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Electrical properties of silica-polyimide composite dielectric thin films prepared via sol-gel reaction and thermal imidization
ELSEVIER
SyntheticMetals
Electrical
85 (1997)
1399-1400
properties of silica-polyimide composite dielectric thin Ghns prepared via sol-gel reaction and thermal imidization Y.Kim*, E.Kang’, Y.S.Kwond, W.J.Cho’, C.Chob, M.Changb, M.ReeC, T.Changc, and C.S. Ha’ ’ Department
of Polymer Science and Engineering, PIWJI Nat&d University, Pusan 669735, South Korea b Department of Physics, Puwn National University, Pusan 609-735, South Korea ’ Department of Chemistry, Pohang University of Science & Technology, Pohang 79G784, South Korea d Department of Electrical Engineering, Dong-A University, Puwn 604-714, South Korea -s--e------
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Abstract Thin dielectric films composedof silica and polyimide were preparedfrom tetmethoxysilane(TEOS) and precursorof poly@-phenylenebiphenyltetde )(BPDA-PDA). Silica particles were generatedfrom TEOS via sol-gel process. BPDA-PDA polyimide was prepared from its flexible and soluble precursors,poly(p-phenylenebiphenyltetmcarboxamiamic acid)(BPDA-PDA PAA), and polyb-phenylene biphenyltetmcarboxamicdiethyl ester)(BPDA-PDA ES), through thermal hnidizalion process. In the presentwork, the electrical propertiesof the silica-polyimidehybrid compositefilms were examinedutihing a capacitancemeasurement by a high resolutionelectrometer/functiongeneratorsystem The effects of TEOS contentsand precursortypes for polyimide matrix of the compositeson the relative dielectric constant, dielectric dissipationfactor, and resistivity of the compositefilms were investigated Keywords:
-----------
sol-gel methcds,spin casting,insulatingfilms, high-temperature methodsfor materialpreparation ---__I__----~----__--~----------__
Introduction Polyimides have been widely used in microelectronic industriesbecauseof their outstandingchsmcteristicssuchas high tensile strength and modulus,low thermal emvity .and dielectric constant, and good rzsktivity againstorganic solvent[l$Z]. I?qeciaIly the aromatic polyimidesare usedas dielectric layers, a-particle tiers, and insulating layers in multi-chip packaging of semiconductors[3]. It is n@ easy, however, for a single polyimide to match its thermophysical prop-sties such as thermal expansivity to other constituent layers. Recently inorganic-organichybrid compositematerials have hen developed as one of the best methods to overcome the problem becausethe inorganic materialsplay a great role in reducing the thermal expansivity of polyimide and improving the mechanical properties[4]. In the present study, the silica-ircorporabl polyimide inorganic-organiccompositethin films were prepared,and the electrical properties of the composite iihns were investigated.
generated
Experimental
Results and d&us&n
The polyimide usedin this work was BPDA-PDA which had been preparedthrough thermal imidization processfrom the respectiveprecursors,BPDA-PDA PAA and BPDA-PDA ES. The molecular weight of the precursors was about 40,000. The silica p&icles as an inorganic material were
Figure 1 shows the effect of TEOS contents on the dielectric constant of the silica/polyimide compositefilms. The dielectirc coxtants of the composite films were increasedwith TEOS contents, regardlessof the polyimide precursortypss, due to the inherent higher dielectric
0379-6779/97/$17.00
0 1997 Elsevier
PII SO379-6779(96)04409-8
Science S.k
All rights reserved
via in-situ sol-gel reaction of TEOS in the solution of polyimide precursorsin N-methyl- 2-pyrrolidone in the presenceof acid catalyst and water[3]. The mixture solutions after sol-gel reaction were spin-coatedonto the slide glass, and sof&&ed at SOT for ca. 3 hr. The s&baked compositefilms were finally converted into the silica-polyimide compositesthrough thermal imidizaiion at 3809c for 1.5 hr with a heating rate of 2”c/min under nitrogen flow. The silica-polyimide composite films were overcoated with gold as an elect&e to measure the electrical properties. The Shea of the gold electrode was 0.216 cm’, and the silver wire was used as a lead cable. The capacitance of the hybrid composite films was measured in the frequency sweep method. The sweep kquency was varied from 1OOHzto 2MHz, and oscillation voltage was 20mV. In addition to the frequency sweep, the voltage sweepwas also conductedon the direct current voltage range of -4ODCV - +4ODCV at the constant frequency of 1OkHz.
