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Heavy ion (Xe and I) irradiation effects on photoresist films
Nuclear Instruments and Methods in Physics Research B 191 (2002) 733–738 www.elsevier.com/locate/nimb
Heavy ion (Xe and I) irradiation effects on photoresist films Irene T.S. Garcia a, F.C. Zawislak b
b,* ,
Naira M. Balzaretti b, M. Nastasi
c
a Centro Universit ario La Salle, 92010-000, Canoas, RS, Brazil Instituto de Fısica, UFRGS, C.P.15051, 91501-970, Porto Alegre, Brazil c Los Alamos National Laboratory, Los Alamos, NM, 87545, USA
Abstract This contribution presents a study of heavy ion irradiation induced chemical, structural and tribological modifications in photoresist films. Novolak–diazoquinone films 400 and 800 nm thick have been irradiated with 800 keV Xeþþ and 4 MeV Iþþ ions respectively in a fluence range of 1013 to 6 1015 ions cm2 . At these energies, both ions have the 1 , but the ratio Se =Sn is ffi1/3 for Xeþþ and ffi3 for Iþþ . A same nuclear Sn plus electronic Se stopping power, ffi200 eV A detailed investigation of the chemical composition and structural modification of the films due to the irradiation was performed using the ERDA, Raman and nanoindentation techniques. The measured hardness H ¼ 13 GPa and Young’s modulus E ¼ 140 GPa for both films and the respective Raman spectra show that, at the largest fluences, both films are transformed into amorphous carbon layers. However, in the region of intermediate fluences the effects of irradiation on H and E are governed by a competition between the nuclear and the electronic stopping powers. The present data are compared with our previous measurements of the same film irradiated with Heþ ions, when the nature of the transferred energy density is mainly of electronic origin. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Ion irradiation; Photoresist; Hardness; Carbonization
1. Introduction The thermal stability and the associated structural changes of AZ 1350 J photoresist films irradiated with He ions have been recently investigated by us [1,2]. Our results show that irradiation with 380 keV He ions transferring an average 3 (fluences of electronic energy density ffi2 eV A the order of 1015 cm2 ) to the whole volume of the photoresist film, produces an effective crosslinking of the polymeric chains with improvement of the
*
Corresponding author. Tel.: +55-51-331-66427; fax: +5551-331-66510. E-mail address: [email protected] (F.C. Zawislak).
thermal stability and increase of hardness (H) and Young’s modulus (E). More recently [3,4], we have also shown that increasing the He fluences to 1016 cm2 (corresponding to a transferred electronic 3 ) produces an addienergy density ffi22 eV A tional increase of H and E but the Raman spectra clearly show that at this fluence the photoresist film is transformed into an amorphous carbon layer. Many works in the literature [5,6] report improvements of mechanical properties in polymers after irradiations with heavy ions and at large fluences, attributing the improvements to the crosslinking mechanism of polymeric chains caused by the irradiation. In the present contribution, we report a detailed study of hardness and Young’s modulus in the AZ-1350J film as function
0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 2 ) 0 0 6 4 3 - 2
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of the fluence for irradiation with heavy ions (Xe and I). Our results show that the large increase of both, H and E is due to the ion-induced carbonization of the photoresist films and depends on the amounts of electronic (Se ) and nuclear (Sn ) energy deposited by the ion. These results, obtained via Raman, ERDA and nanoindentation techniques, are compared to our previous results using light ion (380 keV Heþ ) irradiated films, when the deposited energy is predominantly electronic.
