JP2018129540A - Laser dicing device - Google Patents

Abstract

A laser dicing apparatus capable of detecting a height position of a surface of a wafer quickly, accurately and stably regardless of a processing depth of a modified region. An AF apparatus (height position detecting means) is configured to focus an AF laser beam having a wavelength that can be reflected on the surface of a wafer W by an AF laser light source and a condenser lens. An AF signal processing unit 250 that sends a displacement signal indicating the displacement of the wafer surface to the control unit 50 based on the reflected light of the AF laser light reflected by the surface of W, and an AF laser light irradiation path 242 that is disposed in the AF A focus optical system 206 that adjusts the condensing point of the laser light in the wafer thickness direction, and a 4f optical system 214 disposed between the condensing lens 106 and the focus optical system 206 are provided. [Selection] Figure 1

Description

  The present invention relates to a laser dicing apparatus that divides a wafer on which a semiconductor device, an electronic component, and the like are formed into individual chips.

  Conventionally, in order to divide a wafer having a semiconductor device or electronic component formed on its surface into individual chips, grinding grooves are formed in the wafer with a thin grindstone with a thickness of about 30 μm formed of fine diamond abrasive grains. A dicing machine for cutting wafers has been used.

  In the dicing apparatus, a thin grindstone (hereinafter referred to as a dicing blade) is rotated at a high speed of, for example, 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, chipping occurs on the front and back surfaces of the wafer, and this chipping is a factor that degrades the performance of the divided chips. It was.

  To solve this problem, instead of cutting with a conventional dicing blade, a laser beam is incident on the wafer with the focusing point aligned, and a modified region by multiphoton absorption is formed inside the wafer. A technique of dividing into chips has been proposed (see, for example, Patent Document 1). In such a technique, the height of the wafer surface (position in the thickness direction) is detected using an autofocus mechanism in order to form a modified region formed inside the wafer at a certain depth from the wafer surface. Therefore, it is necessary to control the position of the condensing point of the laser light with high accuracy.

  In the technique disclosed in Patent Document 1, in order to form a modified region (modified layer) uniformly at a predetermined depth inside the wafer, the surface of the wafer is irradiated with a detection laser beam (AF laser beam), Based on the reflected light, the height position of the surface of the wafer is detected, and processing is performed while controlling the condensing point position of the laser beam for processing according to the height position of the surface of the wafer.

  Further, the technique disclosed in Patent Document 1 includes a condensing point position displacing means for displacing the condensing point position of the laser beam for detection, and when the modified region is formed at a deep position from the surface of the wafer. Can adjust the distance between the condensing point position of the detection laser beam and the condensing point position of the processing laser beam. As a result, the irradiation area (spot area) of the detection laser beam irradiated on the wafer surface can be reduced, so the amount of light per unit area of the reflected light of the detection laser beam reflected on the wafer surface can be reduced. It is possible to accurately detect the height position of the surface of the wafer without lowering.

JP 2009-269074 A

  However, in the technology as described above, since a condensing lens (high NA lens) having a high numerical aperture (NA) is generally used, the sensitivity of the autofocus mechanism is extremely high, and the range of high-precision detection is in focus. Limited to the vicinity of the position. For this reason, the measurement range (pull-in range) in which the height position of the surface of the wafer can be detected is extremely narrow. In addition, if the autofocus characteristics differ according to the depth of the modified region formed inside the wafer from the surface of the wafer (hereinafter referred to as “processing depth”), the stability and responsiveness of the autofocus mechanism There is a problem that the detection of the height position of the surface of the wafer cannot be performed quickly, accurately and stably.

  Patent Document 1 discloses a condensing point position displacing means for displacing the condensing point position of the detection laser light, but does not show any suggestion or solution for these problems.

  The present invention has been made in view of such circumstances, and laser dicing capable of quickly and accurately detecting the height position of the surface of the wafer regardless of the processing depth of the modified region. An object is to provide an apparatus.

  In order to achieve the above object, a laser dicing apparatus according to a first aspect of the present invention includes a table for holding a wafer, and a processing laser beam for forming a modified region inside the wafer held by the table. By emitting the processing laser light source, the condensing lens for condensing the processing laser light emitted from the processing laser light source inside the wafer, and moving the condensing lens in the optical axis direction of the processing laser light Condensing lens driving means for displacing the condensing point of the processing laser light condensed by the condensing lens in the wafer thickness direction, and height position detecting means for detecting the height position of the surface of the wafer held on the table And a control means for controlling the condensing lens driving means based on a detection signal from the height position detecting means, a laser dicing apparatus comprising a height position The emitting means includes a detection laser light source that emits a detection laser light having a wavelength that can be reflected on the surface of the wafer, and a detection laser that guides the detection laser light emitted from the detection laser light source to a condenser lens. A light irradiation path, a detection laser light reflection path for guiding reflected light of the detection laser light irradiated and reflected from the condenser lens to the wafer held on the table via the detection laser light irradiation path, and the detection laser light A light splitting unit arranged in the reflection path for splitting the reflected light, a first detector for receiving one of the reflected light split by the light splitting unit, and the other reflected light split by the light splitting unit Based on the second detector, the received light amount limiting means for limiting a part of the reflected light received by the second detector, and the output signals output from the first detector and the second detector, Displacement A displacement signal generating means for sending a displacement signal to the control means, and a condensing point adjusting optical system that is arranged in the detection laser light irradiation path and adjusts the condensing point of the detecting laser light in the wafer thickness direction, The optical distance between the condensing lens and the received light amount limiting means is 30 mm or more and 150 mm or less, and the optical distance between the condensing lens and the condensing point adjusting optical system is 120 mm or less.

