LASER PROCESSING MACHINE

A laser beam irradiation unit of a laser processing machine includes a laser oscillator, an image-forming element that focuses, on a workpiece, a laser beam emitted from the laser oscillator, and a phase modulation unit arranged between the laser oscillator and the image-forming element and configured to cause a phase difference in the laser beam such that the laser beam forms an intensity distribution along a Gaussian distribution in an X-axis direction parallel to each street set on the workpiece and forms an intensity distribution along a top-hat profile at an image-forming point in a Y-axis direction as a width direction of the each street set on the workpiece.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a laser processing machine.

Description of the Related Art

As a method for singulating a workpiece such as a semiconductor wafer, blade dicing that causes a high-speed rotating, thin disk-shaped blade to cut into the workpiece is in common use. Meanwhile, in recent years, laser dicing that performs dicing of a workpiece by applying a laser beam along projected dicing lines (streets) has also been developed and adopted. In this laser dicing, there has been proposed a technology that adjusts lines to be processed, by modifying the profile of an image to be formed by a laser beam on a workpiece, through a mask (see, for example, JP 2010-089094A).

SUMMARY OF THE INVENTION

The use of the method described in JP 2010-089094A makes it possible to apply processing in a desired profile to a workpiece, but on the other hand, blocks most of a laser beam by a mask, thereby leading to a problem that the energy permitted to contribute to the processing is reduced.

The present invention therefore has as an object thereof the provision of a laser processing machine which can process a workpiece with a laser beam of a desired profile without attenuation of its energy that can contribute to the processing.

In accordance with a first aspect of the present invention, there is provided a laser processing machine for applying a laser beam to a workpiece that has a plurality of intersecting streets, along the streets to apply processing to the workpiece. The laser processing machine includes a holding table that holds the workpiece, a laser beam irradiation unit that applies the laser beam to the workpiece held on the holding table, an X-axis direction moving unit that carries out relative processing feed of the workpiece and an image-forming point of the laser beam in an X-axis direction, and a Y-axis direction moving unit that carries out relative indexing feed of the workpiece and the image-forming point of the laser beam in a Y-axis direction orthogonal to the X-axis direction. The laser beam irradiation unit includes a laser oscillator, an image-forming element that focuses, on the workpiece, the laser beam emitted from the laser oscillator, and a phase modulation unit arranged between the laser oscillator and the image-forming element and configured to cause a phase difference in the laser beam such that the laser beam forms an intensity distribution along a Gaussian distribution in the X-axis direction parallel to each street set on the workpiece and forms an intensity distribution along a top-hat profile at the image-forming point in the Y-axis direction as a width direction of the each street set on the workpiece.

Preferably, the phase modulation unit may be a phase plate capable of adjusting a phase of light, and the phase plate may include a recessed portion or a protruding portion formed such that the intensity distribution is formed along the top-hat profile in the Y-axis direction as the width direction of the each street set on the workpiece.

In accordance with a second aspect of the present invention, there is provided a laser processing machine for applying a laser beam to a workpiece that has a plurality of intersecting streets, along the streets to apply processing to the workpiece. The laser processing machine includes a holding table that holds the workpiece, a laser beam irradiation unit that applies the laser beam to the workpiece held on the holding table, an X-axis direction moving unit that carries out relative processing feed of the workpiece and an image-forming point of the laser beam in an X-axis direction, and a Y-axis direction moving unit that carries out relative indexing feed of the workpiece and the image-forming point of the laser beam in a Y-axis direction orthogonal to the X-axis direction. The laser beam irradiation unit includes a laser oscillator, an image-forming element that focuses, on the workpiece, the laser beam emitted from the laser oscillator, and a first phase plate and a second phase plate arranged between the laser oscillator and the image-forming element and configured to cause a phase difference in the laser beam such that the laser beam forms an intensity distribution along a Gaussian distribution in the X-axis direction parallel to each street set on the workpiece and forms an intensity distribution along a top-hat profile at the image-forming point in the Y-axis direction as a width direction of the each street set on the workpiece. The first phase plate and the second phase plate are configured to be movable relative to each other, and an amount of relative movement between the first phase plate and the second phase plate is adjusted on the basis of a beam diameter of the laser beam incident to the first phase plate and the second phase plate.

