IEEE Transactions on Electrical Insulation Vol. EI-21 No.4, August 1986

DIELECTRIC PROPERTIES OF PLASMA-POLYMERIZED HEXAMETHYLDISILOXANE FILMS:1 COMPLEX PERMITTIVITY

T.S. Ramu*, M.R. Wertheimer and J.-E. Klemberg-Sapieha.Groupe des Couches Minces (GCM)

and

Dept. of Engineering Physics, Ecole Polytechnique,Montreal, Quebec, Canada

ABSTRACT

Prompted by our extensive earlier studies of structure andproperties of plasma-polymerized hexamethyldisiloxane (PPHMDSO)films prepared under different fabrication conditions, we haveinvestigated their dielectric properties. The complex per-mittivity C*=E '-ici" has been measured over a wide frequencyrange (10-2 to 104 Hz), as a function of temperature (250C to>3000C) and ambient relative humidity. The principal fabri-cation variable, substrate temperature Ts, was varied from 250Cto 400 0C. Films prepared at Ts=250C show the same instabilitytowards atmospheric oxygen and humidity, and concomitant highdielectric losses, reported in t-he literature by other work-ers. On the other hand, films prepared at TS=4000C show lowlosses (tan6z7xj04), little susceptibility to aging, and lowmoisture absorption. Films deposited at intermediate valuesof T8 display behavior lying between these two extremes. Wecorrelate the observed dielectric properties with film struc-ture and morphology, and describe a hitherto unreported low-fre-quency dielectric relaxation due to absorbed humidity.

I NTRODUCT I ON

Among the earliest applications envisaged for thin,organic films produced in glow discharges (plasma poly-mers) was their use as dielectrids [1]. The electricalproperties of such films is the object of a thoroughrecent review by Gazicki and Yasuda [2]. As stated bythese reviewers, plasma polymers have so far been lesssatisfactory than conventional polymers for use as di-electrics, for example in capacitors, for two main rea-sons: their relatively high dissipation factor (tanS),and their tendency to "age" more rapidly. Both thesecharacteristics may be associated with trapped radicalswhich can react witn atmospheric gases to form polargroups (for example carbonyl or hydroxyl), or withtrapped ionic species. Gazicki and Yasuda [2] discusstechniques used by various authors in attempts to im-prove film stability, and to reduce dielectric losses.

Among the very wide range of possible "monomers" forplasma-polymerized dielectric films (aromatic and ali-

phatic hydrocarbons, halocarbons, organosilicones, andothers), the organosilicones appear to hold much pro-mise: Not only are these films quite stable at ele-vated temperature, but they are a priori more readilycompatible with silicon-based integrated circuits inelectronic applications. It is therefore not surprisingthat numerous earlier investigators have addressed vari-ous aspects of their dielectric properties [3-15]:Some authors have studied the permittivity and lossesof organosilicone plasma-polymerized films under vari-ous fabrication conditions [3-6], while others wereprimarily concerned with their dc conduction character-istics [3,6-13], or the behavior of MPS (metal/plasmapolymer/semiconductor) structures [14,15].

Over the past few years we have conducted detailedstudies of plasma polymerization of organosilicone filmsin microwave discharges; it has been shown [16-18] thatthe control of important fabrication variables such assubstrate temperature s., power density P, and "monomer"flow rate F, allows one to control film composition,morphology, and growth rates over wide ranges. Pilot-

OfBO-9367/86/0BO0-0549$01 .00 @ 1986 IEEE

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IEEE Transactions on Electrical Insulation Vol. EI-21 No.4, August 1986

scale equipment developed in this laboratory [18] andelsewhere [19], based on the proprietary large-volumemicrowave plasma (LMP®)technique, can uniformly coatlarge surface areas (hundreds of cm2 or more) at de-position rates of 30 nm/s or more, evident advantagesfor eventual manufacture of thin-film capacitors.

Recently we have shown [201 that microwave plasmasdiffer fundamentally from the lower frequency dischar-ges used by other investigators, by virtue of theirsubstantially higher population density of very energe-tic electrons. As this portion of the electron energydistribution function (EEDF) is responsible for thecreation of active precursor species in plasma chemicalreactions, the observed ten-fold or higher film growthrates in microwave as opposed to lower frequency plas-mas, can be quite readily understood.

