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On the correlation of “hot” and “cold” electron-hole drop densities in uniaxially stressed silicon
760
World Abstracts on Microelectronics and Reliability
interface states near the edge of the surface inversion region, is proposed and found to be in good agreement with experimental data. Our model also suggests another method of calculating the density of interface states. Fundamental properties of interface states are estimated from experimental data. A self-consistency check is made among the values of equivalent circuit elements to substantiate our model.
Review of RIE induced radiation damage in silicon dioxide. L. M. EPHRATH and D. J. DIMARIA. Solid-St. Technol. 182 (April 1981). Radiation damage in silicon dioxide films exposed to Reactive Ion Etching (RIE) has been investigated. Capacitance-voltage (C-V) and photocurrentvoltage (photo I-V) techniques were used to monitor charge trapping and the location of trapped charge after the films were incorporated into MOS capacitors. Bulk neutral trapping sites caused by penetrating radiation were observed in oxides exposed to CF4, C F 4 + H / and 0 2 plasmas, although the number of radiation induced traps was somewhat lower in oxides etched in CF 4 + H 2. The neutral trapping centers are removed by a 600°C anneal in forming gas. An additional trapping layer within 10nm of the surface of the oxide was detected in oxides exposed to 0 2. These traps which are primarily associated with atomic displacement damage caused by the penetration of ions ( < 4 0 0 e V ) require a 1000°C anneal for their removal. Blanket etched films were also used to study the trapping characteristics of the bulk neutral traps as a function of position in the reactor, rf peak-to-peak voltage, and preRIE high temperature annealing. The ability of gate electrode materials to shield an underlying oxide during RIE was also tested. It was determined that aluminum and n ÷ polysilicon are effective in shielding oxides from RIE induced radiation damage. The role of transport in very small devices for VLSI. D. K. FERRY and H. L. GRUBIN. Microelectron. J. 12 (2) 5 (1981). As VLSI systems become more dense, individual device size is dramatically reduced in the quest for lower power-delay products and faster logic. The role of velocity overshoot becomes important, not only for reducing the transit-time contribution to logic delay, but more importantly for the role it plays in increasing the effective saturation velocity. These considerations reinforce the view that other semiconductors may be more suitable than Si for VLSI. Evaluation of inhomogeneous resistive layers by a four point method. GYORGY FODOR, MIKLOS SZILAGYI and LASZLO ZOMBORY. E lectrocomponent Sci. Technol. 7, 211 (1981). This paper describes the determination of the sheet resistance of a narrow strip located in a homogeneous resistive layer of different resistivity. The application of the method for the evaluation of inhomogeneous layers used for thermoprinter head production is discussed. On the correlation of "hot" and "cold" electron-hole drop densities in uniaxially stressed silicon. J. WAGNER, A. FORCHEL and R. SAUER. Solid-St. Commun. 36, 917 (1980). "Hot" and "cold" electron-hole drops were studied in (100)stressed silicon by intense optical pulse excitation and gated photoluminescence measurements. We obtain varying relative densities of hot and cold EHD electrons either by choosing the delay time of the gate appropriately or by using samples of different impurity concentrations. In all cases, the spectra can entirely be fitted assuming only a homogeneous EHD-phase consisting of both, hot and cold electrons. This result is in agreement with recent theoretical work which-contrary to germanium--finds phase separation in stressed silicon not to be very likely. Substrate response of a floating gate n-channel MOS memory cell subject to a positive linear ramp voltage. HAN-SHENG LEE and DAVID SCOTT LOWRIE. Solid-St. Electron. 24, 267 (1981).
A computer simulated substrate response of an n-channel MOS floating gate transistor to a positive linear ramping gate voltage was investigated. Device parameters, such as the channel length, effective electron mobility, substrate doping level and the gate voltage ramping rate were changed to see their effects on the substrate response. The substrate response was monitored by using the response of the surface potential at the mid-channel point. In the one-dimensional analysis it was found that the surface potential at the midchannel point increased initially and dropped quickly after passing through its peak value and then decreased slowly. The mid-channel surface potential reached a higher peak value if the device had (1) a longer channel length, (2) a lower effective electron mobility, (3) a higher gate voltage ramping rate, or (4) a lower substrate doping level. Solutions show that the conditions for the mid-channel point to reach its peak surface potential faster are: (a) a shorter channel length, (b) a higher effective electron mobility, (c) a higher gate voltage ramping rate, and (d) a lower substrate doping level. ESR studies of thermally oxidized silicon wafers. CHR1STER BRUNSTROM and CHRISTER SVENSSON.Solid-St. Commun. 37, 399 (1981). We have performed ESR measurements on oxidized (111) silicon wafers and found two ESR centers. One, the previously known Pb center, was found to be a two level interface trap by corona bias studies. The other onc, previously known as "damaged silicon" center was found to be a silicon center, probably related to the oxide growth process.
