Laser Beam Machining Method for Substrate Cutting

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Solution Overview

Problem

Existing laser processing methods for cutting semiconductor, piezoelectric, and glass substrates lack accuracy and often result in unnecessary fractures deviating from the intended cut line.

Innovation Solution

A laser processing method that forms a modified region within the substrate using multiphoton absorption, followed by irradiation with laser light that is transmittable through unmodified regions but more absorbable by the modified regions, generating thermal stress to accurately cut the substrate along the intended line without surface melting or unnecessary fractures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If laser light is irradiated to form a modified region within the object, then cutting accuracy is improved, but the object surface may melt or unnecessary fractures may occur

Engineering Contradiction:

Improvecutting accuracyVSAvoidsurface melting and unnecessary fractures

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The cutting process is divided into two distinct steps: first forming a modified region (cutting start region) within the object using multiphoton absorption, then separately irradiating with laser light to generate stress and grow cracks. This segmentation allows each step to be optimized independently, preventing surface melting while achieving accurate cutting.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The modified region is formed in advance within the object before the actual cutting irradiation. This preliminary action creates a predetermined cutting start region that guides subsequent crack growth, ensuring accurate cutting without requiring high energy density that would cause surface melting.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 3:

The patent replaces direct mechanical force application with optical field-based multiphoton absorption to form the modified region. This substitution allows precise internal modification without mechanical contact or excessive heat that would cause surface damage.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Productivity

If high energy laser light is used to cut the object, then cutting speed is improved, but manufacturing precision deteriorates due to surface melting and fractures

Engineering Contradiction:

Improvecutting speedVSAvoidcutting accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The cutting process is segmented into modified region formation and stress-induced crack growth steps. This allows using lower energy density for modified region formation (preventing surface melting) while maintaining efficient crack propagation for adequate cutting speed.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes laser light parameters by using wavelengths that are transmittable through unmodified regions but absorbed by modified regions. This parameter change enables selective heating of the modified region to generate stress and grow cracks without melting the object surface.

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

Enables precise cutting of substrates with minimal force, preventing fractures outside the intended cut line and improving productivity by forming modified regions such as crack, molten, or refractive index change regions for controlled cleavage.

Implementation Method 1

irradiating a wafer-like object to be processed with laser light while locating a light-converging point within the object, so as to form a modified region due to multiphoton absorption within the object

Methodology Applied

Scientific EffectMultiphoton absorption:

Implementation Method 2

irradiating the modified region with laser light transmittable through an unmodified region of the object and more absorbable by the modified region than by the unmodified region after the first step, so as to generate a stress at a portion where the object is cut

Methodology Applied

Scientific EffectThermal stress:

Implementation Method 3

laser light transmittable through an unmodified region of the object and more absorbable by the modified region than by the unmodified region

Methodology Applied

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

Data Source

PatentUS8247734B2Laser beam machining method

Publication Date: 2012.08.21 HAMAMATSU PHOTONICS KK

AI summary

A laser processing method which can accurately cut an object to be processed along a line to cut is provided. A modified region 7 formed by multiphoton absorption forms a cutting start region 8 within an object to be processed 1 along a line 5 along which the object is intended to be cut. Thereafter, the object 1 is irradiated with laser light L2 transmittable through an unmodified region of the object 1, so as to generate fractures 24 from the cutting start region 8 acting as a start point, whereby the object 1 can accurately be cut along the line 5 along which the object is intended to be cut. Expanding an expandable film 19 having the object 1 secured thereto separates individual chips 25 from each other, which can further improve the reliability in cutting the object 1 along the line 5 along which the object is intended to be cut.