JP4968849B2 - Laser processing method - Google Patents

Description

The present invention, for example, relates to Relais chromatography The processing method for forming a linear groove in the sheet material by irradiating a laser beam such as a semiconductor wafer, in particular, in the case of processing the sheet material is adhered to the ultraviolet-curing tape It relates to a suitable technique.

  In the chip manufacturing process of a semiconductor device, a large number of rectangular chip regions are partitioned on the surface of a substantially disk-shaped semiconductor wafer by division lines arranged in a lattice pattern, and electronic devices such as ICs and LSIs are formed in these chip regions. After the circuit is formed, the wafer is subjected to necessary processing such as back grinding, and then the wafer is cut along a division line and divided (diced) to obtain each chip region as a semiconductor chip. The semiconductor chip thus obtained is packaged by resin sealing and widely used in various electric / electronic devices such as mobile phones and PCs (personal computers).

  In recent years, laser dicing has been adopted in which a wafer is diced by irradiating a transparent laser beam along a division line (Patent Document 1). When dicing a wafer, in order to handle a wafer that is difficult to convey, the wafer is attached to a dicing tape and the dicing frame attached to the dicing tape is handled. In this case, after completion of dicing, the chip is peeled off and picked up from the dicing tape. Therefore, an ultraviolet curable type is used for the adhesive of the dicing tape, and when the chip is picked up, the dicing tape is irradiated with ultraviolet rays to reduce the adhesive property of the adhesive, thereby facilitating picking up (Patent Document 2). ).

JP-A-10-305420 JP 2007-142327 A

  However, when the wafer is heated by the laser beam irradiated along the planned dividing line during dicing, the heat is transferred to the surrounding UV-curing adhesive, causing alteration, and even when irradiated with UV, the adhesiveness is not increased. It happens not to drop. When such a phenomenon occurs, the portion that remains heated and sticky adheres to the semiconductor chip during pick-up, and even if an attempt is made to pick up the semiconductor chip during the mounting process, a part of the semiconductor chip is separated from the dicing tape. In some cases, it could not be implemented. This defect occurs even when the processing by laser beam irradiation is groove formation or when the thickness is fully cut.

On the other hand, when the present inventors investigated the ultraviolet curable adhesive used for the dicing tape, it was found that the material was denatured by heating at about 60 ° C., and after the denature, no matter how much ultraviolet rays were irradiated, it was not cured. Accordingly, the present invention is to provide a heat due can avoid the influence of deterioration of the ultraviolet curing adhesive, thus mounting process can be performed smoothly Relais chromatography The processing method generated during laser dicing It is an object.

Laser processing method of the present invention is a laser processing method for performing processing by the laser to the workpiece in a state where the rear surface side holding the stuck to the work in the ultraviolet curing tape having adhesive disposed in the frame, the laser machining on the workpiece Before performing the above, the ultraviolet curing tape is irradiated with ultraviolet rays to reduce the adhesiveness , and laser processing is performed by irradiating a laser beam having a wavelength of 355 nm from the surface side of the workpiece .

  According to the present invention, since the adhesiveness of the ultraviolet curable tape is lowered at the time of processing the workpiece, the influence on the ultraviolet curable tape due to heat generated during laser processing does not matter. As described above, in the present invention, the semiconductor chip or the like can be picked up from the ultraviolet curable tape whose adhesiveness has been reliably lowered, so that the mounting process can be performed smoothly with few pick-up defects.

  Here, the ultraviolet curable tape includes a dicing tape having a surface provided with an ultraviolet curable adhesive, but also includes a resin film having adhesiveness in a semi-cured state. Further, the UV curable tape of the present invention includes a DAF (Die Attach Film) which is provided on the back surface of the wafer for chip mounting on the surface of the dicing tape as described above. In this case, as DAF, a DAF that becomes sticky when heated to a high temperature (for example, 150 ° C. or higher) and loses stickiness at room temperature can be used. When such a DAF is used, the DAF adhered to the ultraviolet curable tape is heated to adhere to the workpiece. In addition, even if DAF is returned to normal temperature, the adhesion state with a workpiece | work is maintained.

  The irradiation conditions of ultraviolet rays before processing are equivalent to the irradiation conditions conventionally performed after processing. That is, the UV irradiation tape reduces the adhesiveness of the UV curable tape by UV irradiation, but does not completely disappear, but the adhesiveness is such that the semiconductor chip or the like is not displaced on the UV curable tape when handling the entire frame to the mounting process. . Therefore, the present invention is particularly effective for laser processing without processing resistance.

