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Production and in-situ analysis of microscale oxide structures in silicon by oxygen implantation
Nuclear Instruments and Methods in Physics Research ßH0/81 (1993) 872-876 North-Holland
K M 11 ,
Beam Interactions with Matarlals &Atoms
Production and in-situ analysis of microscale oxide structures in silicon by oxygen implantation K. Wittmaack
A70MIKA Analysetcchnik
GmbH, Bruckniamtring 6, D-8042 Obcrscldeißhcim, Germany
P, SIMS scanning ion microprobe has been used to investigate the feasibility of focused oxygen beams for the production and analysis of microscale oxide distributiops in Si . Test structures of AI on Si (width about I pm, spacing between 10 and 20 pin) were used to characterize the microanalytical performance of the ion microprobe . To accomplish discrimination between the implanted primary ions and 160 in the native oxide, the experiments were carried out with a mass filtered beam of 1 "O' . The beam diameter achieved at an energy of 10 keV and a beam current of I nA ranged between f and 1 .5 pin. Depth profile .: were recorded in the checkerboard mode with a pixel size down to less than 1 pin. Under these conditions the AI signal from nominally clean Si regions amounted to about 3x 10 -' of the signal from the AI overlayers . Oxides were generated by line scan implantation as well as with a static beam . The sample composition around an in-situ generated oxide spot was deteimiuetl by spdtially resolved depth profiling and is presented in ouasi-three-dimensional form.
1. Introduction Focused ion beams are widely used for the purpose of modifying the composition and structure of materials [t]. Submicron beams arc commonly generated by liquid metal ion sources, which, however, are not applicable to all elements of interest. Ore element tha; cannot be produced in such a source is oxygen . Implantation of oxygen is a commonly employed technique for generating silicon dioxide, either as a near-surface layer [2,3] or as a buries! layer, the latter technique being named SIMOX [4,5]. In view of the incrcasii.ô interest in the fabrication o,' shallow doped layers, low implantation energicc are A primary concern [6-8] . The accurate determination of the profile of shallow distributions constitutes a challenge in materials inA),n [9] .
In this contribution we report on results o!' experiments devoted to exploring the use of focused oxygen ion beams for producing microscale oxide structures directly in an ion nticrcprobe . The generated structures were subsequently analysed in situ by ion imaging and spatially resolved depth profiling.
2. Experiment The measurements were performed using the dual beam ion microprobe ATOMIKA 40(0 110], The base pressure in the analysis chamber was I x 10- to mbar. The O; beam is formed in an immersion lens system
and :s then passed through a Wien filter for mass analysis [II]. Downstream of the Wien filter a set of mass defining object apertures of various sizes is mounted on a rotatable manipulator. An cinzel lens further downstream serves to generate a demagnificd image of the object aperture on the sample (magnificatiou- ~4In the present work we chose an
object aperture with a diameter of 10 pin so that the nominal ruinimum spot size on target was 1 pr. , (de-regarding lens aberrations). 1t is also possible to generate a cross-over of the beam upstream of the object aperture, in which case a minimum spot size of 0.6 fam has been observe(' with a 15 keV O; beam [I()]. To achieve good counting statistics in the SIMS studies reported here, it was desirable to perform measurements at a beam current of about ! nA. This could be achieved at a bean[ energy of 1(1 keV. Discrimination between Ie0 in the native surface oxides and the implanted oxygen was accomplished using primary ions of Ix0' (supply
gas 18 02 eniiched to 97%). Some experiments based on the use of 1804' have idready been reported by other groups [12,13]. Secondary ion mass spectrometry (SIMS) analysis was pcrfornied by taking advantage, of the checkerboard data acquisition technique [14,15]. Depth profiles recorded in this mode can be presented in threedimensional form by sciectmg planes parallel and normal to the original surface [15]. Depending on flic
species of main interest the signal due to either positive or negative secondary ions was recorded.
