GB2381274A

GB2381274A - High resolution patterning method

Info

Publication number: GB2381274A
Application number: GB0125815A
Authority: GB
Inventors: Daniel Robert Johnson; William Norman Damerell; Anthony Willi Kynaston-Pearson; Stephen George Appleton; Gregory Peter Wade Fixter
Original assignee: Qinetiq Ltd
Current assignee: Qinetiq Ltd
Priority date: 2001-10-29
Filing date: 2001-10-29
Publication date: 2003-04-30
Also published as: EP1440181A2; JP2005507461A; WO2003038146A3; WO2003038146A2; GB0125815D0; US20050003101A1

Abstract

An object of the present invention to provide a method of preparing a substrate material such that it is capable of initiating a catalytic reaction over a pre-determined area of its surface. This is achieved by preparing a substrate so that it is capable of sponsoring a catalytic reaction over a pre-determined area of its surface by the steps of <SL> <LI>i) coating some or all of the substrate material with a first layer material, the first layer material comprising a catalytic material; <LI>ii) coating the first layer material with a second layer material, the second layer being incapable of promoting and/or sustaining the desired catalytic reaction; and <LI>iii) using a scribing process to remove a pre-determined pattern of material from the second layer material in order to expose the first layer material. Scribing is carried out by ablating patterns by the use of energetic media such as lasers or electron beams. </SL> After carrying out this process an autocatalytic plating layer may be applied to the exposed areas. The second layer material may be applied as an ink formulation and may include binders and fillers.

Description

HIGH RESOLUTION PATTERNING METHOD This invention relates to a method of forming high resolution patterns of material on a substrate and encompasses the fields of catalytic reactions (especially autocatalytic coating methods) and also scribing methods using energetic media.

"Scribing"refers to the techniques of ablating accurate and narrow patterns or lines in a target material. In such methods an energetic media such as a laser, AFM (Atomic Force Microscope), STM (Scanning Tunnelling Microscope), ion, or electron beam is used to scribe the pattern into the target material.

Autocatalytic plating is a form of electrode-less (electroless) plating in which a metal is deposited onto a substrate via a chemical reduction process. The advantage of this technology is that an electric current is not required to drive the process and so electrical insulators can be coated. Coatings derived by this technique are usually more uniform and adherent than from other processes and can be applied to unusually shaped surfaces (see Deposition ofinorganic Filmsftom Solution, Section III Ch 1 pp 209-229; Thin Film processes (1978) ; Publishers Academic Press and, Smithells Metals Reference Book, 7th Edition (1992) Chapter 32, ppl2-20 ; Publishers Butterworth Heinmann.) Processes exist for the autocatalytic deposition of a large number of metals, particularly cobalt, nickel, gold, silver and copper from a suitable solution bath.

Basically, the solutions contain a salt of the metal to be deposited and a suitable reducing agent, e. g. hypophosphite, hydrazine, borane etc. When a metal substrate, which is catalytic to the reaction, is introduced into the solution bath it becomes covered with a layer of the coating metal which itself is catalytic so that the reaction can continue.

Deposition will only occur if conditions are suitable on the substrate to initiate and then sustain the autocatalytic process. Therefore in cases where the substrate is a plastic or ceramic, for example, additional steps are required to create suitable surface properties. Usually, in such cases the substrate is"sensitised"with a reducing agent,

e. g. SnCIs. Also, the surface may be"activated"with a thin layer of an intermediate catalytic material, e. g. Palladium (itself a candidate metal for autocatalytic deposition), in order to aid the deposition process. Such"deposition promoting materials"are generally referred to in the literature as"sensitisers"and"activators" respectively.

Autocatalytic deposition is generally employed to coat whole surfaces. However, in order to form metal patterns, e. g. for electrical circuits or decorative effects, additional processes such as photolithography followed by etching of surplus metal have to be performed. There are disadvantages to these additional processes, including inflexibility, long lead times, increased costs and the use of excessive materials to provide coatings much of which is then subsequently removed as waste.

