Available online at www.sciencedirect.com Colloids and Surfaces A: Physicochem. Eng. Aspects 313–314 (2008) 497–499 Fabrication of photonic crystals for a,b,∗ hen hangh ROC hangh ROC ed 1 M 07 Abstract We report photo with arrays stam resonance (E proc of 90–110 ◦C er. T embossing t s real © 2007 Else Keywords: E 1. Introduction Nanostructures have been applied to various fields of science and techno tures is on attracted pe Yablonovit periodicall band gaps are not allo The pho require tha hundred na rication me for photoni In this p fabricated b and the em time are cri ∗ Correspon National Cha Tel.: +886 4 7 E-mail ad arrays of pores in the photonic crystals have diameters of several hundred nanometers to meet the requirements of the infrared photonic applications. 0927-7757/$ doi:10.1016/j logy. One of important applications of nanostruc- photonic crystals [1–3]. Photonic crystals have ople much attention since the pioneering works by ch [1] and John [2]. Photonic crystals consisting of y repeating dielectric structures generate photonic so that the photons with the frequencies in the gaps wed to propagate. tonic crystals with the band gaps in infrared spectra t the periodic structure elements have a size of a few nometers. Hot embossing lithography is a unique fab- thod for fabrication of nanostructures and is suitable c applications [4–14]. aper, we present two-dimensional photonic crystals y hot embossing lithography. The embossing stamp bossing conditions of the pressure, temperature and tical for the fabrication of the photonic crystals. The ding author at: Department of Mechatronics Engineering, nghua University of Education, Changhua 50007, Taiwan, ROC. 232105x7126; fax: +886 4 7211149. dress:
[email protected] (Y.-L. Lai). 2. Experimental A silicon wafer was adopted as a stamp for the hot emboss- ing lithography. The silicon stamp was fabricated as shown in Fig. 1. Firstly, the silicon wafer used for the stamp was cleaned and coated with the hexamethyldisilazane (HMDS) for the adhesion enhancement of photoresists. The I-line photore- sist (TOK TMHR ip3650) was spin-coated on the wafer. The soft bake temperature and time were 90 ◦C and 60 s, respec- tively. Secondly, the patterning of photoresist was conducted by I-line optical lithography with a Canon FPA-3000i5+ I- line stepper. The development process was implemented with an AD-10 developer for 60 s. The wafer was post-baked at 120 ◦C and for 90 s. Thirdly, the silicon stamp with elevated profiles was formed by dry etching. We used an Anelva ECR- 6001 electron cyclotron resonance (ECR) etcher. The etch gases included SF6 with a flow rate of 5 sccm, O2 with a flow rate of 5 sccm, and Cl2 with a flow rate of 90 sccm. The chamber pressure was controlled at 3 mTorr. The microwave power was kept at 300 W and the RF power was set at 90 W. – see front matter © 2007 Elsevier B.V. All rights reserved. .colsurfa.2007.05.075 Yeong-Lin Lai , Chi-C a Department of Mechatronics Engineering, National C Changhua 50007, Taiwan, b Graduate Institute of Display Technology, National C Changhua 50007, Taiwan, Received 19 November 2006; accept Available online 13 June 20 on the two-dimensional photonic crystals in polymer membranes for of pores were fabricated by hot embossing lithography. The silicon CR) etcher with the etch gases of SF6, O2 and Cl2. The hot embossing which was higher than the glass transition temperature of the polym ime was kept at 150 s. The reliable stamp and hot embossing processe vier B.V. All rights reserved. lectron cyclotron resonance (ECR); Hot embossing; Infrared; Photonic crystals infrared applications g Chiu a ua University of Education, ua University of Education, ay 2007 nic applications in infrared spectra. The photonic crystals p for embossing was fabricated by an electron cyclotron ess was conducted in a vacuum chamber at a temperature he embossing pressure was controlled at 380 psi and the ize the infrared photonic crystals. 498 Y.-L. Lai, C.-C. Chiu / Colloids and Surfaces A: Physicochem. Eng. Aspects 313–314 (2008) 497–499 Fig. 1. Fabrication flow of silicon stamps. Finally, the photoresist on the stamp was removed by an ozone asher. The fabrication flow of the photonic crystals using the hot embossing lithography consists of three steps, as shown in Fig. 2. At first, the The stamp The next st in a vacuu Fig. 2. Fabric Fi first cleane and then ri was coated silicon stam vacuum ch than the gl Finally, the after the va 3. Results pho abri pho copy y of rofil of th stamp formation for hot embossing was conducted. with an array of pillars was made of a silicon wafer. ep following the stamp formation was hot embossing m chamber. A silicon semiconductor substrate was The were f ricated micros an arra pore p shape ation flow of photonic crystals using hot embossing lithography. ulus of a s The Young 〈1 1 1〉 orie and 0.26 G Silicon has ness of 850 of 2.6 ppm