DE102012214335A1 - Method for ablating a layer - Google Patents

Method for ablating a layer

Info

Publication number
DE102012214335A1
DE102012214335A1 DE102012214335.1A DE102012214335A DE102012214335A1 DE 102012214335 A1 DE102012214335 A1 DE 102012214335A1 DE 102012214335 A DE102012214335 A DE 102012214335A DE 102012214335 A1 DE102012214335 A1 DE 102012214335A1
Authority
DE
Germany
Prior art keywords
laser
radiation
surface
light source
layer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
DE102012214335.1A
Other languages
German (de)
Inventor
Andreas Brand
Jan Nekarda
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Original Assignee
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV filed Critical Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority to DE102012214335.1A priority Critical patent/DE102012214335A1/en
Publication of DE102012214335A1 publication Critical patent/DE102012214335A1/en
Application status is Pending legal-status Critical

Links

Images

Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36Removing material
    • B23K26/40Removing material taking account of the properties of the material involved
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36Removing material
    • B23K26/361Removing material for deburring or mechanical trimming
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00Materials to be soldered, welded or cut
    • B23K2103/16Composite materials, e.g. fibre reinforced
    • B23K2103/166Multilayered materials
    • B23K2103/172Multilayered materials wherein at least one of the layers is non-metallic
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00Materials to be soldered, welded or cut
    • B23K2103/50Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26

Abstract

The invention relates to a method for ablation of at least one layer (13) of a substrate (10), in which laser radiation (210) from at least one first laser (21) acts on at least one partial surface (105) of the surface of the layer (13). wherein the first laser (21) generates pulsed laser radiation (210) having a pulse duration of less than about 50 ns, and at least one second light source (22) which generates pulsed laser radiation (220) with a pulse duration of greater than about 1 ns includes a continuous wave laser or emits incoherent radiation, wherein the light (210) of the first laser (21) impinges at a time when at least the partial surface (105) of the surface is in thermal equilibrium with the environment.

