JP6713203B2 - Laser processing equipment - Google Patents

Description

The present invention relates to a laser processing apparatus that shapes a laser beam cross-sectional shape and a light intensity distribution on a surface of an object to be processed by a beam shaper.

Laser annealing techniques are used to activate the dopants implanted in the semiconductor wafer. For example, the surface layer portion of the semiconductor wafer is heated by applying a pulse laser beam to the semiconductor wafer to activate the dopant. The pulse width and pulse energy density are adjusted to control the anneal depth and anneal temperature.

To adjust the pulse energy density, the average power of the pulsed laser beam is measured, and the pulse energy density is calculated from the measured value of the average power, the pulse repetition frequency, and the area of the beam cross section. The following patent document 1 discloses a laser annealing apparatus.

JP, 2005-170724, A

The average power of the pulse laser beam can be brought close to the target value by adjusting the transmittance of the attenuator based on the ratio of the measured value of the pulse laser beam incident on the object to be processed and the target value. However, it has been found that even if laser processing is performed with the average power matched with the target value, sufficient reproducibility of processing quality may not be obtained.

An object of the present invention is to provide a laser processing apparatus capable of improving the reproducibility of processing quality.

According to one aspect of the invention,
Laser light source,
A beam shaper that is arranged in the path of the laser beam between the laser light source and the object to be processed, and shapes the beam cross section on the surface of the object to be processed,
An attenuator with a variable transmittance arranged in the path of the laser beam between the laser light source and the object to be processed,
A beam profiler for measuring the light intensity distribution of the laser beam at the position of the surface of the processing object,
A laser intensity measuring device for measuring the intensity of the laser beam incident on the object to be processed,
Measurement of the beam profiler, and based on the measurement result of the laser intensity measuring device, have a control unit for adjusting the transmittance of the attenuator,
The control device is a laser that adjusts the transmittance of the attenuator based on a relationship between a portion showing a light intensity equal to or higher than an intensity threshold and a whole light intensity distribution in the light intensity distribution measured by the beam profiler. A processing device is provided.

By using not only the measurement result of the laser intensity measuring instrument but also the measurement result of the beam profiler to adjust the transmittance of the attenuator, the reproducibility of processing quality can be improved.

1A is a schematic view of a laser processing apparatus according to an embodiment, and FIG. 1B is a plan view of a stage of the laser processing apparatus. FIG. 2 is a schematic diagram of the laser processing apparatus in a state where the pulse laser beam is incident on the beam profiler. FIG. 3 is a flowchart of the average power adjustment processing executed by the laser processing apparatus according to the reference example. FIG. 4A is a diagram showing a beam cross-sectional shape on the surface of the object to be processed, and FIG. 4B is a graph showing an example of the light intensity distribution in the width direction of the beam cross section. FIG. 5 is a flowchart of the average power adjustment processing executed by the laser processing apparatus according to the embodiment. FIG. 6 is a graph showing an example of the light intensity distribution in the width direction of the beam cross section.

FIG. 1A shows a schematic diagram of a laser processing apparatus according to an embodiment. The laser light source 10 receives the oscillation command signal S0 from the control device 50 and outputs a pulsed laser beam. A laser diode, for example, is used for the laser light source 10. The laser diode outputs a quasi-continuous oscillation (QCW) laser beam having a wavelength of 808 nm, for example.

An attenuator 11 having a variable transmittance is arranged in the path of the pulsed laser beam output from the laser light source 10. The attenuator 11 attenuates the light intensity of the pulse laser beam based on the set transmittance. The transmittance of the attenuator 11 is commanded by the transmittance command signal S1 from the control device 50. The pulsed laser beam that has passed through the attenuator 11 is introduced into the processing chamber 15 via the beam shaper 12, the folding mirror 13, and the objective lens 14.

A stage 20 is arranged in the processing chamber 15. A chuck mechanism 23 is fixed on the stage 20, and the workpiece 30 is held by the chuck mechanism 23. The processing object 30 is, for example, a semiconductor wafer in which a dopant is ion-implanted. The stage 20 is controlled by the control device 50 to move in a two-dimensional direction parallel to the surface of the processing object 30.

