*4.2.1.1. Plasma process dependence*

**Figure 7** shows the variation in the *k* value of a porous low-*k* dielectric after O2 plasma treatments with various plasma conditions (power, treatment time, and O2 flow rate). The *k* value of the pristine porous low-*k* dielectric was 2.56. The *k* values of porous low-*k* dielectrics increased after plasma treatment. The increasing magnitude increased with increasing the RF power and the treatment time but slightly deceased with increasing the O2 flow rate. More reactive oxygen species (ions and radicals) formation and a deeper penetration depth for a higher RF power and a longer treatment time in an O2 plasma treatment can be responsible for a larger change in the *k* value. The negative dependence on the O2 flow rate can be attributed to the decreased dissociation rate of O2 gas due to a fixed RF power, leading to a decreased reactive oxygen species (ions and radicals) in the plasma.

**Figure 8(a)** compares the leakage current density and the stress electric field for the pristine and O2 plasma-treated low-*k* films. At a lower electric field, the leakage current density increases with increasing the electric field (region I). Then, the leakage current density reaches a plateau without significant variation (region II). Finally, the leakage current density suddenly jumps, whose value is over 10−2 A/cm2 . This electric field is defined as the dielectric breakdown electric field (region III). For O<sup>2</sup> plasma-treated low-*k* dielectrics, a higher leakage current in region I, a longer duration in region II, and a lower breakdown electric field in region III were detected.

O2

breakdown electric field for the O<sup>2</sup>

performance for O2

plasma treatment conditions.

cess parameters in the O2

power and the treatment time of O2

UV curing and followed by a RP H2

Four kinds of low-*k* dielectrics were treated by O2

*4.2.1.2. Low-k dielectric dependence*

plasma-treated low-*k* dielectrics. A higher leakage current density also leads to a lower

Leakage current densities at 1 and 2 MV/cm and dielectric breakdown field of porous low-*k* dielectrics under various O2

low-*k* dielectrics with various treatment conditions. The characteristic dielectric breakdown time was determined from Weibull distribution, representing the time as 63.2% of the sample failed [52]. The degradation in the characteristic dielectric breakdown time becomes serious

low-*k* dielectrics were dense low-*k* (*k* = 3.02; called low-*k*\_1), porogen low-*k* without UV (*k* = 2.92; called low-*k*\_2) and with UV curing (2.56; called low-*k*\_3), and porogen low-*k* with

**Figure 10** compares the change percentage of the *k* value as a function of RF power in O2 plasma process for four different low-*k* films. The increasing magnitude is enlarged with an increase of RF power for all low-*k* dielectrics. The porogen-containing low-*k* dielectrics (low*k*\_2 and low-*k*\_3) have a higher increase in the *k* value as compared to low-*k*\_1. This suggests that porogen plays an important role for the low-*k* dielectrics under plasma irradiation. Furthermore, the highest increase in the *k* value is occurred in the low-*k*\_2 (porogen-containing low-*k* film without UV curing). The UV irradiation on the low-*k* dielectrics not only removes the porogen to form pores but also strengthens the bonding strength of the low-*k* dielectrics

moisture, which provides ionic conduction pathways by releasing mobile ions (H+

**Figure 9** compares the characteristic dielectric breakdown times (T63.2%) for O2

**Figure 8.** (a) Leakage current density versus applied voltage for pristine and O2

with an increase of RF power and treatment time or a reduction of O2

plasma-treated low-*k* dielectrics. The degrading electrical

, OH<sup>−</sup>

plasma-treated low-*k* dielectrics. (b)

Plasma Damage on Low-*k* Dielectric Materials http://dx.doi.org/10.5772/intechopen.79494

plasma-treated

flow rate. All pro-

) [51].

303

plasma-treated low-*k* dielectrics can be attributable to more absorption of

plasma process would degrade low-*k* dielectric properties. The RF

/He plasma treatment (*k* = 2.48; called low-*k*\_4).

plasma treatment cause a more significant degradation.

plasma with various RF powers. The used

**Figure 8(b)** compares the leakage current densities at 1 MV/cm and 2 MV/cm and the breakdown electric field of the O<sup>2</sup> plasma-treated low-*k* dielectrics with various treatment conditions. Similar to the result of *k* value change, a higher RF power, a longer treatment time, and a lower O2 flow rate can result in the largest increase of the leakage current density for

**Figure 7.** Dielectric constant change of porous low-*k* dielectrics under various O2 plasma treatment conditions (standard condition: RF power = 60 W; time = 60 s; oxygen flow = 100 sccm).

**Figure 8.** (a) Leakage current density versus applied voltage for pristine and O2 plasma-treated low-*k* dielectrics. (b) Leakage current densities at 1 and 2 MV/cm and dielectric breakdown field of porous low-*k* dielectrics under various O2 plasma treatment conditions.

O2 plasma-treated low-*k* dielectrics. A higher leakage current density also leads to a lower breakdown electric field for the O<sup>2</sup> plasma-treated low-*k* dielectrics. The degrading electrical performance for O2 plasma-treated low-*k* dielectrics can be attributable to more absorption of moisture, which provides ionic conduction pathways by releasing mobile ions (H+ , OH<sup>−</sup> ) [51].

