JP2012134333A - Method for measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the fact that a work having a thickness deviating from a standard is carried in before starting the processing in a processing device which forms a modified layer in the work by condensing a laser beam.SOLUTION: While holding a work 1 carried in holding means 40, are carried out the two steps of: a first measurement step for measuring the height position of a top face 1a of the work 1 by optical measuring means 70; and a second measurement step for measuring the height position of an adhesive face 10a of a protective tape 10 set on the reference surface. Distance from the top face 1a of the work 1 to the reference surface is detected by the difference between the values obtained by the first measurement step and second measurement step, and a determination is made whether or not the thickness of the work 1 thus carried in deviates from the standard.

Description

  The present invention relates to a measuring method for detecting whether or not the thickness of a workpiece is in conformity with a standard in a processing apparatus that focuses a laser beam inside a workpiece such as a semiconductor wafer to form a modified layer. .

  In the semiconductor device manufacturing process, a large number of rectangular device areas are defined on the surface of a workpiece such as a disk-shaped semiconductor wafer by grid-like division lines, and the surface of these device areas is composed of IC, LSI, or the like. After forming an electronic circuit and then performing necessary processing such as polishing after the back surface is ground, the workpiece is cut and divided along a predetermined division line to obtain a large number of devices from one workpiece.

  The workpiece is generally divided by a cutting device called a dicer that cuts a workpiece by cutting a cutting blade rotated at a high speed into the workpiece. In recent years, a modified layer is formed by condensing and irradiating the workpiece with a laser beam having a wavelength that passes through the workpiece from the surface side along the planned dividing line, and then applying an external force to the modified layer. A method of dividing the work along the planned dividing line is attempted (Patent Document 1, etc.). As an apparatus for performing such laser processing, there is known an apparatus configured to irradiate a laser beam toward a lower workpiece while processing and feeding a workpiece carried and held on a chuck table in a horizontal direction (for example, Patent Document 2). The condensing point of the laser beam is set at a predetermined depth from the surface of the workpiece.

Japanese Patent No. 3408805 JP-A-2005-28423

  As described above, when the modified layer is formed inside the workpiece by laser beam irradiation, the thickness of the workpiece is grasped in advance, and the condensing point of the laser beam is set based on the thickness. However, when a non-standard workpiece with a thickness other than the known value is brought in, the focal point of the laser beam is not positioned as set, and if laser processing is performed as it is, processing failure will occur. A malfunction occurs. Therefore, there has been a demand for a method that can detect that a workpiece having a thickness outside the standard has been carried in before laser processing.

  The present invention has been made in view of the above circumstances, and the main technical problem thereof is that a workpiece having a thickness outside the standard is brought into a processing apparatus for condensing a laser beam inside the workpiece to form a modified layer. It is an object of the present invention to provide a measurement method that can detect the fact before processing.

  The measuring method of the present invention comprises a holding unit having a holding surface for holding a workpiece, a frame surrounding the holding unit and having the same surface as the holding surface, and a laser beam collected inside the workpiece. A measuring device that measures the distance from the upper surface of the workpiece held on the holding surface of the holding means to a reference surface in a processing apparatus comprising: a processing means that forms a modified layer by light; A first measuring step for measuring the height position of the upper surface by an optical method; a second measuring step for measuring the height position of the reference surface by an optical method; the first measuring step; And a step of detecting a distance from the upper surface of the workpiece to the reference surface based on a difference between values obtained by the second measurement step.

  According to the present invention, it is possible to detect whether the thickness of the workpiece conforms to the standard based on the difference between the values obtained by the first measurement process and the second measurement process. Since these measurement steps are performed on the workpiece held by the holding means of the machining apparatus, it is possible to detect before carrying out the laser machining that a workpiece whose thickness is not specified is carried.

  According to the present invention, a notch indicating a crystal orientation is formed in a part of a circular outer periphery of the work, an adhesive surface of a protective tape having a shape along the circular outer periphery is attached to the lower surface of the work, and the reference surface is the cut The form which is the said adhesion surface of the said protective tape exposed by the notch part is included. In addition, the present invention includes a form in which the reference surface is an upper surface of the frame.

