WO2001079589A1

WO2001079589A1 - Method in and apparatus for etching or plating of substrates

Info

Publication number: WO2001079589A1
Application number: PCT/SE2001/000823
Authority: WO
Inventors: Mats Hållberg
Original assignee: Obducat Aktiebolag
Priority date: 2000-04-13
Filing date: 2001-04-12
Publication date: 2001-10-25
Also published as: AU4896701A; SE0001369L; SE0001369D0

Abstract

In a method for processing a substrate (S), for instance by etching or plating, use is made of an apparatus comprising a chamber (1) for receiving the substrate (S), a unit (10) for feeding a processing fluid to the chamber (1) before and/or during processing, and a flushing unit (20) for cleaning the substrate (S) by means of a flushing fluid after completed processing. The flushing unit (20) comprises a flushing fluid tank (21), a cleaning device (20') and a fluid feeding means (22, 24), the fluid feeding means (22, 24) being arranged to feed from the flushing fluid tank (21) the flushing fluid through the chamber (1) for cleaning the substrate (S) received therein, through the cleaning device (20') for cleaning the flushing fluid and back to the flushing fluid tank (21). Thus, the working operations for cleaning the processed substrate (S) are significantly simplified. The cleaning can easily be automated without necessitating expensive auxiliary equipment. Moreover cleaning takes place in an essentially closed environment inside the chamber (1), thereby minimising the environment's exposure to substances which are dangerous to health. Moreover, an essentially closed process with a minimum of emissions of environmentally dangerous residual products, such as metal ions, is made possible.

Description

Method in and apparatus for etching or plating of substrates.

METHOD IN AND APPARATUS FOR ETCHING OR PLATING OF SUBSTRATES.

Field of the Invention

The present invention relates generally to processing of substrates, e.g. by plating or etching. The invention relates specifically to cleaning of a substrate after completed processing.

The present invention is especially usable in electrochemical plating and etching. Therefore the description of background art, as well as objects of the invention and embodiments thereof, will be given with reference to such electrochemical processing, in particular plating. However, the invention is also applicable to other processing of a surface of a substrate, for instance in chemical etching or in dissolving of surface layers, such as resist layers after expo- sure, by means of a solvent or the like. Background Art

It is many cases desirable to produce small structures in a material surface of a substrate. This can be achieved by electrochemical plating of the substrate. Alternatively, the substrate can be subjected to electrochemical etching. In both cases, such electrochemical processing takes place in a cell or container, which defines a chamber containing at least one electrode and an opposite substrate holder. The electrode and the sub- strate holder are connected to a voltage source, which during the electrochemical processing establishes an electrical field between the electrode and a substrate carried by the substrate holder. An electrolyte is received between the electrode and the substrate. In a plating process, ions pass from the electrolyte and are deposited on the surface of the substrate. In an etching process, parts of the surface of the substrate are dissolved and pass to the electrolyte in the form of ions. In one type of plating process, the surface of the substrate can be provided with the desired structure, so that an inverted copy is transferred to the metal layer which is deposited on the substrate acting as a cathode. The thus structured metal layer can then be released from the substrate and used as a stamper (matrix) , for instance in injection moulding of various products, such as CD, CD ROM, DVD etc. and also vinyl records, holograms etc., or in so-called nanoimprint lithography for manu- facturing structures in semiconductor materials etc.

Alternatively, the structured metal layer can be used as a so-called father by a new metal layer being deposited thereon for making an inverted copy which is used either as a stamper as above or as a so-called mother on which a metal layer is deposited in order to form sons which in turn are used as stampers. This type of plating is disclosed in e.g. US-A-5 , 843 , 296 and US-A-5 , 427 , 674. In an alternative plating process, an unstructured substrate is arranged as a cathode in the chamber. By suitable masking of the substrate, a desired structure can be formed on the same during plating. According to one more alternative plating process, an even metal layer is deposited on an unstructured substrate. This plating process thus results in an unstructured raw matrix of high sur- face smoothness which in a separate subsequent step is structured by a suitable method, such as etching. This type of method is disclosed in W099/63535.

