Laser processing method

For modulating laser light for forming a modified region SD3 at an intermediate position between a position closer to a rear face 21 and a position closer to a front face 3 with respect to an object 1, a quality pattern J having a first brightness region extending in a direction substantially orthogonal to a line 5 and second brightness regions located on both sides of the first brightness region in the extending direction of the line 5 is used. After forming modified regions SD1, SD2 at positions closer to the rear face 21 but before forming modified regions SD4, SD5 at positions closer to the rear face 21 while using the front face 3 as a laser light entrance surface, the modified region SD3 is formed at the intermediate position by irradiation with laser light modulated according to a modulation pattern including the quality pattern J.

TECHNICAL FIELD

The present invention relates to a laser processing method for forming a modified region in an object to be processed.

BACKGROUND ART

Known as a conventional laser processing method in the technical field mentioned above is one which irradiates a planar object to be processed with laser light having a wavelength of 1300 nm, so as to form a modified region to become a starting point region for cutting in the object along a line to cut the object (see, for example, Patent Literature 1).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

Here, when the object is a silicon substrate, for example, it exhibits a higher transmittance for the laser light having a wavelength of 1300 nm than for laser light having a wavelength of 1064 nm, whereby a modified region which is easy to generate fractures can be formed by using the laser light having a wavelength of 1300 nm even at a position located deep from the laser entrance surface of the object. This can reduce the number of rows of modified regions when cutting the object by forming a plurality of rows of modified regions in the thickness direction of the object along a line to cut, thereby shortening takt time.

While the use of the laser light having a wavelength of 1300 nm can form modified regions which are easy to generate fractures, the fractures may continuously advance in the thickness direction of the object when forming a plurality of rows of modified regions in the thickness direction of the object, so as to meander on a main face of the object and so forth, thereby lowering the accuracy in cutting the object.

It is therefore an object of the present invention to provide a laser processing method which can reduce the number of rows of modified regions formed in the thickness direction of the object while preventing the accuracy in cutting the object from lowering.

Solution to Problem

For achieving the above-mentioned object, the laser processing method in accordance with the present invention is a laser processing method of irradiating a planar object to be processed with laser light so as to form a modified region to become a starting point region for cutting in the object along a line to cut the object; wherein, when relatively moving a converging point of the laser light along the line while using one main face of the object as a laser light entrance surface, so as to form modified regions at a position closer to the other main face of the object, a position closer to the one main face, and an intermediate position between the position closer to the other main face and the position closer to the one main face, for forming the modified region at the intermediate position after forming the modified region at the position closer to the other main face but before forming the modified region at the position closer to the one main face, the laser light is modulated by a spatial light modulator according to a modulation pattern including a quality pattern having a first brightness region extending in a direction intersecting the line and second brightness regions adjacent to both sides of the first brightness region in an extending direction of the line.

After forming the modified region at the position closer to the other main face but before forming the modified region at the position closer to the one main face, this laser processing method forms the modified region at the intermediate position between the position closer to the other main face and the position closer to the one main face by irradiation with the laser light modulated by the spatial light modulator according to the modulation pattern including the quality pattern mentioned above. Even when laser light having a wavelength longer than 1064 nm is used in order to reduce the number of rows of modified regions, for example, thus forming the modified region at the intermediate position can prevent fractures from continuously advancing in the thickness direction of the object at the time of forming a plurality of rows of modified regions in the thickness direction of the object. When a stress is generated in the object, for example, a fracture occurring from the modified region acting as a start point extends in the thickness direction of the object more easily than in the case where no modified region is formed at the intermediate position, whereby the object can be cut accurately along the line. Hence, this laser processing method can reduce the number of rows of modified regions formed in the thickness direction of the object along the line, while preventing the accuracy in cutting the object from lowering.

By forming a modified region at a position closer to the other main face is meant that the modified region is formed such that the center position of the modified region is shifted from the center position of the object to the other main face, whereas by forming a modified region at a position closer to the one main face is meant that the modified region is formed such that the center position of the modified region is shifted from the center position of the object to the one main face. By forming a modified region at an intermediate position between the position closer to the other main face and the position closer to the one main face is meant that the modified region is formed between the modified region formed at the position closer to the other main face and the modified region formed at the position closer to the one main face (i.e., it does not mean that the modified region is formed such that its center position coincides with the center position of the object in the thickness direction of the object).

Here, in the extending direction of the line, the width of the first brightness region is preferably at a ratio of 20% to 50% of the width of an effective region for modulating the laser light in the modulation pattern. In this case, a modified region which can reliably prevent fractures from continuously advancing in the thickness direction of the object when forming a plurality of rows of modified regions in the thickness direction of the object can be formed at the intermediate position.

In the extending direction of the line, the width of the first brightness region may be narrower or wider than the width of each of the second brightness regions. In either case, a modified region which can reliably prevent fractures from continuously advancing in the thickness direction of the object when forming a plurality of rows of modified regions in the thickness direction of the object can be formed at the intermediate position.

Preferably, the modulation pattern includes the quality pattern, an individual difference correction pattern for correcting an individual difference occurring in a laser processing device, and a spherical aberration correction pattern for correcting a spherical aberration occurring according to a material of the object and a distance from the laser light entrance surface of the object to the converging point when forming the modified region at the intermediate position, and the laser light is modulated by a spatial light modulator according to a modulation pattern including the individual difference correction pattern and spherical aberration correction pattern when forming the modified regions at the position closer to the other main face and the position closer to the one main face. In this case, the modified regions formed at the intermediate position and the positions closer to the other main face and the one main face are easier to generate fractures, whereby the number of rows of modified regions formed in the thickness direction of the object along the line can be reduced more reliably.

