CN111465889A

CN111465889A - Optical system for producing an illumination line

Info

Publication number: CN111465889A
Application number: CN201980006423.5A
Authority: CN
Inventors: B·伯格哈特; H·卡勒特; J·里克特
Original assignee: Inneva Ltd
Current assignee: Inneva Ltd
Priority date: 2018-01-04
Filing date: 2019-01-03
Publication date: 2020-07-28
Anticipated expiration: 2039-01-03
Also published as: CN111465889B; JP2021508857A; JP6813719B1; WO2019134924A1; KR102459299B1; DE102018200078A1; DE102018200078B4; KR20200101987A

Abstract

An optical system for producing an illumination line includes a laser beam source for producing a laser beam along an optical axis. The optical system further comprises a beam shaping device designed to shape the laser beam such that a beam profile of the laser beam has a major axis and a minor axis; and an imaging device arranged in the beam path of the laser beam after the beam shaping device and configured to image the thus shaped laser beam as an illumination line. The beam shaping device has at least one telescope assembly comprising a first lens group and a second lens group, wherein the first lens group and the second lens group have refractive power at least with respect to the minor axis. The optical system further includes first moving means for moving at least one of the first lens group and the second lens group along the optical axis. The optical system further comprises a control unit arranged to control the first moving device to move at least one of the first lens group and the second lens group when the laser beam source generates the laser beam. The present application also proposes a method for generating an illumination line.

Description

Optical system for producing an illumination line

Technical Field

The invention relates to an optical system for producing illumination lines, in particular for example for so-called laser lift-off applications or for devices for processing thin film layers, and to a method for producing illumination lines, in particular for laser lift-off applications or for processing thin film layers.

Background

The techniques described below may be used, for example, in conjunction with laser lift-off applications that separate a plastic substrate from a glass carrier where a laser line (i.e., illumination line) is focused through transparent glass onto the plastic substrate.

LL O Process is used, for example, to separate a flexible O L ED display substrate from a glass carrier, where a plurality of polyimide films of 10-100 μm are bonded to a flat glass substrate, for example, of 0.5mm thickness, and the structure of an O L ED display is built on these polyimide filmsOn a plastic film. At an energy density of 100-500 mJ/cm²Where the plastic substrate remains undamaged and the flexible O L ED display substrate can be used for further processing, such as in a smart phone.

Another application of the described technology relates to the processing of thin film layers. A laser is used for crystallization of a thin film layer used for manufacturing a Thin Film Transistor (TFT), for example. Silicon (Si), more precisely a-Si, is used in particular as the semiconductor to be processed. The semiconductor layer has a thickness of, for example, 50nm, and is typically located on a substrate (e.g., a glass substrate) or other support.

The layer is irradiated with light from a laser, for example a pulsed solid-state laser. Light of a wavelength of, for example, 532nm or 515nm is shaped here into an illumination line, see, for example, DE 102012007601 a1 or WO 2013/156384 a 1. Lasers with wavelengths 343nm and 355nm have also been used for several years for these processes. The laser beam can be shaped by means of a beam shaping device such that the beam profile of the laser beam has a major axis and a minor axis. The laser beam thus formed may then be imaged as an illumination line by means of an imaging device disposed in the beam path of the laser beam after the beam shaping device to produce the illumination line from the light of the laser beam. A corresponding optical system is described, for example, in DE 102015002537.

In particular, the beam shaping means may comprise, for example, anamorphic optics and have different imaging characteristics with respect to the first and second imaging axes. In particular, the beam shaping device is provided for generating a laser beam from the laser light at a position directly in front of the imaging device, the beam profile of the laser beam having a long axis and a short axis, wherein the beam profile has a (maximally) uniform (or substantially uniform) intensity distribution in the long axis. The imaging device then focuses (in particular only) the short axis of the beam profile produced by the beam shaping device immediately before the imaging device to produce the short axis of the illumination line. The imaging device has, however, (substantially) no focusing properties, in particular with respect to the long axis, so that the long axis of the beam profile generated by the beam shaping device immediately before the imaging device can pass through the imaging device almost unchanged and can thus correspond to the long axis of the illumination line.

The illumination line thus also has a short axis and a long axis, as the beam profile of the previously formed laser beam, wherein for the sake of clarity in particular the short axis of the beam profile of the laser beam passes through the imaging device before imaging, corresponding to the short axis of the illumination line, while the long axis of the beam profile corresponds to the (homogenized) long axis of the illumination line. The intensity distribution of the illumination lines along the long axis is ideally rectangular and has a length (or: Half-height-width (halbwertbreit); english: fulllwidth at Half Maximum, abbreviated FWHM), of several 100mm, for example 750mm to 1000mm or more. The intensity distribution along the short axis is generally gaussian and has a FWHM of about 5 to 100 μm. Thereby, the short axis and the long axis form a relatively high aspect ratio

The illumination line is guided over the semiconductor layer in the direction of the short axis with a feed of about 1 to 50mm/s, preferably 10 to 20 mm/s. The intensity of the beam (in the case of a continuous wave laser) or the pulse energy (in the case of a pulsed laser) is set such that the semiconductor layer is melted and re-solidified into a crystallized layer with better electrical properties for a short time (i.e. in the time range of about 50ns to 100 mus).

In addition to the above-described application areas relating to LL O and the fabrication of thin film transistors, there are many other application areas in which it is desirable to generate illumination lines having high aspect ratios to illuminate a substrate.

The quality of the illumination line produced depends inter alia on its spatial intensity distribution integrated along the short axis and/or the long axis and can have an influence on the material of the substrate to be processed with the illumination line. In the crystallization of amorphous silicon layers, therefore, inhomogeneities of the intensity distribution which are very small along the long axis, i.e. local deviations or modulations of the absolute intensity of, for example, an (ideally) uniform intensity distribution in the low single-digit percentage range (e.g. about 2%), have already been caused, spatial inhomogeneities in the crystal structure on one side of the illumination line as it advances (e.g. due to local variations in the grain size) affecting the quality of the thin-film layer and thus also the quality of the thin-film transistor. This leads to the following relationship: the more uniform (i.e., more uniform) the intensity distribution of the illumination lines, the more uniform (i.e., more uniform) the crystal structure of the thin film layer, and thus the more uniform the characteristics of the resulting product, such as a screen-side TFT of a display device (e.g., display, monitor, etc.).