**Figure 9** compares the characteristic dielectric breakdown times (T63.2%) for O2 plasma-treated low-*k* dielectrics with various treatment conditions. The characteristic dielectric breakdown time was determined from Weibull distribution, representing the time as 63.2% of the sample failed [52]. The degradation in the characteristic dielectric breakdown time becomes serious with an increase of RF power and treatment time or a reduction of O2 flow rate. All process parameters in the O2 plasma process would degrade low-*k* dielectric properties. The RF power and the treatment time of O2 plasma treatment cause a more significant degradation.

#### *4.2.1.2. Low-k dielectric dependence*

*4.2.1. O2*

tine and O2

region III were detected.

and a lower O2

down electric field of the O<sup>2</sup>

 *plasma damage*

*4.2.1.1. Plasma process dependence*

**Figure 7** shows the variation in the *k* value of a porous low-*k* dielectric after O2

power and the treatment time but slightly deceased with increasing the O2

of the pristine porous low-*k* dielectric was 2.56. The *k* values of porous low-*k* dielectrics increased after plasma treatment. The increasing magnitude increased with increasing the RF

reactive oxygen species (ions and radicals) formation and a deeper penetration depth for a

**Figure 8(a)** compares the leakage current density and the stress electric field for the pris-

increases with increasing the electric field (region I). Then, the leakage current density reaches a plateau without significant variation (region II). Finally, the leakage current density sud-

current in region I, a longer duration in region II, and a lower breakdown electric field in

**Figure 8(b)** compares the leakage current densities at 1 MV/cm and 2 MV/cm and the break-

tions. Similar to the result of *k* value change, a higher RF power, a longer treatment time,

plasma-treated low-*k* films. At a lower electric field, the leakage current density

ments with various plasma conditions (power, treatment time, and O2

a larger change in the *k* value. The negative dependence on the O2

higher RF power and a longer treatment time in an O2

reactive oxygen species (ions and radicals) in the plasma.

302 Plasma Science and Technology - Basic Fundamentals and Modern Applications

**Figure 7.** Dielectric constant change of porous low-*k* dielectrics under various O2

condition: RF power = 60 W; time = 60 s; oxygen flow = 100 sccm).

to the decreased dissociation rate of O2

denly jumps, whose value is over 10−2 A/cm2

breakdown electric field (region III). For O<sup>2</sup>

plasma treat-

flow rate. More

flow rate). The *k* value

flow rate can be attributed

plasma treatment conditions (standard

plasma treatment can be responsible for

gas due to a fixed RF power, leading to a decreased

. This electric field is defined as the dielectric

plasma-treated low-*k* dielectrics, a higher leakage

plasma-treated low-*k* dielectrics with various treatment condi-

flow rate can result in the largest increase of the leakage current density for

Four kinds of low-*k* dielectrics were treated by O2 plasma with various RF powers. The used low-*k* dielectrics were dense low-*k* (*k* = 3.02; called low-*k*\_1), porogen low-*k* without UV (*k* = 2.92; called low-*k*\_2) and with UV curing (2.56; called low-*k*\_3), and porogen low-*k* with UV curing and followed by a RP H2 /He plasma treatment (*k* = 2.48; called low-*k*\_4).

**Figure 10** compares the change percentage of the *k* value as a function of RF power in O2 plasma process for four different low-*k* films. The increasing magnitude is enlarged with an increase of RF power for all low-*k* dielectrics. The porogen-containing low-*k* dielectrics (low*k*\_2 and low-*k*\_3) have a higher increase in the *k* value as compared to low-*k*\_1. This suggests that porogen plays an important role for the low-*k* dielectrics under plasma irradiation. Furthermore, the highest increase in the *k* value is occurred in the low-*k*\_2 (porogen-containing low-*k* film without UV curing). The UV irradiation on the low-*k* dielectrics not only removes the porogen to form pores but also strengthens the bonding strength of the low-*k* dielectrics

becomes smaller. This implies that the post-remote H2

low-*k* dielectric is becoming ineffective in preventing O<sup>2</sup>

tric, causing the bonding breakage and reaction with moisture.

tric is a key issue to cause the reliability degradation under O2

tion or the post-deposition plasma treatment, using remote H2

and radicals to reach the porous low-*k* dielectrics [54]. Si, MgF2

this study. The height of the gap was fixed at 1 cm. Under O<sup>2</sup>

deduced, resulting in a weaker resistance against O2

plasma treatment.

*4.2.1.3. Plasma component dependence*

As the RF power is increased in O2

layer induced by remote H2

under O2

power in O2

plasma treatment.

/He plasma treatment on the porous

Plasma Damage on Low-*k* Dielectric Materials http://dx.doi.org/10.5772/intechopen.79494 305

plasma damage as a higher RF power.

plasma treatment. Since two

/He plasma to form a surface

was used as a mask in

plasma treatment with different

plasma damage. By means of UV irradia-

, or CaF2

plasma treatment process, the more active oxygen species

/He plasma treatment into a deeper region within the low-*k* dielec-

are produced, and these active species get more energy so as to penetrate the densification

**Figure 11** compares the degradation in the characteristic dielectric breakdown times relative to those of the pristine low-*k* dielectrics as a function of RF power. The stress electric field was 6.8 MV/cm for all low-*k* dielectrics. The reliability performance continuously degrades with RF power. Additionally, for the same RF power, the degradation order is low-*k*\_2 > low*k*\_3 > low-*k*\_4 > low-*k*\_1. This means that porogen, rather than pore, within a low-*k* dielec-

phases (matrix and porogen) coexist in the low-*k* dielectrics, a weaker bonding strength can be

densification layer can alleviate the reliability degradation for the porous low-*k* dielectrics

A "roof" structure, consisting of a top optical mask, is designed to isolate the ions, photons,

masks, the plasma species penetrating into the porous low-*k* dielectric through the gap is summarized in **Table 2**. For the porous low-*k* dielectric under plasma using various masks,

**Figure 11.** Degradation in characteristic dielectric breakdown time of different low-*k* dielectrics as a function of RF

**Figure 9.** Characteristic dielectric breakdown times of porous low-*k* dielectrics under various O2 plasma treatment conditions (standard condition: RF power = 60 W; time = 60 s; oxygen flow = 100 sccm).

