Wafer Protective Film Layout for Backside Laser Die Separation

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Solution Overview

Problem

During the substrate processing for semiconductor wafers, conventional cutting methods like mechanical or laser cutting can damage or contaminate devices due to debris, especially when cutting through metal structures, and the use of protective films can lead to adhesive-related damage or warpage issues, particularly for fragile structures like MEMS.

Innovation Solution

A method involving two protective films, one directly attached to the substrate's front side without adhesive in the central area and the other on the back side, allowing laser cutting through the transparent back film to minimize contamination and warpage by ensuring accurate and reliable formation of modified regions for precise die separation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the adhesive layer is applied only to the peripheral portion of the protective film, then the risk of adhesive damage to devices is reduced, but the substrate may not be sufficiently held during processing due to lack of support in the central portion

Engineering Contradiction:

Improveadhesive damage riskVSAvoidsubstrate holding stability

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The substrate holding function is segmented between two films: the first protective film on the front side provides central area support without adhesive, while the second protective film on the back side with adhesive provides overall substrate attachment. This segmentation resolves both the adhesive damage risk and substrate holding stability requirements.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The solution moves from a single-film approach to a two-film approach, adding the dimension of dual-side protection. The second film on the back side compensates for the reduced adhesive support of the first film, ensuring overall substrate stability during processing.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Ease of manufacture

If laser cutting is performed from the substrate front side, then the cutting process can be carried out, but debris generated in the cutting process damages or contaminates the devices formed in the device area

Engineering Contradiction:

Improvecutting process feasibilityVSAvoiddebris damage and contamination

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The laser cutting direction is inverted from the conventional front-side approach to a back-side approach. The laser beam is applied from the back side of the substrate, allowing cutting while preventing debris from contaminating the device area on the front side. This inversion resolves the contradiction between cutting feasibility and device protection.

Inventive Principle:

Principle #13The other way round (Inversion)

3Ease of manufacture

If stealth laser cutting is performed by forming modified regions in the substrate, then cutting can be achieved, but substrate warpage occurs due to volume increase in modified regions, affecting the accuracy of modified region formation

Engineering Contradiction:

Improvecutting capabilityVSAvoidmodified region formation accuracy

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The second protective film applied to the back side serves as a cushioning layer that suppresses substrate warpage during laser processing. By providing support from the back side, it compensates for the volume expansion in modified regions, maintaining substrate flatness and ensuring accurate formation of modified regions for precise die separation.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 significantly reduces the risk of damage and contamination, enhances the accuracy of modified region formation, and allows for reliable division of substrates into individual dies, even for small die sizes, by preventing warpage and using adhesive-free central contact for the front film.

Implementation Method 1

Laser cutting may be performed, for example, by ablation laser cutting and/or by stealth laser cutting, i.e., by forming modified regions within the substrate by the application of a laser beam

Methodology Applied

Scientific EffectLaser ablation: Laser Ablation

Data Source

PatentUS11842926B2Method of processing a substrate

Publication Date: 2023.12.12 DISCO CORP

AI summary

This invention relates to a method of processing a substrate, having on one side a device area with a plurality of devices. The method includes attaching a first protective film to the one side of the substrate, so that at least a central area of a front surface of the first protective film is in direct contact with the one side of the substrate, and attaching a second protective film to the opposite side of the substrate. After attaching the second protective film, a laser beam is applied to the substrate from the opposite side of the substrate. The substrate and second protective film are transparent to the laser beam. The laser beam is applied to the substrate in a plurality of positions so as to form a plurality of modified regions in the substrate.