Abstract: Compared with UV embossing and micro-contact imprinting, hot embossing technology is the first to be used in nano-imprint lithography, and is access to copying the parallel structure in micro-nano-scale at low cost and relatively faster speed. This paper explores which factors influence some pattern transferring accuracy appearing in the experiment: the adhesion between mold and polymethyl methacrylate, the main factors of affecting embossing plastic flow including imprinting pressure, temperature, time and the plastic filling effect affected by mold pattern, the effect on the viscosity of embossing adhesive by temperature and the effect on the viscosity of embossing adhesive by embossing pressure and time. The parameters affecting the accuracy of pattern transfer are optimized via the IntelliSuite simulation designed specifically for Micro-electro-mechanical systems. A micro-level pattern with high-precision by the use of nano-imprint Obduct machine is eventually made. Copyright © 2014 IFSA Publishing, S. L

Feng Wang

Hongjun Guo

Yan Li

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Sensors & Transducers, Vol. 166, Issue 3, March 2014, pp. 224-228 
  224
     
S S Se e en n ns s so o or r rs s s & & & T T Tr r ra a an n ns s sd d du u uc c ce e er r rs s s
© 2014 by IFSA Publishing, S. L. 
http://www.sensorsportal.com 
 
 
 
 
 
Based on Hot Embossing Lithography Preparation  
of High-Precision Micron-Level Pattern 
 
1* Sumei Jia, 
1 Yan Li, 
2 Feng Wang, 
1 Hongjun Guo 
1 College of Information Engineering, Handan College, Room 401, Unit 2, Block 5, Tongren Garden, 
Hanshan District, Handan City, Hebei Province, 056001, China 
2 E&A College, Hebei Normal University of Science & Technology, Qinhuangdao, 066004, China 
1 Tel.: 13603306856 
E-mail: jiasumei0920@163.com 
 
 
Received: 25 December 2013   /Accepted: 28 February 2014   /Published: 31 March 2014 
 
 
Abstract: Compared with UV embossing and micro-contact imprinting, hot embossing technology is the first to 
be used in nano-imprint lithography, and is access to copying the parallel structure in micro-nano-scale at low 
cost and relatively faster speed.  This paper explores which factors influence some pattern transferring accuracy 
appearing in the experiment: the adhesion between mold and polymethyl methacrylate, the main factors of 
affecting embossing plastic flow including imprinting pressure, temperature, time and the plastic filling effect 
affected by mold pattern, the effect on the viscosity of embossing adhesive by temperature and the effect on the 
viscosity of embossing adhesive by embossing pressure and time. The parameters affecting the accuracy of 
pattern transfer are optimized via the IntelliSuite simulation designed specifically for Micro-electro-mechanical 
systems. A micro-level pattern with high-precision by the use of nano-imprint Obduct machine is eventually 
made. Copyright © 2014 IFSA Publishing, S. L. 
 
Keywords: Nano-imprint lithography, Hot embossing lithography, MEMS, IntelliSuite, Micro-scale patter. 
 
 
 
1. Introduction 
 
Nano-imprint technique comes from soft-
engraving technique development. In order to obtain 
nano-scale pattern, we use rigid die painted nano-
pattern to extrude the polymer film on a chip, then, 
the stamping parts is treated by etching, peeling, and 
other processing, nano-structures and devices are 
made. At present, nano-imprint technology has been 
widely used in the field of microfluidic chip 
manufacturing [1, 2]. 
Nano-imprint technology mainly includes hot 
embossing (HEL), UV embossing (UV-NIL) (Step – 
Flash Imprint (S-FIL)) and micro-contact imprinting 
(μCP) three kinds. Among them, hot-pressing process 
is good at obtaining micro-nano-scale structure of a 
parallel copy, and it is low-cost and fast, the same 
structure can be copied to large surfaces by one 
mode. This paper introduces the process of hot 
embossing, analyzes the factors influencing the 
accuracy of pattern transfer.  
This article describes the process of hot 
embossing, and explores which factors influence 
some pattern transferring accuracy appearing in the 
experiment. The parameters affecting the accuracy of 
pattern transfer are optimized via the IntelliSuite 
simulation designed specifically for MEMS. A 
micro-level pattern with high-precision by the use of 
nano-imprint Obduct machine is eventually made. 
 
 
2. Process of HEL 
 
The process of HEL is illustrated in Fig.  1. 
Initially, the positive silicon mold pattern are 
Article number P_1931Sensors & Transducers, Vol. 166, Issue 3, March 2014, pp. 224-228 
  225
fabricated using HEL technology, including the 
following steps: spin coating and baking of the HEL 
thermoplastic polymer over the two inches silicon 
wafer, imprinting process, residual layer etching by 
an oxygen plasma, depositing film, polymer removal 
and etching. 
 
 
     
 
(a) spin coating                                                                      (b) embossing 
 
     
 
(c) demoulding                                                          (d) residual layer etching 
 
     
 
(e) deposited film                                               (f) polymer removal 
 
 
 
(g) etching 
 
Fig. 1. The process of HEL. 
 
