RTA Treatment - Electrical Characteristics of Al/HfO 2 /Si MIS Capacitors

Chapter 4 Electrical Characteristics of Al/HfO 2 /Si MIS Capacitors

4.4 RTA Treatment

In our experiments, after oxidation process, we could have an additional RTA treatment at 850 for 30 seconds to HfO℃ 2 film. Fig. 4-24 shows 1MHz high

frequency C-V characteristics of n-type HfO2 capacitors with 6.25×10^-6 cm² die areas under 400℃-15 minutes oxidation condition without / with RTA. The device with RTA treatment has smaller accumulation capacitance and smaller slope of C-V curve than without RTA treatment. Fig. 4-25 shows J-V characteristics of n-type HfO2

capacitors with 6.25×10^-6 cm² die areas under 400℃-15 minutes oxidation condition without / with RTA. The device with RTA treatment has larger leakage current than without RTA treatment. From above results, we know that RTA treatment couldn’t improve the quality of HfO2 film in J-V and C-V characteristics. This is due to HfO2

is unit-combined structure and thus couldn’t be enhanced the value of dielectric constant by RTA treatment. In the other hand, high-k material, like Ta2O5, which isn’t unit-combined structure could be enhanced the value of dielectric constant by RTA treatment [16]. In addition, when the temperature rises to 800℃～900 , HfO℃ 2 would change the lattice structure from amorphous type to polycrystalline type and thus increase gate leakage current. Consequently, we don’t suggest using RTA treatment to HfO2 film.

4.5 References

[1] Ben G.. streetman, Sanjay Banerjee, “Solid State Electronic Devices”, 2001.

[2] Gerry Lucovsky Departments of Physics, Electrical and Computer Engineering, and Materials Science and Engineering, NC State University, “Intrinsic limitations on the performance and reliability of high-k gate dielectrics: differences between interfacial and bulk bond-strain in high-k and SiO2 gate stacks.”

[3] R. N. Hall, “Bulk generation current in depleted germanium junctions”, Appl.

Phys. Lett. 29, 202 (1976).

[4] Yea-Dean Sheu and Gilbert A. Hawkins, “Method for reduction in surface generation current in polycrystalline-silicon-gate metal-oxide-semiconductor devices”, J. Appl. Phys. 73, 4694 (1993).

[5] E. Carnes and W. F. Kosonocky, RCA Rev. 33, 327 (1979).

[6] P. J. Caplan and E. H. Poindexter, J. Appl. Phys. 50, 5847 (1979).

[7] R. C. de Wit and J. M. McKenzle, IEEE Trans, Nuci. Sci. NS-16, 352 (1968).

[8] R. H. Pehl, E. E. Haller, and R. C. Cordt, IEEE Trans. Nuci. Sci, NS-20, 494 (1973).

[9] Felice Crupi, Robin Degraeve, Guido Groeseneken, Senior Member, IEEE,

Tanya Nigam, and Herman E. Maes, Fellow, IEEE, “On the Properties of the Gate and Substrate Current after Soft Breakdown in Ultrathin Oxide Layers”, IEEE Transactions on Electron Devices, Vol. 45, No. 11, November 1998

[10] J. Robertson, “Band Offsets of Wide-Band-Gap Oxides and Implications for Future Electronic Devices," J. Vac. Sci. Technol. B, Vol. 18, 2000, p. 1785.

[11] W. Zhu, T.P. Ma, T. Tamagawa, Y. Di, J. Kim, R. Carruthers, M. Gibson, T.

Furukawa, “HfO2 and HfAlO for CMOS ： Thermal Stability and Current Transport”, in IEDM Tech. Dig., 20.4.1-4, 2001.

[12] S. M. Sze, “Physics of Semiconductor Devices”, New York, Wiley, p.406, 1981.

[13] S. S. Gong et al., “Evolution of Qbd for electrons tunneling from the Si/SiO2

interface compared to electron tunneling from the poly Si/SiO2 interface”, IEEE Transactions on Electron Devices, vol. 40, p.1251, 1993.

[14] K. F. Schuegraf et al., “Reliability od Thin SiO2 at direct tunneling voltages”, in IEDM Tech. Dig., p.609, 1994.

[15] Dieter K. Schroder, “Semiconder Material and Device Characterization”

Wiley-INTERSCIENCE, 1998.

