KR20220007139A - MEHTOD AND OPTICAL SYSTEM FOR PROCESSING A SEMICONDUCTOR MATERIAL - Google Patents

Abstract

FIELD OF THE INVENTION The present invention relates to a method and an optical system for processing a layer of semiconductor material, in particular for producing a crystalline semiconductor layer. The method comprises the steps of: 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 into a laser pulse having a short axis and a long axis in the form of a line by using the laser pulse in the form of a line by an imaging device 34 Imaging as an illumination line (36) having a short axis and a long axis on the semiconductor material layer (12) using adjusting the short axis direction, - adjusting the polarization direction of the second laser pulse 86 in the long axis direction of the illumination line 36 , - the illumination line 36 imaged in the semiconductor material layer 12 having a first the first laser pulse 76 for a predetermined time interval Δt selected to have a time-dependent joint strength profile 96 in the form of a pulse having a maximum value M1 and a second maximum value M2. time delaying the two laser pulses (86).

Description

MEHTOD AND OPTICAL SYSTEM FOR PROCESSING A SEMICONDUCTOR MATERIAL

The present invention 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 example, for crystallization of thin film layers for the manufacture of thin film transistors (Thin Film Transistors, abbreviations: TFT). Silicon (abbreviation: Si), more precisely amorphous silicon (abbreviation: a-Si), is used as the semiconductor to be processed. The thickness of the semiconductor layer is, for example, 50 nm, and the semiconductor layer is typically placed on a substrate, for example a glass substrate or other carrier.

The layer is illuminated with light of a laser, such as a pulsed solid-state laser. In this case, for example, light with a wavelength of 343 nm is formed into an illumination line and imaged on the image plane of the semiconductor material. The illumination line has a short axis (narrow axis) and a uniform long beam axis. The uniaxial or narrow axis has a Gaussian or flat intensity distribution.

The illumination line is moved in the uniaxial direction over the semiconductor layer, typically at a traveling speed of about 5-50 mm/s. The power density (in the case of a continuous wave laser) or pulse energy density (in the case of a pulsed laser) of the light beam is, for example, in the case of amorphous silicon, this silicon is partially melted, and then the molten silicon is transferred to unmelted solid silicon on a glass substrate. It is tuned to solidify into a polycrystalline structure based on it. Melting and solidification generally occur on a time scale of 10 to 100 ns, and then cooling the film to room temperature typically takes several 100 μs.

The uniform intensity of the illumination line, ie the uniformity of the integrated spatial intensity distribution along the minor and/or major axes, is particularly important when the amorphous silicon layer is irradiated and converted into a polycrystalline silicon layer. The more uniform the intensity distribution of the illumination line, the more uniform the crystal structure of the thin film layer (eg, the grain size of the polycrystalline layer), and the electrical properties of, for example, the final product formed of the thin film layer, for example, the thin film transistor. it gets better A uniform crystal structure produces a high conductivity, for example due to the high mobility of electrons and positive holes.

Non-uniformities can occur along the minor axis of the beam in particular along the major axis of the beam and perpendicular thereto as the illumination line moves over the semiconductor layer in the minor axis direction. This non-uniformity is called "Mura". The so-called "Scan Mura" occurs non-uniformly along the beam axis and appears as a strip-like non-uniformity extending in the scan or travel direction. Vertically to this, a so-called "Shot Mura" occurs due to fluctuations in intensity and energy density from pulse to pulse.

In order to make the “shot mura” as small as possible, the energy density per laser pulse and the variation of the intensity profile with time are possible, for example, by the use of a laser with very good pulse stability and by superimposing laser beams of multiple laser sources. should be small To make the "scan mura" as small as possible, the intensity of the light lines should be as uniform as possible along the long axis. To “clear” non-uniformities along the long axis, a “scan mura” is created by using a mirror that vibrates about its axis of rotation at a frequency of 10 Hz to 200 Hz, whereby the illumination line is reciprocated by 1 mm to 2 mm in the direction of the long axis during scanning. It is also known to reduce

In addition, in order to prevent oxidation of materials such as silicon by reducing the oxygen concentration to a value of 10 ppm to 20 ppm, during irradiation, the exposed surface of the substrate, i.e. the surface of the material layer to be treated, for example the surface of the semiconductor layer, is not flushed with nitrogen. The resulting so-called "nitrogen mura" is known. For this purpose, a laminar flow of nitrogen is passed directly over the layer of material to be exposed. In this case, the non-uniformity of the laminar flow can lead to the non-uniformity of the crystal structure, so-called "nitrogen mura".

It is known to use the surface interference effect to create a regular polycrystalline grain structure during the crystallization process, whereby a modulated intensity distribution occurs during exposure such that several exposures during the course of the course enhance the grain structure with a wavelength size of approximately the wavelength of light. have. This effect is referred to as "Laser Induced Periodical Pattern Structure (abbreviated as "LIPPS"). For example, at a wavelength of 343 nm, a particle structure of about 0.3 μm to 0.4 μm is produced. In the case of linear polarization, a modulated intensity distribution can be formed only in the polarization direction, ie in the E-field vector direction. Experimental investigations have shown that when light is polarized in the long axis, a regular structure is formed along the beam long axis, and thus, when the light is polarized in the traveling direction, the above effect can be observed in the traveling direction.

The present invention provides an improved method for processing a semiconductor material, in particular a method for producing a uniformly crystallized semiconductor layer. The present invention also provides an improved apparatus for processing semiconductor materials, in particular apparatus for producing uniformly crystallized semiconductor layers. In this case, the uniformly crystallized semiconductor layer is particularly a semiconductor layer having a uniform crystal grain size.

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, is disclosed, the method comprising the steps of:

- 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 into a laser pulse having a short axis and a long axis in the form of a line using a beam forming apparatus;

- Imaging the laser pulse in the form of a line thus formed as an illumination 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 illumination line;

- adjusting the polarization direction of the second laser pulse in the direction of the long axis of the illumination line, and

- a second for a first laser pulse 76 by a predetermined time interval Δt selected such that the illumination line imaged in the semiconductor material layer has a coupling strength profile over time in the form of a pulse having first and second maxima. Time delaying the laser pulse.

The order of the method steps does not indicate the chronological order in which the steps are performed. In general, the adjustment of the direction of polarization, for example in the beam path, takes place where the individual beams, ie the first and second laser beams, are separated. Reshaping, equalization and superposition of the individual beams necessarily occur after the first and second laser beams have been provided. The time delay step may be performed before or after alignment of the polarizations of the first and second laser beams. The time order of the steps may in principle be different.

The semiconductor material to be treated may be a thin layer made of amorphous silicon, for example about 50 nm thick, said layer being 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 described in more detail later. The laser may be, for example, a UV solid-state laser emitting light having a wavelength of 343 nm. A typical temporal full width at half maximum (FWHM) of the first and second laser pulses is 15 ns to 20 ns. The first laser beam and the second laser beam are typically linearly polarized.

In another method step, the polarizations of the first and second pulses are each adjusted to a specific predefined direction, for example using a polarizing device. The first laser pulse is linearly polarized in the short axis direction of the illumination line, and the second laser pulse is linearly polarized in the long axis direction of the illumination line. Pulses emitted from solid state lasers are generally linearly polarized. When the emitted pulses are linearly polarized, according to the present method, the polarization directions of the emitted first and second pulses are respectively rotated in predetermined, defined directions. This can be done by a polarizing device, such as a λ/2 plate, which has a corresponding direction for a beam or pulse impinging on the λ/2 plate. In particular, the polarization direction of the first pulse is rotated in the uniaxial direction as will be explained in more detail later. Thus the polarization of the first pulse is aligned in the uniaxial direction, in particular the polarized light is aligned almost exclusively in the uniaxial direction, for example a ratio of linearly polarized light in a direction perpendicular to the uniaxial direction is 1% (polarization ratio 100:1) , or, for example, arranged so that the polarization ratio is 95:5. The polarization direction of the second pulse is rotated in the long axis direction, as will be explained in more detail later, and is perpendicular to the direction of the minor axis. Thus, the polarization of the second pulse is aligned in the long-axis direction, in particular the polarization is almost exclusively aligned in the long-axis direction, for example, if the proportion of linearly polarized light in the direction perpendicular to the long axis is 1% (polarization ratio 100:1) , or, for example, arranged so that the polarization ratio is 95:5.

