LINDSAY MARTIN PAUL SAUNDERS SPRING 2000 POLYMERS PROJECT THE PHOTORESIST PROCESS AND IT’S APPLICATION TO THE SEMICONDUCTOR INDUSTRY LINDSAY MARTIN PAUL SAUNDERS SPRING 2000 POLYMERS PROJECT

AGENDA Definition of Photoresist and Types Photoresist Raw Materials and Chemistry Overview of Types Photoresist Process Semiconductor Process example Importance of Photoresist Material Corporations producing new photoresist polymers Applications of Photoresist Corporations using Technology Conclusion (Recent Tech involving Photoresist)

DEFINITION OF PHOTORESIST AND TYPES Photoresist is a viscous polymer resin (solution) containing some photochemical active polymer(PAC) Two types of Photoresist Negative Positive Spin coating most common method of putting Photoresist on wafer Photoresist material is irradiated using photons(photolithography), electrons(e-beam lithography) and X-rays(X-ray lithography)

TYPES OF PHOTORESIST AND PROCESS Mask applied to wafer with photoresist material Positive Photoresist Resist is exposed with UV light wherever the underlying material is to be removed Exposure to radiation changes the chemical structure of the resist so that it becomes more soluble in the developer solvent The exposed resist is then washed away by the developer solution, leaving windows of the bare underlying material The mask contains an exact copy of the pattern to remain Whatever goes shows

TYPES OF PHOTORESIST AND PROCESS Negative Photoresist Behaves in opposite manner to positive resist Exposure to irradiation causes the resist to polymerize, and becomes insoluble Negative resist remains on the surface wherever it is exposed, the developer solution removes only the unexposed portions Mask contain the inverse (or photographic “negative”) of the pattern to be transferred

POSITIVE AND NEGATIVE RESIST

TYPES OF PHOTORESIST MATERIALS Can be classified as one or two component One component polymer that undergoes photochemical reaction(polystyrene systems) PMMA(Polymethyl methacrylate) Two component sensitizer molecule(monomeric) dissolved in an inert polymeric matrix(Phenols, Acrylics, meta and para acetoxystyrene, azides) Phenolic resin matrix and diazonaphthoquinone poly cis-isoprene resin matrix and bisazide Phenol-formaldehyde copolymer and diazoquinone

TYPES OF PHOTORESIST MATERIALS(one-component positive) Polymer: polybutene-1-sulfone Radiation leads to chain scission, reduces molecular weight and gives a more soluble material

TYPES OF PHOTORESIST MATERIALS(one-component negative) Polymer: component of glycidyl methacrylate and ethyl acrylate

TYPES OF PHOTORESIST MATERIALS (one-component negative) Crosslinking reaction initiated by e-beam radiation with anion present This propagates to lead to insoluble hmolwt mat

TYPES OF PHOTORESIST MATERIALS(two-component negative) Matrix resin:synthetic rubber (poly cis-isoprene) Sensitizer: bisazide bisazide sensitizer under radiation gives nitrine + nitrogen

TYPES OF PHOTORESIST MATERIALS (two-component negative) Nitrines react to produce polymer linkages less soluble in developer

TYPES OF PHOTORESIST MATERIALS(two-component positive) Matrix resin: Phenol-formaldehyde copolymer (novolak) Sensitizer: diazoquinone

TYPES OF PHOTORESIST MATERIALS (two-component positive) Sensitizer distributed in matrix. Exposure to radiation matrix soluble in base

MICROLITHOGRAPHY PROCESS STEPS Wafer cleaning Thermal Oxidation or Decomposition Silicon wafer is heated and exposed to oxygen forming a SiO2 film on the surface of the wafer Masking(like stencils:create circuit patterns) Photoresist film is applied to wafer Mask is applied Intense light(UV) is projected through the mask Etching(removal of select portions) Wafer is developed (exposed resist is removed) Wafer baked to harden remaining Photoresist pattern Wafer exposed to chemical solution so resist not hardened are etched away

THERMAL OXIDATION

PHOTORESIST LAYER

MASKING AND IRRADIATION

ETCHING PROCESS

ETCHING PROCESS

MICROLITHOGRAPHY PROCESS STEPS Doping Atoms with one less (boron or Al) or one more electron(phosphorus) than silicon introduced Alters the electrical character of silicon P-Type (positive-boron) or N-type(negative-phosphorus) to reflect their conducting characteristics First 4 steps repeated several times Front end of wafer completed (all active devices are formed)

MICROLITHOGRAPHY PROCESS STEPS Dielectric Decomposition individual devices are interconnected using metal depositions and dielectric film (insulators) Passivation Final dielectric layer added to protect(silicon nitride or dioxide) Electrical tests are conducted

DOPING PROCESS

FINAL MICROPROCESSOR

IMPORTANCE OF PHOTORESIST MATERIAL Intense drive towards designing and fabricating material with small dimensions(0.1-1m) Microelectronics business need to build devices containing increasing # of individual circuit elements The Photoresist technology as a step in the microlithography process Photoresist material: Polymeric resins can help create faster and smaller devices Imaging light sources of smaller wavelengths(UV spectrum ranges from 117nm-410nm) Traditional photoresist using 248nm resolve features between 0.25-0.18µm

CORPORATIONS INVOLVED IN NEW POLYMER DESIGNS ASAHI ASHLAND CHEMICAL DOW CHEMICAL DUPONT MERCK AND PRAXAIR MITSUI CHEMICALS SHELL CHEMICALS UNION CARBIDE

APPLICATIONS OF PHOTORESIST (SEMICONDUCTORS) Electronic and Telecommunications industry Television, Radios and Printers Video Cameras and Computers(micro processor) Calculators and watches Cell phones and waveguides Aviation and Aerospace Industry Airplanes, meteorology equip and Spaceships Automobile Industry Cars( microchips trigger inflation of air bags) Traffic lights(signals) Pharmaceutical Industry Lab on a chip Portable blood analyzers(microchip-based sensing devices)

CORPORATIONS USING TECHNOLOGY IBM(Computers) MOTOROLA(Cell phones) HEWLETT PACKARD(calculators, computers and lab on chip) INTEL(micro processor) LUCENT TECH(waveguides) CORNING(waveguides and lab on chip) TEXAS INSTRUMENTS(calculators) SONY (Televisions etc.) BELL LABS(Telecommunications) MICRON TECH FUJITSU

CONCLUSIONS OF PHOTORESIST PROCESS Industry moved from imaging light sources from 350-450-nm down to 248-nm Researching photoresist to support component design <0.18µm and later <0.13µm Target for 2001-03 is to image light source of 193-nm Target after 2003 image light source of 157-nm Smaller wavelengths from light source creates smaller resist images