DE102008038118A1 - Removing layers applied on a transparent substrate with a laser beam, comprises passing the laser beam through a transparent substrate and then reaching the layers from the substrate side - Google Patents

Abstract

The method comprises passing a laser beam (62) through a transparent substrate (11) and then reaching the layers from the substrate side. The wavelength of the laser beam is selected, so that the laser beam is not absorbed by the substrate such as glass or polymer and the absorption of the laser beam by the layer and/or the layer system is high, so that the layer and/or the layer system is removed. The removal process is caused in a single step process by the pressure generated by the absorbed laser energy in a first layer (L1) (12). The layer system is removed by multi-step process. The method comprises passing a laser beam (62) through a transparent substrate (11) and then reaching the layers from the substrate side. The wavelength of the laser beam is selected, so that the laser beam is not absorbed by the substrate such as glass or polymer and the absorption of the laser beam by the layer and/or the layer system is high, so that the layer and/or the layer system is removed. The removal process is caused in a single step process by the pressure generated by the absorbed laser energy in a first layer (L1) (12). The layer system is removed by multi-step process by using laser beam. A pulsed laser or Q-switched laser or mode-locked laser is used. The layer system is solar layers. The laser beam has a wavelength of larger than 1200 nm. The laser beam is produced by neodymium-doped laser, erbium-doped laser, thulium-doped laser, holmium-doped laser or optically parametric amplifier and/or oscillator. In the layer system, the laser energy absorbs by the first layer (L1). The pressure in the first layer is higher than the sum of the pressures, which are generated by the laser energy absorbed in the second layer (L2) (22) and third layer (L3) (32). The expansion energy in the first layer is larger than the binding energy of second, third and other layers. A two-stage process is used, where in the first stage, the second and third layers are removed by a first laser beam with a defined wavelength, which is not absorbed by the substrate and the first layer, and in the second stage, the first layer is removed with a second laser beam with a further wavelength, which is not absorbed by the substrate. The wavelength of the first laser beam lies in the visible region and the wavelength of the second beam is selected around 350 nm. The second harmonic around 670 nm from neodymium-doped laser, which is operated with the wavelength around 1340 nm, is used as first laser beam, and the fundamental around 1340 nm from the neodymium-doped laser is used as second laser beam, and/or the second harmonic from the neodymium-doped laser, which is operated with the wavelength around 1000 nm, is used as first laser beam, and the third harmonic from the neodymium-doped laser is used as second laser beam. An independent claim is included for a plant for removing layers applied on a transparent substrate with a laser beam.

Description

Abstract

This patent application discloses methods and apparatus for removing layers applied to a transparent support with laser beams. The laser beams pass through the carrier and strike the layers, the wavelength of the laser beam being so controlled that the laser beam is substantially not separated from the carrier (FIG. 11 ) are absorbed as glass or polymer and the absorption of the laser beam by the layer ( 12 ) or the layer system ( 12 . 22 and 32 ) is so high that the layer ( 12 ) or the layer system ( 12 . 22 and 32 ) is ablated in the laser beam direction.

State of the art

In our modern society is not thin-film tecnology to think more away. The thin-film technology including holding essentially the technology for the generation and structuring of thin films for defined Functions. Examples of these are: structured electrical conductor tracks in flat display based on thin, conductive and for visible light transmitting layers; electricity generating solar layer system in Thin-film solar; heat dam end Layers and layer system with changeable transmission Building- or car glass.

In In this patent application, plants for beautiful structuring of thin films or thin-film systems on transparent carrier as glass, polymer indicated with lasers.

description

The Principle of structuring or stripping with lasers based on localized and selective ablation initiated by absorbed laser energy becomes.

Basically, there are two variations of ablation processes with respect to the relation of the propagation direction of the laser beams ( 61 . 62 . 63 . 81 . 82 ) and the direction of travel of the removed materials ( 13 . 23 . 14 ). On the one hand, the abraded material flies against the direction of preparation of the laser beams, on the other hand the ablated material flies in the direction of preparation of the laser beams (compare Figures 3, 4, 5 and 6). The second case is also called advancement. The forward removal process is more effective with factors. In the plants of the present patent application, the forward removal process of layers on transmissive substrates ( 11 ) represents the core process.

