JP7817009B2 - Substrate processing method and substrate processing apparatus - Google Patents

Description

The present invention relates to a substrate processing method and a substrate processing apparatus.

GaN devices using GaN (gallium nitride) have a wide bandgap and are therefore widely used in optical devices. Furthermore, GaN devices have excellent electrical properties, such as a high breakdown field and the potential for high electron mobility, which has led to their application in high-frequency devices and power devices.

However, because freestanding GaN substrates are extremely expensive, the mainstream method for manufacturing GaN devices is to use a substrate in which GaN crystals are grown by vapor phase epitaxy on a sapphire or Si (silicon) substrate as the base material. In the following explanation, a substrate in which a layer of GaN is formed on a base material made of a material other than GaN is referred to as a GaN (gallium nitride)-based substrate.

International Publication No. 2005/041283

However, GaN has a different lattice constant than the sapphire used as the base material. For this reason, when GaN is grown on a sapphire substrate, dislocations, a type of lattice defect, are randomly generated, penetrating from the GaN layer to the surface of the sapphire substrate. This causes pits, holes that originate from dislocations and reach the surface, to form on the surface of the GaN layer of the substrate.

In products manufactured using such GaN-based substrates, for example, if pits exist within a p-n junction diode element, the reverse breakdown voltage characteristics may be significantly reduced. Furthermore, if a device is formed on the pits, there is a concern that leakage current may occur. To address this issue, it is conceivable to reduce the pits through surface treatment, but currently no effective method has been found that can reduce only the pits without degrading properties such as surface roughness.

An embodiment of the present invention aims to provide a substrate processing method and substrate processing apparatus that can reduce pit depth while suppressing deterioration of surface roughness on gallium nitride substrates.

A substrate processing method according to an embodiment of the present invention is a method for processing a gallium nitride-based substrate, and includes a wet processing step of processing the substrate with a mixed solution containing phosphoric acid and nitric acid, the mixed solution having a phosphoric acid concentration of 60 to 80 mass % and a nitric acid concentration of 5 to 20 mass % .

A substrate processing apparatus according to an embodiment of the present invention includes a processing tank for performing wet processing on the substrate using a mixed solution containing phosphoric acid and nitric acid, the mixed solution having a phosphoric acid concentration of 60 to 80 mass % and a nitric acid concentration of 5 to 20 mass % , and a temperature adjustment tank for adjusting the temperature of the processing solution supplied to the processing tank.

Embodiments of the present invention can provide a substrate processing method and substrate processing apparatus that can reduce pit depth while suppressing deterioration of surface roughness on gallium nitride substrates.

1 is a configuration diagram of a substrate processing apparatus according to an embodiment; 1 is a flowchart showing a processing procedure of the substrate processing apparatus according to the embodiment. 1 is a graph showing the relationship between the nitric acid concentration and phosphoric acid concentration of the treatment liquid, and the etching rate and surface roughness. 1 is a graph showing the relationship between the nitric acid concentration and phosphoric acid concentration of the treatment solution and the oxidation-reduction potential of the treatment solution after treatment. 1 is a graph showing the relationship between the temperature of the processing liquid and the etching rate and surface roughness. 1 is a graph showing the relationship between the concentration of hydrogen peroxide solution and the concentration of phosphoric acid in the treatment liquid, and the etching rate and surface roughness. 1A and 1B are diagrams showing images of the substrate surface (A) and the cross section (B) taken along the line AA before treatment with a mixed solution of phosphoric acid and nitric acid. 1A and 1B are images of the substrate surface and cross section taken along the line BB, respectively, after treatment with a mixed solution of phosphoric acid and nitric acid. 1A and 1B are images of the surface of a substrate before treatment with a mixed solution of phosphoric acid and hydrogen peroxide solution and a cross section taken along the line CC. 1A and 1B are images of the surface of a substrate after treatment with a mixed solution of phosphoric acid and hydrogen peroxide solution and the cross section taken along the line DD.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[overview]
1, this embodiment relates to a substrate processing apparatus 1 and a substrate processing method, which include a processing tank 10 that performs wet processing on a substrate W such as a wafer using a processing liquid L, and a temperature adjustment tank 20 that adjusts the temperature of the processing liquid L supplied to the processing tank 10. The processing target of this embodiment is a GaN-based substrate W having a GaN layer formed on a base made of a material other than GaN, such as sapphire or silicon.

