Feature-level Compensation & Control. CMP September 15, 2005 A UC Discovery Project

Transcription

1 Feature-level Compensation & Control CMP September 15, 2005 A UC Discovery Project

2 Chemical Mechanical Planarization - Faculty Team Mechanical Phenomena David A. Dornfeld Mechanical Engineering UCB Fiona M. Doyle Materials Science and Engineering UCB Chemical Phenomena Interfacial and Colloid Phenomena Jan B. Talbot Chemical Engineering UCSB Including slurryless planarization - E-CMP

3 Chemical Mechanical Planarization - Student Team Sunghoon Lee ME-UCB Jihong Choi ME-UCB Mechanical Phenomena Alex DeFeo ME-UCB Ling Wang MSE UCB Chemical Phenomena Interfacial and Colloid Phenomena Robin Ihnfeldt Chem Eng UCSB

4 4 CMP Research Description: The major objective of this work continues to be to establish an effective linkage between capable process models for CMP and its consumables to be applied to process recipe generation and process optimization and linked to device design and other critical processes surrounding CMP. Specific issues include dishing, erosion and overpolishing in metal polishing, which have an impact on circuit performance all pattern dependent effects at the chip level wetability effects in polishing, and novel consumable design (pads and abrasives) for optimized performance. We develop integrated feature-level process models which drive process optimization to minimize feature, chip and wafer-level defects. Goals: The final goals remain reliable, verifiable process control in the face of decreasing feature sizes, more complex patterns and more challenging materials, including heterogeneous structures and process models linked to CAD tools for realizing CMP compatible chip design. - CMP

5 5 Year 2 Highlights Developed capability in integrated model for determining and assessing pattern sensitivity. The effects of various common additives on zeta potential for alumina slurries used in copper CMP were determined. The influence of common slurry additives on the colloidal behavior of alumina suspensions used for copper CMP were characterized. Design rules for SMART pad design and fabrication are developed and simulation verification of pad slurry flow characteristics done with initial performance validation tests run. Experiments to provide crucial data for prediction of the galvanic damage sometimes seen during CMP were conducted including measurement of relative reactivity of copper and barrier materials in different slurries. - CMP

6 6 Year 3 Plan Mechanisms for coupling of chemical and mechanical phenomena in CMP (M22 YII.7) Use kinetic data for weight changes during passivation by peroxide to develop dynamic model for response after abrasion of surface layers and creation of new copper surface. Wetting and adhesion studies on two phase or multiphase surfaces (M7 [carried forward, with modifications, from year 1] YII.8) Study the effects of wetting and adhesional behavior of metals, low-k dielectrics and other phases on their polishing behavior, using isolated materials and for standard feature set from the cooperative photomask activity. Explore modification of the wetting and adhesional behavior through judicious selection of pad material, and optimized use of surfactants and other solvents. Further develop basic understanding of agglomeration/dispersion effects (M23 YII.9) Relate colloidal chemistry to surface charge and particle size distribution changes. Develop SMART prototyping methodology (M24 YII.10) Determine best manufacturing processes for prototyping pads for use in validation testing based on common photomask design. Integrate SMART pad design criteria into comprehensive model (M25 YII.11) Develop capability in integrated model for determining process-based or device design-based criteria for SMART-pad and other commercial surface and property specifications, specially for assessing pattern sensitivity. Basic material removal model development (Milestone Added, YII.12) Continue development of process model with attention to low down force applications/non-prestonian material removal as well as subsurface damage effects. - CMP

7 Cu CMP An overview of CMP research in Bulk Cu CMP Barrier polishing W CMP Oxide CMP Poly-Si CMP [oxidizer], [complexing agent], [corrosion inhibitor], ph Bulk Cu slurry Barrier slurry W slurry Oxide slurry Poly-Si slurry Doyle Dornfeld model Talbot Chemical reactions Mechanical material removal mechanism in abrasive scale Physical models of material removal mechanism in abrasive scale Abrasive type, size and concentration Pad asperity density/shape Pad mechanical properties in abrasive scale Pattern Topography Pad properties in die scale Slurry supply/ flow pattern in die scale Wafer scale pressure NU Wafer scale velocity profile Wafer bending with zone pressures Slurry supply/ flow pattern in wafer scale Pad groove MIT model Models of WIDNU Models of WIWNU model design goal Better planarization efficiency Better control of WIWNU Smaller WIDNU Small dishing & erosion Reducing scratch defects Reducing Fang Reducing slurry usage Uniform pad performance thru it s lifetime Longer pad life time Ultra low-k integration E-CMP Fabrication Pad design Test Fabrication technique Pad development