L'168-5g3X/93/$06 .00 C 1993 - Elsevier Science Publishers B.V. All rights reserved
K. Wttunaack / Mi-cale oxide structurer in St by O in :pla .tttuion
3 . Results and discussion First we characterized the microanalytical performance of the ion microprobe by performing an incomplctc depth profile on a test pattern of vapour deposited AI on Si [16]. Fig . I shows a raster scanning Al' ion image of one particular section of this sample, recorded with a digital image processor. The image reflects some nonunifermity of the line width (nominal width I wm), which, ho,-,ever, was not considered serious for the present work. The data acquisition area in the subsequent depth profiling experiment covered 25°Jo of the total bombarded area, i .e., a central 60 x 60 Rm 2 region in the image of fig . 1 . Accordingly, the three stripes and a small upper fraction of the number "I .G" happened to fall into the gated area. Using the checkerboard data acquisition mode one can distinguish between signals from the AI stripes ("in") and from outside this area ("out"). The depth profiles shown in fig. 2 were derived by summation over typicai:y 20 to 100 acquisition cells ("pixels"), out of a total of 16 x 16 pixels per checkerboard plane (see fig . 6). To ease coirparison all integrated signals arc normalized to the integration time per pixel . Several observations are noteworthy . i) After an initial rise due to surface cleaning, the ="SiI signal from Si ("Si) decreases by a factor of
Fig. I . Raster scanning AI' image of a test pattern of AI on Si, recorded with a 10 kcV 1 "O' beam at I nA. The sparing of the At bars is 20 wm .
873
10 4
10 3
0 ~ t0 t rit z
w i
to o
te It (Y- Ai' ~a.'. Si' measured in the central 60 gm x60 pm section of the image show,[ in fig. (bombardment time 8 s per data acquisition cycle). The curves labeled "in" and "out" relate to integration of signals from the At pattern and from outside of this area, respectively. Fig. 2. De-,!h pn,filt1
about 8 and then increases again. This well-known behaviour [171 reflects the removal of the native surface oxide and the concurrent beam induced oxidation . The buildup of oxygen is also evident from the profile iabclieù "0,,u , . ii) to contrast to 2 "Si' the ='AI' signal from AI ("AI ,") chanics rather little during bombardment with '"O,+, even though 180n, (not shown) increases almost as much as `O_t (factor of 2 difference by the end of the ptofilc). This could imply that the sensitivity of the AI' signal to changes in oxygen cot!ccntration-is relatively small compared to Si', an interpretation that might relate to the difference in ionization potential (AI : 5 .99 eV, Si: 8.15 eV). iii) The positive secondary ion signal at mass numher 27 from Si ("AI ,") decreases rapidly during the initial period of surface cleaning and oxide removal, thcr passes through a flat minimum and finally increases with a very small gradient, which is essentially the same as for AI , . The irdaximum-to-minimum ratio is 15, i .e . higher than for SiWe interpret the AI , profile tentatively as being due to two coutribe0ove" (a) the intial sputter removal of a surface contamination layer containing Al and other impurities, and (b) a backgrounJ due bombardment of the Al stripes with primary ions from the beam tail . Mass interference between AI and C 2 H, (from an assumed hydrocarbon surface contamination layer) might also he worth considering . Illd . SEWCONDUCTOR MODIFICATION (d)
K Wittmaack / Microscale oxidestructures in Si by O implantation
874
Fig . I %hows the ratio of the (normalized) At signals ftont the regions outside and inside the At pattern. Afr completion of surface cleaning Al_,/All,, reaches an apparently stationary level of 3.5 x 10 - '. For the given pattern of the sample, this measured dynamic range of almost 300 apparently represents the limit that can be achieved in small area analysis. The problems encountered in this type of measurement have been discussed in some detail previously [18]. We now turn to the main ion beam modification aspect of this work, i .e. in-situ production and analysis of microscale oxide structures by oxygen bombardment . Fig. 4 shows a raster scanning t "O - ion image of line scans produced by implantation of and subsequcr" analysis with `s0,-` . The spacing between the lines is 1G Win. Note that the width of the recorded lines is the result of a convolution of the beam profile with itself. Accordingly, the measured lines arc significantly broader than the true width of the implanted lines . For depth profile analysis a single oxide spot was produced by implantation, t;iQh a static t"OZ beam (almost complete oxidation). The results relating to integration of the 1'0 - signals over regions inside and outside the implanted area are labelled O , and O respectively, in fig . 5 . As cxpc,tcd, O , starts from a very high level due to implantation prior to analysis whereas with O , one observes the well-known pronounced signal buildup [19]. Concurrently, the tn 0 , sig -aal decreases due to the removal of the surface oxide . Note that the maximum yield enhancement that can be achieved with negative secondary ions by implanting oxygen is significantly smaller than for positive
Fig . 4 . Raster scanning 1"0 - image of thtce lines generated by implantation of "0,* . The line spacing is 10 Win. species [19] . Accordingly, the "dynamic range" in the depth profile for O, is only about 100. A quasi-three-dimensional display of the `O - distribution is presented in fig . 6. Three different two-di;mensional images are shown. The checkboard image to the right relates to plane no. 6 of the depth profile . The .mplanted oxygen spot in the centre of the image
10 -t
a YI O
v N
Z
10 0
10 10 -3
TTY-T1
0
too zee 300 400 500 TIME (number of cycle)
Fig . 3 . Ratio of the AI signals from outside the AI pattrrn to the signal from within this area.
