Laser processing equipment

Abstract

[Problem] To provide a laser processing apparatus that can accurately measure the height of the upper surface of a wafer regardless of its type or surface condition. [Solution] The laser processing apparatus includes: a laser oscillator that emits laser light; a concentrator that focuses the laser light emitted by the laser oscillator and positions the concentrator point on the wafer; a concentrator position adjuster disposed between the laser oscillator and the concentrator and adjusting the position of the concentrator point; and an upper surface position detector that detects the position of the upper surface of the wafer. The upper surface position detector includes: a detection light source that emits detection light with a wide wavelength band; and a selector that selects a detection light of a specific wavelength from the detection light emitted by the detection light source.

Description

Technical Field

[0001] This invention relates to a laser processing apparatus. Prior Technology

[0002] A wafer with multiple components such as ICs and LSIs formed on the front side by intersecting multiple predetermined dividing lines is diced into individual component chips by a laser processing device after being ground to the desired thickness on the back side.

[0003] The laser processing apparatus includes: a chuck stage for holding a wafer; a laser beam irradiation unit for irradiating the wafer held on the chuck stage with laser beams; and a feed mechanism for feeding the chuck stage and the laser beam irradiation unit in the X-axis direction and the Y-axis direction orthogonal to the X-axis direction, and for irradiating the wafer with laser beams with high precision along the predetermined dicing lines.

[0004] Furthermore, in the process of positioning the focal point of a laser beam with a wavelength that is penetrable to the wafer inside the wafer corresponding to the predetermined dicing line, and irradiating the wafer with the laser beam to form a modified layer inside the wafer, and then applying external force to the wafer to dice it into individual component wafers, it is necessary to position the focal point of the laser beam at an appropriate and correct position from the upper surface of the wafer. The applicant has developed a technique for controlling the position of the focal point of the laser beam while measuring the position (upper surface height) of the upper surface of the wafer (for example, see Patent Documents 1 and 2).

[0005] The technology disclosed in Patent Document 1 is a first type of technology, which irradiates the upper surface of the wafer with the detection light emitted by the detection light source at an incident angle α, and has the ability to measure the position of the reflected light reflected on the upper surface of the wafer, and calculate the position of the upper surface of the wafer by means of the position of the reflected light detected by the image sensor.

[0006] The technology disclosed in Patent Document 2 is a second type of technology, which uses a detection light source to irradiate the upper surface of a wafer held on a chuck stage through a condenser. The reflected light reflected from the upper surface of the wafer is split into a first optical path and a second optical path. The position of the upper surface of the wafer is calculated by comparing the intensity of the reflected light passing through the slit mask disposed in the first optical path with the intensity of the reflected light guided to the second optical path. [Known Technical Documents] [Patent Literature]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2005-313182 [Patent Document 2] Japanese Patent Application Publication No. 2007-152355 Summary of the Invention

[0008] [The problem that the invention aims to solve] However, depending on the type and surface condition of the wafer, there may be situations where the detection light emitted from the detection light source cannot be sufficiently reflected on the upper surface of the wafer. In such cases, there is a problem that the height of the upper surface of the wafer cannot be measured properly and accurately. Although this problem is more common in Type I measuring instruments, it can also occur in Type II measuring instruments.

[0009] Therefore, the object of the present invention is to provide a laser processing apparatus that can appropriately and accurately measure the height of the upper surface of a wafer regardless of the type and surface condition of the wafer.

[0010] [Technical means to solve the problem] According to the present invention, a laser processing apparatus is provided, comprising: a chuck stage for holding a wafer; a laser beam irradiation unit for irradiating the wafer held on the chuck stage with laser beams; and a feed mechanism for feeding the chuck stage and the laser beam irradiation unit in an X-axis direction and a Y-axis direction orthogonal to the X-axis direction. The laser beam irradiation unit comprises: a laser oscillator for emitting laser beams; a concentrator for focusing the laser beams emitted by the laser oscillator and positioning the concentrator point on the wafer held on the chuck stage; and a concentrator point position adjuster disposed on the laser oscillator. The laser processing apparatus includes: a detection light source that emits detection light with a wide wavelength band; and a selector that selects a detection light of a specific wavelength from the detection light emitted by the detection light source. The laser processing apparatus uses the selector to select the detection light of a specific wavelength from the detection light emitted by the detection light source and guides it to the upper surface of the wafer held on the chuck stage. The upper surface position of the wafer is calculated by the reflected light reflected from the upper surface of the wafer.

[0011] Preferably, the selector includes a plurality of bandpass filters that allow detection light of different specific wavelengths to pass through, and selects any one of the plurality of bandpass filters and positions it in the optical path of the detection light to select the detection light of a specific wavelength. Preferably, the selector selects the detection light of the wavelength with the maximum amount of light received.

