Radial Spot Array Illumination for Wafer Pitch Uniformity
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Solution Overview
Problem
Current systems for generating an array of spots on an inclined surface suffer from pitch errors due to uneven spacing, which can be difficult to correct and result in reduced sensitivity or throughput, especially near the center of a wafer.
Innovation Solution
A system and method utilizing a diffractive optical element and a focusing lens to split and focus beams onto a surface at an oblique illumination angle, ensuring uniform spacing and alignment of spots in the radial direction, thereby minimizing pitch errors and enhancing sensitivity and throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If tangential spot placement is used, then the spots are aligned with the scanning direction, but the pitch becomes uneven especially near the center of the wafer
Solution Approach 1:
The patent transitions from symmetric tangential spot placement to asymmetric radial spot placement. The spots are arranged along the radial direction of the wafer rather than following the tangential scanning path, which fundamentally changes the geometric relationship between spots and eliminates the pitch error that occurs with tangential arrangement.
Solution Approach 2:
The patent changes the illumination angle parameter from oblique (non-normal) to substantially normal incidence. This parameter change allows the beam to be focused onto the wafer surface in the radial direction, achieving uniform pitch across all spots including those near the center.
2Manufacturing precision
If the pitch error changes from edge to center, then the spot spacing varies across the wafer, but correcting it results in loss of sensitivity or throughput
Solution Approach 1:
The patent applies preliminary optical design and calculation to pre-determine the optimal spot arrangement and illumination parameters before actual scanning. By calculating the radial spot positions and normal illumination angle in advance, the system achieves uniform pitch across the entire wafer surface without requiring real-time correction that would reduce throughput.
3Manufacturing precision
If normal incidence illumination is used, then the pitch uniformity is improved, but the illumination angle changes from oblique to normal
Solution Approach 1:
The patent deliberately changes the illumination angle parameter from oblique to substantially normal incidence. This parameter change is achieved through optical design that directs the beam perpendicular to the wafer surface, enabling uniform radial spot placement while maintaining optimal illumination intensity for inspection.
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
The solution effectively generates a radial spot array with small spot sizes and a large number of spots across a large field, maintaining uniformity and sensitivity while reducing pitch errors, and is compatible with a wide laser wavelength bandwidth.
Implementation Method 1
The diffractive optical element may be configured to split a beam into a plurality of beams by generating a plurality of diffraction orders
Implementation Method 2
The focusing lens may be configured to focus at least some of the plurality of beams on the surface in the plurality of spots
Data Source
AI summary
A system which may be used to generate a plurality of spots on a surface is provided. The spots may be aligned with the incident plane of oblique illumination. The system may include a diffractive optical element configured to split a beam into a plurality of beams by generating a plurality of diffraction orders. The system may also include a focusing lens configured to focus at least some of the plurality of beams on the surface in the plurality of spots. At least some of the plurality of beams may be focused on the surface at an oblique illumination angle. The system may also include an illumination source positioned off-axis relative to an optical axis of the diffractive optical element. Using the system, a plurality of spots may be generated on an inclined surface.