JP2007253120A - Ultrasonic cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic cleaning method capable of enhancing the removal performance of polluted organic matter. <P>SOLUTION: A cleaning solution containing microbubbles is fed to a substrate A via a slit 19 of a cleaning head 11, and ultrasonic waves are emitted to be converged toward the slit 19, thereby cleaning the substrate A. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic cleaning method for cleaning an object to be cleaned such as a glass substrate of a liquid crystal display device, a glass substrate for a photomask, a substrate for an optical disk, and a semiconductor wafer.

  In the manufacturing process of liquid crystal display devices and semiconductors, ultrasonic cleaning is performed to quickly and reliably remove contaminants such as particles adhering to the surface of a glass substrate or wafer (hereinafter referred to as a substrate) ( For example, Patent Document 1).

The ultrasonic cleaning apparatus disclosed in Patent Document 1 includes a processing liquid supply source that supplies a processing liquid onto a substrate, a microbubble generator that generates microbubbles in the processing liquid, and a processing liquid that includes microbubbles. It is comprised from the ultrasonic transducer | vibrator which irradiates an ultrasonic wave. Then, the processing liquid is supplied from the upper part of the substrate while rotating. The processing solution is contained microbubbles supplied by the micro-bubble generator, ultrasound 5～100MH _Z is irradiated to the treatment solution.
Japanese Patent Laying-Open No. 2005-93873 (see FIG. 1)

However, ultrasonic cleaning device disclosed in Patent Document 1, microbubbles crushing on the substrate surface in view of the damage to the substrate is set high and 5～100MH _Z frequency of the ultrasonic wave to be irradiated . For this reason, particle absorptivity can be obtained by stirring the microbubbles with ultrasonic waves, but since the microbubbles cannot be positively crushed by ultrasonic waves, the amount of radicals generated is small, and the performance of removing contaminating organic substances is reduced. There was a problem that became low.

  Then, an object of this invention is to provide the ultrasonic cleaning method which can also improve the removal performance of a contaminated organic substance in view of such a situation.

  In order to achieve the above object, as a result of earnest research, the inventor has improved the generation efficiency of radicals while maintaining the removal performance of contaminant particles on the substrate, and promotes the decomposition performance of contaminated organic matter, thereby improving the cleaning effect. Has led to a significant improvement.

  In the ultrasonic cleaning method according to claim 1, a cleaning liquid containing microbubbles is supplied to an object to be cleaned through a slit formed in the cleaning head body, and ultrasonic waves are focused so as to be focused toward the slit. The object to be cleaned is cleaned by irradiation.

  The cleaning liquid is preferably one in which excess gas dissolved in pure water is degassed by a degassing membrane module, and then gas is supplied to pure water in a microbubble state by a microbubble supply device. As the type of gas, ammonia that exhibits alkalinity after dissolution has a negative zeta potential and is therefore suitable for removing particulate contamination. Hydrogen gas, oxygen gas, ozone gas, etc. are preferable because they increase the generation of radicals. Moreover, since argon gas is non-condensable and has low thermal conductivity, it generates high thermal energy when the microbubbles are crushed. Therefore, it can be used in combination with other gases to improve the generation of radicals.

Ultrasonic cleaning method according to claim 2 is the invention of claim 1, wherein the ultrasonic waves, and less than 1 MH _Z.

  According to a third aspect of the present invention, there is provided the ultrasonic cleaning method according to the first aspect of the present invention, wherein the ultrasonic wave is a single frequency, and the ultrasonic wave is irradiated intermittently.

  According to a fourth aspect of the present invention, in the first aspect of the invention, the ultrasonic wave is a combination of a plurality of frequencies.

  According to a fifth aspect of the present invention, in the ultrasonic cleaning method of the fourth aspect, the frequency of the ultrasonic wave is 5 to 800 KHz and 1 MHz or more.

  The ultrasonic cleaning method according to a sixth aspect is characterized in that, in the invention according to any one of the first to fifth aspects, the focused position of the ultrasonic wave is in front of the surface of the object to be cleaned.

  The ultrasonic cleaning method according to a seventh aspect of the present invention is the ultrasonic cleaning method according to any one of the first to sixth aspects, wherein the cleaning liquid is formed in the cleaning liquid film forming region formed on the cleaning target by the cleaning liquid supplied to the cleaning target The ratio of the gap distance of the slit to the distance is 0.8 or less.

