Surface charges and surface potential in silicon surface inversion layers

The effect of interface charges on the channel conductance in MOS transistors has been investigated. It has been found that, by measuring the conductance as a function of temperature, it is possible to determine both the "fixed" interface charge which is independent of the surface potential and the charge trapped in surface states whose occupancy is a function of the surface potential. The characteristics of the two charge components are discussed. It appears that neither a continuous nor a delta-function energy distribution alone is adequate to describe the observed surface-state density.     

Degradation of electron irradiated MOS capacitors

We have investigated the degradation of MOS structure due to high energy electron irradiation as a function of radiation dose and gate bias applied during the irradiation. Devices have been characterized by current–voltage measurements, in order to study charge accumulation also at the gate interface. Three types of oxide charge have been observed: the unstable positive charge, due to trapped holes induced by the electron irradiation; the negative charge in the oxide bulk, deriving from capture of electrons injected during electrical measurements in radiation generated traps; and border traps, at both oxide interfaces.     

Carrier trapping centers and interface states induced by r.f. sputtering of molybdenum electrodes in MOS-structure diodes

Electronic properties of interface and oxide layers of Si MOS diodes with an r.f. sputtered molybdenum metal electrodes have been studied. A remarkable density increase of both oxide charge and interface states by the sputtering has been found. IMA data show that the sputtered Mo atoms are implanted into the SiO₂ less than 100 Å from the surface. It is also found from photo I–V data that the charge centroid in the SiO₂ is shifted to a depth of 100 Å below the SiO₂ surface. The energy distribution of the carrier trapping centers having a capture cross section of the order of 10^?13 to 10^?16 cm² has been observed. The interface states density can be reduced about one order of magnitude by an annealing in N₂ 10 min/H₂ 15 min/N₂ 10 min at 450°C. The mechanism of the increase of the carrier trapping centers and the interface states is also studied. Especially it is concluded that the increase of the interface states originates from the ultraviolet-light irradiation emitted from the plasma during the r.f. sputtering.     

注氟MOSFET电离辐射响应特性

对氢氧合成栅氧化后注F的MOSFET进行了γ射线辐照试验,分析了不同注F剂量的MOSFET电离辐射响应特性。结果表明,在1×10~(15)～1×10~(16)F/cm~2F注量范围内,注F能够明显抑制辐射感生氧化物电荷和界面态的增长,且F注量越高,抑制能力越强,F的注入能减少工艺过程所带来的氧化物电荷和界面态。用Si一F结键替代其它在辐射过程中易成为电荷陷阱的应力键模型对实验结果进行了讨论。可以预测,F在Si/SiO_2界面附近和SiO_2中的行为直接与MOS结构的辐射响应相对应,而F的行为依赖于注F工艺条件。     

MOS栅氧的界面特性和辐照特性研究

通过交流电导法,对经过不同时间N₂O快速热处理(RTP)的MOS电容进行界面特性和辐照特性研究。通过电导电压曲线,分析N₂O RTP对Si-SiO₂界面陷阱电荷和氧化物陷阱电荷造成的影响。结论表明,MOS电容的Si-SiO₂界面陷阱密度随N₂O快速热处理时间先增加再降低;零偏压总剂量辐照使氧化层陷阱电荷显著增加,而Si-SiO₂界面陷阱电荷轻微减少。     

Influence of interface charge inhomogeneities on the measurement of surface state densities in SiSiO2 interfaces by means of the MOS a.c. conductance technique

The relationship between interface charge and surface potential of a MOS capacitor is examined when interface charge inhomogeneities are present. For practical values of the interface charge variance, the relation between interface charge and surface potential is found to be quite linear. High surface state densities and high impurity concentrations tend to damp the potential fluctuations and to increase the linearity. The magnitude of the potential deviation for a given charge deviation increases from flat band to weak inversion and decreases again in strong inversion, due to screening, but the linearity is found to be best in weak inversion.The original Nicollian-Goetzberger analysis of the MOS a.c. conductance technique uses a Gaussian potential distribution and an equivalent circuit consisting of an array of parallel surface state branches connected to a single oxide capacitance. We compare this model with a patchwork model, using a Gaussian interface charge density distribution and an equivalent circuit with distributed oxide capacitance. It is found that in depletion, for practical charge densities, the patchwork model interpretation of conductance peaks does not lead to a very different result than the random charge distribution model interpretation. Both models agree very well on surface state density and variance of the interface charge distribution, but a large discrepancy on the capture cross section of the surface states is possible.     

