Patent Publication Number: US-2009230103-A1

Title: Laser beam processing machine

Description:
FIELD OF THE INVENTION 
     The present invention relates to a laser beam processing machine for forming a plurality of via holes in a workpiece. 
     DESCRIPTION OF THE PRIOR ART 
     In the production process of a semiconductor device, a plurality of areas are sectioned by dividing lines called “streets” which are arranged in a lattice pattern on the front surface of a substantially disk-like semiconductor wafer, and a device such as IC or LSI is formed in each of the sectioned areas. Individual semiconductor chips are manufactured by cutting this semiconductor wafer along the streets to divide it into the areas in which the device is each formed. 
     As a means of reducing the size and increasing the number of functions of an apparatus, a modular structure for connecting the electrodes of a plurality of semiconductor chips which are stacked up in layers is disclosed by JP-A 2003-163323. This modular structure is a structure in which via holes are formed at the positions at which the electrode is formed, in a semiconductor wafer and a conductive material such as aluminum for connecting the electrodes is buried in the via holes. 
     The above via holes in the semiconductor wafer are generally formed by a drill. Therefore, the diameters of the via holes formed in the semiconductor wafer are 100 to 300 μm and hence, drilling of the via holes reduces productivity. 
     To solve the above problem, the present applicants propose a laser beam processing machine capable of forming via holes in a workpiece such as a semiconductor wafer efficiently as JP-A 2006-247674. This laser beam processing machine comprises a chuck table for holding a workpiece, a processing-feed amount detection means for detecting the processing-feed amount of the chuck table holding the workpiece relative to a laser beam application means, a memory means for storing the X and Y coordinate values of the via holes to be formed in the workpiece, and a control means for controlling the laser beam application means based on the X and Y coordinate values of the via holes stored in the memory means and a detection signal from the processing-feed amount detection means. When the point of the X and Y coordinate values of a via hole to be formed in the workpiece reaches a position right below a condenser of the laser beam application means, one pulse of a laser beam is so constituted to be applied. 
     To form a via hole in the workpiece, however, a pulse laser beam must be applied to the same position a plurality of times. When the above-mentioned laser beam processing machine is used, the workpiece must be moved a plurality of times, which is not always satisfactory in the terms of productivity. 
     Further, it is desired that a plurality of grooves can be formed in the workpiece by only moving it in the processing-feed direction without moving (indexing-feeding) it in the indexing-feed direction (Y-axis direction) perpendicular to the processing-feed direction (X-axis direction). 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a laser beam processing machine capable of forming via holes in a workpiece such as a semiconductor wafer or the like efficiently and forming a plurality of grooves by only moving the workpiece in the processing-feed direction. 
     To attain the above object, according to the present invention, there is provided a laser beam processing machine comprising a chuck table for holding a workpiece, a laser beam application means for applying a laser beam to the workpiece held on the chuck table, a processing-feed means for moving the chuck table and the laser beam application means relative to each other in a processing-feed direction (X-axis direction), and an indexing-feed means for moving the chuck table and the laser beam application means relative to each other in an indexing-feed direction (Y-axis direction) perpendicular to the processing-feed direction (X-axis direction), wherein 
     the laser beam application means comprises a laser oscillation means for oscillating a laser beam, a first acousto-optic deflection means for deflecting the optical axis of a laser beam oscillated by the laser beam oscillation means in the processing-feed direction (X-axis direction), and a second acousto-optic deflection means for deflecting the optical axis of a laser beam oscillated by the laser beam oscillation means in the indexing-feed direction (Y-axis direction). 
     The above first acousto-optic deflection means comprises a first acousto-optic device for deflecting the optical axis of a laser beam oscillated by the laser beam oscillation means in the processing-feed direction (X-axis direction), a first RF oscillator for applying RF to the first acousto-optic device and a first deflection angle adjusting means for adjusting the frequency of RF output from the first RF oscillator; and 
     the above second acousto-optic deflection means comprises a second acousto-optic device for deflecting the optical axis of a laser beam oscillated by the laser beam oscillation means in the indexing-feed direction (Y-axis direction), a second RF oscillator for applying RF to the second acousto-optic device, and a second deflection angle adjusting means for adjusting the frequency of RF output from the second RF oscillator. 
     The above first acousto-optic deflection means comprises a first output adjusting means for adjusting the amplitude of RF output from the first RF oscillator, and the above second acousto-optic deflection means comprises a second output adjusting means for adjusting the amplitude of RF output from the second RF oscillator. 
     The laser beam processing machine further comprises a processing-feed amount detection means for detecting the processing-feed amount of the chuck table relative to the laser beam application means, an indexing-feed amount detection means for detecting the indexing-feed amount of the chuck table relative to the laser beam application means, a memory means for storing the X and Y coordinate values of an area to be processed of the workpiece, and a control means for controlling the first acousto-optic deflection means and the second acousto-optic deflection means based on the X and Y coordinate values stored in the memory means and detection signals from the processing-feed amount detection means and the indexing-feed amount detection means. 
     In the laser beam processing machine according to the present invention, since the control means controls the first acousto-optic deflection means based on a detection signal from the processing-feed amount detection means to deflect the optical axis of a laser beam oscillated by the laser beam oscillation means in the processing-feed direction (X-axis direction), a plurality of pulses of the pulse laser beam can be applied to a predetermined position even in a state where the workpiece held on the chuck table is moving in the processing-feed direction, thereby making it possible to form via holes efficiently. 