In addition to the spatial uniformity of the intensity of the illumination lines described above, the temporal uniformity of the intensity (i.e., the variation of the intensity over time during the scan) is of greater significance. The intensity fluctuations of the illumination line over time can result in the area of the illuminated material over which the illumination line is directed being illuminated with a different (i.e., non-uniform or non-uniform) intensity, which can lead to undesirable non-uniform characteristics of the resulting end product.

In this context, it is desirable that the optical characteristics of the illumination line produced remain as constant as possible over time. In particular, it is desirable that the intensity of the illumination line (in particular the overall intensity distribution or at least the maximum intensity) and the full width at half maximum (FWHM) of the illumination line along the minor axis remain as constant as possible over time.

Disclosure of Invention

The object of the present invention is therefore to provide an improved optical system for an apparatus for producing illumination lines, in particular for processing thin film layers, which optical system is capable of producing illumination lines of high quality and constant over time.

The object of the invention is achieved by means of an optical system according to claim 1 and a method according to claim 12.

According to a first aspect of the invention, an optical system for generating illumination lines (in particular an apparatus for processing thin film layers) is proposed. The optical system includes a laser beam source for generating a laser beam along an optical axis. The optical system further comprises a beam shaping device, which is provided for shaping the laser beam such that the beam profile of the laser beam has a long axis and a short axis (in particular oriented perpendicular to the long axis), and a (in particular cylindrical) imaging device, which is located in the beam path of the laser beam after the beam shaping device and which is provided for imaging (or mapping) the thus shaped laser beam (in particular the short axis of the thus shaped laser beam) into an illumination line. The beam shaping means comprises at least one telescope assembly (teleskopandordnung) comprising a first lens group and a second lens group, wherein the first lens group and the second lens group have refractive power at least with respect to the short axis. The optical system further includes first moving means for moving at least one of the first lens group and the second lens group along the optical axis. The optical system further comprises a control unit arranged to control the first moving means to move at least one of the first lens group and the second lens group when the laser beam source generates the laser beam.

The beam profile of the laser beam is understood in particular to mean the beam profile of the laser beam (in particular directly) upstream of the imaging device. A telescope assembly, also called telescopic device, describes the optical arrangement of the lens groups or lenses of the device and their optical properties. In particular, the telescope assembly may be a keplerian telescope or a galilean telescope, as will also be described in detail below. The telescope assembly includes at least a first lens group and a second lens group. A lens group is understood here to mean a lens group which can be a single lens (for example a converging lens or a diverging lens) or a lens group consisting of a plurality of (for example cemented) lenses. In the simplest case, the telescope assembly therefore consists of two individual lenses, each of which acts as an individual lens of the respective lens group. The telescope assembly may be embodied such that the focal point of the first lens group spatially corresponds to the focal point of the second lens group. The first lens group may be composed of a single cylindrical lens or a plurality of cylindrical lenses, for example. This holds true regardless of the arrangement of the first lens group and the second lens group.

Conventionally, the optical axis extends along the z-axis. The first moving means is thus provided for moving the first lens group, the second lens group or both lens groups along the z-axis. For this purpose, the first displacement device may comprise, for example, a linear servomotor or a piezoelectric element.

The words "first" and "second", as used in connection with "first mobile device" and later "second mobile device", are for purposes of distinction only and are not intended to be exclusive. Alternatively, for example, a "first mobile device" may be referred to as a "mobile device" and a "second mobile device" may be referred to as another mobile device.

The control unit may comprise, for example, at least one processor and at least one memory. In the memory instructions may be stored, and the control unit may control the first mobile device in a predefined order based on the instructions. The control unit may also be used to control other elements of the optical system, such as a laser beam source and two shutter elements, which will be described below.

The above-described technique has the effect and advantage that optical changes to the optical system while generating the laser beam can be compensated for by moving or adjusting the telescope assembly. In particular for thermal lens effects caused by the laser beam due to heating of optical components of the optical system, can be compensated for or at least reduced by the movement of the first movement means.

The laser beam source may comprise a laser resonator, a frequency doubled crystal assembly (kristallandnung) located after the laser resonator in a beam path, and a first shutter element disposed between the laser resonator and the crystal assembly in the beam path. The control unit may further be arranged for controlling the first moving means in dependence of the open state of the first shutter element, in particular based on control data stored in a memory of the control unit.

The laser resonator may be, for example, a solid-state laser, which emits, in particular, laser radiation in the infrared range. The laser resonator may comprise, for example, a Nd: YAG laser. Frequency-doubled crystal assemblies may include, for example, crystals for doubling the frequency (also known as SHG crystals) and/or crystals for tripling the frequency (also known as THG crystals). In addition to controlling the first moving means, the control unit may be used to control the first shutter element. The first shutter element may for example comprise a mechanical shutter. The shutter element can be controlled in such a way: causing it to either block the laser beam so that the laser beam source is in a state of not generating the laser beam; or passing the laser beam (e.g., by moving a mechanical shutter out of the beam path) so that the laser beam source is in a state of generating the laser beam. In other words, the first shutter element can be understood as an on/off switch for a laser beam source for frequency-doubled laser radiation, wherein the laser beam source can be caused to generate a laser beam or to stop generating a laser beam by controlling the first shutter element. The duration of exposure of the frequency doubling crystal assembly to the laser beam can be reduced by means of the shutter element to the time it takes to actually irradiate the substrate (e.g., thin film layer) with the laser beam.

Controlling in dependence on the open state of the first shutter element means that the time course of the movement of the first and/or second lens group is related to (in particular triggered by) the closing or opening of the first shutter element. In other words, the control of the opening of the shutter element has a predetermined time relationship with the control of the first moving means. In particular, the control of the first moving means may be triggered by the opening (or opening command) of the shutter element.