Description

  • The invention relates to a method for ablating at least one layer of a substrate, in which laser radiation from at least one first laser acts on at least a partial area of the surface of the layer, wherein the first laser generates pulsed laser radiation having a pulse duration of less than about 50 ns. Methods of the type mentioned can be used for structuring of semiconductor devices.
  • From practice it is known to use photovoltaic cells for the conversion of optical energy into electrical energy. The photovoltaic cell consists essentially of a planar pn diode, in which the space charge zone extends to just below the surface. Incident sunlight thus leads to the formation of electron-hole pairs, which can be tapped as electrical current via the front and rear contacts.
  • To increase the efficiency, i. In order to increase the current efficiency from a predeterminable area, it is also known to provide the surface provided for the entry of light with a structuring. As a result of this structuring, multiple reflections of incident radiation occur, so that a larger proportion of the radiation is absorbed in the space charge zone. In some embodiments, the patterning may be produced by anodic etching of the surface in potassium hydroxide or hydrofluoric acid. A further increase in the efficiency can be achieved by dielectric layers, which deteriorate the reflective properties as a reflection-preventing layer and thus cause an increased absorption of incident radiation.
  • In order to dissipate the electric current from that of the photoelectric cell, electrically conductive contacts are required. At least one contact covers a partial area of the front side in some cell types, so that remaining surface areas are available for absorption of the incident radiation. In order to allow a low contact resistance between the semiconductor and the front side contact and a good mechanical adhesion, a microscopically possible full-surface contacting of the surface in the partial areas of the contacts is desired.
  • Since the dielectric coating is electrically non-conductive, it must first be removed from the surface in the partial areas provided for receiving the front side contact. The removal of the dielectric coating should if possible be such that the crystallinity and the electrical properties of the remaining material are largely left in their original state. In particular, the recombination rate or the lifetime of non-equilibrium charge carriers should be maintained or impaired as little as possible. The lifetime of non-equilibrium charge carriers is essentially determined by the density of deep impurities, which can serve as recombination centers for minority carriers. Such deep impurities can arise on the one hand in contamination of the remaining material with components of the removed layer or by disturbances of the crystal structure. In the case of serious damage, the pn contact can be damaged to such an extent that a short circuit occurs across the photovoltaic cell.
  • In known manufacturing processes, either the dielectric layer is ablated with the pulses of a short-time laser, which is a fast and inexpensive process. However, the crystal quality of the remaining semiconductor material is greatly damaged, so that the photovoltaic cell has a reduced performance. According to other known methods, the dielectric layer is removed by wet or dry chemical etching after the remaining semiconductor surface has been protected with a patterned mask. Although these methods are able to provide better results, but cause a large manufacturing effort and therefore high costs.
  • Based on this prior art, the invention is therefore based on the object of specifying a method for removing a layer on a substrate that is simple and quick to perform.
  • The object is achieved by a method according to claim 1. Advantageous developments of the method are in the dependent claims.
  • According to the invention, it is proposed to use laser radiation for ablation of at least one layer of a substrate. The substrate, in some embodiments of the invention, may be a semiconductor substrate, for example, an elemental semiconductor, germanium, a III-V compound semiconductor, or a II-VI compound semiconductor. In some embodiments of the invention, the substrate may include or consist of silicon, gallium arsenide, gallium nitride, copper indium gallium diselenide or germanium. The substrate may contain dopants at least in some spatial regions in order to set a predeterminable electrical conductivity and / or a predefinable lattice constant. Furthermore, the substrate may contain conventional impurities, for example hydrogen, oxygen, carbon or metals. The substrate may be a semiconductor device or a plurality of Record semiconductor devices in the form of an integrated circuit.
  • The layer may contain or consist of a metal or a dielectric and may be formed, for example, as an antireflection layer, as an electrical conductor or as an electrical connection contact. To this end, in some embodiments of the invention, the layer may contain or consist of silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, aluminum oxide, amorphous silicon, gold, silver, copper or aluminum or their alloys. The layer can be arranged directly on the substrate or can indirectly adhere to the substrate surface with the aid of one or more intermediate layers. In some embodiments of the invention, the layer may be implemented as a multilayer system and may include multiple, thin layers. In some embodiments of the invention, the layer can be applied over the entire surface of the substrate and be removed or ablated on certain, predefinable partial surfaces by the proposed method.
  • The laser radiation used to remove the layer may be selectively absorbed in the layer to be removed or in an underlying layer such that the energy input selectively occurs in that layer without unduly affecting the underlying substrate. The laser radiation provided to remove the layer is pulsed, for example, with a pulse duration of less than about 50 ns, less than about 50 ps, less than about 20 ps, less than about 1 ps, or less than about 100 fs. The material of the layer can evaporate under the action of the laser radiation or be removed in larger clusters or particles. In some embodiments, the material of the layer may flake off under the action of laser radiation in macroscopic particles. To remove the layer, a predeterminable partial area can be irradiated with one or more laser pulses. The number can be defined by the repetition rate, the pulse trains and the feed rate.
  • According to the invention, it is now proposed to anneal the damage to the substrate caused by the action of the laser radiation of the first laser on the substrate by radiation of a second light source.
  • In one embodiment of the invention, this can be achieved by heating the substrate to a predeterminable temperature, for example by the action of infrared radiation from an infrared light source or a heating plate. In that regard, for the purposes of the present description, a heat source of long-wave infrared radiation is referred to as the second light source. This can lead to the conditioning of the surface of the substrate, so that the complex refractive index for the incoming laser radiation is modified, the atoms can recrystallise in a more favorable arrangement, a dopant can diffuse faster in the substrate, or adhering adsorbates can be thermally desorbed. As a result, the size and / or depth of amorphous regions can be reduced and / or the defect density of crystalline material can be reduced. The heating to a predeterminable temperature for a predeterminable time can take place after the action of the laser radiation and / or before and / or at the same time. The heating can take place over the entire surface or only in the irradiated or to be irradiated partial surfaces.
