**2.2 Organic residues and pad debris**

The polished wafers are also contaminated with organic residues (**Figure 3a**), which are originated from the slurry components such as dispersants, additives for the selectivity, complexing agents, corrosion inhibitors, etc. (**Table 1**). One of the main sources of organic residues is insoluble metal complexes. Azole derivatives (more specifically, benzotriazole (BTA)) have been widely used as corrosion inhibitors for metal films during polishing. BTA can strongly chemisorb onto the metal film by forming a chemical bond with a surface metal ion through the nitrogen lone pair electrons [41]. For example, each Cu<sup>+</sup> ion can coordinate with two nitrogen ligands of BTA<sup>−</sup> during the Cu CMP process, which forms a polymeric product with the BTA<sup>−</sup> acting as bridging ligands (**Figure 3b**) [40, 41]. The third nitrogen atom in BTA<sup>−</sup> of Cu-BTA complexes can bind to Cu surfaces, resulting in the polymeric protecting layer on the Cu films [41]. Recently, Seo et al. [20] reported that Cu and Co ions dissolved from Cu and Co films, respectively, can react with BTA and form 4-15 nm Cu-BTA/Co-BTA particles when Co is used as the liner in Cu interconnect structures (**Figure 3c**). These particles adsorb on only Cu surface, not Co film at pH 10 [20]. Since the zeta-potentials of both particles at pH 10 are close to ~0 mV (**Table 3**), there is a negligible electrostatic interaction of Cu-BTA/ Co-BTA particles with Cu and Co films. They suggested that the adsorption of these particles on Cu film is not only attributed to the hydrophobic interaction between particles and Cu film but also the chemisorption via the lone pair electrons on the nitrogen atoms in the Cu-BTA/Co-BTA particles [20, 40]. Other organic additives can also be adsorbed on the films via van der Waals and hydrophobic interactions. In some cases, these may convert hydrophilic to hydrophobic of the film surfaces.

**307**

atoms/cm<sup>2</sup>

(**Table 2**).

**Figure 3.**

*5 × 5* μ*m2*

alkaline medium [45].

**2.3 Metallic impurities**

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

The hydrophobic nature of the film surfaces can attract water droplets containing organic contaminants, leading to the watermarks and more organic residues [42]. These adsorbed organic contaminants affect the wettability and cleanability of the wafer surface, resulting in the poor adhesion of subsequently deposited layers

*(a) Organic residues generated from pad materials and others during polishing. (b) The formation of Cu-BTA complexes during polishing; TEM images of samples collected from the wafer surfaces after the exposure to the slurry components containing hydrogen peroxide, glycine, and BTA. (c) Topographic AFM images of Cu films contaminated with Cu-BTA (upper figure) and Co-BTA complexes (lower figure) at pH 10 in a scan area of* 

*. AFM profiles show the height of Cu-BTA/Co-BTA particles adsorbed on the Cu films. Reprinted with permission from Refs. [3, 40]. Copyright 2010 and 2009 American Chemical Society. Reproduced with* 

Most polishing pads are made of polymeric materials such as polyurethane. During polishing, the pad is conditioned with a diamond conditioner to regenerate the pad asperities and remove the accumulated particles on the pad, but generating 0.2 to 300 μm pad debris [43]. Although in-situ conditioning enables a higher removal rate and better planarity by maintaining stable pad surface properties, it can cause more pad debris compared to ex-situ conditioning [43]. Most of the pad debris is in the range of 0.2 to 0.3 μm. Some of the large pad debris (20-300 μm) are not only very irregular shapes, but also covered by abrasive particles [44]. This pad debris is known as a source of micro-scratches, and it should be completely removed during cleaning. Both hybrid clean (i.e., acidic plus alkaline cleans) and alkaline-clean processes are effective in removing pad debris from the wafer surfaces by the electrostatic repulsion between them in the

The CMP process leaves metallic impurities in the concentrations of 1011-1012

. These contaminants may originate from the abraded metal lines, metal ions in the slurries, the environment of the CMP tool [15]. During the metal CMP process, chelating agents are able to form a metal complex with metal ions on metal surfaces (Cu, W, Co, Ta, TaN, Ti, Ru, etc.). Metal ions dissolved from

