Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
  • G02B19/0095—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with ultraviolet radiation
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0004—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed
  • G02B19/0028—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed refractive and reflective surfaces, e.g. non-imaging catadioptric systems
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
  • G02B19/0047—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source
  • G02B19/0052—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source the light source comprising a laser diode
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
  • G02B19/0047—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source
  • G02B19/0061—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source the light source comprising a LED
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
  • G02B27/0938—Using specific optical elements
  • G02B27/0977—Reflective elements
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
  • H01S3/08—Construction or shape of optical resonators or components thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
  • H01S3/22—Gases
  • H01S3/223—Gases the active gas being polyatomic, i.e. containing two or more atoms
  • H01S3/225—Gases the active gas being polyatomic, i.e. containing two or more atoms comprising an excimer or exciplex

Definitions

• the present invention relates to pulsed, gas discharge lasers.
• the present invention is particularly, but not exclusively, useful as a beam mixer for increasing the intensity symmetry of a high power Excimer gas discharge laser beam.
• TFT's thin film transistors
• TFT's amorphous silicon film that has been deposited on a substrate, e.g., glass
• LCD's liquid crystal displays
• Other applications for crystallized silicon films may include Organic LED (OLED), System on a Panel (SOP), flexible electronics and photovoltaics.
• OLED Organic LED
• SOP System on a Panel
• PVD liquid crystal displays
• high volume production systems may be commercially available in the near future capable of quickly crystallizing a film having a thickness of about 90nm and a width of about 700mm or longer.
• Laser crystallization may be performed using pulsed laser light that is optically shaped to a line beam, e.g., laser light that is focused in a first axis, e.g., the short-axis, and expanded in a second axis, e.g., the long-axis.
• a first axis e.g., the short-axis
• a second axis e.g., the long-axis.
• the first and second axes are mutually orthogonal and both axes are approximately orthogonal to a central ray traveling toward the film.
• An exemplary line beam for laser crystallization may have a beam width at the film of less than about 20 microns, e.g. 3-4 microns, and a beam length of about 700mm, or larger. With this arrangement, the film can be scanned or stepped in a direction parallel to the beam width to sequentially melt and subsequently crystallize a film having a substantial length, e.g.,
• homogenizers e.g. lenslet arrays (so-called fly's eye arrays) or difxusers are typically used in the projection optics downstream of the laser to produce a beam of uniform intensity.
• these homogenizers operate most effectively if the beam input to the homogenizer has a symmetrical intensity profile. Fluctuations in laser beam shape and symmetry may lead to a corresponding degradation in beam uniformity at the exit of beam homogenizers. This non-uniformity, in turn, can undesirably create regions of non-uniformly crystallized silicon.
• Excimer gas discharge laser sources are capable of producing the high power pulses suitable for generating a laser crystallization line beam, as described above.
• a typical excimer laser source may emit a beam having a cross-section with a short axis of about 3mm and a long axis of about 12mm. This beam can then be homogenized and shaped into the line beam, as described above. While the pulse shape and intensity symmetry along the short axis is typically stable and close to
• Gaussian the intensity along the long axis is generally non-symmetrical and unstable from pulse to pulse. Thus, if untreated, these pulses may not be homogenized properly and may result in a line beam having undesirable intensity variations along its length.
• Applicant discloses a beam mixer for increasing intensity symmetry along a selected axis of a beam and a laser source incorporating a beam mixer.
• a beam mixer for increasing intensity symmetry along a selected axis of a beam may include a plurality of mirrors establishing a spatially inverting path.
• the inverting path may have a beginning and an end and may be characterized in that a part of the beam near the first beam edge at the beginning of the path translates to the second beam edge at the end of the path.
• the beam mixer may further include an optic dividing the beam into first and second beam portions; the optic placing the first portion onto the inverting path and recombining the first and second portions onto a common path after the first portion has traveled along the inverting path thereby mixing the beam.
• the optic may be a beam splitter reflecting the first portion of the beam onto the inverting path, and in a particular embodiment, the plurality of mirrors may comprise three mirrors, e.g. three flat mirrors. In one arrangement, the inverting path may extend substantially orthogonal to the common beam path.
