WO2020225016A1

WO2020225016A1 - Method and optical system for processing a semiconductor material

Info

Publication number: WO2020225016A1
Application number: PCT/EP2020/061677
Authority: WO
Inventors: Sebastian Geburt; Hans-Juergen Kahlert
Original assignee: Innovavent Gmbh
Priority date: 2019-05-09
Filing date: 2020-04-28
Publication date: 2020-11-12
Also published as: DE102019112141A1; KR20220007139A; JP2022533566A; CN113811981A

Abstract

The invention relates to a method and an optical system for processing a semiconductor material layer, in particular for creating a crystalline semiconductor layer. The method comprises the following steps: - providing a first laser beam (74) having a first laser pulse (76) and a second laser beam (84) having a second laser pulse (86), - transforming the first laser pulse (76) and the second laser pulse (86), by means of a beam forming device, into a laser pulse in line form having a short axis and a long axis, - imaging the laser pulse that is thus formed in line form, by means of an imaging device, as an illumination line having a short axis and a long axis on the semiconductor material layer, wherein the method furthermore comprises the following steps: - adjusting a polarization direction of the first laser pulse (76) in the direction of the short axis of the illumination line (36), - adjusting a polarization direction of the second laser pulse (86) in the direction of the long axis of the illumination line, and - temporally delaying the second laser pulse (86) in respect of the first laser pulse (76) by a predetermined time interval Δt, which is chosen such that the illumination line imaged on the semiconductor material layer has a combined temporal intensity progression (96) in the form of a pulse having a first maximum (M1) and a second maximum (M2).

Description

Method and optical system for processing a semiconductor material Description

The disclosure relates to a method for processing a semiconductor material, in particular for producing a crystalline semiconductor layer, and an optical system for processing a semiconductor material, in particular for producing a crystalline semiconductor layer.

Lasers are used for the crystallization of thin film layers, for example for the production of thin film transistors (in English: Thin Film Transistor, or TFT for short). The semiconductor to be processed is silicon (Si for short), more precisely amorphous silicon (a-Si for short). The thickness of the semiconductor layer is, for example, 50 nm, which is typically located on a substrate, for example a glass substrate, or on another carrier.

The layer is illuminated with the light of the laser, for example a pulsed solid-state laser. The light is formed into a line of illumination and, as imaged on an image plane of Halbleitermateri ^¬ nm with a wavelength of, for example, 343rd The illumination line has a short (narrow) axis and a homogeneous long beam axis. The short or narrow axis has a Gaussian or a flat intensity distribution.

The line of illumination is moved over the semiconductor layer in the direction of the short axis with a feed rate of typically approx. 5 to 50 mm / s. The power density (in the case of continuous wave lasers) or the pulse energy density (in the case of pulsed lasers) of the light beam is set in such a way that, for example, in the case of amorphous silicon, it partially melts and the melted silicon is then in a polycrystalline structure starting from non-melted solid silicon solidified on the glass substrate. Melting and solidifying typically takes place on a time scale of 10 to 100 ns and the subsequent cooling of the film to room temperature typically takes several 100 ps. When irradiating and converting the layer of amorphous silicon into a layer of polycrystalline silicon, a uniform intensity of the illumination line is particularly important, i.e. the homogeneity of the spatial intensity distribution integrated along the short and / or long axis. The more homogeneous or uniform the intensity distribution of the line of illumination, the more homogeneous or uniform the crystal structure of the thin-film layer (for example the grain size of the polycrystalline layer), and the better, for example, the electrical properties of the end product formed from the thin-film layer, for example the thin-film transistor. A homogeneous crystal structure, for example, results in high conductivity due to a high mobility of electrons and positive charge holes.

Inhomogeneities can occur in particular along the long beam axis and perpendicular to it along the short beam axis when the line of illumination is moved over the semiconductor layer in the direction of the short axis. These inhomogeneities are called “mura”. So-called “scan mura” have their origin in inhomogeneities along the beam axis and occur as strip-shaped inhomogeneities running in the scanning direction or in the feed direction. So-called "shot mura" occur perpendicular to this, which can be traced back to fluctuations in intensity and energy density pulse to pulse.

In order to make the "shot mura" as small as possible, the fluctuation in the energy density and in the temporal intensity curve from laser pulse to laser pulse should be as small as possible, for example by using lasers with very good pulse stability and by superimposing several laser beams Laser sources. In order to make the "scan mura" as small as possible, the intensity of the illumination line should be as homogeneous as possible along the long axis. It is also known to reduce "Scan-Mura", by the illumination line during the scan ^¬ nens mm by means of a vibrating about an axis of mirror having frequencies of 10 Hz to 200 Hz to 1 to 2 mm in the direction of the long axis departures and is pushed in order to "smear" any inhomogeneities along the long axis.

Also known are so-called "nitrogen mura", which can be traced back to the fact that during the irradiation the substrate exposure area, i.e. the surface of the material layer to be processed, for example the semiconductor layer, is flushed with nitrogen in order to reduce the oxygen concentration to values between 10 ppm and To reduce 20 ppm and thus prevent oxidation of the material, such as silicon. For this purpose, a laminar nitrogen flow is passed directly over the material layer to be exposed. Inhomogeneities in the laminar flow can lead to inhomogeneities in the crystal structure, the so-called "nitrogen mura".

In order to generate a regular polycrystalline grain structure during crystallization, it is known that a surface interference effect is used, which leads to a modulated intensity distribution during the exposure and, through repeated exposure during the advance, a grain structure with about the size of the wavelength of the light is reinforced. This effect is called "Laser Induced Periodical Pattern Structure"("LIPPS" for short). At a wavelength of 343 nm, for example, grain structures of approximately 0.3 pm to 0.4 pm result. For linearly polarized light, the modulated intensity distribution can only develop in the direction of polarization, i.e. in the direction of the E-field vector. Experi ^{¬-experimental} investigations show that the regular structure along the long beam axis is then formed, when the light is polarized in the long axis corresponding to the effect in the feed direction is observable when the light is polarized in the direction of the feed direction.

The present disclosure provides an improved method for processing a semiconductor material, in particular a method for producing uniformly crystallized semiconductor layers. The present invention further provides an improved apparatus for processing a semiconductor material, in particular an apparatus for producing uniformly crystallized semiconductor layers. In this case, uniformly crystallized semiconductor layers are in particular semiconductor layers with uniform crystal grain sizes.

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

A method for processing a layer of semiconductor material, in particular for producing a crystalline semiconductor layer disclosed, comprising the following Schrit ^¬ te comprising:

Providing a first laser beam with a first laser pulse and a second laser beam with a second laser pulse, Reshaping the first laser pulse and the second laser pulse, using a beam shaping device, into a laser pulse with a short axis and a long axis in line form,

Imaging of the laser pulse formed in this way in line form, using an imaging device, as an illumination line with a short axis and a long axis on the semiconductor material layer,

Setting a polarization direction of the first laser pulse in the direction of the short axis of the illumination line,

Setting a polarization direction of the second laser pulse in the direction of the long axis of the illumination line, and

temporal delay of the second laser pulse with respect to the first laser pulse by a predetermined time interval At, which is selected such that the illumination line imaged on the semiconductor material layer has a combined temporal intensity profile in the form of a pulse with a first and a second maximum.

The sequence of the method steps given above does not reflect the chronological sequence in which the steps are carried out. Typically, for example, the setting of the polarization direction in the beam path takes place where the individual beams, that is to say the first and second laser beams, are separated. The reshaping, homogenization and superposition of the individual beams necessarily take place after the first and second laser beams have been provided. The step of time delay can occur before or after the alignment of the polarization of the first and second laser beams. The chronological order of the specified steps can in principle also be different.

The semiconductor material to be processed can be, for example, a thin layer with a thickness of approximately 50 nm made of amorphous silicon, which is applied to a carrier such as a glass substrate.

