JP6644422B2 - Laser processing equipment - Google Patents

Description

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

  A laser annealing technique is used for activating a dopant implanted in a semiconductor wafer. For example, by irradiating the semiconductor wafer with a pulsed laser beam, the surface layer of the semiconductor wafer is heated to activate the dopant. The pulse width and pulse energy density (fluence) are adjusted to control the anneal depth and anneal temperature.

  In order to adjust the pulse energy density, the average power of the pulse 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. Patent Literature 1 below discloses a laser annealing apparatus.

JP 2015-170724 A

  By adjusting the transmittance of the attenuator based on the ratio between the measured value of the average power of the pulsed laser beam incident on the object to be processed and the target value, the average power of the pulsed laser beam can be made closer to the target value. However, it has been found that even if the laser processing is performed with the average power equal to the target value, sufficient reproducibility of the 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,
A laser light source ,
Disposed in the path of the laser beam between the previous SL laser light source and the machining object, a beam shaper for shaping the beam cross section at the surface of the workpiece,
And the laser beam transmittance variable attenuator positioned in the path of between the laser light source and the front Symbol machining object,
A beam profiler which measures the light intensity distribution of the laser beam at the position of the surface before Symbol machining object,
A laser processing apparatus comprising: a control device that obtains an area of a beam cross section based on a measurement result of the beam profiler, sets a measured value of the area, and adjusts a transmittance of the attenuator based on the measured value of the area of the beam cross section. Is provided.

  Even if the area of the beam cross section changes from the initial value, it is possible to make the fluence close to the target value. Thereby, the reproducibility of the processing quality can be improved.

FIG. 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 when the pulse laser beam is incident on the beam profiler. FIG. 3 is a flowchart of a power adjustment process performed by the laser processing apparatus according to the reference example. FIG. 4 is a diagram illustrating a beam cross-sectional shape on the surface of the processing object. FIGS. 4B and 4C are examples of light intensity distributions of the beam cross section in the width direction (x direction) and the length direction (y direction), respectively. FIG. FIG. 5 is a flowchart of a fluence adjustment process performed by the laser processing apparatus according to the embodiment.

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

  A variable transmittance attenuator 11 is arranged on the path of the pulse 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 a transmittance command signal S1 from the control device 50. The pulse laser beam transmitted 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 target 30 is, for example, a semiconductor wafer into which a dopant is ion-implanted. The stage 20 moves in a two-dimensional direction parallel to the surface of the workpiece 30 under the control of the control device 50.

  The pulsed laser beam is introduced into the processing chamber 15 through an entrance window 16 provided on a wall surface above the processing chamber 15. When the stage 20 moves, the incident position of the pulsed laser beam moves on the surface of the processing target 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 workpiece 30 can be annealed. By this annealing, the dopant injected into the processing target 30 is activated.

  The beam shaper 12 and the objective lens 14 make the cross-sectional shape of the pulse laser beam on the surface of the processing target 30 long in one direction (long shape), and also adjust the light intensity distribution in the length direction and the width direction. Make uniform. 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. The mirror 20 and the beam profiler 25 are attached to the stage 20 in addition to the chuck mechanism 23. By moving the stage 20, one of a state in which the pulsed laser beam is incident on the processing target 30, a state in which the pulsed laser beam is incident on the mirror 21, and a state in which the pulsed 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. FIG. 2 shows a state in which the pulsed laser beam introduced into the processing chamber 15 is incident on the beam profiler 25.

  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 pulse laser beam reflected by the mirror 21 passes through a window 17 provided on a side wall of the processing chamber 15 and enters a laser intensity measuring device 40 disposed outside the processing chamber 15. A lens 22 is disposed on the path of the pulse 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 photo detector, or the like can be used. The power meter measures the average power (time average of power) of the pulse laser beam. The joule meter measures the energy per one pulse of the pulsed laser beam (pulse energy). The photo detector measures the waveform of the pulsed laser beam. By calibrating the photodetector, the pulse energy can be obtained from the pulse laser beam waveform. The measurement result of the intensity of the pulse laser beam by the laser intensity measuring device 40 is input to the control device 50. Hereinafter, the case where the physical quantity measured by the laser intensity measuring device 40 is the average power will be described.

