Lithography Focus Control for Reconstituted Wafer Topography
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Solution Overview
Problem
Lithographic processing of reconstituted wafers faces challenges due to positional and orientation errors of IC chips, leading to uneven surfaces within the exposure field, which can result in out-of-focus imaging and reduced yield.
Innovation Solution
A method involving a line scanner with height sensor elements to measure the surface topography of reconstituted wafers, adjusting the position and orientation of the wafer relative to the focus plane of the lithography tool to ensure the photoresist layers of IC chips fall within the depth of focus, and performing exposure to pattern the photoresist layers within each exposure field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If IC chips are placed in resin during packaging, then IC chips can be secured in select positions, but positional and orientation errors occur causing uneven surfaces within exposure field
Solution Approach 1:
The patent performs a preliminary scan of the reconstituted wafer surface before lithographic exposure to measure the actual positions and orientations of IC chips. This advance measurement allows the system to determine focus adjustments needed for each exposure field, compensating for surface unevenness caused by chip placement in the resin.
Solution Approach 2:
The patent applies different focus adjustments to different exposure fields based on their specific surface topography. By scanning the wafer and mapping surface heights, the system tailors the focus plane for each exposure field individually, rather than using a uniform focus setting across the entire wafer, thus addressing local variations in surface flatness.
2Productivity
If standard lithographic exposure is performed on reconstituted wafers, then processing can be carried out, but out-of-focus imaging occurs reducing yield
Solution Approach 1:
The patent dynamically adjusts the focus plane for each exposure field based on real-time surface measurements. Rather than using a static focus setting, the system modifies focus parameters on-the-fly according to the measured topography, ensuring that each exposure field is imaged at the optimal focus plane while maintaining processing throughput.
Solution Approach 2:
The patent implements a feedback loop where the surface scan data from the reconstituted wafer is used to determine appropriate focus adjustments for subsequent lithographic exposure. The measured surface topography feeds into the exposure control system, which automatically adjusts focus parameters to compensate for surface variations, thereby maintaining imaging quality.
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
This approach improves the accuracy and yield of lithographic processing by ensuring that all IC chips within an exposure field are in focus, allowing for precise formation of conductive structures and redistribution layers on the IC chips.
Implementation Method 1
performing at least one scan of the reconstituted wafer with a line scanner having a plurality of height sensor elements to measure a surface topography of the reconstituted wafer
Implementation Method 2
performing an exposure with the lithography tool to pattern the photoresist layers of the IC chips in the given exposure field
Data Source
AI summary
A method of processing a reconstituted wafer that supports IC chips includes operably disposing the reconstituted wafer in a lithography tool that has a depth of focus and a focus plane and that defines exposure fields on the reconstituted wafer, wherein each exposure field includes at least one of the IC chips. The method also includes scanning the reconstituted wafer with a line scanner to measure a surface topography of the reconstituted wafer as defined by the IC chips. The method also includes, for each exposure field: i) adjusting a position and/or an orientation of the reconstituted wafer so that a photoresist layers of the IC chips within the given exposure field fall within the depth of focus; and ii) performing an exposure with the lithography tool to pattern the photoresist layers of the IC chips in the given exposure field.