CMP Metal Layer Planarization Over Photoresist
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Solution Overview
Problem
The existing methods for fabricating Digital Micromirror Devices (DMDs) face challenges in achieving a smooth mirror layer, which is critical for maintaining high contrast ratios, as conventional chemical mechanical planarization processes are believed to destroy the metal layer formed over a photoresist layer.
Innovation Solution
A chemical mechanical planarization process is employed to smooth the metal layer without shearing it from the photoresist layer, utilizing specific conditions such as down force, platen speed, and slurry composition to maintain the integrity of the metal layer, allowing for the reduction of surface roughness and precise thickness control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional chemical mechanical planarization process is used on metal layer over photoresist, then planarization may be achieved, but the metal layer is destroyed (sheared from photoresist)
Solution Approach 1:
The patent applies parameter changes by modifying the down force applied during CMP from conventional high values to a controlled range of 0.5-2.0 psi, and adjusting platen speed to 1-5 rpm. These parameter modifications enable planarization to proceed without exceeding the shear strength threshold that would cause metal layer failure, thus resolving the contradiction between achieving smoothness and maintaining integrity
Solution Approach 2:
The patent introduces a photoresist layer as an intermediary protective medium between the metal layer and the CMP polishing pad. This photoresist layer acts as a cushion that distributes the polishing pressure and prevents direct mechanical damage to the metal layer while still allowing the CMP process to achieve the desired planarization effect
2Manufacturing precision
If conventional CMP process is used, then planarization may be attempted, but contrast ratio is reduced due to surface roughness
Solution Approach 1:
By changing the CMP parameters (down force to 0.5-2.0 psi, platen speed to 1-5 rpm), the patent achieves superior surface smoothness with average roughness Ra < 5 nm. This enhanced smoothness directly improves the mirror layer's optical performance, maximizing light reflection efficiency and thereby enhancing the contrast ratio between bright and dark states
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 achievement of a smooth mirror layer with reduced surface roughness, enhancing the contrast ratio and allowing for precise tailoring of the metal layer thickness, thereby improving the performance of the micro pixel array.
Implementation Method 1
chemical mechanical planarization process
Implementation Method 2
chemical mechanical planarization process
Data Source
AI summary
The present invention provides a method for planarizing a metal layer, and a method for manufacturing a micro pixel array. The method for planarizing the metal layer, without limitation, may include the steps of forming a metal layer over a photoresist layer, and then planarizing the metal layer using a chemical mechanical planarization process.