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

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1 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 and Mask scattering (1.5X) BPP-3: Electric fields and Intensity (1.5X) BPP-4: Coupling and Standing Waves in resist (2X) BPP-5: Partial Coherence BPP-6: Integral Representation of Fresnel and Fraunhoffer Each module is a min presentation of about a dozen slides. Suggested reading: Griffin: Plummer, Deal and Chapter 5 Sheats and Smith: , , , , 121 Wong: 31-45, 55-58, 83

2 International Semiconductor Technology Roadmap Semiconductor Industry Association Road Map ASIC vs MPU CD Variation Mean+3s = 10% Alignment Mean+3s = 50% 2002 version is at PDG Fig. Ch 5

3 ASML 5500/90 Tool Fly s Eye Sigma Aperture Mask Port Condenser Lens Light path Hexagonal Light Pipe Output Objective Lens To Wafer

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

5 Parameters for Microlab Projection Printers Working Resolution Tool λ NA σ k 1 θ LEN θ ILL k 1 λ/na λ/(4na) TFR Μ nm deg deg nm nm nm Canon gh 405 GCA-g GCA-i ASML- DUV TFR = Total focus range = 2 x Rayleigh Depth of Focus = 2DOF λ M is the demagnification factor DOF = k L LINEWIDTH = k 1 NA 2 λ ( ) 2 2 NA

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 d of fthe shape of the pin hole with diameter 1.22λ/NA. The peak E is proportional to pin hole area the peak Ii is proportional lto Area 2 or (dimension) i 4.

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

8 Normalized Image of a Point and a Line I(x) = I o [2J 1 (ν)/ν] 2 ν = 2π(λ/NA)(x 2 x 1 ) Point Spread Function Line Spread Function 061λ/NA 0.61λ/NA

9 Resolution ~ Transverse Variation Larger angles give higher resolution φ #1 Resolution = P/2 = λ/(2 sinφ) = 0.5(λ/NA)) λ = 248 nm Assumes one wave is onaxis and the other off-axis λ TRANS = λ/sinφ = 3.22λ = 800nm 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

10 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

11 Depth of Focus in Projection Printing #2 Depth of Focus = λ/(2na 2 ) Result must be modified for a) High NA, and b) Two waves at arbitrary angles. PDG Fig. Ch 5

12 DOF is needed to image over a range of device heights Photo mask Field Oxide Δ Different photo images DOF is also needed for thick resist

13 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 = 05μmandNA=0 0.5μm 0.5. L LINEWIDTH DOF = k 2 λ 0.5μm = k1 = k1 = k1μm NA 0.5 λ 0.5 μm = k2 = k2μm NA ( ) ( )

14 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

15 Various Types of Image Distortion Proximity effect with neighbors ihb Nonlinearity with size End shortening Corner rounding

16 Optical Proximity Correction (OPC) Called Optical Process Proximity Correction (OPP) when compensations for other process effects are included. Wong

17 OPC Feature Design Data: Binary Masks TEMPEST-CF vs. SPLAT-CF differ by 9% TEMPEST-DF vs. SPLAT-DF differ by 6% Perturbation is proportional to OPC area. in nm 1/2 (LE ES corre ection) 1/2 Wave propagation and polarization are 2 nd order for binary masks. CF = Clear Field DF = Dark Field TEMPEST-CF Line end shortening (LES) correction SPLAT-CF SPLAT-DF TEMPEST-DF equiv. size of OPC in l/na (1X) Adam, SPIE Serif

18 Hands On Exploration

19 Lava Applets: Basic Images and Focus Applications => Basic Projection Printing Input various wavelengths, NA, sigma, Input various feature types and sizes Observe k1, k2 scaling, intersection near 30% Applications => Educational => Depth of Focus In the green box on the right advance the angle (say 18 degrees) Observe the depth at which the green off-axis wavefront is a quarter cycle behind the on axis red wavefront. Click on calculate to obtain exact value Observe that the DOF decreases as the inverse of the sine of the angle.

Optical Projection Printing and Modeling

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