JP2012237676A - Light receiving apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light receiving apparatus at comparatively low cost having a function equal to that of a line image sensor.SOLUTION: A light receiving apparatus for detecting light in a detection region includes: a photodetector; light receiving means provided with a mask including an aperture for regulating light incident to the photodetector; moving means for moving the light receiving means over the detection region; and position detection means to detect movement position of the light receiving means.

Description

  The present invention relates to a light receiving device for detecting light in a detection region.

  In the semiconductor device manufacturing process, a plurality of regions are partitioned by dividing lines called streets arranged in a lattice pattern on the surface of a substantially wafer-shaped semiconductor wafer, and devices such as ICs, LSIs, etc. are partitioned in the partitioned regions. Form. Then, the semiconductor wafer is cut along the streets to divide the region in which the device is formed to manufacture individual semiconductor devices.

  As a method of dividing along the street of the above-described semiconductor wafer or the like, there is a laser processing method in which a pulse laser beam having transparency to the wafer is used, and the pulse laser beam is irradiated with a focusing point inside the region to be divided. Has been tried. The dividing method using this laser processing method is to irradiate a pulse laser beam having a wavelength having transparency to the wafer from one side of the wafer to the inside, and irradiate the wafer along the street. The work layer is divided by continuously forming a deteriorated layer and applying an external force along a street whose strength is reduced by the formation of the deteriorated layer. When the altered layer is formed inside along the street formed on the workpiece as described above, it is important to position the condensing point of the laser beam at a predetermined depth position from the upper surface of the workpiece.

  In addition, as a method of dividing a plate-like workpiece such as a semiconductor wafer, a laser processing groove is formed by irradiating a pulse laser beam having a wavelength transmissive to the wafer along a street formed on the wafer. A method of cleaving along the laser-processed groove with a mechanical braking device has been proposed. Even when the laser processing groove is formed along the street formed on the wafer as described above, it is important to position the condensing point of the laser beam at a predetermined height position of the wafer.

  However, plate-like workpieces such as semiconductor wafers have undulations, and their thickness varies, making it difficult to perform uniform laser processing. That is, when forming an altered layer along the street inside the wafer, if the wafer thickness varies, the altered layer is uniformly formed at a predetermined depth position due to the refractive index when irradiating a laser beam. I can't. Further, even when the laser processing groove is formed along the street formed on the wafer, if the thickness varies, the laser processing groove having a uniform depth cannot be formed.

  In order to solve the above-described problems, a height measuring apparatus capable of measuring the upper surface height of a workpiece such as a semiconductor wafer held on a chuck table is disclosed in Patent Document 1 below. The height measuring device disclosed in the following Patent Document 1 uses reflected light of light irradiated to a workpiece by utilizing the fact that white light that has passed through a diffractive means composed of a chromatic aberration lens has a different focal length depending on the wavelength. Since the focal length is obtained by specifying the wavelength, the height position of the workpiece held on the chuck table can be accurately measured.

JP 2011-33383 A

  In the height measuring device described in Patent Document 1, a line image sensor is used to detect the wavelength of reflected light of light irradiated on a workpiece. However, the line image sensor is expensive, which increases the cost of the entire measuring apparatus.

  The present invention has been made in view of the above-described facts, and a main technical problem thereof is to provide a relatively inexpensive light receiving device having a function equivalent to that of a line image sensor.

In order to solve the main technical problem, according to the present invention, a light receiving device for detecting light in a detection region,
A photo detector, and a light receiving means comprising a mask having an aperture for restricting light entering the photo detector;
Moving means for moving the light receiving means over the detection area;
Position detecting means for detecting the moving position of the light receiving means,
A light receiving device is provided.

  The light-receiving device according to the present invention includes a light-receiving unit including an inexpensive photo-detector and a mask having an aperture that restricts light incident on the photo-detector, and a moving unit that moves the light-receiving unit across a detection region. And a position detecting means for detecting the moving position of the light receiving means, it can be constructed relatively inexpensively.

