Electrical Activity of B and As Segregated at the Si-SiO 2 Interface
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Electrical Activity of B and As Segregated at the Si-SiO2 Interface Jens Frühauf1,2, Richard Lindsay3, Andreas Bergmaier2, Wilfried Vandervorst3, Georg Tempel1, Karen Maex3, Günther Dollinger2 and Frederick Koch2 1 Infineon technologies AG, affiliated to IMEC vzw, Kapeldreef 75, B-3001 Leuven, Belgium 2 Technische Universität München, Physik-Department, Garching, Germany 3 IMEC vzw, Leuven, Belgium Corresponding author: [email protected] ABSTRACT During spike annealing of ultra-shallow junctions, large fractions of the dopants form a partially active pile-up at the interface between silicon and the screening oxide layer. In this paper, we show results of sheet resistance, SIMS and high resolution Elastic Recoil Detection measurements to investigate the physical and electrical behaviour of B and As dopant atoms at the interface. Our results show that the fraction of dopants segregated at the interface is as high as 30-50% for B, but is dependent on dose and the type of screening oxide. Concentrations of up to 3e20cm-3 and more of active dopants are found on the Si side of the interface. The presence of nitrogen in the oxide at the interface causes a higher and sharper pile-up. Results indicate that a similar peak is expected for As, with active concentrations above 6e20cm-3. In an HF dip, the pile-up is removed together with the oxide or deactivated during native oxide regrowth. Further experiments show that immediately after removing the screening oxide in an HF dip the sheet resistance for B decreases sharply due to carrier accumulation, then raises to about 6-9% above the initial level depending on the oxide and dopant species. The sharp decrease in resistance is not observed for As. INTRODUCTION To form ultra-shallow junctions, dopants are usually implanted with projected ranges 0.3nm thick and does extent into the oxide and/or silicon. Comparing BF2 implants with different doses, fig. 2a shows that for doses of 1e14cm-2 and 4e14-2, around 30% of the observed dopants have segregated to the interface pile-up. For the 1e15cm-2 implant however, this number increases to 46%. SIMS does not resolve the pile-up in detail (cf. [3]), but confirms the dose within 10%, when integrating over the top 5nm. Only for sample C (with oxynitride), a 30% dose difference is seen between ERD and SIMS. C3.4.2
a)
b) at% 80
Sample B
at% 1.6
O
80 at%
at% 1.6
Sample C
1.4
70
1.2
60
1.2
1
50
1
40
0.8
40
0.8
30
0.6
30
0.6
20
0.4
20
0.2
10
70 60
B as-impl.
50
B
10
0
0 -2
0
2
4
6
1.4
O
0.4
B
0.2
N
0
0
nm 8
-2
0
2
4
6
nm 8
Figure 1 – ERD depth profiles of samples B, C and E (cf. Table I). The concentrations are given on a linear scale in atomic %, on the left scale for the O and N content, on the right scale for the B content. The dashed line indicates the average interface depth. For sample B, the as-implanted profile is shown for comparison. a)
b)
1E+22
1E+24
-3
-3
cm
cm 1E+23
H, x1000
D, 1e15
1E+21
G, x100 1E+22
B, 4e14
F, x10 1E+21
1E+20
1E+20 E, x1
A, 1e14 1E+19
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