Hafnium oxide deposition (CVD): Difference between revisions

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The base of this chemical recipe and processing is Hafnium-Tetrachloride, as it can be seen in the picture.
The equipment required for this process are a CVD and a plasma cleaner for removing impurities after the Hafnium oxide deposition


[[File:High-Quality-Hafnium-Chloride-Hafnium-Tetrachloride-Hfcl4-CAS-No-13499-05-3-with-Best-Price.jpg|200px|Hafnium-Tetrachloride]]
Since HfCl<sub>4</sub> is a solid salt at room temperature, we need to first create a liquid precursor which can be turned into a vapor.


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 process is based on a [https://download.libresilicon.com/papers/HafniumOxide.pdf Japanese paper] and requires a complex precursor.


The equipment required for this process are a CVD and a plasma cleaner for removing impurities after the Hafnium oxide deposition
The synthesis of the [[Hf precursor TDEAH (Hf(NEt2)4)]] is so complex, that it needs its own page.
 
===Precursor injection===
 
[[File:Pressure_TDEAH.png|200px|right|thumb|Vapor pressure]]
 
Introduce TDEAH gas into the deposition chamber using a bubbling system, use N<sub>2</sub> as the carrier gas.


===Chemical properties of Hafnium-Tetrachloride===
To prevent liquefaction of the source before it enters the deposition chamber, maintain the line from the bubbler to the chamber at a temperature of 85°C.


[[File:34591.png|200px|left]]
Heat the bubbling system chamber to 80°C.


The flow rate into the CVD chamber should be 40 sccm.


HfCl<sub>4</sub> can be produced by several related procedures:
===Oxidizer injection===
*The reaction of carbon tetrachloride and hafnium oxide at above 450&nbsp;°C;
:HfO<sub>2</sub>  +  2 CCl<sub>4</sub>  →  HfCl<sub>4</sub>  +  2 COCl<sub>2</sub>
*Chlorination of a mixture of HfO<sub>2</sub> and carbon above 600&nbsp;°C using chlorine gas or sulfur monochloride:
:HfO<sub>2</sub>  +  2 Cl<sub>2</sub>  +  C  →  HfCl<sub>4</sub>  +  CO<sub>2</sub>
*Chlorination of hafnium carbide above 250&nbsp;°C.


The result of those chemical reactions is a crystalline powder with a melting point of 432&nbsp;°C
[[File:HFO2_CVD_setup.png|200px|right|thumb|CVD setup]]


===Processing steps===
Have O<sub>2</sub> in N<sub>2</sub> in a ration 1:99 and feed it into the chamber through a separate nozzle, because otherwise the O<sub>2</sub> decomposes the TDEAH before it can reach the substrate.


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:
The flow rate can be varied between 0 and 20 sccm, for obvious reasons you want it higher than zero, because without oxygen you won't get any oxide.


[[https://en.wikipedia.org/wiki/Cyclohexane|Cyclohexane]]
===Substrate/CVD chamber temperature===
Set a temperature between 300°C and 450°C, in order to control deposition speed.


HfCl<sub>4</sub> + 2 H<sub>2</sub>O
===CVD chamber pressure===
→
Set the pressure within the CVD chamber to 1 torr
HfO<sub>2</sub> + 4 HCl


Since HfCl<sub>4</sub> is a solid salt at room temperature, we dissolve it in water (H<sub>2</sub>O), in a ratio 1:2 and use direct liquid injection for using it in our CVD as the precursor.
===Equipment===


The waste result is hydrochloric acid which needs to be continuously flushed out with a gas like Argon
* Potential CVD furnaces:
** https://www.digiqualsystems.com/products/furnaces/tubular-furnace/horizontal-tubular-furnace/
** https://www.mtixtl.com/ThreeZonesTubeFurnaceHighVacuumMFCGas-OTF-1200X-III-HVC-UL.aspx


===Links===
* Bubblers:
Study HfO<sub>2</sub> formation: https://iopscience.iop.org/article/10.1149/MA2005-02/13/547/pdf
** https://www.mtixtl.com/Bubbler/Evaporatorforliquidsourcesandchemicalprecursors-BL-SS.aspx


DLI: https://www.intechopen.com/chapters/63679
* Mass flow meters
** https://www.mtixtl.com/Liquid-delivery-system.aspx

Latest revision as of 17:33, 14 October 2022

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

Since HfCl4 is a solid salt at room temperature, we need to first create a liquid precursor which can be turned into a vapor.

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

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

Precursor injection

Vapor pressure

Introduce TDEAH gas into the deposition chamber using a bubbling system, use N2 as the carrier gas.

To prevent liquefaction of the source before it enters the deposition chamber, maintain the line from the bubbler to the chamber at a temperature of 85°C.

Heat the bubbling system chamber to 80°C.

The flow rate into the CVD chamber should be 40 sccm.

Oxidizer injection

CVD setup

Have O2 in N2 in a ration 1:99 and feed it into the chamber through a separate nozzle, because otherwise the O2 decomposes the TDEAH before it can reach the substrate.

The flow rate can be varied between 0 and 20 sccm, for obvious reasons you want it higher than zero, because without oxygen you won't get any oxide.

Substrate/CVD chamber temperature

Set a temperature between 300°C and 450°C, in order to control deposition speed.

CVD chamber pressure

Set the pressure within the CVD chamber to 1 torr

Equipment

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