Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/26—Bombardment with radiation
  • H01L21/263—Bombardment with radiation with high-energy radiation
  • H01L21/268—Bombardment with radiation with high-energy radiation using electromagnetic radiation, e.g. laser radiation
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
  • C30B13/16—Heating of the molten zone
  • C30B13/22—Heating of the molten zone by irradiation or electric discharge
  • C30B13/24—Heating of the molten zone by irradiation or electric discharge using electromagnetic waves
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
  • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/08—Devices involving relative movement between laser beam and workpiece
  • B23K26/083—Devices involving movement of the workpiece in at least one axial direction
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/352—Working by laser beam, e.g. welding, cutting or boring for surface treatment
  • B23K26/355—Texturing
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
  • C30B13/28—Controlling or regulating
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/02—Elements
  • C30B29/06—Silicon
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/47—Scattering, i.e. diffuse reflection
  • G01N21/4788—Diffraction
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/8422—Investigating thin films, e.g. matrix isolation method
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/02104—Forming layers
  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02656—Special treatments
  • H01L21/02664—Aftertreatments
  • H01L21/02667—Crystallisation or recrystallisation of non-monocrystalline semiconductor materials, e.g. regrowth
  • H01L21/02675—Crystallisation or recrystallisation of non-monocrystalline semiconductor materials, e.g. regrowth using laser beams
  • H01L21/02686—Pulsed laser beam
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
  • H01L22/10—Measuring as part of the manufacturing process
  • H01L22/12—Measuring as part of the manufacturing process for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N2021/8461—Investigating impurities in semiconductor, e.g. Silicon
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N2021/8477—Investigating crystals, e.g. liquid crystals
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/02104—Forming layers
  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02518—Deposited layers
  • H01L21/02521—Materials
  • H01L21/02524—Group 14 semiconducting materials
  • H01L21/02532—Silicon, silicon germanium, germanium
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/02104—Forming layers
  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02518—Deposited layers
  • H01L21/02587—Structure

Definitions

• the present invention relates in general to melting and recrystallization of thin silicon (Si) layers by pulsed laser irradiation.
• the method relates in particular to methods of evaluating the recrystallized layers.
• Silicon crystallization is a step that is often used in the manufacture of thin- film transistor (TFT) active-matrix LCDs, and organic LED (AMOLED) displays.
• TFT thin- film transistor
• AMOLED organic LED
• the crystalline silicon forms a semiconductor base, in which electronic circuits of the display are formed by conventional lithographic processes.
• crystallization is performed using a pulsed laser beam shaped in a long line having a uniform intensity profile along the length direction (long-axis), and also having a uniform or "top-hat” intensity profile in the width direction (short-axis).
• a thin layer of amorphous silicon on a glass substrate is repeatedly melted by pulses of laser radiation while the substrate (and the silicon layer thereon) is translated relative to a delivery source of the laser-radiation pulses. Melting and re-solidification (re-crystallization) through the repeated pulses, at a certain optimum energy density (OED), take place until a desired crystalline microstructure is obtained in the film.
• OED optimum energy density
• Optical elements are used to form the laser pulses into a line of radiation, and crystallization occurs in a strip having the width of the line of radiation. Every attempt is made to keep the intensity of the radiation pulses highly uniform along the line. This is necessary to keep crystalline microstructure uniform along the strip.
• a favored source of the optical pulses is an excimer laser, which delivers pulses having a wavelength in the ultraviolet region of the electromagnetic spectrum.
• the above described crystallization process, using excimer-laser pulses, is usually referred to as excimer-laser annealing (ELA).
• ELA excimer-laser annealing
• the process is a delicate one, and the error margin for OED can be a few percent or even as small as ⁇ 0.5%
• ELA electroactive polymer styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-S-S-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-st
• the method should be capable at least of being implemented on a production line. More preferably, the method should be capable of being used for quasi real-time evaluation in a feedback loop for automatically adjusting process energy density responsive to data provided by the evaluation.
• the present invention is directed to evaluating the progress of crystallization of semiconductor layer at least partially crystallized by exposure to a plurality of laser-radiation pulses having an energy density on the layer.
