newnergy薄膜淀积技术实用教案

1、第1页/共48页第一页，共49页。半导体工艺中所涉及(shj)的常用薄膜：第2页/共48页第二页，共49页。第3页/共48页第三页，共49页。Evaporation (蒸发(zhngf)）第4页/共48页第四页，共49页。Sputtering (溅射(jin sh)）第5页/共48页第五页，共49页。使用加热、等离子体或紫外线等各种能源，使气态物质(wzh)经化学反应（热解或化学合成）形成固态物质(wzh)淀积在衬底上的方法， 叫做化学汽相淀积(Chemical Vapor Deposition)技术，简称CVD技术。它与真空蒸发和溅射技术并列，是应用较为普遍的一种薄膜淀积技术。特点：1、淀积

2、温度低；2、可以淀积各种电学和化学性质都符合要求的薄膜；3、均匀性好；4、操作简便，适于大量生产；CVD技术(jsh)：第6页/共48页第六页，共49页。CVD的化学反应大致分为两种类型：一是一种气态化合物在一定激活能量下被分解，生成固态物质淀积在衬底上，而其它则为气态物质跑掉，如：SiH4 Si + 2H2另一类是两种气体化合物经化学反应生成新的固态物质和气态物质，如： 3SiH4 + 4NH3 Si3N4 + 12H2第7页/共48页第七页，共49页。CVD的分类：可按淀积温度，反应腔气压或淀积反应的激活方式分类 低温(dwn)CVD (200-500C) 中温CVD（500-1000C)

3、 高温CVD（1000-1300C) 常压CVD 低压CVD 热CVD 等离子体CVD 光CVD等等第8页/共48页第八页，共49页。热CVD系统(xtng)：第9页/共48页第九页，共49页。等离子体(dnglzt)CVD第10页/共48页第十页，共49页。第11页/共48页第十一页，共49页。第12页/共48页第十二页，共49页。Molecular Beam Epitaxy (MBE)分子(fnz)束外延技术MBE自1960年开始就有人提出，是一种超精密和极精确的薄膜生长技术。其利用的是蒸发原理，将分子束射至单晶衬底上生长单晶外延(wiyn)层的方法。第13页/共48页第十三页，共49页。

4、MBE的特点：超高真空；设备中外延生长室真空度可达5x10-11Torr,这样分子平均自由程L较大。例如：P=10-9Torr, L=5x106cm。这样大的自由程使分子碰撞几率很小，薄膜生长均匀，生长速率和组分可精确控制。可以实现低温过程；这样能减少杂质扩散和沾污(zhn w)的几率。利用MBE技术可生长出位错密度102cm-2的外延层。原位监控；MBE设备上安装有许多原位监控仪器，可以实时监控外延薄膜的生长参数以及物理性能。(UHV = Ultra High Vacuum)第14页/共48页第十四页，共49页。PhotolithographyLithography is the proce

5、ss 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 patt

6、ern definition seem simple they are the heart of modern IC fabrication.半导体器件制作(zhzu)第15页/共48页第十五页，共49页。PhotoresistPhoto 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

7、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

8、is exposure to UV makes the photoresist soluble in developing solution.第16页/共48页第十六页，共49页。! Remember: There are two types of photoresist:* NEGATIVE - unexposed areas removed* POSITIVE - exposed areas removedNegative resist is the most often used because it is less affected by etchants although posit

9、ive 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.第17页/共48页第十七页，共49页。光刻的大致工艺流程： 涂胶：一般从高温炉中取出硅片立即涂胶或在180-200C恒温干燥箱中烘烤30分钟后再进行涂胶。要求粘附性能良好，厚度均匀适当。 前烘：在80 C恒温干燥箱中烘10-15

10、分钟。目的是使胶膜体内溶剂充分(chngfn)挥发，使胶膜干燥，以增强胶膜与SiO2膜的粘附性和胶膜的耐磨第18页/共48页第十八页，共49页。曝光与显影：在涂好光刻胶的硅片表面覆盖掩膜版(Mask)，一般利用紫外光进行选择性照射，使光照部分光刻胶发生光化学反应，经显影将部分光刻胶除去得到相应(xingyng)的图形。第19页/共48页第十九页，共49页。坚膜：一般将显影后的硅片放在烘箱中热烘30分钟左右使经显影时软化、膨胀的胶膜坚固。这样可使胶膜与硅片贴得更牢，同时也增强了胶膜本身(bnshn)的抗蚀能力。腐蚀：在用正胶的情况下，利用适当的腐蚀液将SiO2或Al腐蚀掉，而有光刻胶覆盖的区域保

