Laser beam machine with cylindrical lens system

A laser beam processing machine comprising a chuck table for holding a workpiece and a laser beam application means for applying a laser beam to the workpiece held on the chuck table, the laser beam application means comprising a laser beam oscillation means for oscillating a laser beam and a condenser for converging the laser beam oscillated by the laser beam oscillation means, wherein the condenser comprises a first cylindrical lens unit having a first cylindrical lens, a second cylindrical lens unit having a second cylindrical lens which is positioned such that its converging direction becomes perpendicular to the converging direction of the first cylindrical lens, and an interval adjustment mechanism for adjusting the interval between the first cylindrical lens unit and the second cylindrical lens unit.

FIELD OF THE INVENTION

The present invention relates to a laser beam processing machine for carrying out laser processing of a workpiece such as a semiconductor wafer and, more specifically, to a laser beam processing machine capable of adjusting the focal spot shape of a laser beam.

DESCRIPTION OF THE PRIOR ART

In the production process of a semiconductor device, a plurality of areas are sectioned by dividing lines called “streets” 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 each of which the device is formed. An optical device wafer having light receiving devices such as photodiodes or light emitting devices such as laser diodes laminated on the front surface of a sapphire substrate is also cut along streets to be divided into individual optical devices such as photodiodes or laser diodes which are widely used in electric appliances.

As a means of dividing a wafer such as the above semiconductor wafer or optical device wafer along the streets, JP-A 2004-9139 discloses a method in which a groove is formed by applying a pulse laser beam along the streets formed on the wafer, and the wafer is divided along the grooves.

The processing conditions of the laser beam applied to a workpiece can be suitably adjusted depending on the output, wavelength, repetition frequency, focal spot shape, etc. However, it is difficult to suitably change the focal spot shape to a circle or an ellipse whose long axis and short axis differ from each other in length and hence, there arises a problem that the adjustment of the processing conditions is restricted.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a laser beam processing machine capable of easily changing the focal spot shape of a laser beam to a circle or an ellipse whose long axis and short axis differ from each other in length.

To solve the above main technical problem, according to the present invention, there is provided a laser beam processing machine comprising a chuck table for holding a workpiece and a laser beam application means for applying a laser beam to the workpiece held on the chuck table, the laser beam application means comprising a laser beam oscillation means for oscillating a laser beam and a condenser for converging the laser beam oscillated by the laser beam oscillation means, wherein

the condenser comprises a first cylindrical lens unit having a first cylindrical lens, a second cylindrical lens unit having a second cylindrical lens which is positioned such that its converging direction becomes perpendicular to the converging direction of the first cylindrical lens, and an interval adjustment mechanism for adjusting the interval between the first cylindrical lens unit and the second cylindrical lens unit.

The above interval adjustment mechanism comprises a support board, a first support table which is mounted on the support board and holds the first cylindrical lens unit or the second cylindrical lens unit, a second support table which is arranged above the first support table in such a manner that it can move in the vertical direction along the support board, and holds the second cylindrical lens unit or the first cylindrical lens unit, and an adjusting means for adjusting the interval between the first support table and the second support table. The adjusting means comprises a first adjustment plate fixed to the support board, a second adjustment plate which is fixed to the second support table and arranged above the first adjustment plate and an adjusting screw means fitted in the second adjustment plate, and the end of a metering rod which constitutes the adjusting screw means and can move in a vertical direction comes into contact with the top surface of the first adjustment plate.

The above first cylindrical lens unit comprises a lens holding member which is circular and holds the first cylindrical lens, a first frame having a circular hollow for accepting the lens holding member, a second frame for holding the first frame, a turning adjustment means for turning the lens holding member along the inner wall of the circular hollow, and a moving adjustment means for moving the first frame relative to the second frame in a direction perpendicular to the converging direction of the first cylindrical lens; and the above second cylindrical lens unit comprises a lens holding member which is circular and holds the second cylindrical lens, a first frame having a circular hollow for accepting the lens holding member, a second frame for holding the first frame, a turning adjustment means for turning the lens holding member along the inner wall of the circular hollow, and a moving adjustment means for moving the first frame relative to the second frame in a direction perpendicular to the converging direction of the second cylindrical lens.

