Ion microprobe mass spectrometer with cooled electrode target for analyzing traces of fluid

Barrington, A. E.

English

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https://ntrs.nasa.gov/search.jsp?R=19710019387 2020-03-17T03:15:21+00:00Z
United States Patent rill 3,567,927 
1721 Inventor Alfred E. BarringPon 
Lexingala, Mas.  
[21]  Appl. No. 815,367 
I221 Filed Apr. 11,1969 
1451 Patented Mar. 2,1971 
[ 7 3 ]  Assignee the United States of America as represented 
by the Administmtor of the National 
Aeranautia and Space Administration 
[ 5 4 ]  ION MCRBBROBE MASS SIPECTRO1?.IETER FOR 
ANALYZING FLUID MATERIALS 
8 Claims, 2 Drawing h i s .  
[ 5 2 ]  U.S. CI ...................................................... 250/49.5, 
250/41.9 
[ 5  I ]  Int. Cl .................................................... HQlj 37/00; 
GO 1 n 23/00 
I501 Field of Search ......................................... 250141.9 
(ISE), 49.5 ( 2 ) ,  49.5 ( 8 ) ,  49.5 ( 9 )  
is61 References Cited 
UNITED STATES PATENTS 
2,826,701 311 958 Columbe ...................... 250149.5 
2,976,413 311961 Robinson .................. 250/49.5X 
OTHER REFERENCES 
" Mass-spectrometric micro-surface analysis" by the 
Geophysics Corporation of America of Bedford, Mas- 
sachusetts, Received March 25 ,  1963,5 Pages. 250-49.5 
Primary Exuminer- William F. Lindquist 
Attorneys-John R. Manning, Herbert E. Farmer and Garland 
T. Mc Coy 
ABSTRACT: An improved ion microprobe mass spectrometer 
type apparatus is provided that is suitable for analyzing trace 
amounts of a fluid. The present invention utilizes a target elec.. 
trode for holding the sample, and a means for cooling the sur.. 
faces of the target to below a fixed temperature for a deter- 
mined period of time. A stream of sample fluid is directed over 
the cooled surfaces of the target and is condensed thereon 
after which the target surface is sputtered by an incident, high 
intensity primary beam directed obliquely onto the surface 
thereof. Thereafter, means is provided for focusing the electri- 
cally charged ions of sample material that result in a seconda- 
ry beam produced due to the bombardment of the sample 
layer. Additional means is provided to remove the prior 
material from the target surfaces after each analysis, so that 
the target surface is prepared for another sample layer. 
The invention described herein was made by an ennployee 
of the United States Government and may be manufactured 
and used by or for the Government for governmental purposes 
without the payment of any royalties thereon or therefor. 
PATENTED MAR 2 1971 
ALFRED E BARR/NGGJON 
3,567,927 
1 2 
l 3 N  MICROPROBE MASS SPECTROMETER FOR ANA- 4. 16 s'nould be capable of detectang ail chem ca 4-rDrsrlay 
LYZIN@ FLUID MATERIALS elements regardless of the major conaponents o6 the 
- 
matrnx, and 
BACKGROUND OF THE INVENTION 5. it should be capable of diffeferentlat~ng between surfam 
This invention relates to ion probe mass spectrometers and 5 impur~ties and bulk ~mpuritnes 
more pafiacularly to an refrigerated t a g $  elec- Relatnve to the anal~sas of bulk solids and tiiln fiirrs, 
trode in an Ion probe mass spectrometer above-ment~oned requirements are satnsfied by technlquerr 
The development of the non mlcroprobe mass spectrometer e m p l o ~ ~ n g  the mlcroprobe mass spectrometer Yowevcr, 
const~tutes a srgnfficant add~tnon to the range of ~nstrumenta- them stall exists nn the art a need to sat~s'j, tbe above-mep- 
sgon for analysls To a great extent, the ac., 10 tmned requarements relabve to technnques for the ~ R ~ ~ ~ S Y S  ar 
ceptance of the instrument is due to ~ t s  abil~ty to perform non- 
destructive testing on thin films Accordingly, such an instru- 
ment wnll find extensnve use In such diverse fields as geology, SUMMARY OF THE INVEEJ'TlOaI 
metallurgy, semiconductor technology, surface chemrstry, 15 As will be heremafter used, the term "flu-d' is ~ntended to 
crnminology and baology Furthermore, the versatllnty and sen- ~nclude vapors, gases, and mlxtures and S ~ / L I C L ~ F " S  thelreof 
satavxty limst thereof has presently only been approached due In the unproved ion microprobe mass spectrometer type ap- 
