JP6719074B2 - Laser processing area confirmation device and confirmation method - Google Patents

Description

The present invention is a laser for forming a modified region inside a wafer along a planned cutting line of the wafer by irradiating a laser beam with a focusing point inside the wafer having a plurality of devices formed on the surface. The present invention relates to a processing device and a laser processing method.

Conventionally, to divide a wafer with multiple devices formed on the surface into individual chips, a thin grindstone with a thickness of about 30 μm formed with fine diamond abrasive grains is used to cut the wafer by making grinding grooves in the wafer. The dicing device that does this has been used.

In the dicing machine, a thin grindstone (hereinafter referred to as a dicing blade) is rotated at a high speed, for example, at 30,000 to 60,000 rpm to grind the wafer, and the wafer is completely cut (full cut) or incompletely cut (half cut or semi-full). Cut).

However, in the case of grinding with this dicing blade, since the wafer is a highly brittle material, it becomes brittle mode processing, and chipping occurs on the front and back surfaces of the wafer, and this chipping is a factor that reduces the performance of the divided chips. It was

To solve this problem, instead of cutting with a conventional dicing blade, by irradiating a laser beam with the focusing point inside the wafer, the modified region by the multiphoton absorption (modified layer ) Is formed and divided into individual chips (see, for example, Patent Documents 1 and 2).

JP, 2009-34723, A JP, 2010-58128, A

However, in the technique as described above, when forming the modified region by condensing the laser light inside the wafer, the formation position of the modified region formed inside the wafer (particularly the position in the wafer depth direction) is changed. In order to confirm or measure, there is only a method in which the wafer is cut along a planned cutting line and then the cross section of the cut wafer is observed with a microscope. For this reason, it is difficult to verify the product wafer, and it is necessary to separately prepare the wafer for verification. Regarding processing damage, it is necessary to perform processing using a wafer on the back surface of which tin, gold, etc. are vapor-deposited, and then observe the wafer with another microscope, for example to detect a trouble in the middle of a lot. I couldn't.

The present invention has been made in view of the above circumstances, and provides a laser processing apparatus and a laser processing method capable of nondestructively confirming and measuring the formation position and processing damage of a modified region formed inside a wafer. The purpose is to

In order to achieve the above-mentioned object, the laser processing apparatus according to the first aspect of the present invention irradiates a laser beam with a converging point inside the wafer, so that the inside of the wafer is cut along a planned cutting line of the wafer. A laser processing apparatus for forming a modified region on a wafer, which comprises an illumination light source that outputs illumination light in a wavelength range that passes through a wafer, and an objective that collects the illumination light on the wafer and receives reflected light from the focusing point. A lens, a condensing point changing means for changing the condensing point of the objective lens in the wafer depth direction, and an image of reflected light received by the objective lens, and for each condensing point changed by the condensing point changing means. An image capturing unit that acquires a plurality of captured images.

A laser processing apparatus according to a second aspect of the present invention is the laser processing apparatus according to the first aspect, wherein the focusing point changing means changes the focusing point of the objective lens in the wafer depth direction by moving the objective lens in the optical axis direction. It has an objective lens moving means.

A laser processing apparatus according to a third aspect of the present invention is the laser processing apparatus according to the first aspect or the second aspect, wherein the condensing point changing means is a tunable lens arranged on an optical path between the image pickup means and the objective lens. Tunable lens curvature changing means for changing the focal point of the objective lens in the wafer depth direction by changing the curvature of the tunable lens.

A laser processing apparatus according to a fourth aspect of the present invention is the laser processing apparatus according to any one of the first to third aspects, wherein a focusing lens that focuses the laser light inside the wafer and the wafer relative to the laser light. And a moving means for moving the focusing lens. The focusing point of the objective lens is arranged downstream of the focusing point of the focusing lens in the moving direction of the wafer.

A laser processing apparatus according to a fifth aspect of the present invention is the laser processing apparatus according to any one of the first to fourth aspects, wherein the spatial light modulator that modulates the laser light and the depth from the laser light irradiation surface inside the wafer are mutually different. A controller that controls the spatial light modulator so that the laser beams are simultaneously focused on different positions that are different from each other in the moving direction of the wafer, and the spatial light modulator are configured separately, and inside the wafer An aberration correction unit that corrects the aberration of the laser light to be equal to or less than a predetermined aberration at a plurality of positions where the focal points of the laser light are combined.

A laser processing apparatus according to a sixth aspect of the present invention is the laser processing apparatus according to the fifth aspect, wherein the controller condenses the laser light at a first position in the wafer depth direction and the first position is the wafer depth. The spatial light modulator is controlled so that the laser light is focused on the second position which is different in the direction.

A laser processing method according to a seventh aspect of the present invention is a laser for forming a modified region inside a wafer along a planned cutting line of the wafer by irradiating a laser beam with a focusing point inside the wafer. In the processing method, a light receiving step of collecting illumination light of a wavelength range that passes through the wafer on the wafer by the objective lens and receiving reflected light from the light collecting point by the objective lens, and a light collecting point of the objective lens on the wafer Focusing point changing step of changing in the depth direction, and imaging in which the reflected light received by the objective lens is imaged by the imaging means, and a plurality of picked-up images are acquired for each focusing point changed in the focusing point changing step And a process.

