WO1999001592A1

WO1999001592A1 - Method for electrochemical deposition and/or etching and an electrochemical cell of this nature

Info

Publication number: WO1999001592A1
Application number: PCT/BE1998/000102
Authority: WO
Inventors: Bert Raf Celis; Jean-Pierre Paul Julien Clement Frans Celis; Jan Leo Dominique Fransaer
Original assignee: Katholieke Universiteit Leuven; Interuniversitair Microelektronica Centrum vzw IMEC
Current assignee: Katholieke Universiteit Leuven; Interuniversitair Microelektronica Centrum vzw IMEC
Priority date: 1997-07-03
Filing date: 1998-07-03
Publication date: 1999-01-14
Anticipated expiration: 2000-01-03
Also published as: AU8201698A; NL1006463C2

Abstract

Method for the electrochemical deposition or etching off of metals, alloys, composition-modulated layers or composites on an at least partially electrically conductive workpiece which is connected in an electrically conductive manner to a voltage source or current source and is positioned essentially parallel with respect to a counter-electrode, between which there is an electrolyte, characterized in that an electric current is applied between a cathode and an anode when the flow rate of the electrolyte between the anode and the cathode is essentially equal to zero.

Description

METHOD FOR ELECTROCHEMICAL DEPOSITION AND/OR ETCHING AND AN ELECTROCHEMICAL CELL OF THIS NATURE

ffyhj^.i-. of the invention The invention relates in general terms to a method for electrochemical deposition and/or etching and to an electrochemical cell of this nature, for the purpose of depositing or etching metal, metal alloys, composition- modulated layers or composites on or off a workpiece which is at least partially electrically conductive, in accordance with the preamble of Claim 1.

Thus the method and the cell device according to the invention can preferably be used for the production of:

- microelectronic components, such as electrical conductors, resistors, inductive elements, capacitive elements, magnetic elements and switching elements, for example as part of integrated circuits on silicon wafers;

- micro-electromechanical and micro-mechanical systems, for example micro-motors and transmissions;

- micro-analytical systems, for example gas sensors, ion-selective detectors and pressure-detection cells;

- supports for immobilized cell cultures in the biotechnology industry;

- optical and opto-electronic components, for example screen components, photocells, photoelectric generators ;

- plane-parallel metal multilayers with special magnetic, optical, electrical, mechanical properties, such as for example Co/Cu, Co/Ni/Cu multilayers; - dispersion composite layers, for example nickel - silicon carbide layers, nickel-phosphorus- fluoropolymer layers, the carbide particles and polymer particles, respectively, being incorporated in a layer of metal or metal alloy.

Prior art

Electrochemical deposition or etching (referred to below in general terms as electrodeposition) according to the invention is, in general terms, a process in which metals, alloys, composition-modulated layers or composites are deposited on or etched off a workpiece, which is optionally provided with a mask or pattern. The workpiece is placed in or between a suitable aqueous or non-aqueous electrolyte, which comprises ions, charged complexes and/or particles of, inter alia, elements which are deposited. At least part of the surface of the workpiece is electrically conductive and is connected to the negative or positive pole of a current source and/or voltage source and respectively forms the cathode or the anode. A suitable electrode is connected to the opposite pole. When an electric current is flowing between cathode and anode, electrochemical reaction causes a layer of metal, which may contain particles, to be deposited on the cathode or the anode to be partially dissolved. By arranging a resist layer which is non-conductive or less conductive in the form of a pattern (mask) on the conductive substrate, the metal can be selectively deposited on or etched off the remaining parts. This technique is used for producing micropatterns and has been improved numerous times over the course of recent decades in the context of increasing miniaturization and the ever higher demands placed on manufacturing efficiency. The manufacturer of circuits, electromagnetic components and electronic information carriers, in particular, imposes high demands, such as uniformity of thickness and composition and the avoidance of flaws caused by contamination. The uniformity depends on the current distribution over the cathode. This current distribution is affected by the potential applied and the movement of ions. This movement can be caused by convection, electromigration and diffusion. The dimensions of a substrate to which a mask is applied, for example by lithography, demand that the uniformity at three different layers be considered: at the level of the workpiece, at the level of the masks, - at the level of the cavities.