The pulsed laser beam is introduced into the processing chamber 15 through the entrance window 16 provided on the wall surface above the processing chamber 15. When the stage 20 moves, the incident position of the pulse laser beam moves on the surface of the processing object 30. By repeating the movement of the incident position of the pulsed laser beam in the main scanning direction and the movement in the sub scanning direction, the entire surface of the object 30 to be processed can be annealed.

The beam shaper 12 and the objective lens 14 make the cross-sectional shape of the pulsed laser beam on the surface of the processing object 30 long in one direction (long shape), and provide the light intensity distribution in the length direction and the width direction. Homogenize. As the beam shaper 12, a beam homogenizer in which a plurality of cylindrical lens arrays are combined can be used.

FIG. 1B shows a plan view of the stage 20. In addition to the chuck mechanism 23, a mirror 21 and a beam profiler 25 are attached to the stage 20. By moving the stage 20, one of a state in which the pulse laser beam is incident on the processing target 30, a state in which the pulse laser beam is incident on the mirror 21, and a state in which the pulse laser beam is incident on the beam profiler 25 is realized.

FIG. 1A shows a state in which the pulse laser beam introduced into the processing chamber 15 is incident on the mirror 21. A state in which the pulse laser beam introduced into the processing chamber 15 is incident on the beam profiler 25 is shown in FIG.

As shown in FIG. 1A, the pulse laser beam incident on the mirror 21 is reflected by the mirror 21 in the horizontal direction. The pulsed laser beam reflected by the mirror 21 passes through the window 17 provided on the side wall of the processing chamber 15 and enters the laser intensity measuring device 40 arranged outside the processing chamber 15. A lens 22 is arranged in the path of the pulsed laser beam from the mirror 21 to the laser intensity measuring device 40. The lens 22 adjusts the size of the beam cross section of the pulse laser beam on the light receiving surface of the laser intensity measuring device 40.

As the laser intensity measuring device 40, a power meter, a joule meter, a photodetector or the like can be used. The power meter measures the average power (time average of power) of the pulsed laser beam. The Joule meter measures the pulse energy of the pulsed laser beam. The photodetector measures the waveform of the pulsed laser beam. By calibrating the photodetector, the pulse energy can be obtained from the waveform of the pulse laser beam. The measurement result of the laser intensity measuring device 40 is input to the control device 50. Hereinafter, the case where the measured physical quantity of the laser intensity measuring device 40 is the average power will be continued.

As shown in FIG. 2, when the pulse laser beam is incident on the beam profiler 25, the beam profiler 25 measures the light intensity distribution. The measurement result of the beam profiler 25 is input to the control device 50.

A branching device 18 is arranged in the path of the pulsed laser beam between the laser light source 10 and the attenuator 11. Upon receiving the switching signal S2 from the control device 50, the branching device 18 switches between a state in which the pulse laser beam is incident on the attenuator 11 (processing state) and a state in which the pulsed laser beam is incident on the outlet power meter 45 (standby state). The outlet power meter 45 measures the average power of the incident pulsed laser beam. The measurement result of the outlet power meter 45 is input to the control device 50.

The control device 50 controls the output timing of the pulsed laser beam from the laser light source 10, the transmittance of the attenuator 11, the movement of the stage 20, and the state of the branching device 18.

Before describing the embodiments of the present invention, reference examples will be described with reference to FIGS. 3 and 4. The laser processing apparatus according to the reference example has the same configuration as the laser processing apparatus according to the embodiment shown in FIG. 1A.

FIG. 3 shows a flowchart of the power adjustment process executed by the laser processing apparatus according to the reference example. Each process of the flowchart is realized by a processing program stored in the control device 50.

In step ST1, the control device 50 sets the transmittance of the attenuator 11 to the initial value. The initial value of the transmittance is stored in the control device 50 in advance.

