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JUNE 26 MONDAY MORNING
ETCHC-MoM-OR.6 SPUTTERING OF NITRIDES BY LOW-ENERGY IONS OF
DIFFERENT MASSES . S.S. Elovikov, A.S. Mosunov, J. C. Colligon*, Yu.A.Ryzhov,
I.I.Shkarban, V.E.Yurasova, E.Yu.Zykova. Physics Faculty, Moscow State University, Moscow,
119899, Russia. *Manchester Metropolitan University. John Dalton Extension. Manchester M1 5GD,
England, UK
The results of calculations of mass dependence of sputtering yields for nitrides with various ratios
between masses of their components, i.e. BN, AlN, and GaN, are presented. The effect of masses of
bombarding ions with energy from 200 to 2000 eV on sputtering yields, mean energies and energy
spectra of sputtered particles, depths of sputtering origin and number of generations of emitted atoms
for nitrides was investigated and discussed.
Study of sputtering of these nitrides is of interest both for physics of interaction between atomic particles
and solids and from practical viewpoints. BN is an important constructional material due to a
set of useful physical and chemical properties: high hardness and electric strength, good heat conduction,
thermal and chemical stability. AlN is known for strength, elasticity, good heat conduction, and
dielectric strength, and is used in acoustic devices and as a coating in spacecraft components. GaN is
used in light-emitting diodes and other electronic devices. In many of applications, surfaces of nitrides
are subject to various kinds of irradiation, which often leads to degradation of their properties.
Therefore, it is important to know the resistance of these nitrides to the low-energy ion irradiation.
We have used the MD simulation with a mobile single-crystal block of atoms. Polycrystal was simulated
by rotation of single-crystal block through arbitrary angles for every impinging ion. Inelastic
loses were taken into account. Thermal vibrations were considered as uncorrelated. Equations of motion
were integrated using predictor-corrector modified scheme. The interaction potential:
U(r)=a bm (1+a b /r)exp(-r/b),where a bm = 52(Z 1 Z 2 ) 3/4 , a b = (Z 1 Z 2 ) 1/4 /52, b = 0.219Å, Z 1 and Z 2 are the
atomic numbers of the impinging ion and the target atom, respectively. Binding energy E b of surface
atoms was estimated from value of cohesion energy per a bond between atoms in compounds and
was corrected using the experimental results. E b value, thus selected, is: 8.1, 6.8, and 5.4 eV for BN,
AlN, and GaN, respectively.
It was shown that the sputtering yields Y of BN, AlN, and GaN as functions of mass m 1 of normally
incident low-energy ions have a nonmonotonic character with a maximum for small m 1 . For targets
with medium mass of atoms (AlN, GaN), the Y(m 1 ) maximum is observed at m 2 /m 1 = 2 (where m 2 is
the mean atomic mass for compound). In the case of the light-target sputtering (BN), the Y(m 1 )
maximum is at m 2 /m 1 = 1. With increasing E 0 , the Y(m 1 ) maximum is shifted towards heavier masses
and then disappears.
Mean energies Ē 1 of particles sputtered by low-energy ions from AlN and GaN depend nonmonotonically
on m 1 with a maximum at the same values of m 1 as for Y(m 1 ). In BN, Ē 1 has maximum
for the lightest ions.
Energy spectra of a light component of nitrides, which give the main input to sputtering, differ qualitatively
for sputtering by low-energy ions of large and small masses. In the last case, the spectra have
longer high-energy tail and broader maximum of distribution that indicates more favorable conditions
of particle emission with higher energy.
Depths of origin x 0 of sputtered atoms for GaN and AlN increase with decreasing m 1 , particularly
sharp for small m 1 . For greater ion masses, at E 0 = 200 eV, the curves x 0 (m 1 ) reach a constant value at
x 0 ∼ 4 Å for AlN and GaN and slowly grow with m 1 for BN.
Distribution of the sputtering yield over the number of generations of emitted atoms differs significantly
for targets with light and with heavy masses of atoms. So, for BN, these are the tertiary recoils
that give the major contribution to sputtering. In the case of AlN and GaN, the sputtered atoms belong
to primary recoils at lower E 0 and to secondary recoils at higher E 0 .
A special feature of nitride sputtering is that the Y(m 1 ) curves reach saturation for lower values of E 0
than in the case of equivalent single-element target, with atomic mass equal to the mean of the
masses of the two components of the binary compound. This early saturation is caused by the presence
of the lighter component (i.e. N) in nitrides.
We would like to thank the Russian Foundation for Basic Research (grants 05-02-17227 and 05-02-
17870), and INTAS (grant 03-53-5607) for their support.
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