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外文翻譯資料
單片集成MEMS技術(shù)
在過(guò)去的20年中，CMOS技術(shù)已成為集成電路主要制造工藝，制造成本下降的同時(shí)，成品率和產(chǎn)量也得到很大提高，COMS工藝將繼續(xù)以增加集成度和減小特制尺寸向前發(fā)展。當(dāng)今，CMOS集成工藝不僅被利用在集成電路設(shè)計(jì)上，而且，也被利用在很多微傳感器和微執(zhí)行器上，這樣可以把微傳感器與集成電路集成在一起，構(gòu)成功能強(qiáng)大的智能傳感器。隨著微傳感應(yīng)用范圍的不斷擴(kuò)大，對(duì)傳感器的要求也越來(lái)越高，對(duì)未來(lái)微傳感器的主要要求是：微型化和集成化；低功耗和低成本；高精度和長(zhǎng)壽命；多功能和智能化。硅微機(jī)械和集成電路的一體化集成，可以滿足上述要求。目前，集成傳感器的產(chǎn)品多數(shù)采用混合集成，單片集成的比例很小。而實(shí)現(xiàn)單片集成是實(shí)現(xiàn)傳感器智能化的關(guān)鍵，特別是單片集成MEMS傳感器技術(shù)也是當(dāng)今片上系統(tǒng)芯片能否實(shí)現(xiàn)的關(guān)鍵技術(shù)之一?？梢姡瑢?duì)各種單片集成MEMS技術(shù)難點(diǎn)進(jìn)行分析以及給出目前已有的各種單片集成MEMS技術(shù)是非常必要的。
1.單片集成MEMS技術(shù)的優(yōu)勢(shì)和面臨的挑戰(zhàn)
實(shí)現(xiàn)MEMS和CMOS共同工作是分別制造MEMS傳感器和CMOS集成電路，然后，從各自的晶片切開，固定在一個(gè)共同的襯底上，并且，連線鍵合，這樣就實(shí)現(xiàn)兩者的集成，這就是所謂的混合（hybrid）方法。這種方法不會(huì)產(chǎn)生MEMS制造過(guò)程對(duì)CMOS電路的污染，同時(shí)，兩者生產(chǎn)過(guò)程互不干擾。但是，由于信號(hào)經(jīng)過(guò)鍵合點(diǎn)和引線，導(dǎo)致在高頻應(yīng)用時(shí)，信號(hào)傳輸質(zhì)量下降，并且，開發(fā)兩套生產(chǎn)線增加了產(chǎn)品的成本。為了解決一些性能問題，并降低制造成本，提出把MEMS部分做在和CMOS電路同一塊襯底上，也就是產(chǎn)生了與CMOS工藝兼容單片集成MEMS技術(shù)或叫CMOS-MEMS技術(shù)。這種方法相對(duì)混合方法總的來(lái)說(shuō)有如下優(yōu)勢(shì)：第一，性能能得到很大的提高，因?yàn)榧纳娙莺痛當(dāng)_現(xiàn)象可以顯著減?。坏诙?，混合方法需要復(fù)雜的封裝技術(shù)以減小傳感器接口的影響，而單片集成方法需要的封裝技術(shù)相對(duì)簡(jiǎn)單，所以，降低傳感器成本；第三，單片集成傳感器技術(shù)也是陣列傳感器的需要，是克服陣列傳感器與外圍譯碼電路互連瓶頸的一種有效方法；第四，開發(fā)單片集成MEMS產(chǎn)品比開發(fā)混合MEMS產(chǎn)品所需的時(shí)間短，而且，開發(fā)成本低。
單片集成MEMS技術(shù)根據(jù)MEMS器件部分與CMOS電路部分加工順序不同可以分為前CMOS（pre-CMOS）、混合CMOS（intermediate-CMOS）及后CMOS（post-CMOS）集成方法。
post-CMOS方法是在加工完CMOS電路的硅片上，通過(guò)一些附加MEMS微細(xì)加工技術(shù)以實(shí)現(xiàn)單片集成MEMS系統(tǒng)，目前，單片集成MEMS技術(shù)主要以這種方法為主。post-CMOS方法主要問題是MEMS加工工藝溫度會(huì)對(duì)前面的CMOS電路性能產(chǎn)生影響，更為嚴(yán)重的是后面高溫MEMS加工工藝溫度與前面CMOS工藝金屬化不兼容。以目前研究最多的多晶硅作為結(jié)構(gòu)層的MEMS為例，使磷硅玻璃致密化退火溫度為950℃，而使作為結(jié)構(gòu)層多晶硅的應(yīng)力退火溫度則達(dá)到1050℃，這將使CMOS器件結(jié)深發(fā)生遷移。特別是800℃時(shí)淺結(jié)器件的結(jié)深遷移就會(huì)影響器件的性能。另一方面，采用常規(guī)鋁金屬化工藝時(shí)，當(dāng)溫度達(dá)到400-450℃時(shí)，CMOS電路可靠性將受到嚴(yán)重的影響。從以上可以看出：如何克服后面高溫MEMS微結(jié)構(gòu)加工溫度對(duì)前面的已加工完的CMOS電路影響是解決單片集成MEMS系統(tǒng)關(guān)鍵所在。目前，國(guó)際上解決這個(gè)問題基本是通過(guò)3種方式：第一種是以難熔金屬化互連代替鋁金屬化互連，如，伯克利大學(xué)的以鎢代替鋁金屬互連方案，這樣提高容忍后續(xù)加工MEMS所需的高溫；第二種方式是通過(guò)尋找低制作溫度且機(jī)械性能優(yōu)良的材料代替多晶硅作為結(jié)構(gòu)層材料；第三種方式是利用CMOS本身已有結(jié)構(gòu)層作為MEMS結(jié)構(gòu)層。
