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Hydrogenated silicon carbon nitride ?lms obtained by HWCVD,PA-HWCVD and PECVD techniquesI. Ferreira a, * , E. Fortunato a, P. Vilarinho b , A.S. Viana c, A.R. Ramos d ,E. Alves d, R. Martins aa CENIMAT, Departamento de Cie?ncia dos Materiais da Faculdade de Cie?ncias e Tecnologia da UNL and CEMOP-UNINOVACampus da FCT-UNL, 2829-516 Caparica, Portugalb CICECO, Departamento de Engenharia Cera?mica e do Vidro da Universidade de Aveiro, 3810-193 Aveiro, Portugalc ICAT, laborato′ rio de SPM da Faculdade de Cie?ncias, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugald ITN, Instituto Tecnolo′ gicoe Nuclear, Estrada Nacional 10, 2686-953 Sacave′ m, PortugalAvailable online 17 April 2006AbstractHydrogenated silicon carbon nitride (SiCN:H) thin ?lm alloys were produced by hot wire (HWCVD), plasma assisted hot wire (PA-HWCVD) and plasma enhanced chemical vapor (PECVD) deposition techniques using a Ni bu?er layer as catalyst for inducing crys-tallization. The silicon carbon nitride ?lms were grown using C2 H 4, SiH 4 and NH 3 gas mixtures and a deposition temperature of 300 ° C.Prior to the deposition of the SiCN:H ?lm a hydrogen etching of 10 min was performed in order to etch the catalyst material and tofacilitate the crystallization. We report the in?uence of each deposition process on compositional, structural and morphological prop-erties of the ?lms. Scanning Electron Microscope-SEM and Atomic Force Measurement-AFM images show their morphology; the chem-ical composition was obtained by Rutherford Backscattering Spectrometry-RBS, Elastic Recoil Detection-ERD and the structure byInfrared-IR analysis. The thickness of the catalyst material determines the growth process and whether or not islands form. The produc-tion of micro-structured SiCN:H ?lms is also dependent on the gas pressure, gas mixture and deposition process used.ó 2006 Elsevier B.V. All rights reserved.PACS: 81.05.Gc; 73.61.Jc; 81.15. à zKeywords: Amorphous semiconductors; Composition; Films and coatings; FTIR measurements; Nitrogen-containing glass1. IntroductionThe exceptional mechanical, tribological and opticalproperties of ternary SiCN thin ?lm alloys make them suit-able for a wide range of applications. Pro?ting of the wideband gap controllability between 5 eV, for SiN, and 2.8 eV,for SiC [1], SiCN ?lms can be used in optoelectronic appli-cations such UV detection [2,3] or low-voltage white – blueelectroluminescence devices [4]. Due to its low dielectricconstant k, below 5, SiCN ?lms have been successfullyapplied in the protection of metal interconnection of ultralarge-scale integrated circuit (ULSI) [5] as etch stop andhardmask. Crystalline SiCN ?lms were employed in highbreakdown-voltage heterojunction diodes for high-temper-ature [6]. Applications of SiCN to MEMS have been alsoreported [7] making use of its exceptional mechanical prop-erties like high hardness in the range of SiC and SiN mate-rials %30 GPa [1]. Adding together a good chemicalresistance make this ternary alloy particularly interestingfor tribological applications.Several processes were used to produce amorphous orcrystalline SiCN thin ?lms alloys. Amorphous SiCN ?lmsare produced frequently by PECVD-like techniques usingsubstrate temperatures below 600 ° C, while crystallineSiCN ?lms reported have principal deposition process0022-3093/$ - see front matter ó 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.jnoncrysol.2006.02.025* Corresponding author. Tel.: +351 21 294 8564; fax: +351 21 295 7810.E-mail address: imf@fct.unl.pt (I. Ferreira).www.elsevier.com/locate/jnoncrysolJournal of Non-Crystalline Solids 352 (2006) 1361– 1366based on CVD techniques for substrate temperaturesabove 800 ° C.A large