In addition, the second pulse is time-delayed with respect to the first pulse by a predetermined time interval Δt. Typical time delays are 5 ns to 20 ns. In general, the time interval Δt is selected such that two pulses overlap in time to form a single pulse when imaging an illumination line, which will be described later, on the semiconductor material layer. The temporal overlap produces a bond strength profile over time having a first maximum and a second maximum.

In a further method step, the first and second pulses are reformed into laser lines, ie laser pulses in the form of lines, by means of a beam shaping device. The beam shaping apparatus may form anamorphic optics. This may include, for example, a lens array homogenizer based on the principle that the incident laser beam(s) is split into several partial beams and then spatially overlapped. The laser line has a short axis and a long axis.

The laser line thus formed is imaged as an illumination line on the image plane of the semiconductor material by the imaging device. The illumination line also has a minor axis and a major axis, the directions of which define the polarizations of the first and second pulses. In general, the direction of the short axis and the long axis of the illumination line coincides with the direction of the short axis and the long axis of the laser pulse in the form of a line. The length of the illumination line, ie the geometrical extension in the major axis direction, is generally between 100 mm and 1000 mm, for example 100 mm, 250 mm, 750 mm or 1000 mm. This may be longer if the beam shaping apparatus and/or imaging apparatus are properly designed. The width of the illumination line, that is, the geometrical extension in the minor axis direction, is expressed as the full width at half maximum (FWHM) when the Gaussian distribution is 20 μm to 200 μm. In a flat distribution, the width is measured at the point where the strength is 90% (“90% full width”) and is typically between 20 μm and 200 μm.

In a further method step, the illumination line may be moved in a traveling direction relative to the semiconductor material layer. In this case, the first pulse is linearly polarized in the traveling direction because the traveling direction coincides with the minor axis direction. By sweeping the layer of semiconductor material with an illumination line, the entire layer of semiconductor material or at least a larger area of the layer of semiconductor material can be exposed and processed. The carrier with the semiconductor material can for example be arranged on a table movable in the direction of travel and thus can be moved relative to the illumination line. Typical travel speed ranges from 5 mm/s to 50 mm/s.

According to a further aspect, the relative intensities of the first laser pulse and the second laser pulse are such that the ratio of the first maximum to the second maximum in the combined intensity profile over time 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 time-dependent bonding strength profile is a result of superimposing the strength profiles of the first and second pulses over time, by the strength of the first and second pulses, considering the time interval Δt, the time-dependent bonding The ratio of the first maximum to the second maximum in the intensity profile may be adjusted. As described above, for a given range of the ratio of the first maximum to the second maximum, in combination with the defined polarization directions of the first and second pulses, a particularly uniform grain structure within the formed (poly)crystalline semiconductor layer. was found to be formed.

The bond strength profile over time of the illumination line may have a temporal full width at half maximum of 40 ns to 50 ns for a first maximum value of the bond strength profile over time. The relatively long pulse duration affects the crystallization process over several 10 ns and promotes the formation of a uniform grain structure.

According to a further aspect, the first laser and the second laser are designed to emit the first laser beam and the second laser beam, respectively, such that the second laser pulse is emitted with a delay relative to the first laser pulse by a time interval Δt. Controlled. The delay can be achieved, for example, by electronically delaying the trigger signal of the second laser relative to the trigger signal of the first laser.

As an alternative, there is provided a first laser designed to provide a pulse to the laser beam, the laser beam of the first laser being split into a first laser beam component and a second laser beam component, the first laser beam component being the first laser pulse to form a first laser beam having a , and the second laser beam component forms a second laser beam having a second laser pulse. In this alternative, a laser operated in a pulsed mode is provided, the emitted laser beam of which is split into a first laser beam and a 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 is such that the optical path length of the second laser beam from the beam splitting position to the image plane of the semiconductor material is such that the optical path length of the second laser beam from the beam splitting position to the image plane of the semiconductor material is the first laser longer than the optical path length of the beam, which can be achieved by generating a phase shift of the first pulse relative to the second pulse.

It is 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 the longer optical path length of the second pulse.

According to a further aspect, the first laser pulse may be one of a plurality of first laser pulses of a first laser beam, wherein the second laser pulse is a laser of one of a plurality of second laser pulses of a second laser beam and each of the plurality of laser pulses of the second pulsed laser beam is time delayed relative to the other of the plurality of laser pulses of the first pulsed laser beam by a predetermined time interval Δt. The laser(s) are pulsed and emit multiple laser pulses at a specific pulse repetition rate, for example 10 kHz. The laser pulse of the second laser beam is time delayed relative to the first laser pulse so that the first laser pulse and the second laser pulse are always superimposed to be imaged as an illumination line in the form of a pulse having first and second maxima in the semiconductor material. . In other words, the semiconductor material is pulsed exposed by an illumination line at the pulse repetition rate of the laser(s).

The traveling speed, the pulse repetition rate of the first and second laser beams, and the geometric full width at half maximum of the illumination line in the uniaxial direction can be selected such that a point of the semiconductor material is exposed by the illumination line several times. In other words, the semiconductor material moves very slowly with respect to the illumination line and the geometric full width at half maximum of the illumination line in the uniaxial direction is large, so that after a duration corresponding to the pulse repetition rate of the laser beam or a multiple of the pulse repetition rate, the semiconductor material moves to the point where it was previously exposed. It has moved a small distance enough to be exposed once again or several times.

According to another aspect of the disclosed method, there is provided a third laser beam having a third laser pulse and a fourth laser beam having a fourth laser pulse, the first laser pulse, the second laser pulse, the third laser pulse and the second 4 The laser pulse is reshaped by a beam shaping device into a laser pulse having a short axis and a long axis in the form of a line, and the laser pulse in the form of a line, thus formed, is imaged as an illumination line on the image plane of the semiconductor material layer by the imaging device do. Further, the polarization direction of the third laser pulse is adjusted to the short axis direction of the illumination line, the polarization direction of the fourth laser pulse is adjusted to the long axis direction of the illumination line, and the fourth laser pulse is a predetermined time with respect to the third laser pulse Delayed in time by an interval Δt, the predetermined time interval Δt is selected such that an illumination line imaged in the semiconductor material layer has a bond strength profile over time in the form of a pulse having first and second maxima.

According to this aspect of the method, four laser beams are uniformly superimposed and imaged, two of the four laser beams each have a linearly polarized pulse in the uniaxial direction of the illumination line and are temporally synchronized, The other two of the laser beams each have pulses that are linearly polarized in the long axis direction of the illumination line, which are delayed in time with respect to the pulses of the first two laser beams.

According to another aspect of the invention, 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 designed to reshape the first laser pulse of the first laser beam and the second laser pulse of the second laser beam into laser pulses having a short axis and a long axis in the form of a line;

- an imaging device designed to image laser pulses in the form of lines, thus formed, as illumination lines on the layer of semiconductor material;

- a polarizing device designed to align the polarization direction of the first laser pulse to the minor axis direction of the illumination line, and to align the polarization direction of the second laser pulse to the long axis direction of the illumination line, and

- a second laser for a first laser pulse by a predetermined time interval Δt, selected such that the illumination line imaged in the semiconductor material layer has a time-dependent coupling intensity profile in the form of a pulse having first and second maxima It includes a delay device designed to delay the pulse.

