JP2009021448A - Cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method which can minimize generation of fine foreign matter (particles) when cleaning a cleaning-target substrate, for example, a photomask substrate, a photomask blank, a photomask or a manufacturing intermediate product thereof. <P>SOLUTION: The cleaning method of supplying a cleaning solution after foreign matter is removed to the cleaning-target substrate for its cleaning includes a step of removing foreign matter in the cleaning solution. At least in the foreign matter removal step of removing foreign matter by passing the cleaning solution through a filter, air bubbles in the cleaning solution are also removed, and the cleaning solution after the air bubbles are removed and foreign matter is removed is supplied to the cleaning-target substrate for its cleaning. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for cleaning a substrate used for manufacturing a semiconductor device or the like, and more particularly to a cleaning method for cleaning a photomask substrate, a photomask blank, a photomask, or a manufacturing intermediate thereof used in lithography.

  Photomasks used in a wide range of applications including the manufacture of semiconductor integrated circuits such as IC, LSI, and VLSI are basically thin films containing a metal or metal compound on a light-transmitting substrate (photomask substrate). The light-shielding film of the photomask blank on which the light-shielding film is formed is processed 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 the photolithography method used for manufacturing the semiconductor integrated circuit and the like, 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 diffraction of the exposure light. 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 .

  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 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, and 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 by the applicant of the present invention in Patent Document 1, and this method using warm water was washed with water at room temperature. Patent Document 2 shows that the effect of removing sulfate ions is higher than the case.

JP 2004-19994 A JP 2004-53817 A

  By the way, when performing the warm water treatment as described above, it is possible to use a warm water washing tank, but in order to create a cleaner environment, the nozzle is supplied with warm water directly onto the substrate to be cleaned. It is preferable to do. However, when the present inventors have investigated the dried substrate by supplying hot water or the like directly onto the substrate to be cleaned with the nozzle in this way, it is confirmed that defects due to fine foreign matter have occurred. understood. It was also found that the defects tend to increase when washed with warm water than when washed with pure water at room temperature.

  The present invention has been made in view of such problems. When a substrate to be cleaned, such as a photomask substrate, a photomask blank, a photomask, or a production intermediate thereof, is cleaned, fine foreign matter (particles) is removed. It aims at providing the washing | cleaning method which can reduce generation | occurrence | production extremely.

  In order to solve the above problems, the present invention includes a foreign matter removing step for removing foreign matter in the cleaning liquid, and is a cleaning method for cleaning the substrate by supplying the cleaning liquid from which the foreign matter has been removed to the substrate to be cleaned. In the foreign matter removing step of removing the foreign matter in the cleaning liquid by filtering with a filter, the bubbles in the cleaning liquid are also removed, and the cleaning liquid from which the bubbles and foreign matter have been removed is supplied to the substrate to be cleaned. A cleaning method is provided (claim 1).

Thus, in the cleaning method of the present invention, in the foreign matter removing step of removing the foreign matter in the cleaning liquid by filtering the cleaning liquid through the filter, the bubbles in the cleaning liquid are also removed. As a result, fluctuations in the filtration pressure of foreign matter and a reduction in the filtration ability of foreign matters, and generation of dust from the filter can be effectively suppressed.
And, in the cleaning liquid in which bubbles and foreign substances are removed in this way, there are few foreign substances due to bubbles that have been generated in the past, and the amount of foreign substances in the cleaning liquid is significantly reduced than before, By supplying the cleaning liquid to the substrate to be cleaned and cleaning it, particles on the cleaned substrate can be extremely reduced. This makes it possible to obtain a substrate with extremely few defects.

  The removal of bubbles here means that the bubbles are at least separated from the cleaning liquid filtered by the filter.

At this time, the cleaning liquid can be filtered so as to have a flow component in a direction parallel to the filter surface of the filter to remove bubbles.
In this way, if the cleaning liquid is made to flow so as to have a flow component in a direction parallel to the filter surface of the filter, bubbles are more effectively prevented from adhering to the filter, and the bubbles are moved along the filter surface of the filter. Therefore, it is possible to perform filtration while removing bubbles from the cleaning liquid filtered by the filter.
And by setting it as such a method, the removal of a bubble and the removal of a foreign material can be performed efficiently in space-saving.

  Further, the removal of bubbles and the removal of foreign substances in the cleaning liquid can be performed in multiple stages (Claim 3), and the cleaning liquid from which bubbles and foreign substances have been further removed can be supplied to the substrate to be cleaned.

Then, it is possible to eliminate the bubbles in the cleaning liquid out of the system together with the cleaning liquid containing the bubbles (claim 4).
In this way, if the cleaning liquid containing bubbles is excluded, it is possible to more reliably exclude bubbles from the system.