11、存下来。去胶：腐蚀结束后，利用湿法去胶，氧气去胶或等离子体去胶等方法将覆盖在硅片表面(biomin)的保护胶膜去除。第20页/共48页第二十页，共49页。第21页/共48页第二十一页，共49页。Exposure Method:* CONTACT PRINTING - 1x mask required；* DIRECT STEP - 5x mask required；* E-BEAM - no mask required；第22页/共48页第二十二页，共49页。第23页/共48页第二十三页，共49页。第24页/共48页第二十四页，共49页。第25页/共48页第二十五页，共49页。第26页/共48

12、页第二十六页，共49页。X-Ray LithographyX-Ray lithography (XRL) consists of proximity printingof a mask onto a wafer.Advantages1) resolution and process simplicity (linewidth1 m)2) no need for multilevel resist systems used in e-beamlithography3) XRL parallel writing process, e-beam is a serial.第27页/共48页第二十七页，

13、共49页。EtchProcess 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

14、direction only.第28页/共48页第二十八页，共49页。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 bom

15、bardment 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.第29页/共48页第二十九页

16、，共49页。湿法刻蚀特点(tdin)： 选择性高； 生产量大；加工精度：3m 装置成本低；第30页/共48页第三十页，共49页。干法刻蚀特点(tdin): 可控性好； 加工精度高,可达； 可加工设计形状；第31页/共48页第三十一页，共49页。第32页/共48页第三十二页，共49页。对于硅系材料, 最常用(chn yn)的是用在CF4中放电所产生的等离子体来腐蚀Si、多晶硅和Si3N4。主要(zhyo)反应：在刻蚀过程中起主要作用的是原子态F和CF3游离基。近来人们发现在CF4中添加少量(sholing)氧可使Si的腐蚀速率明显提高。这是因为O2与等离子体中的CF3、CF2或CF游离基作用而放

17、出原子态F所致。第33页/共48页第三十三页，共49页。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 i

18、mpurities into only those areas that you desire.第34页/共48页第三十四页，共49页。THERE ARE TWO TECHNIQUES OF DOPING:* SOLID-STATE DIFFUSION* ION IMPLANTATION第35页/共48页第三十五页，共49页。Diffusion:Diffusion is the process whereby particles move from regions of higher concentration to regions of lower concentration. Althou

19、gh this includes the self diffusion phenomena, our interest is in the diffusion of impurity atoms.硅平面扩散工艺是在硅集成电路中广泛使用的一种掺杂技术。其利用(lyng)硅片表面的SiO2作为扩散掩膜，把待掺入的元素从窗口扩散到硅片内。第36页/共48页第三十六页，共49页。固态源扩散装置气态(qti)源扩散装置液态源扩散装置第37页/共48页第三十七页，共49页。扩散原理：空位扩散复合(fh)扩散格子间隙扩散第38页/共48页第三十八页，共49页。Mathematical Model for D

20、iffusion：The basic one-dimensional diffusion process followsFicks first law of diffusion: J = -D N/ xwhere 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 t

21、he continuity equation for the particle flux: N/ t = D 2N/ x2in which the diffusion coefficient D has been assumed to be independent of position. This assumption is violated at high impurity concentrations.第39页/共48页第三十九页，共49页。Two specific types of boundary conditions are important in modeling impuri

22、ty diffusion in silicon.The first is the constant-source diffusion(恒定表面浓度扩散(kusn), in which the surface concentration is held constant throughout the diffusion.N(x,t)=Noerfcx/2(Dt)1/2Where erfc is complementary error function(相补误差函数).第40页/共48页第四十页，共49页。The second is called a limited-source diffusion

23、(限定(xindng)源扩散), in which a fixed quantity of the impurity species is deposited in a thin layer on the surface of the silicon.第41页/共48页第四十一页，共49页。SOLID-STATE DIFFUSION USUALLY CONSISTS OF TWO STEPS:1) PRE-DEPOSITION；2) DRIVE-IN； During the pre-deposition step, impurities are introduced but typically

24、 do not diffuse very far into the substrate. 恒定表面浓度扩散(kusn) 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

25、源扩散(kusn)第42页/共48页第四十二页，共49页。在热扩散中，掺杂原子通过掩膜向硅片中扩散时，除了在深度方向形成一定分布外，在窗口边缘同样有横向扩散。另外，在大面积掺杂时的掺杂量、结深和浓度(nngd)分布可控性重复性等方面，高温扩散法有着一定不足之处，限制了其应用。目前，在低浓度(nngd)高精度掺杂方面已被离子注入技术所替代。第43页/共48页第四十三页，共49页。Ion Implantation:Ions of dopant atoms are accelerated to a high velocity in an electric field and impinge on t

26、arget 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 precisely controlled. The dopant concentration can be carefully controlled by monitoring implantation current.第44页/共48页第四十四页，共49页。Advantages:掺杂深度与浓度精确可控；掺杂