JP4606936B2 - Substrate cleaning method - Google Patents

Description

  The present invention relates to a method for cleaning a substrate or the like using ozone water, which is applied in a cleaning operation of an organic substance or the like adhering to the substrate or the like in a semiconductor or liquid crystal manufacturing process. In more detail, ozone water that can be applied to the removal of resist from a semiconductor or liquid crystal substrate, the removal of organic contaminants, or the removal of an organic masking agent from a quartz plate or the like used in semiconductors or liquid crystals was used. The present invention relates to a substrate cleaning method. Furthermore, it can be applied as a treatment using ozone water such as surface modification.

  As a semiconductor cleaning process, an RCA method developed by an American RCA company in 1970 is known. The cleaning method is a method using four types of cleaning, sulfuric acid / hydrogen peroxide (SPM), dilute hydrofluoric acid (DHF), ammonia / hydrogen peroxide (APM), and hydrochloric acid / hydrogen peroxide (HPM). This cleaning method was an excellent cleaning method with high decontamination capability and reduced surface damage. Therefore, this cleaning method or a modification of this RCA method is still mainstream. However, this method uses concentrated chemicals, and it must be rinsed with pure water every time the cleaning water changes. Therefore, a large amount of pure water is used. Problems such as water pollution and deterioration of the work environment have arisen, such as an increased burden. For this reason, today, a cleaning method that uses a small amount of chemical solution and has a low environmental load is expected.

  Even in the case of a glass substrate related to liquid crystal, it is necessary to perform sufficient cleaning before receiving the substrate when the substrate is received. Cleaning at that time uses pure water, a detergent, a chemical solution, or the like as a cleaning solution, and cleaning methods are performed by various methods such as brush cleaning, ultraviolet irradiation, and ultrasonic cleaning. In the case of a liquid crystal substrate, since the size is very large compared to a semiconductor wafer, the amount of cleaning liquid used is increased.

  These cleaning methods include a batch type and a single wafer type. In the batch type, the substrate to be cleaned is immersed in a cleaning liquid tank for a certain period of time, then washed with pure water, then immersed in another cleaning liquid tank and washed with pure water. This is a method of repeating the cleaning operation as many times as possible. At this time, if the cleaning liquid decreases, it is added, and if the cleaning liquid deteriorates, it is necessary to replace the entire amount. At this time, a large amount of waste water is discharged. Similarly, the pure water that is the rinsing liquid needs to be replaced.

  In the single wafer type, it is not necessary to directly immerse the object to be cleaned, but a large amount of cleaning liquid is used for cleaning each sheet. When the cleaning liquid is circulated and used, the cleaning liquid tank is provided as a service tank, and the waste water is discharged as in the batch type. Moreover, pure water is required as rinse water to remove the cleaning liquid, and the waste water is also discharged.

  As described above, a large amount of waste water is discharged when cleaning semiconductors, liquid crystal substrates, and the like. At present, it is desired to reduce the waste water and to replace it with a safe and less dangerous cleaning liquid. As one of the alternative technologies, ozone water with oxidizing power is attracting attention.

  At present, ozone water is generally used as a disinfectant at about 10 ppm or less, and in the semiconductor industry, water having a relatively low concentration of 10 to 20 ppm is used as cleaning water. However, since the oxidizing power of ozone is very strong, there is an expectation that it will be used for cleaning organic substances such as liquid crystals and wafers in recent years, and application to this field has been attempted.

  However, despite the fact that ozone water has a very strong oxidizing power, ozone can be used only as a disinfectant or for cleaning dust such as simple wafers. The cause was that it was difficult to produce high-concentration ozone water because it was very insoluble in water, and secondly, ozone in ozone water was very easily decomposed. For this reason, ozone is decomposed before reaching the point of use, and the oxidizing power is lost.

