Method and optical system for processing semiconductor materials - Patents.com

Abstract

A method and optical system for processing a semiconductor material layer, particularly for producing a crystalline semiconductor layer, is disclosed, which includes providing a first laser beam (74) having a first laser pulse (76) and a second laser beam (84) having a second laser pulse (86), shaping the first laser pulse (76) and the second laser pulse (86) into linear laser pulses having a minor axis and a major axis using a beam shaping device, and imaging the linear laser pulses (76) and the second laser pulse (86) onto a semiconductor material layer using an imaging device. The polarization direction of the first laser pulse (76) is adjusted to be aligned with the minor axis of the illumination line (36), and the polarization direction of the second laser pulse (86) is adjusted to be aligned with the major axis of the illumination line (36), and the second laser pulse (86) is time-delayed relative to the first laser pulse (76) by a predetermined time interval Δt, where the time interval Δt is selected so that the illumination line imaged onto the semiconductor material layer has a composite time-intensity curve (96) in the form of a pulse having a first maximum value M1 and a second maximum value M2.

Description

[Technical field]

[0001] The present disclosure relates to a method for processing semiconductor materials, in particular for producing crystalline semiconductor layers, and to an optical system for processing semiconductor materials, in particular for producing crystalline semiconductor layers. [Background technology]

[0002] Lasers are used for the crystallization of thin film layers, for example for producing thin film transistors (TFTs). As the semiconductor to be processed, silicon (Si), more precisely amorphous silicon (a-Si), is used. The semiconductor layer has a thickness of, for example, 50 nm, which is typically on a substrate, for example a glass substrate, or another support.

[0003] The layer is irradiated with light from a laser, for example a pulsed solid-state laser. The light, for example having a wavelength of 343 nm, is shaped into an irradiated line and imaged onto an image plane of the semiconductor material. The irradiated line has a short (narrow) axis and a homogeneous long beam axis. The short or narrow axis has a Gaussian or flat intensity distribution.

[0004] The irradiation line is moved in the short axis direction over the semiconductor layer with a feed rate of typically about 5-50 mm / s. The power density (for continuous wave lasers) or pulse energy density (for pulsed lasers) of the light beam is adjusted such that, for example in the case of amorphous silicon, the silicon is partially melted and then the molten silicon solidifies into a crystalline structure, starting from unmelted solid silicon on the glass substrate. This melting and solidification typically occurs on a time scale of 10-100 ns, and the subsequent cooling of the film at room temperature typically takes several hundred μs.

[0005] When irradiating a layer of amorphous silicon to convert it into a layer of polycrystalline silicon, a uniform intensity of the irradiation line, i.e. the homogeneity of the spatial intensity distribution integrated along the short and / or long axis, is particularly important. The more homogeneous or uniform the intensity distribution of the irradiation line, the more homogeneous or uniform the crystal structure of the thin film layer (e.g. the grain size of the polycrystalline layer) and the better the final product formed from the thin film layer, e.g. a thin film transistor. A homogeneous crystal structure results in a high electrical conductivity, e.g. due to a high mobility of electrons and positively charged holes.

[0006] As the irradiation line moves over the semiconductor layer in the short axis direction, non-uniformities may occur, especially along the long beam axis, as well as perpendicularly along the short beam axis. These non-uniformities are called "mura". The so-called "scan mura" is due to non-uniformities along the beam axis and appears as stripe-like non-uniformities extending in the scanning or feed direction. Perpendicular to this, the so-called "shot mura" occurs, which is due to pulse-to-pulse intensity and energy density variations.

[0007] In order to make the "shot unevenness" as small as possible, the fluctuations in the energy density and time-intensity curve between laser pulses must be made as small as possible, for example by using lasers with very good pulse stability and by superimposing the laser beams of several laser sources. In order to make the "scan unevenness" as small as possible, the intensity of the irradiation line must be made as homogeneous as possible along the long axis. In addition, it is also known to reduce the "scan unevenness" by moving the irradiation line back and forth by 1 mm-2 mm with the help of a mirror oscillating around the axis of rotation during scanning, with the result that the unevenness generated along the long axis is "painted out".

[0008] Furthermore, the so-called "nitrogen unevenness" is known, the cause of which is that during irradiation, nitrogen is flowed over the substrate exposure surface, i.e. the surface of the material layer to be processed, e.g. a semiconductor layer, in order to reduce the oxygen concentration there to values ​​of 10 ppm-20 ppm, thus preventing oxidation of materials such as silicon. For this purpose, a laminar flow of nitrogen is passed directly over the material layer to be exposed. Inhomogeneities in the laminar flow can then lead to inhomogeneities in the crystal structure, the so-called "nitrogen unevenness".

[0009] It is known to use the surface interference effect to generate regular polycrystalline structures during crystallization. This effect produces a tuned intensity distribution during exposure, and by repeated exposure during feeding, the grain structure is strengthened approximately with the size of the wavelength of light. This effect is called "Laser-induced periodic surface structure" (abbreviation: LIPPS). For example, for a wavelength of 343 nm, grain structures of about 0.3 μm to 0.4 μm are produced. In the case of linearly polarized light, the tuned intensity distribution can be formed only in the direction of polarization, i.e., in the direction of the electric field vector. Experimental studies have shown that regular structures are formed along the long beam axis only when the light is polarized with its long axis. Similarly, if the light is polarized in the feeding direction, the effect can be observed in the feeding direction. Summary of the Invention [Problem to be solved by the invention]

[0010] The present disclosure provides improved methods for processing semiconductor materials, particularly for producing uniformly crystallized semiconductor layers. The present disclosure further provides improved apparatus for processing semiconductor materials, particularly for producing uniformly crystallized semiconductor layers, where the uniformly crystallized semiconductor layers have, in particular, uniform grain sizes. [Means for solving the problem]

[0011] A method having the features of claim 1 and an optical system having the features of claim 11 are provided.

[0012] A method for processing a layer of semiconductor material, in particular for producing a crystalline semiconductor layer, is disclosed which comprises the steps of: providing a first laser beam having a first laser pulse and a second laser beam having a second laser pulse; shaping the first laser pulse and the second laser pulse into a linear laser pulse having a short axis and a long axis using a beam shaping device; imaging the thus shaped linear laser pulse as an irradiation line having a short axis and a long axis on the semiconductor material layer using an imaging device; Adjusting the polarization direction of the first laser pulse to the minor axis direction of the irradiation line; The polarization direction of the second laser pulse is adjusted to the major axis direction of the irradiation line, The second laser pulse is time delayed with respect to the first laser pulse by a predetermined time interval Δt, which time interval Δt is selected such that the illumination line imaged on the semiconductor material layer has a composite time-intensity curve in the form of a pulse having a first maximum and a second maximum.

[0013] Here, the order of the above-mentioned method steps does not represent the temporal order in which the steps are performed. Typically, for example the adjustment of the polarization direction in the beam path is performed where the individual beams, i.e. the first and second laser beams, are separated. The shaping, homogenization and superposition of the individual beams are always performed after the first and second laser beams are prepared. The time delay step can be performed before or after the alignment of the polarization of the first and second laser beams. In principle, however, the temporal order of the above-mentioned steps can also be different.

[0014] The semiconductor material to be processed may be a thin layer, for example of amorphous silicon, about 50 nm thick, applied to a support such as a glass substrate.

[0015] The first and second laser beams are provided by at least one laser, as will be described in detail later. The laser may be, for example, a solid-state UV laser emitting light at a wavelength of 343 nm. The typical full width at half maximum (FWHM) of the first and second laser pulses is 15 ns to 20 ns. Here, the first and second laser beams are typically linearly polarized.

[0016] In another method step, the polarization of the first and second pulses is adjusted to a specific predefined direction, for example using a polarizing device. Thus, the first laser pulse is linearly polarized in the direction of the short axis of the irradiation line, and the second laser pulse is linearly polarized in the direction of the long axis of the irradiation line. The pulses emitted by solid-state lasers are typically linearly polarized. If the emitted pulses are linearly polarized, the polarization direction of the first and second pulses emitted according to the disclosed method is rotated to a specific predefined direction. This can be done using a polarizing device such as a λ / 2 plate with a corresponding orientation with respect to the beam or pulse impinging on the λ / 2 plate. In particular, the polarization direction of the first pulse is rotated to the direction of the short axis, which will be explained in more detail later. The polarization of the first pulse is thus aligned in the direction of the short axis, so that the polarization is almost exclusively aligned in the direction of the short axis, for example so that the proportion of light linearly polarized in a direction perpendicular to the short axis is 1% (polarization ratio 100:1) or for example so that the polarization ratio is 95:5. The polarization direction of the second pulse is rotated to a major axis perpendicular to the minor axis, as described in more detail below, such that the polarization of the second pulse is aligned along the minor axis so that the polarization is almost exclusively aligned along the major axis, e.g., 1% of the light is linearly polarized perpendicular to the major axis (polarization ratio 100:1), or, e.g., a polarization ratio of 95:5.

[0017] Furthermore, the second pulse is delayed by a predetermined time interval Δt with respect to the first pulse. A typical time delay is between 5 ns and 20 ns. Very typically, the time interval Δt is selected such that both pulses are superimposed in time into a single pulse when an illumination line, which will be described in more detail below, is imaged onto the semiconductor material layer. This superimposition in time results in a composite intensity curve with a first maximum and a second maximum.

[0018] In another method step, the first and second pulses are shaped into a laser line, i.e. a linear laser pulse, using a beam shaping device. The beam shaping device can form an anamorphic optical system. The anamorphic optical system can, for example, comprise a lens array homogenizer, which is based on the principle of splitting an incident laser beam into many partial beams and then spatially superimposing them. The laser line has a short axis and a long axis.