The block block diagram of the height measuring apparatus equipped with the light-receiving device comprised according to this invention. The top view of the mask means which comprises the height measuring apparatus shown in FIG. Explanatory drawing which shows the condensing point of each wavelength in the light condensed with the objective lens which comprises the height measuring apparatus shown in FIG. The perspective view of the light-receiving device comprised according to this invention. The figure which shows the control map stored in the memory of the control means with which the height measuring apparatus shown in FIG. 1 is equipped.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of a light receiving device configured according to the invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram of a height measuring device equipped with a light receiving device constructed according to the present invention. A height measuring device 1 shown in FIG. 1 includes a white light source 2 that emits white light, a diffraction unit 3 that diffracts each wavelength of light emitted by the white light source 2, and light diffracted by the diffraction unit 3. Mask means 4 that shields the central portion of the light and forms light in an annular shape, relay lens 5 that relays an image of the annular light formed by the mask means 4, and annular light transmitted by the relay lens 5 For example, the objective lens 6 that irradiates the workpiece W held on the chuck table C / T of the laser processing apparatus and the mask means 4 and the relay lens 5 to be disposed on the workpiece. A beam splitter 7 that splits the reflected light of the irradiated white light is provided.

  The white light source 2 can be a white light, a light emitting diode (LED), or the like. The diffractive means 3 includes a first chromatic aberration lens 31 and a first chromatic aberration lens 31 and a second chromatic aberration lens 32 disposed on the optical axis at a predetermined interval. The first chromatic aberration lens 31 and the second chromatic aberration lens 32 constituting the diffractive means 3 are each composed of a lens having chromatic aberration such as a gradium lens, and the refractive index differs depending on the wavelength of light. The first chromatic aberration lens 31 constituting the diffractive means 3 forms a focal point for each wavelength of white light incident from the white light source 2 on the optical axis. The second chromatic aberration lens 32 constituting the diffractive means 3 forms light that has passed through the focal point for each wavelength and spread by the first chromatic aberration lens 31 into a substantially parallel light beam (difference angle varies depending on the wavelength). Thus, the diffractive means 3 constituted by the first chromatic aberration lens 31 and the second chromatic aberration lens 32 sequentially shortens the wavelength of the white light emitted from the white light source 2 from the optical axis side toward the outside. Diffraction.

  The mask means 4 comprises a transparent slope 41 such as a glass plate as shown in FIGS. 1 and 2, and a circular shielding mask 411 for shielding light is formed at the center of the surface. The circular shielding mask 411 that shields light is set to a size that shields light having a wavelength longer than 800 nm, for example. In the mask means 4 configured in this way, a circular shielding mask 411 is disposed on the optical axis of light passing through the diffraction means 3. Therefore, the light having passed through the diffracting means 3 is formed into an annular light when light having a wavelength longer than 800 nm is blocked by the circular shielding mask 411 and light having a wavelength of 800 nm or less passes through the mask means 4.

  The relay lens 5 relays the annular light image formed by the mask means 4 to the objective lens 6 as described above. The objective lens 6 collects the annular light transmitted by the relay lens 5 and irradiates the workpiece W held on the chuck table C / T. As shown in FIG. 3, the annular light condensed by the objective lens 6 is blocked by the circular shielding mask 411 as described above, so that light having a wavelength of 800 nm or less is blocked. Focused. The light having a wavelength of 800 nm or less has a short collection wavelength of light having a short wavelength far from the optical axis because the light having a short wavelength is diffracted to the outside by the diffracting means 3. The light distance becomes longer. The positional relationship between the mask means 4 and the relay lens 5 and the objective lens 6 is as follows. The distance from the mask means 4 to the relay lens 5 is (a) and the distance from the relay lens 5 to the objective lens 6 is shown in FIG. (B) and the focal length of the relay lens 5 is (f), the position is set to satisfy the relationship of (1 / a) + (1 / b) = (1 / f).