     In the laser beam processing machine according to the present invention, since the optical axis of a pulse laser beam is deflected in the indexing-feed direction (Y-axis direction) by activating the second acousto-optic deflection means of the laser beam application means to apply the pulse laser beam to the workpiece, a plurality of grooves can be formed in the workpiece or two-dimensional (2-D) processing can be made on the workpiece in the X-axis direction and the Y-axis direction by only moving the workpiece in the processing-feed direction without moving it in the indexing direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a laser beam processing machine constituted according to the present invention; 
         FIG. 2  is a block diagram of a laser beam application means provided in the laser beam processing machine shown in  FIG. 1 ; 
         FIG. 3  is a plan view of a semiconductor wafer as a workpiece; 
         FIG. 4  is a partially enlarged plan view of the semiconductor wafer shown in  FIG. 3 ; 
         FIG. 5  is a perspective view showing a state where the semiconductor wafer shown in  FIG. 3  is affixed to a protective tape mounted on an annular frame; 
         FIG. 6  is an explanatory diagram showing the coordinates in a state where the semiconductor wafer shown in  FIG. 3  is held at a predetermined position of the chuck table of the laser beam processing machine shown in  FIG. 1 ; 
         FIGS. 7(   a ) and  7 ( b ) are explanatory diagrams showing the drilling step using the laser beam processing machine shown in  FIG. 1 ; 
         FIGS. 8(   a ) and  8 ( b ) are enlarged explanatory diagrams showing the details of the drilling step shown in  FIGS. 7(   a ) and  7 ( b ); 
         FIGS. 9(   a ) and  9 ( b ) are explanatory diagrams showing the drilling step which is carried out with the laser beam processing machine shown in  FIG. 1 ; 
         FIGS. 10(   a ) and  10 ( b ) are explanatory diagrams showing another example of the laser processing method which is carried out by using the laser beam processing machine shown in  FIG. 1 ; and 
         FIGS. 11(   a ) and  11 ( b ) are explanatory diagrams showing still another example of the laser processing method which is carried out by using the laser beam processing machine shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A laser beam processing machine constituted according to the present invention will be described in more detail hereinunder with reference to the accompanying drawings. 
       FIG. 1  is a perspective view of a laser beam processing machine constituted according to the present invention. The laser beam processing machine shown in  FIG. 1  comprises a stationary base  2 , a chuck table mechanism  3  for holding a workpiece, which is mounted on the stationary base  2  in such a manner that it can move in a processing-feed direction indicated by an arrow X (X-axis direction), a laser beam application unit support mechanism  4  mounted on the stationary base  2  in such a manner that it can move in an indexing-feed direction indicated by an arrow Y (Y-axis direction) perpendicular to the direction indicated by the arrow X (X-axis direction), and a laser beam application unit  5  mounted on the laser beam application unit support mechanism  4  in such a manner that it can move in a direction indicated by an arrow Z (Z-axis direction). 
     The above chuck table mechanism  3  comprises a pair of guide rails  31  and  31  which are mounted on the stationary base  2  and arranged parallel to each other in the processing-feed direction indicated by the arrow X (X-axis direction), a first sliding block  32  mounted on the guide rails  31  and  31  in such a manner that it can move in the processing-feed direction indicated by the arrow X (X-axis direction), a second sliding block  33  mounted on the first sliding block  32  in such a manner that it can move in the indexing-feed direction indicated by the arrow Y (Y-axis direction), a cover table  35  supported on the second sliding block  33  by a cylindrical member  34 , and a chuck table  36  as a workpiece holding means. This chuck table  36  comprises an adsorption chuck  361  made of a porous material, and a workpiece, for example, a disk-like semiconductor wafer is held on the adsorption chuck  361  by a suction means that is not shown. The chuck table  36  constituted as described above is rotated by a pulse motor (not shown) installed in the cylindrical member  34 . The chuck table  36  is provided with clamps  362  for fixing an annular frame which will be described later. 
     The above first sliding block  32  has, on its undersurface, a pair of to-be-guided grooves  321  and  321  to be fitted to the above pair of guide rails  31  and  31  and, on the top surface, a pair of guide rails  322  and  322  formed parallel to each other in the indexing-feed direction indicated by the arrow Y (Y-axis direction). The first sliding block  32  constituted as described above can move along the pair of guide rails  31  and  31  in the processing-feed direction indicated by the arrow X (X-axis direction) by fitting the to-be-guided grooves  321  and  321  to the pair of guide rails  31  and  31 , respectively. The chuck table mechanism  3  in the illustrated embodiment comprises a processing-feed means  37  for moving the first sliding block  32  along the pair of guide rails  31  and  31  in the processing-feed direction indicated by the arrow X (X-axis direction). The processing-feed means  37  has a male screw rod  371  which is arranged between the above pair of guide rails  31  and  31  parallel to them and a drive source such as a pulse motor  372  for rotary-driving the male screw rod  371 . The male screw rod  371  is, at its one end, rotatably supported to a bearing block  373  fixed on the above stationary base  2  and is, at the other end, transmission-coupled to the output shaft of the above pulse motor  372 . The male screw rod  371  is screwed into a threaded through-hole formed in a female screw block (not shown) projecting from the undersurface of the center portion of the first sliding block  32 . Therefore, by driving the male screw rod  371  in a normal direction or reverse direction with the pulse motor  372 , the first sliding block  32  is moved along the guide rails  31  and  31  in the processing-feed direction indicated by the arrow X (X-axis direction). 
