Semiconductor device manufacturing: process – Introduction of conductivity modifying dopant into... – Plasma
Reexamination Certificate
1998-04-30
2001-02-06
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Introduction of conductivity modifying dopant into...
Plasma
C438S513000, C438S591000, C438S787000, C257S069000
Reexamination Certificate
active
06184110
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the fabrication of MOSFET devices that require an extremely reliable gate oxide process for control of the transistor, and specifically for deep submicron devices that require boron-doped gate polysilicon for the pMOS part of the CMOS flow.
BACKGROUND OF THE INVENTION
Gate oxides that are incorporated into 0.25 &mgr;m CMOS processes are extremely thin, on the order of 3.5 to 4.0 nm thick. Such oxides need to be a highly reliable insulator. Techniques to grow these thin oxide layers involve the use of one or more of the following gases: O
2
(oxygen), H
2
O (water vapor), N
2
O (nitrous oxide), and NO (nitric oxide).
In known prior art, the gate polysilicon is doped with phosphorous to form the N
+
gate for both nMOS and pMOS devices. For smaller channel lengths, i.e., 0.25 &mgr;m and below, it is necessary to form p
+
doped polysilicon gates using boron for the pMOS devices to minimize short channel effects. The diffusion of boron through the gate oxide and into the channel region results in the shifting of threshold voltages and unpredictability in the performance of the ultimate circuit after fabrication, particularly as the device ages. Therefore, in devices where boron is present in the gate polysilicon it becomes necessary for the gate oxide to act as a barrier to the diffusion of boron atoms.
SUMMARY OF THE INVENTION
A method of forming a nitrogen-implanted gate oxide in a semiconductor device includes preparing a silicon substrate; forming an oxide layer on the prepared substrate; and implanting N
+
ions into the oxide layer in a plasma immersion ion implantation apparatus.
An object of the invention is to place nitrogen at the top surface of an oxide layer prior to deposition of the gate polysilicon.
Another object of the invention is to provide nitrogen implantation into an oxide layer to effectively block the diffusion of boron into the oxide layer.
A further object of the invention is to preserve the reliability of a device constructed according to the invention, while maintaining the desired properties of the polysilicon layer.
REFERENCES:
patent: 5629221 (1997-05-01), Chao et al.
patent: 5672541 (1997-09-01), Booske et al.
patent: 5683918 (1997-11-01), Smith et al.
patent: 5953600 (1999-09-01), Gris
Article entitled “Surface Nitridation of Silicon Dioxide with a High Density Nitrogen Plasma”, by R. Kraft, T.P. Schneider, W.W. Dostalik and S. Hattangady published in 1997 American Vacuum Society Technol. B 15(4), Jul./Aug. 1997, pp 967-970.
Article entitled “Separation of Plasma Iimplantation of Oxygen to Form Silicon on Insulator” by X. Lu, S. Lyer, J. Liu, C. Hu and N.A. Cheung, published in 1997 American Institute of Physics Letter 70(13), Mar. 31, 1997, pp. 1748-1750.
Article entitled “The Effects of Nitrogen Implant into Gate Electrode on the Characteristics of Dual-Gate MOSFETs with Ultra-thin Oxide and Oxynitrides” by A.I. Chou, C. Lin, K. Kumar, P. Chowhry, M. Gardner, M. Gilmer, J. Fulford and J.C. Lee published in 1997 IEEE, Sep. 1997, pp. 174-177.
Ma Yanjun
Ono Yoshi
Krieger Scott C.
Lee, Jr. Granvill
Rabdau Matthew D.
Ripma David C.
Sharp Laboratories of America Inc.
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