  In developing the present invention, it was studied from the beginning to use an ultraviolet curable tape having a low adhesive strength. However, preparing such a special UV curable tape is cumbersome and not economical, and subcontractors that only undertake dicing may not be allowed to choose UV curable tape. is there. In addition, UV curable tapes that have DAF adhered to the surface are required to have strong adhesive strength for UV curable adhesives, so it is difficult to find UV curable tapes that go against the demand. .

  Furthermore, with the ultraviolet curable tape as described above, there is a concern that the adhesive strength of the sticking part to the frame will be weak, which will hinder the handling of the frame. In this regard, in the present invention, by selectively irradiating only the part pasting the workpiece with ultraviolet rays, it is possible to selectively weaken the adhesive force of only the part pasting the workpiece, The adhesive force to the frame of the ultraviolet curable tape can be maintained.

  The workpiece in the present invention is not particularly limited. For example, a wafer such as a semiconductor wafer, an adhesive member such as the above-mentioned DAF, a semiconductor product package, a glass-based or silicon-based substrate, and a micron-order accuracy. Various processing materials required are listed. A DAF having a wafer adhered thereto is also included in the work of the present invention. In this case, after dicing the wafer, only the DAF may be diced with a laser. In this case, there is a case where cleaning is not necessary because the generation of cutting waste is less than that of dicing the wafer. Therefore, in the present invention in which it is feared that the processed workpiece is scattered from the ultraviolet curable tape when cleaning or the like using centrifugal force is performed, it is particularly suitable for the above processing.

  According to the present invention, since the adhesiveness of the ultraviolet curable tape is reduced at the time of processing the workpiece, it is possible to reliably pick up a semiconductor chip or the like from the ultraviolet curable tape having reduced adhesiveness. There are few effects that the mounting process can be performed smoothly.

Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.
[1] Workpiece (semiconductor wafer)
FIG. 1 shows a thin plate-like workpiece which is a processing target in the present embodiment. This workpiece is a disk-shaped semiconductor wafer (hereinafter abbreviated as a wafer) made of silicon or the like. The wafer 1 has, for example, a thickness of about 200 μm and a diameter of about 200 mm. An orientation flat 2 is formed on a part of the outer periphery of the wafer 1 as a mark indicating a crystal orientation.

  A plurality of first division lines A extending in the first direction (left and right direction in FIG. 1) and a direction (vertical direction in FIG. 1) perpendicular to the first division line A are formed on the surface of the wafer 1. A plurality of second division planned lines B extending are formed. The division lines A and B are parallel to each other and equally spaced, and are arranged in a lattice pattern.

  A plurality of rectangular chips 3 are partitioned on the surface of the wafer 1 by the respective division lines A and B arranged in a lattice pattern. On the surface of these chips 3, electronic circuits such as IC and LSI (not shown) are formed. Each chip 3 is subjected to processing as necessary such as thinning by back surface grinding on the wafer 1, and then all the planned division lines A and B are cut and the wafer 1 is diced to obtain one chip 3. One is obtained as a piece. The division lines A and B can be cut by full cutting by laser beam irradiation, or by forming a groove by laser beam irradiation and further cutting by laser beam irradiation.

  In the laser processing apparatus 10, the wafer 1 is set horizontally on a disk-shaped chuck table 41 (see FIG. 3) with the surface facing upward, and is divided from the laser head 52 of the laser processing means 50 to the scheduled division lines A and B. A laser beam is radiated along. When the wafer 1 is set on the chuck table 41, the wafer 1 is held by the dicing frame 5 via the dicing tape 4 as shown in FIG.

  The dicing tape 4 is, for example, a circular adhesive tape in which a polyvinyl chloride having a thickness of about 100 μm is used as a base material 4a and an acrylic resin-based ultraviolet curing adhesive 4b is applied on one surface thereof to a thickness of about 5 μm ( (See FIG. 2B). The dicing frame 5 is an annular thin plate member having an inner diameter larger than the diameter of the wafer 1 and is made of a material having rigidity such as metal, and the outer periphery of the adhesive surface (upper surface in FIG. 2) of the dicing tape 4. Attached to the part. The back surface of the wafer 1 is adhered to the central portion of the adhesive surface of the dicing tape 4 and is held by the dicing frame 5 through the dicing tape 4. The wafer 1 held by the dicing tape 4 and the dicing frame 5 in this manner is conveyed by handling the dicing frame 5 and set in the laser processing apparatus 10. Below, the laser processing apparatus 10 is demonstrated.

