Korean Chem. Eng. Res., Vol. 44, No. 5, October, 2006, pp. 520-527 m r i Ž m m i r, q rl 561-756 r rte v v 1 664-14 (2006 9o 5p r, 2006 9o 26p }ˆ) Surface Reaction Modeling for lasma Etching of SiO 2 Thin Film YeonHo Im Nanomaterials Research Center and School of Chemical Engineering and Technology, Chonbuk National University, 664-14, 1-ga, Duckjin-dong, Duckjin-gu, Chonju 561-756, Korea (Received 5 September 2006, accepted 26 September 2006) k l l FC(fluorocarbon) v p l p pml vl q v, e v p q p r d p l p m. SiO 2 e l pp e p mlp q CSTR(continuous stirred tank reactor) rp p l pm nl p e p l. r ˆ q p e v p q pp p pm nl p q ƒ vp rk l m. p ƒ vp e q r r l mp, p e v e p pn l m. s p p ˆ p v o l e m. h Abstract A realistic surface model is presented for prediction of various surface phenomena such as polymer deposition, suppression and sputtering as a function of incidence ion energy in high density fluorocarbon plasmas. This model followed ion enhanced etching model using the well-mixed or continuous stirred tank reactor (CSTR) assumption to the surface reaction zone. In this work, we suggested ion enhanced polymer formation and decomposition mechanisms that can capture SiO 2 etching through a steady-state polymer film on SiO 2 under the suppression regime. These mechanisms were derived based on experimental data and molecular dynamic simulation results from literatures. The model coefficients are obtained from fits to available beam and plasma experimental data. In order to show validity of our model, we compared the model results to high density fluorocarbon plasma etching data. Key words: SiO 2, Etching, Surface Reaction, High Density lasma, Modeling 1. ~ lp p p rqp vr p. p o p q v rp pp, p q p tn p p [1]. p p v rp pn or p e rl ps pp v rp q p p l ~ rp rp r t rp l p rp p. er ~ rp p l p (aspect ratio)p e, p e ˆ p n. p e p o ~ lp s rp r m To whom correspondence should be addressed. E-mail: yeonhoim@chonbuk.ac.kr l v q e ~l p v p [2-3]. v p l e pp p t s l vp p pm p l vl p r. e p e rp p l e l np FC(fluorocarbon) lp ~ n pp, q p (sidewall)p l p [2]. kn, v FC q p l o l ~ lp o t pp, kp p l l p l p pp q p p l er rp m o r r p l n erp [2-3]. k v e l l p v e e, t pms (beam) e q r r p k r p l l [2-10]., e p e 520
p l p v pl t s pms p l e l l p [6-9, 11]. p p e pp Langmuir mel q pp r l er rp p o r rp n p [6-7, 9]. l p e ol FC p lv q p r ˆ e p p rk p [2-3, 9]. p e p ˆ p pv q r r p q p p q tl p [10]. Abraham-Shrauner e p e o e e pl p rr p o Langmuir mep rn q p p rk mp, p t n pqp v e p e lp ep n l r rp o l ˆ p pv m [12]. q v l p v pp vrp q p p ~ l ql e rp l p rp l n erp. l l v v v e, q r r e l l er rp q m p p m. e pp CSTR(continuous stirred tank reactor) rp p l FC q l e l ƒ vp l. l p rk p p, F pm dp l ˆ p Š mp, srp pml vp l e pl e m m. 2. m n e p e p FC(fluorocarbon) ~ n p p e p o q v l np v p n p. Fig. 1p p rp v p ˆ pm (ionization), l (excitation) (dissociation) p