Lehigh University Lehigh Preserve Theses and Dissertatins 1-1-1976 Imprved a.c. prperties in heat treated tantalum xide capacitrs derived frm magnetrn sputtered tantalum eilms cntaining nitrgen. M H. Rttersman Fllw this and additinal wrks at: http://preserve.lehigh.edu/etd Part f the Electrical and Cmputer Engineering Cmmns Recmmended Citatin Rttersman, M H., "Imprved a.c. prperties in heat treated tantalum xide capacitrs derived frm magnetrn sputtered tantalum eilms cntaining nitrgen." (1976). Theses and Dissertatins. Paper 2088. This Thesis is brught t yu fr free and pen access by Lehigh Preserve. It has been accepted fr inclusin in Theses and Dissertatins by an authrized administratr f Lehigh Preserve. Fr mre infrmatin, please cntact preserve@lehigh.edu.
IMPROVED A.C. PROPERTIES IN HEAT TREATED TANTALUM OXIDE CAPACITORS DERIVED EROM MAGNETRON SPUTTERED TANTALUM EILMS CONTAINING NITROGEN by M. H. Rttersman A Thesis Presented t the Graduate Cmmittee f Lehigh University in Candidacy fr the Degree f Master f Science in Electrical Engineering Lehigh University 19 7 6..
PrQuest Number: EP76361 All rights reserved INFORMATION TO ALL USERS The quality f this reprductin is dependent upn the quality f the cpy submitted. In the unlikely event that the authr did nt send a cmplete manuscript and there are missing pages, these will be nted. Als, if material had t be remved, a nte will indicate the deletin. uest PrQuest EP76361 Published by PrQuest LLC (2015). Cpyright f the Dissertatin is held by the Authr. All rights reserved. This wrk is prtected against unauthrized cpying under Title 17, United States Cde Micrfrm Editin PrQuest LLC. PrQuest LLC. 789 East Eisenhwer Parkway P.O. Bx 1346 Ann Arbr, Ml 48106-1346
This thesis is accepted and apprved in partial fulfillment f the requirements fr the degree f Master f Science in Electrical Engineering. (date) Prfessr in Charge Chairman f the Department v? 11 -
TABLE OF CONTENTS List f Figures Abstract I. Intrductin II. Experimental Prcedure i III. Experimental Results A. Dependence f Film Prperties n Nitrgen Cncentratin B. Dependence f Capacitr Prperties n Nitrgen Cncentratin C. Effect f Heat Treatment n Capacitr Prperties (1) Dependence f Capacitr Prperties n Temperature and Perid f Heat Treatment Page (a) 200 C Heat Treatment Up T 19 6 Hurs (b) 250 C Heat Treatment Up T 20 6 Hurs (c) 300 C Heat Treatment Up T 21 5 Hurs (d) 350 C Heat Treatment Up T 24 2 Hurs (2) Dependence Of Dissipatin Factr 25 On Temperature (3) Effects Of Standard Heat Treatment 26 Cnditins Used In Thin Film Circuit Prcessing IV. Discussin 31 V. Cnclusins and Summary 36 References 4-0 Figures 41 Vita 62 iv 1 4 6 11 11 16 19 19 in -
LIST OF FIGURES Figure 1 Magnetic Field Lp in Planar 41 Magnetrn Cathde Figure 2 Cncentratin f Nitrgen in MES Ta 42 as a Functin f Nitrgen Flw Rate Figure 3 Grain Size and d?nn fr Beta-Ta 43 with Nitrgen Dping Figure 4 Lattice Cnstant and Grain Size fr 44 B.C.C. Ta Film as a Functin f Nitrgen Cncentratin Figure 5 Ta+N Resistivity Characterizatin 45 fr VTA Planar Magnetrn Figure 6 Ta+N Thermelectric Pwer 46 Characterizatin fr VTA Planar Magnetrn Figure 7 Ta+N TCR Characterizatin fr 47 VTA Planar Magnetrn Figure 8 Capacitance Variatin with 48 Nitrgen Dping Figure 9 Capacitance Decrease as a Functin 49 f Nitrgen Cncentratin Figure 10 Leakage Current Dependence n 50 Nitrgen Cncentratin fr Ta+N Magnetrn Sputtered Film Figure 11 0.2 Hur, 85 C Step Stress Results 51 fr Magnetrn Sputtered Ta+N Capacitr Film Figure 12 Dependence f Capacitr Prperties 52 n Heat Treatment at 200 C Figure 13 Dependence f Capacitr Prperties 53 n Heat Treatment at 250 C Page IV -
Page Figure 14 Dependence f Capacitr Prperties 54 n Heat Treatment at 300 C Figure 15 Dependence f Capacitr Prperties 55 n Heat Treatment at 350 C Figure 16 Dependence f Dissipatin Factr 56 n Temperature After Heat Treatment at 350 C, 1 Hur fr Capacitrs With Different Nitrgen Cncentratins Figure 17 Percent Change f Capacitance due 57 t Heat Treatment as a Functin f Nitrgen Cncentratin Figure 18 Dependence f TCC n Nitrgen Cn- 58 centratin After Heat Treatment Figure 19 Dependence f Dissipatin Factr 59 n Nitrgen Cncentratin After Heat Treatment Figure 20 50 Vlt Leakage Current Dependence 60 n Nitrgen Cncentratin After Heat Treatment Figure 21 Dependence n 350 C Heat Treatment 61 f Step Stress Results f 230 Vlt TM Capacitrs Cntaining 13 Atm Percent Nitrgen - v -
ABSTRACT Many applicatins f tantalum based precisin RC filters are dependent n the ability f the capacitrs t meet mre stringent requirements. The tw majr items f imprtance are: first, a lwer dissipatin factr t attain a higher circuit Q and t enable peratin at higher frequencies; secnd, an imprved lng-term capacitance stability. Earlier wrkers have shwn that capacitrs based n beta-tantalum films cntaining small cncentratins f nitrgen (abut 3 atm percent) exhibit imprved d.c. characteristics and higher yields than capacitrs made frm pure beta-tantalum. Hwever, these capacitrs cannt be subjected t temperatures abve 200 C withut irreversible harmful changes in their prperties. W. Anders recently fund that by adding larger amunts f nitrgen t the base layer during r.f. sputtering an imprvement in a.c. capacitr prperties was btained during heat treatment between 250 C and 350 C. The purpse f the present study was t evaluate the effect f heat treatment n Ta-film capacitrs as a functin f nitrgen cncentratin in the sputtered film in mre detail. Analytical techniques were used fr determining the film cmpsitin and t ensure that the nitrgen was hmgeneusly distributed thrughut the Ta-films. - 1 -
Planar magnetrn sputtering was used t depsit the films at a rate f 2000 A/minute and the physical prperties f the films were measured as a functin f nitrgen cncentratin up t 34 atm percent. The dependence n nitrgen cncentratin was bserved with respect t capacitr a.c. prperties such as capacitance, dissipatin factr, and temperature cefficient f capacitance (TCC) fr nnheated capacitrs and fr capacitrs receiving varius heat treatment cnditins between 200 C and 350 C. In additin, the d.c. prperties f the capacitrs were investigated and static life testing was perfrmed. It was determined that capacitrs with excellent a.c. prperties culd be btained frm the tantalum films cntaining between 13% and 22% atmic nitrgen and having the b.c.c. crystal structure. Capacitrs fabricated frm this film and heat treated at a temperature between 250 C and 350 C fr ne hur shw a capacitance increase f nly between 1 and 2%. The dissipatin factr and TCC fr these films are abut.0015 and +135 ppm/ C, respectively, as cmpared t.0025 and +200 ppm/ C fr currently prduced beta-tantalum capacitrs. If lightly nitrgen dped capacitrs are subjected t the same heat treatment their capacitance is increased up t 5%, while their dissipatin factr and TCC increase t as much as.01 and +500 ppm/ C, respectively. In additin t the decreased intrinsic lss - 2