  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 on the path of the pulse 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 pulsed laser beam enters the attenuator 11 (processing state) and a state in which the pulsed laser beam enters the exit power meter 45 (standby state). The outlet power meter 45 measures the average power of the incident pulse 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 pulse 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 an embodiment of the present invention, a reference example will be described with reference to FIGS. 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 a power adjustment process performed 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 an 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 pulse laser beam output from the laser light source 10 is measured. Specifically, first, the control device 50 moves the stage 20 so that the pulsed laser beam enters the mirror 21. Thereafter, an oscillation command signal S0 is sent to the laser light source 10 to start outputting a pulse laser beam. When the control device 50 reads the output from the laser intensity measuring device 40, a measured value of the average power of the pulsed laser beam is obtained.

  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 transmittance after adjustment 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 has been adjusted in step ST3, laser processing can be performed with the target average power.

  Next, with reference to FIG. 4A to FIG. 4C, a problem of the annealing process using the laser processing apparatus according to the reference example shown in FIG. 3 will be described.

  FIG. 4A shows a beam cross-sectional shape of the pulsed laser beam on the surface of the processing target 30. The beam cross section 33 has a long 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.

4B and 4C show examples of the light intensity distribution in the width direction (x direction) and the length direction (y direction) of the beam cross section 33, respectively. The horizontal axis in FIG. 4B represents the x coordinate, and the vertical axis represents the light intensity. The horizontal axis of FIG. 4C represents the y coordinate, and the vertical axis represents the light intensity. The center in the width direction of the beam cross section 33 is the origin of the x coordinate, and the center in the length direction is the origin of the y coordinate. An almost top-flat light intensity distribution (beam profile) is realized in two directions, the width direction and the length direction. A line connecting the points where the light intensity is equal to the intensity threshold Ith can be defined as the outer peripheral line of the beam cross section. As intensity threshold Ith, it is possible for example to employ the 1 / e ² times the value of the peak intensity.

When the average power of the pulse laser beam is represented by Pm, the area of the beam cross section 33 is represented by A, and the pulse repetition frequency is represented by f, the fluence (pulse energy density) F is defined by the following equation.
F = Pm / (f × A) (1)
As can be seen from the above equation (1), even if the average power Pm is constant, when the area A of the beam cross section 33 changes, the fluence F also changes. In the reference example shown in FIG. 3, the average power of the pulse laser beam is made to match the target value, but the area A of the beam cross section 33 is not considered. That is, laser processing is performed on the assumption that the area A of the beam cross section 33 is unchanged.

  However, the area A of the beam cross section 33 is not always constant due to a change in optical characteristics due to a rise in the temperature of the beam shaper 12 and aging. Since the fluence F cannot be kept constant due to a change in the area A of the beam cross section 33, it is difficult to ensure reproducibility of the annealing quality.

  Next, a laser processing apparatus according to an embodiment will be described with reference to FIG. 1, FIG. 2, and FIG. In the laser processing apparatus according to the embodiment, as described below, reproducibility of annealing quality can be ensured.

  FIG. 5 is a flowchart illustrating a fluence adjustment process performed by the laser processing apparatus according to the embodiment. Each process in the flowchart is realized by a processing program stored in the control device 50.

  In step ST <b> 11, before starting laser processing, first, a processing target 30 (FIG. 1), for example, a semiconductor wafer into which a dopant has been implanted is transferred to the stage 20. After the transfer, the workpiece 30 is fixed to the chuck mechanism 23.

  In step ST12, the control device 50 performs height adjustment of the processing target 30 and alignment in the in-plane direction.

  After step ST12, in step ST13, it is determined whether or not the current operation mode of the apparatus is “fluence feedback execution mode”. This operation mode is set by the operator. For example, when the current operation mode of the device is the “fluence feedback execution mode”, the fluence feedback process described below is executed. If the operation mode is not the “fluence feedback execution mode”, the laser processing is executed in step ST23 without executing the fluence feedback processing.