2. Experimental part The AZ 1350 JTM photoresist, supplied by Shipley Europe Ltd., is composed of 70% in weight of o-novolak and 30% in weight of diazonaphtoquinone. The films were obtained by spin coating on clean silicon 20 X cm wafers and subsequently heated at 95 °C for 25 min to eliminate the solvent. The atomic composition of the pristine sample is C46:13 H44:86 O7:47 N1:06 S0:44 with a density of 1.3 g cm3 . The irradiation was carried out in the 500 kV (800 keV Xeþþ ) and 3 MV Tandetron (4 MeV Iþþ ions) HVEE accelerators of the Ion Implantation Laboratory – Instituto de Fısica – UFRGS. The irradiation beam current densities were lower than 50 nA cm2 to avoid heating of the material. Films 400 and 800 nm thick were irradiated with 800 keV Xeþþ and 4 MeV Iþþ ions, respectively. At these thicknesses the beam passes over the film and there is no significant changes in the total energy deposition through the depth of the photoresist film. For the irradiation with 800 keV Xeþþ the average nuclear stopping power pre1 ) and dominates (hSe i ¼ 57 and hSn i ¼ 140 eV A for 4 MeV Iþþ ions the average electronic stopping 1 and hSn i ¼ 66 power prevails (hSe i ¼ 138 eV A 1 ) but the total stopping power (hSt i ¼ eV A 1 ) is approximately the hSe i þ hSn i ffi 200 eV A same in both cases, through all the film thickness. The stopping powers of the ions and the projected ranges were calculated by using the TRIM code [7]. The micro-Raman spectra were obtained using a HeNe laser of 10 mW for excitation with k ¼ 632:8 nm. The microbeam of about 2 lm was moved rapidly in a random pattern over the
samples to avoid local heating as well as photodamage of the film by the laser light. The scattered radiation was collected in a region between 500 and 2000 cm1 . The obtained results were normalized by the acquisition time. The hydrogen content was determined by elastic recoil analysis (ERDA) using He ions. An 8-lm polymeric film is placed in front of the Si detector to prevent the forward scattering of the He ions. The hardness and the Young’s modulus of the films were obtained by using the technique described by Oliver and Pharr [8] through the analysis of loading–unloading curves in a nanoindenter machine at the Los Alamos National Laboratories. The loading–unloading curves were measured by varying the load until a predefined value of penetration depth was attained. The maximum depth of penetration reached about 35% of the film thickness.
3. Results and discussion The chemical changes of the irradiated photoresist films are investigated via micro-Raman spectroscopy. The Raman spectra are shown in Figs. 1 and 2, for Xe and I irradiated photoresist films respectively. The pristine as well as the low fluence irradiated films exhibit strong fluorescence background. The fluorescence is due to the conjugated bonds present in the novolak–diazonaphquinone system. The increase of the fluence produces a reduction in the fluorescence in both cases and the spectra develop two wide bands in the region around 1500 cm1 , characteristics of amorphous carbon. The ERDA results, displayed in Fig. 3 for both irradiations, show the decrease of hydrogen with the grow of the irradiation fluences. At the highest fluences, the hydrogen contents, in both irradiations, attains the same values (around 7 at.%). ERDA spectra clearly show the thickness decrease of the films as function of fluence, due to the loss of hydrogen and mainly loss of oxygen [3] or small molecular groups (hydroxyl and methyl groups) promoting the formation of C–C bonds. In Fig. 4, we show H and E values for the pristine and irradiated films as function of fluence.
I.T.S. Garcia et al. / Nucl. Instr. and Meth. in Phys. Res. B 191 (2002) 733–738
735
Fig. 1. Micro-Raman spectra of AZ 1350 J films irradiated with 800 keV Xeþþ .
Both films show a relatively abrupt raise of H and E with the fluence but for Xeþþ irradiated photoresist, where the nuclear stopping dominates, the increase starts at lower fluence (ffi2 1014 Xeþþ cm2 ) than for Iþþ irradiated samples (ffi6 1014 Iþþ cm2 ) when the electronic stopping power prevails. The maximum attained values of hardness and Young’s modulus for both irradiations are, 13 and 140 GPa respectively at the highest fluences. Independently of the ion and nature of the deposited energy (electronic or nuclear), at high fluences and high deposited energy density, both irradiated systems present very similar structures. The structures are characterized by high and analogous values of hardness and Young’s modulus, low hydrogen concentration, and very alike Raman spectra. This behaviour of the irradiated photoresist can be compared with experiments where C60 , a-C and a-C:H films are irradiated in the same regime of total deposited energy density, qt ¼ / (hSe i þ hSn i) [9]. The authors of reference [9] found that after irradiation, the three above carbonaceous systems also end up with the same H ffi 14 GPa and E ¼ 140 GPa and hydrogen
Fig. 2. Micro-Raman spectra of AZ 1350 J films irradiated with 4 MeV Iþþ .