For this purpose, the control unit can be provided for controlling the first displacement device such that, after (in particular immediately after) the first shutter element has opened, the telescope assembly can be displaced continuously from the first position into the second position in order to at least partially compensate for a thermal lens effect caused by heating of the crystal assembly (in particular in a laser).

The control unit can control the first shutter element and the first displacement device, wherein control data are stored in a memory of the control unit, and the control unit moves the telescope assembly from the first position to the second position in dependence on these control data immediately after the first shutter element has opened.

Thermal lens effects can cause the beam waist of a laser beam, for example, generated by a laser, to move along the optical axis. This movement leads to a focal width and focal position on the substrate and thus to an intensity variation in the optical system for generating the illumination line. The control unit may be arranged to compensate for this movement such that the width of the illumination line (in particular along the minor axis) and/or the intensity of the illumination line remains substantially constant.

Control data based on simulation data or calibration data describing the temporal relationship of the thermal lens effect may be stored in the memory of the control unit. The control data for controlling the first moving means may be arranged such that they are able to compensate for the thermal lens effect as good as possible.

The at least one telescope assembly may be, for example, a keplerian telescope or a galilean telescope. The telescope assembly may be arranged to output the substantially collimated incident laser beam as a substantially collimated laser beam. In the case of a keplerian telescope, the telescope assembly can consist of two lens groups of positive refractive power, in particular two separate converging lenses. The image-side focus of the first lens group (which is arranged in the beam path upstream of the second lens group) substantially coincides with the object-side focus of the second lens group (at least one possible position of the telescope assembly). In the case of a galilean telescope, the telescope assembly may consist of a first lens group with negative refractive power (which is disposed in the beam path before the second lens group) and a second lens group with positive refractive power. Here, an object-side focal point of the first lens group substantially coincides with an object-side focal point of the second lens group (located in at least one possible position of the telescope component). Thus, a Galilean telescope can be denoted as a beam expander (e.g., a 1:5 beam expander or a 1:5 telescope).

The telescope assembly may be a keplerian telescope, wherein the first lens group and the second lens group have the same focal length. Alternatively, the focal length of the second lens group may be larger than that of the first lens group, wherein the second lens group is arranged in the beam path after the first lens group, so that the laser beam incident into the telescope assembly is output as a widened laser beam. In addition to the telescope assembly, further telescope assemblies can be provided in the beam path before or after the telescope assembly. For example, a further telescope component can be arranged in the beam path after the telescope component, the first and second lens groups of the telescope component having the same focal length, and the further telescope component being a beam-expanding telescope component (for example a 1:5 telescope).

The second lens group can be arranged in the beam path behind the first lens group, wherein the first movement device is provided for moving the first lens group, while the second lens group is fixedly mounted (in particular with respect to the other elements of the beam shaping device, with respect to the laser beam source and/or with respect to the imaging device).

Thus, the first lens group can be moved by the moving means, while the second lens group is held in their position together with the other (optical) elements of the beam shaping means. It has been found that thermal lens effects can be compensated very effectively by moving the first lens group of the telescope assembly.

The control unit may be arranged for moving the first lens group in the direction of the beam path along the optical axis after the first shutter element is opened.

Further, the optical system may have second moving means for moving the imaging means along the optical axis. The imaging means may refer to, for example, a cylindrical focusing lens or a cylindrical objective lens disposed directly in front of the substrate. The control unit may be configured to control the second moving means to move the imaging device simultaneously with at least one of the first lens group and the second lens group.

The movement of the imaging means may be used to compensate for movement of the focal position (relative to the short axis) along the optical axis due to thermal lens effects and/or due to movement of the first movement means. In the memory of the control unit, corresponding control data can be stored, which define the temporal and spatial course of the movement of the first and/or second mobile means. These control data may be obtained based on prior calibration or prior simulation.

The control unit may be arranged for controlling the second moving means to move the imaging means from the first position to the second position continuously, in particular immediately after the first shutter element is opened.

The imaging device is moved in particular from the first position to the second position to compensate for a movement of the focal position of the short axis of the illumination line in the direction of the optical axis, in particular towards the substrate. Such a movement of the focal position may be caused, for example, by a thermal lens effect and/or by a movement of the first movement means. The movement by the second movement means ensures that the focal position in the direction of the optical axis and thus the width (FWHM) and the intensity of the illumination line remain constant in the imaging plane (the plane of the substrate to be illuminated).

The optical system may further comprise a second shutter element arranged in the beam path after the crystal assembly. The control unit may be arranged for controlling the first shutter element and the second shutter element such that the first shutter element is first open and the second shutter element is closed, the second shutter element being open after a predetermined period of time has elapsed.

Thus, in addition to the correction carried out by the first displacement means, it can be ensured that a change in the optical properties of the optical system immediately after the opening of the first shutter element does not have an effect on the illumination line, since the second shutter element is still in the closed state at this time. The second shutter element is only opened when the thermal lens effect "levels" (or stabilizes to a certain extent), and small changes in the thermal lens effect can be equalized by the first moving means in the state in which the second shutter element is opened, or such changes are small enough that they are insignificant to the process.

According to a second aspect of the invention, a method for generating an illumination line is presented. The method includes generating a laser beam along an optical axis; shaping the laser beam such that a beam profile of the laser beam has a major axis and a minor axis; imaging the thus shaped laser beam as an illumination line; and moving at least one of the first lens group or the second lens group of the telescope assembly along the optical axis during generation of the laser beam, wherein the first lens group and the second lens group have refractive power at least with respect to the short axis.

The statements made above with respect to the optical system of the first aspect apply correspondingly to the method of the second aspect. In particular, the method of the second aspect may be performed with the optical system of the first aspect, wherein all details of the first aspect may also be applied to the second aspect as much as possible.

