HK1072083B - Method and electrode for defining and replicating structures in conducting materials - Google Patents

Description

Method and electrode for determining and replicating structures in conductive material

Technical Field

The invention relates to a novel etching or electroplating method which simplifies the production of applications involving micro-or ultrastructures using specific electrodes.

The present invention relates closely to electrochemical etching, electroplating, photolithography and pattern replication, and is in the field of microscopy and ultra-microscopy.

The method is particularly useful in the production of PWEs (printed wiring boards), PCBs (printed circuit boards), MEMS (micro electro mechanical systems), sensors, flat panel displays, magnetic and optical storage devices. With this method it is possible to produce integrated circuits, different types of conductive polymer structures, semiconductor structures, metal structures, etc. It is even possible to produce silicon 3D-structures using the resulting porous silicon.

Background

The ever-increasing demand for smaller, faster and less expensive microelectronic and microelectromechanical systems requires the development of appropriate production technologies that are effective accordingly.

The addition or subtraction technique is used when producing microstructures and/or ultrastructures on a surface. One common subtractive technique is etching and one common additive technique is electroplating.

Etching methods are generally divided into two subgroups, dry etching and wet etching. In general, dry etching is used for sub-micron structures and/or where straight sidewalls are important. Wet etching is used for large structures where some undercutting is acceptable or sometimes desirable. Wet etching techniques can be divided into chemical etching and electrochemical etching.

An advantage of dry etching compared to wet etching is that anisotropic etch profiles can be created in crystalline and polycrystalline/amorphous materials. Some of the drawbacks of dry etching are high equipment cost, lack of selectivity, problems associated with re-precipitation on the sample, environmentally hazardous chemicals, damage to the surface of the etched sample, and safety and disposal issues.

The advantage of wet etching is that the method is a simple and cheap method. One drawback is that the method does not include any directional driving force, and thus the etch rate is the same in any direction, resulting in an isotropic etch profile. Some other drawbacks are that wet etching baths are generally charged with corrosive, toxic chemicals, which present safety and disposal problems. In many wet etching processes, waste disposal and disposal costs often exceed the actual etching costs, and dry etching is equally applicable.

A detailed description of the above etching method is known to those skilled in the art and will not be described herein. Because of the close relationship between the etching process of the present invention and the electrochemical etching process, some details regarding the latter are described below:

electrochemical etching is a simple and inexpensive etching method that makes it possible to achieve high etching rates and precise process control. In electrochemical etching, an external potential is applied between the etching sample and a counter electrode, both of which are immersed in a liquid etchant. An electrochemical cell is constructed having a working electrode, i.e., the sample, as the anode and a counter electrode as the cathode. As shown in fig. 1. An external potential is applied to drive the oxidation process at the working electrode. The corresponding reduction at the cathode is usually the generation of hydrogen. As electrolyte and etchant, a neutral salt solution or a very dilute mixture of conventional etchants can be used. The applied potential and the resulting electric field result in a vertically oriented etch.

One problem facing designers of electrochemical etch cells is the reduction of resistance losses in the electrolyte due to charge transfer, and it is desirable that the electrode spacing be small. A small distance, which makes the electrode non-uniformity very small, may result in a relatively large ad, which may result in a non-uniform current density distribution. The result is that some portions of the sample are over-etched and some portions are not etched to the desired depth. Since no contact between the sample and the counter electrode is allowed, it is not possible to have any mechanical support to keep the electrodes in place over the whole surface.

Another problem in electrochemical etching is the non-uniform current density distribution, which results from the accumulation of current from non-etched areas due to the fact that all counter electrode portions are in contact with the electrolyte, not just in the desired areas on the etched part.

A second approach to pattern transfer, additive techniques, is to add material to the structure formed over the substrate using a deterministic pattern step. Electrodeposition (the term "electroplating" is also used by those skilled in the art), physical vapor deposition, and chemical vapor deposition are examples of additive methods. It is known in the art that electroplating can be used to produce well-defined patterns, vertical sidewalls and high aspect ratio structures. However, a general industrial problem also exists with known electroplating methods, i.e. the non-uniform current density distribution causes the deposition rate to be dependent on the pattern surrounding each electroplated structure. In addition, such current density differences also result in different material compositions when electroplating the alloy, and also in differences in the height of the plated structures on the substrate. Until now, these undesired non-uniform current distributions typically have to be adjusted in subsequent process steps using planarization (planarization) methods.

When the purpose of etching is to etch away selected portions of the etched material to provide a structure, the etched material that is not to be etched away is typically coated with an etch resist, i.e., a so-called masking layer or resist layer. The main technique for defining the pattern to be etched is photolithography, and a general etch-resistant layer is photoresist. The photoresist is exposed to electromagnetic radiation and developed to transfer the desired pattern for etching. Each etch sample must be resist coated, pre-baked, exposed, developed and baked hard before the etch process can begin.

