Presentation Details
Kinematic and Static Equilibrium Analysis of Five-Pin and Three-Pin Graphite Boat Designs for Stable PECVD Wafer Handling

Siddhant Kaushik.

University of California, Berkeley, Berkeley, CA, USA

Abstract


Plasma arcing and wafer misalignment remain important failure modes in PECVD graphite boats used for silicon wafer handling. In this study, a baseline five-pin graphite boat was compared with a redesigned three-pin gravity-wedge configuration using kinematic design principles, static equilibrium analysis, and MATLAB-based pin-location optimization. In the five-pin configuration, the wafer was nominally supported at five contact locations; however, production observations showed that the wafer did not seat deterministically on all pins. Instead, the active contact condition shifted with robotic placement, machining variation, wafer tolerance, and thermal loading. This resulted in incomplete wafer support, repeated wafer misalignment over more than 100 loading cycles, and process aborts in over 45% of the production test runs. By contrast, the redesigned three-pin gravity-wedge configuration was developed to provide exact and repeatable constraint for the critical in-plane wafer motions. Reaction-force analysis showed positive support forces at both room temperature and 500°C, while the selected asymmetric layout preserved a positive gravity-driven wedging force. These results indicate that replacing the baseline five-pin geometry with a properly positioned three-pin gravity-wedge configuration is a more robust path to reducing wafer misalignment and improving PECVD wafer-handling reliability.

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