For the removal process safely (without damaging the carrier material ( 11 )) and to design effectively (with the least possible use of laser energy), the choice of the wavelengths) of the laser beams is decisive. The core idea of this patent application is that used in the system for structuring via ablation laser beams whose wavelength is chosen so that the laser beams are not substantially from the support materials ( 11 ), such as glass or polymer, so that the carrier material is not damaged by the laser beams, and the absorption of laser beams by the layers ( 12 . 22 . 32 ) or layer system is so high that the removal process is possible.

In The following are examples of such plants using the example of production of thin-film solar explained.

In principle, a thin film solar consists of three layers: the front contact layer ( 12 ) (the first layer, L1), the semiconductor layer ( 22 ) (the second layer, L2) and the back contact layer ( 32 ) (the third layer, L3). The three-layer system (L1, L2 and L3) is applied in succession to glass slides. For the selection of the wavelength for forward removal, the absorption of the layers and the carrier is crucial. The absorption dependence of glass is shown in Figure 1. It can be seen that glass has good transmission from 400 nm to 2600 nm. Even at a wavelength around 350 nm, the glass has relatively low absorption.

The front contact layers L1 ( 12 ) are electrically conductive and have high transmission for light in the wavelength range from 400 nm to about 900 nm (see Figure 2). The most commonly used front contact layers L1 ( 12 ) are TCO, ZnO or ITO layers with a thickness of a few 100 nm. In order to divide the large-area contact layers into narrow contact strips, solid-state lasers are used which emit light with a wavelength of 1 μm (see Figure 3). Here, the L1 is structured in the form of narrow strips by creating thin lines by ablation with laser beams ( 13 ). As Figure 2 shows, the front contact layers L1 ( 12 ) high absorbances for wavelengths around 350 nm or for wavelengths longer than 1250 nm. In systems according to this present patent application, therefore, lasers with wavelengths around 350 nm z. B. 355 nm or 347 nm or with wavelength longer than 1200 nm, z. B. 1340 nm used. Laser beams with a wavelength around 1300 nm can be generated with a Nd: doped laser. Also, the wavelength around 1500 nm has high absorption. The wavelength can be generated among other things by Er: doped laser. The highest absorption is at a wavelength around 2000 nm. Laser beams of this wavelength can be doped with a Tm:, or ei Ho: doped, or an optical parametric amplifier or oscillator, which is pumped with a wavelength of 1 micron, generated.

As shown in Figure 1, glass also has very high transmission for wavelengths longer than 1200 nm for visible light. Therefore, it is advantageous to use lasers with wavelengths longer than 1200 nm for ablation of front contact layers L1 (FIG. 12 ) to use.

To the three-layer system is built, it must be in the border area with a Width to be completely removed by 1 cm for insulation. This allows solar cells without short circuit in Frame to be installed.

For the edge stripping be u. a. Belt sanders or sandblast machines used. This will damage the glass surface and generate more waste. One glass forming beautiful and environmentally friendly process makes the stripping with lasers In this case, pulsed high-power lasers with a wavelength of 1 μm are used.

During the stripping process via forward removal, the laser beam first strikes the front contact conductor L1 through the support. The absorbed laser energy E1 in L1 heats L1 and even ionizes it. This results in expansion pressure wave with the pressure P1 in L1. When the laser energy is metered so that the pressure P1 and the energy E1 of the pressure wave become so large, all three layers L1, L2 and L3 are jumped off ( 33 ). In this review of the one-step process, the energies E2 and E3 absorbed by the L2 and L3 and thus generated pressures P2 and P3 are to be kept smaller than P1 by selecting the wavelength and by balancing the absorption. A reliable one-step removal of all layers can be realized if P1 is higher than the sum of P2 and P3.

If the energy of the pressure wave in L1 is called the expansion energy E _x and the energy required to jump up L2 and L3 is taken to be the binding energy E _b , E _x > E _b must apply to a complete application L1, L2 and L3.