  In the laser dicing apparatus according to the second aspect of the present invention, in the first aspect, a 4f optical system is disposed between the condensing lens and the condensing point adjusting optical system.

  In the laser dicing apparatus according to the third aspect of the present invention, in the first aspect or the second aspect, the first detector receives the total amount of one reflected light divided by the light dividing means, and the second detector The other reflected light divided by the light splitting means is limited by the received light amount limiting means, and a part of the reflected light is received.

  The laser dicing apparatus according to a fourth aspect of the present invention is the laser dicing apparatus according to the first aspect or the second aspect, wherein the height position detection means opens on the optical axis of the detection laser light reflection path as the light dividing means and the received light amount limiting means. The first detector receives the reflected light reflected by the reflecting surface of the perforated mirror, and the second detector receives the reflected light that has passed through the opening of the perforated mirror. Receive light.

  According to the present invention, the height position of the surface of the wafer can be detected quickly, accurately and stably regardless of the processing depth of the modified region. As a result, even if there is variation in the wafer surface, it is possible to accurately form the modified region at a predetermined processing depth from the wafer surface.

Schematic showing a configuration example of a laser dicing apparatus according to an embodiment of the present invention Perspective view showing wafer mounted on frame via tape Conceptual diagram explaining the modified region formed near the condensing point inside the wafer Graph showing output characteristics of AF signal Diagram showing how the focusing point of the AF laser light changes in the wafer thickness direction The flowchart which showed the flow of the dicing method using the laser dicing apparatus of this embodiment. The flowchart which showed the detailed flow of the calibration operation | movement shown in FIG. Flowchart showing the detailed flow of the real-time machining operation shown in FIG. The figure which showed the evaluation result (output characteristic of AF signal for every processing depth) by simulation The figure which showed the evaluation result (output characteristic of AF signal for every processing depth) by simulation The figure which showed the evaluation result (output characteristic of AF signal for every processing depth) by simulation The figure which showed the result evaluated about the relationship between optical distance D0, D1 and AF characteristic Schematic showing another configuration example of the laser dicing apparatus Schematic showing the main part of another configuration example of the laser dicing apparatus

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

  FIG. 1 is a schematic view showing a configuration example of a laser dicing apparatus according to an embodiment of the present invention. As shown in FIG. 1, the laser dicing apparatus 10 includes a stage 12, a laser head 20, a control unit 50, and the like.

  The stage 12 is configured to be movable in the XYZθ directions and holds the wafer W by suction. As shown in FIG. 2, a dicing sheet S having an adhesive material is attached to one surface of the wafer W, and the wafer W is placed on the stage 12 while being integrated with the frame F via the dicing sheet S.

  The laser head 20 irradiates the wafer W with a processing laser beam L1 for forming a modified region inside the wafer W.

  The control unit 50 includes a CPU, a memory, an input / output circuit unit, and the like, and controls the operation of each unit of the laser dicing apparatus 10.

  In addition, the laser dicing apparatus 10 includes a wafer transfer means, an operation plate, a television monitor, an indicator lamp, and the like (not shown).

  On the operation plate, switches and a display device for operating operations of each part of the laser dicing apparatus 10 are attached. The television monitor displays a wafer image captured by a CCD camera (not shown) or displays program contents and various messages. The indicator lamp displays the operation status such as processing end, emergency stop, etc. during processing of the laser dicing apparatus 10.

  Next, the detailed configuration of the laser head 20 will be described.

  As shown in FIG. 1, the laser head 20 includes a processing laser light source 100, a collimating lens 102, a dichroic mirror 104, a condenser lens 106, an AF device (autofocus device) 200, and the like.

The processing laser light source 100 emits processing laser light L1 for forming a modified region inside the wafer W. For example, the processing laser light source 100 emits laser light having a pulse width of 1 μs or less and a peak power density at the condensing point of 1 × 10 ⁸ (W / cm ² ) or more.

  On the first optical path of the processing laser light L1, a collimator lens 102, a dichroic mirror 104, and a condensing lens 106 are arranged in this order from the processing laser light source 100 side. The dichroic mirror 104 transmits the processing laser light L1 and reflects AF laser light L2 emitted from an AF device 200 described later. The second optical path of the AF laser light L2 is bent by the dichroic mirror 104 so as to share a part of the optical path with the first optical path of the processing laser light L1, and the condenser lens 106 is disposed on the shared optical path. The

  The processing laser light L 1 emitted from the processing laser light source 100 is collimated by the collimating lens 102, passes through the dichroic mirror 104, and then is condensed inside the wafer W by the condensing lens 106. The position of the focusing point of the processing laser beam L1 in the Z direction (wafer thickness direction position) is moved by moving the focusing lens 106 in the Z direction (the optical axis direction of the processing laser beam L1) by the first actuator 108. Adjusted. The first actuator 108 is an example of a condensing lens driving unit. Although details will be described later, the driving of the first actuator 108 is controlled by the control unit 50 so that the distance between the condenser lens 106 and the surface of the wafer W is constant.

