View source for Specific Process Knowledge/Characterization/XRD/XRD SmartLab/ALD deposited alumina and titania XRR

'''Feedback to this page''': '''[mailto:labadviser@nanolab.dtu.dk?Subject=Feed%20back%20from%20page%20http://labadviser.nanolab.dtu.dk/index.php/Specific_Process_Knowledge/Characterization/XRD/XRD_SmartLab/ALD_deposited_alumina_and_titania_XRR click here]'''

<i>This page is written by <b>Evgeniy Shkondin @DTU Nanolab</b> if nothing else is stated. <br>
All images and photos on this page belongs to <b>DTU Nanolab</b>.<br>
The fabrication and characterization described below were conducted in <b>2019</b> by <b>Sarah Elisabeth Hussein El Dib (s135170)</b> and <b>Evgeniy Shkondin, DTU Nanolab</b> as a part of the master project in collaboration with the DTU Photonics Department. The  <b>XRR fitting results has been corrected in november 2021.</b><br></i>


==Purpose of the work==

The prepared samples were investigated by X-ray Reflectivity (XRR) method. The idea is to investigate the initial growth of Al<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> on conventional Si samples (with native oxide) and measure the thickness of the layers in the range of 1 to 10 nm, where Spectroscopic Ellipsometry can be limited. 

The deposition of ultrathin layers (with thickness below 10 nm) is difficult to characterize with ellipsometry alone, because of the model complexity. The prepared samples consist of a thin ALD film, but in order to properly distinguish it, the native oxide and surface moisture (with adventitious carbon contamination) should be taken into account since whey both have thicknesses comparable to ALD ultra-thin layer. For this purpose, the XRR method was employed.


Page has been updated in January 2022 with minor densities correction.

==Deposition characteristics==

A sequence of samples has been made by deposition Al<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> on flat natively oxidized Si (100) samples. The thickness setpoints were chosen to be <b>2</b>, <b>4</b>, <b>6</b>, and <b>8</b> nm, and a number of cycles calculated from the published growth rates which were verified for thicker films (20-100nm).

===Deposition of Al<sub>2</sub>O<sub>3</sub>===

The standard recipe for deposition of Al<sub>2</sub>O<sub>3</sub> on flat and high aspect ratio structures has been used.

<b>Equipment: ALD-1</b>

<b>Recipe: AL2O3</b>

<b>Assumed deposition rate: 0.097 nm/cycle</b>

<b>Temperature: 200 <sup>o</sup>C</b>

{| border="2" cellspacing="2" cellpadding="5"  align="none"
|- 
|
!TMA
!H<sub>2</sub>O
|-
!Nitrogen flow
|150 sccm
|200 sccm
|-
!Pulse time
|0.1 s
|0.1 s
|- 
!Purge time	
|3.0 s
|4.0 s
|-
|}

<b>Number of cycles:</b> <b>20</b>, <b>40</b>, <b>60</b>, <b>80</b> for 2nm, 4nm, 6 nm and 8 nm respectively.

===Deposition of TiO<sub>2</sub>===

The standard recipe for deposition of amorphous TiO<sub>2</sub> on flat and high aspect ratio structures has been used.

<b>Recipe: amorphous TiO2</b>,

<b>Equipment: ALD-2</b>

<b>Assumed deposition rate: 0.0385 nm/cycle</b>

<b>Temperature: 150 <sup>o</sup>C</b>

{| border="2" cellspacing="2" cellpadding="5"  align="none"
|- 
|
!TiCl<sub>4</sub>
!H<sub>2</sub>O
|-
!Nitrogen flow
|150 sccm
|150 sccm
|-
!Pulse time
|0.1 s
|0.1 s
|- 
!Purge time	
|4.0 s
|6.0 s
|-
|}

<b>Number of cycles:</b> <b>52</b>, <b>104</b>, <b>156</b>, <b>208</b> for 2nm, 4nm, 6 nm and 8 nm respectively.

