Contact preparation at low temperatures is possible with the use of a copper-titanium eutectic alloy. Contacts formed with this alloy are ohmic on p-type silicon carbide and rectifying on n-type

Shier, J. S.

English

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ember 1970	 Brief 70-10444 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U .S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Copper—Titanium Eutectic Alloy Improves Electrical and Mechanical

Contact to Silicon Carbide 
With increased requirements for electronic equip-
ment operating at elevated temperatures, there has 
been considerable interest in wide bandgap semi-
conductors such as silicon carbide. The hexagonal 
(alpha) form of SiC has many desirable qualities. The 
semiconductor is chemically stable and mechanically 
rugged and its bandgap of 2.9 eV is more suitable for 
high temperature operation than silicon (1.2 eV) or 
gallium arsenide (1.4 eV). However, the chemical 
stability and hardness of SiC have required excessively 
high temperature processes to form electrical contacts 
which have ohmic resistance and are not rectifying. 
The high temperature causes the contact to penetrate 
deeply into the material. Also, during cooldown there 
is a tendency for the contact to shear or break away 
from the SIC surface because of the differences in 
thermal expansion coefficients. 
Tungsten	 Alloy 
Tab Contact	 (5-10 Microns) 
Substrate	 Silicon Carbide Device 
Cross Section of Contact Formation on S. C. Device 
After considerable research and experimentation, 
acceptable ohmic contacts were made with the ad-
dition of a copper-titanium (Cu-Ti) eutectic alloy
between the top metal tab and the SiC surface (see 
fig.). An alloy composition of 71 atomic % Cu and 
29 atomic % Ti (eutectic between the intermetallic 
compounds TiCu 2
 and TiCu 3 ) melts at 880°C and 
readily wets the semiconductor surface. An alloy layer 
of 5 to 10 microns, applied to the SiC surface, pene-
trates 300 to 500 angstroms into the SiC material. 
Tungsten is used as the tab because of similar thermal 
expansion properties and the ability to resist dissolving 
in the eutectic alloy. 
Contacts formed with Cu-Ti alloy are ohmic on 
p-type SiC and rectifying on n-type. Current-voltage 
characteristics of a typical p-n junction device have 
shown that contact resistance is a few hundred ohms. 
Contact preparation at low temperatures is impor-
tant if metal or oxide films which are susceptible to 
high temperatures are present in a device structure. 
In addition, the shallow penetration enables this pro-
cess to be used for preparing contacts on thin epitaxial 
films. 
Notes: 
1. SiC devices, such as diodes, transistors and elec-
troluminescent arrays, will have widespread ap-
plication in electronics technology when acceptable 
performance levels and reliability have been 
achieved. 
2. Requests for further information may be directed 
to:
Technology Utilization Officer 
Headquarters 
National Aeronautics 
and Space Administration 
Washington, D.C. 20546 
Reference: B70-10444
(L011 (i,iucd toe rietri) 
fhis document was prepared under the sponsorship of the National
	 Governmãnt assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19700000428 2020-03-17T00:49:55+00:00Z
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546.
Source: J. S. Shier 
Electronics Research Center 
(ERC-10256) 
Brief 70-10444	 0	 Category 04


Copper-titanium eutectic alloy improves electrical and mechanical contact to silicon carbide

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