Laser processing equipment

Abstract

To provide a laser processing device capable of properly measuring an upper surface height of a wafer regardless of the kind and surface state of the wafer.SOLUTION: A laser processing device includes: an oscillator 24 that oscillates a laser beam LB1; a light collector 26 that condenses the laser beam LB1 oscillated by the oscillator 24 and positions a light focus spot P on a wafer W; a light focus spot position adjuster 28 which is arranged between the oscillator 24 and the light collector 26 and adjusts a position of the light focus spot P; and an upper surface position detector 30 for detecting an upper surface position of the wafer W. The upper surface position detector 30 includes a detecting light source 61 that emits a detection light LB2 of a wide wavelength band and selection means 62 for selecting the detection light LB2 of a specific wavelength from the detection light LB2 emitted by the detecting light source 61. The upper surface position detector 30 selects the detection light LB2 of the specific wavelength via the selection means 62 out of the detection light LB2 emitted by the detecting light source 61, guides it to the upper surface of the wafer W, and calculates the upper surface position of the wafer W with the reflection light reflected by an upper surface of the wafer W.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a laser processing device. [Background technology]

[0002] A wafer has a plurality of devices such as ICs and LSIs formed on its surface, separated by planned dividing lines. The back surface is ground to the desired thickness, and then the wafer is divided into individual device chips using a laser processing machine.

[0003] The laser processing device includes a chuck table that holds a wafer, a laser beam application means that applies a laser beam to the wafer held on the chuck table, and a feed means that feeds the chuck table and the laser beam application means for processing in the X-axis direction and in the Y-axis direction that is perpendicular to the X-axis direction, and can apply the laser beam to the planned dividing line of the wafer with high precision.

[0004] Furthermore, in a technology in which the focal point of a laser beam having a wavelength that is transparent to the wafer is positioned within the intended dividing line, the laser beam is irradiated onto the wafer to form a modified layer, and then an external force is applied to the wafer to divide the wafer into individual device chips, it is necessary to position the focal point of the laser beam at an appropriate position from the top surface of the wafer, and the applicant has filed a patent application for a technology to control the position of the focal point of the laser beam while measuring the top surface position (top surface height) of the wafer (see, for example, Patent Documents 1 and 2).

[0005] The technology disclosed in Patent Document 1 is a first type in which detection light emitted from a detection light source is irradiated onto the top surface of the wafer at an incident angle α, and an image sensor is provided that measures the position of the light reflected from the top surface of the wafer, and the position of the top surface of the wafer is calculated based on the position of the reflected light detected by the image sensor.

[0006] The technology disclosed in Patent Document 2 is a second type in which detection light emitted by a detection light source is irradiated onto the top surface of a wafer held on a chuck table through a condenser, the light reflected from the top surface of the wafer is split into a first optical path and a second optical path, and the intensity of the reflected light that has passed through a slit mask arranged in the first optical path is compared with the intensity of the reflected light that has been guided to the second optical path to calculate the top surface position of the wafer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-313182 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-152355 Summary of the Invention [Problem to be solved by the invention]

[0008] However, depending on the type and surface condition of the wafer, the detection light emitted from the detection light source may not be sufficiently reflected by the top surface of the wafer. In such cases, the problem of not being able to properly measure the height of the top surface of the wafer arises. This problem is often seen in the first type of measuring instrument, but it can also occur in the second type of measuring instrument.

[0009] An object of the present invention is to provide a laser processing apparatus that can properly measure the upper surface height of a wafer regardless of the type of wafer or the surface condition. [Means for solving the problem]

[0010] According to the present invention, there is provided the following laser processing apparatus that solves the above-mentioned problems. "A laser processing apparatus including a chuck table for holding a wafer, a laser beam application means for applying a laser beam to the wafer held on the chuck table, and a feed means for feeding the chuck table and the laser beam application means in an X-axis direction and a Y-axis direction perpendicular to the X-axis direction, the laser beam application means comprises an oscillator for emitting a laser beam, a condenser for condensing the laser beam oscillated by the oscillator and positioning the condensing point on the wafer held on the chuck table, a condensing point position adjuster disposed between the oscillator and the condenser for adjusting the position of the condensing point, and an upper surface position detector for detecting the position of the upper surface of the wafer; The upper surface position detector includes a detection light source that emits detection light in a wide wavelength band, and a selection means that selects detection light of a specific wavelength from the detection light emitted by the detection light source. a combiner that combines the detection light emitted by the detection light source and that has passed through the selection means and a first beam splitter in this order between the oscillator and the light-focusing point position adjuster; and filter means that transmits only light that corresponds to the specific wavelength selected by the selection means from the light that is guided from the combiner to the first beam splitter and reflected by the first beam splitter. Including, the selection means includes a plurality of bandpass filters that transmit detection light of specific wavelengths different from each other, and selects one of the plurality of bandpass filters and positions it in the optical path of the detection light to select the detection light of the specific wavelength; the filter means includes a plurality of band pass filters that transmit reflected light of specific wavelengths different from each other, and selects a band pass filter from the plurality of band pass filters that transmits the same wavelength as the wavelength selected by the selection means and positions it in the optical path of the reflected light to transmit the reflected light of the specific wavelength; The detection light having a specific wavelength is selected by the selection means from the detection light emitted by the detection light source, and the selected detection light is guided to the upper surface of the wafer held on the chuck table and reflected from the upper surface of the wafer. The light transmitted through the filter means The present invention provides a laser processing device that calculates the upper surface position of a wafer by the above method.

[0011] Applicable The selection means preferably selects the detection light having the wavelength at which the amount of received light is maximum.