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

*permission from Ref. [20]. Copyright 2019 IOP Publishing.*

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

#### **Figure 3.**

*Emerging Contaminants*

**Abrasive particles**

**Dielectric CMP**

**2.2 Organic residues and pad debris**

pair electrons [41]. For example, each Cu<sup>+</sup>

ligands of BTA<sup>−</sup>

with the BTA<sup>−</sup>

**Table 3.**

atom in BTA<sup>−</sup>

The polished wafers are also contaminated with organic residues (**Figure 3a**), which are originated from the slurry components such as dispersants, additives for the selectivity, complexing agents, corrosion inhibitors, etc. (**Table 1**). One of the main sources of organic residues is insoluble metal complexes. Azole derivatives (more specifically, benzotriazole (BTA)) have been widely used as corrosion inhibitors for metal films during polishing. BTA can strongly chemisorb onto the metal film by forming a chemical bond with a surface metal ion through the nitrogen lone

**Materials pHIEP**

**Silica 2.5** [22**] Ceria 7.3 [**23**] Alumina ~7.0** [24**]**

**SiO2 2.5** [25**]**

**Si3N4 ~**5**.**0 [26**] Poly-Si ~3.3** [27**]**

**W ~0.5** [24**] (WOx) TaN/TiN ~4.0 [**27**]/~3.6 [**28**] Ru 4.2-5.2 [**29**] (RuOX)**

**Metal CMP Cu The IEPs of CuO and Cu(OH)2 are 8.5 and 9.5,** 

**Consumables Polishing pad The IEPs of IC1000 and Politex are ~ 3.2 and 4,** 

**Organic residues Cu-BTA ~10 [**20**]**

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

**PVA brush ~2.5** [15**]**

**Co-BTA ~10 [**31**]**

during the Cu CMP process, which forms a polymeric product

of Cu-BTA complexes can bind to Cu surfaces, resulting in the

polymeric protecting layer on the Cu films [41]. Recently, Seo et al. [20] reported that Cu and Co ions dissolved from Cu and Co films, respectively, can react with BTA and form 4-15 nm Cu-BTA/Co-BTA particles when Co is used as the liner in Cu interconnect structures (**Figure 3c**). These particles adsorb on only Cu surface, not Co film at pH 10 [20]. Since the zeta-potentials of both particles at pH 10 are close to ~0 mV (**Table 3**), there is a negligible electrostatic interaction of Cu-BTA/ Co-BTA particles with Cu and Co films. They suggested that the adsorption of these particles on Cu film is not only attributed to the hydrophobic interaction between particles and Cu film but also the chemisorption via the lone pair electrons on the nitrogen atoms in the Cu-BTA/Co-BTA particles [20, 40]. Other organic additives can also be adsorbed on the films via van der Waals and hydrophobic interactions. In some cases, these may convert hydrophilic to hydrophobic of the film surfaces.

acting as bridging ligands (**Figure 3b**) [40, 41]. The third nitrogen

ion can coordinate with two nitrogen

**respectively [**24**].**

**and 11.4, respectively [**24**].**

**respectively [**30**].**

**Co The IEPs of CoO, Co3O4, and Co(OH)2 particles are 9.2, 9.5,** 

**306**

*(a) Organic residues generated from pad materials and others during polishing. (b) The formation of Cu-BTA complexes during polishing; TEM images of samples collected from the wafer surfaces after the exposure to the slurry components containing hydrogen peroxide, glycine, and BTA. (c) Topographic AFM images of Cu films contaminated with Cu-BTA (upper figure) and Co-BTA complexes (lower figure) at pH 10 in a scan area of 5 × 5* μ*m2 . AFM profiles show the height of Cu-BTA/Co-BTA particles adsorbed on the Cu films. Reprinted with permission from Refs. [3, 40]. Copyright 2010 and 2009 American Chemical Society. Reproduced with permission from Ref. [20]. Copyright 2019 IOP Publishing.*

The hydrophobic nature of the film surfaces can attract water droplets containing organic contaminants, leading to the watermarks and more organic residues [42]. These adsorbed organic contaminants affect the wettability and cleanability of the wafer surface, resulting in the poor adhesion of subsequently deposited layers (**Table 2**).

