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The effect of implant species on defect anneal kinetics part I: Silicon and phosphorus implantation
496
Nuclear Instruments and Methods in Physics Research B21 (1987) 496-498 North-Holland, Amsterdam
T H E E F F E C T O F I M P L A N T S P E C I E S O N D E F E C T A N N E A L K I N E T I C S P A R T I: SILICON AND PHOSPHORUS IMPLANTATION S. P R U S S I N ~) a n d K e v i n S. J O N E S 2) ~TT.R.W. Electronics Group, Redonda Beach, CA 90278, USA ")Dept. of Materials Science and Mineral Engineerin~ University of California, Berkeley, CA 94720, USA
The role of implant species on defect anneal kinetics was investigated by comparing the defect structures resulting from 5 × 10tS/cm2 implantations of phosphorus and silicon at 50 key into {100} silicon surfaces. Plan-view and cross-sectional TEM analyses were used. For the silicon implant, annealing at 900°C resulted in little change in the concentration and size of the dislocation loops with time. For the phosphorus implant, a significant loss in dislocation loop concentration was found together with an increase in loop diameter. Possible explanations for this effect are discussed.
1. Introduction
2. Experimental
The fraction of the implant energy which is lost by nuclear processes is, for a given ion species, a function of its mass. For two ions with very similar masses, such as Si + and P+, we expect to find very similar depositions of damage density. For implant doses of 5 × 10tS/cm 2 at 50 keV into (100) silicon wafers we obtain structures with surface amorphous layers 105 nm thick and similar end of range damage in the crystalline material just beyond the amorphous/crystalline interface. Low temperature recrystallization, e.g. 550°C, permits regrowth of the amorphous layer with only the end of range or category II [1] damage remaining.
In this study we implanted 100 mm {100} commercially polished p-type wafers with 5 X 1 0 1 5 / c m 2 P+ and Si + at 50 keV. After a recrystallization anneal, 4 h at 550°C, the wafers were subjected to a furnace anneal at 900°C in dry nitrogen for 30 min, 1, 2 and 4 h. Plan-view and cross-sectional TEM specimens were prepared and examined. All plan-view micrographs were taken under dark field conditions using a g04o two beam reflecting condition and are at the magnification labeled in fig. 1. All cross-sectional TEM micrographs were taken under bright field conditions using a g22o two beam reflecting condition and are at the magnification labeled in fig. 2.
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Fig. 1. Plan-view TEM micrograph of 5 × 10xs Si + cm -2 implant annealed 30 rain at 900°C. 0168-583X/87/$03.50 © Elsevier Science Pubfishers B.V. (North-Holland Physics Publishing Division)
Fig. 2. Cross-sectional TEM micrograph of 5 × 1015 Si + cm -2 implant annealed 30 rain at 900°C.
S. Prussin, K.S. Jones / Effect of implants on defect anneal kinetics
497
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Fig. 3. Plan-view TEM micrograph of 5 × 1015 Si+ cm -2 implant annealed 4 h at 9000C.
Fig. 5. Plan-view TEM micrograph of 5 × 1015 P+ cm -2 implant annealed 30 rain at 900"C.
Fig. 4. Cross-sectional TEM micrograph of 5 x 1015 Si + cm -2 implant annealed 4 h at 900°C.
Fig. 6. Cross-sectional TEM micrograph of 5 × 1015 P+ cm -2 implant annealed 30 rain at 900°C.
3. Results
show the effect of annealing this sample for 4 h at 9000C. The longer annealing time appears to have increased the diameter of the loops slightly and decreased their concentration also slightly, but relatively little change has occurred. Figs. 5 and 6, corresponding to a 30 rain anneal for the P+ implant, suggest that even for this short period the dislocation loops have undergone some solution and that the remainder have expanded in
Figs. 1 and 2 illustrate the array of dislocation loops found for the Si + implants after 30 rain in plan-view and cross-section respectively. This is a good example of the category II defect structure. The dislocation loops are extrinsic and located slightly deeper than where the amorphous/crystalline interface had been. Figs. 3 and 4
VII. RANGE/DAMAGE/SHALLOW JUNCTIONS
498
S. Prussin, K.S. Jones / Effect of implants on defect anneal kinetics
Fig. 7. Plan-view TEM micrograph of 5 x 10Is P+ cm -2 implant annealed 4 h at 900°C.
size. Figs. 7 and 8 illustrate the effect of a 4 h anneal onthe P+ implant. We note a very significant loss in concentration and an increase in size.
