Characterization of oxygen and nitrogen rapid thermal annealing ...

S. Lee et al.: Characterization of oxygen and nitrogen rapid thermal annealing processes for ultra-low-k SiCOH filmsremoval. 3,5 In this work, we investigated rapid thermalannealing (RTA) processing for formation of porosity byremoving hydrocarbon in the PECVD-deposited films.Furnace annealing typically requires long processing times,on the order of 1 h, while RTA systems require about aminute due to their fast temperature ramp-up rate. Therefore,productivity can be increased significantly with anRTA process. 9,10 Changes in molecular structure are correlatedwith hardness and modulus of films in this work.II. EXPERIMENTALThe SiCOH film was deposited using a PECVD system,which is described in detail elsewhere. 3,5 The basepressure of the deposition chamber was approximately10 −6 Torr. DMCPSO and CHex were vaporized in bubblersoperated at 75 and 45 °C, respectively, and thoseprecursors were introduced into the deposition chamberusing helium (99.99%) carrier gas. A radio-frequencypower of 13.56 MHz was delivered to the lower electrode.The films were deposited both on highly borondopedP + (

S. Lee et al.: Characterization of oxygen and nitrogen rapid thermal annealing processes for ultra-low-k SiCOH filmsFIG. 2. Elemental composition of as-deposited SiCOH film shown byAES depth profiling.decreased from 2.4 to as low as 1.85 as the treatmenttemperature was increased up to 550 °C. In the RTOprocess, the k value of 2.15 was obtained at the processingtemperature of 550 °C. The change in film thicknesswith RTA temperature variation is summarized inFig. 3(b). Little change of the film thickness was observedup to 300 °C. However, as the treatment temperaturewas increased to 350 and 400 °C both in the RTNand in the RTO processes, respectively, the films showedthickness reductions of 25% and 48%. Above 450 °C, nochange in thickness was observed. Similar thickness reductionwas reported by Grill and Neumayer in furnaceheat-treatment. 11Figure 4 shows the hardness and elastic modulus ofthe ultra-low-k SiCOH films as a function of treatmenttemperature. For RTO-treated films, the hardness andmodulus were decreased with a treatment temperatureof 400 °C. Above 450 °C, the hardness and moduluswere increased again. RTN-treated films show similarFIG. 3. RTA-treated SiCOH films: (a) k values and (b) thicknessretention (n), as a function of treatment temperature.FIG. 4. Mechanical strength of the SiCOH films: (a) hardness and (b)elastic (Young’s) modulus as functions of treatment temperature.858J. Mater. Res., Vol. 23, No. 3, Mar 2008

S. Lee et al.: Characterization of oxygen and nitrogen rapid thermal annealing processes for ultra-low-k SiCOH filmsto 450 °C, the reduction in the dielectric constant k isdue mainly to hydrocarbon removal in the film. We believethat the higher k values of RTO films than in RTNfilms were due to the large O–H peak contained in theFTIR spectra.We correlated the variation in the dielectric constantand mechanical strength with structural modificationsabove 400 °C in this work. Figure 7(a) shows the deconvolutionof the Si–CH 3 bending band of the as-depositedSiCOH films before RTN and RTO processing. Relativeoxygen content in the O–Si–CH 3 structure is analyzed indetail; O–Si–(CH 3 ) 3 , O 2 Si–(CH 3 ) 2 , O 3 Si–(CH 3 ), andO 4 Si are defined here as M, D, T, and Q group, respectively,as in other reports. 15,16 Their peak positions are1250, 1260, 1270, and 1280 cm −1 , respectively. However,no M-group peak was observed for as-depositedSiCOH films. Figure 7(b) shows the relative area of theD- and T-group signal intensities divided by Si–CH 3peak intensity (in percent) as a function of the treatmenttemperature by RTN and RTO. The relative T-groupfraction in the Si–CH 3 peak (T group/Si–CH 3 ) was increasedfrom 36% to 50% in RTO-treated films and from35% to 44% in RTN-treated films as the treatment temperaturewas increased from 400 to 550 °C. As shown inFig. 7(b), the relative T-group fraction in the Si–CH 3peak in RTO-treated files was significantly higher than inRTN-treated films above 400 °C. However, the relativeD-group fraction in the Si–CH 3 peak (D group/Si–CH 3 )was decreased from 50% to 37% in RTO-treated filmsand from 53% to 42% in RTN-treated films as the treatmenttemperature was increased from 300 to 550 °C. Weattribute the increase of the T group to the cross-linkingof the oxidized Si–O bonding induced by the radiationenergy in the RTA system. Figure 7(c) shows that hardnessand relative area of the T groups/Si–CH 3 peak (%)in the FTIR spectrum as a function of RTN and RTOtreatment temperature. Notably, the hardness increasedfrom 0.1 to 0.44 GPa, and the T groups in the FTIRspectrum increased from 46% to 50% in RTO-treatedfilms. We believe that structural change from D to Tgroup can be attributed to the increase in hardness in theSiCOH films.FIG. 7. (a) Deconvolution of the Si–CH 3 bending band of the asdepositedSiCOH film. (b) Relative area of D and T groups/Si–CH 3peak (%) in the FTIR spectrum as a function of RTN and RTO treatmenttemperature. (c) Hardness and relative area of the T groups/Si–CH 3 peak (%) in the FTIR spectrum as a function of RTN and RTOtreatment temperature.peak intensity of the SiCOH films saturated in the RTNand RTO films. The reduction of CH x and Si–CH 3 peakintensity is considered as an evidence for the removal ofthe thermally unstable hydrocarbon fragments. 3,12,14 UpIV. CONCLUSIONWe investigated ultra-low-k SiCOH films heat-treatedby RTA processing. A minimum dielectric constant (k)of 1.85 was achieved with the RTN process, and a k valueof 1.98 was achieved with the RTO process after deposition.Hardness and modulus values of 0.44 and 3.95GPa were achieved with the RTO process. Improvementsin hardness and modulus are attributed to oxygen incorporationin the Si–CH 3 structure. In addition to improvementsin hardness and modulus, processing time andthermal budget can be significantly reduced with RTA860J. Mater. Res., Vol. 23, No. 3, Mar 2008