f the dielectric, the series resistance f the b.c.c. tantalum electrde is apprximately ne half f that btained frm beta-tantalum films, enabling extensin f applicatin t higher frequency. The d.c. prperties f these capacitrs, unlike thse f capacitrs made frm cnventinally sputtered lightly dped film, are uncmprmised as a result f the heat treatment. D.C. static life testing at 65 vlts, 85 C n capacitrs andized t 230 vlts reveals an,exceptinally lw failure rate. The results will be explained by a discussin f physical mechanisms ccurring during heat treatment. - 3 -
I. INTRODUCTION Many high precisin RC filter applicatins in the Bell System require capacitr prperties nt presently achieved with tantalum film capacitrs. The tw majr items f imprtance are the lng-term stability f the capacitance fr high precisin RC prduct and a decreased lss factr t achieve higher circuit Q and t enable peratin at higher frequencies. In attempts t imprve capacitr stability, wrkers at Bell Labratries develped a prcess sequence cnsisting f a 230 vlt preandizatin f beta-ta film, fllwed by heat treatment fr 5 hurs at 250 C with a subsequent reandizatin t 230 vlts, and a pst-stabi- lizatin f 200 C fr 1 hur after cunterelectrde delineatin. This prcess resulted in capacitrs which shwed imprved stability during thermcmpressin bnd- ing r parametric aging at 85 C. Hwever, the dissipatin factr was increased and subsequent evaluatin f the prcess by the Western Electric Cmpany n actual prduct revealed that it was a prcess which was difficult t re- prducibly cntrl. 2 3 Kumagai et al and Huttemann et al have shwn that the additin f small cncentratins f nitrgen (2-4 atm percent) while sputtering tantalum has a beneficial effect n ptimizing capacitr d.c. prperties and reli- 4 -
ability. Hwever, wrking temperatures fr these capaci- trs are very limited in high stability applicatins, and even shrt expsures t temperature abve 200 C during circuit fabricatin cause irreversible increases in capaci- tance and dissipatin factr. H 5 Recently, W. Anders ' f the Siemens Cmpany has shwn that tantalum films having the b.c.c. crystal structure and cntaining an estimated nitrgen cncen- tratin f between 5 and 15% fabricated int capacitrs and heat treated t temperatures between 250 C and 350 C have imprved temperature stability. Fr a heat treatment time f between 30 and 60 minutes, imprvements in capaci- tr stability were bserved after a small initial increase (abut 1%). This was accmpanied by a lwer and mre stable dissipatin factr (abut.0015) and a decreased and stable TCC (abut +135 ppm/ C). In additin, the ca- pacitrs exhibited a capacitance decrease f nly abut 7.5% frm capacitrs made frm undped film. Anders' results have significant implicatins twards the imprvement in the characteristics f present prduct. Even mre imprtantly they ffer great prmise fr the utilizatin f tantalum based filter circuits in applicatins having mre stringent frequency and stability requirements. The majr purpse f the present study was t evaluate the effect f heat treatment n the a.c. - 5 -
prperties f Ta-film capacitrs as a functin f nitrgen cncentratin in mre detail, as well as t investigate the effect n the d.c. prperties which had nt been reprted by Anders. In additin, it was desired t carry ut a detailed investigatin f the electrical and structural prperties f the tantalum films and their dependence n nitrgen cncentratin. This was imprtant because the recently develped planar magnetrn sputtering apparatus was used t depsit the films used in this wrk. It was therefre necessary t determine what differences exist between this methd and cnventinal sputtering techniques currently used. The depsitin rate f tantalum by d.c. r a.c. techniques currently used has been limited t abut 200 A/minute. In cases where high prduct thrughput is required, substantial cst savings can result frm an increase in depsitin rate f an rder f magnitude r mre. This has particular significance fr the depsitin f tantalum capacitr andes which have a nminal thickness f between 3000 and 4000 A. II. EXPERIMENTAL PROCEDURE The films were depsited in a vacuum lck inline type sputtering apparatus cntaining a planar magnetrn cathde and ande assembly purchased frm VTA, Incrprated f Bulder, Clrad. The cathde and ande
assemblies are cnstructed f aluminum and cpper, respectively and are water-cled (with deinized water t reduce crrsin). The cathde assemblies huse a series f permanent bar magnets 'arranged t frm a ring which is encmpassed by a lping magnetic field, as shwn in Figure 1. The magnetic field f abut 300 gauss exists perpendicular t the electric field during sputtering, s that the secndary electrns emitted frm the cathde traverse a spiral path arund the ring surce. This results in far mre inizing cllisins with the sputtering gas, causing high discharge currents and allwing sputtering t take place at very lw pressures (between 1 and 2 millitrr). The desired 5" x 8" x 1/4" rectangular tantalum target is clamped t the cathde surface and the target material is erded frm the area belw the magnetic ring during sputtering. Due t the enhanced inizatin, relatively lw vltages may be used between cathde and ande, typically between 300-600 vlts. The pwer supply requirements fr planar magnetrn sputtering call fr a means f cntrlling the current, and this is accmplished with the incrpratin f a saturable cre reactr. The ande may be perated in either f three mdes - grunded, biased psitive thrugh a fixed resistr t grund, r flating psitive with respect t grund. Since the substrates rest n a tray which is at grund - 7 -
