A study on Al2O3 passivation in GaN MOS-HEMT by pulsed stress

This paper studies systematically the drain current collapse in AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors （MOS-HEMTs） by applying pulsed stress to the device. Low-temperature layer of Al2O3 ultrathin film used as both gate dielectric and surface passivation layer was deposited by atomic layer deposition （ALD）. For HEMT, gate turn-on pulses induced large current collapse. However, for MOS-HEMT, no significant current collapse was found in the gate turn-on pulsing mode with different pulse widths, indicating the good passivation effect of ALD Al2O3. A small increase in Id in the drain pulsing mode is due to the relieving of self-heating effect. The comparison of synchronously dynamic pulsed Id - Vds characteristics of HEMT and MOS-HEMT further demonstrated the good passivation effect of ALD Al2O3.     

SiNx薄膜热物性参数实验测量与分析研究

采用一种新的实验测量方案，将金属加热单元与温度探测单元合二为一，间接获得了在半导体和微电子学MEMS领域内有重要用途的SiN_x薄膜的导热系数、发射率、比热容和热扩散系数，并对实验结果进行了不确定度分析，为微电子电路设计和掩模成型工艺等提供了可靠的热物性数据. 实验结果表明，薄膜的导热系数、发射率、热扩散系数远比相应体材质低，而且还与温度、厚度有关，尺寸效应显著，而比热容则与体材质相差不大. 关键词： 微尺度传热 热物性参数 x薄膜')" href="#">SiN_x薄膜 测量技术     

The defect density of a SiNx/In0.53Ga0.47As interface passivated using (NH4)2Sx

Passivation of the electronic defect states at a SiN_x/InGaAs interface has been achieved using (NH₄)₂S_x treatments of the InGaAs surface. The X-ray photoelectron spectroscopy technique was used to investigate the mechanism of sulfur passivation. The results indicate that sulfur treatment can effectively erase the native oxides, and S-In, S-Ga and S-As bondings are formed after sulfidation. The fabrication of Au/SiN_x/InGaAs metal–insulator–semiconductor diodes has been achieved by depositing a layer of SiN_x on (NH₄)₂S_x-treated n-InGaAs using the plasma enhanced chemical vapor deposition technique. The effect of passivation on the InGaAs surface before and after annealing was evaluated by current–voltage and capacitance–voltage measurements. The results indicate that the SiN_x passivation layer exhibits good insulative properties. The annealing contributes to the decrease of the fixed charge density and the minimum surface state density, which are 4.5×10¹¹ cm^-2 and 3.92×10¹¹ cm^-2 eV^-1, respectively. A 256×1 InP/InGaAs/InP heterojunction short-wavelength infrared detector, fabricated with the sulfidation plus a SiN_x passivation layer, has shown a good response uniformity of 4.81%. PACS 73.20.At; 73.40.Kp; 73.40.Rw; 81.40.Rs; 71.55.Eq     

Passivation of InP-based HBTs

The surface effects, the (NH₄)₂S and low-temperature-deposited SiN_x passivations of InP-based heterostructure bipolar transistors (HBTs) have been investigated. The surface recombination current of InP-based HBTs is related to the base structures. The (NH₄)₂S treatment for InGaAs and InP removes the natural oxide layer and results in sulfur-bonded surfaces. This can create surface-recombination-free InP-based HBTs. Degradation is found when the HBTs were exposed to air for 10 days. The low-temperature-deposited SiN_x passivation of InGaAs/InP HBTs causes a drastic decrease in the base current and a significant increase in the current gain. The improvement in the HBT performance is attributed to the low deposition temperature and the effect of N₂ plasma treatment in the initial deposition process. The SiN_x passivation is found to be stable. S/SiN_x passivation of InGaAs/InP HBTs results in a decrease in the base current and an increase in the current gain. The annealing process can cause the base current to decrease further and the current gain increase.     