  Decomposition of ozone is generally said to be self-decomposition because it occurs even with ozone alone, and the rate of self-decomposition is very fast with ozone water produced from ultrapure water. Is known to be less than 1 minute. However, by adding chemicals such as carbon dioxide and isopropyl alcohol, the self-decomposition rate can be suppressed, and there is data that extends about 15 to 20 times in half-life.

  Regarding the increase in the concentration of ozone water, that is, the production of high-concentration ozone water, as can be seen in Patent Document 1, it is possible to easily produce ozone water of 100 to 150 ppm by using a multistage countercurrent contact device. ing. Furthermore, as described in Patent Document 2, it is becoming possible to produce ozone water having a high temperature by adding steam to the ozone water.

  As described above, high-concentration ozone water can be produced, high-temperature ozone water that is considered to contribute to the oxidation rate can be produced, and a method capable of suppressing the self-decomposition rate has been established. However, such a condition is necessary but not sufficient for cleaning an organic substance of a semiconductor or a liquid crystal substrate, for example, a photoresist (hereinafter referred to as “resist”).

  In the resist cleaning of the wafer substrate by the experiments of the present inventors, the resist cleaning was attempted by pouring ozone water from a nozzle fixed on the wafer. At the initial stage of water pouring, the resist was peeled off at a relatively high speed. I begin, but after a certain period of time, I have experienced a sharp decline in cleaning ability.

  The reason for this is that the injected ozone water spreads concentrically around the water injection point, but the ozone water rises with a diameter of about several tens of millimeters and becomes difficult to flow around. To avoid this, if ozone water is poured into the center of the rotating shaft while the wafer is placed on a rotating table of a spinner and rotated, the ozone water easily flows to the surroundings due to centrifugal force, and the cleaning power is about doubled. It was possible to raise. It is understood that this method has the effect of increasing the liquid velocity of the ozone water flowing on the cleaning surface by causing the substrate to rotate, causing disturbance on the cleaning surface, and improving the cleaning ability.

  The above method requires high-speed rotation in order to increase the cleaning efficiency, and such operations are not problematic for small wafers, but when applied to large liquid crystal substrates, the substrate is subjected to centrifugal force. Becomes unbearable and makes it very difficult to rotate. In addition, since ozone water having a high temperature is used to increase the reaction rate, ozone scatters and the effective utilization of ozone also deteriorates.

  In addition, the method of irradiating the substrate with ultraviolet rays as a device for enhancing the reaction has been found to have a relatively good effect, but the effect is still limited to about 1.5 times that of the fixed water injection. was there.

On the other hand, there is a method in which a water tank for ozone water is provided and the cleaning treatment is performed in a batch manner.
1. Although autolysis can be suppressed, it is necessary to supply a large amount of expensive ozone water in order to maintain a high ozone concentration. 2. In order to increase the reaction rate, the temperature of the ozone water is increased, so that the loss due to ozone scatter is large. 3. In the water tank, generation of gas due to decomposition of ozone, and ozone and other source gases are supersaturated, and these gases adhere to the substrate surface and inhibit the reaction.

  As described above, there are many problems in the current technology for cleaning substrates and the like with ozone water, and further improvement is required for practical use.

Proceedings of the 14th Annual Meeting of the Japan Ozone Society, p. 101-104 “Ozone self-decomposition in ultrapure water for semiconductor cleaning” June 24, 2004 Published by Japan Ozone Association JP 2000-167366 A JP 2004-89971 A

  As described above, ozone in ozone water has a very fast self-decomposition rate, and because of the unique properties of ozone water, such as ozone being very difficult to dissolve in water, When surface treatment or the like is performed, the ozone concentration decreases before reaching the use point, or ozone is diffused during the cleaning operation, so that the use efficiency of ozone water is lowered.

  Moreover, even if an attempt is made to improve the utilization efficiency of ozone water by rotating the substrate to be cleaned to increase the disturbance of the ozone water on the cleaning surface, the efficiency is still low and needs to be further improved. . Further, it is difficult to rotate a large substrate.