Here, wet etching is considered effective for deburring the edge surfaces of GaN patterns. Furthermore, wet etching of GaN is considered to cause less damage to the substrate surface than dry etching. However, wet etching has a slow etching rate, even when using chemicals regulated at approximately 100°C, so batch etching is more effective. However, no matching etchant has been found that can reduce pit depth without deteriorating surface roughness.

For example, when GaN grows on a sapphire substrate, the growth plane is the (0001) plane (hereafter referred to as the C-plane) of the crystal, and so pits are formed that are deeper in the C-axis direction. If etching proceeds only in the C-plane direction, the pits will become shallower, but no processing solution has been found that can selectively anisotropically etch in the C-plane direction. Existing etching solutions result in isotropic etching that also etches in directions other than the C-plane direction, which increases the pit diameter and depth, making it impossible to reduce the pits.

After extensive research, the inventors were able to select a chemical solution and processing conditions that result in a processing solution L that can etch Ga and N in the GaN layer without selectivity and that can perform anisotropic etching in the C-plane direction of the crystal. In other words, the inventors discovered a processing solution L that can wet-etch a GaN layer with pits in the processing tank 10, suppress the expansion of pits that exist randomly on the surface of the GaN layer, reduce their depth, and maintain or improve surface roughness.

[composition]
A substrate processing apparatus 1 according to this embodiment will be described with reference to the block diagram of Fig. 1. The substrate processing apparatus 1 includes a processing bath 10, a temperature adjustment tank 20, a blending bath 30, a supply mechanism 40, a rinse bath 80, a waste liquid tank 90, and a control device 100.

(Treatment tank)
The processing tank 10 is a tank that performs wet processing on substrates W using a processing liquid L. The processing liquid L is a mixed liquid containing phosphoric acid ( _H3PO4 ) and _nitric acid ( _HNO3 ), and is capable of etching gallium (Ga) and nitrogen (N) without selectivity. The processing liquid L is also capable of anisotropic etching in the C-plane direction of the crystal. A plurality of substrates W that have been transported in cassettes (not shown) are loaded into the processing tank 10 together with the cassettes, and are immersed in the processing liquid L to be wet processed.

(Temperature control tank)
The temperature adjustment tank 20 is a tank that adjusts the temperature of the processing liquid L to be supplied to the processing bath 10. The temperature adjustment tank 20 is provided with a heater 21, which is a heating unit, and is capable of heating the processing liquid L. The heater 21 is, for example, a drop-in type. However, it may also be an in-line heater.

The temperature adjustment tank 20 is also provided with a temperature sensor 22 and a concentration sensor 23. The temperature sensor 22 detects the temperature of the processing liquid L in the temperature adjustment tank 20. The concentration sensor 23 detects the concentration of _H3PO4 , _HNO3 , or _DIW (ultrapure water) in the processing liquid L in the temperature adjustment tank 20. The concentration sensor 23 may be provided in the processing bath 10 to detect the concentration of the processing liquid L that has changed due to the wet processing in the processing bath 10.

The temperature adjustment tank 20 and the processing tank 10 are connected via piping 11, which is a path for supplying processing liquid L, temperature-adjusted in the temperature adjustment tank 20, to the processing tank 10, and piping 15, which is a path for returning processing liquid L from the processing tank 10 to the temperature adjustment tank 20. Pipe 11 is equipped with a valve 12, pump 13, and filter 14. Pipe 15 is equipped with a valve 16. This allows processing liquid L supplied to the processing tank 10 by the pump 13 via piping 11 to return to the temperature adjustment tank 20 via piping 15, so that the desired temperature can be maintained while circulating the processing liquid L between the processing tank 10 and the temperature adjustment tank 20.

