An anneal adds nothing and removes nothing. It gives atoms the energy to move, react, and settle, turning as-deposited films into stable, well characterized parts of a device. This guide explains what anneals do, the main ambients, furnace versus rapid thermal annealing, and how to choose the right conditions. A thermal anneal is a controlled heat treatment that holds a wafer at a chosen temperature, for a chosen time, in a chosen gas, to bring about a beneficial change in a film or structure. Unlike deposition or etching, an anneal usually adds and removes nothing; it simply gives atoms the energy to move, react, and reorganize. In MEMS fabrication, anneals are used to densify deposited films, passivate interfaces, relieve or stabilize film stress, form and improve metal contacts, and activate implanted dopants such as the boron in a piezoresistive pressure sensor. The result of an anneal is set by four variables, temperature, time, ambient gas, and the ramp and cool rate, balanced against the thermal budget that the rest of the device can tolerate. Four variables set the result. Temperature, time at temperature, the ambient gas, and the ramp and cool rate together decide what the anneal does to the film. - Nitrogen, nitrogen with oxygen, and forming gas anneals, run in a horizontal furnace. - Nitrogen anneal to densify PECVD oxide and nitride films so they stay stable through later high temperature processing. - Forming gas anneal, recommended after dry chlorinated oxidation, to passivate dangling bonds at the silicon to oxide interface and secure the full benefit of the oxide. - Processed on both sides, on 50, 100, 125, 150, and 200mm wafers from about 100 to 2,000µm thick, in silicon, silicon on insulator, and quartz. - The published thermal anneal process runs at 450 °C, well suited to densification, interface passivation, and metal contact alloying, and compatible with aluminum metal. - Annealing integrates with RVM thermal oxidation, LPCVD and PECVD films, and metal deposition; for higher temperature anneals, discuss your thermal budget with the team. Dopant activation for piezoresistors, activating and driving in implanted boron and repairing implant damage in pressure and force sensors. Metal contact alloy and sinter, a forming gas anneal that lowers contact resistance and forms reliable ohmic contacts. PECVD film densification, a nitrogen anneal that stabilizes deposited oxide and nitride against later thermal cycling. Interface passivation, a forming gas anneal that neutralizes dangling bonds at the silicon to oxide interface and improves dielectric quality. Film stress relief and stabilization for membranes, cantilevers, and other released structures. Polysilicon anneal, activating dopants and relieving stress in structural polysilicon layers. Bond strengthening for fusion bonded and silicon on insulator wafers. Yes. RVM provides nitrogen, nitrogen with oxygen, and forming gas anneals in a horizontal furnace, commonly to densify PECVD films and to passivate the silicon to oxide interface after oxidation.
