The MIS capacitors measurement

In order to measure the C-V characteristics of our MIS capacitors, we used HP 4284A precision LCR meter in our experiments. We swept the gate bias from inversion region to accumulation region to obtain the curve at the frequency of 50 kHz from -2V to 1V. And the leakage current of our MIS capacitors were analyzed from the current-voltage (I-V) characteristics measured by an HP4156A semiconductor parameter analyzer.

The hysteresis will also be discussed in this experiment. The name of Hysteresis was borrowed from electromagnetic. It is means that 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 hysteresis phenomenon is similar to the C-V curve in the MIS capacitor device. When we apply a voltage in reverse, it will not fit the original C-V curve measured previously. It is due to the interface traps which can trap charges to have impact on the flat band voltage and C-V curve. The C-V characteristics for hysteresis extraction were measured by sweeping the voltage from accumulation to inversion (-2V→1V) and then sweeping back (1V→-2V) at a frequency of 50 kHz.

24 

Chapter 4

Results and Discussion

4.1 PDA treatment and without PDA treatment characteristics of ZrO

/HfO

gate stake dielectrics

Fig. 4-1 and Fig. 4-2 shows the comparison of C-V curves of the samples with and without PDA treatment on ZrO2 film in O2 ambient at 500°C for 5 minute. In addition, Fig. 4-2 shows the C-V characteristics of Si surface (before ZrO2 film deposited) treated CF4 plasma and DC bias 20W for 10 sec.

The characteristics of samples with PDA treatment were improved than samples without treatment. Post deposition annealing could reduce the interface trap density exhibited by more sharp C-V characteristics. The C-V curve of O2-treated PDA 500°C capacitors was kink free and exhibited good interface properties.        

Fig. 4-3 and Fig. 4-4 showed the leakage current density comparison of samples with and without PDA treatment. In addition, Fig. 4-4 shows the J-V characteristics of Si surface (before ZrO2 film deposited) treated CF4 plasma and DC bias 20W for 10 sec.

It can be observed that the samples which treated by PDA treatment present the smaller leakage current density than the leakage current density without PDA treatment.

Form leakage density current reveled that a suitable PDA temperature can further improve the dielectric properties.

The hysteresis of C-V characteristics was shown in Fig. 4-5, Fig. 4-6, Fig.4-7, and Fig. 4-8 for the samples with and without PDA treatment. The hysteresis phenomenon of the C-V curves can be observed for all samples, which is caused by the existence of negative charges trapped in the dielectric defect states when the capacitors are stressed.

The samples without PDA treatment revealed large hysteresis. Indicate O2-treated PDA 500°C sample exhibited almost hysteresis-free characteristics.

Fig. 4-9 and Fig. 4-10 showed the C-V and the J-V characteristics of samples with various process treatments such as PDA treatment and fluorination treatment. We compared with these treatment and without on electrical characteristics.

In this chapter, we demonstrate that samples treated by PDA treatment and fluorination treatment were the best choice and PDA process can effectively improve gate dielectric quality.

4.2 Electrical characteristics for ZrO

/HfO

with nitridation plasma treatment

The various surface treatments such as without treatment, nitridation, and PDA treatment are compared and studied.

4.2.1Electrical characteristics for ZrO

/HfO

with N

plasma treatment but without PDA treatment on ZrO

Fig. 4-11 reveals the capacitance-voltage (C-V) characteristics of samples treated in N2 plasma for 30 sec and 90 sec.The capacitor treated in N2 for 90 sec shows the maximum capacitance density among these samples with different process treatment.In addition, the capacitors treated for 30 sec also present the larger values than the capacitors without whole plasma nitridation process.

This phenomenon indicates that the N2 plasma treatment was workable to improve the capacitance. The factor of improvement might be from that the nitrogen incorporation in the HfO2 dielectrics, which could enhance the electronic polarization as well as the ionic polarization, so the dielectric constant of the HfO2 thin films increases just as Hf-silicate thin film and SiO2 thin film.

The J-V characteristics of samples treated by N2 plasma with 30 sec and 90 sec from 0V to -2V are described in Fig. 4-12. It can be observed that the samples which treated in N2 plasma all present the smaller leakage current density than the leakage current density without whole plasma nitridation process. The gate leakage current

26 

density treated in N2 for 90 sec shows the minimum current density among these conditions. The lower leakage shows that the weak structure of interface must be fixed by the plasma nitridaiton.

