JP5681453B2 - Measuring method and measuring device - Google Patents

Description

  The present invention relates to a measuring method and a measuring apparatus for measuring the thickness of a protective film formed on a workpiece surface.

  As a method of dividing a workpiece such as a semiconductor wafer along the street, a method of dividing the workpiece by laser processing is known (see, for example, Patent Document 1). In the laser processing method of Patent Document 1, the semiconductor wafer is continuously processed along the streets by the thermal energy generated in the irradiation region by irradiating the semiconductor wafer with the laser beam. In the irradiated area on the semiconductor wafer, thermal energy may concentrate and debris (work scraps) may be generated, and this debris adheres to the bonding pads of the LSI, etc., and there is a problem that the quality of the semiconductor chip is degraded. .

  In order to solve this problem, the present applicant has devised a laser processing method in which a water-soluble protective film is formed on the surface of the semiconductor wafer and the semiconductor wafer is irradiated with a laser beam through the protective film (see, for example, Patent Document 2). . In the laser processing method of Patent Document 2, since the semiconductor wafer is processed through the protective film, debris scattered by the laser processing can be attached to the protective film. Then, by removing the protective film to which the debris is attached in the cleaning process, the adhesion of the debris to the surface of the semiconductor wafer is suppressed, and the deterioration of the quality of the semiconductor chip is prevented.

JP-A-6-120334 JP 2004-322168 A

  In order to process a semiconductor wafer through a protective film by laser processing, it is preferable that the thickness of the protective film is constant. That is, the thickness of the protective film affects the laser processing result. If the protective film is too thin, the semiconductor wafer cannot be sufficiently protected from debris, and if the protective film is too thick, laser processing is hindered. For this reason, there has been a demand for a method for accurately measuring the thickness of the protective film on the semiconductor wafer before laser processing. However, a conventional measuring device that performs the measuring method is large and expensive, and the measuring device is used as a processing device. There was a problem that it was difficult to prepare as many units as possible or to incorporate them into processing equipment.

  The present invention has been made in view of such points, and an object of the present invention is to provide a measurement method and a measurement apparatus that can accurately measure the thickness of a protective film formed on a workpiece surface more simply than a conventional measurement apparatus. .

The measurement method of the present invention includes an absorbent that absorbs light of the wavelength of the laser in order to protect the surface of the workpiece from processing waste generated when laser processing is performed by irradiating the workpiece with a laser beam in the ultraviolet wavelength range . A measurement method for measuring the thickness of a protective film formed of a water-soluble resin, the protective film forming step of forming the protective film on a workpiece surface with a water-soluble resin containing the absorbent so as to have a predetermined thickness And after the protective film forming step, the protective film formed on the work surface is irradiated with light having a wavelength of 250 nm or more and 380 nm or less that is absorbed by the absorbent, and an intensity measuring step for measuring a reflection intensity, By performing the intensity measurement step while changing the thickness of the protective film formed in the protective film formation step, a map representing the change in the reflection intensity with respect to the thickness change of the protective film is created. When measuring the thickness of the protective film applied to the surface of the work, including the map making step, measure the reflection intensity by irradiating the protective film with light having a wavelength absorbed by the absorbent, A protective film thickness measuring step of measuring the thickness of the protective film based on a map is performed. Another measuring method of the present invention is an absorbent that absorbs light of the wavelength of the laser in order to protect the surface of the workpiece from processing waste generated when the workpiece is subjected to laser processing by irradiating the workpiece with a laser beam in the visible light wavelength range. A method for measuring the thickness of a protective film formed of a water-soluble resin containing phosphine, wherein the protective film is formed on the surface of the workpiece with a predetermined thickness by the water-soluble resin containing the absorbent. A film forming step and an intensity measuring step of measuring the reflection intensity by irradiating the protective film formed on the work surface with light having a wavelength of 460 nm or more and 650 nm or less absorbed by the absorbent after the protective film forming step. And a map representing the change in the reflection intensity with respect to the thickness change of the protective film by performing the intensity measuring step while changing the thickness of the protective film formed in the protective film forming step. When measuring the thickness of the protective film applied to the surface of the workpiece, including a map production step to be produced, measure the reflection intensity by irradiating the protective film with light having a wavelength absorbed by the absorbent, A protective film thickness measuring step of measuring the thickness of the protective film based on the map is performed.

Measuring device of the present invention, by the above measuring method, including the absorber that absorbs light of a wavelength of the laser to protect the surface of the workpiece from the swarf generated during the laser processing a workpiece water-soluble resin a measuring device for measuring the thickness of the protective film formed by a light irradiation unit for irradiating light of a wavelength which the absorbent is absorbed by the protective film formed on the surface of the workpiece, the light irradiation A light receiving unit that receives the reflected light of the light irradiated by the unit and obtains a reflection intensity, a storage unit that stores a map that represents a change in the reflection intensity with respect to a change in the thickness of the protective film, And calculating means for obtaining the thickness of the protective film based on the reflection intensity and the map stored in the storage means.

