JP4739170B2 - Substrate drying method - Google Patents

Description

  The present invention relates to a method for drying a substrate used for manufacturing a semiconductor device or the like, and more particularly to a method for drying a photomask substrate, a photomask blank, a photomask, and their production intermediates used in lithography.

  Photomasks used in a wide range of applications including the manufacture of semiconductor integrated circuits such as ICs, LSIs, and VLSIs are basically photomasks in which a light-shielding film made of a metal compound thin film is formed on a light-transmitting substrate. The blank light-shielding film is obtained by processing into a predetermined light-shielding film pattern using an electron beam photolithography method or the like. In recent years, along with market demands such as higher integration of semiconductor integrated circuits, pattern miniaturization has rapidly progressed. In response to this, in order to increase the resist resolution in the exposure process, the exposure wavelength is shortened and the aperture of the lens is increased. This is dealt with by increasing the number.

  In a photolithography method used for manufacturing the semiconductor integrated circuit, a photomask in which a light shielding portion made of a metal compound is formed on a substrate transparent to exposure light is used as an original drawing for printing a circuit pattern on a photoresist. . However, when a photomask is used for exposure of a very fine pattern, extremely fine foreign matter and haze are also defective. Therefore, the photomask and the material for manufacturing the photomask are required to be extremely clean. It is done.

Photomasks are binary masks with a light-shielding part that blocks the exposure light almost completely, and the light phase is reversed with respect to the light-transmitting part while attenuating the light, thereby preventing a decrease in contrast between light and dark due to exposure light diffraction Halftone phase shift masks and the like have been put into practical use, but these have a light shielding portion of a chromium compound or a metal silicide compound on a transparent substrate such as quartz or CaF ₂ .

  Further, the photomask is formed by forming a thin film of the light shielding film material on the transparent substrate as described above, forming a resist pattern thereon by an electron beam lithography method, and transferring the pattern to the light shielding material by etching. Although manufactured, as described above, since extremely high cleanliness is required, strict cleaning is performed in each step.

  However, when high energy rays such as ArF excimer laser light are used as exposure light, ammonium sulfate microcrystals are formed from sulfate ions and ammonium ions remaining on the substrate, and these are counted as defects as particles. Was found and became a problem.

  It is clear that the major cause of this problem is sulfate ions, but it is well known that sulfate ions are difficult to remove. The method of rinsing the photomask material with heated pure water was previously proposed in Patent Document 1, but this method using warm water has a higher effect of removing sulfate ions than using normal temperature water. It is shown in Patent Document 2.

By the way, when a photomask substrate, a photomask blank intermediate, a photomask blank, a photomask, or the like is cleaned, there is a spin drying method as a drying method capable of drying while suppressing contamination of foreign substances (Patent Document 3). reference).
The spin drying method is a method in which a substrate to be dried is rotated at a high speed and dried while blowing water droplets on the surface by centrifugal force. However, when drying is performed only by rotation of the material, a long drying time is required. Thus, Patent Document 1 discloses that the drying time can be shortened by raising the substrate temperature by treating the substrate to be dried with warm water in advance.

  However, when the finer foreign substance defect was investigated about the board | substrate dried using the warm water process in this way, it turned out that there is a case where a foreign substance defect increases rather than the case where it processes with the normal temperature pure water. Therefore, although the treatment with heated pure water is simple and effective in reducing sulfate ions, it is necessary to solve the above-mentioned problem that the minute foreign matters increase.

JP 2004-19994 A JP 2004-53817 A JP-A-2-237029

  The present invention has been made in view of such problems. Even if the substrate after cleaning, for example, a photomask substrate, a photomask blank, a photomask, or the like is treated with warm water and dried, minute foreign matter (particles) is extremely generated. It is an object of the present invention to provide a substrate drying method capable of obtaining a small number of substrates.

The present invention has been made to solve the above problems, and is a method for drying a substrate after cleaning, and at least after performing a step of treating the substrate with heated pure water, the surface temperature of the substrate A method for drying a substrate is provided, in which a step of lowering is performed, followed by a drying step .

  As described above, by performing the process of lowering the surface temperature of the substrate, a large amount of finer particles based on mist is not generated on the substrate even if the cleaned substrate is dried after being subjected to hot water treatment. Accordingly, the hot water treatment removes sulfate ions that cause defects and prevents the increase of particles based on mist. Therefore, it is possible to obtain an extremely clean substrate with reduced defects and particles.

