Advanced Issues and Technology (AIT) Modules Purpose: Explain the top advanced issues and concepts in optical projection printing and electron-beam lithography. h AIT-1: LER and Chemically Amplified Resists * AIT-2: Resolution Enhancement and PSM AIT-3: Small Features and Defects AIT-4: Aberrations AIT-5: Maskless, High-NA, Immersion, EUV, Imprint Each module is a 20-25 min presentation of about a dozen slides. Suggested reading: Griffin: Plummer, Deal and Chapter 5 Sheats and Smith: 214-232, Wong: 34-37, 71-90, Fig 4.1, Fig. 4.10,
OPC Scatterbars or Assist Features Main Feature The isolated main pattern now acts somewhat more like a periodic line and space pattern which has a higher quality image especially with focus when off-axis illumination is used. The bars must be small enough that the image at their location does not print. Add nonprinting adjacent features A typical size is about 1/3 of the minimum feature size and they are placed about a minimum feature size from the feature edge.
Scattering Bar Simulation with TEMPEST λ=193nm Mag=4X CD Incident radiation target =130nm SB CD E y TE : E y polarization z-axis y-axis μm Image CD x-axis With SB E x μm TM : E x polarization Aerial Scatterbars improve DOF Defocus μm μm Adam, SPIE 4000-72
Scattering Bar Aerial Image and Design λ=193nm, NA=0.7, σ=0.6, Mag=4X, CD target =130nm Norm malized Inten nsity 1.2 1 0.8 0.6 0.4 0.2 Aerial Image (Best focus) SPLAT TE TM Intensity 1 0.8 0. 6 0.4 0.2 Intensity dip of SB SPLAT TE TM Perturbation model 0 0 0.1 0.2 0.3 0.4 0.5 (μm) 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Size of SB (λ/na) - Observe that the scatter bars (also the main feature) appear wider in TM (field perpendicular) excitation than in TE (field parallel) and narrower with SPLAT simulation (scalar theory) Adam, SPIE 4000-72
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 4000-72 Serif
High-Fidelity Audio System Off-Axis Analogy The lateral spatial variation across a wafer of an off-axis light ray is analogous the temporal variation of a note in a Hi-Fi audio system. More rapid variations (spatial or temporal) from higher frequencies (spatial or temporal) allow sharper artifacts t (spatial {lithography feature} or temporal {drum beat}) to be produced. Just as it is difficult to improve upon the pulse width times bandwidth product it is difficult to improve upon the feature size times NA product. BUT IN RESOLUTION ENHANCEMENT WE TRY TO GET A FACTOR OF TWO INCREASE ANYWAY.
Resolution Enhancement Techniques Resolution Enhancement Emphasizes High Frequencies Conventional Illumination Binary Mask Modified Illumination 0 Frequency 0 Frequency Phase Mask Lens Capture 0 0 Frequency Frequency 0 0 Frequency In-Lens Filter Frequency Bokor, Neureuther, Oldham, Circuits and Devices, 1996
Two Ray Infinite DOF Ray # 1 θ 1 θ 2 k y Ray # 2 k x Pitch When θ 1 =θθ 2 the contributions from Ray #1 and Ray #2 track each exactly with axial distance and an INFINITE depth of focus is produced. Period = Pitch = Δk Transverse = = λ 2sin θ 2k 0 Δ 2π k Transverse sin( θ ) sin( θ ) = NA λ ( θ ) 2 NA Doubled Resolution! With infinite DOF
Strategy to improve both resolution and DOF Since the small features or edges are are most important emphasize the high-frequency off-axis ray to improve resolution. σ SPOT = λ Pitch NA Since the change in the image with focus comes from the relative phase change among the rays with axial distance, utilize rays at similar azimuthal angles that track in phase with focus to improve DOF.
Top Hat General Shapes Illumination Schemes Annular DOF, Contacts k 1 = 0.67 k 1 = 0.55 σ k = 1.3 k = 1.7 IN = 0.55 2 2-1 1-1 1σ OUT = 0.85 Pupil Pupil Quadruple H,V lines, DOF k 1 = 0.45 k 2 = 2.0 Dipole V lines, DOF k 1 = 0.35 k 2 = 3.0-1 1-1 1 Pupil Pupil The k1 factor is inversely proportional to the lateral separation of the illumination k 1 = 1/(2 x separation) H lines and contacts formed via a double exposure
Annular Illumination: k 1 =0.4 Large DOF L = S = 0.4 σ IN = 0.5 σ OUT = 0.8 DOF = 2.0 Contrast = 0.61
Quadrapole Illumination 0.4 l/na Line equal Space (Dense) DOF =1 σ x =σ y =0.6 σ POLE = 0.1 Higher contrast than annular for Manhattan geometries as there are no illumination components near either σ x =0 or σ y = 0
Quadrapole Optimization Dipole illumination i i can print 0.707 smaller lines but lines only.