Localized anodic thinning of GaAs structures. D. W. SHAW and R. E. WILLIAMS. Solid-St, Electron. 24, 281 (1981}. The self-limiting characteristics of anodic thinning for GaAs FET structures is not realized when applied to selected areas as with patterned wafers. An approach that circumvents this problem is described. Vibrational properties of crystalline and amorphous Ge I _ xSix alloys. BALK. AGRAWAL. Solid-St. Commun. 37, 271 (1981). A five-atom cluster Bethe lattice method treating the shortrange order with proper statistical effects has been proposed for understanding the crystalline and amorphous alloys. Numerical results for Gel_xSi x alloys are in excellent agreement with the experimental data. In the system studied the network is random but the nearest-neighbour coordination should be treated exactly. The long-range coordination is seen to be concentration-dependent in the crystalline alloys but concentration-independent in the amorphous alloys. Transport equations for the analysis of heavily doped semiconductor devices. M. S. LUNDSTROM, R. J. SCHWARTZ and J. L. GRAY. Solid-St. Electron. 24, 195 (1981). Transport equations for use in analyzing heavily doped semiconductor devices are considered. These transport equations describe the effects of the nonuniform band structure and the influence of Fermi-Oirac statistics, which are important in heavily doped semiconductors. Previous workers [1, 2] have derived transport equations in terms of the nonuniform band structure. These equations, however, are not convenient for use in semiconductor device analysis because the band structure of heavily doped semiconductors is not well known. In this paper, the transport equations of Marshak and van Vliet [1, 3] are recast into a simple, Boltzmann-like form in which the effects associated with the nonuniform band structure and degenerate carrier concentrations are described by two parameters, the effective gap shrinkage, Ate, and the effective asymmetry factor, 7. The experimental determination of both of these parameters is also discussed. Finally, Adler's contention [4], that some important features of semiconductor device operation can be modeled accurately by using an electrically measured AG with an arbitrarily chosen 7, is considered. The validity of this
World Abstracts on Microelectronics and Reliability
interface states near the edge of the surface inversion region, is proposed and found to be in good agreement with experimental data. Our model also suggests another method of calculating the density of interface states. Fundamental properties of interface states are estimated from experimental data. A self-consistency check is made among the values of equivalent circuit elements to substantiate our model.
Review of RIE induced radiation damage in silicon dioxide. L. M. EPHRATH and D. J. DIMARIA. Solid-St. Technol. 182 (April 1981). Radiation damage in silicon dioxide films exposed to Reactive Ion Etching (RIE) has been investigated. Capacitance-voltage (C-V) and photocurrentvoltage (photo I-V) techniques were used to monitor charge trapping and the location of trapped charge after the films were incorporated into MOS capacitors. Bulk neutral trapping sites caused by penetrating radiation were observed in oxides exposed to CF4, C F 4 + H / and 0 2 plasmas, although the number of radiation induced traps was somewhat lower in oxides etched in CF 4 + H 2. The neutral trapping centers are removed by a 600°C anneal in forming gas. An additional trapping layer within 10nm of the surface of the oxide was detected in oxides exposed to 0 2. These traps which are primarily associated with atomic displacement damage caused by the penetration of ions ( < 4 0 0 e V ) require a 1000°C anneal for their removal. Blanket etched films were also used to study the trapping characteristics of the bulk neutral traps as a function of position in the reactor, rf peak-to-peak voltage, and preRIE high temperature annealing. The ability of gate electrode materials to shield an underlying oxide during RIE was also tested. It was determined that aluminum and n ÷ polysilicon are effective in shielding oxides from RIE induced radiation damage. The role of transport in very small devices for VLSI. D. K. FERRY and H. L. GRUBIN. Microelectron. J. 12 (2) 5 (1981). As VLSI systems become more dense, individual device size is dramatically reduced in the quest for lower power-delay products and faster logic. The role of velocity overshoot becomes important, not only for reducing the transit-time contribution to logic delay, but more importantly for the role it plays in increasing the effective saturation velocity. These considerations reinforce the view that other semiconductors may be more suitable than Si for VLSI. Evaluation of inhomogeneous resistive layers by a four point method. GYORGY FODOR, MIKLOS SZILAGYI and LASZLO ZOMBORY. E lectrocomponent Sci. Technol. 7, 211 (1981). This paper describes the determination of the sheet resistance of a narrow strip located in a homogeneous resistive layer of different resistivity. The application of the method for the evaluation of inhomogeneous layers used for thermoprinter head production is discussed. On the correlation of "hot" and "cold" electron-hole drop densities in uniaxially stressed silicon. J. WAGNER, A. FORCHEL and R. SAUER. Solid-St. Commun. 36, 917 (1980). "Hot" and "cold" electron-hole drops were studied in (100)stressed silicon by intense optical pulse excitation and gated photoluminescence measurements. We obtain varying relative densities of hot and cold EHD electrons either by choosing the delay time of the gate appropriately or by using samples of different impurity concentrations. In all cases, the spectra can entirely be fitted assuming only a homogeneous EHD-phase consisting of both, hot and cold electrons. This result is in agreement with recent theoretical work which-contrary to germanium--finds phase separation in stressed silicon not to be very likely. Substrate response of a floating gate n-channel MOS memory cell subject to a positive linear ramp voltage. HAN-SHENG LEE and DAVID SCOTT LOWRIE. Solid-St. Electron. 24, 267 (1981).