0
rr . 1 30 40 10 20 TIME (number of cyc1o)
Fig. 5 . C^rth -rnfile" of 1 "n - and 1 "O - , measured ir,,-,ide and outside ~in oxide spot generated by implantation with a static beam of n1 0 : (bombardment time 4 s per data acquisition cycle).
K Wittntoack / Microscafe oxide structures in Si bu O imeant-,!inn
875
420 <= 392 - 4218 364 - 392 336 - 364 308 - 336 280 - 308 i : "i' aii. ''`..' " 252 - 280 .. 224 - 252 tttt 196 - 224 168 `'' - 196 140 - 168 ¬i _¬ _ 112 - 140 lt iü ü 84 - 112 ,_, 56 - 84 28 - 56 < 28 Fig . 6. Quasi-three-dimensional display of the 18 0 - depth profile for the same area as in fig. 5 . The checkerboard signal distribution in plane no. 6 is shown on the right-hand panel (16x 16 pixels, corresponding to 15 üm x 15 Wm) . The two images on the left-hand side show the signal distribution in planes normal to the sample surface (laterally resolved depth profiles). The location of the two planes is indicated on the checkerboard image by small open squares. The colour aide of the intensities (counts per pixel) is shown below the checkerboard . is clearly visible. The side length of this image is 15 Wm, subdivided into 16 pixels, i .e . each pixel has a width of only 0.94 Wm . Two images in the direction normal to the surface are ~hn%vn or tilc left-hand side. They may be referred to as spatially resolved deptii profiles. The intersection of these images with plane no. 6 is marked in the checkerboard image by small open squares (cross-cut and diagonal cut, respectively) . Inspection of the depth profile images suggests that the width of the implanted spot increases in the course of depth profiling, r-,)tably tovra~ds completion of oxidation in the non-implanted region. This broadening might in part be due to bombardment induced lateral diffusion of oxygen. The magnitude of the observed effect (diffusion length of the order of 1 gm) appears to be too large for diffusion being the only source of broadening (note, however, that very little is currently
known about high-fluence bombardment induced lateral diffusion) . At this stage it appears more likely that the broadening is due to a superposition of oxygen from the tail of the implanted spot and the oxygen incorporated during analysts. Quantitative data analysis will b: somewhat complicated because, at high concentrations; the O - signal varies nonlinearly with oxygen concentration [19]. 4. Conclusion It has been shown that microscale oxide structures can be generated by implantation at a relatively low energy of 5 keV/O atom . Due to the rather large beam current of I :nA the actual size of the structure generated here was about I .S gm . Production of sub111d. SEMICONDUCTOR MODIFICATION (d)
K Wittmaack /Microscale oxide stractntres in Si by Oimplantation
876
micron features should be possible at lower beam currents and/or higher beam energies .