A laser processing method according to an eighth aspect of the present invention is the laser processing method according to the seventh aspect, wherein in the focusing point changing step, the focusing point of the objective lens is changed in the wafer depth direction by moving the objective lens in the optical axis direction. Including steps.

A laser processing method according to a ninth aspect of the present invention is the laser processing method according to the seventh aspect or the eighth aspect, wherein the converging point changing step includes a curvature of a tunable lens arranged on an optical path between the imaging means and the objective lens. By changing the focal point of the objective lens in the wafer depth direction.

A laser processing method according to a tenth aspect of the present invention is the laser processing method according to any one of the seventh to ninth aspects, wherein a modified region is formed inside the wafer by a laser beam, and the objective lens is collected by a focusing point changing step. While changing the light spot in the wafer depth direction, a plurality of picked-up images are acquired for each condensing point changed in the converging point changing step in the imaging step.

A laser processing method according to an eleventh aspect of the present invention is the laser processing method according to any one of the seventh aspect to the tenth aspect, wherein the laser light is modulated by the spatial light modulator and the laser light modulated by the spatial light modulator is used. The focusing step of focusing inside the wafer, the moving step of moving the wafer relative to the laser light, and the depth from the laser light irradiation surface inside the wafer are different from each other, and in the moving direction of the wafer. A control process that controls the spatial light modulator so that the laser light is simultaneously focused on a plurality of positions separated from each other, and is configured separately from the spatial light modulator, and the focusing point of the laser light is aligned inside the wafer. An aberration correction step of correcting the aberration of the laser light to be equal to or less than a predetermined aberration at a plurality of positions.

A laser processing method according to a twelfth aspect of the present invention is the laser processing method according to the eleventh aspect, wherein in the control step, the laser light is focused at a first position in the wafer depth direction and the first position is the wafer depth. The spatial light modulator is controlled so that the laser light is focused on the second position which is different in the direction.

According to the present invention, the formation position and processing damage of the modified region formed inside the wafer can be confirmed and measured nondestructively.

The block diagram which showed the outline of the laser processing apparatus which concerns on the 1st Embodiment of this invention. Conceptual diagram showing how the modified region is formed inside the wafer Conceptual view of how cracks extend from the modified region formed inside the wafer in the wafer depth direction Schematic diagram showing multiple captured images captured by an infrared camera The figure which showed an example of the captured image containing an upper modified layer and a lower modified layer. Graph showing the relationship between the amount of aberration correction and the total crack length Graph showing the relationship between aberration correction and crack bottom length FIG. 3 is a conceptual diagram showing how a modified region is formed inside a wafer, and is a diagram for explaining another form of two positions (focusing positions) where laser light is focused. The block diagram which showed the outline of the laser processing apparatus which concerns on the 2nd Embodiment of this invention. The block diagram which showed the outline of the laser processing apparatus which concerns on the 3rd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a configuration diagram showing an outline of a laser processing apparatus according to a first embodiment of the present invention. As shown in FIG. 1, the laser processing apparatus 1 of the present embodiment mainly includes a wafer moving unit 11, a laser head 20, a control unit 60 and the like.

The wafer moving unit 11 includes a suction stage 13 that holds the wafer W by suction, and an XYZθ table 12 that is provided on the main body base 16 of the laser processing apparatus 1 and that moves the suction stage 13 precisely in the XYZθ directions. The wafer W is precisely moved by the wafer moving unit 11 in the XYZθ directions in the drawing. The wafer moving unit 11 is an example of moving means.

A back grind tape (hereinafter, BG tape) having an adhesive material is attached to the surface of the wafer W on which the device is formed, and the wafer W is placed on the suction stage 13 so that the back surface faces upward. The thickness of the wafer W is not particularly limited, but is typically 700 μm or more, and more typically 700 to 800 μm.

The wafer W may be mounted on the suction stage 13 in a state in which a dicing sheet having an adhesive material is attached to one surface of the wafer W and the wafer W is integrated with the frame via the dicing sheet.

The laser head 20 includes a processing optical system for irradiating the wafer W with a processing laser beam L, and an observation optical system for confirming or measuring a formation position of a modified region formed inside the wafer W and processing damage. It has a system.

The processing optical system of the laser head 20 includes a laser light source 22, a spatial light modulator 28, a condenser lens 38, and the like.

The laser light source 22 outputs a processing laser beam L for forming a modified region inside the wafer W under the control of the control unit 60. The conditions of the laser light L are, for example, a semiconductor laser-excited Nd:YAG laser as a light source, a wavelength of 1.1 μm, a laser light spot cross-sectional area of 3.14×10 ⁻⁸ cm ² , and an oscillation mode of Q switch pulse. The repetition frequency is 80 to 120 kHz, the pulse width is 180 to 380 ns, and the output is 8 W.

