Optical Projection Printing and Modeling

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1 Optical Projection Printing and Modeling Overview of optical lithography, concepts, trends Basic Parameters and Effects (1-14) Resolution Depth of Focus; Proximity, MEEF, LES Image Calculation, Characterization (15-39) Includes Hands On simulation using LAVA, SIMPL_display Technology Advances (40-52) Resolution Enhancement, Immersion, Double Patterning, EUV, Imprint Suggested reading and sources: Griffin: Plummer, Deal and Chapter 5 Sheats and Smith: , , , , 121 Wong RET: 31-45, 55-58, 83; Chris Mack Simulation Examples 1

2 ASML 5500/ nm Wavelength Tool Fly s Eye Sigma Aperture Mask Port Condenser Lens Light path Hexagonal Light Pipe Output Objective Lens To Wafer 2

3 EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006 Projection Printer Examples Wafer Mask Stepper Mask Scanner Wafer Sheats and Smith 3

4 Optical Projection Printing Parameters #0 Key Parameters: λ, NA, σ Wavelength λ = 248 nm) Numerical Aperture NA = sin (θ) = 0.5 Partial Coherence Factor σ = (NAc/NAo) = 0.3 4

5 Parameters for Microlab Projection Printers Working Resolution Tool λ nm NA σ k 1 θ LEN deg θ ILL deg k 1 λ/na nm λ/(4na) nm TFR nm Μ Canongh GCA-g GCA-i ASML- DUV Ann TFR = Total focus range = 2 x Rayleigh Depth of Focus = 2DOF λ M is the demagnification factor DOF = k L LINEWIDTH = k 1 NA λ ( ) 2 2 NA 5 5

6 Optical System Point Spread Function Mask Lens Wafer Image of a pin hole (Diffraction limited) Relationship for electric fields The small pinhole due to its size diffracts uniformly over all angles. Pin hole This diffraction uniformly fills the lens pupil. The lens re-phases the remaining emerging rays so that they re-converge at the wafer with the same relative phases and uniform magnitude. The electric field at the waver is thus the inverse Fourier transform of a disk = Airy Function. The intensity is the time average of the square of the electric field = (Airy function) 2 The pattern shape is independent of the shape of the pin hole with diameter 1.22λ/NA. The peak E is proportional to pin hole area the peak I is proportional to Area 2 or (dimension) 4. 6

7 Resolution in Projection Printing f = focal distance d = lens diameter Point spread function Null position F# = f/d f f 1.22λ = 0.61λ = d d 2 λ NA Minimum separation of a star to be visible. PDG Fig. Ch 5 7

8 Resolution ~ Transverse Variation Larger angles give higher resolution φ #1 Resolution = P/2 = λ/(2 sinφ) = 0.5(λ/NA)) λ = 248 nm λ TRANS = λ/sinφ = 3.22λ = 800nm Assumes one wave is onaxis and the other off-axis The most useful rays in forming an image are those with the same pitch as the pattern Wave graphic by Ongi Englander and Kien Lam 8

9 Depth of Focus: Phase change on vertical axis Plane of Best Focus 4.75λ 5.0λ Plane of Rayleigh l/4 Defocus Wave graphic by Ongi Englander and Kien Lam Observe phase along a vertical line 9

10 EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006 Depth of Focus in Projection Printing Ray Angle View #2 Depth of Focus = λ/(2na2) Result must be modified for a) High NA, and b) Two waves at arbitrary angles. PDG Fig. Ch 5 10

11 Normalized Parameters For any wavelength λ and numerical aperture NA. λ L LINEWIDTH = k1 DOF = k NA λ = 365, 248,193, 157, 13.4 nm NA = 0.167, 0.38, 0.5, 0.63, 0.7, 0.75, λ ( ) 2 2 NA Instead of recalculation for every new combination of λ and NA a universal catalog of image behavior can be utilized if we first determine the k 1 and k 2 factors in the actual system for the linewidth and defocus and look up results in a data based based on λ = 0.5µm and NA =0.5. λ 0.5µ m L LINEWIDTH = k1 = k1 = k1µ m NA 0.5 λ 0.5µ m DOF = k2 = k2 = k2µ m NA ( ) ( ) 11

Optical Proximity Effect - lateral influence function E-field Point Spread Function for Coherent Imaging: illuminator Condenser lens mask Finite size of

12 Optical Proximity Effect - lateral influence function E-field Point Spread Function for Coherent Imaging: illuminator Condenser lens mask Finite size of projection lens (i.e. low-pass filter) images point on mask as Airy pattern on wafer. [Airy = IFT (disk) = f(l/na)] Projection lens wafer λ/na 12

13 Various Types of Image Distortion Proximity effect with neighbors Nonlinearity with size End shortening Corner rounding Wong RET 13

14 Optical Proximity Correction (OPC) Called Processl Proximity Correction (PPC) when compensations for other process effects are included. Wong RET 14

Purpose: Explain the top 10 phenomena and concepts. BPP-1: Resolution and Depth of Focus (1.5X)

Basic Projection Printing (BPP) Modules Purpose: Explain the top 10 phenomena and concepts key to understanding optical projection printing BPP-1: Resolution and Depth of Focus (1.5X) BPP-2: Bragg condition