Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2003-05-14
2004-09-07
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S301000, C257S411000
Reexamination Certificate
active
06787863
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing it. More particularly, the present invention relates to a semiconductor device such as a MOS field effect transistor or MOS capacitor, which contains a silicon substrate and an insulating film adjacent thereto, and operates by applying a voltage to an electrode in opposition to a silicon substrate with an insulating film interposed there between, and its manufacturing method.
2. Description of the Related Art
MOS field effect transistors (MOSFET) and DRAM capacitors are required to have insulating films that have superior properties. On the other hand, accompanying the growing levels of integration of semiconductor devices in recent years, MOSFET gate insulating films are being required to be increasingly thin due to the requirements of the scaling rule, and MOSFET having a gate length of 100 nm or less are required to have a gate insulating film having a film thickness of 2.0 nm or less. Similarly, the insulating films of DRAM capacitors are being required to be increasingly thin.
In the past, silicon thermal oxidation films were used for the gate insulating films of MOSFET and the gate insulating films of DRAM capacitors. However, efforts to reduce the thickness of these silicon thermal oxidation films have encountered several problems. For example, in the case of the gate insulating film of a MOSFET, as the thickness of the silicon thermal oxidation film decreases, leakage current ends up increasing due to direct tunnel current. In order to solve such problems, it is necessary to develop a satisfactory insulating film having a high dielectric constant that can inhibit leak current even if the equivalent oxide thickness (EOT) is small.
Examples of satisfactory insulating films having a high dielectric constant that are currently considered most likely to take the place of silicon thermal oxidation films from the viewpoint of their thermal stability include high dielectric constant, metal oxide insulating films such as hafnium oxide or zirconium oxide. However, hafnium oxide and zirconium oxide films are readily permeable to oxygen. Consequently, when these films are formed by deposition in a furnace, trace amounts of residual oxygen in the furnace diffuse through the formed thin film and react with silicon at the interface with the silicon substrate of the lower layer, which in turn ends up causing the formation of an interface layer having a low dielectric constant.
According to a method proposed in the past to avoid this problem, a silicon nitride film is pre-formed on a silicon substrate in the form of an oxygen diffusion barrier layer by low pressure chemical vapor deposition (LPCVD) or plasma nitridation, and a hafnium oxide layer or zirconium oxide layer is deposited thereon. For example, the formation of a silicon nitride film as an oxygen diffusion barrier layer for hafnium oxide by plasma CVD is described in H. Ota, et al., HfO
2
MIS Structures with a Silicon Nitride Barrier Layer, Extended Abstracts of International Workshop on Gate Insulator, IWGI 2001, Nov. 1-2, 2001, Tokyo, pp. 188-190.
The dielectric constant of silicon nitride films used as an oxygen diffusion barrier layer is comparatively low. Consequently, in the case the silicon nitride film of the barrier layer is thick, the dielectric constant of the overall insulating film stack, including the hafnium oxide film or zirconium oxide film formed thereon, ends up decreasing considerably. Thus, a silicon nitride film for use as an oxygen diffusion barrier layer is required to be as thin as possible.
However, in the case of the previously proposed vacuum chemical vapor deposition or plasma nitridation, it was extremely difficult to accurately form a thin silicon nitride film in the form of a layer on the order of several molecules thick that is effective in inhibiting the decrease in the dielectric constant in terms of the overall insulating film stack. In addition, it was also difficult to ensure adequate thin film quality and uniform film thickness.
A known method that is effective in forming a thin film only one molecule or several molecules thick is atomic layer deposition (ALD) method. For example, the formation of a zirconium oxide film by ALD is described in K. Kukli, et al., Low-Temperature Deposition of Zirconium Oxide-Based Nanocrystalline Films by Alternate Supply of Zr[OC(CH
3
)
3
]
4
and H
2
O, Chem. Vap. Deposition, Vol. 6, No. 6, pp. 297-302 (2000). The formation of a silicon nitride gate insulating film by ALD is described in A. Nakajima, et al., Low-temperature formation of silicon nitride gate dielectrics by atomic-layer deposition, Applied Physics Letters, Vol. 79, No. 5, pp. 665-667 (2001). However, the use of a silicon nitride film grown by ALD as an oxygen diffusion barrier layer for the gate insulating layer of a MOSFET as in the present invention has heretofore not been known.
SUMMARY OF THE INVENTION
Thus, an object of the present invention is to provide a semiconductor device that uses a high dielectric constant insulating film in the manner of a gate insulating film formed on a silicon substrate, and a thin film having superior film quality and uniform film thickness as an intermediate layer in the manner of a barrier layer and so forth between the insulating film and the silicon substrate.
The semiconductor device provided by the present invention comprises a silicon substrate and an insulating film adjacent thereto and which operates by applying a voltage to an electrode opposed to the silicon substrate with the insulating film interposed between, and includes a MOSFET, MOS capacitor, particularly DRAM capacitor, and so forth.
More specifically, the semiconductor device of the present invention is a semiconductor device in which a thin intermediate layer formed by ALD is provided between the silicon substrate and the insulating film, and the thickness of the intermediate layer is 0.2-1 nm.
REFERENCES:
patent: 2003/0001187 (2003-01-01), Basceri et al.
Hiroyuki Ota, et al., “HfO2MIS Structures with a Silicon Nitride Barrier Layer”,Extended Abstracts of International Workshop on Gate Insulator IWGI 2001, Nov. 1-2, 2001, Tokyo, Japan.
Kaupo Kukli, et al., “Low-Temperature Deposition of Zironium Oxide-Based Nanocrystalline Films by Alternate Supply of Zr[OC(CH3)3]4and H2O”,Chemical Vapor Deposition, vol. 6, No. 6, pp. 297-302, 2000.
Anri Nakajima, et al., “Low-Temperature Formation of Silicon Nitride Gate Dielectrics by Atomic-Layer Deposition”,Applied Physics Letters, vol. 79, No. 3, pp. 665-667, Jul. 30, 2001.
Ngo Ngan V.
Semiconductor Technology Academic Research Center
Staas & Halsey , LLP
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