Thin-Oxide Mos Capacitance Studies of Fast Surface States

Hunter, W. R.; Eaton, D. H.; Sah, C. T.

doi:10.1063/1.1653369

Cited by 23 publications

(2 citation statements)

References 10 publications

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“…The flatband voltage value is nearly --0.8V and discrepancy from the A1-Si work function difference (14) is less than 0.05V. No hump caused by the interface state density distribution (15,16) can be observed in this capacitance curve. These facts prove the quality of the thin oxide films described in this paper.…”

Section: Resultsmentioning

confidence: 76%

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Formation and Properties of Thin Tunnelable SiO2 Films Using a Vaporized O 2 Source at Liquid N 2 Temperature

Horiuchi

Kamigaki

Hagiwara

1978

J. Electrochem. Soc.

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A high temperature (700~176 oxidation process for the formation of thin tunnelable SiO2 (20-70A) is described. This oxidation process uses liquid 02 at liquid N2 temperature as a source of oxidant and oxygen is vaporized just before the furnace tube to supply a water-free oxidant ambient. The activation energy (20.2 keal/mole) of oxidation rate differs from that previous (43.9 kcal/mole) which has been evaluated for thin oxide growth using the 02/N2 partial pressure method. By the use of this technique we can control thickness to ~_0.5~ accuracy. The rate of oxidation has been found to be governed by the inverse-logarithmic growth law, i.e., Mott-Cabrera's fieldassisted diffusion law. Electrical characteristics, such as dynamic conductance, capacitance, and tunnel current, are measured and discussed. The increment of the oxidation temperature is found to result in the decrease of surfacestate density at the Si-SiO2 interface. The process described enables the way for wider application of thin oxide devices.There has been a good deal of recent interest in thin oxide nonvolatile memory devices such as metalnitride-oxide silicon (MNOS) devices. This is because of the proposed use of MNOS devices in electrically alterable read-only memories as well as for various other applications (1). In these devices, a thin tunnelable oxide plays a very important role in governing several properties of the memory actions, such as switching speed, retention characteristics, and degradation phenomena. Although there is a considerable amount of information available about the kinetics and electrical properties of relatively thick (0.02-1 #m) SiO2 layers (2-4), there has been comparatively little published on thin (<200A) SiO2 films (5-7). Most importantly, there is little information on the reproducibility of the formation and quality control of thin tunnelable oxides.This paper presents a study of the growth of thin tunnelable oxides (20-80A) on freshly etched Si at 700~176 in dry oxygen. It describes the successful development of a technique for reproducibly ~abricat-ing thin tunnelable SiO2 films (on Si) and for improving the Si-SiO2 interface properties. Experimental ProceduresSample preparation.--Most of the single crystal silicon wafers in this study were 8-12 ~2-cm p-type with a chemmechanically polished (100) face. Conductance measurements were carried out using sample wafers of 0.002 ~2-cm p+ +-type or 0.009 l~-cm n + +-type (111) face. The wafers were cleaned by a standard ammoniacal peroxide process as a preoxidation wafer treatment after the field oxide was etched off to expose the gate region. Wafers for studying the rate of formation of thin tunnelable SiO2 films did not have a field oxide, so only the cleaning sequence was carried out.All thickness measurements were made ellipsometrically. The films formed in air during 7-10 min measurement time on freshly etched Si wafers were measured to be about 6.0A (assuming that the films were SiO2 films). In this study, the refractive indexes of nsio2 = 1.47 and nsi = 4.08-0.02...

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Section: Resultsmentioning

confidence: 76%

“…No hump caused by the interface state density distribution (15,16) can be observed in this capacitance curve. These facts prove the quality of the thin oxide films described in this paper.…”

Section: Resultsmentioning

confidence: 81%

Formation and Properties of Thin Tunnelable SiO2 Films Using a Vaporized O 2 Source at Liquid N 2 Temperature

Horiuchi

Kamigaki

Hagiwara

1978

J. Electrochem. Soc.

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Frequency response of Si–SiO2 interface states on thin oxide MOS capacitors

Eaton¹,

Sah²

1972

Phys. Stat. Sol. (a)

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The frequency dependence of the impedance of interface states on thermally oxidized silicon has been measured using MOS capacitors with very thin (83 Å) oxides on non‐degenerate p‐type silicon. Frequency response of the capacitance and conductance was measured from 10 Hz to 50 MHz at 142, 178, and 220 °K. The frequency response deviates significantly from that predicted by the Shockley‐Read‐Hall model applied to interface states. The high‐frequency portion of the frequency response can be explained by the SRH theory if it is assumed that there exists a variation of oxide charge concentration over the area of the device. At low frequencies the conductance can be explained by a two‐step model consisting of the SRH process plus elastic tunneling between interface states and traps located in the oxide. This model was previously employed by Fu and Sah in connection with I/f noise. The two‐step model, modified to account for areal variation of oxide charge concentration, explains the observed frequency response at all three temperatures over six decades of frequency.

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Frequency response of the surface state admittance in weakly inverted thin SiO2–Si MOS capacitors

Katto

Sah

1972

Phys. Stat. Sol. (a)

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The frequency response of surface states in the weak inversion region has been studied using MOS capacitors with very thin oxide on p‐type silicon. To account for the conductance and capacitance data, an exact formula is derived for the Shockley‐Read‐Hall (SRH) centers having interaction not only with the majority carrier band but also with the minority carrier band located at the surface of the semiconductor. The energy distribution of surface states and the random spatial variation of the surface potential are taken into account. Accurate data are obtained on devices fabricated on p‐type silicon substrates with a very thin oxide (about 35 Å) in the energy range of 0.32 to 0.73 e V at room temperature. Good agreement between the experimental and the theoretical conductance‐ and capacitance‐frequency characteristics is obtained. The time constant for the SRH transitions of holes in the weak inversion region is evaluated by the exact formula, and shown to be exponentially dependent on the surface potential precisely as in the depletion region.

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Thin-Oxide Mos Capacitance Studies of Fast Surface States

Cited by 23 publications

References 10 publications

Formation and Properties of Thin Tunnelable SiO2 Films Using a Vaporized O 2 Source at Liquid N 2 Temperature

Formation and Properties of Thin Tunnelable SiO2 Films Using a Vaporized O 2 Source at Liquid N 2 Temperature

Frequency response of Si–SiO2 interface states on thin oxide MOS capacitors

Frequency response of the surface state admittance in weakly inverted thin SiO2–Si MOS capacitors

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