  FIG. 3 is a conceptual diagram illustrating a modified region formed in the vicinity of a condensing point inside the wafer. 3A shows a state where the modified laser beam L1 incident on the inside of the wafer W forms a modified region P at the focal point, and FIG. 3B shows an intermittent pulsed processing laser beam. This shows a state in which the wafer W is moved in the horizontal direction under the light L1, and discontinuous modified regions P, P,. FIG. 3C shows a state in which the modified region P is formed in multiple layers inside the wafer W.

  As shown in FIG. 3A, when the condensing point of the processing laser light L1 incident from the surface of the wafer W is set in the thickness direction of the wafer W, the processing is transmitted through the surface of the wafer W. The energy of the laser beam L1 is concentrated at the condensing point inside the wafer W, and a modified region such as a crack region due to multiphoton absorption, a melting region, or a refractive index changing region is formed near the condensing point inside the wafer W. It is formed. As shown in FIG. 3 (b), the wafer W is formed by irradiating the wafer W with intermittent pulsed processing laser light L1 to form a plurality of modified regions P, P,... Along the dicing street. , The balance of intermolecular forces is lost, and it is cleaved naturally starting from the modified regions P, P,..., Or cleaved by applying a slight external force.

  Further, in the case of a thick wafer W, since the layer of the modified region P cannot be cleaved by one layer, the processing laser beam L1 is collected in the thickness direction of the wafer W as shown in FIG. The light spot is moved, and the modified region P is formed in multiple layers and cleaved.

  In the example shown in FIGS. 3B and 3C, the discontinuous modified regions P, P,... Are formed by the intermittent pulsed laser beam L1 for processing. The continuous modified region P may be formed under the continuous wave of the laser beam L1. When the discontinuous modified region P is formed, it is difficult to cleave as compared with the case where the continuous modified region P is formed. Therefore, the processing laser light L1 depends on the thickness of the wafer W, the safety during transportation, and the like. The continuous wave or the intermittent wave is appropriately selected.

  The AF apparatus 200 irradiates the wafer W with AF laser light (detection laser light) L2, receives the reflected light of the AF laser light L2 reflected from the surface of the wafer W, and converts the received reflected light into the received reflected light. Based on this, the height position (Z direction position) of the surface of the wafer W is detected. The AF device 200 is an example of a height position detection unit.

  The AF apparatus 200 includes an AF light source (detection laser light source) 202, a collimator lens 204, a focus optical system 206, a 4f optical system 214, half mirrors 220 and 222, a condensing lens 224, a mask (light-shielding plate) 226, a first It comprises a detector 228, a second detector 230, an AF signal processor 250, and the like.

  The AF light source 202 includes, for example, an LD (Laser Diode) light source, an SLD (Super Luminescent Diode) light source, and the like. The AF light source 202 has a wavelength that is different from the processing laser light L1 and can be reflected on the surface of the wafer W. A laser beam L2 is emitted.

  The AF laser light L2 emitted from the AF light source 202 is collimated by the collimator lens 204 and reflected by the half mirror 220 via the focus optical system 206. Then, the light is reflected by the dichroic mirror 104 via the 4f optical system 214, condensed by the condenser lens 106, and irradiated onto the wafer W.

  The reflected light of the AF laser light L2 reflected from the surface of the wafer W is refracted by the condenser lens 106, reflected by the dichroic mirror 104, and transmitted through the half mirror 220 via the 4f optical system 214. Further, the reflected light is branched into a first branch path 232 and a second branch path 234 by the half mirror 222. The reflected light branched into the first branch path 232 is 100% condensed by the condenser lens 224 and imaged on the light receiving surface of the first detector 228. Then, the first detector 228 outputs an output signal (electric signal) corresponding to the received light amount to the AF signal processing unit 250. On the other hand, the reflected light branched into the second branch path 234 passes through the hole of the mask 226 (the light receiving area is limited) and forms an image on the light receiving surface of the second detector 230. Then, the second detector 230 outputs an output signal (electric signal) corresponding to the received light amount to the AF signal processing unit 250. The half mirror 222 is an example of a light splitting unit. The mask 226 is an example of a received light amount limiting unit.

  Note that a path for guiding the AF laser light L2 emitted from the AF light source to the condenser lens 106 is an AF laser light irradiation path 242 (corresponding to a detection laser light irradiation path). Further, a path for guiding the reflected light of the AF laser light L2 reflected from the surface of the wafer W to the detectors 228 and 230 is an AF laser light reflection path 244 (corresponding to a detection laser light reflection path).

