Thermal Process

Fig. 3-4 and Fig. 3-5 indicate the thermal process flow in sample I and sample II.

In sample I, directly oxidize a thick SiGeN layer (sample I) to form blocking oxide by a dry oxidation process with different time or by a 30 min dry oxidation process followed by a 3 minutes steam treatment in thermal furnace at 900 ℃. In sample II, oxidize the amorphous Si layer capped on the SiGeN layer(sample II) to form blocking oxide by a dry oxidation process with different time or by a 30 min dry oxidation process followed by a 3 minutes steam treatment in thermal furnace at 900 ℃. The steam treatment means let in H2O into thermal furnace, the same as wet oxidation. Owing to its smaller size and lower activation energy than O₂ molecules, H₂O molecules are more permeable through the blocking oxide and can passivate dangling bonds in the blocking oxide. The purpose of steam treatment is to strengthen the blocking oxide and improve its quality.

Figure 3-1 (a) Sample structure of sample I (b) Sample structure of sample II.

Si-substrate Tunnel ox. 50A

SiGeN

(a)

Sample I

Si-substrate Tunnel ox. 50A

SiGeN a-Si

Sample II

(b)

Sample I

(a)

(b)

Figure 3-2 The TEM diagram of sample I before thermal oxidation.

Si Substrate

SiGeN Tunnel Oxide

Tunnel Oxide+ SiGeN

Si Substrate

Sample II

Si Substrate Tunnel Oxide SiGeN

a-Si

Tunnel Oxide

SiGeN Si Substrate

a-Si

Directly Oxidize SiGeN Layer to Form Blocking Oxide

Figure 3-4 The thermal process flow of sample I.

Si-substrate Tunnel ox. 50A

SiGeN

Si-substrate a-Si 200A

Blocking ox.

Ge dot Tunnel ox. 50A

SiON Thermal

Oxidation

• Dry

• Dry + steam treatment

Sample I

Oxidize The Amorphous Si Layer Capped on the SiGeN layer to Form Blocking Oxide

Si-substrate Tunnel ox. 50A

SiGeN a-Si

Si-substrate a-Si 200A

Blocking ox.

Tunnel ox. 50A SiON

Thermal Oxidation

•

Dry

•

Dry + steam treatment

Ge dot

Sample II

Chapter 4

Experiment Results and Discussions

4.1 Electrical Characteristics

In previous section, it has been mentioned that there are two methods used to form blocking oxide. In one method, only a dry oxidation process with different time in thermal furnace at 900 ℃ is adopted. In the other method, a dry oxidation process is followed by a 3 minutes steam treatment. Table 4-1 shows the difference conditions performed on sample I and sample II. The Ge nanocrystals embedded SiON layer (the charge storage layer) of a MOIOS memory device is utilized to capture the injected carriers from the channel. When the device is programmed, electrons directly tunnel from the Si substrate through the tunnel oxide by Fowler-Nordheim (F-N) tunneling.

The tunneling electrons are trapped in the forbidden gap of SiON layer and conduction band of Ge nanocrystals in the SiON layer. For the erasion, the holes may tunnel from the valence band of the Si substrate. The tunneling hole recombine with the electrons trapped in the forbidden gap of SiON layer and conduction band of Ge nanocrystals in the SiON layer. The blocking oxide is utilized to prevent the carriers of gate electrode from injecting into the charge-trapping layer by Fowler-Nordheim (F-N) tunneling. The capture of carriers will causes a variation in the threshold voltage and can serve as a memory device.

