Method for finding the correlation between the tool PM and the product yield
View Patent ↗A method for finding the correlation between tool PM (prevention maintenance) and the product yield of the tool is disclosed. The method uses a moving average method to magnify a curve trend that is formed by the product yield data that is captured during a predetermined days before PM and after PM. The magnified curve trend is shown by a Cumulative sum chart. The Cumulative sum chart is analyzed for informing related workers of the effect between the tool PM and the product yield, so as to accurately estimate PM timing. Thereby, via the method, the effect between the tool PM and the product yield may be determined, which serves as an important reference for workers to execute further PM.
1. A method for finding the correlation between prevention maintenance of a tool and the product yield of the tool, the method comprising:
(a) collecting a plurality of product yield data of a plurality lots of wafers that are correspondingly formed from being processed by a plurality of tools of a production line;
(b) according to the aforementioned product yield data, respectively calculating a yield gap between an average yield a predetermined days before the prevention maintenance of the tool and an average yield a predetermined days after the prevention maintenance of the tool;
(c) selecting the tools that has its product yield gap greater than or equal to a predetermined yield threshold;
(d) within the time frame between the predetermined days before the prevention maintenance of the tool and the predetermined days after the prevention maintenance of the tool, selecting the tools that has processed wafer lots in numbers greater than or equal to a predetermined lot count threshold;
(e) finding all the product yield data generated at different time for different wafer lots from each of the tools in step (c) and step (d), and using a moving average method to magnify a curve trend that is formed by the product yield data of each tool which has been captured during the predetermined days before the prevention maintenance of the tool and the product yield data of each tool which has been captured during the predetermined days after the prevention maintenance of the tool, so as to decrease the effect of data noise to subsequent analysis;
(f) displaying every one of the aforementioned magnified curve trend via a format of cumulative sum chart respectively;
(g) through each of the cumulative sum chart, finding a continuous downward trend period number from the product yield data during the predetermined days before the prevention maintenance of the tool, furthermore finding a continuous upward trend period number from the product yield data during the predetermined days after the prevention maintenance, so as to find the tools that has its sum of the continuous downward trend period number and the continuous upward trend period number greater than or equal to a predetermined period threshold; and
(h) for those tools that are greater than or equal to the aforementioned predetermined period threshold, sending a notification information to related workers regarding the effect between the prevention maintenance for those tools and the product yield of those tools.
2. The method according to claim 1 , wherein the predetermined days before the prevention maintenance of the tool and the predetermined days after the prevention maintenance of the tool are equal number of days.
3. The method according to claim 2 , wherein the predetermined days before the prevention maintenance of the tool and the predetermined days after the prevention maintenance of the tool are both 3 days.
4. The method according to claim 1 , wherein a selection equation used in step (c) for selecting the tools comprises:
|Mean_yield(PM pre3 )−Mean_yield(PM post3 )|≧yield gap threshold,
wherein Mean_yield(PM pre3 ) is the average yield a predetermined days before the prevention maintenance, Mean_yield(PM post3 ) is the average yield a predetermined days after the prevention maintenance, and the yield gap of the two average yields must be greater than or equal to the aforementioned predetermined yield gap threshold for a tool to be selected.
5. The method according to claim 4 , wherein the predetermined days before the prevention maintenance of the tool and the predetermined days after the prevention maintenance of the tool are both 3 days.
6. The method according to claim 1 , wherein a selection equation used in step (d) for selecting the tools comprises:
(Lot count pre3 ) and (Lot count post3 )≧Lot count threshold,
wherein (Lot count pre3 ) and (Lot count post3 ) are respectively processed wafer lot numbers during the time frame between the predetermined days before the prevention maintenance of the tool and the predetermined days after the prevention maintenance of the tool, and the wafer lot numbers must be greater than or equal to the aforementioned predetermined lot count threshold for a tool to be selected.
7. The method according to claim 6 , wherein the predetermined days before the prevention maintenance of the tool and the predetermined days after the prevention maintenance of the tool are both 3 days.
8. The method according to claim 1 , wherein a magnification equation used in step (e) for magnifying the curve trend comprises:
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n
-
threshold
+
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Mean
(
YB
period
(
i
)
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YB
period
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YB
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,
wherein the magnification equation magnifies the curve trend that is formed by the product yield data of each tool which has been captured during the predetermined days before the prevention maintenance of the tool and the product yield data of each tool which has been captured during the predetermined days after the prevention maintenance of the tool, and YB period is the product yield of each of the lots of wafers, n is the total number of lots for the wafers, and threshold is the number of period used by the moving average method.
9. The method according to claim 8 , wherein the predetermined days before the prevention maintenance of the tool and the predetermined days after the prevention maintenance of the tool are both 3 days.
10. The method according to claim 1 , wherein a determination equation used in step (g) for finding the tools comprises:
(Trend down periods prePM +Trend up periods postPM )≧period threshold,
wherein Trend down periods prePM is the continuous downward trend period number from the product yield data during the predetermined days before the prevention maintenance of the tool, Trend up periods postPM is the continuous upward trend period number from the product yield data during the predetermined days after the prevention maintenance, and the sum of the two period numbers must be greater than or equal to the predetermined period threshold for finding a tool.