Resist Coating in Deep Recesses via Inversion and Ultrasonic Air Removal
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Solution Overview
Problem
Conventional methods face difficulties in achieving a uniform resist film over the entire inner surface of recesses on substrates, particularly those with large depth-to-width ratios, due to challenges in coating the inner walls of depressions such as VIA holes.
Innovation Solution
A method involving filling the recess with a resist solution, followed by heating to evaporate the solvent, resulting in a continuous resist layer on the inner walls and surface, and subsequent overflow coating to ensure complete coverage, combined with ultrasound air removal and optional surface cleaning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If spray coating is used to coat the inner surface of a depression, then the coating process is simple and fast, but the inner walls of deep recesses cannot be completely covered
Solution Approach 1:
Instead of spraying resist from above onto the depression, the invention inverts the approach by filling the depression with liquid resist from the bottom up, allowing the resist to naturally coat the inner walls through capillary action and gravity, ensuring complete coverage even in deep recesses
Solution Approach 2:
The invention uses liquid resist filling combined with ultrasonic vibration to remove air bubbles and ensure complete wetting of the inner surface, leveraging fluid dynamics to achieve uniform coating in geometries that spray coating cannot access
2Device complexity
If a resist solution is applied to both the substrate surface and cavity in a single step, then the process is simplified, but air trapped in the cavity prevents uniform coating
Solution Approach 1:
The invention applies ultrasonic vibration to the substrate during or after resist filling to mechanically dislodge and remove trapped air bubbles from the cavity, ensuring the resist solution can completely wet the inner surface without air pockets preventing uniform coating
Solution Approach 2:
The invention changes the physical state and properties of the resist solution by controlling temperature, viscosity, and application timing to optimize wetting behavior and air bubble removal, enabling single-step filling that achieves uniform coating despite the complexity of air entrapment
3Ease of manufacture
If conventional coating methods are used on deep recesses, then the process is simple, but the inner walls are not completely covered with resist
Solution Approach 1:
The invention performs preliminary actions by first filling the depression with resist solution before applying resist to the surface, and using ultrasonic vibration to pre-remove air bubbles, ensuring that when the resist dries, complete and uniform coverage of the inner walls is achieved
Solution Approach 2:
The invention uses liquid resist solution as an intermediary medium that can flow into and completely wet the inner surfaces of deep recesses, unlike spray coating which cannot reach all areas, ensuring reliable coating coverage while maintaining process simplicity
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 achieves a continuous and uniform resist layer on the inner walls and surface of recesses, enhancing precision and completeness of the coating, which is advantageous for subsequent processing and contacting in microelectromechanical systems.
Implementation Method 1
the substrate is heated such that the solvent of the resist solution evaporates and the bottom and at least sections of the inner walls of the depression bordering the bottom are coated with the resist
Implementation Method 2
Any air trapped in the cavity by the resist is then removed using, for example, ultrasound
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a method for resist coating the inner surface of a depression (110) in the surface of a substrate (100), in which the depression is filled with a resist solution. Air trapped in the depression is removed by applying ultrasound and/or a nitrogen stream or ultrasound and vacuum. The surface of the substrate is cleaned by centrifugation. The substrate is heated such that the solvent of the resist solution evaporates and the bottom and at least sections of the inner wall (112) of the depression adjacent to the bottom are coated with the resist (131). The surface of the substrate (120) is again coated with a resist such that sections of the inner walls (112) of the depression (110) adjacent to the surface of the substrate (100), for example above a line (133), are also coated, wherein the width of the depression is 10 to 100 µm.Furthermore, a substrate with such a coating is described.