WO2024181433A1 - Substrate processing method - Google Patents

Abstract

A substrate processing method according to the present invention is a substrate processing method which uses a sheet-fed washing machine to remove a photoresist film from the surface of a substrate by using a processing solution, wherein: the substrate is held inside the sheet-fed washing machine; the substrate is rotated around an axis that intersects the plane of the substrate, and a sulfuric acid solution is discharged onto the surface of the substrate as the processing solution; the sulfuric acid solution, which now includes the photoresist separated from the substrate, is collected; the collected sulfuric acid solution is electrolyzed so as to decompose the photoresist; and the sulfuric acid solution, in which the photoresist has now been decomposed, is returned to the sheet-fed washing machine and used again for removing the photoresist film from the surface of the substrate.

Description

Substrate processing method Related Applications

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

The present invention relates to a technique for treating a substrate using a treatment liquid, for example, to a method for treating a substrate in a single-wafer cleaning machine that removes a photoresist film on the substrate surface using a treatment liquid.

For the purpose of surface treatment of various substrates such as semiconductor substrates and glass substrates, cleaning treatment of the substrates with a treatment liquid is widely practiced. For example, in a process for peeling and removing a photoresist film formed on the surface of a semiconductor substrate, a mixture of concentrated sulfuric acid and hydrogen peroxide (Sulfuric acid-hydrogen peroxide mixture: SPM) is used as the treatment liquid. For example, in the technology described in Patent Document 1, in a single-wafer cleaning machine, a substrate is held in a horizontal position and rotated at a predetermined speed, and SPM is discharged from a nozzle arranged above the substrate.
SPM uses an oxidizing agent called peroxomonosulfuric acid ( _H2SO5 ), which is generated by the reaction of sulfuric acid and hydrogen peroxide as shown in formula ( ₁ ). Once used to remove a photoresist film, peroxomonosulfuric acid is no longer consumed. Therefore, in order to reuse this used solution, it is necessary to add hydrogen peroxide again. However, as can be seen from formula (1), when hydrogen peroxide is added, _H2O (water) is produced as a by-product, and the sulfuric acid concentration decreases.
H ₂ SO ₄ + H ₂ O ₂ → H ₂ SO ₅ + H ₂ O Formula (1)

When the sulfuric acid concentration decreases, the photoresist film removal performance drops significantly, so the number of times hydrogen peroxide is added and reused is about one or two times. In addition, since the sulfuric acid concentration is different from that of the original SPM when reused by adding hydrogen peroxide, many semiconductor device manufacturers discard SPM after one use from the viewpoint that manufacturing should be done in the same process, and use large amounts of sulfuric acid and hydrogen peroxide solution to remove photoresist films. The cost of purchasing these chemicals and the large cost required for waste liquid treatment are pushing up the price of semiconductor devices.
Semiconductor manufacturing equipment can be broadly divided into two types: batch and single-wafer. Batch types process many substrates at the same time, while single-wafer types process substrates one at a time.
In recent years, the trend has shifted from mass production of a small variety of products, where many of a single product are produced, to small-variety production of a large variety of products, where many different products are produced in small quantities, and the advantages of the batch system are becoming less and less useful. In addition, as the line width of semiconductor IC circuits has become narrower, there is a demand for the dimensions of impurities such as fine particles to be small and for the amount of impurities adhering per unit area to be small. As a result, the use of single-wafer systems has been increasing in manufacturing equipment, especially cleaning equipment (see, for example, Patent Document 1).