The work referred to in the present invention is not particularly limited. For example, a semiconductor wafer made of silicon, gallium arsenide (GaAs), silicon carbide (SiC), or the like, or a DAF (Die Attach Film) provided on the back surface of the wafer for chip mounting. ), Etc., semiconductor product packages, ceramics and glass, sapphire (Al ₂ O ₃ ) -based or silicon-based inorganic material substrates, various electronic components such as LCD drivers for controlling and driving liquid crystal display devices, and micron Various processing materials that require high processing position accuracy are listed.

  The modified layer in the present invention is a region where the density, refractive index, mechanical strength, or other physical characteristics are different from the surroundings, such as a melt-treated layer, a crack layer. A dielectric breakdown layer, a refractive index change layer, and the like, and further include a single state or a mixed state thereof.

  According to the present invention, there is provided a measuring method capable of detecting, prior to processing, that a workpiece having a non-standard thickness is carried in a processing apparatus that forms a modified layer by condensing a laser beam inside the workpiece. The effect that it is done.

BRIEF DESCRIPTION OF THE DRAWINGS It is the partially expanded plan view which shows the (a) perspective view, (b) sectional drawing, (c) notch part of the workpiece | work which concerns on one Embodiment of this invention by which the protective tape was stuck on the back surface. 1 is an overall perspective view of a processing apparatus according to an embodiment. It is sectional drawing which shows the holding means of a processing apparatus. It is side surface sectional drawing which shows the state which has formed the modified layer inside the workpiece | work by laser processing. It is front sectional drawing which shows the state which has formed the modified layer inside the workpiece | work by laser processing. It is sectional drawing which shows the measuring method of embodiment which uses the adhesion surface of a protective tape as a reference surface. It is sectional drawing which shows the measuring method of embodiment which uses the upper surface of the frame of a holding means as a reference plane. It is sectional drawing which shows the measuring method of embodiment which uses the upper surface of the frame of a preliminary | backup holding means as a reference plane. It is a side view which shows typically the state which hold | maintained the workpiece | work to the holding means, Comprising: It is a figure for demonstrating the problem of the conventional method.

  Hereinafter, an embodiment of the present invention will be described. In the present embodiment, the present invention is applied to a method for measuring the thickness of a workpiece when the workpiece 1 shown in FIG. 1 is carried into the processing apparatus 20 shown in FIG. 2 and laser processing is performed.

(1) Workpiece First, a work 1 according to an embodiment will be described with reference to FIG. The workpiece 1 is a disk-shaped semiconductor wafer such as a silicon wafer, and a large number of device regions 3 are defined on the surface 1a by division lines 2 set in a lattice shape. Is formed. A V-shaped notch 4 called a notch indicating the crystal orientation of the semiconductor is formed at a predetermined location on the outer periphery of the work 1.

  As shown in FIG. 1B, a disc-shaped protective tape 10 having a predetermined thickness is attached to the back surface 1b of the workpiece 1. The protective tape 10 is one in which one side of a base material made of a resin sheet is an adhesive surface 10a, and the back surface 1b of the workpiece 1 is adhered to the adhesive surface 10a. The protective tape 10 has a circular shape having the same diameter as that of the workpiece 1 along the circular outer periphery of the workpiece 1 and is attached so as to cover the entire back surface 1b of the workpiece 1 as shown in FIG. 1 (c). The adhesive surface 10a is exposed upward in the four portions.

(2) Processing Device The workpiece 1 is subjected to laser processing along the planned division line 2 by the processing device 20 shown in FIG. Hereinafter, the basic configuration and operation of the processing apparatus 20 will be described.

  Reference numeral 21 in FIG. 2 denotes a base, and a wall portion 22 is erected on the back side of the base 21 in the drawing. An XY movement table 30 is provided on the base 21 so as to be movable in the X direction and the Y direction. The XY moving table 30 is provided on the base 21 so as to be movable in the Y direction via the guide rail 24 on the X-axis base 31 provided so as to be movable in the X direction via the guide rail 23. The X-axis base 31 moves in the X direction by moving in the X direction, and the XY movement table 30 itself moves in the Y direction by moving in the Y direction. The X-axis base 31 is driven in the X direction by an X-axis drive mechanism 32 that operates a ball screw 32b by a motor 32a, and the XY moving table 30 is driven by a Y-axis drive mechanism 33 that operates a ball screw 33b by a motor 33a. Driven by.

