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Proximity gettering of transition metals in silicon by ion implantation
Abstract
We compare the gettering efficiency of C, 0 and He implantation %o Cz-grown silicon. After the getter implantation, with a projected range of 1.2 pm, we introduce a controlled amount of either Fe or Cu through low-energy implantation. Subsequently, we study the distribution of the impurities for various annealing conditions by means of secondary ion mass spectroscopy.In contrast to the C and 0 implantations which already show gettering behaviour at #relativelylow dose&the He implantation requires a dose in excessof 6 X 10” ions/cm* before observable getteriug occurs. When sufficiently high doses of He are implanted its gettering efficiency significantly exceeds that of comparable C and 0 implantations, i.e, implantations with the same projected ranges and doses,subjected to the same mealing treatment. The shape of the getter profile in the sample implanted with He is strongly influenced by the annealing treatment.
1. Introduction
2. ExperinmitaI
Transition metal ions, such as Fe and Cu, are notorious for their detrimental effect on the characteristicsof electronic devices fabricated in silicon. Therefore, great efforts have been made to minimize their concentration in virgin silicon wafers. Gettering of illese.impurities during processing, either on the back of the wafer or at getter centres in the bulk of the wafer, has ako become an established technique for lowering their concentration in active device areas[l]. With the ongoing miniaturization, however, thermal budgets, and hence also the diffusion distances of impurities, are continuously decreasing. At the same time, the demands imposed on silicon purity have become more stringent. This has initiated researchin proximity gettering, where the getter centres are situated in the direct vicinity of active device areas in order to increase their efficiency. The feasibility of introducing getter centres by means of ion implantation has been demonstrated in the literature. Both carbon and oxygen implantation [2], as weft as ion implantation damage alone [3-51 make collection of at least some of the transition-metal ions possible. Recently, the potential use of He bubbles as getter centres has been demonstrated for the case of Cu contaminated silicon 161. In the present paper, we will compare the gettering efficiency of He, C and 0 implantations for several dosesand annealing strategies,for Cu- and Fe-contaminatedsamples.
l
Correspondingauthor.
0168-583X/95/$09.50 ssDr0168-583x(94)00495.1
0 1995
ElsevierScienceB.V. kli rightsreserved
The getter experiments were performed using 4-in. Czochralski-grown (100) n-type Si wafers, The bulk of these wafers contains in the order of 20 ppm oxygen, which is used for internal gettering [l]. On the front side of the wafer, a phosphorus-doped epitaxial layer has been grown with a thickness of approximately 20 urn; and a resistivity of 11-14 St cm. The back of the wafer has been damaged by sand blasting by the manufacturer which can result in gettering of transition-metal ions as well. For the formation of getter centms in the proximity of the wafer surface we implanted the front sides of ‘the wafers with He, C or 0 ions. The energy of the ions was chosen such as to result in a projected range of approximately 1.2 Frn. This amounted to 240, 650 and 700 keV for He, C and 0 respectively [7]. During implantation, the wafers were kept close to room temperature by means of electrostatical cooling, i.e. a method in which the wafer is electrostatically attracted by a cooling body. The transition”metal c.mtaminants, Fe and Cu, were also introduced through ion implantation, which was done in a separate target chamber in order to prevent cross contamination. In this case an implantation energy of 30 keV was chosen, which resulted in projected ranges of 27.5 and 29.3 mn for Cm and Fe, respectively,[7]. The contaminants were implanted in either the front or the back side of the wafer. In, all the experiments presented here the most abundant; isotope of the contaminant was chosen. After implantation the wafers were divided into samples of approximately 1 cmZ, which were then subjectedto’
thermal cycle of the individual samples is given in the discussionbelow. For the analysis of the getter profiies we resorted ta secondary ion mass spectroscopy (SIMS). A CAMECA ims4f was used, which employed a focused 5.5keV 0: primary ion beam rasteredover a 250 X 2SO-pm2 area and detected positive secondary ions stemming exclusively from the 30-pm diameter centre of the sputtered crater. (In the case of oxygen depth profiling a 14.5-keV Cs+ beam was used and r60- detected.) The depth scale was calibrated by determining the total eroded depth with the aid of a micromechanicalstylus transducerand by assuming a constant erosion rate. This is estimated to be accurate to within 10%. The concentration scale of the profiles was calibrated by means of gauge implantations in silicon reference samples.This implies that a well-defined diluted standard was used for the instrumental-sensitivity determination. !n the case of,the gettered samples, however, the impurity is not distributed randomly throughout the silicon lattice. This could introduce systematicerrors in the determined getter efficiency due to matrix effects. No evidence for this was found for the Fe-containing samples, but for the &-contaminated samples problems did indeed occur. To eliminate matrix effects some of these samples were also investigated with RBS, for which we used samples which were chemicsily etched to the point at which the Si signal no longer obscured the Cu signal. The accuracy of the concentration scaleof the SIMS spectra is estimated to be 10 to 30%. Day-to-day vari:‘ior;:: were observed in the scaling of the SIMS spectra which clearly exceeded the 10% variations normally observed during a single day, probably due to variations in the instrumental settings. Therefore, comparisons were only made for spectra measured on the same day, thus assuringnear-identical instrumental settings. 