The first laser beam and the second laser beam are provided by at least one laser, as will be explained in more detail later. The laser can be, for example, a UV solid-state laser that emits light with a wavelength of 343 nm. Typical half-widths (FWHM, “Full Width at Half Maximum”) of the first and second laser pulses range from 15 ns to 20 ns. The first laser beam and the second laser beam are typically linearly polarized. In a further method step, the polarization of the first and the second pulse is each set in a specific, predefined direction, for example using a polarization device. The first laser pulse is linearly polarized in the direction of the short axis of the illumination line and the second laser pulse is linearly polarized in the direction of the long axis of the illumination line. The pulse emitted by a solid-state laser is typically linearly polarized. If the emitted pulse linearly polarized, the disclosed method is rotated in each case, the polarization direction of the emitted first and second pulse in a predetermined defi ned ^¬ direction according to. This can be carried out by means of a polarization device such as a 1/2 plate with a corresponding orientation with respect to the beam or pulse ^impinging on the 1/2 plate. In particular, the direction of polarization of the first pulse is rotated in the direction of a 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, namely in such a way that the polarization is almost exclusively aligned in the direction of the short axis, for example so that the proportion of linearly polarized light in a direction perpendicular to the short axis is 1% is (Po ^¬ larisa tion ratio 100: 1), or for example so that the polarization ratio of 95: 5. The direction of polarization of the second pulse is rotated in the direction of a long axis, which will also be explained in more detail later and is perpendicular to the direction of the short axis. The polarization of the second pulse is thus aligned in the direction of the long axis, specifically in such a way that the polarization is almost exclusively aligned in the direction of the long axis, for example so that the proportion of linearly polarized light in a direction perpendicular to the long axis 1% (polarization ratio 100: 1), or for example so that the ratio of polarization ^¬ tion 95: 5.

Furthermore, the second pulse is delayed in time with respect to the first pulse by the predetermined time interval At. Typical time delay times are 5 ns to 20 ns. In general, the time interval At is chosen such that when a later-described illumination line is mapped onto the semiconductor material layer, the two pulses are overlaid over time to form a single pulse. The temporal superposition results in a combined temporal intensity profile with a first maximum and a second maximum.

In a further method step, the first and the second pulse are converted into a laser line, that is to say a laser pulse in the form of a line, using a beam shaping device. The beam shaping device can be anamorphic optics form. For example, it can have a lens array homogenizer which is based on the principle that the incident laser beam or beams are split up into many partial beams, which are then spatially superimposed. The laser line has a short axis and a long axis.

The laser line thus formed is imaged as an illumination line on an image plane of the semiconductor material by means of an imaging device. The line of illumination also has a short axis and a long axis, the direction of which is the

Specify the polarization of the first and second pulse. Typically, the directions of the short axis and the long axis of the illumination line coincide with the direction of the short axis and the long axis of the laser pulse in line form

together. The length of the lighting line, that is to say the geometric extension in the direction of the long axis, is typically between 100 mm and 1000 mm, for example 100 mm, 250 mm, 750 mm or 1000 mm. They can be longer if the beam shaping device and / or imaging device entspre ^¬ adapted accordingly. The width of the illumination line, thus the geometric from ^¬ strain in the short axis direction, is given at a Gaussian distribution as a half-value width (FWHM), and is typically pm and 200 pm between 20th In the case of a flat distribution, the width is measured at the point at which the intensity is 90% (“Full Width 90%”) and is also typically between 20 μm and 200 μm.

In a further method step, the illumination line can conductor material layer relative to the ^half-¬ in a feeding direction to be moved. The first pulse is then linearly polarized in the direction of feed, since the feed direction of the Rich ^¬ processing corresponds to the short axis. By sweeping the semiconductor material layer ^¬ with the illumination line, the entire semiconductor material layer or at least a major portion of the semiconductor material layer is exposed and processed it. The carrier with the semiconductor material can be arranged, for example, on a table that can be moved in the feed direction and can thus be moved relative to the illumination line. Typical feed speeds range from 5 mm / s to 50 mm / s.

According to a further aspect, the relative intensity of the first laser pulse and the second laser pulse can be selected so that the ratio of the first maximum to the second maximum in the combined time intensity ^curve in the range from 0.8 to 1.4, in particular is in the range from 0.9 to 1.2, especially 1.0. Since the combined temporal intensity curve results from superimposing the temporal intensity curve of the first and second pulse, the ratio of the first maximum to the second maximum in the combined temporal intensity curve can be set using the intensities of the first and second pulse, taking into account the time interval At will. It has been found that, in combination with the defined polarization direction of the first and second pulse, as described above, particularly homogeneous grain structures have resulted in the (poly) crystalline semiconductor layer formed for the specified range of the ratio of the first maximum to the second maximum .

The combined temporal intensity profile of the illumination line can be a temporal half-width, based on the first maximum of the combined temporal Inten ^¬ sitätsverlaufs having between 40 and 50 ns. The relatively long pulse duration influences the crystallization process over several 10ns and promotes the formation of uniform grain structures.

According to another aspect, a first laser and a second laser are provided ^¬ which are adapted in each case to emit the first laser beam and the second laser beam, and which are controlled so that the second laser pulse by the time interval At is delayed to the first Laser pulse is emitted. The tarry ^¬ tion, for example, by electronically delaying the trigger signal of the second laser with respect to the trigger signal of the first laser can be achieved.

Alternatively, it is provided that a first laser is provided which is adapted to provide a laser beam with a pulse, and that the laser ^¬ ray of the first laser is divided into a first laser beam portion and a second laser beam portion, the first laser beam portion forming the first laser beam of the first laser pulse and the second laser beam portion forms the second laser beam ^¬ with the second laser pulse. In this alternative, a laser is provided which is operated in pulsed mode and whose emitted laser beam is split into the first laser beam and the second laser beam by means of a beam splitter.

In this alternative, the time delay of the second pulse with respect to the first pulse can be achieved in that the optical path length of the second laser beam from the point of beam splitting to the image plane of the semiconductor material than is greater than the optical path length of the first laser beam from the location of the beam splitting to the image plane of the semiconductor material, so that there is a phase shift of the first pulse with respect to the second pulse. In principle it is of course also possible in the variant with two lasers that the time delay of the second pulse with respect to the first pulse is provided by a greater optical path length of the second pulse.

According to a further aspect, the first laser pulse can be a laser pulse of a plurality of first laser pulses of the first laser beam and the second laser pulse can be a laser pulse of a plurality of second laser pulses of the second laser beam, and each of the plurality of laser pulses of the second pulsed laser beam is temporal is delayed with respect to another of the plurality of laser pulses of the first pulsed laser beam by the predetermined time interval At. The laser or lasers are therefore operated in a pulsed manner and emit a large number of laser pulses with a specific pulse repetition rate, for example 10 kHz. The laser pulses of the second laser beam are delayed relative to the first laser pulses so that a first laser pulse and a second laser pulse are always superimposed as an illumination line in the form of a pulse with a first and second maximum on the semiconductor material. In other words, the semiconductor mate rial ^¬ is pulsed at a line of illumination exposed, with the pulse repetition rate of the laser or.

The feed speed, the pulse repetition rate of the first laser beam and the second laser beam and the geometrical half-value width of the illumination line in the short axis direction can be chosen so that a point of the half ^¬ is conductor material repeatedly exposed by a line of illumination. In other words: the semiconductor material moves so slowly relative to the lighting line, and the geometric half-width of the lighting line in the direction of the short axis is so large that after a period of time that corresponds to the pulse repetition rate of the laser beam or a multiple of the pulse repetition rate, the semiconductor material has moved such a small distance that a previously exposed point is exposed again or multiple times. According to yet another aspect of the disclosed method, a third laser beam with a third laser pulse and a fourth laser beam with a fourth laser pulse are provided, the first laser pulse, the second laser pulse, the third laser pulse pulse and the fourth laser pulse, using a beam shaping device, is converted into a laser pulse with a short axis and a long axis in line form, and the laser pulse thus formed in line form, using the imaging device, as the illumination line on an image plane of the semiconductor material layer of the third laser pulse is set in the direction of the short axis of the illumination line, a polarization direction of the fourth laser pulse is set in the direction of the long axis of the illumination line, and the fourth laser pulse is delayed with respect to the third laser pulse by a predetermined time interval At, the predetermined time interval At being selected in this way that the illumination line imaged on the semiconductor material layer has a combined intensity profile over time in the form of a pulse with a first and a second maximum.

According to this aspect of the method, four laser beams are homogeneously ^superimposed and imaged, two laser beams of the four laser beams each having a pulse linearly polarized in the direction of the short axis of the illumination line and being synchronized in time, and the other two of the four laser beams each have a pulse linearly polarized in the direction of the long axis of the illumination line, which is delayed in time with respect to the pulses of the first two laser beams.

