BACKGROUND

The invention relates generally to semiconductor device and integrated circuit fabrication and, more specifically, to structures for an extended-drain metal-oxide-semiconductor device and methods of forming a structure for an extended-drain metal-oxide-semiconductor device.

High-voltage integrated circuits used, for example, in microwave/RF power amplifiers typically require specialized circuit technology capable of withstanding higher voltages. Extended-drain metal-oxide-semiconductor (EDMOS) devices, also known as laterally-diffused metal-oxide-semiconductor (LDMOS) devices, are designed to handle such higher voltages by incorporating additional transistor features, such as an extended drain, that promote the higher voltage handling capability. However, elevated drain voltages make an extended-drain metal-oxide-semiconductor device highly susceptible to damage caused by hot-carrier injection. The damage caused by hot-carrier injection may degrade the linear drain current. Consequently, the ability to use an extended-drain metal-oxide-semiconductor device in automotive applications, as well as other applications, may be restricted.

Improved structures for an extended-drain metal-oxide-semiconductor device and methods of forming an extended-drain metal-oxide-semiconductor device are needed.

SUMMARY

In an embodiment, a structure for an extended-drain metal-oxide-semiconductor device is provided. The structure includes first and second source/drain regions in a substrate, and a gate electrode over the substrate. The gate electrode has a sidewall, and the gate electrode is laterally positioned between the first source/drain region and the second source/drain region. A buffer dielectric layer is formed that includes a dielectric layer having a first portion positioned between the substrate and the gate electrode. The dielectric layer also has a second portion positioned on the substrate laterally between the sidewall of the gate electrode and the first source/drain region. The first portion of the dielectric layer has a first thickness, and the second portion of the dielectric layer has a second thickness that is less than the first thickness.

In an embodiment, a method of forming a structure for an extended-drain metal-oxide-semiconductor device is provided. The method includes forming a dielectric layer of a buffer dielectric layer on a substrate, forming a gate electrode over the substrate that covers a first portion of the dielectric layer, thinning a second portion of the dielectric layer adjacent to a sidewall of the gate electrode, and forming a first source/drain region and a second source/drain region in the substrate. The gate electrode is laterally positioned between the first source/drain region and the second source/drain region, and the second portion of the first dielectric layer is positioned on the substrate laterally between the gate electrode and the first source/drain region. The first portion of the dielectric layer has a first thickness, and the second portion of the dielectric layer has a second thickness that is less than the first thickness.

