Presentation on theme: "Jie Sun EE 518 Instructor: Dr. Jerzy Ruzyllo Apr"— Presentation transcript:
1 Jie Sun EE 518 Instructor: Dr. Jerzy Ruzyllo Apr. 4 2006 Advanced Photoresist TechnologyJie SunEE 518Instructor: Dr. Jerzy RuzylloApr
2 Presentation outline Introduction of Photoresists Roadmap of Photoresist TechnologyPhotoresists Solution for SubmicronlithographySummary
3 Introduction of Photoresists Photoresists Type:Positive: exposed regions dissolve (best resolution)Negative: Unexposed regions dissolve ( Swelling)Photoresists Structure:Resin: a binder that provides mechanical properties (adhesion, chemical resistance)Solvent: used to dissolve the resin, allowing the resin to be applied in a liquid statePhotoactive Compound (PAC): Act to inhibit or promote the dissolution of theresin in the developer. PAC inhibits dissolution in positive resists before lightexposure. After exposure the PAC promotes dissolution of the resin.* George Tech, “Photoresists and Non-optical Lithography”
4 Photoresists Chemistry (1) Positive PhotoresistTwo-component DQN resists:DQN, corresponding to the photo-active compound, diazoquinone (DQ) and resin,novolac (N)Dominant for G-line (436nm) and I- line (365nm) exposure and not suitable for veryshort wavelength exposuresNovolac (N): a polymer whose monomer is an aromatic ring with two methyl groupsand an OH group.dissolves in an aqueous solution easilyDiazoquinone(DQ)20-50 % weightPhotosensitiveDQUVCarboxylic acid ( dissolution enhancer)*Stephen A. Campbell, “ The Science and Engineering of Microelectronic Fabrication”.
5 Photoresists Chemistry (2) Positive PhotoresistDQ molecule will not dissolve in a base developer solution (pH >7).UV light breaks the nitrogen molecule off forming an unstable moleculeTo “stabilize” itself, one of the 6 carbon atoms in the ring pops out of the ring (leaving 5)Once exposed to water (a developer /water mixture), an OH group attaches to the carbon atom, forming an acid.The acid can then react and dissolve with the basic developer solution.Advantage:Unexposed areas unchanged by the presence of the developer, line width and shape of apattern precisely retained.Novolac fairly resistant chemical attack, a good mask for the subsequent plasma etching
6 Performance of Photoresists Resolution (um) - linearity/ minimumSensitivity (mJ/cm2)Focus margin (um)Exposure margin (%)Dry etch resistance(X)Heat resistanceAdhesionStanding wave effect (and bulk effect)(um)BARC (bottom anti-reflective coating) compatibilityProcess margin/stabilityShelf-lifePhotoresists Profile* Han Ku Cho, Samsung Electronics Co., Ltd, “Lithography technology review of what it is and what to be”, March 2003
7 Roadmap of Photoresists Technology * Han Ku Cho, Samsung Electronics Co., Ltd, “Lithography technology review of what it is and what to be”, March 2003
8 Deep UV Photoresist Limitation of Novolac based Photoresist Strongly absorb below 250nm, KrF (248nm) marginally acceptable but not ArF (193nm)Photoresist Solution for Submicron FeaturesPMMAPAGs ( Photoacid generator) replace PACContrast enhancement layers (CELs)Inorganic resist (Ag-doped Ge-Se)Silicon-containing resists (dry developable)Multi-layer photoresist
9 PMMA (Ploymethyl methacrylate) Short-wavelength lithography: deep UV, extreme UV, electron-beam lithographyResin itself is photosensitiveAdvantage: high resolutionDisadvantage:Plasma etch tolerance is very low and thick PMMA to protect the thin filmDissociation changes chemistry of the plasma etch and polymeric deposits on thesurface of the substrate.Low sensitivity: Add PAG (chemically reactive dissociating) or elevate exposuretemperature*Stephen A. Campbell, “ The Science and Engineering of Microelectronic Fabrication”.
10 Contrast enhance layers (CELs) CEM photo-bleachableSpun onto the DQN PR after softbakeFormed in-situ “conformal contact mask”Enhanced contrastImportant for DUV resists with less optical intense and PR radiation absorbtion*
11 Inorganic Resist Advantage: High contrast γ ≈ 7 Produce fine line Process: Ag-doped Ge-SeAg plated on sputtered Ge-SePhotodoping create Ag2Se after exposureDissolved in alkaline solutionDisadvantage:Require thick planarizing underlayer due tothin film naturePineholes and defects from Ge-Se*Stephen A. Campbell, “ The Science and Engineering of Microelectronic Fabrication”.
12 Dry developable: Polysilynes Bi-layer processSilicon-containing resists on top of novolac based resistHighly resistant to plasma processBleaching under DUV exposure due to cross-linked siloxane networkEtch silicon selectively to silicon dioxide in HBr plasma* Roderick R. Kunz, et al, “193 nm Resists and Lithography”, Polymers for Advanced Technologies, Volume 5, p p.12-21
13 Multi-layer Resists and Hard mask Tri-layer processThin layer PR + SiO2 +thicker planarizingOxide layer act as hard maskOxide layer: Dry etchingresistant layer*E.Ong and E.L.Hu, “Multilayer Resists for Fine Line Optical Lithography,” Solid State Technol.
14 Process Comparison for SLR, BLR and MLR * Han Ku Cho, Samsung Electronics Co., Ltd, “Lithography technology review of what it is and what to be”, March 2003
15 SummaryPhotoresists technology: Basic and key technology in lithographyPR chemistry structure changed with wavelength of light sourceSeveral PR solutions for DUV applicationMulti-layer PR replace the single layer for Sub-100nm features