Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – Insulated gate formation
Reexamination Certificate
2000-01-07
2001-03-27
Booth, Richard (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
Insulated gate formation
C438S514000, C438S791000, C438S586000, C156S001000, C257S069000
Reexamination Certificate
active
06207542
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the fabrication of semiconductor devices, and more particularly to establishing field effect transistor (FET) gate insulators.
BACKGROUND OF THE INVENTION
Semiconductor chips or wafers are used in many applications, including as integrated circuits and as flash memory for hand held computing devices, wireless telephones, and digital cameras. Regardless of the application, it is desirable that a semiconductor chip hold as many circuits or memory cells as possible per unit area. In this way, the size, weight, and energy consumption of devices that use semiconductor chips advantageously is minimized, while nevertheless improving the memory capacity and computing power of the devices.
It can readily be appreciated that it is important to electrically isolate various components of an integrated circuit from each other, to ensure proper circuit operation. As one example, in a transistor, a gate is formed on a semiconductor substrate, with the gate being insulated from the substrate by a very thin dielectric layer, referred to as the “gate oxide” or “gate insulator”. As the scale of semiconductor devices decreases, the thickness of the gate insulator layer likewise decreases.
As recognized herein, at very small scales, the gate insulator can be become so thin that otherwise relatively small encroachments into the gate insulator layer by sub-oxides from the substrate and from adjacent polysilicon connector electrodes can reduce the insulating ability of the gate insulator layer. This poses severe problems because under these circumstances, even very minor defects in the substrate can create electron leakage paths through the gate insulator, leading to catastrophic failure of the transistor.
To circumvent this problem, alternatives to traditional gate oxide materials, such as high-k dielectric materials including nitrides and oxynitrides that can be made very thin and still retain good insulating properties, have been proposed. Unfortunately, it is thought that these materials can degrade the performance of the transistor. Nitride, in particular, has been considered undesirable because it promotes unwanted leakage of electrons through the gate insulator layer.
Furthermore, as the gate insulator layer becomes very thin, e.g., on the order of nineteen Angstroms (19 Å), device integration becomes highly complicated. Specifically, it is necessary to etch portions of the polysilicon electrodes down to the substrate, but stopping the etch on a very thin, e.g., 19 Å gate insulator layer without pitting the substrate underneath becomes problematic. Accordingly, the present invention recognizes that it is desirable to provide a gate insulator layer that can be made very thin as appropriate for very small-scale transistors while retaining sufficient electrical insulation properties to adequately function as a gate insulator, and while retaining sufficient physical thickness to facilitate device integration, without degrading performance vis-a-vis oxide insulators.
BRIEF SUMMARY OF THE INVENTION
A method for making a semiconductor device includes providing a semiconductor substrate, and establishing a nitride film over the substrate. The method also includes annealing the substrate with film in ammonia, after which the substrate with film is oxidized in Nitrogen Oxide. Next, FET gates are formed on portions of the film.
Preferably, a Nitrogen Oxide base film is established on the substrate in contact therewith, prior to establishing the nitride film, with the nitride film being subsequently deposited on the base film. In one preferred embodiment, the base film defines a thickness of no more than fifteen Angstroms (15 Å), and more preferably the base film defines a thickness of no more than twelve Angstroms (12 Å). To alleviate degraded electron mobility, Nitrogen is implanted into at least some of the gates.
In accordance with the preferred method, the annealing act is undertaken such that the Nitrogen concentration in the nitride film is greater than the stoichiometric concentration of Nitrogen in the nitride film. Moreover, the annealing act is undertaken such that dangling Nitrogen and Silicon bonds in the nitride film are passivated to thereby decrease the charge concentration in the nitride film to a charge concentration of a thermal oxide film having the same dimensions as the nitride film. In a particularly preferred embodiment, the annealing act is undertaken at temperatures up to eleven hundred degrees Celsius (1100° C.).
Other features of the present invention are disclosed or apparent in the section entitled “DETAILED DESCRIPTION OF THE INVENTION”.
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Advanced Micro Devices , Inc.
Booth Richard
LaRiviere Grubman & Payne, LLP
Luk Olivia
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