450mm FOUP/LPU system in advanced semiconductor manufacturing processes: A study on the minimization of oxygen content inside FOUP when the door is opened

摘要

In the last 15 years, the FOUP/LPU (front opening unified pod (FOUP) and load-port unit (LPU)) module was adopted by major 300 mm wafer semiconductor fabs and proved to be able to create a very high particle free environment for wafer transfer. However, it is not able to provide a moisture, oxygen or airborne molecular contaminants (AMCs) free environment, as the moisture, oxygen or airborne molecular contaminants exhibit in the FOUP through filter, FOUP material, and/or the last processes (in-process). Currently, the technology roadmap of devices has already moved towards the era of sub-20nm, some even to 10nm, node. For those devices made in such a small scale patterns, they are generally very sensitive to moisture, oxygen and other AMCs in the air. An example is that after the processes of etching, the contaminant, as a form of AMC, may evaporate, deposit, and contaminate wafers in the later processes, such as CMP. The deposited AMC may, again, evaporate and deposit on the wafer of next process. Nitrogen gas purge for stationary door-closed FOUP, which is normally when FOUP is at a purge station or a FOUP stocker, has been adopted to minimize sensitive in-process wafers' exposure to those contaminants in many processes. However, gas purge performed when FOUP door is off i.e. FOUP is in open condition, (thereafter referred as “door off” condition) is still rare. Nevertheless, this approach is very urgent is for sub-20nm process. If oxygen is not of concern, Clean Dry Air (CDA) purge instead of nitrogen is an alternative gas. Note that nitrogen is much more expensive than CDA and with potential safety concern. In-processes, such as etching/Chemical Mechanical Polishing (CMP) require FOUP purge while the FOUP door is open to an Equipment Front End Module (EFEM) load-port. This door off condition comes with exceptional challenges as compared to stationary door-closed conditions. To overcome this critical challenge, a new FOUP/LPU purge system is propo- ed. The system includes two uniform purge diffusers plus top-down pure gas curtain created by a so called “flow field former” when FOUP is in door-off condition. Note that a conceptual patent about “flow field former” in this proposal has been applied (under reviewing). In implementation of this project, firstly, a prototype FOUP/LPU purge system will be built in an ISO class 1 (0.1. um) cleanroom. Various environment parameters in the FOUP including temperature, relative humidity, air velocity magnitude, and concentration of particle will be monitored. Visualization on flow pattern in the FOUP and in the vicinity of door edge will be carried out by green-light laser visualization system. Optimized size/dimensions and operation parameters of the flow filed former will be determined based on the overall testing results. The performance of the newly proposed system will be eventually verified in a production line of a prestigious semiconductor fab. The ultimate objective of this project is to prevent cross contamination and surface oxidation with a quickly control of moisture, oxygen and AMCs when FOUP is in door-off condition through an efficient and purge gas saving system.