JP5213112B2 - Laser processing method and laser processing apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for processing a workpiece such as a semiconductor wafer using a laser beam. More specifically, the present invention relates to a technique for forming a modified region on a workpiece.

  In recent years, optical devices such as light emitting diodes have been widely used in electronic devices and the like. In the manufacturing process of this optical device, a light emitting element made of a nitride compound semiconductor layer such as gallium nitride is formed in a matrix on a substrate made of sapphire, and then the substrate on which the plurality of elements are formed. Each element is separated into chips by cutting in a lattice shape along a predetermined street (division planned line).

  For such cutting of a wafer or a substrate, a cutting apparatus that rotates a cutting blade at a high speed to cut a workpiece is usually used. However, a sapphire substrate used in an optical device has a high Mohs hardness. Since it is a difficult-to-cut material and the chip of the optical device is as small as 1 mm square or less, defects are likely to occur. For this reason, when the optical device wafer is cut, the processing is generally performed at a lower speed than in the case of cutting a semiconductor wafer using a silicon substrate, and there is a problem that productivity is low.

  Therefore, conventionally, a method of cutting a sapphire substrate using laser light has been proposed (for example, see Patent Document 1). For example, in the method of manufacturing a semiconductor element described in Patent Document 1, a pulsed laser is focused along a predetermined division surface inside a sapphire substrate to form a modified (deformed) region in a broken line shape, and then an external force Is added to divide the substrate on the plane to be divided.

  In addition, a method of forming a modified region in a substrate with a laser beam and cutting it has been studied for application to various materials other than a sapphire substrate. For example, there is a method for cutting a quartz substrate using this method. It has been proposed (see Patent Document 2). Furthermore, the present applicant has proposed a method for dividing a silicon wafer having a low dielectric constant insulator film formed on its surface using laser light (see, for example, Patent Document 3).

  On the other hand, in a method of forming and cutting a modified region in a workpiece such as a substrate, it is necessary to make the machining position from the workpiece surface constant in order to perform high quality machining. Therefore, conventionally, when machining a workpiece with irregularities on the main surface, measure the flatness of all parts to be machined in advance using, for example, a flatness measuring instrument equipped with a projector and a reflected light receiver. And the method of processing based on the measurement result is proposed (for example, refer to patent documents 4).

  Conventionally, the displacement of the laser beam irradiation surface such as waviness or unevenness and the thickness of the workpiece are measured, and the displacement of the front and back surfaces is obtained from the result. In the case where the focal point position of the laser beam is adjusted based on the above and the modified region on the back side is formed, a processing method for adjusting the focal point position of the laser beam based on the displacement of the back side has also been proposed ( (See Patent Document 5).

  Furthermore, even when there is a region with low reflectivity with respect to the measurement laser beam, the measurement laser beam is irradiated so that the focusing point of the processing laser beam can accurately follow the laser beam irradiation surface of the workpiece. A processing method has also been proposed in which astigmatism is added to the reflected light obtained in this way, and the focal position of the processing laser is adjusted based on a value fed back according to the amount of the reflected light (see Patent Document 6).

JP 2006-245062 A JP 2007-130768 A JP 2007-173475 A JP 2005-193286 A JP 2008-12542 A JP 2008-87053 A

  However, the processing methods described in Patent Documents 4 to 6 described above have a problem that it takes time to measure the flatness because it is necessary to scan all streets with a measuring laser beam or the like.

  In view of the above, a main object of the present invention is to provide a laser processing method and a laser processing apparatus capable of efficiently determining the focal position of the processing laser beam.

  The laser processing method according to the present invention is a laser processing method for forming a modified region in a division line of a work by irradiating the work with a laser beam having a wavelength that passes through the work with a converging point inside the work. Of the plurality of planned division lines in the workpiece, the step of measuring the surface displacement of one planned division line, and the actual measurement value of the surface displacement of the one planned division line, Next, the step of predicting the surface displacement of another division line to be processed and the laser beam is irradiated onto the workpiece while adjusting the condensing point position of the laser beam based on the measured or predicted surface displacement. Process.

  In the present invention, in order to predict the surface displacement of other scheduled division lines to be processed next to this one scheduled division line from the actual measurement value of the surface displacement of one scheduled division line, the surfaces of all the planned division lines There is no need to measure the displacement. For this reason, compared with the conventional processing method, the time required for the measurement of the surface displacement can be greatly shortened.

