Patent Publication Number: US-2012042913-A1

Title: Cleaning apparatus using ultrasonic waves

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cleaning apparatus using ultrasonic waves, and, more particularly, to a cleaning apparatus using ultrasonic waves to separate contaminations from a wafer, which comprises: a housing receiving an oscillator therein; and a rod coupled to a surface of the oscillator to transmit ultrasonic waves produced from the oscillator to a cleaning solution applied onto an upper surface of the wafer, the oscillator including a piezoelectric device bonded to a diffusive layer consisting of a near-field region and a far-field region, and the rod having a diameter-reduced portion to amplify the ultrasonic waves produced from the oscillator for the efficient removal of the contaminations on the wafer to be cleaned. 
     2. Description of the Related Art 
     One of the most basic technologies among semiconductor manufacturing processes is a cleaning technology. A semiconductor is manufactured via several processes to form a desired wafer surface. As each process is performed on a semiconductor wafer by means of semiconductor manufacturing equipment, various contaminations are created and left on the semiconductor wafer and the semiconductor manufacturing equipment. Therefore, it is necessary to clean the semiconductor wafer and the semiconductor manufacturing equipment by a predetermined time interval while performing processes. A cleaning technology is to remove various contaminations caused during the manufacture of a semiconductor by physical and chemical methods. 
     First, a chemical method is to remove contaminations on a wafer surface by washing, etching, oxidation/de-oxidation, etc., and uses various chemicals or gases. In the chemical method, particles attached to a wafer surface are removed by use of a pure or chemical cleaning solution, and organic substances are removed in various manners, for example, they may be dissolved by use of a solvent, they may be removed by use of an oxidizing acid, or they may be carbonized under an atmosphere of oxygen plasma. As occasion demands, the chemical method is performed to etch a wafer surface by a predetermined depth so as to expose a new, clean surface. 
     Next, in a physical method, contaminations attached onto a wafer surface may be peeled off by use of ultrasonic-wave energy, may be brushed off, or may be removed by use of high-pressure water. Generally, when the physical and chemical methods are appropriately combined, a highly efficient cleaning can be accomplished. 
     A representative example of appropriately combining the physical and chemical methods is an ultrasonic cleaning. The ultrasonic cleaning removes contaminations attached to an object to be cleaned by use of physical means (ultrasonic waves) and chemical means (chemical cleaning solution) and prevents re-attachment of the contaminations. Here, a physical way using ultrasonic waves is based on the cavitation (cavity) phenomenon of ultrasonic waves. The cavitation phenomenon is that fine air bubbles are produced and disappear by a pressure of ultrasonic waves as an ultrasonic-wave energy is propagated in a solution. The cavitatoin phenomenon accompanies a very high pressure (several tens to hundreds atmosphere) and a high temperature (several hundreds to thousands degrees centigrade). 
     In the above described phenomenon, with a shock energy caused as air bubbles are repeatedly produced and disappear within an extremely short time (one tens thousandth to one hundreds thousandth second), invisible inner deep portions of an object to be cleaned, which is immersed in a cleaning solution, can be cleaned within a short time. 
     Actually, in addition to the shock energy caused by the cavitation, an agitation effect, thermal action, etc. by ultrasonic radiation pressure have a synergy effect with a detergent, resulting in a high cleaning efficiency. 
     The ultrasonic cleaning is mainly used to clean or rinse an object to be cleaned, such as a glass substrate for a liquid crystal display (LCD) apparatus, a semiconductor wafer, and a magnetic disk for the storage of data. In a conventional ultrasonic cleaning system, an object to be cleaned is introduced into a cleaning vessel, and the cleaning vessel receives a cleaning solution to which ultrasonic waves are transmitted from an oscillating plate as the oscillating plate is activated by an ultrasonic oscillator. Ultrasonic waves apply an oscillation energy to particles on the object to be cleaned, thereby efficiently removing the particles and other contaminations from the object. 
     Recently, with the use of a high-integration semiconductor device, it has been required to form a very fine pattern on a wafer. However, since the pattern on the wafer easily causes a defective semiconductor device even by the attack of super fine particles, the importance of a cleaning process is increasing more and more. 
     Generally, a wafer cleaning is performed by use of ultra-pure water (cleaning solution), brush, and ultrasonic waves. 