  According to the first aspect of the present invention, since the ultrasonic wave is focused and irradiated on the cleaning liquid supplied to the object to be cleaned in a slit shape, the ultrasonic wave can be focused at the optimum position. By focusing in front of the surface of the cleaning object and thereby crushing the microbubbles, radicals can be generated without damaging the object to be cleaned. Hydrogen radicals (H.) and hydroxy radicals (OH.) Are generated from the collapsed microbubbles. These radicals are supplied to the surface of the object to be cleaned together with the microbubbles that have not been crushed. Microbubbles that are not crushed come into contact with and adsorb contaminant particles present on the surface of the object to be cleaned. Since the microbubbles themselves have a negative charge and the object to be cleaned also has a negative charge, the microbubbles adsorbing the contaminating particles are lifted off without reattaching. In addition, radicals generated during the collapse of the microbubbles supplied to the surface of the object to be cleaned act on the contaminated organic matter adhering to the surface of the object to be cleaned, and the contaminated organic matter can be instantly decomposed and removed.

  According to invention of Claim 2, a microbubble can be crushed effectively.

  According to the invention of claim 3, when low frequency ultrasonic waves are continuously supplied, excessive ultrasonic energy is given to the object to be cleaned, but by supplying ultrasonic waves intermittently, the object to be cleaned is supplied. The ultrasonic energy applied upward can be suppressed, and the microbubbles can be effectively crushed.

  According to the invention of claim 4, the microbubbles are crushed by the low frequency ultrasonic wave, the radical generation is promoted, and the generated radical is mixed with the microbubbles remaining without being crushed by the high frequency ultrasonic wave. In this way, the surface of the object to be cleaned is supplied to the surface of the object to be cleaned.

  According to the invention of claim 5, low frequency ultrasonic waves (5 to 800 KHz) that crush the microbubbles and high frequency ultrasonic waves (1 MHz or more) that effectively mix the microbubbles and the generated radicals are combined. By irradiating the cleaning object, it can be effectively cleaned.

  According to the invention of claim 6, since the ultrasonic wave is focused in front of the surface of the object to be cleaned, and the microbubbles are crushed, radicals are generated without damaging the object to be cleaned when the microbubbles are crushed. Can be made. For this reason, the object to be cleaned is not damaged by cavitation that occurs when the microbubbles are collapsed. Therefore, since the frequency of the ultrasonic wave to be irradiated can be lowered and the output can be increased, the amount of radicals generated can be increased, and contaminated organic substances can be decomposed and removed more effectively.

  According to the seventh aspect of the present invention, the cleaning performance can be maintained high by setting the ratio of the slit gap distance (cleaning liquid supply area) to the cleaning liquid film forming area on the object to be cleaned to 0.8 or less. Furthermore, if the ratio of the slit gap distance to the cleaning liquid supply region is set to 0.6 to 0.8, the amount of cleaning liquid to be used can be reduced, and the cleaning efficiency can be further increased.

  Hereinafter, preferred embodiments of an ultrasonic cleaning method according to the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional perspective view conceptually showing an ultrasonic cleaning apparatus 1 for carrying out the ultrasonic cleaning method according to the present invention, and FIG. 2 is a schematic diagram showing the ultrasonic cleaning apparatus 1 shown in FIG. FIG. 3 is a view showing a cleaning liquid film formation region and a cleaning liquid supply region during substrate cleaning, FIG. 3 is an image of cleaning using both microbubbles and ultrasonic waves, and FIG. 4 is a cleaning liquid supply region / cleaning liquid film formation region and contaminant removal rate. It is the graph which showed the relationship.

  The ultrasonic cleaning apparatus 1 shown in FIG. 1 includes an ultrasonic generation unit 10, a cleaning liquid supply unit 20, a substrate transfer unit 30, and the like.

  The ultrasonic generator 10 includes a cleaning head (cleaning head main body) 11. The cleaning head 11 has a box shape having a width wider than the width of the substrate A, and a front end portion (lower portion in the embodiment) is tapered in a cross section in the traveling direction of the substrate A. At the tip of the cleaning head 11, an opening 11a extending in a direction perpendicular to the traveling direction of the substrate A is formed in parallel with the traveling direction surface of the substrate A, and the diaphragm 12 having ultrasonic permeability is formed in the opening 11a. Is arranged. The material of the diaphragm 12 is not particularly limited as long as the material can withstand ultrasonic energy and has chemical resistance (for example, polyester, polyethylene, quartz, etc.).

