JP2009259860A - Laser processing device, and laser processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform processing with excellent processing quality. <P>SOLUTION: A radius of an outer concentric circle is denoted by r<SB>1</SB>, and a radius of an inner concentric circle is denoted by r<SB>2</SB>. Defining the radius and width of an annular laser beam as (r<SB>1</SB>+r<SB>2</SB>)/2 and r<SB>1</SB>-r<SB>2</SB>, a laser processing device includes a laser light source which emits a laser beam; a holding table holding a workpiece; an optical system which generates the annularly-sectioned laser beam from the laser beam emitted by the laser light source and makes it incident on the workpiece held on the holding table; and a controller which varies the output of the laser light source or the width of the annular laser beam in a direction such that when the annular laser beam varies in radius, variation in peak intensity of the annular laser beam in the identical orientation is suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laser processing apparatus that performs processing by irradiating a workpiece with a laser beam, and a laser processing method.

  With reference to FIGS. 6A and 6B, a conventional technique for activation annealing of a semiconductor wafer will be described.

  As shown in FIG. 6A, the activation annealing is performed, for example, by irradiating a semiconductor wafer 51 placed on the precision positioning moving stage 50 with a long and narrow line-shaped laser beam 52. By driving the precision positioning and moving stage 50 to scan the semiconductor wafer 51 in the X-axis direction, the entire surface of the semiconductor wafer 51 is irradiated with a laser beam.

  When the activation annealing of the circular semiconductor wafer 51 is performed using the line-shaped laser beam 52, the laser beam is irradiated to portions other than the semiconductor wafer 51, resulting in poor energy efficiency. In addition, dust or the like may be generated and scattered by the laser beam applied to portions other than the semiconductor wafer 51, and may adhere to the semiconductor wafer 51 and contaminate the semiconductor wafer 51. Furthermore, since the precision positioning / moving stage 50 is expensive, the cost of the entire laser annealing apparatus increases. In addition, it is difficult to shape the linear laser beam 52 that can irradiate the entire surface of the semiconductor wafer 51 only by scanning in the X-axis direction.

  Reference is made to FIG. A short line laser beam 54 may be used for the activation annealing. In this case, the precision positioning moving stage 53 is driven to scan the semiconductor wafer 51 in the X axis direction and the Y axis direction, thereby irradiating the entire surface of the semiconductor wafer 51 with a laser beam.

  When the short line-shaped laser beam 54 is used, energy efficiency can be improved as compared with the case where the long line-shaped laser beam 52 is used. Further, the amount of contamination of the semiconductor wafer 51 can be reduced. However, it is impossible to completely eliminate wasteful energy and contaminants irradiated on portions other than the semiconductor wafer 51.

  Further, since the semiconductor wafer 51 is scanned many times in the X-axis direction and the Y-axis direction, there is a problem that it takes time for the activation annealing. Further, unlike the precision positioning / moving stage 50 that only needs to scan the semiconductor wafer 51 in the X-axis direction, the precision positioning / moving stage 53 needs to scan the semiconductor wafer 51 in the X-axis direction and the Y-axis direction. The laser annealing apparatus using is more expensive. In addition, there is a problem of processing quality at the joint portion at the irradiation position of the line laser beam 54.

  The tip of the heating means is arranged above the central portion of the semiconductor wafer so that the radius of rotation increases from the arrangement position to the center of the arrangement position at a constant moving speed while maintaining a predetermined distance from the semiconductor wafer. An invention of an apparatus and a method for melting and recrystallizing the entire semiconductor layer so as not to cause an unmelted recrystallized portion in the semiconductor layer by moving in a spiral manner is disclosed (for example, Patent Document 1). reference). According to this apparatus or method, a semiconductor layer having a crystal grain size larger than that of the conventional one can be obtained.

JP-A-8-78328

  An object of the present invention is to provide a laser processing apparatus capable of performing processing with high energy efficiency.

  Moreover, it is providing the laser processing apparatus which can process with high time efficiency.

  Furthermore, it is providing the laser processing apparatus which can process with favorable processing quality.

  Furthermore, it is to provide an inexpensive laser processing apparatus.

  Another object of the present invention is to provide a laser processing method capable of performing processing with high energy efficiency.

  Furthermore, it is providing the laser processing method which can process with high time efficiency.

  Another object of the present invention is to provide a laser processing method capable of performing processing with good processing quality.

According to one aspect of the present invention, the radius of the outer concentric circle is r ₁ , the radius of the inner concentric circle is r ₂ , the radius of the annular laser beam is (r ₁ + r ₂ ) / 2, and the width is r ₁ −r. ₂ , a laser light source that emits a laser beam, a holding table that holds a workpiece, and a laser beam that has a ring-shaped cross section are generated from the laser beam emitted from the laser light source, and the holding table When the radius of the ring-shaped laser beam is changed and the optical system that is incident on the workpiece to be processed in a variable radius, the change of the peak intensity in the same direction of the ring-shaped laser beam is suppressed. There is provided a laser processing apparatus having a control device for changing an output of the laser light source or a width of the annular laser beam.

