Conclusions

In conclusion, we have investigated the effect of C I/I on the thermal stability of the NiSi film. Adding C into NiSi significantly enhances the NiSi thermal stability.

Improved efficiency depends on the quantity of the C I/I dose. For the CIA samples implanted with a dose of 5x10¹⁵ cm^-2, the sustainable process temperature can be improved from 700 °C to 850 °C with the tradeoff of ~10 % increase of the Rs values.

Furthermore, it is verified that the C I/I process, regardless of whether As dopants exist, is indeed useful for improving the thermal stability of the NiSi film at high temperatures. Our experimental results show that the agglomeration and phase transformation temperatures increase from 700-750 °C to 800 °C at least.

We also study the influence of the CPIII technology on the formation of the Ni-silicide film. The deposition of the DLC film during the C PIII process plays an important role in forming the Ni-silicide film. When the implantation voltage is equal to 3 kV, the DLC film will become a block layer between the Ni film and the Si substrate and prevent the formation of Ni silicide. Therefore, the silicide formation

temperature must be increased to 800-900 °C to form the Ni-silicide film. When the implantation voltage is increased to 5 kV, the Ni-silicide film can be normally formed at 500 °C. We find that the C3K1M and C5K1M samples exhibit poor thermal stability of NiSi due to insufficient implanted C atoms at the Ni-silicide grain boundary and Ni-silicide/Si interface. A tradeoff exists between the C PIII dose and the thickness of the DLC film. As the C PIII process is applied in the future, the impact of the DLC film must be carefully considered, or the appropriate etching technology must be developed to remove the DLC film.

References

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Table 2-1 Summary of substrate types, experimental splits, and their corresponding

Table 2-2 Summary of the agglomeration and phase transformation temperatures of all samples.

Notations C I/I condition Agglomeration temperature (°C)

500 600 700 800 900 2

3 4 5 6 7 8 9 10 11

CIA: 30 keV/1x10¹⁵ cm^-2 CIA: 30 keV/5x10¹⁵ cm^-2 CIA: 40 keV/1x10¹⁵ cm^-2 CIA: 40 keV/5x10¹⁵ cm^-2 reference1: w/o C I/I

R s (Ω/F)

Tempeture (^oC)

Fig. 2-1 Rs values of the CIA samples and control1 samples as a function of annealing temperaure for 30 sec.

5 μm (a) 600

^o

C

5 μm

5 μm 5 μm

(b) 700

^o

C

(c) 800

^o

C (d) 850

^o

C

Fig. 2-2 Plan-view SEM micrographs of the CIA samples implanted at 40 keV with a dose of 1x10¹⁵ cm^-2: (a) 600 °C, (b) 700°C, (c) 800°C, and (d) 850°C.

30 35 40 45 50 55 60

Fig. 2-3 XRD spectra of the CIA samples implanted at 40 keV with a dose of 1x10¹⁵ cm^-2. The silicide formation temperatures are labeled in the figure.

5 μm

Fig. 2-4 SEM micrographs of the CIA samples implanted at 40 keV with a dose of 5x10¹⁵ cm^-2 with different silicide formation temperatures: (a) 600 °C, (b) 700°C, (c) 800°C, and (d) 850°C.

30 35 40 45 50 55 60

Fig. 2-5 XRD spectra of the CIA samples implanted at 40 keV with a dose of 5x10¹⁵ cm^-2. The silicide formation temperatures are labeled in the figure.

Si substrate 20 nm

NiSi (52 nm) C I/I: 40 keV/5x10¹⁵cm^-2

silicide formation: 500 ^oC

Fig. 2-6 Cross-sectional TEM image of the CIA sample implanted at 40 keV with a dose of 5x10¹⁵ cm^-2 after silicide formation at 500 °C for 30 sec.

0 100 200 300 400 500 silicide formation: 500 ^oC

10⁰

Fig. 2-7 SIMS depth profile of the CIA sample implanted at 40 keV with a dose of 5x10¹⁵ cm^-2 after silicide formation at 500 °C for 30 sec.

500 600 700 800 900

2

Fig. 2-8 Rs values of the w/o CIA samples as a function of annealing temperaure for 30 sec.

