The Effect of Process Parameters on Metal Step Coverage for Aluminum by Evaporation Technique

Abstract

The degree to which deposited metals cover steps over topography is important to the yield and reliability of devices in very large scale integrations (VLSI). In evaporated and sputtered thin films, the most difficult steps to cover are those with straight walls. This is especially true with aluminum and its alloys. Metal to semiconductor contact step coverage has been studied as a function of evaporation process parameters. Contacts of different sizes, ranging from 5um to 20um have been designed and fabricated with the help of Electron Beam Lithography (EBL) system for high-resolution pattern transfer, using a standard CMOS process flow in Micro-fabrication Cleanroom Lab, UniMAP. Throughout the fabrication, wafers underwent the processes such as oxide deposition by PECVD, Lithography by EBL, wet and dry etches, photoresist stripping and so on. Aluminum was then deposited using thermal evaporator with varying process parameters. Characterization included grinding and polishing for cross sectioning, while high power microscope and scanning electron microscopy (SEM) techniques were employed for step coverage measurement. Experimental results shows that 20 μm metal step coverage is the only contact dimension can be investigated. The investigation is including the bottom step coverage and sidewall step coverage.