Monatomic and Cluster Argon Ion XPS Depth Profiling of SrTiO 3 and - - PowerPoint PPT Presentation

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Monatomic and Cluster Argon Ion XPS Depth Profiling of SrTiO 3 and - - PowerPoint PPT Presentation

Nov 07, 2023 43 likes •155 views

Monatomic and Cluster Argon Ion XPS Depth Profiling of SrTiO 3 and HfO 2 Paul Mack, Thermo Fisher Scientific The world leader in serving science Introduction: Depth profiling of metal oxide layers HfO 2 or SrTiO 3 layer on Si substrate

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The world leader in serving science

Paul Mack, Thermo Fisher Scientific

Monatomic and Cluster Argon Ion XPS Depth Profiling of SrTiO3 and HfO2

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Introduction: Depth profiling of metal oxide layers

Sample structure

HfO2 or SrTiO3 Si

~25 nm Substrate

  • HfO2 or SrTiO3 layer on Si substrate
  • Problem
  • What is the stoichiometry of the film as a function of

depth?

  • Traditional monatomic Ar+ sputtering causes changes in
  • xidation state when profiling metal oxides
  • How can we profile through the sample, keeping the

chemistry intact?

  • Argon clusters with ≥2000 atoms are good for profiling

through organic layers with minimal chemical damage

− These large clusters etch too slowly with inorganic materials

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Introduction: Monatomic versus cluster profiling

  • Monatomic ions (Ar+)
  • High energy per atom (200eV – 4keV)
  • High etch rate
  • Deep surface penetration
  • Can damage surface chemistry
  • Ideal for etching inorganic material
  • Cluster ions (Ar+

n)

  • Low energy per atom (1eV – 100eV)
  • Minimal surface penetration
  • Non-damaging to surface chemistry
  • Low etch rate for large clusters
  • Large clusters ideal for etching organic material
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Introduction: Small clusters for inorganic profiling

20 40 60 80 100 500 1000 1500 2000 Energy per atom / eV Number of atoms in cluster

Energy per atom versus cluster size for different beam energies

Higher beam energy 8keV beam

300 atom cluster Same energy per atom

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Monatomic Argon profile - SrTiO3 film on Si

  • Monatomic Argon profile
  • 500eV beam energy
  • Sr:Ti ratio is expected to be 1:1

throughout film but ∼0.75:1 observed instead

  • Monatomic Argon beam is modifying

the stoichiometry of the film

10 20 30 40 50 60 70 80 90 100 100 200 300 400 500 600 Atomic % (%) Etch Time (s)

500eV Ar+ monatomic profile

O Ti Sr Si C

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Monatomic Argon profile – Titanium chemistry SrTiO3 film on Si

450 454 458 462 466 470 474 Binding Energy (eV)

Ti2p spectra as received and during 500eV Ar+ sputter profile

Ti2p3/2 (Ti4+) Ti2p1/2 (Ti4+)

Reduced

  • xidation states,

caused by ion beam damage

  • Monatomic Argon profile
  • Ti2p spectrum from as received surface

shows only peaks due to Ti4+ chemical state (as expected for SrTiO3)

  • After only 90s of 500eV Ar+ profiling, a

significant intensity of lower oxidation states (Ti3+, Ti2+) are observed in the spectrum

  • ∼45% of the Ti2p spectrum is due to

these damaged states after 500eV sputtering

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Argon small cluster profile - SrTiO3 film on Si

10 20 30 40 50 60 70 80 90 100 100 200 300 400 500 600 Atomic % (%) Etch Time (s)

8keV, Ar300

+ cluster profile

O Ti Sr Si C

  • Argon small cluster profile
  • 8keV, Ar300+ small cluster beam
  • Etch rate is comparable to the 500eV

monatomic profile (0.07 nm/s)

  • With small cluster profiling, the Sr:Ti ratio

is much closer to the expected 1:1 value

  • Small cluster beam is much better at

preserving the elemental composition of the SrTiO3 film, compared to the 500eV monatomic beam

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450 454 458 462 466 470 474 Binding Energy (eV)

Ti2p spectra as received, during 8keV Ar300

+ sputter profile

and 500eV monatomic profile

Ti2p3/2 (Ti4+) Ti2p1/2 (Ti4+)

Lower damage from small cluster profiling

  • Argon small cluster profile
  • Ti2p spectrum from as received surface shows
  • nly peaks due to Ti4+ chemical state (as

expected for SrTiO3)

  • After 90s of 8keV Ar300

+ profiling, the damage

to the titanium is considerably lower than was

  • bserved for the 500eV monatomic beam
  • Small cluster profiling only caused the

production of Ti3+ states, whereas monatomic profiling generated Ti3+ and the more reduced Ti2+ state in similar quantities

Argon small cluster profile – Titanium chemistry - SrTiO3 film on Si

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10 20 30 40 50 60 70 80 90 100 Atomic % (%)

500eV monatomic Ar+ profile

O Hf Hfdamaged Si

10 20 30 Etch Depth (nm) 10 12 14 16 18 20 22 24 26 28 30 Binding Energy (eV)

Hfdamaged HfO2 0nm 7nm 12nm

Hf4f spectra from depth profile

  • Significant change in [Hf]/[O] ratio in top few nm,

caused by preferential sputtering of oxygen

  • Damage to Hf chemistry, as observed in Hf4f

spectra (almost 50% on total Hf concentration in film)

  • Prolonged tailing of Hf damaged into Si substrate

Low energy (500eV) monatomic Argon profile - HfO2 film on Si

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  • Sample tilted to give more glancing ion incidence

during sputtering

  • Constant [Hf]/[O] ratio throughout film (minimal

preferential sputtering of oxygen)

  • No significant damage to Hf chemistry, until well

into interface region (much less damage compared to 500eV monatomic mode)

10 12 14 16 18 20 22 24 26 28 30 Binding Energy (eV)

0nm 7nm 12nm HfO2 Hfdamaged

Hf4f spectra from depth profile

10 20 30 40 50 60 70 80 90 100 10 20 30 Atomic % (%) Etch Depth (nm)

8keV Ar150

+ cluster profile

O Hf Hfdamaged Si

Small Argon cluster (8keV, Ar+

150) sputter profile - HfO2 film on Si

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  • Small cluster profiling of HfO2 and

SrTiO3 films

  • Monatomic and Gas Cluster Ion

Source

  • Comprehensive XPS profiling with small

Argon clusters (75-300 atoms) enables HfO2 films to be analysed with lower chemical damage than monatomic Argon

Thermo Scientific Monatomic and Gas Cluster Ion Source (MAGCIS)

Conclusion - HfO2 film on Si