The laser beam source generating the laser beam may comprise a laser resonator, a frequency doubled crystal assembly arranged after the laser resonator in the beam path, and a first shutter element arranged between the laser resonator and the crystal assembly in the beam path. The first lens group or the second lens group may be moved according to an open state of the first shutter element.

The telescope assembly may be continuously moved from the first position to the second position after the first shutter element is opened to at least partially compensate for thermal lens effects due to heating of the crystal assembly.

Thermal lensing causes the beam waist of the laser beam to move along the optical axis. This movement causes compensation for this movement, keeping the width of the illumination line and/or the intensity of the illumination line (in particular the overall intensity distribution or at least the maximum intensity) substantially constant.

Drawings

The invention is further described below with the aid of the accompanying drawings, in which

Fig. 1a, 1b show schematic overview diagrams of the optical system of an apparatus for processing thin-film layers, viewed from different viewing directions;

fig. 2 shows a detail of the laser beam source of the optical system in fig. 1a, 1b, and the movement of the laser beam waist due to thermal lens effect;

FIG. 3 shows a schematic representation of the beam waist shift in the optical system of FIGS. 1a, 1b and the illumination variation of a cylindrical imaging objective associated therewith;

FIG. 4 illustrates the effect of thermal lensing on the intensity and width of illumination lines in the plane of a substrate;

FIG. 5 illustrates the effect of thermal lensing on the intensity and width of illumination lines when an upconversion laser beam is repeatedly turned on and off;

FIG. 6 shows a schematic diagram of the beam path (Gaussian beam propagation) in an optical system according to the present invention;

FIG. 7 illustrates the effect of lens group No. 1 and imaging device No. 5 moving across the width of the illumination line in plane No. 6 for the arrangement of FIG. 6;

FIG. 8 shows a plot of laser beam waist position shift versus time in conjunction with appropriate movement of lens group No. 1 and imaging device No. 5 for the arrangement of FIG. 6; and

fig. 9 shows the timing of controlling the first shutter element and the second shutter element.

Detailed Description

Fig. 1a, 1b show the optical system of an apparatus for processing a film layer and are generally designated by reference numeral 10. Although reference will be made below to optical system 10 of an apparatus for processing thin film layers, the described optical system 10 may be used in any other application where an illumination line is desired. The optical system 10 comprises a beam shaping device 12 arranged to shape the laser beam 14 such that a beam profile 16 of the laser beam 14 has a major axis and a minor axis, and an imaging device 18 located in the beam path of the laser beam 14 after the beam shaping device 12 and arranged to image the thus shaped laser beam 14 as an illumination line 22. Thus, the imaging device 18 produces the short axis of the illumination line 22 from the short axis of the laser beam 14 formed by the beam shaping device 12.

Conventionally, the minor axis in the drawings should be parallel to the x-axis, the major axis parallel to the y-axis, and the optical axis of the optical system 10 parallel to the z-axis. In fig. 1a, the optical system 10 is shown, for example, from above (viewing direction is along the x-direction), while in fig. 1b, for example, from one side (viewing direction is along the y-direction).

The beam-shaping means 12 may for example represent or comprise an anamorphic optical device 42 as shown in fig. 4-6 of DE 102012007601 a 1. In particular, the beam shaping arrangement 12 may comprise one or more of the

components

20, 54, 56, 58, 62, 66, 68, 74 shown in fig. 4-6 of DE 102012007601 a 1.

In other words, the beam shaping device 12 can be described by a first imaging axis x (parallel to the x-axis of the coordinate system), a second imaging axis y (parallel to the y-axis of the coordinate system) perpendicular to the first imaging axis x, and an optical axis z (parallel to the z-axis of the coordinate system) perpendicular to the first imaging axis x and the second imaging axis y. The beam shaping device 12 (e.g., as an anamorphic optic) may have different imaging characteristics with respect to the first and second imaging axes x, y. The beam shaping device 12 may be arranged to generate a laser beam 14 from the laser at a position "16" before the imaging device 18 (see, e.g., fig. 1a, 1b), the beam profile 16 of the laser beam 14 having a major axis y and a minor axis x, wherein the beam profile has a maximally uniform (or substantially uniform) intensity distribution over the major axis y.

In particular, the beam shaping means 12 (in particular as an anamorphic optical device) may comprise (see fig. 1a, 1 b):

a first telescope assembly 20 which is optically effective with respect to the short axis x, i.e. has optical power with respect to the short axis x. The first telescope assembly 20 is composed of a cylindrical lens 23 as a first lens group and a cylindrical lens 24 as a second lens group. The first cylindrical lens 23 receives the laser beam 14 from the laser beam source 26 and focuses it on the first intermediate image 28 with respect to the short axis x. The second cylindrical lens 24 is located after the first cylindrical lens 23 in the beam path and collimates the beam of the first intermediate image 28. As shown in fig. 1b, the first telescope assembly 20 is a 1:1 telescope, which is implemented as a keplerian telescope. Here, the first cylindrical lens 23 and the second cylindrical lens 24 are each a converging lens having substantially the same focal length. The focal point on the image side of the first cylindrical lens 23 substantially coincides with the focal point on the object side of the second cylindrical lens 24.

A cylindrical lens 30, having refractive power with respect to the long axis y, arranged in the beam path after the first telescope assembly 20. The cylindrical lens 30 receives the laser beam 14 from the laser beam source 26 and focuses it onto an intermediate image 32 where the laser beam 14 is unaffected by the first telescope assembly 20 relative to the long axis y.

A cylindrical lens 34, arranged in the beam path after the cylindrical lens 30, having an optical power with respect to the long axis y. The cylindrical lens 34 collimates the light beam of the cylindrical lens 32. As shown in fig. 1a, the cylindrical lens 30 and the cylindrical lens 34 form a keplerian telescope, which is used to expand the laser beam 14 relative to the long axis y.