According to another aspect of the disclosure, an optical system for processing Bear ^¬ is a layer of semiconductor material, in particular for producing a crystalline semiconductor layer is provided, which comprises:

reshape a beam shaping device which is adapted to a first laser pulse of a first laser beam and a second laser pulse of a second laser beam in a ^¬ a short axis and a long axis having laser pulse in line shape,

an imaging device which is set up to image the laser pulse formed in this way in line form as an illumination line on the semiconductor material layer,

a polarization means which is adapted to receive a ^{polarization-¬} onsrichtung of the first laser pulse in the direction of the short axis of the Beleuchtungsli ^¬ never align and aligning a polarization direction of the second laser pulse in the direction of the long axis of the illumination line, and

a delay device which is set up to add the second laser pulse with respect to the first laser pulse by a predetermined time interval At delay, which is selected such that the illumination line imaged on the semiconductor material layer has a combined intensity profile over time in the form of a pulse with a first and a second maximum. The polarization device is designed and arranged in such a way that the first laser pulse almost exclusively contains polarization components in the direction of the short axis of the illumination line (the polarization ratio is, for example, 1: 100), and the second laser pulse almost exclusively contains polarization components in the direction of the long axis of the illumination line ( the polarization ratio is, for example, 1: 100). The polarization device can have a first

Have 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 then arranged in particular in the beam path of the first laser beam and the second polarization device is in particular arranged in the beam path of the second laser beam.

The beam shaping device can form anamorphic optics. For example, it can have a lens array homogenizer which is based on the principle that the incident laser beam or beams are split up into many partial beams, which are then spatially superimposed. The laser line has a short axis and a long axis.

The laser line thus formed is imaged by an imaging device as a BL LEVEL ^¬ processing line on an image plane of the semiconductor material. The lighting line also has a short axis and a long axis, the direction of which is the

Specify the polarization of the first and second pulse. Typically fall Rich ^¬ obligations of the short axis and the long axis of the illumination line with the direction of the short axis and the long axis of the laser pulse in a line form

together.

The polarization device of the optical system can in particular comprise a first K / 2 plate, which is arranged in the beam path of the first laser beam, in particular in front of the beam shaping device, and is oriented with respect to the first laser pulse impinging on the K / 2 plate that the first laser pulse is linearly polarized after passing through the l / 2 plate in the direction of the short axis, and comprise a second K / 2 plate, which is arranged in the beam path of the second laser beam, in particular in front of the beam shaping device, and so with respect to of the first laser pulse striking the 1/2 plate is oriented so that the second laser pulse is linearly polarized in the direction of the long axis after passing through the 1/2 plate. The first 1/2 plate is thus oriented in such a way that it rotates the polarization direction of the linearly polarized first laser beam with the first laser pulse in the direction of the short axis. The second 1/2 plate is oriented in such a way that it rotates the polarization direction of the linearly polarized second laser beam with the second laser pulse in the direction of the long axis.

According to one variant, the delay device can comprise a delay circuit that generates a trigger signal from a second laser which is configured to emit the second laser beam with the second laser pulse in order to delay the time interval At with respect to a trigger signal from a first laser, the first laser for this purpose is set up to emit the first laser beam with the first laser pulse. The second trigger signal may thus of the first trigger signal ^¬ be delayed with respect to electronically.

According to an alternative variant, the delay means may comprise a beam detour, which causes the optical path length of the second laser beam to an image plane of the semiconductor material layer is greater than the optical path ^¬ length of the first laser beam to the image plane of the semiconductor material layer. According to this variant, therefore, the time delay is caused by a different path ^¬ by the second laser pulse has undergone a larger optical path length up to the overlay as the first pulse.

The first and second laser beams of the optical system can be provided by a first and second laser source or, alternatively, by a laser source, the emitted laser beam of which is split into the first laser beam and the second laser beam by means of a beam splitter.

According to a further aspect, the beam shaping means may be adapted to control the first laser pulse of the first laser beam, the second laser pulse of the two ^¬ th laser beam, a third laser pulse of a third laser beam and a fourth laser pulse having a fourth laser beam into a short axis and a long axis To transform the laser pulse into line form, the imaging device can be set up to transform the laser pulse formed in this way into line form as a lighting The polarization device can be configured to linearly polarize the third laser pulse in the direction of the short axis of the illumination line and linearly polarize the fourth laser pulse in the direction of the long axis of the illumination line, and the delay device can do this be set up to delay the fourth laser pulse with respect to the third laser pulse by a predetermined time interval At, which is selected so that the illumination line imaged on the semiconductor material layer has a combined intensity profile over time in the form of a pulse with a first and a second maximum.

According to this aspect, the optical system thus includes a four jet assembly, are superimposed homogeneous at the four laser beams and imaged as a line of illumination on the semiconductor material layer, wherein the polarizing means is arranged and configured such that two laser beams of the four Laserstrah ^¬ len each in the direction having the short axis of the illumination line linear ^¬ polarized pulse and are synchronized in time, and the other two of the four laser beams each of the illumination line are linearly polarized pulse a in the long axis direction, the time-delayed relative to the pulses of the first two laser beams.

The present disclosure further comprises a system for processing a semiconductor material layer, in particular for producing a crystalline semiconductor layer, which comprises the optical system according to an aspect described above and which is designed to move the semiconductor material layer relative to the illumination line in a feed direction, wherein the The direction of advance corresponds to the direction of the short axis of the illumination line. The semiconductor material layer may, for example, by means of a feed device such as a mobile in the direction of feed table on which the carrier with the semiconductor material layer angeord ^¬ net, are moved relative to the exposure line so that large areas of up to the entire semiconductor layer exposed by the illumination line and processed so that can be. The feed direction corresponds to the direction of the health ^¬ zen axis so that the orientation of the polarization of the first pulse and / or third pulse corresponds to the advancing direction. The disclosure is further explained below with reference to the accompanying drawings. In these show: - Figure 1 is a schematic view of a semiconductor material layer having a relative to the semiconductor material layer moving in the feed direction Be ^¬ leuchtungslinie is exposed to the processing of the semiconductor material layer;.

2a to 2c show the line geometry of the illustrated illumination line;

3a and 3b show a schematic view of an optical system for a system for processing semiconductor layers, by means of which an illumination line can be formed and imaged on a semiconductor material;

4 shows a schematic view of an embodiment of the optical system in which the first and second laser beams are provided by beam splitting of a laser beam;

5 shows a schematic view of an embodiment in which four laser beams are provided by four laser sources, the pulses of two laser beams each being emitted with a time delay to the pulses of the other two laser beams;

6 shows a schematic view of an embodiment in which two laser beams are provided by two laser sources, the pulses of one laser beam being delayed in time with respect to the pulses of the other laser beam;

FIG. 7 schematically shows a combined intensity profile of the illumination line over time, which results from homogeneous superimposition of the individual pulses;

8a shows a scanning electron microscope image of a crystalline silicon layer which was produced in accordance with the disclosed method; and

8b shows a scanning electron microscope image of a crystalline silicon layer which has been processed according to a comparative method.

FIG. 1 shows schematically how, according to the disclosed method, a semiconductor material is irradiated with a laser beam to produce homogeneously crystallized layers. A carrier 10, for example a glass substrate, is coated with a layer 12 of the semiconductor material to be processed. In this one In the present example, the semiconductor material to be processed is amorphous silicon. The thickness of the semiconductor material layer 12 is typically around 50 nm.

A laser beam 14 in the form of a line is imaged on the semiconductor material and moved relative to it in a feed direction X so that the laser line 14 sweeps over at least a partial area of the semiconductor material layer 12 and is illuminated in the process. In the example shown here, the carrier 10 with the semiconductor material layer 12 is displaced in space and thus relative to the laser beam 14, which is stationary. The laser line 14 can be moved relative to the semiconductor material layer 12 in such a way that the entire semiconductor material layer 12 is irradiated by the laser line 14. The laser line 14 is typically moved relative to the semiconductor material layer 12 in such a way that a specific area is irradiated several times by a laser line 14. Typical feed speeds are in the range between 5 mm / s and 50 mm / s.

In the exemplary embodiment shown here, the direction of propagation of the laser beam 14 is perpendicular to the surface of the semiconductor material layer 12, i.e. the laser beam 14 here hits the surface of the semiconductor material layer 12 perpendicularly, with an angle of incidence of 0 °.

The line geometry of the laser beam 14 is shown in FIGS. 2a to 2c. In FIGS. 2a to 2c, the intensity is shown as a function of a specific direction. 2a shows the intensity of the laser line in the direction of the long axis, namely an intensity distribution 16 integrated along the short axis (along the x-axis), the intensity distribution 16 thus integrated along the long axis (along the y-axis) is shown. By convention, the short axis should run parallel to the x-axis and the long axis parallel to the y-axis in the figures. As can be seen in this figure, the distribution 16 is approximately rectangular, that is to say ideally formed homogeneously along the long axis. The length of the illumination line in the y direction can typically be between 100 mm and 1000 mm, for example 100 mm, 250 mm, 750 mm or 1000 mm, or more than 1000 mm. In FIGS. 2b and 2c, the intensity of the laser line is shown in the direction of the short axis, namely an intensity distribution 18, 20 integrated along the long axis (i.e. along the y-axis), the intensity distribution thus integrated Distribution along the short axis (i.e. along the x-axis) is shown. The intensity in FIG. 2b has a Gaussian profile 18. As an alternative to this, the intensity, as shown in FIG. 2c, can have a flat profile 20 (“flat-top”), that is to say an approximately rectangular profile.

