JP2008112805A - Pulsed laser heat treatment apparatus and method for controlling same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser thermal treatment apparatus for maintaining accuracy in the thermal treatment to a constant value and also provide a method for controlling the same laser heat treatment apparatus. <P>SOLUTION: The pulsed laser heat treatment apparatus includes a pulsed laser oscillator composed of an excitation source, a pumping chamber, a pulse oscillation mechanism, and a resonator structure to oscillate a pulsed laser light; a variable attenuator for attenuating intensity of a laser beam emitted from the pulse laser oscillator; an optical system for radiating the laser beam which has been adjusted in the intensity thereof with the variable attenuator on a heat treatment object surface, a stage on which the heat treatment object is placed; a measuring instrument for measuring pulse waveform as the time waveform of light intensity of the pulse laser; and a controller for adjusting a pulse width and moreover controlling attenuation rate of the variable attenuator by controlling excitation intensity of the excitation source on the basis of pulse width of the pulse waveform measured with the measuring instrument. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pulse laser processing apparatus and a control method therefor, and more particularly to a pulse laser heat treatment apparatus that performs heat treatment and a control method therefor. The heat treatment is a heat treatment, and includes chemical treatment such as impurity activation and crystallization in a semiconductor, and mechanical treatment such as welding and drilling.

  Heat treatment using a laser, thermal processing, and the like are performed. In order to make the processing accuracy and processing accuracy constant, the energy density on the processing surface and processing surface is monitored and fed back to the laser light source.

  In pulse laser processing, the peak value of the pulse laser beam as well as the pulse energy affects the processing accuracy. Japanese Patent Application Laid-Open No. 2005-101305 teaches that a pulse width and a peak intensity of a pulse laser beam are defined in a marking process for creating a mark on an inorganic nitride member. Japanese Patent Application Laid-Open No. 2003-002822 teaches that in laser welding, the lamp current of a laser oscillator is pulsated so that the peak value is at a level that gives a desired deep penetration. JP-A-8-153924 detects a peak value of a pulse laser beam when a repetition frequency is changed in a Q-switch pulse laser having a variable repetition frequency, and a peak value of an n-th pulse laser beam, and an (n-1) -th pulse laser beam. It is proposed that the driver is controlled based on the result of comparison with the peak value of the pulse laser beam. Japanese Patent Laid-Open No. 2000-126879 measures the relationship between the pulse width or pulse peak value and the pulse output in advance, compares the measured pulse width or pulse peak value with a set value, and controls the laser oscillator. , Teach to make uniform hole drilling with constant pulse output.

JP-A-2005-101305 JP 2003-200222 A JP-A-8-153924 JP, 2000-126879, A The activation of impurities implanted into a semiconductor wafer is performed using a harmonic pulse laser obtained by converting the pulse laser output of a laser diode (LD) pumped solid-state laser using a wavelength conversion element. Has been done. Laser oscillation is performed in a state where the temperature of the wavelength conversion element is kept constant and the current value of the LD is kept constant. The energy density per area on the wafer surface is monitored, and when a change is detected, it is fed back to the LD excitation current of the variable attenuator or the laser light source and controlled to keep the energy density constant.

  However, it has been found that the heat treatment accuracy can change even if the energy density is constant. Typically, the depth of the impurity activated in the semiconductor region doped with the impurity varies. When the depth at which the impurities are activated changes, the performance of the manufactured semiconductor device changes.

  An object of the present invention is to provide a pulse laser heat treatment apparatus capable of keeping the heat treatment accuracy constant, or a control method of the pulse laser heat treatment apparatus.

According to one aspect of the present invention,
A pulse laser oscillator having an excitation source, a pumping chamber, a pulse oscillation mechanism, and a resonator structure, and oscillating a pulse laser beam;
A variable attenuator for attenuating the intensity of the laser beam emitted from the pulse laser oscillator;
An optical system for irradiating the object to be heat-treated with a laser beam whose intensity is adjusted by the variable attenuator;
A stage on which a heat treatment object is placed;
A first measuring instrument capable of measuring a pulse waveform which is a time waveform of the light intensity of the pulse laser beam;
A control device capable of adjusting the pulse width by controlling the excitation intensity of the excitation source based on the pulse width of the pulse waveform measured by the first measuring instrument, and further controlling the attenuation rate of the variable attenuator;
Is provided.

