JP2012156168A - Division method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To condense a laser beam sufficiently in a region to be divided.SOLUTION: Before a reformed layer formation step is run, irregularities 101 existing on the surface of a work 1 are removed by irradiating the surface of a work 1 with a laser beam LB exhibiting absorptivity to the work 1. Since the laser beam LB is scattered by the irregularities 101 existing on the surface of a work 1 when the reformed layer formation step is run, the laser light beam LB can be condensed sufficiently in a region to be divided.

Description

  In the present invention, a modified layer is continuously formed inside a workpiece along a division planned line by irradiating a laser beam having transparency to the workpiece, and an external force is applied to the modified layer. It is related with the dividing method which divides | segments a workpiece | work along.

  In a semiconductor device manufacturing process, a plurality of regions are defined by division lines arranged in a lattice pattern on the surface of a substantially disc-shaped semiconductor wafer, and circuits such as ICs and LSIs are formed in the partitioned regions. The Then, each semiconductor chip is manufactured by dividing each region by dividing the semiconductor wafer along the planned dividing line.

  In recent years, as a method of dividing a semiconductor wafer along a division line, there is a laser processing method that uses a laser beam having transparency to a semiconductor wafer and irradiates the laser beam with a focusing point inside the region to be divided. Used (see Patent Documents 1 and 2). In this laser processing method, a semiconductor wafer is arranged along a planned division line by irradiating a laser beam in the infrared region, for example, having a light converging point from one surface side of the semiconductor wafer and having transparency to the semiconductor wafer. The semiconductor wafer is divided by continuously forming a modified layer inside the wafer and applying an external force along a planned division line whose strength is reduced by the formation of the modified layer.

JP 2005-028423 A Japanese Patent No. 3408805

  However, according to the laser processing method described above, when irregularities are formed on the surface of the semiconductor wafer by etching or grinding with a rough grindstone, the inside of the region to be divided by scattering of the laser beam on the surface of the semiconductor wafer. As a result, the semiconductor wafer may not be divided with high accuracy along the planned dividing line.

  The present invention has been made in view of the above, and an object thereof is to provide a dividing method capable of sufficiently condensing a laser beam inside a region to be divided.

  In order to solve the above-described problems and achieve the object, the dividing method according to the present invention is a method in which a condensing point is positioned inside a position along the work division planned line from the incident surface side having the unevenness of the work. A modified layer forming step of forming a modified layer by irradiating a laser beam having transparency to the workpiece, and applying an external force to the modified layer after the modified layer forming step to align the workpiece along the planned dividing line A dividing step that divides the surface by dividing the surface by irradiating the incident surface with a laser beam having an absorptivity with respect to the workpiece before the modified layer forming step. A flattening step of flattening the incident surface is included.

  The dividing method according to the present invention is characterized in that, in the above invention, the cross-sectional energy distribution of the laser beam irradiated in the planarization step is constant in a direction orthogonal to the processing progress direction.

  According to the dividing method according to the present invention, the laser beam can be sufficiently condensed inside the region to be divided.

FIG. 1 is a schematic perspective view showing a configuration of a laser processing apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of the laser irradiation mechanism shown in FIG. FIG. 3 is a cross-sectional process diagram illustrating a flow of a dividing process according to an embodiment of the present invention. FIG. 4 is a diagram showing a cross-sectional energy distribution of a laser beam in a direction orthogonal to the processing progress direction.

  Hereinafter, a configuration of a laser processing apparatus according to an embodiment of the present invention and a workpiece dividing method using the laser processing apparatus will be described with reference to the drawings.

[Configuration of laser processing equipment]
First, with reference to FIG. 1, the structure of the laser processing apparatus which is one Embodiment of this invention is demonstrated.

