Lsi Logic Corporation

Laique Khan

Sheldon Aronowitz

James O Kimball

Philippe Schoenborn

Lifetime of a short-channel NMOS device is increased by modifying distributions of electrically active LDD dopant at boundaries of the device's LDD regions. The LDD dopant distributions are modified by implanting counter-dopants at the boundaries of the LDD regions. Group III counter-dopants such as boron and group IV elements such as silicon alter activation properties of the LDD dopant. The dopant distributions are modified at the device's n-junctions to reduce the maximum electric field displacement at an interface defined by the device's gate and substrate. The dopant distributions can be further modified to shape the n-junctions such that hot carriers are injected away from the gate.

FETs having lightly doped drain regions that are shaped with counter and noncounter dorant elements

A retrograde well in a CMOS device is formed by using a low energy ion implanter. Dopant atoms are implanted into a bare surface of the device's substrate, in a direction that is orthogonal to the surface of the substrate (for a substrate having a &lt;100&gt; orientation). The well implant can be performed at an energy below 220 keV. Chained implants for a punch-through barrier in the retrograde well can be performed after the well implant. When the substrate is annealed, the punch-through barrier is activated at the same time as the retrograde well.

Method of forming retrograde well structures and punch-through barriers

A novel integrated circuit structure, and process for making same, is disclosed wherein a tapered or gradient doped profile region is provided in a semiconductor substrate between the heavily doped drain region and the channel region in the substrate comprising an MOS device. In the process of the invention, a re-entrant or tapered gate electrode, resembling an inverted trapezoid, is used as a mask during a first doping step at a dosage level higher than normally used to form a conventional LDD region. This doping step forms a doped region having a dopant gradient which gradually increases in dosage level with distance from the channel region. Conventional oxide spacers may then be formed on the sidewalls of the gate electrode followed by conventional high level doping to form the heavily doped source and drain region in the unmasked portions of the substrate between the oxide spacers and the field oxide isolation. Since the doped region beneath the oxide spacers includes a gradient doped profile region, with the lightest level of dopant adjacent the channel region (since more of the tapered gate electrode acted as a mask for the initial implantation), the overall dosage level used in the first implantation step to form the gradient doped profile region may be higher than the dosage level conventionally used to form a conventional LDD region. The resistance of the path between the heavily doped drain contact region and the channel region, which includes the gradient doped profile region, is therefore lower than the resistance of a conventional LDD region.

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Milpitas, CA, United States of America

Laique Khan