Heterogeneous Wafer Bonding with Stress Compensating Polymer Layers

Solution Overview

Problem

Wafer level integration for heterogeneous wafers is challenging due to differences in structure, materials, coefficients of thermal expansion, processing, equipment, mechanical stresses, and thermal considerations, leading to non-planarity and breakage issues that affect manufacturing yields.

Innovation Solution

The method involves creating under bump metallization pads on heterogeneous wafers, applying a conductive means above these pads, and low-temperature bonding them together using stress compensating oxide or polymer layers to minimize stress and warpage, with optional steps like channel creation and precision alignment to enhance bonding strength and planarity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If heterogeneous wafers with different materials and structures are integrated at wafer level, then functional versatility and device capability are improved, but mechanical stress and thermal expansion mismatch cause warpage and breakage

Engineering Contradiction:

Improvefunctional versatilityVSAvoidmechanical strength

Core Design Contradiction:

Adaptability or versatilityVSStrength

Solution Approach 1:

Stress compensating oxide or polymer layers are applied to the wafer surfaces before bonding occurs. This preliminary application of compensating layers allows stress to be counteracted during the bonding process itself, preventing warpage and breakage that would occur with conventional post-bonding stress management approaches

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Stress compensating oxide or polymer layers are introduced as intermediary materials between the heterogeneous wafer surfaces. These intermediary layers act as stress buffers that accommodate the thermal expansion mismatch and mechanical stress differences between dissimilar wafer materials, enabling successful bonding without direct stress transmission between the heterogeneous substrates

Inventive Principle:

Principle #24Intermediary (Mediator)

2Strength

If conventional high temperature bonding is used to join heterogeneous wafers, then bonding strength is improved, but thermal stress and warpage increase

Engineering Contradiction:

Improvebonding strengthVSAvoidthermal stress

Core Design Contradiction:

StrengthVSTemperature

Solution Approach 1:

The bonding process parameters are changed by using low temperature bonding instead of conventional high temperature bonding. This parameter change, combined with stress compensating layers, allows adequate bonding strength to be achieved while significantly reducing thermal stress and warpage that would occur with high temperature processing of heterogeneous wafers

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If wafer level integration is performed without stress compensation, then manufacturing complexity is reduced, but non-planarity and breakage increase

Engineering Contradiction:

Improvemanufacturing complexityVSAvoidplanarity

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

Stress compensating oxide or polymer layers are applied to the wafer surfaces before bonding occurs. This preliminary application of compensating layers allows stress to be counteracted during the bonding process itself, preventing warpage and breakage that would occur with conventional post-bonding stress management approaches

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Stress compensating oxide or polymer layers are introduced as intermediary materials between the heterogeneous wafer surfaces. These intermediary layers act as stress buffers that accommodate the thermal expansion mismatch and mechanical stress differences between dissimilar wafer materials, enabling successful bonding without direct stress transmission between the heterogeneous substrates

Inventive Principle:

Principle #24Intermediary (Mediator)

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 reduces mechanical and thermal stresses between wafers, minimizing warpage and enhancing bonding quality, resulting in more robust multi-layer wafer structures with improved manufacturing yields and reduced defects.

Implementation Method 1

low temperature bonding the two heterogeneous wafers to adhere the under bump metallization pads together via the conductive means

Methodology Applied

Scientific EffectLow temperature bonding: Soldering

Implementation Method 2

applying a conductive means above the under bump metallization pads on at least one of the two heterogeneous wafers; and low temperature bonding the two heterogeneous wafers to adhere the under bump metallization pads together via the conductive means to form a multi-layer wafer pair

Methodology Applied

Scientific EffectStress compensation: Stress Relaxation

Data Source

PatentUS11201138B2Wafer level integration including design/co-design, structure process, equipment stress management and thermal management

Publication Date: 2021.12.14 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A method of manufacturing a multi-layer wafer is provided. Under bump metallization (UMB) pads are created on each of two heterogeneous wafers. A conductive means is applied above the UMB pads on at least one of the two heterogeneous wafers. The two heterogeneous wafers are low temperature bonded to adhere the UMB pads together via the conductive means. At least one stress compensating polymer layer may be applied to at least one of two heterogeneous wafers. The stress compensating polymer layer has a polymer composition of a molecular weight polymethylmethacrylate polymer at a level of 10-50% with added liquid multifunctional acrylates forming the remaining 50-90% of the polymer composition.