==X-ray reflectivity results==

<br clear="all" />
X-ray reflectivity (XRR) profiles for Al<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> films at different number of cycles has been obtained using Rigaku XRD SmartLab equipment. The voltage and current settings for the Cu X-ray tube were standard  40kV and 30mA. The incident optics contained a Ge220x2 monochromator and 5 &deg; Soller slit. Other slits: IS=0.03mm RS1=0.03mm and RS2=0.032mm. Step size: 0.01 and measurement time - 10s for each point. Fitting procesure was performed using commercial GlobalFit software assuming the model based on Si substrate with native oxide followed by the deposited ALD layer with thin moisture surface. The results are summarized in a tables below. 

<gallery caption="Sample model used in XRR analysis." widths="480px" heights="240px" perrow="1">
image:eves_01052020_XRR_sample_model.png|Sample considers to have ALD layer with top moisture deposited on natively oxidized silicon.
</gallery>

===Si reference samples===

Before the depositions of thin films, the Si samples has been analyzed with and without native oxide. It wil be used as a reference. Removing of native oxide has been done using  5% HF solution and rinsing with water. Results are shown below:

<br clear="all" />


<gallery caption="All XRR scans." widths="1200px" heights="600px" perrow="1">
image:eves_Si_with_and_without_native_oxide_XRR_20211118.png|Measuring <b>Si</b> reference sample with and without native oxide.
</gallery>

<br clear="all" />


{| border="2" cellspacing="2" cellpadding="9" colspan="12"
|bgcolor="#98FB98" |'''Physical properties of Si reference sample with and without native oxide'''
|-
|

{| {{table}}
| align="center" | 
{| border="2" cellspacing="2" cellpadding="9"  align="center" 

|-
!colspan="1" style="background:silver; color:black" align="center"|
|colspan="3" style="background:silver; color:black" align="center"|<b>Si native oxide</b>
|colspan="3" style="background:silver; color:black" align="center"|<b>Si substrate</b>
|colspan="5" style="background:silver; color:black" align="center"|<b>Fitting parameters</b>

|-
!style="background:WhiteSmoke; color:black" align="center"|Sample
|style="background:WhiteSmoke; color:black" align="center"|<b>SiO<sub>2</sub> Thickness (nm)</b>
|style="background:WhiteSmoke; color:black" align="center"|<b>SiO<sub>2</sub> Density (g/cm<sup>3</sup>)</b>
|style="background:WhiteSmoke; color:black" align="center"|<b>SiO<sub>2</sub> Roughness (nm)</b>
|style="background:WhiteSmoke; color:black" align="center"|<b>Si Thickness (nm)</b>
|style="background:WhiteSmoke; color:black" align="center"|<b>Si Density (g/cm<sup>3</sup>)</b>
|style="background:WhiteSmoke; color:black" align="center"|<b>Si Roughness (nm)</b>
|style="background:WhiteSmoke; color:black" align="center"|<b>Intensity</b>
|style="background:WhiteSmoke; color:black" align="center"|<b>Background</b>
|style="background:WhiteSmoke; color:black" align="center"|<b>Fitting area (<math>2\Theta</math>)</b>
|style="background:WhiteSmoke; color:black" align="center"|<b>R</b>
|style="background:WhiteSmoke; color:black" align="center"|<b><math>\Chi^2</math></b>

|- 
|style="background:WhiteSmoke; color:black" align="center"|<b>Si without native oxide</b>
| -
| -
| -
|<math>\infty</math>
|<b>2.328</b>
|<b>0.1</b>
|1.23109
|2.95508E-7
|0.4045-2.0
|0.00864
|0.00056

|- 
|style="background:WhiteSmoke; color:black" align="center"|<b>Si with native oxide</b>
|<b>1.6</b>
|<b>1.92</b>
|<b>0.412</b>
|<math>\infty</math>
|<b>2.328</b>
|<b>1.12</b>
|1.18812
|3.22806E-7
|0.4045-6.0
|0.02357
|0.01376

|-
|}
|-  
|}
|}

<br>
<!-- -->

<br clear="all" />


{| border="2" cellspacing="2" cellpadding="5"  align="center"

