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. Thin Solid Films 311 1997 207 211 Concentrtion nd therml relese of hydrogen in morphous silicon crbide films prepred by rf sputtering Y. Suzki,), T. Shikm, S. Yoshiok, K. Yoshii b, K.

UniÕersity, 2-1 Ymd-ok, Suit, Osk 565, Jpn Received 5 November 1996; ccepted 18 June 1997 Abstrct Concentrtion nd therml relese of hydrogen in hydrogented morphous SiC -SiC:H. films were studied.

1 . Thin Solid Films Concentrtion nd therml relese of hydrogen in morphous silicon crbide films prepred by rf sputtering Y. Suzki,), T. Shikm, S. Yoshiok, K. Yoshii b, K. Ysutke b Reserch Lbortory for AdÕnced Technology, Tkmtsu Ntionl College of Technology, 355 Chokushi, Tkmtsu, Kgw 761 Jpn b Precision Science nd Technology DiÕision, Grdute School of Engineering, Osk UniÕersity, 2-1 Ymd-ok, Suit, Osk 565, Jpn Received 5 November 1996; ccepted 18 June 1997 Abstrct Concentrtion nd therml relese of hydrogen in hydrogented morphous SiC -SiC:H. films were studied. The films were prepred onto Si 111. wfers t room temperture by rf plner mgnetron sputtering in gs mixture of rgon t prtil pressures of 0.33 P nd hydrogen from to 1.3 P. The IR mesurements conducted on the films nneled t vrious tempertures for 3600 s suggested tht the hydrogen ws relesed from Si H nd C H bonds in the films t the tempertures bove 600 nd 850 K, respectively. In-situ isochronl nneling for 300 s t vrious tempertures from 323 to 1123 K in the ERDA Elstic Recoil Detection Anlysis. system ws crried out for the specimen hving the hydrogen concentrtion of 7.1=10 27 tomsrm 3. It ws reveled tht three types of hydrogen exist in the films; hydrogen bonded to Si or C toms nd unbonded hydrogen, with the concentrtions of 2.8=10 27, 1.9=10 27 nd 2.4=10 27 tomsrm 3, respectively. The concentrtion of unbonded hydrogen decreses with increse of the hydrogen prtil pressure. q 1997 Elsevier Science S.A. Keywords: Amorphous mterils; Anneling; Hydrogen; Silicon crbide 1. Introduction Hydrogented morphous silicon crbide -SiC:H. films re used in the morphous silicon solr cell w1,2 x, the tndem solr cell wx 3 nd the electroluminescent device wx 4. The structure, opticl nd electricl properties of the films depend on the deposition conditions w5,6 x. Especilly, the hydrogen toms in the films give much influence on some electronic nd opticl properties w7,8 x. Therefore, the mesurement of hydrogen concentrtion nd bonding structure in -SiC:H films nd their therml stbility re importnt for the devices. Hydrogen concentrtion is usully indirectly estimted by infrred IR. bsorption mesurements wx 9 except for the unbonded hydrogen. In this pper, we studied the vrition of hydrogen in -SiC:H film prepred by rf sputtering method in gs mixture of rgon nd hydrogen by using IR spectroscopy nd elstic recoil detection nlysis ERDA. w10,11 x. In ddition, we hve crried out in-situ chrcteriztion of ) Corresponding uthor. hydrogen depth profiles during isochronl nneling of the specimen to obtin the ctivtion energy for detrpping of hydrogen. 2. Experimentl detils A-SiC:H films were prepred by diode-type rf plnr mgnetron sputtering on to Si 111. wfers t room temperture. A sintered silicon crbide disk 75 mm in dimeter ws sputtered t power of 210 W in gs mixture of rgon t prtil pressure P. Ar of 0.33 P, nd hydrogen P. H 2 from to 1.3 P, where the bckground pressure before sputtering ws 6.5=10 y5 P. The distnce from the cthode to the substrte ws 50 mm. Under these conditions, the deposition rte obtined ws bout 0.5 nm s y1. The component rtio of crbon to silicon determined by Auger electron spectroscopy ws nerly unity. IR spectr of s-deposited nd nneled films were mesured using double bem IR spectrophotometer Hitchi Perkin-Elmer The nneling temperture ws in the rnge of K for 3600 s in vcuum of 5=10 y4 P.