Hot-electron reliability improvement using perhydropolysilazane spin-on-dielectric passivation buffer layers for AlGaN/GaN HEMTs

We investigate the effects of perhydropolysilazane spin-on-dielectric (SOD) buffer layer adopted prior to Si₃N₄ passivation on the dc drain current level and degradation after the electrical stress in the AlGaN-GaN high electron mobility transistors (HEMTs). The SOD-buffered HEMTs show ∼1.6 times greater drain current densities (∼257 mA/mm) than those of the devices with conventional-Si₃N₄ passivations (∼155 mA/mm). After the hot electron stresses (step-wise and constant) applied to the devices, it is also found that the SOD-buffered structure produces greatly improved device reliability in terms of the dc current collapse (15% for step-stress and constant stress) compared to the conventional structure (25% for each case). We propose that the enhancement of SOD-buffered structure in dc current collapse is due to the reduction in surface state density at the passivation interface and the suppressed electron trapping.     

Effects of the passivation of SiNx with various growth stoichiometry on the high temperature transport properties of the two-dimensional electron gas in AlxGa1−xN/GaN heterostructures

Effects of the passivation of SiN_x on the high temperature transport characteristics of the two-dimensional electron gas (2DEG) in unintentionally doped Al_xGa_1−xN/GaN heterostructures have been investigated by means of high temperature Hall measurements. The 2DEG density increases much after SiN_x passivation, and the increment is proportional to the Si content in SiN_x layer, indicating that the increment is mainly caused by ionized Si atoms at the SiN/Al_xGa_1−xN interface with dangling bonds or by Si atoms incorporated into the Al_xGa_1−xN layer during the SiN_x growth, which is approved by strain analysis and X-ray photoemission spectroscopy (XPS). There is lower 2DEG mobility at room temperature in a passivated sample than in an unpassivated one. However, the 2DEG mobility becomes to be higher in a passivated sample than in an unpassivated one when the temperature is above 250 °C, which is suggested to be caused by different subband occupation ratios in the triangular quantum well at the heterointerface before and after passivation.     

Surface passivation of In0.83Ga0.17As photodiode with high-quality SiN layer fabricated by ICPCVD at the lower temperature

The surface passivation of low-temperature-deposited SiN_x films has been investigated in PIN type In_0.83Ga_0.17As photodiodes. In contrast to SiN_x films (330 °C) fabricated by PECVD (Plasma enhanced chemical vapor deposition), the low-temperature-deposited SiN_x films (75 °C) fabricated by ICPCVD (Inductively coupled plasma chemical vapor depositon) have a good effect on passivation of In_0.83Ga_0.17As photodiodes, which caused reductions of dark current as large as 2–3 orders of magnitude at the same test temperature 200 K. The effects of low-temperature-deposited SiN_x passivations with lowrate (∼16 nm/min) model were compared to the ones with highrate (∼100 nm/min) model. SiN_x films with lowrate model have a better effect on reducing dark current of the photodiodes. The different SiN_x films were studied by SIMS. The results show that the content of oxides in SiN_x layer fabricated by PECVD is 2 orders of magnitude more than that in SiN_x layer fabricated by ICPCVD which could be the reason that low-temperature-deposited SiN_x passivation leads to higher performance. Further, the dark current density of the photodiodes with lowrate-deposited SiN_x passivations does not show the dependence on the perimeter-to-area(P/A) of the junction.     

使用SiNx原位淀积方法生长的GaN外延膜中的应力研究

采用低压MOCVD系统，在生长过程中使用SiN_x原位淀积的方法产生纳米掩模，并 在纳米掩模上进行选区生长和侧向外延制备了GaN外延薄膜.使用拉曼光谱和光荧光的手段对 GaN外延膜中的残余应力进行了研究.研究发现，用SiN_x原位淀积出纳米掩模后 ，GaN生长将由二维向三维转变，直到完全合并为止.利用拉曼光谱和光荧光谱分别研究了薄 膜中的残余应力，两者符合得很好；这种方法生长出的GaN薄膜的应力分布较传统的侧向外 延更加均匀；并且从中发现随着生长过程中SiN_x原位淀积时间的增加，生长在 其上的GaN外延膜中的残余应力减小.这是因为，随着SiN_x原位淀积时间的增加 ，SiN_x纳米掩模的覆盖度也增大.因此侧向外延区的比例增大，残余应力随之减 小. 关键词： GaN x原位淀积')" href="#">SiN_x原位淀积 拉曼 光荧光 残余应力     

