Trench-gate semiconductor devices and their manufacture

A method according to any one of the preceding claims, wherein the trench is etched in stage (b) through a silicon body portion that has a doping concentration of the first conductivity type that extends from the surface into an underlying area to provide a part of the drain region, and wherein a gate dielectric layer is formed by thermal oxidation of the silicon body portion at the walls of the trench.

A method according to any one of the preceding claims, wherein a channel-accommodating region of a second conductivity type is formed adjacent to the trench-gate using the following sequence of steps:

• removing the first mask part in stage (d) to form a doping window in the insulating overlayer, and
• introducing dopant of the second conductivity type into the body via this doping window so as to form the channel-accommodating region at the doping window and extending laterally below the insulating overlayer to the trench.

A method according to any one of the preceding claims, wherein the gate is provided in a part of the trench below the level of the surface of the body, and the subsequently deposited and etched-back insulating material of stage (d) is left in the upper part of the trench and extends laterally from the trench into the wider window of the first mask part.

A method according to any one of the preceding claims, wherein the first mask in stage (a) is a composite comprising an upper layer part on a lower layer part, the upper layer part is of a different material to the lower layer part so as to etchable from the lower layer part, and the upper layer part is etched away from the lower layer part before providing the insulating overlayer in stage (d).

A method according to any one of the preceding claims, wherein, after providing the insulating overlayer in stage (d), the channel-accommodating region is contacted using the following sequence of steps:

• removing the first mask part to form a contact window in the insulating overlayer,
• introducing dopant of the second conductivity type into the body via the contact window so as to form a more highly doped contact region for the channel-accommodating region, and
• depositing the source electrode to contact the source region and the contact region at the contact window and to extend over the insulating overlayer over the trench-gate.

A method according to any one of the preceding claims, wherein, after removing the first mask part in stage (d) and before providing the source electrode, the insulating material of the insulating overlayer is isotropically etched back a sufficient distance to increase the area of the source region not covered by the insulating overlayer.

A method according to any one of the preceding claims, wherein the gate is provided in the trench before removing the sidewall extensions to re-expose the wider window.

A method according to any one of the preceding claims, wherein, after etching the trench, the sidewall extensions are removed to re-expose the wider window, and then gate material is deposited to fill the wider window and the trench therein and is etched back to be left as the gate in the trench.

A method according to any one of the preceding claims, wherein the first mask comprises silicon nitride, the sidewall extensions comprise silicon dioxide, and the insulating overlayer comprises silicon dioxide.