Thermal behavior study of Sb implanted into photoresist film

Nuclear Instruments and Methods in Physics Research B8! /81 (19931 1316-1314 North-Holland

Beam tntdraetions with Materials &Atoms

Thermal behavior study of Sb impl_arited into photoresist film R .L Maltez, L . Atrtaral, M . Behar and F .C . Zavvislak

Inmituw de Fiska, Unuersidade Federal do Rio Grande do Sud, Catra Arstal 15051. 91501-9711 Porto Alegre, RS, Brazil

The thermal stabiliiy of Sb implanted AZ1350 photoresist films has been investigated ~ , ;a the Rutherford backsc .ttlmring technique. We find that a shallow Sb implantation raises the temperature at whic) the photoresist starts to decompose considerably . Cornpati,un of the present results with thus, of Ag, .`an and Bi into the same pholoresist indicates that not only radiation but also chemical effects have to be considered in order to explain the impro,ment of the photoresist theimel stai lity .

1 . Introduction In recent yct:rs there has been a growing interest in ion implantation of polymers, essentially because of the actual and potential applications in advanced microelectronic technology. Radiation effects on the structure stability and electrical conductivity as well as characterization of the ion implanted profiles have been important topics of these studies [i-5] . It is known that most of the photoresists remain stable up to 150°C . At higher temperatures they start to decompose losing molecular components like H,, COZ , COH, CH 4 , ete. In an earlier work, Okvyama et al . [6] have shown that polymers heavily bombarded with high °nergy Itr ions become more resis'ant tv heat treatments . We have shown [7] that shallow Bi irnnlantgti ,rt (E = 50 keV, - a x 10 14 at ./cm - ) rcsulte;1 in a drastt ", intrcaat. of the temperature at which the polymer started to decompose. It was also shown that a threshold Bi fluence is necessary in order to optimize. the stabilization effect. Finally, it was demonstrated that not only the radiation damage but also chemical effects are important to raise the decomposition temperature of the polymer [7] . More iecently, we have also shown [8? that Ag implantations do not prod,ice any significant improven-,wit on the thermal stability of the AZ1350, while Sn implantation with .A = 3 1014 at./cm= seems to sligh,iy increase the temperature at which the photoresist starts to decompose, and a more significant reduction in the material loss is obtained when the implantation fluence of Sri was A = 5 x 10 14 at./CMZ. We have undertaker. the present experiment in order to further investigate the influence of the chemical and radiation damage effects or. the decomposition temperature of the polymer . 0168-583X/93/$06.110

In the present work we implanted St, under identical conditions as in previous work with Sri and Ag . These elements have similar mass :~ but quite different chemical and physical propertie, . The Rutherford backscattering technique (RBS) w ;, s used to observe the stoichiometric changes as consequence of the ,Stcrmal treatments of the photoresist . 2 . Experimental procedure and data analysis Clear, silicon wafers were spin coated with a 1 .0 win film of the AZ1350 photofesist and then baked for 1 h at 170°C. Small pieces of the wafers were subsequently implanted with 50 keV Sb at fluences of 3 and 5 x 10 14 at ./cm2 . Tile implantations were done using the 400 kV ion implanter at the Institute of Physics, Porto Alegre . The beam current density was G 2(1 nA/cm= in order to avoid excessive heating of the samples . Depth piufttes were obtameu by RbS analysts using 760 keV a particles from the same implanter. The backscattered a particles were detected by a Si(Li) surface barrier detector piaccd at 160° with respect to the beam direction. The electronic resolution of the detection system was 14 keV, The beam spot on the sample was moved whenever the a dose reached 2 x 10 12 a/cm 2 . This procedure was followed to avoid compaction e'l'ects and formation of carbon rich regions as consequence of locally large a irradiation fluences. Under these circumstances no significant changes is the O and C contents,werc detected as a consequence of the a irradiation . The energy to depth transformation was done using the a stopping poweo; as reported in ref. [9] . The analysis of the RBS spectra were performed using the simulation RUMP code program [10]. Further details

v i'iy i - Elsevier Science Publishers B.V . All rights reserved

R. L. Ma:tc :et al / Thertaal hchattor of' Sb tit photo-t fthrt

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Fig. 1 . RBS speLtra of the unimplanted AZ1350 polymer film.

Fig . 2 . RBS spectra of the Sb implanted sample .

of the, experimental setup and data. treatmen . can he found in rel. [4]. The sainpl- :.ere isochronally at ncaled at 15(1, 2011, 25(1, 300 and 350°C, always 20 min in a vacuum better than 10 ' Torr.