[0019] The laser line thus formed is imaged by the imaging device as an illumination line on the image plane of the semiconductor material. This illumination line likewise has a short axis and a long axis, the directions of which specify the polarization of the first and second pulses. Typically, the short and long axes of the illumination line coincide with the short and long axes of the linear laser pulse. The length of the illumination line, i.e. the geometrical extension in the long axis direction, is typically 100 mm to 1000 mm, for example 100 mm, 250 mm, 750 mm or 1000 mm. The length of the illumination line can also be longer if the beam shaping device and / or the imaging device are designed accordingly. The width of the illumination line, i.e. the geometrical extension in the short axis direction, is given as the full width at half maximum (FWHM) of the Gaussian distribution and is typically 20 μm to 200 μm. For a flat distribution, the width is measured at 90% intensity ("90% full width") and is typically 20 μm to 200 μm.

[0020] In another method step, the irradiation line can be moved in a feed direction relative to the semiconductor material layer. The first pulse is then linearly polarized in the feed direction, since the feed direction corresponds to the minor axis direction. The irradiation line sweeps over the semiconductor material layer, so that the entire semiconductor material layer or at least a larger area of ​​the semiconductor material layer can be exposed and thus processed. The support with the semiconductor material can be moved relative to the irradiation line, for example arranged on a table which moves in the feed direction. Typical feed speeds are between 5 mm / s and 50 mm / s.

[0021] According to another embodiment, the relative intensities of the first and second laser pulses can be selected such that the ratio of the first maximum to the second maximum in the combined time-intensity curve is in the range of 0.8 to 1.4, in particular in the range of 0.9 to 1.2, in particular 1.0. Since the combined time-intensity curve results from the superposition of the time-intensity curves of the first and second pulses, the ratio of the first maximum to the second maximum in the combined time-intensity curve can be adjusted by the intensities of the first and second pulses, taking into account the time interval Δt. In combination with a defined polarization direction of the first and second pulses as described above, it has been found that for the above-mentioned range of the ratio of the first maximum to the second maximum, a particularly homogeneous grain structure occurs in the formed (poly)crystalline semiconductor layer.

[0022] The composite time-intensity curve of the irradiated line can have a time-half-width of 40-50 ns relative to the first maximum of the composite time-intensity curve. The relatively long pulse duration allows the crystallization process to be affected over tens of ns, promoting the formation of a uniform grain structure.

[0023] According to another aspect, a first laser and a second laser designed to emit a first laser beam and a second laser beam, respectively, are provided and controlled such that the second laser pulse is emitted delayed with respect to the first laser pulse by a time interval Δt, the delay being achieved, for example, by electronically delaying the trigger signal of the second laser with respect to the trigger signal of the first laser.

[0024] As an alternative to this, it is provided to provide a first laser designed to provide a laser beam having a pulse, and to split the laser beam of the first laser into a first laser beam portion and a second laser beam portion, the first laser beam portion forming the first laser beam having the first laser pulse and the second laser beam portion forming the second laser beam having the second laser pulse. Thus, in this alternative, a laser is provided which is operated in a pulsed mode, and whose emitted laser beam is split by a beam splitter into the first laser beam and the second laser beam.

[0025] In this alternative, the time delay of the second pulse relative to the first pulse is achieved by the optical path length from the location of beam splitting of the second laser beam to the image surface of the semiconductor material being greater than the optical path length from the location of beam splitting of the first laser beam to the image surface of the semiconductor material, resulting in a phase shift of the first pulse relative to the second pulse.

[0026] In principle, it is of course also possible in the variant with two lasers for the time delay of the second pulse relative to the first pulse to be provided by a longer optical path length of the second pulse.

[0027] According to another embodiment, the first laser pulse may be one of the first laser pulses of the first laser beam and the second laser pulse may be one of the second laser pulses of the second laser beam, each of the plurality of laser pulses of the pulsed second laser beam being time-delayed by a respective predetermined time interval Δt with respect to each of the plurality of laser pulses of the pulsed first laser beam. The laser is thus pulsed to emit a plurality of laser pulses at a certain pulse repetition frequency, for example 10 kHz. In this case, the laser pulses of the second laser beam are time-delayed with respect to the first laser pulses, so that the first and second laser pulses are always superimposed and imaged on the semiconductor material as an illumination line in the form of a pulse with a first maximum and a second maximum. In other words, the semiconductor material is exposed to an illumination line pulsed at the pulse repetition frequency of the laser.

[0028] Here, the feed rate, the pulse repetition frequency of the first and second laser beams and the geometrical half-width in the minor axis direction of the irradiation line can be selected such that a location of the semiconductor material is exposed several times by the irradiation line, in other words, the semiconductor material moves so slowly relative to the irradiation line and the geometrical half-width of the irradiation line in the minor axis direction is so large that after a time corresponding to the pulse repetition frequency of the laser beam or a multiple of the pulse repetition frequency, the semiconductor material has moved a very small distance, so that the previously exposed location is exposed again or several times.

[0029] According to another aspect of the disclosed method, a third laser beam having a third laser pulse and a fourth laser beam having a fourth laser pulse are provided, the first laser pulse, the second laser pulse, the third laser pulse and the fourth laser pulse are shaped into a linear laser pulse having a short axis and a long axis by a beam shaping device, and the linear laser pulse thus shaped is imaged as an illumination line on a screen of the semiconductor material layer by an imaging device, further comprising: a polarization direction of the third laser pulse is adjusted to a direction of a short axis of the illumination line, a polarization direction of the fourth laser pulse is adjusted to a direction of a long axis of the illumination line, and the fourth laser pulse is time-delayed with respect to the third laser pulse by a predetermined time interval Δt, the time interval Δt being selected such that the illumination line imaged on the semiconductor material layer has a composite time-intensity curve in the form of a pulse having a first maximum and a second maximum.

[0030] Thus, according to this aspect of the method, four laser beams are uniformly superimposed and imaged, two of the four laser beams each having pulses linearly polarized in the direction of the short axis of the illumination line and time synchronized, and the other two of the four laser beams each having pulses linearly polarized in the direction of the long axis of the illumination line, which pulses are time delayed with respect to the pulses of the first two laser beams.

[0031] According to another aspect of the present disclosure, there is provided an optical system for processing a layer of semiconductor material, in particular for producing a crystalline semiconductor layer, the optical system comprising: a beam shaping device configured to shape the first laser pulse of the first laser beam and the second laser pulse of the second laser beam into a linear laser pulse having a minor axis and a major axis; an imaging device configured to image the shaped linear laser pulse as an illumination line onto the layer of semiconductor material; a polarization device configured to align a polarization direction of the first laser pulse with a minor axis of the illumination line and to align a polarization direction of the second laser pulse with a major axis of the illumination line; and a delay device configured to delay the second laser pulse by a predetermined time interval Δt relative to the first laser pulse, the time interval Δt being selected such that the illumination line imaged on the semiconductor material layer has a composite time-intensity curve in the form of a pulse having a first maximum and a second maximum.

[0032] The polarization device is therefore designed and arranged in such a way that the first laser pulse contains a polarization component almost exclusively along the minor axis of the irradiation line (polarization ratio of, for example, 1:100) and the second laser pulse contains a polarization component almost exclusively along the major axis of the irradiation line (polarization ratio of, for example, 1:100). Here, the polarization device may comprise a first polarization device for the first laser beam with the first laser pulse and a second polarization device for the second laser beam with the second laser pulse. The first polarization device is arranged in particular in the beam path of the first laser beam and the second polarization device is arranged in particular in the beam path of the second laser beam.

[0033] The beam shaping device can form an anamorphic optical system, which may for example comprise a lens array homogenizer, which is based on the principle of splitting an incident laser beam into many partial beams which are then spatially superimposed. The laser line has a minor axis and a major axis.

[0034] The laser line thus formed is imaged by an imaging device onto an image plane of the semiconductor material as an illumination line, which also has a minor axis and a major axis whose directions specify the polarization of the first and second pulses. Typically, the minor and major axes of the illumination line coincide with the minor and major axes of the linear laser pulse.

[0035] The polarizing device of the optical system may in particular comprise a first λ / 2 plate, which is arranged in the beam path of the first laser beam, in particular before the beam shaping device, and oriented such that, for a first laser pulse impinging on the λ / 2 plate, the first laser pulse is linearly polarized in the short axis direction after passing through the λ / 2 plate, and may comprise a second λ / 2 plate, which is arranged in the beam path of the second laser beam, in particular before the beam shaping device, and oriented such that, for a first laser pulse impinging on the λ / 2 plate, the second laser pulse is linearly polarized in the long axis direction after passing through the λ / 2 plate.

[0036] Thus, the first λ / 2 plate is oriented to rotate the polarization direction of the linearly polarized first laser beam having the first laser pulse along the short axis, and the second λ / 2 plate is oriented to rotate the polarization direction of the linearly polarized second laser beam having the second laser pulse along the long axis.

[0037] According to a variant, the delay device comprises a delay circuit, which emits a trigger signal configured to delay the second laser beam with the second laser pulse by a time interval Δt relative to the trigger signal of the first laser, the first laser being configured to emit the first laser beam with the first laser pulse, so that the second trigger signal can be electronically delayed relative to the first trigger signal.

[0038] According to an alternative variant, the delay device may comprise a beam bypass which causes the optical path length of the second laser beam to the image plane of the semiconductor material layer to be greater than the optical path length of the first laser beam to the image plane of the semiconductor material layer, so that according to this variant the time delay is caused by a path difference due to the second laser pulse having traversed a greater optical path length than the first pulse to the superposition.