Most of today's microdevices are composed of a large number of functional layers, each of which must be patterned and arranged in a photolithographic process followed by a pattern transfer process. Fig. 6 shows a general etching method with a photolithography process. Determining the complexity of the pattern lithography process and manufacturing the microscopic devices requires a large number of lithography steps, making it a significant time and cost carrier in the overall production chain.

It is known from european patent publication EP1060299 to use an electrode having a conductive electrode portion at a selected electrode surface portion, and to use a method of etching to create pits at the selectively etched surface portion, wherein the electrode portion is made to constitute an electrode pattern corresponding to the etched pattern. The method differs from the present invention in that the passivation layer formed on the etching material is dissolved using electromagnetic radiation. During etching, the electrodes are placed at a distance from the conductive etching material, which is also different from the present invention. The electrodes of EP1060299 must be transparent to electromagnetic radiation and they cannot compensate for micro-/nano-domain inhomogeneities.

WO9845504 discloses an electroplating method using an electroplated article, an anode and a substrate. The plated article is placed in contact with the substrate. In one embodiment, the external anode is placed separate from the substrate and plated item, all immersed in the electrolyte. According to this disclosure, an electrical potential is applied across the external anode and the substrate causing material to be transfer plated from the anode through the porous carrier of the plated article onto the substrate in a pattern defined by the insulating mask of the plated article. The electrolyte between the plated item and the anode can be agitated to improve the mass transfer of the electroactive ions. In any event, the disclosed methods attempt to overcome the same problems and deficiencies associated with conventional electroplating techniques, namely uneven plating rates due to uneven current density distribution due to different anode surface areas than the corresponding cathode surface areas on the patterned substrate. Thus, the difference in reaction rates among the different cavities results in different heights of the plated microstructures depending on the pattern around each structure. This problem is usually solved by a subsequent planarization step, like grinding or CMP (chemical mechanical polishing). The method described in WO9845504 suffers from the same problems as the usual electroplating methods when electroplating alloys, namely differences in material composition due to non-uniform current density distribution.

Furthermore, the disclosed embodiment which has been mentioned in WO9845504 requires a plated article which is manufactured using a porous material permeable to ions in the electrolyte, which raises a problem of limitation as to how the small size can be determined depending on the pore size of the material.

In a second embodiment disclosed in WO9845504, reference is made to an electroplated article consisting of a patterned masking layer disposed on an anode. The anode may be soluble or insoluble and may include an erodable layer. In the method using a soluble anode, the material thereof is transferred from the anode material in the plated item, and thus the plated item is eroded in use, but can be periodically re-adjusted for reuse. However, this method also suffers from the problem of an uneven current density distribution when the patterned masking layer is still placed on the anode layer as a separate layer, i.e. the current density distribution is only uniform at the beginning of the electroplating process, and when the anode material is consumed the contact surface of the electrolyte with the anode material increases differently in each local plating cell, depending on its size. Moreover, the maximum aspect ratio, i.e. the height/width ratio, of the structures that can be plated is limited by the fact that: erosion of the anode material in the plated article can undercut the insulating pattern masking layer. Undercutting the masking layer during use is also associated with reliability problems because the patterned masking layer can be completely undercut and separated from the plated article if the plating process is not terminated in a timely manner. The described problem is inherently connected with this method, since soluble anode material can be transferred directly from the plated article itself, even in case the plated article consists of different layers of soluble and insoluble material.

Disclosure of Invention

It is an object of the present invention to simplify the production of applications involving microscopic and submicroscopic structures, wherein the etched or plated pattern defined by the conductive electrode, the master electrode, is replicated on a conductive material, i.e. a substrate. In addition, the master electrode should be capable of being reused several times, producing a replica according to the method. More particularly, it is an object of the present invention to avoid unnecessary process steps, such as the above-mentioned planarization process steps, during said production of said structures, and also to precisely control the electrochemical etching or electroplating process, without limitations in terms of maximum aspect ratio of the deposited structures, variations in the material composition of the deposits and reliability problems for mass production.

Generally, this is achieved by using a specific contact electrochemical etching/plating process, known as electrochemical patterning. For simplicity of explanation of the electrochemical pattern replication method of the present invention, it will be referred to as ECPR method hereinafter in this specification. This method is based on a structured electrode device, an electrochemical etching/plating method, and an apparatus for carrying out the method.

