A recent development in the field of electro-mechanics has been the miniaturization of various mechanical devices. Typical of such devices are tiny gears, levers, and valves. These "micro-mechanical" devices are manufactured using integrated circuit techniques, often together with electrical control circuitry. Common applications include accelerometers, pressure sensors, and actuators. As another example, micro-mirrors can be configured for use in spatial light modulators.
For fabricating micro-mechanical devices, as with electrical integrated circuits, a carrier, known as a wafer, has thin-film materials selectively deposited and patterned on it. Thin-film deposition and wet and dry etching are integral parts of the fabrication process. The thin films are patterned to provide structural elements of the micro-mechanical elements. Sacrificial etching is used to provide a "spacer layer", which is a soluble layer that is grown or deposited for later removal from beneath structure that has been patterned above it. The removal is usually by wet etching. The patterned structure is left behind, with an air gap between it and its underlying structure. The air gap permits the formation of elements that move, such as by rotating, bending, or tilting.
One type of micro-mechanical spatial light modulator is a digital micro-mirror device (DMD), which has an array of tiny tilting mirrors. For freedom of movement, each of these mirrors is mounted on one or more post-supported hinges and spaced by means of an air gap, over underlying control circuitry. A typical sequence of steps for manufacturing the mirrors and their hinges is to etch the support posts, provide sacrificial spacer material between the support elements, fabricate the mirrors and hinges on the surface of the spacer material such that each hinge is in contact with its support post, and remove the sacrificial material. Many DMD designs call for the sacrificial material to be provided in a manner that provides a surface that is co-planar with the top surfaces of the support elements. In the past, this has been accomplished by at least two steps that include depositing a layer of sacrificial material over the support elements and selectively etching away the material over the support posts. Typically, the selective etching requires use of a mask.