There are many types of catalytic reaction (including the autocatalytic reaction described above) that can take place over the surface of a substrate material and such reactions can be used to increase the rate of or activate reactions in gas, liquid or solid environments.

The"catalytic materials"that are used in such reactions include"deposition promoting materials" (as defined above) but also include other heterogeneous catalysts and homogeneous catalysts. Heterogeneous catalytic materials include metals such as platinum, rhodium and palladium and metal oxides containing catalytic sites, e. g. perovskite cage structures. These catalysts are used in synthetic or decomposition reactions in organic or inorganic chemistry, for example in the Fischer-Tropsch synthesis of organic molecules from hydrogen and carbon monoxide , cracking, or in the decomposition of hydrocarbons. Homogeneous catalytic materials include enzymes which are used, for example in biochemical testing in diagnostic arrays and for de-compositional analysis of biopoloymers and systems that mimic proteozone behaviour. Homogeneous catalysts also include negative catalysts, commonly known as inhibitors, which moderate reactions.

Generally in such reactions the catalytic material used is either applied to or is effective over the whole of the substrate material and as a consequence the reaction takes place over the whole of the substrate.

It is therefore an object of the present invention to provide a method of preparing a substrate material such that it is capable of initiating a catalytic reaction over a predetermined area of its surface.

Accordingly, this invention provides a method of preparing a substrate such that it is capable of sponsoring a catalytic reaction over a pre-determined area of its surface comprising the steps of : i) coating some or all of the substrate material with a first layer material, the first layer material comprising a catalytic material (as hereinbefore defined) ii) coating the first layer material with a second layer material, the second layer material comprising materials that are unable of promoting and/or sustaining the desired catalytic process iii) using a scribing process (as hereinbefore defined) to remove a pre-determined pattern of material from the second layer material in order to expose first layer material The invention is basically a three stage process which results in a substrate that has been prepared in such a way that it will sponsor a catalytic reaction over only part of its surface. The substrate, which may be any material, for example, metal (s), organic/inorganic compounds, ceramics or polymers, is initially treated with a catalyst material that will allow the substrate to sponsor a catalytic reaction. For example, if the catalyst material is a deposition promoting material then the substrate will be capable of being metal plated via an autocatalytic process. Alternatively, the catalyst may be a reaction promoting material for example aluminium chloride used in the electrophilic substitution in the Friedel-Crafts reaction.

The first layer of catalyst material is then coated with a second layer which is unable to sponsor the desired catalytic reaction. Conveniently, the second layer slightly overlaps the first layer in order to form a seal.

A scribing process, for example a laser scriber, is then used to scribe through the second layer in order to expose user defined areas of the first layer. Conveniently, the scribing process may be tuned to do this without undue damage to the first layer and

materials may be selected to enhance the specificity of the process. Equally, the scribing process may be used to produce grooves, pits or holes through both of the layers which at the same time transfers catalytic material from the first layer into these features for subsequent catalytic reaction.

This invention has a number of advantages over other process. The catalytic reaction will, once initiated, only occur within the scribed areas of the second layer as opposed to other processes which would involve etching in order to create the user defined patterns. There is therefore a reduction in the amount of wasted material.

The lines/patterns of catalytic material are constrained within the profile of the scribed line/groove. This reduces lateral spread of material into areas where there is no requirement for a catalytic reaction. The scribing grooves also offer protection from mechanical damage. In cases where the catalytic reaction involves deposition of a material (e. g. deposition of a metal plating in an autocatalytic reaction) then conveniently a further sealing layer can be added in order to encapsulate the deposited metal pattern.

Conveniently a pattern transfer mechanism such as inkjet printing, screen printing, pen writing or spray printing can be used to apply the first layer to the substrate material. The same (or different) pattern transfer mechanism can also be used to coat the first layer material with the second layer material.

The minimum feature sizes that result from the use of a pattern transfer technique are dependent on the particular mechanism used. For an ink jet printing technique features of the order 20 microns are possible. Screen printing and/or pen writing result in much coarser features being produced, e. g. up to 1000 microns. Features in the range 20-1000 microns are therefore possible depending on the mechanism used.