At this time, when the entire cleaning liquid containing bubbles is excluded from the system, the total amount of the cleaning liquid to be excluded is preferably adjusted according to the total amount of the cleaning liquid from which the bubbles and foreign matter have been removed. ).
In this way, the cleaning liquid can be efficiently removed, and the cost can be prevented from increasing more than necessary.

Then, the total amount of the cleaning liquid to be excluded can be set to be 1 or more times the total amount of the cleaning liquid from which the bubbles and foreign substances have been removed (Claim 6).
As described above, it is preferable that the total amount of the cleaning liquid to be excluded is one or more times the total amount of the cleaning liquid from which the bubbles are removed and the foreign matters are removed, because the bubbles can be more reliably excluded.

In addition, bubbles in the cleaning liquid can be excluded from the system by using a gas-liquid separator (claim 7).
Thus, by using a gas-liquid separator, it is possible to more reliably exclude bubbles from the system.

And after heating the said washing | cleaning liquid to 40 degreeC or more and less than 100 degreeC, the removal of the said bubble and the removal of a foreign material can be performed (Claim 8).
Thus, if the cleaning liquid is heated to 40 ° C. or higher and lower than 100 ° C. and then the bubbles are removed and the foreign matter is removed, the foreign matter caused by the bubbles is generated even in the heated cleaning solution in which bubbles are likely to be generated. Can be prevented, and in particular, a cleaning solution having a high effect of removing sulfate ions can be obtained, and the photomask material can be effectively cleaned.

Further, the substrate to be cleaned can be any one of a photomask substrate, a photomask blank, a photomask, or a production intermediate thereof.
Since a photomask substrate, a photomask blank, a photomask, or a production intermediate thereof requires extremely high cleanliness, it can be suitably cleaned by the cleaning method of the present invention.

  With the cleaning method of the present invention, the generation of particles due to bubbles in the cleaning liquid can be extremely suppressed, so that a substrate with less contamination by particles can be obtained after cleaning, and productivity and yield can be improved. You can plan. In particular, it is suitable for cleaning a photomask substrate, a photomask blank, a photomask, or a production intermediate thereof.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.
Conventionally, when removing sulfate ions remaining on a substrate in a photomask material or the like, it has been known that cleaning with warm pure water is effective. However, the present inventor has conducted extensive research on this cleaning method, and by supplying the heated pure water directly onto the substrate to be cleaned with a nozzle or the like, and conducting a survey on the substrate after drying, It was found that many particles were generated.

Furthermore, it has been discovered that more particles are generated when washed with pure water heated as described above than when washed with pure water at room temperature.
In this way, since the ultrapure water is heated and the substrate to be cleaned is cleaned, a large number of particles are generated particularly when the filtered liquid is used near the cleaning nozzle that is a use point. The present inventor has studied various causes of particles that may increase on the substrate after cleaning by using warm water in the foreign matter removal step of removing foreign matter with a filter.

  As a result of thought and error, it was discovered that the generation of the particles is caused by fine bubbles contained in the cleaning liquid. That is, when bubbles are generated in the cleaning liquid and adhere to the filter used in the foreign matter removing process, the filtration pressure in the filter fluctuates accordingly. Further, it has been found that the fluctuation of the filtration pressure caused by this causes a decrease in the filtering ability of foreign matter or dust generation from the filter, causing the problem of the generation of particles.

As an example, the cleaning liquid (for example, pure water) supplied to the substrate to be cleaned is produced by pure water manufacturing process, the manufactured pure water is heated by the heating process, and then in the cleaning liquid by the foreign matter removing process. The method of preparing by removing the foreign material is mentioned. After the foreign substance removing step, the obtained cleaning liquid is supplied to the substrate to be cleaned and cleaning is performed.
Here, with respect to the bubbles in the cleaning liquid such as pure water, the bubbles are particularly easily generated by heating the cleaning liquid. For example, Japanese Patent Laid-Open No. 4-338282 discloses a gas-liquid separator in the process of heating the cleaning liquid. Is used to eliminate bubbles in the cleaning liquid.

However, according to the inventor's investigation, when the washing liquid is heated, when the washing liquid with a large flow rate is passed through the heating portion, the function of the gas-liquid separator is insufficient and the bubbles cannot be sufficiently eliminated. Alternatively, it has been found that supersaturated gas is taken in as bubbles in the cleaning liquid while the cleaning liquid subjected to the heating process is being sent to the foreign matter removing process.
That is, even if a process for removing bubbles generated in the cleaning liquid from the cleaning liquid in the heating process or the previous pure water production process is performed, the cleaning liquid subjected to the foreign matter removing process includes bubbles. End up.
When such a cleaning liquid is filtered through a filter in the foreign matter removal process, the filtering ability of the foreign matter is reduced due to bubbles in the cleaning liquid, and dust is generated from the filter. When the substrate is cleaned (that is, the conventional cleaning method), many particles are generated.