According to another aspect of the present invention, when the radius of the outer concentric circle is defined as r ₁ , the radius of the inner concentric circle is defined as r _2, and the radius of the annular laser beam is defined as (r ₁ + r ₂ ) / 2. (A) a step of causing an annular laser beam having a first radius to enter the object to be processed; and (b) an annular laser beam having a second radius different from the first radius. And a laser processing method that suppresses a change in peak intensity in the same direction of the annular laser beam when the radius of the annular laser beam changes.

  ADVANTAGE OF THE INVENTION According to this invention, the laser processing apparatus which can process with high energy efficiency can be provided.

  Further, it is possible to provide a laser processing apparatus capable of performing processing with high time efficiency.

  Furthermore, it is possible to provide a laser processing apparatus capable of performing processing with good processing quality.

  Furthermore, an inexpensive laser processing apparatus can be provided.

  In addition, according to the present invention, it is possible to provide a laser processing method capable of performing processing with high energy efficiency.

  Furthermore, it is possible to provide a laser processing method capable of performing processing with high time efficiency.

  In addition, it is possible to provide a laser processing method capable of performing processing with good processing quality.

  With reference to FIGS. 1A and 1B, a laser processing method common to the following embodiments will be described.

  Reference is made to FIG. In the following embodiments, activation annealing of the semiconductor wafer 51 is performed by irradiating the circular semiconductor wafer 51 placed on the fixed stage 60 with a laser beam shaped into an annular shape (ring-shaped or annular shape). I do. Several examples of regions on the semiconductor wafer 51 irradiated with the laser beam shaped into an annular shape are shown as irradiation regions 55a to 55d in this drawing. The irradiation regions 55 a to 55 d are regions surrounded by two circles (concentric circles) centered on the center of the circular semiconductor wafer 51.

  The laser beam shaped into an annular shape is irradiated on the entire surface of the semiconductor wafer 51 while changing the radius and width on the irradiation surface. The irradiation is performed, for example, so that the irradiation region moves from the inside toward the outside along the radial direction of the semiconductor wafer 51 while increasing the radius of the annular laser beam. The irradiation region may be moved from the outside toward the inside along the radial direction of the semiconductor wafer 51 while reducing the radius of the annular laser beam. When the laser beam used for the activation annealing is a pulsed laser beam, the irradiation is performed so that the overlap rate is constant, for example.

For example, in the annular laser beam irradiation region 55e shown in FIG. 1B, when the radius of the outer concentric circle is r ₁ and the radius of the inner concentric circle is r ₂ , the radius of the annular laser beam is (r ₁ + r ₂ ) / 2, and the width is defined by r ₁ -r ₂ .

  By changing the radius of the annular laser beam in this way and scanning the laser beam concentrically with the center of the semiconductor wafer 51 as the center, the semiconductor wafer is not incident on the fixed stage 60. The entire surface of 51 can be irradiated with a laser beam, and activation annealing of the semiconductor wafer 51 can be performed.

  The annular laser beam is incident on the semiconductor wafer 51 under the condition that the light intensity is constant during processing. Further, in the activation annealing, the energy per unit area input to the semiconductor wafer 51 is constant regardless of the location on the semiconductor wafer 51. For this reason, when activation annealing is performed using a pulse laser beam, the number of shots of the laser pulse irradiated on the semiconductor wafer 51 is constant regardless of the location. When activation annealing is performed using a continuous wave laser beam, the irradiation time of the laser beam irradiated onto the semiconductor wafer 51 is constant regardless of the location.

  For this reason, it is possible to prevent the semiconductor wafer 51 from being contaminated by dust generated by irradiating the fixed stage 60 with the laser beam. Moreover, the problem of the processing quality in the joint part of the short line-shaped laser beam irradiation position demonstrated with reference to FIG. 6 (B) does not arise. For this reason, laser annealing with good quality can be realized.

  In addition, since the laser beam is not irradiated on portions other than the semiconductor wafer 51, laser annealing can be performed with high energy efficiency.

  Furthermore, since activation annealing is performed using the fixed stage 60, the time required for the movement and positioning of the semiconductor wafer by the moving stage becomes unnecessary. For this reason, laser annealing can be performed with high time efficiency.

  Further, since an inexpensive fixed stage 60 that holds the semiconductor wafer 51 is used instead of an expensive precision positioning movement stage, laser annealing can be realized with an inexpensive apparatus configuration.

  With reference to FIGS. 2A to 2C, a laser processing method according to the first embodiment will be described.

  FIG. 2A is a schematic diagram showing a laser processing apparatus according to the first embodiment. The laser processing apparatus according to the first embodiment includes a laser light source 10, a variable attenuator 11, an intensity distribution adjuster 12, an axicon lens (conical lens) 13, a lens moving mechanism 13a, an imaging lens 14, a control device 15, and a fixed. A stage 60 is included.