The use of pattern transfer mechanisms to apply the first and second layer materials further reduces the amount of material that needs to be applied to the substrate and therefore further reduces waste material.

Conveniently, the catalytic material can be synthesised from the printing of inks containing reagents that react together at a printed surface or can be contained directly in an ink formulation. The inks may be printed into a user-defined pattern with a chosen pattern transfer mechanism.

The second layer which is deposited onto the first layer comprises a material that is unable to promote the catalytic reaction. This second layer material can conveniently also be applied using a pattern transfer mechanism and can be contained within an ink formulation of its own which is suitable for use with the chosen pattern transfer mechanism. The pattern transfer mechanism used to deposit the second layer material need not be the same as the pattern transfer mechanism used to deposit the first layer material.

Conveniently, the ink formulations, for both the first and second layers, can, in addition to the first and second layer materials, contain binders and fillers which can enhance the properties of the intended catalytic process.

Any organic/inorganic material that will solidify or"set"and be adhered to the printable surface of the substrate may be used as a binder. Examples may be ink solutions containing polymers e. g. poly (vinyl acetate), acrylics, poly (vinyl alcohol) and/or inorganic materials that behave as cements or sol-gels coatings, e. g titanium isopropoxide and other alkoxides.

Fillers comprise insoluble particles contained in the ink that are small enough to transfer from the printer mechanism. Typically, 10-200 nm carbon black particles are added to colour inkjet inks and 1-100 micron graphitic carbon is added to screenprintable inks used in the fabrication of printed electrical conductors. Ceramics, organic dyes or polymer particles may be added to ink to provide colour and/or texture in the printed product e. g. titania, alumina, mica, glass, acrylics. The ink may therefore be formulated with any of these components and include the catalytic material to provide a wide range of properties.

The scribing process can be any one of a range of energetic ablation methods, for example a laser. The chosen scribing process can either be used to expose the first

layer material without causing undue damage or alternatively it may be used to remove (or bum off in the case of a laser scribing process) unwanted materials in the first layer in order to leave a more concentrated form of catalytic material.

The ink formulations for the first and second layers may conveniently be chosen to contain materials that enhance the scribing process. For example, the binders in the two layers may have different melting temperatures to enhance the scribing process.

The ink formulations may also contain fillers that absorb or reflect energy in order to actively assist in the retention of the catalytic material upon the substrate material.

The ink formulations may also contain materials that are sensitive to the particular scribing process that is used. For example, with a laser scribing process there are a large variety of laser types operating at different frequencies that could be used. The laser energy impinging on the target material could therefore be arranged to be reflected, transmitted or absorbed in a particular way dependent on the optical absorption characteristics of the materials contained in the first and second layer materials.

Once the substrate has been prepared in the manner described above then it can be introduced into a reaction environment suitable to initiate the required catalytic process. For example, if the chosen catalytic reaction is an autocatalytic coating method then the final stage of the process is to deposit a metal into the scribed areas.

This can be achieved by immersing the substrate in a suitable autocatalytic solution bath. In general terms the catalysed surface may be exposed to any reaction environment, including gas, vapour, liquid, solution or solid.

Certain catalytic reactions (such as the autocatalytic reaction above) will result in material being deposited onto the prepared substrate and in such cases the process according to the invention can be repeated in order to build up multiple material layers/patterns. Insulator layers can also be added to separate these different layers.

The resolution of the deposited material patterns is limited only by the characteristics of the scribing process.

Autocatalytic reactions are used to deposit metal onto a substrate. Such processes are generally used to deposit whole surfaces. However, the process according to the present invention can be used to deposit metal patterns in a pre-determined user defined manner. To deposit a metal coating the catalytic material is chosen to be a deposition promoting material. The prepared substrate in this case will then be suitable for subsequent metal plating by immersion in a suitable autocatalytic deposition solution.

