WO2015014489A1 - Method for structuring an electrically conducting or semiconducting layer - Google Patents

Abstract

Structuring an electrically conducting or semiconducting layer, by means of which one or a plurality of layer regions (6) of the layer are electrically insulated and/or the electrical conductivity of the one or the plurality of layer regions of the layer can be set purposefully. In the method, the layer between and/or alongside the layer regions (6) to be insulated is locally irradiated with energetic radiation. Alternatively, the one or the plurality of layer regions of the layer intended to be set purposefully in terms of the conductivity thereof is or are irradiated with energetic radiation. For the irradiation of the layer, a radiant intensity below the removal threshold of the layer material and below a melt threshold of the layer material is chosen, in the case of which a modification of the layer material leads to the production of electrically insulating layer properties or purposefully reduced electrical conductivity as layer properties. The modification is effected by introducing trap states for free charge carriers into the layer material or by extracting dopants for free charge carriers from the layer material.

Description

Process for structuring an electrically conductive or semiconductive layer

Technical application

 The present invention relates to a method for structuring an electrically conductive or semiconducting layer, by which one or more

Layer regions of the layer are electrically insulated, or by the electrical conductivity of one or more layer regions is set specifically.

Thin-film electronics, in particular organic electronics, are based on thin layers of electrically conductive, semiconductive or insulating materials. Typical layer thicknesses are between a few 10 nanometers and a few micrometers. Particularly in the case of organic light-emitting diodes, thin-film transistors for LCDs or in thin-film photovoltaics, transparent electrodes are required in order to disconnect or couple in light. For this purpose, mostly transparent,

electrically conductive oxides (TCO) used. Due to its high conductivity at the same time high

Transparency is very often used indium tin oxide (ITO) as electrode material. Also transparent organic, electrically conductive materials are used. Examples of these are PEDOT: PSS (poly-3,4-ethylenedioxythiophene: polystyrene sulfonate) or

Graphs.

The transparent electrodes must be structured according to their application and electrically from each other be isolated. Semiconducting layers must also be isolated between the individual components in order to avoid the so-called cross-talk between the components. In all cases, a structuring of an electrically conductive or semiconductive layer is thus required, by means of which a plurality of layer regions of the layer are electrically isolated from one another.

State of the art

 The structuring of transparent electrodes currently takes place, as a rule, by local removal of the electrically conductive layer. By means of complex wet-chemical processes, the TCO material is locally removed by etching. In this case, the TCO layer must be prepared by means of photoresist and lithography, for example by suitable masking.

Another possibility is to convert an amorphous TCO layer in certain areas selectively into a polycrystalline layer having the required electrical conductivity. The remaining amorphous layer can then be removed with an etching process. After the etching process must

Cleaning steps are carried out. For example, US 2010/0105196 A1 shows a method for structuring an ITO layer, in which initially an amorphous ITO layer is applied and subsequently converted into polycrystalline ITO by irradiation by means of a laser beam in the desired regions. The remaining amorphous ITO is then etched away. Due to the selective removal of the amorphous layer during the etching process, the polycrystalline regions remain unaffected. This method thus produces a structured polycrystalline ITO layer.

Another known technique for structuring a TCO layer is the direct removal of layer areas with energetic radiation, in particular laser radiation. For example, EP 1589579 A2 shows a method for structuring an ITO electrode on a passive matrix display. The OLED-based passive matrix display is structured in one step, in which the ITO layer is combined with the overlying, organic layer

Layers is removed selectively. For this purpose is

Laser radiation in the wavelength range between 248 nm and 355 nm with pulse durations in the picosecond to

Nanosecond range used.

