Approaches, challenges and opportunities for area-selective ALD Adrie Mackus Eindhoven University of Technology Area-selective ALD for bottom-up processing 1 / 37 Top-down Semiconductor fabrication Excavated from solid rock Bricks as building blocks Building technology Subtractive Additive processing Bottom-up Adrie Mackus Tutorial ALD 2017 What is area-selective ALD? What could we do with layered structures with just the right layers? What would the properties of materials be if we could really arrange the atoms the way we want them? ….. when we have some control of the arrangement of things on small scale, we will get an enormously greater range of possible properties that substances can have… Lecture Richard Feynman “There is plenty of room at the bottom” Area-selective ALD = bottom-up fabrication by deposition of atoms at specific locations HOPG Lee et al., Nano Lett. 13, 457 (2013) Haider et al., RSC Adv. 6, 106109 (2016) Kim et al., ACS Nano 10, 4451 (2016) Cao et al., Small 17006483 (2017) Weber et al., Nanotechnology 26, 094002 (2015) 2 / 37 Richard Feynman, American Physical Society meeting, Caltech, Dec 29 1959 Adrie Mackus Tutorial ALD 2017 What is area-selective ALD? Patterned resist Area-selective ALD involving patterning steps Area-selective ALD on a device structure Partially-processed device structure 3 / 37 Adrie Mackus Tutorial ALD 2017 1. Patterning of ALD-grown films – Area-selective ALD by area-deactivation – Area-selective ALD by area-activation 2. Approaches for obtaining area-selective growth – Motivation: self-aligned fabrication – Selective precursor adsorption – Selective co-reactant adsorption 3. Discussion of challenges – Achieve high selectivity – Geometrical effects – Classes of selectivity Outline Growth area Non-growth area 4 / 37 Adrie Mackus Tutorial ALD 2017 Area-selective ALD on SAM-functionalized surface • Patterning by photolithography • Adsorption of octadecyltrichlorosilane (OTS) selfassembled monolayer (SAM) • Area-selective ALD of Co from Co(iPr-AMD)2 + NH3 Co(iPr-AMD)2 NH3 Lee et al., J. Electrochem. Soc. 157, D10 (2010) Kim, Area Selective Deposition workshop, Leuven, Belgium (2016) 5 / 37 Adrie Mackus Tutorial ALD 2017 Area-selective ALD by area-deactivation Blank substrate Areas masked by self-assembled monolayer (SAM) ALD on open areas only • ALD growth deactivation by self-assembled monolayer (SAM) • No growth occurs on the SAM 6 / 37 Book chapter: Nanopatterning by area-selective ALD Lee and Bent, in ALD of nanostructured materials, Wiley, 2012 Adrie Mackus Tutorial ALD 2017 Patterning of ALD-grown films Etching 1. ALD 2. Resist patterning 3. Etching 4. Resist strip 1. Resist patterning 2. ALD 3. Lift-off Lift-off Area-selective ALD by area-deactivation Review paper: The use of ALD in advanced nanopatterning Mackus et al., Nanoscale 6, 10941 (2014) ALD-enabled:Conventional: 7 / 37 1. SAM patterning 2. ALD 3. SAM strip Adrie Mackus Tutorial ALD 2017 Patterning of ALD-grown films Etching 1. ALD 2. Resist patterning 3. Etching 4. Resist strip Conventional: 8 / 37 Review paper: The use of ALD in advanced nanopatterning Mackus et al., Nanoscale 6, 10941 (2014) Adrie Mackus Tutorial ALD 2017 Motivation: Elimination of compatibility issues Not compatible with sensitive CNT surface: • Etching chemicals • Lift-off methods (due to delamination) • Resist films  Bottom-up method desired Graphene / PMMA residue “Clean” graphene 9 / 37 Example: Contacting carbon nanotubes or graphene Avouris, Physics Today 62, 34 (2009) Adrie Mackus Tutorial ALD 2017 Example area-activation: EBID & ALD of Pt Mackus et al., Nanoscale 4, 4477 (2012) US patent: 8,268,532 (2012) Two-step process: • Patterning: ultrathin (<1 ML) seed layer on oxide by EBID • Building: area-selective ALD of Pt (MeCpPtMe3 + O2) on seed layer 2. Building step: Atomic layer deposition (ALD) 1. Patterning step: e-beam induced deposition (EBID) e-beam Half-reaction A Half-reaction B 10 / 37 Adrie Mackus Tutorial ALD 2017 Direct-write ALD of Pt contacts Back-gated (single-wall) CNTFET with direct-write ALD Pt contacts TLM structure on graphene with direct-write ALD Pt contacts • Bottom-up patterning: eliminates use of resists and etching steps 11 / 37 Mackus et al., Appl. Phys. Lett. 110, 013101 (2017) Thissen et al., 2D Mater. 