Preferably, the first phase plate and the second phase plate may each be configured to have a large thickness region and a small thickness region, the first phase plate and the second phase plate may be arranged such that the large thickness region of the first phase plate faces the small thickness region of the second phase plate and the small thickness region of the first phase plate faces the large thickness region of the second phase plate, and the top-hat profile may be adjusted in width by an adjustment of an overlapping width of the small thickness region of the first phase plate and the small thickness region of the second phase plate.

The present invention realizes the hat-top profile by changing the intensity distribution of the laser beam from the Gaussian distribution to an airy disk pattern with the phase modulation unit unlike the related art, that is, without using a mask that attenuates the energy of the laser beam by 60% to 70%, and then allowing the laser beam to form an image, and therefore can perform laser processing of the workpiece with a laser beam of a desired profile without attenuation of its energy that can contribute to the laser processing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the attached drawings, a description will be made in detail regarding embodiments of the present invention. However, the present invention shall not be limited by details that will be described in the subsequent embodiments. The elements of configurations that will hereinafter be described include those readily conceivable to persons skilled in the art and substantially the same ones. Further, the configurations that will hereinafter be described can be combined appropriately. Moreover, various omissions, replacements, and modifications of configurations can be made without departing from the spirit of the present invention.

First Embodiment

A laser processing machine1according to a first embodiment of the present invention will be described with reference toFIGS.1through9.FIG.1is a perspective view illustrating a configuration example of the laser processing machine1according to the first embodiment. As illustrated inFIG.1, the laser processing machine1according to the first embodiment includes a holding table10, a laser beam irradiation unit20, an imaging unit30, an X-axis direction moving unit41, a Y-axis direction moving unit42, a Z-axis direction moving unit43, a display unit50, an input unit60, and a controller70.

As illustrated inFIG.1, a workpiece100to be processed by the laser processing machine1according to the first embodiment is, for example, a disk-shaped semiconductor wafer, an optical device wafer, or the like which is made of a base material such as silicon, sapphire, silicon carbide (SiC), gallium arsenide, or glass. The workpiece100has chip-size devices103formed in regions defined by a plurality of streets102formed in a grid pattern on a planar front surface101as illustrated inFIG.1. In the first embodiment, the workpiece100, as illustrated inFIG.1, includes a self-adhesive tape105bonded to a back surface104on a side opposite to the front surface101, and an annular frame106attached to an outer edge portion of the self-adhesive tape105, but not limited to the foregoing in the present invention. In the present invention, the workpiece100may also be a rectangular package substrate, a ceramic plate, a glass plate, or the like having a plurality of devices sealed with resin.

The holding table10includes a disk-shaped frame body with a recessed portion formed therein and a disk-shaped suction portion fitted in the recessed portion. The suction portion of the holding table10is formed from a porous ceramic or the like having a number of pores, and is connected to a vacuum suction source (not illustrated) via a vacuum suction channel (not illustrated). The suction portion of the holding table10has an upper surface which, as illustrated inFIG.1, acts as a holding surface11. When the workpiece100is placed on the holding surface11, the holding surface11holds the placed workpiece100by suction under a negative pressure introduced from the vacuum suction source. In the first embodiment, the workpiece100is placed on the holding surface11with the front surface101directed upward, and the holding surface11holds the placed workpiece100by suction from a side of the back surface104via the self-adhesive tape105. The holding surface11and an upper surface of the frame body of the holding table10are arranged on the same plane, and lie horizontally with an XY plane that is a horizontal plane.