  The AF signal processing unit 250 indicates a displacement signal indicating a displacement (defocus distance) in the Z direction from the reference position on the surface of the wafer W based on the output signals output from the first detector 228 and the second detector 230. An AF signal (autofocus signal) is generated as (detection signal) and output to the control unit 50. The AF signal processing unit 250 is an example of a displacement signal generating unit.

  Here, the principle of detecting the displacement of the surface of the wafer W will be described.

  The reflected light received by the first detector 228 is collected 100% by the condenser lens 224, so that the amount of received light is constant and the output of the first detector 228 is constant. On the other hand, the reflected light received by the second detector 230 is limited to the central portion of the light receiving region by the mask 226, so the distance from the condenser lens 106 to the surface of the wafer W, that is, the height of the surface of the wafer W is high. The amount of light received by the second detector 230 varies depending on the position (position in the Z direction). Therefore, the output of the second detector 230 changes depending on the height position of the surface of the wafer W irradiated with the AF laser light. Therefore, the displacement of the surface of the wafer W can be detected by utilizing such a property.

  In the AF signal processing unit 250, when the output signals output from the first detector 228 and the second detector 230 are S1 and S2, respectively, the AF signal E is obtained according to the following equation (1).

E = S1 / S2 (1)
FIG. 4 is a graph showing the output characteristics of the AF signal. The horizontal axis shows the displacement (defocus distance) in the Z direction (wafer thickness direction) from the reference position on the surface of the wafer W, and the vertical axis shows the AF signal. The output value is shown. It is assumed that the AF signal is adjusted in advance so as to be a predetermined set value (for example, “5”) at the reference position on the surface of the wafer W.

  As shown in FIG. 4, the output characteristics of the AF signal depend on the defocus distance, and the range in which the output of the AF signal is proportional to the defocus distance is the pull-in range. In addition, the proportionality coefficient (slope) of the linear portion having the proportional relationship is the AF sensitivity. Therefore, if the output of the AF signal is a preset value, it can be seen that the surface of the wafer W is at the same height as the reference position. If the output of the AF signal is not zero, the output of the AF signal is Accordingly, the direction and amount of displacement of the surface of the wafer W can be known.

  The AF signal having such output characteristics is generated by the AF signal processing unit 250 as wafer displacement information indicating displacement in the Z direction from the reference position on the surface of the wafer W, and is output to the control unit 50.

  Based on the AF signal output from the AF signal processing unit 250, the control unit 50 controls the driving of the first actuator 108 so that the distance between the condenser lens 106 and the surface of the wafer W is constant. Thereby, the condenser lens 106 is finely moved in the Z direction (wafer thickness direction) so as to follow the displacement of the surface of the wafer W, and the processing laser light L1 is moved from the surface of the wafer W to a certain distance (depth). Since the condensing point is positioned, the modified region can be formed at a desired position inside the wafer W. The control unit 50 is an example of a control unit.

  By the way, in the configuration in which the condensing lens 106 is disposed on the shared optical path of the first optical path of the processing laser light L1 and the second optical path of the AF laser light L2 as in the present embodiment, When the relative distance between the condensing lens 106 and the wafer W changes in order to change the processing depth, the condensing point of the AF laser light L2 as well as the converging point of the processing laser light L1 is positioned in the Z direction relative to the wafer W Changes.

  For example, as shown in FIG. 5A, when the modified region is formed at a shallow position from the surface of the wafer W, it is assumed that the focal point of the AF laser light L2 coincides with the surface of the wafer W. In such a case, as shown in FIG. 5B, when the relative distance between the condenser lens 106 and the wafer W is changed in order to form a modified region at a deep position from the surface of the wafer W, The condensing point of the AF laser light L2 is greatly deviated from the surface of the wafer W in the Z direction (wafer thickness direction). If the distance between the focal point of the AF laser beam L2 and the surface of the wafer W exceeds the measurement range (the pull-in range), the displacement of the surface of the wafer W cannot be detected. In particular, since the condensing lens 106 is a high NA lens, the measurement range in which the displacement of the surface of the wafer W can be detected is limited to the vicinity of the condensing point (focusing position) of the AF laser light L2. The problem becomes more pronounced.

  Therefore, the AF apparatus 200 of the present embodiment includes a focus optical system 206 that adjusts the focusing point of the AF laser beam L2 in the Z direction (wafer thickness direction) independently of the focusing point of the processing laser beam L1. I have. The focus optical system 206 is an example of a condensing point adjustment optical system.

  The focus optical system 206 is disposed on the second optical path of the AF laser light L2 and at a position independent of the shared optical path with the first optical path of the processing laser light L1. Specifically, it is disposed between the collimating lens 204 and the half mirror 220 in the AF laser light irradiation path 242.

  The focus optical system 206 includes a plurality of lenses including a moving lens configured to be movable along at least the second optical path (AF laser light irradiation path 242). In this example, the focus optical system 206 is from the subject side (wafer W side). In order, the lens includes a fixed lens (positive lens) 208 that is immovable along the second optical path and a moving lens (negative lens) 210 that is movable along the second optical path.

