Voltage coefficient of capacitance (VCC) are very important parameters for MIM capacitor applications, and can be obtained by using a second order polynomial
equation of ( )− = 2 + +1
capacitance, αand β represent the quadratic and linear VCC respectively. The requirement of the quadratic coefficient of capacitance α is smaller than 100 ppm/V2, and the requirement of the linear coefficient of capacitance β is below 1000 ppm/V according to the ITRS roadmap. Low VCC values cause the capacitance to stability.
Figure 3-19, Figure 3-20, and Figure 3-21 shows Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to without PDA and with 400°C、500°C PDA in N2
for 100 KHz, 10 KHz, and 1KHz respectively. We found the sample exhibits VCC values became lager with increasing PDA temperature. Especially the sample with 500°C PDA in N2 clarifies high VCC values. It may be explained that the dielectric traps located around the metal–insulator interface [46]. Figure 3-22, Figure 3-23, and Figure 3-24 shows Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to without PDA and with 400°C、500°C PDA in O2 ambient for 100 KHz, 10
KHz, and 1KHz respectively. The sample with 500°C PDA in O2 ambient can reduce VCC values compare with the sample with 400°C PDA in O2 ambient. It may be explained that PDA process with 500°C O2 ambient reduces traps around the metal–insulator interface. Figure 3-25 shows measured Quadratic VCC, α, versus difference frequency without PDA , with 400°C、500°C PDA in O2 and N2. It is found that the Quadratic VCC decreases with frequency. It may be explained that the carrier mobility becomes smaller with increase frequency, which lead to a higher relaxation time and a smaller capacitance variation [47]. Table 3-1 Summary of Quadratic VCC, α and linear VCC, β extracted from MIM structure (Ta/HfO2/Ta) without and with 400°C、500°C PDA in N2 and O2 ambient PDA process. Maybe dielectric traps located around the metal–insulator interface cause high VCC values. According to this reason, we use plasma process to improve metal–insulator interface defects [48]. Besides, the rapid △C/Co reduction with increasing frequency may be due to the trapped carriers being unable to follow the high frequency signal [49] [50].
Figure 3-26, Figure 3-27, Figure 3-28 shows Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to without plasma and with N2O, NH3 plasma process for 100 KHz, 10 KHz, and 1KHz respectively. We found VCC values of the sample with plasma process become smaller than the sample without plasma process.
It may be explained that plasma process can improve trap defects to reduce VCC values. Figure 3-29 shows measured Quadratic VCC, α, versus difference frequency without plasma and with N2O, NH3 plasma process. The results clarify plasma process can reduce VCC values make the capacitance stability. However the VCC values are still higher than 100 ppm/V2 and 1000 ppm/V, not achieve the requirement of the ITRS roadmap. Table 3-2 Summary of Quadratic VCC, α, and linear VCC, β, extracted from MIM structure (Ta/HfO2/Ta) without plasma and with N2O, NH3
plasma process for variant frequency.
3.4 Summary
In this chapter, we studied PDA effect on MIM structure at first. We met a few questions of large leakage current density under high temperature annealing in N2
ambient. Because of grain growing, we found surface roughness increase with PDA temperature. High Surface roughness gives rise to large leakage current density.
Moreover, PDA temperature increases to cause the capacitance go up, it was attributed grain boundary effect. On condition PDA in O2 ambient, after annealing O2
ambient the leakage current density reduces and capacitance rises were attributed thicker high-k film producing and interface layer growing.
Secondly, we used plasma process improve electric characteristics on MIM. It was found that leakage current density decreases one order, but ensues to reduce capacitance density after plasma process. Especially N2O plasma process reduces capacitance density more than NH3 plasma process. It may be explained that surface roughness with N2Oplasma process was higher than NH3 plasma process.
Finally, form analysis VCC on MIM, we found out that PDA process in N2
ambient causes Quadratic VCC and linear VCC become higher than without PDA and with PDA process in O2 ambient. Especially Quadratic VCC and linear VCC become smaller after 500°C PDA process in O2 ambient. Besides, plasma process can reduce Quadratic VCC, but still not achieve the requirement of the ITRS roadmap.
