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

The abrasive particles are removed from the wafer surfaces by the direct contact 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 without damage [56].

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 provided by the organic residues [60].

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 process make the wafer backside ring signature [57].

#### **Figure 4.**

*(a) Scanning electron microscopy (SEM) images of initial PVA brush and contaminated PVA brush. (b) Wafer backside signature after CMP and cleaning process. Reproduced with permission from Ref. [56]. Copyright 2019 IOP Publishing. Used with the permission of HongJin Kim [57].*

#### **4. Post-CMP cleaning for removing CMP-related to contaminants**

**Table 4** shows traditional post-CMP cleaning solutions that have been widely used to remove CMP-related to contaminants over the past several decades [46]. SC-1 solution is a mixture of NH4OH (29 wt%)/H2O2 (30 wt%)/DIW, which is very useful for removing particles, organic residues, and some metallic contaminants from the water surface through under-cut and particle lift-off or their combination [46]. SC-2 solution consisting of HCl (37%)/H2O2 (30 wt%)/DIW is very effective in removing metallic contaminants via the formation of soluble metal complexes

**311**

with Cl−

**Table 4.**

**Cleaning solution**

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

**Compositions and conditions Contaminant removal**

Particles, organics, and some metallic

contaminants

Organic residues

oxide removal

Metallic contaminants

 ions [46]. Sulfuric acid-peroxide mixture (SPM) of H2SO4 (96 wt%)/H2O2 (30 wt%) is able to remove photoresist and other organic residues by forming a very strong oxidizing agent, which can be expressed as H2SO4 + H2O2 → H2SO5 (Caro's acid) + H2O [61]. Caro's acid can easily dissolve the organic residues during cleaning. Hydrofluoric acid (HF) diluted with H2O (DHF) is useful to remove the oxide layer from the wafers. These traditional cleaning solutions have been modified to meet the post-CMP cleaning process requirements for advanced technology nodes. Some equimolar solutions containing NH4OH and H2O2 (4.20 and 4.13 mol/L, respectively) to remove even 10 nm ceria particles (~99% cleaning efficiencies) from SiO2 films were proposed by Seo et al. [21]. Non-traditional cleaning solutions composed of a bond-breaking reagent, complexing reagent, cleaning additive and pH adjuster were proposed for post STI CMP cleaning process [62, 63]. For postmetal CMP cleaning, the contaminants need to be completely removed while minimizing the individual corrosion of metals, localized pitting, and bimetallic/galvanic corrosion. Many cleaning compositions consisting of oxidizers, complexing agents, cleaning agents, and pH adjuster have been developed so far [20, 31]. However, there are still several cleaning challenges for the future technology nodes, while considerable progress has been made [57]; (1) improvement of cleaning efficiency, (2) the removal of smaller particles from the films, (3) the prevention of cross-contamination by brush scrubbing, (4) the removal of new-types contaminants-very thin metal flake, (5) wafer backside cleaning, (6) universal cleaning solution, (7) environmentally friendly post-CMP cleaning, (8) TMAH-free cleaning solution.

DHF HF, 1:10-1:200 at 25°C Sacrificial oxide removal and native

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

40-75°C

90-40°C

*Traditional cleaning solutions and their conditions.*

SC-1 NH4OH (29 wt%)/H2O2 (30 wt%)/H2O, 1:1:5-1:1:100 at 40-75°C

SC-2 HCl (37%)/H2O2 (30 wt%)/H2O, 1:1:6-1:1:50 at

SPM H2SO4 (96 wt%)/H2O2 (30 wt%), 2:1-4:1 at

**5. Toxicity issues and safety considerations**

complexing agent, corrosion inhibitor, and the slurry pH.