Therefore, the present inventor can remove the bubbles from the cleaning liquid to be filtered by removing the bubbles in the cleaning liquid in the foreign matter removing step, and as a result, filter filtration caused by the bubbles in the cleaning liquid. It has been found that the reduction in capacity and the generation of dust from the filter can be extremely suppressed. The cleaning liquid from which the bubbles and foreign matter have been removed contains almost no foreign matter, and cleaning the substrate to be cleaned using this cleaning solution remarkably causes the generation of particles that have occurred frequently in the past. We found that it can be reduced.
The inventor found the above and completed the present invention.

  Below, although the washing | cleaning method of this invention is demonstrated in detail, referring drawings, this invention is not limited to this. Hereinafter, a foreign substance removing apparatus that can be used in the foreign substance removing step in carrying out the cleaning method of the present invention will be described with reference to FIGS. 1-4. However, the present invention is limited to the case of using these foreign substance removing apparatuses. Instead, various forms of devices can be used. Conventionally, in the foreign matter removing process in which only the removal of foreign matters has been performed, it is only necessary to remove bubbles and obtain a cleaning liquid from which bubbles and foreign matters have been removed.

(First embodiment)
FIG. 1 shows an outline of an example of a foreign matter removing apparatus that can be used in the foreign matter removing step when the cleaning method of the present invention is carried out. A nozzle that is a use point and a substrate to be cleaned that is cleaned with a cleaning liquid sprayed from the nozzle are also illustrated.
The foreign matter removing apparatus 1 has a housing 10. The housing 10 has a cleaning liquid inlet 11 through which, for example, a cleaning liquid sent after a heating process or the like enters the housing 10. A cleaning liquid outlet 14 is provided for the cleaning liquid that has been removed. Furthermore, a filter 12 for filtering the cleaning liquid and removing foreign substances in the cleaning liquid is disposed inside the housing 10.

Here, as shown in FIG. 1, a flow path 17 extending upward in the vertical direction, for example, from the cleaning liquid inlet 11 is provided in the housing 10, and continues to the upper portion 13 of the housing 10. A first filter 12 a is disposed along the flow path 17. That is, the cleaning liquid that enters from the cleaning liquid inlet 11 and flows through the flow path 17 flows so as to have a flow component in a direction parallel to the filter surface of the filter 12a.
A flow path 17 ′ provided on the opposite side of the flow path 17 across the filter 12 a continues to the cleaning liquid outlet 14.
The flow paths 17 and 17 ′ and the filter 12a are not limited to the structure and arrangement as shown in FIG.

An exhaust port 15 is provided in the upper portion 13 of the housing 10. As will be described later, bubbles are removed from the cleaning liquid to be filtered by the filter 12a. The removed bubbles rise to the upper portion 13 of the housing 10 and are directed to the exhaust port 15.
The exhaust port 15 is provided with a gas-liquid separator 16 or an intermittent valve, for example, so that bubbles collected near the exhaust port 15 can be excluded from the system.

  Many gas-liquid separators 16 are already known, and gas-liquid separation membranes that allow only gas molecules to pass therethrough are used, and gas is removed with negative pressure on the outside (for example, JP-A-10-235103). ), And those using a specific gravity difference between gas and liquid (for example, Japanese Patent Application Laid-Open No. 2007-50332), etc. are known. Can do.

On the other hand, as in the gas-liquid separator disclosed in the above-mentioned document, the cleaning liquid and the bubbles are not separated from each other by completely separating the cleaning liquid and the bubbles, and the cleaning liquid and the bubbles are integrated. It is also possible to provide a type that eliminates the cleaning liquid containing bubbles.
For example, in the case of the gas-liquid separator type using the above-described specific gravity difference, not only bubbles are excluded, but bubbles can be excluded from the system together with a certain amount of cleaning liquid. Therefore, the size of the apparatus for complete separation is unnecessary, and the gas-liquid separator can be miniaturized.

In this case, instead of the exhaust port 15 shown in FIG. 1, a drain line 15 ′ as shown in FIG. 2 is provided.
The drain line 15 ′ is further provided with a drain valve 19, which is connected to, for example, a computer. Then, the drain valve 19 is controlled by the computer according to the total amount of cleaning liquid from which bubbles have been removed by the foreign substance removing apparatus 1, that is, the amount of cleaning liquid that is actually supplied to the nozzle of the use point later. The total amount of the cleaning liquid containing bubbles that are excluded from the system through the drain line 15 ′ can be adjusted.

  For example, if the supply of the cleaning liquid at the point of use is controlled by switching on and off, the drain line 15 'can be provided with an on / off type drain valve, and the supply at the point of use When the amount changes, a drain valve that can be controlled to change the removal amount accordingly can be attached.

