Dielectric Optical Coating Lift-Off via Soft Bake Micro-Cracking
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Solution Overview
Problem
Conventional lift-off processes for producing light sensors with dielectric optical coatings are inefficient due to long soak durations required for photoresist removal, which increases costs and reduces process margins.
Innovation Solution
Implementing a soft bake process or thermal shock treatment after dielectric optical coating deposition to create micro-cracks in the coating, facilitating faster and more efficient lift-off by enhancing solvent access through photoresist reflow and delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional lift-off process is used for photoresist removal, then complete removal is achieved, but process duration becomes excessively long (hours)
Solution Approach 1:
The patent applies preliminary action by performing a soft bake process before the lift-off step. This soft bake pre-heats and prepares the photoresist and dielectric optical coating structure, creating micro-cracks and reducing adhesion in advance. As a result, the subsequent lift-off process completes photoresist removal much faster (reducing from hours to minutes) while still achieving complete removal, because the preparatory soft bake has already weakened the bonds that would otherwise require prolonged soaking.
Solution Approach 2:
The patent changes the thermal parameter of the photoresist and coating structure by applying a soft bake process at elevated temperature. This temperature parameter change causes the photoresist to reflow and creates micro-cracks in the dielectric optical coating, fundamentally altering the physical state and adhesion properties of the layers. This parameter change enables rapid solvent penetration and photoresist removal during lift-off without compromising complete removal effectiveness.
2Ease of manufacture
If long soak duration is used for photoresist removal, then complete removal is ensured, but production costs increase
Solution Approach 1:
The soft bake process serves as a preliminary action that prepares the structure for efficient lift-off. By pre-heating the photoresist and creating micro-cracks in the dielectric coating before the actual lift-off, the process reduces the time required for solvent penetration and photoresist removal. This preliminary preparation step significantly shortens the overall lift-off duration from hours to minutes, thereby reducing production costs while maintaining complete photoresist removal through the enhanced solvent access created by the micro-cracks.
3Reliability
If conventional lift-off process is used, then photoresist removal is achieved, but process margins are reduced
Solution Approach 1:
The soft bake process changes the thermal and physical parameters of the photoresist and dielectric optical coating, creating a more favorable state for lift-off. The elevated temperature causes photoresist reflow and micro-crack formation, which fundamentally alters the adhesion characteristics. This parameter change increases process margin by making the lift-off step much more robust and predictable, reducing variability and enabling complete removal with significantly reduced process time, thereby improving both reliability and productivity.
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
Significantly reduces the lift-off process duration from hours to minutes, increasing process margins and reducing production costs while maintaining the spectral response shaping necessary for accurate light sensing.
Implementation Method 1
a soft bake process or thermal shock treatment after dielectric optical coating deposition to create micro-cracks in the coating
Implementation Method 2
a soft bake process or thermal shock treatment after dielectric optical coating deposition to create micro-cracks in the coating
Implementation Method 3
facilitating faster and more efficient lift-off by enhancing solvent access through photoresist reflow and delamination
Data Source
AI summary
Light sensors including dielectric optical coatings to shape their spectral responses, and methods for fabricating such light sensors in a manner that accelerates lift-off processes and increases process margins, are described herein. In an embodiment, a light sensor includes a photodetector sensor region formed in a semiconductor substrate, a dielectric optical coating filter covering the photodetector sensor region, and dummy dielectric optical coating features beyond the photodetector sensor region, wherein the dummy dielectric optical features include one or more dummy corners, dummy islands and/or dummy rings. Alternatively, or additionally, the dielectric optical coating filter includes chamfered corners, which improves the thermal reliability of the dielectric optical coating.