[0012] The upper surface position detector includes: ApplicableIt is desirable to provide a focal point position adjuster and a second beam splitter that splits the reflected light, which is detection light that has passed through the condenser and is reflected by the upper surface of the wafer held on the chuck table, into a first optical path and a second optical path via the combiner and the first beam splitter, a filter that is disposed in the first optical path and passes a portion of the split reflected light, a first light receiving element that receives the reflected light that has passed through the filter, and a second light receiving element that is disposed in the second optical path and receives all of the split reflected light, and to calculate the upper surface position of the wafer by comparing the amount of light received by the first light receiving element and the amount of light received by the second light receiving element. [Effects of the Invention]

[0014] The laser processing apparatus of the present invention is A laser processing apparatus including a chuck table for holding a wafer, a laser beam application means for applying a laser beam to the wafer held on the chuck table, and a feed means for feeding the chuck table and the laser beam application means for processing in an X-axis direction and a Y-axis direction perpendicular to the X-axis direction, the laser beam application means comprises an oscillator for emitting a laser beam, a condenser for condensing the laser beam oscillated by the oscillator and positioning the condensing point on the wafer held on the chuck table, a condensing point position adjuster disposed between the oscillator and the condenser for adjusting the position of the condensing point, and an upper surface position detector for detecting the position of the upper surface of the wafer; The upper surface position detector includes a detection light source that emits detection light in a wide wavelength band, and a selection means that selects detection light of a specific wavelength from the detection light emitted by the detection light source. a combiner that combines the detection light emitted by the detection light source and that has passed through the selection means and a first beam splitter in this order between the oscillator and the light-focusing point position adjuster; and filter means that transmits only light that corresponds to the specific wavelength selected by the selection means from the light that is guided from the combiner to the first beam splitter and reflected by the first beam splitter. Including, the selection means includes a plurality of bandpass filters that transmit detection light of specific wavelengths different from each other, and selects one of the plurality of bandpass filters and positions it in the optical path of the detection light to select the detection light of the specific wavelength; the filter means includes a plurality of band pass filters that transmit reflected light of specific wavelengths different from each other, and selects a band pass filter from the plurality of band pass filters that transmits the same wavelength as the wavelength selected by the selection means and positions it in the optical path of the reflected light to transmit the reflected light of the specific wavelength; The detection light having a specific wavelength is selected by the selection means from the detection light emitted by the detection light source, and the selected detection light is guided to the upper surface of the wafer held on the chuck table and reflected from the upper surface of the wafer. The light transmitted through the filter meansSince the position of the upper surface of the wafer is calculated by the above method, it is possible to select detection light of a specific wavelength that is sufficiently reflected by the upper surface of the wafer, and the height of the upper surface of the wafer can be measured appropriately regardless of the type or surface condition of the wafer. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a perspective view of a laser processing apparatus configured according to the present invention; [Figure 2] FIG. 2 is a block diagram of the laser beam application means shown in FIG. 1. [Figure 3] A perspective view of the first and second galvanometer scanners shown in Figure 2. [Figure 4] 4 is a schematic diagram showing the optical path length of a laser beam passing through the first galvanometer scanner shown in FIG. 3. [Figure 5] Graph showing the relationship between the installation angle of the first and second galvanometer scanners shown in Figure 3 and the change in the optical path length of the laser beam. [Figure 6] 10 is a graph showing the relationship between the optical path length of a laser beam and the change in the distance from the condenser to the focal point. [Figure 7] FIG. 3 is a perspective view of the selection means shown in FIG. 2; [Figure 8] (a) Schematic diagram showing the reflection area when the detection light is irradiated onto the wafer, (b) Schematic diagram showing the reflection area when the focal point of the detection light is positioned lower than in the case shown in (a). [Figure 9] 3 is a graph showing the relationship between the ratio of voltage signals output from the first and second light receiving elements shown in FIG. 2 and the distance from the upper surface of the wafer to the focal point of the detection light. [Figure 10] FIG. 2 is a perspective view of the collector and second top surface position detector shown in FIG. 1; [Figure 11] 2 is a schematic diagram showing a state in which the upper surface position of the wafer is detected by the second upper surface position detector shown in FIG. 1; [Figure 12] 1 is a schematic diagram showing the optical path of the detection light when the upper surface position of the wafer is at a reference position and the optical path of the detection light when the upper surface position of the wafer has shifted by h from the reference position. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a laser processing apparatus constructed according to the present invention will now be described with reference to the drawings.

[0017] (Laser processing equipment 2) 1, the laser processing apparatus 2 includes a chuck table 4 that holds a wafer W, a laser beam application means 6 that applies a laser beam to the wafer W held on the chuck table 4, and a feeding means 8 that feeds the chuck table 4 and the laser beam application means 6 for processing in the X-axis direction indicated by the arrow X in Fig. 1 and in the Y-axis direction (direction indicated by the arrow Y in Fig. 1) that is perpendicular to the X-axis direction. The XY plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.

[0018] (Chuck table 4) The laser processing apparatus 2 of the illustrated embodiment includes an X-axis movable plate 12 mounted on the upper surface of a base 10 so as to be movable in the X-axis direction, a Y-axis movable plate 14 mounted on the upper surface of the X-axis movable plate 12 so as to be movable in the Y-axis direction, a support column 16 fixed to the upper surface of the Y-axis movable plate 14, and a cover plate 18 fixed to the upper end of the support column 16. An elongated hole 18a extending in the Y-axis direction is formed in the cover plate 18. The chuck table 4 is rotatably mounted on the upper end of the support column 16 and extends upward through the elongated hole 18a in the cover plate 18.

