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Estimation of phase separation behavior in nanohybrids by thermal and dielectric analyses
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Colloids and Surfaces A: Physicochem. Eng. Aspects 313–314 (2008) 549–552
Estimation of phase separation behavior in nanohybrids by thermal and dielectric analyses Sung-Kyu Min a , Jae-Mann Park b , Ki-Tae Song c , Bong-Jin Moon d , Do-Young Yoon e , Hee-Woo Rhee f,∗ a
Thin Film Team, Hynix Semiconductor, Kyunggido 467-701, South Korea b T/C ABS/PC Team LG Chem., Deajeon 305-380, South Korea c Cheil Industries Inc., Seoul 135-751, South Korea d Department of Chemistry, Sogang University, Seoul 121-742, South Korea e Department of Chemistry, Seoul National University, Seoul 151-742, South Korea f Department of Chemical & Biomolecular Engineering, Sogang University, Seoul 121-742, South Korea Received 31 October 2006; accepted 25 April 2007 Available online 2 June 2007
Abstract The compatibility between low-k matrix and porogen was characterized by TGA and dielectric analyses. A new low-k matrix has been prepared by copolymerization of methyl trimethoxysilane (MTMS) with [bis(1,2-trimethoxysilyl)ethane, BTMSE 10%] to control its compatibility with porogens. The shift of both decomposition and glass transition temperature (Tg ) of porogen in hybrids was dependent on the content of porogen. As porogen loading increased over critical points, decomposition temperature and Tg of porogen in hybrids approached the corresponding temperature of porogen itself, which implied that large domains as well as nanoscopic domains were formed. In addition, these critical points were much higher for MSSQ copolymer than MSSQ, which meant that MSSQ copolymer produced the smaller pores than MSSQ due to better compatibility. This was also verified by comparing the cross-sectional FE-SEM images of both porous MSSQ and MSSQ copolymer. © 2007 Elsevier B.V. All rights reserved. Keywords: Methyl silsesquioxane (MSSQ); MSSQ copolymer; Porogen; Differential TGA; Dielectric relaxation spectroscopy; Glass transition temperature (Tg )
1. Introduction According to International Technology Roadmap for Semiconductors 2005, low-k materials lower than 2.2 will be required for the 50 nm device generation in 2009 [1]. One of the most promising routes to achieve the material with lower k than 2.2 is to introduce nano-sized pores filled with air (k = 1) into the matrix [2]. This approach is based on the incorporation of a thermally degradable material, called porogen, within a host matrix. One set of materials that have attracted considerable attention are porous organosilicates such as poly(methyl silsesquioxane) (PMSSQ) and macromolecular porogens, such as hyperbranced polyester [3], poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (PEO-b-PPO-b-PEO) triblock copolymers [4] and poly(methyl
∗
Corresponding author. Tel.: +82 2 705 8484; fax: +82 2 711 0439. E-mail address: [email protected] (H.-W. Rhee).
0927-7757/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2007.04.100
methacrylate-co-2-dimethylaminoethyl methacrylate) [5]. For example, Bell lab researchers have reported that porous MSSQ films could have a dielectric constant as low as 1.5 with 50% porogen loading using PEO-b-PPO-b-PEO triblock copolymers [4]. However, when the high porosity was introduced into MSSQ, mechanical properties of porous MSSQ have it questionable in semiconductor fabrication such as chemical mechanical polishing (CMP) since incorporation of higher porosity resulted in poor mechanical strength of porous MSSQ. In this regard, Lee and coworkers [6] have reported that MSSQ copolymer, prepared by copolymerization of methyl trimethoxysilane (MTMS) with a small amount of an ethylene-bridged organosilicate [bis(1,2-trimethoxysilyl) ethane, BTMSE] as a comonomer, exhibited better mechanical properties. It is known that the properties of bulk porogen dispersed with nano-meter size in matrix are quite different from those of porogen itself. Recently, Rhee and coworkers [2,7] have reported that differential thermo gravimetric analysis (DTGA) and dielectric
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relaxation measurement were greatly useful tools to qualitatively estimate the degree of interaction between porogen and matrix by measuring decomposition and glass transition temperature of porogen in hybrid, respectively. In this work, we have investigated that the compatibility of PCL porogen with both MSSQ and MSSQ copolymer was observed by DTGA and dielectric relaxation measurements as a function of porogen loading. Cross-sections of both porous MSSQ and MSSQ copolymer were observed with FE-SEM. 2. Experiment MTMS-co-BTMSE prepolymers were prepared by copolymerization of MTMS with BTMSE and the synthetic procedures were described by Takamura et al. [8]. MSSQ was commercially obtained from Techneglas Co., Ltd. The star-shaped poly(caprolactone) (PCL) with 8-arm was synthesized by the similar procedures reported elsewhere [9].
