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Heating a Wafer – How Difficult Can it Be?
Temperature uniformity in wafer processing has always been an area requiring accurate
measurement and control in silicon based manufacturing. With new materials and scaling
challenges the need for temperature control has increased to the point that any deviation
from requirements can lead to manufacturing failure. Thomas Kupiszewski of Watlow
discusses how thermal design analysis is used in improving existing processes and even
extending the life of equipment.
A
mong the many processes involved in This article presents a case study examining the
fabricating integrated circuits, it is development of a rather unconventional pedestal heater to
deposition and dry etch which levy some of the most address an unusual confluence of thermal and structural
stringent requirements on the temperature uniformity of requirements which proved to be highly coupled and
wafer heaters. Both chemical vapor deposition and planar conflicted. The problem presented here was the
plasma etch often stand out as the most demanding modification of a legacy pedestal heater design for a new
applications of “superuniformity” solutions to the wafer application with an increased process heat load. The
heating problem, reference Figure 1. Common to such legacy heater configuration was characterized by a
processes is the need for a pedestal heater which concentric, dual control zone layout of spiraled heating
supports and transfers thermal energy to a target elements embedded in an aluminum casting.
substrate while maintaining surface temperature and
flatness profiles within acceptable limits over the life of the This product was supported on a bi-metallic shaft
equipment. as depicted in the left half of Figure 2. In the new
Fig. 1 Application domain for “super-uniformity” heating solutions. Optimized with the aid of realistic computer
modeling and simulation, Watlow pedestal heaters have exhibited impressive temperature uniformity performance
in fielded systems
November / December 2009 www.compoundsemiconductor.net 31
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