ewnergy9-薄膜淀積技術(shù).ppt

薄膜淀積技術(shù),半導體工藝中所涉及的常用薄膜：,Evaporation (蒸發(fā)）,Sputtering (濺射）,使用加熱、等離子體或紫外線等各種能源，使氣態(tài)物質(zhì)經(jīng)化學反應（熱解或化學合成）形成固態(tài)物質(zhì)淀積在襯底上的方法， 叫做化學汽相淀積(Chemical Vapor Deposition)技術(shù)，簡稱CVD技術(shù)。它與真空蒸發(fā)和濺射技術(shù)并列，是應用較為普遍的一種薄膜淀積技術(shù)。 特點： 1、淀積溫度低； 2、可以淀積各種電學和化學性質(zhì)都符合要求的薄膜； 3、均勻性好； 4、操作簡便，適于大量生產(chǎn)；,CVD技術(shù)：,CVD的分類： 可按淀積溫度，反應腔氣壓或淀積反應的激活方式分類 低溫CVD (200-500C) 中溫CVD（500-1000C) 高溫CVD（1000-1300C) 常壓CVD 低壓CVD 熱CVD 等離子體CVD 光CVD 等等,熱CVD系統(tǒng)：,等離子體CVD,Molecular Beam Epitaxy (MBE) 分子束外延技術(shù),MBE自1960年開始就有人提出，是一種超精密和極精確的薄膜生長技術(shù)。其利用的是蒸發(fā)原理，將分子束射至單晶襯底上生長單晶外延層的方法。,MBE的特點： 超高真空；設備中外延生長室真空度可達5x10-11Torr,這樣分子平均自由程L較大。例如：P=10-9Torr, L=5x106cm。這樣大的自由程使分子碰撞幾率很小，薄膜生長均勻，生長速率和組分可精確控制。 可以實現(xiàn)低溫過程；這樣能減少雜質(zhì)擴散和沾污的幾率。利用MBE技術(shù)可生長出位錯密度102cm-2的外延層。 原位監(jiān)控；MBE設備上安裝有許多原位監(jiān)控儀器，可以實時監(jiān)控外延薄膜的生長參數(shù)以及物理性能。 (UHV = Ultra High Vacuum),Photolithography Lithography is the process in which a microelectronics patterns are transfer to a substrate. This transfer can be aided by light, electron-beams, ion beams, x-rays, etc. Without the techniques of pattern definition, the fabrication of multiple devices on one semiconductor would be impossible. Although the techniques of pattern definition seem simple they are the heart of modern IC fabrication.,半導體器件制作,Photoresist Photo lithography is a process in which wafer is coated with a light sensitive polymer called photoresist. Polyisoprene is an example of a commonly used photoactive agent. A mask is used to expose selected areas of photoresist to UV light. The UV light induces polymerization in the exposed photoresist. UV causes it to cross link rendering it insoluble in developing solution. Such a photoresist is called a positive photoresist. A negative photoresist shows an opposite behavior. That is exposure to UV makes the photoresist soluble in developing solution.,! Remember: There are two types of photoresist: * NEGATIVE - unexposed areas removed * POSITIVE - exposed areas removed Negative resist is the most often used because it is less affected by etchants although positive resist offers better resolution. Positive resists are more capable of producing the small size of modern device features which are typically below 1.0 m but may be as small as 0.15 m.,光刻的大致工藝流程： 涂膠：一般從高溫爐中 取出硅片立即涂膠或在180- 200C恒溫干燥箱中烘烤 30分鐘后再進行涂膠。要 求粘附性能良好，厚度均 勻適當。 前烘：在80 C恒溫干燥箱中烘10-15分鐘。目 的是使膠膜體內(nèi)溶劑充分揮發(fā)，使膠膜干燥，以 增強膠膜與SiO2膜的粘附性和膠膜的耐磨,曝光與顯影：在涂好光刻膠的硅片表面覆蓋掩膜版(Mask)，一般利用紫外光進行選擇性照射，使光照部分光刻膠發(fā)生光化學反應，經(jīng)顯影將部分光刻膠除去得到相應的圖形。,堅膜：一般將顯影后的硅片放在烘箱中熱烘30分鐘左右使經(jīng)顯影時軟化、膨脹的膠膜堅固。這樣可使膠膜與硅片貼得更牢，同時也增強了膠膜本身的抗蝕能力。,腐蝕：在用正膠的情況下，利用適當?shù)母g液將SiO2或Al腐蝕掉，而有光刻膠覆蓋的區(qū)域保存下來。 去膠：腐蝕結(jié)束后，利用濕法去膠，氧氣去膠或等離子體去膠等方法將覆蓋在硅片表面的保護膠膜去除。,Exposure Method: * CONTACT PRINTING - 1x mask required； * DIRECT STEP - 5x mask required； * E-BEAM - no mask required；,X-Ray Lithography X-Ray lithography (XRL) consists of proximity printing of a mask onto a wafer. Advantages 1) resolution and process simplicity (linewidth1 m) 2) no need for multilevel resist systems used in e-beam lithography 3) XRL parallel writing process, e-beam is a serial.,Etch Process that follows immediately after photolithography step is the removal of material from areas unprotected by photoresist. This process must be selective; that is SiO2 is removed while leaving photoresist and silicon intact. It must also be anisotropic; that is etching should be in one direction only.,Etch Method:,Two types of etching processes are used in practice; namely, chemical and physical etching. In purely