Articles written in Sadhana
Volume 34 Issue 4 August 2009 pp 543-556
Fabrication of Micro-Electro-Mechanical-Systems (MEMS) requires deposition of ﬁlms such as SiO2, Si3𝑁4, ZnO, polysilicon, phosphosilicate glass (PSG), Al, Cr-Au, Pt, etc. for use as structural, sacriﬁcial, piezoelectric and conducting material. Deposition of these materials at low temperature is desirable for fabricating sensors/actuators on temperature-sensitive substrates and also for integrating MEMS structures on silicon in post-CMOS processing procedures. Plasma enhanced chemical vapour deposition (PECVD) and sputtering are amongst potential techniques for preparing ﬁlms for MEMS fabrication at comparatively low temperatures. The sputtering technique has an added advantage that the process is carried out in an inert ambient (argon) and chemically sensitive substrate/sacriﬁcial layers can be used in realization of MEMS. Furthermore, the same system can be used for depositing dielectric, piezoelectric and conducting materials as per requirement in the fabrication sequence. This enables rapid low-cost prototyping of MEMS with minimum fabrication facilities.
In the present work, we report preparation, characterization and application of RF sputtered SiO2, Si3𝑁4 and ZnO ﬁlms for MEMS fabrication. The effect of RF power, sputtering pressure and target-to-substrate spacing was investigated on the structural and other properties of the ﬁlms. The residual stress in the ﬁlms was obtained using wafer curvature measurement technique. The deposition parameters are optimized to obtain low stress ﬁlms of SiO2 and Si3𝑁4. The self-heating of the substrate during deposition was advantageously exploited to obtain highly 𝑐-axis oriented ﬁlms of ZnO without any external heating. A variety of MEMS structures such as cantilever beams, micro-bridges, diaphragms, etc. are demonstrated using bulk, surface and surface-bulk micromachining techniques.
Volume 34 Issue 4 August 2009 pp 563-572
In the present work, we report the preparation of PLZT thin ﬁlms in pure perovskite phase by RF magnetron sputtering without external substrate heating and their integration with micro-cantilevers. The ‘lift-off’ process for patterning different layers of a micro-cantilever including PLZT, Pt/Ti and Au/Cr was employed. The basic requirement of lift-off process is that the deposition temperature should not exceed 200°C otherwise photoresist will burn out. Therefore, one of the aims of the present work was to prepare PLZT ﬁlm at lower deposition temperatures, which can be subsequently annealed to form pure perovskite phase. This also strongly favours the incorporation of ‘lift-off’ process for patterning in the complete process ﬂow. As no external substrate heating was required in the deposition of PLZT ﬁlm, this objective has been successfully accomplished in the present work. The ‘lift-off’ process has been successfully adopted for patterning the composite layers of PLZT/Pt/Ti and Au/Cr using thick positive photo-resist (STR-1045). Different types of cantilever beams incorporating PLZT ﬁlms have been successfully fabricated using ‘lift-off’ process and bulk micromachining technology. The proposed process can be advantageously applied for the fabrication of various MEMS devices.