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Interaction effects between arsenic and boron ions implanted in silicon during furnace annealing and RTA
39/numbers Printed in Great Britain
Vacuum/volume
24Jpages
0042-207X/89$3.00+.00 Pergamon Press plc
205 to 207/I 989
Interaction effects between arsenic and boron ions implanted in silicon during furnace annealing and RTA Li Guohui, University,
Ma Yi, Zhang Tonghe Beijing,
and Luo Yan, Low-energy
Nuclear
Physics Institute,
Beijing Normal
PRC
Furnace annealing of boron and As co-implanted silicon results in a retarded base diffusion. This is mainly due to vacancy undersaturation, the emitter internal electric field and boron-arsenic ion pairing. The influence of implantation damage can be neglected. Using rapid thermal annealing good n-p-n junctions can be formed at 7 700°C for 7 min; the retarded base diffusion can be neglected.
1. Introduction In order to fabricate bipolar circuits boron and arsenic coimplantation has been used. During thermal diffusion the interaction effects between phosphorus and gallium, phosphorus and boron, as well as arsenic and boron have been investigated’. With a boron diffusion base and a phosphorus emitter there is enhanced diffusion of the base. This is the emitter push effect. However, with a boron diffusion base and an arsenic emitter, there is retarded diffusion of the base. The dip of the boron concentration near the emitter junction has been obtained’. Boron and arsenic co-implantation profiles have been discussed by Hofker et ~l*,~. The conditions for and the mechanisms of retarded base diffusion in boron and arsenic co-implantation during furnace annealing and RTA were researched in this work.
a distance of at least the diffusion length of vacancies (l-2 pm at 1000”C)4. Vacancy undersaturation is caused by vacancy concentration reduction. Because boron diffusion is mainly vacancy diffusion, the diffusion of the base was retarded. For As doses of 5 x lOI cm-’ the electrical activity can reach 100% so that the formed ( Vsi AsJ complexes are fewer. Consequently vacancy undersaturation does not occur, and there is no retarded base diffusion. This result indicates that retarded base diffusion is mainly due to ‘long range’ interactions of the vacancy undersaturation condition created by ( Vsi As,) complex formation’.
4000
.
-
2. Experimental results and discussion /
Silicon wafers of orientation (111) with 0.354.4 R-cm resistivity were used. As+ ions, 80-160 keV, at doses of 5 x 10”-1 x lOI cm-* and 60 keV B+ ions at doses of 2 x 1014-3 x 1O’j cm-’ were implanted. After ion implantation, the samples were treated by furnace or halogen light rapid annealing. The junction depths near the single-double implantation interfaces were measured by lapping and electrolysis junction staining. Carrier profiles were measured by the spreading resistance method. The samples were implanted with 150 keV As+ at 1 x lOI cm-*, 60 keV B+ at 3 x lOI cm-’ and were annealed in a furnace at 1000-I 100°C. The base depths were decreased (Figure 2(a)). The retarded base diffusion depth 6 vs annealing time and temperature is shown in Figure l(a), 6 = Xjk-Xj,, here X,, and Xjp are the boron junction depths in double and single implantation, respectively (Figure l(b)). The retarded base diffusion increases with the rise in temperature and annealing time. Photographs of the junction depths of several samples are shown in Figure 2. There was no retarded base diffusion in samples implanted with 70 keV B+ at 1 x lOI cm-’ and 80 keV As+ 5 x lOI cm-’ and annealed at 1000°C for 30 min (Figure 2(b)). At a dose of 1 x lOI cm-’ the vacancy complex (Vs, As,) was formed by the excess arsenic of the emitter. The vacancy concentration decreases outwards towards the emitter region to
M
/
.
I 60
I 40
Annealing time (mln)
(a)
(b)
1
SI
substmte
Figure 1. (a) The retarded base movement @-As+ 150keV 1 x 10’hcm~2; B+ 60keV3 anneal, 1lOO”C, lower 1000°C. O-As+ 150 30 min; B+ 140 keV 3 x 10” cm-* lOOO”C, matic diagram of the retarded base diffusion
1
depth 6 vs annealing time. x 1015cm~2.Uppercurve: keV 1 x 10lb cm-‘, 1 lOo”C, 30 min annealing. (b) Scheunder an As emitter.