     The laser beam processing machine in the illustrated embodiment has a processing-feed amount detection means  374  for detecting the processing-feed amount of the above chuck table  36 . The processing-feed amount detection means  374  is composed of a linear scale  374   a  arranged along the guide rail  31  and a read head  374   b  which is mounted on the first sliding block  32  and moves along the linear scale  374   a  together with the first sliding block  32 . The read head  374   b  of this processing-feed amount detection means  374  supplies one pulse signal for every 1.0 μm to a control means which will be described later in the illustrated embodiment. The control means detects the processing-feed amount of the chuck table  36  by counting the input pulse signals. When the pulse motor  372  is used as a drive source for the above processing-feed means  37 , the processing-feed amount of the chuck table  36  can be detected by counting the drive pulses of the control means (later described) for outputting a drive signal to the pulse motor  372 . When a servo motor is used as the drive source for the above processing-feed means  37 , a pulse signal outputted from a rotary encoder for detecting the revolution of the servo motor is supplied to the control means (later described) which in turn counts the input pulse signals to detect the processing-feed amount of the chuck table  36 . 
     The above second sliding block  33  has, on its undersurface, a pair of to-be-guided grooves  331  and  331  to be fitted to the pair of guide rails  322  and  322  on the top surface of the above first sliding block  32  and can move in the indexing-feed direction indicated by the arrow Y (Y-axis direction) when the to-be-guided grooves  331  and  331  are fitted to the pair of guide rails  322  and  322 , respectively. The chuck table mechanism  3  in the illustrated embodiment has a first indexing-feed means  38  for moving the second sliding block  33  in the indexing-feed direction indicated by the arrow Y (Y-axis direction) along the pair of guide rails  322  and  322  provided on the first sliding block  32 . The first indexing-feed means  38  comprises a male screw rod  381  which is arranged between the above pair of guide rails  322  and  322  parallel to them and a drive source such as a pulse motor  382  for rotary-driving the male screw rod  381 . The male screw rod  381  is, at its one end, rotatably supported to a bearing block  383  fixed on the top surface of the above first sliding block  32  and is, at the other end, transmission-coupled to the output shaft of the above pulse motor  382 . The male screw rod  381  is screwed into a threaded through-hole formed in a female screw block (not shown) projecting from the undersurface of the center portion of the second sliding block  33 . Therefore, by driving the male screw rod  381  in a normal direction or reverse direction with the pulse motor  382 , the second sliding block  33  is moved along the guide rails  322  and  322  in the indexing-feed direction indicated by the arrow Y (Y-axis direction). 
     The laser beam processing machine in the illustrated embodiment has a first indexing-feed amount detection means  384  for detecting the indexing-feed amount of the above second sliding block  33 . This first indexing-feed amount detection means  384  is composed of a linear scale  384   a  arranged along the guide rail  322  and a read head  384   b  which is mounted on the second sliding block  33  and moves along the linear scale  384   a  together with the second sliding block  33 . The read head  384   b  of the indexing-feed amount detection means  384  supplies one pulse signal for every 1 μm to the control means (later described) in the illustrated embodiment. The control means (later described) detects the indexing-feed amount of the chuck table  36  by counting the input pulse signals. When the pulse motor  382  is used as a drive source for the above first indexing-feed means  38 , the indexing-feed amount of the chuck table  36  can be detected by counting the drive pulses of the control means (later described) for outputting a drive signal to the pulse motor  382 . When a servo motor is used as the drive source for the above first indexing-feed means  38 , a pulse signal outputted from the rotary encoder for detecting the revolution of the servo motor is supplied to the control means (later described) which in turn counts the input pulse signals to detect the indexing-feed amount of the chuck table  36 . 
     The above laser beam application unit support mechanism  4  comprises a pair of guide rails  41  and  41  mounted on the stationary base  2  and arranged parallel to each other in the indexing-feed direction indicated by the arrow Y (Y-axis direction) and a movable support base  42  mounted on the guide rails  41  and  41  in such a manner that it can move in the direction indicated by the arrow Y. This movable support base  42  consists of a movable support portion  421  movably mounted on the guide rails  41  and  41  and a mounting portion  422  mounted on the movable support portion  421 . The mounting portion  422  is provided with a pair of guide rails  423  and  423  extending parallel to each other in the direction indicated by the arrow Z (Z-axis direction) on one of its flanks. The laser beam application unit support mechanism  4  in the illustrated embodiment has a second indexing-feed means  43  for moving the movable support base  42  along the pair of guide rails  41  and  41  in the indexing-feed direction indicated by the arrow Y (Y-axis direction). This second indexing-feed means  43  comprises a male screw rod  431  arranged between the above pair of guide rails  41  and  41  parallel to each other and a drive source such as a pulse motor  432  for rotary-driving the male screw rod  431 . The male screw rod  431  is, at its one end, rotatably supported to a bearing block (not shown) fixed on the above stationary base  2  and is, at the other end, transmission-coupled to the output shaft of the above pulse motor  432 . The male screw rod  431  is screwed into a threaded through-hole formed in a female screw block (not shown) projecting from the undersurface of the center portion of the movable support portion  421  constituting the movable support base  42 . Therefore, by driving the male screw rod  431  in a normal direction or reverse direction with the pulse motor  432 , the movable support base  42  is moved along the guide rails  41  and  41  in the indexing-feed direction indicated by the arrow Y (Y-axis direction). 