  If it is determined in step ST13 that the operation mode is the “fluence feedback execution mode”, it is determined in step ST14 whether the operation mode is the “beam cross section measurement mode”. This operation mode is also set by the operator.

  When it is determined in step ST14 that the operation mode is the “beam cross-sectional area measurement mode”, in step ST15, it is determined whether or not the current object 30 (FIG. 1A) is the first lot in the lot. .

  If it is determined in step ST15 that the current processing object 30 is the first one in the lot, in step ST16, the light intensity distribution of the pulse laser beam is measured. The light intensity distribution can be measured by making the pulsed laser beam output from the laser light source 10 incident on the beam profiler 25, as shown in FIG.

  In step ST17, the control device 50 calculates a beam cross-sectional area based on the measured light intensity distribution. For example, the width of the beam section 33 is determined from the light intensity distribution in the width direction (FIG. 4B) of the beam section 33 (FIG. 4A), and the length of the beam section 33 is determined from the light intensity distribution in the length direction (FIG. 4C). The area A can be calculated from the width and the length of the beam section 33.

  In step ST18, it is determined whether or not the area A of the beam cross section 33 is normal. The allowable range of the area A of the beam cross section 33 is stored in the control device 50 in advance. If the measured value of the area A falls within the allowable range, it is determined that the area A is normal, and if it is outside the allowable range, it is determined that the area A is not normal.

  If it is determined that the area A of the beam cross section 33 is not normal, it is considered that some abnormality has occurred in the beam shaper 12 (FIG. 1A), and the laser processing is ended. The control device 50 issues an alarm for notifying the operator of the abnormality.

  In step ST18, when it is determined that the area A of the beam cross section 33 is normal, in step ST19, the measured value of the area A obtained in step ST17 is used as the area A of the beam cross section 33 for fluence calculation. adopt.

  In step ST20, the average power of the pulse laser beam is measured. The measurement of the average power can be performed by making the pulsed laser beam output from the laser light source 10 incident on the laser intensity measuring device 40 as shown in FIG. 1A.

  In step ST21, the fluence F is calculated. The calculation of the fluence F can be performed by the above equation (1). At this time, the measured value is adopted as the area A of the beam section 33 for calculating the fluence (step ST19). Therefore, in step ST21, the fluence F is calculated using the measured value of the area A obtained in step ST17.

  In step ST22, it is determined whether or not the calculated value of the fluence F is normal. The allowable range of the fluence F is stored in the control device 50 in advance. If the calculated value of the fluence F falls within the allowable range, the calculated value of the fluence F is determined to be normal. If the calculated value of the fluence F is out of the allowable range, it is determined that the calculated value of the fluence F is not normal.

  If the calculated value of the fluence F is normal, laser processing is performed in step ST23.

  If it is determined in step ST22 that the calculated value of the fluence F is not normal, the average power is adjusted in step ST24. After adjusting the average power, in step ST20, the average power of the pulse laser beam is measured again. Hereinafter, the method of adjusting the average power in step ST24 will be described.

  As a method of adjusting the average power, one or both of a method of adjusting the transmittance of the attenuator 11 and a method of adjusting the drive current of the laser light source 10 are employed. In step ST24, the control device 50 first adjusts the transmittance of the attenuator 11 so that the calculated value of the fluence F matches the target value of the fluence F. The target value of the fluence F is stored in the control device 50 in advance.

  If it is determined that the measured value of the fluence F does not reach the target value even if the transmittance of the attenuator 11 is set to the rated maximum value, for example, approximately 100%, the control device 50 sets the drive current supplied to the laser light source 10. Increase. The relationship between the increase width of the drive current and the increase width of the average power at the exit of the laser light source 10 is stored in the control device 50 in advance. The increase amount of the drive current can be determined based on the difference between the measured value of the fluence F and the target value, and the relationship between the increase amount of the drive current and the increase amount of the average power.