[0012] Preferably, the upper surface position detector includes: a converging unit that merges the detection light emitted from the detection light source and sequentially passing through the selector and the first beam splitter between the laser oscillator and the focusing point position adjuster; a second beam splitter that, through the converging unit and the first beam splitter, splits the reflected light reflected from the upper surface of the wafer held on the chuck stage by the detection light that has passed through the focusing point position adjuster and the focusing unit into a first optical path and a second optical path; a filter disposed in the first optical path and allowing a portion of the split reflected light to pass through; a first light-receiving element that receives the reflected light that has passed through the filter; and a second light-receiving element disposed in the second optical path and receiving all of the split reflected light, and the upper surface position of the wafer is calculated 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.

[0013] Preferably, the upper surface position detector includes: an irradiation end that irradiates the upper surface of the wafer with the detection light emitted by the detection light source at an incident angle α; a light-receiving end that receives the reflected light from the detection light irradiated from the irradiation end on the upper surface of the wafer; and an image sensor that measures the position of the reflected light received at the light-receiving end, and calculates the position of the upper surface of the wafer by means of the position of the reflected light detected by the image sensor.

[0014] [Invention Benefits] According to the laser processing apparatus of the present invention, a specific wavelength of detection light that is sufficiently reflected on the upper surface of the wafer can be selected, and the height of the upper surface of the wafer can be measured appropriately and accurately regardless of the type and surface condition of the wafer. Simple Explanation of the Diagram

[0015] Figure 1 is a perspective view of the laser processing apparatus according to an embodiment of the present invention. Figure 2 is a block diagram of the laser beam irradiation unit shown in Figure 1. Figure 3 is a perspective view of the first / second current scanner shown in Figure 2. Figure 4 is a schematic diagram showing the optical path length of the laser beam passing through the first current scanner as shown in Figure 3. Figure 5 is a graph showing the relationship between the setting angle of the first / second current scanner shown in Figure 3 and the displacement of the optical path length of the laser beam. Figure 6 is a graph showing the relationship between the optical path length of the laser beam and the displacement of the distance from the concentrator to the focal point. Figure 7 is a perspective view of the selector shown in Figure 2. Figure 8(a) is a schematic diagram showing the reflective area when the detection light shines on the wafer, and Figure 8(b) is a schematic diagram showing the reflective area when the focal point of the detection light is positioned lower than that shown in Figure 8(a). Figure 9 is a graph showing the relationship between the voltage signal ratio output from the first / second light-receiving element shown in Figure 2 and the distance from the upper surface of the wafer to the focal point of the detection light. Figure 10 is a perspective view of the condenser and the second upper surface position detector shown in Figure 1. Figure 11 is a schematic diagram showing the state of detecting the position of the upper surface of the wafer by means of the second upper surface position detector shown in Figure 1. Figure 12 is a schematic diagram showing the optical path of the detection light when the upper surface of the wafer is at the reference position and the optical path of the detection light when the upper surface of the wafer changes only h from the reference position. Implementation

[0016] Hereinafter, a detailed description of the laser processing apparatus according to an embodiment of the present invention will be provided with reference to the drawings.

[0017] As shown in Figure 1, the laser processing apparatus 2 includes: a chuck stage 4 that holds the wafer W; a laser beam irradiation unit 6 that irradiates the wafer W held on the chuck stage 4 with laser beams; and a feed mechanism 8 that feeds the chuck stage 4 and the laser beam irradiation unit 6 along the X-axis direction (indicated by arrow X in Figure 1) and the Y-axis direction (indicated by arrow Y in Figure 1), which is orthogonal to the X-axis direction. Furthermore, the XY plane defined by the X-axis and Y-axis directions is substantially horizontal.

[0018] The laser processing apparatus 2 of this embodiment includes: an X-axis movable plate 12, which is movably mounted on the upper surface of a base 10 in the X-axis direction; a Y-axis movable plate 14, which is movably mounted on the upper surface of the X-axis movable plate 12 in the Y-axis direction; a support column 16, which is fixed to the upper surface of the Y-axis movable plate 14; and a cover plate 18, which is 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. Furthermore, the chuck stage 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 porous, circular suction chuck 20, connected to a suction means (not shown), is disposed at the upper part of the chuck stage 4. Multiple clamps 22 are provided at circumferential intervals around the periphery of the chuck stage 4.

[0020] The chuck stage 4 generates an attractive force on the upper surface of the adsorption chuck 20 using an attraction method, and attracts and holds the wafer W placed on the upper surface of the adsorption chuck 20. Furthermore, the chuck stage 4 rotates around the vertical axis by a chuck stage motor (not shown) built into the support column 16.

[0021] As shown in Figure 2, the laser beam irradiation unit 6 includes: a laser oscillator 24 that emits a processing pulse laser beam LB1; a concentrator 26 that focuses the laser beam LB1 emitted by the laser oscillator 24 and positions the focusing point P on the wafer W held on the chuck stage 4; a focusing point position adjuster 28 that is disposed between the laser oscillator 24 and the concentrator 26 and adjusts the position of the focusing point P; and an upper surface position detector 30 that detects the position of the upper surface of the wafer W.

