Pulse Laser Defect Inspection for Semiconductor Substrates
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Solution Overview
Problem
Existing defect inspection methods for semiconductor substrates face challenges in detecting micro defects of 20 nm or less due to weak scattered light signals being buried in noise, and increasing illuminating power leads to thermal damage, while reducing scan speed limits the number of samples that can be inspected within a certain time.
Innovation Solution
A defect inspection method and device utilizing a pulse dividing unit with an optical dividing unit, delay optical path, and optical integrating unit to adjust light quantity, combined with an optical axis adjusting unit and high-frequency signal removing circuit to detect micro defects without thermal damage, featuring a rotatable sample stage and pulse laser illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If illuminating power is increased to detect micro defects, then defect detection sensitivity is improved, but thermal damage to the sample occurs
Solution Approach 1:
The patent applies periodic pulsed illumination instead of continuous light to inspect the sample surface. By using short-duration light pulses with sufficient intervals, the system accumulates scattered light signals over multiple pulses while allowing thermal dissipation between pulses, thereby detecting micro defects without causing thermal damage.
Solution Approach 2:
The patent employs multiple continuous light pulses to illuminate the sample surface, accumulating scattered light signals from micro defects. By combining signals from multiple pulses, the system achieves high detection sensitivity while maintaining low instantaneous power to avoid thermal damage.
2Measurement precision
If scan speed is reduced to improve detection sensitivity, then defect detection accuracy is improved, but the number of samples that can be inspected within certain time is reduced
Solution Approach 1:
The patent maintains continuous scanning motion while applying multiple light pulses to the same inspection region. This allows the system to accumulate sufficient scattered light signals for high-accuracy detection without reducing scan speed, thereby maintaining both detection accuracy and inspection throughput.
Solution Approach 2:
The patent performs preliminary signal accumulation by applying multiple light pulses before making a detection decision. This preliminary accumulation of useful signals ensures high detection accuracy even during rapid scanning, eliminating the need to reduce scan speed for improved sensitivity.
3Measurement precision
If multiple light pulses are applied to accumulate scattered light signals, then defect detection sensitivity is improved, but thermal damage to the sample increases
Solution Approach 1:
The patent uses periodically spaced light pulses with sufficient intervals between them. This periodic application allows thermal energy to dissipate between pulses while still accumulating enough scattered light signals for sensitive defect detection, resolving the contradiction between signal accumulation and thermal damage prevention.
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 rapid scanning of entire surfaces with precise detection of micro defects without causing thermal damage, improving defect detection sensitivity and throughput.
Implementation Method 1
a pulse dividing unit configured to divide a pulse of a pulse laser emitted from a light source (2), a first beam monitor unit configured to monitor a barycentric position of light intensity of divided-pulse pulse laser emitted from the pulse dividing unit (8)
Implementation Method 2
an optical axis adjusting unit configured to expand a beam after passing through the pulse dividing unit (8) to increase an absolute quantity of an axial displacement of the beam and to suppress fluctuations in angles of the beams
Implementation Method 3
a laser light beam expanding unit (5) disposed on a subsequent stage of the pulse dividing unit (8), configured to expand a diameter of a laser beam
Implementation Method 4
the light is applied to the sample surface, and the light scattered from defects is focused and detected for inspecting defects
Data Source
AI summary
Disclosed is a defect inspection method which makes it possible to scan the entire surface of a sample and detect minute defects without causing thermal damage to the sample. A defect inspection method in which a pulse laser emitted from a light source is subjected to pulse division and irradiated on the surface of a sample which moves in one direction while the divided-pulse pulse laser is rotated, reflection light from the sample irradiated by the divided-pulse pulse laser is detected, the signal of the detected reflection light is processed to detect defects on the sample, and information regarding a detected defect is output to a display screen, wherein the barycentric position of the light intensity of the divided-pulse pulse laser is monitored and adjusted.