  • In another embodiment of the invention, a continuous wave laser un / or an incoherent light source is used as the second light source, with which the partial area irradiated by the first laser supplies energy. The radiation of the second light source is at least partially absorbed by the substrate or a near-surface layer of the substrate. As a result of this energy input, the substrate can recrystallize, a dopant can diffuse in the substrate, or adsorbates adhering can be desorbed. The radiation of the continuous wave laser can impinge temporally after the radiation of the first laser on the already irradiated partial surface. In other embodiments of the invention, the radiation of the continuous wave laser can impinge simultaneously with the first laser and / or be directed in time before the first laser and / or in time after the first laser to the partial surface intended for irradiation. In this case, the continuous wave laser can be switched off with the impact of the radiation of the first laser or the radiation of the continuous wave laser can persist beyond the pulse duration of the first laser.
  • In yet another embodiment of the invention, a second light source may be used which generates pulsed laser radiation having a pulse duration of greater than about 1 ns or greater than about 10 ns. The pulsed laser radiation of the second light source can impinge on the already irradiated partial surface in time after the light pulses of the first laser. In other embodiments of the invention, the pulsed laser radiation of the second light source can impinge on the already irradiated partial area in time before the light pulses of the first laser. Under the pulsed laser radiation of the second light source, the surface can melt and recrystallize. In some embodiments of the invention, delaminated regions in which the layer is unintentionally released from the substrate can be re-bonded under the action of the laser radiation of the second light source, so that a connection of the layer to the underlying substrate exists. Finally, the pulsed Laser radiation of the second light source cause adhering adsorbates are desorbed by thermal or photon-induced desorption or that diffuse dopants or impurities in the substrate and occupy other locations within the microstructure of the substrate.
  • All variants of the method according to the invention have in common that the light of the first laser impinges on the surface at a time at which at least the partial surface of the surface to be irradiated is in thermal equilibrium with the surroundings. If electromagnetic radiation from the second light source arrives before or at the same time, the surface is in the radiation equilibrium, i. a further rise in temperature is no longer present. If the radiation is suitable for making electronic excitations in the solid state, these are in an equilibrium state, i. As many electrons are transferred from the ground state to an excited state per time unit as they change from the excited state back to the ground state. Therein, the proposed method differs from known material processing methods with laser radiation, in which the second light pulse impinges at a time when the interaction of the solid with the first light pulse is not yet completed or the solid is not yet relaxed to an equilibrium state.
  • In some embodiments of the invention, the first laser may have a wavelength of about 250 nm to about 1100 nm. In some embodiments of the invention, the first light source may have a wavelength of about 200 nm to about 2000 nm. This is the average wavelength because the first light source will have a broadband wavelength distribution due to the short duration of the pulse. Said wavelength may be adapted to the absorption behavior of the material of the first layer and / or the material of the substrate or the material of an intermediate layer between the layer and the substrate. In this way it is ensured that the light of the first light source is absorbed at the desired location to effect the ablation of the layer.
  • In some embodiments of the invention, the first light source may have a beam spot size of about 1 μm to about 100 μm, or from about 15 μm to about 50 μm. If a strip or lattice-shaped front side contact of a photoelectric cell is to be generated on the substrate, the width of the beam spot of the light source can directly define the width of the partial area to be liberated by the layer, so that the desired partial areas of the coating can be achieved by simply laterally displacing the beam spot be freed. As a result, the process can be carried out efficiently and with high throughput.
  • In some embodiments of the invention, the first light source may have a pulse duration of from about 10 fs to about 10 ns, or from about 100 fs to about 100 ps. This ensures a sufficiently high energy density and a sufficiently large spectral width of the light pulses to enable an efficient ablation of the layer.
  • In some embodiments of the invention, the second light source may have a wavelength of from about 200 nm to about 400 nm, or from about 1100 nm to about 3000 nm, or from about 200 nm to about 1500 nm. If the second light source is pulsed, this is also a medium wavelength since the radiation has a spectral width which is inversely proportional to the pulse duration. Light of this wavelength is sufficiently strongly absorbed by the substrates mentioned at the outset in order to enable rapid recrystallization and / or desorption of adhering adsorbates and / or reversal of delaminations. As a result, the application of the method can be simplified and / or performed faster.
  • In some embodiments of the invention, the second light source may have a wavelength of about 1.5 μm to about 50 μm. Light or thermal radiation of this wavelength can be used particularly efficiently for heating the substrate, so that the surface melts at least partially and / or due to the elevated temperature, a different refractive index or a different absorption behavior for the laser pulses of the first laser can be generated. Said wavelength range may in some embodiments be generated by an incoherent light source or a heater in contact with the substrate.
  • In some embodiments of the invention, the second light source may have a beam spot size of about 15 μm to about 100 μm. This allows the selective processing of the partial surfaces irradiated by the first light source, so that extensive recrystallization or thermal damage to the remaining substrate is avoided. Since the energy input does not occur in the entire substrate, the speed of execution of the method can be increased.
  • In some embodiments of the invention, the second light source may have a pulse duration of from about 10 ns to about 20 μs, or from about 1 μs to about 10 μs, or from about 100 ns to about 1 μs. The pulse duration of the second light source is thus longer than the pulse duration of the first light source. hereby Non-linear optical effects are suppressed and the surface can recrystallise differently due to the longer exposure time. In particular, the duration of exposure may be longer than the timing of typical diffusion processes, such that the surface is reconstructed in thermal equilibrium with the injected radiation.
  • In some embodiments of the invention, the first laser may have a pulse duration of less than 1 ns, and as the second light source a laser having a pulse duration of more than 1 ns may be used.
  • In some embodiments of the invention, the first laser and / or the laser used as the second light source may emit shaped pulse trains, i. Laser pulses, which have a substructure locally and / or temporally within their pulse duration.
  • In some embodiments of the invention, the first laser and / or the laser used as the second light source may be combined in one device, i. the same laser emits pulse trains with the characteristics of the first laser and temporally coordinated pulse trains with the properties of the second light source.
