JP2011091157A - Laser marking method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser marking method that attains traceability of chip level without producing debris. <P>SOLUTION: In the laser marking method, a reformed region P is formed for each chip C by irradiating the inside of a wafer W with laser light L to mark a product information part 15 associated with the chip C for the each chip C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a laser marking method for marking product information on a chip on which a semiconductor device is formed.

  Wafers on which devices such as semiconductor devices and electronic parts are formed undergo various processes such as grinding and polishing of the front and back surfaces, device formation, and device inspection, and then cut along individual scheduled lines. It is divided into. In the division of a wafer, a dicing apparatus using a blade that is rotated at high speed by a spindle is conventionally used. In recent years, instead of the conventional blade-type dicing device, the laser light emitted from the laser light source is condensed inside the wafer, and the modified region by multiphoton absorption is continuously formed inside the wafer to cleave the wafer. A dicing apparatus (hereinafter referred to as a laser dicing apparatus) is used.

  The device divided in this way is marked with product information such as the function, manufacturing number, and lot number of each device on the back using laser light, and the product information is managed for each chip (for example, patents). Reference 1).

JP 2008-178886 A

  However, in the marking method described in the cited document 1, because the engraving on the back surface using laser ablation, the wafer material evaporated and scattered by laser processing is inevitably generated on the wafer surface, and debris is hardened and cannot be cleaned. . Therefore, problems such as a decrease in adhesion at the time of attaching DAF to the back surface of the wafer occur. In order to prevent this, it has become necessary to apply a debris adhesion prevention coating to the wafer and to add a cleaning process after marking.

  Moreover, in the marking method described in the cited document 1, since the marking is directly engraved on the back surface, if marking is performed before the wafer is thinned by back grinding, the engraved information is lost, and marking is performed after back grinding. In this case, it is necessary to transport the thinned wafer to a marking apparatus, which causes damage. Furthermore, after the chip is packaged, it is difficult to read because the inscription is hidden.

  The present invention has been made in view of such a situation, and provides a laser marking method capable of marking before and after back grinding without generating debris and enabling traceability at the chip level. It is aimed.

In order to achieve the above object, the present invention forms a modified region by irradiating a laser beam for each of the chips inside a wafer on which a large number of chips on which semiconductor devices are formed is formed. It is characterized by marking product information about the chip.
According to the present invention, laser light emitted from a laser light source is condensed inside a wafer on which many chips on which semiconductor devices are formed are formed. A modified region by multiphoton absorption is formed inside the wafer by the condensed laser light. A plurality of laser beams are condensed at different positions, and a plurality of modified regions are formed inside the wafer, whereby product information relating to the chips is marked for each chip.

  Thereby, since the wafer material is not vaporized and scattered on the wafer surface, debris does not occur. Further, marking can be performed before or after back grinding, and the thinned wafer is not conveyed many times, and the marking does not disappear even if back grinding is performed after marking. Furthermore, it is possible to read even after packaging.

  Further, the present invention is characterized in that the product information is represented by a character string, a barcode, or a two-dimensional barcode.

  According to the present invention, the product information marked by the modified region formed for each chip inside the wafer is in the form of a character string, a barcode, or a two-dimensional barcode. As a result, product information can be easily read, and traceability at the chip level is possible.

  As described above, according to the laser marking method of the present invention, the product information is marked by forming a modified region for each chip inside the wafer by laser light, so that debris is not generated and before and after back grinding. Marking is possible, enabling traceability at the chip level.

Perspective view of laser processing equipment Perspective view showing the configuration of the laser head Cross-sectional view showing the state of laser processing Plan view showing the marking state The perspective view of the laser processing apparatus by which the wafer by another embodiment was mounted Cross section of marked wafer Plan view showing the inside of a marked wafer

  Hereinafter, preferred embodiments of a laser marking method according to the present invention will be described in detail with reference to the accompanying drawings. First, the laser processing apparatus used for the laser marking method according to the present invention will be described. FIG. 1 is a perspective view of a laser processing apparatus, FIG. 2 is a perspective view showing a configuration of a laser head, and FIG. 3 is a cross-sectional view showing a state of laser processing.

