Small Feature Reproducibility A Focus on Photolithography UC-SMART Major Program Award Spanos, Bokor, Neureuther Second Annual Workshop 11/8/99 SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Agenda 8:30 – 9:00 Introductions, Overview / Spanos 9:00 – 10:15 Lithography / Spanos, Neureuther, Bokor 10:15 – 10:45 Break 10:45 – 12:00 Sensor Integration / Poolla, Smith, Solgaard, Dunn 12:00 – 1:00 lunch, poster session begins 1:00 – 2:15 Plasma, TED / Graves, Lieberman, Cheung, Aydil, Haller 2:15 – 2:45 CMP / Dornfeld 2:45 – 3:30 Education / Graves, King, Spanos 3:30 – 3:45 Break 3:45 – 5:30 Steering Committee Meeting in room 775A / Lozes 5:30 – 7:30 Reception, Dinner / Heynes rm, Men’s Faculty Club SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Litho Milestones, Year 1 Demonstrate AFM aerial image inspection on 180nm features. Demonstrate Specular Spectroscopic Scatterometry CD metrology for 180nm features. Demonstrate focus classification scheme for 180nm features. Complete 3D device simulations of mask errors and LER effects in gate-level. Threshold voltage shifts, turn-off characteristics, and saturated drain current will be evaluated. Complete a simulation feasibility study and verification experiment on novel in-lens filtering for resolution enhancement. Evaluate the physical basis for novel effects in interaction of light with materials and low voltage electrons with resists. Establish web based simulation capabilities for DUV resists, mask topography effects and electron-beam lithography. SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Litho Milestones, Year 2 Demonstrate AFM aerial image inspection on 50nm features. Demonstrate 150nm Specular Spectroscopic Scatterometry CD metrology. Demonstrate focus classification scheme for 150nm features. Test NMOS devices with programmed mask errors and LER, compare measured characteristics to simulation. Integrate scattering, imaging, resist modeling for analyzing inspection and printabilty of mask non-idealities in the context of use with OPC. Establish a prototype system for process integration including the automatic generation of simulation-designed multi-step, short loop test structures. Establish web based simulation capabilities for optical alignment and advanced electron-beam lithography. SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Outline Simulation and Metrology Lithography Simulator Calibration Scatterometry Plans for Statistical Process Optimization Line Edge Roughness Lithography Simulation SFR Workshop - Lithography 11/8/99

In-situ / On-wafer thin film Metrology Reflectometry / Ellipsometry / Scatterometry Thickness, n & k, chemical composition Run-to-run and real-time monitoring Resist surface analysis for aerial image evaluation Thin film Spin Coat & Soft Bak e Exposure PEB Develop Thickness n and k CD, profile and SFR Workshop - Lithography 11/8/99

Motivation for Parameter Extraction Current lithography simulators are parameter limited as opposed to model limited. Traditional optimization techniques are unsuitable in complex, non-linear, high dimensional problems. Importance of predictive capabilities is increasing with increasing development costs and time-to-market pressures. SFR Workshop - Lithography 11/8/99

Some Critical Parameters in DUV Lithography Simulation Amplification Rate (Pre-exp) Amplification Rate (Activation) Acid Loss Rate (Pre-exp) Acid Loss Rate (Activation) Dill’s A Parameter Dill’s B Parameter Dill’s C Parameter Relative Quencher Conc. PEB Diffusivity (Pre-exp) PEB Diffusivity (Activation) Maximum Develop Rate Minimum Develop Rate Developer Selectivity Developer Threshold PAC Resist Refractive Index (Real) Resist Refractive Index (Imag.) ARC Refractive Index (Real) ARC Refractive Index (Imag.) Relative Focus Amplification Reaction Order Exact values obtained from experiments or resist vendor Narrow range of values available from unpatterned experiments Wide parameter range SFR Workshop - Lithography 11/8/99

Proposed DUV-SCAPE Framework 3: user specified parameter ranges 2: global optimization engine (SAC) 1: unpatterned resist experiments 5: commercial simulation program 6: simulated profile 4: parameter interface front end 7: global optimization engine (SAC) 2: image processing front end 3: experimental profile 1: patterned resist experiments SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Salient Features Unpatterned Resist Models BCAM exposure and bake models Mack develop model Optimization Technique Global optimization theory (Adaptive Simulated Annealing) Patterned Resist Model Existing lithography simulators (e.g. SAMPLE, Prolith, Solid-C, etc.) SFR Workshop - Lithography 11/8/99

