JPWO2008107933A1 - Cleaning apparatus and cleaning method - Google Patents

Abstract

The present invention provides a novel cleaning technique for cleaning a surface of an object to be cleaned having a flat surface. The present invention is particularly suitable for cleaning an object to be cleaned such as a wafer in which a fine structure that is fragile is formed on the surface. In a cleaning apparatus for cleaning a surface of an object to be cleaned having a flat surface, a structure capable of propagating ultrasonic waves and ultraviolet rays, the structure having a flat surface facing the surface, and An ultrasonic vibrator and an ultraviolet irradiation device for irradiating the surface of the object to be cleaned, and for holding the surface of the structure parallel to the surface of the object to be cleaned with a certain distance A mechanism and a cleaning liquid supply mechanism for supplying the cleaning liquid to the space between the two surfaces.

Description

  The present invention relates to a cleaning technique for cleaning a surface of an object to be cleaned having a flat surface. More specifically, the present invention relates to a cleaning apparatus and a cleaning method used for cleaning the surface of a thin plate substrate such as a semiconductor device performed in the manufacturing process of various electronic devices.

  In recent years, in the manufacture of semiconductor elements, the wafer size has been increased. As a result, even in the wafer cleaning process, contaminants such as fine particles removed from the wafer surface are easier to perform a uniform cleaning process within the wafer surface compared to dip cleaning performed using a large cleaning tank. Single-wafer cleaning is becoming mainstream because it has many advantages such as being less likely to re-adhere to the surface, reducing the amount of cleaning liquid and rinsing water used, and starting up the cleaning device in a short time. . Single wafer cleaning is also used for other electronic materials such as glass substrates in the manufacturing process of display devices such as liquid crystal panels.

  In the present specification, contaminants such as fine particles are also simply referred to as fine particles. For example, “pollutant removal” is also simply referred to as “fine particle removal”.

  Electronic materials such as wafers in the manufacturing process of semiconductor elements and glass substrates in the manufacturing process of display devices such as liquid crystal panels are required to have a highly clean surface. Ultrasonic cleaning technology using ultrapure water (also referred to as gas-dissolved water) in which a specific gas is dissolved has been developed instead of cleaning technology that uses water at high temperatures, and has been rapidly adopted in the manufacturing process of various devices in recent years. (For example, refer to Patent Document 1).

  Among them, hydrogen-dissolved water (also referred to as hydrogen water) in which high-concentration hydrogen gas is dissolved in ultrapure water is known to exhibit an extremely excellent particulate removal effect when used in combination with ultrasonic irradiation. ing.

  The reason why an excellent particle removal effect can be obtained by using hydrogen water and ultrasonic irradiation in combination is due to the action of ultrasonic waves in addition to the physical cleaning effect of ultrasonic waves similar to conventional ultrasonic cleaning. This is because very active hydrogen radicals exist in hydrogen water in excess compared to water that does not contain hydrogen, and the hydrogen radicals cause a chemical reaction with the surface of the object to be cleaned or attached foreign matter. The explanation is given.

  Patent document 1 is mentioned as a well-known example of the ultrasonic cleaning technique using gas-dissolved water. Non-patent document 1 can be cited as an example of a research report on the effect of removing fine particles by the combined use of hydrogen water and ultrasonic irradiation.

  In a single wafer type spin cleaning apparatus that cleans a wafer by ultrasonic cleaning, a cleaning liquid is sprayed from the ultrasonic nozzle onto the surface of the wafer, and at the same time, an ultrasonic wave is generated by oscillating a vibrator inside the ultrasonic nozzle, Ultrasonic waves are propagated to the wafer surface using the cleaning liquid ejected from the ultrasonic nozzle as a medium, and the wafer surface is cleaned using ultrasonic energy. FIG. 1 shows an outline of spin cleaning performed using an ultrasonic nozzle. A cleaning liquid 3 is sprayed from the ultrasonic nozzle 2 toward the wafer 1. When the ultrasonic vibrator built in the ultrasonic nozzle 2 is operated, the generated ultrasonic wave propagates to the wafer surface using the cleaning liquid 3 as a medium. The ultrasonic nozzle 2 so that the irradiation point 4, which is the point at which the cleaning liquid 3 ejected from the ultrasonic nozzle 2 hits the wafer surface while the wafer 1 is rotated, reciprocates between the rotation center and the outer periphery of the wafer. , The irradiation point 4 passes through the entire surface of the wafer, and the entire surface of the wafer is cleaned.

  If hydrogen water is used as the cleaning liquid 3, the attached fine particles are cleaned and removed from the surface of the wafer 1 very efficiently.

  In the hydrogen water cleaning described so far, a state where active hydrogen radicals exist in the hydrogen water is created by the action of ultrasonic waves, and the effect of removing fine particles is obtained by the chemical action. On the other hand, it is known that the same effect as that of ultrasonic irradiation can be obtained by irradiation with ultraviolet rays. When hydrogen water is irradiated with ultraviolet rays, water molecules are excited and decomposed by the energy of ultraviolet rays, and as a result, a state in which active hydrogen radicals exist in hydrogen water is created, as in the case of ultrasonic irradiation. It is done.