The spatial light modulator 28 is of a phase modulation type, and receives the laser light L output from the laser light source 22 and modulates the phase of the laser light L in each of a plurality of two-dimensionally arranged pixels. The pattern is presented and the laser light L after the phase modulation is output. This hologram pattern is formed by superimposing a plurality of Fresnel lens patterns having different focusing positions. As a result, as will be described later in detail, the depths from the laser light irradiation surface (the back surface of the wafer W) inside the wafer W are different from each other, and the wafer movement direction (processing feed direction) parallel to the X direction in FIG. The laser light L is simultaneously condensed by the condenser lens 38 at two positions separated from each other by M.

As the spatial light modulator 28, for example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) is used.
) Spatial light modulator (SLM: Spatial Light Modulator) is used. The operation of the spatial light modulator 28 and the hologram pattern presented by the spatial light modulator 28 are controlled by the control unit 60. Since the specific configuration of the spatial light modulator 28 and the hologram pattern presented by the spatial light modulator 28 are already known, detailed description thereof will be omitted here.

The condenser lens 38 is an objective lens (infrared objective lens) that condenses the laser light L inside the wafer W. The condenser lens 38 having a numerical aperture (NA) of 0.6 to 0.8 (for example, 0.65) is used.

The condenser lens 38 is an objective lens with a correction ring for correcting the aberration of the laser light L generated inside the wafer W. A correction ring (not shown) provided on the condenser lens 38 is manually rotatable. When the correction ring is rotated in a predetermined direction, the distance between the lens groups forming the condenser lens 38 is changed. Then, the aberration can be corrected so that the aberration of the laser light L becomes equal to or less than the predetermined aberration at a position of a predetermined depth from the laser light irradiation surface (back surface) of the wafer W. The correction ring of the condenser lens 38 is an example of aberration correction means.

The correction ring of the condenser lens 38 may be electrically driven by a correction ring driving unit (not shown). In this case, the control unit 60 controls the operation of the correction ring drive unit and rotates the correction ring to correct the aberration of the laser light L to a desired state.

The processing optical system of the laser head 20 includes a beam expander 24, a λ/2 wavelength plate 26, a reduction optical system 36, and the like, in addition to the above configuration.

The beam expander 24 expands the laser light L output from the laser light source 22 into a beam diameter suitable for the spatial light modulator 28. The λ/2 wave plate 26 adjusts the polarization plane of the laser light incident on the spatial light modulator 28. The reduction optical system 36 is an afocal optical system (both-side telecentric optical system) including a first lens 36a and a second lens 36b, and collects the laser light L modulated by the spatial light modulator 28 into a condensing lens 38. Reduced projection to.

The observation optical system of the laser head 20 includes an illumination light source 42, a half mirror 44, an observation objective lens 46, an actuator 48, an infrared camera 50, and the like.

The illumination light source 42 is, for example, an LD (Laser Diode) light source or an SLD (Super Luminescent Diode) light source, and outputs illumination light (infrared light) in a wavelength range (infrared range) that transmits the wafer W.

The illumination light output from the illumination light source 42 passes through the half mirror 44 arranged on the optical path thereof, and is irradiated onto the wafer W via the observation objective lens 46. The objective lens 46 for observation has a numerical aperture (NA) of 0.5 to 0.9 (preferably 0.6 to 0.8). Further, the position of the focal point of the observation objective lens 46 in the Z direction (position in the wafer depth direction) is determined by moving the observation objective lens 46 in the Z direction (optical axis direction of the observation objective lens 46) by the actuator 48. Is adjusted by. The actuator 48 is an example of an objective lens moving unit.

The reflected light reflected by the wafer W (that is, the reflected light from the focal point by the observation objective lens 46) is received by the observation objective lens 46. Further, the reflected light received by the observation objective lens 46 is reflected by the half mirror 44 and enters the infrared camera 50.

The infrared camera 50 is an example of an image capturing unit, and captures an image of the wafer W from the laser light incident surface (back surface) side of the wafer W. The infrared camera 50 includes an image sensor (not shown) having sensitivity to the wavelength range of infrared light. Therefore, with the actuator 48, the observation objective lens 46 is moved in the Z direction (the direction of the optical axis of the observation objective lens 46) so that the focusing point of the observation objective lens 46 is aligned inside the wafer W. When the image of the wafer W is taken by 50, the internal state of the wafer W can be confirmed. Further, the internal state of the wafer W can be confirmed by aligning the converging point of the observation objective lens 46 with the surface of the wafer W (the surface opposite to the laser light incident surface). A captured image captured by the infrared camera 50 is stored in a storage unit (not shown) of the laser processing device 1.

As the infrared camera 50, for example, a camera (near infrared camera) having high sensitivity in the near infrared region (wavelength region of 1 μm or more) represented by an InGaAs (indium gallium arsenide) camera is preferably used.

In the present embodiment, as shown in FIG. 1, the observation position of the wafer W by the observation optical system, that is, the imaging position of the wafer W by the infrared camera 50 (the converging point of the observation objective lens 46) is the processing optical system. Is arranged in a straight line on the downstream side (right side in FIG. 1) in the wafer moving direction M with respect to the processing position of the wafer W (converging point of the laser light L by the condensing lens 38). With this configuration, the infrared camera 50 can image the wafer W on the same planned cutting line as the processing position of the wafer W by the processing optical system, and the formation position of the modified region formed inside the wafer W and It is possible to confirm and measure processing damage etc. in real time.