1400
Y. Kim et al. /SyntheticMetals
85
(1997) 1399-1400
constant of silica in comparison with the insulating polyimide. The composite tihns prepared from the polyimide of polyamic acid precursor exhibited higher dielecaic constantsthan those from poly(amic diethyl ester) precursor, meaning that the dielectric constants of the composite films were affected by generatedinorganic particles existing in the solid state films; It was reported that the homogeneous nanometer-sized silica particleswere prepred in the composite films from the polyimide of BPDA-PDAA PAA precursor, whereas heterogeneous micrometer-sizedparticles were prepared in case of the BPDA-PDA ES precursor[5j. Thus, it is not surprisingthat 15 '0 5 the composite films prepared from the polyimide of TEO&t.%) polyamic acid precursorexhibited higher dielectric constanta than those from poly(amic diethyl ester) precursor,due to Fig. 1. The effect of TEOS contents on the dielectric the uniformly distributed nanometer-sizedsilica particles. constantof the silica/polyimidecompositefilms. A: The relative dielectric constantsof the compositefilms was BPDA-PDA PAA precursor, B: BPDA-PDA Fs rangedfrom 1.5 to 4.5. precursor The relative dielectric constant and the dielectric dissipation factor of the silica-polyimidecomposite films were, however, not varied with increasing the sweep frequency in the range between 100 Hz and 2MBz, regalless of polyimide precursortypes and silica contents. e I The composite films showed also no dependenceof dielectric constanton bias voltage within the direct current voltage range of -40DCV - +4ODCV. The compositefilms prepared from the poly(amic diethyl ester) precursor polyimide also showedthe sametreands. Figure 2 shows the dielectric constantsas a function of the bias voltage and TEOS contents. It was observed for both composite films having polyirnide matrices of two different precursorsthat the dissipationfactors were also not dependenton the TEOS contents as well as the bii voltage. The dielectric dissipationfactor was almostin the rangeof 0.01-0.02. BiasVoltage(Vj the current-voltageQ-V) characteristics was FRY, measuredusing the pica-level electrometer. From the I-V Fig. 2. The dependenceof the dielectric constantsof the cbatacteristics,the resistivlty value was e&ma&d. Figure 3 compositefilms on the bii voltage. The polyimide showstypical results at the bias voltage of -23.5 V. It is was preparedfrom poly(amic acid) precursor. seen that the resistivity of the compositefilms decreased with TEOS contents regardlessof precursor types. As expected from the dielectric constant resuts as shown in 6e+13 I Figure 1, the decreasein the reskivity was lesspromineut in the caseof the polyimide matrix preparedfrom polyamic acid precursor than that from poly(amic diethyl ester) precursor,due to the formation of the nanocompoaites in the former polyimide.
‘5*o i
References [l] K.L%iittal, Eds., Polyimide:Synthesis, Chamcter&ion and Applications, Plenum,New York (1983). TummaIa and E.J. Rymaszewsld, Eds., PI RR. Microelectronics Packaging Handbook, Van Nostrand Reinhold,New York (1989). [3] M.Ree, C.W.Chu, and M.J.Goldberg, J.AppL Phys., 75 (1994), 1410. [4] C.E.Sroog,hog. PolymSci., 16 (1!391),561. [5] Y.Kim, PhD. dissertation, Pusan National University, Pusan,Korea(1996).
2
le+13 Oe+O l 0
I
5
I
TE&t.%)
I
I
15
20
Fig. 3. ‘The resistivity of the compositefilms as a function of TEOS contents (bias voltage = -23.5 V); ABPDA-.-FDA PM precursor, B: BPDA-PDA ES precursor.
