3D Micromachining

Lithography steps are followed by a number of subtractive and additive processes, transferring the lithography patterns into ICs or 3D micromachines. Table 3.2 is a partial list of subtractive steps used in building microstructures. In subtractive processes material is removed from the device under construction, usually very selectively, through the use of a resist or other mask pattern (e.g. an oxide or a nitride). 

Such confined etchant layer technique has been applied to achieve effective three-dimensional (3D) micromachining on n-GaAs and p-Si. It operates via an indirect electrochemical process and is a maskless, low-cost technique for microfabrication of arbitrary 3D structures in a single step [109]. It has also been presented that free-standing Si quantum wire arrays can be fabricated without the use of epitaxial deposition or lithography... 

D microfabiication 3D micromachining Fabrication of 3D microfluidic channels Microfab-licatiOTi of three-dimensi(Mial microstructures Three-dimensional patterning... 

The process of micromachining may be assisted by either dry or wet chemical etchants for building high-quality 3D micromachines. As an example, chlorine may be used as an etchant and is... 

Irradiation with ions was used on monocrystalline substrates prior to anodization, in order to manage the porous silicon properties. This allows technique of 3D micromachining of silicon... 

D microfabrication 3D micromachining Microfabrica-tion of three-dimensional microstructures Three-dimensional patterning Fabrication of 3D microfluidic channels... 

D Processing Technology 200 Sensors, Actuators and Passive Components 201 Bulk Micromachining Technology 201 Surface Micromachining of Silicon 205 Summary 205... 

Cheng, Y. Tsai, H. L. Sugioka, K. Midorikawa, K., Fabrication of 3D microoptical lenses in photosensitive glass using femtosecond laser micromachining, Appl. Phys. A. 2006, 85, 11 14... 

C. R. Tellier and S. Durand, Micromachining of(hhl) silicon stractures Experiments and 3D simulation of etched shapes, Sensors Actuators A 60, 168, 1997. 

Fabrication of 3D Metallic and 3D Ceramic Microstructures Based on Electrochemical Micromachining of A1... 

Bulk micromachining relies on several etching techniques and creates projections of planar photolithographic masks in 3 dimensions. Surface micromachining relies on sacrificial layer and wafer bonding techniques. It creates true 3D structures as a stack of 2D patterned layers. Hence, it is more correct to refer to both micromachining techniques as two and a half dimensional (2% D). 

Oxygen plasma cleaning. The integrated surface-micromachined wafer is exposed to an oxygen plasma to remove the photoresist and thus create free 3D structures as shown in Figure 5.2.9. 

Figure 3.1 A typical process sequence used in microfabricating a 3D microstructure. The fabrication tool used is bulk micromachining.

In micromachines, alignment is often even more complex than in IC manufacture. Indeed one not only deals with high-aspect-ratio 3D features, but often needs to align the 3D features on both sides of the wafer, as in the case of wafer to wafer (fusion bonding) [4] or wafer to glass bonding (anodic bonding)... 

The concept of unit removal (UR) was introduced by N. Taniguchi to differentiate the removal phenomena between micromachining and conventional machining [7], UR is defined as the part of worlqjiece removed during one cycle of removal action, i.e., material removal per unit pulse or unit time. When material removal is considered per unit time, it is called material removal rate (MRR). UR can be expressed in terms of one-dimensional, 2D, and 3D values, i.e., length, area, and volume, respectively. Since UR gives the limit of the smallest adjustable dimensions of the product, it should be much smaller than the size of the product. UR of submicrometer order is also required when the object size is very small or when high precision of the product is required. 

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