**2. CMP consumables-induced contaminants**

Some of the CMP related to contaminants, such as residual particles, surface residues, organic residues, and metallic impurities, are common to most CMP processes, which are directly associated with CMP consumables [3, 12, 13]. Various types of CMP-related to contaminants and their impacts in the semiconductor manufacturing process were summarized in **Table 2** [18]. These contaminants are presumably attributed to the chemical reactions of slurry components at the slurry/ pad-wafer interface. The sources and characteristics of the contaminants listed in **Table 2** will be discussed in this section.

#### **2.1 Residual abrasive particles**

Abrasive particle is not only one of the main components in CMP slurries (**Table 1**) [16, 17], but also a common contaminant observed after all CMP processes (**Figure 2a**) [13]. Silica and ceria have been widely employed as abrasive particles for CMP processes [16]. The adsorption of silica abrasives on the films is driven by the electrostatic attractive forces between abrasives and films in a certain


#### **Table 2.**

*Some CMP-related to contaminants and their effects in the semiconductor manufacturing process. Modified and reprinted with permission from Ref. [18], American Vacuum Society.*

pH range. The pHIEP of silica abrasive is about pH 2.5 [22], so the silica particles show a negative surface charge at above pH 2.5 and lead to the contamination of positively charged films that have higher pHIEP values. The preferential adsorption of silica abrasives on Cu and Co films was observed after the Cu CMP process when Co is used as the liner (**Figure 2b**) [20]. As expected, the IEPs of Cu and Co species are much higher than those of TaN and SiO2 films (**Table 3**). W films are covered with a passivation layer in acidic pH range according to the Pourbaix diagram [32]. So, the silica abrasives can remain on the polished W films due to their electrostatic attraction (The pHIEP of WOx is 0.5 as listed in **Table 3**) [24]. In some cases, the alumina particles (pHIEP ~ 7) are used as the abrasive for W CMP, and they are observed on the W films after polishing due to its positive charge in the acidic medium [13, 24]. Co films and other metal films can also be contaminated with the silica abrasive during polishing [14, 15]. These particle contaminants can be controlled by the chemical reactions between slurry components and films being polished. Moreover, silica abrasives are weakly bound to the films and can be easy to be removed by under-cut and particle lift-off or their combination during cleaning [15].

Ceria-based slurry has been widely used for STI CMP to uniformly polish the step height of SiO2, formed by the gap-filling process, and stop on an underlying Si3N4 film [4–6]. Residual ceria abrasives are discovered after STI CMP process (**Figure 2c**) [21, 33]. In contrast with a silica abrasive, ceria abrasive is more strongly coupled with the dielectric materials (in particular, SiO2 film) via the formation of strong Ce-O-Si bonding [4, 34]. It is well known that the surface Ce3+ species are the active sites for the formation of strong Ce-O-Si bonds with SiO2 films during polishing [4, 21]. Various ceria abrasives such as smaller particles with higher surface Ce3+ concentrations [35], the core/shell type Ce3+ rich ceria [36], and metal-doping or coated ceria abrasive [37] have been investigated to improved SiO2 removal rates, but making their removal during cleaning more difficult. Since the pHIEP of the ceria abrasive, SiO2, and Si3N4 films are 7.3, 2.5, and ~ 5.0 (**Table 3**)

**305**

**Figure 2.**

residues are listed in **Table 3**.

*Refs. [20, 21]. Copyright 2019 IOP Publishing.*

"killer defect" [39].

*Chemical Mechanical Planarization-Related to Contaminants: Their Sources and Characteristics*

[38], respectively, the particles can effectively interact with the SiO2 films due to the electrostatic attractions between them. The surface charges of ceria abrasive are different depending on the nature of additives (e.g., dispersant, passivation agent for high selectivity, etc.) and the slurry pH [33]. Positively charged ceria particles, dispersed with amino acid, led significant contamination of negatively charged SiO2 films while negatively charged ceria particles, dispersed with a weak organic acid or poly(acrylic acid), showed a higher level of contamination of Si3N4 films [33]. Thus, cleaning of ceria particles from the wafer surfaces has become more challenging. The pHIEP of abrasive particles, films to be polished, CMP consumables, and organic

*(a) Residual abrasive particles on the wafer surfaces after the CMP process. (b) Atomic force microscopy (AFM) images of adsorbed three different sized ceria particles on the SiO2 films and the corresponding number of particles before and after SC1 cleaning. (c) Topographic AFM images of Cu, Co, TaN, and SiO2 films contaminated with silica slurry at pH 10. Reprinted with permission from Ref. [3]. Copyright 2010 American Chemical Society. Used with the permission of HongJin Kim [19]. Reproduced with permission from* 

These residual particles cause not only an increase in local roughness but also poor photolithography results by blocking the UV light (**Table 2**) [18]. Residual particles on the wafer surfaces can also lead to pinholes in the subsequently deposited film [18]. In some cases, just two residual abrasives on the surfaces can make the device bad [9]. The particle larger than ½ the minimum feature size becomes a

*DOI: http://dx.doi.org/10.5772/intechopen.94292*

*Chemical Mechanical Planarization-Related to Contaminants: Their Sources and Characteristics DOI: http://dx.doi.org/10.5772/intechopen.94292*

#### **Figure 2.**

*Emerging Contaminants*

Particulate Silica or ceria, fine

Organic Buffers,

Metallic Na+

**Table 2.**

fragments of film or pad, etc.

surfactants, etc.