The capacitance-voltage (C-V) hysteresis of sample I (without capped Si layer) with three different conditions A, B, C and D are shown in Fig. 4-1 (a), (b) and Fig. 4-2 (a), (b), respectively. In 30 and 45 minutes short term dry oxidation (condition A and B),

because the thickness is not thick enough and the quality is not good enough, the blocking oxide can’t block the carriers (electrons or holes) tunneling from gate to charge storage layer. When the dry oxidation time is extended to 60 minutes (condition C), the blocking oxide is thick enough to block the carriers from gate and therefore the way carrier injection turns from gate injection to substrate injection. In condition C, the memory windows are ~1.1V under ±3V C-V sweeping, ~2.4V under ±5V C-V sweeping and ~4V under ±7V C-V sweeping. In condition D (30 minutes dry oxidation followed by 3 minutes steam treatment), the memory window is 0.9V under ±10V C-V sweeping. The retention character of sample I with condition C (60 minutes dry oxidation) is shown in Fig. 4-3. The program curve and erase curve in Fig. 4-3 shift toward positive voltage at the same time because positive oxide trapped charges are created during the program/erase cycles in tunnel oxide and they will de-trap with the retention time [4-1]. As the de-trapping of the positive oxide trapped charges, the threshold voltage will shift to positive side. The schematic plot and are shown in Figure 4-4. The endurance characteristic of sample I with condition C (60 minutes dry oxidation) is shown in Fig. 4-5. There is almost no shift in the threshold voltage after 10⁶ program/erase cycles under ±3V operation.

The capacitance-voltage (C-V) hysteresis of sample II (with capped Si layer) with four different conditions A, B, C and D are shown in Fig. 4-6 (a), (b), and 4-7 (a), (b), respectively. The C-V properties are of the same trends as sample I. In 30 and 45 minutes short term dry oxidation (condition A and B) a gate injection is observed. Also, substrate injections are observed in 60 minutes dry oxidation (condition C) and 30 minutes dry oxidation plus a 3-minute steam treatment (condition D). In condition C, the threshold-voltage shift (memory window, ∆Vt) under ±7V C-V sweeping is ~1.7 V and in condition D (30 minutes dry oxidation followed by 3 minutes steam treatment),

sweeping and ~4.2V under ±10V C-V sweeping. The retention and endurance character of sample II with condition D are shown in Fig. 4-8 and Fig. 4-9. The Auger Electron Spectroscopy (AES) analysis of sample II with condition D is shown in Fig. 4-33 (b).

There is a rise in oxygen signal after steam treatment in AES analysis. The SiON dielectric is oxidized by steam to form SiOx. As a result, the Ge nanocrystals are not embedded in SiON but in SiOx. The program and erase curves in Fig. 4-9 shift to negative voltage at the same time because positive oxide trapped charges are created during the program/erase cycles in both tunnel oxide and the SiOx oxidized from SiON film by steam treatment [4-1]. The schematic plot is shown in Figure 4-10. The positive trapped charges in SiOx oxidized from SiON film will increase with the P/E cycles because of its worse quality than tunnel oxide’s. Therefore, the threshold voltage in the Fig. 4-9 will shift to negative side.

4.1.1 Comparing to Other Memories

Figure 4-11 shows the C-V hysteresis of Ge nanocrystals embedded in SiO2 (Ge nanocrystal only) nonvolatile memory proposed by T. C. Chang et al. [4.2]. Fig. 4-12 shows the C-V hysteresis of SONOS memory and the SiNx layer in the ONO stack is deposited by the same PECVD used in this study. The memory windows in the Ge nanocrystal only NVSM are ~0.4V under ±5V C-V sweeping and ~2V under ±10V C-V sweeping. The memory windows in SONOS only NVSM are ~0.2V under ±5 C-V sweeping and ~0.6V under ±10V C-V sweeping. In this study, a combination of Ge nanocrystal and SONOS NVSM is proposed. The memory windows of sample I with condition C are ~1.1V under ±3V C-V sweeping, ~2.4V under ±5V C-V sweeping and

~4V under ±7V C-V sweeping, as shown in Fig. 4-2 (a). Moreover, The memory windows of sample II with condition D are ~0.6V under ±3V C-V sweeping, ~1.8 V under ±7V C-V sweeping and ~4.2V under ±10V C-V sweeping, as shown in Fig. 4-7 (b). The memory windows both in sample I and sample II are larger than Ge nanocrystal

only NVSM or SONOS only NVSM (table. 4-4) and even larger than the Ge nanocrystal NVSM plus SONOS NVSM. It’s inferred that besides charge trapping units in the Ge nanocrystal and the SiON dielectric, there are additional charge trapping units at Ge/SiON interface. The band diagrams are shown in Figure 4-13.

