KHOA H O C - C O N N G U O l - XA H O I
Phirong phap kiem dinh do chan khdng trong oho tao mang mong
Mot he thong che tao mang mong du dit tien the nao di chang niTa, vin khong may huTu ich neu Chung ta Jchong the biet do chan khong cua he thong do. Xac djnh do chan khong cua phong chufa VI the tror thanh mot yeu to' rat quan trong trong cong nghe vi mach. Bai viet nay trmh bay ve mot soap ke tieu bieu va nguyen ly hoat dpng cua chung. Nhihig thiet bj do do chan khong chinh la ap ke thu dien, ap ke nhiet dien va ap ke ion hoa. Ben canh do la nhOhg thong tin ve cac thiet b[ khong kem phan quan trpng trong viec che tao mang mong nhiT bp dieu chmh lUU lutfng
(MFC), mpt so'thiel bj tieu bieu de khao sat chd ro ri va cac yeu to'trong phong chufa khi bcrm, nhiTbo phan ti'ch khi con dil* (RGA) va bp cam bien dp ri bing heli.
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hu dd trinh bay trong nhdng so trUde, linh kien dien td ddi hdi mdng mdng vdi nhijfng tinh ndng khde nhau, va dp chdn khdng cd tdc dpng manh din tinh quang dien td eua mdng mdng. N l u chi nhin mdt phdng chda (chamber) cua he t h i n g c h l tao mdng mdng, chdng ta khd cd t h i dodn dupe chinh xdc dp chdn khdng, nhd't la khi phdng chda d mat dp chdn khdng eao hay cUc eao. Chung ta can nhijfng dung cu hdu hieu vd chinh xdc de do dp chdn khdng. T h i l t hi k i l m dinh dp chdn khdng cd hai nhiem vu: (1) Quylt dinh dp chdn khdng can dung va (2) Xdc dinh cho hi ri. Ve nhiem vu (1), dp chdn khdng thay doi vdi cdc he thd'ng bPm chdn khdng dung. V l nhiem vu (2), sau khi ldp ddt be thing c h l tao mang mdng, dieu trddc tien ehdng ta phai lam Id k i l m sodt xem phdng chda ed bi ri bay khong? Vi day Id chuyen rd't thddng xay ra.SirrdritfennrtfauP
Sd rd ri do n h i l u nguyen nhdn khdc nhau: Cd t h i td phdng chda, khi cd h a t bui hay nhdng vdt cP khi nam tren vdng O rings; do nhijCng ong gas bay cdc phdn noi cae ong gas khdng du chat, vdng dem kin bi tray xxidc, sd n h a khi cua cdc nguyen lieu hay mdng mdng cdn sdt lai trong phdng chda hay do sU nha khi t d tddng eua phdng chda khi phdng chda ddPe bum tdi do chdn khdng trung binh khoang 200 mTorr d i n lO^ Torr. Hien tUpng nay dupe b i i t
dudi ten ri do (virtual leak). Hinh 1 la mdt vi du ve cdc chd't nha ra td bdc tUdng trong phdng chda khi phong nay d dp chdn khdng khoang 200 mTorr.
Phikn tu gas o&ci du i«i
1-216p hydrogen, carbort mono»de ^r4 nHfog«n
5-20 l&p tvuxSc thim thau vio tuj^ng do hi4u lin j vat ly
1- 2 \6p n\j6c Ihiim thiu vio t i n ^ j do hi8u ung h6a hoc
Cek \6f> carbon, mangan«M, hydrogenr mirogw, oxyg«%
tftki b* mat ctia buctuciig
Hinh 1: Nhiing chdt nhd ra tU bUc tUdng cua phdng chUa [1]
De xdc dinh dp ri, dilu trUde tien la dung phdPng phdp thdng thudng, chang ban nbU dung bPm cP bpc bPm phdng chda d i n dp chdn khong sP bp, roi dung nddc xd phdng xit vdo cdc phan dang nghi ngd vd ehd hi ri la nPi cd bpt xd phdng. O nbOrng chd ri nhd hPn, khi dp chdn khdng dat khoang 10-2- 10* Torr, ehdng ta ed the dung isopropanol xit vdo eho nghi ngd vd dp sud't nPi dp k l chdn khdng noi
87
KHOA H O C - C O N N G L f O l - X A HOI
lien vdi phdng chda se tang len. Chung ta cung co the dung bp cam bien dp ri bdng hcli de xac dinh cho hi ri.
