Chapter 3 Electrical Characteristics of Al/HfO 2 or HfAlO x /Si MIS
3.3 Electrical Characteristics with different steps for PDA and post-plasma treatment
3.3.1 Capacitance-Voltage and Current-Voltage Characteristics for HfO 2
Fig 3-11, Fig 3-12 shows the the C-V and J-V characteristics of HfO2 gate dielectrics treated with the same PDA temperature annealing and different PDA temperature annealing. As show in Fig. 3-11, the sample without nitridation can not sustain the high temperature annealing, so nitridation can improve the thermal stability of high-k film. In addition, we observe that the C-V curve of the sample without PDA and treated by N2 plasma directly is distorted at high negative bias voltages owing to the crystallization, we could see that after post deposition anneal, nitridation could effectively improve the thermal stability of the thin film. From Fig.
3-12, we can find the same result, the sample with nitridation after PDA can effectively decrease gate leakage current. It is good evidence to show that the thin
film treated by N2 plasma after post-deposition anneal can make the thin film sustain high thermal stress.
The sample with PDA 600℃ 30sec and PNA 600℃ 60sec has the better C-V curve and lower leakage current. Fig 3-13, Fig 3-14 shows the capacitance-voltage (C-V) and J-V characteristics of HfO2 gate dielectrics after the same PDA temperature and the same PNA temperature. After N
2
plasma nitridation and 800℃, 850℃, 900℃30 sec thermal treatment. We can find the better C-V curve and lower leakage current.
The best condition is “PDA 600℃ 30sec + N
2
plasma treatment + PNA 600℃ 60sec + 800℃ 30 sec thermal treatment.”Fig 3-15, Fig 3-16 shows the capacitance-voltage (C-V) and J-V characteristics of HfO2 gate dielectrics after NH3 plasma nitridation and 800℃, 850℃, 900℃ 30 sec thermal treatment. The capacitor with PDA 600℃ and after plasma treatment annealing 600℃ certainly has the better C-V curve and lower leakage current. But, the capacitance value decreased at negative bias, this was caused by the additional interfacial layer during the thermal process. However, it is particularly noteworthy that nitridatuon can let the HfO2 gate dielectric sustain high temperature (800℃) thermal treatment. The best condition is “PDA 600℃ 30sec + NH3 plasma treatment + PNA 600℃ 60sec + 800℃ 30 sec thermal treatment.” Compare to Fig 3-1, the film without nitridation will breakdown after high temperature (over 800℃) thermal treatment.
Fig 3-17, Fig 3-18 shows the capacitance-voltage (C-V) and J-V characteristics of HfO2 gate dielectrics after N2O plasma nitridation and 800℃, 850℃, 900℃ 30 sec thermal treatment. The capacitor with PDA 600℃ and after plasma treatment annealing 600℃ certainly has the better C-V curve and lower leakage current. But, the capacitance value decreased at negative bias, this was caused by the additional
that nitridatuon can let the HfO2 gate dielectric sustain high temperature (800℃) thermal treatment. The best condition is “PDA 600℃ 30sec + N2O plasma treatment + PNA 600℃ 60sec + 800℃ 30 sec thermal treatment.” Compare to Fig 3-1, the film without nitridation will breakdown after high temperature (over 800℃) thermal treatment.
Chapter 4
Reliability of Al /Ti /HfO 2 /S i MIS Capacitors
4.1 Hysteresis
When a ferromagnetic material is magnetized in one direction, it will not relax back to zero magnetization when the applied magnetizing field is removed. It must be driven back to zero by the additional opposite direction magnetic field. If an alternating magnetic field is applied to the material, its magnetization will trace out a loop called a hysteresis loop. The lack of retrace ability of the magnetization curve is the property called hysteresis and it is related to the existence of magnetic domains in the material. Once the magnetic domains are reoriented, it takes some energy to turn them back again [38]. The hysteresis phenomenon is similar in the C-V curve of the MIS capacitor device. When we apply a voltage in opposite direction, it will not fit the original C-V curve measured previously. It is due to the traps of interface which would trap charges to influence the flat band voltage and C-V curve. [39]
Fig. 4-1 shows the hysteresis of p-type HfO2 gate dielectric which was deposited by sputter system without plasma treatment. Fig. 4-2 shows the hysteresis of p-type HfO2 gate dielectric which was deposited by metal-organic deposition system without plasma treatment. We see that, the hysteresis of the thin film deposited by MOCVD is smaller than the thin film deposited by sputter system. It is a good way to use MOCVD to deposit HfO dielectric, because its interfacial trap density is smaller than
the sample deposited by sputter system.
Fig. 4-3 shows the hysteresis of p-type HfO2 gate dielectrics (MOCVD) with PDA 600℃-30 sec、 N2 plasma treatment 60 sec 、PNA 600℃-60 sec and 800℃-30 sec. The hysteresis is also small after 800℃ annealing, so nitridation could decrease the trap density and let the thin film sustain high thermal stress.
Fig. 4-4 shows the hysteresis of p-type HfO2 gate dielectrics (MOCVD) with PDA 600℃-30 sec、 NH3 plasma treatment 90 sec 、PNA 600℃-60 sec and 800℃
-30 sec. The hysteresis is also small after 800℃ annealing, so nitridation could decrease the trap density and let the thin film sustain high thermal stress.
Fig. 4-5 shows the hysteresis of p-type HfO2 gate dielectrics (MOCVD) with PDA 600℃-30 sec、 N2O plasma treatment 90 sec 、PNA 600℃-60 sec and 800℃
-30 sec. The hysteresis is also small after 800℃ annealing, so nitridation could decrease the trap density and let the thin film sustain high thermal stress.
As a consequence, the plasma treatment can improve the reliability of gate oxide. The limit of hysteresis for transistor in the future generation is about 10 mV or less than it under high frequency C-V measurement. It seems we could use metal-organic deposition to deposit the HfO2 thin film to decrease hysteresis of HfO2
device.