The polarizing device is such that the first laser pulse almost exclusively contains the polarization component in the short axis direction of the illumination line (polarization ratio is, for example 1:100), and the second laser pulse almost exclusively contains the polarization component in the long axis direction of the illumination line. It is designed and arranged to include The polarizer may include a first polarizer for a first laser beam with a first laser pulse, and a second polarizer for a second laser beam with a second laser pulse. In this case, the first polarizer is in particular arranged in the beam path of the first laser beam and the second polarizer is in particular arranged in the beam path of the second laser beam.

The beam shaping apparatus may form anamorphic optics. It may for example have a lens array homogenizer based on the principle that the incident laser beam(s) is split into several partial beams and then spatially overlapped. The laser line has a short axis and a long axis.

The laser line thus formed is imaged as an illumination line on the image plane of the semiconductor material by the imaging device. The illumination line also has a minor axis and a major axis, the directions of which define the polarizations of the first and second pulses. In general, the direction of the short axis and the long axis of the illumination line coincides with the direction of the short axis and the long axis of the laser pulse in the form of a line.

The polarizer of the optical system can in particular comprise a first λ/2 plate and a second λ/2 plate, said first λ/2 plate being arranged in the beam path of the first laser beam, in particular in front of the beam shaping device and for a first laser pulse impinging on a λ/2 plate, the first laser pulse is oriented to be linearly polarized in a uniaxial direction after passing through the λ/2 plate, and the second λ/2 plate is a second laser beam In the beam path of , in particular for a first laser pulse which is disposed in front of the beam shaping device and impinges on the λ/2 plate, the second laser pulse is oriented to be linearly polarized in the long axis direction after passing through the λ/2 plate.

The first λ/2 plate is oriented in such a way that the polarization direction of the first linearly polarized laser beam with the first laser pulse is rotated in the uniaxial direction. The second λ/2 plate is oriented in such a way that the polarization direction of the linearly polarized second laser beam with the second laser pulse is rotated in the major axis direction.

According to a variant, the delay device may comprise a delay circuit for delaying the trigger signal of the second laser designed to emit a second laser beam having a second laser pulse by a time interval Δt with respect to the trigger signal of the first laser. wherein the first laser is designed to emit a first laser beam having a first laser pulse. That is, the second trigger signal may be electronically delayed with respect to the first trigger signal.

According to an alternative variant, the delay device is a beam bypass such that the optical path length of the second laser beam to the image plane of the semiconductor material layer is longer than the optical path length of the first laser beam to the image plane of the semiconductor material layer. may include According to this variant, the time delay is caused by the path difference, whereby the second laser pulse passes through a longer optical path length to overlap than the first pulse.

The first and second laser beams of the optical system are provided by the first and second laser sources or alternatively provided by one laser source and the laser beam emitted from the laser source is provided by means of a beam splitter to the first laser beam and a second laser beam.

According to a further aspect, the beam shaping apparatus lines 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. and the imaging device may be designed to image the laser pulse in the form of a line so formed as an illumination line on the layer of semiconductor material, the polarizing device being the third laser and the delay device may be designed to linearly polarize the pulse in the short axis direction of the illumination line and linearly polarize the fourth laser pulse in the long axis direction of the illumination line, wherein the delay device causes the illumination line imaged in the semiconductor material layer to achieve first and second maximum values. It can be designed to delay the fourth laser pulse with respect to the third laser pulse by a predetermined time interval Δt selected to have a bond strength profile over time in the form of a pulse with

According to this aspect, the optical system includes a four-beam device in which four laser beams are uniformly superimposed and imaged as an illumination line on the semiconductor material layer, and the polarizer is configured such that two laser beams of the four laser beams are each of the illumination line. having linearly polarized pulses in the short-axis direction, synchronized in time, the other two of the four laser beams each have pulses linearly polarized in the long-axis direction of the illumination line, these pulses arranged to be time-delayed with respect to the pulses of the first two laser beams and designed

The present invention also comprises a system for processing a layer of semiconductor material, in particular for producing a crystalline semiconductor layer, comprising an optical system according to the aspect described above and for directing the layer of semiconductor material with respect to an illumination line in a traveling direction. It is designed to move, and the traveling direction corresponds to the minor axis direction of the illumination line. The layer of semiconductor material can be moved relative to the exposure line by means of a traveling device, for example a table movable in the traveling direction, on which a carrier having the layer of semiconductor material is arranged, so that a large area spanning the entire semiconductor layer is covered by the illumination line. can be exposed and processed. In this case, since the traveling direction corresponds to the direction of the minor axis, the polarization direction of the first pulse and/or the third pulse corresponds to the traveling direction.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in detail below with reference to the accompanying drawings.

1 shows a schematic diagram of a semiconductor material layer exposed by an illumination line moved in a travel direction with respect to the semiconductor material layer for processing the semiconductor material layer.
2A-2C show the line geometry of an imaged illumination line.
3A and 3B show schematic diagrams of an optical system for a semiconductor layer processing system capable of forming an illumination line to image on a semiconductor material.
4 shows a schematic diagram of an embodiment of an optical system in which first and second laser beams are provided by beam splitting of a laser beam;
Figure 5 shows a schematic diagram of an embodiment, in which four laser beams are provided by four laser sources, and the pulses of the two laser beams are respectively emitted with a time delay relative to the pulses of the other two laser beams.
6 shows a schematic diagram 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;
7 schematically depicts the bond strength profile over time of an illumination line, resulting from the uniform superposition of individual pulses.
8A is a scanning electron micrograph of a crystalline silicon layer prepared according to the disclosed method.
8B is a scanning electron micrograph of a crystalline silicon layer treated according to a comparative method.

1 schematically illustrates a method for generating a uniformly crystallized layer by irradiating a laser beam on a semiconductor material according to the disclosed method. A carrier 10 , for example a glass substrate, is coated with a layer 12 of semiconductor material to be treated. In this example, the semiconductor material to be processed is amorphous silicon. The thickness of the semiconductor material layer 12 is typically about 50 nm.

A laser beam 14 in the form of a line is imaged on a semiconductor material and moved in a travel direction X with respect to the semiconductor material, such that the laser line 14 sweeps and illuminates at least some area of the semiconductor material layer 12 . . In the example shown here, the carrier 10 with the semiconductor material layer 12 is displaced in space and thus displaced relative to the laser beam 14 being stationary. The laser line 14 may be moved relative to the semiconductor material layer 12 such that the entire semiconductor material layer 12 is irradiated by the laser line 14 . The laser line 14 is generally moved relative to the semiconductor material layer 12 such that a specific area is irradiated by the laser line 14 multiple times. Typical travel speeds are in the range of 5 mm/s to 50 mm/s.

In the embodiment shown here, the direction of propagation of the laser beam 14 is perpendicular to the surface of the semiconductor material layer 12 . That is, the laser beam 14 here impinges at an angle of incidence of 0°, perpendicular to the surface of the semiconductor material layer 12 .

The line geometry of the laser beam 14 is shown in FIGS. 2A-2C . In Figures 2a to 2c the intensity is plotted according to a specific direction.

Figure 2a shows the intensity of the laser line in the major axis direction, i.e. the integrated intensity distribution 16 along the minor axis (x-axis), and the thus integrated intensity distribution 16 is plotted along the major axis (y-axis), have. In general, in the drawings, the minor axis is parallel to the x-axis and the major axis is parallel to the y-axis. As can be seen in this figure, the distribution 16 is formed to be approximately rectangular, ie ideally uniform along the major axis. The length of the illumination line in the y direction may generally be between 100 mm and 1000 mm, for example 100 mm, 250 mm, 750 mm or 1000 mm, or greater than 1000 mm.

2b and 2c respectively show the intensity of the laser line in the minor axis direction, i.e. the integrated intensity distributions 18 and 20 along the major axis (y-axis), and the thus integrated intensity distributions have the minor axis (x-axis). are shown along. In FIG. 2b the intensity has a Gaussian profile 18 . As an alternative to this, the strength as shown in FIG. 2c may have a flat profile 20 (“flat-top”), ie an approximately rectangular profile.