[111 [121
Referenc,,s [1] [2] [3] [41 [5] t6] [7] [81 [91 [101
S. Namba, Nucl . Instr. and Meth. B39 (1989) 504. K. Wittmaack, Appl . Surf. Sci . 9 (1981) 315. W. Reuter, Nw.i . Instr. and Meth . B15 (1986) 173. K. Izumi, M. Doken and H. Ariyoshi, Electron. Lett. 14 (1978)593. A.H . van Ommen, Nucl . Instr . and Meth. B39(1989) 194. O. Vancauwenberghe, N. Herbots, H. Manohoran and M. Ahrens, J. Vac. Sci . Technol. A9 (1991) 1035 . O. Vancauwenberh- N. Herbots and OC. Hellman, J. Vac. Sci. Technol. A1 0(1992) 713. C. Hill, J . Vac. Sci . Technol . BI(1(1992) 289. W. Vandervorst and T. Clarysce, J. Lac. Sci . Technol . BI0 0992) 302. K. Wittmaack, Sec-dary Ion Mass Spectrometry SIMS
(131 [14] 115] [16] [17] [18]
(19]
Vlll, eds. A. Benninghoven et al. (Wiley, Chichester, 1992). K. Wittmaack and J.B . Clegg. Appl . Phys. Lett. 37 (1980) 285. S.D. Lrttlewood and J.A. Kilner. J. Appl. Phys. 63 (1988) 2173. A .E. Morgan and P. Maillot, Secondary Ion Mass Spectrometr,, , SIMS VI, eds. A. Benninghoven, A.M . Huber and II.W. Werner (Wiley, Chichester . 1988) p. 709. R. von Criegern, l . Weitzel and J. Fottner, Secondary Ion Mass Spectrometry SIMS IV, eds. A. Benninghoveu et al. (Springer, Berlin, 1984) p 308. S.M. Daiser, C. Scholte and J.L. Maul, Nucl . Instr . and Meth. B35 (1988) 544. The Al-on-Si test patterns were kindly provided by M. Harde. Heinrich-Hertz-Institut, Berlin . K. Wittmaack, Nucl. instr . and Meth . 168(1980) 343. W. Vandervorst and H.W. Werner, Secondary Ion Mass Spectrometry SIMS VI, eds. A. Benninghoven, A.M . Huber and H.W . Werner (Wiley, Chichester, 1988) p. 4119 . K. Wittmaack, Surf. Sci . 112 (1981) 168 .
K M 11 ,
Beam Interactions with Matarlals &Atoms
Production and in-situ analysis of microscale oxide structures in silicon by oxygen implantation K. Wittmaack
A70MIKA Analysetcchnik
GmbH, Bruckniamtring 6, D-8042 Obcrscldeißhcim, Germany
P, SIMS scanning ion microprobe has been used to investigate the feasibility of focused oxygen beams for the production and analysis of microscale oxide distributiops in Si . Test structures of AI on Si (width about I pm, spacing between 10 and 20 pin) were used to characterize the microanalytical performance of the ion microprobe . To accomplish discrimination between the implanted primary ions and 160 in the native oxide, the experiments were carried out with a mass filtered beam of 1 "O' . The beam diameter achieved at an energy of 10 keV and a beam current of I nA ranged between f and 1 .5 pin. Depth profile .: were recorded in the checkerboard mode with a pixel size down to less than 1 pin. Under these conditions the AI signal from nominally clean Si regions amounted to about 3x 10 -' of the signal from the AI overlayers . Oxides were generated by line scan implantation as well as with a static beam . The sample composition around an in-situ generated oxide spot was deteimiuetl by spdtially resolved depth profiling and is presented in ouasi-three-dimensional form.
1. Introduction Focused ion beams are widely used for the purpose of modifying the composition and structure of materials [t]. Submicron beams arc commonly generated by liquid metal ion sources, which, however, are not applicable to all elements of interest. Ore element tha; cannot be produced in such a source is oxygen . Implantation of oxygen is a commonly employed technique for generating silicon dioxide, either as a near-surface layer [2,3] or as a buries! layer, the latter technique being named SIMOX [4,5]. In view of the incrcasii.ô interest in the fabrication o,' shallow doped layers, low implantation energicc are A primary concern [6-8] . The accurate determination of the profile of shallow distributions constitutes a challenge in materials inA),n [9] .