A second telescope component 36 arranged in the beam path after the cylindrical lens 34, which is optically effective with respect to the short axis x, i.e. has optical power with respect to the short axis x. The second telescope assembly 36 is composed of a cylindrical lens 38 as a first lens group and a cylindrical lens 40 as a second lens group. The first cylindrical lens 38 widens the laser beam 14 relative to the minor axis x and the second cylindrical lens 40 re-collimates the widened laser beam. As shown in FIG. 1b, the second telescope assembly 36 is a beam expanding telescope (e.g., a 1:5 telescope) that is implemented as a Galilean telescope. Here, the first cylindrical lens 38 is a diverging lens and the second cylindrical lens 40 is a converging lens, where the focal points of the first cylindrical lens 38 and the second cylindrical lens 40 substantially coincide or overlap. A virtual second intermediate image (not shown) is created in the beam path before the first cylindrical lens 38.

An anamorphic homogenizing optics 42 arranged in the beam path after the second telescope assembly 36 for homogenizing the laser beam 14 (to the greatest extent) with respect to the long axis y.

A condenser cylindrical lens 44, arranged in the beam path after the anamorphic homogenizing optic 42 and having an optical power with respect to the long axis y, for superimposing the homogenized laser beam on the illumination line 22.

The imaging device 18 is arranged in the beam path after the condenser cylindrical lens 44. The imaging device 18 may for example comprise or represent the component 66 shown in fig. 4 to 6 of DE 102012007601 a 1. In the latter case, the imaging device 18 represents, for example, a focusing cylindrical lens optic 66, which is arranged in the beam path after the condensing cylindrical lens 44, for focusing the laser beam 14 on the illumination line 22 with respect to the short axis x.

Thus, the imaging device 18 arranged after the beam-shaping device 12 picks up the beam profile 16 in front of the imaging device 18 and images the laser beam 14 as an illumination line 22, wherein only the short axis x of the beam profile 16 is (more precisely: only) focused, instead of the homogenized long axis y of the beam profile 16. The imaging device 18 typically images without diffraction limitation, but may also image with diffraction limitation in some embodiments.

Illumination lines 22 produced by optical system 10 may be used for crystallization of thin film layers, such as for fabrication of Thin Film Transistors (TFTs). The illumination lines 22 are applied to the semiconductor layer to be processed and the illumination lines 22 are guided over this semiconductor layer, wherein the intensity of the illumination lines 22 is set such that the semiconductor layer can be melted and re-solidified in a short time to form a crystallized layer with better electrical properties.

As described above, an anamorphic optical assembly is employed to produce the laser beam geometry. The laser beam 14 emitted by the laser beam source 26 is homogenized by means of a cylindrical lens array, for example, in a (long) beam axis y. The other (short) axis x is optically processed as a gaussian beam and the beam waist of the laser beam source 26 is transmitted into the homogenization plane. Fig. 1a, 1b show a typical arrangement and have been described in detail above.

The laser beam 14 is cylindrically broadened (typically by a factor of 2-4) in the axis y to be homogenized and directed to two subsequent lens arrays on top of each other. The uniform long beam axis y occurs at the focal length of the condenser cylindrical lens 44. The waist of the laser beam 14 formed in the laser beam source 26 is recalibrated using the cylindrical 1:1 telescope 20 and widened using another telescope 36 to produce a gaussian mini-beam axis x of the desired width using the focusing objective 18.

Fig. 2 shows a detail of the laser beam source 26 of the optical system 10 in fig. 1a, 1 b. The laser beam source 26 comprises a laser resonator 46 for generating the laser beam 14, which is here, for example, an infrared solid-state laser, in particular a Nd: YAG laser. The laser beam source 26 also comprises a first shutter element 48, which is, for example, an electrically controllable mechanical shutter, arranged in the beam path behind the laser resonator 46 for blocking the laser beam 14 or for letting the laser beam 14 pass through. Laser beam source 26 further includes a converging lens 50 positioned in the beam path after first shutter element 48 for focusing laser beam 14 onto a frequency doubled crystal assembly 52 positioned in the beam path after converging lens 50. Frequency doubling crystal assembly 52 includes an SHG crystal for doubling the frequency of laser beam 14 (or halving the wavelength) and/or a THG crystal for tripling the frequency of laser beam 14.

The laser beam source 26 also includes a converging lens as a re-collimating lens (Rekollimationsiline) 54. The re-collimating lens 54 is adapted to maximize the collimation of the laser beam 14.

One possible way of operating the laser beam source 26 consists in switching on the laser resonator 46 permanently (or at least over a longer period of time, including a plurality of irradiation processes) so that it produces a continuous infrared laser beam 14 that is very constant in time. However, in order to avoid unnecessary permanent exposure of sensitive crystal components 52 (which may cause lifetime limitations due to UV laser generation) and possibly other components of the optical system 10 to (possibly harmful or damaging) laser illumination, the first shutter element 48 is only opened when the illumination line 22 is actually needed to illuminate the substrate. In other words, i.e. when the laser beam 14 happens to be unnecessary, e.g. because of a replacement of the substrate to be irradiated, the laser beam 14 can be switched off by closing the first shutter element 48. In this manner, the duration of exposure of crystal assembly 52 to laser beam 14 may be minimized and the effective lifetime increased.

The above-described mode of operation in which the first shutter element 48 of the laser beam source 26 is opened as desired will be referred to hereinafter as burst mode (burst mode). When it is mentioned below that the laser beam source 26 emits/does not emit the laser beam 14, or that the laser beam source 26 is on/off, it means that the first shutter element 48 is open/closed at this time.

It is important for the application of illumination lines, for example, in lift-off applications (irradiation of a thin film bonded to glass through the glass) and thin-film silicon crystallization applications that the laser beam 14 have a width (FWHM) that remains constant (i.e., constant in time) and a peak intensity.

The use of burst mode can be important in reducing and optimizing laser run time and thus run cost. In a typical lift-off process, the tact time (or cycle time, Tiktzeit) is in the range of 60-100 seconds, for example, for large glass substrates, whereas the laser beam itself only needs about 20-30 seconds for removing the plastic substrate from the glass carrier plate. Unlike the burst mode, in continued operation of the laser beam source 26, the process shutter (see second shutter element 66 described below) is closed and opened, and the laser beam source 26 continues to operate and continue to illuminate the crystal assembly 52.

