is excessively long, for example, more than 100 mm, in the etching liquid 201 above the wafer 10, a large amount of SO ₄ ^{− *} radicals that do not contribute to the PEC etching are unnecessarily generated, so that the etching liquid 201 is used. Efficiency is reduced.

  Next, an experimental example relating to the PEC etching of this embodiment will be described. FIG. 2A and FIG. 2B are graphs showing the results of the first experimental example and the second experimental example, respectively. 2A and 2B also show the results of the reference experimental example.

In the first experimental example, the etching solution 201 in which the 0.001M KOH aqueous solution and the 0.05M K ₂ S ₂ O ₈ aqueous solution were mixed at 1: 1 described as the etching solution 201 of the first example was used. Using. In the second experimental example, the 1M etching of the 0.01M H ₃ PO ₄ aqueous solution and the 0.05M K ₂ S ₂ O ₈ aqueous solution described as the etching solution 201 of the second example was performed. Liquid 201 was used. In the reference experiment example, the etching solution 201 in which the 0.01 M KOH aqueous solution and the 0.05 M K ₂ S ₂ O ₈ aqueous solution were mixed at 1: 1 was used as the etching solution 201 of the reference example. ..

  In this experimental example, by irradiating the etching solution 201 with the UV light 221, it was measured how the pH of the etching solution changes with time. UV light 221 having a peak wavelength of 260 nm was irradiated. In addition, in this experimental example, the wafer 10 is not immersed in the etching solution to perform the PEC etching, and only the pH change of the etching solution is measured. It is considered that the change in pH is almost the same.

  2A and 2B, the horizontal axis represents the time from the start of irradiation with the UV light 221 and the vertical axis represents the pH of the etching solution 201. The time on the horizontal axis can be regarded as the time from the start of PEC etching.

As shown in FIG. 2A, in the reference experimental example, the etching solution 201 of the reference example has a pH of about 12 at the start of etching and is alkaline. As described above, the irradiation of the UV light 221 increases the amount of SO ₄ ²⁻ in the etching solution 201. Therefore, the longer the etching time, the lower the pH of the etching solution 201. The etching solution 201 of the reference example has a pH of 7 when the etching time is 40 minutes and becomes acidic after that.

The PEC etching proceeds by dissolving the generated Ga ₂ O ₃ in an alkali or an acid. Therefore, in the reference experimental example, the etching does not proceed while the etching solution 201 is near neutral. Further, in the reference experimental example, since the pH of the etching solution 201 fluctuates largely with time, the Ga ₂ O ₃ dissolution conditions vary greatly with time. Therefore, it is difficult to maintain the temporal uniformity of PEC etching.

  As shown in FIG. 2A, in the first experimental example, the etching solution 201 of the first example has a pH of 4.4 and is acidic at the start of etching. Therefore, the etching solution 201 of the first example is acidic from the start of etching. Therefore, by using the etching liquid 201 of the first example, it is possible to prevent the PEC etching from stopping due to the etching liquid 201 becoming neutral. Further, the fluctuation range of the pH during the etching period can be reduced as compared with the case where the etching solution 201 of the reference example is used.

  As shown in FIG. 2B, in the second experimental example, the etching solution 201 of the second example has a pH of 2.3 and is acidic at the start of etching. Therefore, like the etching solution 201 of the first example, the etching solution 201 of the second example is acidic from the start of etching. Therefore, by using the etching solution 201 of the second example, as in the etching solution 201 of the first example, the PEC etching does not progress due to the etching solution 201 becoming neutral. In addition, the fluctuation range of the pH during the etching period can be reduced as compared with the case where the etching liquid 201 of the reference example is used.

  As described above, in the present embodiment, as in the first and second examples, by using the acidic etching solution 201 at the start of etching, the state where the etching solution 201 is acidic over the entire etching period is maintained. maintain. This can prevent the PEC etching from stopping due to the etching liquid 201 becoming neutral. Further, as compared with the case where the etching liquid 201 of the reference example is used, during which the etching liquid 201 changes from alkaline to acidic, the fluctuation range of the pH during the etching period can be reduced.

  Further, maintaining the etching solution 201 in an acidic state is preferable from the viewpoint of facilitating the use of a resist mask as the mask 50. On the other hand, when the etching solution 201 is alkaline, the resist is easily peeled off, and thus it is difficult to use the resist mask as the mask 50. When the acidic etching solution 201 is used, a mask material (silicon oxide, silicon nitride, etc.) other than the resist may be used if necessary.