Most improvements- take place at the level of the workpiece and the masks. US-A-31652 , 442 improves the uniformity of thickness by placing the cathode and anode almost in contact with the cell housing and by stirring the electrolyte to and fro in the vicinity of the cathode using a paddle. US-A-4, 304, 641 uses a rotating cathode with an auxiliary cathode and/or a dielectric shield between cathode and anode at its edge. This avoids the deposition being non-uniform at the edge of the cathode.

US-A-5, 516,412 improves the uniformity at the level of the workpiece and partially reduces the risk of contamination and H₂ pits by positioning the cathode and anode vertically. Since the electrolyte is moved, the uniformity of electrodeposition remains a problem with regard to the cavities. The invention described here aims, inter alia, to improve the uniformity at the level of the workpiece and the cavities and to avoid the risk of contamination and H₂ pits. A similar approach applies for the relative etching of material.

In all these known processes, the electrolyte moves with respect to the cathode (anode) in order to counteract depletion (enrichment) of the electrolyte in the vicinity of the cathode (anode) , with the result that the deposition rate (etching rate) and the homogeneity of the electrolyte are increased. If the flow of liquid or the liquid flow rate is uniform or randomly turbulent, this provides better uniformity in deposition on or etching from relatively extensive flat layers. In the thesis "Aanmaak van magnetische microcomponenten bij middel van elektrochemische processen" [Production of magnetic microcomponents using electrochemical processes] by B. CELIS, Catholic University of Leuven, Dep . MTM Thesis Academic Year 1996-1997 and the publication "Shape evolution of elektrodeposited copper bumps with high Peclet numbers" by K. KONDO et al . , J. Electrochem. Soc . , volume 144, No. 2, pp. 466-470, it is clearly demonstrated that with liquid flowing over cavities the. mass transport is no longer uniform over the cavity. As a result, deposition is not uniform- in the cavities. With the cell described by BROWNLOW et al . (1969) in US-A-3 , 480, 522 , the electrolyte is successively stirred in a cycle of 30 seconds by moving the electrodes, monitored until the electrolyte is virtually at a standstill and then metal can briefly be deposited electrolytically. The cell can be used to deposit multilayers using an electrolyte, but this is associated with several major drawbacks: - the deposition rate is low, since the cycle frequency is low and the electrolyte becomes depleted too quickly at the cathode if one were to work with a high current density and a relatively long deposition period, - there are no measures on the workpiece for improving the uniformity at the edge, the contamination debris emanating from the anode can settle on the cathode.

Document US 5,242,556 describes a method for etching a structure flat. The method comprises the use of a negative and positive pulse on the workpiece with respect to a working electrode, followed by a pause in which some of the electrolyte between the workpiece and the working electrode is replaced. The presence of both negative and positive pulses gives rise to partial dissolution and partial deposition on the surface of the workpiece, with the result that the surface roughness is reduced.

Document XP002058762 of Derwent Publications Ltd. (And SU 489 616) describe a similar method for dissolving electrodes by utilizing pulsed currents and electrolyte circulation.

Aims of the invention

The invention relates to an electrochemical cell and a method which seeks to reduce the. abovementioned drawbacks and which can also be used efficiently for depositing metal coatings, alloy coatings, composite coatings and multilayers from one or various electrolytes, and for the electrochemical etching of microstructures . The invention generally aims to produce microstructures in a rapid, reproducible and economical manner by an electrochemical method by means of electrodeposition and/or electrolytic etching on planar, electrically conductive substrates. In particular, the invention aims:

- to deposit, in a reproducible manner, metals, alloys, composition-modulated layers or composites which, for a specific pattern, are uniform in terms of thickness and composition over the entire cathode surface,

- to prevent flaws in the deposition by avoiding contamination and the deposition of debris during electrodeposition,

- to obtain a relatively quick deposition process, so that large volumes can be produced in an automated unit,

- to manufacture multilayers of different or cyclically repeated composition using one or more elec trolytes, - to etch away patterns uniformly and quickly on chemically inert materials.