Typical widths for the intensity in the x direction are between 20 pm and 200 pm. In the case of the Gaussian curve 18 in FIG. 2b, the width is specified as a full width at half maximum, FWHM, in the case of the flattened curve 20 in FIG. 2c as the width that the curve has at an intensity equal to 90 % of the maximum intensity (FW 90%: Full Width at 90%).

If the lighting line 14 is guided over the semiconductor material layer 12 to be processed, such as a-Si, this causes the semiconductor material layer 12 to briefly melt and solidify as a crystalline layer with improved electrical properties.

FIGS. 3a and 3b show schematically an optical system 30 for a system for processing semiconductor layers, by means of which an illumination line 14, as described with reference to FIGS. 1 and 2, can be formed and mapped onto a semiconductor material.

As will be described in more detail later, the optical system 30 comprises a beam shaping device 32 which is set up to shape a laser beam in such a way that a beam profile of the laser beam has a long axis and a short axis, as well as one in the beam path of the laser beam of the beam shaping device 32 downstream imaging device 34 which is set up to image the laser beam shaped in this way as an illumination line 36. In the example shown here, it is shown that four laser beams strike the beam shaping device 32, namely the first laser beam 38, the second laser beam 40, the third laser beam 42 and the fourth laser beam 44. However, according to the present disclosure, two laser beams can also hit the beam shaping device 32 meet, as will be explained later using an example. In principle, the number of laser beams is neither limited to four nor to two, but any other number is possible and covered by the disclosure.

In the example shown here, the laser radiation is the laser radiation emitted by several UV solid-state lasers with a wavelength of 343 nm. In principle, it is however, it is also possible to use other laser sources, in particular other solid-state laser sources, for example solid-state lasers which emit in the green spectral range. In FIGS. 3a and 3b, as in FIGS. 1 and 2, the short axis is shown parallel to the x-axis and the long axis is shown parallel to the y-axis. The optical axis of the optical system runs parallel to the z-axis.

FIG. 3a shows the imaging characteristics of the optical system 30 in the y direction, that is, along the long axis of the reshaped laser beam and the

Illumination line, and FIG. 3b shows the imaging characteristics of the optical system 30 in the x direction, that is to say along the short axis of the reshaped laser beam and the illumination line. The beam shaping device 32 of the optical system 30 of FIGS. 3a and 3b has anamorphic homogenization optics 46 which homogenize the intensity of the incident laser beams in the direction of the y-axis. The anamorphic homogenization optics 46 comprise, for example, two cylindrical lens arrays arranged parallel to one another. The cylindrical lens arrays divide the incident radiation into individual partial bundles and superimpose them over the entire surface so that the laser radiation is largely homogenized. In the case of several incident laser beams, each laser beam is divided into individual sub-bundles and superimposed in a homogenized manner. Such homogenization optics are described in more detail, for example, in the prior art according to DE 42 20 705 A1, DE 38 29 728 A1 or DE 102 25 674 A1, which is included here in the disclosure.

The beam shaping device 32 of the optical system 30 also has a condenser cylinder lens 48 in the beam path behind the anamorphic homogenization optics 46, which is set up to telecentrically direct the laser beams redistributed and homogenized using the anamorphic homogenization optics 46 onto the illumination line 36 and with respect to the long axis , i.e. in the y-direction, to be superimposed there. The combination of the anamorphic homogenization optics 46 and the condenser cylinder lens 48 thus has the effect that the incident laser radiation is imaged in a homogenized manner on the image plane as an illumination line 36. In the beam path behind the condenser cylinder lens 48, the imaging device 34 is arranged, which is set up to focus the laser beams on the illumination line 36 with respect to the short axis, that is to say in the x direction. In other words: the imaging device 34 images the laser beams as the illumination line 36, with only the short axis of the beam profile being homogenized, but not the homogenized long axis of the beam profile. The Abbil ^¬-making device 34 may for example be a Fokussierzylinderlinsenoptik be.

The combination of the anamorphic homogenization optics 46 and the condenser cylinder lens 48 can be anamorphic optics or be part of such optics. In particular, they can be part of an anamorphic optics, as is described in FIGS. 4 to 6 of the document DE 10 2012 007 601 A1, which is included in the present disclosure, with regard to the anamorphic optics 42.

Accordingly, the beam shaping device 32 can furthermore comprise one or more of the following optical elements:

- a first collimation cylinder lens, provided with reference number 54 in DE 10 2012 007 601 A1, for collimation of laser beams emitted with respect to the x-axis,

- a second collimation cylinder lens, provided with reference numeral 56 in DE 10 2012 007 601 A1, for collimation of laser beams emitted with respect to the y-axis,

- a cylinder lens arranged in the beam path behind the first collimation cylinder lens, provided with reference number 58 in DE 10 2012 007 601 A1, for focusing the light beams with respect to the x-axis on an intermediate image, provided with reference number 60 in DE 10 2012 007 601 A1,

- An intermediate collimation cylinder lens arranged in the beam path behind the first collimation cylinder lens 54, provided with reference numeral 58 'in DE 10 2012 007 601 A1, for collimation of the light beams of the first

Intermediate image, and / or

- A further cylinder lens arranged in the beam path behind the first intermediate image, in particular behind the intermediate collimation cylinder lens, provided with reference numeral 62 in DE 10 2012 007 601 A1, for focusing the light beams with respect to the x-axis on a second intermediate image, in DE 10 2012 007 601 A1 is provided with reference numeral 64. The anamorphic homogenization optics 46 described above can, for example, represent or include the component 68 shown in FIGS. 4 to 6 of DE 10 2012 007 601 A1.

The condenser cylinder lens 48 described above can, for example, represent or include the condenser cylinder lens 74 shown in FIGS. 4 to 6 of DE 10 2012 007 601 A1.

Finally, the above-described imaging device 34 can, for example, represent or include the component 66 shown in FIGS. 4 to 6 of DE 10 2012 007 601 A1.

The optical system further includes a polarizing means 50 for each of the anamorphic optics einfal ^¬ lumbar laser beams 38, 40, 42, 44th The Polari ^¬ sationseinrichtung here is an optical system for adjusting the polarization direction of 50, for example, a l / 2 plate in the beam path of each of the incident laser beams 38, 40, 42, 44. The optics 50 is in the beam path in front of the anamorphic optical system or the anamorphic homogenizing 46 arranged. Each incident laser beam passes through the optics 50, so that the laser beam 38, 40, 42, 44 passing through the optics 50 is linearly polarized in a defined direction. More precisely, the laser beam emitted by the laser is already linearly polarized, for example in the example of the UV solid-state laser shown here, and the orientation of the polarization is rotated in a defined direction by means of the optics 50. The optics 50, for example the 1/2 plates, are oriented with respect to the polarization direction of the incident linearly polarized light so that two of the four laser beams are linearly polarized after passing through the optics 50 in the direction of the long axis, and the remaining two of the four laser beams after passing through the optics 50 in the direction of the short axis, are linearly polarized. The feed direction corresponds to the direction of the short axis, so that 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 arranged in the beam path of the first and second laser beams 38, 40, for example the 1/2 plates, are oriented such that the first and second laser beams 38, 40 each in the direction of the short axis , i.e. in the x-direction, in the feed direction, are polarized, and the optics 50 arranged in the beam path of the third and fourth laser beams 42, 44, for example the 1/2 plates, are each oriented so that the third and fourth laser beam 42 , 44 are each polarized in the direction of the long axis, i.e. in the y-direction. In the present example, the lasers are also operated in a pulsed manner, so that the individual pulses of the respective laser beam have the polarization direction of the respective laser beam described above.

The four laser beams 38, 40, 42, 44 can be the emitted laser radiation from four laser sources, ie each laser beam is assigned to a separate laser source.

