TWI896005B - Substrate processing method - Google Patents

Abstract

The present invention relates to a substrate processing method that utilizes a single-wafer cleaning machine and a treatment liquid to remove a photoresist film from a substrate surface. The substrate is held within the single-wafer cleaning machine and rotated about an axis intersecting the surface of the substrate. A sulfuric acid solution is released onto the substrate surface as the treatment liquid. The sulfuric acid solution, containing the photoresist detached from the substrate, is recovered and electrolyzed to decompose the photoresist. The decomposed sulfuric acid solution is then returned to the single-wafer cleaning machine for use in removing the photoresist film from the substrate surface.

Description

Substrate processing method

The present invention relates to a technique for treating substrates using a treatment liquid, for example, to a substrate treatment method using a single-wafer cleaning machine that utilizes the treatment liquid to remove a photoresist film from the substrate surface.

For the purpose of surface treatment of various substrates, such as semiconductor substrates and glass substrates, the industry widely utilizes treatment liquids for cleaning. For example, in the process of stripping and removing photoresist films formed on the surface of semiconductor substrates, a mixture of concentrated sulfuric acid and hydrogen peroxide solution (SPM) is used as the treatment liquid. For example, in the technology described in Patent Document 1, a single-wafer cleaning machine maintains a horizontal position and rotates at a specified speed, while SPM is sprayed from a nozzle positioned above the substrate.

SPM utilizes an oxidizing agent called peroxymonosulfuric acid ( _H2SO5 ) generated by the reaction of sulfuric acid and hydrogen peroxide as shown in formula (1) _. Once used to remove the photoresist film, the peroxymonosulfuric acid is consumed and disappears. Therefore, to reuse the used solution, hydrogen peroxide must be added again. However, as can be seen from formula (1), the addition of hydrogen peroxide will produce _H2O (water) as a byproduct, thereby reducing the sulfuric acid concentration.

H ₂ SO ₄ +H ₂ O ₂ →H ₂ SO ₅ +H ₂ O Formula (1)

Lowering the sulfuric acid concentration significantly reduces photoresist removal performance, so the number of times hydrogen peroxide is added for reuse is limited to one or two times. Furthermore, when hydrogen peroxide is added for reuse, the sulfuric acid concentration differs from that of the original SPM. Therefore, many semiconductor device manufacturers discard SPM after a single use, emphasizing the need to complete manufacturing within the same steps. Consequently, large quantities of sulfuric acid and hydrogen peroxide solutions are used for photoresist removal. The high cost of purchasing these chemicals and the high cost of wastewater disposal drive up the price of semiconductor devices.

Semiconductor manufacturing equipment is generally divided into two types: batch type and single-wafer type. Batch type processes multiple substrates simultaneously, while single-wafer type processes each substrate one by one.

In recent years, the trend has shifted towards low-volume production of multiple varieties of multiple products, rather than mass production of a single product. Consequently, the advantages of batch production have been underutilized. Furthermore, the line widths of semiconductor ICs (integrated circuits) have become thinner, requiring impurities such as microparticles to be smaller and their amount per unit area to be reduced. Consequently, the use of monolithic production has increased in manufacturing equipment, particularly cleaning equipment (e.g., Patent Document 1).

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 5127325

As described in Patent Document 1, SPM is a process that mixes a hydrogen peroxide solution at a flow rate ratio of 0.1 to 0.35 with sulfuric acid at a flow rate of 1. The concentration of the sulfuric acid after mixing is 76.9% to 87.8% by mass.

The inventors of this application have discovered that sulfuric acid solutions are hydrophilic at lower concentrations and hydrophobic at higher concentrations. A concentration exceeding 75% by mass can dissolve photoresist. Furthermore, the lower the sulfuric acid concentration, the higher the temperature required. Furthermore, the inventors have discovered that when using a treatment solution containing an oxidizing agent, such as SPM, the sulfuric acid concentration or temperature required to remove photoresist tends to decrease.

When using sulfuric acid without an oxidizing agent as the treatment solution, the photoresist can be effectively dissolved, although the sulfuric acid concentration or temperature must be slightly increased. However, since the photoresist dissolves in the treatment solution, the sulfuric acid must be decomposed into carbon dioxide and water for repeated use.

When sulfuric acid containing a photoresist is electrolyzed, a strong oxidant called peroxodisulfuric acid (H ₂ S ₂ O ₈ , redox potential 2.01 V) is generated at the anode by the reaction shown in formula (2). This has a higher redox potential than the peroxomonosulfuric acid (redox potential 1.81 V) obtained from SPM (see Table 1 below).

