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1、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
2、? 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 betwe
3、en 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400：1,KOH etching,Relationship between etching rate and temperature? Relationship between etching rate and concentrati
4、on? 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 requ
5、ired 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 accurat
6、ely (1m), and have very uniform and reproducible characteristics,Etch Stops,控制时间 控制掺杂浓度,浓硼掺杂自停止腐蚀技术：KOH、EPW腐蚀，在掺杂浓度小于阈值时，腐蚀速率为常数，大于阈值时，腐蚀速率急剧降低重掺杂导致腐蚀停止。,湿法腐蚀工艺,理论模型：三种,应变模型重掺杂应力使表面SiO2生长速率超过腐蚀速率 复合模型硅表面高浓度空穴存在使氧化反应中产生的电子复合，还原反应因为缺少电子减慢，腐蚀速率降低 电化学模型利用能带理论解释。,缺点：应力大，压阻系数突变，IC不兼容,解决办法: PN结自停止,电钝化,装置：,
7、工作电极（WE）： 接硅 辅助电极（CE）： 腐蚀液中（Pt） 参考电极（RE）： 测硅的电势，（SCE饱和甘汞电极）,IV曲线反应了不同材料、导电类型的普遍特征（Vocp：开路电势；Vpp：钝化势）,电钝化,电钝化腐蚀机制：腐蚀反应分三个区,A区：Vocp附近把Si开始转化为硅复合物Si(OH)22+和H2，无电荷转移，电流为零 B区：VPP附近，开始钝化，电流减小 C区：VOFP附近，氧化物形成，电流迅速接近于零,电钝化,相关参数的影响：晶向、掺杂浓度、温度、腐蚀液配比,光照的影响：产生电子空穴对 N型：Vpp降低，Vocp不变； P型： Vpp降低，Vocp向正方向飘移 尽量避免光照,利
8、用电钝化可以进行停止控制，问题是？,PN结自停止腐蚀,PN结自停止腐蚀：P衬底生长N外延层（结构层） SiO2，SiN掩膜，恒压源加在N区和CE之间，电压略大于Vpp,N区接正极，PN结反偏，电压落在结上，P衬底被正常腐蚀；P衬底被腐蚀掉后，PN结被破坏，外加电压加在N与腐蚀液间，且大于N型硅的钝化势，N型硅被钝化，腐蚀停止,三极系统,N型外延层对腐蚀液电位难于精确控制，影响N层厚度均匀性。需增加参考电极（RE）三极系统 但P型区电位由于缺陷等原因导致短路，引起边界电流，钝化P区。即使理想的PN结也会因双极效应使腐蚀停在离PN结界面几微米处,四电极系统精度可到0.2微米,适当恒压源加在衬底，使
9、腐蚀电势处于P区的Vocp附近 Ve使PN结反偏，外延层电位略大于N区的钝化势Vpp,四极系统,Dielectric Etch Stop,Silicon-On-Insulator (SOI) wafers are becoming and abundant because of their use in IC manufacturing.1 The Si on the insulator (which is usually a silicon dioxide) can be either single-crystal, or polycrystalline The silicon oxide
10、acts as an excellent etch stop because it does not etch appreciably in etchant like KOH or EDP. The thickness of the silicon on top of the insulator can be controlled very accurately with better than 5% uniformity. SOI wafers are typically much more expensive than standard Si wafers.,Silicon Etching
11、 (Anisotropic),KOH EPW TMAH,EDP/EPW湿法腐蚀系统,EPW腐蚀系统：乙二胺（NH2（CH2）2NH2） E 邻苯二酚（C6H2（OH）2） P 水 W,电离反应 ： NH2（CH2）2NH2+H2ONH2（CH2）2NH3+（OH)- 氧化还原：Si+2 (OH)- +4H2OSi(OH)62-+2H2 络合过程： Si(OH)62-+ C6H2（OH）2Si(C6H4O2)32-+6H2O,Ethylene Diamine, Pyrochatechol, Water,EPW反应装置,反应温度：115度，低温下将在硅表面产生不可溶解的残留物，使表面粗糙 带回流：
12、防蒸发 带搅拌,EDP(EPW) (115C) Etch rate (100) = 0.75 m/min Al may be etched R(100) 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,TMA
13、H, 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 slower,ASE Issues,Choosing a method Des
14、ired 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) Con
15、tamination 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,Etch has to be timed, no self stop Hard to control
16、, non-uniform Not reproducible,HNA (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SiO2 HF溶解SiO2形成水溶液H2SiF6,Si+HNO3+6HF=H2SiF6+H2NO2+H2O+H2,HNO3+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