concentration of 5%. Otherwise, the photoresist films irradiated with fluences lower than 6 1013 Xeþþ cm2 and 2 1014 Iþþ cm2 can be considered soft polymeric materials maintaining a structure similar to that of the pristine. The hydrogen contents, hardness, and the Young’s modulus are shown in Fig. 5 as function of the qt for Xeþþ , Iþþ and Heþ irradiated AZ 1350 J films. The data for 380 keV Heþ ions are from references [2,3]. The data presented in Fig. 5 exhibit very similar trends for the three parameters H, E and hydrogen concentration, as function of total deposited energy density. In all the cases there are two tendencies shown by the curves drawn to guide the eyes. The dashed curves represent the data of the films irradiated by 4 MeV Iþþ and 380 keV Heþ ions. The full lines show the data of Xe irradiated films. The main difference between both is that in the case of I and He irradiation the deposited energy is mainly of electronic
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Fig. 3. Hydrogen contents as function of depth for irradiated samples with (a) 4 MeV Iþþ and (b) 800 keV Xeþþ ions.
origin. On the contrary for Xe the deposited energy is mainly nuclear. These results can have the following interpretation. When Sn is larger (800 keV Xeþþ ions), the nuclear collisions of the ions with the film atoms are responsible for atomic displacements, chain scissions, loss of small molecules and consequently for the rapid formation of carbon–carbon bonds resulting in earlier formation of amorphous carbon. On the other hand, when the electronic stopping power dominates the irradiation process, like for He and Iþþ ions, than at the beginning, up to 3 , the a deposited energy density of ffi2–3 eV A dominant mechanism is the ionization which produces a crosslinked three-dimensional network
with improved tribological properties and better thermal stability (see [1]). Increasing the fluence, the nuclear deposited energy density also increases (specially in the case of I) and we observe the carbonization of the photoresist, with more loss of hydrogen and oxygen and finally reaching the amorphous carbon form, as shown by the Raman spectra and by the high values of H and E. The measured hardness of three different polymers (poly(isoquinone), poly(2-vinyl-piridine) and poly(acrilonitrile) irradiated with heavy (Au) and light (He) ions by Pivin [10] shows a similar behaviour as the one observed here, and probably also can be explained in terms of the nuclear and electronic stopping powers.
I.T.S. Garcia et al. / Nucl. Instr. and Meth. in Phys. Res. B 191 (2002) 733–738
737
Fig. 4. (a) Hardness for the pristine, Xe, and I irradiated AZ 1350 J films as function of fluence and (b) Young’s modulus for the same films. The lines are to guide the eyes.
Fig. 5. (a) H contents; (b) hardness; (c) Young’s modulus, as function of qt for AZ1350 J irradiated films with 380 keV Heþ , 800 keV Xeþþ and 4 MeV Iþþ ions. The lines are to guide the eyes.
4. Conclusions
their structure and mechanical properties are due to crosslinking produced by the ionization process. The three-dimensional network formed via crosslinking inhibits the chain motions, improving the tribological properties. However at high fluences, when the transferred total energy density is larger 3 , Xe or I ions produce the same than 100 eV A effect on the tribological parameters, giving H ffi 13 GPa and E ffi 140 GPa for both films. At these fluences the photoresist films show a loss of 85% of the hydrogen and 90% of oxygen [3], the film thicknesses are 40% smaller, and the Raman spectra confirm the transformation of the photoresists into amorphous carbon layers.