8 8 Today s Presentation - see the posters for details - SMART Pad Model-based pad design Initial experimental results Corrosion studies/wettability galvanic corrosion of Ta-Cu couple Wetting studies on multi-phase surfaces Comprehensive model Linkage with model beyond end-point (dishing/erosion) Expansion to copper CMP model Pad development for low down force CMP / E-CMP Study on non-uniform break thru in a die scale in copper Ecmp - CMP

9 9 SMART Pad - Pad Characterization (1) (SEM, x150) (White light Interferometer, x200) 100µm R a = 12.5µm 45µm -45µm 100µm 300µm 500µm 200~300µm - CMP R z = 96.7µm Pore diameter : 30~50 µm Peak to Peak : 200~300µm

10 10 Pad Characterization (2) Peak to Peak 200~300 µm Pores 40~60µm Asperity: Real contact area 10~50 µm 1. Reaction Region (10~15 µm) 2. Transition Region 3. Reservoir Region Simplified Pad Model Reaction region Transition region - CMP Reservoir region

11 11 Defects from Conventional Pads Stress concentration Pad asperity ILD-CMP defects Small asperity 10 µm Cu-CMP defects ILD wafer wafer Over polishing wafer Pressure 50 µm Avg. contact pressure Nominal pressure Large asperity ILD Fang Dishing Erosion Position Rounding wafer wafer - CMP

12 12 Design Rules for a New Pad Design rules for a pad Macro scale Stacked layer (Hard/soft) Slurry channel Micro scale Constant contact area (width:10-50um) The ratio of real contact area (10-15%) Conditioning-less CMP High slurry efficiency Nano scale Compatible features to abrasive Constant re-generation of nano scale surface roughness Channel Nano scale features µm Hard Layer (i.e. high stiffness) 50-70µm Soft Layer (i.e. low stiffness) - CMP

13 13 Fabrication Process 1. Master 2. PDMS Casting 3. PDMS Mold 4. Hard Layer Casting 5. Soft Layer Casting 6. Demolding - CMP New pad

14 14 Simulation of Slurry Flow Type A Without slurry guidance Type B With slurry guidance Area : 4.3^-10 m 2 Flow rate : 3.93^-11 kg/sec - CMP Area : 4.294^-10 m 2 Flow rate : 3.24^-10 kg/sec 8 times more flow rate On contact area

15 15 Results 1 ILD pattern SiO 2 wafer 0.77µm 1.7µm Relative step height (µm) New in 3mins in 7mins in 10mins IC1000/SUBA400 (overpolishing:2500å) New in 10mins in 40mins Type A (squares) (Not planrized) - CMP New In 10min In 20min Type B (V shape) (overpolishing:800å)

16 16 Corrosion - the Problems E O2/H2O Cu 2+ 2H + 2e - 2H 2 O Adsorbed O 2 (-) potential (+) i 0 O2/H2O E cu/cu2+ O 2 +4H + + 4e - =2H 2 O i E corr, Cu corr, Cu Cu = Cu 2+ +2e - (acidic) electrolyte Cu corrosion in areated solution. The nature of copper species depends on the solution chemistry. Continuous corrosion requires electrical and electrolytic conduction paths and the presence of a potential difference i 0 Cu/Cu2+ log I Polarization curves for corrosion reactions, describing the change in reaction rate as each half cell reaction is polarized away from equilibrium state; both the anodic dissolution of metal and cathodic reduction of an oxidant are polarized to a common potential, the corrosion potential, E corr Copper tends to corrode in solutions open to air, barrier materials such as Ta have similar corrosion problems - CMP

17 17 (-) potential (+) M M= M m+ + me - E corr, M i corr, M i corr, M Egalvanic E corr, N i corr, N N log I Cathodic reaction on M M N N= N n+ + ne - Cathodic reaction on N Corrosion of more noble metal, M, is suppressed due to cathodic polarization i corr, N Corrosion of more active metal, N, accelerates due to anodic polarization Galvanic effect: accelerates corrosion of the more active metal, N, because of anodic polarization and suppresses corrosion of the more noble metal, M, because of cathodic polarization A new common potential, called mixed potential, is reached at the steady state of corrosion Galvanic effects lead to more severe corrosion of the more active metal. Damage sensitive to solution chemistry and area ratio effects - CMP (-) potential (+) (-) potential (+) E corr, Mi corr, M E corr, Ni corr, N E corr, Mi corr, M E corr, Ni corr, N i corr, N i corr, N log I Solution chemistry might change the polarization behavior of each material; thereby affecting the preferential galvanic corrosion of the corroding material i corr, N i corr, N log I Increasing the area of the more noble material accelerates corrosion of N