General description of the invention This aim is achieved in accordance with the characterizing part of Claim 1. Surprisingly, it has been found that the electrolyte is preferably at a standstill (flow rate between the electrodes essentially equal to zero) during the electrodeposition in order to obtain uniform deposition at the level of the cavities. The same applies for the anode dissolution (etching) .

Preferably, an intermittent variation in flow rate is imposed on the electrolyte in accordance with a cycle composed of two phases: a first phase where the flow rate is essentially other than zero and a second, subsequent phase where the flow rate is essentially equal to zero.

The electrodeposition (the etching) is preferably carried out by means of a cell which comprises plane- parallel electrodes which are disposed close together and are submerged in an electrolyte. The electrolyte is introduced through one or more openings in the anode or the cathode or between the anode and the cathode or, if appropriate, through an opening at the side between anode and cathode. A valve mechanism and/or a pump is designed in such a manner that the flow rate of the electrolyte between the electrodes can be fully controlled. This mechanism, combined with suitable positioning of anode and cathode, ensure that the flow of liquid between the electrodes can be forcibly accelerated or decelerated and even brought to a standstill. Cyclically, in the first phase the liquid (containing the electrolyte) between the electrodes is partially or completely replaced, and in the second position, when the liquid is virtually, and preferably completely, at a standstill, the electrodeposition (the etching) takes place. The flow rate is intermittently controlled in such a manner that a sufficiently high liquid flow rate is achieved, so that small gas bubbles and any debris are discharged during each cycle, in particular during the first phase of each cycle, in which the flow rate is essentially other than zero. After this, the flow rate gradually decreases, with the result that the flow of liquid is decelerated. A sinu- soidal flow rate, which is easy to realize, preferably meets these characteristics. Controlling the flow of liquid is necessary in order to achieve a high cycle frequency and essentially ensures complete replacement with electrolyte, which if appropriate has been filtered and revitalized, in the space between the electrodes. For this reason, the cell and the method according to the invention are suitable -for operating at high current density and therefore high deposition rate (or etching rate) . Discharging hydrogen bubbles prevents the formation of H₂ pits. The high liquid flow and frequency prevents contamination debris produced at the anode from being able to settle on the cathode. The cell according to the invention may be equipped with an anode which is in conformity with the cathode, an auxiliary cathode and/or a dielectric shield at the edge, thus preventing non-uniform deposition caused by the edge effect. Owing to the fact that the electrodes ^• can be arranged very close to one another, the volume of electrolyte which has to be completely replaced each cycle, if desired, is low. As a result, it is possible selectively to introduce or pump in and to collect various electrolytes, swills or dispersions each cycle. This makes it possible, inter alia, to produce composite coatings and multilayers using one or more electrolytes. To summarize, one can state that the method and the device according to the invention ensure that :

- complex micropatterns can be manufactured quickly, without contamination and with uniform thickness and composition;

- multilayers and/or composite layers can be manufactured using one or more electrolytes. The device and the method according to the invention are referred to below in general terms as "agitation synchronized electrodeposition" (ASE) .

Brief description of the figures

The invention is described below on the basis of a number of embodiments and with reference to the appended drawing, in which: Figure 1 diagrammatically depicts . an ASE system with a cell,

Figure 2 shows -a diagrammatic overview of a control system for ASE,

Figure 3 shows flow rate and electric current diagrams as a function of the cycle time,

Figure 4 shows a plan view of a variant cell design for ASE,

Figure 5 shows a section through the cell illustrated in Figure 4, Figure 6 shows a variant cell design for ASE, in section,

Figure 7 shows a section in the plane of the cathode of the cell in Figure 6, and

Figure 8 shows a section through the cell shown in Figure 6.

Detailed description of the invention

Figure 1 diagrammatically depicts an embodiment of a cell 10 which can be used to carry out an "agitation synchronized electrodeposition" (ASE) method according to the invention with high frequency.