Experiments - Commercial DUV Resist Unpatterned Resist Characterization Experiments Process 4 wafers with flood exposed sites Measure ARC and Resist optical constants - Ellipsometry Measure exposure and PEB parameters - FTIR/DITL Measure develop parameters - DRM Patterned Resist Characterization Experiments Process 1 wafer with a focus-exposure matrix Measure profiles for sub-quarter micron lines using AFM/cross-section CD-SEM/Specular Spectroscopic Scatterometry SFR Workshop - Lithography 11/8/99

Unpatterned Experiments 1 .5 135C 140C Exposure + PEB Parameters Deprotection 120C 110C 0 1 2 3 4 5 6 7 Exposure Dose (mJ/cm2) 3000 Develop Parameters 2000 Develop Rate in A/sec 1000 0 0.5 1 Normalized concentration of unreacted sites SFR Workshop - Lithography 11/8/99

Patterned Experiments: AFM vs Simulation mask 1 mask 2 mask 3 mask 4 mask 5 mask 6 mask 7 mask 8 mask 9 mask 10 Masks 1-10 differ in the line-space ratios 0.25 micron process technology OPC assisted masks -1 Focus +1 -1 Focus +1 SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography What is Scatterometry? Concept: Scattering (Diffraction) of light from features produces strong structure in reflected optical field. Analyze structure to obtain topography information. Periodic structures (gratings) can be numerically modeled “exactly”. Incident Laser Beam Incident Polarized White Light 0th order 0th order 2-q Scatterometry Specular Spectroscopic Scatterometry SFR Workshop - Lithography 11/8/99

Specular Spectroscopic Scatterometry 0th order, broadband detection 1D gratings and 2D symmetric gratings Use spectroscopic ellipsometers sinqm = sinqi+ml/D |sinqm|<1 i +1 -1 D l Cut-Off Pitch 600 300 400 200 250 125 (in nm) SFR Workshop - Lithography 11/8/99

Timbre ProfilerTM Flow Library Generation Electromagnetic Simulation Software Generate Profile Library Generate Signal Library Typical turnaround time = 6-12 hours Compiled Profiler Library Compiled Profiler Library Collect Reflected Signal Timbre ProfilerTM Measurement Ellipsometer / Reflectometer Test Grating (Scribe Lane) Reconstructed Profile Total Measurement + Analysis = 5 seconds/site Load Library on Ellipsometer Ellipsometry Measurement Analysis SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography ProfilerTM Setup Periodic grating on mask (~ 50 mm * 50 mm area - typical spot size of production spectroscopic ellipsometers) line/space specified Provide optical constants for each film in the stack Broadband (240-800 nm) Specify variability expected in process (in CD & thickness) range around nominal in nm Specify spectroscopic ellipsometer / reflectometer angle of incidence Save broadband tan y and cos D values Specify accuracy requirements down to sub-nm (this automatically decides library size) SFR Workshop - Lithography 11/8/99

GTK Interface at http://sfr.berkeley.edu SFR Workshop - Lithography 11/8/99

Matching on tan(Y) and cos(D) Simulated by GTK SFR Workshop - Lithography 11/8/99

Example of 0.25mm Profile Extraction Blue is actual (by Veeco AFM). Red is extracted from GTK Library. SFR Workshop - Lithography 11/8/99

Case I: Resist on ARC on Si (0.18 mm technology) Focus-Exposure Matrix SFR Workshop - Lithography 11/8/99

Profile Extraction over the entire FEM RED is AFM. BLUE is extracted. SFR Workshop - Lithography 11/8/99

Offset between CD-SEM and ProfilerTM as a function of Sidewall Angle D bottom CD (CDSEM - PXM) in nm Sidewall angle in degrees SFR Workshop - Lithography 11/8/99

Case II: Resist on ARC on Metal (0.25 mm technology) TiN Al TiN Ti TEOS Si Focus-Exposure Matrix SFR Workshop - Lithography 11/8/99

Profile Extraction: Resist on ARC on Metal CD-SEM (Bottom CD) Profiler Extraction PXM (Bottom CD) CD (in nm) Correlation* = 0.93 Site Number SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Case III: Etched Metal TiN Al TiN Ti TEOS Si Focus-Exposure Matrix SFR Workshop - Lithography 11/8/99

