WO2009036716A1

WO2009036716A1 - Method and arrangement for producing a laser beam with a linear beam cross section

Info

Publication number: WO2009036716A1
Application number: PCT/DE2008/001181
Authority: WO
Inventors: Michael Stopka
Original assignee: Coherent Gmbh
Priority date: 2007-09-17
Filing date: 2008-07-18
Publication date: 2009-03-26
Also published as: CN101801586A; DE102007044298B3; JP2011501872A; KR20100065326A; CN101801586B; KR101529344B1; JP5548127B2

Abstract

A description is given of a method and an arrangement for producing a laser beam with a linear beam cross section, which has a long and a short cross-sectional beam axis and has an extent in the long axis of at least 200 mm and an extent in the short axis of at most 800 µm, wherein the laser beam emerging from a laser beam source is homogenized separately with respect to the long axis and the short axis, in that the laser beam is homogenized both in relation to the long axis and in relation to the short axis while respectively producing a focal plane, into which there are focused in each case a multiplicity of partial beams which have been created by dividing up the beam cross section of the laser beam and which are subsequently brought together to form a laser beam homogenized in the beam cross section, and the laser beam undergoes telecentric imaging, at least with respect to the long axis, i.e. the laser beam homogenized with respect to the long axis is projected by means of a condensing optical system (LACL) in such a way as to produce a path of rays that can be assigned to the projected laser beam, comprising partial beams of parallel light oriented longitudinally in relation to the direction of propagation. The invention is characterised by the following method steps: projecting the beam cross section that is converging in a homogenizing manner in the short axis by means of a first condensing optical system (SACL1) to produce a homogeneous image field (HFSA1) and producing a first pupil (P1) by means of a first field-lens optical system (SAFL1), into which the focal plane, in which the partial beams divided up with respect to the short axis are focused, is projected and projecting the homogeneous image field (HFSA1) by means of a second condensing optical system (SACL2) in a second image field (HSFA2) as well as projecting the first pupil (P1) by means of a second field-lens optical system (SAFL2) in a second pupil (P2), which corresponds to the entrance pupil of an imaging optical system (p-lens SA) for the telecentric imaging of the laser beam on an imaging plane, onto which the laser beam homogenized with respect to the long axis is projected by means of the condensing optical system (LACL).

Description

Method and arrangement for generating a laser beam with a linear

Beam cross section

Technical area

The invention relates to a method and an arrangement for producing a laser beam having a linear beam cross section, which has a long and a short beam cross-sectional axis and has a long axis extent of at least 200 mm and a short axis extension of at most 800 μm, in which the laser beam emerging from a laser beam source is homogenized separately with respect to the long axis and the short axis, by the laser beam both relative to the long and the short axis forming a respective fissure plane into each of a plurality of partial beams into which the beam cross section the laser beam is separated, is focused, which are subsequently merged to form a homogenized in the beam cross section laser beam. The laser beam is telecentrically imaged at least with respect to the long axis, i. H. the laser beam homogenized with respect to the long axis is imaged by means of a condenser optics in such a way that a beam path which can be assigned to the imaged laser beam and consists of partial beams oriented parallel to the propagation direction is formed,

State of the art

Methods and arrangements of the aforementioned type are used for some time in the industrial production of TFT (thin film transistor) technology based flat screens. One of the measures to be taken is to provide a polycrystalline as large as possible surface Silicon layer, on the basis of which a plurality of arrayed thin-film transistors is processed in the further. To produce the polycrystalline silicon layer, a substrate is coated with amorphous silicon, which is converted by means of a laser-assisted exposure method by controlled local, light-induced heating in polycrystalline silicon by means of a brief melting process. Excimer lasers, for example XeCl lasers, which are able to emit light in the ultraviolet spectral range, which is largely completely absorbed by silicon, are used for such exposure methods known from the literature in a manner known per se, resulting in thermal heating leading to the melting of the amorphous silicon an associated recrystallization of the amorphous silicon in polycrystalline silicon is made possible. In this context, often spoken by ELA (Excimer Laser Annealing). In order to briefly deposit a required energy density for the melting process on the surface of the substrate coated with amorphous silicon by means of a laser beam and at the same time meet the requirements of industrial production, it proved to be expedient to use the laser beam emerging from an excimer laser in a laser beam line cross-sectional shape, for example, with a line length of 370 mm and a line width of 400 .mu.m, which is scanned in this form in a controlled manner for local short-term melting of the amorphous silicon layer over the entire, coated with amorphous silicon substrate surface, scanned or scanned.