  If it is determined in step ST15 that the current processing object 30 is the second or subsequent lot of the lot, the beam for calculating the fluence F is determined in step ST19 without performing the light intensity distribution measurement process. As the area A of the cross section 33, a measured value of the area A obtained at the time of processing the first processing object 30 of the lot is adopted. That is, the light intensity distribution of the pulse laser beam is actually measured only when processing the first processing object 30 of the lot. The reason for omitting the measurement of the light intensity distribution during the processing of the second and subsequent sheets is that the light intensity distribution of the pulsed laser beam does not substantially change during the processing of a plurality of processing objects 30 in one lot. Because it can be.

  If it is determined in step ST14 that the current operation mode is not the beam cross-sectional area measurement mode, it is determined in step ST25 whether or not there is a thinning process. The presence or absence of the thinning process is preset by the operator.

  If it is determined in step ST14 that there is a thinning process, in step ST26, it is determined whether or not the current processing target 30 is a thinning target. If it is determined that the current processing target 30 is a thinning target, laser processing is performed in step ST23 without adjusting the fluence F.

  If it is determined in step ST25 that there is no thinning process, and if it is determined in step ST26 that the current workpiece 30 is not a thinning target, in step ST27, the area of the beam section 33 for fluence calculation is determined. A standard value is adopted as A. This standard value is stored in the control device 50 in advance.

  After step ST27, the processing after step ST20 is executed. In step ST21, the fluence F is calculated using the standard value of the area A.

  Next, excellent effects of the laser processing apparatus according to the embodiment shown in FIG. 5 will be described. In the embodiment, in step ST19, an actually measured value is used as the area A of the beam section 33 for calculating the fluence. For this reason, even when the area A of the beam cross section 33 deviates from the initial value due to a change in the characteristics of the beam shaper 12, the current fluence F can be calculated with high accuracy. Since the average power of the pulse laser beam is corrected based on the fluence F, the fluence F of the current pulse laser beam used for processing can be made to substantially match the target value. This makes it possible to perform laser processing with high reproducibility.

  For example, when the characteristics of the beam shaper 12 (FIG. 1A) are stable and it is considered that the light intensity distribution does not substantially fluctuate, the operation mode of the apparatus is set to the “beam cross section measurement mode”. It is not necessary to keep it. If the average power at the exit of the laser light source 10, the characteristics of the beam shaper 12, and the characteristics of other optical systems are not considered to have changed so much as to affect the processing quality, the operation mode of the apparatus is changed. , The "fluence feedback execution mode" need not be set.

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

Reference Signs List 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 processing object 33 beam cross section 40 laser intensity measuring device 45 Power meter for exit 50 Control device

Claims (4)

A laser light source ,
Disposed in the path of the laser beam between the previous SL laser light source and the machining object, a beam shaper for shaping the beam cross section at the surface of the workpiece,
And the laser beam transmittance variable attenuator positioned in the path of between the laser light source and the front Symbol machining object,
A beam profiler which measures the light intensity distribution of the laser beam at the position of the surface before Symbol machining object,
A laser processing apparatus comprising: a control device that obtains an area of a beam cross section based on a measurement result of the beam profiler, sets a measured value of the area, and adjusts a transmittance of the attenuator based on the measured value of the area of the beam cross section. . further,
A stage that holds the object to be processed at a position where a laser beam output from the laser light source is incident,
And laser intensity measuring device for measuring the intensity of the laser beam incident on the front Symbol machining object has <br/>,
The laser processing according to claim 1, wherein the control device adjusts the transmittance of the attenuator based on a measured value of the laser beam intensity measured by the laser intensity measuring device in addition to the measured value of the area of the beam cross section. apparatus.   The control device calculates the pulse energy density based on the measured value of the laser beam intensity and the measured value of the area of the beam cross section, and sets the measured value as the measured value of the pulse energy density. 3. The laser processing apparatus according to claim 2, wherein the transmittance of the attenuator is adjusted so as to match a target value of the pulse energy density. The laser light source includes a laser diode,
4. The control device according to claim 3, wherein the drive current applied to the laser light source is increased when the pulse energy density of the pulse laser beam is less than a target value even when the transmittance of the attenuator reaches the rated maximum value of the attenuator. The laser processing apparatus according to item 1.

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