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MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
Photo-lithography
Manufacturing
Book: Micro Electro Mechanical System Design by James J Allen
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
What is Lithography?
• Lithography(Greek word) means printing on stone.
• Photo-lithography: light-silicon wafer-printing.
• Components in photolithography:
(1)Mask (2) Photoresist (3)UV exposure system
Lithography is the most widely used method to pattern
layers in microelectronic and MEMS processing. 2
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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Overview of the Photolithography
Process
(1)Mask
(2) Photoresist
(3)UV exposure system
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
Steps Used in
Photolithography
• Surface cleaning
• Spin coating with photoresist
• Soft baking
• Mask alignment
• Exposure
• Development
• Hard baking
• Plasma Etch-Or Add Layer
• Post process cleaning
• Final Inspection
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
Surface Cleaning
• Typical contaminants that must be removed prior to
photoresist coating: dust from scribing or cleaving
(minimized by laser scribing)
• Photoresist residue from previous photolithography
(minimized by performing oxygen plasma ashing)
• Atmospheric dust (minimized by good clean room
practice)
• Bacteria (minimized by good Deionized water system)
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
• films from other sources:
-solvent residue
-H2O residue
-photoresist or developer residue
-silicone
• For particularly troublesome grease, oil, or wax
stains: Start with 2-5 min. soak in 1,1,1-
trichloroethane (TCA) or trichloroethylene (TCE)
with ultrasonic agitation prior to acetone
Surface
Cleaning
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
Spin coating with photoresist
• Wafer is held on a spinner chuck by vacuum and resist is
coated to uniform thickness by spin coating.
• Typically 3000 - 6000 rpm for 15-30 seconds.
• Resist thickness is set by: primarily resist viscosity secondarily
spinner rotational speed
• Most resist thicknesses are 1-2 μm for commercial Si
processes.
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
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• Resist thickness is given by
t =square of( k p )/root of(w),
where,
k = spinner constant
p = resist solids content in percent
w = spinner rotational speed in rpm/1000
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
Stages of Resist Coating
MEHRAN UNIVERSITY
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MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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Stages of Resist Coating
10
MEHRAN UNIVERSITY
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MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
Soft baking
• Used to evaporate the coating solvent.
• Typical thermal cycles:90-100°C for 20 min. in a
convection oven 75-85°C for 45 sec. on a hot plate
• Microwave heating or IR lamps are also used
• Optimizes light absorbance characteristics of
photoresist
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
Soft baking
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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Mask alignment & Exposure
Transfers the mask image to
the resist-coated wafer
Activates photo-sensitive
components of photoresist
Three types of masking
(1) Contact printing
(2) Proximity printing
(3) Projection printing
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
• Contact printing capable of high resolution but has
unacceptable defect densities. May be used in
Development but not manufacturing.
• Proximity printing cannot easily print features below a
few mm in line width.
• Projection printing provides high resolution and low
defect densities and dominates today. The number of
print 50 wafers/hour.
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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Positive resist & Negative
resist
16
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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Development
• Soluble areas of photoresist are dissolved by
developer chemical
• Visible patterns appear on wafer
• Quality measures:
• –line resolution
• –uniformity
• –particles & defects
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
Hard baking
• Used to stabilize and harden the developed
photoresist prior to processing steps that the resist
will mask.
• Postbake removes any remaining traces of the
coating solvent or developer.
• Higher temperature than soft bake (120-150
degree)
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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Plasma Etch-Or Add Layer
19
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
Post process cleaning
• Plasma etching with O2 (ashing)
• Simple solvents are generally sufficient for non- postbaked
photoresists:
• Positive photoresists:
aceton
trichloroethylene (TCE)
• Negative photoresists:
methyl ethyl ketone
methyl isobutyl ketone
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
Final Inspection
• Photoresist has been completely removed
• Pattern on wafer matches mask pattern (positive
resist)
• Quality issues:
–defects
–particles
–step height
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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Photolithography
Requirements• High Resolution
• High PR Sensitivity
• Precision Alignment
• Precise Process Parameters Control
• Low Defect Density
• Photo sensitive material
• Temporarily coated on wafer surface
• Transfer design image on it through exposure
• Very similar to the photo sensitive coating on the film for
camera
Photoresist
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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Negative Photoresist
• Becomes insoluble after
exposure
• When developed, the
unexposed parts dissolved.
