photomasksmyplace.frontier.com/~stevebrainerd1...fwhm : note at 4x. mask blanks use standard i-line...

9/11/2004 ECE580-MPE/MASKS/PHOTOMASKS.PPT

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Photomasks• Photolithography Evolution


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Photomasks: Evolution


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Photomasks

• Photomasks• Substrates: Type : thermal expansion• Chrome• Pellicles• Mask: OPC and PSM• Fabrication: E-Beam or Laser


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Photomasks

• Photomask Information Websites:• http://www.photronics.com/internet/corpcomm/publications/basics101/basics.

htm#section3• http://www.appliedmaterials.com/products/etec_tp.html• http://www.photomask.com/tech/ov.html• http://www.lrsm.upenn.edu/~frenchrh/phase_shift_photomasks.htm• http://www.numeritech.com/nttechnology/• http://www.siliconductor.com/equipment/photo.htm• http://courses.nus.edu.sg/course/phyweets/Projects98/litho-x-

e/mask.html


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Photomaskshttp://www.amat.com/products/about_advanced_maskmaking_process2.html

• Photomask Making:


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Photomasks• Photomask Evolution Compexity and Price$• $500- $1000 $1200- $50000


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PhotomasksSubstrates: Type : Blanks

• There are four types of material used to make photomasks; quartz (the most commonly used and most expensive), LE, soda lime, and white crown. The mask sizes can range from 3 inches square to 7 inches square and 7.25 inches round. The thickness of the masks ranges from 60 mils to 250 mils. Most common size for modern tools is 6 inches square 250 mils thick (older tools 5 inch) The quartz has an absorbing film which need to be conductive for e-beam exposure:

• Binary masks: AR:Chrome oxide 100A (~1%) , Absorber:Chrome 800A, Glue and conductive layer ITO 100A (transparent conductor)0.1% Transmission (ND 3.0)

• APSM : MoSi2: 6 – 8% transmission• Weak phase shift or• Halftone masks


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PhotomasksSubstrates: Glass properties : Thermal Expansion


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Photomasks

• Fabrication: Data = rectangles


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Photomasks• Fabrication: Basics COG type


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Photomasks• Fabrication: Basics COG type


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Photomasks

Some Key layout terms on masks


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Photomasks

Some Key layout terms on masks


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PhotomasksSome Key layout terms on masks: FIDUCIALSFiducials are patterns on reticles used for alignment on wafer steppers. Each brand and model of stepper has specific types of fiducials. The fiducials are located outside of the array or fields.


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PhotomasksPellicles: Defect protection: Particles outside depth of field

Film membrane: Nitrocellulose

Fluoro-Polymer ( DuPontTeflon

AR coatings

Membrane Thicknesses:

2.85um: ghi line

1.20 um: DUV ghi line

0.794 um: ghi line

0.84 um: DUV ghi line


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PhotomasksDefects

• Typical Photomask Defects:


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PhotomasksOPC

Most common effect: line end shortening

• Typical OPC:• Optical Proximity Correction:• Purposely distort mask pattern to

correct for Proximity effects in wafer patterns caused by :

• Optical : diffraction and interference effects: illumination

• Wafer topographical: Underlying features

• Etch effects: Etcher type and chemistry


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PhotomasksOPC

• Optical Proximity Correction features:• Line end extensions• Line width biasing: Inflation or reduction• Serifs: To square up line ends and corners• Hammerheads: To square up and bias line ends• Sub-resolution outriggers: to correct outside linewidth

proximity effects in dense linewidths


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PhotomasksOPC

• Sub-resolution outriggers: Sub-Resolution Assist Features: SRAF


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PhotomasksOPC Special features

• Serifs: To square up line ends and corners• Sub-resolution outriggers:


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PhotomasksOPC Special features

Line end extensionsLine width biasing: Inflation or reductionSerifs: To square up line ends and cornersHammerheads: To square up and bias line ends


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PhotomasksOPC

• Typical OPC:


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PhotomasksOPC


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Photomasks OPChttp://www.mentor.com/dsm/tpapers/vtr.pdf

OPC

on reticle

(chrome)

Un corrected Corrected OPC

OPC pattern on 3 different ReticleWriters = RWA,B,C


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PhotomasksPSM

• PSM: Phase Shift Mask Alternating Aperture type AAPSM


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PSM: Alternating Aperture• AAPSM fabrication process


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PhotomasksPSM

• AAPSM:Phase Shift Mask CD optimization 0 and π windows


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PhotomasksFabrication Tools

http://www.appliedmaterials.com/products/pdf/211654exara.pdf• Ebeam


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• Ebeam


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• Ebeam Writer


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Photomasks Laser Fabrication Tools:AMAT ETEC http://www.amat.com/products/

Applied Materials Corp. Etec Laser Writers:

Alta 3700 :Exposure: raster scanned 363 nm laser to “ write” masks or reticles down to 0.27u spot size FWHM : note at 4X. Mask blanks use standard I-linephotoresist and processing.

Alta 4000 :Exposure: raster scanned 257 nm laser to “ write” masks or reticles down to 0.19u spot size FWHM: note at 4X. Mask blanks use standard DUV CAR photoresist and processing.


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Photomasks Laser Fabrication Tools:AMAT ETEC Alta 3700http://www.amat.com/products/pdf/pb_a3700.pdf

Scanning laser writer system:

photomasksmyplace.frontier.com/~stevebrainerd1...fwhm : note at 4x. mask blanks use standard i-line...

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