Profile Extraction : Etched Metal CD-SEM (Top CD) Correlation = 0.92 CD (in nm) Profiler Extraction PXM (Top CD) Site Number SFR Workshop - Lithography 11/8/99

But What Is Our Real Goal? -- a good profile ? -- or high yield ? We cannot avoid process variations Recipe setting drift: focus ( ~0.2 m), dose, PEB temperature Model and material parameter variation: resist n & k, developer Rmax and Rmin, acid diffusivity System inherent variation: mask OPC feature variation Our goal is to maximize yield for the statistical distribution of parameters and operating points. SFR Workshop - Lithography 11/8/99

Parameter Variation Effect Profile deviation from best setting Operating Point Settings SFR Workshop - Lithography 11/8/99

Parameter and Operating Point Variances Extraction Parameter mean + variation Recipe setting + drift Lithography process Experiment data In-die spatial variation Hierarchical process disturbance extraction SFR Workshop - Lithography 11/8/99

Recipe Optimization with Variations Parameter distributions Spatial variation Simulated Output distributions Profiles within spec. Calibrated Lithography Simulator Operating Point distributions + - Overlapping to get yield RECIPE OPTIMIZER SFR Workshop - Lithography 11/8/99

Recipe Optimization with Multiple Feature Types Poly layer isolated line periodic lines with OPC metal layer elbows combination of above Need to link recipe optimization to circuit performance! SFR Workshop - Lithography 11/8/99

Parameter relationship analysis In reality, all parameters have variations too many dimensions for output distribution calculation Parameter relations can be analyzed to attribute the variation of some parameters to other parameters diffusivity  PEB temperature developer temperature  Rmin and Rmax What are the fundamental reasons behind the variation? Need a comprehensive list of disturbances, linked to physical models, circuit performance. SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Summary Experiment Data Spatial variation filter Param. & op. point variance Param. mean values Calibrated Sim. Eng. Target Specs. of features Recipe of max. yield In-line sensor measurement Maximization of overlapping area SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography What is Next? Extend statistical optimization to other process steps Plasma etching Metallization Device level Circuit level Process simulator for other steps needed Simulator for full process procedure: Avant!, Solid C device model: BSIM3 Circuit simulator: SPICE Study error budgets, linked to circuit performance. SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Outline Simulation and Metrology Line Edge Roughness Lithography Simulation SFR Workshop - Lithography 11/8/99

Defining LER and Defect Specifications SFR Workshop November 08, 1999 Tho Nguyen, Shiying Xiong and J. Bokor Berkeley, CA The objective of this work is to understand and model the impact of lithography/etch line-edge roughness in the gate definition layer, on the electrical behavior of short channel transistors SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Progress Since May Hydrodynamic Model working 3D interaction of Defects Real LER Simulation SFR Workshop - Lithography 11/8/99

Effect of Gate “Errors” on Device Characteristics Cross-section Threshold voltage Turn-off slope Drive current Device reliability n+ n+ Edge roughness Layout views DL Single defects DW SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Base Design Channel Doping Selected at 0.4 Volt Halo Implant Incorporated to Offset Vt rolloff Threshold Swing 70-80 mV/decade @ Vds = 2V and L = 100nm DIBL = 70 mV/V for Vds = 0.05-2V Vt RollOff Characteristics 500 450 Device Length = 200 nm Channel Length = 100 nm Channel Width = 50-200 nm Buried Oxide = 100 nm Si Film Thickness = 250Å Gate Oxide = 30 Å 400 Without Halo Implant 350 With Halo Implant 300 250 0.2 0.4 0.6 0.8 1 1.2 Channel Length (Microns) SFR Workshop - Lithography 11/8/99

