Thickness measuring device

Abstract

The present application provides a thickness measuring device that can easily and accurately measure the thickness of a workpiece. The thickness measuring device measures the thickness of a workpiece held by a chuck table, wherein the thickness measuring device includes: a plurality of image sensors that detect the intensity of light that is spectrally split by a plurality of diffraction graters by each wavelength and generate a spectral interference waveform; and a thickness output unit that outputs thickness information based on the spectral interference waveforms generated by the plurality of image sensors. The thickness output unit includes: a reference waveform recording section that records spectral interference waveforms corresponding to a plurality of thicknesses as reference waveforms; and a thickness determination section that compares the plurality of spectral interference waveforms generated by the plurality of image sensors with the reference waveforms recorded by the reference waveform recording section, and determines the thickness corresponding to each spectral interference waveform based on the reference waveform that matches the waveform.

Description

Technical Field

[0001] The present invention relates to a thickness measuring device for measuring the thickness of a workpiece held by a chuck table. Background Art

[0002] The wafer is divided by a plurality of intersecting predetermined dividing lines and multiple devices such as IC and LSI are formed on the front side. After the wafer is thinned by grinding the back side with a grinding device, it is divided into individual device chips by a cutting device or a laser processing device. The device chips obtained by division are used in electronic devices such as mobile phones and personal computers.

[0003] A grinding device for grinding the back side of a wafer generally includes: a chuck table for holding the wafer; a grinding unit having a rotatable grinding wheel for grinding the wafer held by the chuck table; and a measuring device for measuring the thickness of the wafer held by the chuck table. The grinding device can process the wafer to a desired thickness.

[0004] Furthermore, regarding a measuring device for measuring thickness, when a contact-type measuring device is used in which a probe is brought into contact with the ground surface of the wafer to measure the thickness of the wafer, there is a problem of scratching the ground surface. Therefore, a non-contact-type measuring device is used as follows: the thickness is measured using a spectral interference waveform formed by light reflected from the ground surface of the wafer and light reflected from the surface opposite to the ground surface after passing through the wafer (for example, see Patent Document 1).

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2012-21916

[0006] However, when measuring thickness using waveform analysis based on the spectral interference waveform and waveform function, there are the following problems: The spectral interference waveform must be analyzed using Fourier transform theory, for example, to determine the signal intensity waveform. As the wafer becomes thinner, the accuracy of thickness information derived from the peak value decreases. Furthermore, when the workpiece is made of different materials, the waveform shape of the spectral interference waveform varies depending on the material, making proper waveform analysis difficult. This is particularly true for composite wafers composed of multiple layers, where the spectral interference waveform is formed based on the return light reflected and synthesized from each layer. This makes it difficult to measure the thickness of each layer.

[0007] Furthermore, for example, when measuring a wafer having a two-layer structure in which a relatively thin SiO2 layer, for example, less than 3 μm thick, is laminated on the lower surface of an LN substrate using a measurement device based on spectral interference waveforms, there is a problem: multiple interference lights are formed by the diffraction grating constituting the measurement device, and the thickness information of the LN substrate generated by the interference wave of light reflected from the upper surface of the LN substrate and the reflected light reflected from the lower surface of the LN substrate is combined with the thickness information of the "LN substrate + SiO2 film" generated by the interference wave of light reflected from the upper surface of the LN substrate and the reflected light reflected from the lower surface of the SiO2 film. This makes it impossible to measure the thickness of the LN substrate alone.

[0008] Furthermore, when two or more devices are formed in the planar direction of one layer constituting a wafer, there is a problem that interference waves differ depending on the materials constituting the devices, making it impossible to measure accurate thickness. Summary of the Invention

[0009] Therefore, an object of the present invention is to provide a thickness measuring device capable of easily and accurately measuring the thickness of a workpiece.

[0010] According to the present invention, a thickness measuring device is provided, which measures the thickness of a workpiece held by a chuck worktable, wherein the thickness measuring device comprises: a light source that emits white light; a plurality of condensers that condense the white light emitted by the light source toward the workpiece held by the chuck worktable; a plurality of first optical paths that connect the light source and the condensers; a plurality of light branching portions that are arranged on the plurality of first optical paths and branch reflected light reflected from the workpiece held by the chuck worktable into a plurality of second optical paths; a plurality of diffraction gratings that are arranged on the plurality of second optical paths; and a plurality of image sensors that detect the intensity of light that has been dispersed according to each wavelength by the plurality of diffraction gratings. And generates a spectral interference waveform; and a thickness output unit, which outputs thickness information based on the spectral interference waveform generated by the multiple image sensors, the condenser includes: a plurality of fθ lenses, which are arranged in a manner of sharing the measurement area of ​​the workpiece; and a plurality of scanners, which are arranged corresponding to each of the fθ lenses, the thickness output unit includes: a reference waveform recording unit, which records the spectral interference waveforms corresponding to multiple thicknesses as reference waveforms; and a thickness determination unit, which compares the multiple spectral interference waveforms generated by the multiple image sensors with the reference waveforms recorded by the reference waveform recording unit, and determines the thickness corresponding to each spectral interference waveform based on the reference waveform with consistent waveforms.

