Ultra-pure air system for nano wafer environment

In one embodiment, an air filtration system includes a first ventilation path connected between at least one external air supply and a clean room. The first ventilation path is configured to direct air from the at least one external air supply to the clean room. A second ventilation path is connected to the clean room. The second ventilation path is configured to recirculate air in the clean room. A third ventilation path, separate from the first path, is connected between the at least one external air supply and a tool environment disposed within the clean room. The third ventilation path includes an ultra-pure air filtration unit disposed between the outdoor air supply and the tool environment. The ultra-pure air filtration unit includes a compressor and a dryer.

FIELD OF THE DISCLOSURE

The disclosure relates to a semiconductor wafer fabrication environment, and more specifically, to the control of airborne molecular contamination (AMC) in a semiconductor wafer fabrication environment.

BACKGROUND

Semiconductor wafer processing requires an environment virtually free from AMC and particulate matter so the wafers may be processed without being contaminated. Accordingly, semiconductor processing is performed in clean rooms in which air is highly purified or filtered prior to its introduction into the room. Chemical filters as well as high efficiency particulate air (HEPA) and/or ultra low penetration air (ULPA) filters are commonly employed to filter and purify the air prior to its introduction into the clean room. As wafer processing enters into nano technology, more and more chemical filters are required to meet the tight AMC specification requirements for wafer processing.

FIG. 1is a block diagram of the air flow in a conventional air filtration system100for a clean room. As shown inFIG. 1, the conventional air filtration system100introduces air into the clean room114in two ways: (1) through a make-up air flow102and (2) through a recirculation airflow122. The make-up airflow102takes air from an external (e.g., outdoor) air supply104and passes it through a make-up air treatment unit (ATU)106. In the ATU106, the outdoor air undergoes airborne molecular contamination (AMC) removal treatment by passing through one or more chemical filters. After passing through ATU106, the make-up airflow102is mixed with air from the recirculation flow122. The combined airflow is cooled through dry cooling coil108.

The combined airflow, which includes the filtered outdoor air and the recirculated air, is passed through a fan filter unit (FFU)110where it is once again filtered by one or more chemical filters. The combined air is then blown by the fan of the FFU110into the clean room114. A fan mounted on the tool directs air from the clean room114into the tool environment112. A portion of the air that passes through the tool environment112is dispersed back into the clean room114where it mixes with the air in the clean room114. The mixed air flows into a sub-fabrication air return area116. At the sub-fabrication air return area116, part of the returned air will be discharged to the outdoors, along with some air drawn directly from the tool environment112, after passing through the air abatement system118. The remaining portion of the airflow will be recirculated and mixed with the make-up flow102from the outdoors at the dry cooling coil108. The conventional air purification systems as described above are expensive as they require a large quantity of expensive chemical filters to purify both the make-up airflow102and the recirculation airflow122. Additionally, the conventional systems suffer from cross-contamination between the clean room and the tool environment caused by turbulent air in the clean room114.

Accordingly, an improved air filtration system for nano-wafer environments is desired.

SUMMARY OF THE DISCLOSURE

In one embodiment, an air filtration system comprises a first ventilation path connected between at least one external air supply and a clean room. The first ventilation path is configured to direct air from the at least one external air supply to the clean room. A second ventilation path is connected to the clean room. The second ventilation path is configured to recirculate air in the clean room. A third ventilation path, separate from the first path, is connected between the at least one external air supply and a tool environment disposed within the clean room. The third ventilation path includes an ultra-pure air filtration unit disposed between the outdoor air supply and the tool environment. The ultra-pure air filtration unit includes a compressor and a dryer.

In another embodiment, a method comprises the steps of filtering a first make-up airflow, purifying a second make-up airflow in an ultra-pure air purification unit, combining the first make-up airflow with a first recirculation airflow, and applying the second make-up airflow directly into a tool environment and the combined airflow into a clean room. The ultra-pure air purification unit includes an air compressor and dryer.

In another embodiment, a method for purifying air for a nano-technology process environment comprises the steps of providing air from an external air supply, pre-treating the air at a pre-treatment unit, compressing the air to a pressure such that water vapor and airborne contaminants form a condensate, removing the condensate from the air, post-treating the air at a post-treatment unit, and directing the air into a tool environment within a clean room. The air is directed into the tool room while bypassing an air recirculation path of the clean room.

DETAILED DESCRIPTION

FIG. 2is a flow diagram of one embodiment of a clean room air filtration system. The clean room214may be a Class 100 clean room, e.g., the air in the clean room214contains fewer than 100 particles that are 0.5 μm or larger per cubic foot of air. Note that in other embodiments clean room214may be a classification other than Class 100, or clean room214may be another room type such as, for example, a nano-technology lab or any room where ultra-pure air is used. As illustrated inFIG. 2, the clean room air filtration system includes two airflows: (1) a make-up airflow202and (2) an air recirculation flow222. Each airflow202,222is directed through a separate ventilation path until it is received in the clean room214and tool environment212. Make-up airflow202includes a dedicated airflow for the clean room214and a separate dedicated airflow for the tool environment212where tooling is in direct contact with semiconductor wafers.

