Patent ID: 6406974
Filing Date: 2002-06-18
Classification: H01L

Abstract:
A method of forming a triple N well, comprising:providing a substrate having a first patterned mask layer formed thereon; performing a first ion implantation step to form an annular longitudinal deep N well in the substrate, wherein the first ion implantation step is performed with phosphorus ions implanted with an energy level of about 950 KeV; performing a second ion implantation step to form an annular longitudinal shallow N well in the substrate, the annular longitudinal shallow N well lying above the annular longitudinal deep N well, wherein the second ion implantation step is performed with phosphorus ions implanted with an energy level of about 300 KeV; removing the first patterned mask layer; forming a second patterned mask layer on the substrate; performing a third ion implantation step to form a transversal deep N well surrounded by the annular longitudinal deep N well, the transversal deep N well being connected with the annular longitudinal deep N well to form the triple N well, wherein the third implantation step is performed with phosphorus ions implanted with an energy level of about 950 KeV; performing a fourth ion implantation step to form a cell well surrounded by the triple N well, the cell well lying above the transversal deep N well, wherein the fourth ion implantation step is performed with boron ions implanted with an energy level of about 80 KeV so that an interface between the transversal deep N well and the cell well substantially approaches neutrality while the dopant concentration at the interface is substantially low; and removing the second patterned mask layer.