  A cylindrical table base 34 is fixed on the XY moving table 30, and a vacuum chuck type holding means 40 is rotatably supported on the table base 34 with the Z direction as a rotation axis. As shown in FIG. 3, the holding means 40 has a holding portion 42 made of a porous material and having a holding surface 42a concentric with an upper surface recess 41a of a disk-like frame 41 made of a metal such as stainless steel. It is formed by fitting in a shape. The holding surface 42a and the annular upper surface 41b of the frame body 41 surrounding the holding portion 42 are horizontal and flush with each other. The holding means 40 is rotationally driven in one direction or both directions by a rotation driving mechanism (not shown) housed in the table base 34. The workpiece 1 is placed concentrically on the holding surface 42a of the holding means 40 via the protective tape 10, and is sucked and held by a negative pressure action. In this case, the diameter of the work 1 is larger than the outer diameter of the holding surface 42 a and smaller than the outer diameter of the frame body 41, so that the outer peripheral side of the upper surface 41 b of the frame body 41 is exposed outside the work 1.

  Further, as shown in FIG. 2, on the XY moving table 30, a cylindrical reference table 50 whose axial direction is along the Z direction is disposed close to the holding means 40. The reference table 50 is smaller in diameter than the holding means 40 and has a horizontal upper surface 51 that is mirror-finished at the same height as the holding means 40.

  The workpiece 1 held by the holding means 40 is subjected to laser processing by the processing means 60 fixed to the wall portion 22. The processing means 60 includes a rectangular parallelepiped casing 61 fixed to the wall portion 22 and an irradiation section 62 fixed to the tip of the casing 61, and the laser beam is directed substantially vertically downward from the irradiation section 62. Irradiated. The housing 61 accommodates a laser beam oscillator, an output adjuster for adjusting the output of the laser beam oscillated by the oscillator, and the like. In this case, a laser beam oscillator that can oscillate a pulse laser beam having a wavelength that passes through the workpiece 1 such as YAG or YVO is used. Further, the irradiation unit 62 accommodates a mirror that reflects the optical path of the laser beam vertically downward, an objective lens that condenses the laser beam reflected by the mirror toward the workpiece 1, and the like.

  In the laser processing of the present embodiment, as shown in FIGS. 4 and 5, a laser beam LB having a wavelength that passes through the work 1 is condensed and irradiated along the planned division line 2 from the surface 1 a side. By doing so, the modified layer 5 according to the present invention is formed. In order to perform laser processing along the planned division line 2, the position of the planned division line 2 is detected in advance by, for example, imaging the surface 1a of the workpiece 1 with an imaging means that detects infrared rays, and the detected division planned line is detected. Based on the position 2, the laser beam LB is scanned along the planned division line 2 with a condensing point positioned inside the work 1. An arrow F in FIG. 4 indicates the relative scanning direction of the laser beam LB. Further, when the workpiece 1 is irradiated with the laser beam LB, the thickness of the workpiece 1 held by the holding unit 40 is measured by the measuring unit 70 shown in FIG.

  This measuring means 70 is a generally known non-contact type optical device that irradiates a detection light beam below and receives reflected light from the measurement object, evaluates and calculates the received light, and converts it into a distance. A distance sensor of the type is used.

  The scanning of the laser beam LB along the planned division line 2 is performed by processing feed that rotates the holding means 40 to set the division planned line 2 parallel to the Y direction in FIG. 2 and moves the XY moving table 30 in the Y direction. Made. Further, the division line 2 to be irradiated is switched by index feed for moving the X-axis base 31 in the X direction. Note that the machining feed direction and the index feed direction may be set oppositely, that is, the X direction may be set as the machining feed direction, and the Y direction may be set as the index feed direction, and is not limited.

  When the modified layer 5 is formed along all the planned division lines 2 inside the workpiece 1 by irradiation with the laser beam LB, the holding of the workpiece 1 by the holding means 40 is released, and the workpiece 1 is carried out from the holding means 40.

  The above is the configuration and operation of the processing apparatus 20, and the workpiece 1 after the laser processing is applied to a number of device regions 3, that is, devices along the planned division line 2 by applying an external force to the formed modified layer 5. Divided.

(3) Work Thickness Measuring Method As described above, the thickness of the workpiece 1 to be laser processed is measured by the measuring means 70 on the holding means 40 prior to the laser processing. Hereinafter, the measuring method according to the present invention will be described.

