薄膜制备与表面分析01

null薄膜制备与表面分析 Thin Film Synthesis and Surface Analysis薄膜制备与表面分析 Thin Film Synthesis and Surface AnalysisQing-Yu Zhang State Key Laboratory for Materials Modification by Laser, Ion and Electron Beams 概论  表面及表面科学 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  表面及表面科学概论  表面及表面科学 Since it requires energy 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 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。概论  表面分析技术概论  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 关于××同志的政审材料调查表环保先进个人材料国家普通话测试材料农民专业合作社注销四查四问剖析材料 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  表面分析技术概论  表面分析技术概论  表面分析技术概论  表面分析技术概论  表面分析技术概论  表面分析技术概论  表面分析技术概论  表面分析技术概论  表面分析技术概论  表面分析技术部分表面分析设备的分析范围 概论  表面分析技术概论  表面分析技术概论  真空技术原理概论  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  真空技术原理概论  真空技术原理真空单位 Atmospheres (atm): Scale relative to our atmospheric pressure as 1 atm Pascal (Pa): SI unit equal to N/m2 mBar: Equal to 1x10-8 Pa. Torr or mmHg: Most commonly used pressure unit, based on mercury vacuum gauges.概论  真空技术原理概论  真空技术原理真空的划分Atmospheric: 760 Torr Low Vacuum: 1 to 1x10-3 Torr Medium Vacuum: 1x10-3 to 1x10-5 Torr High Vacuum (HV): 1x10-6 to 1x10-8 Torr Ultra-High Vacuum (UHV): < 1x10-9 Torr 概论  真空技术原理概论  真空技术原理真空的意义 Monolayer Coverage Time For an ideal gas, the time needed for monolayer coverage is given by: tML  1019/ ZA where ZA is impingement rate.概论  真空技术原理概论  真空技术原理真空的意义 Impingement Rate (Flux) For an ideal gas, the impingement rate is given by: ZA = ρ v / 4 where, ρ - the number density of gas molecules v - the mean velocity概论  真空技术原理概论  真空技术原理概论  真空技术原理概论  真空技术原理真空的获得 Ultimate Pressure Low Vacuum (Rough) Pumps Rotary Vane Pumps Sorption Pumps High Vacuum Pumps Diffusion Pumps Turbo Molecular Pumps Ultra-High Vacuum Turbo Molecular Pumps Ion Pumps Titanium Sublimation PumpsOil / Oil-Free Oil Rotary Vane Pumps Diffusion Pumps Turbo Molecular Pumps Oil-Free Turbo Molecular Pumps Ion Pumps Titanium Sublimation Pumps概论  真空技术原理概论  真空技术原理真空的获得 Gas enters the inlet port and is trapped between the rotor vanes and the pump body. The eccentrically mounted rotor compresses the gas and sweeps it toward the discharge port. When gas pressure exceeds atmospheric pressure, the exhaust valve opens and gas is expelled. Atmosphere to 10-3 torr Robust, inexpensive Oil lubricated 概论  真空技术原理概论  真空技术原理真空的获得 LN2 cooled molecular sieve with large surface area Atm to 10-3 Torr (two units working alternately) Quickly becomes saturated Must be baked at >200 °C to remove adsorbed gases Simple, inexpensive, oil-free 概论  真空技术原理概论  真空技术原理真空的获得 Momentum transfer to gas molecules through collision with directed jet of oil molecules Require cooling water, backing pump 10-3 to 10-7 Torr (to 10-9 Torr with LN2 cooling) Advantages Robust High pumping speed for relatively low cost. No vibration or noise. Disadvantages Oil as a pumping medium, high risk of back-streaming oil, cold traps required Potential for serious vacuum problems 概论  真空技术原理概论  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 of the average thermal velocity of molecules. Atmosphere to 10-10 Torr Oil/grease/electromagnetic bearings Most common HV/UHV pump.概论  真空技术原理概论  真空技术原理真空的获得 Advantages Correctly 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. Disadvantage Turbo pump can be noisy and they induce vibration. Turbo pumps are expensive.概论  真空技术原理概论  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 accelerated 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  真空技术原理概论  真空技术原理真空的获得 Advantages Clean, oil-free. No moving parts, no vibrations, quiet. Low power consumption and relatively long operating lives Disadvantage Do not pump noble gases well. Requires “regeneration” of Ti every 4-6 years.概论  真空技术原理概论  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 Torr Inexpensive, reliable Periodic operation - not primary pumping mechanism概论  真空技术原理概论  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  真空技术原理概论  真空技术原理真空的获得 Oxygen free high-purity copper (OFHC) Be-Cu alloy Tantalum, Molybdenum, Tungsten Teflon (gassy) MACOR (machinable glass 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 solders Any type of grease or oils 真空的获得 Common Vacuum Problems Improper cleaning or handling techniques Using incompatible materials Leaks Virtual leaks 概论  真空技术原理概论  真空技术原理真空的获得 概论  真空技术原理概论  真空技术原理真空的获得 概论  真空技术原理概论  真空技术原理真空的获得 Pump Down Typically follows a well-defined sequence according to the types of pumps on the vacuum system For UHV systems, typically requires a few hours to reach a medium vacuum after a vent to air Bake Out Heat 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 recover base pressure.概论  真空技术原理概论  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 Torr Fast, simple, inexpensive. Thermocouple Gauge 概论  真空技术原理概论  真空技术原理真空的测量 Two 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 wire. Measure the current between anode and collector. Operate at 10-4 to 10-11 Torr Sensitive, high accuracy, widely used.Ion Gauge (Bayard-Alpert)概论  真空技术原理概论  真空技术原理真空的测量 Quadrupole mass spectrometer - RGA (residual gas analyzer) 10-4 to <10-14 torr Total pressure mode integrates all ion intensities Partial pressure mode indicates residual vacuum composition Highly accurate, precise Complex, expensive.Mass Spectrometer概论  真空技术原理概论  真空技术原理真空的测量 Typical UHV mass spectrum of residual gases before bakeout.