Preferably, the laser light has a wavelength of 1080 nm or longer. This makes the object exhibit a higher transmittance for the laser light, so that the modified regions formed at the intermediate position, the position closer to the other main face, and the position closer to the one main face are easier to generate fractures, whereby the number of rows of modified regions formed in the thickness direction of the object along the line can be reduced more reliably.

Cutting the object along the line from the above-mentioned modified regions acting as a start point can accurately cut the object along the line. Manufacturing a semiconductor device by cutting the object can yield a highly reliable semiconductor device.

Advantageous Effects of Invention

The present invention can reduce the number of rows of modified regions formed in the thickness direction of the object while preventing the accuracy in cutting the object from lowering.

DESCRIPTION OF EMBODIMENTS

In the following, preferred embodiments of the present invention will be explained in detail with reference to the drawings. In the drawings, the same or equivalent constituents will be referred to with the same signs while omitting their overlapping descriptions.

Before explaining an embodiment of the laser processing method in accordance with the present invention, forming of a modified region for an object to be processed will be described with reference toFIGS. 1 to 6, As illustrated inFIG. 1, a laser processing device100comprises a laser light source101which causes laser light L to oscillate in a pulsating manner, a dichroic mirror103arranged such as to change the direction of the optical axis (optical path) of the laser light L by 90°, and a condenser lens105for converging the laser light L. The laser processing device100also comprises a support table107for supporting an object to be processed1irradiated with the laser light L converged by the condenser lens105, a stage111for moving the support table107, a laser light source controller102for controlling the laser light source101in order to regulate the output, pulse width, and the like of the laser light L, and a stage controller115for controlling the movement of the stage111.

In the laser processing device100, the laser light L emitted from the laser light source101changes the direction of its optical axis by 90° with the dichroic mirror103and then is converged by the condenser lens105into the object1mounted on the support table107. At the same time, the stage111is shifted, so that the object1moves relative to the laser light L along a line to cut5. This forms a modified region in the object1along the line5.

A semiconductor material, a piezoelectric material, or the like is used as a material for the object1, while the line5for cutting the object1is set therefor as illustrated inFIG. 2. Here, the line5is a virtual line extending straight. When forming a modified region within the object1, the laser light L is relatively moved along the line5(i.e., in the direction of arrow A inFIG. 2) while locating a converging point (converging position) P within the object1as illustrated inFIG. 3. This forms a modified region7within the object1along the line5as illustrated inFIGS. 4 to 6, whereby the modified region7formed along the line5becomes a cutting start region8.

The converging point P is a position at which the laser light L is converged. The line5may be curved instead of being straight or a line actually drawn on a front face3of the object1without being restricted to the virtual line. The modified region7may be formed either continuously or intermittently. The modified region7may be formed like lines or dots; it will be sufficient if the modified region7is formed at least within the object1. There are cases where fractures are formed from the modified region7acting as a start point, and the fractures and modified region7may be exposed at outer surfaces (the front face, rear face, and outer peripheral face) of the object1.

Here, the laser light L is absorbed in particular in the vicinity of the converging point within the object1while being transmitted therethrough, whereby the modified region7is formed in the object1(i.e., internal absorption type laser processing). Hence, the front face3of the object1hardly absorbs the laser light L and thus does not melt. In the case of forming a removing part such as a hole or groove by melting it away from the front face3(surface absorption type laser processing), the processing region gradually progresses from the front face3side to the rear face side in general.

By the modified region are meant regions whose physical characteristics such as density, refractive index, and mechanical strength have attained states different from those of their surroundings. Examples of the modified region include molten processed regions, crack regions, dielectric breakdown regions, refractive index changed regions, and their mixed regions. Further examples of the modified region7include an area where the density has changed from that of an unmodified region in a material of the object and an area formed with a lattice defect (which may collectively be referred to as a high-density transitional region).

The molten processed regions, refractive index changed regions, areas where the modified region has a density different from that of the unmodified region, or areas formed with a lattice defect may further incorporate a fracture (microcrack) therewithin or at an interface between the modified region and an unmodified region. The incorporated fracture may be formed over the whole surface of the modified region or in only a part or a plurality of parts thereof. Examples of the object1include those containing or constituted by silicon, glass, LiTaO3, and sapphire (Al2O3).

Here, a plurality of modified spots (processing scars) are formed along the line5, so as to produce the modified region7. The modified spots, each of which is a modified part formed by a shot of one pulse of pulsed laser light (i.e., one pulse of laser irradiation: laser shot), gather to form the modified region7. Examples of the modified spots include crack spots, molten processed spots, refractive index changed spots, and those mixed with at least one of them. As for the modified spots, it will be preferred if their size and the length of fractures generated thereby are controlled as appropriate in view of required accuracy in cutting, required flatness in the cut section, thickness, kind, and crystal orientation of the object, and the like.

An embodiment of the laser processing method in accordance with the present invention will now be explained.FIG. 7is a plan view of the object in an embodiment of the laser processing method in accordance with the present invention. As illustrated inFIG. 7, the object1having a planar form comprises a silicon substrate11and a functional device layer16formed on a front face11aof the silicon substrate11.

The functional device layer16includes a plurality of functional devices15formed into a matrix in directions parallel and perpendicular to an orientation flat6of the silicon substrate Examples of the functional devices15include semiconductor operating layers formed by crystal growth, light-receiving devices such as photodiodes, light-emitting devices such as laser diodes, and circuit devices formed as circuits.

