Wafer Thinning via Recess Grinding and Dry Etching Splitting

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Solution Overview

Problem

The existing methods for thinning wafers by grinding result in reduced rigidity, making them difficult to handle, and the removal of annular reinforcement portions using cutting blades can lead to wafer breakage due to bending forces, while avoiding these forces limits the number of devices that can be obtained from the wafer.

Innovation Solution

A method involving a grinding step to form a recess and annular projecting portion on the wafer's backside, followed by a splitting groove formed using dry etching at the boundary between the recess and annular projecting portion, allowing for separation without cutting into the wafer and enabling secure device extraction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a cutting blade is used to remove the annular reinforcement portion by cutting into the joining portion between the recess and annular projecting portion, then the annular reinforcement portion can be removed, but the R-shape exerts a bending force on the cutting blade causing wafer breakage

Engineering Contradiction:

Improveremoval of annular reinforcement portionVSAvoidwafer integrity

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent replaces the mechanical cutting blade with a laser beam to remove the annular reinforcement portion. The laser beam ablates the material without physical contact, eliminating the bending force problem caused by the R-shape while maintaining effective removal of the reinforcement portion.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the method parameter from mechanical cutting to laser ablation. This parameter change allows the removal process to overcome the geometric constraint of the R-shape by using a non-contact energy field instead of a physical tool that would be deflected by the curved surface.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the cutting blade avoids the R-shape by cutting into a flat region of the bottom surface, then wafer breakage is prevented, but the device region is narrowed reducing the number of devices that can be obtained

Engineering Contradiction:

Improvewafer integrityVSAvoidnumber of devices per wafer

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

By replacing the mechanical cutting blade with a laser beam, the system can precisely target and remove material at the boundary between the recess and annular projecting portion without the blade deflection problem. This enables full utilization of the device region while maintaining wafer integrity through contactless processing.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Length of moving object

If the wafer is thinned by grinding the back side, then the wafer can be made thinner to realize smaller and lighter devices, but the wafer rigidity is greatly lowered making it difficult to handle

Engineering Contradiction:

Improvewafer thicknessVSAvoidwafer rigidity

Core Design Contradiction:

Length of moving objectVSStrength

Solution Approach 1:

The patent applies local quality by creating a recess only in the central device region while leaving the peripheral marginal region with its original thickness as an annular reinforcement portion. This localized thinning approach reduces the overall wafer thickness for smaller devices while maintaining peripheral rigidity for easy handling.

Inventive Principle:

Principle #3Local quality

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 prevents wafer breakage and allows for the secure production of a sufficient number of devices by forming splitting grooves through dry etching, eliminating the need to avoid the boundary between the recess and annular projecting portion, thus maintaining wafer integrity and efficiency.

Implementation Method 1

a back side of a wafer is ground, for example, by use of a grinding wheel smaller than the wafer in diameter to form a recess corresponding to the device region

Methodology Applied

Scientific EffectAbrasion: Abrasion

Implementation Method 2

the splitting groove is formed by dry etching

Methodology Applied

Scientific EffectDry etching:

Data Source

PatentUS9887091B2Wafer processing method

Publication Date: 2018.02.06 DISCO CORP

AI summary

A method of processing a wafer includes: a grinding step of grinding a back surface of the wafer to form, on the back side of the wafer, a recess corresponding to a device region and an annular projecting portion corresponding to a peripheral marginal region; and a splitting groove forming step of forming, after the grinding step is conducted, a splitting groove for splitting the device region and the peripheral marginal region from each other at the boundary between the recess and the annular projecting portion, the splitting groove extending from the front surface of the wafer to reach the back surface of the wafer. The splitting groove is formed by dry etching.