Backside Illuminated Sensor Substrate Thickness Variation

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Solution Overview

Problem

Backside illuminated image sensors face challenges in uniformly sensing different wavelengths of light due to varying effective absorption depths in the substrate, with blue light experiencing a more shallow absorption depth compared to red light, leading to uneven light sensitivity across pixels.

Innovation Solution

The solution involves a semiconductor substrate with varying absorption depths beneath each pixel type (red, green, and blue) and the use of color filters and microlenses to optimize light exposure, along with a planarization layer and metal layers to enhance light sensitivity uniformity across different wavelengths.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a uniform substrate thickness is used in backside illuminated sensors, then manufacturing is simplified, but light sensitivity becomes uneven across different wavelengths

Engineering Contradiction:

Improvesubstrate manufacturing simplicityVSAvoidlight sensitivity uniformity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The substrate is engineered with spatially varying thickness: thinner regions (first thickness) beneath blue pixels for shallow absorption, and thicker regions (second thickness) beneath red pixels for deep absorption. This local differentiation enables each pixel type to optimally sense its corresponding wavelength while maintaining a single manufacturing process.

Inventive Principle:

Principle #3Local quality

2Illumination intensity

If the substrate is thinned to allow light transmission, then backside illumination is enabled, but mechanical strength and structural integrity are reduced

Engineering Contradiction:

Improvelight transmission capabilityVSAvoidsubstrate mechanical strength

Core Design Contradiction:

Illumination intensityVSStrength

Solution Approach 1:

The substrate thickness parameter is varied across different regions to optimize both light transmission and mechanical strength. By controlling the thickness distribution (thinner under blue pixels, thicker under red pixels), the design achieves adequate light transmission for backside illumination while maintaining sufficient structural integrity through strategically placed thicker regions.

Inventive Principle:

Principle #35Parameter changes

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 results in a more even distribution of light sensitivity across pixels for different wavelengths, improving the performance and spectral response of backside illuminated sensors.

Implementation Method 1

different wavelengths of radiation to be sensed experience different effective absorption depths in the substrate. For example, blue light experiences a more shallow effective absorption depth, as compared to red light.

Methodology Applied

Scientific EffectLight absorption: Absorption (EM radiation)

Data Source

PatentUS8790954B2Method of making wafer structure for backside illuminated color image sensor

Publication Date: 2014.07.29 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

An integrated circuit device is provided. The integrated circuit device can include a substrate; a first radiation-sensing element disposed over a first portion of the substrate; and a second radiation-sensing element disposed over a second portion of the substrate. The first portion comprises a first radiation absorption characteristic, and the second portion comprises a second radiation absorption characteristic different from the first radiation absorption characteristic.