Bd cam bien dd ri bang heli (Helium leak detector)
Day la thiet bi hdu hieu de do va xac dinh dp ri trong phdng chda. Cd hai each de theo ddi dp ri trong he thdng che tao mang mdng:
Dd Id hd bdng each danh hpi vdi heli: Sau khi bo"m phdng chda den dp chan khdng sP bp, chung ta qud dp phong chda vdi heli, sau dd dung ddu dd d l tim chd ri. Gidi ban phat hien cua phUPng phdp nay vao khoang >x\0 ** mluir.lJsci:.
Dd Id hd vdi dp ri cam bien chan khdng: Mpt khi phdng chda da chan khdng kin, chdng ta xit nhdng cho cd t h i ri vdi heli d l tim cho ri. Tiep theo dd, pho ke khdi lUpng se dupe dung d l theo ddi heli (amu = 4). Gidi han phdt hien cua loai thiet hi nay vao khodng 5x10'- mbar.L I sec.
Bd phan tich khi cdn tax (Besidual gas analyzer (BGAl
Dung cu nay b i i n thai td t h i l t hi dd lo bd dung heli vd thudng dupe sd dung trong viec do dp sud't cue bp cua eac chd't khi trong phdng chda. Thudng thi bd phdn tich RGA dUpc noi vdi phdng chda bdng mpt gd vanb cd kich thude 2,75 inches (khoang 7 cm). Thilt hi nay ed ba bp phdn chinh: Nguon ion, bp lpc khdi lupng b i n eUc va bp cam biin ion. Phdn td cua chd't khi td nguon ion hi ion hda vd dupe tdch rdi ra tuy theo k h i i lUpng trong bd lpc khoi lUpng.
Va lupng ion d nhdng khoi ldpng khdc nhau cd t b i do dupe. RGA thudng boat ddng d dp chdn khdng cao khoang 10"^ Torr d l trdnh sU xung dot gida ion tao thanh vdi nhdng phdn td chd't khi. Mpt ed'u tao dien binh cua bd RGA ddPe bilu thi d hinh 2.
Ion ngudn B9 Ipc kh6i lirgng O^u (Am bi4n
Ngudn ion: Day irium bpc vdi chd't thorium oxide hay yttrium oxide dUPe dung ldm spfi filamdng.
Spi filamdng nay dUpe nung ndng d l phdng thich ra electron. Nhdng electron ndy dpi phd cdc chat khi mdi den, tao ra dien tich. Dipn trddng se ddpe dung de dieu k h i l n nhdng phdn td tich dien hay bi ion hda. Ion tren andt bi keo di bdi ldpng dien the noi thau kinh tap trung vd tao ra mdt chum ion (beam). Thau kinh tap trung nay ddpe gid d dien the am dd'i vdi andt. Chum ion ndy se di vdo bp lpc khdi lupng; nhdng phan cdn lai dap vdo thdu kinh p dau ra, trd thdnh trung tinh vd tao nen dong dien chay.
Bp lpc khdi lupng bd'n cUc: B i n cdc ndy nam song song vdi nhau tao thdnh mdt hinh vuong. Bp lpc khdi lupng ndy loai ra td't ed ion, trd nhiing ion cd ty so khdi ldpng dien tich (mass-to-ebarge ratio) ddc biet.
