Dummy Wafer Availability Control in Substrate Processing
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Solution Overview
Problem
In substrate processing systems, the frequent replacement of dummy wafers due to limited use numbers disrupts lot processing, leading to increased variation in processing conditions and decreased production yield, as the system often runs out of usable dummy wafers before completing a lot of product wafers.
Innovation Solution
A method and control unit that calculate the required number of dummy wafers for the next lot based on processing conditions and add it to the used number, prohibiting the start of lot processing if the total exceeds the maximum usable number, ensuring adequate dummy wafers are available to maintain consistent processing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If dummy wafers are repeatedly used in substrate processing, then processing capacity increases, but dummy wafers become damaged or contaminated exceeding their limited usable number
Solution Approach 1:
The control unit calculates the required number of dummy wafers for the next lot in advance before lot processing starts, and compares it with the remaining usable dummy wafers. This preliminary check prevents the situation where dummy wafers would be exhausted during processing, ensuring continuous operation without interruption for wafer replacement.
2Reliability
If dummy wafer carriers are replaced when dummy wafers reach limited use number, then fresh dummy wafers are available, but all dummy wafers in the carrier are destroyed even if some remain usable
Solution Approach 1:
The system tracks the usage count of each individual dummy wafer separately rather than treating all wafers in a carrier uniformly. The control unit identifies specifically which dummy wafers have reached their limited use number and need replacement, while leaving other usable dummy wafers in the carrier untouched. This selective replacement approach reduces waste of still-usable dummy wafers.
3Productivity
If lot processing continues without checking dummy wafer availability, then processing efficiency is maintained, but lot processing must be stopped to replace dummy wafers causing yield decrease
Solution Approach 1:
The control unit continuously monitors the usage status of dummy wafers and the current lot processing state. When a dummy wafer reaches its limited use number during lot processing, the control unit detects this condition and automatically replaces the dummy wafer with a new one, then resets the usage counter. This feedback mechanism ensures continuous processing without interruption, maintaining both efficiency and reliability.
4Reliability
If dummy wafers are replaced during lot processing, then usable dummy wafers are restored, but temperature in processing chamber changes causing variation in product wafer processing
Solution Approach 1:
The control unit checks dummy wafer availability and performs replacements before lot processing starts, rather than during processing. By anticipating the need for dummy wafer replacement in advance and completing it beforehand, the system avoids temperature fluctuations in the processing chamber that would occur during mid-processing replacement, thereby maintaining consistent processing conditions for product wafers.
Data Source
AI summary
A lot processing start determining method includes: storing, in a memory, processing conditions of each lot in a first substrate vessel and a maximum usable number of dummy substrates in a second substrate vessel; counting the used number the dummy substrates in the second substrate vessel; and calculating the number of dummy substrates required to process all substrates of a next lot in the first substrate vessel based on the processing conditions of each lot which are stored in the memory, adding the calculated number of the dummy substrates of the next lot to the counted used number of the dummy substrates, and determining whether the added value exceeds the maximum usable number of the dummy substrates stored in the memory. The method further includes prohibiting start of processing the next lot when the added value is determined to exceed the maximum usable number of the dummy substrate.