Transistor with asymmetric spacers
A field-effect transistor device including an asymmetric spacer assembly allows lower parasitic capacitance on the drain side of the device and lower resistance on the source side. The asymmetric spacer assembly is formed by a self-aligned process, resulting in less gate/junction overlap on the drain side of the device and greater gate/junction overlap on the source side of the device. Asymmetric transistors having small gate lengths can be obtained without overlay/misalignment issues.
1. An asymmetric field-effect transistor device, comprising:
a semiconductor substrate including a channel region;
a doped source region operably associated with the channel region;
a doped drain region operably associated with the channel region;
a first doped extension region within the semiconductor substrate and extending between the channel region and the doped source region;
a second doped extension region within the semiconductor substrate and extending between the channel region and the doped drain region;
a gate electrode operatively associated with the channel region, the gate electrode including a drain side and a source side;
a gate dielectric layer between the gate electrode and the channel region;
a first drain side dielectric spacer extending over the drain side of the gate electrode, a portion of the second doped extension region extending beneath the first drain side dielectric spacer;
a second drain side dielectric spacer adjoining the first drain side dielectric spacer, the second drain side spacer being discrete from the first drain side spacer, a further portion of the second doped extension region extending beneath the second drain side dielectric spacer, the first drain side dielectric spacer being positioned between the gate electrode and the second drain side dielectric spacer;
a source side dielectric spacer extending over the source side of the gate electrode, a portion of the first doped extension region extending beneath the source side dielectric spacer, the first drain side dielectric spacer and the second drain side dielectric spacer having a combined thickness exceeding the thickness of the source side dielectric spacer;
wherein the first and second drain side dielectric spacers and the source side dielectric spacer are configured such that the gate electrode overlaps a larger area of the first doped junction between the doped source region and the channel region than the second doped junction between the doped drain region and the channel region.
2. The asymmetric field-effect transistor device of claim 1 , wherein:
the first drain side dielectric spacer comprises a first dielectric material,
the second drain side dielectric spacer and the source side dielectric spacer comprise a second dielectric material, the first dielectric material having a lower dielectric constant than the second dielectric material.
3. The asymmetric field-effect transistor device of claim 1 , further including:
an electrically conductive drain contact electrically connected to the drain region and adjoining the second drain side dielectric spacer; and
an electrically conductive source contact electrically connected to the source region and adjoining the source side dielectric spacer.
4. The asymmetric field-effect transistor device of claim 3 , wherein the gate dielectric layer further adjoins the first drain side dielectric spacer and the source side dielectric spacer.
5. The asymmetric field-effect transistor device of claim 4 , wherein the second drain side dielectric spacer and the source side dielectric spacer are thicker than the first drain side dielectric spacer.
6. The asymmetric field-effect transistor device of claim 1 , wherein the semiconductor substrate is comprised of a semiconductor fin.
7. The asymmetric field-effect transistor device of claim 1 , wherein the second drain side dielectric spacer and the source side dielectric spacer have thicknesses between four and eight nanometers and are thicker than the first drain side dielectric spacer.