Papers by Keyword: Hydrogen Termination

Abstract: This work aims to summarize previous results reported in literature on atomic level properties of the wet chemically treated hydrogen-terminated silicon surfaces and of the Si oxidation, in comparison to a model system of ultraclean Si surfaces prepared in ultrahigh vacuum (UHV) conditions. A literature review shows that a proper wet chemical treatment of Si(111) provides an atomically smooth, high-quality surface, similar to the model template obtained in UHV conditions after high temperature heating. However, it seems that Si(111) is an exception among semiconductor surfaces concerning the effects of wet chemistry. Although the insulator films grown by the atomic layer deposition (ALD) have replaced the thermal oxide of SiO₂ in many applications, still an intermediate SiO₂ layer is formed and often grown intentionally beneath the ALD film to improve the device performance. However, a detailed atomic structure of the SiO₂/Si interface is still debatable, which might be due to differences in atomic level smoothness of the used Si(100) starting surfaces.

Abstract: 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.

Abstract: This paper presents synthesized diamond films by using combustion activated chemical vapor deposition (CACVD) techniques. The characteristics of diamond films have been studied at wide ranges of temperature (30-400°C). The resistance of diamond films has been determined for hydrogen termination times of 5, 10, 15, and 20 minutes, and at the operation temperatures of 500, 600, and 700°C. The investigation found that, at 30°C a synthesized diamond film has a high resistance (1010 ), whereas at high temperatures (100-400°C) the resistance has decreased from 4.04 M to 2.42 M. The result obtained from the hydrogen termination showed that the resistance has decreased by 105-106  (at 30°C). Summarily, it can be stated that the higher the hydrogen termination times and operation temperatures, the lower the resistance of diamond films.

Abstract: We investigated Si surfaces modified by wet-chemical and electrochemical treatments using pulsed photoluminescence (PL) and infrared spectroscopic ellipsometry during and after processing, both also in surface mapping techniques. Etching of oxidized Si surfaces by HF containing solutions lead to an enhancement in PL due to hydrogenation of the surface what improves the surface passivation and reduces the recombination loss of charge carriers via surface/interface states. PL measurements show that the H-terminated surface is attacked soon by HF or H2O species increasing again the recombination loss. Hence, a narrow time window for this type of processing exists. Nitrogen purging or exchanging the etching solution by a non-etching solution under negative bias decelerated the defect formation in HF solutions. Grafting of organic molecules (exchanging the H-Si by a C-Si bond) induces only small amounts of defects at the interface but stabilizes PL on a high level (i.e. surface recombination is low) for much longer times than for H-terminated Si surfaces.

Abstract: We have investigated the techniques to improve the channel mobility of SiC MOSFETs and found that the hydrogen termination of dangling bonds at a MOS interface is very effective in improving the channel mobility, particularly that of the interface fabricated on a (11-20) face wafer. A high channel mobility of MOSFET on the (11-20) face was achieved to 244cm2/Vs by new process which can terminate dangling bonds by hydrogen. The vertical MOSFET, which is prepared using this process, has a low on-resistance of 5.7 mΩcm2 and a breakdown voltage of 1100 V. The channel resistance is estimated at 0.58 mΩcm2.