1063-7397/04/3305- © 2004 MAIK “Nauka /Interperiodica”
Russian Microelectronics, Vol. 33, No. 5, 2004, pp. 298–302. Translated from Mikroelektronika, Vol. 33, No. 5, 2004, pp. 366–371.
Original Russian Text Copyright © 2004 by Snitovsky.
In microwave bipolar junction transistors, metals
used for making ohmic contacts to active regions are
mostly characterized by a large free energy (16.9, 11.4,
and 7.4 eV for Al, Cr, and Mo, respectively). They also
show good adhesiveness and high penetration capacity.
The latter results in the metal diffusing through a thin
layer under annealing. For example, this occurs in
near-emitter regions about 0.12
m thick, in which case
the emitter junction is short-circuited [1, 2].
This raises an important issue of making ohmic con-
tacts to shallow diffusion regions, which might be
doped with phosphorus.
The goal might be achieved by orienting the emitter
along the <110> direction in the Si(111) plane .
However, with remnants of SiO
in contact win-
dows, the problem remains of how to make reliable
ohmic contacts to the emitter and base [4, 5]. The oxide
is responsible for inhomogeneous metal–silicon con-
tacts, the interaction occurring mostly via pores in the
Regrettably, the metal–silicon dioxide interface has
received much less attention than the SiO
. It should be emphasized that physical and chemical
processes at the metal–silicon dioxide interface may
disturb the operation of integrated circuits and charge-
coupled devices; they may also be a reason for other
problems, such as high contact resistances to the emit-
ter and base. The metal–oxide interaction is also impor-
tant in Schottky-barrier junctions, effectively determin-
ing the junction parameters.
Previously transliterated as
In addition, the contact resistance of the ﬁrst
metallization layer is largely dependent on the qual-
ity to which the semiconductor surface has been pre-
This study represents an attempt to understand the
inﬂuence of silicon-surface processing in contact win-
dows on the electrical parameters of silicon microwave
bipolar junction transistors, including the contact resis-
of Al/Mo contacts to the emitter and base. We
also try to explain the results obtained in terms of phys-
ical and chemical processes at the Mo/SiO
Real-world surfaces are essentially inhomogeneous.
This is due to a variety of interrelated factors [14, 15].
First, consider structural inhomogeneity. One rea-
son for it is that different surface regions may have dif-
ferent crystallographic orientations and so may differ in
adsorption capacity and reactivity. Another reason is
macroscopic structural imperfections such as growth
steps, ﬁssures, pores, scratches, dislocations, and etch
pits. Moreover, surfaces inevitably have microscopic
imperfections such as vacancies, interstitials, and sub-
Second, account should be taken of chemical inho-
mogeneity. Owing to their saturated nature, surface
atoms combine with ambient molecules to form a wide
range of compounds strongly bound to the surface.
Molecular processes that may occur on a surface are to
a certain degree dependent on its chemical composi-
Third, all the macroscopic and electronic properties
of a surface should be seen in relation to its interaction
Silicon-Surface Restructuring under Cleaning as a Method
for Improving Al/Mo-to-Si Contact Resistance
and Microwave-BJT Parameters
Yu. P. Snitovsky
Belarussian State University of Informatics and Radioelectronics, Minsk, Belarus
Received December 10, 2003
—For microwave BJTs, the inﬂuence is experimentally studied of different surface-cleaning processes
on the Al/Mo-to-Si contact resistance and BJT parameters. Two processes are identiﬁed as optimal. One of them
includes preliminary H
O treatment, vacuum furnace annealing, H
and treatment with 1% hydroﬂuoric acid. The other includes rapid light annealing followed by treatment with
1% hydroﬂuoric acid. It is concluded that the resultant silicon-surface restructuring provides a lower contact
resistance, more intimate metal–semiconductor contact, and better BJT parameter values.
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