Although not shown, the laser head 20 has an alignment optical system for performing alignment with the wafer W, and an automatic optical system for maintaining a constant distance (working distance) between the wafer W and the condenser lens 38. A focus unit and the like are provided.

The control unit 60 includes a CPU, a memory, an input/output circuit unit, etc., and controls the operation of each unit of the laser processing apparatus 1. Specifically, the thickness of the wafer W and the feed speed of the wafer W are controlled, and the operation of each part (the wafer moving part 11, the laser head 20, etc.) is controlled under optimum conditions to form the modified region.

Further, the control unit 60 controls the operation of the spatial light modulator 28 and causes the spatial light modulator 28 to present a predetermined hologram pattern. Specifically, two positions different from each other inside the wafer W (that is, two positions having different depths from the laser light irradiation surface and separated from each other in the wafer moving direction M parallel to the X direction in FIG. 1). ) Causes the spatial light modulator 28 to present a hologram pattern for modulating the laser light L so that the laser light L is simultaneously condensed by the condenser lens 38. The hologram pattern is derived in advance based on the formation position of the modified region, the wavelength of the laser light L to be irradiated, the refractive index of the condenser lens 38 and the wafer W, and is stored in the control unit 60.

In addition, when the control unit 60 confirms or measures the formation position of the modified region formed inside the wafer W and the processing damage, the condensing point by the observation objective lens 46 is a minute step (for example, 2 μm) in the Z direction. The drive of the actuator 48 is controlled so as to move at intervals.

In addition to this, the laser processing apparatus 1 is composed of a wafer transfer means (not shown), an operation plate, a television monitor, an indicator lamp and the like.

Switches and display devices for operating the operations of the respective parts of the laser processing apparatus 1 are attached to the operation plate. The television monitor displays a captured image (wafer image) captured by the infrared camera 50, or displays program content, various messages, and the like. The indicator lamp displays an operation status such as during processing of the laser processing apparatus 1, processing completion, and emergency stop.

The operation of the laser processing apparatus 1 of the present embodiment configured as above will be described. Here, a case where a silicon substrate having a thickness of 775 μm is processed as the wafer W will be described as an example.

First, the correction ring provided in the condenser lens 38 is manually (or electrically) rotated to cause the laser light L to be condensed inside the wafer W at a position where the laser light L is condensed (processing depth of the modified region). The aberration correction amount is adjusted so that the aberration is less than or equal to the predetermined aberration. In the present specification, the “aberration correction amount” is a value converted into the depth from the laser light irradiation surface of the wafer W. That is, for example, when the aberration correction amount is 500 μm, it means that the aberration of the laser light is minimum at a position where the depth from the laser light irradiation surface of the wafer W is 500 μm. In this example, as will be described later in detail, when the thickness of the wafer W is 775 μm, the aberration correction amount by the correction ring is preferably set to 500 μm.

Next, after the wafer W to be processed is placed on the suction stage 13, the alignment of the wafer W is performed using an alignment optical system (not shown).

Next, while the XYZθ table 12 is processed and fed in the wafer moving direction M (that is, the wafer W is relatively moved in the wafer moving direction M with respect to the laser light L), the laser head 20 moves toward the wafer W. The laser light L is irradiated.

At this time, the laser light L output from the laser light source 22 has its beam diameter expanded by the beam expander 24, is reflected by the first mirror 30, and is changed in polarization direction by the λ/2 wavelength plate 26 to perform spatial light modulation. It is incident on the container 28.

The laser light L incident on the spatial light modulator 28 is modulated according to a predetermined hologram pattern presented on the spatial light modulator 28. At that time, the control unit 60 spatially modulates the hologram pattern for modulating the laser light L so that the laser light L is simultaneously condensed by the condenser lens 38 at two different positions inside the wafer W. The control for causing the container 28 to present is performed.

The laser light L emitted from the spatial light modulator 28 is sequentially reflected by the second mirror 31 and the third mirror 32, passes through the first lens 36a, and is further reflected by the fourth mirror 33 and the fifth mirror 34. It is reflected, passes through the second lens 36b, and is incident on the condenser lens 38. As a result, the laser light L emitted from the spatial light modulator 28 is reduced and projected onto the condenser lens 38 by the reduction optical system 36 including the first lens 36a and the second lens 36b. Then, the laser light L incident on the condenser lens 38 is condensed by the condenser lens 38 at two different positions inside the wafer W.

FIG. 2 is a conceptual diagram showing how the modified region is formed inside the wafer W. As shown in FIG. 2, the laser light L modulated by the spatial light modulator 28 has different depths from the laser light irradiation surface (back surface of the wafer W) inside the wafer W by the condenser lens 38, and The light is focused at two positions separated from each other in the wafer moving direction M at the same time. As a result, modified regions P1 and P2 due to multiphoton absorption are formed in the vicinity of the respective focusing positions. When the modified regions P1 and P2 are formed, cracks K1 and K2 extending from the modified regions P1 and P2 in the wafer depth direction (wafer thickness direction) are formed.

