Influence of Confinement and Antiplasticization on the Dynamics

Influence of Confinement and Antiplasticization on the Dynamics of Polymers Robert Riggleman Tommy Knotts and Juan J. de Pablo Center for Nano. Technology and Department of Chemical and Biological Engineering University of Wisconsin- Madison This work is based in part by a grant from the Semiconductor Research Corporation under Grant Number 2005 -OC-985 task number 985. 008. 1

Summary I. Computational resources available to our group II. Influence of Confinement and Antiplasticization on the Dynamics of Polymers III. Development of a Mesoscale DNA Model 2

Grid Laboratory of Wisconsin Initially funded as a collaboration of six research groups Each group contributes machines, has access to other group’s machines Group priority on owned machines Idle machines available to all Each site administers their own machines Resources: 1200 2. 8 GHz Xeon cpus 200 1. 8 GHz Opteron cpus 1000 ~1 GHz cpus in general Condor pool 3

Group Resources & Requirements Timeline of de Pablo group resources: 2002 – 130 private cpus 2003 – 170 private cpus 2004 – 160 private + 130 GLOW = 290 Total 2005 – 140 private + 190 GLOW = 330 Total 2006 – 150 private + 250 GLOW = 400 Total Use of Condor enables our group to function as well as it does Submit jobs and forget about them Substantial use of Standard Universe Typical number of jobs: 400 -500 total in queue 350 -400 running at any given time (including private, non-Condor pool) Introduction of GLOW in 2004 greatly expanded our resources 4

II. Influence of Confinement and Antiplasticization on the Dynamics of Polymers 5

Introduction Gordon Moore Chairman Emeritus, Intel Corporation Moore’s Law predicts that the number of transitors on a chip doubles every 18 -24 months This requires smaller features to be produced on cpu chips There are many challenges facing the semiconductor industry as they attempt to fabricate next-generation chips 6

Chemically amplified resist technology at the sub-32 node Acid Photoacid Expose generator (PAG) Reacted polymer Bake (120~140 o. C) Develop Etch Pawloski, AJ, et al, J. of Vac. Sci. and Tech. , 22, 869 (2004) Polymer chain The semiconductor industry has the goal of producing chips with features smaller than 45 nm within the next five years Properties of photoresist materials change when they are confined to such small geometries Current technology will have to be modified in order to achieve stable structure on nanoscopic lengthscales Segmental motion PAG 7

Introduction Being able to reproduce stable structures with lengthscales less than 40 nm is critical Physical properties of polymers are known to change when they are confined to small lengthscales Decrease in Tg causes a decrease in the stiffness, increase in the dynamics in polymers Can lead to collapse during the rinsing step of photolithography! - Mattson, J, Forrest, JA, Boerjesson, L, Phys. Rev. E 62 5187 (2000) - Stoykovich, MP, Cao, HB, Yoshimoto, K, Ocola, LE, Nealey, PF, Adv. Mat. 15 1180 (2003) 300 nm 8

Plasticizers and Antiplasticizers Plasticizer Antiplasticizer • • Decreases Tg Decreases the density Decreases the elastic constants Ex: Water in poly(styrene), adipic acid polyesters in poly(lactide acid) (shown below) Martino V. P. , Proc. 8 th Poly. Adv. Tech. Int. Sym. (2005) Decreases Tg Increases the density Increases the elastic constants Ex: water in poly(amide), organophosphates in an epoxy, Epon 825 (below) Zerda, AS, et al, Poly. Sci. and Engr. , 11, 2125 (2004) 9

Multiscale Modeling Glass-forming polymer ~0. 5 nm O C 30 - 50 nm 2. 0 - 5. 0 nm C CH 2 O CH 3 Coarse-grained polymer chain (500 - 1000 mers) Monomer unit of PMMA (100 g/mol) Statistical segment (~10 mers) Photoresist nanostructures 40 mers 10

Coarse-Grained Model Small inclusion Glycerol ~2 nm Molecular Dynamics U (Interaction energy) solvent polymer r ~2 nm ~1 nm - All interactions are assumed to be pairwise - Forces on all particles calculated at each timestep: Fij = - (d. U/drij) Interparticle distance, r [nm] - Positions of each particle updated based on Newton’s equations of motion - Procedure repeated to obtain equilibrium results 11

Procedure Computational Time Required Begin with 5 initial configurations per system and equilibrate at high temperature with molecular dynamics 3 weeks/system: ~30 weeks total Cool each system to the temperatures of interest (10 T’s / system x 5 configs x 2 systems) 1 week/config: ~100 weeks total Equilibrate at each temperature (10 T’s / system x 5 configs x 2 systems) 1 week/config: ~100 weeks total Production runs at each temperature, data analysis (10 T’s / system x 5 configs x 2 systems) 2 weeks/config: ~200 weeks total ~ 430 weeks or 8. 3 years Real time: ~ 11 weeks 12

