Abstract:
An object of the present invention is to provide a laser annealing method and apparatus capable of performing uniform beam emission. By means of the present invention, uniform beam application to a sample can be achieved because a linear cross-sectional configuration can be created in an optical system with a beam having a Gaussian distribution while areas of strong light intensity are avoided by rotating the beam from a laser light source at a prescribed angle by means of rotating means even when the beam pattern of the beam from the laser light source has a non-uniform intensity distribution.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a laser annealing method and apparatus. 
   BACKGROUND OF THE INVENTION 
   High-power lasers such as excimer lasers, YAG lasers, and the like are presently becoming widespread not only in research applications, but in industrial applications as well. These fields of industrial utilization are expanding not only into general materials processing, but also into the medical and semiconductor fields. 
   When materials processing is performed using an excimer laser or similar beam, the beam is transformed in a linear cross-sectional dimension by means of an optical system, with scanning in the latitudinal direction (width direction). 
   The longitudinal direction and the latitudinal direction of the beam cross-section are each severally divided by a cylindrical lens to obtain a high degree of uniformity in the longitudinal direction and latitudinal direction of the beam pattern when the laser beam is transformed to a linear cross-sectional configuration. 
     FIG. 7  is a conceptual diagram of an apparatus operating according to the conventional laser annealing method (refer to Japanese Patent Application Laid-open No. H8-195357). 
   The apparatus  1  depicted in the diagram is designed such that a beam  2  from a YAG laser (not shown) is divided into four parts in a vertical direction by a lens group  3  comprising four cylindrical lenses  3   a - 3   d , further subdivided into seven parts in a horizontal direction by a lens group  4  comprising seven cylindrical lenses  4   a - 4   g , and combined by a paired lens  7  comprising a pair of cylindrical lenses  7   a  and  7   b  disposed orthogonally to the generatrix, yielding a beam pattern whose light intensity is uniform in the longitudinal direction and the latitudinal direction. (Lens groups  3  and  7  comprise a homogenizer  15 .) A beam  8  whose light intensity is uniformized is deflected by a reflecting mirror  9  towards a sample  10  and focused by a cylindrical lens  11  such that the sample  10  placed on a translation stage  13  that moves in the direction of arrow  12  is irradiated by a linear beam  14 . 
   Due to the occurrence of transverse expansion when a YAG laser is used in this arrangement, the shape of the beam in the direction of the minor axis may correspond to that of a Gaussian beam. 
     FIG. 8A  is a block diagram of a pulse YAG laser (hereafter referred to as “YAG laser”) as a laser light source, and  FIG. 8B  is an arrow view of a laser amplifier on the output side of the YAG laser depicted in  FIG. 8A  in the direction of arrow A.  FIG. 9A  is a diagram depicting the beam pattern of the YAG laser;  FIG. 9B  is an intensity distribution diagram of the beam pattern along the line  9 B— 9 B depicted in  FIG. 9A ; and  FIG. 9C  is an intensity distribution diagram of the beam pattern along the line  9 C— 9 C depicted in FIG.  9 A. In  FIGS. 9B and 9C , distance is plotted on the horizontal axis, and light intensity is plotted on the vertical axis. 
   It is apparent from  FIG. 9B  that the beam  24  of the YAG laser has a Gaussian distribution  24   a , and from  FIG. 9C  that the light intensity thereof has large peaks  36  and  37  on both ends (the top and bottom ends in FIG.  9 A). 
   This is because flash lamps  32  and  35  for excitation are disposed at both sides of NdYAG rods  31  and  34 . 
   A description will now be given of the YAG laser depicted in  FIGS. 8A and 8B . 
   The YAG laser  20  comprises an output laser oscillator  21  for oscillating a pulsed YAG laser, two laser amplifiers  22  and  23 , and reflecting mirrors  25  and  26  for deflecting the path of the beam  24  from the output laser oscillator  1  and inputting the resultant beam into the laser amplifier  22  of the preceding stage. 
   The output laser oscillator  21  comprises a resonator comprising a total reflection mirror  27  and a diffusion (output) mirror  28 , an NdYAG rod  29  disposed at the central axis of the resonator; and a flash lamp  30  for generating pulsed light flashes as excitation light arranged parallel with (in the y-axis) and beneath the NdYAG rod  29 . 