Phase-Shifting Mask Types Alternating (Strong) Attenuating (Weak) Used for Contacts 6% to 10% gives slope improvement of 30%. Sidelobe issue. Phase Edge Requires second trim mask exposure. Chromeless (Only 0 order)
Attenuating Phase-Shifting Masks Intensity of 6% comes from an electric field of -0.25 Going from positive electric fields to negative electric fields increases edge slope and creates darker intensity near edge.
Phase-Shifting Mask P P Perfect Null P P/2 Frequency doubled Sheats and Smith
Phase-Shifting Mask: Electric Fields Sheats and Smith
Alternating Phase-Shifting Mask 0.7 Alternating 0 and 180 regions, σ = 0.3 In Focus 1 RU Defocus 0 180 0 180 The period on the wafer is ½ the period of the mask. The region < 0.3 intensity is about 1/3 of the period.
Phase-Edge (Perfect Null) 1.5 λ/na 0 and 180 regions, σ = 0.3 In Focus 0 180 1 RU Defocus 0 180 The width is about 0.3λ/NA. Great depth of focus.
Phase-Edge Masks Is trim or conjugate shifter better?
Focus Monitor 1.5 l/na 0 and 90 regions with 0.4 λ/na chrome, σ = 0.3 In Focus 1 RU Defocus 0 Cr 90 0 Cr 90 The shift is nearly linear with focus.
Phase-Edge Simulation in SPLAT 1.5 λ/na 0 and 180 regions, σ = 0.3 In Focus 0 180 SPLAT INPUT FILE # Phase Edge DOF=0.0 2: 0.5 3: 0.5 4: 0.0 5: 0.3 0.0 6:303000 3.0 3.0 0.0 7: 0.0 0.0 1.5 3.0 at 1.0 7: 1.5 0.0 1.5 3.0 at 1.0 <180.0> 10:; 14: 0.0 1.5 3.0 1.5 'twolines.txt' 0:end; Implicit Symmetry for statement 7
Appropriate RETs for Various Patterns pˆ is the mask period in λ/na From Wong, RET in OL.
TEMPEST Instantaneous Electric Fields
Alt-PSM Intensity Imbalance: Edge Effects Δ IEDM, 1992 Wong
Photomask Polarization Effects When openings reach the size of 2 wavelengths polarization effects occur and they also are somewhat worse with off-axis illumination. However, for binary masks they are mitigated by the fact that the chrome is only about 80nm thick. The attached data shows that at λ = 193 nm and 80 nm of chrome the effects are probably not measurable for 1.5λ (300nm) openings. For 1.0λ (200nm) openings the desired TE polarization is favored by a factor of 1.2 for both the 0 th and 1 st orders.
Order Magnitudes: FDTD (Normalized) 0 th Order Magnitude 0.6 0.5 0.4 0.3 0.2 01 0.1 Cr = 80nm Zeroth Order Magnitude (cr = 80nm @ 193 nm Lambda) Normalized λ TE Polarization TM Polarization 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Mask Pitch (4x) (um) Magnitude Cr = 200nm Zeroth Order Magnitude (cr = 200 nm @ 193 nm Lambda) 0.6 0.5 0.4 0.3 0.2 TE Polarization 0.1 λ TM Polarization 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Mask Pitch (4x) (um ) 1st Order Magn nitude 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 First Order Magnitude (cr = 80nm @ 193nm Lambda) Normalized λ TE Polarization TM Polarization 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Mask Pitch (4x) (um) agnitude Ma First Order Magnitude (cr = 200nm @ 193 nm Lambda) Normalized 0.5 0.45 0.4 0.35 0.3 0.25 02 0.2 0.15 TE Polarization 0.1 TM Polarization 0.05 λ 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Mask Pitch (4x) (um) Data from Neureuther, Sematech 2003 Situation is worse for Attenuated masks due to their thickness, Progler, SPIE 05
Resolution Enhancement: In-Lens Filter cos ( ) 2 2 2 j2πβ r j2πβ r 2πβr = 0.5e + 0.5e Defocus away and toward the lens. The cos(2πβr 2 ) filter creates dual defocused images that are very effective in increasing the total focal range of contact patterns. Fukuda Fukuda, JVST B Hitachi Nov/Dec 91