[0019] A circular porous suction chuck 20 connected to suction means (not shown) is disposed on the upper end portion of the chuck table 4. A plurality of clamps 22 are provided on the periphery of the chuck table 4 at intervals in the circumferential direction.

[0020] In the chuck table 4, a suction force is generated on the upper surface of the suction chuck 20 by a suction means, and the wafer W placed on the upper surface of the suction chuck 20 is suction-held. The chuck table 4 is rotated around an axis in the vertical direction by a chuck table motor (not shown) built into the support 16.

[0021] (Laser beam irradiation means 6) As shown in FIG. 2, the laser beam application means 6 includes an oscillator 24 that oscillates a processing pulse laser beam LB1, a condenser 26 that condenses the laser beam LB1 oscillated by the oscillator 24 and positions a focal point P on the wafer W held on the chuck table 4, a focal point position adjuster 28 that is disposed between the oscillator 24 and the condenser 26 and adjusts the position of the focal point P, and an upper surface position detector 30 that detects the position of the upper surface of the wafer W.

[0022] (Oscillator 24, Concentrator 26) 1, the laser beam application means 6 includes a housing 32 that extends upward from the upper surface of the base 10 and then extends substantially horizontally. The oscillator 24 is disposed inside the housing 32. The laser beam LB1 emitted by the oscillator 24 may have a wavelength (e.g., 1064 nm) that is transparent to the wafer W. The condenser 26 is attached to the lower surface at the tip of the housing 32.

[0023] (Focusing point position adjuster 28) 2, the focal point position adjuster 28 includes first and second lenses 34, 36 arranged at an interval from each other, a first galvanometer scanner 38 that reflects the laser beam LB1 that has passed through the first lens 34, and a second galvanometer scanner 40 that reflects the laser beam LB1 that has been reflected by the first galvanometer scanner 38 and directs it to the second lens 36. A direction-changing mirror 42 that directs the laser beam LB1 that has passed through the second lens 36 to the condenser 26 is provided between the second lens 36 and the condenser 26.

[0024] (First Galvanometer Scanner 38) Explaining with reference to FIG. 3 together with FIG. 2, the first galvanometer scanner 38 has a pair of first and second mirrors 44, 46 installed parallel to each other and facing each other at a predetermined distance, and an angle adjustment actuator 48 (see FIG. 3) that adjusts the installation angles of the first and second mirrors 44, 46.

[0025] 2, the first mirror 44 reflects the laser beam LB1 that has passed through the first lens 34 toward the second mirror 46. The second mirror 46 reflects the laser beam LB1 that has been reflected by the first mirror 44 toward the second galvanometer scanner 40.

[0026] 3, the rotation shaft 48a of the angle adjustment actuator 48 is connected to both the first and second mirrors 44, 46. The angle adjustment actuator 48 changes the installation angles of the first and second mirrors 44, 46 with respect to the optical axis of the laser beam LB1 while maintaining the parallel state of the first and second mirrors 44, 46.

[0027] (Second Galvanometer Scanner 40) Similar to the first galvanometer scanner 38, the second galvanometer scanner 40 has a pair of third and fourth mirrors 50, 52 that are installed parallel to each other and facing each other at a predetermined distance, and an angle adjustment actuator 54 that adjusts the installation angles of the third and fourth mirrors 50, 52.

[0028] The third mirror 50 reflects the laser beam LB1 reflected by the second mirror 46 of the first galvanometer scanner 38 toward the fourth mirror 52. The fourth mirror 52 reflects the laser beam LB1 reflected by the third mirror 50 toward the second lens 36.

[0029] The rotation shaft 54a of the angle adjustment actuator 54 is connected to both the third and fourth mirrors 50, 52. The angle adjustment actuator 54 changes the installation angles of the third and fourth mirrors 50, 52 with respect to the optical axis of the laser beam LB1 while maintaining the parallel state of the third and fourth mirrors 50, 52.

[0030] As described above, the laser beam LB1 oscillated by the oscillator 24 passes through the first lens 34 and is then reflected by the first and second mirrors 44, 46. As shown in FIG. 4, if the distance between the first mirror 44 and the second mirror 46 is d, then: m1=d / cosθ m2=m1cos2θ=(d / cosθ)cos2θ Since it is expressed as m1+m2=(d / cosθ)(1+cos2θ)=2dcosθ This becomes:

[0031] If the distance between the third mirror 50 and the fourth mirror 52 is also d as above, the optical path length of the laser beam LB1 changes as (m1 + m2) × 2. For example, if the distance d is 2 mm and the angle θ is 47.5 degrees as the reference (the optical path length change is 0), the optical path length change of the laser beam LB1 will be as shown in Figure 5. In the example shown in Figure 5, when the angle θ changes from 40 degrees to 57.5 degrees, the optical path length changes from +0.73 mm to -1.1 mm. In other words, the optical path length change over the above angle range is 1.83 mm.

[0032] Next, the relationship between the change in the optical path length and the change in the focal point position of the laser beam LB1 focused by the condenser 26 will be described.

[0033] As shown in Figure 2, if the optical path length from the focal point D of the first lens 34 to the second lens 36 is d1, the optical path length from the second lens 36 to the condenser 26 is d2, the focal length of the second lens 36 is f1, and the focal length of the condenser 26 is f2, then the distance d3 from the condenser 26 to the focal point P can be calculated using the following equation (1).