• a beam mixer for altering an intensity profile along a selected axis of a beam may comprise an optical inverting means for translating a part of the beam near the first beam edge at a first location along the beam to the second beam edge at a second location along the beam; and a means for directing a first portion of the beam to the inverting means, directing a second portion onto a common beam path and directing an output of the inverting means onto the common beam path.
• the directing means may comprise a beam splitter and in a particular embodiment the beam splitter may reflect about 40 to 60 percent of light incident upon the beam splitter to the inverting means.
• the inverting means may comprise a plurality of mirrors and in one arrangement, the plurality of mirrors may be three flat mirrors.
• the three flat mirrors may include a first mirror, second mirror and third mirror with the first mirror oriented to receive a beam from the directing means at an angle of incidence of approximately thirty degrees, the second mirror oriented to receive a beam from the first mirror at an angle of incidence of approximately thirty degrees, and the third mirror oriented to receive a beam from the second mirror at an angle of incidence of approximately thirty degrees.
• An additional aspect of an embodiment may include a laser source comprising: an oscillator producing a beam, an amplifier amplifying the beam and a beam mixer increasing intensity symmetry along a selected axis of the beam.
• the amplifier may output an amplified beam and the beam mixer may be positioned to increase intensity symmetry along a selected axis of the amplified beam.
• the oscillator may output a seed beam and the beam mixer may be positioned to increase intensity symmetry along a selected axis of the seed beam and produce an output for amplification by the amplifier.
• Fig. 1 shows a simplified perspective view of a beam mixer, shown, for the purposes of illustration, mixing a beam having a white half and a black half as incident on the mixer;
• Fig. 2 illustrates a typical beam profile along an axis of a beam exiting an excimer discharge laser
• Fig. 3 illustrates a symmetric beam profile
• Fig. 4 shows a first embodiment of a laser source having a beam mixer
• Fig. 5 shows another embodiment of a laser source having a beam mixer.
• a beam mixer 10 is shown for operation on a beam 12 (which for illustrative purposes has been shown as having an upper white half and a lower black half).
• the beam mixer 10 can be used to alter the intensity profile of a beam, e.g. improving intensity symmetry along a selected axis of a beam, can be used to reduce beam coherency, or both.
• the beam mixer 10 includes a beam splitter 14 and mirrors 16a-c.
• the beam is initially incident upon the beam splitter 14 whereupon a portion of the beam is directed, via reflection, toward mirror 16a and the remainder is transmitted (with substantially no change in direction) through the beam splitter 14 and exits the beam mixer on an output beam path.
• a beam splitter reflecting about forty to sixty percent of the incident light, e.g. fifty percent, may be used.
• about fifty percent of the initial beam incident upon the beam splitter 14 is directed toward the mirror 16a.
• mirrors 16a-c are typically flat, maximum reflectivity mirrors.
• mirror 16a may be positioned and oriented to receive light from the beam splitter 14 at an angle of incidence of approximately thirty degrees.
• mirror 14b may be positioned and oriented to receive light reflected from mirror 14a at an angle of incidence of approximately thirty degrees
• mirror 14c may be positioned and oriented to receive light reflected from mirror 14b at an angle of incidence of approximately thirty degrees.
• the output beam path includes a combined beam containing the portion of the initial beam 12 that passed through the beam splitter 14 and the portion of light from mirror 16c that is reflected from the beam splitter 14.
• the light on the path from the beam splitter 14 to mirror 16a includes a combined beam containing the portion of the initial beam 12 that is reflected by the beam splitter 14 and the portion of light from mirror 16c that is transmitted through the beam splitter 14.
• the beam entering the beam mixer 10 in Fig. 1 is shown having a rectangular cross-section that defines a long axis 18.
• This type of beam is typical of a laser beam produced by an excimer laser with the long axis corresponding to the direction from one discharge electrode to the other.
• a typical beam may have dimension of about 3mm by 12mm.
• the intensity profile in the long axis 18 is typically unsymmetrical (see graph 50 Fig. 2) whereas the intensity profile in the short axis (i.e. the axis normal to the long axis) is approximately Gaussian (see graph 52 on Fig. 3).
• the beam mixer 10 shown is particularly suitable for improving symmetry of a high power excimer discharge laser, it is to be appreciated that it can be used in conjunction with other types of laser systems and for other applications, for example, the beam mixer may be used to reduce coherency in a beam generated by a solid state laser.