  The second actuator 212 is a driving unit that changes the interval between the lens groups constituting the focus optical system 206. In this example, the second actuator 212 moves the moving lens 210 of the focus optical system 206 along the second optical path. When the moving lens 210 moves along the second optical path, the AF laser light L2 is moved in accordance with the moving direction and moving amount of the moving lens 210 while the position of the focusing point of the processing laser light L1 in the Z direction is fixed. The position of the condensing point in the Z direction changes. That is, the relative distance between the focusing point of the processing laser beam L1 and the focusing point of the AF laser beam L2 changes.

  Based on the AF signal output from the AF signal processing unit 250, the control unit 50 adjusts the focal point of the AF laser light L2 to be near the surface of the wafer W (specifically, the output of the AF signal is The driving of the second actuator 212 is controlled so that the setting value is set in advance.

  As a result, as shown in FIG. 5A to the state shown in FIG. 5B, the relative distance between the condenser lens 106 and the wafer W is changed in order to change the processing depth of the modified region. Even when the distance changes, the processing laser light L1 is condensed as shown in FIG. 5C by changing the distance between the lens groups constituting the focus optical system 206 as described above. It is possible to make the focal point of the AF laser light L2 coincide with the surface of the wafer W in a state where the position of the point in the Z direction is fixed.

  Therefore, even when the processing depth of the modified region changes, the focusing point of the AF laser light L2 can be adjusted to the surface of the wafer W, so that the AF laser light reflected from the surface of the wafer W The position in the Z direction (height position) of the surface of the wafer W can be accurately detected without reducing the amount of reflected light of L2 per unit area.

  In the present embodiment, as shown in FIG. 1, a 4f optical system 214 is disposed between the focus optical system 206 and the condenser lens 106. The 4f optical system 214 includes a first relay lens 216 and a second relay lens 218, and the distance between the first relay lens 216 and the condenser lens 106 is equal to the focal length f1 of the first relay lens 216. The distance between the second relay lens 218 and the focus optical system 206 is equal to the focal length f2 of the second relay lens 218, and the distance between the first relay lens 216 and the second relay lens 218 is Are arranged at a position equal to the sum of the focal lengths (f1 + f2).

  According to such a configuration, a surface conjugate with the exit pupil of the condensing lens 106 can be disposed at a position physically separated from the condensing lens 106. Therefore, the condensing lens 106 and the focus optical system 206 are arranged. Can be easily set within a desired range.

  Next, a dicing method using the laser dicing apparatus 10 of this embodiment will be described. FIG. 6 is a flowchart showing a flow of a dicing method using the laser dicing apparatus 10 of the present embodiment.

  As shown in FIG. 6, the laser dicing apparatus 10 executes a calibration operation for measuring the output characteristics of the AF signal prior to a real-time machining operation described later (step S10).

  After the calibration operation is completed, the laser dicing apparatus 10 adjusts the Z-direction position of the condensing point of the processing laser beam L1 so as to follow the displacement of the surface of the wafer W, and the modified region is formed inside the wafer W. A real-time machining operation for forming a shape is executed (step S12).

  FIG. 7 is a flowchart showing a detailed flow of the calibration operation shown in FIG. The AF signal output from the AF signal processing unit 250 is set in advance in a state where the focus optical system 206 is adjusted so that both the processing laser light L1 and the AF laser light L2 are condensed on the surface of the wafer W. It is assumed that the position of the mask 226 in the optical axis direction is adjusted in advance so that the set value is obtained.

  First, the control unit 50 controls the driving of the second actuator 212 to move the moving lens 210 of the focus optical system 206 to a position corresponding to the processing depth of the modified region (step S20). A memory unit (not shown) of the control unit 50 holds a correspondence relationship between the processing depth of the modified region and the position of the moving lens 210 of the focus optical system 206.

  Subsequently, the control unit 50 controls the movement of the stage 12 to move the reference position on the surface of the wafer W directly below the condenser lens 106 (step S22). The reference position on the surface of the wafer W is a position where the condensing point of the AF laser light L2 is coincident and is a reference position for displacement in the Z direction on the surface of the wafer W. For example, a predetermined position of a central portion excluding the outer peripheral portion of the wafer W is set as a reference position.

  Subsequently, the control unit 50 controls the driving of the second actuator 212 so that the AF signal output from the AF signal processing unit 250 becomes a preset setting value so that the moving lens 210 of the focus optical system 206 is reached. Is moved along the second optical path (step S24). As a result, as shown in FIG. 5B, even when there is a deviation between the focal point of the AF laser light L2 and the reference position of the surface of the wafer W, as shown in FIG. The condensing point is adjusted so that the condensing point of the laser beam L2 coincides with the reference position on the surface of the wafer W. Note that the control unit 50 rewrites the position of the moving lens 210 of the focus optical system 206 held in the memory unit (not shown) to the position (correction position) of the moving lens 210 after the condensing point adjustment.

  Subsequently, the control unit 50 controls the driving of the first actuator 108 to move the AF signal output from the AF signal processing unit 250 while moving the condenser lens 106 over the entire movable range along the Z direction. The output characteristic is measured, and the output characteristic is held in a memory unit (not shown) as a lookup table (step S26).

