Optical Sensor Manufacturing with Low-Alpha Glass Substrate
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Solution Overview
Problem
The manufacturing of optical sensors using light transmissive substrates that emit low levels of α rays or crystal materials is hindered by warping and cracking issues due to thermal expansion, leading to reduced yield rates and reliability concerns.
Innovation Solution
A method involving a light transmissive substrate with low α-ray emitting members attached to a semiconductor wafer, fixed using a similar linear expansion coefficient glass and an organic adhesive, to minimize α-ray influence and prevent warping, involving a borosilicate glass with a linear expansion coefficient matching the silicon substrate and a low-α-ray glass for absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light transmissive substrate formed of a crystal that emits no α rays or a glass that emits small amounts of α rays is fixed to a wafer, then the influence of α rays to the image pickup device chip is reduced, but warping of the wafer or light transmissive substrate or both occurs due to thermal expansion
Solution Approach 1:
The patent applies parameter changes by carefully selecting a glass material whose linear expansion coefficient matches that of the silicon wafer. This parameter matching prevents differential thermal expansion during manufacturing processes, thereby eliminating warping while maintaining low α-ray emission properties of the glass substrate.
Solution Approach 2:
The patent employs a composite material approach by using a specifically formulated glass that combines two critical properties: low α-ray emission and a linear expansion coefficient matched to silicon. This composite glass material simultaneously addresses both the radiation protection requirement and the thermal expansion compatibility requirement.
2Object-affected harmful factors
If a light transmissive substrate formed of a crystal that emits no α rays or a glass that emits small amounts of α rays is fixed to a wafer, then the influence of α rays to the image pickup device chip is reduced, but a crack or peeling occurs if warping takes place between the fixed light transmissive substrate and the wafer
Solution Approach 1:
By changing the material parameter (linear expansion coefficient) to match between the glass substrate and silicon wafer, the patent prevents warping that would otherwise lead to mechanical stress, cracking, or peeling during thermal cycles in manufacturing and operation, thereby ensuring long-term reliability.
Solution Approach 2:
The patent applies beforehand cushioning by pre-matching the thermal expansion coefficients of the bonded materials. This preventive measure eliminates the root cause of future mechanical failures (warping-induced cracking and peeling) before they can occur during manufacturing or device operation.
3Productivity
If WLCSP is obtained by fixing a wafer-state semiconductor substrate including image pickup devices and a light transmissive substrate together and dividing the fixed substrates into individual chips, then the manufacturing cost can be reduced and a small and thin optical sensor can be realized, but warping occurs due to thermal expansion
Solution Approach 1:
The patent enables cost-effective WLCSP manufacturing by selecting a glass substrate with a linear expansion coefficient matched to silicon. This parameter matching prevents warping during the wafer-level bonding and subsequent dicing processes, ensuring high yield and manufacturing precision while maintaining the cost and size advantages of WLCSP technology.
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 reduces the impact of α rays on the image pickup device chip and suppresses warping, enhancing the reliability and yield of optical sensors by matching thermal expansion coefficients and using a low-α-ray glass for absorption, thereby improving the manufacturing process.
Implementation Method 1
each of the plurality of light transmissive members emitting α rays in an amount smaller than or equal to 0.05 c/cm2·h
Implementation Method 2
fixing the light transmissive substrate onto the semiconductor wafer by a fixing member
Data Source
AI summary
A method of manufacturing an optical sensor includes providing a semiconductor wafer including a plurality of pixel areas, providing a light transmissive substrate including a light transmissive wafer with a plurality of light transmissive members attached thereto, the plurality of light transmissive members being arranged on a first main surface of the light transmissive wafer and each of plurality of light transmissive members emitting α rays, an amount of the α rays being smaller than or equal to 0.05 c/cm2·h, fixing the light transmissive substrate onto the semiconductor wafer together by a fixing member, and dividing the semiconductor wafer and the light transmissive substrate that are fixed together into individual pieces.