Fig. 1. Differential TGA curves of the PCL and its hybrids with both MSSQ and its copolymer as a function of porogen loading: (a) 10 wt% (b) 30 wt% and (c) 40 wt%.
For differential TGA experiments, inorganic matrix and organic porogen were dissolved in n-butyl acetate at 30 wt% and mixed together to make proper ratios of porogen to matrix from 0 wt% to 40 wt%. In order to fabricate porous low-k films, the prepared hybrid solution was spun on a Si wafer at 2500 rpm for 30 s and cured at 250 ◦ C for 30 min and at 430 ◦ C for 1 h, respectively. The heating rate was 3 ◦ C/min and the nitrogen atmosphere was employed during curing procedure. For the dielectric relaxation measurement, the hybrid solution was spin-coated on a glass substrates with patterned bottom Al electrodes and cured according to mentioned curing cycle. Next, the cured samples were slowly cooled to room temperature and finally a top electrode was evaporated on the cured sample at 5 × 10−5 Torr or less. The dimensions of Al electrodes were ˚ in thickness. 5 mm in diameter and 1000 A TGA analysis on hybrid samples was done with Thermogravimetric Analyzer TGA 2950 (TA instruments). The
Fig. 2. Dielectric relaxation result for (a) PCL at different frequencies, PCL hybrids in (b) MSSQ and (c) its copolymer as a function of loading.
S.-K. Min et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 313–314 (2008) 549–552
heating rate was 3 ◦ C/min, and the dates were collected from 30 ◦ C to 500 ◦ C under nitrogen atmosphere. The dielectric relaxation measurements were conducted with LCR meter (Hewlett-Packard 4194A) interfaced with IBM PC. The frequency ranged from 10 kHz to 500 kHz and the amplitude was 0.1 V. tan δ was acquired during heating cycles and temperature varied from −200 ◦ C to 200 ◦ C at a rate of 5 ◦ C/min. Dielectric constants of porous MSSQ copolymer films were measured with metal–insulator–semiconductor (MIS) configuration using (Hewlett-Packard 4284A). The thickness of hybrids and porous films was obtained by ␣-step profiler (Model 25087) and a variable angle multi-wavelength ellipsometer (L116C, Gaertner Scientific Corp.), respectively. The morphology of porous organosilicate film was observed with an FE-SEM (JSM-633OF, JEOL, Japan). 3. Results and discussion Thermogravimetric properties were measured on poly(caprolactone) porogen and its hybrids with both MSSQ and its copolymer as a function of porogen loading as shown in Fig. 1. When porogen loading in both matrices was 10 wt%, PCL was decomposed at higher temperature than that of pure porogen, which might indicate that PCL molecules were nano-dispersed in matrix. The 30 wt% porogen loading in MSSQ caused the appearance of a shoulder around 290 ◦ C and the remarkable growth of this shoulder at 40 wt% PCL, which might suggest that starting from 30 wt% porogen loading, PCL molecules began to form not only nanoscopic domains but also large domains which will be verified with observation of
551
FE-SEM images. On the other hand, decomposition of porogen in MSSQ copolymer occurred at higher temperature than that of porogen itself. It meant that porogen domains might be smaller in MSSQ copolymer than MSSQ. Dielectric relaxation measurements are considered as another powerful tool to estimate the degree of interaction between porogen and matrix by measuring glass transition temperature (Tg ) of porogen [2]. In this study, we have performed dielectric relaxation measurements on porogen and its hybrids with MSSQ and its copolymer cured at 250 ◦ C for 2 h. Fig. 2(a) shows tan δ of PCL porogen as a function of frequency on heating cycle. The dielectric loss of porogen increased with a frequency and the loss peaks around −60 ◦ C and −90 ◦ C represented glass (or β) relaxation and sub-glass (or γ) relaxation, respectively. In addition, the stepwise change of dielectric loss