pre-CMOS集成方法是先制造MEMS結(jié)構(gòu)后制造CMOS電路，這種集成CMOS技術(shù)雖然克服post-CMOS方法中MEMS高溫工藝對(duì)CMOS電路的影響，但由于存在垂直的微結(jié)構(gòu)，所以，存在傳感器與電路互連臺(tái)階覆蓋性問題，而且，在CMOS電路工藝過(guò)程中對(duì)微結(jié)構(gòu)的保護(hù)也是一個(gè)需要考慮的問題。甚至已優(yōu)化微調(diào)的CMOS工藝流程，例如：柵氧化可能被重?fù)诫s的結(jié)構(gòu)層影響。另外，MEMS工藝過(guò)程中不能有任何的金屬或其他的材料，如壓電材料聚合物等，使得這種方法只適合一些特殊應(yīng)用。
intermediate-CMOS是在CMOS電路生產(chǎn)過(guò)程中插入一些MEMS微細(xì)加工工藝來(lái)實(shí)現(xiàn)單片集成MEMS的方法。這種方法已很成熟，并已有很多商品化產(chǎn)品，也是研究最早一種單片集成方法，是解決pre-CMOS和post-CMOS方法存在問題有效方法，但是，由于需要對(duì)現(xiàn)有的標(biāo)準(zhǔn)CMOS或BiCMOS工藝進(jìn)行較大的修改，因此，這種方法的使用有一定限制。
2.單片集成MEMS的主要技術(shù)現(xiàn)狀
目前，單片集成MEMS技術(shù)主要以post-CMOS技術(shù)為主，通過(guò)一系列的與CMOS工藝兼容的表面微細(xì)加工和體加工實(shí)現(xiàn)單片集成MEMS。又可分為2種：一種是在CMOS結(jié)構(gòu)層上面再淀積一層結(jié)構(gòu)層的微加工；另一種是直接以CMOS原有的結(jié)構(gòu)層作為MEMS結(jié)構(gòu)層的微加工。
2.1 淀積新的結(jié)構(gòu)材料作MEMS結(jié)構(gòu)的集成技術(shù)
2.1.1 多晶硅作為結(jié)構(gòu)層的集成表面微細(xì)加工技術(shù)
這種工藝典型代表是伯克利大學(xué)開發(fā)模塊集成CMOS與MEMS工藝（modular integration of CMOS with micro-structures，MICS），這種方法是以多晶硅為微結(jié)構(gòu)層，磷硅玻璃（PSG）作為犧牲層的表面微細(xì)加工技術(shù)。采用難熔金屬鎢的金屬化互連代替鋁金屬化互連以承受后面的生產(chǎn)多晶硅微結(jié)構(gòu)所需要的高溫，但是，在600℃時(shí)，鎢容易與硅形成反應(yīng)，伯克利大學(xué)是通過(guò)在接觸孔上放一層TiN阻擋層來(lái)解決這一問題的。MICS工藝基本流程是：完成鎢金屬化的CMOS工藝后，淀積300×10-10nm低溫氧化物（LTO），然后，低壓化學(xué)氣相淀積200×10-10nm的氮化硅薄膜保護(hù)已生產(chǎn)的CMOS電路，腐蝕完微結(jié)構(gòu)與CMOS電路的接觸孔后，淀積第1層現(xiàn)場(chǎng)摻雜多晶硅（350×10-10）作為CMOS電路與微結(jié)構(gòu)的互連線，再在上面淀積1um厚的PSG作為犧牲層以及淀積厚度為2um多晶硅結(jié)構(gòu)層。通過(guò)在第2層多晶硅上再淀積一層0.5um的PSG，以及在氮?dú)猸h(huán)境下的1000℃快速退火1min來(lái)降低作為結(jié)構(gòu)層的多晶硅應(yīng)力。最后，刻蝕多晶硅結(jié)構(gòu)圖形以及腐蝕掉其下面的犧牲層（PSG）以釋放微結(jié)構(gòu)。
2.1.2 以其他材料作結(jié)構(gòu)層集成表面微細(xì)加工技術(shù)
多晶硅鍺不僅有與多晶硅相似的優(yōu)良機(jī)械性能，而且，淀積溫度低與CMOS工藝兼容，所以，目前被廣泛研究。伯克利大學(xué)開發(fā)的基于硅鍺結(jié)構(gòu)層的工藝與MICS工藝基本相似。主要技術(shù)革新：第一，保護(hù)層采用不同的材料，以前MICS工藝采用835℃的LPCVD氮化硅，而現(xiàn)在則是采用兩層LTO和中間夾一層不定型硅（a-Si）作為CMOS電路保護(hù)層，其中，a-Si分兩步淀積，第一步淀積在450℃；第二步淀積則在410℃，這樣溫度是不會(huì)損壞鋁金屬化CMOS電路；第二，采用低淀積溫度多晶硅鍺作為結(jié)構(gòu)層材料，其低壓化學(xué)氣相淀積（LPCVD）溫度只有400℃，采用快速退火溫度也僅為550℃，時(shí)間為30s。而MICS工藝淀積多晶硅結(jié)構(gòu)溫度則超過(guò)600℃。從以上兩點(diǎn)可知，由于整個(gè)后續(xù)MEMS加工溫度不超過(guò)450℃，所以，不會(huì)對(duì)鋁金屬化互連CMOS電路產(chǎn)生很大的影響。