The hysteresis of C-V characteristics are shown in Figs. 4-13 and 4-14 for the samples with 30 and 90 sec N2 plasma treatment , respectively. The hysteresis characteristic could be improved by various plasma nitridation process.

4.2.2 Electrical characteristics for HfO

with N

plasma treatment and PDA treatment on ZrO

Fig. 4-15 reveals the capacitance-voltage (C-V) characteristics of MIS capacitor treated in N2 plasma for 30 sec and 90 sec with PDA treatment. The capacitor treated in N2 for 90 sec with PDA treatment shows the maximum capacitance density among these samples with different process treatment.In addition, the capacitors treated for 30 sec also present the larger values than the capacitors without whole plasma nitridation process.

      The J-V characteristics of MIS capacitor treated in N2 plasma for 30 sec and 90 sec with PDA treatment from 0V to -2V are described in Fig. 4-16. The gate leakage current density treated in N2 plasma 90 sec with PDA treatment shows the minimum current density among these conditions.

The hysteresis of C-V characteristics are shown in Fig. 4-17, and Fig. 4-18 for the samples with PDA treatment and with 30 and 90 sec N2 plasma treatment , respectively.

The hysteresis characteristic could be improved by various plasma nitridation process.

4.2.3 Short summary

Fig. 4-19 and Fig. 4-20 shows the comparison of C-V curves of the samples with and without PDA treatment on ZrO2 film in O2 ambient at 500°C for 5 minute.

Fig. 4-21 and Fig. 4-22 showed the leakage current density comparison of samples with and without PDA treatment.

Fig. 4-23 and Fig. 4-24 showed the C-V and the J-V characteristics of samples with various process treatments such as PDA treatment, fluorination treatment, and nitridation treatment. We compared with these treatment and without on electrical characteristics.

In this chapter, we demonstrate that samples treated by PDA treatment and nitridation treatment were the best choice.

4.3 Electrical characteristics for HfO

with CF

plasma treatment and N

plasma treatment

There are four kinds of plasma treatment with different source gas (i.e. CF4, N2, NH3, and N2O) and they were treated for different process time (i.e. 10 sec, 20sec, 30sec, 40sec, and 120sec).

4.3.1 Electrical characteristics for HfO

with CF

plasma treatment and N

plasma treatment but without PDA treatment

Fig. 4-25 reveals the capacitance-voltage (C-V) characteristics of MIS capacitor treated in CF4 plasma for 10 sec and N2 plasma for 30 sec and 90 sec. The capacitor treated in CF4 for 10 sec and N2 for 90 sec shows the maximum capacitance density among these samples with different process times. In addition, other samples which treated in CF4 plasma and N2 plasma all present the larger values than the capacitors without whole plasma process. This phenomenon indicates that dual plasma treatment was workable to improve the capacitance. The factor of improvement might be from that the fluorine and nitrogen can repair defect and dangling bonds.

The J-V characteristics of MIS capacitor treated in CF4 plasma for 10 second and N2 plasma for 30 sec and 90 sec from 0V to -2V are described in Fig. 4-26. The gate leakage current density treated N2 plasma 90 sec shows the minimum current density among these conditions. The lower leakage shows that the weak structure of interface must be fixed by the plasma nitridaiton.

28 

The hysteresis of C-V characteristics are shown in Fig. 4-27, and Fig.4-28 for the samples with fluorination and with 30 and 90 sec N2 plasma treatment , respectively.

The hysteresis characteristic could be improved by various plasma nitridation process. 

4.3.2 Electrical characteristics for HfO

with CF

plasma treatment, N

plasma treatment and PDA treatment

Fig. 4-29 reveals the capacitance-voltage (C-V) characteristics of MIS capacitor treated in CF4 plasma for 10 sec and N2 plasma for 30 sec and 90 sec with PDA treatment. The capacitor treated in CF4 for 10 sec and N2 for 90 sec with PDA treatment shows the maximum capacitance density among these samples with different process times. In addition, other samples which treated in CF4 plasma and N2 plasma all present the larger values than the capacitors without whole plasma process. 