  In this laser processing method, for example, when the length of one division planned line and the length of another division planned line are different from each other, such as a semiconductor wafer, the length of the one division planned line and the other division Based on the ratio with the length of the planned line, the surface displacement of the other divided planned line can be predicted.

  In addition, after the modified region is formed in the one division line, the surface displacement of the other division line can be predicted.

  Furthermore, the surface displacement of a plurality of division lines to be processed thereafter may be predicted from the actual measurement value of the surface displacement of the one division line.

  On the other hand, the laser processing apparatus according to the present invention is a laser processing apparatus that forms a modified region in a work division planned line, and measures the surface displacement of the work holding means and the work division planned line. The surface displacement detection means that performs the analysis, and the surface displacement of one of the planned division lines measured by the surface displacement detection means predicts the surface displacement of another planned division line that is processed after the planned division line And laser light irradiation means for irradiating the workpiece with laser light, the relative movement of the holding means and the laser light irradiation means, and the laser based on the measured or predicted surface displacement While adjusting the light condensing point position, the inside of the work is irradiated with laser light having a wavelength that passes through the work.

  In the present invention, there is provided analysis means for predicting the surface displacement of another scheduled division line to be processed after the one scheduled division line from the surface displacement of the one scheduled division line measured by the surface displacement detecting means. Therefore, it is not necessary to actually measure all the division lines in the workpiece by the surface displacement detection means. As a result, the time required to measure the surface displacement of the planned division line is shortened, so that the focal position of the processing laser beam can be determined in a short time.

  Further, the analyzing means can predict the surface displacement of the other scheduled division line based on the ratio of the length of the one scheduled division line and the length of the other scheduled division line.

  Furthermore, the analysis means may predict the surface displacement of a plurality of division lines to be processed thereafter from the actual measurement value of the surface displacement of the one division line.

  According to the present invention, since the surface displacement of another division line to be processed next is predicted from the actually measured value of one division line, the time required for measuring the surface displacement is shortened, and the laser beam for processing is efficiently obtained. The focal position can be determined.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. In addition, this invention is not limited to embodiment shown below. FIG. 1 is a diagram showing a configuration of a laser processing apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view showing a workpiece to be processed, and FIG. 3 is a diagram schematically showing the surface displacement of the workpiece.

  As shown in FIG. 1, the laser processing apparatus 1 of the present embodiment includes a holding unit 2 that holds a workpiece 10, a laser beam irradiation unit 3 that irradiates a predetermined position of the workpiece 10 with a laser beam, and a surface displacement of the workpiece 10. From the surface displacement detection means 4 for measuring the surface displacement of the one division planned line measured by the surface displacement detection means 4, the surface displacement of the other division lines to be processed after this one division planned line is calculated. Analyzing means 51 for prediction is provided.

  The holding means 2 in the laser processing apparatus 1 of this embodiment is, for example, a chuck table that holds a workpiece by suction using negative pressure, and can be moved in the x direction and the y direction perpendicular to the x direction by a feeding means. It has become. Specifically, a ball screw 23a is arranged between a pair of guide rails 22a and 22b arranged parallel to each other on the base 21, and a motor 23b is attached to one end of the ball screw 23a. The other end is rotatably supported by the bearing block 23c.

  A sliding block 24 is placed on the guide rails 22a and 22b and the ball screw 23a. On the sliding block 24, a pair of guide rails 25a and 25b and a ball screw 26a are parallel to each other. Has been placed. The ball screw 26a also has a motor 26b attached to one end, and the other end is rotatably supported by the bearing block 26c. Further, a sliding block 27 is placed on the guide rails 25 a and 25 b and the ball screw 26 a, and the holding means 2 is installed on the sliding block 27.

  In the feeding means constituted by these members, when the ball screw 23a is driven by the motor 23b, the sliding block 24 is guided and moved by the guide rails 22a and 22b, whereby the holding means 2 is moved in the x direction. Moving. On the other hand, when the ball screw 26a is driven by the motor 26b, the sliding block 27 is guided and moved by the guide rails 25a and 25b, thereby moving the holding means 2 in the y direction.

  Further, the laser beam irradiation means 3 in the laser processing apparatus 1 of the present embodiment is disposed above the holding means 2, and for example, a laser beam having a wavelength that passes through the workpiece 10 such as a YAG laser oscillator or a YVO laser oscillator. And an optical component such as a mirror and a condenser lens for irradiating the workpiece 10 with the oscillated laser light.

