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1993_JCG_Davis.pdf

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JournalofCrystalGrowth132(1993)513—522 o,CRYSTAL North-Holland GROWTH

Numerical modeling of particle dynamics in a rotating disk chemical vapor deposition reactor

R.W. Davis, E.F. Moore and M.R. Zachariah

Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA

Received 22 December 1992; manuscript received in final form 10 May 1993

Particle contamination is considered to be one of the major pro DIem areas in the processing of semiconductors via chemical vapor deposition (CVD). Thus it is very important to acquire an understanding of particle transport processes in CVD reactors.

This paper addresses this issue by presenting the results of a numerical simulation of particle dynamics in a rotating disk CVD reactor. The background flowfield calculation employs the full axistmmetric Navier—Stokes equations, while individual particle trajectories are computed by accounting for inertial, thermophoretic and gravitational effects. The results of this simulation are analyzed to determine under what conditions particles greater than 1 ~sm in diameter impact and thus contaminate the deposition substrate. It is shown that particle size and injection location as well as flow direction (with or against gravity) and disk characteristics (temperature and rotation rate) all play important roles here. The results for various parameter combinations are presented and discussed, as is the concept of a global type of particle contamination parameter.

Introduction

Particle contamination is considered to be one of the major limitations in the efficient processing of semiconductors during chemical vapor deposi- tion (CVD). For micro-electronics fabrication of feature sizes less than 1 ~.tm,as much as 75% of the yield loss can be attributed to particle con- tamination of the wafer. Since one of the major goals of the semiconductor industry is shrinkage of feature size, the particle contamination issue assumes great importance. There are two major sources of particle contamination: (1) cleanroom air, process gases and people in the cleanroom, and (2) new particle formation inside the CVD reactor through chemical and physical processes. Because of the extensive effort applied to control- ling entry of particulates into the process, the first of these sources has largely been eliminated. At present, more than 80% of the total contami- nant particles come from the chemical processing steps and the mechanical movement of equip- ment.

In order to develop methods for controlling contaminant motions inside CVD reactors, it is

first necessary to understand the particle dynam- ics involved. Of particular concern is the question of under what conditions particles impact and i:hus contaminate the deposition substrate. The purpose of the present paper is to address this issue in the context of gm-size particles in the vertical rotating disk CVD reactor. The results of a numerical simulation of flow and particle dy- namics in this type of reactor will be presented. These results indicate the major parameters in- fluencing whether or not particles greater than 1 j~min diameter impact the substrate, and thus provide possible mechanisms for contaminant control.

2. Vertical rotating disk CVD reactor

The configuration selected for this study is the vertical rotating disk CVD reactor (fig. 1). This configuration has been the subject of numerous

0022-0248/93/$06.00 © 1993 — Elsevier Science Publishers B.V. All rights reserved

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 Supercritical Fluid Extraction 1993_JCG_Davis.pdf Page 001
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