Further, as shown in FIG. 1, a flow path 18 extending downward in the vertical direction from the upper portion 13 is provided inside the housing 10, and a filter 12 b is disposed along the flow path 18. Yes. The cleaning liquid from which bubbles are excluded from the system is filtered by the filter 12b.
A flow path 18 ′ provided on the opposite side of the flow path 18 across the filter 12 b continues to the cleaning liquid outlet 14.
The flow paths 18 and 18 'and the filter 12b are not limited to the structure and arrangement as shown in FIG.

The cleaning liquid outlet 14 is connected to the nozzle of the cleaning device at the point of use, so that the cleaning liquid from which bubbles and foreign matter have been removed can be supplied to the substrate to be cleaned. A cleaning apparatus for ejecting the cleaning liquid onto the substrate to be cleaned can be, for example, the same as the conventional one.
In addition, in order to improve reliability, it is preferable that the foreign matter removing device 1 is disposed in the vicinity of the cleaning device (use point), for example, at a position within 1 meter.

  Further, in front of the foreign matter removing apparatus 1, a pure water manufacturing apparatus for manufacturing pure water as a cleaning liquid in a pure water manufacturing process, a heating apparatus for heating pure water manufactured in a heating process, and the like. Is arranged. However, for example, if a heated cleaning solution is not required, the heating device can be omitted.

Hereinafter, the cleaning method of the present invention including the foreign matter removing step performed using the foreign matter removing apparatus 1 as described above will be described.
As a substrate to be cleaned, for example, a transparent photomask substrate such as a SiO ₂ substrate (for example, JP-A-2002-318450) or a calcium fluoride substrate (for example, JP-A-2001-19596) as a photomask substrate, A reflective photomask substrate such as a titanium-doped SiO ₂ substrate (for example, US Patent Publication No. 2002/157421), or a photomask blank in which a single layer or a multilayer film for imparting light shielding properties to the photomask substrate is formed ( For example, a photomask (for example, Japanese Patent Application Laid-Open No. 2007-33470) that becomes an original drawing of a semiconductor circuit diagram in lithography in which baking by pattern irradiation is performed can be given. Manufacturing intermediates in the mask manufacturing process It may be subject to a cleaning method of the invention.

  In particular, like the above-described photomask blank and photomask, a film containing silicon, transition metal-containing silicon or chromium, and a light element selected from oxygen, nitrogen, carbon, etc., is formed on the substrate by sputtering or the like. In a filmed substrate, particularly a film containing chromium, the surface has a large amount of adsorption of inorganic salts such as ammonium and sulfate ions, and the cleaning method of the present invention can be applied particularly effectively in order to remove these ions.

  When the above-described photomask blank is used as a substrate to be cleaned, UV cleaning (for example, Japanese Patent Laid-Open No. 63-271938) or ozone water treatment (Japanese Patent Laid-Open No. 2003-50453) is performed before cleaning. Then, the wettability of water can be improved, which is more preferable in applying the present invention. Further, when UV irradiation is performed in an atmosphere with oxygen such as in the air, oxygen is ozonized, which is more preferable.

  In addition, the cleaning method of the present invention can be applied after the substrate to be cleaned is cleaned with cleaning water to which megasonic is applied. At this time, pure water to which megasonic is applied may be used, or functional water (such as ammonia hydrogen water) applied with megasonic may be used.

In addition, procedures, such as a pure water manufacturing process and a heating process performed before a foreign material removal process, are not specifically limited, It can carry out similarly to the past.
Here, a case where pure water is used as a cleaning liquid and a substrate to be cleaned is a photomask material, that is, a photomask substrate, a photomask blank, a photomask, or a production intermediate thereof is described, but the present invention is not limited thereto. The cleaning method of the present invention can be carried out using a variety of cleaning liquids and a substrate to be cleaned.

Further, the heating process may be performed as necessary. The cleaning liquid can be applied to the foreign matter removing step without heating, or can be applied to the foreign matter removing step after being heated to, for example, 40 ° C. or higher and lower than 100 ° C., particularly 55 ° C. or higher and 95 ° C. or lower.
As described above, when the cleaning liquid is heated, bubbles are likely to be generated in the cleaning liquid. However, in the cleaning method of the present invention, the bubbles can be removed together with the foreign substance removing step, and the bubbles and foreign substances can be removed. Therefore, it is really effective in preventing the generation of particles due to bubbles, and a high cleaning effect can be obtained.
In particular, it becomes a cleaning liquid capable of effectively removing sulfate ions, and is suitable for cleaning a photomask material.

  The cleaning liquid that has been subjected to the foreign matter removal process through various processes in this manner first enters the housing 10 from the cleaning liquid inlet 11 of the foreign matter removal apparatus 1 and passes through the flow path 17. Since the filter 12a is disposed along the flow path 17, the cleaning liquid flows so as to have a flow component in a direction parallel to the filter surface of the filter 12a.