  FIG. 1 is a schematic perspective view showing a configuration of a laser processing apparatus according to an embodiment of the present invention. As shown in FIG. 1, a laser processing apparatus according to an embodiment of the present invention includes a holding mechanism 2 for holding a workpiece 1, an X direction that is a machining feed direction, and a Y that is an index feed direction. XY drive mechanism 4 for moving in the direction, laser irradiation mechanism 5 for irradiating the workpiece 1 held by the holding mechanism 2 with a laser beam, and the operation of each part constituting the laser processing apparatus to control the laser processing apparatus And a control device 6 for overall control.

The workpiece 1 is configured by a substantially disk-shaped plate-like object. The surface side of the workpiece 1 is partitioned in a grid pattern by dividing lines 11 orthogonal to each other, and devices are formed in the partitioned areas. The workpiece 1 is not particularly limited. For example, semiconductor wafers such as silicon wafers, GaAs wafers, and SiC wafers, adhesive members such as DAF (Die Attach Film) provided on the back side of the wafer for chip mounting, and semiconductor product packages. Examples thereof include inorganic material substrates such as ceramics, glass and sapphire (Al ₂ O ₃ ), various electronic parts such as liquid crystal display drivers, and various processing materials that require micron-order processing position accuracy.

  The holding mechanism 2 mainly includes a chuck table having a size corresponding to the workpiece 1, and sucks and holds the workpiece 1 placed on the holding surface 21 which is the upper surface by a suction unit (not shown). The workpiece 1 is carried into the holding mechanism 2 by, for example, a surface side up by a conveying means (not shown), and is sucked and held on the holding surface 21. In this way, the holding mechanism 2 that holds the workpiece 1 on the holding surface 21 is provided at the upper end of the cylindrical member 22, and the Z direction (vertical direction) is axially centered by a pulse motor (not shown) disposed in the cylindrical member 22. It is configured to be freely rotatable.

  The XY drive mechanism 4 includes two stages of sliding blocks 41 and 42. The holding mechanism 2 is mounted on the two-stage sliding blocks 41 and 42 via the cylindrical member 22. The XY drive mechanism 4 includes a processing feed mechanism 43 configured by a ball screw 431, a pulse motor 432, and the like, and the sliding block 41 can freely move in the X direction by the processing feed mechanism 43. Then, the processing feed mechanism 43 is driven to move the sliding block 41, and the holding mechanism 2 moves in the X direction with respect to the laser irradiation mechanism 5, whereby the holding mechanism 2 and the laser irradiation mechanism mounted on the sliding block 41 are moved. 5 are relatively moved along the X direction.

  The XY drive mechanism 4 includes an index feeding mechanism 44 configured by a ball screw 441, a pulse motor 442, and the like, and the sliding block 42 can be freely moved in the Y direction by the index feeding mechanism 44. Then, the indexing feed mechanism 44 is driven to move the sliding block 42, and the holding mechanism 2 moves in the Y direction with respect to the laser irradiation mechanism 5, whereby the holding mechanism 2 mounted on the sliding block 42 and the laser irradiation mechanism. 5 are relatively moved along the Y direction.

  In the present embodiment, the holding mechanism 2 and the laser irradiation mechanism 5 are relatively moved by moving the holding mechanism 2 in the X direction and the Y direction. On the other hand, the laser irradiation mechanism 5 may be moved in the X direction and the Y direction without moving the holding mechanism 2. In addition, both the holding mechanism 2 and the laser irradiation mechanism 5 are moved in the reverse direction along the X direction, and both the holding mechanism 2 and the laser irradiation mechanism 5 are moved in the reverse direction along the Y direction so that they are relatively moved. A configuration may be adopted.

  A processing feed amount detecting means 45 for detecting the processing feed amount of the holding mechanism 2 is attached to the processing feed mechanism 43. The processing feed amount detection means 45 includes a linear scale arranged along the X direction, a reading head arranged on the sliding block 41 and reading the linear scale by moving together with the sliding block 41, and the like. Similarly, an index feed amount detection means 46 for detecting the index feed amount of the holding mechanism 2 is attached to the index feed mechanism 44. The index feed amount detection means 46 is configured by a linear scale disposed along the Y direction, a reading head disposed on the sliding block 42 and reading the linear scale by moving together with the sliding block 42, and the like.

