Offset Bond Pad Isolation Structure for BSI-CIS Light Leakage Control
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Solution Overview
Problem
The fabrication of back-side illuminated CMOS image sensors (BSI-CIS) is complicated and costly due to the need for dielectric structures around bond pads, which can increase light reflection and decrease the reliability of the bond, while placing bond pads on the substrate surface can affect photodetector efficiency and reliability.
Innovation Solution
A bond pad isolation structure is laterally offset from photodetectors, surrounded by a ring-shaped dielectric structure that extends from the front-side to the back-side of the substrate, electrically isolating the bond pad from other devices and reducing current leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dielectric structures are placed around bond pads, then electrical isolation is improved, but light reflection increases and manufacturing complexity increases
Solution Approach 1:
The patent extracts the dielectric structure from the bond pad region by laterally offsetting it, removing the harmful interaction between dielectric materials and incident light while preserving the electrical isolation function through alternative positioning
Solution Approach 2:
The patent transitions from vertical stacking (dielectric over bond pad) to lateral separation (dielectric offset from bond pad), using spatial repositioning to eliminate light reflection while maintaining electrical isolation through the offset configuration
2Reliability
If dielectric structures are placed around bond pads, then electrical isolation is improved, but device complexity increases
Solution Approach 1:
The patent merges the bond pad isolation function with the photodetector isolation structure, using a shared offset dielectric configuration to achieve both electrical isolation objectives simultaneously and reduce overall device complexity
Solution Approach 2:
The offset dielectric structure serves multiple functions: it provides electrical isolation for the bond pad, maintains isolation for photodetectors, and reduces light reflection, thereby simplifying the overall device architecture through multi-functionality
3Reliability
If bond pads are placed on substrate surface, then electrical connection is improved, but photodetector efficiency decreases
Solution Approach 1:
The patent segments the substrate into distinct functional regions with lateral offset: bond pad regions for electrical connection and photodetector regions for light sensing, allowing each to optimize its performance without interfering with the other
Data Source
AI summary
Various embodiments of the present disclosure are directed towards a method for forming a semiconductor device including a shallow trench isolation (STI) structure disposed between a first side and a second side of the semiconductor substrate. An intermetal dielectric structure comprising a first metal interconnect is on the second side. A first etching process is performed to form a first trench extending from the first side of the semiconductor substrate to the STI structure. An etch stop layer is deposited on the first side. A dielectric material is deposited into the first trench to form a dielectric spacer. A second trench is etched during a second etching process. The second trench is aligned with the first trench and extends through the STI structure to the first metal interconnect. A conductive material is deposited into the second trench to form a contact pad that contacts the first metal interconnect.