Method for forming a semiconductor device having a strained channel and a heterojunction source/drain

Abstract

A semiconductor device (10) is formed by positioning a gate (22) overlying a semiconductor layer (16) of preferably silicon. A semiconductor material (26) of, for example only, SiGe or Ge, is formed adjacent the gate over the semiconductor layer and over source / drain regions. A thermal process diffuses the stressor material into the semiconductor layer. Lateral diffusion occurs to cause the formation of a strained channel (17) in which a stressor material layer (30) is immediately adjacent the strained channel. Extension implants create source and drain implants from a first portion of the stressor material layer. A second portion of the stressor material layer remains in the channel between the strained channel and the source and drain implants. A heterojunction is therefore formed in the strained channel. In another form, oxidation of the stressor material occurs rather than extension implants to form the strained channel.

Description

CROSS REFERENCE TO RELATED APPLICATION [0001] This application is related to our copending U.S. Patent Application, (Attorney Docket No. SC-13377TP) entitled “Double Gate Device Having A Heterojunction Source / Drain and a Strained Channel”, filed simultaneously herewith and assigned to the assignee hereof.FIELD OF THE INVENTION [0002] This invention relates generally to semiconductor, and more specifically, to making semiconductor devices having very small dimensions. BACKGROUND OF THE INVENTION [0003] Semiconductor devices, such as transistor structures, continue to be scaled to smaller dimensions as process lithography improves. However, different challenges have been encountered in the scaling of transistor structures much below 100 nm. Additionally, when transistor dimensions on the order of 100 nm and smaller are used, implants cannot be adequately controlled with conventional semiconductor fabrication equipment. Channel dopant fluctuations adversely affect device uniformity wit...

AI Technical Summary

Problems solved by technology

However, different challenges have been encountered in the scaling of transistor structures much below 100 nm.

Additionally, when transistor dimensions on the order of 100 nm and smaller are used, implants cannot be adequately controlled with conventional semiconductor fabrication equipment.

Channel dopant fluctuations adversely affect device uniformity within circuits.

However, channel doping is not an efficient method for ultra-thin devices due to the large amount of channel impurities that are required.

Therefore, highly doped ultra-thin devices are even more susceptible to threshold voltage fluctuations.

Additionally, high channel doping concentrations degrade both electron and hole mobility and promote source / gate and drain / gate junction leakage.

However, when thin-body devices are being implemented, the depth available for the stressor material is insufficient to adequately strain the channel.

Another issue with this technique is that the silicon material is recessed with an etch process.

Stopping the etch process at a desired depth is a challenge and subject to variation.

Additionally, re-growth of the stressor material on the remaining ultra-thin silicon is problematic.

Additionally, this method does not apply to the known FINFET structures or any thin-body transistor devices.

Therefore, another issue with this approach is that the presence of SiGe in the transistor's channel increases the transistor's off-state current leakage.

Additionally, this method does not apply to the known FINFET structures or any vertical thin body double gate transistor.

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