Chemical-mechanical Planarization - Application

Application

Shallow trench isolation (STI), a process used to fabricate semiconductor devices, is a technique used to enhance the isolation between devices and active areas. Moreover, STI has a higher degree of planarity making it essential in photolithographic applications, depth of focus budget by decreasing minimum line width. To planarize shallow trenches, a common method should be used such as the combination of resist etching-back (REB) and chemical mechanical polishing (CMP). This process comes in a sequence pattern as follows. First, the isolation trench pattern is transferred to the silicon wafer. Oxide is deposited on the wafer in the shape of trenches. A photo mask, composed of silicon nitride, is patterned on the top of this sacrificial oxide. A second layer is added to the wafer to create a planar surface. After that, the silicon is thermally oxidized, so the oxide grows in regions where there is no Si3N4 and the growth is between 0.5 and 1.0 µm thick. Since the oxidizing species such as water or oxygen are unable to diffuse through the mask, the nitride prevents the oxidation. Next, the etching process is used to etch the wafer and leave a small amount of oxide in the active areas. In the end, CMP is used to polish the SiO2 overburden with an oxide on the active area.