pp k ps pm p. l l FC v l rp ps (, F) pms p m. FC v l pp k e l p p rp mlp p [2, 3]. Fig. 2(a) Žl p p e p e p 521 Fig. 1. Schematic of plasma-surface interactions in fluorocarbon plasma. ml vp l v e pp ˆ, k l p d (sputtering) mll r e. v (deposition) lr(suppression) m lp Fig. 2(b)m p e op FC lp q l q pl p v, tn p p p r l e erp., lr mlp rp p ~ p rrp p e k l p(bowing) p rp m p p. l l lr mlp q l ps p CSTR rp p l p l m. p p s SiO 2 pp k e l llv p r r ep n m. kn, l p q r r e rp l l lr mll SiO 2 p v ps p p nl q SiO 2 l pm l p p rk m. l l rk p p p el n p v e m. 2-1. SiO 2 Ž m 2-1-1. ps p e pl ps p p Fig. 2m p v m vrrp r p q l p l e l vrrp. p p l q r r [10] e [3]l rp, l l CSTR rp p l p p m. Fm Fig. 2. (a) The etching yield as a function of ion energy based on the observed experimental trends. (b) Schematic of the model that describes the SiO 2 etching mechanism in the suppression regime. Korean Chem. Eng. Res., Vol. 44, No. 5, October, 2006
522 p l Table 1. Reaction set for SiO 2 etching in fluorocarbon plasma Reaction rocess Flux dependence Surface coverage Rate coefficient Reaction sets for SiO 2 etching in ion-induced layer Reaction with F atoms [1] SiO 2 2F SiO F (g) 2 Neutral adsorption on clean SiO 2 Γ F θ SiO2 s F [2] SiO 2 F 2F I SiF O (s) 2SiO 4(g) 2(g) 2(*) Ion-enhanced chemical etching θ F Y MF [3] SiO 2 CF F SiO (s) (s) 2 x1(g) Recombination of CFx with F Γ F K Reactions with fluorocarbon species [4] SiO CF SiO CF x(g) 2 x(s) Neutral adsorption on clean SiO 2 θ SiO2 s CFx [5] SiO [CF ] I SiO x n 2 (s) Ion-activated polymer decomposition (1-θ T ) [6] SiO [CF ] I SiO x 2 2 [ ] n Ion-enhanced polymer formation θ [CFx]2 Y M [7] SiO [CF ] I SiO x 2 2 [ ] θ [CFx]2 Y MC site formation by ion bombardment [8] SiO [CF ] F I SiO x 2 (s) 2 [ ] θ [CFx]2 Y MF [9] I 2SiO 2 (s) SiF 2CO SiO x(g) 2(g) 2(*) Ion-enhanced chemical etching by Y ME Reaction sets for fluorocarbon deposition Reaction with F atoms [10] [ ] F I n(s) [CF (s) x ] n 1(s) Ion-enhanced etching of polymer θ F/ Y F Reactions with fluorocarbon species [11] [ ] CF [CF ] n(s*) x(s) x n1(s) olymer deposition * / s CFx [12] I [ ] n(s) [ ] n 1(s) consumption by ion bombardment / Y C [13] I [ ] n(s) [ ] n(s*) Ion-activated polymerization site formation / Y S p e q p pe p Table 1 p [1], [4]m [11]l ˆ l. e pp ps (F, ) p š p(surface coverage, θ) r (sticking coefficient), ps p pv kp (1-θ)l r (S) v. l l l ps p p p p p l ˆ r m. š pp q p CSTR rp p p p. ps d(γ)l ep p p p. Γ ADS = SΓ( 1 θ) p pel n r p l p n m. r m l p v pl l ps l (beam) e l l p [11, 13-15]., Gray p e p e p mlp CSTR r l r p m, l l r e l rn l r. l, Gogolides p Gray p e p q l q ˆ p pv m. l l p p p pn m, Table 2l l v ps l r ˆ l. 2-1-2. pm nl p r d (ion-enhanced chemical sputtering) e p e pp Table 1p [2]m [9]p pe p F l v d(sheath) mll pml p SiF x s p ˆ p p [9, 15]. p e rp pmp nl p r d p, e p rp p p. ER = Y θ SiFx o44 o5 2006 10k (1) (2) Table 