ptential, the ande is perated in either the biased r flating mdes, thereby eliminating electrn bmbardment f the substrates and its assciated heating effect. The tantalum target furnished by Materials Limited, Incrp- rated has a purity f 99.99%. It was determined that the pwer delivered t the cathde shuld nt exceed 1 KW in rder t avid warpage f the tantalum target due t ex- cessive heating. The depsitin rate has been fund t exhibit a linear dependence n sputtering pwer, result- ing in a depsitin rate f 2000 A/minute at 1 KW-. The argn flw rate was maintained at 10 sec/minute, as mni- tred by a Hastings-Raydist mass flwmeter. The back- grund pressure befre admissin f argn was in the lw _7 10 trr range and cnsisted mainly f water vapr, as bserved n a mass spectrmeter residual gas analyzer. The sputtering vltage was chsen t be 500 vlts, as initial experiments revealed stable undped film prper- ties cnfrming t present specificatins t exist at this vltage. A series f sputter runs was made using nitrgen flw rates ranging frm 0.2 t 5.5 sec/minute. The flw rates were increased in 0.1 sec/minute incre- ments up t 2.0 sec/minute, after which larger incre- ments were used. Fifteen minutes f presputtering were used t establish equilibrium between successive runs while the substrates were in the lad chamber. During
this time the substrates were degassed at abut 100 C in the lad chamber by infrared lamps fr ne minute. After entry f the substrates int the main chamber, an additinal five minutes f presputtering ensued. The substrates were then mved under the target and 3500 A f tantalum was depsited nt 3.75" x 4.5" x.048" substrates f 7059 glass cated with thermally frmed Ta 0 underlay, at a depsitin rate f 2000 A/minute, fr each f the different nitrgen levels. After transferring substrates int the unlad chamber, they were immediately remved, as they are nly slightly heated during the depsitin prcess. Althugh n actual temperature measurements were made, the substrates were cl t the tuch. Previus wrk n NiCr-Pd high rate sputtering revealed that at an equivalent pwer f 1 KW the substrate temperature reached nly abut 85 C fr an equivalent sputter time. The film electrical prperties such as resistivity, thermelectric pwer, and temperature cefficient f resistance (TCR) were measured fr the varius sputter runs as a functin f nitrgen flw rate. X-ray diffractmeter traces were btained t determine crystal structure, interplanar spacing f the majr crystal planes, and size f the crystallites. In-depth prfiling by Auger Electrn Spectrscpy, using electrn micrprbe analysis - 9
as a reference, was perfrmed t determine nitrgen cn- centratin, hmgeneity with film depth, and pssible cn- taminatin by incrpratin f undesirable elements. The films were prcessed int a 28 spt capaci- 2 tr pattern (capacitr area = 0.1 cm ) using an andizatin vltage f 230 vlts and e-gun evaprated NiCr-Pd-Au cunterelectrde film. Fur 1" x 3" 28 capacitr sub- strates were derived frm each large substrate by laser scribing and separatin. Initial measurements f capacitance and dissi- patin factr were made n all substrates at 1 KHz and at temperatures f -40 C, +25 C, and +65 C. The TCC was calculated frm values measured at +25 C and -40 C and at +25 C and +65 C. Initial measurements f the d.c. prper- ties such as 50 vlt, 1 minute leakage current and step stress breakdwn vltage at 85 C in 0.2 hur, 5 vlt steps were perfrmed. The substrates were divided int fur grups in such a manner that capacitrs frmed frm tantalum cntain- ing each nitrgen cncentratin were represented by ne substrate in each grup. Each f the fur grups was heat treated at a different temperature; namely, 200 C, 250 C, 300 C, and 350 C. The substrates were remved frm their respective vens at cumulative intervals f 1/3 hur up t ne hur, and at 1 hur intervals thereafter. At each - 10 -
interval, measurements f capacitance, dissipatin factr, and TCC were perfrmed. In additin, at intervals crre- spnding t thse frequently used fr resistr aging n RC circuits (e.g., 1 hur at 350 C, 4 hurs at 300 C, r 5 hurs at 250 C), d.c. leakage measurements at 50 vlts were als perfrmed. Step stress testing at 0.2 hur and 2 hur intervals in 5 vlt steps was als perfrmed fr capacitrs heat treated at 350 C fr ne hur. In addi- tin, anther grup f capacitrs was subjected t d.c. static life testing at 65 vlts, 85 C. The capacitrs were heat treated and tested fr a ttal time crrespnd- ing t ne hur lnger than the usual time prescribed fr the varius resistr stabilizatin cnditins. III. EXPERIMENTAL RESULTS A. Dependence f Film Prperties n Nitrgen Cncentratin The results f Auger analysis f Ta films sputtered at nitrgen flw rates between 0.2 and 5.5 sec/ minute are shwn in Figure 2. Oxygen and carbn are un- detectable in all films, except fr expected surface cn- taminatin. At nitrgen flw rates belw 0.5 sec/minute, nly traces f nitrgen peaks whse amplitudes lie within the nise level appear. At 0.5 sec/minute, the first quantitative measurement shws abut 1.5 atm percent nitrgen. The nitrgen level gradually increases t 5.3 atm percent at a flw rate f 1.2 sec/minute, where the - 11 -
b.c.c. phase is initially bserved. A sudden steep increase in nitrgen cncentratin ccurs between 1.2 and 1.3 sec/minute, after which a regin f fairly cnstant nitrgen cncentratin, hereafter referred t as a "plateau regin", ccurs up t a flw rate f 2.1 sec/minute. The average nitrgen cncentratin in the plateau regin is abut 13.5 atm percent. Further increase in nitrgen flw rate results in the predictable increase in nitrgen cncentratin, which reaches 34 atm percent at 5.5 sec/ minute. All measurements were taken at a film depth f 1200 A. The in-depth cncentratin prfile fr nitrgen, hwever, shws less than 1.0 atm percent variatin even fr sputter remval f the entire 3500 A thick film. The crystal structure f films which cntain between zer and 4 atm percent nitrgen is that f betatantalum with n detectable b.c.c. phase. The dependence n nitrgen flw rate f the grain size and d nn interplanar spacing fr the beta-tantalum is shwn in Figure 3. The nitrgen cncentratin is nt pltted because it is very lw ver a large prtin f the flw rate range where the reslutin f the Auger analytical equipment des nt permit meaningful analysis. The grain size is bserved t decrease frm abut 320 A t 180 A just befre the transitin t the b.c.c. phase. The d n _ spacing shws a 12 -
