1. 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

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)

3. 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)

4. 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

5. 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

6. POSITIVE AND NEGATIVE RESIST

7. 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

8. 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

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

10. 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

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

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

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

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

15. 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

16. THERMAL OXIDATION

17. PHOTORESIST LAYER

18. MASKING AND IRRADIATION

19. ETCHING PROCESS

20. ETCHING PROCESS

21. 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)

22. 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

23. DOPING PROCESS

24. FINAL MICROPROCESSOR

25. 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 µm

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

27. 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)

28. 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

29. CONCLUSIONS OF PHOTORESIST PROCESS
Industry moved from imaging light sources from nm down to 248-nm
Researching photoresist to support component design <0.18µm and later <0.13µm
Target for 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