The mechanical properties, hardness and Young’s modulus, of ion irradiated photoresist films have been investigated in terms of the electronic and nuclear slowing down processes. The films have been irradiated with 800 keV Xe ions with Se =Sn ffi 1=3 and 4 MeV Iþþ with Se =Sn ffi 3. Our results show that both H and E increase more rapidly with the fluence (and with the average total deposited energy density) when irradiated with Xe ions. This faster increase is due to the larger Sn of Xe which is more efficient to transform the photoresist into amorphous carbon via nuclear displacements of atoms and radicals, scission of bonds and consequent loss of volatile molecular fragments. In the irradiation with 4 MeV Iþþ the Se is larger and at lower and medium fluences the mechanism of ionization dominates the transformation of the photoresist, and the modifications of
References [1] I.T.S. Garcia, F.C. Zawislak, D. Samios, Nucl. Instr. and Meth. Phys. Res. B 148 (1999) 1111.
738
I.T.S. Garcia et al. / Nucl. Instr. and Meth. in Phys. Res. B 191 (2002) 733–738
[2] I.T.S. Garcia, D. Samios, F.C. Zawislak, J.A.H. da Jornada, C.E. Foerster, F.C. Serbena, C.M. Lepienski, Mat. Res. Proc. Symp. 585 (2000) 289. [3] I.T.S. Garcia, Irradiacß~ao e implantacß~ao i^ onica em filmes fotossensıveis compostos de poli(fenolformaldeıdo) e diazonaftoquinona, PGCIMAT-UFRGS, Ph.D. thesis, 2001. [4] C.M. Lipienski, I.T.S. Garcia, C.E. Foerster, F.C. Serbena, F.C. Zawislak, Nucl. Instr. and Meth. Phys. Res. B 175– 177 (2001) 668.
[5] E.H. Lee, G.R. Rao, M.B. Lewis, L.K. Mansur, J. Mater. Res. 9 (1994) 1043. [6] L. Guzman, R. Celva, A. Miotello, E. Voltolini, F. Ferrari, M. Sdamis, Surf. Coat. Technol. 103/104 (1988) 37. [7] J.F. Ziegler, J.F. Biersack, U. Littmark, in: The Stopping and Range of Ions in Solids, Vol. 1, Pergamon, New York, 1985. [8] W.C. Oliver, G.M. Parr, J. Mat. Res. 7 (1992) 1564. [9] D.L. Baptista, F.C. Zawislak, in press. [10] J.C. Pivin, Thin Solid Films 263 (1995) 185.
Heavy ion (Xe and I) irradiation effects on photoresist films Irene T.S. Garcia a, F.C. Zawislak b
b,* ,
Naira M. Balzaretti b, M. Nastasi
c
a Centro Universit ario La Salle, 92010-000, Canoas, RS, Brazil Instituto de Fısica, UFRGS, C.P.15051, 91501-970, Porto Alegre, Brazil c Los Alamos National Laboratory, Los Alamos, NM, 87545, USA
Abstract This contribution presents a study of heavy ion irradiation induced chemical, structural and tribological modifications in photoresist films. Novolak–diazoquinone films 400 and 800 nm thick have been irradiated with 800 keV Xeþþ and 4 MeV Iþþ ions respectively in a fluence range of 1013 to 6 1015 ions cm2 . At these energies, both ions have the 1 , but the ratio Se =Sn is ffi1/3 for Xeþþ and ffi3 for Iþþ . A same nuclear Sn plus electronic Se stopping power, ffi200 eV A detailed investigation of the chemical composition and structural modification of the films due to the irradiation was performed using the ERDA, Raman and nanoindentation techniques. The measured hardness H ¼ 13 GPa and Young’s modulus E ¼ 140 GPa for both films and the respective Raman spectra show that, at the largest fluences, both films are transformed into amorphous carbon layers. However, in the region of intermediate fluences the effects of irradiation on H and E are governed by a competition between the nuclear and the electronic stopping powers. The present data are compared with our previous measurements of the same film irradiated with Heþ ions, when the nature of the transferred energy density is mainly of electronic origin. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Ion irradiation; Photoresist; Hardness; Carbonization
1. Introduction The thermal stability and the associated structural changes of AZ 1350 J photoresist films irradiated with He ions have been recently investigated by us [1,2]. Our results show that irradiation with 380 keV He ions transferring an average 3 (fluences of electronic energy density ffi2 eV A the order of 1015 cm2 ) to the whole volume of the photoresist film, produces an effective crosslinking of the polymeric chains with improvement of the
*
Corresponding author. Tel.: +55-51-331-66427; fax: +5551-331-66510. E-mail address: [email protected] (F.C. Zawislak).
