Throughout the wafer manufacturing process, there are several steps that involve the use of ultrapure water (UPW), both in chemical bath mixtures, and in the rinse process following these chemical processes. These include standard cleans, wet etch, and Chemical Mechanical Planarization (CMP). Furthermore, the wafer is often redundantly cleaned to remove contaminants and prepare the surface between processes. These wet standard cleaning operations can account for as much as one third of the total processing steps, depending on the type of product.Wet cleans and other wet processes, such as some etch processes, solvent processes and CMP, utilize only UPW for the process chemistry and subsequent rinses. In fact, more than 3000 gallons of UPW can be used to process each eight inch wafer from start to finish. Standard wet cleans consume about 60% of the total UPW used in wafer processing, while etch processes, which typically use acids, consume 20%. Solvent processes use 10%, and process tool cleaning steps consume approximately 10%.

The UPW generation process is a series of chemical engineering unit operations designed to remove contaminants from water to achieve an ultrapure level. These contaminants include particles, organic compounds, dissolved ions, and dissolved gases. The final UPW quality that must be achieved is often the highest of any industry. This is due to the fact that any contaminants that remain on the wafer surface can render a device non-functional; the dimensions of the device structure are so small that virtually any molecule of contaminant can be detrimental.

Water Quality Parameter	Units	Typical Municipal Water Supply	Typical Ultrapure Water Product
Resistivity	M Ohms-cm	0.004	>18
pH	units	8	6
TOC	ppb	3500	<10
Ammonium	ppb	300	<1
Calcium	ppb	22000	<1
Magnesium	ppb	4000	<1
Potassium	ppb	4500	<1
Silica	ppb	4780	<10
Sodium	ppb	29000	<1
Chloride	ppb	15000	<1
Fluoride	ppb	740	<1
Sulfate	ppb	42000	<1