Therefore, in hydrogen water cleaning, if ultrasonic water and ultraviolet light are simultaneously irradiated to hydrogen water, hydrogen radicals are generated in hydrogen water more efficiently than when only ultrasonic waves are irradiated. There is a possibility that an effect of removing fine particles superior to the case of irradiating with 1 is obtained.
Japanese Patent Publication No. 2821887 (Claims) Published Patent No. 2003-181394 (Claims) Publication No. 2003-31540 (Claims) Morita et al., "Particle Removable Mechanism of Hydrogen Water Megalogical Irradiation", 5th International Symposium on Silicon Surface Ultracleaning Process Fifth International Symposium on Ultra Clean Processing of Silicon Surfaces), UCPSS2000, Solid State Phenomena Vols. 76-77 (2001) pp. 245-250, Ostende, Belgium, September 2000

  In recent semiconductor devices, the wiring width and interval have been miniaturized. Therefore, in the middle of the manufacturing process, the object to be cleaned in which a fine structure (pattern) that is very fragile is formed must be cleaned. The number of cases that must be increased is increasing. For example, a semiconductor device having an interlayer insulating film made of an insulating material made of porous silica (also referred to as porous silica) in which fine pores called pores are uniformly distributed inside for the purpose of reducing the value of relative dielectric constant On the other hand, this case corresponds to a case where a fine pattern having a width of 100 nm or less between the grooves is formed by reactive dry etching or the like.

  When ultrasonic cleaning is performed on such an object to be cleaned using an ultrasonic nozzle, the pattern of the surface of the object to be cleaned is destroyed by the energy given by the ultrasonic wave, and a phenomenon called pattern collapse may occur. is there. This phenomenon also occurs when hydrogen water cleaning and ultrasonic irradiation are combined. In order to avoid such a problem, it is possible to reduce the energy of the ultrasonic wave irradiated per unit area of the surface of the object to be cleaned according to the structural strength of the pattern formed on the surface of the object to be cleaned. Necessary.

  In the cleaning apparatus using the ultrasonic nozzle as shown in FIG. 1, the ultrasonic vibrator built in the ultrasonic nozzle is driven so that damage to the structure on the wafer surface by the ultrasonic wave can be reduced. In many cases, the ultrasonic oscillator for adjusting the output is provided with a mechanism capable of adjusting the drive output, and the drive output can be set small within a certain range. If the drive output is still too large, it is conceivable to modify the electronic circuit of the ultrasonic oscillator so that it can be driven with a smaller output.

  However, even if the drive output can be reduced by modifying the electronic circuit of the ultrasonic oscillator, the ultrasonic vibrator built in the ultrasonic nozzle has inherent vibration conditions determined by the shape and structure, and there is a drive output. Below the lower limit, there is a problem that stable vibration is not established. In the case of a high frequency, if the drive output of the ultrasonic transducer falls below a certain level, the attenuation of the ultrasonic wave in the cleaning liquid ejected from the ultrasonic nozzle becomes abruptly intense. The case that does not reach will come out. As described above, when the ultrasonic nozzle is used, it is generally difficult to irradiate the wafer surface with the ultrasonic wave by operating the vibrator with a very small driving output.

  On the other hand, recently, for such a problem, an ultrasonic irradiation method using a vibrating body has been proposed in order to reduce ultrasonic damage to the wafer as much as possible.

  FIG. 2 shows an example of ultrasonic cleaning using a vibrating body. The upper side of FIG. 2 is a schematic perspective view, and the lower side is a schematic cross-sectional view. In the example shown in FIG. 2, the ultrasonic transducer 6 is installed on one of the flat surfaces of the vibrating body 5 that is a triangular prism-shaped member. The vibrating body 5 is held so that another flat surface of the vibrating body 5 faces the surface to be cleaned of the wafer 1 in parallel with a small distance. The cleaning liquid 3 is supplied from the nozzle 7 so that the gap generated between the vibrating body 5 and the wafer 1 is completely filled with the cleaning liquid 3. When the ultrasonic transducer 6 is driven in this state, the generated ultrasonic wave propagates through the vibrating body 5 and is transmitted to the cleaning liquid 3 from the entire surface of the vibrating body 5 facing the wafer 1. And reaches the surface of the wafer 1 to be cleaned. The manner of vibration of the surface facing the wafer 1 is determined by the manner of vibration of the ultrasonic vibrator 6 and the shape and material of the vibrator 5, and these are predicted by simulation in advance, and the design of the vibrator 5 according to the purpose. It is reflected in. FIG. 2 shows an example in which a ceramic vibrating body having a triangular prism shape is employed, but the material and shape (structure) of the vibrating body are various.

  In the method using such a vibrating body, the entire surface of the vibrating body vibrates due to the ultrasonic vibration generated by the ultrasonic vibrator, so that the vibration energy is dispersed and irradiated per unit area of the surface to be cleaned. The energy of the ultrasonic wave is greatly reduced compared to the case of the ultrasonic nozzle, and the effect of reducing the ultrasonic damage given to the surface of the object to be cleaned can be obtained.

  Even in such a cleaning method using a vibrating body, if hydrogen water is used as the cleaning liquid 3, a very excellent particle removal effect can be obtained as compared with the case of using ultrapure water in which hydrogen gas is not dissolved. (See Patent Documents 2 and 3).

  As described above, when hydrogen water cleaning is performed using an ultrasonic nozzle, the object to be cleaned has a pattern with a very small structural strength that causes pattern collapse. However, it has been found that the cleaning can be performed without causing pattern collapse if the vibrating body is used to reduce the energy of the ultrasonic wave irradiated per unit area and gently perform the hydrogen water cleaning. However, the damage to the pattern and the effect of particle removal are in a trade-off relationship with each other, and if the ultrasonic energy irradiated per unit area is reduced, pattern collapse will not occur, but the effect of particle removal is It became clear that it would be reduced to an insufficient level.