The J-V characteristics of MIS capacitor treated in CF4 plasma for 10 sec and N2

plasma for 30 sec and 90 sec with PDA treatment from 0V to -2V are described in Fig.

4-30. The gate leakage current density treated in CF4 plasma 10 sec and N2 plasma 90 sec with PDA treatment shows the minimum current density among these conditions.

The hysteresis of C-V characteristics are shown in Fig. 4-31 and Fig. 4-32 for the samples with fluorination, PDA treatment, and with 30 and 90 sec N2 plasma treatment, respectively. The hysteresis characteristic could be improved by various plasma nitridation process.

4.3.3 Short summary

Fig. 4-33 and Fig. 4-34 shows the comparison of C-V curves of the samples with and without PDA treatment on ZrO2 film in O2 ambient at 500°C for 5 minute. 

Fig. 4-35 and Fig. 4-36 shows the comparison of C-V curves of the samples with and without PDA treatment on ZrO2 film in O2 ambient at 500°C for 5 minute. 

Fig. 4-37 and Fig. 4-38 showed the C-V and the J-V characteristics of samples with various process treatments such as PDA treatment, fluorination treatment, and

nitridation treatment. We compared with these treatment and without on electrical characteristics.

In this chapter, we demonstrate that samples treated by PDA treatment, fluorination, and nitridation treatment were the best choice.

4.4 Electrical characteristics for HfO

with CF

plasma treatment and N

O plasma treatment

There are four kinds of plasma treatment with different source gas (i.e. CF4, N2, NH3, and N2O) and they were treated for different process time (i.e. 10 sec, 20sec, 30sec, 40sec, and 120sec).

4.4.1 Electrical characteristics for HfO

with CF

plasma treatment and N

O plasma treatment but without PDA treatment

Fig. 4-39 reveals the capacitance-voltage (C-V) characteristics of MIS capacitor treated in CF4 plasma for 10 sec and N2O plasma for 30 sec and 90 sec. The capacitor treated in CF4 for 10 sec and N2O for 90 sec shows the maximum capacitance density among these samples with different process times. In addition, other samples which treated in CF4 plasma and N2O plasma all present the larger values than the capacitors without whole plasma process. This phenomenon indicates that dual plasma treatment was workable to improve the capacitance. The factor of improvement might be from that the fluorine and nitrogen can repair defect and dangling bonds.

The J-V characteristics of MIS capacitor treated in CF4 plasma for 10 second and N2O plasma for 30 sec and 90 sec from 0V to -2V are described in Fig. 4-40. The gate leakage current density treated N2O plasma 90 sec shows the minimum current density among these conditions. The lower leakage shows that the weak structure of interface must be fixed by the plasma nitridaiton.

The hysteresis of C-V characteristics are shown in Fig. 4-41 and Fig.4-42 for the samples with fluorination and with 30 and 90 sec N2O plasma treatment , respectively.

30 

The hysteresis characteristic could be improved by various plasma nitridation process. 

4.4.2 Electrical characteristics for HfO

with CF

plasma treatment, N

O plasma treatment and PDA treatment

Fig. 4-43 reveals the capacitance-voltage (C-V) characteristics of MIS capacitor treated in CF4 plasma for 10 sec and N2O plasma for 30 sec and 90 sec with PDA treatment. The capacitor treated in CF4 for 10 sec and N2O for 90 sec with PDA treatment shows the maximum capacitance density among these samples with different process times. In addition, other samples which treated in CF4 plasma and N2O plasma all present the larger values than the capacitors without whole plasma process. 

The J-V characteristics of MIS capacitor treated in CF4 plasma for 10 sec and N2O plasma for 30 sec and 90 sec with PDA treatment from 0V to -2V are described in Fig. 4-44. The gate leakage current density treated in CF4 plasma 10 sec and N2O plasma 90 sec with PDA treatment shows the minimum current density among these conditions.

The hysteresis of C-V characteristics are shown in Fig. 4-45, and Fig.4-46 for the samples with fluorination, PDA treatment, and with 30 and 90 sec N2O plasma treatment , respectively. The hysteresis characteristic could be improved by various plasma nitridation process.

