1063-7397/01/3003- $25.00 © 2001 MAIK “Nauka /Interperiodica”
Russian Microelectronics, Vol. 30, No. 3, 2001, pp. 191–194. Translated from Mikroelektronika, Vol. 30, No. 3, 2001, pp. 223–227.
Original Russian Text Copyright © 2001by Snitovskii.
Wet etching is widely used in semiconductor device
manufacturing and serves various functions: from sur-
face cleaning to etching of mesas and grooves on mul-
tilayer semiconductor structures [1–3].
As IC features shrink, requirements imposed on the
quality of starting materials and production technology
become ever more stringent [4, 5]. Along with material
perfection and the density of defects introduced during
various process steps, the IC yield depends on the over-
all process purity, namely, on the purity of gaseous
energy suppliers, clean-room environment, deionized
water, chemicals, etc. [4–7].
Ultrapure technology (ultrapure process environ-
ment, ultrapure wafer surface, and precise control of
process parameters) is a key factor in the successful
development of ULSI ICs [3, 6, 7].
In [6, 7], the idea of wafer processing in a closed
manufacturing system (CMS), where the wafers are
transported between reactors in a nitrogen-ﬁlled chan-
nel without being in contact with air, has been put for-
ward. This idea is based on experimental data accord-
ing to which such conditions allow a considerable
decrease in the
In this work, we report results on wafer cleaning in
equipment that simulates CMS conditions. The addi-
tional effect of cavitation in the liquid etchant is dis-
When silicon wafers are cleaned by wet etching,
they are usually at rest. Reaction products (hence,
molecular, ionic, and atomic contaminants ) are not
entrained by the liquid but are redistributed over the
surface. Therefore, even the heated etchant does not
sweep them away from the etchant–wafer interface.
The liquid ﬂow rate  depends on the liquid prop-
erties (such as viscosity, surface tension, and evapora-
tion-related parameters), the presence of (soluble or
suspended) solid or gaseous impurities, the interface
condition (purity, as well as the presence of gas-ﬁlled
cracks or scratches), and the crystallographic orienta-
tion of the surface.
By heating a liquid at constant pressure or by
decreasing the pressure at constant temperature under
static or dynamic (i.e., during motion) conditions, one
can bring up the liquid to the state where vapor, gas, or
vapor–gas bubbles (cavities) begin to grow .
The bubble may grow with a moderate rate if dis-
solved gases diffuse into it or merely if the gas inside
the bubble expands with increasing liquid temperature
or decreasing liquid pressure.
Bubble growth due to an increase in the liquid tem-
perature is called evaporation; if the driving force of
bubble growth is a dynamic decrease in the pressure
(with the temperature remaining virtually constant),
such a process is called cavitation .
If the pressure rises during bubble growth, the
growth will be terminated and the bubbles start shrink-
ing. Eventually, they collapse and disappear because of
gas dissolution and/or vapor condensation.
Collapse takes place sharply if the bubbles, or cavi-
ties, contain a small amount of gas or gradually if the
gas content is considerable.
Thus, cavitation involves a variety of processes
from bubble nucleation to bubble collapse . It may
evolve in both a moving liquid and a liquid during rest.
Also, the process may occur both in the volume and at
the solid–liquid interface.
Thus, we can conclude that (1) the cleaning efﬁ-
ciency will be improved if the wafers are in a dynamic
state, (2) the cleaning efﬁciency will be improved if
contaminants (etching products) are swept away from
Silicon Surface Cleaning by Wet Etching for IC Production
in a Closed Manufacturing System
Yu. P. Snitovskii
Belarussian State University of Information Science and Radio Engineering, ul. Brovki 17, Minsk, 220072 Belarus
Received April 10, 2000
—Silicon wafer cleaning by wet etching in model equipment meeting requirements for a closed man-
ufacturing system is considered. Theoretical grounds for the new production technology, including chemical
treatment, rinsing in water, and drying in a single process, are discussed. It is shown that the cleaning efﬁciency
is improved if a heated gas (such as nitrogen) passes through the etchant, causing the wafers to vibrate, rotate
in the horizontal plane, or reciprocate in the vertical plane. Also, the heated gas exerts a cavitation effect on the
wafer surface. The degree of surface contamination after chemical etching, rinsing, and drying is reported.