The present study is based on the dielectric charac-terization of plasma-polymerized organosilicon filmsproduced in LMP apparatus. In this first of two com-panion papers we discuss the complex permittivity £C '-ic" and its dependence on fabrication conditions,ambient temperature and humidity, and measurement fre-quency. The object is to elucidate dielectric lossmechanisms, and to optimize fabrication conditions forproducing chemically and physically stable films havingthe lowest possible dielectric losses. In the compan-ion paper [21] we report dielectric breakdown studieson the same sample materials.

EXPER I MENTAL

The LMP apparatus used to produce films by microwave(2.45 GHz) discharge has been described elsewhere [18].Plasma polymer (PP) of hexamethyldisiloxane (HMDSO), theonly "monomer" used in the present study, was depositedon aluminum-coated glass substrates with the guardedelectrode geometry shown in Fig. 1: the dielectric filmthickness is between 200 and 500 nm, while that of thetop electrode (also of aluminum) is typically about 50nm. The effective area of the electrodes was so chosenas to yield a capacitance of at least 4 nF.

1~~~~~~~

Fig. 1: SampZe geometry used for measuring e* : h,Z,g designate high, voZtage, Zaw voZtage, and guardeZectrodes, respectiveZy; a = gZass substrate;d = dielectric fiZm.

The dielectric parameters cE' and tan6 have been stud-ied over the temperature range from 25 to 300 °C, andover a frequency range from 10 mHz to 10 kHz. Two in-struments were used to cover this wide frequency range,namely a Solartron, model 1170 Frequency Response Analy-ser (from 10 mHz to 1 kHz) and a General Radio, model1615 transformer-ratio-arm bridge (from 50 Hz to 10 kHz).In both cases the measurement accuracy is better than1%, both in tan6 and in capacitance.

Based on earlier investigations [18] the magnitude ofthe applied microwave power was kept constant at 600 W,corresponding to a power density in the plasma of 0.4W/cm3, while the pressure and monomer flowrate were 0.2Torr and 40 ml/min, respectively. The substrate tem-perature, also an important fabrication parameter [17,18] was varied over the range from 250C to 4000C. De-position rates under these conditions varied from -22to -5 nm/s, film thicknesses being determined by inter-ferometry or profilometry as described earlier [16-18].Some samples were annealed in vacuum at their respectivedeposition temperature for 3 to 5h. As mentioned above,the response of F* to variations in fabrication condi-tions is a primary objective of this study; equally im-portant, however, are the effects of sample exposure toelevated temperature and relative humidity: the effectof temperature cycling (annealing) on the properties offilms has been studied over the temperature range be-tween 25 and 3000C, both in air and under vacuum. Theaging characteristics of PPHMDSO, a measure of the di-electric's long-term stability, has been assessed byfollowing the evolution of tan6 of specimens heated inair at 3000C for durations of up to 250 h.

RESULTS

Effect of Substrate Temperature (T.) on e*(f) and E*(T)

As in earlier work [18], we have studied the morpholo-gy of films produced at different fabrication conditionsby scanning electron microscopy (SENI). Figs. 2 (a) and(b), micrographs of PPHMDSO films produced at T,= 500Cand 250 0C, respectively, show a decrease in the numberdensity of spheroidal particles with rising T's; this hasbeen discussed in detail elsewhere [18].

Typical data for the temperature response and the ef-fect of thermal cycling on the relative permittivityK'=cl/Eo and the dissipation factor tan6 (=c`/c') areshown in Fig. 3. In this experiment, a virgin specimenproduced at TS=250C was heated in a temperature-controlledoven in air up to 260 0C, kept at this temperature for 4h, and then slowly cooled. There is seen to be hystere-sis in both K' and tan6., both quantities attaining somewhat lower values after the temperature cycle. Fig. 4depicts the isothermal (25°C) frequency response of K'and tan6 for a number of samples, produced under differ-ent conditions: curves "a"l and "b" pertain to a samplesimilar to that of Fig, 3, before and after annealingin air at 3000C, respectively. Curves "c" and "d" per-tain to a sample produced at T5=2000C, without furthertreatment, and following an 8h anneal in vacuum at 2000C, respectively, Finally, curve "e" corresponds to asample produced at T,= 400 °C, followed by the same treat-ment as "d". In all cases, a well-defined minimum intan6 is observed at low audio frequency, similar to datareported by Segui [7].