2H ₂ SO ₄ →H ₂ S ₂ O ₈ +2H ⁺ +2e ^-Formula (2)

If the peroxydisulfuric acid is heated to a high temperature, it becomes a sulfuric acid radical SO ₄ ^- according to formula (3). This can cause the photoresist (denoted as R) dissolved in the sulfuric acid to be transformed into an organic radical R as shown in formula (4), thereby increasing the reactivity and ultimately decomposing into carbon dioxide and water.

S ₂ O ₈ ^2- →2SO ₄ ^- ． Formula (3)

SO _4- ^． +R→R． +HSO ₄ ^-Formula (4)

After removing the photoresist, the sulfuric acid can be used again to remove the photoresist film.

The present invention was developed against the backdrop of the above circumstances, and one of its objectives is to provide a substrate processing method that can repeatedly use a sulfuric acid solution after removing photoresist and the like from the substrate.

One aspect of the present invention provides a substrate processing method for removing a photoresist film from a substrate surface using a single-wafer cleaner and a treatment liquid. This substrate processing method comprises holding a substrate within the single-wafer cleaner, rotating the substrate about an axis intersecting the substrate surface, and releasing a sulfuric acid solution as the treatment liquid onto the substrate surface. The sulfuric acid solution containing the photoresist detached from the substrate is recovered, electrolyzed, and the recovered sulfuric acid solution is returned to the single-wafer cleaner to remove the photoresist film from the substrate surface.

According to the above-described substrate processing method, photoresist films can be effectively removed by contacting a sulfuric acid solution with the surface of a rotating substrate within a single-wafer cleaning machine. Furthermore, the sulfuric acid solution containing the removed photoresist decomposes the photoresist through electrolysis, and the electrolyzed sulfuric acid solution can be reused for substrate processing. This maintains the photoresist film removal performance, allowing for the recycling of the sulfuric acid solution, significantly reducing chemical consumption.

The sulfuric acid concentration of the sulfuric acid solution released onto the substrate is preferably 85% to 96% by mass.

The temperature of the sulfuric acid solution released onto the substrate is preferably set to 130°C to 200°C when the sulfuric acid concentration of the sulfuric acid solution exceeds 95% to 96% by mass, 150°C to 200°C when the sulfuric acid concentration exceeds 90% to 95% by mass, and 170°C to 200°C when the sulfuric acid concentration is 85% to 90% by mass.

Preferably, a sulfuric acid solution heated in a heating unit is released onto the surface of the substrate as the treatment solution. In this case, the oxidant concentration in the sulfuric acid solution before heating in the heating unit is preferably set to less than 0.5 g/L. Furthermore, the redox potential of the sulfuric acid solution before heating in the heating unit is preferably less than 1,100 mV.

One purpose of the aforementioned substrate processing method is to remove photoresist and the like from substrates using a sulfuric acid solution. The sulfuric acid solution containing the photoresist is electrolyzed to decompose the photoresist, and the resulting sulfuric acid solution is repeatedly used. During the electrolysis of the sulfuric acid solution, the oxidant is consumed by the photoresist decomposition, leaving the sulfuric acid solution with virtually no oxidant (the oxidant concentration is less than 0.5 g/L). This sulfuric acid solution is supplied to a cleaning chamber, where it comes into contact with the substrate to remove the photoresist. In this manner, the sulfuric acid solution can be repeatedly used for cleaning. The oxidant concentration can be easily controlled by pre-calculating and performing electrolysis, or by measuring the oxidant concentration in the sulfuric acid solution before supplying it to the cleaning chamber.

A sulfuric acid solution with an appropriately controlled concentration and temperature can provide superior cleaning performance comparable to that of a sulfuric acid solution containing persulfuric acid. Therefore, by supplying a sulfuric acid solution containing virtually no oxidants to the cleaner, substrates can be cleaned without excessively burdening the electrolytic process. Furthermore, the cleaner utilizes various components, and if persulfuric acid, with its high redox properties, comes into contact with these components, it can cause premature degradation and increase the frequency of component replacement. For example, while fluororesin tubing, commonly used in single-piece cleaning machines, has excellent heat and chemical resistance, there's a risk of premature component degradation when the process fluid is heated to high temperatures or pressurized, and when oxidizing agents are present. Therefore, using a sulfuric acid solution that contains virtually no oxidizing agents during cleaning can help prevent component degradation.

In another aspect of the substrate processing method of the present invention, the sulfuric acid solution is released by spraying the sulfuric acid solution from a nozzle.

In another aspect of the substrate processing method of the present invention, the recovered sulfuric acid solution is cooled to 20°C to 60°C and the electrolysis is performed.

