Abstract:
A cleaning apparatus includes a cleaning tank for reserving cleaning fluid, an object to be cleaned being immersed in the cleaning fluid, a vibrator for vibrating the cleaning fluid in the cleaning tank, and two micro-vibration sources for minutely vibrating the object to be cleaned in two different directions.

Description:
This application is a divisional application filed under 37 CFR § 1.53(b) of parent application Ser. No. 09/098,751, filed Jun. 17,1998, and now U.S. Pat. No. 6,085,764. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an apparatus and method for cleaning an object to be cleaned, such as a wafer or the like, using for example ultrasonic vibration. 
     DESCRIPTION OF THE RELATED ART 
     A cleaning apparatus, in which an object to be cleaned such as a wafer is immersed in cleaning fluid and the cleaning fluid is ultrasonically vibrated or oscillated, is well known. In order to enhance the cleaning power of such kinds of ultrasonic cleaning apparatus, various attempts have been made. 
     In, for example, Japanese Unexamined Patent Publication No. 6(1994)-320124, is described an ultrasonic cleaning apparatus that enhances the ultrasonic cleaning power by pouring fine air-bubbles into the cleaning fluid. Also, in Japanese Unexamined Patent Publication No. 8(1996)-141527, is described an ultrasonic cleaning apparatus in which the residue is exfoliated and removed by using an ultrasonic vibrator that vibrates at different frequencies. Furthermore, in Japanese Unexamined Patent Publication No. 8(1996)-108155 is described a cleaning apparatus that cleans an object to be cleaned with the object obliquely attached to the ultrasonic vibrator. 
     As mentioned above, according to the conventional cleaning apparatuses, the residue and dirts adhered to the object to be cleaned can be removed to some extent. However, polished tailings and residues confined in a groove of the object to be cleaned could not positively be removed. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a cleaning apparatus and a cleaning method that can substantially positively remove polished tailings and residues confined in grooves of the object to be cleaned. 
     According to the present invention, a cleaning apparatus includes a cleaning tank for reserving cleaning fluid, an object to be cleaned being immersed in the cleaning fluid, a vibrator for vibrating the cleaning fluid in the cleaning tank, and two micro-vibration sources for minutely vibrating the object to be cleaned in two different directions. 
     Furthermore, according to the present invention, a cleaning method for cleaning an object to be cleaned, has a step of immersing the object in cleaning fluid, a step of vibrating the cleaning fluid, and a step of minutely vibrating the object in two different directions during the vibration of the cleaning fluid. 
     The cleaning fluid in the cleaning tank is vibrated by a vibrator and, at the same time, an object to be cleaned is minutely vibrated in two different directions. Cleaning non-uniformities due to the vibrator cavitation can be removed by minutely vibrating the object to be cleaned in two different directions by two micro-vibration sources. 
     It is preferred that the vibrator produces pressure distribution in the cleaning fluid in the cleaning tank, and that at least one of the micro-vibration sources presents to the object micro-vibration in a direction vertical and/or parallel to an advance direction of the pressure distribution. 
     It is also preferred that the two micro-vibration sources presents to the object micro-vibrations in two directions orthogonal to each other. Such crossing of vibration directions at right angle can facilitate the removal of polished tailings and residues confined in grooves or the like. 
     It is preferred that the vibrator produces pressure distribution in the cleaning fluid in the cleaning tank, and that at least one of the micro-vibration sources is rocked in a direction parallel to an advance direction of the pressure distribution. 
     It is further preferred that the cleaning tank has a wall to which the vibrator is attached, and that the two micro-vibration sources are rocked in a direction vertical to a surface of the wall of the cleaning tank. When the vibrator is attached to one wall surface of the cleaning tank, a sound pressure distribution is generated between this wall surface and opposite wall surface of the cleaning tank in the cleaning fluid in the cleaning tank. A larger cleaning effect is obtained at the maximum point in the sound pressure change and a smaller cleaning effect is obtained at the minimum point in the sound pressure change, thereby generating a cleaning non-uniformities. When the wall surface to attach the vibrator is a bottom surface, the opposite wall surface is a fluid surface. Oscillation of the minute vibration source in a direction vertical to this attaching wall surface oscillates the object to be cleaned along this sound pressure distribution. Accordingly the object does not remain only at the maximum or minimum point in the sound pressure change, thereby removing the cleaning non-uniformities. 
     It is preferred that the micro-vibration sources consist of oscillating horns. 
     Preferably, the vibrator is an ultrasonic oscillator and/or the micro-vibration sources are ultrasonic oscillators. 
     Further, objects and advantages of the present invention will be apparent from description of the preferred embodiments of the invention in the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 schematically shows a constitution of a preferred embodiment of a cleaning apparatus according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, a reference numeral  10  denotes a cleaning tank in which cleaning fluid  11  is stored. Also, reference numerals  12 ,  13 ,  14  and  15  denote an ultrasonic vibrator attached to a bottom wall  10   a  of the tank  10 , first and second ultrasonic oscillating horns, and a wafer, i.e. an object to be cleaned, attached to the first and second ultrasonic oscillating horns  13  and  14  through a support member  16 , respectively. 