4.4.3 Short summary

Fig. 4-47 and Fig. 4-48 shows the comparison of C-V curves of the samples with and without PDA treatment on ZrO2 film in O2 ambient at 500°C for 5 minute. 

Fig. 4-49 and Fig. 4-50 shows the comparison of J-V curves of the samples with and without PDA treatment on ZrO2 film in O2 ambient at 500°C for 5 minute. 

Fig. 4-51 and Fig. 4-52 showed the C-V and the J-V characteristics of samples with various process treatments such as PDA treatment, fluorination treatment, and nitridation treatment. We compared with these treatments and without on electrical

characteristics.

In this chapter, we demonstrate that samples treated by PDA treatment, fluorination, and nitridation treatment were the best choice.

4.5 Electrical characteristics for HfO

with CF

plasma treatment and NH

plasma treatment

There are four kinds of plasma treatment with different source gas (i.e. CF4, N2, NH3, and N2O) and they were treated for different process time (i.e. 10 sec, 20sec, 30sec, 40sec, and 120sec).

4.5.1 Electrical characteristics for HfO

with CF

plasma treatment and NH

plasma treatment but without PDA treatment

Fig. 4-53 reveals the capacitance-voltage (C-V) characteristics of MIS capacitor treated in CF4 plasma for 10 sec and NH3 plasma for 30 sec and 90 sec. The capacitor treated in CF4 for 10 sec and NH3 for 90 sec shows the maximum capacitance density among these samples with different process times. In addition, other samples which treated in CF4 plasma and NH3 plasma all present the larger values than the capacitors without whole plasma process. This phenomenon indicates that dual plasma treatment was workable to improve the capacitance. The factor of improvement might be from that the fluorine and nitrogen can repair defect and dangling bonds.

The J-V characteristics of MIS capacitor treated in CF4 plasma for 10 second and NH3 plasma for 30 sec and 90 sec from 0V to -2V are described in Fig. 4-54. The gate leakage current density treated NH3 plasma 90 sec shows the minimum current density among these conditions. The lower leakage shows that the weak structure of interface must be fixed by the plasma nitridaiton.

The hysteresis of C-V characteristics are shown in Fig. 4-55, and Fig.4-56 for the samples with fluorination and with 30 and 90 sec NH3 plasma treatment , respectively.

The hysteresis characteristic could be improved by various plasma nitridation process. 

32 

4.5.2 Electrical characteristics for HfO

with CF

plasma treatment, NH

plasma treatment and PDA treatment

Fig. 4-57 reveals the capacitance-voltage (C-V) characteristics of MIS capacitor treated in CF4 plasma for 10 sec and NH3 plasma for 30 sec and 90 sec with PDA treatment. The capacitor treated in CF4 for 10 sec and NH3 for 90 sec with PDA treatment shows the maximum capacitance density among these samples with different process times. In addition, other samples which treated in CF4 plasma and NH3 plasma all present the larger values than the capacitors without whole plasma process.

The J-V characteristics of MIS capacitor treated in CF4 plasma for 10 sec and NH3 plasma for 30 sec and 90 sec with PDA treatment from 0V to -2V are described in Fig. 4-58. The gate leakage current density treated in CF4 plasma 10 sec and NH3

plasma 90 sec with PDA treatment shows the minimum current density among these conditions.

The hysteresis of C-V characteristics are shown in Fig. 4-59, and Fig. 4-60 for the samples with fluorination, PDA treatment, and with 30 and 90 sec NH3 plasma treatment, respectively. The hysteresis characteristic could be improved by various plasma nitridation process.

4.5.3 Short summary

Fig. 4-61 and Fig. 4-62 shows the comparison of C-V curves of the samples with and without PDA treatment on ZrO2 film in O2 ambient at 500°C for 5 minute.

Fig. 4-63 and Fig. 4-64 shows the comparison of J-V curves of the samples with and without PDA treatment on ZrO2 film in O2 ambient at 500°C for 5 minute.

Fig. 4-65 and Fig. 4-66 showed the C-V and the J-V characteristics of samples with various process treatments such as PDA treatment, fluorination treatment, and nitridation treatment. We compared with these treatment and without on electrical characteristics.