采用鋁作為結(jié)構(gòu)層材料也會(huì)獲得很大成功，最為成功的是德州儀器開發(fā)低溫表面微細(xì)加工技術(shù)，并用這種技術(shù)成功生產(chǎn)了數(shù)字微鏡設(shè)備（DMD）。技術(shù)革新主要表現(xiàn)在采用濺射鋁作為結(jié)構(gòu)層材料，并且，采用光致抗蝕劑作為犧牲層，這種低溫后處理使得已生產(chǎn)的下面SRAM單元不被破壞 。
鋯鈦酸鉛（PZT）電材料因具有優(yōu)良的壓電性能、熱釋電性能、鐵電性能和介電性能而被廣泛應(yīng)用在鐵電存儲(chǔ)器中以及作為高介質(zhì)材料。同時(shí)，還可以利用鋯鈦酸鉛壓電效應(yīng)制作微傳感器以及微執(zhí)行器。PZT薄膜工藝與硅集成工藝兼容，如，目前的基于金屬有機(jī)化學(xué)氣相淀積（OCVD）方法制作PZT薄膜溫度已降低到430~75℃，這個(gè)溫度還在降低，因此，采用這種材料作為結(jié)構(gòu)層是很有希望與CMOS工藝集成的。
2.2 以原CMOS結(jié)構(gòu)層作MEMS結(jié)構(gòu)的集成技術(shù)
2.2.1 犧牲鋁的微加工技術(shù)
如果CMOS金屬化合物用作犧牲材料，則可能存在和CMOS工藝完全兼容的表面微細(xì)加工丁藝，這種方法被稱作犧牲鋁蝕刻（sacrificial aluminum etching，SALE）。在許多CMOS工藝過(guò)程中，都采用了兩層由鋁合金構(gòu)成的金屬層。第1層金屬作為犧牲層被清除，可以制造出電介質(zhì)金屬化合物；第2層由金屬和鈍化物組成，第2層金屬介于兩個(gè)電介質(zhì)之間，適當(dāng)結(jié)構(gòu)化后，便可以作為反射鏡、電極、熱電阻或電熱調(diào)節(jié)器。其基本工藝過(guò)程包括：（1）保護(hù)電氣連接觸點(diǎn)不受到蝕刻；（2）腐蝕犧牲鋁層；（3）涮洗清除徼結(jié)構(gòu)里面的蝕刻劑；（4）烘干微機(jī)構(gòu)。
2.2.2 單晶體硅活化蝕刻和金屬化法
單體硅活化蝕刻和金屬化法（single crystal reactiveetching and metallization，SCREAM）可用于制造，梁、橋這樣的結(jié)構(gòu)，甚至可以用單晶硅制造更復(fù)雜的結(jié)構(gòu)。這種方法始于制造完的CMOS電路硅片，首先，淀積一層覆蓋接觸孔的氧化硅，這層氧化物保護(hù)CMOS電路免受后面工藝影響，并通過(guò)反應(yīng)離子蝕刻（RIE）圖形化這層氧化物遮蔽層；然后，RIE蝕刻硅溝槽，深度可達(dá)到10um，氧化硅薄膜淀積下來(lái)，覆蓋在側(cè)面和水平面上。通過(guò)反應(yīng)離子蝕刻掉水平面上的氧化物，而使豎直面受到保護(hù)，第二次反應(yīng)離子蝕刻硅；最后，各向同性蝕刻硅，釋放出懸浮的微結(jié)構(gòu)，同時(shí)，蝕刻接觸孔氧化物，并濺射金屬，這層金屬化淀積物使大縱橫比的粱變成電容性元素，用厚的抗蝕劑作掩蔽模圖形化金屬層。由于SCREAM的每一步均在低于300℃的溫度下進(jìn)行的，因此，是與CMOS電路兼容的。
2.2.3大縱橫比的CMOS-MEMS工藝
Gamegle Melloa大學(xué)開發(fā)的與CMOS兼容干法蝕刻方法，它應(yīng)用各向同性硅蝕刻產(chǎn)生絕緣薄膜，CMOS介質(zhì)和金屬化層在這個(gè)工藝中不僅用作金屬互連，而且，還作為微機(jī)械結(jié)構(gòu)尾?；竟に囘^(guò)程為：首先，標(biāo)準(zhǔn)的CMOS工藝采用三層金屬0.5upmN阱工藝實(shí)現(xiàn)；其次，金屬層1和2被用作電活性層，而第3層作為微機(jī)械加工的蝕刻掩模。應(yīng)用化合物CHF3／O2的反應(yīng)離子蝕刻（RIE），使整個(gè)芯片上的鈍化層被清除掉，在第3層金屬斷開區(qū)域，CMOS薄膜夾層被一直蝕刻至基底，而上面覆蓋有第3層金屬的CMOS薄膜夾層則保留完好；最后，采用SP6／O2等離子在不蝕刻微結(jié)構(gòu)側(cè)壁情況下各向同性蝕刻硅襯底。狹窄的絕緣層和導(dǎo)電層融為一體制造出梁和橋，例如：梳狀驅(qū)動(dòng)器這樣的微結(jié)構(gòu)。
2.2.4 體加工CMOS-MEMS工藝
主要是通過(guò)蝕刻硅襯底等體加工技術(shù)來(lái)形成所需的MEMS結(jié)構(gòu)，這種技術(shù)主要以蘇黎世大學(xué)為主?？梢詮恼嫖g刻硅襯底，也可以從反面蝕刻硅襯底，利用各向異性腐蝕（100）方向的特性，從硅的正面蝕刻是可以得到未封閉的微結(jié)構(gòu)，如，梁和支撐膜等，可選用的蝕刻劑可以是氫氧化四甲基銨水溶液（TMATH）或乙烯二胺溶液（EDP）。通過(guò)從已完成的硅片背部蝕該硅片可以得到封閉的介電薄膜，需要一個(gè)額外的掩模定義膜片的大小，通常采用的燭刻劑是KOH。
采用XeF2干法蝕刻的post-CMOS工藝也得到很大的發(fā)展。XeP2是一種各向異性硅蝕刻劑，蝕刻速度很高，它是惰性氣體氙的一種稀有化合物。XeP2既不蝕刻IC絕緣層，也不蝕刻鋁合金金屬化合物，因此，和CMOS完全兼容。經(jīng)過(guò)適當(dāng)?shù)膮^(qū)域設(shè)計(jì)、連接和加掩模，在指定部位打開絕緣層，使基底硅局部暴露給蝕刻劑。因?yàn)閄eF2即不蝕刻陶瓷，也不蝕刻塑料，從而適合集成CMOS微系統(tǒng)的微加工。使用這種方法可在已完成的CMOS芯片上無(wú)掩模蝕刻出微機(jī)構(gòu)。
