Interlaced Laser Scanning for Wafer Edge Thermal Stress Reduction
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Solution Overview
Problem
Thermal processing for semiconductor wafers faces challenges in minimizing thermal budget and reducing thermal stress at the wafer edge, which can lead to breakage due to non-uniform heating and high temperature gradients, and also experiences non-uniform scanning issues due to opposite direction scanning of adjacent rows.
Innovation Solution
The method involves interlacing the scanning of adjacent rows in the same direction with a cool-down period, allowing for continuous laser operation and optimizing the overlap percentage to minimize thermal history and uniformity variations, using a beam scanning pattern where rows in one half of the wafer are scanned in one direction and then translated to the other half for scanning in the opposite direction, with specific stepping distances to ensure adequate cooling time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If rapid thermal processing is used to reduce thermal budget and minimize thermal diffusion, then manufacturing precision is improved, but thermal stress at wafer edge increases causing breakage
Solution Approach 1:
The patent applies local quality by implementing different scanning directions for different regions of the wafer. The first half of the wafer is scanned in one direction while the second half is scanned in the opposite direction, creating region-specific thermal histories that reduce edge stress concentrations while maintaining the overall rapid thermal processing benefits for circuit feature precision.
2Productivity
If conventional serpentine scanning is used to cover the entire wafer surface, then productivity is maintained, but scanning uniformity deteriorates due to opposite direction scanning of adjacent rows
Solution Approach 1:
The patent segments the wafer surface into two distinct halves for scanning purposes. By dividing the wafer into a first half and a second half, each scanned in opposite directions, the patent eliminates the uniformity issues caused by conventional serpentine scanning while maintaining complete coverage and processing productivity.
3Manufacturing precision
If laser is turned on and off frequently to scan different rows, then scanning uniformity is improved, but laser lifetime decreases
Solution Approach 1:
The patent implements continuous laser operation by scanning the first half of the wafer and then the second half without turning off the laser. This continuous operation maintains scanning uniformity through the interlaced pattern while significantly extending laser lifetime by eliminating frequent on-off cycling.
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 reduces thermal stress at the wafer edge, enhances scanning uniformity, and prolongs laser lifetime by allowing continuous operation, thereby improving process yield and maintaining high precision in thermal processing.
Implementation Method 1
Rapid thermal processing (RTP) uses radiant lamps which can be very quickly turned on and off to heat only the wafer and not the rest of the chamber
Implementation Method 2
The Jennings and Markle versions use CW diode lasers to produce very intense beams of light that strike the wafer as a thin long line of radiation
Data Source
AI summary
The time between illumination of adjacent zones of a workpiece edge is extended by a long cool-down period or delay, by interlacing a radiation beam scanning pattern. During the cool-down period, the beam successively scans (along the fast axis) two rows separated by about half the wafer diameter, and travels back and then forth (along the slow axis) across the distance between the two rows, while the radiation beam source continuously generates the beam.