     The laser beam processing machine in the illustrated embodiment comprises a second indexing-feed amount detection means  433  for detecting the indexing-feed amount of the movable support base  42  of the above laser beam application unit support mechanism  4 . This second indexing-feed amount detection means  433  comprises a linear scale  433   a  arranged along the guide rail  41  and a read head  433   b  which is mounted on the movable support base  42  and moves along the linear scale  433   a . The read head  433   b  of this second indexing-feed amount detection means  433  supplies one pulse signal for every 1 μm to the control means (later-described) in the illustrated embodiment. The control means detects the indexing-feed amount of the laser beam application unit  5  by counting the input pulse signals. When the pulse motor  432  is used as a drive source for the above second indexing-feed means  43 , the indexing-feed amount of the laser beam application unit  5  can be detected by counting the drive pulses of the control means (later described) for outputting a drive signal to the pulse motor  432 . When a servo motor is used as the drive source for the above second indexing-feed means  43 , a pulse signal outputted from the rotary encoder for detecting the revolution of the servo motor is supplied to the control means (later described), which in turn counts the input pulse signals to detect the indexing feed-amount of the laser beam application unit  5 . 
     The laser beam application unit  5  in the illustrated embodiment comprises a unit holder  51  and a laser beam application means  52  secured to the unit holder  51 . The unit holder  51  has a pair of to-be-guided grooves  511  and  511  to be slidably fitted to the pair of guide rails  423  and  423  provided on the above mounting portion  422  and is supported in such a manner that it can move in the direction indicated by the arrow Z (Z-axis direction) by fitting the to-be-guided grooves  511  and  511  to the above guide rails  423  and  423 , respectively. 
     The laser beam application unit  5  in the illustrated embodiment has a moving means  53  for moving the unit holder  51  along the pair of guide rails  423  and  423  in the direction indicated by the arrow Z (Z-axis direction). The moving means  53  comprises a male screw rod (not shown) arranged between the pair of guide rails  423  and  423  and a drive source such as a pulse motor  532  for rotary-driving the male screw rod. By driving the male screw rod (not shown) in a normal direction or reverse direction with the pulse motor  532 , the unit holder  51  and the laser beam application means  52  are moved along the guide rails  423  and  423  in the direction indicated by the arrow Z (Z-axis direction). In the illustrated embodiment, the laser beam application means  52  is moved up by driving the pulse motor  532  in the normal direction and moved down by driving the pulse motor  532  in the reverse direction. 
     The above laser beam application means  52  comprises a cylindrical casing  521  arranged substantially horizontally, a pulse laser beam oscillation means  6 , a transmission optical system  7 , a first acousto-optic deflection means  81  for deflecting the optical axis of a laser beam oscillated by the pulse laser beam oscillation means  6  in the processing-feed direction (X-axis direction) and a second acousto-optic deflection means  82  for deflecting the optical axis of a laser beam oscillated by the pulse laser beam oscillation means  6  in the indexing-feed direction (Y-axis direction) installed in the casing  521 , as shown in  FIG. 2 . The laser beam application means  52  has a processing head  9  for applying a pulse laser beam passing through the first acousto-optic deflection means  81  and the second acousto-optic deflection means  82  to the workpiece held on the above chuck table  36 . 
     The above pulse laser beam oscillation means  6  is constituted by a pulse laser beam oscillator  61  composed of a YAG laser oscillator or YVO4 laser oscillator and a repetition frequency setting means  62  connected to the pulse laser beam oscillator  61 . The above transmission optical system  7  comprises suitable optical elements, such as a beam splitter. 
     The above first acousto-optic deflection means  81  comprises a first acousto-optic device  811  for deflecting the optical axis of a laser beam oscillated by the laser beam oscillation means  6  in the processing-feed direction (X-axis direction), a first RF oscillator  812  for generating RF (radio frequency) to be applied to the first acousto-optic device  811 , a first RF amplifier  813  for amplifying the power of RF generated by the first RF oscillator  812  to apply it to the first acousto-optic device  811 , a first deflection angle adjusting means  814  for adjusting the frequency of RF generated by the first RF oscillator  812 , and a first output adjusting means  815  for adjusting the amplitude of RF generated by the first RF oscillator  812 . The above first acousto-optic device  811  can adjust the deflection angle of the optical axis of a laser beam according to the frequency of the applied RF and the output of a laser beam according to the amplitude of the applied RF. The first deflection angle adjusting means  814  and the first output adjusting means  815  are controlled by the control means which will be described later. 
     The above second acousto-optic deflection means  82  comprises a second acousto-optic device  821  for deflecting the optical axis of a laser beam oscillated by the laser beam oscillation means  6  in the indexing-feed direction (Y-axis direction: direction perpendicular to the sheet in  FIG. 2 ) perpendicular to the processing-feed direction (X-axis direction), a second RF oscillator  822  for generating RF to be applied to the second acousto-optic device  821 , a second RF amplifier  823  for amplifying the power of RF generated by the second RF oscillator  822  to apply it to the second acousto-optic device  821 , a second deflection angle adjusting means  824  for adjusting the frequency of RF generated by the second RF oscillator  822  and a second output adjusting means  825  for adjusting the amplitude of RF generated by the second RF oscillator  822 . The above second acousto-optic device  821  can adjust the deflection angle of the optical axis of a laser beam according to the frequency of the applied RF and the output of a laser beam according to the amplitude of the applied RF. The above second deflection angle adjusting means  824  and the second output adjusting means  825  are controlled by the control means which will be described later. 
     The laser beam application means  52  in the illustrated embodiment comprises a laser beam absorbing means  83  for absorbing a laser beam not deflected by the first acousto-optic device  811  as shown by a one-dot chain line in  FIG. 2  when RF is not applied to the above first acousto-optic device  811 . 
     The above processing head  9  is attached to the end of the casing  521  and has a direction changing mirror  91  for changing the direction of a pulse laser beam passing through the above first acousto-optic deflection means  81  and the second acousto-optic deflection means  82  to a downward direction, and a condenser lens  92  for converging a laser beam whose direction has been changed by the direction changing mirror  91 . 
