Laser processing device control device, laser processing device, and laser annealing method

Abstract

To provide a control device for a laser annealing device capable of performing annealing with a desired pulse energy density without reducing energy utilization efficiency.SOLUTION: A laser processing device, by which a pulse laser beam outputted from a laser oscillator is incident to a processing object via a beam size adjustment optical system, is controlled by a control device. The control device comprises: a function for acquiring a density target value of pulse energy of a pulse laser beam to be used for processing; a function for calculating an area target value of a beam spot on a surface of the processing object in such a manner that the pulse energy density on the surface of the processing object becomes the density target value based on the pulse energy of the pulse laser beam outputted from the laser oscillator and the density target value; and a function for controlling the beam size adjustment optical system in such a manner that an area of the beam spot on the surface of the processing object becomes the area target value.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a control device for a laser processing device, a laser processing device, and a laser annealing method. [Background technology]

[0002] Laser annealing using a pulsed laser beam is used for annealing to activate dopants doped in a semiconductor wafer, annealing to crystallize an amorphous semiconductor layer formed on a glass substrate, etc. (For example, Patent Document 1, etc.) In laser annealing, a beam spot is scanned over the surface of the workpiece to anneal almost the entire area of ​​the workpiece.

[0003] To perform optimal annealing, it is preferable to optimize the energy density per pulse (pulse energy density).The pulse energy density can be optimized by attenuating the laser beam output from the laser oscillator using a variable attenuator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-202242 Summary of the Invention [Problem to be solved by the invention]

[0005] If the pulse laser beam output from the laser oscillator is attenuated in order to optimize the pulse energy density, the energy utilization efficiency will decrease. An object of the present invention is to provide a laser annealing apparatus, a control device therefor, and a laser annealing method that are capable of performing annealing at a desired pulse energy density without decreasing the energy utilization efficiency. [Means for solving the problem]

[0006] According to one aspect of the present invention, A control device for controlling a laser processing device that causes a pulsed laser beam output from a laser oscillator to be incident on a processing object via a beam size adjustment optical system, Before laser processing, A function of acquiring a target value for the density of the pulse energy of the pulse laser beam used during processing; based on the pulse energy of the pulse laser beam output from the laser oscillator and the density target value, so that the pulse energy density on the surface of the object to be processed becomes the density target value; Before laser processing, a function of calculating a target area value of the beam spot on the surface of the workpiece; The area of ​​the beam spot on the surface of the workpiece is set to the target area value. , before laser processing a function of controlling the beam size adjusting optical system; A control device is provided.

[0007] According to another aspect of the present invention, a laser oscillator that outputs a pulsed laser beam; a beam size adjusting optical system that is arranged on a path of the pulsed laser beam from the laser oscillator to the workpiece and that changes the area of ​​the beam spot on the surface of the workpiece; an input device for inputting laser processing conditions; a control device for controlling the beam size adjusting optical system; Equipped with The control device Before laser processing, a function of acquiring a target value of pulse energy density input to the input device; Before laser processing, a function of calculating a target area value of a beam spot on the surface of the workpiece based on the pulse energy of the pulse laser beam output from the laser oscillator and the target density value so that the pulse energy density on the surface of the workpiece becomes the target density value; The area of ​​the beam spot on the surface of the workpiece is set to the target area value. , before laser processinga function of controlling the beam size adjusting optical system; A laser processing apparatus having the following is provided.

[0008] According to yet another aspect of the present invention, determining a target value of pulse energy density at a surface of the workpiece; Before laser processing, determining an area of ​​a beam spot on the surface of the workpiece based on pulse energy of a pulse laser beam output from a laser oscillator and the target value so that a pulse energy density on the surface of the workpiece becomes the target value; A pulsed laser beam is irradiated onto the workpiece under conditions that the area of ​​the beam spot on the surface of the workpiece becomes a determined area. and start the laser processing. A laser annealing method is provided. [Effects of the Invention]

[0009] By adjusting the target value of the beam spot area based on the target value of the pulse energy density, laser processing can be performed at the target pulse energy density even if the pulse energy is kept constant. Even if the target value of the pulse energy is reduced, there is no need to reduce the pulse energy, so a decrease in energy utilization efficiency can be suppressed. Furthermore, by expanding the beam spot area when the target value of the pulse energy density is reduced, the time required for laser processing can be shortened. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a laser processing apparatus according to one embodiment. [Figure 2] FIG. 2A is a schematic diagram showing the movement of the beam spot of a pulsed laser beam on the surface of a workpiece, and FIG. 2B is a schematic diagram showing the movement of the beam spot when the width Lx is longer than that of the beam spot shown in FIG. 2A. [Figure 3]FIG. 3 is a flowchart showing the procedure of the laser processing method according to this embodiment. [Figure 4] 4A to 4C are diagrams showing the movement of the beam spot and the laser irradiation conditions during laser processing. DETAILED DESCRIPTION OF THE INVENTION

