4MEMS工艺湿法腐蚀

MEMS工艺--腐蚀董海峰改编自美国西北大学ChangLiu教授《微机电系统》课程相关课件2012.10考核方式考核方式Þ课上关上手机Þ上课不出勤，必须提出具体意见纪律要求纪律要求Þ提出问题或发表评论(≤10个/人):每个满分5分Þ回答问题(≤10个/人):每个满分5分Þ问题、评论和回答重复得0分回顾*ThinFilmsImplantDiffusionEtchTest/SortPolishPhotoPatternedwafer腐蚀工艺•湿法腐蚀•干法腐蚀KOHetching•Relationshipbetweenetchingrateandtemperature?•Relationshipbetweenetchingrateandconcentration?•SelectivityofKOHetching?•Etchingstopmethod?KOHetching•Relationshipbetweenetchingrateandtemperature?•Relationshipbetweenetchingrateandconcentration?•SelectivityofKOHetching?•Etchingstopmethod?KOHetching•Relationshipbetweenetchingrateandtemperature?•Relationshipbetweenetchingrateandconcentration?•SelectivityofKOHetching?•Etchingstopmethod?KOHetching•Relationshipbetweenetchingrateandtemperature?•Relationshipbetweenetchingrateandconcentration?•SelectivityofKOHetching?•Etchingstopmethod?晶面的选择性通常{111}面腐蚀速率最慢，与{100}比可达400：1(100)Planeyz111(110)Planexyz111(111)PlaneFeaturesthatareallconvexKOHetching•Relationshipbetweenetchingrateandtemperature?•Relationshipbetweenetchingrateandconcentration?•SelectivityofKOHetching?•Etchingstopmethod?EtchStops•Often,itisrequiredthatoneetcharegionofsiliconandstoponawell-defined“etch-stop”thatthenstopstheetchabruptly.•Thereareseveraletchstoptechniques？•Theseetchstopsallowonetocontrolthethicknessofamicrostructureaccurately(1µm),andhaveveryuniformandreproduciblecharacteristics停止层技术（1）„控制时间停止层技术（2）--重掺杂„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。停止层技术（2）--重掺杂•浓硼自停止HeavilydopedHeavilydopedLightlydopedPN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停止层技术（3）--电钝化•Silicon-On-Insulator(SOI)wafersarebecomingandabundantbecauseoftheiruseinICmanufacturing•TheSiontheinsulator(whichisusuallyasilicondioxide)canbeeithersingle-crystal,orpolycrystalline•ThesiliconoxideactsasanexcellentetchstopbecauseitdoesnotetchappreciablyinetchantlikeKOHorEDP.•Thethicknessofthesiliconontopoftheinsulatorcanbecontrolledveryaccuratelywithbetterthan5%uniformity.•SOIwafersaretypicallymuchmoreexpensivethanstandardSiwafers.DielectricSingle-CrystalSi(SOI)DielectricPolycrystallineSi停止层技术（4）--介质停止层各向同性腐蚀•Creatingstructureswithroundsurfaces•Thinning/RemovingsiliconwafersSiIC’sIsotropically-EtchedDiaphragmReleasedShellsBoronDopedSisubstrateEtchSiusingHNAandanitridemaskBorondopeshellstodesireddepthReleaseshellsinEDP/KOHzEtchhastobetimed,noselfstopzHardtocontrol,non-uniformzNotreproducibleSiO2etching•HF•HFvapor•BHFSi3N4etching•Si3N4：HF，H3PO4（180度）其他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？，王水湿法腐蚀小结•可行性：可以腐蚀几乎所有材料！•速率：腐蚀温度和浓度对速率影响较大•选择性：腐蚀速率差异较大，可以方便地选择掩膜材料•方向：腐蚀基本为各向同性，某些腐蚀液有晶面选择性•其他：因为大部分器件的结构是硅材料，因此对硅的湿法腐蚀研究最多，包括自停止性的研究Microguitar–CornellUniversityIBMSuperconetipSandiaPhotoniclatticeStereoLithography!