In another aspect of the substrate processing method of the present invention, the sulfuric acid solution after the electrolysis is passed through a filter that removes particles of a specified diameter.

The following explains the contents stipulated in this section.

Sulfuric acid concentration: 85% to 96% by mass

When removing photoresist films, the concentration of the sulfuric acid solution is not limited to a specific range. The ideal concentration is 85% to 96% by mass. If the concentration is too low, the hydrophobicity of the solution will weaken, slowing the dissolution of the photoresist. While a high concentration of sulfuric acid is not a problem, the concentration of commercially available sulfuric acid used for semiconductors is 96% by mass.

Sulfuric acid solution temperature: 130°C~200°C

When removing photoresist, the temperature of the sulfuric acid solution is not limited to a specific range, but ideally, it should be set between 130°C and 200°C. If the temperature of the sulfuric acid solution is too low, the photoresist dissolution rate will be slow. If the temperature of the sulfuric acid solution is too high, it will not only increase the load on the heating unit, but also require the components used in the single-wafer cleaning machine to be reselected with higher heat resistance.

The ideal temperature is 130°C to 200°C when the sulfuric acid concentration exceeds 95% to 96% by mass, 150°C to 200°C when the concentration exceeds 90% to 95% by mass, and 170°C to 200°C when the concentration is 85% to 90% by mass.

Sulfuric acid solution temperature during electrolysis: 20°C~60°C

After removing the photoresist film, the ideal temperature for electrolysis in the sulfuric acid solution should be between 20°C and 60°C. If the temperature of the sulfuric acid solution is too low, the diffusion rate of sulfate ions will be slow, resulting in a slower generation of peroxodisulfuric acid. On the other hand, if the temperature of the sulfuric acid solution is too high, the diffusion rate of substances in the solution will increase, and the generated peroxodisulfuric acid will be reduced at the cathode, failing to increase the peroxodisulfuric acid concentration.

1: Processing system

2: Single-chip cleaner

3: Substrate holding unit

4: Nozzle

5: Recycling Department

6: Recovery device storage tank

7A: Liquid delivery line

7B: Liquid collecting line

8: Heating section

10A: Electrolysis device

10B: Electrolysis device

10C: Electrolysis device

11A: Electrolyte delivery line

11B: Electrolyte return line

12: Cooler

13: Pump

14: Filter

100:Substrate

L: Sulfuric acid

Figure 1 is a schematic diagram showing an example of the structure of a device used in an embodiment of the present invention.

Figure 2 is the potential-pH diagram of arsenic.

Figure 3 shows the relationship between oxidant concentration and redox potential.

Below, one embodiment of the present invention is described based on the accompanying drawings.

The processing system 1 includes a single-wafer cleaning machine 2 for treating substrates using chemical liquids, and further includes a liquid collection mechanism for recovering the used chemical liquids.

The single-wafer cleaning machine 2 comprises a substrate holder 3 that holds a substrate 100 used to manufacture semiconductor devices with its surface horizontal and rotates it around a longitudinal axis; and a nozzle 4 that is located above the held substrate 100 and sprays a chemical solution downward.

In this embodiment, the substrate holder 3 holds the substrate 100 so that its surface is horizontal. However, the substrate is not limited to being held horizontally; a substrate holder can also be used that holds the substrate surface tilted relative to the horizontal. Furthermore, a substrate holder can be used that can dynamically change the tilt angle or tilt direction during substrate rotation. The rotation axis of the substrate holder 3 can be either a vertical axis or an axis that is angled relative to the vertical direction.

The nozzle 4 sprays the chemical solution onto the surface of the held substrate 100. The nozzle 4 can be fixed in position or adjusted radially or vertically relative to the substrate 100. Adjustment can be performed before spraying or dynamically during spraying.

The lower portion of the single-wafer cleaner 2 is the recovery unit 5, which recovers the chemical solution sprayed onto the substrate 100.

Treatment system 1 comprises a recovery device storage tank 6; a liquid feed line 7A, which supplies the chemical solution in recovery device storage tank 6 to nozzle 4; and a liquid collection line 7B, which returns the chemical solution from recovery section 5 to recovery device storage tank 6. Both liquid feed line 7A and liquid collection line 7B are equipped with pumps (not shown) for transporting the treatment liquid. Liquid feed line 7A is also equipped with a heating unit 8 for heating the transported treatment liquid. The configuration of heating unit 8 is not particularly limited; an appropriate heater, etc., may be used.

