Field and high‐temperature dependence of the long term charge loss in erasable programmable read only memories: Measurements and modeling

High‐temperature charge transport across an oxide‐nitride‐oxide sandwich of erasable programmable read only memories is mainly governed by the oxide conductivity as experimentally determined. It was verified in the examined devices that charge loss is not due to mobile ions. Since hole injection from the control gate into the nitride can be blocked by a 70‐A‐thick top oxide we conjecture that charge loss is due to leakage of electrons; however, the observed leakage current is too large to be explained by pure electrode‐limited charge transport (Richardson emission and direct tunneling). It was also verified that field gain on asperities and along edges cannot increase the charge loss current to the required range. Numerical evaluation of trap tunneling and resonant tunneling indicated that both mechanisms are weakly temperature dependent while charge loss has a typical activation energy of 1.2 eV in the range of 250–350 °C. Consequently, a multiphonon‐assisted tunneling mechanism is proposed where electrons stored on the floating gate tunnel to oxide traps, then are emitted into the nitride. The coupling of the trap level to oxide phonons results in virtual energy levels in the oxide which allow for more effective transition paths. As a consequence of the electron‐phonon coupling, the emission occurs close to the oxide conduction‐band edge at temperatures between 250 and 350 °C, producing a strong temperature dependence for the mechanism.

[1]  B. Ricco,et al.  Novel Mechanism for Tunneling and Breakdown of Thin SiO 2 Films , 1983 .

[2]  G. Sery,et al.  High-temperature charge loss mechanism in a floating-gate EPROM with an oxide-nitride-oxide (ONO) interpoly stacked dielectric , 1991, IEEE Electron Device Letters.

[3]  R. Williams,et al.  The effect of electrical conduction of Si3N4on the discharge of MNOS memory transistors , 1978, IEEE Transactions on Electron Devices.

[4]  K. K. Young,et al.  Charge transport and trapping characteristics in thin nitride-oxide stacked films , 1988, IEEE Electron Device Letters.

[5]  Analysis of mechanism for resonant tunneling via localized states in thin SiO2 films , 1988 .

[6]  J. Simmons.  Richardson-Schottky Effect in Solids , 1965 .

[7]  M. White,et al.  Determination of the trapped charge distribution in scaled silicon nitride MONOS nonvolatile memory devices by tunneling spectroscopy , 1991 .

[8]  F. Liou,et al.  IIIB-7 evidence of hole flow in silicon nitride for positive gate voltage , 1984 .

[9]  W. Lui,et al.  Exact solution of the Schrodinger equation across an arbitrary one‐dimensional piecewise‐linear potential barrier , 1986 .

[10]  P. Lai,et al.  Simplified closed‐form trap‐assisted tunneling model applied to nitrided oxide dielectric capacitors , 1992 .

[11]  Z. Weinberg.  Hole conduction in Si3N4 films on Si , 1976 .

[12]  S. Nozaki,et al.  Conduction and charge trapping in polysilicon-silicon nitride-oxide-silicon structures under positive gate bias , 1988 .

[13]  Ingemar Lundström,et al.  Theory of the thin-oxide m.n.o.s. memory transistor , 1970 .

[14]  K. Yoshikawa,et al.  Bottom-oxide scaling for thin nitride/oxide interpoly dielectric in stacked-gate nonvolatile memory cells , 1992 .

[15]  Changhua Tan,et al.  Calculations of resonant tunneling levels across arbitrary potential barriers , 1992 .

[16]  S. Nozaki,et al.  Study of carrier trapping in stacked dielectrics , 1986, IEEE Electron Device Letters.

[17]  R. Fowler,et al.  Electron Emission in Intense Electric Fields , 1928 .

[18]  C. Svensson.  The conduction mechanism in silicon nitride films , 1977 .

[19]  Z. Weinberg,et al.  A review of recent experiments pertaining to hole transport in Si3N4 , 1978, IEEE Transactions on Electron Devices.

[20]  Simon M. Sze,et al.  Current Transport and Maximum Dielectric Strength of Silicon Nitride Films , 1967 .

