Polyimide sacrificial layer and novel materials for post-processing surface micromachining

Abstract

We present a low-temperature post-processing module, utilizing polyimide as a sacrificial layer and novel materials such as PECVD SiC and metals (sputtered aluminium and titanium) as structural layers. The use of spin-on polyimide allows an all-dry final release step overcoming stiction problems often encountered in wet sacrificial etching processes. The spinning and curing procedure has been tailored to the specific needs of the IC-compatible post-process module. For the patterning of the polyimide, thin films of aluminium, PECVD silicon oxide or silicon carbide are employed as a mask layer. Anisotropic etching of the mask film and of the polyimide layer is accomplished by RIE. After patterning the structural layer, sacrificial etching of the polyimide is done using an isotropic dry etch process in high-density oxygen plasma. An underetch rate of 4 μm min−1 is achieved. Compatibility with different structural materials is tested and test structures are designed and realized in a fully post-processing surface micromachining module.

Residue-free plasma etching of polyimide coatings for small pitch vias with improved step coverage

“…When PI is used as sacrificial layer, isotropic etching is used in order to release the top functional layer. 8 PI is also very often used as dielectric layer, or as substrate material for flexible applications. In this case, different types of etching are required for the fabrication of electrical vias running through the PI layer.…”

Integrated MEMS: Opportunities & Challenges

“…One PECVD layer with good mechanical properties is SiC (Pakula, 2004). With these low temperatures layers such as polyimides (Bagolini, 2002) can be used as sacrificial layer.…”

Micro‐ and nanomechanical structures for silicon carbide MEMS and NEMS

“…Using the same PSG-based release process, a surfacemicromachined sensor capable of measuring from 10 mbar up to 5 bar, has been reported. The reported sensitivity is Figure 16 Schematic cross-sectional diagrams showing the key fabrication steps for a surface micromachined a-SiC : H capacitive pressure sensor: (a) Al and polyimide deposition and patterning to form lower electrode and sacrificial layer, (b) a-SiC : H deposition, (c) Al deposition and pattering, (d) a-SiC : H deposition and patterning to form sensor membrane, (e) etch window definition for membrane release, and (f) release and window capping [161].…”