[0011] Preferably, the reference waveform recording section includes multiple material differentiation reference waveform recording sections that record reference waveforms according to the materials constituting the workpiece. The thickness determination section of the thickness output unit compares the spectral interference waveform generated by the image sensor with the reference waveforms recorded by the multiple material differentiation reference waveform recording sections included in the reference waveform recording section, and selects the material differentiation reference waveform recording section to which the reference waveform with the consistent waveform belongs.

[0012] The workpiece is preferably a composite wafer comprising at least layer A and layer B. The workpiece comprising multiple materials is preferably a composite wafer comprising at least layer A and layer B, wherein layer B is composed of multiple materials in the planar direction. The light source is preferably selected from any of a superluminescent diode light source, an amplified spontaneous emission light source, a supercontinuum light source, a light-emitting diode light source, a halogen light source, a xenon light source, a mercury light source, and a metal halide light source.

[0013] The thickness measuring device is preferably provided in the processing device.

[0014] According to the thickness measuring device of the present invention, the thickness of a workpiece can be measured easily and accurately. Furthermore, even for a workpiece having a multi-layer structure, the thickness can be measured accurately according to the material of each layer.

[0015] In addition, according to the processing device equipped with the thickness measuring device of the present invention, the thickness of the workpiece can be measured easily and with high precision. Moreover, even if the workpiece has a multi-layer structure, the thickness can be measured with good precision according to the material of each layer, and the workpiece can be efficiently processed to the desired thickness. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is an overall perspective view of a grinding device equipped with a thickness measuring device according to an embodiment of the present invention.

[0017] Figure 2 It shows Figure 1 A schematic block diagram of the optical system included in the thickness measurement device described.

[0018] Figure 3 Is shown by Figure 2 The thickness measuring apparatus shown is a top view showing the relationship between the wafer and the fθ lens when measuring the thickness of the wafer.

[0019] Figure 4 It shows that it is equipped with Figure 1 The following is a schematic conceptual diagram of a material classification reference waveform recording unit of a thickness measurement device.

[0020] Figure 5(a) is a conceptual diagram showing an example of a spectral interference waveform generated based on a light intensity signal detected by an image sensor. Figure 5 (b) shows the comparison with Figure 5 A conceptual diagram of a method of determining thickness based on a reference waveform matching the spectral interference waveform shown in (a).

[0021] Figure 6 yes Figure 1 A conceptual diagram of a thickness recording unit provided in the thickness measuring device shown.

[0022] Figure 7 (a) is a conceptual diagram of another example of a spectral interference waveform generated based on a light intensity signal detected by an image sensor. Figure 7 (b) is the control and Figure 7 A conceptual diagram of a method of determining thickness based on a reference waveform matching the spectral interference waveform shown in (a).

[0023] Description of labels

[0024] 1: Grinding device; 2: Device housing; 21: Main unit; 22: Vertical wall; 3: Grinding unit; 31: Moving base; 4: Spindle unit; 41: Spindle housing; 42: Rotating spindle; 5: Grinding wheel; 51: Grinding tool; 6: Grinding unit feed mechanism; 7: Chuck table mechanism; 71: Chuck table; 8: Thickness measuring device; 8A: Measuring housing; 8B: Light source; 80: First optical system; 80a: First optical path; 81: Condenser; 81A: fθ lens; 82: Light branching unit; 83: Collimating lens; 84: Reflector; 85: Scanner; 86: Collimating lens; 87: Diffraction grating; 88: Focusing lens; 89: Image sensor; 90: Second optical system; 90a: First optical path; 91: Condenser; 91A: fθ lens; 92: Light branching section; 93: Collimating lens; 94: Reflector; 95: Scanner; 96: Collimating lens; 97: Diffraction grating; 98: Focusing lens; 99: Image sensor; 10: Wafer; 14: Protective tape; 100: Thickness output unit; 110: Thickness determination section; 112: Control section; 120: Reference waveform recording section; 130: Thickness recording section; 140: Display unit. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments of a thickness measuring device and a grinding device including the thickness measuring device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0026] exist Figure 1 1 shows an overall perspective view of a grinding apparatus 1 including a thickness measuring apparatus 8 according to the present embodiment, and a wafer 10 as a workpiece whose thickness is measured by the thickness measuring apparatus 8 according to the present embodiment. Figure 1The wafer 10 shown is, for example, a composite wafer in which a first layer 10A (layer A) and a second layer 10B (layer B) are formed of different materials.

