Gabriele Seguini,1,* M. Ceresoli,1,2 F. Zanenga,1 T. J. Giammaria,1,3 V. Gianotti,3 D. Antonioli,3 K. Sparnacci,3 M. Laus,3 M. Perego.1,*

1. Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, I-20864 Agrate Brianza, Italy.2. Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, I-20133 Milano, Italy.

3. Dipartimento di Scienze e Innovazione Tecnologica (DISIT), Università del Piemonte Orientale ‘A. Avogadro’, INSTM, UdR Alessandria, Viale T. Michel 11, I-15121 Alessandria, Italy.* gabriele.seguini@mdm.imm.cnr.it, michele.perego@mdm.imm.cnr.it

Solvent assisted rapid thermal treatment in low molecular weight asymmetric and symmetric PS-b-PMMA thin films

F. Ferrarese Lupi, T. J. Giammaria, G. Seguini, F. Vita, O. Francescangeli, K. Sparnacci, D. Antonioli, V. Gianotti, M. Laus, M. Perego, "Fine Tuning of Lithographic Masks through Thin Films of PS-b-PMMA with Different Molar Mass by Rapid Thermal Processing" , ACS Appl. Mater. Interfaces 10, 7180–7188 (2014)

M. Perego, F. Ferrarese Lupi, M. Ceresoli, T. J. Giammaria, G. Seguini, E. Enrico, L. Boarino, D. Antonioli, V. Gianotti, K. Sparnacci, M. Laus,"Ordering dynamics in symmetric PS-b-PMMA diblock copolymer thin films during rapid thermal processing" , J. Mater. Chem. C 2, 6655–6664 (2014)

M. Ceresoli, F. Ferrarese Lupi, G. Seguini, K. Sparnacci, V. Gianotti, D. Antonioli, M. Laus, L. Boarino, M. Perego,"Evolution of lateral ordering in symmetric block copolymer thin films upon rapid thermal processing " , Nanotechnology 25, 275601 (2014)

K. Sparnacci, D. Antonioli, V. Gianotti, M. Laus, F. Ferrarese Lupi, T. Jacopo Giammaria, G. Seguini, M. Perego,"Ultrathin Random Copolymer-Grafted Layers for Block Copolymer Self-Assembly " , ACS Appl. Mater. Interfaces 7, 10944–10951 (2015)

M. Ceresoli, F. G. Volpe, G. Seguini, D. Antonioli, V. Gianotti, K. Sparnacci, M. Laus, M. Perego ,"Scaling of correlation length in lamellae forming PS-b-PMMA thin films upon high temperature rapid thermal treatments" , J. Mater. Chem. C 3, 8618--8624 (2015)

The self-assembly of block copolymers (BCPs) into a nanometric ordered structure and the chemical similarity with the photoresist materials employed in standard photolithographicprocesses have triggered the application of BCPs as template masks.Polystyrene-block-polymethylmethacrylate (PS-b-PMMA) can form nanodomains perpendicularly oriented with respect to the substrate since the weakly unbalanced surface interactionsare easily neutralized by grafting the appropriate functional poly(styrene-random-methylmethacrylate) P(S-r-MMA) random copolymer (RCP) to the surface.In this work, the self-assembly and the lateral organization of a cylinder forming asymmetric and of a lamellar forming symmetric PS-b-PMMA BCP over a P(S-r-MMA) RCP grafted layer isaccomplished by a fine tuning of the annealing temperature (Tann) and time (tann) using a Rapid Thermal Process (RTP) machine.

2: P(S-r-MMA)

3: PS-b-PMMA

1: Surface cleaning: ’Piranha’

4: RTP

Cylinder forming asymmetric BCP:PS-b-PMMAPS fraction = 0.7, Mn = 54,000 g mol-1RCPs: P(S-r-MMA)• w-Br, PS = 0.62, thin, Mn = 1,700 g mol-1• w-Br, PS = 0.61, thick, Mn = 69,000 g mol-1

Tann = 310 °C, tann = 60 s

Lamellar forming symmetric BCP:PS-b-PMMAPS fraction = 0.5, Mn = 51,000 g mol-1RCP: P(S-r-MMA) • w-Br, PS = 0.58, Mn = 13,200 g mol-1

Tann = 310 °C, tann = 60 s

SEM images: tann = 10 s, Tann = 250 - 350 °C.Corresponding orientation color maps obtained by a software analysis.

The grain size monotonically increases with Tann.

x(tann), Tann = 250 - 350 °C

The lower edge of the grey area (Itcorresponds to processing conditionsleading to inhomogeneous polymericfilms) indicates the combination ofprocessing parameters: tann = 10/30 s, Tann= 330 °C, tann = 60/100 s, Tann = 310 °C,corresponding to the highest x values.

Time–Temperature-Superposition (TTS)principle on the x(tann) curves, holding thex(tann) curve at Tann = 250 °C as the reference.

The TTS procedure generates a single mastercurve at Tann = 250 °C describing the evolutionof x(tann).

• the occurrence of inhomogeneous regionsin the polymeric film hampers theinvestigation of lateral order evolution at hightemperature for long tann.

• the exponential growth of the x turns intothe plateau values indicating the system isentering a slow coarsening regime.

The solvent content in the total RCP+BCP system before the RTP treatments is RCP-dependent, it is less for the thin RCP than for the thick RCP.

The amount oftrapped toluene forevery condition(simple RCP vs. totalRCP+BCP systemeither for thin RCPor thick RCP) of thestarting system.

The amount oftrapped toluene inthe total RCP+BCPsystem after thespinning of the BCPover the RCP is muchhigher than in thesimple RCP.

Four different behaviorsare identified after RTP:1. Limited lateral order ●2. Ordered nanodomains

begin to appear ●3. Ordered nanodomains ●4. Inhomogeneity ●

These four behaviors:• Are RCP-independent,• Appear for the same (tann,

Tann) combinations,• d ≈ 13 nm, L0 ≈ 28 nm.

x(tann), Tann = 160 - 220 °CThe different behaviorbetween the thin RCPand the thick RCP beginto appear at shorter tannas Tann increases.

TTS (ref: Tann = 160 °C)• thick RCP: a power lawwith exponent 1/3.• thin RCP: differentdependence where thegrowth slows and stops.

Tann=220 °C

The short-rangecharacteristics of the BCPare RCP- independent. The kinetics of thegrain coarsening (long-range) of the BCP areRCP-dependent.

The residual amount oftrapped toluene for thethick RCP even at thelongest tann (900 s) is higherthan that for thin RCP evenat the shortest tann (1 s).

Fast and slowcoarsening regimes ofthe lamellar structures.

The competition between self-assembling and polymer degradation processes was investigated through the quantification of the lateral ordering. This systematic analysis indicates that the two processes occur on a different time scale. RTP takes advantages of very fast heating rate that allows reaching the target temperature in a very short amount of time, preventing any kind of degradation during the transient regime. The ordering evolution depends on capacity of the solvent reservoir in the total RCP + BCP system. Indeed, this content increases with the RCP thickness.The combination of solvent reservoir and RTP thermal processing allows reaching micrometer scale correlation lengths.

Patent protection related to this work is pending.

Methods