205
Li Guohui et al: Interaction effects between arsenrc and boron
5
c L 04
Depth (pm)
Si Substrate (b)
.
’ “-
-
.A_
Figure 3. The carnrr profiles of LRTA at II00 C. (B ’ NJ keV 3 x IO cm ?: As. 150 kcV I x IO’” cm ‘). x--B implantation IO s annealing. e---As+ B implantation IO s annealing. n-B implantation I min annealing. m-As + B implantation I min unnealing.
60 keV Si + implantation at I x IO” cm ’ The same base junction depths wcrc obtained in samples of single boron and silicon boron double implantation (Figure 2(c)). The damage of the implanted layer dots not influence the base junction depth. Therefore for retarded base diffusion the influence of implantation damage can be neglected. The carrier profiles of RTA samples at I 100 C for IO s and I min were measured by the spreading resistance method (Figurc 3). For the IO s annealing time samples, the arsenic electrical activity was lower but the B junction was dccpencd. This is due to the boron transient enhanced diffusion cffcct. However the base junction depths wcrc smaller than those of single boron implanted samples. In this case the boron cnhanccd diffusion was reduced by As implantation. When the implanted samples wcrc annealed at 1100°C for 1 min the arsenic atoms were mostly activated and good n p n junctions were formed. The dip of the B carrier profile near the emitter junction disappeared. In thih situation the transient enhanced diffusion cffcct was reduced so that the retarded base diffusion disappcarcd. If the annealing time was increased, the retarded base diffusion would be similar to that of thermal diffusion. retarded
base diffusion.
was used to replace As implantation.
depth photographs ( xX00). (a) R’ 60 keV 3 x IO“ I x IOlh cm- 2, II00 C 15 min annealing. (b) B. 70 kcV I x IO“ cm ‘; As’ X0kcV 5 x IO“ cm 2~ 1000 c‘ 30 min annealing. (c) B’ 60 kcV 3 x IO“ cm ‘. Si ’ 60 keV I x IO’” cm ‘. 1000 C 30 min annealing. Figure 2.
cm
‘. As’
Junction 150 keV
For samples implanted with As and annealed at 1100 C the retarded base diffusion is grcatcr than for the simultaneously annealed samples (Figure I (a)). This is because boron moved to the emitter under the influence of the emitter junction electrical field in the narrower base (within 2000 A). In this case. because thcrc is emitter boron-arsenic ion pairing, the diffusion of boron is decreased. Thercforc when the base width is 1000-2000 A, the two factors mentioned above are dominant. So as to research the influence of implantation damage in the 206
3. Conclusion
During furnace annealing, a retarded base ditfusion was found for boron and arsenic co-implanted silicon at arsenic doses 01 I x IO” cm ‘. This is mainly due to vacancy undersaturation
Li Guohui et a/: Interaction
effects between
arsenic and boron
by (V,, As,) complex formation. When the base region is narrower the emitter junction electric field and the boron-arsenic ion pairing have a larger influence. Implantation damage can be neglected. During light rapid thermal annealing (RTA) for 10 s, a smaller retarded base diffusion was obtained ; this is not so for RTA for 30-60 s, and probably results from the implanted arsenic reducing the boron transient enhanced diffusion within 10 s.
created
References
‘A F W Willoughby, Impurity Doping Processe.~ in Silicon (Edited by F F Y Wang), p 1. North-Holland, Amsterdam (1981). *Ma Yi, Chinese J Semiconductors, 7,210 (1986). ’ W K Hofkor, Application of Ion Beam to Materials (Edited by G Carter et a/), p 13. Institute of Physics, London (1975). 4 R B Fair, Solid-State Electron, 7, 17 (1974). ‘R B Fair, Jappl Phys, 44,283 (1973).
