Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – With pn junction isolation
Reexamination Certificate
1998-12-10
2001-03-13
Saadat, Mahshid (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
With pn junction isolation
C257S506000, C257S508000, C257S649000, C257S762000, C257S767000, C257S774000
Reexamination Certificate
active
06201291
ABSTRACT:
BACKGROUND OF THE INVENTION
DESCRIPTION
The invention relates to a semiconductor device comprising a semiconductor body which includes at least an active element with a pn junction, the surface of the semiconductor body being provided with an electrically insulating layer on which a conductor track is situated, which is made of a metal having a lower resistivity than aluminium, which electrically insulating layer is provided with an aperture which contains a metal which electrically connects the conductor track to the active element or to an aluminium conductor track, the walls and the bottom of said aperture being provided with an electroconductive layer forming a diffusion barrier for the metal. The invention also relates to a simple method of manufacturing such a device.
Such a device is, for example, an IC (=Integrated Circuit). The active elements used in successive generations of such an IC are becoming smaller and smaller. In this connection, also the conductor tracks, which are responsible for the electric connection of the elements, are becoming ever smaller. If very small conductor tracks are made of aluminium, the resistance of the conductor tracks becomes too high. As a result, it is necessary to manufacture the conductor tracks from a metal having a better resistivity, such as copper, silver or gold.
Such a device is known from United States patent specification EP 0.751.566, published on Jan. 2, 1997. This patent document shows an IC comprising a copper conductor track on an electrically insulating layer, which conductor track is connected to an underlying aluminium conductor track via an aperture in the insulating layer which is also filled with copper. The side walls and the bottom of the aperture are provided with an electroconductive layer, which comprises tantalum nitride and forms a diffusion barrier for the copper. Also the copper conductor track is surrounded by such a layer.
A disadvantage of the known device is that the electroconductive layer, which serves as a diffusion barrier for copper, adversely affects the resistance of a conductor track or connection. The material of such a barrier has a higher resistivity than, for example, copper, and the barrier must be sufficiently thick if it is to serve as a diffusion barrier. In addition, undesirable interaction may occur between the material of the barrier and, for example, copper. Besides, the impact of these drawbacks becomes relatively large as the conductor tracks become smaller. Also the manufacture of such a device is relatively complex.
SUMMARY OF THE INVENTION
Therefore, it is an object of the invention to provide a device of the type mentioned in the opening paragraph, which does not have the above drawbacks and which comprises very small conductor tracks, for example of copper, and which can be readily manufactured.
To achieve this, a device of the type mentioned in the opening paragraph is characterized in accordance with the invention in that the electrically insulating layer comprises a sub-layer which forms a diffusion barrier for the metal and which extends, outside the aperture, throughout the surface of the semiconductor body.
The invention is based on the surprising realizations that if a diffusion barrier does not directly border on the conductor track, the provision of said diffusion barrier has no consequences for the dimensions and the manufacture of a conductor track, and that, in such a case, the barrier may also comprise a non-electroconductive material. By providing the insulating layer, throughout the surface of the semiconductor body, with a sub-layer which forms a barrier for the diffusion of, for example, copper, it is precluded that copper from a conductor track can penetrate the semiconductor body, and hence it is precluded that, for example, copper can adversely affect the service life of charge carriers in the active elements. As the sub-layer is contiguous to the electroconductive barrier layer present in the aperture, the entire semiconductor body is shielded from the metal. By virtue of the electrically insulating character of the sub-layer, this does not lead to electrical problems such as short-circuits. Consequently, in a device in accordance with the invention, the conductor tracks do not have to be provided with a sheath forming a barrier for the metal. If the conductor tracks are provided with a sheath, then this can be used for other functions such as, if necessary, ensuring a good adhesion between the metal and the adjoining insulating material and, if necessary, protecting the conductor track against impurities. Such functions may require a smaller thickness of the material or another material than the function of diffusion barrier for a metal like copper. Such functions also become easier to optimize because they are fulfilled independently of the metal-barrier function. The most important advantage, in this connection, is that the resistance of the conductor tracks of a metal like copper can be very low, even if the dimensions of the conductor tracks are very small. In addition, the manufacture of such a device is relatively simple.
In a very favorable embodiment of a device in accordance with the invention, the conductor track is covered with a further electrically insulating layer on which a further conductor track is situated which is made from the same metal as the first conductor track. Since also the further conductor track does not have to be surrounded by a sheath serving as a diffusion barrier for the metal, the advantage of the present invention is further increased.
In a preferred embodiment of a method in accordance with the invention, the sub-layer serving as a barrier is situated within the electrically insulating layer. Since an electrically insulating layer which can act as a diffusion barrier for a metal has a high dielectric constant, it is desirable for a good, i.e. rapid, operation of the device that such a capacitance-increasing layer is as far removed as possible from overlying and underlying conductor tracks or from underlying active elements. This is achieved by arranging the sublayer within the electrically insulating layer, preferably approximately in the middle of said layer.
Metals having a (much) lower resistivity than aluminium are, for example, copper, silver or gold, or an alloy of one or more of these metals. Very suitable electrically insulating materials which also form a good diffusion barrier for said metals are oxides, nitrides, fluorides or carbides. For example, the sub-layer may advantageously comprise aluminium oxide or magnesium oxide. Suitable nitrides are nitrides of aluminium or boron. Also silicon carbide or boron carbide can be used.
A method of manufacturing a semiconductor device comprising a semiconductor body which includes at least an active element with a pn junction, the surface of the semiconductor body being provided with an electrically insulating layer on which a conductor track is formed of a metal having a lower resistivity than aluminium, which electrically insulating layer is provided with an aperture, the side walls and the bottom of which are provided with an electroconductive layer which forms a diffusion barrier for the metal, and said aperture being provided with an electroconductive material which electrically connects the conductor track to another conductor track of aluminium or to the active element, is characterized in accordance with the invention in that the electrically insulating layer is provided with a sub-layer which forms a diffusion barrier for the metal and which extends, outside the aperture, throughout the surface of the semiconductor body. Such a method enables a semiconductor device in accordance with the invention to be obtained in a simple manner.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 4985750 (1991-01-01), Hoshino
patent: 5510651 (1996-04-01), Maniar et al.
patent: 5739579 (1998-04-01), Chiang et al.
patent: 5900672 (1999-05-01), Chan et al.
pat
Groen Wilhelm A.
Klee Mareike K.
Kordic Srdjan
Mutsaers Cornelis A. H. A.
Biren Steven R.
Saadat Mahshid
U.S. Philips Corporation
Warren Matthew E.
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