substrate which appears :n the RRS spectrum indicates that the film has become thinn :r (the observable th .zkncss of the film at 350'C is =15000 A) as a --on,eaucncc of the loss of material . In our previous work, we had shown that Ag irmplantation with ~6 = 3 x 10 14 and 5 x 10 14 at ./cm 2 and the Sri implantation performed with 0= 3 x 10 14 at ./c,2 do not alter significantly the thermal behavior of the implanted AZ1350 samples . The situation changes when the AZ1350 film is Sri implanted with tb = 5 x 10 14 at ./cm =. Annealings up to 256'C do not produce any major change in the photoresim composition . At 300'C there is 15% oxygen a,Ed 5`7 carbon Final!, at 350'C et. ., .d° rL ° !csscs are 30 and 15% respectively. .The C and O ms ,es as function of the tcmperaturt. for the nonimplanted and the Sri and Ag implanted AZ1350 samples are summp.rized in table 1 . The Sb implantati- performed in this work, show a similar trend as those observed with Sri, but a still lower carbon and oxygen loss is treasured. At 350°C the C (30°,.) and C (15îb) !usses for the 5 X 10 14 Sn/cm : sample arc reduced to O (24%) and C (13%) rcspcctivcty, foi Sb itm,4.nted at santz °". ::-n:: (fig. 2) .

3 . Results 'f nc analysis of the RBS spectra of the unimplantcd AZ1350 films perie)rmed with the RUMP simulation program show that up to 2110'C there is no significant c' -inge in the chemical composition of the polymer fisat . Hcrvcver at higher temperatures there is a drastic change as illustiated by fib. 1 vb :ch shows the RBS spectra corre~rondi,ng to the nowtnncalcd and anneale.1 at 300 and 350'C AZ1350 ..aniples . At 2511°C the data show, in the sibnil .cant rcgior= of 1.UMP simulation (from the surface up to -2400 Â), a con sidcrable and uniform boss of oxygen around 2(1% . The corrcsp tnding C lose is of the order of 10% . With increasing tcmperatu , e there is a large material loss and imady at 350°C three main features can be observed : (i) the oxygt,n loss i" i rovnd 50L, 60 the C content is reduced by 20% and (iii) the Si edge of the

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Table I Carbon (C) and oxygen (O) rciative losses (in e/) as it ftenctio,E of the annealing temperature . Results for Sn and Ag implanted ions and 0uences Temperatut~ oci

Nonimplanted

l

2(H) 2511 3()0 350

c 7 15 20

_o

5 20 35 47

Implanted

Sn [x 1() 14 at /cm 2 l

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ô 10 30 12

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Ag [ x 10 14 at ./cm 2 l =3 di= 5 c ô c

_ 15 30

_ 12 17

17

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45

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25

22 e0 52

Va. NOVEL TECHNIQUES (a)

R. L. Maltez et ai. / Thermal belmcior ofS'b in plrotoresist film

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Table 2 Carbon li') and oxygen (O) relative tosses (in %) as a function of the annealing temperature for Sb simples Temperature [°C1

Sb

5 X 10 14 at./cmZ 0=3x 101° at ./C,2 C O C O 7 18 4 5 20 10 10 9 32 '3 14

200 250 300 350

The total C and O losses as function of the temp,.ralure for the Sb implanted sample arc summarized in table 2. For t.omparison in fig. 3 we show the oxygen Posses corresponding to the nonimplanted, Sri and Sb implanted, as described in tables 1 and 2, as well as the results of the Bi implantation taken from [7]. From this figure we can see that the most effective reduction in the material loss appears after Bi implaination . i~or chemically similar elements (Sh. Bi) the stronger protection mechanism is attributed with higher damage caused by the heavier Bi ions . 4. Discussion and conclusions The present and our previous results on Sri and Ag shay. some special futures. First, results of the Ag implantations do not show any significant improvement on the thermal stability of the AZ1350 photoresist. The amount of oxygen and carbon lost from Ag implanted samples is similar if not a little bit larger than in the casc of the nonimplante .l ones. Remarkable is that the Sri implanted sample with 0 = 3 x 10 1 ° at./cmZ seems 60 __-50 V)40 U) O

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250 300 850 400 TEMP ( 'C) Fig . 3 . Oxygen loss as a function of temperature for Sb, Sri and Bi implanted samples.

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to exhibit a slightly inL-)rovcd thermal stability. However a more effective r ~duction in the material loss is only obtained when the mplantation fluencc of Sri was 0=5x 10 1 ° at ./cm =. Finally, concerning Sb implantation, an even higher reduction in the material loss is observed. In order to gain more insight, we 1 epresent in fig . 4 the oxygen loss as a function of the depth for the Sb implanted sample with 0 = 3 x 10 1 ' at ./cm= : as implanted, after annealing at 200, 300 and 350°C . The figure shows several interestir ;> c .;tires . First there is a considcrabl loss of oxygen as a consequence of the implantation process . This loss occurs from the surface i p to = 1000 74. It is interesting to remark that the oxyger, 1nss profile does not resemble (neither in shepe, nor in depth) the damage profile as predicted by Ziegler, Biersack and Littmark (see ref. [11]). Up to Zù0°C there is an at:ditional loss, but we do not observe any change in the oxygen loss profile . At the temperature of 300°C the analysis of the RBS spectrum shows

r V1 O i Z W CD Y X

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Fig. 4 . Oxygen loss as a function of the depth for the Sb inif.',anted. ~b = 1x 10 1° at . /cm Z AZ 1350 m+mple.

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DIPTH ( A ) Fig. 5 . Oxygen loss as :+ function of the depth for the Sb implanted (0 = 5 x 101° at./cm Z ) AZI350 sample.