SyntheticMetals
Electrical
85 (1997)
1399-1400
properties of silica-polyimide composite dielectric thin Ghns prepared via sol-gel reaction and thermal imidization Y.Kim*, E.Kang’, Y.S.Kwond, W.J.Cho’, C.Chob, M.Changb, M.ReeC, T.Changc, and C.S. Ha’ ’ Department
of Polymer Science and Engineering, PIWJI Nat&d University, Pusan 669735, South Korea b Department of Physics, Puwn National University, Pusan 609-735, South Korea ’ Department of Chemistry, Pohang University of Science & Technology, Pohang 79G784, South Korea d Department of Electrical Engineering, Dong-A University, Puwn 604-714, South Korea -s--e------
---~__-
--
---------__---------
Abstract Thin dielectric films composedof silica and polyimide were preparedfrom tetmethoxysilane(TEOS) and precursorof poly@-phenylenebiphenyltetde )(BPDA-PDA). Silica particles were generatedfrom TEOS via sol-gel process. BPDA-PDA polyimide was prepared from its flexible and soluble precursors,poly(p-phenylenebiphenyltetmcarboxamiamic acid)(BPDA-PDA PAA), and polyb-phenylene biphenyltetmcarboxamicdiethyl ester)(BPDA-PDA ES), through thermal hnidizalion process. In the presentwork, the electrical propertiesof the silica-polyimidehybrid compositefilms were examinedutihing a capacitancemeasurement by a high resolutionelectrometer/functiongeneratorsystem The effects of TEOS contentsand precursortypes for polyimide matrix of the compositeson the relative dielectric constant, dielectric dissipationfactor, and resistivity of the compositefilms were investigated Keywords:
-----------
sol-gel methcds,spin casting,insulatingfilms, high-temperature methodsfor materialpreparation ---__I__----~----__--~----------__
Introduction Polyimides have been widely used in microelectronic industriesbecauseof their outstandingchsmcteristicssuchas high tensile strength and modulus,low thermal emvity .and dielectric constant, and good rzsktivity againstorganic solvent[l$Z]. I?qeciaIly the aromatic polyimidesare usedas dielectric layers, a-particle tiers, and insulating layers in multi-chip packaging of semiconductors[3]. It is n@ easy, however, for a single polyimide to match its thermophysical prop-sties such as thermal expansivity to other constituent layers. Recently inorganic-organichybrid compositematerials have hen developed as one of the best methods to overcome the problem becausethe inorganic materialsplay a great role in reducing the thermal expansivity of polyimide and improving the mechanical properties[4]. In the present study, the silica-ircorporabl polyimide inorganic-organiccompositethin films were prepared,and the electrical properties of the composite iihns were investigated.
generated
Experimental
Results and d&us&n
The polyimide usedin this work was BPDA-PDA which had been preparedthrough thermal imidization processfrom the respectiveprecursors,BPDA-PDA PAA and BPDA-PDA ES. The molecular weight of the precursors was about 40,000. The silica p&icles as an inorganic material were
Figure 1 shows the effect of TEOS contents on the dielectric constant of the silica/polyimide compositefilms. The dielectirc coxtants of the composite films were increasedwith TEOS contents, regardlessof the polyimide precursortypss, due to the inherent higher dielectric
0379-6779/97/$17.00
0 1997 Elsevier
PII SO379-6779(96)04409-8
Science S.k
All rights reserved
via in-situ sol-gel reaction of TEOS in the solution of polyimide precursorsin N-methyl- 2-pyrrolidone in the presenceof acid catalyst and water[3]. The mixture solutions after sol-gel reaction were spin-coatedonto the slide glass, and sof&&ed at SOT for ca. 3 hr. The s&baked compositefilms were finally converted into the silica-polyimide compositesthrough thermal imidizaiion at 3809c for 1.5 hr with a heating rate of 2”c/min under nitrogen flow. The silica-polyimide composite films were overcoated with gold as an elect&e to measure the electrical properties. The Shea of the gold electrode was 0.216 cm’, and the silver wire was used as a lead cable. The capacitance of the hybrid composite films was measured in the frequency sweep method. The sweep kquency was varied from 1OOHzto 2MHz, and oscillation voltage was 20mV. In addition to the frequency sweep, the voltage sweepwas also conductedon the direct current voltage range of -4ODCV - +4ODCV at the constant frequency of 1OkHz.
