TMAH+Triton中Si湿法腐蚀机理研究现状

在微机电系统(MEMS)领域硅各向异性湿法腐蚀是制作许多元器件的一项重要技术,加入非离子型表面活性剂的腐蚀液可以在硅基片上制作出各种形状,但是对于真正的腐蚀机理还有待进一步研究。介绍了硅湿法腐蚀机理的研究现状,通过不同腐蚀条件下得出的不同腐蚀结果分析其腐蚀机理。介绍了当非离子型表面活性剂加入碱性溶液时固体表面的活性剂吸附层结构,重点介绍了表面活性剂Triton X-100加入各向异性碱性腐蚀剂四甲基氢氧化铵(TMAH)后对活性剂吸附状态和硅腐蚀速率产生影响的根本原因。不同晶向硅表面的H基和OH基数量会影响其表面活性剂的吸附能力,硅在纯TMAH腐蚀液和加入活性剂Triton后的TMAH腐蚀液中的腐蚀速率存在一定差异,高质量分数的TMAH下加入不同体积分数的Triton时,不同晶面在活性剂吸附和腐蚀速率上也存在不同,给出了出现这些现象的机理分析。研究硅腐蚀机理可以为器件设计提供有效的理论支持,有助于制作更多新的MEMS结构。     

碘过饱和KOH溶液对硅(110)晶面腐蚀的改善

将非金属元素碘作为硅的KOH腐蚀液的添加物,在对(100)和(110)单晶硅片的各向异性腐蚀中,获得了更为丰富的异向腐蚀特性和更为光滑的腐蚀表面。当温度在95℃,KOH腐蚀液中碘的摩尔比为0.5时,得到了粗糙度均小于10nm的Si-(100)和(110)光洁表面,两晶面的腐蚀速率均为1.4μm/min。这两晶面在相同的条件下同时达到最佳光洁度,说明腐蚀速率是获得高光洁度表面的关键。实验还证明碘在热碱溶液中的稳定性和持久性要高于现在已被大量研究的双氧水和过硫等,尤其是对硅(110)表面光洁度的改善具有积极的促进作用。     

用于高灵敏度红外探测器的超薄硅膜的研制

超薄、平整的硅膜对于制作高灵敏度红外探测器是非常重要的。这种超薄硅膜的各向异性腐蚀技术，包括有机溶液EPW和无机溶液KoH及KoH IPA(异丙醇)。从腐蚀速率、腐蚀表面质量、腐蚀停特性、腐蚀边缘形貌及腐蚀工艺的角度分析比较了两种腐蚀系统，分别制作出了约1μm厚的平整超薄硅膜，并研究了不同掩膜材料在腐蚀液中的抗蚀性，为高灵敏度红外探测器的制作奠定了工艺基础。     

一种新的铝和铝-铜-硅的干法腐蚀技术

本文介绍一种新的干腐蚀技术,即铝的“反应掩蔽溅射腐蚀”技术。这种工艺技术可刻蚀微细线条的铝和铝-铜-硅合金膜图形,没有目前通用的反应溅射腐蚀方法存在的许多麻烦问题。这种技术把淀积和腐蚀包含在一个工艺过程之中,在三氧化二铝、铝和铝-铜-硅合金被腐蚀的同时,所有其他材料表面却被涂敷上一层SiOx膜。这在本质上产生特别大(铝/掩模和铝/衬底)的腐蚀速率比。此外,腐蚀气体不含有通常会产生浸蚀和钻蚀现象的氯。事实上,这种腐蚀技术兼有反应溅射腐蚀和非反应溅射腐蚀的优点。本文介绍的腐蚀气体是四氟化硅/氧混合气体。研究结果表明,大多数添加的杂质气体对腐蚀的影响非常小。但是,添加水或氢气则可明显地影响腐蚀特性。文章示出了用光致抗蚀剂作掩蔽层采用四氟化硅/氧/氢混合气体进行反应掩蔽溅射腐蚀的典型腐蚀剖面。     

激光直接金属沉积316L不锈钢表面粘粉工艺研究

为了探究激光直接金属沉积316L不锈钢的表面粉末粘附工艺规律, 利用高速摄像机分析粉末粘附类型, 采用单因素试验的方法, 定量研究了单道多层沉积中的送粉速率、送粉气流量和线能量密度对粉末粘附的影响规律。结果表明, 粉末粘附主要包括熔池熔液逸出和未熔粉末粘附两种类型; 随着送粉速率的增加和送粉气流量的减小, 薄壁件侧表面粉末粘附程度增加, 而粉末粘附程度则对激光线能量密度的变化不敏感; 激光功率700W、扫描速率700mm/min、送粉量13.54g/min、送粉气流量14L/min、离焦量+22mm时, 激光直接金属沉积薄壁件表面粉末粘附较少。研究结果能够成为改善316L不锈钢增材制件表面质量的重要依据。     