According to another aspect of the invention,
(A) a step of measuring a pulse waveform which is a time waveform of the light intensity of the pulse laser beam emitted from the pulse laser device provided with the excitation source;
(B) obtaining a pulse width of the pulse waveform;
(C) obtaining a variation of the excitation intensity of the excitation source necessary to match the pulse width to a specified value;
(D) taking the variation and adjusting the pulsed laser device;
(E) irradiating the adjusted light emitted from the pulse laser device onto a stage on which an object to be processed is placed, and measuring an energy density;
(F) adjusting a variable attenuator so that the energy density matches a specified value;
A method for controlling a pulsed laser heat treatment apparatus is provided.

  Even if the pulse energy density per area is constant, the processing accuracy can change if the pulse waveform changes. Heat treatment accuracy can be improved by monitoring the pulse width of the pulse waveform, adjusting the pulse width by feedback, and adjusting the energy density by adjusting the variable attenuator.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1A is a block diagram schematically showing a configuration of a pulse laser heat treatment apparatus according to a first embodiment of the present invention.

The harmonic solid-state pulse laser 10 includes a pumping chamber 12, a Q switch 14, a wavelength conversion element 15, a shutter 16, and a dichroic mirror DM on the optical path between the pair of end mirrors EM1 and EM2. The end mirrors EM1 and EM2 are composed of a dielectric multilayer film formed on a quartz substrate. The end mirror EM1 is a perfect reflection mirror for the fundamental wave, and the end mirror EM2 is a perfect reflection mirror for the fundamental wave and the second harmonic. The pumping chamber 12 receives the emitted light from the laser diode 13 that is an excitation light source, and generates an excitation state. The pumping chamber 12 is made of, for example, an Nd: YAG crystal having an oscillation wavelength of 1064 nm, an Nd: YLF crystal having an oscillation wavelength of 1047 nm or 1053 nm, or an Nd: YVO ₄ crystal having an oscillation wavelength of 1064 nm. The wavelength with the highest absorption coefficient of the Nd: YLF crystal is 792 nm or 797 nm depending on conditions. The wavelength with the highest absorption coefficient of the Nd: YAG crystal and the Nd: YVO ₄ crystal is 808 nm. Even a wavelength slightly deviated from the wavelength having the highest absorption coefficient can be used as a sufficient excitation light source. Therefore, the excitation laser diode 13 is composed of a semiconductor laser diode having an oscillation wavelength of 780 nm to 820 nm.

The Q switch 14 is formed of, for example, an acousto-optic crystal, and generates a traveling wave or a standing wave by a sound wave generated from a transducer of a piezo element. The incident light having a predetermined wavelength is diffracted by the periodic arrangement of the refractive index. The Q switch for generating pulse oscillation can be constituted by a Pockels cell using an electro-optic crystal such as ADP or KDP in addition to the acousto-optic element. The shutter 16, which is an optional component, is composed of, for example, a mechanical shutter made of stainless steel and has a function of blocking a predetermined optical path between the end mirrors EM1 and EM2. The wavelength conversion element 15 is formed of, for example, a LiB ₃ O ₅ (LBO) crystal, receives a fundamental wave, and generates a second harmonic having a half wavelength.

As a wavelength conversion element, in addition to LBO crystal, βBaB ₂ O ₄ (BBO) crystal, KTiPO ₄ (KTP) crystal, BiB ₃ O ₆ (BIBO) crystal, MgO: LiNbO ₃ crystal, KDP crystal, DKDP crystal, KD ^* P A crystal, LiIO ₃ crystal, LiNbO ₃ crystal, or the like can also be used.