1400
Y. Kim et al. /SyntheticMetals
85
(1997) 1399-1400
constant of silica in comparison with the insulating polyimide. The composite tihns prepared from the polyimide of polyamic acid precursor exhibited higher dielecaic constantsthan those from poly(amic diethyl ester) precursor, meaning that the dielectric constants of the composite films were affected by generatedinorganic particles existing in the solid state films; It was reported that the homogeneous nanometer-sized silica particleswere prepred in the composite films from the polyimide of BPDA-PDAA PAA precursor, whereas heterogeneous micrometer-sizedparticles were prepared in case of the BPDA-PDA ES precursor[5j. Thus, it is not surprisingthat 15 '0 5 the composite films prepared from the polyimide of TEO&t.%) polyamic acid precursorexhibited higher dielectric constanta than those from poly(amic diethyl ester) precursor,due to Fig. 1. The effect of TEOS contents on the dielectric the uniformly distributed nanometer-sizedsilica particles. constantof the silica/polyimidecompositefilms. A: The relative dielectric constantsof the compositefilms was BPDA-PDA PAA precursor, B: BPDA-PDA Fs rangedfrom 1.5 to 4.5. precursor The relative dielectric constant and the dielectric dissipation factor of the silica-polyimidecomposite films were, however, not varied with increasing the sweep frequency in the range between 100 Hz and 2MBz, regalless of polyimide precursortypes and silica contents. e I The composite films showed also no dependenceof dielectric constanton bias voltage within the direct current voltage range of -40DCV - +4ODCV. The compositefilms prepared from the poly(amic diethyl ester) precursor polyimide also showedthe sametreands. Figure 2 shows the dielectric constantsas a function of the bias voltage and TEOS contents. It was observed for both composite films having polyirnide matrices of two different precursorsthat the dissipationfactors were also not dependenton the TEOS contents as well as the bii voltage. The dielectric dissipationfactor was almostin the rangeof 0.01-0.02. BiasVoltage(Vj the current-voltageQ-V) characteristics was FRY, measuredusing the pica-level electrometer. From the I-V Fig. 2. The dependenceof the dielectric constantsof the cbatacteristics,the resistivlty value was e&ma&d. Figure 3 compositefilms on the bii voltage. The polyimide showstypical results at the bias voltage of -23.5 V. It is was preparedfrom poly(amic acid) precursor. seen that the resistivity of the compositefilms decreased with TEOS contents regardlessof precursor types. As expected from the dielectric constant resuts as shown in 6e+13 I Figure 1, the decreasein the reskivity was lesspromineut in the caseof the polyimide matrix preparedfrom polyamic acid precursor than that from poly(amic diethyl ester) precursor,due to the formation of the nanocompoaites in the former polyimide.
‘5*o i
References [l] K.L%iittal, Eds., Polyimide:Synthesis, Chamcter&ion and Applications, Plenum,New York (1983). TummaIa and E.J. Rymaszewsld, Eds., PI RR. Microelectronics Packaging Handbook, Van Nostrand Reinhold,New York (1989). [3] M.Ree, C.W.Chu, and M.J.Goldberg, J.AppL Phys., 75 (1994), 1410. [4] C.E.Sroog,hog. PolymSci., 16 (1!391),561. [5] Y.Kim, PhD. dissertation, Pusan National University, Pusan,Korea(1996).
2
le+13 Oe+O l 0
I
5
I
TE&t.%)
I
I
15
20
Fig. 3. ‘The resistivity of the compositefilms as a function of TEOS contents (bias voltage = -23.5 V); ABPDA-.-FDA PM precursor, B: BPDA-PDA ES precursor.