     The laser beam application means  52  in the illustrated embodiment is constituted as described above. When RF is not applied to the first acousto-optic device  811  and the second acousto-optic device  821 , a pulse laser beam oscillated by the pulse laser beam oscillation means  6  is guided to the laser beam absorbing means  83  as shown by the one-dot chain line in  FIG. 2  through the transmission optical system  7 , the first acousto-optic device  811  and the second acousto-optic device  821 . Meanwhile, when RF having a frequency of, for example, 10 kHz is applied to the first acousto-optic device  811 , the optical axis of a pulse laser beam oscillated by the pulse laser beam oscillation means  6  is deflected and converged at a focal point Pa as shown by the solid line in  FIG. 2 . When RF having a frequency of, for example, 20 kHz is applied to the first acousto-optic device  811 , the optical axis of a pulse laser beam oscillated by the pulse laser beam oscillation means  6  is deflected as shown by the broken line in  FIG. 2  and converged at a focal point Pb which shifts from the above focal point Pa by a predetermined distance in the processing-feed direction (X-axis direction). When RF having a predetermined frequency is applied to the second acousto-optic device  821 , the optical axis of a pulse laser beam oscillated by the pulse laser beam oscillation means  6  is converged at a position which shifts from the above focal point Pa by a predetermined distance in the indexing-feed direction (Y-axis direction, direction perpendicular to the sheet in  FIG. 2 ) perpendicular to the processing-feed direction (X-axis direction). 
     The laser beam processing machine in the illustrated embodiment comprises an image pick-up means  11  which is mounted on the front end of the casing  521  and detects the area to be processed by the above laser beam application means  52 . This image pick-up means  11  comprises an illuminating means for illuminating the workpiece, an optical system for capturing the area illuminated by the illuminating means, and an image pick-up device (CCD) for picking up an image captured by the optical system. A signal of the picked-up image is supplied to the control means which will be described later. 
     Returning to  FIG. 1 , the laser beam processing machine in the illustrated embodiment comprises the control means  10 . The control means  10  is composed of a computer which comprises a central processing unit (CPU)  101  for carrying out arithmetic processing based on a control program, a read-only memory (ROM)  102  for storing the control program, etc., a read/write random access memory (RAM)  103  for storing data on the design values of the workpiece and the results of operations both of which will be described later, a counter  104 , an input interface  105  and an output interface  106 . Detection signals from the above processing-feed amount detection means  374 , the first indexing-feed amount detection means  384 , the second indexing-feed amount detection means  433 , the image pick-up means  11 , etc. are input to the input interface  105  of the control means  10 . Control signals are output from the output interface  106  of the control means  10  to the pulse motor  372 , the pulse motor  382 , the pulse motor  432 , the pulse motor  532 , the laser beam application means  52 , etc. The above random access memory (RAM)  103  has a first storage area  103   a  for storing data on the design values (later described) of the workpiece, a second storage area  103   b  for storing data on the detection values (later described), and other storage area. 
     The laser beam processing machine in the illustrated embodiment is constituted as described above, and its operation will be described hereinbelow. 
       FIG. 3  is a plan view of a semiconductor wafer  20  as the workpiece to be processed by a laser beam. The semiconductor wafer  20  shown in  FIG. 3  is a silicon wafer, a plurality of areas are sectioned by a plurality of dividing lines  201  arranged in a lattice pattern on the front surface  20   a , and a device  202  such as IC or LSI is formed in each of the sectioned areas. The devices  202  are the same in constitution. A plurality of electrodes  203  ( 203   a  to  203   j ) are formed on the surface of each device  202  as shown in  FIG. 4 . In the illustrated embodiment, electrodes  203   a  and  203   f , electrodes  203   b  and  203   g , electrodes  203   c  and  203   h , electrodes  203   d  and  203   i , and electrodes  203   e  and  203   j  are at the same positions in the X-axis direction. A via hole is formed respectively in the plurality of electrodes  203  ( 203   a  to  203   j ). The intervals A between adjacent electrodes  203  ( 203   a  to  203   j ) in the X-axis direction (horizontal direction in  FIG. 4 ) and the intervals B between adjacent electrodes in the X-axis direction (horizontal direction in  FIG. 4 ) with the dividing line  201  interposed therebetween, that is, between the electrodes  203   e  and  203   a  out of the electrodes  203  formed on each device  202  are the same in the illustrated embodiment. The intervals C between adjacent electrodes  203  ( 203   a  to  203   j ) in the Y-axis direction (vertical direction in  FIG. 4 ) and the intervals D between adjacent electrodes in the Y-axis direction (vertical direction in  FIG. 4 ) with the dividing line  201  interposed therebetween, that is, between the electrodes  203   f  and  203   a  and between the electrodes  203   j  and  203   e  out of the electrodes  203  formed on each device  202  are the same in the illustrated embodiment. The design value data of the semiconductor wafer  20  constituted as described above, which include the numbers of devices  202  disposed in rows E 1  to En and columns F 1  to Fn shown in  FIG. 3  and the above intervals A, B. C and D, are stored in the first storage area  103   a  of the above random access memory (RAM)  103 . 
     An embodiment of laser processing for forming a via hole in the electrodes  203  ( 203   a  to  203   j ) of each device  202  formed on the above semiconductor wafer  20  by using the above laser beam processing machine will be described hereinunder. 
     The semiconductor wafer  20  constituted as described above is put on a protective tape  22  which is composed of a synthetic resin sheet such as a polyolefin sheet and mounted on an annular frame  21  in such a manner that the front surface  20   a  faces up as shown in  FIG. 5 . 
