ICP刻蚀4H-SiC栅槽工艺研究

为避免金属掩膜易引起的微掩膜,本文采用SiO2介质作为掩膜,SF6/O2/Ar作为刻蚀气体,利用感应耦合等离子体刻蚀(ICP)技术对4H-SiC trench MOSFET栅槽刻蚀工艺进行了研究。本文详细研究了ICP刻蚀的不同工艺参数对刻蚀速率、刻蚀选择比以及刻蚀形貌的影响。实验结果表明:SiC刻蚀速率随着ICP功率和RF偏压功率的增大而增加;随着气体压强的增大刻蚀选择比降低;而随着氧气含量的提高,不仅刻蚀选择比增大,而且能够有效地消除微沟槽效应。刻蚀栅槽形貌和表面粗糙度分别通过扫描电子显微镜和原子力显微镜进行表征,获得了优化的栅槽结构,RMS表面粗糙度0.4nm。     

InP/InGaAsP异质结ICP刻蚀表面损伤(英文)

本文详细研究了采用Cl_2/H_2刻蚀气体时,ICP刻蚀系统对InP/InGaAsP材料表面损伤的影响。通过设计特殊结构的InP/InGaAsP多量子阱结构,测量刻蚀区域及非刻蚀区域的光荧光强度的变化,并结合高斯深度分布模型对刻蚀损伤进行定量研究。详细研究ICP刻蚀系统中的压强、ICP功率、RF功率以及Cl_2/H_2刻蚀气体组分对损伤程度的影响。基于这些结果优化得到一组低损伤参数,最终实现刻蚀损伤深度小于16nm。     

硅基外延β-SiC薄膜在不同刻蚀气体中的等离子体刻蚀研究

用等离子体刻蚀（PE)工艺，以四氟化碳（CF4）和六氟化硫（SF6）以及它们与氧气（O2）的混合气体作为刻蚀气体分别对Si基外延生长的β-SiC单晶薄膜进行了刻蚀工艺研究。结果表明在同样刻蚀工艺条件下，以SF6＋O2作为刻蚀气体要比以CF4＋O2作为刻蚀气体具有更高的刻蚀速率；在任何气体混合比条件下经SF6＋O2刻蚀后的样品表面都不会产生富碳（C）表面的残余SiC层；而经CF4＋O2刻蚀后的样品表面是否产生富C表面残余SiC层则与气体混合比条件有关，但刻蚀后的样品表面更为细腻。文中还对不同刻蚀气体下的刻蚀产物进行了讨论比较。     

InAs/GaSb超晶格红外探测器台面的ICP刻蚀研究

采用分子束外延方法在GaSb衬底上生长InAs/GaSb超晶格红外薄膜材料,为获得台面结构,采用电感耦合等离子体(ICP)刻蚀技术和Cl2/Ar刻蚀气体,分别研究了不同刻蚀时间、不同气体比例及不同功率对GaSb、InAs及InAs/GaSb超晶格刻蚀速率和刻蚀形貌的影响。结果表明,由于刻蚀产物InCl x的低挥发性阻挡了Cl2的刻蚀,InAs的刻蚀速率低于GaSb;Cl2比例在20%~40%时,刻蚀表面粗糙度最小,明显低于湿法腐蚀造成的表面损伤,有助于形成良好的欧姆接触和减小器件的表面漏电流。     

HfO2薄膜的反应离子刻蚀特性研究

研究了HfO2薄膜在CHF3/Ar和SF6/Ar等气体中的反应离子刻蚀机理.结果表明刻蚀气体的组分和射频偏压对刻蚀速率有较大影响,而气体流量影响不大.CHF3和SF6与HfO2的反应产物具有较好的挥发性,Ar的引入不仅可以打破分子之间的键合促进刻蚀产物的形成,而且通过轰击加快产物从材料表面解吸,从而提高HfO2刻蚀速率.AFM测量结果表明刻蚀降低了HfO2表面粗糙度,显示刻蚀工艺对材料的低损伤.     