Since the laser beam processing machine of the present invention comprises the interval adjustment mechanism for adjusting the interval between the first cylindrical lens unit and the second cylindrical lens unit to adjust the interval between the first cylindrical lens unit and the second cylindrical lens unit, a focal spot having a circular section and a focal spot having an elliptic section can be formed, and further, the ratio of the long axis to the short axis of the focal spot having an elliptic section can be suitably changed. Therefore, the shape of a focal spot suitable for laser processing can be suitably selected.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of a laser beam processing machine constituted according to the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1is a perspective view of a laser beam processing machine constituted according to the present invention. The laser beam processing machine shown inFIG. 1comprises a stationary base2, a chuck table mechanism3for holding a workpiece that is mounted on the stationary base2in such a manner that it can move in a processing-feed direction indicated by an arrow X, a laser beam application unit support mechanism4that is mounted on the stationary base2in such a manner that it can move in an indexing-feed direction indicated by an arrow Y perpendicular to the direction indicated by the arrow X, and a laser beam application unit5mounted on the laser beam application unit support mechanism4in such a manner that it can move in a direction indicated by an arrow Z.

The above chuck table mechanism3comprises a pair of guide rails31and31, which are mounted on the stationary base2and arranged parallel to each other in the processing-feed direction indicated by the arrow X, a first sliding block32mounted on the guide rails31and31in such a manner that it can move in the processing-feed direction indicated by the arrow X, a second sliding block33mounted on the first sliding block32in such a manner that it can move in the indexing-feed direction indicated by the arrow Y, a cover table35supported on the second sliding block33by a cylindrical member34, and a chuck table36as a workpiece holding means. This chuck table36comprises an adsorption chuck361made of a porous material, and a workpiece, for example, a disk-like semiconductor wafer, is held on the adsorption chuck361by a suction means that is not shown. The chuck table36constituted as described above is rotated by a pulse motor (not shown) installed in the cylindrical member34.

The above first sliding block32has, on its undersurface, a pair of to-be-guided grooves321and321to be fitted to the above pair of guide rails31and31and, on the top surface, a pair of guide rails322and322formed parallel to each other along the indexing-feed direction indicated by the arrow Y. The first sliding block32constituted as described above can move along the pair of guide rails31and31in the processing-feed direction indicated by the arrow X by fitting the to-be-guided grooves321and321to the pair of guide rails31and31, respectively. The chuck table mechanism3in the illustrated embodiment comprises a processing-feed means37for moving the first sliding block32along the pair of guide rails31and31in the processing-feed direction indicated by the arrow X. The processing-feed means37comprises a male screw rod371arranged between the above pair of guide rails31and31parallel thereto and a drive source such as a pulse motor372for rotary-driving the male screw rod371. The male screw rod371is, at its one end, rotatably supported to a bearing block373fixed onto the above stationary base2and is, at the other end, transmission-coupled to the output shaft of the above pulse motor372. The male screw rod371is 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 block32. Therefore, by driving the male screw rod371in a normal direction or reverse direction with the pulse motor372, the first sliding block32is moved along the guide rails31and31in the processing-feed direction indicated by the arrow X.

The above second sliding block33has, on its undersurface, a pair of to-be-guided grooves331and331to be fitted to the pair of guide rails322and322formed on the top surface of the above first sliding block32and can move in the indexing-feed direction indicated by the arrow Y by fitting the to-be-guided grooves331and331to the pair of guide rails322and322, respectively. The chuck table mechanism3in the illustrated embodiment comprises a first indexing-feed means38for moving the second sliding block33in the indexing-feed direction indicated by the arrow Y along the pair of guide rails322and322formed on the first sliding block32. The first indexing-feed means38comprises a male screw rod381which is arranged between the above pair of guide rails322and322parallel thereto and a drive source such as a pulse motor382for rotary-driving the male screw rod381. The male screw rod381is, at its one end, rotatably supported to a bearing block383fixed onto the top surface of the above first sliding block32and is, at the other end, transmission-coupled to the output shaft of the above pulse motor382. The male screw rod381is 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 block33. Therefore, by driving the male screw rod381in a normal direction or reverse direction with the pulse motor382, the second sliding block33is moved along the guide rails322and322in the indexing-feed direction indicated by the arrow Y.