|- 
!colspan="6" border="none" style="background:silver; color:black;" align="center"| Fitting of Delta and Beta values
|-
|style="background:WhiteSmoke; color:black" rowspan="2"|<b>Sample</b>
|colspan="2" border="none" style="background:WhiteSmoke; color:black"|<b>SiO<sub>2</sub></b>
|colspan="2" border="none" style="background:WhiteSmoke; color:black"|<b>Si</b>

|-
|style="background:WhiteSmoke; color:black"|<b>Delta</b>
|style="background:WhiteSmoke; color:black"|<b>Beta</b>
|style="background:WhiteSmoke; color:black"|<b>Delta</b>
|style="background:WhiteSmoke; color:black"|<b>Beta</b>

|-
|<b>Si without native oxide</b>
| -
| -
|7.5796E-6
|1.7601E-7

|-
|<b>Si with native oxide</b>
|6.2243E-6
|8.1116E-8
|7.5796E-6
|1.7601E-7

|}


<br>
<!-- -->

<br clear="all" />

===Thin films samples===

Below is an overview of all samples in total. XRR spectra are shifted in respect to each other in y-direction for better comparison.
The reader can click on [[Specific Process Knowledge/Characterization/XRD/XRD SmartLab/ALD deposited alumina and titania XRR/Individual XRR for Al2O3 and TiO2|XRR Spectra for individual samples]] to see them in highere resolution.

<gallery caption="All XRR scans." widths="600px" heights="800px" perrow="2">
image:eves_Al2O3_all_XRR_20211118.png|All <b>Al<sub>2</sub>O<sub>3</sub></b> samples scan.
image:eves_TiO2_all_XRR_20211118.png| All <b>TiO<sub>2</sub></b> samples scan.
</gallery>



====Fitting resilts for Al<sub>2</sub>O<sub>3</sub>====





{| border="2" cellspacing="2" cellpadding="3" colspan="13"
|bgcolor="#98FB98" |'''XRR results for Al<sub>2</sub>O<sub>3</sub> layers'''
|-
|

{| {{table}}
| align="center" | 
{| border="2" cellspacing="2" cellpadding="3"  align="center" style="width:1500px" 

|-
!colspan="1" style="background:silver; color:black;" align="center" |
|colspan="3" style="background:silver; color:black;" align="center" |<b>Top layer (moisture)</b>
|colspan="3" style="background:silver; color:black;" align="center" |<b>Main layer</b>
|colspan="3" style="background:silver; color:black;" align="center" |<b>Si native oxide</b>
|colspan="3" style="background:silver; color:black;" align="center" |<b>Si substrate</b>

|-
!style="background:WhiteSmoke; color:black;" align="center" |Number of cycles
|style="background:WhiteSmoke; color:black;" align="center" |<b>Moisture thickness (nm)</b>
|style="background:WhiteSmoke; color:black;" align="center" |<b>Moisture density (g/cm<sup>3</sup>)</b>
|style="background:WhiteSmoke; color:black;" align="center" |<b>Moisture roughness (nm)</b>
|style="background:WhiteSmoke; color:black;" align="center" |<b>Al<sub>2</sub>O<sub>3</sub> thickness (nm)</b>
|style="background:WhiteSmoke; color:black;" align="center" |<b>Al<sub>2</sub>O<sub>3</sub> density (g/cm<sup>3</sup>)</b>
|style="background:WhiteSmoke; color:black;" align="center" |<b>Al<sub>2</sub>O<sub>3</sub> roughness (nm)</b>
|style="background:WhiteSmoke; color:black;" align="center" |<b>SiO<sub>2</sub> thickness (nm)</b>
|style="background:WhiteSmoke; color:black;" align="center" |<b>SiO<sub>2</sub> density (g/cm<sup>3</sup>)</b>
|style="background:WhiteSmoke; color:black;" align="center" |<b>SiO<sub>2</sub> roughness (nm)</b>
|style="background:WhiteSmoke; color:black;" align="center" |<b>Si thickness (nm)</b>
|style="background:WhiteSmoke; color:black;" align="center" |<b>Si density (g/cm<sup>3</sup>)</b>
|style="background:WhiteSmoke; color:black;" align="center" |<b>Si roughness (nm)</b>

