Feature Level Compensation and Control: Chemical Mechanical Planarization Investigators Fiona M. Doyle, Dept. of Materials Science and Engineering David A. Dornfeld, Dept. of Mechanical Engineering University of California, Berkeley Jan B. Talbot, Dept. of Chemical Engineering, University of California, San Diego F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Students Involved in CMP Effort Mechanical Aspects Andrew Chang (RAPT Technologies) Yongsik Moon (Applied Materials) Jianfeng Luo(Cypress Semiconductor) Inkil Edward Hwang Sunghoon Lee Jihong Choi Chemical Aspects Serdar Aksu (Suleyman Demiril University, Isparta, Turkey) Ling Wang Interfacial and Colloid Aspects Tanuja Gopal (UCSD) F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Outline Objective of FLCC effort in CMP Background on CMP Mechanical phenomena Interfacial and colloidal phenomena Chemical phenomena Modeling efforts Future work F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Objective of FLCC effort in CMP F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Aim Insure uniform, global planarization with no defects by means of optimized process recipes and consumables Idealized single-phase CMP processes are now well understood in terms of the fundamental physical-chemical phenomena controlling material removal The challenge is to extend this to heterogeneous structures that are encountered when processing product wafers with device features F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Approach Develop integrated feature-level process models, encompassing upstream and downstream processes These models will drive process optimization and the development of novel consumables to minimize feature-level defects We will require the capability of faithfully predicting defects and non-idealities at feature boundaries. F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Background on CMP F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

CMP Process Schematic Pad Pad Wafer Carrier table Wall Pore Wall Pore F : down force Oscillation w w : wafer rotation conditioner Wafer Carrier slurry feed head Retainer ring Backing film Wafer table pad Pore Wall Wall Pore w p :pad rotation Pad Pad Abrasive particle Electro plated diamond conditioner Typical pad F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Multilevel Metalization Applications of CMP – ILD, Metal and STI CMP Interconnection (ILD CMP) Via formation (Metal CMP) Shallow Trench Isolation (STI CMP) Multilevel Metalization F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Idealized CMP ‘Softened’ surface by chemical reaction Silicon wafer Abrasive particle Polishing pad Pad asperity F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Wafer Geometry and Materials CMP Parameters Input Parameters Output Parameters Wafer Pad Fiber Structure Conditioning Compressibility Modulus Material Removal WIWNU (Within-Wafer Non-Uniform Material Removal) Slurry pH Oxidizers Buffering Agents, Abrasive Concentration Abrasive Geometry and Size Distribution CMP Die WIDNU (Within-Die Non-Uniform Material Removal) Wafer Geometry and Materials Surface Surface Quality Roughness, Scratching Process Pressure Velocity Temperature Slurry Flow Polish Time F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Interactions between Input Variables Velocity V Vol Chemically Influenced Wafer Surface Wafer Abrasive particles on Contact area with number N Abrasive particles in Fluid (All inactive) Polishing pad Pad asperity Active abrasives on Contact area Interactions Wafer Pad Abrasive Slurry chemical - √ Source: J. Luo and D. Dornfeld, IEEE Trans: Semiconductor Manufacturing, 2001 Recognize that wafer is heterogeneous, and there may not be a single interaction between it and other input variables F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Chemical Mechanical Planarization Mechanical Phenomena Chemical Phenomena Interfacial and Colloid Phenomena F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Mechanical Phenomena F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Gap effects on “mechanics” Eroded surface by chemical reaction --- softening Silicon wafer Delaminated by brushing ‘Small’ gap Abrasive particle Polishing pad Pad-based removal Silicon wafer Polishing pad Abrasive particles ‘Big’ gap Slurry-based removal F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Stribeck Curve and Characteristics of slurry film thickness Wafer Direct contact Film thickness Polishing pad Direct contact Semi-direct contact Hydroplane sliding Elasto- hydrodynamic lubrication Hydrodynamic lubrication Semi-direct contact Friction coefficient Boundary lubrication Hershey number(= ) Hydroplane sliding Stribeck curve F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Mechanical and Chemical Material Removal Effects vs Slurry Film Thickness Source: Yongsik Moon and David A. Dornfeld, “Investigation of Material Removal Mechanism and Process Modeling of Chemical Mechanical Polishing (CMP),” Engineering Systems Research Center (ESRC), Technical Report 97-11, University of California at Berkeley (September 1997) F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Effect of gap on CMP - material removal Material removal per sliding distance Preston’s equation: MRR vs sliding distance, A/meter (C=Preston’s coefficient P = pressure, V=velocity, h=removed height, s=sliding distant t= time) F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Increasing Line Density Proposed Pattern-Pad Contact Mode Increasing Line Density Direct Contact Increasing Hershey Number Semi-direct or Hydroplaning Contact Pad Slurry Oxide Wafer F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Die Layout Num of Features Line Pitch (mm) Density (%) 1 2000 13 2 1250 24 3 440 60 500 66 5 200 75 A B C D E F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Increasing Line Density Results – Line Density Effect Increasing Line Density Increasing Hershey Number F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Scale effects – Abrasives/Pad UR100 from Rodel Abrasive particle(<0.1m) 100m End fibrils 400m Vertically oriented pores Urethane impregnated polyester felt 1500m F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

