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

The basic reaction we want to make use of, according to https://patents.google.com/patent/CN100356519C/en (original Chinese version: https://patents.google.com/patent/CN100356519C), is as following:

HfCl₄ + C₆ H₁₁ → HfO₂, HCl

Since HfCl₄ is a solid salt at room temperature, we dissolve it in Cyclohexane (C₆ H₁₁), with a concentration range of 0.01-1.0M, and use direct liquid injection for using it in our CVD as the precursor.

The waste result is hydrochloric acid, CO₂ and H₂O which needs, to be continuously flushed out with a gas like Argon

Links

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