to the availablllty of only a meager number of standards for paratus herein presented, a target electrode for holei,ng the 
use therewith. sample is cooled below a fixed temperatule and mannta~ned at 
The prior a n  has found that the mlcroprobe mass spec- 20 the lowered temperature for a predetemlned penod of tune 
tm'rteter is readily adapted to the analysis of lmpurlty distribu- A stream of fluid is darected over the cooled s u ~ a c e s  of 
laon In solid films h a v W  a thickness of less than about 100 target and deposited thereon Means 1s prov ceil hr P T C P ~ U C L I T ~  
microns, a detailed dnscusslon and descnptlon of which is an Intense beam of ions of a chemrcally Inert gas ana Ib; l x J s  
found ~n the publ~catlon entitled, "Progress in Nuclear ener- ing and accelerating the beam The deposrte$ aa-gel tper 
gy," ~ernes  IX,  Analytical Chemistry by 8. E Barrtngton, R. F. 25 obliquely bombarded by the beam to sputter or ronaze the 
K. Herzog and P. Poschenrneder published 1966 Per- atoms of the sample. These sputtered ions have d reiatevely 
gamon Press gn general, the prlor art apparatus has a primary 10, veloclty and are seEectlvely focused ~neo an a ~ a E y ~ e r  if 
source of noble gas ions integral with a target chamber, amass desired, heating means may be employed Po clean "r~re target 
and an ion detector. A well-ea~@ed, mercuq diffuu- surfaces after an analysts The target e l e c ~ ~ o d e  be of spy 
slon pump is provided to pump down the target chamber, 30 conventional design and fabricatton 
while the primary source Is evacuated by means of In one embodiment, the cooflng means 1s pneegpal v41ih 
mercury di'usion pump. The sect'on " then evacu- target electrode and consnsts of a structure havmng a channei: 
ated a combinatton zeobte soptaon sputter- formed therein for the flow of refrigerant ehererhnough In 
aon pump, mounted for continuous operation, nf desnred another embod~ment, both the cooling means aqc! the heatnng The Instrument Is 'aerated in the test Inode fntroduclng 35 means are an integral part of the electrode are sand- 
a mounted '' a target electrode the target 
w~ched between the sample hoid~ng surfaces 'The heater 
and reducnng the target pressure to less c$evlce may be of conventional electrncaE despgq and fabstca- 
about Torr. A low arc Is then In the tlon, to a source of power by means 06 cenver- 
duop~asrnatron ion source which is maintained at a pressure of tional clrcultry 
about 0 02 Tour of a noble gas such as Argon, Xenon or the 40 Thus, one ns able to provlde an improved methoa for a~raiy7 lake. The resultnng arc is then focused and severely constricted Ing trace amounts of by dlreclrng a stredm nirav >b -mDie 
an ax la"~  'lsposed magnetmc Re'd to a very dense over the surfaces of a target ejeckroae whrch hSiS beCn plasma Next, the ~ntensefied beam IS passed through a plnhole 
In the anode and acceEepated by a conacally shaped electrode below a fixed temperature After the analys~c ri7e : iruz* sir- 
The beam 1s then electmstat~caliy deflected so as t~ bombard 45 E;a:i: ;: ~ ~ e ~ ~ ~ ~ $ a i n ' n g  """'" '" 
the target at an oblnque angle of lncldence Thas then causes a 
nigher rate of sputtering than normal impact No chemical All or just a portion of the fluld may be collected for dnaiv-  
reaction occurs and the target electrode remains uncon- sis, if des~red If the sample nuld is a gas m~xture, depend~rg  
'arnnnated due to the noble gas ions on the temperature of the target surfaces, ail the fluid nay be 
The secondary ions of material resulting from the 50 condensed or the flurd may be fractkonalb c~c~densec ,  i a e r e ~ v  
sputtering of the sample layer, are next focused electrostati- P'Qv"~"~ the practlt'oner of the invention advarrage a 
cally Into a mass spectrometer, where the ~onlzed maternal IS Select"e system for the of unknown' 
separated In a magnetic sector thenr respecrave The se'ect'on of 'he re'lgerant used 1' d e t e r ~ 1 ~ e . g  c'1efl.Y 
mass-to-charge ratios The sorted rons ate then sorted again the o~erat lonal  or the rEec- 