The lines5are formed like grids in the object1so as to pass between the functional devices15,15adjacent to each other. The object1is cut along the lines5into chips, each of which becomes a semiconductor device having one functional device15.

FIG. 8is a structural diagram illustrating a laser processing device in one embodiment of the laser processing method in accordance with the present invention. As illustrated inFIG. 8, this laser processing device300comprises a laser light source202, a reflective spatial light modulator203, a 4 f optical system241, and a condensing optical system204. The reflective spatial light modulator203, 4 f optical system241, and condensing optical system204are accommodated in a housing234, while the laser light source202is held in a housing231containing the housing234.

The laser light source202, for which a fiber laser is used, for example, emits laser light L which is pulsed laser light having a wavelength of 1080 nm or longer, for example. Here, the laser light source202is secured to a top plate236of the housing234with screws or the like so as to emit the laser light L horizontally.

The reflective spatial light modulator203, for which a spatial light modulator (SLM) made of a liquid crystal on silicon (LCOS) is used, for example, modulates the laser light L emitted from the laser light source202. Here, the reflective spatial light modulator203modulates the laser light L horizontally incident thereon, while reflecting it obliquely upward with respect to the horizontal direction.

FIG. 9is a partial sectional view of the reflective spatial light modulator in the laser processing device ofFIG. 8. As illustrated inFIG. 9, the reflective spatial light modulator203comprises a silicon substrate213, a drive circuit layer914, a plurality of pixel electrodes214, a reflecting film215such as a dielectric multilayer mirror, an alignment film999a, a liquid crystal layer216, an alignment film999b, a transparent conductive film217, and a transparent substrate218such as a glass substrate, which are stacked in this order.

The transparent substrate218has a front face218aextending along an XY plane, while the front face218aconstitutes a front face of the reflective spatial light modulator203. The transparent substrate218is mainly composed of a light-transmitting material such as glass, for example, and transmits therethrough the laser light L having a predetermined wavelength incident thereon from the front face218aof the reflective spatial light modulator203to the inside of the latter. The transparent conductive film217is formed on a rear face218bof the transparent substrate218and mainly composed of a conductive material (e.g., ITO) which transmits therethrough the laser light L.

The plurality of pixel electrodes214are arranged two-dimensionally according to the arrangement of a plurality of pixels on the silicon substrate213along the transparent conductive film217. Each pixel electrode214is made of a metal material such as aluminum, for example, while its front face214ais processed flat and smooth. The plurality of pixel electrodes214are driven by an active matrix circuit provided with the drive circuit layer914.

The active matrix circuit is disposed between the plurality of pixel electrodes214and the silicon substrate213and controls the voltage applied to the pixel electrodes214according to a light image to be issued from the reflective spatial light modulator203. An example of such an active matrix circuit has a first driver circuit for controlling pixel rows each aligning in the X direction and a second driver circuit for controlling pixel columns each aligning in the Y direction, which are not depicted, and is constructed such that a controller250applies a predetermined voltage to the pixel electrode214of a pixel designated by both of the driver circuits.

The alignment films999a,999bare arranged on both end faces of the liquid crystal layer216, respectively, so as to align a group of liquid crystal molecules in a fixed direction. As the alignment films999a,999b, those made of a polymer material such as polyimide, whose surfaces coming into contact with the liquid crystal layer216have been subjected to rubbing, for example, are employed.

The liquid crystal layer216is arranged between the plurality of pixel electrodes214and the transparent conductive film217and modulates the laser light L according to an electric field formed between each pixel electrode214and the transparent conductive film217. That is, when the active matrix circuit applies a voltage to a given pixel electrode214, an electric field is formed between the transparent conductive film217and this pixel electrode214.

The electric field is applied to the reflecting film215and the liquid crystal layer216at a ratio of their respective thicknesses. The alignment direction of liquid crystal molecules216achanges according to the magnitude of the electric field applied to the liquid crystal layer216. The laser light L entering the liquid crystal layer216through the transparent substrate218and transparent conductive film217, if any, is modulated by the liquid crystal molecules216awhile passing through the liquid crystal layer216, then reflected by the reflecting film215, and thereafter modulated again by the liquid crystal layer216before being taken out.

This adjusts the wavefront of the laser light L incident on and transmitted through a modulation pattern (image for modulation), so that individual rays constituting the laser light L vary in phases of components in a predetermined direction orthogonal to their advancing direction.

Returning toFIG. 8, the 4 f optical system241adjusts the wavefront form of the laser light L modulated by the reflective spatial light modulator203. The 4 f optical system241has first and second lenses241a,241b.

The lenses241a,242bare arranged between the reflective spatial light modulator203and the condensing optical system204such that the distance (optical path length) between the reflective spatial light modulator203and the first lens241aequals the focal length f1of the first lens241a, the distance (optical path length) between the condensing optical system204and the second lens241bequals the focal length f2of the lens241b, the distance (optical path length) between the first and second lenses241a,241bequals f1+f2, and the first and second lenses241a,241bconstitute a double-telecentric optical system. This 4 f optical system241can inhibit the laser light L modulated by the reflective spatial light modulator203from changing its wavefront form through spatial propagation and thereby increasing aberration.

The condensing optical system204converges the laser light L modulated by the 4 f optical system241into the object1. The condensing optical system204, which includes a plurality of lenses, is placed on a bottom plate233of the housing231while interposing therebetween a drive unit232composed of a piezoelectric device and the like.