2. Coefficients and parameters for the SiO 2 surface model Value S F 0.02 S CFx 0.9 S F/[CFx] 0.1 S CFx/[CFx] 0.1 S CFx/ 0.1 S F/ 0.01 K 0.0153 Y MF E >, 0.0457 ( E ), =4.0eV E>, 0.0361 ( E ), =4.0eV Y M /2< E <, 0.0361 ( E ), = 128 ev, Y ME E < /2, E >, 0.0150 0.0305 ( E E ), =4.0eV E >, 0.0456 ( E ), = 20.0 ev Y F E >, 0.020 ( E ), =4.0 ev Y C E >, 0.45 ( E ), = 35.0 ev Y S E >, 0.020 ( E ), =4.0 ev l, Y, θ SiFx m pm r d p(chemical sputtering yield), SiF x p š p pm d ˆ. e pp pml v ps p v pep [9]. Y = Y O ( E ) Y O m e p m e pp eq pm p l v(threshold energy) p, k e p Table 2l ˆ l. 2-1-3. r d (physical sputtering) e p e pp r d nl p l v pml p r d l p p (3)
. p e r d d p p. ER = Y( 1 θ) l, Ym 1 θ, r d p(physical sputtering yield), v l SiO 2p p pm d ˆ. r d pp pml v ps p, r d p e o Table 2l ˆ l. 2-1-4. pm nl p q v (ion-enhanced polymer formation and decomposition) e l s p pm l p q e pp ppˆ [2-3,11]. Gray p e e p k v l tn sp CF 2m Ar p m e pml vl p e m špp m [13]. p p e p e p CF 2p v e p q pp l Fig. 2(a)p d mll r q m v pn p [16]. e rl tn l p Fig. 2(a)p lr mll, p p rp p mlp v p. e q r r p p ml l q p r ˆ e e p ƒ vp rk p [2-3, 10]. kv v ƒ vl ~rp p r r p erp. l l Fig. 2(a)p r mlp o pm l p q pl p ˆ Table 1p [5-8] p p rk m., Table 1p pe [5] e l p q pm l p l e p e p q. p r ep p q p r ˆ e p p. Table 1l n q v p(y M, Y MC ) p p llrp [11], q p( )p Oehrleinp e m l m [17]. l l n p p Table 2l r l ˆ l. v p l Žp p pmp l v p nl q v pp. l Chae Schaepkens p l v pml p q v e p m [9, 18]. p l p p mp q s p l q v p. l l v mll p p p rn mp, Table 1p [10-13] Table 2l pe p ˆ l. 2-2. SiO 2 rym Ž m l l rk p v l k r s l e p r~ mll p p pp, Table 1 2l p l pe p ˆ l. rk p l l e o l F, q p špl r ˆ ve p p p. e p e p 523 (4) dθ -------- F = S (5) F ( 1 θ T )Γ F 2Y MF θ F d ------------ = S CFx ( 1 θ T ) θ [ CFx]2Γ I K Γ F 2Y ME S CFx [ CFx] dθ -------- = Y MS [ CFx] l, θ T = θ F p., [ CFx] m θ F [ CFx] e l ol F p š pp p, r ˆ ve p p. d [ CFx ] ------------------------- = S CFx [ CFx] ( Y M Y MC ) [ CFx] (8) dθ -------------------- F [ CFx ] = S (9) F [ CFx] [ CFx] Γ F Y MF θ F [ CFx] (5~9)ep lr d mll r ˆ e p v e l p e p. e p o p p p rp, = Γ F, =, Var = K 2Y ME S CFx, Var1 = Y M Y MC S F/[CFx] Var2=1Y MC Var1/Y M S CFx/[CFx] /Y M S CFx/[CFx] / Y MF (5~9)ep l s l šp p p. = 1 2Y MF S F R ---------------------------------------------------------------------------------------------------------------------------------------------- F Var2 Var2 Y Y MS MC S F [ CFx]2 VarVar1 S CFx [ 1 2Y MF S F ] (10) θ F = 1 [Var Y MC S F [ CFx]2 VarVar1 S CFx ] (11) = Var1 S CFx CFx [ CFx] = Y M θ F [ CFx] = S F [ CFx] [ ] Y MF Korean Chem. Eng. Res., Vol. 44, No. 5, October, 2006 (6) (7) (12) (13) (14) p e p e e pp lr d mll rn, s e p(si oq /pm)p p p. EY = θ F Y MF Y ME ( 1 θ T ) (15) e e p q pp l er q p l l p pm t s l r p k. l l p ˆ p v o v dl pm t s l r pn mp, q l ps p p pm (ion scattering) p evrp p l d p.