The holding table10is disposed movably in an X-axis direction, which is parallel to a horizontal direction, by the X-axis direction moving unit41, and is also disposed movably in a Y-axis direction, which is parallel to the horizontal direction and is orthogonal to the X-axis direction, by the Y-axis direction moving unit42. The holding table10is moved along the X-axis direction and the Y-axis direction by the X-axis direction moving unit41and the Y-axis direction moving unit42, respectively, so that the workpiece100held on the holding table10is moved in the X-axis direction and the Y-axis direction, respectively, relative to an image-forming point330(seeFIG.2) of a laser beam203(seeFIG.2) formed by the laser beam irradiation unit20and to the imaging unit30. The holding table10is disposed rotatably about a Z-axis, which is parallel to a vertical direction and is orthogonal to the XY plane, by a rotary drive source (not illustrated). The holding table10is appropriately rotated by the rotary drive source to adjust its direction about the Z-axis such that the streets102in desired one of the directions of the workpiece100held on the holding surface11become parallel to the X-axis direction.

FIG.2is a cross-sectional view illustrating a configuration example of the laser beam irradiation unit20ofFIG.1.FIG.3is a graph illustrating an example of an intensity distribution of a laser beam201emitted by a laser oscillator21ofFIG.2.FIGS.4and5are a perspective view and a top view, respectively, which illustrate a phase modulation unit22ofFIG.2.FIGS.6and7are graphs illustrating examples of intensity distributions of a laser beam202and the laser beam203both formed by the laser beam irradiation unit20ofFIG.2.FIG.8is a top view illustrating an example of an intensity profile of the laser beam203formed by the laser beam irradiation unit20ofFIG.2.FIG.9is a top view illustrating an example of the image-forming point330of the laser beam203formed by the laser beam irradiation unit20ofFIG.2. It is to be noted that, in the graphs illustrated inFIGS.3,6, and7, the abscissas each indicate the position in the Y-axis direction, which is a width direction of the streets102, as plotted using an optical path as an origin, and the ordinates indicate the intensities of the laser beams201,202, and203, respectively. It is also to be noted that, in a frame ofFIG.8, a horizontal direction in the plane of the paper sheet represents the position in the X-axis direction parallel to the streets102, a vertical direction in the plane of the paper sheet represents the position in the Y-axis direction, the dot density represents the intensity of the laser beam203, and a higher dot density indicates a higher intensity of the laser beam203.

The laser beam irradiation unit20, as illustrated inFIG.2, has the laser oscillator21, the phase modulation unit22, and an image-forming element23. The laser oscillator21emits the laser beam201of a wavelength having absorptivity for the workpiece100, along a Z-axis direction toward the workpiece100held on the holding table10. The laser beam201forms an intensity distribution301, centering at the optical path, along a Gaussian distribution in both the X-axis direction and, as illustrated inFIG.3, the Y-axis direction. The laser beam201is in a pulse form, for example, of a 5 mm beam diameter and a 355 nm wavelength in the first embodiment, but not limited to this in the present invention.

The phase modulation unit22, as illustrated inFIG.2, is arranged between the laser oscillator21and the image-forming element23on the optical path of the laser beam201emitted from the laser oscillator21. As illustrated inFIGS.2,4, and5, the phase modulation unit22is a phase plate capable of adjusting the phase of light. The phase plate is formed in a plate shape sufficiently larger than the beam diameter of the laser beam201in both the X-axis direction and the Y-axis direction, and has a pair of a first surface25and a second surface26parallel to the XY plane and orthogonal to the optical path of the laser beam201emitted from the laser oscillator21. As the phase modulation unit22, one obtained, for example, by forming synthetic quartz which has a refractive index of 1.449 into a plate shape of a 6 mm thickness is used, for example. The first surface25is directed upward in the Z-axis direction, and the second surface26is directed downward in the Z-axis direction.

In the phase modulation unit22, a recessed portion27is formed in the first surface25such that an intensity distribution302along such an airy disk pattern as illustrated inFIG.6is formed in the Y-axis direction. The recessed portion27is specifically a groove which extends along the X-axis direction over a length sufficiently greater than the beam diameter of the laser beam201, is symmetrical with respect to a plane that includes the optical path of the laser beam201, and is parallel to an X-axis, and which has a quadrilateral (rectangular) shape in a cross-section along a YZ plane. The recessed portion27has a width28in the Y-axis direction, which is dimensioned to allow the laser beam201to straddle the recessed portion27in a width direction, specifically, has a predetermined dimension narrower than the beam diameter of the laser beam201. The width28of the recessed portion27is determined on the basis of the beam diameter of the laser beam201and a desired value of a width310(seeFIG.7) of a top-hat profile of a below-described intensity distribution303(seeFIG.7) of the laser beam203to be applied to the workpiece100.