  For example, a pulsed laser beam 30 that is a second harmonic (wavelength 527 nm) of an Nd: YLF laser is emitted from a laser light source 10 including an Nd: YLF laser oscillator. The cross-sectional shape of the pulse laser beam 30 is circular, for example, and the light intensity in the cross-section has a Gaussian distribution. The pulse laser beam 30 is incident on a variable attenuator 11 that can attenuate the light intensity of the incident laser beam (time average value of energy passing through a unit area per unit time) with a variable attenuation factor, and the light intensity is attenuated. After the light intensity in the beam cross section is made uniform by the intensity distribution controller 12, the light enters the axicon lens 13 that forms a beam whose cross section perpendicular to the beam traveling direction is an annular shape. The axicon lens 13 is held by the lens moving mechanism 13a so as to be movable in the traveling direction (optical axis direction) of the pulse laser beam 30. The pulse laser beam 30 shaped into an annular shape by the axicon lens 13 is incident on the semiconductor wafer 51 held on the fixed stage 60 through the imaging lens 14, and activation annealing of the semiconductor wafer 51 is performed. The imaging lens 14 images (transfers) the pulse laser beam 30 on the virtual surface 40 on the optical path of the pulse laser beam 30 onto the semiconductor wafer 51. Unlike the XY stage and the like, the fixed stage 60 does not have a function of moving the semiconductor wafer 51. For this reason, the semiconductor wafer 51 is spatially fixed during the activation annealing period. The control unit 15 controls the attenuation rate of the light intensity of the pulse laser beam 30 by the variable attenuator 11 and the movement of the axicon lens 13 by the lens moving mechanism 13a.

  With reference to FIG. 2 (B), the structure and effect | action of the intensity distribution regulator 12 are demonstrated. FIG. 2B is a cross-sectional view of the intensity distribution adjuster 12 as seen from a line of sight orthogonal to the optical axis of the laser beam incident thereon. The intensity distribution controller 12 includes a lens 12a (intensity conversion lens) and a lens 12b (phase correction lens) which are two aspheric lenses. As will be described below, the intensity distribution adjuster 12 indicates the intensity distribution in the beam cross section when the intensity distribution in the cross section is a Gaussian distribution and the cross section is circular, and the intensity is within the beam cross section. Close to a constant distribution (top flat distribution).

  The pulsed laser beam 30 emitted from the variable attenuator 11 enters the lens 12a. As shown in the graph at the left end of FIG. 2B, the intensity of the incident light in the beam cross section is high at the center of the beam cross section and decreases as it goes toward the periphery. The lens 12a is thin at the portion where the center of the beam cross-section is incident, and becomes thicker from the position toward the edge of the lens. The lens 12a has the maximum thickness at a certain position, and is thinned from the position where the thickness is maximum to the edge of the lens. Become. The lens 12a acts as a concave lens on the central portion of the beam cross section to diffuse the incident light, and acts as a convex lens on the peripheral portion of the beam cross section to converge the incident light.

  Thereby, in the cross section of the laser beam radiate | emitted from the lens 12a, the intensity | strength of a center part falls relatively and the intensity | strength of a peripheral part rises relatively. On the virtual plane 12c that is a predetermined distance away from the lens 12a, the intensity in the beam cross section is substantially constant as shown in the graph at the right end of FIG.

  After passing through the virtual surface 12c, the light at the central portion of the beam cross section is further diffused and the light at the peripheral portion is further converged by the action of the lens 12a. Therefore, a uniform intensity distribution cannot be maintained within the cross section of the laser beam that has passed through the virtual plane 12c. In order to maintain a uniform intensity distribution, the lens 12b is disposed in the vicinity of the virtual surface 12c.

  The lens 12b is thick at the part where the center of the beam cross-section is incident, and becomes thinner as it goes from the position toward the edge of the lens. Become. The lens 12b acts as a convex lens on the central part of the beam cross section and acts as a concave lens on the peripheral part of the beam cross section, so that the laser beam emitted from the lens 12b has a parallel intensity having a substantially uniform intensity in the beam cross section. Can be light.

  Note that FIG. 2B shows an example of an intensity distribution controller, and a similar function can be realized by using, for example, a DOE.

  FIG. 2C is a schematic perspective view including the axicon lens 13. A pulse laser beam 30 that is a parallel beam having a uniform light intensity distribution is incident on the axicon lens 13. The pulse laser beam 30 spreads along the direction of the generatrix of the cone, and is shaped into a laser beam that travels in the direction of the central axis of the cone as a whole and is emitted from the axicon lens 13. A cross section obtained by cutting the laser beam along a plane perpendicular to the traveling direction has an annular shape. The radius of the annular laser beam increases as the distance from the axicon lens 13 in the beam traveling direction increases. On the other hand, the width of the annular laser beam is constant regardless of the distance from the axicon lens 13 and is equal to the radius of the pulsed laser beam 30 incident on the axicon lens 13.