The flow of the cleaning liquid will be further described with reference to FIG. FIG. 3 is an explanatory diagram for explaining how the cleaning liquid flows when the cleaning liquid is flowed so as to have a flow component in a direction parallel to the filter surface.
When air bubbles in the cleaning liquid try to adhere to the filter 12a when passing through the vicinity of the filter 12a filled with the cleaning liquid, the bubbles are resisted by surface tension. At this time, as described above, if the cleaning liquid flows so as to have a flow component in a direction parallel to the filter surface of the filter 12a through the flow path 17, the bubbles do not adhere to the filter 12a. It moves along the filter surface (in the case of FIG. 3, it moves upward). Since the cleaning liquid flowing in the flow path 17 has a flow component in a direction parallel to the filter surface, for example, compared with a case where the cleaning liquid flows only in a direction perpendicular to the filter surface, the filtration amount of the cleaning liquid in the filter 12a Therefore, it is possible to move away from the filter surface more effectively without attaching bubbles.

Then, as shown in FIG. 3, the cleaning liquid in a certain unit volume (A) near the filter surface at a certain point in time passes partly through the filter 12a (a) at the next time, but the rest of the filter 12a. It moves in a direction parallel to the filter surface (b).
However, this is not limited to the case where the flow of the cleaning liquid has a component in a direction parallel to the filter surface, and the filter 12a is arranged in parallel to the flow path 17 as shown in FIG. For example, even when the filter 12a is disposed obliquely with respect to the flow path 17, the cleaning liquid has a flow component in a direction parallel to the filter surface of the filter 12a.

  As described above, it is possible to prevent bubbles from adhering to the filter 12a and rapidly increasing the filtration pressure. Therefore, it is possible to prevent a reduction in the ability to remove foreign substances in the cleaning liquid, and it is possible to prevent dust generation from the filter due to a change in filtration pressure. Since the filter 12a has both the function of removing bubbles and removing foreign substances, it is not necessary to provide a means for removing bubbles more than necessary, and a desired cleaning liquid can be obtained in a small space.

The cleaning liquid filtered by the filter 12 a passes through the flow path 17 ′ toward the cleaning liquid outlet 14.
On the other hand, the air bubbles away from the filter surface of the filter 12a further move up the upper portion 13 of the housing 10 and go to the exhaust port 15 (or the drain line 15 ′).

  When the foreign substance removing apparatus having the exhaust port 15 as shown in FIG. 1 is used, the collected air bubbles are separated from the cleaning liquid by, for example, the gas-liquid separator 16 and excluded from the system.

Further, when a foreign matter removing apparatus having a drain line 15 ′ as shown in FIG. 2 is used, the collected bubbles are removed from the system together with the cleaning liquid, through the gas-liquid separator and the drain line 15 ′.
If the bubbles are eliminated together with the cleaning liquid in this way, it is not necessary to completely separate the bubbles from the cleaning liquid. For example, a simpler and more compact gas-liquid separator can be used, and the cleaning of the present invention can be performed in a small space. The method can be carried out, and bubbles can be more reliably excluded from the system.

When the cleaning liquid containing bubbles is excluded from the system as described above, the total amount of the cleaning liquid to be excluded is the total amount of the cleaning liquid in which the bubbles are removed and the foreign substances are removed in the foreign matter removing process, that is, the substrate to be cleaned later. It can adjust according to the quantity of the washing | cleaning liquid supplied. For example, the drain valve 19 of the drain line 15 ′, the nozzle as a use point, and a computer connected thereto are used to open and close the drain valve 19 according to the amount supplied from the nozzle to the substrate to be cleaned. It can be done by adjusting.
In this way, the cleaning liquid can be efficiently removed, the unnecessary cleaning liquid can be prevented from being removed out of the system, the cleaning liquid can be efficiently removed for each bubble, and the cost can be improved. it can.

  At this time, the total amount of the cleaning liquid to be excluded is not particularly limited and can be determined each time. For example, if the amount of the cleaning liquid supplied to the substrate to be cleaned is one or more times as a guide, bubbles are more appropriately Can be excluded from the system.

  In addition, the cleaning liquid that has not been filtered by the filter 12a flows through the upper portion 13 of the housing 10 and the flow path 18, and after being filtered by the filter 12b, travels from the flow path 18 'to the cleaning liquid outlet 14.

As described above, it is possible to obtain a cleaning liquid from which bubbles are removed and foreign matters are removed by the foreign matter removing step using the foreign matter removing apparatus 1. In this cleaning liquid, the amount of foreign matter caused by bubbles generated in the conventional method is remarkably reduced.
In the next cleaning step, the cleaning liquid is supplied to the substrate to be cleaned for cleaning. The method for supplying the cleaning liquid to the substrate to be cleaned is not particularly limited. For example, the cleaning liquid can be supplied by a nozzle or the like using a cleaning device similar to the conventional one.

  Therefore, by the cleaning method of the present invention, generation of particles due to bubbles can be significantly suppressed as compared with the conventional case, and the substrate can be cleaned with less contamination by particles. Thereby, the yield and productivity of a product can be improved.