thermal stability and increase of hardness (H) and Young’s modulus (E). More recently [3,4], we have also shown that increasing the He fluences to 1016 cm2 (corresponding to a transferred electronic 3 ) produces an addienergy density ffi22 eV A tional increase of H and E but the Raman spectra clearly show that at this fluence the photoresist film is transformed into an amorphous carbon layer. Many works in the literature [5,6] report improvements of mechanical properties in polymers after irradiations with heavy ions and at large fluences, attributing the improvements to the crosslinking mechanism of polymeric chains caused by the irradiation. In the present contribution, we report a detailed study of hardness and Young’s modulus in the AZ-1350J film as function
0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 2 ) 0 0 6 4 3 - 2
734
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of the fluence for irradiation with heavy ions (Xe and I). Our results show that the large increase of both, H and E is due to the ion-induced carbonization of the photoresist films and depends on the amounts of electronic (Se ) and nuclear (Sn ) energy deposited by the ion. These results, obtained via Raman, ERDA and nanoindentation techniques, are compared to our previous results using light ion (380 keV Heþ ) irradiated films, when the deposited energy is predominantly electronic.
2. Experimental part The AZ 1350 JTM photoresist, supplied by Shipley Europe Ltd., is composed of 70% in weight of o-novolak and 30% in weight of diazonaphtoquinone. The films were obtained by spin coating on clean silicon 20 X cm wafers and subsequently heated at 95 °C for 25 min to eliminate the solvent. The atomic composition of the pristine sample is C46:13 H44:86 O7:47 N1:06 S0:44 with a density of 1.3 g cm3 . The irradiation was carried out in the 500 kV (800 keV Xeþþ ) and 3 MV Tandetron (4 MeV Iþþ ions) HVEE accelerators of the Ion Implantation Laboratory – Instituto de Fısica – UFRGS. The irradiation beam current densities were lower than 50 nA cm2 to avoid heating of the material. Films 400 and 800 nm thick were irradiated with 800 keV Xeþþ and 4 MeV Iþþ ions, respectively. At these thicknesses the beam passes over the film and there is no significant changes in the total energy deposition through the depth of the photoresist film. For the irradiation with 800 keV Xeþþ the average nuclear stopping power pre1 ) and dominates (hSe i ¼ 57 and hSn i ¼ 140 eV A for 4 MeV Iþþ ions the average electronic stopping 1 and hSn i ¼ 66 power prevails (hSe i ¼ 138 eV A 1 ) but the total stopping power (hSt i ¼ eV A 1 ) is approximately the hSe i þ hSn i ffi 200 eV A same in both cases, through all the film thickness. The stopping powers of the ions and the projected ranges were calculated by using the TRIM code [7]. The micro-Raman spectra were obtained using a HeNe laser of 10 mW for excitation with k ¼ 632:8 nm. The microbeam of about 2 lm was moved rapidly in a random pattern over the
samples to avoid local heating as well as photodamage of the film by the laser light. The scattered radiation was collected in a region between 500 and 2000 cm1 . The obtained results were normalized by the acquisition time. The hydrogen content was determined by elastic recoil analysis (ERDA) using He ions. An 8-lm polymeric film is placed in front of the Si detector to prevent the forward scattering of the He ions. The hardness and the Young’s modulus of the films were obtained by using the technique described by Oliver and Pharr [8] through the analysis of loading–unloading curves in a nanoindenter machine at the Los Alamos National Laboratories. The loading–unloading curves were measured by varying the load until a predefined value of penetration depth was attained. The maximum depth of penetration reached about 35% of the film thickness.