Here, the two positions (focusing positions) where the laser light L is focused will be described in detail. In the present embodiment, the first position Q1 in the wafer depth direction inside the wafer W (right side in FIG. 2). Laser beam L is focused on a second position Q2 (focus point on the left side in FIG. 2) which is different from the first position Q1 in the wafer depth direction. It

Further, in the present embodiment, the second position Q2 is arranged on the upstream side (left side in FIG. 2) in the wafer moving direction M with respect to the first position Q1 and the first position from the laser light irradiation surface of the wafer W. It is arranged at a position deeper than the position Q1. An example of the distance (interval) between the first position Q1 and the second position Q2 is 50 μm in the wafer depth direction. The distance in the wafer moving direction M is 30 μm.

By moving the wafer W relative to the laser light L in this state, as shown in FIG. 3, along the movement loci of the two focus points (focus positions Q1 and Q2) of the laser light L. The modified regions P1 and P2 are formed inside the wafer W. As a result, the modified regions P1 and the modified regions P2 are formed inside the wafer W one by one along the planned cutting line of the wafer W in a state of being overlapped with each other at a predetermined interval.

When the modified region P1 and the modified region P2 are formed in such a manner that they are overlapped at a predetermined interval, the two modified regions P1 and P2 overlapping in the wafer depth direction are delayed with time. As shown in FIG. 3, the impact at the time of forming the reformed region P1 to be formed connects the crack K1 of the reformed region P1 and the crack K2 of the reformed region P2, and further the crack K2 extending from the reformed region P2 to the wafer. The W extends toward the surface (the surface of the wafer W) opposite to the laser light irradiation surface.

That is, by modulating the laser light L by the spatial light modulator 28, the laser light L is simultaneously focused at different positions inside the wafer W, so that the throughput from the surface of the wafer W is not reduced. The crack can be extended to a desired position between the target surface indicating the position of the final thickness T2 of the wafer W and the surface of the wafer W. 2 and 3, T1 represents the initial thickness of the wafer W (775 μm in this example).

When the reformed regions P1 and P2 are formed line by line along the planned cutting line, the XYZθ table 12 is indexed and fed by one pitch in the Y direction, and the reformed regions P1 and P2 are similarly formed on the next line. ..

When the modified regions P1 and P2 are formed along all the planned cutting lines parallel to the X direction, the XYZθ table 12 is rotated by 90°, and the lines orthogonal to the previous line are all similarly modified regions P1. , P2 are formed.

As a result, the modified regions P1 and P2 are formed along all the planned cutting lines. The modified regions P1 and P2 have the same position on the plane (the position when viewed from the back surface or the front surface of the wafer W) and are both formed along the planned cutting line, but in the thickness direction of the wafer W (wafer Only the position in the depth direction) is different.

After the modified regions P1 and P2 are formed along the planned cutting line as described above, the back surface of the wafer W is ground by using a grinding device (not shown) to obtain a thickness (initial thickness) T1 of the wafer W. A backside grinding step is performed to process the above into a predetermined thickness (final thickness) T2 (for example, 30 to 50 μm).

After the back surface grinding step, an expanding tape (dicing tape) is attached to the back surface of the wafer W, the BG tape attached to the front surface of the wafer W is peeled off, and a tension is applied to the expanding tape attached to the back surface of the wafer W. Then, an expanding step of adding and expanding the mixture is performed.

As a result, the wafer W is cut with the crack extending to the front surface side of the wafer W as a starting point. That is, the wafer W is cut along the planned cutting line and divided into a plurality of chips.

Here, in the laser processing apparatus 1 according to the present embodiment, as shown in FIG. 1, the laser light L is formed inside the wafer W while forming the modified region along the planned cutting line along the planned cutting line. Wafer processing confirmation processing for confirming the formed position of the modified region and the processing damage is performed in real time.

In the wafer processing confirmation processing, the infrared camera 50 takes an image from the laser light incident surface (back surface) side of the wafer W on the same planned cutting line as the modified region formed inside the wafer W by the processing optical system.

At this time, the control unit 60 controls the drive of the actuator 48 to move the observation objective lens 46 in the optical axis direction (Z direction) in minute steps (for example, about 2 μm) (that is, the observation objective lens 46 An image is picked up by the infrared camera 50 while moving the position of the focal point (focal point) in minute steps in the wafer depth direction. In the present embodiment, the position of the focusing point of the observation objective lens 46 is changed from the laser light incident surface (back surface) of the wafer W to the device surface (front surface). As a result, as shown in FIG. 4, a plurality of picked-up images (XY images at the positions of the respective converging points) 62 (62-1, each of which has a different position in the wafer depth direction for each converging point of the observation objective lens 46). 62-2,..., 62-n) are sequentially acquired by the infrared camera 50. The plurality of captured images 62 sequentially acquired by the infrared camera 50 are stored in the storage unit (not shown) of the laser processing device 1. In addition, each captured image stored in the storage unit can be displayed on the television monitor according to a user operation.