524 p l p pml vl q v l Fm q q l š p (θ F/, */ )p op e p p ep r ˆ vep p. dθ F ------------ = S F ( 1 )Γ F Y F θ F (16) dθ * ------------- = Y S ( 1 ) S CFx θ * (17) l, θ F θ * = 1p ep. op ep l l p p šp p lp p. S F S CFx/ = ------------------------------------------------------------------------------------------------------------ S F S CFx/ S CFx/Y F Y F Y S θ F θ * Y F Y S = ------------------------------------------------------------------------------------------------------------ S F S CFx/ S CFx/Y F Y F Y S srp v p(v oq /pm)p p. (18) (19) Fig. 4. Surface coverage for SiO 2 vs radical to ion flux ratio. Surfacecoverage with polymer(θ p, thin curves), with F atom (θ p, dashed curves) and with radical on SiO 2 surface. DY = S CFx R c θ * Y S ( 1 ) Y F θ F o44 o5 2006 10k (20) p p e v r l l s p šp, e v l r p lp pp, n p Table 2l ˆ l. 3. y SiO 2p pp v p tn r p t s p d, pm d pm l v l p m p. l l p prp p o t s pm d pl p ˆ l. Fig. 3p pr l p l šp p ˆ. pml v p rp v rs p 100 ev r m. v l SiO 2 l q pp qp e F d l, Fm špp r v m. p p v v e q p. Fig. 4 pr m 100 evp pml vl eˆl Fig. 3. Surface coverages vs F atom to ion flux ratio. Surface coverage with polymer(θ p, thin curves), with F atom (θ F, dashed curves) and with radical on SiO 2 surface. špp ˆ. d v l q špp v, e l vrrp l p špp p mlp sq m. po d v l l špp v, p dl q v v špp p. p p l l re p t s d l p p rp m p k p. Fig. 5 pr l m pml v l q p špp ˆ. Fig. 5(a)l p pml vl SiO 2 p q mr, p pml vl v l q špp v m. 100 }l pml v v q špp 1l or e pp pl v k. e p vrrp l p p p špp pml v v l v l p m. p m p sl pml v F/C pl e pp e q p, l l re p m pml v l m p q ˆ ppp k p. Fig. 6p l l re p Fm dp l ˆ p p. Fig. 6(a) / pl špp m p, s F/C pl e p., p F dm p dl špp p Fm p p pl p r kvp rp m p. Fig. 6(b)l q špp / pl p ˆ. p po F d rp p qp e v p. p p špp pn l e pl Fig. 7l ˆ l. 100 evp pr pml vl Fm dp l e pp p F dm rp p dl p e pp ˆ l. p rp špl e rp p r rp r l o q p p r ˆp. l l rk p ˆ p pv o r rp n
e p e p 525 Fig. 5. Surface coverage as functions of and ion energy. (a) polymer surface coverage, (b) surface coverage. Fig. 6. Surface coverage as functions of and (Ion erergy is 100 ev). (a) CFx surface coverage, (b) polymer surface coverage. p v, lr d mll v e pl Oehrlein e [17] m. p m Fig. 8 l ˆ } mll e r q p m. 70 ev p p pml vl q v p m, pml v 0l ovl q p šp v m. Fig. 8p 70 125 ev v lr m lp ˆ l l rk q v ƒ v p ˆ p k p. kn, 125 ev p p d ml e m r q p ppp k p. 4. l l s p r p, er rp m o FC v l SiO 2 e l p p m. p o s e l llv p e p v SiO 2m q p l p ƒ v p rk m. p l n p p e q r r p Š lrp, Fig. 7. SiO 2 etching yield as functions of and (Ion erergy is 100 ev). n p p e llr. l l llv ps p šp p v r Korean Chem. Eng. Res., Vol. 44, No. 5, October, 2006
526 p l Fig. 8. SiO 2 etching yield as a function of ion energy ( =10 and =10). Experimental data ( ) are from Oehrlein et al. [16]. p l rp p mp, srp rk p e m l ˆ p pv m. p ~ p o n p p e rl l r p p np p. p p 2006 l qvo ll p l vo ld. o44 o5 2006 10k k DY : deposition yield (deposited atom/ion) EY : etch yield (Si atoms/ion) : F atom to ion flux ratio : radical to ion flux ratio K : recombination coefficient of with F S F : sticking coefficient of F atoms on clean SiO 2 S CFx : sticking coefficient of radicals on clean SiO 2 S F/[CFx] : sticking coefficient of F radicals on chemisorbed S CFx/[CFx] : sticking coefficient of radicals on chemisorbed S CFx/ : sticking coefficient of radicals on polymer S F/ : sticking coefficient of F radicals on polymer Y MF : ion-enhanced chemical etching yield : ion-activated polymer decomposition yield Y M : ion-enhanced polymer formation yield Y ME : ion-enhanced etch yield by : physical sputtering yield Y F : ion-enhanced etch yield of polymer with F atoms Y C : consumption yield by ion bombardment : ion-activated polymer site creation yield Y S m m Γ F : fluorine radical flux : radical flux θ F θ F/ * / : ion flux : fluorine surface coverage : surface coverage : polymer surface coverage : fluorine surface coverage on polymer : activated polymer surface coverage on polymer y 1. Sze, S. M., VLSI Technology, 2 nd ed., McGraw-Hill, New York, NY(1983). 