occurred at around 40 ◦ C, which corresponded to the melting temperature of porogen. Fig. 2(b) and (c) present tan δ of PCL hybrids with both MSSQ and its copolymer as a function of porogen loading, which were obtained at 100 kHZ on heating cycle with 5 ◦ C/min. The glass transition temperatures of porogens in both matrices were dependent on contents of porogen. Fig. 2(b) shows that when the porogen loading in MSSQ increased to 16%, Tg of porogen occurred at around 40 ◦ C, which was much higher than that of porogen itself by ∼100 ◦ C. For 20% porogen in MSSQ, its β relaxation appeared at corresponding temperature of the pure porogen. It suggests that starting from this porogen loading large porogen domains along with nanoscopic domains began to form in MSSQ. Fig. 2(c) compares that the glass relaxation of porogen in cured copolymer was observed at higher temperature until porogen loading increased to 35%. Such an increased
Fig. 3. Cross-sectional FE-SEM images of porous MSSQ and its copolymer prepared at different PCL loadings.
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S.-K. Min et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 313–314 (2008) 549–552
temperature so that smaller porogen domains and pores were formed in the copolymer than MSSQ. Fig. 4 shows the k values of porous MSSQ copolymer as a function of porogen loading. As the porogen loading increased, the dielectric constant of the copolymer linearly decreased to as low as about 1.8 at 50% porogen loading. 4. Conclusions
Fig. 4. Dielectric constant of porous copolymer as a function of porogen loading.
critical point implies that porogen molecules were more compatible with MSSQ copolymer than MSSQ. In addition, when this critical point was compared with TGA results, dielectric relaxation measurement was more sensitive to detect the compatibility between porogen and matrix since Tg measurement was based on the PCL chain mobility. It was also found that crystallization of PCL polymer was suppressed to be nano-phase domains due to the confinement effect of matrix. Fig. 3(a) and (b) show the cross-sectional FE-SEM images of porous PMSSQ prepared by sintering 10% and 30% of porogen, respectively. Ten percent porogen loading resulted in no visible pores in porous MSSQ samples, while 30% porogen loading presented larger pores than the other. When porogen loading in MSSQ was low, porogen domains were dispersed in matrix with smaller size due to thermodynamical reason. However, the increase in porogen loading above the critical point led to decrease in the compatibility between two phases so that micro-phase domains began to be formed in matrix. Fig. 3(c) and (d) show porous MSSQ copolymer images of obtained by sintering at corresponding porogen content as the porous MSSQ. The increase in porogen loading up to 30% resulted in no visible pores, which indicates that MSSQ copolymer produced the smaller pores than MSSQ at higher porogen loading. Since the relatively larger amount of Si–OH end groups, present initially in the copolymer, should lead to higher miscibility with PCL porogen, the phase separation could be hindered until at higher
The differential TGA and dielectric relaxation measurement also showed that properties of porogen in hybrids were dependent on the porogen loading. As porogen loading increased over critical points, porogen in both MSSQ and its copolymer showed the decomposition and glass transition temperature at similar temperature as the pure porogen but these critical points were higher for the copolymer than MSSQ. It indicated that PCL porogen formed smaller nano-sized domains in the copolymer than MSSQ, which was confirmed by comparing the cross-sectional FE-SEM images of both porous MSSQ and its copolymer. Acknowledgment This work was supported by Brain Korea 21 Program by the Ministry of Education, Korea. References [1] Semiconductor Industry Association, The International Technology Roadmap for Semiconductor, San Francisco, 2005. [2] C.V. Nguyen, K.R. Cater, C.J. Hawker, J.L. Hedrick, R.D. Miller, H.W. Rhee, D.Y. Yoon, Chem. Mater. 