(mixing tank)
The blending tank 30 is a tank that blends the treatment liquid _L to be supplied to the temperature adjustment tank ₂₀ by mixing the first chemical liquid, the second chemical liquid, and DIW so that the concentration of _H3PO4 is 60 to 80 mass % and the concentration of HNO3 is 5 to 20 mass %. The blending tank 30 is connected to the temperature adjustment tank 20 via a pipe 31 that is provided with a valve 32. The pipe 31 is a path that supplies the treatment liquid L blended in the blending tank 30 to the temperature adjustment tank 20.

The first chemical liquid is a liquid containing _H3PO4 , for example, _a liquid consisting of _H3PO4 and _DIW , and the second chemical liquid is a liquid containing _HNO3 , for example, a liquid consisting of _HNO3 and DIW. The first chemical liquid can be a relatively high concentration liquid containing about 85% _H3PO4 , _and the second chemical liquid can be a relatively high concentration liquid containing about 69% _HNO3 , but the concentrations are not limited to these.

(Supply mechanism)
The supply mechanism 40 is a mechanism that supplies the first chemical liquid, the second chemical liquid, and DIW to the blending tank 30. The supply mechanism 40 has a first chemical liquid supply tank 50, a second chemical liquid supply tank 60, and a DIW supply tank 70. The first chemical liquid supply tank 50 is a tank that stores the first chemical liquid. The second chemical liquid supply tank 60 is a tank that stores the second chemical liquid. The DIW supply tank 70 is a tank that stores DIW.

The first chemical supply tank 50, the second chemical supply tank 60, and the DIW supply tank 70 are connected to the blending tank 30 via pipes 51, 61, and 71 equipped with valves 52, 62, and 72, respectively. Pipes 51, 61, and 71 also branch into pipes 53, 63, and 73 equipped with valves 54, 64, and 74, which are connected to the temperature adjustment tank 20.

(Rinse tank)
The rinse tank 80 is a tank for cleaning, i.e., rinsing, the substrate W that has been processed in the processing tank 10. The cleaning liquid used for the rinse process is DIW. The DIW supply tank 70 is connected to the rinse tank 80 via a pipe 75 having a valve 76 and a filter 77, so that the DIW for the rinse process can be supplied from the DIW supply tank 70.

Although not shown, a transfer mechanism is provided between the processing tank 10 and the rinsing tank 80 to transfer cassettes containing multiple substrates W from the processing tank 10 to the rinsing tank 80 in a single batch. The transfer mechanism has a wafer chuck that holds and moves multiple substrates W in a single batch.

(waste liquid tank)
The waste liquid tank 90 is a tank into which the processing liquid L in the processing tank 10 and the processing liquid L in the temperature adjustment tank 20 are discharged. The processing tank 10 and the temperature adjustment tank 20 are connected to the waste liquid tank 90 via pipes 18 and 24 having valves 19 and 25, respectively.

(Control device)
The control device 100 is a computer that controls each part of the substrate processing apparatus 1. The control device 100 has a processor that executes programs, a memory that stores various information such as the programs and operating conditions, and a drive circuit that drives each element. An input device for inputting information and a display device for displaying information are connected to the control device 100.

The control device 100 has a mechanism control unit 110, a temperature control unit 120, a concentration determination unit 130, and a usage history determination unit 140. The mechanism control unit 110 controls the valves 12, 16, 19, 25, 32, 52, 54, 62, 64, 72, 74, 76, the pump 13, etc. The temperature control unit 120 controls the temperature of the heater 21 so that the temperature detected by the temperature sensor 22 becomes a predetermined temperature, which is a standard set in advance in a memory, etc.

The concentration determination unit 130 determines whether the concentration detected by the concentration sensor 23 is within a set concentration range, which is a standard previously set in memory or the like. If the concentration determination unit 130 determines that the concentration is outside the set concentration range, the mechanism control unit 110 controls valves 54, 64, and 74 to adjust the flow rate of the first chemical liquid, second chemical liquid, or DIW supplied to the temperature adjustment tank 20. Alternatively, it controls valves 52, 62, and 72 to adjust the flow rate of the first chemical liquid, second chemical liquid, or DIW supplied to the blending tank 30.

