Developing the No.1 Silicon Fabricating Technology in the World
Advanced technology about grooves with the width of 1 micrometer and the depth of 50 micrometers
Denso Corporation developed the novel multiple etching technology in its Research Laboratories to solidly form Micro Electro Mechanical Systems (MEMS), such as micro motors and micro mirrors, on silicon substrates. This technology makes it possible to form thin, deep grooves on a silicon substrate. Its advantage is to increase the aspect ratio, which is the ratio of the depth of the groove to the width. Since there is a general problem with the width of a groove becoming larger when the silicon is chipped to a certain depth, it was impossible to make the aspect ratio more than 25 until now.
In their research, Denso found that the combination between oxidizing plasma and non-oxidizing plasma suppresses the etching of silicon in a lateral direction. Their newly-developed multiple etching technology is one that optimizes these conditions, and chips the groove only in a vertical direction by covering a special protection layer to the side wall of the groove. This multiple process, that is, the repetition of the process of forming the protection layer and digging the groove, results in permanent etching, in principle. However, because the supply of plasma decreases as the silicon is deeply etched, the deepest groove confirmed to be fabricated so far had a width of 1 micro meter, and a depth of 50 micro meters (aspect ratio = 50).
This technology can be applied to the fabrication not only of actuators, (e.g. motors), and sensors for MEMS devices in the next generation, but can also be applied to micro channels for analysis of micro liquid, variable micro capacitors, and so on. Although it is reported that a micro motor with the thickness of 2 micrometers and the diameter of a few hundred micrometers driven with static electrical power has been fabricated on a silicon wafer, there is a problem with its torque being small. Application of the multiple etching technology increases the thickness of a micro motor, and more static electrical power can be used, which means a 25 times torque can be obtained with the same diameter.