|- 
|<b>20</b> 
|1.22
|0.99
|0.46
|<p style="color:red;"><b>2.11</b></p>
|<p style="color:red;"><b>3.30</b></p>
|<p style="color:red;"><b>1.04</b></p>
|1.33
|1.60
|1.01
|<math>\infty</math>
|2.328
|0.02

|- 
|<b>40</b>  
|1.01
|1.82
|0.36
|<p style="color:red;"><b>4.00</b></p>
|<p style="color:red;"><b>2.88</b></p>
|<p style="color:red;"><b>0.41</b></p>
|2.10
|2.11
|0.50
|<math>\infty</math>
|2.328
|0.31

|- 
|<b>60</b>  
|1.00
|1.80
|0.37
|<p style="color:red;"><b>6.29</b></p>
|<p style="color:red;"><b>2.86</b></p>
|<p style="color:red;"><b>0.40</b></p>
|2.07
|2.10
|0.48
|<math>\infty</math>
|2.328
|0.27

|- 
|<b>80</b>  
|0.99
|1.85
|0.38
|<p style="color:red;"><b>8.46</b></p>
|<p style="color:red;"><b>2.97</b></p>
|<p style="color:red;"><b>0.46</b></p>
|2.02
|2.10
|0.56
|<math>\infty</math>
|2.328
|0.38

|-
|}
|-
|}
|}


<br clear="all" />


{| border="2" cellspacing="2" cellpadding="5"  align="center"

|- 
!colspan="14" border="none" style="background:silver; color:black;" align="center"| Fitting parameters
|-
|style="background:WhiteSmoke; color:black" rowspan="2"|<b>Sample</b>
|colspan="2" border="none" style="background:WhiteSmoke; color:black"|<b>Moisture</b>
|colspan="2" border="none" style="background:WhiteSmoke; color:black"|<b>Al<sub>2</sub>O<sub>3</sub></b>
|colspan="2" border="none" style="background:WhiteSmoke; color:black"|<b>Si native oxide</b>
|colspan="2" border="none" style="background:WhiteSmoke; color:black"|<b>Si substrate</b>
|colspan="5" border="none" style="background:WhiteSmoke; color:black"|<b>Fitting parameters</b>

|-
|style="background:WhiteSmoke; color:black"|<b>Delta</b>
|style="background:WhiteSmoke; color:black"|<b>Beta</b>
|style="background:WhiteSmoke; color:black"|<b>Delta</b>
|style="background:WhiteSmoke; color:black"|<b>Beta</b>
|style="background:WhiteSmoke; color:black"|<b>Delta</b>
|style="background:WhiteSmoke; color:black"|<b>Beta</b>
|style="background:WhiteSmoke; color:black"|<b>Delta</b>
|style="background:WhiteSmoke; color:black"|<b>Beta</b>
|style="background:WhiteSmoke; color:black"|<b>Intensity</b>
|style="background:WhiteSmoke; color:black"|<b>Background</b>
|style="background:WhiteSmoke; color:black"|<b>Fitting area (<math>2\Theta</math>)</b>
|style="background:WhiteSmoke; color:black"|<b>R</b>
|style="background:WhiteSmoke; color:black"|<b><math>\Chi^2</math></b>

|-
|<b>20 cycles</b>
| 3.2291E-6
| 7.4986E-8
| 1.0491E-5
| 1.2221E-7
| 5.1604E-6
| 6.7251E-8
| 7.5796E-6
| 1.7601E-7
| 1.15165
| 4.1694E-7
| 0.3846 - 5.000
| 0.02218
| 0.01138

|-
|<b>40 cycles</b>
| 5.9060E-6
| 1.3693E-7
| 9.1612E-6
| 1.0654E-7
| 6.8125E-6
| 8.8635E-8
| 7.5669E-6
| 1.7544E-7
| 1.11031
| 1.24726E-8
| 0.3714 - 5.000
| 0.02677
| 0.01663

