Assessing the Oxidative Degradation of N-Methylpyrrolidone (NMP) in Microelectronic Fabrication Processes by Using a...

Area of Science:

• Materials Science
• Chemical Engineering
• Microelectronic Fabrication

Background:

• Corrosion of metal features and deposition of by-products are observed during recording head device construction.
• N-methylpyrrolidone (NMP) use in photoresist removal has been implicated as a contributing factor to these issues.

Purpose of the Study:

• To investigate the role of NMP in metal corrosion during photolithography lift-off.
• To identify the chemical mechanisms responsible for corrosion and device performance degradation.
• To propose a method for mitigating NMP-induced corrosion in microelectronic fabrication.

Main Methods:

• A multiplatform analytical approach was employed, including pH monitoring, liquid chromatography/UV detection (LC/UV), inductively coupled plasma optical emission spectroscopy (ICP-OES), and LC/mass spectrometry (LC/MS).
• Reaction conditions mimicking photoresist removal processes were simulated.
• Experiments were conducted under both standard and inert atmosphere conditions.

Main Results:

• NMP oxidation was confirmed to occur under conditions simulating photoresist removal processes.
• NMP oxidation was shown to lower the solution pH, facilitating the dissolution of transition metals on wafer substrates.
• Performing the process in an inert atmosphere suppressed NMP oxidation and stabilized pH, preventing metal dissolution.
• The observed metal dissolution negatively impacts microelectronic device performance.

Conclusions:

• The study confirms NMP oxidation as a cause of metal corrosion and performance issues in microelectronic devices.
• Implementing an inert atmosphere during the photolithography lift-off stage is a viable and affordable method to enhance recording head quality.
• pH should be considered a key process input variable (KPIV) in the design of new photoresist removal processes.