In an etching process, the substrate, which is arranged as an anode in the chamber, can be structured by suitable masking thereof. Alternatively, an electrode surface can be caused to move in a given pattern over the substrate. Different types of electrochemical etching are known from e.g. EP-A-392 738, O98/10121 and EP-A-563 744. Like in plating, the structured substrate can be used directly as a stamper, for instance in injection moulding or in nanoimprint lithography, or be used for making a mother etc.

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ring the substrate from the plating chamber to the flushing unit .

The above problems are also to be found in prior-art apparatus for chemical or electrochemical etching, and dissolution of a surface layer, for instance an exposed resist layer, on a substrate. Object of the Invention

It is an object of the present invention to wholly or at least partly overcome the above problems according to prior-art technique, and in particular to provide a method in processing a substrate as well as a processing apparatus which minimises the emission of environmentally dangerous residual products .

It is also an object to reduce the operator's expo- sure to substances which are injurious to health during cleaning of the processed substrate.

One more object is to minimise the risk of contamination of the processing fluid, i.e. the electrolyte, the etchant or the solvent, during cleaning of a substrate processed with this processing fluid. Summary of the Invention

These and other objects that will be evident from the following description are now achieved by a method and an apparatus according to the independent claims. Preferred embodiments are defined in the dependent claims .

An advantage of the inventive method is that the substrate is flushed with a flushing fluid in situ in the processing chamber. Thus, the working operations for cleaning the processed substrate are significantly simplified. The cleaning can easily be automated without necessitating expensive auxiliary equipment. Moreover, the cleaning takes place in an essentially closed environment inside the chamber, which means that the envi- ronment's exposure to substances dangerous to health is minimised. Thanks to the fact that the flushing fluid after passing the chamber is cleaned by means of a clean-

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.

According to another preferred embodiment, especially intended for electrochemical plating, the ion concentration of the processing fluid, i.e. the electrolyte, in the second tank is adjusted by a dosed supply of alkaline anions and metal ions which are identical with metal ions present in the electrolyte. This embodiment is particularly preferred when using a dimensionally stable anode in the chamber. Thus, a constant metal ion content can easily be maintained in the electrolyte. Preferably, a filter is arranged between the second tank and the first tank, so that undissolved residues of the added ions can be prevented from reaching the first tank and from this the chamber. Preferably, the anions and metal ions can be supplied as a slurry of an alkaline metallic salt. The supply of the alkaline metallic salt is controlled preferably based on the pH of the electrolyte received in the first or second tank. Consequently, simple and accurate control is allowed. During the plating process, hydrogen ions in fact form at the anode in proportion to the amount of deposited metal ions on the substrate, which means that the pH also indicates the metal ion content of the electrolyte. It is preferred for the alkaline metallic salt to contain anions in the form of carbonate ions, hydroxide ions, oxide ions or oxide hydroxide ions since these are capable of neutralising the formed hydrogen ions without giving rise to undesired residual products in the electrolyte.

According to another preferred embodiment, the flushing fluid is cleaned after passing the chamber in the cleaning device by separating ions dissolved in the flushing fluid, and said ions are recirculated to the processing fluid, preferably to the second tank. This permits an essentially fully closed process with minimum amounts of residual products. The recirculation of the ions can take place manually or automatically.

According to another preferred embodiment, the flushing fluid fed through the chamber is directed during a first period of time to the first or the second tank and during a subsequent second period of time via the cleaning device to the flushing fluid tank. Thus, the amount of processing fluid that is admixed to the flush- ing fluid can be minimised. This is advantageous since as a rule it is easier to remove flushing liquid, typically water, from the processing fluid than processing fluid from the flushing fluid.