[0027] The grinding device 1 shown in the figure includes a device housing 2. The device housing 2 has a substantially rectangular parallelepiped main portion 21 and an upright wall 22 provided at the rear end of the main portion 21 and extending upward. A grinding unit 3, serving as a grinding unit, is mounted on the front surface of the upright wall 22 so as to be movable in the vertical direction.

[0028] The grinding unit 3 includes a movable base 31 and a spindle unit 4 mounted on the movable base 31. The movable base 31 is configured to slidably engage with a pair of guide rails provided on the upright wall 22. The spindle unit 4, which serves as the grinding unit, is mounted on the front surface of the movable base 31, which is slidably mounted on the pair of guide rails provided on the upright wall 22, via a support portion protruding forward.

[0029] The spindle unit 4 includes a spindle housing 41, a rotating spindle 42 rotatably mounted on the spindle housing 41, and a servo motor 43 as a driving source for rotating the rotating spindle 42. The rotating spindle 42 is rotatably supported on the spindle housing 41, and one end thereof (at Figure 1 A grinding wheel 5 is mounted on the lower surface of the grinding wheel mount 44. A grinding tool 51 composed of multiple segments is mounted on the lower surface of the grinding wheel 5.

[0030] The illustrated grinding device 1 includes a grinding unit feed mechanism 6 that moves the grinding unit 3 vertically along the pair of guide rails. The grinding unit feed mechanism 6 includes an externally threaded rod 61 disposed in front of the upright wall 22 and extending substantially vertically, and a pulse motor 62 serving as a drive source for rotating the externally threaded rod 61. The grinding unit feed mechanism 6 includes a bearing component (not shown) that is threadedly engaged with the externally threaded rod 61, which is disposed on the back side of the movable base 31. When the pulse motor 62 rotates forward, the grinding unit 3 and the movable base 31 are lowered together. When the pulse motor 62 rotates reversely, the grinding unit 3 and the movable base 31 are raised together.

[0031] A chuck table mechanism 7 serving as a chuck table for holding the wafer 10 is provided in the main portion 21 of the device housing 2. The chuck table mechanism 7 comprises: a chuck table 71; a cover member 72 that covers the periphery of the chuck table 71; and folding units 73 and 74 that are provided in front and behind the cover member 72. The chuck table 71 is configured to operate an unillustrated suction unit to attract and hold the wafer 10 on the upper surface (holding surface) of the chuck table 71. In addition, the chuck table 71 is configured to be rotatable by an unillustrated rotation drive unit and to be moved by an unillustrated chuck table moving unit. Figure 1 The workpiece placement area 70 a shown in the figure moves between the workpiece placement area 70 a and the grinding area 70 b facing the grinding wheel 5 (along the X-axis direction shown by the arrow X).

[0032] The servo motor 43, pulse motor 62, and chuck table moving unit (not shown) are controlled by a control unit (not shown). In the illustrated embodiment, a notch is formed on the outer periphery of the wafer 10 to indicate the crystal orientation. A protective tape 14 is attached to the front side of the wafer 10 where the first layer 10A (layer A) is formed, serving as a protective member. The protective tape 14 is held downwardly on the upper surface (holding surface) of the chuck table 71.

[0033] The thickness measuring device 8 has a measuring housing 8A. As shown in the figure, on the upper surface of the main portion 21 of the rectangular parallelepiped shape constituting the device housing 2, the thickness measuring device 8 is arranged on the side of the path of the chuck table 71 moving between the workpiece loading area 70a and the grinding area 70b. It is movably arranged in the area where the chuck table 71 moves between the workpiece loading area 70a and the grinding area 70b, and is configured to measure the thickness of the wafer 10 held on the chuck table 71 by irradiating white light from above. On the lower surface of the front end portion of the measuring housing 8A, there are two condensers 81 and 91 that converge and irradiate white light for thickness measurement. These condensers 81 and 91 face the chuck table 71 positioned directly below. The condensers 81 and 91 are configured to be reciprocatingly movable in the direction indicated by the arrow Y in the figure (Y-axis direction) together with the measuring housing 8A through a driving unit not shown in the figure. For the optical system constituting the thickness measuring device 8 housed in the measuring housing 8A, refer to Figure 2 A more detailed explanation is given.

[0034] like Figure 2 As shown, the optical system constituting the thickness measuring device 8 includes a light source 8B that emits white light having a wide wavelength range toward the chuck table 71. Light emitted from the light source 8B is guided toward the first optical system 80 and the second optical system 90.