  For this reason, it is necessary to delicately adjust the intensity of the ultrasonic energy in order to irradiate the object to be cleaned with the strongest possible ultrasonic wave within a range in which pattern collapse does not occur. However, since the vibrating body also has specific vibration conditions determined by the material and structure, simply adjusting the drive output of the ultrasonic vibrator will continuously change the intensity of the ultrasonic energy emitted from the vibrating body. It turned out to be very difficult to make fine adjustments. Optimized to irradiate ultrasonic waves with the energy of the optimal strength for the object to be cleaned if the highest particle removal effect is to be obtained without causing pattern collapse using a vibrating body. Although it is necessary to newly design and prepare a vibrating body having a material and a structure, such a response is impossible in practice.

  Therefore, attention has been focused on a method of irradiating hydrogen water with ultrasonic waves using a vibrating body and simultaneously irradiating with ultraviolet rays. In this way, more hydrogen radicals are generated in the hydrogen water by the action of the ultraviolet rays that are irradiated at the same time, and as a result, a higher particle removal effect can be obtained compared to the case of irradiating only ultrasonic waves. Therefore, it is expected that the magnitude of the energy per unit area of the ultrasonic wave irradiated from the vibrating body can be more easily kept to a level that does not cause pattern collapse. The presence or absence of occurrence of pattern collapse is determined only by the intensity of the energy of ultrasonic waves to be irradiated. Therefore, it is considered that pattern collapse does not occur by adding ultraviolet irradiation.

  However, as a result of the experiment, in FIG. 2, a portion of the hydrogen water (that is, the cleaning liquid 3) that is supplied from the nozzle 7 and spreads on the surface of the wafer 1 that is not hidden by the vibrating body 5 that radiates ultrasonic waves. It is impossible to enhance the effect of removing fine particles even when irradiated with ultraviolet rays of various wavelengths and intensities compared to the case where only the ultrasonic waves are irradiated by the vibrator 5. There was found. That is, not only when the hydrogen water at a position away from the vibrating body 5 is irradiated with ultraviolet rays, but also when the ultraviolet water is irradiated on the hydrogen water that is in contact with the vibrating body 5 at the outer edge portion of the vibrating body 5, the effect of removing fine particles changes I didn't. There was no effect of the ultraviolet ray on the portion hidden by the vibrating body 5 that does not pass through the ultraviolet ray (that is, does not propagate).

  From this result, it is possible to generate hydrogen radicals in hydrogen water by irradiating ultraviolet rays to excite water molecules. However, the fine particles adhering to the surface of the object to be cleaned can be obtained only by the action of hydrogen radicals. It is estimated that they cannot be separated. In addition, it is estimated that the hydrogen radical obtained by the irradiation of ultraviolet rays does not have a force or a lifetime that affects the portion that is not directly irradiated with ultraviolet rays (that is, the portion hidden by the vibrating body 5 that does not allow the passage of ultraviolet rays). The

  In view of such a situation, the present invention aims to provide a technique capable of effectively cleaning an object to be cleaned even when a fine structure (also referred to as a pattern) that is fragile is formed on the surface. It is said. Still other objects and advantages of the present invention will become apparent from the following description.

  According to one aspect of the present invention, in a cleaning apparatus for cleaning a surface of an object to be cleaned having a flat surface, the structure is capable of propagating ultrasonic waves and ultraviolet rays, and is a flat surface facing the surface. A structure having a smooth surface, an ultrasonic vibrator and an ultraviolet irradiation device for irradiating the surface of the object to be cleaned, and a predetermined distance between the surface of the structure and the surface of the object to be cleaned And a cleaning liquid supply mechanism for supplying a cleaning liquid to the space between the two surfaces.

  According to the aspect of the present invention, a novel cleaning apparatus for cleaning the surface of an object to be cleaned having a flat surface is provided.

  The cleaning liquid supply mechanism has a conducting tube portion that passes through the structure and opens on the surface of the structure, the interval is 1 mm or less, the cleaning liquid is hydrogen, oxygen, or a noble gas substance. And a gas-dissolved water obtained by dissolving a substance selected from the group consisting of these in water, the structure is quartz glass, and the wavelength of ultraviolet rays irradiated from the ultraviolet irradiation device is 170 to 250 nm. The vibration frequency of the ultrasonic wave emitted from the ultrasonic vibrator is 1 MHz or more, and the cleaning device has a mechanism for rotating the cleaning object while maintaining the interval. The cleaning device has a mechanism for moving the structure while maintaining the interval, the cleaning target is a semiconductor device, and the surface of the cleaning target is It has an uneven width of the convex portion is 100nm or less between the grooves, are preferred.

  According to still another aspect of the present invention, there is provided a method for cleaning a surface of an object to be cleaned having a flat surface using the cleaning device according to the claim, wherein the cleaning liquid is supplied to the space. Meanwhile, there is provided a cleaning method in which the surface of the object to be cleaned is irradiated with ultrasonic waves from the ultrasonic transducer and ultraviolet rays from the ultraviolet irradiation device through the surface of the structure. The cleaning is preferably performed in a state where the space is filled with the cleaning liquid.

  According to the aspect of the present invention, a novel cleaning method for cleaning a surface of an object to be cleaned having a flat surface is provided.

  The present invention provides a novel cleaning technique for cleaning a surface of an object to be cleaned having a flat surface. The present invention is particularly suitable for cleaning an object to be cleaned such as a semiconductor device in which a fine structure that is fragile is formed on the surface.