3. Results and discussion Fig. 1 shows the Cu distribution obtained by means of SIMS for samples implanted with He, C or 0, up to a dose of 1 X 1016 ions/cm’, and contaminated with 1 X lOI4 &/cm’ in the front side of the sample. The sampleswere subjected to identical annealing treatments, viz. 25 min at 95O’C in dry N,. The heating rate of the furnace was fixed at 10°C per minute. After the annealing, the samples were cooled to room temperature, initially at a rate of 5°C per minute, but ultimately at a iower rate due to the intrinsic co,oling rate of the furnace. The Cu content of the peak in the depth profile of the He-implanted sample significantly exceedsthat of the other two, and the C-implanted sample gettered more Cu than the O-implanted sample. We have to keep in mind that the implanted getter centres had to compete with both the getter action of oxygen precipitates in the bulk of the wafer and that of the damage on the back
1x10” 0
400
800 depth
1200
f600
2000
(nm)
Fig. 1. Cu distributionas determinedwith the aid of SIMS for Si samplesimplantedwith Be (solidcurve),C (dashedcurve)or 0 (da&cd-dottedcurve) up to a dose of 1X lOI6 ions/cm2 and annealedfor 25 min at 950°Cin dry N2. The sampleshavebeen intentionallycontaminatedwith 1X 1Or4Cu/cm’. of the wafer. However, this holds for all three samples, which means that the conclusion that the getter efficiency of the He-implanted sample under the given annealing conditions exceedsthat of the other two is justified. When we look more closely at the SIMS profiles, we see that the O-implanted sample displays two Cu peaks RBS measurementsshow that the 0 implantation results in a buried amorphous layer. During the annealing the oxygen preferentially precipitates in the originally amorphous layer and displays a slightly enhanced oxygen concentration near the original amorphous-to-crystalline interfaces in the SIMS depth profile. Furthermore, the implantation damage is most resistantto annealing near these interfaces. Both effects can contribute to the double getter peak. In the case of the carbon implanted sample (which was heavily damaged after implantation but not up to the point at which it was amorphous), the Cu profile approximately duplicates the implanted C distribution. The most salient features of the He-implanted sample are a sharp central getter peak accompanied by two wing-like structures. The shape of the wing-like structures is strongly influenced by the annealing strategy. After implantation, the He is more or less randomly distributed throughout the implanted layer apart from the gaussian depth distribution. Annealing at sufficiently high temperatures causes the He to become mobile in the silicon lattice and to precipitate in the form of He bubbles [S]. When the temperature exceeds N SOO*Csignificant amounts of He are released from the sample [81, presumably leaving empty bubbles behind. To determine the influence of annealing on the getter profile we first treated the sample at a temperature of 100, 300, 500 or 700°C for one hour in dry Nz before subjecting it to a final annealing treatment at a temperature of 950°C for 25 min in dry Nz. In the latter annealing treatment the samples were brought to 600°C within several minutes,
g’ x which the temperature was increased by 10% per minute to the final temperature. The samples that have been pte-annealed at 100,500 and 700°C all display a very sharp Cu distribution without wing-like strucrures(see Fig. 2), identical to a sample that has been subjected to annealing at high temperature only. The sample that has been pre-annealed at 300°C, on the other hand, shows a broad distribution of getter peaks. The shape of the Cu profile varies considerably with the position on the sample. Apparently a broad distribution of stable He bubbles develops during the low-temperature annealing treatment, which does not contract upon high-temperature annealing. It is, however, not yet possible to rule out that the presenceof already gettered Cu on the inside surface of the bubbles (61 influences their size distribution by immobilizing the bubbles duricg low-temperature annealing in the same way as oxygen coverage does [9l. To determine the minimum He dose required for getter behaviour we implanted a series of samples with doses varying from 1 X 10” to 1 x 1016 He/cm*. The front sides of these wafers were then contaminated with either 1 X 1013 or 1 X ?Q14 Cu/cm*. Then the samples were annealed for 25 min rtt 950°C as described for the samples of Fig. 2. Fig. 3 shows the Cu content of the ps.~r ;n the SIMS profile as a function of the implanted He dose. For both Cu contamination levels we see a sharp transition from non-observable to significant gettering around a da= of 6 X 1015 He/cm’ (the arrows in Fig* 3’ indicate that the getter efficiency is below the SEM5 detection limit). Above this dose, both curves appear to saturate at a getter efficiency of approximately 70%. We note that identical gettering behaviour is observed when these samples are contaminated via the back of the waier.1 The remaining Cu is probably gettered internally or at the back of the sample.