R.L. hialtez

.t et al. / Thenru:f beltn~ ior of Sb in photo-

that thtr : is a nonuniform oxygen loss which uccui~ . from the surface up to - 1500 A. Finally at 350°C an additional lo.,s is observed . but the maximum depth, basically remains unchanged . With increasing temlccraturcs not :-nly them. i s an additional oxygen loss, but this loss seems not to be confined to a fixed death . This kind of hchavior is also observed for Sn and Ag implanted samples . The oxygen loss profile of the sample with Lhe flucnce (,b = 5 x 10 14 Sb/cm=) in fig, 5 shows an additi,nal feature . Up to temperatures of 3P0°C a well d-fined peak in the t ,.,ygcn- loss profile is observed ar, , und the depth of 300 A. This behavior is also vetificd with a flucnce of 3 x 101,1 Sb/cm =, with a slig.~t dislocation of the maxiiit.m toward deeper regions as the temperature of the polymer was raised. It is imp, , rtar, to note that this profile was also observed for t' , c cases of Sri and Ag implantations, but it is not d'spl . vt d in. the fig. 4 of our previous paper [8]. These pun , of oxygen loss scale with the range of the implanted ms. iloh:,r et al . [7] have suggested that in addition t;t the iaiiation damage, chemical effects (due to bonding of the implanted ions with the molecules of the photoresist) should play an important role in the thermal behavior of implanted photoresists. Our results confirm this hypothesis. The Ag and Sn implantations produce similar damage, however only Sn scents to be cffectlve as inhibitor of the thermal degradation of the photoresist. Due to similar ion masses, the datragc produced by Sb implantation is very similar to Sri . Thus, the more effective Sb protection against thermal decomposition measured in this work :. ._e fig . 3) sc.^.ms to be associated with chemical effects A further comparison of the present r- c'. ;,r-vious published results allows us to draw other conclusions. First, there is a threshold fluence O,h needed to inhibit the thermal decor :,)osition of the photoresist . Tlrs fluence depends on both, the type of photoresist and on ihc implanted ion species. For AZ111 photoresist thn Bi threshold flucnce was reportt,d to be 0th = 1014 Bi/cm 2 [7) . This number changes to 0 = 3x '.0 14 Bi/cm z for the AZ1350 polymer. For Sri the ~, h is 5 x 10 14 Sr,/cm=, while in the p!escnt case we found that for Sb, the 0  , is also 5 x 10 14 Sh/cm= .

fil.

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Besides the above conclusions. a °omparison of the present and previous data show that tai is more effective in the inhibition mechanism . We showed on average Bi is - 30 an(: - 20%n more effective in protecting the polymer film relative to Sn and Sb . respectively . This is another clear indication that chemical effects play an important role in the decomposition pzocess of implanted photoresist films . In summary, the results of the present experiment .;how that chemical effects play a crucial role it raising the decomposition temperature .1f implanted photci,:sists. On one side, we have shown that Sb implanted at a threshold flucnce is able to inhibit the material io: .s which occurs as a c,,nsequcncc of thermal treatment &r polymer. On the other band, we assume, ~n the case of expectation A similar chemical effects (b)th Sb and Bi arc VA elements of the periodic table) different damage levels can explain differences in d°gr,Aation protection after implantation .

References [11 T. Venkatesan, Nuci. Instr . and Meth . B7/8 (1985) 461 . [2) W !, Brown. Radiat . Eff . 99 (1987) 281 . [3) 7 . Venkatesan, i. . Cal-s-, B .S Fitnan and Cl Foti, in: Ion Implantation m Insulators, ed . P. Mazzoldi kNorthHt,lland, Amsterdam, 1987) chap. 8. 141 R n Guimarâes, L. Amaral, M . Behar, D. Fiotk and F.C. Zawislak, J . Water . Res . 3 (1988) 1422 . [51 R.B . Guimarâes, L. Amaral, R.P . Livi, J.P. de Souza, M . Behar and F .C. Zawislak, Nud . Instr. and Mah . B32 (1988) 419. [61 Y. Okayama, T . Hashimoto and T Yoguchi, J . Electrochem . Soc. 125 (1978) 1 293 . [7] M . Behar, L. Amaral, F.C . Zawislak, R .B . Guimarâes and D. Fink Nucl . Instr. and Meth. B46 (1090) 350. 181 R .L . Maltez, L. Amaral, 'A . Behar, R .B . Guim -tes, J MR. dog Santos and F.C. Zawisla:., Nucl . Instr . and Meth. B65 (1992) 423. [91 J .F. Ziegler, J.P . Bi :rsack and U . Littmark, in: The Stopping and Range of Icns n Solids, ed . J.F. Ziegler (Pergamon, New York, 1985) . (101 R .L. Doolittle, Nucl . Instr. and Meth . B15 (1986) 227 . [111 R .B. Guimarâes, L. Amaral, M . Behar, F .C . Zawislak and D . Fink, J . Appl. Phys. 63 ;1988) 2502.

Va. NOVEL TECHNIQUES (a)