  According to these configurations, since the protective film includes an absorbent that absorbs light having the wavelength of the processing laser, irradiation with light having a wavelength that is absorbed by the absorbent can change the reflection intensity with respect to the change in the thickness of the protective film. A representing map is created. Based on this map, the thickness of the protective film can be accurately measured from the reflection intensity obtained by irradiating light having a wavelength absorbed by the absorbent. Therefore, laser processing can be performed in a state where the thickness of the protective film is kept constant, and adhesion of debris to the work can be suppressed and deterioration of the work quality can be prevented.

  In the measurement method according to the invention, the wavelength of light absorbed by the absorbent includes at least 250 nm to 380 nm, or 460 nm to 650 nm.

  According to the present invention, the protective film formed on the workpiece surface includes an absorbent that absorbs light of the wavelength of the laser, so that the thickness of the protective film can be accurately measured by the light of the wavelength absorbed by the absorbent. Can be measured more simply.

It is a figure which shows embodiment of the measuring method which concerns on this invention, and is a perspective view of a laser processing apparatus. It is a figure which shows embodiment of the measuring method which concerns on this invention, and is a schematic diagram of the optical system of the thickness measurement process of a laser processing apparatus. It is a figure which shows embodiment of the measuring method which concerns on this invention, and is a figure which shows the relationship between the thickness of a protective film, and the reflection intensity of a wafer. It is a figure which shows embodiment of the measuring method which concerns on this invention, and is a flowchart of operation | movement of a laser processing apparatus. It is a modification of the measuring method which concerns on this invention, and is a schematic diagram of the optical system of the thickness measurement process of a laser processing apparatus.

  A laser processing apparatus to which a measurement method according to the present invention is applied will be described with reference to FIG. FIG. 1 is a perspective view of a laser processing apparatus according to an embodiment of the present invention. The laser processing apparatus to which the measurement method of the present invention is applied is not limited to the configuration shown in FIG. The laser processing apparatus may have any configuration as long as it performs laser processing on the workpiece. In addition, the measurement method of the present invention is not limited to the configuration applied to the laser processing apparatus shown in FIG. 1. For example, the measurement method may be applied to a measurement apparatus dedicated to film thickness measurement that is separate from the laser processing apparatus. Good.

  As shown in FIG. 1, the laser processing apparatus 1 is configured to form a protective film 61 (see FIG. 2) for preventing debris adhesion on the wafer W and to laser-process the wafer W after the film formation. ing. The wafer W is formed in a substantially disc shape, and is partitioned into a plurality of regions by streets (division planned lines) (not shown) arranged in a lattice pattern on the surface. Devices such as IC and LSI are formed in each area partitioned by the street. Further, the wafer W is supported by the annular frame 62 via the sticking tape 63 and is carried into and out of the laser processing apparatus 1 while being accommodated in the cassette 2.

In the present embodiment, a wafer W such as a silicon wafer (Si), gallium gallium (GaAs), or silicon carbide (SiC) will be described as an example of the workpiece. However, the present invention is not limited to this configuration. For example, adhesive members such as DAF (Die Attach Film) provided on the back surface of the wafer W for chip mounting, semiconductor product packages, ceramic, glass, sapphire (Al ₂ O ₃ ) inorganic material substrates, liquid crystal display drivers, etc. The various electrical parts and various processing materials that require micron-order processing position accuracy may be used as the workpiece.

  The laser processing apparatus 1 includes a rectangular parallelepiped bed portion 3, a carry-in stand 4 provided on the side of the bed portion 3, and a standing wall portion 5 standing upright behind the bed portion 3 and the carry-in stand 4. Yes. The loading table 4 is provided with a loading / unloading mechanism 11 on which the cassette 2 is placed on the front side. A protective film 61 is formed on the surface of the wafer W on the rear side, and a protective film is formed for cleaning the processed wafer W. A mechanism 12 is provided. Beside the loading / unloading mechanism 11 and the protective film forming mechanism 12, a chuck table 13, a laser processing unit 14 for laser processing the wafer W on the chuck table 13, and a protective film 61 of the wafer W before the laser processing. A thickness measuring unit 15 for measuring the thickness is provided.

  On the upper surface of the loading table 4, a push-pull mechanism 16 for loading and unloading the wafer W with respect to the cassette 2 placed on the loading / unloading mechanism 11 is provided. A pair of guide rails 17 for slidably guiding the wafer W when the push-pull mechanism 16 is driven are provided on the upper surface of the loading table 4. Between the pair of guide rails 17 and the protective film forming mechanism 12, a transfer mechanism 18 that transfers the wafer W by the bed portion 3 and the loading table 4 is provided.