       FIG. 1  illustrates the configuration of a conventional ultrasonic cleaning apparatus, which is designed to clean a surface of a semiconductor wafer  105  by use of ultrasonic waves and cleaning water (or cleaning solution). The conventional ultrasonic cleaning apparatus comprises a cleaning solution injector  106  having a nozzle-shaped lower end, and a supply tube  102  connected to the sidewall of the injector  106  to supply a cleaning solution  103  into the injector  106 . 
     If the cleaning solution  103  is supplied into the injector  106  through the supply tube  102 , an oscillator  101  sends ultrasonic waves to the cleaning solution  103 , thereby injecting the cleaning solution  103  with the ultrasonic waves onto an object to be cleaned that is located below the cleaning solution injector  106 . During the injection of the cleaning solution, the object to be cleaned is rotated by a rotating shaft  104  such that the overall surface of the object can be cleaned. 
     In the above described conventional cleaning apparatus, however, since the cleaning solution  103  is injected from the cleaning solution injector  106  after being previously combined with the ultrasonic waves within the cleaning solution injector  106 , there is a problem in that an excessively large amount of cleaning solution  103  is consumed as compared to the resulting cleaning effect. 
     Further, the ultrasonic waves have a great change in strength even if cleaning conditions, such as an operating frequency, cleaning solution condition, electricity consumption, and cooling conditions, are temporarily changed during a cleaning operation. Furthermore, since the high-pressure cleaning solution is injected through the nozzle-shaped lower end of the injector  106 , it may cause a serious damage to a local or overall region of a semiconductor wafer surface. 
       FIG. 2  illustrates the configuration of another conventional ultrasonic cleaning apparatus. The conventional ultrasonic cleaning apparatus shown in  FIG. 2  comprises an elongated horizontal oscillating rod  110  to be disposed above a semiconductor wafer  114  with a predetermined gap, an oscillator  111  coupled to one end of the oscillating rod  110  to provide the oscillating rod  110  with an ultrasonic oscillating energy, and a cleaning water discharger  113  to discharge cleaning water  116  into the gap between the oscillating rod  110  and the semiconductor wafer  114 . 
     To rotate the semiconductor wafer  114 , the conventional ultrasonic cleaning apparatus further comprises a rotating plate  112  on which the semiconductor wafer  114  is disposed, and a rotating shaft  115  coupled to the rotating plate  112 . In operation, the oscillating rod  110 , which is disposed above the semiconductor wafer  114 , emits longitudinal ultrasonic waves while the semiconductor wafer  114  is rotated by the rotating shaft  115  and the rotating plate  112 , and simultaneously, the cleaning water  116  is sprayed over the semiconductor wafer  114 , to allow the overall surface of the semiconductor wafer  114  to be cleaned in an ultrasonic cleaning manner. 
     In the above described conventional ultrasonic cleaning apparatus shown in  FIG. 2 , however, since the oscillating rod  110  has a cantilever structure, the cleaning operation is performed only below an axial direction of the oscillating rod  110 . This causes a difference in the strength of ultrasonic waves along the oscillating rod  110 , making it impossible to achieve a uniform cleaning of, in particular, a finely patterned wafer. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a cleaning apparatus using ultrasonic waves, which comprises: a housing receiving therein an oscillator, which produces ultrasonic waves as a piezoelectric device is contracted and expanded upon receiving power during a cleaning of contaminations on a wafer; and a rod coupled to a surface of the oscillator to transmit the ultrasonic waves to cleaning water applied onto an upper surface of the wafer, the piezoelectric device being bonded to a surface of a diffusive layer consisting of a near-field region in which the ultrasonic waves propagate straight and a far-field region in which the ultrasonic waves are diffused and overlapped, to complete the oscillator, and the rod having a diameter-reduced portion to amplify the ultrasonic waves produced from the oscillator for the efficient removal of the contaminations on the wafer. 
     Additional objects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description of preferred embodiments of the invention. Also, the objects and/or advantages of the invention will be realized by means and combinations of the following claims. 
     In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a cleaning apparatus using ultrasonic waves comprising: a tube; a housing coupled to an end of the tube and disposed perpendicular to a wafer to be cleaned while maintaining a gap with the wafer; and an oscillator provided in the housing at a position to face the wafer and used to produce ultrasonic waves. 