The recessed portion27has a depth29in the Z-axis direction, which has a predetermined dimension capable of causing a predetermined phase difference (for example, a phase difference of π/2) in the laser beam201, which passes through the phase modulation unit22, by a difference in the thickness of the laser beam201in the direction of its optical path, the difference being equivalent to the depth29formed by the recessed portion27. The depth29of the recessed portion27is determined according to the refractive index of a base material of the phase modulation unit22, and is, for example, approximately 395 nm if the base material of the phase modulation unit22is synthetic quartz.

Owing to the formation of the recessed portion27of the shape as mentioned above, the phase modulation unit22induces no modulation in phase on the laser beam201incident from the first surface25because the laser beam201does not straddle a step formed by the recessed portion27, in the X-axis direction in which the recessed portion27extends. In the Y-axis direction in which the step is formed by the recessed portion27, on the other hand, the laser beam201straddles the step formed by the recessed portion27. A phase difference is therefore caused by the step of the recessed portion27to induce a modulation in phase, so that the intensity distribution302along the airy disk pattern can be formed. This allows the phase modulation unit22to form the intensity distribution301along the Gaussian distribution like the laser beam201in the X-axis direction, and also to cause the phase difference in the laser beam201incident from the first surface25such that the intensity distribution302is formed along the airy disk pattern in the Y-axis direction.

When the laser beam201is incident from the first surface25, the phase modulation unit22emits, from the second surface26, the laser beam202with the intensity distribution301formed along the Gaussian distribution in the X-axis direction and the intensity distribution302formed along the airy disk pattern in the Y-axis direction. It is to be noted that, as will be mentioned below, the intensity distribution302along the airy disk pattern is converted, as a result of the formation of an image through the image-forming element23, into the intensity distribution303along the top-hat profile at the image-forming point330as illustrated inFIG.7.

The phase modulation unit22includes the recessed portion27formed in the first surface25in the first embodiment. Without being limited to this configuration in the present invention, a protruding portion may be formed on the first surface25. It is to be noted that the protruding portion in this alternative extends in the X-axis direction, and its cross-sectional shape along the YZ plane is rectangular, has a width of a dimension similar to that of the width28of the recessed portion27, and has a height of a dimension similar to that of the depth29of the recessed portion27. Even if the protruding portion is formed instead of the recessed portion27as described above, the phase modulation unit22induces a modulation in phase similar to that in the formation of the recessed portion27. When the laser beam201is incident from the first surface25, the laser beam202is therefore emitted from the second surface26with the intensity distribution301formed along the Gaussian distribution in the X-axis direction and the intensity distribution302formed along the airy disk pattern in the Y-axis direction. Further, the phase modulation unit22is not limited to these configurations in the present invention, and the recessed portion27or the protruding portion may be formed in or on the second surface26instead of the first surface25, or may be formed in or on each of the first surface25and the second surface26.

Further, in the phase modulation unit22, the depth29of the recessed portion27may be set to be the same as the plate thickness of the phase modulation unit22. In other words, the phase modulation unit22may be formed in a shape such that a gap of a width similar to the width28in the Y-axis direction is formed extending through in the direction of the optical path of the laser beam201and the laser beam201passes the phase plate on sides of only its outer peripheries in the Y-axis direction.

The image-forming element23focuses the laser beam202emitted from the laser oscillator21and modulated in phase by the phase modulation unit22, and forms an image on the workpiece100held on the holding table10, thereby forming the image-forming point330. As described above, the image-forming element23focuses the laser beam202having the intensity distribution301formed along the Gaussian distribution in the X-axis direction and the intensity distribution302formed along the airy disk pattern in the Y-axis direction, thereby converting the laser beam202into the laser beam203having the intensity distribution301formed along the Gaussian distribution in the X-axis direction and the intensity distribution303formed along the top-hat profile in the Y-axis direction as illustrated inFIG.7.

