Method of controlling film stress in MEMS devices
View Patent ↗A structural film, typically of silicon, in MEMS or NEMS devices is fabricated by depositing the film in the presence of a gas other than nitrogen, and preferably argon as the carrier gas.
1. A method of fabricating a structural silicon film in MEMS or NEMS devices, comprising:
depositing said silicon film using an SiH 4 -based precursor gas in the presence of phosphine as a dopant and argon as a carrier gas by LPCVD at a deposition temperature less than 580° C.; and
wherein the deposited silicon film has a tensile stress.
2. A method as claimed in claim 1 , wherein the silicon is deposited by an in-situ doped process.
3. A method as claimed in claim 1 , wherein the silicon film is deposited as amorphous silicon.
4. A method as claimed in claim 1 , wherein the silicon is deposited in a batch deposition system.
5. A method as claimed in claim 1 , wherein the silicon film is an amorphous film deposited in a horizontal LPCVD furnace under the following deposition conditions:
high purity precursors: SiH 4 at a partial pressure of 744 mTorr and 1% Ar at a partial pressure of 106 mTorr;
deposition pressure <1000 mTorr;
20 minute pause during deposition cycle:
point-of-use gas purifiers for SiH 4 and PH3/Ar.
6. A method as claimed in claim 1 , wherein at least one deliberate pause is implemented during the deposition of the silicon film to deliberately introduce impurities locally.
7. A method as claimed in claim 6 , wherein multiple pauses are implemented during the deposition of the silicon film.
8. A method as claimed in claim 6 , wherein said at least one pause is implemented during the deposition of the film, and the silicon film is subsequently annealed to modify the stress gradient.
9. A method as claimed in claim 1 , wherein the deposited film is subsequently subjected to an anneal step to modify the mechanical stress values of the silicon film.