the defects are significant. These include the perturbation of point defect concentrations due to: 1. Impurity diffusion. 2. Stress fields from impurity atomic size misfit. 3. Electrical fields and charge concentration. 4. Precipitation and precipitate solution. Phosphorus diffusion has been credited with affecting the point defect concentration in such phenomena as emitter-dip effect [2]. The smaller tetrahedral covalent radius of phosphorus relative to silicon has been shown to lead to highly stressed areas [3]. The role of charge concentration on impurity diffusion has been attributed to its effect on the charged point defect concentrations. For a Gaussian distribution with a projected standard deviation of 0.0256 #m, we expect to find a peak phosphorus concentration of 7.8 × 102°/cm3. This is compared to the solid solubility of phosphorus at 900°C of 6.5 X 102°/cm3 [4]. Recent experimental work on the defect annealing kinetics for gallium implants suggests that precipitation may play the significant role in enhancing the defect anneal kinetics [5].
5. Conclusions 4. Discussion
The role of the implant species on the defect annealing kinetics suggests that factors in addition to the thermodynamic equilibrium driving force for solution of
From this experiment it is apparent, that the implant species plays a very significant role in the defect annealing kinetics. As discussed, the species may affect the defect kinetics in several ways. These include stress, diffusion, electric field and precipitation effects. As phosphorus imparts most of these effects it is not possible from this experiment alone to determine the dominant species-related factor influencing the defect kinetics. It can only be concluded that due to the limited reactions in the silicon implant, the driving force toward thermodynamic equilibrium is not a dominant effect at 900°C. The discussion of the species effect which dominates the defect annealing kinetics is further expanded upon in part II of this paper.
References
Fig. 8. Cross-sectional TEM micrograph of 5 × 1015 P+ cm -2 implant annealed 4 h at 900°C.
[1] S. Prussin and Kevin S. Jones, in: Materials Issues in Silicon Integrated Circuit Processing, eds., M. Strathman, J. Stimmel and M. Wittmer, Vol. 71, Proc. Mater. Res. Soc. (1986). [2] A.F.W. Willoughby, Impurity Doping, ed., F.F.Y. Wang (North-Holland, New York, 1981) p. 1. [3] S. Prussin, J. Appl. Phys. 32 (1961) 1876. [4] F.A. Trumbore, Bell Systems Technical Journal 39 (1962) 210. [5] S. Prussin and Kevin S. Jones (unpublished).
Nuclear Instruments and Methods in Physics Research B21 (1987) 496-498 North-Holland, Amsterdam
T H E E F F E C T O F I M P L A N T S P E C I E S O N D E F E C T A N N E A L K I N E T I C S P A R T I: SILICON AND PHOSPHORUS IMPLANTATION S. P R U S S I N ~) a n d K e v i n S. J O N E S 2) ~TT.R.W. Electronics Group, Redonda Beach, CA 90278, USA ")Dept. of Materials Science and Mineral Engineerin~ University of California, Berkeley, CA 94720, USA
The role of implant species on defect anneal kinetics was investigated by comparing the defect structures resulting from 5 × 10tS/cm2 implantations of phosphorus and silicon at 50 key into {100} silicon surfaces. Plan-view and cross-sectional TEM analyses were used. For the silicon implant, annealing at 900°C resulted in little change in the concentration and size of the dislocation loops with time. For the phosphorus implant, a significant loss in dislocation loop concentration was found together with an increase in loop diameter. Possible explanations for this effect are discussed.
1. Introduction
2. Experimental
The fraction of the implant energy which is lost by nuclear processes is, for a given ion species, a function of its mass. For two ions with very similar masses, such as Si + and P+, we expect to find very similar depositions of damage density. For implant doses of 5 × 10tS/cm 2 at 50 keV into (100) silicon wafers we obtain structures with surface amorphous layers 105 nm thick and similar end of range damage in the crystalline material just beyond the amorphous/crystalline interface. Low temperature recrystallization, e.g. 550°C, permits regrowth of the amorphous layer with only the end of range or category II [1] damage remaining.
In this study we implanted 100 mm {100} commercially polished p-type wafers with 5 X 1 0 1 5 / c m 2 P+ and Si + at 50 keV. After a recrystallization anneal, 4 h at 550°C, the wafers were subjected to a furnace anneal at 900°C in dry nitrogen for 30 min, 1, 2 and 4 h. Plan-view and cross-sectional TEM specimens were prepared and examined. All plan-view micrographs were taken under dark field conditions using a g04o two beam reflecting condition and are at the magnification labeled in fig. 1. All cross-sectional TEM micrographs were taken under bright field conditions using a g22o two beam reflecting condition and are at the magnification labeled in fig. 2.
C',* ,~
~
•
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•
0
o"
~ fit
.~ jk,~
o
.
.