Most polishing pads are made of polymeric materials such as polyurethane. During polishing, the pad is conditioned with a diamond conditioner to regenerate the pad asperities and remove the accumulated particles on the pad, but generating 0.2 to 300 μm pad debris [43]. Although in-situ conditioning enables a higher removal rate and better planarity by maintaining stable pad surface properties, it can cause more pad debris compared to ex-situ conditioning [43]. Most of the pad debris is in the range of 0.2 to 0.3 μm. Some of the large pad debris (20-300 μm) are not only very irregular shapes, but also covered by abrasive particles [44]. This pad debris is known as a source of micro-scratches, and it should be completely removed during cleaning. Both hybrid clean (i.e., acidic plus alkaline cleans) and alkaline-clean processes are effective in removing pad debris from the wafer surfaces by the electrostatic repulsion between them in the alkaline medium [45].

#### **2.3 Metallic impurities**

The CMP process leaves metallic impurities in the concentrations of 1011-1012 atoms/cm<sup>2</sup> . These contaminants may originate from the abraded metal lines, metal ions in the slurries, the environment of the CMP tool [15]. During the metal CMP process, chelating agents are able to form a metal complex with metal ions on metal surfaces (Cu, W, Co, Ta, TaN, Ti, Ru, etc.). Metal ions dissolved from

metal surfaces or metal residues may be the main source for metallic contaminants (**Table 2**). These metallic cations not only are affected by the surface charge, but also can be precipitated on the surface of Si devices, which is expressed by ≡Si-OH(s) + Men+(aq) ↔ ≡ SiOMe(n−1)+ (s) + H+ (aq). Heavy metals (Cu, Fe, Ni, Cr, Co, and Mo) that deposited on the wafer surface by the galvanic reaction can diffuse into the Si devices during heat treatments and cause excessive leakage currents, resulting in the device degradation and reliability problems [46]. Other metals (Al, group II metals, and Ti) may have much lower diffusivities and may not diffuse significantly into the Si devices [39]. Metal ions such as Cu, Co, Fe, Al, Zn, and Mg can hydrolyze in the alkaline based cleaning solution and form insoluble metal hydroxides that are remained on the wafer surfaces [15]. Cu electromigration occurs through the movement of Cu atoms or Cu ions when there is a strong electrical current [47]. The undesirable metallic particles can cause short circuits between metal lines, whereas the metal hydroxides may cause open circuits [39].

Mobile ions such as alkaline metals (Na+ and K+ ) originated from the slurry components such as salts and NaOH/KOH (pH adjuster) [18] (**Table 2**) can cause flatband shifts and surface-related leakage currents due to their electrical characteristics of high mobility [39]. Fe ions have been used as a catalyst for W CMP slurry [8]. Fe ions (Fe3+, Fe(CN)6 3−, Fe(CN)6 4−, etc.) and FeOx caused from W CMP slurries are observed on the polished wafers (**Table 2**) [18, 48]. Acidic cleaning solutions are useful for removing metallic impurities and suppressing the adsorption of metallic species. Critical metallic impurities on the Si device continue to decrease as the device feature shrinks down. For the current technology nodes, the acceptable metallic contaminants are less than 108 atoms/cm2 and approach the limit of detection [46].

Some metallic contaminants directly come from the metal interconnect lines. After the Cu CMP process, pyramid-shaped Cu particles (Cu, CuO, and CuOH) detached from the Cu films are discovered on the surface [49] Metal flakes such as Ti or W-Ti on the top of the replace metal gate (RMG) after W RMG CMP process are observed [50, 51]. Metals at partially filled can be broken during the RMG CMP process, and they are a source of metal flake. These metal flakes are trapped inside the brush and re-deposit to the wafer surface by the cross-contamination process. In some cases, the delamination of metal films is occurred at the wafer edge due to the edge over erosion or a poor adhesion between metal and barrier film, which is another source of metal flakes [50, 51]. These metal flakes are known as a potential killer defect in the current RMG technologies.