2. SiO2 550 nm film deposited at furnace Wet Oxidation.
3. Bottom electrode Tantalum 100 nm deposited by Reactive Sputter (RS) and is patterned by mask
4. The HfO2 thin film 5 nm deposited by RS
5. Post deposit annealing, PDA: 400°C, 500°C, 600°C, in N2 or O2 60 sec.
6. Finally, Top Electrode deposited 100 nm by RS and is patterned by metal mask
Figure 3-1 Flow chart for the fabrication of HfO2 thin films with PDA Technology
1. Silicon substrate, RCA clean and HF dip to remove native oxide.
2. SiO2 550 nm film deposited at furnace Wet Oxidation.
3. Bottom electrode Tantalum 100 nm deposited by Reactive Sputter (RS) and is patterned by mask
4. Plasma N2O and NH3 treatment on Bottom electrode
5. The HfO2 thin film 5 nm deposited by RS
6. Finally, Top Electrode deposited 100 nm by RS and is patterned by metal mask
Figure 3-2 Flow chart for the fabrication of HfO2 thin films with Plasma Technology
Voltage (V)
Figure 3-3 The comparison of (a) and (b) C-V characteristics of MIM structure (Ta/HfO2/Ta) without PDA and with 400°C, 500°C , 600°C PDA in N2.
Voltae (V)
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
J (A/cm2 )10
-910
-810
-710
-610
-510
-410
-310
-210
-110
010
1AS
N2 400oC N2 500oC N2 600oC
Figure 3-4 The J-V curves characteristics of MIM structure (Ta/HfO2/Ta) without PDA and with 400°C, 500°C, 600°C PDA in N2
(a)
(b)
Figure 3-5 (a) and (b) AFM topography of HfO2/Ta structure without PDA.
(a)
(b)
Figure 3-6 (a) and (b) AFM topography of HfO2/Ta structure with 400°C PDA in N2
(a)
(b)
Figure 3-7 (a) and (b) AFM topography of HfO2/Ta structure with 500°C PDA in N2
(a)
(b)
Figure 3-8 (a) and (b) AFM topography of HfO2/Ta structure with 600°C PDA in N2
AS-dep. 400 500 600
RMS (A)
5 10 15 20 25 30
Figure 3-9 the relationship between surfaces roughness relate to difference PDA temperature of HfO2/Ta structure
Voltage (V)
Figure 3-10 (a) and (b) C-V characteristics of MIM structure (Ta/HfO2/Ta) without PDA and with 400°C, 500°C, 600°C PDA in O2
Voltage (V)
Figure 3-11 the J-V curves characteristics of MIM structure (Ta/HfO2/Ta) without PDA and with 400°C, 500°C, 600°C PDA in O2
PDA Temperature (
oC)
AS-dep. 400 500 600
Figure 3-12 the relationship between capacitance densities relate to difference PDA temperature
PDA Temperature (
oC)
AS-dep. 400 500 600
J (A/cm2 ) @ -1V
10
-1110
-1010
-910
-810
-710
-610
-510
-410
-310
-210
-1N2 O2 AS-dep.
Figure 3-13 leakage current characteristics as a function of PDA temperatures with 400°C, 500°C and 600°C deposition in N2 andO2.
Voltage (V)
Figure 3-14 the comparison of (a) C-V and (b) J-V characteristics of MIM structure (Ta/HfO2/Ta) without PDA and with N2O, NH3 plasma process on Ta electrode.
Figure 3-15 AFM topography of Ta bottom electrode without plasma process
Figure 3-16 AFM topography of Ta bottom electrode with N2O plasma process, 600s
Figure 3-17 AFM topography of Ta bottom electrode with NH3 plasma process, 600s
AS-dep. N2O Plasma NH3 Plasma
RMS (A)
6 8 10 12 14
Figure 3-18 the relationship between surfaces roughness relate to without and with plasma process on Ta electrode
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
Figure 3-19 Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to without PDA and with 400°C、500°C PDA in N2 for 100 KHz
Figure 3-20 Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to without PDA and with 400°C、500°C PDA in N2 for 10 KHz
Figure 3-21 Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to without PDA and with 400°C、500°C PDA in N2 for 1 KHz
Figure 3-22 Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to without PDA and with 400°C、500°C PDA in O2 for 100 KHz
Figure 3-23 Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to
Figure 3-24 Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to without PDA and with 400°C、500°C PDA in O2 for 1 KHz
Frequency (Hz)
1K 10K 100k
α (ppm/V2 )
0 5000 10000 15000 20000 25000 30000 35000 40000
AS-dep.