0
400
800 c.apth
1200 (nm)
1600
2000
Fig. 2. Cu depth profile obtained by means of SIMS for samples implanted with 1 X 10 I6 He/cm’ for two different annealing strategies. The solid cmve represents a sample which was first annealed at 300°C for 1 h in dry N2 and then at 950°C for 25 min in dry Nz. The dashed curve represents a sample which was
subjectedto the latterannealingtreatmentonly.
PO I 1x10" 0
I 2
, 4 He dose
/ 6 (x10”
/ 8
I 10
ions/cm’)
Fig. 3. Cu content of the getter peak in the SIMS profile as a function of the total implanted He dose. The cirdes and squares represent SIMS measurements of samples contaminated with 1 X lOI and 1 X 10T3 Cu/cm’, respectively. The triangle represents a result obtained by means of RBS. The datepoints accompanied by an arrow represent measurements for which no detectable gettering was observed. The dashed curve is intended to guide the eye.
In the caseof the sample implanted with 1 X 10’” He/cm* the getter efficiency was also determined by means of RBS (triangle in Fig. 3). Both measurementsagree well within the experimental accuracy. When we lower the dose of the C and 0 implantation to 1 x lOI ions/cm’ and anneal the samplesas described for the previous two experiments, getter action is still observed. In the case of Cu the efficiency of the C implantation is reduced by approximately a factor of 5. The efficiency of the 0 implantation remains approximately the same, probably becausein the caseof this dose, the implantation damage remaining after annealing is relatively greater than in the case of the high-dose implantatim due to the absenceof complete amorphization of the implanted layer. For the low-dose implantations the Cu profile for both C and 0 implanted samples more or less follows the distribution of the implanted ions. Finally, we repeated the previous experiment for C, 0 and He implantations but this time in Fe-contaminated silicon (see Fig. 4). Again, 6: or 0 was implanted up to a dose of 1 X lOI ions/cm’, followed by au annealing treatment iden% to that in the previously described experiment. The sampleswere contaminated with 1 X 1013 Fe/cm’. The observed getter behaviour has changed dramatically compared with that of the Cu-contaminated sample, The C implantation displays a very irr&ular and irreproducible getter profile, which appearsto be related to the implantation damage rather than to the C distribution. Similar behaviour is observed for the 0 implaniation. For crtmparison of the gettering behaviour we also show the resultsobtained for a 1 X 10’6-He/cm2 implantation wl$ch shows excellent gettering behaviour after an identical annealkg treatment. As in the caseof Cu, the Fe is concenIII. SILICON
l%e C and 0 impkmtations, on the other band, appear to result in gettering on the implantation damage rather than on the implanted ions. Accordingly, He implantation appears to be most suitable for use in proximity gettering despite the fact that relatively high implantation doses are required.
depth
(nm)
Fig. 4. SIIAS depth &file of Fe ir. samples implanted with either O/cm2 (dashed curve) or 1X10i5 C/cm* (thin solid curve). The Fe distribution in a sample implanted with 1 X 10” He/cm’ (thick solid curve) is also given for comparison. All samples have been contaminated with 1 X lOI Fe/cm*. 1~10’~
trated in a very narrow region around the projected range of the implantation, which makes it the only practical getter implantation for this impurity even though higher irq$srtation doses are necessary.
