Gravure par voie humide de nitrure de silicium Si3N4. Attaque chimique avec acide phosphorique H3PO4.
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Silicon Nitride Removal Si3N4

In the semiconductor manufacturing process a silicon nitride, Si3N4 layer with a pattern is used as a mask to grow field oxide, SiO2 that displays the negative pattern. The nitride pattern is then removed in a wet chemical batch process using hot phosphoric acid, H3PO4.

Nitride mask

Targets of this process are:

To achieve this, it is crucial to control the etch rate, process time and selectivity as precise as possible.

The process time is easily controlled by using automatic wet stations. It is however a little more difficult to maintain a good and repeatable etch rate and sufficient selectivity. It requires quite some effort in measuring, software and adjustment.

The important parameters for the etch rate, or etching speed, are concentration and temperature of the phosphoric acid.

The selectivity is the ratio of etch rate in the material that you want to etch to the etch rate in the material that you don't want to etch. Typical for our case our case: nitride etch rate : oxide etch rate which is about 9:1 in 160°C H3PO4.

As higher temperature increases the etch rate but decreases the selectivity, 160°C is a good compromise.

The chemical reaction:

Si3N4 + 6 H2O Pfeil H3PO4 3 SiO2 + 4 NH3

Interesting, that the phosphoric acid only acts as a catalyst and is not actually consumed. Can it be used forever?

Our ZEUS/J.E.T. wet benches offer a repeatable and precise nitride removal process. technology

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