The width310of the top-hat profile of the intensity distribution303can be set at a desired value equivalent to the width of processed grooves, which are to be formed along the streets102, by appropriately setting the width28of the recessed portion27.

The laser beam203formed through the image-forming element23forms an intensity profile320having a breadth equivalent to the width310of the intensity distribution303in the Y-axis direction as illustrated inFIG.8. When this laser beam203is applied to each street102on the workpiece100, the image-forming point330of a profile equivalent to the intensity profile320is formed as illustrated inFIG.9.

As described above, the laser beam irradiation unit20emits, from the laser oscillator21, the laser beam201with the intensity distribution301formed along the Gaussian distribution, forms the laser beam203with the intensity distribution301formed along the Gaussian distribution in the X-axis direction and the intensity distribution303formed along the top-hat profile in the Y-axis direction through the phase modulation unit22and the image-forming element23, and applies the laser beam203to the workpiece100held on the holding table10, to form the image-forming point330on the workpiece100.

The image-forming element23included in the laser beam irradiation unit20is disposed movably in the Z-axis direction by the Z-axis direction moving unit43. When the image-forming element23included in the laser beam irradiation unit20is moved in the Z-axis direction by the Z-axis direction moving unit43, the image-forming point330of the laser beam203, the image-forming point330being formed by the laser beam irradiation unit20, and the imaging unit30are moved in the Z-axis direction relative to the workpiece100held on the holding table10.

The imaging unit30includes an imaging device that images the front surface101and streets102of the workpiece100held on the holding table10, processed grooves formed in the front surface101, and the like. The imaging device is, for example, a charge-coupled device (CCD) imaging device or a complementary metal oxide semiconductor (CMOS) imaging device. In the first embodiment, the imaging unit30is arranged adjacent to the laser beam irradiation unit20in such a manner as to be movable integrally with the image-forming element23included in the laser beam irradiation unit20.

The imaging unit30images the workpiece100which is held on the holding table10and has not yet been subjected to laser processing, to acquire an image to be used in performing a positional registration, in other words, an alignment or the like between the workpiece100and the laser beam irradiation unit20(image-forming point330), and outputs the acquired image to the controller70. In addition, the imaging unit30also images the workpiece100which is held on the holding table10and has been subjected to the laser processing, and acquires an image to be used in automatically checking if the processed grooves fall within the streets102and any large chipping or the like has occurred, in other words, in performing a kerf check, and outputs the acquired image to the controller70.

The X-axis direction moving unit41carries out relative processing feed, in the X-axis direction, of the workpiece100held on the holding table10and the image-forming point330of the laser beam203to be applied by the laser beam irradiation unit20. The Y-axis direction moving unit42carries out relative indexing feed, in the Y-axis direction, of the workpiece100held on the holding table10and the image-forming point330of the laser beam203to be applied by the laser beam irradiation unit20. The Z-axis direction moving unit43carries out relative movement, in the Z-axis direction, of the workpiece100held on the holding table10and the image-forming point330of the laser beam203to be applied by the laser beam irradiation unit20. The X-axis direction moving unit41, the Y-axis direction moving unit42, and the Z-axis direction moving unit43detect the relative positions in the X-axis direction, the Y-axis direction, and the Z-axis direction of the holding table10and the laser beam irradiation unit20, and output the detected relative positions to the controller70.

The display unit50is disposed on a cover (not illustrated) of the laser processing machine1with a side of a display screen directed outward, and displays a screen of setting of irradiation conditions and the like for the laser beam203in the laser processing machine1, a screen presenting the results of processing, including an alignment, autofocusing, an automatic light adjustment, a kerf check, and the like, such that an operator can visually recognize them. The display unit50includes a liquid crystal display device or the like. The display unit50is provided with the input unit60to be used when the operator inputs command information and the like regarding various operations of the laser processing machine1, laser beam irradiation conditions, the display of images, and so on. The input unit60with which the display unit50is provided is configured by at least one of a touch panel incorporated in the display unit50, a keyboard, or the like.

