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APPROACH — Two main cleaning approaches: (1) W surface charge reversal, using cleaning additives able to adsorb at the W surface. Other cleaning additives prevent residue redeposition. (2) Particle charge reversal and electrosteric protection using organic additives à strongly negative charged surfaces à best cleaning. SUMMARY — • Two main approaches followed: (1) reverse W surface charge; (2) particle charge reversal. • Latter approach results in strongly negative charged surfaces and best cleaning. • AG W-100 represents a significant improvement in cleaning. • CIP2 shows the best performance on W, SiN and SiO 2 blankets. • This feature enables advanced node W cleaning for memory devices. Post-CMP cleaners for tungsten at advanced nodes Ruben R. Lieten, Daniela White, Thomas Parson, Shining Jenq, Don Frye, Michael White — Entegris, Inc. Lieve Teugels, Herbert Struyf — imec SCOPE OF WORK — • Design of formulated post-CMP cleaners for W plugs with TiN as barrier liner, dielectrics SiO 2 and Si 3 N 4 , for use at 10 nm technology node (40 nm metal pitch) INTRODUCTION — • W bulk and barrier CMP slurries consist of: — (a) abrasive particles (fumed alumina or silica: fumed or colloidal) — (b) oxidizer (usually H 2 O 2 ): W à W(VI)O 3 for removal by slurry abrasive — (c) H 2 O 2 decomposition accelerator — (d) W corrosion protection additive • Particle charge in low pH W CMP slurries are usually positive (isoelectric point, pH IEP Al2O3 = 6-8 and pH IEP SiO2 = 2-4). • W surface is always negatively charged at pH >3 (pH IEP W = 2-3, ) à strong electrostatic attraction W surface and residual particles during PCMP cleaning. Significant surface contamination after CMP: abrasive particles, organic residue, pad debris, metal cations. RESULTS AND DISCUSSION — • Corrosion: Minimized Galvanic corrosion by using new and specific ligands that adsorb on metal or barrier liner à additional passivation less noble material • Particle cleaning: Upon mixing with AG-W100, all nanoparticle dispersions reversed charges from positive to negative (Al 2 O 3 , WO 3 , SiN) or became more negatively charged (SiO 2 , SiC) à strong repulsion (from Zeta Potential) • Organic residue cleaning: — Contamination takes place during post-CMP rinsing with DI water — Organics disappeared after 1‘ cleaning of SiN with AG-W100 (FTIR-ATR) • Defectivity: 300 mm CMP + brush cleaning — AMAT Reflexion ® LK polishing tool with integrated brush cleaner (Desica) — IC1010 pad, silica abrasive slurry (100 nm particle size), PVA brushes — Defect inspection by laser light scattering (SP3, KLA-Tencor Corp.) — dAmmonia as reference (W and other metals are significantly etched) — dAmmonia dissolves some of the SiO 2 surface and particles — Significant progress in removal of organic residues — AG W-100 represents a significant improvement in cleaning — CIP2: unique cleaning additive designed to disperse silica and prevent reattachment to SiO 2 surface Component TABLE 1: PLANARCLEAN ® AG-W100 FORMULATION ADDITIVES LIST – FUNCTION AND MECHANISM A B & C D Function Non-TMAH pH adjustor Complexing agents Dispersing agents Mechanism W surface hydroxylation and good wetting Negative surface charge surface of wafer and contamination Surface modification of particles to prevent agglomeration and re-precipitation Prevent aggregation and control etch rate Entegris ® , the Entegris Rings Design™ , Pure Advantage™ and PlanarClean ® are trademarks of Entegris, Inc. Reflexion ® is a registered trademark of Applied Materials, Inc. ©2016 Entegris, Inc UCPSS–2016 www.entegris.com AG- W100-1 AG- W100-2 CIP2 W105 CIP1 dAmmonia 16000 14000 12000 10000 8000 6000 4000 2000 0 Figure 1: Number of defects (particles and organic residue) pareto on silicon-nitride blanket wafers (bobom figure is a zoom in of top figure). Figure 2: Number of defects (particles and organic residue) pareto on W blanket wafers. Figure 3: Number of defects (particles and organic residue) pareto on SiO 2 blanket wafers. Number of defects pareto ( ≥ 60 nm defects) 2D organic Topography Slurry ball cluster Slurry ball 2D cluster AG- W100-1 AG- W100-2 CIP2 W105 CIP1 dAmmonia 40 35 30 25 20 15 10 5 0 Number of defects pareto ( ≥ 100 nm defects) 2D silica Slurry cluster Slurry ball 2D flat 2D cluster AG- W100-1 AG- W100-2 CIP1 CIP2 350 300 250 200 150 100 50 0 Number of defects pareto ( ≥ 60 nm defects) AG- W100-1 AG- W100-2 CIP2 W105 CIP1 dAmmonia 2000 1800 1600 1400 1200 1000 800 600 400 200 0 Number of defects pareto ( ≥ 65 nm defects) 2D organic Slurry ball cluster Slurry ball 2D cluster Slurry ball Slurry cluster Silica Organic-silica Organic Si sub. Si sub. Figure 4: W post-CMP cleaning formulation – mechanistic design concepts CMP slurry abrasive: • Al 2 O 3 ζ > 0 mV; • Surface-treated silica (ST-SiO 2 )–ζ > 0 mV; • Silica (ζ > 0 mV) •W ζ reversal • Non-TMAH additive for organic residue removal Post-CMP surface Primary approach (1) (2) Figure 5: Tunability of the galvanic corrosion W/TiN for PlanarClean AG W-100 type formulations abs (1) [A] CIP-2 -100 -0.75 -0.50 0.50 -0.25 0.25 -0.00 W TiN W passivating layer abs (1) [A] CIP-1 0.001 0.0001 0.00001 0.000001 0.0000001 0.00000001 0.001 0.0001 0.00001 0.000001 0.0000001 0.00000001 -100 -0.75 -0.50 0.50 -0.25 0.25 -0.00 W TiN Different ph organic solvent pH adjustor ζ mV 30 20 10 0 -10 -20 -30 -40 -50 Al203 SiO2 WO3 Si3N4 SiC z, mV, control z, mV in AG-W100 Figure 6: Zeta Potential, ζ , (mV) for slurry abrasives (alumina, silica), W and dielectrics surfaces in contact with AG-W100 formulation. Si3N4 control (clean) Baseline Formamide contact angle (degrees) 14 12 10 8 6 4 2 0 AGW-100 z% D AGW-100 baseline AGW-100 y% D AGW-100 x% D Post-CMP (slurry con- taminated) Clean hydrophilic Dirty Figure 7: Formamide contact angle measurements on contaminated and cleaned SiN surfaces.