The metal coating which is deposited into the scribed grooves by the autocatalytic deposition process may subsequently be coated with further metals through electroless deposition, provided the first autocatalytically deposited metal coating surface can catalyse or ion exchange with the subsequent metals. For example the exposed areas of a sensitised substrate may be autocatalytically coated with a layer of nickel which could then be further coated, via a further electroless process, with a coating of copper. Alternatively, if the first electroless coating is copper a further coating of tin may be deposited.

It is also possible for the autocatalytic deposition solution to contain two different metal salts which are then co-deposited onto a sensitised substrate at the same time, for example nickel and copper.

An autocatalytically deposited metal pattern may also be further coated with a wide range of metals or compounds by electrodeposition, provided there are continuous electrical paths in the pattern to act as the cathode of an electrolytic bath. An example is the electrodeposition of"chromium"plate onto nickel to prevent tarnishing.

Conveniently, the deposition promoting material can be contained in an ink formulation suitable for use with the chosen pattern transfer mechanism.

Conveniently, the ink formulations, for both the first and second layers, can, in addition to the first and second layer materials, contain binders and fillers which variously can enhance the properties of the final metal coating, enhance the adhesion

of the electroless metal to the substrate and which can provide porous and textured surface effects, which can change the mechanical, thermal, electrical, optical, and catalytic properties of depositing metal.

The inclusion of binders in the ink formulation may additionally serve to prevent loss of adhesion from the printed substrate of the deposition promoting agent during electroless coating. The inclusion of fillers may serve to improve contact between the deposition promoting agent and the autocatalytic solution bath.

As an alternative to including binders and fillers within the ink formulation the substrate may incorporate a porous layer which can influence the adhesion, scratch resistance and texture of the subsequent electroless metal coating. However, it may also be preferable to have an impervious substrate surface to maintain the integrity and resolution of the printed feature according to need.

The deposition promoting material may comprise a reducing agent (a"sensitiser") such as SnCb, glucose, hydrazine, amine boranes, borohydride, aldehydes, hypophosphites, tartrates.

As an alternative to, or as well as, a reducing agent, the deposition promoting material could be an activator such as a colloidal dispersion of a catalytic material. For example palladium, cobalt, nickel, steel or copper could be added to an ink formulation to catalyse a particular metal deposition.

As a further alternative, the deposition promoting material could be one that is able to ion exchange with the catalytic material contained within the autocatalytic solution bath. For example, Ni or Fe could be added directly to an ink formulation. Once the coated substrate is introduced into the autocatalytic solution bath the deposition promoting material undergoes ion exchange with the metal in the autocatalytic solution, thereby nucleating deposition of the electroless coating.

Where a chemical reducing agent is deposited onto a substrate to become the deposition promoting agent, the method may conveniently comprise a further step of immersing the now"sensitised"substrate into an intermediate solution bath of

reducible metal ions (prior to the final autocatalytic solution bath), to provide an "activating"metal overlayer on the deposition promoting agent. This further step has the effect of aiding the deposition promoting material and promoting easier deposition of certain metals (such as copper, nickel and cobalt).

For example, for the case of an ink formulation containing SnClz as the deposition promoting material, once the substrate material has had the SnClx applied to it, it can be immersed into an intermediate solution bath comprising a dilute aqueous solution ofPdCl. This causes the deposition of Pd metal onto the areas of the substrate coated with the deposition promoting material. If the Pd"activated"substrate is now immersed into an autocatalytic solution then autocatalytic deposition will take place onto the Pd metal. Such an intermediate step is useful in cases where the metal to be deposited from the autocatalytic deposition bath is either copper, nickel or cobalt.

As an alternative to the above the ink formulation could contain PdClx instead of SnCl2. Following deposition of this onto the substrate, an intermediate step could be to convert the PdCl2 on the surface of the substrate to Pd metal by immersion in a dilute aqueous solution ofSnClx. The application of the second layer material, scribing process and immersion in an autocatalytic deposition bath could then take place as before.