  Further, the configuration and method of the surface displacement detection means 4 are not particularly limited as long as the surface displacement indicating surface waviness or unevenness of the workpiece 10 can be detected. For example, a laser is disposed above the holding means 2. A configuration in which a laser beam irradiation unit including an oscillator and a laser beam detection unit including a sensor are installed, and a laser beam having a wavelength reflected by the surface of the workpiece 10 is irradiated to the workpiece 10 and the reflected light is detected. It can be. In this case, the amount of reflected light is measured in the laser light detection unit, and the change in the distance from the surface of the workpiece 10 to the laser light detection unit, that is, the surface displacement of the workpiece 10 can be obtained from the change in the value.

  The analysis means 51 in the laser processing apparatus 1 of the present embodiment includes an input interface 52, a read only memory (ROM) 53 that stores a control program, and a random access memory (ROM) that stores measurement and prediction results of surface displacement. Along with a storage means 54 comprising a RAM), a counter 55, an output interface 56, etc., it is provided in the control section 5 and connected to the surface displacement detection means 4. In addition, this control part 5 can be comprised by a computer, for example.

  The analysis means 51 receives the surface displacement data of one division planned line measured by the surface displacement detection means 4 and, based on the value, one or a plurality of division schedules to be processed after the one division planned line. Predict line surface displacement. As a method for predicting the surface displacement, for example, an actual measurement value of the surface displacement in one division planned line is based on a ratio between the one division planned line length and the length of another division line to be processed thereafter. A method of enlarging or reducing can be applied. Note that the scheduled division line predicted by the analyzing unit 51 is not limited to the planned division line to be processed next to the actually measured one scheduled division line, but a plurality of divisions to be processed after the one scheduled division line. The surface displacement can be predicted in the same way for the planned line.

  Examples of the workpiece 10 to be processed by the laser processing apparatus 1 described above include various types of semiconductor wafers, adhesive tapes such as DAF (Die Attach Film), inorganic materials such as glass, silicon and sapphire, metal materials, and plastics. Examples include substrates, semiconductor product packages, and various processing materials that require micron-order accuracy. As shown in FIG. 2, these workpieces 10 are supported by the opening of the ring frame 11 via the adhesive tape 12 and placed on the holding means 2 in this state.

  Next, the operation of the laser processing apparatus 1 according to the present embodiment, that is, a method for processing the workpiece 10 using the laser processing apparatus 1 will be described. In the laser processing method of this embodiment, first, the workpiece 10 supported by the ring frame 11 is placed on the holding means 2 with the processing surface facing up. Next, the surface displacement of the one scheduled division line is measured by the surface displacement detection means 4. For example, when the workpiece 10 is the semiconductor wafer shown in FIG. 2, the measurement laser beam having a reflectivity with respect to the workpiece 10, for example, a wavelength of 635 nm is irradiated along the division line 10a, and the amount of the reflected light is irradiated. Measure changes.

  This measurement result is input to the analysis means 51 provided in the control unit 5, and the analysis means 51 calculates the surface displacement of the planned division line 10 a. Further, the analysis means 51 obtains the surface displacement of the planned division line 10b based on the surface displacement of the planned division line 10a. Specifically, as shown in FIG. 3, the measured values of the surface displacement of the planned division line 10a are proportionally distributed based on the ratio of the length of the planned division line 10a to the length of the planned division line 10b.

At this time, when the planned division line 10b is longer than the planned division line 10a, the measured value of the surface displacement is expanded by proportional distribution. For example, when five pieces of measurement data are expanded to nine pieces, new values (a ₁₂ , a ₂₃ , a, respectively) are measured between the actually measured values (a ₁ , a ₂ , a ₃ , a ₄ , a ₅ ). ₃₄ , a ₄₅ ) are complemented to obtain (a ₁ , a ₁₂ , a ₂ , a ₂₃ , a ₃ , a ₃₄ , a ₄ , a ₄₅ , a ₅ ). The complementary values a ₁₂ , a ₂₃ , a ₃₄ , and a ₄₅ are calculated based on the measured values before and after that and the ratio between the length of the planned division line 10a and the length of the planned division line 10b.

Note that the values a ₁₂ , a ₂₃ , a ₃₄ , and a _{45 to be} complemented can be calculated based on measured values at one point before and after the values, but the present invention is not limited to this. For example, You may calculate from the measured value of each two points before and behind. Specifically, if the value a ₂₃ to be complemented is calculated, it can be calculated from a total of four points, the previous measured values a ₁ and a ₂ and the subsequent measured values a ₃ and a ₄ .