*and reprinted with permission from Ref. [18], American Vacuum Society.*

, K+

pH range. The pHIEP of silica abrasive is about pH 2.5 [22], so the silica particles show a negative surface charge at above pH 2.5 and lead to the contamination of positively charged films that have higher pHIEP values. The preferential adsorption of silica abrasives on Cu and Co films was observed after the Cu CMP process when Co is used as the liner (**Figure 2b**) [20]. As expected, the IEPs of Cu and Co species are much higher than those of TaN and SiO2 films (**Table 3**). W films are covered with a passivation layer in acidic pH range according to the Pourbaix diagram [32]. So, the silica abrasives can remain on the polished W films due to their electrostatic attraction (The pHIEP of WOx is 0.5 as listed in **Table 3**) [24]. In some cases, the alumina particles (pHIEP ~ 7) are used as the abrasive for W CMP, and they are observed on the W films after polishing due to its positive charge in the acidic medium [13, 24]. Co films and other metal films can also be contaminated with the silica abrasive during polishing [14, 15]. These particle contaminants can be controlled by the chemical reactions between slurry components and films being polished. Moreover, silica abrasives are weakly bound to the films and can be easy to be removed by under-cut and particle lift-off or their combination during

*Some CMP-related to contaminants and their effects in the semiconductor manufacturing process. Modified* 

**Contaminants Dielectric CMP Metal CMP Effects**

pad, etc.

,Ca2+, etc. WxOy, Cu2+, Al3+, Fe3+, IO4−, I−

Fe(CN)6

Silica or alumina, metal hydroxide precipitates, fine fragments of film or

Buffers, surfactants, inhibitors, etc.

/I2, Fe(CN)6

4−, etc.

3−,

1. Cause local roughness an block

photolithography 2. Pinholes in new grown films: metal precipitates leads to metallic contamination 3. Shorts by conductive particles

1. **A**ffects wettability and cleanability 2. Outgassing

1. Alkali metal ions: high mobility influences electrical

characteristics 2. Copper: fast diffuser in Si 3. Many metals can form silicide, and/or affect the oxidation 4. Noble metal ions cause etching

of Si

3. Poor adhesion of deposited layers

Ceria-based slurry has been widely used for STI CMP to uniformly polish the step height of SiO2, formed by the gap-filling process, and stop on an underlying Si3N4 film [4–6]. Residual ceria abrasives are discovered after STI CMP process (**Figure 2c**) [21, 33]. In contrast with a silica abrasive, ceria abrasive is more strongly coupled with the dielectric materials (in particular, SiO2 film) via the formation of strong Ce-O-Si bonding [4, 34]. It is well known that the surface Ce3+ species are the active sites for the formation of strong Ce-O-Si bonds with SiO2 films during polishing [4, 21]. Various ceria abrasives such as smaller particles with higher surface Ce3+ concentrations [35], the core/shell type Ce3+ rich ceria [36], and metal-doping or coated ceria abrasive [37] have been investigated to improved SiO2 removal rates, but making their removal during cleaning more difficult. Since the pHIEP of the ceria abrasive, SiO2, and Si3N4 films are 7.3, 2.5, and ~ 5.0 (**Table 3**)

**304**

cleaning [15].

*(a) Residual abrasive particles on the wafer surfaces after the CMP process. (b) Atomic force microscopy (AFM) images of adsorbed three different sized ceria particles on the SiO2 films and the corresponding number of particles before and after SC1 cleaning. (c) Topographic AFM images of Cu, Co, TaN, and SiO2 films contaminated with silica slurry at pH 10. Reprinted with permission from Ref. [3]. Copyright 2010 American Chemical Society. Used with the permission of HongJin Kim [19]. Reproduced with permission from Refs. [20, 21]. Copyright 2019 IOP Publishing.*

[38], respectively, the particles can effectively interact with the SiO2 films due to the electrostatic attractions between them. The surface charges of ceria abrasive are different depending on the nature of additives (e.g., dispersant, passivation agent for high selectivity, etc.) and the slurry pH [33]. Positively charged ceria particles, dispersed with amino acid, led significant contamination of negatively charged SiO2 films while negatively charged ceria particles, dispersed with a weak organic acid or poly(acrylic acid), showed a higher level of contamination of Si3N4 films [33]. Thus, cleaning of ceria particles from the wafer surfaces has become more challenging. The pHIEP of abrasive particles, films to be polished, CMP consumables, and organic residues are listed in **Table 3**.

These residual particles cause not only an increase in local roughness but also poor photolithography results by blocking the UV light (**Table 2**) [18]. Residual particles on the wafer surfaces can also lead to pinholes in the subsequently deposited film [18]. In some cases, just two residual abrasives on the surfaces can make the device bad [9]. The particle larger than ½ the minimum feature size becomes a "killer defect" [39].


#### **Table 3.**

*The pHIEP of abrasive particles, films to be polished, CMP consumables, and organic residues.*