For the effectiveness of the stripping Therefore, the absorption at L1, L2 and L3 is relevant. Ideally the entire laser energy is essentially completely absorbed by L1 and Thus, the complete stripping will take place at once, if the complete layer system by the pressure P1, which by absorption generated by laser energy in the front contact layer, blown away becomes. Therefor it is crucial that the wavelength so to choose that the laser beam is effectively absorbed in L1. The wavelength around 350 nm met this requirement. Even better are laser beams with wavelength longer than 1200 nm, since the Täger as glass has high transmission at wavelength longer than 1200 nm.

As Figure 2 shows, the front contact layers L1 ( 12 ) high absorbances for wavelengths around 350 nm or for wavelengths longer than 1250 nm. In systems according to this present patent application, therefore, lasers with wavelengths around 350 nm z. B. 355 nm or 347 nm or with wavelength longer than 1200 nm, z. B. 1340 nm used. Laser beams with a wavelength around 1300 nm can be generated with a Nd: doped laser. Also, the wavelength around 1500 nm has high absorption. The wavelength can be generated among other things by Erzdotierten laser. The highest absorption is at a wavelength around 2000 nm. Laser beams of this wavelength can be generated with a Tm: doped, or a Ho: doped, or an optical parametric amplifier or oscillator pumped at a wavelength of 1 μm.

A In particular, clean stripping is achieved when the pressure, which is generated by absorption of front contact layers L1, significantly higher is the sum of the pressures, which is produced by the absorption in the other two layers L2 and L3 become.

If the energy of the pressure wave in L1 is called the expansion energy E _x and the energy required to jump up L2 and L3 is taken to be the binding energy E _b , E _x > E _b must apply to a complete application L1, L2 and L3. In this way, the layers L2 and L3 are removed cold (without significant temperature). This is particularly desirable in terms of possible electrical shorting due to thermal damage of L2 and melt of L3.

Depending on the thickness of the respective layers, it may be that the single-stage removal process discussed above can not lead to complete delamination of the layer system, since the maximum expansion energy E _x z which can be generated in the pressure wave in L1. B. due to the limited thickness of L1 and thus disposable energy smaller than the binding energy E _b . In this case, a two-stage or multistage removal process has to be considered. In the case of solar cells, according to this present invention, in the first stage, preferably, the L2 and L3 are removed by a laser. In this case, the wavelength of the laser to be used is selected so that the laser beam absorbs only insignificantly from the carrier and L1 and that most of the laser energy is absorbed by L2. The pressure wave generated in L2 leads to ablation ( 23 ) of the L2 and L3.

In analogy, the relationship of Drü P2> P3 in L2 and L3. Furthermore, it must be said that the expansion energy generated in L2 is higher than the binding energy of L3.

L1 is for visible light almost transparent and the semiconductor layer L2 has high absorption for visible light on. That is why it is advantageous to use a laser wavelength in the range 400 nm to 800 nm for to choose the distance from L2 and L3. Due to availability of high power lasers at 532 nm (second harmonic of 1064 nm) nm Nd: doped laser), it is close to this laser for the distance to use from L2 and L3.

To L1 remains in the first process stage. The remaining L1 is removed in the second process stage with a laser beam. Due to the absorption behavior is according to this present invention a laser with one wavelength around 350 nm or longer used as 1000 nm. After the two process stages, the complete layer system is created removed and thus the edge area isolated.

For the realization of the two-stage process for the first stage the second harmonic with a wavelength around 530 nm can be used by a pulsed Nd: doped laser. For the second Level can The pulsed Nd: doped laser with a wavelength around 1060 nm directly verwedent become. Also pulsed Yb: doped lasers like disk lasers and fiber lasers and their harmnoischen can be used in the two-step process.

Nd: doped Lasers can operated at the relatively strong line around 1340 nm. Pulsed Nd: doped Lasers around 1340 nm and their second harmonic around 670 nm can be found in the two-step process for the removal of the layer L1 in the second stage and for used the removal of layers L2 and L3 in the first stage become.

Of Further can the laser beams with appropriate wavelengths in fiber laser or by means of optical parametric processes or up or down conversion to be generated.

Depending on The absorption behavior will be different wavelength for an effective Processing required. This wavelength can be replaced by z. B. frequency doubling, Up-conversion or / and Raman process or optical parameteric processes are generated.