The above laser beam application unit support mechanism4comprises a pair of guide rails41and41which are mounted on the stationary base2and arranged parallel to each other in the indexing-feed direction indicated by the arrow Y and a movable support base42mounted on the guide rails41and41in such a manner that it can move in the direction indicated by the arrow Y. This movable support base42consists of a movable support portion421movably mounted on the guide rails41and41and a mounting portion422mounted on the movable support portion421. The mounting portion422is provided with a pair of guide rails423and423extending parallel to each other in the direction indicated by the arrow Z on one of its flanks. The laser beam application unit support mechanism4in the illustrated embodiment comprises a second indexing means43for moving the movable support base42along the pair of guide rails41and41in the indexing-feed direction indicated by the arrow Y. This second indexing means43comprises a male screw rod431arranged between the above pair of guide rails41and41parallel thereto and a drive source such as a pulse motor432for rotary-driving the male screw rod431. The male screw rod431is, at its one end, rotatably supported to a bearing block (not shown) fixed on the above stationary base2and is, at the other end, transmission coupled to the output shaft of the above pulse motor432. The male screw rod431is 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 portion421constituting the movable support base42. Therefore, by driving the male screw rod431in a normal direction or reverse direction with the pulse motor432, the movable support base42is moved along the guide rails41and41in the indexing-feed direction indicated by the arrow Y.

The laser beam application unit5in the illustrated embodiment comprises a unit holder51and a laser beam application means52secured to the unit holder51. The unit holder51has a pair of to-be-guided grooves511and511to be slidably fitted to the pair of guide rails423and423formed on the above mounting portion422and is supported in such a manner that it can move in the direction indicated by the arrow Z when the to-be-guided grooves511and511are fitted to the above guide rails423and423, respectively.

The laser beam application unit5in the illustrated embodiment comprises a moving means53for moving the unit holder51along the pair of guide rails423and423in the direction indicated by the arrow Z. The moving means53comprises a male screw rod (not shown) arranged between the pair of guide rails423and423and a drive source such as a pulse motor532for rotary-driving the male screw rod. By driving the male screw rod (not shown) in a normal direction or reverse direction with the pulse motor532, the unit holder51and the laser beam application means52are moved along the guide rails423and423in the direction indicated by the arrow Z. In the illustrated embodiment, the laser beam application means52is moved up by driving the pulse motor532in a normal direction and moved down by driving the pulse motor532in the reverse direction.

The illustrated laser beam application means52has a cylindrical casing521that is secured to the above unit holder51and extends substantially horizontally. The laser beam application means52comprises a pulse laser beam oscillation means522and a transmission optical system523installed in the casing521as shown inFIG. 2and a processing head6for applying a pulse laser beam oscillated by the pulse laser beam oscillation means522to the workpiece held on the above chuck table, which is attached to the end of the casing521. The above pulse laser beam oscillation means522comprises a pulse laser beam oscillator522acomposed of a YAG laser oscillator or YVO4laser oscillator and a repetition frequency setting means522bconnected to the pulse laser beam oscillator522a. The transmission optical system523has suitable optical elements such as beam splitter, etc.

The above processing head6is composed of a direction changing mirror61and a condenser7, as shown inFIG. 3. The direction changing mirror61changes the direction of the pulse laser beam that is oscillated from the above pulse laser beam oscillation means522and irradiated through the transmission optical system523toward the condenser7. The condenser7in the illustrated embodiment comprises a first cylindrical lens unit8ahaving a first cylindrical lens81a, a second cylindrical lens unit8bhaving a second cylindrical lens81bpositioned such that its converging direction becomes perpendicular to that of the first cylindrical lens81a, and an interval adjustment mechanism for adjusting the interval between the first cylindrical lens unit8aand the second cylindrical lens unit8b, which will be described later. The above direction changing mirror61, the first cylindrical lens unit8a, the second cylindrical lens unit8band the interval adjustment mechanism later described are installed in a processing head housing60secured to the end of the above casing521as shown inFIG. 4.

