THE PHOTORESIST PROCESS AND IT

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THE PHOTORESIST PROCESS AND ITS APPLICATION TO
THE SEMICONDUCTOR INDUSTRY

• LINDSAY MARTIN
• PAUL SAUNDERS
• SPRING 2000
• POLYMERS PROJECT

2
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)

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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)

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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

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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

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POSITIVE AND NEGATIVE RESIST
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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

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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

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TYPES OF PHOTORESIST MATERIALS(one-component
negative)

• Polymer component of glycidyl methacrylate and
  ethyl acrylate

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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

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TYPES OF PHOTORESIST MATERIALS(two-component
negative)

• Matrix resinsynthetic rubber (poly cis-isoprene)
• Sensitizer bisazide
• bisazide sensitizer under radiation gives nitrine
  nitrogen

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TYPES OF PHOTORESIST MATERIALS (two-component
negative)

• Nitrines react to produce polymer linkages less
  soluble in developer

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TYPES OF PHOTORESIST MATERIALS(two-component
positive)

• Matrix resin Phenol-formaldehyde copolymer
  (novolak)
• Sensitizer diazoquinone

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TYPES OF PHOTORESIST MATERIALS (two-component
positive)

• Sensitizer distributed in matrix. Exposure to
  radiation matrix soluble in base

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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 stencilscreate 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

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THERMAL OXIDATION
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PHOTORESIST LAYER
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MASKING AND IRRADIATION
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ETCHING PROCESS
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ETCHING PROCESS
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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-phospho
  rus) to reflect their conducting characteristics
• First 4 steps repeated several times
• Front end of wafer completed (all active devices
  are formed)

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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

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DOPING PROCESS
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FINAL MICROPROCESSOR
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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

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CORPORATIONS INVOLVED IN NEW POLYMER DESIGNS

• ASAHI
• ASHLAND CHEMICAL
• DOW CHEMICAL
• DUPONT
• MERCK AND PRAXAIR
• MITSUI CHEMICALS
• SHELL CHEMICALS
• UNION CARBIDE

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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)

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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

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CONCLUSIONS OF PHOTORESIST PROCESS

• Industry moved from imaging light sources from
  350-450-nm down to 248-nm
• Researching photoresist to support component
  design lt0.18µm and later lt0.13µm
• 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