Wafer Measurement Timing Control for Laser Charge Neutralization
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Solution Overview
Problem
The challenge of sample charging in semiconductor wafer measurement devices leads to reduced measurement accuracy due to pattern edge disappearance and contamination from laser light irradiation, which cannot be fundamentally eliminated by increasing scanning speed.
Innovation Solution
A measurement device with a controlled laser light irradiation system, using a shutter and controller to adjust the timing of light exposure to maintain consistent irradiation across multiple measurement points, thereby reducing the impact of laser light on pattern shape and enhancing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the scanning speed of the electron beam is increased to reduce sample charging, then the throughput is improved, but the measurement accuracy deteriorates due to insufficient charge neutralization
Solution Approach 1:
The laser light irradiation is performed in advance before the electron beam scanning to pre-neutralize the sample charging. This preliminary charge neutralization allows the electron beam to scan at higher speeds without accumulating excessive charge, thereby improving throughput while maintaining measurement accuracy.
Solution Approach 2:
Laser light is introduced as an intermediary substance to mediate between the electron beam and the sample. The laser photons interact with the sample to generate secondary electrons that neutralize the positive charge accumulated by the electron beam, enabling high-speed scanning without sacrificing measurement precision.
2Measurement precision
If laser light irradiation is applied to remove sample charging, then the measurement accuracy is improved, but the pattern shape changes due to damage or contamination
Solution Approach 1:
Only the minimum necessary amount of laser light irradiation is applied to achieve charge neutralization. By controlling the irradiation dose to be just sufficient for removing sample charging without excess, the pattern shape is preserved while still improving measurement accuracy.
Solution Approach 2:
The irradiation amount of laser light is precisely controlled by adjusting parameters such as light intensity and irradiation duration. This parameter optimization ensures that the laser light removes sample charging effectively while preventing pattern damage or contamination that would occur with excessive irradiation.
3Reliability
If the amount of laser light irradiation is increased to remove sample charging, then the charge neutralization effect is improved, but the pattern damage and contamination increase
Solution Approach 1:
The system monitors the sample charging state and adjusts the laser light irradiation amount accordingly. This feedback control ensures that the irradiation dose is optimized to achieve charge neutralization while preventing pattern damage, as the irradiation is increased only to the extent necessary and no further.
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 enables highly accurate dimension measurement by minimizing the side effects of laser light irradiation, ensuring consistent light exposure across all measurement points and reducing variations in measurement results.
Implementation Method 1
a charged particle optical system, a stage, and a detector configured to detect signal electrons emitted when the wafer placed on the stage is irradiated with a charged particle beam from the charged particle optical system
Implementation Method 2
an irradiation optical system including a laser light source, an optical element configured to irradiate a region including a field of view of the charged particle optical system with light from the laser light source
Data Source
AI summary
The invention enables highly accurate dimension measurement while reducing a side effect caused by laser light irradiation.A measurement device for measuring a dimension of a predetermined pattern on a wafer at a plurality of measurement points, includes: an imaging unit 101 including a charged particle optical system and a detector 108; an image processing unit 111 configured to create a scanning image in response to a detection signal from the detector; an irradiation optical system 120 including a laser light source 121 and a shutter 122 configured to control irradiation toward the region with light from the laser light source; and a controller 112 configured to control the imaging unit and the irradiation optical system. The controller performs time adjustment such that an irradiation amount of light from the laser light source from when the shutter is opened to start the irradiation with the light from the laser light source to when the imaging unit starts imaging of the scanning image is equal at the plurality of measurement points.