Structure and fabrication of field-effect transistor having nitrided gate dielectric layer with tailored vertical nitrogen concentration profile
AssigneeNational Semiconductor Corporation
InventorsPrasad Chaparala, D. Courtney Parker
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Abstract
A gate dielectric layer (500, 566, or 700) of an insulated-gate field-effect transistor (110, 114, or 122) contains nitrogen having a vertical concentration profile specially tailored to prevent boron in the overlying gate electrode (502, 568, or 702) from significantly penetrating through the gate dielectric layer into the underlying channel zone (484, 554, or 684) while simultaneously avoiding the movement of nitrogen from the gate dielectric layer into the underlying semiconductor body. Damage which could otherwise result from undesired boron in the channel zone and from undesired nitrogen in the semiconductor body is substantially avoided.
Claims34
A structure comprising a primary field-effect transistor comprising:
- a channel zone of a semiconductor body;
- a pair of source/drain zones situated in the semiconductor body and laterally separated by the channel zone;
- a gate dielectric layer overlying the channel zone, having lower and upper gate dielectric surfaces, being of an average gate dielectric thickness, and comprising semiconductor material, oxygen, and nitrogen at a gate dielectric nitrogen concentration (i) which reaches a maximum concentration of 2×1021-6×1021 atoms/cm3 along a maximum-nitrogen-concentration location in the gate dielectric layer when the normalized depth into the gate dielectric layer is at a normalized maximum-nitrogen-concentration depth value of no more than 0.2 and (ii) which drops to 1×1020 atoms/cm3 when the normalized depth is at a higher value of up to 0.9, the normalized depth being the actual depth below the upper gate dielectric surface divided by the average gate dielectric thickness;
- and
- a gate electrode overlying the gate dielectric layer above the channel zone.
A method of fabricating a structure comprising a primary field-effect transistor, the method comprising:
- forming a gate dielectric layer along a semiconductor body;
- defining a gate electrode above, and vertically separated by the gate dielectric layer from, a portion of the semiconductor body intended to be a channel zone;
- and
- introducing semiconductor dopant into the semiconductor body to form a pair of source/drain zones laterally separated by the channel zone such that, upon completion of fabrication of the transistor, the gate dielectric has lower and upper gate dielectric surfaces, is of an average gate dielectric thickness, and comprises semiconductor material, oxygen, and nitrogen at a gate dielectric nitrogen concentration (i) which reaches a maximum concentration of 2×1021-6×1021 atoms/cm3 along a maximum-nitrogen-concentration location in the gate dielectric layer when the normalized depth into the gate dielectric layer is at a normalized maximum-nitrogen-concentration depth value of no more than 0.2 and (ii) which drops to 1×1020 atoms/cm3 when the normalized depth is at a higher value of up to 0.9, the normalized depth being the actual depth below the upper gate dielectric surface divided by the average gate dielectric thickness.
A method as in claim 191 wherein, upon completion of fabrication of the transistor, the nitrogen in the gate dielectric layer constitutes 6-12% of the gate dielectric layer by mass.
Dependencies are inferred from the claim text.