  In addition, in order to maintain the alkaline state of the etching solution 201 of the reference example, it is possible to consider a mode in which the PEC etching is prevented from progressing by continuing to exchange the etching solution 201 before reaching neutrality. However, in this aspect, the labor for exchanging the etching solution 201 is complicated. By using the etching solution 201 of the first example and the second example, it is possible to perform a long time (for example, preferably 30 minutes, more preferably 60 minutes, still more preferably 90 minutes) without exchanging the etching solution 201. As described above, more preferably 120 minutes or more) can be easily performed without exchanging the etching solution 201, that is, using the same etching solution 201.

Further, by not exchanging the etching solution 201, it is possible to suppress the stirring of the etching solution 201. By not stirring the etching liquid 201, it is possible to enhance temporal uniformity of the supply state of S ₂ O ₈ ²⁻ , SO ₄ ^{− *} radicals and the like to the surface to be etched 20, and thus etching was performed. It becomes easy to improve the flatness of the surface (improve in-plane uniformity). This is also an advantage when etching for a long time. In the present embodiment, it is not essential to keep the etching solution 201 stationary, and PEC etching may be performed while flowing the (acidic) etching solution 201 as necessary. When the etching solution 201 is supplied, the same etching solution 201 may be circulated (the etching solution 201 is not replaced), or new etching solution 201 may be continuously supplied (the etching solution 201 is replaced). It may be.

By using the etching liquid 201 of the second example, the following effects can be further obtained. Etchant 201 of the second example, as an example of a weak acid having greater than 0 less than 7 acid dissociation constant pK _a, including H 3 PO _4. By using the etching solution 201 of the second example, the buffering action of the weak acid can be utilized in the acidic region where the pH is more than 0 and less than 7, so that the decrease range of the pH during the etching period is reduced, in other words, during the etching period. It becomes easy to bring the pH of the solution close to a constant value. The first acid dissociation constant pK _a1 of H ₃ PO ₄ is 2.12.

Therefore, by using the etching solution 201 of the second example, it is possible to further reduce the temporal variation of the pH of the etching solution 201, as compared with the aspect using the etching solution 201 of the first example, and thus the Ga ₂ O ₃ content of It is possible to reduce temporal fluctuations in the dissolution conditions. Therefore, it becomes easier to maintain the temporal uniformity of the PEC etching.

  From the viewpoint of reducing the temporal change in the pH of the etching solution 201, one guideline can be stated as follows. The decrease range of the pH of the etching solution 201 at the end of etching with respect to the pH of the etching solution 201 at the start of etching is, for example, preferably 4 or less, more preferably 3 or less, still more preferably 2 or less, still more preferably 1.5. Hereafter, it is more preferable to set it to 1 or less.

In addition, from this point of view, as another standard, the following can be said. The decrease range of the pH of the etching solution 201 with respect to the pH of the etching solution 201 at the start of etching is, for example, preferably 4 or less when the S ₂ O ₈ ²⁻ contained in the etching solution 201 is changed to SO ₄ ^2−. , More preferably 3 or less, further preferably 2 or less, further preferably 1.5 or less, and further preferably 1 or less.

In the etching solutions 201 of the first and second examples, the pH of the etching solution 201 when S ₂ O ₈ ²⁻ is all changed to SO ₄ ²⁻ (that is, the limit when the etching time is increased) PH is about 1.5).

When a weak acid is contained like the etching liquid 201 of the second example, it is more preferable to select the following conditions. The pH of the etching solution 201 in the etching starting time, difference from the acid dissociation constant pK _a of the weak acid, for example, preferably ± 1 or less, more preferably is at plus or minus 0.5. Buffering action of a weak acid is greater in the vicinity of the acid dissociation constant pK _a of the weak acid. Therefore, the pH of the etching solution 201 in the etching starting time, by reducing the difference from the acid dissociation constant pK _a of the weak acid, it is easy to utilize the buffering effect of the weak acid.

Further, pH of the etching solution 201 in the etching start point is preferably higher than the acid dissociation constant pK _a of the weak acid. Thus, as the PEC etching proceeds, gradually pH of the etching solution 201 is reduced, because the approaches the acid dissociation constant pK _a of the weak acid, it is easily to longer use the buffer action of the weak acid Become.

