A New Thin Film Growth/Regrowth Process Design and Experimental Comparisons with Molecular Dynamic Analyses
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A NEW THIN FILM GROWTH/REGROWTH PROCESS DESIGN AND EXPERIMENTAL COMPARISONS WITH MOLECULAR DYNAMIC ANALYSES TAKAKO K. OKADA%, SHIGERU KAMBAYASHI*, MOTO YABUKI*, YOSHITAKA TSUNASHIMA*, YUICHI MIKATA** and SHINJI ONGA* ULSI Research Center, Toshiba Corporation, Kawasaki, 210, Japan 0*Integrated Circuit Advanced Process Engineering Department, Toshiba Corporation ABSTRACT A new concept of thin film growth/regrowth process design taking atomic motions into account using molecular dynamics is proposed. In the system, a modified many-body Tersoff-type interatomic potential for silicon has been adopted. The mathematical derivation of higher order derivatives was rigorously treated. Among many applications, the solid phase growth process was studied. It has been found from simulation studies that the solid phase growth of crystalline silicon proceeded along the [110] direction layer by layer. Furthermore, it has been obtained that all the atoms are activated in an extremely thin amorphous silicon film. Based on simulated results, an experiment using an extremely thin amorphous silicon film was carried out. It has been found that the perfect spherical silicon crystals with a uniform size and spacing can be grown from a thin amorphous silicon film. INTRODUCTION A deep understanding of the atomistic mechanisms, energetics, and dynamics of a thin film growth/regrowth process is indispensable for future process designing in scaled devices. Otherwise, technical problems in an advanced process can not be settled. From this viewpoint, the authors have developed a new simulation system employing the molecular dynamics (MD) method in order to examine the dynamic processes in microscopic scales. In this work, as one of many applications, individual atom motions during the crystallization process of amorphous silicon were mainly examined by solving Newtonian equations using an effective empirical silicon potential developed by TersoffP). Amorphous silicon has been formed by a rapid quenching method using the Andersen constant-external-pressure form of molecular dynamics2). The following matters are discussed; (i) details of the newly developed simulation system, (ii) accuracy and validity of the system, (iii) applications to the solid phase growth process of crystalline silicon. Furthermore, several experiments on solid phase growth were carried out to compare with the simulated results. Experimental results are also presented. THE MODEL Let us consider silicon atoms enclosed in a MD cell with periodic boundary conditions. In constant-external-pressure molecular dynamics, the Lagrangian equation presented by Andersen is used which has the form L( p, p, Q, Q
1 2 -LL
21
n_,pi2- U(Lp) +
-Q-
2
2 with
.62 PFQ
l]
Q
1
pi = ri/L = ri/Q 3 ,
(1.2)
where m is the mass of an atom, ri is the position vector of particle i, U is the potential energy, PE is the external pressure, Q is the volume of the MD cell, and M is a constant. The equations of motion derived from the Lagrangian in Eq. (1.1) are given by F
2.Q
=ML 3
S=
P-
PE(1.4
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