In a particularly advantageous manner, for such a homogeneous recrystallization of a correspondingly shaped laser beam with a pronounced homogeneity in the distribution of the light intensity both along the long and along the short axis of the rectangular line beam cross section required. Moreover, it is advantageous to form the beam profile with respect to the light intensity distribution along the short axis with large steepness on both sides, so that the light intensity is approximated as close as possible to a rectangular profile to be regarded as an ideal with respect to the short beam cross-sectional axis The beam intensity plateau reaches with the plateau value up to the lateral flanks and drops steeply at the flanks.

Representative of a related art, reference is made to US 2005/0035103 A1, in which a notable summary of the current state of the art with respect to ELA method can be found and from the particular reference to their Figure 1 an excimer laser arrangement with an optical arrangement arranged in the beam path according to ordered and also beam-shaping optical arrangement for generating a laser beam with a linear beam cross-section in the aforementioned sense is shown. Thus, a telephoto arrangement helps to adapt the rectangular beam cross section emerging from the excimer laser to the input aperture of a homogenizer in the beam path which is capable of separately homogenizing the laser beam rectangular in the beam cross section relative to its short and also long beam cross section axis with respect to the light intensity distribution. First, the laser beam passes through a so-called long axis homogenizer, which consists of a first arrangement of parallel cylindrical lenses and this in the beam path downstream of a second array of parallel cylindrical lenses, the focal points or lines of the cylindrical lenses of the first arrangement between the first and second Arrangement of

Cylinder lens arrangements are. Downstream of the cylindrical lens arrangements in the beam path, a condenser lens is provided for imaging the beam cross-section which is rectangular in the long axis. The following is a short axis homogenizer, which also provides a first arrangement of mutually parallel cylindrical lenses, followed in the beam path of a second array of parallel aligned cylindrical lenses, the axes of the cylindrical lenses of the short axis homogenizer are oriented orthogonal to the cylindrical lens axes of the long axis homogenizer. Likewise with the long-axis homogenizer, the focal points or lines of the respective first arrangement of cylindrical lenses are also located between the two cylindrical lens arrangements in the case of the short-axis homogenizer. For further illustration of the short axis Homogenized beam cross section, a condenser lens and a field lens are subsequently provided, which image the beam cross section, which is homogenized in the short axis, into the region of a slit lens. Finally, an optical magnifying glass arrangement ensures a reduction in the beam cross-sectional shape in the short axis, and ultimately the laser beam, which is now linearly formed and homogenized in the beam cross section, is imaged onto the substrate surface coated with amorphous silicon. Further details can be found in the aforementioned US 2005/0035103 A1. In addition, the publications US 2006/0209310 A1 and US 2007/0091978 A1 may also be mentioned, in which exemplary embodiments for the optical laser beam homogenization with subsequent transfer of the laser beam into a laser beam with a linear beam cross section are to be taken, which, however, compared to the aforementioned US 2005 / 0035103 A1 reveal no fundamental changes.

