Techniques for impressing a voltage with an electron beam

An insulated conductive region, such as a doped semiconductor region in a semiconductor substrate and/or a metal conductor carried insulated on a substrate is subjected to non-destructive testing to determine the electrical integrity of the region. The outer portion of the insulating material may be, for example, a passivating layer and is provided with a metal film which extends over a conductive region to be tested. An electrical potential is applied to the metal film and the structure is subjected to electron beam radiation of sufficient energy level to provide a diffusion cloud which extends from the metal film to the region undergoing tests to form an electrical connection therewith. A voltage measurement taken at the region, with respect to a reference provides an indication of the electrical integrity of the tested region.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is concerned with techniques for providing 
non-destructive testing of an insulated electrical region, and is more 
particularly concerned with impressing a voltage into an electric 
component of an integrated circuit, which has a passivating layer of 
electrically insulating material, through the utilization of an electron 
beam. 
2. Description of the Prior Art 
It is well known in the art that an electron beam can be used for proximity 
testing of the function of electronic components, particularly of 
integrated circuits. For this purpose, the integrated circuit is mounted 
into the sample chamber of a scanning electron microscope. The primary 
electron beam triggers secondary electrons on the surface of the 
component, the energy of which can be measured with a spectrometer. 
In order to check such electronic components, voltages can be impressed 
from the exterior. For this purpose, mechanical probes are placed on 
conducting areas of the component. It is, however, customary in case of 
such components having a base of semiconductor material, to provide the 
surface, for the sake of passivation, with a layer of electrically 
insulating material, for example, silicon oxide (SiO) or silicon dioxide 
(SiO.sub.2). The passivating layer covers the electrically conducting 
areas of the component and prevents contacting by a mechanical probe 
without destruction of the surface layer. 
With the primary electron beam of a scanning electron microscope, it is 
possible to inject charges into the surface of the insulating passivating 
layer. This injection charge carriers into the isolator can be used for 
analysis of leakage currents, as suggested in "Scanning Electron 
Microscopy", Part IV-IITRI, Chicago/USA, SEM, April 1976, pp. 515-520. A 
tampering into the electrical behavior of the circuit is thus, however, 
not possible. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide for non-destructive 
testing of electrical components by the impression of voltages into 
electron components having a passivating layer of electrically insulating 
material. 
The aforementioned object is achieved according to the present invention in 
that the passivating layer is at least partially provided with a metal 
film, which is connected to a supply voltage and upon which an electron 
beam is directed. The acceleration voltage of the electron beam is 
selected such that it builds up a diffusion cloud within the passivating 
layer, and that the diffusion cloud by means of its beam-induced 
conductivity connects the component with the metal film in an electrically 
conducting manner. The electron beam thereby serves only as a circuit 
breaker for shortcircuiting and for production of the conductive 
connection between the metal film and the conducting area, for example, a 
conductor of an integrated circuit. By means of the impressed voltage, one 
obtains information concerning the function and operation of the 
component, as well as information about errors present, for example, an 
interruption in the conductive path, in a simple manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, an amplifier circuit is illustrated which comprises 
two transistors 2 and 4 which, for amplification, are connected in tandem 
and in each case are arranged in series with a respective load resistor 6 
and 8 between a supply voltage of, for example, 5 volts and 0 volts. The 
amplifier circuit includes an input E and an output A. A main electrode of 
the transistor 2 which carries the load current is connected by way of a 
conductor 16 with the control electrode of the transistor 4. In a 
practical embodiment, the amplifier circuit can, for example, be a portion 
of an integrated circuit, which contains the connecting conductor 16 as a 
conductive path. 
In order to check the operation of the integrated circuit, as represented 
in FIG. 2, a voltage is to be impressed from the exterior of the circuit 
to the conductive path 16, which voltage then serves as a control voltage 
for the transistor 4 and allows the amplified signal to appear at the 
output A, as long as the conductive path 16, or further conducting 
conductors of the transistor 4, contain no interruptions. 