In this chapter, we demonstrate that samples treated by PDA treatment, fluorination, and nitridation treatment were the best choice.

Fig. 4-67 shows the capacitance-voltage (C-V) characteristics of MIS capacitors combined CF4 plasma treatment with N2, NH3, or N2O plasma treatment at optimal condition.It is indicated that the capacitance treated in CF4 plasma for 10 sec and N2

plasma for 90 sec shows the most excellent value among these samples. The films with the N2 plasma treatments showed higher capacitances than those with the N2O plasma treatments, because the N2O treatment caused increased growth of the interfacial silicate layer. The samples treated in NH3 plasma exhibited the highest interface trap density compared with the samples treated by the other treatments. It was due to the hydrogen related traps (-H, -OH, and N-H) formed on the surface of Si substrate. This suggests that remote-plasma N2 treatment is the optimal process to obtain an increased dielectric constant.

The J-V characteristics of MIS capacitors combined CF4 plasma treatment with N2, NH3, or N2O plasma treatment at optimal condition in Fig. 4-68. The gate leakage current density treated in CF4 plasma 10 sec and N2O plasma 90 sec shows the minimum current density among these conditions. The samples with nitridation and PDA treatments demonstrated lower leakage current due to the Si-O and Si-N bonds formation. The bonding strength comparisons as below: Si-O bond is 8.42 eV. Si-N bond is 4.75 eV. Si-Si bond is 3.38 eV. Si-H bond is 3.18 eV. We understood that bonding strength of Si-N and Si-O bonds are so stronger that the leakage current was lower. The leakage current of samples without plasma treatment is large due to the poor interfacial layer characteristic.

34 

Chapter 5

Conclusions and future work

5.1 Conclusions

In this thesis, various surface treatments such as PDA (post deposition annealing), fluorination, and nitridation are present. It is evidence that the ZrO2(interfacial layer) treated by PDA treatment at 500 °C for 5 min can effectively reduce leakage current, hysteresis, and can improve capacitance value. After PDA treatments, the high K dielectric quality was improved, and the reliability therefore superior.

The next chapters, characteristics of MIS capacitors that combine CF4 plasma treatment with N2, NH3, or N2O plasma treatment have been investigated. Most of the plasma treatment samples can promote the electrical characteristics and reliability until the plasma damage or the growth of interfacial layer happened. Among these treatments, the samples treated in CF4 plasma for 10 sec and N2, NH3, or N2O plasma for 90 sec represent significantly great improvement, such as good capacitance, reduced leakage current and smaller C-V hysteresis. In addition, the N²O or NH3 plasma treatment has the lower leakage current than N2 plasma for HfO². The reason is that the samples using N²O plasma treatment will introduce oxygen bonding to form additional interfacial layer so that the capacitance will be lower. But, the thicker oxidation layer generates a good resistance against leakage current. The bonding strength comparisons as below: Si-O bond is 8.42 eV. Si-N bond is 4.75 eV. Si-Si bond is 3.38 eV. Si-H bond is 3.18 eV. We understood that bonding strength of Si-N and Si-O bonds are so stronger that the leakage current was lower. The samples treated in NH3 plasma exhibited the highest interface trap density compared with the samples treated by the other treatments. It was due to the hydrogen related traps (-H, -OH, and N-H) formed on the surface of Si substrate. Finally, in this thesis, the various surface treatments such as without treatment,

PDA treatment, fluorination, and nitridation are compared and studied. We demonstrate that samples treated by PDA treatment at 500 °C for 5 min, CF4 plasma pretreatment for 10 sec, and N2 plasma treatment for 90 sec were the best choice.

5.2 Future work

Although the effect of the PDA treatment, plasma nitridation, and fluorination to the electrical characteristics and reliabilities of ZrO2/HfO2 stack dielectric thin films has been examined in this research, there are still several issues that could investigated in the future:

1. The reason of leakage current mechanism:

We must try to research the mechanism for leakage current with SE, FP, F-N tunneling effect in Hf-based thin film further. Therefore, we can realize the mechanism

We must try to research the mechanism for leakage current with SE, FP, F-N tunneling effect in Hf-based thin film further. Therefore, we can realize the mechanism