In an effort to increase the line shape of the beam cross-section along its long axis, ultimately also for reasons as large as possible, befilmte with amorphous silicon substrate surfaces to edit economically by way of ELA method, arises increasingly the problem of field curvature due to different Focus depths leads to a blurred image along the laser line, the degree of blurring increases with increasing distance from the center of the image to the image edge areas. Moreover, this aberration is even more evident when the depth of field of the imaging system is approximately of the same or smaller magnitude as the positional shift of the focal points caused by the field curvature, especially in the image border areas, compared to the focal position in the center of the image. If, however, a telecentric image is used to image the laser beam along its long axis, ie the partial beams which can be assigned to the laser beam are directed parallel to one another after passing through the condenser optics downstream of the long axis homogenizer, then it is possible to disadvantageously form the ones forming with respect to the long axis Appearance occurring imaging error due to the field curvature to minimize. such Optical structures for the realization of long-dimensioned laser lines with line lengths of typically 450 mm and more, however, require for the realization of telecentric imaging optics, large distances between the long-axis homogenizer and the Langachsenkondensoroptik. However, this raises problems in the imaging of the laser beam along its short axis, it is true over the entire line length of the laser beam along the short axis as close as possible to an ideal rectangular profile approximated light intensity distribution, ie to realize a profile with a possible defined half line width and a pronounced edge steepness ,

Presentation of the invention

The invention has for its object to provide a method for producing a laser beam with a linear beam cross section, which has a long and a short beam cross-sectional axis and an extension in the long axis of at least 200 mm, preferably more than 400 mm, and an extension in the short Axial of at most 800 microns, preferably 400 .mu.m, in which the emerging from a laser beam source laser beam is homogenized separately with respect to the long axis and the short axis by the laser beam both relative to the long and the short axis to produce a respective Fokiebene, in in each case a plurality of partial beams, in which the beam cross section of the laser beam is separated, is focused, which are subsequently combined to form a homogenized in the beam cross section laser beam and the laser beam at least with respect to the long axis undergoes a telecentric imaging, ie with respect to the lan gen axis homogenized laser beam is imaged by means of a condenser optics such that a the laser beam imaged beam path consisting of longitudinally oriented to the propagation direction partial beams of parallel light, such that the beam profile along the short axis despite the large imaging distances with a sharp as possible drawn rectangular profile, ie can be mapped to a mapping plane with the greatest possible edge steepness and a defined line half-width. In particular, it is necessary to take optical measures that allow a largely independent variation of the Beam profile with respect to the short axis in terms of edge steepness and line half-width along the entire length of the linear laser beam cross-section can be made. Furthermore, it is necessary to provide a corresponding arrangement for generating a laser beam, which corresponds to the requirements described above.

The solution of the problem underlying the invention is specified in claim 1. A solution according to the invention is the subject of claim 6. The invention further advantageous features forming the subject of the invention are the subject of the dependent claims and the further description, in particular with reference to the exemplary embodiments.

According to the solution, a method for generating a laser beam with a linear beam cross section according to the features of the preamble of claim 1 is characterized in that in the beam path for beam shaping and beam imaging of the laser beam cross section in the short axis at least two-stage optical imaging is performed with the one hand, a spatial Bridging the caused by the telecentric beam guidance long distance between the Kurzachsenhomogenisierer and an imaging plane is made possible, in which preferably is provided with the amorphous Si layer substrate, and on the other hand, an independent adjustment for the slope and line half width is created.

According to the solution, the two-stage imaging is realized by two optical imaging branches arranged one after the other in the beam path, of which the first optical imaging branch consists of the cylindrical lens arrangements of the short axis homogenizer, a subsequent short axis condensing optics and a short axis field lens optical system following the beam path. Here, the individual optical units are coordinated and arranged so that on the one hand the Kurzachsenkondensoroptik generates a homogeneous image field and on the other hand, the subsequent field lens optics which is sharply imaged between the two cylinder arrangements of the Kurzachsenhomogenisierers Foci into which the partial beams separated with respect to the short axis are imaged in the form of a line array are imaged in a first pupil plane.

The second imaging branch, which is arranged downstream of the first imaging branch in the beam path, images the homogeneous image field generated in the context of the first homogeneous branch into a second homogeneous image field by means of a second condenser optic, wherein at the same time the foci of the short axis homogenizer depicted in the first pupil by means of a second field lens optic is imaged in a second pupil, which corresponds to the entrance pupil of an imaging optics for telecentric imaging of the laser beam onto an imaging plane, to which at the same time the homogenized with respect to the long axis laser beam is imaged by means of Langachsenkondensoroptik. Thus, the second imaging branch consists exclusively of a Kurzachsenkondensoroptik and a short-axis field lens optics.