碳氟感应耦合等离子体的SiO2介质刻蚀的研究

使用感应耦合等离子体技术,通过改变源气体流量比R(R=[C4F8]/{[C4F8] [Ar]})、射频源功率、自偏压等条件进行了SiO2介质刻蚀实验研究。碳氟等离子体的特征由朗谬探针和发射光谱技术来表征。结果表明,SiO2的刻蚀速率随放电源功率和射频自偏压的增大而单调上升,与R的关系则存在R=8%处的刻蚀速率峰值。C2基团的发射谱线强度随R的变化类似于SiO2刻蚀速率对R的依赖关系,对此给出了解释。在此基础上,对SiO2介质光栅进行了刻蚀。结果显示,在较大的R及自偏压等条件下,刻蚀后的槽形呈轻微的锥形图案,同时光刻胶掩膜图形出现分叉。结合扫描电镜技术对此进行了分析,认为光刻胶表面与侧面的能量传递和聚合物再沉积是导致出现上述现象的原因。     

无机酸刻蚀多孔氮化碳的合成及光催化性能

通过合理的形貌调控使石墨相氮化碳(g-C_3N_4)低维化和多孔化,是提高其光催化活性的有效途径.采用高温煅烧方法制备了HCl、HNO_3和H_2SO_4刻蚀的g-C_3N_4,并对它们进行了结构形貌表征、形成机理探究和光催化降解罗丹明B测试,还给出了活性增强机理.结果显示:酸刻蚀g-C_3N_4具有和g-C_3N_4相同的基本晶体结构,但是呈薄片状,且表面出现了大量纳米孔,这些孔是由无机酸阻碍前驱体中N—H键参与热缩聚反应所致,按照HCl、HNO_3、H_2SO_4的顺序阻碍作用依次增强,对应的孔径依次增大,结构边缘(C)_2—N—H基团的XPS特征峰强度也依次增加;经过40 min光反应,g-C_3N_4和HCl、HNO_3、H_2SO_4刻蚀的g-C_3N_4对罗丹明B的降解率分别为45%、 56%、 52%和95%,H_2SO_4刻蚀的g-C_3N_4光催化活性最高;酸刻蚀引起的薄片和多孔结构不仅增加了g-C_3N_4的比表面积,促进了暗条件下对罗丹明B的吸附,还通过量子限域效应提高了其光吸收能力,拓宽了禁带宽度,有效促进了光生电荷的分离.因此,酸刻蚀克服了g-C_3N_4的缺点,为探寻其光催化活性的提高方法提供了有价值的启发.     

聚变堆中H刻蚀碳氢薄膜的分子动力学模拟

使用分子动力学方法模拟了低能H原子与碳氢薄膜的作用过程,以了解基于核聚变装置中等离子体与C基材料的相互作用机制。模拟中使用REBO(reactive empirical bond order)势函数来描述C-H体系中原子间的相互作用,并使用Berendsen热浴来控制体系的温度。文中着重探讨了入射能量对低能H原子刻蚀碳氢薄膜的影响,入射能量分别为0.3,1,5和10eV。模拟结果显示随着入射能量的增加,H原子的吸附率增加,C原子和H原子的刻蚀率增加。同一能量下H原子比C原子更易发生刻蚀。通过讨论发现在H原子与碳氢薄膜作用过程中,当能量大于1 eV时,由于入射的H原子先沉积在表面并与表面原子发生反应形成碳氢化合物,然后在后续入射粒子的轰击下碳氢化合物在表面发生解吸附现象,从而导致了C原子的刻蚀,因此C原子的刻蚀发生主要是化学增强的物理溅射。     

CdZnTe晶片4种化学钝化工艺效果的比较

常用于X射线和γ射线探测器中的CdZnTe(CZT)晶片经机械抛光后表面存在损伤层和许多肉眼看不到的划痕,采用溴甲醇(Br2-CH3OH)腐蚀可有效去除损伤层和划痕,使表面变得光亮平整.但经Br2-CH3OH腐蚀的表面富Te而产生较大的表面漏电流,为此,采用H2O2溶液,NH4F/H2O2溶液,KOH-KCl溶液+NH4F/H2O2溶液二步法和溴水4种湿法化学钝化工艺,对CZT晶片表面进行了钝化处理,并对比了其钝化效果.结果表明:二步法钝化效果最好,表面漏电流降低4个数量级,NH4F/H2O2对CZT晶片表面的钝化效果较好,表面漏电流降低3个数量级.     