[21]  G. Sery,et al.  Physical origin of long-term charge loss in floating-gate EPROM with an interpoly oxide-nitride-oxide stacked dielectric , 1991, IEEE Electron Device Letters.

[22]  Carver A. Mead,et al.  The Effect of Trapping States on Tunneling in Metal Semiconductor Junctions , 1969 .

[23]  D. Dimaria,et al.  Interface effects and high conductivity in oxides grown from polycrystalline silicon , 1975 .

[24]  M. Lenzlinger,et al.  Fowler‐Nordheim Tunneling into Thermally Grown SiO2 , 1969 .

[25]  D. Frohman-Bentchkowsky,et al.  Charge Transport and Storage in Metal‐Nitride‐Oxide‐Silicon (MNOS) Structures , 1969 .

[26]  A. Schenk.  An improved approach to the Shockley-Read-Hall recombination in inhomogeneous fields of space-charge regions , 1992 .

[27]  G. Sery,et al.  A scaling methodology for oxide-nitride-oxide interpoly dielectric for EPROM applications , 1990 .

[28]  C. M. Svensson,et al.  Properties of MNOS structures , 1972 .

[29]  J. W. Gadzuk.  Resonance Tunneling Through Impurity States in Metal‐Insulator‐Metal Junctions , 1970 .

[30]  C. Duke,et al.  Field Emission through Atoms Adsorbed on a Metal Surface , 1967 .

[31]  M. Willander,et al.  Evanescent channels in calculation of phonon‐assisted tunneling spectrum of a semiconductor tunneling structure , 1993 .

[32]  G. Lucovsky.  On the photoionization of deep impurity centers in semiconductors , 1993 .

[33]  S.T. Wang.  On the I-V characteristics of floating-gate MOS transistors , 1979, IEEE Transactions on Electron Devices.

[34]  P. Liu,et al.  A theoretical model for the current-voltage characteristics of a floating-gate EEPROM cell , 1993 .

[35]  M. Pulver,et al.  Tunnel mechanism in MNOS structures , 1970 .

[36]  A. Schenk.  A model for the field and temperature dependence of Shockley-Read-Hall lifetimes in silicon , 1992 .

[37]  H. Araki,et al.  ONO inter-poly dielectric scaling for nonvolatile memory applications , 1991 .

[38]  P. Pipinys,et al.  Release of electrons from traps by an electric field with phonon participation , 1976 .

[39]  Kun Huang,et al.  Theory of light absorption and non-radiative transitions in F-centres , 1950, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[40]  S. Manzini,et al.  Charge transport and trapping in silicon nitride-silicon dioxide dielectric double layers , 1985 .

[41]  J. O'dwyer.  Current-Voltage Characteristics of Dielectric Films , 1966 .

[42]  N. Hwang,et al.  Tunneling and thermal emission of electrons from a distribution of deep traps in SiO/sub 2/ (nMOSFET) , 1993 .

[43]  Milton Abramowitz,et al.  Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables , 1964 .

[44]  J. C. Penley.  Tunneling through Thin Films with Traps , 1962 .

[45]  Z. Weinberg,et al.  Hole conduction and valence‐band structure of Si3N4 films on Si , 1975 .

[46]  Yutaka Hayashi,et al.  Carrier conduction in ultrathin nitrided oxide films , 1986 .

[47]  Roberto Menozzi,et al.  Evaluation of E2PROM data retention by field acceleration , 1991 .

[48]  Yuji Ando,et al.  Calculation of transmission tunneling current across arbitrary potential barriers , 1987 .

[49]  M. Bass,et al.  Flexible infrared‐transmissive metal waveguides , 1976 .

[50]  S. Kohyama,et al.  Characteristics and reliability of the SEPROM cell , 1984, IEEE Transactions on Electron Devices.

[51]  Susumu Kohyama,et al.  A Thermionic Electron Emission Model for Charge Retention in SAMOS Structure , 1982 .

[52]  K. Ando,et al.  Mechanism of leakage current through the nanoscale SiO2 layer , 1994 .

[53]  Ingemar Lundström,et al.  Trap‐assisted charge injection in MNOS structures , 1973 .

[54]  S. M. Sze,et al.  Physics of semiconductor devices , 1969 .