Atomic Layer Deposition of Niobium Nitride Thin Film with Nbcl and NH

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Atomic layer deposition of niobium nitride thin film with NbCl5 and NH3 Moo-Sung Kim1, Se-Won Lee1, and Sergei Ivanov2 Atomic: Layer Deposition of Niobium Nitride Motivation

Key Properties Metal Nitride Work Function, • Thermodynamically stable toward Cu eV • High melting point TiN 5.05 – 5.15 • Chemically inert VN 5.05 – 5.15 • Good mechanical properties, such as hardness and toughness

• Low resistivity, good adhesion NbN 4.95 • Lower work function compared to TiN Potential Applications HfN 4.70 – 4.80 • Barrier layer • Metal gate TaN 4.70 – 4.80 • Electrode material Project goals R. Fujii et al, Vacuum, 2006, 80, p. 832-835 • Study ALD of NbN on various substrates • Confirm good process conformality

2 ALD Conference 2020 | June 2020 Atomic Layer Deposition of Niobium Nitride ALD precursor and ALD tool

• Niobium pentachloride, NbCl5, was evaluated as a potential precursor for the deposition of NbNx films

• Deposition on Si, SiO2, Al2O3 and TiN substrates was investigated • The impact of chamber pressure and wafer temperature on ALD process was studied

Tool Configuration NbNx Film Characterization

Chamber Pressure 1-30 Torr Thickness and Resistivity: XRF, 4 point probe 80oC NbCl 5 Film Composition: RBS, XPS, SIMS Wafer T 300-500oC Film properties: XRR and XRD

The deposition tool is CN-1 Surface morphology and single 200mm wafer with 300 sccm Conformality: SEM & TEM showerhead

3 ALD Conference 2020 | June 2020 Atomic Layer Deposition of Niobium Nitride Saturation Behavior at 350°C and 20 torr

• NbCl5 showed good saturation behavior independent of substrate • More variability was observed during ammonia saturation study on AlOx • 3/30/5/30 was used as a reference recipe for film saturation

NbCl5/Ar/NH3/Ar = x/30/5/30 x100 cycles NbCl5/Ar/NH3/Ar = 3/30/x/30 x100 cycles

4 ALD Conference 2020 | June 2020 Atomic Layer Deposition of Niobium Nitride The Impact of Chamber Pressure on Growth Rate

• Deposition rate increased with increase in chamber pressure • No significant impact of substrate on film thickness

NbCl5/Ar/NH3/Ar = 3/30/5/30 x100 cycles

5 ALD Conference 2020 | June 2020 Atomic Layer Deposition of Niobium Nitride GPC and Wafer Temperature Dependence at 10 torr NbNx Film Thickness vs. Cycle # at Different Wafer Temperatures • No nucleation delay and good linearity observed 300°C up to ~ 450°C 300oC • Above 450°C more variation between substrates was observed, likely due to minor reactivity of

NbCl5 with substrates

400°C 400oC

500°C 500oC

6 ALD Conference 2020 | June 2020 Characterization of Niobium Nitride Film Film Resistivity

• Resistivity of NbNx film decreased gradually as the deposition temperature increased. The resistivity at 350°C was ~ 1,900 uohm-cm, whereas it was ~700 uohm-cm at 500°C • No improvement in film resistivity with increase in chamber pressure was observed

NbNx Film Resistivity vs. Wafer T NbNx Film Resistivity vs. Chamber P Chamber P = 20 torr Wafer T = 350oC 3000 3000

2500 2500

2000 2000

1500 1500

1000 1000

Resistivity (uohm‐cm) 500

0 0 300 350 400 450 500 550 0 10203040 Wafer temperature (C) Chamber pressure (Torr)

7 ALD Conference 2020 | June 2020 Characterization of Niobium Nitride Film XPS and RBS Analysis

• Discrepancy between XPS and RBS analysis was observed at all testing conditions • XPS profile showed Nb-rich films, likely due to preferential sputtering of nitrogen

• RBS profile showed N-rich film, more consistent with Nb4N5 structure • XRD and SIMS analyses were also conducted to confirm film composition