  • In some embodiments of the invention, the beam spot of the first light source may be scanned over at least a portion of the surface of the layer, wherein the feed corresponds to about 90% to about 100% of the beam spot size. This means that the track resulting from the screening is composed of individual points, each point corresponding to the point of impact of one or more pulses of the laser radiation of the first laser. The number of impinging pulses may be between 1 and about 5,000 in some embodiments of the invention.
  • In some embodiments of the invention, the beam spot of the second light source may be scanned over at least a portion of the surface of the layer, wherein the feed corresponds to about 40% to about 60% or about 1% to about 60% of the beam spot size. This results in that a partial surface is irradiated several times, so that on the one hand forms a smooth edge of the irradiated partial surface and on the other hand due to the longer exposure time a longer time is available, in which the surface can recrystallize.
  • In some embodiments of the invention, the radiation of the second light source may hit the surface delayed in time after the radiation of the first light source. This feature has the effect that the excitation of the substrate or of the layer caused by the first light source has completely decayed and the substrate or the irradiated partial area of the substrate is again in equilibrium with the surroundings. The material properties of the substrate, such as refractive index, temperature, Fermi level or carrier density is thus not affected by the intensity, duration or wavelength of the laser pulses of the first laser. In some embodiments of the invention, this may be the case when the radiation of the second light source strikes the surface by more than 1 ns or more than 100 ns or more than a 1 μs delayed after the radiation of the first light source.
  • In some embodiments of the invention, the radiation of the second light source may hit the surface in time prior to the radiation of the first light source. This feature has the effect that the excitation of the substrate or of the layer caused by the second light source effects a conditioning of the surface for the arrival of the radiation of the first laser, whereby the substrate or the irradiated partial area of the substrate is in equilibrium with the surroundings located. The material properties of the substrate, such as, for example, refractive index, temperature, Fermi level or carrier density, are thus influenced by the intensity, duration and / or wavelength of the radiation of the first light source, but no longer change in time. In some embodiments of the invention, this may be the case when the radiation of the first laser strikes the surface by more than 1 ns or more than 100 ns or more than a 1 μs delayed after the radiation of the first laser.
  • In some embodiments of the invention, the beam spot of the second light source may follow the beam spot of the first light source at a predeterminable temporal or spatial distance. In some embodiments of the invention, the predeterminable distance may be greater than 2 μm or greater than 200 μm or greater than 1 mm so that the beam spots do not overlap. In this way, both light sources can be moved simultaneously over the surface of the substrate, wherein a complex adjustment of the two light sources is required only once at the beginning of the process. When the first laser is scanned over the surface of the substrate, the beam spot of the second laser then follows in its trace, without the need for time-consuming adjustment of the second laser or position control of the beam spot. The process can be carried out easier, more reliable or faster.
  • In some embodiments of the invention, the beam spot of the second light source may be larger than the beam spot of the first laser. This results in that the edge regions of the beam spot of the first laser are reliably detected by the radiation of the second light source and a improved quality of the substrate or the layer can be ensured in these areas.
  • In some embodiments of the invention, the first light source and the second light source may be mounted on a common mount. This ensures that the relative position of both beam spots remains unchanged during the performance of the method.
  • In some embodiments of the invention, the point of incidence of the beam spot of the second light source can be regulated to a predefinable desired value with a control device. This allows the independent guiding of the first and the second light source, so that the method can be carried out with the greatest possible flexibility. For position control of the beam spot, in some embodiments of the invention, an optical microscope can be used which detects the position of the partial areas irradiated by the first laser. In a further embodiment of the invention, alternatively or cumulatively, attitude control systems can be used which detect a photocurrent or a fluorescence signal and in this way recognize whether the point of incidence of the beam spot of the second light source lies on the layer or on the already irradiated partial area of the substrate.
  • In some embodiments of the invention, the radiation of the second light source may impact the surface at the same time as the radiation of the first laser. In this case, the radiation of the first light source impinges on the surface only when the surface is in equilibrium with the radiation of the second light source, for example at least 1 ns or at least 100 ns or at least 1 μs after switching on the second light source. In this case, advantageously, a faster process control can be ensured if the restructuring of the surface caused by the second light source takes place simultaneously with the removal of the layer by the radiation of the first laser.
  • In some embodiments of the invention, the surface may have a roughness of about 1 μm to about 5 μm. It has surprisingly been found that the ablation of the layer is reliably possible even when the surface of the substrate has a roughness, although in this case different crystal orientations and / or a different reflection behavior for the incoming laser pulses is present. Thus, the proposed method can be used completely surprisingly in the production of photovoltaic cells, which ideally have a structuring or a roughness to reduce reflection losses.
  • The invention will be explained in more detail with reference to figures without limiting the general inventive concept. Hereby shows:
  • 1 the schematic representation of the surface of a known photovoltaic cell.
  • 2 shows the effect of irradiation with pulsed laser radiation.
  • 3 shows the application of a self-organizing electrical contact.
  • 4 shows the inventive irradiation of the surface with a first laser.
  • 5 shows the result after the process step according to 4 ,
  • 6 shows the irradiation according to the invention with a second light source.
  • 7 shows that after the process step of 6 Result obtained.
  • 8th shows an apparatus for carrying out the proposed method.
  • 9 shows a light micrograph of irradiated patches according to the invention.
  • 10 shows an electron micrograph of a substrate according to a first embodiment of the in 4 explained method step.
  • 11 shows the part of the 10 after the in 6 explained method step.
  • 12 shows an electron micrograph of a substrate according to a second embodiment of the in 4 explained method step.
  • 13 shows the part of the 12 after the in 6 explained method step.
  • 14 shows the change in the service life of the minority carriers before carrying out the method, after the first method step and after the second method step.
  • Based on 1 to 3 the fabrication of a front-side contact of a photoelectric cell will be explained.