In the removal processes by means of laser radiation, adjacent layers are damaged. In addition, patches may appear at the edge of the ablated areas that are several tens of nm high, as well

unwanted deposits of erosion products (debris) on the unprocessed layer. The thickness of the

Subsequent semiconductive layer is often of the same order of magnitude, so that the conductive

Edge jams or the debris pierce the semiconductive layer. This can lead to short circuits and component failure. Therefore edge edgings must be avoided by selecting suitable process windows for these processes. The debris has to go through

Cleaning processes are removed. From Itoh, E., Torres, I., Hayden, C, Taylor, DM: "Excimer laser micropatterned photobleaching as a means of isolating polymer electronic devices", In: Synthetic Metals, 2006, 129-134, a method is known in which the conductivity of a layer of poly (3-hexylthiophene) (P3HT) is reduced by up to two orders of magnitude by UV irradiation by means of an excimer laser with a beam intensity below the ablation threshold. The reduced conductivity is due to a decrease in the π-onjugation by either breaking of chains or photooxidation of the polymer.

In US 2002/0058366 AI is a method for

Conversion of amorphous silicon into polycrystalline

Silicon disclosed in which the silicon is locally melted by means of pulsed laser radiation, the absorption coefficient in amorphous silicon is greater than their absorption coefficient in polysilicon.

The object of the present invention is to provide a method for structuring a

electrically conductive or semiconducting layer

which does not cause edge deposits or deposits of erosion products and can be easily performed without the need for subsequent purification processes.

Presentation of the invention

 The object is achieved with the method according to

Claim 1 solved. Advantageous embodiments of the method are the subject of the dependent Claims or can be taken from the following description and the exemplary embodiments.

In the proposed method for structuring an electrically conductive or semiconductive layer, by which one or more layer regions of the layer are electrically insulated or by which an electrical conductivity of one or more layer regions of the layer is deliberately adjusted, the layer between and / or next to the layer areas to be isolated or the one or more

Layer regions whose or their conductivity is set, irradiated with energetic radiation, preferably with laser radiation. For the irradiation of the layer with the energetic radiation, a beam intensity below the ablation threshold of the layer material and below a threshold of the layer material is selected, in which the layer between and / or next to the layer regions to be insulated by a modification of the layer material electrically insulating properties receives or in which the one or more layer regions whose or whose conductivity is to be adjusted specifically, obtained by a modification of the layer material, the conductivity to be set. The modification takes place by introducing case states for free charge carriers (electrons or holes) into the layer material and / or by dissolving out dopants, which lead to free charge carriers in the layer material. Under a specific adjustment of the conductivity is the

Setting the conductivity to a given value or range of values understood. Dot dopants are generally understood to mean atoms or parts of molecules which supply free charge carriers. For example, in semiconducting materials, these can be electron acceptors that are free

generate mobile holes, or electron donors that generate free-moving electrons.

The dissolution of the dopants is preferably carried out in intrinsically semiconducting materials as well as in organic conductors, for example in TCOs (for example ITO) or organic semiconductors, which are distinguished by specific

Molecule parts are doped.

In intrinsically conductive materials, trap states are preferred, for example in the form of impurities, lattice defects or grain boundaries

be introduced.

Under the dissolution becomes general

understood that the dopants from the irradiated

Layer or layer areas are removed, which are isolated or their conductivity adjusted. The dopants can either escape from the layer, so that they no longer in the

Sample containing the irradiated layer areas are, or are shifted in the layer

(Dislocation), so that largely undoped areas or areas with reduced doping remain. The dislocation of the dopants, for example, in inorganic semiconductors and organic

Semiconductors done. In organic semiconductors, bonds to dopants are formed during irradiation. Particles broken up and created new bonds or doping parts of the molecule leave the layer.

The proposed method is thus based on the local modification of the layer material by means of energetic radiation, in particular laser radiation. For this purpose, the electrically conductive or semiconducting layer, for example an organic layer or a TCO layer, is irradiated below its removal threshold, so that no removal of material takes place by the irradiation. In addition, the irradiation also takes place below the threshold, i. there is no melting of the layer by the irradiation. By a caused by the irradiation

 Changes in the irradiated areas of the layer are destroyed in one alternative of the method, the electrical conductivity or the semiconductor properties. Thus, individual areas can be electrically isolated from each other, without removing the originally conductive or semiconducting layer.