[16] Hung-Yu Chen, “Characteristics of Ultra-thin Ta2O5 Gate Insulator”, 2003.

T able 4-1 Measurem ent results of HfO

capacitors with 6.25×10

-6

cm

die area.

W a fer T y pe Oxidation T emperatur e & Ti m e

200 ℃ 15min 300 ℃ 15min 400 ℃ 15min 400 ℃ 30min 500 ℃ 15min 500 ℃ 30min EOT 17.3 17.4 23.8 23.9 P Jg (A/cm

) @ -1 V

N/A N/A 2.3×10

-4

1.9×10

-4

8.8×10

-7

8.6×10

-8

EOT 9.2 21.8 21.9 24.3 25.5 N Jg (A/cm

) @ 1 V

N/A 7.8×10

-2

8.0×10

-4

8.0×10

-4

1.1×10

-6

7.8×10

-7

T able 4-2 Measurem ent results of HfO

capacitors with 2.5×10

-5

cm

die area.

W a fer T y pe Oxidation T emperatur e & Ti m e

200 ℃ 15min 300 ℃ 15min 400 ℃ 15min 400 ℃ 30min 500 ℃ 15min 500 ℃ 30min EOT 21.0 21.4 29.1 29.9 P Jg (A/cm

) @ -1 V

N/A N/A 2.1×10

-4

1.7×10

-4

1.9×10

-6

2.2×10

-7

EOT 1 1.3 27.4 28.6 31.3 33.4 N Jg (A/cm

) @ 1 V

N/A 5.9×10

-2

1.0×10

-3

8.0×10

-4

3.0×10

-6

8.4×10

-7

T able 4-3 Measurem ent results of HfO

capacitors with 1×10

-4

cm

die area.

W a fer T y pe Oxidation T emperatur e & Ti m e

200 ℃ 15min 300 ℃ 15min 400 ℃ 15min 400 ℃ 30min 500 ℃ 15min 500 ℃ 30min EOT 22.3 23.2 30.3 32.0 P Jg (A/cm

) @ -1 V

N/A N/A 2.0×10

-4

1.6×10

-4

3.5×10

-6

4.4×10

-7

EOT 13.2 28.9 29.8 33.7 36.4 N Jg (A/cm

) @ 1 V

N/A 4.8×10

-2

1.3×10

-3

1.1×10

-3

1.0×10

-5

2.3×10

-6

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5

p-type 400⁰C 15min

Capacitance (µF/cm2 )

Gate Voltage (V)

Area = 1E-4 cm² Area = 2.5E-5 cm² Area = 6.25E-6 cm²

Fig. 4-1 1MHz high frequency C-V characteristics of p-type HfO2 capacitors with different die areas under 400℃ 15 minutes oxidation condition.

-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5

Fig. 4-2 1MHz high frequency C-V characteristics of p-type HfO

capacitors

with 6.25×10

^-6

cm

die area under different oxidation conditions.

Fig. 4-3 C-V characteristics of SiO2, (SiO2)0.5(Si3N4)0.5 and Si3N4 NMOSFET.

(Gerry Lucovsky, NC State University, 2003)

10^-5 10^-4

12 16 20 24 28 32 36

40 p-type 400⁰C 15min p-type 400⁰C 30min p-type 500⁰C 15min p-type 500⁰C 30min

EOT (A)

Die Area (cm²)

Fig. 4-4 EOT of p-type HfO2 capacitors with different die areas.

Fig. 4-5 EOT of p-type and n-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation conditions.

HfO₂ HfSiO

SiO₂ SiO₂

Si-substrate

Fig. 4-6 Illustration of HfO2 capacitor.

300 400 500

8 10 12 14 16 18 20 22 24

26 Area = 6.25E-6 cm²

p-type oxidation 15 min p-type oxidation 30 min n-type oxidation 15 min n-type oxidation 30 min

EOT (A)

Oxidation Temperature (⁰C)

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 10^-7

10^-6 10^-5 10^-4

p-type 400⁰C 15min

Area = 1E-4 cm² Area = 2.5E-5 cm² Area = 6.25E-6 cm²

Gate Leakage (A/cm2 )

Gate Voltage (V)

Fig. 4-7 J-V characteristics of p-type HfO2 capacitors with different die areas under 400℃ 15 minutes oxidation condition from 0 V to -1 V.