• Cheaper
Positive Photoresist
• Becomes soluble after exposure
• When developed, the exposed
parts dissolved
• Better resolution
Photoresist
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
• Polymer
• Solvents
• Sensitizers
• Additives
POLYMER
• Solid organic material
• Transfers designed pattern to wafer surface
• Changes solubility due to photochemical reaction when exposed
to UV light.
• Positive PR: from insoluble to soluble
• Negative PR: from soluble to insoluble
Photoresist Composition
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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MEHRAN UNIVERSITY
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SOLVENTS
• Dissolves polymers into liquid
• Allow application of thin PR layers by spinning.
SENSITIZERS
• Controls and/or modifies photochemical reaction of resist
during exposure.
• Determines exposure time and intensity.
ADDITIVES
• Various added chemical to achieve desired process results, such
as dyes to reduce reflection..
Photoresist Composition
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
• Most negative PR are polyisoprene type
• Exposed PR becomes cross-linked polymer
• Cross-linked polymer has higher chemical etch resistance.
• Unexposed part will be dissolved in development solution.
Negative Resist
Disadvantages
• Polymer absorbs the development
solvent
• Poor resolution due to PR swelling
• Environmental and safety issues
due to the
main solvents xylene.
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
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• Exposed part dissolve in developer solution
• Image the same that on the mask
• Higher resolution
• Commonly used in IC fabs
Positive Resist
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
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Comparison of Photoresists
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
• High resolution
– Thinner PR film has higher the resolution
– Thinner PR film, the lower the etching and ion
implantation resistance
• High etch resistance
• Good adhesion
• Wider process latitude
– Higher tolerance to process condition change
Requirement of Photoresist
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
• Photoresist must be able to withstand process conditions
• Coating, spinning, baking, developing.
• Etch resistance
• Ion implantation blocking
Photoresist Physical Properties
Photoresist Performance Factor
• Resolution • Adhesion
• Expose rate, Sensitivity and Exposure Source
• Process latitude/ liberty • Pinholes
• Particle and Contamination Levels
• Step Coverage • Thermal Flow
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
MEHRAN UNIVERSITY
OF ENGINEERING & TECHNOLOGY, JAMSHORO
MASTERS IN MANUFACTURING
• The smallest opening or space that can produced in a photoresist layer.
• Related to particular processes including expose source and developing
process.
• Thinner layer has better resolution.
• Etch and implantation barrier and pinhole-free require thicker layer
• Positive resist has better resolution due to the smaller size of polymer.
Resolution Capability

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Photolithiography Mannufacturing

  • 1. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Photo-lithography Manufacturing Book: Micro Electro Mechanical System Design by James J Allen
  • 2. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING What is Lithography? • Lithography(Greek word) means printing on stone. • Photo-lithography: light-silicon wafer-printing. • Components in photolithography: (1)Mask (2) Photoresist (3)UV exposure system Lithography is the most widely used method to pattern layers in microelectronic and MEMS processing. 2
  • 3. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Overview of the Photolithography Process (1)Mask (2) Photoresist (3)UV exposure system
  • 4. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Steps Used in Photolithography • Surface cleaning • Spin coating with photoresist • Soft baking • Mask alignment • Exposure • Development • Hard baking • Plasma Etch-Or Add Layer • Post process cleaning • Final Inspection
  • 5. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Surface Cleaning • Typical contaminants that must be removed prior to photoresist coating: dust from scribing or cleaving (minimized by laser scribing) • Photoresist residue from previous photolithography (minimized by performing oxygen plasma ashing) • Atmospheric dust (minimized by good clean room practice) • Bacteria (minimized by good Deionized water system)
  • 6. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING • films from other sources: -solvent residue -H2O residue -photoresist or developer residue -silicone • For particularly troublesome grease, oil, or wax stains: Start with 2-5 min. soak in 1,1,1- trichloroethane (TCA) or trichloroethylene (TCE) with ultrasonic agitation prior to acetone Surface Cleaning
  • 7. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Spin coating with photoresist • Wafer is held on a spinner chuck by vacuum and resist is coated to uniform thickness by spin coating. • Typically 3000 - 6000 rpm for 15-30 seconds. • Resist thickness is set by: primarily resist viscosity secondarily spinner rotational speed • Most resist thicknesses are 1-2 μm for commercial Si processes.