  On the other hand, conventionally, even if the process of removing bubbles from the system was performed in the pure water production process and the heating process, which are the previous processes, it was not performed in the subsequent foreign substance removal process. For this reason, as described above, the supersaturated gas bubbles are not generated in the cleaning liquid while the bubbles are not sufficiently removed in the heating process or the like, or while the cleaning liquid is being sent to the foreign matter removing process. As a result, when the cleaning liquid is filtered with a filter in the foreign matter removing step, the filtration pressure is reduced due to the bubbles. As a result, many foreign substances are contained in the cleaning liquid despite the foreign substance removing step.

(Second embodiment)
FIG. 4 shows an outline of an example of another foreign matter removing apparatus that can be used in the foreign matter removing step when the cleaning method of the present invention is carried out.
This foreign matter removing device 2 is provided with one more filter as compared with the foreign matter removing device 1 of FIG. 1, and has a multi-stage structure comprising the filter 12a, the flow paths 17, 17 ′, and the exhaust port 15 of FIG. It is the structure provided in.
In addition, each part itself of the foreign material removal apparatus 2 of FIG. 4 can be made the same as that of the foreign material removal apparatus 1 of FIG.

  If the foreign matter removing step in the cleaning method of the present invention is performed using such a foreign matter removing device 2, it is possible to remove bubbles and remove foreign matters in multiple stages. Can be further reduced. Therefore, it is possible to clean the substrate to be cleaned with a higher degree of cleanliness, further suppress contamination by particles, and increase yield and productivity.

In addition, the removal of bubbles and the removal of foreign substances can be further performed, and the number of stages can be appropriately determined as necessary.
Moreover, the washing | cleaning process after a foreign material removal process, etc. are not specifically limited, For example, it can carry out in the same procedure as the past.

(Third embodiment)
FIG. 5 shows an outline of an example of still another foreign matter removing apparatus that can be used in the foreign matter removing step.
This foreign matter removing apparatus 3 has a cylindrical housing 30 and is provided with a cleaning liquid inlet 31 that opens in the horizontal direction and a cleaning liquid outlet 34 opposite thereto. A filter 32 is disposed inside the housing 30, and the cleaning liquid entering the housing 30 is filtered by the filter 32, flows through the flow path 37 ′, and exits from the cleaning liquid outlet 34.

  Further, as shown in FIG. 5, a drain line 35 ′ is provided on the same side as the cleaning liquid outlet 34 of the housing 30. However, the position where the drain line 35 'is provided is not particularly limited, and a plurality of drain lines 35' may be provided. As will be described later, it suffices if the cleaning liquid is provided at a position where the flow of the cleaning liquid can be generated so as to have a flow component in a direction parallel to the filter surface of the filter 32.

When performing the foreign substance removal process in the cleaning method of the present invention using such a foreign substance removing apparatus 3, it is performed while removing a part of the cleaning liquid from the drain line 35 '.
If an attempt is made to filter the cleaning liquid through the filter 32 without removing a part of the cleaning liquid from the drain line 35 ′ (that is, the conventional method), the cleaning liquid is filtered with a flow direction substantially perpendicular to the filter surface near the interface of the filter 32. The filtered cleaning liquid is sent to the use point through the cleaning liquid outlet 34. When such a foreign matter removing step is performed, the conventional problem caused by bubbles cannot be solved.
However, when the cleaning liquid is sent to the use point, the drain line 35 ′ is opened and a part of the cleaning liquid is removed through the flow path 37, so that the cleaning liquid flows in the direction parallel to the filter surface near the interface of the filter 32. Can be made. Accordingly, bubbles in the cleaning liquid can be removed without adhering to the filter 32, and further, the entire cleaning liquid can be excluded from the drain line 35 ′. On the other hand, the cleaning liquid filtered by the filter 32 is subjected to the removal of bubbles and the removal of foreign matters, and then proceeds to the substrate to be cleaned through the cleaning liquid outlet 34.
In this way, it is possible to obtain a cleaning liquid from which bubbles in the cleaning liquid have been removed and foreign substances have been removed, and the cleaning liquid can be supplied to the substrate to be cleaned and cleaned in the cleaning process.

As described above, for example, the cleaning method of the present invention can be performed using the foreign matter removing apparatus 1-3. However, as described above, the cleaning method of the present invention is not limited to these, and in the foreign matter removing step. In addition, it is sufficient that the bubbles are removed together with the removal of the foreign matter, and the foreign matter removing device of various forms can be used.
For example, using a gas-liquid separator or the like disposed immediately before the position of the filter, and removing the bubbles in the cleaning liquid using the gas-liquid separator, By filtering the cleaning liquid by the above, it is possible to obtain a cleaning liquid from which bubbles and foreign matters have been removed.