[0011] A laser processing device according to one embodiment will be described with reference to FIGS. 1 is a schematic diagram of a laser processing apparatus according to this embodiment. Two laser oscillators 10 output pulse laser beams based on commands from a control device 30. The pulse laser beams output from the two laser oscillators 10 are combined into one pulse laser beam by a beam combiner 12. The pulse laser beam output from one of the laser oscillators 10 is reflected by a mirror 11 and enters the beam combiner 12.

[0012] The pulsed laser beam combined by the beam combiner 12 passes through an attenuator 13, a beam expander 14, and a beam size adjusting optical system 15, is reflected by a mirror 18, passes through a condenser lens 21, and is incident on a workpiece 50. The workpiece 50 is held on a movable stage 22 such as an XY stage. The movable stage 22 moves the workpiece 50 in two directions in a horizontal plane based on commands from a control device 30. The workpiece 50 is, for example, a semiconductor wafer into which dopant ions have been implanted, and activation annealing of the dopant is performed by irradiating the workpiece with a pulsed laser beam.

[0013] A measuring instrument 20 is attached to a movable stage 22. By moving the movable stage 22 and positioning the measuring instrument 20 at the incident position of the pulsed laser beam, it is possible to measure the beam profile of the pulsed laser beam at the position of the surface of the workpiece 50. The measurement results of the beam profile are input to the control device 30.

[0014] The laser oscillator 10 may be, for example, a fiber laser oscillator, a laser diode, or a solid-state laser oscillator. The attenuator 13 attenuates the pulse laser beam at a predetermined attenuation rate. The beam expander 14 adjusts the beam size at the incident position of the beam size adjustment optical system 15. The beam size adjustment optical system 15 shapes the beam spot on the surface of the workpiece 50 and homogenizes the intensity distribution. Furthermore, the beam size adjustment optical system 15 changes the area of ​​the beam spot in response to a command from the control device 30.

[0015] The beam size adjusting optical system 15 can, for example, shape the beam spot on the surface of the workpiece 50 into a rectangle and change its area. A pair of cylindrical lens arrays 15A is arranged to change the dimension of the beam spot in the major axis direction, and another pair of cylindrical lens arrays 15B is arranged to change the dimension in the minor axis direction.

[0016] The pulsed laser beam incident on the beam size adjustment optical system 15 passes through the minor axis cylindrical lens array 15B, the major axis cylindrical lens array 15A, and the convex lens 15C, and is output from the beam size adjustment optical system 15. When the major axis adjustment mechanism 15D changes the spacing between the pair of major axis cylindrical lens arrays 15A in response to a command from the control device 30, the dimension of the beam spot in the major axis direction changes. Similarly, when the minor axis adjustment mechanism 15E changes the spacing between the pair of minor axis cylindrical lens arrays 15B, the dimension of the beam spot in the minor axis direction changes.

[0017] Laser processing conditions and various commands are input to the input device 31. The control device 30 controls the movable stage 22 based on the laser processing conditions input to the input device 31 so that the pulsed laser beam is incident on a target position on the surface of the workpiece 50. Furthermore, it controls the output timing of the pulsed laser beam from the laser oscillator 10.

[0018] Next, movement of the beam spot during laser processing will be described with reference to Fig. 2A. Fig. 2A is a schematic diagram showing movement of the beam spot 40 of the pulsed laser beam on the surface of the workpiece 50 (Fig. 1). In this embodiment, the path of the pulsed laser beam is fixed, and the workpiece 50 is moved, thereby moving the beam spot 40 relative to the workpiece 50. Fig. 2A shows the relative movement of the beam spot 40 with respect to the workpiece 50.

[0019] An xyz Cartesian coordinate system is defined with the surface of the workpiece 50 as the xy plane. The shape of the beam spot 40 is a rounded rectangle that is longer in the y direction. The dimension (length) of the beam spot 40 in the y direction is denoted as Ly, and the dimension (width) in the x direction is denoted as Lx.