**Figure 10.** Change percentage in dielectric constant of different low-*k* dielectrics as a function of RF power in O2 plasma treatment.

[53]. Therefore, the resistance to O2 plasma damage can be reinforced. To enhance plasma resistance for porous low-*k* dielectrics, a RP H2 /He plasma treatment seems to be a possible method to alleviate the increase in the *k* value upon O2 plasma process. The RP H2 /He plasma treatment can form a densification layer on the low-*k* dielectric's surface without damaging film's properties. This formation densification layer can effectively resist O<sup>2</sup> plasma damage and prevent active oxygen species to penetrate into the film. However, as the RF power further increases in O2 plasma treatment process, the difference in the *k* value in low-*k*\_3 and low-*k*\_4 becomes smaller. This implies that the post-remote H2 /He plasma treatment on the porous low-*k* dielectric is becoming ineffective in preventing O<sup>2</sup> plasma damage as a higher RF power. As the RF power is increased in O2 plasma treatment process, the more active oxygen species are produced, and these active species get more energy so as to penetrate the densification layer induced by remote H2 /He plasma treatment into a deeper region within the low-*k* dielectric, causing the bonding breakage and reaction with moisture.

**Figure 11** compares the degradation in the characteristic dielectric breakdown times relative to those of the pristine low-*k* dielectrics as a function of RF power. The stress electric field was 6.8 MV/cm for all low-*k* dielectrics. The reliability performance continuously degrades with RF power. Additionally, for the same RF power, the degradation order is low-*k*\_2 > low*k*\_3 > low-*k*\_4 > low-*k*\_1. This means that porogen, rather than pore, within a low-*k* dielectric is a key issue to cause the reliability degradation under O2 plasma treatment. Since two phases (matrix and porogen) coexist in the low-*k* dielectrics, a weaker bonding strength can be deduced, resulting in a weaker resistance against O2 plasma damage. By means of UV irradiation or the post-deposition plasma treatment, using remote H2 /He plasma to form a surface densification layer can alleviate the reliability degradation for the porous low-*k* dielectrics under O2 plasma treatment.

#### *4.2.1.3. Plasma component dependence*

[53]. Therefore, the resistance to O2

increases in O2

treatment.

resistance for porous low-*k* dielectrics, a RP H2

method to alleviate the increase in the *k* value upon O2

plasma damage can be reinforced. To enhance plasma

treatment can form a densification layer on the low-*k* dielectric's surface without damaging

**Figure 10.** Change percentage in dielectric constant of different low-*k* dielectrics as a function of RF power in O2

and prevent active oxygen species to penetrate into the film. However, as the RF power further

plasma treatment process, the difference in the *k* value in low-*k*\_3 and low-*k*\_4

film's properties. This formation densification layer can effectively resist O<sup>2</sup>

**Figure 9.** Characteristic dielectric breakdown times of porous low-*k* dielectrics under various O2

conditions (standard condition: RF power = 60 W; time = 60 s; oxygen flow = 100 sccm).

304 Plasma Science and Technology - Basic Fundamentals and Modern Applications

/He plasma treatment seems to be a possible

/He plasma

plasma

plasma treatment

plasma damage

plasma process. The RP H2

A "roof" structure, consisting of a top optical mask, is designed to isolate the ions, photons, and radicals to reach the porous low-*k* dielectrics [54]. Si, MgF2 , or CaF2 was used as a mask in this study. The height of the gap was fixed at 1 cm. Under O<sup>2</sup> plasma treatment with different masks, the plasma species penetrating into the porous low-*k* dielectric through the gap is summarized in **Table 2**. For the porous low-*k* dielectric under plasma using various masks,

**Figure 11.** Degradation in characteristic dielectric breakdown time of different low-*k* dielectrics as a function of RF power in O2 plasma treatment.

the thickness reduction, the Si–CH3 group extraction, the Si–OH/H–OH bond formation, the top modification layer formation, the WCA value declination, the dielectric constant increment, and the dielectric breakdown field degradation were detected. The results indicate that all ions, photons, and radicals in the plasma cause negative impact on the porous low-*k* dielectrics, but they have different contributions. The maximum change is in the case of without mask. In Si mask case, the photons and the ions are blocked so that only oxygen radicals can react with the porous low-*k* dielectrics. Its plasma damage is less minor. In MgF2 mask or CaF2 mask, photons can penetrate but depends on the wavelength. With an addition of photon effect, the changes in the physical and electrical properties for the porous low-*k* dielectrics slightly increase. Furthermore, as ions are added in the plasma to react with the porous low-*k* dielectrics (without mask case), the changes become significant. This implies that the synergy between the radicals, the photons, and the ions in the plasma induces the highest degradation in the porous low-*k* dielectrics.

