TRANSPORT OF SUBMICRON PARTICLES FROM A LEAK TO A PERPENDICULAR SURFACE IN A CHAMBER AT REDUCED PRESSURE

At subatmospheric pressure, thermodynamic conditions of semiconductor manufacturing processes change rapidly during pump down or venting ope rations. Important insights regarding the behavior of particles in rea l equipment can be obtained using simplified models and idealized expe riments under static conditions. Experimental and theoretical studies were performed in order to understand the particle transport into a ch amber and the particle deposition behavior on a free-standing wafer at reduced pressure (down to 10(2) Pa). The transport mechanisms taken i nto account were convection, diffusion and external forces such as sed imentation and thermophoresis. To model these particle transport proce sses, the analogy between the governing equations of momentum, energy and mass was applied to the extended diffusion equation. In their nond imensional form, the results of the numerical calculation give detaile d information about velocity, temperature and particle concentration b oundary layer thickness as well as their distributions. In particular, the influence of external forces on the particle concentration field in the vicinity of the Surface was investigated. The experimental stud y consisted of the generation of a monodisperse, fluorescent latex aer osol, the injection of the aerosol through a tiny capillary at the top of a vertical chamber at subatmospheric pressure and the deposition o f the particles on a cooled, free-standing wafer in the chambers cente r. The deposited particles were detected and counted by an optical mic roscope connected to an image processing unit. This paper presents the results from particle transport and deposition experiments conducted in a chamber while varying the pressure level and the temperature of t est surface. Copyright (C) 1996 Elsevier Science Ltd.