In step ST2, the average power of the pulsed laser beam output from the laser light source 10 is measured. Specifically, first, the controller 50 moves the stage 20 so that the pulse laser beam is incident on the mirror 21. Then, the oscillation command signal S0 is sent to the laser light source 10 to start the output of the pulsed laser beam. The controller 50 reads the output from the laser intensity measuring device 40 to obtain a measurement value of the average power of the pulsed laser beam.

In step ST3, the control device 50 adjusts the transmittance of the attenuator 11 based on the measured value of the average power and the target value of the average power. Specifically, the adjusted transmittance is calculated by multiplying the current transmittance by the ratio of the target value to the measured value of the average power. The target value of the average power is stored in the control device 50 in advance.

In step ST4, laser processing is performed under the control of the control device 50. Since the transmittance of the attenuator 11 is adjusted in step ST3, laser processing can be performed with the target average power.

Next, with reference to FIG. 4A and FIG. 4B, problems of the annealing process by the laser processing apparatus according to the reference example shown in FIG. 3 will be described.

FIG. 4A shows a beam cross-sectional shape on the surface of the processing object 30. The beam cross section 33 has an elongated shape that is long in one direction. An xy orthogonal coordinate system is defined in which the length direction of the beam cross section 33 is the y direction and the width direction is the x direction.

FIG. 4B shows an example of the light intensity distribution in the width direction (x direction) of the beam cross section 33. The abscissa represents the x coordinate in the unit of “μm”, and the ordinate represents the light intensity in an arbitrary unit. The center of the beam cross section 33 (FIG. 4A) in the width direction is the origin of the x coordinate. The light intensity distribution has a skirt portion outside the beam cross section. As an example, the line connecting the points where the light intensity is equal to the intensity threshold value Ith can be defined as the outer peripheral line of the beam cross section.

The pulse laser beam having the light intensity distribution shown by the solid line in FIG. 4B has a higher light intensity inside the beam cross section than the pulse laser beam having the light intensity distribution shown by the broken line. On the other hand, in the skirt portion, the pulse laser beam having the light intensity distribution shown by the broken line has a higher light intensity than the pulse laser beam having the light intensity distribution shown by the solid line. Such a difference in the light intensity distribution may occur due to fluctuations in the characteristics of the beam shaper 12.

Normally, the position of the laser intensity measuring device 40 is adjusted so that the beam cross section is located at the center of the light receiving surface of the laser intensity measuring device 40. In this state, the foot portion of the light intensity distribution also enters the light receiving surface of the laser intensity measuring device 40. Therefore, the average power measured by the laser intensity measuring device 40 also includes the power of the skirt portion.

Only the laser energy in the beam cross section contributes to the laser annealing, and the laser energy in the foot portion does not contribute to the laser annealing. Therefore, in order to perform annealing with high reproducibility, the average power in the beam cross section must be constant. However, in the reference example shown in FIG. 3, the average power including the skirt portion matches the target value. If the light intensity distribution deviates from the initial shape, the average power in the beam cross section will not reach the target value even if the measured value of the average power is matched with the target value. Therefore, reproducibility of the annealing process cannot be ensured.

For example, when the measured values of the average power of the light intensity distribution indicated by the solid line shown in FIG. 4B and the light intensity distribution indicated by the broken line are the same, the average power in the beam cross section is equal to that of the light intensity distribution indicated by the solid line. Is bigger.

Next, a laser processing apparatus according to an embodiment will be described with reference to FIGS. 1, 2, 5, and 6. In the examples described below, it is possible to perform annealing with high reproducibility.

FIG. 5 shows a flowchart of the power adjustment processing executed by the laser processing apparatus according to the embodiment. Each processing of the flowchart is executed by a processing program stored in the control device 50.

The processes of steps ST1 and ST2 are the same as steps ST1 and ST2 of the reference example shown in FIG.

In step ST10, the light intensity distribution of the pulse laser beam is measured. Specifically, after measuring the average power in step ST2, the control device 50 controls the branching device 18 so that the pulsed laser beam output from the laser light source 10 enters the outlet power meter 45. Then, the stage 20 (FIG. 1) is moved so that the pulsed laser beam enters the beam profiler 25. In this state, the branching device 18 is controlled so that the pulse laser beam is incident on the beam profiler 25. Thereby, the beam profiler 25 measures the light intensity distribution of the pulsed laser beam. The measured light intensity distribution is the cumulative light intensity distribution of a plurality of shots.

