PSPI Layer UV Inspection for Accurate Height Metrology

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Solution Overview

Problem

The Photo-Sensitive Polyimide (PSPI) layer above a radiation reflecting layer in wafers causes double reflections, leading to inaccurate height measurements in 3D metrology, especially for low-profile bumps, due to the second reflected radiation from the lower layer, which complicates automatic optical inspection methods.

Innovation Solution

Employing a system that uses ultraviolet light at specific wavelengths below 400 nanometers to illuminate the PSPI layer, allowing for high-resolution and accurate height measurements by eliminating the second reflection from the internal Silicon surface, and incorporating a dual illumination mode with white light and ultraviolet light sources to differentiate between reflections from the top and bottom of the object.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a PSPI layer is positioned above a radiation reflecting layer for wafer applications, then the wafer structure provides necessary functional properties, but double reflections occur causing inaccurate height measurements in 3D metrology

Engineering Contradiction:

Improvewafer structure functionalityVSAvoidheight measurement accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent changes the wavelength parameter of the illumination radiation to ultraviolet range (below 400 nanometers). The PSPI layer absorbs UV radiation, preventing it from reaching the lower reflecting layer, thereby eliminating the second reflection path while maintaining the structural functionality of the wafer

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If conventional illumination methods are used for 3D metrology, then the inspection process is simple, but height measurement accuracy deteriorates due to second reflected radiation from the lower layer

Engineering Contradiction:

Improveinspection process simplicityVSAvoidbump height measurement accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The illumination wavelength is changed from visible light to ultraviolet radiation below 400 nanometers. This parameter change causes the PSPI layer to absorb the radiation, blocking the second reflection path and enabling accurate height measurements while maintaining operational simplicity

Inventive Principle:

Principle #35Parameter changes

3Loss of information

If the PSPI layer is illuminated with radiation that passes through it, then the lower reflecting layer can be detected, but this creates harmful second reflected radiation that introduces height errors

Engineering Contradiction:

Improvelower layer detection capabilityVSAvoidsecond reflected radiation causing height errors

Core Design Contradiction:

Loss of informationVSObject-generated harmful factors

Solution Approach 1:

The patent converts the PSPI layer's radiation transmission property into a blocking property by selecting ultraviolet wavelengths. The same PSPI layer that would normally transmit radiation and cause second reflections now absorbs UV radiation, converting the harmful reflection path into a blocked path while maintaining wafer functionality

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

By changing the illumination wavelength to ultraviolet below 400 nanometers, the interaction between radiation and PSPI layer changes from transmission to absorption, eliminating the harmful second reflected radiation while preserving necessary wafer properties

Inventive Principle:

Principle #35Parameter changes

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 enables precise height measurement of objects with PSPI layers by reducing ambiguity and increasing measurement resolution, effectively addressing the challenges of low-profile bump inspection and improving the accuracy of 3D metrology in semiconductor wafer applications.

Implementation Method 1

the PSPI layer absorbs the radiation, preventing it from reaching the lower layer

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Data Source

PatentUS10823669B2Inspecting an object that includes a photo-sensitive polyimide layer

Publication Date: 2020.11.03 CAMTEK LTD

AI summary

A method for determining a property of an object positioned on a photo-sensitive polyimide layer, wherein the photo-sensitive polyimide layer is positioned on a lower layer that is a radiation reflecting layer, the method may include illuminating, by an illumination unit, an area of the photo-sensitive polyimide layer with first ultraviolet radiation; sensing, by a first sensor, a first reflected ultraviolet radiation that was reflected from the area; and determining, by a processor, based at least in part on the first reflected ultraviolet radiation, the property of the object.