  In the cleaning head 11, the ultrasonic vibrator 14 is held on the ceiling by the SUS partition wall 13, and the ultrasonic vibrator is connected to the power supply 15. An acoustic lens 16 is disposed on the lower surface of the ultrasonic transducer 14. The cleaning head 11 is filled with the ultrasonic wave propagation liquid B.

  Further, a cooling device 17 is attached to the cleaning head 11, and the cooling device is communicated with the cleaning head 11 by a pipe 17a, and the ultrasonic wave propagation liquid B is circulated and cooled.

  A cover 18 is formed at the tip of the cleaning head 11 so as to cover the tip. A slit 19 is formed in the bottom wall of the cover 18. The length of the slit 19 is longer than the width of the substrate A.

  The cleaning liquid supply unit 20 includes a cleaning liquid storage tank 21. The cleaning liquid storage tank 21 is connected to the cover 18 by a cleaning liquid supply pipe 22, and the cover 18 is connected to the cleaning liquid storage tank 21 by a cleaning liquid return pipe 23.

  The cleaning liquid storage tank 21 is connected to a cleaning liquid generator 24 through a pipe 24a. Further, a microbubble generator 25 is disposed in the cleaning liquid storage tank 21, and the microbubble generator 25 is connected to a gas supply source 26 through a pipe 25a.

  In the cleaning liquid supply unit 20, the cleaning liquid deaerated by the degassing membrane module in the cleaning liquid generator 24 is supplied to the cleaning liquid storage tank 21, and is also supplied from the gas supply source 26 in the cleaning liquid storage tank 21. The generated gas is generated in a microbubble state by the microbubble generator 25 and supplied into the cleaning liquid. Therefore, microbubbles are dissolved in the cleaning liquid supplied to the cleaning liquid supply pipe 22. Note that an air vent 27 is disposed in the cleaning liquid return pipe 23.

  The substrate transport unit 30 includes transport means 31 such as a belt conveyor, which is installed along the cleaning liquid supply pipe 22 below the cleaning liquid supply pipe 22. The substrate A is transported by the transport means 31. It is conveyed so as to cross the lower part of the slit 19 of the cleaning head 11.

  In the ultrasonic cleaning device 1 configured as described above, the ultrasonic transducer 14 is vibrated in the ultrasonic generator 10 to generate ultrasonic waves. This ultrasonic wave is focused by the acoustic lens 16, transmitted to the diaphragm 12 via the ultrasonic wave propagation liquid B, passes through the diaphragm, and is irradiated into the cover 18.

  On the other hand, the cleaning liquid is supplied from the cleaning liquid storage tank 21 into the cover 18 via the cleaning liquid supply pipe 22 by a pump (not shown). A part of the cleaning liquid is supplied linearly from the slit 19 onto the substrate A.

  The cleaning liquid supplied onto the substrate A is irradiated with linear ultrasonic waves that have passed through the diaphragm 12, and contaminants on the substrate A are removed by the ultrasonic waves and the microbubbles in the cleaning liquid.

  Next, the operation of the ultrasonic cleaning apparatus 1 configured as described above will be described.

  The ultrasonic cleaning apparatus 1 supplies a cleaning liquid containing microbubbles to the substrate A through a slit 19 formed in the cleaning head 11 and irradiates ultrasonic waves so as to be focused toward the slit 19. The substrate A is cleaned.

  Thereby, according to the ultrasonic cleaning apparatus 1, since the ultrasonic wave is focused in front of the surface of the substrate A at the optimum position and thereby the microbubbles are crushed, damage to the object to be cleaned is caused when the microbubbles are crushed. And can generate radicals. Hydrogen radicals (H.) and hydroxy radicals (OH.) Are generated from the collapsed microbubbles. These radicals are adsorbed in contact with the contaminating particles present on the surface of the substrate A together with the microbubbles that have not been crushed. Since the microbubbles themselves have a negative charge and the substrate A also has a negative charge, they are lifted off without reattaching. Further, the radicals supplied to the substrate A act on the contaminated organic matter adhering to the surface of the substrate A, and the contaminated organic matter can be instantly decomposed and removed.

Further, since the ultrasonic is less than 1 MH _Z, it is possible to effectively collapse the microbubbles.

