Acousto-Optical Device Scanning for Optical Crosstalk Suppression
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Solution Overview
Problem
Existing acousto-optical device (AOD) scanning techniques face challenges in minimizing optical crosstalk and system complexity while maintaining accurate defect detection on semiconductor wafers, particularly due to overlapping spot scans and the need for high-power lasers and multiple photomultiplier tubes (PMTs).
Innovation Solution
The method involves forming co-linear scans with predetermined spacing using acousto-optical devices (AODs) and diffractive optical elements (DOEs) to separate and adjust spot sizes and scan lengths, allowing for efficient isolation of scattered light and reducing crosstalk through programmable AODs and adjustable magnification changers, thereby optimizing the inspection system's design and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional AOD scanning techniques are used to scan the wafer surface, then the scan rate can be achieved, but optical crosstalk occurs due to overlapping spot scans
Solution Approach 1:
The patent applies dynamics by making the AOD programmable and adjustable in real-time. The AOD parameters (frequency, amplitude, phase) are dynamically modified between scans to change spot position, size, and spacing. This allows the system to adapt the scanning pattern to prevent overlap and crosstalk while maintaining high scan rates, resolving the contradiction between productivity and harmful optical effects.
Solution Approach 2:
The patent changes multiple parameters of the AOD including operating frequency, drive amplitude, and phase to control spot characteristics. By adjusting these parameters, the system modifies spot size and spacing to prevent overlapping while maintaining fast scanning. This parameter control enables the system to achieve both high productivity and minimal optical crosstalk.
2Measurement precision
If high-power lasers and multiple PMTs are used to maintain accurate defect detection, then detection accuracy is improved, but system complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the need for high-power lasers and multiple PMTs by using programmable AOD to prevent optical crosstalk at its source. By controlling spot spacing and preventing overlap through AOD parameter adjustment, the system removes the requirement for complex high-power laser systems and multiple detector tubes, thereby reducing system complexity while maintaining detection accuracy.
Solution Approach 2:
The programmable AOD acts as an intermediary between the light source and the wafer surface. It controls and shapes the light spots to prevent overlap, thereby eliminating optical crosstalk without requiring complex detection systems. This intermediary device simplifies the overall system by replacing the need for multiple PMTs and high-power lasers with a single programmable AOD that manages light delivery precisely.
3Productivity
If spot spacing is reduced to increase scan coverage, then productivity improves, but optical crosstalk increases due to overlapping scans
Solution Approach 1:
The patent uses dynamic adjustment of AOD parameters to maintain optimal spot spacing throughout the scanning process. As the scan progresses and spots move closer together, the system dynamically modifies AOD frequency and amplitude to adjust spot size and spacing, preventing overlap even when scan coverage is increased. This dynamic control enables both high productivity and minimal crosstalk.
Solution Approach 2:
The system changes AOD operating parameters including frequency, amplitude, and phase to control spot characteristics. By adjusting these parameters, the system can reduce spot size or increase spacing between spots to prevent overlap while maintaining dense scan coverage. This parameter control resolves the contradiction between increased productivity through greater scan coverage and prevention of optical crosstalk.
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 effectively minimizes optical crosstalk, enhances defect detection accuracy, and reduces system complexity and costs by allowing for flexible spacing between co-linear scans and the use of inexpensive collectors, while maintaining high scan rates and throughput.
Implementation Method 1
An oscillating electric signal can drive sound transducer 121 and causes it to vibrate. In turn, this vibration creates sound waves in quartz plate 122. As a result of the sound waves, incoming light 124 to quartz plate 122 is diffracted into a plurality of directions
Implementation Method 2
a diffractive optical element (DOE) to separate and adjust spot sizes and scan lengths
Data Source
AI summary
A method of scanning a sample includes simultaneously forming a plurality of co-linear scans. Each scan is formed by a sweep of a spot by an acousto-optical device (AOD). The co-linear scans are separated by a predetermined spacing. A first plurality of swaths are formed by repeating the simultaneous forming of the plurality of co-linear scans in a direction perpendicular to the co-linear scans. The first plurality of swaths have an inter-swath spacing that is the same as the predetermined spacing. The predetermined spacing can be a scan length or an integral number of scan lengths. A second plurality of swaths can be formed adjacent to the first plurality of swaths. Forming the second plurality of swaths can be performed in an opposite direction to that of the first plurality of swaths or in a same direction. An inspection system can implement this method by including a diffractive optical element (DOE) path after a magnification changer.