In burst mode operation, the operation of the UV laser can be reduced from 60-100 seconds to 20-30 seconds, and potentially reduce the operating cost to 1/4-1/2(Faktor 2-4).

If the external (outside the laser resonator 46) frequency doubled laser beam source 26 is operated in burst mode, a thermal lens (refractive index change due to radial temperature characteristics) is formed in the frequency doubling crystal (SHG and THG)52 in the first 10-20 seconds as the pulse sequence begins (i.e., immediately following the opening of the first shutter element 48), which then remains substantially stable until the end of the pulse sequence. The thermal lens results in the generation of a laser beam waist that optically characterizes the laser beam 14 at another location of the laser (beam quality, location, beam waist diameter, and divergence angle). The beam position can vary here from a few centimeters to half a meter or even more, depending on how the focusing of the IR laser beam 14 in the frequency doubled crystal assembly 52 is designed. Fig. 2 shows how the position of the beam waist travels from position 56 to position 58 after about t 10-20 seconds immediately after the start of the pulse sequence (t 0, first shutter element 48 is open). At position 58, the optical system 10 and in particular the thermal lens formed is in thermal equilibrium, the position of the beam waist not changing significantly with the first shutter element 48 still open.

The virtual origin (waist) of the emitted laser beam 14 is moved by the thermal lens (particularly in the z direction along the optical axis).

The change in beam waist position has substantially no effect on the long beam axis y to be homogenized.

But the small beam axis x of the resulting beam bundle is propagated with a gaussian beam, and therefore the waist location in the laser beam source 26 has an effect on the beam waist in the focal spot of the objective lens 18.

Typically, in the beam arrangement as shown in fig. 1a, 1b, a line width (full width at half maximum) of 10-100 μm FWHM is generated (along the minor axis x). For this purpose, the laser beam is transmitted optically in the 1:1 telescope (first telescope assembly 20) and then widened 1:1 to 1:5 in the further telescope (second telescope assembly 36). The laser beam 14 is focused in the homogenized plane by means of a cylindrical objective 18 (see fig. 3, in which the assembly according to fig. 1b is shown).

The components are arranged such that a change in the beam waist position has virtually no effect on the position of the focal point behind the focusing lens 18 within a set depth of field. But in principle the position of the focal spot (along the optical axis z) is shifted. However, the variation in the position of the beam waist in the laser beam source 26 has a significant effect on the illumination of the cylindrical focusing objective 18 (imaging device 18). For gaussian beam propagation, the following formula holds for the focal spot diameter:

d(1/e²)＝4fλM²/(πD(1/e²))。

here, D is the focal diameter, and D is the diameter (1/e) of the laser beam 14 on the imaging device 18²) F is the focal length, M²Is the beam mass number of the laser beam 14 and λ is the wavelength.

If the diameter D on the focusing objective lens 18 is made smaller by moving the beam waist (see fig. 2 and 3), the focal point diameter D becomes larger. As a result, the peak intensity of the gaussian distribution in the plane of the illumination line 22 decreases.

This phenomenon has been observed in the optical system according to fig. 1a, 1b from the laser beam 14 of the laser beam source 26. With the pulse sequence switched on (first shutter element 48 open), a focus can be observed, which increases by about 10% in width d, typically 10-20 seconds. The width and intensity of the focal spot is then stabilized.

This phenomenon is a result of the thermal lens generated in the crystal assembly 52 and is shown in fig. 4. At time t, 720 seconds, first shutter element 48 is open and laser beam source 26 generates laser beam 14. As can be seen from the upper curve (intensity, left scale) in fig. 4, the initial intensity of the illumination line 22 drops from a maximum value in about the first 10 seconds to a value at which the maximum degree remains constant during the subsequent illumination (first shutter element 48 remains open). Similarly, the width along the minor axis x of the illumination line 22 (lower curve, FWHM, right scale) is an initial value when the laser beam 14 is switched on, and then rises to a value that remains maximally constant during subsequent illumination in about the first 10 seconds.

As shown in fig. 5, the above-described behavior of the illumination line 22 is reproducible and will occur when the laser beam source 26 is repeatedly turned on and off, i.e., the first shutter element 48 is repeatedly turned on and off (in a repeated burst mode).

The crystal assembly 52 in the laser beam source 26 is actively stabilized at the nominal temperature to effectively tune the frequency conversion (index of refraction adjustment). Slightly different balance values can be aligned for different burst mode-sequences.

According to the invention, the optical system 10 further comprises first displacement means 60 (see e.g. fig. 1a, 1b) adapted to reduce the above-mentioned effects of variations in the intensity and width (FWHM) of the illumination line 22, and preferably to compensate completely.

In other words, according to the invention, the 1:1 telescope (first telescope component 20) and/or the 1:1 … 5 telescope (second telescope component 36) are specifically detuned in order to compensate for the beam waist position variations described above in such a way that the peak intensity and the beam width on the substrate (i.e. in the plane of the illumination line 22) do not change or only change very slightly (for example < 1%).

In the examined embodiment, it is shown that the first telescope assembly 20(1:1 telescope) is particularly suitable for this. In a particular arrangement, a 0.1-0.2mm adjustment is sufficient. Since the temporal relationship of the beam waist position change is reproducible for a particular burst mode-sequence, the time-dependent adjustment of the fixed adjustment of the first lens group 23 (i.e. the converging lens 23 positioned closer to the laser beam source 26 in the arrangement of fig. 1a, 1b) is used with the start of the pulse sequence (i.e. with the opening of the first shutter element 48). A linear drive or, for example, also a piezo drive is suitable as first displacement device 60.

The movement of the focal point with respect to the short axis x after focusing the objective lens 18 is typically 20-100 μm along the optical axis z, which is part of the typical depth of field. In principle, however, it is also possible to move the imaging device 18 (focusing objective 18) simultaneously, likewise by means of the second displacement device 62.

