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The ALD window for titanium dioxide (TiO<sub>2</sub>) ranges from 120 <sup>o</sup>C to 350 <sup>o</sup>C. 

A low temperatures between 120 <sup>o</sup>C and 150 <sup>o</sup>C an amorphous TiO<sub>2</sub> layer is grown in the ALD, and at higher temperatures between 300 <sup>o</sup>C and 350 <sup>o</sup>C an anatase TiO<sub>2</sub> layer is grown. At temperatures between 150 <sup>o</sup>C and 300 <sup>o</sup>C the TiO<sub>2</sub> layer will be a mixture of both amorphous and anatase TiO<sub>2</sub>.

For Si wafers, amorphous TiO<sub>2</sub> is best grown on wafers with native oxide, and anatase TiO<sub>2</sub> is best grown on wafers without native oxide (removed using HF).



====TiO<sub>2</sub> standard recipe====

<b>Recipe</b>: TiO2

<b>Temperature</b>: 120 <sup>o</sup>C - 350 <sup>o</sup>C

{| border="2" cellspacing="2" cellpadding="5"  align="none"
|- 
|
!TiCl<sub>4</sub>
!H<sub>2</sub>O
|-
!Nitrogen flow
|150 sccm
|200 sccm
|-
!Pulse time
|0.1 s
|0.1 s
|- 
!Purge time	
|4.0 s
|5.0 s
|-
|}


====TiO<sub>2</sub> deposition rates====

In the graphs below the TiO<sub>2</sub> thickness as function of the number of cycles for deposition temperatures between 150 <sup>o</sup>C and 350 <sup>o</sup>C can be seen. From the equations the number of cycles required for a certain thickess to be deposited can be calculated. All results have been obtained for Si wafers with native oxide.  

<gallery caption="Titanium dioxide thickness as function of number of cycles" widths="300px" heights="300px" perrow="3">
image:ALD_TiO2_grow_rate_150C.jpg| Temperature 150 <sup>o</sup>C.
image:ALD_TiO2_grow_rate_250C.jpg| Temperature 250 <sup>o</sup>C.
image:ALD_TiO2_grow_rate_350C.jpg| Temperature 350 <sup>o</sup>C.
</gallery>

Evgeniy Shkondin, DTU Danchip, April-May 2014.


====TiO<sub>2</sub> results====

Some some SEM images of TiO<sub>2</sub> deposited on a Si surface at different temperatures between 150 <sup>o</sup>C and 350 <sup>o</sup>C are shown below. Some of samples have been treated with HF (hydrofluoric acid) to remove the native oxide layer just before the ALD deposition.

<gallery caption="Titanium dioxide deposited at different temperatures on a Si surface" widths="250px" heights="180px" perrow="3">
image:TiO2 150C 1200 cycles Si_HF_treated.jpg| Temperature 150 <sup>o</sup>C, 1200 cycles, HF treated.
image:TiO2 150C 1200 cycles Si_untreated.jpg| Temperature 150 <sup>o</sup>C, 1200 cycles.
image:TiO2 250C 750cycles_Si_untreated.jpg| Temperature 250 <sup>o</sup>C, 750 cycles.
</gallery>
<gallery caption="" widths="250px" heights="180px" perrow="5">
image:TiO2 1000 cycles 300C Si_HF.jpg| Temperature 300 <sup>o</sup>C, 1000 cycles, HF treated.
image:TiO2 1000 cycles 300C Si_un.jpg| Temperature 300 <sup>o</sup>C, 1000 cycles.
image:TiO2 350C 1250 cycles Si_HF_treated.jpg| Temperature 350 <sup>o</sup>C, 1250 cycles, HF treated.
</gallery>

XPS measurements of TiO<sub>2</sub> deposited at 120 <sup>o</sup>C and 300 <sup>o</sup>C are shown below. From the XPS measurements it can be calculated that at temperatures below 120 <sup>o</sup>C the TiO<sub>2</sub> layer will be contaminated with about 1-3 % chlorine molecules from the TiCl<sub>4</sub> precursor. This can be also seen as small white dots in the SEM image of the amorphous TiO<sub>2</sub> layers above.

[[image:XPS_TiO2.jpg|320x320px|left|thumb|XPS measurements of titanium dioxide.]]

<br clear="all" /> 

Evgeniy Shkondin, DTU Danchip, 2014.


====TiO<sub>2</sub> deposition on trenches====

For TiO<sub>2</sub> deposition on trenches more information can be found here:

*[[Specific Process Knowledge/Thin Film deposition/ALD/TiO2 deposition using ALD/TiO2 deposition on trenches using ALD|TiO<sub>2</sub> deposition on trenches using ALD]]