Effect of the Si SiO2 Interface on Diffusion in SiO2

Transcription

1 Vol. 26, No. 5, pp , 2005 Si SiO2 SiSiO2 CREST-JST NTT Effect of the SiSiO2 Interface on Diffusion in SiO2 Shigeto FUKATSU, KoheiM.ITOH, Masashi UEMATSU, Akira FUJIWARA,Hiroyuki KAGESHIMA,Yasuo TAKAHASHI and Kenji SHIRAISHI Keio University and CREST-JST, 3141 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa NTT Basic Research Laboratories, NTT Corporation, 31 Morinosato-Wakamiya, Atsugi, Kanagawa Institute of Physics, University of Tsukuba, 111 Tennodai, Tsukuba, Ibaraki (Received November 1, 2004) Using 30 Si-implanted 28 SiO2 and nat SiO2 28 SiO2 structures, Si self-diffusion in SiO2 was studied as a function of temperature and SiO2 thickness ( nm). Si self-diffusivity increased by about one order of magnitude with decreasing SiO2 thickness from 650 to 200 nm with a SiN layer, i.e., the shorter the distance between the 30 Si diffusers and the SiSiO2 interface became, the higher Si self-diffusivity became. The dependence of Si self-diffusion in SiO2 on the distance is caused by SiO generated at the SiSiO2 interface and diffusing into SiO2. Siself-diffusion in SiO2 was modeled taking into account the effect of SiO molecules. The simulated results showed good agreement with the experimental profiles. Furthermore, the simulation predicts that the self-diffusivity would increase for a longer annealing time because more SiO molecules should be arriving from the interface. Such time-dependent diffusivity was indeed found in our follow-up experiments, and the experimental profiles were also fitted by thesimulation using a single set of parameters. 1 SiO2 Si 1 Si kitoh@appi.keio.ac.jp SiSiO2 Si 30 Si SiSiO2 Si SiSiO2 Si SiO Si Si 9

2 Fig. 1. The sample structures employed in this study: ( a) 30 Si-implanted 28 SiO2 and (b) nat SiO2 28 SiO2 isotope hetero structures Si 800 nm CVDchemical vapor deposition Si Isonics SIMS 28 Si 28 Si : 29 Si : 30 Si : : Si 28 Si : 29 Si : 30 Si92.2 : 4.7 : Si 1, nm 28 SiO2 50 kev 30 Si cm nm300 nm650 nm 28 SiO2 nat SiO2 750 nm CVD nat SiO2 SiO2 SiN 30 nm Fig. 1ab 5mm1,1501,250 Ar Si O2 5keV SIMS ZOMBIE 9 3 Fig. 2a 28 SiO2 30 Si Fig. 2. Experimental and simulated 30 Si depth profiles and simulated 28 SiO profiles in (a) 30 Si-implanted 28 SiO2 (b) nat SiO2 28 SiO2 isotope hetero structures. In SIMS profiles of 30 Si-implanted 28 SiO2, theincrease of 30 Si concentration close to the surface (020 nm) is due to nat SiN layer, and that deep in the bulk (160 nm) in the 200-nm-thick sample is 30 Si that diffused from nat Si substrates (800 nm below the 28 Si epilayer) during the thermal oxidation to prepare the sample. SIMS SiN Si 10 SiN 28 SiO2 10

3 251 SiSiO2 Si Fig. 2b 750 nm SIMS nat SiO2 28 SiO2 SiSiO2 SiSiO2 Si Si Fig. 3 SiN DSi SD 30 Si SiSiO2 650 nm DSi SD Si Si SiO2 Si cm 2 2 Fig. 3. Comparison of the temperature dependencies of the Si self-diffusivity (DSi SD )found in this study with those reported previously in the literature. Filled squares (), filled circles (), and filled triangles ( ) represent the present results for the siliconnitride-capped samples with 200-, 300-, and 650-nmthick 28 SiO2 layers, respectively. The previously reported values are for Si self-diffusion in 170-nmthick 28 SiO2 using implanted 30 Si as markers (), 6) isotope heterostructures with 650-nm-thick 28 SiO2 (), 7) and isotope heterostructures with 200-nmthick 28 SiO2 (). 8) Si 28 SiO2 200 nm DSi SD SiN nat SiO2 28 SiO2200 nm 8 SiSiO2 SiN SiSiO2 Si Si Si SiN Si 2 SiN D Si SD D Si SD DSi SD exppvdkt P Vd SiO SiO2 650 nm DSi SD Fig. 3 SiN nm 6 SiN SiO2 650 nm SiN 200 nm Si SiN Fig. 2b SiSiO2 Si Si SiSiO2 SiSiO2 2SiO SiO SiO2 Si SiN SiO Si 4SiO2 Si 28 Si 28 SiO22 28 SiO 28 SiO 30 Si 30 Sis 28 SiOi 28 Sis 30 SiOi 1 s SiO2 Si Si i SiO 11

4 kick-out 1Si Si 30 Sis 28 Sis 28 Sis 30 Sis 2 28 SiO2 30 Si 30 Si 28 SiO 30 SiO ZOMBIE 9 13 SIMS SiO DSiO 5 Fig Si 30 Si 30 SiOi 30 Si 2 30 Sis DSiO 28 SiO2 30 Si SIMS 1, h 28 SiO nm cm 2 s 1,250 DSiO 28 SiO2 30 Si SIMS Fig. 2a 28 SiO 1 28 SiO 30 Si 30 Si 28 SiO 28 SiO2 30 Si 28 SiO2 SiO 30 Si 28 SiO SiO DSiO DSiO exp5.2 evktcm 2 s DSiO Si 257 SiO 34 Fig. 4 DSiO SD exp6.2 evktcm 2 s DSiO SD thdsio SiO 5 Si SiO2 Si Si 1,100 DSiO cm 2 s 10 2DSiOt nm Fig. 4. Temperature dependencies of the Si diffusion coefficients obtained in this study with those reported previously in the literature. Filled circles () andfilled squares ()representthe present results for DSiO and DSiO SD,respectively. The previously reported values are DSi SD (th) from refs. 7 (in thermally grown SiO2), 2 (fused silica), and 5 (quartz), and the SiO diffusivities from refs. 3 and 4 (thermally migrated impurities and defect evolutions as markers, respectively). 1nm SiO SiN Si 1 nm High-κ 28 Si 28 SiO2 30 Si 28 SiO 30 Si 30 Si 28 SiO 300 nm 1,250 6h24 h Fig. 5 6h cm 2 s24 h cm 2 s 4 SiO 28 SiO 12

5 253 Fig. 5. Simulated and experimental 30 Si depth profiles and simulated 28 SiO profiles in the 300-nm-thick sample after annealing of 6 and 24 h at 1,250. Theselfdiffusivity, assuming a constant diffusion coefficient, shows time-dependence, that is, cm 2 sfor 6hand cm 2 sfor24 h. DSiO 200 nm 1, h 168 h 2 DSiO SiO2 Si SiSiO2 SiO2 DSi SD DSi SD thdsio SD CSiOxtC O SiO SiO2 6B SiSiO2 SiO SiO B SiO B Fig. 6. B diffusion profiles before and after the annealing at 1,250 for 6 h. Si nm 30 nm SiN B cm 2 B SIMS Fig. 6 B Si B Si SiO 14 7 SiO2 Si SiSiO2 SiSiO2 SiO SiO2 Si SiO Si Si SIMS B SiO2 13

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