Integrity Assessment of Ceramic CVD Liners Against Plasma Loading

During the development of aluminum oxide liners for plasma enhanced CVD process, cracking was observed near the bottom and in the mid-section close to the zone of maximum power deposition. Major cracks were observed to run along the circumferential direction across the cylindrical liner and were caused by excessive tensile stresses resulting from temperature gradients or temperature transients induced by different operating conditions. Because of the pre-mature failure, a detailed characterization of the temperature profile was carried out on two ceramic liners using a combination of measurement and numerical modeling. Numerical modeling was performed using CFD-PLASMA and CFD-ACE+ numerical tools, heat transfer and stress finite element analysis (MSC NASTRAN). Results were in turn, used to obtain a better understanding the cause of the pre-mature failure. A probabilistic failure assessment procedure was used to explain the cause of the failure. Temperature gradients or temperature transients could be induced by different operating cycles. Temperature gradients could also occur across the wall thickness of the liner due to heating inside and cooling outside the liner, and along the inside wall in the axial direction due to non-uniform power intensity during normal material processing and cleaning cycles. Design improvement concepts were suggested in terms of more stringent material parameter and better cooling to alleviate any future potential failure.