Alternatively, the laser beams 38, 40, 42, 44 can have been created by beam splitting a laser beam emitted by a laser source into a first partial beam and a second partial beam by means of a beam splitter. The beam splitter can be designed in such a way that it splits into the first partial beam, the transmitted beam, and in the second partial beam, the transmitted beam, for example of approximately 50% each. For example, polarizing optics can be used for this, for example what is known as a thin-film polarizer. Thin-film polarizers are optical substrates with a special coating that allows light with p-polarization (plane of oscillation of the electrical vector parallel to the plane of the incident beam and the perpendicular on the substrate surface) to pass and light with s-polarization (plane of oscillation of the electrical vector perpendicular ^¬ right to the plane of the incident beam and the perpendicular on the substrate surface) reflected. By means of a 1/2 plate in the beam path in front of the thin-film polarizer, the polarization direction of the laser beam emitted by the laser source can be rotated so that equal proportions of p- and s-polarization occur in the laser beam in front of the thin-film polarizer, in order to achieve a division of in to achieve about 50%. The 1/2 plate in front of the thin-film polarizer can, however, also be rotated in such a way that different proportions of p- and s-polarization occur in the laser beam in front of the thin-film polarizer, in order to achieve a division different from 50%. In principle, the relative intensity of the first partial beam to the second partial beam can be adjusted by means of the orientation of the 1/2 plate.

Such an arrangement is shown schematically in FIG. A linearly polarized laser beam 52 emitted by a laser source strikes a ½ plate 54 which is arranged in the beam path in front of the beam splitter 56, here a thin-film polarizer. The 1/2 plate 54 is oriented so that the relative proportions of s and p polarization in the laser beam after the 1/2 plate corresponds to the desired relative intensity of the two partial beams 58, 60 after the beam splitter 56, as described generally above . The first partial beam 58 can then, for example, be the first laser be beam 38 of the arrangement of Figures 3a and 3b, and the second partial beam 60 can then be, for example, the third laser beam 42 of Figures 3a and 3b. The second partial beam 60 is deflected by means of a reflective element 62 such that it runs parallel to the first partial beam 58. In addition, a 1/2 plate 64 is arranged in the beam path behind the beam splitter 56 in the beam path of the first partial beam and the second partial beam, which the 1/2 plates 50 from Figures 3a and 3b in the beam path of the first laser beam 38 and the third

Laser beam 42 correspond. That is, the downstream ½ plate 64 in the beam path of the first partial beam 58 serves for polarization in the direction of the short axis. The downstream ½ plate 64 in the beam path of the second partial beam 60 then serves for polarization in the direction of the long axis.

The second and fourth laser beams 40, 44 can be provided with a further arrangement corresponding to the arrangement in FIG. 4 with a beam splitter 56 by beam splitting. The downstream 1/2 plates 64 are then again oriented such that they polarize a third and fourth partial beam in the direction of the short axis and in the direction of the long axis. The four laser beams of FIGS. 3a and 3b can therefore alternatively be provided by 2 laser sources, the emitted laser beams of which are then divided into a first and second partial beam 58, 60 or a third and fourth partial beam by beam splitting.

The optical system 30 from FIGS. 3a and 3b can also be used, as already described above, to superimpose a number other than 4 laser beams, for example 2 laser beams. The 2 laser beams can then be provided by 2 laser sources in accordance with the 4 laser beams, or by a laser source, the emitted laser beam of which is then split into a first partial beam and a second partial beam by means of an arrangement corresponding to or the same as in FIG.

The optical system 30 of FIGS. 3a and 3b is also set up in such a way that the pulses of different polarization are each offset in time with respect to one another with a predetermined time interval Δt. When using separate laser sources for each laser beam, this can be achieved by electronically delaying the trigger signals from the laser sources. When laser beams are provided by means of partial beams, the time delay can be achieved by a beam detour. As shown in FIG. 4, the second partial beam 60 covers a path which is longer by the path As than the first partial beam 58. The path As can be chosen so that that a time delay arises by the predetermined time interval At of the second partial beam 60 with respect to the first partial beam 58. The predetermined time interval is preferably 10 ns to 20 ns.

By means of the optical system 30 described above, at least one laser pulse polarized in the direction of the short axis and one laser pulse polarized in the direction of the long axis are superimposed on the illumination line in a homogenized manner, the one in the direction of the long axis polarized pulse is delayed by the time interval At with respect to the pulse polarized in the direction of the short axis. When four laser beams are superimposed, two laser beams are polarized in the direction of the short axis and 2 laser beams are polarized in the direction of the long axis, whereby the laser beams with polarization in the direction of the short axis are synchronized and the laser beams with polarization in the direction of the long axis are synchronized of the laser beams with polarization in the direction of the short axis are delayed in time by the same time interval At. By superimposing two (or more) simultaneously synchronized laser beams from two (or more) different laser sources, possible fluctuations in the energy density from pulse to pulse can be reduced, which lead to different crystallization results when the illumination line is shifted in the direction of the short axis pulse to pulse and can lead to inhomogeneities in the crystal structure along the direction of movement ("shot mura"). It should be noted that the combined intensity distribution of two (or more) such superimposed laser beams (laser pulses) due to existing time jitter, ie a short-term temporal Deviation of the intensity from an ideal value, over which time (from combined intensity distribution to combined intensity distribution) can vary and thus lead to inhomogeneities in the crystal structure. In particular, the inhomogeneities are due to the fact that when combining two (or more) lasers Each laser source has an independent time jitter. It is therefore advantageous to use (pulsed) laser sources with the smallest possible time jitter in the ns range.

The anamorphic homogenizing optics 46 are designed in such a way that each incoming light beam is split up into partial beams and is superimposed in a homogenized manner in the direction of the long axis. That means, every single ray creates a homogeneous line. In the above-described pulsed arrangement with 2 laser beams, both the laser pulse, which is polarized in the direction of the short axis and precedes in time, is superimposed and imaged as a homogeneous line, as well as the laser pulse, which is polarized in the direction of the long axis and is delayed in time with respect to the first pulse. In the arrangement with 4 laser beams, each of the laser pulses that are polarized in the direction of the short axis and are temporally ahead are superimposed and imaged as a homogeneous line, as are each of the laser pulses that are polarized in the direction of the long axis and temporally with respect to the first pulses are delayed.

This is explained again in more detail using the method disclosed.

In FIG. 5, the disclosed method is exemplified using an arrangement with four laser sources, i. 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 each provided to provide a first laser beam 74 with a first laser pulse 76 and a second laser beam 78 with a second laser pulse 80, the first and second laser pulses 76, 80 being synchronized with trigger signals 82 first and second laser sources 66, 68 are emitted simultaneously. The third and fourth laser sources 70, 72 are provided to each provide a third laser beam 84 with a third laser pulse 86 and a fourth laser beam 88 with a fourth laser pulse 90, the trigger signals 92 of the third and fourth laser sources 70, 72 each around the time interval At can be delayed electronically, for example by means of an electronic delay circuit 94, so that the third and fourth laser pulses 86, 90 are each emitted with a time delay by the time interval At with respect to the first pulse 76 and the second pulse 80 and propagate with a time delay. According to the disclosed method, the first laser pulse 76 and the second laser pulse 80 are furthermore linearly polarized in the direction of the feed direction, i.e. in the direction of the x-axis, that is, the polarization is aligned in the feed direction, and the third laser pulse 86 and the fourth laser pulse 90 are linearly polarized in the direction of the long axis, i.e. the polarization is aligned in the direction of the long axis, for example by means of the 1/2 plates 50 described with reference to FIGS. 3a and 3b. The first to fourth laser pulses 76, 80, 86, 90 typically have a time width at half maximum (FWHM) in the range of 15 ns to 20 ns. Typical times for the time interval At are between 10 ns and 20 ns.

The four laser beams 74, 78, 84, 88 with the four laser pulses 76, 80, 86, 90 are then converted into a laser pulse having a short axis and a long axis in line form, for example by means of the method based on FIGS. 3a and 3b The laser pulse thus formed is then imaged as an illumination line 36 on an image plane of the semiconductor material, for example by means of the imaging device 34 described with reference to FIGS. 3a and 3b.

In FIG. 6, the disclosed method is described by way of example using an arrangement with two laser sources. The first laser source 66 corresponds to the first laser source of Figure 5, and the second laser source 70 corresponds to the third laser source of Figure 5. Accordingly, the trigger signal 92 of the second laser source 70 electronically with respect to the trigger signal 82 of the first laser source 66 to the Zeitin ^¬ interval At delayed, so that the second laser pulse 86 propagates delayed by the time interval At with respect to the first laser pulse 76. Furthermore, the first laser pulse 76 is linearly polarized in the direction of the short axis of the laser pulse formed later or the line of illumination in the form of a line, and the second laser pulse 86 is linearly polarized perpendicular thereto in the direction of the long axis, for example by means of the FIGS. 3a and 3b l / 2 plate 80. the described direction of the short axis corresponds to the direction of feed, with the later shaped BL LEVEL ^¬ tung line 36 with respect to the is moved to be processed semiconductor material 12th Analogous to the method in FIG. 5, the two laser beams 74, 84 with the two laser pulses 76, 86 are then converted into a laser pulse with a short axis and a long axis in line form, for example by means of the beam shaping device 32 described with reference to FIGS. 3a and 3b. The laser pulse formed in this way is then imaged as an illumination line 36 on an image plane of the semiconductor material 12, for example by means of the imaging device 34 described with reference to FIGS. 3a and 3b.

