Effects of Pad Properties on Cu Dishing During CMP Caprice Gray PhD Student, Mechanical Engineering Tufts University, Medford, MA Intel Intern Presentation 8/18/05

Overview Goal: Investigate Cu line dishing during CMP using polishing pads with varying properties Motivation: How do pad properties affect dishing as design rules shrink? Topics Covered: –Automated dishing analysis for higher data throughput –Evaluated 9 different pad –Pad Properties Evaluated Fiber size Pad hardness Hydrophobicity (Surface Tension) Fibrous vs. Porous

Experimental Overview Cu Ta Silicon Cu FW ILD up region ConstantsVariablesResponses Platen/Wafer Rotation Rate Slurry Flow Slurry Type Starting Cu/Ta layer thickness and topography Pad Type (9 types) Pattern Density (20%- 70%) Feature Width ( um) Polish time (0-6min) Dishing/Dishing Rate Erosion

Polishing Pads Polyurethane impregnated Polyester felt Felt Nylon Microporous polyurethane Silk Tangled Polyester Fibrous Porous Soft Hard Polyurea/ Polyurethane Nanocomposit Elastomer/ WSP Alloy Mohair Microfiber

Analysis Process Polish Wafers (vary polish time) Profile features and save data Data Evaluation attain average dishing Change Pads Data Modeling and effect screening

Automated Data Evaluation Import Raw Data Isolate region of interest and apply data smoothing filter Isolate features and calculate dishing Isolate feature width region Calculate average dishing and Erosion for each feature width 0 Dishing Erosion

Dishing Rate Results

Dishing is Predictable Dishing Rate is a function of: Feature Width Feature Density Pad “Pad” is a convolution of many material properties Hardness Fiber/Pore Size Hydrophobicity Asperity Geometry Grooving Compressibility Density Material

Evaluation of Variables Feature Width > 2um Feature Width < 2um Contact Angle* (Hydrophobicity) Fiber/Pore Size (um) Pad Hardness (Shore D) Feature Density 0 20% 70% Dishing Rate (A/min) 800 Dishing Rate (A/min) Pores Fibers * Soft Fibrous Pads Only No Effect

Summary and Conclusions A LabView interface was developed to automate data analysis Summary of design rule affects on Dishing Rates (DR) –Feature Width↓  DR↓ –Large Features  Large DR variation pad to pad –Small Features  Small DR variation pad to pad –Feature Density has minimal affect on DR Summary of pad property affects on DR –Hardness↓  DR↑ for large features –Fiber size↑  DR↓ more so for large features –Hydrophobicity↑  DR↓ for porous pads, for large features –Hydrophobicity↑  DR↑ for fiberous pads, more so for large features Recommendations –Large Features (FW > 2 um): Allied, JSR –Small Features (FW < 2 um): Allied, SUBA IV, TWI 711, (Polytex) –All Feature Scales (0.32um – 20 um): Allied, TWI 711, SUBA IV Future Work –Determine the relationship between other pad properties and dishing –Examine erosion data –Is there different selectivity on the pads? (Cu vs. Ta vs. Oxide polish rates)

Dishing Rate Normalized to Bulk Rate Oxide Polishing Pad

Dishing Rate and Feature Density

Effect of Feature Density by Pad

Dishing Rate and Pad Hardness

Normalized Dishing Rate with Pad Hardness

Dishing Rate and Fiber Size

Dishing Rate and Contact Angle Soft Fiberous Porous Brushlon and TWI 711 behave completely differently Brushlon- fiberous, high dishing rate, contact angle = 0 TWI 711 – intermediate dishing rate (between allied and SUBA,90+ contact angle

Soaks in near different grove-drop locations. Otherwise, no soak. Contact Angle Images Polyurethane WSP Elastomer Tangled Polyester Nanocomposit Microfiber-initial Porous Felt Microfiber – 1 min Fibrous Felt Soaks in Soaks in quickly Soaks in Soaks in quickly Soaks in Does not soak in

Processing Interface

Evaluating Erosion Data Long Scans Length  Scan Leveling Drift  Inaccurate Erosion Data Can examine erosion amplitude –See planarity in time across entire structure –Lose information about feature width effects Must Evaluate shorter scans for accurate erosion data

Erosion Amplitudes

Erosion v Dishing SUBA IV TWI 711

Erosion Through Material Layers Unpolished Ta no Cu No Ta or Cu Overpolished Wafer Can optically identify the presence on Ta inside Cu lines, but not outside the lines