In step ST11, the control device 50 calculates the effective power ratio based on the light intensity distribution measured in step ST10. The definition of the effective power ratio will be described below with reference to FIG.

FIG. 6 shows an example of the light intensity distribution in the width direction (x direction) of the beam cross section. A region surrounded by a line connecting the positions where the light intensity is equal to the intensity threshold value Ith is defined as a beam cross section 33 (FIG. 4A). Within the beam cross section 33, an almost top-flat light intensity distribution is obtained. A skirt portion 34 having a light intensity sufficiently weaker than the peak intensity extends outside the beam cross section 33. A1 represents a value obtained by integrating the light intensity in the beam cross section 33 in the width direction (x direction). A2 represents a value obtained by integrating the light intensity of the skirt portion 34 in the width direction.

A region in the beam cross section 33 having a light intensity equal to or higher than the intensity threshold value Ith contributes to annealing, and a skirt portion 34 having a light intensity lower than the intensity threshold value Ith does not substantially contribute to annealing. Effective power ratio Re
Re=A1/(A1+A2)
It is defined as. That is, the effective power ratio is the integral value A1 of the light intensity of the portion showing the light intensity of the intensity threshold Ith or more in the light intensity distribution measured by the beam profiler 25 and the integral value A1+A2 of the entire light intensity distribution. Defined by the ratio. The effective power ratio can be considered as the ratio of the power effectively used for annealing to the laser power incident on the processing target 30 (FIG. 1A).

In step ST12 (FIG. 5), the control device 50 determines, based on the relationship between the entire light intensity distribution and a portion of the light intensity distribution measured by the beam profiler 25, which indicates a light intensity equal to or higher than the intensity threshold Ith. The transmittance of the attenuator 11 is adjusted. More specifically, the control device 50 adjusts the transmittance of the attenuator 11 (FIG. 1A) based on the measured value and target value of the average power of the pulsed laser beam and the measured value and standard value of the effective power ratio. .. Hereinafter, an example of the adjusting method will be specifically described.

The target value Pt of the average power and the standard value Rs of the effective power ratio are stored in the control device 50 in advance. The target value Pt of the average power can be determined from the conditions under which the optimum processing is performed by performing a plurality of evaluation experiments with different average powers. The effective power ratio of the pulse laser beam used in this evaluation experiment is adopted as the standard value Rs.

The transmittance of the attenuator 11 set in step ST1 is expressed as Tm, the average power of the pulsed laser beam measured in step ST2 is expressed as Pm, and the effective power ratio measured in step ST11 is measured. Notated as Rm. When the measured value of the average power at the exit of the laser light source 10 is expressed as P0, the measured value Pm of the average power is
Pm=P0×Tm (1)
It is expressed as

The adjusted value of the transmittance of the attenuator 11 after the adjustment in step ST12 is expressed as Tc. Assuming that the average power of the pulsed laser beam at the exit of the laser light source 10 does not substantially fluctuate in a short time, the average power Pc on the surface of the processed object after the transmittance adjustment is
Pc=P0×Tc (2)
It is expressed as

In order to perform the annealing under the optimum conditions, the effective power after adjusting the transmittance may be made equal to the optimum effective power in the evaluation experiment. That is, the following formula may be satisfied.
Pc×Rm=Pt×Rs (3)
Here, it is assumed that the characteristics of the beam shaper 12 (FIG. 1) do not change in a short time and the effective power ratio is substantially constant.

The following equations are derived from the above equations (1), (2) and (3).
Tc=(Pt/Pm)×(Rs/Rm)×Tm (4)

The transmittance adjustment value Tc of the attenuator 11 can be obtained based on the equation (4). The attenuator 11 may be adjusted so that this transmittance becomes equal to the adjustment value Tc.

