第六讲-湿法腐蚀课件.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,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,Example,Silicon Etching(Anisotropic),KOH,EPW,TMAH,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?,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?,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)=35,Etch masks:SiO2 0.2 nm/min,Si3N4 0.1 nm/min,Boron doped etch stop,50 slower,Carcinogenic,corrosive,Is there safe alternative?,Silicon Etching(Anisotropic),KOH,EPW,TMAH,TMAH,TMAH,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:SiO,2,Si,3,N,4,0.05-0.25 nm/min,Boron doped etch stop,up to 40 slower,ASE Issues,Choosing a method,Desired shapes,Etch depth and uniformity,1,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 potential,outline,Si,-Anisotropic,-KOH,TMAH,EPW,-Isotropic,-HNA,SiO2-Glass,PSG,-Isotropic,-HF,BHF,Si3N4,-Isotropic,-Boiled H3PO4,Example,ISE Applications,Creating structures with round surfaces,Thinning/Removing silicon wafers,Si,ICs,Isotropically-Etched,Diaphragm,Released,Shells,Boron Doped,Si substrate,Etch Si using HNA and a nitride mask,Boron dope shells to desired depth,Release shells in EDP/KOH,Etch has to be timed,no self stop,Hard to control,non-uniform,Not reproducible,HNA(,H,F+H,N,O3+,A,cetic 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,+,Si,2+,Si,2+,+,2OH,-,Si（OH）,2,氢被释放形成SiO,2,HF溶解SiO,2,形成水溶液H,2,SiF,6,Si+HNO,3,+6HF=H,2,SiF,6,+H,2,NO,2,+H,2,O+,H,2,HNO,3,+H,2,O=2H,2,NO,2,+,2OH,-,+,2h,+,湿法腐蚀工艺,H,2,O、HAC的作用：稀释剂或缓冲剂,HAC的作用是控制HNO,3,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、,HNO,3,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、,HNO,3,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,Example,SiO,2,etching,HF,HF vapor,BHF,outline,Si,-Anisotropic,-KOH,TMAH,EPW,-Isotropic,-HNA,SiO2-Glass,PSG,-Isotropic,-HF,BHF,Si3N4,-Isotropic,-Boiled H3PO4,Example,Si,3,N,4,etching,Si,3,N,4,：HF，,H,3,PO,4,（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，BHF,TiSi：HF，BHF,CoSi,2,：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,+,Si,2+,吸附来自水中的OH,-,：,Si,2+,+,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,