It is a schematic diagram which shows the mode of the spin cleaning performed using an ultrasonic nozzle. It is a schematic diagram which shows the mode of the ultrasonic cleaning using a vibrating body. It is a schematic diagram explaining the fundamental structure of the washing | cleaning apparatus which is one Example of this invention. It is a schematic diagram explaining the mode of washing | cleaning by the washing | cleaning apparatus which is one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wafer 2 Ultrasonic nozzle 3 Cleaning liquid 4 Irradiation point 5 Vibrating body 6 Ultrasonic vibrator 7 Nozzle 11 Structure 12 Irradiation surface 13 Cable 14 Ultraviolet irradiation apparatus 15 Ultraviolet lamp 16 Lamp house 17 Nitrogen gas 18 Through-hole 19 Opening 20 Tube

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, tables, examples and the like. In addition, these figures, tables, examples, etc., and explanations are only examples of the present invention, and do not limit the scope of the present invention. It goes without saying that other embodiments may belong to the category of the present invention as long as they match the gist of the present invention. In the drawings, the same reference numeral represents the same element.

  In the present invention, the wafer will be mainly described. However, it is needless to say that the present invention can be applied to a semiconductor device in which various structures are provided on a substrate. In a semiconductor device, in particular, an interlayer insulating film is provided in the multilayer structure, and a wiring pattern is often embedded in a groove provided therein, but such a wiring pattern is easily damaged by ultrasonic cleaning. It can be said that it is a suitable cleaning object of the present invention.

  As a result of the study, as described above, it has been clarified that the synergistic effect cannot be obtained even when the ultrasonic water and the ultraviolet light are separately irradiated at different positions on the object to be cleaned. This seems to mean that it is necessary to simultaneously irradiate hydrogen water with ultrasonic waves and ultraviolet rays at the same position on the object to be cleaned.

  That is, in cleaning by a technique using a combination of ultrasonic waves and ultraviolet rays (for example, hydrogen water cleaning), in order to separate fine particles from the surface of the object to be cleaned, even if they are weak against fine particles, Since it is good, it is considered that the premise is that the physical force such as the ultrasonic wave acts and the fine particles are shaken and floated from the surface of the object to be cleaned. In addition, the active hydrogen radicals generated by ultrasonic waves and ultraviolet rays chemically inactivate both the surface of the object to be cleaned and the fine particles to inactivate them, thereby reducing the interaction between the two. It is estimated that it becomes easy to detach from the surface of the object to be cleaned.

  The present invention has been completed based on such examination results. However, the above is only an inference, and the correctness is irrelevant to the contents of the present invention.

  The cleaning apparatus according to the present invention is used for cleaning the surface of an object to be cleaned having a flat surface (this surface is also referred to as “cleaning surface” in the present specification). This cleaning apparatus is a structure capable of propagating ultrasonic waves and ultraviolet rays, and has a flat surface (this surface is also referred to as an “irradiation surface” in this specification) opposite to the cleaning surface. An ultrasonic vibrator and an ultraviolet irradiation device for irradiating the cleaning surface, a mechanism for holding the irradiation surface parallel to the cleaning surface with a certain distance, and between the two surfaces And a cleaning liquid supply mechanism for supplying a cleaning liquid to a space (this space is also referred to as a “cleaning space” in the present specification). In the present invention, “can transmit ultraviolet rays” is synonymous with “can transmit ultraviolet rays”.

  According to the present invention, the ultrasonic wave generated by operating the ultrasonic vibrator propagates through the structure, is irradiated from the irradiation surface toward the cleaning liquid, and is transmitted to the underlying cleaning surface. At this time, since the entire irradiation surface vibrates, the vibration energy is dispersed, and the ultrasonic energy irradiated per unit area of the object to be cleaned can be reduced, thereby forming on the surface of the object to be cleaned. It is possible to prevent the fragile fine pattern thus formed from being damaged by ultrasonic damage.

  In addition, ultraviolet rays generated by operating an ultraviolet irradiation device that is connected to or close to the structure are transmitted through the structure and the same as the ultrasonic wave from the irradiation surface toward the cleaning liquid. The position is irradiated. If gas-dissolved water, particularly hydrogen water, is used for this cleaning liquid, the effect of removing fine particles can be enhanced as compared with the case where only ultrasonic waves are irradiated. Moreover, pattern collapse can be prevented or suppressed by adding ultraviolet irradiation.

  In the present invention, the “cleaning device” may be any device as long as the above requirements are satisfied. A known cleaning apparatus can be modified and used.

  The object to be cleaned according to the present invention has a flat surface, but there is no particular limitation, and it can be generally adopted when a clean surface is required and cleaning is required in the semiconductor industry. However, it is particularly suitable for application of the present invention to a semiconductor device that requires a particularly clean surface. In the present invention, the semiconductor device includes a wafer unless it departs from the spirit of the present invention or unless otherwise noted.

  The “flat surface” of the object to be cleaned according to the present invention does not exclude fine irregularities on the surface. The degree of “flatness” may be non-flat within a limit where ultrasonic waves can be propagated from the irradiation surface and the effect of the cleaning according to the present invention can be exhibited during the cleaning in the above configuration. Specifically, for example, the surface of the wafer is said to be flat, but generally has fine unevenness called a pattern, and the present invention is particularly excellent for cleaning when such unevenness is present. Demonstrate the effect. That is, such irregularities do not deny the above-mentioned “flatness”. The above structure also has a “flat surface”, but can be considered in the same manner as the “flat surface” of the object to be cleaned.