The controller70controls operations of the individual elements of the laser processing machine1to make the laser processing machine1perform laser processing or the like by applying the laser beam203to the workpiece100. The controller70includes a computer system in the first embodiment. This computer system has a computation processing unit having a microprocessor such as a central processing unit (CPU), a storage device having a memory such as a read only memory (ROM) or a random access memory (RAN), and an input/output interface device. The computation processing unit of the controller70performs computation processing according to a computer program stored in the storage device of the controller70, and outputs control signals to the individual elements of the laser processing machine1via the input/output interface device of the controller70to control the laser processing machine1.

A description will be made of one example of operation processing by the laser processing machine1according to the first embodiment. The laser processing machine1first performs a positional registration, in other words, an alignment between the workpiece100and the laser beam irradiation unit20(image-forming point330) by holding the workpiece100on the holding surface11of the holding table10, rotating the holding table10with the rotary drive source to make an adjustment such that the streets102in desired one of the directions of the workpiece100on the holding table10become parallel to the X-axis direction, and capturing, with the imaging unit30, an image of the workpiece100on the holding table10.

The laser processing machine1next subjects the workpiece100to laser processing (what is generally called ablation processing) along each street102with the laser beam203by carrying out, with the X-axis direction moving unit41, processing feed of the workpiece100held on the holding table10, relative to the image-forming point330of the laser beam203along the street102while applying, from the laser beam irradiation unit20, the laser beam203with the intensity distribution301formed along the Gaussian distribution in the X-axis direction and the intensity distribution303formed along the top-hat profile in the Y-axis direction.

The laser processing machine1according to the first embodiment, which is configured as described above, realizes the top-hat profile at the image-forming point330by converting the intensity distribution of the laser beam201from the Gaussian distribution into the airy disk pattern through the phase modulation unit22(phase plate) without using a mask which attenuates the energy of a laser beam by 60% to 70%, unlike the related art, and then focusing the resulting laser beam203. The laser processing machine1according to the first embodiment therefore exhibits advantageous effects in that the workpiece100can be subjected to laser processing with a laser beam of a desired profile without attenuating its energy that contributes to the laser processing.

Further, the laser processing machine1according to the first embodiment can suppress damage to the devices103and an uneven wear of a cutting blade during blade dicing as a subsequent step by setting the intensity distribution in the top-hat profile in the width direction (Y-axis direction) of each street102formed on the workpiece100, and can also effectively perform removal of, for example, a test element group (TEG) chip as an evaluation device which is present on the street102, by converting the intensity distribution into the Gaussian distribution in the processing feed direction (X-axis direction) along the street102.

As the recessed portion27or the protruding portion is formed such that the phase modulation unit22forms the airy disk pattern in the Y-axis direction, the laser processing machine1according to the first embodiment can suitably realize the irradiation of the laser beam203with the intensity distribution formed as the Gaussian distribution in the X-axis direction and also the intensity distribution formed in the top-hat profile in the Y-axis direction.

Second Embodiment

A laser processing machine1-2according to a second embodiment of the present invention will be described with reference toFIGS.10to12.FIG.10is a cross-sectional view illustrating a configuration example of a laser beam irradiation unit20-2of the laser processing machine1-2according to the second embodiment.FIG.11is a perspective view illustrating a phase modulation unit22-2ofFIG.10.FIG.12depicts a bottom view and a top view illustrating the phase modulation unit22-2ofFIG.10. Described more specifically,FIG.12illustrates a bottom view of a first phase plate81on an upper side of the paper sheet, and also illustrates a top view of a second phase plate82on a lower side of the paper sheet. InFIGS.10to12, portions identical to those of the first embodiment are identified by the same reference numerals, and their description is omitted.

The laser processing machine1-2according to the second embodiment is different from the laser processing machine1according to the first embodiment in that the laser beam irradiation unit20has been changed to the laser beam irradiation unit20-2. The laser beam irradiation unit20-2is different from the laser beam irradiation unit20in that the phase modulation unit22has been changed to the phase modulation unit22-2. With regard to the rest of the configurations, the laser processing machine1-2according to the second embodiment is similar to the laser processing machine1according to the first embodiment.