  By moving the axicon lens 13 by the lens moving mechanism 13a, the radius of the annular laser beam at the position of the virtual surface 40 changes. While changing the radius of the annular laser beam at the position of the virtual plane 40 for each laser pulse, the beam cross section at that position is imaged on the semiconductor wafer 51 by the imaging lens 14. The laser beam can be scanned concentrically around the center of the semiconductor wafer 51.

  By moving the axicon lens 13 in the direction opposite to the traveling direction of the pulse laser beam 30, the radius of the annular irradiation region on the semiconductor wafer 51 is increased for each laser pulse, and the inner side along the radial direction of the semiconductor wafer 51 is increased. Beam scanning can be performed from the outside toward the outside. Conversely, by moving the axicon lens 13 in the same direction as the traveling direction of the laser beam 30, the radius of the annular irradiation region on the semiconductor wafer 51 is decreased for each laser pulse, while the radial direction of the semiconductor wafer 51 is increased. It is possible to scan the beam from the outside toward the inside along.

  The control device 15 controls the axicon lens 13 so that each laser pulse is incident on the semiconductor wafer 51 under the condition that the light intensity in the beam irradiation region becomes a constant value common to all the laser pulses during processing. The attenuation rate of the variable attenuator 11 is controlled according to the movement. Further, in the processing, the incidence of the laser beam on the semiconductor wafer 51 is controlled so that the energy per unit area input to the semiconductor wafer 51 is constant regardless of the location on the semiconductor wafer 51.

  In the first embodiment, since the width of the annular irradiation region on the semiconductor wafer 51 is constant regardless of the radius, the attenuation factor of the variable attenuator 11 is reduced when the radius of the annular irradiation region is increased. To do.

  In this way, the semiconductor wafer 51 is irradiated with the laser beam without causing the laser beam to be incident on the fixed stage 60, and activation annealing of the semiconductor wafer 51 is performed.

  With reference to FIGS. 3A and 3B, a laser processing method according to the second embodiment will be described.

  FIG. 3A is a schematic view showing a laser processing apparatus according to the second embodiment. In place of the axicon lens 13 held movably, two axicon lenses 13x and 13y fixedly arranged on the optical path of the laser beam are provided. The laser processing apparatus according to the first embodiment is different from the laser processing apparatus according to the first embodiment in that the reduction imaging optical system 16 is included.

  FIG. 3B is a schematic perspective view including axicon lenses 13x and 13y. The axicon lenses 13x and 13y are arranged coaxially (so that the central axes coincide) so that the apexes of the conical portions face each other. The pulse laser beam 30 spreads along the generatrix direction of the cone by the axicon lens 13x, is shaped into a laser beam that travels in the direction of the central axis of the cone as a whole, and then enters the side surface of the conical portion of the axicon lens 13y. To do. The laser beam emitted from the axicon lens 13y becomes a parallel beam that travels in a direction parallel to the central axis of the cylindrical surface.

  A cross section obtained by cutting the laser beam along a plane perpendicular to the traveling direction has an annular shape. The radius and width of the annular laser beam are constant regardless of the distance from the axicon lens 13y in the beam traveling direction. The width of the annular laser beam is equal to the radius of the pulsed laser beam 30 incident on the axicon lens 13x.

  The ring-shaped parallel beam emitted from the axicon lens 13 y enters the enlargement / reduction imaging optical system 16. The enlargement / reduction imaging optical system 16 enlarges and reduces the ring-shaped beam while maintaining the ratio of the radius and the width constant, and forms an image on the semiconductor wafer 51.

  The enlargement / reduction imaging optical system 16 forms (transfers) an annular cross section of a parallel beam on the semiconductor wafer 51 while changing the imaging (transfer) magnification for each laser pulse. The laser beam can be scanned concentrically around the center of the semiconductor wafer 51.

  By increasing the imaging magnification of the enlarging / reducing imaging optical system 16 for each laser pulse, beam scanning can be performed from the inside to the outside along the radial direction of the semiconductor wafer 51. Conversely, by reducing the imaging magnification for each laser pulse, beam scanning can be performed from the outside toward the inside along the radial direction of the semiconductor wafer 51.

  The control device 15 responds to the imaging magnification so that each laser pulse is incident on the semiconductor wafer 51 under the condition that the light intensity in the beam irradiation region is equal to a constant value common to all laser pulses during processing. Thus, the attenuation rate of the variable attenuator 11 is controlled. When increasing the imaging magnification, the attenuation factor of the variable attenuator 11 is reduced. Further, the scanning of the laser beam is controlled so that the absolute value of the speed at which the radius of the annular laser beam incident on the semiconductor wafer 51 expands is proportional to the width of the annular laser beam. Further, in the processing, the incidence of the laser beam on the semiconductor wafer 51 is controlled so that the energy per unit area to be introduced into the semiconductor wafer 51 is constant regardless of the location on the semiconductor wafer 51.