An example of a captured image including an upper modified layer (modified region P1) and a lower modified layer (modified region P2) among a plurality of captured images obtained by the infrared camera 50 in the wafer processing confirmation process is shown in FIG. Shown in.

When the modified region P1 and the modified region P2 are properly formed in the wafer depth direction (Z direction), as shown in FIG. The modified region can be confirmed in the captured image at the position in the wafer depth direction.

On the other hand, when the modified region P1 and the modified region P2 are not properly formed in the wafer depth direction, the modified region cannot be confirmed in the captured image at the desired position in the wafer depth direction.

Therefore, it is determined from the plurality of captured images captured by the infrared camera 50 whether the captured image in which the modified region P1 or the modified region P2 is confirmed is the captured image at the desired wafer depth direction position. Thus, it is possible to confirm whether or not the reformed region forming positions such as the positions of the reformed regions P1 and P2 in the wafer depth direction and the intervals between the reformed regions P1 and P2 are appropriate.

In the present embodiment, this determination process is automatically performed by the control unit 60. The control unit 60 detects the three-dimensional positional relationship between the modified regions P1 and P2 inside the wafer W by performing image processing on each captured image by the image processing unit 60a provided therein. As a result, not only the wafer depth direction position (Z direction position) of each of the modified regions P1 and P2 but also the processing feed direction position (X direction position) and the index feed direction position (Y direction position) are formed at appropriate positions. It is possible to easily determine whether or not it has been done. Therefore, it is possible to confirm the positional deviation in the horizontal direction (X direction and Y direction) of the incident point of the laser light L with respect to the planned cutting line.

Further, the processing damage caused on the device surface side of the wafer W is confirmed from the imaged image picked up by the infrared camera 50 when the position of the converging point of the observation objective lens 46 is set at or near the device surface of the wafer W. can do.

As described above, according to the present embodiment, while forming the modified region inside the wafer W by the laser beam L along the planned cutting line, the formation position and processing of the modified region formed inside the wafer W are performed. Wafer processing confirmation processing for confirming and measuring damage is performed in real time. In the wafer processing confirmation process, as described above, while changing the position of the focal point (focal point) of the observation objective lens 46 in the wafer depth direction, the infrared camera 50 is used for each focal point of the observation objective lens 46. Then, a plurality of captured images are sequentially acquired. This makes it possible to non-destructively confirm and measure the formation position and processing damage of the modified region formed inside the wafer W from the plurality of captured images acquired by the infrared camera 50 without destroying the wafer W. it can.

Further, in the present embodiment, it is possible to preferably employ a configuration in which the result of confirmation or measurement in the wafer processing confirmation process is feedback-controlled to the formation position of the modified region and the laser processing condition. With this configuration, it is possible to form a modified region suitable for dividing the wafer while automatically correcting the forming position of the modified region and the laser processing conditions, and it is also possible to prevent processing damage. , You can get stable quality chips.

Note that, in the present embodiment, as an example, the mode in which the above-described determination process is automatically performed by the image processing unit 60a provided in the laser processing apparatus 1 is shown, but the invention is not limited to this, and the infrared camera 50 acquires the determination process, for example. A plurality of captured images may be displayed on the television monitor so that the user can confirm and measure the formation position of the modified region formed inside the wafer W and the processing damage.

Further, in the present embodiment, while the laser light L is simultaneously condensed by the condenser lens 38 at a plurality of positions by using the spatial light modulator 28, the laser light L is condensed by the correction ring of the condenser lens 38. Since the aberration at the point-matching position is corrected to be equal to or less than the predetermined aberration, even if the wafer W is thick, the laser light L can be efficiently focused at a deep position in the wafer depth direction. Is possible. Further, cracks generated when the modified regions P1 and P2 overlapping in the wafer depth direction are sufficiently extended to the surface (front surface of the wafer W) opposite to the laser light irradiation surface of the wafer W. it can. Therefore, the wafer W can be efficiently divided into chips, and stable quality chips can be efficiently obtained.

Here, an experiment conducted by the present inventors to verify the above effects will be described.

In this experiment, the laser processing apparatus 1 of the above-described embodiment was used as an example. In addition, as a comparative example, an apparatus having the same configuration as that of Patent Document 2 described above, that is, a spatial light modulator is used to focus laser light at two different positions inside the wafer while each position is adjusted. For correcting aberration in (1st comparative example) and a device for correcting aberration using a correction ring without using a spatial light modulator (that is, by converging laser light at one focus position) (Second Comparative Example) was used.

As an experimental condition, for a wafer (silicon substrate) having a thickness of 775 μm, when the modified region is formed while changing the aberration correction amount in each apparatus, the total crack length (the crack length The total length) and the crack lower end length (the length of the crack extending from the lower end of the modified region to the wafer surface side) were measured (see FIG. 3 ).

FIG. 6 is a graph showing the relationship between the aberration correction amount and the total crack length. FIG. 7 is a graph showing the relationship between the aberration correction amount and the crack bottom length. 6 and 7, the horizontal axis represents the aberration correction amount, and the vertical axis represents the total crack length and the crack lower end length generated by the respective devices.

