Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-01-18
2001-08-28
Le, Vu A. (Department: 2824)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S400000, C438S410000, C438S510000, 43, 43, 43, 43
Reexamination Certificate
active
06281119
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for making contact with semiconductor components as well as to a corresponding semiconductor component fabricated by the method according to the invention.
During the production of semiconductor components, individual cells of the semiconductor component are connected to one another and to terminals leading to the outside. That is usually accomplished through the use of one or more interconnect planes made of aluminum. In order to connect the interconnect planes to switching elements in the semiconductor, contact holes are etched through the insulator layers on the actual semiconductor substrate to establish electrical contact between the interconnect plane and the elements of the cell.
During the fabrication of contact holes, it is necessary to take account of certain requirements of the subsequent contact-making. During the fabrication of a contact hole with a rectangular cross-sectional profile, problems having to do with edge coverage frequently arise in the production of an Al layer for the contact-making. The Al layers often have constrictions at the edges. At those points, there may then be an intensified transport of material in the conductor and consequently interconnect breaks, due to the increased current density.
A contact hole having a rectangular cross-sectional profile and a contact hole with beveled edges are discussed in detail below with reference to
FIGS. 2 and 3
. However, the prior art methods do not permit high contact hole density to be achieved on the semiconductor in conjunction with high reliability of electrical contacts and the prior art semiconductor components do not have reliable electrical contacts.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for making contact with a semiconductor layer and a semiconductor structure having a plurality of layers, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type, in which the method enables a higher contact hole density to be achieved on the semiconductor in conjunction with increased reliability of electrical contacts and in which the semiconductor component has more reliable electrical contacts.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for making contact with at least one covered semiconductor layer through a contact hole, which comprises providing the at least one semiconductor layer; covering the at least one semiconductor layer with an insulator layer having a surface; producing the contact hole in the insulator layer for making contact with the at least one covered semiconductor layer; producing a heavily doped polysilicon layer on the surface of the insulator layer while at least partially filling the contact hole with heavily doped polysilicon; and applying a metal layer on the heavily doped polysilicon layer for establishing an ohmic connection to the outside.
In accordance with another mode of the invention, the surface of the polysilicon layer is planarized prior to the application of the metal layer, with the result that the surface of the polysilicon is essentially planar.
In accordance with a further mode of the invention, in order to ensure that better simultaneous contact is made with a plurality of semiconductor layers lying one above the other by a polysilicon layer, a conductor layer is applied on the surface of the insulator layer and the surface of the contact hole prior to the production of the polysilicon layer.
With the objects of the invention in view, there is also provided a semiconductor structure having a plurality of layers, comprising at least one semiconductor layer for electrical connection to the outside; an insulator layer disposed above the at least one semiconductor layer, the insulator layer having at least one contact hole formed therein for exposing the at least one semiconductor layer; and an electrically conductive contact layer at least partially filling the contact hole, the contact layer including a first layer made of a heavily doped polysilicon and a second layer disposed on the first layer and made of a metallic conductor.
In accordance with another feature of the invention, the contact layer includes a conductor layer between the layer made of polysilicon and the surface of the semiconductor structure in the contact hole. In other words, a thin, conductive layer is provided directly on the structure surface, which establishes an ohmic contact with the n
+
-type and p
+
-type zones in e.g. FET cells and also makes ohmic contact with the (n
+
-type) polysilicon filling.
In accordance with a concomitant feature of the invention, a plurality of semiconductor regions are connected through the use of the contact hole. In particular, the semiconductor structure may be formed of a MOS-FET having a source region and a channel region which are both connected to one another and to the outside through the use of the contact layer according to the invention.
The advantage of the semiconductor structure produced by the method according to the invention is that additional processing of the contact hole such as beveling of the edges, is no longer necessary. Furthermore, the formation of shrink holes and cracking in the connecting conductor no longer occur. Moreover, better Na shielding of the component is afforded. When, as in the prior art, metal is used as the contact layer, Na atoms diffuse into the semiconductor structure. The Na atoms can then accumulate at the gate in the case of a MOS structure, and thus influence the threshold voltage of the transistor. Since Na diffuses into polysilicon to a very much lesser extent, making contact by using polysilicon thus forms an additional barrier to Na. Finally, the method according to the invention has the advantage of permitting additional processing steps for beveling the edges of the contact hole to be omitted.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for making contact with a semiconductor layer and a semiconductor structure having a plurality of layers, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
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Tihanyi Jenoe
Werner Wolfgang
Greenberg Laurence A.
Infineon - Technologies AG
Le Vu A.
Lerner Herbert L.
Luu Pho
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