注氟加固PMOSFET的电离辐射响应与时间退火效应

研究了注F加固PMOSFET的总剂量辐照响应特性和辐照后由氧化物电荷、界面态变化引起的阈电压漂移与时间、温度、偏置等退火条件的关系，发现一定退火条件下注F加固PMOSFET由于界面态密度、特别是氧化物电荷密度继续增加，使得电路在电高辐照后继续损伤，探讨了加速MOS器件电离辐照感生界面态生长的方法。     

The effects of gamma irradiation on low-pressure chemical-vapor-deposited silicon dioxide metal-oxide-silicon structures

The effects of gamma irradiation on as-deposited, oxygen-annealed, and dual-dielectric gate (undoped polysilicon/oxide) low-pressure chemical-vapor-deposited (LPCVD) silicon dioxide (SiO₂) metal-oxide-silicon (MOS) structures were investigated. As-deposited LPCVD SiO₂ MOS structures exhibit the largest shift in flatband voltage with gamma irradiation. This is most likely due to the large number of bulk oxide traps resulting from the nonstochiometric nature of as-deposited LPCVD SiO₂. Dual-dielectric (undoped polysilicon/annealed LPCVD SiO₂) MOS structures exhibit the smallest shift in flatband voltage and increase in interface state density compared to as-deposited and oxygen-annealed LPCVD SiO₂ MOS structures. The interface state density of dual-dielectric MOS structures increases from 5 × 10¹⁰ eV cm⁻² to 2–3 × 10¹¹ eV cm⁻² after irradiation to a gamma total dose level of 1 Mrads(Si). This result suggests that the recombination of atomic hydrogen atoms with silicon dangling bonds, either along grain boundaries or in crystallites of the undoped polysilicon layer in dual-dielectric (undoped polysilicon/annealed LPCVD SiO₂) MOS structures, probably reduces the number of atomic hydrogen atoms reaching the Si/SiO₂ interface to generate interface states.     

Thin oxide mos damage generated after treatment in a merie reactor

The effect of magnetized non-uniform helium plasma on the properties of thin oxide (11–13 nm) MOS structures has been investigated by means of the HLFCV technique. The plasma reactor system used is like a magnetically enhanced reactive ion etcher. The damage creation for MOS structures with various Al gate thicknesses was determined as a function of discharge parameters and plasma exposure time. The creation of a large amount of defects in the form of a fixed oxide charge and interface states is found; the build-up plasma damage process is very rapid, particularly during the first 5–30 s of the plasma exposure time and it depends essentially on the Al gate thickness. It is established that build-up damage depends on the plasma non-uniformity, but the non-uniformity is neither the only nor the dominating factor.     

Charge-pumping characterization of SiO2/Si interface invirgin and irradiated power VDMOSFETs

The applicability of charge-pumping technique to characterize the oxide/silicon interface in standard power Vertical Double-diffused (VD)MOS transistors is studied. Qualitative analysis of the charge-pumping threshold and flat-band voltage distributions in the VDMOS structure, supported with rigorous transient numerical modeling of the charge-pumping effect, shows that the measurements can be carried out in the subthreshold region. This conclusion is confirmed by various experimental results. The characteristics, i.e. charge-pumping current versus gate top level, is studied in detail. The changes in the characteristics after γ-ray irradiation are analyzed. A charge-pumping-based method for separate extraction of interface state density and density of charge trapped in the oxide after irradiation of VDMOSFETs is proposed. The validity and limitations of the method are studied by experiments and modeling     

Temperature dependence of turn-on voltage of gold-doped MOSFETs

The temperature dependence of the turn-on voltage of gold-doped and control n- and p-channel MOSFETs has been measured. To account for the large positive shift of turn-on voltage, VT Au, of gold treated n- and p-channel devices, it has been proposed that the gold eliminates the fast interface traps of continuous energy distribution, and that additional acceptor states very close to the valence band can cause additional charge QA Au, which can dominate the effect of acceptor and donor levels of gold ions in the silicon surface space charge region, and can also over-compensate the surface state charge, Qss. To fit the theoretical VT Auversus T curve to experimental curves, an accumulation of electrically active gold within the surface space charge region has been considered in n-channel devices and depletion in p-channel devices.     

CMOS／SIMOX器件总剂量辐照的研究

在新材料ＳＩＭＯＸ上制作ＣＭＯＳ器件,并采用静态Ｉ－Ｖ技术,研究了ＣＭＯＳ／ＳＩＭＯＸ在（６０）Ｃｏ－γ电离辐照场中辐照感生界面态、氧化物正电荷、阈值电压、静态漏电流等参数的变化。结果表明,在辐照过程中,氧化物正电荷增加较多,界面态增加较少,且ＮＭＯＳ和ＰＭＯＳ＂导通＂辐照偏置是最恶劣偏置。     

Capacitance voltage measurements on n-type InAs MOS diodes

The electrical properties of the interface between pyrolytically deposited SiO₂ and InAs have been investigated by measuring the admittance of Al-SiO₂-InAs MOS diodes at room temperature and 77°K. The room temperature measurements yield a rather high surface state density of 2·5 × 10¹² states/eV/cm². The surface state density undergoes an anomalous decrease to 2·8 × 10¹¹ states/eV/cm² at 77°K. A charge which is linearly dependent on the voltage across the oxide is trapped in the oxide. Conduction through the oxide causes the diodes to enter a deep depletion condition at 77°K.     