  The loading / unloading mechanism 11 adjusts the loading / unloading position of the wafer W in the height direction by moving up and down with the cassette 2 placed. The push-pull mechanism 16 is configured to be movable in the front-rear direction, and is provided with a clamping portion 23 that clamps an annular frame 62 around the wafer W. The clamping part 23 has a pair of parallel plates spaced apart in the vertical direction and is driven by an air actuator (not shown).

  The protective film forming mechanism 12 has a film forming table 26 that holds the wafer W in the center of the opening 25 formed on the upper surface of the loading table 4. The film forming table 26 is a vacuum chuck type that holds the wafer W by suction, and is provided with four clamp portions 27 that hold the annular frame 62 around the film forming table 26. The clamp unit 27 is supported in a pendulum form on a support plate extending from four sides of the film formation table 26, and is clamped by the centrifugal force acting by the rotation of the film formation table 26 to clamp the wafer W.

  A liquid resin supply unit 28 is provided in the vicinity of the film formation table 26 on the upper surface of the carry-in table 4. The liquid resin supply unit 28 applies a liquid resin to the upper surface of the wafer W on the film formation table 26. The wafer W is coated with a water-soluble resin such as polyvinyl alcohol (PVA) containing an absorbent that absorbs light having a laser wavelength as a liquid resin. In this case, during processing using a laser beam in the ultraviolet wavelength region (for example, a wavelength of 355 nm), an ultraviolet absorber that absorbs light in the ultraviolet region (for example, a wavelength of 250 nm or more and 380 nm or less) is added as an absorbent. In this case, for example, benzophenone-based, benzotriazole-based, triazine-based, and benzoate-based plastic additives are used. In addition, when processing using a laser beam (for example, a wavelength of 533 nm) in the visible light wavelength region, a light absorber that absorbs light in the visible light range (for example, a wavelength of 460 nm or more and 650 nm or less) is added as an absorbent. . In this case, for example, a water-soluble dye compound or a water-soluble dye compound is used. The protective film forming mechanism 12 forms the film by lowering the film forming table 26 and rotating it at high speed inside the loading table 4 to spread the liquid resin over the entire surface of the wafer W.

  Further, the protective film forming mechanism 12 also functions as a cleaning mechanism for removing the protective film 61 from the processed wafer W. A cleaning nozzle (not shown) is provided inside the carry-in table 4. When the processed wafer W is placed on the film forming table 26, the protective film forming mechanism 12 lowers the film forming table 26 into the loading table 4 through the opening 25. The film formation table 26 rotates and rotates at a high speed in the loading table 4, and the cleaning water is sprayed to clean and remove the protective film 61 of the water-soluble resin from the wafer W. Thereafter, the film forming table 26 is rotated at a high speed, and the spray of the cleaning water is stopped to dry the wafer W.

  The transport mechanism 18 includes a pivot shaft 31 extending in the vertical direction, an extendable arm 32 supported on the upper end of the pivot shaft 31, and a suction holding unit that is provided at the tip of the extendable arm 32 and holds the wafer W by suction. 33. The rotation shaft 31 is configured to be movable up and down and rotatable, and the extendable arm 32 is configured to be extendable and contractable in the extending direction. The position of the suction holding portion 33 in the horizontal plane is adjusted by the rotation of the rotation shaft 31 and the expansion / contraction of the extendable arm 32, and the position adjustment in the height direction is performed by the vertical movement of the rotation shaft 31.

  The transport mechanism 18 picks up the wafer W on the pair of guide rails 17 and places the wafer W on the film formation table 26 before the laser processing. Pick up and place on the chuck table 13. After the laser processing, the transfer mechanism 18 picks up the processed wafer W on the chuck table 13 and places it on the film forming table 26, and picks up the cleaned wafer W on the film forming table 26. Return to the pair of guide rails 17.

  A chuck table moving mechanism 35 is provided on the upper surface of the bed portion 3 to process and feed the chuck table 13 in the X-axis direction and index and feed it in the Y-axis direction. The chuck table moving mechanism 35 includes a pair of guide rails 36 extending in the X-axis direction on the bed 3 and parallel to each other, and a motor-driven X-axis table 37 slidably installed on the pair of guide rails 36. have. The chuck table moving mechanism 35 extends in the Y-axis direction on the X-axis table 37 and is parallel to each other, and a motor-driven Y-axis that is slidably installed on the pair of guide rails 38. And a table 39.