3.發(fā)展趨勢(shì)
單片集成MEMS技術(shù)已開發(fā)10多年了，已得到了迅猛發(fā)展，也涌現(xiàn)出各種MEMS制造服務(wù)組織和企業(yè)，從而可以獲得一些組織或直接由特殊集成電路制造商提供MEMS加工。代表微系統(tǒng)IC技術(shù)發(fā)展方向的組織包括美國(guó)的MOSIS.Europractice和歐洲的TIMACMP；美國(guó)北卡羅納州的Croons集成微系統(tǒng)公司除了提供基本的CMOS工藝以外，還提供體微加工和表面徽加工、LIGA工藝以及多用戶微機(jī)電系統(tǒng)工藝等；美國(guó)桑迪亞國(guó)家實(shí)驗(yàn)室開發(fā)的超平面多層多晶硅工藝也已商品化；在歐洲從事特殊應(yīng)用集成電路制造技術(shù)研究的包括奧地利微系統(tǒng)公司和瑞士的EM微電子公司。還有很多基于傳感器的特殊硅工藝也已經(jīng)被研究出來(lái)，如，德國(guó)的羅伯特博施公司和挪威的SensoNor公司等。從目前來(lái)看，集成MEMS技術(shù)將有如下趨勢(shì)：
（1）post-CMOS集成方法仍將是未來(lái)的主要開發(fā)技術(shù)，并將現(xiàn)有實(shí)驗(yàn)室已開發(fā)的各種post-CMOS單片集成MEMS技術(shù)產(chǎn)業(yè)化；
（2）在集成MEMS系統(tǒng)上集成更多的復(fù)雜的電路包括數(shù)字接口和微控制器，這樣得到功能更強(qiáng)大、價(jià)格便宜的智能系統(tǒng)；
（3）開發(fā)封裝技術(shù)保護(hù)CMOS芯片免受環(huán)境的影響，不僅需要開發(fā)適應(yīng)MEMS集成系統(tǒng)的封裝，而且，也需要開發(fā)能適應(yīng)封裝的單片MEMS集成技術(shù)。
4.結(jié)束語(yǔ)
單片集成MEMS是實(shí)現(xiàn)智能傳感器的關(guān)鍵，也是IC業(yè)發(fā)展的一個(gè)重要方向。雖然目前各種方法都還存在一些問題，但是，隨著對(duì)其不斷的研究與CMOS工藝兼容性各種問題也會(huì)一一解決。本文對(duì)單片集成MEMS技術(shù)對(duì)工藝提出的要求進(jìn)行了討論，并對(duì)目前各種單片集成MEMS技術(shù)特點(diǎn)、工藝流程進(jìn)行了介紹，同時(shí)，還給出未來(lái)單片集成MEMS技術(shù)未來(lái)發(fā)展趨勢(shì)。
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外文翻譯資料
Monolithically integrated MEMS technology
In the past 20 years, CMOS technology has become a major integrated circuit manufacturing technology, manufacturing costs decline at the same time, yield and production has also been greatly improved, COMS technology will continue to increase integration and reduce development of a special size. Today, CMOS integrated process not only be used in the design of integrated circuits, but also to be used in many micro-sensors and micro-actuator, so it can be integrated circuits and micro-sensor integrated with a powerful, intelligent sensors. With micro-sensor constantly expanding the scope of application of the sensor increasingly high demands of the future microsensor the main requirements are: miniaturization and integration of low-power and low-cost high-precision and long life; - and intelligent. Micromachined silicon integrated circuits and the integration of integration, to meet the above-mentioned