Modified three-step process controls the concentration of lithium diffused as a dopant into the base region of a diffused n-on-p silicon solar cell wafer. Part of the surface layer of the base region of the p-type silicon containing the diffused dopant is removed, prior to redistributing the remaining portion of the dopant into the bulk of the wafer

Bartholomay, W. C.

Topfer, A. R.

English

NASA Technical Reports Server

Diffused Lithium Portion of 
Removed 
Surface 
n 
-
p-Type Silicon with 
Lithium Diffusant 
n-Type Layer 
p-Type Silicon 
Lithium-Oil Suspension
August 1967	 -	 Brief 67-10303 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Process Controls Introduction of Selected Impurities
into Semiconductor Wafers
The problem: 
To devise a process for controlling the concentration 
of lithium diffused as a dopant, or impurity, into the 
base region of a diffused n-on-p silicon solar cell 
wafer. 
The solution: 
A modified three-step process in which part of the 
surface layer of the base region of the p-type silicon 
containing the diffused dopant (lithium) is removed, 
prior to redistributing the remaining portion of the 
dopant into the bulk of the silicon wafer. 
How it's done: 
Lithium is diffused into the base region of the 
silicon wafer using a coating of lithium suspended in 
oil as the diffusant source. Part of the surface layer 
on the base region is then chemically or mechanically 
removed to a depth less than that of the total pene-
tration of the diffused lithium. The diffusant in the 
remaining portion of the surface layer is redistributed 
throughout the bulk of the silicon wafer by heat 
treatment.
Notes: 
1. The advantages of this process are that the final 
impurity concentration in the wafer can be closely 
controlled by adjusting the amount of surface layer 
removed, and the effects of surface alloying, gen-
erally encountered in the diffusion of metallic 
impurities as lithium, are eliminated. 
2. This process, which has been specifically used for 
lithium doping of diffused n-on-p solar cell wafers, 
can be applied to other dopants and semiconductor 
materials. 
3. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B67-10303 
Patent status: 
No patent action is contemplated by NASA. 
Source: A. R. Topfer and W. C. Bartholomay 
of Radio Corporation of America 
under contract to 
Goddard Space Flight Center 
(QSFC-523) 
Category 01 
This document was prepared under the sponsorship of the National	 Government 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.
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Process controls introduction of selected impurities into semiconductor wafers

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