On the other hand, when the planned division line 10b is shorter than the planned division line 10a, the measured value of the surface displacement is reduced by proportional distribution. For example, when 5 pieces of measurement data (a ₁ , a ₂ , a ₃ , a ₄ , a ₅ ) are reduced to 3 pieces, (a ₁ , a ₃ , a ₅ ) are obtained, and the actual measurement values are set at predetermined intervals. Thin out. The interval at which data is thinned when reducing the actual measurement value is determined based on the ratio between the length of the planned division line 10a and the length of the planned division line 10b.

  FIG. 4 is a graph showing measured values and predicted values of the surface displacement of the planned division line, with the horizontal axis representing the position in the planned division line and the vertical axis representing the surface displacement. Note that the values shown in FIG. 4 are values actually measured for one division planned line arbitrarily selected from the division planned lines provided at intervals of 0.24 mm on a wafer having a diameter of 76.2 mm (3 inches). And a value predicted from an actual measurement value of another adjacent division planned line. When comparing the actual measurement value and the predicted value shown in FIG. 4, the surface displacement of the planned division line predicted by the above-described method showed the same tendency as the actual measurement value, and the difference was 1 μm or less. That is, according to the method of the present embodiment, it is possible to accurately predict the surface displacement of the planned division line.

  Further, by applying this method, the processing time can be greatly shortened. Specifically, a workpiece on which a line to be divided is provided on a 3-inch wafer with a pitch of 0.24 mm in the x direction and a pitch of 0.48 mm in the y direction is set to 600 mm / second per line. When performing one pass of surface displacement measurement and three passes of laser light irradiation, the time required for processing is reduced by about 205 seconds / sheet compared to the case of measuring all lines by setting the surface displacement measurement interval to 9 lines. can do.

  The surface displacement of the planned division line 10b predicted by the analysis unit 51 is stored in the storage unit 54 together with the surface displacement of the planned division line 10a actually measured by the surface displacement detection unit 4. Thereafter, the surface displacement of the planned division line to be processed next to the planned division line 10b is measured by the surface displacement detecting means 4 or predicted based on the actual measurement value of the planned division line 10a. This process is repeated a plurality of times to determine the surface displacements of all the planned division lines.

  At this time, after measuring the surface displacement of the planned division line 10a and then predicting a plurality of planned division lines to be processed thereafter, the value of the surface displacement of the planned division line 10b predicted from the measured value of the planned division line 10a. Based on the above, the surface displacement of the division line to be processed next may be predicted. Moreover, based on the actual measurement value of the division | segmentation planned line 10a, the surface displacement of each division | segmentation planned line can also be estimated separately, respectively.

  The interval for actually measuring the planned division lines can be appropriately set according to the pitch between the respective divided lines, the allowable error range, the flatness of the workpiece 10, the position in the workpiece 10, and the like. For example, a substantially circular workpiece such as a semiconductor wafer has a large difference in length between adjacent division lines near the end portion, but a small difference between adjacent division lines near the center portion. When machining such a workpiece, it is also possible to measure the surface displacement of all the planned dividing lines at the end and predict the surface displacement only for the planned dividing line at the central portion.

  After that, while adjusting the focal position based on the actually measured or predicted surface displacement, the division line of the workpiece 10 is irradiated with a processing pulse laser beam having a wavelength of, for example, 1064 nm and having transparency to the workpiece. As a result, a modified region is formed on the planned division line, and the workpiece 10 is divided starting from the modified region.

  In the laser processing method of the present embodiment, the laser beam is irradiated after measuring the surface displacement of all the division lines, but the present invention is not limited to this, and the surface displacement measurement or You may perform prediction and laser beam irradiation for every line. Specifically, after measuring the surface displacement of the scheduled division line 10a and performing laser irradiation based on the measured value, the surface displacement of the scheduled division line 10b can be predicted. Furthermore, while the laser beam irradiating means 3 irradiates one scheduled division line with the laser beam, the analyzing means 51 predicts the surface displacement of one or more scheduled division lines to be processed thereafter, and It is also possible to irradiate a laser beam continuously to the scheduled division line.

  Also, each step described above, specifically, the step of measuring the surface displacement of one planned division line, the surface displacement of another planned division line to be processed next from the actual measurement value of the surface displacement of one planned division line And the step of irradiating the workpiece 10 with the laser beam while adjusting the condensing point position of the laser beam based on the measured or predicted surface displacement is, for example, a measurement / stored in the ROM 53 of the control unit 5. It is automatically executed by executing an analysis program and a control program.