[0034]

number

[0035] The focal point D of the first lens 34 coincides with the focal length of the first lens 34 when the laser beam LB1 oscillated by the oscillator 24 is a parallel beam.

[0036] In equation (1), when specific numerical values ​​are assigned to the focal length f1 of the second lens 36, the focal length f2 of the condenser 26, and the optical path length d2 from the second lens 36 to the condenser 26, the distance d3 from the condenser 26 to the focal point P becomes a function of the optical path length d1 from the focal point D of the first lens 34 to the second lens 36. In other words, when the optical path length d1 is changed, the position of the focal point P changes.

[0037] For example, if the focal length f1 of the second lens 36 is 12.7 mm, the focal length f2 of the condenser 26 is 2 mm, and the optical path length d2 is 20 mm, and the state in which the optical path length d1 matches the focal length f1 (12.7 mm) of the second lens 36 is taken as the reference (displacement of the focal point P is 0), the displacement of the focal point P with respect to the displacement of the optical path length d1 will be as shown in Figure 6.

[0038] Therefore, under the above conditions, when the angle θ changes within a range from 40 degrees to 57.5 degrees, the optical path length changes within a range from +0.73 mm to -1.1 mm, and correspondingly, the distance d3 from the condenser 26 to the focal point P changes within a range from -20 μm to +28 μm. That is, in the focal point position adjuster 28, the angle adjustment actuators 48, 54 adjust the installation angles of the first to fourth mirrors 44, 46, 50, 52, thereby adjusting the vertical position of the focal point P.

[0039] (Top surface position detector 30) 2, the top surface position detector 30 of the illustrated embodiment includes a first top surface position detector 56, a second top surface position detector 58, and a selection unit 60 that selects either the first top surface position detector 56 or the second top surface position detector 58. Note that the top surface position detector 30 does not need to include both the first and second top surface position detectors 56, 58, and it is sufficient if it includes either the first or second top surface position detector 56, 58.

[0040] (First upper surface position detector 56) The first upper surface position detector 56 includes a detection light source 61 that emits detection light LB2 in a wide wavelength band, and a selection means 62 that selects detection light LB2 of a specific wavelength from the detection light LB2 emitted by the detection light source 61. The selection means 62 selects detection light LB2 of a specific wavelength from the detection light LB2 emitted by the detection light source 61, and guides it to the upper surface of the wafer W held on the chuck table 4, and calculates the upper surface position of the wafer W based on reflected light LB2' reflected by the upper surface of the wafer W.

[0041] (Detection light source 61) The detection light source 61 emits light having a wavelength in the range of 100 to 2000 nm, for example, as the wide wavelength band detection light LB2. Note that the wide wavelength band of the detection light LB2 is not limited to the above range (100 to 2000 nm) as long as it is a range that allows selective extraction of multiple detection lights with mutually different wavelengths.

[0042] (Selection means 62) As shown in FIG. 7, the selection means 62 includes a plurality of bandpass filters 63a to 63j, a support plate 64 that supports the plurality of bandpass filters 63a to 63j, and a motor 65 that rotates the support plate 64.

[0043] The bandpass filters 63a to 63j are each configured to transmit detection light LB2 of a specific wavelength different from one another. For example, the bandpass filter 63a may be configured to transmit light of wavelengths of 100 nm, 300 nm, 500 nm, 700 nm, 900 nm, 1100 nm, 1300 nm, 1500 nm, 1700 nm, and 1900 nm.

[0044] The number of bandpass filters in the selection means 62 and the wavelengths transmitted by the bandpass filters in the selection means 62 can be set arbitrarily.

[0045] The selection means 62 rotates a support plate 64 using a motor 65 to select one of the plurality of bandpass filters 63a to 63j and position it in the optical path of the detection light LB2. This makes it possible to select the detection light LB2 of a specific wavelength that is sufficiently reflected by the upper surface of the wafer W from the detection light source 61, which has a wide wavelength band. The selection means 62 also selects the detection light LB2 of a wavelength different from the wavelength of the processing laser beam LB1 oscillated by the oscillator 24.

[0046] The selection means 62 preferably selects detection light of a wavelength that maximizes the amount of light received by the first and second light receiving elements 72, 74 or the light receiving end portion 86, which will be described later, depending on the type of wafer W and the surface condition of the wafer W. This is because the height of the top surface of the wafer W can be measured more accurately.

[0047] As shown in FIG. 2, the first top surface position detector 56 includes a combiner 67 that combines the detection light LB2 emitted by the detection light source 61, which has passed through the selection means 62 and the first beam splitter 66 in this order, between the oscillator 24 and the focal point position adjuster 28; a second beam splitter 68 that splits the detection light LB2', which has passed through the focal point position adjuster 28 and the collector 26 and is reflected by the top surface of the wafer W held on the chuck table 4, into a first optical path OP1 and a second optical path OP2 via the combiner 67 and the first beam splitter 66; a filter 70 that is disposed on the first optical path OP1 and passes a portion of the split reflected light LB2'; a first light-receiving element 72 that receives the reflected light LB2' that has passed through the filter 70; and a second light-receiving element 74 that is disposed on the second optical path OP2 and receives all of the split reflected light LB2'.

[0048] The combiner 67 may be composed of a dichroic half mirror. The combiner 67 passes the laser beam LB1 oscillated by the oscillator 24, and reflects the detection light LB2 emitted by the detection light source 61 and passed through the first beam splitter 66, toward the focus position adjuster 28. The first and second light receiving elements 72 and 74 output voltage signals corresponding to the amount of received light to the control means 76.