Typical widths for intensity in the x-direction range from 20 μm to 200 μm. In the case of the Gaussian profile 18 of FIG. 2b , the width is the width the curve has at the intensity corresponding to 90% of the maximum intensity (FW 90%: full width at 90%) in the flat profile 20 of FIG. 2c , the full width at half maximum ( Full Width at Half Maximum, FWHM).

When the illumination 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.

3A and 3B schematically show an optical system 30 for a semiconductor layer processing system, capable of imaging a semiconductor material by forming the illumination line 14 described with reference to FIGS. 1 and 2 .

As will be described in more detail later, the optical system 30 includes a beam shaping apparatus 32 designed to form a laser beam in such a way that the beam profile of the laser beam has a major axis and a minor axis, and a beam shaping apparatus in the beam path of the laser beam. and (32) an imaging device (34) disposed downstream and designed to image the laser beam so formed as an illumination line (36). In the embodiment shown here, four laser beams, a first laser beam 38 , a second laser beam 40 , a third laser beam 42 and a fourth laser beam 44 32) crashes. However, according to the present invention, two laser beams may impinge on the beam shaping apparatus 32 as will be described later with reference to one embodiment. In principle, the number of laser beams is not limited to four or two, any other number is possible and encompassed by the present invention.

The laser radiation in the embodiment shown here is laser radiation with a wavelength of 343 nm emitted by a plurality of UV solid lasers. However, 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.

In FIGS. 3A and 3B as in FIGS. 1 and 2 , the minor axis is shown parallel to the x-axis and the major axis is shown parallel to the y-axis. The optical axis of the optical system is parallel to the z-axis.

Fig. 3a shows the imaging characteristics of the optical system 30 in the y-direction, ie along the long axis of the reshaped laser beam and illumination line, and Fig. 3b shows the short axis in the x-direction, ie the reshaped laser beam and illumination line. shows the imaging characteristics of the optical system 30 along

The beam shaping apparatus 32 of the optical system 30 of FIGS. 3A and 3B has an anamorphic equalization optical system 46 that equalizes the intensity of the incident laser beam in the y-axis direction. Anamorphic equalization optics 46 includes, for example, an array of two cylinder lenses arranged parallel to each other. A cylinder lens array divides the incident radiation into individual partial bundles and superimposes them on the entire plane, resulting in a highly uniformized laser radiation. In the case of multiple incident laser beams, each laser beam is divided into individual partial bundles and overlapped in a uniformed manner. Such homogenizing optics are described in more detail in the prior art, for example according to DE 42 20 705 A1, DE 38 29 728 A1 or DE 102 25 674 A1 incorporated in the present invention.

The beam shaping device 32 of the optical system 30 has a condenser cylinder lens 48 in the beam path behind the anamorphic equalization optics 46 , the condenser cylinder lens 48 being redistributed by the anamorphic equalization optics 46 . It is designed to telecentrically redirect the homogenized and homogenized laser beam to an illumination line 36 and superimpose therewith respect to the major axis, ie in the y-direction. The combination of anamorphic equalization optics 46 and condenser cylinder lens 48 thus has the effect that the incident laser radiation is imaged in a uniformed manner in the image plane as illumination lines 36 .

An imaging device 34 is arranged in the beam path behind the condenser cylinder lens 48 , said imaging device being designed to focus the laser beam on an illumination line 36 with respect to a single axis, ie in the x-direction. In other words, the imaging device 34 images the laser beam as the illumination line 36 , and only the short axis of the beam profile is equalized, not the uniform long axis of the beam profile. Imaging device 34 may be, for example, focusing cylinder lens optics.

The combination of anamorphic equalization optics 46 and condenser cylinder lens 48 may be or be part of anamorphic optics. They may in particular be part of anamorphic optics as described in connection with anamorphic optics 42 in FIGS. 4 to 6 of document DE 10 2012 007 601 A1 incorporated in the present invention.

Accordingly, the beam shaping apparatus 32 may further include one or more of the following optical elements:

- a first collimating cylinder lens denoted by reference numeral 54 in DE 10 2012 007 601 A1 for collimating an emitted laser beam with respect to the x-axis;

- a second collimating cylinder lens denoted by reference numeral 56 in DE 10 2012 007 601 A1 for collimating the emitted laser beam with respect to the y-axis;

- 58 in DE 10 2012 007 601 A1, arranged in the beam path behind the first collimating cylinder lens, for focusing the light beam with respect to the x-axis on the intermediate image denoted 60 in DE 10 2012 007 601 A1 cylinder lens marked with

- an intermediate collimating cylinder lens, designated 58' in DE 10 2012 007 601 A1, arranged in the beam path behind the first collimating cylinder lens 54, for collimating the light beam of the first intermediate image, and/or

- arranged in the beam path behind the first intermediate image, in particular behind the intermediate collimating cylinder lens, for focusing the light beam with respect to the x-axis on a second intermediate image, denoted by reference 64 in DE 10 2012 007 601 A1, Additional cylinder lens marked with reference 62 in DE 10 2012 007 601 A1.

The anamorphic homogenization optics 46 described above can represent or comprise the component 68 shown in FIGS. 4 to 6 of DE 10 2012 007 601 A1, for example.

The aforementioned condenser cylinder lens 48 may represent or comprise, for example, the condenser cylinder lens 74 shown in FIGS. 4 to 6 of DE 10 2012 007 601 A1.

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

The optical system also has a polarizer 50 for each of the laser beams 38 , 40 , 42 , 44 incident on the anamorphic optics. The polarizer is here an optical device 50 for adjusting the polarization direction 50 , for example a λ/2 plate in the beam path of each of the incident laser beams 38 , 40 , 42 , 44 . The optics 50 are disposed in the beam path in front of anamorphic optics or anamorphic equalization optics 46 . Each incident laser beam passes through the optics 50 so that the laser beams 38 , 40 , 42 , 44 that pass through the optics 50 are linearly polarized in a defined direction. More precisely, the laser beam emitted by the laser is already linearly polarized and the direction of polarization is rotated in the direction defined by the optical device 50 , for example as in the example of the UV solid-state laser shown here. The optical device 50, for example a λ/2 plate, is linearly polarized after two of the four laser beams pass through the optical device 50 in the major axis direction with respect to the polarization direction of the incident linearly polarized light, and among the four laser beams The other two are oriented to be linearly polarized after passing through the optical device 50 in the uniaxial direction. In this case, since the traveling direction corresponds to the direction of the minor axis, the remaining two of the four laser beams are linearly polarized in the traveling direction. More precisely, according to the invention, an optical arrangement 50 , for example a λ/2 plate, arranged in the beam path of the first and second laser beams 38 , 40 is applied to the first and second laser beams 38 . , 40 , respectively oriented in the uniaxial direction, ie in the x-direction, in the travel direction, and arranged in the beam path of the third and fourth laser beams 42 , 44 , for example The [lambda]/2 plate is respectively oriented such that the third and fourth laser beams 42 and 44 are each polarized in the major axis direction, ie in the y-direction. In this example, the laser is also pulsed, so that the individual pulses of each laser beam have the aforementioned polarization direction of each laser beam.

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

Alternatively, the laser beams 38 , 40 , 42 , 44 may be generated by splitting a laser beam emitted from a laser source into a first partial beam and a second partial beam by a beam splitter. The beam splitter may be designed to split into a first partial beam, a transmitted beam and a second partial beam, a transmitted beam, for example about 50% each. For this purpose, for example, polarizing optics can be used, for example so-called thin-film polarizers. A thin film polarizer passes light with p-polarization (the plane of oscillation of an electric vector parallel to the plane of the incident beam and normal to the substrate surface) and s-polarization (the plane of the incident beam and an electric vector perpendicular to the normal to the substrate surface). It is an optical substrate with a special coating that reflects light with an oscillating plane). With the λ/2 plate in the beam path in front of the thin film polarizer, the polarization direction of the laser beam emitted from the laser source is approximately 50% of the p-polarization and s-polarization in the beam path in front of the thin film polarizer. It can be rotated to achieve segmentation. However, the λ/2 plate in front of the thin film polarizer can be rotated so that different ratios of p-polarization and s-polarization occur to achieve a split other than 50%. In principle, the relative intensity of the first partial beam to the second partial beam can be adjusted via the orientation of the λ/2 plate.