[0039] The first and second laser beams of the optical system can be provided by a first and second laser source, or alternatively can be provided by a laser source whose emitted laser beam is split into the first and second laser beams using a beam splitter.

[0040] According to another aspect, the beam shaping device is configured to shape the first laser pulse of the first laser beam, the second laser pulse of the second laser beam, the third laser pulse of the third laser beam, and the fourth laser pulse of the fourth laser beam into a linear laser pulse having a short axis and a long axis, the imaging device is configured to image the linear laser pulse thus shaped as an illumination line on the semiconductor material layer, the polarizing device is configured to linearly polarize the third laser pulse in a short axis direction of the illumination line and the fourth laser pulse in a long axis direction of the illumination line, and the delay device is configured to delay the fourth laser pulse by a predetermined time interval Δt with respect to the third laser pulse, the time interval Δt being selected such that the illumination line imaged on the semiconductor material layer has a composite time-intensity curve in the form of a pulse with a first maximum and a second maximum.

[0041] Thus, according to this aspect, the optical system includes a four-beam configuration in which four laser beams are uniformly superimposed and imaged onto the semiconductor material layer as an illumination line, two of the four laser beams each having pulses linearly polarized along a minor axis of the illumination line and time synchronized, and two other of the four laser beams each having pulses linearly polarized along a major axis of the illumination line and time delayed with respect to the pulses of the first two laser beams.

[0042] The present disclosure further includes a system for processing a semiconductor material layer, in particular for producing a crystalline semiconductor layer, comprising an optical system according to the above-mentioned embodiment, which is designed to move the semiconductor material layer relative to the irradiation line in a feed direction, where the feed direction corresponds to the minor axis direction of the irradiation line. The semiconductor material layer can be moved relative to the irradiation line using a feed device, e.g. a table movable in the feed direction, so that a large area or even the entire semiconductor material layer can be exposed and thus processed by the irradiation line. In this case, the feed direction corresponds to the minor axis direction, so that the polarization orientation of the first pulse and / or the third pulse corresponds to the feed direction.

[0043] The present disclosure will now be described in detail with reference to the accompanying drawings. [Brief description of the drawings]

[0044] [Figure 1] FIG. 1 shows a schematic diagram of a layer of semiconductor material exposed to a line of radiation moving in a feed direction relative to the layer of semiconductor material for processing the layer of semiconductor material. [Figure 2a] FIG. 2a shows the line shape of the imaged illumination line. [Figure 2b] FIG. 2b shows the line shape of the imaged illumination line. [Figure 2c] FIG. 2c shows the line shape of the imaged illumination line. [Figure 3a] FIG. 3a shows a schematic diagram of an optical system for a system for processing a semiconductor layer, capable of shaping and imaging a line of radiation onto the semiconductor material. [Figure 3b] FIG. 3b shows a schematic diagram of an optical system for a system for processing a semiconductor layer, capable of shaping and imaging a line of radiation onto the semiconductor material. [Figure 4] FIG. 4 shows a schematic diagram of an embodiment of an optical system in which a first laser beam and a second laser beam are provided by beam splitting of a laser beam. [Diagram 5]FIG. 5 shows a schematic diagram of an embodiment in which four laser beams are provided by four laser sources, with the pulses of two laser beams being emitted with a time delay relative to the pulses of the other two laser beams. [Figure 6] FIG. 6 shows a schematic diagram of an embodiment in which two laser beams are provided by two laser sources, with the pulses of one laser beam being time delayed with respect to the pulses of the other laser beam. [Figure 7] FIG. 7 shows diagrammatically the composite time-intensity curve of an illumination line resulting from a homogeneous superposition of individual pulses. [Figure 8a] FIG. 8a shows a scanning electron microscope image of a crystalline silicon layer produced by the disclosed method. [Figure 8b] FIG. 8b shows a scanning electron microscope image of a crystalline silicon layer produced by a comparative method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] In Fig. 1, it is shown diagrammatically how a semiconductor material is irradiated by a laser beam to produce a homogeneous crystallized layer according to the disclosed method. A support 10, for example a glass substrate, is coated with a layer 12 of the semiconductor material to be treated. In this example, the semiconductor material to be treated is amorphous silicon. The thickness of the semiconductor material layer 12 is typically about 50 nm.

[0046] The linear laser beam 14 is imaged on the semiconductor material and moves in a feed direction x relative to the semiconductor material, so that the laser line 14 brushes and irradiates at least a partial area of ​​the semiconductor material layer 12. In the example shown, the support 10 carrying the semiconductor material layer 12 is moved in space relative to the stationary laser beam 14. The laser line 14 can be moved relative to the semiconductor material layer 12 such that the entire semiconductor material layer 12 is irradiated by the laser line 14. Typically, the laser line 14 is moved relative to the semiconductor material layer 12 such that a certain area is irradiated by the laser line 14 multiple times. A typical feed speed is in the range of 5 mm / s to 50 mm / s.

[0047] The propagation direction of the laser beam 14 is in the embodiment shown perpendicular to the surface of the semiconductor material layer 12. That is, the laser beam 14 strikes the surface of the semiconductor material layer 12 perpendicularly here, at an incidence angle of 0°.

[0048] The line shape of the laser beam 14 is shown in Figures 2a-c, where the intensity is plotted as a function of a particular direction.

[0049] FIG. 2a shows the intensity of the laser line in the major axis direction, i.e. the intensity distribution 16 integrated along the minor axis (along the x-axis), and the thus integrated intensity distribution 16 is shown along the major axis (along the y-axis). By convention, the minor axis runs parallel to the x-axis in the figure, and the major axis runs parallel to the y-axis. As can be seen in this figure, the distribution 16 is approximately rectangular and therefore ideally homogeneous along the major axis. The length of the illumination line in the y-direction may typically be 100 mm to 1000 mm, for example 100 mm, 250 mm, 750 mm or 1000 mm, or more than 1000 mm.

[0050] Figures 2b and 2c show the intensity of the laser line in the minor axis direction, i.e. the intensity distribution integrated along the major axis (and thus along the y-axis) 18, 20, respectively, and the intensity distribution thus integrated is shown along the minor axis (i.e. along the x-axis). In this case, the intensity in Figure 2b has a Gaussian curve 18. Alternatively, the intensity may have a flat curve 20 ("flat top"), i.e. an approximately rectangular curve, as shown in Figure 2c.

[0051] Typical widths of the intensity in the x-direction are between 20 μm and 200 μm. For the Gaussian curve 18 in Fig. 2b the width is shown as the Full Width at Half Maximum (FWHM) and for the flattened curve 20 in Fig. 2c it is shown as the width that the curve has at an intensity corresponding to 90% of the maximum intensity (FW90%: Full Width at 90%).

[0052] When the irradiation line 14 is guided over a layer 12 of semiconductor material to be processed, such as a-Si, the layer 12 of semiconductor material melts for a short period of time and then solidifies as a crystalline layer with improved electrical properties.

[0053] 3a and 3b show a schematic of an optical system 30 for a system for processing a semiconductor layer, which is capable of shaping and imaging a line of irradiation 14 onto the semiconductor material, as described with respect to FIGS. 1 and 2.

[0054] The optical system 30 includes a beam shaper 32 configured to shape the laser beam such that the beam profile of the laser beam has a major axis and a minor axis, as described below, and an imaging device 34 arranged after the beam shaper 32 in the beam path of the laser beam, configured to image the thus shaped laser beam as an illumination line 36. In the example shown, four laser beams are shown to impinge on the beam shaper 32, namely a first laser beam 38, a second laser beam 40, a third laser beam 42 and a fourth laser beam 44, as described below by way of example. However, also according to the present disclosure, two laser beams may impinge on the beam shaper 32, as described below by way of example. In principle, the number of laser beams is not limited to four or two, any other number is possible and is encompassed by the present disclosure.

[0055] In the example shown, the laser beam is a 343 nm laser beam emitted by a number of solid-state UV lasers, but in principle it is also possible to use other laser sources, in particular other solid-state laser sources, for example solid-state lasers emitting in the green spectral range.

[0056] In Figures 3a and 3b the minor axis is shown parallel to the x-axis and the major axis parallel to the y-axis, as already seen in Figures 1 and 2. The optical axis of the optical system runs parallel to the z-axis.

[0057] FIG. 3a shows the imaging characteristics of optical system 30 in the y direction, i.e. along the major axis of the shaped laser beam and illumination line, and FIG. 3b shows the imaging characteristics of optical system 30 in the x direction, i.e. along the minor axis of the shaped laser beam and illumination line.

[0058] The beam shaping device 32 of the optical system 30 of Fig. 3a and Fig. 3b comprises an anamorphic homogenizing optics 46, which homogenizes the intensity of the incident laser beam in the y-axis direction. The anamorphic homogenizing optics 46 comprises, for example, two cylindrical lens arrays arranged parallel to each other. The cylindrical lens arrays split the incident beam into individual partial beams which are superimposed all over, as a result of which the laser beam is approximately homogenized. In the case of several incident laser beams, each laser beam is split into individual partial beams which are homogenized and superimposed. Such kind of homogenizing optics is described in more detail, for example, in German patent application DE 4220705 A1, German patent application DE 3829728 A1 or German patent application DE 10225674 A1, which are hereby incorporated in the present disclosure.

