1、q 真空的基本知識(shí)真空的基本知識(shí)q 稀薄氣體的基本性質(zhì)稀薄氣體的基本性質(zhì)q 真空的獲得真空的獲得q 真空的測量真空的測量第四章 薄膜制備技術(shù) 為了使被研究的樣品不被周圍氣氛所污染，為了使被研究的樣品不被周圍氣氛所污染，獲取獲取“原子清潔原子清潔”的表面，薄膜制備和襯底表面形的表面，薄膜制備和襯底表面形成過程往往是在真空或超高真空中進(jìn)行的。目前，成過程往往是在真空或超高真空中進(jìn)行的。目前，人們所廣泛使用的薄膜制備系統(tǒng)都具有真空系統(tǒng)。人們所廣泛使用的薄膜制備系統(tǒng)都具有真空系統(tǒng)。F 真空：真空： 低于一個(gè)大氣壓的氣體空間。低于一個(gè)大氣壓的氣體空間。F 真空單位：真空單位： 帕斯卡（帕斯卡（Pasca

2、l）：）：Pa 托（托（Torr）：）：1Torr=133.322Pa 舊的單位：舊的單位： Torr mmHg bar atm 1、 毫米汞柱（mmHg）：1mmHg=133.3Pa。2、 托（Torr）：1Torr=133.3Pa。3、 毫巴（mbar）：1mbar=7.510-1Torr=102Pa. Atmospheric: 760 Torr Low Vacuum: 1 to 1x10-3 Torr 真空的劃分真空的劃分 Medium Vacuum: 1x10-3 to 1x10-5 Torr High Vacuum (HV): 1x10-6 to 1x10-8 Torr Ultra-

3、High Vacuum (UHV): 200 C to remove adsorbed gasesSimple, inexpensive, oil-free沸石 擴(kuò)散泵擴(kuò)散泵(Diffusion Pumps)依靠被抽氣體向蒸汽流擴(kuò)散進(jìn)行工作的. 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)q Ad

4、vantages Robust（高效） High pumping speed for relatively low cost. No vibration or noise.q Disadvantages Oil as a pumping medium, high risk of back-streaming oil, cold traps（冷阱）required Potential for serious vacuum problems 渦輪分子泵渦輪分子泵 Turbo Molecular PumpsMolecules mechanically pumped by collision with

5、 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 TorrOil/grease/electromagnetic bearingsMost common HV/UHV pump.qAdvantages Correctly

6、 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. qDisadvantage Turbo pump can be noisy and they induce vibration. Turbo pumps are expensive. 離子泵離子泵 Ion PumpsHigh voltage between anode and cathode (5 kV)Electrons are capt

7、ured 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

8、Torr to 10-11 TorrqAdvantages Clean, oil-free. No moving parts, no vibrations, quiet. Low power consumption and relatively long operating livesqDisadvantage Do not pump noble gases well. Requires “regeneration” of Ti every 4-6 years. Heated Ti filament evaporates Ti film onto cooled surface. Ti gett

9、ers reactive gases by reaction. Operate at 10-8-10-11 Torr Inexpensive, reliable Periodic operation - not primary pumping mechanism 升華泵升華泵 Titanium Sublimation Pumps 真空材料真空材料 Outgassing rates （除氣速率） Producing “virtual” leaks （產(chǎn)生氣體虛漏） Mechanical stability（機(jī)械穩(wěn)定性） Temperature stability（溫度穩(wěn)定性） Conductiv

10、ity（熱導(dǎo)率） Chemical inertness（化學(xué)惰性） Weldability（可焊接性）真空材料應(yīng)考慮的問題：真空材料應(yīng)考慮的問題：輔助材料：輔助材料： Oxygen free high-purity copper (OFHC無氧高導(dǎo)電性銅) Be-Cu alloy Tantalum（鉭）, Molybdenum（鉬）, Tungsten （鎢） Teflon (gassy)（聚四氟乙烯，特氟龍） MACOR (machinable glass composite) Alumina（氧化鋁） Quartz, pyrex (gassy耐熱玻璃) mu-metal magnetic

11、shielding (Co, Ni, Fe) Molybdenum disulfide（二硫化鉬） (lubricant)mu：機(jī)組避免使用高蒸氣壓材料：避免使用高蒸氣壓材料： Zn, Cd: especially be careful of fasteners, bolts （緊固件、螺栓） Brass（黃銅） Certain solders（焊料） Any type of grease or oils（油脂）系統(tǒng)和管道的連接：系統(tǒng)和管道的連接：氟橡膠氟橡膠密封圈密封圈Pump Down（抽氣）抽氣） Typically follows a well-defined sequence acc

