Browse Prior Art Database

Method for the complete or epitaxial metal silicidation of a MOSFET

IP.com Disclosure Number: IPCOM000030145D
Publication Date: 2004-Jul-29
Document File: 6 page(s) / 275K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for the complete or epitaxial metal silicidation of a metal oxide semiconductor field-effect transistor (MOSFET). Benefits include improved functionality, improved performance, improved yield, and improved process robustness.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 32% of the total text.

Method for the complete or epitaxial metal silicidation of a MOSFET

Disclosed is a method for the complete or epitaxial metal silicidation of a metal oxide semiconductor field-effect transistor (MOSFET). Benefits include improved functionality, improved performance, improved yield, and improved process robustness.

Background

              Conventional MOSFET technology uses a single metal layer (typically, Ni) deposited on a patterned Si substrate to form nickel silicide in exposed Si regions. The Si wafer is annealed so NiSi is formed by chemical reaction at the Ni/Si interfaces but no reaction occurs where Ni contacts insulators, such as SiO2 or Si3N4 (see Figure 1).

              The unreacted metal is selectively removed with a chemical etchant. The highly conductive layers of NiSi are left behind on the gate lines and the source and drain regions of the MOSFET (see Figure 2).

      Alternatively, Co/Ni bilayers form metal silicide gate electrodes on negative-channel metal oxide semiconductor (NMOS) and positive-channel metal oxide semiconductor (PMOS) devices. Shallow silicide regions are maintained in the source/drain regions of the transistors.

              Subsequent processes include capping the devices with an insulating film and further annealing the wafers to improve the resistance of the NiSi regions. This process results in low-resistance source and drain junctions and contacts, which improve MOS performance. However, MOS performance can be further enhanced if the interface between the silicide and the Si can be made smooth and coherent. Additionally, Ni diffuses very rapidly in Si, and the conventional process does not adequately control Ni diffusion in the active regions of a MOSFET.

General description

              The disclosed method enables the formation of nickel silicide on a MOSFET. The entire silicon gate area can be covered or the silicide can cover the source and drain regions. The silicide lowers the external resistance and improves the drive current of the device. The method uses a metal, such as Co, interlayer or underlayer and a thin Ni film. The  metal layer mediates the formation of nickel silicide on the diffusion and polysilicon gate surfaces of a MOSFET. The ratio of the film thicknesses and subsequent thermal budget determines its effectiveness for MOS device performance.

              In the case of expitaxil silicidation, the Ni silicide on the source/drain regions of the MOSFET is epitaxially aligned to the substrate.

              The key elements of the disclosed method include the following:

•             Use of a metal stack (Co/Ni) instead of a single metal film to form silicide

•             Use of predoped p+ poly-silicon to enhance silicidation of poly-silicon films

•             When the silicidation is complete, silicide consumes all of a poly-silicon gate (≥800A) while leaving the gate oxide intact

•             When the silicidation is complete, the silicide in source/drain regions is shallow (~300A)

•...