The laser processing apparatus300also comprises a surface observation unit211for observing the front face3of the object1and an AF (AutoFocus) unit212for finely adjusting the distance between the condensing optical system204and the object1, which are accommodated in the housing231.

The surface observation unit211has an observation light source211afor emitting visible light VL1and a detector211bfor receiving and detecting reflected light VL2of the visible light VL1reflected by the front face3of the object1. In the surface observation unit211, the visible light VL1emitted from the observation light source211ais reflected by a mirror208and dichroic mirrors209,210and transmitted through a dichroic mirror238, so as to be converged by the condensing optical system204to the object. The reflected light VL2reflected by the front face3of the object1is converged by the condensing optical system204, so as to be transmitted through and reflected by the dichroic mirrors238,210, respectively, and then transmitted through the dichroic mirror209, so as to be received by the detector211b.

The AF unit212emits AF laser light LB1and receives and detects reflected light LB2of the AF laser light LB1reflected by the front face3of the object1, thereby acquiring displacement data of the front face3(position (height) data of the front face3in the thickness direction of the object1) along the line5. Then, when forming the modified region7, the AF unit212drives the drive unit232according to thus obtained displacement data, so as to move the condensing optical system204to and fro in its optical axis along undulations of the front face3of the object1.

The laser processing apparatus300further comprises the controller250, constituted by CPU, ROM, RAM, and the like, for controlling the laser processing apparatus300. The controller250controls the laser light source202, so as to adjust the output, pulse width, and the like of the laser light L emitted from the laser light source202. When forming the modified region7, the controller250controls the positions of the housing231and stage111and the driving of the drive unit232so that a simultaneous converging position of the laser light L relatively moves along the line5while being located at a predetermined distance from the front face3of the object1.

When forming the modified region7, the controller250also applies a predetermined voltage between each pixel electrode214and the transparent conductive film217, so as to cause the liquid crystal layer216to display a predetermined modulation pattern. This allows the reflective spatial light modulator203to modulate the laser light L desirably.

A case where the object1is processed by the above-mentioned laser processing apparatus300will now be explained. Here, a case where the planar object1is irradiated with the laser light L while locating the converging point P within the object1so as to form the modified region7to become a starting point region for cutting along the line5will be explained by way of example.

First, an expandable tape is attached to a rear face21of the object1, and the object1is mounted on the stage111. Subsequently, while irradiating the object1with the laser light L in a pulsating manner from the front face3employed as the laser light irradiation surface, the object1is moved relative to (scanned with) the laser light L along the line5, so as to form the modified region7.

That is, in the laser processing device300, the laser light L emitted from the laser light source202advances horizontally within the housing231and then is reflected downward by a mirror205a, whereby its light intensity is adjusted by an attenuator207. Thereafter, the laser light L is horizontally reflected by a mirror205band, with its intensity distribution homogenized by a beam homogenizer260, enters the reflective spatial light modulator203.

The laser light L incident on the reflective spatial light modulator203is transmitted through and modulated according to the modulation pattern displayed on the liquid crystal layer216and then is emitted obliquely upward with respect to the horizontal direction. Subsequently, the laser light L is reflected upward by a mirror206aand then, after its polarization direction is changed by a half-wave plate228so as to orient along the line5, horizontally by a mirror206b, so as to enter the 4 f optical system241.

Subsequently, the wavefront form of the laser light L is adjusted so that it enters the condensing optical system204as parallel light. Specifically, the laser light L is transmitted through and converged by the first lens241aand then reflected downward by a mirror219, so as to diverge through a confocal point O. The diverged laser light L is transmitted through the second lens241b, so as to be converged again to become parallel light.

The laser light L passes through the dichroic mirrors210,238in sequence, so as to enter the condensing optical system204, thereby being converged into the object1mounted on the stage111. As a result, a modified spot is formed at a predetermined depth in the thickness direction within the object1.

Then, the converging point P of the laser light L is relatively moved along the line5, so that the modified region7is formed by a plurality of modified spots. Thereafter, the expandable tape is expanded, so as to cut the object1along the line5from the modified region7acting as a starting point region for cutting, whereby a plurality of cut chips are obtained as semiconductor devices (e.g., memories, ICs, light-emitting devices, and light-receiving devices).

A laser processing system400equipped with the above-mentioned laser processing device300will now be explained. As illustrated inFIG. 10, the laser processing system400comprises personal computers (hereinafter referred to as “PCs”)401,402, a controller403, and the laser processing device300. As mentioned above, the laser processing device300irradiates the object1with the laser light L modulated by the reflective spatial light modulator203, so as to form the modified region7in the object1.

A storage unit (a memory, a hard disk, or the like)401aof the PC401stores conditions for forming the modified region7for the object1as a database. When a user inputs a desirable forming condition by operating the PC401, this forming condition is fed into the controller403through a LAN (Local Area Network).

When fed with a condition for forming the modified region7for the object1, the controller (pattern assignment means)403chooses one or a plurality of element patterns for the modified region according to the forming condition and assigns the chosen element patterns to the PC402through the LAN. Here, the element patterns are patterns to become elements for a modulation pattern for subjecting the laser light to a predetermined modulation in the reflective spatial light modulator203in the laser processing device300, while a plurality of kinds of element patterns are stored as a database in a storage unit (a memory, a hard disk, or the like)402aof the PC402.