The linear geometry of the thus formed illumination line 36 was the basis of the Figu ^¬ ren explained 2a to 2c. The combined intensity profile over time, that is to say the intensity of the superimposed and mutually delayed pulses as a function of time, of the illumination line formed in this way will now be explained with reference to FIG. In FIG. 7, the combined intensity profile 96 over time is shown as an example for the method disclosed in FIG. 6 with two laser beams. FIG. 7 also shows both the combined intensity of the two laser beams 74, 84 and the intensity of the pulses for each individual laser beam as a function of time. In FIG. 7, the intensity profile marked with the reference number 98 corresponds to the intensity profile of the first laser pulse 76 of the first laser beam 74, the intensity profile marked with the reference number 100 corresponds to the intensity profile of the second laser pulse 86 of the second laser beam 84, and the intensity profile marked with the reference number 96 the combined temporal intensity profile of the first and second pulse 76, 86. The first and the second laser pulse 76, 86 each have a time width at half maximum (FWHM) that is between 15 ns and 20 ns. As can also be seen in FIG. 7, the second laser pulse 86 is delayed in time with respect to the first laser pulse 76, specifically by a period of approximately 10 ns to 20 ns. In FIG. 7 the duration is approximately 20 ns. This results in a pulse profile in the combined time intensity profile 96 which has a first maximum M1 and a second maximum M2 and which has a widened pulse duration 102 in relation to the individual pulse duration, namely a total pulse length of 40 ns to 50 ns. The total pulse length 102 again corresponds to a temporal half-width, specifically the temporal half-width based on the first maximum ("Full Width at Half Maximum of First Maximum"), ie the width of the pulse at the point where the intensity of the first pulse is half of the maximum value Ml.

As is also shown in Figure 7, the maximum intensity Ml of the first laser pulse 76 is greater than the maximum intensity M2 of the second, time-delayed laser pulse 86.Specifically, the intensity of the first laser pulse 76 is set relative to the intensity of the second laser pulse 86 so that that the ratio of the first maximum Ml to the second maximum M2 of the combined intensity curve 96 over time, the ratio M1 / M2, is between 1 / 1.2 and 1 / 0.7, that is between 0.8 and 1.4. In the embodiment in which each laser beam is provided by a separate laser source, this can be achieved in that the intensities of the individual laser beams are matched to one another. In the arrangement shown schematically in FIG. 4, in which the two laser beams are provided by splitting a laser beam, the relative intensity can be adjusted by changing the s and p components of the light beam in front of the thin-film polarizer 56 by rotating the 1/2 plate accordingly 54 can be achieved.

As already described in detail above, according to the present disclosure, the first laser pulse 76 is linearly polarized in the direction of the short axis, that is to say in the direction of advance, and the second laser pulse 86 is linearly polarized in the direction of the long axis. One finding on which the present disclosure is based is that the above-described linear polarization of the first and second pulses 76, 86 has a positive effect on the homogeneity of the semiconductor material layer 12 processed with the laser line. It has been found that with a polarization of the temporally first pulse in the direction of the advance and the temporally delayed pulse in the direction of the long axis, very homogeneous 50 nm to 60 nm thick layers of crystalline silicon with a regular grain structure result. The ratio of the first maximum M1 to the second maximum M2 of the combined intensity profile over time was approximately 1: 1, that is to say between 0.8 and 1.4.

In contrast, with an interchanged polarization, i.e. with a linear polarization of the first pulse in the direction of the long axis and the second, delayed pulse in the direction of the short axis, this positive effect could not be observed.

This finding should be illustrated by the following experimental data:

The semiconductor material to be processed was a 50 nm thin layer of amorphous silicon on a glass substrate as a carrier. The optical arrangement used was a line beam arrangement with four UV solid-state lasers which emit light with a wavelength of 343 nm. The four lasers were operated with a pulse repetition rate of 10 kHz. The pulse length of the emitted pulses, i.e. the time half-value width, was between 15 ns and 20 ns. The energy of a laser pulse was up to 20 mJ. The energy density on the substrate, that is to say on the silicon layer, was 220 mJ / cm ² . Analogous to the method of Figure 5, the plurality of first and second laser pulses from a first and second laser of the four lasers were synchronized by synchronized trigger signals from the laser sources, so that a first laser pulse was emitted at the same time as a second laser pulse. The plurality of third and fourth laser pulses of the third and fourth laser was delayed by 10 ns to 20 ns in each case with respect to the plurality of first and second laser pulses. The intensities of the four laser beams were set so that a ratio of 1/1 resulted for the ratio of the first maximum to the second maximum in the combined intensity curve over time (M1 / M2). The laser pulses of the four laser beams were transformed into a laser line with an arrangement corresponding to FIGS. 3a and 3b and imaged as an illumination line on the amorphous silicon. The line of illumination was moved with respect to the semiconductor layer at a feed rate of 20 mm / s, specifically in the direction of the short axis of the line of illumination. The length of the line of illumination in the direction of the long axis was 90 mm with a homogeneity of 1.5% (2o). The length of the illumination line in the direction of the short axis was 67 μm with a homogeneity of 3% (2o). The total pulse length of the combined intensity curve over time was 45 ns (“Full Width at Half Maximum of First Maximum”).

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

In a 2nd experiment (experiment b)) the pulses of the first and second laser beams were linearly polarized in the direction of the long axis, and the pulses of the delayed third and fourth laser beams were polarized in the direction of the short axis.

FIG. 8a shows an image of the silicon surface recorded with a scanning electron microscope after the laser exposure according to experiment a), and FIG. 8b shows an image of the silicon surface recorded with a scanning electron microscope after the laser exposure according to experiment b). In both images, the feed direction was in the direction of the x-axis (short axis of the line of illumination), that is to say in the vertical direction with regard to FIGS. 8a and 8b.

FIG. 8a shows that a regular grain structure results perpendicular to the feed direction, that is to say in the y direction, in the direction of the long axis. In particular, it can be seen that the grains are arranged in vertically running rows which are approximately equally spaced, with a spacing of approximately 0.35 μm, corresponding to the wavelength of the UV laser. In other words: the grain structure shows a stripe pattern running in the direction of advance, the stripes being equally spaced and thus producing a homogeneity in the direction of the long axis. The grain size in the direction of the long axis (y-direction) therefore exhibits great homogeneity. In the direction of the short axis (x direction), there is less homogeneity compared to the long axis. In contrast, FIG. 8b shows that there is no pronounced homogeneity, neither in the direction of the short axis (x direction) nor in the direction of the long axis (y direction). The grain structure appears disordered in comparison to the grain structure of FIG. 8a, both in terms of the orientation and in terms of the size of the grains.

As already described above, the laser crystallization process is based on the partial melting of the a-Si layer and the subsequent solidification starting from non-melted solid silicon on the glass substrate in a crystalline structure. Melting and solidifying takes place on a time scale from 10 ns to 100 ns and the subsequent cooling of the film to room temperature over several 100 ps. The pulse repetition rate of 10 kHz corresponds to a period of 100 ps. Since the pulse repetition rate, the feed rate and the pulse width of the illumination 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. from several consecutive pulses, and the period corresponding to the pulse repetition rate is smaller than the time that the film needs to cool down to room temperature, the semiconductor material is repeatedly irradiated with UV light during the crystallization process. In addition, the relatively long exposure comes through a pulse due to the relatively long laser pulse temporal profile over meh ^¬ eral 10 ns. This multiple exposure promotes the formation of uniform grain structures.

As mentioned in the introduction, it is also known that the polarization of the laser light, in particular in combination with the multiple exposure described above, can have a positive effect on the regular polycrystalline silicon grain structure. This is due to a surface interference effect ("Laser Induced Periodical Pattern Structure", LIPSS), which results in a modulated intensity distribution. It has been shown that a regular structure is formed along the long axis when the light is directed in the direction of the long axis is linearly polarized, accordingly the effect in the feed direction can be observed if the light is linearly polarized in the direction of the short axis (feed direction).

