ALD Silicon Nitride Passivation for PV Undercut Control

The passivation layer is divided into three distinct silicon nitride layers with different thicknesses and etching rates. The first layer (20-50nm) has the lowest etching rate, the second layer (50-200nm) has medium etching rate, and the third layer (200-500nm) has the highest etching rate. This segmentation allows each layer to serve different functions: the first layer prevents PV undercut at critical interfaces, the second layer provides transition, and the third layer offers general protection, collectively solving the etching uniformity problem while maintaining manufacturability.

Different layers of the passivation structure are assigned different etching rates through controlled deposition parameters. The first silicon nitride layer is specifically engineered with lower etching rate to protect critical areas during etching, while subsequent layers have progressively higher etching rates for easier removal where needed. This local differentiation of material properties enables precise control over the etching process and eliminates dark spots.

The passivation layer is constructed as a composite structure with three silicon nitride layers, each with different thicknesses and etching characteristics. This composite approach allows the overall thickness to be reduced to meet cell gap requirements while the multi-layer configuration provides enhanced mechanical strength and stress distribution, preventing film breakage that would occur with a single thin layer.

By segmenting the passivation layer into three thinner sub-layers rather than one thick layer, the overall thickness is reduced to accommodate cell gap requirements. Simultaneously, the segmented structure distributes mechanical stress across multiple interfaces, preventing concentration of stress that would lead to breakage in a single thin layer.

The first silicon nitride layer with the lowest etching rate is deposited in advance to serve as a protective barrier against PV undercut during the etching process. This preliminary protective layer counteracts the harmful etching effect at critical interfaces before the actual contact hole etching begins, preventing dark spots while allowing the use of efficient etching processes.

The etching rate parameters of the three silicon nitride layers are specifically optimized to create a gradient structure. The first layer has the lowest etching rate to resist undercut, while subsequent layers have progressively higher rates. This parameter differentiation enables selective etching behavior that prevents PV undercut during high-speed manufacturing, maintaining display quality without sacrificing productivity.