[0049] The control means 76 is composed of a computer and controls the operation of the laser processing device 2. The control means 76 includes a central processing unit (CPU) that performs calculations according to a control program, a read-only memory (ROM) that stores the control program etc., and a readable and writable random access memory (RAM) that stores the calculation results etc.

[0050] The first top surface position detector 56 in the illustrated embodiment further includes a filter means 78 that transmits only the light that corresponds to the wavelength of the reflected light LB2′ (the specific wavelength selected by the selection means 62) from the light that is guided from the combiner 67 to the first beam splitter 66 and reflected by the first beam splitter 66; a cylindrical lens 80 that one-dimensionally focuses the reflected light LB2′ that is split onto the first optical path OP1 by the second beam splitter 68; and a focusing lens 82 that focuses 100% of the reflected light LB2′ that is split onto the second optical path OP2 by the second beam splitter 68.

[0051] The configuration of the filter means 78 may be the same as the configuration of the selection means 62 described above, and although not shown, it includes a plurality of bandpass filters, a support plate that supports the plurality of bandpass filters, and a motor that rotates the support plate.

[0052] Then, the filter means 78 selects a bandpass filter from the plurality of bandpass filters that transmits the same wavelength as the wavelength selected by the selection means 62, and positions it in the optical path of the reflected light LB2'. This allows only light corresponding to the wavelength of the reflected light LB2' (the specific wavelength selected by the selection means 62) to pass through.

[0053] Only a specific wavelength of the wide wavelength band detection light LB2 emitted by the detection light source 61 is selected by the selection means 62, passes through the first beam splitter 66, and is then reflected by the junction 67 toward the focus position adjuster 28 and is guided to the collector 26 via the focus position adjuster 28 and the direction changing mirror 42. The detection light LB2 of the specific wavelength collected by the collector 26 is then reflected by the upper surface of the wafer W held on the chuck table 4.

[0054] For example, as shown in FIG. 8(a), when the focal point Pa of the detection light LB2 is relatively close to the upper surface of the wafer W, the detection light LB2 is reflected by an area S1 irradiated on the upper surface of the wafer W.

[0055] The reflected light LB2' reflected by the upper surface of the wafer W passes through the condenser 26, the direction-changing mirror 42, the focal point position adjuster 28, the condenser 67, and the first beam splitter 66, as shown by the dashed line in Figure 2, and reaches the filter means 78.

[0056] Like the reflected light LB2' of the detection light LB2, the reflected light of the processing laser beam LB1 also reaches the filter means 78, but the reflected light of the processing laser beam LB1 is blocked by the filter means 78. As described above, the filter means 78 passes only light corresponding to the wavelength of the reflected light LB2' of the detection light LB2. Therefore, only the reflected light LB2' of the detection light LB2 passes through the filter means 78.

[0057] The reflected light LB2' that passes through the filter means 78 is split into a first optical path OP1 and a second optical path OP2 by the second beam splitter 68. The reflected light LB2' that is split into the first optical path OP1 is focused one-dimensionally by the cylindrical lens 80, and its cross section becomes elliptical. The reflected light LB2' that has been focused into an elliptical cross section is restricted to a predetermined unit length by the filter 70, and a portion of the reflected light LB2' that is split into the first optical path OP1 is received by the first light receiving element 72. A voltage signal corresponding to the amount of received light is then output from the first light receiving element 72.

[0058] 8(b), when the focal point Pa of the detection light LB2 is deeper than the position shown in FIG. 8(a), the detection light LB2 is reflected by an area S2 irradiated onto the upper surface of the wafer W. The area S2 is larger than the area S1 (S2>S1). Therefore, the length of the major axis of the reflected light related to the area S2 when the cross section is narrowed into an ellipse by the cylindrical lens 80 of the first optical path OP1 is longer than the length of the major axis of the reflected light related to the area S1 when the cross section is narrowed into an ellipse.

[0059] As described above, the reflected light LB2' whose cross section has been narrowed to an elliptical shape in the first optical path OP1 is restricted to a predetermined unit length by the filter 70 and is received by the first light receiving element 72. For this reason, the amount of light received by the first light receiving element 72 when the reflected light related to the area S2 is received is less than the amount of light received by the first light receiving element 72 when the reflected light related to the area S1 is received.

[0060] In this way, the amount of reflected light received by the first light receiving element 72 increases as the focus point Pa of the detection light LB2 is closer to the top surface of the wafer W, and decreases as the focus point Pa is farther from the top surface of the wafer W. Therefore, when the top surface position (reflection position) of the wafer W changes, the amount of light received by the first light receiving element 72 changes, and the voltage signal output from the first light receiving element 72 also changes.

[0061] On the other hand, the reflected light LB2' branched onto the second optical path OP2 is 100% condensed by the condenser lens 82, and therefore all of the reflected light LB2' branched onto the second optical path OP2 is received by the second light receiving element 74. Therefore, even if the upper surface position (reflection position) of the wafer W changes, the amount of light received by the second light receiving element 74 does not change. Therefore, the amount of light received by the second light receiving element 74 is greater than the amount of light received by the first light receiving element 72, and the voltage signal output from the second light receiving element 74 is constant.

[0062] The relationship between the ratio (V2 / V1) of the voltage signals output from the first and second light receiving elements 72, 74 and the distance from the top surface of the wafer W to the focal point Pa of the detection light LB2 is, for example, as shown in the graph of FIG.

[0063] 9 represents the distance (μm) from the upper surface of the wafer W to the focal point Pa when the focal point Pa is positioned inside the wafer W. The vertical axis of FIG. 9 represents the ratio (V2 / V1) of the voltage signal V1 output from the first light receiving element 72 to the voltage signal V2 output from the second light receiving element 74.