The LIPPS effect has been discussed in numerous publications, for example in the references (1) to (4) given below. It is assumed that the modulated intensity distribution is caused by an interaction of the incident light beam with the light beams diffracted on the surface and in the direction of the surface a resulting periodic distribution of the pulse energy density arises. The periodic pulse energy distribution has the form of so-called "ripples", which are spaced apart by an amount of l / (1 ± sinO) for laser light with a wavelength l and an angle of incidence Q. For perpendicular incidence of light (0 = 0 °) this results a spacing in the order of magnitude of the wavelength 1. The "ripples" extend in a direction perpendicular to the E-field vector, that is, to the polarization direction of the light beam or light pulse and have a periodicity in the direction of the E-field vector. Along the "ripples" the pulse energy density is at a minimum or a maximum. The periodic pulse energy density causes the spatially periodic temperature distribution on the exposed semiconductor material layer, wherein the perio ^¬ sized temperature distribution is similar to the periodic pulse energy density distribution. In periodic temperature distribution also has yet to the thermal diffusion in the It has also been found that the periodic distribution of the pulse energy density varies with the thickness of the semiconductor material layer due to multiple reflections in the interior of the semiconductor material layer.

In summary, it can be stated that, according to these observations, in order to obtain a periodicity or regularity in the direction of the long axis, the E-field vector must be in the direction of the long axis, i.e. the light or the light pulse in the direction of the long axis must be linearly polarized.

Accordingly, it has previously been assumed that each pulse at least contain an amount of polarization in the direction of the long axis to be able must generate to a control ^¬ uniform grain structure in the direction of the long axis.

According to the present disclosure, it has now been found that, with regard to the homogeneity of the polycrystalline silicon grain structure, it is particularly advantageous if the temporal first pulse 76 or the temporal first pulses 76, 80 is polarized in the direction of the short axis, i.e. in the feed direction, and the second delayed pulse 86 or the second delayed pulses 86, 90 is polarized in the direction of the long axis.

A possible explanation for the fact that regular grain structures are promoted when the second pulse is polarized in the long axis could be that this light in the long axis generates the interference modulation (LIPPS) with the laser wavelength and thus supports the structured grain formation in this direction . Is the second pulse in the direction of linearly polarized-, no interference ^¬ modulation forms in the long axis.

An attempt to explain why the polarization of the light in the first maximum, i.e. the first pulse, in the direction of the short axis (feed direction) is advantageous for the grain structure, could be that in this period of irradiation the film in the long axis is heated more evenly than as if there were a polarization component in the direction of the long axis, since the interference modulation does not occur there, and only the second pulse component generates the partially liquid phase in a structured manner and promotes the grain structure.

It was also observed that when setting the polarization of the first pulse in the feed direction, i.e. in the direction of the short axis, and of the second delayed pulse in the direction of the long axis according to experiment a), the size of the energy density process window is 20 to 25 itύ / cm ² increased (for an energy density process window of 210 to 230 or 235 mJ / cm ² ), compared to an exposure in which the first pulse and the second, delayed pulse have the same polarization distribution in the two directions. In this case, only about 10 mJ / cm ^{2 were} observed for the size of the energy density process window (for an energy density process window of 215 to 225 mJ / cm ² ).

Finally, it was found that with an "optical delay", as shown for example in FIG. 4, advantageous results compared to an "electronic delay", as shown for example in FIGS. 5 and 6 can be achieved. In particular, it was found that the inhomogeneities in the crystal structure in the direction of movement (“shot mura”) can be reduced with an “optical delay” compared to an “electronic delay”.

As has already been explained above, when two (or more) simultaneously synchronized laser beams from two (or more) different laser sources are superimposed, fluctuations in the intensity distribution due to existing time jitter between the laser sources can result.

If, for example, a combined intensity curve 96 over time, as shown in FIG. 7 for two laser pulses 76, 86, is considered and formed for four laser pulses, the intensity curve 98 of the first laser pulse 76 is made up of the combined The intensity profile 98 of two first laser pulses 76, 80 combined, and the intensity profile 100 of the second laser pulse 86 from the combined intensity profile 100 of two second laser pulses 86, 90. It is possible to use pulsed laser sources with the smallest possible time jitter (for example in ns Range) to minimize variations from the combined intensity profile 98 to the combined intensity ^profile 98 or from the combined intensity profile 100 to the combined intensity profile 100. Since the two first laser pulses 76, 80 and the two second laser pulses 86, 90 originate from different laser sources both in a device with optical delay and in a device with electronic delay, there is no such "smearing" due to time jitter different situation for electronic and optical delay.

The combined temporal intensity profile 96 of FIG. 7 is then obtained by superimposing the (combined) intensity profiles 98, 100. As shown in FIG. 7, the pulse widths and delays are selected so that the leading pulse 98 or the leading one Pulse combination 98 is superimposed with the following pulse 100 or the following pulse combination 100. This creates a first maximum Ml which is practically not influenced by the delayed pulse 100 or the delayed pulse combination 100 (since the delayed pulse 100 or the delayed pulse combination 100 makes little or no contribution to the maximum Ml of the combined intensity loss 96) , and a second maximum M2, the position and characteristics of which are clearly influenced by the delayed pulse 100 or the delayed pulse combination 100.

An existing, varying time jitter between the first pulse 98 and the second, time-delayed pulse 100 is thus mapped in a varying position and form of the maximum M2, in particular in the position and form of the maximum M2 from the combined intensity profile 96 to the combined intensity profile 96 The crystallization process can be based on these changes in intensity in the combined course of time with grain structure deviations, eg Deviations in the grain size react.

With the optical delay by beam splitting and the provision of an optical delay path, unlike the electronic delay, it can be achieved (for example in combination with pulsed laser sources with the smallest possible time jitter) that the leading pulse 98 and the delayed pulse 100 have a practically identical time jitter. As a result, when the pulses 98, 100 or the pulse combinations 98, 100 are superimposed, a fluctuation in the intensity profile is minimized and a homogeneous conversion of the amorphous semiconductor layer into a polycrystalline semiconductor layer is achieved over large areas.

To achieve a typical time delay of 20 ns for a second pulse 100 compared to a first pulse 98, an additional optical path of approx.

6 m necessary. This additional optical path can be achieved, for example, with the aid of a long focal length spherical telescope, which is located in the deceleration path (for example in the beam path of the second partial beam 60 of FIG. 4).

is arranged and has conjugate levels at the input and output of the delay line. In this way, the laser beam (partial beam 60 of FIG. 4) can be imaged in a controlled manner over a large distance. For a 1: 1 image, for example, a telescope can be provided in which the focal length of the lens is identical to the focal length of the eyepiece. The delay path can also be designed in such a way that it (its length) can be changed, for example with the aid of displaceably arranged deflection elements such as mirrors. In this way, a pulse length that is optimal for the crystallization process can be set. Instead of obtaining the time-delayed laser beam or laser pulse by beam splitting and subsequent optical delay, the disclosure also provides for a UV laser source to be used in which two UV laser beams are generated from an IR source by generating the third harmonic wavelength (343 nm) is obtained from an IR laser beam (1030 nm). Such a UV laser source uses the unconverted IR pulse energy (typically 50%) in the first SHG ("second harmonic generation") / THG ("third harmonic generation") crystal in a second SHG / THG crystal to generate the second UV laser beam to create. These two UV rays do not have any varying time jitter to one another. One of the two UV laser beams can then be optically delayed as described above, for example with the aid of a long-focal spherical telescope. With this solution, no beam splitting is necessary.

It has also been shown that the formation of the periodic structure in the long axis is more successful the smaller the angular distribution of the laser light in the long axis in the delayed pulse 100. It is assumed that this is due to the dependence of the periodic pulse energy density distribution explained above with regard to the LIPPS effect due to the resulting interference along the surface. is to be returned (l / (1 ± sine), where Q is the angle of incidence to the surface normal), which varies less, i.e. is sharper, the smaller the angular distribution of the incident light. The rays in the delayed pulse are linearly polarized in the direction of the long axis. For this reason, the delay is preferably set for laser beams that are imaged close to the optical axis. Conversely, this means that the rays imaged at a distance from the optical axis should mainly be rays of the leading pulse with polarization perpendicular to the long axis.

References (1) to (4):

(1) P. van der Wilt, "Excimer-LASER Annealing: Microstructure Evolution and a Novel Characterization Technique, SID 2014 Digest pl94

(2) S. Horita, H. Kaki, K. Nishioka, "Surface modification of an amorphous Si thin film crystallized by a linear polarized Nd: YAG pulse 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

Structure on Solids: A Universal Phenomenon ", Phys. Rev. Lett. 49, 1955-1958

(1982) and S.E. Clark and D.C. Emmony, "Ultraviolet laser-induced periodic surface structures", Phys. Rev. B 40, 2031-2041 (1989)

(4) J. F. Young, J. S. Preston, H. M. van Driel, and J. E. Sipe, "Laser-induced periodic surface structure. II. Experiments on Ge, Si, AI, and brass", Phys. Rev. B 27, 1155-1172 (1983).

