Optical Inspection Illumination Intensity Adjustment for Detectability
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Solution Overview
Problem
Conventional optical inspection methods for detecting micro foreign matters or defects on semiconductor substrates face reduced detectability at the outer peripheral parts due to higher linear velocities, leading to shorter light interaction times and increased risk of thermal damage from increased illumination intensity.
Innovation Solution
An optical inspection apparatus with a movable stage that adjusts the brightness of the light beam based on the scanning speed, ensuring consistent (brightness×scanning time) values across the surface, thereby maintaining detectability while preventing thermal damage by increasing illumination intensity only where necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If constant angular velocity scanning is used to shorten inspection time, then productivity is improved, but detectability at the outer peripheral part deteriorates due to higher linear velocity reducing light interaction time
Solution Approach 1:
The patent applies local quality by adjusting the illumination intensity according to the radial position on the substrate. The outer peripheral region receives higher illumination intensity to compensate for the reduced light interaction time caused by higher linear velocity, while the inner region maintains lower intensity. This position-dependent illumination adjustment ensures uniform detectability across the entire substrate surface while maintaining constant angular velocity scanning for high productivity.
2Measurement precision
If illumination intensity is increased to enhance detectability at the outer peripheral part, then measurement precision is improved, but thermal damage risk increases
Solution Approach 1:
The patent implements local quality by applying different illumination intensities to different radial regions of the substrate. The illumination intensity is increased only in the outer peripheral region where higher linear velocity reduces detectability, while the inner region maintains lower intensity. This localized intensity adjustment enhances detectability where needed without subjecting the entire substrate to high illumination levels, thereby preventing thermal damage.
3Measurement precision
If linear velocity is reduced at the outer peripheral part to improve detectability, then measurement precision is improved, but inspection throughput decreases
Solution Approach 1:
The patent applies parameter changes by adjusting the illumination intensity parameter according to the radial position rather than changing the scanning velocity parameter. The linear velocity is maintained at constant angular velocity for high throughput, while the illumination intensity is increased in the outer peripheral region to compensate for the reduced light interaction time. This parameter substitution allows maintaining productivity while improving detectability.
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 detectability for foreign matters or defects across the entire surface without compromising inspection throughput or causing thermal damage, by dynamically adjusting the illumination spot intensity according to the scanning speed, particularly at the outer peripheral parts.
Implementation Method 1
scattered light from a foreign matter which possibly sticks to the semiconductor substrate that is fed on rotation or translation is detected
Implementation Method 2
An ellipsoidal mirror is used for detecting the scattered light, which is arranged in such a way that the primary focal position of the ellipsoid thereof is set at a detecting position on the semiconductor substrate while the secondary focal position thereof is set at an light receiving surface of a light receiving element
Data Source
AI summary
An optical inspection apparatus irradiates a light beam onto the outer surface of an object to be inspected, in the form of an illumination spot having an illumination intensity which is higher in the outer peripheral part of the object to be inspected than in the inner peripheral part thereof while uniformly maintains a temperature rise caused by the irradiation of the light beam, over the outer surface of the object to be inspected, in order to prevent the effective entire signal value of a scattered light signal from lowering, without lowering the linear speed of a movable stage for the object to be inspected in the outer peripheral part of the object to be inspected, thereby it is possible to prevent lowering of the detectability for a foreign matter or a defect, for preventing lowering of inspection throughput.