11 (11) (1999) 3080. [3] C.V. Nguyen, C.J. Hawker, R.D. Miller, E. Huang, J.L. Hedrick, Macromolecules 33 (2000) 4281. [4] S. Yang, P.A. Mirau, E.K. Lin, H.J. Lee, D.W. Gidley, Chem. Mater. 13 (2001) 2762. [5] Q.R. Huang, W. Volksen, E. Huang, M. Toney, C.W. Frank, R.D. Miller, Chem. Mater. 14 (9) (2002) 3676. [6] H.W. Ro, K.H. Char, S.H. Chu, M.Y. Jin, W.C. Kim, J.K. Lee, S.K. Min, H.W. Rhee, D.Y. Yoo, D.Y. Yoon, Abstracts of Papers of the American Chemical Society 224 (2002) U376-U376 127-POLY Part 2. [7] S.K. Min, J.M. Park, K.T. Song, M.Y. Jin, D.Y. Yoon, H.W. Rhee, Mol. Cryst. Liq. Cryst. 406 (2003) 389–396. [8] N. Takamura, T. Gunji, H. Hatano, Y.J. Abe, J. Polym. Sci. 37 (1999) 1017. [9] M. Trollsas, J.L. Hedrick, D. Mecerreyes, R. Jerome, H. Ihre, A. Hult, Macromolecules 30 (1997) 8505.
Colloids and Surfaces A: Physicochem. Eng. Aspects 313–314 (2008) 549–552
Estimation of phase separation behavior in nanohybrids by thermal and dielectric analyses Sung-Kyu Min a , Jae-Mann Park b , Ki-Tae Song c , Bong-Jin Moon d , Do-Young Yoon e , Hee-Woo Rhee f,∗ a
Thin Film Team, Hynix Semiconductor, Kyunggido 467-701, South Korea b T/C ABS/PC Team LG Chem., Deajeon 305-380, South Korea c Cheil Industries Inc., Seoul 135-751, South Korea d Department of Chemistry, Sogang University, Seoul 121-742, South Korea e Department of Chemistry, Seoul National University, Seoul 151-742, South Korea f Department of Chemical & Biomolecular Engineering, Sogang University, Seoul 121-742, South Korea Received 31 October 2006; accepted 25 April 2007 Available online 2 June 2007
Abstract The compatibility between low-k matrix and porogen was characterized by TGA and dielectric analyses. A new low-k matrix has been prepared by copolymerization of methyl trimethoxysilane (MTMS) with [bis(1,2-trimethoxysilyl)ethane, BTMSE 10%] to control its compatibility with porogens. The shift of both decomposition and glass transition temperature (Tg ) of porogen in hybrids was dependent on the content of porogen. As porogen loading increased over critical points, decomposition temperature and Tg of porogen in hybrids approached the corresponding temperature of porogen itself, which implied that large domains as well as nanoscopic domains were formed. In addition, these critical points were much higher for MSSQ copolymer than MSSQ, which meant that MSSQ copolymer produced the smaller pores than MSSQ due to better compatibility. This was also verified by comparing the cross-sectional FE-SEM images of both porous MSSQ and MSSQ copolymer. © 2007 Elsevier B.V. All rights reserved. Keywords: Methyl silsesquioxane (MSSQ); MSSQ copolymer; Porogen; Differential TGA; Dielectric relaxation spectroscopy; Glass transition temperature (Tg )
1. Introduction According to International Technology Roadmap for Semiconductors 2005, low-k materials lower than 2.2 will be required for the 50 nm device generation in 2009 [1]. One of the most promising routes to achieve the material with lower k than 2.2 is to introduce nano-sized pores filled with air (k = 1) into the matrix [2]. This approach is based on the incorporation of a thermally degradable material, called porogen, within a host matrix. One set of materials that have attracted considerable attention are porous organosilicates such as poly(methyl silsesquioxane) (PMSSQ) and macromolecular porogens, such as hyperbranced polyester [3], poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (PEO-b-PPO-b-PEO) triblock copolymers [4] and poly(methyl
∗
Corresponding author. Tel.: +82 2 705 8484; fax: +82 2 711 0439. E-mail address: [email protected] (H.-W. Rhee).