[0022] As shown in Figure 1, the laser beam irradiation unit 6 includes a housing 32 that extends upward from the upper surface of the base 10 and then extends substantially horizontally. A laser oscillator 24 is disposed inside the housing 32. The laser beam LB1 emitted by the laser oscillator 24 can be a wavelength (e.g., 1064 nm) that is penetrating to the wafer W. A concentrator 26 is mounted on the lower front surface of the housing 32.

[0023] Referring to FIG2, the focusing point position adjuster 28 includes: first and second lenses 34 and 36, which are equally spaced apart from each other; a first current scanner 38 that reflects the laser light LB1 that has passed through the first lens 34; and a second current scanner 40 that reflects the laser light LB1 reflected by the first current scanner 38 and guides it to the second lens 36. Furthermore, a direction conversion mirror 42 is provided between the second lens 36 and the focusing lens 26 to guide the laser light LB1 that has passed through the second lens 36 to the focusing lens 26.

[0024] Referring to Figures 2 and 3, the first current scanner 38 has: a pair of first / second reflectors 44, 46, which are equally spaced and arranged parallel to each other; and an angle adjustment actuator 48 (refer to Figure 3) that adjusts the setting angle of the first / second reflectors 44, 46.

[0025] As shown in Figure 2, the first reflector 44 reflects the laser beam LB1 that has passed through the first lens 34 toward the second reflector 46. The second reflector 46 then reflects the laser beam LB1 reflected by the first reflector 44 toward the second current scanner 40.

[0026] As shown in Figure 3, the rotation axis 48a of the angle adjustment actuator 48 is connected to both the first and second reflectors 44 and 46. Moreover, while maintaining the parallel state of the first and second reflectors 44 and 46, the angle adjustment actuator 48 changes the setting angle of the first and second reflectors 44 and 46 relative to the optical path of the laser beam LB1.

[0027] The second current scanner 40, like the first current scanner 38, has: a pair of third / fourth reflectors 50, 52, which are equally spaced and arranged parallel to each other; and an angle adjustment actuator 54, which adjusts the setting angle of the third / fourth reflectors 50, 52.

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

[0029] The rotation axis 54a of the angle adjustment actuator 54 is connected to both the third and fourth reflectors 50 and 52. Moreover, while maintaining the parallel state of the third and fourth reflectors 50 and 52, the angle adjustment actuator 54 changes the setting angle of the third and fourth reflectors 50 and 52 relative to the optical path of the laser beam LB1.

[0030] As described above, the laser beam LB1 emitted by the laser oscillator 24 is reflected by the first lens 34 and then by the first / second reflecting mirrors 44 and 46. As shown in Figure 4, if the distance between the first reflecting mirror 44 and the second reflecting mirror 46 is set as d, it is represented as follows: m1=d / cosθ m2=m1cos2θ=(d / cosθ)cos2θ, Therefore, it becomes: m1+m2=(d / cosθ)(1+cos2θ)=2dcosθ.

[0031] If the distance between the third reflector 50 and the fourth reflector 52 is also set to d as described above, then the optical path length of the laser beam LB1 varies by (m1 + m2) × 2. For example, if the distance d is set to 2 mm, and the state with an angle θ of 47.5 degrees is taken as the reference (displacement of optical path length 0), then the displacement of the optical path length of the laser beam LB1 is shown in Figure 5. In the example shown in Figure 5, if the angle θ varies from 40 degrees to 57.5 degrees, then the optical path length varies from +0.73 mm to -1.1 mm. That is, the displacement of the optical path length within the above angle range is 1.83 mm.

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

[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 set as d1, the optical path length from the second lens 36 to the condenser 26 is set as d2, the focal distance of the second lens 36 is set as f1, and the focal distance of the condenser 26 is set as f2, then the distance d3 from the condenser 26 to the focusing point P can be obtained by the following formula (1).

[0034] [Mathematical Expression 1]

[0035] Furthermore, when the laser beam LB1 emitted by the laser oscillator 24 is parallel, the focal point D of the first lens 34 is at the same distance from the focal point of the first lens 34.

[0036] In equation (1), if specific values ​​are applied to each of the focal distance f1 of the second lens 36, the focal distance f2 of the condenser 26, and the optical path length d2 from the second lens 36 to the condenser 26, then the distance d3 from the condenser 26 to the focusing 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. That is, once the optical path length d1 changes, the position of the focusing point P will change.

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

[0038] Therefore, under the conditions described above, if the angle θ varies from 40 degrees to 57.5 degrees, the optical path length varies from +0.73 mm to -1.1 mm, and correspondingly, the distance d3 from the condenser 26 to the focusing point P shifts from -20 μm to +28 μm. That is, the focusing point position adjuster 28 uses angle adjustment actuators 48 and 54 to adjust the setting angles of the first to fourth reflectors 44, 46, 50, and 52, thereby adjusting the vertical position of the focusing point P.

