利用MOSFET亚阈I—V特性进行辐射感生界面陷阱的测量

本文利用ＭＯＳＦＥＴ亚阈Ｉ－Ｖ曲线对加固和非加固ＭＯＳＦＥＴ的辐射感生界面陷阱密度进行了测量,分析和讨论了辐射感生的界面陷阱密度依赖于辐射总剂量和辐射剂量率的变化关系。     

SiO_2/SiC界面陷阱对SiC MOSFET开关损耗的影响

位于SiO_2/SiC界面处密度较高的陷阱,不仅俘获SiC MOSFET沟道中的载流子,而且对沟道中的载流子形成散射、降低载流子的迁移率,因而严重影响了SiC MOSFET的开关特性。目前商业化的半导体器件仿真软件中迁移率模型是基于Si器件开发,不能体现SiO_2/SiC界面处的陷阱对沟道中载流子的散射作用。通过引入能正确反映界面陷阱对载流子作用的迁移率模型,利用半导体器件仿真软件研究了界面陷阱对SiC MOSFET动态特性的影响。结果表明,随着界面陷阱密度的增加,SiC MOSFET开通过程变慢,开通损耗增加,而关断过程加快,关断损耗减小;但是由于沟道载流子数量的减少、导通电阻的增加,总损耗是随着界面陷阱密度的增加而增加。     

不同剂量率LC54HC04RH电路的电离辐射效应

对 L C54HC0 4 RH电路在不同辐射剂量率进行了电离辐射实验。分析了该电路的阈值电压随辐射剂量率的变化关系。实验结果表明 :在辐射剂量率处于 3× 10 -4 Gy(Si) / s到 1.98×10 -1Gy(Si) / s范围内 ,辐射感生界面陷阱电荷随辐射剂量率的减少而增加。辐射感生界面陷阱电荷是导致该电路在空间辐射环境下失效的主要原因。     

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。     

热载流子诱生MOSFET/SOI界面陷阱的正向栅控二极管技术表征

本文完成了热载流子诱生MOSFET/SOI界面陷阱正向栅控二极管技术表征的实验研究 .正向栅控二极管技术简单、准确 ,可以直接测得热载流子诱生的平均界面陷阱密度 ,从而表征器件的抗热载流子特性 .实验结果表明 :通过体接触方式测得的MOSFET/SOI栅控二极管R G电流峰可以直接给出诱生的界面陷阱密度 .抽取出来的热载流子诱生界面陷阱密度与累积应力时间呈幂指数关系 ,指数因子约为 0 787     

热载流子诱生MOSFET／SOI界面陷阱的正向机控二极管技术表征

本文完成了热载流子诱生MOSFET/SOI界面陷阱正向栅控二极管技术表征的实验研究。正向栅控二极管技术简单、准确，可以直接测得热载流子诱生的平均界面陷阱密度，从而表征器件的抗热载流子特性。实验结果表明：通过体接触方式测得的MOSFET/SOI栅控二级管R-G电流峰可以直接给出诱生的界面陷阱密度。抽取出来的热载流子诱生界面陷阱密度与累积应力时间呈幂指数关系，指数因子约为0.787。     

AlGaN/GaN异质结辐射感生界面态电荷对二维电子气输运的影响

根据荷电中心与自由载流子间的库仑散射作用,给出了异质结辐射感生界面态电荷对二维电子气(2DEG)迁移率的散射模型.计算了在不同沟道电子面密度下,界面态电荷密度与其所限制的迁移率之间的关系.运用马德森定则分析了辐射感生界面态电荷散射对总迁移率的影响.分析表明,辐射感生界面态电荷在累积到一定量后,会显著影响迁移率,一定程度上提高2DEG密度能抑制界面态电荷散射的作用     

AlGaN/GaN异质结辐射感生界面态电荷对二维电子气输运的影响

根据荷电中心与自由载流子间的库仑散射作用,给出了异质结辐射感生界面态电荷对二维电子气(2DEG)迁移率的散射模型.计算了在不同沟道电子面密度下,界面态电荷密度与其所限制的迁移率之间的关系.运用马德森定则分析了辐射感生界面态电荷散射对总迁移率的影响.分析表明,辐射感生界面态电荷在累积到一定量后,会显著影响迁移率,一定程度上提高2DEG密度能抑制界面态电荷散射的作用.     