According to a preferred embodiment, the flushing fluid fed through the chamber is transferred to a secondary tank, and the flushing fluid is supplied from the secondary tank to the flushing fluid tank via the cleaning device, which collects the ions dissolved in the flushing fluid. By contaminated flushing fluid being sup- plied to the secondary tank, flushing fluid of a desirable quality is always available in the flushing fluid tank. Moreover the flushing fluid can be kept at a given level in the flushing fluid tank, for instance by means of an overflow connected to the secondary tank, in order to minimise the risk of production troubles during the flushing of the substrate.

It is also preferred for a subatmospheric pressure to be generated in the chamber during processing. The risk of processing fluid leaking from the chamber is thus easily eliminated. Furthermore the sealing of the chamber can be simplified since the subatmospheric pressure automatically strives to keep the parts of the chamber together .

According to a preferred embodiment, the processing fluid circulating between the first and second tanks passes through an ejector, which during generation of a subatmospheric pressure in the chamber draws electrolytes from this and thus causes the processing fluid to circulate between the first tank and the chamber. Consequently the number of pumps or the like can be minimised since one pump can perform the circulation of processing fluid both between the first and second tanks and between the OJ ) to to Y→ t→

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3 Y→ TJ CD Yi Oi Y→ rt μ- Φ C rt μ- Φ φ i CO 3 Y→ t→ φ CQ Ω i

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Φ tr Φ Φ Φ 3 Ω tr rt tr μ- l-h Ω Oi C • t→- h Y→ rt φ CO C Ω 3 Ωi μ- 3 H Ω. φ Ω

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01 O Hi 0 μ 0 H 01 01 01 tr Ωi co μ- a CD Φ tr 0i Hi O t→ 3 Hi Hi 3 φ Oi 3

3 0 o μ, §^■ Yi rt Ω 3 Φ μ- 0 3 tr Φ a Y→ X μ- fj¹ rt l-h O a ø o^* fj¹ ^ μ^j μ- Φ 0 Φ μ- μ- Ω Ω 0 3 Ω 3 Φ μ- Ω a o O tr LQ Φ Φ TJ Φ Y→ Yi CD TJ Φ

Φ μ- Y→ 3 o Oi 3 Ω C 0 X D CD 0 a 3 tr X μ- Φ Yi μ i C Φ μ- rt § Φ^• Yi μ> CD 0 φ μ- O CD μ 3 μ. μ 0 rt CQ 01 r μι Ω a o t→- 0 μ- i •

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opposite cathode holder (not shown) , which carries the substrate S which is to be plated. A voltage source (not shown) is connected to the anode 2 and the cathode holder in order to establish during the plating process an elec- trical field between the anode 2 and the substrate S, which acts as a cathode. An electrolyte feeding system 10 communicates with the chamber 1 to feed an electrolyte through the chamber 1 during plating. A flushing water system 20 also communicates with the chamber 1 in order to feed flushing water through the chamber 1 after completed plating, for washing of the plated substrate S. Valves 30, 31, 32 are arranged to selectively control the feeding of electrolyte and flushing water to and from the chamber 1. The flushing water system 20 comprises a cleaning device 20' which is designed to separate ions from incoming flushing water. A conduit 33 extends from the cleaning device 20' to the electrolyte feeding system 10 for transferring separated ions to the same. The electrolyte feeding system 10 contains a concentrating device 10' which is designed to separate water from the electrolyte. A conduit 34 extends from the concentrating device 10' to the flushing water system 20 for transferring separated fluid to the same.

The apparatus shown in Fig. 1 generally operates in the following fashion. During plating, the valves 30, 32 are closed and the valve 31 open, and electrolyte is circulated continuously between the electrolyte feeding system 10 and the chamber 1. The system continuously conditions the electrolyte, inter alia with regard to its metal ion content, pH and temperature. After completed plating, the plated substrate S is flushed in situ in the chamber 1 by the valve 30 being opened and flushing water being pumped into the chamber 1. A non-return valve 35 prevents flushing water from flowing into the electrolyte feeding system 10. During a first period of time, the flushing water is allowed to press electrolyte out of the chamber 1 and into the system 10. When almost all the electrolyte has been pressed out, the valve 31 is closed and the valve 32 is opened, so that flushing water and the remaining electrolyte are allowed to circulate between the flushing water system 20 and the chamber 1. The plated substrate S is flushed clean from electrolyte. The cleaning device 20' of the system continuously cleans the flushing water received from the chamber 1. In the meantime the concentrating device 10' operates to separate any flushing water admixed to the electrolyte and transfer this to the cleaning device 20' of the system