The master electrode is placed in intimate contact with the substrate with a partial etch/plating bath formed in the open or closed cavity between the master electrode and the substrate. An arrangement of internal counter electrode surfaces within each localized electrochemical etching or plating cell, each cell defined by the walls of the insulating pattern layer, achieves uniform current density distribution regardless of the pattern. In order to realize the internal counter electrode principle of ECPR in closed-cell electrochemical micro-and nanocells, a pre-deposition of soluble anode material in the cavities in the master electrode is performed before ECPR plating and during ECPR etching is performed to plate excess ions in the electrolyte resulting from substrate etching. This results in a uniform ECPR current density distribution without any pattern dependency of the application, solving the above-mentioned prior art related drawbacks, i.e. different deposition rates depending on the plating pattern. Furthermore, ECPR does not require subsequent planarization because the deposited structures have the same height when plated using the ECPR method. ECPR also solves the problem of limited maximum aspect ratio of the deposited structures per plating cycle and the reliability limitations associated with the prior art. In addition, FCPR also solves the above-mentioned problem of different material compositions of different structures when plating alloys, which problem depends on the pattern around each structure. Thus, the object of the present invention is satisfied. Another advantage of the ECPR process is that it enables highly well controlled anisotropic etch profiles, etch rates and surface finish and uniformity, the possibility of precise process control, minimized undercutting, environmentally friendly processes (due to the use of electrolytes or very dilute etchants), and low cost when used for etching.

Another object is to design a master electrode for use in the ECPR method.

This is achieved by integrating the counter electrode and the pattern of defined structures of the electrochemical etching/plating bath into one device, the master electrode. This master electrode works well both as counter electrode and as pattern master electrode in the etching/plating bath used in the ECPR process. The substrate, the sample on which the pattern is etched or plated, is operated as a working electrode in an etching/plating cell used in ECPR processes.

This master electrode is used in combination with the ECPR method, and several copies can be created in the conductive material by electrochemically removing or adding material in each of the localized electrochemical micro-or nano-cells defined by the master electrode.

Still other objects and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following preferred embodiments.

Drawings

The invention will now be described more closely by way of example and with reference to the accompanying drawings. In the drawings:

fig. 1 is a cross-sectional view of an etching bath used in general electrochemical etching.

Fig. 2a-2f are cross-sectional views illustrating a process for producing a master electrode based on an open local electrochemical cell according to the invention.

Fig. 3 is a cross-sectional view of an etching/plating bath of the present invention.

Fig. 4a is a cross-sectional view of an etching bath wherein the master electrode and the substrate are compressed to form a closed partial etching bath according to the present invention.

Fig. 4b is a cross-sectional view of an etch bath in which a pattern has been etched on a substrate according to the present invention.

Figure 5a is a cross-sectional view of a plating cell in which the master electrode and substrate are compressed to form a closed partial plating cell in accordance with the present invention.

Figure 5b is a cross-sectional view of an electroplating cell wherein the pattern is replicated on a substrate according to the present invention.

FIG. 6 is a flow chart of a micro-production method with photolithography.

FIG. 7 is a flow chart of the ECPR method of the present invention.

FIG. 8 is a cross-sectional view of a main apparatus used when single-sided etching/plating is performed by the ECPR method according to the present invention.

Figure 9a is a side view of another embodiment of an apparatus used in etching/plating using ECPR methods according to the present invention.

Figure 9b is an end view of the same device shown in figure 9 a.

Fig. 10a and 10b are cross-sectional views of different designs and exemplary combinations of materials for the master electrode material in accordance with the present invention.

Detailed Description

The master electrode 8 of the present invention operates as both the counter electrode 1 and the patterned master electrode, while the substrate 9 operates as the working electrode 2 in the etching/plating bath shown in fig. 3 used in the ECPR method of the present invention.

Furthermore, in the present description reference is made to an exemplary etching or plating method, but it should be noted that it is obvious to a person skilled in the art that the same also relates to and applies correspondingly to a respective plating or etching method.

Main electrode structure

The purpose of the master electrode 8 is to provide a well defined electrical connection of the pre-deposited anode material to all the partial plating cells 12 formed when compressing the master electrode 8 and the substrate 9 and at the same time providing electrical insulation to the areas where electrochemical action is not desired, i.e. at the contact areas between the insulating pattern 3 and the substrate 9. In order to enable well-defined pattern transfer, even for relatively rough substrate surfaces, generally over the entire substrate surface, locally in the insulating structure of each pattern layer in contact with the substrate surface, a suitable property is required. This is satisfied by the overall macro-scale overall master electrode flexibility and the presence of a compressible elastomer layer 20, 21 within the local micro-scale master electrode structure.