[0039] As shown in FIG2, the upper surface position detector 30 of this embodiment includes: a first upper surface position detector 56; a second upper surface position detector 58; and a selection unit 60, which selects either the first upper surface position detector 56 or the second upper surface position detector 58. Furthermore, the upper surface position detector 30 does not need to include both the first and second upper surface position detectors 56 and 58, but only either the first or second upper surface position detector 56 or 58 is required.

[0040] The first upper surface position detector 56 includes: a detection light source 61 that emits a detection light LB2 with a wide wavelength band; and a selector 62 that selects a detection light LB2 of a specific wavelength from the detection light LB2 emitted by the detection light source 61, and guides the detection light LB2 of a specific wavelength from the detection light LB2 emitted by the detection light source 61 to the upper surface of the wafer W held on the chuck stage 4, and calculates the position of the upper surface of the wafer W by the reflected light LB2' reflected from the upper surface of the wafer W.

[0041] The detection light source 61 emits light with a wavelength in the range of, for example, 100 to 2000 nm, as a wide-band detection light LB2. Furthermore, the wide-band detection light LB2 is not limited to the above range (100 nm to 2000 nm), as long as it is a range of multiple detection lights with different wavelengths that can be selectively selected.

[0042] As shown in Figure 7, the selector 62 has: a plurality of bandpass filters 63a~63j; a support plate 64 that supports the plurality of bandpass filters 63a~63j; and a motor 65 that rotates the support plate 64.

[0043] Multiple bandpass filters 63a-63j each allow detection light LB2 of different specific wavelengths to pass through. For example, bandpass filter 63a can be configured to allow light with a wavelength of 100 nm to pass through, bandpass filter 63b to allow light with a wavelength of 300 nm, bandpass filter 63c to allow light with a wavelength of 500 nm, bandpass filter 63d to allow light with a wavelength of 700 nm, bandpass filter 63e to allow light with a wavelength of 900 nm, bandpass filter 63f to allow light with a wavelength of 1100 nm, bandpass filter 63g to allow light with a wavelength of 1300 nm, bandpass filter 63h to allow light with a wavelength of 1500 nm, bandpass filter 63i to allow light with a wavelength of 1700 nm, and bandpass filter 63j to allow light with a wavelength of 1900 nm.

[0044] The number of bandpass filters in selector 62 and the wavelength of the bandpass filters in pass-through selector 62 can be arbitrarily set.

[0045] Then, in selector 62, the support plate 64 is rotated by motor 65 to select any one of the multiple bandpass filters 63a-63j and position it in the optical path of the detection light LB2. In this way, a specific wavelength of detection light LB2 that is sufficiently reflected from the upper surface of the wafer W can be selected from the wide-wavelength detection light LB2 emitted by the detection light source 61. Selector 62 selects the detection light LB2 with a wavelength different from the processing laser light LB1 emitted by the laser oscillator 24.

[0046] The selector 62 preferably selects the detection light with the maximum light intensity in the first / second light-receiving elements 72, 74 or the light-receiving end 86, as described later, according to the type of wafer W and the surface condition of the wafer W. This allows for a more accurate measurement of the height of the upper surface of the wafer W.

[0047] As shown in Figure 2, the first upper surface position detector 56 includes: a converging unit 67, which merges the detection light LB2 emitted from the detection light source 61 and sequentially passing through the selector 62 and the first beam splitter 66 between the laser oscillator 24 and the focusing point position adjuster 28; a second beam splitter 68, which splits the reflected light LB2' into a first optical path OP1 and a second optical path OP2 through the converging unit 67 and the first beam splitter 66, wherein the reflected light LB2' is the detection light LB2 that has passed through the focusing point position adjuster 28 and the focusing unit 26 and is reflected on the upper surface of the wafer W held on the chuck stage 4; a filter 70, which is disposed in the first optical path OP1 and allows a portion of the split reflected light LB2' to pass through; a first light receiving element 72, which receives the reflected light LB2' that has passed through the filter 70; and a second light receiving element 74, which is disposed in the second optical path OP2 and receives the entire split reflected light LB2'.

[0048] The converging element 67 can be constructed from a dichroic half mirror. The converging element 67 allows the laser beam LB1 emitted from the laser oscillator 24 to pass through, and reflects the detection beam LB2 emitted from the detection light source 61 (i.e., the detection beam LB2 that has already passed through the first beam splitter 66) towards the focusing point position adjuster 28. The first / second light-receiving elements 72 and 74 output voltage signals corresponding to the amount of light received to the controller 76.

[0049] The controller 76 is composed of a computer and controls the operation of the laser processing device 2. The controller 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 read-write random access memory (RAM) that stores the calculation results, etc.

[0050] The first upper surface position detector 56 of this embodiment further includes: a filter 78 that allows only light corresponding to the wavelength of the reflected light LB2' (a specific wavelength selected by the selector 62) to pass through in the light guided from the converger 67 to the first beam splitter 66 and reflected by the first beam splitter 66; a cylindrical lens 80 that performs one-dimensional focusing on the reflected light LB2' that is split into the first optical path OP1 by the second beam splitter 68; and a condenser lens 82 that performs 100% focusing on the reflected light LB2' that is split into the second optical path OP2 by the second beam splitter 68.

