Semiconductor devices, in particular field-effect controlled switching devices such as a Junction Field Effect Transistor (JFET), a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and an Insulated Gate Bipolar Transistor (IGBT) have been used for various applications including but not limited to use as switches in power supplies and power converters, electric cars, air-conditioners, and even stereo systems. Such semiconductor devices are typically manufactured on wafer-level. With increasing wafer-size manufacturing costs per chip typically decrease. Larger silicon-wafers, i.e. silicon-wafers with a diameter of at least 12″, are currently only available as magnetic Czochralski grown silicon wafers. Silicon-wafers with a diameter of 8″ are also available as float zone grown silicon wafers, but are comparatively expensive and may have a comparatively large resistance variation due to striations.
To avoid or at least to reduce concentration and size of unwanted crystal originated particles (COPs) that may facilitate formation generation centers in the wafer resulting in an enhanced leakage current and weakening of later formed gate dielectrics, special conditions of the magnetic Czochralski process may be used during the crystal growing. In particular, the speed of crystal growth (rate of pulling) may be reduced. This increases costs. Furthermore, A-swirls and crystal dislocations may occur at low speed of crystal growth due to an increased concentration of interstitial silicon (Si).
Another possibility for reducing COPs consists in adding nitrogen during the crystal growth. Nitrogen atoms may avoid the agglomeration of vacancies in the Si-lattice and with it the formation of COPs. However, particularly with regard to power semiconductor devices, it is desirable to form n-type doping regions in the wafer by proton implantation. However, proton implantation may activate electrically inactive nitrogen pairs by the transformation of nitrogen pairs into single nitrogen atoms in the silicon wafer which may result in partial compensation of n-type doping, reducing the life-time of charge recombination centers and/or reducing the charge-carrier life-time, because single substitutional nitrogen atoms have a deep energy level in the band-gap of silicon.
Accordingly, there is a need to improve manufacturing of semiconductor devices, in particular of power semiconductor devices.
USPTO Backgrounds
USPTO Backgrounds