JP2008249854A - Method of cleaning photomask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem, wherein a photoresist left undeveloped which is a foreign matter deposited on a photomask, cannot be removed easily by either a liquid chemical or a gas-liquid flow of two fluids, wherein pure water and air are mixed, and cannot be removed easily, when being redeposited on the photomask by using the gas-liquid flow of two fluids which is apt to cause mist spattering. <P>SOLUTION: A photomask 1 is cleaned by executing a step of placing the photomask 1 on a table 3, rotating at a low speed and spraying the liquid chemical and a step of spraying the gas-liquid flow of two fluids. Thereafter, a drying step is executed, while making the table 2 rotate at a high speed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a photomask cleaning method and a cleaning apparatus used for manufacturing semiconductors, LCD color filters, and the like.

  In the manufacture of semiconductors, color filters for LCDs, and the like, ultraviolet irradiation is performed through a photomask. Therefore, if there are defects or foreign matter on the photomask, they are projected during transfer. Therefore, it is necessary to remove foreign matters on the front surface (back surface) of the photomask.

  In order to remove such foreign matter adhering to the photomask, various photomask cleaning methods such as chemical immersion and coating (spinning method, etc.) have been proposed, but in order to remove the firmly attached foreign matter. In addition, it is necessary to perform cleaning with a physical action such as a brush.

  However, in physical cleaning with a brush or the like, the pattern of the photomask may be damaged if the brush is pushed too hard. Therefore, it is necessary to make fine adjustments such as the amount of pressing of the brush, and when foreign matter is firmly attached to the photomask, it is difficult to remove it by one cleaning.

Therefore, a cleaning method using two fluids in which a liquid and a gas are mixed has been proposed. For example, Patent Document 1 discloses a cleaning method having a two-fluid jet nozzle that ejects mist-like minute water droplets onto a wafer at high speed. In the present invention, the wafer rotates while being held so as to face the nozzle. Then, the nozzle is scanned a plurality of times from the center of the wafer to the outside, and the ejection speed in the second and subsequent scans is made faster than the ejection speed in the first scan.
JP 2004-335671 A

  In most cases, the foreign matter adhering to the photomask is a photoresist which is a photosensitive object. In general, a photoresist is often an adhesive substance, and often cannot be easily removed by simply immersing it in a chemical solution or applying a physical impact with two fluids.

  Further, in the case of two fluids, water droplets are often in a fine mist form. When the mist droplets adhere to the object to be cleaned, they become fine water marks and are difficult to remove.

  The photomask cleaning method of the present invention has been conceived in view of the above problems. Specifically, in the photomask cleaning method of the present invention, a processing liquid and an antistatic two-fluid gas-liquid are jetted onto the photomask, and the chemical liquid that has come into contact with the photomask is rotated while rotating the photomask. The photomask is removed and dried by rotating at high speed.

  As described above, according to the present invention, the cleaning process is performed while rotating the photomask, and then drying is performed by high-speed rotation. It can be removed, and the photomask cleaning effect can be improved.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the drawings. FIG. 1 is a side view showing an example of a photomask cleaning apparatus for carrying out the cleaning method of the present invention. FIG. 2 is a top view of FIG.

  The processing tank 4 has a turntable 3 on which a photomask is placed. The rotary table 3 is supported by the rotary shaft 2 and can be rotated at a predetermined speed by a control system and a drive unit (not shown). Further, the treatment tank 4 has a shape in which the bottom surface becomes higher as it is closer to the rotation shaft 3. By adopting such a shape, various liquids applied to the photomask are guided to the outer peripheral portion and easily drained.

  The rotary table 3 on which the photomask 1 is placed is preferably composed of a thin member as long as the strength can be maintained so that the lower surface of the photomask can be easily cleaned and the processing solution behind the photomask 1 can be easily cleaned.

  Above the processing tank 4, there are a chemical liquid discharge nozzle 7 and a two-fluid gas-liquid discharge nozzle 6 for discharging the chemical liquid onto a photomask placed on a rotary table. The chemical solution discharge nozzle and the two-fluid gas-liquid discharge nozzle are provided on one column.