-1.0 -0.8 -0.6 -0.4 -0.2 0.0

Fig. 4-8 J-V characteristics of p-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation conditions from 0 V to -1 V.

Fig. 4-9 Measured and simulated J-V characteristics of NMOSFET with SiO2

gate insulator. The dotted line indicates the 1 A/cm² limit for leakage current. (S. H. Lo, et. al (IBM), IEEE EDL 1997)

8 10 12 14 16 18 20 22 24 26

10^-8 10^-7 10^-6 10^-5 10^-4 10^-3 10^-2 10^-1 10⁰

10¹ p-type 400⁰C 15min

area = 6.25E-6 cm² p-type 400⁰C 15min area = 2.5E-5 cm²

p-type 400⁰C 15min area = 1E-4 cm²

n-type 300⁰C 15min area = 6.25E-6 cm² n-type 300⁰C 15min area = 2.5E-5 cm²

n-type 300⁰C 15min area = 1E-4 cm² Gate Leakage (A/cm2 ) at |V g|= 1 V

EOT (A)

Fig. 4-10 Gate leakage at ∣ Vg ∣ = 1 V of n -type and p-type HfO

capacitors

with different die area.

8 10 12 14 16 18 20 22 24 26 Gate Leakage (A/cm2 ) at |Vg|= 1 V

EOT (A)

with 6.25×10

^-6

cm

die area under different oxidation condition.

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Fig. 4-12 J-V characteristics of n-type and p-type HfO

capacitors with 6.25×10

^-6

cm

die area from -1 V to +1 V.

Al HfO

₂

Silicon

+ + + + +

Generation current

(Inversed minority carrier)

(a)

(b)

N-type substrate Al gate

HfO₂

Space charge region Minority carrier

- V

Fig. 4-13 Illumination of leakage current under negative bias. (a) energy band diagram (b) cross-section view

0 2 4 6 8 10

n-type 400⁰C 30min

Area = 1E-4 cm² Area = 2.5E-5 cm² Area = 6.25E-6 cm² Gate Leakage (A/cm2 )

Gate Voltage (V)

Fig. 4-14 J-V characteristics of n-type HfO

capacitors with different die areas under 400℃ 15 minutes oxidation condition from 0 V to +10 V.

-10 -8 -6 -4 -2 0

Fig. 4-15 J-V characteristics of p-type HfO

capacitors with 6.25×10

^-6

cm

die

area under different oxidation conditions from 0 V to -10 V.

Fig. 4-16 Gate current as a function of the gate voltage for four oxide degradation stages in a 2000 µm² SiO2 NMOSFET. After SBD, a large increase of the substrate current is observed in the whole voltage range. (Felice Crupi, et. al, IEEE Transactions on Electron Devices, 1998)

-1.0 -0.8 -0.6 -0.4 -0.2 0.0

10^-7 10^-6 10^-5 10^-4 10^-3 10^-2 10^-1 10⁰

p-type 400⁰C 15min area = 6.25E-6 cm² Gate Leakage (A/cm2 )

Gate Voltage (V)

Fresh SILC SBD HBD

Fig. 4-17 Four oxide degradation stages of p-type HfO

capacitors with 6.25×10

^-6

cm

die area under 400℃ 15 minutes oxidation condition.

0.9eV

4.1eV 4.05eV

8.9eV

Al SiO₂ Silicon

Vacuum level

Fig. 4-18 Energy band diagram of SiO2 capacitors with Al gate.

2.82eV

4.1eV 4.05eV

5.7eV

Al HfO₂ Silicon

Vacuum level

Fig. 4-19 Energy band diagram of HfO2 capacitors with Al gate.

Al HfO₂ Silicon

Fig. 4-20 Conduction mechanism in the oxide for MIS structure.

Fig. 4-21 Schottky plot of n-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation condition.

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32

Fig. 4-22 Fowler-Nordheim plot of n-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation condition.

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Fig. 4-23 Frenkel-Poole plot of n-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation condition.

-0.5 0.0 0.5 1.0 1.5 0.0

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

n-type 400⁰C 15min area = 6.25E-6 cm² Capacitance (µF/cm2 )

Gate Voltage (V) without RTA

with RTA

Fig. 4-24 1MHz high frequency C-V characteristics of n-type HfO2 capacitors with 6.25×10^-6 cm² die areas under 400℃ 15 minutes oxidation condition without / with RTA.

