| AVS 58th Annual International Symposium and Exhibition | |
| Nanometer-scale Science and Technology Division | Tuesday Sessions |
| Session NS-TuP |
| Session: | Nanometer-scale Science and Technology Division Poster Session |
| Presenter: | Kenji Odaka, National Institute of Advanced Industrial Science and Technology (AIST), Japan |
| Authors: | K. Odaka, National Institute of Advanced Industrial Science and Technology (AIST), Japan A. Kurokawa, National Institute of Advanced Industrial Science and Technology (AIST), Japan Y. Azuma, National Institute of Advanced Industrial Science and Technology (AIST), Japan L. Zhang, National Institute of Advanced Industrial Science and Technology (AIST), Japan T. Fujimoto, National Institute of Advanced Industrial Science and Technology (AIST), Japan |
| Correspondent: | Click to Email |
We would report on the XRR (X-ray reflectivity) analysis to observe the density distribution of the SiO2 thin film which is thermally grown on Si (100) at 1000 ℃. The results show the non-uniform distribution in depth, and once the high density SiO2 was formed during ramp-up it would remain under the following 1000 ℃ oxidation.
Experimental We measured XRR using an apparatus equipped with a shower of high purity N2 to protect a specimen from contamination for a few hours of measurement. We analyzed the data with a fitting method [1], [2] which is well established to evaluate thicknesses, densities, and surface roughness of laminated layers of a specimen. We assumed a two-layer-fitting model consisting of a transition layer and an upper layer where each had uniform density in it. We oxidized a H-terminated Si (100) specimen of 15x15 mm2 in dry O2 flow at 1 atm. with a quartz tube furnace. The ramp rate was 33 Kmin-1. We kept specimens at 1000 ℃ for 0 through 120 min to form SiO2 films of 7.4 through 95.9 nm.
Results We measured XRR for the as grown samples. Then we etched the 95.9 nm sample with dilute HF solution and measured XRR at some thicknesses. The densities of the etched samples as a function of the thickness coincided with those of the as-grown samples. The transition layer was 1 nm thick and about 2.46 gcm-3 in density for all the samples. The upper layer density changed from 2.35 to 2.25 gcm-3 as the thickness increased. The upper layer density obtained above was an averaged value in its thickness according to our assumption. The density between the two- neighboring-measured points of the etched data might correspond to the real density distribution in depth. The results were as follows. The pre-formed layer of 7.4 nm including the transition layer which grew during the ramp-up process had density of 2.35 gcm-3 or more. The density of the main layer formed at 1000 ℃ decreased rapidly to 2.25 gcm-3 at 20 nm, however the non-uniformity occurred mainly within 10 nm. The pre-formed layer remained stable at 1000 ℃ in 1 atm. O2 for 120 min. The thermal SiO2 films had stoichiometric composition. [3] The non-uniformity might be caused by change in structure of SiO2-network.
Conclusions The XRR analysis revealed the non-uniform density distribution of the thermally grown SiO2 thin films which may originate from structural change in SiO2-network near SiO2/Si interface region.
[1] Paratt, L. G., Phys. Rev. 95 (1954) 359. [2] Awaji, N., Ohkubo, S., Nakanishi, T., Sugita, Y., Takasaki, K., and Komiya, S., Jpn. J. Appl. Phys. 35 (1996) 67. [3] Kurokawa, A., Odaka, K. and Ichimura, S., Abstract 47th Ann. Meeting Vac. Soc. Jpn. (2006) in Japanese.