OLED Displaying Substrate Via-Hole Layout to Prevent Over-Etching

The patent applies preliminary action by forming a protective layer on the metal layer before the etching process. This protective layer is etched along with the flat layer and passivation layer to form via holes, but it initially protects the metal layer from oxidation during etching. The protective layer is then selectively removed only in the via hole regions, allowing electrical connection while preventing harmful oxidation on the metal surface that would affect subsequent processing and signal transmission.

The protective layer serves as an intermediary between the etching process and the metal layer. It mediates the conflict by being present during etching to prevent direct contact between the etching chemistry and metal surface, thus preventing oxidation. The intermediary is then selectively removed where needed (in via holes) to establish electrical connection, while leaving the metal surface protected in other areas for subsequent metal film layer overlapping.

The protective layer is formed preliminarily across the entire metal layer surface before etching. During the etching process to create via holes through the flat layer and passivation layer, the protective layer remains in place to protect the metal surface. This preliminary protective action allows the etching to proceed to the required depth for electrical connection without causing over-etching variations, as the protective layer uniformly prevents excessive etching across all regions.

The protective layer provides beforehand cushioning against over-etching. By being present before the etching process, it cushions or limits the etching depth to prevent penetration into the metal layer. This prior cushioning effect ensures uniform etching depth control across all via holes, preventing the depth variations and over-etching that would otherwise occur in regions where via holes need to be etched deeper.

The via hole formation process is segmented into two independent stages: first, forming via holes through the flat layer and passivation layer to the metal layer; second, removing the protective layer only in the via hole regions. This segmentation allows different via holes to be formed to different depths as needed for electrical connection adaptability, while the etching process itself remains simple and uniform. The complexity of handling different via hole depths is transferred to the selective protective layer removal step rather than the etching step.

The protective layer acts as an intermediary that simplifies the etching process. It allows all via holes to be etched using the same simple process parameters, while the intermediary's selective removal afterward creates the required depth variations for different electrical connection needs. This intermediary approach decouples the etching process complexity from the via hole depth variation requirements, making the overall process easier to control.