[0051] The filter 78 can be configured in the same way as the selector 62 described above. Although not shown in the figure, 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, filter 78 selects a bandpass filter from a plurality of bandpass filters that allows the wavelength that is the same as the wavelength selected in selector 62 to pass through, and positions it in the optical path of the reflected light LB2'. In this way, only light corresponding to the wavelength of the reflected light LB2' (the specific wavelength selected by selector 62) passes through.

[0053] The wide-wavelength detection light LB2 emitted by the detection light source 61 is selected by the selector 62 to be of a specific wavelength and passes through the first beam splitter 66. It is then reflected by the converger 67 toward the focusing point position adjuster 28 and guided to the focusing point position adjuster 28 and the direction conversion mirror 42. Then, the detection light LB2 of a specific wavelength focused by the focusing point 26 is reflected on the upper surface of the wafer W held on the chuck stage 4.

[0054] For example, as shown in Figure 8(a), when the focal point Pa of the detection light LB2 is closer to the upper surface of the wafer W, the detection light LB2 is reflected over the area S1 of the upper surface of the wafer W.

[0055] The reflected light LB2' reflected from the upper surface of wafer W is shown as a dashed line in Figure 2. It passes through the condenser 26, the direction conversion mirror 42, the condenser position adjuster 28, the converger 67 and the first beam splitter 66, and finally reaches the filter 78.

[0056] Furthermore, although the reflected light from the processing laser beam LB1 and the reflected light LB2' from the detection beam LB2 both reach the filter 78, the reflected light from the processing laser beam LB1 is blocked by the filter 78. This is because the filter 78 only allows light corresponding to the wavelength of the reflected light LB2' from the detection beam LB2 to pass through. Therefore, only the reflected light LB2' from the detection beam LB2 passes through the filter 78.

[0057] The reflected light LB2', which has passed through filter 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' split into the first optical path OP1 is focused one-dimensionally by cylindrical lens 80, and its cross-section is elliptical. The reflected light LB2' with its elliptical cross-section is limited to a predetermined unit length by filter 70, and a portion of the reflected light LB2' split into the first optical path OP1 is received by the first light-receiving element 72. Then, a voltage signal corresponding to the amount of light received is output from the first light-receiving element 72.

[0058] Furthermore, as shown in Figure 8(b), when the focal point Pa of the detection light LB2 is deeper than that shown in Figure 8(a), the detection light LB2 is reflected over an area S2 on the upper surface of the wafer W. Area S2 is larger than area S1 (S2>S1). Therefore, the length of the major axis of the reflected light over area S2, when its profile is narrowed into an ellipse by the cylindrical lens 80 of the first optical path OP1, becomes longer than the length of the major axis of the reflected light over area S1, when its profile is narrowed into an ellipse.

[0059] As described above, the reflected light LB2', whose cross-section is narrowed into an ellipse in the first optical path OP1, is limited to a predetermined unit length by the filter 70 and received by the first light-receiving element 72. Therefore, compared to the amount of light received by the reflected light of area S1 when it is received by the first light-receiving element 72, the amount of light received by the reflected light of area S2 when it is received by the first light-receiving element 72 becomes less.

[0060] The amount of reflected light received by the first light-receiving element 72 is determined by the proximity of the focusing point Pa of the detection light LB2 to the upper surface of the wafer W, and the amount of light received by the focusing point Pa to the distance from the upper surface of the wafer W. Therefore, if the position of the upper surface of the wafer W (reflection position) 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, since the reflected light LB2', which is split into the second optical path OP2, is 100% focused by the condenser lens 82, all of the reflected light LB2' split into the second optical path OP2 is received by the second light-receiving element 74. Therefore, even if the position of the upper surface (reflection position) of the wafer W changes, the amount of light received by the second light-receiving element 74 will not change. Therefore, the amount of light received by the second light-receiving element 74 is greater than that 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 voltage signal ratio (V2 / V1) output from the first / second light-receiving elements 72 and 74 and the distance from the upper surface of the wafer W to the focusing point Pa of the detection light LB2 is, for example, as shown in the graph in Figure 9.

[0063] The horizontal axis of Figure 9 represents the distance (μm) from the upper surface of wafer W to the focal point Pa when the focal point Pa is located inside wafer W. The vertical axis of Figure 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 upper surface of the wafer W, the voltage signal ratio (V2 / V1) is "3", and when the focal point Pa is located at a depth of 40 μm from the upper surface of the wafer W, the voltage signal ratio (V2 / V1) is "6".

[0065] Then, in the first upper surface position detector 56, the controller 76 calculates the upper surface position of the wafer W by comparing the amount of light received by the first light-receiving element 72, which varies due to the upper surface position of the wafer W, with the amount of light received by the second light-receiving element 74, which does not vary due to the upper surface position of the wafer W, using the position of the focusing point Pa of the detection light LB2 as a reference.