It has been recognized that the separate mapping in both optical branches, each having a condenser optics and a field lens optics, the prerequisite is created to vary the beam profile of the short axis with respect to the edge steepness and the line half-width separately. to optimize specifically. This can, as the further embodiments will show, be achieved by axial displacement of the individual condenser and / or field lens optics associated with the optical imaging branches. In addition, a rotation of an optics contained along the imaging branches opens at least an influence on the line half-width.

The solution according to the concept as well as a concrete arrangement along the imaging beam path arranged optical elements will be described below with reference to the embodiments. Brief description of the invention

The invention will now be described by way of example without limitation of the general inventive idea by means of embodiments with reference to the drawings. Show it:

1 beam path with optical elements for illustrating the imaging of the laser beam cross-section with respect to the short axis,

2 optical path with optical elements to illustrate the image of the laser beam with respect to the long axis,

3a, b show diagrams illustrating the separate adjustability of the edge steepness and line half width with respect to the short axis.

Ways to carry out the invention, industrial usability

In Fig. 1, the beam path for illustrating the beam forming and beam imaging of a laser beam with respect to its short axis for the purpose of generating a line beam cross section with a line length, i. with a maximum extension along the long axis of more than 200 mm, preferably greater than 450 mm, and a maximum line width of 800 microns, preferably 400 microns shown. FIG. 2, which shows only a view rotated by 90 ° relative to the beam path according to FIG. 1, illustrates the beam shaping along the long axis. Furthermore, reference can be made to both figures at the same time.

Let it be assumed that the laser beam L emerging from an excimer laser is matched to the input aperture of a homogenizer H composed of a long-axis LAH and a short-axis homogenizer SAH by means of suitable imaging optics, for example a telephoto lens.

The beam path illustrated in FIGS. 1 and 2 provides a beam direction from left to right to the so-called long-axis homogenizer Cylinder lens arrangement LAH1 and LAH2 before. Together with the long-axis condenser lens LACL they form an afocal optical system and represent a telecentric imaging optics, the laser beam homogenized in the long beam cross-sectional axis after passing through the long-axis condenser lens LACL parallel to the optical axis and parallel to the image plane HFLA, in the example to be exposed , disposed with substrate coated with amorphous silicon, generates an image field homogenized in the long axis. In addition, due to the telecentric imaging along the long axis, the image aberrations resulting from field curvature can be suppressed at least very greatly. Thus, the long-axis condenser lens LACL is placed at a distance from the cylindrical lens arrangement of LAH2 and LAH1, so that each sub-beam separated by this long-axis homogenizer results in a parallel sub-beam after the condenser lens, with all the parallel sub-beams superimposed in the imaging plane HFLA.

Due to the chosen optical focal lengths of the above-described long-axis optical elements, the distance d is typically 3 meters or more in length, a relatively large distance to be bridged to the HFLA imaging plane to image the beam cross-section to be homogenized in the short axis. For this purpose, the Langachshomogenisierer LAH the so-called short axis homogenizer SAH, consisting of a first cylindrical lens SAH1 and a second Zylinderlinsenanordnung SAH2 downstream, where it is provided to Längsachshomogenisierer a lying between two cylindrical lens assemblies SAH1 and SAH2 Fokiebene, in which by the first Zylinderlinsenanordnung SAH1 divided into partial beams short beam cross section is focused in the form of a spot or line array.

The short-axis homogenizer is followed by a short-axis condenser lens SACL1, by means of which an image field HFSA1 homogenizing forming along the short beam cross-sectional axis is generated. The homogenized Image field HFSA1 has a largely rectangular-shaped beam profile in the short axis, which is to be further imaged in the image plane HFLA. A short axis field lens SAFL1 is provided in the beam path upstream of the homogenized image field HFSA1, by which a pupil P1 is defined, in which the focus plane lying between the two cylindrical lens arrangements SAH1 and SAH2 of the short axis homogenizer is sharply imaged. The optical components described above with respect to the imaging of the short axis homogenized laser beam profile, namely SAH1, SAH2, SACL1 and SAFL1 form the so-called first imaging branch I, which is used to generate the homogenized image field HFSA1.