XPS Profile of NbNx deposited at 350°C RBS Profile of NbNx deposited at 350°C

70 Nb

60 C1s N1s N 50 Nb3d O1s 40 Atomic % (%) % Atomic N Si2p Nb 30 Cl2p 20 Cl x10 10

0 0 20 40 60 80 100 120 140 160 180 200 220

Etch Time (s)

8 ALD Conference 2020 | June 2020 Characterization of Niobium Nitride Film SIMS Analysis

• According to SIMS analysis films deposited on Si substrate were nitrogen-rich, consistent with RBS data

• However, films deposited on SiO2 substrate showed composition more consistent with NbN. Further investigation is needed to confirm this observation. However, RBS of the film deposited on SiO2 at 500oC also confirmed this observation (Nb=49.0; N=50.1)

9 ALD Conference 2020 | June 2020 Characterization of Niobium Nitride Film XRD and XRR Analysis

• All films deposited about 350°C were polycrystalline

• XRD results showed peaks correlated with Nb4N5 structure • Relative peak intensities of 111 and 200 reflections changed with deposition temperatures but no obvious effect of chamber pressure or substrate was observed • Film density measured by XRR was ~ 6.7 g/cm3 at 350°C and increased to 7.3 g/cm3 at 500°C wafer temperature

XRD Pattern vs. Deposition Temperature and Substrate XRD Pattern vs. Chamber Pressure Chamber Pressure = 20 torr Wafer T = 350(p°C, Si substrate )@ 12000 10 torr (200) 10000 20 torr 30 torr (111) 500°C, on SiO 8000 2 Si 450°C, on SiO (220) 2 6000 (311) (222) ° 350 C, on SiO2 4000 500oC, on Si Intensity (cps) 450°C, on Si 2000 ° 350 C, on Si 0 30 35 40 45 50 55 60 65 70 75 80 2‐theta (degree)

10 ALD Conference 2020 | June 2020 Characterization of Niobium Nitride Film Step Coverage Optimization

NbNx Step Coverage vs. Wafer Temperature • The effect of wafer temperature and chamber and Chamber Pressure pressure on step coverage (SC) were studied • SC improved at lower chamber pressure • Best SC was at 450°C and 10 torr

3/30/5/30 x 500cy, NH3 Thermal ALD; AR ~ 15-18 M/T = Middle Thk/Top Thk (%) Top THK = 18.0 nm B/T = Bottom Thk/Top Thk (%) Middle = 17.5 nm (SC ~ 97%) Bottom = 17.0 nm (SC ~ 93%)

11 ALD Conference 2020 | June 2020 Atomic Layer Deposition of Niobium Nitride Film Summary and Conclusions

• ALD saturation characteristics, linearity of growth and ALD thermal window were investigated on

various substrates such as Si, SiO2, Al2O3 and TiN. • The ALD window of NbNx film was observed from 400 to 450°C with ALD deposition rate in 0.35- 0.40 Å/cycle range. • Best step coverage was observed at 450oC wafer temperature and 10 torr chamber pressure, ~ 95 % in trench pattern with A/R > 17 • The resistivity of NbNx film decreased gradually as the deposition temperature increased. It was 1900 μohm-cm at 350°C and decreased to 700 μohm-cm at 500°C wafer temperature

• The chemical composition correlated best with Nb4N5 at all conditions on Si substrate. Interestingly, Nb/N ratio was ~ 1/1 on SiO2 substrate based on RBS and SIMS analyses. This observation will have to be investigated further to explain potential effect of the substrate on stoichiometry of NbNx film. • The Cl impurities decreased with increase in deposition temperature and were <0.6 at % at 500°C.

12 ALD Conference 2020 | June 2020 Moo-Sung Kim1 and Se-Won Lee1 Merck Performance Materials 82 Jangjagol-ro, Danwon-gu Ansan City, 15601, S. Korea

Sergei Ivanov2 EMD Performance Materials 357 Marian Avenue Tamaqua, PA 18252, USA