[0059] The beam shaping device 32 of the optical system 30 further includes a focusing cylinder lens 48 in the beam path following the anamorphic homogenizing optic 46, which is configured to direct the laser beam redispersed and homogenized by the anamorphic homogenizing optic 46 telecentrically to the illumination line 36 where it overlaps with respect to the long axis, i.e., in the y-direction. Thus, the combination of the anamorphic homogenizing optic 46 and the focusing cylinder lens 48 homogenizes the incoming laser beam as the illumination line 36 on the image plane.

[0060] In the beam path after the focusing cylindrical lens 48, an imaging device 34 is arranged, which is set to focus the laser beam in the short axis, i.e. in the x-direction, into an illumination line 36. Or in other words, the imaging device 34 images the laser beam into an illumination line 36, in which case only the short axis of the beam profile is homogenized, but not the homogenized long axis of the beam profile. The imaging device 34 can be, for example, a focusing cylindrical lens system.

[0061] The combination of the anamorphic homogenizing optics 46 and the focusing cylindrical lens 48 may be an anamorphic optics or a part of such an optics, which may be part of the anamorphic optics described in particular in figures 4 to 6 of German patent application DE102012007601A1, which is included in the present disclosure with respect to the anamorphic optics 42.

[0062] The beam shaping device 32 may further include one or more of the following optical elements: A first collimation cylindrical lens, designated by the reference number 54 in the German patent application DE 10 201 2007 601 A1, for collimation of the emitted laser beam with respect to the x-axis. A second collimation cylindrical lens, designated by the reference number 56 in the German patent application DE 10 201 2007 601 A1, for collimation of the emitted laser beam with respect to the y-axis. a cylindrical lens, referenced 58 in German patent application DE 10 201 2007 601 A1, arranged in the beam path after the first collimation cylindrical lens in order to focus the light rays in relation to the x-axis into an intermediate image, referenced 60 in German patent application DE 10 201 2007 601 A1 an intermediate collimation cylinder lens, designated by the reference number 58' in the German patent application DE 10 2012 007 601 A1, arranged in the beam path after the first collimation cylinder lens 54 for collimating the light rays of the first intermediate image, and / or a further cylinder lens, referenced 62 in German patent application DE102012007601A1, arranged in the beam path after the first intermediate image, in particular after the intermediate collimation cylinder lens, in order to focus the light rays in relation to the x-axis into an intermediate image, referenced 60 in German patent application DE102012007601A1.

[0063] The above-mentioned anamorphic homogenizing optics 46 may for example be or include an element 68 shown in FIGS. 4 to 6 of German patent application DE102012007601A1.

[0064] The above-mentioned focusing cylindrical lens 48 may for example be or include a focusing cylindrical lens 74 as shown in Figures 4 to 6 of German patent application DE102012007601A1.

[0065] Finally, the aforementioned imaging device 34 can be or include, for example, an element 66 shown in FIGS. 4 to 6 of German patent application DE 10 2012007601 A1.

[0066] The optical system further comprises a polarizing device 50 for each of the laser beams 38, 40, 42, 44 incident on the anamorphic optical system. The polarizing device here is an optical system for adjusting the polarization direction 50, for example a λ / 2 plate in the beam path of each incident laser beam 38, 40, 42, 44. The optical system 50 is arranged in the beam path before the anamorphic optical system or the anamorphic homogenizing optical system 46. Each incident laser beam passes through the optical system 50, and the laser beams 38, 40, 42, 44 passing through the optical system 50 are linearly polarized in a defined direction. More precisely, the laser beams emitted from the lasers are already linearly polarized, for example in the example of a solid-state UV laser shown here, and the polarization direction is rotated to a defined direction by the optical system 50. In this case, the optical system 50, for example the λ / 2 plate, is oriented with respect to the polarization direction of the linearly polarized incident light such that two of the four laser beams are linearly polarized after passing through the optical system 50 in the long axis direction, and the remaining two of the four laser beams are linearly polarized after passing through the optical system 50 in the short axis direction. In this case, the feed direction corresponds to the minor axis direction, and the remaining two of the four laser beams are linearly polarized in the feed direction. More precisely, according to the present disclosure, the optics 50, e.g. a λ / 2 plate, arranged in the beam paths of the first laser beam 38 and the second laser beam 40 are oriented such that the first laser beam 38 and the second laser beam 40 are polarized in the minor axis direction, i.e. in the x-direction or feed direction, respectively, and the optics 50, e.g. a λ / 2 plate, arranged in the beam paths of the third laser beam 42 and the fourth laser beam 44 are oriented such that the third laser beam 42 and the fourth laser beam 44 are polarized in the major axis direction, i.e. in the y-direction, respectively. In this example, the lasers are furthermore pulsed, with the individual pulses of the respective laser beams having the above-mentioned polarization direction of the respective laser beam.

[0067] The four laser beams 38, 40, 42, 44 may be laser beams emitted from four laser sources, and thus each laser beam is assigned to a separate laser source.

[0068] Alternatively, the laser beams 38, 40, 42, 44 may result from splitting a laser beam emitted by a laser source into a first and a second partial beam using a beam splitter. The beam splitter can be designed to split the first partial beam, i.e. the transmitted beam, and the second partial beam, i.e. the transmitted beam, by about 50% each. For this purpose, for example, polarizing optics, for example so-called thin film polarizers, can be used. Thin film polarizers are optical substrates with a special coating that passes p-polarized light (plane of vibration of the electric vector parallel to the plane of the incident beam and the normal on the substrate surface) and reflects light with s-polarized light (plane of vibration of the electric vector perpendicular to the plane of the incident beam and the normal on the substrate surface). By rotating the polarization direction of the laser beam emitted by the laser source by a λ / 2 plate in front of the thin film polarizer in the beam path, an equal proportion of p-polarized light and s-polarized light occurs in front of the thin film polarizer in the beam path, thereby achieving a split of about 50%. However, the λ / 2 plate in front of the thin film polarizer can also be rotated so that a different proportion of p- and s-polarized light occurs in front of the thin film polarizer in the beam path, achieving a split different from 50%. In principle, the relative intensity of the first partial beam with respect to the second partial beam can be adjusted by the orientation of the λ / 2 plate.

[0069] Such an arrangement is shown diagrammatically in Fig. 4. A linearly polarized laser beam 52 emitted by a laser source impinges on a λ / 2 plate 54 arranged in the beam path before a beam splitter 56, here a thin-film polarizer. The λ / 2 plate 54 is generally oriented in the beam path such that the relative proportion of s-polarized and p-polarized light of the laser beam after the λ / 2 plate corresponds to the desired relative intensity of both partial beams 58, 60 after the beam splitter 56, as described above. In this case, the first partial beam 58 can be, for example, the first laser beam 38 of the arrangement of Figs. 3a and 3b, and the second partial beam 60 can be, for example, the third laser beam 42 of Figs. 3a and 3b. The second partial beam 60 is deflected by a reflecting element 62 to run parallel to the first partial beam 58. In addition, after the beam splitter 56 in the beam path, a λ / 2 plate 64 is arranged in the beam path of the first and second partial beam, respectively, which corresponds to the λ / 2 plate 50 in the beam path of the first laser beam 38 and the third laser beam 42 in Figures 3a and 3b. The λ / 2 plate 64 arranged later in the beam path of the first partial beam 58 is used for polarization in the minor axis direction. The λ / 2 plate 64 arranged later in the beam path of the second partial beam 60 is then used for polarization in the major axis direction.

[0070] The second laser beam 40 and the fourth laser beam 44 can be provided by beam splitting in an alternative arrangement corresponding to the arrangement of Fig. 4 but with a beam splitter 56. A subsequent λ / 2 plate 64 is again oriented to polarize the third and fourth partial beams in the minor and major axis directions, respectively. Alternatively, the four laser beams of Fig. 3a and 3b can be provided by two laser sources, the laser beams emitted from which are split into the first partial beam 58 and the second partial beam 60 or the third and fourth partial beams, respectively.

[0071] The optical system 30 of Figures 3a and 3b can also be used, as already mentioned above, for superimposing other numbers of laser beams than four, for example two laser beams, in which case the two laser beams can be provided by two laser sources corresponding to four laser beams, or by one laser source, splitting into a first and a second partial beam by beam splitting, using an arrangement corresponding to Figure 4 or the same arrangement.

[0072] Furthermore, the optical system 30 of Fig. 3a and Fig. 3b is set up such that the pulses of different polarizations are time-shifted from each other by a predefined time interval Δt. This can be achieved by electronically delaying the trigger signals of the laser sources when using separate laser sources for each laser beam. When providing the laser beams using partial beams, the time delay can be achieved by a beam detouring. As shown in Fig. 4, the second partial beam 60 travels a longer distance than the first partial beam 58. The path Δs can be selected such that there is a time delay of the second partial beam 60 with respect to the first partial beam 58 by a predefined time interval Δt. This predefined time interval is preferably between 10 ns and 20 ns.

[0073] Using the optical system 30 described above, at least one short-axis polarized laser pulse and one long-axis polarized laser pulse are imaged in a homogeneous superposition on the illumination line, with the long-axis polarized pulse being delayed by a time interval Δt with respect to the short-axis polarized pulse. The superposition of four laser beams results in two short-axis polarized laser beams and two long-axis polarized laser beams, with the long-axis polarized laser beams being time-synchronized and the short-axis polarized laser beams being time-delayed by the same time interval Δt. By superposing two (or more) time-synchronized laser beams from two (or more) different laser sources, possible variations in energy density between pulses can be reduced. Such variations can lead to different crystallization results when the illumination line is shifted in the short axis direction between pulses, leading to inhomogeneities in the crystal structure along the direction of travel ("shot mura"). It should be noted in this case that the combined intensity distribution of two (or more) laser beams (laser pulses) superimposed in this way can change over time (between the combined intensity distributions) due to the presence of time jitter, i.e. short-term time deviations of the intensity from the ideal value. In particular, these non-uniformities arise when combining two (or more) laser sources, each of which has a time jitter independent of the other. It is therefore advantageous to use (pulsed) laser sources with as small a time jitter as possible in the ns range.

