Backside Illuminated CMOS Sensor Cavity Etching
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Solution Overview
Problem
The existing fabrication methods for backside-illuminated (BSI) semiconductor image sensors require costly mechanical grinding or chemical-mechanical planarization processes to remove semiconductor materials, which are inefficient and costly.
Innovation Solution
A BSI image sensor design featuring a cavity etched into the semiconductor substrate allows light to reach the light sensing elements with minimal attenuation, incorporating micro-optical devices, anti-reflective films, and vias for electronic signal communication, fabricated without mechanical grinding or CMP processes, using etching techniques like wet or dry etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mechanical grinding or CMP process is used to remove semiconductor materials for BSI image sensor, then the light sensing elements can be located close to the backside surface, but the fabrication cost increases and the process becomes complex
Solution Approach 1:
The patent replaces mechanical grinding and CMP processes with a chemical etching process using KOH solution. The etching process selectively removes semiconductor material to form cavities, achieving the required precision for light sensing element positioning without mechanical intervention. This substitution eliminates expensive precision machine tools and reduces fabrication complexity.
Solution Approach 2:
The patent changes the processing parameter from mechanical removal to chemical etching. By controlling etching time, temperature, and solution concentration, the cavity depth and shape are precisely controlled to position light sensing elements close to the backside surface. This parameter-based control achieves manufacturing precision while simplifying the fabrication process.
2Manufacturing precision
If mechanical grinding or CMP process is used to remove semiconductor materials for BSI image sensor, then the light sensing elements can be located close to the backside surface, but the fabrication process becomes complex
Solution Approach 1:
The patent replaces mechanical grinding and CMP processes with a chemical etching process using KOH solution. The etching process selectively removes semiconductor material to form cavities, achieving the required precision for light sensing element positioning without mechanical intervention. This substitution eliminates expensive precision machine tools and reduces fabrication complexity.
Solution Approach 2:
The patent changes the processing parameter from mechanical removal to chemical etching. By controlling etching time, temperature, and solution concentration, the cavity depth and shape are precisely controlled to position light sensing elements close to the backside surface. This parameter-based control achieves manufacturing precision while simplifying the fabrication process.
3Ease of operation
If light travels through metallization layers in FSI image sensor, then the image can be received on the front side, but light energy is reflected back reducing sensor sensitivity
Solution Approach 1:
The patent inverts the traditional FSI architecture by implementing BSI architecture where light enters through the backside of the substrate. This inversion allows light to reach photodiodes directly without passing through metallization layers, eliminating reflection losses and improving sensitivity while maintaining image reception capability.
Solution Approach 2:
The patent changes the light entry dimension from the front side to the backside of the substrate. By forming cavities on the backside and positioning photodiodes to face the backside surface, light can travel directly through the substrate thickness to reach sensing elements, avoiding the harmful path through metallization layers.
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 distance light travels through the semiconductor material, enhancing sensitivity and reducing fabrication costs by eliminating the need for expensive mechanical processes, while achieving high device integration and efficient signal processing.
Implementation Method 1
The presence of the cavity allows the image light reaching the light sensing elements through the cavity base surface such that a distance traveled by the image light from outside the semiconductor substrate is shorter
Implementation Method 2
The cavity is formed by etching on the semiconductor substrate
Data Source
AI summary
This invention discloses a backside illuminated image sensor without the need to involve a mechanical grinding process or a chemical-mechanical planarization process in fabrication, and a fabricating method thereof. In one embodiment, an image sensor comprises a semiconductor substrate, a plurality of light sensing elements in the semiconductor substrate, and a cavity formed in the semiconductor substrate. The light sensing elements are arranged in a substantially planar manner. The cavity has a base surface overlying the light sensing elements. The presence of the cavity allows the image to reach the light sensing elements through the cavity base surface. The cavity can be fabricated by etching the semiconductor substrate. Agitation may also be used when carrying out the etching.