In this section, the physical and electrical characteristics of MOS capacitors using MOCVD HfAlO dielectric were discussed.
2-3-1 C-V Characteristic
Fig. 2-4~2-11 show the relationship between the sweep voltage and capacitance for Hf1-xAlxO MOS Capacitors. We have several conditions for Hf1-xAlxO MOS capacitors. Then we measure C-V curves, and use a systematic methodology to extract the accurate flat band voltage of Hf1-xAlxO MOS capacitors for interfacial state density (Fig. 2-21).We found that the higher PDA temperature, the thicker dielectric, the higher interface density, therefore the capacitance decreases. We also found that the H1A2 C-V curves are better than others.
2-3-2 I-V Characteristic
We also measure I-V curves, such as Fig. 2-12~2-19 illustrate. We found that the more Hf component the more leakage current, and higher PDA temperature the higher gate leakage current. This is because that more Hf component more grain boundaries.
Fig. 2-20 shows that the gate leakage current comparison between H1A2 and Al2O3
sample with the same condition (As-dep., 600oC PDA and 800oC PDA). We found
15
that they are almost the same.
2-3-3 CET Characteristic
From the C-V illustrations (Fig. 2-4~2-11), we not only can calculate the Vfb for each sample, but also the CET for each sample. So we plot the Fig. 2-22 which shows the relationship between the gate leakage current Jg@Vfb-2V(A/cm2) and each sample for all conditions. We discovered that the more Hf component the higher gate leakage current Jg@Vfb-2V(A/cm2), this is because that the more Hf component the more grain boundaries. The Fig. 2-23 shows the relationship between the gate leakage current Jg@Vfb-2V(A/cm2) and the CET for each samples with all PDA conditions.
We found that the Al-rich-Hf1-xAlxO capacitors are better than Hf-rich-Hf1-xAlxO ones in the relationship between gate leakage current and CET.
From the two pictures (Fig. 2-22 and 2-23), we extract the Al-rich-Hf1-xAlxO capacitors are better, so we discuss the Al-rich-Hf1-xAlxO characteristics especially.
Fig.2-24 shows the relationship between CET (nm) and each Al-rich samples with all PDA conditions, Fig. 2-25 shows the relationship between the gate leakage current Jg@Vfb-2V(A/cm2) and each Al-rich-Hf1-xAlxO samples with all PDA conditions, and Fig. 2-26 shows the relationship between the gate leakage current Jg@Vfb-1.5V(A/cm2) and each Al-rich-Hf1-xAlxO samples with all PDA conditions. From Fig. 2-24 and Fig.
2-25, we can combine them to the Fig. 2-27 which shows that the relationship between the gate leakage current Jg@Vfb-2V(A/cm2) and the CET for each samples with all PDA conditions. We can obviously find the two samples H1A2 (As-dep.) and H1A2 (700oC PDA) with the lowest CET and the lowest gate leakage current Jg@Vfb-2V(A/cm2) from Fig. 2-27, so we decided the four conditions (H1A2 As-dep., H1A2 700oC PDA, Al2O3 As-dep., and Al2O3 700oC PDA) are our the best blocking layer for SONOS-type memory in next chapter. We cast the characteristics of
16
Al-rich-Hf1-xAlxO dielectrics capacitors in Table 2-3.
2-4 Summary
In this chapter, we observed that Al-rich Hf1-xAlxO dielectric capacitors have lower interfacial state density, lower gate leakage current Jg@Vfb-2V(A/cm2) and Jg@Vfb-1.5V(A/cm2), and lower CET than Hf-rich ones at the same condition.
Therefore we optimized the condition for the SONOS-type memory blocking layer.
According to our data, we choose A (Al2O3: As-dep. and 700oC PDA) and H1A2 (HfAlO: As-dep. and 700oC PDA) for our blocking layer of SONOS-type memory.
Dielectric
Table 2-1 Selected material and electrical properties of high-k gate dielectrics.
Data compiled from Robertson [2.5], Gusev et al. [2.4], Hubbard and Schlom [2.3], and other sources.
Fig. 2-1 Bandgap and band alignment of high k gate dielectrics with respect to silicon. Data from Robertnson [2.5], with permission. The dashed line represents 1eV above/below the conduction/valence bends.
Fig. 2-2 The process flow of the Hf1-xAlxO MOS capacitors. On the right: the different flow rates and the dielectric Hf/Al component ratio analyzed by XPS method.
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Sample
Split Condition H H10A1 H8A1 H6A1 H2A1 H1A1 H1A2 A
As-dep. ■ ■ ■ ■ ■ ■ ■ ■
600oC PDA ● ● ● ● ● ● ● ●
700oC PDA ▲ ▲ ▲ ▲
800oC PDA ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆
900oC PDA ★ ★ ★ ★
Table 2-2 Split table for MIS Capacitors using MOCVD Hf1-xAlxO Dielectric.
0 2 4 6 8 10
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Hf/Al ratio in Hf 1-xAl xO
Hf/Al precursor rate
Fig. 2-3 The relationship between Hf/Al precursor rate and Hf/Al ratio in Hf1-xAlxO.
18
-3 -2 -1 0 1 2 3
Fig. 2-4 The C-V curves of Al2O3 dielectric MOS capacitor.
-3 -2 -1 0 1 2 3
Fig. 2-5 The C-V curves of H1A2 (Hf/Al = 0.11) dielectric MOS capacitor.
19
-3 -2 -1 0 1 2 3
Fig. 2-6 The C-V curves of H1A1 (Hf/Al = 0.23) dielectric MOS capacitor.