Alternatively, the change caused by the irradiation becomes the conductivity of the

targeted irradiated layer material, in particular selectively reduced. It has the

However, irradiated layer region still has a conductivity, so that adjacent to the irradiated layer region layer areas are not isolated from each other. In particular, the conductivity of the irradiated layer region is above 0.004 S / cm. Under a specific adjustment of the conductivity, the adjustment of the conductivity to a predetermined to understand the conductivity value or range. In this case, preference is given to parameters of the energetic radiation, for example pulse number per position,

Pulse energy, fluence, wavelength and pulse duration, chosen such that the conductivity of the irradiated layer region compared to in the lateral direction, i. Although in the layer direction, adjacent layer areas reduced but not destroyed.

 This can be achieved, for example, by selecting the penetration depth of the energetic radiation, which may be dependent on wavelength, irradiation duration, dose, number of pulses per position and / or fluence, to be smaller than the layer thickness. Thus, the irradiated layer region is not modified over the entire layer thickness, but only over a depth that is smaller than the layer thickness, so that the layer region is not completely deactivated / isolated, but retains a specifically adjustable via the penetration depth conductivity. Alternatively or in combination, the number or the density of the introduced case states or of the dissolved-out dopants and thus a conductivity of the irradiated layer region can be influenced in a targeted manner by irradiating the layer and / or the one or more layer regions under predetermined atmospheric conditions For example, a certain process gas atmosphere, a pressure of the atmosphere, the chemical effect of

Atmosphere, e.g. reducing or oxidizing

Atmosphere, or a treatment of the layer under liquid is selected. The energy input required in each case for both variants of structuring depends on the layer material and can easily be determined by preliminary experiments with different energies or intensities of the energetic beam and irradiation times. Preferably, the radiation is pulsed for the irradiation

Laser radiation used, wherein the local modification can be done both with a single laser pulse as well as with a sequence of laser pulses. The pulse durations are preferably in the nanosecond range or at even shorter pulse durations. However, longer pulses or cw laser radiation can also be used.

Under structuring, the proposed method thus either produces smaller electrically conductive or semiconducting layers

Regions understood from a larger layer region of an electrically conductive or semiconducting layer, which are separated from each other via electrically insulating regions, or the generation of smaller electrically conductive or semiconducting regions with specifically set or modified, in particular reduced, conductivity understood. The method can be used to isolate several electrically conductive or semiconductive layer areas from one another. Even an electrical isolation of only a single layer area is possible. Both methods can also be used side by side in a layer, i. in a part of the layer becomes the

Conductivity is destroyed (insulation) and in another part of the layer, the conductivity is targeted

set, in particular reduced, but without destroying the conductivity. A modification of the layer material is a change in the solid state structure and / or the chemical composition of the layer material

Understood. The erosion threshold denotes the limit intensity of the energetic beam, from which a removal of the layer material by the beam occurs. The wavelength of the laser radiation preferably used for the irradiation is preferably in the ultraviolet ray range, particularly preferably at a wavelength of ^ 300 nm, but may also be at other wavelengths, i. in the visible or infrared

Wavelength range are. To the electric

the insulating properties over the entire layer thickness with the irradiation, the

Wavelength depends on the respective

Layer material chosen so that it still completely penetrates the layer despite the absorption required. Electrically insulating properties are understood as meaning an electrical conductivity of <0.004 S / cm.

The proposed method can be added

Wavelengths of> 300 nm are particularly advantageous for structuring ITO layers or PEDOT: use PSS layers. However, the method is not based on these layer materials or on transparent

Limited layers or electrodes. The semiconducting properties of organic semiconductors can also be destroyed by the proposed irradiation below the erosion threshold or can be selectively changed or adjusted, in particular reduced, with respect to the conductivity. With TCOs (eg ITO) an increase of the conductivity can be achieved. in this connection the number of trap states at the grain boundaries is reduced. With the radiation used, in particular with laser radiation in the deep ultraviolet spectral range, the responsible for the semiconductor properties π-electron systems are destroyed. Individual regions of an organic semiconductor layer can thus be isolated from one another, whereby the unwanted cross-talk is avoided. Depending on the respective semiconductive or electrically conductive layer, for example, bonds are broken in the modification, parts of the molecule dissociate and the layer escapes. Especially with inorganic layers there is a dislocation of the electrical

Conducting responsible dopants instead. In addition, the modification can be made by using

be reinforced suitable process gases. Thus, for example, electron acceptors can be introduced into an n-conducting layer of electron acceptors or into a p-conducting layer by thermal diffusion during irradiation from the gas phase, which act as additional trap states.