  In the configuration shown in the figure, a dichroic mirror DM1 that completely reflects the fundamental wave and transmits the second harmonic is disposed between the shutter 16 and the wavelength conversion element 15. The fundamental wave traveling from the pumping chamber is completely reflected by the dichroic mirror DM1 and travels toward the wavelength conversion element 15. The fundamental wave reflected by the end mirror EM2 and passed through the wavelength conversion element 15 is again completely reflected by the dichroic mirror DM1 and travels toward the pumping chamber 12. The harmonic generated by the wavelength conversion element 15 passes through the dichroic mirror DM1 in the direction from the end mirror EM2 toward the dichroic mirror DM1, and is extracted downward in the figure. The solid-state pulse laser 10 oscillates pulse laser light having a pulse width of 100 nsec to 300 nsec by a Q switch.

  The pulse laser beam emitted from the harmonic solid-state pulse laser 10 is subjected to predetermined attenuation by a variable attenuator 20 having a variable attenuation factor, and an XY stage via an optical system 21 such as a zoom lens 17, a homogenizer 18, and an imaging optical system 19. An object to be irradiated on ST, for example, a semiconductor wafer WF is irradiated. The optical system 21 forms a spatial beam shape according to the content of the heat treatment.

  In the vicinity of the exit of the harmonic solid-state pulse laser 10, a photodetector PD and a power meter PM1 are arranged. The photodetector PD receives, for example, a laser pulse reflected by the switching mirror SM via an attenuator (attenuator with fixed attenuation factor) EXT. The photodetector PD is formed of, for example, a silicon photodiode, and can detect a temporal change (pulse waveform) of the pulsed light intensity and supply the detection signal S1 to the control device CTL. The power meter PM1 can receive the laser pulse reflected by the switching mirror SM, measure the laser output emitted by the harmonic solid-state pulse laser 10, and supply the detection signal S3 to the control device CTL. A power meter PW2 is provided on the stage ST, and the incident energy density per area on the stage can be detected, and the detection signal S2 can be supplied to the control device CTL.

  The control device CTL determines the operating state of the laser heat treatment apparatus from the time waveform of the received light intensity signal S1 and the energy density signal S2. The control device CTL controls the drive current of the excitation laser diode LD and the attenuation factor of the variable attenuator 20 via the control signals CTL1 and CTL2.

  In heat treatment in which the object to be processed is irradiated with laser light to increase the temperature of the irradiated part, the peak value of the pulsed laser light on the irradiated part is closely related to the temperature reached by the irradiated part. I think that. The constant energy of the pulsed laser light only means that the total energy irradiated is constant. If the irradiated portion is a material having high thermal conductivity, it is considered that the temperature rise due to laser light irradiation and the temperature drop due to heat radiation occur simultaneously. Even if the total area (energy density) of the pulse waveform, which is the time waveform of the light intensity of the pulse laser beam, is the same, the heat treatment effect will be different if the pulse waveform is different. The inventor studied to control both the pulse waveform of the pulse laser beam and the irradiation energy.

FIG. 1B schematically shows a temporal waveform of the pulse laser beam intensity. It is assumed that the intensity waveform of the output pulse laser beam when the excitation laser diode LD is driven with a reference current is WV0. When the drive current of the excitation laser diode LD is increased, that is, when the excitation intensity is increased, the peak value increases and the pulse width decreases as shown by the pulse waveform WV1. When the drive current of the excitation laser diode LD is decreased, that is, when the excitation intensity is decreased, the peak value is decreased and the pulse width is increased as indicated by the waveform WV2. Thus, the pulse width and the peak value of the pulse are related to each other. The pulse width may be a half width, a width at an intensity of 1 / e of the peak value, or a width at an intensity of 1 / e ² of the peak value.

  Although the energy of the pulse laser beam of the laser heat treatment apparatus is the same, the area of the pulse waveform is the same as the state where the content of the heat treatment changes, but the peak is low and wide, and the peak is high and wide. It is conceivable that is narrow.