  The laser irradiation mechanism 5 is for irradiating the workpiece 1 sucked and held on the holding surface 21 with a laser beam and performing laser processing along the position where the workpiece 1 is to be processed. The control device 6 is constituted by a microcomputer having a built-in memory for holding various data necessary for the operation of the laser processing apparatus.

[Configuration of laser irradiation mechanism]
Next, the configuration of the laser irradiation mechanism 5 will be described with reference to FIG.

  FIG. 2 is a block diagram showing the configuration of the laser irradiation mechanism shown in FIG. As shown in FIG. 2, the laser irradiation mechanism 5 includes an oscillator 51, an intensity adjustment unit (attenuator) 52, an energy distribution adjustment unit 53, a mirror element 54, and a condenser lens 55. The oscillator 51 is for oscillating a laser beam having a predetermined wavelength, and includes, for example, a laser beam oscillator composed of a YAG laser oscillator, a YVO4 laser oscillator, or the like, an oscillator that oscillates a laser beam in the infrared wavelength region, and the like. The intensity adjustment unit 52 includes a half-wave plate 521, a motor 522, a polarization beam splitter 523, and an absorber 524.

  The half-wave plate 521 is disposed at the subsequent stage of the oscillator 51 so as to be rotatable by the motor 522. The half-wave plate 521 changes the linear polarization direction of the laser beam LB oscillated by the oscillator 51 according to the rotation angle. The polarization beam splitter 523 transmits a laser beam having a predetermined linear polarization direction out of the laser beams that have passed through the half-wave plate 521 toward the polarization direction setting unit 53 and has a linear polarization direction other than the predetermined linear polarization direction. Is branched to the absorber 524 side. The absorber 524 is for absorbing the laser beam branched by the polarization beam splitter 523, and may be made of, for example, a matte black metal in order to absorb the laser beam satisfactorily.

  The energy distribution adjusting unit 53 is a generally known homogenizer using a diffractive optical element or the like, and a cross-sectional energy distribution in a direction orthogonal to the processing progress direction of a laser beam whose cross-sectional energy distribution is a Gaussian distribution in a direction orthogonal to the processing progress direction. Is converted into a laser beam that is constant within the processing range. The mirror element 54 is for reflecting the laser beam that has passed through the half-wave plate 531 toward the condenser lens 55 side. The condensing lens 55 is disposed so as to face the work 1, positions a condensing point inside the work 1, and condenses the laser beam reflected by the mirror element 54.

[Division method]
Next, with reference to FIG. 3 and FIG. 4, a work dividing method using the laser processing apparatus will be described. FIG. 3 is a cross-sectional process diagram illustrating a flow of a dividing process according to an embodiment of the present invention. FIG. 4 is a diagram showing a cross-sectional energy distribution of a laser beam in a direction orthogonal to the processing progress direction.

  When the workpiece 1 is divided using the laser processing apparatus, first, as shown in FIG. 3A, the workpiece 1 is moved along the surface of the workpiece 1 that is the incident surface of the laser beam LB (in the direction of arrow A1). On the other hand, by irradiating the laser beam LB having the absorptivity, the unevenness 101 existing on the surface of the workpiece 1 is removed, and the surface of the workpiece 1 is planarized (a planarization step). When the workpiece 1 is a silicon wafer, a laser beam having a wavelength of 355 [nm] can be used as a laser beam that absorbs the workpiece 1.

  In order to uniformly flatten the surface of the work 1, the cross-sectional energy distribution on the surface of the work 1 of the laser beam irradiated in the flattening step is in a direction perpendicular to the processing progress direction as indicated by a solid line R1 in FIG. Although it is desirable to be constant within the processing range (flattening range), a Gaussian distribution may be formed in a direction orthogonal to the processing progress direction as indicated by a one-dot chain line R2 in FIG.