  A chuck table 13 is provided above the Y-axis table 39. Note that nut portions (not shown) are formed on the back sides of the X-axis table 37 and the Y-axis table 39, and ball screws 41 and 42 are screwed into these nut portions. Drive motors 43 and 44 are coupled to one end portions of the ball screws 41 and 42, respectively, and the ball screws 41 and 42 are rotationally driven by the drive motors 43 and 44, respectively.

  The chuck table 13 includes a θ table 45 that can rotate around the Z axis on the upper surface of the Y-axis table 39, and a work holding unit 46 that is provided on the top of the θ table 45 and holds the wafer W by suction. The work holding unit 46 is a vacuum chuck type that holds the wafer W by suction, and has a suction surface formed of a porous ceramic material on the upper surface. The suction surface is a surface that sucks the wafer W through the sticking tape 63 by a negative pressure, and is connected to a suction source through a pipe inside the θ table 45.

  Around the work holding portion 46, four clamp portions 48 are provided via a pair of support arms extending radially outward from the four sides of the θ table 45. The four clamp portions 48 are driven by an air actuator to clamp and fix the annular frame 62 around the wafer W from four directions.

  An arm portion 51 protrudes from the front surface of the standing wall portion 5 erected on the rear side of the chuck table 13. A measuring head 52 of the thickness measuring unit 15, a processing head 53 of the laser processing unit 14, and an imaging head 54 for alignment are provided side by side on the distal end side of the arm portion 51. The measuring head 52 emits measuring light for measuring the thickness of the protective film 61 of the wafer W. A laser beam for processing the wafer W is irradiated from the processing head 53. Imaging light is emitted from the imaging head 54. Various optical systems are provided in the measurement head 52, the processing head 53, the imaging head 54, the arm portion 51, and the standing wall portion 5.

  The measuring light is adjusted to a wavelength that can be absorbed by the protective film 61 of the wafer W formed of a water-soluble resin containing an absorbent. For example, when laser processing is performed in the ultraviolet wavelength region, as described above, an absorbent capable of absorbing light in the ultraviolet wavelength region is used, and therefore the wavelength of the measurement light is adjusted within the ultraviolet range. Further, when laser processing is performed in the visible light wavelength range, an absorbent capable of absorbing visible light is used, so that the wavelength of the measurement light is adjusted within the visible light range. The thickness measurement unit 15 measures the thickness of the protective film 61 by receiving the reflected light from the wafer W that has been reduced by the absorption of the measurement light. In this case, the thickness of the protective film 61 is measured with reference to a map indicating the change in the reflection intensity with respect to the change in the thickness of the protective film 61 stored in the control unit 19 in the bed 3 in advance. Then, when the thickness of the protective film 61 is within the predetermined range, laser processing is started by the laser processing unit 14, and when the thickness of the protective film 61 is outside the predetermined range, the protective film 61 in the protective film forming mechanism 12. Is reformed.

  As described above, in the laser processing unit 14, only the wafer W with the protective film 61 having a constant thickness is laser processed. Therefore, the trouble caused by the thickness of the protective film 61 at the time of laser processing is improved, the adhesion of debris to the wafer W is suppressed, and the quality deterioration of the wafer W is prevented. At this time, since the absorber that absorbs the light having the wavelength of the laser is added to the protective film 61, the protective film 61 is also removed together with the processing of the wafer W during the laser processing. For this reason, the protective film 61 is not peeled off due to the pressure of the thermal decomposition product of the wafer W, and debris adhesion due to the peeling of the protective film 61 is also prevented.

  The measurement position by the thickness measurement unit 15 and the processing position by the laser processing unit 14 are adjusted by alignment processing by the imaging head 54. The imaging head 54 images the surface of the wafer W with an imaging element such as a CCD and outputs the captured image to the control unit 19 in the bed unit 3. The control unit 19 performs the alignment process by matching the reference pattern stored in advance in the storage unit with the chip pattern included in the captured image. By this alignment process, the thickness of the protective film 61 at the same position of the wafer W is measured every time when measuring the thickness. Therefore, variations in the measurement result due to the difference in the material (substrate, device) on the wafer surface can be suppressed. Laser processed along the street with high accuracy.

  The control unit 19 performs overall control of the laser processing apparatus 1 and includes a processor (calculation unit) that executes various processes, a storage unit (storage unit), and the like. The storage unit is configured by one or a plurality of storage media such as a ROM (Read Only Memory) and a RAM (Random Access Memory) depending on the application. The storage unit stores control programs used for thickness measurement processing, alignment processing, and laser processing. Further, the storage unit stores a map used for the thickness measurement process and a reference pattern used for the alignment process.

  With reference to FIG. 2, the optical system of the thickness measurement process of a laser processing apparatus is demonstrated. FIG. 2 is a schematic diagram of an optical system for thickness measurement processing of the laser processing apparatus according to the embodiment of the present invention. The laser processing laser optical system and the alignment processing reading optical system are not described in detail, but have general configurations.