硅各向异性浅槽腐蚀实验研究

通过实验分析,对比了异丙醇(IPA)和超声波对Si(100)面在KOH溶液和四甲基氢氧化氨(TMAH)溶液中的浅槽腐蚀速率及其表面形态的影响。实验结果表明,IPA能降低TMAH溶液的腐蚀速率,但IPA在KOH溶液中腐蚀速率降低不明显;IPA加入到较高浓度的KOH溶液中,会在Si表面产生较大小丘,恶化了Si腐蚀表面的质量,但在TMAH溶液中加入一定量的IPA会改善腐蚀表面的质量;超声波能加快腐蚀速率并能改善Si腐蚀表面质量,但对于加入IPA的较高浓度KOH溶液,超声波未能消除Si腐蚀表面的小丘,另外,超声波还能减弱腐蚀过程中微尺寸沟槽的尺寸效应;在腐蚀条件和配比一定情况下,TMAH溶液的腐蚀质量比KOH溶液好。     

用于X射线闪烁屏的硅微通道阵列整形技术

为制备用于X射线闪烁屏的高开口面积比硅微通道阵列,研究了四甲基氢氧化铵(TMAH)溶液温度和质量分数对硅(100)晶面和(110)晶面腐蚀速率的影响.通过金相显微镜观测硅微通道端面尺寸并计算腐蚀速率,分析了硅(100)晶面和(110)晶面腐蚀速率比对硅微通道阵列孔形的影响,探讨了TMAH溶液温度和质量分数与硅微通道阵列开口面积比的关系.研究表明,硅(100)晶面和(110)晶面的腐蚀速率比是影响硅微通道阵列开口面积比的主要因素.当硅(100)晶面与(110)晶面腐蚀速率比大于√2时,得到具有高开口面积比的正方形硅微通道阵列.使用质量分数为1％的TMAH溶液在40℃的溶液温度下,制备出开口面积比大于81％的正方形硅微通道阵列.通过高温填充CsI (TI)制备出基于硅微通道的X射线闪烁屏,X射线成像结果表明通道整形技术有助于提高闪烁屏的性能.     

在等离子腐蚀中的一种新的钻蚀现象

硅和硅介质膜的腐蚀是在硅衬底表面上形成精细图形的一种基本技术。本文的目的是报导在硅、硅介质膜和铬膜气体等离子腐蚀时所观察到的一种新的腐蚀方法。众所周知,钻蚀现象是由于采用溶液的通常湿化学腐蚀方法的一种固有现象,因为腐蚀是以中心位于光致抗蚀剂的边缘按两维的正向推进。因此,当光致抗蚀剂掩模图形宽度和腐蚀的图形宽度分别定为 W_1和 W_2时,钻蚀的量△W=(W_1—W_2)/2在通常湿化学腐蚀方法的情况下总是正的。氟利昂—14气体等离子可以腐蚀硅和硅介质膜,同时腐蚀速率按下列次序:多晶     

含添加剂的各向异性腐蚀液中实现小掩膜下高硅尖的腐蚀

各向异性KOH溶液腐蚀硅尖具有简单、易于实现、成本低廉、(100)晶面腐蚀速率均匀等优点.然而在40%KOH溶液中削角速率和(100)晶面的腐蚀速率之比约为1.6~1.9,并且该比值随着KOH浓度的减小而增大.如此高的削角速率会给AFM探针的制作带来技术上的困难.而对腐蚀场发射器件和隧道式传感器的硅尖阵列来说,高的削角速率会减少单位面积内的硅尖数量.本文通过在氢氧化钾(KOH)或者四甲基氢氧化胺(TMAH)溶液中添加适当的添加剂(如异丙醇(IPA)、1,5戊二醇或碘)降低了削角速率,在较小直径的掩膜下腐蚀出高硅尖.实验结果还表明:在TMAH基腐蚀液中每个硅尖的八个快腐蚀面的削角速率几乎相等,硅尖直径偏差较KOH溶液中腐蚀的硅尖直径偏差更小,因此成品率得到了提高.     