according to their energy, by means of an electrostatlc 55 trade. C~nvenhonal refrngerants may be emoloyeo, lsrovided 
analyzer The nntenslty of the Don current correspondnng to a they are compatible for use with the apparatus, such as corn- 
glven mass peak 1s then measured with an electron rnultlpller pressed gases or CrYQgennC fluids, for examde Tiqd~, for 
~ n b  a vnbratlng reed electrometer ih spectrum 1s obtaaned, study of atmospheric gases, ~t may be de3nrabie crrnrnate 
elPt?er when :he potentaal whach the surfirce ions are the known major fractlon of the atmosphere w%cL C ~ P U  c t e ~ a  
accelerated 1s changed, together with the potential of the 60 mask the Presence of the trace ' w e  3'1% 
trostatlc analyzer, or when the magnetude of the magnerlc deposzted on the target Accordlngi~, an operat or*?: 'eI-.lPera- 
Geld ;? changed at constapt ton accelePaelng potential A per- ture 1s selected such that the known major cornporents ~f ebc 
manent record of the spectrum ns obtanned by synchronlzrng atmosphenc gas stream will not be ~o~-~deased an qoi lc l fa~ 
the horazgntaE sweep of an X-V recorder with the parameter on the target surfaces, yet allow~ng the lesser cor-sc-e?rc o 
varied and maklng the vert~cal deflection proportional to the 65 be deposited Hence, the operatlonal CemPCra'I re 01 lay- 
,on current get surfaces wdl be at, or below, about ciyope- c fl,ic t e T -  
&n order to determnne the chemical composltron of the wlde peratures which may be employed to prev~ae the cidilrabre 
varrety of ma er:aEs encocrtered IR ~rzsent-day technology operational temperature for the analysas of at-nuspr'eri~ gaoel 
pad to detec trace-co~bam~cants in the parts-per-mlllion such as inquld nitrogen, Plquad oxygen, llqugd hel ti.. 210~ : 
range, it has been proposed that modern analytncal techn~ques 70 nitrogen is preferred as a refrigerant becausc * $ *n--r ccm- 
should sat~sfy the following requlremeots mercially avariabie and is safer to ose Whcn c r{oe r  c ICU L C  
: The sensitnvety Eamt should exceed one part per rnnllnon, are employed as refragerants, the use o' raCciz -a-rcii -\. 
2 ~t should work equally well for materrals which may be equipment isobv~ated 
conductors, semnconductors and ~nsulators, The apparatus may also be employed 'lo. an >lv-i- - 2 no- 
3 :e should be nondestructive, 75 malEy conbustnble or explosive atmosphe r, SJ - 2. --e  0 7  
3,567,927 
3 4 
jgen rlch a'mosphere of a manned space craft, where the use onto the surface of the target electrode 26, wh~ch solidifies 
3~ coyvent onar soark d~scharge type analyzers would be and forms the sampie layer 28. 
T-eci~ded S r f ~ e r m o r e ,  those possessed of an ion Referring now to FIG 2, there is shown a sectional vlew of 
T ~ ~ C S O P I - O ~ ~  mass SOectrometer would be encouraged to mod,- the target electrode 26 of FIG. 1 that is prov~ded wnth an anput 
3") rie aopaVahl accosdnng to the teachings of the present das- 5 refrigeration line 36, the exit line 38 and a communicating 
i: osure '0 Q ~ ( ~ ~ ~  the advantages offered for the study and portlon 44 which allows the refrlgerant to cnrcuPate and C O O P  
a~ilaiysis af "u,m presently unobtaanable from the apparatus of the electrode 26 Addittonally, to cleanse the target after an 
he pr 0- analysss, there 1s shown a heatnng element 46 2nd a pair of 
Accord qgly, lt e an object of the present nnventnon to pro- leads .68,50 for prov~dlng suitable power to operate the ele- 
ap ~np-oved method and apparatus for the analysis of ment46 
i3~1is Whale there has been descr~bed what IS presently consndered 
S.li"lnot\~a object of the present invention is to provade a the preferred embodiment the Invention It w119 be obvnous 
v n  2 3oc an6 apparatus for the analysis of trace amounts of a to those skilled In the art, that various changes and modlfica- 
tions may be made therein without depart~ng from the inven- 2 s 
--h5 eeFitLse\ rnventlon whnc- are believed lo be novel 15 tnve concept contained therein and it IS, therefore, aimed to 
;-e w~ch pa*lcuPaslty In the appended clarms The In- 'Over a'1 changes and modifications as "" with'n the 
Y ,n lor tsc;", '?owser, both as to 11s organlzatnon and method SF'"" and Of the invention I claim 