  As shown in FIG. 1, the laser processing apparatus 1 is provided with a wafer table 3 which is rotated in the θ direction by a moving shaft (not shown) on an X moving shaft 2 as moving means. A wafer W on which product information marking is performed is placed on the wafer table 3. A large number of chips C on which devices such as semiconductor devices and electronic components are formed are formed on the wafer W.

  A laser head 5 is provided on a Y movement axis 4 as movement means provided so as to be orthogonal to the X movement axis 2 at the upper part of the wafer table 3. The laser head 5 is attached to the Z moving shaft 6 and moved together with the image pickup means 7 in the vertical direction.

  As shown in FIG. 2, the laser head 5 includes a laser oscillator 8, a collimating lens 9, mirrors 10, 10, a first rotating mirror 12, a second rotating mirror 13, an f-θ lens 14, and the like.

  The first rotating mirror 12 and the second rotating mirror 13 are respectively arranged along two orthogonal axes (for example, X and Y axis directions), and a galvanometer mirror having a driving unit so that the mirror rotates around the axis. A so-called mechanism is provided.

  The laser light L oscillated from the laser oscillator 8 is converted into a parallel light beam in the horizontal direction by the collimator lens 9, then the traveling direction is changed by the mirrors 10 and 10, and the rotation angle between the first rotating mirror 12 and the second rotating mirror 13. It is possible to swing in two axial directions by changing.

  The f-θ lens 14 changes the direction so that the traveling direction of the laser light L swayed in the two axial directions by the first rotating mirror 12 and the second rotating mirror 13 is perpendicular to the two axes. . The laser beam L whose direction has been changed by the f-θ lens 14 is collected by a condensation lens (not shown) and is incident on the wafer W.

  The laser beam L incident on the wafer W is condensed inside the wafer W, and the energy is concentrated at the condensing point as shown in FIG. 3A, and a crack region and a melting region due to multiphoton absorption near the condensing point. Then, a modified region P such as a refractive index changing region is formed.

  As the laser light L, for example, a laser light capable of realizing 1.0 × 10 7 W / cm 2 or more which is an energy density necessary for forming the modified region P is used.

  As shown in FIG. 3B, a plurality of modified regions P are formed by focusing the laser beam L at a desired depth and position inside the workpiece W by moving the focusing point of the laser beam L using a galvano mirror mechanism. . As shown in FIG. 4, a plurality of modified regions P are formed so as to have a shape such as a character string, a barcode, or a two-dimensional barcode, and a product information section related to the chip C for each of the formed chips C. 15 is marked inside the workpiece W.

  In the formation of the modified region P, the X movement axis 2, the Y movement axis 4, and the Y movement axis 4 shown in FIG. 1 are used without using the galvanometer mirror mechanism including the first rotation mirror 12, the second rotation mirror 13, and the f-θ lens 14. The laser beam L and the wafer W are relatively moved in the X, Y, Z, and θ directions by the Z moving shaft 6 and the θ rotation moving shaft, and the laser beam L is condensed at an arbitrary depth and position. Also good.

  Alternatively, a plurality of modified regions P may be formed by irradiating a plurality of laser beams L at the same time or irradiating a plurality of laser beams L having different wavelengths, pulse widths, and energies with a time difference.

  Next, the laser marking method according to the present invention will be described. In the laser marking method, a wafer W on which a large number of chips C on which devices such as semiconductor devices and electronic components are formed is first placed on the wafer table 3.

  As shown in FIG. 1, a protection sheet (not shown) is attached to the front surface of the wafer W, and the wafer W is suction-mounted on the wafer table 3 with the back surface facing the laser head 5. The wafer W may be either thinned after the back grinding process or unthinned before the back grinding process, and the laser light L is incident from the back side.

  In addition, as shown in FIG. 5, the wafer W sucked and mounted on the wafer table 3 is a wafer before or after the dicing process that is mounted on the frame F via the tape T attached to the back surface side. W may be used, and laser light L is incident on such a wafer W from the surface side.

  After the wafer W is placed on the wafer table 3, the alignment pattern of each chip C formed on the surface of the wafer W is imaged by the imaging means 7, and alignment is performed. As shown in FIG. 1, when imaging is performed by the imaging unit 7 from the back side of the wafer W and alignment is performed by the imaging unit 7 by irradiating light having a wavelength that passes through the wafer W in order to capture an alignment pattern on the front surface. Image. Specifically, if the wafer W is a silicon wafer, imaging is performed by irradiating light having a wavelength of 310 nm or more (less than 4 eV), more preferably, a wavelength of 1 μm or more (less than 1.2 eV).