The plasma-induced damage mechanism is that the bonds inside the porous low-*k* dielectrics are broken by ion bombardment and then easily react with radicals to form the new bonds or Si–OH/H–OH bonds with a higher *k* value (~80). As for the contribution of photons, photons can weaken or broken the low-*k* dielectric's bonds, assisting the chemical reaction of radicals. The photons with a higher energy cause more bonding breakage, inducing a more degradation. Therefore, a higher degradation in the porous low-*k* dielectric underneath MgF2 mask during O2 plasma treatment was detected due to extra photon transmission with 120–250 nm wavelength.

indicating that radicals cause the greater degradation in the dielectric reliability than the other two plasma components. However, this finding is still needed to be demonstrated by more experiments which can be treated under the individual plasma component. The synergy between radicals, photons, and ions causes a considerable degradation. Getting rid of one or two components from the plasma environment is a workable strategy for the low-*k* dielec-

**Figure 12.** Characteristic dielectric breakdown time versus electric field for porous low-*k* dielectrics under O2

/He plasma treatments on the porous low-*k* dielectrics (*k* = 2.56) using CCP and RP systems at various operation temperatures (25–350°C) were investigated. The *k* value of porous low-*k*

ment in CCP system, and the increasing magnitude increased with increasing the operation temperature. However, as the operation temperature is raised above 250°C, the increasing rate of the *k* value tends to alleviate. This phenomenon can be explained by transforming Si–OH bonds to Si–O–Si bonds at an elevated temperature above 200°C. For porous low-*k*

slightly reduced with an increase of the operation temperature. Furthermore, as the operation temperature is elevated to 350°C, the *k* value was reduced to be lower than 2.56. The

trics turns to be positive by raising the operation temperature to 350°C. As a consequence, a

/He plasma treatment in CCP and RP systems as a function of the operation

/He plasma in RP system, the increase in the *k* value was lower owing

depletion and Si–OH formation. Additionally, the *k* value was

/He plasma treatment in RP system on porous low-*k* dielec-

/He plasma treat-

plasma

307

Plasma Damage on Low-*k* Dielectric Materials http://dx.doi.org/10.5772/intechopen.79494

/He plasma treatment in RP

tric's reliability improvement.

treatment with various masks.

*)/helium (He) plasma damage*

"damage-free" resist strip processing can be obtained by using H2

temperature is presented in **Figure 13**. An increased *k* was detected after H2

*4.2.2. Hydrogen (H2*

dielectrics treated by H2

to a relatively small Si–CH3

result suggests that the effect of H<sup>2</sup>

chamber at elevated temperatures.

films after H<sup>2</sup>

H2

**Figure 12** plots the characteristic dielectric breakdown times (T63.2%) versus the applied electric field for O<sup>2</sup> plasma-treated low-*k* dielectrics with various masks. In a fixed electric field, the order of T63.2% is pristine > Si mask > MgF2 mask > CaF2 mask > without mask, indicating that all ions, photons, and radicals in the plasma cause the dielectric reliability degradation. For example, in an electric field of 6.8 MV/cm, the dielectric lifetime degradation ratios are 43.17, 66.41, and 82.18% for Si mask, MgF2 mask, and without mask cases, respectively, corresponding to radical, radicals + photon, and ions + photons + radical effects. By simple calculation, the contributions of radicals, photons, and ions were 43.17, 23.24, and 15.77%, respectively,


**Figure 12.** Characteristic dielectric breakdown time versus electric field for porous low-*k* dielectrics under O2 plasma treatment with various masks.

indicating that radicals cause the greater degradation in the dielectric reliability than the other two plasma components. However, this finding is still needed to be demonstrated by more experiments which can be treated under the individual plasma component. The synergy between radicals, photons, and ions causes a considerable degradation. Getting rid of one or two components from the plasma environment is a workable strategy for the low-*k* dielectric's reliability improvement.

#### *4.2.2. Hydrogen (H2 )/helium (He) plasma damage*

the thickness reduction, the Si–CH3

306 Plasma Science and Technology - Basic Fundamentals and Modern Applications

in the porous low-*k* dielectrics.

tric underneath MgF2

field for O<sup>2</sup>

plasma treatment.

group extraction, the Si–OH/H–OH bond formation, the

plasma treatment was detected due to extra photon

mask, and without mask cases, respectively, correspond-

mask > without mask, indicating that

mask or CaF2

top modification layer formation, the WCA value declination, the dielectric constant increment, and the dielectric breakdown field degradation were detected. The results indicate that all ions, photons, and radicals in the plasma cause negative impact on the porous low-*k* dielectrics, but they have different contributions. The maximum change is in the case of without mask. In Si mask case, the photons and the ions are blocked so that only oxygen radicals can

mask, photons can penetrate but depends on the wavelength. With an addition of photon effect, the changes in the physical and electrical properties for the porous low-*k* dielectrics slightly increase. Furthermore, as ions are added in the plasma to react with the porous low-*k* dielectrics (without mask case), the changes become significant. This implies that the synergy between the radicals, the photons, and the ions in the plasma induces the highest degradation

The plasma-induced damage mechanism is that the bonds inside the porous low-*k* dielectrics are broken by ion bombardment and then easily react with radicals to form the new bonds or Si–OH/H–OH bonds with a higher *k* value (~80). As for the contribution of photons, photons can weaken or broken the low-*k* dielectric's bonds, assisting the chemical reaction of radicals. The photons with a higher energy cause more bonding breakage, inducing a more degradation. Therefore, a higher degradation in the porous low-*k* dielec-