o, opc-at o-, togel~aer wath further objects and advantages g. Apparatus for the analysis of trace amounts of materaais kcseoC ~ , a y  best be understood by reference to the f~llowlng 20 having a source of prlmary ions, a target electrode for retaln- 
:escslptaos 'arcen 3 1  conjunction with the following drawrngs a layer of sample for testlng, means for dlrectlng an 
BRIEF DESCRIPTION OF THE DRAWINGS s~fied primary Ion beam obl~quely onto the surface of s a d  tar- get to sputter a port~on of the sample layer, a mass analyzer 
F;G P ss a scbernatac representatnon of an improved Ion and means for dlrect~ng the secondary ions of the sputtered 
probe ~ h i l s s  pectrometer apparatus 25 mater~al to said analyzer for analys~s, the ~mprovement for the 
"IG 2 ~s t;aawverse, sectional vlew of the structure of the anal~sls of fluid materials which CQmprnses 
.,arger eiectrodc of FIG 1 a means for cryogenically cool~ng the surface of said target 
electrode to below a fixed temperature, and 
D8; ABLEiCB DESCRIPTION OF THE PREFERRED b means for directing a stream of fluid to be analyzed over 
EMBODIMENTS 30 the cooled surface of the electrode to condense and 
solidlfy a layer of the stream thereon Referring now lo FIG 1, thehe 1s shown a duoplasmatron The apparatus ofclalm 1 further comprlslng 
lor source 10 of eiectrically charged bodnes which produces a heater means for cleanlng the target electrode by t.eatlng psrrnary: !learn 112 which rs ax~ally dasposed, wlth respect to a the surface thereof to volat~lize the tested sample layer 
bcas2?g magnet 14 and pevendIcuPar to an 18 35 3. The apparatus of claim 2 whereln the heater means is In- 
o - ~ e c  n an anode 16 The beam 12 is focused by the magnet tegral wath the target electrode 
14 anla pasqes "ramugh apenure 16 into a chamber 20 where ~t 4 ~h~ apparatus of 1 the coollng means Is an 
5 "0r41erI 13~d shaped by an ekctrostatlc lens 22 A deflection Integral of said target electrode 
V-enaqs 24 I~":+C ?cj beam 12 obliquely onto the surface of a 5 The apparatus of claim 1 wherein the prlmav beam con- 
*a;gt. e'<:~* ode j; Q which has been previously coated w~th  a 40 ~ 1 s t ~  of noble gas Ions 
1-yzr of a solrl>fiei", sampie flu~d 28 The impingement of the 6 A method of analyzing trace amounts of flula maternals 
qt3.q ,, onto the sarnpie layer 28 causes a portnon of the layer comprising the steps of 
98 o be qpittered prodbcnng a secondary beam 30 w h ~ h  con- cryogenically coohng the surface of a target electrode to 
q V S  I O ~ I Z C C I  >3n?~Ie  naterlal from the sampie layer 28 A below a fixed temperature, 
se 2s' ve T, cu\vg lsicans 32 dlrects the relatively low charged 45 directing a stream of fluid to be analyzed over the cooled 
OD* 01 be 3aam 30 nro a mass analyzer 34 for anaiysls surface of the electrode to condense and soladtfy a layer 
thcsorclnng ~3 2 - 9  method of the present ~nventlon, trace of the stream thereon, 
nTi3bat.s c, a flu16 such as a gas, may be analyzed by first d~recting an lntenslfied primary Ion beam o~lrquely onto the 
c-nlr 7g ihb: 3~rSacer of the target electrode 26 The electrode surface of sald tlrget to sputter a portion of the layer, and 
2 6 T 1311. g e r ~ t d  33 mtroduclng a su~table refrngerant from a 50 mass analyzing the resultant secondary ~ o n s  of the sputtered 
I ~ L L T C ~  (noi S S ~ C W Y ~  mko an Input refrigerat~on llne 36 From a layer 
r.e 36 I: 33ws lato a channel pn the target electrode 26  7 The method of claim 6 comprising the further step of 
7 hcteafter ahe refr*gerant to exit through a line 38 heatang the surface of the target electrode Po volatlllze the 
"\Text a fJij*:! sample stream as introduced into a target chamber layer 
40 .Tom a samulc source (not shown) by means of a fluid line 55 8 The method ofclalm 6 ~ h e r e l n  the PrImarY beam con- 
42 a w  dircckeci s t e r  the prevaously cooled surfaces of the tar- sists of gas Ions 
_YC* eic,en-ede 26 W portion of the flund stream ns condensed 


Ion microprobe mass spectrometer for analyzing fluid materials Patent

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