Three-Dimensional Simulation of Contact Hole Metallization using Aluminum Sputter Deposition at Elevated Temperatures

Abstract

A three dimensional D simulation program has been developed which is capable of simulating layer deposition on D geometries In this paper we present the application of the tool to the simulation of aluminum sputter deposition at elevated temperatures It is assumed that due to the higher temperature surface di usion of the atoms is possible In consequence the step coverage is better than for cold sputter deposition To model surface di usion a transport coe cient K is introduced as parameter which can be related to the di usion length Simulation results for di erent values of K are shown It turned out that if K is far larger than the dimension of the contact hole void free lling of the hole is achieved Introduction Current and future generations of integrated circuits require processes capable of lling high aspect ratio contact holes and vias Conventional sputtering at low temperature leads to only poor step coverage resulting in incomplete lling of the contact holes and vias This problem gets worse as the aspect ratios of the holes increase Thus speci c techniques have to be developed which are suitable for lling the holes One possibility is to carry out the sputtering process at an elevated temperature allowing surface di usion of the metal atoms before they are incorporated into the growing layer In consequence the atoms are distributed more uniformly over the entire structure leading to improved contact ll Model and D Implementation In this paper we present an approach to model surface di usion during re ow sputtering at elevated temperatures For this purpose a D simulator which had originally been developed for the simulation of low pressure chemical vapor deposition LPCVD processes was extended In LPCVD simulation particles from gas space which hit the surface are incorporated into the growing layer with a certain probability the so called sticking coe cient For sputter deposition a sticking coe cient equal to can be assumed i e no desorption of the metal atoms from the surface takes place The geometry is described by a set of triangles which are shifted according to the growth rates calculated from the particle ux of atoms arriving from the gas volume at this triangle To include surface di usion particle transport between neighboring triangles i e between triangles with one side in common has to be taken into account A transport coe cient K depending on temperature and process time is introduced as the model parameter The rate of particle exchange between neighboring triangles is proportional to K It has been shown that the di usion length is of the same order of magnitude as K For each surface triangle a dynamical equilibrium between positive and negative particle uxes is assumed The positive uxes are due to particles arriving from the gas volume or neighboring triangles the negative uxes are due to particle consumption by incorporation into the growing lm or due to particles di using to neighboring triangles The corresponding equations are solved numerically on the triangular surface grid A system of linear equations in the layer growth rates has to be solved The elements of the system matrix depend on the geometry i e the shape and orientation of the triangles and the solid angles open to the gas volume with respect to the di erent triangles and on the transport coe cient K Figure D simulation of aluminum sputter deposition with negligible surface di usion into a cubic contact hole The bars represent m