[2] Laser processing apparatus The laser processing apparatus 10 has a base 11, and an XY moving table 12 is provided on the base 11 so as to be movable in the horizontal X-axis direction and the Y-axis direction. Yes. The chuck table 41 is installed on the XY moving table 12, and when the XY moving table 12 moves in the X-axis direction or the Y-axis direction, the laser head 52 moves to the scheduled division lines A and B of the wafer 1. A laser beam is radiated along.

  The XY movement table 12 includes an X-axis base 20 provided on the base 11 so as to be movable in the X-axis direction, and a Y-axis base 30 provided on the X-axis base 20 so as to be movable in the Y-axis direction. It consists of a combination. The X-axis base 20 is slidably attached to a pair of parallel guide rails 21 that are fixed on the base 11 and extend in the X-axis direction, and an X-axis drive mechanism 24 that operates a ball screw 23 by a motor 22. Is moved in the X-axis direction. On the other hand, the Y-axis base 30 is slidably attached to a pair of parallel guide rails 31 fixed on the X-axis base 20 and extending in the Y-axis direction, and the Y-axis for operating the ball screw 33 by the motor 32. It is moved in the Y-axis direction by the drive mechanism 34.

  A cylindrical chuck base 40 is fixed to the upper surface of the Y-axis base 30, and a chuck table 41 is rotatably supported on the chuck base 40 with the Z-axis direction (vertical direction) as a rotation axis. Yes. The chuck table 41 is of a general well-known vacuum chuck type that holds the wafer 1 by vacuum suction and is rotated in one direction or both directions by a rotation drive mechanism (not shown) housed in the chuck base 40. Be made. Around the chuck table 41, a pair of clamps 42 for detachably holding the dicing frame 5 are disposed at positions separated from each other by 180 °. These clamps 42 are attached to the chuck base 40.

  In the XY movement table 12 in this case, the state in which the X-axis base 20 moves in the X direction is the processing feed that irradiates the laser beam irradiation along the planned division line A or B. The state in which the Y-axis base 30 moves in the Y-axis direction is the indexing direction for switching the division planned line A (B) to be irradiated with the laser beam. The machining feed direction and the indexing direction may be set oppositely, that is, the Y-axis direction may be set as the machining direction, and the X-axis direction may be set as the indexing direction.

  Next, the laser processing means 50 will be described. The laser processing means 50 has a rectangular parallelepiped casing 51 extending in the Y-axis direction toward the upper side of the chuck table 41, and the laser head 52 is provided at the tip of the casing 51. The casing 51 is provided on the column 13 erected on the upper surface of the base 11 so as to be movable up and down along the vertical direction (Z-axis direction). The vertical drive mechanism (not shown) housed in the column 13 is provided. Can be moved up and down.

  In the casing 51, a pulse laser beam oscillator composed of a YAG laser oscillator or a YVO4 laser oscillator is accommodated as a component of the laser processing means 50 (not shown). The casing 51 also houses auxiliary equipment such as an output adjuster and a repetition frequency device for adjusting the output (pulse energy) of the laser beam oscillated by the pulse laser beam oscillator. Further, the laser head 52 accommodates a mirror that changes the direction of the pulse laser beam irradiated horizontally from the laser beam oscillator, a lens that collects the laser beam whose direction is changed by the mirror, and the like. .

  As shown in FIG. 3, an imaging unit 60 is disposed at the tip of the casing 51 and next to the laser head 52. The image pickup means 60 picks up and detects an irradiation region of the laser beam emitted from the laser head 52, and includes an illuminating means and an optical system for illuminating a workpiece (here, a wafer) set on the chuck table 41. An image sensor such as a CCD for imaging an elephant captured by the optical system is provided.

  Next, reference numeral 70 in FIG. 3 denotes an ultraviolet irradiation means. The ultraviolet irradiation means 70 includes a work table 71 attached to the base 11. An arm 72 extending in the X-axis direction is provided at the upper edge of the work table 71 so as to be movable in the Y-axis direction. A chuck 73 that holds the edge of the dicing frame 5 is attached to the tip of the arm 72. Yes. On the other hand, step portions 71 a extending in the Y-axis direction are formed on both sides of the upper surface of the work table 71. By placing the edge of the dicing frame 5 on the stepped portion 71 a, the dicing frame 5 is lifted from the upper surface of the work table 71, and the dicing frame 5 can be gripped by the chuck 73. The chuck 73 moves the dicing frame 5 in and out of the ultraviolet irradiation unit 80 and the cassette 90 described below.

