JP5116382B2 - Laser processing method - Google Patents

Description

  The present invention relates to a laser processing method for irradiating a laser beam along a predetermined division line formed on a workpiece such as a semiconductor wafer and forming a deteriorated layer along the predetermined division line inside the wafer.

  In the semiconductor device chip manufacturing process, a plurality of rectangular areas are defined on the surface of a substantially disk-shaped semiconductor wafer by dividing lines arranged in a lattice pattern, and electronic circuits such as ICs and LSIs are formed in these rectangular areas. Alternatively, after forming a microelectromechanical element called MEMS (Micro Electro Mechanical System), the wafer is cut along a division line to obtain a rectangular region as a semiconductor chip.

  As a means for cutting the wafer, a dicing method is generally used in which a thin disk-shaped blade rotated at a high speed is cut into the wafer. This dicing method has an advantage that a flat and sharp cut surface can be obtained. However, the width of the line to be divided between chips needs to be larger than the thickness of the blade to be used (mainly about 10 to 30 μm). Therefore, the cutting allowance is relatively large, which is disadvantageous in terms of improving the productivity by obtaining as many chips as possible per wafer.

  On the other hand, in recent years, a translucent laser beam is irradiated along the planned dividing line to the inside of the wafer to form a deteriorated layer having reduced physical strength, and then an external force is applied to the wafer along the planned dividing line. A laser method has also been adopted in which a wafer is cleaved and individual chips are obtained (see Patent Document 1). In this laser method, the cutting allowance is much smaller than that in the dicing method, which is advantageous in terms of productivity.

  By the way, when the wafer is divided into chips, an adhesive tape called a dicing tape is attached in advance to the back surface of the wafer in order to prevent chip dispersion and protect the chuck table. Furthermore, by attaching a metal frame to the outer periphery of the dicing tape, handling of the wafer is facilitated, and in that state, the wafer is cleaved in a braking process in which an external force is applied after laser beam irradiation in the laser method. Is called.

JP-A-10-305420

  As an apparatus for irradiating a laser beam to a division line of a wafer attached to a dicing tape, for example, a holding means for holding the wafer, a laser beam irradiating means for irradiating the wafer with a laser beam, a holding means, and a laser beam irradiation There is a laser processing apparatus having a moving means for relatively moving the means. The wafer is held on the holding means of this laser processing apparatus, and the laser beam irradiation means irradiates the laser beam to the division line of the wafer and moves the holding means and the laser beam irradiation means relative to each other, thereby changing the quality inside the wafer. A layer is formed.

  At this time, if the laser beam is irradiated to the edge of the wafer, the laser beam may be irradiated on the dicing tape or the holding unit slightly outside the wafer edge due to a mechanical control error of the moving unit. When the laser beam is applied to the dicing tape or the holding means, heat is generated by the energy of the laser beam, and a hole is opened in the irradiated portion. As described above, when a large number of holes are formed on the extension line of the dicing tape to be divided, the external force is not transmitted well to the wafer in the braking process, which may cause cleaving failure. In particular, in small chip size devices such as LED chips such as sapphire wafers and discrete semiconductors that are single-function semiconductor elements, the holes become fine perforations, and when external force is applied, the holes are connected, and the dicing tape is located at the hole position. May be cut and cannot be cleaved.

  Therefore, the present invention provides a method for laser processing of a wafer that prevents laser beam from being irradiated to the outside of the wafer and that can perform laser processing without the dicing tape and holding means being affected by the laser beam. It is aimed.

In the laser processing method of the present invention, the holding means is held so that one surface of the plate-like workpiece is exposed, and the laser beam irradiation means arranged opposite to the holding means and the holding means are relatively translated. While irradiating the laser beam from the laser beam irradiation means along the scheduled division line formed on the workpiece, the workpiece has substantially the same shape and the same dimension as the workpiece around the workpiece. The inner edge is formed with an outer edge that is spaced from the outer edge of the workpiece and has a height that exceeds the thickness of the workpiece, and a flange that extends inwardly from the upper end of the outer edge. The laser beam shielding member having the opening is disposed so as to surround the workpiece.

