The (almost) completely automated 12”-lithography

Abstract

A fundamental aspect for the economic success of a semiconductor production is a low level of costs per wafer. A substantial part of these costs per wafer is accounted by personnel costs. For this reason, it is desirable to reach the lowest possible level of personnel costs. Mainly this is achieved by increasing the degree of the factory automation. To increase the degree of factory automation, various approaches are conceivable and in use. We were at the time the first 12”-fab worldwide and we were equipped with an OHT (Overhead Hoist Transfer) system of the first generation to transport to and load wafer pods on process equipment and wafer stockers. That means, that the complete wafer handling took place automatically. Viewed with a certain distance, the fab as a whole showed a high level of automation. However, in the lithography it was necessary to handle reticles manually. Figure 1 shows the distribution between the automated wafer handling and the manual done parts reticle handling and necessary tool assist. The efforts for manual reticle handling and the resulting personnel costs contradicted the requirements of a highly automated manufacturing. An investigation about possible reticle automation scenarios by using AGV (Automated Guided Vehicles) or OHT to improve the lithography automation level resulted in non-acceptable investments in relation to the saved personnel costs. As a result, further activities to automate reticle handling have been avoided. But driven by the end of live situation of the used OHT system, a retrofit of the system in 2017 offered the possibility to install additionally to the lot OHT system a reticle OHT option. In conjunction with the findings of the above investigation, this new situation led to the decision to install this option to save the personnel costs of manual reticle handling. Introductory in this paper, we would like to compare briefly conceivable automation scenarios by using AGV and OHT systems. We describe the advantages and disadvantages of both systems arising from our present situation. We justify why only the use of an OHT makes sense for us. The main part of the paper is dedicated to the way from the ended OHT hardware startup to the running automated reticle handling. First of all, we introduce the machinery used. The majority of the exposure equipment was not intended for OHT loading by tool manufacturer. We explain the modifications needed to allow a reticle loading of the exposure tools by OHT. One key factor in getting the system up and running is the control of the exposure tools by host commands. These sequences are used to enable the tool operation without operator-tool interaction. Based on the reticle load and unload strategy, we explain basics of our used exposure tool control. Another key factor is the system control algorithm. The whole reticle operation is controlled by a rule based dispatching system. The rules used combine robustness and necessary performance emphasizing the robustness of the system. The limitations of this rule based dispatching system are discussed and the use of a mathematical solver system recommended. An important aspect of the introduction of the system is the fact that the exposure systems, the OHT and the reticle stockers were used to create a network of machines. This machine network requires functional monitoring approaches that are new to us. We consider possibilities to display status information of this complex network as simply as possible. The aim is to enable fast and efficient troubleshooting within the network. Furthermore, this newly created machine network entails some intrinsic risks. The main risk of complete failure due to the failure of a sub component and ways to minimize this risk are discussed. A summary of the practical experiences during the construction phase of several months completes the main part of this work. It is expected that in continuous operation the demands on the performance and the robustness of the system will increase. In conclusion, we would like to point out possibilities for future system optimization. Based on the current state of knowledge and the implementation costs we will try to evaluate these. Finally, we would like to comment on the title's restriction "almost". We explain why a completely automated lithography, which means including the additional automation of tool assists, is not possible from our current perspective.