12、ording 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 airBake 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

13、 order to lower the outgassing rates at room temperature. Generally it takes another day to cool and recover base pressure. 熱電偶真空計(jì)熱電偶真空計(jì)Heat filament with a constant current.Measure filament temperature with thermocouple.Gas molecules collide with and cool the filament.Voltage increases to keep fila

14、ment at constant current.Atm to 10-4 TorrFast, simple, inexpensive. 熱電偶真空計(jì)熱電偶真空計(jì)熱電偶真空計(jì)的規(guī)管主要由加熱燈絲C與D（鉑絲）和用來測量熱絲溫度的熱電偶A與B（鉑銠或康銅-鎳鉻）組成。熱電偶熱端接熱絲，冷端接儀器中的毫伏計(jì)，從毫伏計(jì)中可以測出熱偶電動(dòng)勢。1）測量的壓強(qiáng)是被測容器的真實(shí)壓強(qiáng)；2）能連續(xù)測量，并能遠(yuǎn)距離讀數(shù)；3）結(jié)構(gòu)簡單，容易制造；4）即使突然遇到氣壓急劇升高，也不會(huì)燒毀。熱電偶真空計(jì)的優(yōu)點(diǎn)：熱電偶真空計(jì)的優(yōu)點(diǎn)：1）標(biāo)準(zhǔn)曲線因氣體種類而異，故對于空氣測量得到的標(biāo)準(zhǔn)曲線不能直接用于其他氣體；2）由于熱慣性

15、，壓強(qiáng)變化使熱絲溫度的改變將滯后，讀數(shù)亦必定滯后；3）受外界的影響很大，所以規(guī)管必須安裝在不易受熱輻射或?qū)α鳠岬奈恢茫?）老化現(xiàn)象嚴(yán)重，必須經(jīng)常校準(zhǔn)。熱電偶真空計(jì)的缺點(diǎn)：熱電偶真空計(jì)的缺點(diǎn)： 電離真空計(jì)規(guī)管電離真空計(jì)規(guī)管具有足夠能量的電子在運(yùn)動(dòng)中與體分子碰撞，可能引起分子的電離，產(chǎn)生正離子及電子。而電子在一定的“飛行”路程中與分子碰撞次數(shù)，又正比于分子的密度，一定溫度下也正比于氣體壓強(qiáng)，故產(chǎn)生的正離子數(shù)也正比于壓強(qiáng)。由此可見，電離現(xiàn)象是與壓強(qiáng)有關(guān)的現(xiàn)象，可作為一種真空測定的依據(jù)。熱陰極電離真空計(jì)是測量極高真空的儀器，測量范圍為0.1110-5 Pa1）測出的是總壓強(qiáng)2）反應(yīng)迅速，可連續(xù)讀數(shù)，還

16、可以遠(yuǎn)距離控制；3）可測很低的壓強(qiáng)。一般的電離計(jì)就可測量到510-5 Pa；4）規(guī)管小，易于連接到被測量處；5）一般電離真空計(jì)的校準(zhǔn)曲線范圍寬，通常在101 105 Pa之間；6）對機(jī)械振動(dòng)不敏感；熱陰極電離真空計(jì)的原理熱陰極電離真空計(jì)的原理熱陰極電離真空計(jì)的優(yōu)點(diǎn)熱陰極電離真空計(jì)的優(yōu)點(diǎn)1）靈敏度與氣體的種類有關(guān)；2）壓強(qiáng)大于10-1 Pa時(shí)，燈絲易于燒毀，但一旦真空系統(tǒng)突然漏氣，如不設(shè)置專門保護(hù)線路，規(guī)管燈絲往往立即燒毀；3）在工作時(shí)產(chǎn)生化學(xué)清除作用及電清除作用，造成壓強(qiáng)的改變，影響測量準(zhǔn)確度；4）玻璃殼、電極的放氣，會(huì)導(dǎo)致產(chǎn)生測量誤差；熱陰極電離真空計(jì)的缺點(diǎn)：熱陰極電離真空計(jì)的缺點(diǎn)： 質(zhì)譜儀真空計(jì)質(zhì)譜儀真空計(jì) 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,