Method for Forming Shielded Gate Trench FET with Multiple Channels

Abstract

A method of forming a field effect transistor (FET) includes the following steps. A pair of trenches extending into a semiconductor region of a first conductivity type is formed. A shield electrode is formed in a lower portion of each trench. A gate electrode is formed in an upper portion of each trench over but insulated from the shield electrode. First and second well regions of a second conductivity type are formed in the semiconductor region between the pair of trenches such that the first and second well regions are vertically spaced from one another and laterally abut sidewalls of the pair of trenches. The gate electrode and the first shield electrode are formed relative to the first and second well regions such that a channel is formed in each of the first and second well regions when the FET is biased in the on state.

1 - 22 . (canceled) 
     
     
         23 . A method of forming a field effect transistor (FET), the method comprising:
 forming a pair of trenches extending into a semiconductor region of a first conductivity type;   forming a shield electrode in a lower portion of each trench;   forming a gate electrode in an upper portion of each trench over but insulated from the shield electrode; and   forming first and second well regions of a second conductivity type in the semiconductor region between the pair of trenches such that the first and second well regions are vertically spaced from one another and laterally abut sidewalls of the pair of trenches,   wherein the gate electrode and the first shield electrode are formed relative to the first and second well regions such that a channel is formed in each of the first and second well regions when the FET is biased in the on state.   
     
     
         24 . The method of  claim 23  wherein the first well region is laterally directly next to the gate electrode in each trench, and the second well region is laterally directly next to the first shield electrode in each trench. 
     
     
         25 . The method of  claim 23  further comprising:
 forming a shield dielectric lining lower sidewalls and bottom of each trench;   forming a gate dielectric lining upper sidewalls of each trench;   forming source regions of the second conductivity type flanking upper sidewalls of each trench; and   forming a heavy body region of the first conductivity type extending in the first well region.   
     
     
         26 . The method of  claim 23  wherein the first well region extends over the second well region, and the first region is formed before the second well region. 
     
     
         27 . The method of  claim 26  wherein the first well region extends over the second well region, the method further comprising:
 forming a third well region of the first conductivity type in the semiconductor region between the pair of trenches, the third well region abutting sidewalls of the pair of trenches, the third well region being vertically spaced from the second well region.   
     
     
         28 . The method of  claim 27  wherein the first well region is laterally directly next to the gate electrode in each trench, and the second and third well regions are laterally directly next to the first shield electrode in each trench.