Reliability

The effects of constant-voltage stress on capacitance, leakage current and ∆C/C0 of Al/TiTaO/TaN capacitor were investigated. After constant-voltage stress, the leakage current of a TiTaO MIM capacitor was lower than fresh one, as shown in Fig. 3-11. It was supposed that there is generation of the electron traps in the high-κ TiTaO dielectric and in the TaTiO/metal interface. And then, the trapped charges decrease the carrier mobility of electrons in the dielectric and lower the charge injection from the top electrode by electrostatic scattering, which in turn produces a smaller leakage current, according to a free-carrier-injection model [3-10]. Fig.3-11 also shows the thermal equilibrium-band diagram of Al/TiTaO/TaN structure after the constant-voltage stress.

Fig. 3-12 shows the C-V characteristics of the TiTaO MIM capacitors before and after constant-voltage stress. It can be seen that the capacitance density decreases with increasing stress time for the TiTaO MIM capacitors, and the curves have positive shift along voltage axis. Because the trapped charges in the dielectric will cause the voltage shift. Fig. 3-13 shows the ∆C/C0 characteristics below 1 MHz obtained from the data shown in Fig. 3-12 before and after constant-voltage stress. We can also find out that the ∆C/C0 decreases with increasing stress time as the same as the capacitance values. For this phenomenon, we can use electrode polarization mechanism that implies hopping carriers whose mobility is field dependent to clearly explain it [3-11]. The equation of this mechanism will be

( )

⎟⎟

(

ρ+

)

^{( ) ϖ σ ×⎢⎣⎡ ⎜⎝⎛ κ ⎟⎠⎞− ⎥⎦⎤} density of the mobile charges. Parameter ρ is the “blocking parameter,” that accounts for electrode transparency. For ohmic contacts, ρ is large (no space charge). On the contrary, for blocking contacts, ρ is weak (no charge transfer at the electrodes in ac). σ is the factor of

hopping distance of mobile charges and n is about the empirical Jonscher universal law, where 2n = 0~1 [3-11]. These are all verified experimental factors.

This equation (7) predicts that ∆C/C0 should decrease with frequency (ω^-2n) and should increase with the leakage current (σ0). Fig. 3-14 shows the characteristics of the VCC-α values versus constant-voltage-tress time at different frequencies. We can find out that the VCC-α becomes worse after constant-voltage stress and becomes better at higher frequency.

Altogether, the leakage current of a TiTaO MIM capacitor was lower, its capacitance and

∆C/C0 became smaller and the VCC-α was worse than before after the constant-voltage stress.

-5 -4 -3 -2 -1 0 1 2 3 4 5

Fig.3-1 C-V and J-V characteristics of the TiTaO MIM capacitors measured from 10 kHz to 1 MHz. The data were measured by HP 4156A and HP4284A precision LCR meter.

-2 -1 0 1 2 0

4 8 12 16 20 24

Al/TiTaO/TaN MIM at 1 MHz Al/TiTaO/TaN MIM at 500 kHz Al/TiTaO/TaN MIM at 100 kHz Al/TiO

₂

/TaN MIM at 1 MHz

Cap a citan ce D ensit y (fF/ µ m

2

)

Bias (V)

Fig.3-2 The C-V characteristics of TiO2 and TiTaO MIM capacitors measured at different frequency. High capacitance density of 23 fF/µm² of TiTaO MIM capacitors were measured at 1 MHz with small capacitance variation.

-4 -2 0 2 4 10

^-8

10

^-6

10

^-4

10

^-2

10

⁰

Al/TiO2/TaN Al/TaTiO/TaN

Bias (V) C u rr ent D e n si ty (A /cm

2

)

Bottom TaN Electron Injection Top Al electron Injection

Fig.3-3 The J-V characteristics of TiO2 and TiTaO MIM capacitors. The leakage current is lower for the TiTaO capacitors.

0.0 -0.5 -1.0 -1.5 -2.0 0

1x10

⁴

2x10

⁴

3x10

⁴

Gate injection @1MHz C=23 fF/

µ

m

²α

=1983 (ppm/V

²

)

C=14 fF/

µ

m

²α

=1459 (ppm/V

²

)

Bias (V)

∆

C/C (ppm)

Fig.3-4 The characteristics of ∆C/C0 for the TiTaO MIM capacitors with dielectric thicknesses of 17nm and 29nm. The data were measured at 1 MHz.

0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 0

1x10

⁴

2x10

⁴

3x10

⁴

Electric field (MV/cm)

∆

C/C (ppm)

C=23 fF/

µ

m

²α

=1983 (ppm/V

²

) C=14 fF/

µ

m

²α

=1459 (ppm/V

²

)

Fig.3-5 The polts of ∆C/C0 versus electric field (E) with different dielectric thickness. The reason for no matching together is that there are different gauge of trapped charges in the interface of the different thicknesses.

20 40 60 80 100 120 140

Fig.3-6 The characteristics of the Normalized capacitance of the TiTaO MIM capacitors as an approximate linear function of temperature.

0.5 1.0 2.0 5.0

-0.5j 0.5j

-1.0j 1.0j

-2.0j 2.0j

-5.0j 5.0j

S

₁₂

S

21

Fig.3-7 The measured scattering parameters of TiTaO MIM capacitors from 50 MHZ to 10 GHz.

