Mark Imaging Across Mask Layers Using SWIR and Reflective Light
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Solution Overview
Problem
Existing image acquisition methods struggle to capture clear images of overlay or alignment marks in semiconductor processes due to layers with low visible light transmittance and high short wavelength infrared transmittance, making it difficult to differentiate between marks covered and not covered by these layers.
Innovation Solution
An image acquisition method and device that utilizes both penetrative and reflective light beams to determine the presence of a mask layer, employing short wavelength infrared and visible light beams to acquire clear images of marks, respectively, by comparing optical signals and adjusting autofocusing based on layer coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If visible light is used to acquire images of marks, then the image acquisition process is simple, but marks covered with low visible light transmittance layers cannot be imaged clearly
Solution Approach 1:
The patent changes the wavelength parameter of light from visible light to short wavelength infrared light. Since the mask layer has high SWIR transmittance, using SWIR light allows penetration through the mask layer to image marks underneath, resolving the contradiction between operational simplicity and image clarity for covered marks.
Solution Approach 2:
The patent introduces a new dimension of wavelength spectrum by incorporating SWIR light in addition to visible light. This dimensional expansion allows the system to overcome the transmittance limitation of the mask layer while maintaining the simplicity of the imaging process.
2Device complexity
If only one type of light beam is used for image acquisition, then the device structure is simple, but the system cannot differentiate between marks covered and not covered by mask layers
Solution Approach 1:
The patent segments the light beam acquisition process into two distinct paths: one using visible light (which reflects off the mask layer surface) and another using SWIR light (which penetrates the mask layer). This segmentation enables differentiation between covered and uncovered marks while keeping each individual light path simple.
Solution Approach 2:
The patent uses the mask layer itself as an intermediary element to enable differentiation. By comparing the reflection characteristics at the mask layer interface for different wavelengths, the system can detect mark coverage status without requiring additional complex detection mechanisms.
3Measurement precision
If SWIR light is used to penetrate mask layers, then marks under low transmittance layers become visible, but the device requires multiple light beam paths and detectors
Solution Approach 1:
The patent merges the SWIR light path with the visible light path by using a single detector that can detect both wavelength ranges. The optical system combines multiple light beam paths into a unified detection framework, reducing overall device complexity while maintaining the ability to image marks through mask layers.
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
Enables the acquisition of clear images of marks regardless of layer transmittance properties, improving overlay measurement and wafer alignment accuracy in semiconductor processes.
Implementation Method 1
acquiring a first optical signal by emitting a penetrative light beam, which is capable of penetrating a mask layer, to a measurement target mark
Implementation Method 2
acquiring a second optical signal by emitting a reflective light beam, which reflects from the mask layer, to the measurement target mark
Implementation Method 3
layers having low visible light transmittance and high short wavelength infrared (SWIR) transmittance
Data Source
AI summary
An image acquisition method includes acquiring a first optical signal by emitting a penetrative light beam, which can penetrate a mask layer, to a measurement target mark that is one of marks on a sample, acquiring a second optical signal by emitting a reflective light beam reflecting from the mask layer to the measurement target mark, determining whether the measurement target mark is covered with the mask layer by comparing the first optical signal and the second optical signal, and acquiring a mark image by emitting a first light beam, which penetrates the mask layer, to the measurement target mark when the measurement target mark is covered with the mask layer, and acquiring a mark image by emitting a second light beam different from the first light beam to the measurement target mark when the measurement target mark is not covered with the mask layer.