     As the cleaning fluid, pure water and cleaning fluid containing a water soluble detergent, solvent or the like can be used. The ultrasonic vibrator  12  attached to the bottom surface  10   a  of the tank  10  vibrates the cleaning fluid  11  in a direction vertical to the fluid surface from this bottom surface  10   a , namely in upward and downward directions in FIG.  1 . In the embodiment, 28 kHz of the vibration frequency is selected. It is apparent that the ultrasonic vibrator  12  may be attached to the wall surface of the cleaning tank  10  other than the bottom wall thereof. Although it is the most preferable that the vibration frequency is 28 kHz, it is not limited thereto. The vibration frequency may range from 26 to 40 kHz. 
     In the present embodiment, the first and second ultrasonic oscillation horns  13  and  14  minutely vibrate the wafer  15  in orthogonal directions to each other. That is the first ultrasonic oscillating horn  13  performs an ultrasonic vibration in the upward and downward directions in FIG. 1, and the ultrasonic oscillating horn  14  performs an ultrasonic vibration in the left and right directions in FIG.  1 . To the first and second ultrasonic oscillating horns  13  and  14  are secured both end portions of the support member  16 , to which the wafer  15  is attached so that it is immersed in the cleaning fluid  11 . In the embodiment, the wafer  15  is attached to the support member  16  in a manner that the surface of the wafer  15  is positioned in parallel to the upward and downward directions and perpendicularly to the vibration direction of the second ultrasonic oscillating horn  14 , as shown in FIG.  1 . 
     The horns  13  and  14  vibrate in orthogonal directions to each other. Nevertheless, the horns  13  and  14  can be designed so as to vibrate in optional two different directions with each other. The oscillation frequency of the horns  13  and  14  of the embodiment is set to 19.5 kHz. The 19.5 kHz of this oscillation frequency is particularly preferable. However, the frequency is not limited to 19.5 kHz and may be in a range of 14 to 30 kHz. Furthermore, it can be understood by those skilled in the art that the horns  13  and  14  may be oscillated at different frequencies with each other. As the horns  13  and  14 , for example, a horn type oscillators for an ultrasonic cleaning machine, commercially available from Kaijo Co. Ltd. can be used. 
     The ultrasonic horns  13  and  14  are integral with the support member  16  and wafer  15  and are rocked in upward and downward directions, as shown in FIG.  1 . This rocking operation is carried out at, for example, 20 strokes per minute by a motor or the like. As the amplitude of the rocking of the horns  13  and  14 , more than a half of the diameter of the wafer  15  can be selected. For example, if the diameter of the wafer  15  is 75 mm, the horns  13  and  14  are rocked at an amplitude of about 40 mm. It is preferred that the rocking direction is a direction perpendicular to the wall surface of the cleaning tank  10 , to which wall the ultrasonic vibrator  12  is attached. In the embodiment in FIG. 1, this wall surface is the bottom wall  10   a  of the cleaning tank  10 . 
     Operations of the ultrasonic cleaning apparatus of the embodiment will hereinafter be described with reference to a case of cleaning the wafer  15  for a thin-film magnetic head after the chemical mechanical polishing (CMP) process. 
     The CMP-processed wafer  15  is set to the support member  16  so that the surface of the wafer  15  is positioned in parallel to the upward and downward directions and perpendicularly to the vibration direction of the second ultrasonic oscillating horn  14 , as shown in FIG.  1 . In this conditions, the ultrasonic vibrator  12  and the first and second ultrasonic oscillating horns  13  and  14  vibrate to clean the wafer  15 . In addition, the horns  13  and  14  are rocked in upward and downward directions. 
     The wafer  15  is cleaned by cavitation in the cleaning fluid, formed by vibration of the ultrasonic vibrator  12  while ultrasonically vibrating the wafer  15  itself in two directions mentioned above by the horns  13  and  14 . Consequently, tailings of polished pad, residues and the like confined in respectively deep grooves on the element formation surface of the wafer  15  can be effectively removed. Such tailings, residues and the like could not be conventionally removed by only cavitation produced by the vibrator  12  attached to the bottom surface of the cleaning tank  10 . In the present invention, after such tailings, residues and the like confined in the above mentioned groove are first detached by the two directional ultrasonic vibration, they are then removed by the force of cavitation formed by the vibrator  12 . Since in particular the ultrasonic vibrations generated by the horns  13  and  14  are performed in two direction perpendicular to each other, detachment of the tailings of polished pad, residue and the like produced during the CMP process is effectively carried out. 
     Furthermore, since the vibrator  12  is attached to the bottom surface  10   a  of the cleaning tank  10 , a sound pressure distribution  17  is generated between the fluid surface and the bottom surface  10   a  in the fluid  11  in the cleaning tank  10  as shown in FIG.  1 . Cavitation is generated also at the maximum point  18  in change of the sound pressure, thereby resulting in an improved cleaning effect. On the other hand, at the minimum point  19  in the change of the sound pressure a cleaning effect is poor thereby generating the cleaning non-uniformities. However, according to the embodiment, the horns  13  and  14  are rocked in upward and downward directions. Thus, the wafer  15  is also rocked along the sound pressure distribution  17  and does not stop at only the maximum point  18  or minimum point  19  in the change of the sound pressure. Therefore, cleaning non-uniformities and the like are remarkably removed. 
     Table 1 shows the number of remaining polished tailings confined in grooves in one wafer after the CMP process, actually measured before and after ultrasonic cleaning. Table 1 also shows the number of removal of the remaining tailings by the cleaning and the rate of the removal calculated from the measured result. In the cleaning for this measurement, in addition to the ultrasonic vibration by the vibrator  12 , the wafer  15  was rocked in upward and downward directions. If the cleaning was carried out by only ultrasonic vibration by the horns  13  and  14 , the rate of removal of the polished pad tailings was 30 to 40%. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                   
                 THE 
                   
