Redistribution Layer Step Height Control via Dummy TSV Alignment
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Solution Overview
Problem
Conventional redistribution layers (RDLs) using aluminum face challenges with step height issues due to poor step coverage in physical-vapor deposition, requiring additional processes for alignment marks, which can lead to seam problems.
Innovation Solution
The solution involves forming a substrate with dummy TSVs for alignment and functional TSVs, where a redistribution layer is created with step heights over functional TSVs less than a predetermined value and over dummy TSVs greater than this value, using a method that includes forming TSVs, planarizing, and depositing a dielectric layer followed by forming the RDL over the remaining dielectric layer and exposed TSV ends.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If physical-vapor deposition is used to deposit aluminum film for RDL, then the deposition process is simple and cost-effective, but poor step coverage is achieved leading to seam issues
Solution Approach 1:
The patent performs preliminary planarization by removing the dielectric layer from over the TSVs before depositing the aluminum RDL. This pre-prepares the surface to reduce step height, allowing the subsequent PVD process to achieve adequate step coverage without requiring complex deposition techniques
Solution Approach 2:
The patent changes the physical parameters of the substrate surface by planarizing and removing dielectric material, thereby reducing the step height parameter. This parameter modification enables the PVD process to achieve sufficient step coverage that would otherwise be unattainable with the original larger steps
2Measurement precision
If additional processes are added to generate alignment marks for aluminum RDL lithography, then alignment accuracy is improved, but process complexity and seam issues increase
Solution Approach 1:
The patent makes the TSVs serve multiple functions: they act as both electrical interconnects and as alignment marks for lithography. By forming TSVs that protrude through the substrate, they provide natural alignment features for the aluminum RDL patterning process, eliminating the need for separate alignment mark structures
Solution Approach 2:
The patent merges the function of electrical interconnection and alignment reference into a single structure (the TSV). This consolidation eliminates the need for separate alignment mark processes while maintaining alignment accuracy, thereby reducing overall process complexity
3Measurement precision
If step height is increased to improve alignment mark visibility, then alignment accuracy is improved, but seam issues in aluminum film are worsened
Solution Approach 1:
The patent performs preliminary planarization to reduce the step height before aluminum deposition. This pre-reduction of step height ensures that when the aluminum RDL is deposited, the film can continuously bridge across the TSVs without forming seams, while the TSVs still protrude sufficiently to serve as alignment marks
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 seam issues and improves alignment accuracy, enhancing the manufacturing efficiency and reliability of RDLs by controlling step heights and utilizing dummy TSVs as alignment marks.
Implementation Method 1
such as may be attributable to poor step coverage attainable with physical-vapor deposition (PVD) of the aluminum film
Data Source
AI summary
An apparatus comprising a substrate with multiple electronic devices. An interconnect structure formed on a first side of the substrate interconnects the electronic devices. Dummy TSVs each extend through the substrate and form an alignment mark on a second side of the substrate. Functional TSVs each extend through the substrate and electrically connect to the electronic devices. A redistribution layer (RDL) formed on the second side of the substrate interconnects ones of the dummy TSVs with ones of the functional TSVs. Step heights of the RDL over the functional TSVs are less than a predetermined value, whereas step heights of the RDL over the dummy TSVs are greater than the predetermined value.