[0035] Next, first refer to Figure 2 The first optical system 80 will be described. Light generated by the light source 8B is guided along the first optical path 80a. The white light, which is connected to the first optical path 80a by the light branching section 82 that guides the reflected light traveling backward along the first optical path 80a toward the second optical path 80b, passes through the collimator lens 83 and is then collimated. The light path is then changed by the reflector 84 and directed to the scanner 85, which is controlled by a control signal from the thickness output unit 100. The scanner 85 is configured, for example, as a galvano mirror. The scanner 85 changes the optical path of the white light along the first optical path 80a to the desired direction, as indicated by arrow R1 in the figure. This white light is guided toward the fθ lens 81A held by the lens barrel that constitutes the condenser 81, thereby appropriately changing the focusing position on the wafer 10 on the chuck table 71. The scanner 85 is not limited to the galvano mirror described above and may also be configured using a polygon mirror, a resonant scanner, or the like.

[0036] Light source 8B can be, for example, a halogen lamp that emits white light. In the present invention, a "light source that emits white light" refers to a light source that irradiates with light having a wavelength of 400 nm to 800 nm, commonly known as visible light. Light source 8B is not limited to the aforementioned halogen lamp. Light source 8B can be appropriately selected from commonly known light sources that can emit white light, such as superluminescent diode light sources, amplified spontaneous emission light sources, supercontinuum light sources, light-emitting diode light sources, xenon light sources, mercury light sources, and metal halide light sources. Light branching unit 82 can be a polarization-maintaining fiber coupler, a polarization-maintaining fiber circulator, a single-mode fiber coupler, a single-mode fiber coupler circulator, or the like.

[0037] A collimating lens 86, a diffraction grating 87, a focusing lens 88, and an image sensor 89 are arranged along the path of the second optical path 80b branched off by the optical branching section 82. The collimating lens 86 parallelizes the reflected light, which is reflected from the wafer 10 held by the chuck table 71 and then travels back through the first optical path 80a and is then guided from the optical branching section 82 to the second optical path 80b. The diffraction grating 87 diffracts the reflected light, which has been parallelized by the collimating lens 86, and transmits the diffracted light corresponding to each wavelength to the image sensor 89 via the focusing lens 88. The image sensor 89 is a so-called linear image sensor with light-receiving elements arranged in a linear pattern. It detects the intensity of each wavelength of the reflected light diffracted by the diffraction grating 87 and transmits the light intensity signal to the thickness output unit 100. In addition, a portion of the first optical path 80a from the light source 8B to the collimator lens 83 and a portion of the second optical path 80b from the light branching unit 82 to the image sensor 89 are formed by optical fibers.

[0038] Next, refer to Figure 2Next, the second optical system 90 will be described. The second optical system 90 has substantially the same structure as the first optical system 80, and detailed descriptions of the respective structures will be omitted as appropriate.

[0039] Light generated by light source 8B is guided toward first optical path 90a disposed on the side of second optical system 90. The white light, which is connected to first optical path 90a by light branching section 92 that guides reflected light traveling backward in first optical path 90a toward second optical path 90b, passes through collimating lens 93 to be parallelized. The light path is then changed by reflector 94 and guided toward scanner 95, which is controlled by a control signal from thickness output unit 100. The white light, whose light path is changed by scanner 95 to a desired direction as indicated by arrow R2 in the figure, is guided toward fθ lens 91A held by condenser 91. The condensing position on wafer 10 on chuck table 71 is appropriately changed to focus the white light at a desired position.

[0040] A collimating lens 96, a diffraction grating 97, a focusing lens 98, and an image sensor 99 are arranged along the path of the second optical path 90b branched off by the optical branching unit 92. The collimating lens 96 parallelizes the reflected light, which is reflected by the wafer 10 held by the chuck table 71 and then travels back through the first optical path 90a and is then guided from the optical branching unit 92 to the second optical path 90b. The diffraction grating 97 diffracts the reflected light, which has been parallelized by the collimating lens 96, and transmits the diffracted light corresponding to each wavelength to the image sensor 99 via the focusing lens 98. The image sensor 99 is a so-called linear image sensor with light-receiving elements arranged in a linear pattern. It detects the intensity of each wavelength of the reflected light diffracted by the diffraction grating 97 and transmits the light intensity signal to the thickness output unit 100.

[0041] As can be understood from the above description, the thickness measuring device 8 of this embodiment has a light source 8B that emits white light, and has: two condensers 81, 91 that condense the white light emitted by the light source 8B onto the wafer 10 held by the chuck table 71; two first optical paths 80a, 90a that connect the light source 8B with the condensers 81, 91; and two light branching parts 82, 92 that are arranged on the two first optical paths 80a, 90a and branch the reflected light reflected from the wafer 10 held by the chuck table 71 to the two second optical paths 80a, 90a. Optical paths 80b, 90b; two diffraction gratings 87, 97, which are arranged in the two second optical paths 80b, 90b; two image sensors 89, 99, which detect the intensity of the light separated according to each wavelength by the two diffraction gratings 87, 97 and generate a spectral interference waveform; and a thickness output unit 100, which outputs thickness information based on the spectral interference waveform generated by the two image sensors 89, 99. In addition, fθ lenses 81A, 91A are respectively arranged in the two condensers 81, 91. The condenser 81 and the condenser 91 are set to share the measurement area on the chip 10 through the fθ lens 81A and fθ lens 91A respectively arranged. Regarding this, refer to the following Figure 3 Provide explanation.