Patent No. 5127325

As described in Patent Document 1, the SPM mixes hydrogen peroxide water at a flow rate ratio of 0.1 to 0.35 to sulfuric acid 1. The sulfuric acid concentration after this mixing is 76.9% by mass to 87.8% by mass.
The inventors of the present application have found that a sulfuric acid solution is hydrophilic when its concentration is low, and hydrophobic when its concentration is high, and that a photoresist can be dissolved when its concentration exceeds 75 mass %, and that the lower the sulfuric acid concentration, the higher the sulfuric acid temperature must be.Furthermore, the inventors have found that the use of a treatment solution containing an oxidizing agent such as SPM acts to lower the sulfuric acid concentration or sulfuric acid temperature at which photoresist can be removed.
When sulfuric acid without oxidizing agent is used as the treatment liquid, the sulfuric acid concentration or sulfuric acid temperature must be increased slightly, but photoresist can be effectively dissolved. However, since the photoresist dissolves in the treatment liquid, it is necessary to decompose the photoresist in the sulfuric acid into carbon dioxide and water and remove it in order to reuse it repeatedly.

When the sulfuric acid that has dissolved the photoresist is electrolyzed, the reaction shown in formula (2) at the anode produces peroxodisulfuric acid (H ₂ S ₂ O ₈ , redox potential: 2.01 V), a strong oxidizing agent with a higher redox potential than peroxomonosulfuric acid (redox potential: 1.81 V) obtained by SPM (see Table 1 below).
2H ₂ SO ₄ → H ₂ S ₂ O ₈ + 2H ⁺ + 2e ^- Formula (2)
When this peroxodisulfuric acid is heated to a high temperature, it becomes the sulfate radical SO ₄ ^- . according to formula (3). As a result, the photoresist (referred to as R) dissolved in the sulfuric acid is converted into the organic radical R. as shown in formula (4), which increases its reactivity and ultimately allows it to be decomposed into carbon dioxide and water.
S ₂ O ₈ ^2- → 2SO ₄ ^-・ Formula (3)
SO ₄ ⁻ · + R → R· + HSO ₄ ⁻ Equation (4)
The sulfuric acid used to remove the photoresist can be reused to remove a photoresist film.

The present invention was made against the background of the above circumstances, and one of its objectives is to provide a substrate processing method that enables repeated use of the sulfuric acid solution that has been used to remove photoresist and other substances from a substrate.

One aspect of the present invention provides a substrate processing method for removing a photoresist film on a substrate surface with a processing liquid using a single-wafer cleaning machine. This substrate processing method holds the substrate in a single-wafer cleaning machine, rotates the substrate around an axis intersecting the surface of the substrate, and releases a sulfuric acid solution as the processing liquid onto the substrate surface, recovers the sulfuric acid solution containing the photoresist that has been detached from the substrate, electrolyzes the recovered sulfuric acid solution to decompose the photoresist, and returns the sulfuric acid solution containing the decomposed photoresist to the single-wafer cleaning machine again and uses it to remove the photoresist film on the substrate surface.

According to the above-mentioned substrate processing method, the photoresist film can be effectively removed by contacting the sulfuric acid solution with the surface of the substrate rotating in the single-wafer cleaning machine. The sulfuric acid solution containing the removed photoresist is then electrolyzed to decompose the photoresist, and the electrolyzed sulfuric acid solution can be reused for substrate processing. This allows the sulfuric acid solution to be recycled without changing the photoresist film removal performance, thereby achieving a significant reduction in the amount of chemicals used.
The sulfuric acid concentration of the sulfuric acid solution discharged onto the substrate is preferably 85% by mass to 96% by mass.
The temperature of the sulfuric acid solution discharged onto the substrate is preferably 130° C. to 200° C. when the sulfuric acid concentration of the sulfuric acid solution is from 95% by mass to 96% by mass, 150° C. to 200° C. when the sulfuric acid concentration is from 90% by mass to 95% by mass, and 170° C. to 200° C. when the sulfuric acid concentration is from 85% by mass to 90% by mass.