  As shown in FIG. 2, the optical system of the laser processing apparatus is provided with a measurement light source 55 for measuring the thickness of the protective film 61 of the wafer W. The measurement light source 55 is set to be able to oscillate measurement light having a wavelength absorbed by the absorbent (in this embodiment, a laser beam is used). A half mirror 56, a mirror 57, and a condenser lens 58 are disposed on the optical path of the measurement light emitted from the measurement light source 55. The half mirror 56 is configured to transmit the measurement light emitted from the measurement light source 55 and guide it to the mirror 57, and guide the reflected light from the wafer W to the light receiving unit 59 via the mirror 57. The measurement light source 55, the half mirror 56, the mirror 57, and the condenser lens 58 function as a light irradiation unit that irradiates the measurement light toward the protective film 61.

  The light receiving unit 59 converts the reflection intensity from the wafer W into a voltage signal by a light receiving element (not shown) or the like and outputs the voltage signal to the control unit 19. The control unit 19 creates a reflection intensity map based on the voltage signal during preliminary measurement before the machining head 53 of the laser machining apparatus 1 is operated, and uses the map when the machining head 53 of the laser machining apparatus 1 is operated. The thickness of the protective film is measured. The condensing lens 58 is configured to be drivable in the optical axis direction, and adjusts the collection point of the measurement light. At this time, the measurement light is condensed, so that when the thickness of the protective film 61 formed on the surface of the wafer W with the uneven surface is measured, light scattering is suppressed and the measurement is efficiently performed. In addition, the condensing lens 58 is comprised with the single lens or the combination lens. Details of the map creation process and the measurement process will be described later.

  The measurement light emitted from the measurement light source 55 passes through the half mirror 56, is reflected by the mirror 57 toward the condenser lens 58, is condensed by the condenser lens 58, and is applied to the protective film 61 of the wafer W. Is done. The protective film 61 absorbs the measurement light by the absorbent and reduces the reflection intensity of the measurement light from the wafer W. Then, the reflected light from the wafer W is incident on the mirror 57 via the condenser lens 58, reflected by the mirror 57 and the half mirror 56, and incident on the light receiving unit 59. In this embodiment, the optical system used for the thickness measurement process, the laser processing process, and the alignment process is individually provided. However, the optical system may be configured by a common optical system. In this case, the processing laser beam may be used by setting the irradiation energy per unit area as measurement light low.

  Here, the relationship between the thickness of the protective film and the reflection intensity of the wafer will be described with reference to FIG. FIG. 3 is a diagram showing the relationship between the thickness of the protective film and the reflection intensity of the wafer. In FIG. 3, the solid line is an actually measured intensity curve when the protective film contains an absorbent, the broken line is an ideal intensity curve when the protective film does not contain an absorbent, and the dots are actual measured when the protective film does not contain the absorbent. Data are shown respectively. Here, it is assumed that an ultraviolet absorbent is used as the absorbent, and light having an ultraviolet wavelength is used as the measurement light.

  The thickness measurement unit 15 irradiates the wafer W with measurement light in the ultraviolet wavelength region, whereby the reflection intensity of the wafer W is obtained through the protective film 61. Further, by changing the presence or absence of the ultraviolet absorber and the thickness of the protective film 61 while maintaining the wavelength of the measurement light, for example, a measurement result as shown in FIG. 3 is obtained. As indicated by the solid line, when the protective film 61 contains an ultraviolet absorber, the reflection intensity of the wafer W decreases linearly as the thickness of the protective film 61 increases. This is because the amount of measurement light absorbed by the ultraviolet absorber increases as the thickness of the protective film 61 increases. In the present invention, the thickness of the protective film 61 of the wafer W is measured using the change in the reflection intensity with respect to the change in the thickness of the protective film 61.

  On the other hand, as shown by the broken line, when the protective film 61 does not contain an ultraviolet absorber, the protective film 61 is protected by interference between reflected light from the surface of the protective film 61 and reflected light from the bottom surface of the protective film 61 (wafer W surface). As the thickness of the film 61 increases, the film 61 attenuates while repeatedly increasing and decreasing. Therefore, the reflection intensity does not change linearly with respect to the thickness of the protective film 61 due to the influence of reflected light, and it is difficult to measure the thickness of the protective film 61. In this case, it is conceivable to correct the reflection intensity in consideration of interference caused by reflected light. However, in practice, it is difficult to correct interference due to reflected light because the reflection intensity varies irregularly as indicated by dots without ideally increasing or decreasing as indicated by a broken line.

