Multiple-Buffer OHT Vehicle for Fast Wafer Carrier Handover
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Solution Overview
Problem
Overhead hoist transport systems in semiconductor fabrication facilities face significant delays and inefficiencies due to the time-consuming transfer of transport carriers between storage and processing tools, leading to idle time and wafer wastage, as they take around 180 seconds to remove a completed carrier and an additional 120 seconds to bring a new one, causing wafers to become unusable if not processed promptly.
Innovation Solution
A multiple-buffer OHT vehicle is introduced, which includes a single inner volume with multiple buffers or multiple inner volumes coupled together, allowing for efficient storage, transfer, and exchange of transport carriers, reducing the average time for carrier exchange to 40 seconds by operating in air storage, pre-transfer, and exchange transfer modes, and increasing storage capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single-buffer OHT vehicle is used, then the device complexity is low, but the productivity is reduced due to long carrier exchange time (180+120=300 seconds)
Solution Approach 1:
The OHT vehicle is segmented into multiple independent buffers (first buffer, second buffer, third buffer) that can operate independently. Each buffer can load, store, or unload carriers autonomously, allowing parallel operations that reduce total carrier exchange time from 300 seconds to approximately 40 seconds while maintaining manageable device complexity through modular architecture.
Solution Approach 2:
The system performs preliminary actions by pre-loading carriers into buffers before they are needed at load ports. The controller predicts future carrier needs and proactively transfers carriers to appropriate buffers, eliminating waiting time and ensuring immediate availability of carriers when processing tools require them, thus dramatically improving productivity.
2Loss of time
If multiple buffers are added to increase storage capacity, then the loss of time is reduced, but the device complexity increases
Solution Approach 1:
The buffer system is designed with dynamic reconfigurability where buffers can be selectively activated or deactivated based on real-time operational needs. The controller dynamically assigns carriers to different buffers and adjusts buffer usage patterns, allowing the system to adapt to varying workload demands and minimize transfer delays without permanently increasing operational complexity.
Solution Approach 2:
The multiple buffers act as intermediary storage zones between the load port and the OHT vehicle's main storage. These intermediate buffers reduce transfer delays by providing nearby staging areas for carriers, minimizing the distance and time required to move carriers between loading/unloading points and main storage, while the controller manages the intermediary buffer system efficiently.
3Productivity
If carrier exchange time is reduced, then the productivity increases, but the use of energy increases due to more frequent operations
Solution Approach 1:
The multiple-buffer system enables continuous useful action by eliminating idle time during carrier exchanges. While one buffer is being loaded or unloaded, other buffers can simultaneously perform opposite operations or remain stationary. This continuity ensures the OHT vehicle is constantly engaged in productive activity rather than repeatedly stopping and starting, improving throughput while optimizing energy usage through sustained motion.
Data Source
AI summary
Some implementations described herein provide a method that includes loading, from a load port and into a first buffer of a multiple-buffer overhead hoist transport (OHT) vehicle, a first transport carrier storing one or more processed wafers. The method includes unloading to the load port, while the first buffer retains the first transport carrier, and from a second buffer of the multiple-buffer OHT vehicle, a second transport carrier storing one or more wafers for processing. In other implementations, the method includes loading, into a first buffer of the multiple-buffer OHT vehicle, a first transport carrier storing one or more wafers for processing, while a semiconductor processing tool, associated with a load port, is processing one or more wafers associated with a second transport carrier. The method includes positioning the multiple-buffer OHT vehicle above the load port while the multiple-buffer OHT vehicle retains the first transport carrier in the first buffer.