高场应力及栅应力下AlGaN/GaN HEMT器件退化研究

采用不同的高场应力和栅应力对AlGaN/GaN HEMT器件进行直流应力测试,实验发现：应力后器件主要参数如饱和漏电流,跨导峰值和阈值电压等均发生了明显退化,而且这些退化还是可以完全恢复的;高场应力下,器件特性的退化随高场应力偏置电压的增加和应力时间的累积而增大;对于不同的栅应力,相对来说,脉冲栅应力和开态栅应力下器件特性的退化比关态栅应力下的退化大.对不同应力前后器件饱和漏电流,跨导峰值和阈值电压的分析表明,AlGaN势垒层陷阱俘获沟道热电子以及栅极电子在栅漏间电场的作用下填充虚栅中的表面态是这些不同应 关键词： AlGaN/GaN HEMT器件 表面态(虚栅) 势垒层陷阱 应力     

Effective surface passivation of crystalline silicon using ultrathin Al2O3 films and Al2O3/SiNx stacks

We measure surface recombination velocities (SRVs) below 10 cm/s on p‐type crystalline silicon wafers passivated by atomic–layer–deposited (ALD) aluminium oxide (Al₂O₃) films of thickness ≥10 nm. For films thinner than 10 nm the SRV increases with decreasing Al₂O₃ thickness. For ultrathin Al₂O₃ layers of 3.6 nm we still attain a SRV < 22 cm/s on 1.5 Ω cm p‐Si and an exceptionally low SRV of 1.8 cm/s on high‐resistivity (200 Ω cm) p‐Si. Ultrathin Al₂O₃ films are particularly relevant for the implementation into solar cells, as the deposition rate of the ALD process is extremely low compared to the frequently used plasma‐enhanced chemical vapour deposition of silicon nitride (SiN_x). Our experiments on silicon wafers passivated with stacks composed of ultrathin Al₂O₃ and SiN_x show that a substantially improved thermal stability during high‐temperature firing at 830 °C is obtained for the Al₂O₃/SiN_x stacks compared to the single‐layer Al₂O₃ passivation. Al₂O₃/SiN_x stacks are hence ideally suited for the implementation into industrial‐type silicon solar cells where the metal contacts are made by screen‐printing and high‐temperature firing of metal pastes. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High-electric-field-stress-induced degradation of SiN passivated AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated by employing SiN passivation, this paper investigates the degradation due to the high-electric-field stress. After the stress, a recoverable degradation has been found, consisting of the decrease of saturation drain current I_Dsat, maximal transconductance g_m, and the positive shift of threshold voltage V_TH at high drain-source voltage V_DS. The high-electric-field stress degrades the electric characteristics of AlGaN/GaN HEMTs because the high field increases the electron trapping at the surface and in AlGaN barrier layer. The SiN passivation of AlGaN/GaN HEMTs decreases the surface trapping and 2DEG depletion a little during the high-electric-field stress. After the hot carrier stress with V_DS=20 V and V_GS=0 V applied to the device for 10⁴ sec, the SiN passivation decreases the stress-induced degradation of I_Dsat from 36% to 30%. Both on-state and pulse-state stresses produce comparative decrease of I_Dsat, which shows that although the passivation is effective in suppressing electron trapping in surface states, it does not protect the device from high-electric-field degradation in nature. So passivation in conjunction with other technological solutions like cap layer, prepassivation surface treatments, or field-plate gate to weaken high-electric-field degradation should be adopted.     

Structural evolution of SiNx films deposited by ECR and its light emission

Structural and optical properties of a-SiN_x films deposited by electron cyclotron resonance chemical vapor deposition (ECRCVD) have been investigated. The Fourier transform infrared (FTIR) spectroscopy shows the structural evolution of the SiN_x films, which are defined as Si-rich SiN_x and N-rich SiN_x films, also confirmed by Raman spectroscopy. The origin of the light emission for SiN_x films may be attributed to two mechanisms, i.e., quantum confinement effect (QCE) and transition of defect energy levels. The correlation between light emission and structures of SiN_x films is discussed.     