It is preferable that a sulfuric acid solution heated by a heating unit is discharged onto the surface of the substrate as the treatment liquid. In this case, it is preferable that an oxidizing agent concentration in the sulfuric acid solution before heating by the heating unit is less than 0.5 g/L. It is also preferable that an oxidation-reduction potential of the sulfuric acid solution before heating by the heating unit is less than 1,100 mV.
The above substrate processing method has an object to remove photoresist and the like from a substrate using a sulfuric acid solution, electrolyze the sulfuric acid solution containing the photoresist to decompose the photoresist, and repeatedly use the sulfuric acid solution from which the photoresist has been removed. In this case, in the electrolysis of the sulfuric acid solution, the oxidizing agent is used up in the decomposition of the photoresist, and the electrolyzed sulfuric acid solution contains almost no oxidizing agent (oxidizing agent concentration is less than 0.5 g/L). Such a sulfuric acid solution is supplied into a cleaning machine and further contacted with a substrate to remove the photoresist. In this way, the cleaning process can be performed by repeatedly using the sulfuric acid solution. The concentration of the oxidizing agent can be easily controlled by predicting the concentration of the oxidizing agent before electrolysis or by measuring the concentration of the oxidizing agent in the sulfuric acid solution before it is supplied to the cleaning machine.

Sulfuric acid solutions with appropriate concentration and temperature settings perform cleaning actions that are superior to those containing persulfuric acid. By supplying a sulfuric acid solution that contains almost no oxidizing agents to the cleaning machine, it is possible to clean substrates without placing an excessive burden on the electrolytic process. In addition, various parts are used in cleaning machines, and if persulfuric acid, which has high oxidation-reduction properties, comes into contact with the parts, the parts deteriorate relatively quickly, which can lead to problems such as increased frequency of replacement. For example, fluororesin tubes, which are commonly used in the piping of single-wafer cleaning machines, have excellent heat and chemical resistance, but when the processing liquid is heated to a high temperature or pressurized, if an oxidizing agent is present in the processing liquid, the deterioration of the parts may progress quickly. Therefore, by using a sulfuric acid solution that contains almost no oxidizing agents during cleaning, the deterioration of the parts can be suppressed.

In another aspect of the substrate processing method of the present invention, the sulfuric acid solution is discharged by ejection from a nozzle.
In another embodiment of the substrate processing method of the present invention, the recovered sulfuric acid solution is cooled to 20° C. to 60° C., and then electrolysis is performed.
In another aspect of the substrate processing method of the present invention, the sulfuric acid solution that has been electrolyzed is passed through a filter that removes particles of a predetermined diameter.

The contents stipulated in this section are explained below.
Sulfuric acid concentration: 85% by mass to 96% by mass
When removing the photoresist film, the concentration of the sulfuric acid solution is not limited to a specific range, but the sulfuric acid concentration is preferably 85% by mass to 96% by mass. If the sulfuric acid concentration is too low, the hydrophobicity of the sulfuric acid solution will be weakened, and the dissolution rate of the photoresist will be slow. In addition, although there is no problem if the sulfuric acid solution concentration is too high, the sulfuric acid concentration commercially available for semiconductors is 96% by mass.

Sulfuric acid solution temperature: 130℃~200℃
When removing the photoresist film, the temperature of the sulfuric acid solution is not limited to a specific range, but it is preferable to set it to 130° C. to 200° C. If the temperature of the sulfuric acid solution is too low, the dissolution rate of the photoresist is slow. If the temperature of the sulfuric acid solution is too high, not only will the load on the heating section increase, but it will also become necessary to select components in the single-wafer cleaning machine that are more heat-resistant.
When the sulfuric acid concentration of the sulfuric acid solution is more than 95% by mass to 96% by mass, the temperature is set to 130° C. to 200° C., when the sulfuric acid concentration is more than 90% by mass to 95% by mass, the temperature is set to 150° C. to 200° C., and when the sulfuric acid concentration is more than 85% by mass to 90% by mass, the temperature is set to 150° C. to 200° C. In this case, it is preferable to set the temperature at 170 to 200°C.