Fig. 6 shows gaussian beam propagation in the actual beam path. The beam diameter and the focal position can be determined for the respective waist start positions in the laser beam source 26 by means of beam propagation.

Fig. 7 illustrates the adjustment of the cylindrical lens 38 to compensate for the change in beam waist, with the associated adjustment of the imaging device 18 for the configuration shown in fig. 6. When the depth of field is not significantly greater than the adjustment amount, it may be necessary to move the imaging device 18 at the same time. Depth of field range the beam quality (number of dimensions M) of the laser beam 14²) Or by possible processing/reduction of the beam quality by the beam-switching optics.

Fig. 7 shows in detail the appropriate change of position of the first cylindrical lens 23 of the first telescopic mirror assembly 20 ("telescopic lens shift", right scale). The appropriate change in position of the imaging device 18 is also shown ("focus lens shift", right scale). Fig. 7 also shows the resulting full width at half maximum ("FWHM") of the illumination line 22 relative to the minor axis x, where it can be seen that this value remains substantially constant and thus enables an almost complete compensation of the thermal lens effect.

Fig. 8 shows the same variation of the first telescopic mirror assembly 20 and the imaging device 18 as in fig. 7, and additionally shows the variation of the beam waist position ("waist position in laser", left scale).

Thus, according to the invention, as soon as the laser beam source 26 is switched on, i.e. as soon as the first shutter element 48 of the laser beam source 26 is opened (or immediately), the associated first displacement device 60 displaces at least one of the

cylindrical lenses

23, 24, 38 and 40 along the optical axis z. It has proven advantageous here to move the first cylindrical lens 23 of the first telescopic mirror assembly 20, alternatively or additionally one of the

cylindrical lenses

24, 38 and/or 40 can also be moved in a similar manner.

Further, the movement of the imaging device 18 by the second moving device 62 is described in the above-described examples of fig. 7 and 8, but the movement is optional.

In order to control the movement of the first displacement device 60 and, if appropriate, the second displacement device 62, a control unit 64 is provided (see fig. 1a, 1 b). The control unit 64 is responsible for controlling the laser beam source 26 in addition to controlling the movement of the respective moving means 60, 62. More specifically, the control unit 64 controls the timing of turning the laser beam source 26 on and off or the timing of turning the first shutter element 48 on and off. An optional second shutter element 66, which will be described below, may also be controlled by the control unit 64.

The control unit 64 includes a memory in which control data is stored, and the first moving device 60 (and the second moving device 62, if necessary) performs movement of the first cylindrical lens 23 (and the imaging device 18, if necessary) in accordance with these control data. In particular, data defining the timing of movement of each

mobile device

60, 62 may be backed up. Accordingly, the data stored in the memory of the control unit 64 may represent the curves shown in fig. 7 and 8, which describe the position of the first cylindrical lens 23 with respect to time. The same is true for the curve describing the position of the imaging device 18 versus time.

The control data may be obtained based on prior calibration or may be obtained by calculation and/or simulation, as described in connection with fig. 6.

In particular, the control unit 64 may be arranged to move the first cylindrical lens 23 (in particular immediately after the first shutter element 48 opens) according to a predetermined position-time relationship. Optionally, the control unit 64 is arranged for moving the imaging device 18 (in particular immediately after the opening of the first shutter element 48) according to a predetermined position-time relationship.

Furthermore, the control unit 64 may also control other functions and/or elements of the optical system 10 or the device comprised by the optical system 10.

In addition to the above-described technique of moving the lens of one of the

telescope assemblies

20, 36, the optical system 10 may optionally further comprise a second shutter element 66 (see fig. 1a, 1b) according to an embodiment of the present invention. Second shutter element 66 is located anywhere in the beam path after the crystal assembly, such as directly after laser beam source 26. The second shutter element 66 is controlled by the control unit 64.

More precisely, the control unit 64 is provided for controlling the first shutter element 48 and the second shutter element 66, first with the first shutter element 48 open and the second shutter element 66 closed; after a predetermined period of time (e.g., in the range of 10-20 seconds) has elapsed, second shutter element 66 opens. This sequence ensures that a strong change in the waist position immediately after the laser beam source 26 is switched on (i.e. immediately after the first shutter element 48 is opened) does not lead to a strong change in the beam intensity or beam width of the illumination line 22, since at the time of this strong initial change (for example within the first 10 seconds after the first shutter element 48 is opened) the second shutter element 66 remains closed and no illumination line 22 is produced at this time. Until after the thermal lens effect has stabilized to a certain extent, the second shutter element 66 is not opened and the illumination line 22 is produced, the intensity and width of which remain constant to the greatest extent. Corresponding to the above description, slight variations that may occur in the beam waist position after the predetermined period of time may be compensated by the movement of the first moving device 60 and, if necessary, the second moving device 62.

Fig. 9 illustrates the above-described technique employing the second shutter element 66. The intensity of the illumination line 22 is plotted against time. For greater clarity, fig. 9 also shows the intensity of illumination line 22 when second shutter element 66 is closed and therefore does not produce illumination line 22 at all. The intensity shown at this time is the intensity that the illumination line 22 would have if the second shutter element 66 was open.

Fig. 9 shows a time period 68 in which the laser beam source 26 is switched on, i.e. in which the first shutter element 48 is open. During this time the intensity initially reaches a maximum and then drops off sharply during the first 10-20 seconds until a substantially steady state is reached, see also fig. 4 and 5. However, as shown by time period 70, at the beginning (for a predetermined time period 72 after the first shutter element 48 is opened) the second shutter element 66 is still in a closed state and no illumination line 22 is generated. Until after time period 72, second shutter element 66 (process shutter) does not open and produce illumination line 22 in time period 74. Fluctuations in the intensity and/or width (FWHM) of the illumination line 22 will be compensated for by moving the at least one

lens group

23, 24, 38, 40 of the at least one

telescope assembly

20, 36 as described in detail above.

It is also possible in one example to not provide the first and second moving means 60, 62 and to compensate for the thermal lens effect only by controlling the second shutter element 66, as already described in connection with fig. 9.