In this case, it is preferable to perform the step of lowering the surface temperature of the substrate by rinsing with pure water that is not heated .

  By rinsing with pure water that is not heated in this way, the surface temperature of the substrate can be lowered very simply and with cleanliness maintained, and an increase in the number of particles on the substrate can be prevented.

The drying step is preferably performed by spin drying .
By performing spin drying in this manner, foreign matter contamination can be suppressed to a lower level and drying can be performed.

Moreover, it is preferable to perform the drying prevention process of the surface of the said board | substrate after performing the process of processing the said board | substrate with the heated pure water until it starts the said drying process .
Thus, if the drying prevention treatment is performed after the hot water treatment so that the substrate surface is not dried, it is possible to prevent the occurrence of dry spots caused by drying of high-temperature water droplets. Therefore, it is possible to obtain a substrate with extremely high cleanliness with reduced dry spots.

In this case, the drying prevention treatment is performed by rinsing with pure water which is heated or not heated until the step of lowering the surface temperature of the substrate is started, and is heated after the step of lowering the surface temperature of the substrate. It is preferable to carry out by rinsing with pure water .
By rinsing with pure water heated or not heated in this manner, drying of the substrate surface can be easily prevented.

Moreover, the board | substrate which performed the process processed with the material containing a sulfuric acid or a sulfate can be used as the said board | substrate .
Sulfate ions remain on the substrate that has been subjected to the process of treating with a material containing sulfuric acid or a sulfate, which is likely to cause defects. If such a substrate is dried by the drying method of the present invention, the hot water treatment removes sulfate ions that cause defects, and the process of lowering the surface temperature of the substrate prevents the increase of particles based on mist. In addition, it is possible to obtain an extremely clean substrate in which defects based on sulfate ions and particles based on mist are reduced.

Moreover, the said board | substrate can be either a photomask board | substrate, a photomask blank, a photomask, and those manufacture intermediates .
Since a photomask substrate, a photomask blank, a photomask, and production intermediates thereof require extremely high cleanliness, they can be suitably dried by the drying method of the present invention.

In this case, the substrate can be used in lithography using an exposure light source having a wavelength of 200 nm or less .

  In particular, when the substrate is exposed with such a high energy beam, ammonium sulfate microcrystals are likely to be formed due to sulfate ions remaining on the substrate, resulting in defects. Therefore, it is necessary to remove sulfate ions by hot water treatment. According to the drying method of the present invention, sulfate ions are removed by the hot water treatment, and the increase of particles caused by the hot water treatment is prevented, so that a highly reliable substrate with reduced defects and particles can be obtained. it can.

  As described above, if the substrate drying method of the present invention is used, the hot water treatment removes sulfate ions that cause defects, and the increase in particles caused by the hot water treatment is prevented. It is possible to obtain an extremely clean substrate in which particles based on defects and mist due to hot water treatment are reduced. Accordingly, when a substrate such as a photomask substrate, a photomask blank, a photomask, or a production intermediate thereof dried by the drying method of the present invention is used in a photomask manufacturing process, a device manufacturing process, etc., productivity and yield are improved. Improvements can be made.

Hereinafter, the present invention will be described in more detail.
Substrates such as photomask substrates, photomask blanks, and photomasks are in contact with sulfate ions in the cleaning process, for example, a sulfuric acid-containing cleaning solution such as a resist stripping solution, or a surfactant containing sulfate. Many. In addition, since sulfate ions are highly adherent to the substrate, sulfate ions are accidentally adsorbed in the working atmosphere, and sulfate ions are observed on the substrate surface even when the above treatment is not performed. Sometimes.

In this way, sulfate ions remaining on the substrate react with ammonium ions to form ammonium sulfate microcrystals, which become particles, and a phenomenon of pattern defects has been found, which is problematic.
In order to solve this problem, a method of removing sulfate ions remaining on the substrate by rinsing the substrate with warm water has been performed.

However, the present inventor has found a phenomenon in which fine particles increase when the above-mentioned substrate subjected to hot water treatment is spin-dried. In addition, this phenomenon is not seen in the board | substrate which performed the normal temperature washing | cleaning liquid and the pure water rinse.
As a cause of this phenomenon, the present inventor strongly suspected the reattachment of water droplets to the substrate surface, and presumed that the mist originated from it.

