JP6037390B2 - Laser processing equipment - Google Patents

Description

  The present invention relates to a laser processing apparatus that forms a modified layer inside a workpiece by irradiating the workpiece with a laser beam.

  In recent years, as a method of dividing a plate-like workpiece such as a semiconductor wafer into individual devices, a condensing point of a laser beam having a wavelength (for example, 1064 nm) that is transmissive to the workpiece corresponds to a division planned line. A method is proposed in which a modified layer is formed in the workpiece by irradiating the workpiece with a laser beam along the planned dividing line, and then the workpiece is cleaved by a mechanical braking device. (For example, refer to Patent Document 1 below). By using this method, a fragile modified layer can be formed inside the workpiece without scattering debris generated during laser processing.

  However, the outer periphery of the workpiece is subjected to arc-shaped chamfering from the front surface to the back surface, and when the condensing point of the laser beam positioned inside the workpiece is irradiated to the chamfered region, Since the laser beam is not completely transparent to the workpiece, the chamfered part is ablated and debris is generated, and the debris adheres to the objective lens of the condenser, and the objective lens is There is a problem of contamination. The same problem may occur when foreign matter such as dust adheres to the surface of the workpiece corresponding to the division line or the upper surface of the workpiece is covered with a film. That is, debris may be generated when a foreign substance or the like is instantaneously heated and burned by a laser beam, and the debris may adhere to the objective lens. Therefore, it is necessary to periodically clean the objective lens.

  In addition, if the workpiece has undulations and the thickness varies, the refractive position in the thickness direction of the workpiece varies at each location where the laser beam hits when the workpiece is irradiated with the laser beam. Therefore, a uniform modified layer cannot be formed at a predetermined depth. Therefore, in order to form a uniform modified layer at a predetermined depth inside the workpiece, the following Patent Document 2 discloses a means for detecting the height position of the surface of a region irradiated with a laser beam, and a collection of laser beams. A laser processing apparatus including an actuator that functions as a light spot position adjusting unit has been proposed. This actuator can finely adjust the objective lens of the condenser in a direction perpendicular to the upper surface of the workpiece by applying a voltage.

Japanese Patent No. 3408850 JP 2010-52014 A

  However, when periodically cleaning the objective lens, an extra vertical force is applied to the condenser while the voltage is applied to the actuator as described above (for example, a piezo element or a voice coil motor). If this happens, an overvoltage or overcurrent may occur and the actuator control circuit may be damaged. Further, in the case of a piezo element, a load is applied to the insulator between the electrodes, which may cause a dielectric breakdown, causing a short circuit between the electrodes and failure.

  The present invention has been made in view of the above circumstances, so that the objective lens mounted on the condenser can be cleaned without causing problems in the actuator of the laser beam condensing point position adjusting means. Therefore, the present invention has a problem to be solved.

  The present invention relates to a holding means for holding a workpiece, an oscillator that oscillates a laser beam having a wavelength that is transmissive to the workpiece, and a workpiece that holds the laser beam oscillated from the oscillator in the holding means. A laser beam irradiating means having a condenser having an objective lens for condensing inside the object, a measuring means for measuring the surface displacement of the laser beam irradiation area of the workpiece, and a laser beam based on the measurement result of the measuring means. A focusing point position adjusting unit that adjusts the focusing point position in a direction perpendicular to the workpiece, the focusing point position adjusting unit supporting the collector An actuator for moving the condenser in a direction perpendicular to the workpiece; and a focusing point of the laser beam by controlling a voltage applied to the actuator based on a measurement result of the measuring means And a control means for adjusting the location, and control means, characterized by interrupting the power supply to the actuator of said population point position adjusting means in the maintenance mode for performing maintenance of the condenser unit.

The laser processing apparatus according to the present invention includes a condensing point position adjusting unit that adjusts a condensing point position of a laser beam in a direction perpendicular to the workpiece, and is in a maintenance mode for cleaning an objective lens of the concentrator. Since the power supply to the actuator is automatically cut off by the control of the control means constituting the condensing point position adjusting means, the actuator can be moved up and down with the objective lens when cleaning the objective lens. No overvoltage or overcurrent occurs in the actuator, and no malfunction occurs in the actuator. Further, when the actuator is constituted by a piezo element, no load is applied to the insulator between the electrodes, so that dielectric breakdown does not occur and the actuator is not damaged.
Therefore, the periodic maintenance of the objective lens can be safely performed without damaging the actuator, so that the processing defect due to the debris adhering to the objective lens does not occur and the good processing accuracy is maintained. be able to.

It is a perspective view which shows the structure of a laser processing apparatus. It is sectional drawing which shows the structure of a laser beam irradiation means and a condensing point position adjustment means.

  A laser processing apparatus 1 shown in FIG. 1 has a base 2, and a side wall 3 extending in the Z-axis direction is erected on the rear side of the base 2 in the Y-axis direction. The laser processing apparatus 1 includes a holding means 10 that holds and rotates a workpiece.