[0020] Laser processing is performed by alternately repeating a scanning process in which the surface of the workpiece 50 is scanned in the x direction with a pulsed laser beam and a stepping operation in which the beam spot 40 is moved in the y direction. In the scanning operation, the distance that the beam spot 40 moves in the x direction during one pulse repetition period of the pulsed laser beam is denoted as Wx. The moving distance Wx is shorter than the dimension of the beam spot 40 in the x direction (hereinafter referred to as width Lx). Therefore, the beam spot 40 of a given shot partially overlaps with the beam spot 40 of the previous shot in the x direction. The ratio of the dimension of the overlapping portion in the x direction, i.e., Lx - Wx, to the width Lx of the beam spot 40 is called the overlap ratio in the scanning operation.

[0021] The movement distance of the beam spot 40 in the y direction in one step operation is denoted as Wy. The movement distance Wy is shorter than the dimension of the beam spot 40 in the y direction (hereinafter referred to as the length Ly). Therefore, the area scanned in one scanning operation partially overlaps in the y direction with the area scanned in the previous scanning operation. The ratio of the dimension of the overlapping portion in the y direction, i.e., Ly-Wy, to the length Ly of the beam spot 40 is called the overlap ratio in the step operation.

[0022] The control device 30 controls the beam size adjusting optical system 15 to change the length Ly and width Lx of the beam spot 40. For example, the control device 30 controls the major axis adjusting mechanism 15D to change the length Ly of the beam spot 40, and the control device 30 controls the minor axis adjusting mechanism 15E to change the width Lx of the beam spot 40.

[0023] 2B is a schematic diagram showing the movement of the beam spot 40 when the width Lx is increased compared to the beam spot 40 shown in FIG. 2A. Increasing the width Lx increases the area of ​​the beam spot 40. If the area of ​​the beam spot 40 is increased under the condition that the energy per pulse of the pulsed laser beam (hereinafter referred to as pulse energy) is the same, the energy density per pulse (hereinafter referred to as pulse energy density) decreases.

[0024] Next, a method for performing laser processing using the laser processing apparatus according to this embodiment will be described with reference to Fig. 3. Fig. 3 is a flowchart showing the procedure of the laser processing method according to this embodiment.

[0025] When laser irradiation conditions such as peak power, pulse width, and pulse energy density are input to the input device 31, the control device 30 acquires these laser irradiation conditions from the input device 31 (step S1). The values ​​of peak power and pulse width may be stored in advance in the control device 30. The value of pulse energy density input as a laser irradiation condition is referred to as a density target value. The peak power may be determined based on the rated value of the peak power of the laser oscillator 10. For example, when two laser oscillators 10 are used, the peak power may be set to approximately twice the rated value of the peak power of the laser oscillators 10.

[0026] Based on the peak power, pulse width, and density target value, the control device 30 calculates the area of ​​the beam spot 40 so that the pulse energy density becomes the density target value (step S2). The area value obtained by calculation is referred to as the area target value.

[0027] Once the target area value of the beam spot 40 is determined, the dimensions Lx and Ly of the beam spot 40 in the scanning direction (x direction) and stepping direction (y direction) of the beam spot 40 are determined (step S3). As an example, the dimension Ly in the y direction is given as a fixed value in advance, and the dimension Lx in the x direction is determined from the target area value and the dimension Ly. Alternatively, the ratio between the dimensions Lx and Ly may be determined in advance, and the dimensions Lx and Ly may be determined from this ratio and the target area value.

[0028] The control device 30 controls the beam size adjusting optical system 15 so that the dimensions Lx and Ly of the beam spot 40 become the values ​​determined in step S3 (step S4). The control device 30 operates the movable stage 22 (FIG. 1) to position the measuring device 20 on the path of the pulsed laser beam and cause the laser oscillator 10 to output the pulsed laser beam. The control device 30 acquires the measurement results from the measuring device 20, and determines the dimensions Lx and Ly of the beam spot 40 from the measurement results, and calculates the area (step S5).

[0029] The measured value of the area of ​​the beam spot 40 calculated from the measurement results is compared with the target area value, and it is determined whether the difference between them is within the allowable range (step S6). If the difference between them is outside the allowable range, the beam size adjustment optical system 15 is controlled again to fine-tune the dimensions Lx and Ly of the beam spot 40 (step S4). If the difference between them is within the allowable range, laser processing is performed with the current dimensions of the beam spot 40 (step S7).

[0030] Next, the excellent effects of this embodiment will be described with reference to Figures 4A to 4C. Figures 4A to 4C are diagrams showing the movement of the beam spot 40 and the laser irradiation conditions during laser processing. Figure 4A shows the case where the target pulse energy density value is E0, and Figures 4B and 4C show the case where the target pulse energy density value is E1, which is smaller than E0.