In a further alternative, the intermediate step could be omitted by using a"reduced" complex as the deposition promoting material, i. e. the deposition promoting material could be formulated to contain a combination of chemical species comprising both a reducing agent and an activator. For example, both SnCl2 (sensitiser) and PdCl (activator) could be added to the ink formulation. Following deposition of this first layer material onto the substrate the first layer material could then be coated with the second layer material, scribed using an appropriate scribing process and the substrate could then be introduced immediately into the autocatalytic deposition solution to deposit the metal of choice.

A variant of the above"reduced"complex option would be to use two sequential printing mechanisms, one containing the sensitiser material and the other containing a compound of a metal that can be reduced to an activator material. For example, if a

sensitiser like SnCl2 dissolved and contained in an ink having a binder is printed onto a printed ink layer containing dissolved PdClz and binder, then the two reagents will react whilst solvated to form a reduced complex containing catalytic Pd metal at the interface between the pril1. d layers. In the instance that the sensitiser is unable to promote a reaction in the autocatalytic solution bath, then the layer containing the sensitiser is also suitable as the second layer (as before defined). Otherwise another layer unable to sponsor reaction may be preferred to seal in both the sensitiser and activator materials. Once again the catalytic activator material is then accessed through a scribing process.

Embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure la shows the three stage preparation process described above as applied to a substrate material to be used in an autocatalytic plating process.

Figure 1 b shows the final stage of depositing a metal plating on the substrate depicted in Figure la.

Figure 2 shows the complete process of producing a metalised substrate.

Turning to Figure la, a substrate 1 has been partially coated with a first layer material 3 which comprises an electroless deposition promoting material. The first layer 3 has been subsequently coated with a second layer material 5 which is unable to promote electroless deposition. The first and second layers (3,5) may have been applied via a suitable pattern transfer mechanism, e. g. inkjet printing, to the substrate.

The second layer 5 overlaps the first layer 3 and forms a seal 7 with the substrate 1 below.

A suitable scribing mechanism (e. g. laser scribing) has removed material (depicted by the scribed groove 9) from the second layer to expose the material in the first layer.

Figure 1 b shows the substrate material from Figure la after it has been immersed in a suitable autocatalytic deposition solution bath. A metal 11 has now been deposited into the scribed groove 9.

Turning to Figure 2, an ink jet printing system 21 coats a substrate 23 with an ink formulation containing a deposition promoting material in a user determined pattern 25. This first layer comprising the deposition promoting material is then coated with a second layer of material that cannot promote autocatalytic deposition.

A scribing mechanism 27 then ablates part of the second layer of material on the coated substrate to produce grooves 29 in which the first layer of deposition promoting material is exposed.

The"scribed"substrate is then immersed into an autocatalytic solution 31 to produce a user defined metallic pattern 33.

Claims

CLAIMS 1. A method of preparing a substrate such that it is capable of sponsoring a catalytic reaction over a pre-determined area of its surface comprising the steps of : i) coating some or all of the substrate material with a first layer material, the first layer material comprising a catalytic material (as hereinbefore defined) ii) coating the first layer material with a second layer material, the second layer material being incapable of promoting and/or sustaining the desired catalytic reaction iii) using a scribing process (as hereinbefore defined) to remove a pre-determined pattern of material from the second layer material in order to expose the first layer material
2. A method of preparing a substrate such that it is capable of sponsoring a catalytic reaction as claimed in Claim 1 wherein the second layer material overlaps the first layer material in order to form a seal.
3. A method of preparing a substrate such that it is capable of sponsoring a catalytic reaction as claimed in either Claim 1 or Claim 2 wherein a pattern transfer mechanism is used to print the first layer material onto the substrate.
4. A method of preparing a substrate such that it is capable of sponsoring a catalytic reaction as claimed in any preceding claim wherein a pattern transfer mechanism is used to print the second layer material onto the first layer material.
5. A method of preparing a substrate such that it is capable of sponsoring a catalytic reaction as claimed in Claim 3 and/or Claim 4 wherein the pattern transfer mechanism is ink-jet printing.
6. A method of preparing a substrate such that it is capable of sponsoring a catalytic reaction as claimed in any preceding claim wherein the catalytic material is contained within an ink formulation.

