真空技术原理

1、薄膜制备与表面分析Thin Film Synthesis and Surface Analysis概论 表面及表面科学 固体的表面、或者说界面， 在人们的社会实践中起着极为重要的作用。表面科学的研究，对整个科学技术的发展具有重要的意义。表面科学包括表面物理、表面化学、表面电子学、表面生物学等。 概论 表面及表面科学固体表面：物体与真空或气体的界面。固体表面可以指从单一的第一个原子层到几个原子层厚度的表面层，甚至深达几个微米的表面层。在热力学平衡的条件下，固体表面的化学组成、微观结构、原子振动状态等均会与固体内部产生一定的差异。概论 表面及表面科学 Since it requires energ

2、y to terminate the bonding, the surface is energetically less stable than the bulk. This energy is known as the surface free energy. In the case of liquid interfaces, this energy is called surface tension. 概论 表面分析技术 表面分析技术是人们为了获取表面的物理、化学等方面的信息而采用的一些实验方法和手段。SampleExcitationsourceEnergy SelectorSignal

3、 DetectorEvent概论 表面分析技术一般地说，它是利用一种探测束如电子束、 离子束、光子束、中性粒子束等，有时还加上电场、磁场、热等的作用，来探测材料的形貌、化学组成、原子结构、原子状态、电子状态等方面的信息。 概论 表面分析技术探测粒子 发射粒子分析方法名称简称 主要用途 e e低能电子衍射 LEED结构e e反射式高能电子衍射 RHEED结构e e俄歇电子能谱 AES成分e e扫描俄歇探针 SAM微区成分e e电离损失谱 ILS成分e 能量弥散x射线谱 EDXS成分e e俄歇电子出现电势谱 AEAPS成分e 软x射线出现电势谱SXAPS成分e e消隐电势谱DAPS成分e e电子能

4、量损失谱EELS原子及电子态e I电子诱导脱附ESD吸附原子态及成分e e透射电子显微镜TEM形貌e e扫描电子显微镜SEM形貌ee扫描透射电子显微镜STEM形貌概论 表面分析技术探测粒子 发射粒子分析方法名称简称 主要用途 I I离子探针质量分析IMMA微区成分I I静态次级离子质谱SSIMS成分I n次级中性离子质谱SNMS成分I I离子散射谱ISS成分、结构I I卢瑟福背散射谱RBS成分、结构I e离子中和谱INS最表层电子态I 离子激发x射线谱IEXS原子及电子态概论 表面分析技术探测粒子 发射粒子分析方法名称简称 主要用途 ex射线光电子谱XPS成分、化合态 e紫外线光电子谱UPS分

5、子及固体电子态 e同步辐射光电子谱SRPES成分、原子及电子态红外吸收谱IR原子态拉曼散射谱RAMAN原子态 扩展x射线吸收谱精细结构SEXAFS结构 角分辨光电子谱ARPES原子及电子态结构 I光子诱导脱附谱PSD原子态概论 表面分析技术探测粒子 发射粒子分析方法名称简称 主要用途 Ee场电子显微镜FEM结构EI场离子显微镜FIM结构EI场离子显微镜-原子探针AP-FIM结构及成分Ee场电子发射能量分布FEED电子态Ee扫描隧道显微镜STM形貌Tn热脱附谱TDS原子态n中性粒子碰撞诱导辐射SCANIIR成分n n分子束散射MBS结构、原子态AWAW声显微镜AM形貌概论 表面分析技术部分表面分

6、析设备的分析范围 概论 表面分析技术XPS AES ILS ISS RBS SIMS 测氢 NoNoNoNoNoYes元素灵敏度均匀性 GoodGoodBadGoodGoodBad最小可检测灵敏度 10-2-10-310-2-10-310-910-2-10-310-2-10-310-4-10-5定量分析 GoodYesBadBadGoodBad化学态判断 GoodYesYesBadBadBad谱峰分辨率 GoodGoodGoodBadBadGood识谱难易 GoodGoodGood-表面探测深度 MLsMLsMLsMLML-mML- MLs空间分辨率 BadGoodGoodBadBadGood

7、无损检测 YesYesYesNoYesYes理论数据完整性 GoodYesBadYesGoodBad概论 真空技术原理为了使被研究的样品不被周围气氛所污染，获取“原子清洁”的表面，表面分析过程往往是在真空或超高真空中进行的。目前，人们所广泛使用的很多表面分析设备都具有真空系统。薄膜制备设备往往涉及真空系统。概论 真空技术原理真空单位Atmospheres (atm): Scale relative to our atmospheric pressure as 1 atmPascal (Pa):SI unit equal to N/m2mBar:Equal to 1x10-8 Pa. Torr