Such a device is schematically illustrated in FIG. 4 . A linearly polarized laser beam 52 emitted from the laser source impinges on a λ/2 plate 54 disposed in the beam path in front of a beam splitter 56 (here a thin film polarizer). The λ/2 plate 54 is such that the relative ratios of the s-polarization and the p-polarization of the laser beam after the λ/2 plate are the desired relative ratios of the two partial beams 58, 60 after the beam splitter 56, as described above. Oriented to correspond to intensity. The first partial beam 58 can then be, for example, the first laser beam 38 of the apparatus of FIGS. 3A and 3B , and the second partial beam 60 , for example, of FIGS. 3A and 3B . It may be a third laser beam 42 . The second partial beam 60 is deflected by the reflective element 62 to be parallel to the first partial beam 58 . In addition, in the beam path of the first laser beam 38 and the third laser beam 42 , the λ/2 plate 64 corresponding to the λ/2 plate 50 of FIGS. 3A and 3B is formed by the beam splitter 56 . respectively in the beam path of the first partial beam and the second partial beam in the rear beam path. That is, the downstream λ/2 plate 64 in the beam path of the first partial beam 58 is used for polarization in the uniaxial direction. A downstream λ/2 plate 64 in the beam path of the second partial beam 60 is used for polarization in the long axis direction.

The second and fourth laser beams 40 , 44 can be provided beam split by a further device corresponding to the device of FIG. 4 , with a beam splitter 56 . In this case, the downstream λ/2 plates 64 are oriented in such a way that they polarize the third and fourth partial beams in the short axis direction and the long axis direction, respectively. Alternatively, the four laser beams of FIGS. 3a and 3b may be provided by two laser sources, the laser beams emitted from the first and second partial beams 58, respectively by beam splitting, respectively. 60) or into third and fourth partial beams.

The optics 30 of FIGS. 3A and 3B can be used to superimpose a number of laser beams other than 4, for example two laser beams, as already described above. The two laser beams may be provided by two laser sources corresponding to four laser beams, or may be provided by one laser source, and the laser beams emitted from the laser sources correspond to or identical to FIG. 4 . It is split into a first partial beam and a second partial beam by beam splitting by the apparatus.

The optical system 30 of FIGS. 3a and 3b is also designed in such a way that pulses of different polarizations are time-offset with respect to each other at a predetermined time interval Δt. When using a separate laser source for each laser beam, this can be achieved by electronically delaying the trigger signals of the laser sources. A time delay can be achieved by beam detour when the laser beams are provided as partial beams. As shown in FIG. 4 , the second partial beam 60 covers a path longer than the first partial beam 58 by the path Δs. The path Δs may be selected such that a time delay occurs with respect to the first partial beam 58 by a predetermined time interval Δt of the second partial beam 60 . The predetermined time interval is preferably 10 ns to 20 ns.

With the optical system 30 described above, at least one laser pulse polarized in the short axis direction and the laser pulse polarized in the long axis direction are superimposed on the illumination line in a uniform manner and imaged, and the long axis direction polarized pulse is imaged in the short axis direction. It is delayed by a time interval (Δt) for a pulse polarized as . When four laser beams are superimposed, two laser beams are polarized in the short axis direction and two laser beams are polarized in the long axis direction, the short axis polarized laser beams are synchronized at the same time, and the long axis polarized laser beams are polarized in the short axis direction It is delayed by the same time interval (Δt) for the polarized laser beams. By superimposing two (or more) simultaneously synchronized laser beams of two (or more) different laser sources, variations in energy density from pulse to pulse can be reduced. The fluctuation of the energy density causes different crystallization results when the illumination line is moved in the uniaxial direction per pulse and can cause non-uniformity of the crystal structure along the movement direction (“shot mura”). In this case, the combined intensity distribution of two (or more) superimposed laser beams (laser pulses) over time ( It should be noted that the bond strength distribution may be different), which may lead to non-uniformity of the crystal structure. In particular, the non-uniformity is due to the fact that when two (or more) laser sources are combined, each laser source has time jitter independent of each other. It is therefore desirable to use a (pulse) laser source with as little time jitter as possible in the ns range.

The anamorphic equalization optical system 46 is designed such that each incident light beam is split into partial beams and overlapped in a uniformed manner in the major axis direction. That is, each individual beam forms a uniform line. In the above-described pulse device with two laser beams, not only the short-axis polarized and temporally advanced laser pulses but also the long-axis polarized and time-delayed laser pulses with respect to the first pulse are superimposed and imaged as uniform lines. In an apparatus with four laser beams, each of the short-axis polarized and temporally advanced laser pulses as well as each of the long-axis polarized and time delayed laser pulses with respect to the first pulse is superimposed and imaged as a uniform line.

This is explained in more detail using the disclosed method.

In FIG. 5 , the disclosed method uses an apparatus having four laser sources: a first laser source 66 , a second laser source 68 , a third laser source 70 and a fourth laser source 72 . It is exemplarily described. The first laser source 66 and the second laser source 68 are respectively a first laser beam 74 with a first laser pulse 76 and a second laser beam 78 with a second laser pulse 80 , respectively. The first and second laser pulses 76 , 80 are simultaneously emitted by synchronized trigger signals 82 of the first and second laser sources 66 , 68 . The third and fourth laser sources 70 and 72 provide a third laser beam 84 with a third laser pulse 86 and a fourth laser beam 88 with a fourth laser pulse 90, respectively. The trigger signals 92 of the third and fourth laser sources 70, 72 are respectively delayed electronically by a time interval Δt, for example by an electronic delay circuit 94, so that the third and fourth The fourth laser pulses 86 and 90 are emitted with a time delay by a time interval Δt with respect to the first laser pulse 76 and the second laser pulse 80, respectively, and propagate with a time delay. According to the disclosed method, the first laser pulse 76 and the second laser pulse 80 are linearly polarized in the traveling direction, ie in the x-axis direction, ie the polarization is aligned in the traveling direction, and the third laser pulse 86 . The first to fourth laser pulses 76, 80, 86, 90 have a temporal full width at half maximum (FWHM) that is typically in the range of 15 ns to 20 ns. A typical time for the time interval Δt is between 10 ns and 20 ns.

The four laser beams 74 , 78 , 84 , 88 with four laser pulses 76 , 80 , 86 , 90 are formed for example by means of the beam shaping device 32 described with reference to FIGS. 3A and 3B . It is reshaped into a laser pulse having a short axis and a long axis in the form of a line. The laser pulse thus formed is subsequently imaged as an illumination line 36 on the image plane of the semiconductor material, for example by means of the imaging device 34 described with reference to FIGS. 3A and 3B .

6 , the disclosed method is illustrated by way of example using an apparatus having two laser sources. 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 . Accordingly, the trigger signal 92 of the second laser source 70 is electronically delayed relative to the trigger signal 82 of the first laser source 66 by a time interval Δt, so that the second laser pulse 86 is The propagation is delayed by a time interval Δt with respect to the first laser pulse 76 . In addition, the first laser pulse 76 is linearly polarized in the minor axis direction of an illumination line in the form of a laser pulse or line formed later, and the second laser pulse 86 is, for example, as described with reference to FIGS. 3A and 3 . By the λ/2 plate 80, it is linearly polarized in the long axis direction perpendicular to it. The minor axis corresponds to the traveling direction in which the illumination line 36 to be formed later moves relative to the semiconductor material layer 12 to be processed. Similar to the method of FIG. 5 , the two laser beams 74 , 84 with two laser pulses 76 , 86 are formed for example by means of the beam shaping apparatus 32 described with reference to FIGS. 3 a and 3 . , is reshaped into a laser pulse with a short axis and a long axis in the form of a line. The laser pulses thus formed are subsequently imaged as illumination lines 36 on the image plane of the semiconductor material layer 12 , for example by means of the imaging device 34 described with reference to FIGS. 3A and 3B .

