Meaning
Deposition uniformity measurements evaluate the ability of a manufacturing process to coat the bottom and sidewalls of deep contact holes or trenches on a substrate. During semiconductor manufacturing, step coverage is defined as the ratio of film thickness at the step sidewall or bottom to the thickness on the top surface. It is a fundamental metric in physical vapor deposition and chemical vapor deposition processes.
This uniformity ensures the electrical continuity of thin-film metal lines and insulation layers.
Measurement Protocol
Evaluating the thin-film layer across microstructures requires advanced microscopic analysis. To assess step coverage, technicians utilize scanning electron microscopy or transmission electron microscopy to measure the cross-section of a deposited wafer. These measurements are taken at several points across the chip to confirm the uniformity of the deposited film.
This analysis allows engineers to optimize deposition parameters before starting high-volume production.
Process Factor
The physical parameters of the deposition chamber directly affect the metal distribution. High gas pressures or low temperature settings during deposition will reduce the step coverage of the metal film. Adjusting the power and gas flow helps maintain a uniform coating over complex features.
Quality Standard
Poor deposition uniformity leads to thin areas on trench walls that can break under electrical stress. In high-density memory or processor chips, inadequate step coverage causes localized high resistance and early electromigration failure. To prevent these field failures, semiconductor foundries enforce strict quality limits on the thickness of sidewall layers.
A wafer that does not meet the specified minimum coverage is rejected and scrapped, preventing bad chips from entering the supply chain. This control process ensures the long-term reliability of the manufactured microelectronic devices.