Furthermore, treatment system 1 includes electrolysis devices 10A, 10B, and 10C for electrolyzing the chemical solution. Electrolysis devices 10A, 10B, and 10C are arranged in parallel, and are connected to their liquid inlet sides with an electrolyte supply line 11A for transporting sulfuric acid. The starting end of electrolyte supply line 11A is located within the recovery device storage tank 6. A cooler 12 and a pump 13 are provided on electrolyte supply line 11A to cool the sulfuric acid.

Electrolyte return line 11B is connected to the liquid outlet of electrolysis units 10A, 10B, and 10C. The front end of electrolyte return line 11B is located within the recovery unit storage tank 6. A filter 14 is installed on electrolyte return line 11B to capture particles contained in the sulfuric acid.

Next, the processing method using processing system 1 is described.

During semiconductor device manufacturing, a substrate 100 with residual photoresist film is placed on a substrate holder 3 and held. A recovery device storage tank 6 contains sulfuric acid L, which serves as a chemical solution. The concentration of sulfuric acid L is preferably set to 85% to 96% by mass.

Sulfuric acid L contained in the recovery device storage tank 6 is transported via a liquid delivery line 7A by a pump (not shown), heated by a heating unit 8, preferably to a temperature of 130-200°C, and then supplied to the nozzle 4. At this time, the substrate 100 is held by the substrate holder 3 and rotated with the substrate surface facing upward. The sulfuric acid ejected from the nozzle 4 ideally has this temperature.

The sulfuric acid sprayed from the nozzle 4 contacts the surface of the substrate 100, removing the photoresist film remaining on the surface of the substrate 100 and dissolving it into the sulfuric acid.

The sulfuric acid containing the photoresist is recovered by the recovery unit 5. The recovery unit 5 can be configured in a container shape, etc.

The sulfuric acid that has been moved to the recovery section 5, while still containing photoresist components, is returned to the recovery device storage tank 6 via a pump (not shown) through the liquid collection line 7B.

Following this action, the sulfuric acid L returned to the recovery device storage tank 6 is transported to the electrolysis unit via electrolyte feed line 11A by pump 13. At this point, the sulfuric acid is cooled by cooler 12, preferably to a temperature between 20°C and 60°C. Ideally, the sulfuric acid should be at this temperature when introduced into the electrolysis unit.

The sulfuric acid transported by the electrolyte supply line 11A contains the photoresist components removed from the substrate 100 and is branched and transported to the electrolysis devices 10A, 10B, and 10C.

In electrolysis devices 10A, 10B, and 10C, a voltage is applied between electrodes (not shown) to electrolyze sulfuric acid passing through them. The voltage and current during electrolysis can be set appropriately.

Electrolysis of sulfuric acid generates peroxodisulfuric acid, a strong oxidizing agent. This decomposes the photoresist dissolved in the sulfuric acid into carbon dioxide and water. The sulfuric acid containing peroxodisulfuric acid is then supplied to the sulfuric acid storage tank 6 of the recovery unit via an electrolyte return line 11B and a pump (not shown). This decomposes the photoresist contained in the sulfuric acid returning from the single-wafer cleaner 2.

Furthermore, the sulfuric acid used to remove photoresist contains not only the photoresist but also the implanted elements or molecules. As shown in Figure 2, arsenic (As), the most commonly used ion in semiconductor device manufacturing, forms particles in the form of _As₂O₃ . Therefore, it is removed by filter 14, which can capture particles smaller than _As₂O₃ , approximately 5 nm in diameter. Furthermore, filter 14 can be used with a particle size suitable for removal.

The sulfuric acid contained in the recovery device's storage tank 6 decomposes the photoresist and is then supplied to the nozzle 4 via a pump (not shown) via a liquid delivery line 7A. The sulfuric acid is heated to 130-200°C by a heating unit 8 and used to remove the photoresist film from the substrate 100.

Furthermore, while the sulfuric acid solution returning from electrolysis units 10A, 10B, and 10C contains a small amount of peroxodisulfuric acid (oxidizing agent), this is consumed by the decomposition of the photoresist in the recovery unit's storage tank 6. Furthermore, the residual peroxodisulfuric acid, less than 0.5 g/L, is accelerated by heating in heating unit 8, resulting in virtually no residual peroxodisulfuric acid remaining in the sulfuric acid when it is ejected from nozzle 4.

Furthermore, if the oxidant concentration is less than 1 g/L, the redox potential will not reach 1,100 mV, as shown in Figure 3, which is roughly equivalent to that of a sulfuric acid bath.

The above process allows for the repeated use of sulfuric acid, significantly reducing the amount of chemicals required for the process. Specifically, high-concentration sulfuric acid can be used instead of SPM as the treatment solution for stripping and removing the organic, hydrophobic photoresist film, while electrolysis decomposes the photoresist dissolved in the sulfuric acid into carbon dioxide and water.