  The cleaning method of the present invention can obtain a high effect particularly when cleaning with warm water, but cleaning with warm water is particularly advantageous in the following cases. In other words, if the substrate to be cleaned is cleaned with a sulfuric acid-containing cleaning solution such as a resist stripping solution or a sulfuric acid or sulfate-containing material such as a surfactant containing sulfate, the substrate should be cleaned with warm water. Thus, sulfate ion removal can be satisfactorily achieved. In the case of cleaning for the purpose of removing sulfate ions, the treatment time with warmed hot water can be appropriately adjusted according to the size of the substrate to be cleaned, the supply amount of hot water supplied per unit time, and the like. In general, it is preferable to supply hot water onto the substrate to be cleaned for about 30 seconds to 20 minutes.

  Thus, particularly when the substrate to be cleaned is intended for lithography used with an exposure light source having a wavelength of 200 nm or less, it is necessary to suppress sulfate ion contamination as described above. By performing the hot water cleaning by the method, it is possible to obtain a cleaning substrate that suppresses sulfate ion contamination to a low level and has little particle contamination, and can obtain particularly preferable effects.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this.
Example 1
For a device that can supply cleaning liquid to the spin cleaning / drying machine, clean the photomask substrate, and spin dry, install a line heater in front of this device to supply the cleaning liquid so that the supplied cleaning liquid can be heated. I made it. Further, the foreign matter removing apparatus shown in FIG. 4 was attached at a position immediately before the warm water heated by the line heater was sent to the spin cleaning apparatus. In addition, the spin cleaning apparatus can be sufficiently ventilated with clean air so that mist cannot enter the apparatus even when hot water is used.

Next, as a substrate to be cleaned, a light shielding film 26 nm made of CrN (Cr: N = 9: 1 (atomic ratio)) and CrON (Cr: N: O = 4: 5: 1 (atomic ratio)) are formed on the main surface. A quartz substrate having an antireflection film of 20 nm formed by sputtering and having no defects of 0.2 μm or more is set in the spin cleaning / drying machine, and irradiated with Xe excimer UV light having a wavelength of 172 nm in air for 3 minutes. Spin cleaning was performed for 4 minutes with aqueous ammonia hydrogen water (ammonia concentration 2 ppmm hydrogen concentration 1.4 ppm) to which a megasonic output of 100 W was applied at a frequency of 1.5 MHz (the above processing is the same in other examples and comparative examples described later). Done).
Next, it is heated to 60 ° C. with a line heater, washed with 1 L of pure water subjected to the foreign matter removing process using the foreign matter removing apparatus for 10 minutes, and spin-dried at 1000 rpm for 30 seconds after washing. went.
Note that the total amount of the cleaning liquid removed from the drainage line in the foreign matter removing step was set so that 1 L of cleaning liquid was removed while 1 L of cleaning liquid was supplied from the cleaning nozzle per minute.

  After performing this treatment, the number of surface defects on the substrate was measured using MAGICS manufactured by Lasertec Corporation. As a result, 65 defects having a diameter of 0.2 μm or more were found.

(Example 2)
In the spin cleaning / drying machine of Example 1, the foreign matter removing apparatus having the drainage line shown in FIG. 5 and capable of adjusting the amount of the cleaning liquid removed from the drainage line in conjunction with the amount of the cleaning liquid supplied to the cleaning apparatus was attached.
The substrate to be cleaned similar to that of Example 1 was subjected to the same treatment, and then heated to 60 ° C. with a line heater, and pure water subjected to the foreign matter removing process using the foreign matter removing apparatus was added for 10 minutes every minute. 1 L was supplied and washed, and after washing, spin drying was performed at 1000 rpm for 30 seconds.
Note that the total amount of the cleaning liquid removed from the drainage line in the foreign matter removing step was set so that 1 L of cleaning liquid was removed while 1 L of cleaning liquid was supplied from the cleaning nozzle per minute.

  After this treatment, the number of surface defects on the dried substrate was measured in the same manner as in Example 1. As a result, there were 213 defects having a diameter of 0.2 μm or more.

(Example 3)
Using the apparatus of Example 2, the same processing was performed on the substrate to be cleaned similar to Example 1, and then heated to 60 ° C. with a line heater, and subjected to the foreign substance removing process using the foreign substance removing apparatus. Water was supplied at a rate of 1 L per minute for 10 minutes for cleaning, and after cleaning, spin drying was performed at 1000 rpm for 30 seconds.
In the foreign matter removing step, the total amount of the cleaning liquid removed from the drainage line was set so that 2.8 L of cleaning liquid was excluded while 1 L of cleaning liquid was supplied from the cleaning nozzle per minute.

  After this treatment, the number of surface defects on the dried substrate was measured in the same manner as in Example 1. As a result, there were no defects having a diameter of 0.2 μm or more.

