Wafer Backside N2 Purge for High-Viscosity Photoresist Coating
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High viscosity liquid photoresist materials used in semiconductor manufacturing often result in 'cotton candy' residue and bubbles on the backside of semiconductor wafers due to negative pressure during rotation, leading to electrical shorting and contamination issues, which existing double coating processes fail to fully address.
Innovation Solution
A method involving a gas purge, specifically using nitrogen (N2) gas, is applied during the photolithographic process to remove defects and contamination by creating an air flow that dislodges and expels residue from the backside of the wafer, ensuring a clean and dry surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high viscosity liquid photoresist is used to coat semiconductor wafer, then photoresist can better cover bump structures and achieve higher aspect ratios, but photoresist cotton candy and bubbles form on the backside of the wafer due to negative pressure during rotation
Solution Approach 1:
The harmful photoresist cotton candy and bubbles are extracted and removed from the wafer backside using a gas purge system. The gas flow extracts these contaminants from the negative pressure zone created during wafer rotation, preventing them from causing electrical shorts while maintaining the benefits of high viscosity photoresist coating.
Solution Approach 2:
A gas (such as nitrogen or compressed air) is introduced as an intermediary medium between the wafer backside and the environment. This gas flow acts as a mediator to counteract the negative pressure effects, prevent photoresist vapor condensation, and carry away cotton candy contaminants during the spin coating process.
2Manufacturing precision
If wafer rotation speed is increased to improve photoresist distribution, then coating uniformity improves, but negative pressure increases causing more cotton candy formation
Solution Approach 1:
Gas purge is introduced as an intermediary to counteract the increased negative pressure effects of higher rotation speeds. The gas flow balances the pressure differential, allowing faster rotation for better coating uniformity without proportionally increasing cotton candy formation.
Solution Approach 2:
A pneumatic gas purge system is used to apply positive pressure to the wafer backside, counterbalancing the negative pressure generated during high-speed rotation. This pneumatic counter-pressure prevents photoresist vapor condensation and reduces cotton candy formation while maintaining coating uniformity.
3Object-generated harmful factors
If double coating process is used to reduce photoresist contamination, then some cotton candy is reduced, but the process complexity increases and complete contamination removal is not achieved
Solution Approach 1:
The gas purge is applied during the coating process itself as a preliminary action to prevent cotton candy formation before it can cause contamination. This prevents the need for subsequent cleaning steps, simplifying the overall process while achieving complete contamination removal.
Solution Approach 2:
The gas purge operates continuously throughout the spin coating process, maintaining constant protection against cotton candy formation and contamination. This continuous action eliminates the need for separate remediation steps required by discontinuous double coating approaches.
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
The gas purge effectively reduces photoresist defects and contamination, achieving a clean, dry, and contaminant-free semiconductor wafer surface, enhancing the quality of electrical interconnects and reducing the risk of electrical shorting.
Implementation Method 1
The rotation of the semiconductor wafer creates a negative pressure, which tends to form photoresist cotton candy... A common design goal for a semiconductor device is to reduce the footprint and profile... The gas purge effectively reduces photoresist defects and contamination
Implementation Method 2
A method involving a gas purge, specifically using nitrogen (N2) gas, is applied during the photolithographic process to remove defects and contamination by creating an air flow that dislodges and expels residue from the backside of the wafer
Data Source
AI summary
A semiconductor manufacturing device has an outer cup and inner cup with a wafer suction mount disposed within the outer cup. A photoresist material is applied to a first surface of a semiconductor wafer disposed on the wafer suction mount while rotating at a first speed. A gas port is disposed on the inner cup for dispensing a gas oriented toward a bottom side of the semiconductor wafer. The gas port purges a second surface of the semiconductor wafer with a gas to remove contamination. The second surface of the semiconductor wafer is rinsed while purging with the gas. The gas can be a stable or inert gas, such as nitrogen. The contamination is removed from the second surface of the semiconductor wafer through an outlet between the inner cup and outer cup. The semiconductor wafer rotates at a second greater speed after discontinuing purge with the gas.