Semiconductor device manufacturing: process – Repair or restoration
Reexamination Certificate
2002-09-17
2004-07-13
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Repair or restoration
C438S005000, C438S012000
Reexamination Certificate
active
06762066
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method in which a semiconductor structure is produced on a substrate. A protective layer is applied to the semiconductor structure in order to protect the semiconductor structure from being impaired during subsequent processing steps. At least one intermediate process is carried out for further fabrication of the semiconductor structure or for fabrication of a further semiconductor structure that is to be formed on the substrate. The protective layer remains on the semiconductor structure or is removed from the semiconductor structure that is to be protected, for example in order for it to be structured further.
The substrate is, for example, a semiconductor wafer. However, ceramic substrates or thin-film substrates are also used.
One process is the processing of the substrate under constant process conditions in a processing installation, e.g. the execution of an oxidation step, the deposition of a layer, the application of a photomask, exposure, developing, etching, and/or ion implantation.
By way of example, to fabricate what are known as bipolar complementary metal oxide semiconductor circuits (BICMOS circuits), it is necessary to protect semiconductor structures in one base technology, while the semiconductor structures of the other base technology are being produced. Under certain circumstances, a repeated change between the regions that are in each case to be protected and the regions which are in each case to be processed may be necessary.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for fabricating a semiconductor structure using a protective layer, and a semiconductor structure which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, which provides an improved method for fabrication of the semiconductor structure using a protective layer.
With the foregoing and other objects in view there is provided, in accordance with the invention, a fabrication method. The method includes providing a given structure being either a substrate or a semiconductor structure; applying a protective layer to the given structure; carrying out at least one intermediate process and the intermediate process leading to a formation of cracks in the protective layer resulting in an impairment of a protective action of the protective layer; applying a repair layer to the protective layer; and removing the repair layer before an application of further layers and/or before carrying out subsequent process steps.
The invention is based on the consideration that the known protective layers in principle ensure sufficient protection to, for example, avoid damage to the semiconductor structure that is to be protected. However, the protective layer is usually applied to a topological surface, i.e. to an uneven surface, for example with height differences of over 100 nm. While the intermediate processes are being carried out, the chemical and mechanical properties of the protective layer are influenced.
By way of example, heat causes a shrinkage of the protective layer, so that tensile forces are formed in the lateral direction. The tensile forces lead to the formation of shear forces and possibly also of notch effects in particular at the locations at which height differences occur in the protective layer. On account of the lateral forces, cracks and gaps may form in the protective layer.
By way of example, on a wafer with a diameter of, for example, 6″ or 12″ (inches) only three or four such cracks are formed. The cracks are highly disruptive in particular because they reduce the effectiveness of the protective layer, so that components that are unable to function are fabricated or long-term reliability problems arise. Deposits that penetrate into the crack often only diffuse very slowly to the semiconductor structure, where they lead to delayed failures that only occur in the end product. The crack is, for example, only a few nanometers wide and only a few nanometers deep. The length of the crack is, for example, a few nanometers, a few tens of nanometers or a few hundred nanometers.
Moreover, the invention is based on the consideration that only with great difficulty is it possible to reduce the number of cracks, since measures aimed at avoiding the formation of cracks are highly complex.
Therefore, in the method according to the invention, a protective layer that is of a thickness at which cracks occur during the intermediate processes is applied. In other words, the formation of cracks is accepted in the method according to the invention. However, in the method according to the invention, a repair layer is applied to the protective layer whose protective action has been impaired, and the repair layer increases the protective effect of the protective layer again in such a way that the repaired protective layer once again effectively protects the semiconductor structure which is to be protected during subsequent processes.
In the method according to the invention, the repair layer is removed again, for example, by a fixed-time etch or an end-point etch, before further layers are applied and/or before the subsequent processes are carried out, in order for the substrate to be processed further. However, residues of the repair layer remain in the cracks in the protective layer and also, in the case of relatively deep cracks, in the semiconductor structure which is to be protected or in a substrate which is to be protected. The residues in fact increase the protective effect of the protective layer. Moreover, it is only possible for residues of the repair layer to remain in the cracks in the protective layer if the protective layer has not been removed during removal of the repair layer.
Therefore, the result of the use of the method according to the invention is that even with a simple procedure, i.e. when a relatively thin protective layer is applied and, for example, when a protective layer which contains only one material is applied, a high protective action and therefore a high yield are nevertheless achieved after the repair. In particular, the particularly critical delayed failures are avoided. The application of a further layer with a complete protective action is dispensed with.
In a refinement of the method according to the invention, the thickness of the repair layer is significantly less than the thickness of the protective layer. By way of example, the thickness of the repair layer is less than approximately one-third of the thickness of the protective layer, less than approximately one-tenth of the thickness of the protective layer or less than approximately one-hundredth of the thickness of the protective layer. A repair layer for repairing a 100 nm (nanometer) thick protective layer has a thickness of, for example, 20 nm.
In one configuration, the thickness of the repair layer is half the maximum crack width, so that even the crack that has the greatest crack width is just still reliably filled. When all the cracks have been filled, the deposition of the repair layer is ended without the thickness of the repair layer being increased still further. The application of such a thin repair layer can be carried out quickly and easily. Moreover, a thin repair layer can be removed more easily than a thicker repair layer.
In a further refinement of the method according to the invention, the repair layer contains the same material as the material of the protective layer. The result of this is that the protective layer and the deposits of the repair layer that are present in the cracks have uniform etching properties. In this way, it is possible to effectively prevent the cracks from being etched open during subsequent etching operations. In one configuration, the repair layer is applied using the same process as the protective layer. This measure too leads, for example, to uniform etching properties of protective layer and repair layer. By way of example, the protective layer used may be TEOS (tetraethyl orthosilica
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Picardat Kevin M.
Stemer Werner H.
LandOfFree
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