Wafer Thinning via Side Surface Protective Structure

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Solution Overview

Problem

Conventional wafer thinning processes often result in chipping or breaking during the thinning of semiconductor wafers due to uneven stress distribution, particularly when the wafers are thinned to less than 300 μm, and existing solutions like forming a step structure require additional tools and increase manufacturing costs.

Innovation Solution

A protective structure is formed on the side surface of the wafer before the thinning process to provide uniform thickness and alleviate stress, using materials like epoxy resin with added particles for enhanced hardness, which can be applied via spin coating and cured thermally or with light energy, without altering the wafer profile.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the wafer is thinned to a thickness less than 300 μm, then the wafer thinning technology can be used for BSI photo-sensor and chip packaging, but the problem of wafer chipping or breaking easily occurs during the thinning process

Engineering Contradiction:

Improvewafer thicknessVSAvoidwafer integrity

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

A protective structure is formed on the side surface of the wafer before the thinning process to provide mechanical support and prevent chipping or breaking during thinning. The protective structure acts as a cushion that compensates for the reduced structural integrity of the thinned wafer, allowing achieving thickness less than 300 μm while maintaining wafer integrity.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The protective structure serves as an intermediary element between the wafer and the external environment during the thinning process. It provides mechanical support and distributes stress, preventing direct contact between the fragile thinned wafer and potential damage sources, thus resolving the contradiction between reducing wafer thickness and maintaining wafer integrity.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a step structure is provided near the edge of the wafer to avoid chipping, then the chipping problem can be prevented, but additional cutting tools are required and manufacturing costs increase

Engineering Contradiction:

Improvewafer integrityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The protective structure is formed using a coating process instead of mechanical cutting methods. This replaces the mechanical system (grinding wheel, cutting tools) with a deposition/coating process, eliminating the need for additional cutting tools and reducing manufacturing complexity while still preventing chipping during thinning.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

Instead of changing the geometric profile of the wafer (step structure), the invention changes the material parameters by adding a protective layer on the side surface. This parameter change approach (adding protective material) achieves the same chipping prevention effect without the complexity of step structure formation.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If a step structure is provided near the edge of the wafer to reduce uneven stress, then chipping can be prevented, but additional mask and etching steps are required which increase manufacturing costs

Engineering Contradiction:

Improvewafer integrityVSAvoidprocess steps

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The protective structure is formed using a coating process instead of lithography and etching processes. This replaces the complex photochemical system (mask, lithography, etching) with a simpler deposition/coating process, reducing the number of process steps while achieving the same stress distribution effect.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention extracts only the essential function of the step structure (providing mechanical support and stress distribution) and implements it through a simpler means (protective coating on side surface). This extracts the core benefit while eliminating the unnecessary complexity of lithography and etching steps.

Inventive Principle:

Principle #2Taking out (Extraction)

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

The method effectively prevents chipping during the thinning process by providing uniform stress distribution and reducing production costs compared to conventional step structure formation methods.

Implementation Method 1

which can be applied via spin coating and cured thermally or with light energy

Methodology Applied

Scientific EffectSpin coating: Spin Coating

Implementation Method 2

cured thermally or with light energy

Methodology Applied

Scientific EffectThermal curing: Heat Treatment

Data Source

PatentUS8278189B2Method for thinning wafer

Publication Date: 2012.10.02 UNITED MICROELECTRONICS CORP

AI summary

The present invention provides a method of thinning a wafer. First, a wafer is provided. The wafer includes an active surface, a back surface and a side surface. The active surface is disposed opposite to the back surface. The side surface is disposed between the active surface and the back surface and encompasses the peripheral of the wafer. Next, a protective structure is formed on the wafer to at least completely cover the side surface. Last, a thinning process is performed upon the wafer from the back surface.