Bp edm bien ion: Cd t h i d dang cup Faraday' (Faraday cup), bp nhdn dien td (EM)" bay dddi sd k i t hpp eua hai dang nay.
o a u do lay mau gas gan phien ba' dan i w a l e t i
Hani hA !nj Di^n ngu6n
Hinh 2: Cdu tgo cda bd RGA (Hdng Inficon)
liiiih :>: l\(l\ lap dat vol phong chua inguon: Transpector CIS2. i-lcmg ill/icon) 12J
Hinh 3 gidi thieu mot phdng chilu kit noi vdi RGA. Vdi phdPng phdp dung bp RGA, dd lieu thddng ddPc trinh bdy bang tam bilu do vdi ty s l khIi Iddng dien tich (mass-to-eharge ratio) d true X vd pho cam dp (spectra sensitivity) d true Y. RGA dUPe diing d l tim nhdng nguyen t l trong phdng chda cua he t h i n g c h l tao mdng mong. Bang 1 liet kd ty so dong vi (isotope ratios) cua vdi nguyen t l tieu bieu.
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KHOA HOC ^"^
KHOA H O C - C O N N G U O l - XA HOI
Ty SO dong vj
Thftnh p h i n
c
N
O
F Ne
Na Al Si
P S
Cl
Ar
Khdi lif(?ng
12 13 14 15 16 17 18 19 20 21 22 23 27 28 29 30 31 32 33 34 36 35 37 36 38 40
Ty s6 luong d6i
98.892 1 108 99.63
0 37 99.759 0,0374 0.2039 100.0 90.92 0.257 8.82 100.0 100.0 92.27 4.68 3.05 100.0 95.06 0.74 4.18 0.016
75.4 24.6 0.337 0.063 99.600
Bdng 1: Ty sd dong vi cua vdi nguyen td tiiu bieu
Mpt vi du ve ede dong vi eua argon td bilu do RGA dUPc bilu thi d hinh 4.
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Lam the nao phan biet hai phan tir cd cung khdi lutmg trong RGAP
Vi du nhu N^ va CO cd cdng khdi lUpng 28. Hai phan td nay co the phan biet dUpe bdng each dung cracking mo hinh (cracking patterns). N^ thUdng dupe thu gom lai dUdi dang '^^ cd khd^i lUpng bdng 28; nhUng khoang 6-7% cua phdn td nay bien thanh dang ^i va ^ vdi khoi lUpng bang 14. Dong vi N'-'cung CO mpt dinh nhd vdi khoi lUpng 15. Trong khi dd con eo dinh nhd '^^0,0 y^j j^j^g'j i^/gng theo thd tu bang 12, 16 va 14. Tuy theo khoi lUpng cua cdc dinh nay, chung ta co t h i phdn biet dUpe sU khac nhau gida hai phdn td N^ va CO. Dudi day la vai dinh nghia ve nhdng td thudng de cap nhieu trong bp RGA:
Cracking mo hinh
Hinh 5 bieu hien cracking mo binh cua khi methane (CH^).
Hlnh 4: Ddng vi cua argon [3]
Hlnh 5: Cracking md hinh cua methane trong bg RGA [3]
Ty so khoi Idctng - di?n tich (Mass-to-charge ratio: mie) Id gi?
Ty so m/e la ty so gida phdn td lUpng va so electrons rdi khdi ed'u true nguyen td. Vi du nhU, carbon dioxide (COg) cd phan td lUpng bang 44;
khi mpt electron rdi khdi, phdn td hi ion hda don le ed m/e bang 44/1 hay 44. Trong khi dd vdi sU rdi khdi eua hai h a t electron, phdn td hi ion hai
KHOA H O C - C O N N G U O l - X A HOI
lan cd m/e = 44/2 = 22.
Dam vi khdi Idgfng nguyen td (Atomic mass unit) Id gi?