20. Subsequently the apparatus is ready to perform a new plating process. The plating apparatus is suitably controlled by a main control unit (not shown) .

The construction and function of the apparatus in Fig. 1 will now be described in more detail with reference to Fig. 2.

The electrolyte feeding system 10 comprises a first tank 11, which via a feeding duct 12 communicates with the chamber 1, and a second tank 13, which via a pump 14, an ejector 15 and a particle filter 16 communicates with the first tank 11. The suction side of the ejector 15 communicates with an electrolyte outlet of the chamber 1. The first tank 11 has an overflow 17 which communicates with the second tank 13. The concentrating device 10' of the system 10 comprises an air fan 11' which communicates with the upper part of the second tank 13, and a cooling tower 12' extending from the upper part of the tank 13. The first tank 11 is provided with a heater 18A for heating the electrolyte, a temperature sensor 18B and a pH meter 18C.

In the preferred embodiment, the anode 2 (Fig. 1) in the chamber 1 is a dimensionally stable anode which is essentially inert relative to the electrolyte. The metal ions in the electrolyte which are consumed during plating are replaced in this case by means of a compensating device 40 which prepares a water-based slurry containing corresponding metal ions. A pump 41 is designed for dosed supply of the slurry to the second tank 13.

The choice of electrolyte is of course controlled by which metal is to be deposited on the substrate S (Fig. 1) . In nickel plating, the electrolyte can be based on e.g. nickel sulphamate and water. In this case hydrogen ions are formed at the anode 2 during plating while at the same time nickel ions are precipitated on the substrate S. These hydrogen ions are neutralised by supply- ing an alkaline substance. This takes place by means of the compensating device 40, which prepares the slurry of an alkaline metallic salt, in this case nickel carbonate, nickel hydroxide, nickel oxide or nickel oxide hydroxide. The anions of the salt react with the hydrogen ions and form, depending on the salt chosen, water or carbon dioxide. Owing to the metal ions and the alkaline substance being supplied in the form of a salt, metal ions can be supplied in a controlled fashion to the electrolyte based on the pH of the electrolyte measured by the meter 18C.

The flushing water system 20 comprises a clean water tank 21, which via a feeding pump 22 and the valve 30 communicates with the feeding duct 12 and the chamber 1, and a secondary tank 23, which via a pump 24 and the cleaning device 20' communicates with the clean water tank 21. The cleaning device 20' is an ion filter, for instance a filter for reverse osmosis. The cleaning device 20' is designed to separate ions from the flushing water and has an ion outlet which via the duct 33 is con- nected to the compensating device 40 for transferring ion concentrate to this. The cleaning water tank 21 has an overflow 25 which communicates with the secondary tank 23. The secondary tank 23 communicates with the cooling tower 12' via the duct 34 for receiving condensed water from the same.

The plating chamber 1 has a pressure-controlled outlet (not shown) which is closed at subatmospheric pressure in the chamber 1 and is open at pressure above atmospheric in the same. For instance, the plating chamber 1 may consist of two parts which are held together at internal subatmospheric pressure and which automatically are separated at internal pressure above atmospheric. A collecting vessel 50 is arranged under the plating chamber 1 for receiving electrolyte and flushing water from the pressure-controlled outlet, as will be described in more detail below. The collecting vessel 50 communicates via the respective valves 31, 32 with the first tank 11 and the secondary tank 23.