4. CQnclusEons In ;he case of G-contaminated silicon, He, C and 0 implantations show sigi%caur gertering behaviour, v:hich is clearly related to the distribution of the implanted ions. When the implanted dose exceeds 6-8 X 10” ions/cm’, He implantation results in the most efficient getter centre for the present annealing strategy. In the case of Fe-contaminated silicon He implantation results in similar gettering efficiencies as in the case of &-contaminated samples.
We gratefully acknowledge .ioep Huizinga for anneaiing the samples, Frank Hakkens for the RBS measurements and Gerald van Hoften for his excellent technical assistance.
References
01 T.E. Seidel, in: Materials Issues in Silicon Integrated Circuit Processing, eds. M. Wittner, J. Stimmell, and M. Stratllman (Materials Research Society, Pittsburgh, 1986) p. 3. RI H. Wong, N.W. Cheung, P.K. Chu, J. Liu and J.W. Mayer, Appl. Phys. L&t. 52 (1988) 1023. [31 T.M. Buck, K.A. Pickar, J.M. Poate and C.-M. Hsieh, Appl. Phys. Len. 21 (1972) 485. 141 T.E. SeideI, R.L. Meek and A.G. Cullis, J. Appl. Phys. 46 (1975) 600. I51 T. Kuroi, Y. Kawasaki, S. Komori, K Fukumoto, M. Inuishi, K. Tsukamoto, H. Shinyashiki and T. Shingyoji, Jap. J. Appl. Phys. 32 (19931303. 161S.M. Myers, D.M. Bishop, D.M. Follstaedt, H.J. Stein and W.R. Wacpier, Mat. Res. Sot. Symp. Vol. 283 (1993) 549. I71 J.F. Ziegler, J.P. Biersack and U. Littmark, The Stopping and Range of Ions in Solids vol. 1, ed. J.F. Ziegler (Pergamon, 1985). t81 C.C. Ciriffioen, J.H. Evans, P.C. de Jong and A. van Veen, Nucl. Instr. and Meth. B 27 (1987) 417. c91 J.H. Evans, A. van Veen and CC. Griffioen, Nucl. Instr. and Meth. B 28 (1987) 360.
We compare the gettering efficiency of C, 0 and He implantation %o Cz-grown silicon. After the getter implantation, with a projected range of 1.2 pm, we introduce a controlled amount of either Fe or Cu through low-energy implantation. Subsequently, we study the distribution of the impurities for various annealing conditions by means of secondary ion mass spectroscopy.In contrast to the C and 0 implantations which already show gettering behaviour at #relativelylow dose&the He implantation requires a dose in excessof 6 X 10” ions/cm* before observable getteriug occurs. When sufficiently high doses of He are implanted its gettering efficiency significantly exceeds that of comparable C and 0 implantations, i.e, implantations with the same projected ranges and doses,subjected to the same mealing treatment. The shape of the getter profile in the sample implanted with He is strongly influenced by the annealing treatment.
1. Introduction
2. ExperinmitaI
Transition metal ions, such as Fe and Cu, are notorious for their detrimental effect on the characteristicsof electronic devices fabricated in silicon. Therefore, great efforts have been made to minimize their concentration in virgin silicon wafers. Gettering of illese.impurities during processing, either on the back of the wafer or at getter centres in the bulk of the wafer, has ako become an established technique for lowering their concentration in active device areas[l]. With the ongoing miniaturization, however, thermal budgets, and hence also the diffusion distances of impurities, are continuously decreasing. At the same time, the demands imposed on silicon purity have become more stringent. This has initiated researchin proximity gettering, where the getter centres are situated in the direct vicinity of active device areas in order to increase their efficiency. The feasibility of introducing getter centres by means of ion implantation has been demonstrated in the literature. Both carbon and oxygen implantation [2], as weft as ion implantation damage alone [3-51 make collection of at least some of the transition-metal ions possible. Recently, the potential use of He bubbles as getter centres has been demonstrated for the case of Cu contaminated silicon 161. In the present paper, we will compare the gettering efficiency of He, C and 0 implantations for several dosesand annealing strategies,for Cu- and Fe-contaminatedsamples.
l
Correspondingauthor.