  The ultraviolet irradiation unit 80 is supported by a pair of guide rails 81 so as to be movable in the vertical direction (Z-axis direction), and is driven by a ball screw 82 and a motor 83 that rotates the ball screw 82. FIG. 4 is a sectional view showing details of the ultraviolet irradiation unit 80. As shown in FIG. 4, the ultraviolet irradiation unit 80 is a box-shaped unit whose side faces in the Y-axis direction are opened, and a support frame extending in the Y-axis direction is provided at the upper end of the inner side surface located in the X-axis direction. 84 is attached. The support frame 84 supports the dicing frame 5, and the dicing frame 5 held by the chuck 73 in a state where the height of the support frame 84 and the height of the stepped portion 71 a of the work table 71 are matched with each other. It slides on and off with respect to the ultraviolet irradiation unit 80.

  A plate 85 is installed below the ultraviolet irradiation unit 80, and an LED 86 that is an ultraviolet irradiation light source is provided on the plate 85. The LED 86 is configured by arranging, for example, about 1000 UV-400s manufactured by Keyence Corporation, and adheres the wafer 1 among the dicing tape 4 that adheres the dicing frame 5 accommodated above the LED 86. UV light is irradiated to the part. Here, the wavelength of ultraviolet rays can be about 365 nm, and the illuminance per LED can be about 26000 mW / cm 2.

  A cassette 90 is detachably mounted on the ultraviolet irradiation unit 80 having the above configuration. The cassette 90 has a box-like shape with open side surfaces facing the Y-axis direction, and a plurality of supporting frames (not shown) extending in the Y-axis direction are attached to the inner side surface located in the X-axis direction. A plurality of dicing frames 5 are accommodated. Then, the dicing frame 5 gripped by the chuck 73 is slid on the support frame with the height of the support frame and the height of the above-described stepped portion 71a being brought into and out of the cassette 90.

  Next, reference numeral 100 in FIG. 3 denotes a robot hand for carrying the dicing frame 5 on which the dicing tape 4 and the wafer 1 are mounted. A partition 101 extending upward is attached to a side surface of the base 11, and a Y-axis base 102 is supported on the partition 101 by a guide rail 103 so as to be movable in the Y-axis direction. The Y-axis base 102 is moved in the Y-axis direction by a ball screw 104 and a motor 105 that rotates the ball screw 104.

  An arm 106 that protrudes in the X-axis direction and bends downward from the tip is attached to the Y-axis base 102. The lower end portion 106a that is bent downward of the arm 106 is configured to be extendable in the vertical direction, and a vacuum chuck 107 is attached to the lower end portion 106a. The vacuum chuck 107 includes four vacuum pads 107a having conical inner surfaces, and sucks the dicing frame 5 by vacuum suction from the inner surfaces of the vacuum pads 107a.

[3] Operation of Laser Processing Apparatus Next, the operation of the laser processing apparatus having the above configuration will be described.
As shown in FIG. 2, a plurality of wafers 1 held by the dicing frame 5 via the dicing tape 4 are accommodated in the cassette 90, and the cassette 90 is mounted on the ultraviolet irradiation unit 80. Then, the ultraviolet irradiation unit 80 is moved by the rotation of the ball screw 82, and, for example, the lowermost wafer 1 in the cassette 90 is stopped at a position facing the chuck 73. Then, the arm 72 moves to the wafer 1 side and grips the dicing frame 5 that supports the wafer 1. The chuck 73 moves in the Y-axis direction, and the dicing frame 5 is extracted from the cassette 90 together with the wafer 1 and placed on the stepped portion 71 a of the work table 71.

  Next, when the ultraviolet irradiation unit 80 is raised and the support frame 84 of the ultraviolet irradiation unit 80 is matched with the height of the stepped portion 71a, the chuck 73 moves to the ultraviolet irradiation unit 80 side and the dicing frame 5 is supported. 84. In this state, ultraviolet rays are irradiated from the LED 86 toward the wafer 1 to reduce the adhesive force of the ultraviolet curable adhesive 4 b provided on the surface of the dicing tape 4. Next, the chuck 73 moves in the Y-axis direction, and the dicing frame 5 is extracted from the ultraviolet irradiation unit 80 together with the wafer 1 and placed on the stepped portion 71 a of the work table 71.

  Subsequently, the Y-axis base 102 of the robot hand 100 moves in the Y-axis direction and stops so that the vacuum chuck 107 is positioned directly above the wafer 1. Then, the vacuum chuck 107 is lowered, the dicing frame 5 is sucked by the vacuum pad 107a, and is lifted and moved to the chuck table 41 side. At that time, the chuck table 41 is moved so that the center thereof overlaps the movement locus of the center of the vacuum chuck 107, and the vacuum chuck 107 descends when it reaches just above the chuck table 41. The vacuum chuck 107 stops the vacuum suction when the dicing frame 5 is placed on the chuck table 41, and the wafer 1 faces the surface on which the chip 3 is formed on the chuck table 41 operated in vacuum. Are concentrically mounted and adsorbed and held by a vacuum suction action. The dicing frame 5 is held by the clamp 42.