8、or mmHg:Most commonly used pressure unit, based on mercury vacuum gauges.概论 真空技术原理真空的划分Atmospheric: 760 TorrLow Vacuum: 1 to 1x10-3 TorrMedium Vacuum: 1x10-3 to 1x10-5 TorrHigh Vacuum (HV): 1x10-6 to 1x10-8 TorrUltra-High Vacuum (UHV): 200 C to remove adsorbed gasesSimple, inexpensive, oil-free概论 真空

9、技术原理真空的获得Momentum transfer to gas molecules through collision with directed jet of oil moleculesRequire cooling water, backing pump10-3 to 10-7 Torr (to 10-9 Torr with LN2 cooling)AdvantagesRobustHigh pumping speed for relatively low cost. No vibration or noise.DisadvantagesOil as a pumping medium,

10、high risk of back-streaming oil, cold traps requiredPotential for serious vacuum problems概论 真空技术原理真空的获得Molecules mechanically pumped by collision with angled high speed turbine blades (rotor). Several rotor arranged in a series spinning at 30,000-60,000 rpm.Rotor tangential velocity is on the order

11、of the average thermal velocity of molecules. Atmosphere to 10-10 TorrOil/grease/electromagnetic bearingsMost common HV/UHV pump.概论 真空技术原理真空的获得AdvantagesCorrectly operated they do not back-stream oil into the vacuum system at any time.They can be started and stopped in a few minutes time. Disadvanta

12、ge Turbo pump can be noisy and they induce vibration. Turbo pumps are expensive.概论 真空技术原理真空的获得High voltage between anode and cathode (5 kV)Electrons are captured in anode and spiral due the to magnetic field (longer path-length).Gas molecules are ionized by collisions with electrons and are accelera

13、ted to cathode.Ions embedded in cathode material (titanium) and sputter titanium atoms from surface.Sputtered Ti atoms act as getter for reactive gases.10-4 Torr to 10-11 Torr概论 真空技术原理真空的获得AdvantagesClean, oil-free.No moving parts, no vibrations, quiet.Low power consumption and relatively long opera

14、ting livesDisadvantage Do not pump noble gases well.Requires “regeneration” of Ti every 4-6 years.概论 真空技术原理真空的获得Heated Ti filament evaporates Ti film onto cooled surface.Ti getters reactive gases by reaction.Operate at 10-8-10-11 TorrInexpensive, reliablePeriodic operation - not primary pumping mech

15、anism概论 真空技术原理真空的获得Materials ConsiderationsOutgassing rates Producing “virtual” leaks Mechanical stability Temperature stabilityConductivity Chemical inertness Weldability概论 真空技术原理真空的获得Oxygen free high-purity copper (OFHC) Be-Cu alloyTantalum, Molybdenum, Tungsten Teflon (gassy) MACOR (machinable gl

16、ass composite) Alumina Quartz, pyrex (gassy) mu-metal magnetic shielding (Co, Ni, Fe) Molybdenum disulfide (lubricant)Compatible Materials 概论 真空技术原理Materials to be Avoided (high vapor pressures) Zn, Cd: especially be careful of fasteners, bolts Brass Certain soldersAny type of grease or oils真空的获得Com

17、mon Vacuum ProblemsImproper cleaning or handling techniquesUsing incompatible materialsLeaksVirtual leaks 概论 真空技术原理真空的获得概论 真空技术原理真空的获得概论 真空技术原理真空的获得Pump DownTypically follows a well-defined sequence according to the types of pumps on the vacuum systemFor UHV systems, typically requires a few hours t

18、o reach a medium vacuum after a vent to airBake OutHeat the chamber to temperatures between 100oC and 200oC for 1 - 2 days.Rapidly remove adsorbed gases from the chamber walls at high temperatures in order to lower the outgassing rates at room temperature.Generally it takes another day to cool and r

19、ecover base pressure.概论 真空技术原理真空的测量Heat filament with a constant current.Measure filament temperature with thermocouple.Gas molecules collide with and cool the filament.Voltage increases to keep filament at constant current.Atm to 10-4 TorrFast, simple, inexpensive.Thermocouple Gauge概论 真空技术原理真空的测量Tw

20、o identical heated filaments; one sealed at HV, one exposed to system.Current flows through Wheatstone bridge circuit.Pressure difference indicated by meter (non-linear).Atm to 10-4 torr.Simple, reliable, inexpensive.Pirani Gauge概论 真空技术原理真空的测量Heated filament produces electrons via thermionic emission.Electrons are accelerated towards anode grid.Many electrons pass through the grid and create positive ions from collisions with gas molecules.Ions are accelerated to collector w