Dynamic Spin Coating Speed Control for Uniform Resist Films
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Solution Overview
Problem
In the photolithography process for semiconductor device manufacturing, the miniaturization of circuits leads to thinner resist films, requiring reduced amounts of expensive resist solution, but conventional spin coating methods result in coating mottles and uneven film formation due to rapid spreading of the solution on the wafer.
Innovation Solution
A coating treatment method involving gradual acceleration and deceleration of the substrate's rotation speed during spin coating, with continuous change in rotation speed from a first speed to a higher second speed, and subsequent deceleration for planarization and drying, while the nozzle discharges the solution from the center and then moves off-center, ensuring uniform application and reduced solution usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the resist solution is supplied to the center of the wafer which is rotated at high speed, then the coating treatment can be performed, but the resist solution rapidly spreads outward from the center, causing coating mottles in a streak shape near the center of the wafer
Solution Approach 1:
The rotation speed of the wafer is dynamically changed during the coating process. The coating solution is supplied at a first rotation speed, then the rotation speed is increased to a second speed after supply stops. This dynamic speed adjustment prevents rapid outward spreading of the solution while maintaining coating efficiency.
Solution Approach 2:
The rotation speed parameter is changed in two stages: first at a lower speed during solution supply, then increased to a higher speed after supply stops. This parameter change controls the spreading behavior of the coating solution, preventing streak-shaped mottles while maintaining productivity.
2Loss of substance
If the amount of resist solution supplied to the wafer is reduced, then the cost is reduced and thinner films can be formed, but coating mottles are more likely to occur and the coating becomes non-uniform
Solution Approach 1:
By dynamically adjusting the rotation speed (lower speed during supply, then higher speed after supply), the coating solution spreads more controllably. This allows reduced solution amounts to be used without causing coating mottles or non-uniformity, achieving both cost reduction and quality maintenance.
Solution Approach 2:
The rotation speed parameter is optimized in two stages to control solution spreading. This enables the use of smaller amounts of resist solution while maintaining coating uniformity, as the controlled speed change prevents rapid outward spreading that would cause mottles with reduced solution volumes.
3Speed
If the rotation speed of the wafer is increased during coating solution supply, then the coating solution spreads faster, but coating mottles and streak shapes are formed near the center
Solution Approach 1:
The rotation speed is not kept constant but dynamically changed. The coating solution is supplied at a first rotation speed, then the speed is increased to a second speed after supply stops. This dynamic adjustment prevents the formation of streak-shaped mottles while maintaining efficient coating process speed.
Solution Approach 2:
The rotation speed is increased after the coating solution supply stops, not during the supply process. This preliminary action (speed increase after supply) allows the solution to be deposited first, then spread uniformly as the speed increases, preventing mottles during the critical deposition phase.
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 uniform resist solution application and thinner film formation, reducing coating mottles and minimizing solution usage, thereby enhancing the quality and cost-effectiveness of the resist coating process.
Implementation Method 1
a so-called spin coating treatment method of applying a resist solution on a surface of a wafer by supplying the resist solution from a nozzle to a center portion of the wafer which is rotated at high speed and diffusing the resist solution on the wafer by a centrifugal force
Implementation Method 2
a third step of accelerating, after the second step, the rotation of the substrate to dry the coating solution on the substrate
Data Source
AI summary
The present invention includes: a first step of discharging a coating solution from a nozzle to a center portion of the substrate to apply the coating solution on a surface of the substrate while rotating the substrate; a second step of decelerating, after the first step, the rotation of the substrate and continuously rotating the substrate; and a third step of accelerating, after the second step, the rotation of the substrate to dry the coating solution on the substrate, wherein: the substrate is rotated at a fixed speed of a first speed immediately before the first step; and in the first step, the rotation of the substrate which is at the first speed before start of the first step is gradually accelerated after the start of the first step so as to make the speed continuously change, and the acceleration of the rotation of the substrate is gradually decreased so as to make the speed of the rotation of the substrate converge in a second speed higher than the first speed at end of the first step.