requirements. At present, the majority of products integrated sensor using hybrid integrated, monolithic integration of a very small percentage. And the realization of single-chip integration is the key to achieving intelligent sensors, in particular monolithic integrated MEMS sensor technology is today's system-on-chip can achieve one of the key technologies. Clearly, monolithic integration of the various technical difficulties analysis of MEMS and have already given the various monolithic integration of MEMS technology is essential.
1. Monolithic integration of MEMS technology advantages and the challenges facing。
MEMS and CMOS achieve working together, the separate manufacturing CMOS MEMS sensors and integrated circuits, and then cut from their chips, fixed in a common substrate, and, bonded connection, thereby bringing the two integration, This is the so-called mixed (hybrid) method. This method does not produce MEMS manufacturing process for CMOS circuits pollution At the same time, both the production process Noninterference. However, due to signal bonding point and fuses, resulting in high-frequency applications, decline in the quality of signal transmission, and to develop two production lines to increase the cost of the product. In order to address some performance issues, and lower manufacturing costs, and proposed to do in the part of MEMS and CMOS circuits with a substrate, which is produced compatible with CMOS technology or monolithic integrated MEMS technology called CMOS-MEMS technology. This method relative hybrid method generally have the following advantages: First, the performance can be greatly improved, because parasitic capacitance and crosstalk phenomenon can be significantly reduced; second, hybrid method requires sophisticated technology to reduce packaging Sensor Interface affected, and monolithic integration requires packaging technology is relatively simple and therefore, lower cost sensors; third, monolithic integrated sensor array sensor technology is the need to overcome the array sensor and external decoding circuit an effective interconnect bottleneck; Fourth, the development of monolithic integrated mixed development of MEMS products than MEMS products for a short time, and to develop low cost.