[0066] The second upper surface position detector 58, like the first upper surface position detector 56, includes: a detection light source 61 that emits a wide-wavelength detection light LB2; and a selector 62 that selects a specific wavelength of detection light LB2 from the detection light LB2 emitted by the detection light source 61. The selector 62 selects a specific wavelength of detection light LB2 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 stage 4. The upper surface position of the wafer W is calculated by the reflected light LB2” reflected from the upper surface of the wafer W.

[0067] Referring to Figures 10 and 11, the second upper surface position detector 58 includes: an illumination end 84 that illuminates the upper surface of the wafer W with the detection light LB2 emitted by the detection light source 61 at an incident angle α (see Figure 11); a light-receiving end 86 that receives the reflected light LB2” reflected from the detection light LB2 irradiated from the illumination end 84 on the upper surface of the wafer W; and an image sensor 88 that measures the position of the reflected light LB2” received at the light-receiving end 86 (see Figure 11).

[0068] The second upper surface position detector 58 of this embodiment includes a U-shaped housing 90 as shown in FIG. 10. The housing 90 is supported on the outer shell 32 of the laser beam irradiation unit 6 by means of a suitable bracket (not shown). Then, an irradiation end 84 and a light-receiving end 86 are provided on this housing 90. The irradiation end 84 and the light-receiving end 86 are arranged as shown in FIG. 11, sandwiching the condenser 26 and spaced apart in the Y-axis direction.

[0069] As shown in Figure 2, the wide-wavelength detection light LB2 emitted by the detection light source 61 is selected by the selector 62 to a specific wavelength and then guided to the housing 90 of the second upper surface position detector 58 by the first beam splitter 66. Then, the detection light LB2 of the specific wavelength guided to the housing 90 is irradiated from the irradiation end 84 at an incident angle α to the upper surface of the wafer W held on the chuck stage 4, as shown in Figure 11.

[0070] As shown in Figure 11, the incident angle α is the angle between a straight line perpendicular to the upper surface of the chuck stage 4 and the detection light LB2 irradiated from the irradiation end 84. The incident angle α is set to be greater than the focusing angle β of the condenser 26 and less than 90 degrees (β<α<90). Furthermore, the irradiation position of the detection light LB2 irradiated from the irradiation end 84 is almost the same as the irradiation position of the processing laser light LB1 irradiated from the condenser 26 onto the wafer W.

[0071] The light-receiving end 86 is positioned such that the detection light LB2, irradiated from the irradiation end 84, is positively reflected from the upper surface of the wafer W and propagates forward. As shown in Figure 12, the image sensor 88 is positioned such that the angle between the image sensor 88 and the straight line perpendicular to the upper surface of the chuck stage 4 is α.

[0072] Furthermore, as shown in Figure 10, the housing 90 is provided with angle adjustment knobs 92 and 94 for adjusting the tilt angle of the irradiation end 84 and the light-receiving end 86. By rotating the angle adjustment knobs 92 and 94, the incident angle α of the detection light LB2 irradiated from the irradiation end 84 and the light-receiving angle of the light-receiving end 86 can be adjusted.

[0073] In the case where the position on the upper surface of wafer W is indicated by the solid line in Figure 12, the detection light LB2 irradiated from the irradiation end 84 is reflected on the upper surface of wafer W and received at point A of the image sensor 88. Furthermore, in the case where the position on the upper surface of wafer W is indicated by the two-point chain line in Figure 12, the detection light LB2 irradiated from the irradiation end 84 is reflected on the upper surface of wafer W as shown by the two-point chain line and received at point B of the image sensor 88. The data detected by the image sensor 88 is output to the controller 76.

[0074] Then, based on the position of the reflected light LB2” detected by the image sensor 88, the controller 76 calculates the position of the upper surface of the wafer W. Specifically, based on the distance H between point A and point B detected by the image sensor 88, the displacement h (h=Hcosα) of the upper surface of the wafer W is calculated.

[0075] For example, when the position of the upper surface of the wafer W at point A of the image sensor 88 when the reflected light LB2” is detected is set as the reference position h0, since the displacement h of the upper surface position of the wafer W at point B of the image sensor 88 when the reflected light LB2” is detected can be calculated as described above using h=Hcosα, the upper surface position h1 of the wafer W at point B when the reflected light LB2” is detected can be obtained using h1=h0-h. Thus, in the second upper surface position detector 58, the upper surface position of the wafer W is calculated based on the position of the reflected light LB2” detected by the image sensor 88.

[0076] Referring to FIG2, the selection unit 60 includes: a first / second shutter 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 positioned by the first actuator at an allowable position (shown by the solid line in Figure 2) that allows the detection light LB2 that has passed through the first beam splitter 66 to pass through, and at a blocking position (shown by the two-point chain line in Figure 2) that blocks the detection light LB2 that has passed through the first beam splitter 66.

[0078] The second shutter 98 is positioned by the second actuator at an allowable position (shown by the solid line in Figure 2) that allows the detection light LB2 reflected by the first beam splitter 66 to pass through, and at an obstruction position (shown by the two-point chain line in Figure 2) that blocks the detection light LB2 reflected by the first beam splitter 66.

