Specific Process Knowledge/Thin film deposition/Deposition of Titanium Nitride/Deposition of Titanium Nitride using Lesker sputter tool

Deposition Characteristics

This page presents the results of TiN deposition using reactive sputtering by Lesker sputter tool. The fabrication and characterization was conducted in 2019 by Evgeniy Shkondin, DTU Nanolab. The prepared samples were investigated by X-ray Photoelectron Spectroscopy (XPS) and Spectroscopic Ellipsometry. Several parameters influens the quality of the films. The analysis included variations of power, pressure, substrate temperature and N₂/Ar ratio.

In short, the key to prepare high quality, stochiometric, conducting TiN layers is to apply following deposition parameters:

• High power in the range 220W-250W
  Lesker sputter tool uses 2-inch targets. For Ti source, the highest allowed power is 250W. Deposition rate increases by using high power and it lower incorporation of oxygen in the film.

• Low pressure (1-2 mTorr)
  Lowering the pressure improves stochiometry and lower the oxygen content.

• High substrate temperature (400°C)
  Generally, the substrat temperatre affects the density.

• Work with N₂ concentration in the range 20-50%
  The higher the nitrogen concentration the lower the deposition rate, and it will result issues in respect to oxygen contamination.

The investigation is mainly based on two powers - 110W and 220W in pressure range between 1 to 14 mTorr. Substrate temperature was kept at 400°C with N₂/Ar ratio 20/80%.

Spectroscopic Ellipsometry

Drude-Lorentz model

Drude-Lorentz is commonly used to fit TiN complex dielectric function.

$\epsilon (E)=\epsilon _{\infty }+\epsilon _{Drude}(E)+\sum _{n}\epsilon _{Lorentz}(E)$
where: $\epsilon _{\infty }$ is a high-frequency dielectric constant.

The Drude term can be written as follow:

$\epsilon _{Drude}(E)={\frac {-\hbar ^{2}}{\epsilon _{o}\rho (\tau E^{2}+i\hbar E)}}$
where: $\epsilon _{o}$ - dielectric permittivity of vacuum, $\hbar$ - Planck constant, $\rho$ - resistivity, $\tau$ - scattering time.

Lorentz oscillator term is given by:

$\epsilon _{Lorentz}(E)={\frac {Amp_{n}Br_{n}En_{n}}{En_{n}^{2}-E^{2}-iEBr_{n}}}$
where: $n$ - number of oscillator, $Amp$ - Amplitude, $Br$ - Broadening of each oscillator, $En$ - Center energy of the Lorentz oscillator.

Dielectric function analysis

High Power. Deposition time: 20min				Drude term		Lorentz oscillator - 1			Lorentz oscillator - 2			Lorentz oscillator - 3
Power (W)	Pressure (mTorr)	Thickness (nm)	$\epsilon _{\infty }$	$\rho$ (Ohm cm)	$\tau$ (fs)	$Amp_{1}$	$Br_{1}$ (eV)	$En_{1}$ (eV)	$Amp_{2}$	$Br_{2}$ (eV)	$En_{2}$ (eV)	$Amp_{3}$	$Br_{3}$ (eV)	$En_{3}$ (eV)
220	1	87.01	3.489	7.5618·10-5	1.008	192.557054	0.0213	6.321	9.689831	2.7132	5.604	-	-	-
220	2	66.13	2.609	2.017·10-4	1.141	2.083940	0.8848	3.492	8.125820	3.2412	5.944	15.781023	0.9923	1.053
220	4	66.40	1.934	6.6567·10-4	1.041	2.439534	1.3777	3.724	4.677488	4.0837	6.160	12.110575	0.9458	0.959
220	6	75.11	1.347	2.587·10-3	0.655	2.303432	1.7123	3.942	1.934678	5.4051	6.420	7.712139	0.9659	0.883
220	8	81.94	1.271	4.273·10-3	0.242	2.038004	1.7074	4.062	1.614453	5.6564	6.677	5.212949	0.8602	0.895
220	10	82.59	1.138	5.257·10-3	0.323	1.672949	1.6265	4.186	1.433617	7.9416	7.058	4.294563	0.8546	0.902
220	12	82.40	1.090	5.807·10-3	0.443	1.450316	1.5414	4.262	1.368362	9.1405	7.128	3.787770	0.8471	0.906
220	14	81.88	1.089	5.838·10-3	0.468	1.415215	1.5370	4.266	1.349390	9.2650	7.074	3.579245	0.8420	0.909
Low Power. Deposition time: 40min				Drude term		Lorentz oscillator - 1			Lorentz oscillator - 2			Lorentz oscillator - 3
Power (W)	Pressure (mTorr)	Thickness (nm)	$\epsilon _{\infty }$	$\rho$ (Ohm cm)	$\tau$ (fs)	$Amp_{1}$	$Br_{1}$ (eV)	$En_{1}$ (eV)	$Amp_{2}$	$Br_{2}$ (eV)	$En_{2}$ (eV)	$Amp_{3}$	$Br_{3}$ (eV)	$En_{3}$ (eV)
110	2	37.28	1.951	3.4619·10-4	0.719	2.294032	2.7712	4.298	8.807626	4.6007	7.311	14.494131	1.0222	1.025
110	4	32.42	2.024	9.724·10-4	0.890	5.185267	3.5747	4.958	7.900142	2.2325	7.115	12.284271	0.8444	1.012
110	6	34.12	1.907	2.109·10-3	1.119	3.946173	3.4395	4.953	4.368733	1.9486	7.189	7.063107	0.8046	0.983
110	8	35.58	1.694	2.661·10-3	1.292	2.990718	3.3861	4.928	3.091825	2.0160	7.163	4.843337	0.7813	0.980
110	10	37.02	1.526	2.741·10-3	1.592	2.521075	3.5788	4.959	2.664635	2.1239	7.295	3.751751	0.7497	0.975