The insulating pattern layer 3 can be made of an electrically insulating material which is chemically inert in the electrolyte used, making high aspect ratio structures possible, and which is easily patterned using i.e. UV, X-ray, electron beam, laser or etching/plating in combination with an insulating method. Examples of insulating materials that can be used are polyimide, SU-8, SC 100, MRL 6000, ED-resist and Teflon materials. In another embodiment, the insulating portion is fabricated by anodizing a conductive material, such as a metal.

The counter electrode 1 comprises a conductive electrode layer 1'. Alternatively, the conductive electrode layer may also comprise a flexible conductive foil 1 ", a solid metal sheet or a thin conductive layer on the mechanical support layer 23. The conductive electrode layers 1', 1 "are deposited on the mechanical support layer 23 or the elastomer layer 21 and have a very high surface uniformity, both planarity and high surface uniformity properties being combined. The decisive material properties of the conductive electrode layers 1', 1 "are high conductivity, chemical inertness in the use of an electrolyte, good electrochemical material deposition of the seed layer, and a suitable method for depositing or otherwise incorporating the layer into the integrated master electrode structure. Non-limiting examples of conductive electrode layer 1', 1 "materials used are stainless steel, platinum, palladium, titanium, gold, graphite, chromium, aluminum and nickel.

According to one embodiment, the master electrode is produced using the general microfabrication process described in FIG. 6. Different embodiments of master electrodes for use in the ECPR process are depicted in fig. 10a-10 h. All different embodiments of the electrode layers 1', 1 "can be combined with all different combinations of insulating pattern layer 3, soft elastomer layers 20, 21, mechanical support layer 23 and intermediate metal layer 22. All of these configurations can be used for either the open cavity concept or the closed cavity concept. These concepts will be further explained in this document.

The main electrode of the open cavity structure can be manufactured by the following method.

A master electrode for use in an open cavity configuration can be fabricated in two main steps. In a first step, the counter electrode layer 1 is shaped and prepared to meet different regulatory requirements, such as are decisive for a successful ECPR processing method. After these requirements are met, the insulating pattern layer 3 is deposited and patterned on the counter electrode layer 1.

In a preferred embodiment, titanium has been chosen as the primary electrode material because it is inert in the electrolyte used. In addition, anodic polarization can form dense TiO in the contact area₂An insulating outer layer. It is also possible to use other materials as mentioned above.

Since the main electrode 8 is in contact with the working electrode 2, some portions of the main electrode, the insulating pattern layer 3 on the contact surface, and the main electrode surface 11, must be made of an insulating material. The insulating pattern layer 3 prevents an area, which is not desired to be etched, from contacting the etchant.

All the production steps of the main electrode 8 are carried out using the usual microfabrication method known in the art, in which the characteristic steps are shown in fig. 6.

Thus, as indicated previously, the master electrode 8 shown in figures 2a-2e is fabricated from two layers of titanium foil 16 with a sacrificial photoresist layer 17 in between to form the gas/electrolyte transfer channels. An example of how such a master electrode can be manufactured is as follows:

1. the starting material, i.e. the sample in fig. 6, is a 4 micron Ti-foil layer 16. The 1 micron sacrificial photoresist layer 17 is electrochemically deposited as shown in figure 2 a. To form the fluid channels, the resist was formed into squares 4 microns wide, separated by 1 micron resist lines, as shown in FIG. 2 b. A second 3 micron Ti-foil layer 16 is deposited over the sacrificial photoresist layer 17 as shown in figure 2 c.

2. The two long sides of the "sandwich" shown in fig. 2c are coated with ED-resist 18 as shown in fig. 2 d. According to the pattern determination process shown in fig. 6, the master electrode face 11 is patterned with the desired master electrode pattern and the outer face 10 is patterned with 1 micron holes.

3. The double-sided electrochemical etching is performed according to the pattern transfer process shown in fig. 6. The outer face 10 is etched to a sacrificial photoresist layer and the main electrode face 11 is etched to a depth of 3 microns leaving 1 micron for the air wells. A new layer of ED-resist is deposited. The contact area is exposed and developed. This contact area is anodically polarized to form isolated TiO₂As shown in fig. 2 e.

4. The photoresist is rinsed thoroughly in an alkaline solution to dissolve the outer layer and the sacrificial layer as shown in figure 2 f.

All manufacturing steps outside the main electrode 8, 10, are standardized, independent of which main structure is used. A common standard masking layer may be used. The masking layer of the main electrode face 11 must be chosen for each specific main structure. The master electrode is ready to be mounted in an etching bath.

A closed hole master is produced in the same manner as the process described above for making an open hole master, except for the sacrificial photoresist layer. Several material combinations are shown in FIGS. 10a-10 h.