strange dependence n nitrgen frm the undped cnditin t the pint where nitrgen is initially intrduced int the sputtering atmsphere at a flw rate f nly 0.1 sec/ minute. A decrease in the d spacing ccurs frm 2.701 A t 2.677 A, a result which at this time is nt fully understd. Hwever, it is pssible that the additin f nitrgen t the plasma inhibits the srptin f energetic argn neutrals int the tantalum film, thereby shrinking the previusly expanded lattice. As additinal nitrgen is admitted the d spacing is bserved t increase t 2.696 A, a change f 0.7% as cmpared t abut 0.4% in high vltage sputtered Western Electric Cmpany prductin films. This expansin is due t the incrpratin f nitrgen atms at interstitial sites within the tantalum lattice. Figure 4 shws the variatin f crystallite grain size and lattice cnstant (a) with increasing nitrgen cncentratin fr the nitrgen-induced b.c.c. phase. The grain size is bserved t decrease fairly linearly with increasing nitrgen cncentratin frm abut 85 A at 8 atm percent t 40 A at 22 atm percent. The b.c.c. lattice cnstant increases linearly frm abut 3.3494 A t 3.4238 A ver the same range f nitrgen cncentratins. Gmelin's Handbuch n the chemistry f tantalum gives the lattice cnstant f pure bulk tantalum as being between 3.259 and 3.298 A, depending n the reference surce. The - 13 -
literature value f 3.298 A fr zer nitrgen cncentra- tin pltted in Figure 4 cnfrms t the same linear de- pendence as the experimental values btained frm the films in this wrk. The slpe f the curve results in a 0.18% change in the lattice cnstant per atm percent nitrgen. This is in reasnable agreement with the value f 0.15% per 7 atm percent nitrgen fund in the literature fr lattice cnstant measurements n bulk tantalum with interstitial nitrgen. Hwever, it shuld be pinted ut that the slubility limit fr nitrgen in bulk b.c.c. tantalum is nly abut 4 atm percent. Due t the rapidly decreasing crystallite size, exact measurements f "d" spacing at nitrgen cncentratins beynd 22 atm percent are nt pssible because f the very wide peaks btained n the diffractmeter. Fr films sputtered at 5.5 sec/minute N, the grain size is estimated t be abut 23 A and the d spacing is estimated t be abut 2.44 A. It is interesting t nte that these films which have the electrical prper- ties f Ta N still shw a diffuse b.c.c. crystal structure withut bservable traces f the hexagnal Ta N phase, even thugh electrn micrprbe analysis reveals that the film cntain 34 atmic percent nitrgen. Figures 5 thrugh 7 reveal the resistivity, thermelectric pwer, and TCR as a functin f bth nitr- gen flw rate and cncentratin, respectively. The beta- 14 -
tantalum crystal structure exists thrugh the flw range between 0 and 1.0 sec/minute (up t 4.2 atm percent N~). In this range the film electrical prperties underg very little change. The resistivity and TCR shw sme randm scattering abut 200 yftcm and -140 ppm/ C, respectively. The thermelectric pwer shws a small linear decrease frm +4.8 t +4.4 yv/ C. A sharp transitin regin fllws between flw rates f 1.0 and 1.2 sec/minute, crrespnding t nitrgen cncentratins between 4 and 5 atm percents, where a change in crystal structure frm beta t b.c.c. takes place. In this regin minima in resistivity and thermelectric pwer are attained at apprximately 60 pficm and +3.0 yv/ C, respectively, while the TCR attains a value f +700 ppm/ C. Further increase in nitrgen flw rate between 1.3 and 2.1 sec/minute, crrespnding t the nitrgen cncentratin "plateau" regin f 13.5 atm percent, results in a similar "plateau" regin fr all three film prperties, a phenmenn nt previusly bserved in sputtered Ta films. The resistivity in this regin is abut 100 vificm, the TCR is apprximately +450 ppm/ C, and the thermelectric pwer is in the rder f +3.6 yv/ C. Fllwing the "plateau" regin the film electrical prperties shw a similar dependence n nitrgen flw rate t high vltage, lw rate sputtered films. At 5.5 sec/minute N, crrespnding t - 15 -
a nitrgen cncentratin f 34 atm percent, the therm- pwer f -1.8 yv/ C is in reasnable agreement with that f Ta? N films sputtered by d.c. dide high vltage sputter- ing, the resistivity f 300 vjftcm is smewhat lwer, and the TCR f -125 ppm/ C is mre negative. Hwever, it is t be remembered that the crystal structure f this film is still predminantly b.c.c. Ta. B. Dependence f Capacitr Prperties n Nitrgen Cncentratin Capacitance measurements as a functin f ni- trgen flw rate are shwn in Figure 8. Undped Ta films, when andized t 230 vlts, with a capacitr area f 2 0.1 cm result m a capacitance value f 5650 pf when measured at 1 KHz. The capacitance decreases by nly 0.9% at a flw rate f 1.2 sec/minute, after which a sharp drp ccurs between flw rates f 1.2 and 1.3 sec/ minute, crrespnding t the sudden jump in N cncentra- tin which was bserved in the as-sputtered film. The capacitance at this pint is abut 5250 pf, a 7% decrease frm the undped cnditin. The capacitance remains relatively cnstant ver the range f nitrgen flw rates frm 1.3 t 2.1 sec/minute, previusly referred t as the "plateau" regin. Further increase in nitrgen flw rate results in the mntnic decrease f the capacitance density bserved previusly in capacitrs made frm lw rate sputtered films. The relatinship f percent change - 16 -
in capacitance t actual nitrgen cncentratin is shwn in Figure 9. It is bserved that the relatinship b- tained is nn-linear. At abut 14 atm percent, in the "plateau" regin, the capacitance decrease is nly abut 7%, crrespnding t a 0.5% decrease in capacitance per atm percent nitrgen. Fr higher cncentratins f nitr- gen (up t 26 atm percent) the slpe f the curve steadily increases, appraching 2.2% change in capacitance per atm 3 percent nitrgen. Huttemann et al fund a linear rela- tinship t exist between zer and 20 atm percent nitrgen cntent, shwing a decrease in capacitance f 1% per atm percent nitrgen. It is felt that pssible explanatins fr the discrepancy are: first, the nitrgen cncentratin might nt have been as hmgeneusly distributed thrugh the film thickness as in this wrk; secnd, that imprve- ments in the Auger technique nw give greater accuracy in determining nitrgen cncentratin, especially at very lw levels. The dissipatin factr f the capacitrs at 1 KHz varies slightly between.0027 and.0023. Because the lwer values ccur fr nitrgen cncentratins between 13 and 14 atm percent, it is assumed that the lwer sheet resistance at this level ffers a slight cntributin twards lwering the dissipatin factr. Leakage current measurements fr the varius ni- trgen cncentratins perfrmed at 50 vlts fr 1 minute - 17 -