**Figure 12** plots the characteristic dielectric breakdown times (T63.2%) versus the applied electric

all ions, photons, and radicals in the plasma cause the dielectric reliability degradation. For example, in an electric field of 6.8 MV/cm, the dielectric lifetime degradation ratios are 43.17,

ing to radical, radicals + photon, and ions + photons + radical effects. By simple calculation, the contributions of radicals, photons, and ions were 43.17, 23.24, and 15.77%, respectively,

**Table 2.** Change of physical and electrical characteristics of porous low-*k* dielectrics using different masks under O<sup>2</sup>

mask > CaF2

plasma-treated low-*k* dielectrics with various masks. In a fixed electric field, the

react with the porous low-*k* dielectrics. Its plasma damage is less minor. In MgF2

mask during O2

transmission with 120–250 nm wavelength.

order of T63.2% is pristine > Si mask > MgF2

66.41, and 82.18% for Si mask, MgF2

H2 /He plasma treatments on the porous low-*k* dielectrics (*k* = 2.56) using CCP and RP systems at various operation temperatures (25–350°C) were investigated. The *k* value of porous low-*k* films after H<sup>2</sup> /He plasma treatment in CCP and RP systems as a function of the operation temperature is presented in **Figure 13**. An increased *k* was detected after H2 /He plasma treatment in CCP system, and the increasing magnitude increased with increasing the operation temperature. However, as the operation temperature is raised above 250°C, the increasing rate of the *k* value tends to alleviate. This phenomenon can be explained by transforming Si–OH bonds to Si–O–Si bonds at an elevated temperature above 200°C. For porous low-*k* dielectrics treated by H2 /He plasma in RP system, the increase in the *k* value was lower owing to a relatively small Si–CH3 depletion and Si–OH formation. Additionally, the *k* value was slightly reduced with an increase of the operation temperature. Furthermore, as the operation temperature is elevated to 350°C, the *k* value was reduced to be lower than 2.56. The result suggests that the effect of H<sup>2</sup> /He plasma treatment in RP system on porous low-*k* dielectrics turns to be positive by raising the operation temperature to 350°C. As a consequence, a "damage-free" resist strip processing can be obtained by using H2 /He plasma treatment in RP chamber at elevated temperatures.

**Figure 13.** Dielectric constant of H2 /He plasma-treated low-*k* dielectrics operated in CCP and RP systems as a function of operation temperature.

on porous low-*k* dielectrics in RP system at 350°C efficiently removes porogen residues from

≡Si– CH3 + 2H → ≡Si–H + CH4 ΔH<sup>r</sup> = −411 KJ/mole (2)

≡Si–O–Si≡ + 2H → ≡Si–H + ≡Si–OH ΔH<sup>r</sup> = −325 KJ/mole (3)

assumed to be 25°C. The negative enthalpies of reactions (2) and (3) represent that the reactions are exothermic and presumably occurred at room temperature [57]. Assuming that the amount of H atoms remains unchanged at an elevated temperature, these two reactions would become less favored with an increase of the reaction temperature according to Chatelier's

temperature. The discrepancy can be explained by the fact that only H radical is considered to react with the low-*k* dielectric for reactions (2) and (3). However, H ions and VUV photons

and VUV photons, the above two reactions become possible because the bonding energies

H radicals can react with the porous low-*k* dielectric. According to FT-IR result, only Si–CH3

and Si–O–Si bonds are weaken. Furthermore, at an elevated temperature, ions and

temperature. However, FT-IR analysis revealed that the losses of CH3

is the estimated enthalpy. The reaction temperature of these two reactions is

/He plasma operated in CCP system. Due to the presence of H ions

reactive plasma species and porous low-*k*

/He plasma-treated low-*k* dielectrics operated in CCP

Plasma Damage on Low-*k* Dielectric Materials http://dx.doi.org/10.5772/intechopen.79494 309

and Si–O–Si groups should be stronger at a lower

/He plasma in CCP system at a higher

and Si–O–Si bonds, causing a violent

/He plasma treatment in RP system, only

and Si–O–Si groups

porous low-*k* dielectrics, resulting in a better reliability.

**Figure 14.** (a) Breakdown field. (b) Dielectric breakdown time of H<sup>2</sup>

and RP systems as a function of operation temperature.

The mechanism about the reaction between H2

principle. Therefore, the scission of Si–CH3

were higher for porous low-*k* dielectrics treated by H2

photons can gain more energy and easily break Si–CH3

response for reactions (2) and (3). In the case of H2

dielectrics can be described as [56]:

where ΔH<sup>r</sup>

can be produced in H2

of Si–CH3

**Figure 14(a)** and **(b)** shows the breakdown field and the dielectric breakdown time, respectively, of porous low-*k* dielectrics under H2 /He plasma treatment in the CCP or RP systems at various operation temperatures. Both results indicate that H2 /He plasma-treated low-*k* dielectrics in RP system exhibited a higher breakdown field and a longer breakdown time as compared to those in CCP system, indicating that deep UV light radiation and ion bombardment induced from H2 /He plasma treatment in CCP system on the low-*k* dielectric can accelerate the degradation of reliability. The trends of temperature dependence of reliability characteristics were different for H<sup>2</sup> /He plasma treatments in the CCP and RP systems. The breakdown field and the breakdown time of H<sup>2</sup> /He plasma-treated low-*k* dielectrics in CCP system were decreased, while those in CCP system were improved as the operation temperature is raised. Furthermore, H2 /He plasma-treated low-*k* dielectrics operated in CCP system displayed a strong temperature dependence of reliability, implying that the reaction induced by radicals is not enhanced by increasing the temperature. However, with the assistance of deep UV light radiation and ion bombardment, the reaction becomes stronger at a higher operation temperature. As the operation temperature of H2 /He plasma treatment in RP system was raised to 350°C, the reliability performance of the plasma-treated low-*k* dielectrics exceeded that of the pristine samples. A better reliability for H<sup>2</sup> /He plasma-treated low-*k* films operated in RP system at 350°C can be attributable to another mechanism because the scission of Si–CH3 bonds was still detected although the decreasing ratio was reduced. H2 /He plasma treatment on porous low-*k* dielectrics in RP system at evaluated temperatures reportedly removes carbon-based porogen residues, which are formed inside the porous low*k* structure due to non-optimized incorporation of porogen molecules and non-optimized UV curing [55]. The removal of porogen residues from porous low-*k* dielectrics has also been demonstrated to promote reliability for low-*k* dielectrics. Therefore, H2 /He plasma treatment

**Figure 14.** (a) Breakdown field. (b) Dielectric breakdown time of H<sup>2</sup> /He plasma-treated low-*k* dielectrics operated in CCP and RP systems as a function of operation temperature.

on porous low-*k* dielectrics in RP system at 350°C efficiently removes porogen residues from porous low-*k* dielectrics, resulting in a better reliability.

The mechanism about the reaction between H2 reactive plasma species and porous low-*k* dielectrics can be described as [56]:

**Figure 14(a)** and **(b)** shows the breakdown field and the dielectric breakdown time, respec-

dielectrics in RP system exhibited a higher breakdown field and a longer breakdown time as compared to those in CCP system, indicating that deep UV light radiation and ion bom-

accelerate the degradation of reliability. The trends of temperature dependence of reliabil-

CCP system were decreased, while those in CCP system were improved as the operation

system displayed a strong temperature dependence of reliability, implying that the reaction induced by radicals is not enhanced by increasing the temperature. However, with the assistance of deep UV light radiation and ion bombardment, the reaction becomes stronger at

in RP system was raised to 350°C, the reliability performance of the plasma-treated low-*k*

low-*k* films operated in RP system at 350°C can be attributable to another mechanism because

/He plasma treatment on porous low-*k* dielectrics in RP system at evaluated temperatures reportedly removes carbon-based porogen residues, which are formed inside the porous low*k* structure due to non-optimized incorporation of porogen molecules and non-optimized UV curing [55]. The removal of porogen residues from porous low-*k* dielectrics has also been

/He plasma treatment in the CCP or RP systems

/He plasma treatments in the CCP and RP systems.

/He plasma-treated low-*k* dielectrics operated in CCP

/He plasma-treated low-*k* dielectrics in

/He plasma treatment in CCP system on the low-*k* dielectric can

/He plasma-treated low-*k* dielectrics operated in CCP and RP systems as a function

bonds was still detected although the decreasing ratio was reduced.

/He plasma-treated low-*k*

/He plasma treatment

/He plasma-treated

/He plasma treatment

tively, of porous low-*k* dielectrics under H2

ity characteristics were different for H<sup>2</sup>

temperature is raised. Furthermore, H2

The breakdown field and the breakdown time of H<sup>2</sup>

bardment induced from H2

**Figure 13.** Dielectric constant of H2

of operation temperature.

the scission of Si–CH3

H2

at various operation temperatures. Both results indicate that H2

308 Plasma Science and Technology - Basic Fundamentals and Modern Applications

a higher operation temperature. As the operation temperature of H2

dielectrics exceeded that of the pristine samples. A better reliability for H<sup>2</sup>

demonstrated to promote reliability for low-*k* dielectrics. Therefore, H2

$$\text{=Si-CH}\_3 + 2\text{H} \rightarrow \equiv \text{Si-H} + \text{CH}\_4 \quad \Lambda\\\text{H}\_x = -411 \text{ K} \text{/mole} \tag{2}$$

$$\equiv \text{Si-O-Si} \equiv +2\text{H} \rightarrow \equiv \text{Si-H} + \equiv \text{Si-OH} \quad \Lambda\\\text{H}\_{\text{r}} = -325 \text{ K} \text{J/mole} \tag{3}$$

where ΔH<sup>r</sup> is the estimated enthalpy. The reaction temperature of these two reactions is assumed to be 25°C. The negative enthalpies of reactions (2) and (3) represent that the reactions are exothermic and presumably occurred at room temperature [57]. Assuming that the amount of H atoms remains unchanged at an elevated temperature, these two reactions would become less favored with an increase of the reaction temperature according to Chatelier's principle. Therefore, the scission of Si–CH3 and Si–O–Si groups should be stronger at a lower temperature. However, FT-IR analysis revealed that the losses of CH3 and Si–O–Si groups were higher for porous low-*k* dielectrics treated by H2 /He plasma in CCP system at a higher temperature. The discrepancy can be explained by the fact that only H radical is considered to react with the low-*k* dielectric for reactions (2) and (3). However, H ions and VUV photons can be produced in H2 /He plasma operated in CCP system. Due to the presence of H ions and VUV photons, the above two reactions become possible because the bonding energies of Si–CH3 and Si–O–Si bonds are weaken. Furthermore, at an elevated temperature, ions and photons can gain more energy and easily break Si–CH3 and Si–O–Si bonds, causing a violent response for reactions (2) and (3). In the case of H2 /He plasma treatment in RP system, only H radicals can react with the porous low-*k* dielectric. According to FT-IR result, only Si–CH3