We noted above that both annealing (in air or vacuum)and deposition at elevated T. can lead to a significantreduction in tan6. This is depicted, in a more syste-

550_

Ramu et al.: Complex permittivity of hexamethyldisiloxane

60

a

b40~~~~~~~~~~~

20

1 2 3 4

109,0f (Hz)

Fig. 4: Isothermal (T = 25°C) frequency response oftan6 for PPHMDSO samples produced under differentconditions: (a) Ts= 25°C; (b) Ts= 25°C, anneaZedin air at 300 C; (c) T = 200°C; (d) T5= 200°C, thenannealed for 8 hours in vacuum at 200 C. (e) T. =4000C, follZaed by the same anneal as in (d).

matic manner, in Fig. 5: samples represented by opensymbols were deposited at the indicated values of Tsfollowed immediately by an 8 h anneal in air at 3000C.

Pig. 2: Scanning electron micrographs of PPHMDSOfiZms produced at (a) Ts= 500C, (b ) Ts= 2500C,

4

3

10-Xso

U

2

1

50 100 150 200 250

T (0C)

Fig. 3: Effect of temperature cycling on the complexpermittiVity K*[= K' (1 - j tan6)] of a virginPpHMDSo film (TC=250C) at 1 kHz.

0

4

3

0 100 200 300 400

TS( C)

Fig. 5: K' and tan6 for PPHMDSO samples produced atdifferent Ts. Open synboZs: sampZes were anneaZedin air at 3000C for 8 h; full syibolZs: no furthertreatment after deposition.

I

a

4

3

2

551

552 IEEE Transactions on Electrical Insulation Vol. EI-21 No.4, August 1986

Full symbols, on the other hand, represent sampleswhich had not received the additional annealing treat-ment. In both cases tan6 is seen to decrease systema-tically, especially in the range 25<T, 250°C. The re- 16lative benefit of the annealing treatment decreaseswith rising T., as one may expect. Note that K 'changeslittle over the range of T. values investigated. 12

Fig. 6 shows the variations of C and tanS at differ-ent ambient temperatures (and constant measurement /frequency, f=1 kHz), for sample materials produced at - 8four Ts values, ranging from 50 to 400°C. Note that 60the sample produced at T,=400°C shows the least amountof variation with T and, of course, the lowest valueof tan6. 4

24 - x

20

16 I i I | _

co 60

-x 4

0

0 100 200 300

T (C)

Fig. 6: Temperature response of C and tanS of sam-

ples produced at different TS: x500C; 150OC;A 25006C; A 400 0C.

Finally, Fig. 7 illustrates the relative resistanceto "aging" of sample materials produced at differentT5: samples were kept in air at 300°C for periods ofup to 10 days, and their tanS values were monitoredduring this period. The hatched areas for T,=100 and2500C correspond to the limits of variation observedfor several samples prepared under the nominally identi-cal fabrication conditions. In the case of all fourTS values, samples are seen to undergo "aging", that is,an increase in tanS with time.. For T5=4000C, however,this effect is least pronounced, and tanS reaches anasymptote after two or three days; for T,=25 and 100 0C,tanS does not yet appear to have reached its asymptoticlimit, even after 10 days. This "aging" effect is evi-dently contrary to the drop in tanS when virgin samplesare first annealed (see Figs. 3 to 5); in other words,tanS has a minimum (after roughly 8 h at 300°C) which,for simplicity, has not been shown in Fig. 7.

0

0 2 4 6 8 10

Time ( days )

Fig. 7: Effect on tanS of aging in air at 300°C,for sampZes produced at different Ts: x T = 25°C;

Tsf; = 100°C; A Ts = 250°C; 7s = 400°C.

E'ffect of reZative hurnmd-ity onr *(f)

The rise in tanS with decreasing frequency below 50Hz (Fig. 4) suggests the presence of a very low fre-quency relaxation. In order to study this further,E*(f) has been measured between 10-2 and 102 Hz: Fig. 8shows the results of dielectric relaxation at room tem-perature on a series of samples prepared at three dif-ferent substrate temperatures (T,=25, 100 and 2500°C)which had been conditioned for 24 h at different levelsof relative humidity. Peaks in tanS, the amplitude andcentral frequency of which rise substantially with in-creasing relative humidity (RH), are observed in allthree cases,

We note, further, that the position (fm)of the losspeak shifts to higher frequency with rising T. (at con-stant RH) and with rising RH for a given T.. The ampli-tude (tan6)max of the loss peak, on the other hand, isseen to drop considerably with increasing T..