  The beam splitter 7 transmits the annular light having passed through the mask means 4 toward the relay lens 5 as indicated by a solid line, and also reflects the reflected light reflected by the workpiece W held on the chuck table C / T. As shown by a broken line, the light is reflected and dispersed at an angle of 90 degrees.

  The reflected light dispersed by the beam splitter 7 reaches the light receiving device 10 through the light separating means 8 and the diffraction grating 9 that allow the reflected light having the wavelength passing through the optical axis to pass. The light separating unit 8 includes a first condenser lens 81, a mask 82, and a second condenser lens 83. The first condensing lens 81 is a lens having no chromatic aberration, such as an achromatic lens, and condenses the reflected light dispersed by the beam splitter 7. The mask 82 is provided at a condensing point position of the first condensing lens 81 and includes a pinhole 821 through which reflected light collected by the first condensing lens 81 passes. The pinhole 821 may have a diameter of 10 to 100 μm. The second condenser lens 83 is a lens having no chromatic aberration, such as an achromatic lens, and condenses the reflected light that has passed through the pinhole 821 of the mask 82. The diffraction grating 9 converts the reflected light collected by the second condenser lens 83 into diffracted light and separates it for each wavelength. The diffracted light converted by the diffraction grating 9 is irradiated toward the light receiving device 10. The light receiving device 10 will be described with reference to FIGS. 1 and 4.

  The light receiving device 10 shown in FIGS. 1 and 4 includes a light receiving means 11, a moving means 12 that moves the light receiving means 11 over a detection region, and a position detecting means 13 that detects the moving position of the light receiving means 11. Yes. The light receiving means 11 enters the moving base 111, the photo detector housing case 112 disposed on the moving base 111, the photo detector 113 disposed in the photo detector housing case 112, and the photo detector 113. It consists of a mask 114 having an opening 114a for restricting light.

  The moving means 12 for transferring the light receiving means 11 over the detection region includes a stationary base 121 and a pair of the diffracted light diffracted by the diffraction grating 9 on the stationary base 121 along the spectral direction. It includes guide rails 122 and 122, a male screw rod 123 disposed in parallel between the pair of guide rails 122 and 122, and a drive source such as a pulse motor 124 for driving the male screw rod 123 to rotate. The moving base 111 of the light receiving means 11 is supported on the pair of guide rails 122 and 122 constituting the moving means 12 so as to be movable along the guide rails 122 and 122. That is, a pair of guided grooves 111a and 111a that are fitted to the pair of guide rails 122 and 122 are provided on the lower surface of the movable base 111, and the pair of guided grooves 111a and 111a are connected to the pair of guide rails. The movable base 111 is supported so as to be movable along the guide rails 122 and 122 by being fitted to 122 and 122. One end of the male screw rod 123 is rotatably supported by a bearing block 125 fixed to the stationary base 121, and the other end is connected to the output shaft of the pulse motor 124. The male screw rod 123 is screwed into a through female screw hole 111c formed in a female screw block 111b provided to protrude from the lower surface of the central portion of the moving base 111. Accordingly, when the male screw rod 123 is driven to rotate forward and backward by the pulse motor 124, the moving base 111 on which the light receiving means 11 is disposed is moved along the guide rails 122 and 122.

  The position detecting means 13 for detecting the moving position of the light receiving means 11 is provided on the stationary base 121 along a pair of guide rails 122, 122 and on the moving base 111. The reading head 132 moves along the linear scale 131 together with the moving base 111. In the illustrated embodiment, the reading head 132 of the position detecting means 13 sends a pulse signal of one pulse to the control means 20 every 1 μm. And the control means 20 calculates | requires the wavelength of the diffracted light set corresponding to the pulse number from a reference position by counting the input pulse signal. When the pulse motor 124 is used as the drive source of the moving means 12, the movement position of the light receiving means 11 is detected by counting the drive pulses of the control means 20 that outputs a drive signal to the pulse motor 124. You can also.

