A Model of a Combined Film Deposition and Ion Bombardment for Coatings Formation
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A MODEL OF A COMBINED FILM DEPOSITION AND ION BOMBARDMENT FOR COATINGS FORMATION Z.A.ISKANDEROVA, T.D.RADJABOV, R.Yu. LEIDERMAN AND F. K. TUKFATULLIN Institute of Electronics, Uzbek Academy of Sciences, Academgorodok, 700143, Tashkent, USSR
ABSTRACT The mathematical model of a combined film deposition and and high dose ion implantation for coating formation has been developed. Calculations of concentration profiles of implanted element in the film and substrate depending on different parameters of the model have been carried out.
INTRODUCTION The combined deposition and ion irradiation method for improved films and coatings has recently found a wide applica-
tion. Preliminary ion-beam treatment of the substrate, simultaneous or alternating film deposition and ion bombardment from a source or at glow discharge, ion implantation at a (specific) intermediate of final stage of multi-layer structure formation, and also various combinations of the above techniques are used /1-8/. This often achieves composition and structure controlled coatings with improved adhesion and better mechanical and physico-chemical characteristics /1,3,5,7,9/. In many cases, the effect is
determined by not only an altered
film structure but production of film-substrate interfaces and new phases or compounds in the coating proper as well, resulting from ion implantation, especially to high fluences. Here, the concentration level and distribution of an impurity to be implanted play a decisive role and this is the subject of
this paper.
A MATHEMATICAL MODEL The simplest mathematical model of a combined deposition and bombardment process is based on the first
/10-12/
S•(•,)
order equation
-•V(ýJ2- n (., t) -- 1(t) f(-x).(1
Here n(t,i) is the density of an impurity to be implanted (atom c&-3); V(t)z a(t)-o(ti, where - (t(is the rate of the de-
position-induced move of the surface; o(t) is the surface sputtering rate; Z(t) is the ion flux density (ion cm- 2 s- 1 );FfY) is the function of ion ranýe distribution. With the initial condition nf(xo) =0 and VW0): 0, the solu-
tion of eq. (1) is nz,)I
'S(S(XJ,
whereB(x) =1 if xO
sV(.s, )F(X
1
i,
S,
(x) =0? if x < 0. Equation (2)
(2)
is valid
(neglecting diffusion and ion mixing) provided n(xt)/No 4- 1, where IV. is the atomic density of the film substance. To
estimate the implanted particle concentration for high irradiation doses, we shall proceed from a more general equation
Mat. Res. Soc. Symp. Proc. Vol. 128. '1989 Materials Research Society
170
where the
T& is the effective atomic volume of implanted species, JZ/ oX'JyFK) integral known to be the function of the layer
"swelling" at the expense of the ions-at-rest trapped by the film /13-15/. Strictly speaking, both V[t) and F(ri) are the functionals of n(x,t ) : V(t) -V(t; ne'o, t)) , F(r) -F('x, n(z.,t)) . In the examples below, however, the values of J2n(6o,t,)is small enough (or rigorously equal to zero) that the Vit) dependence on n(ot) can be neglected. To obtain solutions in an analytical and fairly simple form, we
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