The moisture uptake in PPHMDSO has been studied bymeasuring the change. in capacitance of samples maintainedat known levels of RH. In Fig. 9 we plot the specificchange in capacitance, AC/C as a function of RH. Theplots are seen to be linear for all sample materials,and they can be characterized by a moisture absorptionindex defined by

cCl-c2)/Cl 1 ACRHH -RH C jH]

1 2

(1)

Values of obtained from Fig. 9 are listed in Table 1;for comparison we have included in this table data takenfrom the literature [6].

I II

II

Ramu et al.: Complex permittivity of hexamethyldisiloxane

Table 1

Moisture absorption index 6 for PPHMDSO samples preparedunder different fabrication conditions.

DISCUSSION4-

Effect of Substrate Termrperature and Anneal,ing Treatments

In their review paper on the electrical properties ofplasma polymers, Gazicki and Yasuda [2] state: "It ap-pears that both aging problems and humidity sensitivity

.L.. contribute to the dielectric instability of plasma-polymerized thin films, and that this instability is the

2 major factor inhibiting the technological applicationsof these films", They list and discuss the techniqueswhich have been used by various investigators in at-tempts to overcome the instability problem, namely:

(1) annealing post-treatment, primarily under vacuum;

Fig. 8: Dielectric relaxation at differentrelative humidities (RH) for three different sam-.ple materials: (a) T.= 25°C; (b) Ts= 150°C;(c) Ts= 250 0C. 1: 8% RH; 2: 65% RH; 3: 100%RH.

60

40

20

Relative humidity ( % )

Fig. 9: Effect of anbient relative hwmdity on mois-ture uptake, measured by capacitance change AC/C,for samples produced at different Ts: x 25°C;

100°C; A 250°C; A 400 0C.

(2) hydrogen plasma post-treatment;

(3) incorporation into the film of antioxidizing stabil-izers; and

(4) lowering the mean kinetic energy of ions in theplasma during film deposition.

Although most of these approaches have shown some par-tial successes, so far none was able to improve the filmsdielectric properties to the point of being comparableto those of "conventional" polymeric materials.

In the present paper we have added to the list a newapproach towards solving the instability problem, name-ly the use of elevated substrate temperature Ts duringfilm deposition. Although heated substrates (2500C<T <

400%C) are routinely used for the plasma deposition oinorganic films such as amorphous silicon (a-Si:H) [22],and silicon nitride or oxide [23,24], this approach doesnot appear to have occurred to earlier workers in thepresent field, Yet, the results described above strong-ly suggest that this appears to be by far the most promi-sing solution to the instability problem: in theirTable 1, Gazicki and Yasuda [2] summarize values of K'and tan6 (at 20%C and 1 kHz) for various plasma polymers,the appropriate literature references, and dielectricproperties of corresponding conventional polymers. The"best" plasma polymer cited is that obtained from ethy-lene (PPE), tan6 z5x10-4, while for PPHMDSO they citethe results of Tuzov et al, [6], tan6 - 10 2. Referringto Fig. 4 for PPHMDSO deposited at TS=400QC (curve "e"),not only is our 1 kHz result (tan6=7x104) an order ofmagnitude lower than the best results of the Soviet work-ers [4], but it rivals the result for PPE. Elsewhere

60

40

20

0

30

20

10

0

x

0-do

lo0- 4T (°C ) Calculated from Fig. (9)

25 70.6100 35.5250 21.5400 5.4

Tuzov [6] 22.0B ~ ~~~~~~~ I

20

10

0

(C)

-2 0 1

loglof(Hz)

~I

55

IEEE Transactions on Electrical Insulation Vol. EI-21 No.4, August 1986

[25] we report a comparison of our results for a varie-ty of plasma-deposited materials, including PPHMDSO.

