Membrane processing for water treatment in the semiconductor industry


It is the aim of high-purity water production to either fully eliminate organic and ¡florganic compounds, particles, and microorganisms from the water or to reduce their concentrations to values below the detection limits of the most advanced analysis methods. Currently, this problem is solved by means of a multi-stage process chain, in which membrane technology plays a special role atseveral points. With the introduction of the 0.25 micron (pm) and 0.18 pm wafer technology, the requirements for the high-purity water treatment plants with regard to the specification as well asflexibility, safety, andleadtimewillbe even higher.


Product cycle times in the microelectronics industry are approximately 2 years. This requires an increasing demand on the high-purity water quality. Table A shows how high-purity water specifications have developed over the past decades as the structure of integrated circuits have changed.


Large quantities of high-purity water are required for wafer production; the demand of high-purity water even increases with the wafer size. For instance, the production of a 200-millime- ter (mm) wafer with a 16 MB DRAM needs 4 to 5 cubic meters (m3) of highpu rity water. Therefore, state-of-the-art wafer fabs commonly consume 100 to 300 m3 of high-purity water per hour.


Semiconductor High-Purity Water Systems

Figure 1 shows an example of a commonly used high-purity water treatment system in the semiconductor industry for 0.35-pm and 0.25-pm structures, respectively. Membrane processes are highlighted to show their leading role.

The raw water is first fed into the pretreatment system to remove suspended solids and to condition the water for the next step. The components applied in this step may vary dependent on the raw water quality. The goal is to getwaterto at least drinking water quality.


Then the water is fed to a reverse osmosis (RO) plant. Most of the ionic and organic substances are removed in this step. The pure waterflowing offthe RO plant (permeate) is collected and ozonated in a tank from where it is pumped through an ultraviolet(UV) system in order to remove the residual total organic carbon (100) and to sterilize the water. The UV radiation has the ability to destroy certain bondings in molecules, thus decomposing them. In the vacuum degasifier, dissolved gases, in particular oxygen and carbon di- oxide, are removed. A reduction of oxygen down to a level of 10 parts per billion (ppb) and lower is feasible.


A further red uction of the oxygen can be achieved by using a catalytic oxygen removal process. The oxygen can be red uced down to a level of less than ppb.

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