硅基N沟道VDMOS不同偏置下总剂量效应研究

通过⁶⁰Co γ射线辐照试验,研究了不同栅极和漏极偏置下硅基N沟道VDMOS器件的总剂量效应,获得了器件的电学特性与低频噪声特性随辐射总剂量的变化规律。试验结果表明：受辐射诱生的氧化物陷阱电荷与界面陷阱电荷的影响,在栅极偏置为+20 V时,器件的电学特性随累积剂量的增大而退化明显。通过退火试验发现,相比于导通电阻和正向压降,阈值电压、漏电流、亚阈值摆幅和输出电容对于总剂量辐射更加敏感。而在低频噪声特性方面,辐照后器件的沟道电流归一化噪声功率谱密度与正栅极偏置呈现正相关性,与负栅极偏置呈现负相关性。在不同漏极偏置条件下,辐照后器件的沟道电流归一化噪声功率谱密度降低,且基本重合。依据噪声模型,认为N沟道VDMOS内部局域电场分布对辐射感生陷阱电荷的形成影响显著,导致器件Si/SiO₂界面或者附近的载流子与陷阱交换引起的沟道电流波动不同,成为低频噪声主要来源。研究结果可为N沟道VDMOS器件的辐射效应评估、筛选和抗辐射加固设计提供参考。     

MOSFET的低温(77°K)电离辐照特性

本文采用MOSFET的亚阈外推测量技术,研究MOSFET在低温(77°K),~(60)Coγ射线辐照下,辐照感生氧化层电荷和界面态。在77°K辐照下,n沟道MOSFET辐照感生氧化层电荷比室温更加明显。77°K时,辐照感生界面态的增加是室温辐照下的20％左右。p沟MOSFET在77°K辐照下,处于截止偏置的退化大于导通偏置。导通偏置辐照时,未观察到界面态的产生。     

MOS器件辐照引入的界面态陷阱性质

通过分析总剂量辐照产生的界面陷阱的施主和受主性质 ,用半导体器件模拟软件 Medici模拟了NMOS、PMOS器件加电下辐照后的特性。结果表明 ,对于 NMOSFET,费米能级临近导带 (N沟晶体管反型 )时 ,受主型界面态为负电荷 ,施主型界面态陷阱为中性 ,使界面态陷阱将引起的阈值电压漂移 ;而对 PMOSFET,当费米能级临近价带 (P沟晶体管反型 )时 ,施主型界面态陷阱带正电荷 ,受主型界面态陷阱为中性 ,界面态陷阱将引起负的阈值电压漂移。理论模拟的转移特性与测试结果吻合。文中从器件工艺参数出发 ,初步建立了总剂量电离辐照模型 ,该模型对于评估器件总剂量加固水平提供了一种理论方法     

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.     

HCl氧化物MOS结构质子辐照诱导的界面陷阱效应

用微分电容法研究质子辐照HCl氧化物铝栅MOS结构诱导的界面陷阱,栅氧化层在1 160℃很干燥的、含0～10％HCl的气氛中热生长而成,质子辐照能量为120～300keV,注入总剂量范围为8×10~(13)～1×10~(16)p/cm~2。结果表明,辐照诱导的界面陷阱能级密度随质子能量、剂量增加而增加。然而,氧化层中掺入6％HCl时,辐照诱导的界面陷阱明显减少。这样,已能有效地改变MOS器件的抗辐照性能。实验结果可用H~+二级过程解释。     

PMOS剂量计的稳定性研究

在室温条件下 ,研究了辐照偏置、总剂量和剂量率对 PMOS剂量计辐照剂量记录 -阈电压的稳定性影响 ,观察了辐照后阈电压在不同栅偏条件下的变化趋势和幅度。分析认为慢界面陷阱中电荷的“充放电”是造成不稳定的首要原因。结果表明 ,该种由慢界面态造成的阈电压变化在每次开机测量下具有重复性。讨论了在 PMOS剂量计中提高稳定性的办法。     

辐射加固54HC系列集成电路的研制

在分析电离辐射引起场区隔离失效机理及场区电离辐射加固技术的基础上，开发了一套适用于研制辐射加固５４ＨＣ系列和辐射加固大规模集成电路的ＣＭＯＳ工艺技术。辐射实验结果表明，该技术可比非加固电路的抗总剂量辐射能力提高两个数量级。     