     The semiconductor wafer  20  supported to the annular frame  21  through the protective tape  22  is placed on the chuck table  36  of the laser beam processing machine shown in  FIG. 1  in such a manner that the protective tape  22  side comes into contact with the chuck table  36 . The semiconductor wafer  20  is suction-held on the chuck table  36  through the protective tape  22  by activating the suction means that is not shown. The annular frame  21  is fixed by the clamps  362 . 
     The chuck table  36  suction-holding the semiconductor wafer  20  as described above is brought to a position right below the image pick-up means  11  by the processing-feed means  37 . When the chuck table  36  is positioned right below the image pick-up means  11 , the semiconductor wafer  20  on the chuck table  36  is in a state of being located at a coordinate position shown in  FIG. 6 . In this state, alignment work is carried out to check whether the dividing lines  201  formed in a lattice pattern on the semiconductor wafer  20  held on the chuck table  36  are parallel to the X-axis direction and the Y-axis direction or not. That is, an image of the semiconductor wafer  20  held on the chuck table  36  is picked up by the image pick-up means  11  to carry out image processing such as pattern matching, etc. for the alignment work. 
     Thereafter, the chuck table  36  is moved to bring a device  202  at the most left end in  FIG. 6  in the topmost row E 1  out of the devices  202  formed on the semiconductor wafer  20  to a position right below the image pick-up means  11 . Further, the upper left electrode  203   a  in  FIG. 4  out of the electrodes  203  ( 203   a  to  203   j ) formed on the device  202  is brought to a position right below the image pick-up means  11 . After the image pick-up means  11  detects the electrode  203   a  in this state, its coordinate values (a 1 ) are supplied, as a first processing-feed start position coordinate value to the control means  10 . And, the control means  10  stores the coordinate values (a 1 ) in the second storage area  103   b  of the random access memory (RAM)  103  as the first processing-feed start position coordinate values (a processing-feed start position detecting step). Since there is a predetermined space between the image pick-up means  11  and the processing head  9  of the laser beam application means  52  in the X-axis direction at this point, a value obtained by adding the interval between the above image pick-up means  11  and the processing head  9  is stored as an X coordinate value. 
     After the first processing-feed start position coordinate values (a 1 ) of the device  202  in the topmost row E 1  in  FIG. 6  are detected as described above, the chuck table  36  is moved (indexing-fed) a distance corresponding to the interval between the dividing lines  201  in the Y-axis direction and brought in the X-axis direction to bring a device  202  at the most left end in the second row E 2  from the topmost in  FIG. 6  to a position right below the image pick-up means  11 . Further, the upper left electrode  203   a  in  FIG. 6  out of the electrodes  203  ( 203   a  to  203   j ) formed on the device  202  is brought to a position right below the image pick-up means  11 . After the image pick-up means  11  detects the electrode  203   a  in this state, its coordinate values (a 2 ) are supplied as second processing-feed start position coordinate values to the control means  10 . And, the control means  10  stores the coordinate values (a 2 ) in the second storage area  103   b  of the random access memory (RAM)  103  as the second processing-feed start position coordinate values. Since there is a predetermined space between the image pick-up means  11  and the processing head  9  of the laser beam application means  52  in the X-axis direction at this point as described above, a value obtained by adding the interval between the image pick-up means  11  and the processing head  9  is stored as an X coordinate value. The above indexing-feed and processing-feed start position detecting steps are repeated up to the bottom row En in  FIG. 6  to detect the processing-feed start position coordinate values (a 3  to an) of the devices  202  formed in the rows and store them in the second storage area  103   b  of the random access memory (RAM)  103 . 
     Next comes the step of drilling a via hole in the electrodes  203  ( 203   a  to  203   j ) formed on each device  202  of the semiconductor wafer  20 . In the drilling step, the processing-feed means  37  is first activated to move the chuck table  36  so as to bring the first processing-feed start position coordinate values (a 1 ) stored in the second storage area  103   b  of the above random access memory (RAM)  103  to a position right below the processing head  9  of the laser beam application means  52 .  FIG. 7(   a ) shows a state of the first processing-feed start position coordinate values (a 1 ) being positioned right below the processing head  9 . The control means  10  controls the above processing-feed means  37  to move (processing-feed) the chuck table  36  in the state shown in  FIG. 7(   a ) in the direction indicated by the arrow X 1  at a predetermined moving rate, and activates the laser beam application means  52  to apply a pulse laser beam from the processing head  9  for a predetermined time at the same time. The focal point P of a laser beam applied from the processing head  9  is set to a position near the front surface  20   a  of the semiconductor wafer  20 . At this point, the control means  10  outputs a control signal to the first deflection angle adjusting means  814  and the first output adjusting means  815  of the first acousto-optic deflection means  81  based on a detection signal sent from the read head  374   b  of the processing-feed amount detection means  374  for a predetermined time during which a pulse laser beam is applied. That is, the control means  10  controls the frequency of RF generated by the first RF oscillator  812  to a range of, for example, 10 to 20 kHz and outputs a control signal to ensure that the amplitude of RF generated by the first RF oscillator  812  becomes a predetermined value. The first RF oscillator  812  outputs RF based on control signals from the first deflection angle adjusting means  814  and the first output adjusting means  815 . The power of RF output from the first RF oscillator  812  is amplified by the first RF amplifier  813  and applied to the first acousto-optic device  811 . As a result, the first acousto-optic device  811  deflects the optical axis of a pulse laser beam oscillated by the pulse laser beam oscillation means  6  to a range from the position shown by the solid line in  FIG. 2  up to the position shown by the broken line in  FIG. 2 . 
