In chip cleaning agents, the role of a film-forming agent is to enhance the cleaning effect and prevent secondary contamination by forming a uniform protective film on the chip surface. The following are its core functions and technical principles:
01
Core Functions of Film Agents
(1) Anti-corrosion Protection
Metal Layer Protection: After cleaning, the metal on the chip surface (such as Al, Cu) may be exposed to air and oxidize or corrode. Film-forming agents (e.g., silane coupling agents, benzotriazole) form an inert thin film that isolates oxygen and moisture, inhibiting metal corrosion.
Example: BTA (benzotriazole) is used in copper interconnects to prevent discoloration by forming a dense organic film.
(2) Anti-Particle Adhesion
Reducing Surface Energy: Film-forming agents chemically bond (e.g., silane reacts with Si-OH) or physically adsorb to modify the chip surface properties, making it hydrophobic instead of hydrophilic, thereby reducing adhesion of particles (such as SiO₂, photoresist residue).
Example: Fluorosilanes (e.g., FDTS) form a low surface energy film after HF cleaning to prevent particle redeposition.
(3) Enhanced Lubricity
Reducing Friction Damage: After chemical mechanical polishing (CMP), film-forming agents can repair micro-scratches on the surface, reducing mechanical wear risks in subsequent processes (such as testing and packaging).
Example: Long-chain silanes (e.g., octadecyltrichlorosilane) form a molecular-level lubricating layer.
(4) Stable Cleaning Effect
Prolonging Cleanliness Duration: Film-forming agents can delay the secondary adsorption of contaminants after cleaning. For example, after RCA cleaning, a silane film can maintain surface cleanliness for several hours, avoiding contamination during storage.
02
Technical Principles
(1) Chemical Bonding Mechanism
Silane-based Film-forming Agents: Hydrolyze to form Si-OH, which condenses with hydroxyl groups (Si-OH) on the chip surface to form covalent Si-O-Si bonds for chemical adsorption.
Reaction: Si-CH₂CH₂CH₂Si(OH)₃ → Si-O-Si (on chip surface) + H₂O
Phosphate-based Film-forming Agents: Coordinate and chelate with metal oxides (e.g., Al₂O₃) to form stable chelation films.
(2) Physical Barrier Mechanism
Polymer Film-forming Agents (e.g., polydimethylsiloxane): Spread through van der Waals forces to form a continuous thin film that fills surface micro-voids and blocks contaminant penetration.
03
Application Scenarios
Post-wet cleaning treatment: After SC1/SC2 cleaning, silane film-forming agents (e.g., HMDS) are used to prevent moisture retention leading to oxidation.
Etching/Polishing Protection: After CMP, fluorosilane films are sprayed to avoid dicing fluid contamination.
Temporary Storage Protection: During wafer transfer or testing, film-forming agents provide short-term (several hours to days) anti-contamination protection.
04
Precautions
Compatibility: Must not react adversely with cleaning agents (e.g., hydrofluoric acid, ozone water); for example, avoid silane hydrolysis failure under alkaline conditions.
Thickness Control: Film thickness is typically at the nanometer level (e.g., 1–5 nm); excessive thickness may cause photolithography alignment errors or degrade electrical performance.
Removability: Must be easily removable before subsequent processes (e.g., bonding, metal deposition), commonly using UV decomposition or solvent cleaning.
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