Semiconductor electric circuit device with plural-layer aluminum base metallization

A pure aluminum outer layer is provided to facilitate bonding with aluminum bonding wires having a diameter of 50 .mu.m or greater without formation of troublesome slivers upon bonding. Beneath that a copper-bearing aluminum layer with 1 to 4% copper content is provided. A third layer beneath the copper-bearing layer containing up to 1% silicon can be added below the copper-bearing layer to promote adhesion at contact window edges.

This invention relates to a semiconductor electric circuit device, 
particularly of the monolithic integrated circuit type having a 
monocrystalline semiconductor chip or wafer body of silicon and zones of 
different conductivity and/or conductivity type in various surface areas 
of the body for provision of components of the circuit device. Such 
devices are conventionally partly covered by an insulating layer, usually 
of silicon oxide, which leaves uncovered, by windows therein, areas of the 
body or zones thereof for contact therewith, and there is also generally 
provided, above the insulating layer where that is also present, a 
patterned metallization layer providing circuit paths, contact through the 
contact windows of the insulating layers, and areas for application of 
external contact wires or other connection devices. Bonding wires are 
commonly provided to make contact with the metallization layer in suitable 
areas of the latter, in order to provide the necessary external 
connections to the circuit and components provided on or in the 
semiconductor body. These bonding wires are generally attached to the 
metallization layer by a pressure-bonding procedure. 
Semiconductor electric circuit devices of the above-described kind are 
already known in which the metallization is composed of an aluminum layer 
and the bonding wires are made of aluminum wire. In such devices, 
particularly in the case of relatively thick aluminum wires (thickness&gt;50 
.mu.m), difficulty has been found in applying the bonding wires. Through 
friction of the wire against the aluminum layer, bond slivers are formed 
in the bonding operation which can lead to the formation of short-circuits 
between the various conducting paths of the metallization. 
It is an object of the present invention to avoid the above-mentioned 
disadvantages of the known devices without resort to expedients bringing 
other disadvantages, as in the case of increased corrosion of aluminum and 
copper and poor quality of covering and of adherence to the window edges. 
SUMMARY OF THE INVENTION 
Briefly, the metallization layer is made up of at least three distinct 
layers, an outer layer of highly pure aluminum, a layer underlying the 
outer layer of copper-containing aluminum having a copper content of 
between 1 and 4% by weight and an inner layer beneath the copper-bearing 
aluminum layer made of aluminum that preferably has a small silicon 
content, up to 1% of silicon by weight. The inner layer just mentioned has 
an adhesion-promoting function that allows the steep edges or steps at the 
rim of contact windows to be better bridged over by the metallization path 
than in the case of metallization of which the bottom layer is 
copper-bearing aluminum. 
Preferably the outer layer has a thickness of 0.5 to 1.5 .mu.m, the layer 
immediately underlying it likewise, and the inner layer, a thickness of 
0.3 to 0.5 .mu.m. The bonding wires can be of aluminum and preferably have 
a thickness not less than 50 .mu.m.

FIG. 1 shows, in section, a part of a semiconductor electric circuit device 
constituted as a monolithic integrated circuit that has a monocrystal 
semiconductor wafer body 10 of silicon. The body 10 consists mainly of a 
substrate 11 and an epitaxial layer 13 that is grown on the substrate 11 
in manufacture. Between the epitaxial layer 13 and the substrate 11 is a 
conductive layer produced by diffusion of a suitable impurity and this 
layer is interrupted in a few places not shown in the drawing, so that in 
such places the substrate 11 and the epitaxial layer 13 come together at a 
common boundary. 
In the epitaxial layer 13, there is a zone 14 that has been produced by 
diffusion of a suitable significant impurity, which zone accordingly has a 
different conductivity or a different conductivity type compared to the 
corresponding quality of the epitaxial layer 13. The semiconductor body 10 
is covered with a silicon oxide layer 15 on the surface of the body in 
which the zone 14 has been diffused. As partly shown in the righthand 
portion of FIG. 1, a contact window has been etched through the insulating 
layer 15 above the zone 14 of the semiconductor body. The system 
consisting of the semiconductor body 10 and the silicon oxide layer 15 is 
partly covered with a metallization 16. This metallization 16 forms an 
ohmic contact with the zone 14 over part or all of the contact window 
above mentioned and serves to provide electrical connection between the 
zone 14 and other zones provided in the semiconductor body 10 in portions 
of that body that are not shown in the drawing. 
The metallization layer 16 also serves to provide an external connection 
for the zone 14. For this purpose, a bonding wire 17 is provided that has 
been press-bonded with the metallization layer 16 at or near its end and 
leads to a circuit point, not shown in the drawing, that is beyond the 
edge of the semiconductor body 10. The bonding wire 17 is an aluminum wire 
and has a thickness equal to or greater than 50 .mu.m. 
In order to prevent the formation of bond slivers at the time of bonding, 
the metallization 16, in the illustrative embodiment shown in FIG. 1, is 
made up of two distinct layers, an outer layer of highly pure aluminum 
facing the bonding wire 17 and an underlying layer 16b consisting of 
copper-bearing aluminum with a copper content of from 1 to 4%. The outer 
layer 16 has a thickness between 0.5 and 1.5 .mu.m and the underlying 
layer 16b likewise has a thickness of 0.5 to 1.5 .mu.m. 
FIG. 2 shows the three-layer metallization 16 of the present invention that 
contains, in addition to the outer layer 16a and the layer 16b immediate 
underlying the outer layer, a third layer 16c serving as an 
adhesion-providing layer, for improving the adhesion of the metallization 
16 to the system 10,15 lying below it. The adhesion-providing layer 16c 
consists of aluminum and can advantageously contain up to 1% of silicon. 
The adhesion-providing layer 16c has a thickness between 0.3 and 0.5 
.mu.m. 
Although the invention has been described with respect to particular 
illustrative embodiments, it is to be understood that the invention is not 
strictly limited thereto. Thus, for example, another aluminum layer of 
different additive metal content could be provided, in addition to the 
copper-bearing aluminum layer, between the inner and outer aluminum layers 
16c and 16a of FIG. 3 without departing from the present inventive 
concept.