## 1 Introduction  
Within the realm of complementary metal oxide semiconductor microelectromechanical systems (CMOS-MEMS) fabrication, following the construction of CMOS circuitry upon the silicon substrate, MEMS structures (e.g., sensors, actuators) are subsequently established atop this circuitry. However, this integration process frequently necessitates modifications to the underlying layers [1], or the formation of intricate features that are potentially unattainable through conventional lithography or etching alone. In such scenarios, laser ablation emerges as a valuable tool. The advantageous nature of laser ablation in post-CMOS-MEMS processing stems from its inherent precision, minimal collateral damage to surrounding regions, and its versatility in addressing a diverse range of materials commonly employed in MEMS fabrication. Nevertheless, meticulous control over laser parameters such as power, wavelength, and pulse duration is paramount to mitigate the potential for undesirable effects, including thermal damage and unintentional material alterations. The emergence of laser ablation in the 1960s, coinciding with the development of lasers, initially served as a cornerstone for fundamental research in physics, particularly in understanding laser-material interactions. Early applications focused on ablating or removing material from surfaces using high-powered lasers. Subsequent advancements in laser technology propelled the development of diverse laser types, each with unique characteristics and applications. Excimer lasers, for instance, with their short wavelengths and high energies, excel at precise material removal [2]. This technological evolution broadenedthe reach of laser ablation into various fields, including microelectronics, semiconductor fabrication, medical device manufacturing [3], and cultural heritage preservation. Within the realm of material processing, laser ablation has become a pivotal technique for micro-machining, surface structuring, thin film deposition, and even micro/nano-scale feature creation with intricate patterns. Ongoing research and development in laser technology continue to refine laser ablation methods. The introduction of new laser sources, such as femtosecond lasers, enables even finer control and minimal thermal damage, unlocking the potential for novel applications and deeper integration across various industries. Our investigation leverages the TSMC/TSRI D35 common use process, which employs distinct materials for each layer (poly, oxide, via, metal, and silicon nitride (passivation)) to accommodate diverse design configurations. We meticulously fine-tuned a comprehensive array of laser parameters encompassing wavelengths, energy levels, interval time, pulse shots, and pad position, with the explicit objective of precisely removing silicon nitride [4]. The unique properties of Si\({}_{3}\)N\({}_{4}\), including its high mechanical strength, thermal stability, chemical inertness, and superior electrical insulating capabilities, have propelled its widespread adoption across various industries. In microelectronics, Si\({}_{3}\)N\({}_{4}\) serves as a crucial passivation layer, insulator, or mask material due to its exceptional electrical insulation properties, safeguarding underlying semiconductor devices from external influences. Furthermore, its compatibility with CMOS technology makes Si\({}_{3}\)N\({}_{4}\) an extensively utilized structural material in MEMS fabrication, offering both mechanical stability and resilience, while seamlessly integrating with the underlying CMOS circuitry. Prior to the widespread adoption of laser ablation for Si\({}_{3}\)N\({}_{4}\) removal in post-processing of CMOS-MEMS devices, several alternative methods were employed. Chemical etching, utilizing solutions such as hydrofluoric acid (HF), offered selective removal of silicon nitride while minimizing effects on other materials. Dry etching techniques, including reactive ion etching (RIE) and plasma-enhanced chemical vapor deposition (PECVD), were also implemented.