The storage unit (pattern storage means)402astores an individual difference correction pattern (D-01) for correcting an individual difference occurring in the laser processing device300(e.g., a distortion occurring in the liquid crystal layer216in the reflective spatial light modulator203) as an element pattern. The storage unit402aalso stores spherical aberration correction patterns (S-0001to S-1000) for correcting the spherical aberration occurring at the converging point P of the laser light L as element patterns. Since the spherical aberration occurring at the converging point P of the laser light L varies depending on materials of the object1and the distance from the laser light entrance surface of the object1to the converging point P of the laser light L, the spherical aberration correction patterns are set with the material and distance serving as parameters and stored in the storage unit402a.

The storage unit402afurther stores quality patterns (J-01to J-10) as element patterns. As illustrated inFIG. 11, each quality pattern has a first brightness region R1extending in a direction substantially orthogonal to the line5and second brightness regions R2located on both sides of the first brightness region R1in the extending direction of the line5.

In the case where the modified regions7are formed at a position closer to the rear face21of the object1, a position closer to the front face3of the object1, and an intermediate position between the position closer to the rear face21and the position closer to the front face3in the order of the position closer to the rear face21, the intermediate position, and the position closer to the front face3(or in the order of the position closer to the front face3, the intermediate position, and the position closer to the rear face21), the quality pattern is used when forming the modified region7at the intermediate position. That is, the quality pattern is used when forming the modified region7at the intermediate position after forming the modified region at the position closer to the rear face21but before forming the modified region at the position closer to the front face3(or after forming the modified region at the position closer to the front face3but before forming the modified region at the position closer to the rear face21).

Returning toFIG. 10, the PC (pattern creation means)402reads one or a plurality of kinds of element patterns for the modified region7from the storage unit402aaccording to the assignment of element patterns by the controller403. That is, according to the condition for forming the modified region7for the object1, the PC402acquires one or a plurality of kinds of element patterns for the modified region7from the storage unit402a.

When one kind of element pattern is acquired, the PC402employs the one kind of element pattern as a modulation pattern for forming the modified region7corresponding thereto. When a plurality of kinds of element patterns are acquired, the PC402employs a composite pattern combining the plurality of element patterns as the modulation pattern for forming the modified region7corresponding thereto. After thus creating the modulation pattern, the PC402outputs the modulation pattern in association with the modified region7to the laser processing device300through a DVI (Digital Visual Interface).

When forming a plurality of kinds of modified regions7in the object1(e.g., when a plurality of rows of modified regions7juxtaposed in the thickness direction of the object1are formed with respect to one line to cut5), the PC402creates a modulation pattern for each of all the kinds of modified regions7and then outputs the modulation pattern in association with its corresponding modified region7to the laser processing device300.

The above-mentioned quality pattern will now be explained in more detail. As illustrated inFIG. 11, in the extending direction of the line5, the width of first brightness region R1is at a ratio of 20% to 50% of the width of an effective region R for modulating the laser light L in the modulation pattern. However, in the extending direction of the line5, the width of the first brightness region R1may be narrower than the width of each of the second brightness regions R2(see, for example, J-01inFIG. 10) or wider than the latter (see, for example, J-10inFIG. 10). The effective region R of the quality pattern is a region corresponding to the part of laser light L incident on the condensing optical system204(the part incident on the entrance pupil of the condensing optical system204).

Any of the average brightness of the first brightness region R1and that of the second brightness regions R2may be higher than the other as long as they differ from each other. From the viewpoint of increasing the difference in brightness between the first and second brightness regions, however, it will be preferred if the average brightness of the first brightness region R1and that of the second brightness region R2deviate from each other by 128 gradations when the brightness of each pixel constituting the quality pattern is expressed by 256 gradations.

An example of laser processing methods performed in the above-mentioned laser processing system400will now be explained with reference toFIG. 12. First, a user operates the PC401, so as to input a condition for forming the modified region7for the object1(step S01). Here, the thickness and material of the object1are set to 200 μm and silicon, respectively. Two rows of modified regions SD1, SD2are set as a plurality of rows of modified regions7formed in juxtaposition in the thickness direction of the object1with respect to one line to cut5. For forming the modified region SD1, the distance (depth) from the laser light entrance surface of the object1to the converging point P of the laser light L and the output of the laser light L are set to 180 μm and 0.6 W, respectively. For forming the modified region SD2, the distance and output are set to 70 μm and 0.6 W, respectively.

When the condition for forming the modified region7for the object1is fed into the controller403, the latter chooses one or a plurality of element patterns for each of the modified regions SD1, SD2according to the forming condition and assigns the element patterns in association with their corresponding modified regions SD1, SD2to the PC402(step S02). This allows the PC402to acquire appropriate element patterns easily and reliably.

When the element patterns are assigned for each of the modified regions SD1, SD2, the PC402chooses the element patterns in association with their corresponding modified regions SD1, SD2from the storage unit402a(step S03). Here, the individual difference correction pattern D-01and spherical aberration correction pattern S-0025are chosen as element patterns in association with the modified region SD2, while the individual difference correction pattern D-01and spherical aberration correction pattern S-0060are chosen as element patterns in association with the modified region SD1.

Subsequently, for forming the modified regions SD1, SD2, the PC402combines a plurality of kinds of element patterns in association with each of the modified regions SD1, SD2corresponding thereto and employs the resulting composite pattern as a modulation pattern (step S04). Here, the individual difference correction pattern D-01and spherical aberration correction pattern S-0025are combined so as to create a modulation pattern SD-002for forming the modified region SD2, while the individual difference correction pattern D-01and spherical aberration correction pattern S-0060are combined so as to create a modulation pattern SD-001for forming the modified region SD1.

Next, the PC402outputs thus created modulation patterns SD-001, SD-002in association with their corresponding modified regions SD1, SD2to the laser processing device300(step S05). When fed with the modulation patterns SD-001, SD-002in association with their corresponding modified regions SD1, SD2, the laser processing device300performs laser processing (step S06).