CMP pad topography (IC1400 K-Groove) 1.Pore 2.Wall 3.Groove (side view) Pad Wafer Pore Wall Abrasives 300um Topography of pad surface (source : Rodel (Zygo profile)) New pad (open pores/smooth wall) After CMP (glazed pores/smooth wall) After Conditioning (open pores/rough wall) After Stabilization (open pores/rough wall) F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

New Conditioned Glazed The Need for Conditioning Pad becomes glazed during polishing Pad Porosity and Surface Roughness are affected Slurry transport, contact area and by-product removal deteriorate Conditioning needed to break up glazed areas New Conditioned Glazed Source: B. J. Hooper, UCD, Dublin, 2001 F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Schematic of SMART pad 200um Top View 50um(space) Groove & Pore Hard Material (i.e. high stiffness) Wall Side View Soft Material (i.e. low stiffness) Protrusion for rough wall F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Model Implementation - Pad Design Pad Wafer Pore Wall Abrasives SMART pad surface 200um Polymer pad surface Polyethylene pad surface F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Interfacial and colloidal phenomena F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Mass Transfer Process (a) movement of solvent into the surface layer under load imposed by abrasive particle (b) surface dissolution under load (c) adsorption of dissolution products onto abrasive particle surface (d) re-adsorption of dissolution products (e) surface dissolution without a load (f) dissolution products washed away or dissolved Dissolution products Abrasive particle Surface Surface dissolution Ref. L. M. Cook, J. Non-Crystalline Solids, 120, 152 (1990). F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Electrical Double Layer of Abrasive Particles Diffuse Layer + a Shear Plane Particle Surface Potential at surface usually stems from adsorption of lattice ions, H+ or OH- Potential is highly sensitive to chemistry of slurry Slurries are stable when all particles carry same charge; electrical repulsion overcomes Van de Waals attractive forces If potentials are near zero, abrasive particles may agglomerate Potential  Distance 1/ F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Colloidal effects Glass polishing rate (mm/min) Oxide Isoelectric point Maximum polishing rates for glass observed compound IEP ~ solution pH > surface IEP (Cook, 1990) Polishing rate dependent upon colloidal particle - W in KIO3 slurries (Stein et al., J. Electrochem. Soc. 1999) Polishing rate (A/min) Colloid oxide F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Chemical phenomena F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Potential-pH diagram, with {CuT} = 10-5, {LT} = 10-2 Chemistry of Glycine-Water System pKa1=2.350 pKa2=9.778 +H3NCH2COOH  +H3NCH2COO-  H2NCH2COO- Cation: H2L+ Zwitterion: HL Anion: L- H-O-H N-H2 H2-C O O=C C-H2 H2-N C=O Cu2+ Cu(II) glycinate complexes Cu(H3NCH2COO)2+ : CuHL2+ Cu(H2NCH2COO)+ : CuL+ Cu(H2NCH2COO)2 : CuL2 Cu (I) glycinate complexes Cu(H2NCH2COO)-2 : CuL2- Potential-pH diagram, with {CuT} = 10-5, {LT} = 10-2 F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Cu-Glycine Using electrochemical control of oxidation, see passivation only at high pH, where a solid oxide forms Using hydrogen peroxide as a chemical oxidant, see passivation at pH 4 and 9, where no solid oxide expected F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Copper concentration, mg/l, and dissolved copper, nm, in unbuffered aqueous glycine (pH 4.5) F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Modeling Efforts F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