  Further, an upper pure water discharge nozzle 5 for rinsing is provided in the upper part of the processing tank 4. A lower pure water discharge nozzle 8 is provided on the lower side of the turntable 3, and the placed photomask can be rinsed with pure water simultaneously on the upper side and the lower side.

  Here, the chemical solution discharge nozzle 7 and the two-fluid gas-liquid discharge nozzle 6 may be installed below the rotary table. However, the discharge of the chemical solution from the lower side of the rotary table 3 has a reason that it cannot be sufficiently ejected due to the arm portion of the rotary table 3 and a chuck for fixing the photomask, and the chemical solution or the like by the subsequent rinsing. It is preferable not to do this because there is a possibility that it cannot be completely removed. When cleaning the backside of the photomask, it is preferable to turn the photomask over.

  The chemicals used to clean the photomask include nonionic, anionic or cationic surfactants, potassium hydroxide (KOH), sodium hydroxide (NaOH), tetramethylammonium hydroxide ( Examples include alkaline aqueous solutions such as TMAH), pure water, and the like, but it is necessary to select an appropriate chemical solution that is easily dissolved depending on the type of photoresist with which the photomask contacts.

The two-fluid gas-liquid used for cleaning the photomask is obtained by discharging pure water and air simultaneously. As pure water to be used, pure water bubbling CO ₂ is preferably used in order to prevent damage to the mask pattern due to generation of static electricity.

  Next, the cleaning method of the present invention using such a cleaning apparatus will be described. The photomask 1 is placed on the turntable 3 with the surface in contact with the photoresist as the upper side. While the fixed photomask is slowly rotated, the chemical solution is ejected from the chemical solution discharge nozzle 7. The chemical is sprayed to spread over the entire surface of the photoresist. This is a chemical solution application process. Next, the photomask is washed with a two-fluid gas-liquid.

  When jetting the processing liquid, the two-fluid gas-liquid, or pure water onto the photomask 1, the photomask is jetted while slowly rotating. The rotation speed of the photomask is preferably 200 rpm or less, more preferably 100 rpm or less. By rotating the photomask, the chemical liquid and the two-fluid gas-liquid that are always in contact with the photomask are renewed, and the processing liquid is prevented from being scattered and becoming mist droplets by slowly rotating the photomask.

  The two-fluid gas-liquid is a mixture of liquid and gas, has a physical impact action, and can remove deposits. However, on the other hand, a rotating photomask results in very fine droplets or air droplets (mist droplets), which cannot be easily removed as fine water traces or bubble traces when attached to the photoresist. Therefore, when using chemical liquid, two-fluid gas-liquid, or pure water, the rotary table is slowly rotated. The step of ejecting the two-fluid gas-liquid is a two-fluid gas-liquid ejecting step.

  Regarding the discharge method of chemical liquid and two-fluid gas-liquid, install a plurality of nozzles to increase the area where the chemical liquid and two-fluid gas-liquid contact and increase the cleaning effect, and install an appropriate number of nozzles and shake the nozzles. There is a method of bringing the chemical liquid and the two-fluid gas-liquid into contact with the entire surface of the photomask by moving them, but either discharge method may be used.

  After washing with a chemical solution or two-fluid gas-liquid, rinsing is performed by washing with water. At this time, rinsing is performed using both the upper pure water discharge nozzle 5 and the lower pure water discharge nozzle 8. This is a rinsing step. Washing with water from the lower surface is effective in removing the chemical solution around the back.

  After rinsing, a drying process is performed in which water on the photomask is spun off and dried by rotating the photomask at a high speed. The rotation speed of the photomask is preferably 200 to 1000 rpm, more preferably 300 to 600 rpm. After removing most of the water droplets up to about 200 rpm in advance, the photomask may be dried by increasing the number of rotations up to 300 to 600 rpm.

  It is preferable to increase the rotation speed over the first time immediately after rinsing because the generation of mist splashes can be suppressed. The number of rotations is preferably accelerated from 3 rpm / sec to 6 rpm / sec. If the acceleration is higher than this, the rinsed pure water will scatter finely and become mist droplets.