|-
|<b>60 cycles</b>
| 5.8344E-6
| 1.3527E-7
| 9.0960E-6
| 1.0578E-7
| 6.7815E-6
| 8.8233E-8
| 7.5669E-6
| 1.7544E-7
| 0.92337
| 2.27778E-7
| 0.3714 - 5.000
| 0.02671
| 0.01677

|-
|<b>80 cycles</b>
| 6.0443E-6
| 1.4036E-7
| 9.4679E-6
| 1.1029E-7
| 6.8062E-6
| 8.8700E-8
| 7.5796E-6
| 1.7601E-7
| 0.98482
| 6.13396E-8
| 0.3714 - 5.000
| 0.02601
| 0.01598

|}


<br>
<!-- -->

<br clear="all" />


<br clear="all" />


====Fitting resilts for TiO<sub>2</sub>====





{| border="2" cellspacing="2" cellpadding="3" colspan="13"
|bgcolor="#98FB98" |'''XRR results for TiO<sub>2</sub> layers'''
|-
|

{| {{table}}
| align="center" | 
{| border="2" cellspacing="2" cellpadding="3"  align="center" style="width:1500px" 

|-
!colspan="1" style="background:silver; color:black"|
|colspan="3" style="background:silver; color:black"|<b>Top layer (moisture)</b>
|colspan="3" style="background:silver; color:black"|<b>Main layer</b>
|colspan="3" style="background:silver; color:black"|<b>Si native oxide</b>
|colspan="3" style="background:silver; color:black"|<b>Si substrate</b>

|-
!style="background:WhiteSmoke; color:black"|Number of cycles
|style="background:WhiteSmoke; color:black"|<b>Moisture thickness (nm)</b>
|style="background:WhiteSmoke; color:black"|<b>Moisture density (g/cm<sup>3</sup>)</b>
|style="background:WhiteSmoke; color:black"|<b>Moisture roughness (nm)</b>
|style="background:WhiteSmoke; color:black"|<b>TiO<sub>2</sub> thickness (nm)</b>
|style="background:WhiteSmoke; color:black"|<b>TiO<sub>2</sub> density (g/cm<sup>3</sup>)</b>
|style="background:WhiteSmoke; color:black"|<b>TiO<sub>2</sub> roughness (nm)</b>
|style="background:WhiteSmoke; color:black"|<b>SiO<sub>2</sub> thickness (nm)</b>
|style="background:WhiteSmoke; color:black"|<b>SiO<sub>2</sub> density (g/cm<sup>3</sup>)</b>
|style="background:WhiteSmoke; color:black"|<b>SiO<sub>2</sub> roughness (nm)</b>
|style="background:WhiteSmoke; color:black"|<b>Si thickness (nm)</b>
|style="background:WhiteSmoke; color:black"|<b>Si density (g/cm<sup>3</sup>)</b>
|style="background:WhiteSmoke; color:black"|<b>Si roughness (nm)</b>

|- 
|<b>52</b> 
|0.41
|1.00
|1.01
|<p style="color:red;"><b>2.54</b></p>
|<p style="color:red;"><b>3.80</b></p>
|<p style="color:red;"><b>1.02</b></p>
|1.31
|1.55
|1.01
|<math>\infty</math>
|2.328
|0.01

|- 
|<b>104</b>  
|0.57
|0.80
|0.60
|<p style="color:red;"><b>5.09</b></p>
|<p style="color:red;"><b>3.45</b></p>
|<p style="color:red;"><b>0.02</b></p>
|2.01
|2.13
|0.43
|<math>\infty</math>
|2.328
|0.20

|- 
|<b>156</b>  
|0.54
|0.78
|0.61
|<p style="color:red;"><b>7.54</b></p>
|<p style="color:red;"><b>3.42</b></p>
|<p style="color:red;"><b>0.45</b></p>
|2.04
|2.10
|0.41
|<math>\infty</math>
|2.328
|0.21