YtA ~"
-1
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. ~
-
y
•
0 ~
"
,
•.
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,
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Fig. 1. Plan-view TEM micrograph of 5 × 10xs Si + cm -2 implant annealed 30 rain at 900°C. 0168-583X/87/$03.50 © Elsevier Science Pubfishers B.V. (North-Holland Physics Publishing Division)
Fig. 2. Cross-sectional TEM micrograph of 5 × 1015 Si + cm -2 implant annealed 30 rain at 900°C.
S. Prussin, K.S. Jones / Effect of implants on defect anneal kinetics
497
#
•
¢"
¢.,
•
h
L
Fig. 3. Plan-view TEM micrograph of 5 × 1015 Si+ cm -2 implant annealed 4 h at 9000C.
Fig. 5. Plan-view TEM micrograph of 5 × 1015 P+ cm -2 implant annealed 30 rain at 900"C.
Fig. 4. Cross-sectional TEM micrograph of 5 x 1015 Si + cm -2 implant annealed 4 h at 900°C.
Fig. 6. Cross-sectional TEM micrograph of 5 × 1015 P+ cm -2 implant annealed 30 rain at 900°C.
3. Results
show the effect of annealing this sample for 4 h at 9000C. The longer annealing time appears to have increased the diameter of the loops slightly and decreased their concentration also slightly, but relatively little change has occurred. Figs. 5 and 6, corresponding to a 30 rain anneal for the P+ implant, suggest that even for this short period the dislocation loops have undergone some solution and that the remainder have expanded in
Figs. 1 and 2 illustrate the array of dislocation loops found for the Si + implants after 30 rain in plan-view and cross-section respectively. This is a good example of the category II defect structure. The dislocation loops are extrinsic and located slightly deeper than where the amorphous/crystalline interface had been. Figs. 3 and 4
VII. RANGE/DAMAGE/SHALLOW JUNCTIONS
498
S. Prussin, K.S. Jones / Effect of implants on defect anneal kinetics
Fig. 7. Plan-view TEM micrograph of 5 x 10Is P+ cm -2 implant annealed 4 h at 900°C.
size. Figs. 7 and 8 illustrate the effect of a 4 h anneal onthe P+ implant. We note a very significant loss in concentration and an increase in size.
the defects are significant. These include the perturbation of point defect concentrations due to: 1. Impurity diffusion. 2. Stress fields from impurity atomic size misfit. 3. Electrical fields and charge concentration. 4. Precipitation and precipitate solution. Phosphorus diffusion has been credited with affecting the point defect concentration in such phenomena as emitter-dip effect [2]. The smaller tetrahedral covalent radius of phosphorus relative to silicon has been shown to lead to highly stressed areas [3]. The role of charge concentration on impurity diffusion has been attributed to its effect on the charged point defect concentrations. For a Gaussian distribution with a projected standard deviation of 0.0256 #m, we expect to find a peak phosphorus concentration of 7.8 × 102°/cm3. This is compared to the solid solubility of phosphorus at 900°C of 6.5 X 102°/cm3 [4]. Recent experimental work on the defect annealing kinetics for gallium implants suggests that precipitation may play the significant role in enhancing the defect anneal kinetics [5].
5. Conclusions 4. Discussion
The role of the implant species on the defect annealing kinetics suggests that factors in addition to the thermodynamic equilibrium driving force for solution of
From this experiment it is apparent, that the implant species plays a very significant role in the defect annealing kinetics. As discussed, the species may affect the defect kinetics in several ways. These include stress, diffusion, electric field and precipitation effects. As phosphorus imparts most of these effects it is not possible from this experiment alone to determine the dominant species-related factor influencing the defect kinetics. It can only be concluded that due to the limited reactions in the silicon implant, the driving force toward thermodynamic equilibrium is not a dominant effect at 900°C. The discussion of the species effect which dominates the defect annealing kinetics is further expanded upon in part II of this paper.
References
Fig. 8. Cross-sectional TEM micrograph of 5 × 1015 P+ cm -2 implant annealed 4 h at 900°C.
[1] S. Prussin and Kevin S. Jones, in: Materials Issues in Silicon Integrated Circuit Processing, eds., M. Strathman, J. Stimmel and M. Wittmer, Vol. 71, Proc. Mater. Res. Soc. (1986). [2] A.F.W. Willoughby, Impurity Doping, ed., F.F.Y. Wang (North-Holland, New York, 1981) p. 1. [3] S. Prussin, J. Appl. Phys. 32 (1961) 1876. [4] F.A. Trumbore, Bell Systems Technical Journal 39 (1962) 210. [5] S. Prussin and Kevin S. Jones (unpublished).