A New Flexible Rapid Thermal Processing System

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Introduction Rapid thermal processing (RTP) technology is a necessary ingredient to achieve the concepts of a programmable factory with flexible equipment. Because of its low thermal budget it is eminently suited for performing thermal steps in submicron ULSI manufacturing. The temperature and process environment can be changed very quickly. The acceptance of Rapid Thermal Processing in the IC industry has been restricted by temperature nonuniformity, mainly caused by the nonuniform nature of wafer radiation heat loss, convective cooling, as well as inappropriate lamp design. In the commercially available RTP equipment once the lamp array, the reflector and chamber geometries are chosen, the light flux distribution is fixed, and there is no possibility of further control of the spatial flux profile. Various methods, such as guard rings, specially shaped reflectors, have been tried to compensate for the nonuniform heat loss. However, these methods have been unable to solve this problem fully. At Stanford University extensive work has been done on equipment design, sensors and control to overcome this problem. In our earlier work we had demonstrated that through the use of multizone lamps with multi-variable control improved temperature uniformity can be achieved [1,2]. However, in that work the lamp development was done through extensive experimentation and past experience. Although substantial improvement was obtained over the linear lamp approach, the lamp design was not fully optimized with significant scope for improvement. In this paper a "virtual reactor" methodology has been demonstrated through the development of a new lamp system for single wafer Rapid Thermal Multiprocessing (RTM) reactor using a newly developed three-dimensional thermal simulator. Given the equipment configuration, e.g., the lamp array, a three-dimensional simulator is used to predict the wafer temperature profiles for various lamp array designs for different processing conditions. The only experimental input needed is the spatial light flux distributions of the individual tungsten-halogen bulbs making the lamp array. Using the simulator the design of the lamp array can be optimized to obtain the best possible temperature uniformity. Based on this approach, a new RTP system with an adjustable reflector and multi-variable control has been designed. We also describe a new acoustic sensor which non-invasively allows a complete wafer temperature tomography tinder all process conditions. The presently available temperature 307 Mat. Res. Soc. Symp. Proc. Vol. 389 0 1995 Materials Research Society

measurement techniques are either invasive or are seriously dependent upon wafer surface conditions which changes during processing. The acoustic temperature sensor infers the temperature by measuring the velocity of sound through the bulk of the wafer and hence is insensitive to wafer surface conditions and the process environment. Problems of the conventional approach The problems of RTP can be understood through modeling and simulation of the ther