Furthermore, in the above embodiment, the photoresist film is described as the object to be removed from the substrate. However, the object to be removed is not limited to the photoresist film, and can be broadly used to include any object that can be removed by sulfuric acid and decomposed by electrolysis.

[Example 1]

The following describes an embodiment of a processing method using the processing system 1 shown in FIG1 .

Sulfuric acid with a concentration of 85% to 96% by mass is placed in the recovery device's storage tank 6. The sulfuric acid is heated to 130°C to 200°C and then sprayed onto the substrate. The sulfuric acid sprayed onto the substrate is recovered using a liquid collection line. Simultaneously, the sulfuric acid circulates through the electrolysis device. After decomposing the photoresist, the sulfuric acid is heated to 130°C to 200°C and sprayed onto the substrate again.

In each test case, photoresist was removed from the substrate using sulfuric acid at the concentrations and temperatures shown in Table 2. Each sulfuric acid did not contain an oxidizing agent. The removal capability was evaluated under the following conditions, and the results are shown in Table 2.

Substrate: 300mm silicon wafer

Photoresist: For ArF, thickness 1000nm

Implant: As, 1.0×10 ¹⁵ atoms/cm ²

Nozzle output: 0.9L/min

Processing time: Up to 90 seconds

Electrolysis conditions: (1) Sulfuric acid solution temperature 40°C

(2) Current density 1.5A/ ^dm2

Although detailed descriptions of the embodiments of the present invention are provided, these descriptions are intended only to clarify the specific examples of the technical content of the present invention. The present invention should not be construed as limited to these specific examples. The scope of the present invention is solely defined by the scope of the accompanying patent applications.

[Related Applications]

This application claims priority based on Japanese Patent Application No. 2023-29373 filed on February 28, 2023, the entire contents of which are incorporated herein by reference.

1: Processing system

2: Single-chip cleaner

3: Substrate holding unit

4: Nozzle

5: Recycling Department

6: Recovery device storage tank

7A: Liquid delivery line

7B: Liquid collecting line

8: Heating section

10A: Electrolysis device

10B: Electrolysis device

10C: Electrolysis device

11A: Electrolyte delivery line

11B: Electrolyte return line

12: Cooler

13: Pump

14: Filter

100:Substrate

L: Sulfuric acid

Claims (8)

A substrate processing method employing a single-wafer cleaning machine and a treatment liquid to remove a photoresist film from a substrate surface is disclosed. The substrate is held within the single-wafer cleaning machine and rotated about an axis intersecting the substrate surface. A sulfuric acid solution is released onto the substrate surface as the treatment liquid. The sulfuric acid solution containing the photoresist detached from the substrate is recovered, electrolyzed to decompose the photoresist, and then returned to the single-wafer cleaning machine to remove the photoresist film from the substrate surface. In the substrate processing method of claim 1, a sulfuric acid solution heated by a heating unit is released onto the surface of the substrate as the processing liquid, and the oxidizing agent concentration in the sulfuric acid solution before heating by the heating unit is set to less than 1 g/L. In the substrate processing method of claim 1, a sulfuric acid solution heated by a heating unit is released onto the surface of the substrate as the processing liquid, and the oxidizing agent concentration in the sulfuric acid solution before heating by the heating unit is set to less than 0.5 g/L. In the substrate processing method of any one of claims 1 to 3, a sulfuric acid solution heated by a heating unit is released onto the surface of the substrate as the processing liquid, and the redox potential of the sulfuric acid solution before heating by the heating unit is less than 1,100 mV. The substrate processing method of any one of claims 1 to 3, wherein the sulfuric acid solution released onto the substrate has a sulfuric acid concentration of 85% to 96% by mass, and the temperature of the sulfuric acid solution released onto the substrate is set to 130°C to 200°C when the sulfuric acid concentration of the sulfuric acid solution exceeds 95% to 96% by mass, 150°C to 200°C when the sulfuric acid concentration exceeds 90% to 95% by mass, and 170°C to 200°C when the sulfuric acid concentration is 85% to 90% by mass. In the substrate processing method according to any one of claims 1 to 3, the sulfuric acid solution is released by spraying the sulfuric acid solution from a nozzle. The substrate processing method according to any one of claims 1 to 3, wherein the recovered sulfuric acid solution is cooled to 20°C to 60°C and the electrolysis is performed. The substrate processing method according to any one of claims 1 to 3 is characterized in that the sulfuric acid solution after the electrolysis is passed through a filter that removes particles of a specified diameter.