  When a plurality of modified region layers are formed inside the wafer W, the processing from step S20 to step S26 is executed for each processing depth of the modified region.

  Through the above processing, the control unit 50 refers to the lookup table held in the memory unit (not shown) in the real-time processing operation in step S12 of FIG. Since the displacement (defocus distance) in the Z direction from the reference position on the surface of the wafer W can be easily obtained from the output value of the signal, the processing efficiency (throughput) in the real-time processing operation can be improved.

  FIG. 8 is a flowchart showing a detailed flow of the real-time machining operation shown in FIG.

  First, the control unit 50 controls the driving of the second actuator 212 to move the moving lens 210 of the focus optical system 206 to a position corresponding to the processing depth of the modified region, similarly to step S20 of FIG. (Step S30). At this time, the control unit 50 moves to the position (correction position) of the moving lens 210 held in the memory unit (not shown). As a result, the focal point of the AF laser light L2 coincides with the reference position on the surface of the wafer W, and the AF apparatus 200 can detect displacement in the Z direction with reference to the reference position on the surface of the wafer W. It becomes.

  Subsequently, the control unit 50 controls the movement of the stage 12 to move the wafer W sucked and held on the stage 12 to a predetermined processing start position (step S32).

  Subsequently, after the processing laser light source 100 is turned on, the control unit 50 performs dicing with the processing laser light L1 emitted from the processing laser light source 100 while moving the wafer W in the horizontal direction (XY direction). A modified region is formed inside the wafer W along the street (step S34).

  At this time, the control unit 50 turns on the AF light source 202 at substantially the same time as the timing at which the processing laser light source 100 is turned on, or at a timing earlier than that. Thereby, the processing laser beam L1 and the AF laser beam L2 are condensed toward the wafer W by the condenser lens 106. The AF laser light L2 emitted from the AF light source 202 is reflected on the surface of the wafer W, and the reflected light is imaged on the light receiving surfaces of the detectors 228 and 230, respectively. The AF signal processing unit 250 generates an AF signal indicating the displacement in the Z direction from the reference position on the surface of the wafer W based on the output signals output from the detectors 228 and 230 and outputs the AF signal to the control unit 50.

  Then, the control unit 50 controls the driving of the first actuator 108 based on the AF signal output from the AF signal processing unit 250, thereby adjusting the Z-direction position of the condensing point of the processing laser light L1. However, a modified region is formed inside the wafer W.

  Subsequently, the control unit 50 determines whether or not the formation of the modified region has been completed for all the dicing streets of the wafer W (step S36). If the formation of the modified region is not completed for all the dicing streets (in the case of No), the process moves to the next dicing street (step S38), and the processing from step S34 to step S36 is repeated for the dicing street. . On the other hand, when the formation of the modified region is completed for all dicing streets (in the case of Yes), the process proceeds to the next step S40.

  Subsequently, the control unit 50 determines whether or not the modified region has been formed for all the processing depths (step S40). If the formation of the modified region is not completed for all the processing depths, the process moves to the next processing depth (step S42), and the processing from step S30 to step S40 is repeated. On the other hand, when the formation of the modified region is completed for all the processing depths, the real-time processing operation is ended.

  In this manner, by forming the modified region at a desired position inside the wafer, the wafer W can be divided into a plurality of chips starting from the modified region.

  By the way, as a result of intensive studies by the inventor, in order to obtain a stable autofocus characteristic (AF characteristic) regardless of the processing depth, the optical relationship between the exit pupil of the condenser lens 106 and the focus optical system 206 is obtained. It has been found that the distance D0 and the optical distance D1 between the exit pupil of the condenser lens 106 and the mask 226 are important parameters.

  For example, when the optical distance D1 between the exit pupil of the condenser lens 106 and the mask 226 is set to zero, the AF signal output does not change even if the relative distance between the condenser lens 106 and the wafer W changes. The displacement from the reference position on the surface of the wafer W cannot be detected. If the optical distance D1 is too long, the AF sensitivity increases but the pull-in range becomes narrow.

  The same applies to the optical distance D0 between the exit pupil of the condenser lens 106 and the focus optical system 206. At the object position serving as a reference for the condenser lens 106 (when the focal point of the AF laser light L2 is aligned with the surface of the wafer W), the light beam emitted from the focus optical system 206 becomes a parallel light beam. When the modified region is formed, the wafer W approaches the condenser lens 106, and a convergent light beam is emitted from the focus optical system 206. At this time, if the optical distance D0 between the exit pupil of the condensing lens 106 and the focus optical system 206 is large, the beam diameter on the condensing lens 106 side becomes small, and the entire aperture of the condensing lens 106 can be used. become unable. As a result, the change of the AF signal becomes slow (that is, the rate of change of the output of the AF signal with respect to the defocus distance becomes small), and the AF sensitivity is lowered. That is, a phenomenon occurs in which the AF sensitivity changes for each processing depth of the modified region.

  Here, a simulation was performed using a model substantially equivalent to the laser dicing apparatus 10 of the present embodiment described above, and the results of evaluating the change in AF characteristics at each processing depth are described with reference to FIGS. 9 to 11. explain.