• the crystallization produces first and second groups of periodic surface features on the layer in respectively first and second directions perpendicular to each other, the form of the first and second groups of periodic features depending on the energy density of the laser-radiation pulses to which the semiconductor laser has been exposed.
• an evaluation method comprises delivering light to an area of the crystallized semiconductor layer such that first and second portions of the light are diffracted by respectively the first and second groups of periodic features.
• the amplitudes of the first and second diffracted light portions are separately measured.
• the energy density on the layer of the laser-radiation pulses is determined from the measured amplitudes of the first and second diffracted light portions.
• FIG. 1 is a graph schematically illustrating measured peak amplitude as a function of pulse energy density in rolling and transverse direction for fast Fourier transforms (FFTs) of scanning laser microscope images of ELA crystallized silicon layers.
• FFTs fast Fourier transforms
• FIG. 2 is a graph schematically illustrating measured peak amplitude as a function of pulse energy density in rolling and transverse directions for FFTs of scanning laser microscope images of A-ELA crystallized silicon layers.
• FIG. 3 is a graph schematically illustrating measured peak amplitude as a function of pulse number in rolling and transverse direction for fast Fourier transforms (FFTs) of scanning laser microscope images of A-ELA crystallized silicon layers.
• FFTs fast Fourier transforms
• FIG. 4 is a polarized-light microscope image of an area of an ELA crystallized silicon layer illustrating ridges formed transverse to and parallel to the rolling direction (RD) of the layer during crystallization.
• FIG. 5 is a conoscopic microscope image of an area of a crystallized layer similar to that of FIG. 4 depicting horizontal and vertical bands of light formed by diffracted light from respectively transverse-direction and rolling- direction ridges.
• FIG. 6 is a graph schematically illustrating measured amplitude as a function of pulse-energy density for diffracted light from transverse-direction and from rolling-direction ridges of ELA crystallized layers.
• FIG. 7 is a graph schematically illustrating measured amplitude as a function of pulse number for diffracted light from transverse-direction and from rolling-direction ridges of A-ELA crystallized layers for EDs of 410, 415, and 420 mJ/cm 2 .
• FIGS. 8 and 8 A schematically illustrate one preferred embodiment of an apparatus in accordance with the present invention for separately measuring the amplitude of diffracted light from transverse-direction and from rolling-direction ridges of ELA crystallized layers.
• FIG. 9 schematically illustrates one preferred embodiment of ELA apparatus in accordance with the present invention including the apparatus of FIG. 8 cooperative with a variable attenuator for adjusting pulse energy density on a silicon layer responsive to the measured amplitude of diffracted light from transverse-direction and from rolling-direction ridges of the ELA crystallized layer.
• FIG. 10 schematically illustrates another preferred embodiment of an ELA apparatus in accordance with the present invention similar to the apparatus of FIG. 9, but wherein the apparatus of FIG. 8 is replaced by another preferred embodiment of an apparatus in accordance with the present invention for separately measuring the amplitude of diffracted light from transverse-direction and from rolling-direction ridges of the ELA crystallized layer.
• protrusions are formed as a result of the expansion of Si upon solidification; they are formed especially between three or more solidification fronts colliding during lateral growth.
• the protrusions are often not randomly located. Rather, they are aligned due to processes of ripple formation collectively referred to in the literature as laser- induced periodic surface structures (LIPSS).
• LIPSS laser- induced periodic surface structures
• the ripples thus consist of series of well aligned protrusions.
• the ripple formation is only observed within an energy density window (range) in which partial melting of the film is achieved.
• the ripple periodicity is on the order of the wavelength of the incident light, for example, around 290-340 nm for XeCl excimer lasers. Because of these small dimensions, ripples cannot or can at best hardly be resolved using conventional optical microscopy techniques.
• ELA processed films consists of elongated darker colored regions interspersed with brighter regions. Close inspection of the darker regions shows that they consist of more strongly rippled (ordered) regions having higher protrusions, while in between are regions having less order and/or lower protrusions.
• the more ordered regions are herein referred to as ridges, while the regions in between are referred to as valleys. It is an inventive finding that the formation of ridges appears to be correlated to that of ripples with the typical orientation of ridges being in a direction perpendicular to the ripple direction.
• the inventive method and apparatus rely on measuring light-diffraction from ridges in a thin Si film (layer) that are formed as a result of the ELA process.