The plating apparatus shown in Fig. 2 operates as follows. During plating, the valves 30, 31, 32 are closed. The pump 14 feeds electrolyte from the second tank 13 through the ejector 15 to the first tank 11. The ejector 15 draws electrolyte from the chamber 1 into the first tank 11, and the suction effect of the ejector 15 causes electrolyte to circulate in a loop between the first tank 11 and the chamber 1. This loop is designed in such manner that a subatmospheric pressure is established in the chamber 1. The filter 16 separates any particles in the electrolyte. Via the overflow 17, a stable electrolyte level is established in the first tank 11. The compensating device 40 feeds the slurry to the second tank 13 based on the output signal of the pH meter 18C. The concentrating device 10' separates continuously or intermittently water from the electrolyte in the second tank 13 and transfers this water to the secondary tank 23. After the plating has been completed, the plated substrate S is flushed in situ in the chamber 1 by the pump 14 being stopped, the valve 30 being opened and the feeding pump 22 being started to pump flushing water into the chamber 1. The non-return valve 35 prevents the flushing water from flowing into the first tank 11. The water flowing into the chamber 1 increases the pressure in the chamber 1 so that its pressure-controlled outlet

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Φ 3 01 μ. 3 tr Ω 0 Hi rt øi C øi μ. a Yi X 01 Oi Φ 3 φ Φ i o CD

• a

Oi CO 3 μ- rt Φ Φ C 3 01 y→ 3 3 < l-h 0 D ti a Ωi CD rt Φ Hi CD Ω. y→ • TJ μ- a Oi CO 0 i Φ X TJ CQ 0i Y→ Yt, 01 rt to ^■<: Ωi CQ μj tr CQ μ- rt Φ

H CO cr rt 0 Yi Φ Hi 3 Oi Φ Hi TJ O tr TJ Oi CQ X φ Φ Φ CD Yi tr Y→ rt tr 0 m Φ μ- 3 Ω ft Φ CO H φ ^ Ω. Φ O X 01 0 i 3 • rt Ω C 0⁾ Ω 3 Φ CQ 01 tr

Φ tr 0 Y→ > 0 0 μ- H- rt CD μ CQ μ- < 0 X 01 0 cr ft 0 Oi <! Ω. rt rt σι Φ cr Φ 3 3 μ- Φ Y→ < Ωi Ω tr <! Yi i i Φ Ω 3 3 CQ φ 3 μ- øi o cr Φ 0 CQ øi CQ tr Φ C μ- o Ω μ- Φ c φ to ? rt rt μ 3 Y→ 0 rt rt • Φ

01 Oi Ω- 0 a 0 Φ Yi 01 Φ PL O øi Ω. t→- TJ Φ rt CQ Y→ CO 0i μ. 01 μ- < c 01 tr t→

CD c TJ μ- Hi a μ- 01 - Y→ a a CD 3 tr CQ rt to 3 01 μ. a Φ rt 3 φ Φ μ- CD TJ Hi 0 a rt Y→ rt 01 rt rt rt μ- rt Φ cr 0i > μ- rt 01 ^ CD X rt Ω

Ω Φ Oi μ- rt rt LQ tr rt rt TJ a Oi tr 0 3 3 Yi ^ cr a Φ 3 LO 0 φ rt

O i Φ tr Φ tr tr Oi o μ- φ 0i 01 Φ rt Y→ rt Oi rt Φ CO Hi t→ Y→ rt μ|

TJ 01 Ωi φ 01 Φ O 3 a ft Ω- rt μ- t→ tr 3 Φ tr rt CO 0⁾ y→ t→ φ tr 0

Hi rt Yi X Ωi Oi 01 CQ H tr Φ tr 3 Φ Φ Φ ^ Φ • Φ a Φ μ- rt . Ω Φ Y→ μ- 0 c TJ t→- tr o C a μ- Φ Φ CO Ω Oi X 0 Ωi y→ X Ω Q tr rt ^

3 i-i CD Y→ CD Φ TJ Ω Y→ rt rt Hi a 01 c H Φ rt Φ ≤ Yi CO rt

0⁾ X 3 φ rt rt O μ 01 CO rt CD 3 Ω to i-i tr 0 øi Φ rt CD Φ 0 a Φ tr co 0 Φ 3 i 3 Φ

ciples of the invention can also be applied to chemical etching of a substrate, and to dissolving a surface layer on a substrate, for instance after exposing a resist layer, for masking the substrate before a subsequent etching or plating step.