  That is, when the substrate is rinsed with warm water, water vapor (higher than the ambient temperature) evaporated from the warm water is cooled to the atmosphere and becomes supersaturated to form water droplets (mist, mist). It is considered that this mist adheres again on the substrate due to the influence of the air current (downward air current or pump effect by rotation) and causes particles.

  In this case, in the process of drying the mist attached to the substrate, the substances contained in the mist, such as the substance that became the core of the mist formation, agglomerate with water evaporation and solidify, and are counted as foreign particles. The Further, not only substances contained in the mist but also foreign substances on the surface of the substrate are dissolved and aggregated in the attached mist, which may be counted as particles.

  In order to solve this problem, it is only necessary to lower the temperature of the substrate to be dried that has been subjected to hot water treatment so as to suppress the generation of water vapor so that high temperature water droplets are less likely to be present on the substrate surface. That is, the present inventor has conceived that after the hot water treatment, the substrate surface may be actively subjected to a low temperature treatment, for example, rinsing with pure water that has not been heated, and the present invention has been completed.

  That is, the present invention is a method for drying a substrate after cleaning, and at least after the step of treating the substrate with heated pure water, the step of lowering the surface temperature of the substrate is performed, and then the drying step is performed. A method for drying a substrate is provided.

  In this way, by performing the process of lowering the surface temperature of the substrate after the substrate is treated with warm water, it is possible to suppress the generation of a large amount of water vapor, thereby suppressing the generation of mist and making it difficult for the mist to adhere to the substrate surface. Can be. Thereby, it is possible to prevent a large amount of particles from being generated on the substrate. Therefore, according to the method of the present invention, the sulfate ion causing the defect is removed by the hot water treatment, and the increase of particles caused by the hot water treatment is prevented, so that the defect based on the sulfate ion and the particle based on the mist are prevented. It is possible to obtain a reduced and extremely clean substrate.

The step of lowering the surface temperature of the substrate is not limited to this, but is preferably performed by rinsing with pure water that is not heated. This is because rinsing using pure water that is not heated can be performed with a very simple apparatus while maintaining the cleanliness of the substrate. In addition, pure water here means water that has reduced the possibility of residue remaining due to evaporation by ion exchange, etc., as well as so-called ultrapure water, which contains carbon dioxide gas that is usually used in the production of electronic materials In addition, so-called functional water such as ozone water and hydrogen water is also included.
Further, the step of lowering the surface temperature of the substrate can be performed using, for example, air blow or volatile alcohol.

Moreover, the said drying process is not limited to this, It can carry out by spin drying.
Spin drying is a method in which a substrate to be dried is rotated at high speed to dry the surface while blowing off water droplets on the surface. Although this method is a preferable method in which water droplets are not concentrated and dried on the substrate surface, it is difficult to generate particles due to foreign matter aggregation. However, the present invention can be preferably applied because it easily causes mist problems due to the structure of the apparatus.

  Furthermore, in the case of spin drying, if rinsing is performed using pure water that is not heated, and if the spin drying is started immediately, the main water droplets on the surface are removed by the start of spinning, and then the target is dried at the stage where the sprinkling starts. Spin drying can be performed in a state where the surface temperature is increased by the latent heat of the substrate body, and not only the generation of particles can be suppressed, but also the effect of shortening the drying time can be obtained at the same time.

  Other than spin drying, warm air drying, reduced pressure drying, drying with an infrared lamp, or the like can be used.

  Moreover, it is preferable to perform the drying prevention process of the surface of the said board | substrate after performing the process of processing the said board | substrate with the heated pure water until it starts the said drying process.

  This dry prevention treatment is performed by rinsing with pure water that has been heated or not heated until the step of lowering the surface temperature of the substrate, and pure water that is not heated after the step of lowering the surface temperature of the substrate. Can be carried out by rinsing with

  Performing the anti-drying process on the surface of the substrate means performing a process that does not actively dry the substrate surface in order to maintain the wetness of the substrate surface. For example, it is possible to perform rinsing using pure water that is not heated as a drying prevention treatment after the hot water treatment. In this case, this rinsing also serves as a step of lowering the surface temperature of the substrate.

  In this way, if the substrate surface is wet after the hot water treatment and before the drying process is started, the mist reattached on the substrate flows out from the substrate together with the rinse water. Therefore, even if mist is generated, the possibility that the reattached water droplets remain on the substrate and cause an increase in particles is reduced. Furthermore, it is possible to prevent the occurrence of dry spots caused by drying of high-temperature water droplets. Therefore, it is possible to obtain a substrate with extremely high cleanliness with reduced dry spots.

