Etching a substrate: processes – Forming or treating mask used for its nonetching function
Reexamination Certificate
2000-12-21
2004-03-16
Olsen, Allan (Department: 1763)
Etching a substrate: processes
Forming or treating mask used for its nonetching function
C216S013000, C216S037000, C216S058000, C216S067000, C427S456000, C427S534000, C427S537000
Reexamination Certificate
active
06706201
ABSTRACT:
The invention relates to a method of manufacturing metallised substrate materials which are suitable for use in the manufacture of electrical circuit carriers which may be used in the gigahertz range (Ghz).
For the manufacture of high-density electrical circuits, circuit carriers which have a plurality of conductor track levels are used. These circuits serve to connect to one another, besides so-called passive components, for example resistors and capacitors, also active components, i.e. integrated semiconductor circuits, in order to construct an electrical circuit. In recent times, the active components have been fitted even without housings directly onto the circuit carriers, for example by the semiconductor circuits being bonded with bond wires directly or via so-called TAB (tape automated bonding) connectors to the connection points. By this means, higher conductor track densities can be achieved than with housed semiconductor circuits, since the housings take up considerable space on the circuit carriers, which space cannot be used for the circuit.
For some time now, circuit carriers of this sort for new types of semiconductor components have been used, for example of multichip modules (MCM). These components are distinguished by a higher functional density than traditional active components.
Higher and higher requirements are made of the techniques for manufacturing the circuit carriers for these components. On the one hand narrower and narrower electrical conductor tracks are formed in smaller and smaller distances from one another. On the other hand, components are also needed for applications with increasing thermal load on account of the rising complexity of the wiring density. A further requirement consists in manufacturing components with particularly high, switching frequencies. The standard clock frequencies in office computers, for example, are in the region of several hundred megahertz (MHz). In the meantime, clock frequencies in the semiconductor circuits of more than 1 GHz are aimed at, the intention being that the electrical signals should be transmitted without noticeable losses and distortion of the signal form. In overcoming the problems arising here, the materials for the manufacture of the circuit carriers play an essential role, since their dielectric constant &egr; and, the dielectric loss factor (tan &dgr;) largely determine the utilisable frequency range.
For the manufacture of the circuit carriers, for example multichip modules, amongst other things known manufacturing methods from printed circuit board technology are used. For example, dielectric substrates made of an epoxy resin material which is reinforced with glass fiber mats can be used for this purpose. On the outer sides of these laminates, copper layers are normally provided, from which the conductor tracks are formed by etching and if necessary by electrolytic metal deposition processes. Materials of this kind are very suitable also for the manufacture of multilayer circuit carriers, by a plurality of laminates provided with a circuit pattern being connected to one another.
For the manufacture of particularly high-density circuit patterns, dielectric substrates provided without outer copper layers are preferably used. The copper layers required for producing the conductor tracks are applied to the laminates by means of metallisation processes. One of the possible manufacturing methods consists in forming metal layers by decomposing volatile metal compounds in a glow discharge. With this method, strongly bonded metal layers can be formed on the substrate surfaces.
For example, in DE P 35 10 982 A1 a process for manufacturing electrically conductive structures, e.g. conductor tracks, on non-conductors is described, in which a metallic film is deposited by the decomposition of organometallic compounds in a glow discharge zone. As non-conductors, ceramics, for example aluminium oxide and silicone oxide ceramics, glass, synthetics, for example polyimide foil and composite materials are mentioned. As decomposable compounds, organic copper, organic tin and organic palladium compounds are mentioned. The use of nickel tetracarbonyl and molybdenum hexacarbonyl is described as unutilisable on account of the high toxicity of these compounds.
Furthermore, in DE P 38 06 587 A1 a method for manufacturing securely adhering metal structures on polyimide surfaces is described. To this end, organometallic compounds are formed in a glow discharge forming a metallic film. Metals of the I, and VIII, subgroup of the periodic system can be used. Compounds of palladium, platinum, gold, copper, ruthenium and iridium are expressly proposed. The metal layers, for example of palladium, are then coated with additional metal layers, for example with copper or nickel, these additional layers being formed in an electroless metallisation bath. To improve the adhesion of the metal layers to the dielectric, the latter is cleaned and etched by means of suitable plasma processes before the formation of the first metal layers.
In DE P 44 38 791 A1 a further method for depositing metal layers on polyimide surfaces is described. Palladium, platinum, copper, gold and silver are mentioned as metals which may be deposited in the glow discharge zone. In contrast to the previously-described process, additional metal layers are formed in an electroless metallisation bath adjusted either acid or neutral. By this means, a sufficiently high adhesive strength can be maintained on the polyimide material even during and after thermal stressing of the polymer/metal bond.
In WO 9612051 A1 a method for depositing metal layers on polyimide surfaces is also described in which the first metal layer is produced through decomposition of volatile metal compounds by means of a glow discharge process. As metals which may be deposited, in particular palladium, copper, gold and platinum are mentioned as well as other metals which can form a catalytic metal layer for the subsequent electroless metal deposition. The metal layers are here formed in the presence of a gas mixture which contains inert gases and oxygen. This provides a solution to the problem that the metal layers formed, after a conventionally undertaken tempering treatment for consolidating the layers on the substrate with aqueous alkaline solutions, for example a solution to develop photoresist layers applied to the metal layers, are brought into contact. In the previously known methods, the adhesive strength of the metal layers sank abruptly with treatment of this kind to very low values. Here the metal layers detached themselves completely from the polyimide surfaces in individual cases.
A method for coating polyimide surfaces is also described in the scientific article “Thin Palladium Films Prepared by Metal-Organic Plasma-Enhanced Chemical Vapour Deposition” in Thin Solid Films, Volume 157 (1988), pages 81-86, by E. Feurer and H. Suhr. In order to manufacture palladium layers which are as pure as possible, the depositing and subsequent treatment conditions were varied. A coating in a pure argon plasma led to layers contaminated with carbon. Through subsequent oxygen treatment in plasma, a very pure palladium layer could be obtained. By further after-treatment in a hydrogen plasma, the metal content of the layer was not substantially increased. By means of a different manufacturing method through deposition from an oxygen plasma, it was in fact possible to obtain a layer free of carbon. However, the layer consisted not of palladium but of palladium oxide. The oxide layer was converted into pure palladium by subsequent treatment in a hydrogen plasma.
It has been shown that polyimide admittedly has excellent thermal stability in relation to traditional epoxy resin materials which are usually used for the manufacture of printed circuit boards. However the dielectric properties of this polymer (&egr;, tan &dgr;) is not good enough for many applications, such that high frequency applications in the GHz range cannot be realised in every case with circuit carriers manufactured from this materi
Heinz Roland
Klusmann Eckart
Meyer Heinrich
Schulz Ralf
Atotech Deutschland GmbH
Olsen Allan
Paul & Paul
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