4.2 Mechanism of Ge Nanocrystals Formation

Kan et al. adopted a two-step RTA process executed on a Si0.54Ge0.46 film to form Ge nano-dots embedded in SiOx dielectric [4.3-4.4] and the 950 N℃ 2 RTA would reduce the Ge atoms and the nanocrystals grew based on the Ostwald ripening mechanism [4.5]. Besides, a method of Ge nano-dots segregated downward until they reach the tunnel oxide surface by Si0.8Ge0.2 layer being wet oxidized in an APCVD reactor has been proposed [4.6-4.8]. In this work, the formation of Ge nanocrystals is only by one step of oxidation of the silicon-germanium-nitride layer, which is simpler than the previous research [4.9] and high-throughput and low cost potentially for industrial consideration.

A thermal furnace process is introduced to form blocking oxide (SiOx or SiON) and segregate Ge atoms in this study. During 900 dry oxidation process, ℃ Si in the SiGeN film more easily combine with O2 than Ge to form SiOx. Because of the low solid solubility of Ge in silicon oxide, the Ge atoms will be segregated downward until they reach the tunnel oxide surface [4.6-4.8] and nucleate to form Ge nano-dots (or Ge nanocrystal) near the tunnel oxide(or gate oxide). Therefore, the SiGeN film will be oxidized to form SiOx film (as blocking oxide); meanwhile, the Ge in the SiGeN film will be segregated to form Ge nano-dots (or Ge nano-crystal) embedded by SiON dielectric near the tunnel oxide.

4.2.1 Directly Oxidize SiGeN Layer as Blocking Oxide ( Sample I )

The different bonds’ wave numbers of Fourier Transform Infrared Rays (FTIR) spectrum are shown in table 4-2 and 4-3 [4.8]. The FTIR spectra of sample I before and after thermal oxidation process are shown in Figure 4-14. The weak bonds such as Si-H, Ge-H, N-H disappear after 900℃ dry oxidation and the appearance of Si-O after oxidation means the SiGeN layer has been oxidized to form SiOx as blocking oxide.

The transmission electron microscope (TEM) diagrams and Auger Electron Spectroscopy (AES) analysis before oxidation and after oxidation with condition A(dry 30 minutes), C(dry 60minutes) are shown in Fig. 4-15 (a), (b) and Fig. 4-16 (a), (b), respectively. The TEM diagram as shown in Fig. 4-15 (a), there is no Ge nanocrystal present in the as-deposited SiGeN film before oxidation and Fig. 4-15 (b) shows that all of the three elements, Si, Ge and N are present in the as-deposited SiGeN film before oxidation. The Ge nanocrystals appear in the TEM diagram after oxidation as shown in Fig. 4-16 (a) and there is a rise of Ge and N signal between 500 and 1300 second in Fig.

4-16 (b), which reveals that the Ge nanocrystals are imbedded in SiON dielectric.

The Raman spectra of sample I before and after 30 minutes thermal oxidation process in O2 ambiance are shown in Figure 4-17. In the Raman spectrum of SiGeN film in sample I before oxidation, there is a broad distribution signal which means that the as-deposited SiGeN film is amorphous and a signal peak of Ge crystal appears after 30 minutes thermal oxidation. The appearance of the signal peak of crystal Ge represents that the Ge atoms in SiGeN film were segregated and nucleated forming Ge nanocrystal while dry oxidation. The Raman spectra of 30 minutes short term and 60 minutes long term dry oxidation are shown in Fig. 4-18 (a) and (b). In comparison with crystal Si substrate signal peak (~520 cm^-1), the intensity of crystal Ge peak (~300 cm^-1) increase with the extension of dry oxidation time, which reveals that the longer oxidation time makes not only more Ge atoms to be segregated from the thickening

blocking oxide, but also more time for Ge atoms to nucleate. The intensity of crystal Ge after 60 minutes oxidation is even stronger than that of crystal Si substrate.