#### **2.4 Pad contamination**

In some cases, the by-products are generated during the metal CMP process, and they are discovered on the pad surface [52, 53]. Han et al. observed the large stain on the pad after the polishing of Cu films [52]. The brown-colored by-products are formed and accumulated on the pores and grooves of the polishing pad, which is able to disturb the slurry transportation during polishing. These contaminants are caused by the chemical reactions between the slurry components and Cu films. They suggested that an additional pad cleaning step will be required to remove these by-products from the polishing pad and improve the pad lifetime [52]. Later, Lu et al. reported the pink by-products remained on the polishing pad after Co CMP process [53]. They compared Raman spectroscopy of by-products with that of the precipitates (Co-BTA particles) made from a mixture of Co(NO3)2 and BTA. Both samples showed the same Raman peaks, indicating that by-products observed on the polishing pad are Co-BTA particles.

**309**

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

When water evaporates from the hydrophobic surfaces, it leaves the residues containing organic residues, particles, and metallic impurities that were present in the evaporation water layer, which is known as "watermark". Watermarks are observed in hydrophobic regions or Mixed hydrophobic and hydrophilic areas [32, 54]. During the Si CMP and cleaning process, the oxidation of Si occurs in the presence of O2 in the water (Si + O2 → SiO2), and it is dissolved into water

). The dissolved species may precipitate to form

−

the residues containing Si and O. Watermarks that may contain organic residues and Cu oxide particles have also been one of the challenges for Cu CMP and cleaning process. Such watermarks tend to cause significant degradation in device performance [15]. IPA-based Marangoni drying process was proposed and used to eliminate watermarks [55]. The addition of surfactants that can convert hydrophobic to hydrophilic of the films will prevent the formation of watermarks after

**3. Brush-induced cross-contamination during post CMP cleaning**

between wafers and PVA brushes during post CMP cleaning. The brush is compressed to the wafer surfaces, and then the particle contaminants are removed by the physical force of the compressed brush. However, the surface and inside the pore structure of PVA brushes are contaminated with the particles, organic residues, and pad debris (**Figure 4a**), which can be transported to the next wafers and cause cross-contamination of the wafers during the brush scrubbing [56, 58]. More cross-contamination is observed on the wafer surfaces when the contact pressure and contact area between the brush and the wafer increase [59]. Also, the longer brush contact time (lower brush rotation speed) results in more cross-contaminated particles on the wafers. Before brush scrubbing, brush soaking treatment and break-in and their optimized process may be useful to reduce the cross-contamination and improve the cleaning efficiency [58]. Also, the ultrasonication method with DIW was very effective in removing the contaminants from the PVA brushes

The abrasive particles are removed from the wafer surfaces by the direct contact

The ring-shaped CuO residue is rarely observed at the wafer center region after the Cu barrier CMP process with acid-based slurries [60]. Chelating agents in the acidic medium are able to effectively form water-soluble complexes with Cu ions and pull them into the slurries. More polymers or corrosion inhibitors are added at lower pH slurry, which may lead to conductive organic residues during polishing. These organic residues can be dissolved in the cleaning solutions and move between the brush and wafer surfaces during cleaning when there is a direct solid–solid contact between them, making an electrical circuit [60]. Cu2+ ions released from the Cu films during cleaning can transfer to the brush, and they react with oxygen in the ambient environment to convert to CuO residue where the electro circuit is

Particle contaminants at the backside surface of wafers are also reported (**Figure 4b**) [57]. The wafer backside surface contacts with the slurries during polishing and cleaned with brush scrubbing and nozzle. Cleaning solutions are dispensed from an overhead nozzle onto the wafer backside. The locations of the wafer backside ring signature are well-matched with the inner ring, outer ring, and clean nozzle, which means that the polishing and the downstream surface cleaning

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

(SiO2 + H2O → H2SiO3 → H+ HSiO3

**2.5 Watermarks**

drying [42].

without damage [56].

provided by the organic residues [60].

process make the wafer backside ring signature [57].

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

#### **2.5 Watermarks**

*Emerging Contaminants*

circuits [39].

≡Si-OH(s) + Men+(aq) ↔ ≡ SiOMe(n−1)+ (s) + H+

Mobile ions such as alkaline metals (Na+

acceptable metallic contaminants are less than 108

killer defect in the current RMG technologies.

the polishing pad are Co-BTA particles.

slurry [8]. Fe ions (Fe3+, Fe(CN)6

limit of detection [46].