Improved resistive switching phenomena observed in SiNx‐based resistive switching memory through oxygen doping process

The improvement of resistive switching (RS) phenomena of silicon‐nitride (SiN_x)‐based resistive random access memory (ReRAM) cells through oxygen doping process was investigated. As a result, compared to un‐doped SiN_x films, the oxygen doped SiN_x (SiN_x:O₂)‐based ReRAM cells show a lower current (～0.3 μA) level at a high resistance state and a smaller variation of operating voltage through the reduction of leakage current in the SiN_x:O₂ film by combining silicon dangling bonds and doped oxygen ions. Therefore, we believe that the oxygen doping process in SiN_x films can effectively improve the RS characteristics of SiN_x‐based ReRAM cells. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

沉积参数对SiNx薄膜结构及阻透性能的影响

利用直流脉冲磁控溅射法在室温下制备无氢SiN_x薄膜.通过傅里叶变换红外光谱、台阶仪、紫外—可见分光光度计、接触角测量仪、透湿测试仪等表征技术,分析了N₂流量、Si靶溅射功率等实验参数对SiN_x薄膜成分、结构、及阻透性能、透光性能、接触角等性能的影响.研究结果表明,Si靶溅射功率固定时,在低N₂流量条件下,或N₂流量固定时,在高Si靶溅射功率条件下,制备的SiN _{关键词： x}')" href="#">SiN_x 磁控溅射 微观结构 阻透性能     

RHEED studies during growth of TiN/SiNx/TiN trilayers on MgO(0 0 1)

TiN/SiN_x/TiN(0 0 1) trilayers have been deposited on MgO(0 0 1) substrates using ultra-high vacuum based reactive magnetron sputtering and studied by in situ reflection high energy electron diffraction (RHEED). Depositions were carried out at 500 °C and 800 °C, with SiN_x layer thicknesses between 3 and 300 Å. Here, we find that SiN_x(0 0 1) layers grown at 800 °C exhibit 1 × 4 surface reconstructions along orthogonal 〈1 1 0〉 directions up to a critical thickness of ∼9 Å, where an amorphous phase forms. Growth of TiN overlayers on the reconstructed SiN_x(0 0 1) layers yield RHEED patterns indicating the growth of (0 0 1)-oriented epitaxial layers with a 1 × 1 reconstruction. For the case of amorphous SiN_x layers the TiN overlayers grow polycrystalline.     

Si-rich SiNx rear passivated c-Si solar cell with a novel antimony Local Back Surface Field formed by Laser Fired Contact

Local Back Contact (LBC) crystalline silicon solar cell with novel antimony (Sb) Local Back Surface Field (LBSF) are reported. The Sb LBSF is formed at low temperature with a Laser Fired Contacts (LFC) process. To improve the solar cell parameters of Sb LBSF, the rear passivation layer with SiN_x is optimized by varying the refractive index. The Si-rich SiN_x with a refractive index (n) of 2.7 possesses high lifetime of 2 ms with reduced absorption at a longer wavelength. The increase in lifetime is analyzed with Si–H bond concentration by FTIR. A 100 nm thick Sb layer with low laser power of 44 mW resulted in a junction depth of 500 nm with a carrier concentration of 5 × 10²⁰ cm^?3. The improved rear passivation with Si-rich SiN_x, the optimized Sb thickness yielded the best electrical results, with open circuit voltage (V_oc) of 643 mV and efficiency of 19.25%, compared to the reference cell with V_oc of 625 mV and efficiency of 18.20%.     

