Devices using poly-Ge film as the channel material have been fabricated and the fundamental characteristics of devices also have been demonstrated. However, due to
34
small grain size formed by SPC method and the implanted damage, the advantages of Ge film are rarely observed. Hence, there are a lot of works ahead to further enhance the performance of devices. To improve the performance, some beneficial suggestions are listed as follows for the future works.
(1) Replace SPC method by using MIC or MILC method to form larger grain size Ge film. With larger grain size, the performance of devices can be further improved due to the decrease of grain boundaries and defects.
(2) Decrease the Ni film thickness to the extent that it is fully consumed by Ge or increase the annealing time in order to form NiGe for 30 nm poly-Ge film. By using nickel monogermanide as S/D material or using MIDA technique to activate dopants, device performance is expected to be drastically enhanced, because the parasitic resistance can be further decreased and the issue of implanted damage is reduced to a lesser extent
(3) The thickness of poly-Si film may affect the crystallinity of poly-Ge which is deposited onto the poly-Si film. Hence, by changing the thickness of poly-Si film, there should be an optimal thickness for achieving better performance.
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Angle(2θ)
10 20 30 40 50 60 70 80 90
Intensity( A.U.)
0 200 400 600 800 1000 1200 1400 1600
fresh Ge 400oC_2h annealing 450oC_2h annealing 500oC_2h annealing
Ge(111) Ge(220) Ge(311)
Fig. 2-1 XRD profiles of SPC samples at various annealing temperatures from 400 ℃ to 500 ℃ for 2 hours. The XRD intensity profile of fresh Ge film is shown as a reference.
42
Angle(2θ)
10 20 30 40 50 60 70 80 90
Inte nsi ty(A.U.)
0 1000 2000 3000 4000
fresh Ge 500oC_30min annealing
500oC_1h annealing 500oC_2h annealing 500oC_3h annealing 500oC_6h annealing
Fig. 2-2 XRD profiles of SPC samples annealed at 500 ℃ for various annealing times from 30 minutes to 6 hours. The XRD intensity profile of fresh Ge film is shown as a reference.
43
~5nm
(a)
(b)
Fig. 2-3 (a) shows the TEM cross-sectional view of poly-Ge film annealed at 500 ℃ for 1 hour. The circled area in the image indicates the grain size, and (b) presents the diffraction pattern of the poly-Ge film.
44
~5nm
Fig. 2-4 TEM cross-sectional view of poly-Ge film annealed at 500 ℃ for 6 hours.
45
(a)
(b)
Fig. 2-5 AFM images of Ge films annealed at 500 ℃ for 1 hour for (a) without protection of oxide capping layer, and (b) with protection of capping layer during annealing.
46
with capping without capping 0
1000 2000 3000 4000 5000
Sheet Resistanc e( Ω /□ )
500oC_1h annealing
Fig. 2-6 The difference of sheet resistance between Ge film with oxide capping layer and without capping layer during annealing.
47
Angle(2θ)
1 hour_annealing in N2
250oC
Angle(2θ)
10 20 30 40 50 60 70 80 90
Intensi ty(A.U .)
0 200 400 600 800 1000 1200 1400 1600 1800
Ni MIC at 350oC_1 hour SPC at 500oC_1 hour
Fig. 2-8 Comparison of XRD profiles between Ni MIC annealed at 350 ℃ for 1 hour and SPC at 500 ℃ for 1 hour.
~20nm
Fig. 2-9 TEM cross-sectional view of poly-Ge film formed by Ni MIC.
49
50
dose(cm-2)
undoped 5e+15 1e+15 5e+14 8e+13 3e+13 0
Fig. 2-10 (a) The sheet resistance of three types (p-type, n-type, and undoped) MIDA samples annealed at 350 ℃ for 1 hour with different implanted dose. (b) The comparison of sheet resistance between three types of MIDA samples and thermally activated samples annealed at 350 ℃ for 1 hour and 500 ℃ for 1 hour, respectively.
Angle(2θ)
20 30 40 50 60 70
Intensi ty(A.U.)
0 1000 2000 3000 4000 5000 6000
Ni_30min annealing
250oC 300oC 350oC 375oC 400oC 450oC 500oC
poly-Ge (111) NiGe (111) NiGe (120) NiGe (021) NiGe (211) NiGe (121) NiGe (002)
Fig. 2-11 The XRD spectra of the NiGe samples annealed at various temperature from 250 ℃ to 500 ℃.
51
Temperature(oC)
200 250 300 350 400 450 500 550