多弧离子镀制备TiCN/Al复合铝箔及温度敏感性

为提高电容器用铝箔的比电容并降低传统刻蚀铝箔生产过程中的环境污染,采用多弧离子镀技术制备了一种新的电容器,用TiCN/Al复合铝箔电极材料,研究了C2H2和H2流量比及沉积后冷却方式对TiCN/AI复合铝箔比电容的影响.通过扫描电镜和x射线衍射分析了不同温度下铝箔表面的微观结构和物相变化规律,探讨了TiCN/Al复合铝...     

Electrical and structural characterization of AlGaN/GaN field-effect transistors with recessed gate

Performance of AlGaN/GaN heterostructure field-effect transistors (HFETs) with recessed gate was investigated and compared with non-recessed counterparts. Optimal dry etch conditions by plasma assisted Ar sputtering were found for ∼6 nm gate recess of a 20 nm thick AlGaN barrier layer. A decrease of the residual strain after the gate recessing (from −0.9 GPa to −0.68 GPa) was evaluated from the photoluminescence measurement. The saturation drain current at the gate voltage V_G = 1 V decreased from 1.05 A/mm to 0.85 A/mm after the recessing. The gate voltage for a maximal transconductance (240−250 mS/mm) has shifted from −3 V for non-recessed HFETs to −0.2 V for recessed counterparts. Similarly, the threshold voltage increased after the gate recessing. A decrease of the sheet charge density from 1 × 10¹³ cm⁻² to 4 × 10¹² cm⁻² at V_G = 0 V has been evaluated from the capacitance measurements. The RF measurements yielded a slight increase of the cut-off frequencies after the gate recessing. All these indicate that the gate recessing is a useful tool to optimize the AlGaN/GaN HFET performance for high-frequency applications as well as for the preparation of normally-off devices.     

Low-Energy Defectless Dry Etching of the AlGaN/AlN/GaN HEMT Barrier Layer

A method of defectless dry etching of an AlGaN barrier layer is proposed, which consists in repeated plasmachemical oxidation of AlGaN and removal of the oxide layer by means of reactive ion etching in inductively coupled BCl₃ plasma. Using the proposed etching technology, AlGaN/AlN/GaN high-electron-mobility transistors (HEMTs) with a buried gate have been successfully fabricated for the first time. It is shown that the currents of obtained HEMTs are independent of the number of etching cycles, while the gate operating point shifts toward positive voltages up to obtaining transistors operating in the enhancement mode.     

Reactive ion etching of GaN and AlGaN/GaN assisted by Cl2/BCl3

This work reports on the latest results of etching of different Al _x Ga_1?x N/GaN heterostructures in relation to percentage composition of aluminum. The etching processes were carried out in a reactive ion etching (RIE) system using the mixture of BCl₃/Cl₂/Ar. The topography of the heterostructures surfaces and the slope were controlled using atomic force microsopy (AFM) technique. The photoluminescence spectra were used to determine the surface damage and to calculate the Al content in AlGaN/GaN heterostructures commonly used for high electron mobility transistors (HEMTs) fabrication.     

Surface acoustic wave excitation on SF6 plasma-treated AlGaN/GaN heterostructure

In this work, we introduce a new modified approach to the formation of interdigital transducer (IDT) structures on an AlGaN/GaN heterostructure. The approach is based on a shallow recess-gate plasma etching of the AlGaN barrier layer in combination with “in-situ” SF₆ surface plasma treatment applied selectively under the Schottky gate fingers of IDTs. It enables one to modify the two-dimensional electron gas (2DEG) density and the surface field distribution in the region of the IDTs, as is needed for the excitation of a surface acoustic wave (SAW). The measured transfer characteristics of the plasma-treated SAW structures revealed the excitation of SAW at zero bias voltage due to fully depleted 2DEG in the region of the IDTs. High external bias voltages are not necessary for SAW excitation. SIMS depth distribution profiles of F atoms were measured to discuss the impact of SF₆ plasma treatment on the performance of the AlGaN/GaN-based IDTs.     