   The laser amplifier  22  of the preceding stage comprises an NdYAG rod  31  disposed along the optical axis of the beam  24  from the reflecting mirror  26 , and a flash lamp  32  arranged parallel with (in the y-axis) and beneath the NdYAG rod  31 . 
   The later-described laser amplifier  23  comprises a NdYAG rod  34  disposed along the optical axis of the beam  33  arriving from the laser amplifier  22  of the preceding stage, and a flash lamp  35  arranged parallel with (in the y-axis) and beneath the NdYAG rod  34 . 
   For this reason, the strong portions of the light intensity from the excitation light of the flash lamps  32  and  35  are superimposed on both ends of the beam  24  (depicted by the broken line) emitted from the YAG laser  20  and provided with the Gaussian distribution  24   a,  thus generating large peaks  36  and  37  as depicted in  FIG. 9A  on the upper and lower ends (in the y-axis) of the beam pattern  38 . 
   A linear beam having large, streaked peaks on both latitudinal (in the direction of arrow  12 ) ends thereof in the manner depicted in  FIG. 10  is radiated to the sample  10  when a beam  24  having large peaks  36  and  37  is directly transformed to a linear cross-sectional configuration with the aid of cylindrical lens groups  3 - 6  or a paired lens  7  such as those depicted in  FIG. 7. A  resulting problem is that the sample  10  undergoes ablation (a phenomenon in which scattering and surface roughening occur in areas within the portion of the sample  10  exposed to the beam  14  that are irradiated by the streaked-peaks, specifically, the longer ends).  FIG. 10  is a diagram depicting the light intensity (along the line  10 — 10 ) of a linear cross-sectional beam applied to a sample  10  from a laser annealing apparatus as depicted in FIG.  7 . 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a laser annealing method and apparatus capable of performing uniform beam emission, overcoming the aforementioned problems. 
   The laser annealing method of the present invention comprises transforming the cross-sectional configuration of a beam from a laser light source to a linear cross-sectional configuration by means of an optical system, and annealing a sample by applying the resulting linear cross-sectional beam thereto, wherein the laser annealing method entails transforming the beam from the laser light source to a linear cross-sectional configuration by means of an optical system after being rotated by rotating means at a prescribed angle. 
   The laser annealing apparatus of the present invention comprises a laser light source and an optical system for transforming the cross-sectional configuration of a beam from the laser light source to a linear configuration and annealing a sample by applying the resulting linearly configured beam thereto, wherein rotating means for rotating the cross-sectional configuration of the beam from the laser light source about the central axis of the beam at a prescribed angle are provided in the laser annealing apparatus between the laser light source and the optical system thereof. 
   In addition to the above structure, the optical system of the laser annealing apparatus of the present invention may comprise a plurality of cylindrical lens groups arranged parallel to one another and orthogonal with respect to the optical axis of the beam, and designed for dividing the beam in the arrangement direction; and a lens disposed on the transmission side of the cylindrical lens groups and designed for combining the divided beam. 
   In addition to the above structure, the rotating means of the laser annealing apparatus of the present invention may comprise a first mirror for deflecting the beam from the laser light source orthogonally with respect to the optical axis of the beam; a second mirror for deflecting the reflected beam from the first mirror orthogonally with respect to the plane containing the optical axis of the beam from the laser light source and the optical axis of the reflected beam from the first mirror; a third mirror for deflecting the reflected beam from the second mirror orthogonally within a plane identical to the plane containing the optical axis of the reflected beam from the first mirror and the optical axis of the reflected beam from the second mirror; and a fourth mirror for deflecting the reflected beam from the third mirror orthogonally within a second plane. 
   In addition to the above structure, the fourth mirror of the laser annealing apparatus of the present invention may be provided to a moving means capable of moving along the direction of the optical axis of the reflected beam from the third mirror. 
   In addition to the above structure, the rotating means of the laser annealing apparatus of the present invention may comprise a first mirror for deflecting the beam from the laser light source orthogonally with respect to the optical axis of the beam; and a second mirror for deflecting the reflected beam from the first mirror orthogonally with respect to a first plane containing the optical axis of the beam from the laser light source and the optical axis of the reflected beam from the first mirror. 