四甲基氢氧化铵在MEMS中的应用

通过各向异性腐蚀硅杯实验,研究了四甲基氢氧化铵（TMAH）腐蚀液的特性,包括硅（100）面腐蚀速率与溶液浓度、温度的关系,不同腐蚀条件下硅杯的表面状况,并确定了制作硅杯的最佳工艺条件。通过测试硅杯结构多晶硅压力传感器的输出特性,证明了TMAH确实是一种性能优良的各向异性腐蚀剂。     

过硫酸铵在TMAH体硅刻蚀中的作用

为了提高低浓度下四甲基氢氧化铵(TMAH)体硅刻蚀的质量,通过对质量分数为5%的TMAH进行研究,发现合适的过硫酸铵(AP)添加方式和添加量能够在不降低刻蚀速率的条件下提高体硅刻蚀质量。通过SEM,EDS和XRD对AP的作用机理进行深入分析,发现加入AP能使刻蚀底面生成"伪掩膜",并确定其成分为低温石英晶体。这些"伪掩膜"能够选择性地覆盖于刻蚀底面金字塔小丘的交界区域,使刻蚀底面相对凹陷的部分被保护,而金字塔顶相对凸出的部分则被刻蚀,从而在宏观上达到了降低粗糙度的效果。在此基础上得到了"两步法"的优化刻蚀工艺,结合该工艺已成功制备出深度485μm,平均刻蚀速率1.01μm/min,底面粗糙度仅为0.278μm硅杯微结构。     

恒温磁力搅拌下KOH刻蚀Si的研究

采用恒温磁力搅拌的方法,在KOH溶液中湿法刻蚀Si。在掩模层为SiO2时,研究了刻蚀速率随KOH浓度与温度的变化关系。结果表明:在110℃、30%的KOH溶液下,刻蚀Si(100)可以得到4.0μm/min的刻蚀速率,Si(100):SiO2的刻蚀速率比为550:1,Si(100):Si(111)的刻蚀速率比为90:1,而且可以得到光滑的刻蚀表面与形状。     

基于多孔硅牺牲层技术的压阻式加速度传感器的分析和设计

分析并设计了一种利用高选择自停止的多孔硅牺牲层技术制作压阻式加速度传感器的工艺,并利用外延单晶硅作为传感器的结构材料,这种工艺能精确地控制微结构的尺寸.利用多孔硅作牺牲层工艺,使用加入硅粉和(NH4 ) 2 S2 O8的TMAH溶液通过在薄膜上制作的小孔释放多孔硅,能很好地保护未被覆盖的铝线.该工艺和标准的CMOS工艺完全兼容.     

Study of electrochemical etch-stop for high-precision thickness control of single-crystal Si in aqueous TMAH : IPA : pyrazine solutions

In this paper, we describe a method of controlling the thickness of single-crystal Si membranes, fabricated by wet anisotropic etching in aqueous tetramethyl ammonium hydroxide (TMAH) : isopropyl alcohol (IPA) : pyrazine solutions. The Si surface of the etch-stopped microdiaphragm is extremely flat with no noticeable taper or nonuniformity. The benefits of the electrochemical etch-stop method for the etching of n epilayer-embedded p-type single-crystal Si(0 0 1) wafers in aqueous TMAH became apparent when the reproducibility of the microdiaphragm’s thickness in mass production was realized. The results indicated that the use of the electrochemical etch-stop method for the etching of Si in aqueous TMAH provided a powerful and versatile alternative process for the fabrication of high-yield Si microdiaphragms (20 ± 0.26 μm s.d). With etch-stop, the pressure sensitivity of devices fabricated on the same wafer can be controlled to within ±2.3% s.d.     

基于多孔硅牺牲层技术的压阻式加速度传感器的分析和设计

分析并设计了一种利用高选择自停止的多孔硅牺牲层技术制作压阻式加速度传感器的工艺,并利用外延单晶硅作为传感器的结构材料,这种工艺能精确地控制微结构的尺寸.利用多孔硅作牺牲层工艺,使用加入硅粉和(NH4)2S2O8的TMAH溶液通过在薄膜上制作的小孔释放多孔硅,能很好地保护未被覆盖的铝线.该工艺和标准的CMOS工艺完全兼容.     

Etch characteristics of KOH, TMAH and dual doped TMAH for bulk micromachining of silicon

High precision bulk micromachining of silicon is a key process step to shape spatial structures for fabricating different type of microsensors and microactuators. A series of etching experiments have been carried out using KOH, TMAH and dual doped TMAH at different etchant concentrations and temperatures wherein silicon, silicon dioxide and aluminum etch rates together with <100> silicon surface morphology and <111>/<100> etch rate ratio have been investigated in each etchant. A comparative study of the etch rates and etched silicon surface roughness at different etching ambient is also presented.From the experimental studies, it is found that etch rates vary with variation of etching ambient. The concentrations that maximize silicon etch rate is 3% for TMAH and 22 wt.% for KOH. Aluminum etch rate is high in KOH and undoped TMAH but negligible in dual doped TMAH. Silicon dioxide etch rate is higher in KOH than in TMAH and dual doped TMAH solutions. The <111>/<100> etch rate ratio is highest in TMAH compared to the other two etchants whereas smoothest etched silicon surface is achieved using dual doped TMAH. The study reveals that dual doped TMAH solution is a very attractive CMOS compatible silicon etchant for commercial MEMS fabrication which has superior characteristics compared to other silicon etchants.     