Effects of ionizing radiation on oxidized silicon surfaces and planar devices

This paper examines in detail the effects of high and low energy electron, X-ray, and ultraviolet radiation on oxidized silicon surfaces and planar devices. Two permanent effects of ionizing radiation on oxidized silicon surfaces are distinguished: 1) The buildup of a positive space charge within the oxide, and 2) The creation of fast surface states at the oxide-silicon interface resulting in increased surface recombination velocity. The dependence of these effects on dose and dose rate, on bias applied during irradiation, and on structural parameters is discussed and a theory is presented which accounts for the observed features of the space-charge buildup. This theory involves trapping of holes which are generated within the oxide by the radiation. It is shown that all details of the experimental observations can be accounted for by assuming a high density of hole traps near the oxide-silicon interface which decays rapidly with distance into the oxide. Radiation-induced changes in the characteristics of MOS and junction field-effect transistors, p-n junction diodes, and p-n-p and n-p-n transistors are reported and examined in terms of the above two effects. It is shown that the charge buildup causes shifts in the operating point of MOS transistors, catastrophic increases in the reverse current of p-n junctions, and variations in their breakdown voltage. The increase in fast surface-state density is responsible for the lowering of the transconductance of MOS transistors and, in combination with the space-charge buildup, for the degradation of the current gain in bipolar transistors. It is shown that junction field-effect transistors are relatively insensitive to both effects of ionizing radiation and therefore offer the most promise for use in ionizing radiation environments.     

Observation of near-interface oxide traps with the charge-pumpingtechnique

In studies of MOS devices with the charge pumping technique, the authors have encountered a low-frequency increase in the charge recombined per cycle, which they attribute to the charging and discharging of traps located within a tunneling distance of the Si-SiO ₂ interface, i.e., near-interface oxide traps. MOS devices subjected to ionizing radiation as well as ultrathin tunnel oxide polysilicon-oxide-nitride-oxide-silicon (SONOS) nonvolatile memory devices possess a high density of near-interface oxide traps. When the charge recombined per cycle is examined as a function of frequency, a breakpoint is observed at a particular frequency with an inverse equivalent to a trap-to-trap tunneling time constant     

Correlation between most 1/f noise and CCD transfer inefficiency

The 1/f noise in MOS transistors has been investigated and is shown to correlate with charge transfer inefficiency experiments on surface-channel CCDs. Both independent phenomena can be quantitatively explained by the same interface state model. The oxide trap density turns out to vary by more than a factor 10. The 1/f noise is compared with McWhorter's number fluctuation model and with the mobility fluctuation model. The oxide trap density is calculated from the charge transfer inefficiency in surface CCDs. Both the quantitative agreement between oxide trap density and 1/f noise and the observed dependence of 1/f noise on gate voltage here give strong arguments in favour of the McWhorter model. The investigated MOS transistors fall into a category that cannot be explained by the present mobility fluctuation model.     

InSb阳极氧化膜界面特性研究

用阳极氧化的方法在InSb衬底上生长氧化膜,并在阳极氧化膜上镀Cr/Au电极以制备MOS器件,通过分析77 K时MOS器件C-V特性,得出InSb-阳极氧化膜界面的掺杂浓度、界面态密度,氧化层中的固定电荷密度可动电荷密度等重要参数,分析其界面特性和制备工艺的关系,为InSb表面的钝化工艺提供参考。     

总剂量辐照SiO2/6H-SiC引起的界面势垒变化

辐照会引起MOS器件电介质氧化物与半导体界面势垒变化,影响其工作性能和可靠性。测量了n型6H-SiC MOS电容辐照105rad(Si)剂量前后的I-V曲线,通过Fowler-Nordheim(F-N)隧道电流拟合,得到了界面势垒的大小,辐照前的为2.596 eV,辐照后降为1.492eV。界面势垒变化主要是由辐照产生的界面态引起的。     

Characterization of ultra-thin SiO2 by capacitance-voltage and charge pumping measurements

In this paper, we present results on electrical measurements of ultra thin SiO₂ layers (from 3.5 nm down to 1.7 nm), used as gate dielectric in metal-oxide-semiconductors (MOS) devices. Capacitance-voltage (C-V) measurements and simulations on MOS capacitors have been used for extracting the electrical oxide thickness. The SiO₂/Si interface and oxide quality have been analyzed by charge pumping (CP) measurements. The mean interface traps density is measured by 2-level CP, and the energy distribution within the semiconductor bandgap of these traps are investigated by 3-level charge pumping measurements. A comparison of the energy distribution of the SiO₂/Si interface traps is made using classical and quantum simulations to extract the surface potential as a function of the gate signal. When the gate oxide thickness <3.5 nm, we prove that it is mandatory to take into account the quantum effects to obtain a more accurate energy distribution of the SiO₂/Si interface traps. We also explain the increase of the apparent interface traps density measured by 2-levels CP with the increase of the oxide thickness, for transistors made from the same technological process.     

Stress induced degradation features of very thin gate oxides

The degradation features of very thin gate oxide after Fowler-Nordheim stress have been studied. Bulk oxide, cathodic and anodic regions have been analysed from the charge build-up point of view, as well as the stress induced generation of Si/SiO₂ fast interface state density. A physical interpretation of experimental results has been proposed, involving two types of stress induced positive charge building up at interface regions. It is shown that a critical oxide thickness exists, under which the degradation mechanisms could be considerably different.