The reason for the substantial reduction in tan6 andother favorable film characteristics, to be discussedbelow, we feel, is rather complex: We have shown [17,18] that organosilicone films become more and more"inorganic" in character as T. is raised, and that theirstructure becomes dense and homogeneous, with few spher-oidal inclusions (see also Fig. 2). Not only does ele-vated Ts permit more rapid recombination of free radi-cals during film formation (and during subsequent va-cuum annealing), but the resulting reduction in carboncontent [18] presumably results in a lesser density ofpossible sites for subsequent formation of polar (car-bonyl) moieties. Furthermore, the enhanced surface mo-bility of active species at elevated T., impedes thenucleation and growth of spheroidal particles. The im-portance of film structure and morphology will be ad-dressed again below.

Other benefits derived from deposition at elevatedTs, evidenced by Figs. 4 to 7 are the following:

(1) material deposited at a particular, elevated valueof Ts is presumably stable for subsequent use to atleast that temperature. Consequently, films deposited,for example, at Ts=4000C are suitable as dielectricsin high-temperature applications;

(2) this is further underlined by the much lesser ten-dency for high .s films to "age" irreversibly, as isillustrated by Fig. 7;

(3) films deposited at the highest value of Ts investi-gated here, 400°C, have the lowest values of D(tan6)/Dfand D(tan6)/DT (see Figs. 4 and 6, respectively), Thisis important in avoiding possible "thermal run-away"conditions, a distinct possibility in the results ofearlier workers [5,6], 3(tan6)/DT being high at eleva-ted ambient temperatures;

(4) we have noted that K' is quite stable as a functionof measurement temperature and frequency; the observedvalue, between 3.5 and 4.5, is in good agreement withthe results of the Soviet workers [5,6];

(5) finally, the reduced sensitivity to humidity, mani-fested in Figs. 8 and 9, is an issue of sufficient im-portance to merit detailed discussion. This is thesubject of the section below.

Effecl of reLative hwmdity

From Fig. 8 (especially 8a) we note a loss peak witha width of between one and two decades in frequency,which shifts towards higher frequency (and grows in am-plitude) as the moisture content in the film is in-creased. This Debye-like dispersion is a well-knowncharacteristic of absorbed water in heterogeneous di-electrics [26-29]; the amplitude (tan6)max of the losspeak decreases significantly with rising T. [Figs. 8(b)and (c)], as we have already pointed out. An inspectionof scanning electron micrographs, Figs. 2(a) and (b)(see also Ref. 18, Fig. 5) shows that films containlarge numbers of spheroidal particles having dimensionsof the order of 0.1 pm, the size and spatial frequencyof which decrease with rising Ts [18]. The interfacesof these spheroids are regions of relatively low den-sity, where moisture can readily absorb. Absorbed(bound) water and the dense spheroids of PPHMDSO thusconstitute a two-component system, equivalent to a di-electric continuum containing a uniform distribution of

conducting spheroids. Sillars [29] has given an expres-sion for the relaxation frequency fm of such a system,namely,

fn = 0l + AV2(C1-o2)27rE0o[K1 ' + AV2(K2'-K1 ) ]

(2)

where subscripts 1 and 2 refer to the dielectric andaater, respectively, A is the depolarizing coefficientof the spheroids, a and K7 are the conductivity andrelative permittivity, respectively, and V2 the volumefraction of moisture.

In the present case V <<1 a c<a2 and K1 t<<K2, so thatfm can be approximate: by:

(3)AV2mc[ 2

fm 2TE:o [Kl + AV2K 2']

It can be seen,therefore, that an increase in absorbedhumidity causes an increase in fm, that is, a shift inthe position of (tan6)Max to higher frequency; also,the magnitude of (tan6)max increases with V2. As bothof these features are confirmed experimentally by Fig.8, we conclude that Maxwell-Wagner-Sillars (MWS) [26,29] theory provides at least a semi-quantitative de-scription of the present situation, Complete elimina-tion of spheroidal inclusions can presumably be achieved,for example, by deposition at sufficiently high Ts, andsuch microscopically homogeneous films should be quiteinsensitive to humidity. Such a trend is, indeed, mani-fested by the data in Fig, 9 and in Table 1, where 6drops sharply with rising T.s

Numerous authors [6,30,31] have observed the moisturesensitivity of plasma-polymerized films, and have evensuggested putting them to use as moisture-sensing de-vices. To the best of our knowledge, however, the low-frequency relaxations reported here, their relationshipto relative humidity, and the links between 6 and filmmorphology have not been recognized by earlier workers.

