Photomasks. Photolithography Evolution 9/11/2004 ECE580- MPE/MASKS/PHOTOMASKS.PPT

Transcription

1 Photolithography Evolution 1

2 : Evolution 2

3 Photomasks Substrates: Type : thermal expansion Chrome Pellicles Mask: OPC and PSM Fabrication: E-Beam or Laser 3

4 Photomask Information Websites: htm#section

5 Photomask Making: 5

6 Photomask Evolution Compexity and Price$ $500- $1000 $1200- $

7 Substrates: 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 7

8 Substrates: Glass properties : Thermal Expansion 8

9 Fabrication: Data = rectangles 9

10 Fabrication: Basics COG type 10

11 Fabrication: Basics COG type 11

12 Some Key layout terms on masks 12

13 Some Key layout terms on masks 13

14 Some Key layout terms on masks: FIDUCIALS Fiducials 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. 14

15 Pellicles: Defect protection: Particles outside depth of field Film membrane: Nitrocellulose Fluoro-Polymer ( DuPont Teflon AR coatings Membrane Thicknesses: 2.85um: ghi line 1.20 um: DUV ghi line um: ghi line 0.84 um: DUV ghi line 15

16 Defects Typical Photomask Defects: 16

17 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 Photomasks OPC Most common effect: line end shortening 17

18 OPC 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 18

19 OPC Sub-resolution outriggers: Sub-Resolution Assist Features: SRAF 19

20 OPC Special features Serifs: To square up line ends and corners Sub-resolution outriggers: 20

21 OPC Special 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 21

22 OPC Typical OPC: 22

23 OPC 23

24 OPC OPC pattern on 3 different Reticle Writers = RWA,B,C OPC on reticle (chrome) Un corrected Corrected OPC 24

25 PSM PSM: Phase Shift Mask Alternating Aperture type AAPSM 25

26 PSM: Alternating Aperture AAPSM fabrication process 26

27 PSM AAPSM:Phase Shift Mask CD optimization 0 and π windows 27

28 Fabrication Tools Ebeam 28

29 Ebeam Photomasks Fabrication Tools 29

30 Fabrication Tools Ebeam Writer 30

31 Laser Fabrication Tools:AMAT ETEC 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-line photoresist 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. 31

32 Laser Fabrication Tools:AMAT ETEC Alta Scanning laser writer system: 32