4, 025046 (2017) Adrie Mackus Tutorial ALD 2017 Area-deactivation versus area-activation Requires a subtractive patterning step Bare substrate Areas masked by photoresist or SAM No ALD on the masking material Surface modification ALD on activated areas only Completely additive process 12 / 37 Review paper: The use of ALD in advanced nanopatterning Mackus et al., Nanoscale 6, 10941 (2014) Adrie Mackus Tutorial ALD 2017 Patterning of ALD-grown films Etching 1. ALD 2. Resist patterning 3. Etching 4. Resist strip 1. Resist patterning 2. ALD 3. Lift-off 1. SAM patterning Lift-off Area-selective ALD by area-deactivation Area-selective ALD by area-activation 2. ALD 3. SAM strip 1. Patterning of activation layer 2. ALD ALD-enabled:Conventional: 13 / 37 Subtractive Additive Review paper: The use of ALD in advanced nanopatterning Mackus et al., Nanoscale 6, 10941 (2014) Adrie Mackus Tutorial ALD 2017 1. Patterning of ALD-grown films – Area-selective ALD by area-deactivation – Area-selective ALD by area-activation 2. Approaches for obtaining area-selective growth – Motivation: self-aligned fabrication – Selective precursor adsorption – Selective co-reactant adsorption 3. Discussion of challenges – Achieve high selectivity – Geometrical effects – Classes of selectivity Outline Growth area Non-growth area 14 / 37 Adrie Mackus Tutorial ALD 2017 The challenge of alignment at the nanoscale • Alignment becomes extremely challenging in future technology nodes Resist film patterned by lithography Alignment Patterned sample After etching + resist strip Edge placement error 15 / 37 Adrie Mackus Tutorial ALD 2017 Area-selective ALD: • Fewer lithography and etch steps • Eliminates alignment issues • Self-aligned fabrication scheme Motivation: Enabling self-aligned fabrication Patterned sample Selective deposition 16 / 37 Adrie Mackus Tutorial ALD 2017 Area-selective ALD on a specific material • Growth area = material on which deposition should occur • Non-growth area = material(s) on which no deposition should occur Differences in nucleation behavior are often exploited to achieve area-selective ALD Linear growth on growth area Nucleation delay on non-growth area Selective growth Number of cycles Thickness Growth area Non-growth area Growth area Non-growth area 17 / 37 Adrie Mackus Tutorial ALD 2017 Selective precursor adsorption • Adsorption of TiCl4 is the most endothermic reaction (1.30 eV) • Chemoselective adsorption of precursor allows for area-selective ALD of films of a few nanometers thick Longo et al., J. Vac. Sci. Technol. B, 32 O3D112-1 (2014) DFT of adsorption on H-terminated Si XPS after 10 cycles (with H2O) 18 / 37 Adrie Mackus Tutorial ALD 2017 Selective adsorption of SAM Chen and Bent, Adv. Mater. 18, 1086 (2006)19 / 37 Adrie Mackus Tutorial ALD 2017 Precursor blocking by SAM prior to deposition 20 / 37 Dodecanethiol (DDT) Octadecanethiol (ODT) Chen et al., Chem. Mater. 