The acid dissociation constant pK _a of the weak acid contained in the etching solution 201, pH of the etching solution 201 in the case where the _S ² _O ^{8 2-} contained in the etching solution 201 changes all the _SO ^{4 2-(hereinafter,} extreme (Also referred to as pH). As a result, the buffer action of the weak acid can be utilized while the pH of the etching liquid 201 approaches the extreme pH.

  FIG. 3A and FIG. 3B are graphs showing the results of the third experimental example, showing the relationship between the etching time and the etching depth in PEC etching under various conditions. The slope of the graph represents the etching rate.

In FIG. 3A, the result (square plot) of etching of the processing object 100 on which the mask 50 made of silicon oxide (SiO ₂ ) is formed by the etching solution 201 of the reference example, and the mask 50 made of silicon oxide. The etching result (triangle plot) of the second example etching liquid 201 on the processed object 100 on which the mask was formed, and the second example etching liquid 201 on the processed object 100 on which the resist mask 50 was formed. The results of etching (circular plot) are shown. The wavelength of the UV light 221 (λ _UVC ) was 260 nm, and the irradiation intensity (I) was 4 mW / cm ² . The distance L (d _electrolyte ) from the surface 20 to be etched to the upper surface 202 of the etching solution 201 was 5 mm.

  It can be seen that PEC etching can be performed at substantially the same etching rate when the etching liquid 201 of the reference example is used and when the etching liquid 201 of the second example is used. Further, when the etching liquid 201 of the second example is used, it can be seen that PEC etching can be performed at substantially the same etching rate regardless of whether the mask 50 is formed of silicon oxide or resist. Since the etching liquid 201 of the reference example is alkaline, it is difficult to use the resist mask 50.

  FIG. 3B shows another result obtained by performing etching with the etching liquid 201 of the second example on the processing target 100 on which the resist mask 50 is formed. Similar to the result shown in FIG. 3A, it can be understood that the PEC etching using the resist mask can be favorably performed by using the etching liquid 201 of the second example.

  Next, a fourth experimental example will be described. FIG. 4A is a laser microscope image showing the result of forming a resist mask having a line-and-space pattern with a width of 10 μm and performing PEC etching with the etchant 201 (using phosphoric acid) of the second example. .. The dark areas of the laser microscope image show the etched areas.

  FIG. 4B is a scanning electron microscope (SEM) image of the etched region of the sample shown in FIG. The root mean square (RMS) surface roughness of the etched area in a 5 μm square area was 2.76 nm.

  FIG. 5A shows various data obtained by atomic force microscope (AFM) measurement of the sample shown in FIG. FIG. 5B is an AFM image of another sample in which a resist mask is formed and etching is performed using the etching liquid 201 (using phosphoric acid) of the second example.

From these experimental examples, the inventors of the present application have found that PEC etching can be performed by using S ₂ O ₈ ²⁻ as an oxidant that receives electrons and using the etching solution 201 that is acidic from the start of etching. Obtained. Moreover, in order to prepare such an etching solution 201, it was found that phosphoric acid, which is a weak acid, can be preferably used. Furthermore, the inventor of the present application has also found that it is possible to favorably perform PEC etching using a resist mask by using such an etching solution 201. Performing PEC etching using such an etching solution 201 and using a resist mask for the PEC etching have not been proposed so far, and are the first proposals made by the present inventor.

  As described above, according to the present embodiment, the PEC etching is performed using the etching solution 201 that is acidic from the etching start time, and thus the PEC etching is performed using the etching solution 201 that is alkaline at the etching start time. Compared with the case, it is possible to perform PEC etching in which the time variation of etching conditions is suppressed. Further, by using such an acidic etching solution 201, it becomes easy to use a resist mask as the mask 50.

<Modification>
Next, a modified example of the above embodiment will be described. In the above-described embodiment, by using the etching liquid 201 of the first example (FIG. 2A), compared to the case of using the etching liquid 201 of the second example (FIG. 2B), the etching start time The mode in which the pH is high, that is, the range in which the fluctuation range of the pH during the etching period is large is exemplified. In this modification, a mode in which the pH at the start of etching can be lowered even when the etching liquid 201 of the first example is used, that is, a range in which the fluctuation range of the pH during the etching period can be reduced is exemplified.

FIG. 6 is a schematic view of the PEC etching apparatus 200, which illustrates the pretreatment process added in this modification. In the pretreatment step, before the step of etching the wafer 10 (FIG. 1B), the etching liquid 201 is irradiated with UV light 221 in a state where the wafer 10 is not immersed in the etching liquid 201, This is a step of lowering the pH of the etching liquid 201 by changing a part of S ₂ O ₈ ²⁻ to SO ₄ ²⁻ .