  Only by controlling the driving current of the excitation laser diode, the width only decreases when the peak value of the pulsed light is increased, and the width only increases when the peak value of the pulsed light is decreased. If the peak values are matched, the widths are not matched, and if the widths are matched, there is a high possibility that the peak values are not matched. Another parameter is the attenuation factor of the variable attenuator 20. The intensity of the laser pulse light on the irradiated surface is adjusted by a variable attenuator. Although the pulse width does not change, the peak value of the pulse can be adjusted with a variable attenuator. For example, the waveform WV1 can be selected and the attenuation factor of the variable attenuator can be increased to make the peak value the same as the waveform WV0. When there is a certain attenuation factor of the variable attenuator, the waveform WV2 can be selected to reduce the attenuation factor of the variable attenuator so that the peak value is the same as the peak value of the waveform WV0. The variable attenuator 20 only changes the attenuation rate (peak value) of the light intensity, and the pulse width is maintained.

 Therefore, if the pulse width is first matched with the specified value and then the peak value is matched with the specified value, both the width and the peak value will match the specified value. The intensity waveform of the laser pulse is usually fixed in a certain shape. If the width of the pulse width and the peak value match, the area (energy) also matches, or if the pulse width and the area match, the peak value can also be expected to match. That is, if the pulse width and the peak value or energy density of the pulse are adjusted to match the specified value, the accuracy of the heat treatment will be improved.

Hereinafter, the contents of the control will be described with reference to FIGS. 2A and 2B. For the target heat treatment, the peak value of the pulse waveform of the pulse light, the pulse width, and the output power P _WO at the laser exit are defined based on preliminary experiments and the like using the excitation intensity as a parameter.

FIG. 2A shows an example of a lookup table LUT that lists measurement values measured in advance. The drive current I _LD of the pumping laser diode is varied, the peak value of the pulse waveform of the emitted pulse light intensity at each value Ep, the pulse width Wd, it is listed the output power Pwo at the laser exit. Look-up table LUT1 is the excitation diode drive current I _LD around a first reference current, a table when changing in a certain range. Look-up table LUT2 is a pumping diode drive current I _LD about a second reference current, a table when changing in a certain range. Control is performed in one of the tables. In addition, a new table can be created. By using such a look-up table, the pulse width of the current pulse light is measured, and when it is different from the specified value, it can be seen how the drive current is adjusted to obtain the desired pulse width. Instead of the look-up table, the relationship between the drive current, the pulse width, the energy density, and the like may be formulated.

FIG. 2B shows a control flowchart. In the first step 31, a time-varying waveform of the pulsed light intensity is measured. Since the purpose is to measure the pulse width, the measurement position may be before or after the variable attenuator. In the second step 2, the pulse width is calculated from the pulse waveform of the measured pulsed light intensity. In a third step 33, a variation ΔI _LD of the driving current of the pumping laser diode necessary for matching with the pulse width of the prescribed pulse light intensity is obtained using a lookup table or a mathematical expression. The solid-state pulse laser is driven by changing the drive current of the excitation laser diode by ΔI _LD . In the fourth step 34, the energy density on the stage ST is measured. In a fifth step 35, the energy density variation ΔPw required to obtain the prescribed energy density is determined. Next, in step 36, it is determined whether or not ΔPw can be realized by adjusting the attenuation factor of the variable attenuator 20. The output power Pwo at the laser exit can be referred to. If possible, the variable attenuator is adjusted in step 37 to achieve the specified energy density. If not possible, the process proceeds to step 38 and an alarm is issued. The control flowchart is not limited to that shown in FIG. 2B.

As shown in FIG. 2C, a step 38 may be provided between the third step 33 and the fourth step 34, and a branch may be created depending on the value of ΔI _LD . If the value of ΔI _LD is within the allowable error range between −δ1 and δ2, the process proceeds to step 34, and if it exceeds the allowable error, the process returns to step 31 with the drive current adjusted. When the pulse width needs to be adjusted, the value of ΔI _LD exceeds the allowable error at first, so the control returns to step 31 again after adjusting ΔI _LD . If the adjustment is successful, the pulse width almost coincides with the specified value, and the value of ΔI _LD falls within the allowable error range. Therefore, the process goes from step 38 to step 34. Other points are the same as the flow of FIG. 2B.

  FIG. 3 is a block diagram showing the configuration of the pulse laser heat treatment apparatus according to the second embodiment. When compared with the first embodiment, the photodetector PD is moved onto the stage ST from the vicinity of the pulse laser device emitting portion.