CONCLUSIONS

An extensive review of the literature, including thepatent literature, suggests that a strong interest hasexisted for more than twenty years in potential applica-tion of plasma-polymers as thin film dielectrics. Aspointed out by Gazicki and Yasuda [2], however, the filmschemical instability and concomitant dielectric lossesappear so far to have discouraged commercial implementa-tion. Several techniques have been tested by earlierworkers in efforts to overcome Che instability problem,but none of them appears to have had the desired impact.

In this paper we show, for the case pf PPHMDSO, thatdeposition at elevated substrate temperature Ts can leadto tan6 values as low as 7xlO-4 , to excellent resistanceto aging (tested by heating the dielectric in air forextended periods of time), and to a low value of themoisture absorption index 6. Similar results may beachieved with other organosilicones; a comparison ofdifferent materials is published elsewhere [25].

In the companion paper [22] we show that tanS is notthe only dielectric property of the PPHMDSO films whichimproves markedly with increasing T5, but that this ap-plies also to the dielectric breakdown properties. We

54

Ramu et al.: Complex permittivity of hexamethyldisiloxane

have already pointed out that microwave plasmas arecapable of substantially higher deposition rates thanlower frequency plasmas [20], and that the LMP processused here is suitable for uniformly coating large sur-face areas. Considering all these favorable factorstogether, we feel, warrants reexamining the technologi-cal future of plasma-polymerized dielectric films.

ACKNOWLEDGMENTS

The authors gratefully acknowledge numerous fruitfuldiscussions with Prof. H.P. Schreiber, and with membersof the GCM, particularly E. Sacher, A. Yelon, and A.Okoniewski.

This work is supported by the Natural Sciences andEngineering Research Council of Canada (NSERC) and bythe Fonds FCAR of Quebec.

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[3] J.S. Sandved and K. Kristiansen, "Glow DischargePolymerization of Organic Silicones" Vacuum, Vol.27, pp. 235-239, 1977.

[4] B.V. Tkachuk, L.V. Perova and V.M. Kolotyrkin,"The Dielectric Properties of Organosilicon Filmsand the Effect of y-Radiation on their Structure"Vysokomol. Soyed., Vol. A13, pp. 828-832, 1971,[English Translation: Polym. Sci. USSR, Vol. 13,pp. 935-940, 1971].

[5] B.V. Tkachuk, V.M. Kolotyrkin and G.G. Kirei,"Thermal Degradation of Polymer Films of MethylSiloxanes" Vysokomol. Soyed., Vol. A10, pp. 585-591, 1968, [English Translation: Polym. Sci. USSR,Vol. 10-, pp. 683-691, 1968].

[61 L.S. Tuzov, V.M. Kolotyrkin and N.N. Tunitskii,"Stability of the Dielectric Properties of PolymerFilms Formed in Glow Discharge"l Int. Chem. Engg.,Vol. 11, pp. 60-64, 1971.

[7] Y. Segui, "Contribution a 1'e'Aude des mecanismesde conduction dans les films minces de polymere.Application a la passivation de composants asemi-conducteur", Ph.-D. thesis, Universite PaulSabatier, Toulouse 1978.

[8] A.K. Tsapuk, V.M. Kolotyrkin, "Polymerization ofSilicone Oil on the Electron Irradiated Surfaceof Solid" Vysokomol. Soyed., Vol. 7, pp. 1802-1806,1965, [English Translation: Int. Chem. Engg. Vol.7, pp. 1985-1989, 1965].

[9] H.T. Mann, "Electrical Properties of Thin PolymerFilms: Part I, Thickness 500-2500 A", J. Appl.Phys., Vol. 35, pp. 2173-2179, 1964.

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[12] J. Tyczkowski and M. Kryszewski, "ElectricalConduction in Plasma-Polymerized OrganosiliconFilms: Influence of Water and Oxygen", J. Appl.Polym. Sci.: Appl. Polym. Symp., Vol. 38, pp.149-161, 1984.

[13] A. Okoniewski and A. Yelon, "Conduction Mechan-isms in Polysiloxane Films Deposited by MicrowaveGlow Discharge", J. ApplL Phys., Vol. 58, pp.414-419, 1985.