Real 3D LER Construction and Simulation Real 3D LER Created by Matlab and incorporated into simulator language LER defined by band-limited white spectrum. 2 parameters: RMS roughness, correlation length Process simulation used for self- aligned S/D doping Current digitized LER resolution is 0.5-1nm due to limited memory 160 SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Simulation Results Hydrodynamic model has been successfully turned on in ISE simulator With hydro on, Ion is ~ 30% higher Simulations of “real” 3D LER has been successful ( @ W = 50nm) I_V Curves for Different Real 3D LER Zoom View of Leakage Current 25 % increase in Ioff for 5nm rms roughness 140% increase in Ioff for 9nm rms roughness SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Simulation Results Defect shows 3D interaction for channel width less than 100nm To study LER, we have to use 3D models Intel Work (T. Linton, et al. 1999): Simulation of square-wave modulation of LER with Neuman boundary conditions Shows similar 3D interaction Leakage control by length adjustment with reasonable Ion reduction SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Milestone Status June 1999 Complete 3D device simulations of mask errors and LER effects in gate-level. Threshold voltage shifts, turn-off characteristics, and saturated drain current will be evaluated. Status: Late. Student (Tho Nguyen) started Jan. 1999. Second student (Shiying Xiong) started Sept. 1999. Expect completion March 2000. June 2000 Test NMOS devices with programmed mask errors as well as varied LER and compare measured characteristics with simulation results. Status: Delayed. No company fab support. Will start Microlab run Jan. 2000 if unable to arrange support from company fab. SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Proposal for 2000-2002 Simulation Effect of LER on GIDL Effect of LER in isolation edge Device reliability Extend to 50 nm CD Experiments Complete gate roughness experiment for 100 nm CD Isolation roughness experiment Extend to 50 nm CD?? SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Outline Simulation and Metrology Line Edge Roughness Lithography Simulation SFR Workshop - Lithography 11/8/99

Konstantinos Adam Prof. Andrew Neureuther UC Berkeley Implications of Polarization, Corner Rounding, OPC Design and OPC Fidelity on Aerial Images Konstantinos Adam Prof. Andrew Neureuther UC Berkeley Use EM theory and rigorous TEMPEST simulations to investigate photomask technology issues Current Investigations scattering bars - polarization effects corners - interior versus exterior OPC features - placement and corner rounding SFR Workshop - Lithography 11/8/99

Scattering Bar Simulation with TEMPEST l=193nm Mag=4X CDtarget=130nm |Ey| CD SB x-axis z-axis Incident radiation y-axis TE : Ey polarization mm |Ex| TM : Ex polarization mm mm SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography SB Aerial Images l=193nm, NA=0.7, s=0.6, Mag=4X, CDtarget=130nm Aerial Image (Best focus) 0.1 0.2 0.3 0.4 0.5 0.6 0.8 1 1.2 1.4 SPLAT TE TM No SB SB size = 0.18l/NA Normalized Intensity (mm) - Observe that the scatter bars (also the main feature) appear wider in TM excitation than in TE and narrower with SPLAT simulation (scalar theory) SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography SB Design Graphs Intensity dip of SB CD Control with SB Size Control 0.05 0.1 0.15 0.2 0.25 0.3 0.35 .2 .4 .6 .8 1 SPLAT TE TM Perturbation model 0.1 0.2 0.3 110 120 130 140 150 160 SPLAT TE TM Intensity CD (nm) Size of SB (l/NA) Size of SB (l/NA) SFR Workshop - Lithography 11/8/99

Corner Rounding (Clear Field Mask) - |Ey| Near fields Square mm Rounded l=193nm Mag=4X CDtarget=130nm Eincident (TE) Eincident (TE) x-axis y-axis SFR Workshop - Lithography 11/8/99

Corner Rounding Design Graph 0.04 0.08 0.12 0.16 0.2 2 4 6 8 10 radius of curvature in l/NA LES increase from reference in nm Clear field mask Dark field mask - LES increase versus radius of curvature is quadratic, i.e. it is proportional to the area missing from the corner due to the roundness SFR Workshop - Lithography 11/8/99

External OPC – |Ey| Near Fields Example: 0.1l/NA Square OPC and “Mouse Ear” OPC with radius=0.06l/NA Reference Square OPC “Mouse Ear” OPC mm SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography OPC Design Graph 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 5 10 15 20 25 non-overlapping area in mm2 (1X) LES correction in nm x10-3 Square OPC “Mouse ear” OPC Data for OPC displaced along the diagonal SFR Workshop - Lithography 11/8/99

Resist modeling, Simulation and Line-End Shortening effects Mosong Cheng Prof. Andrew Neureuther, UC Berkeley Use experiment and simulation to investigate photoresist performance and provide mechanism based models, characterization methodology, accurate profile simulation and support models/fast algorithms for including resist in OPC Current investigations chemically amplified resist modeling - LES and SFR K2G electric-field-enhanced post-exposure bake fast imaging algorithm for 2-dimensional OPC SFR Workshop - Lithography 11/8/99