stamp beca Fig. 4. Pressu lithography. g. 3. Photonic crystal with a pore diameter of 490 nm. d by trichloroethylene, acetone and isopropylalcohol nsed with de-ionized water. A polymer membrane on the cleaned silicon semiconductor substrate. The p was hot-embossed into the polymer membrane in a amber. The hot embossing temperatures were higher ass transition temperature of the polymer material. stamp was separated from the polymer membrane cuum chamber was cooled down. and discussion tonic crystals with different geometric dimensions cated by the hot embossing lithography. The fab- tonic crystals were observed by scanning electron . Fig. 3 shows the fabricated photonic crystal with the pores. The diameter of the pores is 490 nm. The e of the photonic crystal corresponds to the pillar e stamp made by a silicon wafer. The Young’s mod- ilicon wafer depends on the wafer orientation [15]. ’s moduli are 129.5 and 186.5 GPa for 〈1 0 0〉 and ntations, respectively. The Poisson ratios are 0.28 Pa for 〈1 0 0〉 and 〈1 1 1〉 orientations, respectively. a yield strength of 2600–6800 MPa, a Knoop hard- –1100 kg/mm2, and a thermal expansion coefficient /K. The silicon wafer is suitable for a hot embossing use of its unique material properties. re and temperature profiles with respect to time for hot embossing Y.-L. Lai, C.-C. Chiu / Colloids and Surfaces A: Physicochem. Eng. Aspects 313–314 (2008) 497–499 499 Fi Fi Before removal of stamp clean of the stam asher with under a hig was able to tion to the the ashing active chem to an excite excited N2O ashing of th uniform, ac The fabr ing proces embossing pressure an hot emboss to the emb applied. The pressure was released until the temperature level was decreased to the room temperature. The embossing temper- ature was in the range of 90–110 ◦C. The embossing pressure and time were 380 psi and 150 s, respectively. The advantage of the short hot embossing time achieved is able to provide high throughput for mass production. pho 5. T emb s of wit ic b ir ge ted b nclu -dim ogra e ar ted o the d tim hot tche ic ap g. 5. Photonic crystal with a pore diameter of 540 nm. The in Fig. of the pattern crystal photon on the genera 4. Co Two ing lith with th fabrica but als sure an of the ECR e photon g. 6. Photonic crystal with a pore diameter of 400 nm. hot embossing, an ozone asher was used for the the photoresist on the stamp in order to keep the . Any particle or residual photoresist on the surface p might damage the results of the hot embossing. The an O2 feed gas generated a mixture of ozone and O2 h-voltage high-frequency supply power. The ozone strip the photoresist on the silicon stamp. In addi- O2 feed gas, an N2O feed gas was added to enhance effect. Although N2O in the normal state was not an ical, the molecular structure of N2O was changed d state under a strong alternating electric field. The associated with the ozone affectively enhanced the e photoresist. In this work, the silicon stamp with a curate and stable profile was successfully produced. ication of the photonic crystals using the hot emboss- s depended not only on the stamp but also on the pressure, temperature and time. Fig. 4 shows the d temperature profiles with respect to time for the ing lithography. When the vacuum chamber reached ossing temperature, the embossing pressure was Acknowled This wo Council of E-018-001 Reference [1] E. Yablo [2] S. John, [3] D.F. Siev Joannop [4] H.-C. Sc [5] S.Y. Ch 3114–31 [6] X.C. Sha (2005) 4 [7] S.Y. Cho [8] K. Seuna tron. Eng [9] K.B. Yoo [10] T. Bailey J.G. Eke [11] B. Cui, T [12] L. Guo, [13] K. Hasu 2341–23 [14] P.W. Lee [15] M.J. Ma ization, s tonic crystal with a pore diameter of 540 nm is shown he profiles of the photonic crystals were the results ossing temperature, pressure and time as well as the the stamps. Fig. 6 shows the fabricated photonic h a pore diameter of 400 nm. The properties of the and gaps of the photonic crystals were dependent ometric dimensions. A photonic waveguide can be y removing a row or column of pores in the arrays. sion ensional photonic crystals fabricated by hot emboss- phy have been demonstrated. The photonic crystals rays of pores in the polymer membranes have been according to not only the high-quality silicon stamp proper embossing conditions of temperature, pres- e. The silicon wafer was processed to be the stamp embossing lithography by an I-line stepper and an r. The photonic crystals obtained were suitable for plications in infrared regions. gements rk was supported in part by the National Science the Republic of China under Contracts NSC 93-2215- and NSC 94-2215-E-018-006. s novitch, Phys. Rev. Lett. 58 (1987) 2059–2062. Phys. Rev. Lett. 58 (1987) 2486–2489. enpiper, E. Yablonovitch, J.N. Winn, S. Fan, P.R. Villeneuve, J.D. oulos, Phys. Rev. Lett. 80 (1998) 2829–2832. heer, H. Schulz, Microelectron. 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