• the method offers an indirect measure of the degree of rippling that can be used for monitoring or controlling the ELA process in quasi real-time.
• a method is described looking more directly at the ripples themselves, albeit using microscopy techniques that are relatively slow compared to more conventional optical microscopy techniques used for measuring diffraction from ridges.
• Ripples are commonly not formed in one direction only.
• the ripples are predominantly formed in a direction parallel to the scan direction, and also in a direction perpendicular to the scan direction (the line direction).
• the ripples are periodic and are described herein by the direction of their periodicity, using terminology common in metallurgy, wherein the rolling direction (RD) corresponds with the scanning direction and the transverse direction (TD) corresponds with the line-direction. Accordingly, since ripples oriented in the scan direction are periodic in the transverse direction, they are termed TD ripples. Similarly ripples oriented in the line direction are periodic in the rolling direction and are termed RD ripples.
• TD ripples have a spacing roughly equal to the wavelength of the light, while RD ripples are spaced approximately /(l ⁇ sin9), with the ⁇ /(1- sinB) spacing typically dominant, wherein ⁇ is the angle of incidence of laser-radiation on the layer, which in ELA typically is about 5 or more degrees.
• Ripple formation is instrumental in obtaining uniform poly-Si films, because the grain structure tends to follow the surface periodicity.
• ripples are present, ideally, a very ordered film consisting predominantly of rectangular grains sized roughly ⁇ by /(l-sin9) is formed. At lower energy density (ED), grains are smaller and at higher ED, grains are larger.
• SSG super-lateral growth
• FIG. 1 is a graph schematically illustrating amplitude of corresponding RD and TD transform peaks as a function of energy density (ED) in millijoules per square centimeter (mJ/cm 2 ) in pulses for a total of 25 overlapping pulses in an ELA process.
• ED energy density
• mJ/cm 2 millijoules per square centimeter
• FIG. 2 is a graph similar to the graph of FIG. 1 but for crystallization by an A- ELA process of 25 pulses.
• the RD ripples show stronger periodicity than for ELA and its peak periodicity is better defined than in the case of the ELA process.
• FIG. 3 is a graph schematically illustrating RD and TD peak amplitudes as a function of pulse number at an ED of 420 mJ/cm 2 , which is somewhat less than the empirically determined OED. It can be seen that periodicity increases steadily in the TD direction up to a pulse number of about 22. In the RD direction, there is very little growth of periodicity until after about 15 pulses have been delivered.
• FIG. 4 is a polarization microscope image in reflected light. Ridges that are oriented in the transverse direction (which are correlated to ripples in the RD direction, or in other words, following the periodicity based definition, the "TD-ripples") can clearly be seen. Ridges that are oriented in the rolling direction (and correlated to "RD ripples") are less prominent but still evident, as would be expected from the above discussed FFT analysis.
• the ridges are not strictly periodic. However, the ridges have a characteristic spacing that can typically range between about 1.5 ⁇ and about 3.0 ⁇ , or about an order of magnitude larger than the spacing between the ripples.
• the ridges are referred to in the direction of periodicity, i.e., RD ridges are oriented in the transverse direction and TD ridges are oriented in the rolling direction.
• FIG. 5 is a conoscopic microscope image of a layer such as that depicted in FIG. 4. This was taken using a commercially available microscope with the eyepiece removed to allow an image of the back focal plane of the objective to be recorded. In this example, the image was recorded with a simple mobile-telephone camera. The microscope was used in a transmitted light configuration. A first polarizer was located in the illumination light path ahead of the sample and a second polarizer (analyzer) was located after the sample with the polarization direction at 90-degrees to that of the first polarizer. [0033] The center of the conoscopic image corresponds to the optical axis of the microscope system and the distance from the optical axis (center spot) corresponds to the angle over which the light travels. Accordingly, the conoscopic image provides information on the direction of light in the microscope.
• a condenser diaphragm was set close to a minimum aperture to limit the angular distribution of incident light on the sample and consequently to restrict the image of the aperture to the center of the conscopic image.
• the remainder of the image is formed by light diffracted from the TD and RD ridge groups formed by the crystallization.
• the polarizer and analyzer together, act to minimize the brightness of the central spot relative to the rest of the image.