  The pulse waveform of the pulse laser beam on the stage ST (irradiation surface) is measured using the photodetector PD. Since the pulse width of the pulse waveform does not change before and after the variable attenuator, the detection of the pulse width is the same as in the first embodiment. The other points are the same as in the first embodiment.

  Note that the peak value of the pulse waveform measured by the photodetector PD is a measured value on a part of the laser beam irradiation surface, but since it is a value on the irradiation surface, the peak value of the pulse laser light that directly controls the heat treatment is measured it can. When the pulse width is multiplied by the peak value, the parameter represents the area of the pulse waveform (can be approximated). Instead of the energy density measurement in the flowcharts of FIGS. 2B and 2C, the peak value of the pulse laser beam on the irradiation surface or the peak value and the pulse width may be measured. The object to be controlled is a pulse width and a peak value of the pulse, or a parameter (pulse width × peak value) representing the pulse width and the area of the pulse.

  Note that the pulse waveform of the pulse laser beam intensity is not limited to the harmonic laser that becomes narrower as the peak value is higher.

 As shown in FIG. 4A, a pulsed laser apparatus in which a pumping chamber 13 and a Q switch 14 are disposed between an end mirror EM1 and a partially reflecting mirror PM of a complete reflecting mirror, and the pumping chamber 13 is irradiated with pumping light from the pumping LD12. Can also be used as the laser 10 in FIGS. 1A and 3.

  As shown in FIG. 4B, the excitation source of the pumping chamber 13 may use a lamp 13x instead of the laser diode. When the excitation intensity is increased, the time waveform of the pulsed light intensity has a high peak value and a narrow width as in the case of laser diode excitation.

  As shown in FIG. 4C, the object to be processed is obtained by depositing a semiconductor layer aS such as amorphous silicon on a glass substrate GL, and the heat treatment may be crystallization of the semiconductor layer.

  As shown in FIG. 4D, the object to be processed is a multilayer substrate in which an insulating layer DL and a wiring metal layer WL are stacked, and the heat treatment may be performed by drilling a metal layer or an insulating layer. Thus, the heat treatment may be a chemical heat treatment such as impurity activation or crystallization, or a mechanical heat treatment such as drilling, cutting, or welding.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. The shutter 16 in FIGS. 1A and 3 may be omitted. The photodetector PD may be any detector that can measure a time-varying waveform of the pulse laser beam intensity. The beam shape can be selected according to the purpose, and the contents of the optical system 21 can be changed and corrected. It will be apparent to those skilled in the art that various modifications, substitutions, improvements, combinations, and the like are possible.

1A and 1B are a block diagram schematically showing the configuration of the pulse laser heat treatment apparatus according to the first embodiment, and a graph showing a waveform change of the pulse laser light. FIG. 2A is a lookup table used for control, and FIGS. 2B and 2C are flowcharts of two types of control. FIG. 3 is a block diagram schematically showing the configuration of the pulse laser heat treatment apparatus according to the second embodiment. 4A and 4B are block diagrams showing modifications of the solid-state pulse laser device, and FIGS. 4C and 4D are sectional views showing modifications of the heat treatment object.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Solid-state pulse laser apparatus 12 Pumping chamber 13 (Excitation) Laser diode 13x (Excitation) lamp 14 Q switch 15 Wavelength conversion element 16 Shutter 17 Zoom lens 18 Homogenizer 19 Imaging optical system 20 Variable attenuator 21 Optical system M Mirror EM End Mirror DM Dichroic mirror PM Partial mirror ST (XY) stage PD Photodetector PM Power meter CTL Controller WV Waveform GL Glass substrate aS Semiconductor layer DL Insulating layer WL Wiring metal layer

Claims (16)