An essentially planar workpiece, which is electrically connected to the cathode 6, is preferably (plane- ) parallel with respect to an anode surface 5. The electrodes 5, 6 are positioned in suitable holders 4, which are provided with the necessary lead-through for the wiring and contacts for conducting the electric current from a galvanostat or a potentiostat to the electrodes 5, 6.

Conductors 18 are inert, electrically insulated and sealed off at the necessary locations with respect to an electrolyte 7, and are produced in accordance with the known rules of the prior art .

The electrodes 5, 6 rest in a receptacle 3 and are submerged in the electrolyte 7. The receptacle 3 is surrounded by a casing 15 which contributes to thermo- static insulation for the electrolyte 7. A casing 15 is insulated and provided with a double wall, through which a thermostating liquid 14 - can flow. A circuit for the thermostating liquid 14 passes via a thermostating element 11. The electrolyte 7 is pumped between cathode 6 and anode 5 via pump 1, through narrow openings 2 which are situated in the anode or the cathode. The size of these openings is preferably less than 1/5 of the cathode/anode distance and the openings are sufficiently far removed from one another to keep the electric current distribution as uniform as possible. In the design depicted in Figures

4, 5, 6, 7, in which the electrolyte is pumped between anode and cathode from the side, there is no problem of current distribution around the electrolyte feed, since the feed is not above the cathode or the workpiece. Feed line 8 is made from material which is sufficiently strong not to be deformed by the pressure and vacuum brought about during pumping. One-way valves 9 are provided, irrespective of the action of the pump or in the feed line. As a result, the pump flow rate controls the flow between the electrodes while the electrolyte is being changed. The inlet to the discharge line 19 is disposed in such a manner that the discharge flow does not cause any turbulence during electrodeposition between the electrodes. This inlet is at a deep position, preferably the deepest position, in the receptacle, in order to extract any debris which has settled and to filter it out of the electrolyte. Liquid-level detector 13 in receptacle 3 checks that cathode and anode are always submerged in the electrolyte. The electrolyte may be discharged continuously or discontinuously, in phase or counterphase with the feed.

This can be carried out using one or more pumps equipped with the necessary distribution line, expansion vessels and valve mechanisms and known measurement and control equipment which, for reasons of clarity, are not shown in Figure 1. A simple, efficient layout, which is depicted in Figure lb, shows a pump (1) which pumps out and feeds in the electrolyte, discontinuously in counterphase. If the pump is driven with a uniform, rotational movement via shaft 22 and motor 26, the flow rate D is sinusoidal, as illustrated in Figure 3a. The arrangement shown in Figure 1 and the cycle time diagram shown in Figure 3a indicate that the electrolyte flows between the electrodes only during the delivery stroke in time phase 1 Tl of the cycle. During the second phase T2, the suction stroke, the electrolyte between the electrodes is virtually at a standstill and the receptacle is partially emptied. By driving the pump at a varying angular velocity using a stepper motor or motor 26, it is possible to control the instantaneous flow rate, the period time and the relationship between phase time 1 and 2 and the cycle frequency, as shown, for example, in Figures 3a, 3b, 3c. As a result, it is possible to optimize the course of the flow rate, taking into account the visco-elastic properties of the electrolyte 7, the geometry of and distance between cathode and anode, in such a manner that it is possible, within the shortest period of time, to refresh the electrolyte 7 between the electrodes 5, 6 and then to bring it to a standstill. It is also possible to alter the time of phase 2 in order to obtain a better deposition efficiency and/or a controlled composition. Via a detector 21, the position of the piston 29 of the pump is detected. If necessary, the detection signal is delayed, so that the electrodeposition takes place at the same time as the electrolyte between anode and cathode is at a standstill in time phase 2 of the cycle. Figure 2 diagrammatically depicts the synchronization. Figure 2 shows: the detector 21, the pump 1, the pulse delay 23, the function generator 24, the galvanostat or potentiostat 25, the cell 26, the feed line 8, the discharge line 12, the electrical connections 18 between the electrodes and galvanostat or potentiostat. Together with the galvanostat or potentiostat, the function generator allows the current or voltage to be modulated during phase 2, for example as shown in Figures 3d, 3e, 3f .