2 208 Y. Suzki et l.rthin Solid Films Fig. 1. Hydrogen depth profile in -SiC:H film 154-nm-thick prepred t H prtil pressure of 0.33 P obtined by ERDA. 2 Fig. 3. Anneling temperture dependence of the integrted intensity... H v rv dv, which is due to the vibrtions of Si H bonds. In ERDA w12,13 x, the recoiled hydrogen from elstic collisions with the bombrding 6.06 MeV 19 F 3q ions trverses through the 0.5=2 mm 2 collimtor nd is t the fixed forwrd ngle of 408 with n energy below 0.4 MeV. A 6.2-mm-thick Mylr bsorber ws used s prticle filter to shield the silicon surfce brrier detector SSBD. from the forwrd scttered nlysis bem nd other recoiled hevy ion bems. The typicl bem current of 19 F 3q on the smples ws 5 10 prticle nnompere pna.. The depth scle pplied to the smple ws obtined using Brgg s lw for stopping power bsed on the elew14,15x nd Andersen nd mentl vlues tbled by Ziegler Ziegler w16 x. In-situ isochronl nneling for 300 s t vrious tempertures from 323 to 1123 K ws crried out in the ERDA system. 3. Results nd discussion 3.1. Hydrogen depth profile by ERDA A hydrogen depth profile in the 154-nm-thick -SiC:H film prepred t PH 2 of 0.33 P obtined by ERDA is shown in Fig. 1. The surfce of the -SiC:H film nd the interfce between the film nd silicon substrte re indi- cted by broken lines. The depth profile of hydrogen concentrtion in the film ws uniform t 7.1=10 27 tomsrm IR bsorption results Fig. 2 shows IR bsorption coefficient v. vs. wvenumber for s-deposited -SiC:H film prepred t PH 2 of 0.33 P. This figure shows brod bsorption bnds t round 800, 2100 nd 2800 cm y1, which re due to the stretching mode vibrtions of Si C, Si H nd C H bonds, respectively wx 8. In ddition, shoulder on the bsorption bnd is shown t round 1000 cm y1, which is due to the rocking nd wgging mode vibrtions of C H bonds. The concentrtion of C H bonds is estimted by using the bsorption spectr t round 1000 cm y1 which ws seprted from the bsorption t round 800 cm y1. Using the vlue of v., the concentrtion of bonds in the film, N is given by w17x IR v. NIR sas H dv 1. v where As is conversion fctor which depends on the bonding stte, which will be estimted lter, nd the integrtion is over the bsorption bnd. Thus the integrted Fig. 2. Typicl IR bsorption spectrum of -SiC:H film prepred t H 2 prtil pressure of 0.33 P. Fig. 4. Anneling temperture dependence of the integrted intensity... H v rv dv, which is due to the vibrtions of C H bonds.

3 intensity H v. rv. d v. is directly proportionl to the concentrtion of bonds in the films w8,18 x. Figs. 3 nd 4 show chnges of the integrted intensities H v. rv. dv., which re due to the vibrtions of Si H nd C H bonds, with increse of nneling temperture for the smples prepred in the sme condition in Fig. 2. These figures show the integrted intensities decrese with increse of nneling temperture from 600 to 1000 K nd from 850 to 1100 K for Si H nd C H, respectively. These results men tht the hydrogen which ws bonded to Si or C toms is relesed t different rnges of tempertures In-situ isochronl nneling in the ERDA system nd the kinemticl nlysis of hydrogen relese Y. Suzki et l.rthin Solid Films In-situ isochronl nneling for 300 s t vrious tempertures from 323 to 1123 K in the ERDA system ws crried out in order to mesure precise trnsition of hydrogen density in the film directly. Fig. 5 shows the vrition of hydrogen depth profiles during the isochronl nneling. The surfce of the film nd the interfce between the film nd Si substrte re indicted by broken lines. In this figure, it is seen tht the hydrogen does not diffuse into the Si substrte, but is relesed from surfce of the smple with incresing temperture. At 1073 K, hydrogen is no longer detected. The verge hydrogen concentrtions deduced from Fig. 5 re plotted ginst nneling tempertures in Fig. 6. In Fig. 6, open circles nd solid lines show the experimentl results nd the clculted, respectively. The hydrogen concentrtion decreses with Fig. 5. Chnge in the hydrogen depth profile of -SiC:H film prepred t H 2 prtil pressure of 0.33 P during in-situ isochronl nneling for 300 s t the tempertures from 323 to 1123 K in ERDA system. Fig. 6. Chnge in hydrogen concentrtion in -SiC:H film with the nneling temperture, obtined from the hydrogen depth profiles seen in Fig. 5. Open circles nd solid line show the experimentl results nd the clculted, respectively. increse of nneling temperture. Three chrcteristic regions re seen where the hydrogen concentrtion decreses drsticlly t the nneling tempertures round 350, 700 nd 950 K. These tempertures re in good greement with the integrted intensities of IR bsorption bnds s shown in Figs. 3 nd 4. Thus, it cn be sid tht three types of hydrogen bonds re distributed in the films; the first type is the unbonded, which corresponds to the relese round 350 K, the second nd third types re the hydrogen bonded to Si or C tom, which correspond to the relese t tempertures round 700 or 950 K, respectively. The solid line in Fig. 6 ws clculted under the ssumptions w19x tht the detrpping is rte limiting process nd tht the relese process obeys the first-order kinetics; the hydrogen toms escpe from the surfce of the film, nd diffusion is independent of the hydrogen concentrtion. In this cse, the ctivtion energy is expressed by generlized form of the Arrhenius eqution w20 x, / ye D NsN0exp ytn expž 2. kt where N is the hydrogen concentrtion in the film fter nneling for time t t temperture T, N0 is the initil hydrogen concentrtion, ED is the ctivtion energy for detrpping, n is the detrpping ttempt frequency nd k is the Boltzmnn constnt. Since three types of hydrogen bonds re present in these films, three kinds of the initil hydrogen concentrtion N 1, N2 nd N 3, re to be considered. The experimentl results in Fig. 6 were fitted by Eq.. 2 where the ctivtion energy ED nd the detrpping ttempt frequency n re obtined through the reltion of 1rT vs. lnyln NrN.4 in the three chrcteristic re- 0

