Multiproject wafer processes

Shallow holes, approximately 0.75 pm deep, which do not go all the way through the 2 pm thick oxide, are defined using the DIMPLE mask. These dimple holes are later filled in with Polyl to form tiny stalactites that hang down from the bottom of Polyl to limit the amount of surface area contact between Polyl and PolyO. Surface forces such as van der Waals and capillarity dominate on a microscale, which can lead to surfaces sticking together. This is so prevalent in microelectromechanical 

After patterning the Oxide2 layer with anchors and vias, the second layer of released structural polysilicon is deposited, annealed, and patterned following the procedures used for Polyl. Poly2 is 1.5pm thick and has a compressive residual stress of —10 MPa and a resistance of 20 O/D. A common use for this structural layer is to provide constraints for features defined in Polyl, such as a hub that constrains a rotor in an electrostatic motor [9], [10] or a staple that constrains a pin in a hinge [11], [12]. It is also possible to make a 

The final layer is a 0.5 pm thick gold metal layer on top of Poly2 for wires, bond pads, bimorphs, and potentially as an optically reflective surface. The gold is deposited on top of a thin (20 nm) chrome layer to promote adhesion. It is not possible to deposit gold on top of the Polyl layer. For a flat mirror to be formed, the stress-induced curvature from the metallization should be comprehended in the design [13]. 

2 Sandia Ultra-planar Multilevel MEMS Technology V 

This process has been used in early prototyping of MEMS mirror arrays for applications in adaptive optics, optical switching, and deformable grating arrays [16], [17]. The SUMMiT IV process was transferred from Sandia National Laboratories to Fairchild Semiconductor International but has since been discontinued. Fairchild was the only company that offered this technology for foundry manufacturing. 

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Lay out a tunable Fabry-Perot optical filter in a multiproject wafer process as shown in Figure 4.24. The top Bragg mirror should be composed of a stack of dielectric films and should be flat to within a fraction of a wavelength of light that will be filtered. 

Design a fluidic pump in a multiproject wafer process. The pump should have a volumetric flow rate of 20 nL/s for water through a 100 pm X 100 pm microchannel that is 1 mm long. What pressure difference is required to achieve this flow rate Before starting, perform a literature search to see what has been done in the past. 

The book ends with a case study of a commercial MEMS device, a deformable mirror for applications in adaptive optics, first prototyped using the PolyMUMPS process, that eventually went on to become a product offered by Boston Micromachines Corporation. This case study demonstrates that there is a path-to-the-sea from MEMS prototyping in a standard multiproject wafer fabrication process to commercialization of a robust MEMS product. Once the prototype was designed, fabricated, and tested using a multiproject wafer fabrication process, PolyMUMPS,... 

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