Specific Process Knowledge/Thin film deposition/ALD2 (PEALD)/TiN plasma deposition using ALD2

This page is written by Evgeniy Shkondin @DTU Nanolab if nothing else is stated.
All images and photos on this page belongs to DTU Nanolab.
The fabrication and characterization described below were conducted in 2021 by Evgeniy Shkondin, DTU Nanolab.

Deposition of TiN is a standard, well explored ALD process. In any book where ALD is explained or scientific reviews on a subject, the TiN process is mentioned as a standard example of nitride deposition with the corresponding reaction mechanism. In any facility where you find an ALD tool, you will also find an TiN process since the film is very popular in many applications due to the ease of deposition, excellent uniformity, strict thickness control, and reliability. At DTU Naolab you can use ALD-2 for the deposition of TiN with thermal or plasma methods.

TiN ALD deposition using TiCl4 and plasma NH₃

TiN can be deposited in the range between 300 °C to 500 °C. At this moment we did not explored the tamperatures below 300^oC. The maximum temperature can be 500 °C.

TiN recipes

TiN plasma Nanolab Standard

Maximum deposition thickness: 100 nm

Temperature: 300 °C - 500 °C

	TiCl4	NH3
Gas flow	60 sccm (N2)	100 sccm (Ar) + 100 sccm (NH3)
Pulse time	0.1 s	8.6
Purge time	5.0 s	8.0 s

Plasma source settings
RF power (W)	Ar carrier flow (sccm)	Plasma gas flow (sccm)	t1 stabilization (s)	t2 RF Power on (s)
3000	100	100	1	7

Note! Remember to obey the relation: [Pulse time - (t₁+t₂)] > 0.5 s

This is a standard recipe of TiN. It is suitable for coating the flat samples and structures with an aspect ratio of around up to 1:10.

Deposition characteristics

The deposition rate for TiN depends on the temperature, see the ALD-window graph below. The uniformity, thickness, refractive index has been obtained using Ellipsometer VASE.

Deposition rate

• 
  Deposition rate of TiN at 350 °C. Substrate: Silicon 6" wafer with 300nm dry SiO₂ (C-1 furnace).
  $Thickness(nm)=0.0264\cdot N+2.48$
• 
  Deposition rate of TiN at 400 °C. Substrate: Silicon 6" wafer with 300nm dry SiO₂ (C-1 furnace).
  $Thickness(nm)=0.0327\cdot N+1.75$
• 
  Deposition rate of TiN at 450 °C. Substrate: Silicon 6" wafer with 300nm dry SiO₂ (C-1 furnace).
  $Thickness(nm)=0.0343\cdot N-0.16$
• 
  Deposition rate of TiN at 500 °C. Substrate: Silicon 6" wafer with 300nm dry SiO₂ (C-1 furnace).
  $Thickness(nm)=0.0317\cdot N+10.03$
• 
  Deposition rate of TiN in a temperature range 350 °C - 500 °C.

Sheet resistance

• 
  Deposition rate of Al₂O₃ at 100 °C. Substrate: Silicon 4" wafer with native oxide.
  $SheetResistance(\mathrm{\Omega }/sq)=10.4+\frac{92060}{t^2}$, where t is a thickness.

Uniformity across 150 mm wafer

Recipe "TiN plasma Nanolab Standard" Samples: 150mm ssp-Si

Results have been obtained for <150> 100 mm Si wafers with native oxide, based on ellipsometry study.

Sample	Minimum thickness (nm)	Maximum thickness (nm)	Average thickness (nm)	Standard deviation	Uniformity (%)
Reference, 300 nm Dry SiO2 from C1	292.46	298.33	295.43	1.46	0.99
450°C / 1000 cycles	31.59	44.18	35.20	2.53	17.88
450°C / 2000 cycles	62.77	84.33	69.22	4.42	15.57
450°C / 3000 cycles	92.13	120.00	103.52	6.69	13.52
450°C / 4000 cycles	127.84	159.26	137.05	6.61	11.46

• 
  Uniformity across 100mm wafer. Deposition at 100°C
• 
  Uniformity across 100mm wafer. Deposition at 100°C
• 
  Uniformity across 100mm wafer. Deposition at 150°C
• 
  Uniformity across 100mm wafer. Deposition at 200°C
• 
  Uniformity across 100mm wafer. Deposition at 250°C

Optical functions

Results have been obtained for <100> 100 mm Si wafers with native oxide, based on ellipsometry study. Cauchy model has been implemented for refractive index fitting.

