Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2003-03-07
2004-11-09
Zurnda, David A. (Department: 2829)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S571000, C438S584000, C438S597000, C438S621000, C438S931000
Reexamination Certificate
active
06815351
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for contacting a semiconductor configuration.
The invention relates, in particular, to a semiconductor configuration which is composed of a given polytype of silicon carbide at least in specific semiconductor regions, in particular the semiconductor regions which are to be contacted. The semiconductor regions that are to be contacted are in particular p-conducting.
Silicon carbide (SiC) in monocrystalline form is a semiconductor material having outstanding physical properties that seem to make this semiconductor material interesting particularly for power electronics, even for applications in the kV range, inter alia due to its high breakdown field strength and its good thermal conductivity. Since the commercial availability of monocrystalline substrate wafers, especially ones made of 6H and 4H silicon carbide polytypes, has risen, silicon carbide-based power semiconductor components, such as e.g. Schottky diodes, are now also receiving more and more attention. Other silicon carbide components which are becoming increasingly widespread are pn diodes and transistors such as, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors).
Stable ohmic contacts to semiconductor regions of different conduction types are indispensable for the functioning of these components. In this case, the lowest possible contact resistances are sought in order to minimize undesirable losses at the semiconductor-metal junction.
The overview paper “Ohmic contacts to SiC” by G. L. Harris et al. from “Properties of Silicon Carbide” ed. by G. L. Harris INSPEC, 1995, pages 231-234 contains a summary of contacting methods for silicon carbide of different polytypes and conduction types. With regard to the contact-connection of p-conducting SiC, the overview paper and the cross-references cited reveal the current state of the art generally accepted by experts, which is outlined below:
Aluminum is predominately used for contact-connecting p-conducting SiC. Since aluminum is soluble in small amounts in SiC and acts as an acceptor, a zone highly doped with aluminum can be produced in a boundary region between the aluminum-containing contact region and the semiconductor region made of SiC. In order to avoid evaporation of the aluminum, which melts at a temperature as low as 659° C., during a subsequent thermal treatment for forming the ohmic contact, at least one covering layer made of a material having a higher melting point, such as e.g. nickel, tungsten, titanium or tantalum, is applied to the aluminum.
In order to be able to exploit the advantageous contact properties of a specific contact material on p-conducting SiC, these methods of the prior art consequently require a second layer which protects the underlying first layer. The first and second layers are applied by separate, successive technological process steps with different materials in each case.
The paper “Titanium and Aluminium-Titanium Ohmic Contacts to p-Type SiC”, Solid-State Electronics, Vol. 41, No. 11, 1997, pages 1725-1729, discloses an aluminum-titanium alloy as material for an ohmic contact on p-conducting SiC. The alloy used in this case has a proportion by weight of 90% for aluminum and correspondingly a portion by weight of 10% for titanium. The contact made of the aluminum-titanium alloy is not covered with a further layer. The paper reports on problems with reproducibility and with very thin contact layers. With thin contact layers, in particular, the aluminum may volatilize from the aluminum-titanium alloy.
The paper “Ohmic Contacts to p-type SiC with improved thermal stability”, by Liu, S., et al., 7
th
International Conference on Silicon Carbide, III-Nitrides and Related Materials Stockholm, September 1997 describes an ohmic contact on p-conducting SiC which is produced through the use of a layer structure including an aluminum layer, a nickel layer and a tungsten layer. After this layer structure has been applied, a heat-treatment process is carried out, in the course of which, inter alia, the aluminum and the nickel are mixed together, but a material composition that is homogeneous over the depth of the contact region is not formed. Moreover, this mixing also takes place only in the presence of the third layer made of tungsten. During the heat-treatment process, a considerable proportion of tungsten in turn diffuses from this third layer right into the boundary region of the ohmic contact and of the p-conducting SiC. In this case, however, the tungsten can then lead to impairment of the ohmic contact behavior.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for contacting a semiconductor configuration which overcomes the above-mentioned disadvantages of the heretofore-known semiconductor configurations and methods of this general type and which provide an improved contact-connection of p-conducting SiC in comparison with conventional configurations and methods. In this case, the contact on the p-conducting semiconductor region should have a low contact resistance and should be thermally stable.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor configuration with an ohmic contact-connection, including:
at least one p-conducting semiconductor region composed of silicon and carbon in a form of silicon carbide;
at least one p-type contact region adjoining the at least one p-conducting semiconductor region and composed of a material having nickel as a first material component and aluminum as a second material component, the at least one p-type contact region having a substantially uniform material composition throughout; and
a boundary region extending into the at least one p-conducting semiconductor region and into the at least one p-type contact region, the boundary region being composed substantially exclusively of the silicon and the carbon of the at least one p-conducting semiconductor region and of the nickel and the aluminum of the at least one p-type contact region.
In other words, the semiconductor configuration according to the invention includes:
a) at least one p-conducting semiconductor region made of silicon carbide and
b) at least one p-type contact region adjoining the p-conducting semiconductor region, in which case
c) the p-type contact region is composed of a material having nickel as a first material component and aluminum as a second material component,
d) an approximately identical or uniform material composition is present in the p-type contact region, and
e) practically exclusively the silicon and the carbon of the p-conducting semiconductor region and the nickel and the aluminum of the p-type contact region are present in a boundary region, which extends into the p-conducting semiconductor region and into the p-type contact region.
With the objects of the invention in view there is also provided, a method for contacting a semiconductor configuration, the method includes the steps of:
providing at least one p-conducting semiconductor region formed of silicon carbide; and
applying a material having nickel as a first material component and aluminum as a second material component on the at least one p-conducting semiconductor region for forming at least one substantially homogeneous p-type contact region on the at least one p-conducting semiconductor region, by simultaneously applying both, the first material component and the second material component such that a given mixture ratio of the first material component and the second material component is established at an interface between the at least one p-conducting semiconductor region and the at least one p-type contact region prior to a heat-treatment process.
In other words, the method according to the invention includes:
a) at least one substantially homogeneous p-type contact region is formed on at least one p-conducting semiconductor region made of silicon carbide by
b) a material having nickel and aluminum as a first and a second material component,
Friedrichs Peter
Peters Dethard
Schörner Reinhold
Greenberg Laurence A.
Locher Ralph E.
Sarkar Asok Kumar
SiCED Electronics Development GmbH & Co. KG
Stemer Werner H.
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