Modeling for Resist Reflow of an Elongated Contact Hole

Abstract

Resist reflow is a simple and cost effective technique by which the resist is baked above the glass transition temperature (Tg) after the typical contact hole pattern has been exposed, baked, and developed. The resist reflow method can obtain very high resolution without the loss of process margin compared to any other resolution enhancement technique that can make the same line width. However, it is difficult to predict the results of thermal flow and process optimization. If the results of reflow could be exactly predicted, we could save great time and cost. Thus, in order to optimize the layout design and process parameters, we develop a simple resist flow model that can predict the resist reflow as a function of the contact hole size, the initial shape, and the reflow temperature for normal and elongated contact holes. The basic fluid equation is used to express the flow of the resist, and the variations of the viscosity and the density as functions of the reflow temperature and time are considered. Moreover, the surfaces tension and gravity are considered. In order to build a basic algorithm, we assume that the fluid is incompressible, irrotational, and Newtonian. First, we consider the boundary movement of a side wall, and we think of the basic equations for a free surface flow of a fluid as the 2-dimensional time-dependent Navier-Stokes equations with the mass conservation equation. The surface tension acting on the interface, the pressure difference, and the gravity force that enables the resist flow are also included.