The first cylindrical lens unit8awill be described with reference toFIGS. 5 to 7.FIG. 5is a perspective view of the first cylindrical lens unit8a, andFIG. 6is an exploded perspective view of the first cylindrical lens unit8ashown inFIG. 5.

The first cylindrical lens unit8ashown inFIG. 5andFIG. 6comprises the first cylindrical lens81a, a lens holding member82for holding the first cylindrical lens81a, a first frame83for holding the lens holding member82, and a second frame84for holding the first frame83.

The first cylindrical lens81ahas a semicircular section as shown inFIG. 7. The focal distance of this first cylindrical lens81ais set to 80 mm in the illustrated embodiment. The lens holding member82for holding the first cylindrical lens81ais circular and made of a synthetic resin in the illustrated embodiment. The first cylindrical lens81ais embedded in the lens holding member82made of a synthetic resin in such a manner that its top surface and bottom surface are exposed. A projecting piece821is formed from one position of the outer peripheral surface of the lens holding member82as shown inFIG. 6.

The above first frame83has, as shown inFIG. 6, a shape of square with a side length E, and a circular hollow831for accepting the above lens holding member82and a working chamber832for accepting the projecting piece821formed on the lens holding member82are formed in the top surface of the first frame83. A hole831bis formed in the center portion of the bottom wall831aof the circular hollow831. A recess832bwhich is a spring seat is formed in the wall surface832aforming the working chamber832. A screw hole832cis formed on the axis line of the recess832bin the first frame83. The lens holding member82is, as shown inFIG. 5, fitted in the circular hollow831of the first frame83thus constituted, and the projecting piece821is fitted in the working chamber832. Therefore, the lens holding member82fitted in the circular hollow831of the first frame83can turn along the inner wall of the circular hollow831as far as the projecting piece821can move within the working chamber832. A compression coil spring85is interposed between the above recess832band the projecting piece821. A first adjustment screw86is screwed into the above screw hole832c, and the end of the first adjustment screw86is designed to be brought into contact with the projecting piece821. Therefore, when the first adjustment screw86is moved forward by rotating in one direction, the lens holding member82is turned in one direction against the spring force of the compression coil spring85, and when the first adjustment screw86is moved backward by rotating in the other direction, the lens holding member82is turned in the other direction by the spring force of the compression coil spring85. Thus, the projecting piece821formed on the lens holding member82, the first adjustment screw86and the compression coil spring85function as a turning adjustment means for turning the lens holding member82along the inner wall of the circular hollow831.

The above second frame84is rectangular, and a rectangular hollow841for accepting the first frame83is formed in the top surface of the second frame84as shown inFIG. 6. This rectangular hollow841has a width A corresponding to the length E of one side of the above square first frame83and a length B larger than the length E of one side of the first frame83. The rectangular hollow841is sectioned by a bottom wall842aand side walls842b,842c,842dand842e. A hole842fis formed in the center portion of the bottom wall842a. A recess842gwhich is a spring seat is formed in the inner surface of the side wall842dsectioning the rectangular hollow841. A screw hole842his formed in the side wall842eopposite to the side wall842dhaving the recess842g. A prolonged hole842jfor accepting insertion of the first adjustment screw86is formed in the side wall842bof the second frame84. The above first frame83is fitted to the rectangular hollow841of the second frame84constituted as described above, as shown inFIG. 5. A compression coil spring87is interposed between the recess842gformed in the inner surface of the above side wall842dand the side wall of the first frame83. A second adjustment screw88is screwed into the screw hole842hformed in the side wall842e, and the end of the second adjustment screw88is designed to be brought into contact with the side wall of the first frame83. Therefore, when the second adjustment screw88is moved forward by rotating in one direction, the first frame83is moved in one direction against the spring force of the compression coil spring87and when the second adjustment screw88is moved backward by rotating in the other direction, the first frame83is moved in the other direction by the spring force of the compression coil spring87. Thus, the second adjustment screw88and the compression coil spring87function as a moving adjustment means for moving the first frame83relative to the second frame84in a direction perpendicular to the converging direction of the first cylindrical lens81a.