A very important part of the ECPR process is the use of a suitable insulating layer. One of the benefits of this method is that it no longer requires a resist to be applied on each sample, but rather the resist should be on the reused primary electrode. To make this a beneficial point, the resist needs to withstand several processing cycles. In addition to this, the resist should also determine how small structures can be made, what electrolyte volume to sample depth ratio can be had, and how easily all structures can be kept in contact with the sample. Electrodeposition photoresist is often used for lithographic processes, and ED resist is also suitable for these etching methods because deposition can be controlled to very precise thicknesses.

The specific embodiments of the master electrode of the present invention are in no way limited to the exemplary structures shown in figures 2a-2i, 10a-10h, nor to the materials considered suitable for the listing in the foregoing description.

Base material

An electrically conductive material resistant to electrochemical stresses, such as copper, may be used as the base material.

Electrolyte

The electrolyte is decisive for controlling the electrochemical process and its different properties. Conductivity, ion mobility, ionic environment, relaxation, mobility, diffusion and transport number are important concepts.

When using an electrolytic etchant, there is no or little chemical etching effect and the negative impact on the replicated structure should be negligible. The presence of chemical etching depends on the presence or absence of a chemical oxidizing agent in the electrolyte solution.

One important issue that must be addressed with electrolytes is to optimize the mass transfer of electroactive ions in a local electrochemical cell, which must occur to achieve an optimized ECPR process. The electrolyte optimization that leads to optimized mass transfer is described below after the description of the ECPR process.

If one wishes to prevent matrix material deposition and wishes to cause the etching process to stop in a natural manner, a reducing component, such as a metal ion, may be added to the electrolyte solution. When a reducing component is added, a reduction process occurs in the electrolyte, and when there is an equilibrium between the reducing component and the deposition component, a natural stop of the etching process occurs.

ECPR method

The substrate 9 and the master electrode 8 are brought together in close contact to form an etching bath as shown in fig. 4 a.

They can be installed in an apparatus in which the ECPR process is to be carried out. Such a device will be described in more detail below. One of the main problems is to bring the electrodes into the correct position and to provide them with a proper contact once they are brought into contact.

The insulating pattern layer 3 determines the distance between the counter electrode 1 portion of the main electrode and the substrate 9. Due to the fact that the distance is short and precise over the whole surface, the problems of non-uniform current density distribution and non-etched areas are solved. It also minimizes the resistive losses in the electrolyte due to charge transfer.

Since the master electrode 8 controls the electric field and the ionic movement in the etching/plating solution in the vertical direction, the structure will be replicated on the substrate 9.

Since the master electrode 8 is in close contact with the substrate 9, there are open or closed cavities between the electrode surfaces, partially etching the pool 12. The cavities are open or closed depending on how the master electrode 8 used is constructed with or without the sacrificial resist layer 17. This document considers that these cavities will be further closed. These very small and well controlled spaces between the electrodes allow for efficient etching with high accuracy. Each partial etching bath 12 has a surface on the main electrode 8 which corresponds to the surface of the substrate 9 which should be etched away, so that fluctuating current density distribution problems in the vicinity of large insulating areas with adjacent small structures are avoided.

According to the invention, there is thus provided an ECPR method for etching selected portions of the surface defined by the master electrode described above.

Figures 3, 4a and 4b illustrate different steps in an ECPR etching method according to the invention. These steps are as follows:

1. the main electrode 8 and the substrate 9 are immersed in an electrolyte solution 6, which will be described below, as shown in fig. 3.

2. They are compressed and form an etching bath with a partial etching bath 12, which is filled with an electrolyte solution 6. This is shown in fig. 4 a. It is also possible to coat one of the surfaces with a very thin layer of electrolyte solution before compressing the electrode, for example by immersing the surfaces in the electrolyte solution before the compressing step, or by adding the electrolyte solution to the etching bath through a layer on the outer face 10 of the main electrode 8 after compressing the electrode.

3. An external pulsed voltage is applied to the entire etching cell with or without additional ultrasound, wherein the substrate 9 becomes the anode and the main electrode 8 becomes the cathode.

4. Figure 4 shows how the pattern 3 defined by the master electrode 8 is replicated on the substrate 9. The etched away material is deposited on the master electrode 8, the deposited material 13, all in each of the partial electrochemical cells.

5. Since some of the matrix material etched away from the anode is deposited in the structure on the master electrode 8 and is thus eventually filled with matrix material, the deposition material 13, it is important to have a method of easily cleaning the master electrode. After many etch cycles, a cleaning process is normally performed. The deposited material 13 is etched away from the master electrode 8.