Effects of differential etching and masking resist preparation on the quality of the reactive-ion-etched aluminum and aluminum alloys

The conventional method used for aluminum (Al) and aluminum alloy (Al + Si, Al + Si + Cu) delineation in integrated circuits is mainly by wet chemical etching. Because of its isotropic characteristic, wet chemical etching becomes inadequate for patterning Al metal lines with linewidths narrower than about 4 Μm. In this work, Al and Al alloys (Al + 2% Si; Al + 1% Si + 1% Cu) were reactively etched in SiCl₄ plasma using patterned photoresist as the etch-mask. Resist patterns were generated either by conventional processing methods or by tri-level resist techniques which included hard-baking (200°C, ≤ 30 min), and two consecutive reactive ion etchings in CF₄ and 0₂ plasmas. Masking resists prepared by the tri-level resist technique retained their integrity during exposure to a SiCl₄ plasma, and significantly improved resolution and fidelity of pattern transfer from resist to underlying Al or Al alloy film. The substrate surface of the reactively etched Al + Si + Cu sample was considerably rougher than that of the Al or Al + Si sample due to the high concentration of Cu accumulated at the metal/substrate region during RIE process.     

Bulk micromachining of silicon in TMAH-based etchants for aluminum passivation and smooth surface

The fabrication of silicon based micromechanical sensors often requires bulk silicon etching after aluminum metallization. All wet silicon etchants including ordinary undoped tetramethyl ammonium hydroxide (TMAH)-water solution attack the overlaying aluminum metal interconnect during the anisotropic etching of (100) silicon. This paper presents a TMAH-water based etching recipe to achieve high silicon etch rate, a smooth etched surface and almost total protection of the exposed aluminum metallization. The etch rate measurements of (100) silicon, silicon dioxide and aluminum along with the morphology studies of etched surfaces are performed on both n-type and p-type silicon wafers at different concentrations (2, 5, 10 and 15%) for undoped TMAH treated at various temperatures as well as for TMAH solution doped separately and simultaneously with silicic acid and ammonium peroxodisulphate (AP). It is established through a detailed study that 5% TMAH-water solution dual doped with 38 gm/l silicic acid and 7 gm/l AP yields a reasonably high (100) silicon etch rate of 70 μm/h at 80 °C, very small etch rates of SiO₂ and pure aluminum (around 80 Å/h and 50 Å/h, respectively), and a smooth surface (±7 nm) at a bath temperature of 80 °C. The etchant has been successfully used for fabricating several MEMS structures like piezoresistive accelerometer, vaporizing liquid micro-thruster and flow sensor. In all cases, the bulk micromachining is carried out after the formation of aluminum interconnects which is found to remain unaffected during the prolonged etching process at 80 °C. The TMAH based etchant may be attractive in industry due to its compatibility with standard CMOS process.     

Reactive sputter etching of Al in BCl3

Etching of Al is studied in pure BCl₃ as well as in mixtures with other gases in the reactive sputter etching mode in a cryopumped system. Etch rate, selectivity with respect to positive photoresist, SiO₂ and Si and etch profiles are investigated as a function of gas composition, gas pressure, flow rate and plasma power. Plasma chemical processes are monitored by quadrupole mass spectroscopy as well as by optical emission spectroscopy. Perfectly square Al-profiles can be etched if etch rates are kept below 1000 A/min. Al-patterns running over steep steps can also be clearly defined if a certain amount of overetching can be tolerated. The experimental data indicate that the etch process is reactant supply limited. Anisotropic etching is achieved by either a ‘surface inhibitor mechanism’ or the formation of a sidewall protecting film.     

Modeling magnetically enhanced RIE of aluminum alloy films usingneural networks

Aluminum (Al) and its alloy films are widely used for fabricating VLSI interconnections. The discharge behavior of a magnetically enhanced reactive ion etching (MERIE) of Al(Si) has been modeled using neural networks. A 2^6-1 fractional factorial experiment was employed to characterize etch variations with RF power, pressure, magnetic field and gas mixtures of Cl₂, BCl₃, and N₂. Responses of an Al(Si) film etched in a chlorine-based plasma include etch rate, selectivity to oxide, anisotropy and bias of critical dimension (CD). The generalization accuracy of the models, measured by the root-mean squared error (RMS) on a test set, are 285 Å/min for etch rate, 5.58 for oxide selectivity, 0.08 for anisotropy, and 3.82 Å/min for CD bias. Al(Si) etch rate was found to be chlorine-dependent with significantly affected by magnetic field variations. For the other etch responses, RF power was dominant. Gas additives such as BCl₃ and N₂ were seen to have conflicting effects on etch outputs. Predicted Al(Si) etch behaviors from neural process models were in qualitative good agreement with reported experimental results