  In this way, during the thickness measurement process during operation of the processing head 53 of the laser processing apparatus 1, the thickness of the protective film 61 is measured with reference to the reflection intensity map as shown by the solid line in FIG. This map is created at the time of preliminary measurement before the processing head 53 of the laser processing apparatus 1 is operated. Specifically, a plurality of wafers W having different thicknesses of the protective film 61 are prepared from a wafer W on which the protective film 61 is not formed to a wafer W on which the protective film 61 is formed thicker, and each wafer W has an ultraviolet wavelength region. Irradiate the measurement light. Then, by receiving the reflected light from the wafer W through the protective film 61, reflection intensity data corresponding to the change in the thickness of the protective film 61 is input to the control unit 19. The control unit 19 creates and stores a map from the reflection intensity data.

  The map production process is performed each time the type of wafer W to be processed changes. This is because the reflection intensity of the wafer W changes because the material differs depending on the type of wafer. Note that the map shown by the solid line in FIG. 3 is merely an example, and the wavelength of the measurement light, the film thickness of the measurement target, and the like can be changed as appropriate.

  Here, the operation of the laser processing apparatus will be described with reference to FIG. FIG. 4 is a flowchart of the operation of the laser processing apparatus according to the embodiment of the present invention. Prior to the operation of the processing head 53 of the laser processing apparatus 1, preliminary measurement is performed and a map of reflection intensity is created. Here, the wafer W for map preparation in which the protective film 61 is not formed by the transport mechanism 18 is transported to the protective film forming mechanism 12, and the protective film 61 is formed on the surface of the wafer W so as to have a predetermined thickness ( Protective film forming step: Step S01). In the protective film forming step, it is confirmed that the protective film 61 has a predetermined thickness using a conventional film thickness measuring device. Next, the wafer W is transported to the chuck table 13 by the transport mechanism 18, and the reflected light of the wafer W is measured through the protective film 61 by irradiating the wafer W with measurement light having a wavelength absorbed by the absorbent. (Strength measuring step: Step S02). Then, by repeating the spectrum measurement process as many times as necessary while changing the thickness of the protective film 61 formed on the wafer W in the protective film forming process, the reflection intensities of the plurality of wafers W having different protective film 61 thicknesses are measured. The measurement result is input to the control unit 19, and a map representing the change in the reflection intensity with respect to the change in the thickness of the protective film 61 is prepared (map preparation step). And preliminary measurement is complete | finished when a map preparation process is complete | finished. The measurement position of the protective film 61 is adjusted by the alignment process by the imaging head 54.

  Next, when the processing head 53 of the laser processing apparatus is operated, the wafer W to be processed is pulled out from the cassette 2 onto the pair of guide rails 17 by the push-pull mechanism 16 and the wafer W is protected by the transport mechanism 18. The film is transferred to the film forming table 26 of the forming mechanism 12. In the protective film forming mechanism 12, a protective film 61 is formed on the surface of the wafer W to be processed so as to have a predetermined thickness (step S03). Here, the liquid resin is applied from the liquid resin supply unit 28 to the wafer W on the film formation table 26. Then, the film formation table 26 is rotated at a high speed inside the loading table 4, whereby the entire surface of the wafer W is formed with the liquid resin.

  Next, the wafer W is transferred to the chuck table 13 by the transfer mechanism 18, and is positioned below the measurement head 52 by the chuck table 13. When the wafer W is positioned below the measuring head 52, the thickness of the protective film 61 of the wafer W is measured (protective film thickness measuring step: step S04). Here, alignment processing is performed by the imaging head 54, and the measurement position of the measurement head 52 is adjusted to an arbitrary position on the protective film 61. The measurement head 52 irradiates the protective film 61 with measurement light, and the reflection intensity from the wafer W reduced by the absorption of the measurement light by the protective film 61 is detected. Then, the control unit 19 measures the thickness of the protective film 61 based on the reflection intensity map.

  Next, the controller 19 determines whether or not the thickness of the protective film 61 is within a predetermined range (step S05). Here, for example, the thickness of the protective film 61 measured in the protective film thickness measuring step is compared with the upper and lower thresholds for determination predetermined in the map making step. When the thickness of the protective film 61 is not less than the lower threshold and not more than the upper threshold, the protective film 61 having an appropriate thickness is determined to be within the predetermined range. When the thickness of the protective film 61 is smaller than the lower limit threshold or larger than the upper limit threshold, it is determined that the protective film 61 is too thick or too thin and is out of the predetermined range. Note that the determination processing in step S05 is performed at several places (for example, five places) on the protective film 61. Moreover, the determination process should just be able to identify abnormality of the thickness of the protective film 61, for example, may determine from the thickness variation of several places.