0927-7757/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2007.04.100
methacrylate-co-2-dimethylaminoethyl methacrylate) [5]. For example, Bell lab researchers have reported that porous MSSQ films could have a dielectric constant as low as 1.5 with 50% porogen loading using PEO-b-PPO-b-PEO triblock copolymers [4]. However, when the high porosity was introduced into MSSQ, mechanical properties of porous MSSQ have it questionable in semiconductor fabrication such as chemical mechanical polishing (CMP) since incorporation of higher porosity resulted in poor mechanical strength of porous MSSQ. In this regard, Lee and coworkers [6] have reported that MSSQ copolymer, prepared by copolymerization of methyl trimethoxysilane (MTMS) with a small amount of an ethylene-bridged organosilicate [bis(1,2-trimethoxysilyl) ethane, BTMSE] as a comonomer, exhibited better mechanical properties. It is known that the properties of bulk porogen dispersed with nano-meter size in matrix are quite different from those of porogen itself. Recently, Rhee and coworkers [2,7] have reported that differential thermo gravimetric analysis (DTGA) and dielectric
550
S.-K. Min et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 313–314 (2008) 549–552
relaxation measurement were greatly useful tools to qualitatively estimate the degree of interaction between porogen and matrix by measuring decomposition and glass transition temperature of porogen in hybrid, respectively. In this work, we have investigated that the compatibility of PCL porogen with both MSSQ and MSSQ copolymer was observed by DTGA and dielectric relaxation measurements as a function of porogen loading. Cross-sections of both porous MSSQ and MSSQ copolymer were observed with FE-SEM. 2. Experiment MTMS-co-BTMSE prepolymers were prepared by copolymerization of MTMS with BTMSE and the synthetic procedures were described by Takamura et al. [8]. MSSQ was commercially obtained from Techneglas Co., Ltd. The star-shaped poly(caprolactone) (PCL) with 8-arm was synthesized by the similar procedures reported elsewhere [9].
Fig. 1. Differential TGA curves of the PCL and its hybrids with both MSSQ and its copolymer as a function of porogen loading: (a) 10 wt% (b) 30 wt% and (c) 40 wt%.
For differential TGA experiments, inorganic matrix and organic porogen were dissolved in n-butyl acetate at 30 wt% and mixed together to make proper ratios of porogen to matrix from 0 wt% to 40 wt%. In order to fabricate porous low-k films, the prepared hybrid solution was spun on a Si wafer at 2500 rpm for 30 s and cured at 250 ◦ C for 30 min and at 430 ◦ C for 1 h, respectively. The heating rate was 3 ◦ C/min and the nitrogen atmosphere was employed during curing procedure. For the dielectric relaxation measurement, the hybrid solution was spin-coated on a glass substrates with patterned bottom Al electrodes and cured according to mentioned curing cycle. Next, the cured samples were slowly cooled to room temperature and finally a top electrode was evaporated on the cured sample at 5 × 10−5 Torr or less. The dimensions of Al electrodes were ˚ in thickness. 5 mm in diameter and 1000 A TGA analysis on hybrid samples was done with Thermogravimetric Analyzer TGA 2950 (TA instruments). The
Fig. 2. Dielectric relaxation result for (a) PCL at different frequencies, PCL hybrids in (b) MSSQ and (c) its copolymer as a function of loading.
