Products and Technology - MEMS-CET Technology Overview

CET Technology

The HF/Alcohol CET process employs a reduced pressure, gas phase isotropic etch for removal of sacrificial SiO2 layers to release flexures or other MEMS devices. The process is generally carried out at pressures between 75 and 350 torr providing CONTROLLED, residue-free etching (mitigating "runaway" or uncontrolled conditions). Typical vertical and lateral oxide etch rates are in the 0.1 - 10 microns/minute range

Primaxx offers the broadest range of MEMS dry etch release products, from lab systems to multi-chambered cluster tools for high volume production.

Why Gas Phase Dry Etch Release?

  • Eliminates process problems associated with Wet Bench and Supercritical Drying technologies.
  • Eliminates stiction and contamination, with device yields that are typically ~ 100%.
  • No complex waste management issues, smaller footprint, lower process consumables, lower cost of ownership when compared with Wet Bench technology.

Why Reduced Pressure?

  • Maximum feature penetration without localized loading effects.
  • Broadest process window for optimizing productivity and etch results for a variety of oxide films.
  • Keeps etch byproducts in the gas phase insuring high selectivities to metals including aluminum.
  • Initial pump down step allows surface moisture desorption insuring reproducible process starting conditions.

CET Process Overview

During the MEM-CET process, hydrogen fluoride gas and alcohol vapor/nitrogen gas mixture are injected into the processing module's reactor chamber. Chemical ionization of this mixture results in the formation of the active chemical species. HF etching of the oxide on the wafer surface produces silicon fluoride gas and water vapor, and generally consumes the remaining dopants and impurities in the oxide layer. These gaseous reaction products are pumped out of the reactor chamber by purging with nitrogen gas.

Alcohol vapor acts as a catalyst for the etch step and is not consumed in the reaction. Without alcohol, etching will not occur, and the etch rate can be closely controlled by controlling the its flow rate. The silicon substrate is not etched at all in this reaction, since the etch rates for silicon are many times slower than those for silicon oxide. Alcohol also scavenges water vapor from the wafer surface, which, if not removed, could allow the buildup of reaction products and the possible generation of oxide particles. Alcohol vapor keeps the wafer surface dry, allowing the reaction products to be pumped away.

By virtue of reduced pressure operation, this gas phase etch process provides maximum feature penetration, for example removing 0.05 micron thick sacrificial oxide layers underneath small structures, a feat generally not possible with wet etch technology. The Primaxx CET process also eliminates contamination and stiction-creating conditions since no liquids are used in contact with the MEMS devices; this typically results in significantly increased device yields, especially for 3D elements.

Primaxx has developed gas phase etch release processes for a wide range of MEMS products from accelerometers and gyroscopes, to bolometers and 3D mirrors, to thermal and pressure sensors.