Undoped Silicate Glass – USG
Undoped silicate glass has a high deposition rate at low temperatures, and has similar properties to silicon dioxide. This means it is easy to deposit via plasma enhanced CVD (PECVD), HDP-CVD or SACVD. It’s most common as an insulator and passivation layer in multilevel IMD applications.
Borophosphosilicate Glass – BPSG
Borophosphosilicate glass (BPSG) is a coating made from a mixture of oxygen and hydrides of silicon (silane – SiH4), boron (diborane – B2H6), and phosphorus (phosphine – PH3). It is also called a doped oxide film because it is similar to silicon dioxide with the addition boron and phosphorus, which change its thermal properties. The addition of hydrides drastically lowers the melting point of glass, which make this process very useful when a wafer has limited thermal capabilities.
BPSG is applied to wafers via different chemical vapor deposition (CVD) techniques. The most effective and common deposition technique is PECVD, although other CVD processes will also work. Atmospheric pressure CVD (APCVD), subatmospheric pressure CVD (SACVD), low pressure CVD (LPCVD) and high density plasma CVD (HDP-CVD) are some of the other CVD processes that will apply BPSG to a wafer.
The ratio of oxygen to hydrides in the deposition chamber is usually between 40:1 and 60:1, which significantly lowers the deposition temperature of BPSG when compared to other doped oxide films. To deposit these films, the furnace temperature is 360°C – 390°C , with an optimal deposition temperature of around 370°C.
In order to ensure these wafers will properly insulate inter-metal dielectrics and maintain their high flatness qualities, these wafers often undergo a process called ‘reflow’, which takes place either in a furnace or through rapid thermal annealing (RTA). Because of their temperature sensitivity, these wafers are not subject to temperatures above 900°C to prevent damage and imperfections. This also means RTA is performed at a lower temperature.
Borophosphosilicate glass protects the underlying silicon substrate and conductive paths in semiconductors and helps with device planarization. This makes BPSG most valuable in semiconductor device fabrication, inter-metal dielectrics (IMD), and pre-metal dielectrics (PMD).
SVM offers BPSG deposition on 200mm (8″) wafers. For more information on BPSG or to request a quote, please CONTACT SVM today.