CMP Modeling Roadmap Objectives from Industrial Viewpoint - VMIC 2001 Models are not reliable enough to be used as verification of process Usefulness of modeling is the ability to give feedback for “what-if” scenarios (predicting “polishability” of new mask designs) in lieu of time-consuming DOE tests Models should give some performance prediction for realistic, heterogeneous pattern effects Models should predict not only wafer scale phenomena but also have some capability to capture feature/chip scale interaction F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Current Status of Modeling Efforts Abrasive Particle Interaction Pattern Density Effects – STI Pattern Density Effects – Copper Pattern Density Effects – Oxide Hydrodynamics Pad Stress Dynamics Kinematics Material Removal – Chemistry Material Removal – Slurry/Abrasive/Pad Environmental Issues Modeling Aspect Feature/ Particle- Level Chip/Die-Level Wafer-Level Global Interaction Scale 50% 40% 20% 90% 30% < 5% < 5 % Estimated Completion F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Literature Review of Modeling of CMP   MRR Non-uniformity Slurry/Water usage Abrasive Concentration Other Chemical Effluent Energy References Wafer Level Feature Level Die Level Empirical Model Preston              Preston, 1927 Boning              Boning, et al, 1997-1998 (4) Others             Various (10) incl. Burke, Runnels, Zhao Individual Model Tribology             Various (11) Kinematic              Various (2) Pad              Various (4) Chemical               Various (6) Integrated Model               F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Motivations for a Comprehensive Material Removal Model Identify the most important input parameters related to Slurry Abrasives, Wafer, and Polishing Pad except the down pressure P0 and velocity V Investigate the interactions between the input parameters Develop material removal rate formulation to consider the roles of the input parameters and their interactions Model as a basis for process design and optimization (including environmental impacts) F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Past 2-D Material Removal Rate (MRR) Models Experimental Model [1]: Preston’s Equation P0 V MRR= KeP0V + MRR0 where Ke an all-purpose coefficient, MRR0 a fitting parameter, P0, down pressure, and V, the relative Velocity. Wafer Pad Analytical Model Considering Wafer-Pad Contact Area[2]: Zhao’s Equation P0 V Wafer MRR= Ke(P0-Pth)2/3V, where Pth a fitting parameter. Active abrasive number is proportional to contact area. Contact area  P02/3 Contact Area A *All with an all purpose factor Ke to represent the roles and interactions of other input variables except the down pressure and velocity 1Preston, 1917, J. of Glass Soc. 2. Zhao et. al., 1999, Applied Physics F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Sub-Model not Included in Current Model Mechanical Model Wafer-Pad Interaction Abrasive-Pad Interaction Abrasive-Wafer Interaction Model of Wafer Properties Model of Pad Properties Model of Slurry Abrasive Properties Force Applied on Abrasives Number of Active Abrasives Material Removal by a Single Active Abrasive Chemical Model Mechanical-Chemical Interaction Model: Relationship not Included in Current Model or Unimportant Relationship Strong Relationship Included in Current Model Weak Relationship Included in Current Model Sub-Model Model Output MRR Consumable Parameters including: Slurry Abrasive Concentration, Abrasive Size Distribution, Slurry Oxidizer Type and Concentration, PH, Pad Topography and Pad Material (Hardness and Young’s Modulus), Wafer Materials and Process Parameters including Down Pressure, Relative Velocity, Slurry Temperature and so on. Wafer-Chemical Interaction: Passivation Rate Model Abraded Material-Chemical Interaction (Dissolution) Model Inputs and Outputs Wafer Surface Hardness Model Chemical-Pad Interaction Model Chemical-Slurry Abrasive Interaction Model Enhancement of Mechanical Elements (Indentation, Leading Edge Area) on Passivation Competition between Mechanical Removal and Passivation F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Three Different Regions of Material Removal Rate With Increase of Material Removal Rate abrasives growth rate removal rate F 2a 2 (a) (b) (c) Shaped area is leading edge with aggressive chemical reaction softer surface harder   Different layer removed with increase of abrasive weight concentration/material removal rate: (a) small MRR < GR of Upper Layer (removed material is upper layer) (b) MRR= GR of Upper layer (upper layer is removed as formed) (c) MRR> GR (part of removed materials is the upper softer layer which is removed as formed, and part of removed materials is the bottom harder layer) F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Particle-Scale Material Removal Model Wafer-Scale Pressure and Velocity Distribution Die-Scale Pressure Distribution Model Consumable Parameters Layout Density Macroscopic Contact Mechanics Model (Weight Function) Pattern Density Window and Effective Pattern Density Material Removal Rate Surface Quality Die-Scale Topography (both vertical & lateral directions) Upper Stream Wafer-Scale Topography Wafer-Scale Topography Upper Stream Die-Scale Topography CMP Tool Configurations Pattern Density Effect Dishing Erosion Include device design Dummy Filling Circuit Performance ECAD Process Modeling “Roadmap” F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Process Models - Basis for Environmental Analysis F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

F.M. Doyle, D.A. Dornfeld, J.B. Talbot Future Work F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003

Chemical and interfacial effects CMP of heterogeneous surfaces Characterize the effect of different slurry additives on the etching of copper when adjacent to diffusion barrier materials, advanced low-k dielectrics and other relevant phases Explicitly consider autocatalytic effects, e.g. dissolved metal ions catalyzing decomposition of H2O2 Investigate the ability of different slurries to wet different phases, and the effect of surfactants in modifying wetting behavior Consider coupling of chemical and mechanical phenomena through mechanisms such as: zeta potential modifications, hydration, dehydration, and sorption of species, particularly organic surfactants and polymers F.M. Doyle, D.A. Dornfeld, J.B. Talbot November 3, 2003