The effect | action of the height measuring apparatus 1 mentioned above is demonstrated.
The white light (R) emitted from the white light source 2 enters the first chromatic aberration lens 31 constituting the diffractive means 3 as shown by a solid line in FIG. The first chromatic aberration lens 31 forms a focal point for each wavelength of white light incident from the white light source 2 on the optical axis. The light having the focal point corresponding to each wavelength formed on the optical axis in this way enters the second chromatic aberration lens 32, and the second chromatic aberration lens 32 is focused on each wavelength by the first chromatic aberration lens 31. The light that has passed and spread is formed into a light beam that is substantially parallel (the spread angle varies depending on the wavelength). In this way, the diffractive means 3 constituted by the first chromatic aberration lens 31 and the second chromatic aberration lens 32 sequentially shortens the wavelength of the white light emitted from the white light source 2 from the optical axis side (inner side) toward the outer side. Diffraction to be The white light diffracted by the diffraction means 3 in this way is blocked by the mask means 4 with light having a wavelength longer than, for example, 800 nm by the circular shielding mask 411, and light with a wavelength of 800 nm or less is formed into annular light. .

  As described above, for example, light having a wavelength longer than 800 nm is blocked by the circular shielding mask 411 by the mask means 4, and the light having a wavelength of 800 nm or less formed in an annular shape is transmitted through the beam splitter 7 to the relay lens 5. The light enters, and the relay lens 5 relays the annular light image to the objective lens 6. The objective lens 6 collects the annular light transmitted by the relay lens 5 and irradiates the workpiece W held on the chuck table C / T. As shown in FIG. 3, the annular light condensed by the objective lens 6 is blocked by the circular shielding mask 411 as described above, so that light having a wavelength of 800 nm or less is blocked. Focused. The light with a wavelength of 800 nm or less has a shorter light collection distance with a longer wavelength closer to the optical axis and a light collection distance with a shorter wavelength farther from the optical axis. Accordingly, the white light (R) irradiated to the workpiece W is reflected on the upper surface of the workpiece W, and among these, the light with the wavelength whose focal point matches the upper surface of the workpiece W has the smallest diameter. reflect.

  Reflected light (R1) having a wavelength that matches the focal point reflected by the upper surface of the workpiece W passes through the objective lens 6 and the relay lens 5 as shown by the broken line, and is split by the beam splitter 7 to be separated into light. The light enters the first condenser lens 81 that constitutes. The reflected light (R 1) that has entered the first condenser lens 81 is condensed and passes through the pinhole 821 of the mask 82, and is collected again by the second condenser lens 83 and reaches the diffraction grating 9. . The reflected light having a wavelength that does not match the focal point on the upper surface of the workpiece W has a large diameter. Therefore, even if the reflected light is condensed by the first condenser lens 81, it is blocked by the mask 82 and passes through the pinhole 821. Is only a few. The reflected light that has reached the diffraction grating 9 is converted into diffracted light corresponding to the wavelength, and irradiates the light receiving device 10. In the embodiment shown in FIG. 1, the wavelength of 500 nm is set corresponding to the position indicated by the solid line of the opening 114a of the mask 114 constituting the light receiving device 10 as indicated by the broken line (500 nm of the linear scale 131 in the light receiving device 10). Irradiating the target position). Further, the wavelength of 300 nm is indicated by a one-dot chain line, and the position of the opening 114a of the mask 114 constituting the light-receiving device 10 is indicated by the one-dot chain line (a position set corresponding to 300 nm of the linear scale 131 in the light-receiving device 10). ). The wavelength of 700 nm is indicated by a two-dot chain line, and the position of the opening 114a of the mask 114 constituting the light receiving device 10 is indicated by the two-dot chain line (a position set corresponding to 700 nm of the linear scale 131 in the light receiving device 10). ). The light receiving device 10 detects the movement position of the light receiving means 11 at the time when the photo detector 113 receives light through the opening 114a of the mask 114, and sends a detection signal to a control means described later. That is, the position detection unit 13 outputs a pulse signal to the control unit 20 from the read head 132 that moves on the linear scale 131. The control means 20 obtains the wavelength of the reflected light based on the number of pulses from the reference position sent from the reading head 132 of the position detection means 13 to the moving position of the light receiving means 11 when the photodetector 113 receives light. And the control means 20 calculates | requires the focal distance with respect to the wavelength of the light irradiated from the objective lens 6 based on the wavelength of reflected light, The height of the upper surface of the workpiece W hold | maintained at the chuck table C / T. Find the position.

