Multi-channel backside wafer inspection with local focus control
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Solution Overview
Problem
Backside semiconductor wafer inspection systems face challenges due to wafer sag and warp caused by gravity and surface tension, limiting the effectiveness of existing multi-channel inspection systems which only provide global focus correction, leading to less than ideal inspection results.
Innovation Solution
A multi-channel inspection system with individually adjustable focus channels, using positional sensors and actuation assemblies to correct for wafer shape and position changes, allowing for real-time or near real-time focus adjustments based on pre-mapped wafer profiles and shape measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a backside inspection system supports the wafer at the edge in an unrestrained state, then the wafer can be inspected without front-side damage, but the wafer displays significant sag and warp due to gravity and surface tension
Solution Approach 1:
The patent applies local quality by providing individual focus adjustment for each inspection channel rather than global focus correction. Each channel can independently compensate for local variations in wafer shape, allowing the system to maintain focus despite sag and warp while keeping the wafer unrestrained at the edges.
Solution Approach 2:
The system changes the focus parameter dynamically for each channel based on measured wafer shape. By adjusting focus positions individually for each channel according to local wafer topography, the system compensates for shape variations without requiring mechanical restraint of the wafer.
2Measurement precision
If single channel optical systems are used for backside inspection, then focus can be maintained, but inspection throughput is limited
Solution Approach 1:
The inspection system is segmented into multiple independent inspection channels, each capable of individual focus adjustment. This segmentation allows parallel inspection of different wafer regions while maintaining focus quality in each channel, thereby increasing throughput without sacrificing measurement precision.
Solution Approach 2:
The system introduces dynamic focus adjustment capability where each channel can independently adapt its focus position in real-time based on wafer shape measurements. This dynamic adaptation enables multiple channels to operate simultaneously with optimal focus, multiplying the throughput compared to a single static channel system.
3Device complexity
If prior multi-channel systems provide global focus correction, then system complexity is reduced, but the ability to correct for sag and warp in a given wafer is limited
Solution Approach 1:
The focus correction system is segmented into multiple independently controllable channels, each capable of individual adjustment. This segmentation increases the system's ability to correct local variations in wafer shape while maintaining manageable complexity through modular architecture.
Solution Approach 2:
Instead of applying a single global focus correction to all channels, the system applies local quality by allowing each channel to have its own focus adjustment. This enables precise correction of local sag and warp variations across different wafer regions, significantly improving focus correction accuracy.
Data Source
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AI summary
A system for inspecting a backside surface of a wafer with multi-channel focus control includes a set of inspection sub-systems including a first inspection sub-system positioned and an additional inspection sub-system. The first and additional inspection sub-systems include an optical assembly, an actuation assembly, where the optical assembly is disposed on the actuation assembly, and a positional sensor configured to sense a position characteristic between a portion of the optical assembly and the backside surface of the wafer. The system also includes a controller configured to acquire one or more wafer profile maps of the backside surface of the wafer and adjust a first focus position of the first inspection sub-system or an additional focus position of the additional inspection sub-system based on the received one or more wafer profile maps.