  Hereinafter, as one embodiment of the present invention, a case where a cleaned substrate is treated with heated pure water, a treated with pure water not heated, and a spin drying step will be described in order. Is not limited to these.

  The substrate used is not particularly limited, and examples thereof include precision substrates such as a photomask substrate, a photomask blank, a photomask, and production intermediates thereof. More specifically, a photomask substrate transparent to exposure light such as quartz and calcium fluoride for manufacturing a photomask, and a photomask in which an optical film such as a phase shift film is formed on the photomask substrate Blank production intermediates, photomask blanks formed by combining phase shift films, light-shielding films, etc. alone or in combination, photomask intermediates obtained by etching photomask blanks by lithography, or photomasks that have been processed It is.

  The substrate cleaning performed before the hot water treatment according to the present invention is not particularly limited, and conventionally used cleaning can be performed. For example, immersion cleaning with hot sulfuric acid, scrub cleaning with a surfactant, shower cleaning with hydrofluoric acid aqueous solution, potassium hydroxide aqueous solution, and ultrapure water can be used.

  However, particularly when the substrate is washed with a sulfuric acid-containing cleaning solution such as a resist stripping solution, or a material containing sulfuric acid such as a surfactant containing sulfate, sulfate ions are generated by the drying method of the present invention. In addition, since an increase in particles due to mist is also prevented, it is preferable because a substrate with extremely high cleanliness with reduced defects and particles can be obtained. In particular, if the substrate is used in lithography using an exposure light source having a wavelength of 200 nm or less, extremely high cleanliness is required, and therefore the method of the present invention can be suitably used.

The substrate thus cleaned is treated with heated pure water.
The method for performing the warm water treatment is not particularly limited, and for example, the substrate may be immersed in a warm water tank, or warm water may be supplied to the substrate before the drying treatment on the spin dryer.

  When the process of treating with heated pure water, the process of treating with pure water without heating, and the spin drying process are continuously performed on a spin dryer, a line for supplying heated pure water to the substrate and heating A spin dryer having a line for supplying pure water that has not been used can be used. Further, the drying apparatus preferably has an exhaust line, and it is preferable that mist can be prevented from staying in the apparatus for a long time when high-temperature pure water is supplied.

  The heated pure water is preferably controlled at 40 ° C. or more and less than 100 ° C., more preferably 60 ° C. or more and less than 95 ° C. Since the processing time is related to the size of the substrate, the supply amount of hot water supplied per unit time, and the like, it is necessary to adjust appropriately, but it is generally preferable to supply hot water on the substrate for about 30 seconds to 20 minutes. . Thereby, in particular, sulfate ions remaining on the substrate surface can be removed.

Next, the substrate is treated with pure water that is not heated.
This treatment serves both as a step for lowering the surface temperature of the substrate and a drying prevention treatment for the surface of the substrate. By treating the substrate with pure water without heating, it is possible to suppress the generation of a large amount of water vapor from the substrate surface, etc. and also when mist is generated while high-concentration water vapor in the drying apparatus is exhausted. The substrate surface can be covered with pure water so that the substrate surface is not contaminated.
The pure water used at this time may be pure water that is normally managed in a state preferably used for photomask production, and the temperature is sufficient within the control temperature. For example, the thing of about 10-35 degreeC can be used.

  The supply amount of pure water is not particularly limited and can be appropriately selected depending on conditions. For example, in the case of processing into pure water immediately after treatment with pure water without heating, the minimum amount for flowing hot water on the surface is sufficient. In addition, when processing is performed under conditions where it takes time to move to spin drying after treatment with pure water without heating, the surface temperature is lowered so that the water remaining on the surface does not become high again due to the latent heat of the substrate. What is necessary is just to select a flow rate.

  The supply time of pure water is not particularly limited, and can be appropriately selected depending on conditions. However, it is preferable to supply pure water that has not been heated for a period of time during which high-temperature steam that generates mist is exhausted from the inside of the spin drying apparatus, because adhesion of mist and drying of the substrate surface are prevented.