Moi nguyen to hda hpc ed nhdng dong vi khde nhau nhu dUpe t h i hien trong bang 1. Chdng ban nhu dong vi cua carbon la ',JC.','C,',^C. Moi dong vi cd khdi ldpng hpi khdc nhau. Gia tri trung binh cua nbdlig khdi ldpng nay ddpe dinh nghia Id khdi ldpng nguyen td trung binh (average atomic mass) hay thudng gpi tdt la atomic mass unit (amu). Chang han nhu amu cua carbon Id 12,01, hydrogen (1,008) va nitrogen (14,01). 1 amu = 1,66 x 10 '•* ,i,'
Ap ke thu dien (Capacitance manometer)
Cdu tao cua dp ke thu dien dPpc the hien d hinh 6.
Diafam Do chan khong
c i n do
Dien cUc co dinh
Hinh 6 (a): Cdu tgo cua dp ki' thu diin
Dung cu ndy dung d l do dp sud't vdi dO chinh xdc
± 0.1% d i n lO'-^Torr. Nguyen tdc boat ddng eua dp k l ndy ed t h i cdt nghia nhd sau: Thay dli dp suat trong phdng chda se tao ra sd di dpng eua mdng diafam ddn hIi (flexible diaphragm) khi so sdnh vdi mpt mdng khde dddc gid d mpt vi tri nhd't dinh.
Mdng diafam ndy Id mpt tam kim loai, thddng lam bdng chdt Inconel. Dp thu didn (capacitance) ddpe do bang khodng cdch eua hai mdng diafam. Dilm ylu eua loai dp k l ndy Id gid ddt, de thay dli vdi nhiet dp vd loai chd't khi dung. Hinh 6(b) Id mpt dp k l thu dien hipn bdn tren tbi trUdng.
Ap kd nhidt didn (Thermocouple gauges)
Loai dung cu ndy ed t h i do dp suat trong khoang td 760 d i n lO'^ Torr. Cd t h i dung d l do dp chdn khdng sp bp cua bPm ho trp, chang ban nhd bpm turbo hay do dp sud't eua phdng chda luc ede bPm dang hoat ddng. Spi ddy den ddpe dun ndng va nhiet dien dung d l do nhiet dp eua spi ddy den.
Nhiet dp nay thddng tdng len vdi dp giam eua dp sud't. Loai dp k l nay re hpn nhdng khdng chinh xdc.
Ap ke Chan khdng Pirani (Pirani gauges)
Cdu tao eua dp k l chdn khdng Pirani ddpe the hien d hinh 7.
Cofliptnutor
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Hlnh 7 (a): Sa do cda dp ki' chdn khdng Pirani (compensa- tor: Bd phdn bd; manometer: Ap ke); (b) Ap ke hiin bdn
trin thi trUdng (Model 945, Hdng MKS) [5]
Hlnh 6 (b): Ap ke thu diin hien bdn tren thi trudng (Baratron, Model 631 C cua Hdng MKS) [4]
Cau tao eua loai dp k l nay dUa vdo mang Iddi Wheatstone. R, trong hinh 7 (a) dung de dilu chinh sU thdng bang cua dp k l . Gia tdng dp suat se gia tang sU hao nhiet do sU giam gid tri dien trd (resistance) eua day ndng va clu Wheatstone
on Hoat tfong ^. ,^, . ,^ „„..
KHOA HOC "^
K H O A H O C - C O N N G U O I - X A HOI
trd t h a n h md't thang bdng. K i t qua la nhilu ndng ldpng phdn tdn trong day ndng, dan den sU gia tdng dien t h i . Dien t h i nay cang tang thi day dien cdng ndng hPn va mang ludi Wheatstone trd thanh thdng bang trd lai. Mdi dp sud't deu ddpe do d mot nhiet dp ddy ndng nhd't dinh.
Bd dieu chinh luu lutmg (Mass flow controller -MFC)
Loai dung cu nay rd't can t h i l t trong cac he t h i n g c h l tao mang mdng, dung de do vd dieu ehinh luu lupng chd't long, chat khi d mdt pham vi nhd't dinh.