  The structure according to the present invention may be made of any material as long as it can propagate ultrasonic waves and ultraviolet rays. Actually, since there are many materials that can propagate ultrasonic waves, it is important to be a material that can propagate (that is, pass through) ultraviolet rays. The degree to which ultrasonic waves and ultraviolet rays can be propagated can be appropriately determined according to the actual situation. Furthermore, since the structure according to the present invention also comes into contact with the cleaning liquid, it should not be affected by being dissolved by the cleaning liquid.

  As such a material, a so-called transparent glass-like inorganic substance can be considered. Among these, quartz glass is particularly preferable because it has a high degree of propagation of ultrasonic waves and ultraviolet rays and at the same time has excellent chemical resistance.

Quartz glass is a glass made of quartz (SiO ₂ ) and means a material having high SiO ₂ purity. It is also called synthetic quartz glass, fused silica, fused silica, silica glass or the like. In classical manufacturing methods, crystal powder is obtained by melting, cooling, and vitrifying at 2000 ° C or higher, but now it is generally manufactured from silicon tetrachloride gas by chemical vapor deposition (CVD). Has been.

  Since these quartz glasses have an impurity content of ppb level and extremely high purity, they do not cause large absorption if they are ultraviolet rays (especially ultraviolet rays having a wavelength of about 170 nm). Quartz glass shows significant absorption for ultraviolet rays with wavelengths shorter than this. In such cases, the use of fluoride crystals such as calcium fluoride and magnesium fluoride is suitable, but these materials are difficult to machine and have poor chemical resistance compared to quartz glass. However, it is not suitable for use in contact with a cleaning liquid as in the present invention. In addition, those added with impurities such as boron also belong to the category of quartz glass according to the present invention.

The shape of the structure according to the present invention can be arbitrarily selected. What is necessary is just to choose an optimal thing from the relationship with an ultrasonic transducer | vibrator, an ultraviolet irradiation device, and arrangement | positioning of a cleaning surface. For example, a triangular prism shape as shown in FIG. 2 or a cylindrical shape as shown in FIG. The area of the irradiated surface can also be determined arbitrarily. For example, in the case of a wafer, it is generally in the range of about 400 to 2500 mm ² .

  The structure, shape, energy strength, and the like of the ultrasonic transducer according to the present invention are not particularly limited as long as they can be applied to the present invention. The vibration frequency of the ultrasonic wave irradiated from this ultrasonic vibrator is set to the highest possible frequency from the viewpoint of damage to the pattern when cleaning an object to be cleaned (for example, a wafer) on which a fragile fine pattern is formed. It is preferable. Specifically, the frequency is preferably at least 1 MHz or more, and more preferably 3 MHz or more. In the region of 1 MHz or higher, for example, it is easy to clean by reducing damage to a fragile fine pattern formed on the wafer surface. The ultrasonic transducer according to the present invention is generally directly attached to the structure, but may be partially embedded in the structure.

  The structure, shape, energy strength, and the like of the ultraviolet irradiation apparatus according to the present invention are not particularly limited as long as they can be applied to the present invention. It is preferable that the wavelength of the ultraviolet rays irradiated from the present ultraviolet irradiation device is in the range of 170 to 250 nm. If it is this range, the transmittance | permeability to the structure which consists of quartz glass etc. will be high, and it will become possible to supply sufficient energy required for decomposition | disassembly of a water molecule. When the wavelength is longer than 250 nm, it is considered that the energy of photons becomes insufficient for decomposing water molecules and cannot contribute to the generation of hydrogen radicals.

  There is no particular limitation on the “mechanism for holding the irradiation surface parallel to the cleaning surface with a certain interval” according to the present invention, and a known mechanism can be adopted. The “certain interval” is determined in accordance with the actual situation, but is generally in the order of mm in order to suppress the attenuation of ultrasonic energy and efficiently transmit it to the cleaning surface. For example, it is preferable to set the “certain interval” to 1 mm or less. The lower limit is not particularly limited as long as it does not hinder the cleaning liquid from flowing into and out of the cleaning space and the irradiation surface and the cleaning surface are not in contact with each other.

  The “cleaning liquid supply mechanism for supplying the cleaning liquid to the cleaning space” according to the present invention is not particularly limited, and a known mechanism can be employed. In general, a method in which a cleaning liquid is supplied near the structure according to the present invention and the cleaning liquid moves into the cleaning space by moving the object to be cleaned can be adopted.

  As a method superior to such a method, there can be mentioned a method in which the cleaning liquid supply mechanism has a conducting tube portion that passes through the inside of the structure and opens to the irradiation surface.

  In general, since the distance between the cleaning surface and the irradiation surface is set to be very small, it is difficult to efficiently flow the cleaning liquid from the outside of the structure into the cleaning space sandwiched between the two. There are many cases where air bubbles are caught from the part. However, with such a structure, the cleaning liquid can be reliably fed into the cleaning space, and the supply amount can be easily adjusted. For this reason, compared with the method of moving the cleaning liquid into the cleaning space by moving the object to be cleaned, the “certain interval” can be made narrower, and therefore the effect of ultrasonic waves and ultraviolet rays can be further increased. Specifically, it is easy to narrow down to about 0.1 mm.

Any shape may be sufficient as a conduction | electrical_connection pipe part, and it is practical that it is a cylindrical body which has a circular cross section. The cross-sectional area of the conducting tube portion may be determined as appropriate. In general, when the area of the irradiation surface is about 400 to 2500 mm ² as in the case of a wafer, it is about 4 to 25 mm ^2. It is preferable.