207
Vacuum/volume
24Jpages
0042-207X/89$3.00+.00 Pergamon Press plc
205 to 207/I 989
Interaction effects between arsenic and boron ions implanted in silicon during furnace annealing and RTA Li Guohui, University,
Ma Yi, Zhang Tonghe Beijing,
and Luo Yan, Low-energy
Nuclear
Physics Institute,
Beijing Normal
PRC
Furnace annealing of boron and As co-implanted silicon results in a retarded base diffusion. This is mainly due to vacancy undersaturation, the emitter internal electric field and boron-arsenic ion pairing. The influence of implantation damage can be neglected. Using rapid thermal annealing good n-p-n junctions can be formed at 7 700°C for 7 min; the retarded base diffusion can be neglected.
1. Introduction In order to fabricate bipolar circuits boron and arsenic coimplantation has been used. During thermal diffusion the interaction effects between phosphorus and gallium, phosphorus and boron, as well as arsenic and boron have been investigated’. With a boron diffusion base and a phosphorus emitter there is enhanced diffusion of the base. This is the emitter push effect. However, with a boron diffusion base and an arsenic emitter, there is retarded diffusion of the base. The dip of the boron concentration near the emitter junction has been obtained’. Boron and arsenic co-implantation profiles have been discussed by Hofker et ~l*,~. The conditions for and the mechanisms of retarded base diffusion in boron and arsenic co-implantation during furnace annealing and RTA were researched in this work.
a distance of at least the diffusion length of vacancies (l-2 pm at 1000”C)4. Vacancy undersaturation is caused by vacancy concentration reduction. Because boron diffusion is mainly vacancy diffusion, the diffusion of the base was retarded. For As doses of 5 x lOI cm-’ the electrical activity can reach 100% so that the formed ( Vsi AsJ complexes are fewer. Consequently vacancy undersaturation does not occur, and there is no retarded base diffusion. This result indicates that retarded base diffusion is mainly due to ‘long range’ interactions of the vacancy undersaturation condition created by ( Vsi As,) complex formation’.
4000
.
-
2. Experimental results and discussion /
Silicon wafers of orientation (111) with 0.354.4 R-cm resistivity were used. As+ ions, 80-160 keV, at doses of 5 x 10”-1 x lOI cm-* and 60 keV B+ ions at doses of 2 x 1014-3 x 1O’j cm-’ were implanted. After ion implantation, the samples were treated by furnace or halogen light rapid annealing. The junction depths near the single-double implantation interfaces were measured by lapping and electrolysis junction staining. Carrier profiles were measured by the spreading resistance method. The samples were implanted with 150 keV As+ at 1 x lOI cm-*, 60 keV B+ at 3 x lOI cm-’ and were annealed in a furnace at 1000-I 100°C. The base depths were decreased (Figure 2(a)). The retarded base diffusion depth 6 vs annealing time and temperature is shown in Figure l(a), 6 = Xjk-Xj,, here X,, and Xjp are the boron junction depths in double and single implantation, respectively (Figure l(b)). The retarded base diffusion increases with the rise in temperature and annealing time. Photographs of the junction depths of several samples are shown in Figure 2. There was no retarded base diffusion in samples implanted with 70 keV B+ at 1 x lOI cm-’ and 80 keV As+ 5 x lOI cm-’ and annealed at 1000°C for 30 min (Figure 2(b)). At a dose of 1 x lOI cm-’ the vacancy complex (Vs, As,) was formed by the excess arsenic of the emitter. The vacancy concentration decreases outwards towards the emitter region to
M
/
.
I 60
I 40
Annealing time (mln)
(a)
(b)
1
SI
substmte
Figure 1. (a) The retarded base movement @-As+ 150keV 1 x 10’hcm~2; B+ 60keV3 anneal, 1lOO”C, lower 1000°C. O-As+ 150 30 min; B+ 140 keV 3 x 10” cm-* lOOO”C, matic diagram of the retarded base diffusion
1
depth 6 vs annealing time. x 1015cm~2.Uppercurve: keV 1 x 10lb cm-‘, 1 lOo”C, 30 min annealing. (b) Scheunder an As emitter.