  After the alignment of the wafer W is completed, the modified region P is formed by irradiating the wafer W with the laser light L, and the product information portion 15 for each chip is marked. In the formation of the modified region P, the galvanometer mirror mechanism including the first rotating mirror 12, the second rotating mirror 13, and the f-θ lens 14 shown in FIG. 2, or the X moving axis 2, the Y moving axis 4 shown in FIG. The modified region P is formed by converging the laser light L at a desired depth and position inside the wafer W by the moving mechanism using the Z moving shaft 6 and the θ rotational moving shaft.

  As shown in FIG. 4, a plurality of modified regions P are formed so as to have a shape such as a character string, a barcode, or a two-dimensional barcode, and for each chip C formed by these, product information about the chip C is formed. The part 15 is marked inside the chip C.

  Thereby, processing by the laser beam L is not performed on the front surface or the back surface of the wafer, and the material on the front surface or the back surface of the wafer is not vaporized and scattered, so that debris does not occur and adhere to the front or back surface of the wafer. In addition, it is possible to mark before back grinding, after back grinding and after dicing, and the thinned wafer will not be transported many times, and the marking will not disappear even if back grinding after marking. . Furthermore, product information can be read even after packaging, and traceability at the chip level becomes possible.

  In addition, the position where the product information part 15 is formed by the modified region P may be an arbitrary position for each chip C. Further, the depth at which the product information section 15 is formed may be an arbitrary position, and is preferably formed at a depth in the vicinity of the device D as shown in FIG. By forming the product information part 15 in the vicinity of the device D, an effect of gettering for capturing transition metal contamination is obtained, and copper (Cu), iron (Fe), nickel (Ni) adhering to the back surface of the wafer are obtained. , Heavy metal impurities such as chromium (Cr) are prevented from entering the wafer.

  Next, an embodiment of the laser marking method according to the present invention will be described. The wafer W shown in FIG. 7 has a large number of chips C on which devices such as semiconductor devices and electronic components are formed, and the chip C in the wafer W is used as the product information section 15 for each chip C by the laser marking method according to the present invention. The matrix number indicating the position of is marked.

  The wafer W is divided into individual chips through various processes such as a back grinding process and a dicing process, and then packaged to become a semiconductor product or an electronic component. At this time, the product information part 15 of defective products generated after commercialization is read and totaled for each matrix number.

  For example, when the chip C1 which is a defective product is generated along the grinding mark GM, it is understood that the defect is caused by the grinding process, and the defective product is reduced by reducing the grinding mark GM. It becomes possible. Thus, according to the laser marking method of the present invention, traceability at the chip level becomes possible.

  As described above, according to the laser marking method according to the present invention, product information is marked for each chip inside the wafer by laser light, so that the wafer material is not vaporized and scattered, and debris does not occur. Marking can be performed before or after back grinding, and the thinned wafer is not transported many times. Even if back grinding is performed after marking, the marking does not disappear. Furthermore, it is possible to read even after packaging, and traceability at the chip level is possible.

  DESCRIPTION OF SYMBOLS 1 ... Processing part, 2 ... X movement axis, 3 ... Wafer table, 4 ... Y movement axis, 5 ... Laser head, 6 ... Z movement axis, 7 ... Imaging means, 8 ... Laser oscillator, 9 ... Collimating lens, 10 ... Mirror, 12 ... first rotating mirror, 13 ... second rotating mirror, 14 ... f-theta lens, 15 ... product information section, C, C1 ... chip, D ... device, F ... frame, G ... grinding mark, L ... Laser beam, P ... Modified area, T ... Tape, W ... Wafer

Claims (2)

  Irradiating a laser beam for each chip inside a wafer on which a large number of chips each having a semiconductor device formed are formed to form a modified region, thereby marking product information about the chip for each chip. Laser marking method.   The laser marking method according to claim 1, wherein the product information is represented by a character string, a barcode, or a two-dimensional barcode.

Images