4 210 Y. Suzki et l.rthin Solid Films Fig. 8. Hydrogen concentrtions in -SiC:H films prepred under vrious H 2 prtil pressures PH 2 rnging from to 1.3 P. Open circles indicte totl hydrogen concentrtions s mesured by ERDA, nd br chrts indicte the concentrtions of Si H nd C H bonds which were estimted from the IR bsorption spectr, using the conversion fctors estimted from the N nd N vlues Section Htched region then indictes unbonded hydrogen concentrtions. Fig. 7. Chnges in the concentrtions of three types of hydrogen in the film;. the unbonded hydrogen,. b the hydrogen bonded to Si tom nd. c tht to C tom. N 1, N2 nd N3 indicte the initil hydrogen concentrtions of such three types of hydrogen. gions. The initil concentrtions N 1, N2 nd N 3, were determined from itertive clcultion. The initil hydrogen concentrtions N 1, N2 nd N3 thus determined bsed on Eq. 2 re 2.4 = 10, 2.8 = 10 nd 1.9 = 10 tomsrm 3, respectively, nd the ctivtion energies re ev 1.27=10 J, 0.44 ev 7.05=10 J. nd y ev 2.08 = 10 J., respectively. Fig. 7, b nd c show the clculted concentrtions of those three types of hydrogen s function of nneling temperture. We determined the conversion fctors As for Si H nd C H bonds in -SiC:H film bsed on Eq.. 1 using the vlues of H v. rv. dv shown in Figs. 3 nd 4 nd N 2, N 3. The conversion fctors As determined were 3.2=10 23 nd 6.4=10 22 m y2 for Si H nd C H, respectively. the unbonded hydrogen concentrtion hs peked in the rnge of PH 2 from 0.13 to 0.33 P. The rdicls in the plsm during smple preprtion were observed by opticl emission mesurements w21 x. Fig. 9, b shows the opticl emission intensity of rdicls of. Ar ) 415 nm. nd b. H ) 652 nm. nd H ) 486 nm. b for vrious hydrogen prtil pressures P. In Fig. 9, it is seen H Concentrtions of three types of hydrogen in -SiC:H films prepred t Õrious H prtil pressures 2 Fig. 8 shows the chnge of hydrogen concentrtion in -SiC:H films with vrious hydrogen prtil pressures P H 2 rnging from to 1.3 P. In this figure, open circles indicte totl hydrogen concentrtions s mesured by ERDA, nd br chrts indicte the concentrtions of Si H nd C H bonds which were estimted from the IR bsorption spectr, using the conversion fctors estimted from the N nd N vlues Section Htched region then indictes unbonded hydrogen concentrtions. It is seen tht Fig. 9. The opticl emmission intensity of rdicls of. Ar ) 415 nm. nd. b H ) 652 nm. nd H ) 486 nm. b for vrious hydrogen prtil pressures P H 2.