Monolithic integration of MEMS technology under some of MEMS devices and CMOS circuit can be divided into different order processing before CMOS (pre-CMOS), mixed CMOS (intermediate-CMOS), and after the CMOS (post-CMOS) integrated approach.
Post-CMOS approach is in the processing of silicon CMOS circuits End, through some additional MEMS micro-processing technology to achieve monolithic integrated MEMS system, at present, monolithic integration of MEMS technology in this way mainly based. Post-CMOS approach is the main issue on MEMS processing temperature CMOS circuit performance in front of an impact on more serious is that the technology behind high-temperature MEMS processing temperature and metal CMOS process ahead of incompatibility. In the present study as the most polysilicon layer structure of the MEMS example, the densification of phosphorus glass annealing temperature is 950 ℃ due to a structural polysilicon layer of stress annealing temperature reached 1050 ℃, which will enable CMOS devices junction depth migration occurred. In particular 800 ℃ shallow junction devices junction depth migration will affect device performance. On the other hand, the conventional aluminum metallization process, when the temperature reaches 400-450 ℃, the reliability of CMOS circuits will be severely affected. From the above we can see that: how to overcome behind high-temperature MEMS processing temperature on the micro-structure of the front end processing has been the impact of CMOS circuits integrated MEMS single-chip solution is key to the system. At present, the international community is essential to resolve this issue through three ways: First is the interconnection of refractory metals instead of aluminum metal interconnect, for example, the University of Berkeley to replace tungsten aluminum metal interconnect programmes, such follow-up increased tolerance MEMS processing for high temperature; The second is produced by finding low temperature mechanical properties and excellent substitute materials as structural polysilicon layer; third way is to use its existing structure CMOS MEMS layer as a layer structure.
Pre-CMOS integrated approach is to create structure MEMS manufacturing CMOS circuits, although this integrated CMOS technology to overcome post-CMOS method of high-temperature MEMS Technology on CMOS circuits affected, but because of the existence of micro-vertical structure, and therefore, there sensor and circuit interconnection level coverage, but also in the process of CMOS circuits on the micro-structure protection is also a need to consider the issue. Even fine-tune the optimization of CMOS process, such as: gate oxide may be heavily doped layer impact of the structure. In addition, the MEMS technology can not process any of the metal or other materials, such as piezoelectric polymers, and so on, makes this method only suitable for some special applications.
Intermediate-CMOS circuits in the CMOS production process to insert some MEMS micro-processing technology to achieve monolithic integrated MEMS approach. This approach has been very mature and have a lot of commercialization of products, is the first study of a single-chip integration method is to solve the pre - and post-CMOS CMOS method effective method problems, but due to the need for the existing standard CMOS or larger BiCMOS process changes, therefore, the use of this method is limited.
2.The main monolithic integrated MEMS technology status
At present, the monolithic integration of MEMS technology mainly to post-CMOS technologies, through a series of compatible with CMOS process on the surface micro-machining and processing to achieve monolithic integration of MEMS. Can be divided into two kinds: one is in the top layer CMOS structure to a structure layer deposition micro-machining; the other is directly CMOS layer structure as the original structure of the MEMS micro-machined.