S.-K. Min et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 313–314 (2008) 549–552
heating rate was 3 ◦ C/min, and the dates were collected from 30 ◦ C to 500 ◦ C under nitrogen atmosphere. The dielectric relaxation measurements were conducted with LCR meter (Hewlett-Packard 4194A) interfaced with IBM PC. The frequency ranged from 10 kHz to 500 kHz and the amplitude was 0.1 V. tan δ was acquired during heating cycles and temperature varied from −200 ◦ C to 200 ◦ C at a rate of 5 ◦ C/min. Dielectric constants of porous MSSQ copolymer films were measured with metal–insulator–semiconductor (MIS) configuration using (Hewlett-Packard 4284A). The thickness of hybrids and porous films was obtained by ␣-step profiler (Model 25087) and a variable angle multi-wavelength ellipsometer (L116C, Gaertner Scientific Corp.), respectively. The morphology of porous organosilicate film was observed with an FE-SEM (JSM-633OF, JEOL, Japan). 3. Results and discussion Thermogravimetric properties were measured on poly(caprolactone) porogen and its hybrids with both MSSQ and its copolymer as a function of porogen loading as shown in Fig. 1. When porogen loading in both matrices was 10 wt%, PCL was decomposed at higher temperature than that of pure porogen, which might indicate that PCL molecules were nano-dispersed in matrix. The 30 wt% porogen loading in MSSQ caused the appearance of a shoulder around 290 ◦ C and the remarkable growth of this shoulder at 40 wt% PCL, which might suggest that starting from 30 wt% porogen loading, PCL molecules began to form not only nanoscopic domains but also large domains which will be verified with observation of
551
FE-SEM images. On the other hand, decomposition of porogen in MSSQ copolymer occurred at higher temperature than that of porogen itself. It meant that porogen domains might be smaller in MSSQ copolymer than MSSQ. Dielectric relaxation measurements are considered as another powerful tool to estimate the degree of interaction between porogen and matrix by measuring glass transition temperature (Tg ) of porogen [2]. In this study, we have performed dielectric relaxation measurements on porogen and its hybrids with MSSQ and its copolymer cured at 250 ◦ C for 2 h. Fig. 2(a) shows tan δ of PCL porogen as a function of frequency on heating cycle. The dielectric loss of porogen increased with a frequency and the loss peaks around −60 ◦ C and −90 ◦ C represented glass (or β) relaxation and sub-glass (or γ) relaxation, respectively. In addition, the stepwise change of dielectric loss occurred at around 40 ◦ C, which corresponded to the melting temperature of porogen. Fig. 2(b) and (c) present tan δ of PCL hybrids with both MSSQ and its copolymer as a function of porogen loading, which were obtained at 100 kHZ on heating cycle with 5 ◦ C/min. The glass transition temperatures of porogens in both matrices were dependent on contents of porogen. Fig. 2(b) shows that when the porogen loading in MSSQ increased to 16%, Tg of porogen occurred at around 40 ◦ C, which was much higher than that of porogen itself by ∼100 ◦ C. For 20% porogen in MSSQ, its β relaxation appeared at corresponding temperature of the pure porogen. It suggests that starting from this porogen loading large porogen domains along with nanoscopic domains began to form in MSSQ. Fig. 2(c) compares that the glass relaxation of porogen in cured copolymer was observed at higher temperature until porogen loading increased to 35%. Such an increased
Fig. 3. Cross-sectional FE-SEM images of porous MSSQ and its copolymer prepared at different PCL loadings.