5 Y. Suzki et l.rthin Solid Films tht the intensities of H ) nd H ) b increse nd the inten- sity of Ar ) decreses with increse of P H 2, respectively. The unbonded hydrogen concentrtion decreses in ccor- ) dnce with the increse of hydrogen rdicls H nd H ). b in the plsm. 4. Summry nd conclusions Concentrtion nd therml relese of hydrogen in the hydrogented morphous SiC -SiC:H. films were studied using IR spectroscopy nd elstic recoil detection nlysis ERDA.. The results obtined re s follows:. 1 Hydrogen depth profiles of s-deposited films by the ERDA method showed tht the totl hydrogen concentrtions in the films rnged from 5.3 to 7.1=10 27 tomsrm The IR mesurements conducted on the films nneled t vrious tempertures for 3600 s suggested tht the hydrogen ws relesed from Si H nd C H bonds in the films t the tempertures from 600 to 1000 K nd from 850 to 1100 K, respectively.. 3 In situ isochronl nneling for 300 s t vrious tempertures from 323 to 1123 K in the ERDA system ws crried out for the film hving the hydrogen concentrtion of 7.1=10 27 tomsrm 3. Three types of hydrogen bonds exist in the film; the first type is the unbonded, the second nd third types re the hydrogen bonded to Si or C tom. The initil concentrtions nd the ctivtion energies for therml relese of three types of hydrogen were determined to be 2.4 = 10 27, 2.8 = nd 1.9 = tomsrm, nd ev 1.27=10 J., 0.44 ev y19 =10 J nd 1.3 ev 2.08=10 J., respectively.. 4 The conversion fctors As for the Si H nd C H bonds in -SiC:H film were 3.2=10 23 nd 6.4=10 22 m y2, respectively. The unbonded hydrogen concentrtion decresed in ccordnce with the increse of hydrogen ) rdicls H nd H ). in the plsm. b Acknowledgements We would like to cknowledge Professor K. Our, Osk University, for his kind coopertion with the ERDA mesurements. References wx 1 G. Gnguly, A. Mtsud, Mter. Res. Proc wx 2 S. Tsud et l., Jpn. J. Appl. Phys wx 3 G.A. Hirt, T. Nishimoto, H. Okmoto, Y. Hmkw, IEEE Electron Devices wx 4 F. Demichelis, G. Crovini, C.F. Pirri, E. Tresso, G. Amto, U. Cosci, G. Ambrosone, P. Rv, Thin Solid Films wx 5 H. Shiri, D. Ds, J. Hnn, I. Shimizu, Appl. Phys. Lett wx 6 Y. Suzki, S. Inoue, I. Hsegw, K. Yoshii, H. Kwbe, Thin Solid Films wx 7 C.H. Ling, C.Y. Kwok, K. Prsd, J. Vc. Sci. Technol. A wx 8 F. Demichelis, F. Giorgis, C.F. Pirri, E. Tresso, Phil. Mg. B wx 9 W.A. Lnford, M.J. Rnd, J. Appl. Phys w10x P.M. Red, C.J. Sofield, Thin Solid Films w11x A. Turos, O. Meyer, Nucl. Instr. Meth. b w12x K. Umezw, T. Kuroi, J. Ymne, F. Shoji, K. Our, T. Hnw, Nucl. Instr. Meth. b w13x T. Kuroi, K. Umezw, J. Ymne, F. Shoji, K. Our, T. Hnw, Jpn. J. Appl. Phys w14x J.F. Ziegler, Stopping Cross-Sections for Energetic Ions in All Elements, Pergmon, New York, w15x J.F. Ziegler, Nucl. Instr. Meth w16x H.H. Andersen, J.F. Ziegler, Hydrogen Stopping Powers nd Rnges in All Elements, Pergmon, New York, w17x S. Inoue, K. Yoshii, M. Umeno, H. Kwbe, Thin Solid Films w18x F. Demichelis, C.F. Pirri, E. Tresso, G. Benedetto, Phil. Mg. B w19x F.M. Lord, J.S. Kittelberger, Surf. Sci w20x A.H.M. Holtslg, A.V. Silfhout, Surf Sci w21x A. Mtsud, M. Mtsumur, S. Ymski, H. Ymmoto, T. Imur, H. Okushi, S. Iizim, K. Tnk, Jpn. J. Appl. Phys L183.

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