Hafnium oxide deposition (CVD)

The base of this chemical recipe and processing is Hafnium-Tetrachloride, as it can be seen in the picture.

You might notice that Hafnium-Tetrachloride is a solid crystal at room temperature, which is kind of a problem considering that we wanna use it as a vapor in our CVD furnace, in order to react it with oxide for obtaining a Hafnium-Oxide thin film layer.

The equipment required for this process are a CVD and a plasma cleaner for removing impurities after the Hafnium oxide deposition

Chemical properties of Hafnium-Tetrachloride

HfCl₄ can be produced by several related procedures:

• The reaction of carbon tetrachloride and hafnium oxide at above 450 °C;

HfO₂ + 2 CCl₄ → HfCl₄ + 2 COCl₂

• Chlorination of a mixture of HfO₂ and carbon above 600 °C using chlorine gas or sulfur monochloride:

HfO₂ + 2 Cl₂ + C → HfCl₄ + CO₂

• Chlorination of hafnium carbide above 250 °C.

The result of those chemical reactions is a crystalline powder with a melting point of 432 °C

Processing steps

Since HfCl₄ is a solid salt at room temperature, we need to first create a liquid precursor, and use direct liquid injection for using it in our CVD.

The process is based on a Japanese paper and requires a complex precursor.

The synthesis of this the Hf precursor TDEAH (Hf(NEt2)4) is so complex, that it needs its own page.

Links

Study HfO₂ formation: https://iopscience.iop.org/article/10.1149/MA2005-02/13/547/pdf

A Japanese paper how they grew it with an LPCVD: http://www.trichemical.com/topics/Manuscript%20revisions.pdf