  When it is determined that the thickness of the protective film 61 is within the predetermined range (step S05: Yes), laser processing is started (step S06). Here, the exit of the processing head 53 is aligned with the street of the wafer W, and a laser beam is irradiated along the street. In this case, since the protective film 61 of the wafer W is formed to have an appropriate thickness, problems due to the thickness of the protective film 61 are improved, and debris adhesion to the wafer W is suppressed and deterioration of the quality of the wafer W is prevented. The Further, since the protective film 61 contains an absorbent that absorbs the laser beam, the wafer W is laser processed while the protective film 61 is removed by the laser beam. Thereby, adhesion of debris resulting from peeling of the protective film 61 is also prevented.

  Next, when all the streets of the wafer W are processed, the processed wafer W is transferred from the chuck table 13 to the film forming table 26 of the protective film forming mechanism 12 by the transfer mechanism 18. In the present embodiment, since the water-soluble resin is used as the protective film 61, the protective film is cleaned and removed from the processed wafer W by the protective film forming mechanism 12 (step S07). Here, the debris is washed out together with the protective film 61 from the surface of the wafer W by rotating the film forming table 26 at a high speed while spraying cleaning water inside the carry-in table 4. Then, the cleaned wafer W is transferred from the film forming table 26 to the pair of guide rails 17 by the transfer mechanism 18, and the wafer W is accommodated in the cassette 2 by the push-pull mechanism 16.

  On the other hand, when it is determined that the thickness of the protective film 61 is outside the predetermined range (step S05: No), it is determined whether or not the number of times the protective film 61 is formed on the wafer W in the protective film thickness measurement step is equal to or less than the predetermined number n. (Step S08). When it is determined that the number of formations of the protective film 61 is equal to or less than the predetermined number n (step S08: Yes), the protective film 61 is transferred to the protective film forming mechanism 12, and the protective film 61 is washed away from the wafer W by the cleaning process similar to step S07. (Step S09), the process returns to Step S03, and the protective film 61 is formed again. If it is determined that the number of formations of the protective film 61 is greater than the predetermined number n (step S08: No), an error is output by the control unit 19 and the laser processing apparatus 1 is stopped (step S10). The number of formations of the protective film 61 is counted during the protective film forming process in step S03, but may be configured to be counted during the thickness measurement of the protective film 61 in step S04 and during the determination process in step S05. Further, when processing a plurality of wafers W, the laser processing apparatus 1 repeats the number of processes during operation (step S03 to step S10).

  As described above, according to the measurement method according to the present embodiment, the wafer W is irradiated with the light absorbed by the absorbent based on the map representing the change in the reflection intensity with respect to the change in the thickness of the protective film 61. Therefore, the thickness of the protective film 61 can be measured with high accuracy and more simply than the conventional measuring device. Accordingly, it becomes easy to prepare as many measuring devices as the number of processing devices or to incorporate them into the processing devices, and laser processing can be performed with the thickness of the protective film 61 kept constant, and adhesion of debris to the wafer W is suppressed. Thus, quality degradation of the wafer W can be prevented.

  As the optical system, for example, a projecting optical system as shown in FIG. 5 may be used. FIG. 5 shows an optical system for thickness measurement used when laser processing is performed with visible light, but it can also be applied to an optical system for thickness measurement used when laser processing is performed with ultraviolet light. It is. As shown in FIG. 5, a white light source 65 is provided on the irradiation system side of the optical system as a measurement light source for measuring the thickness of the protective film 61 of the wafer W. The white light source 65 is configured to irradiate the surface of the wafer W at an angle, and there is no measurement light on the optical path of the measurement light including light having a wavelength that is absorbed by the light absorber emitted from the white light source 65. A condensing lens 66 for adjusting the focal point is disposed. The white light source 65 and the condensing lens 66 function as a light irradiation unit that irradiates the measurement light toward the protective film 61.

  On the light receiving side of the optical system, a light receiving unit 69 that receives reflected light from the wafer W and measures the reflection intensity is provided. On the optical path of the reflected light from the surface of the wafer W toward the light receiving unit 69, a band pass filter 67 that blocks light other than an arbitrary wavelength and a light that passes through the band pass filter 67 is collected on the light receiving surface of the light receiving unit 69. An optical lens 68 is disposed. In addition, the condensing lenses 66 and 68 are comprised with the single lens or the combination lens.

  The measurement light emitted from the white light source 65 is condensed by the condensing lens 66 and irradiated obliquely to the surface of the wafer W. The protective film 61 absorbs the measurement light by the absorbent and reduces the reflection intensity of the measurement light from the wafer W. Then, the reflected light from the wafer W enters the light receiving unit 69 via the band pass filter 67 and the condenser lens 68. In addition, it is good also as a structure which disperse | distributes reflected light with a spectrometer instead of the band pass filter 67, and acquires the light of arbitrary wavelengths.

