PSG (Phosphorosilicate Glass) and BPSG (Borophosphorosilicate Glass) are examples of doped oxides and are useful as filling layers. Doped Oxides (glasses) can be made to “flow” or smooth out. This is particularly useful for smooth interconnects (prevents sharp edges which tend to break metal lines) or for partial global planarization for subsequent lithography steps. The following reactions occur during doped oxide deposition.
LPCVD of Silicon Nitride
Silicon Nitride is used for encapsulation; a process which seals up the device/circuit against contamination from air, moisture, plastics used in packaging etc. It is sometimes used for a dielectric isolation layer and as gate dielectric. Oxide/nitride mixtures known as oxynitrides are useful in FLASH memories. The following reactions occur during doped oxide deposition.