Molecular dynamics simulations of wafer bonding
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Molecular dynamics simulations of wafer bonding Kurt Scheerschmidt Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle/Saale, Germany, [email protected] Tel: +49-345-5582910, Fax: +49-345-5582917
ABSTRACT Molecular dynamics simulations using empirical potentials have been employed to describe atomic interactions at interfaces created by the macroscopic wafer bonding process. Investigating perfect or distorted surfaces of different semiconductor materials as well as of silica enables one to study the elementary processes and the resulting defects at the interfaces, and to characterize the ability of the potentials used. Twist rotation due to misalignment and bonding over steps influence strongly the bondability of larger areas. Empirical potentials developed by the bond order tight-binding approximation include π-bonds and yield enhanced interface structures, energies, and transferability to new materials systems. INTRODUCTION Wafer bonding, i.e. the creation of interfaces by joining two wafer surfaces, has become an attractive method for many practical applications to microelectronics, micromechanics or optoelectronics [1,2]. The macroscopic properties of bonded materials are mainly determined by the atomic processes at the interfaces during the transition from the adhesion state to the chemical bonding. Thus, the description of the atomic processes is of increasing interest to support the experimental investigations or to predict the bonding behaviour. While, in principle, it is now possible to predict material properties by using quantum-theoretical ab initio calculations with a miminum of free parameters, the only method to simulate atomic processes with macroscopic relevance is the molecular dynamics (MD) method using suitably fitted manybody empirical potentials. Such simulations enable a sufficiently large number of particles and relaxation times up to µs to be considered. However, the electronic structure and the nature of the covalent bonds can only be described indirectly. Therefore, it is of importance to find physically motivated semiempirical potentials starting mostly with the moments of the electron density and using tight-binding representations [3-5]. The MD simulations have successfully been used to describe ultra-high-vacuum bonding experiments for Si(100) [6], hydrogen passivated hydrophobic bonding processes [7], and to analyze the defect structure at bonded interfaces [8-10]. Simulations for SiC [11] were possible using the Tersoff [12] potential, whereas the predictions of the bondability of diamond have been performed using a bond-order potential [13]. Simulations of the bonding of amorphous silica (aSiO2) surfaces [14,15] may be the basis or a first step to describe hydrophilic wafer bonding. Conventional transmission (TEM) and high resolution electron microscopy (HREM) structure I2.3.1
imaging has been applied to investigate the resulting interfaces and the defect structures at an atomic level [16], the MD relaxed structures are the basis to calculate TEM and HREM i
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