Around the wavelength of the laser beam to adapt to the absorption behavior of the workpiece, can be nonlinear Frequency conversion crystals such as frequency doubling, tripling be used.

diode laser are the most compact and effective beam sources. Their integration In the laser processing head the process simplifies the whole insbesoderes.

by virtue of the flexible design The laser beam can be generated by a fiber laser. there For example, one end of the fiber laser can be mounted directly on the machining head become. Thus, the laser beam is introduced directly into the laser head.

It was nachgewiessen that the removal of the max. effective energy efficiency with a rotationally symmetric Gaussian beam only 37%, with a one-dimensional Top-hat beam, which in one direction is a homogeneous intensity distribution and in the other Direction a Gaussian intensity distribution has only 48%, while the achievable max. Energy efficiency with a two-dimensional top-hat beam, which has a homogeneous intensity distribution in both directions is 100%. In order to a laser beam of rectangular top hat intensity distribution the highest Effizeinzer at the removal or order is achieved, it is advantageous the light-guiding core rectangular form.

One annährender Top-hat-ray can with a diaphragm from a beam with z. B. Gaussian beam profile be cut out. But that's a big loss too connected. With a low loss, a top-hat beam can by means of a waveguide integrator, an array of lens array, a diffractive optic or a Arrangement of phase delay plates and Beamdisplacer be generated outside the laser oscillator.

Proceeding lossless can be a top-hat beam with a fiber laser, whose light-guiding Core has a rectangular cross-section, is generated.

to Generation of laser beams with a rectangular cross-section and a top hat intensity distribution and can Mode hood can be used with a rectangular cross-section. Further lossless can be a top-hat beam with a microlaser, the one gain volume has a rectangular cross section and the reinforcement over the cross section substantially is homogeneous, can be generated. When pumping with diode laser the pump beams to shape that way have a rectangular cross section in laser crystals and a top hat intensity profile exhibit. The pumping area and the fashions can be designed so that a multimode laser beam is generated, which has a substantially top-hat intensity profile.

The laser beam may be after the beam Mung is focused with an optic from a single lens or multiple lenses on the workpiece. An improved rendering of a top hat intensity distribution on the workpiece is achieved when the top hat intensity distribution is achieved by means of optics, e.g. B. a telescope is displayed.

The depth of field a laser beam is limited. Is the laser beam at a great distance over the workpiece moved, so it is necessary to use the laser and its shaping and Take imaging optics. The entrainment The laser and its shaping optics is associated with effort. Around To avoid this, the workpiece is arranged in a plane, their normal at a defined angle to the direction of movement stands. The angle is determined so that the laser beam z. B. with a telescope always sharp enough on the workpiece is mapped.

Of the Laser beam has a certain area in the propagation direction, where good processing results can be achieved. For a workpiece whose Form must deviate from a level the beam and the workpiece relatively positioned in the beam propagation direction (longitudinal). It is more flexible and practical when the beam is in relation to the workpiece is positioned. This can be done by means of an autofocus unit. she consists essentially of a long-term position detector unit (Distance sensor) and a servo circuit.

For large-area ablation The laser beam and the workpiece are relative to a scanner or an axis system or a robot moves.

Figure 7 shows an embodiment. The laser beam ( 81 ) of a laser with a defined wavelength is determined by an optical system ( 67 ) and a deflection mirror on the workpiece ( 71 ). Ideally, the laser beam has a rectangular cross section ( 68 ). Thus, the layers with each pulse in the form of a rectangle ( 70 ). Will the workpiece ( 71 ) as ( 73 ), the edge region ( 78 ) without the layers.

A simple realization of the two-stage process is present when the one laser beam with one wavelength for the first process step and the other laser beam with a different wavelength for the second process step in the direction of the relative movement arranged one behind the other be that the L2 and L3 are removed first, and L1 shortly afterwards Will get removed. A compact construction can be realized by the two beams with a common optic in the direction of movement offset on the workpiece be imaged or focused.

Figure 8 shows an embodiment of the two-stage process. The laser ( 66 ) sends in this case two laser beams ( 82 and 83 ) of different wavelengths, z. 532 nm and 1064 nm or around 670 nm and 1340 nm. The laser beam ( 82 ) with the shorter wavelength is used for the process step and thus generates the ablation of L2 and L3 ( 76 ). The remaining layer (L1, 75 ) is emitted by the laser beam ( 83 ) with the longer wavelength in the second process stage. After that the border area ( 78 ) without layers (L1, L2 and L3).