     In accordance with another aspect of the present invention, the above and other objects can be accomplished by the provision of a cleaning apparatus using ultrasonic waves comprising: a hollow housing: an oscillator coupled to the housing at a position to face a wafer to be cleaned and used to produce ultrasonic waves; and a constant-diameter rod having an end coupled to a surface of the oscillator, the rod being disposed perpendicular to an upper surface of the wafer to transmit the ultrasonic waves, produced from the oscillator, to cleaning water applied onto the upper surface of the wafer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view illustrating the configuration of a conventional ultrasonic cleaning apparatus; 
         FIG. 2  is a view illustrating the configuration of another conventional ultrasonic cleaning apparatus;. 
         FIG. 3  is a sectional view illustrating the pole structure of a piezoelectric device according to the present invention; 
         FIG. 4  is a plan view of  FIG. 3 ; 
         FIG. 5  is a sectional view illustrating the configuration and basic principle of an oscillator according to the present invention; 
         FIG. 6  is an explanatory view illustrating the basic principle of the oscillator according to the present invention; 
         FIG. 7  is a plan view of  FIG. 5 ; 
         FIG. 8  is a perspective view illustrating an embodiment of the oscillator according to the present invention; 
         FIG. 9  is a perspective view illustrating an embodiment of the piezoelectric device according to the present invention; 
         FIG. 10  is a perspective view illustrating a cleaning apparatus according to a first embodiment of the present invention; 
         FIG. 11  is a perspective view illustrating a cleaning apparatus according to a second embodiment of the present invention; 
         FIG. 12  is a perspective view illustrating an alternative embodiment of  FIG. 11 ; 
         FIG. 13  is a perspective view illustrating a cleaning apparatus according to a third embodiment of the present invention; 
         FIG. 14  is a perspective view illustrating an alternative embodiment of  FIG. 13 ; and 
         FIG. 15  is a perspective view illustrating a cleaning apparatus according to a fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the terms or words used in the following description should not be analyzed by typical or dictionary means. The definitions of these terms should be analyzed by means and concepts corresponding to technical ideas of the present invention based on the principle that an inventor can appropriately define the concept of terms for explaining the invention in the most preferable manner. 
     Accordingly, since the embodiments disclosed herein and configurations illustrated in the drawings are only the most preferable embodiment and are not intended to represent all technical items of the invention, it should be appreciated that other various equivalents and modifications capable of substituting for the disclosed embodiments exist at the filing time point of the invention. 
     Hereinafter, a cleaning apparatus using ultrasonic waves according to preferred embodiments of the present invention will be described in detail with reference to  FIGS. 3 to 15 . 
     As shown, to efficiently separate contaminations from a wafer  70  to be cleaned, the cleaning apparatus comprises an oscillator  30 , which is prepared by bonding a piezoelectric device  10  to a surface of a diffusive layer  22  consisting of a near-field region  20  and a far-field region  21 . The cleaning apparatus uses ultrasonic waves generated from the oscillator  30 , and further comprises a rod having a diameter-reduced portion to amplify the ultrasonic waves. In summary, the cleaning apparatus using ultrasonic waves comprises a tube  41 , the rod  42  or  42 ′, a housings  40  or  43 , and the oscillator  30 . 
       FIG. 3  is a sectional view illustrating the pole structure of the piezoelectric device according to the present invention, and  FIG. 4  is a plan view of  FIG. 3 . As shown in  FIGS. 3 and 4 , the piezoelectric device  10  includes a piezoelectric ceramic plate  11  of various shapes, a positive pole  14  formed at one surface of the plate  11 , and a negative pole  12  formed at the other surface of the plate  11 . The positive pole  14  consists of a plurality of positive pole pieces  13  deposited on the plate  11  to be vertically and horizontally spaced apart from each other by a predetermined interval. 
     The piezoelectric device  10  may be configured in various manners. In one example, the positive pole  14 , which consists of the plurality of positive pole pieces  13 , is arranged on one surface of the plate  11  and the negative pole  12  is formed throughout the other surface of the plate  11 . In another example, the positive pole  14 , which consists of the plurality of positive pole pieces  13 , is formed on an upper surface of the plate  11 , and the negative pole  12  extends throughout a lower surface and a sidewall of the plate  11 . In yet another example, the piezoelectric device  10  may include a plurality of piezoelectric ceramic units each including a single positive pole piece and a negative pole arranged at opposite surfaces of the plate  11 . 