In this contribution we report on results o!' experiments devoted to exploring the use of focused oxygen ion beams for producing microscale oxide structures directly in an ion nticrcprobe . The generated structures were subsequently analysed in situ by ion imaging and spatially resolved depth profiling.
2. Experiment The measurements were performed using the dual beam ion microprobe ATOMIKA 40(0 110], The base pressure in the analysis chamber was I x 10- to mbar. The O; beam is formed in an immersion lens system
and :s then passed through a Wien filter for mass analysis [II]. Downstream of the Wien filter a set of mass defining object apertures of various sizes is mounted on a rotatable manipulator. An cinzel lens further downstream serves to generate a demagnificd image of the object aperture on the sample (magnificatiou- ~4In the present work we chose an
object aperture with a diameter of 10 pin so that the nominal ruinimum spot size on target was 1 pr. , (de-regarding lens aberrations). 1t is also possible to generate a cross-over of the beam upstream of the object aperture, in which case a minimum spot size of 0.6 fam has been observe(' with a 15 keV O; beam [I()]. To achieve good counting statistics in the SIMS studies reported here, it was desirable to perform measurements at a beam current of about ! nA. This could be achieved at a bean[ energy of 1(1 keV. Discrimination between Ie0 in the native surface oxides and the implanted oxygen was accomplished using primary ions of Ix0' (supply
gas 18 02 eniiched to 97%). Some experiments based on the use of 1804' have idready been reported by other groups [12,13]. Secondary ion mass spectrometry (SIMS) analysis was pcrfornied by taking advantage, of the checkerboard data acquisition technique [14,15]. Depth profiles recorded in this mode can be presented in threedimensional form by sciectmg planes parallel and normal to the original surface [15]. Depending on flic
species of main interest the signal due to either positive or negative secondary ions was recorded.
L'168-5g3X/93/$06 .00 C 1993 - Elsevier Science Publishers B.V. All rights reserved
K. Wttunaack / Mi-cale oxide structurer in St by O in :pla .tttuion
3 . Results and discussion First we characterized the microanalytical performance of the ion microprobe by performing an incomplctc depth profile on a test pattern of vapour deposited AI on Si [16]. Fig . I shows a raster scanning Al' ion image of one particular section of this sample, recorded with a digital image processor. The image reflects some nonunifermity of the line width (nominal width I wm), which, ho,-,ever, was not considered serious for the present work. The data acquisition area in the subsequent depth profiling experiment covered 25°Jo of the total bombarded area, i .e., a central 60 x 60 Rm 2 region in the image of fig . 1 . Accordingly, the three stripes and a small upper fraction of the number "I .G" happened to fall into the gated area. Using the checkerboard data acquisition mode one can distinguish between signals from the AI stripes ("in") and from outside this area ("out"). The depth profiles shown in fig. 2 were derived by summation over typicai:y 20 to 100 acquisition cells ("pixels"), out of a total of 16 x 16 pixels per checkerboard plane (see fig . 6). To ease coirparison all integrated signals arc normalized to the integration time per pixel . Several observations are noteworthy . i) After an initial rise due to surface cleaning, the ="SiI signal from Si ("Si) decreases by a factor of
Fig. I . Raster scanning AI' image of a test pattern of AI on Si, recorded with a 10 kcV 1 "O' beam at I nA. The sparing of the At bars is 20 wm .