[0042] exist Figure 3 FIG2 shows a top view of fθ lenses 81A and 91A positioned above wafer 10 held on chuck table 71. In this embodiment, when measuring the thickness of wafer 10, white light is emitted from two fθ lenses 81A and 91A while wafer 10 and chuck table 71 are rotated together in the direction indicated by arrow R3. As shown in the figure, fθ lenses 81A and 91A are positioned so that the centers of fθ lenses 81A and 91A do not align with each other in the radial direction as viewed from the center of wafer 10.

[0043] When scanners 85 and 95 are driven to illuminate wafer 10 with white light from fθ lenses 81A and 91A, the area for irradiating white light from fθ lenses 81A and 91A to the desired position is the central area, excluding outer ineffective areas 81B and 91B. Outer ineffective areas 81B and 91B encompass the lens barrels of condensers 81 and 91. Thus, when measuring the thickness of wafer 10 by irradiating the entire area of ​​wafer 10 with white light through fθ lenses 81A and 91A, fθ lens 81A is allocated to irradiating inner area L1 of wafer 10, while fθ lens 91A is allocated to irradiating outer area L2 of wafer 10. More specifically, while wafer 10 is rotated in the direction indicated by R3 as described above, scanner 85 scans white light in the direction indicated by R1, and scanner 95 scans white light in the direction indicated by R2. In this way, by arranging the fθ lenses 81 and 91 so as to share the measurement area on the chip 10 and combining the driving of the scanners 85 and 95 arranged corresponding to the fθ lenses 81 and 91 with the rotation of the chip 10 toward the arrow R3, the entire area on the chip 10 can be irradiated with white light.

[0044] return Figure 2 Continuing the explanation, the thickness output unit 100 is composed of a computer, and the thickness output unit 100 has (detailed illustrations omitted): a central processing unit (CPU), which performs calculations according to a control program; a read-only memory (ROM), which stores the control program, etc.; a read-write random access memory (RAM), which is used to temporarily store the detected values, calculation results, etc.; and an input interface and an output interface.

[0045] The thickness output unit 100 generates a spectral interference waveform based on the light intensity signal for each wavelength transmitted from the image sensors 89 and 99. This spectral interference waveform is temporarily stored in a RAM (not shown). The thickness output unit 100 further includes a thickness determination unit 110 that determines the thickness of the wafer 10 based on this spectral interference waveform, and a reference waveform recording unit 120 that records spectral interference waveforms corresponding to a plurality of thicknesses as reference waveforms. The thickness determination unit 110 includes a comparison unit 112 that compares the spectral interference waveform detected by the image sensors 89 and 99 and stored in the RAM with the reference waveform recorded by the reference waveform recording unit 120. The chuck table 71 includes a position detection unit 75 that detects the X coordinate (left-right direction in the figure) and Y coordinate (perpendicular to the drawing) of the chuck table 71. The scanners 85 and 95 are driven and controlled based on the coordinate position of the chuck table 71 detected by the position detection unit 75, accurately controlling the position of the white light emitted from the fθ lenses 81A and 91A. The thickness information determined by the thickness determination unit 110 is associated with the X and Y coordinates of the wafer 10 held by the chuck table 71 detected by the position detection unit 75 and recorded in the thickness recording unit 130. The thickness information stored in the thickness recording unit 130 can be appropriately output to the display unit 140. The thickness determination unit 100 of this embodiment is configured within a control unit (not shown) that includes various control programs for controlling the grinding apparatus 1.

[0046] Reference Figure 4 The reference waveform recording unit 120 will be described in more detail. The reference waveform recording unit 120 includes, for example, material-specific reference waveform recording units 122a to 122l, which record reference waveforms corresponding to the material of the workpiece. Material-specific reference waveform recording unit 122a records the thickness (μm) of the Si (silicon) wafer and, corresponding to the thickness, a reference waveform of a spectral interference waveform. This reference waveform of the spectral interference waveform is generated based on the light intensity signal detected by the image sensors 89 and 99 when the Si wafer is irradiated with white light from the condensers 81 and 91 of the thickness measurement device 8. Similarly, material classification reference waveform recording section 122b records the thickness (μm) and reference waveform of the spectral interference waveform for LN (lithium niobate) wafers, material classification reference waveform recording section 122c records the thickness (μm) and reference waveform of the spectral interference waveform for GaN (gallium nitride) wafers, and material classification reference waveform recording section 122d records the thickness (μm) and reference waveform of the spectral interference waveform for SiO2 (silicon dioxide) wafers. Note that material classification reference waveform recording sections 122a-122d record reference waveforms corresponding to wafers made of a single material; however, some data has been omitted for ease of explanation.