• Fig. 1 shows that the beam extends along the axis 18 from a first edge 20 to a second edge 22.
• Fig. 1 also shows that the mirrors 16a-c establishing a spatially inverting path which has a beginning 24 and an end 26.
• the inverting path may be characterized in that a part of the beam near the first beam edge 20 at the beginning 24 of the inverting path translates to the second beam edge at the end 26 of the inverting path. More specifically, for the mixer 10 shown, a photon at the 'top' of the beam which strikes mirror 16a translates and leaves mirror 16c at the 'bottom' of the beam. Since the inverting path constitutes a delay path, there will be some temporal stretching of the pulse, however, this can be minimized by minimizing the delay path.
• Fig. 4 illustrates a laser source (generally designated 100) having an oscillator 102 which produces a beam 104 and an amplifier 106 which receives and amplifies the beam 104.
• Fig. 4 also shows that the source 100 may include a beam mixer 10', as described above, for increasing intensity symmetry along a selected axis of the beam.
• the amplifier 106 outputs an amplified beam 108 which is feed into the beam mixer 10'.
• the oscillator may be a pulsed gas discharge laser, such as a KrF excimer laser, an XeF excimer laser, an ArF excimer laser or molecular fluorine laser and may or may not be line narrowed using a dispersive optic such as one or more gratings, prisms, etalons, etc.
• a dispersive optic such as one or more gratings, prisms, etalons, etc.
• Other types of lasers may be used, such as cavity dumped lasers, mode-locked or Q- spoiled.
• the oscillator may be pulsed or continuous, and may be a CO 2 gas discharge laser, dye laser, or solid state laser, e.g. fiber laser, diode laser, etc.
• the amplifier may be may be pulsed or continuous and may be an excimer laser, molecular fluorine laser, CO2 gas discharge laser, dye laser, or solid state laser, e.g. fiber laser, diode laser, etc. More than one amplifier may be used, in series or in parallel.
• Fig. 5 shows another embodiment in which a laser source (generally designated 200) having an oscillator 202 which produces a seed beam 204 and an amplifier 206.
• the source 200 may include a beam mixer 10", as described above, for increasing intensity symmetry along a selected axis of the seed beam.
• the oscillator 202 outputs a seed beam 204 which is feed into the beam mixer 10".
• the mixed beam 208 is then feed into the amplifier 206 which amplifies the beam 208 and outputs and amplified beam 210.
• the oscillator may be a pulsed gas discharge laser, such as a KrF excimer laser, an XeF excimer laser, an ArF excimer laser or molecular fluorine laser and may or may not be line narrowed using a dispersive optic such as one or more gratings, prisms, etalons, etc.
• a dispersive optic such as one or more gratings, prisms, etalons, etc.
• Other types of lasers may be used, such as cavity dumped lasers, mode-locked or Q-spoiled.
• the oscillator may be pulsed or continuous, and may be a CO 2 gas discharge laser, dye laser, or solid state laser, e.g. fiber laser, diode laser, etc.
• the amplifier may be pulsed or continuous and may be an excimer laser, molecular fluorine laser, CO 2 gas discharge laser, dye laser, or solid state laser, e.g. fiber laser, diode laser, etc. More than one amplifier may be used, in series or in parallel.
• a single beam mixer 10', 10" is shown in Figs. 4 and 5, for altering an intensity profile along a selected axis of a beam, it is to be appreciated that two beam mixes could be employed, in series, with a first beam mixer altering an intensity profile along a first axis of a beam and a second beam mixer altering an intensity profile along a second axis of a beam.
• the first and second axes could be orthogonal.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Lasers (AREA)
• Recrystallisation Techniques (AREA)

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• 2006
  • 2006-06-05 US US11/447,380 patent/US7433372B2/en active Active
• 2007
  • 2007-05-14 TW TW096117040A patent/TWI344014B/zh active
  • 2007-05-22 JP JP2009514300A patent/JP2009540567A/ja active Pending
  • 2007-05-22 WO PCT/US2007/012389 patent/WO2007145791A2/en not_active Ceased
  • 2007-05-22 KR KR1020087030013A patent/KR101389722B1/ko active Active
  • 2007-05-22 EP EP07809174.1A patent/EP2036168B1/en not_active Ceased

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