873
10 4
10 3
0 ~ t0 t rit z
w i
to o
te It (Y- Ai' ~a.'. Si' measured in the central 60 gm x60 pm section of the image show,[ in fig. (bombardment time 8 s per data acquisition cycle). The curves labeled "in" and "out" relate to integration of signals from the At pattern and from outside of this area, respectively. Fig. 2. De-,!h pn,filt1
about 8 and then increases again. This well-known behaviour [171 reflects the removal of the native surface oxide and the concurrent beam induced oxidation . The buildup of oxygen is also evident from the profile iabclieù "0,,u , . ii) to contrast to 2 "Si' the ='AI' signal from AI ("AI ,") chanics rather little during bombardment with '"O,+, even though 180n, (not shown) increases almost as much as `O_t (factor of 2 difference by the end of the ptofilc). This could imply that the sensitivity of the AI' signal to changes in oxygen cot!ccntration-is relatively small compared to Si', an interpretation that might relate to the difference in ionization potential (AI : 5 .99 eV, Si: 8.15 eV). iii) The positive secondary ion signal at mass numher 27 from Si ("AI ,") decreases rapidly during the initial period of surface cleaning and oxide removal, thcr passes through a flat minimum and finally increases with a very small gradient, which is essentially the same as for AI , . The irdaximum-to-minimum ratio is 15, i .e . higher than for SiWe interpret the AI , profile tentatively as being due to two coutribe0ove" (a) the intial sputter removal of a surface contamination layer containing Al and other impurities, and (b) a backgrounJ due bombardment of the Al stripes with primary ions from the beam tail . Mass interference between AI and C 2 H, (from an assumed hydrocarbon surface contamination layer) might also he worth considering . Illd . SEWCONDUCTOR MODIFICATION (d)
K Wittmaack / Microscale oxidestructures in Si by O implantation
874
Fig . I %hows the ratio of the (normalized) At signals ftont the regions outside and inside the At pattern. Afr completion of surface cleaning Al_,/All,, reaches an apparently stationary level of 3.5 x 10 - '. For the given pattern of the sample, this measured dynamic range of almost 300 apparently represents the limit that can be achieved in small area analysis. The problems encountered in this type of measurement have been discussed in some detail previously [18]. We now turn to the main ion beam modification aspect of this work, i .e. in-situ production and analysis of microscale oxide structures by oxygen bombardment . Fig. 4 shows a raster scanning t "O - ion image of line scans produced by implantation of and subsequcr" analysis with `s0,-` . The spacing between the lines is 1G Win. Note that the width of the recorded lines is the result of a convolution of the beam profile with itself. Accordingly, the measured lines arc significantly broader than the true width of the implanted lines . For depth profile analysis a single oxide spot was produced by implantation, t;iQh a static t"OZ beam (almost complete oxidation). The results relating to integration of the 1'0 - signals over regions inside and outside the implanted area are labelled O , and O respectively, in fig . 5 . As cxpc,tcd, O , starts from a very high level due to implantation prior to analysis whereas with O , one observes the well-known pronounced signal buildup [19]. Concurrently, the tn 0 , sig -aal decreases due to the removal of the surface oxide . Note that the maximum yield enhancement that can be achieved with negative secondary ions by implanting oxygen is significantly smaller than for positive
Fig . 4 . Raster scanning 1"0 - image of thtce lines generated by implantation of "0,* . The line spacing is 10 Win. species [19] . Accordingly, the "dynamic range" in the depth profile for O, is only about 100. A quasi-three-dimensional display of the `O - distribution is presented in fig . 6. Three different two-di;mensional images are shown. The checkboard image to the right relates to plane no. 6 of the depth profile . The .mplanted oxygen spot in the centre of the image
10 -t
a YI O
v N
Z
10 0
10 10 -3
TTY-T1
0
too zee 300 400 500 TIME (number of cycle)
Fig . 3 . Ratio of the AI signals from outside the AI pattrrn to the signal from within this area.
0
rr . 1 30 40 10 20 TIME (number of cyc1o)
Fig. 5 . C^rth -rnfile" of 1 "n - and 1 "O - , measured ir,,-,ide and outside ~in oxide spot generated by implantation with a static beam of n1 0 : (bombardment time 4 s per data acquisition cycle).