[0074] The anamorphic homogenizing optics 46 is designed such that each incoming beam is split into partial beams, which are homogenized in the long axis direction and superimposed, i.e. the individual beams produce a homogenous line. In the pulsed configuration with two laser beams described above, both the laser pulses polarized in the short axis direction and preceding in time, as well as the laser pulses polarized in the long axis direction and delayed in time with respect to the first pulse, are superimposed and imaged as homogenous lines. Thus, in the configuration with four laser beams, both the laser pulses polarized in the short axis direction and preceding in time, as well as the laser pulses polarized in the long axis direction and delayed in time with respect to the first pulse, are superimposed and imaged as homogenous lines.

[0075] The above will be explained again in more detail based on the disclosed method.

[0076] 5 illustrates the disclosed method based on an example configuration with four laser sources, namely a first laser source 66, a second laser source 68, a third laser source 70 and a fourth laser source 72. The first laser source 66 and the second laser source 68 are adapted to provide a first laser beam 74 having a first laser pulse 76 and a second laser beam 78 having a second laser pulse 80, respectively, which are emitted simultaneously by a synchronous trigger signal 82 of the first laser source 66 and the second laser source 68. The third laser source 70 and the fourth laser source 72 are adapted to provide a third laser beam 84 having a third laser pulse 86 and a fourth laser beam 88 having a fourth laser pulse 90, respectively, and the trigger signals 92 of the third laser source 70 and the fourth laser source 72, respectively, are electronically delayed by a time interval Δt, for example by an electronic delay circuit 94, so that the third laser pulse 86 and the fourth laser pulse 90 are emitted and propagated with a time delay of the time interval Δt relative to the first pulse 76 and the second pulse 80, respectively. Further according to the disclosed method, the first laser pulse 76 and the second laser pulse 80 are linearly polarized in the feed direction, i.e., in the x-axis direction, and thus the polarization is aligned in the feed direction, for example by using the λ / 2 plate 50 described with reference to Figures 3a and 3b. The first to fourth laser pulses 76, 80, 86, and 90 typically have a full width at half maximum (FWHM) in the range of 15 ns to 20 ns. A typical duration of the time interval Δt is 10 ns to 20 ns.

[0077] The four laser beams 74, 78, 84, 88 having four laser pulses 76, 80, 86, 90 are then shaped into linear laser pulses having a short axis and a long axis, for example using the beam shaping device 32 described with reference to Figures 3a and 3b, which are then imaged as an illumination line 36 onto an image plane of the semiconductor material, for example using the imaging device 34 described with reference to Figures 3a and 3b.

[0078] In Fig. 6, the disclosed method is illustrated by way of example on the basis of a configuration with two laser sources, where the first laser source 66 corresponds to the first laser source in Fig. 5, and the second laser source 70 corresponds to the third laser source in Fig. 5. The trigger signal 92 of the second laser source 70 is electronically delayed by a time interval Δt with respect to the trigger signal 82 of the first laser source 66, so that the second laser pulse 86 propagates delayed by a time interval Δt with respect to the first laser pulse 76. Furthermore, the first laser pulse 76 is linearly polarized in the minor axis direction of the subsequently shaped linear laser pulse or irradiation line, for example by means of the λ / 2 plate 80 described with reference to Figs. 3a and 3b, and the second laser pulse 86 is linearly polarized perpendicularly to the minor axis direction, where the minor axis direction corresponds to the feed direction in which the subsequently shaped irradiation line 36 moves relative to the semiconductor material 12 to be processed. 5, the two laser beams 74, 84 with the two laser pulses 76, 86 are then shaped into linear laser pulses having a short axis and a long axis, for example using the beam shaping device 32 described with reference to Figures 3a and 3b, which are then imaged as an illumination line 36 onto an image plane of the semiconductor material 12, for example using the imaging device 34 described with reference to Figures 3a and 3b.

[0079] The linear shape of the thus shaped illumination line 36 has been explained with reference to Figures 2a to 2c. The resultant time-intensity curve of the thus shaped illumination line 36, i.e. the intensity as a function of time of the superimposed and mutually time-delayed pulses, is explained with reference to Figure 7. In Figure 7, a resultant time-intensity curve 96 is shown as an example of the method using two laser beams as disclosed in Figure 6. In Figure 7, the intensity of the pulses of the individual laser beams is further shown as a function of time, alongside the resultant intensity of both laser beams 74, 84.

[0080] In FIG. 7, the intensity curve labeled with reference number 98 corresponds to the intensity curve of the first laser pulse 76 of the first laser beam 74, the intensity curve labeled with reference number 100 corresponds to the intensity curve of the second laser pulse 86 of the second laser beam 84, and the intensity curve labeled with reference number 96 corresponds to the combined temporal intensity of the first and second pulses 76 and 86. The first and second laser pulses 76 and 86 each have a full width at half maximum (FWHM) of 15 ns to 20 ns. As can further be seen in FIG. 7, the second laser pulse 86 is time delayed with respect to the first laser pulse 76 by a duration of about 10 ns to 20 ns. In FIG. 7, this duration is about 20 ns. This results in a pulse curve with a first maximum M1 and a second maximum M2 in the combined temporal intensity curve 96. This pulse curve has a pulse duration 102 that is wider than the single pulse duration, resulting in a total pulse length of 40 ns to 50 ns. The total pulse length 102 again corresponds to the temporal half-width, i.e. the full width at half maximum with respect to the first maximum ("Full Width at Half Maximum of First Maximum"), i.e. the pulse width at the time when the intensity of the first pulse has half of its maximum value M1.

[0081] As also shown in FIG. 7, the maximum intensity M1 of the first laser pulse 76 is greater than the maximum intensity M2 of the second time delayed laser pulse 86. In particular, the intensity of the first laser pulse 76 is adjusted relative to the intensity of the second laser pulse 86 such that the ratio of the first maximum M1 to the second maximum M2 of the composite time intensity curve 96, i.e. the ratio M1 / M2, is between 1 / 1.2 and 1 / 0.7, i.e. between 0.8 and 1.4. This can be achieved in embodiments where each laser beam is provided by a separate laser source by tuning the intensities of the individual laser beams to each other. In the configuration where the two laser beams are provided by splitting a single laser beam, as shown diagrammatically in FIG. 4, the relative intensities can be achieved by varying the s and p components of the light beam by correspondingly rotating the λ / 2 plate 54 in front of the thin film polarizer 56.

[0082] As already described in detail above, in accordance with the present disclosure, the first laser pulse 76 is linearly polarized in the short axis, or transmission, direction, and the second laser pulse 86 is linearly polarized in the long axis.

[0083] One of the findings underlying the present disclosure is that the linear polarization of the first and second pulses 76 and 86 described above has a positive effect on the homogeneity of the semiconductor material layer 12 treated with the laser line. It was found that if, for example, the first pulse in time is polarized in the feed direction and the pulse delayed in time is polarized in the longitudinal direction, a very homogeneous layer thickness of 50 nm to 60 nm of crystalline silicon with a regular grain structure results. In this case, the ratio of the first maximum M1 to the second maximum M2 of the composite time-intensity curve was about 1:1, i.e. 0.8 to 1.4.

[0084] In contrast, in the case of the opposite polarization, ie the first pulse was linearly polarized in the long axis direction and the second delayed pulse was linearly polarized in the short axis direction, this positive effect could not be observed.

[0085] This finding is clarified based on the following experimental data.

[0086] The semiconductor material to be processed was a 50 nm thin layer of amorphous silicon coated on a glass substrate as support. The optical setup used was a line beam configuration with four solid-state UV lasers emitting light with a wavelength of 343 nm. The four lasers were driven at a pulse repetition rate of 10 kHz. The pulse length, i.e. the temporal half-width, of the emitted pulses was between 15 ns and 20 ns. The energy of the laser pulses was up to 20 mJ. The energy density of the substrate, i.e. the silicon layer, was 220 mJ / cm. 2 Similar to the method of FIG. 5, the multiple first and second laser pulses of the first and second lasers of the four lasers were time-synchronized by the synchronized trigger signals of the laser sources so that the first laser pulse was emitted simultaneously with the second laser pulse, respectively. The multiple third and fourth laser pulses of the third and fourth lasers were time-delayed by 10 ns to 20 ns with respect to the multiple first and second laser pulses, respectively. The intensities of the four laser beams were adjusted so that the ratio (M1 / M2) of the first maximum and the second maximum in the composite time-intensity curve was 1 / 1.

[0087] The laser pulses of the four laser beams were shaped into laser lines by configurations corresponding to Fig. 3a and Fig. 3b and imaged as irradiation lines on the amorphous silicon. The irradiation lines were moved in the direction of the short axis of the irradiation line with a feed rate of 20 mm / s relative to the semiconductor layer. The length of the irradiation line in the long axis direction was 90 mm with a homogeneity of 1.5% (2σ). The length of the irradiation line in the short axis direction was 67 μm with a homogeneity of 3% (2σ). The total pulse of the composite time-intensity curve was 45 ns long ("full width at half maximum about the first maximum").