  The required time for drying is preferably 60 to 300 sec, more preferably 90 to 150 sec. Since water droplets are removed by rotating the photomask mask at a high speed, it is desirable that the drying time be as short as possible so that the water droplets on the photomask can be completely removed and the photomask is not recontaminated by mist splashes.

  In the cleaning apparatus for carrying out the method of the present invention, it is preferable that the upper side of the mounted photomask is open. When performing the drying process, it is better to prevent re-adhesion of mist droplets, and it is easier for mist droplets to escape when the treatment tank is open than when the treatment tank is sealed, and re-apply to the photomask. This is because adhesion hardly occurs.

  The photomask cleaning method of the present invention has a high cleaning effect because a new processing liquid always contacts the photomask by rotating the photomask. Further, it is characterized in that the foreign matter firmly adhered to the photomask can be removed and cleaned without damaging the photomask by jetting two fluid gas-liquid.

Hereinafter, the present invention will be described in more detail using preferred embodiments, but the efficacy of the present invention is not limited by the embodiments used.
Example 1
The nozzle for discharging the chemical solution 7 and pure water 5 used in this example is a chevron-distributed flat spray pattern with both ends tapered, 0.9 L / min when the pressure is 0.1 MPa, and the spray angle is 50 °. The thing which is is used.

The two-fluid gas-liquid discharge nozzle 6 is of a flat cone type in which the discharge nozzle has a tip shape and the spray pattern is thin and sharp. When the hydraulic pressure is 0.3 MPa (air pressure 0.3 MPa), the spray amount is 0.6 L / min, the air consumption (CDA) is discharged at a rate of 49 L / min, and the spray angle is 60 ° Was used. The average particle diameter of the spray discharged from the two-fluid gas-liquid discharge nozzle was 20 to 250 μm. The pure water used for the two-fluid gas-liquid was pure water having a static electricity generation amount of 50 V or less by CO ₂ bubbling in order to prevent pattern damage of the photomask due to static electricity generation.

  Six chemical solution discharge nozzles 7 for discharging the chemical solution are installed on the upper side of the photomask 1 so that the nozzles at both ends cover the half surface of the photomask, and the photomask rotates at 50 rpm to apply the detergent to the entire surface. The mechanism was able to. Further, the chemical solution discharge nozzle was positioned 154 mm from the upper surface of the photomask 1.

  The upper pure water discharge nozzles 5 are installed on the upper side of the photomask and on a support column different from the detergent nozzle. Six nozzles at both ends are equally installed so as to cover the half surface of the photomask. It was set as the mechanism which can apply | coat detergent on the whole surface by rotating at 50 rpm. The upper pure water discharge nozzle was positioned 154 mm from the upper surface of the photomask 1. In addition, the lower pure water discharge nozzles 8 are installed at three positions so that the angle can be adjusted from the lower surface of the photomask 1 so that pure water can be jetted onto the back surface of the photomask 1.

  Three two-fluid gas-liquid discharge nozzles 6 are installed above the photomask 1 and on the same support column as the chemical liquid discharge nozzle, and the middle nozzle is installed at the center position of the photomask. The position of the two-fluid gas-liquid discharge nozzle 6 is adjusted to be 50 mm above the photomask.

  The two-fluid gas-liquid discharge nozzle 6 reciprocally swings 20 times in a scan manner at 3 deg / sec on the upper surface of the photomask 1 and can spray two fluids on the entire surface by rotating the photomask at 50 rpm. The mechanism. Further, the two-fluid nozzle was installed at a position of 154 mm from the upper surface of the photomask 1.

  The photomask is used for the structure of the color filter, and the main foreign matter is a resist. Therefore, TMAH, which is sometimes used as a developing solution, was used as the chemical solution used for cleaning.

  If foreign matter is present on the front surface (back surface) of the photomask, it is projected during transfer, so it is necessary to remove the foreign matter on the front surface (back surface) of the photomask. Therefore, when a foreign substance adheres to the photomask, the mask must be cleaned.