**2.4 Pad contamination**

metal surfaces or metal residues may be the main source for metallic contaminants (**Table 2**). These metallic cations not only are affected by the surface charge, but also can be precipitated on the surface of Si devices, which is expressed by

Cr, Co, and Mo) that deposited on the wafer surface by the galvanic reaction can diffuse into the Si devices during heat treatments and cause excessive leakage currents, resulting in the device degradation and reliability problems [46]. Other metals (Al, group II metals, and Ti) may have much lower diffusivities and may not diffuse significantly into the Si devices [39]. Metal ions such as Cu, Co, Fe, Al, Zn, and Mg can hydrolyze in the alkaline based cleaning solution and form insoluble metal hydroxides that are remained on the wafer surfaces [15]. Cu electromigration occurs through the movement of Cu atoms or Cu ions when there is a strong electrical current [47]. The undesirable metallic particles can cause short circuits between metal lines, whereas the metal hydroxides may cause open

and K+

components such as salts and NaOH/KOH (pH adjuster) [18] (**Table 2**) can cause flatband shifts and surface-related leakage currents due to their electrical characteristics of high mobility [39]. Fe ions have been used as a catalyst for W CMP

3−, Fe(CN)6

slurries are observed on the polished wafers (**Table 2**) [18, 48]. Acidic cleaning solutions are useful for removing metallic impurities and suppressing the adsorption of metallic species. Critical metallic impurities on the Si device continue to decrease as the device feature shrinks down. For the current technology nodes, the

Some metallic contaminants directly come from the metal interconnect lines. After the Cu CMP process, pyramid-shaped Cu particles (Cu, CuO, and CuOH) detached from the Cu films are discovered on the surface [49] Metal flakes such as Ti or W-Ti on the top of the replace metal gate (RMG) after W RMG CMP process are observed [50, 51]. Metals at partially filled can be broken during the RMG CMP process, and they are a source of metal flake. These metal flakes are trapped inside the brush and re-deposit to the wafer surface by the cross-contamination process. In some cases, the delamination of metal films is occurred at the wafer edge due to the edge over erosion or a poor adhesion between metal and barrier film, which is another source of metal flakes [50, 51]. These metal flakes are known as a potential

In some cases, the by-products are generated during the metal CMP process, and they are discovered on the pad surface [52, 53]. Han et al. observed the large stain on the pad after the polishing of Cu films [52]. The brown-colored by-products are formed and accumulated on the pores and grooves of the polishing pad, which is able to disturb the slurry transportation during polishing. These contaminants are caused by the chemical reactions between the slurry components and Cu films. They suggested that an additional pad cleaning step will be required to remove these by-products from the polishing pad and improve the pad lifetime [52]. Later, Lu et al. reported the pink by-products remained on the polishing pad after Co CMP process [53]. They compared Raman spectroscopy of by-products with that of the precipitates (Co-BTA particles) made from a mixture of Co(NO3)2 and BTA. Both samples showed the same Raman peaks, indicating that by-products observed on

(aq). Heavy metals (Cu, Fe, Ni,

) originated from the slurry

4−, etc.) and FeOx caused from W CMP

and approach the

atoms/cm2

**308**

When water evaporates from the hydrophobic surfaces, it leaves the residues containing organic residues, particles, and metallic impurities that were present in the evaporation water layer, which is known as "watermark". Watermarks are observed in hydrophobic regions or Mixed hydrophobic and hydrophilic areas [32, 54]. During the Si CMP and cleaning process, the oxidation of Si occurs in the presence of O2 in the water (Si + O2 → SiO2), and it is dissolved into water (SiO2 + H2O → H2SiO3 → H+ HSiO3 − ). The dissolved species may precipitate to form the residues containing Si and O. Watermarks that may contain organic residues and Cu oxide particles have also been one of the challenges for Cu CMP and cleaning process. Such watermarks tend to cause significant degradation in device performance [15]. IPA-based Marangoni drying process was proposed and used to eliminate watermarks [55]. The addition of surfactants that can convert hydrophobic to hydrophilic of the films will prevent the formation of watermarks after drying [42].