A description is subsequently given of the above second cylindrical lens unit8bwith reference toFIG. 8andFIG. 9.FIG. 8is a perspective view of the second cylindrical lens unit8bandFIG. 9is an exploded perspective view of the second cylindrical lens unit8bshown inFIG. 8.

The second cylindrical lens unit8bshown inFIG. 8andFIG. 9comprises the second cylindrical lens81b, a lens holding member82for holding the second cylindrical lens81b, a first frame83for holding the lens holding member82and a second frame84for holding the first frame83, like the above first cylindrical lens unit8a. Since the lens holding member82, the first frame83and the second frame84constituting the second cylindrical lens unit8bare substantially identical to the lens holding member82, the first frame83and the second frame84constituting the above first cylindrical lens unit8a, the same reference symbols are given to the same members and their detailed descriptions are omitted. The second cylindrical lens81bconstituting the second cylindrical lens unit8bhas a focal distance of 40 mm in the illustrated embodiment.

The first cylindrical lens unit8aand the second cylindrical lens unit8bconstituted as described above are set in the interval adjustment mechanism10shown inFIG. 10. A description of the interval adjustment mechanism10is given below.

The interval adjustment mechanism10shown inFIG. 10comprises a support board11, a first support table12installed at the lower end of the support board11, and a second support table13arranged in such a manner that it can move in the vertical direction along the front surface of the support board11.

A guide groove111is formed in the center portion of the front surface of the support board11in the vertical direction. A first adjustment plate112is fixed to the intermediate portion of the side wall of the support board11. The first support table12projects from the front surface of the support board11at a right angle. A hole121is formed in the center portion of this first support table12. Positioning rails122and123each extending from the front surface of the support board11at a right angle are formed at the both side ends of the first support table12. The interval between the positioning rails122and123is set to a size corresponding to the width of the second frame84constituting the above second cylindrical lens unit8b.

The above second support table13is composed of a support portion14and a table portion15installed at the lower end of the support portion14. The support portion14has on the back a to-be-guided rail141that is to be fitted to the guide groove111formed in the above support board11. By fitting this to-be-guided rail141to the guide groove111, the second support table13is supported to the support board11in such a manner that it can move in the vertical direction along the guide groove111. A second adjustment plate142positioned above the first adjustment plate112is fixed to the top end of the support portion14. The above table portion15projects from the front surface of the support portion14at a right angle. A hole151is formed in the center portion of the table portion15. Positioning rails152and153each extending parallel to the front surface of the support portion14are formed at the front and rear ends of the table portion15. The interval between the positioning rails152and153is set to a size corresponding to the width of the second frame84constituting the above first cylindrical lens unit8a.

An adjusting screw means16is fitted in the above second adjustment plate142. This adjusting screw means16comprises a support cylinder161mounted on the second adjustment plate142, a metering rod162installed in the support cylinder161in such a manner that it can move in the vertical direction, and an adjusting dial163for moving the metering rod162in the vertical direction and has the same structure as a micrometer. In the thus constituted adjusting screw means16, the end (lower end) of the metering rod162comes into contact with the top surface of the first adjustment plate112to restrict the position in the vertical direction of the support portion14constituting the second support table13. Therefore, by moving the metering rod162in the vertical direction by turning the adjusting dial163in one direction or the other direction, the position in the vertical direction of the support portion14, that is, the interval between the table portion15installed at the lower end of the support portion14and the first support table12can be changed. At this point, the movement of the metering rod162is adjusted based on scales on the support cylinder161and the adjusting dial163to suitably adjust the interval between the table portion15of the second support table13and the first support table12.

