This paper addresses the design of an Automated Material Handling System (AMHS) for wafer lots in the photolithography workshop of a 200mm wafer manufacturing facility (fab) that was not initially built to have such a system. Lots transportation has to be performed using an Overhead Hoist Transport (OHT) system that was already chosen to transport reticles in the workshop. The main objective is to propose a decision support tool to characterize the AMHS elements including lot handling, transportation as well as the storage space design. A simulation-based approach is proposed to evaluate different scenarios and propose an effective AMHS design. Experimental results based on real instances confirm the capability of the proposed AMHS design to support the workshop activity.
After the migration in the semiconductor manufacturing from High Volume-Low Mix to Low Volume-High Mix, 200mm wafer manufacturing facilities (fabs) have encountered many challenges to remain on the competitive edge. Typical 200mm fabs were built in the last 1990s without incorporating the automated handling tools to transfer the parts through their complex production process. Establishing an automated handling system in such previously-built fabs renders chip producers to various constraints such as space limitation, clean rooms requirements and technology of production tools. Accordingly, the considered 200mm fab operates in a semi-automated mode; meaning that the lot transportation and storage are performed by operators, however, lot loading/unloading and production tool setting are automated. Corresponding decision makers (DMs) start modernizing their 200mm fabs in order to integrate an AMHS into the existing infrastructure to serve the current production system. DMs start this integration from the bottleneck area in 200mm fab, namely photolithography. An operation of a lot in this area requires an auxiliary resource called a reticle for processing.
The remainder of this paper is organized as follows. A literature review is illustrated in Section 2. In Section 3, we present the problem statement. Section 4 is dedicated to the description of the simulation-based approach used to solve the problem. Simulation results and analysis are summarized in Section 5. Section 6 analyzes the interaction between the transport of lots and reticles. Conclusions are given in Section 7.
Problem Statement
The structure of the simulation model.
In the considered photolithography area lots and reticles are manually handled. There are more than 4000 reticles, and when they are not used, pods (multi-reticles containers) are stored in specific locations. Lots are transported by operators and stored at shelves. Given this high number, handling tasks are tedious and challenging. In fact, lots and reticles management requires physical efforts and continuous concentration of operators to verify that the right reticle or lot is properly delivered to the right tool at the right time. To handle this problem, the integration of AMHS based OHT system was already decided to automate the transportation of reticles (Ben-Salem et al. 2016). In this paper, we focus on the lot transportation problem using the same OHT system.