4-1 Characterization of H-NIL nanoimprint results
The mold for our researches are usually fabricated by the e-beam and Lift-off process. However , the fringe of the metal hole array or star-like patterns are easily damaged and generated defects during the mold fabrication and imprint processes. Beside , they are not that easy to be characterized with SEM or AFM. Therefore , our researches are focused primarily on grating patterns.
4-1-1 H-NIL fabrication results
When we designed the layout of the mold patterns , we always put a larger marker nearby the desire patterns for the convenience of observation under SEM and AFM. However , there are many unexpected distorted line and bobbles nearby or inside the desire patterns after imprinting. After many tests , we found that these distorted patterns were caused by the marker pattern. Besides , their correlation will be redused when the desire patterns are far apart fromeach other (as shown in Fig.29).
Therefore , we put the marker away from the desire patterns to avoid the correlation between the desire patterns and the marker. After that , we do obtain good H-NIL results with our home-made nanoimprintor , as shown in Fig. 30.
At the same time , the H-NIL mold are spin coated with BA-m thin film for the anti-sticking layer. The anti-sticking layer has served the purpose well for preventing the adhesion between resist and mold.
er 4. Re
4-1-2 Fracture induced structuring results
During the investigation of H-NIL process , we uncovered some inter
sults might be similar to Fracture induced structuring (FIS) results reported by Chou et.al in 2007[17].
peeled off the sandwich structure of o blank substrates within a PMMA polymer film , nano-scale grating patte
, as shown in Fig.32；the other has a pitch size
2
Fig.34 ; the nanogratings fabricated with this method is e esting phenomena. After some imprint tests with the same mold , there are some parallel patterns appear on some local area , as shown in Fig. 31(b). And this phenomenon became more clear when the mold was reused for several times , as shown in Fig. 31(c). We speculated that this phenomenon may resulted from the losing of anti-sticking layer (BA-m ~ 30nm) after a couple of tests. So , this re
On the other hand , when we tw
rns can be self-assembled. During these tests , we found two nanogratings with different pitch size on the sample. One is similar with Chou et al’s experimental results with a grating period of
larger than the previous one , as shown in Fig.33.
The patterns which was shown in Fig. 32 is more clear and uniform when thicker resist film was applied. Such nanogratings are generally found in around few cm area. In summary , the phenomenon of FIS is resulted from the facture of polymer (or crack propagation of polymer) , as shown in
easier than any other fabrication process. However , we must peel off th
On the other hand , the other nanogratings shown as Fig. 33 are enerally dispersed on local breaking edge. Besides , these structures were
ical force applied on UV-NIL should be g
distorted along the breaking edge and the grating direction of each different block are usually different. We concluded that the results come from the uneven peeling force because the sample was peeled off manually.
4-2 Characterization of UV-NIL nanoimprint results
The UV-NIL was proceeded with two different UV curin resis s the PAK-01-60 , the other is SU-8-2000.5. In the beginning of our experiment , we tried UV-NIL with PAK-01-60. It is a high resolution、
low adhesive UV-NIL resist. However , we can only get poor results with this resist. Therefore , we tested with SU-8 resist. Unfortunately , we still can not get good UV-NIL result. Both results show that the depth is
ch is less than the depth of the metal grating (~80 nm) on the mold. On the other hand , we tried U
rent half-pitch size grating (250 nm and 70 nm Al metal grating , as shown in Fig. 35) patterned mold and different thickness of UV resist , but we all get similar results. The gratings have round shape instead of vertical edge. The only difference between them is that the smaller metal grating patterned mold produces a rougher surface , as shown in Fig.
36~38. Therefore , we conclude that it is due to insufficient mechanical force , the illustration is as shown in Fig. 39.
In general , the mechan
lower than H-NIL. However , when we proceed UV-NIL processes with our home-made nanoimprintor , the imprint force was exercised in max.
pressure (0.7 MPa , larger than 0.4MPa of H-NIL process) , but it is still not enough for pressing the mold to reach the bottom.
(a) (b) (c)
(d) (e) (f)
(g) (h) (i)
(j)
Fig. 29 The geometric patterns between the star-like pattern and marker (a)~(j) represent the distance far away from marker , and (a) is the closest to marker.