   In addition to the above structure, the second mirror of the laser annealing apparatus of the present invention may be provided to a moving means capable of moving along the direction of the optical axis of the reflected beam from the first mirror. 
   In addition to the above structure, the laser light source of the laser annealing apparatus of the present invention preferably comprises a YAG laser light source, an Nd glass laser, or a Q-switch solid-state laser. 
   By means of the present invention, uniform beam emission can be achieved because a beam having a Gaussian distribution can be utilized and a linear cross-sectional configuration formed in an optical system by rotating the beam from a laser light source at a prescribed angle with the aid of rotating means even when the beam pattern of the beam from the laser light source has a nonuniform intensity distribution. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a conceptual diagram depicting an embodiment of the laser annealing apparatus adopting the laser annealing method of the present invention; 
       FIG. 2A  is a side view of the rotating means used in the laser annealing apparatus depicted in  FIG. 1 ; 
       FIG. 2B  is a plan view of  FIG. 2A ; 
       FIG. 3A  is a cross-sectional view of a beam incident on the rotating means depicted in  FIG. 2A ; 
       FIG. 3B  is a cross-sectional view of a beam exiting the rotating means depicted in  FIG. 2A ; 
       FIG. 4A  is a diagram depicting the intensity distribution of the incident light; 
       FIG. 4B  is a diagram depicting the optical path of a beam passing through the homogenizer; 
       FIG. 4C  is a diagram depicting the intensity distribution of the beam along the line  4 C— 4 C after passing through the homogenizer; 
       FIG. 5  is a diagram depicting the light intensity along the line  5 — 5  of a linear cross-sectional beam applied to a sample from the laser annealing apparatus depicted in  FIG. 1 ; 
       FIG. 6A  is a conceptual diagram depicting another embodiment of the rotating means depicted in  FIGS. 2A and 2B ; 
       FIG. 6B  is a plan view of  FIG. 6A ; 
       FIG. 7  is a conceptual diagram of an apparatus operating according to the conventional laser annealing method; 
       FIG. 8A  is a block diagram of a pulse YAG laser as the laser light source; 
       FIG. 8B  is an arrow view of a laser amplifier on the output side of the YAG laser depicted in  FIG. 8A  in the direction of arrow A; 
       FIG. 9A  is a diagram depicting the beam pattern of the YAG laser; 
       FIG. 9B  is an intensity distribution diagram of the beam pattern along the line  9 B— 9 B depicted in  FIG. 9A ; 
       FIG. 9C  is an intensity distribution diagram of the beam pattern along the line  9 C— 9 C depicted in  FIG. 9A ; and 
       FIG. 10  is a diagram depicting the light intensity along the line  10 — 10  of a linear cross-sectional beam applied to a sample from the laser annealing apparatus depicted in FIG.  7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described in detail hereafter based on the accompanying figures. 
     FIG. 1  is a conceptual diagram depicting an embodiment of the laser annealing apparatus adopting the laser annealing method of the present invention. The present embodiment is described with reference to a case in which a Near Field pulse YAG laser is used as the laser light source. 
   The laser annealing apparatus  40  depicted in the same diagram comprises a Near Field pulse YAG laser (hereafter referred to as “YAG laser”)  20  (as seen in FIG.  8 A); rotating means  42  for rotating a beam  41  from the YAG laser  20  at a prescribed angle; a lens group  44  for dividing the beam  43  from the rotating means  42  into four parts in a horizontal direction (the number of divisions is not limited), composed of cylindrical lenses  44   a - 44   d ; a cylindrical lens  46  for transforming the beam from the lens group  44  into a linear cross-sectional configuration by combining the beam, disposed orthogonally to the generatrix; a total reflection mirror  51  for deflecting the beam  49  from the cylindrical lens  46  towards a sample  50 ; a cylindrical lens  53  for laser annealing by focusing the beam  52  from the total reflection mirror  51  and applying the beam to the sample  50 ; and a translation stage  56  that moves in the latitudinal direction (the direction of the arrow  55 ) of the linear cross-sectional beam  54  focused on the sample  50 . The lens group  44  and the cylindrical lens  46  also comprise a homogenizer  57  as the optical system. 
