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Submitted on 1 Jan 1989
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DOPING PROFILE INSPECTION IN SILICON BY LOW ACCELERATION VOLTAGE SEM-EBIC
R. Kuhnert
To cite this version:
R. Kuhnert. DOPING PROFILE INSPECTION IN SILICON BY LOW ACCELERATION VOLTAGE SEM-EBIC. Journal de Physique Colloques, 1989, 50 (C6), pp.C6-185-C6-185.
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REVUE DE PHYSIQUE APPLIQU~E
Colloque C6, Supplbment au n06, Tome 24, Juin 1989
DOPING PROFILE INSPECTION IN SILICON BY LOW ACCELERATION VOLTAGE SEM-EBIC
R. KUHNERT
Siemens AG, Research laboratories, 0-8000 Miinchen 83, F.R.G.
EBIC micrographs of sectional planes are a common tool for the delineation of p/n-junctions. The EBIC contrast has been inter- preted based on models originating from van Roosbroeck /1/ in which the specimen is characterized by a recombination velocity at the sectional plane and a bulk recombination parameter (e.g.
the minority carrier diffusion length).
In this work, VLSI devices are inspected at low primary electron accelerating voltages. The EBIC contrast is manifestly dependent on the preparation of the sectional plane (cleaving or lapping with subsequent ion milling with argon or oxygen and with or without additional annealing) and in neither case can be explained by van Roosbroeck's model, since the EBIC maximum does not coincide with the space charge area of the p/n-junction.
Thus, a new model is developed, based on the following assumptions :
A sectional plane introduces surface states, and as a result the fermi level is pinned. The electric field perpendicular to the sectional plane can be expressed in Schottky's approximation.
The minority carrier lifetime beneath the sectional plane is drastically reduced by damage introduced by lapping and sputtering or cleaving. Thus, the carrier separation is governed by the electric field, not by diffusion.
Depending on specimen preparation on p-type silicon an inversion channel may transport minority carriers to the n-type region where they can be detected as beam induced current. On n-type silicon a minority carrier channel does not exist and, thus, a beam induced current can not be detected.
As a result of these assumptions, the collection efficiency q can be expressed as a function of Fermi level position at the sectional plane @B,*, (measured from the top of the valence band) , the surface llfetimg Ts, the surface mobility ps, the primary electron extrapolated range RG, and the (p-type) doping concentration NA.
For discussion the dopinq profiles of several specimens were measured with SIMS or calculated with a numerical, simulation program (SUPKEM 111) and the model calculations are compared to EBIC measurements. For drain profile inspection a resolution of 50 nm is achieved.
reference :
/1/ : W. van Roosbroeck : "Injected Current Carrier Transport in a Semi-InfPnite, Semiconductor and the Determination of Lifetimes and Surface Recombination Velocitiesw, J.Appl.Phys. = ( 4 ) , 380-391, (1955)
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989639