O2 4000C O2 5000C N2 4000C N2 5000C
Figure 3-25 Quadratic VCC, α, versus difference frequency without PDA , with 400°C、500°C PDA in N2 and 400°C、500°C PDA in O2
Frequency(Hz) α (ppm/V2) β (ppm/V)
Table 3-1 Summary of Quadratic VCC, α and linear VCC, β extracted from MIM structure (Ta/HfO2/Ta) without and with 400°C、500°C in N2, 400°C、500°C in O2
PDA.
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
Figure 3-26 Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to without plasma and with N2O, NH3 plasma process for 100 KHz
dC/C 0 (ppm)
Figure 3-27 Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to
without plasma and with N2O, NH3 plasma process for 10 KHz
Figure 3-28 Normalized C-V curves (△C/Co) of MIM structure (Ta/HfO2/Ta) relate to without plasma and with N2O, NH3 plasma process for 1 KHz
Figure 3-29 Quadratic VCC, α, versus difference frequency without plasma and α (ppm/V2 )
2 3
Frequency (Hz)
α (ppm/V2) β (ppm/V)
1K 14215 17200
10K 8277 10536
As-dep.
100K 5139 7025
1K 4961 19557
10K 2910 12374
N2O Plasma Treatment
100K 1908 8869
1K 6776 19037
10K 3914 11834
NH3 Plasma Treatment
100K 2402 8045
Table 3-2 Summary of Quadratic VCC, α, and linear VCC, β, extracted from MIM structure (Ta/HfO2/Ta) without plasma and with N2O, NH3 plasma process for variant frequency.
CHAPTER 4
Conclusions and Suggestions
For Future Work
4.1 Conclusions
In the first part of this thesis, MIM capacitors have been successfully fabricated with HfO2 as the dielectric layer. Describe as follows
Firstly, we also discussed Characteristics of HfO2 Gate Dielectrics Deposited on Tantalum Metal. We found MIM (Ta/HfO2/Ta) structure achieve a high capacitance density (~25.67fF/cm2). However, the poorer frequency dispersion for MIM (Ta/HfO2/Ta) structure was produced especially at 1 MHz. Besides, we speculate that the conduction mechanism of MIM structure is Frenkel-Poole Emission. The leakage currents of Ta/HfO2/Ta capacitors are very small compared to TiN/Al2O3/TiN structure. The capacitance density of Ta/HfO2/Ta capacitors is higher than TiN/Al2O3/TiN structure.
In the second part of this thesis, we deposited HfO2 thin film on Ta metal electrode using these optimum conditions. Several important phenomena were observed and summarized follows. Firstly, we focused on PDA effect on MIM
structure. Large leakage current density was observed under high temperature annealing at deference ambient. Secondly, plasma treatment on bottom metal can reduce the leakage current density. However, capacitance density was gone up.
Thirdly, we analyze VCC (Voltage coefficient of capacitance) in the MIM capacitor with PDA process. We found out that the process of 500°C PDA in O2 ambient causes VCC becomes smaller. Finally, we found out the process of plasma treatment on bottom metal can reduces Quadratic VCC, but increases linear VCC.
4.2 Recommendations for Future Works
In this thesis, we used PDA process and plasma technology to improve electric Characteristics on MIM (Ta/HfO2/Ta). We got better results than TiN/Al2O3//TiN structure. However, VCC values still is very high according to ITRS roadmap.
Besides, the mechanism of the variation of α and β values is unclear and more work needs to be done. After plasma treatment was processed, PDA 400°C in N2 was carried out for MIMmay be improved to electrics characteristics.
In the future, Pt can be chosen as buffer layer in MIM structure (Ta/HfO2/Ta) due to its inactive property. If all of the improvement on Ta could not become better results, maybe we should replace Ta with other metal material, such as Pt, Ir.
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個人簡歷
姓名 : 許修豪 性別 : 男
出生年月日 : 民國 68 年 3 月 14 日 籍貫 : 台灣省台南市
住址 : 台南市前鋒路 56 巷 16 號
學歷 :
國立彰化師範大學工業教育學系學士 (87.9–92.6) 國立交通大學電子工程研究所碩士 (93.9–95.6)
碩士論文題目 :
高介電常數材料二氧化鉿於金屬-絕緣體-金屬電容之研究
Investigation of High-K Material HfO2 On Metal-Insulator-Metal Capacitor