  The present invention is intended to solve the above problems when cleaning a substrate or the like with ozone water, and even with a large substrate or the like without using a spin cleaning machine, the cleaning area per unit ozone water is increased, It is an object of the present invention to provide a cleaning method that can improve cleaning efficiency and efficiently perform substrate cleaning and the like.

First aspect of the present invention, the cover plate facing onto the cleaning surface of the substrate to be processed object, the substrate was placed and cover plate of the treatment object in a state of wearing the inclination angle, the substrate and the cover plate Is set to 2 mm or less, and ozone water is allowed to flow from the bottom to the top at an average flow rate of 0.1 m / s or more in the gap. The gap between the substrate and the cover plate is preferably 1 mm or less, and the average flow rate of ozone water is preferably 0.5 m / s or more.
The average flow rate of ozone water in the present invention is obtained by dividing the flow rate of ozone water by the cross-sectional area of the ozone water flow path.

  The invention according to claim 2 is the method for cleaning a substrate, wherein the ozone water is heated ozone water. This is to increase the cleaning efficiency of the substrate, etc. For this purpose, ozone water and water vapor are mixed and supplied immediately before use, or ozone water is passed through a heating device and supplied after heating. It is sufficient to adopt means such as The heating degree of ozone water is preferably 30 ° C. or higher, more preferably 50 ° C. or higher.

  The invention according to claim 3 is the substrate cleaning method according to claim 1 or 2, wherein the ozone concentration of ozone water is 50 ppm or more. This is to increase the cleaning efficiency of the substrate and the like.

  A fourth aspect of the present invention is the substrate cleaning method according to any one of the first to third aspects, wherein a gap between the substrate and the cover plate is 1 mm or less. This is for further improving the cleaning efficiency of the substrate and the like by further suppressing ozone diffusing and flowing ozone water at a higher speed.

Effects and effects of the invention

The present invention has been completed as a result of intensive studies in order to solve the problems of the prior art described above. In the present invention, it covers the upper cleaned surface of the substrate to be treated object with the covering plate, by flowing ozone water at a high speed in a gap formed by the substrate and the cover plate, wash the organic adhesion substances on the substrate Thus, the cleaning speed can be improved, and the area that can be cleaned per unit ozone water, that is, the cleaning efficiency can be remarkably increased. In addition, by installing the substrate to be processed and the cover plate at an inclined angle and flowing ozone water, the influence of the retention of fine air bubbles generated by decomposition of ozone water can be reduced. It becomes possible. In particular, ozone water is more preferably flowed from the bottom to the top of the gap.

  Therefore, if the cleaning scale of the substrate is the same, the scale of the ozone gas generator in the apparatus for producing ozone water can be made smaller, which contributes to the reduction of energy required for the production of ozone gas and the reduction of equipment costs. Will do.

  The present invention makes it possible to treat a large area such as a substrate uniformly, which is practically significant.

  With the cleaning method of the present invention, a cleaning speed that is about 4 times that of the cleaning method without a cover plate and about 2 times that of the spin cleaning method is achieved.

  When ozone water is used as the cleaning liquid, it is necessary to fully understand the nature of the ozone water. First, ozone water has a very fast self-decomposition rate. Although it differs depending on the level of pure water in which ozone is dissolved and the concentration of ozone water, high-concentration ozone water dissolved in ultrapure water used at the semiconductor level has a half-life of less than 1 minute. Yes. Therefore, it must be supplied near the point of use and processed as quickly as possible.

  Second, by dissolving ozone in pure water under pressure, it is possible to produce higher-concentration ozone water. The ozone concentration decreases by scattering. Therefore, in order to suppress the dispersion of ozone, it is desirable to process in a pressurized state as much as possible.

  Further, it is desirable to increase the turbulence by flowing ozone water at a high speed on the cleaning surface in order to enhance the cleaning effect.