(a)
(b)
(c)
Fig. 30 (a) The SEM and AFM image of the Si mold (b) the SEM images of imprint results (c) the AFM image of the imprint data
(a)
(b)
(c)
Fig. 31 (a) These images represents the first imprint (b) the images after
(a)
(b)
Fig. 32 (a) The FIS by peeling from 130 nm thick PMMA film (b) The FIS by peeling from 300 nm thick PMMA film
0 Fig. 33 The structures appear near the breaking edge by peeling from 13
(a)
(b)
Fig. 34 (a) The basic three modes of fracture (b) the illustration of fracture induced structuring with polymer resist thin film
Fig. 35 The SEM images of the ITO patterned mold (a) is the 250 nm
Fig .36 The result of UV-NIL with PAK-01-60 resist and 250 nm metal grating patterned mold
The result of UV-NIL with SU-8 resist and 2
Fig .37 50 nm metal grating
patterned mold
Fig. 38 The result of UV-NIL with SU-8 resist and 70 nm metal grating patterned mold
Fig. 39 The illustration shows the UV-NIL process with the insufficient
Chapter 5. Conslusion
5-1 Improvement of NIL techniques
In summary , we built up a home-made nanoimprint tool that can work both in H-NIL and UV-NIL modes. We can fabricate any patterns on Si or transparent ITO、quartz substrate by combing the nanoimprintor with e-beam lithography technology. Therefore , we can applied our techniques on other nano researches , such as solar cell、photonics、
bio-senser…etc..
The uniformity of imprinting force is one of our concern in our f H-NIL tralized , at least 50% of the area shows good pattern uniformity , as shown in Fig.40(1). However , we can’t control the imprinting results of the edges. This phenomenon is similar with the other commercial bonding nanoimprint systems[22]. The uniformity of the edge on the sample is usually not well-controlled during the imprinting process.
This problem seems happened in all those systems using pneumatic system to provide the imprint force.
We counted the defects between the middle and periphery of the patterns. From the results , we conclude that the defects are easily generated in the periphery of the patterns , however , the middle of the imprinting patterns have less defect (Fig.40). On the other hand , the
generate mprinting process. The uniformity of our home-made nanoimprintor is good for the simple imprinting.
home-made equipment. In our imprinting results , the available area o results are cen
UV-NIL results are generally more uniform and no apparent defects are d during the i
During the research of the H-NIL processes with our home-made teresting results which we r ted to the FIS. The phenomenon is conclusively resulted from the factu
On the other hand , the result for UV-NIL is satisfied because of he insufficient imprint force of our home-made nanoimprintor. With more
5-2
ith nanoimprint technique[23][24][25]. Most
nanoimprintor , we uncovered some in att ibu
re of polymer. This process has the potential application for the fabrication of large-area nanograting patterns.
efforts , we should be able to improve our pneumatic system to make this process more controllable.
Future goal on solar cell
As the increasing needs for green energy , people now pay more and more attention on solar energy because it is the most important source of regenerative energy and represents mankind’s only inexhaustible energy source. However , most of the solar cells (Table3) require large areas and high ordered structures inside the modules to improve the conversion efficiency. There are a lot of groups investigated in fabricating large-area anti-reflection layer on Si wafer w
of the researches presented good anti-reflection properties with these imprinted polymer layers. However , there is no report on the fabrication of the real P-N solar cell devices with nanoimprint technique , nor tests of the properties of the solar cell device. Therefore , we can dedicated this method to the solar cell applications.
process that is relatively inexpensive and easy. With further improvement , we can combine this techniques with solar cell devices and provide a promising technique for the fabrication of high efficiency solar cell.