[0031] As shown in Figure 4A, laser processing is performed under conditions where the pulse energy is set to P0 and the area of ​​the beam spot 40 is set to S0. The pulse energy P0 is determined, for example, from the rated value of the laser oscillator 10 (Figure 1). The area S0 of the beam spot 40 is determined to satisfy P0 / S0 = E0. The dimensions of the beam spot 40 in the x and y directions are denoted as Lx and Ly, respectively. The movement distance of the beam spot 40 in the x direction between shots is denoted as Wx.

[0032] 4B shows the laser irradiation conditions in a conventional laser processing method according to a comparative example. Conventionally, even if the target pulse energy density value is reduced from E0 to E1, the area of ​​the beam spot 40 remains S0, and the pulse energy density is adjusted to the target density value E1 by reducing the pulse energy from P0 to P1. The pulse energy is reduced, for example, by increasing the attenuation of the pulse laser beam using the attenuator 13 (FIG. 1). The pulse energy P1 is determined to satisfy P1 / S0=E1. The x-direction dimension Lx, y-direction dimension Ly, and movement distance Wx of the beam spot 40 are the same as those in the laser processing shown in FIG. 4A.

[0033] 4C shows laser irradiation conditions in the laser processing method according to the embodiment. Even if the target value of the pulse energy density is reduced from E0 to E1, the pulse energy is not changed, and the area of ​​the beam spot 40 is increased from S0 to S1. The area S1 of the beam spot 40 is determined so as to satisfy P0 / S1=E1.

[0034] The area of ​​the beam spot 40 can be enlarged by increasing the dimension Lx of the beam spot 40 in the x-direction. When laser processing is performed under conditions where the overlap rate is constant, the movement distance Wx of the beam spot 40 becomes longer than in the case of laser processing shown in Fig. 4A. This makes it possible to shorten the laser processing time.

[0035] 4B, the laser energy is not used effectively because the attenuation of the pulse laser beam by the attenuator 13 (FIG. 1) is increased. In contrast, in the embodiment shown in FIG. 4C, the pulse energy is not reduced even if the target value of the pulse energy density is reduced, so the reduction in the laser energy utilization efficiency is suppressed.

[0036] Next, a modification of the above embodiment will be described. In the above embodiment, as shown in Figures 2A and 2B, when changing the area of ​​the beam spot 40, the dimension Ly in the y direction is fixed and the dimension Lx in the x direction is changed, but conversely, the dimension Lx in the x direction may be fixed and the dimension Ly in the y direction may be changed.

[0037] It is also possible to determine multiple candidate values ​​for the dimension Ly and select one from the multiple candidate values ​​based on the area of ​​the beam spot 40. In this case, the value of the other dimension Lx can be calculated from the area of ​​the beam spot 40 and the selected candidate value of the dimension Ly. Conversely, it is also possible to determine multiple candidate values ​​for the dimension Lx.

[0038] The ratio between the dimensions Lx and Ly may be determined in advance, and the dimensions Lx and Ly may be determined from the area of ​​the beam spot 40.

[0039] In the above embodiment, pulsed laser beams output from two laser oscillators 10 (FIG. 1) are combined, but a single laser oscillator 10 may also be used. Also, in the first embodiment, the measuring instrument 20 is attached to the movable stage 22, but the mirror 18 may be a partial reflecting mirror, and the measuring instrument 20 may be placed at a position where the pulsed laser beam that has passed through the partial reflecting mirror is incident. In this case, it is preferable to adjust the beam spot at the position where the measuring instrument 20 is placed so that it is the same size as the beam spot on the surface of the workpiece 50.

[0040] The above-described embodiments are merely illustrative, and the present invention is not limited to the above-described embodiments. For example, it will be obvious to those skilled in the art that various modifications, improvements, combinations, etc. are possible. [Explanation of symbols]

[0041] 10 Laser oscillator 11. Mirror 12 Beam combiner 13 Attenuator 14 Beam Expander 15 Spot size adjustment optics 15A Long-axis cylindrical lens array 15B Short-axis cylindrical lens array 15C convex lens 15D long axis adjustment mechanism 15E Short axis adjustment mechanism 18 Partially Reflecting Mirror 20. Measuring instrument (beam profiler) 21 Condenser lens 22 Movable stage 30 Control device 31 Input / Output Devices 40 beam spots 50 Processing object