  In the present invention, after understanding the characteristics of the above-mentioned ozone water, a treatment method of covering the cleaning surface of the substrate to be treated with a cover plate and flowing ozone water at a high speed through a gap formed between the substrate and the cover plate. Invented. By covering the substrate with a cover plate, it is possible to perform processing in a state close to a sealed state rather than an open state, it is possible to maintain a pressurized state for a long time, and to suppress ozone scatter. . In addition, by flowing ozone water at a high speed through a narrow gap formed by the substrate and the cover plate, it was realized that the ozone water flowing on the cleaning surface has a good cleaning effect.

As a reference example for describing the embodiment of the present invention, FIG. 1 and FIG. 2 illustrate the case where the resist is peeled off with ozone water. However, these reference examples do not restrict the present invention at all. It is merely an example.

The substrate 5 to be processed is placed on the substrate support plate 6 of FIG. 1, and the cover plate 3 is placed opposite the substrate cleaning surface to form a gap 4 through which ozone water flows on the substrate cleaning surface. Install. The cover plate 3 is provided with an ozone water supply nozzle 1, and the substrate is cleaned by flowing ozone water through the gap between the substrate and the cover plate. In FIG. 1, the ozone water supply nozzle is described as a plurality of openings. However, the present invention is not limited to this. For example, ozone water may be supplied from a slit opening in the short side direction of the substrate .

Then, in the embodiment of the present invention, it is to establish the state of beveled angle instead of horizontally substrate and cover plate of the treatment object, to flow upward direction to flow ozone water from below. This reduces or eliminates the influence of stagnant gas generated by decomposition of ozone water .

  Further, the surface corresponding to the substrate side of the cover plate may be roughened by embossing or the like to create a disturbance. Although the material of the support plate and the cover plate is not specified, it is desirable to use a fluororesin, stainless steel, vinyl chloride resin, glass, or the like that is resistant to ozone water.

FIG. 2 shows a reference example of a processing method for cleaning a large glass substrate or the like. The substrate 10 to be processed is placed on the substrate support plate 12 in FIG. 2, and the cover plate 10 is opposed to the substrate cleaning surface to form a gap for flowing ozone water on the substrate cleaning surface. Install. The cover plate 10 is provided with an ozone water supply port nozzle 8 corresponding to the object to be processed, an ozone water outlet 9 is provided around the nozzle, and the substrate is cleaned by flowing ozone water between the substrate and the cover plate. Like that.

The gap between the substrate and the cover plate, that is, the thickness of the ozone water can be adjusted by arranging a spacer having an appropriate thickness on the periphery of the substrate support plate 6 or cover plate 3, or by the end portions of the substrate support plate and cover plate. Is fixed by an elastic body, and a method of providing a constant interval by using a screw member or the like from one back side can be employed. Alternatively, a method of automatically adjusting the gap between the substrate and the cover plate by using the pressure of ozone water and the weight of the cover plate without providing a spacer can be employed. These are only required to maintain the gap in a constant state, and do not specify a method or means.
The outlet of the ozone water after the cleaning treatment should be appropriately provided with openings at both ends, outlets arranged around the ozone water supply port on the cover plate, spacers arranged around the substrate support plate, etc. To do.

  As ozone water used in the present invention, in addition to ozone water in which ozone is dissolved in tap water, ion exchange water, pure water, ultrapure water, etc., ozone water containing acid or alkali is used. Also good. This is because use of ozone water containing acid or alkali is expected to improve the cleaning efficiency of the substrate and the like.

  Further, in the above substrate cleaning method, the ozone water may contain carbon dioxide, isopropyl alcohol, acetone, acetic acid, formic acid, methyl alcohol, ethyl alcohol, or the like as a self-decomposition inhibitor. This is to efficiently use ozone by adding an inhibitor that suppresses the self-decomposition of ozone.