  According to the present invention, when the workpiece is held by the holding means, the laser beam shielding member having an opening having substantially the same shape and the same size as the workpiece is disposed so as to surround the workpiece. To do. Since this laser beam shielding member shields the laser beam, the laser beam is not irradiated to the region covered with the laser beam shielding member of the dicing tape or the holding means. Thus, even if the laser beam is irradiated slightly outside the edge of the workpiece due to a mechanical control error of the moving unit, the dicing tape and the holding unit are not affected by the laser beam and the hole is not opened. As a result, for example, when a braking process is performed after laser beam irradiation using a dicing tape, an external force can be reliably transmitted to the workpiece, and occurrence of cleaving defects can be suppressed.

  In the present invention, the distance of the gap formed between the inner edge portion of the opening of the laser beam shielding member and the outer edge portion of the workpiece is preferably set within 0.1 mm. By making the gap as fine as 0.1 mm, it is possible to suppress the influence on the dicing tape and the holding means irradiated with the laser beam. Accordingly, the workpiece can be irradiated with the laser beam without considering the influence of the laser beam on the dicing tape and the holding means.

Further, as described above, the laser beam shielding member of the present invention has a height that is separated from the outer edge portion of the workpiece and exceeds the thickness of the workpiece on the inner edge portion of the opening of the laser beam shielding member. an outer rim having, that have a overhanging portion extending from the upper end of the outer edge to the inside is formed. The overhanging length of the buttock may be the length that covers the outer edge of the work piece or the length that matches the outer edge of the work piece. Thus, it is reliably prevented that the laser beam hits the laser beam shading member when it comes out and hits the dicing tape or the holding means. Moreover, even if it is outside the outer edge of the workpiece, the laser beam is not affected as long as the distance is within 0.1 mm from the outer edge as described above. Thus, by making the laser beam shielding member into a bowl shape, a sufficient distance can be secured between the workpiece and the outer edge portion, so that the workpiece is prevented from coming into contact with the laser beam shielding member. Can do. As a result, the laser beam shielding member can be easily disposed around the workpiece, and damage to the workpiece due to contact between the workpiece and the laser beam shielding member can be suppressed.

  According to the present invention, since the laser beam shielding member is disposed in a state surrounding the workpiece, irradiation of the laser beam to the dicing tape and the holding means outside the workpiece can be prevented. It is possible to reliably transmit the external force to the workpiece in the cutting process and to suppress the occurrence of cleaving defects.

First, a basic form approximate to the present invention will be described with reference to the drawings.
[1] Semiconductor Wafer Reference numeral 1 in FIG. 1 indicates a disk-shaped semiconductor wafer irradiated with a laser beam by the laser processing method of the basic form. A plurality of rectangular semiconductor chips (devices) 3 are defined on the surface of the wafer 1 by grid-like division lines 2, and on the surface of the semiconductor chips 3, an unillustrated electronic device such as an IC or LSI is provided. A circuit is formed. A V-shaped notch 4 indicating the crystal orientation of the semiconductor is formed at a predetermined location on the peripheral surface of the wafer 1.

The wafer 1 is irradiated with a laser beam inside along the planned division line 2 by the laser processing method of the basic form to form a deteriorated layer, and the deteriorated layer is cut to be separated into individual semiconductor chips 3. . The laser processing method of the basic form is preferably implemented using the laser processing apparatus shown in FIG.

[2] Formation of Altered Layer by Laser Processing Apparatus The wafer 1 has a surface side on which a semiconductor chip 3 is formed on a dicing tape 62 in which a dicing frame 61 is stuck around as shown in FIG. The wafer 1 is held on a horizontal chuck table (not shown) provided in the laser processing apparatus 10 with the laser beam shielding member 70 surrounding the wafer 1. Adhering the wafer 1 and the laser beam light shielding member 70 (hereinafter, abbreviated as a light shielding member) to the dicing tape 62 relates to the present invention, and will be described in detail later.

  A laser head 21 that irradiates a laser beam vertically downward is disposed above the chuck table. The chuck table is installed on an XY movement table 13 provided on the base 12 of the laser processing apparatus 10 so as to be movable in the horizontal X-axis direction and the Y-axis direction. By moving in the Y-axis direction, a laser beam is emitted from the laser head 21 to the planned division line 2.

  The XY moving table 13 includes an X-axis base 30 provided on the base 12 so as to be movable in the X-axis direction, and a Y-axis base 40 provided on the X-axis base 30 so as to be movable in the Y-axis direction. It consists of a combination. The X-axis base 30 is slidably attached to a pair of parallel guide rails 31 that are fixed on the base 12 and extend in the X-axis direction, and an X-axis drive mechanism 34 that operates a ball screw 33 by a motor 32. Is moved in the X-axis direction. On the other hand, the Y-axis base 40 is slidably attached to a pair of parallel guide rails 41 extending in the Y-axis direction fixed on the X-axis base 30, and the Y-axis that operates the ball screw 43 by the motor 42. It is moved in the Y-axis direction by the drive mechanism 44.