  9 to 11 show the output characteristics of the AF signal for each processing depth when the optical distances D0 and D1 are set to predetermined values, respectively. The unit of D0 and D1 is mm.

  FIG. 9 shows the output characteristics of the AF signal when D0 = 0 and D1 = 80, and the curves of the output characteristics of the AF signal for each processing depth are substantially the same. That is, the AF sensitivity is high, the pull-in range is wide, and stable AF characteristics can be obtained regardless of the processing depth.

  FIG. 10 shows output characteristics of the AF signal when D0 = 0 and D1 = 0. It is the figure which showed AF characteristic. As shown in FIG. 10, when D0 = 0 and D1 = 0, the AF signal is always a constant value regardless of the defocus distance and does not operate as an AF function. As is apparent from this result, it is understood that the optical distance D1 between the condenser lens 106 and the mask 226 needs to be at least larger than zero (that is, D1> 0).

  FIG. 11 is a diagram showing AF characteristics when D0 = 120 and D1 = 80. As shown in FIG. 11, when the processing depth is 0 μm, good AF characteristics are shown. However, as the processing depth increases, the slope of the AF signal becomes gradual, and the AF sensitivity gradually decreases. Further, as can be seen from the comparison with the results shown in FIG. 9, when the optical distance D0 is increased, the variation in AF characteristics for each processing depth increases. Therefore, the optical distance D0 needs to be as small as possible.

  FIG. 12 shows the result of further detailed evaluation of the relationship between the optical distances D0 and D1 and the AF characteristics. FIG. 12 shows the evaluation results when the optical distances D0 and D1 are each changed by 20 mm in the range of 0 to 200 mm.

  As can be seen from the results shown in FIG. 12, the optical distance D0 between the exit pupil of the condenser lens 106 and the focus optical system 206 is preferably set to 120 mm or less (more preferably 40 mm or less). By setting within this range, stable AF characteristics can be obtained regardless of the processing depth.

  The optical distance D1 between the exit pupil of the condenser lens 208 and the mask 226 is an important parameter for improving the AF sensitivity and the pull-in range. That is, in order to increase the AF sensitivity, the optical distance D1 is desirably 20 mm or more. Moreover, in order to widen the drawing-in range, it is desirable that it is within 160 mm. By setting within this range, the AF sensitivity is high and the pull-in range can be widened, and good AF characteristics can be obtained.

  As described above, according to the present embodiment, the optical distance D0 between the exit pupil of the condenser lens 106 and the focus optical system 206 and the optical distance D1 between the exit pupil of the condenser lens 106 and the mask 226 are described above. By setting the desired range, the AF sensitivity is high, the pull-in range is wide, and stable AF characteristics can be obtained regardless of the processing depth. As a result, it becomes possible to detect the height position of the surface of the wafer W quickly, accurately and stably.

  In order to obtain good AF characteristics, it is necessary to set the optical distances D0 and D1 within the above-described desired range. However, it is difficult to arrange in this way in the actual device configuration. There are many. On the other hand, in the present embodiment, by disposing the 4f optical system 214 on the second optical path between the dichroic mirror 104 and the half mirror 220, a point conjugate with the exit pupil of the condenser lens 106 is set to the outside. The above conditions can be achieved.

  In the above-described embodiment, the 4f optical system 214 is disposed between the dichroic mirror 104 and the half mirror 220, that is, a common path between the AF laser light irradiation path 242 and the AF laser light reflection path 244. Although the configuration in which the 4f optical system 214 is arranged is not limited to this, for example, a configuration as shown in FIG.

  FIG. 13 is a schematic diagram illustrating another configuration example of the laser dicing apparatus 10. In FIG. 13, the same or similar components as those in FIG.

  In the configuration example shown in FIG. 13, the half mirror 260 is arranged between the dichroic mirror 104 and the 4f optical system 214, and only the optical path between the condenser lens 106 and the focus optical system 206 is 4f. The optical system 214 is arranged.

  The AF laser light L2 emitted from the AF light source 202 is irradiated on the surface of the wafer W through the AF laser light irradiation path 242 similar to the configuration shown in FIG.

  On the other hand, the reflected light of the AF laser light L2 reflected from the surface of the wafer W is refracted by the condenser lens 106 and reflected by the dichroic mirror 104, unlike the AF laser light reflection path 244 shown in FIG. After that, the light is reflected by the half mirror 260 disposed in front of the 4f optical system 214 and guided to the half mirror 222. The light is received by the first detector 228 and the second detector 230 in the same manner as the configuration shown in FIG.

  In other words, in the configuration example shown in FIG. 13, the reflected light of the AF laser light L2 reflected from the surface of the wafer W is not transmitted through the 4f optical system 214 but the first detector 228 and the second detector 230. Each is configured to receive light.

  Even in such a configuration, as in the above-described embodiment, the optical distance D0 between the exit pupil of the condenser lens 106 and the focus optical system 206, and the optical distance between the exit pupil of the condenser lens 106 and the mask 226 are similar. By setting D1 within the desired range described above, AF sensitivity is high, the pull-in range is wide, and stable AF characteristics can be obtained regardless of the processing depth. As a result, it becomes possible to detect the height position of the surface of the wafer W quickly, accurately and stably.