The line geometry of the illumination line 36 thus formed has been described with reference to FIGS. 2A-2C . The coupled intensity profile over time of the illumination line thus formed, ie the intensity of superimposed and time delayed pulses over time, will now be described with reference to FIG. 7 . In FIG. 7 , a bond strength profile 96 over time is shown as an example for the method with two laser beams disclosed in FIG. 6 . 7 also shows the combined intensity of the two laser beams 74 and 84 over time and the intensity of the pulses for each individual laser beam.

In FIG. 7 , the intensity profile denoted by reference numeral 98 corresponds to the intensity profile of the first laser pulse 76 of the first laser beam 74 , and the intensity profile denoted by reference numeral 100 corresponds to that of the second laser beam 84 . Corresponding to the intensity profile of the second laser pulse 86 , the intensity profile denoted by reference numeral 96 corresponds to the combined intensity profile over time of the first and second pulses 76 , 86 . The first and second laser pulses 76 and 86 each have a temporal full width at half maximum (FWHM) of 15 ns to 20 ns. Also, as can be seen in FIG. 7 , the second laser pulse 86 is time delayed relative to the first laser pulse 76 by a duration of approximately 10 ns to 20 ns, specifically, specifically. In FIG. 7, the duration is about 20 ns. This is, in the joint strength profile over time 96, a total pulse duration 102 with a first maximum M1 and a second maximum M2 and extended for individual pulse durations, i.e. between 40 ns and 50 ns. Create a pulse profile with a pulse length. The total pulse length 102 is the temporal full width, in particular the temporal full width at half maximum of first maximum (“Full Width at Half Maximum of First Maximum”), that is, the point at which the intensity of the first pulse is half the maximum value M1. corresponds to the width of the pulse.

As shown in FIG. 7 , the maximum intensity M1 of the first laser pulse 76 is greater than the maximum intensity M2 of the time-delayed second laser pulse 86 . Specifically, the intensity of the first laser pulse 76 relative to the intensity of the second laser pulse 86 is the first maximum (M1) versus the second maximum (M2) of the combined intensity profile 96 over time. is adjusted so that the ratio of M1/M2 lies between 1/1.2 and 1/0.7, ie between 0.8 and 1.4. In embodiments where each laser beam is provided by a separate laser source, this may be achieved by matching the intensities of the individual laser beams to each other. In the device schematically shown in Fig. 4, in which two laser beams are provided by splitting one laser beam, the s-component and p of the light beam in front of the thin film polarizer 56 by rotating the λ/2 plate 54 - Relative strength can be achieved by changing the components.

As described above, according to the present invention, the first laser pulse 76 is linearly polarized in the short axis direction, that is, the traveling direction, and the second laser pulse 86 is linearly polarized in the long axis direction.

The knowledge underlying the present invention is that the aforementioned linear polarization of the first and second pulses 76 , 86 has a positive effect on the uniformity of the semiconductor material layer 12 processed with the laser line. It has been found that when the first pulse is temporally polarized in the traveling direction and the time-delayed pulse is polarized in the long axis direction, very uniform 50 nm to 60 nm thick crystalline silicon layers with regular grain structure are produced. The ratio of the first maximum (M1) to the second maximum (M2) of the bond strength profile over time was approximately 1:1, ie 0.8 to 1.4.

In contrast, this positive effect could not be observed when the polarization was reversed, i.e., when 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 knowledge 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 device used was a line beam device with four UV solid-state lasers emitting light with a wavelength of 343 nm. Four lasers were operated at a pulse repetition rate of 10 kHz. The pulse length of the emitted pulses, that is, the temporal full width at half maximum, was 15 ns to 20 ns. The energy of the laser pulse was up to 20 mJ. The energy density on the substrate, ie the silicon layer, was 220 mJ/cm 2 . Similar to the method of FIG. 5 , a large number of first and second laser pulses from the first and second of the four lasers are synchronized simultaneously by a synchronized trigger signal from the laser source, such that the first laser pulse It was emitted simultaneously with the second laser pulse. The large number of third and fourth laser pulses of the third and fourth lasers were time delayed by 10 ns to 20 ns, respectively, with respect to the large number of first and second laser pulses. The intensities of the four laser beams were adjusted so that the ratio (M1/M2) of the first maximum to the second maximum in the time-dependent bonding intensity profile was 1/1.

The laser pulses of the four laser beams were reformed into laser lines by the apparatus according to FIGS. 3a and 3b and imaged as illumination lines on amorphous silicon. The illumination line was moved at a traveling speed of 20 mm/s with respect to the semiconductor layer, in particular in the short axis direction of the illumination line. The illumination line length in the major axis direction was 90 mm and the uniformity was 1.5% (2σ). The illumination line length in the minor axis direction was 67 μm and the uniformity was 3% (2σ). The total pulse length of the bond strength profile over time was 45 ns ("Full Width at Half Maximum of First Maximum).

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

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

8a shows a photograph of the silicon surface taken with a scanning electron microscope after laser exposure according to experiment a). 8b shows a photograph of the silicon surface taken with a scanning electron microscope after laser exposure according to experiment b). In both pictures, the direction of travel was the direction of the x-axis (short axis of the illumination line), ie the direction perpendicular to FIGS. 8A and 8B .

Fig. 8a shows that a regular grain structure is generated in the longitudinal direction, perpendicular to the propagation direction, ie in the y-direction. In particular, it can be seen that the particles are arranged in vertical rows spaced at approximately equal intervals, in particular approximately 0.35 μm apart corresponding to the wavelength of the UV laser. In other words, the grain structure exhibits a strip pattern extending in the traveling direction, and the strips are evenly spaced, thereby providing uniformity in the long axis direction. Therefore, the particle size in the long axis direction (y-direction) has a large uniformity. In the short axis direction (x-direction) there is less uniformity compared to the long axis.

In contrast, FIG. 8b shows that there is no apparent uniformity in both the minor axis direction (x-direction) and the major axis direction (y-direction). The particle structure appears chaotic compared to the particle structure of FIG. 8A with respect to the direction and size of the particles.

As already described above, the laser crystallization process is based on partial melting of an a-Si layer and subsequent solidification based on unmelted solid silicon on a glass substrate of crystalline structure. Melting and solidification occur on a time scale of 10 ns to 100 ns, after which the film is cooled to room temperature over several 100 µs. A pulse repetition rate of 10 kHz corresponds to a period of 100 μs. The pulse repetition rate, rate of travel, and pulse width of the illumination line in the direction of travel depend on the number of times a point of semiconductor material is exposed during the course of exposure, i.e., by multiple successive pulses, with a period corresponding to the pulse repetition rate allowing the film to return to room temperature. Because it is designed in such a way that it takes less time to cool, the semiconductor material is repeatedly irradiated by UV light during the crystallization process. Also, there is a relatively long exposure with one pulse due to the relatively long laser pulse profile spanning several 10 ns. This multiple exposure promotes the formation of a uniform grain structure.

As mentioned in the introduction, it is also known that the polarization of laser light, especially in combination with the multiple exposures 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) that results in a modulated intensity distribution. It has been shown that when light is linearly polarized in the long axis direction, a regular structure is formed along the long axis, and when light is linearly polarized in the short axis direction (traveling direction), the above effect can be observed in the traveling direction.

