Low temperature oxidation of silicon (111) 7 × 7 surfaces

Schell-Sorokin, A. J.; Demuth, J. E.

doi:10.1016/0039-6028(85)90673-9

Cited by 101 publications

(35 citation statements)

References 80 publications

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“…Since our calculation for a free SiO molecule (148 meV) slightly underestimates its experimental value of 154 meV, the present Si-O(ad) stretching mode can be well identified as the origin of the metastable EELS peak. In fact, Schell-Sorokin and Demuth [28] attributed the metastable EELS peak to a diatomiclike SiO species, but Ibach et al [1] and Edamoto et al [2] disputed this SiO assignment by reasoning that a SiO species bonded to the surface would not give such a high frequency comparable to that of a free SiO molecule. However, the present Si-O(ad) unit in the ad-ins configuration appears quite similar to a free SiO molecule vibrationally as well as structurally (as evidenced by the nearly identical Si-O bond lengths).…”

Section: Department Of Physics Pohang University Of Science and Techmentioning

confidence: 98%

Identification of the Initial-Stage Oxidation Products on Si(111)-(7×7)

Lee

Kang

1999

Phys. Rev. Lett.

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Density functional theory calculations are used to study the initial-stage adsorption of O 2 molecules on the Si͑111͒-͑7 3 7͒ surface. Contrary to experimental suggestions, we find no evidence of metastable O 2 molecular states on this surface, i.e., O 2 molecules dissociate spontaneously without any barrier. Our electronic and vibrational analysis reveals that the resulting atomic-oxygen products can explain the "molecular" features reported in previous experiments. [ S0031-9007(99) PACS numbers: 68.35.Bs, 68.35.Ja, 73.20.At Chemisorption of oxygen molecules on silicon surfaces has been a subject of both fundamental and technological importance as a model for the initial stage of silicon oxidation. In most cases, however, the adsorption-induced chemical and geometrical complexity has greatly hindered experimental or theoretical identifications of the atomic structure of the reaction products, and thus many structural and spectroscopic issues still remain unresolved.Of particular interest among such examples is the socalled "molecular precursor" model for the initial-stage chemisorption of O 2 molecules on the Si͑111͒-͑7 3 7͒ surface, which was proposed to explain the observed oxygen-induced metastable features: In their vibrational electron energy loss spectroscopy (EELS) studies, Ibach et al. [1] and Edamoto et al.[2] found a loss peak at 149-155 meV that was extinguished by 400 K annealing. Later Höfer et al. [3,4] reported in their ultraviolet photoelectron spectroscopy (UPS) studies two metastable spectra at 2.1 and 3.9 eV which were also quenched by ϳ400 K annealing. These metastable features have been ascribed to chemisorbed O 2 states (i.e., molecular precursors), and the reported lifetime at room temperature varies from ϳ10 min in early studies [3,4] to several hours in recent studies [5][6][7]. The concept of O 2 molecular precursors on Si͑111͒-͑7 3 7͒ has been put forward in a more concrete but controversial way in recent scanning tunneling microscopy (STM) studies: Oxygeninduced bright sites in STM topographs are the most numerous product at low O 2 exposures and are known to be quite stable at room temperature and to survive heating up to 600 K [8][9][10][11][12][13][14]. These bright sites have usually been assigned to atomic-oxygen species [8][9][10][11][12]. Recently, however, Dujardin et al.[13] emphasized their molecular origin by identifying the bright sites with the metastable state that gives a 3.9 eV UPS peak. Furthermore, initiated by the Dujardin et al.'s molecular assignment, Hwang et al. [14] interpreted even the motion of the bright sites at 300 365 ± C as hopping of single O 2 molecules. Despite these experimental proposals, however, the structural identification of the O 2 molecular precursors is yet to be done. Previous theoretical studies [15][16][17][18] were based either on the unreconstructed Si surface structure or on a qualitative theoretical scheme, and so more elaborate theoretical studies are needed.In this Letter, we report an atomistic identification of the initial-sta...

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Section: Department Of Physics Pohang University Of Science and Techmentioning

confidence: 98%

Identification of the Initial-Stage Oxidation Products on Si(111)-(7×7)

Lee

Kang

1999

Phys. Rev. Lett.