The make-up airflow for the clean room214is received from an external (e.g., outdoor) air supply204a, which passes through air treatment unit (ATU)206. Although the example ofFIG. 2uses outdoor air for the external air supplies204aand204b, other embodiments may use a different external air source, such as air from a compressed air storage reservoir, or air from a central ventilation system.

In the ATU206, the air received from the external air supply204aundergoes temperature and humidity control through HVAC coils and one or more humidifiers. ATU206may also include a pre-filter, a medium filter, and a high efficiency particulate air (HEPA) filters to remove particles contaminants from the air. Once the air is filtered, it is combined with air from the recirculation airflow222at a dry cooling coil208, where the air is cooled. The recirculation airflow222is directed through a ventilation path that is separate from the paths of the make-up airflows202, and continuously recirculates air from below the clean room214and tool environment212to be recombined with air from make-up airflow202for the clean room214. The combined dry cooled air passes through the fan and filter unit (FFU)210where it is once again filtered prior to being directed into the clean room214by one or more fans.

The make-up airflow202for the tool environment212is a directed along a separate ventilation path between an external air supply204band the tool environment212. Accordingly, the make-up airflow for the tool room212is filtered separately from the air that is directed into the clean room214. The dedicated airflow for the tool environment212is received from external air supply204band undergoes ultra-pure air (UPA) treatment at UPA treatment unit220. In some embodiments, external air supplies204aand204bare separate and distinct from each other. In other embodiments, external air supplies204aand204bmay be the same external air supply, connected via two separate and distinct ventilation paths for providing the air to ATU206and UPA treatment unit220, respectively.

In one embodiment, UPA treatment unit220includes a pre-treatment unit220a, an air compressor and dryer unit220b, and a post-treatment unit220c. Pre-treatment unit202amay include an ionizer and a photo-catalyst. Additionally, a humidifying component may be included in the pre-treatment unit220ato enhance the performance of the compressor and dryer unit220b.

Air from the pre-treatment unit220ais received at the compressor and dryer unit220b. The compressor may be an industrial air compressor that increases the pressure of the air in the compressor to a pressure above that of the external atmosphere until water vapor and airborne contaminants are condensed into a liquid condensate. The air contaminants are dissolved in the pressurized water vapor and removed through a drain located in UPA treatment unit220. The compressed air is dried in a dryer, which also enhances the purity of the air. The dryer may be an industrial compressed air dryer configured to remove additional condensate and airborne contaminants from the air. In some embodiments, the dryer may be a refrigerated air dryer which further reduces the dew point of the compressed air to remove airborne contaminants.

The compressed and dried air may then enter a post-treatment unit220c. Post-treatment unit220cmay include one or more chemical and/or physical filters, e.g., HEPA, ultra-low penetration air (ULPA) filter, and the like, to further purify the air. The air from the post-treatment unit220cis then directed into the tool environment212where it may be applied directly to the tooling or another point of use.

FIG. 3illustrates one example of a clean, dry air (CDA) measurement of the air through various stages of the ultra-purification treatment in accordance with the embodiment shown inFIG. 2. As shown inFIG. 3, the UPA treatment unit220reduces the amount of contaminants including, but not limited to, fluoride, chloride, nitrate, phosphorus, sulfate, and ammonium from the external air. The compressor purification also reduces the amount of organic contaminates in the air, such as, for example, toluene, ethane, ethyl acetate, cyclohexanone, xylene, acetone, and ethlybenzene. To increase the purity of the air, the UPA treatment unit220may also incorporate additional air purification techniques to reduce AMCs, such as, for example, air-washers, chemical filters, photo-catalyst filters, and ultra-violet radiation at the pre-treatment unit220aand/or post-treatment unit220c.

By isolating the make-up airflows202for the tool environment212and the clean room214, the chance of contamination of the tool environment212by locally borne contaminants caused by turbulent airflow in the clean room214is reduced. Additionally, separating the make-up airflow for the clean room214reduces the amount of air that requires ultra-pure air treatment. Purifying with the UPA treatment unit220reduces the number of chemical filters that may be installed in the FFU210to filter the air for the clean room214. Reducing the number of chemical filters through which the air passes reduces the likelihood of experiencing an undesired pressure drop in the clean room214, which may occur when multiple chemical filters are used to purify an airflow in conventional clean room air filtration systems.

As shown inFIG. 2, the air from the clean room214and tool environment212get mixed in clean room214and flow into the sub-fabrication air return area216. A portion of the air received in the sub-fabrication air return area216is diverted back into the clean room214as part of the recirculation airflow222. The remainder of the air received in the sub-fabrication air return area216, along with some of the air directly removed from the tool environment212, is removed through the air abatement system218, which discharges the air to the outdoors.