Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
1999-02-12
2001-03-13
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S238000
Reexamination Certificate
active
06200844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to a method of manufacturing a dielectric film of a capacitor in a dynamic random access memory (DRAM), and more particularly to a method for improving the charge storage ability of the capacitor.
2. Description of the Related Art
Typically, a single DRAM cell comprises a metal-oxide-semiconductor (MOS) and a capacitor used to store signals therein. As more charges stored in the capacitor, the less the effect of the noise is when the data are read by a reading amplifier. Additionally, the refreshing frequency is reduced as the charges stored in the capacitor are increased. Currently, the method of increasing the charges storage ability includes: (1) increasing the surface of the capacitor to increase the amount of the charges stored in the capacitor, but this decreases the integration of the DRAM; (2) choosing a proper dielectric material to form a dielectric layer of the capacitor with a relatively high permittivity to increase the amount of the charges stored per unit surface area of the capacitor; and (3) decreasing the thickness of the dielectric layer.
Conventionally, the dielectric film of the capacitor is an oxide-nitride-oxide (ONO) dielectric layer, which is a sandwich structure of an oxide layer, a silicon nitride layer and an oxide layer. The method of forming the ONO dielectric layer comprises the steps of forming a native oxide layer on the lower electrode, which is the storage electrode, and forming a silicon nitride layer on the oxide layer. An oxide layer is formed on the silicon nitride layer. The native oxide layer is naturally formed and cannot be easily removed. The dielectric constant of the native oxide layer is lower than the dielectric contact of the nitride layer. The dielectric constant of the dielectric film of the capacitor thus cannot be decreased.
SUMMARY OF THE INVENTION
The invention provides a method of manufacturing a dielectric film for a capacitor in a DRAM. In the invention, the native oxide layer is removed using a rapid ramp process at a pressure lower than 10
−5
torr. A nitridation is performed to form a dielectric layer on the surface of a storage electrode. A silicon nitride layer is formed on the dielectric layer. The rapid ramp process is started at a temperature of about 450-550° C. The temperature is raised at a rate of about 80-120° C./minute. The rapid ramp process is stopped at about 700-850° C. The nitridation is performed using a source gas, such as ammonia at about 700-850° C. for a relatively long time of about 10-60 minutes. The dielectric layer comprises silicon nitride or silicon-oxy-nitride. An oxide layer is further formed on the silicon nitride layer. The oxide layer is formed by, for example, a rapid thermal process. A gas used in the rapid thermal process can be selected from a group comprising nitrogen monoxide (N
2
O), oxygen and combinations of nitrogen monoxide (N
2
O) and oxygen. The dielectric film structure of the capacitor of the invention can be a double-layer structure, such as silicon nitride/silicon oxide or a mono-layer structure, such as silicon nitride.
The method of the invention removes a native layer on the storage electrode in a short time. The method of the invention thus has a low thermal budget. Moreover, the nitration process is performed on the surface of the storage electrode without the native layer to prevent another native layer forming, on the storage electrode. The dielectric film formed according to the invention has no native layer so that the dielectric constant of the capacitor is increased and the capacitance stored in every unit area is increased.
REFERENCES:
patent: 5663087 (1997-09-01), Yokozawa
patent: 5846859 (1998-12-01), Lee
patent: 5917213 (1999-06-01), Iyer et al.
patent: 6057189 (2000-05-01), Huang et al.
Blakely & Sokoloff, Taylor & Zafman
Nelms David
Nhu David
United Microelectronics Corp.
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