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Kinetics of large B clusters in crystalline and preamorphized silicon
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10.1063/1.3639280
/content/aip/journal/jap/110/7/10.1063/1.3639280
http://aip.metastore.ingenta.com/content/aip/journal/jap/110/7/10.1063/1.3639280
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(Color online) Schematic representations of (a) the energetics of the several BIC configurations (B n I m ) referred to the perfect lattice and (b) the main features of the proposed model which includes four main regions. (a) Oblique (red) and vertical (blue) arrows represent the formation/dissolution paths for the different configurations through the trapping/emission of mobile species boron-interstitial (Bi) and Si interstitial (I), respectively. (b) Gray and white arrows distinguish between formation and dissolution paths, respectively, whereas solid and dashed arrows indicate high and low probability paths, respectively.

Image of FIG. 2.
FIG. 2.

(Color online) Experimental data [15] and simulation results for the evolution of the normalized clustered B dose as a function of the second annealing step time at 900 °C for samples S1 (1 × 1019 B/cm3 B box), S2 (5 × 1019 B/cm3 B box) and S3 (2 × 1020 B/cm3 B box) implanted with 20 keV, 1014 Si ions/cm2. The inclusion of very stable BICs with more than four B atoms in the model—represented as normalized dose of large BICs in the figure—allow us to capture the firstly faster and later slower regimes of dissolution observed experimentally for high B concentration samples S2 and S3.

Image of FIG. 3.
FIG. 3.

(Color online) Simulated time evolution of the doses of electrically active B, Si Is stored in Si interstitial defects, B atoms and Is stored in BICs (both small and large BICs) and B atoms and Is stored in large BICs, as extracted from simulation for sample S3. This figure includes the evolution of doses during (a) the 20 keV, 1014 Si ions/cm2 implant at room temperature, (b) the first step annealing at 815 °C for 5 min, and (c) the second step annealing at 900 °C. Dashed line represents the instant at which the end of the ramp up (at 50 °C/s) to the target temperature of the first step annealing at 815 °C is reached.

Image of FIG. 4.
FIG. 4.

(Color online) Simulated depth profiles for crystalline Si samples implanted with 500 eV B ions to a dose of 1 × 1015 B/cm2 and subsequently annealed at 650 °C for 10 s (pre-stabilization annealing step) and then spike annealed at 1050 °C and 1100 °C using a 250 °C/s ramp-up rate. Simulations evidence the presence of a characteristic B concentration peak at a depth of ∼2 nm, in agreement to experiments [13], typically associated to the formation of BICs. As the thermal budget increases, the B concentration peak decreases and the tail region of the B profile broadens, similarly to experimental SIMS profiles [13].

Image of FIG. 5.
FIG. 5.

(Color online) Simulated time evolution of the doses of electrically active B, Si Is stored in Si interstitial defects, B atoms and Is stored in BICs (both small and large BICs) and B atoms and Is stored in large BICs, as extracted from simulation of a crystalline Si sample implanted with 500 eV B ions to a dose of 1 × 1015 B/cm2. This figure includes the evolution of doses during (a) the B implant at room temperature, (b) the pre-stabilization annealing step at 650 °C for 10 s using a 250 °C/s ramp-up rate, and (c) the second step spike annealing at 1050 °C using a 250 °C/s ramp-up rate. Dashed lines represent the end of the ramp up to the target temperatures.

Image of FIG. 6.
FIG. 6.

(Color online) Electrically active B concentration and the ratio of groups with two, three, or four B atoms resulting after low-temperature SPER theoretical simulations as a function of B concentration. Simulations lead to an electrically active B concentration around 2 × 1020 B/cm3, in very good agreement with the experimental reported value for low-temperature SPER [7 and 8]. Group of two B atoms has the highest probability at the lower B concentration whereas groups containing three or four B atoms become more likely as B concentration increases.

Image of FIG. 7.
FIG. 7.

(Color online) Evolution of the experimental (symbols) and simulated (lines) electrically active B dose as a function of annealing time for (a and c) LB (12 keV, 3 × 1015 B/cm2) and (b and d) HB (26 keV, 2 × 1016 B/cm2) samples during anneals at (a–b) 850 °C and (c–d) 1000 °C performed after SPER. Two different types of simulation are considered: dashed lines represent simulations performed by using our previous model for BICs (which only included small BICs) whereas solid lines correspond to simulations performed by using our full extended model for BICs (which shows a better agreement with experimental data).

Image of FIG. 8.
FIG. 8.

EFTEM images of the HB sample annealed at (a) 850 °C, 10 000 s and (b) 1100 °C, 30 s obtained by selecting the plasmon loss peak centered at 22 eV and by a 4-eV-wide energy slit. (c) B chemical map obtained by selecting the Boron K edge centered at 180 eV for the sample annealed at 1100 °C for 30 s. EFTEM images evidences (a) the formation of large BIC configurations after annealing at 850 °C for 10 000 s, which are very stable since (b) they survive after very intense annealing at 1100 °C, 30 s. The comparison between images (b) and (c) indicates that the observed defects are rich in B atoms.

Image of FIG. 9.
FIG. 9.

(Color online) Time evolution of experimental (a) sheet resistance and active B dose and (b and c) hole mobility as extracted from Hall measurements for HB sample during anneals at 850 °C and 1000 °C performed after SPER. The simulated time evolution of the dose of BICs during anneals is also included. Experiments indicate that sheet resistance and active B dose initially evolve with opposite trends, as it has been generally assumed. However, at long time anneals an “anomalous” behavior (marked with ovals) is observed, since the active B dose decreases at the same time that sheet resistance also decreases (large oval, 850 °C) or remains approximately constant (small oval, 1000 °C), contrary to expected. This apparently “anomalous” behavior is due to the high increase in mobility observed at long time anneals, contrary to the expected small range of variation of mobility (marked with dashed lines and estimated through Masetti’s expression [19]). A correlation between the high increase in mobility and the high decrease in the simulated density of BICs is observed. This suggests that mobility could be degraded by the presence of large densities of BICs.

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/content/aip/journal/jap/110/7/10.1063/1.3639280
2011-10-14
2014-04-17
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Kinetics of large B clusters in crystalline and preamorphized silicon
http://aip.metastore.ingenta.com/content/aip/journal/jap/110/7/10.1063/1.3639280
10.1063/1.3639280
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