17, 536 (2005) Minaye Hasehemi et al., ACS Appl. Mater. Interfaces 8, 33264 (2016) Role of SAMs is twofold: 1. Remove hydroxyl groups from the surface 2. Prevent precursor molecules from reaching the surface • At some point selectivity is lost, due to desorption or degradation of SAM XPS on Cu Diethylzinc + H2O Adrie Mackus Tutorial ALD 2017 Minaye Hasehemi and Bent, Adv. Mater. Interfaces 3, 1600464 (2016) Regeneration of SAM 21 / 37 Reference Re-dosing • Results in area-selective ALD of 3 x thicker ZnO films SAM molecule Adrie Mackus Tutorial ALD 2017 Precursor blocking during every ALD cycle Use of inhibitor molecules during every ALD cycle: • Co-dosing during precursor pulse (Engstrom and co-workers) • ABC-type cycle (Mameli et al.) Benefit: compatible with plasma-assisted or ozone-based ALD MSc report Taewon Suh, Cornell University, 2017 Mameli et al., submitted Co-dosing inhibitor ABC-type cycle with inhibitor 22 / 37 Triethylamine (TEA) TEMAZ Acetylacetone (Hacac) BDEAS Adrie Mackus Tutorial ALD 2017 Approaches for selective precursor adsorption 23 / 37 1a. Selective precursor adsorption Growth area Non-growth area HH H H H H H H H H H AB cycles Growth area Non-growth area AB cycles 1b. Precursor blocking prior to deposition 1c. Precursor blocking during every cycle Growth area Non-growth area ABC cycles Adrie Mackus Tutorial ALD 2017 Precursor Co- reactant SAM Inhibitor Approaches for achieving area-selective growth 1) Precursor exposure 2) Purge 3) Co-reactant exposure 4) Purge Half-reaction I Half-reaction II Half-reaction I 1. Selective precursor adsorption on growth area a. Selective precursor adsorption b. Precursor blocking prior to deposition c. Precursor blocking during every cycle 24 / 37 Half-reaction II 2. Selective co-reactant adsorption on growth area Adrie Mackus Tutorial ALD 2017 • O-O bond breaking: Dissociative chemisorption of O2 Catalytic activation of the co-reactant 25 / 37 Pt H3C CH3 CH3 CH3 200-300 ˚C + O2 gas Pt ALD process: MeCpPtMe3 Aaltonen et al., Electrochem. Solid-State Lett. 6, C130 (2003) Freyschlag and Madix., Materials Today 14, 134 (2011) Adrie Mackus Tutorial ALD 2017 • Selective adsorption of O2 on metal growth area • Precursor ligands are not eliminated from non-growth area • Approach for metal-on-metal deposition Catalytic activation of the co-reactant 25 / 37 Aaltonen et al., Electrochem. Solid-State Lett. 6, C130 (2003) Mackus et al., Chem. Mater. 24, 1752 (2012) Adrie Mackus Tutorial ALD 2017 Catalytic activation of the co-reactant has been used extensively for the synthesis of core/shell and bimetallic particles • Area-selective ALD of Pd on Pt, Pt on Pd, Pd on Ru, etc. Core/shell synthesis by metal-on-metal ALD Weber et al., Nanotechnology 26, 094002 (2015) Lu et al., Nat. Commun. 5, 3264 (2014) 26 / 37 Pd/Pt core/shell Pd/Pt core/shellRu deposition on Pd or Pt Motivation for area-selective ALD: Controlled synthesis of nanostructures Adrie Mackus Tutorial ALD 2017 Approaches for achieving area-selective growth 1) Precursor exposure 2) Purge 3) Co-reactant exposure 4) Purge Half-reaction I Half-reaction II Half-reaction I 1. Selective precursor adsorption on growth area a. Selective precursor adsorption b. Precursor blocking prior to deposition c. Precursor blocking during every cycle 27 / 37 Half-reaction II 2. Selective co-reactant adsorption on growth area a. Catalytic activation of co-reactant on the growth area Adrie Mackus Tutorial ALD 2017 1. Patterning of ALD-grown films – Area-selective ALD by area-deactivation – Area-selective ALD by area-activation 2. Approaches for obtaining area-selective growth – Motivation: self-aligned fabrication – Selective precursor adsorption – Selective co-reactant adsorption 3. Discussion of challenges – Achieve high selectivity – Geometrical effects – Classes of selectivity Outline Growth area Non-growth area 28 / 37 Adrie Mackus Tutorial ALD 2017 Main challenge: achieve high selectivity Number of cycles Thickness Growth area Non-growth area 29 / 37 • Selectivity in ALD refers to ratio of amount of material deposited on growth and nongrowth areas • It is extremely challenging to obtain area-selective ALD with a high selectivity due to growth initiation at defects and impurities • Potential solution: combine area-selective ALD with atomic layer etching (ALE) Vallat et al, J. Vac. Sci. Technol. A 35, 01B104 (2017) Adrie Mackus Tutorial ALD 2017 Combination of area-selective ALD and ALE • Starting point: deposition occurs at a faster rate on the growth area • ALE is performed to remove any deposited atoms from the non-growth area • Supercycle is repeated until the desired thickness is reached Growth area Non-growth area Adrie Mackus Tutorial ALD 2017 30 / 37 Growth area Non-growth area Number of cycles Thickness Geometrical effects Ras et al. JACS 130, 11252 (2008) Chopra et al, Chem Mater. 