  First, the photomask 1 was placed on the turntable 3 with the surface facing the resist at the time of exposure. The turntable 3 has a pin chuck 9 having a height of 100 mm, and a gap is provided between the turntable 3 and the photomask 1. The size of the photomask 1 was 800 mm × 960 mm × 8 mm, and the material was quartz glass.

  The photomask 1 was rotated at 50 rpm, and TMAH was sprayed at 0.9 L / min for 120 seconds from the chemical solution discharge nozzle 7 located at a position 154 mm above the photomask 1. Thereafter, the air pressure is 0.2 MPa, the liquid pressure is 0.2 MPa, and the spray amount is 0 from the two-fluid gas-liquid discharge nozzle 6 that is installed on the same column as the chemical liquid discharge nozzle 7 and is located 50 mm above the photomask 1. Two-fluid gas-liquid was ejected at a rate of 0.5 L / min and a consumption air amount of 36 L / min. At this time, the two-fluid gas-liquid was sprayed on the upper surface of the photomask 1 in a range of 18 degrees while reciprocating 20 times in a 3 des / sec scan.

  As a result, the two-fluid gas-liquid can be ejected over the entire upper surface of the photomask 1. Further, this method requires less utility usage.

  After the two-fluid spraying, the rotation speed of the photomask 1 was set to 60 rpm, and pure water was immediately discharged from the upper pure water nozzle to the photomask 1 for 300 seconds at a flow rate of 0.9 L / min. At the same time, pure water was discharged from the lower pure water discharge nozzle 8 on the lower side of the photomask 1 at a flow rate of 0.9 L / min to remove TMAH that had turned to the back surface of the photomask. At this time, pure water completely covered the upper surface of the photomask 1.

  After rinsing TMAH with pure water, the rotation of the photomask 1 was set to 200 rpm over 30 seconds to remove most of the pure water adhering to the photomask 1. The acceleration of the photomask at this time was 4.6 rpm / sec, and no mist splash was generated. Thereafter, the rotational speed of the photomask 1 was set to 450 rpm over 30 seconds, and the photomask 1 was rotated at this rotational speed for 40 seconds. Thereafter, the rotation of the photomask 1 was stopped over 30 seconds, and the pure water adhering to the photomask 1 was completely removed. In the drying process of the photomask 1, CDA was sprayed at 30 L / min from the upper and lower surfaces of the photomask 1 at the center of rotation so that the pure water at the center of the photomask was easily removed.

  Thereafter, the photomask 1 was turned over, fixed, and rotated at 60 rpm, and pure water was discharged from the upper pure water discharge nozzle 5 at a flow rate of 0.9 L / min for 240 seconds. Also at this time, pure water was discharged from the back surface of the photomask 1 in the same manner as described above. The subsequent drying process was also performed by the same operation as described above.

(Example 2)
Spraying from the two-fluid gas-liquid discharge nozzle 6 was changed to an air pressure of 0.2 MPa and a hydraulic pressure of 0.3 MPa. That is, the air pressure was the same and the hydraulic pressure was increased. At this time, the amount of fog was 0.9 L / min, and the amount of air consumed was 24 L / min. Under this condition, the photomask was cleaned by the same procedure as in Example 1.

(Example 3)
Spraying from the two-fluid gas-liquid discharge nozzle 6 was changed to an air pressure of 0.3 MPa and a liquid pressure of 0.3 MPa. That is, the air pressure and the hydraulic pressure were higher than those in Example 1. The spray amount at this time was 0.6 L / min and the air consumption was 49 L / min. The other conditions were the same as in Example 1 to clean the photomask.

Example 4
Six two-fluid nozzles 6 are installed at equal intervals so that the two-fluid gas-liquid discharge nozzle 6 can be sprayed on the upper surface of the photomask 1 without performing a scanning motion, and the photomask is cleaned under the same conditions as in the third embodiment. Went.

(Comparative Example 1)
In Comparative Example 1, only the chemical solution and the rinsing were performed under the same conditions as in Example 1 without using the two-fluid gas-liquid discharge nozzle 6.

  About the above Example and the comparative example, it was confirmed with the following method whether the photomask wash | cleaned on each condition was in the clean state.

