Wafer Inspection Microscope With Oblique Optics for Clear Front-Side Imaging
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Solution Overview
Problem
Conventional observation methods for semiconductor wafers face challenges in achieving clear imaging of the front surface due to absorption of illumination light by the wafer material and scattering of light by saw marks on the back surface, leading to reduced light transmission and noise in images.
Innovation Solution
An observation method using a microscope with a lighting unit that irradiates the back surface of the wafer with a light beam having transmissivity for the wafer material, where the focal point is positioned at a predetermined location on the front surface or interior, and an imaging unit with an objective lens having an optical axis inclined obliquely to the condenser lens, allowing for increased light transmission and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a light beam of wavelength having transmissivity for the workpiece is used to image the front surface through the back surface, then light transmission is improved, but the light beam is absorbed in the interior of the workpiece and does not reach the front surface
Solution Approach 1:
The patent changes the wavelength parameter of the illumination light beam to match the transmissivity characteristics of the specific workpiece material. By selecting a wavelength that the workpiece material transmits well, the patent optimizes light transmission through the workpiece while minimizing absorption losses in the interior.
Solution Approach 2:
The patent transitions from conventional oblique lighting to a configuration where the illumination optical axis and imaging optical axis are separated in space. The lighting unit is positioned at a location different from the imaging unit, allowing illumination light to enter the workpiece from one dimension while the imaging unit captures reflected light from another dimension, thereby reducing absorption path length.
2Measurement precision
If oblique lighting is used to observe the workpiece, then imaging capability is improved, but the illumination light beams are absorbed in the interior of the workpiece and do not reach the front surface
Solution Approach 1:
The patent positions the lighting unit and imaging unit at different spatial locations with their optical axes separated. This dimensional separation allows the illumination light to strike the workpiece at an optimized angle while the imaging unit captures reflected light from a different angle, improving both imaging capability and reducing absorption losses.
Solution Approach 2:
The patent optimizes the inclination angle between the illumination optical axis and imaging optical axis to balance imaging capability with light transmission efficiency. By adjusting this angular parameter, the patent achieves clear imaging while minimizing the path length that illumination light must travel through the workpiece interior.
3Productivity
If the workpiece is ground to thin the device chips, then processing capability is improved, but saw marks are formed that scatter the illumination light beam and cause noise in the image
Solution Approach 1:
The patent changes the wavelength parameter of the illumination light to one that is less susceptible to scattering by saw marks. By selecting a wavelength that penetrates better through the ground surface irregularities, the patent reduces scattering effects and improves image quality while maintaining processing capability.
Solution Approach 2:
The patent accepts the presence of saw marks as an inevitable byproduct of grinding but converts this harmful factor into a manageable condition by selecting illumination parameters that minimize their negative impact. The specific wavelength selection and optical configuration transform the scattering issue into a controlled parameter that does not significantly degrade image quality.
4Measurement precision
If multiple light sources are arranged along the outer peripheral portion of a lens barrel for dark field microscopy, then imaging capability is improved, but the illumination light beams are absorbed in the interior of the workpiece
Solution Approach 1:
The patent extracts the lighting function from the conventional position within or near the lens barrel and places it in a separate location. By positioning the lighting unit independently at a different spatial location with a separated optical axis, the patent reduces the path length of illumination light through the workpiece interior, thereby minimizing absorption while maintaining dark field imaging capability.
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 enhances light transmission to the front surface, reducing noise and improving image clarity by focusing light at a single point within the wafer, even for thick silicon wafers with high dopant concentrations.
Implementation Method 1
a condenser lens capable of focusing the light beam from the light source at a predetermined position on the other side or in the interior of the object
Implementation Method 2
detecting reflected light from the object by an imaging unit including an objective lens having an optical axis inclined obliquely to an optical axis of a condenser lens of the lighting unit
Implementation Method 3
irradiating the object with the light beam from a lighting unit that is capable of irradiating the light beam with a wavelength having transmissivity for the object
Data Source
AI summary
An observation method for irradiating one side of an object, the object having a plate shape, the one side, and the other side, with a light beam, and observing the other side of the object or an interior of the object includes a holding step of holding the object at the other side on a holding surface of a holding table, and a detection step of irradiating the object with the light beam from a lighting unit capable of applying the light beam with a wavelength having transmissivity for the object, with a focal point of the light beam being positioned at a predetermined position on the other side or in the interior, and detecting reflected light from the object by an imaging unit including an objective lens having an optical axis inclined obliquely to an optical axis of a condenser lens of the lighting unit.