Multiple-Buffer OHT Carrier Exchange for Faster Wafer Handoffs
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Solution Overview
Problem
Overhead hoist transport systems in semiconductor fabrication facilities face significant delays due to the time-consuming transfer of transport carriers, leading to idle time for load ports and potential wafer wastage, as wafers become unusable if not processed promptly after etching or ashing operations.
Innovation Solution
A multiple-buffer OHT vehicle system that includes a single inner volume with multiple buffers or coupled inner volumes, allowing for efficient storage, transfer, and exchange of transport carriers, reducing the time to remove completed carriers and provide new ones, 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 seconds)
Solution Approach 1:
The OHT vehicle is segmented into multiple independent buffers (first buffer, second buffer, etc.) within a single inner volume. Each buffer can independently hold transport carriers, allowing parallel operations of loading and unloading carriers simultaneously. This segmentation enables the carrier exchange time to be reduced from 180 seconds to 40 seconds by eliminating sequential waiting time.
Solution Approach 2:
The system performs preliminary action by pre-loading transport carriers into buffers before they are needed at load ports. The controller can load carriers into buffers in advance and position the OHT vehicle at load ports when carriers are required, ensuring continuous operation without idle time. This preliminary preparation of carriers in buffers eliminates waiting time and maintains continuous processing flow.
2Productivity
If multiple buffers are added to increase storage capacity, then the productivity improves, but the device complexity increases
Solution Approach 1:
Multiple buffers within the OHT vehicle serve universal functions: they can all hold transport carriers, be loaded with carriers, and positioned at load ports. The controller manages all buffers using the same control logic and communication protocol, making the system multi-functional rather than complex. Each buffer is interchangeable and can perform the same operations, simplifying the overall management despite having multiple units.
Solution Approach 2:
Multiple buffers are nested within a single OHT vehicle body, with each buffer contained within the vehicle's inner volume. This nesting arrangement allows multiple storage compartments to occupy the space of a single vehicle, effectively increasing storage capacity and enabling parallel carrier handling without requiring separate vehicles or external storage facilities.
3Loss of time
If carrier exchange time is reduced, then the loss of time is minimized, 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 at load ports. While one buffer is being unloaded at a load port, another buffer can be loaded with carriers in preparation. This continuous operation ensures that the OHT vehicle is always engaged in productive work (transporting carriers), minimizing non-productive idle time and optimizing the energy-to-work ratio despite increased operational frequency.
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.