More specifically in the laser processing device300, when forming the modified region SD1, the modulation pattern SD-001is displayed on the liquid crystal layer216of the reflective spatial light modulator203through the controller250, whereby the laser light L is modulated by the modulation pattern SD-001. When forming the modified region SD2, the modulation pattern SD-002is displayed on the liquid crystal layer216of the reflective spatial light modulator203through the controller250, whereby the laser light L is modulated by the modulation pattern SD-002.

Since the modulation pattern thus includes the individual difference correction pattern and spherical aberration correction pattern when forming each of the modified regions SD1, SD2, states of forming the modified regions can be inhibited from fluctuating because of the individual difference occurring in the laser processing device300and the spherical aberration generated at the converging point P of the laser light L. Here, it is preferable to form the modified region SD2located closer to the laser light entrance surface of the object1after forming the modified region SD1located farther from the laser light entrance surface of the object1.

Another example of laser processing methods performed in the above-mentioned laser processing system400will now be explained with reference toFIG. 13. First, the user operates the PC401, so as to input a condition for forming the modified region7for the object1(step S11). Here, the thickness and material of the object1are set to 300 μm and silicon, respectively. Three rows of modified regions SD1, SD2, SD3are set as a plurality of rows of modified regions7formed in juxtaposition in the thickness direction of the object1with respect to one line to cut5. For forming the modified region SD1, the distance (depth) from the laser light entrance surface of the object1to the converging point P of the laser light L and the output of the laser light L are set to 260 μm and 0.6 W, respectively. For forming the modified region SD2, the distance and output are set to 180 μm and 0.6 W, respectively. For forming the modified region SD3, the distance and output are set to 70 μm and 0.6 W, respectively. Here, the quality pattern is set to “yes” for forming the modified region SD2.

When the condition for forming the modified region7for the object1is fed into the controller403, the latter chooses one or a plurality of element patterns for each of the modified regions SD1, SD2, SD3according to the forming condition and assigns the element patterns in association with their corresponding modified regions SD1, SD2, SD3to the PC402(step S12). This allows the PC402to acquire appropriate element patterns easily and reliably.

When the element patterns are assigned for each of the modified regions SD1, SD2, SD3, the PC402chooses the element patterns in association with their corresponding modified regions SD1, SD2, SD3from the storage unit402a(step S13). Here, the individual difference correction pattern D-01and spherical aberration correction pattern S-0025are chosen as element patterns in association with the modified region SD3. The individual difference correction pattern D-01, spherical aberration correction pattern S-0060, and quality pattern J-03are chosen as element patterns in association with the modified region SD2. The individual difference correction pattern D-01and spherical aberration correction pattern S-0100are chosen as element patterns in association with the modified region SD1.

Subsequently, for forming the modified regions SD1, SD2, SD3, the PC402combines a plurality of kinds of element patterns in association with each of the modified regions SD1, SD2, SD3corresponding thereto and employs the resulting composite pattern as a modulation pattern (step S14). Here, the individual difference correction pattern D-01and spherical aberration correction pattern S-0025are combined so as to create a modulation pattern SD-003for forming the modified region SD3. The individual difference correction pattern D-01, spherical aberration correction pattern S-0060, and quality pattern J-03are combined so as to create a modulation pattern SD-002for forming the modified region SD2. The individual difference correction pattern D-01and spherical aberration correction pattern S-0100are combined so as to create a modulation pattern SD-001for forming the modified region SD1.

Next, the PC402outputs thus created modulation patterns SD-001, SD-002, SD-003in association with their corresponding modified regions SD1, SD2, SD3to the laser processing device300(step S15). When fed with the modulation patterns SD-001, SD-002, SD-003in association with their corresponding modified regions SD1, SD2, SD3, the laser processing device300performs laser processing (step S16).

More specifically in the laser processing device300, when forming the modified region SD1, the modulation pattern SD-001is displayed on the liquid crystal layer216of the reflective spatial light modulator203through the controller250, whereby the laser light L is modulated by the modulation pattern SD-001. When forming the modified region SD2, the modulation pattern SD-002is displayed on the liquid crystal layer216of the reflective spatial light modulator203through the controller250, whereby the laser light L is modulated by the modulation pattern SD-002. When forming the modified region SD3, the modulation pattern SD-003is displayed on the liquid crystal layer216of the reflective spatial light modulator203through the controller250, whereby the laser light L is modulated by the modulation pattern SD-003.

Since the modulation pattern thus includes the individual difference correction pattern and spherical aberration correction pattern when forming each of the modified regions SD1, SD2, SD3, states of forming the modified regions can be inhibited from fluctuating because of the individual difference occurring in the laser processing device300and the spherical aberration generated at the converging point P of the laser light L. Here, it is preferable to form the modified region SD1farther from the laser light entrance surface of the object1, the modified region SD2located in the middle, and the modified region SD3located closer to the laser light entrance surface of the object1in this order.

In the case where the modified regions SD1, SD2, SD3are formed in this order, the modulation pattern includes the quality pattern in addition to the individual difference correction pattern and spherical aberration correction pattern when forming the modified region SD2at the intermediate position. Thus modulating the laser light L by using the quality pattern so as to form the modified region SD2at the intermediate position can prevent fractures from continuously advancing in the thickness direction of the object1when forming the modified regions SD1, SD2, SD3in the thickness direction of the object1. When a stress is generated in the object1, fractures generated from the modified region acting as a start point extend in the thickness direction of the object1more easily than in the case where the modified region SD2is not formed at the intermediate position, whereby the object1can be cut accurately along the line5. The modified region SD3located closer to the laser light entrance surface of the object1, the modified region SD2located in the middle, and the modified region SD1located farther from the laser light entrance surface of the object1may also be formed sequentially in this order.