[0064] In the example shown in Figure 9, when the focal point Pa is located at a depth of 10 μm from the top surface of the wafer W, the ratio of the voltage signals (V2 / V1) is "3," and when the focal point Pa is located at a depth of 40 μm from the top surface of the wafer W, the ratio of the voltage signals (V2 / V1) is "6."

[0065] In the first upper surface position detector 56, the control means 76 calculates the upper surface position of the wafer W based on the position of the focal point Pa of the detection light LB2 by comparing the amount of light received by the first light receiving element 72, which changes depending on the upper surface position of the wafer W, with the amount of light received by the second light receiving element 74, which does not change depending on the upper surface position of the wafer W.

[0066] (Second upper surface position detector 58) The second upper surface position detector 58, like the first upper surface position detector 56, includes a detection light source 61 that emits detection light LB2 in a wide wavelength band, and a selection means 62 that selects detection light LB2 of a specific wavelength from the detection light LB2 emitted by the detection light source 61, and the selection means 62 selects detection light LB2 of the specific wavelength from the detection light LB2 emitted by the detection light source 61, guides it to the upper surface of the wafer W held on the chuck table 4, and calculates the upper surface position of the wafer W based on reflected light LB2″ reflected by the upper surface of the wafer W.

[0067] Explaining with reference to Figures 10 and 11, the second top surface position detector 58 includes an irradiation end portion 84 (see Figure 11) that irradiates the top surface of the wafer W with detection light LB2 emitted by the detection light source 61 at an incident angle α, a light-receiving end portion 86 that receives reflected light LB2" that is formed when the detection light LB2 irradiated from the irradiation end portion 84 is reflected by the top surface of the wafer W, and an image sensor 88 (see Figure 11) that measures the position of the reflected light LB2" received by the light-receiving end portion 86.

[0068] The second upper surface position detector 58 of the illustrated embodiment includes a U-shaped casing 90 as shown in Fig. 10. The casing 90 is supported on the housing 32 of the laser beam application means 6 via an appropriate bracket (not shown). The casing 90 is provided with an application end portion 84 and a light-receiving end portion 86. The application end portion 84 and the light-receiving end portion 86 are spaced apart in the Y-axis direction, with the condenser 26 sandwiched between them, as shown in Fig. 11.

[0069] 2, a wide wavelength band of detection light LB2 emitted by the detection light source 61 is selected by the selection means 62, and only a specific wavelength is then selected, and the selected light is then guided to the casing 90 of the second top surface position detector 58 via the first beam splitter 66. Then, the detection light LB2 of the specific wavelength guided to the casing 90 is irradiated onto the top surface of the wafer W held on the chuck table 4 from the irradiation end 84 at an incident angle α, as shown in FIG.

[0070] 11, the incident angle α is the angle between a line perpendicular to the upper surface of the chuck table 4 and the detection light LB2 irradiated from the irradiation end portion 84. The incident angle α is set to be larger than the collection angle β of the collector 26 and smaller than 90 degrees (β<α<90). The irradiation position of the detection light LB2 by the irradiation end portion 84 substantially coincides with the irradiation position of the processing laser beam LB1 irradiated onto the wafer W from the collector 26.

[0071] The light-receiving end portion 86 is disposed at a position where the detection light LB2 irradiated from the irradiating end portion 84 travels after being specularly reflected by the upper surface of the wafer W. As shown in Fig. 12, the image sensor 88 is disposed so that the angle formed between the image sensor 88 and a line perpendicular to the upper surface of the chuck table 4 is α.

[0072] 10, the casing 90 is provided with angle adjustment knobs 92, 94 for adjusting the inclination angles of the irradiating end 84 and the light-receiving end 86. By rotating the angle adjustment knobs 92, 94, it is possible to adjust the incident angle α of the detection light LB2 irradiated from the irradiating end 84 and the light-receiving angle of the light-receiving end 86.

[0073] 12, the detection light LB2 emitted from the irradiation end portion 84 is reflected by the upper surface of the wafer W and received at point A of the image sensor 88. When the upper surface of the wafer W is positioned as shown by the two-dot chain line in FIG. 12, the detection light LB2 emitted from the irradiation end portion 84 is reflected by the upper surface of the wafer W as shown by the two-dot chain line and received at point B of the image sensor 88. Data detected by the image sensor 88 is output to the control means 76.

[0074] Then, based on the position of the reflected light LB2" detected by the image sensor 88, the position of the upper surface of the wafer W is calculated by the control means 76. Specifically, based on the distance H between points A and B detected by the image sensor 88, the displacement h of the position of the upper surface of the wafer W is calculated (h = H cos α).

[0075] For example, if the position of the top surface of the wafer W when the image sensor 88 detects the reflected light LB2" at point A is taken as the reference position h0, the displacement h of the top surface position of the wafer W when the image sensor 88 detects the reflected light LB2" at point B can be calculated by h = H cos α as described above, and therefore the top surface position h1 of the wafer W when the reflected light LB2" is detected at point B can be found by h1 = h0 - h. In this way, in the second top surface position detector 58, the top surface position of the wafer W is calculated from the position of the reflected light LB2" detected by the image sensor 88.

[0076] (Selection Department 60) Referring to FIG. 2, the selection unit 60 includes first and second shutters 96, 98, a first actuator (not shown) that moves the first shutter 96, and a second actuator (not shown) that moves the second shutter 98.

