Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Flip chip
Reexamination Certificate
2000-02-18
2001-02-20
Williams, Alexander O. (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Flip chip
C257S737000, C257S738000, C257S774000, C257S758000, C257S700000, C257S784000, C257S693000, C257S686000, C257S687000, C361S719000, C361S437000, C361S762000, C361S790000, C174S261000, C174S255000, C174S264000, C174S250000, C439S331000, C439S333000
Reexamination Certificate
active
06191489
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for manufacturing a layer arrangement having at least one bump, especially for a flip chip or similar connection, wherein several layers made of solid material are stacked into a layer stack. At least one recess is made in the stack transverse to the coating planes of the layers, into which a bump material is filled or applied. In addition, the invention relates to a layer arrangement with a layer stack having several layers made of solid material and having a recess extending transverse to the coating planes of the layers. A bump is arranged in the recess, which is provided especially for a flip chip or similar connection, and has a projection projecting on the surface of the layer stack, wherein the bump is made of a continuous one-piece bump material.
A process of this type and a layer arrangement manufactured according to it are already known from the book
Flip Chip Technologies
, John H. Lau, McGraw-Hill (1996). In the process, on a portion of the surface of a substrate made of a semiconductor material, an aluminum layer functioning as a connection path is first applied in certain areas. After that, the substrate is coated with a passivation layer, which covers the aluminum layer and the surface area of the substrate adjoining it. To expose the aluminum layer, a recess is then made in the passivation layer. On the aluminum layer and areas of the passivation layer laterally adjoining it, adhesive layers are applied, which are to improve the adhesion of additional layers to be applied and the bump material to be brought into the recess. Onto the adhesive layers, a copper layer is applied, which should make it more difficult for moisture to penetrate into the layer stack, and a gold layer is applied, which functions as an oxidation barrier. Next, the bump material is brought into the recess, for example, by vacuum evaporation through a metal mask, by plating, dispersion, or imprinting.
With the adhesive layers located between the substrate and the bump material, a better adhesion of the bump to the substrate is indeed achieved to a certain extent. However, the mechanical solidity of the layer arrangement manufactured according to the process is nevertheless in need of improvement. In practice, the moisture resistance of the layer arrangement has additionally proven to be problematic, since moisture can get under the bump material and can cause corrosion on the bump material and/or the layers of the layer stack. On the one hand, the mechanical solidity of the layer arrangement is thereby weakened, and on the other hand, the moisture can also change the electrical properties of the layer arrangement. In particular, there is the danger in a bump functioning as an electrical connection contact, that the moisture will cause electrical leak currents or short circuits.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to create a layer arrangement of the type described at the outset, in which the bump adheres to the layers of the layer stack especially well. In a bump comprising an electrically conducting material, the layer arrangement should in addition make possible a small electrical resistance between the bump and the layers. In addition, an object of the invention is to provide a process for manufacturing a layer arrangement of this type.
The object is achieved in regard to the process in that a recess is made in the layer stack extending over several of its layers, and that a profiling is created on the lateral boundary wall of the recess by removing layer material of different layers of the layer stack. The profiling has at least two indentations, proceeding in layers from the surface of the layer stack adjoining the recess to the interior of the recess, and has at least one projection located between them. The bump material is brought into the recess after the manufacture of the profiling in such a way that it grasps behind the indentations.
The boundary wall of the recess is thus provided with a profile by the layer-wise removal of layer material, and the bump material is introduced into the recess in a manner such that it catches in the open spaces of the profiling or between the respective profiling projections and indentations adjacent to each other. In an advantageous manner, a form-fitting connection thereby results between the bump and the layer stack, such that lateral projections of the bump grasp behind the indentations of the boundary wall of the layer stack. The bump material thus engages in a comb-like manner into the profiling of the boundary wall formed by the layer stack. A good adhesion of the bump into the layer stack and thus a correspondingly great strength of the connection between the bump and the layer stack is thereby achieved. In an expedient way, the bump material is introduced into the recess completely, so that a continuous single-piece, mechanically-stable bump results, which is macroscopically homogeneous and free of border surfaces. When seen microscopically, the bump material can have non-homogeneities, for example if the bump material is made of an elastic plastic mass, in which metal or similar solid particles are included.
By the toothing between the layer stack and the bump material, resulting from the projections and indentations of the profiling made in the boundary wall, a good moisture resistance of the layer arrangement is additionally achieved. In particular, the danger is reduced that moisture from the surface of the layer arrangement proceeds along the surface of the boundary wall of the recess, which forms the border area between the layer stack and the bump, gets to the rear side of the bump, and causes corrosion there.
The layers of the layer arrangement can be manufactured, for example, by vapor deposition, by a chemical reaction on the surface of the layer stack, in particular by oxidation of layer material, by galvanic deposition (plating) of layer material, or other coating processes known per se from planar technology. A good mechanical connection can thereby be achieved between the respectively-neighboring, adjoining layers of the layer stack.
Since the bump material is first brought into the recess after the production of the layer arrangement, the process additionally allows a simple manufacture of the layer arrangement. In particular, the recess can be introduced in one operation into several or even all layers of the layer stack, for example by an etching process. By introducing the bump into the layer stack, an intervention into the manufacturing process of the layer stack can be avoided.
An especially advantageous embodiment of the invention provides that a liquid or flowable bump material is introduced into the recess and is then solidified, in particular by hardening, curing, and/or drying of a solvent contained in the bump material. The bump material can thereby be filled into the recess in a simple way such that, even in the area of the open spaces or recesses formed between respectively adjacent indentations and projections of the boundary wall, a complete filling and thus a good form-fitting connection of the bumps to the layer stack can be achieved. The bump material may be, for example, a casting compound which is poured into the recess. The liquid or flowable bump material can be introduced into the recess, for example, by imprinting of the layer stack, in particular using a screen printing process. The bump material can thereby be introduced simultaneously in a simple way into a plurality of recesses located in the layer stack.
Another embodiment of the invention provides that the bump material is plated onto the lateral boundary wall and/or the bottom of the recess. The bump material can then reach especially well into the area of the indentations of the boundary wall of the recess. The plating of the bump material can be done without current or using an external electrical field.
A preferred, especially advantageous embodiment of the invention provides that the layer stack is brought into contact with an etchant to create t
Gahle Hans-Jurgen
Igel Gunter
Lehmann Mirko
Akin Gump Strauss Hauer & Feld L.L.P.
Micronas GmbH
Williams Alexander O.
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