As can be seen from FIGS. 6 and 7, in the example, the total crack length becomes longer over all aberration correction amounts, and the crack lower end length also becomes longer, as compared with the first comparative example and the second comparative example. Results were obtained.

In particular, when the aberration correction amount is 500 μm, in the example, the total crack length is about 250 μm and the crack lower end length is about 80 μm, which is a very excellent result as compared with the first comparative example and the second comparative example. Has been obtained. From this result, in the laser processing apparatus 1 of the present embodiment, when processing the wafer W having the thickness of 775 μm, the aberration correction amount by the correction ring is 500 μm (that is, the laser light irradiation surface of the wafer W (wafer W Is preferably set so that the aberration is minimized at a position where the depth from the back surface) is 500 μm. Then, the spatial light modulator 28 modulates the laser light so that the laser light L is simultaneously focused by the condenser lens 38 at two positions having different depths in the vicinity of this depth (500 μm). The cracks extending in the wafer depth direction can be sufficiently extended from the modified region formed inside the wafer W. As a result, the wafer can be efficiently divided into chips, and stable quality chips can be efficiently obtained.

In addition, in the present embodiment, the mode in which the aberration correction unit is configured by the correction ring provided in the condenser lens 38 has been described, but the present invention is not limited to this, and the condenser lens 38 and the spatial light modulator 28 are not included. A correction optical system may be arranged on the optical path of the laser light L between them (for example, between the condenser lens 38 and the second lens 36b). In this case, the aberration of the laser light L generated inside the wafer W can be corrected by changing the distance between the plurality of lens groups forming the correction optical system by a driving unit (not shown).

Further, instead of using the objective lens with the correction ring, as the condenser lens 38, a correction function is incorporated in advance so that the aberration of the laser light L is minimized at a predetermined position inside the wafer W in the depth direction of the wafer. An objective lens (infrared objective lens) may be used. In this case, the aberration correction amount is fixed depending on the thickness of the wafer W and the laser beam focusing position (processing depth of the modified region), but for example, the aberration is corrected at a position where the aberration correction amount is 500 μm. By using the smallest objective lens, the crack can be sufficiently extended from the modified region in the wafer depth direction.

Further, in the present embodiment, the laser light L is simultaneously focused inside the wafer W at two different positions in the wafer depth direction, and the modified regions P1 and P2 are simultaneously formed at the respective focusing positions. A method of dividing the wafer W into individual chips by performing a backside grinding step of grinding the backside of the wafer W after performing the two-step processing is not limited to this. The laser processing may be performed a plurality of times while changing the position (the processing depth of the modified region) where the laser light L is focused inside. At that time, the correction pattern for correcting the aberration inside the wafer W is added to the hologram pattern presented to the spatial light modulator 28 according to the processing depth of the modified region (in this case, the correction pattern of the correction ring is used to cancel the correction). By superimposing the pattern), it is possible to perform appropriate aberration correction even on a portion relatively deep from the laser light irradiation surface of the wafer W.

Further, in the present embodiment, as shown in FIG. 2, the second position Q2 is the first position as the positional relationship between the two positions (condensing positions) Q1 and Q2 where the laser light L is condensed. The structure is arranged upstream of the position Q1 in the wafer movement direction M (left side in FIG. 2) and deeper than the first position Q1 from the laser light irradiation surface of the wafer W. However, the configuration is not limited to this, and as shown in FIG. 8, a configuration opposite to that shown in FIG. That is, the second position Q2 is arranged on the upstream side (left side in FIG. 8) in the wafer movement direction M with respect to the first position Q1 and is shallower than the first position Q1 from the laser light irradiation surface of the wafer W. It may be arranged at a position.

Further, in the present embodiment, the spatial light modulator 28 modulates the laser light L so that the laser light L is simultaneously condensed by the condenser lens 38 at two different positions inside the wafer W. The position at which the laser light L is focused is not limited to two, and may be three or more.

Further, in the present embodiment, a reflective spatial light modulator (LCOS-SLM) is used as the spatial light modulator 28, but the spatial light modulator 28 is not limited to this, and may be a MEMS-SLM or DMD (deformable mirror device) or the like. It may be. Further, the spatial light modulator 28 is not limited to the reflective type and may be a transmissive type. Further, as the spatial light modulator 28, a liquid crystal cell type, an LCD type or the like can be mentioned.

(Second embodiment)
Next, a second embodiment of the present invention will be described. The description of the parts common to the first embodiment will be omitted, and the description will focus on the characteristic parts of the present embodiment.

FIG. 9 is a configuration diagram showing an outline of the laser processing apparatus according to the second embodiment. In FIG. 9, constituent elements common or similar to those in FIG. 1 are designated by the same reference numerals, and description thereof will be omitted.

In the second embodiment, in the observation optical system of the laser head 20, a tunable lens 52 is arranged on the optical path of reflected light between the half mirror 44 and the infrared camera 50. The tunable lens 52 changes the focal point of the observation objective lens 46 in the wafer depth direction (Z direction) by changing its curvature under the control of the control unit 60. The control unit 60 is an example of a tunable lens curvature changing unit.