It may also be noted that in some applications there may be reason to operate with a pressure above atmospheric in the processing chamber.

In some applications, the chamber need not be conti- nuously passed by a processing fluid during processing.

For example, it may in some kind of electrochemical etching be sufficient to supply processing fluid to the chamber before the actual processing starts.

Claims

1. A method in processing a substrate (S) in a cham- ber (1) , comprising the steps of, before and/or during processing, supplying a processing fluid, such as an electrolyte, an etchant or a solvent, to the chamber (1) and, after completed processing, flushing the substrate (S) with a flushing fluid, c h a r a c t e r i s e d in that the substrate (S) is flushed in situ in the chamber (1) by feeding the flushing fluid through the chamber (1) from a flushing fluid tank (21) , and cleaning the flushing fluid, after passing the chamber (1) , by means of a cleaning device (20') and recirculating the flushing fluid to the flushing fluid tank (21) .

2. A method as claimed in claim 1, comprising the steps of separating from the processing fluid any flushing fluid admixed thereto, and via the cleaning device (20') recirculating the thus separated flushing fluid to the flushing fluid tank (21) .

3. A method as claimed in claim 1 or 2 , comprising the steps of circulating, during processing, processing fluid between a first processing fluid tank (11) and the chamber (1) and simultaneously circulating processing fluid between the first processing fluid tank (11) and a second processing fluid tank (13) .

4. A method as claimed in claim 3, comprising the step of separating in the second tank (13) from the processing fluid any flushing fluid admixed thereto and, via the cleaning device (20'), recirculating the thus-separated flushing fluid to the flushing fluid tank (21) .

5. A method as claimed in claim 4, wherein the step of separating any flushing fluid admixed to the processing fluid comprises supplying a gas flow above the pro- cessing fluid in the second tank (13) , and in a condenser (12') receiving and cooling the gas flow to form a condensate containing the admixed flushing fluid.

6. A method as claimed in any one of claims 3-5, comprising the step of adding in a dosed manner to the flushing fluid in the second tank (13) alkaline ions and metal ions which are identical with metal ions present in the processing fluid, preferably as a slurry of an alkaline metal salt.

7. A method as claimed in claim 6, wherein the addition of the alkaline to the salt is controlled based on the pH of the processing fluid contained in the first or the second tank (11, 13) .

8. A method as claimed in any one of claims 3-7, comprising the step of keeping the processing fluid at a given level in the first tank (11) .

9. A method as claimed in any one of claims 3-8, wherein the flushing fluid, after passing the chamber

(1), is cleaned by means of the cleaning device (20') by separating ions dissolved in the flushing fluid, and wherein said ions are recirculated to the processing fluid, preferably to the second tank (13) . 10. A method as claimed in any one of claims 3-9, comprising the steps of directing, during a first period of time, the flushing fluid fed through the chamber (1) to the first or the second tank (11, 13), and directing, during a subsequent second period of time, the flushing fluid fed through the chamber (1) via the cleaning device (20') to the flushing fluid tank (21).

11. A method as claimed in any one of claims 1-10, comprising the steps of transferring the flushing fluid fed through the chamber (1) to a secondary tank (23) , and supplying the flushing fluid from the secondary tank (23) to the flushing fluid tank (21) via the cleaning device (20') which collects ions dissolved in the flushing fluid.

12. A method as claimed in claim 11 in combination with claim 4 or 5 , comprising the step of transferring the flushing fluid separated from the processing fluid to the secondary tank (23) .