  Further, in the above-described embodiment, the map format data is used as the measurement data indicating the relationship between the thickness of the protective film and the reflection intensity. However, the present invention is not limited to this configuration. The measurement data may be data indicating the relationship between the thickness of the protective film and the reflection intensity. For example, the measurement data may be tabular data indicating the change in the reflection intensity from the wafer with respect to the change in the thickness of the protective film.

  In the above-described embodiment, the protective film is formed of a water-soluble resin containing an absorbent, but is not limited to this configuration. The protective film may be formed of a resin material other than the water-soluble resin as long as it contains an absorbent and can be cleaned.

  The embodiment disclosed this time is illustrative in all respects and is not limited to this embodiment. The scope of the present invention is shown not by the above description of the embodiments but by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

  As described above, the present invention has an effect that the thickness of the protective film can be accurately measured by light having a wavelength absorbed by the absorbent, and is particularly applied to a laser processing apparatus that divides a workpiece by laser processing. It is useful for measuring methods and measuring devices.

1 Laser processing equipment (measuring equipment)
DESCRIPTION OF SYMBOLS 11 Loading / unloading mechanism 12 Protective film formation mechanism 13 Chuck table 14 Laser processing unit 15 Thickness measurement unit 16 Push pull mechanism 18 Conveyance mechanism 19 Control part (memory | storage means, calculation means)
28 Liquid Resin Supply Unit 52 Measurement Head 53 Processing Head 54 Imaging Head 55 Measurement Light Source (Light Irradiation Unit)
56 Half mirror (light irradiation part)
57 Mirror (light irradiation part)
58, 66 Condensing lens (light irradiation part)
59 Light-receiving part 61 Protective film 65 White light source (light irradiation part)
W wafer (work)

Claims (3)

In order to protect the surface of the workpiece from the processing waste generated when laser processing is performed by irradiating the workpiece with a laser beam in the ultraviolet wavelength range, the workpiece is formed of a water-soluble resin containing an absorbent that absorbs light of the wavelength of the laser. A measurement method for measuring the thickness of a protective film,
A protective film forming step of forming the protective film so as to have a predetermined thickness on the workpiece surface by the water-soluble resin containing the absorbent;
After the protective film forming step, an intensity measuring step of measuring the reflection intensity by irradiating the protective film formed on the workpiece surface with light having a wavelength of 250 nm or more and 380 nm or less absorbed by the absorbent;
Including a map creating step of creating a map representing a change in the reflection intensity with respect to a thickness change of the protective film by performing the intensity measuring step while changing a thickness of the protective film formed in the protective film forming step,
When measuring the thickness of the protective film applied to the surface of the workpiece,
A protective film thickness measuring step is performed in which the protective film is irradiated with light having a wavelength that is absorbed by the absorbent, the reflection intensity is measured, and the thickness of the protective film is measured based on the map. Measuring method. In order to protect the surface of the workpiece from the processing waste generated when laser processing is performed by irradiating the workpiece with a laser beam in the visible light wavelength range, the workpiece is formed of a water-soluble resin containing an absorbent that absorbs light of the laser wavelength. A measuring method for measuring the thickness of the protective film,
A protective film forming step of forming the protective film so as to have a predetermined thickness on the workpiece surface by the water-soluble resin containing the absorbent;
After the protective film forming step, an intensity measuring step of measuring the reflection intensity by irradiating the protective film formed on the workpiece surface with light having a wavelength of 460 nm or more and 650 nm or less absorbed by the absorbent;
Including a map creating step of creating a map representing a change in the reflection intensity with respect to a thickness change of the protective film by performing the intensity measuring step while changing a thickness of the protective film formed in the protective film forming step,
When measuring the thickness of the protective film applied to the surface of the workpiece,
A protective film thickness measuring step is performed in which the protective film is irradiated with light having a wavelength that is absorbed by the absorbent, the reflection intensity is measured, and the thickness of the protective film is measured based on the map. Measuring method. An aqueous solution comprising the absorbent that absorbs light of the wavelength of the laser in order to protect the surface of the workpiece from machining waste generated when the workpiece is laser processed by the measurement method according to claim 1 or 2 . A measuring device for measuring the thickness of the protective film formed of a conductive resin,
A light irradiation section for irradiating the protective film light formed on the work surface of the wavelength of the absorber absorbs,
A light receiving unit that receives reflected light of the light irradiated by the light irradiation unit and obtains a reflection intensity;
Storage means for storing a map representing a change in the reflection intensity with respect to a change in the thickness of the protective film;
A measuring apparatus comprising: a calculating unit that obtains the thickness of the protective film based on the reflection intensity acquired by the light receiving unit and the map stored by the storage unit.

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