Igfet with silicide contact on ultra-thin gate

Abstract

An IGFET with a silicide contact on an ultra-thin gate is disclosed. A method of forming the IGFET includes forming a gate over a semiconductor substrate, forming a source and a drain in the substrate, depositing a contact material over the gate, and reacting the contact material with the gate to form a silicide contact on the gate and consume at least one-half of the gate. By consuming such a large amount of the gate, a relatively thin gate can be converted into an ultra-thin gate with a thickness on the order of 100 to 200 angstroms. Preferably, the bottom surface of the gate is essentially undoped before reacting the contact material with the gate, and reacting the contact material with the gate pushes a peak concentration of a dopant in the gate towards the substrate so that a heavy concentration of the dopant is pushed to the bottom surface of the gate without being pushed into the substrate. As exemplary materials, the contact material is a refractory metal such as titanium, the gate is polysilicon, and the dopant is arsenic.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to integrated circuit manufacturing, and more particularly to forming insulated-gate field-effect transistors with silicide contacts.[0003] 2. Description of Related Art[0004] An insulated-gate field-effect transistor (IGFET), such as a metal-oxide semiconductor field-effect tnansistor (MOSFET), uses a gate to control an underlying surface channel joining a source and a drain. The channel, source and drain are located in a semiconductor substrate, with the source and drain being doped oppositely to the substrate. The gate is separated from the semiconductor substrate by a thin insulating layer such as a gate oxide. The operation of the IGFET involves application of an input voltage to the gate, which sets up a transverse electric field in order to modulate the longitudinal conductance of the channel.[0005] In typical IGFET processing, the source and drain are formed by introducing dopants of a second conductivity t...

AI Technical Summary

Benefits of technology

[0015] By consuming such a large amount of the gate, a relatively thin gate can be converted into an ultra-thin gate with a thickness on the order of 100 to 200 angstroms. This provides for extremely low gate resistance.

[0018] A key advantage of the invention is that a highly miniaturized IGFET can be provided with an ultra-thin polysilicon gate having a well-controlled doping profile, thereby providing a low-resistance gate as well as the desired threshold voltage and drain current.

Problems solved by technology

Although refractory metals and their silicides have adequately high melting points, they usually do not provide suitable replacements for polysilicon as the gate.

For instance, the oxides of refractory metals are typically of poor quality, and in some cases volatile (Mo and W oxides).

In addition, it may be difficult to obtain consistent threshold voltages due to impurities in the sources of the refractory metals.

Otherwise, implanting a substantial amount of such dopants into the channel region may produce unwanted changes to the threshold voltage.

Furthermore, even if a thicker titanium layer is applied, it becomes difficult to form titanium silicide contacts with a thickness that exceeds 1000 angstroms, which in turn limits the amount of polysilicon that will be consumed.

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