13. A method as claimed in claim 11 or 12, comprising the step of keeping the flushing fluid at a given level in the flushing fluid tank (21) by recirculating flushing fluid to the secondary tank (23) . 14. A method as claimed in any one of claims 1-13, comprising the step of generating a subatmospheric pressure in the chamber (1) during processing.

15. A method as claimed in claim 3, wherein the processing fluid circulating between the first and second tanks (11, 13) passes through an ejector (15), which during generation of a subatmospheric pressure in the chamber (1) draws processing fluid therefrom and thus causes processing fluid to circulate between the first tank (11) and the chamber (1) . 16. A method as claimed in claim 15, comprising the steps of interrupting, after completed processing, the circulation of processing fluid between the first and second tanks (11, 13), and thus also interrupting the circulation of processing fluid between the first tank (11) and the chamber (1) , supplying flushing fluid from the flushing fluid tank (21) to the chamber (1) so that a pressure above atmospheric is generated in the chamber (1), which is consequently opened and allows the flushing fluid to flow down into a collecting vessel (50) , direct- ing during a first period of time the flushing fluid from the collecting vessel (50) to the first or the second tank (11, 13), and during a subsequent second period of time directing the flushing fluid from the collecting vessel (50) via a cleaning device (20') to the flushing fluid tank (21) .

17. An apparatus for processing a substrate, comprising a chamber (1) for receiving the substrate (S) , a unit (10) for supplying a processing fluid, such as an electrolyte, an etchant or a solvent, to the chamber (1) before and/or during processing, and a flushing unit (20) for cleaning the substrate (S) by means of a flushing fluid after completed processing, c h a r a c t e r i s - e d in that the flushing unit (20) comprises a flushing fluid tank (21), a cleaning device (20') and a fluid feeding means (22, 24), the fluid feeding means (22, 24) being adapted to feed from the flushing fluid tank (21) the flushing fluid through the chamber (1) for cleaning the substrate (S) contained therein, through the cleaning device (20') for cleaning the flushing fluid and back to the flushing fluid tank (21) .

18. An apparatus as claimed in claim 17, wherein the feeding unit (10) for processing fluid comprises a fluid separating means (10') which is designed to separate from the processing fluid any flushing fluid admixed thereto, the fluid separating means (10') being in fluid communication with the flushing fluid tank (21) via the cleaning device (20') for recirculating thus separated flushing fluid.

19. An apparatus as claimed in claim 17 or 18, wherein the feeding unit (10) for processing fluid comprises a first processing fluid tank (11) , a second pro- cessing fluid tank (13) and a feeding means (14, 15) for processing fluid, which is designed to circulate processing fluid between the first tank (11) and the chamber (1) and simultaneously circulate processing fluid between the first and second tanks (11, 13) . 20. An apparatus as claimed in claim 19, wherein the first processing fluid tank (11) comprises a level control means (17) , preferably an overflow which is connected to the second tank (11) and which is adapted to maintain a given level of the processing fluid in the first tank (11) .

21. An apparatus as claimed in claim 19 or 20, wherein a fluid separating means (10') is allocated to the second tank (13) and designed to separate from the processing fluid any flushing fluid admixed thereto, the fluid separating means (10') being in fluid communication with the flushing fluid tank (21) via the cleaning device (20') for recirculating thus separated flushing fluid.

22. An apparatus as claimed in claim 21, wherein the fluid separating means (10') comprises a pump means (11') which is adapted to supply a gas flow above the processing fluid in the second tank (13) and a condenser (12') which is adapted to receive from the second tank (13) the gas flow and cool the same to form a condensate containing the admixed flushing fluid.

23. An apparatus as claimed in any one of claims 19-22, comprising a conditioning means (40, 41) which is designed to add in a dosed manner to the processing fluid in the second tank (13) alkaline anions and metal ions which are identical with metal ions present in the processing fluid, preferably as a slurry of an alkaline metallic salt. 24. An apparatus as claimed in claim 23, comprising a pH meter (18C) which in the first or second tank (11, 13) is adapted to measure the pH of the processing fluid, the conditioning means (40, 41) being designed to control, based on said pH, the supply of the alkaline metal - lie salt.