4.2.2 Oxidize Capped Amorphous Si Layer as Blocking Oxide ( Sample II )

The FTIR spectra of sample II before and after thermal oxidation process are shown in Figure 4-19. The same as sample I, the weak bonds such as Si-H, Ge-H, N-H disappear after 900℃ dry oxidation and the appearance of Si-O after oxidation means the SiGeN layer has been oxidized to form SiOx as blocking oxide. The transmission electron microscope (TEM) diagrams and Auger Electron Spectroscopy (AES) analysis before oxidation and after oxidation with condition A(dry 30 minutes), C(dry 60minutes) are shown in Fig. 4-20 (a), (b), Fig. 4-21 (a), (b), Fig. 4-22 (a), (b), respectively. Also, the TEM diagram as shown in Fig. 4-20 (a), there is no Ge nanocrystal present in the as-deposited SiGeN film before oxidation and Fig. 4-20 (b) shows that all of the three elements, Si, Ge and N are present in the as-deposited SiGeN film before oxidation. In the Raman analysis as shown in Fig. 4-23, there is a Ge crystal peak but in the TEM diagram (Fig. 4-20(a)), there is no Ge nanocrystal present in the oxidized SiGeN film because the oxidation time is not long enough for Ge atoms to be segregated and to nucleate and this phenomenon is also observed by Kan et al. in their study [4.2]. After a longer oxidation period, the Ge nanocrystals appear in the TEM diagram, as shown in Fig. 4-22 (a) and there is a rise of Ge and N signal between 100 and 400 second in Fig.

4-22 (b), which reveals that the Ge nanocrystals are imbedded in SiON dielectric.

The Raman spectra of sample II before and after 30 minutes thermal oxidation process in O2 ambiance are shown in Figure 4-24. In the Raman spectrum of SiGeN film in sample II before oxidation, there is a broad distribution signal which means that the deposited SiGeN film is amorphous and a signal peak of Ge crystal appears after 30 minutes thermal oxidation. The appearance of the signal peak of crystal Ge represents

nanocrystal while oxidation. The Raman spectra of 30 minutes short term and 45 minutes longer term dry oxidation are shown in Fig. 4-25 (a) and (b). The same as sample I, in comparison with crystal Si substrate signal peak (~520 cm^-1), the intensity of crystal Ge peak (~300 cm^-1) increase with the extension of dry oxidation time, which reveals that the longer oxidation time makes not only more Ge atoms to be segregated from the SiGeN layer, but also more time for Ge atoms to nucleate. The intensity of crystal Ge after 45 minutes oxidation is even as strong as that of crystal Si substrate.

Besides, there is a Si-Ge signal appear in Fig. 2-25 (a), (b) and the peak decays with the extension of oxidation time, but it’s not present in sample I. Therefore, it’s inferred that the Si-Ge bonds are produced in the amorphous/SiGeN interface during the PECVD film deposition process.

4.3 Role of Steam Treatment

The steam treatment means let in H2O into thermal furnace at 900℃, the same as wet oxidation. After the dry oxidation, a 3-minute steam treatment is performed on both sample I and sample II; the results are demonstrated in this section. It’s believed that owing to its smaller size and lower activation energy than O2 molecules, H2O molecules are more permeable through the blocking oxide and passivate dangling bonds in blocking oxide. The purpose of steam treatment is to strengthen the blocking oxide and improve its quality.

4.3.1 Directly Oxidize SiGeN Layer as Blocking Oxide ( Sample I )

The capacitance-voltage (C-V) hysteresis and I-V characteristics of sample I (without capped Si layer) with four different conditions (A, B, C, D) are shown in Fig.