  The chuck table is of a generally known vacuum chuck type that holds a workpiece (in this case, the wafer 1) by vacuum action and is rotatably supported on the Y-axis base 40, not shown. It is rotated in one direction or both directions by a rotation drive mechanism. The chuck table is moved in the X-axis direction and the Y-axis direction as the X-axis base 30 and the Y-axis base 40 move.

The wafer 1 held on the chuck table is rotated by rotating the chuck table so that each division line 2 extending in one direction is parallel to the X-axis direction and each division line 2 extending in the other direction perpendicular to the X-axis direction. Is parallel to the Y-axis direction, and this state is fixed by stopping the chuck table. While maintaining this state, the X-axis base 30 and the Y-axis base 40 of the XY moving table 13 are appropriately moved, and the laser beam emitted from the laser head 21 is projected from the surface side along the scheduled division line 2. The inside of the wafer 1 is irradiated. In this basic form, the focal position of the laser beam is set inside the wafer 1, and the altered layer is formed at the focal position.

  The laser head 21 is provided at the tip of a casing 22 that extends in the Y-axis direction toward the chuck table. The casing 22 is provided on the column 14 erected on the upper surface of the base 11 so as to be movable up and down along the vertical direction (Z-axis direction), and is driven up and down (not shown) housed in the column 14. It is moved up and down by the mechanism.

  The laser head 21 is connected to a pulse laser oscillator composed of a YAG laser oscillator or a YVO4 laser oscillator so that the laser oscillated by the laser oscillator is irradiated as a laser beam vertically downward from the laser head 21. It has become. The laser oscillated by the laser oscillator has good transparency to the inside of the wafer and forms a deteriorated layer with certainty so that it can be easily cleaved. For example, the output is 1 to 5 W, and the wavelength is the light transmission of the workpiece. It is selected according to sex.

  The irradiation position of the laser beam from the laser head 21 is controlled based on the imaging of the microscope 24 attached to one side of the casing 22 via the arm 23. The microscope 24 moves up and down together with the laser head 21 as the casing 22 moves up and down to adjust the focus. Prior to laser beam irradiation, the wafer 1 held on the chuck table is moved below the microscope 24 and a surface pattern image is taken by the microscope 24. Then, the imaged pattern image of the wafer surface is taken in by an image processing means (not shown), and the division line 2 to be cut is detected by the image processing means. Further, based on the data of the scheduled division line 2 detected by the image processing means, the movement operation of the chuck table and the XY movement table 13 and the operation of laser beam irradiation from the laser head 21 are controlled. If an infrared microscope is used as the microscope 24, the back surface side is exposed and the wafer 1 is held on the chuck table, and in this state, the inside of the wafer 1 is transmitted from the back surface of the wafer 1 and a pattern image of the surface is taken. Thus, the division line 2 can be recognized. Thereby, it is possible to irradiate the laser beam from the back side of the wafer 1.

  In the laser processing apparatus 10 described above, the laser beam is irradiated from the laser head 21 onto the planned division line 2 while moving the X-axis base 30 in the X-axis direction, thereby causing the wafer along the planned division line 2 parallel to the X-axis direction. An altered layer is formed inside. Further, by irradiating the laser beam from the laser head 21 to the planned division line 2 while moving the Y-axis base 40 in the Y-axis direction, an altered layer is formed inside the wafer along the planned division line 2 parallel to the Y-axis direction. It is formed. When irradiating the laser beam, the casing 22 is moved up and down to adjust the vertical position of the laser head 21 in order to form a deteriorated layer by aligning the focal point inside the wafer. Is set to the target height.

  As described above, the laser beam is irradiated along all the planned division lines 2 parallel to the X-axis direction and the Y-axis direction, and a deteriorated layer is formed inside the wafer. After the deteriorated layer is formed, the wafer 1 is set to an external force applying device such as a braking device via the dicing tape 62 and the dicing frame 61, and external force such as applying tension to the dicing tape 62 is applied. As a result, the division line 2 is cut and separated into individual semiconductor chips 3.