2.1 Deposition of new structural materials for the structure of integrated MEMS technology
2.1.1 Polysilicon layer structure as the surface micro-machining technology integration
This process is typical of modules developed at the University of Berkeley Integrated CMOS and MEMS Technology (modular integration of CMOS with micro-structures, MICS), this method is for the micro-structural polysilicon layer, phosphorus silicon glass (PSG) as a sacrificial layer The surface micro-machining technology. A refractory metal tungsten metal interconnect instead of aluminum metal interconnect to bear behind the polysilicon production needs of micro-structure of high-temperature, but at 600 ℃, tungsten and silicon form easily response by the University of Berkeley in the Contacts release a TiN barrier layer to address this problem. MICS process is the basic process: the completion of tungsten metal CMOS process, the deposition of 300 × 10-10nm low-temperature oxide (LTO), and then, low pressure chemical vapor deposition 200 × 10-10nm protection of the silicon nitride film has been produced CMOS circuits, micro-structure and corrosion End CMOS circuit contact hole, No. 1 layer deposition scene doped polysilicon (350 × 10-10), as CMOS circuits and micro-structure of interconnection lines, in the above deposition to a um PSG thick as a sacrificial layer thickness and deposition of 2 um polysilicon layer structure. No. 2 through another layer polysilicon deposition of a layer of 0.5 um PSG, as well as nitrogen environment in the 1000 ℃ rapid thermal annealing for 1 min as a structure to reduce stress polysilicon layer. Finally, the structure of graphics and polysilicon etching out its corrosion layer below the sacrifices (PSG) for the release of micro-structure.
2.1.2 Other materials for the structure of the surface micro-machining technology integration
Polycrystalline silicon germanium polysilicon not only with the excellent mechanical properties similar, and, low temperature deposition compatible with the CMOS process, therefore, is being extensively studied. Developed at the University of Berkeley-based structural layer of silicon germanium technology and MICS technology similar. Major technological innovations: First, the protective layer using different materials, before 835 ℃ MICS process is the LPCVD silicon nitride, and now it is using a two-tier LTO and intermediate folder is not a stereotypical silicon (a-Si) as a CMOS circuit protective layer, in which the two-step deposition of a-Si, the first step in the deposition 450 ℃; step deposition in the 410 ℃, this will not damage the temperature of aluminum metal CMOS circuit; Second, the low amylin plot structure as a temperature polysilicon layer of germanium materials, the low pressure chemical vapor deposition (LPCVD) temperature only 400 ℃ using rapid thermal annealing temperature of only 5.5 ℃ for 30 s. MICS and the temperature polysilicon deposition of more than 600 ℃. From the above two points, we can see that the whole follow-up MEMS processing temperature does not exceed 450 ℃, therefore, not of aluminum metal interconnect CMOS circuits have greatly affected.
Aluminum used as a structural material will be a great success, the most successful is the Texas Instruments developed cryogenic surface micro-machining technology, and use this technology successfully produced digital micromirror device (DMD). Technical innovation in the use of sputtering performance as aluminum structural material, and using photoresist as a sacrificial layer, which makes low-temperature post-processing production has been below the SRAM cells were not damaged.
Lead zirconate titanate (PZT) of the material has an excellent result piezoelectric properties, pyroelectric properties of ferroelectric properties and dielectric properties and is widely used in ferroelectric memory, as well as high-dielectric materials. At the same time, we can also use lead zirconate titanate piezoelectric effect produced micro-sensors and micro-actuators. PZT thin film silicon technology and integration technology compatible, such as the present based on the metal-organic chemical vapor deposition (OCVD) Methods PZT thin films temperature has been reduced to 430 to 75 ℃, the temperature is lower, therefore, use of such materials as structural layer is a very hopeful and CMOS process integration.
2.2 CMOS structure to the original layer to the structure of integrated MEMS technology
2.2.1 Sacrifice aluminum micro-machining technology
If CMOS metal compounds used for the expense of materials, there may be fully compatible with CMOS technology and surface micro-machining small art, this method is called sacrifice aluminum etching (sacrificial aluminum etching, SALE). In many CMOS process, use two layers of aluminum alloy by a metal layer. No. 1 as a sacrificial layer of metal was removed, can create metal dielectric compounds; Layer 2 and passivation of the metal component, 2-layer metal between two dielectric between appropriate structure, they could serve as a mirror electrodes, heat or electric resistance regulator. The basic process include: (1) the protection of electrical contacts are not connected etching (2) corrosion sacrifice aluminum layer; (3) removal rinsed Boundary structure inside the etching agent; (4)-drying bodies.
2.2.2 Monocrystal silicon etching and metal activation method.
Monomer silicon etching and metal activation method (single crystal reactiveetching and metallization, SCREAM) can be used for manufacturing, beam, the bridge structure, and even silicon can be used to create more complex structures. This approach starts at the End manufacture silicon CMOS circuits, first of all, a layer of coverage deposition contact hole silicon oxide, oxide layer to protect it from the back of CMOS circuits affected, and through reactive ion etching (RIE) of this graphics Oxide layer shielding layer; then RIE etching silicon trench, the depth of up to 10 um, silicon oxide thin film deposition down, and the level of coverage in the side surface. By reactive ion etching of the oxide surface level off due to a vertical surface to be protected, the second reactive ion etching silicon; Finally, the isotropic etch silicon, the release of the microstructure of a suspension, at the same time, etching contact hole oxides, and Sputtering metal, this layer of metal deposition to the aspect ratio of the beam into a capacitive elements with thick resist masking agent for the graphics mode of metal layers. As each step of SCREAM are below 300 ℃ under the temperature and, therefore, is compatible with CMOS circuits.
