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BOE (Buffered Oxide Etch)
NH4F used as buffer agent , F - ion supplier,so the F- concentration keeps stable ,that means the Etch rate keeps stable.
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SC1
Components: NH4OH:H2O2:H2O=1:2:$ Temperature: 30C
NH4OH:H2O2::H2O=1:2:50 Function: Particle removal NH4OH:H2O2::H2O=1:2:30 Function: PR removal
Electrical repulsion mechanism
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SC2
Components: HCl:H2O2:H2O=1:1:50 Temperature: 30C Function: metal contamination removal Mechanism : SC2 provides a low pH environment. Alkaline ions (Na, K, Li metals), hydroxide of Al, Mg, Fe, Zn (insoluble in NH4OH SC1), and residual trace metal (Au/Cu not completely desorbed by SC1) will be dissolved in SC2.
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BOE etch Polymer residue
metal
metal
•dielectric
There is some Polymer residue after etch ,so Polymer residue needs to be removed with metal and dielectric not been affected .
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H3PO4 (Phosphoric Acid)
Components: H3PO4 Temperature: 160C Function: Nitride strip, ER = 50 A/min Mechanism:Si3N4 + 6H2O --------> 4NH3
3SiO2 +
(H3POe often added to improve wetting, based on the capillary mechanism.
Benefit compared to DHF: 1) Low selectivity oxide etch for DRAM contact pre-clean 2) Prevent photo resist liftoff for KV, Dual gate process
WET ETCH &CLEAN Chemical
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Differences between 49%HF, HF(50:1) ,DHF(100:1) The Etch rate: 49%HF >HF(50:1)>DHF(100:1) on the same condition to the same material . In Backside etch , 49%HF is used to etch the nitride on the back side deposited at Diffusion ,which is much thick ,about 1600A. DHF (100:1) Etch rate is the lowest among the three chemicals,so it is used to preclean ,that is to etch a very thin oxide layer. As to oxide etch , HF(50:1) etch rate is in a reasonable range ,so it is suitable to etch oxide layer completely and safely.
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SC1 to remove Particle Mechanism: oxidation and electrical repulsion
Oxidation
Dissolutio n
Surfac e etching
Electrical repulsion
Oxidation mechanism
There is a thin Oxide layer on the surface of SiN ,so need to remove this Oxide layer with HF before SiN etch.
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