When a laser beam201is incident from a first surface86, the phase modulation unit22-2, similarly to the phase modulation unit22, emits, from a second surface89, a laser beam202with an intensity distribution301formed along a Gaussian distribution in the X-axis direction and an intensity distribution302formed along an airy disk pattern in the Y-axis direction.

As illustrated inFIG.10, the phase modulation unit22-2has a first phase plate81, a second phase plate82, and a moving unit83. As illustrated inFIGS.10,11, and12, the first phase plate81is formed in a plate shape, and has a large thickness region84and a small thickness region85. The first phase plate81has the first surface86parallel to the XY plane, and in a surface on a side opposite to the first surface86, a step of a depth92is formed in the Z-axis direction along a boundary between the region84and the region85. As illustrated inFIGS.10,11, and12, the second phase plate82is formed in a plate shape, and has a large thickness region87and a small thickness region88. The second phase plate82has the second surface89parallel to the XY plane, and in a surface on a side opposite to the second surface89, a step of a depth93is formed in the Z-axis direction along a boundary between the region87and the region88. The region85and the region88have a greater width in the Y-axis direction than that of the region84and the region87, respectively. As the first phase plate81and the second phase plate82, those which are each formed, for example, with a material similar to and in a plate shape of a size and a thickness substantially similar to those of the phase modulation unit22in the first embodiment are used. The depth92and the depth93are set to be equal in the second embodiment, and are approximately a half of the depth29of the first embodiment.

As illustrated inFIGS.10,11, and12, the first phase plate81and the second phase plate82are arranged such that the region84of the first phase plate81faces the region88of the second phase plate82, the region87of the second phase plate82faces the region85of the first phase plate81, and there is a region in which the region85of the first phase plate81and the region88of the second phase plate82overlap in the Z-axis direction. The first phase plate81is arranged above the second phase plate82such that the first surface86is directed upward in the Z-axis direction and the stepped surface on the side opposite to the first surface86faces, in the Z-axis direction, the stepped surface on the side opposite to the second surface89of the second phase plate82. The second phase plate82is arranged below the first phase plate81such that the second surface89is directed downward in the Z-axis direction and the stepped surface on the side opposite to the second surface89faces, in the Z-axis direction, the stepped surface on the side opposite to the first surface86of the first phase plate81.

The moving unit83supports the first phase plate81and the second phase plate82movably relative to each other in the Y-axis direction. The moving unit83relatively moves the first phase plate81and the second phase plate82in the Y-axis direction such that the boundary (step) between the region84and the region85and the boundary (step) between the region87and the region88are symmetrical with respect to a plane which includes an optical path of the laser beam201and is parallel to the X-axis, in other words, such that the region in which the region85of the first phase plate81and the region88of the second phase plate82overlap in the Z-axis direction includes the optical path of the laser beam201and is symmetrical with respect to the plane parallel to the X-axis. When the moving unit83moves the first phase plate81in a direction toward the optical path of the laser beam201, for example, the moving unit83moves the second phase plate82in a direction toward the optical path of the laser beam201. When the moving unit83moves the first phase plate81in a direction away from the optical path of the laser beam201, on the other hand, the moving unit83moves the second phase plate82in a direction away from the optical path of the laser beam201. The moving unit83is controlled by the controller70.

In the phase modulation unit22-2, a width (in other words, an overlapping width)91in the Y-axis direction of the region in which the region85of the first phase plate81and the region88of the second phase plate82overlap in the Z-axis direction is determined on the basis of the beam diameter of the laser beam201incident to the first phase plate81and the second phase plate82and a desired value of the width310of the top-hat profile of the intensity distribution303of the laser beam203to be applied to the workpiece100, and on the basis of the width91, the amount of the relative movement between the first phase plate81and the second phase plate82by the moving unit83is determined. The phase modulation unit22-2can adjust the width310of the top-hat profile of the intensity distribution303of the laser beam203to be applied to the workpiece100, to the desired value by adjusting the width91through an adjustment of the amount of the relative movement between the first phase plate81and the second phase plate82by the moving unit83. The width91is adjusted, for example, to be approximately equal to the width28of the recessed portion27of the first embodiment.

