PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Advanced Photoresist TechnologyAdvanced Photoresist TechnologyJie SunEE 518Instructor: Dr. Jerzy RuzylloApr. 4 2006Presentation outlinePresentation outline Introduction of Photoresists Roadmap of Photoresist Technology Photoresists Solution for Submicron lithography SummaryIntroduction of PhotoresistsPhotoresists 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 state Photoactive Compound (PAC): Act to inhibit or promote the dissolution of the resin in the developer. PAC inhibits dissolution in positive resists before light exposure. After exposure the PAC promotes dissolution of the resin.* George Tech, “Photoresists and Non-optical Lithography”Photoresists Chemistry (1) Positive Photoresist  Two-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 very short wavelength exposures Novolac (N): a polymer whose monomer is an aromatic ring with two methyl groups and an OH group. dissolves in an aqueous solution easily  Diazoquinone(DQ) 20-50 % weight Photosensitive DQ UVCarboxylic acid ( dissolution enhancer)*Stephen A. Campbell, “ The Science and Engineering of Microelectronic Fabrication”.Photoresists Chemistry (2) Positive Photoresist 1. DQ molecule will not dissolve in a base developer solution (pH >7).2. UV light breaks the nitrogen molecule off forming an unstable molecule3. To “stabilize” itself, one of the 6 carbon atoms in the ring pops out of the ring (leaving 5)4. Once exposed to water (a developer /water mixture), an OH group attaches to the carbon atom, forming an acid.5. 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 a pattern precisely retained. Novolac fairly resistant chemical attack, a good mask for the subsequent plasma etching Resolution (um) - linearity/ minimum Sensitivity (mJ/cm2) Focus margin (um) Exposure margin (%) Dry etch resistance(X) Heat resistance  Adhesion Standing wave effect (and bulk effect)(um) BARC (bottom anti-reflective coating) compatibility Process margin/stability Shelf-lifePerformance of PhotoresistsPhotoresists Profile* Han Ku Cho, Samsung Electronics Co., Ltd, “Lithography technology review of what it is and what to be”, March 2003Roadmap of Photoresists Technology* Han Ku Cho, Samsung Electronics Co., Ltd, “Lithography technology review of what it is and what to be”, March 2003Deep UV Photoresist Limitation of Novolac based PhotoresistStrongly absorb below 250nm, KrF (248nm) marginally acceptable but not ArF (193nm)Photoresist Solution for Submicron Features PMMA PAGs ( Photoacid generator) replace PAC Contrast enhancement layers (CELs) Inorganic resist (Ag-doped Ge-Se) Silicon-containing resists (dry developable) Multi-layer photoresistPMMA (Ploymethyl methacrylate)  Short-wavelength lithography: deep UV, extreme UV, electron-beam lithography Resin itself is photosensitive Advantage: high resolution Disadvantage:  Plasma etch tolerance is very low and thick PMMA to protect the thin film Dissociation changes chemistry of the plasma etch and polymeric deposits on the surface of the substrate. Low sensitivity: Add PAG (chemically reactive dissociating) or elevate exposure temperature*Stephen A. Campbell, “ The Science and Engineering of Microelectronic Fabrication”.Contrast enhance layers (CELs)  CEM photo-bleachable  Spun onto the DQN PR after softbake  Formed in-situ “conformal contact mask”  Enhanced contrast  Important for DUV resists with less optical intense and PR radiation absorbtion* http://www.microsi.com/photolithography/data_sheets/CEM%20365iS%20Data%20Sheet%Inorganic Resist Advantage: High contrast γ ≈ 7Produce fine lineProcess: Ag-doped Ge-Se Ag plated on sputtered Ge-Se  Photodoping create Ag2Se after exposure Dissolved in alkaline solution Disadvantage: Require thick planarizing underlayer due to thin film nature Pineholes and defects from Ge-Se*Stephen A. Campbell, “ The Science and Engineering of Microelectronic Fabrication”.Dry developable: Polysilynes  Bi-layer process Silicon-containing resists on top of novolac based resist Highly resistant to plasma process Bleaching under DUV exposure due to cross-linked siloxane network Etch 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.12-21Multi-layer Resists and Hard mask  Tri-layer process Thin layer PR + SiO2 + thicker planarizing  Oxide layer act as hard mask Oxide layer: Dry etching resistant layer *E.Ong and E.L.Hu, “Multilayer Resists for Fine Line Optical Lithography,” Solid State Technol.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 2003Summary  Photoresists technology: Basic and key technology in lithography PR chemistry structure changed with wavelength of light source Several PR solutions for DUV application Multi-layer PR replace the single layer for Sub-100nm