The flow rate can be adjusted based on the determination result of the concentration determination unit 130, for example, as follows. When the concentration sensor 23 detects a decrease in the concentration of any one of the first chemical liquid, the second chemical liquid, or DIW, the valves 54, 64, and 74 corresponding to the chemical liquid or DIW whose concentration has been detected are controlled to supply the chemical liquid or DIW whose concentration has been detected to the temperature control tank 20 in accordance with the decrease in concentration, or to increase the supply amount. Furthermore, when the concentration sensor 23 detects an increase in the concentration of any one of the first chemical liquid, the second chemical liquid, or DIW, the valves 54, 64, and 74 corresponding to the chemical liquid or DIW other than the chemical liquid or DIW whose concentration has been detected to increase are controlled to supply the chemical liquid or DIW other than the chemical liquid or DIW whose concentration has been detected to the temperature control tank 20 in accordance with the increase in concentration, or to increase the supply amount.

The usage history determination unit 140 measures the number of times or duration of use of the processing liquid L and determines whether the number of times or duration has exceeded a predetermined standard set in a memory or the like. If the usage history determination unit 140 determines that the predetermined number of times or duration has exceeded, the mechanism control unit 110 controls the valve 19 to drain the processing liquid L in the processing bath 10 into the waste liquid tank 90. The mechanism control unit 110 also controls the valve 25 to drain the processing liquid L in the temperature adjustment tank 20 into the waste liquid tank 90. The processing liquid L is supplied again from the supply mechanism 40, as described above.

[Operation]
The operation of this embodiment as described above will be described with reference to the flowchart of Fig. 2. Note that a substrate processing method for processing a substrate W and a substrate manufacturing method for manufacturing a substrate W in the following procedure are also aspects of this embodiment.

First, if there is no processing liquid L in the temperature adjustment tank 20 (NO in step S01), the following preparatory operation is performed before the substrate W is loaded into the processing bath 10. That is, the processing liquid L is prepared by supplying the first chemical liquid from the first chemical liquid supply tank 50, the second chemical liquid from the second chemical liquid supply tank 60, and the DIW from the DIW supply tank 70 to the blending tank 30 (step S02). At this time, the processing liquid L is prepared so that the concentration of _H3PO4 in the processing liquid _L is 60 to 80 mass % and the concentration of _HNO3 is 5 to 20 mass %.

The prepared treatment liquid L is supplied to the temperature adjustment tank 20 and circulated between it and the treatment bath 10 (step S03), and its temperature is adjusted by heating with the heater 21 until it reaches a predetermined temperature (approximately 100°C) (step S04: NO) (step S05).

When it is determined from the detected values of the temperature sensor 22 and concentration sensor 23 in the temperature adjustment tank 20 that the processing liquid L in the processing bath 10 has reached a predetermined temperature and concentration (YES in step S04), the multiple substrates W stored in the cassettes are loaded into the processing bath 10 together (step S06). Since the multiple substrates W have been loaded into the processing bath 10 together, they are immersed in the processing liquid L and undergo wet etching until the preset processing time has elapsed (NO in step S07).

Even during processing, the temperature is maintained by circulating the processing liquid L between the processing tank 10 and the temperature adjustment tank 20 (steps S08 and S09). Furthermore, because the processing tank 10 is an open system and the temperature of the processing liquid L is high, the components of the cleaning liquid that evaporate and become gaseous within the processing tank 10 during processing are constantly discharged through a duct (not shown). If the concentration determination unit 130 determines that the concentration detected by the concentration sensor 23 installed in the temperature adjustment tank 20 is outside the reference concentration range (YES in step S08), the supply mechanism 40 adjusts the concentration by supplying the missing components of the processing liquid L to the temperature adjustment tank 20 as needed until the concentration falls within the reference concentration range (NO in step S08) (step S09).