  Furthermore, since the ultrasonic wave is a single frequency and the ultrasonic wave is irradiated intermittently, the ultrasonic energy applied to the object to be cleaned can be suppressed, and the microbubbles can be effectively crushed.

  In addition, since the ultrasonic wave is a combination of multiple frequencies, the microbubbles are crushed by low-frequency ultrasonic waves and radical generation is promoted, and the generated radicals remain without being crushed by the high-frequency ultrasonic waves. The mixed microbubbles can be mixed and supplied to the surface of the substrate A. For this reason, damage to the substrate A is reduced and cleaning is performed efficiently.

  Furthermore, since the frequency of the ultrasonic waves is 5 to 800 KHz and 1 MHz or higher, low frequency ultrasonic waves (5 to 800 KHz) that crush the microbubbles and high frequency ultrasonic waves (1 MHz or higher) that effectively mix the microbubble radicals. The substrate A can be irradiated in combination. Thereby, the substrate A can be effectively cleaned.

  Further, since the focused position of the ultrasonic wave is in front of the surface of the substrate A, the microbubbles are thereby crushed. Therefore, radicals can be generated without damaging the substrate A when the microbubbles are crushed. For this reason, the substrate A is not damaged by cavitation that occurs when the microbubbles are collapsed. Therefore, since the frequency of the ultrasonic wave to be irradiated can be lowered and the output can be increased, the amount of radicals generated can be increased, and contaminated organic substances can be decomposed and removed more effectively.

  Furthermore, since the ratio of the gap distance of the slit to the distance in the direction of the cleaning object in the cleaning liquid film forming region formed on the substrate A by the cleaning liquid supplied to the substrate A is 0.8 or less, the cleaning performance is maintained high. Can do. Furthermore, if the ratio of the slit gap distance to the cleaning liquid supply region is set to 0.6 to 0.8, the amount of cleaning liquid to be used can be reduced, and the cleaning efficiency can be further increased.

The cross-sectional perspective view which showed notionally the apparatus for implementing the ultrasonic cleaning method which concerns on this invention FIG. 2 is a schematic diagram illustrating the ultrasonic cleaning apparatus illustrated in FIG. 1, illustrating a cleaning liquid film formation region and a cleaning liquid supply region during substrate cleaning. Image of cleaning using both microbubbles and ultrasonic waves Graph showing the relationship between the cleaning liquid supply area / cleaning liquid film forming area and the contaminant removal rate

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Ultrasonic cleaning apparatus, 10 ... Ultrasonic generating part, 11 ... Cleaning head, 11a ... Opening, 12 ... Diaphragm, 13 ... Septum, 14 ... Ultrasonic vibrator, 15 ... Power supply, 16 ... Acoustic lens, 17 ... Cooling Equipment: 17a ... Pipe, 18 ... Cover, 19 ... Slit, 20 ... Cleaning liquid supply section, 21 ... Cleaning liquid reservoir, 22 ... Cleaning liquid supply pipe, 23 ... Cleaning liquid return pipe, 24 ... Cleaning liquid generator, 24a ... Pipe, 25 ... Microbubble generator, 25a ... pipe, 26 ... gas supply source, 27 ... air vent, 30 ... substrate transport unit, 31 ... transport means, A ... substrate, B ... ultrasonic wave propagation liquid

Claims (7)

  A cleaning liquid containing microbubbles is supplied to the object to be cleaned through a slit formed in the cleaning head body, and the object to be cleaned is cleaned by irradiating ultrasonic waves so as to be focused toward the slit. An ultrasonic cleaning method characterized by the above. The ultrasound ultrasonic cleaning method according to claim 1, characterized in that less than 1 MH _Z.   The ultrasonic cleaning method according to claim 1, wherein the ultrasonic wave is irradiated at a single frequency intermittently.   The ultrasonic cleaning method according to claim 1, wherein the ultrasonic wave is a combination of a plurality of frequencies.   The ultrasonic cleaning method according to claim 4, wherein the ultrasonic frequency is 5 to 800 KHz and 1 MHz or more.   The ultrasonic cleaning method according to claim 1, wherein the ultrasonic focusing position is in front of the surface of the object to be cleaned.   The ratio of the gap distance of the slit to the distance in the direction of movement of the cleaning liquid film forming region formed on the cleaning object by the cleaning liquid supplied to the cleaning object is 0.8 or less. Item 7. The ultrasonic cleaning method according to any one of Items 1 to 6.

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