Impact of molecular size in sub 10nm nanoimprint
lithography based on computational study
R. Sakata1, M. Yasuda1, K. Tada2, Y. Miyashita1, M. Shirai1, H. Kawata1, Y. Hirai1
1

Physics and Electronics Engineering, Osaka Prefecture University, Sakai, 599-8537, Japan
2
National Institute of Technology, Toyama College, Toyama, 939-8630, Japan
E-mail: hirai@pe.osakafu-u.ac.jp

Introduction
Progresses for industrial application of NIL have been reported in sub 20nm scale integrated
systems [1]. Beside those technical progress, scientific issues comes out. Several experimental
results have been reported about viscosity increment in squeezed liquid resin [2]. As the pattern
width becomes narrow down to molecular size of the resist polymer, mechanical behaviors
become important in nanoimprint process, however we could hardly investigate the moleculebehaviors in experimentally. So, computational study is one of the effective approaches toinvestigate the dynamics in nano scale spaces.
In this work, the impacts of molecular size of polymer on required pressure for imprinting andevaluate line edge roughness of the pattern after de-molding using molecular dynamics
simulations and investigate.
Molecular dynamics Simulation
To investigate polymer deformation and de-molding process, computational simulation basedon the molecular dynamics study is carried using in-house software. We investigate impact ofmolecular diameter (ie. molecular weight) to pattern width on process conditions and imprinted
results. Polymethylmethacrylate (PMMA) is used as an examined resist polymer in various
molecular weights. Figure 1 shows schematics of the computational system. The Si mold ispressed to PMMA resist, where the molecular weights are varied. Table 1 shows molecule
radius in various molecular weight Mn of PMMA. The required forces to fill the polymer into
the pattern cavity are calculated for various molecular weight of the PMMA. Also, the lineedge roughness of the imprinted pattern after de-molding are investigated.
Results and discussion
Impact of the relative cavity width w/Φ on the required pressure for imprinting and the lineedge roughness of the pattern after de-molding are shown in Fig.2. , where w is pattern cavity
width and Φ is molecular diameter of PMMA. The required pressure increases when therelative cavity width w/Φ is reduced below around 3 as shown in Fig.2 (a). Also, the line edge
roughness (LER) increases when the relative cavity width is reduced as shown in Fig.2 (b).
Those results are explained by the large deformation of the polymer chain related with therelative cavity width w/Φ.
Reference:[1]
T. Higashiki, Proc. of SPIE Advanced lithography (San Jose, 2019) [10958-9],[2]
S. Ito, ACS Appl. Mater. Interfaces, 9 (2017) 6591.

3.0[nm]

Si moldｚPMMAｘ

Si substrate
ｙ4.0[nm]b) Demolding
T=300 Ka) Press
T=400 KFig. 1. Schematics of the systems.
Table. 1 Molecular diameter (PMMA)
Molecular weight[g/mol]
Mw
500
1500
4000
8000

Diameter of molecularchain [nm]
Φ1.1
1.6
2.2
2.8

Line edge roughness [nm]Pressure [a.u,]150
Mw=8000
Mw=4000
Mw=1500
Mw=500100

500123w/Φ

456

1
0.9
0.8
0.7
0.6
0.5
0.4
0.30.1● Mw=500△ Mw=1500□ Mw=4000■ Mw=8000
0.5

1w/Φ

5Figure 2. Impact of relative cavity width w/Φ on the required pressure (a) and line edge
roughness of the pattern after de-molding (b), where w is pattern cavity width and Φ ismolecular diameter of PMMA.

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