[0079] Then, in the selection section 60, the detection light LB2, which is split by the first beam splitter 66, is selected by the first shutter 96 and the second shutter 98.

[0080] Specifically, when the first upper surface position detector 56 is selected by the selection unit 60, the first shutter 96 is positioned in the permissible position by the first actuator, and the second shutter 98 is positioned in the blocked position by the second actuator.

[0081] In this way, the detection light LB2 emitted from the detection light source 61 and passing through the first beam splitter 66 is guided to the first upper 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 upper surface position detector 56 is selected.

[0082] Furthermore, when the second upper surface position detector 58 is selected by the selection unit 60, the first shutter 96 is positioned in the blocking position by the first actuator, and the second shutter 98 is positioned in the permissible position by the second actuator.

[0083] In this way, the detection light LB2 emitted from the detection light source 61 and passing 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 upper surface position detector 58. Therefore, the second upper surface position detector 58 is selected.

[0084] As shown in Figure 1, the feed mechanism 8 includes: an X-axis feed mechanism 100, which feeds the chuck table 4 relative to the laser beam irradiation unit 6 in the X-axis direction; and a Y-axis feed mechanism 102, which feeds the chuck table 4 relative to the laser beam irradiation unit 6 in the Y-axis direction.

[0085] The X-axis feed mechanism 100 includes: a ball screw 104 connected to an X-axis movable plate 12 and extending in the X-axis direction; and a motor 106 that rotates the ball screw 104. The X-axis feed mechanism 100 converts the rotational motion of the motor 106 into linear motion via the ball screw 104 and transmits it to the X-axis movable plate 12, causing the X-axis movable plate 12 to move along the guide rail 10a on the base 10 in the X-axis direction. This allows the chuck stage 4 to perform machining feed in the X-axis direction.

[0086] The Y-axis feed mechanism 102 includes: a ball screw 108 connected to a Y-axis movable plate 14 and extending in the Y-axis direction; and a motor 110 that rotates the ball screw 108. The Y-axis feed mechanism 102 converts the rotational motion of the motor 110 into linear motion via the ball screw 108 and transmits it to the Y-axis movable plate 14, causing the Y-axis movable plate 14 to move along the guide rail 12a on the X-axis movable plate 12 in the Y-axis direction. This allows the chuck table 4 to perform machining feed in the Y-axis direction.

[0087] As shown in Figure 1, the laser processing apparatus 2 further includes a camera unit 112, which detects the area to be laser-processed by means of the laser beam irradiation unit 6. The camera unit 112 is mounted on the lower front surface of the housing 32 of the laser beam irradiation unit 6. The images captured by the camera unit 112 are output to the controller 76.

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

[0089] In this embodiment, firstly, the wafer W is placed on the upper surface of the chuck stage 4. Next, the suction means connected to the suction chuck 20 is operated to hold the wafer W by suction from the upper surface of the suction chuck 20. Then, the X-axis feed mechanism 100 is operated to position the chuck stage 4 directly below the camera unit 112.

[0090] If the chuck stage 4 is positioned directly below the camera unit 112, the camera unit 112 is used to capture an image of the wafer W. Next, based on the image of the wafer W captured by the camera unit 112, the positional relationship between the wafer W and the condenser 26 is adjusted. At this time, the laser beam LB1 is aimed at the area to be laser-processed, and the focal point P of the laser beam LB1 is adjusted to a predetermined position (e.g., a position at a predetermined depth from the upper surface of the wafer W).

[0091] Next, the support plate 64 is rotated by the motor 65 of the selector 62 to select any one of the multiple bandpass filters 63a~63j and position it in the optical path of the detection light LB2. In this way, a specific wavelength of detection light LB2 that is sufficiently reflected on the upper surface of the wafer W can be selected from the wide wavelength band of detection light LB2 emitted by the detection light source 61.

[0092] From the viewpoint of more accurately measuring the height of the upper surface of wafer W, it is preferable to select the detection light of the wavelength at which the light received by the first / second light-receiving elements 72, 74 or the light-receiving end 86 is maximized. Therefore, multiple detection lights LB2 of specific wavelengths selectable by selector 62 can be pre-irradiated onto the upper surface of wafer W to confirm that the light received is maximized.

[0093] Next, either the first or second upper surface position detector 56 or 58 is selected by the selection unit 60. Then, the processing laser beam LB1 is irradiated from the condenser 26 while the chuck stage 4 is moved by the feed mechanism 8, so that the focal point P of the processing laser beam LB1 passes sequentially through the processing area of ​​the wafer W.

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

[0095] When the first upper surface position detector 56 has been selected, if the wafer W is irradiated with a detection light LB2 of a specific wavelength, the voltage signal of the amount of light received by the first light-receiving element 72 and the voltage signal of the amount of light received by the second light-receiving element 74 will be transmitted to the controller 76.

