Continuing the discussion from Poor Resist Adhesion after developing:
The issues of poor resist adhesion to your substrate is a common one, so making a summary tech note here. Please let me know what you found to be best practices as well.
Resist will not adhere well if there is anything between the resist and the substrate, and this mostly includes things not visible to the human eye, and may not even be visible in a microscope (bright field or dark field). So here are some ways to clean.
If the wafer is brand new in the wafer box, and was not exposed to cleanroom air until you are about to use it, this is the only time that cleaning might not be advisable. Any processing however, even cleaning, can add some contaminants. Processing includes dicing the wafer into chips.
The following processes used together or apart will all improve adhesion. All of these methods should be user right before spinning the resist.
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Acetone + IPA Solvent Clean- Using either chemical baths or the spray bottles at the spinner, clean first with Acetone, and then Immediately after (not letting the acetone dry) clean with IPA. This is a first pass on wafer/chip cleaning.
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O2 plasma clean- using a RIE (Reactive Ion Etcher) or plasma asher, you can expose the wafer or chip to a gentle O2 plasma (50-100Watts 30-60 seconds). This helps in 2 ways: it removes any organic residues, and can also help to drive off some of the water molecules that might be on the surface due to the heat of the plasma. This also serves to make the surface of the substrate hydrophilic, ( chemically adding hydroxyl groups (OH) promoting liquid resist adhesion.
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Baking on a hotplate- Prebaking the wafer at 100C to 150C for 1-3 minutes before spinning resist served to drive off any moisture that has deposited on the wafer. (Water is always bad for adhesion.). Make certain to let the wafer cool for a couple of minutes before resist spinning
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Piranha Clean - This is a more aggressive step that involved using sulfuric acid and Hydrogen peroxide to remove the organics from the surface of the wafer. Like O2 cleaning, this also serves to make the surface of the substrate hydrophilic (OH Groups), further promoting liquid resist adhesion.
All of these methods should be user right before spinning the resist.
Depending on the resist and the substrate (resist-substrate pair) you can use other primers other than cleaning to promote adhesion. These include HMDS (hexamethyldisilazane, which actually makes the surface hydrophobic), or Surpass, both of which can be spun onto the wafer before the resist. But these are very dependent on the resist-substrate pair, and perhaps the subject of another tech note.
If you have other thoughts on this please reply below!