  Next, the X-axis base 20 is moved in the X-axis direction, and the wafer 1 is positioned at a position deviating from the focal point of the laser beam irradiated from the laser head 52 in the X direction. Further, the Y-axis base 30 is moved in the indexing direction (Y-axis direction) so that the Y-axis direction position of one first scheduled division line A matches the focal point of the laser beam. Further, the vertical position of the casing 51 is adjusted so that the focal point of the laser beam irradiated from the laser head 52 is set at a position where a groove having a predetermined depth is formed in the first division line A.

  Subsequently, processing feed is performed to move the X-axis base 20 in a direction in which the wafer 1 is directed toward the laser head 52. During the process feed, one division line A passes through the focal point of the laser beam, and during this time, a laser beam is emitted from the laser head 52 at a constant output, so that a groove having a predetermined depth is formed on the division line A. It is formed. In this way, grooves having a predetermined depth are formed in all the division lines A. Next, the chuck table 41 is rotated by 90 °, and grooves having a predetermined depth are formed in all the division lines B in the same manner as described above. In this case, the depth of the groove formed at one time or a plurality of times is set to be equal to or greater than the thickness of the wafer 1 (full cut), or the depth of the groove formed at one time or a plurality of times is set to the wafer 1. Either of these methods can be employed, in which the thickness is made shallower than that (grooving), and the laser beam is changed and the full cutting is performed in the next processing.

  When all the division lines A and B are cut as described above, the dicing is completed. The wafer 1 separated into a plurality of semiconductor chips 3 by dicing is transferred together with the dicing frame 5 to the next mounting process. At that time, the UV curable adhesive 4b of the dicing tape 4 has a reduced adhesive force but is not completely lost. When handling the entire frame to the mounting process, the semiconductor chip or the like is positioned on the UV curable tape. It remains sticky enough not to slip. In addition, by selectively irradiating only the part where the work is pasted, the adhesive strength of only the part where the work is pasted is selectively weakened. Adhesive strength is maintained. Further, when the semiconductor chip 3 is mounted, since the adhesive force of the ultraviolet curable adhesive 4b is reduced, the semiconductor chip 3 is surely picked up from the dicing tape 4 and the mounting process can be performed smoothly.

  A silicon wafer having a thickness of 50 μm was adhered to a dicing tape (manufactured by Lintec, D650 UV tape), and the ultraviolet curable adhesive of the dicing tape was irradiated with ultraviolet rays. Next, the silicon wafer was grooved with a laser and then fully cut with a laser. The conditions for laser processing are as follows.

<Grooving conditions>
Light source: LD excitation Q switch Nd: YV04
Wavelength: 355nm
Average output: 1W
Repetition frequency: 100 kHz
Processing feed rate: 600mm / s
2 passes for 1 cutting planned line <Full cut processing conditions>
Light source: LD excitation Q switch Nd: YV04
Wavelength: 355nm
Average output: 10W
Repeat frequency: 10 kHz
Processing feed rate: 200 mm / s
2 passes for 1 cut line

  Mounting was performed on a semiconductor chip diced under the above conditions, and the success rate of the pickup was investigated. As a result, the success rate was 98%. For comparison, when the test was performed under the same conditions as described above except that the ultraviolet irradiation was performed after the wafer was diced, the success rate of the pickup was 60%.

It is a top view of the semiconductor wafer processed by the method concerning one embodiment of the present invention. It is a perspective view which shows the state which hold | maintained the semiconductor wafer shown in FIG. 1 to the dicing frame via the dicing tape. It is a perspective view which shows the laser processing apparatus for enforcing the laser processing method of one Embodiment. It is sectional drawing which shows the detail of an ultraviolet irradiation unit.

Explanation of symbols

1 ... Semiconductor wafer (work)
4 ... Dicing tape ( UV curable tape)
5 ... Dicing frame (frame)
41 ... Chuck table (holding means)
50 ... Laser processing means 70 ... Ultraviolet irradiation means 80 ... Ultraviolet irradiation unit

Claims (1)

In the laser processing method of processing the workpiece with a laser in a state of holding the workpiece with the back side adhered to the ultraviolet curable tape having adhesiveness arranged in the frame,
Before performing laser processing on the workpiece, the UV curable tape is irradiated with ultraviolet rays to reduce adhesiveness, and the laser processing is performed by irradiating a laser beam having a wavelength of 355 nm from the surface side of the workpiece. A laser processing method characterized by the above.

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