AlGaN/GaN-based diodes and gateless HEMTs for gas and chemical sensing

The characteristics of Pt/GaN Schottky diodes and Sc/sub 2/O/sub 3//AlGaN/GaN metal-oxide semiconductor (MOS) diodes as hydrogen and ethylene gas sensors and of gateless AlGaN/GaN high-electron mobility transistors (HEMTs) as polar liquid sensors are reported. At 25/spl deg/C, a change in forward current of /spl sim/6 mA at a bias of 2 V was obtained in the MOS diodes in response to a change in ambient from pure N/sub 2/ to 10% H/sub 2// 90% N/sub 2/. This is approximately double the change in forward current obtained in Pt/GaN Schottky diodes measured under the same conditions. The mechanism appears to be formation of a dipole layer at the oxide/GaN interface that screens some of the piezo-induced channel charge. The MOS-diode response time is limited by the mass transport of gas into the test chamber and not by the diffusion of atomic hydrogen through the metal/oxide stack, even at 25/spl deg/C. Gateless AlGaN/GaN HEMT structures exhibit large changes in source-drain current upon exposing the gate region to various polar liquids, including block co-polymer solutions. The polar nature of some of these polymer chains lead to a change of surface charges in gate region on the HEMT, producing a change in surface potential at the semiconductor/liquid interface. The nitride sensors appear to be promising for a wide range of chemicals, combustion gases and liquids.     

Etch damage characteristics of TiO2 thin films by capacitively coupled RF Ar plasmas

Etch damage of TiO₂ thin films with the anatase phase by capacitively coupled RF Ar plasmas has been investigated. The plasma etching causes a mixed phase of anatase and rutile or the rutile phase. The effect of Ar plasma etching damage on degenerating TiO₂ thin films is dependent on gas pressure and etching time. The physical etching effect at a low gas pressure (1.3 Pa) contributes to the degradation: the atomic O concentration at the thin film surface is strongly increased. At a high gas pressure (13-27 Pa) and long etching time (60 min), there are a variety of surface defects or pits, which seem to be similar to those for GaN resulting from synergy effect between particle and UV radiation from the plasmas. For the hydrophilicity, the thin film etched at the high gas pressure and a short etching time (5 min) seems to have no etch damage: its contact angle property is almost similar to that for the as-grown thin film, and is independent of the black light irradiation. This result would probably result from formation of donor-like surface defects such as oxygen vacancy.     

Characteristics of 4H-SiC Pt-gate metal-semiconductor field-effect transistor for use at high temperatures

The 4H-SiC Pt recessed gate metal-semiconductor field-effect transistor (MESFET) was fabricated by reactive ion etching (RIE) for device isolation. The device exhibited a pinch-off voltage of − 9 V, transconductance (g_m) of 19.2 mS/mm, and gate breakdown voltage of − 115 V at room temperature. The characteristics of this MESFET were investigated at high temperatures. It was shown that the MESFET can operate at 560 °C. The time dependence of the I_DS of a MESFET was also investigated at 400 °C in an Ar atmosphere. The change of I_DS (V_G = 0 V) was less than 5%, for the duration of 200 h.     

Reactive ion etching of ZnS films for thin-film electroluminescent devices

Reactive ion etching (RIE), employing CH₄/H₂/Ar plasmas, of ZnS films grown by metalorganic chemical vapor deposition (MOCVD) is reported. The etching rates are investigated as functions of the plasma parameters: pressure, RF power and relative composition of reactive gases. It is found that the amount of CH₄ in a CH₄/H₂/Ar gas discharge will decide whether the polymer will be produced. The optimum composition of the mixed gas is 1CH₄/7H₂/4Ar, when the pressure, RF power and total flow rate are 30 mTorr, 245 W and 30 sccm, respectively. The etching mechanism is also proposed. The quality of the etched surfaces under these conditions is examined by X-ray photoelectron spectroscopy. It is found that the amount of overt damage is small under these etching conditions. A dot-matrix thin-film electroluminescent device employing a ZnS:Mn phosphor layer is also fabricated by this etching process.     

Deep etch-induced damage during ion-assisted chemical etching of sputtered indium-zinc-oxide films in Ar/CH4/H2 plasmas

Plasma etch damage to sputtered indium-zinc-oxide (IZO) layers in the form of changes in the film stoichiometry was investigated using Auger Electron Spectroscopy (AES). While damage resulting from pure chemical etching processes is usually constrained to the surface vicinity, ion-assisted chemical etching of IZO in Ar/CH₄/H₂ plasmas produces a Zn-rich layer, whose thickness (∼ 50 nm) is well-above the expected stopping range of Ar ions in IZO (∼ 1.5 nm). Based on AES depth profiles as a function of plasma exposure time, it is concluded that the observed Zn enrichment and In depletion deep into the IZO film are driven by the implantation of hydrogen atoms.