A computer simulated substrate response of an n-channel MOS floating gate transistor to a positive linear ramping gate voltage was investigated. Device parameters, such as the channel length, effective electron mobility, substrate doping level and the gate voltage ramping rate were changed to see their effects on the substrate response. The substrate response was monitored by using the response of the surface potential at the mid-channel point. In the one-dimensional analysis it was found that the surface potential at the midchannel point increased initially and dropped quickly after passing through its peak value and then decreased slowly. The mid-channel surface potential reached a higher peak value if the device had (1) a longer channel length, (2) a lower effective electron mobility, (3) a higher gate voltage ramping rate, or (4) a lower substrate doping level. Solutions show that the conditions for the mid-channel point to reach its peak surface potential faster are: (a) a shorter channel length, (b) a higher effective electron mobility, (c) a higher gate voltage ramping rate, and (d) a lower substrate doping level. ESR studies of thermally oxidized silicon wafers. CHR1STER BRUNSTROM and CHRISTER SVENSSON.Solid-St. Commun. 37, 399 (1981). We have performed ESR measurements on oxidized (111) silicon wafers and found two ESR centers. One, the previously known Pb center, was found to be a two level interface trap by corona bias studies. The other onc, previously known as "damaged silicon" center was found to be a silicon center, probably related to the oxide growth process.
Localized anodic thinning of GaAs structures. D. W. SHAW and R. E. WILLIAMS. Solid-St, Electron. 24, 281 (1981}. The self-limiting characteristics of anodic thinning for GaAs FET structures is not realized when applied to selected areas as with patterned wafers. An approach that circumvents this problem is described. Vibrational properties of crystalline and amorphous Ge I _ xSix alloys. BALK. AGRAWAL. Solid-St. Commun. 37, 271 (1981). A five-atom cluster Bethe lattice method treating the shortrange order with proper statistical effects has been proposed for understanding the crystalline and amorphous alloys. Numerical results for Gel_xSi x alloys are in excellent agreement with the experimental data. In the system studied the network is random but the nearest-neighbour coordination should be treated exactly. The long-range coordination is seen to be concentration-dependent in the crystalline alloys but concentration-independent in the amorphous alloys. Transport equations for the analysis of heavily doped semiconductor devices. M. S. LUNDSTROM, R. J. SCHWARTZ and J. L. GRAY. Solid-St. Electron. 24, 195 (1981). Transport equations for use in analyzing heavily doped semiconductor devices are considered. These transport equations describe the effects of the nonuniform band structure and the influence of Fermi-Oirac statistics, which are important in heavily doped semiconductors. Previous workers [1, 2] have derived transport equations in terms of the nonuniform band structure. These equations, however, are not convenient for use in semiconductor device analysis because the band structure of heavily doped semiconductors is not well known. In this paper, the transport equations of Marshak and van Vliet [1, 3] are recast into a simple, Boltzmann-like form in which the effects associated with the nonuniform band structure and degenerate carrier concentrations are described by two parameters, the effective gap shrinkage, Ate, and the effective asymmetry factor, 7. The experimental determination of both of these parameters is also discussed. Finally, Adler's contention [4], that some important features of semiconductor device operation can be modeled accurately by using an electrically measured AG with an arbitrarily chosen 7, is considered. The validity of this