T. Garcia, A. Dahl, T. Le, L. Majid
University of New Mexico,
United States
Keywords: statistical process control, measurement system analysis, gage reproducibility and repeatability, MEMS fabrication
Summary:
For consistent Micro-Electromechanical Systems (MEMS) fabrication, detailed control of etch profiles, thin-film thickness, and dimensional uniformity are critical in order to achieve consistent actuation behavior. However, release related variability often hinders yield and reproducibility in MEMS thermal actuators (bimorph cantilevers). This work seeks to identify and quantify key sources of that variability by applying Statistical Process Control (SPC) and Measurement System Analysis (MSA) to assess process variation, operator influence, and manufacturability in MEMS bimorph cantilevers fabricated, comparing and contrasting xenon difluoride (XeF2) and potassium hydroxide (KOH) release methods. Building on prior mask design and etch characterization work, this study focuses on the reproducibility of etch depth and undercut uniformity which determine how completely the structures are released. In addition, key release geometry parameters such as release hole size, spacing, and open area are analyzed to understand their influence on etch performance and structure integrity. This work compares XeF2 isotropic vapor-phase etching, which offers high selectivity release, with anisotropic KOH wet etching of crystalline Si (100 wafers) to evaluate how each affects release structure integrity and actuation reliability. Reliability is evaluated through functional go/no-go release testing and optical displacement measurements (in-plane or out-of-plane motion) to correlate release quality with actuator performance. Comparative analysis presented will show how the two different processes affect release completeness, etched surface morphology, and process repeatability. Profilometry, optical and scanning electron microscopy are used to quantify geometric parameters, while an abbreviated Gage R&R evaluates measurement precision across multiple measurement systems. The MSA determines whether instrument and operator variation remain below an acceptable threshold to validate subsequent future SPC findings. Within wafer and wafer-to-wafer uniformity analysis provides a basis for setting up small volume production SPC charts. These analyses highlight trends such as etch depth consistency, process centering, and potential drift sources including alignment accuracy or etch rate process fluctuations. Process capability indices (Cp, Cpk) are presented to quantify predicted manufacturability in bimorph cantilever designs. Emphasis is placed on the repeatability of the XeF2 and KOH etch release process and characterizations, providing a basis for subsequent design rules including release hole size, and hole distribution pattern enabling successful release of bimorph cantilever devices. By integrating MSA and SPC, this study aims to establish a quantitative framework for evaluating fabrication repeatability, identifying key sources of variation, and validating measurement reliability. These results will guide process parameter selection and measurement practices to support more consistent, high yield fabrication of MEMS bimorph cantilevers.