Initial Oxidation Processes on Hydrogenated Silicon Surfaces Studied by In Situ Raman Spectroscopy

Abstract

The influence of the solution pH on H-terminated silicon surfaces in different electrolytes was investigated by in situ confocal Raman microscopy. This study provides Raman evidence that the initial oxidation of the hydrogenated silicon surface could occur by two paths. In the lower pH solution, the H-terminated silicon surface could be directly oxidized by the attack of OH Ϫ ; in the higher pH solution, the surface oxidation occurs in the second layer by the insertion of OH Ϫ into the back bond of Si-H ͑Si-Si͒, in which an intermediate species of uO 3 SiH could be found. In the study of the influence of electrolytes, it was found that F Ϫ ion could assist and accelerate the oxidation reaction, while the attack of OH Ϫ ion is essential to the initial oxidation processes. By taking advantage of Raman spectroscopy in the study of the low frequency region and analyzing the results from various samples, the assignment of the band located at about 629 cm Ϫ1 is discussed in detail and attributed to the vibrations of the silicon hydride and multiphonon structure.Wet chemical etching and oxidation of silicon are crucial to the semiconductor industry in the manufacturing of integrated circuits. An in situ investigation of the wet chemical etching and oxidation processes is highly desirable. Vibrational spectroscopies are important tools in characterizing the local bonding environments in semiconductors. There are a wealth of reports on the hydrogen bonding on the flat silicon surfaces of various crystal faces and on polycrystalline by using IR spectroscopy. 1-4 This technique is highly sensitive, and has provided detailed information of the surface configurations, such as silicon oxides and silicon hydrides. Furthermore, IR can identify covalently bonded hydrogen to be distributed among four different environments in the hydrogenated silicon: monohydride ͑ϵSi-H͒, dihydride (ϭSiH 2 ), trihydride (-SiH 3 ), and polymeric hydride (SiH 2 ) n . 1-4 However, there is presently no consensus about the details of the mechanism involved for etching or oxidation processes, and consequently, controversy has developed over the veracity of several proposed models. 4-7 Moreover, it is difficult for IR spectroscopy to provide the low frequency vibrational ͑Ͻ650 cm Ϫ1 ͒ information. Thus, to unravel the detailed mechanism for the above processes, a complementary technique, such as Raman spectroscopy, is highly desirable.Raman spectroscopy has some unique advantages over other spectroscopic techniques on the study of the silicon surface. First it can provide simultaneously the signal from the surface species and the silicon substrate. Second, it can detect vibrational bands in the low frequency region easily, which may be helpful to elucidate the mechanism of the etching and oxidation processes. Third, Raman spectroscopy can be conveniently used to monitor the reaction processes in situ in the aqueous solution because the Raman signal of water is very weak. Therefore, even a thick solution layer over the silicon surface will not severely i...

Enhanced-Raman scattering from silicon nanoparticle substrates

“…It can be seen that both the first and second-order bands are broadened, weakened and red-shifted compared to that of spectra a and the third-order band is even difficult to identify let alone the fourth-order band. Meanwhile, on the roughened silicon surfaces (sample c and d), weak bands at about 1922 and 1927 cm À1 , which could be assigned to the fourth-order phonon process, were clearly observed together with the band centered at 2121 cm À1 from silicon hydrides (-SiH x or -O x SiH y ) [19]. Besides the dramatic variation in intensity for the Raman bands of those phonon processes, one can also observe the difference in the band shape and frequency.…”

“…Silicon electrodes were prepared according to the method reported previously [18][19][20]. In brief, a commercially available n-type Si (1 1 1) (8.6 or 0.015 X cm) wafer with optically polished face was firstly cut into 0.5 cm  0.5 cm pieces and sealed in a Teflon sheath with epoxy resin to form a silicon working electrode.…”

Analytical TEM characterization of the interfacial layer between ALD HfO2 film and silicon substrate

“…before the loading substrate into reactors, partial SiO 2 island growth may occur at HFtreated Si surface [28] probably due to nonuniform H-termination (passivation) of Si. Uniform SiO 2 growth can be expected at room temperature in solutions with high OH À content [29] or in oxygen at above 200 1C [30] whereas in the latter case assistance of ozone is required for effective oxidation. In our ALD process, all treatments before the loading substrates into the hot-wall ALD reactor were made at room temperature in air ambient.…”

Investigation of SiC and C Nanostructures Obtained by MWCVD

“…The second-order silicon peak is observed in the region of 486.9, 501.1, and 504.6 cm -1 in all three spectra. Groups within 282.5-300.6 cm -1 and 662.9-666.4 cm -1 correspond to silicon oxide [6]. In addition, shift of silicon carbide peaks in the region of 780.8-787.7 cm -1 are observed, which correspond to the transverse mode, while the longitudinal mode is observed in the range of 921.4-934.9 cm -1 .…”

“…There are intense peaks of silicon carbide in the region of 795.1 and 972.7 cm -1 , which can indicate the formation of silicon carbide film with a 3C-SiC structure [5]. Peaks in the region of 614.4 and 663.4 cm -1 correspond to silicon oxide [6]. One can note a peak within 1432.4 cm -1 , which belongs to CH 3 groups [7].…”