  • The figures show a section through a substrate 10 which is based on at least one Surface a structuring 101 having. The structuring 101 For example, it can be produced by etching, for example in potassium hydroxide solution or by machining, for example micro-milling or micro-grinding. The pitch of the peaks to the valleys may be between about 1 μm and about 5 μm in some embodiments of the invention. The structuring 101 may be regular or irregular, ie statistical.
  • The substrate 10 For example, in some embodiments of the invention, it may be a silicon monocrystal. The substrate may contain dopants to obtain a desired conductivity. The 1 to 3 show, by way of example, the side provided for the entry of light into a front-side-contacted photovoltaic cell, which is subsequently referenced as the upper side. The opposite underside can be provided over the entire surface with an electrical contact to dissipate the resulting electric current. On the top of the solar cell also electrical contacts must be arranged to dissipate the resulting current. However, these can occupy only partial areas of the top, so that a part of the top is still available for light entry. Upon illumination of the top, electron-hole pairs are formed in the emitter layer 12 , which is formed by a dopant over the surface of the substrate 10 diffused. The emitter layer 12 may be about 20 nm to about 300 μm deep into the substrate 10 protrude.
  • To further increase the current efficiency is on top of the substrate 10 a layer 13 arranged, which may be formed as an interference filter and which reduces reflections of incident solar radiation and / or passivated the surface. For this purpose, the layer 13 Silicon nitride or silica or silicon oxynitride included. The layer 13 may have a thickness of about 50 nm to about 100 nm. Accordingly, the structuring is formed 101 the top of the substrate 10 also on the surface of the layer 13 from.
  • Because the layer 13 consists of a dielectric and thus an insulating material, this must be in those sub-areas 105 are removed, in which the electrical contact 15 should be arranged. This can be done by irradiation with pulsed laser radiation 210 made from a first laser, so that the layer 13 in the irradiated areas into fragments 130 decomposes, which subsequently from the surface of the substrate 10 can be removed or flake off.
  • The subarea 105 can subsequently with a nucleation layer 14 be provided, which contains nickel, for example, so that the electrical contact 15 galvanic on the surfaces 105 can be raised.
  • This on the basis of 1 to 3 explained, known per se method has the disadvantage that the laser radiation 210 also to damage the emitter layer 12 and / or damage to the substrate 10 can lead. For example, the substrate 10 in the subareas 105 become at least partially amorphous, constituents of the layer 13 can the substrate 10 in the partial area 105 contaminate and / or thermomechanical pressure can dislocations in the crystal material of the substrate 10 be generated. As a result, the life of non-equilibrium charge carriers or minority carriers can drop sharply, so that the current efficiency and thus the efficiency of the photovoltaic cell decreases.
  • Based on 4 to 7 the process of the invention is explained in more detail. Identical components are provided in the figures with the same reference numerals, so that the following description is limited to the essential differences. Also in the 4 to 7 is a substrate 10 shown a structuring 101 has as previously described.
  • In the first process step, laser radiation hits 210 of a first laser on a partial surface 105 in the surface of the substrate 10 on. The laser radiation 210 has a pulse duration of less than about 30 ps and a mean wavelength of about 355 nm. The diameter of the beam spot on the substrate 10 can be about 35 microns. The energy density of the laser radiation 210 can be greater than 10 mJ / cm 2 .
  • This causes the layer 13 in fragments 130 decomposes, which subsequently from the surface of the substrate 10 peel off. Furthermore, it forms in the substrate 10 a damaged surface layer 120 which may at least partially have an amorphous structure and / or in which the dopant of the emitter layer 12 the substrate 10 has left and / or in which components of the shift 13 have diffused.
  • 5 shows the cross section through the substrate 10 after irradiation by the laser radiation 210 , Visible are the listed damages in a surface layer 120 , which are attached to the surface of the substrate 10 borders. In these areas may be the deteriorated quality of the substrate 10 lead to a reduction in performance of the device. Furthermore, in 5 schematically shown that residues 135 the layer 13 stick to the surface. These radicals 135 can galvanic deposition of the contact 15 hinder and / or worsen the quality of the electrical contact.
  • According to the invention, in this exemplary embodiment, it is now proposed to use laser radiation in chronological order 220 from a second laser on the partial surface 105 to act. The laser radiation 220 has a longer pulse duration, which may be 25 ns or 1 μs, for example. The number of impinging pulses may be between 1 and about 5,000 in some embodiments of the invention. In some embodiments of the invention, the laser radiation 220 be generated with a continuous wave laser. The compared to the laser radiation 210 longer exposure time of the radiation 220 causes the fragments 135 be desorbed from the surface by thermal and / or photon-stimulated desorption. Furthermore, the surface of the substrate 10 in the surface layer 120 recrystallize and / or dopants of the emitter layer 12 can diffuse to lattice sites and thus into electronically effective positions. When the laser radiation 220 time after the radiation 210 acting on the surface, this happens at a time when the effects of the laser radiation 210 have already decayed, ie that of the laser radiation 210 excited electrons of the substrate 10 are back in the ground state and those of the laser radiation 210 excited lattice vibrations have subsided. This may, for example, have occurred after a time duration of more than 1 ns or more than 10 ns or more than 1 μs.
  • 7 shows the surface of the substrate 10 after carrying out the second method step, which in 6 was explained. As can be seen, the emitter layer is 12 at least partially restored and the surface is in the subarea 105 of adhering residues 135 the layer 13 freed. The improved crystal quality in the range 120 can make itself felt in a longer life of the minority carrier.
  • In some embodiments of the invention, the laser radiation 210 also at the same time as the radiation 220 impinge, so the radiation 220 for setting a desired reflection behavior or absorption behavior of the substrate 10 or for instantaneous healing of the radiation 210 Induced defects can be used.
  • 8th shows an embodiment of an apparatus for carrying out the method according to the invention. The device according to 8th is of course only to be seen as an example and may vary in other embodiments of the invention. In particular, not all components shown must be present in each embodiment of the invention.
  • 8th shows a first laser 21 for generating the pulsed laser radiation 210 , This one can be on a mount 25 be mounted, showing the exact adjustment of the laser 21 allows and optionally the pivotability or displaceability of the laser 21 allows. In addition, the mount 25 in an embodiment of the invention, the second light source 22a carry the radiation 220 generated. The light source 22a may also be a laser, which generates the laser pulses already described in more detail with a pulse duration of more than about 10 ns. In other embodiments of the invention, the light source 22a be a continuous wave laser or emit non-coherent radiation, which is the partial surface 105 of the substrate 10 heated temporarily and thus allows recrystallization and / or desorption of adhering adsorbates. The light source 22a can on the mount 25 relative to the first laser 21 be adjusted so that when moving the laser beam 210 over the surface of the substrate 10 the laser beam 220 in the track of the laser beam 210 follows. In other embodiments of the invention, the light source 22a regardless of the light source 21 be moved and for example via a control device 28 in the track of the laser beam 210 be guided. For this purpose, the control device 28 measure a photocurrent or a fluorescence signal and thereby detect if the laser beam 220 on the dielectric or metallic coating 13 or the semiconductive surface in the subarea 105 incident.