K Wittntoack / Microscafe oxide structures in Si bu O imeant-,!inn
875
420 <= 392 - 4218 364 - 392 336 - 364 308 - 336 280 - 308 i : "i' aii. ''`..' " 252 - 280 .. 224 - 252 tttt 196 - 224 168 `'' - 196 140 - 168 ¬i _¬ _ 112 - 140 lt iü ü 84 - 112 ,_, 56 - 84 28 - 56 < 28 Fig . 6. Quasi-three-dimensional display of the 18 0 - depth profile for the same area as in fig. 5 . The checkerboard signal distribution in plane no. 6 is shown on the right-hand panel (16x 16 pixels, corresponding to 15 üm x 15 Wm) . The two images on the left-hand side show the signal distribution in planes normal to the sample surface (laterally resolved depth profiles). The location of the two planes is indicated on the checkerboard image by small open squares. The colour aide of the intensities (counts per pixel) is shown below the checkerboard . is clearly visible. The side length of this image is 15 Wm, subdivided into 16 pixels, i .e . each pixel has a width of only 0.94 Wm . Two images in the direction normal to the surface are ~hn%vn or tilc left-hand side. They may be referred to as spatially resolved deptii profiles. The intersection of these images with plane no. 6 is marked in the checkerboard image by small open squares (cross-cut and diagonal cut, respectively) . Inspection of the depth profile images suggests that the width of the implanted spot increases in the course of depth profiling, r-,)tably tovra~ds completion of oxidation in the non-implanted region. This broadening might in part be due to bombardment induced lateral diffusion of oxygen. The magnitude of the observed effect (diffusion length of the order of 1 gm) appears to be too large for diffusion being the only source of broadening (note, however, that very little is currently
known about high-fluence bombardment induced lateral diffusion) . At this stage it appears more likely that the broadening is due to a superposition of oxygen from the tail of the implanted spot and the oxygen incorporated during analysts. Quantitative data analysis will b: somewhat complicated because, at high concentrations; the O - signal varies nonlinearly with oxygen concentration [19]. 4. Conclusion It has been shown that microscale oxide structures can be generated by implantation at a relatively low energy of 5 keV/O atom . Due to the rather large beam current of I :nA the actual size of the structure generated here was about I .S gm . Production of sub111d. SEMICONDUCTOR MODIFICATION (d)
K Wittmaack /Microscale oxide stractntres in Si by Oimplantation
876
micron features should be possible at lower beam currents and/or higher beam energies .
[111 [121
Referenc,,s [1] [2] [3] [41 [5] t6] [7] [81 [91 [101
S. Namba, Nucl . Instr. and Meth. B39 (1989) 504. K. Wittmaack, Appl . Surf. Sci . 9 (1981) 315. W. Reuter, Nw.i . Instr. and Meth . B15 (1986) 173. K. Izumi, M. Doken and H. Ariyoshi, Electron. Lett. 14 (1978)593. A.H . van Ommen, Nucl . Instr . and Meth. B39(1989) 194. O. Vancauwenberghe, N. Herbots, H. Manohoran and M. Ahrens, J. Vac. Sci . Technol. A9 (1991) 1035 . O. Vancauwenberh- N. Herbots and OC. Hellman, J. Vac. Sci. Technol. A1 0(1992) 713. C. Hill, J . Vac. Sci . Technol . BI(1(1992) 289. W. Vandervorst and T. Clarysce, J. Lac. Sci . Technol . BI0 0992) 302. K. Wittmaack, Sec-dary Ion Mass Spectrometry SIMS
(131 [14] 115] [16] [17] [18]
(19]
Vlll, eds. A. Benninghoven et al. (Wiley, Chichester, 1992). K. Wittmaack and J.B . Clegg. Appl . Phys. Lett. 37 (1980) 285. S.D. Lrttlewood and J.A. Kilner. J. Appl. Phys. 63 (1988) 2173. A .E. Morgan and P. Maillot, Secondary Ion Mass Spectrometr,, , SIMS VI, eds. A. Benninghoven, A.M . Huber and II.W. Werner (Wiley, Chichester . 1988) p. 709. R. von Criegern, l . Weitzel and J. Fottner, Secondary Ion Mass Spectrometry SIMS IV, eds. A. Benninghoveu et al. (Springer, Berlin, 1984) p 308. S.M. Daiser, C. Scholte and J.L. Maul, Nucl . Instr . and Meth. B35 (1988) 544. The Al-on-Si test patterns were kindly provided by M. Harde. Heinrich-Hertz-Institut, Berlin . K. Wittmaack, Nucl. instr . and Meth . 168(1980) 343. W. Vandervorst and H.W. Werner, Secondary Ion Mass Spectrometry SIMS VI, eds. A. Benninghoven, A.M . Huber and H.W . Werner (Wiley, Chichester, 1988) p. 4119 . K. Wittmaack, Surf. Sci . 112 (1981) 168 .