The LIPPS effect has been discussed in numerous publications, such as, for example, references (1) to (4) below. It is assumed that the modulated intensity distribution arises from the interaction of the incident light beam with the light beam diffracted at and toward the surface and the resulting periodic distribution of pulse energy density. The periodic pulse energy density distribution has the form of a so-called "ripple", spaced apart by an amount of λ/(1 ± sinΘ) for a laser light having a wavelength λ and an angle of incidence Θ. In the case of normal incidence of light (Θ = 0°), an interval of about the wavelength λ occurs. "Ripple" extends in a direction perpendicular to the E-field vector, ie perpendicular to the polarization direction of the light beam or light pulse, and has periodicity in the E-field vector direction. The pulse energy density is minimum or maximum along the "ripple". The periodic pulse energy density causes a spatially periodic temperature distribution in the exposed semiconductor material layer, which is similar to the periodic pulse energy density distribution. In the case of a periodic temperature distribution, the thermal diffusion of the semiconductor material layer must also be considered. It was also found that the periodic distribution of the pulse energy density varies with the thickness of the semiconductor material layer due to multiple reflections inside the semiconductor material layer.

In summary, these observations indicate that there must be an E-field vector in the long-axis direction to obtain periodicity or regularity in the long-axis direction, that is, light or light pulses must be linearly polarized in the long-axis direction.

Therefore, it has been assumed so far that each pulse must contain at least a portion of the polarization in the long axis direction to be able to create a regular grain structure in the long axis direction.

According to the present invention, temporally first pulse 76 or temporally first pulses 76, 80 is polarized in the short-axis direction, ie in the traveling direction, and the second delayed pulse 86 or second delayed pulses ( 86, 90) has been found to be particularly preferable with respect to the uniformity of the polycrystalline silicon grain structure when it is polarized in the long-axis direction.

A possible explanation for the fact that regular particle structure is promoted when the second pulse is polarized in the long axis is that the light in the long axis can generate interferometric modulation (LIPPS) with a laser wavelength to support structured particle formation in this direction. will be. If the second pulse is linearly polarized in the traveling direction, no interferometric modulation is formed in the long axis.

An explanation of why polarization of the first maximum value of light in the minor direction (direction of travel), i.e. the first pulse, is desirable for the particle structure is that during this period of irradiation the film in the major axis does not undergo coherent modulation there, so that the polarization component is shifted in the major axis direction. It is heated more uniformly than there is, and only the second pulse component may be to structuring and creating a partial liquid phase and to promote particle structure.

Also, according to experiment a), when adjusting the polarization of the first pulse in the traveling direction, i.e., the short-axis direction, and the polarization of the second delay pulse in the long-axis direction, the size of the energy density process window is different between the first pulse and the second delay pulse. was observed to increase (for energy density process windows of 210 to 230 or 235 mJ/cm 2 ) from 20 to 25 mJ/cm 2 , compared to exposure with the same polarization distribution in both directions. In this case, the size of the energy density process window was only about 10 mJ/cm 2 (for an energy density process window of 215-225 mJ/cm 2 ).

Finally, it has been found that favorable results are achieved in the case of "optical delay", for example as shown in FIG. 4, compared to, for example, "electronic delay", as shown in FIGS. 5 and 6 . In particular, it has been found that the non-uniformity of the crystal structure in the direction of movement (“shot mura”) can be reduced in the case of “optical delay” compared to “electron delay”.

As already explained above, when two (or more) laser beams synchronized at the same time from two (or more) different laser sources are superimposed, the fluctuation of the intensity distribution due to the existing time jitter of the laser sources is can occur

For example, when observing the bond strength profile 96 over time as shown for two laser pulses 76 and 86 in FIG. 7 and forming for four laser pulses, the first laser pulse 76 ) consists of a combined intensity profile 98 of two first laser pulses 76 , 80 , and an intensity profile 100 of a second laser pulse 86 consists of two second laser pulses. It consists of a bond strength profile (100) of (86, 90). In this case, by means of a pulsed laser source with the smallest possible temporal jitter (eg, in the ns range), it is possible to minimize variation from coupling strength profile 98 or from coupling strength profile 100 to coupling strength profile 100 . do. Because the two first laser pulses 76, 80 or the two second laser pulses 86, 90 come from different laser sources in the device with optical delay and the device with electronic delay, " No other situation appears for electronic and optical retardation with regard to "blurring".

The bond strength profile 96 over time of FIG. 7 is obtained by superimposing the (bonding) strength profiles 98 , 100 . As shown in FIG. 7 , the pulse width and delay are selected such that the preceding pulse 98 or preceding pulse combination 98 overlaps the subsequent pulse 100 or subsequent pulse combination 100 . In this case, delayed pulse 100 or delayed pulse combination 100 (because delayed pulse 100 or delayed pulse combination 100 contributes little or no contribution to the maximum value M1 of the combined strength profile 96) A first maximum (M1) not actually affected by 100), and a second maximum (M2) having a position and shape greatly influenced by the delayed pulse 100 or delayed pulse combination 100 occurs. do.

Thus, the existing varying time jitter between the first pulse 98 and the second time delayed pulse 100 is dependent on the varying location and shape of the maximum value M2, in particular the maximum value ( M2) is imaged on the location and morphology. The crystallization process can respond to the change in strength over time with particle structure variations, for example particle size variations.

In the case of optical delay by splitting the beam and providing an optical delay line, unlike electronic delay (for example in combination with a pulsed laser source with the smallest possible time jitter), the leading pulse 98 and the delayed pulse 100 are In practice it is possible to have the same time jitter. As a result, when the pulses 98, 100 or the pulse combinations 98, 100 are superimposed, the fluctuation of the intensity profile is minimized, and uniform conversion from the amorphous semiconductor layer to the polycrystalline semiconductor layer is achieved over a wide surface.

An additional optical path of about 6 m is needed to achieve a typical time delay of 20 ns of the second pulse 100 to the first pulse 98 . This additional optical path is for example arranged in a delay line (eg, the beam path of the second partial beam 60 in FIG. 4 ) and with the aid of a long focal spherical telescope having conjugate planes at the input and output of the delay line. can be achieved. In this way, the laser beam (partial beam 60 in FIG. 4 ) can be imaged in a controlled manner over a long distance. In the case of a 1:1 image, for example, a telescope may be provided in which the focal length of the objective is equal to the focal length of the eyepiece. The delay line can also be designed in such a way that the delay line (its length) can be changed with the aid of a deflecting element arranged displaceably like a mirror, for example. Due to this, the optimal pulse length for the crystallization process can be adjusted.

Instead of obtaining time delayed laser beams or laser pulses by beam splitting and subsequent optical delay, two UV laser beams are obtained by generating a third harmonic wavelength (343 nm) from an IR laser beam (1030 nm) with an IR source according to the present invention. Use a UV laser source. This UV laser source uses the unconverted IR pulse energy (typically 50%) in the first SHG (“second harmonic generation”)/THG (“third harmonic generation”) crystal in the second SHG/THG crystal to produce 2 Generate a UV laser beam. These two UV beams do not have varying time jitter with respect to each other. One of the two UV laser beams can be optically retarded as described above, for example with the aid of a long-focal spherical telescope. This solution eliminates the need for beam splitting.

In addition, it was shown that the formation of the periodic structure of the long axis in the delayed pulse 100 was more successful as the angle distribution of the long axis of the laser light was smaller. It is assumed that this is due to the dependence of the periodic pulse energy density distribution described above in relation to the LIPPS effect (λ/(1 ± sinθ)) due to the interference occurring along the surface. In the above equation, θ is the angle of incidence with respect to the surface normal, and the smaller the angular distribution of the incident light, the less the angle of incidence varies. That is, it is sharper. A beam of delayed pulses is linearly polarized in the long axis direction. Accordingly, the delay is preferably adjusted for the laser beam being imaged close to the optical axis. Conversely, this means that the beams imaged away from the optical axis should be beams of a preceding pulse with a polarization perpendicular to the major axis.

References (1) to (4):

(1) P. van der Wilt, “Excimer-LASER Annealing: Microstructure Evolution and a Novel Characterization Technique, SID 2014 Digest p194

(2) S. Horita, H. Kaki, K. Nishioka, "Surface modification of an amorphous Si thin film cystallized by a linear polarized Nd: YAG pulse laser beam", Journal of Applied Physics 102, 013501 (2007)

(3) H.M van Driel, J.E. Sipe, 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, "Ultravioletlaser-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 peiodic surface structure. II. Experiments on Ge, Si, Al and brass", Phys. Rev. B 27, 1155-1172 (1983).