-3 -2 -1 0 1 2 3
Fig. 2-7 The C-V curves of H2A1 (Hf/Al = 0.55) dielectric MOS capacitor.
20
-3 -2 -1 0 1 2 3
Fig. 2-8 The C-V curves of H6A1 (Hf/Al = 3) dielectric MOS capacitor.
-3 -2 -1 0 1 2 3
Fig. 2-9 The C-V curves of H8A1 (Hf/Al = 4) dielectric MOS capacitor.
21
-3 -2 -1 0 1 2 3
Fig. 2-10 The C-V curves of H10A1 (Hf/Al = 5.67) dielectric MOS capacitor.
-3 -2 -1 0 1 2 3
Fig. 2-11 The C-V curves of HfO2 dielectric MOS capacitor.
22
-4 -3 -2 -1 0 Gate leakage current J g
(
A/cm2)
Fig. 2-12 The I-V curves of Al2O3 dielectric MOS capacitor.
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 Gate leakage current J g
(
A/cm2)
Fig. 2-13 The I-V curves of H1A2 (Hf/Al = 0.11) dielectric MOS capacitor.
23
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0
Fig. 2-14 The I-V curves of H1A1 (Hf/Al = 0.23) dielectric MOS capacitor.
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0
Gate leakage current J g
(
A/cm2)
Voltage(V)
Fig. 2-15 The I-V curves of H2A1 (Hf/Al = 0.55) dielectric MOS capacitor.
24
-4 -3 -2 -1 0
Fig. 2-16 The I-V curves of H6A1 (Hf/Al = 3) dielectric MOS capacitor.
-4 -3 -2 -1 0 Gate leakage current J g
(
A/cm2)
Fig. 2-17 The I-V curves of H8A1 (Hf/Al = 4) dielectric MOS capacitor.
25
-4 -3 -2 -1 0 Gate leakage current J g
(
A/cm2)
H10A1 As-dep.
600oC PDA 800oC PDA
Fig. 2-18 The I-V curves of H10A1 (Hf/Al = 5.67) dielectric MOS capacitor.
-4 -3 -2 -1 0 Gate leakage current J g
(
A/cm2)
Fig. 2-19 The I-V curves of HfO2 dielectric MOS capacitor.
26
-3 -2 -1 0
Fig. 2-20 The gate leakage current comparison between H1A2 and Al2O3 with the same condition (As-dep., 600oC PDA and 800oC PDA).
1011 1012 1013
Al-rich-Hf1-xAlxO (x=0.8-1) Hf-rich-Hf1-xAlxO (x=0-0.25)
Interfacial state density D it(cm-2 eV-1 )
Al
Fig. 2-21 The relationship between interfacial state density Dit and PDA conditions.
27
10-10
Hf-rich-HfxAl1-xO (x=0.75-0.85) Al-rich-Hf
xAl
1-xO (x=0.1-0.2)
PDA conditions
Gate leakage current J g@V FB-2 V(A/cm2 )
900oC
Fig. 2-22 The relationship between the gate leakage current Jg@Vfb-2V(A/cm2) and each sample for all conditions.
20 30 40 50 60 70 80
Hf-rich-Hf1-xAlxO (x=0-0.25)
Al-rich-Hf1-xAlxO (x=0.8-1)
CET (nm)
Gate leakage current J g@V FB-2 V(A/cm2 )
Fig. 2-23 The relationship between the gate leakage current Jg@Vfb-2V(A/cm2) and the CET for each samples with all PDA conditions.
28
1
Fig. 2-24 The relationship between CET (nm) and each Al-rich-Hf1-xAlxO samples with all PDA conditions.
10-10
Hf/Al = 3.5/6.5 (H2A1)
Hf/Al = 1.9/8.1 (H1A1)
Hf/Al = 1.0/9.0 (H1A2)
PDA conditions
Gate leakage current J g@V FB-2 V(A/cm2 )
Fig. 2-25 The relationship between the gate leakage current Jg@Vfb-2V(A/cm2) and each Al-rich-Hf1-xAlxO samples with all PDA conditions.
29
10-9 10-8 10-7 10-6
Hf/Al = 3.5/6.5 (H2A1)
Hf/Al = 1.9/8.1 (H1A1)
Hf/Al = 1.0/9.0 (H1A2) 900oC PDA conditions
Gate leakage current J g@V FB-1.5 V(A/cm2 )
800oC 700oC
600oC As-dep.
Fig. 2-26 The relationship between the gate leakage current Jg@Vfb-1.5V(A/cm2) and each Al-rich-Hf1-xAlxO samples with all PDA conditions.
2 3 4 5 6 7
Gate leakage current J g@V FB-2 V(A/cm2 )
Hf/Al = 1.0/9.0 (H1A2) Hf/Al = 1.9/8.1 (H1A1)
CET (nm)
Hf/Al = 3.5/6.5 (H2A1)
Fig. 2-27 The relationship between the gate leakage current Jg@Vfb-2V(A/cm2) and the CET for each samples with all PDA conditions.
30
31
Al2O3(As-dep.) 44.8 0.89 1.3x1011 1.9x10-9 6.3x10-10
H1A2(As-dep.) 28.2 0.6 4x10
11
H1A1(As-dep.) 35.3 0.3 4.2x1012 3.7x10
-9
1.7x10
-9
H1A1(700oC PDA) 37.3 0.62 4.7x1012 10-7 8.1x10-9
H2A1(As-dep.) 35.9 0.44 10
12 Table 2-3 The characteristics of Al-rich-Hf1-xAlxO dielectrics capacitors.