resulted in median leakage currents averaging less than 0.5 nanamps ver the entire range, as shwn in Figure 10. Furteen capacitrs were tested fr each nitrgen cncentratin. T»he leakage current values are well belw the requirement f 12 nanamps, and very little dependence n nitrgen cncentratin can be bserved. Step stress measurements, hwever, d exhibit sme dependence n nitrgen cncentratin. The median breakdwn vltages at 85 C are shwn in Figure 11 as a functin f nitrgen cncentratin. Fr very light dping levels (belw 1.5 atm percent) the breakdwn vltage averages abut 105 vlts. The reductin in breakdwn vltage frm the 125 vlts bserved fr the undped film is nt understd at this time. With increasing nitrgen flw rate, especially in the b.c.c. "plateau" regin and beynd, the median breakdwn vltage again increases, averaging abut 125 vlts. It is bth wrthwhile and interesting t nte that althugh n bservable quantities f metallic r gaseus reactive impurities (such as N, C, r 0) culd be fund in the bulk films, as indicated by the high thermpwers, capacitrs having lw d.c. leakages can be reprducibly fabricated frm the magnetrn sputtered film. This test result is cntrary t that btained frm capacitrs frmed frm undped tantalum film depsited by high
3 vltage, lw rate sputtering and als by magnetrn sput- tering as reprted by ther wrkers. p Eighty capacitrs made frm the authr's film shw nly a few failures after 10,000 hurs f testing at 65 vlts and 85 C. The reasns fr these remarkable results are nt fully understd at the present time. C. Effect f Heat Treatment n Capacitr Prperties (1) Dependence f Capacitr Prperties n Temperature and Perid f Heat Treatment (a) 200 C Heat Treatment Up T 6 Hurs The dependence f a.c. capacitr prperties n heat treatment time at 200 C fr different nitrgen cncentratins in the tantalum film is shwn in Figure 12. It is bserved that all prperties d nt change appreciably after the first hur f heat treatment. Capacitrs with less than 1.5 atm percent nitrgen, hwever, still cntinue t shw increases in capacitance t abut 0.75% after 6 hurs. Capacitrs with nitrgen cncentratins between 1.5 t 22 atm percent exhibit a fairly cnstant capacitance after increasing by 0.5% within the first 2 hurs. The TCC fr capacitrs made frm films cntaining between zer and 22 atm percent drps and stabilizes at values between 150-165 ppm/ C after 1 hur f heat treatment. The - 19 -
dissipatin factr similarly decreases and reaches a fairly cnstant level after the first hur f heating. The values are between.0018 and.0021 fr nitrgen levels up t 3.2 atm percent and between.0015 t.0017 fr nitrgen cncentratins between 13 and 22 atm percent, respectively. (b) 250 C Heat Treatment Up T 6 Hurs A.C. capacitr prperties as a functin f time f heat treatment at 250 C are shwn in Figure 13. After the first 20 minutes f heat treatment it becmes apparent that the mechanisms which cause the changes in prperties f capacitrs with lw nitrgen cncentratins (< 1.5 atm percent) are different frm thse which are respnsible fr changing the prperties f capacitrs with higher nitrgen cncentratins, up t 22 atm percent. In samples cntaining nitrgen cncentratins between 10 and 22 atm percent, the capacitance levels ff within the first hur at an increase f between 0.8 and 1.2% fr unheated capacitrs; while capacitrs cntaining less than 1.5 atm percent nitrgen shw a sharper increase cntinuing t 2% after 6 hurs. The TCC and dissipatin factr 20 -
shw inflectin pints after 20 minutes f heat treatment fr the lw nitrgen level capacitrs. The TCC, after initially falling t 170 ppm/ C, rises again t 220 ppm/ C in the fllwing 20 minutes, and eventually reaches 230 ppm/ C after 6 hurs. Hwever, capacitrs cntaining greater than 3.2 percent nitrgen retain the lwer TCC, between 135-150 ppm/ C, bserved after 1 hur f heat treatment. The dissipatin factr, likewise, shws a sizeable increase fr lw nitrgen capacitrs. After drpping t.0020 frm.0028 in the first 20 minutes, the lsses increase t a dissipatin factr f.0034 after 6 hurs. Capacitrs with nitrgen cntent f 3.2 atm percent and higher exhibit nly a decreasing dissipatin factr, levelling ff at a value between.0014 and.0015 after the first hur f heat treatment. (c) 300 C Heat Treatment Up T 5 Hurs Similar trends ccur in capacitrs cntaining different nitrgen cncentratins during heat treatment at 300 C, as depicted in Figure 14. The majr difference between heat treatment at 250 C and 300 C is that the changes in the prperties frm the nn-heat treated cnditin are - 21 -
much mre severe, especially fr capacitrs derived frm film cntaining lw nitrgen levels, up t 2.5 atm percent in this case. The prperties, after initially increasing t a fairly cnstant value between 20 minutes and 1 hur f heating, abruptly increase again t much higher values, especially fr the capacitrs made frm films cntaining the lwest»nitrgen cncentratins (less than 1.5 atm percent). In the wrst case the capacitance increases after 2 hurs f heat treatment by abut 3.75%, after which it increases mre gradually t 4.6% after the next 3 hurs. Capacitrs cntaining tantalum with nitrgen cncentratins between 10 and 19%, hwever, d nt shw appreciable increases in capacitance beynd the first 20 minutes f heat treatment. Fr times f 20 minutes and 5 hurs at 300 C, the average increase in capacitance is abut 1.25% and 1.5%, respectively. The TCC fr lightly dped capacitr film (< 1.5 atm percent N ) des nt shw the decrease bserved during the entire 6 hur heating perid at 200 C and during the initial 20 minute perid at 250 C. The TCC f these capacitrs, after initially levelling ff at abut +250 ppm/ C between 20-22 -
minutes and 1 hur, increases sharply again and reaches a value f +500 ppm/ C after 5 hurs f heat treatment. Similar type behavir is bserved, althugh t a lesser extent, in capacitrs cntaining tantalum with up t 2.5 atm percent nitrgen. A majr difference in TCC behavir ccurs in capacitrs with nitrgen cntent between 10 and 22 atm percent. The TCC in this case decreases t abut +140 ppm/ C in the first 20 minutes and remains practically invariant thrugh the 5 hurs f heat treatment. Much larger increases in the dissipatin factr ccur fr capacitrs with the lw nitrgen cncentratins at 300 C than at 250 C, especially fr capacitrs with less than 1.5 atm percent nitrgen. The initial decrease in d.f. which ccurred at 250 C and which remained at 200 C was nt bserved at 300 C. As in the case f the change in capacitance and TCC dependence, the dissipatin factr increases initially, remains relatively cnstant between 20 minutes and 1 hur, and then sharply rises. Capacitrs with less than 1.5 atm percent nitrgen attain a d.f. f.0065 after 2 hurs and.0084 after 5 hurs. On the ther hand, capacitrs cntaining - 23 -