Sulfuric acid solution temperature during electrolysis: 20°C to 60°C
The sulfuric acid solution from which the photoresist film has been removed is desirably kept at 20° C. to 60° C. when electrolyzing. If the temperature of the sulfuric acid solution is too low, the diffusion rate of sulfate ions is slow, and the rate of production of peroxodisulfuric acid is slow. If the temperature of the sulfuric acid solution is too high, the diffusion rate of substances in the sulfuric acid solution is fast, and the generated peroxodisulfuric acid is reduced at the cathode, making it impossible to increase the concentration of peroxodisulfuric acid.

1 is a schematic diagram showing an example of an apparatus used in an embodiment of the present invention. FIG. 1 is a Pourbey diagram for arsenic. FIG. 1 is a graph showing the relationship between oxidant concentration and oxidation-reduction potential.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
The processing system 1 includes a single-wafer cleaning machine 2 that processes substrates with chemicals, and further includes a liquid collection system for recovering the chemicals used.

The single-wafer cleaning machine 2 has a substrate holding section 3 that can hold a substrate 100 used in the manufacture of semiconductor devices with its surface horizontal and rotate it around a vertical axis of rotation, and a nozzle 4 that is positioned above the held substrate 100 and sprays a chemical solution downward.
In this embodiment, the substrate holder 3 holds the substrate 100 so that the surface thereof is horizontal. However, the present invention is not limited to a substrate holder that holds the substrate surface horizontally, and a substrate holder that holds the substrate surface at an angle relative to the horizontal direction may also be used. A substrate holder that can dynamically change the tilt angle and tilt direction while the substrate is rotating may also be used. The rotation axis of the substrate holder 3 may be a rotation axis that is aligned along the vertical direction, or may be a rotation axis that is angled relative to the vertical direction.

The nozzle 4 discharges the chemical solution onto the surface of the held substrate 100. The position of the nozzle 4 may be fixed, or the radial position and the vertical position may be adjustable with respect to the substrate 100. The adjustment may be performed before discharge, or may be performed dynamically during discharge.
The lower portion of the single wafer cleaning machine 2 serves as a recovery section 5 for recovering the chemical solution discharged onto the substrate 100 .

The treatment system 1 has a recovery device storage tank 6, a liquid delivery line 7A that supplies the chemical liquid in the recovery device storage tank 6 to the nozzle 4, and a liquid collection line 7B that returns the chemical liquid in the recovery section 5 to the recovery device storage tank 6. The liquid delivery line 7A and the liquid collection line 7B are provided with pumps (not shown) that deliver the treatment liquid. In addition, the liquid delivery line 7A is provided with a heating section 8 that heats the treatment liquid being delivered. The configuration of the heating section 8 is not particularly limited, and an appropriate heater or the like can be used.

The treatment system 1 further includes electrolysis devices 10A, 10B, and 10C that electrolyze the chemical solution. The electrolysis devices 10A, 10B, and 10C are arranged in parallel, and an electrolyte solution delivery line 11A that delivers sulfuric acid is connected to the inlet side of the electrolysis devices 10A, 10B, and 10C. The start end of the electrolyte solution delivery line 11A is arranged in the recovery device storage tank 6, and a cooler 12 that cools the sulfuric acid and a pump 13 are interposed in the electrolyte solution delivery line 11A.
An electrolyte return line 11B is connected to the discharge side of the electrolysis devices 10A, 10B, and 10C, and the tip side of the electrolyte return line 11B is disposed in the recovery device storage tank 6. A filter 14 that captures particles contained in the sulfuric acid is disposed in the electrolyte return line 11B.

Next, a processing method using the processing system 1 will be described.
A substrate 100 on which a photoresist film remains during the manufacture of a semiconductor device is placed and held on a substrate holder 3. A recovery device storage tank 6 contains sulfuric acid L as a chemical liquid. The concentration of sulfuric acid L is preferably 85% by mass to 96% by mass.
The sulfuric acid L contained in the recovery device storage tank 6 is sent by a pump (not shown) through a liquid sending line 7A, heated to preferably 130 to 200° C. by a heating unit 8, and supplied to the nozzle 4. At this time, the substrate 100 is held by a substrate holding unit 3 and rotated with the substrate surface facing upward. The sulfuric acid discharged from the nozzle 4 desirably has the above temperature.
The sulfuric acid discharged from the nozzle 4 comes into contact with the surface of the substrate 100, removing the photoresist film remaining on the surface of the substrate 100 and incorporating it into the sulfuric acid.
The sulfuric acid containing the photoresist is collected in the collection section 5. The collection section 5 can be configured in the shape of a container or the like.

