Doped Silicate Glass Deposition by Atomic Layer Deposition
Publication Date: 2010-Aug-04
The IP.com Prior Art Database
Disclosed herein are non-limiting embodiments of methods, apparatus, and compounds which may be used in the manufacture of semiconductor, photovoltaic, LCD-TFT, or flat panel type devices.
In the manufacture of semiconductor devices in particular, Borophosposilicate glass (BPSG) is a silicate glass doped with boron and phosphorous. BPSG is usually used as a premetal dielectric widely used for device planarization.
Usually, SiO2 – silicon dioxide – is used as a diffusion mask to protect diffused junctions from impurity contamination, as a surface insulator to separate devices and metal interconnections or as simple dielectric film. The use of SiO2 as a mask plays an important role in preventing diffusion of elements such as Na+ or H+ which can diffuse rapidly even (at low temperature) in lightly doped p regions for example that can be detrimental for the device.
SiO2 is thus usually preferable deposited at low temperature to avoid impurities diffusion for example with simple reaction between silane and oxygen in chemical vapor deposition process. In addition, uniformity of the deposited film on the silicon wafer is more and more challenging. This can require complex system as describe dfor example by Alberti and al. US4098923 where they deposit phosphosilicate glass.
Phosphosilicate (PSG) or phosphorous doped glass is usually employed as a flow glass layer in the semiconductor industry meaning that the deposited film will nicely follow the contours of the surface. As the geometries of the integrated circuits formed on a wafer have reduced and become more and more complex with 3D structures for instance, it is more and more difficult to obtain this flow deposition without using high temperatures that helps soften the glass, thereby leading to non desirable dopant diffusion.
The dopant concentration will shift the temperature at which the glass softens: the higher the concentration is, the lower the temperature needed. However when the phosphorous doping is too high the risk of diffusion out of the glass increases.
Alternatively, boron doping has been used in combination with the phosphorous doping to overcome those problems. Very recently, the art has advanced that a combination of phosphorous and boron doping into the SiO2 glass provides the advantages of a low flow temperature when reducing the risks of phosphorous diffusion (phosphorous diffusion also leads to another issue: phosphorous in glass is hygroscopic which means that the tendency to attract moisture can lead to the formation of phosphoric acid within the glass that can damage the metal interconnects).
BPSG formation is already described by Kern and al (US3481781 and the article: “Chemical Vapor Deposited Borophosphate glass for silicon device applications Volume 43, RCA review September 1982). They describe a CVD process using silane, diborane, and phosphine. However, they report als...