Claims

1. A control device for controlling a laser processing device that causes a pulsed laser beam output from a laser oscillator to be incident on a processing object via a beam size adjustment optical system, A function of acquiring a target value of the density of the pulse energy of the pulse laser beam used during processing before the laser processing; a function of calculating a target area value of a beam spot on the surface of the object to be processed before laser processing, based on the pulse energy of the pulse laser beam output from the laser oscillator and the target density value, so that the pulse energy density on the surface of the object to be processed becomes the target density value; a function of controlling the beam size adjusting optical system before laser processing so that the area of ​​the beam spot on the surface of the processing object becomes the area target value; A control device comprising:

2. moreover, a function of acquiring measurement results from a measuring instrument that measures a beam profile of the pulsed laser beam on the surface of the object to be processed; a function of determining whether or not a difference between the area of ​​the beam spot determined from the measurement result obtained from the measuring instrument and the target area value is within an allowable range, and if the difference is outside the allowable range, controlling the beam size adjustment optical system so that the area of ​​the beam spot approaches the target area value; The control device according to claim 1 , comprising:

3. Furthermore, a function of controlling the beam size adjustment optical system so that the area of ​​the beam spot approaches the target area value, then moving the measuring instrument onto the path of the pulsed laser beam, causing the laser oscillator to emit the pulsed laser beam, and calculating the area of ​​the beam spot from the measurement result by the measuring instrument; A function of comparing the calculated value of the beam spot area with the target area value, and starting laser processing if the difference between the two is within the tolerance range, and if not, readjusting the beam size adjustment optical system. The control device according to claim 2 , comprising:

4. A control device described in any one of claims 1 to 3, wherein the function of acquiring the density target value is realized by acquiring the density target value input into an input device from the input device.

5. a laser oscillator that outputs a pulsed laser beam; a beam size adjusting optical system that is arranged on a path of the pulsed laser beam from the laser oscillator to the workpiece and that changes the area of ​​the beam spot on the surface of the workpiece; an input device for inputting laser processing conditions; a control device for controlling the beam size adjusting optical system; Equipped with The control device A function of acquiring a target value of pulse energy density input to the input device before laser processing; a function of calculating a target area value of a beam spot on the surface of the object to be processed based on the pulse energy of the pulse laser beam output from the laser oscillator and the target density value before laser processing, so that the pulse energy density on the surface of the object to be processed becomes the target density value; a function of controlling the beam size adjusting optical system before laser processing so that the area of ​​the beam spot on the surface of the processing object becomes the area target value; A laser processing device having:

6. Further, a measuring instrument is provided to measure a beam profile of the pulse laser beam at the position of the workpiece, The laser processing apparatus of claim 5, wherein the control device further has a function of determining whether a difference between the area of ​​the beam spot determined from the measurement results obtained from the measuring instrument and the target area value is within an acceptable range, and if the difference is outside the acceptable range, controlling the beam size adjustment optical system so that the area of ​​the beam spot approaches the target area value.

7. The method further comprises a movable stage that holds the object to be processed and is capable of performing a scanning operation to scan the surface of the held object to be processed in a predetermined direction with a pulse laser beam output from the laser oscillator, 7. The laser processing apparatus according to claim 5, wherein the control device has a function of controlling the scanning operation of the movable stage so that the beam spot of one shot of the pulsed laser beam has an overlapping portion with the beam spot of the immediately preceding shot in the predetermined direction, and the ratio of the dimension of the overlapping portion in the predetermined direction to the dimension of the beam spot in the predetermined direction is constant.

8. The laser processing apparatus described in Claim 7, wherein the control device further has the function of controlling the scanning operation of the movable stage so that the movement distance in the specified direction of the object to be processed held on the movable stage during one repetition period of the pulses of the pulsed laser beam output from the laser oscillator is shorter than the dimension in the specified direction of the beam spot of the pulsed laser beam.

9. determining a target value of pulse energy density at a surface of the workpiece; Before laser processing, an area of ​​a beam spot on the surface of the object to be processed is determined based on the pulse energy of a pulse laser beam output from a laser oscillator and the target value so that the pulse energy density on the surface of the object to be processed becomes the target value; A laser annealing method in which the laser processing is started by irradiating a pulsed laser beam onto the object under conditions such that the area of ​​the beam spot on the surface of the object becomes a determined area.

10. A laser annealing method as described in Claim 9, wherein in the laser processing, the object to be processed is scanned in a predetermined direction with a pulsed laser beam, and the beam spot of one shot of the pulsed laser beam has an overlapping portion with the beam spot of the immediately preceding shot in the predetermined direction, and scanning is performed so that the ratio of the dimension of the beam spot in the predetermined direction to the dimension of the overlapping portion in the predetermined direction is constant.

Images