The sulfuric acid that has moved to the recovery section 5 is returned to the recovery device storage tank 6 via a liquid collection line 7B while still containing the photoresist components by a pump (not shown).
Along with this operation, the sulfuric acid L returned to the recovery device storage tank 6 is sent to the electrolysis device side by the pump 13 through the electrolyte sending line 11A. At this time, the sulfuric acid is cooled by the cooler 12 to preferably 20° C. to 60° C. It is desirable that the sulfuric acid has the above temperature when it is introduced into the electrolysis device.

The sulfuric acid sent through the electrolyte sending line 11A contains the photoresist components removed from the substrate 100, and is branched and sent to the electrolysis devices 10A, 10B, and 10C.
In the electrolysis devices 10A, 10B, and 10C, a voltage is applied between electrodes (not shown) to electrolyze sulfuric acid passing between the electrodes. The voltage and current during electrolysis can be set appropriately.

The electrolysis of sulfuric acid produces peroxodisulfuric acid, a strong oxidizing agent, which breaks down the photoresist dissolved in the sulfuric acid into carbon dioxide and water. Furthermore, sulfuric acid containing peroxodisulfuric acid is supplied to the sulfuric acid in the recovery device storage tank 6 by a pump (not shown) via the electrolyte return line 11B, which breaks down the photoresist contained in the sulfuric acid returned from the single-wafer cleaning machine 2.

The sulfuric acid used to remove the photoresist contains the implanted elements or molecules in addition to the photoresist. Arsenic (As), which is the most widely used element in semiconductor device manufacturing, turns into fine _{particles as As2O3 as} shown in Fig. 2, and is removed by a filter 14 capable of capturing fine particles of about 5 nm, which are smaller than the particle diameter of As. The filter 14 may be one that has an appropriate particle diameter that can be removed.

The sulfuric acid contained in the recovery device storage tank 6 has the photoresist decomposed therein, and is supplied again to the nozzle 4 by a pump (not shown) via the liquid supply line 7A. At this time, the sulfuric acid is heated to 130 to 200° C. by the heating unit 8 and used to remove the photoresist film from the substrate 100.
Although a small amount of peroxodisulfuric acid (oxidizing agent) is contained in the sulfuric acid solution returned from the electrolysis devices 10A, 10B, and 10C, this is consumed due to the decomposition of the photoresist in the recovery device storage tank 6. In addition, the decomposition of less than 0.5 g/L of peroxodisulfuric acid remaining in the sulfuric acid is promoted by the heating of the heating unit 8, and almost no peroxodisulfuric acid remains in the sulfuric acid when it is discharged from the nozzle 4.
Furthermore, when the oxidizing agent concentration is less than 1 g/L, the oxidation-reduction potential is less than 1,100 mV as shown in FIG. 3, which is almost the same as that of a sulfuric acid bath.

The above operation allows sulfuric acid to be reused repeatedly, making it possible to significantly reduce the amount of chemicals required for processing. In other words, high-concentration sulfuric acid can be used instead of SPM as the processing liquid in the process of peeling and removing photoresist films, which are organic and hydrophobic, and the photoresist dissolved in sulfuric acid can be decomposed into carbon dioxide and water by electrolysis.

In the above embodiment, a photoresist film is described as the object to be removed from the substrate, but the object to be removed is not limited to a photoresist film, and can be anything that can be removed with sulfuric acid and decomposed by electrolysis.