S. Lee et al.: Characterization of oxygen and nitrogen rapid thermal annealing processes for ultra-low-k SiCOH filmsprocessing when it is compared with furnace thermalprocesses. Therefore, RTA-treated ultra-low-k SiCOHfilms have the potential to become a strong candidate innew low-k interconnect development.ACKNOWLEDGMENTThis work was supported by the Science ResearchCenter (SRC) program (Center for Nanotubes and NanostructuredComposites) of Ministry of Science and Technology(MOST)/Korea Science and Engineering Foundation(KOSEF).REFERENCES1. M. Bohr: Interconnect scaling—the real limiter to high performanceULSI, in Technical Digest of the International ElectronDevice Meeting, Washington, DC (IEEE, Piscataway, NJ, 1995),pp. 241–244.2. A. Milella, J.L. Delattre, F. Palumbo, F. Fracassi, and R. d’Agostino:From low-k to ultralow-k thin-film deposition by organosiliconglow discharges. J. Electrochem. Soc. 153, F106 (2006).3. S. Lee, J. Yang, S. Yeo, J. Lee, J. Lee, D. Jung, J. Boo, H. Kim,and C. Chae: Effect of annealing temperature on dielectric constantand bonding structure of low-k SiCOH thin films depositedby plasma enhanced chemical vapor deposition. Jpn. J. Appl.Phys. 46(2), 536 (2007).4. J. Cui, J.M. Madsen, and C.G. Takoudis: A thermal processingsystem for microelectric materials. Meas. Sci. Technol. 15, 2099(2004).5. J. Yang, S. Lee, H. Park, D. Jung, and H. Chae: Characterizationof low-dielectric constant plasma polymer films deposited byplasma-enhanced chemical vapor deposition using decamethylcyclopentasiloxaneand cyclohexane as the precursors. J. Vac. Sci.Technol., A 24, 165 (2006).6. L. Wang, M. Ganor, S.I. Roklin, and A. Grill: Nanoindentationanalysis of mechanical properties of low to ultralow-dielectricconstant SiCOH films. J. Mater. Res. 20(8), 2080 (2005).7. K. Kinoshita, A. Nakano, J. Kawahara, N. Kunimi, and Y. Hayashi:Vapor phase reactions in polymerization plasma for divinylsiloxanebis-benzocyclobutenefilm deposition. J. Vac. Sci. Technol. A. 24,2192 (2006).8. Y. Shioya, H. Shimoda, K. Maeda, T. Ohdaira, R. Suzuki, andY. Seino: Low-k SiOCH film deposited by plasma-enhancedchemical vapor deposition using hexamethyldisiloxane and watervapor. Jpn. J. Appl. Phys. 44, 3879 (2005).9. C.Y. Chang and S.M. Sze: ULSI Technology (McGraw-Hill Companies,Inc., New York, 1996), p. 145.10. J.M. Shieh, S.C. Chang, B.T. Dai, and M.S. Feng: Investigation ofsuperfilling and electrical characteristics in low-impurityincorporatedCu metallization. Jpn. J. Appl. Phys. 41, 5104(2002).11. A. Grill and D. Neumayer: Structure of low-dielectric constant toextreme low-dielectric constant SiCOH films: Fourier transforminfrared spectroscopy characterization. J. Appl. Phys. 94, 6697(2003).12. D.D. Burkey and K.K. Gleason: Temperature-resolved Fouriertransform infrared study of condensation reactions and porogendecomposition in hybrid organosilicon–porogen films. J. Vac. Sci.Technol., A 22, 61 (2004).13. J. Yang, C. Shim, and D. Jung: Effects of post-deposition in-situheat treatment on the properties of low-dielectric constant plasmapolymer films deposited using decahydronaphthalene and tetraethylorthosilicate as the precursors. J. Mater. Res. 17(6), 1248(2002).14. L.M. Han, J.S. Pan, S.M. Chen, N. Balasubramanian, J. Shi,L.S. Wong, and P.D. Foo: Characterization of carbon-doped SiO 2low k thin films: Preparation by plasma-enhanced chemical vapordeposition from tetramethylsilane. J. Electrochem. Soc. 148, F148(2001).15. Y. Lin, T.Y. Tsui, and J.J. Vlassak: Octamethylcyclotetrasiloxanebased,low-permittivity organosilicate coatings. J. Electrochem.Soc. 153, F144 (2006).16. A.D. Ross and K.K. Gleason: Effects of condensation reactions onthe structural, mechanical, and electrical properties of plasmadepositedorganosilicon thin films from octamethylcyclotetrasiloxane.J. Appl. Phys. 97, 113707 (2005).J. Mater. Res., Vol. 23, No. 3, Mar 2008 861