In MEMS fabrication, stiction is a core bottleneck that limits yield and performance. During micro/nano structure formation, from lithography and etching to deposition and release, unwanted adhesion may occur between microstructures and the substrate or between neighboring microstructures. This can damage devices, cause functional failure and increase manufacturing cost.
At the micro/nano scale, van der Waals forces, capillary forces and electrostatic forces become dominant. During wet etching release, residual liquid evaporation can generate capillary forces and cause release stiction. In dry processes such as plasma etching, charge accumulation may create electrostatic attraction. Surface contamination and residual structural stress caused by mismatched process parameters can also intensify stiction.
Process-parameter optimization is the foundation for reducing stiction. In lithography, suitable photoresist should be selected and spin-coating and baking parameters should be optimized to ensure uniform coatings without bubbles. In etching, wet processes require careful control of solution concentration, temperature and time, while dry etching should adjust plasma power and gas ratio to reduce charge accumulation. In release steps, gradient drying can replace direct drying to lower capillary-force risk.
Surface modification is an important method for improving anti-stiction performance. Self-assembled monolayers (SAMs) can form low-surface-energy films on microstructures and are compatible with many MEMS processes. Plasma treatment can remove contamination and change surface properties. Diamond-like carbon (DLC) films and PTFE coatings deposited by PVD or CVD can also enhance anti-stiction behavior, though coating thickness must be controlled to preserve device accuracy.
Stiction can also be reduced through structural design. Hollowed structures, support posts or micro-bumps can reduce contact area. Sacrificial-layer isolation can be introduced in areas prone to adhesion, then removed precisely to realize non-contact release.
Environmental control is also essential. MEMS fabrication requires strict temperature, humidity and cleanliness control. A typical environment may maintain temperature around 23±2°C and relative humidity around 40%±5% to reduce capillary adhesion. Cleanroom cleanliness and anti-static, anti-contamination packaging help reduce particles, charge accumulation and surface contamination.
Stiction in MEMS fabrication is caused by multiple factors and must be addressed through coordinated process optimization, surface modification, structural design and environmental management. Future anti-stiction materials, advanced processes and intelligent control systems will continue to improve MEMS yield and reliability.