Instead of the deflecting mirror ( 69 ) scanner can be used for fast movement of the laser beam over the workpiece to generate the required ablation area.

For one efficient removal process is used with process gas such as compressed air, to quickly blow off the removed materials from the process zone. This increases also the process quality, since the probability of return is reduced by process gas.

to Collecting the removed materials becomes a suction unit used. To the removed materials for recycling or for the environment harmless make a filtration system behind the suction unit switched on.

Claims (19)

Method for removing layers applied to a transparent support with at least one laser beam, wherein the laser beam passes through the support and strikes the layers from the support side, the wavelength of the laser beam being so controlled that the laser beam is substantially not separated from the support ( 11 ) are absorbed as glass or polymer and the absorption of the laser beam by the layer ( 12 ) or the layer system ( 12 . 22 and 32 ) is so high that the layer ( 12 ) or the layer system ( 12 . 22 and 32 ) is removed. Method for removing layers according to the claim 1, characterized in that the removal in a single-stage Process essentially by that of absorbed laser energy in the first layer L1 generated pressure is effected. Method for removing layers according to the claim 1, characterized in that the layer system by a multi-stage process layer for Layer is removed by laser beam. Method for removing layers after a the claims 1 to 3, characterized in that a pulsed laser, or a quality-slated one or a mode locked laser is used. Method for removing layers after a the claims 1 to 4, characterized in that it is in the layer system is about solar layers. Method for removing layers after a the claims 1 to 5, characterized in that a laser beam with a wavelength around 350 nm is used. Method for removing layers after a the claims 1 to 5, characterized in that a laser beam with a wavelength greater than 1200 nm used. Method for removing layers according to claim 7, characterized in that a laser beam from a Nd: doped Laser, or from a Er: doped laser, or from a Tm: doped laser, or from a Ho: doped laser, or from an optical parametric one amplifier or oscillator is generated. Method for removing layers after a the claims 1 to 8, characterized in that in a layer system the laser energy is substantially absorbed by the first layer L1. Method for removing layers according to the claim, characterized in that the pressure generated in the layer L1 higher than the sum of the pressures, which is generated by the energy absorbed in L2 and L3 in L2 and L3 are. Method for removing layers after a the claims 9 to 10, characterized in that the expansion energy in L1 greater than the binding energy of L2, L3 and other layers. Method for removing layers according to the claim 5, characterized in that a two-step process is used is, wherein in the first stage, the L2 and L3 by a first Laser beam with a defined wavelength, which is essentially not from the carrier and the L1 is absorbed, and at the second Level the L1 with a second laser beam of a different wavelength, the essentially not absorbed by the carrier will be removed. Method for removing layers according to the claim 12, characterized in that the wavelength of the first laser beam is visible in the area and the wavelength of the second beam is longer than 1000 nm selected becomes. Method for removing layers according to the claim 12, characterized in that the wavelength of the first laser beam is visible in the area and the wavelength of the second beam to 350 nm selected becomes. Method for removing layers according to the claim 12, characterized in that as the first laser beam second harmonic used at 670 nm from a Nd: doped laser that's at the wavelength is operated at 1340 nm, and that as the second laser beam used fundamentally around 1340 nm from the same Nd: doped laser becomes. Method for removing layers according to the claim 12, characterized in that as the first laser beam second harmonic is used by a Nd: doped laser, the at the wavelength is operated at 1000 nm, and that as the second laser beam third harmonic is used by the same Nd: doped laser. Device for stripping according to the method of one of claims from 1 to 16, consists of at least one laser beam source, one Movement unit for the relative movement between the laser beam and the workpiece, one Suction unit for the suction of the removed layer material. Plant for stripping according to claim 17, characterized characterized in that process gas to blow away from the removed layer material is used. Plant for stripping according to claim 17 or 18, characterized in that a sensor unit for determining the position of the workpiece and a servo unit for adjusting the relative position of workpiece and the Strahlkaustik.