The above second cylindrical lens unit8bis set on the first support table12of the interval adjustment mechanism10constituted as described above, as shown inFIG. 11. That is, the second frame84of the second cylindrical lens unit8bis placed between the positioning rails122and123of the first support table12. The second cylindrical lens unit8bplaced at a predetermined position on the first support table12is fixed on the first support table12by a suitable fixing means that is not shown. The converging direction of the second cylindrical lens81bof the second cylindrical lens unit8bplaced on the first support table12is set to the direction indicated by the arrow X inFIG. 11.

The above first cylindrical lens unit8ais set on the table portion15of the second support table13of the interval adjustment mechanism10. That is, the second frame84of the first cylindrical lens unit8ais placed between the positioning rails152and153of the table portion15constituting the second support table13. The first cylindrical lens unit8aplaced at a predetermined position on the table portion15of the second support table13is fixed onto the table portion15of the second support table13by a suitable fixing means that is not shown. The converging direction of the first cylindrical lens81aof the first cylindrical lens unit8aplaced on the table portion15of the second support table13is set to the direction indicated by the arrow Y inFIG. 11.

Returning toFIG. 1, an image pick-up means17for detecting the area to be processed by the above laser beam application means52is attached to the front end portion of the casing521constituting the above laser beam application means52. This image pick-up means17is constituted by an image pick-up device (CCD) and supplies an image signal to a control means that is not shown.

The laser beam processing machine in the illustrated embodiment is constituted as described above, and its function will be described hereinunder.

The focal spot shape of a laser beam irradiated by the above-described laser beam application means52will be first described with reference toFIGS. 12(a) to12(c) andFIGS. 13(a) to13(c).

When the interval between the first cylindrical lens81aand the second cylindrical lens81bis set to 40 mm as shown inFIGS. 12(a) and12(b), as the focal distance of the first cylindrical lens81ais set to 80 mm in the illustrated embodiment, the focal point P1of a laser beam L converged by the first cylindrical lens81ais at a position 40 mm below the second cylindrical lens unit8bas shown inFIG. 12(a). Meanwhile, as the focal distance of the second cylindrical lens81bis set to 40 mm in the illustrated embodiment, the focal point P2of the laser beam L converged by the second cylindrical lens81bis at a position 40 mm below the second cylindrical lens unit8bas shown inFIG. 12(b). The focal point P1and the focal point P2are thus in the same position. As a result, the laser beam L having a circular section applied to the first cylindrical lens81ais converged in the direction indicated by the arrow Y by the first cylindrical lens81aand in the direction indicated by the arrow X by the second cylindrical lens81b, thereby forming a focal spot S1having a circular section at the focal points P1and P2as shown in the enlarged view ofFIG. 12(c). Therefore, when the workpiece is set at the focal points P1and P2, the workpiece can be processed by means of the focal spot S1having a circular section.

Next, when the interval between the first cylindrical lens81aand the second cylindrical lens81bis set to 20 mm as shown inFIGS. 13(a) and13(b), as the focal distance of the first cylindrical lens81ais set to 80 mm, the focal point P1of the laser beam L converged by the first cylindrical lens81ais at a position 60 mm below the second cylindrical lens unit8bas shown inFIG. 13(a). Meanwhile, as the focal distance of the second cylindrical lens81bis set to 40 mm, the focal point P2of the laser beam L converged by the second cylindrical lens81bis at a position 40 mm below the second cylindrical lens unit8bas shown inFIG. 13(b). Therefore, the laser beam L to be converged by the second cylindrical lens81bis converged at the focal point P2and is expanded in the direction indicated by the arrow X until it reaches the above focal point P1. As a result, at the position of the focal point P1, a focal spot S2having an elliptic section is formed as shown in the enlarged view ofFIG. 13(c). The long axis D1of the elliptic focal spot S2is formed in the direction indicated by the arrow X. The ratio of the long axis D1to the short axis D2of the focal spot S2having an elliptic section can be adjusted by changing the interval between the first cylindrical lens81aand the second cylindrical lens81b. Therefore, when the workpiece is set at the position of the focal point P1, the workpiece can be processed by means of the focal spot S2having an elliptic section.

A description is subsequently given of a processing method for forming a groove in the workpiece by means of the focal spot S2having an elliptic section shown inFIGS. 13(a) to13(c) with reference toFIG. 1andFIG. 14.