The modulation patterns (individual correction pattern, spherical aberration correction pattern, and quality pattern) will now be explained.FIG. 14is a first diagram illustrating a cut section obtained when cutting the object from modified regions acting as a start point. Here, using the front face3of the object1made of silicon having a thickness of 625 μm as a laser light entrance surface, modified regions SD1to SD7were formed in the descending order of their distance from the front face3. For forming the modified regions SD1to SD7, a spherical aberration correction pattern which could correct the spherical aberration at the converging point P of the laser light L when forming the modified region SD7located closest to the front face3serving as the laser light entrance surface was used, and the laser light L was modulated by a modulation pattern including the spherical aberration correction pattern in addition to an individual difference correction pattern. As a result, it has been seen as indicated by arrows on the right side ofFIG. 14that fractures generated at the time of forming each of the modified regions SD1to SD7, the modified regions SD1to SD5in particular, are hard to extend in the thickness direction of the object1.

FIG. 15is a second diagram illustrating a cut section obtained when cutting the object from modified regions acting as a start point. Here, using the front face3of the object1made of silicon having a thickness of 625 μm as a laser light entrance surface, modified regions SD1to SD7were formed in the descending order of their distance from the front face3. For forming the modified regions SD1to SD7, a spherical aberration correction pattern which could correct the spherical aberration at the converging point P of the laser light L when forming the modified region SD7located closest to the front face3serving as the laser light entrance surface was used, and the laser light L was modulated by a modulation pattern including the spherical aberration correction pattern in addition to an individual difference correction pattern. As a result, it has been seen as indicated by arrows on the right side ofFIG. 15that fractures generated at the time of forming each of the modified regions SD1to SD7, the modified regions SD3to SD5in particular, are hard to extend in the thickness direction of the object1.

In view of the results ofFIGS. 14 and 15, spherical aberration correction patterns which could correct the spherical aberration at the converging point P of the laser light L when forming the respective modified regions were used (i.e., the spherical aberration correction pattern was changed depending on the modified regions).FIG. 16is a third diagram illustrating a cut section obtained when cutting the object from modified regions acting as a start point. Here, using the front face3of the object1made of silicon having a thickness of 400 μm as a laser light entrance surface, modified regions SD1to SD4were formed in the descending order of their distance from the front face3. For forming the modified regions SD1to SD4, respective spherical aberration correction patterns which could correct the spherical aberration at the converging point P of the laser light L were used, and the laser light L was modulated by modulation patterns including the respective spherical aberration correction patterns in addition to the individual difference correction pattern. As a result, it has been seen as indicated by arrows on the right side ofFIG. 16that fractures generated at the time of forming the modified regions SD1to SD4have equal lengths among the modified regions SD1to SD4and extend in the thickness direction of the object1more easily than in the cases ofFIGS. 14 and 15. However, there was a case where the following problem occurred in a part of a cut section.

FIG. 17is a fourth diagram illustrating a cut section obtained when cutting the object from modified regions acting as a start point. While the modified regions SD1to SD4were formed under a forming condition equal to that in the case ofFIG. 16, fractures continuously advanced in the thickness direction of the object1in the process of forming the modified regions SD1to SD4in sequence as indicated by the arrow on the right side ofFIG. 17. As a result, twist hackles T occurred at the cut section of the object1and so forth, whereby the cut section meandered on the front face3side in particular.

Therefore, a quality pattern was used in addition to the individual difference correction pattern and spherical aberration correction pattern when forming the modified region at the intermediate position.FIG. 18is a fifth diagram illustrating a cut section obtained when cutting the object from modified regions acting as a start point. Here, using the front face3of the object1made of silicon having a thickness of 400 μm as a laser light entrance surface, modified regions SD1to SD5were formed in the descending order of their distance from the front face3. For forming the modified regions SD1, SD2located closer to the rear face21and the modified regions SD4, SD5located closer to the front face3, respective spherical aberration correction patterns S which could correct the spherical aberration at the converging point P of the laser light L were used, and the laser light L was modulated by modulation patterns including the respective spherical aberration correction patterns S in addition to the individual difference correction pattern D. For forming the modified region SD3at the intermediate position between the respective positions closer to the rear face21and front face3, the laser light L was modulated by a modulation pattern including a quality pattern J in addition to the individual difference correction pattern D and spherical aberration correction pattern S.

As a result, fractures generated at the time of forming the modified regions SD1, SD2reached the rear face21of the object1but failed to join with fractures generated at the time of forming the modified region SD3. Fractures generated at the time of forming the modified regions SD4, SD5reached the front face3of the object1but failed to join with the fractures generated at the time of forming the modified region SD3. This has made it possible to reduce the number of rows of modified regions7formed in the thickness direction of the object1along the line5, while preventing the accuracy in cutting the object1from lowering.

FIG. 19is a schematic view of converging spots of laser light for forming a modified region. When the laser light L was modulated by a modulation pattern including an individual difference correction pattern and a spherical aberration correction pattern, a converging spot CS1of the laser light L became a circular region as illustrated inFIG. 19(a). When the laser light L was modulated by a modulation pattern including a quality pattern in addition to the individual difference correction pattern and spherical aberration correction pattern, on the other hand, a converging spot CS2of the laser light L attained a form in which a plurality of dot-like regions were juxtaposed along the extending direction A of the line5(i.e. the relative moving direction of the laser light L) as illustrated inFIG. 19(b). There were cases where the dot-like regions adjacent to each other partly overlapped and were spaced apart from each other.

