Composite Spacer Structure for Optoelectronic Device Chip
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Solution Overview
Problem
Traditional wafer-level chip scale packaging (WLCSP) methods for digital imaging devices face challenges in achieving precise control of spacer thickness, leading to significant thickness variations and optical performance issues, as well as inadequate structural strength to withstand environmental stresses.
Innovation Solution
A composite spacer structure incorporating an adhesive material with dispersed particles, which can be conductive or insulating, is used to provide a robust and uniform spacing between substrates, allowing for precise optical focus control and enhanced mechanical resilience.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a thick photoresist layer is used for spacers in WLCSP, then the spacer height can be achieved, but severe wafer uniformity issue occurs with ±(10-20)％ thickness variation across the wafer
Solution Approach 1:
The patent uses a composite spacer structure consisting of a first spacer layer (photoresist) and a second spacer layer (different material) with different refractive indices. This composite structure enables lithography penetration through the first layer while the second layer provides the final spacer height, achieving both sufficient height and uniform thickness control within ±2.5% variation.
2Ease of manufacture
If traditional single-material spacer structure is used, then manufacturing is simpler, but the structure lacks sufficient strength to resist tensile or compressive stress and shearing force
Solution Approach 1:
The patent employs a composite spacer structure with a first spacer layer made of photoresist material and a second spacer layer made of a different material. This composite construction provides enhanced mechanical strength to resist tensile, compressive, and shearing forces while maintaining manufacturability through established lithography processes.
3Length of stationary object
If thick photoresist layer is used for spacers, then the spacer height is sufficient, but the thickness variation causes severe defocus issue when pixel size is smaller than 2.2 μm
Solution Approach 1:
The composite spacer structure with two layers of different materials allows the first layer to be penetrated by lithography light while the second layer provides the precise final height. This achieves spacer heights sufficient for optical performance while controlling thickness variation within ±2.5%, preventing defocus issues in high-resolution sensors with pixel sizes below 2.2 μm.
4Reliability
If the package layer is bonded with another substrate through adhesive, then the cavity is formed, but the laminated structure does not provide enough strength to resist environmental stresses
Solution Approach 1:
The composite spacer structure with a first photoresist layer and a second material layer provides enhanced mechanical strength to the bonded package structure. This composite construction resists environmental stresses including tensile, compressive, and shearing forces that would otherwise cause cracking or delamination in traditional single-material structures.
Data Source
AI summary
An optoelectronic device chip, and a method for making the chip, are disclosed. The chip comprises a device substrate, an optically transparent upper substrate, and a composite spacer layer which includes an adhesive material and a plurality of particles dispersed in said adhesive material. The distance between the device substrate and the upper substrate is controlled by the thickness of the composite spacer layer so that the variation is within the depth of focus of optical system.