Enhanced rear‐side reflection and firing‐stable surface passivation of silicon solar cells with capping polymer films

Low refractive index polymer materials have been investigated with a view to form the back surface mirror of advanced silicon solar cells. SiO_x:H or AlO_y SiO_x:H polymer films were spun on top of an ultra‐thin (<10 nm) atomic‐layer‐deposited (ALD) Al₂O₃ layer, itself deposited on low‐resistivity (1 Ω cm) p‐type crystalline silicon wafers. These double‐layer stacks were compared to both ALD Al₂O₃ single layers and ALD Al₂O₃/plasma‐enhanced chemical vapour deposited (PECVD) SiN_x stacks, in terms of surface passivation, firing stability and rear‐side reflection. Very low surface recombination velocity (SRV) values approaching 3 cm/s were achieved with ALD Al₂O₃ layers in the 4–8 nm range. Whilst the surface passivation of the single ALD Al₂O₃ layer is maintained after a standard firing step typical of screen printing metallisation, a harsher firing regime revealed an enhanced thermal stability of the ALD Al₂O₃/SiO_x:H and ALD Al₂O₃/AlO_y SiO_x:H stacks. Using simple two‐dimensional optical modelling of rear‐side reflection it is shown that the low refractive index exhibited by SiO_x:H and AlO_y SiO_x:H results in superior optical performance as compared to PECVD SiN_x, with gains in photogenerated current of ～0.125 mA/cm² at a capping thickness of 100 nm. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of interfaces density and thermal processes on mechanical stress of PECVD silicon nitride

The paper focuses on a particular silicon nitride thin film (SiN_x) produced by plasma enahanced chemical vapor deposition (PECVD) technique with high deposition rate (26 nm/min) and low values of mechanical stress (<100 MPa). This was perfomed with mixed frequency procedure varying the modulation of high frequency at 13.56 MHz and low frequency at 308 kHz of RF power supply during the deposition, without changing the ratio of reaction gases. Low stress silicon nitride is commonly obtained by tailoring the thickness ratio of high frequency vs. low frequency silicon nitride layers.The attention of this work was directed to the influence of the number of interfaces per thickness unit on the stress characteristics of the deposited material. Two sets of wafer samples were deposited with low stress silicon nitride, with a thickness of 260 nm and 2 μm, respectively. Thermal annealing processes at 380 and 520 °C in a inert enviroment were also performed on the wafers.The Stoney–Hoffman model was used to estimate the stress values by wafer curvature measurement with a mechanical surface profilometer: the stress was calculated for the as-deposited layer, and after each annealing process.The thickness and the refractive index of the SiN_x were also measured and charaterized by variable angle spectra elliposometry (VASE) techinique.The experimental measurements were performed at the MT-LAB, IRST (Istituto per la Ricerca Scientifica e Tecnologica) of Bruno Kessler Foundation for Research in Trento.     

a-SiNx/nc-Si/a-SiNx双势垒结构中的电荷隧穿和存储效应

在等离子体增强化学气相沉积系统中利用大氢稀释逐层淀积技术制备nc-Si量子点阵列,用硅烷和氨气混合气体淀积氮化硅层,制备了a-SiN_x/nc-Si/a-SiN_x不对称双势垒结构,其中隧穿和控制a-SiN_x层的厚度分别为3和20 nm.利用电导-电压和电容-电压测量研究结构中的载流子隧穿和存储特性.在同一样品中观测到由于电荷隧穿引起的电导峰和由于电荷存储引起的电容回滞现象.研究结果表明,合理地选择隧穿层和控制栅层的厚度,就能够实现载流子发生共振隧穿进入到nc-Si量子点中,并被保存在nc-Si量子点中. 关键词： nc-Si量子点 电导峰 存储效应     

Interface of anodic sulfide-oxide on n-type InSb

A novel anodic sulfidization process for forming native sulfide-oxide films on n-type InSb is described. The results of Auger electron spectroscopy analysis indicate that native sulfide-oxide films are formed from aqueous sulfide solutions. The measured capacitance-voltage characteristics of metal-insulator-semiconductor devices indicate that the films have a low fixed surface charge density of the order of 3×10¹⁰ cm^–2 and small hysteresis. The native sulfide-oxide films leave the surface of n-type InSb practically at flatband and in this respect are superior to the passivation layers of anodic oxide and direct plasma SiN _x . The interface between InSb and its native sulfide-oxide in combination with plasma CVD SiN _x has excellent electrical properties.