4-26 (a), (b), (c), (d) and Fig. 4-27, respectively. With the extension of oxidation time from 30 minutes to 60 minutes, the C-V hysteresis turns form gate injection (clockwise)

to substrate injection (counterclockwise) and the leakage current density (J) in the I-V diagram decrease from 10^-3 order to 10^-9 order, which means the blocking oxide is thick enough and its quality is good enough after a long enough dry oxidation. However, the leakage current density characteristic of 30 minutes short term dry oxidation followed by a 3 minutes steam treatment is comparable with 60 minutes long term dry oxidation, which reveals that an extra 3 minutes steam treatment can improve the blocking oxide quality.

The TEM diagrams and Auger Electron Spectroscopy (AES) analysis after oxidation with condition D (30 minutes dry oxidation plus 3 minutes steam treatment) are shown in Fig. 4-28 (a) and (b). Owing to the rapid oxidation rate of steam treatment, the Si atoms in SiGeN film are oxidized so fast that there is on enough time for Ge atoms to be segregated toward the tunnel oxide and therefore the Ge clusters are present throughout the oxidized SiGeN film, as shown in Fig. 4-28 (a). Furthermore, the N signal in the AES spectrum, as shown in Fig. 4-28 (b), almost decays to zero after steam treatment. This represents that the SiON dielectric by which the Ge nano-crystal is surrounded is oxidized to become SiOx and also explains the endurance characteristic without steam treatment (Fig. 4-5) is better that with a steam treatment (Fig. 4-9) because of the oxide trapped charges present in the SiOx dielectric after P/E cycles.

The Raman spectra before and after steam treatment are compared in figure 4-29.

There is a dramatic drop in the Ge signal peak and there is also a rise in the germanium oxide (Ge2O) signal after a steam treatment. The same situation is also observed in 60 minutes dry oxidation with and without steam treatment cases, as shown in Fig. 4-30.

These show that the introduction of steam treatment will oxidize a part of Ge nanocrystal to become germanium oxide by which the Ge nanocrystals are surrounded.

The capacitance-voltage (C-V) hysteresis and I-V characteristics of sample II (with capped Si layer) with four different conditions (A, B, C, D) are shown in Fig. 4-31 (a), (b), (c), (d) and Fig. 4-32, respectively. With the extension of oxidation time from 30 minutes to 60 minutes, the C-V hysteresis turns form gate injection (clockwise) to substrate injection (counterclockwise) and the leakage current density (J) in the I-V diagram decrease from 10^-2 order to 10^-9 order, which means the blocking oxide is thick enough and its quality is good enough after a long enough dry oxidation. The same as sample I (without capped Si layer), the leakage current density characteristic of 30 minutes short term dry oxidation followed by a 3 minutes steam treatment is comparable with 60 minutes long term dry oxidation, which reveals that an extra 3 minutes steam treatment can improve the blocking oxide quality. The TEM diagrams of 60 minutes dry oxidation and 30 minutes dry oxidation plus 3 minutes steam treatment are shown in figure 4-33 (a) and (b). The thickness of blocking oxide after 60 minutes dry oxidation (~260 A) is thicker than that after 30 minutes dry oxidation (~200A) plus 3 minutes steam treatment but the I-V characteristic after 30 minutes oxidation (~200A) plus 3 minutes steam treatment is comparable with that after 60 minutes long term dry oxidation. This proves that the blocking oxide quality after 30 minutes dry oxidation followed by a 3-minute steam treatment is better than that after 60 minutes long term dry oxidation.

The TEM diagrams and Auger Electron Spectroscopy (AES) analysis after oxidation with condition D (30 minutes dry oxidation plus 3 minutes steam treatment) are shown in Fig. 4-34 (a) and (b). In Fig. 4-34 (a), because there is an amorphous capped Si layer in sample II before oxidation, the Ge nanocrystals are confined only between tunnel oxide and blocking oxide after oxidation. As a result, the distribution of Ge nanocystals differ form the case in sample I with the same oxidation condition (Fig.