Resist-model-based line-end shortening simulation APEX-E , UVIIHS, K2G parameter-extraction methodology Simulation flow Problem: Top to Top underestimates diffusion Problem: Micro-stepper at Berkeley has insufficient image quality SFR Workshop - Lithography 11/8/99

K2G resist: DRM curves and reaction/diffusion/outgasing model DRM curves, dissolution rate is lower at the top if no TARC. Collaboration with Jacek Tyminski Nikon Reaction/diffusion/outgasing model SFR Workshop - Lithography 11/8/99

K2G resist: modeling and simulation Modeling methodology Extracting dissolution parameters Large-area exposure Extracting reaction rate Resist profile simulation Extracting diffusivity Fitting with DRM data Fitting DRM curves Resist profile simulation SFR Workshop - Lithography 11/8/99

Electric-field-enhanced post-exposure bake Goal: shorten PEB time, improve vertical resist profile uniformity, reduce lateral acid diffusion. Principle: vertical electric field enhance the vertical movement of photo-acid, hence enhance the reaction cross-section. PEB time as well as lateral acid diffusion can be reduced. Experimental Setup Al foil wafer Al foil Hotplate Resist E photoacid SFR Workshop - Lithography 11/8/99

Electric-field-enhanced post-exposure bake: status Experiment done in summer 1999, on UVII resist using JEOL. RESIST RESIST UVII resist, 0.5µm L/S, dose 20µC/cm2, PEB with 100kHz, 3.3V AC, 140oC, 60sec. UVII resist, 0.5µm L/S, dose 20µC/cm2, nominal PEB,140oC, 90sec. SFR Workshop - Lithography 11/8/99

SFR Workshop - Lithography Fast resist imaging algorithm for 2-dimensional OPC(submitted to SPIE’99) Assume 2-D reaction/diffusion. Let f(x,y,t)=Cas(x,y,t), g(x,y,t)=Ca(x,y,t). Contains Spatial Laplacian and Uses 3rd Order Splines Time-advancing scheme Based on NT Aliasing and NL Relaxation Very Fast as only requires repeated multiplication with fixed coefficients Iterative solve c2,d2, to minimize the error E. SFR Workshop - Lithography 11/8/99

Fast resist imaging algorithm: simulating flow and tuning parameters Simulating and tuning flow: resist profile Mask pattern aerial image Resist imaging SPLAT Resist parameter tuner Method of Feasible Direction Differential SEM picture Extract resist parameters by tuning the image to fit with SEM picture. SFR Workshop - Lithography 11/8/99

Progress on Milestones Year 1 simulate in-lens filtering (Done) resist exposure mechanisms (Not Started =>DARPA/SRC) web simulation resist and mask effects (In Progress 70%) Year 2 Integrate scattering, imaging and resist (Expanded by 3X in the number of effects characterized, In Progress 70%) process flow generator for test structures (Not Started) web alignment and e-beam (alignment Ongoing 30%, e-beam Not Started => DARPA/SRC) SFR Workshop - Lithography 11/8/99

Future Opportunities in Lithography Photomask EM effects (How to move faster?) impact of non-idealities inspection and repair Chemically-Amplified Resists models that work methodology to calibrate models for production Optical Systems high NA low k1 SFR Workshop - Lithography 11/8/99

Targeted Opportunities in Photomasks and Optics Attenuating phase-shifting masks high refractive index and physical height of the attenuating material adversely influences light in adjacent areas Alternating phase-shifting masks 3D problematical structures - resonate ridges and cross-talk between features inside the photomask Phase-shifting mask repair guidelines for adequate repair - height, slope, river bed, stain Optics role of laser bandwidth in image quality high NA thin-film polarization effects SFR Workshop - Lithography 11/8/99

Targeted Opportunities in Resists and Tools Complete comparison of Simulation and SEM's of printed features in K2G resist, quantify the accuracy of the resist model. Complete coding of the fast but approximate image processing like algorithm and assess speed and accuracy against rigorous simulation in STORM. Initiate tool-process-dependent line-end shortening investigation by identifying key factors contributing to line-end shortening and suggesting approaches for control and compensation tuning. SFR Workshop - Lithography 11/8/99