As an alternative, the phase modulation unit22-2may also be set such that the small thickness region85of the first phase plate81has a thickness of zero and the small thickness region88of the second phase plate82has a thickness of zero. In other words, the phase modulation unit22-2may be configured in such a form that the first phase plate81includes only the large thickness region84, the second phase plate82includes only the large thickness region87, and the laser beam201passes the phase plates (regions84and87) on sides of only their outer peripheries in the Y-axis direction.

As described above, the laser processing machine1-2according to the second embodiment is different from the laser processing machine1according to the first embodiment in that the phase modulation unit22has been changed to the phase modulation unit22-2. When the laser beam201is incident from the first surface86, the phase modulation unit22-2, similarly to the phase modulation unit22, emits, from the second surface89, the laser beam202with the intensity distribution301formed along the Gaussian distribution in the X-axis direction and the intensity distribution302formed along the airy disk pattern in the Y-axis direction. The laser processing machine1-2according to the second embodiment therefore exhibits advantageous effects similar to those of the laser processing machine1according to the first embodiment.

Further, the phase modulation unit22-2has the first phase plate81and the second phase plate82, which are movable relative to each other in the Y-axis direction. The laser processing machine1-2according to the second embodiment is therefore adaptable to various beam diameters of the laser beam201emitted from the laser oscillator21, by adjusting the width (in other words, the overlapping width)91in the Y-axis direction of the region in which the small thickness region85of the first phase plate81and the small thickness region88of the second phase plate82overlap in the Z-axis direction, through the adjustment of the amount of the relative movement between the first phase plate81and the second phase plate82. It is hence possible for the laser processing machine1-2according to the second embodiment to perform laser processing by changing the beam diameter and also to compensate for deteriorations, individual differences, and the like of the laser oscillator21.

Modification

A laser processing machine1or1-2according to a modification of the present invention will be descried with reference toFIGS.13to16.FIGS.13and14are graphs illustrating examples of an intensity distribution and an intensity profile of a laser beam203formed by a laser beam irradiation unit20or20-2of the laser processing machine1or1-2according to the modification. The abscissas and the ordinates inFIGS.13and15are similar to those inFIGS.3,6, and7. The horizontal directions, the vertical directions, and the dot densities inFIGS.14and16are similar to those inFIG.8. InFIGS.13to16, portions identical to those of the first embodiment or the second embodiment are identified by the same reference numerals, and their description is omitted.

If the various widths, depths, and the like of the phase modulation unit22or22-2of the laser beam irradiation unit20or20-2are set such that the laser beam203of the intensity distribution303and the intensity profile320is formed when the beam diameter of the laser beam201is targeted at 0.9 mm, setting of the beam diameter of the laser beam201at a value greater than the target, that is, 1.4 mm, forms an intensity profile325with a peak separated into two in the Y-axis direction as illustrated inFIGS.15and16. On the other hand, setting of the beam diameter of the laser beam201at a value greater even slightly than that target, that is, 1.0 mm, forms an intensity profile324with a peak spreading slightly in the Y-axis direction as illustrated inFIGS.13and14. The laser processing machine1or1-2according to the modification may subject the workpiece100to laser processing by the laser beam203that forms the intensity distribution304or305and intensity profile324or325as described above.

It is to be noted that the present invention shall not be limited to the above-described embodiments. In other words, the present invention can be practiced with various changes or modifications within the scope not departing from the spirit of the present invention. For example, the phase modulation units22and22-2are configured by the single phase plate and the two phase plates, respectively. However, the present invention is not limited to the use of such a single phase plate or such two phase plates, and may use a spatial optical modulator that adjusts optical characteristics of the laser beam201emitted from the laser oscillator21, that is, a liquid crystal on silicon-spatial light modulator (what is generally called an LCOS-SLM).