  In this way, the semiconductor wafer 51 is irradiated with the laser beam without causing the laser beam to be incident on the fixed stage 60, and activation annealing of the semiconductor wafer 51 is performed.

  With reference to FIGS. 4A and 4B, a laser processing method according to the third embodiment will be described.

  FIG. 4A is a schematic view showing a laser processing apparatus according to the third embodiment. A laser processing apparatus according to the second embodiment in that a torus type lens (annular cylindrical lens) 17 is provided on the optical path of the laser beam between the axicon lens 13y and the magnification / reduction imaging optical system 16. Is different. The laser processing apparatus according to the third embodiment includes a lens moving mechanism 17a that holds the torus lens 17 so as to be movable in the laser beam traveling direction (optical axis direction). Furthermore, the laser processing apparatus according to the third embodiment does not include a variable attenuator.

  FIG. 4B is a schematic perspective view including the torus type lens 17. The axicon lenses 13x and 13y are arranged coaxially (so that the central axes coincide with each other) so that the apexes of the conical portions are opposed to each other. The emitted laser beam enters the torus lens 17. The torus-type lens 17 is a donut-type special lens, and its radius is equal to the radius of the incident ring-shaped parallel beam. The torus lens 17 has a width equal to or greater than the width of the incident ring-shaped parallel beam.

  The laser beam emitted from the torus type lens 17 is a laser beam having a circular shape in cross section perpendicular to the traveling direction of the beam. The width of the annular laser beam decreases as the distance along the direction of travel of the laser beam increases. On the other hand, the radius of the annular laser beam is constant regardless of the distance along the traveling direction of the laser beam.

  In the laser processing method according to the third embodiment, the torus type lens 17 is moved in a direction parallel to the traveling direction of the laser beam by the lens moving mechanism 17a, and is applied onto the semiconductor wafer 51 by the enlargement / reduction imaging optical system 16. The width of the annular beam at the transfer position (conjugate position) is changed. With this as one parameter, the width of the annular beam irradiated onto the semiconductor wafer 51 can be controlled. Further, by changing the imaging (transfer) magnification of the enlargement / reduction imaging optical system 16, the radius and width of the annular beam irradiated on the semiconductor wafer 51 can be changed.

  The control device 15 moves and enlarges / reduces the torus type lens 17 by the lens moving mechanism 17a so that the product of the radius and width of the annular incident beam on the semiconductor wafer 51 is always constant during the activation annealing. The imaging (transfer) magnification of the imaging optical system 16 is controlled for each laser pulse. By performing such control, the light intensity in the beam irradiation region on the semiconductor wafer 51 can be set to an equal constant value common to all laser pulses during processing. Further, the scanning of the laser beam is controlled so that the absolute value of the speed at which the radius of the annular laser beam incident on the semiconductor wafer 51 expands is proportional to the width of the annular laser beam. Further, in the processing, the incidence of the laser beam on the semiconductor wafer 51 is controlled so that the energy per unit area to be introduced into the semiconductor wafer 51 is constant regardless of the location on the semiconductor wafer 51.

  The laser beam scanning on the semiconductor wafer 51 is the same as in the second embodiment. By increasing or decreasing the imaging (transfer) magnification of the enlarging / reducing imaging optical system 16 for each laser pulse, a concentric circle is formed around the center of the semiconductor wafer 51 along the radial direction of the semiconductor wafer 51. A laser beam can be scanned.

  In this way, the semiconductor wafer 51 is irradiated with the laser beam without causing the laser beam to be incident on the fixed stage 60, and activation annealing of the semiconductor wafer 51 is performed.

  In the laser processing methods according to the first and second embodiments, the control device 15 determines that each laser pulse is a semiconductor wafer under the condition that the light intensity in the beam irradiation region is equal to a constant value common to all laser pulses. The attenuation factor of the variable attenuator 11 was controlled so as to enter the beam 51. In a laser processing apparatus that performs these laser processing methods, there is an advantage that a simple apparatus configuration can be adopted.

  However, when the area of the beam irradiation region is small, such as when irradiating an annular laser beam with a small radius, the attenuation factor of the variable attenuator 11 must be increased to reduce the pulse energy of the laser pulse.

  On the other hand, in the laser processing method according to the third embodiment, since it is not necessary to attenuate the light intensity of the laser beam emitted from the laser light source 10 with a variable attenuator, activation annealing is performed with high energy efficiency and high productivity. It can be performed. This also applies to the laser processing method according to the fourth embodiment described below.

  With reference to FIGS. 5A to 5C, a laser processing method according to the fourth embodiment will be described.