  According to the study of the inventors of the present invention, when the surface of a silicon wafer having an arithmetic average roughness Ra of about 0.60 [um] is flattened by dry etching, it is orthogonal to the processing progress direction. A laser beam having a wavelength of 355 [nm], a repetition frequency of 80 [kHz], an output of 0.6 [W], and a feed rate of 100 [mm / s] in which the cross-sectional energy distribution is constant in the processing range (flattening range) in the direction. It was found that the surface of a silicon wafer having a width of about 100 [um] can be flattened (within Ra = 0.05 [um]) by irradiating with one pass. However, the repetition frequency is within the range of 1 to 1000 [kHz], the output is within the range of 0.1 to 4 [W], and the feed rate is within the range of 20 to 300 [mm / s], and the conditions are appropriately combined. It is considered that the surface of a silicon wafer having a width of about 15 to 150 [um] can be planarized by one-pass irradiation.

  When the flattening step shown in FIG. 3A is completed, the condensing point is positioned inside the position along the planned division line of the work 1 from the surface side of the work 1 as shown in FIG. 3B. Then, the modified layer 102 is formed by irradiating the workpiece 1 with a laser beam LB having transparency (along the arrow A2) along the planned division line (modified layer forming step). The modified layer means a region where the density, refractive index, mechanical strength and other physical characteristics are different from those of the surroundings, and includes a melt treatment region, a crack region, a dielectric breakdown region, Examples include a refractive index changing region and a region in which these regions are mixed.

  When the modified layer forming step shown in FIG. 3B is completed, finally, as shown in FIG. 3C, the dicing tape 100 affixed to the back side of the work 1 is orthogonal to the planned dividing line ( By expanding in the direction of arrow A3), an external force is applied to the modified layer 102 to divide the workpiece 1 into individual devices D along the planned division line 11. Thereby, a series of division | segmentation processes are complete | finished.

  As is clear from the above description, according to the dividing step which is an embodiment of the present invention, the laser beam LB having an absorptivity with respect to the workpiece 1 on the surface of the workpiece 1 before executing the modified layer forming step. To remove the unevenness 101 existing on the surface of the workpiece 1. As a result, when the modified layer forming step is performed, the laser beam LB is scattered by the unevenness 101 existing on the surface of the workpiece 1, so that the laser beam LB cannot be sufficiently condensed inside the region to be divided. Can be suppressed.

  The embodiment to which the invention made by the present inventors has been described has been described above, but the present invention is not limited by the description and drawings that form part of the disclosure of the present invention according to the above embodiment. That is, other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above-described embodiments are all included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Work 2 Holding mechanism 4 XY drive mechanism 5 Laser irradiation mechanism 6 Control apparatus 11 Dividing schedule line 21 Holding surface 22 Cylindrical member 41, 42 Sliding block 43 Processing feed mechanism 44 Indexing feeding mechanism 45 Processing feeding amount detection means 46 Indexing feeding amount detection Means 51 Oscillator 52 Strength adjustment section (attenuator)
53 Polarization direction setting unit 54 Mirror element 55 Condensing lens 100 Dicing tape 101 Concavity and convexity 102 Modified layer 431, 441 Ball screw 432, 442 Pulse motor 521, 531 1/2 wavelength plate 522, 532 Motor 523 Polarizing beam splitter 524 Absorber D device LB laser beam

Claims (2)

Forming a modified layer by positioning a condensing point from the incident surface side of the workpiece with irregularities on the inside of the position along the planned dividing line of the workpiece and irradiating the workpiece with a laser beam having transparency Process,
A dividing step of applying an external force to the modified layer after the modified layer forming step to divide the workpiece along the planned dividing line,
Before the modified layer forming step, the method includes a flattening step of flattening the incident surface by irradiating the incident surface with a laser beam having absorptivity with respect to a workpiece to remove the unevenness. How to split.   2. The dividing method according to claim 1, wherein the cross-sectional energy distribution of the laser beam irradiated in the flattening step is constant in a direction orthogonal to the processing progress direction.

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