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S.-K. Min et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 313–314 (2008) 549–552
temperature so that smaller porogen domains and pores were formed in the copolymer than MSSQ. Fig. 4 shows the k values of porous MSSQ copolymer as a function of porogen loading. As the porogen loading increased, the dielectric constant of the copolymer linearly decreased to as low as about 1.8 at 50% porogen loading. 4. Conclusions
Fig. 4. Dielectric constant of porous copolymer as a function of porogen loading.
critical point implies that porogen molecules were more compatible with MSSQ copolymer than MSSQ. In addition, when this critical point was compared with TGA results, dielectric relaxation measurement was more sensitive to detect the compatibility between porogen and matrix since Tg measurement was based on the PCL chain mobility. It was also found that crystallization of PCL polymer was suppressed to be nano-phase domains due to the confinement effect of matrix. Fig. 3(a) and (b) show the cross-sectional FE-SEM images of porous PMSSQ prepared by sintering 10% and 30% of porogen, respectively. Ten percent porogen loading resulted in no visible pores in porous MSSQ samples, while 30% porogen loading presented larger pores than the other. When porogen loading in MSSQ was low, porogen domains were dispersed in matrix with smaller size due to thermodynamical reason. However, the increase in porogen loading above the critical point led to decrease in the compatibility between two phases so that micro-phase domains began to be formed in matrix. Fig. 3(c) and (d) show porous MSSQ copolymer images of obtained by sintering at corresponding porogen content as the porous MSSQ. The increase in porogen loading up to 30% resulted in no visible pores, which indicates that MSSQ copolymer produced the smaller pores than MSSQ at higher porogen loading. Since the relatively larger amount of Si–OH end groups, present initially in the copolymer, should lead to higher miscibility with PCL porogen, the phase separation could be hindered until at higher
The differential TGA and dielectric relaxation measurement also showed that properties of porogen in hybrids were dependent on the porogen loading. As porogen loading increased over critical points, porogen in both MSSQ and its copolymer showed the decomposition and glass transition temperature at similar temperature as the pure porogen but these critical points were higher for the copolymer than MSSQ. It indicated that PCL porogen formed smaller nano-sized domains in the copolymer than MSSQ, which was confirmed by comparing the cross-sectional FE-SEM images of both porous MSSQ and its copolymer. Acknowledgment This work was supported by Brain Korea 21 Program by the Ministry of Education, Korea. References [1] Semiconductor Industry Association, The International Technology Roadmap for Semiconductor, San Francisco, 2005. [2] C.V. Nguyen, K.R. Cater, C.J. Hawker, J.L. Hedrick, R.D. Miller, H.W. Rhee, D.Y. Yoon, Chem. Mater. 11 (11) (1999) 3080. [3] C.V. Nguyen, C.J. Hawker, R.D. Miller, E. Huang, J.L. Hedrick, Macromolecules 33 (2000) 4281. [4] S. Yang, P.A. Mirau, E.K. Lin, H.J. Lee, D.W. Gidley, Chem. Mater. 13 (2001) 2762. [5] Q.R. Huang, W. Volksen, E. Huang, M. Toney, C.W. Frank, R.D. Miller, Chem. Mater. 14 (9) (2002) 3676. [6] H.W. Ro, K.H. Char, S.H. Chu, M.Y. Jin, W.C. Kim, J.K. Lee, S.K. Min, H.W. Rhee, D.Y. Yoo, D.Y. Yoon, Abstracts of Papers of the American Chemical Society 224 (2002) U376-U376 127-POLY Part 2. [7] S.K. Min, J.M. Park, K.T. Song, M.Y. Jin, D.Y. Yoon, H.W. Rhee, Mol. Cryst. Liq. Cryst. 406 (2003) 389–396. [8] N. Takamura, T. Gunji, H. Hatano, Y.J. Abe, J. Polym. Sci. 37 (1999) 1017. [9] M. Trollsas, J.L. Hedrick, D. Mecerreyes, R. Jerome, H. Ihre, A. Hult, Macromolecules 30 (1997) 8505.