Trench MIS device with thick oxide layer in bottom of gate contact trench
A trench MIS device includes a thick dielectric layer at the bottom of the trench. The thick dielectric layer can be formed by the deposition or thermal growth of a dielectric material, such as silicon dioxide, on the bottom portion of the trench. The thick dielectric layer, which reduces the capacitance between the drain and gate of the device, can be formed in both the active areas of the device, where the switching function is performed, and in the inactive areas where, among other things, contacts are made to the gate electrode.
1. A trench MIS device formed in a semiconductor substrate and comprising and active region and an inactive region, said active region comprising:
a first trench containing a first conductive gate material;
a source region in said substrate; and
a body region adjacent a side wall of said trench, said trench being lined with a thin insulating layer adjacent said body region;
said inactive region comprising:
a second trench containing a second conductive material, said second conductive material being in electrical contact with said first conductive material;
a relatively thin insulating layer on a side wall of said second trench;
a relatively thick insulating layer on a bottom of said second trench; and
a gate bus in contact with said second conductive material.
2. The trench MIS device of claim 1 wherein said relatively thin insulating layer covers a corner region between said bottom and said side wall of said second trench.
3. The trench MIS device of claim 1 comprising a transition region between said relatively thick insulating layer and said relatively thin insulating layer, said transition region comprising a graduated insulating layer abutting said relatively thick and relatively thin insulating layers, a thickness of said graduated insulating layer decreasing gradually in the direction from said relatively thick insulating layer towards said relatively thin insulating layer.