  As shown in FIG. 6, the measurement method of the present embodiment irradiates the upper surface of the workpiece 1 held on the holding means 40, that is, the surface 1 a with the first detection light beam L <b> 1 from the measuring means 70 to the surface from the measuring means 70. The distance d1 to 1a is measured, and this distance d1 is recognized as the height position H1 of the surface 1a of the workpiece 1 (first measurement step). Next, the adhesive surface 10a of the protective tape 10 exposed upward by the notch 4 is set as a reference surface, and the adhesive surface 10a is irradiated with the second detection light beam L2 from the measuring unit 70 and from the measuring unit 70. The distance d2 to the adhesive surface 10a is measured, and this distance d2 is recognized as the height position H2 of the adhesive surface 10a. In each measurement process, in order to irradiate the detection light beams L1 and L2 from the measurement means 70 to the target position, the XY movement table 30 is moved in the X direction or the Y direction, and the holding means 40 is rotated as necessary. Thus, the detection can be performed by positioning the optical axes of the detection light beams L1 and L2 at the target positions.

  Next, from the difference (d2-d1) between the height position H1 of the surface 1a of the workpiece 1 and the height position H2 of the adhesive surface 10a of the protective tape 10, the distance from the surface 1a of the workpiece 1 to the adhesive surface 10a of the protective tape 10 is determined. Find the distance. In this case, the distance (d2-d1) is the thickness of the workpiece 1. In the laser processing step, the condensing point position of the laser beam LB set as the depth from the surface 1a is set on the basis of the height position of the surface 1a of the workpiece 1 measured here.

  In the measurement method, the adhesive surface 10a of the protective tape 10 is used as a reference surface, but the reference surface may be set on the upper surface 41b of the frame 41 of the holding means 40. That is, as shown in FIG. 7, the upper surface 41b exposed to the outside of the work 1 is irradiated with the second detection light beam L2 from the measuring means 70 to measure the distance d3 from the measuring means 70 to the upper surface 41b, and this distance d3. Is recognized as the height position H3 of the upper surface 41b of the frame body 41 (second measurement step). Then, from the difference (d3−d1) between the height position H1 of the surface 1a of the workpiece 1 and the height position H3 of the upper surface 41b of the frame body 41 measured in the first measurement step, the frame body 41 from the surface 1a of the workpiece 1 is obtained. The distance to the upper surface 41b of is determined. In this case, since the protective tape 10 is affixed to the back surface 1b of the work 1, when the thickness of the protective tape 10 is t, the thickness of the work 1 is obtained by “(d3-d1) −t”. .

  Further, the reference surface may be set on the upper surface 51 of the reference table 50. In that case, as shown in FIG. 8, the distance d4 from the measuring means 70 to the upper surface 51 is measured by irradiating the upper surface 51 of the reference base 50 with the second detection light beam L2 from the measuring means 70, and this distance d4. Is recognized as the height position H4 of the upper surface 51 (second measurement step). Then, the distance from the surface 1a of the workpiece 1 to the upper surface 51 is determined from the difference (d4-d1) between the height position H1 of the surface 1a of the workpiece 1 and the height position H4 of the upper surface 51 measured in the first measurement step. Ask. Even in this case, the thickness of the work 1 is obtained by “(d4−d1) −t” in consideration of the thickness t of the protective tape 10.

  The reference surface for irradiating the second detection light beam L2 is not limited to the above-described embodiment as long as it is a horizontal reflecting surface having a certain height at which the thickness of the workpiece 1 can be detected. Note that the upper surface 41b of the frame body 41 may be ground together with the holding surface 42a, and the detected light beam is not sufficiently reflected if the ground surface is left, so at least the portion irradiated with the detected light beam L2 is mirror-finished. Thus, the detection light beam L2 may be sufficiently reflected. Further, if the adhesive surface 10a of the protective tape 10 is used as a reference surface as described above, the thickness measurement value of the workpiece 1 becomes more accurate because it is not affected by variations in the thickness of the protective tape 10.

  In the present embodiment, the height position value (H1) of the workpiece 1 obtained in the first measurement step and the height position value (H2, H3 or H4) of the reference surface obtained in the second measurement step. Based on the difference, the thickness of the workpiece 1 can be detected. The thickness measuring step of the workpiece 1 can be performed on the workpiece 1 held by the holding means 40. For this reason, when a workpiece having a thickness outside the standard is loaded, this is performed before laser processing. Can be detected. If the loaded workpiece has a thickness outside the standard, the workpiece is unloaded from the holding means 40 and the next workpiece is loaded. In the above embodiment, the thickness of the workpiece 1 is obtained. However, if at least a difference between the height position value of the upper surface of the workpiece 1 and the height position value of the reference surface is detected, the thickness of the workpiece 1 is detected. It is possible to determine whether the length is out of specification.