  • In some embodiments of the invention, alternatively or cumulatively to the light source 22a a long-wave infrared source 22b be present, for example, a hot plate. This allows the substrate 10 be brought to a predetermined temperature, resulting from thermal excitation of the electrons in the substrate 10 can influence the refractive index and / or the recrystallization of the surface and / or the desorption of adhering particles or adsorbates.
  • The substrate 10 and / or the infrared source 22b can be mounted on a movable holder to allow relative movement between the substrate 10 and the laser beams 210 and or 220 to enable. In this case, the mount 25 also be immobile.
  • 9 shows a light micrograph of the surface of a substrate 10 , Visible are partial areas 105 on which the laser radiation 210 has hit. This will make the layer 13 at least incompletely removed, leaving the underlying substrate 10 is exposed. Because the beam profile of the laser radiation 210 is approximately Gaussian, the intensity decreases towards the edge. This causes that in the border areas 106 a lower intensity impinges, which causes the coating 13 delaminated, ie the adhesion to the surface of the substrate 10 loses. In addition, the interface is at least partially amorphous or too rapidly solidified with too many defects or defect states. However, the intensity is not big enough for the layer 13 also completely from the substrate 10 to solve. In these areas, the function of the layer 13 as passivation layer or reflection-reducing layer limited or not present, since this effect is lost due to the increased distance to the substrate.
  • The right part of the picture shows the surface after the laser radiation 220 the second light source on the surface of the substrate 10 has acted. As can be clearly seen, the previously delaminated areas 107 removed or completely disappeared. The laser radiation has the original adhesion between the layer 13 and the substrate 10 restored, so that the previously described defects are at least partially healed. In some embodiments of the invention, the laser radiation 220 thus the delaminated areas 106 between the layer 13 and the substrate 10 repair.
  • 9 further shows that the laser radiation 210 of the first laser 21 is moved with a feed over the surface of the substrate, which corresponds in about 90 to about 100% of the beam diameter. This results in individual, approximately circular limited partial areas 105 , which are connected at their points of contact. In contrast, the laser radiation 220 the second light source are moved overlapping over the surface, so that individual faces 105 and 106 several times with the laser radiation 220 can interact.
  • The 10 and 11 show a first embodiment of a substrate according to the invention after performing the first method step and after performing the second method step according to the present invention. The substrate contains silicon, which is provided with a statistically oriented surface topography in an etching process. On the surface is a layer 13 applied, which contains silicon nitride. As in 10 it can be seen, the layer 13 in subareas 105 by the action of the laser radiation 210 be removed. At the same time the laser radiation leads 210 however, incomplete removal of the layer 13 so that individual impact locations are not contiguous to the layer 13 are liberated. Partial surfaces of the layer 13 may already be delaminated, but are still insufficiently adherent to the surface. Furthermore, it can be seen that on the surface by the laser pulses an irregular surface texture was applied, which corresponds approximately to the intensity maxima of an interference pattern of the laser radiation. Due to the shortness of the applied pulses, the material of the substrate solidifies faster than the plastically deformable material can flow. This leads to a multiplicity of crystal defects and subsequently to deep impurities and inhomogenization of the pn junction, which accelerate the recombination of minority charge carriers. This reduces the efficiency of the photovoltaic cell.
  • 11 shows the surface after exposure to the laser radiation 220 the second light source. The laser radiation 220 leads to a substantial removal of the layer 13 from the faces 105 as well as to a recrystallization of the surface, which is subsequently smooth and clearly defect poorer.
  • The in 10 and 11 described facts will be described below with reference to 12 and 13 for a second substrate explained. The substrate 10 which is in 12 and 13 was etched in potassium hydroxide to structuring 101 to create. Also in this case forms the laser radiation 210 Ribs of molten material in the faces 105 , Likewise is in 12 visible that the layer 13 was only incompletely removed.
  • Both defects are in 13 by the action of radiation 220 from the second light source largely healed. The layer 13 is still present on the substrate only in a very small area. The ribs showing the defect density in the irradiated patches 105 increase significantly, are in 13 considerably reduced.
  • The positive effect of the inventively proposed second process step can be determined by 14 understand again. 14 shows in the left part of the picture the same section of a substrate 10 , The uppermost representation corresponds to the untreated substrate, as in 1 shown. In the middle representation was divided into subareas 31 and 32 of the substrate with laser radiation 210 in some subareas 105 the layer 13 removed, as based on the 2 and 4 is explained. The two subregions of the substrate 10 are as rectangles 31 and 32 entered in the figure.
  • In the lowest representation, the surface area became 32 with laser radiation 220 edited as based on 6 described. The surface area 31 is still in the state after the previous process step as a comparison area.
  • The left part of the picture 14 shows the mean lifetime of the minority carriers in the substrate 10 coded on a scale of 50 to 130 μs in gray scale. In the uppermost diagram, the untreated substrate shows a mean lifetime of the minority charge carriers of 120 μs. In the middle illustration, after the sections 31 and 32 with laser radiation 210 were treated in lines of 30 microns wide and 1 mm apart, the average lifetime of the charge carriers decreases to about 53 microseconds. This is essentially based on the 5 . 10 and 12 attributed defects.
  • In the lowest representation was in the subarea 32 the basis of 6 described second method step performed. As a result, the average life of the charge carriers increases again to 74 μs. In the comparison field 31 the lifetime of the charge carriers is unchanged.
  • In the right part of the picture 14 In each case, the change in the average life of the charge carriers is shown. In the upper figure it can be seen that the lifetime decreases by about 50% through the first method step. In the lower part of the picture it can be seen that the lifetime in the comparison field 31 remains unchanged, whereas in the field 32 an increase of about 40% is recorded.
  • Of course, the invention is not limited to the embodiments shown in the figures. The above description is not to be considered as limiting, but as illustrative. Features of different embodiments of the invention described above in detail may be combined to form other embodiments. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. If the claims and the above description define "first" and "second" features, then this term serves to distinguish two similar features without prioritizing them.