When the preset processing time has elapsed (YES in step S07), the substrates W are unloaded from the processing bath 10 together with the cassette (step S10). Even after the processing time has elapsed and the substrates W are unloaded, the processing liquid L continues to circulate in order to maintain the temperature of the processing liquid L in the processing bath 10. The substrates W contained in the cassette are transported to the rinse bath 80 by a transport mechanism, and the cassette is loaded into the rinse bath 80 together, where they are rinsed with DIW (step S11).

If the usage history determination unit 140 determines that the number of uses or the usage time of the processing liquid L has not exceeded the predetermined number of uses or the predetermined time (NO in step S12), and if processing of the planned number of substrates W has not been completed (NO in step S14), it performs the processing from step S01 onwards on the substrates W contained in the next cassette.

If the usage history determination unit 140 determines that the use of the processing liquid L has exceeded the predetermined number of times or the predetermined time (YES in step S12), the mechanism control unit 110 controls the valves 19 and 25 to discharge the processing liquid L in the processing bath 10 and the temperature adjustment tank 20 into the waste liquid tank 90 (step S13). If the processing of the planned number of substrates W has not been completed (NO in step S14), the processing from step S01 onwards is performed on the substrates W contained in the next cassette.

When the planned number of substrates W have been processed (YES in step S14), the processing ends. Note that although the flowchart in FIG. 2 shows the rinsing process (step S11) after the substrates W are removed in step S10, the processing liquid discharge process (steps S12 and S13), and the transition to processing of the next substrate W (step S14) in chronological order, these processes can be performed in parallel. Also, while an example has been shown in which the processing liquid L from the processing bath 10 and the temperature adjustment tank 20 is discharged in the processing liquid discharge process (steps S12 and S13), it is also possible to discharge only one of the processing liquids L, for example, only the processing liquid L from the processing bath 10.

[Test Results]
Test results showing the effects of the wet etching according to this embodiment are described below. The substrate W used in the test was a sapphire substrate (550 μm) with a GaN film (2 μm) formed thereon, measuring 200 mm (200 mm × 200 mm). The following (1), (3), (4), and (5) are based on the results of immersing the substrate _W in a treatment solution containing 73% _H3PO4 and 10% _HNO3 at 95°C for 5 hours.

(1) Relationship between Treatment Solution Concentration, Etching Rate, and Surface Roughness Figure 3 is a graph showing the relationship between the etching rate (left vertical axis ₎ and surface roughness (right vertical axis) of the GaN layer of a GaN substrate versus the compounding ratio of _H3PO4 to _HNO3 ( _HNO3 concentration on the horizontal axis) in an etching solution at 95°C. The surface roughness is expressed as surface Ra (arithmetic mean roughness). The surface Ra before the etching process was 0.09 nm.

_{When H3PO4} was used in a concentration range of at least 60-73 mass% and _HNO3 in a concentration range of at least 10-20 mass%, the etching rate increased to 0.28-0.37 nm/h, and the surface Ra fluctuated between 0.10-0.13 nm. Since the surface Ra before treatment was 0.09 nm, the surface Ra deteriorated slightly, but the pit depth decreased. Maintaining this level of surface Ra is believed to minimize product problems. Compared to etching with _{a single H3PO4} solution ( ₈₅ % _H3PO4 , 0% _HNO3 ) and a single _HNO3 solution (0% _H3PO4 , 70% _{HNO3 )} , the mixed solution of _H3PO4 and _HNO3 improved the etching rate without significantly affecting the surface Ra.

In particular, as the _HNO3 concentration increases from 0% to 10%, the etching rate rises sharply, demonstrating that adding even a small amount of _HNO3 is effective. Furthermore, the etching rate also rises sharply as the _{H3PO4 concentration} increases from 36% to 60%. Therefore, considering the decrease in surface Ra, it can be said that _{a H3PO4} concentration of 60-80% and a _HNO3 concentration of 5-20% are effective in improving the etching rate.