 
3. Experiment 
 
3.1. Equipments & Materials 
 
Equipment: P6708D spin coater; nano-imprint 
obduct machine; DM RXE HC Metallurgical 
Microscopy; BOC EDWARDS AUTO306 vacuum 
coating machine; MMM vacuum drying oven; 
1530VP field emission scanning electron microscope 
(SEM); Oxford Plasmalab 80 plus RIE; Nanoscope 4 
scanning probe microscopy. 
Material: PMMA particles purchased from 
ACROS, (glass transition temperature is 105°C, 
molecular weight Mw=35K; glass transition 
temperature is 122 °С, molecular weigh Mw=350 K), 
1H, 1H, 2H, 2H-perfluorodecylsilane (F13–TCS) 
purchased from perimed, anisole (molecular weigh: 
18.14), acetone solution (analytically pure), HF 
solution (analytically pure), HCL solution 
(analytically pure), H2O2 solution (analytically pure), 
H2SO4  solution (analytically pure), 2 inches P-type 
polished silicon wafers etc. 
 
 
3.2. Equipments Processes 
 
Nano embossing experiments conducted in clean 
room, Initially, Configuration Mw=35  K and 
Mw=350  K of PMMA plastic, (PMMA particles 
dissolved in anisole 10 % (wt)), spin coating over the 
two inches silicon wafer, in order to complete curing 
PMMA plastic, baking 1h at 170 °С in vacuum oven. 
After drying, scanning probe microscopy (SPM) 
measures the film thickness is 1  μm. In the 
experimental processes, temperature range   
190 °С~200 °С; pressure range of 40~50 Bar; time 
range of 180~540 s, mold release temperature range 
80 °C~90 °C. 3 impressing conditions are shown   
in Table 1. 
 Sensors & Transducers, Vol. 166, Issue 3, March 2014, pp. 224-228 
  226
Table 1. Embossing condition. 
 
Experiment PMMA  (Mw)  Embossing 
Pressure (Bar) 
Embossing 
Time(s) 
Mold removal 
temperature 
(°C) 
Embossing 
Temperature 
(°C) 
1  350  K  40  300 90 190 
2  350  K  50  300 80 190 
3  35  K 50  500 80 200 
 
 
3.3. Some Problems of Microscale  
Pattern Transfer 
 
There are concave mold box array and line 
graphics on micron size mold graphics. The width of 
square array is 5 μm, the depth of step is 0.7 μm, and 
interval period is 4  μm. The mold graphics is 
illustrated in Fig. 2.  
 
 
 
 
(a) 
 
 
 
(b) 
 
Fig. 2. (a) the metallographic microscope bright field 
image of mold box array; (b) the SEM image of the line. 
 
 
3.3.1. The Adhesion between Mold  
and PMMA 
 
Fig. 3 illustrates the torn line because of excessive 
adhesive force between mold and PMMA. 
In 2001, the founder of hot stamping technology 
Stephen Y Chou has realized the adhesion between 
PMMA and mold and put forward a 1H, 1H, 2H,   
2H-Perfluoro octyl trichlorosilane (F13-TCS) 
prepared Si anti-adhesive layer. We used 1H, 1H, 2H, 
2H-Perfluoro octyl trichlorosilane (F13-TCS) 
materials to prepare anti-adhesive layer of mold by 
vapor phase in this study, and the effect is very good. 
 
 
 
 
(a) 
 
 
 
(b) 
 
Fig. 3. (a) the metallographic microscope bright field 
image of torn line; (b ) the metallographic microscope dark 
field image of torn line. 
 
 
3.3.2. The Embossing Plastic Fluidity 
 
Incompletely plastic filling effect is shown in 
Fig. 4. We must take into account the above factors 
of affecting embossing plastic fluidity. 
 
 
 
 
Fig. 4. The phenomenon of PMMA plastic  
incompletely fluidity. Sensors & Transducers, Vol. 166, Issue 3, March 2014, pp. 224-228 
  227
3.3.2.1. The Effect on the Viscosity of 
Embossing Adhesive by Temperature 
 
Temperature is higher than the glass transition 
temperature of embossing adhesive in hot embossing 
process, but the temperature is too high, molecular 
chain structure of embossing adhesive may be 
damaged, which makes graphics cause a lot of 
embossing defects. The low temperature will lead to 
incomplete filling and insufficient embossing plastic 
fluidity. Equation (1) illustrates the ratio of polymer 
viscosity relationship varies with temperature. 
 