variety of alloys SixCyN z can be obtaineddepending on the gas mixture and on carbon and nitrogensources. Extra alloying elements such oxygen and hydrogenare of great importance and a source of complication forunderstanding its role on the main mechanical, opticalstructural and electrical properties.In this paper we compare the structure, morphology andcomposition of SiCN:H ?lms produced by HWCVDassisted or not by rf plasma and compared it to the ?lmsobtained by PECVD technique. This leads to the produc-tion of SiCN:H crystalline ?lms by PA-HWCVD withoutincorporation of oxygen.2. ExperimentalThe Six N yCz:H ?lms were produced by hot wire chemi-cal vapor deposition (HWCVD), plasma assisted HWCVD(PA-HWCVD) and plasma enhanced chemical vapor depo-sition (PECVD) using a gas mixture of silane (SiH 4 ), ethyl-ene (C2H 4) and ammonia (NH 3) without hydrogendilution. For the HWCVD process the ?lament tempera-ture was kept at 1900 ° C while for the PECVD componentan rf power of 130 W was applied. A gas mixture consistingof SiH 4 /C 2H 4/NH 3 was fed into the reactor in the propor-tion of 10/50/200 sccm, respectively. The system employedwas described in a previous work [8]. The ?lms were depos-ited on normal glass and crystalline silicon (c-Si) substratesand on thin (50 or 100 A?) Ni covered layer c-Si high resis-tivity wafer and glass substrates. The ?lms compositionwas analyzed by RBS and by ERD. He-RBS spectra wereobtained with 2 Schottky barrier detectors placed in IBMgeometry at 140° and 180° scattering angles, with resolu-tions of 15 and 20 keV respectively, using 2.0 MeV He +beam. ERD spectra were obtained with a Schottky barrierdetector placed at 24° scattering angle in IBM geometry,with 20 keV resolution, using a 2.0 MeV He + beam. Toprevent backscattered He + particles from hitting theERD detector, a Kapton ?lter with 8.2 · 1019 at/cm 2 wasplaced in front of it. IR absorption spectra were acquiredwith FTIR equipment in the wavenumber range of 400–4000 cm à 1. SEM images were taken with a Hittachi-S400apparatus on ?lms covered with a very thin carbon conduc-tive layer. Tapping mode AFM experiments were per-formed in a Multimode AFM microscope coupled to aNanoscope IIIa Controller. Commercial etched silicon tipswith typical resonance frequency of a.c. 300 Hz, have beenused as AFM probes.3. ResultsThe FTIR spectra obtained for HWCVD, PA-HWCVDand PECVD ?lms are shown in Fig. 1. The main assignedvibrations are related to: N–H (%3300 cm à 1 ), C–H(%2800 cmà 1) and C–N (%2100– 2150cm à 1) stretchingmodes; N–H 2 wagging modes (%1500 cmà 1); Si –N (stretch-ing)/Si –O (rocking) modes (%450 cm à 1); and a strongabsorption band in the wavelength range of 600–1300 cmà 1, due to SiC, SiN, SiO, Si – CHx , C–N vibrationmodes [5,9,10] . An enlargement and deconvolution of thespectra in this region was performed in order to obtain therelative intensity, position and area of each peak. That isshown in Fig. 1(b) and summarized in Table 1.Although similar deposition parameters were used forthe ?lms production, IR data show that the process rulesthe species incorporated into the ?lm and therefore its com-position. The main di?erence between the three processemployed is related to the incorporation of C and N. OnHWCVD ?lms C and N is preferentially bonded to siliconatoms due to the fact that SiC and SiN peaks are the mostintense. Signi?cant N–H x bonds are also present bothrevealed by the N–H x bending and stretching bonds. Sinceno peak related to C–N stretching modes is observed, werelate the peaks at 1000– 1030cmà 1 to the presence ofSiO or Si – CHx – Sibonds. On the other hand, PECVD ?lmsshow less C bonded to Si (weak SiC peak), an importantamount of N is bonded to Si but major C and N arebonded in the hydroxyl groups (Si – CHx – Si;N–H x, C– H).For PA-HWCVD ?lms an intermediate situation, as faras composition is concerned, is achieved. Still a highamount of C and N bonded to Si but inferior to that one500 1000 1500 2000 2500 3000 3500 40000.00.20.40.60.81.0aSi-N/Si-ON-H2/C-NC-NSi-H/Si-H2N-HC-HxNormalizedIntensity(a.u.)Wavenumber (cm-1)Wavenumber (cm -1)HWCVDPA-HWCVDPECVD600 700 800 900 1000 1100 1200 1300 1400010101PECVDNormalizedintensity(a.u.)HWCVDbSi-CHx-SiC-NSiON-H x Si-CH 3SiNSiCPA-HWCVDFig. 