Prof. Christopher K. ber Department of Materials Science and Engineering, Cornell University, Ithaca NY Current Status of Inorganic Nanoparticle Photoresists Markos Trikeriotis, Marie Krysak, Yeon Sook Chung, Christine uyang, Emmanuel Giannelis (Cornell) Brian Cardineau, Robert Brainard (CNSE, Albany) CRNELL Mark Neisser, Kyoungyong Cho (Sematech)
Presentation verview Introduction to inorganic photoresists Lithographic performance highlights: EUV patterning Etching and pattern transfer Versatile resist platform: Dual-tone capability Alternative formulations EUV absorbance optimization CRNELL
Inorganic Photoresist Platform Why Inorganic Photoresist? High resolution: High aspect ratio Pattern collapse X Thinner film: Improved patterning ü Poor pattern transfer X High etch-resistance photoresist: Improved pattern transfer ü Advantages: Nanoparticles are soluble in PGMEA and other common coating solvents. Choice of the organic ligands can alter the photoresist chemistry: both positive tone and negative tone patterning. EUV absorbance, sensitivity and etch resistance can be fine-tuned by changing the combination and ratios of metal oxide, organic ligand and photoactive compound CRNELL
Resist Formulation Spin coating solvent: PGMEA HfMAA or ZrMAA: 5-10% w/v propylene glycol monomethyl ether acetate Photoactive compound: 1-10% w/w relative to nanoparticle mass Me Me Photoinitiator or PAG dimethoxy phenyl acetophenone CRNELL
Absorption optimization Film absorption depends on atomic composition and density µ = N A ρ MW i x iσ α i rganic/inorganic hybrid Inorganic: Hf 2 Zr 2 high density materials Hf has higher absorbance than Zr at 13.5 nm rganic: Lower density Photo absorption crosssection (cm 2 /mol) Zr Hf Absorption optimization: Hf:Zr ratio rganic content film density 0 10 20 30 40 50 60 70 80 Atomic Number CRNELL
EUV Lithography Highest EUV sensitivity reported to date! SuMMIT analysis: CD = 26.1 ± 0.11 nm LWR = 6.0 ± 0.10 nm LER = 3.8 ± 0.07 nm SuMMIT analysis: CD = 21.5 ± 0.58 nm LWR = 9.0 ± 0.18 nm LER = 5.6 ± 0.18 nm Zr-MAA + PAG Dose: 4.2 mj/cm 2 Half pitch 34nm 32nm 30nm 28nm Zr-MAA + PAG Dose: 16.5 mj/cm 2 CRNELL
Etch Resistance / Pattern Transfer Etch rate comparison of PHST and Hf-MAA resist 2 plasma treatment has no detrimental effect on pattern transfer 200 Film thickness (nm) 150 100 50 4.4 nm/sec 0.17 nm/sec PHST HfMAA SF 6 / 2 pattern transfer 0 0 30 60 90 120 150 Time (sec) HfMAA has 25 times better etch resistance than PHST CF 4 pattern transfer CRNELL
E-beam and 193i Lithography HfMAA + DPAP 193 dry, negative tone, 150nm HfMAA + DPAP E-beam, negative tone HfMAA + DPAP 193 immersion, negative tone, 40nm CRNELL
Inorganic Photoresist Platform Metal oxide nanoparticles with organic surface ligands Many possible combinations of inorganic cores, organic ligands and photoactive compounds Photoactive compound Inorganic cores to date: Zr 2 or Hf 2, other metal oxides can be used rganic shell: Carboxylic and sulfonic acids bind strongly. Tailored ligands. Photoactive compounds: Photoradical initiator or PAG CRNELL
First Hypothesized Mechanism Negative tone: Crosslink MAA via radical mechanism Positive tone unlikely Hf 2 H H Hf 2 H H H Hf 2 Hf 2 Hf 2 Hf 2 CRNELL
Dual-Tone Photoresist Dual-tone photoresist: Dual-Tone Capability The same Hf or Zr based films can be patterned on both tones only by changing the postexposure processing (+) HfMAA (-) (+) ZrMAA (-) CRNELL
Alternative Cores and Ligands H H Hf 2 H H H ü Dual-tone ü EUV ü E-beam, 193, DUV Alternative ligands: HfMAA H H Zr 2 H H H ü Dual-tone ü EUV ü E-beam, DUV ZrMAA H H Hf 2 H H H ü Dual-tone ü E-beam, DUV HfIBA CRNELL
Synthesis and Characterization 100 98 96 Film FT-IR of Hf-MAA 94 92 90 88 86 84 Transmittance (%) 82 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm-1) 30 25 Particle size - DLS 2-3 nm Hf- MAA Zr- MAA Number (%) 20 15 10 5 0 1 10 100 Particle diameter (nm) rganic content TGA Controlled MAA concentration CRNELL
Negative tone Not CAR Mechanism rganic alcohol developer, no PEB Photoinitiator or photoacid generator aids ligand crosslinking IR also suggests a change in the bonds corresponding to the binding ligands Positive tone Aq. base developer, PEB needed Solubility of unexposed regions is changed with PEB IR of Hf-MAA with 5 wt% PAG Difference between unexposed and exposed films 1.01 1.005 1 0.995 0.99 0.985 0.98 Transmittance (%) 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 0.975 1000 Wavenumber (cm-1) CRNELL
Summary Highly sensitive, high resolution EUV resist based on Hf-xide and Zr-xide Excellent etch resistance Both negative (expected) and positive (unexpected) tone New non-car mechanism for pattern formation ther cores and ligands possible and this will lead to further improvements CRNELL