Claims (11)

  1. Method for ablating at least one layer ( 13 ) from a substrate ( 10 ), in which laser radiation ( 210 ) of at least one first laser ( 21 ) on at least one partial surface ( 105 ) the surface of the layer ( 13 ), wherein the first laser ( 21 ) pulsed laser radiation ( 210 ) having a pulse duration of less than about 50 ns, characterized in that at least one second light source ( 22 ), which pulsed laser radiation ( 220 ) is generated with a pulse duration of more than about 1 ns or contains a continuous wave laser or emits non-coherent radiation, the light ( 210 ) of the first laser ( 21 ) impinges at a time at which at least the partial area ( 105 ) of the surface is in thermal equilibrium with the environment.
  2. Method according to claim 1, characterized in that the first laser ( 21 ) has a wavelength of about 200 nm to about 2000 nm and / or the first laser ( 21 ) has a beam spot size of about 2 microns to about 100 microns and / or the first laser ( 21 ) has a pulse duration of about 10 fs to about 1 ns.
  3. Method according to one of claims 1 or 2, characterized in that the second light source ( 22 ) has a wavelength of about 200 nm to about 2000 nm or from about 3 microns to about 25 microns and / or the second light source ( 22 ) has a beam spot size of about 2 microns to about 100 microns and / or the second light source ( 22 ) has a pulse duration of from about 1 ns to about 1000 ns.
  4. Method according to one of claims 1 to 3, characterized in that the beam spot of the first laser ( 21 ) at least over a partial area ( 105 ) the surface of the layer is screened, wherein the feed corresponds in about 90% to about 100% of the beam spot size.
  5. Method according to one of claims 1 to 4, characterized in that the beam spot of the second light source ( 22 ) is rastered over at least a portion of the surface of the layer, wherein the feed corresponds in about 1% to about 60% of the beam spot size.
  6. Method according to one of claims 1 to 5, characterized in that the radiation ( 220 ) of the second light source ( 22 ) delayed after the radiation ( 22 ) of the first laser ( 21 ) hits the surface and / or that the radiation of the second light source ( 22 ) delayed by more than 1 ns or more than 100 ns after the radiation of the first laser ( 21 ) hits the surface.
  7. Method according to claim 6, characterized in that the beam spot of the second light source ( 22 ) the beam spot of the first laser ( 21 ) follows at a predeterminable distance.
  8. Method according to one of claims 6 or 7, characterized in that the point of impact of the beam spot of the second light source ( 22 ) with a control device ( 28 ) is regulated to a predefinable setpoint.
  9. Method according to one of claims 1 to 5, characterized in that the radiation ( 220 ) of the second light source ( 22 ) coincident with the radiation of the first laser ( 21 ) on the surface ( 105 ) meets.
  10. Method according to one of claims 1 to 9, characterized in that the surface ( 120 ) a roughness ( 101 ) from about 1 μm to about 5 μm and / or that the layer ( 13 ) contains or consists of a dielectric.
  11. Method according to one of claims 1 to 10, characterized in that it forms at least one process step in the manufacture of a photovoltaic cell.
DE102012214335.1A 2012-08-10 2012-08-10 Method for ablating a layer Pending DE102012214335A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE102012214335.1A DE102012214335A1 (en) 2012-08-10 2012-08-10 Method for ablating a layer