[0047] In the reference waveform recording unit 120, in addition to the above-mentioned material differentiation reference waveform recording units 122a to 122d that record reference waveforms corresponding to a single material, there can also be material differentiation reference waveform recording units 122k and 122l that assume that the chip as the workpiece is a composite chip with multiple layers (first layer (upper layer), second layer (lower layer)) made of different materials.

[0048] Figure 4 The material differentiation reference waveform recording unit 122k records the reference waveform of the spectral interference waveform generated when the first layer is layer A (LN) and the second layer is layer B (SiO2 layer) and white light is irradiated from the concentrators 81 and 91 in a matrix table formed according to each thickness of the A layer and the B layer. The matrix table records the reference waveform in such a manner that the horizontal axis corresponds to the thickness (μm) of the A layer and the vertical axis corresponds to the thickness (μm) of the B layer, and the thicknesses of the A layer and the B layer can be determined respectively based on the reference waveform. In addition, the material differentiation reference waveform recording unit 122l records the reference waveform of the spectral interference waveform generated when the first layer is layer C (LN) and the second layer is layer D (GaN) and white light is irradiated from the concentrators 81 and 91 in the same manner as the material differentiation reference waveform recording unit 122k in a matrix table formed according to each thickness of the C layer and the D layer. Figure 4 In the figure, the reference waveform recording unit 120 is shown as including two material-specific reference waveform recording units 122k and 122l related to composite wafers. However, further material-specific reference waveform recording units assuming composite wafers composed of other material combinations may be recorded in advance. Furthermore, the reference waveforms recorded in the reference waveform recording unit 120 can be obtained as theoretical waveforms through computer calculations.

[0049] The grinding apparatus 1 and the thickness measuring device 8 of this embodiment have substantially the above-described configurations. Hereinafter, an embodiment in which the thickness of the wafer 10 is measured using the thickness measuring device 8 provided in the grinding apparatus 1 will be described.

[0050] First, when performing the grinding process, the operator sets the target finished thickness of the wafer 10 using the operation panel of the grinding device 1. Figure 1As shown, a protective tape 14 is attached to the front side of the wafer 10, and the wafer 10 is placed with the protective tape 14 facing downward on the chuck table 71 positioned in the workpiece mounting area 70a. Furthermore, the wafer 10 is attracted and held on the chuck table 71 by operating the suction unit (not shown). If the wafer 10 is attracted and held on the chuck table 71, the moving unit (not shown) is operated to move the chuck table 71 from the workpiece mounting area 70a side to the direction indicated by the arrow X1 in the X-axis direction, and positioned directly below the thickness measuring device 8. Furthermore, the thickness measuring device 8 is moved in the direction indicated by the arrow Y, so that the fθ lenses 81A, 91A of the condensers 81, 91 of the thickness measuring device 8 are adjusted as shown in FIG. Figure 3 As described above, the chuck table 71 is positioned on the inner region L1 and the outer region L2 of the wafer 10 and is positioned at the thickness measurement position of the wafer 10 held by the chuck table 71. Furthermore, the chuck table 71 can be positioned at the thickness measurement position before, during, or after the grinding process, and thickness measurement can be performed at any time.

[0051] If the wafer 10 is positioned directly below the thickness measuring device 8, the white light oscillated by the light source 8B is converged by the condensers 81 and 91 and the focusing position of the white light is scanned in the directions of R1 and R2 by the scanners 85 and 95 while being irradiated onto the wafer 10 according to the instruction signal of the thickness output unit 100. At this time, the wafer 10 is rotated one circle at a prescribed rotation speed together with the chuck table 71. Here, a plurality of spectral interference waveforms are generated based on the respective light intensity signals from the image sensors 89 and 99. Figure 5 (a) shows the spectral interference waveform W1 generated by the image sensor 99 when white light is irradiated at the coordinate (x1, y1) on the chip 10 held by the chuck worktable 71. If the spectral interference waveform W1 is generated in this way, it is recorded in the RAM of the thickness output unit 100, and the spectral interference waveform W1 stored in the RAM is compared with the reference waveforms of each material classification reference waveform recording section 122a to 122l recorded in the reference waveform recording section 120 by the comparison section 112 of the thickness determination section 110. As a result, the reference waveform Wa, which is determined to have a waveform and phase consistent with the spectral interference waveform W1, belongs to Figure 5 Material differentiation reference waveform recording section 122k in reference waveform recording section 120 shown in (b) is selected. Specifically, wafer 10 is determined to be a two-layer composite wafer in which first layer 10A (layer A) is LN (lithium niobate) and second layer 10B (layer B) is SiO2. The thickness (TA1) of first layer 10A at coordinate (x1, y1) is 4.00 μm, and the thickness (TB1) of second layer 10B is 0.27 μm.