[0088] In a first experiment (experiment a)), the pulses 76, 80 of the first laser beam 74 and the second laser beam 78 were linearly polarized in the short axis direction, and the delayed pulses 86, 90 of the third laser beam 84 and the fourth laser beam 88 were linearly polarized in the long axis direction.

[0089] In a second experiment (experiment b)), the pulses of the first and second laser beams were linearly polarized along the long axis, and the delayed pulses of the third and fourth laser beams 84 and 86 were linearly polarized along the short axis.

[0090] Figure 8a shows an image of the silicon surface taken with a scanning electron microscope after laser exposure according to experiment a), and Figure 8b shows an image of the silicon surface taken with a scanning electron microscope after laser exposure according to experiment b). In both images, the feed direction was along the x-axis (the short axis of the irradiation line), i.e. vertically in Figures 8a and 8b.

[0091] Figure 8a shows that a regular grain structure occurs perpendicular to the feed direction, i.e. in the y or long axis direction. In particular, it can be seen that the grains are arranged in vertically extending rows with approximately equal spacing of about 1.5 μm, corresponding to the wavelength of the UV laser. In other words, the grain structure shows stripes extending in the feed direction, which are equally spaced, resulting in homogeneity along the long axis. Thus, the grain size along the long axis (y direction) has a large homogeneity. Along the short axis (x direction) there is less homogeneity compared to the long axis.

[0092] In contrast, Figure 8b shows that there is no significant homogeneity along either the short axis (x-direction) or the long axis (y-direction). The grain structure appears more disordered compared to the grain structure in Figure 8a, both in terms of grain orientation and size.

[0093] As already mentioned above, the laser crystallization process is based on the partial melting of the a-Si layer and subsequent solidification into a crystalline structure, starting from unmelted solid silicon on a glass substrate. This melting and solidification takes place on a time scale of 10-100 ns, and the subsequent cooling of the film at room temperature usually takes several hundred microseconds. A pulse repetition frequency of 10 kHz corresponds to a period of 100 microseconds. The pulse repetition frequency, the feed rate and the pulse width of the irradiation line in the feed direction are dimensioned in such a way that a point of the semiconductor material is exposed several times during the exposure process, i.e. by several successive pulses, and the period corresponding to the pulse repetition frequency is shorter than the time required to cool the film to room temperature, so that the semiconductor material is repeatedly irradiated with UV light during the crystallization process. In addition to this, the exposure by the pulses is relatively long due to the relatively long time course of the laser pulses, which is several tens of nanoseconds. This multiple exposure promotes the formation of a uniform grain structure.

[0094] As mentioned at the beginning, it is furthermore known that the polarization of the laser beam, especially in combination with the above-mentioned multiple exposure, can have a positive effect on the regular polycrystalline silicon grain structure. This is due to surface interference effects ("Laser-induced periodic surface structures", LIPPS) which give rise to a tailored intensity distribution. It thus turns out that if the light is linearly polarized in the long axis direction, regular structures are formed along the long axis, and if the light is linearly polarized in the short axis direction (feed direction), a corresponding effect can be observed in the feed direction.

[0095] The LIPPS effect has been discussed in several publications, for example in the references (1)-(4) listed below. In these publications, it is assumed that the tailored intensity distribution is generated by the interaction of the incident light beam with light beams polarized on and towards the surface, and the periodic distribution of the pulse energy density caused thereby. The periodic pulse energy density distribution has the form of so-called "ripples", which are spaced apart by an order of magnitude λ / (1±sinΘ) for a light laser beam with wavelength λ and angle of incidence Θ. Thus, for normal incidence (Θ=0°), a separation of the order of magnitude of the wavelength λ occurs. In this case, the "ripples" extend in a direction perpendicular to the electric field vector, i.e. in the direction of the polarization of the light beam or light pulse, and are periodic in the direction of the electric field vector. The pulse energy density is either a minimum or a maximum along the "ripples". The periodic pulse energy density induces a spatially periodic temperature distribution on the exposed semiconductor material layer, which is similar to the periodic pulse energy density distribution. In addition, the thermal diffusion in the semiconductor material layer must be taken into account in the periodic temperature distribution. It was also confirmed that the periodic distribution of the pulse energy density changes depending on the thickness of the semiconductor material layer due to multiple reflections inside the semiconductor material layer.

[0096] Thus, collectively, these observations confirm that to obtain longitudinal periodicity or regularity, the electric field vector must be longitudinal, and therefore the light or light pulses must be linearly polarized in the longitudinal direction.

[0097] Therefore, it has been assumed in the past that in order to be able to generate a particle structure that is regularly oriented in the longitudinal direction, each pulse must contain a longitudinal polarization component.

[0098] It has now become apparent from the present disclosure that it is particularly advantageous in terms of homogeneity of the polycrystalline silicon grain structure if the first pulse in time 76 or the first pulse in time 76, 80 is polarized in the short axis direction, i.e. in the feed direction, and the second delayed pulse 86 or the second delayed pulse 86, 90 is polarized in the long axis direction.

[0099] One possible explanation for the promotion of regular grain structures when the second pulse is polarized in the long axis is that light in this long axis creates laser wavelength interferometric modulation (LIPPS), thereby encouraging structured grain formation in this direction. If the second pulse is linearly polarized in the feed direction, no interferometric modulation is formed in the long axis.

[0100] An attempt to explain why light at the first maximum, and therefore the polarization of the first pulse along the short axis (in the feed direction), is favorable for grain structuring would be that in this time section of irradiation the film is heated more uniformly in the long axis than in the presence of a long-axis polarization component, since there is no interference modulation and it is only the second pulse component that structures and creates a partial liquid phase, promoting grain structuring.

[0101] Furthermore, if the polarization of the first pulse is adjusted to the sending direction, i.e., the short axis direction, and the polarization of the second delayed pulse is adjusted to the long axis direction according to experiment a), the size of the energy density process window is 20-25 mJ / cm 2 (The energy density process window is 210-230-235mJ / cm 2 ), in comparison to an exposure in which the first and second delayed pulses have the same polarization distribution in both directions, the energy density process window in this case is approximately 10 mJ / cm 2 (The energy density process window is 215-225mJ / cm 2 ) was observed.

[0102] Finally, it was confirmed that, for example, the "optical delay" shown in Figure 4 can provide advantageous results compared to the "electronic delay" shown in Figures 5 and 6. In particular, it was confirmed that the non-uniformity of the crystal structure in the direction of motion ("shot unevenness") can be reduced in the "optical delay" compared to the "electronic delay."

[0103] As already mentioned above, the superposition of two (or more) time-synchronized laser beams from two (or more) different laser sources may result in fluctuations in their intensity distribution with respect to each other due to the presence of time jitter in the laser sources.

[0104] For example, if one looks at the composite time-intensity curve 96 shown in Fig. 7 for two laser pulses 76, 86 and forms it for four laser pulses, the intensity curve 98 of the first laser pulse 76 is composed of the composite intensity curve 98 of the two first laser pulses 76, 80, and the composite intensity curve 100 of the second laser pulse 86 is composed of the composite intensity curve 100 of the two second laser pulses 86, 90. In this case, it is possible to minimize the variation between the composite intensity curves 98 or 100 by a pulsed laser source with the smallest possible time jitter (for example in the ns range). Since the first laser pulses 76, 80 and the second laser pulses 86, 90 originate from different laser sources in both devices with optical and electronic delays, there is no different situation with electronic and optical delays in terms of "smearing" due to the presence of this time jitter.

[0105] The composite time-intensity curve 96 of Fig. 7 is obtained by superposition of the (combined) intensity curves 98, 100. As shown in Fig. 7, the pulse widths and delays are selected such that a leading pulse 98 or a leading composite pulse 98 is superimposed with a trailing pulse 100 or a trailing composite pulse 100. The resulting first maximum M1 is hardly influenced by the delayed pulse 100 or the delayed composite pulse 100 (because the delayed pulse 100 or the delayed composite pulse 100 has no or little contribution to the maximum M1 of the composite intensity curve 96), whereas the position and occurrence of the second maximum M2 is clearly influenced by the delayed pulse 100 or the delayed composite pulse.

[0106] This existing and changing time jitter is imaged in the changing position and occurrence of the maximum M2 between the first pulse 98 and the second time delayed pulse 100, and in particular in the changing position and occurrence of the maximum M2 between the composite intensity curves 96. The crystallization process can respond to these intensity changes by deviations in the grain structure, e.g., grain size.

[0107] In this case, by using beam splitting in the optical delay as opposed to electronic delay and providing an optical delay section (e.g. in combination with a pulsed laser source with the lowest possible time jitter), it can be achieved that the leading pulse 98 and the delayed pulse 100 have approximately the same time jitter, thereby minimizing the fluctuations of the intensity curve when the pulses 98, 100 or composite pulses 98, 100 are superimposed and a homogeneous conversion of the amorphous semiconductor layer into a polycrystalline semiconductor layer is achieved over a large area.

[0108] To achieve a typical time delay of 20 ns of the second pulse 100 with respect to the first pulse 98, an additional optical path of about 6 m is required. This can be achieved, for example, by using a spherical telescope with a long focal length. It is arranged in the delay section (for example in the beam path of the second partial beam 60 in FIG. 4) and has conjugate planes at the entrance and exit of the delay section. In this way, the laser beam (partial beam 60 in FIG. 4) can be imaged in a controlled manner over a long distance. For example, for a 1:1 imaging, a telescope can be provided in which the focal length of the lens is the same as the focal length of the eyepiece. Furthermore, the delay section can be designed in such a way that it is variable (its length) by means of a deflection element, for example a movably arranged mirror. This allows the pulse length to be adjusted to be optimal for the crystallization process.