Alternatively, in one embodiment of the

proposed method, the modification of an n-type layer in that electrons onators are released from the layer. Accordingly, in one embodiment of the proposed

Method, the modification of a p-type layer carried out in that electron acceptors are released from the layer.

In one embodiment of the proposed

Procedure, the irradiation can also be done with laser radiation different laser or wavelengths simultaneously or immediately after each other. Also, this can reduce the electrical conductivity to form the insulating properties.

The proposed method becomes a

Material modification in the electrically conductive or semiconducting layer generated by the electrically conductive or semiconductive layer regions

can be isolated from each other without this

 Remove or remove material. Since the structuring by means of modification is not on the

Based on the removal of the layer, the disadvantages associated with the removal do not arise. Thus, the proposed method avoids both edge drops and debris consisting of erosion products. This makes it possible to dispense with a subsequent cleaning step. Since the structuring is carried out by means of modification below the removal threshold of the layer material, a lower pulse energy than for the removal of the layer is required. This offers the advantage that the proposed modification by means of energetic or laser radiation can be done much faster than a removal by means of laser radiation. For example, the layer can be processed to a high degree in parallel by splitting laser pulses of high pulse energy into a plurality of partial beams by diffractive optical elements, through which a simultaneous modification of different layer areas can then take place. In a further embodiment, the technique of

Use mask projection, in which large areas are structured by means of individual laser pulses can. Thus, especially when using excimer laser radiation, the area that with a

individual pulse can be structured, increased by the proposed method of pure modification by more than a factor of 10 compared to the area that would be required for a removal of the corresponding areas. The scaling of the surface is possible by a simple change of the imaging ratio in the mask projection. Furthermore, the resolution of the structures produced can also be achieved

Increase mask mapping and mask projection techniques. The low pulse energy required for modification, compared to a removal, also reduces the risk of damaging the surrounding material or adjacent layers.

Another preferred embodiment involves beam deflection by means of fast scanners. Under a fast scanner becomes here a system

understood that moves the laser beam over the sample with up to several 100 m / s (polygon scanner).

In a further embodiment of the method according to the invention, a wavelength of the energetic radiation, preferably the laser radiation, is selected such that its penetration depth is greater than a layer thickness of the layer. This ensures a modification of the layer over the entire layer thickness. If the penetration depth is chosen smaller than the layer thickness, the layer can not be completely deactivated or isolated. In a further preferred embodiment of the method according to the invention, a conductivity gradient or conductivity profile is generated in a section of the layer by varying at least one parameter of the energetic radiation. The at least one parameter is selected from a group of parameters that includes number of pulses per point, pulse energy, fluence, wavelength and pulse duration. The conductivity profile can be adjusted in the vertical and / or in the lateral direction of the layer. The conductivity profile in the lateral direction, ie in the layer direction, can be, for example, stepped by stepwise variation of at least one parameter or gradually by continuous change

at least one parameter of the energetic radiation can be adjusted. A conductivity gradient or course can be achieved, for example, by irradiating the section of the layer in the lateral direction with energy radiation of different penetration depth, so that the modified regions reach different depths.

Alternatively or in combination, the conductivity gradient or course in the lateral direction can also be achieved by varying the

Parameters, e.g. Fluence, number of pulses per site, the number or density of the trap states or of the released dopants is varied. The inventive method thus allows in this embodiment, the targeted and flexible adjustment of the conductivity. In this way, in the operation of the electrically conductive or semiconducting layer, the local

Current density distribution and thus the flow of current in the layer are selectively influenced or controlled. The The method can therefore be used particularly advantageously for this purpose, for example by being transparent

To produce electrodes with a gradient conductivity distribution to avoid voltage peaks at corners.