Effect of Inclusions on Density and Tg 5 wt % Solvent Pure PMMA Density [gm/cm 3] Tg Tg increase density decrease Tg Temperature [K] 13

Elastic Modulus of Bulk Systems with Inclusions Shear Modulus (GPa) 5 wt % Solvent Pure PMMA Solvent increase G’ at low T Antiplasticization! Temperature [K] 14

Molecular Motion Near Tg Results of previous studies have shown: Upon cooling, relaxation requires that larger domains to move cooperatively Example of 1 D cooperative motion Size of domains increases as T decreases Cooperative regions shown to behave as 1 -D strings Hypothesis Antiplasticized Polymer: - Smaller cooperatively rearranging regions - Weak T dependence Pure Polymer: - Larger cooperative regions - Strong T dependence Particles replace the position of each other along a 1 dimensional string Initial position Final position 15

Cooperatively Rearranging Regions Pure Polymer Large, extended clusters of mobile particles Polymer + Antiplasticizer Smaller, isolated mobile particles 16

Cooperative Rearrangements: Bulk ftotal = 0. 296 Effect of Antiplasticization: Shorter string length Weaker temperature dependence 17

Free-Standing Thin Film: Density Profiles Macroscopic 5 wt. % at T/Tg = 1. 58 h y Local density of Polymer [g/cm 3] Nanoscopic h ≈ 30 nm 0 4 8 12 16 20 24 28 32 Local density of Inclusion [g/cm 3] Polymer + inclusion Air 36 40 z [nm] z x Periodic boundaries in x and y directions 18

Thin Film Cooperative Regions Air Surface Region Air Pure Polymer Cooperative regions exist near free surfaces Films are strongly heterogeneous Polymer + Antiplasticizer Homogeneous distribution of cooperative regions 19

Cooperative Rearrangements: Films T = 1. 5 Tg Probability T = 1. 9 Tg Antiplasticized Polymer Pure Polymer -10 -5 0 5 10 z-position (nm) Pure polymer films strongly heterogeneous Antiplasticizer homogenizes the freestanding film: eliminates surface effects R. A. Riggleman et al. , Phys. Rev. Lett. , 97 (2006) 045502 Glass Transition Temperature Ratios: Pure Antiplas. (5%) TG/TG, bulk: 0. 72 0. 99 20

Elimination of Confinement Effects: Experimental Evidence Thin PS films with various amounts of additives Pyrene makes the system a stronger glass former More homogeneous system Smaller cooperative regions Pyrene shown to eliminate confinement effects in PS films 9% Pyrene 2% Pyrene 0. 2% Pyrene Oligomeric PS did not eliminate confinement effects Specific additives must be used! Ellison C. J. et al. , Phys. Rev. Lett. , 92 095702 (2004) 21

Summary and Conclusions Chemically amplified resists contain a substantial amount of low molecular weight additives Plasticizers or antiplasticizers Developed a unique model to study the effects of antiplasticization in polymeric melts Shown that antiplasticization: Stiffens the bulk material Reduces the size of the cooperatively rearranging regions Eliminates the effects of confinement in photoresists 22

III. Parameterization of a Mesoscale Model for Molecular Simulations of DNA 23

Time/Length Scales and Existing Models 1 nm 10 nm Atomistic 1 mm 100 nm xp persistence length 3. 4 nm 10 mm Coarse graining 100 mm contour length L Rg radius of gyration 2 nm CHARMM, AMBER, etc. 24 Jendrejack et al. , J Chem Phys 116: 7752 -7759 (2002).

Gō-like Model q Objectives/Features of Molecular Model q Allow and describe hybridization q Reduce the number of sites q Reproduce thermal and mechanical experimental data q Include coulombic interactions and salt effects q Simple to understand implement 25

Proposed Model Intramolecular Intermolecular Computational time to develop and characterize: > 19 years 26

“Long” DNA and Mechanical Properties 0. 5 mm Smith, Cui, and Bustamante, Science, 271: 795 -799 (1996). q Persistence Length, lp q q q Model System q q 2 nm Chen et al. , Macromolecules 38: 6680 -6687 (2005). l-phage DNA Experimental lp ~ 45 nm; sim ~30 nm q 1489 bp fragment of l-phage DNA Digest l DNA with Sty. I 0. 5 mm 27

Group Computational Demands Since April 2006, on UW-GLOW: >75 years of cpu time! 28

Acknowledgements Yioryos Papakonstantopoulos, Dr. Kenji Yoshimoto, Dr. Jack Douglas Tommy Knotts Prof. Juan de Pablo University of Wisconsin Condor Team Semiconductor Research Corporation through Grant Number 295 -OC-985, NSF NIRT funding, and UW-NSEC Questions ? 29