An embodiment of a processing method using the processing system 1 of FIG. 1 will be described below.
Sulfuric acid with a concentration of 85% to 96% by mass is placed in the recovery device storage tank 6 in advance, and the sulfuric acid is heated to a temperature of 130°C to 200°C before being sprayed onto the substrate. The sulfuric acid sprayed onto the substrate is recovered using a liquid collection line. At the same time, the sulfuric acid is circulated to the electrolysis device. The sulfuric acid that has decomposed the photoresist is heated to a temperature of 130°C to 200°C and sprayed onto the substrate again.
In each test example, the photoresist on the substrate was removed using sulfuric acid at the sulfuric acid concentration and heating temperature shown in Table 2. Each sulfuric acid did not contain an oxidizing agent, and the removability was evaluated under the following conditions, and the results are shown in Table 2.

Substrate: φ300 mm Si wafer Photoresist: ArF type, thickness 1000 nm
Implant: As, 1.0×10 ¹⁵ atoms/cm ²
Discharge rate from nozzle: 0.9 L/min
Treatment time: up to 90 seconds Electrolysis conditions: (1) Temperature of sulfuric acid solution: 40°C
(2) Current density 1.5A/dm ²

Although the embodiments of the present invention have been described in detail, these are merely examples used to clarify the technical content of the present invention, and the present invention should not be interpreted as being limited to these examples, and the scope of the present invention is limited only by the scope of the attached claims.

REFERENCE SIGNS LIST 1 Processing system 2 Single-wafer cleaning machine 3 Substrate holder 4 Nozzle 5 Recovery unit 6 Recovery unit storage tank 7A Liquid delivery line 7B Liquid collection line 8 Heating unit 10A Electrolysis unit 10B Electrolysis unit 10C Electrolysis unit 11A Electrolyte delivery line 11B Electrolyte return line 12 Cooler 13 Pump 14 Filter 100 Substrate L Sulfuric acid

Claims (7)

A substrate processing method for removing a photoresist film on a substrate surface with a processing liquid using a single-wafer cleaning machine, comprising the steps of:
Holding the substrate in a single wafer cleaning machine;
The substrate is rotated around an axis intersecting a surface of the substrate, and a sulfuric acid solution is discharged onto the surface of the substrate as the treatment liquid;
Recovering the sulfuric acid solution containing the photoresist removed from the substrate;
The recovered sulfuric acid solution is electrolyzed to decompose the photoresist;
the sulfuric acid solution in which the photoresist has been decomposed is returned to the single-wafer cleaning machine and used to remove the photoresist film on the surface of the substrate. A sulfuric acid solution heated by a heating unit is discharged as the processing liquid onto the surface of the substrate;
2. The substrate processing method according to claim 1, wherein the oxidizing agent concentration in the sulfuric acid solution before heating by the heating part is less than 0.5 g/L. A sulfuric acid solution heated by a heating unit is discharged as the processing liquid onto the surface of the substrate;
3. The substrate processing method according to claim 1, wherein the oxidation-reduction potential of the sulfuric acid solution before heating by the heating part is less than 1,100 mV. The sulfuric acid concentration of the sulfuric acid solution discharged onto the substrate is 85% by mass to 96% by mass;
The substrate processing method according to any one of claims 1 to 3, wherein a temperature of the sulfuric acid solution discharged onto the substrate is set to 130°C to 200°C when the sulfuric acid concentration of the sulfuric acid solution is from 95% by mass to 96% by mass, 150°C to 200°C when the sulfuric acid concentration is from 90% by mass to 95% by mass, and 170°C to 200°C when the sulfuric acid concentration is from 85% by mass to 90% by mass. The substrate processing method according to any one of claims 1 to 4, wherein the sulfuric acid solution is discharged by ejection from a nozzle. The substrate processing method according to any one of claims 1 to 5, wherein the recovered sulfuric acid solution is cooled to 20°C to 60°C and electrolysis is performed. The substrate processing method according to any one of claims 1 to 6, wherein the electrolyzed sulfuric acid solution is passed through a filter that removes particles of a predetermined diameter.

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