A.S. Polukhin, T.K.Zuyeva, A.I. Solodovnik
One of the basic tendencies of the power semiconductors development is substitution of discrete devices in hermetic glass-to-metal packages for modules, where the structures of power semiconductor devices (thyristors, triacs, transistors, diodes etc.) are soldered on an insulating ceramic substrate and encapsulated into a plastic case. These structures fabricated by world productors have one-sided passivation; anode blocking p-n junction is exposed on the upper surface of the structure through the peripheral separating area, so called, vertical insulation. Such structures are more reliable as compared to structures with double-side mesa  and allow direct soldering on a metallized ceramic substrate without thermal compensator. That's why the tendency of increase of modules current and growth of blocking voltage was designated.
Well-established solid-state diffusion is used for making of vertical isolation by the majority of manufacturers as the most mastered process. The square-law dependence between diffusion term and p-n junction depth essentially lengthens the process of deriving of a vertical isolation on thick wafers of high-ohmic silicon used to manufacture of high-voltage devices, so electrophysical parameters of the initial silicon are changed for worse.