0.0 0.2 0.4 0.6 0.8 1.0

10^-9 10^-8 10^-7 10^-6

n-type 400⁰C 15min area = 6.25E-6 cm² without RTA

with RTA

Gate Leakage (A/cm2 )

Gate Voltage (V)

Fig. 4-25 J-V characteristics of n-type HfO2 capacitors with 6.25×10^-6 cm² die areas under 400℃ 15 minutes oxidation condition without / with RTA.

Chapter 5 Reliability of Al/HfO ₂ /Si MIS Capacitors

5.1 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 [1].

The hysteresis phenomenon is similar in the C-V curve of the MIS capacitor device. Fig. 5-1 shows the hysteresis of p-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation conditions. Hysteresis of p-type HfO2 capacitors are about 20～30 mV. Oxidation temperature seems not influence hysteresis for p-type HfO2 capacitors. Longer oxidation time makes hysteresis a little larger. Fig. 5-2 shows the hysteresis of n-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation conditions. We see that, for n-type HfO2 capacitors, oxidation temperature influences hysteresis hardly. Atoms getting higher energy under higher oxidation temperature could reverse more easily. Thus hysteresis is smaller under higher oxidation temperature. Comparing to p-type HfO2 capacitor, n-type HfO2 capacitor appears much larger hysteresis. However, the limit of hysteresis for transistor in the future generation is less than 10 mV under high frequency C-V measurement. It seems we need to find some method to decrease hysteresis of HfO2 device.

5.2 Uniformity

Fig. 5-3 and 5-4 show the distribution of p-type and n-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation conditions. Measurements were made on 15 capacitors per wafer. Breakdown voltage at 50 % cumulative failure for p-type HfO2 capacitors under 400℃-15 minutes, 400℃-30 minutes, 500℃-15 minutes and 500℃-30 minutes oxidation condition are 6.10 V, 6.20 V, 7.30 V and

7.45 V respectively. Breakdown voltage at 50 % cumulative failure for n-type HfO2

capacitors under 400℃-15 minutes, 400℃-30 minutes, 500℃-15 minutes and 500℃-30 minutes oxidation condition are 3.55 V, 3.60 V, 4.80 V and 5.15 V respectively. We could find that devices under higher oxidation temperature and longer oxidation time have larger breakdown voltage because of thicker thickness and stronger chemical bonding. The uniformity of HfO2 film on a p-type substrate wafer is excellent under all oxidation condition. HfO2 film on an n-type substrate wafer shows a little worse uniformity under the same oxidation condition.

5.3 Constant Current Stress (CCS)

To study the reliability of HfO2 film, stressing the film with a constant voltage or a constant current are two common methods. In our experiments, we use constant current stress (CCS) to test the reliability of HfO2 film. Fig. 5-5 shows gate voltage shift of p-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation conditions as a function of stress time during Jg = 1 A/cm² CCS stress. Capacitors under 400℃-15 minutes and -30 minutes oxidation condition have very similar EOT (i.e. 17.3 Å and 17.4 Å). However, we find that there is a 0.8 V drop between these two devices at the beginning gate voltage applied for. The larger initial gate voltage means device under 400℃-15 minutes oxidation condition has better capability of resisting current tunneling. In addition, gate voltage of these two devices both becomes slightly larger during the stressing period. This might result from that detrapping action fixes the defects in HfO2 film and enhances the capability of resisting current tunneling. After stressing 30 seconds, SBD happens to p-type capacitor under 400℃-30 minutes oxidation condition, indicating that the worst capability of resisting current tunneling. P-type HfO2 capacitor under higher oxidation temperature and longer oxidation time has larger gate voltage shift after 100 seconds CCS stress and thus has worse reliability. Fig. 5-6 shows gate voltage shift of n-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation conditions as a function of stress time during Jg = 1 A/cm² CCS stress. Like p-type HfO2 capacitor, n-type HfO2 capacitor under 400℃-15 minutes oxidation condition has better capability of resisting current tunneling than under 400℃-30 minutes oxidation condition. Detrapping doesn’t occur to all of n-type HfO2 capacitors. Gate voltage shift of these four devices after 100 seconds CCS stress don’t have obviously difference and are about 0.3 V. Thus the reliability is almost the same for n-type HfO2

capacitors under different oxidation conditions.

