Surface micromachining is a process used to create integrated circuits and sensors with up to 100 layers of circuit patterns on a chip. It uses selected materials and wet and dry etching processes to form the layers. This process is used in motion sensors, accelerometers, gyroscopes, and consumer electronics. The process uses crystalline silicon chip substrates or cheaper glass or plastic substrates. Wet and dry etching processes are used to engrave the circuit designs into the layers.
Surface micromachining is a manufacturing process used to develop integrated circuits and sensors of various kinds. The use of surface micromachining techniques allows for applications of up to nearly 100 finely applied layers of circuit patterns on a chip. By comparison, only five or six layers are possible using standard micromachining processes. This allows many more functions and electronics to be incorporated into each chip for use in motion sensors, accelerometers that activate airbags in a car crash, or for use in navigation system gyroscopes. Surface micromachining uses selected materials and both wet and dry etching processes to form the layers of the circuit boards.
Parts of the circuitry made using this method were first used in accelerometers, which activated airbags in vehicles in the event of an accident. Micromachined surface sensors in vehicles also provide rollover protection via tilt control and are used in anti-lock braking systems. This circuit is also used in high performance gyroscopes in guidance control systems and navigation systems. Because circuits produced using this method produce small, precise circuits, it is possible to combine multiple functions on one chip for uses in motion sensing, flow sensing, and some consumer electronics. In photography, when shooting with a video camera, these chips give image stabilization during movement.
The surface micromachining process uses crystalline silicon chip substrates as the foundation on which to build layers or can be started on cheaper glass or plastic substrates. Usually, the first layer is silicon oxide, an insulator, which is etched to the desired thickness. A layer of photosensitive film is applied over this layer and ultraviolet (UV) light is applied across the circuit pattern overlay. Subsequently, this wafer is developed, rinsed and cooked for the subsequent etching process. This process is repeated multiple times to apply multiple layers, with careful monitoring and precise etching techniques applied to each layer, to produce the final layered chip design.
The actual surface micromachining process of the engraving is done by one or a combination of multiple machining processes. Wet etching is done using hydrofluoric acids to etch circuit designs into the layers, cutting through unprotected insulating materials; the unetched areas of that layer are then electrolysed to isolate the layer from the next one applied. Dry etching can be done alone or in combination with chemical etching, using an ionized gas to bombard the areas to be etched. Manufacturers use dry plasma etching when a large portion of the layer needs to be etched in a circuit design. Additionally, another plasma combination of chlorine with gaseous fluorine can produce deep vertical cuts through a layer’s film masking materials, as is often necessary when manufacturing microactuator sensor chips.
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