       FIG. 5  is a sectional view illustrating the configuration and basic operation principle of the oscillator according to the present invention.  FIG. 6  is an explanatory view illustrating the basic operation principle of the oscillator according to the present invention.  FIG. 7  is a plan view of  FIG. 5 . As shown in  FIGS. 5 to 7 , the diffusive layer  22  is bonded to a surface of the piezoelectric device  10  such that a surface of the diffusive layer  22  is bonded to the negative pole  12  of the piezoelectric device  10 . The diffusive layer  22  includes the near-field region  20  and the far-field region  21 , and is bonded to the negative pole  12  of the piezoelectric device  10 . 
     In  FIG. 5 , a distance from the surface of the diffusive layer  22 , to which the piezoelectric device  10  is bonded, to the boundary where the near field region  20  ends and the far-field region  21  begins is represented by N=D 2 −λ 2 /4 λ. Here, D is a width of each positive pole piece  13 . Also, the diffusion angle of sound from the boundary of the near-field region  21  and the near-field region  21  into the far-field region  21  is represented by sin γ 0 =1.2 λ/D. That is, the smaller the width of the positive pole piece  13 , the greater the diffusion angle sin γ 0 . 
     Accordingly, the adjustment of a far-field by the overlap of ultrasonic waves to be diffused over an object to be cleaned is possible. The diffusive layer  22  may be bonded, at a surface thereof, with a plurality of piezoelectric devices  10 . 
     The diffusive layer  22  may be made of quartz, stainless-steel, Teflon, aluminum, steel, or the like. 
     The positive pole pieces  13  and the piezoelectric device  10  may have any one shape selected from among a square, a circle, a triangle, a rectangle, a parallelogram, etc. Also, the diffusive layer  22  may have any one shape selected by a user from among a square, a circle, a polygon, etc. 
     An oscillator, to which a near field is applied, is applicable to the portion A of  FIG. 6  using a relatively uniform sound field, and an oscillator, to which a far-field is applied, is applicable to the portion B of  FIG. 6  forming a relatively uniform sound filed by the overlap of ultrasonic waves emitted from a piezoelectric device. 
       FIG. 8  is a perspective view illustrating an embodiment of the oscillator  30  according to the present invention.  FIG. 9  is a perspective view illustrating an embodiment of the piezoelectric device  10  according to the present invention. As shown in  FIGS. 8 and 9 , the diffusive layer  22  includes the near-field region  20 , in which ultrasonic waves propagate straight, and the far-field region  21  in which ultrasonic waves are diffused and overlapped. The piezoelectric device  10  is bonded to a surface of the diffusive layer  22 , to produce ultrasonic waves by contraction and expansion thereof. 
     As shown in  FIG. 8 , the oscillator  30  may be configured in various manners. For example, the oscillator  30  may include the diffusive layer  22 , which consists of the far-field region  21  and the near-field region  20 , and the piezoelectric device  10 , or may include an ultrasonic wave transmitter  23  and the piezoelectric device  10 . 
     It will be appreciated that all the piezoelectric device  10  bonded to a surface of the ultrasonic wave transmitter  23 , the ultrasonic wave transmitter  23 , and the diffusive layer  22  may have any one cross section selected by a user from among a square, a circle, etc. 
     The piezoelectric device  10  may be comprised of a plurality of piezoelectric devices  10  vertically and horizontally spaced apart from one another by a predetermined interval. Also, the piezoelectric device  10 , as described above, may have any one shape selected by a user from among a circle, a square, etc. 
       FIG. 9  illustrates the detailed configuration of the piezoelectric device  10  to be bonded to the ultrasonic wave transmitter  23  or the diffusive layer  22 . 
       FIG. 10  is a perspective view illustrating a cleaning apparatus according to a first embodiment of the present invention. As shown in  FIG. 10 , the cleaning apparatus comprises a cylindrical hollow housing  40  receiving therein the oscillator  30  disposed on an end surface thereof. More specifically, the oscillator  30  is positioned as close as possible to a wafer  70  to be cleaned. 
     A tube  41  is coupled to a position of the housing  40  opposite to the end surface of the housing  40  maintaining a gap with the wafer  70 . 
