Multi-Layer Light Shielding for Optical Fingerprint Sensors
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Solution Overview
Problem
Existing optical fingerprint sensors face challenges in production yield and reliability due to issues with the light shielding layer, which can collapse if too soft or crack if too rigid, affecting the semiconductor device's performance.
Innovation Solution
A multi-layer light shielding structure is implemented, with varying hardness levels between the bottom and top layers to prevent collapse and cracking, ensuring the light shielding layer's stability during the planarization process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the light shielding layer is made soft to prevent cracking, then reliability improves, but collapse occurs during planarization
Solution Approach 1:
The light shielding layer is divided into multiple sub-layers (first light shielding layer and second light shielding layer) with different hardness characteristics. The first layer provides softness to prevent cracking, while the second layer provides hardness to maintain shape stability during planarization, resolving the contradiction between reliability and shape retention.
Solution Approach 2:
Different regions of the light shielding layer are given different hardness properties. The bottom layer (first light shielding layer) is made softer to prevent cracking at the interface with the transparent pillar, while the top layer (second light shielding layer) is made harder to resist collapse during subsequent planarization processes.
2Manufacturing precision
If the light shielding layer is made rigid to maintain shape, then manufacturing precision improves, but cracking occurs during planarization
Solution Approach 1:
The light shielding layer is segmented into multiple layers with different mechanical properties. The first light shielding layer has lower hardness to prevent cracking, while the second light shielding layer has higher hardness to maintain shape precision during planarization, thus resolving the contradiction between manufacturing precision and reliability.
Solution Approach 2:
The light shielding layer is constructed as a composite structure with at least two different materials having different hardness values. This composite approach allows the structure to simultaneously achieve the flexibility needed to prevent cracking and the rigidity needed to maintain manufacturing precision.
3Device complexity
If a single-layer light shielding structure is used, then device complexity is reduced, but production yield decreases due to collapse or cracking
Solution Approach 1:
The light shielding layer is divided into multiple functional layers, each optimized for specific requirements. This segmentation increases structural complexity but eliminates the collapse-cracking problem that plagues single-layer designs, thereby significantly improving production yield despite the added complexity.
Solution Approach 2:
The hardness parameter of the light shielding layer is varied across different layers. By changing the hardness parameter from the first layer to the second layer, the structure achieves optimal performance for both crack prevention and shape retention, resolving the yield issue without requiring overly complex multi-component structures.
Data Source
AI summary
A method for forming a semiconductor device is provided. The method includes forming a sensor pixel array in a substrate, forming several transparent pillars over the substrate, and forming a light shielding layer over the substrate to cover the transparent pillars. The sensor pixel array has several sensor pixels, and each of the transparent pillars is correspondingly disposed on one of the sensor pixels of the sensor pixel array. The light shielding layer is a multi-layer structure. The method further includes performing a planarization process to expose the top surface of the transparent pillars.