  As shown in FIG. 1, an X-axis direction feeding unit 20 is disposed below the holding unit 10. The X-axis direction feeding means 20 includes a ball screw 21 extending in the X-axis direction, a motor 22 connected to one end of the ball screw 21, a pair of guide rails 23 extending parallel to the ball screw 21, and a moving base that supports the holding means 10. And a table 24. One surface of the movable base 24 is in sliding contact with the pair of guide rails 23, and a ball screw 21 is screwed to a nut formed at the center of the movable base 24. Then, when the ball screw 21 is rotated by being driven by the motor 22, the moving base 24 is guided by the guide rail 23 and moved in the X-axis direction, and the holding means 10 can be moved in the same direction.

  On the upper surface of the base 2, Y-axis direction feeding means 30 is disposed in a direction orthogonal to the X-axis direction feeding means 20. The Y-axis direction feeding means 30 is arranged on a ball screw 31 extending in the Y-axis direction, a motor 32 connected to one end of the ball screw 31, a pair of guide rails 33 arranged in parallel to the ball screw 31, and the guide rails 33. And a movable base 34 provided. One surface of the moving base 34 is in sliding contact with the pair of guide rails 33, and a ball screw 31 is screwed into a nut formed at the center of the moving base 34. Then, when the ball screw 31 is driven by the motor 32 to rotate, the moving base 34 is guided by the guide rail 33 and moves in the Y-axis direction, and the X-axis direction feeding means 20 is placed on the moving base 34. It is possible to move the holding means 10 disposed in the same direction.

  As shown in FIG. 1, laser beam irradiation means 40 for irradiating a workpiece with a laser beam is disposed in front of the side wall 3. The laser beam irradiation means 40 shown in FIG. 2 includes an oscillator 41 that oscillates a laser beam having a wavelength that is transmissive to the workpiece. The oscillator 41 includes an oscillation source 42 that is oscillated from the oscillation source 42. A deflection mirror 44 is disposed on the optical path of the laser beam. The deflection mirror 44 can deflect the laser beam 43 oscillated from the oscillation source 42 in a direction perpendicular to the workpiece.

  At the lower end of the oscillator 41, a condenser 45 for condensing the laser beam is disposed. An objective lens 46 for condensing the laser beam at a predetermined position inside the workpiece is disposed at the tip of the condenser 45.

  As shown in FIG. 1, a measuring unit 50 that measures surface displacement such as irregularities on the upper surface of the workpiece is disposed adjacent to the oscillator 41 of the laser beam irradiation unit 40. The measuring means 50 includes at least a light projecting unit that projects measurement light and a light receiving unit that receives reflected light of the measurement light. And the measuring means 50 measures the light quantity of the reflected light of the measurement light projected from the light projecting unit by the light receiving unit, and measures the surface height position of the workpiece in the laser beam irradiation region based on the measured value. it can.

  The laser processing apparatus 1 includes a condensing point position adjusting unit 60 that adjusts the condensing point position of the laser beam based on the measurement result of the measuring unit 50. As shown in FIG. 2, the condensing point position adjusting unit 60 includes an actuator 61 that supports the concentrator 45 from below and moves the concentrator 45 in a direction perpendicular to the workpiece, and the measuring unit 50. Control means 62 is provided for controlling the voltage applied to the actuator 61 based on the measurement result to adjust the focal point position of the laser beam.

  The actuator 61 is composed of a piezo element that expands and contracts in a direction perpendicular to the holding surface of the holding means 10 by applying a voltage. By adjusting the voltage applied to the piezo element, the condenser 45 can be moved in the vertical direction, and the position of the objective lens 46 can be finely adjusted. The configuration of the actuator 61 is not limited to a piezo element, and may be configured by, for example, a voice coil motor that enables linear movement. That is, the actuator 61 is configured by an element that deforms or moves by adjusting the magnitude and polarity of the applied voltage. On the other hand, when the actuator 61 is deformed or moved by applying some force to the actuator itself, an electromotive force is generated, which may cause overvoltage or overcurrent in the control circuit of the actuator 61.

  The control means 62 is a computer provided with at least a CPU and a storage element such as a memory. On the other hand, as shown in FIG. 2, the control unit 62 is connected with a switch 70 for switching between a maintenance mode for performing the maintenance operation of the condenser 45 of the laser beam irradiation unit 40 and a normal operation mode. The maintenance mode refers to a state in which the operation of the laser beam irradiation unit 40 and the condensing point position adjusting unit 60 can be stopped and the condenser 45 can be cleaned, for example. When the operator presses the switch 70 to switch to the maintenance mode, the control means 62 is configured to automatically cut off voltage application (energization) to the actuator 61.

  Next, an operation example of the laser processing apparatus 1 will be described. The workpiece W shown in FIG. 2 is an example of a workpiece to be laser processed, and is not particularly limited. First, the workpiece W is conveyed to the holding means 10. Thereafter, the X-axis direction feeding unit 20 is operated, and the holding unit 10 holding the workpiece W is moved in the X-axis direction and moved below the measuring unit 50.

