Spin coating is a well-known and widely used technique in semiconductor manufacturing, especially when it comes to applying photosensitive polymers like photoresist to semiconductor wafers. This method is integral to many steps in producing semiconductors. However, another less common but equally important method involves coating glass-like films known as Spin-On Glass (SOG). Though less practiced, SOG has significant applications, including doping the substrate, planarizing films, and serving as an interlayer dielectric.
Differences Between Photoresist Coating and Spin-On Glass (SOG)
While both photoresist coating and SOG share similar applications, they require different considerations, particularly around cleanliness and defect prevention. One of the key differences is that photoresist polymers don’t crystallize into solid glass-like particles. In contrast, SOG can form hard deposits that may only be removed with hydrofluoric acid (HF), a less-than-ideal process in terms of safety and cost.
Cleanliness is vital for both processes, but especially for SOG, where glass particles can cause defects that severely impact yield. Maintaining clean process chambers with a simple and safe solvent like isopropyl alcohol (IPA) involves innovative techniques, including using specialized dispense methods.
The Challenge of Defects and Cleanliness in SOG Processing
The build-up of unwanted materials is not typically yield-critical for photoresist, but for SOG, it can be disastrous. SOG almost always requires multiple bake stages to remove solvents and consolidate the glass film. This step introduces additional complexity in terms of wafer handling and the need for controlled, staged heating.
At our company, we’ve studied and addressed the challenges of SOG through specialized tools designed to resolve these potential yield-busting issues, providing solutions to wafer fabrication teams who rely on SOG in their processes.
Key Challenges and Our Solutions for Spin-On Glass (SOG)
1. Preventing Particulate Redeposition in the Spin Bowl
Keeping the spin bowl clean is critical to avoid particulate redeposition on the wafer during the spin-coating process. We’ve developed a unique solution that creates a “waterfall-like” IPA rinse inside the spin bowl during the spin-off process. This descending film of IPA ensures that any glass-like droplets leaving the wafer are carried away to a drain, preventing contamination. The innovative design wets even the nearly horizontal surfaces of the spin bowl, ensuring thorough cleaning and preventing defect buildup. (Note: See the image above)
2. Maintaining Clean Dispense Systems
One of the most common sources of defects in SOG processing comes from dirty dispense systems. To counter this, we’ve designed a dispense system where both the bottle and all associated tubing are swapped out entirely when the bottle is replaced. This ensures a perfectly clean dispense system every time, with no need for manual cleaning. The tubing is inexpensive and disposable, eliminating contamination risks. Even the suck-back feature is designed to prevent drying SOG from forming on the inner wall of the dispense tube, ensuring flawless operation.
3. Automating Multi-Coating Processes
Building up film thickness with SOG often requires multiple coatings, which can be a challenge if left to manual operation. Our tools are designed to automate this process, enabling multiple coatings without requiring operator intervention. This ensures consistent application while increasing throughput and reducing potential human error.
4. Efficient Staged Heating for High Throughput
SOG films require staged heating to remove solvents and solidify the glass film. Our tools utilize a unique wafer handling system that stages the bake process within a single hot plate. By programming the wafer to descend towards the hot plate in stages, we can achieve multiple temperature zones in one tool. This eliminates the need for robots to move wafers from one hot plate to another, saving time and reducing wafer stress by minimizing heating and cooling cycles. Instead, the wafer heats progressively, resulting in more uniform films and less stress on the material.
Conclusion: Solving the Spin-On Glass (SOG) Problem
Our SOG tools are designed to solve the complex issues associated with SOG processing. From maintaining clean spin bowls to ensuring defect-free dispensing and automating multi-stage bakes, we have developed solutions that deliver high yield and efficiency. By addressing each of these challenges, we help semiconductor manufacturers improve their processes and achieve better results in wafer fabrication.
Get in touch to learn more about solutions designed for your needs.