[0077] The first shutter 96 is configured to be positioned by a first actuator at an allowance position (position shown by a solid line in Figure 2) where it allows the detection light LB2 that has passed through the first beam splitter 66 to pass, and at a blocking position (position shown by a two-dot chain line in Figure 2) where it blocks the detection light LB2 that has passed through the first beam splitter 66.

[0078] The second shutter 98 is configured to be positioned by a second actuator at an allowance position (position shown by a solid line in Figure 2) where it allows the detection light LB2 reflected by the first beam splitter 66 to pass through, and at a blocking position (position shown by a two-dot chain line in Figure 2) where it blocks the detection light LB2 reflected by the first beam splitter 66.

[0079] In the selection unit 60, the detection light LB2 split by the first beam splitter 66 is selected by a first shutter 96 and a second shutter 98.

[0080] Specifically, when the selection unit 60 selects the first upper surface position detector 56, the first actuator positions the first shutter 96 in the allowable position, and the second actuator positions the second shutter 98 in the blocking position.

[0081] As a result, the detection light LB2 emitted from the detection light source 61 and passed through the first beam splitter 66 is guided to the first top surface position detector 56. On the other hand, the detection light LB2 emitted from the detection light source 61 and reflected by the first beam splitter 66 is blocked by the second shutter 98. Therefore, the first top surface position detector 56 is selected.

[0082] Furthermore, when the selection unit 60 selects the second upper surface position detector 58, the first actuator positions the first shutter 96 in the blocking position, and the second actuator positions the second shutter 98 in the permitting position.

[0083] As a result, the detection light LB2 emitted from the detection light source 61 and passed through the first beam splitter 66 is blocked by the first shutter 96. On the other hand, the detection light LB2 emitted from the detection light source 61 and reflected by the first beam splitter 66 is guided to the second top surface position detector 58. Therefore, the second top surface position detector 58 is selected.

[0084] (Feeding means 8) As shown in FIG. 1, the feed means 8 includes an X-axis feed means 100 that feeds the chuck table 4 in the X-axis direction relative to the laser beam application means 6 for processing, and a Y-axis feed means 102 that feeds the chuck table 4 in the Y-axis direction relative to the laser beam application means 6 for processing.

[0085] (X-axis feed means 100) X-axis feed means 100 has a ball screw 104 connected to X-axis movable plate 12 and extending in the X-axis direction, and a motor 106 that rotates ball screw 104. X-axis feed means 100 converts the rotational motion of motor 106 into linear motion using ball screw 104 and transmits it to X-axis movable plate 12, moving X-axis movable plate 12 in the X-axis direction along guide rails 10a on base 10. As a result, chuck table 4 is fed for processing in the X-axis direction.

[0086] (Y-axis feed means 102) The Y-axis feed means 102 has a ball screw 108 that is connected to the Y-axis movable plate 14 and extends in the Y-axis direction, and a motor 110 that rotates the ball screw 108. The Y-axis feed means 102 converts the rotational motion of the motor 110 into linear motion using the ball screw 108 and transmits it to the Y-axis movable plate 14, moving the Y-axis movable plate 14 in the Y-axis direction along the guide rails 12a on the X-axis movable plate 12. As a result, the chuck table 4 is fed for processing in the Y-axis direction.

[0087] 1, the laser processing apparatus 2 further includes an imaging means 112 that detects a portion to be processed by the laser beam application means 6. The imaging means 112 is attached to the lower surface of the tip of the housing 32 of the laser beam application means 6. The image captured by the imaging means 112 is output to the control means 76.

[0088] Next, a method for processing the wafer W using the laser processing device 2 as described above will be described.

[0089] In the illustrated embodiment, first, the wafer W is placed on the upper surface of the chuck table 4. Next, the suction means connected to the suction chuck 20 is activated to suction-hold the wafer W on the upper surface of the suction chuck 20. Next, the X-axis feed means 100 is activated to position the chuck table 4 directly below the imaging means 112.

[0090] Once the chuck table 4 is positioned directly below the imaging means 112, the wafer W is imaged by the imaging means 112. Next, the positional relationship between the wafer W and the condenser 26 is adjusted based on the image of the wafer W imaged by the imaging means 112. At this time, the processing laser beam LB1 is aimed at the part to be processed that is to be laser processed, and the focal point P of the processing laser beam LB1 is adjusted to a predetermined position (for example, a position at a predetermined depth from the top surface of the wafer W).

[0091] Next, the motor 65 of the selection means 62 rotates the support plate 64, and one of the multiple bandpass filters 63a to 63j is selected and positioned in the optical path of the detection light LB2. This makes it possible to select the detection light LB2 of a specific wavelength that is sufficiently reflected by the upper surface of the wafer W from the detection light source 61, which has a wide wavelength band.

[0092] In this case, from the viewpoint of measuring the height of the upper surface of the wafer W more accurately, it is preferable to select the detection light of a wavelength at which the amount of light received is maximized by the first and second light receiving elements 72, 74 or the light receiving end portion 86. For this reason, it is preferable to irradiate the upper surface of the wafer W with detection light LB2 of a plurality of specific wavelengths selectable by the selection means 62 in advance, and confirm the wavelength at which the amount of light received is maximized.

[0093] Next, the selection unit 60 selects either the first or second upper surface position detector 56, 58. Next, the processing laser beam LB1 is irradiated from the condenser 26 while the chuck table 4 is moved by the feeding means 8 so that the focal point P of the processing laser beam LB1 passes through the processing portion of the wafer W in sequence.

[0094] Furthermore, the wafer W is irradiated with detection light LB2 of a specific wavelength selected by the selection means 62 to detect the top surface position of the wafer W. Then, based on the detection result of the top surface position of the wafer W, the height of the focal point P of the processing laser beam LB1 is adjusted.