  There is no particular limitation on the cleaning liquid according to the present invention, and a known cleaning liquid can be applied. However, a gas dissolution in which a substance selected from the group consisting of hydrogen, oxygen, a rare gas substance, and a mixture thereof is dissolved in water. Water is preferable for improving the cleaning effect. Hydrogen water is particularly preferable. Various conditions such as the method for preparing these gas-dissolved water and the gas concentration in the gas-dissolved water can be appropriately selected according to the actual conditions, but in general, the higher the possible, the better the effect of removing fine particles. It is easy to obtain. For example, in the case of hydrogen water, the saturation solubility of hydrogen gas in water at 20 ° C. is 1.6 mg / L. However, if the concentration is 1.2 mg / L or more, a very good effect of removing fine particles can be obtained. Obtainable. The “water” in the present invention preferably contains as little impurities as possible. Such a thing can be selected from what is called pure water or ultrapure water.

  The supply of the cleaning liquid according to the present invention only needs to flow continuously without delay so that the fresh cleaning liquid is always in contact with the cleaning surface, and the supply speed is the interval between the irradiation surface and the cleaning surface, etc. It can be determined appropriately according to the actual situation. In the case of a wafer, generally it is often about 100 to 1000 mL / min.

  In the cleaning apparatus according to the present invention, a desired surface region of the cleaning object is cleaned by moving at least one of the cleaning object and the structure. In general, a mechanism for rotating the object to be cleaned and a mechanism for moving the structure are employed while maintaining the above-mentioned interval. In order to simplify the mechanism, the object to be cleaned is rotated at a constant rotational speed, and the structure is often moved at a constant speed. Accordingly, the motion of the structure may be reduced at the peripheral part of the rotation. The movement of the structure is generally a movement through the center of rotation. With such a configuration, for example, the entire surface of the wafer can be cleaned uniformly. In these cases, the degree of “maintaining the interval” can be appropriately determined according to the object to be cleaned.

  The cleaning apparatus according to the present invention can be particularly preferably used when the cleaning surface has irregularities in which the width of the convex portion between the grooves is 100 nm or less. In such a case, with the conventional cleaning device, the cleaning surface is easily damaged, but with the cleaning device according to the present invention, it is possible to clean well without damaging the cleaning surface by a combination of ultrasonic waves and ultraviolet rays. The surface can be cleaned. Note that the larger the aspect ratio between the height and the width of the convex portion between the grooves, the more easily the cleaning surface is easily damaged, and thus the effect of the present invention is easily exhibited. In this sense, this aspect ratio is preferably 2 or more. The upper limit is considered to be limited by the actually required cleaning effect. In addition, said "height of a convex part" is the length from the top part of a convex part to the bottom of a recessed part, when an unevenness | corrugation is repeated.

  When cleaning the cleaning surface using the cleaning device according to the present invention, while supplying the cleaning liquid to the cleaning space, the ultrasonic wave from the ultrasonic vibrator and the ultraviolet light from the ultraviolet irradiation device are applied to the irradiation surface. The cleaning surface is irradiated through. By this method, even if the cleaning surface is an object to be cleaned having unevenness including thin protrusions as described above, cleaning can be suitably performed.

  In order to exhibit a uniform cleaning effect, it is preferable to perform cleaning in a state where the cleaning space is filled with the cleaning liquid. Here, “the cleaning space is filled with the cleaning liquid” means that no bubbles are involved in the cleaning space. In this state, it is sufficient to check visually, but more reliably, by changing the conditions such as the supply rate of the cleaning liquid amount, and selecting a supply rate that enables spotless (ie, homogeneous) cleaning. Can be achieved.

  Next, examples of the present invention will be described in detail.

[Example 1]
FIG. 3 is a diagram illustrating a basic configuration of a cleaning apparatus according to an embodiment of the present invention. The upper side of FIG. 3 is a schematic cross-sectional view of the device cut in the horizontal direction, and the lower side is a schematic cross-sectional view of the device cut in the vertical direction. In this embodiment, the structure 11 has a cylindrical shape, and has a diameter of about 50 mm and a height of about 30 mm. As the material of the structure 11, transparent synthetic quartz glass was selected, and ultraviolet rays having a wavelength of 170 nm or more that do not cause significant absorption by the synthetic quartz glass were used.

  In the columnar structure 11 having a height of about 30 mm used in this example, it was confirmed by measurement that a transmittance of about 60% with respect to the intensity of the light source can be obtained if the wavelength is 170 nm or more. It was.

  In this embodiment, the ultraviolet irradiation device 14 is connected to one surface of the columnar structure 11 (the surface opposite to the irradiation surface 12). The other surface of the structure 11 is the irradiation surface 12, and the ultraviolet rays generated by the ultraviolet irradiation device 14 are transmitted through the structure 11 and irradiated from the irradiation surface 12 toward the cleaning surface.

  An ultraviolet lamp 15 was housed inside the lamp house 16 of the ultraviolet irradiation device 14. In addition, the bottom of the lamp house 16 has a large opening so that the surface of the structure 11 (the surface opposite to the irradiation surface 12) faces the ultraviolet lamp 15 directly.

  When ultraviolet light having a short wavelength passes through the atmosphere, it is strongly absorbed and attenuated by oxygen in the atmosphere, so that the space inside the lamp house 16 is replaced with dry nitrogen gas 17 to make the oxygen concentration as low as possible. . The oxygen concentration inside the lamp house 16 is preferably lowered to 0.01% by volume or less.

As described above, the wavelength of the ultraviolet light emitted from the ultraviolet lamp 15 is preferably a wavelength in the range of 170 to 250 nm because of the absorption characteristics of the synthetic quartz glass. In this example, an experiment was performed using an excimer lamp with a wavelength of 172 nm or 222 nm or a low-pressure mercury lamp including a line spectrum with a wavelength of 185 nm. Irradiation intensity of ultraviolet rays was set to approximately 100 mW / cm ^{2 at} the position of the irradiation surface 12 in any experiment.

