Fabrication process and aluminum/GaAs (gallium arsenide) coupling are used to produce Schottky diodes that have high cutoff frequencies and can withstand operating temperatures in excess of 500 C

Dickens, L. E.

Kim, H. B.

Trageser, F. G.

English

NASA Technical Reports Server

Semiconductor 
Material Figure 1 
June 1975	 B75-10101 
NASA TECH BRIEF S	 Marshall Space Flight Center 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
High-Performance Schottky Diodes Endure High Temperatures' 
The problem: 
Microwave, GaAs (gallium arsenide) Schottky 
barrier diodes must have high cutoff frequency to 
yield high performance. The diodes of this quality, 
however, have low tolerance to elevated temperature. 
Because of this two problems are created. One occurs 
during fabrication: Since the Schottky contacts are 
sensitive to high temperature, they must be formed 
after the alloying of the ohmic contacts. The GaAs is 
fragile, and much of it is lost during the subsequent 
photoetching steps. The second problem is due to low 
diode resistance to RF-pulse power burnout. At the 
high temperatures generated by the RF, contact 
metals such as gold or platinum are not suitable 
because much diffusion occurs between these metals 
and the GaAs. 
The solution: 
An improved fabrication process , and a new 
aluminum/ GaAs coupling are- used to produce 
Schottky diodes that have high cutoff frequencies and 
can withstand operating temperatures in excess of 
5000 C. 
How it's done:. 
The fabrication steps are shown in the illustrations. 
The starting material is a wafer of lowresistivity 
semiconductor material. A thin epitaxial layer of 
n-type GaAs is grown on the surface of this material. 
The typical thickness of this layer is 0.5 to 3.0 jAm.. 
Next, a thin layer of insulating material (typically 
silicon dioxide) is deposited on the epitaxial growth of 
GaAs to a thickness of 30 pm (see Figure 1). 
After the deposition of the insulating layer, 
openings for the diode junctions are formed in the 
layer by standard masking and etching techniques 
(see Figure 2). This is followed by the formation of an 
Al/Mo/Au Schottky barrier. The barrier is formed by
sequential deposition using RF sputtering (see Figure 
3). First, an Al metallization is formed in the openings 
with an overlay over the insulating layer for strong 
adhesion. Next, a diffusion barrier layer of Mo is 
formed, followed by a contact layer of Au. 
Insulating 
n-Type GaAs	 Material 
— 
Figure 2 
Figure 3 
AMR
Ohmic . I . I 
Figure 4 
Figures 1 through 4: Diode Fabrication Steps 
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Aeronautics and Space Administration. Neither the United Stales 	 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=19750000101 2020-03-19T20:06:31+00:00Z
With most of the processing steps completed, the 
semiconductor is reduced in thickness from approx-
imately 0.020 in. (0.51 mm) to approximately 0.005 
in. (0.13 mm) by lapping and etching its bottom 
surface. Next, an ohmic contact is formed on this 
layer by applying a Sn/Ni/Au layer by plating. This 
layer is then alloyed at temperatures ranging from 
450° to 500° C. The wafers are scribed and separated 
into chips. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Marshall Space Flight Center 
Code ATO1 
Marshall Space Flight Center, Alabama 35812 
Reference: B75-10101
Patent status: 
Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code CCO1 
Marshall Space Flight Center, Alabama 35812 
Source: L. E. Dickens, F. G. Trageser, and

H. B. Kim of
Westinghouse Electric Corp. 
under contract to

Marshall Space Flight Center 
(MFS-23184)
is 
Categories: 01 (Electronics - Components 
and Circuitry) 
04 (Materials) 
B75-10101
	 08 (Fabrication Technology)


High-performance Schottky diodes endure high temperatures

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