总剂量加固对SOINMOS器件抗辐射特性的影响

采用埋层改性工艺对部分耗尽SOI NMOS器件进行总剂量加固,通过测试器件在辐射前后的电学性能研究加固对SOI NMOS器件抗辐射特性的影响。加固在埋氧层中引入电子陷阱,辐射前在正负背栅压扫描时,电子陷阱可以释放和俘获电子,导致背栅阈值电压产生漂移,漂移大小与引入电子陷阱的量有关。通过加固可以有效提高器件的抗总剂量辐射特性,电子陷阱的量对器件的抗辐射性能具有显著影响。     

Total ionizing dose effects in shallow trench isolation oxides

The peaked evolution of leakage current with total ionizing dose observed in transistors in 130 nm generation technologies is studied with field oxide field effect transistors (FOXFETs) that use the shallow trench isolation as gate oxide. The overall radiation response of these structures is determined by the balance between positive charge trapped in the bulk of the oxide and negative charge in defect centers at its interface with the silicon substrate. That these are mostly interface traps and not border traps is demonstrated through dynamic transconductance and variable-frequency charge-pumping measurements. These interface traps, whose formation is only marginally sensitive to the bias polarity across the oxide, have been observed to anneal at temperatures as low as 80 °C. At moderate or low dose rate, the buildup of interface traps more than offsets the increase in field oxide leakage due to oxide-trap charge. Consequences of these observations for circuit reliability are discussed.     

The effect of oxide layer thickness on the quantification of 1.5 MeV γ–radiation induced interface traps in the Ag/SiO2/Si MOS devices

This work presents the effect of varied thickness of oxide layer and radiation dose on electrical characteristics of Ag/SiO₂/Si MOS devices irradiated by 1.5 MeV γ–radiations of varied doses. SiO₂ layers of 50, 100, 150 and 200 nm thickness were grown on Si substrates using dry oxidation and exposed to radiation doses of 1, 10 and 100 kGy. The exposure to radiation resulted in generation of fixed charge centers and interface traps in the SiO₂ and at the Si/SiO₂ interface. Capacitance-conductance-voltage (C-G-V) and capacitance-conductance-frequency (C-G-f) measurements were performed at room temperature for all MOS devices to quantify the active traps and their lifetimes. It is shown that accumulation and minimum capacitances decreased as the thickness of SiO₂ layer increased. For the unexposed MOS devices, the flat band voltage V_FB decreased at a rate of −0.12 V/nm, density of active traps increased by 4.5 times and depletion capacitance C_DP, increased by 2.5 times with the increase of oxide layer thickness from 50 to 200 nm. The density of active traps showed strong dependence on the frequency of the applied signal and the thickness of the oxide layer. The MOS device with 200 nm thick oxide layer irradiated with 100 kGy showed density of active interface traps was high at 50 kHz and was 3.6×10¹⁰ eV⁻¹ cm⁻². The relaxation time of the interface traps also increased with the exposure of γ–radiation and reached to 9.8 µs at 32 kHz in 200 nm thick oxide MOS device exposed with a dose of 100 kGy. It was inferred that this was due to formation of continuum energy states within the band gap and activation of these defects depended on the thickness of oxide layer, applied reverse bias and the working frequency. The present study highlighted the role of thickness of oxide layer in radiation hard environments and that only at high frequency, radiation induced traps remain passivated due to long relaxation times.     

Post-irradiation formation of Si-SiO2 interface states in a hydrogen atmosphere at room temperature

Si MOSFETs were irradiated with x-rays and then exposed to various partial pressures of H₂ at either room temperature or 125 °C. The number of interface traps and the net positive oxide trapped charged were measured during the hydrogen exposure using spectroscopic charge pumping techniques. During the hydrogen exposure the gate electrode was held at a positive bias to maintain a field of 0.65 MV/cm across the gate oxide. It was found that during the room temperature hydrogen exposure the number of interface traps increased by a factor of about two. The change in the oxide trapped charge during hydrogen exposure indicated that the decrease in the number of positively charged oxide traps was approximately the same as the increase in the number of interface traps. The time evolution and bias dependence of these changes are explained by a model that we previously proposed. In this model positively charged radiation induced defects in the oxide crack the H₂ to form H⁺. Under positive gate bias the H⁺ then drifts to the Si-SiO₂ interface where it forms an interface state, while at the same time removing positive charge from the oxide.