As an alternativey which is not shown in Figure 1, the electrodeposition can be synchronized with the aid of a liquid flow detector, which detects the liquid flow (standstill) in the feed line just upstream of the anode. Commercially available flow detectors based on various detection principles, such as LASER-Doppler, pressure difference detector and others, are suitable for this purpose. As an alternative, a function generator, coupled to drive electronics for the pump motor and the electric current source for the electrodeposition, can synchronize the system in the correct sequence. The cell 10 may be provided with an auxiliary cathode 16 with suitable current balancing with respect to the cathode or an electrically non-conductive current reflector 17 in order to keep the electrodeposition uniform at the edge of the cathode. Overall, the entire process: synchronization, electrolyte revitalization, filtering, thermostating, electrolyte flow rates and motor control of the pump(s), electrolyte level, electric current/voltage function for deposition, can be controlled by means of control unit 28.

It is essential to the invention that preferably at least 50%, and more preferably at least 80%, of the electrochemical material is deposited at the moment at which the electrolyte between cathode and anode is virtually at a standstill, so that at least 80% of the electric current for electrodeposition is supplied in time phase 2. By allowing the electrodeposition to take place while the electrolyte is at a standstill, the uniformity of deposition is increased in terms of thickness and composition at the level of the microcavities . These are required if a complex microstructure is being produced in a resist layer in the form of a mask.

It is essential to the invention that preferably at least 50%, and more preferably at least 80%, of the electrolyte between the cathode and anode is replaced each cycle by filtered and revitalized electrolyte. This replacement proceeds more quickly if the -volume between cathode and anode is low. This is achieved by making the distance between cathode -and anode as small as possible. Taking into account the visco-elastic properties and the density of the electrolyte and the surface tensions between electrolyte and cathode surface and anode surface, the distance (H) shown in Figure 1 between cathode and anode is preferably less than 10 mm, and more preferably between 0.5 and 3 mm. This prevents convection during phase 2 and provides a quick flow-through during phase 1 of the cycle.

It is essential to the invention that the frequency of refreshing and electrodeposition is preferably higher than 0.1 cycles/second for the following reasons:

- H₂ gas bubbles cannot develop into large entities at the same location on the cathode, since they are discharged each cycle by the flow, so that hydrogen pits are prevented,

- contamination particles emanating from the anode are removed by the flow before they can become deposited on the cathode,

- the frequent refreshing of the electrolyte at the surface of the cathode makes it possible to work with relatively high average current densities, with the result that the deposition process is efficient, - completely replacing the electrolyte in good time means that there is little risk of it becoming depleted, and the composition remains sufficiently homogeneous to achieve uniform deposition in terms of thickness and composition at the level of the workpiece.

By way of example, the uniformity of deposition is illustrated on the basis of the layout shown in Figure 1, in which the distance (H) between _ cathode and anode is 2 mm, the pumping sequence is completely sinusoidal, as in Figure 3 , and the volume pumped between the electrodes during phase 1 is 50 ml, the total cycle lasts 1700 msec and the deposition time lasts 833 msec during phase 2. What is being produced are cores for a microinductor having a thickness of 6 μm and a composition of Ni (81% by weight) and Fe (19% by weight) distributed over a 4-inch Si wafer provided with a Cu seed layer and the necessary photoresist masks. Deposition is carried out galvanostatically with a current density of 100 mA/cm² at 60°C. The bath composition is as follows: FeCl*4H₂0 3 g/1, NaCl 30 g/1, saccharine 3 g/1, NiCl₂»6H₂0 50 g/1, B(OH)₃ 30 g/1, at pH 2.5. It is established in this method that the thickness deviation is less than 4% over identical masks, irrespective of where the mask is situated on the wafer and taking into account deviations in the primary current distribution. The example is not limited to the electrochemical deposition of this composition and the use of this specific electrolyte. The uniformity can also be obtained with other electrolytes, electrolytes mixed with dispersions of charged particles and others.