Fig. 5a and 5b show different steps of the ECPR plating method according to the invention. The electroplating method is almost the same as the etching method except for the following steps:

1. before the electrodes 8, 9 are compressed and immersed in the electrolyte solution, a plating material 15 is deposited on the master electrode 8 in the cavities defined by the insulating pattern layer 3. After the plating structure has reached a certain height, the space formed by the partial plating bath 14 between the main electrode 8 and the substrate 9 will be filled with the electrolyte solution 6, as shown in fig. 5 a.

2. When an external pulse voltage is applied to the plating cell 14, in which the master electrode 8 becomes an anode and the substrate 9 becomes a cathode, the pattern defined by the master electrode 8 is reproduced on the substrate 9. The plating material 15 deposited on the master electrode 8 is plated on the base material 9 as shown in fig. 5 b. Since all of the plating material that can be plated onto the substrate is deposited onto the master structure from the beginning, the amount of plating material plated onto the substrate can be very accurately controlled.

The main advantage of using the ECPR method is a uniform current density distribution in the shape and the adjacent cells in each local electrochemical cell, and in the entire substrate, which is generally independent of the cell size according to the pattern. As mentioned in the brief description of the invention above, this solves the problem of non-uniform height of the plated structures, non-uniform material composition when plating alloys, and the need for subsequent planarization processes. It is also possible to deposit structures with high aspect ratios, i.e. height/width ratios, and to enable high reliability mass production methods.

Optimal mass transfer of electroactive ions in these cells must occur to obtain an optimized ECPR process. Mass transfer of a material from one location to another in a solution results from a potential or chemical difference between the two locations, or from the movement of a volume element (volume element) in the solution. There are three mass transfer modes, migration, diffusion and convection. This is the case for thin layer electrochemical cells, which have a much larger a/V ratio than conventional macro cells. A high a/V ratio means that the friction per unit volume is high, causing all the electrolyte volume to become a stagnant layer. This means that no forced convective mass transfer takes place, except when ultrasound is used, only diffusion and migration mechanisms are involved for material transfer. This involves closing the hole main electrodes. In the open hole master there is micro-convection because of the sacrificial resist layer, wherein the channels in the layer allow for the micro-convection mechanism.

The following effects may optimize mass transfer:

1. electrolyte solution

The parameters adjusted in solution are pH and electroactive/supporting electrolyte ratio.

In one embodiment, an acid copper electrolyte is used as the electrolyte solution. Adding H₂SO₄Or dilute NaOH changes its pH. Several experiments were performed to determine the optimum pH. In this embodiment, a defined pH of 2 to 5 is satisfactory.

The combination of a higher concentration of electroactive species with no or little supporting electrolyte compared to a standard electrolyte may also improve mass transfer. Electroactive concentrations of 10-1200mM are preferred.

ECPR processes involve simultaneous electrochemical etching and electrodeposition. Electrodeposition is a reverse electrochemical etching process in which ions in the electrolyte are reduced and deposited on the cathode. The same conditions were applied and the same parameters controlled both processes. With conventional electroplating methods, there is a tendency to achieve higher deposition rates at the top of the cavities than at the bottom when filling high aspect ratio structures. This may cause voids and thus adversely affect the mechanical and electrical properties of the microstructure. The geometry of the local electrochemical cell and the use of additives is a solution that can be "upside down" filled without any voids. The addition of additives allows the electrolyte to achieve sufficiently controlled electrodeposition. Additives are often used in electroplating processes to homogenize the plating. It contains several active components, but it is primarily attracted to the high current density areas to prevent pillar formation, but initially forms pillars covering the high current density areas. This proves to be the key to the problem, as soon as it is used, a clean solid matrix material is produced on the cathode. Several commercially available systems were tested to obtain satisfactory results. Desirable additives are wetting agents, which lower surface tension; promoters, which are molecules capable of locally increasing the current density they absorb; inhibitors, which are polymers that tend to form current-inhibiting films across the substrate surface (chlorides may sometimes be used as co-inhibitors), and leveling agents, which are current-inhibiting molecules with a mass transfer-dependent distribution.

To avoid too high a concentration of electroactive species at the anode, which gives a locally saturated compound and a solid salt deposit, the counter ions are exchanged with ions that provide a higher solubility product. Additionally, a chelating agent, such as EDTA, may be added to dissolve more of the metal ions without causing any further precipitation.

2. Voltage of

The pulsed voltage is chosen because it enhances mass transport and interferes with the formation of a blocking layer at the electrode-solution interface. Tests were performed to determine what frequency, pulse hold time to pause time ratio, and potential to use. Two periodic pulse reverse voltage (PPR) and composite waveforms were successfully used. Frequencies of 2-20kHz have been tested with satisfactory results, although higher frequencies are possible. In the described embodiment, a frequency of 5kHz is preferred. The potential is 0-10V.