3. Results and discussion The chemical changes of the irradiated photoresist films are investigated via micro-Raman spectroscopy. The Raman spectra are shown in Figs. 1 and 2, for Xe and I irradiated photoresist films respectively. The pristine as well as the low fluence irradiated films exhibit strong fluorescence background. The fluorescence is due to the conjugated bonds present in the novolak–diazonaphquinone system. The increase of the fluence produces a reduction in the fluorescence in both cases and the spectra develop two wide bands in the region around 1500 cm1 , characteristics of amorphous carbon. The ERDA results, displayed in Fig. 3 for both irradiations, show the decrease of hydrogen with the grow of the irradiation fluences. At the highest fluences, the hydrogen contents, in both irradiations, attains the same values (around 7 at.%). ERDA spectra clearly show the thickness decrease of the films as function of fluence, due to the loss of hydrogen and mainly loss of oxygen [3] or small molecular groups (hydroxyl and methyl groups) promoting the formation of C–C bonds. In Fig. 4, we show H and E values for the pristine and irradiated films as function of fluence.
I.T.S. Garcia et al. / Nucl. Instr. and Meth. in Phys. Res. B 191 (2002) 733–738
735
Fig. 1. Micro-Raman spectra of AZ 1350 J films irradiated with 800 keV Xeþþ .
Both films show a relatively abrupt raise of H and E with the fluence but for Xeþþ irradiated photoresist, where the nuclear stopping dominates, the increase starts at lower fluence (ffi2 1014 Xeþþ cm2 ) than for Iþþ irradiated samples (ffi6 1014 Iþþ cm2 ) when the electronic stopping power prevails. The maximum attained values of hardness and Young’s modulus for both irradiations are, 13 and 140 GPa respectively at the highest fluences. Independently of the ion and nature of the deposited energy (electronic or nuclear), at high fluences and high deposited energy density, both irradiated systems present very similar structures. The structures are characterized by high and analogous values of hardness and Young’s modulus, low hydrogen concentration, and very alike Raman spectra. This behaviour of the irradiated photoresist can be compared with experiments where C60 , a-C and a-C:H films are irradiated in the same regime of total deposited energy density, qt ¼ / (hSe i þ hSn i) [9]. The authors of reference [9] found that after irradiation, the three above carbonaceous systems also end up with the same H ffi 14 GPa and E ¼ 140 GPa and hydrogen
Fig. 2. Micro-Raman spectra of AZ 1350 J films irradiated with 4 MeV Iþþ .
concentration of 5%. Otherwise, the photoresist films irradiated with fluences lower than 6 1013 Xeþþ cm2 and 2 1014 Iþþ cm2 can be considered soft polymeric materials maintaining a structure similar to that of the pristine. The hydrogen contents, hardness, and the Young’s modulus are shown in Fig. 5 as function of the qt for Xeþþ , Iþþ and Heþ irradiated AZ 1350 J films. The data for 380 keV Heþ ions are from references [2,3]. The data presented in Fig. 5 exhibit very similar trends for the three parameters H, E and hydrogen concentration, as function of total deposited energy density. In all the cases there are two tendencies shown by the curves drawn to guide the eyes. The dashed curves represent the data of the films irradiated by 4 MeV Iþþ and 380 keV Heþ ions. The full lines show the data of Xe irradiated films. The main difference between both is that in the case of I and He irradiation the deposited energy is mainly of electronic
736
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Fig. 3. Hydrogen contents as function of depth for irradiated samples with (a) 4 MeV Iþþ and (b) 800 keV Xeþþ ions.
origin. On the contrary for Xe the deposited energy is mainly nuclear. These results can have the following interpretation. When Sn is larger (800 keV Xeþþ ions), the nuclear collisions of the ions with the film atoms are responsible for atomic displacements, chain scissions, loss of small molecules and consequently for the rapid formation of carbon–carbon bonds resulting in earlier formation of amorphous carbon. On the other hand, when the electronic stopping power dominates the irradiation process, like for He and Iþþ ions, than at the beginning, up to 3 , the a deposited energy density of ffi2–3 eV A dominant mechanism is the ionization which produces a crosslinked three-dimensional network
with improved tribological properties and better thermal stability (see [1]). Increasing the fluence, the nuclear deposited energy density also increases (specially in the case of I) and we observe the carbonization of the photoresist, with more loss of hydrogen and oxygen and finally reaching the amorphous carbon form, as shown by the Raman spectra and by the high values of H and E. The measured hardness of three different polymers (poly(isoquinone), poly(2-vinyl-piridine) and poly(acrilonitrile) irradiated with heavy (Au) and light (He) ions by Pivin [10] shows a similar behaviour as the one observed here, and probably also can be explained in terms of the nuclear and electronic stopping powers.