[0109] Instead of obtaining time-delayed laser beams or laser pulses by beam splitting and subsequent optical delay, the present disclosure envisages using a UV laser source to generate two UV laser beams from an IR source by generating the third harmonic (343 nm) from an IR laser beam (1030 nm). Such a UV laser source uses the unconverted IR pulse energy (usually 50%) in a first SHG ("second harmonic generation") / THG ("third harmonic generation") crystal to generate a second UV laser beam in a second SHG / THG crystal. Both of these UV beams do not have time jitter that changes with respect to each other. One of the two UV laser beams can then be optically delayed as described above, for example using a long focal length spherical telescope. Therefore, no beam splitting is required in this solution.

[0110] Furthermore, it was found that the formation of periodic structures in the long axis is more successful when the angular distribution of the laser beam in the long axis in the delayed pulse 100 is smaller. This is because, as explained above for the LIPPS effect, the periodic pulse energy density distribution is dependent on the interference occurring along the surface (λ / (1±sinθ), where θ is the angle of incidence with respect to the surface normal). The smaller the variation, i.e. the sharper the angle, the smaller the angular distribution of the incident light. The beam in the delayed pulse is linearly polarized in the long axis direction. Therefore, the delay is preferably adjusted for the laser beam imaged close to the optical axis. Conversely, this means that the beam imaged away from the optical axis must be the beam of the preceding pulse, which has mainly a polarization perpendicular to the long axis.

[0111] References (1)~(4) (1) P. van der Wilt, "Excimer laser annealing: microstructural evolution and new characterization techniques", SID2014, Digest, p.194 (2) S. Hotta, H. Kawataka, K. Nishioka, "Surface modification of amorphous Si thin film crystallized by linearly polarized Nd:YAG pulsed laser beam", Journal of Applied Physics, 102, 013501 (2007) (3) H.M. van Driel, J.E. Sipe, and J.F. Young, "Laser-induced periodic surface structures in solids: a universal phenomenon," Physical Review Letters, 49, 1955-1958 (1982); and S.E. Clark and D.C. Emmony, "Ultraviolet-laser-induced periodic surface structures," Physical Review B, 40, 2031-2041 (1989). (4) JF Young, JS Preston, HM van Driel, JE Sipe, "Laser-induced periodic surface structures, second experiments with Ge, Si, Al, and brass", Physical Review B, 27, 1155-1172 (1983) [Example 1] A method for processing a layer of semiconductor material, in particular for producing a crystalline semiconductor layer, comprising the steps of: providing a first laser beam (74) having a first laser pulse (76) and a second laser beam (84) having a second laser pulse (86); shaping the first laser pulse (76) and the second laser pulse (86) into a linear laser pulse having a minor axis and a major axis using a beam shaping device; and imaging the thus shaped linear laser pulse onto the semiconductor material layer (12) using an imaging device (34) as an illumination line (36) having a short axis and a long axis; Furthermore, the method comprises: adjusting a polarization direction of the first laser pulse (76) to a minor axis direction of the illumination line (36); adjusting the polarization direction of the second laser pulse (86) to the major axis of the illumination line (36); and delaying the second laser pulse (86) by a predetermined time interval Δt relative to the first laser pulse (76), the time interval Δt being selected such that the illumination line (36) imaged on the semiconductor material layer (12) has a composite time-intensity curve (96) in the form of a pulse having a first maximum (M1) and a second maximum (M2). [Example 2] 2. The method of claim 1, comprising moving the illumination line (36) in a feed direction relative to the layer of semiconductor material (12), and the first laser pulse (76) is linearly polarized in the feed direction. [Example 3] The method according to embodiment 1 or 2, wherein the relative intensities of the first laser pulse (76) and the second laser pulse (86) are such that the ratio of the first maximum (M1) to the second maximum (M2) in the composite time-intensity curve (96) is in the range of 0.8 to 1.4, in particular in the range of 0.9 to 1.2, in particular 1.0. [Example 4] 4. The method according to any one of claims 1 to 3, wherein the composite time-intensity curve (96) of the irradiation line (36) has a time half-width (102) of 40 to 50 ns based on the first maximum of the composite time-intensity curve. [Example 5] 5. The method of any one of claims 1 to 4, comprising providing a first laser (66) and a second laser (70), the first laser (66) and the second laser (70) designed to emit the first laser beam (74) and the second laser beam (84), respectively, and controlled such that the second laser pulse (86) is emitted with a time interval Δt delayed relative to the first laser pulse (76). [Example 6] providing a first laser configured to provide a laser beam (52) having pulses; 5. The method of any one of claims 1 to 4, comprising splitting the laser beam (52) into a first laser beam portion (58) and a second laser beam portion (60), wherein the first laser beam portion (58) forms the first laser beam (74) with the first laser pulse (76) and the second laser beam portion (60) forms the second laser beam (84) with the second laser pulse (86). [Example 7] 7. The method of claim 6, wherein an optical path length from a position of beam splitting of the second laser beam portion (60) to the semiconductor material layer (12) is greater than an optical path length from a position of beam splitting of the first laser beam portion (58) to the semiconductor material layer (12). [Example 8] 8. The method of any one of claims 1 to 7, wherein the first laser pulse (76) is one laser pulse of a plurality of first laser pulses of the first laser beam (74) and the second laser pulse (86) is one laser pulse of a plurality of second laser pulses of the second laser beam (84), each of the plurality of laser pulses of the pulsed second laser beam (84) being time delayed by a respective predetermined time interval Δt with respect to the other plurality of laser pulses of the pulsed first laser beam (74). [Example 9] The method according to example 8 with reference to any one of examples 2 to 7, wherein the feed rate, the pulse repetition frequency of the first laser beam (74) and the second laser beam (84) and the geometric half-width (36) of the irradiation line (36) in the minor axis direction are selected such that a portion of the semiconductor material layer (12) is exposed several times by the irradiation line (36). [Example 10] providing a third laser beam (78) having a third laser pulse (80) and a fourth laser beam (88) having a fourth laser pulse (90); shaping the first laser pulse (76), the second laser pulse (86), the third laser pulse (80), and the fourth laser pulse (90) into a linear laser pulse having a minor axis and a major axis using a beam shaping device; and imaging the thus shaped linear laser pulse onto the semiconductor material layer (12) using an imaging device (36) as an illumination line (36) having a short axis and a long axis; moreover, adjusting the polarization direction of the third laser pulse (80) to the minor axis direction of the illumination line (36); adjusting a polarization direction of the fourth laser pulse (90) to a major axis direction of the illumination line (36); and delaying the fourth laser pulse (90) by a predetermined time interval Δt relative to the third laser pulse (80), the time interval Δt being selected such that the illumination line (26) imaged on the semiconductor material layer (12) has a composite time-intensity curve (96) in the form of a pulse having a first maximum (M1) and a second maximum (M2). [Example 11] An optical system (30) for processing a layer of semiconductor material (12), in particular for producing a crystalline semiconductor layer, comprising: a beam shaping device (32) configured to shape the first laser pulse (76) of the first laser beam (74, 38) and the second laser pulse (86) of the second laser beam (84, 40) into a linear laser pulse having a minor axis and a major axis; an imaging device (34) configured to image the thus shaped linear laser pulse onto the layer of semiconductor material (12) as an illumination line (36) having a minor axis and a major axis; Furthermore, the optical system (30) a polarization device (50) configured and arranged to align a polarization direction of the first laser pulse (76) with a minor axis of the illumination line (36) and to align a polarization direction of the second laser pulse (86) with a major axis of the illumination line (36); a delay device (94) configured to delay the second laser pulse (86) by a predetermined time interval Δt relative to the first laser pulse (76), the time interval Δt being selected such that the line of illumination (26) imaged onto the layer of semiconductor material (12) has a composite time-intensity curve (96) in the form of a pulse having a first maximum (M1) and a second maximum (M2). [Example 12] The polarizing device is a first λ / 2 plate (50), which is disposed in the beam path of the first laser beam (74, 38), in particular before the beam shaping device (32), and is oriented with respect to the first laser pulse (76) impinging on the λ / 2 plate (50) such that the first laser pulse (76) is linearly polarized in a minor axis direction after passing through the λ / 2 plate (50); The optical system (30) of Example 11, further comprising a second λ / 2 plate (50) arranged in the beam path of the second laser beam (84, 40), in particular before the beam shaping device (32), and oriented such that, with respect to the second laser pulse (86) impinging on the λ / 2 plate (50), the second laser pulse (86) is linearly polarized in the short axis direction after passing through the λ / 2 plate (50). [Example 13] The optical system (30) of Example 11 or 12, wherein the delay device includes a delay circuit (94) that emits a trigger signal (92) configured to delay the second laser beam (84, 40) having the second laser pulse (86) by a time interval Δt relative to a trigger signal (82) of a first laser (66), and the first laser (66) is configured to emit the first laser beam (74) having the first laser pulse (76). [Example 14] The optical system (30) of Example 11 or 12, wherein the delay device includes a beam bypass path (Δs) that makes the optical path length of the second laser beam (84, 40) to the image plane of the semiconductor material layer (12) longer than the optical path length of the first laser beam (74, 38) to the image plane of the semiconductor material layer (12). [Example 15] the beam shaping device (32) is configured to shape the first laser pulse (76) of the first laser beam (74), the second laser pulse (86) of the second laser beam (84), the third laser pulse (80) of the third laser beam (78), and the fourth laser pulse (90) of the fourth laser beam (88) into linear laser pulses having a minor axis and a major axis; the imaging device (34) is configured to image the thus shaped linear laser pulse onto the layer of semiconductor material (12) as the irradiation line (36) having a minor axis and a major axis; the polarization device (50) is configured and arranged to align a polarization direction of the third laser pulse (80) with a minor axis of the illumination line (36) and to align a polarization direction of the fourth laser pulse (90) with a major axis of the illumination line (36); The optical system (30) of any one of Examples 11 to 14, wherein the delay device (94) is set to delay the fourth laser pulse (80) by a predetermined time interval Δt relative to the third laser pulse (80), the time interval Δt being selected such that the irradiation line (36) imaged on the semiconductor material layer (12) has the composite time-intensity curve (96) in the form of a pulse having the first maximum (M1) and the second maximum (M2). [Example 16] A system for processing said layer of semiconductor material (12), in particular for producing a crystalline semiconductor layer, comprising: A system comprising an optical system (30) according to any one of Examples 11 to 15, the system being designed to move the semiconductor material layer (12) relative to the irradiation line (36) in a feed direction, the feed direction corresponding to a minor axis direction of the irradiation line (36).