group was found to reduce, and the concentration of Si–O–Si bond almost kept unchanged for H2 /He plasma-treated low-*k* dielectrics, implying that reaction (2) is favored over reaction (3) because of a lower dissociation energy of Si–CH3 bond. Additionally, the reduction amount of Si–CH3 bond is relatively small and no temperature dependence effect, indicating that reaction (2) is relatively weak even at a higher temperature for H2 /He plasma treatment in RP system.

**Figure 16(a)** plots the measured dielectric breakdown fields of NH<sup>3</sup>

formance than the pristine low-*k* dielectric. Moreover, the breakdown field of the NH<sup>3</sup>

**Figure 16(b)** compares T63.2% values as a function of applied electric field for the pristine and plasma-treated low-*k* dielectrics. All plasma-treated samples had shorter dielectric breakdown times and a wider distribution as compared to the pristine low-*k* dielectric. The reduction of the dielectric breakdown time may be caused by an accumulation of defects owing to

**Figure 16.** (a) Breakdown field. (b) Dielectric breakdown time as a function of electric field of porous low-*k* dielectrics

/N2

dielectric that was plasma treated with pure NH3

plasma-treated low-*k* dielectrics decreases as the NH3

**Figure 15.** Change in dielectric constant of porous low-*k* dielectrics after NH3

*k* dielectrics. All NH3

highest leakage current.

after various NH3

/N2

plasma treatments.

/N2

Plasma Damage on Low-*k* Dielectric Materials http://dx.doi.org/10.5772/intechopen.79494

gas has the lowest breakdown field and the

plasma-treated samples had a poorer dielectric breakdown per-

/(N2 + NH3

/N2 and O2

plasma treatments.

plasma-treated low-

) ratio increases. The low-*k*

/N2

311

In addition to the above reactions (2) and (3), H2 plasma can break Si–CH3 and Si–O–Si bonds to create Si dangling bonds. The subsequent air exposure makes these Si dangling bonds transform to Si–OH bonds. If OH- bonds are weak or physically bonded, dehydroxylation of Si–OH bonds can occur to form Si–O–Si bonds at a higher temperature [58]. This can be explained by the reduction of Si–OH bonds for H2 /He plasma-treated low-*k* films operated at temperatures above 250°C.

#### *4.2.3. Ammonia (NH3 )/nitrogen (N2 ) plasma damage*

The effect of the NH<sup>3</sup> /N2 ratio in plasma treatment on the porous low-*k* dielectrics (*k* = 2.56) was investigated. The reaction mechanism between the porous low-*k* dielectric and NH3 /N2 plasma can be described as follows: in pure N2 gas plasma, only N, N2 , and N2 \* active species are generated, and no hydrogen species is produced. Physical bombardment by N radicals is favorable, roughing the film's surface. Moreover, the weak bonds in the low-*k* dielectric, such as Si–H, Si–CH3 , and C–Hx bonds, can be broken by these active species in the plasma, forming Si–N and C–N bonds. As NH3 gas was added into the plasma, other active species in addition to the N, N2 , and N2 \* active species, such as H, NH2 , NH4 , and N2 H, may be generated. The Si–CH3 group in the low-*k* dielectric is broken to form Si dangling bonds. This dangling bond easily absorbs H or NH2 species to form Si–H or Si–NH2 bonds due to a lower reaction energy, which is thermodynamically favorable [59–62]. The Si–H and Si–NH2 bonds are not stable in air and easily react with ambient air to form Si–OH, which is more hydrophobic and has a higher *k* value. As the portion of NH3 in the plasma increases, the number of H and NH2 active species increases accordingly. At the same time, the amount of the generated N, N2 , and N2 \* active species is limited because more energy is required to generate these active species. These changes in the plasma result in the significant replacement of –CH3 groups by H and NH2 active species, the formation of more Si–OH bonds, and the reduction of Si–N and C–N bonds.

**Figure 15** shows the changes in the *k* value of NH3 /N2 plasma-treated low-*k* dielectrics upon O2 plasma treatment. After NH3 /N2 plasma treatment, the *k* value of the plasma-treated low-*k* dielectrics increases. Under pure NH3 or pure N2 gas plasma treatment conditions, the increase is larger. This can be attributed to more formation of Si–OH bonds or Si–N/C–N bonds on the surface layer for pure NH3 or pure N2 gas plasma treatment, respectively. Treatment with O2 plasma increases the *k* values of all NH3 /N2 plasma-treated low-*k* dielectrics by the replacement of Si–CH3 and Si–H bonds with Si–O bonds [63]. The increase in the *k* value becomes larger with the NH3 /N2 gas ratio. The pure N2 gas plasma-treated sample exhibits a smaller increase in the *k* value owing to the formation of protective Si–N/C–N layer. This layer suppresses the penetration of oxygen radical into the low-*k* dielectric.