R _P C

R _S L _S2

L _S1

Fig.3-8 The equivalent circuit model for capacitor extraction. The C and RP are the capacitance and its parallel resistance, and the LS and RS are the parasitic inductance and resistance from transmission lines connected between capacitor body and probing pads.

100k 1M 10M 100M 1G 10G 10

¹

10

²

10

³

10

⁴

10

⁵

0 5 10 15 20 25 30

C

∆ C/C

α β

Frequency (Hz)

C a p a ci ta n ce D e n s it y (f F / µ m

2

)

∆ C/C (p pm ), α ( pp m /V

2

) , β ( pp m /V ) 23 fF/ µ m

²

Fig.3-9 Frequency dependent capacitance density, ∆C/C0, α and β for a TiTaO MIM capacitor.

0.0 0.5 1.0 1.5 2.0 10

¹

10

²

10

³

10

⁴

10

⁵

50 MHz 100 MHz 1 GHz 10 GHz 100 kHz 500 kHz 1 MHz

Bias (V)

∆ C/ C ( ppm )

23 fF/ µ m

²

Increasing Frequency

Fig.3-10 The ∆C/C0-V characteristics of a TiTaO MIM capacitor. The data for frequencies >1 MHz were obtained from the S-parameters.

0 100 200 300 400 500 10

^-6

10

^-5

10

^-4

10

^-3

10

^-2

stressed @-1.5V for first time

stressed @-1.5V after 5 hours for second time stressed @-1.5V after 10 hours for thrid time

A l T aTiO x TaN

1.5V C o nst vo ltag e stress

electron trap p ing

A l T aTiO x TaN

1.5V C o nst vo ltag e stress

electron trap p ing

Gate current density (A/cm

2

)

Stress Time (s)

Fig.3-11 The J-V characteristics of Al/TiTaO/TaN capacitors, measured at 1 MHz. The inserted figure is the band diagram of Al/TiTaO/TaN structure.

1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 22.5

23.0 23.5 24.0

Positive shift along the voltage axis Capacitor Size=30

µ

m x 30

µ

m

C=23 fF/

µ

m

²

@1MHz

C

H

( fF/ um

2

)

Voltage(V)

As-stressed

Stressed @-1.5V 500s Stressed @-1.5V 1000s Stressed @-1.5V 2000s

Fig.3-12 The C-V characteristics of a TiTaO MIM capacitor were measured at 1 MHz before and after constant-voltage stress.

1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 0

1x10

⁴

2x10

⁴

3x10

⁴

4x10

⁴

As-stressed α=1983 (ppm/V²) Stressed @-1.5V 500s α=2241 (ppm/V²) Stressed @-1.5V 1000s α=2743 (ppm/V²) Stressed @-1.5V 2000s α=4203 (ppm/V²)

∆

C/C (ppm )

Voltage(V)

Fig.3-13 The ∆C/C0-V characteristics of a TiTaO MIM capacitor were obtained from the formula (6).

0 500 1000 1500 2000 0

1000 2000 3000 4000 5000 6000 7000

Capacitor Size=30

µ

m x 30

µ

m C=23 fF/

µ

m

²

;Stressed@-1.5V

100 kHz 500 kHz 1M Hz

VCC

α

Stress time(sec)

Fig.3-14 The characteristics of VCC-α versus stress time of a TiTaO MIM capacitor at different frequency.

Chapter 4 Conclusion

According to ITRS roadmap (2006), the typical requirements for year 2010 of RF (0.8G

~ 10G) capacitor are capacitance density of 5 fF/µm², voltage linearity of less than 100 ppm/V² , and leakage current of less than 10^-8 A/cm², respectively. We have achieved high 23 fF/µm² capacitance density, < 1.8% capacitance reduction to RF frequency range from 100 kHz to 10 GHz, and ∆C/C0 ≦ 550 ppm, low α of 81 ppm/V² and β of 98 ppm/V at 1 GHz by using high-κ TiTaO MIM capacitors and processed at 400^oC. It can also provide a low leakage current of 1.89 × 10^-6 A/cm² at -1V. All this indicate that it is very suitable for use in silicon IC applications, although the leakage current of the Al/TiTaO/TaN MIM capacitor structure is higher than 10^-8 A/cm². However, we can solve this problem by replacing top metal electrode which have higher work function than Al, or increase thickness to improve the leakage current at the cost of the degraded capacitance density.

The effects of constant voltage stress on capacitance, leakage current and VCC-α of Al/TaTiO/TaN capacitor were also investigated. We can find out that the decreasing leakage current, decreasing capacitance at low voltage, and increasing VCC-α during the stress time.

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Vita

姓名：陳冠麟 性別：男

出生年月日：民國 70 年 10 月 22 日 籍貫：台灣省彰化市

住址：彰化縣彰化市台化街 86 巷 14 號 學歷：國立中山大學電機系

(民國 89 年 9 月~民國 94 年 6 月) 國立交通大學電子研究所固態電子組 (民國 94 年九月~民國 96 年 6 月)

論文題目：

高介電常數金屬-絕緣層-金屬電容電性及其可靠度之研究

The Research of Electric Characteristics and Reliability of High-κ MIM Capacitors

在文檔中 高介電常數金屬-絕緣層-金屬電容電性及其可靠度之研究 (頁 35-0)