The ozone water does not specify the production method, and a known method for producing ozone water can be used. In particular, as in the method described in JP-A-2000-167366, in a packed tower system in which a plurality of packed layers partitioned by a gas backflow prevention plate are provided in the tower and water and ozone gas are in countercurrent contact, It is possible to produce high-concentration ozone water, which is preferable.
In particular, when the high concentration ozone water produced under pressure is used for the substrate cleaning method of the present invention using the above packed tower method, the pressure of the ozone water flowing in the gap formed by the substrate and the cover plate is When ozone drops, ozone easily diffuses. By adjusting the number and size of the ozone water outlets, the total area of the ozone water outlet is reduced and pressure is applied to the cleaning surface of the substrate. You may make it process. Further, as the concentration of ozone water, the higher the ozone concentration, the better the reactivity. In particular, when stripping the resist, the ozone water concentration is preferably 50 ppm or more.

A glass substrate having a shape of 100 mm × 300 mm □ and coated with 1 μm of a high heat resistant g-line positive photoresist was used as a cleaning target. Ozone water was produced using a packed tower method according to Japanese Patent Application Laid-Open No. 2000-167366, supplying ozone gas to the lower part of the tower, supplying ion exchange water from the upper part of the tower, and an absolute pressure of 0.3 MPa. Using ozone water with an ozone water concentration of 100 ppm, the cleaning conditions are an ozone water flow rate of 1.5 L / min and an ozone water temperature of 80 ° C. The gap between the substrate and the cover plate was adjusted to 0.2 mm with a spacer, and the average flow rate of the flowing cleaning water was set to 1.25 m / s. The results of this test are shown as ◯ in FIG.
In FIG. 3, the horizontal axis represents the cleaning time (seconds), and the vertical axis represents the resist stripping area (mm ² ). In the present invention, the cleaning speed increases rapidly when the cleaning time exceeds 60 seconds. I understand.

A glass substrate having a shape of 100 mm × 200 mm □, 50 mm × 400 mm □, 20 mm × 1000 mm □ is used as a cleaning target, an ozone water flow rate is 0.5 L / min, a cleaning time is 120 seconds, and other conditions are as in Example 1. And so on. The result of testing the effect of changing the flow rate of ozone water by adjusting the spacer to adjust the gap between the substrate and cover plate to be constant at 0.4 mm, and the flow path width of ozone water to 100 mm, 50 mm, and 20 mm. Is shown in FIG.
In FIG. 4, the horizontal axis represents the flow rate of ozone water (m / s), the vertical axis represents the resist peeling area (mm ² ), and when the gap between the substrate and the cover plate is the same, the flow rate is 0.2 m / s. It can be seen that the resist stripping area improves rapidly from the vicinity.

A glass substrate having a shape of 100 mm × 200 mm □, 50 mm × 400 mm □, 20 mm × 1000 mm □ is used as a cleaning target, an ozone water flow rate is 0.5 L / min, a cleaning time is 120 seconds, and other conditions are the same as in Example 1. The same was done. The gap between the substrate and the cover plate is changed to 0.2 mm, 0.4 mm, and 1.0 mm by adjusting the spacer, ozone water is flowed in the longitudinal direction, and the flow rate is kept constant at 0.42 m / s. FIG. 5 shows the results of testing the effect of the gap between the two. In FIG. 5, the horizontal axis is the gap (mm) between the substrate and the cover plate, the vertical axis is the resist peeling area (mm ² ), and when the flow rate is the same, the gap between the substrate and the cover plate should be made smaller. It can be seen that the resist peeling area is improved.

A glass substrate having a shape of 100 mm × 300 mm □ is used as the object to be cleaned, the flow rate of ozone water is 1.5 L / min, the gap between the substrate and the cover plate is adjusted with a spacer to 0.2 mm, and other conditions are the same as in Example 1. The same was done. The test was performed using heated ozone water (80 ° C.) produced by mixing ozone water at a temperature of 20 ° C. and ozone water and water vapor. The test results are shown in FIG. In FIG. 6, the horizontal axis represents the cleaning time (seconds), the vertical axis represents the resist peeling area (mm ² ), and the heated ozone water at 80 ° C. (Δ mark) is the ozone water at 20 ° C. (◯ mark). It can be seen that the peeling efficiency is greatly improved as compared with FIG.