  FIG. 5A is a schematic view showing a laser processing apparatus according to the fourth embodiment. The laser processing apparatus according to the fourth embodiment does not include a torus type lens and a lens moving mechanism that holds the torus type lens movably, and moves the axicon lens 13y in the laser beam traveling direction (optical axis direction). The laser processing apparatus according to the third embodiment is different from the laser processing apparatus according to the third embodiment in that a lens moving mechanism 13b that can be held is provided.

  5B and 5C are schematic perspective views including the axicon lenses 13x and 13y. As described with reference to FIG. 3 (B), the axicon lenses 13x and 13y are arranged coaxially so that the apexes of the conical portions face each other (the central axes coincide). A parallel laser beam having a circular cross section perpendicular to the beam exits the axicon lens 13y.

  When the distance between the axicon lenses 13x and 13y varies, the radius of the annular laser beam emitted from the axicon lens 13y changes. FIG. 5B shows a case where the distance between the axicon lenses 13x and 13y is small, and FIG. 5C shows a case where the distance between the two is large. As can be seen from both figures, as the distance between the axicon lenses 13x and 13y increases, the radius of the annular laser beam emitted from the axicon lens 13y increases.

  On the other hand, the width of the annular laser beam is constant even when the distance between the axicon lenses 13x and 13y varies, and is equal to the radius of the pulsed laser beam 30 incident on the axicon lens 13x.

  Further, since the annular laser beam emitted from the axicon lens 13y is a parallel beam, the radius and width of the annular laser beam are equal to those when the axicon lens 13y is emitted, regardless of the distance in the beam traveling direction.

  The annular laser beam emitted from the axicon lens 13 y enters the enlargement / reduction imaging optical system 16. By moving the axicon lens 13y in a direction parallel to the traveling direction of the laser beam by the lens moving mechanism 13b, an annular laser beam having a constant width is incident on the enlargement / reduction imaging optical system 16 while changing the radius. Can be made.

  In the laser processing method according to the fourth embodiment, the axicon lens 13y is moved in the direction parallel to the traveling direction of the laser beam by the lens moving mechanism 13b, and is applied onto the semiconductor wafer 51 by the enlargement / reduction imaging optical system 16. The radius of the annular beam at the transfer position (conjugate position) is changed. With this as one parameter, the radius of the annular beam irradiated onto the semiconductor wafer 51 can be controlled. Further, by changing the imaging (transfer) magnification of the enlargement / reduction imaging optical system 16, the radius and width of the annular beam irradiated on the semiconductor wafer 51 can be changed.

  The control device 15 moves the axicon lens 13y by the lens moving mechanism 13b and enlarges / reduces so that the product of the radius and width of the annular incident beam on the semiconductor wafer 51 is always constant during the activation annealing. The imaging (transfer) magnification of the imaging optical system 16 is controlled for each laser pulse. By performing such control, the light intensity in the beam irradiation region on the semiconductor wafer 51 can be set to an equal constant value common to all laser pulses during processing. Further, the scanning of the laser beam is controlled so that the absolute value of the speed at which the radius of the annular laser beam incident on the semiconductor wafer 51 expands is proportional to the width of the annular laser beam. Further, in the processing, the incidence of the laser beam on the semiconductor wafer 51 is controlled so that the energy per unit area to be introduced into the semiconductor wafer 51 is constant regardless of the location on the semiconductor wafer 51.

  The scanning of the laser beam on the semiconductor wafer 51 is the same as in the second and third embodiments. By increasing or decreasing the imaging (transfer) magnification of the enlarging / reducing imaging optical system 16 for each laser pulse, a concentric circle is formed around the center of the semiconductor wafer 51 along the radial direction of the semiconductor wafer 51. A laser beam can be scanned.

  In this way, the semiconductor wafer 51 is irradiated with the laser beam without causing the laser beam to be incident on the fixed stage 60, and activation annealing of the semiconductor wafer 51 is performed.

  In the laser processing method according to the fourth embodiment, no torus type lens is used. For this reason, activation annealing can be performed with an inexpensive apparatus configuration as compared with the third embodiment.

  In the laser processing method according to the fourth embodiment, the exit-side axicon lens 13y is moved in a direction parallel to the traveling direction of the laser beam, but the incident-side axicon lens 13x may be moved.

  As mentioned above, although this invention was demonstrated along the Example, this invention is not limited to these.

  For example, in the embodiment, a pulsed laser beam is used, and the light intensity in the beam irradiation region on the semiconductor wafer is controlled to be an equal constant value common to all the laser pulses. A continuous wave laser beam may be used to control the light intensity in the beam irradiation region on the semiconductor wafer to be constant.

  The light intensity does not have to be strictly constant. When the radius of the annular laser beam changes, the output of the laser light source or the width of the annular laser beam is changed in such a direction as to suppress the change of the peak intensity in the same direction (radial direction) of the annular laser beam. The effect will be obtained.

