Page 200 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

180 MICROSTEREOLITHOGRAPHY FOR MEMS

and therefore post-CMOS batch fabrication is also feasible (Ikuta et al. 1996; Zissi
1996).
Different MSL systems have been developed in recent years to improve upon their
precision and speed. Basically, scanning MSL (Ikuta and Hirowatari 1993; Zissi el al.
1996; Katagi and Nakajima 1993; Zhang et al. 1999; Maruo and Kawata 1997) and
projection MSL (Bertsch et al. 1997; Nakamoto and Yamaguchi 1996; Monneret et al.
1999) are the two major approaches that have been taken. Scanning MSL builds the solid
microparts in a point-by-point and line-by-line fashion (Figure 7.8), whereas projection
MSL builds one layer with each exposure (Figure 7.9), thus speeding up the building
process by a significant factor (Beluze et al. 1999). The details of the two approaches are
presented in Sections 7.3 and 7.4.
Another research effort in MSL is the incorporation of a broad spectrum of mate-
rials to create MEMS with new special functions. The MSL fabrication of polymer

Z-stage

Y- stage

Figure 7.8 Principle of scanning MSL, that is, a vector-by-vector approach. From Beluze et al.
(1999)

Focusing optics -*

Photoreactor

Figure 7.9 Principle of projection MSL, that is, a plane-by-plane approach. From Beluze et al.
(1999)