PI Baking Wafers and Annealing
PI Baking Wafers and Annealing
In the semiconductor manufacturing field, each process step is crucial, forming a complex and precise production system. PI baking wafers and annealing are two key stages that significantly impact the performance, stability, and yield of the final products. These steps affect not only the surface quality of the wafers but also their intrinsic electrical characteristics and mechanical strength.
PI Baking Wafers
Purpose
PI baking wafers is an important initial step in semiconductor manufacturing, aimed at removing contaminants from the wafer surface and forming a stable protective film through high-temperature processing in an industrial oven. This protective film, known as polyimide (PI) film, effectively isolates the wafers from oxygen and moisture in the air, preventing surface oxidation and providing additional protection in subsequent processes, ensuring the purity and stability of the wafers.
Process
In the preparation stage, the wafers to be baked are placed in a drying oven, the door is closed, and the heating system is activated. The temperature inside the oven is gradually raised. Once it reaches above 200°C, high-purity nitrogen gas is introduced to displace oxygen and moisture, preventing oxidation of the wafer surface. A PI solution is then evenly applied to the rotating wafer surface, forming a thin film. The baking continues for a specific time (usually between 10 minutes to 1 hour) to cure the PI film, ensuring it adheres firmly to the wafer surface. Finally, after heating, the heating system is turned off, allowing the oven to cool to room temperature before removing the baked wafers.
Principle
The principle of PI baking wafers relies on high-temperature baking and chemical reactions, which decompose organic materials and impurities in the PI solution into gases carried away by the nitrogen, thereby cleaning the wafer surface. By creating an oxygen-free and dry environment, the PI solution is uniformly coated on the rotating wafer surface, forming an even film. Under sustained high temperatures in the industrial oven, the PI film gradually cures and adheres firmly, creating a solid barrier that protects the wafer surface from oxidation and contamination, enhancing stability and reliability.
Annealing
Purpose
Annealing is another critical process in semiconductor manufacturing, aimed at optimizing the microstructure and physical properties of the wafers through high-temperature treatment. In this process, wafers are placed in an annealing furnace and subjected to high temperatures for a period, followed by cooling. This step is essential for eliminating residual stress within the wafers, promoting grain growth, and enhancing their mechanical and electrical properties.
Process
In the preparation stage, the wafers that have undergone PI baking are placed in the annealing furnace, the door is closed, and the heating system is activated. During the heating stage, the temperature in the furnace is gradually increased, maintaining it above 600°C for a specific duration (usually a few minutes to several tens of minutes) to allow sufficient grain development at high temperatures. After heating, the system is turned off, and the temperature in the furnace is allowed to cool to room temperature before removing the treated wafers.
Principle
The working principle of annealing is based on atomic diffusion and lattice rearrangement. At high temperatures, atoms within the wafers undergo vigorous movement, facilitating atomic diffusion and leading to grain growth. Simultaneously, high-temperature treatment effectively eliminates residual stress, stabilizing the lattice structure. This process not only enhances the physical properties of the wafers but also lays a foundation for optimizing their electrical performance.
PI baking wafers and annealing are two essential processes in semiconductor manufacturing. PI baking wafers protect the purity and stability of the wafer surface by removing contaminants and forming a protective film, while annealing improves overall quality and performance by optimizing the microstructure and physical properties. These two processes complement each other and are indispensable, providing robust support for high quality and efficiency in semiconductor manufacturing.