Reduced mask count process for manufacture of mosgated device
View Patent ↗A process for forming a power MOSFET enables the connection a metal gate electrode to the conductive polysilicon gates in the active area without an additional mask step. In the process, a groove is formed in the field oxide during the active area mask step. Conductive polysilicon is then formed over the active area and into the groove. At least one window is formed over the groove along with the mask window for forming the channel and source implant windows, and the polysilicon is etched to the silicon surface in the active area, but a strip is left in the groove. This strip is contacted by gate metal during metal deposition. Thus, gate metal is connected to the polysilicon without an added mask step.
1. A process for connecting a metal gate contact in a MOSgated device, comprising the steps of:
forming an oxide layer on a surface of a silicon substrate, said silicon substrate having an active surface area;
after said step of forming said oxide layer, opening a groove in a portion of said oxide layer;
in a common mask step with said step of opening a groove, opening said active surface area in said oxide layer;
forming a layer of polysilicon over said oxide layer, over at least a portion of said active surface area and into said groove;
forming a polyoxide layer over an exposed surface of said layer of polysilicon;
after said step of forming a polyoxide layer, masking a portion of an exposed surface of the polyoxide layer in a common mask step providing a masked area and unmasked areas, said unmasked areas defining a plurality of openings, at least one of said plurality of openings being over a first portion of said groove and at least another of said openings being over said active surface area, wherein said masked area shields a second portion of said groove and a portion of said layer of polysilicon during a subsequent step of etching; and
after said step of masking, etching the polyoxide layer and said layer of polysilicon in said unmasked areas, including a portion of said layer of polysilicon formed into said first portion of said groove, leaving a strip of polysilicon in said first portion of said groove such that said strip of polysilicon is connected to said portion of said layer of polysilicon shielded by said masked area; and
forming a gate contact in a common metallization step with said formation of at least one source electrode, such that said gate contact is electrically coupled with said strip of polysilicon in said bottom of said groove, said strip of polysilicon is electrically coupled with said portion of said layer of polysilicon and said portion of said layer of polysilicon forms at least one gate electrode in said active surface area of said silicon substrate.
2. The process of claim 1 , further comprising masking, implanting and diffusing channel and source impurities through said plurality of openings and into said silicon exposed after said step of etching.
3. The process of claim 1 , further comprising implanting and diffusing source impurities into said active surface area exposed by said at least another of said plurality of openings.
4. A process for connecting a metal gate in a MOSgated device, comprising the steps of:
opening a groove in a portion of an oxide layer which is atop a portion of a silicon substrate, said substrate having an active area adjacent said portion of said silicon under said oxide layer;
forming a layer of polysilicon over said oxide layer into said groove and over at least a portion of said active area;
masking over said layer of polysilicon in a common mask step, said mask including unmasked areas, said unmasked areas defining a plurality of openings, at least one of said plurality of openings being over a first portion of said groove, leaving a second portion of said groove masked; and
etching a portion of said layer of polysilicon under said plurality of openings, leaving a strip of polysilicon in a bottom of said first portion of said groove such that said strip is connected to said layer of polysilicon in said second portion of said groove; and
depositing a metal gate contact on said strip of polysilicon in said bottom of said first portion of said groove.
5. The process of claim 4 , wherein said depositing a metal gate contact is conducted without an extra mask.