Wet Chemical Cleaning in BEOL: Principles and Mechanisms of EKC Post-Etch Residue Removal

The cleaning question: remove the residue, preserve the stack

Post-etch wet cleaning must remove unwanted material while preserving the exposed dielectric, metal and interfaces. “EKC” identifies a family of named cleaning formulations, not one universal reaction or the generic name for all post-etch cleaners. The formulation and the residue must both be specified before a mechanism can be assigned.

For BEOL integration, cleaning success has two parts: sufficient residue removal and acceptable change to the functional stack. A surface that looks clear can still have lost material or changed chemically. [P1][P2]

Different residues call for different mechanisms

Resist-derived material, fluorocarbon-rich sidewall deposits and metal-containing etch products are not chemically identical. A solvent may dissolve or swell an accessible organic fraction while a cross-linked or inorganic-rich fraction remains. Reactive components may change the residue’s chemistry or help release it, but their presence and role depend on the formulation. [P1]

The cited fluorocarbon study found incomplete removal by the tested solvents alone and improved removal after a particular UV pretreatment. This supports a conditional mechanism involving polymer modification before wet removal. It does not show that all EKC products contain fluoride, use UV or remove every residue by the same pathway. [P1]

Selectivity includes the material underneath

Removing a deposit by attacking the supporting dielectric is different from selectively removing the deposit itself. A cavity can appear cleaner because its sidewall has receded. That may be unacceptable when preserving dimensions and interfaces is essential. The cited studies distinguish this lift-off risk from effective polymer removal. [P1][P2]

Chemical access also matters: a liquid must reach the relevant sidewall or bottom, and removed species must leave the feature. Evidence from a blanket film cannot automatically establish performance inside a patterned opening. Residue composition, geometry and exposure history must remain part of the comparison. [P1]

Metal compatibility and corrosion

An exposed metal or barrier can react with the cleaning solution even if the residue is being removed. Assess metal loss, surface chemistry and the actual material combination rather than assuming a cleaner is compatible because it worked on a different stack. The cited fluorocarbon work notes compatibility limits for some hydroxylamine-containing solutions with certain low-k materials and copper; this is a limitation of particular combinations, not a verdict on all products. [P1]

The transition out of the cleaning bath is part of this assessment. Carried-over chemistry can continue reacting during solution exchange. A complete evaluation includes the rinse and drying sequence and any residues left by that sequence, rather than only the immersion endpoint.

Low-k compatibility and physical assistance

Carbon-containing porous low-k dielectrics can be vulnerable to changes in composition and surface chemistry. Removing resist or polymer while also removing useful dielectric groups is not selective cleaning. A material’s appearance alone cannot establish that its dielectric properties were preserved. [P2]

Physical assistance can help detach residues, but force applied to a fragile patterned structure can also cause damage. The cited work describes removal improvements and mechanical limits in specific experiments. It does not justify a universal megasonic step or a transferable operating recipe. [P2]

Rinsing belongs to the process

Rinsing exchanges the cleaning liquid and transports dissolved or detached material away. It is not equivalent to proving that the original residue has been chemically removed. Poor exchange, redeposition or a remaining surface film can still affect the next interface. Drying then determines what remains as the liquid leaves.

The all-wet resist/BARC study evaluates a complete sequence that includes rinsing, drying and dielectric-property measurements. It supports reviewing those operations together, while its particular solvents and conditions cannot be generalized to every EKC formulation or BEOL stack. [P3]

Locate the handoff to metal formation

For the detailed surface-preparation explanation, open the 28nm course step. It follows V1M2 etch and leads to barrier and seed deposition, separating residue removal from low-k damage recovery. Full Step text requires 28nm course access; free registration alone does not unlock it. The step identifies no EKC formulation. The public overview and the existing three-stop topic remain sequence comparisons; the topic omits cleaning.

Use the public 28nm Flow overview to locate dielectric opening before subsequent barrier, seed and metal formation. The existing dual-damascene topic compares three teaching stops: V1M2 etch, M2 copper electrochemical plating and M2 copper CMP. It deliberately leaves intervening operations outside its three-stop view; it contains no cleaning stop and demonstrates no EKC formulation. Anonymous topic entry at the first stop permits two summary stops; free registration opens all three full teaching stops. Detailed Step permissions remain separate.

For deciding what the observed material is and whether it is residue or damage, continue with the residue-removal article. That diagnostic question precedes the choice of cleaning mechanism.