chemical etching material is removed by dissolution which is highly selective but not anisotropic. In purely physical method material is removed by bombardment of high energy ions which is inherently anisotropic but unselective. As an example, SiO2 which is used as a mask for drive in diffusion is removed by exposure to hydrogen fluoride. Hydrogen fluoride reacts with SiO2 to form volatile SiF4 which is swept away by inert argon gas.,濕法刻蝕特點： 選擇性高； 生產(chǎn)量大；加工精度：3m 裝置成本低；,干法刻蝕特點: 可控性好； 加工精度高,可達0.2m； 可加工設計形狀；,對于硅系材料, 最常用的是用在CF4中放電所產(chǎn)生的 等離子體來腐蝕Si、多晶硅和Si3N4。,主要反應：,在刻蝕過程中起主要作用的是原子態(tài)F和CF3游離基。近來人們發(fā)現(xiàn)在CF4中添加少量氧可使Si的腐蝕速率明顯提高。這是因為O2與等離子體中的CF3、CF2或CF游離基作用而放出原子態(tài)F所致。,Doping (Diffusion and Ion Implantation),Doping is a general term which refers to the introduction of impurities into a semiconductor medium. Doping used independently is nonselective, whereas if used in conjunction with pattern definition, it can be selective; introducing impurities into only those areas that you desire.,THERE ARE TWO TECHNIQUES OF DOPING: * SOLID-STATE DIFFUSION * ION IMPLANTATION,Diffusion:,Diffusion is the process whereby particles move from regions of higher concentration to regions of lower concentration. Although this includes the self diffusion phenomena, our interest is in the diffusion of impurity atoms. 硅平面擴散工藝是在硅集成電路中廣泛使用的一種摻雜技術(shù)。其利用硅片表面的SiO2作為擴散掩膜，把待摻入的元素從窗口擴散到硅片內(nèi)。,固態(tài)源擴散裝置 氣態(tài)源擴散裝置 液態(tài)源擴散裝置,擴散原理： 空位擴散 復合擴散 格子間隙擴散,Mathematical Model for Diffusion： The basic one-dimensional diffusion process follows Ficks first law of diffusion: J = -D N/ x where J is the particle flux of the donor or acceptor impurity species, N is the concentration of the impurity, and D is the diffusion coefficient. Ficks second law of diffusion may be derived using the continuity equation for the particle flux: N/ t = D 2N/ x2 in which the diffusion coefficient D has been assumed to be independent of position. This assumption is violated at high impurity concentrations.,Two specific types of boundary conditions are important in modeling impurity diffusion in silicon. The first is the constant-source diffusion(恒定表面濃度擴散), in which the surface concentration is held constant throughout the diffusion. N(x,t)=Noerfcx/2(Dt)1/2 Where erfc is complementary error function(相補誤差函數(shù)).,The second is called a limited-source diffusion(限定源擴散), in which a fixed quantity of the impurity species is deposited in a thin layer on the surface of the silicon.,SOLID-STATE DIFFUSION USUALLY CONSISTS OF TWO STEPS: 1) PRE-DEPOSITION； 2) DRIVE-IN； During the pre-deposition step, impurities are introduced but typically do not diffuse very far into the substrate. 恒定表面濃度擴散 Before the drive-in, a layer of oxide is deposited to cap the wafer thus preventing impurities from escaping. During the drive-in, the wafer is heated and the impurities diffuse further into the wafer until the desired profile is reached.限定源擴散,在熱擴散中，摻雜原子通過掩膜向硅片中擴散時，除了在深度方向形成一定分布外，在窗口邊緣同樣有橫向擴散。另外，在大面積摻雜時的摻雜量、結(jié)深和濃度分布可控性重復性等方面，高溫擴散法有著一定不足之處，限制了其應用。目前，在低濃度高精度摻雜方面已被離子注入技術(shù)所替代。,Ion Implantation: Ions of dopant atoms are accelerated to a high velocity in an electric field and impinge on target wafer. The ions penetrate through the oxide layer and enter into silicon. Penetration depths of 500 to 5000 A are easily achieved. Penetration depth depends on size of ion and energy applied. The ions do not penetrate the photoresist layers which are typically 10,000 A thick. By manipulating the acceleration voltage, the average implantation depth can be pr