Planar Passivation Layers for Thick Metal Thermal Cracking
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Solution Overview
Problem
Standard passivation layers for thick metals are prone to cracking during temperature cycling tests due to mismatched thermal expansion coefficients, limiting design flexibility and increasing stress intensity factors.
Innovation Solution
A fully flat passivation scheme is implemented using High Density Plasma Silicon Dioxide (HDP SiO2) and Silicon Rich Oxide (SRO) layers, followed by Chemical Mechanical Planarization and a silicon nitride layer, with titanium nitride barrier layers to minimize stress and prevent cracking, allowing for thicker metallization without adhering to restrictive design rules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard passivation layers are used for thick metals, then the passivation layer can be formed, but cracks arise during temperature cycling tests due to mismatched thermal expansion coefficients
Solution Approach 1:
The passivation layer is divided into multiple sub-layers (first passivation layer, second passivation layer, third passivation layer) with different material compositions and thicknesses. Each layer serves a specific function: the first layer provides stress relief, the second layer provides planarization, and the third layer provides final protection. This segmentation allows the structure to accommodate thermal expansion differences without cracking.
Solution Approach 2:
The patent uses composite material structures where different dielectric materials are combined in a layered configuration. The first passivation layer uses a dielectric material with specific mechanical properties, while subsequent layers use different materials optimized for their respective functions. This composite approach enables the passivation structure to handle thermal stress while maintaining planarity and protection.
2Reliability
If metal slots or numerous design rule constraints are implemented to reduce passivation cracks, then cracking is reduced, but design flexibility is limited and design rules become more complex
Solution Approach 1:
Instead of using metal slots or restrictive design rules, the patent segments the passivation function into multiple layers that can be deposited conformally over continuous metal structures. This allows designers to route thick metal layers freely without needing to insert slots or adhere to complex spacing rules, while still preventing cracks through the layered structure's inherent stress management capabilities.
Solution Approach 2:
The patent changes the parameters of the passivation structure by introducing multiple layers with varying thicknesses and material properties. The first layer has greater thickness to provide stress relief, while subsequent layers have reduced thickness for planarization. This parameter variation enables crack prevention without imposing constraints on metal layer design, thereby maintaining design flexibility.
3Area of stationary object
If the passivation layer is made conformal to thick metal layers, then complete coverage is achieved, but stress intensity factors increase during temperature cycling
Solution Approach 1:
The conformal passivation layer is segmented into multiple sub-layers with different thickness profiles. The first layer maintains conformality for complete coverage, while subsequent layers are planarized to reduce stress concentration. This segmentation allows the structure to achieve both complete coverage and reduced stress intensity during thermal cycling.
Solution Approach 2:
The patent addresses the stress problem by transitioning from a single-layer conformal structure to a multi-layer structure with vertical dimensionality. By adding the height dimension through layered construction with varying thicknesses, the solution distributes stress more effectively while maintaining complete surface coverage, thereby reducing stress intensity factors during temperature cycling.
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 solution effectively reduces stress-induced cracking and eliminates passivation layer failures during thermal events and temperature cycling, enabling more flexible design options for thick metallization without additional design constraints.
Implementation Method 1
depositing over said metal component a substantially planar High Density Plasma Silicon Dioxide (HDP SiO2) layer
Implementation Method 2
followed by Chemical Mechanical Planarization
Implementation Method 3
titanium nitride barrier layers to minimize stress and prevent cracking
Data Source
AI summary
A method of forming a semiconductor device, the method including the steps of providing a metal component having a top surface, and providing a passivation layer over the metal component such that an outer layer of the passivation layer is substantially planar and does not extend below the top surface of the metal component.