Example 4
Using the apparatus of Example 2, the same processing was performed on the substrate to be cleaned similar to Example 1, and then heated to 80 ° C. with a line heater, and subjected to a foreign substance removing process using the foreign substance removing apparatus. Water was supplied at a rate of 1 L per minute for 10 minutes for cleaning, and after cleaning, spin drying was performed at 1000 rpm for 30 seconds.
In the foreign matter removing step, the total amount of the cleaning liquid removed from the drainage line was set so that 2.8 L of cleaning liquid was excluded while 1 L of cleaning liquid was supplied from the cleaning nozzle per minute.

  After this treatment, when the number of surface defects on the dried substrate was measured in the same manner as described above, there were 5 defects having a diameter of 0.2 μm or more.

(Comparative Example 1)
Using the apparatus of Example 2, the same processing was performed on the substrate to be cleaned similar to Example 1, and then heated to 60 ° C. with a line heater, and subjected to the foreign substance removing process using the foreign substance removing apparatus. Water was supplied at a rate of 1 L per minute for 10 minutes for cleaning, and after cleaning, spin drying was performed at 1000 rpm for 30 seconds.
The drain line was closed and the amount of cleaning liquid to be removed was zero. That is, it was cleaned by a conventional method without removing bubbles in the cleaning liquid.

  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 1334.

As can be seen from the above Examples 1-4 and Comparative Example 1, the cleaning method of the present invention was carried out, and bubbles were removed together in the foreign matter removing step, and the cleaning liquid from which bubbles and foreign matters were removed was used. In Example 1-4 in which the substrate to be cleaned was cleaned, the number of defects in the cleaned substrate could be suppressed to about 200 at the maximum.
However, in the comparative example 1 in which the cleaning method of the present invention is not performed and the foreign matter is simply removed in the foreign matter removing step as in the prior art, the number of defects has reached about 1300.
Thus, it can be seen that the number of defects can be remarkably suppressed by the cleaning method of the present invention.

  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.

In the cleaning method of this invention, it is the schematic which shows the outline of an example of the foreign material removal apparatus which can be used at a foreign material removal process. It is the schematic which shows the outline of an example of another foreign material removal apparatus which can be used at the foreign material removal process in the washing | cleaning method of this invention. It is explanatory drawing for demonstrating the flow of a washing | cleaning liquid. It is the schematic which shows the outline of an example of another foreign material removal apparatus which can be used at the foreign material removal process in the washing | cleaning method of this invention. It is the schematic which shows the outline of an example of another foreign material removal apparatus which can be used at the foreign material removal process in the washing | cleaning method of this invention.

Explanation of symbols

1, 2, 3 ... Foreign matter removing device, 10, 30 ... Housing,
11, 31 ... Cleaning liquid inlet, 12 (12a, 12b), 32 ... Filter,
13 ... upper part of housing 14, 34 ... cleaning liquid outlet,
15 ... exhaust port, 15 ', 35' ... drainage line,
16 ... gas-liquid separator, 17, 17 ', 18, 18', 37, 37 '... flow path,
19 ... Drain valve.

Claims (9)

A cleaning method that includes a foreign matter removal step of removing foreign matter in the cleaning liquid, and supplies the cleaning liquid from which the foreign matter has been removed to the substrate to be cleaned.
At least in the foreign matter removing step of removing the foreign matter in the cleaning liquid by filtering the cleaning liquid with a filter, the bubbles in the cleaning liquid are removed together,
A cleaning method comprising: supplying a cleaning liquid from which bubbles and foreign substances have been removed to a substrate to be cleaned.   The cleaning method according to claim 1, wherein the cleaning liquid is flowed so as to have a flow component in a direction parallel to a filter surface of the filter, and filtered while removing bubbles.   The cleaning method according to claim 1 or 2, wherein the bubbles in the cleaning liquid and foreign substances are removed in multiple stages.   The cleaning method according to any one of claims 1 to 3, wherein the bubbles in the cleaning liquid are excluded from the system together with the cleaning liquid containing the bubbles. When the entire cleaning liquid containing bubbles is excluded from the system, the total amount of the cleaning liquid to be excluded is
The cleaning method according to claim 4, wherein the cleaning method is adjusted in accordance with a total amount of the cleaning liquid from which the bubbles and foreign matters have been removed.   6. The cleaning method according to claim 5, wherein the total amount of the cleaning liquid to be excluded is at least one times the total amount of the cleaning liquid from which the bubbles and foreign substances have been removed.   The cleaning method according to any one of claims 1 to 6, wherein bubbles in the cleaning liquid are excluded from the system by using a gas-liquid separator.   The cleaning method according to any one of claims 1 to 7, wherein the bubbles and foreign matters are removed after the cleaning liquid is heated to 40 ° C or higher and lower than 100 ° C.   The cleaning method according to any one of claims 1 to 8, wherein the substrate to be cleaned is any one of a photomask substrate, a photomask blank, a photomask, or a production intermediate thereof.

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