Shielded gate trench MOSFET with ESD diode manufactured using two poly-silicon layers process
A SGT MOSFET having ESD diode and a method of manufacturing the same are disclosed. The SGT trench MOSFET according to the present invention, has n+ doped shielded electrode in an N channel device and requires only two poly-silicon layers, making the device can be shrunk with reducing shielded gate width for Rds reduction without increasing switching loss and having dynamic switching instability.
1. A SGT MOSFET comprising:
an epitaxial layer of a first conductivity type extending over a substrate;
a plurality of first type trenches formed in said epitaxial layer in an active area, each of said first type trenches being filled with a shielded gate structure comprising a first poly-silicon layer in a lower portion to serve as a shielded electrode and a second poly-silicon layer in an upper portion to serve as a gate electrode, wherein said shielded electrode is insulated from said epitaxial layer by a first insulating film and said gate electrode is insulated from said epitaxial layer by a gate insulating film which has a thickness less than said first insulating film, wherein said shielded electrode and said gate electrode are insulated from each other by a second insulating film;
an ESD clamp diode comprising said second poly-silicon layer formed on top of said epitaxial layer and multiple second type trenches, wherein each of said second type trenches is filled with said first poly-silicon layer as a single electrode;
said ESD clamp diode being isolated from said epitaxial layer by said gate insulating film, and being isolated from said single electrode by said second insulating film, said single electrode being isolated from said epitaxial layer by said first insulating film;
said first and second poly-silicon layers being doped with said first conductivity type; and
trenched anode (cathode) contacts of said ESD clamp diode being located above said multiple second trenches.
2. The SGT MOSFET of claim 1 , wherein said ESD clamp diode is consisted of at least one pair of back to back Zener diodes comprising multiple alternatively arranged doped regions of said first conductivity type and doped regions of a second conductivity type opposite to said first conductivity type.
3. The SGT MOSFET of claim 1 , wherein said active area further comprises source regions of said first conductivity type and body regions of a second conductivity type, wherein said source regions and said body regions are connected to a source metal through trenched source-body contacts filled with a contact metal plug which is tungsten metal layer padded by a barrier layer of Ti/TIN or Co/TiN or Ta/TiN.
4. The SGT MOSFET of claim 1 , wherein said shielded electrode is connected to an outlet part for the shielded electrode to further be shorted to a source metal through a trenched shielded electrode contact filled with a contact metal plug, wherein said outlet part for the shielded electrode is formed by said first poly-silicon layer in a third type trench and said contact metal plug is tungsten metal layer padded by a barrier layer of Ti/TIN or Co/TiN or Ta/TiN.
5. The SGT MOSFET of claim 1 , wherein said gate electrode is connected to a wider gate electrode to further be shorted to a gate metal through a trenched gate contact filled with a contact metal plug, wherein said wider gate electrode is formed at a same step as said gate electrode in a fourth type trench having a greater trench width than said first type trenches and said contact metal plug is tungsten metal layer padded by a barrier layer of Ti/TIN or Co/TiN or Ta/TiN.