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。     

高性能高温压力传感器

研究了决定多晶硅压力传感器性能的两项关键技术：各向异性腐蚀硅杯和温度自补偿。通过研 究四甲基氢氧化铵（ＴＭＡＨ）腐蚀液特性，及在不同腐蚀条件下硅杯表面状况，确定了制作高质量硅杯的工艺 条件。通过优化掺杂浓度，改善了传感器的温度特性，基本上实现自补偿。测试结果表明，多晶硅压力传感器 综合精度达０．ｌ％～０．２％ＦＳ，灵敏度温度系数绝对值小于３ × １０－４／℃，有广阔的应用前景。     

深硅杯湿法腐蚀中金属保护工艺研究

提出了一种新的采用聚酯胶膜保护金属图形的硅湿法腐蚀工艺,解决了深硅杯湿法腐蚀中金属保护难题,允许在器件完成所有IC工艺后再进行深硅杯湿法腐蚀。通过工艺试验研究,增加贴膜前的预处理和贴膜后的热压等工艺,能够有效延长掩膜的保护时间,在TMAH湿法腐蚀工艺条件下掩膜能够坚持6h,且成功实现了对硅280μm的深刻蚀。新工艺与IC工艺兼容,简单可靠,也能进行圆片级批量腐蚀。     

TMAH单晶硅腐蚀特性研究

TMAH是一种具有优良的腐蚀性能的各向异性腐蚀剂,选择性好,无毒且不污染环境,最重要的是TMAH与CMOS工艺相兼容,符合SOC的发展趋势。TMAH正逐渐替代KOH和其他腐蚀液,成为实现MEMS工艺中微三维结构的主要腐蚀剂。本文着重介绍了TMAH的特性、工艺条件及应用。     

无氨氮化硅薄膜在MEMS硅腐蚀中的应用

研究了等离子体增强化学汽相淀积(PECVD)生长的无氨氮化硅薄膜作为掩蔽层在MEMS硅腐蚀工艺中的应用。比较了PECVD不同工艺条件(衬底温度和功率)以及不同四甲基氢氧化铵(TMAH)硅腐蚀液温度对无氨氮化硅薄膜硅腐蚀掩蔽效果的影响。通过优化无氨氮化硅薄膜生长条件和硅腐蚀液温度,得到了高质量的氮化硅薄膜,颗粒以及针孔密度较少,0.2μm以上颗粒度小于100,提高了硅腐蚀掩蔽选择比。实验结果显示优化生长条件的氮化硅薄膜(衬底温度350℃,功率30 W),在85℃的TMAH硅腐蚀液中,硅的腐蚀速率为68μm/h,氮化硅薄膜腐蚀速率为33.2 nm/h,硅与氮化硅的腐蚀选择比为2 048,满足MEMS体硅腐蚀工艺对于掩膜特性的要求。     

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.     

Ar离子激光增强硅各向异性腐蚀速率的研究

研究了Ａｒ离子激光器与硅各向异性腐蚀技术相结合制造硅杯的方法。结果表明，激光照射能增强浸于ＫＯＨ溶液中硅的化学腐蚀速率，在入射光强为４．６Ｗ，ＫＯＨ溶液浓度为０．２２ｍｏｌ，温度为９０℃的条件下，得到＜１００＞硅的腐蚀速率为２１μｍ／ｍｉｎ，是无激光照射时硅各向异性腐蚀速率的多倍。进而讨论了硅在ＫＯＨ溶液中腐蚀速率对激光光强的依赖关系以及实验温度对腐蚀速率的影响问题。     

TMAH湿法腐蚀工艺制备微台面结构北大核心

针对目前四甲基氢氧化铵（TMAH）湿法腐蚀工艺制备微台面结构工艺可控性差、需要添加添加剂、溶液使用周期短及工艺维护繁琐、无法实现大尺寸晶圆工程化应用等问题,研究了无添加剂时,微台面的腐蚀形貌与TMAH溶液质量分数和循环速率之间的关系,提升了大尺寸晶圆凸角腐蚀尺寸的均匀性及表面质量,6英寸（1英寸=2.54 cm）硅晶圆内,凸角腐蚀尺寸不均匀性小于5%,台面高度不均匀性小于3%,且腔体底部平整光亮,腐蚀速率较快,实现了工程化应用。当TMAH溶液pH值为12.2-12.6时,微台面结构制备工艺稳定可控、维护简单,实现了高质量微台面结构的可批量化生产。     

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.     

元素半导体

Y99-61799-345 0007270微型光机系统用硅薄膜研究=An investigation of sill-COn thin membrances for MOMS[会,英]/Miiller,R.&Obreja,p.//Proceedings of 1998 International Semicon-ductor Conference,Vol.2.—345～348(UG)介绍了作为具有光探测器的压力传感器一部分的薄膜(小于10μm)制备的实验结果,以及其表面粗糙度研究成果。在不同温度和不同的 KOH 和 TMAH 溶液浓度情况下,实现了各向异性腐蚀。研究了作为腐蚀期间掩模材料的硅弹性体。参8     

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。     

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.     

MEMS工艺中TMAH湿法刻蚀的研究

TMAH具有刻硅速率高、晶向选择性好、低毒性和对CMOS工艺的兼容性好等优点，而成为MEMS工艺中常用的刻蚀剂。但TMAH在刻蚀过程中合形成表面小丘，影响表面光滑性。文章重点研究了MEMS工艺中的TMAH湿法刻蚀获得光滑刻蚀表面的工艺。实验结果表明，要获得理想的刻蚀效果，刻蚀液配方和刻蚀条件的选择是非常重要的因素，实验中也得到了一些与其它报道不同的数据。     

Texturization of mono-crystalline silicon solar cells in TMAH without the addition of surfactant

Etching was performed on(100) silicon wafers using silicon-dissolved tetramethylammonium hydroxide (TMAH) solutions without the addition of surfactant.Experiments were carried out in different TMAH concentrations at different temperatures for different etching times.The surface phenomena,etching rates,surface morphology and surface reflectance were analyzed.Experimental results show that the resulting surface covered with uniform pyramids can be realized with a small change in etching rates during the et...     

Texturization of mono-crystalline silicon solar cells in TMAH without the addition of surfactant

Texturization of mono-crystalline silicon solar cell by chemical anisotropic etching is still a key issue due to metal ions contamination and consumption of large amount of isopropyl alcohol (IPA) in a conventional mixture of potassium hydroxide (KOH) or sodium hydroxide (NaOH) and IPA. In this study, etching was performed on (100) silicon wafers using silicon-dissolved tetramethylammonium hydroxide (TMAH) solutions without addition of surfactant. Experiments were carried out in different TMAH concentration solutions at different temperatures for different etching time. The surface phenomena, etching rates, surface morphology and surface reflectance have been analyzed. Experimental results show that the resulted surface covered with uniform pyramids can be realized due to small changes of etching rates during the etching process. The etching mechanism has been explained basing on the experimental results and the theoretical considerations. It was suggested that all the components in the TMAH solutions play important roles in the etching process. Moreover, TMA+ ions may increase the wettability of the textured surface. A good textured surface can be obtained on conditions that the absorption of OH- /H2O is equilibrium with that of TMA+/SiO2(OH)22-.     

Effects of etching conditions on surface morphology of periodic inverted trapezoidal patterned Si(100) substrate

In this paper, the anisotropic etching process of Si(100) wafers in tetramethyl ammonium hydroxide (TMAH) solution with isopropyl alcohol (IPA) is investigated in detail. An inverted trapezoidal pattern is developed. A series of experiments are performed by changing TMAH concentration, IPA concentration, etching temperature and etching time. The structure of inverted trapezoidal patterns and roughness of the bottom surface are characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that with TMAH concentration increases, the roughness of bottom surface will decrease. The addition of IPA into TMAH solution improves the morphology of the bottom surface significantly. Low temperature is beneficial to get a smooth bottom surface. Furthermore, etching time can change the bottom surface roughness. A model is proposed to explain the etching processes. The hillock area ratio of the bottom surface has the same tendency as the etching area ratio. Finally, smooth silicon inverted trapezoidal patterns are obtained for epitaxial growth of GaN-based light emitting diode (LED) devices.     

Optical and electrical properties of porous silicon layer formed on the textured surface by electrochemical etching

Porous silicon(PS) layers were formed on textured crystalline silicon by electrochemical etching in HF-based electrolyte.Optical and electrical properties of the TMAH textured surfaces with PS formation are studied. Moreover,the influences of the initial structures and the anodizing time on the optical and electrical properties of the surfaces after PS formation are investigated.The results show that the TMAH textured surfaces with PS formation present a dramatic decrease in reflectance.The longer the anodizing time is,the lower the reflectance.Moreover,an initial surface with bigger pyramids achieved lower reflectance in a short wavelength range.A minimum reflectance of 3.86%at 460 nm is achieved for a short anodizing time of 2 min.Furthermore,the reflectance spectrum of the sample,which was etched in 3 vol.%TMAH for 25 min and then anodized for 20 min,is extremely flat and lies between 3.67%and 6.15%in the wavelength range from 400 to 1040 nm.In addition,for a short anodizing time,a slight increase in the effective carrier lifetime is observed.Our results indicate that PS layers formed on a TMAH textured surface for a short anodization treatment can be used as both broadband antireflection coatings and passivation layers for the application in solar cells.     

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.     

Applications of Inverted Pyramids Corroded by TMAH in PERL Silicon LED

In this paper,a novel and reliable structure of the side passivated emitter and the rear locally-diffused(PERL)silicon light emitting diodes(LEDs)is proposed.The inverted pyramids surface,the important interface in this structure,is given according to the experiment.The results show that the inverted pyramids surface has a low refection about 8%,in the anisotropic etching 70 ℃,5% TMAH concentration,corrosion time of 90 min or 30 min.Low refection means high light emitting rate.Most of the structure and manu...     

背照式CMOS图像传感器的硅减薄湿法刻蚀工艺

针对背照式CMOS图像传感器制作工艺,提出了一种采用氢氧化四甲基铵液进行湿法刻蚀的背部硅片减薄工艺。分析了硅减薄工艺的整体流程,针对化学机械研磨后的湿法刻蚀工艺进行了实验。通过调整反应时间、硅片转速、喷嘴速度和摆幅,得到最优刻蚀参数,使厚度均值达到目标值,平整度控制在一定范围内。该湿法刻蚀工艺中,首先对硅片表面形貌进行修正,接着对硅片进行整体刻蚀,达到目标厚度,最后通过减薄得到BSI背部硅片。采用该硅片制作的图像传感器的成像质量得到提高。