In principle, in the proposed method also different kind of energy radiation than

Laser radiation are used. So can the

Modification, for example, can also be achieved by means of electron beam machining. However, this processing must be performed in contrast to the processing with laser radiation in a vacuum. The proposed method can be used above all in thin-film electronics, in particular in large-scale, organic electronics. In these areas of electronics, individual thin layers with different electrical properties are used. The individual layers must be structured according to their application.

Corresponding application examples are in

Introduction to the description of the technical field of application mentioned. Of course, the proposed method is not limited to these applications.

Brief description of the drawings

The proposed method will be explained in more detail using exemplary embodiments in conjunction with the drawings. Hereby show: Fig. 1 is a schematic representation of

 Irradiation of an electrically conductive layer according to the proposed

 Method;

Fig. 2 is a comparison of the structuring of

 electrically conductive layer by means of a) laser ablation and by means of b) the proposed method; and

Fig. 3 is a schematic representation of a

 correspondingly structured region of an electrically conductive layer in plan view.

Ways to carry out the invention

 In the proposed method, an electrically conductive or semiconducting layer is structured such that electrically conductive regions of a specific geometry, for example, conductor tracks or the

Application appropriately shaped electrodes are formed, which are separated by electrically insulating areas. FIG. 1 shows a highly schematic example of an implementation of the proposed method. In the figure is a

Substrate 2 to recognize, for example, a glass substrate on which a corresponding electrically conductive layer 1 is applied. This layer may, for example, be an ITO layer or a PEDOT: PSS layer

act, which is electrically conductive and transparent. In the proposed method, this layer 1 in the present example with a laser beam 3 of a Lasers 4 irradiated, which is guided via a scanning device 5 over the areas to be irradiated. The corresponding optics, in particular the focusing optics for the laser beam 3, are not shown here. During irradiation, it is also possible to modify several areas in parallel via a mask projection at the same time or by splitting the laser beam into a plurality of partial beams. The laser intensity is chosen in each case so that no material removal takes place, but the layer material is modified so that the electrical conductivity or the semiconductor properties of the layer 1 in the irradiated areas are destroyed. So the electrical conductivity is in one

ITO layer, for example. A layer thickness of 100 nm, reduced by irradiation with individual laser pulses in the ultraviolet spectral range by more than five orders of magnitude. In this case, for example, pulses with 30 ns

Come pulse duration at the wavelengths 193 nm, 248 nm or 266 nm at a pulse energy in the range of 10-500 mJ / cm ² are used. The modification is accompanied by a negligible increase in roughness. When using laser radiation of longer wavelengths multiphoton interactions or local thermal processes lead to the elimination of electrical conductivity. Also, the combination may be

Electron excitation using ultraviolet radiation of low intensity and the subsequent thermal or linear excitation by means of longer wavelengths lead to the desired modification. In another example, the electrical conductivity of a layer of the organic conductor PEDOT: PSS is modified by the irradiation by means of individual pulses of wavelengths less than 300 nm below the erosion threshold so that it is destroyed. The optical penetration depth of the radiation must be greater than the layer thickness, so that the layer is modified in its full thickness. In the case of a 100 nm thick PEDOT: PSS layer, this can be achieved, for example, with laser pulses having a wavelength of 248 nm. At a pulse energy of 330 mJ / cm ² , the electrical conductivity of the layer in the

irradiated layer areas are completely destroyed.

FIG. 2 shows a schematic representation of a comparison of the known laser structuring by means of material removal in partial image a) with the proposed method in partial image b), in which the laser structuring takes place by means of material modification. From the figure it can be seen that in the previous technique of laser structuring by means of material removal at the edges of the electrically conductive regions 6, undesired edge drops 8 occur. Furthermore, unwanted deposits of debris 7 on the surface of the electric

caused conductive areas ^' 6. In contrast, in the proposed method neither erosion products nor edge throws are produced. Rather, the proposed method is merely a modified

Layer region 9 between the electrically conductive layer regions 6 generates, which is electrically insulating. Thus, there is no layer removal and also no removal of the layer material between the electrically conductive regions 6, for example by etching.