Toxic gases (e.g., PH3, AsH3) and the III–V containing liquid (in particular, As) can be generated during the polishing of III–V materials such as GaAs, InGaAs, InAs, and InP, which poses an environment, health, and safety (EHS) risk. Exposure to inorganic As can cause irritation of the stomach and intestines, decrease in the production of red and white blood cells, skin changes and lung irritation [64, 65]. Hence, one of the goals of the CMP processes of III–V materials is to achieve high planarity without generating toxic by-products. Also, Ru film can be converted to highly volatile RuO4 (a toxic gas) in the acidic pH during polishing. Compounds of Ru stain the skin very strongly, and the ingested Ru is retained strongly in bones. The addition of chelating agents may help to reduce the formation of highly volatile RuO4 during polishing. The formation of toxic by-products during polishing must be avoided by controlling slurry chemistry such as oxidizer,

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


**Table 4.**

*Emerging Contaminants*

**310**

**Figure 4.**

**4. Post-CMP cleaning for removing CMP-related to contaminants**

*IOP Publishing. Used with the permission of HongJin Kim [57].*

**Table 4** shows traditional post-CMP cleaning solutions that have been widely used to remove CMP-related to contaminants over the past several decades [46]. SC-1 solution is a mixture of NH4OH (29 wt%)/H2O2 (30 wt%)/DIW, which is very useful for removing particles, organic residues, and some metallic contaminants from the water surface through under-cut and particle lift-off or their combination [46]. SC-2 solution consisting of HCl (37%)/H2O2 (30 wt%)/DIW is very effective in removing metallic contaminants via the formation of soluble metal complexes

*(a) Scanning electron microscopy (SEM) images of initial PVA brush and contaminated PVA brush. (b) Wafer backside signature after CMP and cleaning process. Reproduced with permission from Ref. [56]. Copyright 2019* 

*Traditional cleaning solutions and their conditions.*

with Cl− ions [46]. Sulfuric acid-peroxide mixture (SPM) of H2SO4 (96 wt%)/H2O2 (30 wt%) is able to remove photoresist and other organic residues by forming a very strong oxidizing agent, which can be expressed as H2SO4 + H2O2 → H2SO5 (Caro's acid) + H2O [61]. Caro's acid can easily dissolve the organic residues during cleaning. Hydrofluoric acid (HF) diluted with H2O (DHF) is useful to remove the oxide layer from the wafers. These traditional cleaning solutions have been modified to meet the post-CMP cleaning process requirements for advanced technology nodes.

Some equimolar solutions containing NH4OH and H2O2 (4.20 and 4.13 mol/L, respectively) to remove even 10 nm ceria particles (~99% cleaning efficiencies) from SiO2 films were proposed by Seo et al. [21]. Non-traditional cleaning solutions composed of a bond-breaking reagent, complexing reagent, cleaning additive and pH adjuster were proposed for post STI CMP cleaning process [62, 63]. For postmetal CMP cleaning, the contaminants need to be completely removed while minimizing the individual corrosion of metals, localized pitting, and bimetallic/galvanic corrosion. Many cleaning compositions consisting of oxidizers, complexing agents, cleaning agents, and pH adjuster have been developed so far [20, 31]. However, there are still several cleaning challenges for the future technology nodes, while considerable progress has been made [57]; (1) improvement of cleaning efficiency, (2) the removal of smaller particles from the films, (3) the prevention of cross-contamination by brush scrubbing, (4) the removal of new-types contaminants-very thin metal flake, (5) wafer backside cleaning, (6) universal cleaning solution, (7) environmentally friendly post-CMP cleaning, (8) TMAH-free cleaning solution.

#### **5. Toxicity issues and safety considerations**

Toxic gases (e.g., PH3, AsH3) and the III–V containing liquid (in particular, As) can be generated during the polishing of III–V materials such as GaAs, InGaAs, InAs, and InP, which poses an environment, health, and safety (EHS) risk. Exposure to inorganic As can cause irritation of the stomach and intestines, decrease in the production of red and white blood cells, skin changes and lung irritation [64, 65]. Hence, one of the goals of the CMP processes of III–V materials is to achieve high planarity without generating toxic by-products. Also, Ru film can be converted to highly volatile RuO4 (a toxic gas) in the acidic pH during polishing. Compounds of Ru stain the skin very strongly, and the ingested Ru is retained strongly in bones. The addition of chelating agents may help to reduce the formation of highly volatile RuO4 during polishing. The formation of toxic by-products during polishing must be avoided by controlling slurry chemistry such as oxidizer, complexing agent, corrosion inhibitor, and the slurry pH.