  In addition, the laser light source is designed so that the variation coefficient of the peak intensity in the same direction of the annular laser beam is 10% or less, more preferably 5% or less, and even more preferably 2% or less. It would be possible to suitably perform the activation annealing by changing the output or the width of the annular laser beam. Here, the variation coefficient is obtained by dividing the standard deviation by the average value, and the unit is represented by “%”. In this connection, the product of the radius and width of the annular incident beam on the semiconductor wafer 51 is made to be substantially constant during the activation annealing so that the variation coefficient of the peak value of the light intensity is within the range. That's fine.

  In the embodiment, the energy per unit area to be input to the semiconductor wafer is a constant value independent of the location on the semiconductor wafer, but the variation coefficient of the input energy per unit area is 20% or less. If it is more preferably 10% or less, and even more preferably 5% or less, there will be no problem.

  Furthermore, in the embodiment, the fixed stage 60 that does not have the function of moving the semiconductor wafer 51 is used. However, for example, the semiconductor wafer 51 may be held on an XY stage. With the XY stage, activation annealing can be performed without moving the semiconductor wafer 51 in the X direction or the Y direction.

  In the first and second embodiments, the intensity of the laser beam is adjusted using the variable attenuator. However, the intensity of the laser beam itself emitted from the laser oscillator may be changed without using the variable attenuator. .

  Furthermore, in the embodiment, the semiconductor wafer 51 is irradiated with the annular laser beam uniformed in the circumferential direction and the radial direction. For example, the annular laser beam uniformized at least in the circumferential direction is irradiated on the semiconductor wafer. 51 may be irradiated.

  It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like are possible.

  It can be suitably used for laser processing in general, particularly laser annealing.

(A) And (B) is a figure for demonstrating the laser processing method common to an Example. (A)-(C) are the figures for demonstrating the laser processing method by a 1st Example. (A) And (B) is a figure for demonstrating the laser processing method by the 2nd Example. (A) And (B) is a figure for demonstrating the laser processing method by the 3rd Example. (A)-(C) are the figures for demonstrating the laser processing method by the 4th Example. (A) And (B) is a figure for demonstrating the prior art of activation annealing of a semiconductor wafer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Laser light source 11 Variable attenuator 12 Intensity distribution controller 12a, 12b Aspherical lens 12c Virtual surface 13 Axicon lens 13a, 13b Lens moving mechanism 13x, 13y Axicon lens 14 Imaging lens 15 Control apparatus 16 Enlarging / reducing imaging optics System 17 Torus type lens 17a Lens moving mechanism 30 Laser beam 40 Virtual planes 50, 53 Precision positioning moving stage 51 Semiconductor wafer 52, 54 Line-shaped laser beams 55a-55e Irradiation area 60 Fixed stage

Claims (24)