Dielectric function $\epsilon (E)$ can be rearranged in order to separate real and complex parts: $\epsilon (E)=\epsilon _{1}+i\epsilon _{2}$ . Here, $\epsilon _{1}$ is a real part of the permittivity, and $\epsilon _{2}$ is imaginary part describing optical losses.

DC power 220W

• DC Power 220W
• 
  Elemental procent presence as a function of process pressure (110W).

DC power 110W

• DC Power 110W
• 
  Elemental procent presence as a function of process pressure (110W).

XPS analysis

XPS measurements of all samples has been performed using ….

High resolution scans of individual elements

DC power 220W

• DC Power 220W
• 
  Ti 2p scan.
• 
  O 1s scan.
• 
  N 1s scan.

DC power 110W

• DC Power 110W
• 
  Ti 2p scan.
• 
  O 1s scan.
• 
  N 1s scan.

Stochiometry and N₂/Ti ratio

• Stochiometry
• 
  Elemental procent presence as a function of process pressure (110W).
• 
  Elemental procent presence as a function of process pressure (220W).
• 
  N/Ti ratio for 220W and 110W deposition power.

Films elemental composition

Atomic concentration......

Power (W)	Pressure (mTorr)	Ti (At. %)	N (At. %)	O (At. %)	C (At. %)
220	14	35.20	27.26	33.34	4.20
220	12	35.93	27.71	34.00	2.36
220	10	36.02	27.68	33.34	2.96
220	8	36.23	27.74	32.93	3.10
220	6	35.74	28.49	32.08	3.69
220	4	36.19	29.78	30.05	3.98
220	2	37.12	32.33	26.08	4.47
220	1	42.51	39.27	16.75	1.48
110	10	35.31	26.76	33.84	4.08
110	8	35.86	27.01	32.91	4.22
110	6	35.64	27.24	32.03	5.09
110	4	34.74	27.35	30.34	7.56
110	2	37.18	30.26	27.08	5.48

Effect of substrate temperature

High Power. Deposition time: 10min					Drude term		Lorentz oscillator - 1			Lorentz oscillator - 2			Lorentz oscillator - 3
Temperature (oC)	Power (W)	Pressure (mTorr)	Thickness (nm)	$\epsilon _{\infty }$	$\rho$ (Ohm cm)	$\tau$ (fs)	$Amp_{1}$	$Br_{1}$ (eV)	$En_{1}$ (eV)	$Amp_{2}$	$Br_{2}$ (eV)	$En_{2}$ (eV)	$Amp_{3}$	$Br_{3}$ (eV)	$En_{3}$ (eV)
20	220	2	41.06	2.574	6.5701·10-4	0.815	5.851313	6.8806	6.711	14.513401	1.0293	1.038	-	-	-
400	220	2	46.09	2.692	2.1618·10-4	0.697	1.087128	1.3685	3.824	8.301574	3.5998	6.291	10.301534	1.0371	1.104

• Effect of substrate temperature. Deposition time 10 min. Power 220W. Pressure 2 mTorr
• 
  Real part of permittivity (220W, 2 mTorr).
• 
  Imaginary part of permittivity (220W, 2 mTorr).

Effect of N₂/Ar ratio

High Power. Deposition time: 20min					Drude term		Lorentz oscillator - 1			Lorentz oscillator - 2			Lorentz oscillator - 3
N2 (flow (%))	Power (W)	Pressure (mTorr)	Thickness (nm)	$\epsilon _{\infty }$	$\rho$ (Ohm cm)	$\tau$ (fs)	$Amp_{1}$	$Br_{1}$ (eV)	$En_{1}$ (eV)	$Amp_{2}$	$Br_{2}$ (eV)	$En_{2}$ (eV)	$Amp_{3}$	$Br_{3}$ (eV)	$En_{3}$ (eV)
20	220	1	87.01	3.489	7.5618·10-5	1.008	192.557054	0.0213	6.321	9.689831	2.7132	5.604	-	-	-
80	220	1	39.88	1.926	1.6566·10-4	0.761	7.288805	4.9948	6.061	48.12146	0.5020	0.442	-	-	-

• Effect of substrate temperature. Deposition time 10 min. Power 220W. Pressure 2 mTorr
• 
  Real part of permittivity (220W, 2 mTorr).
• 
  Imaginary part of permittivity (220W, 2 mTorr).
• 
  Elemental procent presence as a function of process pressure (110W).