FIG. 3 shows an example of a plan view of a section of a correspondingly structured layer region, for example for producing parallel, electrically transparent electrodes on a glass substrate. In the figure, the electrically conductive regions 6 can be seen, which form the electrodes and modified by the corresponding

 Layer regions 9 are electrically isolated from each other. Such processing of parallel areas can, for example, by mask projection of a corresponding

Exposure structure or by parallel processing with multiple partial beams of a laser done.

LIST OF REFERENCE NUMBERS

1 electrically conductive layer 2 substrate

 3 laser beam

 4 lasers

 5 scanning device

 6 electrically conductive areas 7 debris

 8 edge throw

 9 modified layer area

Claims

claims Method for structuring an electrically conductive or semiconductive layer (1), by the one or more layer regions (6) of the layer (1) are electrically insulated or by the electrical conductivity of one or more layer regions of the layer (1) is set specifically, in which the layer (1) between and / or adjacent to the layer regions (6) to be insulated is irradiated with energetic radiation, or in which the one or more layer regions of the layer (1), whose or their conductivity is to be adjusted specifically, with energetic Radiation is irradiated, wherein for the irradiation of the layer (1) with the energetic radiation, a beam intensity below the removal threshold of the layer material and below a threshold of the Layer material is selected, in which the layer (1) between and / or adjacent to the insulating layer regions (6) by a modification of the layer material electrically insulating properties or in which the one or more layer regions of the layer (1), whose or their conductivity is targeted to adjust, by a modification of the layer material the get adjusted conductivity, and wherein the modification by introducing Fall conditions for free charge carriers in the Layer material and / or by dissolving out dopants for free charge carriers from the Layer material takes place. Method according to claim 1, characterized, that the irradiation of the layer (1) with Laser radiation (3) takes place as energetic radiation. Method according to claim 1 or 2, characterized, the irradiation of the layer (1) takes place with pulsed laser radiation (3). Method according to one of claims 1 to 3, characterized that the irradiation of the layer (1) with Laser radiation (3) of a wavelength in ultraviolet spectral range occurs. Method according to claim 4, characterized, that the irradiation of the layer (1) with Laser radiation (3) of a wavelength ^ 300 nm takes place. Method according to one of claims 1 to 3, characterized that the irradiation of the layer (1) with Laser radiation (3) from at least two lasers simultaneously or immediately one after the other of which a first laser is laser radiation (3) in a first spectral range and a second laser laser radiation (3) with a generated over the first laser larger wavelength. Method according to one of claims 1 to 6, characterized that the layer (1) is exposed during the irradiation of a gas atmosphere or a gas flow of a process gas, by means of thermal diffusion in an n-type Layer (1) electron acceptors or in a p-type layer (1) electron donors are introduced into the layer (1). Method according to one of claims 1 to 6, characterized that the layer (1) during the irradiation of a liquid is partially or completely covered, by means of thermal Diffusion in an n-type layer (1) Electron acceptors or in a p-type layer (1) electron donors are introduced into the layer (1). Method according to one of claims 1 to 6, characterized that with n-type layers electron donors are released from the layer, and / or that in p-type layers Electron acceptors are released from the layer. Method according to one of claims 1 to 9, characterized that the irradiation of the layer (1) by means of Mask projection takes place. Method according to one of claims 1 to 9, characterized that the irradiation of the layer (1) takes place in parallel with a plurality of laser beams, the meet different places on the layer (1). Method according to one of claims 1 to 9, characterized in that the irradiation of the layer by means of a laser beam, which is deflected by means of a fast scanner. Method according to one of claims 1 to 12 for structuring a layer (1) of an optically transparent organic or inorganic Material. Method according to one of claims 1 to 13, characterized in that in the layer by variation of at least one parameter of energetic radiation in a section of the layer (1) a conductivity gradient or Conductivity is generated, and that the at least one parameter from a Group of parameters comprising pulse rate per digit, pulse energy, fluence, wavelength and pulse duration. 15. The method according to any one of claims 1 to 14, characterized in that the conductivity is selectively reduced. 16. The method according to any one of claims 1 to 13,  characterized in that a wavelength of the energetic radiation is chosen such that the optical penetration depth is greater than one  Layer thickness of the layer is.