Buried Pad Structure for Backside Illuminated Image Sensors
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Solution Overview
Problem
Backside illuminated image sensors face challenges in minimizing the level difference between the substrate and the pad structure, which affects the uniformity of coatings and can lead to defects in image formation due to reflected light from the pad structure.
Innovation Solution
The semiconductor device design includes a pad structure that is almost buried in the substrate with a protruding part, minimizing the level difference and using a via structure and isolation insulating layers to ensure electrical connectivity and uniform coating processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the landing pad is formed to protrude from the substrate, then electrical connection is achieved, but a level difference occurs between the landing pad and substrate surface
Solution Approach 1:
The pad structure is divided into multiple segments: a pad electrode embedded in the substrate, an intermediate connection structure, and an upper pad portion. This segmentation allows the pad to maintain electrical connectivity while minimizing protrusion height, resolving the contradiction between reliable connection and flat surface profile.
Solution Approach 2:
The pad electrode is nested within the substrate, with the intermediate connection structure bridging between the embedded electrode and the upper pad portion. This nesting approach allows electrical connection through the substrate while keeping the external profile flat, eliminating the level difference problem.
2Reliability
If the pad structure protrudes from the substrate, then connection is established, but light reflection occurs causing image defects
Solution Approach 1:
By segmenting the pad structure into embedded and external portions, the reflective surface area is minimized. The critical connection function is maintained through the embedded pad electrode and intermediate structure, while the reduced external protrusion decreases light reflection and associated image defects.
3Reliability
If the pad structure protrudes from the substrate, then electrical connection is achieved, but coating uniformity deteriorates
Solution Approach 1:
The segmented pad structure separates the electrical connection function (embedded in substrate) from the external profile (minimally protruding). This allows coating processes to apply uniform layers across the substrate surface without being disrupted by significant pad protrusions, while electrical connectivity is maintained through the embedded architecture.
Data Source
AI summary
A semiconductor device includes a substrate, a circuit layer formed on a first surface of the substrate and including a via pad and an interlayer insulating layer covering the via pad, a via structure configured to fully pass through the substrate, partially pass through the interlayer insulating layer and be in contact with the via pad, a via isolation insulating layer configured to pass through the substrate and be spaced apart from outer side surfaces of the via structure in a horizontal direction and a pad structure buried in the substrate and exposed on a second surface of the substrate opposite the first surface of the substrate.