This seems to be because of the fact that the laser light L is diffracted in the reflective spatial light modulator203by the quality pattern having the first brightness region R1extending in a direction substantially orthogonal to the line5and the second brightness regions R2located on both sides of the first brightness region R1in the extending direction of the line S. Irradiation with the laser light L having thus constructed converging spot CS2can form modified regions7which can prevent fractures from continuously advancing in the thickness direction of the object1when forming a plurality of rows of modified regions7in the thickness direction of the object1.

As explained in the foregoing, the laser processing method performed in the laser processing system400uses the quality pattern having the first brightness region R1extending in a direction substantially orthogonal to the line5and the second regions R2located on both sides of the first brightness region R1in the extending direction of the line5for modulating the laser light L for forming the modified region7at the intermediate position between the position closer to the rear face21and the position closer to the front face3with respect to the object1. That is, after forming the modified region7at the position closer to the rear face21but before forming the modified region7at the position closer to the front face3while using the front face3as the laser light entrance surface (or after forming the modified region7at the position closer to the front face3but before forming the modified region7at the position closer to the rear face21while using the rear face21as the laser light entrance surface), the modified region7is formed at the intermediate position by irradiation with the laser light L modulated by the reflective spatial light modulator203according to the modulation pattern including the quality pattern. Even when the laser light L having a wavelength longer than 1064 nm is used in order to reduce the number of rows of modified regions7, for example, thus forming the modified region7at the intermediate position can prevent fractures from continuously advancing in the thickness direction of the object1at the time of forming a plurality of rows of modified regions7in the thickness direction of the object1. When a stress is generated in the object1, for example, a fracture occurring from the modified region7acting as a start point extends in the thickness direction of the object1more easily than in the case where the modified region7is not formed at the intermediate position, whereby the object1can be cut accurately along the line5. Hence, this laser processing method can reduce the number of rows of modified regions7formed in the thickness direction of the object1along the line5, while preventing the accuracy in cutting the object1from lowering, thereby shortening the takt time.

Here, in the extending direction of the line5, the width of the first brightness region R1is preferably at a ratio of 20% to 50% of the width of the effective region R for modulating the laser light L in the modulation pattern. In this case, the modified region7that can reliably prevent fractures from continuously advancing in the thickness direction of the object1when forming a plurality of rows of modified regions7in the thickness direction of the object1can be formed at the intermediate position. In the extending direction of the line5, the width of the first brightness region R1may be narrower or wider than the width of each of the second brightness regions R2.

Preferably, the laser light L is modulated by the reflective spatial light modulator203according to a modulation pattern including a quality pattern, an individual difference correction pattern, and a spherical aberration correction pattern when forming the modified region7at the intermediate position and according to a modulation pattern including the individual difference correction pattern and spherical aberration correction pattern when forming the modified regions7at the positions closer to the rear face21and the front face3. In this case, the modified regions7formed at the intermediate position and the positions closer to the rear face21and the front face3are easier to generate fractures, whereby the number of rows of modified regions7formed in the thickness direction of the object1along the line5can be reduced more reliably.

Preferably, the laser light L has a wavelength of 1080 nm or longer. This makes the object1exhibit a higher transmittance for the laser light L, so that the modified regions7formed at the intermediate position and the positions closer to the rear face21and the front face3are easier to generate fractures, whereby the number of rows of modified regions7formed in the thickness direction of the object1along the line5can be reduced more reliably.

Cutting the object1along the line5from the above-mentioned modified regions7acting as a start point can accurately cut the object1along the line5. Manufacturing a semiconductor device by cutting the object1can yield a highly reliable semiconductor device.

Though preferred embodiments of the present invention have been explained in the foregoing, the present invention is not limited thereto.

For example, as illustrated inFIG. 20, the number of rows of modified regions7formed at positions closer to the rear face21, the number of rows of modified regions7formed at positions closer to the front face3, and the number of rows of modified regions7formed at intermediate positions can be varied according to the thickness and material of the object1. The number of rows of modified regions7formed at positions closer to the rear face21can be determined such that fractures can be generated from the modified regions7to the rear face21, while the number of rows of modified regions7formed at positions closer to the front face3can be determined such that fractures can be generated from the modified regions7to the front face3. The number of rows of modified regions7formed at intermediate positions can be determined such that fractures can be prevented from advancing continuously in the thickness direction of the object1when forming a plurality of rows of modified regions7in the thickness direction of the object1.

Not only the quality pattern, individual difference correction pattern, and spherical aberration correction pattern, an astigmatism correction pattern for correcting the astigmatism at the converging point P of the laser light L and the like may also be used as element patterns to become elements of a modulation pattern.

The reflective spatial light modulator is not limited to the LCOS-SLM, but may also be a MEMS-SLM, a DMD (deformable mirror device), or the like. The spatial light modulator is not limited to the reflective one, but may be a transmissive one. Examples of the spatial light modulator include those of liquid crystal cell and LCD types. The reflective spatial light modulator203may use the reflection of pixel electrodes of the silicon substrate instead of the dielectric multilayer mirror.

INDUSTRIAL APPLICABILITY

The present invention can reduce the number of rows of modified regions formed in the thickness direction of the object while preventing the accuracy in cutting the object from lowering.

REFERENCE SIGNS LIST