     As described above, the oscillator  30 , disposed on the end surface of the housing  40 , may include the ultrasonic wave transmitter  23  and the piezoelectric device  10  deposited on a surface of the ultrasonic wave transmitter  23 , or may include the diffusive layer  22  consisting of the near-field region  20  and the far-field region  21  and the piezoelectric device  10  bonded to a surface of the diffusive layer  22 . 
     As the oscillator  30  receives electricity from a power source through an electric wire  51 , the piezoelectric device  10  is contracted and expanded upon receiving the electricity to thereby produce ultrasonic waves. 
     More specifically, the oscillator  30  to produce ultrasonic waves is oriented perpendicular to an upper surface of the wafer to move over the upper surface of the wafer  70  while maintaining a predetermined gap with the wafer  70 . The ultrasonic waves produced by the oscillator  30  are transmitted to cleaning water  61  applied onto the upper surface of the wafer  70  to be cleaned, so as to separate contaminations from the wafer  70 . 
       FIG. 11  is a perspective view illustrating a cleaning apparatus according to a second embodiment of the present invention.  FIG. 12  is a perspective view illustrating an alternative embodiment of  FIG. 11 . As shown in  FIGS. 11 and 12 , to transmit ultrasonic waves to the cleaning water  61  applied onto the upper surface of the wafer  70  to be cleaned, differently from  FIG. 10 , a cylindrical rod  42  may be coupled to a surface of the oscillator  30 . 
     The rod  42  may have a smaller or larger diameter than that of the oscillator  30 , or may have the same diameter as that of the oscillator  30 . 
     With the present embodiment, ultrasonic waves produced by the oscillator  30  are propagated in a longitudinal direction of the rod  42 , which is oriented perpendicular to the wafer  70  while maintaining a predetermined gap with the wafer  70 , thereby being transmitted to the cleaning water  61  applied onto the upper surface of the wafer  70 . 
     When using the oscillator  30  related to the far-field region  21 , furthermore, the diffusion and overlap effects of the ultrasonic waves can be enhanced. 
     In the above described embodiments, the housing  40  or  43  has a hollow tubular shape having any one cross section selected from among a square, a circle, a polygon, etc. 
       FIG. 13  is a perspective view illustrating a cleaning apparatus according to a third embodiment of the present invention.  FIG. 14  is a perspective view illustrating an alternative embodiment of  FIG. 13 . In the present embodiment, the rod  42  as shown in  FIGS. 11 and 12  is replaced by a rod  42 ′ having a diameter-reduced portion. The use of the rod  42 ′ having a diameter-reduced portion has the effect of allowing the ultrasonic waves, which will be transmitted to the cleaning water  61  applied onto the upper surface of the wafer  70 , to be aggregated and amplified as they approach the wafer  70 . 
       FIG. 15  is a perspective view illustrating a cleaning apparatus according to a fourth embodiment of the present invention. As shown in  FIG. 15 , the piezoelectric device  10  is bonded to the diffusive layer  22  having a rectangular cross section. 
     The cleaning apparatus of the present embodiment can separate contaminations on the wafer  70  while moving on the surface of the wafer  70 , to which the cleaning water  61  was previously applied. 
     In the above description of the preferred embodiments of the present invention, the diffusive layer  22 , the ultrasonic wave transmitter  23 , and the rods  42  and  42 ′ may be made of any one material selected by a user from among glassy solids including quartz, sapphire, diamond and glassy carbon, metals including stainless steel, titanium, aluminum and steel, and other glassy materials or metals coated with a chemical resistance material such as Teflon, etc. 
     In the drawings, reference numeral  60  denotes a cleaning water discharger. 
     As apparent from the above description, the present invention provides a cleaning apparatus using ultrasonic waves, which comprises: a housing receiving therein an oscillator, which produces ultrasonic waves as a piezoelectric device is contracted and expanded upon receiving power during a cleaning of contaminations on a wafer; and a rod coupled to a surface of the oscillator to transmit the ultrasonic waves to cleaning water applied onto an upper surface of the wafer. The piezoelectric device is bonded to a surface of a diffusive layer consisting of a near-field region in which the ultrasonic waves propagate straight and a far-field region in which the ultrasonic waves are diffused and overlapped, to complete the oscillator. Also, the rod has a diameter-reduced portion to amplify the ultrasonic waves produced from the oscillator for the efficient removal of the contaminations on the wafer. 
     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.