4-28 (a)). Furthermore, the same phenomenon is observed that comparing to the case

before steam treatment in Fig. 4-21 (b), the N signal in the AES spectrum, as shown in Fig. 4-34 (b), decreases after steam treatment. This means that the SiON dielectric by which the Ge nano-crystal is surrounded is oxidized to become SiOx and also explains the endurance characteristic without steam treatment (Fig. 4-5) is better that with a steam treatment (Fig. 4-9) because of the oxide trapped charges present in the SiOx dielectric after P/E cycles again.

The Raman spectra before and after steam treatment are compared in figure 4-35.

Also, there is a dramatic drop in the Ge signal peak and there is also a rise in the germanium oxide (Ge2O) signal after a steam treatment. The same situation is also observed in 60 minutes dry oxidation with and without steam treatment cases, as shown in Fig. 4-36. These show that the introduction of steam treatment will make a part of every Ge precipitate formed during dry oxidation be oxidized to become germanium oxide by which the Ge nanocrystals are surrounded. Besides, the Si-Ge signal present in Fig. 4-25 (a), (b) disappear after steam treatment because of the good oxidizing ability of steam and the Si-Ge bonds are oxidized to form silicon oxide and germanium oxide.

Conditions of Thermal Process

Table 4-1 Conditions of thermal process.

Condition

O2 thermal oxidation

3 min steam treatment

A 30 min No

B 45 min No

C 60 min No

D 30 min Yes

Wave Number ( cm^-1 ) MODE

3380 N-H stretch mode

650-900 N-H wagging mode

909,964,993 NH2 bending mode

1568 NH2 scissor mode

1042 C-N stretch mode

1468 C-H bending mode

2850,2922,2955 C-H stretch mode

2044 Si-H stretch mode

1543 Si-H bending mode

650 Ge-H bending mode

800-1000 Ge-O stretch

1126-1128 Si-O stretch

503-505, 820 Si-O bending

450 Si-O rocking

3600, 3665 SiO-H stretch

3470,3515 GeO-H stretch

Table 4-2 The different bonds’ wave numbers of Fourier Transform Infrared

Rays (FTIR) spectra.

Table 4-3 The different bonds’ wave numbers of Fourier Transform Infrared

Rays (FTIR) spectra.

ΔV

_TH under 5V

ΔV

_TH under 7V

ΔV

_TH under 10V

Ge Nanocrystal

NVM 0.4 X 1

SiNx NVM 0.2 0.6 X

Oxidized capped

a-Si SiGeN NVM X 1.8 3.2

Oxidized SiGeN

NVM 2.4 4 X

Table 4-4 The memory windows of different memories.

Sample I

(w/o Capped Si layer)

Figure 4-1 The C-V diagrams of sample I with (a) condition A and (b) condition B. Both diagrams are gate injection.

Vg ( V )

Dry oxidation 30 min

-10VÙ10V

Dry oxidation 45 min

-10VÙ10V

(a)

(b)

Sample I

(w/o Capped Si layer)

Figure 4-2 The C-V diagrams of sample I with (a) condition C and (b)

Vg ( V )

Dry oxidation 60 min

Vg ( V )

Dry oxidation 30 min + steam treatment 3 min

-10VÙ10V

(a)

(b)

Sample I

(w/o Capped Si layer)

Retention

Figure 4-3 The retention character of sample I with condition C (60 min dry oxidation).

t ( sec )

10⁰ 10¹ 10² 10³ 10⁴ 10⁵ 10⁶ 10⁷

Threshold Voltage V TH ( V )

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

Program Erase

Sample I

(w/o Capped Si layer)

Figure 4-4 The de-trapping schematic plot of positive oxide trapped charges in tunnel oxide.

P-substrate Blocking ox.

Al Al

Positive oxide trapped charges in tunnel ox.

detrapping with the retention time.