|- 
|<b>208</b>  
|0.52
|1.10
|0.41
|<p style="color:red;"><b>9.68</b></p>
|<p style="color:red;"><b>3.38</b></p>
|<p style="color:red;"><b>0.38</b></p>
|2.10
|2.07
|0.42
|<math>\infty</math>
|2.328
|0.41

|-
|}
|-
|}
|}


<br clear="all" />


{| border="2" cellspacing="2" cellpadding="5"  align="center"

|- 
!colspan="14" border="none" style="background:silver; color:black;" align="center"| Fitting parameters
|-
|style="background:WhiteSmoke; color:black" rowspan="2"|<b>Sample</b>
|colspan="2" border="none" style="background:WhiteSmoke; color:black"|<b>Moisture</b>
|colspan="2" border="none" style="background:WhiteSmoke; color:black"|<b>Al<sub>2</sub>O<sub>3</sub></b>
|colspan="2" border="none" style="background:WhiteSmoke; color:black"|<b>Si native oxide</b>
|colspan="2" border="none" style="background:WhiteSmoke; color:black"|<b>Si substrate</b>
|colspan="5" border="none" style="background:WhiteSmoke; color:black"|<b>Fitting parameters</b>

|-
|style="background:WhiteSmoke; color:black"|<b>Delta</b>
|style="background:WhiteSmoke; color:black"|<b>Beta</b>
|style="background:WhiteSmoke; color:black"|<b>Delta</b>
|style="background:WhiteSmoke; color:black"|<b>Beta</b>
|style="background:WhiteSmoke; color:black"|<b>Delta</b>
|style="background:WhiteSmoke; color:black"|<b>Beta</b>
|style="background:WhiteSmoke; color:black"|<b>Delta</b>
|style="background:WhiteSmoke; color:black"|<b>Beta</b>
|style="background:WhiteSmoke; color:black"|<b>Intensity</b>
|style="background:WhiteSmoke; color:black"|<b>Background</b>
|style="background:WhiteSmoke; color:black"|<b>Fitting area (<math>2\Theta</math>)</b>
|style="background:WhiteSmoke; color:black"|<b>R</b>
|style="background:WhiteSmoke; color:black"|<b><math>\Chi^2</math></b>

|-
|<b>52 cycles</b>
| 3.2558E-6
| 7.5605E-8
| 1.1697E-5
| 5.7265E-7
| 5.0270E-6
| 6.5513E-8
| 7.5796E-6
| 1.7601E-7
| 1.20038
| 8.88999E-9
| 0.3846 - 5.000
| 0.02639
| 0.01450

|-
|<b>104 cycles</b>
| 2.5465E-6
| 5.9040E-8
| 1.0612E-5
| 5.1877E-7
| 6.9037E-6
| 8.9823E-8
| 7.5669E-6
| 1.7544E-7
| 1.12213
| 1.89786E-7
| 0.3846 - 5.000
| 0.01616
| 0.00516

|-
|<b>156 cycles</b>
| 2.5465E-6
| 5.9040E-8
| 1.0527E-5
| 5.1462E-7
| 6.8032E-6
| 8.8515E-8
| 7.5669E-6
| 1.7544E-7
| 1.18524
| 6.07729E-8
| 0.3846 - 5.000
| 0.02059
| 0.00854

|-
|<b>208 cycles</b>
| 3.5635E-6
| 8.2621E-8
| 1.0393E-5
| 5.0808E-7
| 6.6905E-6
| 8.7048E-8
| 7.5669E-6
| 1.7533E-7
| 1.21905
| 6.06500E-8
| 0.3846 - 5.000
| 0.01954
| 0.00725

|}


<br>
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<br clear="all" />
<br clear="all" />

====Graphical illustration of thickness dependence for Al2O3 and TiO2 ultrathin layers====


<gallery caption="Deposition rate in the initial stage." widths="600px" heights="450px" perrow="2">
image:eves_Al2O3_general_20211118.png|<b>Al<sub>2</sub>O<sub>3</sub></b> samples.
image:eves_TiO2_general_20211118.png|<b>TiO<sub>2</sub></b> samples.
</gallery>