  • 8. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING • Resist thickness is given by t =square of( k p )/root of(w), where, k = spinner constant p = resist solids content in percent w = spinner rotational speed in rpm/1000
  • 9. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Stages of Resist Coating
  • 10. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Stages of Resist Coating 10
  • 11. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Soft baking • Used to evaporate the coating solvent. • Typical thermal cycles:90-100°C for 20 min. in a convection oven 75-85°C for 45 sec. on a hot plate • Microwave heating or IR lamps are also used • Optimizes light absorbance characteristics of photoresist
  • 12. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Soft baking
  • 13. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Mask alignment & Exposure Transfers the mask image to the resist-coated wafer Activates photo-sensitive components of photoresist Three types of masking (1) Contact printing (2) Proximity printing (3) Projection printing
  • 14. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING
  • 15. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING • Contact printing capable of high resolution but has unacceptable defect densities. May be used in Development but not manufacturing. • Proximity printing cannot easily print features below a few mm in line width. • Projection printing provides high resolution and low defect densities and dominates today. The number of print 50 wafers/hour.
  • 16. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Positive resist & Negative resist 16
  • 17. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Development • Soluble areas of photoresist are dissolved by developer chemical • Visible patterns appear on wafer • Quality measures: • –line resolution • –uniformity • –particles & defects
  • 18. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Hard baking • Used to stabilize and harden the developed photoresist prior to processing steps that the resist will mask. • Postbake removes any remaining traces of the coating solvent or developer. • Higher temperature than soft bake (120-150 degree)
  • 19. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Plasma Etch-Or Add Layer 19
  • 20. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Post process cleaning • Plasma etching with O2 (ashing) • Simple solvents are generally sufficient for non- postbaked photoresists: • Positive photoresists: aceton trichloroethylene (TCE) • Negative photoresists: methyl ethyl ketone methyl isobutyl ketone
  • 21. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Final Inspection • Photoresist has been completely removed • Pattern on wafer matches mask pattern (positive resist) • Quality issues: –defects –particles –step height
  • 22. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Photolithography Requirements• High Resolution • High PR Sensitivity • Precision Alignment • Precise Process Parameters Control • Low Defect Density • Photo sensitive material • Temporarily coated on wafer surface • Transfer design image on it through exposure • Very similar to the photo sensitive coating on the film for camera Photoresist
  • 23. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Negative Photoresist • Becomes insoluble after exposure • When developed, the unexposed parts dissolved. • Cheaper Positive Photoresist • Becomes soluble after exposure • When developed, the exposed parts dissolved • Better resolution Photoresist
  • 24. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING • Polymer • Solvents • Sensitizers • Additives POLYMER • Solid organic material • Transfers designed pattern to wafer surface • Changes solubility due to photochemical reaction when exposed to UV light. • Positive PR: from insoluble to soluble • Negative PR: from soluble to insoluble Photoresist Composition
  • 25. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING SOLVENTS • Dissolves polymers into liquid • Allow application of thin PR layers by spinning. SENSITIZERS • Controls and/or modifies photochemical reaction of resist during exposure. • Determines exposure time and intensity. ADDITIVES • Various added chemical to achieve desired process results, such as dyes to reduce reflection.. Photoresist Composition
  • 26. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING • Most negative PR are polyisoprene type • Exposed PR becomes cross-linked polymer • Cross-linked polymer has higher chemical etch resistance. • Unexposed part will be dissolved in development solution. Negative Resist Disadvantages • Polymer absorbs the development solvent • Poor resolution due to PR swelling • Environmental and safety issues due to the main solvents xylene.
  • 27. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING • Exposed part dissolve in developer solution • Image the same that on the mask • Higher resolution • Commonly used in IC fabs Positive Resist
  • 28. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING Comparison of Photoresists
  • 29. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING • High resolution – Thinner PR film has higher the resolution – Thinner PR film, the lower the etching and ion implantation resistance • High etch resistance • Good adhesion • Wider process latitude – Higher tolerance to process condition change Requirement of Photoresist
  • 30. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING • Photoresist must be able to withstand process conditions • Coating, spinning, baking, developing. • Etch resistance • Ion implantation blocking Photoresist Physical Properties Photoresist Performance Factor • Resolution • Adhesion • Expose rate, Sensitivity and Exposure Source • Process latitude/ liberty • Pinholes • Particle and Contamination Levels • Step Coverage • Thermal Flow
  • 31. MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO MASTERS IN MANUFACTURING • The smallest opening or space that can produced in a photoresist layer. • Related to particular processes including expose source and developing process. • Thinner layer has better resolution. • Etch and implantation barrier and pinhole-free require thicker layer • Positive resist has better resolution due to the smaller size of polymer. Resolution Capability