According to FIG. 2, the amplifier circuit of FIG. 1 is arranged upon a 
base 10 of semiconductor material, for example n-conducting silicon. The 
semiconductor body 10 includes a p-conducting area 12, which, for example, 
can be produced by diffusion of p-conducting doping material. The region 
12 can function, for example, as a resistor or as a conductive path within 
the semiconductor material of the integrated circuit. The surface of the 
semiconductor body 10 is provided with an oxide layer 14, which serves as 
a protective layer and, for example, can consist of silicon oxide (SiO) or 
silicon dioxide (SiO.sub.2) and have a thickness of, for example, 
approximately 1 .mu.m. The protective layer 14 carries the conductive path 
16 of the amplifier. The surface of the component is also provided with an 
insulating layer 20, also having a thickness of, for example, 
approximately 1 .mu.m, which serves as a passivating layer and represents 
a protection against mechanical damage, as well as the protection against 
corrosion of the conductive paths, for example the conductive path 16 of 
the component. 
The passivating layer 20 is at least partially provided with a metal film 
22 as a covering, which can consist of aluminum or of gold, and which is 
deposited according to the particular purpose. The thickness of the metal 
film 22 is also calculated so that, on the one hand, its conductivity is 
sufficient for limiting the voltage drop within the film, and, on the 
other hand, that one obtains a sufficient penetration depth of the 
electron beam into the component. The thickness can therefore be 
approximately an order of magnitude less than the thickness of the 
passivating layer 20 and, for example, can amount to 0.1 .mu.m. The metal 
film 22 is connected to a voltage source 24 so that a voltage U is 
delivered and is available for impression into the electrically conducting 
areas of the component. The voltage U should, for example, be impressed to 
the conductive path 16 with a primary electron beam S.sub.1 of a scanning 
electron microscope. For this purpose, the primary electron beam S.sub.1 
is directed upon the metal film 22 above the conductive path 16 with an 
acceleration voltage of the primary electron of, for example, U.sub.PE =10 
kV. By means of the primary electrons, a diffusion cloud 26 arises in the 
passivating layer 20. The electrons diffused in all directions and release 
electron-hole pairs. The oxide becomes electrically conductive and thereby 
forms an electrically conducting connection between the conductive path 16 
and the metal film 22. The voltage U is thereby impressed on the 
conductive path 16 and can be checked, whether the component reacts to the 
impressed voltage, for example by the connection of a voltage-sensitive 
instrument to the output A (FIG. 1). 
Further, a connection of the metal film 22 with the doped region 12 is 
possible. For this purpose, the primary electrons must penetrate the two 
insulating areas 14 and 20, in addition to the metal film 22. Therefore, a 
primary electron beam S.sub.2 is directed toward the region 12 with a 
correspondingly higher acceleration voltage of, for example, U.sub.PE =15 
kV upon the metal film above the region 12. A corresponding diffusion 
cloud 28 forms in the metal film 22 and in the two insulating layers and 
extends to the diffusion region 12. The external voltage U is thus 
impressed on the region 12 of the component by means of the beam-induced 
conductivity arising within the diffusion cloud 28, and the electron beam 
S.sub.1 or S.sub.2 serves only as a circuit breaker. The beam therefore 
produces the local beam-induced conductivity and thereby causes the 
electrical contact between the metal film 22 and the corresponding 
portions of the integrated circuit. As with the conductive path 16, the 
electron beam S.sub.2, and the resulting voltage U provided to the region 
12, will provide a response at the output A, assuming that the component 
is without interruptions, or other flaws which would, of course, degrade 
the voltage. 
Although I have described my invention by reference to a particular 
illustrative embodiment thereof, many changes and modifications of the 
invention may become apparent to those skilled in the art without 
departing from the spirit and scope of the invention. I therefore intend 
to include within the patent warranted hereon all such changes and 
modifications as may reasonably and properly be included within the scope 
of my contribution to the art.