3. Ultrasonic wave

Ultrasound may be used with pulsed voltages to enhance mass transfer by micro-convection.

A mechanical solution that performs the function described in this document is a key part of the invention. The purpose of the machine is to compress the two electrode surfaces, the main electrode and the substrate, creating micro/ultramicro cavities in which the electrochemical cell is formed. To make micro/ultra micro-scale and macro-scale surface similar, mechanically soft layers of large scale similar properties and plane parallelism can be combined with a soft layer in the master electrode that provides conditions for micro-and nano-scale similar properties. Thus, ECPR processing can use curved and pitted substrates with somewhat higher surface roughness.

Before the electrodes 8, 9 are compressed to create the local etching cells 12, all the gas must be extracted from the solution, from the solid/liquid interface between the main electrode 8/electrolyte 6 and the electrolyte 6/substrate 9. In one embodiment, the gas is evacuated using a vacuum system, and in another embodiment, the gas is evacuated using ultrasound. A combination of the two bubble removal methods may also be used. The evacuated gases and electrolytes are processed with a buffer volume chamber connected between the reaction chamber and the vacuum system.

In order to be able to carry out the ECPR process, the master electrode 8 and the substrate 9 must be electrically contacted in the same machine solution. This is achieved by contacting the outer face 10 of the main electrode 8, the front, i.e. the contact face, of the substrate 9. However, the present invention does not rely on such a configuration.

There are two mechanical embodiments that can achieve the desired ECPR processing action.

Fig. 8 shows a first specific embodiment, which is based on a membrane solution in which the pressed membrane 24 is expanded against the main electrode 8 or the substrate 9. The medium 19 in the pressure volume may be a gas or a liquid. Bubbles can be removed by a combination of ultrasound and vacuum, or by using ultrasound alone. In this particular embodiment, the electrical contact to the master electrode 8 is provided by the outer face 10, i.e. by the membrane 24, while the electrical contact to the substrate 9 is provided from the front. The nature of the expanded membrane ensures plane parallelism when a uniform pressure is applied in a suitable manner. Both soft and hard master electrodes and substrates may be used in this embodiment.

The second embodiment is based on a cylinder shown in fig. 9 with a movable piston not shown in the figure. The whole system is closed. The two electrodes 8, 9 are compressed pneumatically using a combination of vacuum and overpressure, or hydraulically using a hydraulic piston, or mechanically using screws to apply pressure. And removing bubbles by adopting a mode of combining ultrasonic waves and vacuum. In this embodiment, an electrically conductive moving bar is used, with electrical contact 26 to the main electrode being provided from the outer face 10 and contact to the substrate 25 being provided from the front. Two soft elastomer layers placed between the sample and the piston ensure plane parallelism, one being more compressible than the other. These elastomer layers may also be placed behind the master electrode 8, i.e. between the master electrode and the cylinder wall. Both soft and hard master electrodes and substrates may be used in this embodiment.

The invention is in no way limited to the specific embodiments illustrated and described above, several modifications being feasible within the scope of protection of the invention.

Claims (35)

1. An electrochemical pattern replication method for producing micro-and ultrastructures of electrically conductive material on a substrate (9), whereby an etched or plated pattern is replicated, the pattern being defined by an electrically insulating patterned material, said method comprising:

using an electrochemical process that causes the pattern to be transferred to the substrate (9),

the electrochemical process comprises dissolving a material on the surface of the anode and depositing the material on the surface of the cathode, characterized in that:

placing a master electrode (8) in close contact with the substrate (9) and determining the pattern with the master electrode (8), and

the dissolution and deposition of the material is carried out in a partial etching bath (12) or a partial plating bath (14) and in the substrate (9) formed in open or closed cavities defined by the insulating pattern layer (3) of the master electrode (8),

the master electrode (8) is an anodic surface, the substrate is a cathodic surface and the dissolved material is a predeposited material on the master electrode in a local plating bath (14), or

The substrate (9) is the anode surface, the master electrode is the cathode surface and the cavities are partial etch pools (12).

2. The method according to claim 1, characterized in that the following steps are used:

filling the cavities on the main electrode (8) with an electrolyte solution (6);

compressing the substrate (9) and the master electrode (8) into intimate contact to produce a localised etch bath (12) containing the electrolyte solution (6); and

an external voltage is applied between a base material (9) as an anode and a main electrode (8) as a cathode.

3. The method according to claim 1, characterized in that the following steps are used: pre-depositing a plating material (15) in cavities on the master electrode (8) and filling the cavities with an electrolyte solution (6);

compressing the substrate (9) and the master electrode (8) into intimate contact to produce a localised plating bath (14) containing the electrolyte solution (6); and

an external voltage is applied between a base material (9) as a cathode and a main electrode (8) as an anode.

