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We have investigated dislocation behavior in the surface area of surface-oxygen-concentration controlled Si wafers treated by a high temperature rapid thermal oxidation (HT-RTO). The HT-RTO process allows us to precisely control the interstitial oxygen concentration ([O i ]) in the surface area of the Si wafers. Sizes of rosette patterns, generated by nano-indentation and subsequent thermal annealing at 900 °C for 1 h, were measured for the Si wafers with various [O i ]. It was found that the rosette size decreases in proportion to the − 0.25 power of [O i ] in the surface area of the Si wafers, which were higher than [O i ] of 1 × 10 17 atoms/cm 3 . On the other hand, [O i ] of lower than 1 × 10 17 atoms/cm 3 did not affect the rosette size very much. These experimental results demonstrate the ability of the HT-RTO process to suppress the dislocation movements in the surface area of the Si wafer.

The atomic-scale surface roughness of Si(110) reconstructed via high-temperature Ar annealing is immediately increased by non uniform accidental oxidation during the unloading process (called reflow oxidation) during high-temperature Ar annealing. In particular, for a reconstructed Si(110) surface, characteristic line-shaped oxidation occurs at preferential oxidation sites appearing in pentagonal pairs in the directions of Si[-112] and/or [-11-2]. We previously reported that the roughness increase of reconstructed Si(110) due to reflow oxidation can be restrained by replacing Ar gas with H2 gas at 1000&#176C during the cooling to 100&#176C after high-temperature Ar annealing. It was speculated that preferential oxidation sites on reconstructed Si(110) were eliminated by H2 gas etching and hydrogen termination of dangling bonds. Thus, it is necessary to investigate the effect of H2 gas etching and hydrogen termination behavior on the reconstructed Si(110) surface structure. In this study, we evaluated in detail the relationship between the temperature at which the H2 gas replaces the Ar in high-temperature Ar annealing and the reconstructed Si(110) surface structure. The maximum height of the roughness on the reconstructed surface was the same as if Ar gas was used when the H2 gas introduction temperature was 200&#176C, although the amount of reflow oxidation was decreased to 70% by hydrogen termination. Furthermore, line-shaped oxidation still occurs when H2 gas replaces Ar at this low temperature. Therefore, we conclude that oxidation is caused by slight Si etching at low temperatures, and thus the preferential oxidation sites on the reconstructed structure must be eliminated by hydrogen etching in order to form an atomically smooth Si(110) surface.

It is well known that a smooth surface of Si wafers can be obtained by Si surface reconstruction via high-temperature annealing. However, there remains a possibility of smooth Si surfaces deteriorating by accidental oxidation (called reflow oxidation) during the unloading process, i.e., taking out Si wafers from a vertical furnace after high-temperature annealing. Therefore, we considered it important to investigate the atomic-scale effects of oxidation on surface steps and terraces on Si wafers during the unloading process. We examined the effect of unloading temperature on oxide formation on Si (100) and Si (110) surfaces. The change in surface roughness was also measured. Our results indicated a significant improvement in the root mean square values of the surface roughness of terraces on the reconstructed surface. Moreover, this improvement was dependent on the decrease in the oxidation layer thickness in the case of low-temperature unloading. Furthermore, for suppressing reflow oxidation, we replaced the injected Ar gas with H2 in the cooling process during high-temperature Ar annealing and evaluated the thickness of the reflow oxidation layer and surface structure of Si (100) and Si (110). H2 annealing during the cooling process resulted in the formation of H-terminated Si surfaces, and this formation effectively suppressed reflow oxidation. However, the H2 atmosphere also caused etching of the reconstructed Si surfaces. Atomic force microscopy measurements revealed that in spite of the etching, Si (100) and Si (110) surface roughness drastically decreased because of subsequent roughness variation, regarded as being caused by oxidation. In the case of Si (110), characteristic line oxidation was effectively suppressed, resulting in a smooth terrace-and-step structure. In summary, the obtained results suggested that our method is effective for restraining the increase in atomic-scale surface roughness due to oxidation.

A high-temperature annealing method was developed to obtain an atomically flat surface for Si(1 0 0). Maintaining a smooth reconstructed surface is very important for restricting accidental oxidation during the unloading process (i.e., reflow oxidation) after high-temperature annealing. We evaluated the thickness of the reflow oxidation layer and the surface structure obtained on a Si(1 0 0) wafer when we replaced the injected Ar gas with H 2 during the cooling process after high-temperature Ar annealing. A H-terminated Si(1 0 0) surface was formed by H 2 annealing during the cooling process, and this formation effectively suppressed reflow oxidation. However, the H 2 atmosphere also caused etching of the reconstructed Si(1 0 0) surface; nevertheless, atomic force microscopy (AFM) measurements revealed that the Si(1 0 0) surface roughness drastically decreased when subsequent roughness variation regarded as being caused by the oxidation occurred. The results suggest that our method is effective in restraining increases in surface roughness at the atomic level that are caused by oxidation.

第22回宇宙構造・材料シンポジウム（2006年12月1日. 宇宙航空研究開発機構宇宙科学研究本部 (JAXA)(ISAS)）, 相模原市, 神奈川県, 22nd Symposium on Aerospace Structure and Materials (December 1, 2006. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000019021

We studied the phase stability and photorefractive properties of a new poly(N-vinylcarbazole) (PVK)-based photorefractive polymer composite by modifying the structure of a nonlinear optical chromophore (NLO), 4-butoxy-3-propyl-1-(4-nitrophenyazo)benzene. The shelf life of a sample with a modified NLO, 4-(2-ethylhexyloxy)3-propyl-1-(4-nitrophenyazo) benzene was extended by more than five months even though it had a low glass transition temperature (Tg) of -19C. This material also had a short photorefractive response time constant of 33 ms and a high diffraction efficiency of 49% at an electric field of 100V/m and a total writing intensity of 942mW/cm2. These desirable characteristics are believed to be due to the following reasons: first, the new chromophore acts as a plasticizer, thereby enhancing the orientation of the NLO and second, the solubility of the chromophore in a polymer matrix increases, inhibiting crystallization and providing a high optical quality. 2006 The Japan Society of Applied Physics.

We studied the temperature dependencies of electric field-induced birefringence, conductivity, and photorefractive properties of two poly(n-vinylcarbazole) (PVK)-based composites with different nonlinear optical chromophores: 2,5-dimethyl-4-(4'-nitrophenylazo)anisole (DMNPAA) and its derivative, 4-butoxy-3-propyl-1-(4'-nitrophenyazo) benzene (m3p4). Both composites showed similar temperature dependencies; the photorefractive responses were faster at higher temperatures and the diffraction efficiencies increased with temperature and then began to decrease. Such behavior is consistent with the measured temperature dependencies of the field-induced birefringence and the conductivity. We found that the m3p4 composite exhibited a faster photorefractive response rate than the DMNPAA composite when compared at the same reduced temperature T-Tg, where T is the temperature of the measurement and Tg is the glass transition temperature. The results indicate that one can enhance the total photorefractive response rate by changing the nonlinear optical chromophore.

We studied the electric-field-induced birefringence, the photoconductivity and the photorefractive properties of photorefractive polymer composites based on N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD). Photorefractive response rate is improved in TPD-based photorefractive polymer, composed of TPD, polystyrene (PS), 4-butoxy-3-propyl-1-(4'-nitrophenylazo)benzene (m3p4) and C60. We obtained the photorefractive response time of as fast as 3.2 ms (@I = 837 mW/cm2, E = 40 V/m). The photoconductivity of TPD-based photorefractive polymer is found to be greater than that of the PVK-based one.