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102012214335.1A DE102012214335A1 (en) 2012-08-10 2012-08-10 Method for ablating a layer
PCT/EP2013/066623 WO2014023798A2 (en) 2012-08-10 2013-08-08 Method for ablating a layer

Publications (1)

Publication Number Publication Date
DE102012214335A1 true DE102012214335A1 (en) 2014-02-13

Family

ID=49000920

Family Applications (1)

Application Number Title Priority Date Filing Date
DE102012214335.1A Pending DE102012214335A1 (en) 2012-08-10 2012-08-10 Method for ablating a layer

Country Status (2)

Country Link
DE (1) DE102012214335A1 (en)
WO (1) WO2014023798A2 (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102015114240A1 (en) * 2015-08-27 2017-03-02 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Apparatus and method for processing a semiconductor substrate by means of laser radiation
CN106744674A (en) * 2017-01-11 2017-05-31 兰州空间技术物理研究所 A kind of manufacture method of across the yardstick function micro-nano structure in surface

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102005045704A1 (en) * 2005-09-19 2007-03-22 Gebr. Schmid Gmbh & Co. Method and device for processing substrates, in particular solar cells
US20090166562A1 (en) * 2006-06-07 2009-07-02 Micah James Atkin Production of microfluidic devices using laser-induced shockwaves
US20110300692A1 (en) * 2008-10-29 2011-12-08 Oerlikon Solar Ag, Trubbach Method for dividing a semiconductor film formed on a substrate into plural regions by multiple laser beam irradiation
US8158493B2 (en) * 2008-03-21 2012-04-17 Imra America, Inc. Laser-based material processing methods and systems

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102004013475B4 (en) * 2004-03-18 2007-01-25 Lasertec Gmbh Method and device for removing material
US7169687B2 (en) * 2004-11-03 2007-01-30 Intel Corporation Laser micromachining method
DE102009026410A1 (en) * 2009-05-20 2011-03-17 Carl Baasel Lasertechnik Gmbh & Co. Kg Method for separating silicon solar cells

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102005045704A1 (en) * 2005-09-19 2007-03-22 Gebr. Schmid Gmbh & Co. Method and device for processing substrates, in particular solar cells
US20090166562A1 (en) * 2006-06-07 2009-07-02 Micah James Atkin Production of microfluidic devices using laser-induced shockwaves
US8158493B2 (en) * 2008-03-21 2012-04-17 Imra America, Inc. Laser-based material processing methods and systems
US20110300692A1 (en) * 2008-10-29 2011-12-08 Oerlikon Solar Ag, Trubbach Method for dividing a semiconductor film formed on a substrate into plural regions by multiple laser beam irradiation

Also Published As

Publication number Publication date
WO2014023798A3 (en) 2014-06-12
WO2014023798A9 (en) 2014-04-03
WO2014023798A2 (en) 2014-02-13

Similar Documents

Publication Publication Date Title
JP5193058B2 (en) Back contact solar cell
ES2354400T3 (en) Formation of a high quality back contact with a field in the local located rear surface.
US7781856B2 (en) Silicon-based visible and near-infrared optoelectric devices
US7390689B2 (en) Systems and methods for light absorption and field emission using microstructured silicon
US5897331A (en) High efficiency low cost thin film silicon solar cell design and method for making
JP2013157641A (en) Metal wiring contact structure and method for patterning layers
FI117608B (en) A method for performing integrated laser structuring of thin-film solar cells
EP2164107A2 (en) Apparatus and method for fabrication of silicon-based detectors having laser-microstructured sulfur-doped surface layers
JP2007201304A (en) Solar cell and its manufacturing method
Röder et al. Add‐on laser tailored selective emitter solar cells
ES2267815T3 (en) Procedure to produce a metallic semiconductor contact through a dielectric layer.
KR20110138394A (en) Apparatus and method for solar cells with laser fired contacts in thermally diffused doped regions
Hilali et al. Development of screen-printed silicon solar cells with high fill factors on 100/spl Omega//sq emitters
US7354792B2 (en) Manufacture of silicon-based devices having disordered sulfur-doped surface layers
Knorz et al. Selective laser ablation of SiNx layers on textured surfaces for low temperature front side metallizations
Haas et al. High speed laser processing for monolithical series connection of silicon thin‐film modules
US7259321B2 (en) Method of manufacturing thin film photovoltaic modules
CN101689580B (en) Solar cells
JP5643294B2 (en) Local metal contacts by local laser conversion of functional films in solar cells
CN102439728B (en) Form the method for the structure in solar cell
US5011567A (en) Method of fabricating solar cells
AU2006317517A1 (en) High efficiency solar cell fabrication
JP2012508473A (en) Solar battery
Dobrzański et al. Surface texturing of multicrystalline silicon solar cells
JPH08191152A (en) Solar cell and production thereof

Legal Events

Date Code Title Description
R012 Request for examination validly filed
R079 Amendment of ipc main class

Free format text: PREVIOUS MAIN CLASS: B23K0026060000

Ipc: B23K0026360000

R082 Change of representative

Representative=s name: ANDRAE WESTENDORP PATENTANWAELTE PARTNERSCHAFT, DE

Representative=s name: FRIESE GOEDEN PATENTANWAELTE PARTGMBB, DE

Representative=s name: FRIESE GOEDEN, DE

Representative=s name: FRIESE GOEDEN PATENTANWAELTE, DE

R016 Response to examination communication
R082 Change of representative

Representative=s name: FRIESE GOEDEN PATENTANWAELTE PARTGMBB, DE

Representative=s name: FRIESE GOEDEN, DE

Representative=s name: FRIESE GOEDEN PATENTANWAELTE, DE