**Figure 16(a)** plots the measured dielectric breakdown fields of NH<sup>3</sup> /N2 plasma-treated low*k* dielectrics. All NH3 /N2 plasma-treated samples had a poorer dielectric breakdown performance than the pristine low-*k* dielectric. Moreover, the breakdown field of the NH<sup>3</sup> /N2 plasma-treated low-*k* dielectrics decreases as the NH3 /(N2 + NH3 ) ratio increases. The low-*k* dielectric that was plasma treated with pure NH3 gas has the lowest breakdown field and the highest leakage current.

group was found to reduce, and the concentration of Si–O–Si bond almost kept unchanged

to create Si dangling bonds. The subsequent air exposure makes these Si dangling bonds transform to Si–OH bonds. If OH- bonds are weak or physically bonded, dehydroxylation of Si–OH bonds can occur to form Si–O–Si bonds at a higher temperature [58]. This can be

*) plasma damage*

was investigated. The reaction mechanism between the porous low-*k* dielectric and NH3

are generated, and no hydrogen species is produced. Physical bombardment by N radicals is favorable, roughing the film's surface. Moreover, the weak bonds in the low-*k* dielectric,

lower reaction energy, which is thermodynamically favorable [59–62]. The Si–H and Si–NH2 bonds are not stable in air and easily react with ambient air to form Si–OH, which is more

generate these active species. These changes in the plasma result in the significant replace-

is larger. This can be attributed to more formation of Si–OH bonds or Si–N/C–N bonds on the

increase in the *k* value owing to the formation of protective Si–N/C–N layer. This layer sup-

or pure N2

/N2

/N2

and Si–H bonds with Si–O bonds [63]. The increase in the *k* value becomes

\* active species, such as H, NH2

tion (3) because of a lower dissociation energy of Si–CH3

310 Plasma Science and Technology - Basic Fundamentals and Modern Applications

In addition to the above reactions (2) and (3), H2

explained by the reduction of Si–OH bonds for H2

*)/nitrogen (N2*

, and C–Hx

, and N2

groups by H and NH2

**Figure 15** shows the changes in the *k* value of NH3

the reduction of Si–N and C–N bonds.

plasma treatment. After NH3

surface layer for pure NH3

dielectrics increases. Under pure NH3

plasma increases the *k* values of all NH3

/N2

, and N2

hydrophobic and has a higher *k* value. As the portion of NH3

/N2

or pure N2

gas ratio. The pure N2

presses the penetration of oxygen radical into the low-*k* dielectric.

/N2

plasma can be described as follows: in pure N2

forming Si–N and C–N bonds. As NH3

This dangling bond easily absorbs H or NH2

that reaction (2) is relatively weak even at a higher temperature for H2

/He plasma-treated low-*k* dielectrics, implying that reaction (2) is favored over reac-

bond is relatively small and no temperature dependence effect, indicating

plasma can break Si–CH3

ratio in plasma treatment on the porous low-*k* dielectrics (*k* = 2.56)

gas plasma, only N, N2

group in the low-*k* dielectric is broken to form Si dangling bonds.

active species increases accordingly. At the same time, the amount

species to form Si–H or Si–NH2

\* active species is limited because more energy is required to

active species, the formation of more Si–OH bonds, and

plasma treatment, the *k* value of the plasma-treated low-*k*

gas plasma treatment, respectively. Treatment with O2

plasma-treated low-*k* dielectrics by the replace-

gas plasma-treated sample exhibits a smaller

bonds, can be broken by these active species in the plasma,

gas was added into the plasma, other active species

, NH4

bond. Additionally, the reduction

/He plasma-treated low-*k* films operated at

, and N2

, and N2

in the plasma increases, the

plasma-treated low-*k* dielectrics upon

gas plasma treatment conditions, the increase

/He plasma treatment

and Si–O–Si bonds

/N2

\* active species

H, may be

bonds due to a

for H2

amount of Si–CH3

temperatures above 250°C.

*4.2.3. Ammonia (NH3*

The effect of the NH<sup>3</sup>

such as Si–H, Si–CH3

in addition to the N, N2

generated. The Si–CH3

number of H and NH2

of the generated N, N2

ment of –CH3

ment of Si–CH3

larger with the NH3

O2

in RP system.

**Figure 16(b)** compares T63.2% values as a function of applied electric field for the pristine and plasma-treated low-*k* dielectrics. All plasma-treated samples had shorter dielectric breakdown times and a wider distribution as compared to the pristine low-*k* dielectric. The reduction of the dielectric breakdown time may be caused by an accumulation of defects owing to

**Figure 15.** Change in dielectric constant of porous low-*k* dielectrics after NH3 /N2 and O2 plasma treatments.

**Figure 16.** (a) Breakdown field. (b) Dielectric breakdown time as a function of electric field of porous low-*k* dielectrics after various NH3 /N2 plasma treatments.

plasma-induced damage. Furthermore, the reductions in the dielectric breakdown time were significant in stronger stressing electric fields. Additionally, the T63.2% values of plasma-treated low-*k* dielectrics decreased as the NH3 /(N2 + NH3 ) ratio increased, which is correlated well with the moisture contents in the plasma-treated dielectrics. This indicates that the moisture content in a low-*k* dielectric plays an important role in reducing the dielectric breakdown time. The low-*k* dielectric that was plasma treated with pure N2 gas had the longest low-*k* dielectric because the formed amide-like or nitride-like layers on the surface retard low-*k* dielectric breakdown.

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