28, 4928 (2016) • Mushroom-type growth: Patterns broaden in lateral direction • SAMs form defects at regions with high curvature 31 / 37 Adrie Mackus Tutorial ALD 2017 Classes of selectivity Examples of reported area-selective ALD processes Metal-on-metal • Pd on Pt – Cao et al., Chem. Cat. Chem. 8, 326 (2016) Dielectric-on-dielectric • HfO2 on SiO2 – Guo et al., ACS Appl. Mater. Interfaces 8, 19836 (2016) • In2O3 on SiO2 – Mameli et al., Chem. Mater. 29, 921 (2017) • ZnO on SiO2 – Minaye Hashemi et al., ACS Appl. Mater. Interfaces 8, 33264 (2016) Semiconductor-on-semiconductor • WS2 on Si – Heyne et al., Nanotechnology 28, 04LT01 (2017) Dielectric-on-semiconductor • ZnO on Si – Haider et al., J. Phys. Chem. C 120, 26393 (2016) Metal-on-semiconductor • W on Si – Lemaire et al., J. Chem. Phys. 146, 052811 (2017) Metal-on-dielectric ? Dielectric-on-metal ? Mayberry, 15th ALD conference (ALD 2015) Delabie et al., 2nd Area Selective Deposition workshop (ASD 2017) 32 / 37 Classes of materials refers to surface termination Adrie Mackus Tutorial ALD 2017 Surfaces to take into account 1. Growth area 2. Non-growth area 1. Growth area 2. Non-growth area 3. Deposited material 33 / 37 Adrie Mackus Tutorial ALD 2017 Surfaces to take into account Dielectric Metal Dielectric Metal Metal Starting point: • Dielectric growth area • Metal non-growth area After covering dielectric growth area: • Two metal surfaces Example: metal-on-dielectric with metal non-growth area Difficult classes: • Metal-on-dielectric with metal non-growth area • Dielectric-on-metal with dielectric non-growth area Metal 33 / 37 Adrie Mackus Tutorial ALD 2017 H2O O2 plasma Modification of non-growth area Dielectric Metal Dielectric Metal Dielectic, Metal oxide Example: dielectric-on-dielectric with metal non-growth area Metal oxide Character of the non-growth area changes due to exposure to precursor/co-reactant 34 / 37 Adrie Mackus Tutorial ALD 2017 Modification of non-growth area 1. Growth area 2 Non-growth area 4. Exposed non-growth area 3. Deposited material Character of the non-growth area changes due to exposure to precursor/co-reactant TiO2 from TiCl4 and Ti(OiPr)4 ZrO2 ALD using ethanol as co-reactant Atanasov et al. JVSTA 34, 01A148 (2016) Selvaraj et al, JVSTA 32, 010601 (2014) 34 / 37 Adrie Mackus Tutorial ALD 2017 Area-selective ALD on a device structure Carver et al., ECS JSST 4, N5005 (2016) • A device structure consists of many more materials 35 / 37 Adrie Mackus Tutorial ALD 2017 ALD for semiconductor fabrication Area-selective ALD for self-aligned fabrication has the potential to become the next ALD-enabled innovation in semiconductor fabrication Key ALD-enabled innovations in semiconductor fabrication 36 / 37 Adrie Mackus Tutorial ALD 2017 Summary Motivation for area-selective ALD • Elimination of compatibility issues • Enable self-aligned fabrication • Controlled synthesis of complex nanostructures Patterning of ALD-grown films 1. Area-selective ALD by area-deactivation 2. Area-selective ALD by area-activation Main approaches for area-selective ALD 1a. Selective precursor adsorption 1b. Precursor blocking prior to deposition 1c. Precursor blocking during deposition 2a. Catalytic activation of the co-reactant Challenges for area-selective ALD • Achieve sufficiently high selectivity • Eliminate lateral broadening Growth area Non-growth area 37 / 37 Review paper: The use of ALD in advanced nanopatterning Mackus et al., Nanoscale 6, 10941 (2014) Adrie Mackus Tutorial ALD 2017