18 Potential, E (V) um-thick electrolyte Bulk electrolyte 1 um 5 um ANODE CATHODE Radius, r (cm) 18 The Problems Simulated potential and current distribution, E. McCafferty, JES 124 (12), Local current density Bulk electrolyte 5 um 1 um 0.1 um ANODE CATHODE Radius, r (cm) expected structures Anode Cathod e Galvanic corrosion in thin-layer of solution Anode Cathod e Galvanic corrosion in bulk solution The characteristic pronounced corrosion at the phase boundary in galvanic corrosion is due to the steep potential gradient and high current density at the boundary between two phases solution θ Hydrophobic surface θ: contact angle for characterizing the wetting of a surface by a specific solution; zero or small contact angles = good wetting Hydrophilic surface θ θ? The accessibility and distribution of electrolyte (ions and water) on surfaces may affect galvanic corrosion. The wettability of materials may affect the distribution of the solution on surfaces - CMP

19 19 Experimental Study Experimental setup and samples Potentiostat pressure Slurry delivery Ref. electrode sample 2 Slurry film sample 1 Sample and sample carrier Polisher Polishing pad Rotating platen Galvanic currents and potentials will be measured with or without polishing, to investigate the effects of surface modification by chemicals and mechanical force on the polarity and galvanic current; area ratio of Cu:Ta is to be varied using different sample assemblies with different relative areas - CMP Cu wires for electrode connection Cu Pt Ta sample assembly capable electrochemical control and measurement

20 20 Results of electrochemical measurements Area ratio effect, without polishing Potential, V vs SCE DI H 2 O Ta:Cu=3.9:6.0 (cm 2 ) Ta:Cu=2.6:6.0 (cm 2 ) Ta:Cu=3.9:4.5 (cm 2 ) ph9 buffer glycine Time, s H 2 O 2 Galvanic Current,A 1.6x x x x x x x x x10-6 Ta:Cu=2.6:6.0 (cm 2 ) Ta:Cu=3.9:6.0 (cm 2 ) Ta:Cu=3.9:4.5 (cm 2 ) H 2 O Time,s in ph=9 carbonate buffer, 0.01M glycine and 0.3%H 2 O 2 - CMP

21 21 Results of electrochemical measurement Effects of [H 2 O 2 ], ph=9, without polishing Mixed Potential, V vs SCE % 0.1% 0.6% 1.0% carbonate buffer H 2 O 2, 30 wt% stock glycine sltn Galvanic Current, A 2.0x x x x % 0.1% 0.6% 1.0% Time,s in ph=9 carbonate buffer, 0.01M glycine and varying [H 2 O 2 ] - CMP

22 22 Effects of polishing on galvanic currents and potentials Masako Kodera, etc., J. Electrochem. Soc., 152 (6) G506-G510 (2005) - CMP

23 23 Contact angle measurement Kruss Contact Angle Measuring System (Goniometry approach) The basic elements of a goniometer include a light source, sample stage, lens and image capture. Based on the image of the liquid drop, contact angle can be assessed directly by measuring the angle formed between the solid and the tangent to the drop surface Sessile drop method: Angle between the baseline of the drop and the tangent at the drop boundary is measured. The contact angles as function of solution chemistry on Ta/TaN, Cu and dielectric material (TEOS or SiO 2 ) will be explored - CMP

24 24 Comprehensive CMP Model - Statistical representation of CMP pad surface - Interaction between wafer topography and pad asperities - Hertzian contact model for elastic pad deformation - Linkage with conventional chip-scale pattern density model process parameters wafer topography pad surface condition chemical reactions MRR( x, y) V = C p E * 3 / 2 z( x, y) 7 / 4 ε ( x, y, δ ) PHD( δ ) dδ z pad ρ( x, y) D κ p 1 / 4 H 3 / 2 w abrasive size pad material properties thin film properties R pattern density effect - CMP

25 25 Effect of Pad Asperity Height Distribution rough pad smooth pad σ = 3µm, α = 3µm σ = 6µm, α = 3µm Oxide thickness (µm) Oxide thickness (µm) Time (x10sec) Time (x10sec) Lower planarization efficiency, Higher removal rate Higher planarization efficiency, Lower removal rate - CMP

26 26 Effect of Nominal Down Pressure low pressure high pressure - CMP

27 27 Oxide Test Pattern Wafer for Model Calibration and Verification 4 inch wafer (11 dies across the diameter) 8 mm 20 nm Si Si 3 N 4 CVD nitride 8 mm Pattern nitride (mask #1) 2.5 µm Line width : 20 µm SiO 2 CVD Oxide 50% 100% 0.5 µm 10% 20% 0% 50% Etch oxide (mask #2) 0% 20% 0% 10% - CMP

28 28 Model vs. Experiment (Oxide CMP) highest point in the die (measured) lowest point in the die (measured) highest point in the die (model) lowest point in the die (model) Experiment : t=0min t=2min t=4min t=8min Model : - CMP

29 29 Comparison of Final Oxide Thickness Variation Over the Test Die model prediction experiment RMS error = 30.8 nm (100 measurement sites) - CMP