tantalum with nitrgen cntent between 10 and 22 atm percent exhibit a decrease in d.f. after 20 minutes f heat treatment, t a cnstant level f.0015 fr up t 5 hurs f heat treatment. (d) 350 C Heat Treatment Up T 2 Hurs At 350 C the changes in prperties are even larger with time f heat treatment fr capacitrs with lw nitrgen dped tantalum, as shwn in Figure 15. In the wrst case (< 1.5 atm percent N ) the capacitance increases by 3.7% in the first 20 minutes, and t 5% by the end f 1 hur. Similar, but less extensive, increases prevail with increasing nitrgen cncentratin, until at 22 atm percent nitrgen the ttal increase after 1 hur is nly 1.75%. At the next measuring perid f 2 hurs cumulative, a decrease was bserved in all cases frm the 1 hur measured value, indicating that prlnged expsure t 350 C can result in a different mechanism ccurring within the dielectric. Capacitrs with nitrgen cncentratins between 13 and 22 atm percent still exhibit the best stability after an initial shift in prperties during the first 20 minutes f heat treatment. The TCC as well as the dis- - 24 -
sipatin factr shw rapidly increasing values fr capacitrs with lw nitrgen cncentratins, reaching ver 500 ppin/ 0 C and.0084, respectively, after ne hur. Hwever, gd results are again btained fr mre heavily nitrided capacitrs (13-22 atm percent N ). The TCC drps t abut +14 5 ppm/ C in the first 20 minutes and remains relatively cnstant fr 2 hurs f heating, while the dissipatin factr drps t.0015 and then increases fairly linearly t.0017 after 1 hur and t.0019 after 2 hurs at 350 C. (2) Dependence Of Dissipatin Factr On Temperature A dependence f the dissipatin factr n temperature f measurement was nted in capacitrs subjected t varius heat treatments. The strngest dependence was bserved in capacitrs which underwent the 350 C heat treatment. Figure 16 reveals the d.f. dependence after 1 hur at 350 C based n the three measurement temperatures f -40 C, +25 C, and +65 C. While the dependence befre heat treatment is bserved t be independent f nitrgen cncentratin, varying frm.0016 at -40 C t.0026 at +65 C, there is a marked dependence n nitrgen cncentratin after heat treatment fr capacitrs cntaining tantalum with lw nitrgen levels up t - 25 -
3.2 atm percent, as discussed previusly. In ad- ditin, there appears t be a gradual increase in slpe f the linear dependencies btained as a functin f decreasing nitrgen cncentratin. In the case f capacitrs cntaining between 10-22 atm percent nitrgen, where the dissipatin factr has decreased after heat treatment, the temperature de- pendence is very slight between -40 C and +25 C, changing frm.0013 t.0015 in this range. Between +25 C and +65 C, hwever, a psitive change in slpe is bserved which results in a dissipatin factr f.0024 at 65 C. The same mechanism that causes the difference in slpe f the dissipatin factr in the tw different temperature ranges may als accunt fr a slight difference in the TCC value btained in the tw temperature ranges, abut 130 ppm/ C in the lw range and abut 140 ppm/ C in the higher range. (3)i;Effects Of Standard Heat Treatment Cnditins Used In Thin Film Circuit Prcessing All capacitrs exhibited an increase in capaci- tance after the varius standard heat treatments. The percent increase, based n the value C befre c heat treatment, was dependent n bth nitrgen cn- centratin in the tantalum ande material and n the heat treatment cnditins. Figure 17 reveals that - 26 -
the change in capacitance decreases as a functin f decreasing temperature during heat treatment. In the case f capacitrs frmed frm beta-ta with nly trace amunts f nitrgen, the capacitance increase is 5% fr capacitrs heat treated at 350 C fr 1 hur. Capacitrs frmed frm equivalent film but heat treated at decreasing temperatures shwed a 4.7% increase after 300 C, 4 hurs, a 2% increase after 250 C, 5 hurs, and an increase f nly 0.73% after 200 C, 6 hurs. In cntrast, capacitrs frmed frm b.c.c. Ta cntaining interstitial nitrgen be- tween 10 and 22 atm percent exhibited a much lwer capacitance increase. The 350 C heat treatment pr- duces a capacitance change f abut 2%, while the 300 C, 250 C, and 200 C treatments result in respec- tive capacitance changes f apprximately 1.5, 1.0, and 0.5 percents. Parametric aging studies in a temperature range f 65-150 C as well as studies f the effect f simulated TC bnding n heat treated capacitrs with abut 14 atm percent nitrgen cn- tent are being carried ut by ther wrkers at Bell Labratries. The results btained s far indicate 9 a marked imprvement m capacxtr stability. The variatin f TCC with nitrgen cncentratin fr the different heat treatment cnditins, as well - 27 -
as n heat treatment, is depicted in Figure 18. Fr unheated capacitrs the TCC averages abut +210 ppm/ C and remains cnstant irrespective f nitrgen cncentratin. The 350 C, 1 hur and 300 C, 4 hur treatments, hwever, cause the TCC t be increased t the vicinity f +500 ppm/ C fr capacitrs frmed frm tantalum with nly trace amunts f nitrgen. The shift in TCC cntinues t be tward larger values fr films cntaining up t 3.5 atm percent nitrgen. At nitrgen cncentratins exceeding 3.5 atm percent, the shift in TCC is reversed and the values after heat treatment are smaller than the riginal 210 ppm/ C. At a nitrgen level f abut 13 atm percent, crrespnding t the "plateau regin" f the previus memrandum, the TCC attains a value f abut +140 ppm/ C and remains essentially cnstant as the nitrgen cntent is increased t 22 atm percent. Heat treatment at 250 C fr 5 hurs prduces a similar effect except that the TCC never exceeds +230 ppm/ C, even fr lightly dped film. The 200 C, 6 hur heat treatment results in a shift tward lwer TCC values independent f nitrgen cncentratin. The TCC value f abut +150 ppm/ C is very clse t that fund in capacitrs - 28 -