5 μm 5 μm (b) 800

^o

C (c) 850

^o

C

5 μm (a) 700

^o

C

Fig. 2-9 SEM micrographs of the w/o CIA samples implanted at 30 keV with a dose of 1x10¹⁵ cm^-2 with different silicide formation temperatures: (a) 700 °C, (b) 800°C, and (c) 850°C.

Fig. 2-10 XRD spectra of the w/o CIA samples implanted at 30 keV with a dose of 1x10¹⁵ cm^-2. The silicide formation temperatures are labeled in the figure.

5 μm

Fig. 2-11 SEM micrographs of the w/o CIA samples implanted at 30 keV with a dose of 5x10¹⁵ cm^-2 with different silicide formation temperatures: (a) 600 °C, (b) 700°C, (c) 800°C, and (d) 850°C.

Fig. 2-12 XRD spectra of the w/o CIA samples implanted at 30 keV with a dose of 5x10¹⁵ cm^-2. The silicide formation temperatures are labeled in the figure.

500 600 700 800 900 0

100 200 300 400

TNS

reference2

R s (Ω/F)

Tempeture (^oC)

Fig. 2-13 Rs values of the TNS samples and control2 samples as a function of annealing temperaure for 30 sec.

5 μm 5 μm 5 μm

5 μm 5 μm

(a) 500

^o

C (b) 600

^o

C (c) 700

^o

C

(d) 800

^o

C (e) 850

^o

C

Fig. 2-14 SEM micrographs of the TNS samples implanted at 7 keV with a dose of 5x10¹⁵ cm^-2 with different silicide formation temperatures: (a) 500 °C, (b) 600°C, (c) 700°C, (d) 800°C, and (e) 850°C.

5 μm 5 μm 5 μm

5 μm 5 μm

(a) 500

^o

C (b) 600

^o

C (c) 700

^o

C

(d) 800

^o

C (e) 850

^o

C

Fig. 2-15 SEM micrographs of the control2 samples with different silicide formation temperatures: (a) 500 °C, (b) 600°C, (c) 700°C, (d) 800°C, and (e) 850°C.

500 600 700 800

2 3 4 5 6

C5As35 C1As35 C0As35

R s (Ω/F)

Tempeture (^oC)

Fig. 2-16 Rs values as a function of silicide formation temperature with As I/I energy at 35 keV and different C I/I doses.

4 μm (a) 600

^o

C

4 μm

4 μm 4 μm

(b) 700

^o

C

(c) 750

^o

C (d) 800

^o

C

Fig. 2-17 SEM micrographs of the C0As35 samples with different silicide formation temperatures: (a) 600 °C, (b) 700 °C, (c) 750 °C, and (d) 800 °C.

4 μm (a) 600

^o

C

4 μm

4 μm 4 μm

(b) 700

^o

C

(c) 750

^o

C (d) 800

^o

C

Fig. 2-18 SEM micrographs of the C1As35 samples with different silicide formation temperatures: (a) 600 °C, (b) 700 °C, (c) 750 °C, and (d) 800 °C.

4 μm (a) 600

^o

C

4 μm

4 μm 4 μm

(b) 700

^o

C

(c) 750

^o

C (d) 800

^o

C

Fig. 2-19 SEM micrographs of the C5As35 samples with different silicide formation temperatures: (a) 600 °C, (b) 700 °C, (c) 750 °C, and (d) 800 °C.

40 45 50 55 60 65 70 75

10¹ 10² 10³ 10⁴ 10⁵ 10⁶ 10⁷ 10⁸

700^oC 750^oC 800^oC

Intensity (arb. unit)

2θ (deg)

NiSi(304) Si(400) NiSi 2(400)

Si

Fig. 2-20 XRD spectra of the C1As35 samples. The silicide formation temperatures are labeled in the figure.

40 45 50 55 60 65 70 75

Fig. 2-21 XRD spectra of the C5As35 samples. The silicide formation temperatures are labeled in the figure.

500 600 700 800

Fig. 2-22 Rs values as a function of silicide formation temperature with As I/I energy at 85 keV and different C I/I doses.

