Optical Sensor Wafer Bonding Stress Mitigation

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Solution Overview

Problem

Conventional methods for integrating biometric sensors in electronic devices face challenges due to high stress and thermal effects, leading to performance degradation in optical sensors, particularly in fingerprint recognition systems, where infrared cut-off filters and silicon microelectromechanical systems (MEMS) structures cause wafer bonding issues and impact optical properties.

Innovation Solution

A novel sensing apparatus is developed, featuring a silicon MEMS structure bonded onto a passive oxide layer over a CMOS image sensor (CIS) wafer with a buried oxide layer and an infrared cut-off filter (IRCF) on top, where the MEMS structure is formed separately and aligned fusion bonded onto the CIS wafer, and the IRCF is patterned with metal pads outside its design, mitigating stress and thermal effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the infrared cut-off filter (IRCF) is deposited directly on the CMOS image sensor (CIS) wafer before wafer bonding, then the optical filtering function is achieved, but the high stress in the IRCF induces a high bow surface that makes smooth wafer bonding more difficult

Engineering Contradiction:

Improveoptical filtering functionVSAvoidwafer bonding smoothness

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent segments the wafer bonding process into two distinct stages: first bonding the IRCF to the carrier wafer, then bonding the CIS wafer to the carrier wafer. This segmentation allows the IRCF to be bonded under controlled conditions without directly affecting the final CIS wafer bonding quality, resolving the contradiction between achieving optical filtering and maintaining bonding smoothness

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a carrier wafer as an intermediary substrate. The IRCF is first bonded to this carrier wafer, which acts as a buffer that absorbs the stress and bowing effects. This intermediary approach allows the IRCF to maintain its optical filtering function while preventing stress transmission to the CIS wafer during the final bonding process

Inventive Principle:

Principle #24Intermediary (Mediator)

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 enhances the signal-to-noise ratio of incident light and reduces performance degradation, resulting in improved accuracy and reliability of biometric data detection by minimizing stress and thermal impacts on the optical sensors.

Implementation Method 1

a passive oxide layer over the CIS wafer, where a silicon MEMS structure is bonded onto the passive oxide layer. In addition, the sensing apparatus includes a buried oxide layer over the silicon MEMS structure

Methodology Applied

Scientific EffectOxide layer insulation: Dielectric

Implementation Method 2

an infrared cut-off filter (IRCF) over the buried oxide layer... enhances the signal-to-noise ratio of incident light

Methodology Applied

Scientific EffectInfrared light absorption: Absorption (EM radiation)

Implementation Method 3

the MEMS structure is formed separately and aligned fusion bonded onto the CIS wafer

Methodology Applied

Scientific EffectThermal bonding: Welding

Data Source

PatentUS11514707B2Optical sensor and methods of making the same

Publication Date: 2022.11.29 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Optical sensors and their making methods are described herein. In some embodiments, a described sensing apparatus includes: an image sensor; a collimator above the image sensor, wherein the collimator includes an array of apertures; and an optical filtering layer above the collimator, wherein the optical filtering layer is configured to filter a portion of light to be transmitted into the array of apertures.