  Synthetic quartz glass can propagate ultrasonic vibrations well. An ultrasonic transducer 6 is installed at one place on the side surface of the structure 11 and is connected to an ultrasonic oscillator (not shown) by a cable 13. The high-frequency electrical signal generated in the ultrasonic oscillator was transmitted to the ultrasonic vibrator 6 through the cable 13, and the ultrasonic vibrator 6 operated to generate ultrasonic waves. The generated ultrasonic wave propagated inside the structure 11. FIG. 4 shows a state in which one ultrasonic transducer 6 is connected to the structure 11, but the number of the ultrasonic transducers 6 is not limited to one. A plurality may be installed around 11.

  The ultrasonic vibration frequency generated by the ultrasonic vibrator 6 is preferably as high as possible from the viewpoint of damage to the pattern when the object to be cleaned on which a fragile fine pattern is formed is cleaned. In the present embodiment, the ultrasonic transducer 6 vibrates at a frequency of 3 MHz and an output of 3 W.

  A through hole 18 bent in an L shape was formed inside the structure 11, and one outlet reached the opening 19 at the center of the irradiation surface 12. Moreover, the tube 20 was connected from the exit of the other side of the through-hole 18, and the tip was connected to the hydrogen water supply apparatus.

  In this example, a wafer is used as an object to be cleaned. As will be described later, in this embodiment, cleaning must be performed by supplying hydrogen water to a cleaning space formed between the irradiation surface 12 and the surface of the wafer 1 in a state of being very close to each other. However, since the irradiation surface 12 is very close to the wafer 1, it is very difficult to send hydrogen water into the cleaning space from the outside of the structure 11. Therefore, in this embodiment, the hydrogen water supplied from the opening 19 is supplied to the irradiation surface by sending hydrogen water to the central opening 19 of the irradiation surface 12 through the through hole 18 provided in the structure 11. In a small cleaning space between the wafer 12 and the wafer 1, it spreads in a stable and uniform flow from the center of the irradiation surface 12 toward the outer edge without involving bubbles or the like. It was made possible to stably fill the cleaning space between them with the cleaning liquid.

  The state of cleaning according to this embodiment will be further described with reference to FIG. The upper part was supported from the structure 11 so that the irradiation surface 12 was parallel to the surface of the wafer 1 as the object to be cleaned. In consideration of absorption and attenuation of ultraviolet rays in hydrogen water, it is preferable that the irradiated surface 12 and the wafer 1 be as close as possible to obtain a higher removal effect of fine particles and the like. In this example, it was set to about 0.3 mm.

  With the irradiation surface 12 approaching the wafer 1, the hydrogen water supply device is operated to guide the hydrogen water 3 from the tube 20 to the through hole 18, and from the opening 19 at the center of the irradiation surface 12, the irradiation surface 12. And a cleaning space sandwiched between the wafer 1 and the wafer 1. The hydrogen water 3 spread in a stable and uniform flow from the position of the opening 19 at the center of the irradiation surface 12 toward the outer edge of the irradiation surface 12 in this gap. By doing so, it was possible to prevent bubbles and the like from being caught between the irradiation surface 12 and the wafer 1.

  The amount of the hydrogen water 3 supplied from the opening 19 per unit time may flow continuously without stagnation so that the fresh hydrogen water 3 is always in contact with the irradiation surface 12. May be determined as appropriate according to the distance between the tube 20 and the diameter of the tube 20 or the through hole 18.

  In a state where the cleaning space between the irradiation surface 12 and the wafer 1 is completely filled with the hydrogen water 3, the ultraviolet lamp 15 in the ultraviolet irradiation device 14 is turned on, and at the same time, the ultrasonic vibrator 6 is operated, Ultraviolet rays and ultrasonic waves were simultaneously irradiated from 12 to the hydrogen water 3 so that the removal of fine particles proceeded on the surface of the wafer 1 by the action of the hydrogen water.

  In this state, the wafer 1 is rotated at a constant speed with a straight line passing through the center of the wafer 1 as a rotation axis, and at the same time, the distance between the irradiation surface 12 and the wafer 1 is set at the upper part from the structure 11. The wafer was moved at a constant speed parallel to the surface of the wafer 1 while being kept constant.

  The ultraviolet rays only have to be irradiated almost uniformly within the irradiation surface 12, and it is not necessary to strictly manage the in-plane distribution of the irradiation intensity. In addition, regarding ultrasonic waves, it is only necessary that vibrations occur substantially uniformly within the surface of the irradiation surface 12, and it is not necessary to strictly manage the in-plane distribution of vibration intensity. In any case, a weak ultrasonic wave that does not break a fragile fine pattern formed on the surface of the wafer 1 from each point of the irradiation surface 12 toward the hydrogen water 3 and further toward the wafer 1. In addition, it was possible to irradiate simultaneously with ultraviolet rays having energy large enough to decompose water molecules. As a result, fine particles could be efficiently removed from the surface of the wafer 1 without causing pattern collapse.

Specifically, the following experiment was conducted. In the experiment, washing was performed using two types of samples. One is a sample used to confirm the occurrence of pattern collapse for the purpose of evaluating the magnitude of damage caused by ultrasonic waves. From a porous silica on an 8 inch (about 200 mm) diameter Si wafer. An insulating material having a uniform thickness of 200 nm is formed, and a stripe-like uniform pattern of L (line) / S (space) = 65/65 nm is formed on the insulating material film by dry etching. What was formed was used. 65 nm of this space corresponds to the width of the convex portion in the present invention. The height in this case was the length from the top of the convex part to the bottom of the concave part, and was 195 nm. That is, the aspect ratio was 3.
After washing, the pattern was observed using a polarizing microscope, and the presence or absence of pattern collapse was confirmed.

