Wetting behavior of plasma treated low-k films in dHF cleans solutions

• Dilute HF wetting was measured on porous low-k films as a function of time.
• Wetting for unashed low-k differed from ashed samples.
• Increasing HF concentration showed stronger wetting.
• Droplet spreading occurred for higher HF concentrations.
• Droplet evaporation was affected by ashing and HF concentration.

Post-ash and post-etch cleaning of low-k structures require significant wetting of their surfaces. This work focuses on the interactions between dilute HF cleaning chemistries (dHF—1:50 to 1:1000) on porous low-k surfaces (k = 2.3) as a function of time. Wetting of these solutions was measured by a contact angle goniometer within a high humidity environment. Because ashing low-k films can change their surface chemistry and structure, the contact angles of dHF on N2/H2 and O2 ashed porous low-k films were measured as well. Ellipsometry has shown that 1:50 HF removes an ash-damaged layer from the low-k. Based on thickness loss measurements (ellipsometry and profilometry), the composition of the dilute HF droplet changes minimally as it etches the dielectric surface. Under more concentrated dHF solutions, changes in contact angle, droplet radius, and volume indicate that the droplet spreads for an initial period and then reaches a steady state, perhaps due to the creation of an etch inclusion on the surface. The steady state volume changes show volume loss rates similar to those expected from evaporation; however, the total volume losses are less than expected from only evaporative processes.

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