The second optical imaging branch II following in the beam path has only a second short-axis condenser lens SACL2 and a second short-axis field lens SAFL2 following in the beam path. Here, the second short-axis condenser lens SACL2 is used to image the first homogeneous image field HFSA1 and the generation of a second homogeneous image field HFSA2 in a spatial plane along the beam path, in which a slot-shaped diaphragm arrangement is preferably mounted. The slot size is usually larger than the actual beam cross section of the homogeneous image field HFSA2. The second short-axis field lens SAFL2, on the other hand, forms the pupil P1 into the pupil P2, which at the same time corresponds to the entrance pupil of an imaging optics p-lens SA. Typically, the imaging optics consists of a reduction optics with which the short axis of the laser beam cross-section, for example, is zoomed down onto the imaging plane HFLA in a fivefold manner.

Of very significant importance is the provision of a respective condenser lens and a field lens within the two above-mentioned two optical imaging branches I and II, whereby the possibility is created that form within the homogeneous image fields HFSA1 and HFSA2 almost rectangular shaped beam profiles in the short axis whose edge steepness and line half width can be influenced separately from each other. Thus it could be shown that by axially shifting the field lens position, In particular, the short-axis field lens SAFL2 within the second imaging branch along its optical axis, a variation of the line half width can be achieved with a constant or almost constant edge steepness. This is shown in FIG. 3 a, along whose ordinate light intensity values and along their abscissa deflection paths in mm are plotted. The three graphs shown in the diagram represent, starting from a normal position 1, the light profile on displacement of the short-axis field lens SAFL2 by 20 mm to the right (see graph 2) and 20mm to the left (see graph 3 relative to the normal position). It turns out that in all three positions, the edge steepness of the beam profile remains largely the same, despite variation of the line half-width.

In contrast, by axially displacing the short-axis condenser lens SACL2, it is possible to change the edge steepness while the line half width remains constant. This can be seen from the diagram according to FIG. 3b, whose axis dimensioning is identical to that according to the diagram in FIG. 3a. Here, too, the three different beam profile profiles differ by a different axial position of the short-axis condenser lens 2.

LIST OF REFERENCE NUMBERS

LAH long axis homogenizer

LAH1 First cylindrical lens arrangement of the long axis homogenizer

LAH2 Second cylindrical lens arrangement of the long axis homogenizer

SAH short axis homogenizer

SAH1 First cylindrical lens arrangement of the short axis homogenizer

SHA2 Second cylindrical lens arrangement of the short axis homogenizer

SACL1 short-axis condenser lens

SAFL1 short-axis field lens

HFSA1 First homogeneous image field with respect to the short axis

P1 first pupil

LACL long-axis condenser lens

SACL2 short-axis condenser lens

SAFL1 short-axis field lens

HFSA2 Second homogeneous image field with respect to the short axis

P2 Second pupil p-lens SA reduction optics,

HFLA image plane

H homogenizer

Claims

claims

A method of producing a laser beam having a linear beam cross section having a long and a short beam cross-sectional axis and having a long axis extension of at least 200 mm and a short axis extension of a maximum of 800 μm using a laser beam source emanating laser beam separately with respect to the long axis and the short axis is homogenized by the laser beam both relative to the long and the short axis to produce a respective Fokiebene, in each of which a plurality of partial beams, in which the beam cross section of the laser beam is separated which are subsequently combined to form a laser beam homogenized in the beam cross section, and the laser beam undergoes a telecentric imaging at least with respect to the long axis, i. H. the laser beam homogenized with respect to the long axis is imaged by means of a condenser optic (LACL) in such a way that a beam path which can be assigned to the imaged laser beam and consists of partial beams oriented parallel to the propagation direction is formed, characterized by the following method steps:

Imaging the beam cross-section homogenizingly converging in the short axis by means of a first condenser optics (SACL1) for generating a homogeneous image field (HFSA1) and generating a first pupil (P1) by means of a first field lens optic (SAFL1) into which the foci into which the reference plane are focused on the short axis split partial beams, is mapped, and

Imaging the homogeneous image field (HFSA1) by means of a second condenser optics (SACL1) into a second image field (HSFA2) and imaging the first pupil (P1) by means of a second field lens optic (SAFL2) into a second pupil (P2) corresponding to the entrance pupil of an imaging optic ( p-lens SA) for telecentric imaging of the laser beam onto an imaging plane onto which the long axis homogenized laser beam is imaged by means of condenser optics (LACL).

2. Method according to claim 1, characterized in that by axially displacing the first condenser lens (SACL1) along the beam direction, a variation of a slope steepness attributable to the short axis, i. 10 - 90% of the central beam plateau is made possible, without influencing a line half value width assignable to the short axis.

3. The method of claim 1 or 2, characterized in that by axial displacement of the first field lens optics (SAFL1) along the beam direction, a variation of the short axis assignable line half-width without affecting a short axis assignable edge steepness is made possible.

4. The method according to any one of claims 1 to 3, characterized in that a laser beam is generated with a linear beam cross-section with an extension of at least 450 mm and an extension in the short axis of at least 100 microns.

5. The method according to any one of claims 1 to 4, characterized in that the second image field (HSFA2) is imaged in the region of a slit-shaped diaphragm arrangement.

6. An apparatus for producing a laser beam having a linear beam cross-section, which has a long and a short beam cross-sectional axis and has a length in the long axis of at least 200 mm and a short axis extension of at most 800 microns, with a laser, the one A laser telescope, along the beam direction of which the following components influencing the laser beam are arranged: a telescope unit for adapting the beam cross section widths of the laser beam to the input aperture of a homogenizer following in the beam path, which homogenizes the light intensity distribution of the laser beam Laser beam separated along the long and along the short axis of the beam cross-section makes a first telecentric imaging optics for telecentric imaging of the long axis homogenized laser beam on a

Figure plane and a second imaging optics for imaging the longitudinal axis of the short axis homogenized laser beam to the imaging plane, characterized in that the second imaging optics has at least two in the beam direction successively arranged pairs of optics, each consisting of a Kondensoroptik and a field lens optics that the first optics in the beam direction Pair has a first condenser optics (SACL1) for generating a homogeneous image field (HFSA1) and a first field lens optics (SAFL1) for generating a first pupil (P1), and in that the second optics pair downstream of the first optic pair in the beam direction second condenser optics (SACL1) for imaging the homogenous image field (HFSA1) into a second homogeneous image field (HSFA2) and a second field lens optic (SAFL2) for imaging the first pupil (P1) into a second pupil (P2), the entrance pupil of an imaging optic ( p-lens SA) for telecentric imaging of the laser beam on e corresponds to the image plane.

7. The device according to claim 6, characterized in that the first condenser optics (SACL1) and / or the first field lens optics (SAFL1) are arranged in a controlled movable manner in the beam direction.

8. Apparatus according to claim 6 or 7, characterized in that the first condenser optics (SACL1) and / or the first field lens optics (SAFL1) are arranged to be controlled rotatable about an axis oriented orthogonal to the beam direction.

9. Device according to one of claims 6 to 8, characterized in that the first and second condenser optics (SACL1, SACL2) each as a condenser lens and the first and second field lens optics (SAFL1, SAFL2) are each formed as a field lens.

10. The device according to one of claims 6 to 9, characterized in that the telecentric imaging optics for telecentric imaging of the long axis homogenized laser beam on an imaging plane consists exclusively of the following optical components: provided with respect to the long axis Homogenisierungsoptik (LAH1, LAH2) and a long-axis condenser lens (LACL).

11. Device according to one of claims 6 to 10, characterized in that a preceding in the beam direction of the imaging plane slit-shaped diaphragm arrangement is provided.