The Chemical Mechanical Planarization (CMP) process (polishing and substrate cleaning) results in defects that can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. This work will focus on the rationale design of p-CMP cleaning systems for emerging materials (silicon carbide (SiC)) that activate the cleaning chemistry via external stimuli such as megasonic energy. More specifically, using megasonic energy in the presence of supramolecular assemblies such as micelles and vesicles was employed for a “soft” (low shear force) defect removal process. Results indicate a correlation between the structure of the “soft” cleaning additives and induced megasonic energy on overall simulated defect removal. It was determined that effective particle removal was a second-order kinetic process with a concentration dependency (i.e. above and below the critical micelle concentration (CMC)) emerging as a key driver for the defect removal rate. Although, one apparent drawback is the generation of post-cleaning carbon residue due to the adsorption of the supramolecular structures to the SiC substrate.

The development of post-chemical mechanical planarization (p-CMP) cleaning processes is critical for the continued miniaturization of integrated circuit and logic device architecture. In order for further extension of Moore’s Law, the minimization of critical defects is essential. This work focuses on the development of surface-active cleaning chemistries via the implementation of an α,β-unsaturated carboxylic acid additive to create synergy at the liquid-brush-wafer interface. More specifically, the implementation of itaconic acid (ItA) will chemically activate an organic residue (i.e., Cu(I)-BTA film) resulting in effective removal at significantly reduced CoF. This work demonstrates that the conjugated structure present in ItA significantly enhances the removal of organic residues at the surface of a Cu substrate without the expense of effective SiO2 removal resulting in little to no p-CMP cleaning induced defectivity.

Chemical Mechanical Planarization (CMP) is a critical process step in extending Moore’s Law and must be understood at a deeper, mechanistic level to limit defects that are detrimental to shrinking feature size. Specifically, Cu CMP utilizes a nanoparticle dispersion (slurry) composed of SiO2 abrasive nanoparticles, complexing agent, oxidizer, and a corrosion inhibitor. Slurry components must work in synergy to chemically modify the Cu surface while unwanted topography is removed by mechanical abrasion. The CMP process can cause various defects, and they can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. Adsorbed particles, polish residues, pad debris, and other foreign materials can have catastrophic impacts on device performance as line width decreases to the atomic scale. Upon the completion of the CMP process, removal of unwanted particle residue/organic contaminants is achieved using oxidation/reduction reactions, etching, or encapsulation chemistry coupled with ultrasonic methods or polyvinyl alcohol (PVA) brush cleaning. The nature of the current cleaning techniques has been known to provide insufficient cleaning capacity for next generation devices. This presentation will explore two fundamentally different approaches to post-CMP cleaning for Cu processes. First, the implementation of supramolecular cleaning chemistries to traditional PVA brush scrubbing was explored for the removal of SiO2 nanoparticles from a Cu surface. This work explored a structure activity relationship between the type of supramolecular cleaning chemistry used and its ability to effectively “encapsulate” nanoparticle contaminants. Initial results indicate that the anionic and non-ionic micelle show some corrosive behavior due to non-uniform passivation layers formed at the Cu surface during cleaning. This behavior is not seen with the cationic micelle suggesting its effective surface adsorption to the contaminant particle which can ultimately be removed via brush contact. Secondly, current cleaning chemistries typically utilize an undercutting mechanism to remove organic residues (i.e., BTA), however, this requires harsh oxidation and can result in scratches/erosion. Therefore, an approach to chemically activate the residue in an “overcutting” mechanism can improve cleaning performance with reduced defectivity. More specifically, this work will explore the use of α-β-unsaturated ketones as cleaning agents to initiate the nucleophilic attack and subsequent removal of BTA via a Michael’s Addition reaction. This mechanism will be evaluated via dynamic Tafel analysis, contact angle, atomic force microscopy, and cleaning performance to correlate interfacial interactions/reactions to p-CMP performance.

Wide band gap (WBG) materials (i.e., Silicon Carbide (SiC)) have attracted much attention in the semiconductor arena because of their intrinsic properties (i.e. high capacitance, thermal stability, and wear resistance). In order to achieve the desired removal rate and surface planarity during the Chemical Mechanical Planarization (CMP) process of SiC substrates high shear force and chemically aggressive conditions are employed. Although effective this process can result in significant surface contamination/defectivity (i.e., organic residue, abrasive particles, etc.) post-polish. Current methods of post-CMP cleaning for SiC substrates implement a Polyvinyl Alcohol (PVA) brush scrubbing to aid in surface contaminate removal. A balance of controlled shear force and interfacial adsorption/redox reactions are necessary to effectively remove rouge contaminates without any generation of secondary defects. This research focuses on development of a “soft” (low-shear force) post-CMP cleaning process for SiC which uses transient cavitation effects via megasonic energy coupled with catalytic complexes to enhance reactive oxygen species (ROS) generation. More specifically, hydroxyl radical (*OH) generating organometallic complexes were incorporated into the cleaning fluid to increase ROS and provide additional surface-active chemistries to disrupt the defects non-covalent surface binding energy. Initial results show increased ROS generation (which is complex structure dependent) improved defect removal efficiency under static megasonic conditions with no changes to the surface energy of the final polished SiC substrate.

As integrated circuits (ICs) and logic devices continue to shrink according to Moore’s Law, the demand for enhanced Chemical Mechanical Planarization (CMP) processes has increased dramatically. More specifically, an area that has gained tremendous attention is Shallow Trench Isolation (STI) CMP. The process of STI involves the electrical isolation of active components that require exposure by removing the bulk oxide (i.e., TEOS) overburden from the deposition process. Traditional STI slurry formulations are comprised of a CeO2 nanoparticle dispersion, rate enhancers, selectivity and rheology modifiers, and pH adjusters. Due to the presence of defect states (i.e., oxygen vacancies (Ovacs)) on the surface of CeO2 nanoparticles, their photocatalytic properties can be exploited to induce redox reactions. Specifically, the reduction of Ce4+ to Ce3+ leads to the formation of additional Ovacs on the surface of CeO2, which causes hard adsorption of CeO2 nanoparticles to TEOS surfaces. Significant work has been conducted on optimizing the post-CMP (p-CMP) cleaning process by creating low shear force environments via charge transfer chemistries to remove CeO2 adsorbed to TEOS. As a result, this work presents the design of responsive polymeric composites that may be employed in the brush scrubbing of TEOS to enhance particle removal while minimizing shear and compressive forces. This will ultimately limit secondary defectivity and induce more efficient cleaning of nanoparticles from the dielectric material. To monitor the cleaning process, coefficient of friction (CoF), shear force (SF), defect measurements via profilometry, particle removal efficiency (PRE), and Ce4+/Ce3+ ratio measurements will be utilized. Using a UV/Vis spectroscopic technique to monitor the Ce4+/Ce3+ ratio, initial results show a correlation between the oxidation state of CeO2 and PRE. Additionally, using a non-traditional polymeric brush during cleaning has shown higher PRE while maintaining lower shear force environments.