Nanoindentation Characterization of PECVD Silicon Nitride on Silicon Subjected to Mechanical Fatigue Loading

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Nanoindentation Characterization of PECVD Silicon Nitride on Silicon Subjected to Mechanical Fatigue Loading Z-K Huang, K-S Ou, and K-S Chen Department of Mechanical Engineering National Cheng-Kung University Tainan, Taiwan, 70101 ABSTRACT In this work, the mechanical properties of PECVD silicon nitride deposited on silicon substrates by two different processing conditions were investigated. Indentation method was primary used for qualitatively examining the effect of process conditions to the achieved mechanical properties. The experimental results indicated that the residual stress, fracture toughness and interfacial strength, as well as the fatigue crack propagation were strongly depended on the processing conditions such as deposition temperatures and chamber pressures. Preliminary results indicated that the specimen deposited at a lower temperature and a lower pressure exhibited a much less residual tensile stress and a better interface strength. On the other hand, it was found that RTA could enhance the interfacial strength but the generated high tensile strength could actually reduce the equivalent toughness and leads to structural reliability concerns. In summary, the characterization results should be possible to provide useful information for correlating the mechanical reliability with the processing parameters for future structural design optimization and for improving the structural integrity of PECVD silicon nitride films for MEMS and IC fabrication. INTRODUCTION PECVD nitride films are important and common structural materials used in microsystems applications such as transduction structures, barriers, and mask layers. The mechanical properties of silicon nitride are therefore essential for overall device reliability assessments. In particular, the fatigue and interfacial properties of PECVD nitride coated silicon structures subjected to thermo-mechanical loading will influence the structural longevity of integrated circuits or MEMS actuators. As a result, it is desired to perform characterization to understand the influence of processing and operating conditions such as deposition parameters and thermal annealing as well as service loading for structural longevity concerns. Our previous investigation [1] on PECVD silicon nitride using nanoindentation technique indicated that the residual stress and the fracture toughness, as well as the interfacial strength were major controlling factors for governing the mechanical reliability issue and these factors strongly depend on deposition and post-deposition thermal processing parameters. In this work, a further investigation was conducted by using PECVD nitrides fabricated by two different process conditions followed by a rapid thermal annealing (RTA). In addition to the residual stress and interface delamination characterizations preformed in our previous work, the mechanical fatigue tests also implemented in this work to further evaluate the longevity of silicon nitride films subjected to repeat mechanical loadings, which could be a concern for MEMS sensor