cntaining 10-22 atm percent N and heated at 250 C, 300 C, and 350 C. The dependence f the dissipatin factr, at 25 C, n nitrgen cncentratin fr the varius heat treatment cnditins, as well as fr n heat treatment, is shwn in Figure 19. Fr capacitrs which have nt received any heat treatment, the dissipatin factr is fairly cnstant ver the entire range f nitrgen cncentratin, varying nly slightly between.0025 and.0022, with the lwer values tending t ccur at the higher nitrgen levels. The shift in dissipatin factr during heat treatment is the greatest fr lw nitrgen cncentratin (belw 10 atm percent). Fr heat treatment temperatures f 300 C and 350 C, the dissipatin factr attains a value f abut.0084, where the nitrgen cntent within the tantalum film is negligible. Fr heat treatment temperatures f 250 C and 200 Q, C, the crrespnding values are.0034 and.0027, respectively, fr the minimum nitrgen cncentratin. At nitrgen cncentratins exceeding 10 atm percent, the dissipatin factr shws a drp after the heat treatment and becmes essentially independent f nitrgen cntent, levelling ff at abut.0017 fr heat treatments f 250 C, 300 C, and 350 C and at abut.0015 fr the 200 C heat treatment. - 29 -
The d.c. leakage current dependence n nitrgen cncentratin at 50 vlts fr the varius heat treatment cnditins, as well as fr n heat treatment, is shwn in Figure 20. It is bserved that, irrespective f nitrgen cncentratin r heat treatment, all capacitrs have leakage currents well belw the specified maximum f 12 nanamps, accrding t Western Electric Cmpany requirements. The capacitrs which have nt received heat treatment have median leakage current values averaging abut 0.5 nanamps fr tantalum cntaining frm near zer t 22 atm percent nitrgen. The varius heat treatments have the effect f generally decreasing the leakage current ver mst f the range f nitrgen cncentratins, especially fr nitrgen cncentratins exceeding 13 atm percent (the plateau regin and beynd). Fr capacitrs exhibiting imprved a.c. characteristics (N cncentratins between 13 and 22 atm percent), the average leakage current fr the varius heat treated capacitrs is abut 0.15 nanamps. Hwever, capacitrs heat treated at 300 C fr 4 hurs have leakage currents even an rder f magnitude less fr nitrgen cncentratins between 15 and 19 atm percent. Step stress data were btained n capacitrs with tantalum cntaining 13 atm percent nitrgen - 30 -
which had received the 350 C, 1 hur heat treatment and cmpared t the data n cntrls which had re- ceived n heat treatment. The distributins f failure vltage are shwn in Figure 21. Fr 0.2 hur steps the initial median breakdwn vltage * befre heat treatment was 140 vlts. After heat treatment at 350 C fr ne hur, the median break- dwn vltage was reduced slightly, by 7% t 130 vlts. These values are well abve the 90 vlt minimum median breakdwn vltage requirement f the Western Electric Cmpany. In additin, data were btained frm a 2 hur step stress test frm the same tw respective grups. The median break- dwn vltages were 135 vlts and 130 vlts fr nn- heat treated and 350 C, 1 hur heat treated capaci- trs, respectively. A d.c. static life test is currently under way, and the results thrugh 2000 hurs f testing at 65 vlts, 85 C are mst en- curaging, shwing abut 3% failure n capacitrs withut heat treatment and 6.5% n heat treated capacitrs, mst f which ccurred during the first 2 hurs f testing. IV. DISCUSSION In rder t discuss pssible mechanisms which can lead t the results described in this wrk, sme f - 31 -
the majr bservatins t be cnsidered will first be summarized belw. (1) While there is a decrease in the capacitance density (dielectric cnstant) as a functin f increasing nitrgen cncentratin in the sputtered tantalum andes, the dissipatin factr and TCC are essentially independent f nitrgen cncentratin befre the capacitrs are subjected t heat treatment. (2) Heat treatment at temperatures between 200 C and 350 C prduces an increase in capacitance whse magnitude is dependent n bth temperature and nitrgen cncentratin. (3) Heat treatment at 200 C results in a decrease f dissipatin factr and TCC whse magnitude is practically independent f nitrgen cncentratin. (M-) Heat treatment at temperatures between 250 C and 350 C can result in an increase r decrease f dissipatin factr and TCC, depending n the nitrgen cncentratin in the sputtered tantalum film. At the higher temperatures mre nitrgen. - 32 -
is required in rder t btain a decrease in these prperties, and the magnitude f the increase in lightly dped tantalum is greater. (5) In capacitrs which shw a decrease in d.f. and TCC, limiting values are btained, which are abut.0015 and +140 ppm/ C, respectively. The bservatins utlined abve indicate that at least tw mechanisms can ccur during heat treatment which affect the a.c. lsses, and subsequently the TCC f Ta^Or capacitrs. The first mechanism appears t be practically independent f nitrgen cncentratin in the tantalum film and results in decreases in the dissipatin factr and TCC when the heat treatment temperature des nt exceed 200 C. The secnd mechanism which prduces an increase in dissipatin'factr and TCC, alng with far greater increases in capacitance, is dependent n the nitrgen cncentratin in the tantalum film, ttally swamping ut the effect f the first mechanism fr capacitrs with lw nitrgen cncentratins. The secnd mechanism can be explained by a cm- parisn with wrk dne by Smyth et al ' n the heat treatment f andic xides n bulk tantalum. They pstu- lated that a cnductivity gradient exists in andically - 33 -
frmed tantalum xide after expsure t heat treatment at temperatures between 200 C and 400 C. The explanatin fr the cnductivity gradient is that xygen is extracted frm the Ta^O^ and diffuses acrss the xide-tantalum interface int the tantalum, creating xygen vacancies r excess tantalum in the xide. The cnductivity f the xide is therefre greatest near the tantalum-xide interface and diminishes in the directin f the xidecunterelectrde interface. The prtin f the xide which is affected increases with time and temperature f heat treatment. The capacitance is therefre increased by virtue f the heat treatment, because a prtin f the xide which was previusly a gd insulating dielectric is nw shunted by an effective resistance, resulting in an effectively thinner dielectric. Smyth attributes the increase in dissipatin factr t an increase in series resistance, ccurring in the xygen depleted regin f the xide. Hwever, the increased lsses may als be due t a large number f free Ta ins r ther cnductive cmpunds f Ta distributed thrughut the xide as a result f the heat treatment. This culd als affect the dielectric cnstant because f the different plarizability f the inhmgeneus dielectric, as m the Maxwell-Wagner type f structure. 12-34 -