0168-583X/95/$09.50 ssDr0168-583x(94)00495.1
0 1995
ElsevierScienceB.V. kli rightsreserved
The getter experiments were performed using 4-in. Czochralski-grown (100) n-type Si wafers, The bulk of these wafers contains in the order of 20 ppm oxygen, which is used for internal gettering [l]. On the front side of the wafer, a phosphorus-doped epitaxial layer has been grown with a thickness of approximately 20 urn; and a resistivity of 11-14 St cm. The back of the wafer has been damaged by sand blasting by the manufacturer which can result in gettering of transition-metal ions as well. For the formation of getter centms in the proximity of the wafer surface we implanted the front sides of ‘the wafers with He, C or 0 ions. The energy of the ions was chosen such as to result in a projected range of approximately 1.2 Frn. This amounted to 240, 650 and 700 keV for He, C and 0 respectively [7]. During implantation, the wafers were kept close to room temperature by means of electrostatical cooling, i.e. a method in which the wafer is electrostatically attracted by a cooling body. The transition”metal c.mtaminants, Fe and Cu, were also introduced through ion implantation, which was done in a separate target chamber in order to prevent cross contamination. In this case an implantation energy of 30 keV was chosen, which resulted in projected ranges of 27.5 and 29.3 mn for Cm and Fe, respectively,[7]. The contaminants were implanted in either the front or the back side of the wafer. In, all the experiments presented here the most abundant; isotope of the contaminant was chosen. After implantation the wafers were divided into samples of approximately 1 cmZ, which were then subjectedto’
thermal cycle of the individual samples is given in the discussionbelow. For the analysis of the getter profiies we resorted ta secondary ion mass spectroscopy (SIMS). A CAMECA ims4f was used, which employed a focused 5.5keV 0: primary ion beam rasteredover a 250 X 2SO-pm2 area and detected positive secondary ions stemming exclusively from the 30-pm diameter centre of the sputtered crater. (In the case of oxygen depth profiling a 14.5-keV Cs+ beam was used and r60- detected.) The depth scale was calibrated by determining the total eroded depth with the aid of a micromechanicalstylus transducerand by assuming a constant erosion rate. This is estimated to be accurate to within 10%. The concentration scale of the profiles was calibrated by means of gauge implantations in silicon reference samples.This implies that a well-defined diluted standard was used for the instrumental-sensitivity determination. !n the case of,the gettered samples, however, the impurity is not distributed randomly throughout the silicon lattice. This could introduce systematicerrors in the determined getter efficiency due to matrix effects. No evidence for this was found for the Fe-containing samples, but for the &-contaminated samples problems did indeed occur. To eliminate matrix effects some of these samples were also investigated with RBS, for which we used samples which were chemicsily etched to the point at which the Si signal no longer obscured the Cu signal. The accuracy of the concentration scaleof the SIMS spectra is estimated to be 10 to 30%. Day-to-day vari:‘ior;:: were observed in the scaling of the SIMS spectra which clearly exceeded the 10% variations normally observed during a single day, probably due to variations in the instrumental settings. Therefore, comparisons were only made for spectra measured on the same day, thus assuringnear-identical instrumental settings. 3. Results and discussion Fig. 1 shows the Cu distribution obtained by means of SIMS for samples implanted with He, C or 0, up to a dose of 1 X 1016 ions/cm’, and contaminated with 1 X lOI4 &/cm’ in the front side of the sample. The sampleswere subjected to identical annealing treatments, viz. 25 min at 95O’C in dry N,. The heating rate of the furnace was fixed at 10°C per minute. After the annealing, the samples were cooled to room temperature, initially at a rate of 5°C per minute, but ultimately at a iower rate due to the intrinsic co,oling rate of the furnace. The Cu content of the peak in the depth profile of the He-implanted sample significantly exceedsthat of the other two, and the C-implanted sample gettered more Cu than the O-implanted sample. We have to keep in mind that the implanted getter centres had to compete with both the getter action of oxygen precipitates in the bulk of the wafer and that of the damage on the back
1x10” 0
400
800 depth
1200
f600
2000
(nm)