According to the second embodiment, the focusing point of the observation objective lens 46 is moved in the wafer depth direction at a high speed by the tunable lens 52, and the focusing point of the observation objective lens 46 is moved by the actuator 48 to the wafer. It becomes possible to move a minute distance in the depth direction with high accuracy. Therefore, as compared with the case where the focusing point of the observation objective lens 46 is changed only by the actuator 48 as in the first embodiment, the focusing point of the observation objective lens 46 can be moved at high speed and with high accuracy. Therefore, the imaging time of the wafer W by the infrared camera 50 can be shortened, and the throughput for the wafer processing confirmation process can be improved.

In the second embodiment, as an example, the mode in which the tunable lens 52 and the actuator 48 are used in combination as the means (focus point changing means) for changing the focus point of the observation objective lens 46 is shown. However, without being limited to this, for example, the actuator 48 may not be provided, and the converging point of the observation objective lens 46 may be changed only by the tunable lens 52.

(Third Embodiment)
Next, a third embodiment of the present invention will be described. The description of the parts common to the first embodiment will be omitted, and the description will focus on the characteristic parts of the present embodiment.

FIG. 10 is a configuration diagram showing an outline of a laser processing apparatus according to the third embodiment. In FIG. 10, the same or similar components as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

In the third embodiment, a part of the observation optical system in the laser head 20 is arranged coaxially with the optical axis of the processing optical system. Specifically, a half mirror 44 is disposed between the condenser lens 38 and the second lens 36b on the optical path of the processing optical system, and the condenser lens 38 is shared by the processing optical system and the observation optical system. Has been done. Therefore, the laser light L output from the laser light source 22 is focused inside the wafer W by the condenser lens 38 via the spatial light modulator 28 and the like, and is also reflected inside the wafer W. The reflected light of the light L passes through the condenser lens 38, is reflected by the half mirror 44, and enters the infrared camera 50. Further, the Z-direction position of the condensing point by the condensing lens 38 (position in the wafer depth direction) is adjusted by moving the condensing lens 38 in the Z direction (optical axis direction of the condensing lens 38) by the actuator 54. It

According to the third embodiment, since a part of the observation optical system in the laser head 20 is arranged coaxially with the optical axis of the processing optical system, the imaging position of the wafer W by the infrared camera 50 is processed. It is set at the same position as the processing position of the wafer W by the optical system. Therefore, when the reformed region is formed inside the wafer W by the laser light L, the formation position of the reformed region can be instantly and accurately confirmed and measured by the infrared camera 50 simultaneously with the formation of the reformed region. Become.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above examples, and it is needless to say that various improvements and modifications may be made without departing from the scope of the present invention. ..

10... Laser processing device, 11... Wafer moving part, 12... XYZθ table, 13... Adsorption stage, 20... Laser head, 22... Laser light source, 24... Beam expander, 26... λ/2 wavelength plate, 28... Spatial light Modulator, 36... Reduction optical system, 38... Condensing lens, 42... Illumination light source, 44... Half mirror, 46... Observation objective lens, 48... Actuator, 50... Infrared camera, 52... Tunable lens, 54... Actuator , 60... Control unit, 60a... Image processing unit

Claims (6)

A device for confirming a laser processing area formed inside a workpiece,
An illumination light source that outputs illumination light in a wavelength range that passes through the workpiece,
An objective lens that collects the illumination light on the workpiece and receives reflected light from a light collection point,
Focusing point changing means for changing the focusing point of the objective lens in the depth direction of the workpiece,
An image capturing unit that captures the reflected light received by the objective lens, and acquires a plurality of captured images for each of the focus points changed by the focus point changing unit.
A device for confirming a laser processing area, which comprises: The condensing point changing means has an objective lens moving means for changing the condensing point of the objective lens in the depth direction by moving the objective lens in the optical axis direction.
The laser processing area confirmation device according to claim 1. The condensing point changing unit changes the curvature of the tunable lens disposed on the optical path between the imaging unit and the objective lens, and the condensing point of the objective lens by changing the curvature of the tunable lens. Tunable lens curvature changing means for changing in the depth direction,
The device for confirming a laser processing region according to claim 1 or 2. A method for confirming a laser processing area formed inside a workpiece, comprising:
A light receiving step of collecting illumination light of a wavelength range that passes through the object to be processed with an objective lens and receiving reflected light from a condensing point with the object lens;
A focusing point changing step of changing the focusing point of the objective lens in the depth direction of the workpiece;
An image capturing step of capturing the reflected light received by the objective lens with an image capturing means, and acquiring a plurality of captured images for each of the focus points changed in the focus point changing step;
The method of confirming the laser processing area including. The condensing point changing step includes a step of changing the condensing point of the objective lens in the depth direction by moving the objective lens in the optical axis direction.
The method for confirming a laser processing area according to claim 4. In the condensing point changing step, the condensing point of the objective lens is changed in the depth direction by changing a curvature of a tunable lens arranged on an optical path between the imaging unit and the objective lens. Including the step of
The method for confirming a laser processing area according to claim 4 or 5.