1. Overview of spin coating technology
Spin coating is a process that uses centrifugal force to evenly spread the coated material and form a thin film by rotating the substrate at high speed. This technology is widely used in semiconductors, photovoltaics, display panels and other fields, and can prepare uniform coatings with nano- to micron-level thicknesses.
The core principle of spin coating technology is based on a three-step process, in which the liquid chemical material is precisely distributed onto the surface of the rotating substrate, followed by the centrifugal force generated by the high-speed rotation to drive the liquid to spread evenly, while the solvent volatilizes and solidifies to form a thin film. Film thickness is mainly determined by rotational speed and material viscosity, and thickness control with nanometer precision can be achieved by adjusting these two parameters.The process achieves uniform film formation through the synergistic effect of physical centrifugation and chemical volatilization, where the rotational speed determines the centrifugal force (which affects the uniformity of spreading) and the viscosity affects the fluid shear stress (which correlates with the stability of the film thickness), which together constitute the controllable core variables of the spin coating process.
2. Key influencing factors and optimization measures
| factor | effect | Optimization suggestions |
| Environmental conditions | Temperature, humidity, and particulate matter can cause coating defects (e.g., bubbles, streaks). | In the clean room (Class 1000 or less), control temperature and humidity (23±2°C, 40-60% RH). |
| Material quality | The purity, freshness and viscosity of chemicals directly affect the uniformity of film formation. | Use high-purity reagents and avoid prolonged storage; Pre-filtration (0.2 μm membrane) removes particulate impurities. |
| Substrates & Equipment | Surface contamination or misalignment of suction cups can lead to uneven or peeling of the coating. | The substrate needs to be ultrasonic cleaned (e.g., acetone, IPA); The suction cup is selected to match the size, and the vacuum degree is ≥-80kPa. |
3. Detailed explanation of the operation process
1. Substrate fixation and alignment
Suction cup selection – ensure that the substrate completely covers the suction cup (recommended coverage area ≥ 90%) to avoid deflection when rotating at high speeds.
Alignment Calibration – Adjusted with an optical aligner, the deviation is controlled within ±0.1mm.
2. Static Dispensing
Steps:
Dispensing – dropwise adding material to the center of the substrate (droplet diameter ≈ 50% of the substrate diameter).
Spread at low speed—rotate at 500-1000 rpm for 3-5 seconds to allow the initial expansion of the liquid.
High-speed film deposition – up to 2000-6000 rpm (viscosity adjustment) for 30-60 seconds.
Edge treatment – spray solvent (0.5-1ml/s) in rotation to remove edge build-up (beads).
3. Dynamic Dispensing
It is suitable for high-viscosity materials, and the uniformity of film formation is better (within ±1%).
Steps:
The substrate is rotated at a low speed of 300-500 rpm and dispensed synchronously.
Continue to add until the edges of the substrate are covered, then switch to high-speed mode.
4. Common problems and solutions
| issue | Possible causes | Resolution |
| The film thickness is uneven | Unstable rotational speed or uneven substrate | calibrate the hinge; Check the substrate flatness (≤0.01mm). |
| Edges pile up | The solvent evaporates too quickly | Optimized rotational acceleration (1000-3000 rpm/s). |
| Pinholes/bubbles | The ambient humidity is too high or the material is not adequately degassed | Pre-baked substrate (80°C/10min); Reduce ambient humidity. |
5. Quality inspection and process optimization
The quality control of the spin coating process is achieved by precision instrumentation, using an ellipsometry (±0.1nm) or step meter to measure the film thickness, a full surface scan to verify uniformity (≥95%), and a design of experiments (DOE) to optimize the speed-viscosity parameter combination. It is recommended to develop standardized operating procedures (SOPs) and regularly maintain critical equipment (e.g. Vacuum Pumps, speed sensors) to ensure process stability.
Through strict parameter control and environmental management, spin coating technology can stably produce high-performance films to meet the stringent requirements of the manufacture of precision electronic devices such as semiconductors and display panels. With the advantages of repeatability and controllability, this technology has become one of the core processes for the preparation of micro and nano thin films.