[3] Adhesion of Wafer and Light-shielding Member to Dicing Tape Before holding the wafer 1 on the laser processing apparatus 10, the wafer 1 is attached to the dicing tape 62 with a dicing frame 61 attached around as shown in FIG. Worn. Next, around the wafer 1, a ring-shaped light shielding member 70 having an opening 71 having substantially the same shape and the same size as the wafer 1 surrounds the periphery of the wafer 1 on the dicing tape 62. Affixed. When the wafer 1 and the light shielding member 70 are attached to the dicing tape 62, a gap formed between the inner edge 72 of the opening 71 of the light shielding member 70 and the outer edge 1a of the wafer 1 as shown in FIG. The distance of W2 is set within 0.1 mm. In order to achieve this, the inner diameter of the light shielding member 70 is set when the inner diameter of the light shielding member 70 is set larger than the outer diameter of the wafer 1 within a range of 0.2 mm and the light shielding member 70 is adhered to the dicing tape 62. What is necessary is just to ensure the clearance gap W2 between 72 and the outer edge part 1a of the wafer 1 over a perimeter. In this way, the wafer 1 is adhered to the dicing tape 62 and held on a horizontal chuck table provided in the laser processing apparatus 10. The width in the radial direction of the light shielding member 70 is about 3 to 5 mm. Further, the thickness of the light shielding member 70 is about 1 to 3 mm. The light shielding member 70 is required to shield the laser beam L and not melt even if the heat of the laser beam L is absorbed to some extent. From this viewpoint, aluminum or stainless steel is preferably used as the material of the light shielding member 70. Moreover, it is preferable that the surface of the light shielding member 70 is roughened in order to diffuse the irradiated laser beam when the laser beam L is irradiated.

According to the basic mode, since the light shielding member 70 is disposed so as to surround the periphery of the wafer 1, the laser beam L is not irradiated to the area covered with the light shielding member 70 of the dicing tape 62 or the chuck table. Conventionally, the laser beam L is irradiated slightly outside the outer edge portion 1a of the wafer 1 due to mechanical control errors of the X-axis drive mechanism 34 and the Y-axis drive mechanism 44, and the dicing tape 62 has a hole 63 as shown in FIG. Sometimes opened. However, in this basic form, as shown in FIG. 5, even if the laser beam L is irradiated slightly outside the outer edge portion 1a of the wafer 1, the light shielding member 70 blocks the laser beam L and the dicing tape 62 underneath it. The chuck table is not affected and the dicing tape 62 does not open. As a result, when the braking process is performed after the irradiation with the laser beam L using the dicing tape 62, an external force can be reliably transmitted to the wafer 1, and the occurrence of cleaving defects can be suppressed.

Moreover, in the said basic form, it is difficult to stick to the dicing tape 62 without a gap between the wafer 1 and the light shielding member 70. Therefore, a gap W2 is generated between the outer edge 1a of the wafer 1 and the inner edge 72 of the light shielding member 70, and there is a possibility that the laser beam is irradiated to the dicing tape 62 in the gap W2. However, by setting the distance of the gap W2 within 0.1 mm, the influence of the gap W2 on the dicing tape 62 and the chuck table can be suppressed. Conventionally, as shown in FIG. 4, a hole has been formed at a location about 0.1 mm outside (distance W <b> 1) from the outer edge 1 a of the wafer 1. Therefore, the dicing tape 62 is not affected by the laser beam L as long as the distance is within 0.1 mm from the outer edge portion 1 a of the wafer 1.

[4] Embodiment of the Present Invention Although the light shielding member 70 of the above basic form has a rectangular shape with a simple cross-sectional shape, the present invention is characterized by a bowl-shaped light shielding member as shown in FIG. The invention can achieve the same effects as the basic embodiment. Hereinafter, the hook-shaped light shielding member 73 according to an embodiment of the present invention will be described.

  An inner edge 75 of the opening 74 of the light shielding member 73 shown in FIG. 6 is separated from the outer edge 1a of the wafer 1 and has an outer edge 76 having a height exceeding the thickness of the wafer 1, and the outer edge. A flange 77 extending inward from the upper end of 76 is formed.