[0052] As described above, while the chuck table 71 is rotated, the focusing position of the white light is scanned in the directions of R1 and R2 by the scanners 85 and 95, thereby irradiating the entire area of ​​the wafer 10 with white light. n ,y J )) measures the thickness TA1 to TAn of the first layer 10A and the thickness TB1 to TBn of the second layer 10B corresponding to each coordinate position. The measured thickness information is consistent with the XY coordinates ((x1, y1) to (x n ,y J ))Recorded together Figure 6 The thickness recording unit 130 is shown, and the display unit 140 displays the thickness as needed. Once the thickness of the entire wafer 10 is recorded in the thickness recording unit 130, it is possible to evaluate whether the wafer 10 has reached the desired thickness or has been processed to a uniform thickness through grinding, as needed. When the thickness measurement is performed during grinding, the chuck table 71 moves to the grinding area 70b facing the grinding wheel 5, and grinding is performed to a predetermined thickness.

[0053] The thickness measurement device 8 of the above-described embodiment includes a thickness determination unit 110. This unit compares the spectral interference waveform generated based on the light intensity signal detected by the image sensors 89 and 99 with the reference waveform recorded in the reference waveform recording unit 120, thereby determining the thickness based on the reference waveform that matches the waveform. The reference waveform recording unit 120 includes multiple material-specific reference waveform recording units (122a to 122l) that record reference waveforms corresponding to the material of the workpiece. This allows for highly accurate thickness measurement based on the material of the workpiece. Furthermore, even for workpieces composed of two or more layers, the thickness can be accurately measured individually based on the material of each layer. In addition, in the above-mentioned embodiment, the concentrator includes two small-diameter fθ lenses 81A and 91A arranged in a manner to share the measurement area of ​​the workpiece and two scanners 85 and 95 arranged corresponding to each fθ lens, thereby eliminating the need to use expensive fθ lenses with a large diameter and weight. Instead, inexpensive fθ lenses that are smaller and lighter than the radius of the chip 10 can be used, and the thickness of the entire surface of the chip 10 can be measured at low cost and efficiently.

[0054] According to the present invention, various modifications are provided, not limited to the above-mentioned embodiment. For example, the thickness measuring device 8 in the above-mentioned embodiment includes a first optical system 80 and a second optical system 90, and thus includes two condensers 81, 91, two first optical paths 80a, 90b, two light branching parts 82, 92 from which the two second optical paths 80b, 90b are branched, two diffraction gratings 87, 97, and two image sensors. However, the present invention is not limited to this, and may include more than three optical systems depending on the size of the wafer 10. For example, Figure 3 As shown, when measuring the thickness of a chip 10' (shown by a dotted line) that is larger than the chip 10, the thickness measuring device 8 is provided with a third optical system having the same structure as the first optical system 80 and the second optical system 90 according to the size of the chip 10'. In addition to the two fθ lenses 81A and 91A, a third fθ lens B (shown by a dotted line) corresponding to the outermost area L3 of the chip 10' is provided. By using this fθ lens B, the thickness of the area L3 is measured while scanning and irradiating white light in the direction indicated by R4.

[0055] In addition, in the above embodiment, an example of measuring the thickness is shown in the case where the wafer 10 is a composite wafer composed of the first layer 10A and the second layer 10B, but the present invention is not limited to this, and the thickness of a workpiece (wafer) composed of a single material can also be measured. Figure 7 (a) shows the spectral interference waveform W2 generated by the image sensor 89 (or image sensor 99) when white light is irradiated on a wafer made of a single material. If the spectral interference waveform W2 is generated in this way, it is recorded in the RAM of the thickness output unit 100, and the spectral interference waveform W2 stored in the RAM is compared with the reference waveforms of the material-differentiating reference waveform recording sections 122a to 1221 recorded in the reference waveform recording section 120 by the comparison section 112 of the thickness determination section 110. As a result, the reference waveform Wb whose waveform and phase are consistent with the spectral interference waveform W2 is determined to belong to Figure 7 Material differentiation reference waveform recording section 122b in reference waveform recording section 120 shown in (b) is selected. In other words, it is confirmed that the wafer irradiated with white light is made of a single material, an LN substrate. If the thickness determination section 110 determines that the shape of spectral interference waveform W2 matches reference waveform Wb belonging to material differentiation reference waveform recording section 122b, the thickness (20 μm) corresponding to the position where reference waveform Wb is recorded in material differentiation reference waveform recording section 122b is determined as the thickness of wafer 10. This can be output from thickness output section 100 to display section 140 and stored in RAM.