2.2.3 Large aspect ratio of CMOS-MEMS Technology
Gamegle Melloa University and the development of CMOS-compatible dry etching method, which isotropic silicon etch applications have insulation film, CMOS dielectric and metal layers in this process, not only for the metal interconnect, but also as a micro-mechanical structure tail. Basic process: First, the standard CMOS process using three-metal process to achieve 0.5 upmN Well, secondly, metal layers 1 and 2 were used as electrical activity layer, and layer 3 as a micro-machining etching mask. Application of the compound CHF3/O2 reactive ion etching (RIE), the entire chip passivation layer to be removed, in the three-tier regional disconnect metal, CMOS laminated film has been etched to the basement, and above covered with Layer 3 CMOS metal thin film laminated retained intact; Finally, the use of SP6/O2 plasma etching in the micro-structural wall not under isotropic etch silicon substrate. Narrow insulating layer and conductive layer fused to create beams and bridges, such as: Comb drive the micro-structure.
2.2.4 Processing CMOS-MEMS Technology
Mainly through the etching of silicon substrates, such as processing technology to form the necessary MEMS structure, the technology mainly to the University of Zurich-based. Can be viewed in a positive etching silicon substrate, but also from negative etching silicon substrate, using anisotropic etching (100) in the direction of the characteristics of the silicon etching could be positive not closed micro-structure, such as beams and support film , the choice of etching can be tetramethyl ammonium hydroxide solution (TMATH) or ethylene diamine solution (EDP). From what has been done through the back of the silicon wafer of silicon can be pitting the closure of the dielectric film, the need for a definition of additional patch mask the size of the commonly used candle is engraved on KOH.
XeF2 dry etching using the post-CMOS technology has also made great development. XeP2 is an anisotropic etching of silicon, etching at high velocity, it is an inert gas xenon rare compounds. XeP2 neither IC insulating layer etching, etching aluminum or metal compounds, therefore, and CMOS compatible. After the appropriate regional design, connectivity and processing mask, opened in designated parts insulating layer, so that local exposure to silicon substrate etching agent. XeF2 because that is not etched ceramic, not plastic etching and thus suitable for CMOS integrated micro-processing system. In the use of this method can be completed with CMOS chip micro-etching mask institutions.
3.Development Trend
Monolithically integrated MEMS technology has been developing for more than 10 years, has been the rapid development has also seen the emergence of a MEMS manufacturing services organizations and enterprises, which will be some special organizations or directly from the IC manufacturers to provide MEMS processing. IC Microsystems representative of the direction of technology development organizations, including the United States and Europe TIMACMP MOSIS.Europractice; North Kaluona state Croons Integrated Microsystems Inc., in addition to providing the basic CMOS process, the body also provides micro-machining and surface emblem processing, LIGA process, as well as multi-user MEMS technology; the United States Sandia National Laboratory development of the multi-storey hyperplane polysilicon technology has been commercialized in Europe in the application-specific integrated circuit manufacturing technology research, including Austria Microsystems and Switzerland's EM Microelectronics. There are many special silicon-based sensor technology has also been finding out, for example, Germany's Luobaitebo Oxfam and the Norwegian SensoNor companies. Judging from the current situation, integrated MEMS technology will have the following trends:
(1) post-CMOS integrated approach will continue to be the main future development of technology, and the existing laboratories have developed various post-CMOS single-chip integrated MEMS technology industry;
(2) in the integrated MEMS system more complex integrated circuit including digital interfaces and microcontrollers, so that a more powerful, cheaper intelligent systems;
(3) the development of CMOS chip packaging technology protection against environmental impacts, not only need to develop a system to integrate the MEMS package, but also need to adapt to the development of the single-chip package integrated MEMS technology.
4.Concluding remarks
Monolithic Integrated Intelligent MEMS sensor is the key to the development of IC industry is an important direction. Although various methods are some problems still exist, however, with its constant research and CMOS process compatibility problems will be all the solutions. In this paper, monolithic integration of MEMS technology to the requirements were discussed, and monolithic integration of various characteristics of MEMS technology, a process, at the same time, also gives future monolithic integration of MEMS technology development trend of the future.
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