The above-described technique offers the possibility of compensating for thermal lensing and in particular the movement of the beam waist of the laser beam 14 associated therewith in a reliable, simple and reproducible manner. In this way, the substrate can be irradiated with a constant intensity and a constant beam width, so that stable material properties and thus better material quality are obtained.

The drawings or portions thereof are not necessarily to scale. In particular, the minor axis x of the beam profile 16, for example in FIG. 1b, appears to be longer than the major axis y in FIG. 1 a.

In the drawings, the same reference numerals are used for the same elements or elements functioning in the same manner unless otherwise specified. Furthermore, the features shown in the figures may also be combined arbitrarily.

Claims

1. An optical system (10) for producing an illumination line (22), comprising:

-a laser beam source (26) for generating a laser beam (14) along an optical axis (z);

-a beam shaping device (12) arranged for shaping the laser beam (14) such that a beam profile (16) of the laser beam (14) has a major axis (y) and a minor axis (x); and

-imaging means (18) arranged after said beam shaping means (12) in the beam path of said laser beam (14) for imaging the thus shaped laser beam (14) as an illumination line (22);

wherein the beam shaping device (12) has at least one telescope assembly (20), which telescope assembly (20) comprises a first lens group (23) and a second lens group (24), wherein the first lens group (23) and the second lens group (24) have a refractive power at least with respect to the minor axis (x);

the optical system (10) comprises first moving means (60) for moving at least one of said first and second lens groups along an optical axis (z); and

the optical system (10) further comprises a control unit (64), the control unit (64) being arranged for controlling the first moving means (62) for moving at least one of the first lens group and the second lens group when the laser beam source (26) generates the laser beam.

2. The optical system (10) according to claim 1, wherein the laser beam source (26) comprises a laser resonator (46), a frequency-doubled crystal assembly (52) located after the laser resonator (46) in the beam path, and a first shutter element (48) arranged between the laser resonator (46) and the crystal assembly (52) in the beam path, and

the control unit (64) is provided for controlling the first movement means (60) in dependence on the open state of the first shutter element (48).

3. The optical system (10) according to claim 2, wherein the control unit (64) is arranged for controlling the first moving means (60) such that the telescopic mirror assembly (20) is continuously movable from a first position to a second position after the first shutter element (48) is opened to at least partially compensate for a thermal lens effect caused by heating of the crystal assembly (52).

4. Optical system (10) according to claim 3, wherein the thermal lens effect causes a beam waist of the laser beam (14) to move along an optical axis (z), and the control unit (64) is arranged for compensating such a movement such that a width of the illumination line (22) and/or a maximum intensity of the illumination line (22) remains substantially constant.

5. The optical system (10) according to any one of claims 2 to 4, wherein the at least one telescope assembly (20) is a Keplerian telescope or a Galilean telescope, and

the telescope assembly (20) is arranged to output a substantially collimated incident laser beam as a substantially collimated laser beam.

6. The optical system (10) according to claim 5, wherein the telescope assembly (20) is a Keplerian telescope and the first lens group (23) and the second lens group (24) have the same focal length, or

The second lens group (40) is disposed behind the first lens group (38) in the beam path, and the focal length of the second lens group (40) is larger than that of the first lens group (38), so that the laser beam incident into the telescope assembly (36) is output as a widened laser beam.

7. The optical system (10) according to any one of claims 2 to 6, wherein the second lens group (24) is disposed after the first lens group (23) in a beam path;

the first moving means (60) is provided for moving the first lens group (23); and

the second lens group (24) is fixedly mounted.

8. The optical system (10) according to claim 7, wherein the control unit (64) is arranged for moving the first lens group (23) in the direction of the beam path along the optical axis (z) after the first shutter element (48) is opened.

9. The optical system (10) according to any one of claims 2 to 8, further comprising:

second moving means (62) for moving the imaging means (18) along the optical axis (z);

wherein the control unit (64) is arranged for controlling the second moving means (62) to move the imaging means (18) simultaneously with at least one of the first lens group and the second lens group.

10. The optical system (10) according to claim 9, wherein the control unit (64) is arranged for controlling the second moving means (62) to continuously move the imaging device (18) from the first position to the second position after the first shutter element (48) is opened.

11. The optical system (10) according to any one of claims 2 to 10, further comprising:

a second shutter element (66) disposed in the beam path after the crystal assembly (52);

wherein the control unit (64) is provided for controlling the first shutter element (48) and the second shutter element (66) such that the first shutter element (48) is first opened and the second shutter element (66) is closed, and after a predetermined period of time has elapsed, the second shutter element (66) is opened.

12. A method for producing an illumination line, comprising:

-generating a laser beam (14) along an optical axis (z);

-shaping the laser beam (14) such that a beam profile (16) of the laser beam (14) has a major axis (y) and a minor axis (x);

-imaging the laser beam (14) thus shaped into an illumination line (22); and

-moving at least one of a first lens group (23) or a second lens group (24) of a telescope assembly (20) along an optical axis (z) during generation of the laser beam (14), wherein the first lens group (23) and the second lens group (24) have a refractive power at least with respect to the minor axis (x).

13. The method according to claim 12, wherein the laser beam source (26) generating the laser beam (14) comprises a laser resonator (46), a frequency-doubled crystal assembly (52) arranged in the beam path after the laser resonator (46), and a first shutter element (48) arranged in the beam path between the laser resonator (46) and the crystal assembly (52), and

the first lens group (23) or the second lens group (24) moves according to an open state of the first shutter element (48).

14. The method according to claim 13, wherein the telescope assembly (20) is continuously moved from the first position to the second position after the first shutter element (48) is opened to at least partially compensate for a thermal lens effect caused by heating of the crystal assembly (52).

15. The method of claim 14, wherein the thermal lens effect causes a beam waist of the laser beam (14) to move along an optical axis (z), and wherein such movement causes compensation for such movement such that a width of the illumination line (22) and/or a maximum intensity of the illumination line (22) remains substantially constant.