_{R 1} radius of outer concentric circles, the radius of the inner concentric circle and _{r 2,} the radius of the annular laser beam _{(r 1 + r 2) /} 2, when defining the width _r 1 -r _2,
A laser light source for emitting a laser beam;
A holding table for holding the workpiece;
An optical system that generates a laser beam having a ring-shaped cross-section from the laser beam emitted from the laser light source, and that makes the radius variable incident on the workpiece held by the holding table;
When the radius of the annular laser beam is changed, the output of the laser light source or the width of the annular laser beam is changed in a direction to suppress the change in peak intensity in the same direction of the annular laser beam. A laser processing apparatus.   The control device changes the output of the laser light source or the width of the annular laser beam so that the variation coefficient of the peak intensity in the same direction of the annular laser beam is 10% or less. The laser processing apparatus as described in.   The control device changes the output of the laser light source or the width of the annular laser beam so that the variation coefficient of the peak intensity in the same direction of the annular laser beam is 5% or less. The laser processing apparatus as described in.   The control device changes the output of the laser light source or the width of the annular laser beam so that the variation coefficient of the peak intensity in the same direction of the annular laser beam is 2% or less. The laser processing apparatus as described in.   In the processing, regardless of the location on the processing object held by the holding table, the control device is such that the coefficient of variation of energy per unit area to be input to the processing object is 20% or less. The laser processing apparatus of any one of Claims 1-4 which control the said optical system.   In the processing, regardless of the location on the processing object held on the holding table, the control device is such that the coefficient of variation of energy per unit area to be input to the processing object is 10% or less. The laser processing apparatus of any one of Claims 1-4 which control the said optical system.   In the processing, regardless of the location on the processing object held on the holding table, the control device is such that the coefficient of variation of energy per unit area to be input to the processing object is 5% or less. The laser processing apparatus of any one of Claims 1-4 which control the said optical system. The optical system includes an axicon lens that is held so as to be movable in a direction parallel to the optical axis direction of the laser beam and that generates a laser beam having a ring-shaped cross section.
The laser processing apparatus according to claim 1, wherein the control device adjusts an intensity of a laser beam emitted from the laser light source in accordance with the movement of the axicon lens. The optical system is
Two axicon lenses that are arranged coaxially so that the apexes of the conical portion face each other and generate a laser beam having a ring-shaped cross section;
Imaging with variable imaging magnification that enlarges or reduces the ring-shaped beam generated by the two axicon lenses while keeping the ratio of the radius and width constant, and forms an image on the workpiece. Including an optical system,
The laser processing apparatus according to claim 1, wherein the control device adjusts an intensity of a laser beam emitted from the laser light source in accordance with an imaging magnification of the imaging optical system. The optical system is
Two axicon lenses that are arranged coaxially so that the apexes of the conical portion face each other and generate a laser beam having a ring-shaped cross section;
An annular cylinder that is held so as to be movable in a direction parallel to the optical axis direction of the annular laser beam generated by the two axicon lenses and changes the width without changing the radius of the annular laser beam. A lens,
Imaging optics with variable imaging magnification, which expands and contracts an annular beam emitted from the annular cylindrical lens, while maintaining a constant ratio of radius to width, and forms an image on the workpiece. Including
The controller is configured to move the annular cylindrical lens and to form an imaging magnification of the imaging optical system so that the product of the radius and width of the annular laser beam on the workpiece is substantially constant. The laser processing apparatus of any one of Claims 1-7 which controls these. The optical system is
Two axicon lenses that are coaxially arranged so that the apexes of the conical portions face each other and are variable in distance, and that generate a laser beam having a ring-shaped cross section;
A ring-shaped beam generated by the two axicon lenses is enlarged and reduced while the ratio of the radius and the width is kept constant, and the image is formed on the object to be processed with a variable imaging magnification. An image optical system,
The control device determines the distance between the two axicon lenses and the imaging optical system so that the product of the radius and width of the annular laser beam on the workpiece is substantially constant. The laser processing apparatus according to claim 1, wherein the magnification is controlled.   The control device is configured so that the absolute value of the speed at which the radius of the annular laser beam incident on the workpiece held by the holding table expands is proportional to the width of the annular laser beam. The laser processing apparatus according to any one of claims 9 to 11, which controls scanning of the annular laser beam on the processing object.   The optical system includes a homogenizing optical system that makes a ring-shaped laser beam whose light intensity is uniformed in a circumferential direction incident on a workpiece held on the holding table. The laser processing apparatus according to item 1.   The optical system includes a homogenizing optical system that makes a ring-shaped laser beam whose light intensity is uniformed in a circumferential direction and a radial direction incident on a workpiece held on the holding table. The laser processing apparatus according to any one of the above. When the radius of the outer concentric circle is defined as r ₁ , the radius of the inner concentric circle is defined as r _2, and the radius of the annular laser beam is defined as (r ₁ + r ₂ ) / 2,
(A) a step of causing an annular laser beam having a first radius to enter a workpiece;
(B) having a ring-shaped laser beam having a second radius different from the first radius incident on the object to be processed;
A laser processing method for suppressing a change in peak intensity in the same direction of the annular laser beam when the radius of the annular laser beam changes.   The laser processing method according to claim 15, wherein a change in peak intensity is suppressed so that a variation coefficient of the peak intensity in the same direction of the annular laser beam is 10% or less.   The laser processing method according to claim 15, wherein a change in peak intensity is suppressed so that a variation coefficient of the peak intensity in the same direction of the annular laser beam is 5% or less.   The laser processing method according to claim 15, wherein a change in peak intensity is suppressed so that a variation coefficient of the peak intensity in the same direction of the annular laser beam is 2% or less.   In processing, a laser beam is incident on the processing object so that a variation coefficient of energy per unit area to be input to the processing object is 20% or less regardless of a place on the processing object. Item 19. The laser processing method according to any one of Items 15 to 18.   In processing, a laser beam is incident on the processing object so that a variation coefficient of energy per unit area to be input to the processing object is 10% or less regardless of a place on the processing object. Item 19. The laser processing method according to any one of Items 15 to 18.   In processing, a laser beam is incident on the processing object so that a variation coefficient of energy per unit area input to the processing object is 5% or less regardless of a place on the processing object. Item 19. The laser processing method according to any one of Items 15 to 18.   The laser processing method according to any one of claims 15 to 21, wherein in the steps (a) and (b), the area of the region where the annular laser beam is incident on the workpiece is different. When the radius of the outer concentric circle is defined as r ₁ , the radius of the inner concentric circle is defined as r _2, and the width of the annular laser beam is defined as r ₁ -r ₂ , in steps (a) and (b), the radius The laser processing method according to any one of claims 15 to 21, wherein a ring-shaped laser beam having a substantially equal product with the width is incident on a processing object.   24. The annular laser beam is scanned on the workpiece so that the absolute value of the speed at which the radius of the annular laser beam expands is proportional to the width of the annular laser beam. The laser processing method according to any one of the above.

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