Wafer Dicing via Laser-Induced Deteriorated Layer

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Solution Overview

Problem

The existing methods for cutting semiconductor and optical device wafers along dividing lines result in a large area ratio of dividing lines to wafer, reducing productivity and causing a deteriorated layer that weakens the transverse rupture strength of the chips.

Innovation Solution

A wafer processing method involving the formation of a deteriorated layer on the back surface of the wafer using a pulse laser beam, followed by dividing the wafer along the lines and grinding the back surface to remove the deteriorated layer, thereby maintaining the transverse rupture strength of the chips.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a cutting blade with thickness of about 20 μm is used to cut the wafer along the dividing lines, then the wafer can be divided into individual chips, but the dividing lines must have a width of about 50 μm, resulting in a large area ratio of dividing lines to wafer and reduced productivity

Engineering Contradiction:

Improvewafer cutting efficiencyVSAvoidarea ratio of dividing lines to wafer

Core Design Contradiction:

ProductivityVSArea of stationary object

Solution Approach 1:

The patent replaces the mechanical cutting blade system with a laser processing system. The laser beam processes the dividing lines from the back surface of the wafer, allowing for much narrower processing width compared to the mechanical blade thickness. This substitution eliminates the need for wide dividing lines required by mechanical cutting, thereby reducing the area ratio of dividing lines to wafer and improving productivity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the processing dimension by approaching the dividing lines from the back surface of the wafer rather than from the front surface. This dimensional change allows the laser to process the dividing lines with minimal width while still achieving complete separation, as the laser can access the entire length of the dividing lines from the opposite side without being constrained by the blade thickness.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Strength

If a pulse laser beam is applied from the back surface of the wafer to form a deteriorated layer along the dividing lines, then the transverse rupture strength of chips is maintained by removing the deteriorated layer, but an additional grinding step is required

Engineering Contradiction:

Improvetransverse rupture strength of chipsVSAvoidnumber of processing steps

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The patent applies the laser beam in advance to form a deteriorated layer along the dividing lines before the final cutting step. This preliminary action weakens the material along the dividing lines, facilitating easier and cleaner separation during the subsequent cutting process. The deteriorated layer is then removed by grinding to ensure high transverse rupture strength of the final chips.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent converts the potentially harmful effect of the laser-induced deteriorated layer (which could weaken the chips) into a beneficial effect. By intentionally creating the deteriorated layer along the dividing lines, the laser enables precise and clean separation. The subsequent removal of this deteriorated layer through grinding transforms what would be a defect into a feature that ensures high chip strength, as the separation path is cleanly defined without residual damage to the chip bodies.

Inventive Principle:

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

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 method effectively reduces the area ratio of dividing lines to wafer, improving productivity and ensuring the transverse rupture strength of the chips by removing the deteriorated layer, resulting in chips with enhanced strength.

Implementation Method 1

applying a pulse laser beam capable of passing through the workpiece with its focusing point set to the inside to continuously form a deteriorated layer along the dividing lines in the inside of the workpiece

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

applying a laser beam capable of passing through the wafer along the dividing lines from the back surface of the wafer

Methodology Applied

Scientific EffectOptical transmission: Light

Data Source

PatentUS7682858B2Wafer processing method including formation of a deteriorated layer

Publication Date: 2010.03.23 DISCO CORP

AI summary

A wafer processing method for dividing a wafer having function elements in area sectioned by dividing lines formed on the front surface in a lattice pattern into individual chips along the dividing lines, comprising a deteriorated layer forming step for forming a deteriorated layer on the side of the back surface of a position at a distance corresponding to the final thickness of the chip from the front surface of the wafer by applying a laser beam capable of passing through the wafer along the dividing lines from the back surface of the wafer; a dividing step for dividing the wafer into individual chips along the dividing lines by applying external force to the wafer in which the deteriorated layer has been formed along the dividing lines; and a back surface grinding step for grinding the back surface of the wafer divided into individual chips to the final thickness of the chip.