Blog

The photoresist solution is a particularly difficult fluid to filter, but this must be done to exacting standards, in order to ensure transfer of patterns onto thin films. Not only must the photoresist be filtered, but so also must the solvents used in developing the resist.

Particulate contaminants in photoresist are either undissolved polymers or manufacturing debris from the process of making the photoresist chemicals. Negative photoresist is formulated from high molecular weight products that are often difficult to dissolve and remove from the surface of the wafers. Positive photoresist, by its nature, is unstable with highly photoreactive groups. These can form reaction by-products along with auto-polymerized gels. The gel slugs are a source of pin holing image distortion, and oxide-island formation during the etch process.

Point-of-use filtration for photoresists is essential, and should be done at the last possible point, because in addition to impurities that may be present or formed during the photolithographic process, dispensing of the photoresist can also introduce particulate contaminants. Automatic dispensing machines can generate particles from pumps, valves, nozzles, tubing and residual photoresist deposited on these parts. Membrane filters are recommended for this application also, because they are highly efficient at removing substantial amounts of the gelatinous deformable polymers, along with the hard particles that are contained in the photoresist. As with chemicals the recommended pore size is 0.2um.

A prefilter should be used ahead of the membrane filter in order to reduce the pressure drop when filtering through the membrane, thus reducing the size of the housing needed for the filter cartridges. This will increase the life of the process system and take the load off the membrane filter that performs the removal of the finer particulates. As for the chemicals used to develop photoresists, continuous recirculation and membrane filtration are the preferred techniques. Strict temperature and atmospheric control must be maintained. Compressed air and water are two separate, but essential,
tools in the production of electronic components and systems.

Look for more information, please click here.