  While the holding unit 10 moves below the measuring unit 50, the measuring unit 50 projects measurement light toward the workpiece W held by the holding unit 10, and the workpiece W in the irradiation region of the laser beam is projected. The displacement in the thickness direction of the surface W1 is measured. Then, after measuring the surface displacement of the workpiece W by the measuring unit 50, the measured value is stored in the storage element provided in the control unit 62. For example, when the workpiece is a semiconductor wafer, the surface displacement is measured and stored in the control means 62 along all or part of the streets defining the formed device.

  Next, while the X-axis direction feeding unit 20 further moves the holding unit 10 in the X-axis direction, a laser beam 43 is irradiated downward from the laser beam irradiation unit 40 to form a modified layer inside the workpiece W. To do. At this time, the condensing point position adjusting means 60 adjusts the condensing point position of the laser beam irradiated to the workpiece W in order to form a modified layer at a predetermined depth inside the workpiece W. Match the inside of the workpiece W. Specifically, the control unit 62 shown in FIG. 2 controls the voltage applied to the actuator 61 based on the measurement value measured by the measurement unit 50. For example, when irradiating a laser beam to a portion where the surface W1 of the workpiece W is formed in a convex shape, the laser beam irradiation means 40 is pulled upward by expanding the actuator 61 by increasing the applied voltage. As a result, the condenser 45 supported by the actuator 61 moves in the vertical direction following the surface displacement of the workpiece W, so that the condensing point position of the laser beam via the objective lens 46 is set to the workpiece. Fine adjustment can be made so as to be positioned at a predetermined depth inside W.

  In this way, while adjusting the condensing point position of the laser beam, the laser beam irradiation means 40 shown in FIG. 2 irradiates the laser beam 43 along the planned division line of the workpiece W, and divides it into the workpiece W. A modified layer serving as a starting point is formed. The laser beam 43 only needs to be transmissive so as to reach the inside of the workpiece W. For example, a YAG laser having a wavelength of 1064 nm can be used.

  When the workpiece W is irradiated with the laser beam 43, debris is generated and may adhere to the objective lens 46 of the condenser 45. Therefore, the maintenance work of the condenser 45 is periodically performed to remove the debris. To do. Therefore, the worker periodically presses the switch 70 to shift to the maintenance mode, and performs maintenance work such as debris removal.

  Since the control means 62 automatically cuts off the power to the actuator 61 by shifting to the maintenance mode, the condenser 45 is moved up and down by cleaning the objective lens 46 of the condenser 45 in the maintenance mode, for example. Even if it is moved to, an overvoltage or an overcurrent does not occur in the control circuit of the actuator 61. Further, when the actuator 61 is composed of a piezo element, no load is applied to the insulator between the electrodes, so that the dielectric breakdown does not occur and the actuator 61 is not damaged. After the collector 45 is cleaned in this way, laser processing can be resumed.

As described above, in the maintenance mode in which the objective lens 46 of the condenser 45 is cleaned, the energization to the actuator 61 is automatically cut off by the control of the control means 62 constituting the condensing point position adjusting means 60. Therefore, even if the condenser 45 is moved up and down together with the objective lens 46 when the objective lens 46 is cleaned, no overvoltage or overcurrent occurs in the actuator 61, and no malfunction occurs in the actuator 61. Further, when the actuator 61 is composed of a piezo element, no load is applied to the insulator between the electrodes, so that the dielectric breakdown does not occur and the actuator 61 is not damaged.
Therefore, in the laser processing apparatus 1, the periodic maintenance of the objective lens 46 can be safely performed without damaging the actuator 61, so that a processing defect occurs on the workpiece due to the debris adhering to the objective lens 46. Therefore, good processing accuracy can be maintained.

1: Laser processing device 2: Base 3: Side wall 10: Holding means 20: X-axis direction feeding means 21: Ball screw 22: Motor 23: Guide rail 24: Moving base 30: Y-axis direction feeding means 31: Ball screw 32: Motor 33: Guide rail 34: Moving base 40: Laser beam irradiation means 41: Oscillator 42: Oscillation source 43: Laser beam 44: Deflection mirror 45: Condenser 46: Objective lens 50: Measuring means 60: Focusing point position adjusting means 61: Actuator 62: Control means 70: Switch W: Workpiece

Claims (1)

Holding means for holding the workpiece, an oscillator for oscillating a laser beam having a wavelength that is transmissive to the workpiece, and the laser beam oscillated from the oscillator inside the workpiece held by the holding means Laser beam irradiation means comprising a condenser having an objective lens for condensing, measurement means for measuring the surface displacement of the laser beam irradiation area of the workpiece, and the focal point position of the laser beam based on the measurement results of the measurement means A laser beam focusing device that adjusts the vertical position with respect to the workpiece, and a laser processing device comprising:
The condensing point position adjusting means includes an actuator that supports the concentrator and moves the concentrator in a direction perpendicular to the workpiece;
Control means for adjusting the condensing point position of the laser beam by controlling the voltage applied to the actuator based on the measurement result of the measuring means,
The laser processing apparatus characterized in that the control means cuts off the power supply to the actuator of the focusing point position adjusting means in a maintenance mode for performing maintenance work of the condenser.

Images