Bp dilu ehinh luu lUpng nay gom ed luu lupng k l , bp dilu chinh vd van. MFC thudng cd setpoint td 0-100% vd gid tri chinh xdc nam trong khoang td 0-90% eua pham vi ndy. MFC thudng dupe ldp ddt gida nguon gas va phdng chda. Don vi thudng dung la seem (standard cubic meter per minute) dupe dinh nghia nhU la ddng chdy cd dung lUpng 1 cm^
chd't khi trong mpt phut d nhiet dp 0°C (273K) vd d dp sud't 1 at (atmosphere).
CiiOn cAm bien vftglanlH«t
Tdi hO thing chan khAng
.< Ranh iC n h t e h s
Hlnh 8: Sa do tdng qudt cua mgt MFC [6]
Ap kd ion hda (Ionization gauge)
Cdu tao cua dp k l ion hda dupe t h i hien qua hinh 9. T h i l t hi thdng dung nhd't la dp k l Bayard- Albert.
Nguyen ly boat ddng nhU sau: Mdt spi ddy den ndng dung d l cung cd'p electron vd nhdng electrons nay hi thu hut bdi mang lUdi nap vdi didn dUPng.
Ldp v6 thuy tinh
' Odu thu ion
Lirti
S^i t<Sc dftn
.xiM.
Hlnh 9 (a): Cdu tgo cua dp ki' ion hoa [2]; (b) Ap ke hien bdn tren thi trUdng (Hdng Varian) [7]
Nhdng electron nay va vdo phan td chd't khi va ion boa nhdng phdn td nay. Ion se chay den catdt, k i t qua la ddng dien dat dupc va ddng dien nay se ty le vdi dp sud't trong phdng chda. Bayard- Alpert gauge dupe dung de do dp chdn khdng trong khoang 10"^-10"^ Torr.
Trong so' tdi chdng ta se de cap d i n tinh nang vd ed'u trdc eua mang mong va cdc phUPng phdp de do cdc tinh ndng nay.
Chii thich va tai lieu tham khao
'Clip Faraday: Dung mot tam kim loai hay dien cue co hinh thii nhU cdi Clip, n d ma chum ion co the va triing. Khi ion dap vao detectcf, ion trd thinh trung tinh, k6o dong dien t\i mach dien noi liin hai dien cUc. Clip Faraday vCtng ch^c or dp suat cao, on dinh nhiing co khuyet diem la cho dong di?n nho, \km thcfi gian ddp tjtng thap hom.
" Bp nhan di$n tiJf (EM): Hoat dong nhijf mot bp tien khuech dai (in situ preamplifier) diing de tSng do nhay. Ion vifa den dUcfc gia toe va chay vao EM bfing mgt di|n th§' am cao (khoang 1 kV hay hem niia). Khi va cham, mpt hay nhieu dipn til thii cfi'p di/dc phong thich ra, va nhdng electron nay se dupc gia toe den be mSt thuf hai c6 di?n the l(Jn hcfn, ket qua la nhieu electron di/pc tao them ra. Bg EM phan ijfng nhanh, co dp nhay cao hcfn Faraday cup. Diem yeu cija loai detectP nay la gid ddt va khong the diing d dp sud't cao.
1. L.I.Maissel and R. Giang, Handbook of Thin film Technology, McGraw-Hill.
2. http://www.inficon.com/download/en/RGA-etch_process_
monitoring_technote. pdf
3. J. F. O'Hanlon, A User's Guide to Vacuum TechnologyWiley- Interscience Publication.
4. http://www.mksinst.com/docs/UR/pmcTl.pdf
5. http://www.mksinst.com/product/product.aspx?ProductID=453 6. S. Wolf, Microchip Manufacturing, Lattice Press.
7. http://en.wikipedia.org/wiki/Hot_filament_ionization_gaug
c-.^' -. n on 1 ^ l^^iii €#111 91