5.4 Measured at High Temperature

As shown in figure 5-7, C-V characteristics of n-type HfO2 capacitors with 6.25×10^-6 cm² die area under 300℃-15 minutes oxidation condition are measured at 25℃, 75℃ and 125℃ At higher measurement temperature, HfO. 2 capacitor has flatter accumulation region, steeper slope of C-V curve and smaller hysteresis. In addition, flat band voltage shifts to more negative at higher measurement. Fig. 5-8 shows J-V characteristics of n-type HfO2 capacitors with 6.25×10^-6 cm² die area under 300℃-15 minutes oxidation condition measured at 25℃, 75℃ and 125℃ from 0 V to 1 V. At higher measurement temperature, HfO2 capacitor has larger gate leakage current due to the higher energy of electrons. Besides, gate leakage current at VG = 1V has smaller increase from 75℃ to 125℃ than from 25 to 75℃ ℃. This hints that gate leakage current becomes to saturate at high measurement temperature. Fig. 5-9 shows J-V characteristics of p-type HfO2 capacitors with 6.25×10^-6 cm² die area under 400℃-15 minutes oxidation condition measured at 25℃, 75℃ and 125℃ from 0 V to -10 V. We find that HfO2 capacitor generates breakdown more easily at higher measurement temperature. This is attributed to electrons have higher energy at higher temperature and result in harder damage in HfO2 film.

5.5 Reference

[1] HyperPhysics, C.R Nave Georgia University, 2002.

-2 -1 0

p-type 400⁰C 15min Area = 6.25E-6 cm²

p-type 400⁰C 30min Area = 6.25E-6 cm²

p-type 500⁰C 15min Area = 6.25E-6 cm²

p-type 500⁰C 30min Area = 6.25E-6 cm²

Capacitance (µF/cm2 )

Gate Voltage (V)

Fig. 5-1 Hysteresis of p-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation conditions. (a) 400℃ 15 minutes (b) 400℃ 30 minutes (c) 500℃ 15 minutes (d) 500℃ 30 minutes

-1.0 -0.5 0.0 0.5 1.0 n-type 300⁰C 15min

Area = 6.25E-6 cm² n-type 400⁰C 15min

Area = 6.25E-6 cm² n-type 400⁰C 30min

Area = 6.25E-6 cm² n-type 500⁰C 15min

Area = 6.25E-6 cm²

Capacitance (µF/cm2 )

Gate Voltage (V)

Fig. 5-2 Hysteresis of n-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation conditions. (a) 300℃ 15 minutes (b) 400℃ 15 minutes (c) 400℃ 15 minutes (d) 500℃ 15 minutes

Breakdown voltage,IV_BDI(V)

Ln [-Ln (1-F(t))]

p-type 400℃ 15min p-type 400℃ 30min p-type 500℃ 15min p-type 500℃ 30min

Cumulative Failure Percent (%)

Fig. 5-3 Distribution of the breakdown voltage for p-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation conditions.

Breakdown voltage,IV_BDI(V)

Ln [-Ln (1-F(t))]

n-type 400℃ 15min n-type 400℃ 30min n-type 500℃ 15min n-type 500℃ 30min

Cumulative Failure Percent (%)

Fig. 5-4 Distribution of the breakdown voltage for n-type HfO2 capacitors with 6.25×10^-6 cm² die area under different oxidation conditions.

0 20 40 60 80 100 under different oxidation conditions as a function of stress time during Jg = 1 A/cm² CCS stress. under different oxidation conditions as a function of stress time during Jg = 1 A/cm² CCS stress.

-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0

n-type 300⁰C 15min area = 6.25E-6 cm²

Fig. 5-7 C-V characteristics of n-type HfO2 capacitors with 6.25×10^-6 cm² die area under 300℃ 15 minutes oxidation condition measured at 25℃, 75℃ and 125℃.

n-type 300⁰C 15min area = 6.25E-6 cm²

Fig. 5-8 J-V characteristics of n-type HfO2 capacitors with 6.25×10^-6 cm² die area under 300℃ 15 minutes oxidation condition measured at 25℃, 75℃ and 125℃ from 0 V to 1 V.