4 μm

Fig. 2-23 SEM micrographs at the agglomeration temperature with As I/I energy at 85 keV and various C I/I doses: (a) C0As85 at 700 °C, (b) C1As85 at 750

Fig. 2-24 XRD spectra at the phase transformation temperature with As I/I energy at 85 keV and various C I/I doses.

C PIII: 3 kV/5 min

amorphous Si (27 nm) oxide

capping layer

DLC film (4 nm)

20 nm

Fig. 2-25 Cross-sectional TEM image of the C PIII sample implanted at 3 kV for 5 min.

500 600 700 800 900

0 100 200 300 400

C PIII: 3 kV/1 min C PIII: 5 kV/1 min

R s (Ω/F)

Tempeture (^oC)

Fig. 2-26 Rs values of the C3K1M and C5K1M samples as a function of annealing temperaure for 30 sec.

30 35 40 45 50 55 60 65 70 75

Fig. 2-27 XRD spectra of the C3K1M samples. The silicide formation temperatures are labeled in the figure.

5 μm 5 μm 5 μm

5 μm 5 μm

(a) 500

^o

C (b) 600

^o

C (c) 700

^o

C

(d) 800

^o

C (e) 900

^o

C

Fig. 2-28 SEM micrographs of the C3K1M samples with different silicide formation temperatures: (a) 500 °C, (b) 600 °C, (c) 700 °C, (d) 800 °C, and (e) 900

°C.

30 35 40 45 50 55 60 65 70 75

Fig. 2-29 XRD spectra of the C5K1M samples. The silicide formation temperatures are labeled in the figure.

5 μm 5 μm 5 μm

5 μm 5 μm

(a) 500

^o

C (b) 600

^o

C (c) 700

^o

C

(d) 800

^o

C (e) 900

^o

C

Fig. 2-30 SEM micrographs of the C5K1M samples with different silicide formation temperatures: (a) 500 °C, (b) 600 °C, (c) 700 °C, (d) 800 °C, and (e) 900

°C.

Chapter 3

Electrical Characteristics of

Nickel-Silicide-Contacted Junctions with Carbon Ion Implantation

3.1 Introduction

For sub-100-nm technology nodes, a self-aligned Ni silicide technology is useful to reduce the S/D parasitic resistance in MOSFETs owing to several advantages [1].

The scaling of the junction depth is essential to control the SCE of MOSFETs.

Therefore, the relatively thin silicide S/D contacts having good high-temperature stability are required for ultra-shallow S/D junctions. In chapter 2, we have demonstrated that the thermal stability of the NiSi/Si structure can be improved by high-dose C I/I. In the past, the advantages and disadvantages of C atoms in Si were extensively researched. Many studies focused on ultra-shallow junction formation by co-implanting C ions into the Si substrate [2-5]. Carbon atoms can act as traps and capture Si self-interstitials to form C-Si complexes, and ultra-shallow junctions are achieved by eliminating the interstitial-assisted dopant diffusion. However, the corresponding junction characteristics were not reported in these papers. Only a few papers reported the C-doped pn junction characteristics [6-8]. S. Lombardo et al.

found that C-Si complexes belonged to neutral scattering centers and recombination-generation centers in the Si band gap. In addition, an interstitial C

atom is another deep-level center in Si [8]. Once the C-Si complexes and interstitial C atoms locate within the junction depletion region, the C-doped junction characteristics deviate from the ideal characteristics [6, 8]. C. F. Tan et al. reported that doping C atoms into Si can reduce junction leakage owing to the elimination of secondary defects [7]. Therefore, C atoms in Si have strong effects on the electrical characteristics of ultra-shallow junctions.

The impact of the C I/I process on the current-voltage (I-V) characteristics of the Ni-silicide-contacted Schottky junctions has not been previously reported and will be discussed later in this chapter. Moreover, the I-V characteristics of the Ni-silicide-contacted n⁺/p shallow junctions have not been studied in detail. In this chapter, we demonstrate and discuss the trade-off between the thermal stability of the NiSi film and the I-V characteristics of the Ni-silicide-contacted n⁺/p shallow junction.

Some methods of fabricating the Ni-silicide-contacted n⁺/p shallow junctions with both good thermal stability and excellent I-V characteristics are proposed.

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