4. A method according to any of claims 1-3, characterized in that the distance between the master electrode (8) and the substrate (9) is determined by the thickness of the insulating pattern layer (3).

5. A method according to claim 2, characterized by the further step of cleaning the main electrode (8) after a number of etching cycles.

6. A method according to claim 5, characterized in that the cleaning step is an etching process, in which the deposited material (13) on the master electrode is etched away.

7. Method according to any of the preceding claims, characterized in that a pulsed voltage between the main electrode (8) and the substrate (9) is used.

8. The method of claim 7, wherein the frequency is 2-20 kHz.

9. The method of claim 7, wherein the frequency is 5 kHz.

10. The method of claim 7, wherein the pulsed voltage is a periodic pulse-reversed voltage.

11. The method of claim 7, wherein the pulsed voltage has a complex waveform.

12. A method according to claim 2 or 3, characterized in that the electrolyte (6) is free of supporting electrolyte and high concentration of electroactive species and is free of chemical oxidizing agent.

13. A method according to claim 2 or 3, characterized in that the counter ions in the electrolyte solution (6) are exchanged for counter ions providing higher solubility.

14. A method according to claim 2 or 3, characterized in that an electrolyte solution (6) is used in which the concentration of electroactive ions is 10-1200mM and/or in that a chelating agent is used.

15. The method of claim 14, wherein the chelating agent is EDTA.

16. A method according to claim 2 or 3, characterized in that an additive system is used in the electrolyte solution (6), which comprises wetting agents, promoters, inhibitors and/or levelling agents.

17. A method according to any of claims 2 or 3, characterized in that the electrolyte solution (6) contains acid copper and the pH of the electrolyte (6) is 2-5.

18. Method according to claim 12, characterized in that the electrolyte solution (6) used is an optimized electrolyte in a partial etching bath (12) or a partial plating bath (14).

19. An electrode suitable for use in an etching or plating process, characterized in that a counter electrode (1) and a pattern defining the structure of an electrochemical etching or plating cell are integrated into a main electrode (8), wherein the counter electrode (1) is a conductive electrode layer (1') or a flexible conductive foil (1 ") and the pattern defining the structure is an insulating pattern layer (3) applied to the counter electrode (1).

20. The electrode according to claim 19, characterized in that the counter electrode (1) is inert.

21. An electrode according to claim 19 or 20, characterized in that a layer (20) of a soft elastomer is applied on the insulating pattern layer (3).

22. The electrode according to claim 19 or 20, characterized in that the counter electrode (1) is applied to a mechanical support layer (23).

23. An electrode according to claim 22, characterized in that a layer (21) of an electrically conductive elastomer is applied between the counter electrode (1) and the mechanical support layer (23).

24. An electrode according to claim 21, characterized in that an intermediate metal layer (22) is applied between the insulating pattern layer (3) and the soft elastomer layer (20).

25. Electrode according to claim 19, characterized in that the flexible conductive foil (1 ") is made of titanium.

26. An electrode according to claim 24 or 25, characterized in that the master electrode (8) comprises two counter electrodes (1) with a sacrificial photoresist layer (17) between the two counter electrodes (1), and in that the contact part of the master electrode, i.e. the structure of the insulating pattern layer (3), is electrochemically anodically polarized, creating a barrier layer.

27. A device for carrying out the method as claimed in claim 1, characterized by a main electrode (8) and means for producing a suitable contact between the main electrode (8) and the substrate (9).

28. The device of claim 27 wherein said component is one or more elastomeric layers in a master electrode configuration.

29. A device according to claim 27 or 28, wherein said member is associated with a suitable membrane.

30. A device according to claim 27, characterized in that there are a plurality of electrically conductive members for electrical connection with the main electrode (8) on the outer face (10) and with the substrate (9) on the contact face (11).

31. A device according to claim 27, wherein the main electrode is held in the device by an applied vacuum.

32. A device according to claim 30, characterized in that said electrically conductive member for electrical connection is an electrically conductive member (28) applied to the outer face (10) of the main electrode (8).

33. A device according to claim 27 or 28, wherein the main electrode is held in the device by pressure applied to the conductive member, said pressure being provided by a suitable membrane and/or piston.

34. The apparatus of claim 33, wherein said pressure is applied by a suitable membrane in combination with a container containing a gas or liquid.

35. The device according to claim 27 or 28, characterized in that the bubbles are removed from the electrolyte solution and/or the container using externally applied vacuum, ultrasound, or a combination of vacuum and ultrasound.