Individual ''fingerprint'' signals are produced when system photoexcites chips. ''Fingerprints'' are analyzed for characteristics associated with defects, including many not visible to the naked eye. Electromagnetic radiation photogenerates free electrons and holes in semiconductor chip. These carriers produce electrical signals at terminals. Signals vary depending on what defects are present

Hall, T. C.

English

NASA Technical Reports Server

October 1973
	
B73.10327 
•	 NASA TECH BRIEF Marshall Space Flight Center 
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 National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Laser Scanner for Testing Semiconductor Chips 
The problem: 
In general, semiconductor chips are examined visually 
before capping. This method successfully screens out 
bulk surface defects. However, visual examination is sub-
ject to human error and provides no means for discover-
ing flaws not connected with surface irregularities. 
The solution:
How it's done: 
Electromagnetic radiation photogenerates free elec-
trons and holes in a semiconductor chip. These carriers 
produce electrical signals. at the terminals. The signals 
vary depending on what defects are present. In this 
system (see figure), the electromagnetic radiation is sup-
plied by a two-power-level laser. A high-power mode ex-
cites the chip, and a low-power mode generates a final 
When a laser scanning system photoexcites the chips, 
individual "fingerprint" signals are produced. The 'Tin-
	 ____________[J..•.____ 
Simult 
Eyepiece To Allow Two
aneous Viewing gerprints" are analyzed for characteristics associated and Registration of 
eye.
Laser
(Two-Power Level) 
with defects, including many not visible to the naked 	
 
Semi- 
transparent 
 
Full 
•-f)1)fl)))))))))))))))fl) Reflecting Mirror
Mirror
Binocular Head _•t.	
Inverted Microscope 
(1) 
Oscillating Mirror 
(Frame Rate Frequency)
 
V-Direction	 *(2)
Separate 
Microscope 
X-Direction 
Rotating Mirror 
(Line Rate Frequency)
Binocular 
*Optomechanil	 Heads 
Raster Generator 
Consisting of These 
Two Elements Separate Mechanical 
Stages (X-Y-Z Movement)
Reference 
Chip 
Sample Chip ( Reference Chip 
O Output To 
Differential I 
iuI0\..	
mple	
__cI., 	
utput (To 
\\ ) Amplifier) 
I Differential 
Amplifier) L	 Chip 
Optomechanical Arrangement for the Laser Scanning System
(continued overleaf) 
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.
https://ntrs.nasa.gov/search.jsp?R=19730000327 2020-03-17T07:03:20+00:00Z
display. The laser radiation is rasterized, and the signal 
from the chip appears as a raster on a cathode-ray tube 
(CRT). 
The laser generates a raster by two rotating mirrors. 
The beam is split and directed to one eyepiece of each of 
two separate pairs of binoculars. The binoculars focus 
the beam on the sample chip and on a reference chip 
where it stimulates an electrical signal. A third pair of 
binoculars is used visually to align the chips. 
The "fingerprint" of a device will vary with the leads 
that are selected for output; each pair of leads has its 
own characteristic CRT display. 
The signal from the two chips is processed by a dif-
ferential amplifier, the output of which intensifies and 
modulates the raster on the cathode-ray tube. In the 
unlikely event that the chips are precisely the same, the 
amplifier will have a zero output; otherwise, the greater 
the chip difference, the greater the signal. The actual 
reference chip may be replaced by a computer program, 
and an automated examination can be performed in 
exactly the same manner for each chip.
Note:	
V 
Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Right center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B73-10327 
Patent status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code A&PS-PAT 
Marshall Space Flight Center, Alabama 35812 
Source: T. C. Hall of

Hughes Aircraft Company

under contract to

Marshall Space Flight Center

(MFS.22693)
. 
1^i'_e 
B73-10327 Category 02


Laser scanner for testing semiconductor chips

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