     FIG. 2A  is a side view of the rotating means used in the laser annealing apparatus depicted in  FIG. 1 ; and  FIG. 2B  is a plan view of FIG.  2 A.  FIG. 3A  is a cross-sectional view of a beam incident on the rotating means depicted in  FIG. 2A ; and  FIG. 3B  is a cross-sectional view of a beam exiting the rotating means depicted in FIG.  2 A. 
   The rotating means  42  may comprise, for example, a first mirror  60  for deflecting the beam  41  from the YAG laser orthogonally and upward with respect to the optical axis of the beam  41 ; a second mirror  62  for deflecting the beam  61  reflected by the first mirror  60  orthogonally with respect to a first plane containing the optical axis of the beam  41  and the optical axis of the beam  61  reflected by the first mirror  60 ; a third mirror  64  for deflecting the beam  63  reflected by the second mirror  62  orthogonally and downward within a plane identical to a second plane containing the optical axis of the beam  61  reflected by the mirror  60  and the optical axis of the beam  63  reflected by the second mirror  62 ; a fourth mirror  66  for deflecting the beam  65  reflected by the third mirror  64  orthogonally within the second plane; and moving means  67  for moving the fourth mirror  66  upward and downward along the direction of the optical axis of the beam  65  reflected by the third mirror  64 . 
   The moving means  67  for adjusting the height of the beam  43  comprises a rail  69  mounted along the breadboard  68  of the rotating means  42 ; and a support  70  for supporting the fourth mirror  66 , slidably mounted to the rail  69 ,  71 , shown by the broken line, is a cover. 
   When the laser annealing apparatus  40  depicted in  FIG. 1  is activated, the beam (see  FIG. 3A ) from the YAG laser (see  FIG. 8 )  20  enters the first mirror  60  of the rotating means  42 , reflects vertically upward, and enters the second mirror  62 . The beam  61  incident on the second mirror  62  is rotated 90 degrees (see  FIG. 3B ) by being reflected horizontally along the breadboard  68 . The rotated beam enters the third mirror  64 . The beam  63  thus incident on the third mirror  64  is reflected vertically downward to enter the fourth mirror  66 . The beam  65  thus incident on the fourth mirror  66  is then reflected horizontally along the breadboard  68  and enters the lens group  44  as the beam  43 . 
   The beam  43  incident on the lens group  44  enters the cylindrical lens  46  after being divided into four parts. The beam incident on the cylindrical lens  46  assumes a configuration wherein the beam pattern has a linear form with uniform light intensity in the longitudinal direction (see FIG.  5 ). 
   The operating principle of the homogenizer  57  will now be described. 
     FIGS. 4A ,  4 B, and  4 C are diagrams for describing the operating principle of a homogenizer. The case considered here is that of an incident beam having a Gaussian-type intensity distribution.  FIG. 4A  is a diagram depicting the intensity distribution of incident light;  FIG. 4B  is a diagram depicting the optical path of a beam passing through the homogenizer; and  FIG. 4C  is a diagram depicting the intensity distribution of the beam along the line  4 C— 4 C after passing through the homogenizer. In  FIGS. 4A and 4C , light intensity is plotted on the horizontal axis, and distance is plotted on the vertical axis. 
   A beam having a Gaussian distribution as depicted in  FIG. 4A  is focused along the line  4 C— 4 C through the optical paths L 1   a , L 1   b , L 2   a , L 2   b , L 3   a , and L 3   b  during passage through the lens  81  and the lens group  80  comprising the three cylindrical lenses  80   a - 80   c  depicted in FIG.  4 B. The beam B 1  transmitted in the light paths L 1   a  and L 1   b , the beam B 2  transmitted in the light paths L 2   a  and L 2   b , and the beam B 3  transmitted in the light paths L 3   a  and L 3   b  are thus superimposed to form a beam B 4  having a substantially flat intensity distribution along the line  4 C— 4 C. 
