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Solvent (or solution) cleaning of clean wafers includes acetone wash, isopropyl alcohol (IPA) wash and de-ionized (DI) water wash, followed by drying in nitrogen.

What's the purpose of using DI water? Isn't it increases the overall (undesired) humidity on the wafer?

Sparkler
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  • ions cause electrostatic discharge under high E field excitation , also it is a contaminant where residue causes defects. DI is used after each cleaning process with blow dry in order to remove residue from previous cleaners in a 3 cleaning step for least residues – Tony Stewart EE75 Nov 04 '16 at 01:07
  • If you dry it then how can the humidity increase? – Ignacio Vazquez-Abrams Nov 04 '16 at 01:09
  • @TonyStewart.EEsince'75 I meant why water at all (obviously di is better than non di) – Sparkler Nov 04 '16 at 01:17
  • @IgnacioVazquez-Abrams acetone and ipa are highly volatile, while water is not. Nitrogen drying will not get rid of all the water introduced. – Sparkler Nov 04 '16 at 01:18
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    Because water is a (cheap and plentiful) polar solvent, versus the two non-polar solvents. – Ignacio Vazquez-Abrams Nov 04 '16 at 01:19
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    I would think water would do a good job of removing any trace alcohol or other contaminant residue left behind when the alcohol evaporates. The combination of those three solvents probably does a good job of removing virtually any contaminants. You can get just about anything as dry as you desire by heating it over 100C for an extended period. This is how moisture tests are done. Weigh the sample, heat and repeat until its weight stabilizes at a new value. Weight difference is moisture driven off. – user57037 Nov 04 '16 at 01:47

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Acetone is hygroscopic. So is isopropanol. Neither will be completely devoid of water, so water must always be removed by evaporation. The difficulty is, if any ionic solids are present, THOSE would remain after evaporation (and if those solids are hygroscopic, the 'drying' would be temporary, a little conductive saltwater puddle can reoccur later). So, the rinse water needn't be 'pure', a little alcohol in it won't hurt. But it oughtn't be (for instance) salty.

Deionized water is cheap and disposable, and (in conjunction with an 'air knife' or other droplet-removal scheme) mobilizes ionic contaminants and removes them from the wafer.

Whit3rd
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