     The processing conditions in the above drilling step are set as follows, for example. 
     Light source: LD excited Q switch Nd: YVO4 
     Wavelength: 355 nm 
     Repetition frequency: 50 kHz 
     Output: 3 W 
     Focusing spot diameter: 15 μm 
     Processing-feed rate: 100 mm/sec 
     When the drilling step is carried out under the above processing conditions, a hole having a depth of about 5 μm per one pulse of the pulse laser beam can be formed in the silicon wafer. Therefore, to form a via hole in a silicon wafer having a thickness of 50 μm, 10 pulses of the pulse laser beam must be applied. Consequently, 10 pulses of the pulse laser beam must be applied to the first processing-feed start position coordinate values (a 1 ) of the semiconductor wafer  20  held on the chuck table  36  which is moved at a feed rate of 100 mm/sec under the above processing conditions. 
     The method of applying 10 pulses of the pulse laser beam to the first processing-feed start position coordinate values (a 1 ) of the semiconductor wafer  20  when the semiconductor wafer  20  is moved at a processing-feed rate of 100 mm/sec will be described with reference to  FIGS. 8(   a ) and  8 ( b ). 
     Since the repetition frequency of the pulse laser beam under the above processing conditions is 50 kHz, 50,000 pulses (50,000 pulses/sec) of the pulse laser beam are applied for one second. Therefore, the time for applying 10 pulses of the pulse laser beam is 1/5,000 sec. Meanwhile, the semiconductor wafer  20  which moves in the direction indicated by X 1  at a processing-feed rate of 100 mm/sec moves 20 μm for 1/5,000 sec. Therefore, the laser beam application means  52  is activated for 1/5,000 sec during which the semiconductor wafer  20  moves 20 μm, and the first deflection angle adjusting means  814  controls the frequency of RF output from the first RF oscillator  812  in 10 stages for 1/5,000 sec to ensure that the focal point of the pulse laser beam is brought to a position at the first processing-feed start position coordinate values (a 1 ) during this time. That is, in a state where the first processing-feed start position coordinate values (a 1 ) of the semiconductor wafer  20  is positioned right below the condenser lens  92  as shown in  FIG. 8(   a ), RF having a frequency of, for example, 10 kHz is applied to the first acousto-optic device  811  to apply the optical axis of the pulse laser beam as shown by the solid line and at the same time, the optical axis of the laser beam is deflected in the direction shown by X 1  in 10 stages from the position shown by the solid line up to the position shown by the broken line while the semiconductor wafer  20  moves 20 μm. The deflection of the optical axis of the laser beam can be carried out by controlling the frequency of RF applied to the first acousto-optic device  811  of the first acousto-optic deflection means  81  based on a detection signal from the read head  374   b  of the processing-feed amount detection means  374 , as described above. As a result, since 10 pulses of the pulse laser beam can be applied to the first processing-feed start position coordinate values (a 1 ) even in a state of the semiconductor wafer  20  moving in the processing-feed direction X 1 , a via hole  204  is formed at the first processing-feed start position coordinate values (a 1 ) of the semiconductor wafer  20  as shown in  FIG. 8(   b ). In the above drilling step, the amplitude of RF output by the first RF oscillator  812  may be controlled by the first output adjusting means  815  to adjust the output of the pulse laser beam. 
     Meanwhile, the control means  10  receives a detection signal from the read head  374   b  of the processing-feed amount detection means  374  and counts the detection signals by means of the counter  104 . And, when the count value of the counter  104  reaches a value corresponding to the interval A between the electrodes  203  in the X-axis direction in  FIG. 4 , the control means  10  activates the laser beam application means  52  to carry out the above drilling step. Subsequently, the control means  10  activates the laser beam application means  52  to carry out the above drilling step each time the count value of the counter  104  reaches a value corresponding to the interval A or B between the electrodes  203  in the X-axis direction in  FIG. 4 . After the above drilling step is carried out on the electrode  203   e  at the most right end in  FIG. 4  out of the electrodes  203  formed on the device  202  at the most right end in the row E 1  of the semiconductor wafer  20 , as shown in  FIG. 7(   b ), the operation of the above processing-feed means  37  is suspended to stop the movement of the chuck table  36 . As a result, a hole  204  is formed in each of the electrodes  203  (not shown) of the semiconductor wafer  20 , as shown in  FIG. 7(   b ). 
     Thereafter, the control means  10  controls the above first indexing-feed means  38  or the above second indexing-feed means  43  to move (indexing-feed) the processing head  9  of the laser beam application means  52  in the indexing-feed direction perpendicular to the sheet in  FIG. 7(   b ). Meanwhile, the control means  10  receives, from a read head  433   b  of the second indexing-feed amount detection means  433 , a detection signal and counts the detection signals by means of the counter  104 . When the count value of the counter  104  reaches a value corresponding to the interval C between the electrodes  203  in the Y-axis direction in  FIG. 4 , the operation of the second indexing-feed means  43  is suspended to stop the movement of the processing head  9  of the laser beam application means  52 . As a result, the processing head  9  is positioned right above the electrode  203   j  (see  FIG. 4)  opposed to the above electrode  203   e . This state is shown in  FIG. 9(   a ). In the state shown in  FIG. 9(   a ), the control means  10  controls the above processing-feed means  37  so as to move (processing-feed) the chuck table  36  in the direction indicated by the arrow X 2  in  FIG. 9(   a ) at a predetermined moving rate and activates the laser beam application means  52  to carry out the above drilling step at the same time. Then, the control means  10  counts a detection signal from the read head  374   b  of the processing-feed amount detection means  374  by means of the counter  104  as described above and activates the laser beam application means  52  to carry out the above drilling step each time the count value reaches the interval A or B between the electrodes  203  in the X-axis direction in  FIG. 4 . After the above drilling step is carried out on the electrode  203   f  formed on the device  202  at the most left end in the row E 1  of the semiconductor wafer  20  as shown in  FIG. 9(   b ), the operation of the above processing-feed means  37  is suspended to stop the movement of the chuck table  36 . As a result, a hole  204  is formed in each of the electrodes  203  (not shown) of the semiconductor wafer  20 , as shown in  FIG. 9(   b ). 