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7. A method of preparing a substrate such that it is capable of sponsoring a catalytic reaction as claimed in Claim 6 wherein the ink formulation contains additional binders and/or fillers capable in use of enhancing the catalytic reaction.
8. A method of preparing a substrate such that it is capable of sponsoring a catalytic reaction as claimed in any preceding claim wherein the scribing process is performed by a laser.
9. A method of depositing a material onto a substrate in a user defined pattern by means of a catalytic reaction comprising the steps of : i) preparing a substrate such that it is capable of sponsoring a catalytic reaction as claimed in any of claims 1 to 8 and ii) exposing the prepared substrate from step (i) to a suitable reagent environment such that the catalytic reaction deposits material at the surface of the first layer material.
10. A method of depositing a material onto a substrate in a user defined pattern by means of a catalytic reaction as claimed in claim 9 wherein the steps (i) and (ii) are repeated in order to deposit multiple layers of material onto the substrate.
11. A method of metal plating a substrate by an autocatalytic deposition process comprising the steps of : i) preparing a substrate material according to any of the preceding claims wherein the catalytic material in the first layer material is a deposition promoting material (as hereinbefore defined) which is capable, once the coated substrate is introduced into an autocatalytic solution, of facilitating the deposition of a metal coating from an autocatalytic solution onto the substrate, and ii) introducing the prepared substrate material from step (i) into an autocatalytic deposition solution, the autocatalytic deposition solution comprising a metal salt and a reducing agent.
12 A method of metal plating a substrate by an autocatalytic deposition process as claimed in Claim 11 comprising the further step of introducing the coated substrate

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from step (ii) of Claim 11 into a further autocatalytic solution comprising a further metal salt and a reducing agent.
13. A method of metal plating a substrate by an autocatalytic deposition process as claimed in Claim 11 comprising the further step of introducing the coated substrate material from step (ii) of Claim 11 into an electrolytic bath in order to electrodeposit a further metal.
14. A method of metal plating a substrate by an autocatalytic deposition process as claimed in Claim 11 wherein the autocatalytic solution contains two or more metals salts in solution.
15. A method of metal plating a substrate by an autocatalytic deposition process as claimed in Claim 11 wherein the deposition promoting material comprises a reducing agent.
16. A method of metal plating a substrate by an autocatalytic deposition process as claimed in Claim 11 wherein the deposition promoting material is SnClz
17. A method of metal plating a substrate by an autocatalytic deposition process as claimed in Claim 11 wherein the deposition promoting material comprises an activator comprising a colloidal dispersion of a catalytic material which is capable, once the substrate is introduced into an autocatalytic solution, of initiating and sustaining an autocatalytic reaction.
18 A method of metal plating a substrate by an autocatalytic deposition process as claimed in Claim 11 wherein the method additionally comprises the step of introducing the substrate after it has been coated with the deposition promoting material into an aqueous metal salt solution with which the deposition promoting material will react to reduce the metal from the aqueous metal solution onto those parts of the substrate that have been coated with the deposition promoting material, the reduced metal being selected such that it is capable, once the treated substrate is introduced into an autocatalytic solution, of catalysing the deposition of a further metal from an autocatalytic deposition solution

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19. A method of preparing a substrate material for subsequent metal plating by an autocatalytic deposition process as claimed in Claim 15 wherein the deposition promoting material comprises a combination of reducing agent and activator.
20. A method of preparing a substrate material for subsequent metal plating by an autocatalytic deposition process as claimed in any of Claims 11 to 19 wherein the substrate material comprises an impermeable surface layer.
21. A method of preparing a substrate material for subsequent metal plating by an autocatalytic deposition process as claimed in any of Claims 11 to 19 wherein the substrate material comprises a porous surface layer.