Claims

1. 1. A method for processing a layer of semiconductor material, comprising: providing a first laser beam (74) having a first laser pulse (76) and a second laser beam (84) having a second laser pulse (86); shaping the first laser pulse (76) and the second laser pulse (86) into a linear laser pulse having a minor axis and a major axis using a beam shaping device; and imaging the thus shaped linear laser pulse onto the semiconductor material layer (12) using an imaging device (34) as an illumination line (36) having a short axis and a long axis; Furthermore, the method comprises: adjusting a polarization direction of the first laser pulse (76) to a minor axis direction of the illumination line (36) by a first polarizing device (50, 64); adjusting the polarization direction of the second laser pulse (86) to a longitudinal direction of the illumination line (36) by a second polarizing device (50, 64); and delaying the second laser pulse (86) by a predetermined time interval Δt relative to the first laser pulse (76), the time interval Δt being selected such that the irradiation line (36) imaged on the semiconductor material layer (12) has a composite time-intensity curve (96) in the form of a pulse having a first maximum (M1) and a second maximum (M2).

2. 2. The method of claim 1, comprising moving the illumination line (36) in a feed direction relative to the layer of semiconductor material (12), and wherein the first laser pulse (76) is linearly polarized in the feed direction.

3. 3. The method of claim 1, wherein the relative intensities of the first laser pulse (76) and the second laser pulse (86) are such that a ratio of the first maximum (M1) to the second maximum (M2) in the composite time-intensity curve (96) is in the range of 0.8 to 1.

4.

4. 4. The method of claim 1, wherein the resultant time-intensity curve (96) of the illumination line (36) has a time half-width (102) of 40 to 50 ns relative to the first maximum of the resultant time-intensity curve.

5. 5. The method of claim 1, further comprising providing a first laser (66) and a second laser (70), the first laser (66) and the second laser (70) designed to emit the first laser beam (74) and the second laser beam (84), respectively, and controlled such that the second laser pulse (86) is emitted with a time interval Δt delayed relative to the first laser pulse (76).

6. Providing a first laser configured to provide a laser beam (52) having pulses; 5. The method of claim 1, further comprising splitting the laser beam (52) into a first laser beam portion (58) and a second laser beam portion (60), wherein the first laser beam portion (58) forms the first laser beam (74) with the first laser pulse (76) and the second laser beam portion (60) forms the second laser beam (84) with the second laser pulse (86).

7. 7. The method of claim 6, wherein an optical path length from a location of beam splitting of the second laser beam portion (60) to the semiconductor material layer (12) is greater than an optical path length from a location of beam splitting of the first laser beam portion (58) to the semiconductor material layer (12).

8. 8. The method of claim 1, wherein the first laser pulse (76) is one laser pulse of a plurality of first laser pulses of the first laser beam (74) and the second laser pulse (86) is one laser pulse of a plurality of second laser pulses of the second laser beam (84), each of the plurality of laser pulses of the pulsed second laser beam (84) being time delayed by a respective predetermined time interval Δt with respect to the other plurality of laser pulses of the pulsed first laser beam (74).

9. 9. The method according to claim 8 with reference to any one of claims 2 to 7, wherein the feed rate, the pulse repetition frequencies of the first laser beam (74) and the second laser beam (84) and the geometric half-width (36) of the irradiation line (36) in the minor axis direction are selected such that a portion of the semiconductor material layer (12) is exposed several times by the irradiation line (36).

10. providing a third laser beam (78) having a third laser pulse (80) and a fourth laser beam (88) having a fourth laser pulse (90); shaping the first laser pulse (76), the second laser pulse (86), the third laser pulse (80), and the fourth laser pulse (90) into a linear laser pulse having a minor axis and a major axis using a beam shaping device; and imaging the thus shaped linear laser pulse onto the semiconductor material layer (12) using an imaging device (34) as an illumination line (36) having a short axis and a long axis; moreover, adjusting the polarization direction of the third laser pulse (80) to a minor axis direction of the illumination line (36) by a third polarizing device (50, 64); adjusting a polarization direction of the fourth laser pulse (90) to a longitudinal direction of the illumination line (36) by a fourth polarizing device (50, 64); and delaying the fourth laser pulse (90) by a predetermined time interval Δt relative to the third laser pulse (80), the time interval Δt being selected such that the irradiation line (36) imaged on the semiconductor material layer (12) has a composite time-intensity curve (96) in the form of a pulse having a first maximum (M1) and a second maximum (M2).

11. An optical system (30) for processing a layer of semiconductor material (12), comprising: a beam shaping device (32) configured to shape the first laser pulse (76) of the first laser beam (74, 38) and the second laser pulse (86) of the second laser beam (84, 40) into a linear laser pulse having a minor axis and a major axis; an imaging device (34) configured to image the thus shaped linear laser pulse onto the layer of semiconductor material (12) as an illumination line (36) having a minor axis and a major axis; Furthermore, the optical system (30) a polarization device (50, 64) comprising a first polarization device (50, 64) and a second polarization device (50, 64), the first polarization device (50, 64) being set and arranged to align a polarization direction of the first laser pulse (76) with a minor axis direction of the illumination line (36) and the second polarization device (50, 64) being set and arranged to align a polarization direction of the second laser pulse (86) with a major axis direction of the illumination line (36); a delay device (94) configured to delay the second laser pulse (86) by a predetermined time interval Δt relative to the first laser pulse (76), the time interval Δt being selected such that the illumination line (26) imaged onto the semiconductor material layer (12) has a composite time-intensity curve (96) in the form of a pulse having a first maximum (M1) and a second maximum (M2).

12. The first and second polarizing devices are a first λ / 2 plate (50, 64), the first λ / 2 plate (50) being arranged in a beam path of the first laser beam (74, 38), in particular before the beam shaping device (32), and oriented with respect to the first laser pulse (76) impinging on the λ / 2 plate (50) such that the first laser pulse (76) is linearly polarized in a minor axis direction after passing through the λ / 2 plate (50); 12. The optical system (30) of claim 11, further comprising a second λ / 2 plate (50, 64), the second λ / 2 plate (50) being arranged in the beam path of the second laser beam (84, 40), in particular before the beam shaping device (32), and oriented with respect to the second laser pulse (86) impinging on the λ / 2 plate (50) such that the second laser pulse (86) is linearly polarized in a short axis direction after passing through the λ / 2 plate (50).

13. 13. The optical system (30) of claim 11 or 12, wherein the delay device includes a delay circuit (94) configured to emit a trigger signal (92) configured to delay the second laser beam (84, 40) having the second laser pulse (86) by a time interval Δt relative to a trigger signal (82) of a first laser (66), the first laser (66) configured to emit the first laser beam (74) having the first laser pulse (76).

14. 13. The optical system (30) of claim 11 or 12, wherein the delay device includes a beam bypass (Δs) that causes an optical path length of the second laser beam (84, 40) to an image plane of the semiconductor material layer (12) to be greater than an optical path length of the first laser beam (74, 38) to an image plane of the semiconductor material layer (12).

15. the beam shaping device (32) is configured to shape the first laser pulse (76) of the first laser beam (74), the second laser pulse (86) of the second laser beam (84), the third laser pulse (80) of the third laser beam (78), and the fourth laser pulse (90) of the fourth laser beam (88) into linear laser pulses having a minor axis and a major axis; the imaging device (34) is configured to image the thus shaped linear laser pulse onto the semiconductor material layer (12) as the irradiation line (36) having a minor axis and a major axis; the polarization device (50) comprises a third polarization device (50, 64) and a fourth polarization device (50, 64), the third polarization device (50, 64) being set and arranged to align a polarization direction of the third laser pulse (80) with a minor axis direction of the illumination line (36), and the fourth polarization device (50, 64) being set and arranged to align a polarization direction (90) of the fourth laser pulse with a major axis direction of the illumination line (36); 15. The optical system (30) of claim 11, wherein the delay device (94) is set to delay the fourth laser pulse (80) by a predetermined time interval Δt relative to the third laser pulse (80), the time interval Δt being selected such that the irradiation line (36) imaged onto the semiconductor material layer (12) has the composite time-intensity curve (96) in the form of a pulse having the first maximum (M1) and the second maximum (M2).

16. A system for processing the layer of semiconductor material (12), comprising:

16. A system comprising an optical system (30) according to any one of claims 11 to 15, the system being designed to move the semiconductor material layer (12) relative to the irradiation line (36) in a feed direction, the feed direction corresponding to a minor axis direction of the irradiation line (36).

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