     After the holes  204  are formed in the electrodes  203  on the devices  202  in the row E 1  of the semiconductor wafer  20  as described above, the control means  10  activates the processing-feed means  37  and the second indexing-feed means  43  to bring the second processing-feed start position coordinate values (a 2 ) stored in the second storage area  103   b  of the above random access memory (RAM)  103  out of the electrodes  203  formed on the devices  202  in the row E 2  of the semiconductor wafer  20  to a position right below the processing head  9  of the laser beam application means  52 . Then, the control means  10  controls the laser beam application means  52 , the processing-feed means  37  and the second indexing-feed means  43  to carry out the above drilling step on the electrodes  203  formed on the devices  202  in the row E 2  of the semiconductor wafer  20 . Thereafter, the above drilling step is also carried out on the electrodes  203  formed on the devices  202  in the rows E 3  to En of the semiconductor wafer  20 . As a result, a hole  204  is formed in each of all the electrodes  203  formed on the devices  202  of the semiconductor wafer  20 . 
     In the above drilling step, the pulse laser beam is not applied to the semiconductor wafer  20  in the areas of the intervals A and the areas of the intervals B in the X-axis direction in  FIG. 4 . Thus, since the pulse laser beam is not applied to the semiconductor wafer  20 , the above control means  10  stops RF to be applied to the first acousto-optic device  811  of the first acousto-optic deflection means  81 . As a result, a pulse laser beam oscillated by the pulse laser beam oscillation means  6  is applied and absorbed by the laser beam absorbing means  83  as shown by the one-dot chain line in  FIG. 2  and hence, is not guided to the above processing head  9 , whereby the pulse laser beam is not applied to the semiconductor wafer  20 . 
     As described above, in the laser beam processing machine in the illustrated embodiment, by adjusting the frequency of a high-frequency current to be applied to the first acousto-optic device  811  of the first acousto-optic deflection means  81  based on a detection signal from the read head  374   b  of the processing-feed amount detection means  374 , a plurality of pulses of the pulse laser beam can be applied to a predetermined processing position even in a state of the semiconductor wafer  20  being moved in the processing-feed direction. Therefore, the holes  204  can be formed efficiently. 
     Further, in the above drilling step, the amplitude of RF oscillated from the first RF oscillator  812  is adjusted by controlling the first output adjusting means  815  of the first acousto-optic deflection means  81  to adjust the amplitude of RF to be applied to the first acousto-optic device  811 , thereby making it possible to suitably adjust the output of the pulse laser beam. 
     Another embodiment of laser processing by activating the first acousto-optic deflection means  81  and the second acousto-optic deflection means  82  of the above-described laser beam application means  52  will be described with reference to  FIGS. 10(   a ) and  10 ( b ) 
     That is, when the optical axis of a pulse laser beam is deflected in the X-axis direction and the Y-axis direction sequentially by activating the first acousto-optic deflection means  81  and the second acousto-optic deflection means  82  in a state where the workpiece held on the above chuck table  36  has been moved in the processing-feed direction and further when a pulse laser beam is applied to the workpiece by adjusting the output of the pulse laser beam so as to form a plurality of holes  204  by 2-D processing such as trepanning, etc. as shown in  FIG. 10(   a ), a hole  205  having a desired size can be formed, as shown in  FIG. 10(   b ). 
     Still another embodiment of laser processing by activating the second acousto-optic deflection means  82  of the above-described laser beam application means  52  will be described with reference to  FIGS. 11(   a ) and  11 ( b ). 
     That is, the workpiece W is brought to a position right below the condenser lens  92  as shown in  FIG. 11(   a ) and moved (processing-fed) in the direction perpendicular to the sheet while a pulse laser beam is applied to the workpiece W to form a groove  206 . Then, the second acousto-optic deflection means  82  of the above laser beam application means  52  is activated to deflect the optical axis of a pulse laser beam in the indexing-feed direction (Y-axis direction) as shown in  FIG. 11(   b ) and the workpiece W is moved (processing-fed) in the direction perpendicular to the sheet while the pulse laser beam is applied thereto, thereby making it possible to form a plurality of grooves  206  in the workpiece W by only moving the workpiece W in the processing-feed direction without moving it in the indexing-feed direction. When the above groove  206  is to be formed, the first acousto-optic deflection means  81  is activated to change the output of the pulse laser beam at a predetermined position, thereby making it possible to change the depth of the groove  206  at the predetermined position. 
     Further, when the optical axis of the pulse laser beam is deflected for every other pulse by synchronizing a control for the absorption of the pulse laser beam oscillated by the pulse laser beam oscillation means  6  by the laser beam absorbing means  83  with the repetition frequency of the pulse laser beam without deflecting the optical axis of the pulse laser beam oscillated by the pulse laser beam oscillation means  6  by the first acousto-optic deflection means  81  of the laser beam application means  52  shown in  FIG. 2 , the pulse laser beam having a predetermined repetition frequency can be applied to the workpiece without changing its pulse width.