12: semiconductor material layer
30: optical system
32: beam forming device
34: imaging device
36: light line
66: first laser
70: second laser
74: first laser beam
76: first laser pulse
80: third laser pulse
84: second laser beam
86: second laser pulse
88: fourth laser beam
90: fourth laser pulse
94: delay device
96: strength profile

Claims (16)

A method for processing a layer of semiconductor material, the method comprising:
- 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) into a laser pulse having a short axis and a long axis in the form of a line using a beam shaping device (32);
- imaging the laser pulse in the form of a line thus formed as an illumination line (36) having a short axis and a long axis on the semiconductor material layer (12) by means of an imaging device (34);
the method
- adjusting the polarization direction of the first laser pulse (76) to the minor axis direction of the illumination line (36);
- adjusting the polarization direction of the second laser pulse (86) to the long axis direction of the illumination line (36);
- such that the illumination line 36 imaged in the semiconductor material layer 12 has a bond strength profile over time 96 in the form of a pulse having a first maximum M1 and a second maximum M2. time delaying the second laser pulse (86) with respect to the first laser pulse (76) by a selected predetermined time interval Δt. The method of claim 1,
The method is
- moving the illumination line (36) in a direction of travel relative to the layer of semiconductor material (12), wherein the first laser pulse (76) is linearly polarized in the direction of travel,
Way. 3. The method according to claim 1 or 2, wherein the relative intensities of the first laser pulse (76) and the second laser pulse (86) are in a time-dependent joint intensity profile (96) versus the first maximum (M1). and the ratio of the second maximum (M2) is selected to be in the range from 0.8 to 1.4. 2. The method of claim 1, wherein the bond strength profile over time (96) of the illumination line (36) has a temporal full width at half maximum (102) of 40-50 ns for the first maximum value of the bond strength profile over time. Way. The method of claim 1,
The method is
- designed to emit said first laser beam 74 and said second laser beam 84 respectively, said second laser pulse 86 relative to said first laser pulse 76 by a time interval Δt The method further comprising the step of providing a first laser (66) and a second laser (70) controlled to be emitted with a delayed release. The method of claim 1,
The method is:
- providing a first laser designed to provide a pulse to the laser beam (52);
- splitting the laser beam (52) into a first laser beam component (58) and a second laser beam component (60);
further comprising,
The first laser beam component 58 forms the first laser beam 74 with the first laser pulse 76 and the second laser beam component 60 forms the second laser pulse 86 forming the second laser beam (84) with 7. The method of claim 6,
The optical path length of the second laser beam component 60 from the beam splitting position to the semiconductor material layer 12 is the first laser beam component 58 from the beam splitting position to the semiconductor material layer 12 . longer than the optical path length of the method. The method of claim 1,
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 a plurality of the second laser beams 84 . one of the second laser pulses of , and each of the plurality of laser pulses of the second laser beam 84 is one of the plurality of laser pulses of the first laser beam 74 by a predetermined time interval Δt A method, which is time-delayed relative to the other. 9. The method of claim 8,
The traveling speed, the pulse repetition rate of the first laser beam 74 and the second laser beam 84, and the geometric full width at half maximum of the illumination line 36 in the short axis direction are determined when a point of the semiconductor material layer 12 is illuminated. selected to be exposed multiple times by line (36). The method of claim 1, wherein the method
- providing a third laser beam (78) with a third laser pulse (80) and a fourth laser beam (88) with a fourth laser pulse (90);
- The first laser pulse 76, the second laser pulse 86, the third laser pulse 80 and the fourth laser pulse 90 are shortened by using the beam shaping device 32 and reforming with a laser pulse having a long axis,
- imaging the laser pulse in the form of a line thus formed as an illumination line (36) having a short axis and a long axis on the semiconductor material layer (12) by the imaging device (34),
the method
- adjusting the polarization direction of the third laser pulse (80) to the minor axis direction of the illumination line (36);
- adjusting the polarization direction of the fourth laser pulse (90) to the long axis direction of the illumination line (36), and
- a predetermined predetermined value selected such that the illumination line 36 imaged on the semiconductor material layer 12 has a bond strength profile over time in the form of a pulse having a first maximum M1 and a second maximum M2. time delaying the fourth laser pulse (90) with respect to the third laser pulse (80) by a time interval Δt. An optical system (30) for processing a layer of semiconductor material (12), the optical system (30) comprising:
- Reshaping 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 laser pulse having a short axis and a long axis in the form of a line a beam forming device 32 designed to
- an imaging device (34) designed to image a laser pulse in the form of a line thus formed as an illumination line (36) having a short axis and a long axis on said layer of semiconductor material (12);
The optical system 30 is
- designed to align the polarization direction of the first laser pulse 76 with the short axis direction of the illumination line 36 and align the polarization direction of the second laser pulse 86 with the long axis direction of the illumination line 36 a polarizing device 50 and disposed thereon; and
- such that the illumination line 36 imaged on the semiconductor material layer 12 has a bond strength profile 96 over time in the form of a pulse having a first maximum M1 and a second maximum M2. and a delay device (94) designed to delay the second laser pulse (86) with respect to the first laser pulse (76) by a selected predetermined time interval (Δt). 12. The method of claim 11,
The polarizer is
In the beam path of the first laser beam 74 , 38 , for the first laser pulse 76 disposed in front of the beam shaping device 32 and impinging the first λ/2 plate 50 , the a first λ/2 plate (50) oriented to be linearly polarized in the uniaxial direction after a first laser pulse (76) has passed through the λ/2 plate (50), and
In the beam path of the second laser beam 84 , 40 , for the second laser pulse 86 disposed in front of the beam shaping device 32 and impinging on the second λ/2 plate 50 , the an optical system (30) comprising a second λ/2 plate (50) oriented such that a second laser pulse (86) is linearly polarized in the long axis direction after passing through the λ/2 plate (50). 13. The method according to claim 11 or 12,
The delay device triggers the trigger signal 92 of the second laser 70 designed to emit the second laser beam 84 , 40 having the second laser pulse 86 , the trigger signal 92 of the first laser 66 . a delay circuit (94) for delaying a signal (82) by a time interval Δt, the first laser (66) delaying the first laser beam (74) with the first laser pulse (76) An optical system (30) designed to emit. 13. The method according to claim 11 or 12,
The delay device is such that the optical path length of the second laser beam (84, 40) to the image plane of the semiconductor material layer (12) is the first laser beam (84, 40) to the image plane of the semiconductor material layer (12) an optical system (30) comprising a beam detour (Δs) that is greater than the optical path length of 74, 38). 12. The method of claim 11,
The beam shaping device 32 includes 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 beam 78 ) is designed to reform the third laser pulse 80 of and the fourth laser pulse 90 of the fourth laser beam 88 into a laser pulse having a short axis and a long axis in the form of a line,
the imaging device 34 is designed to image a laser pulse in the form of a line so formed as the illumination line 36 having a short axis and a long axis on the semiconductor material layer 12,
The polarizer 50 aligns the polarization direction of the third laser pulse 80 to the minor axis direction of the illumination line 36 and sets the polarization direction of the fourth laser pulse 90 to that of the illumination line 36 . designed and positioned to align in the longitudinal direction;
The delay device 94 determines the coupling strength over time in the form of a pulse in which the illumination line 36 imaged on the semiconductor material layer 12 has a first maximum M1 and a second maximum M2. An optical system (30) designed to delay the fourth laser pulse (90) with respect to the third laser pulse (80) by a predetermined time interval (Δt) selected to have a profile (96). A system for processing a layer of semiconductor material (12) comprising:
comprising the optical system (30) according to claim 11;
The system is designed to move the layer of semiconductor material (12) with respect to an illumination line (36) in a traveling direction, the direction of travel corresponding to a minor axis direction of the illumination line (36).

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