[0096] In this case, the controller 76 calculates the position of the upper surface of the wafer W by comparing the amount of light received by the first light-receiving element 72 with the amount of light received by the second light-receiving element 74. Then, based on the calculated position of the upper surface of the wafer W, the controller 76 controls the angle adjustment actuators 48 and 54 of the first / second current scanners 38 and 40 of the focus point position adjuster 28 to adjust the height of the focus point P of the processing laser beam LB1.

[0097] On the other hand, if the second upper surface position detector 58 has been selected, and a detection light LB2 of a specific wavelength is irradiated onto the wafer W, the position information of the reflected light LB2 detected by the image sensor 88 of the second upper surface position detector 58 will be transmitted to the controller 76.

[0098] In this scenario, the controller 76 calculates the position of the upper surface of the wafer W 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 controller 76 controls the angle adjustment actuators 48 and 54 of the first / second current scanners 38 and 40 of the focus point position adjuster 28 to adjust the height of the focus point P of the processing laser beam LB1.

[0099] Therefore, since the distance from the upper surface of the wafer W to the focal point P of the laser beam LB1 for processing remains fixed, the required laser processing (e.g., the formation of a modified layer) can be performed at a predetermined depth from the upper surface of the wafer W and parallel to the upper surface of the wafer W.

[0100] As described above, in the laser processing apparatus 2 of this embodiment, the selector 62 selects a specific wavelength of detection light LB2 that is sufficiently reflected from the upper surface of the wafer W from the wide-wavelength detection light LB2 emitted by the detection light source 61. Therefore, regardless of the type or surface condition of the wafer W, the height of the upper surface of the wafer W can be measured appropriately and accurately, and the focusing point P of the processing laser light LB1 can be positioned appropriately and accurately based on the appropriately and accurately measured upper surface height of the wafer W.

[0101] 2: Laser processing equipment 4: Chuck platform 6: Laser beam irradiation unit 8: Feed mechanism 24: Laser Oscillator 26: Concentrator 28: Focus point position adjuster 30: Upper surface position detector 61: Light source for testing 62: Selector 63a~63j: Bandpass filters 66: First beam splitter 67: Convergence device 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 Light Path OP2: Second optical path LB1: Pulsed laser beam for processing LB2: Detection light

Claims

1. A laser processing apparatus comprising: a chuck stage for holding a wafer; a laser beam irradiation unit for irradiating the wafer held on the chuck stage with laser beams; and a feed mechanism for feeding the chuck stage and the laser beam irradiation unit in an X-axis direction and a Y-axis direction orthogonal to the X-axis direction, the laser beam irradiation unit comprising: a laser oscillator for emitting laser beams; a concentrator for focusing the laser beams emitted by the laser oscillator and positioning the concentrator point on the wafer held on the chuck stage; a concentrator point position adjuster disposed between the laser oscillator and the concentrator and adjusting the position of the concentrator point; and an upper surface position detector for detecting the upper surface position of the wafer, the upper surface position detector comprising: a detection light source for emitting detection light with a wide wavelength band; and a selector for selecting a detection light of a specific wavelength from the detection light emitted by the detection light source. The system comprises: a converging unit that merges detection light emitted from the detection light source and sequentially passing through the selector and the first beam splitter between the laser oscillator and the focusing point position adjuster; and a filter unit that, among the light guided from the converging unit to the first beam splitter and reflected by the first beam splitter, allows only light corresponding to a specific wavelength selected by the selector to pass through. The selector includes a plurality of bandpass filters that allow detection light of different specific wavelengths to pass through, and selects any one of the plurality of bandpass filters and positions it in the optical path of the detection light to select the specific wavelength of detection light. The filter unit has a plurality of bandpass filters that allow reflected light of different specific wavelengths to pass through, selects a bandpass filter from the plurality of bandpass filters that allows the wavelength of the same wavelength selected by the selector to pass through, and positions it in the optical path of the reflected light to allow the specific wavelength of reflected light to pass through. The laser processing apparatus uses a selector to select a specific wavelength of detection light from the detection light emitted by the detection light source, guides it to the upper surface of the wafer held on the chuck stage, and calculates the position of the upper surface of the wafer by using the light that passes through the filter unit in the reflected light reflected from the upper surface of the wafer.

2. The laser processing apparatus as described in claim 1, wherein, The selector selects the detection light with the maximum light intensity at the wavelength.

3. The laser processing apparatus as described in claim 1, wherein, The upper surface position detector includes: a second beam splitter that, through the combiner and the first beam splitter, splits the reflected light, which has passed through the focusing point position adjuster and the focusing device, into a first optical path and a second optical path reflected at the upper surface of the wafer held on the chuck stage; a filter disposed in the first optical path and allowing a portion of the split reflected light to pass through; and a first light-receiving element that receives the reflected light that has passed through the filter. And a second light-receiving element, which is disposed in the second optical path and receives all of the diverted reflected light, and the position of the upper surface of the wafer is calculated by comparing the amount of light received by the first light-receiving element with the amount of light received by the second light-receiving element.

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