High-Aspect Ratio Trench Metallization Without Metal Mask Defects
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Solution Overview
Problem
Conventional methods face challenges in patterning vertical sidewalls with aspect ratios greater than 20 in silicon substrates using conventional photoresists, often resulting in re-sputtering and defects due to metal masking, and traditional metal filling techniques require expensive cleanroom processing.
Innovation Solution
A method involving a patterned photoresist on a mask layer using a Bosch process to form high-aspect ratio trenches with vertical sidewalls, followed by filling these trenches with a mixture of high-Z nano-particles in a carrier fluid using screen printing or roll printing, reducing processing steps and equipment costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photoresists are used to pattern vertical sidewalls in silicon substrates, then the patterning process is simple and cost-effective, but the maximum achievable aspect ratio is limited to below 20
Solution Approach 1:
The patterning process is segmented into two distinct stages: first forming a mask layer pattern, then depositing photoresist and performing a second patterning step. This segmentation allows each stage to be optimized independently, enabling achievement of aspect ratios greater than 20 while maintaining process simplicity.
Solution Approach 2:
A mask layer is deposited and patterned before the photoresist application. This preliminary action creates a robust foundation that enables subsequent formation of high-aspect ratio structures with vertical sidewalls, overcoming the limitations of direct photoresist patterning.
2Manufacturing precision
If metal masking is employed to achieve high aspect ratios, then the aspect ratio can be increased beyond 20, but re-sputtering and re-deposition of metal into etched regions occurs causing defects
Solution Approach 1:
A non-metallic mask layer material is used as an intermediary between the substrate and the photoresist. This intermediary material prevents direct metal-photoresist interaction during etching, eliminating re-sputtering and re-deposition defects while still enabling high aspect ratio formation.
Solution Approach 2:
The problematic metal masking step is extracted and replaced with a non-metallic mask layer approach. This removal of the metal masking function eliminates the source of re-sputtering and re-deposition defects while maintaining the ability to achieve aspect ratios greater than 20.
3Manufacturing precision
If traditional metal filling techniques are used to fill deep trenches, then complete filling can be achieved, but expensive cleanroom processing equipment is required
Solution Approach 1:
A disposable mixable paste formulation is used for filling trenches instead of requiring expensive cleanroom metal deposition equipment. The paste can be applied using simple dispensing or printing methods, dramatically reducing processing costs while achieving complete trench filling.
Solution Approach 2:
Traditional mechanical vacuum deposition systems (sputtering, evaporation) are replaced with a chemical paste filling approach. The paste is applied through simple dispensing, printing, or dipping methods, eliminating the need for expensive cleanroom equipment while achieving complete trench filling.
4Manufacturing precision
If conventional trench filling methods are used, then complete filling of deep trenches can be achieved, but the processing time and complexity increase significantly
Solution Approach 1:
A mixable paste with optimized rheology is used that can be rapidly applied and cured. The paste formulation allows for quick filling of deep trenches using simple dispensing or printing methods, dramatically reducing processing time compared to traditional multi-step metal deposition processes.
Solution Approach 2:
The paste utilizes phase transition from liquid to solid through curing (thermal or chemical). This phase transition enables complete filling of deep trenches in a single step followed by rapid curing, eliminating the need for slow, multi-step conventional filling processes.
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 enables the fabrication of high-aspect ratio metallized structures with reduced processing complexity and cost, achieving aspect ratios greater than 20:1, suitable for applications like X-ray imaging and MEMS devices, with scalable and flexible fabrication across various substrate sizes.
Implementation Method 1
The photoresist layer is patterned to form a pattern
Implementation Method 2
The mask layer is etched through the pattern to expose the substrate. The substrate is etched through the pattern to form a structure comprising a plurality of trenches having vertical sidewalls
Implementation Method 3
The carrier fluid is cured to the solid state to form the metallized grid structure
Implementation Method 4
A plurality of nano-particles are suspended within the cured carrier fluid
Data Source
AI summary
The present techniques relate to various aspects of forming and filling high-aspect ratio trench structures (e.g., trench structures having an aspect ratio of 20 or greater, including aspect ratios in the range of 20:1 up to and including 50:1 or greater) combined with trench opening widths ranging from 0.5 micron to 50 microns. By way of example, patterned substrate described herein includes a substrate, a mask layer deposited on the substrate, and a photoresist layer deposited on the mask layer. The photoresist layer is patterned to form a pattern and the mask layer is etched through the pattern to expose the substrate. The substrate is etched through the pattern to form a structure comprising a plurality of trenches having vertical sidewall. The photoresist layer remains on the mask layer during etching of the substrate.