[0095] When the first upper surface position detector 56 is selected, when detection light LB2 of a specific wavelength is irradiated onto the wafer W, a voltage signal relating to the amount of light received by the first light receiving element 72 and a voltage signal relating to the amount of light received by the second light receiving element 74 are sent to the control means 76.

[0096] In this case, the upper surface position of the wafer W is calculated by the control means 76 based on a comparison between the amount of light received by the first light receiving element 72 and the amount of light received by the second light receiving element 74. Then, based on the calculated upper surface position of the wafer W, the angle adjustment actuators 48, 54 of the first and second galvanometer scanners 38, 40 of the focal point position adjuster 28 are controlled by the control means 76 to adjust the height of the focal point P of the processing laser beam LB1.

[0097] On the other hand, when the second top surface position detector 58 is selected, when the detection light LB2 of a specific wavelength is irradiated onto the wafer W, position information of the reflected light LB2″ detected by the image sensor 88 of the second top surface position detector 58 is sent to the control means 76.

[0098] In this case, the position of the upper surface of the wafer W is calculated by the control means 76 based on the position information of the reflected light LB2" detected by the image sensor 88. Then, based on the calculated position of the upper surface of the wafer W, the angle adjustment actuators 48, 54 of the first and second galvano scanners 38, 40 of the focal point position adjuster 28 are controlled by the control means 76 to adjust the height of the focal point P of the processing laser beam LB1.

[0099] This keeps the distance from the top surface of the wafer W to the focal point P of the processing laser beam LB1 constant, making it possible to perform the required laser processing (for example, forming a modified layer) parallel to the top surface of the wafer W at a predetermined depth from the top surface of the wafer W.

[0100] As described above, in the laser processing apparatus 2 of the illustrated embodiment, the selection means 62 selects the detection light LB2 of a specific wavelength that is sufficiently reflected by the upper surface of the wafer W from the detection light source 61, among the detection light LB2 of a wide wavelength band. Therefore, regardless of the type or surface condition of the wafer W, the upper surface height of the wafer W can be properly measured, and the focal point P of the processing laser beam LB1 can be properly positioned based on the properly measured upper surface height of the wafer W. [Explanation of symbols]

[0101] 2: Laser processing equipment 4: Chuck table 6: Laser beam irradiation means 8:Feeding means 24: Oscillator 26: Concentrator 28:Focusing point position adjuster 30: Top surface position detector 61: Detection light source 62: Selection method 63a~63j: Bandpass filters 66: First beam splitter 67: Combiner 68: Second beam splitter 70: Filter 72: First light receiving element 74: Second light receiving element 84: Irradiation end 86: Light receiving end 88: Image sensor W: Wafer OP1: First optical path OP2: Second optical path LB1: Pulsed laser beam for processing LB2: Detection light

Claims

1. A laser processing apparatus including a chuck table for holding a wafer, a laser beam application means for applying a laser beam to the wafer held on the chuck table, and a feed means for feeding the chuck table and the laser beam application means for processing in an X-axis direction and a Y-axis direction perpendicular to the X-axis direction, the laser beam application means comprises an oscillator for emitting a laser beam, a condenser for condensing the laser beam oscillated by the oscillator and positioning the condensing point on the wafer held on the chuck table, a condensing point position adjuster disposed between the oscillator and the condenser for adjusting the position of the condensing point, and an upper surface position detector for detecting the position of the upper surface of the wafer; the top surface position detector includes a detection light source that emits detection light in a wide wavelength band; a selection means that selects detection light of a specific wavelength from the detection light emitted by the detection light source; a combiner that combines the detection light emitted by the detection light source and that has passed through the selection means and a first beam splitter in this order between the oscillator and the light-focusing point position adjuster; and a filter means that transmits only light that corresponds to the specific wavelength selected by the selection means from the light that is guided from the combiner to the first beam splitter and reflected by the first beam splitter; the selection means includes a plurality of bandpass filters that transmit detection light of specific wavelengths different from each other, and selects one of the plurality of bandpass filters and positions it in the optical path of the detection light to select the detection light of the specific wavelength; the filter means includes a plurality of band pass filters that transmit reflected light of specific wavelengths different from each other, and selects a band pass filter from the plurality of band pass filters that transmits the same wavelength as the wavelength selected by the selection means and positions it in the optical path of the reflected light to transmit the reflected light of the specific wavelength; A laser processing device that selects detection light of a specific wavelength from the detection light emitted by the detection light source by the selection means, directs the selected detection light to the upper surface of the wafer held on the chuck table, and calculates the position of the upper surface of the wafer by the light that is reflected from the upper surface of the wafer and that passes through the filter means.

2. 2. The laser processing apparatus according to claim 1, wherein said selection means selects the detection light of the wavelength at which the amount of received light is maximum.

3. The upper surface position detector includes:

2. The laser processing apparatus according to claim 1, further comprising: a second beam splitter that splits the detection light, which has passed through the focus position adjuster and the condenser and is reflected by the top surface of the wafer held on the chuck table, into a first optical path and a second optical path via the combiner and the first beam splitter; a filter that is disposed in the first optical path and passes a portion of the split reflected light; a first light receiving element that receives the reflected light that has passed through the filter; and a second light receiving element that is disposed in the second optical path and receives all of the split reflected light, and the laser processing apparatus calculates the top surface position of the wafer by comparing the amount of light received by the first light receiving element and the amount of light received by the second light receiving element.

Images