(2) Relationship between treatment solution concentration and oxidation-reduction potential of etching solution after treatment Figure 4 is a graph showing the relationship between the compounding ratio of _{H3PO4 to HNO3} ( _HNO3 concentration on the horizontal axis) at an etching solution temperature of ₉₅ °C and the oxidation-reduction potential (vertical axis) of the etching solution after processing the GaN layer of the substrate. The potential of _H3PO4 alone (85%) tends to be low, while the potential of _HNO3 alone (70%) tends to be high. In the case of a mixed solution of _H3PO4 and _HNO3 , the potential was close to that _{of HNO3} . A high oxidation-reduction potential is preferable, but _HNO3 alone has a low etching rate as shown in Figure 3, making it unsuitable for practical use.

In the case of a mixed solution containing 73% _{H3PO4 and} 10% _HNO3 , the potential was 1.25 V, the second highest after _HNO3 alone, and in this case, the etching rate was the highest. This confirmed that the type of treatment solution affects the oxidation-reduction potential. In particular, as the _HNO3 content increased from 0% to 10%, the potential rose sharply, indicating that adding even a small amount of _HNO3 is effective, and that at least 5% or more _HNO3 is effective.

(3) Relationship between Treatment Solution Temperature and Etching Rate and Surface Roughness Figure 5 is a graph showing the relationship between the temperature (horizontal axis) of the treatment solution, which is a mixture of 73 _{% H3PO4} and 10% _HNO3 , and the etching rate (left vertical axis) and surface Ra (right vertical axis) of the GaN layer on the substrate. When the temperature of the treatment solution was 50 to 95°C, the etching rate improved as the temperature increased, but no correlation with temperature was observed at temperatures above 110°C.

At temperatures above 110°C, the volatilization of _HNO3 , which has a boiling point of 82.6°C, caused the influence of _{H3PO4 ,} which has a boiling point of 158°C, to become dominant, so the etching rate approached the etching rate of _{H3PO4 alone} , and the pit depth on the substrate surface and the surface Ra also deteriorated. Considering the rate of increase in etching rate from 50°C to 70°C and the rate of decrease in etching rate from 95°C to 110°C, it can be said that the treatment liquid is preferably at 60 to 100°C, and more preferably at 70 to 95°C. It can be said that deterioration of surface Ra is also suppressed within this temperature range.

(4) Relationship between the concentration of the treatment solution, which is a mixture of _{H3PO4 and H2O2} , and the etching rate and surface roughness _. Figure 6 shows, as a comparative example, the relationship between the etching rate (left vertical axis ₎ and surface Ra ( _right vertical _axis ) of the GaN layer of the substrate versus the compounding ratio of _H3PO4 to _H2O2 ( _hydrogen peroxide solution) ( _H2O2 concentration on the horizontal axis) under etching solution conditions of 95° _C . In the concentration range of 44 to 71% _H3PO4 and 5 to 15% _H2O2 , the etching rate increased in proportion to _{the H2O2 concentration} , from 0.09 to 0.31 nm/h. However, the surface Ra deteriorated to 0.10 to 0.26 nm, with the pit depth accelerating in proportion to _{the H2O2 concentration} . This is thought to be because the mixed solution of H ₃ PO ₄ and H ₂ O ₂ results in isotropic etching.

(5) Substrate Surface and Cross-Sectional Shape Before and After Treatment Figures 7 and 8 are images of the surface (A) and cross-section (B) of the GaN layer of a substrate W before and after immersion in the treatment solution under the above conditions. As shown in Figure 7(A), the substrate W before treatment has a wavy surface shape with multiple pits P scattered throughout. Checking the cross-section of the deepest pit P within the measurement surface revealed that, as shown in Figure 7(B), a pit P with a depth of about 2 nm existed before etching. As shown in Figures 8(A) and (B), the pits P almost disappeared after etching, demonstrating an improvement in the surface shape.

Therefore, it can be seen that the mixed solution of _H3PO4 and _HNO3 has _the property of enabling anisotropic etching that etches only in the C-plane direction, and can reduce the depth of pits present on the substrate surface. In other words, as the etching removes the layer in the C-plane direction, the pits P are reduced in depth. Note that the depth range shown in Figure 7(B) is 0.14 to 2.26 nm, and the depth range shown in Figure 8(B) is 0.33 to 1.08 nm, so it can be seen that the depth is clearly reduced after processing, and the pits P are almost completely eliminated.

