Phosphoric Acid in Semiconductor Production

Phosphoric Acid is used in Semiconductor Production. In the semiconductor manufacturing process, phosphoric acid can be used as a solvent for etching, for example: a mixture of phosphoric acid and hydrogen peroxide can convert InGaAs to InP to achieve the purpose of etching.

Ga2O3 Etchants

References: (2 [sec. 4.3.2], 8, 98, 99).
Ga2O3 thickness typically ~<50 Å.
1:1 – HCL : H2O — (10 sec.)
1:20 – H2SO4 : H2O — (30 sec.)
1:40 – H3PO4 : H2O — (20 sec.)


References: (4, 9, 10, 99).
Reaction rate limited.
InP etch rate with 1:1 ~2.5 µm/minute.
GaInP etch rate with 1:1 ~0.60 µm/minute.

H3PO4 : H2O2 : H2O

References: (13, 98, 99).
Reaction rate limited.
GaAs etch rate with 3:1:25 ~0.30 µm/minute.
InGaAs etch rate with 1:1:8 ~0.40 µm/minute.
InGaAs and InAlAs etch rates with 1:1:38 ~0.10 µm/minute.

Phosphoric Acid in Semiconductor Production

The  production of Semiconductor Grade H3PO4

As the extreme requirement on imputiies, ALL Semiconduct grade Phosphoric acid is made from Element Phosphorus (P4) by thermal process, which won’t introduce impurity if with qualified raw materials. In contrast, wet-process phosphoric acid contains a lot of impurites, and it’s always a challenge to purify wet-process phosphoric acid on technology and engineering.  Many failed cases happened when trying to purify web-process phosphoric acid to technical or food grade products. A famous case was the project in Idaho. Technicians adopted the tehcnology from Europe that purify wet-process phosphoric acid to food grade acid when using the rock phosphorus from North Africa.  Unfortunately technicians was always unsucceessful to purify the qualified acid. Finally the project has to transfer to produce agriculture acid instead.

Therefore, the thermal-process phosphoric acid is only option to make semiconduction grade acid.

Another challege is that any parts contacting phosphoric acid couldn’t introduce impurities into acid. As phosphoric acid is middle-strong acid,   the glass or ceramic equipment including pipes, pumps and tanks is used in the production of Semiconduction grade Phosphoric acid.