Method for removing residues formed during the manufacture of MEMS devices
View Patent ↗A method of removing residues from an integrated device, in particular residues resulting from processing in HF vapor, is disclosed wherein the fabricated device is exposed to dry water vapor for a period of time sufficient to dissolve the residues in the dry water vapor.
1. A method of making a MEMS integrated device with moving mechanical parts, comprising:
performing an anhydrous vapor release step to release the moving mechanical parts in said MEMS device, said release step comprising subjecting a partially fabricated MEMS device including sacrificial material to hydrogen fluoride vapor to remove said sacrificial material;
subsequently performing a cleaning step to remove fluoride residues created in the release step wherein the MEMS device is placed in a chamber containing dry water vapor wherein the pressure/temperature ratio of the water vapor lies in the range of about 0.005 to 0.007 atm/K and wherein there is no condensation on the MEMS device, and wherein the MEMS device is exposed in said chamber to said dry water vapor for a period of time sufficient dissolve said fluoride residues in said dry water vapor, and
wherein ammonium fluorosilicate is formed during said release step, and prior to performing said cleaning step, said MEMS device is subjected to an evaporation step to remove said ammonium fluorosilicate.
2. A method as claimed in claim 1 , wherein the temperature is about 121° C. and the pressure is about 2 atmospheres.
3. A method as claimed in claim 2 , wherein said fabricated device is exposed to said dry water vapor for a period of about 4 hours.
4. A method as claimed in claim 1 , wherein the temperature is about 133° C.
5. A method as claimed in claim 1 , wherein the residues comprise ammonium bifluoride (NH 4 HF 2 ).
6. A method as claimed in claim 1 , wherein the residues comprise a metal fluoride solid compound at room temperature.
7. A method as claimed in claim 6 , wherein the residues comprise aluminum fluoride (AlF 3 ) solid crystal; a titanium fluoride (TiF 3 or TiF 4 ) solid crystal; a copper fluoride (CuF 2 ) solid crystal; a tantalum fluoride (TaF 5 ) solid crystal; a tungsten fluoride (WF 4 ) solid crystal; a cobalt fluoride (CoF 2 ) solid crystal, a nickel fluoride (NiF 2 ) solid crystal, or a combination thereof.
8. A method as claimed in claim 1 , wherein the exposure to dry water vapor is performed with multiple passes.
9. A method as claimed in claim 1 , wherein the exposure to dry water vapor is performed in a multi-step process.