After P/E cycles

Sample I

(w/o Capped Si layer)

Endurance

Figure 4-5 The endurance character of sample I with condition C (60 min dry oxidation).

P/E cycles

10

⁰

10

¹

10

²

10

³

10

⁴

10

⁵

10

⁶

10

⁷

10

⁸

10

⁹ Threshold Voltage VTH ( V )

-3 -2 -1 0 1 2 3

Program Erase

Sample II

Dry oxidation 30 min

-10VÙ10V

Dry oxidation 45 min

-10VÙ10V

(a)

(b)

Sample II

(with Capped Si layer)

Figure 4-7 The C-V diagrams of sample II with (a) condition C and (b) condition D. Both diagrams are substrate injection.

Vg ( V )

Dry oxidation 60 min

(a)

Dry oxidation 30 min + steam treatment 3 min

(b)

t ( sec )

10⁰ 10¹ 10² 10³ 10⁴ 10⁵ 10⁶ 10⁷

Threshold Voltage V TH ( V )

-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2

Erase Program

Sample II

(with Capped Si layer)

Retention

Figure 4-8 The retention character of sample II with condition D (30 min

dry oxidation + 3 min steam treatment).

Sample II

(with Capped Si layer)

Endurance

Figure 4-9 The endurance character of sample II with condition D (30 min dry oxidation + 3 min steam treatment).

P/E cycles

10

⁰

10

¹

10

²

10

³

10

⁴

10

⁵

10

⁶

10

⁷

Thresho ld Vol tage V

TH

( V )

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

Program Erase

Sample I

(w/o Capped Si layer)

Figure 4-10 The schematic plot of positive oxide trapped charges in the SiOx oxidized from SiGeN film.

P-substrate Blocking ox.

Al

P-substrate Blocking ox.

Al

Positive oxide trapped charges in the SiOx oxidized from SiGeN film increase with the P/E cycles.

Al

Al

Ge dot

Fresh

After P/E

cycles

The Ge Nanocrystal Only NVM

Figure 4-11 The C-V hysteresis of Ge nanocrystals embedded in SiO

2

(Ge nanocrystal only) nonvolatile memory proposed by T. C. Chang et al. [3.1]

Voltage (V)

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

C/Cox

0.0 0.2 0.4 0.6 0.8 1.0 1.2

2~(-4)V -4~2V 5~(-5)V -5~5V 10~(-10)V -10~10V

The SONOS Only NVM

Figure 4-12 The C-V hysteresis of SONOS memory.

VG ( V )

-6 -4 -2 0 2 4

C/C ox

0.0 0.2 0.4 0.6 0.8 1.0 1.2

-7V <=> 7V -5V <=> 5V

Figure 4-13 The band diagrams of SONOS, Ge nanocrystal and SONOS+

Ge nanocrystal NVSMs.

SONOS

nanocrystal

ox.

ox.

ox.

ox.

ox.

ox.

SiNx

Ge

Ge

SONOS + nanocrystal

Sample I

(w/o Capped Si layer)

FTIR

Figure 4-14 The Fourier Transform Infrared Rays (FTIR) spectra of sample I before and after thermal oxidation process.

Wave Number ( cm^-1 )

500 1000 1500 2000 2500 3000 3500 4000

Intensity ( a.u )

Sample I

(w/o Capped Si layer) Before Oxidation

(a)

(b)

Figure 4-15 (a) The TEM diagram and (b) AES analysis of sample I before oxidation.

Si Substrate

SiGeN Tunnel Oxide

Time ( Seconds )

0 400 800 1200 1600

MCounts/eV/ Sec

0 1

2 ^{N KL1}

O KL1 Ge LM2 Si KL1

SiGeN / SiO₂ / Si

Sample I

(w/o Capped Si layer) After 60 min Oxidation

(a)

(b)

Figure 4-16 (a) The TEM diagram and (b) AES analysis of sample I after

Si Substrate

Tunnel Oxide Ge

Time ( Seconds )

0 400 800 1200 1600 2000 2400

MCounts/eV/Sec

0 1 2

3 N KL1

O KL1 Ge LM2 Si KL1 SiGeN / SiO2 / Si

After 900C 60min Oxidation

Sample I

(w/o Capped Si layer)

Raman Analysis

Figure 4-17 The Raman spectra of sample I before and after dry oxidation process. A peak of Ge crystal appeared after oxidation.