[14] D. Brosset, Bui Ai, and Y. Segui, "New Method ofGaAs Passivation with Thin Polymer Films", Appl.Phys. Lett., Vol. 33, pp. 87-89, 1978.

[15] M. Maisonneuve, Y. Segui and Bui Ai, "ElectricalProperties of Metal-Polymer (Polysiloxane) -

Silicon Structures and Application of Polysilo-xane to the Passivation of Semiconductor Devices",Thin Solid Films, Vol. 33, pp. 35-41, 1976.

[16] A.M. Wrobel, M.R. Wertheimer, J. Dib and H.P.Schreiber, "Polymerization of Organosilicones inMicrowave Discharges" J. Macromol. Sci. -Chem.,Vol. A14, pp. 321-337, 1980.

[17] A.M. Wrobel, J.E. Klemberg-Sapieha, M.R. Wertheimerand H.P. Schreiber "Polymerization of Organosili-cones in Microwave Discharges II Heated Sub-strates", J. Macromol. Sci.-Chem., Vol. A15, pp.197-213, 1981.

[18] M.R. Wertheimer, J.E. Klemberg-Sapieha and H.P.Schreiber "Advances in Basic and Applied Aspectsof Microwave Plasma Polymerization", Thin SolidFilms, Vol. 115, pp. 109-124, 1984.

[19] J. Kieser and M. Neusch "Industrial MicrowavePlasma Polymerization", ThinSolid Films, Vol.118, pp. 203-210, 1984.

[20] M.R. Wertheimer, M. Moisan, "A Comparison ofMicrowave and Lower Frequency Plasmas for ThinFilm Deposition and Etching", J. Vac. Sci. Technol.Vol. A3, pp. 2643-2649, 1985.

[21]. T.S. Ramu and M,R.. Wertheimer, "Dielectric Pro-perties of Plasma-Polymerized Hexamethyldisilo-xane Films: II Breakdown", IEEE Trans. Electr.Insul., Vol. E121, pp. 557-563, 1985.

[22] M.H. Brodsky (ed .), "Amorphous Semiconductors",Springer, New York, 1979.

[23] J.R. Hollahan and R.S. Rosler, "Plasma Depositionof Inorganic Thin Films", In J.L. Vossen and W.Kern (eds,), "Thin Film Processes", Academic Press,New York, 1978, Chap. IV-1.

[24] N.G. Einspruch and D.M. Brown (eds.)., "VLSI Elec-tronics Microstructure Science, Vol. 8: PlasmaProcessing for VLSI", Academic Press, New York,1984.

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[25] T.S. Ramu, M..R. Wertheimer and J.E. Klemberg-Sapieha, "Dielectric Properties of Plasma-Deposi-ted Thin Films: A Comparison of Different Ma-terials", IEEE Conf. on Electr. Insul. and Di-electric Phenomena (CEIDP), Amherst N.Y., Oct.1985.

[26] L.K.H. Van Beek, "Progress in Dielectrics", Vol.7, p. 70, (Heywood, London, 1967).

[27] J.B. Hasted, "Progress in Dielectrics", Vol. 3,p. 101 (Heywood, London, 1961).

[28] L. Paquin, H. St-Onge and M.R. Wertheimer, "TheComplex Permittivity of Polyethylene/Mica Compo-sites", IEEE Trans. Electr. Insul., Vol. El-17,pp. 399-404, 1982.

[29] R.W. Sillars, "The Properties of a dielectriccontaining semiconducting particles of variousshapes", J.I.E.E., Vol. 80, p. 378, 1937.

[30] G. Sawa, 0. Ito, S. Morita and M. Ieda, "Dielec-tric Properties Polystyrene Formed in Glow Dis-charge", J. Polym. Sci., Polym. Phys. Ed., Vol.12, pp. 1231-1234, 1974.

[31] N. Inagaki, "Plasma Polymerized Films Sensitiveto Moisture", in H. V. Boenig (ed.) "Advances inLow-Temperature Plasma Chemistry, Technology,Applications", Vol. 1, pp. 80-91, 1984.

*Permanent address: Dept. of High Voltage Engineering,Indian Institute of Science, Bangalore, India,

Manuscript was received on 12 June 19 85, in revisedform 15 Novenier 1985.

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