  By the way, conventionally, only the height position of the upper surface of the workpiece is detected, and the condensing point of the laser beam into the workpiece is set based on the detected value. However, this method has the following problems, for example. FIG. 9A shows a phenomenon in which the height position of the holding surface 42a of the holding means 40 becomes higher than usual due to the thermal expansion of the apparatus, and the workpiece 1 held by the holding means 40 has a standard thickness. belongs to. On the other hand, in FIG. 9B, the upper surface of the holding means 40 has a normal height, but the held workpiece 1 is thicker than the standard, and the height position of the upper surface 1a of the workpiece 1 is that of (a). It is the same as work 1. In such a situation, the height position of the upper surface 1a of the work 1 measured by irradiating the upper surface 1a of the work 1 with the detection light beam L from the measuring means 70 is the same and higher than the standard, so it is determined as an error. The That is, the workpiece 1 on the (a) side is judged to be an error even though the thickness is in accordance with the standard, and laser processing is canceled, so a useless operation occurs. However, in this embodiment, since the distance from the upper surface 1a of the workpiece 1 to the reference surface is detected, it can be seen that the workpiece 1 on the (a) side has a thickness according to the standard, and therefore, it is possible to avoid unnecessary operations. can do.

  Normally, when laser processing is performed inside a workpiece with a thickness outside the standard, processing may be defective and it may be difficult to form a modified layer normally, so laser processing is not performed again. . This is due to the following reason. That is, for example, if a workpiece thicker than the standard is irradiated with a laser beam at a focal point as set, the focal point does not reach an appropriate depth, and the modified layer is formed relatively near the surface. Even if the laser beam is again irradiated into the workpiece from the surface side, the already formed modified layer hinders the transmission of the laser beam and the laser beam does not converge to the target depth. In this respect, if the measurement method of the present embodiment is applied, it is possible to prevent a processing defect from being caused, and thus to obtain an advantage of improving productivity.

  In the processing means 60 of the above embodiment, the objective lens that is accommodated in the irradiation unit 62 and condenses the laser beam inside the workpiece is used as an objective lens that condenses the oscillated laser beam as a detection beam for thickness measurement. It can also be used. Thus, if the processing means 60 is used, it is not necessary to provide the measuring means 70 independently. When the thickness of the workpiece is measured by the laser beam irradiated from the irradiation unit 62, the objective of the irradiation unit 62 is confirmed by confirming the degree of reflection of the laser beam irradiated at the time of measuring the thickness of the workpiece. It can be used as a material for determining whether or not the lens is contaminated.

1 ... Work 1a ... Work surface (upper surface)
5 ... Modified layer 10 ... Protective tape 10a ... Adhesive surface (reference surface) of protective tape
20 ... Processing device 40 ... Holding means 41 ... Frame 41b ... Upper surface (reference surface) of frame
42 ... Holding part 42a ... Holding surface 60 ... Processing means H1 ... Height position H2, H3, H4 ... Working surface height position LB ... Laser beam

Claims (3)

A holding means having a holding portion having a holding surface for holding a work and a frame surrounding the holding portion and having the same surface as the holding surface; and a modified layer by condensing a laser beam inside the work In a processing apparatus constituted by processing means to form,
A measuring method for measuring a distance from an upper surface of a work held on a holding surface of the holding means to a reference surface,
A first measuring step for measuring the height position of the workpiece upper surface by an optical method;
A second measuring step for measuring the height position of the reference surface by an optical method;
Detecting the distance from the upper surface of the workpiece to the reference surface by the difference between the values obtained by the first measurement step and the second measurement step;
A measurement method comprising: The workpiece is formed with a notch indicating the crystal orientation in a part of the circular outer periphery,
The adhesive surface of the protective tape with a shape along the circular outer periphery is attached to the lower surface of the workpiece,
The measurement method according to claim 1, wherein the reference surface is the adhesive surface of the protective tape exposed by the notch portion.   The measurement method according to claim 1, wherein the reference surface is an upper surface of the frame.

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