Hf precursor TDEAH (Hf(NEt2)4)

This is the structure of the organic precursor for Hafnium oxide deposition in a CVD (Hafnium_oxide_deposition_(CVD))

as described in the following Japanese paper

WARNING! This chemical reacts VIOLENTLY with water and humidity in general! Caution is required when dealing with it!

Chemical properties of Hafnium-Tetrachloride

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

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

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.

Atmospheric requirements

Since this mixture and its components react with oxygen and humidity, we need to use a Schlenk tube setup for mixing it, because we can only do it in an inert atmosphere.

Chemical reaction

We combine lithium diethylamide (Et₂NLi) with Hafnium tetrachloride (HfCl₄), using a Schlenker tube setup.

With a temperature of 117°C and a pressure of 0.04 torr the following reaction will occur within an inert atmosphere (Argon/Nitrogen):

HfCl₄ + Et₂NLi → TDEAH (Hf(NEt₂)₄)

The yield typically is around 60%

The waste products will be some carbon hydrates (not the stuff in white bread)