Superjunction device and fabrication method therefor
View Patent ↗A super-junction device and a method of fabricating such a device are disclosed, in which a pillar of a second conductivity type situated at an interface between a transition region and a core region is narrowed in width across at least an upper thickness thereof, thereby reducing peak electric field strength in the transition region, increasing voltage endurance of the transition region and preventing the occurrence of avalanche breakdown first in the transition region. Additionally, a dopant ion concentration profile increasing in the direction from the transition region to the core region is created across upper portions of some pillars of the second conductivity type in the core region, which increases the presence of the dopant of the second conductivity type around the surface of the core region and thus stops a vertical electric field before it can reach wells of the second conductivity type. That is, an effective epitaxial thickness of the core region is reduced, which results in lower voltage endurance thereof. In this way, it is ensured that avalanche breakdown occurs first in the core region, resulting in improved EAS performance.
1 . A super-junction device comprising an epitaxial layer of a first conductivity type, the epitaxial layer defining a core region, a termination region surrounding the core region and a transition region interposed between the core region and the termination region, the epitaxial layer containing a number of pillars of the first conductivity type and a number of pillars of a second conductivity type in the core and transition regions, which are arranged alternately, wherein upper portions of some of the pillars of the second conductivity type in the core region in proximity to the transition region exhibit a dopant ion concentration profile increasing from the transition region to the core region in a direction parallel to a surface of the epitaxial layer, and wherein a width at least at the upper portion of a pillar of the second conductivity type positioned at an interface between the transition region and the core region is less than a width of the pillar of the second conductivity type in the core region,
wherein a dopant ion concentration of the upper portion of each pillar of the second conductivity type in the core region is higher than that of any other non-upper portion of all pillars of the second conductivity type in the core region, and the dopant ion concentration of the upper portion of each pillar of the second conductivity type in the core region is higher than a dopant ion concentration of any portion of the pillar of the second conductivity type at the interface between the transition region and the core region,
wherein the epitaxial layer of the first conductivity type is a stack of multiple epitaxial layers, and wherein the width of the portion of the pillar of the second conductivity type at the interface between the transition region and the core region provided by the topmost two of the multiple epitaxial layers is 7-14% less than the width of the pillars of the second conductivity type in the core region,
wherein the upper portion of the pillar at the interface between the transition region and the core region has a reduced width, while the remainder of the pillar has a width equal to the width of the pillar of the second conductivity type in the core region.
2 . The super-junction device of claim 1 , wherein a portion of the pillar of the second conductivity type at the interface between the transition region and the core region provided by the topmost two of the multiple epitaxial layers is narrower in width than the pillars of the second conductivity type in the core region.
3 . The super-junction device of claim 1 , wherein the pillars of the second conductivity type in the core region are numbered from 1 to n in the direction from the transition region to the core region, in which the upper portions of the pillars of the second conductivity type numbered from 1 to i exhibit the increasing dopant ion concentration profile, and the dopant ion concentrations of the upper portions of the pillars of the second conductivity type numbered from i to n are equal, where n is a natural number greater than 1 and 1<i<n.
4 . The super-junction device of claim 1 , further comprising:
wells of the second conductivity type residing on top of the pillars of the second conductivity type in the core and transition regions;
gates provided on the epitaxial layer of the first conductivity type in the core region;
source regions provided in the wells of the second conductivity type on opposing sides of the gates; and
a drain region formed on a backside of the epitaxial layer of the first conductivity type.
5 . The super-junction device of claim 1 , further comprising:
a number of pillars of the first conductivity type and a number of pillars of the second conductivity type, which are arranged alternately in the epitaxial layer of the first conductivity type in the termination region; and
a main junction residing on top of at least one of the pillars of the second conductivity type in the termination region in proximity to the transition region.