A variant of the ASE system according to the invention is the cell 50 shown in Figure 4. This cell can be used for a plurality of wafers or workpieces or a large workpiece where centrally no deposition is required, for example a magneto-optical disc, if the necessary recess is arranged in the cathode holder for this purpose. The cell is shown in Figures 4 and 5 in a very simple form, for example for 3 wafers. Figure 4 shows a plan view of the system and Figure 5 shows a cross-section on line AB in Figure 4. The wafers or workpieces 56 lie in one plane, disposed concentrically around the feed opening 58 for the electrolyte, and essentially plane-parallel to the anode 55. In order to ensure that the electrolyte flows through uniformly, the surface of the holder for the anode 51 and the anode lie in the same plane. With the exception of the electric contact (s) and attachment elements 52 for the cathode 56, if these are present on this surface, the surface of the cathode, of the auxiliary cathode 59 and of the cathode holder 57 lie- in the same plane. The holders for the electrodes 54 are provided with the necessary connections and contacts 49 for conducting the electric current from the galvanostat or potentiostat to the electrodes. These are inert, electrical and sealed at those locations with respect to the electrolyte and are made in accordance with the rules of the prior art . The electrodes rest in a receptacle 63 and are submerged in the electrolyte 67, the level being monitored by a detector 53. A spacer tube 64 ensures that the electrodes are positioned in a plane-parallel manner. The inlet to the discharge line 69 lies at the deepest point of the receptacle in order to discharge any settled debris and to subject the electrolyte to aftertreatment , in particular to filter it. An isostatic chamber 68, which ensures that the radial flow is identical in all directions, may be arranged around the inlet 58. This chamber is a cylindrical ring comprising random capillary openings and passages made of inert material and is made, for example of cemented teflon, polyethylene, polymethylmethacrylate and glass beads with a diameter of less than 1 mm. This cell 50 is connected to a drive system 20, as shown in Figure lb and Figure 2. A variant cell design for ASE according to the invention is shown in Figure 6, Figure 7 and Figure 8. Figure 7 shows a section in the plane of the cathode surface. Figure 6 is a cross-section through the cell on line AB in Figure 7. Figure 8 is a cross-section on line CD in Figure 7. In this cell, the electrolyte is introduced between cathode and anode from the side. In this design, if desired, the anode and the introduction device may be rotated, between each cycle or a plurality of cycles or during phase 1, as desired through 180° or less, continuously or discontinuously, with respect to the cathode. Obviously, it is easy for a person skilled in the art to produce a variant arrangement in which only the injection device can be rotated with respect to the cathode .

It is essential to this design that the direction of electrolyte flow with respect to the workpiece can be changed during phase 1 or between cycles and that the electrolyte is at a standstill during phase 2. This cell 70 may be disposed both horizontally and vertically, and in all intermediate positions, with the cathode 76 always below the anode 75 except when in the vertical position. In this example, the cell is disposed at 20° with respect to the horizontal. The anode holder 71 and the electrolyte injection head 89 and the isostatic chamber 88 are fixed to one another and can be rotated through at least 180° about the axis 98 for the purpose of changing the direction of flow of the electrolyte. They may also be raised in the direction of the axis for the purpose of replacing the electrodes . The electromechanical rotation and lifting mechanism 99 may be designed in various ways by the person skilled in the art . The holder for the wafer and auxiliary cathode 72 is fixed to the bottom of the receptacle 74, which in this example is also tilted by 20°. The electric current conductors for the cathodes 97 pass, sealed and isolated, via the cathode holder, through following the bottom of the receptacle towards the galvanostat or potentiostat. In the anode holder 71, there are resilient, electrically non-conductive pins 102 made of inert material, to which an electrically conductive bridging ring 103 is attached. The bridging ring fits just over the edge of the wafer and forms a bridge between the cathode contact ring 104 and the wafer 76. When the anode holder 71 has been placed on the cathode holder, the ring presses onto the wafer and the cathode contact ring, with the result that the wafer is connected, via the electrical conductor 97, to the galvano-potentiostat . When the anode holder is raised, the wafer comes to lie completely free, so that it becomes possible to load, process and unload the wafers completely automatically. In order to ensure that the electrolyte flows through uniformly, the surface of the cathode 77 and of the cathode holder 78 preferably lies plane-parallel to the surface of the anode 79.