• the two polarizers form a pair of crossing bands of extinction, known as isogyres, in the conoscopic image.
• the actual image represented in gray-scale in FIG. 5 is a colored image.
• the horizontal band is a bluish color and the vertical band is a greenish color.
• the coloring of the bands can be quite uniform and is believed to be indicative of a high diffraction efficiency at those wavelengths and lower diffraction efficiency at other wavelengths.
• the uniformity of the coloring of the bands is believed to be a result of variable spacing of the ridges. There may be some spectral overlap between the spectra of the horizontal and vertical bands.
• the microscope objective was a 20X objective. A fragmented edge of the central spot where the intensity gradient is high gives an indication of the image pixel size. The larger squares in the dark quadrants are an artifact of JPEG image-compression.
• FIG. 6 is a graph schematically illustrating RD ridge diffraction intensity (solid curve) and TD ridge diffraction intensity (dashed curve) as a function of pulse ED for a silicon layer area crystallized by 25 overlapping pulses in an ELA process.
• the intensity of ridges was not measure directly. Instead, a measure for diffraction band intensity was devised based on the observation that the bands have different color and that color information is still present in the regular microscope image.
• a commercially available raster graphics editor was used to determine the mean brightness of the blue and green channels of polarized light images as a measure of the diffraction of RD ridges and TD ridges, respectively.
• a disadvantage of this approach is that the image color channels do not provide optimized filtering to see the band brightness so that there is quite a significant cross-talk between the two signals. Also the signal of the non- diffracted central spot is superimposed on these color channels so that they have a higher noise level. Even so, the difference clearly shows a trend, with the OED found when the ratio of the green channel brightness to the blue channel brightness reaches a maximum, as depicted in FIG. 6 by the dotted curve.
• CMOS array or CCD array similar to the image of FIG. 5 can be electronically processed, using appropriate software, to gather measurement data only from the diffraction bands.
• This has an advantage that the measurement would be insensitive to the actual color and diffraction efficiency of the diffracted light bands in the image, as the spatial information is essentially independent of this.
• the actual diffraction efficiency may be a function of film thickness and deposition parameters.
• FIG. 7 is a graph schematically illustrating RD-ridge diffraction-intensity (solid curves) and TD-ridge diffraction-intensity (dashed curves) as a function of pulse number and ED for pulses sequentially delivered to the same area of a layer being crystallized.
• the trend here is similar to that of the graph of FIG. 3.
• the three ED values in each case are 410 mJ/cm 2 , 415 mJ/cm 2 , and 420 mJ/cm 2 , i.e., selected at intervals of little over 1% of the ED.
• FIG. 8 schematically illustrates one preferred embodiment 20 of apparatus in accordance with the present invention for evaluating a crystallized silicon layer.
• a crystallized silicon layer 22 being evaluated is supported on a glass panel 24.
• a microscope 26 set up for Kohler illumination includes a lamp or light source 28 delivering a beam 29 of white light.
• a condenser diaphragm 30 provides for control of the numerical aperture of the light cone of beam 29.
• a partially reflective and partially transmissive optical element 32 directs beam 29 onto layer 22 at normal incidence to the layer as depicted in FIG. 8.
• a portion 34 of the light beam is reflected from layer 22 and portions 36T are diffracted.
• the suffix T means that the light is diffracted by above-described transverse- direction (TD) ridges formed during crystallization of the layer.
• FIG. 8A depicts apparatus 20 in a plane perpendicular to the plane of FIG. 8 and illustrates light 36R diffracted by above-described rolling-direction (RD) ridges formed during crystallization of the layer.
• the reflected and diffracted light is transmitted through element 32.
• the reflected light is blocked by a stop 38.
• the diffracted light by-passes stop 38 and is incident on an optical detector element 52 in a detector unit 50.
• An electronic processor 54 is provided in detector unit 50 and is arranged to determine the amplitude of the diffracted light received by the detector.
• Detector element 52 can be a pixelated detector such as a CCD array or a CMOS array as discussed above, recording a conoscopic image of the diffracted light (see FIG. 7) from which the diffracted light intensity can be determined by processor 54 by spatial analysis.
• the detector element can be a one or more photo-diode elements recording aggregate diffracted light.