  Specifically, for example, as understood from FIG. 2A, when the etching solution 201 of the first example is used, irradiation of the UV light 221 is performed for 20 minutes before the etching is started, whereby the pH of the etching solution 201 is changed. To 2.5. Then, by immersing the wafer 10 in the etching liquid 201 and starting the etching, the pH at the start of the etching becomes 2.5, for example.

  In this modification, the pH of the etching liquid 201 is lowered to a predetermined pH in advance by the pretreatment step, and then the etching is started. As a result, as compared with the case where the pretreatment step is not performed, the range of decrease in pH can be reduced from the etching start time to the etching end time, and thus fluctuations in etching conditions can be suppressed.

<Other Embodiments>
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 modified examples, and various modifications, improvements, combinations and the like can be made without departing from the spirit of the invention.

For example, the etching liquid 201 that contains S ₂ O ₈ ²⁻ and is acidic at the start of etching is not limited to the above-described first and second examples. As such an etching solution 201, for example, only a K ₂ S ₂ O ₈ aqueous solution can be used. In this case, the concentration of the K ₂ S ₂ O ₈ aqueous solution may be 0.025M, for example.

In the above description _has exemplified the manner for supplying the S ₂ ^{O 8 2-from} potassium peroxodisulfate _{(K 2 S 2 O 8)} , S 2 O 8 2- , the other example, sodium peroxodisulfate It may be supplied from (Na ₂ S ₂ O ₈ ), ammonium peroxodisulfate (ammonium persulfate, (NH ₄ ) ₂ S ₂ O ₈ ), or the like.

  Note that PEC etching can 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 for 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, PEC etching can be performed by generating holes by irradiation with UV light 221 to generate Al oxide or In oxide and dissolving these oxides in acid (or alkali). it can. The peak wavelength of the UV light 221 (365 nm or less) may be appropriately changed depending on the composition of the group III nitride to be etched. Based on the PEC etching of GaN, when Al is contained, shorter wavelength UV light may be used, and when In is contained, longer wavelength UV light can be used. It should be noted that impurities such as conductivity type determining impurities may be added to the group III nitride to be PEC-etched, if necessary.

<Preferred embodiment of the present invention>
Hereinafter, preferred embodiments of the present invention will be additionally described.

(Appendix 1)
Providing an etching object having at least a surface composed of a group III nitride,
The object to be etched is immersed in an etching solution containing peroxodisulfate ions, and the surface of the object to be etched is irradiated with ultraviolet light through the etching solution to convert the peroxodisulfate ions to sulfate ions. Etching radicals in the group III-nitride by generating radicals and holes in the group III-nitride,
Have
In the step of etching the group III-nitride, the etching solution is made acidic during the period when the group III-nitride is etched by making the etching solution acidic at the start of etching the group III-nitride. A method for manufacturing a structure, which maintains a certain state.

(Appendix 2)
The decrease range of the pH of the etching solution at the end of the etching with respect to the pH of the etching solution at the start is preferably 4 or less, more preferably 3 or less, still more preferably 2 or less, still more preferably 1.5. Hereinafter, the method for producing the structure according to Appendix 1, which is more preferably 1 or less.

(Appendix 3)
When the peroxodisulfate ions contained in the etching solution are all converted to sulfate ions, the decrease range of the pH of the etching solution with respect to the pH of the etching solution at the start point is preferably 4 or less, more preferably 3 The method for producing a structure according to appendix 1 or 2, which is preferably 2 or less, more preferably 1.5 or less, still more preferably 1.5 or less.

(Appendix 4)
The etchant is 0 include a weak acid having an acid dissociation constant pK _a of less than super 7, a manufacturing method of a structure according to any one of Appendices 1 to 3.

(Appendix 5)
5. The method for producing a structure according to appendix 4, wherein the weak acid is phosphoric acid.

(Appendix 6)
Of pH of the etchant in the beginning, the difference for the acid dissociation constant pK _a of the weak acid is, preferably ± 1 or less, and more preferably not more than plus or minus 0.5, according to Appendix 4 or 5 structure Body manufacturing method.

(Appendix 7)
The pH of the etching solution at the start is higher than said acid dissociation constant pK _a of the weak acid, the manufacturing method of the structure according to any one of Appendices 4-6.

(Appendix 8)
Acid dissociation constant pK _a of the weak acid is higher than said pH of the etchant when the said peroxodisulfate ions contained in the etching solution is all changed into sulfate ions, according to any one of Appendices 4-7 Manufacturing method of the structure.