               
               
                   
                 THE NUMBER OF 
                 NUMBER 
                 RATE 
               
               
                   
                 REMAINING TAILINGS 
                 OF 
                 OF 
               
               
                   
                 OF POLISHED PAD 
                 REMOVAL 
                 REMOVAL 
               
             
          
           
               
                   
                 BEFORE 
                 AFTER 
                 BY 
                 BY 
               
               
                   
                 CLEANING 
                 CLEANING 
                 CLEANING 
                 CLEANING 
               
               
                   
                   
               
             
          
           
               
                 CLEANING 
                 306 
                 65 
                 241 
                 78.8% 
               
               
                 ONLY BY 
               
               
                 ULTRASONIC 
               
               
                 CAVITATION 
               
               
                 CLEANING 
                 280 
                 1 
                 279 
                 99.6% 
               
               
                 BY 
               
               
                 ULTRASONIC 
               
               
                 CAVITATION 
               
               
                 PLUS 
               
               
                 TWO 
               
               
                 DIREC- 
               
               
                 TIONAL 
               
               
                 ULTRASONIC 
               
               
                 VIBRATIONS 
               
               
                   
               
             
          
         
       
     
     As apparent from Table 1, the rate of removal of the tailings by the (leaning, which was obtained in a case where the wafer  15  was cleaned only by cavitation due to the ultrasonic vibrator  12  is 78.8%. On the other hand, the rate of removal of the tailings by clearing, which was obtained by using two directional ultrasonic vibration by the horns  13  and  14  with the above-mentioned cavitation due to the vibrator  12  is 99.6%. Therefore, the effect of using both the ultrasonic oscillating horns  13  and  14  and the ultrasonic vibrator  12  is 20% higher than that of using only the latter. 
     In the embodiment described above, as an object to be cleaned, a wafer for a thin-film magnetic head was used. However, in the cleaning apparatus according to the present invention, other various wafers and various objects to be cleaned other than the wafer can be naturally used. 
     Many widely different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiment described in the specification, except as defined in the appended claims.