In step ST4, laser processing is performed under the control of the control device 50. The effective power of the pulsed laser beam during laser processing agrees with the optimum value obtained in the evaluation experiment. Therefore, laser processing with high reproducibility can be performed.

In the above-described embodiment, the light intensity distribution in the width direction of the beam cross section 33 (FIG. 4A) is used as the light intensity distribution that is the basis for calculating the effective power ratio. In other words, the effective power ratio was calculated by integrating the light intensity distribution in the width direction of the beam cross section 33 (FIG. 4A). The area of the skirt portion extending in the length direction (y direction) from both ends of the beam cross section 33 in the length direction is sufficiently smaller than the area of the skirt portion extending on both sides in the width direction. Therefore, the value obtained by dividing the light intensity of the skirt portion spreading on both ends in the length direction by the area is sufficiently smaller than the value by dividing the light intensity of the skirt portion spreading on both sides in the width direction by the area. Therefore, by utilizing the effective power ratio obtained based on the power obtained by integrating the light intensity distribution in the width direction, sufficiently high reproducibility can be ensured.

When the ratio of the dimension of the beam cross section in the x direction to the dimension of the y direction is close to 1, for example, when the beam cross section is close to a circle or a square, the two-dimensional light intensity distribution is used as the basis for calculating the effective power ratio. May be used. In this case, the effective power ratio is calculated by dividing the light intensity distribution by the area.

When the measured value Pm of the average power measured in step ST2 is out of the allowable range, the controller 50 may issue an alarm. When this alarm is issued, the operator preferably performs maintenance on the laser light source 10 and the like. When the measured value Rm of the effective power ratio obtained in step ST11 is out of the allowable range, the control device 50 may issue an alarm. When this alarm is issued, the operator preferably performs maintenance of the beam shaper 12 and the like.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

10 laser light source 11 attenuator 12 beam shaper 13 folding mirror 14 objective lens 15 processing chamber 16 entrance window 17 window 18 branching device 20 stage 21 mirror 22 lens 23 chuck mechanism 25 beam profiler 30 workpiece 33 beam cross section 34 skirt portion 40 laser Strength measuring device 45 Outlet power meter 50 Control device

Claims (5)

Laser light source,
A beam shaper that is arranged in the path of the laser beam between the laser light source and the object to be processed, and shapes the beam cross section on the surface of the object to be processed,
An attenuator with a variable transmittance arranged in the path of the laser beam between the laser light source and the object to be processed,
A beam profiler for measuring the light intensity distribution of the laser beam at the position of the surface of the processing object,
A laser intensity measuring device for measuring the intensity of the laser beam incident on the object to be processed,
Measurement of the beam profiler, and based on the measurement result of the laser intensity measuring device, have a control unit for adjusting the transmittance of the attenuator,
The control device is a laser that adjusts the transmittance of the attenuator based on a relationship between a portion showing a light intensity equal to or higher than an intensity threshold and a whole light intensity distribution in the light intensity distribution measured by the beam profiler. Processing equipment. Furthermore, laser processing apparatus of claim 1, the laser beam output from the laser light source to have a stage for holding the workpiece in a position to incident. The control device, of the light intensity distribution measured by the beam profiler, the effective power that is the ratio of the integrated value of the light intensity of the portion showing the light intensity equal to or higher than the intensity threshold and the integrated value of the entire light intensity distribution. based on the measured values of the ratio, the laser machining apparatus according to claim 1 or 2 for adjusting the transmittance of the attenuator. A standard value of the effective power ratio is stored in the control device,
The controller, the ratio of the standard value of the effective power ratio and the measured value, and based on the transmittance of the attenuator at the time of measurement, calculates the adjustment value of the transmittance of the attenuator,
The laser processing apparatus according to claim 3, wherein the transmittance of the attenuator is adjusted so that the transmittance becomes the adjustment value. The beam shaper makes the beam cross-sectional shape on the surface of the processing object long in one direction,
The control device, wherein the light intensity distribution measured by the beam profiler, laser processing apparatus according to any one of claims 1 to 4 using the light intensity distribution in the width direction of the beam cross-section.

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