(1)
(2)(a)
(b)
(c)
(d)
(e)
(f)
(3)
Fig. 40 (1)The illustration shows the layout of the imprint result , the red frame represents the mold imprinting area (2) (a)~(f) represents the imprint result in different place (3) the simple calculation of the defects in the middle and periphery of the nano-grating patterns
ble 1 Comparison of advantages and disadvantages of anti-sticking layers prepared by different methods[21]
Method Advantage Disadvantage
Ta
Spin coating 1.Easy to fabricate 2.Thick film formation
2.Hard to make a uniform coating on patterned surfaces
3.Can waste up to 98% of process materials
Liquid SAM 1.Relatively cheap process 2.Strong chemical bonding
1.Insufficient wetting for nano-structures
2.Low reproducibility and reliability in a large area
3.Waste of organic chemicals
4.Substrates dependant Vapor SAM 1.Easier to fabricate than
liquid process
Table 2 The overall parameters of imprint process by our home-made nanoimprintor
UV
H-NIL -NIL FIS
Mold Si ITO glass Si
Process Lift-off、RIE Lift-off ×
Resist Spin speed(rpm) 4000~5000 3000~6000 3000~4000 1000~5000
Bubble density
after spin coat Low High Low Low
Prebake tem. 100℃ × 95℃ 100℃
Prebake time 1 min × 2 min 1 min
thickness(nm) 170~130 80~70 120~80 300~130
Imprint tem. 120-160℃ RT RT 120-160℃
Imprint time 7 min 5 min 5 min 7 min
Exposure time × 10 min 10 min ×
PEB tem. × × 95℃ ×
Preimprint force 0.1MPa 0.1MPa 0.1MPa 0.1MPa
Imprint force 0.4MPa 0.6MPa 0.6MPa 0.4MPa Mold size ~ 4cm 2 2 cm 2 2 cm2 ~ 4cm2 Base pressure 50 mtorr↓ 50 mtorr↓ 50 mtorr↓ 50 mtorr↓
ASL BA-m × DDTS ×
Classification Effic
Table 3. The classification and parameters of different types of solar cell
a b c
(amorphous)h 9 1.07 0.859 63.0
nanocrystalline)
e sensitised (submodu 26.5 6.145
Organi 3.0±0.1 001 (ap) 9.68 52.4
(t)=total = designated area. d. FF = fill factor. e. Fh unhofer Insti ur Solare Energiesysteme；JQA = japan Quality Assurance；AIST = Japanese National Institute of Advanced Industrial
CIGS=CuInGaSe2；a morphous silico drogen alloy. b. Ef c = efficiency. c. ) = aperture area
area；(da) illumination G-ISE = Fra tut f
Reference
[1]http://www.itrs.net/
.sematech.org/
[2] http://www
[3] Stephen Y. Chou, Peter R.krauss, Preston J. Rrnstrom, A . Phys (21), pp3114 99
nder, M. Otto, B. Hadam, B. Spangenberg, and H. Kurz,
tronic Engineer .53 3– 000
[8]Mingtao Li, Hua Tan, Lei Chen, Jian
Technol. B Vol.21, pp.660-663, 2003
ho, S.W. Lee, B. J. d T chno ,Vol.
urn, et al., "Step ash L raph New High Resol tion Patte ning," Proc. of SPIE, Vol.3676, 79, 1999.
Whitesides . C nt. l.37, p 50-575 ppl . Lett. Vol.67 -3116, 1 5
[4]M. Be
Microelec ing Vol , pp.23 236, 2 [5]Y. Xia, G Angew. Chem. Int. Vol.37,
[12] Stephen Y. Chou Chris Keimel & Jian Gu, Nature Vol.417, pp835 - 837, 2002
[13] Xiaogan Liang ,Wei Zhang, Mingtao Li, Qiangfei Xia, Wei Wu,
Haixiong Ge, Xinyu Huang, Stephen Y. Chou, Nano Letters Vol.5, 5
andis, C Perret, M Fink, F Reuther and D
[15 ction, NJ, USA 08552
illiam B.
n Y. Chou, Nature Nanotechnology Vol. 2,
[1 ukai, Frederic Diana, Brian Gerardot,
logy Vol.2, pp500-506, 2007
[22] Nils ROOS', Thomas Luxbacher", Thomas Glinsner", Karl Pfeiffef, 43, -435, 2001
, Technol. B, Vol.21(6), pp.2874-2876, 2003
No.3, pp527-530, 200 [14] N Chaix, C Gourgon, S L
Mecerreyes, Nanotechnology Vol.17, pp4082–4087, 2006 ] Nanonex Corporation, Monmouth Jun
[16] M. Bender, M. Otto, B. Hadam, B. Spangenberg, and H. Kurz, Microelectronic Engineering Vol.53, pp.233–236, 2000
[17] Leonard F. Pease III, Paru Deshpande, Ying Wang, W Russel and Stephe
pp545-548, 2007
8] Nicholas A. Melosh, Akram Bo
Antonio Badolato, Pierre M. Petroff, James R. Heath, Nature Vol.300, pp112-115, 2003
[19] James R. Heath, Nicholas A. Melosh , Akram Boukai, Science 300, pp.112-115, 2003
[20] Jinan Chai, Dong Wang, Xiangning Fan And Jillian M. Buriak, Nature Nanotechno
[21] Ahmed Busnaina,2007, ”Nanomanufacturing Handbook” , CRC Press/Taylor & Francis, Boca Raton
Hubert Schu1z', Hella-C. Scheer, Proceedings of SPIE, Vol 43 pp.427
[23]Zhaoning Yu,He Gao, Wei Wu, Haixiong Ge, and Stephen Y. Chou J. Vac. Sci.
[25] Lee, Do-Hwan Kim, and Sang-Shin Lee, 90, pp. 063111, 2007
Seh-Won Ahn, Ki-Dong
Ieee Photonics Technology Letters, Vol.17, pp.2122-2124, 2005