Wave Number ( cm^-1 )

250 300 350 400 450

Intensity ( x 103 )

0 5 10 15 20 25

after 30 min oxidation SiGeN film

Ge

30min dry oxidastion for w/o capped a-Si

Raman Shift ( cm^-1 )

200 400 600 800 1000 1200

Intensity ( a.u )

60min dry oxidastion for w/o capped a-Si

Raman Shift ( cm^-1 )

200 400 600 800 1000 1200

Intensity ( a.u )

Figure 4-18 The Raman spectra of sample I with (a) 30 min short term and

Sample II

(with Capped Si layer)

Figure 4-19 The Fourier Transform Infrared Rays (FTIR) spectra of sample II before and after 60 min thermal oxidation process.

Wave Number ( cm^-1)

500 1000 1500 2000 2500 3000 3500

Intensity ( a.u )

Time ( Seconds )

0 100 200 300 400 500 600

MCounts/eV/Sec

0 1 2

N KL1 O KL1 Ge LM2 Si KL1

a-Si / SiGeN / SiO2 / Si

Sample II

(with Capped Si layer)

Before Oxidation

(a)

(b)

Figure 4-20 (a) The TEM diagram and (b) AES analysis of sample II before

Si Substrate

Tunnel Oxide SiGeN

a-Si

Sample II

(with Capped Si layer) After 30 min Oxidation

(a)

(b)

Figure 4-21 (a) The TEM diagram and (b) AES analysis of sample II after 30 min oxidation.

Time ( Seconds )

After 900C 30min Oxidation

SiGeN

Tunnel ox.

Si substrate

Time ( Seconds )

After 900C 60min Oxidation

Sample II

(with Capped Si layer) After 60 min Oxidation

(a)

(b)

Figure 4-22 (a) The TEM diagram and (b) AES analysis of sample II after

Si substrate Tunnel oxide

Ge

Blocking oxide

Sample II

(with Capped Si layer)

Raman Analysis

Figure 4-23 The Raman spectrum of sample II with 30 min dry oxidation.

30min dry oxidation for capped a-Si

Raman Shift ( cm^-1 )

200 400 600 800 1000 1200

Intensity ( a.u )

0 500 1000 1500 2000 2500

Ge

Si-Ge

Si

Sample II

(with Capped Si layer)

Raman Analysis

Figure 4-24 The Raman spectra of sample II before and after dry oxidation process. A peak of Ge crystal appeared after oxidation.

Wave Number ( cm^-1 )

250 300 350 400

Intensity ( x103 )

0 1 2 3 4

Oxidized SiGeN SiGeN

Ge

Sample II

(with Capped Si layer)

(a)

(b)

Figure 4-25 The Raman spectra of sample II with (a) 30 min short term and (b) 45 min longer term dry oxidation.

30min dry oxidation for capped a-Si

Raman Shift ( cm^-1 )

200 400 600 800 1000 1200

Intensity ( a.u )

45min dry oxidation for capped a-Si

Raman Shift ( cm^-1 )

200 400 600 800 1000 1200

Intensity ( a.u )

Sample I

(w/o Capped Si layer)

Figure 4-26 The C-V hysteresis of sample I with four different conditions (a) A, (b) B, (c) C, (d) D.

Dry oxidation 30 min

-10VÙ10

Dry oxidation 45 min -10VÙ10

Dry oxidation 60 min

Vg ( V )

Vg ( V )

在文檔中 含鍺摻雜氮化矽薄膜在非揮發性記憶體應用之研究 (頁 38-0)