• optional filter elements 39 and 40 are provided having pass-bands selected to correspond to the particular colors of the TD and RD diffracted light, as discussed above. These can be moved in or out of the diffracted- light path as indicated in FIG. 8 by arrows A.
• another spectral filter (not shown) can be provided for limiting the bandwidth of light from source 28 to those colors which are diffracted. This will reduce noise due to scattered light (not shown) from layer 22, that is able to by-pass stop 38 and mix with the diffracted light.
• FIGS 8 and 8 A optics of microscope 26 including collector lens optics for light source 28, (infinity- corrected) objective optics, and tube lens optics are not shown, for convenience of illustration. Additionally, the microscope can be provided with a Bertrand lens to directly observe the conoscopic image and "eye pieces" (or oculars). The form and function of such optics in a microscope is well known to those familiar with the optical art, and a detailed description thereof is not necessary for understanding principles of the present invention.
• a transmitted light microscope may be used. Such a microscope setting does not have a beamsplitter but does require a separate condenser lens ahead of the sample.
• the beam stop 38 may be placed in the back focal plane of the objective or in any conjugate plane thereof after the sample.
• the beam stop is best placed in a conjugate plane to the back focal plane of the objective that is located after the beamsplitter so as to not also block the incoming light.
• FIG. 9 schematically illustrates one preferred embodiment 60 of an excimer laser annealing apparatus in accordance with the present invention.
• Apparatus 60 includes an excimer laser 64 delivering a laser beam 65. Beam 65 is transmitted through a variable attenuator 66 to beam-shaping optics 68 which deliver a shaped beam 69 via a turning mirror 70 to projection optics 72. The projection optics project the beam onto layer 22 at non- normal incidence as discussed above. Glass panel 24 including layer 22 is supported on a translation stage 62 which moves the layer and panel in a direction RD relative to the projected laser beam.
• Processing unit 54 determines from the amplitude of the TD-ridge diffracted and RD ridge diffracted light components observed by detector element 52 and an electronic look-up table created from experimental curves such as the curves of FIG. 6 and FIG. 7 whether the layer has been crystallized with pulses above or below the OED.
• the energy density in the projected laser beam is initially controlled at the nominal OED.
• the delivered energy density may drift with time, which is usually recorded as an apparent drift of the OED. If the OED appears to have drifted to a lower value than nominal, the ED will be below the OED; there will be a lower density of ridges in both directions as discussed above; and, accordingly, both the diffraction signals will be reduced in magnitude.
• a signal is then sent from processing unit 54 to attenuator 66 to reduce the pulse energy delivered to the layer.
• processing unit 54 can deliver information concerning the apparent OED drift for display on a monitor to an operator, and the operator can manually adjust the pulse-energy delivered to layer 22.
• FIG. 10 schematically illustrates another preferred embodiment 60A of excimer laser annealing apparatus in accordance with the present invention.
• Apparatus 60A is similar to apparatus 60 of FIG. 9 with an exception that diffraction measuring apparatus 20 thereof is replaced by an alternative diffraction measuring apparatus 21 which includes a directional light source 80 such as a laser beam 82.
• the light from the laser is incident on layer 22 at non-normal incidence as depicted in FG. 10, producing a reflected beam 82R and diffracted light 84.
• the reflected beam 82R is optionally blocked by stop 38 and diffracted light is detected by detector element 52 and can be processed by processing unit 54 as described above depending on the form of detector element 52.
• the inventive method and apparatus may thus be used to find OED from a panel containing multiple scans each at a different ED for example with ED 10, 5, or even just 2 mJ/cm 2 apart.
• a microscope according to the present invention may be mounted inside an annealing chamber of laser annealing apparatus.
• the microscope may include a zoom-lens assembly to change the magnification.
• the panel can be scanned underneath the microscope to allow the panel to be measured at one or multiple locations per condition.
• the microscope may additionally be provided with a stage to make movements in the transverse direction.
• An automatic focusing arrangement may be added but this will not be necessary for a conoscopic image as this has a larger depth of focus than the ELA process.
• Fully crystallized panels can also be measured (either online or offline) in one or more locations to detect the quality of the process so that the crystallization of further panels may be interrupted if necessary. If sufficient measurements are carried out, a map of defects (mura) may be obtained.

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