(6) Substrate Surface and Cross-Sectional Shape Before _and After Treatment with a Mixture of _{H3PO4 and H2O2} Figures 9 and 10 show, as a comparative example, images of the surface ( _A ) and cross-section ( _B ) of the GaN layer of a substrate before and after immersion for 5 hours in a mixture of 44% _{H3PO4 and} 15% _H2O2 , which does not contain HNO3, at 95°C. As shown in Figures 9(A) and 10(A), it can be seen that the pits P have increased to a clearly visible level after treatment compared to before treatment. Furthermore, as shown in Figure 9(B), the pits P were about 2 nm deep before treatment, but as shown in Figure 10(B), they became about 5.5 nm deep after treatment, indicating a deterioration in the pit shape.

In other words, the mixed solution of 44% _{H3PO4 and} 15% _H2O2 has the property of isotropic etching, which etches in directions other than the C-plane direction, and therefore leads to _an increase in the depth and diameter of pits present on the substrate surface. For this reason, a processing solution containing _{only H3PO4} etches in directions other than the C-plane direction, so it is not possible to reduce the depth of pits P, and instead enlarges existing pits P and increases the number of pits P.

[effect]
(1) The substrate processing method of this embodiment is _a method for processing GaN-based substrates W, and includes a wet processing step in which the substrates W are wet-processed with a processing liquid L that is a mixed liquid containing _H3PO4 and _HNO3 and that can etch Ga and N without selectivity. The substrate processing apparatus 1 of this embodiment also includes a processing tank 10 _that performs the wet processing on the substrates W with the processing liquid L that is a mixed liquid containing _H3PO4 and _HNO3 and that can etch Ga and N without selectivity, and a temperature adjustment tank 20 that adjusts the temperature of the processing liquid L supplied to the processing tank 10. Therefore, by anisotropically etching the surface of the GaN-based substrates W, it is possible to reduce pit depth while suppressing deterioration in surface roughness.

(2) In the substrate processing method of this embodiment, the processing solution L has _{an H3PO4} concentration of 60 to 80 mass % and an _HNO3 concentration of 5 to 20 mass %. The substrate processing apparatus 1 also has a blending tank ₃₀ that blends the processing solution _L to _be supplied to the temperature adjustment tank 20 by mixing a first chemical solution containing _H3PO4 and a second chemical solution containing _HNO3 so that the _H3PO4 concentration is 60 to 80 mass % and the _HNO3 concentration is 5 to 20 mass %. Optimizing the concentrations of _H3PO4 and _HNO3 in this way enables wet processing that is excellent in terms of etching rate, oxidation-reduction potential, and surface roughness.

(3) In the substrate processing method of this embodiment, the temperature of the processing liquid L in the wet processing step is 70 to 100°C. Furthermore, the temperature adjustment tank 20 maintains the temperature of the processing liquid L at 70 to 100°C. This enables wet processing with an excellent etching rate.

(4) The system includes a concentration sensor 23 that detects the concentration of the chemical or DIW in the processing liquid L that has changed due to temperature adjustment in the temperature adjustment tank 20 or wet processing in the processing bath 10, and a supply mechanism 40 that supplies the chemical or DIW to the temperature adjustment tank 20 or processing bath 10 so that the concentration detected by the concentration sensor 23 falls within a reference concentration range. Therefore, the concentration of the processing liquid L, which changes due to temperature adjustment or wet processing, can be maintained at an appropriate value, thereby reducing the expansion or increase of pits.

(5) The system includes a usage history determination unit 140 that determines whether the number of uses or usage time of the processing liquid L has reached a predetermined threshold, and a discharge unit that discharges the processing liquid from the processing tank 10 or the temperature adjustment tank 20 when the usage history determination unit 140 determines that the number of uses or usage time has reached the predetermined threshold. This prevents deterioration of the processing liquid L and enables processing at an appropriate concentration, thereby reducing the expansion and growth of pits.

