Laser Pulse Multiplier for Semiconductor Inspection Metrology

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Current semiconductor inspection and metrology systems face challenges with pulsed laser sources, particularly in UV wavelengths, where high repetition rates are needed to reduce peak power and enhance data acquisition, but modifying existing UV lasers is costly and time-consuming.

Innovation Solution

A pulse multiplier system using a polarizing beam splitter and wave plate, with a ring cavity configuration, splits input laser pulses into equal energy pulse trains, increasing repetition rate while minimizing peak power and maintaining energy balance, allowing for high-speed inspection and metrology with off-the-shelf lasers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a pulsed laser is used with high repetition rate and greatest pulse width to achieve sufficient time-averaged radiance, then the instantaneous peak power per pulse decreases reducing damage to optics and wafer, but the available CW light sources at UV wavelengths with sufficient radiance are not available

Engineering Contradiction:

Improvedamage reduction to optics and waferVSAvoidradiance at UV wavelength

Core Design Contradiction:

ReliabilityVSIllumination intensity

Solution Approach 1:

The patent divides a single high-energy laser pulse into multiple lower-energy pulses using a ring cavity with beam splitters. The input pulse is segmented into N output pulses distributed around the ring cavity, each with reduced peak power but collectively providing the required time-averaged radiance for UV illumination while minimizing damage to optical components and wafers.

Inventive Principle:

Principle #1Segmentation

2Productivity

If the repetition rate of laser subsystem is increased by improving laser medium, pump system, and driving electronics, then the pulse repetition rate increases leading to better signal-to-noise ratios and sampling, but it requires significant investment of time and money to modify existing UV laser components

Engineering Contradiction:

Improvepulse repetition rateVSAvoidcost and time to modify laser components

Core Design Contradiction:

ProductivityVSEase of manufacture

Solution Approach 1:

The patent introduces a ring cavity system with beam splitters as an intermediary component between the existing laser source and the inspection system. This intermediary device multiplies the pulse repetition rate without requiring modification of the laser medium, pump system, or driving electronics, thereby achieving higher productivity with minimal investment in modifying existing UV laser components.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Illumination intensity

If a single laser pulse is used for inspection, then the peak power is high providing sufficient radiance, but the number of pulses collected per data acquisition is limited reducing signal-to-noise ratio

Engineering Contradiction:

Improvepeak power per pulseVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Illumination intensityVSMeasurement precision

Solution Approach 1:

The ring cavity system enables continuous circulation and utilization of laser pulses around the cavity multiple times. Each pulse is distributed to multiple detection points and can be reused in subsequent cycles, increasing the effective number of pulses collected per data acquisition. This continuous utilization improves signal-to-noise ratio through better averaging while maintaining sufficient peak power for UV illumination.

Inventive Principle:

Principle #20Continuity of useful action

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 system effectively doubles the repetition rate of laser pulses while reducing peak power, enabling better signal-to-noise ratios and reduced damage to optics and wafers, facilitating high-speed inspection and metrology with minimal energy loss.

Implementation Method 1

The wave plate receives light from the polarized beam splitter and generates first and second sets of pulses. In one embodiment, the wave plate includes a half-wave plate, which can be set at 27.3678 degrees. In another embodiment, the wave includes a quarter-wave plate. Notably, the first set of pulses has a different polarization than the second set of pulses.

Methodology Applied

Scientific EffectPolarization: Polarisation

Implementation Method 2

Methodology Applied

Scientific EffectWave plate polarization transformation: Polarisation

Implementation Method 3

The set of mirrors create the ring cavity, which includes the polarizing beam splitter and the wave plate.

Methodology Applied

Scientific EffectLight reflection: Reflection

Data Source

PatentUS10193293B2Semiconductor inspection and metrology system using laser pulse multiplier

Publication Date: 2019.01.29 KLA CORP

AI summary

A pulse multiplier includes a polarizing beam splitter, a wave plate, and a set of multi-surface reflecting components (e.g., one or more etalons and one or more mirrors). The polarizing beam splitter passes input laser pulses through the wave plate to the multi-surface reflecting components, which reflect portions of each input laser pulse back through the wave plate to the polarizing beam splitter. The polarizing beam splitter reflects each reflected portion to form an output of the pulse multiplier. The multi-surface reflecting components are configured such that the output pulses exiting the pulse multiplier have an output repetition pulse frequency rate that is at least double the input repetition pulse frequency.