  In order to prevent drying spots, it is preferable that the substrate does not dry once between the hot water treatment and the start of drying. Therefore, it is preferable to treat the substrate with pure water that is not heated until the drying starts after the substrate is treated with warm water. Therefore, it is preferable that a line for supplying at least pure water that is not heated is installed in the spin dryer. By using such an apparatus, it is possible to obtain an effect of reducing the drying time due to the latent heat of the main body while reducing the temperature of only the surface to prevent mist without lowering the temperature of the main body of the substrate to be dried.

Next, the substrate is spin-dried.
The spin drying itself is already known as described above, and can be performed by a known method. The number of rotations and time are set depending on the size of the apparatus and the substrate. For example, as an example of a 152 mm square substrate, drying can be performed by spin-drying at a rotation number of about 1000 rpm for 2 minutes.

  By performing the treatment as described above, the hot water treatment removes sulfate ions that cause defects, and also prevents the increase in particles caused by the mist caused by the hot water treatment, thus obtaining a substrate with extremely high cleanliness. be able to.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not limited by these description.

  Four photomask blank production intermediates were prepared by forming a silicon oxynitride film containing molybdenum on the outermost surface of a 152 mm square quartz substrate. The intermediate product was subjected to a washing process by a general method, rinsed with water at room temperature, and spin-dried at 1000 rpm for 2 minutes.

  Next, the surface particle | grains of the obtained board | substrate were measured using the defect detection apparatus (Lasertec company make MAGICS), and the position was pinpointed. The number of defects of 0.06-0.1 μm for each specified substrate was 44 for substrate A, 38 for substrate B, 36 for substrate C, and 48 for substrate D.

Example 1
Pure water heated to 70 ° C. is supplied to the substrate A, which is a photomask blank production intermediate model obtained above, for 10 minutes before drying in a spin dryer, and then pure water at 23 ° C. for 150 seconds. After the temperature of the substrate surface was lowered, spin drying was performed at 1000 rpm for 30 seconds.
When the number of surface defects of the substrate dried by this processing step was measured in the same manner as described above, it was 23, and 5 defects were observed at positions different from the defects observed before the processing.

(Example 2)
Pure water heated to 90 ° C. is supplied to the substrate B, which is a photomask blank manufacturing intermediate model obtained above, for 10 minutes before drying in a spin dryer, and then pure water at 23 ° C. for 150 seconds. After the temperature of the substrate surface was lowered, spin drying was performed at 1000 rpm for 30 seconds.
When the number of surface defects of the substrate dried by this processing step was measured in the same manner as described above, it was 15 and 3 defects were observed at positions different from the defects observed before the processing.

(Comparative Example 1)
After supplying pure water heated to 70 ° C. for 10 minutes before the drying treatment in the spin dryer, the substrate C, which is a photomask blank manufacturing intermediate model obtained above, is spin-dried at 1000 rpm for 30 seconds as it is. went.
When the number of surface defects of the substrate dried by this treatment step was measured in the same manner as described above, it was 1184.

(Comparative Example 2)
Pure water heated to 90 ° C. is supplied to the substrate D, which is the photomask blank manufacturing intermediate model obtained above, for 10 minutes before drying in a spin dryer, and then spin-dried at 1000 rpm for 30 seconds. went.
When the number of surface defects of the substrate dried by this treatment step was measured in the same manner as described above, it was 2737.

  From the above results, it was confirmed that by performing a process of lowering the surface temperature of the substrate after the substrate was treated with warm water, an increase in the number of particles was prevented and a dry substrate with extremely high cleanliness was obtained.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Claims (5)

A method for drying a substrate after cleaning, at least after performing a process of treating a substrate that is one of a photomask substrate, a photomask blank, a photomask and a production intermediate thereof with heated pure water, A method for drying a substrate, comprising performing a step of lowering the surface temperature of the substrate by rinsing with pure water that is not heated , and then performing a drying step by spin drying . After performing the step of treating with pure water was the substrate heated, until the start of the drying process, the substrate according to claim 1, characterized in that the drying-preventing treatment of the surface of said substrate Drying method. Pure water that is not heated after the step of lowering the surface temperature of the substrate is performed by rinsing with pure water that is heated or not heated until the step of lowering the surface temperature of the substrate is started. The method for drying a substrate according to claim 2 , wherein the substrate is rinsed by using a substrate. The substrate drying method according to any one of claims 1 to 3 , wherein a substrate subjected to a treatment with a material containing sulfuric acid or a sulfate is used as the substrate. The method for drying a substrate according to any one of claims 1 to 4, wherein the substrate is used in lithography using an exposure light source having a wavelength of 200 nm or less.