[0056] In addition, in the above embodiment, an example of measuring the thickness of the wafer 10 for each layer is shown in the case where the wafer 10 is a composite wafer composed of two layers, wherein the first layer 10A (A layer) is LN (lithium niobate) and the second layer 10B (B layer) is SiO2. However, for example, a composite wafer in which the second layer 10B (B layer) is composed of two or more materials in the plane direction may also be used. For example, the thickness measuring device 8 of this embodiment may also measure the thickness of the following composite wafer: Figure 3 In the illustrated example, a composite wafer is formed of two layers, wherein first layer 10A is LN (lithium niobate) and second layer 10B is SiO2, in region L1 on wafer 10. Furthermore, in region L2 on wafer 10, first layer 10A is LN (lithium niobate) and second layer 10B is GaN (gallium nitride). In this case, the thicknesses of first layer 10A and second layer 10B are measured with reference to material classification reference waveform recording unit 122k based on the spectral interference waveform generated by image sensor 89 when region L1 on wafer 10 is irradiated with white light via condenser 81 provided in first optical system 80. Furthermore, the thicknesses of first layer 10A and second layer 10B are measured with reference to material classification reference waveform recording unit 122l based on the spectral interference waveform generated by image sensor 99 when region L2 on wafer 10 is irradiated with white light via condenser 91 provided in second optical system 90.

[0057] In the above embodiment, an example in which the thickness measuring device 8 is provided in the grinding device 1 is shown. However, the present invention is not limited thereto, and the thickness measuring device 8 may be a device independent of the grinding device 1 .

Claims

1. A thickness measuring device for measuring the thickness of a workpiece held by a chuck table, wherein: The thickness measuring device has: a light source emitting white light; a plurality of condensers for converging the white light emitted by the light source onto a workpiece held by the chuck table; a plurality of first optical paths connecting the light source and the condenser; a plurality of light branching parts arranged on the plurality of first optical paths and branching the reflected light reflected from the workpiece held by the chuck table into a plurality of second optical paths; a plurality of diffraction gratings disposed on the plurality of second optical paths; a plurality of image sensors that detect the intensity of light dispersed for each wavelength by the plurality of diffraction gratings and generate a spectral interference waveform; and a thickness output unit configured to output thickness information based on the spectral interference waveforms generated by the plurality of image sensors; The plurality of concentrators comprises: a plurality of fθ lenses arranged so as to share a measurement area of ​​the entire surface of the workpiece; and a plurality of lens barrels for holding the plurality of fθ lenses, wherein the lens barrels serve as an ineffective area for white light irradiation; A plurality of scanners are provided corresponding to the fθ lenses. The thickness output unit contains: a reference waveform recording unit that records spectral interference waveforms corresponding to a plurality of thicknesses as reference waveforms; and a thickness determination unit that compares the plurality of spectral interference waveforms generated by the plurality of image sensors with the reference waveforms recorded by the reference waveform recording unit and determines the thickness corresponding to each spectral interference waveform based on the reference waveform having the same waveform; The entire surface of the workpiece except for the ineffective area is shared by the plurality of fθ lenses.

2. The thickness measuring device according to claim 1, wherein: The reference waveform recording unit includes a plurality of material-specific reference waveform recording units for recording reference waveforms according to the materials constituting the workpiece. The thickness determination unit of the thickness output unit compares the spectral interference waveform generated by the image sensor with the reference waveforms recorded in the material-differentiating reference waveform recording unit, and selects the material-differentiating reference waveform recording unit to which the reference waveform with the same waveform belongs.

3. The thickness measuring device according to claim 1 or 2, wherein: The workpiece is a composite wafer including at least an A layer and a B layer.

4. The thickness measuring device according to claim 1 or 2, wherein: The workpiece including a plurality of materials is a composite wafer including at least an A layer and a B layer, wherein the B layer is composed of a plurality of materials in a planar direction.

5. The thickness measuring device according to claim 1 or 2, wherein: The light source is any one of a superluminescent diode light source, an amplified spontaneous emission light source, a supercontinuum light source, a light emitting diode light source, a halogen light source, a xenon light source, a mercury light source, and a metal halide light source.

6. The thickness measuring device according to claim 1 or 2, wherein: At least two fθ lenses are arranged at positions where the centers of the two fθ lenses do not coincide with each other but are offset in the radial direction of the workpiece.

7. The thickness measuring device according to claim 1 or 2, wherein: The thickness measuring device also has a rotation drive unit for rotating the chuck table. By combining the driving of the scanner with the rotation of the chuck table holding the workpiece, the entire area on the workpiece is irradiated with white light.

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