Specific Process Knowledge/Lithography/LiftOff: Difference between revisions
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== Process information == | |||
Lift-off is used for lift-off using resists that are soluble in NMP (''N''-Methyl-Pyrrolidone), supplied in the cleanroom as "Remover 1165". Both AZ 5214E and AZ nLOF are soluble in NMP. | Lift-off is used for lift-off using resists that are soluble in NMP (''N''-Methyl-Pyrrolidone), supplied in the cleanroom as "Remover 1165". Both AZ 5214E and AZ nLOF are soluble in NMP. | ||
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===Poor metal adhesion=== | |||
''This experiment was done by Gustav E. Skands(ges@sbtinstruments.com)'' | |||
This entry details an observed issue with metal adhesion during a Ti/Pt deposition (10/160 nm) and lift-off process within DTU Nanolab. The employed photoresist was TI Spray from MicroChemicals, which is believed (but not confirmed) to share many properties with AZ5214E. The thickness of the resist was approximately 5 µm, and it was spray coated onto the substrate using the Spray Coater. | |||
'''Root cause:''' | |||
The core of the adhesion challenge was linked to the choice of photoresist developer. 2.08% TMAH facilitated excellent resist pattern development, but subsequent metal adhesion during the deposition process was consistently poor, observed across both Wordentec and both Temescal systems. This occurred despite the absence of any visible residues on the substrate surface. Attempts to enhance adhesion, including a descum procedure using 70 mL/min O2 and 70 mL/min N2, 150W, 5 minutes, prior to deposition, were unsuccessful. | |||
'''Solution:''' | |||
Changing the developer to AZ351B (2 minutes development time in beaker) in the process provided significant improvements. Although AZ351B exhibited reduced selectivity in dissolving the soluble vs. insoluble resist, thereby compromising the precision of the resist pattern, it considerably improved the adhesion properties of the deposited metal. | |||
A dual developer approach—using TMAH (3x 60s development in Developer: TMAH UV-lithography followed by a 30 second development step in AZ351B—was therefore implemented. This approach leveraged the high-resolution patterning capability of TMAH and the superior adhesion characteristics provided by AZ351B. | |||
The different adhesion properties observed with the two developers suggest underlying molecular interactions that may inhibit or promote metal-substrate bonding. It is hypothesized that TMAH may leave molecular residues that, although not detectable through optical inspection, could create a barrier to adhesion at the molecular level. Conversely, AZ351B appears to modify or clear these residues, thereby enhancing adhesion. | |||
A descum step of 70 mL/min O2 and 70 mL/min N2, 150W, 5 minutes, was still performed immediately before deposition. However, it is unknown if this has an effect. | |||
Process temperature considerations | |||
The process incorporated a deposition temperature of 50°C, which was maintained without further comparative analysis against room temperature deposition due to the successful outcomes achieved and considerations of operational cost efficiency. | |||