Phosphoric acid
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Phosphoric acid is a weak acid with the chemical formula H3PO4. It is often used to etch Silicon nitride. Phosphoric acid is commonly encountered as an 85% aqueous solution. In appearance, it is a colourless, odourless, and non-volatile viscous liquid. Phosphoric acid will severely irritate the skin and damage the eyes.
Contents
Equipment
Phosphoric acid can be used at the following benches
- Acid Bench 02 - tank
- Acid Bench 73 - hotplate
- Acid Bench 92
Storage Locations
Phosphoric acid is stored in the passthroughs in
- 1436
- 1440A
- 1480C
Processes
- Hot Phosphoric Acid for Etching Silicon Nitride
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Process SOPs
- Acid Bench 02 SOP has information about the tank of phosphoric acid in the lab.
- According to "Etch Rates for Micromachining Processing Part II" by Williams, phosphoric acid at 160C will have an etch rate of 4.5 nm/min.
Hazardous Waste
Never aspirate or drain a liquid that is heated. Wait til the solution has cooled to room temperature before disposing. Phosphoric acid can go down any drain that has an acid waste neutralization system.
Technical Data Sheet
- There are currently no data sheets for this chemical.
Safety Data Sheet
References
- KR Williams, K Gupta, M Wasilik, "Etch Rates for Micromachining Processing - Part II", JMEMS vol. 12 No 6, Dec 2003
- Vossen, John L., and Werner Kern. Thin Film Processes. Academic Press, 1991.
- https://www.microtechprocess.com/wp-content/uploads/2018/04/MTS_Nitride.pdf