Etching a substrate: processes – Etching of semiconductor material to produce an article...
Reexamination Certificate
2002-02-04
2004-05-18
Kunemund, Robert (Department: 1765)
Etching a substrate: processes
Etching of semiconductor material to produce an article...
C216S033000, C216S041000, C165SDIG119, C438S455000, C438S456000
Reexamination Certificate
active
06736983
ABSTRACT:
The invention relates to a method of manufacturing micro-components having at least one individual layer, which can be used in the chemical industry inter alia for synthesis reactions and in other fields, for example as reactors for generating hydrogen for energy conversion (fuel cells), as well as heat exchangers, mixers and evaporators.
In the literature, there have been reports for some years now of chemical microreactors which have advantages in comparison with the traditional production plants for manufacturing chemical compounds. Here it is a question of an arrangement of reaction cells, the dimensions of which range between a few micrometers and several millimeters, and thus are very much smaller than the traditional reactors. These reaction cells are so designed that in them physical, chemical or electrochemical reactions can take place. In contrast to a traditional porous system (heterogeneous catalysis), the dimensions of these cells are defined by their construction, therefore may be manufactured systematically by means of a technical method. The arrangement of individual reaction cells in the assembly of the reactor is ordered, particularly periodically in one, two or three dimensions. Amongst the chemical microreactors are counted, in a wider sense, also the necessary supply and discharge structures for the fluids (liquids, gases) and sensors and actuators, for example valves which control the flow of substance through the individual cells, and heating elements.
The use of chemical microreactors for generating hydrogen for fuel cells for the conversion of energy has been described for example by R. Peters et al. in “Scouting Study about the Use of Microreactors for Gas Supply in a PEM-Fuel Cell System for Traction”, Proc. of the 1
st
Int. Conf. on Microreaction Technology, Frankfurt, 1997.
This concept for chemical microreactors has also been applied to heat exchangers. In this case, at least two fluid channels separate from one another are present in the heat exchanger and serve to transfer heat from fluid in the one channel to fluid in the other channel.
There is a series of proposals for the manufacture of chemical microreactors or heat exchangers:
For example the LIGA-process (lithography, electroforming, moulding) is used. In this process a plastics material layer, mostly polymethyl methacrylate (PMMA) is exposed to synchrotron radiation and then developed. The structure produced in this way is filled with metal by means of an electrolytic process. The metal structure can then be multiplied in further method steps by means of plastics moulding (plastics injection moulding). This method was described by W. Ehrfeld and H. Lehr in Radiat. Phys. Chem., Vol. 45, pages 349 to 365.
The methods which have been developed in the semiconductor industry for structuring silicon surfaces have also been adopted for manufacturing of microreactors. For instance in “Microfabricated. Minichemical Systems: Technical Feasibility”, DECHEMA Monographs, Volume 132, pages 51 to 69 a method is described by J. J. Lerou et al. in which three etched silicon wafers and two end wafers are connected to one another on the outer sides. Furthermore, a heat exchanger filled with polycrystalline silver particles is used which was also configured as a microreactor.
In the same way, the method of manufacturing microreactors which is described in U.S. Pat. No. 5,534,328 also proceeds from etched silicone wafers which are joined into a stack. However, other materials are also mentioned for the microreactors, for example metals, polymers, ceramics, glass and composite materials. To carry out catalytic reactions it is proposed inter alia that the walls of the reaction channels in the reactors be coated with a catalytic layer.
In EP 0 212 878 A1, a method of manufacturing a heat exchanger is described in which the flow channels of the heat medium are formed in steel plates by chemical etching. The steel plates are then welded to one another by diffusion bonding.
In WO-A-9215408, a method of manufacturing microstrainers is described in which perforations are etched in a certain pattern through plasma technology into a flat carrier coated with an etch-resistant layer. Several of these perforated carriers are then connected to one another.
In DE 197 08 472 A1, a method of manufacturing chemical microreactors is described in which fluid channels are formed in individual planes, by substrates provided with metal surfaces being structured by means of photolithographic techniques or screen printing methods, and the channel structures obtained being formed by methods of removing or depositing metal. The individually produced planes are then combined to form a stack and securely connected to one another. For example, the channels can be produced by partial etching away of the metal layer on the substrate.
The previously known methods for manufacturing chemical microreactors and heat exchangers have manifold disadvantages. For example complicated and/or expensive techniques are necessary for producing the channels. In some cases, the manufacture of reactors is limited exclusively to silicone as a material.
It is frequently also necessary to produce a functional coating on the channel walls to set pre-determined properties of the micro-components. Thus for example a microreactor can be produced from a heat exchanger manufactured from copper, by the channels being coated with a metal layer deposited in an electroless manner, for example with palladium. In chemical reaction technology, the functional surface layers serve for example the catalysis of chemical reactions. Subsequent coating of the flow channels in the planes by means of a galvano-technical method is however frequently not possible since the functional layers in this case cannot be applied electrolytically on account of the electrical shielding by the reactor or heat exchanger itself. In electroless metallisation, also, it has emerged that secure coating is not possible since the metallisation baths usually used react very sensitively to different flow speeds of the metallisation fluid on the surfaces to be coated. Under these conditions, inter alia those surface regions past which the metallisation fluid flows slowly are metallised in an electroless manner whilst surface regions past which the fluid flows at a high speed are not coated with metal. With very narrow channels, problems can occur in electroless metal deposition which is based on the very high bath load (surface to be coated per bath volume), such that only inadequate layer qualities are produced. Possibly a layer formation with total covering of the surface becomes completely impossible. Moreover by means of electroless methods only certain metals can be deposited.
Gas deposition methods for applying layers are in this case practically unusable.
In the cases in which the functional layers are applied before the individual layers are joined to form the micro-component, the connection of the individual component layers has proved to be problematic since no reliable connection can be produced between the individual layers. Frequently the components produced from the individual layers have leaks from which fluid which is under relatively high pressure penetrates outwards from the channels.
Furthermore the functional layers are not stable in relation to the joining temperatures usually used to join together the individual layers. The functional layers, particularly in cases in which the material has a lower melting or transition temperature than the temperature during joining, are damaged or even destroyed. In particular also noble metals such as platinum, iridium, palladium and gold can be applied to form the functional layers. These metals admittedly have a higher melting point than the copper usually used as a basic material for the micro-component and should therefore be thermally resistant in a joining process in which the basic materials of two individual layers are welded to one another. However, in this and other similarly layered cases, it has been noticed that for example in diffus
Cramer Konrad
Meyer Heinrich
Thies Andreas
Ahmed Shamim
Atotech Deutschland GmbH
Bonini, Jr. Frank J.
Earley III John F. A.
Harding Earley Follmer & Frailey
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