I.T.S. Garcia et al. / Nucl. Instr. and Meth. in Phys. Res. B 191 (2002) 733–738
737
Fig. 4. (a) Hardness for the pristine, Xe, and I irradiated AZ 1350 J films as function of fluence and (b) Young’s modulus for the same films. The lines are to guide the eyes.
Fig. 5. (a) H contents; (b) hardness; (c) Young’s modulus, as function of qt for AZ1350 J irradiated films with 380 keV Heþ , 800 keV Xeþþ and 4 MeV Iþþ ions. The lines are to guide the eyes.
4. Conclusions
their structure and mechanical properties are due to crosslinking produced by the ionization process. The three-dimensional network formed via crosslinking inhibits the chain motions, improving the tribological properties. However at high fluences, when the transferred total energy density is larger 3 , Xe or I ions produce the same than 100 eV A effect on the tribological parameters, giving H ffi 13 GPa and E ffi 140 GPa for both films. At these fluences the photoresist films show a loss of 85% of the hydrogen and 90% of oxygen [3], the film thicknesses are 40% smaller, and the Raman spectra confirm the transformation of the photoresists into amorphous carbon layers.
The mechanical properties, hardness and Young’s modulus, of ion irradiated photoresist films have been investigated in terms of the electronic and nuclear slowing down processes. The films have been irradiated with 800 keV Xe ions with Se =Sn ffi 1=3 and 4 MeV Iþþ with Se =Sn ffi 3. Our results show that both H and E increase more rapidly with the fluence (and with the average total deposited energy density) when irradiated with Xe ions. This faster increase is due to the larger Sn of Xe which is more efficient to transform the photoresist into amorphous carbon via nuclear displacements of atoms and radicals, scission of bonds and consequent loss of volatile molecular fragments. In the irradiation with 4 MeV Iþþ the Se is larger and at lower and medium fluences the mechanism of ionization dominates the transformation of the photoresist, and the modifications of
References [1] I.T.S. Garcia, F.C. Zawislak, D. Samios, Nucl. Instr. and Meth. Phys. Res. B 148 (1999) 1111.
738
I.T.S. Garcia et al. / Nucl. Instr. and Meth. in Phys. Res. B 191 (2002) 733–738
[2] I.T.S. Garcia, D. Samios, F.C. Zawislak, J.A.H. da Jornada, C.E. Foerster, F.C. Serbena, C.M. Lepienski, Mat. Res. Proc. Symp. 585 (2000) 289. [3] I.T.S. Garcia, Irradiacß~ao e implantacß~ao i^ onica em filmes fotossensıveis compostos de poli(fenolformaldeıdo) e diazonaftoquinona, PGCIMAT-UFRGS, Ph.D. thesis, 2001. [4] C.M. Lipienski, I.T.S. Garcia, C.E. Foerster, F.C. Serbena, F.C. Zawislak, Nucl. Instr. and Meth. Phys. Res. B 175– 177 (2001) 668.
[5] E.H. Lee, G.R. Rao, M.B. Lewis, L.K. Mansur, J. Mater. Res. 9 (1994) 1043. [6] L. Guzman, R. Celva, A. Miotello, E. Voltolini, F. Ferrari, M. Sdamis, Surf. Coat. Technol. 103/104 (1988) 37. [7] J.F. Ziegler, J.F. Biersack, U. Littmark, in: The Stopping and Range of Ions in Solids, Vol. 1, Pergamon, New York, 1985. [8] W.C. Oliver, G.M. Parr, J. Mat. Res. 7 (1992) 1564. [9] D.L. Baptista, F.C. Zawislak, in press. [10] J.C. Pivin, Thin Solid Films 263 (1995) 185.