-10 -8 -6 -4 -2 0 10^-8

10^-6 10^-4 10^-2 10⁰ 10²

p-type 400⁰C 15min area = 6.25E-6 cm²

measured at 25⁰C measured at 75⁰C measured at 125⁰C Gate leakage (A/cm2 )

Gate Voltage (V)

Fig. 5-9 J-V characteristics of p-type HfO2 capacitors with 6.25×10^-6 cm² die area under 400℃ 15 minutes oxidation condition measured at 25℃, 75℃ and 125℃ from 0 V to -10 V.

Chapter 6 Conclusion and Future Work

6.1 Conclusion

The Al/HfO2/Si MIS capacitors were fabricated by DC sputter 20 Å hafnium on p-type and n-type silicon substrate and proceeds under 200℃～500℃ and 15～30 minutes oxidation conditions. Devices with different die areas under different oxidation conditions are performed and discussed.

We couldn’t get effective C-V characteristics of p-type HfO2 capacitors under 200℃ and 300℃ oxidation condition, and of n-type HfO2 capacitors under 200℃

oxidation condition. The size of die area doesn’t influence the flat band voltage.

Higher oxidation temperature and longer oxidation time make the more negative flat band voltage shift. N-type HfO2 capacitor with 6.25×10^-6 cm² die area under 300℃-15 minutes oxidation condition has the smallest EOT of 9.2 Å. Device under higher oxidation temperature has thicker interfacial layer and stronger chemical bonding. Thicker physical thickness and stronger chemical bonding both contribute to the decrease of gate leakage current. Thus, higher oxidation temperature could results in larger EOT and less gate leakage current. Longer oxidation time slightly increases EOT and decreases gate leakage current. Under the same oxidation condition, p-type HfO2 capacitor has smaller EOT and smaller gate leakage current than n-type HfO2

capacitor. HfO2 layer grown on p-type substrate has better quality of resisting gate leakage than on n-type substrate. EOT of devices with different die areas on the same wafer should be the same in fact. With the same EOT, using HfO2 instead of SiO2 for gate insulator could decrease gate leakage current more than 2~3 orders. Device with thinner thickness and weaker chemical bonding generates breakdown more easily. In addition, like SiO2, thicker HfO2 shows more abrupt breakdown characteristics compared to thinner HfO2. Like SiO2 NMOSFET, HfO2 capacitor has four degradation stages. This hints HfO2 might have similar breakdown mechanism with SiO2. Schottky emission occurs at very low gate bias and F-N tunneling occurs at higher gate bias than both Schottky emission and Frenkel-Poole emission. In addition, n-type HfO2 capacitors under 300℃-15 minutes oxidation condition always generate Schottky emission, F-N tunneling or Frenkel-Poole emission earliest because of smallest EOT. RTA treatment couldn’t improve the quality of HfO2 film, because HfO2 is unit-combined lattice structure and thus couldn’t be enhanced the value of

dielectric constant by RTA treatment. When the temperature rises to 800℃～900℃, HfO2 would change the lattice structure from amorphous type to polycrystalline type and thus increase gate leakage current.

Hysteresis of p-type HfO₂ capacitors are about 20 ～ 30 mV. Oxidation temperature seems not influence hysteresis for p-type HfO2 capacitors. Longer oxidation time makes hysteresis a little larger. For n-type HfO2 capacitors, higher oxidation temperature effectively decreases hysteresis. P-type HfO2 capacitor has much smaller hysteresis than n-type HfO2 capacitor. Uniformity of p-type HfO2

capacitor is excellent under all oxidation condition and a little better than of n-type HfO2 capacitor. P-type HfO2 capacitor under 400℃-15 minutes oxidation condition has better capability of resisting current tunneling than under 400℃-30 minutes oxidation condition. P-type HfO2 capacitor under lower oxidation temperature and shorter oxidation time has better reliability. Reliability is almost the same for n-type HfO2 capacitors under different oxidation conditions. At higher measurement temperature, HfO2 capacitor has flatter accumulation region, steeper slope of C-V curve and smaller hysteresis. In addition, flat band voltage shifts to more negative at higher measurement. HfO2 capacitor also has larger gate leakage current due to the higher energy of electrons and generates breakdown more easily at higher measurement temperature.

6.2 Future Work

The HfO2 capacitor fabricated by our method mentioned above could provide an ultra thin dielectric layer of 9.2 Å EOT for n-type and 17.3 Å EOT for p-type. Their leakage current and film quality are acceptable for the use of devices in next generation. We think by technically and carefully controlling the oxidation condition, such as temperature and time, will effectively improve the quality of HfO2 film.