Resist Coating Speed Control for Uniform Film Thickness
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Solution Overview
Problem
The existing spin coating methods struggle to achieve uniform film thickness on semiconductor wafers when the amount of resist solution is reduced, as rapid drying leads to thinner outer circumference films compared to central films, making it difficult to adjust the thickness uniformly.
Innovation Solution
A resist coating method involving a multi-step rotational speed control: initially rotating the substrate at a first speed, then reducing it to a second speed after solution supply, further reducing it to a third speed or halting, and finally increasing to a fourth speed to spin off the residue, allowing for precise film thickness adjustment and reduced resist solution consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the amount of resist solution dropped on the wafer is reduced, then resist consumption is reduced, but the thickness of the coated film becomes non-uniform
Solution Approach 1:
The patent applies dynamic rotational speed control during the spin coating process. The substrate rotation speed is varied in multiple stages: initially rotating at a first speed during resist solution application, then reducing to a second speed after application ends, and finally increasing to a third speed for spin-off. This dynamic adjustment allows the resist solution to spread uniformly across the wafer surface even with reduced solution amounts, achieving both low resist consumption and uniform film thickness.
2Manufacturing precision
If the rotational speed is rapidly reduced after resist solution supply, then the film thickness can be adjusted, but the resist solution returns from the outer circumference toward the center
Solution Approach 1:
The patent implements a multi-stage rotational speed control sequence with distinct phases. After resist solution supply ends, the rotation speed is reduced to a second speed (but not immediately to a stop or low speed), maintained for a predetermined period, and then further adjusted to a third speed for spin-off. This periodic, staged action prevents the harmful effect of solution return while still achieving film thickness adjustment, by avoiding rapid deceleration that would cause centrifugal force reversal.
3Quantity of substance
If the amount of resist solution is small, then the drying progresses rapidly, but the thickness of the outer circumference portion becomes thinner than the central portion
Solution Approach 1:
The patent uses dynamic rotational speed adjustment to control the spreading and drying of resist solution. During the coating phase, the substrate rotates at a first speed that allows sufficient spreading. After supply ends, the speed is reduced to a second speed to prevent rapid drying and maintain fluidity for uniform distribution. This dynamic control ensures that even with small solution amounts, the resist has adequate time to spread uniformly before drying, achieving uniform thickness across the entire wafer surface including the outer circumference.
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 minimizes resist solution consumption while ensuring uniform film thickness across the wafer by controlling the rotational speed in multiple steps, preventing excess solution return and allowing for precise film thickness adjustment, even with minimal solution application.
Implementation Method 1
The dropped resist solution spreads radially outward toward the circumference of the semiconductor wafer by centrifugal force
Implementation Method 2
the semiconductor wafer is continuously rotated while decreasing the rotational speed to spin off and dry the resist solution spread over the wafer surface
Data Source
AI summary
A resist coating method supplies a resist solution to substantially the center of a target substrate to be processed while rotating the target substrate at a first rotational speed, then reduces a rotational speed of the target substrate to a second rotational speed lower than the first rotational speed, reduces the rotational speed of the target substrate to a third rotational speed lower than the second rotational speed or until rotational halt to adjust the film thickness of the resist solution, and accelerates the rotation of the target substrate to a fourth rotational speed higher than the third rotational speed to spin off a residue of the resist solution.