A glass substrate with a shape of 100 mm x 300 mm □ is used as the object to be cleaned, the flow rate of ozone water is 1 L / min, the cleaning time is 120 seconds, the gap between the substrate and the cover plate is adjusted to 0.2 mm, and other conditions are implemented Same as Example 1. The test was conducted with ozone water concentrations of 50, 100, and 150 ppm. The test results are shown in FIG. In FIG. 7, the horizontal axis represents the ozone water concentration (ppm), and the vertical axis represents the resist stripping area (mm ² ). It can be seen that the higher the ozone water concentration, the higher the resist stripping efficiency.

Comparative Example 1 and Comparative Example 2

  As a comparative example 1, without using a cover plate, using a glass substrate having a shape of 200 mm × 200 mm □ as an object to be cleaned, supplying ozone water to one point in the center of the substrate, and removing the resist; Further, as Comparative Example 2, a test result of resist stripping by supplying ozone water to one point at the center of the substrate while rotating the same type substrate at 1000 rpm is shown in FIG. The cleaning conditions were the same as in Example 1, and the same type of resist applied to the substrate was used.

In FIG. 3, the horizontal axis represents the cleaning time and the vertical axis represents the resist stripping area, and the inclination represents the resist stripping rate. As can be seen from these test results, in the fixed point supply of Comparative Example 1 (Δ mark), the peeling speed is 70 mm ² / sec, which is very slow. However, when the substrate of Comparative Example 2 (□ mark) is rotated, the peeling occurs. It can be seen that the speed is 130 mm ² / sec, which is considerably faster. However, in the examples of the present invention, although the resist peeling speed at the initial stage of supplying ozone water is slightly slow, the peeling speed suddenly increases from 60 to 90 seconds as the processing time, and the peeling speed is 60 to 90 seconds. in 300 mm ² / sec, becomes 600 mm ² / sec at 90 to 120 seconds, about 2.1 times when compared with the peeling area of 120 seconds in Comparative example 2, the cleaning time only slightly extended, resist stripping area It is clear that the difference between is large. In the case of a disk-shaped substrate, this effect is exhibited by a large substrate having a diameter of 100 to 150 mm or more.

Also, the resist stripping efficiency is 2500 mm ² / L and 4400 mm ² / L in Comparative Examples 1 and ² , whereas in the examples of the present invention, the stripping efficiency is even larger, 9300 mm ² / L. The superiority of the invention is clear.

1 shows an example of a conceptual diagram of an apparatus for carrying out the present invention. It shows another example of an apparatus conceptual diagram for carrying out the present invention. It is a test result of Example 1 and Comparative Examples 1 and 2 of the present invention. It is a test result of Example 2 of this invention. It is a test result of Example 3 of this invention. It is a test result of Example 4 of this invention. It is a test result of Example 5 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ozone water supply nozzle 2 Ozone water 3 Cover plate 4 Gap 5 Substrate 6 Substrate support plate 7 Spacer 8 Ozone water supply nozzle 9 Ozone water outlet 10 Cover plate 11 Spacer 12 Substrate support plate

Claims (4)

The cover plate is placed facing the cleaning surface of the substrate to be processed, with the substrate to be processed and the cover plate being inclined, and the gap between the substrate and the cover plate is set to 2 mm or less. The substrate cleaning method is characterized in that ozone water is caused to flow from the bottom to the top at an average flow rate of 0.1 m / s or more in the gap.   The method for cleaning a substrate according to claim 1, wherein the ozone water is heated ozone water.   The substrate cleaning method according to claim 1 or 2, wherein the ozone concentration of ozone water is 50 ppm or more.   The method for cleaning a substrate according to claim 1, wherein a gap between the substrate and the cover plate is 1 mm or less.

Images