205
Li Guohui et al: Interaction effects between arsenrc and boron
5
c L 04
Depth (pm)
Si Substrate (b)
.
’ “-
-
.A_
Figure 3. The carnrr profiles of LRTA at II00 C. (B ’ NJ keV 3 x IO cm ?: As. 150 kcV I x IO’” cm ‘). x--B implantation IO s annealing. e---As+ B implantation IO s annealing. n-B implantation I min annealing. m-As + B implantation I min unnealing.
60 keV Si + implantation at I x IO” cm ’ The same base junction depths wcrc obtained in samples of single boron and silicon boron double implantation (Figure 2(c)). The damage of the implanted layer dots not influence the base junction depth. Therefore for retarded base diffusion the influence of implantation damage can be neglected. The carrier profiles of RTA samples at I 100 C for IO s and I min were measured by the spreading resistance method (Figurc 3). For the IO s annealing time samples, the arsenic electrical activity was lower but the B junction was dccpencd. This is due to the boron transient enhanced diffusion cffcct. However the base junction depths wcrc smaller than those of single boron implanted samples. In this case the boron cnhanccd diffusion was reduced by As implantation. When the implanted samples wcrc annealed at 1100°C for 1 min the arsenic atoms were mostly activated and good n p n junctions were formed. The dip of the B carrier profile near the emitter junction disappeared. In thih situation the transient enhanced diffusion cffcct was reduced so that the retarded base diffusion disappcarcd. If the annealing time was increased, the retarded base diffusion would be similar to that of thermal diffusion. retarded
base diffusion.
was used to replace As implantation.
depth photographs ( xX00). (a) R’ 60 keV 3 x IO“ I x IOlh cm- 2, II00 C 15 min annealing. (b) B. 70 kcV I x IO“ cm ‘; As’ X0kcV 5 x IO“ cm 2~ 1000 c‘ 30 min annealing. (c) B’ 60 kcV 3 x IO“ cm ‘. Si ’ 60 keV I x IO’” cm ‘. 1000 C 30 min annealing. Figure 2.
cm
‘. As’
Junction 150 keV
For samples implanted with As and annealed at 1100 C the retarded base diffusion is grcatcr than for the simultaneously annealed samples (Figure I (a)). This is because boron moved to the emitter under the influence of the emitter junction electrical field in the narrower base (within 2000 A). In this case. because thcrc is emitter boron-arsenic ion pairing, the diffusion of boron is decreased. Thercforc when the base width is 1000-2000 A, the two factors mentioned above are dominant. So as to research the influence of implantation damage in the 206
3. Conclusion
During furnace annealing, a retarded base ditfusion was found for boron and arsenic co-implanted silicon at arsenic doses 01 I x IO” cm ‘. This is mainly due to vacancy undersaturation
Li Guohui et a/: Interaction
effects between
arsenic and boron
by (V,, As,) complex formation. When the base region is narrower the emitter junction electric field and the boron-arsenic ion pairing have a larger influence. Implantation damage can be neglected. During light rapid thermal annealing (RTA) for 10 s, a smaller retarded base diffusion was obtained ; this is not so for RTA for 30-60 s, and probably results from the implanted arsenic reducing the boron transient enhanced diffusion within 10 s.
created
References
‘A F W Willoughby, Impurity Doping Processe.~ in Silicon (Edited by F F Y Wang), p 1. North-Holland, Amsterdam (1981). *Ma Yi, Chinese J Semiconductors, 7,210 (1986). ’ W K Hofkor, Application of Ion Beam to Materials (Edited by G Carter et a/), p 13. Institute of Physics, London (1975). 4 R B Fair, Solid-State Electron, 7, 17 (1974). ‘R B Fair, Jappl Phys, 44,283 (1973).
207