Electric semiconductor element with a contact hole

Details Electric semiconductor element with a contact hole Electric semiconductor element with a contact hole

2002-07-25

2004-09-07

Potter, Roy (Department: 2822)

Active solid-state devices (e.g., transistors, solid-state diode

Combined with electrical contact or lead

Of specified material other than unalloyed aluminum

C257S774000

Reexamination Certificate

active

06787905

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an electric semiconductor component including a monocrystalline semiconductor substrate, an insulation layer arranged on the surface of the semiconductor substrate and penetrated by a contact hole in at least one location, and a contact element that contacts the semiconductor substrate through the contact hole and is made of a material in which the semiconductor material of the substrate is soluble in an anisotropic dissolving process.
BACKGROUND INFORMATION
Such semiconductor components in which the semiconductor substrate is silicon and the material of the contact element is aluminum are widely used in general. One problem in establishing contact between aluminum and silicon in the area of the contact holes in such components is the solid-state reaction of aluminum with silicon occurring. For a high conductivity of the contact between the two, it is necessary to remove the oxide film which is naturally present between aluminum and silicon in the contact hole. This is accomplished by a temperature treatment in the range of 300° C. to 500° C. At these temperatures, metallurgical reactions of aluminum with silicon occur due to the solid-state solubility of each substance in the other at locations where the oxide has been removed. The solubility of silicon in aluminum is on the order of a few percent (e.g., 0.48% at T=450° C.), depending on the temperature. The diffusion of silicon in polycrystalline aluminum is very high because of accelerated diffusion along grain boundaries. Therefore, in the course of the temperature treatment, not only is the direct contact hole area saturated with silicon, but also the adjacent aluminum conductor regions become saturated with silicon. Depending on the temperature, a large quantity of silicon may be dissolved away from the surface of the semiconductor component and may migrate into the aluminum contact structure. In a temperature treatment at 450° C. for three minutes, for example, the diffusion length of the silicon atoms amounts to approximately 40 &mgr;m. The silicon atoms dissolved out of the crystal are replaced by aluminum atoms migrating out of the contact structure. They form “spikes”, which are deposits of aluminum having a silicon content. The dimensions of these spikes become larger as the size of the contact hole becomes smaller and the volume of aluminum to be saturated in relation to it becomes larger. These spikes may greatly distort electric fields in the area of the contact hole or may lead to total failure of the component if they extend to a pn junction of the component.
To avoid this problem, it is described D. H. Widmann, H. Mader, H. Friedrich,
Technologie hochintegrierter Schaltungen [Technology of Highly Integrated Circuits],
Berlin, Springer 1996, for example, that silicon-doped aluminum may be used as the material for the contact structures of electronic components. The silicon concentration of the doped aluminum is greater than the solid-state solubility of silicon in aluminum, based on the highest process temperatures reached in the temperature treatment. This concentration may be approximately 1% silicon.
However, this method cannot be used for contacting in contact holes on high-resistance n-type silicon (donor concentration less than 10
20
cm
−3
). Epitaxial silicon deposits are formed in the contact hole area on cooling. These silicon deposits are doped with aluminum and therefore are p-conducting. Because of the formation of the pn junction, they have a negative effect on the contact resistance with increasing degrees of coverage in the contact hole. Therefore, aluminum without added silicon as the metallic coating is used for contacting high-resistance n-type silicon. To produce a conductive junction in the contact hole, the occurrence of spikes must be accepted.
SUMMARY
An object of the present invention is to limit the formation of spikes in a contact hole of a semiconductor component to a great extent by the configuration of the edges of the contact hole. It is not necessary to add additional structures, foreign substances, etc.
There are various configuration possibilities for the edges, which are referred to as diffusion stop structures. Curved segments are the first possibility. For example, a contact hole may be circular as a whole, or it may be composed of overlapping intersecting circles. The effect of the circular segment is based on the fact that it is composed of a plurality of linear segments, each having different directional indices, based on crystalline size dimensions, and that the dissolving process progresses differently along the individual linear segments until reaching the respective areas in the crystalline interior that present the greatest resistance to the dissolving process. The smaller the radius of such a circle, the shorter the corresponding linear segments and also the smaller the spikes that may emanate from a single linear segment.
A similar effect is achieved when the conventional straight bordering lines of a contact hole are replaced by microstructured sections. These microstructured sections may have a crenellated or sawtooth pattern, for example. The dissolving process proceeds regularly from a linear segment of the edge and progresses until reaching sparingly soluble crystal planes. Microstructuring achieves the result that the individual fronts where the dissolving process occurs are shortened in comparison with a rectilinear edge, and that accordingly only a smaller volume of the semiconductor material may be dissolved before reaching planes of the crystal that dissolve only slowly or not at all. The resulting spikes may be shorter as the microstructure becomes finer. An edge length of the structure elements may be 2 &mgr;m or less.
However, it is also possible to prevent or at least largely suppress the development of spikes on rectilinear edges of the contact holes. The anisotropy of the dissolving process implies that the semiconductor material has at least one class of crystal planes that are subject to little or no attack in the dissolving process. A class is understood to refer to a family of crystal planes the Miller's indices of which arise from one another through permutation and/or sign reversal. All the planes of such a class are equivalent from a crystallographic standpoint. Rectilinear sections of the edges of a contact hole may be arranged so that they intersect such crystal planes of the class extending beneath the contact hole in the semiconductor substrate.
A contact hole may also be configured so that all its edges fulfill the above-mentioned requirement. Such a contact hole may be in the form of an equilateral triangle or overlapping, intersecting equilateral triangles.
The substrate of the semiconductor component may be a <111> silicon substrate because the <111>plane of silicon is hardly subject to attack by dissolving in aluminum.
It is also possible to restrict the formation of spikes on such a substrate by the contact hole having edges that are rotated by ±15° toward the lines of intersection of the <11{overscore (1)}> plane, the <1{overscore (1)}1> plane or the <{overscore (1)}11> plane with the surface.


REFERENCES:
patent: 27 51 667 (1978-05-01), None

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