Polishing Stop Layer for Uniform Electrical Contact Exposure
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Solution Overview
Problem
The existing process for reestablishing electrical contact on electronic chips is non-uniform due to inhomogeneous mechanical-chemical polishing, leading to issues like short circuits and open circuits, particularly in regions with varying chip density and substrate wear, causing overetching and insufficient polishing.
Innovation Solution
A method involving a stack of flattening layers with a first material for selective chemical etching, an intermediate layer, and a second material, where the intermediate layer acts as a polishing stop to reduce non-uniformity by controlling the polishing process, ensuring uniform exposure of electrical contact pads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mechanical-chemical polishing is performed on the flattening layer, then the surface is flattened and electrical contact is reestablished, but the polishing becomes non-uniform causing overetching at the center and insufficient polishing at the edges
Solution Approach 1:
The flattening layer is divided into multiple segments with different materials (first flattening layer material and second flattening layer material) that have different etching rates. This segmentation allows the polishing process to be controlled differently across the substrate surface, preventing non-uniform polishing and ensuring reliable electrical contact across all regions.
Solution Approach 2:
Different regions of the flattening layer are assigned different material compositions tailored to their specific polishing needs. Regions prone to overetching use materials with lower etching rates, while regions needing more polishing use materials with higher etching rates. This local customization of material properties ensures uniform polishing across the entire substrate.
2Ease of manufacture
If a single-material flattening layer is used, then the process is simple, but selective chemical etching cannot control the polishing rate variations across the substrate
Solution Approach 1:
The flattening layer is constructed as a composite structure with multiple materials having different etching characteristics. This composite approach enables precise control over the polishing process by leveraging the different etching rates of the constituent materials, achieving high manufacturing precision while managing the increased structural complexity.
3Productivity
If polishing continues until reaching the passivation layer, then electrical contact pads are exposed, but overetching causes short circuits and underetching leaves open circuits
Solution Approach 1:
The flattening layer is designed with predetermined thickness and material composition that anticipates the polishing process. By pre-configuring the layer to be removed during polishing, the process automatically stops at the correct depth (exposing the passivation layer without penetrating it) without requiring complex real-time monitoring or adjustment, thus maintaining both efficiency and reliability.
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 significantly limits the non-uniformity of mechanical-chemical polishing, reducing the risk of short and open circuits by maintaining consistent polishing across the substrate, even in areas with varying chip density and substrate wear.
Implementation Method 1
mechanical-chemical polishing using selective chemical etching between the second material and the material of the intermediate layer
Implementation Method 2
polishing the stack, by mechanical-chemical polishing, until reaching the passivation layer coating the electrical contact pads
Data Source
Figure 1~3
Figure 4a~4f
Figure 5~6c
AI summary
A method for re-establishing electrical contact, comprising the steps: a) providing electronic chips (P), surmounted by electrical contact pads (1), and formed on a substrate (2); the pads (1) and the substrate (2) being coated with a passivation layer (3); b) forming a stack on the passivation layer (3), comprising: - a first flattening layer (4), made of a first material allowing selective chemical etching with respect to the passivation layer (3), and formed on the passivation layer (3) so as to be flush with the top of the pads (1); - a second flattening layer (5), made of a second material; - an interlayer layer (CI), made of a material allowing selective chemical etching of the second material; c) polishing the stack, by mechano-chemical polishing, until reaching the passivation layer (3) coating the pads (1);d) etch the passivation layer (3) coating the studs (1) so as to expose the top of the studs (1).;