Semiconductor Wafer Orientation Flat Detection via Optical Arc Measurement
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Solution Overview
Problem
Existing methods for pre-alignment of semiconductor wafers with multiple orientation flats of the same size fail to appoint a reference orientation flat, as they rely on length differentiation which is not feasible when all flats have the same size.
Innovation Solution
A method and apparatus that detect each orientation flat by rotating the semiconductor wafer, measure the length of circular arcs between them, and appoint the orientation flat next to the longest circular arc as the reference, using an optical sensor to determine the light quantity and calculate the lengths of these arcs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple orientation flats of the same size are provided on a semiconductor wafer, then the wafer can be clearly identified and distinguished, but it becomes impossible to appoint a reference orientation flat using conventional length-based methods
Solution Approach 1:
The invention changes the parameter used for reference orientation flat appointment from flat length to circular arc length between flats. Since all orientation flats have the same length, conventional methods fail. By measuring the circular arc lengths between consecutive flats and selecting the flat adjacent to the longest arc, the system can reliably appoint a reference flat even when all flats are identical in size.
2Productivity
If conventional pre-alignment methods are used on wafers with multiple equal-sized orientation flats, then the alignment process can be completed, but the reference orientation flat cannot be correctly appointed
Solution Approach 1:
The invention replaces the mechanical/conventional length measurement method with an optical measurement system. An optical sensor detects the positions of multiple orientation flats, and the control unit calculates circular arc lengths between them. This substitution enables precise measurement and correct identification of the reference flat in cases where conventional methods fail.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the certain appointment of a reference orientation flat even when multiple orientation flats have the same length, ensuring successful pre-alignment during semiconductor wafer treatment processes.
Implementation Method 1
an optical sensor having a light emitting element and a light receiving element, disposed in the neighborhood of rotating body R. When a light beam from the light emitting element passes through the outside of an orientation flat of rotating semiconductor wafer W, the light quantity of the light beam which passed through the outside is detected by the light receiving element.
Data Source
AI summary
Disclosed is a method for appointing an orientation flat, in which when there are a plurality of orientation flats with the same length, any one from among the orientation flats of the same length can be certainly appointed as a reference orientation flat. In the disclosed method, three orientation flats at three positions are detected, respectively, through the rotation of a semiconductor wafer, the lengths of three circular arcs between the three orientation flats are obtained, respectively, and then an orientation flat at the right side of the longest circular arc from among the three circular arcs is appointed as a reference orientation flat. Accordingly, it is possible to certainly appoint a reference orientation flat even though there exist a plurality of circular arcs with the same length.