  As described above, in the laser processing apparatus and the laser processing method of the present embodiment, one or a plurality of planned division lines to be processed next to this one planned division line is determined from the actual measurement value of the surface displacement of the one planned division line. Since the surface displacement is calculated, it is not necessary to actually measure the surface displacement of all the division lines. Thereby, compared with the conventional processing method, the time required for the measurement of the surface displacement can be shortened. In addition, as in the present embodiment, the surface displacement can be predicted accurately and efficiently by proportionally allocating the actual measurement values according to the lengths of the planned division lines. As a result, it is possible to greatly improve the work efficiency related to the determination of the focal position of the processing laser beam.

  Furthermore, the laser processing apparatus and laser processing method of the present embodiment can be applied to the processing of various workpieces described above. In particular, the laser processing apparatus and the laser processing method of the present embodiment increase the accuracy of surface displacement prediction as the interval between the lines to be divided is narrower. Therefore, an optical device wafer in which a large number of minute elements are formed on a sapphire substrate is used. As described above, this method is suitable for machining a workpiece having a large number of division lines and having a narrow interval between the division lines.

  In the present embodiment, the case where laser processing is performed by the laser processing apparatus 1 has been described as an example. However, the present invention is not limited to this, and the surface displacement of the line to be divided can be measured. It can be connected to analysis means such as a computer that predicts the surface displacement of other scheduled division lines to be processed after one scheduled division line, and the focal position of the laser beam is adjusted based on the measured or predicted surface displacement Various possible laser processing devices can be used.

It is a figure which shows the structure of the laser processing apparatus which concerns on embodiment of this invention. It is a perspective view which shows the workpiece | work of a process target. It is a figure which shows the surface displacement of a workpiece | work typically. It is a graph which shows the actual value and predicted value of the surface displacement of a division | segmentation line by taking the position in a division | segmentation planned line on a horizontal axis, and taking surface displacement on a vertical axis | shaft.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser processing apparatus 2 Holding means 3 Laser beam irradiation means 4 Surface displacement detection means 5 Control part 10 Work 10a, 10b Scheduled division line 11 Ring frame 12 Adhesive tape 21 Base 22a, 22b, 25a, 25b Guide rail 23a, 26a Ball screw 23b, 26b Motor 23c, 26c Bearing block 24, 27 Sliding block 51 Analysis means 52 Input interface 53 Read only memory (ROM)
54 memory means 55 counter 56 output interface

Claims (5)

A laser processing method for forming a modified region in a division planned line of the workpiece by irradiating the workpiece with a laser beam having a wavelength that passes through the workpiece while aligning a condensing point inside the workpiece,
Measuring the surface displacement of one of the plurality of planned division lines in the workpiece;
From the measured value of the surface displacement of the one scheduled division line, based on the ratio of the length of the one scheduled division line and the length of the other division planned line to be processed next to the one divided division line, Predicting the surface displacement of other lines to be split;
Irradiating the workpiece with the laser beam while adjusting the focal point position of the laser beam based on the measured or predicted surface displacement;
A laser processing method. After forming the modified region in the one dividing line, the laser processing method according to claim 1, characterized in that predicting the surface displacement of the other division lines. 3. The laser processing method according to claim 1, wherein the surface displacement of a plurality of scheduled division lines to be processed thereafter is predicted from an actual measurement value of the surface displacement of the one scheduled division line. A laser processing apparatus for forming a modified region in a work division line,
Holding means for holding the workpiece;
Surface displacement detecting means for measuring the surface displacement at the division line of the workpiece;
From the surface displacement of one division planned line measured by the surface displacement detection means, the ratio between the length of the one division planned line and the length of another division line to be processed after this one division planned line Based on the analysis means for predicting the surface displacement of the other division line,
Laser light irradiation means for irradiating the workpiece with laser light,
The holding means and the laser light irradiation means are moved relative to each other, and the work is transmitted through the work while adjusting the focal point position of the laser light based on the measured or predicted surface displacement. A laser processing apparatus that irradiates laser light of a wavelength to be used. The laser processing apparatus according to claim 4 , wherein the analysis unit predicts the surface displacement of a plurality of scheduled division lines to be processed thereafter from an actual measurement value of the surface displacement of the one scheduled division line.

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