After cleaning the photomask, the glass substrate was exposed using a Hitachi High-Tech exposure machine LE8000A under the conditions of a proximity gap of 120 μm and an exposure amount of 40 mJ / cm ² . As a glass substrate, a non-alkali glass of 730 × 920 mm is coated with a black paste, semi-cured in an oven at 135 ° C. for 165 seconds, and further a positive resist (Rohm & Haas SC32A) is coated with a slit die coater, What was baked at 90 ° C. for 165 seconds was used.

  After the exposure, a 23 ° C. aqueous solution containing 2% by weight of TMAH was used as a developer, and the substrate was dipped in the developer for 60 seconds to effect a positive resist phenomenon and black paste etching.

If there are defects or foreign matter in the photomask, they are projected during exposure, so that a development residue (black defect) occurs in the shape of the photomask defect or foreign matter. The remaining development was confirmed with a Takano pattern inspection apparatus to determine the degree of photomask cleaning. When n = 3 was evaluated in the evaluation by the substrate, and a development residue having the same shape was present in the same part, it was assumed that foreign matter was present on the photomask. The results of Examples 1 to 4 and Comparative Example 1 are shown in Table 1.

  The “two-fluid condition” represents the values of the hydraulic pressure and air pressure of the two-fluid gas-liquid in units of MPa (megapascal). “Remaining development” is the number of remaining development on the glass substrate. The utility usage is expressed as L / min (liter per minute) of pure water and air consumption (CDA) of two fluids.

  Comparing the example and the comparative example, in Comparative Example 1 in which the two-fluid gas-liquid was not used, there were five development residues, whereas in the cleaning method using the two-fluid gas-liquid, the number was three or less. Therefore, the development residue that cannot be obtained only by the chemical solution can be removed by using the two-fluid gas-liquid.

  Next, looking at between Examples 1 to 4 using two-fluid gas-liquid, compared with Example 1, Example 2 in which the liquid pressure of pure water was increased reduced the remaining development from 3 to 2. . On the other hand, in Example 3 in which the hydraulic pressure and the air pressure are higher than those in Example 1, the remaining development is reduced from 3 to 0. From this, the cleaning effect is improved when the discharge condition of the two-fluid gas-liquid is not only the liquid pressure but also the air pressure is increased.

  Further, when Example 3 and Example 4 are compared with each other, the remaining number of developments is 0, so the cleaning effect is considered to be the same. However, the utility usage amount of the third embodiment may be approximately half that of the fourth embodiment. This indicates that the amount of utility usage is smaller when three nozzles are swung than when six fixed two-fluid gas-liquid discharge nozzles are installed.

  From the above results, by using the two-fluid gas-liquid, it was possible to completely remove the strong foreign matter adhering to the photomask and to clean the photomask without recontamination with mist splashes. . In addition, the number of two-fluid gas-liquid discharge nozzles was changed to three and oscillated to reduce the service amount by half, and an equivalent cleaning effect was obtained.

It is a side view which shows an example of the washing | cleaning apparatus which implements the washing | cleaning method of this invention. FIG. 2 is a top view of FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photomask 2 Rotating table rotating shaft 3 Rotating table 4 Treatment tank 5 Upper pure water discharge nozzle 6 Upper 2 fluid gas-liquid discharge nozzle 7 Upper chemical liquid discharge nozzle 8 Lower pure water discharge nozzle 9 Spacer

Claims (4)

A chemical application process for injecting a chemical solution that dissolves the residual coating film on the photomask;
A two-fluid gas-liquid injection step of ejecting two-fluid gas-liquid on the photomask;
A photomask cleaning method comprising: a rinsing step of ejecting pure water after the two-fluid gas-liquid injection step. The photomask cleaning method according to claim 1, wherein the rinsing step is performed simultaneously on the back side of the photomask. The photomask cleaning method according to claim 1, further comprising a drying step of rotating the photomask while rotating the photomask after the rinsing step. The photomask cleaning method according to claim 3, wherein the rotation number of the photomask during the drying step is higher than the rotation number of the photomask before the rinsing step.

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