(6) The system includes a rinse tank 80 that collectively rinses multiple substrates W that have been wet-processed in the processing tank 10 with pure water, and a transport mechanism that collectively transports multiple substrates W from the processing tank 10 to the rinse tank 80. Therefore, efficient batch processing is possible regardless of the etching rate.

[Modification]
The present embodiment can also be modified as follows. For example, a liquid level sensor may be installed in the temperature adjustment tank 20, and when a certain amount of the processing liquid L is reduced, the concentration of the processing liquid L may be measured by the concentration sensor 23, and the missing component may be supplied from the supply mechanism 40 to the blending tank 30. The blending tank 30 may be omitted, and the liquid from the supply mechanism 40 may be supplied directly to the temperature adjustment tank 20.

Other Embodiments
The above describes the embodiments of the present invention and modifications of each part, but these embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These novel embodiments described above can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and modifications are included within the scope and spirit of the invention, and are also included in the invention described in the claims.

1 Substrate processing apparatus 10 Processing tank 11, 15, 18, 24, 31, 51, 53, 61, 63, 71, 73, 75 Pipes 12, 16, 19, 25, 32, 52, 54, 62, 64, 72, 74, 76 Valve 13 Pump 14, 77 Filter 20 Temperature adjustment tank 21 Heater 22 Temperature sensor 23 Concentration sensor 30 Blending tank 40 Supply mechanism 50 First chemical liquid supply tank 60 Second chemical liquid supply tank 70 DIW supply tank 80 Rinse tank 90 Waste liquid tank 100 Control device 110 Mechanism control unit 120 Temperature control unit 130 Concentration determination unit 140 Usage history determination unit

Claims (8)

A method for processing a gallium nitride based substrate, comprising:
A substrate processing method comprising: a wet processing step of processing the substrate with a processing solution that is a mixed solution containing phosphoric acid and nitric acid, the processing solution having a phosphoric acid concentration of 60 to 80 mass % and a nitric acid concentration of 5 to 20 mass % . The substrate processing method according to claim 1, characterized in that the temperature of the processing liquid in the wet processing step is 70 to 100°C. a treatment tank for performing wet treatment on a gallium nitride substrate using a treatment solution containing a mixed solution containing phosphoric acid and nitric acid, the treatment solution having a phosphoric acid concentration of 60 to 80 mass % and a nitric acid concentration of 5 to 20 mass % ;
a temperature adjustment tank that adjusts the temperature of the processing solution to be supplied to the processing tank;
A substrate processing apparatus comprising: a concentration sensor for detecting a concentration of phosphoric acid, nitric acid, or pure water that has changed due to the temperature adjustment in the temperature adjustment tank or the wet treatment in the treatment tank;
a supply mechanism that supplies at least one of phosphoric acid, nitric acid, and pure water to the temperature adjustment tank or the treatment tank so that the concentration detected by the concentration sensor falls within a reference concentration range;
4. The substrate processing apparatus according to claim 3 , further comprising: 5. The substrate processing apparatus according to claim 3 , wherein the temperature adjustment tank adjusts the temperature of the processing liquid to 70.degree. C. to 100.degree. C. 6. The substrate processing apparatus according to claim 3, further comprising a blending tank that blends the processing liquid to be supplied to the temperature adjustment tank by mixing a first chemical liquid containing phosphoric acid and a second chemical liquid containing nitric acid so that the phosphoric acid concentration is 60 to 80 mass % and the nitric acid concentration is 5 to 20 mass %. a determination unit that determines whether the number of uses or the duration of use of the treatment liquid reaches a predetermined threshold;
a discharge unit that discharges the treatment liquid in the treatment bath or the temperature adjustment tank when the determination unit determines that the number of uses or the duration of use has reached a predetermined threshold value;
7. The substrate processing apparatus according to claim 3, further comprising: a rinse tank for rinsing the plurality of substrates that have been collectively wet-processed in the processing tank with pure water;
a transfer mechanism that transfers a plurality of the substrates collectively from the processing bath to the rinse bath;
8. The substrate processing apparatus according to claim 3, further comprising: