第六讲-湿法腐蚀ppt课件.ppt

第六讲 湿法腐蚀/刻蚀outline Si-Anisotropic -KOH, TMAH, EPW-Isotropic-HNA SiO2-Glass, PSG-Isotropic-HF, BHF Si3N4-Isotropic-Boiled H3PO4 ExampleSilicon Etching (Anisotropic) KOH EPW TMAHKOH etching Relationship between etching rate and temperature? Relationship between etching rate and concentration? Selectivity of KOH etching? Whats corner compensation? Etching stop method?KOH etching Relationship between etching rate and temperature? Relationship between etching rate and concentration? Selectivity of KOH etching? Whats corner compensation? Etching stop method?KOH etching Relationship between etching rate and temperature? Relationship between etching rate and concentration? Selectivity of KOH etching? Whats corner compensation? Etching stop method?通常111面腐蚀速率最慢，与100比可达400：1KOH etching Relationship between etching rate and temperature? Relationship between etching rate and concentration? Selectivity of KOH etching? Whats corner compensation? Etching stop method?KOH etching Relationship between etching rate and temperature? Relationship between etching rate and concentration? Selectivity of KOH etching? Whats corner compensation? Etching stop method?Etch Stops Often, it is required that one etch a region of silicon and stop on a well defined “etch-stop” that then stops the etch abruptly. There are several etch stop techniques, including concentration-dependent, electrochemical, and dielectric. These etch stops allow one to control the thickness of a microstructure accurately ( R(110) R(111)Etch ratio (100)/(111) = 35Etch masks: SiO2 0.2 nm/min, Si3N4 0.1 nm/minBoron doped etch stop, 50 slowerCarcinogenic, corrosiveIs there safe alternative?Silicon Etching (Anisotropic) KOH EPW TMAHTMAHTMAH, Tetramethyl ammonium hydroxide, 10-40 wt.% (90C) Etch rate (100) = 0.5-1.5 m/min Al safe, IC compatible (PH value related, 13 to 12, 1um/min to 1nm/min) Etch ratio (100)/(111) = 10-35 Etch masks: SiO2 , Si3N4 0.05-0.25 nm/min Boron doped etch stop, up to 40 slowerASE Issues Choosing a method Desired shapes Etch depth and uniformity1 Surface roughness Process compatibility Safety, cost, availability Etch rate variation due to wet etch set-up Loss of reactive species through consumption Evaporation of liquids (concentration change) Poor mixing (etch product blocks diffusion of reactants) Contamination Applied potentialoutline Si-Anisotropic -KOH, TMAH, EPW-Isotropic-HNA SiO2-Glass, PSG-Isotropic-HF, BHF Si3N4-Isotropic-Boiled H3PO4 ExampleISE ApplicationsCreating structures with round surfacesThinning/Removing silicon wafersSiICsIsotropically-EtchedDiaphragmReleasedShellsBoron DopedSi substrateEtch Si using HNA and a nitride maskBoron dope shells to desired depthRelease shells in EDP/KOHlEtch has to be timed, no self stoplHard to control, non-uniformlNot reproducibleHNA (HF+HNO3+Acetic Acid(HAC) Creating structures with round surfaces Thinning/Removing silicon wafers 去除表面损伤 清洗炉管湿法腐蚀工艺反应过程：Si+2h+Si2+Si2+ + 2OH-Si（OH）2氢被释放形成SiO2HF溶解SiO2形成水溶液H2SiF6Si+HNO3+6HF=H2SiF6+H2NO2+H2O+H2HNO3+H2O=2H2NO2+2OH-+2h+湿法腐蚀工艺H2O、HAC的作用：稀释剂或缓冲剂HAC的作用是控制HNO3的溶解度，在使用时间内使氧化速率保持常数（h+的固容度一定）湿法腐蚀工艺不同组分对腐蚀速率的影响： HF高、HNO3低 腐蚀速率由HNO3浓度控制 开始阶段困难，易变，在一定周期内硅表面缓慢生长氧化层，腐蚀受氧化-还原反应控制，趋于依赖晶向 HF低、HNO3高： 腐蚀速率受HF溶解形成的SiO2的速率控制 反应有自钝化特点，表面覆盖SiO2（3050A） 基本限制来自去除硅的复合物 腐蚀各向同性、抛光作用湿法腐蚀工艺 HF：HNO3=1：1与稀释剂有关 稀释剂低于10%，对其不敏感 稀释剂10%30%，随稀释剂速率增加降低 稀释剂高于30%，微小的浓度变化导致腐蚀速率很大变化 多种比例可供选择，用于腐蚀硅 HF溶液对硅也有溶解作用，但速率很慢，小于1A/Min湿法腐蚀工艺室温下HNA对硅的常用腐蚀剂湿法腐蚀工艺outline Si-Anisotropic -KOH, TMAH, EPW-Isotropic-HNA SiO2-Glass, PSG-Isotropic-HF, BHF Si3N4-Isotropic-Boiled H3PO4 ExampleSiO2 etching HF HF vapor BHFoutline Si-Anisotropic -KOH, TMAH, EPW-Isotropic-HNA SiO2-Glass, PSG-Isotropic-HF, BHF Si3N4-Isotropic-Boiled H3PO4 ExampleSi3N4 etching Si3N4：HF，H3PO4（180度）湿法腐蚀工艺对其它材料的腐蚀剂：Al；H3PO4（40度），其它酸Ti：HF，BHFTiSi：HF， BHFCoSi2：HF（慢）Au：KI？，王水小结湿法腐蚀工艺湿法腐蚀是最早应用于IC 和MEMS的技术1970各向同性腐蚀各方向上有相同的腐蚀速率 HNA：HF+HNO3+H2O +HAC（CH3COOH）各向异性腐蚀腐蚀速率依赖于单晶晶向 KOH+肼（联胺） 乙二胺+邻苯二酚（EDP） 通常腐蚀是在有掩膜条件下进行，或结合自停止腐蚀技术完成，以获得所需图形湿法腐蚀工艺机理：电化学反应（氧化还原反应） 硅片表面存在微观的阴极、阳极； 在阳极发生氧化，阴极还原腐蚀机理 空穴到达半导体表面；Si+2h+Si2+ 吸附来自水中的OH-： Si2+ + 2OH-Si（OH）2 Si（OH）2与溶液中的络和剂反应 副产物在腐蚀剂中溶解湿法腐蚀工艺对腐蚀速率的影响： 反应速率限制：腐蚀速率受制于化学反应速率 扩散限制：腐蚀速率受制于反应剂的输运 通过液体到达或离开表面 反应速率限制条件下： 工艺与反应温度、反应剂比率关系密切 扩散限制下：激活能较低（通常几KJ/mol） 对反应温度不敏感 溶液搅拌十分重要提高到达表面的反应剂浓度 提高反应速率 稳定反应速率 均匀反应速率湿法腐蚀工艺 到达表面的少子数的限制： 限制腐蚀反应中的溶解速率，使电子或空穴耗尽 光照、加电可产生电子空穴对提高腐蚀速率 其它影响： 晶向、半导体类型、搀杂浓度、晶格缺陷等 腐蚀的方向性：同性、异性、晶向。