   The homogenizer is thus capable of forming a beam having a different intensity distribution by dividing the beam in the cylindrical lens group  80  and combining the beam again. The intensity distribution of the beam along the line  4 C— 4 C can also be freely adjusted by adjusting the light path after division. 
   The x-axis direction and the y-axis direction of the beam are divided and a substantially flat characteristic beam is obtained in the homogenizer  15  of FIG.  7 . 
   A case will now be considered in which a homogenizer  57  for dividing only the x-axis direction is used, as in FIG.  1 . When a beam enters the homogenizer through the beam pattern  38  having large intensity peaks  36  and  37  on the upper and lower ends thereof as shown in  FIG. 3A , a linear cross-sectional beam having strong light intensity at both ends in the latitudinal direction thereof is obtained as previously described, because of the absence of division along the y-axis thereof. In contrast, when a beam that is rotated 90 degrees as depicted in  FIG. 3B  enters the homogenizer, a beam whose latitudinal direction naturally has a Gaussian-distributed light intensity is obtained because the light intensity along the y-axis direction thereof assumes a Gaussian distribution. A substantially flat characteristic beam as depicted in  FIG. 5  is also ultimately obtained because of division thereof by means of the homogenizer, although the light intensity of the beam will have large peaks at both ends in the x-axis method. 
   The beam  49  from the lens group  44  and the cylindrical  46  depicted in  FIG. 1  is reflected towards the sample  50  (downward in the figure) by the reflecting mirror  51 , focused in the cylindrical lens  53 , and applied to the sample  50 . No ablation occurs because a linear cross-sectional beam with a uniform light intensity is applied to the sample  50 . Being able to operate with fewer lenses in comparison to the conventional laser annealing apparatus depicted in  FIG. 7  also makes further miniaturization possible. 
     FIG. 6A  is a conceptual diagram depicting another embodiment of the rotating means depicted in  FIGS. 2A and 2B .  FIG. 6B  is a plan view of FIG.  6 A. 
   The difference with respect to the rotating means depicted in  FIGS. 2A and 2B  is that this structure comprises only two mirrors. 
   Specifically, the rotating means  90  comprises a first mirror  91  for deflecting the beam  41  from the laser light source orthogonally with respect to the optical axis of the beam  41 ; and a second mirror  93  for deflecting the beam  92  reflected by the first mirror  91  orthogonally with respect to a first plane containing the optical axis of the beam  41  from the laser light source and the optical axis of the beam  92  reflected by the first mirror  91 . The second mirror  93  is provided to a moving means  94  capable of moving along the direction of the optical axis of the beam  92  reflected by the first mirror  91 . The moving means  94  is designed to adjust the height of the beam  43  and is composed of a rail  96  mounted along the breadboard  95  of the rotating means  90 , and a support  97  designed to support the second mirror  93  and slidably mounted to the rail  96  in the same manner as shown in  FIGS. 2A and 2B .  98 , shown by the broken line, is a cover. 
   Not only does using this type of rotating means  90  yield the same effects as the rotating means  42  depicted in  FIGS. 2A and 2B , but operating with only two mirrors enables further miniaturization. 
   By means of the present invention above:
         (1) An irregular state of distribution of a linear beam in which strong areas of intensity occur at both ends, as seen in the beam pattern of a YAG laser, can be overcome; and   (2) The direction of the Gaussian distribution in the original beam can be utilized directly, without division or processing, because the direction of the intensity distribution of the beam pattern can be rotated.       

   The present embodiment was described with reference to a 90 degree angle of rotation, but the present invention is in no way limited by this option alone and can be used as long as it is possible to obtain an angle of rotation that allows deviations in the intensity distribution of the beam to be corrected. The present embodiment was also described with reference to a Near Field pulse YAG laser as a laser light source, but the present invention is in no way limited by this option alone and may be adapted to laser light sources whose beam patterns have a nonuniform intensity distribution, such as Nd glass lasers, Q-switch solid-state lasers, and the like. 
   The claim of priority for the present application is based on Japanese Patent Application No. 2001-5579 (filed Jan. 12, 2001), and the details of the Japanese Application are contained in the description of the present application. 
   INDUSTRIAL APPLICABILITY 
   The present invention is applicable to a laser annealing method and apparatus.