The electrolyte is injected between anode and cathode at height H, which is preferably less than 10 mm. The inlet 88 comprises an isostatic chamber with a spray head comprising capillary passages 89 which ensure that the flow is uniformly distributed over the cathode surface. The flow of liquid leaves the space between the electrodes at outlet 80. Anode holder 71 and cathode holder 92 are made to match and cylindrically recessed 92, so that anode holder can rotate freely with respect to the cathode holder and can move in the direction of the axis 98, with the result that H can be reduced to virtually 0, can reciprocate cyclically or can be set at a height H. The holder of the anode 71 is provided with a sealing ring 81 and a lead-through for the electrically conductive clamping bolt 83 which is attached to the anode and serves to clamp the anode tightly to the sealing ring 81, via the screw 84. This prevents the electrolyte in the hollow cylinder 85, at the rear of the anode, flowing onto the electrically conductive clamping bolt. The electric conductor 101, which passes from the hollow cylinder of the anode holder 85 to the galvanostat or potentiostat, is formed on this bolt. The revitalized, filtered and thermostated electrolyte is fed, via line and duct 93, to the isostatic chamber 88 and the injection piece 89. The electrolyte is discharged at the deepest point of the receptacle 93, in order to pump out any debris which has settled and to filter it out of the electrolyte. The receptacle 73 has a double jacket for a thermostating circuit 100. Level detector 96 ensures that the electrodes are submerged in the electrolyte 94 and are coupled to the control system 28. In order to prevent the wafer from adhering to the bridging ring and in order to hold it entirely stably during the processing, it is sucked onto the plate of the cathode holder 106 by means of vacuum. In this plate, fine passages are connected, via vacuum line 105, to an automatically controlled vacuum pump. Sealing ring 107 ensures that -the vacuum is maintained and prevents electrolyte from seeping in on the rear side of the wafer. This cell 70 is connected to a system 20 as shown in Figure lb and Figure 2 for ASE.

This cell design according to the invention makes it possible to use ASE at high frequency, with various liquid flow directions and makes it possible to completely automate the actions: positioning of the wafer, electrochemical processing and removal of the wafer.

An example of the ASE method for etching is explained below.

By way of example, the uniformity of electrochemical etching is applied using the layout as illus- trated in Figure 1, under conditions which are comparable to those indicated for the example relating to Figure 1. The material to be etched off is of the high-alloy type, such as stainless steel, 316L, Haynes 188 and Elgiloy being materials which are chemically difficult to etch in environmentally-friendly electrolytes (for example, avoidance of NOx emission) . Applying an anodic potential to the said material, submerged in a less aggressive electrolyte, does in face allow the anodic dissolution of the said material to be achieved in a controlled manner. The method is carried out in a 1 to 6 M NaN0₃ electrolyte to which, if appropriate, 10% of glycerine has been added, at 1 V and for a total treatment duration of 1 mm. The high-alloy substrate material is covered with a chemically inert photosensitive resist layer in which a pattern of holes has been made by lithographic methods. It is established here that at those holes where the substrate material is in contact with the electrolyte those parts which have been etched away present a substantial reduction in the undercutting and that the walls along the parts which have been etched away are straighter and flatter by comparison with electrolytic etching tests carried out without using the cell shown in Figure 1. The example is not limited to the electrochemical etching of these materials and the use of these specific electrolytes. -

All these cells are made in accordance with the rules of the prior art, with the result that, if appro- priate, use can be made of an auxiliary cathode (8) thief ring and/or current reflection ring (10) with a modified power supply in order to obtain uniform deposition at the edge of the workpiece (6) . With the exclusion of the cell illustrated in Figures 1 and 2, these are not shown in the rest of the drawings,

- the current-bearing lines to the cathode (s) and the anode are electrically and chemically inert with respect to the electrolyte and are in electrical contact with the respective electrodes,

- the holder of the workpiece is designed in such a manner that the workpiece is easy to put in place and only that part of the cathode which faces the anode is in electrical contact with the electrolyte,

- a thermostating, revitalizing and filtering unit can be accommodated in the feed and discharge circuit, optionally with automatic control, in such a manner that contamination- free and revitalized electrolyte at the correct temperature is pumped between the electrodes, - all the materials used in the cell, feed and discharge lines and pump which come into contact with the electrolyte are chemically inert with respect to the electrolyte, with the exception of the electrodes.