A pulse laser oscillator having an excitation source, a pumping chamber, a pulse oscillation mechanism, and a resonator structure, and oscillating a pulse laser beam;
A variable attenuator for attenuating the intensity of the laser beam emitted from the pulse laser oscillator;
An optical system for irradiating the object to be heat-treated with a laser beam whose intensity is adjusted by the variable attenuator;
A stage on which a heat treatment object is placed;
A first measuring instrument capable of measuring a pulse waveform which is a time waveform of the light intensity of the pulse laser beam;
A control device capable of adjusting the pulse width by controlling the excitation intensity of the excitation source based on the pulse width of the pulse waveform measured by the first measuring instrument, and further controlling the attenuation rate of the variable attenuator;
A pulsed laser heat treatment apparatus. A second measuring instrument arranged on the stage for measuring the irradiation energy density;
The pulse laser heat treatment apparatus according to claim 1, further comprising: controlling the attenuation rate of the variable attenuator based on the irradiation energy density measured by the second measuring instrument, and adjusting the irradiation energy density.   The pulse laser heat treatment apparatus according to claim 1, wherein the first measuring instrument is disposed on the stage.   The pulse laser according to claim 3, wherein the control device controls an attenuation rate of the variable attenuator and adjusts an irradiation energy density based on a product of a pulse width and a peak value of a pulse waveform measured by the first measuring instrument. Heat treatment equipment. A second measuring instrument arranged on the stage and capable of measuring an irradiation energy density;
The control device further includes an attenuation of the variable attenuator based on a product of a pulse width and a peak value of the pulse waveform measured by the first measuring instrument or an irradiation energy density measured by the second measuring instrument. The pulse laser heat treatment apparatus according to claim 3, wherein the rate is controlled and the irradiation energy density is adjusted.   The pulse laser heat treatment apparatus according to any one of claims 1 to 5, wherein the control device determines a change in the drive current of the excitation source necessary for making the width of the time waveform coincide with a specified value.   The pulse laser heat treatment apparatus according to any one of claims 1 to 6, further comprising a look-up table based on a result measured in advance by the control device.   8. The pulse laser according to claim 7, further comprising a third measuring device for measuring an output of the laser beam emitted from the pulse laser oscillator, wherein the look-up table records an output of the laser beam emitted from the pulse laser oscillator. Heat treatment equipment.   The pulse laser heat treatment apparatus according to claim 8, wherein the control device determines an adjustable range of the variable attenuator by referring to an output laser beam output of the lookup table.   The pulse laser heat treatment apparatus according to claim 1, wherein the heat treatment target is a semiconductor wafer into which impurities are ion-implanted, a substrate on which a semiconductor layer is deposited, or a processing target. (A) a step of measuring a pulse waveform which is a time waveform of the light intensity of the pulse laser beam emitted from the pulse laser device provided with the excitation source;
(B) obtaining a pulse width of the pulse waveform;
(C) obtaining a variation of the excitation intensity of the excitation source necessary to match the pulse width to a specified value;
(D) taking the variation and adjusting the pulsed laser device;
(E) irradiating the adjusted light emitted from the pulse laser device onto a stage on which an object to be processed is placed, and measuring an energy density;
(F) adjusting a variable attenuator so that the energy density matches a specified value;
Control method of pulse laser heat treatment apparatus including   The method of controlling a pulse laser heat treatment apparatus according to claim 11, wherein the step (e) measures an energy density on the stage.   The pulse laser heat treatment according to claim 11, wherein the step (a) and the step (e) measure the pulse waveform on the stage, and the step (e) measures at least a peak value of the pulse waveform and calculates an energy density. Control method of the device.   When the variation obtained in step (c) exceeds a predetermined range, after step (d), the process returns to step (a), and steps (b) and (c) are performed again. The method of controlling a pulse laser heat treatment apparatus according to claim 11, wherein the process proceeds from step (d) to step (e) when the variation is within the predetermined range. (G) After the step (f), the method further includes a step of irradiating a pulsed laser with an ion-implanted semiconductor wafer, a substrate on which a semiconductor layer is deposited, or an object to be processed as an object to be heat-treated. The control method of the pulse laser heat processing apparatus of any one of Claims 1.   The method of controlling a pulse laser heat treatment apparatus according to any one of claims 11 to 14, wherein an alarm is generated when the step (f) cannot be performed.

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