A semiconductor wafer W as the workpiece is first placed on the chuck table36of the laser beam processing machine shown inFIG. 1. The semiconductor wafer W is suction-held on the chuck table36by activating a suction means that is not shown. Streets are formed in a lattice pattern on the front surface of the semiconductor wafer W and a device such as IC or LSI is formed in a plurality of areas sectioned by the lattice pattern-like streets. The chuck table36suction-holding the semiconductor wafer W is brought to a position right below the image pick-up means17by the processing-feed means37. After the chuck table36is positioned right below the image pick-up means17, alignment work for detecting the area to be processed of the semiconductor wafer W is carried out by the image pick-up means17and the control means that is not shown. That is, the image pick-up means17and the control means (not shown) carry out image processing such as pattern matching, etc. to align a street formed in a predetermined direction of the semiconductor wafer W with the condenser7of the laser beam application means52for applying a laser beam along the street, thereby performing the alignment of a laser beam application position. The alignment of the laser beam application position is also carried out on streets formed on the semiconductor wafer W in a direction perpendicular to the above predetermined direction.

After the alignment of the laser beam application position is carried out by detecting the street formed on the semiconductor wafer W held on the chuck table36as described above, as shown inFIG. 14(a), the chuck table36is moved to a laser beam application area where the condenser7of the laser beam application means52is located so as to bring one end (left end inFIG. 14(a)) of the predetermined street to a position right below the condenser7. The long axis D1shown inFIG. 13(c) of the focal spot S2having an elliptic section of the laser beam irradiated from the condenser7is aligned with the street. The focal point P1of the pulse laser beam applied from the condenser7is set to a position near the front surface (top surface) of the semiconductor wafer W. The moving means53for moving the laser beam application means52in the direction indicated by the arrow Z along the guide rails423and423is used to set the focal point P1to a position near the front surface (top surface) of the semiconductor wafer. The chuck table36, that is, the semiconductor wafer W is then moved in the direction indicated by the arrow X1inFIG. 14(a) at a predetermined processing-feed rate while a pulse laser beam of a wavelength having absorptivity for the semiconductor wafer W is applied from the condenser7of the laser beam application means52. When the other end (right end inFIG. 14(b)) of the street reaches a position right below the condenser7, the application of the pulse laser beam is suspended, and the movement of the chuck table36, that is, the semiconductor wafer W is stopped. As a result, a groove G is formed along the street in the semiconductor wafer W as shown inFIG. 14(b) (groove forming step).

To form a hole such as a via hole in the workpiece such as the semiconductor wafer W by using the focal spot S1having a circular section shown inFIG. 12(c), the via hole-forming position of the semiconductor wafer W held on the chuck table36is brought to a position right below the condenser7. The focal points P1and P2of the pulse laser beam irradiated from the condenser7are set to a position near the front surface (top surface) of the semiconductor wafer W. The moving means53for moving the laser beam application means52along the guide rails423and423in the direction indicated by the arrow Z is used to set the focal points P1and P2to a position near the front surface (top surface) of the semiconductor wafer W. Then, a predetermined number of pulses of the pulse laser beam of a wavelength having absorptivity for the semiconductor wafer W are applied from the condenser7of the laser beam application mans52to form a hole such as a via hole at a predetermined position of the semiconductor wafer W.

As described above, since the laser beam processing machine of the present invention comprises the interval adjustment mechanism10for adjusting the interval between the first cylindrical lens unit8aand the second cylindrical lens unit8bto adjust the interval between the first cylindrical lens unit8aand the second cylindrical lens unit8b, the focal spot S1having a circular section and the focal spot S2having an elliptic section can be formed, and the ratio of the long axis D1to the short axis D2of the focal spot S2having an elliptic section can be suitably changed. Therefore, the shape of the focal spot suitable for application of laser processing can be suitably selected. The length of the short axis D2of the focal spot S2having an elliptic section can be changed by suitably changing the lens holding member for holding the cylindrical lens having a different focal distance and holding it in the first frame.