  As shown in FIG. 5, the control means 20 includes a memory that stores a control map in which the relationship between the wavelength of light collected by the objective lens 6 and the focal length is set. Then, the control means 20 refers to the control map shown in FIG. 5 stored in the memory, and the reflected light obtained based on the number of pulses sent from the read head 132 of the position detection means 13 constituting the light receiving device 10. The focal length corresponding to the wavelength of. Therefore, the position corresponding to the focal length from the objective lens 6 is the height position of the upper surface of the workpiece W held on the chuck table C / T. For example, in the control map shown in FIG. 5, when the wavelength of the reflected light obtained based on the pulse signal sent from the read head 132 of the position detecting means 13 constituting the light receiving device 10 is 500 nm, the objective lens 6, the height position of the upper surface of the workpiece W held on the chuck table C / T is 29.4 mm below the objective lens 6. In the illustrated embodiment, for the wavelength of white light from 300 nm to 700 nm, for example, the interval between the condensing points every 100 nm is 5 μm, which is obtained based on the pulse signal sent from the reading head 132. When the wavelength of the reflected light is 400 nm, the height position of the upper surface of the workpiece W held on the chuck table C / T is 29.395 mm below the objective lens 6 and constitutes the light receiving device 10. When the wavelength of the reflected light obtained based on the pulse signal sent from the reading head 132 of the position detecting means 13 is 300 nm, the height of the upper surface of the workpiece W held on the chuck table C / T The position is 29.390 mm below the objective lens 6. On the other hand, when the wavelength of the reflected light obtained based on the pulse signal sent from the reading head 132 is 600 nm, the height position of the upper surface of the workpiece W held on the chuck table C / T is When the wavelength of the reflected light obtained based on the pulse signal sent from the reading head 132 is 700 nm, which is 29.405 mm below the objective lens 6, the object to be held on the chuck table C / T is held. The height position of the upper surface of the workpiece W is 29.410 mm below the objective lens 6. As described above, in the height measuring device 1 in the illustrated embodiment, the condensing point of each wavelength of the white light condensed by the objective lens 6 changes linearly, so that the objective lens 6 and the chuck table C are changed. The distance to the upper surface of the workpiece W held at / T, that is, the height position of the upper surface of the workpiece W held at the chuck table C / T can be accurately measured.

  The light receiving device 10 provided in the height measuring device 1 described above is a light receiving means including a photo detector 113 that is less expensive than a line image sensor and a mask 114 having an opening 114a that restricts light incident on the photo detector 113. 11, the moving means 12 that moves the light receiving means 11 over the detection region, and the position detecting means 13 that detects the moving position of the light receiving means 11, can be configured relatively inexpensively.

1: Height measuring device 2: White light source 3: Diffraction means 31: First chromatic aberration lens 32: Second chromatic aberration lens 4: Mask means 41: Transparent slope 411: Circular shielding mask 5: Relay lens 6: Objective lens 7: Beam splitter 8: Light separating means 9: Diffraction grating 10: Light receiving device 11: Light receiving means 111: Moving base 112: Photo detector housing case 113: Photo detector 114: Mask 12: Moving means 121: Stationary base 122, 122: A pair of guide rails 123: Male screw rod 124: Pulse motor 13: Position detection means 131: Linear scale 132: Reading head 20: Control means

Claims (1)

A light receiving device for detecting light in a detection region,
A photo detector, and a light receiving means comprising a mask having an aperture for restricting light entering the photo detector;
Moving means for transferring the light receiving means over the detection area;
Position detecting means for detecting the moving position of the light receiving means,
A light receiving device characterized by that.

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