  In the above-described embodiment, as shown in FIG. 1, the reflected light of the AF laser light L2 is branched into two branch paths 232 and 234 using the half mirror 222, and the first detector 228 and the second detection are detected. However, the present invention is not limited to this. For example, a configuration as shown in FIG.

  FIG. 14 is a schematic view showing a main part of another configuration example of the laser dicing apparatus 10. In FIG. 14, the same or similar components as those in FIG.

  In the configuration example shown in FIG. 14, a perforated mirror 264 having an opening 264 a is disposed on the optical axis of the AF laser light reflection path 244. Among the reflected light of the AF laser light L2, a part of the reflected light passes through the opening 264a formed in the perforated mirror 264 and is received by the second detector 230, and the other reflected light is received by the perforated mirror 264. Are reflected by the reflecting surface in the peripheral portion of the light, condensed by the condenser lens 224, and received by the first detector 228. That is, the total amount of reflected light of the AF laser light L2 is the sum of the amounts of light received by the first detector 228 and the second detector 230, respectively.

  Therefore, when the output of the first detector 228 is S1 and the output S2 of the second detector 230, the AF signal E generated by the AF signal processing unit 250 can be obtained as E = (S1 + S2) / S2. Similarly to the above-described embodiment, the height position of the surface of the wafer W can be detected.

  A split mirror may be arranged instead of the perforated mirror 264. In this case, the reflected light of the AF laser light L2 is divided into two paths by the dividing mirror, and the divided reflected lights are detected by the first detector 228 and the second detector 230, respectively. Accordingly, it is possible to detect the height position of the surface of the wafer W by obtaining the AF signal in the same manner as when the perforated mirror 264 is used.

  Further, in the above-described embodiment, a part of the reflected light of the AF laser light L2 branched to the second branch path 234 using the half mirror 222 is discarded by shielding with the mask 226, but FIG. In the configuration example shown, the reflected light of the AF laser light L2 can be efficiently used without being discarded, and the detection accuracy of the height position of the surface of the wafer W can be improved.

  The embodiments of the present invention have been described above. However, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the scope of the present invention. .

  DESCRIPTION OF SYMBOLS 10 ... Laser dicing apparatus, 12 ... Stage, 20 ... Laser head, 50 ... Control part, 100 ... Processing laser light source, 102 ... Collimating lens, 104 ... Dichroic mirror, 106 ... Condensing lens, 108 ... 1st actuator, 200 ... AF device, 202 ... AF light source, 204 ... collimating lens, 206 ... focus optical system, 212 ... second actuator, 214 ... 4f optical system, 220 ... half mirror, 222 ... half mirror, 224 ... condensing lens, 226 ... Mask, 228 ... Detector, 230 ... Detector, 242 ... AF laser light irradiation path, 244 ... AF laser light reflection path, 250 ... AF signal processing section, 264 ... Perforated mirror, L1 ... Processing laser light , L2 ... AF laser light

Claims (2)

A table for holding a workpiece, a processing laser light source for emitting a processing laser beam for forming a modified region inside the workpiece held by the table, and a laser beam emitted from the processing laser light source Further, the condenser lens that condenses the processing laser light inside the workpiece, and the condenser lens is condensed by moving the condenser lens in the optical axis direction of the processing laser light. Condensing lens driving means for displacing the condensing point of the processing laser beam in the workpiece thickness direction, and height position detection for detecting the height position of the laser beam irradiation surface of the workpiece held on the table And a control means for controlling the condenser lens driving means based on a detection signal from the height position detecting means, a laser dicing apparatus comprising:
The height position detecting means is
A detection laser light source that emits a detection laser beam having a wavelength that can be reflected with respect to the laser light irradiation surface of the workpiece;
A detection laser light irradiation path for guiding the detection laser light emitted from the detection laser light source to the condenser lens;
A detection laser light reflection path for guiding reflected light of the detection laser light irradiated and reflected from the condenser lens to the workpiece held on the table via the detection laser light irradiation path;
A light splitting means for splitting the reflected light disposed in the detection laser light reflecting path;
A first detector that receives one of the reflected lights divided by the light dividing means;
A second detector for receiving the other reflected light divided by the light dividing means;
A received light amount limiting means for limiting a part of the reflected light received by the second detector;
Displacement signal generating means for sending a displacement signal indicating the displacement of the laser light irradiation surface of the workpiece to the control means based on output signals output from the first detector and the second detector;
A condensing point adjusting optical system that is disposed in the detection laser light irradiation path and adjusts the condensing point of the detecting laser light in the workpiece thickness direction;
A 4f optical system disposed between the condensing lens and the condensing point adjusting optical system;
A laser dicing apparatus comprising: The height position detection means includes a perforated mirror having an opening on the optical axis of the detection laser light reflection path as the light dividing means and the received light amount limiting means,
The first detector receives the reflected light reflected by the reflecting surface of the perforated mirror,
The second detector receives the reflected light that has passed through the opening of the perforated mirror.
The laser dicing apparatus according to claim 1.

Images