The other is a sample used for the purpose of evaluating the effect of removing fine particles. A thermal oxide film having a thickness of 100 nm is formed on a Si wafer having a diameter of 8 inches (about 200 mm). Silica (SiO ₂ ) particles having an average particle size of 0.15 μm were deposited almost uniformly on the surface of the oxide film as a model of fine particles to be removed. The total number of silica particles was adjusted to about 30,000 per wafer.

  Using a wafer surface inspection apparatus, the number of silica particles adhering to the wafer surface before and after cleaning was measured, and how much silica particles were removed by the cleaning (removal rate) was calculated.

  Among the lamps described above, an excimer lamp having a wavelength of 172 nm was used for irradiation with ultraviolet rays.

  As the cleaning liquid, hydrogen water in which hydrogen gas was dissolved at a concentration of 1.5 mg / L in ultrapure water was used. The supply rate was 600 mL / min.

  The wafer was rotated at 200 rpm, and the irradiation surface was reciprocated on the wafer between the center of the wafer and the outer edge of the wafer at a speed of 2 cm / second. The cleaning time per wafer was all set to 90 seconds.

  The other conditions were set to the same conditions as described above, and cleaning was performed.

  Table 1 shows the results of washing.

水素ガス溶解の欄で、「あり」と書かれている場合には上記条件を採用した。「あり」と書かれていない条件においては、洗浄液として、水素ガスを溶解させていない超純水を使用した。

When “Yes” is written in the hydrogen gas dissolution column, the above conditions were adopted. Under conditions where “Yes” is not written, ultrapure water in which hydrogen gas is not dissolved is used as the cleaning liquid.

  First, paying attention to the removal rate of silica particles, it is understood that the removal rate is almost the same as that of ultrapure water unless the ultrasonic wave and the ultraviolet ray are irradiated to the hydrogen water (condition number 2).

  Irradiation of ultrapure water with ultraviolet rays did not change the removal rate (condition number 3), but even when hydrogen water was irradiated with ultraviolet rays, the removal rate did not change (condition number 4). That is, it is understood that the effect of removing fine particles cannot be obtained only by irradiating hydrogen water with ultraviolet rays.

  When the ultrapure water is irradiated with ultrasonic waves, the removal rate is higher than when it is not irradiated (condition number 5). However, even when ultraviolet rays are irradiated at the same time, the removal rate is almost the same as when only ultrasonic waves are used (conditions Number 6). It is understood that it is necessary to dissolve hydrogen gas in ultrapure water in order to create a state in which hydrogen radicals exist in hydrogen water.

  When the hydrogen water is irradiated with ultrasonic waves, the effect of washing with hydrogen water appears, and the removal rate increases (condition number 7), but when the ultraviolet rays are simultaneously irradiated there, the removal rate is further increased dramatically (conditions) 8).

  Furthermore, no pattern collapse occurred at any condition.

  The present invention can be used for cleaning the surface of a cleaning object having a flat surface such as a semiconductor device.

Claims (12)

In a cleaning apparatus for cleaning the surface of an object to be cleaned having a flat surface,
A structure capable of propagating ultrasonic waves and ultraviolet rays, the structure having a flat surface facing the surface;
An ultrasonic vibrator and an ultraviolet irradiation device for irradiating the surface of the object to be cleaned;
A mechanism for holding the surface of the structure parallel to the surface of the object to be cleaned at a certain interval;
A cleaning liquid supply mechanism for supplying a cleaning liquid to the space between the two surfaces,
The cleaning liquid is gas-dissolved water in which a substance selected from the group consisting of hydrogen, oxygen, a rare gas substance, and a mixture thereof is dissolved in water.
Cleaning device. The cleaning apparatus according to claim 1, wherein the cleaning liquid supply mechanism includes a conductive pipe portion that passes through the structure and opens on the surface of the structure. The cleaning apparatus according to claim 1 or 2, wherein the interval is 1 mm or less. The cleaning device according to claim 1, wherein the structure is quartz glass. The cleaning apparatus according to any one of claims 1 to 4, wherein a wavelength of ultraviolet rays irradiated from the ultraviolet irradiation device is in a range of 170 to 250 nm. The cleaning apparatus according to claim 1, wherein a vibration frequency of ultrasonic waves irradiated from the ultrasonic vibrator is 1 MHz or more. The cleaning apparatus according to claim 1, further comprising a mechanism that rotates the object to be cleaned while maintaining the interval. The cleaning apparatus according to claim 1, further comprising a mechanism that moves the structure while maintaining the distance. The cleaning apparatus according to claim 1, wherein the object to be cleaned is a semiconductor device. The cleaning apparatus according to any one of claims 1 to 9, wherein the surface of the object to be cleaned has irregularities in which a width of a convex portion between the grooves is 100 nm or less. A method for cleaning a surface of an object to be cleaned having a flat surface using the cleaning device according to claim 1, wherein the ultrasonic vibration is supplied while supplying the cleaning liquid to the space. A cleaning method of irradiating the surface of the object to be cleaned with ultrasonic waves from a child and ultraviolet rays from the ultraviolet irradiation device through the surface of the structure. The cleaning method according to claim 11, wherein the cleaning is performed in a state where the space is filled with the cleaning liquid.

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