(Appendix 9)
9. The method for manufacturing a structure according to any one of appendices 1 to 8, wherein the etching liquid is not exchanged during a period in which the group III nitride is etched.

(Appendix 10)
10. The method for manufacturing a structure according to any one of appendices 1 to 9, wherein the etching liquid is not stirred during the period when the group III nitride is etched.

(Appendix 11)
The period for which the Group III nitride is etched is preferably 30 minutes, more preferably 60 minutes, further preferably 90 minutes or more, and further preferably 120 minutes or more. Manufacturing method of the structure.

(Appendix 12)
The method for producing a structure according to any one of appendices 1 to 11, wherein the pH of the etching solution is measured during the period in which the group III nitride is etched.

(Appendix 13)
When measuring the pH of the etching solution, the probe of the pH meter, the shadow of the ultraviolet light, the probe is arranged at a position where it is not reflected on the surface of the etching target, the structure of the appendix 12, Production method.

(Appendix 14)
Before the step of etching the group III nitride, the etching solution is irradiated with ultraviolet light in a state where the etching target is not immersed in the etching solution, so that a part of the peroxodisulfate ion is removed. 14. The method for manufacturing a structure according to any one of appendices 1 to 13, further comprising a step of lowering the pH of the etching solution by changing to sulfate ions.

(Appendix 15)
15. The structure according to any one of appendices 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). Body manufacturing method.

(Appendix 16)
16. The method of manufacturing a structure according to attachment 15, wherein the mask is a resist mask.

(Appendix 17)
An etching object having at least a surface composed of a group III nitride;
A mask formed on the surface (on a portion of the surface);
Have
The intermediate structure immersed in an acidic etching solution containing peroxodisulfate ions.

(Appendix 18)
18. The intermediate structure according to appendix 17, wherein the mask is a resist mask.

(Appendix 19)
19. The intermediate structure according to appendix 17 or 18, wherein the surface is irradiated with ultraviolet light through the etching liquid.

DESCRIPTION OF SYMBOLS 10 ... Etching object, 20 ... Etching surface 20, 21 ... Etching area, 50 ... Mask, 100 ... Processing object, 200 ... PEC etching device, 201 ... Etching solution, 202 ... Etching solution upper surface, 210 ... Container, 220 ... Light source, 221 ... UV light, 230 ... pH meter, 231 ... Probe, 240 ... Support stand

Claims (22)