• 
  Refractive index of 100 nm Al₂O₃ deposited on silicon at different temperatures.
• 
  Optical transmission of 100 nm Al₂O₃ deposited on fused silica wafer at 200C.

Spectroscopic Ellipsometry

• 
  Refractive index of 100 nm Al₂O₃ deposited on silicon at different temperatures.
• 
  Optical transmission of 100 nm Al₂O₃ deposited on fused silica wafer at 200C.
• 
  Refractive index of 100 nm Al₂O₃ deposited on silicon at different temperatures.
• 
  Optical transmission of 100 nm Al₂O₃ deposited on fused silica wafer at 200C.
• 
  Refractive index of 100 nm Al₂O₃ deposited on silicon at different temperatures.
• 
  Optical transmission of 100 nm Al₂O₃ deposited on fused silica wafer at 200C.
• 
  Refractive index of 100 nm Al₂O₃ deposited on silicon at different temperatures.
• 
  Optical transmission of 100 nm Al₂O₃ deposited on fused silica wafer at 200C.
• 
  Refractive index of 100 nm Al₂O₃ deposited on silicon at different temperatures.
• 
  Optical transmission of 100 nm Al₂O₃ deposited on fused silica wafer at 200C.
• 
  Refractive index of 100 nm Al₂O₃ deposited on silicon at different temperatures.
• 
  Optical transmission of 100 nm Al₂O₃ deposited on fused silica wafer at 200C.
• 
  Refractive index of 100 nm Al₂O₃ deposited on silicon at different temperatures.
• 
  Optical transmission of 100 nm Al₂O₃ deposited on fused silica wafer at 200C.
• 
  Refractive index of 100 nm Al₂O₃ deposited on silicon at different temperatures.
• 
  Optical transmission of 100 nm Al₂O₃ deposited on fused silica wafer at 200C.
• 
  Refractive index of 100 nm Al₂O₃ deposited on silicon at different temperatures.
• 
  Optical transmission of 100 nm Al₂O₃ deposited on fused silica wafer at 200C.
• 
  Refractive index of 100 nm Al₂O₃ deposited on silicon at different temperatures.
• 
  Optical transmission of 100 nm Al₂O₃ deposited on fused silica wafer at 200C.

X-ray photoelectron spectroscopy

XPS measurements of all samples has been performed using the XPS NEXSA equipment. The purpose of the investigation is to get an idea about the film stoichiometry, composition and possible contamination. Since the XPS NEXSA also offers REELS and ISS analysis these measurements were also performed.

The XPS Nexsa is equipped with the MAGCIS or Mono Atomic and Gas Cluster Ion Source that allows to sputter off material from the sample either using single argon atoms with energies up to 4 keV or by using ionized clusters of argon atoms (between 75 and 2000 atoms) with energies up to 8 keV. For this analysis, the native carbon contamination has been removed by Ar clusters at 4keV and a size of 300 atoms. The moisture level has been sputtered off by implementing 25 levels at 5 s each.

After the surface has been cleaned, the film has been measured, so the survey, valence region, and high-resolution elements (Al, O, and C) scan have been acquired.

• 
  Survey scan after removal of the native carbon.
• 
  Survey scan after removal of the native carbon.

• 
  Al 2p signal. High resolution scan. 100°C.
• 
  Al 2p signal. High resolution scan. 150°C.
• 
  Al 2p signal. High resolution scan. 200°C.
• 
  Al 2p signal. High resolution scan. 250°C.
• 
  Al 2p signal. High resolution scan. 100°C.
• 
  Al 2p signal. High resolution scan. 150°C.
• 
  Al 2p signal. High resolution scan. 200°C.
• 
  Al 2p signal. High resolution scan. 250°C.
• 
  Al 2p signal. High resolution scan. 100°C.
• 
  Al 2p signal. High resolution scan. 150°C.
• 
  Al 2p signal. High resolution scan. 200°C.
• 
  Al 2p signal. High resolution scan. 250°C.
• 
  Al 2p signal. High resolution scan. 100°C.
• 
  Al 2p signal. High resolution scan. 150°C.
• 
  Al 2p signal. High resolution scan. 200°C.
• 
  Al 2p signal. High resolution scan. 250°C.

Stoichiometry results

No traces of carbon has been found.

Stoichiometry results for TiN deposited with TiCl4 and NH3 plasma.
Temperature °C	500	450	400	350
Ti (At. %)	43.97	45.40	45.58	45.25
N (At. %)	35.19	38.81	38.51	39.90
O (At. %)	20.84	15.79	15.03	13.53
Cl (At. %)	0	0	0.88	1.33