Claims

1. A method for processing a semiconductor material layer, in particular for producing a crystalline semiconductor layer, with the following steps:

Providing a first laser beam (74) with a first laser pulse (76) and a second laser beam (84) with a second laser pulse (86),

Reshaping the first laser pulse (76) and the second laser pulse (86) by means of a beam shaping device (32) into a laser pulse with a short axis and a long axis in line form,

Imaging of the laser pulse thus formed in line form, using an imaging device (34), as an illumination line (36) with a short axis and a long axis on the semiconductor material layer (12),

the method further comprising the steps of

Setting a polarization direction of the first laser pulse (76) in the direction of the short axis of the illumination line (36),

Setting a polarization direction of the second laser pulse (86) in the direction of the long axis of the illumination line (36), and

time delay of the second laser pulse (86) with respect to the first laser pulse (76) by a predetermined time interval At, which is selected such that the illumination line (36) imaged on the semiconductor material layer (12) has a combined temporal intensity profile (96) in the form of a Has pulse with a first maximum (Ml) and a second maximum (M2).

2. The method of claim 1, comprising

Moving the line of illumination (36) relative to the semiconductor material layer (12) in a feed direction, the first laser pulse (76) being linearly polarized in the feed direction.

3. The method according to claim 1 or 2, wherein the relative intensity of the first laser pulse (76) and the second laser pulse (86) is selected so that the ratio of the first maximum (Ml) to the second maximum (M2) in the combined The time intensity curve (96) is in the range from 0.8 to 1.4, in particular in the range from 0.9 to 1.2, in particular 1.0.

4. The method according to any one of the preceding claims, wherein the combined temporal intensity curve (96) of the illumination line (36) has a temporal half-width (102), based on the first maximum of the combined temporal intensity curve, between 40 and 50 ns.

5. The method according to any one of the preceding claims, comprising

Provision of a first laser (66) and a second laser (70), which are designed to emit the first laser beam (74) and the second laser beam (84), and which are controlled in such a way that the second laser pulse (86) is emitted delayed by the time interval At to the first laser pulse (76).

6. The method according to any one of claims 1 to 4, comprising

Providing a first laser which is designed to provide a laser beam (52) with a pulse,

Splitting the laser beam (52) into a first laser beam component (58) and a second laser beam component (60), the first laser beam component (58) forming the first laser beam (74) with the first laser pulse (76) and the second laser beam component (60) forms the second laser beam (84) with the second laser pulse (86).

7. The method of claim 6, wherein

the optical path length of the second laser beam component (60) from a point of beam splitting to the semiconductor material layer (12) is greater than the optical path length of the first laser beam component (58) from the point of beam splitting to the semiconductor material layer (12).

8. The method according to any one of the preceding claims,

wherein the first laser pulse (76) is one of a plurality of first laser pulses of the first laser beam (74) and the second laser pulse (86) is one of a plurality of second laser pulses of the second laser beam (84), and each of the plurality of laser pulses of the second pulsed laser beam (84) each time delayed with respect to another of the plurality of laser pulses of the first pulsed laser beam (74) by the predetermined time interval At.

9. The method according to claim 8, based on one of claims 2 to 7,

wherein the feed rate, a pulse repetition rate of the first laser beam (74) and the second laser beam (84) and a geometric half width of the illumination line (36) in the direction of the short axis are selected so that a point of the semiconductor material layer (12) is exposed several times by an illumination line (36).

10. The method according to any one of the preceding claims, comprising

- Providing a third laser beam (78) with a third laser pulse

(80) and a fourth laser beam (88) with a fourth laser pulse (90),

Transforming the first laser pulse (76), the second laser pulse (86), the third laser pulse (80) and the fourth laser pulse (90) using the beam shaping device (32) into a laser pulse with a short axis and a long axis in Uniform shape,

Imaging of the laser pulse thus formed in line form, using the imaging device (36), as the illumination line (36) with a short axis and a long axis on the semiconductor material layer (12),

the method further comprising the steps of

- Setting a polarization direction of the third laser pulse (80) in

Direction of the short axis of the lighting line (36),

Setting a polarization direction of the fourth laser pulse (90) in the direction of the long axis of the illumination line (36), and

time delay of the fourth laser pulse (90) with respect to the third laser pulse (80) by a predetermined time interval At, which is selected so that the illumination line (26) imaged on the semiconductor material layer (12) has a combined temporal intensity profile (96) in the form of a Has pulse with a first maximum (Ml) and a second maximum (M2). 11. Optical system (30) for processing a semiconductor material layer (12), in particular for producing a crystalline semiconductor layer, comprising:

a beam shaping device (32) which is set up to convert a first laser pulse (76) of a first laser beam (74, 38) and a second laser pulse (86) of a second laser beam (84, 40) into one having a short axis and a long axis To transform the laser pulse into line form,

an imaging device (34) which is configured to image the laser pulse thus formed in line form as an illumination line (36) with a short axis and a long axis on the semiconductor material layer (12), the optical system (30) further comprising

- A polarization device (50) which is set up and arranged to align a polarization direction of the first laser pulse (76) in the direction of the short axis of the illumination line (36) and a polarization direction of the align the second laser pulse (86) in the direction of the long axis of the illumination line (36), and

a delay device (94) which is set up to delay the second laser pulse (86) with respect to the first laser pulse (76) by a predetermined time interval At which is selected such that the illumination line (36) imaged on the semiconductor material layer (12) a combined temporal

Intensity curve (96) in the form of a pulse with a first maximum (Ml) and a second maximum (M2).

12. Optical system (30) according to claim 11,

wherein the polarization device

comprises a first 1/2 plate (50), which is arranged in the beam path of the first laser beam (74, 38), in particular in front of the beam shaping device (32), and so with respect to the first one impinging on the 1/2 plate (50)

Laser pulse (76) is oriented so that the first laser pulse (76) is iinear-polarized after passing through the ½ plate (50) in the direction of the short axis, and

comprises a second 1/2 plate (50) which is arranged in the beam path of the second laser beam (84, 40), in particular in front of the beam shaping device (32), and so with respect to the second laser pulse impinging on the 1/2 plate (50) (86) is oriented so that the second laser pulse (86) is linearly polarized in the direction of the long axis after passing through the 1/2 plate (50).

13. Optical system (30) according to claim 11 or 12,

wherein the delay device comprises a delay circuit (94) which receives a trigger signal (92) of a second laser (70) which is set up to emit the second laser beam (84, 40) with the second laser pulse (86) in order to set the time interval At with respect to a trigger signal (82) of a first laser (66), wherein the first laser (66) is set up to emit the first laser beam (74) with the first laser pulse (76).

14. Optical system (30) according to claim 11 or 12,

wherein the delay device comprises a beam detour (As) which causes the optical path length of the second laser beam (84, 40) up to the image plane of the semiconductor material layer (12) to be greater than the optical path length of the first laser beam (74, 38) up to the image plane of the semiconductor material layer (12).

15. Optical system (30) according to one of claims 11 to 14,

wherein the beam shaping device (32) is set up to generate the first laser pulse (76) of the first laser beam (74), the second laser pulse (86) of the second laser beam (84), a third laser pulse (80) of a third laser beam (78) and a to convert the fourth laser pulse (90) of a fourth laser beam (88) into a laser pulse having a short axis and a long axis in line form,

wherein the imaging device (34) is set up to image the laser pulse thus formed in line form as the illumination line (36) with a short axis and a long axis on the semiconductor material layer (12),

wherein the polarization device (50) is set up and arranged to align a polarization direction of the third laser pulse (80) in the direction of the short axis of the illumination line (36) and a polarization direction of the fourth laser pulse (90) in the direction of the long axis of the illumination line (36) align, and where

the delay device (94) is set up to delay the fourth laser pulse (90) with respect to the third laser pulse (80) by a predetermined time interval At, which is selected such that the illumination line (36) imaged on the semiconductor material layer (12) combined one time intensity curve (96) in the form of a pulse with a first maximum (Ml) and a second maximum (M2).

16. System for processing a semiconductor material layer (12), in particular for producing a crystalline semiconductor layer, comprising

an optical system (30) according to any one of claims 11 to 15,

wherein the system is designed to move the semiconductor material layer (12) relative to the illumination line (36) in a feed direction, the feed direction corresponding to the direction of the short axis of the illumination line (36).