25. An apparatus as claimed in any one of claims 19-24, wherein the cleaning device (20') is designed to separate ions dissolved in the flushing fluid, and wherein the feeding unit (10) for processing fluid comprises a means (40) for recirculating said ions to the processing fluid, preferably in the second tank (13) .

26. An apparatus as claimed in any one of claims 19-25, wherein the flushing unit (20) further comprises a secondary tank (23), and wherein the fluid feeding means (22, 24) is designed to transfer the flushing fluid fed through the chamber (1) to the secondary tank (23), and feeding the flushing fluid from the secondary tank (23) to the flushing fluid tank (21) via the cleaning device (20') which is designed to collect ions dissolved in the flushing fluid.

27. An apparatus as claimed in claim 26 in combination with claim 21 or 22, wherein the fluid separating ω t t y→ I-¹ o o

Oi TJ

Ω c rt 3 μ- TJ

<

Oi 3 rt φ øi Oi cr P t→ CQ

Φ

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3 rt X

Φ tr μ Φ i 3 c

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0 rt Ω tr Φ

Φ CQ

CQ „ ,

Ω μ- μ- 3 ° | LQ

Ω c μ-

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fluid between the first and second tanks (11, 13) and thus also interrupt the circulation of processing fluid between the first tank (11) and the chamber (1), after which the fluid feeding means (22, 24) is activatable to feed flushing fluid from the flushing fluid tank (21) to the chamber (1) for generating a pressure above atmospheric in the same and opening a fluid outlet of the same, a collecting vessel (50) being adapted to receive flushing fluid flowing out of the fluid outlet of the chamber (1) , and a valve means (31, 32) being controllable^' to direct, during a first period of time, the flushing fluid from the collecting vessel (50) to the first or the second tank (11, 13) and to direct, during a subsequent second period of time, the flushing fluid from the collecting vessel (50) via the cleaning device (20') to the flushing fluid tank (21) .

33. A method in processing a substrate (S) in a chamber (1) , comprising the steps of supplying, before and/or during processing, a processing fluid, such as an electrolyte, an etchant or a solvent, to the chamber (1) and, after completed processing, flushing the substrate (S) with a flushing fluid, c h a r a c t e r i s e d in that the substrate (S) is flushed in situ in the chamber (1) by flushing fluid being fed through the chamber (1) from a flushing fluid tank (21) , and that the flushing fluid after passing the chamber (1) is cleaned by means of a cleaning device (20') and recirculated to the flushing fluid tank (21) , which also comprises the steps of circulating, during processing, processing fluid between a first processing fluid tank (11) and the chamber (1) and simultaneously circulating processing fluid between the first processing fluid tank (11) and a second processing fluid tank (13) .

34. An apparatus for processing a substrate, com- prising a chamber (1) for receiving the substrate (S) , a unit (10) for supplying a processing fluid, such as an electrolyte, an etchant or a solvent, to the chamber (1) before and/or during processing, and a flushing unit (20) for cleaning the substrate (S) by means of a flushing fluid after completed processing, c h a r a c t e r i s e d in that the flushing unit (20) comprises a flushing fluid tank (21), a cleaning device (20') and a fluid feeding means (22, 24), the fluid feeding means (22, 24) being adapted to feed from the flushing fluid tank (21) the flushing fluid through the chamber (1) for cleaning the substrate (S) contained therein, through the cleaning device (20') for cleaning the flushing fluid and back to the flushing fluid tank (21) , and the feeding unit (10) for processing fluid comprising a first processing fluid tank (11) , a second processing fluid tank (13) and a feeding means (14, 15) for processing fluid, which is designed to circulate processing fluid between the first tank (11) and the chamber (1) and simultaneously circulating processing fluid between the first and second tanks (11, 13) .