Wafer Division via Back-Side Laser Ablation

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Solution Overview

Problem

The existing wafer processing methods for dividing wafers into individual device chips face issues such as delamination of low-k films, reduced productivity, debris scattering, thermal strain, and decreased device forming area due to the use of laser grooves and cutting blades, which affect device quality and productivity.

Innovation Solution

A method involving attaching an adhesive tape to the wafer, back grinding to reduce thickness, forming cut grooves on the back side using a cutting blade, and applying a laser beam from the back side to divide the wafer along these grooves, eliminating the need for multiple laser grooves on the front side and reducing thermal strain.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a laser beam is applied to the front side of the wafer to remove the functional layer from each division line, then the cutting blade can cut through without interference, but at least two laser processed grooves must be formed which reduces productivity

Engineering Contradiction:

Improvecutting qualityVSAvoidwafer division speed

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent applies the laser beam from the back side of the wafer instead of the front side, inverting the conventional approach. This allows the laser to process through the adhesive tape and substrate to remove material at the division lines without requiring multiple passes, thereby improving productivity while maintaining cutting quality.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The adhesive tape is attached to the front side of the wafer before laser processing. This preliminary action protects the front side functional layers from laser damage and debris while enabling efficient back-side laser processing that removes material in a single pass.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the laser beam is applied to the front side of the wafer to form laser processed grooves, then the functional layer can be removed, but debris may scatter and stick to the front side of the wafer causing degradation in device quality

Engineering Contradiction:

Improvefunctional layer removalVSAvoiddebris contamination

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent processes the wafer from the back side instead of the front side, inverting the conventional approach. This prevents debris from scattering onto the front side functional layers, eliminating contamination while still achieving effective material removal at the division lines.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The adhesive tape is used to extract and contain debris generated during laser processing. The tape captures scattered particles before they can contaminate the front side of the wafer, maintaining device quality while enabling effective material removal.

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If the laser beam is applied in plural passes along each division line to form laser processed grooves, then the functional layer can be completely removed, but thermal strain remains in the wafer causing reduction in die strength

Engineering Contradiction:

Improvefunctional layer removal completenessVSAvoiddie strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The adhesive tape is attached before laser processing, providing thermal insulation and mechanical support. This preliminary preparation allows for more efficient single-pass or reduced-pass laser processing that removes the functional layer completely while minimizing thermal strain accumulation in the wafer.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Processing from the back side allows for more efficient material removal with fewer laser passes compared to front-side processing. The laser energy is more effectively coupled through the substrate, achieving complete functional layer removal in fewer passes and reducing cumulative thermal strain.

Inventive Principle:

Principle #13The other way round (Inversion)

4Reliability

If the spacing between the two laser processed grooves is larger than the width of the cutting blade, then the functional layer can be removed, but the width of each division line must be increased causing decrease in device forming area

Engineering Contradiction:

Improvefunctional layer removalVSAvoiddevice forming area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent processes from the back side, allowing the laser to effectively remove material with tighter spacing between processing lines. This back-side approach provides better control and efficiency, enabling narrower division lines that preserve more device forming area while still achieving complete functional layer removal.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The adhesive tape preparation enables more precise and efficient laser processing with optimal parameter settings. This preliminary setup allows for tighter groove spacing that reduces division line width while maintaining complete functional layer removal, thereby maximizing device forming area.

Inventive Principle:

Principle #10Preliminary 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

This approach improves productivity by preventing cutting blade deviation and debris scattering, maintains device quality, and allows for a higher device forming area without thermal strain or delamination, enabling efficient division of wafers into individual device chips.

Implementation Method 1

attaching an adhesive tape to the front side of a wafer

Methodology Applied

Scientific EffectAdhesion: Adhesive

Implementation Method 2

grinding the back side of the wafer to thereby reduce the thickness of the wafer

Methodology Applied

Scientific EffectAbrasion: Abrasion

Implementation Method 3

cutting the back side of the wafer along each division line by using a cutting blade

Methodology Applied

Scientific EffectMechanical cutting:

Implementation Method 4

applying a laser beam to the bottom of the cut groove from the back side of the wafer along each division line

Methodology Applied

Scientific EffectLaser ablation: Laser Ablation

Data Source

PatentUS10049934B2Wafer processing method

Publication Date: 2018.08.14 DISCO CORP

AI summary

A wafer processing method divides a wafer into individual device chips along division lines. The method includes attaching an adhesive tape to the front side of the wafer and attaching a peripheral portion of the adhesive tape to an annular frame having an inside opening for receiving the wafer, thereby supporting the wafer through the adhesive tape to the annular frame; grinding the back side of the wafer to reduce the thickness of the wafer; cutting the back side of the wafer along each division line by using a cutting blade to form a cut groove having a depth not reaching the front side of the wafer; and applying a laser beam to the bottom of the cut groove from the back side of the wafer along each division line to divide the wafer to obtain the individual device chips.