مطالعه شبیه سازی برای تقسیم اتوماتیک انتقال مواد طراحی سیستم پیشنهادی برای فاب 300 میلی متری نیمه هادی

With the increase in the size and weight of 300-mm wafers, the factory area must be enlarged accordingly. Due to the flow of material over long distances, the elimination of manual wafer handling has become necessary. Consequently, an automated material handling system (AMHS) is required for 300-mm semiconductor manufacturing facilities. The design of an AMHS must not only be capable of meeting numerous complex material handling requirements, but it must also simplify control and reduce capacity loss. In this study, a segmented dual-track bidirectional loop (SDTBL) design for an AMHS is proposed. The configuration is based on a double-loop flow path structure that is divided into non-overlapping segments, each containing a certain number of vehicles operating in bidirectional mode. A transfer buffer is set to enable conversion between segments and connect each independent zone. This structure eliminates congestion and blocking without requiring additional investment by operating vehicles on mutually exclusive tracks. The segmentation strategies and steps for two scenarios are developed in this research, and a simulation is performed to evaluate the performance of each segmented strategy. The simulation results show that the proposed strategies can reduce the cycle time and increase stocker utilization by up to 55.55% and 39.39%, respectively, while the throughput remains the same. The proposed design has great potential for practical application

The trend in semiconductor wafer fabrication facilities (fabs) has been progressing from 200-mm to 300-mm wafers. While the unit cost of a manufactured 300-mm wafer is approximately 45% higher than that of a similarly manufactured 200-mm wafer, the larger wafer has a 40% lower die cost due to its higher die count [9]. A 300-mm fab costs between approximately 2 and 4 billion US dollars, of which some 70% is invested in process tools. Due to the high tool costs, many programs, such as SEMATECH in the USA, have been initiated to improve the operational efficiency and advance manufacturing technologies associated with the wafer process. A 300-mm wafer travels approximately 8–10 miles during processing and 250 process tools are typically used for the several hundred individual process steps performed on the wafer [1]. The material handling of a 300-mm wafer is highly automated in order to improve fab productivity [12]. A fab is usually equipped with an overhead-monorail automated material handling system (AMHS) in conjunction with automated storage/retrieval systems (stockers) for interbay automation and intrabay material handling automation. The general layout envisioned by I300I for 300-mm fabs had the configuration of a spine [25], similar to those of an AMHS, which forms a material flow-loop within the facility. The commonly adopted technology in an AMHS for a 300-mm fab is to use an overhead hoist transport (OHT) and overhead hoist vehicle (OHV) for inter- and intrabay material handling, respectively. The central aisle is typically designed with two physically separate loops so as to allow unimpeded two-way travel along the central spine of the facility, with crossover turntables for reversing travel direction [18] and [27]. The AMHS configuration with a spine layout is considered to be the standard design for a 300-mm fab, although several variations on component design, such as for the power system or the vehicle type, may be utilized by different AMHS suppliers. The present study explores the segmented AMHS design for a 300-mm fab. The segmented design concept is based on the tandem automated guided vehicle (AGV) design [4] and [5]. The term segmented bidirectional single-loop (SBSL) denotes a single-loop flow path divided into non-overlapping single carrier segments. In the present study, the SBSL proposed by Sinriech et al. [21] is used as the base concept. This concept is combined with a dual-track device that provides more options to the segmented zones. Therefore, a segmented dual-track bidirectional loop (SDTBL) design for an AMHS is proposed in this work. The configuration is based on a double-loop flow path structure that is divided into non-overlapping segments, each containing a certain number of vehicles operating in bidirectional mode. In the SDTBL design, transfer buffers are located at both ends of each segment as input/output buffers. Thus, a carrier can deposit loads that are headed to other segments and can pick up loads from other segments. The carrier has the capability to travel clockwise or counterclockwise on each segment depending on which direction produces the shortest path to the destination point. Due to the tandem design concept, each segmented loop is served by one carrier and is free from the transportation blocking problem. Thus, the SDTBL system can reduce time loss stemming from congestion, blocking, and interference. Notably, the reduction in time loss can lead to additional economic benefits. The SDTBL flow structure was designed in an attempt to improve the performance of a single-loop flow path system and does not require carrier selection (only one carrier per segment), routing, or intersection flow scheduling. In addition, no mutual carrier interaction is possible, making the SDTBL system relatively simple to control and advantageous in industrial applications. The present work serves as a pilot study for the adoption of the segmented design in an AMHS. A practical application is adopted in order to provide an empirical illustration. The case problem is formulated by simulation. Heuristics are proposed to generate several different segmented design scenarios, and the performance of each is subsequently evaluated by simulation. The remainder of this paper is organized as follows: Pertinent literature is reviewed in Section 2, while background information for the case study is provided in Section 3. Details of the proposed methodologies and an empirical illustration are discussed in Sections 4 and 5, respectively, and conclusions and future research opportunities are addressed in the final section.

As wafer size increases, the demand for larger factory sizes also increases and the distance over which material must be transported will inevitably increase. When the moving distance increases, travel management becomes very important. Therefore, the focus of this study was to rearrange the current moving paths without adding additional transportation equipment in order to make the transportation system more efficient. Two scenarios of SDTBL design with four segment strategies to assign each vehicle to a moving segment were proposed in order to eliminate vehicle congestion, blocking, or interference. Simulation experiments were also conducted to evaluate the impacts of throughput, cycle time, stocker utilization, and vehicle utilization. According to the experimental data, the segment strategies improve the cycle time by 27.49–55.55% under the same throughput. The segment strategies also increase the transfer possibilities and thus, stocker utilization increases. The maximum stocker utilization was also improved by 14.2–39.9% since the segment strategy reduces the travel distance of empty vehicles. The maximum vehicle utilization was improved by 1.7–45.8%. The segment strategy not only improves all indices, but can allow the overall system to sustain a higher workload. During the experiment with the base case, it was found that only 0.9 h of lot release interval time could be sustained. In contrast, the segment strategy can sustain a lot release interval time of up to 0.7 h, indicating a 1.285 times improvement in system productivity. The two strategies were discussed only under feasible conditions; optimal segmented strategies were not examined. The performance of these segment strategies were evaluated and analyzed, thus allowing for the future development of an optimal segmented strategy to create an optimal design. Although the segment range in this study was fixed, future research should include flexible segment ranges adjusted according to a change in time. Also, both the layout for optimal planning and the maximal segment length to determine optimal locations for the stockers, which will allow the segmented design to have the greatest performance, should be considered in future research