1. (a) FTIR spectra of SiCN ?lms produced by di?erent processes,HW-CVD PA-HWCVD and PECVD; (b) expansion of the same spectrain the wavenumber range of 600– 1400cmà 1. Dashed lines represent thedeconvoluted peaks.1362 I. Ferreira et al. / Journal of Non-Crystalline Solids 352 (2006) 1361– 1366shown by HWCVD ?lms appears and the Si –H and SiO/C– N/Si – CHx– Sipeaks are enhanced when compared toboth HWCVD and PECVD ?lms.The FTIR measurements we supplemented by RBS andERD analysis shown in Fig. 2.Fig. 2 shows the depth pro?le obtained for the elementsdetected by RBS and EDR analyses, after data simulation,of the samples produced by PA-HWCVD (Fig. 2(a)) andHWCVD (Fig. 2(b)). The average percentage of elementsdetected is shown in Table 2.Under similar deposition conditions used for the ?lmsproduction we get Si0.24 C0.11 N 0.35 :H 0.30 and Si0.22 C 0.16 -N 0.23 O 0.05 :H 0.33 for PA-HWCVD and HWCVD ?lms,respectively. So far, HWCVD ?lms have more carbonincorporation and lower nitrogen content but some poros-ity is revealed by the presence of oxygen in contrast to thePA-HWCVD ?lms. On the other hand, results also reveal athin Ni layer at the glass interface. That layer correspondsto the 5 nm Ni layer used as catalyst for inducing crystalli-zation. The inset of the graphs in Fig. 2(a) and (b) evidencea 5 nm layer corresponding to the thickness of the depos-ited Ni layer. Therefore we conclude that Ni was not con-sumed during the deposition process.Not only is the composition in?uenced by the depositionprocess, but also the ?lm morphology is quite di?erent.Fig. 3 shows the SEM cross section images of the PECVD(Fig. 3(a)), PA-HWCVD (Fig. 3(b)), and HWCVD(Fig. 3(c)) ?lms deposited on Ni 5 nm covered glass andc-Si substrates. The ?lms of Fig. 3(a) are compact, havelow surface roughness and are amorphous while Fig. 3(b)exhibit compact ?lms but with high surface roughnessformed by isles with variable dimensions that are indepen-dent of the substrate used, glass or Si-c, if covered with thinNi layer. SEM images of Fig. 3(c) shows ?lms, depositedon Si + Ni 5 nm substrate, that are compact, structuredand crystalline with a cone-like surface. When depositedon glass, the ?lms are amorphous with a smooth surface.The real dimensions of the isles are supported by AFMdata that is exhibited in Fig. 4, for PA-HWCVD ?lms.There a 3D pro?le image is shown in Fig. 4(a) and the sec-tion analysis across the line displayed is shown in Fig. 4(b).Table 1Summary data of the peak position, area and respective modes obtained for HWPA, PA-HWCVD and PECVD ?lms whose IR spectra are shown inFig. 1(b)Peak position (cm à 1 ) Modes Relative areaHWPA PA-HWCVD PECVD%690– 710 Si –H rocking and wagging 8 14 –%830– 832 SiC stretching and wagging 133 53 7.9%900– 940 SiN stretching 85 69 39%1000 – 1030 SiO (stretching)/C –N(wagging)/Si – CHx – Si(bending) 30 88 53%1130 – 1160 N–H x (bending) 44 40 95%1250 Si – CH3 (bending) 2.2 1.7 0.9Fig. 2. Depth pro?le obtained from RBS and ERD spectra for samplesproduced by (a) PA-HWCVD; and (b) HWCVD. The inset displays amagni?cation of the region were Ni is present.Table 2Results of the composition obtained by RBS and ERD for PA-HWCVD and HWCVD ?lmsSample C at.% N at.% O at.% H at.% Si at.