Poly si p1p2 and p3 deposition are high temperature

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Poly-Si (P1,P2, and P3) deposition are high temperature steps ( 650-800 o C), Al metallization will melt if used for CMOS interconnects. Tungsten can withstand this high temperature. (b) (5 points) Why is silicon nitride used as the passivation layer for the CMOS instead of silicon oxide ? During sacrificial layer (usually oxide) etch for MEMS release, silicon nitride passivation layer will protect the CMOS area from etching. (c) (5 points) What is the purpose of the Etch Hole shown in the MEMS structure ? Etch holes allow etchant having easy access to sacrificial layer underneath , shortening lateral undercut etching time (d) (5 points) What is the function of the Limit Stop shown in the MEMS structure? Electrostatic deflection more than ~1/3 of gap height will collapse the beam towards the bottom. The Limit Stop can prevent excessive deflection. The Limit stop also minimize the contact area during MEMS release (stiction problem)
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