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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 Ciencia dos Materiais da Faculdade de Ciencias e Tecnologia da UNL and CEMOP-UNINOVACampus da FCT-UNL, 2829-516 Caparica, Portugalb CICECO, Departamento de Engenharia Ceramica e do Vidro da Universidade de Aveiro, 3810-193 Aveiro, Portugalc ICAT, laborato′ rio de SPM da Faculdade de Ciencias, 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 SiCNH 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 buer 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 SiCNH lm a hydrogen etching of 10 min was performed in order to etch the catalyst material and tofacilitate the crystallization. We report the inuence 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 SiCNH lms is also dependent on the gas pressure, gas mixture and deposition process used. 2006 Elsevier B.V. All rights reserved.PACS 81.05.Gc; 73.61.Jc; 81.15. 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. Proting 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 2006 Elsevier B.V. All rights reserved.doi10.1016/j.jnoncrysol.2006.02.025* Corresponding author. Tel. 351 21 294 8564; fax 351 21 295 7810.E-mail address imffct.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 SiCNH 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 SiCNH crystalline lms by PA-HWCVD withoutincorporation of oxygen.2. ExperimentalThe Six N yCzH lms were produced by hot wire chemi-cal vapor deposition HWCVD, plasma assisted HWCVDPA-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 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 1 , C–H2800 cm 1 and C–N 2100– 2150cm 1 stretchingmodes; N–H 2 wagging modes 1500 cm 1; Si –N stretch-ing/Si –O rocking modes 450 cm 1; and a strongabsorption band in the wavelength range of 600–1300 cm 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. 1b 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 dierence 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. Signicant 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– 1030cm 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-HxNormalizedIntensitya.u.Wavenumber cm-1Wavenumber cm -1HWCVDPA-HWCVDPECVD600 700 800 900 1000 1100 1200 1300 1400010101PECVDNormalizedintensitya.u.HWCVDbSi-CHx-SiC-NSiON-H x Si-CH 3SiNSiCPA-HWCVDFig. 1. a FTIR spectra of SiCN lms produced by dierent processes,HW-CVD PA-HWCVD and PECVD; b expansion of the same spectrain the wavenumber range of 600– 1400cm 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 prole obtained for the elementsdetected by RBS and EDR analyses, after data simulation,of the samples produced by PA-HWCVD Fig. 2a andHWCVD Fig. 2b. 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. 2a 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 inuenced by the depositionprocess, but also the lm morphology is quite dierent.Fig. 3 shows the SEM cross section images of the PECVDFig. 3a, PA-HWCVD Fig. 3b, and HWCVDFig. 3c lms deposited on Ni 5 nm covered glass andc-Si substrates. The lms of Fig. 3a are compact, havelow surface roughness and are amorphous while Fig. 3bexhibit 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. 3c 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 prole image is shown in Fig. 4a and the sec-tion analysis across the line displayed is shown in Fig. 4b.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. 1bPeak position cm 1 Modes Relative areaHWPA PA-HWCVD PECVD690– 710 Si –H rocking and wagging 8 14 –830– 832 SiC stretching and wagging 133 53 7.9900– 940 SiN stretching 85 69 391000 – 1030 SiO stretching/C –Nwagging/Si – CHx – Sibending 30 88 531130 – 1160 N–H x bending 44 40 951250 Si – CH3 bending 2.2 1.7 0.9Fig. 2. Depth prole obtained from RBS and ERD spectra for samplesproduced by a PA-HWCVD; and b HWCVD. The inset displays amagnication 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. 4b 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. 5a showsthe SEM top view images of a SiCN lm deposited on Ni1 nm covered Si-c substrate. Fig. 5b and c shows theimage of the same lm deposited on Ni 5 nm and Ni10 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 dierence 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 lmsproduced without ammonia gas have a very low growthrate 0.6 A/s [8] compared to the 5–6 A/s obtained forthese SiCNH lms. Besides that, CH x species have alsoan etching eect 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 dierent 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 buer 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 eect of Ni onthe inducing crystallization which has to be conrmed bymicro X-ray diraction 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 Ni5 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 nmcovered 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 SiCNlms was also reported by Gang et al. [11], being dependenton the N/H 2 ratio used, in