The light shielding member 73 has an extension length to the inside of the flange portion 77 that covers the outer edge portion 1a of the wafer 1 shown in FIG. 6A, and the outer edge portion 1a of the wafer 1 shown in FIG. There are three forms of matching lengths or lengths in which a gap W4 is formed between the front end surface 77a of the flange portion 77 and the outer edge portion 1a of the wafer 1 shown in FIG. In the case of FIG. 6A, the length W3 covering the outer edge portion 1a of the wafer 1 is set to 0.5 mm or less as the formation region of the deteriorated layer capable of separating the wafer 1 into chips in the braking process. Moreover, in the case of FIG.6 (c), the clearance gap W4 is set to the distance within 0.1 mm similarly to the said basic form.

In the case where the flange portion 77 of the light shielding member 73 has a length that covers the outer edge portion 1a of the wafer 1 or a length that matches the outer edge portion 1a of the wafer 1 as shown in FIGS. It is reliably prevented that the laser beam L hits the light shielding member 73 and hits the dicing tape 62 or the chuck table when it goes out from the outer edge portion 1a of the wafer 1. Moreover, even if there is a gap W4 between the front end surface 77a of the flange 77 and the outer edge 1a of the wafer 1 as shown in FIG. 6C, if the distance is set within 0.1 mm as in the above basic mode, Not affected by the laser beam L. Further, since the light shielding member 73 is formed in a bowl shape, a sufficient distance can be ensured between the wafer 1 and the outer edge portion 76, so that the wafer 1 can be prevented from contacting the light shielding member 73. As a result, the light shielding member 73 can be easily disposed around the wafer 1, and damage to the wafer 1 due to contact between the wafer 1 and the light shielding member 73 can be suppressed.

In the above basic form, one wafer is attached to one dicing tape. However, in the case of a relatively small wafer such as a sapphire wafer, a plurality of pieces are attached on the dicing tape 62 having the same size as the basic form. Laser processing can be performed. At this time, the light shielding member has a plurality of openings 79 (four in the drawing) as in the other embodiment shown in FIG. 7, and the wafer is disposed inside the openings 79. In the figure, a light shielding member 78 having a rectangular cross section of the opening 79 is shown.

When adhering a plurality of such small wafers to the dicing tape 62, they are arranged so that the planned dividing lines extending in two directions perpendicular to each other are along the two directions X and Y, respectively. Thereby, it is possible to irradiate a plurality of wafers with a laser beam at a time, and to irradiate each wafer in the XY directions. For this reason, the laser beam irradiation operation can be performed efficiently. Thereafter, the light shielding member 78 is attached to the dicing tape 62. At this time, the distance between the outer edge portion of the wafer and the inner edge portion 80 of the opening 79 is set to 0.1 mm or less as in the basic mode. When the wafer and the light shielding member 78 are adhered to the dicing tape, the wafer is held on the chuck table of the laser processing apparatus 10 and the laser beam is irradiated onto the division line of the wafer.

It is a perspective view of the semiconductor wafer separated into the some semiconductor chip by the basic form approximated to this invention. It is a whole perspective view of the laser processing apparatus which can implement suitably the method concerning the basic form. It is a perspective view which shows the state which affixed the wafer and the light-shielding member on the dicing tape. It is sectional drawing which shows the state which has irradiated the laser beam to the wafer by the conventional method. It is sectional drawing which shows the state which has irradiated the laser beam to the wafer by the method of the same basic form. It is sectional drawing which shows the state which has irradiated the laser beam to the wafer in one Embodiment of this invention . It is a perspective view which shows the light-shielding member of other embodiment .

1 ... wafer (workpiece)
2 ... Divided lines 21 ... Laser head (laser beam irradiation means)
70, 73, 78 ... light shielding member (laser beam light shielding member)
71, 74, 79 ... opening
76 ... Outer edge
77 ... Buttocks

Claims (2)

The laser beam is held by the holding means so that one surface of the plate-shaped workpiece is exposed, and the laser beam irradiation means and the holding means are arranged to face the holding means, and the laser light beam is relatively translated. In irradiating the laser beam along the planned division line formed on the workpiece from the irradiation means,
The workpiece has substantially the same shape and dimensions as the workpiece, and the inner edge of the workpiece is spaced from the outer edge of the workpiece and exceeds the thickness of the workpiece. A laser beam shading member having an opening in which an outer edge having a height and a flange extending inward from the upper end of the outer edge is disposed so as to surround the workpiece. A laser processing method.   The distance of the clearance gap formed between the inner edge part of the said opening part of the said laser beam light shielding member and the outer edge part of the said to-be-processed object is set to 0.1 mm or less. Laser processing method.

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