Obviously, these cells may be disposed next to one another in a battery, whether or not in the same one, and replacement of the workpieces may be automated using standard principles.

Although this invention has been described with reference to advantageous-embodiments, it will be clear to the person skilled in the art that amendments in form and details may be made without deviating from the spirit and scope of the invention.

Claims

1. Method for the electrochemical deposition of metals, alloy, composition-modulated layers or composites on an at least partially electrically conductive workpiece which is connected in an electrically conductive manner to a voltage source or current source and is positioned essentially parallel with respect to a counter-electrode, between which there is an electrolyte, characterized in that an electric current is applied_^ between a cathode and an anode when the flow rate of the electrolyte between the anode and the cathode is essentially equal to zero.

2. Method for etching off metals, alloy, composition- modulated layers or composites on an at least partially electrically conductive workpiece which is connected in an electrically conductive manner to a voltage source or current source and is positioned essentially parallel with respect to a counter-electrode, between which there is an electrolyte, characterized in that an electric current is applied between a cathode and an anode when the flow rate of the electrolyte between the anode and the cathode is essentially equal to zero.

3. Method according to Claim 1 or 2 , characterized in that the flow rate of the electrolyte between the anode and the cathode follows an intermittent cycle of two phases, the flow rate being essentially other than zero in the first phase and the flow rate being essentially equal to zero in a subsequent second phase.

4. Method according to Claim 3, characterized in that the frequency of the cycle of the flow rate of the electrolyte is greater than 0.1 Hz.

5. Method according to one of the preceding Claims 1- 4, characterized in that the electrolyte is transported in a circuit, the electrolyte being subjected to a treatment after it has passed between the anode and the cathode and before it is reintroduced, at least in part, between the anode and the cathode, which treatment is preferably a revitalization or a filtering.

6. Method according to one of Claims 3-5, characterized in that at least 50%, and more preferably at least 80%, is deposited or etched off at the moment at which the electrolyte between the cathode and the anode has a flow rate which is essentially equal to zero.

7. Method according to one of Claims 3-6, characterized in that at least 50%, and preferably at least 80%, of the electrolyte between the cathode and the anode is replaced each cycle.

8. Electrochemical cell comprising a .workpiece which is at least partially electrically conductive and is connected in an electrically conductive manner to a cathode, and an anode, between which there is an electrolyte, characterized in that the electrodes are disposed parallel to one another at a distance which is at most equal to 10 mm and preferably lies between 0.5 and 3 mm.

9. Cell according to Claim 8, characterized in that a device which controls the flow rate, such as a pump, is provided for controlling the flow rate of the electrolyte between the anode and the cathode in an intermittent cycle.

10. Cell according to Claim 8 or 9, characterized in that a galvanostat, a potentiostat, a current source or a voltage source is provided, which can provide electric current in an intermittent flow.

11. Cell according to one of Claims 8, 9 or 10, characterized in that at least one of the electrodes, the cathode and/or the anode, is provided with cavities for the passage of the electrolyte, which cavities preferably have a diameter which is less than 1/5 of the distance between the anode and the cathode.

12. Cell according to one of Claims 8-11, characterized in that a circuit line is provided for the electrolyte, to which line a treatment unit is connected.

13. Cell according to one of Claims 8-12, characterized in that an assembly comprising the anode or the cathode and an introduction facility for the electrolyte is provided, which assembly is axially rotatable.

14. Cell according to one of Claims 8-13, characterized in that a current-reflection ring made from an inert material which is not electrically conductive is provided at one edge of the cathode and/or the anode.

15. Cell according to one of Claims 8-14, characterized in that an auxiliary electrode is arranged around the cathode and/or the anode.