2. Schaepkens, M. and Oehrlein, G. S., A Review of SiO 2 Etching Studies in Inductively Coupled Fluorocarbon lasmas, J. Electrochem. Soc., 148(3), C211-C221(2001). 3. Standaert, T. E. F. M., Hedlund, C., Joseph, E. A., Oehrlein, G. S. and Dalton, T. J., Role of Fluorocarbon Film Formation in the Etching of Silicon, Silicon Dioxide, Silicon Nitride, and Amorphous Hydrogenated Silicon Carbide, J. Vac. Sci. Technol. A, 22(1), 53-60(2004). 4. Im, Y. H., Hahn, Y. B. and eaton, S. J., A Leval Set Approach to Simulation of Etch rofile Evolution in a High Density lasma Etching System, J. Vac. Sci. Technol. B, 19(3), 701-710(2001). 5. Cho, B. O., Hwang, S. W., Kim, I. W. and Moon, S. H., Expression of the Si Etch Rate in a CF 4 lasma with Four Internal rocess Variables, J. Electrochem. Soc., 146(1), 350-358(1999). 6. Butterbaugh, J. W., Gray, D. C. and Sawin, H. H., lasma-surface Interactions in Fluorocarbon Etching of Silicon Dioxide, J. Vac. Sci. Technol. B, 9(3), 1461-1470(1991). 7. Chang, J.. and Sawin, H. H., Molecular-beam Study of the lasma-surface Kinetics of Silicon Dioxide and hotoresist Etching with Chlorine, J. Vac.Sci. Technol. B, 19(4), 1319-1327(2001). 8. Kimura, Y., Coburn, J. W. and Graves, D. B., Vacuum Beam Studies of Fluorocarbon Radicals and Argon Ions on Si and SiO 2 Surfaces, J. Vac. Sci. Technol. A, 22(6), 2508-2517(2004). 9. Chae, H., Vitale, S. V. and Sawin, H.GH., Silicon Dioxide Etching Yield Measurements with Inductively Coupled Fluorocarbon lasmas, J. Vac. Sci. Technol. A, 21(2), 381-387(2003). 10. Humbird, D., Graves, D. B., Hua, X. and Oehrlein, G. S., Molecular Dynamics Simulations of Ar -induced Transport of Fluorine Through Fluorocarbon Films, Appl. hys. Lett., 84(7), 1073-1075 (2004). 11. Gogolides, E., Vauvert,., Kokkoris, G., Turban, G. and Boudouvis, A. G., Etching of SiO 2 and Si in Fluorocarbon lasmas: A Detailed Surface Model Accounting for Etching and Deposition, J. Appl. hys., 88(10), 5570-5584(2000). 12. Abraham-Shrauner, B., Simulaneous Multilayer lasma Etching and Deposition of Fluorocarbon Layers on Silicon, J. Appl. hys., 94(8), 4776-4780(2003). 13. Gray, D. C., Tepermeister, I. and Sawin, H. H., henomenological Modeling of Ion-enhanced Surface Kinetics in Fluorinebased lasma Etching, J. Vac. Sci. Technol. B, 11(4), 1243-1257 (1993). 14. Gray, D. C., Sawin, H. H. and Butterbaugh, J. W., Quantification of Surface Film Formation Effects in Fluorocarbon lasma Etching of olysilicon, J. Vac. Sci. Technol. A, 9(3), 779-785(1991). 15. Butterbaugh, J.GW., Gray, D.GC. and Sawin, H.GH., lasma-surface Interactions in Fluorocarbon Etching of Silicon Dioxide, J.
e p e p 527 Vac. Sci. Technol. B, 9(3), 1461-1470(1991). 16. Jin, W. and Sawin, H. H., rofile Evolution Simulation of Oxide Fencing during Via-First Dual Damascene Etching rocess, J. Electrochem. Soc., 150(11), G711-G717(2003). 17. Oehrlein, G. S., Zhang, Y., Vender, D. and Haverlag, M., Fluorocarbon High-density lasmas. I. Fluorocarbon Film Deposition and Etching Using CF 4 and CHF 3, J. Vac. Sci. Technol. A, 12(2), 323-332(1994). 18. Schaepkens, M., Oehrlein, G. S. and Cook, J. M., Effect of Radio Frequency Bias ower on SiO 2 Feature Etching in Inductively Coupled Fluorocarbon lasmas, J. Vac. Sci. Technol. B, 18(2), 848-855(2000). Korean Chem. Eng. Res., Vol. 44, No. 5, October, 2006