Fig. 1. Cu distributionas determinedwith the aid of SIMS for Si samplesimplantedwith Be (solidcurve),C (dashedcurve)or 0 (da&cd-dottedcurve) up to a dose of 1X lOI6 ions/cm2 and annealedfor 25 min at 950°Cin dry N2. The sampleshavebeen intentionallycontaminatedwith 1X 1Or4Cu/cm’. of the wafer. However, this holds for all three samples, which means that the conclusion that the getter efficiency of the He-implanted sample under the given annealing conditions exceedsthat of the other two is justified. When we look more closely at the SIMS profiles, we see that the O-implanted sample displays two Cu peaks RBS measurementsshow that the 0 implantation results in a buried amorphous layer. During the annealing the oxygen preferentially precipitates in the originally amorphous layer and displays a slightly enhanced oxygen concentration near the original amorphous-to-crystalline interfaces in the SIMS depth profile. Furthermore, the implantation damage is most resistantto annealing near these interfaces. Both effects can contribute to the double getter peak. In the case of the carbon implanted sample (which was heavily damaged after implantation but not up to the point at which it was amorphous), the Cu profile approximately duplicates the implanted C distribution. The most salient features of the He-implanted sample are a sharp central getter peak accompanied by two wing-like structures. The shape of the wing-like structures is strongly influenced by the annealing strategy. After implantation, the He is more or less randomly distributed throughout the implanted layer apart from the gaussian depth distribution. Annealing at sufficiently high temperatures causes the He to become mobile in the silicon lattice and to precipitate in the form of He bubbles [S]. When the temperature exceeds N SOO*Csignificant amounts of He are released from the sample [81, presumably leaving empty bubbles behind. To determine the influence of annealing on the getter profile we first treated the sample at a temperature of 100, 300, 500 or 700°C for one hour in dry Nz before subjecting it to a final annealing treatment at a temperature of 950°C for 25 min in dry Nz. In the latter annealing treatment the samples were brought to 600°C within several minutes,
g’ x which the temperature was increased by 10% per minute to the final temperature. The samples that have been pte-annealed at 100,500 and 700°C all display a very sharp Cu distribution without wing-like strucrures(see Fig. 2), identical to a sample that has been subjected to annealing at high temperature only. The sample that has been pre-annealed at 300°C, on the other hand, shows a broad distribution of getter peaks. The shape of the Cu profile varies considerably with the position on the sample. Apparently a broad distribution of stable He bubbles develops during the low-temperature annealing treatment, which does not contract upon high-temperature annealing. It is, however, not yet possible to rule out that the presenceof already gettered Cu on the inside surface of the bubbles (61 influences their size distribution by immobilizing the bubbles duricg low-temperature annealing in the same way as oxygen coverage does [9l. To determine the minimum He dose required for getter behaviour we implanted a series of samples with doses varying from 1 X 10” to 1 x 1016 He/cm*. The front sides of these wafers were then contaminated with either 1 X 1013 or 1 X ?Q14 Cu/cm*. Then the samples were annealed for 25 min rtt 950°C as described for the samples of Fig. 2. Fig. 3 shows the Cu content of the ps.~r ;n the SIMS profile as a function of the implanted He dose. For both Cu contamination levels we see a sharp transition from non-observable to significant gettering around a da= of 6 X 1015 He/cm’ (the arrows in Fig* 3’ indicate that the getter efficiency is below the SEM5 detection limit). Above this dose, both curves appear to saturate at a getter efficiency of approximately 70%. We note that identical gettering behaviour is observed when these samples are contaminated via the back of the waier.1 The remaining Cu is probably gettered internally or at the back of the sample.
0
400
800 c.apth
1200 (nm)
1600
2000
Fig. 2. Cu depth profile obtained by means of SIMS for samples implanted with 1 X 10 I6 He/cm’ for two different annealing strategies. The solid cmve represents a sample which was first annealed at 300°C for 1 h in dry N2 and then at 950°C for 25 min in dry Nz. The dashed curve represents a sample which was
subjectedto the latterannealingtreatmentonly.
PO I 1x10" 0
I 2
, 4 He dose
/ 6 (x10”
/ 8
I 10
ions/cm’)
Fig. 3. Cu content of the getter peak in the SIMS profile as a function of the total implanted He dose. The cirdes and squares represent SIMS measurements of samples contaminated with 1 X lOI and 1 X 10T3 Cu/cm’, respectively. The triangle represents a result obtained by means of RBS. The datepoints accompanied by an arrow represent measurements for which no detectable gettering was observed. The dashed curve is intended to guide the eye.
