Water Soluble PVA Mask for Laser Plasma Substrate Dicing
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Solution Overview
Problem
Conventional dicing techniques for thin semiconductor substrates face challenges such as microcrack formation, delamination, and precise ablation depth control, and plasma dicing is limited by high implementation costs and masking issues due to substrate topography and material selectivity.
Innovation Solution
A hybrid dicing process combining femtosecond laser scribing and plasma etching, using a water-soluble mask layer of poly-vinyl alcohol (PVA) to protect ICs and pattern the substrate, allowing for precise exposure and etching of regions between ICs without damaging the underlying layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional scribing or sawing is used for thin substrate singulation, then the substrate can be separated into individual devices, but microcrack formation, delamination, and chipping occur
Solution Approach 1:
The patent replaces mechanical scribing and sawing processes with a hybrid laser-plasma system. A femtosecond laser performs contactless ablation to create precise scribe lines, followed by plasma etching to complete the separation. This eliminates mechanical contact that causes microcracks, delamination, and chipping in thin substrates.
Solution Approach 2:
The patent utilizes phase transition of water-soluble mask material (PVA) through laser heating. The laser rapidly heats the PVA mask above its glass transition temperature, causing it to soften and facilitate cleaner separation. This controlled phase transition enables precise ablation without damaging underlying device layers.
2Productivity
If plasma dicing is used, then singulation can be achieved, but implementation cost increases and masking becomes problematic
Solution Approach 1:
The patent introduces a water-soluble PVA mask as an intermediary layer between the laser and substrate. This mask absorbs laser energy preferentially, enabling controlled ablation and protecting sensitive device layers from direct laser exposure. The mask can be easily removed by water rinsing, simplifying the overall process compared to traditional plasma masking methods.
Solution Approach 2:
The patent changes the physical state and properties of the PVA mask through controlled laser heating. By adjusting laser parameters (pulse duration, energy density, scanning speed), the mask material undergoes controlled softening and ablation, enabling precise pattern transfer without requiring complex masking steps.
3Ease of manufacture
If laser scribing is used to pattern the mask, then lithography can be eliminated, but precise control of kerf width and ablation depth is required
Solution Approach 1:
The patent implements a feedback-controlled laser system with real-time monitoring of ablation depth and kerf width. Sensors detect process parameters and dynamically adjust laser power, scanning speed, and pulse frequency to maintain precise dimensional control. This closed-loop control enables consistent singulation quality without traditional lithography alignment steps.
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 method effectively singulates ICs with minimal thermal damage, eliminates the need for lithography, and reduces costs by enabling precise control over kerf width and ablation depth, while maintaining the integrity of the substrate and passivation layers.
Implementation Method 1
The mask material has a glass transition temperature between 50 C and 150 C
Implementation Method 2
The mask and substrate are patterned with a laser scribing process
Implementation Method 3
a laser scribing process to provide a patterned mask with gaps, exposing regions of the substrate between the ICs
Implementation Method 4
The substrate is then plasma etched through the gaps in the patterned mask to singulate the ICs into chips
Implementation Method 5
a water soluble mask layer of a poly-vinyl alcohol (PVA) over a front side of a silicon substrate
Data Source
AI summary
Methods of dicing substrates having a plurality of ICs are disclosed. A method includes forming a mask comprising a water soluble material layer over the semiconductor substrate. The mask is patterned with a femtosecond laser scribing process to provide a patterned mask with gaps. The patterning exposes regions of the substrate between the ICs. The substrate is then etched through the gaps in the patterned mask to singulate the IC and the water soluble material layer is washed off.