% Thickness · 1015 at/cm 2PA-HWCVD 11 35 0 30 24 11600HWCVD 16 23 5 33 22 29500I. Ferreira et al. / Journal of Non-Crystalline Solids 352 (2006) 1361– 1366 1363We observe that isles are cone-like shape and their dimen-sions are variable from few nanometers to several microns.The big one observed in the image of Fig. 4(b) is about2.5 l m in diameter and around 200 nm in height. Also wehave observed that the surface morphology is dependenton the Ni thickness as shown in Fig. 5. Fig. 5(a) showsthe SEM top view images of a SiCN ?lm deposited on Ni(1 nm) covered Si-c substrate. Fig. 5(b) and (c) shows theimage of the same ?lm deposited on Ni (5 nm) and Ni(10 nm) covered glass, respectively, obtained in sampleregion absent of isle. Surface morphology is dependenton Ni thickness, some grains appear to be involved bythe amorphous tissue in Si-c substrate covered with a Ni1 nm layer, while in glass substrates with Ni 5 nm and10 nm layer we observed agglomerates that are smotherthan the former.4. DiscussionThe comparison process (keeping the same depositionparameters) evidenced that HWCVD lead to a high incor-poration into the SiCN ?lms, of SiC and SiN bonds. As therf plasma is coupled to HWCVD process the C and Nstarts to be incorporated in hydroxyl groups. Thereforefor ?lms grown by the PECVD the carbon and nitrogenare predominantly bonded to hydroxyl groups (Si – CHx–Si; N– H, C– H). This di?erence in the ?lms compositionis attributed to the gas dissociation occurring in each pro-cess. It is well accepted and demonstrated that in HWCVDprocess the species containing hydrogen are highly dissoci-ated giving rise to ionized species like Si, C, C 2 or N [8] .Additionally, NH 3 has low dissociation energy comparedto C 2H 4 and high reactivity with carbon enhancing theincorporation of Cx N y species and so it is responsible forincreasing carbon content. This explains why SiC ?lms(produced without ammonia gas) have a very low growthrate ($ 0.6 A?/s [8]) compared to the 5–6 A?/s obtained forthese SiCN:H ?lms. Besides that, CH x species have alsoan etching e?ect on the ?lm growth, and so its contributionto this growth mechanism cannot be disregarded. Althoughwith FTIR measurements we cannot conclude about thepresence of a SiCN ternary compound, it reveals that SiCand SiN bonds are the basis bonds for ?lms deposited byHWCVD and PA-HWCVD techniques. PECVD ?lmsseem to be formed by di?erent separated phase, since C–N, N–H and Si – CHx– Sibonds are predominant, suggest-ing that a ternary alloy is not obtained.SEM images have revealed that Ni is crucial for induc-ing crystallization since without that we observe a compact,smooth and featureless ?lm. When a thin Ni bu?er layer isused a high roughness surface is obtained, independently ofSi-c or glass substrate used. The origin of these isles isunknown but certainly related to catalyst e?ect of Ni onthe inducing crystallization which has to be con?rmed bymicro X-ray di?raction investigation in further work. ForHWCVD ?lms produced on (Si + Ni 5 nm) substrate it isquite evident the presence of a crystalline material beingobtained a laminated like surface in the region of the layerbreak. The isle shown, in the SEM image, is also compactwith a diameter of the order of 6 l m and height aroundFig. 3. SEM cross section view images of (a) PECVD ?lm deposited on Ni(5 nm) covered glass and on Ni (5 nm) covered Si-c substrates; (b) PA-HWCVD ?lm deposited on Ni (5 nm) covered glass and on Ni (5 nm)covered Si-c substrates; (c) HWCVD ?lm deposited on Ni (5 nm) coveredSi-c and on glass substrates.1364 I. Ferreira et al. / Journal of Non-Crystalline Solids 352 (2006) 1361– 13662.4 l m. The formation of this isle-like features in SiCN?lms was also reported by Gang et al. [11], being dependenton the N/H 2 ratio used, in