AFM Metallization Inspection for Chip Fabrication Process

The atomic force microscope Tosca 400 was used to characterize the polyimide and metallized aluminium thin films for quality control in semiconductor chip manufacturing.

Chip fabrication in semiconductor industry often involves numerous steps of processes for the deposition of multiple functional layers using various deposition methods to achieve the desired chip performance. Metallization is one of the major steps that deposits a thin metal layer as a conductive pattern to connect various components in a chip or produces a so-called bonding pad for the bonding of wire leads from a package to a chip. Besides copper, aluminium is the most widely used material for metallization. Aluminium has a good conductivity, good adhesion on SiO2, low electrical resistance and good contact with a wire bond. It is easy to deposit and also easy to pattern in single deposition and etching processes (1) (2). Polyimide, a synthetic polymer, is very commonly used as adhesive or as insulating layer in various steps during the chip fabrication process. It is light, flexible and has good mechanical and adhesive strength to materials commonly used in microelectronics (Si, Cu, Al, Au, etc.). In the meantime, polyimide has excellent electrical, chemical and heat resistance (3). It is very important for chip manufacturers to control the quality of both polyimide and metallized aluminium thin films. One of the key control parameters for the coating quality is the surface roughness which has a large influence on the adhesive strength between layers.

Too weak adhesion between layers may result in malfunction of the chip during its further fabrication process or application.
Atomic force microscopy, utilizing a sharp probe to scan across the surface and recording images, provides high resolution in both lateral and vertical direction. It is an ideal tool for chip manufacturers to monitor the surface roughness of the thin film and ensure the quality during the chip fabrication. In this report we use the AFM Tosca 400 from Anton Paar to characterize both polyimide and metallized aluminium thin films.

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