In the case f capacitrs with tantalum cntain- ing interstitially disslved nitrgen in excess f between 10 and 13 atm percent, even with a heat treatment tem- perature as high as 350 C, the xygen cannt easily be extracted frm the Ta.O. dielectric, as the majrity f interstitial sites in the tantalum lattice have already been filled by the nitrgen. Therefre, the dielectric remains fairly hmgeneus thrughut mst f the rigi- nal thickness and the capacitance is shifted nly slightly upward. The first mechanism, which prduces a decreasing TCC and dissipatin factr practically independent f ni- trgen cntent when the capacitrs are treated at nly 200 C, is prbably identical t the ne which causes simi- lar results in mre heavily nitrided capacitrs heat treated at higher temperatures. Evidently, a temper- ature f nly 200 C is insufficient t cause sizeable extractin f xygen frm the dielectric t the underlying tantalum. Therefre, the secnd mechanism discussed abve is nt appreciably bserved, even fr very lightly ni- trided capacitrs. The decreased dissipatin factr and TCC may be due t a decrease in inic cnductivity caused by the remval f species such as H 0 r citric acid ins frm the bulk f the xide which have been incrprated 13 during andic xidatin. Yamazaki et al reprted n - 35 -
the frequency characteristics f Ta^O,. capacitrs having different values f TCC and tan 6 at 1 KHz attributable t different preparatin methds nt specified. In each case decreases in TCC and tan 6 were bserved as a functin f increasing frequency. The remarkable result btained was that a limiting value f between +130 and +140 ppm/ C ccurred in each case. Hwever, the samples which had higher TCC and lss factr at 1 KHz required a higher frequency t attain the limiting value f TCC. The dissipatin factr was als bserved t decrease with increasing frequency until the pint where the series resistance tk effect. Yamazaki attributed his results t less actin f separated tantalum ins and decrease f plarizatin at the higher frequencies. Hwever, trapped water r citrate mlecules culd prbably have caused the same effect, as their diples are unable t respnd t the higher frequencies. It, therefre, appears that the true value f TCC f the intrinsic andic xide f tantalum is between +130 and +140 ppm/ C. V. CONCLUSIONS AND SUMMARY It has been shwn that by subjecting finished TM capacitrs t heat treatment between 250 C and 350 C, imprved a.c. prperties can be btained when the nitrgen cntent in the sputtered tantalum is between 10 and 22 atm percent. The nted imprvements are a lwering - 36 -
f the dissipatin factr and TCC t.0015 and +140 ppm/ C, respectively, as cmpared t.0023 and +200 ppm/ C in TM capacitrs frmed frm beta-ta lightly dped with nitr- gen. These imprvements are accmpanied by a slight in- crease f capacitance, whse magnitude is dependent n the temperature f heat treatment, being abut 2% fr the highest heat treatment temperature f 350 C. It is ex- pected that this aging prcess will inhibit future changes in capacitance in subsequent TC bnding r lng-term aging,.... 9 as indicated by preliminary aging experiments. Analysis f the dependencies f the a.c. prper- ties n perid f heat treatment fr the varius heat treatment temperatures and nitrgen cncentratins sug- gests that at least tw mechanisms ccur during heat treatment. It appears that ne mechanism results in a cnductivity gradient due t xygen diffusin ut f the Ta^O^ int the tantalum, as pstulated by Smyth, causing an increase in lsses and TCC after treatment a ( t temper- atures greater than 200 C. The magnitude f this effect, hwever, decreases as the nitrgen cntent f the tantalum film increases. It is prpsed that this is due t the fact that, as the interstitial sites in the tantalum lat- tice becme saturated with nitrgen, a barrier is set up t xygen diffusin. - 37 -
A secnd mechanism is evident, because the lsses and TCC decrease practically independent f nitrgen cncentratin at 200 C and decrease nly in the case f nitrgen cncentratins in excess f abut 10 atm percent fr higher heat treatment temperatures. It is pstulated that this is due t the remval f water r pssibly citrate mlecules ut f the bulk f the xide. Due t the fact that xygen diffusin int the tantalum is minimal at 200 C, even fr un-nitrided film, and even at 350 C fr mre heavily nitrided film, the secnd mechanism predminates fr these cases. The d.c. prperties f the heat treated capacitrs have been measured t cnfrm with present prduct specificatins. The 50 vlt leakage current after heat treatment up t 350 C is equal t r in mst cases lwer than the current measured befre heat treatment. The average value f leakage current fr capacitrs which exhibit imprved a.c. characteristics is abut 0.15 na. The step stress breakdwn results are equally encuraging. Capacitrs receiving the 350 C, 1 hur heat treatment had a median breakdwn vltage f 130 vlts, as cmpared t m vlts befre heat treatment in the 0.2 hur step stress test. D.C. static life testing thrugh 200 hurs has s far exhibited lw failure rates, averaging abut 4.5%. - 38 -
It has als been shwn that by using planar magnetrn sputtering t prduce the base tantalum film certain distinct advantages are btained ver cnventinal sputtering techniques. In additin t a decade increase in depsitin rate, there is minimal heating f the substrate. Fr the depsitin f alpha-tantalum film anther distinct advantage is the ccurrence f a "plateau regin" where the nitrgen cncentratin is virtually cnstant at abut 13.5 atm percent, as a functin f increasing flw rate ver a wide range, in this case 1.3 t 2.1 sec/minute. This feature wuld prvide excellent cntrl ver film and capacitr prperties in a prductin situatin. The values f film prperties t be mnitred fr prduct cntrl are a resistivity f abut 100 pftcm, a TCR f abut +400 ppm/ C, and a thermpwer f +3.6 JJV/ C. The capacitance density r dielectric cnstant f andic xides prduced frm this film is reduced by abut 7% frm an xide cntaining n nitrgen. The majr cnclusin f this wrk is that TM capacitrs cntaining between 10 and 22 atm percent nitrgen and heat treated at temperatures between 250 C and 350 C exhibit imprved a.c. prperties, permitting extensin f applicatin t higher frequencies withut sacrificing excellent'd.c. prperties. In additin, the lng-term stability f capacitance fr high precisin RC prduct is expected t be greatly imprved. - 39 -