  () ()
() ()
10
0 20
log
cT T
cT T
η
μ
−− 
=  +− 
,  (1) 
 
where  η is the viscosity of the polymer, T is the 
absolute temperature, τ0 and η0 are the values of τ and 
η at reference temperature respectively. Temperature 
T0=Tg (Tg is the glass transition temperature of 
embossing adhesive), the constant c1=17.44 K, 
c2=51.6  K [3]. Viscosity ration of embossing 
adhesive decreases exponentially with the embossing 
temperature increase. The smaller molecular weight 
of embossing adhesive and the smaller embossing 
viscosity, embossing plastic fluidity is better. 
However, higher temperature damages the embossing 
equipment and the embossing base badly. And the 
demoulding temperature is low, too high temperature 
will greatly increase the embossing cycle. 
 
 
3.3.2.2. The Effect on the Viscosity of 
Embossing Adhesive by Embossing 
Pressure and Time 
 
L. J. Heyderman et al. deduced (1) which is about 
transfer time [4]: 
 
 
22
2
11
2
fo
f
hh
tS
P
η
−
=∗ ,  (2) 
 
where tf is the embossing time, η is the viscosity of 
polymer, S for the graphical area, hf the polymer 
height after embossing, h0 is the initial polymer 
height, P is the pressure. When the average molecular 
weight, thickness, template size and imprint 
temperature are constant, the embossing pressure and 
time selection depends on the viscosity of the 
polymer. Yoshihiko Hirai et al. deduce (3) by 
experiment [5]. 
 
 
2 f n t
P
η
∝ ,  (3) 
 
When viscosity is constant, increasing the 
embossing pressure will shorten the embossing time. 
However, increasing the temperature is more 
effective than increasing the pressure. The ratio of 
polymer viscosity changes with exponential 
relationship by temperature. 
We conducted embossing tests under the 
conditions of experiment 2 of Table 1. There are 
many central holes in each array element, or near the 
center, as shown specifically in Fig. 2 (a). 
We simulated embossing process by MEMS-
specific design software IntelliSuite under the 
conditions of experiment 2 of Table 1. 
Fig. 5 illustrates the simulation results. 
 
 
 
 
(a) 
 
 
 
(b) 
 
Fig. 5. Force simulation results. 
 
 
It is clear that upward force is largest within the 
region box array. In order to facilitate viewing the 
simulation results, Y-axis values are enlarged 
10 times, Fig. 5(b) illustrates the result. 
Residual PMMA is removed by RIE, pattern is 
transferred to the silicon wafer by use of Cu mask, 
Fig. 6 shows the result. 
 
 
 
 
Fig. 6. Pattern transferred to the silicon wafer. Sensors & Transducers, Vol. 166, Issue 3, March 2014, pp. 224-228 
  228
Fig. 6 shows pattern transferred to the silicon 
wafer has been severely deformed. We find optimal 
conditions and prepare high-precision micro-level 
graphics via comprehensive analysis on the 
embossing plastic fluidity and test equipment 
limitations. Fig. 7 shows the embossing result. 
 
 
 
 
Fig. 7. High-precision micro-level graphics. 
 
 
4. Conclusions 
 
Hot embossing technology is a new type of 
micro-nano structure manufacturing technology. Its 
applications are not limited to the manufacture of 
micro-electronic structures, the rapid development of 
micro fluidic chip greatly broadens its application 
scope [6]. Some relevant parameters are analyzed, 
and polymer filling processes are simulated by 
MEMS-specific design software IntelliSuite. Micron 
high-resolution graphics are prepared by nano-
imprint Obduct machine. 
Acknowledgements 
 
This work is sponsored by the Key Basic 
Research Project of Hebei basic application research 
plan (13960306D) and science and technology 
research and development plan project of   
Handan (1220103080). 
 
 
References 
 
[1].  P. Yager, T. Edwards, E. Fu, et al., Micro fluidic 
diagnostic technologies for global public health, 
Nature, Vol. 422, Issue 7101, 2006, pp.412-418. 
[2].  E. Abad, S. Merino, A. Retolaza, et al., Design and 
fabrication using nanoimprint lithography of a 
nanofluidic device for DNA stretching applications, 
Microelectronic Engineering, Vol. 85, Issue 5-6, 
2008, pp. 818-821.  
[3]. D. W. van Krevelen, Properties of polymers, 
Elsevier, Amsterdam, 1990. 
[4].  L. J. Heyderman, H. Schift, C. David, et al., Flow 
behaviour of thin polymer films used for hot 
embossing lithography, Microelectronic Engineering, 
Vol. 54, Issue 3-4, 2000, pp. 229-245. 
[5].  Y. Hirai, Y. Onishi, T. Tanabe, et al., Pressure and 
resist thickness dependency of resist time evolutions 
profiles in nanoimprint lithography, Microelectronic 
Engineering, Vol. 85, Issue 5-6, 2008, pp. 842-845. 
[ 6 ] .   L .  P .  W a n g ,  P .  G .  S h a o ,  J .  A .  v a n  K a n ,  e t  a l . ,  
Development of elastomeric lab-on-a-chip devices 
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2014 Copyright ©, International Frequency Sensor Association (IFSA) Publishing, S. L. All rights reserved. 
(http://www.sensorsportal.com) 
 
 
 
 
 
 
 
 

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