In the caseof the sample implanted with 1 X 10’” He/cm* the getter efficiency was also determined by means of RBS (triangle in Fig. 3). Both measurementsagree well within the experimental accuracy. When we lower the dose of the C and 0 implantation to 1 x lOI ions/cm’ and anneal the samplesas described for the previous two experiments, getter action is still observed. In the case of Cu the efficiency of the C implantation is reduced by approximately a factor of 5. The efficiency of the 0 implantation remains approximately the same, probably becausein the caseof this dose, the implantation damage remaining after annealing is relatively greater than in the case of the high-dose implantatim due to the absenceof complete amorphization of the implanted layer. For the low-dose implantations the Cu profile for both C and 0 implanted samples more or less follows the distribution of the implanted ions. Finally, we repeated the previous experiment for C, 0 and He implantations but this time in Fe-contaminated silicon (see Fig. 4). Again, 6: or 0 was implanted up to a dose of 1 X lOI ions/cm’, followed by au annealing treatment iden% to that in the previously described experiment. The sampleswere contaminated with 1 X 1013 Fe/cm’. The observed getter behaviour has changed dramatically compared with that of the Cu-contaminated sample, The C implantation displays a very irr&ular and irreproducible getter profile, which appearsto be related to the implantation damage rather than to the C distribution. Similar behaviour is observed for the 0 implaniation. For crtmparison of the gettering behaviour we also show the resultsobtained for a 1 X 10’6-He/cm2 implantation wl$ch shows excellent gettering behaviour after an identical annealkg treatment. As in the caseof Cu, the Fe is concenIII. SILICON
l%e C and 0 impkmtations, on the other band, appear to result in gettering on the implantation damage rather than on the implanted ions. Accordingly, He implantation appears to be most suitable for use in proximity gettering despite the fact that relatively high implantation doses are required.
depth
(nm)
Fig. 4. SIIAS depth &file of Fe ir. samples implanted with either O/cm2 (dashed curve) or 1X10i5 C/cm* (thin solid curve). The Fe distribution in a sample implanted with 1 X 10” He/cm’ (thick solid curve) is also given for comparison. All samples have been contaminated with 1 X lOI Fe/cm*. 1~10’~
trated in a very narrow region around the projected range of the implantation, which makes it the only practical getter implantation for this impurity even though higher irq$srtation doses are necessary.
4. CQnclusEons In ;he case of G-contaminated silicon, He, C and 0 implantations show sigi%caur gertering behaviour, v:hich is clearly related to the distribution of the implanted ions. When the implanted dose exceeds 6-8 X 10” ions/cm’, He implantation results in the most efficient getter centre for the present annealing strategy. In the case of Fe-contaminated silicon He implantation results in similar gettering efficiencies as in the case of &-contaminated samples.
We gratefully acknowledge .ioep Huizinga for anneaiing the samples, Frank Hakkens for the RBS measurements and Gerald van Hoften for his excellent technical assistance.
References
01 T.E. Seidel, in: Materials Issues in Silicon Integrated Circuit Processing, eds. M. Wittner, J. Stimmell, and M. Stratllman (Materials Research Society, Pittsburgh, 1986) p. 3. RI H. Wong, N.W. Cheung, P.K. Chu, J. Liu and J.W. Mayer, Appl. Phys. L&t. 52 (1988) 1023. [31 T.M. Buck, K.A. Pickar, J.M. Poate and C.-M. Hsieh, Appl. Phys. Len. 21 (1972) 485. 141 T.E. SeideI, R.L. Meek and A.G. Cullis, J. Appl. Phys. 46 (1975) 600. I51 T. Kuroi, Y. Kawasaki, S. Komori, K Fukumoto, M. Inuishi, K. Tsukamoto, H. Shinyashiki and T. Shingyoji, Jap. J. Appl. Phys. 32 (19931303. 161S.M. Myers, D.M. Bishop, D.M. Follstaedt, H.J. Stein and W.R. Wacpier, Mat. Res. Sot. Symp. Vol. 283 (1993) 549. I71 J.F. Ziegler, J.P. Biersack and U. Littmark, The Stopping and Range of Ions in Solids vol. 1, ed. J.F. Ziegler (Pergamon, 1985). t81 C.C. Ciriffioen, J.H. Evans, P.C. de Jong and A. van Veen, Nucl. Instr. and Meth. B 27 (1987) 417. c91 J.H. Evans, A. van Veen and CC. Griffioen, Nucl. Instr. and Meth. B 28 (1987) 360.