Providing an etching object having at least a surface composed of a group III nitride,
In a state where the etching object is immersed in an etching solution containing peroxodisulfate ion, the surface of the etching object is irradiated with light through the etching solution to convert the peroxodisulfate ion into a sulfate ion radical. And etching holes in the group III nitride, thereby etching the group III nitride.
Have
In the step of etching the group III-nitride, the etching solution is made acidic during the period when the group III-nitride is etched by making the etching solution acidic at the start of etching the group III-nitride. Keep a certain state ,
A method of manufacturing a structure , wherein the etching is performed with a resist mask formed on the surface . Providing an etching object having at least a surface composed of a group III nitride,
In a state where the etching object is immersed in an etching solution containing peroxodisulfate ion, the surface of the etching object is irradiated with light through the etching solution to convert the peroxodisulfate ion into a sulfate ion radical. And etching holes in the group III nitride, thereby etching the group III nitride.
Have
In the step of etching the group III-nitride, the etching solution is made acidic during the period when the group III-nitride is etched by making the etching solution acidic at the start of etching the group III-nitride. Keep a certain state ,
The method for manufacturing a structure , wherein 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 light is 2.76 nm or less . Of pH of the etchant at the end of the etching, decline relative to the pH of the etchant in the beginning is 4 or less, the manufacturing method of the structure according to claim 1 or 2. Said pH of said contained in the etching solution peroxodisulfate ions all the etchant in the case of changes to a sulfate ion, a decline relative to the pH of the etchant in the beginning is 4 or less, claim 1 4. The method for manufacturing the structure according to any one of 3 above. The etchant is 0 include a weak acid having an acid dissociation constant pK _a of less than super 7, a manufacturing method of a structure according to any one of claims 1-4. The method for manufacturing a structure according to claim 5 , wherein the weak acid is phosphoric acid. Said pH of the etchant at the beginning, the difference for the acid dissociation constant pK _a of the weak acid, is plus or minus 1 or less, the manufacturing method of the structure according to claim 5 or 6. The pH of the etching solution at the start is higher than said acid dissociation constant pK _a of the weak acid, the manufacturing method of the structure according to any one of claims 5-7. Acid dissociation constant pK _a of the weak acid is higher than said pH of the etchant when the said peroxodisulfate ions contained in the etching solution is all changed into sulfate ions, to any one of claims 5-8 A method for producing the described structure. During said group III period nitride is etched, not replace the etching solution, the manufacturing method of the structure according to any one of claims 1-9. During said group III period nitride is etched, not performed agitation of the etchant, the manufacturing method of the structure according to any one of claims 1-10. Period in which the III-nitride is etched is 30 minutes or more, the manufacturing method of the structure according to any one of claims 1 to 11. During the period in which the III-nitride is etched, measuring the pH of the etchant, the manufacturing method of the structure according to any one of claims 1 to 12. 14. The 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 the shadow of the light of the probe does not appear on the surface of the etching object. Production method. Before the step of etching the Group III nitride, the etching solution is irradiated with light in a state where the etching target is not immersed in the etching solution, so that part of the peroxodisulfate ion is sulfated. by varying the ion, the step of lowering the pH of the etchant further comprises a method for manufacturing a structure according to any one of claims 1-14. An etching object having at least a surface composed of a group III nitride;
A resist mask formed on the surface,
Have
An intermediate structure, which is immersed in an acidic etching solution containing peroxodisulfate ions with the resist mask formed on the surface . The intermediate structure according to claim 16, wherein the surface is irradiated with light through the etching liquid. At least the surface is composed of a group III nitride, the etching object resist mask on the surface is formed, and configured containers so as to house in a state of being immersed in an acidic etching solution containing peroxodisulfate ions ,
In a state where the etching solution is acidic, the surface of the etching object, a light source configured to start irradiating light through the etching solution,
Manufacturing apparatus for a structure having a. At least the surface of the etching object composed of a group III nitride, and configured containers so as to house in a state of being immersed in an acidic etching solution containing peroxodisulfate ions,
In a state where the etching solution is acidic, the surface of the etching object, a light source configured to start irradiating light through the etching solution,
Have a,
The surface of the etching object is irradiated with the light in a state where the etching object is immersed in the etching solution in the container, and the root mean square surface roughness in a 5 μm square area of the surface is set to 2 An apparatus for manufacturing a structure , which is configured to etch the surface of the etching object so as to have a thickness of 0.76 nm or less . Providing an etching object having at least a surface composed of a group III nitride,
In a state where the etching object is immersed in an etching solution containing peroxodisulfate ions, the surface of the etching object is irradiated with light through the etching solution to convert the peroxodisulfate ions into sulfate ion radicals. And etching holes in the group III nitride, thereby etching the group III nitride.
Have
In the step of etching the group III-nitride, the etching solution is made acidic during the period when the group III-nitride is etched by making the etching solution acidic at the start of etching the group III-nitride. Keep a certain state,
Measuring the pH of the etchant during the period in which the III-nitride is etched,
A method for manufacturing a structure, wherein when measuring the pH of the etching solution, the probe of a pH meter is arranged at a position where a shadow of the light due to the light is not reflected on the surface of the etching object. Providing an etching object having at least a surface composed of a group III nitride,
In a state where the etching object is immersed in an etching solution containing peroxodisulfate ions, the surface of the etching object is irradiated with light through the etching solution to convert the peroxodisulfate ions into sulfate ion radicals. And etching holes in the group III nitride, thereby etching the group III nitride.
Have
In the step of etching the group III-nitride, the etching solution is made acidic during the period when the group III-nitride is etched by making the etching solution acidic at the start of etching the group III-nitride. Keep a certain state,
Before the step of etching the Group III nitride, the etching solution is irradiated with light in a state where the etching target is not immersed in the etching solution, so that part of the peroxodisulfate ion is sulfated. A method of manufacturing a structure, further comprising the step of lowering the pH of the etching solution by changing it into ions. A container configured to house an etching target whose surface is composed of a group III nitride in a state of being immersed in an acidic etching solution containing peroxodisulfate ion;
In a state where the etching solution is acidic, the surface of the etching object, a light source configured to start irradiating light through the etching solution,
Have
A pH meter for measuring the pH of the etching solution,
The structure manufacturing apparatus, wherein the probe of the pH meter is arranged at a position where a shadow of the probe caused by the light is not reflected on the surface of the etching object.