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“…On the Si(111) 7 × 7 surface, direct imaging of the reaction sites by STM [1][2][3] has proved the existence of several types of chemisorption geometries. Recent tip-induced chemical-bond breaking [4] unambiguously identified the presence of the molecular precursor state, which was previously indicated by high-resolution electron energy loss spectroscopy [5], photoelectron spectroscopy [1,6], and electron-stimulated desorption [7] studies. Although the Si(100) surface is more important from a technological point of view and has a much simpler surface reconstruction, i.e., the 2 × 1 dimer structure, STM has not been able to provide atomically resolved images of oxygeninduced structures.…”

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confidence: 90%

STM study of the initial oxidation stage of Ge(100) 2×1

Fukuda¹,

Ogino²

1998

Applied Physics A: Materials Science & Processing

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The initial stage of oxygen chemisorption on the Ge(100) surface was studied by scanning tunneling microscopy. By using a defect-free surface and in situ oxidation, oxygen-induced products could be unambiguously determined. Two types of bright products and two types of dark products were identified. One of the bright products is a major product and it protrudes at the center of the dimer. Since this product was observed even after annealing at 300 • C, it is a stable product. The other bright product is a bright spot at one of the dimer atoms, and dimer buckling is stabilized near this product. The two dark products are similar to the missing dimer defects in filled-state images, but they appeared as bright spots in empty-state images. After annealing of the oxygen-chemisorbed surfaces, the dark product aligned in the dimer row with a 2× periodic structure inside.The invention of scanning tunneling microscopy and its descendants opened up a new era for semiconductor technology. One fruitful application of these microscopies is the atomistic investigation of chemical reactions on semiconductor surfaces with gaseous molecules. Oxidation is one of the key technologies for semiconductors and a detailed understanding of oxidation is vital for studying the interface formation between substrates and oxide layers. On the Si(111) 7 × 7 surface, direct imaging of the reaction sites by STM [1-3] has proved the existence of several types of chemisorption geometries. Recent tip-induced chemical-bond breaking [4] unambiguously identified the presence of the molecular precursor state, which was previously indicated by high-resolution electron energy loss spectroscopy [5], photoelectron spectroscopy [1, 6], and electron-stimulated desorption [7] studies. Although the Si(100) surface is more important from a technological point of view and has a much simpler surface reconstruction, i.e., the 2 × 1 dimer structure, STM has not been able to provide atomically resolved images of oxygeninduced structures. Over the past 10 years, several authors * To whom correspondence should be addressed have attempted to identify the initial chemisorption geometries on the Si(100) surface by using STM. However, since oxygen first reacts with surface defects rather than with perfect dimers [8,9] and since the substrate atoms are ejected by the oxygen reaction [10], it has been difficult to acquire a clear picture of chemisorption products that is comparable to the theoretically predicted structure.We present here an STM study of the initial oxygen chemisorption on the Ge(100) 2 × 1 surface. The Ge(100) 2 × 1 surface has atomic and electronic structures quite similar to those of the Si(100) 2 × 1 surface [11,12], and therefore we would expect to see similar oxygen adsorption. A theoretical calculation suggests almost the same chemisorption configurations, but it gives only 25% of the adsorption energy compared to Si dimers [13]. Therefore, one would expect that the exothermic effect [14] would be less pronounced on the Ge(100) surface. Experimentally...

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“…The Si͑111͒-͑7 ϫ 7͒ sample was then cooled down to 45 K before the oxygen exposure, i.e., 10 K above the desorption temperature of condensed O 2 multilayers. 15,20,21 The quality of the O 2 gas was confirmed by a quadrupole mass spectrometer. Figure 2 shows the O 1s core-level spectrum of a 10 Langmuir ͑L; 1 L=1ϫ 10 −6 Torrϫ s͒ O 2 exposed Si͑111͒-͑7 ϫ 7͒ surface, recorded 45 min after the exposure using h = 665 eV.…”

Section: Methodsmentioning

confidence: 99%

Adsorption and reaction processes of physisorbed molecular oxygen on Si(111)-(7×7)

2005

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The adsorption and reaction processes of physisorbed oxygen molecules on a Si͑111͒-͑7 ϫ 7͒ surface have been investigated using time-resolved O 1s core-level photoemission measurements at 45 K. Physisorbed oxygen molecules are only observed at 45 K and lower temperatures on a Si͑111͒-͑7 ϫ 7͒ surface. At the dosage when the dangling bonds are saturated by chemisorbed oxygen, the coverage of the physisorbed species increases drastically. This result indicates that oxygen species, which are chemisorbed on top of adatoms, modifies the potential energy curve for an oxygen molecule approaching the surface such that physisorbed oxygen molecules are stabilized. Further, the longer lifetime at a higher dosage indicates that an intermolecular force plays a role for the stabilization of this species. Taking these results into account, an oxidation stagedependent gas-surface interaction for an oxygen molecule approaching the Si͑111͒ surface is suggested.

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Low temperature oxidation of silicon (111) 7 × 7 surfaces

Cited by 101 publications

References 80 publications

Identification of the Initial-Stage Oxidation Products on Si(111)-(7×7)

Identification of the Initial-Stage Oxidation Products on Si(111)-(7×7)

STM study of the initial oxidation stage of Ge(100) 2×1

Adsorption and reaction processes of physisorbed molecular oxygen on Si(111)-(7×7)

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