Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Grooved and refilled with deposited dielectric material
Reexamination Certificate
1998-01-12
2001-05-29
Chaudhuri, Olik (Department: 2823)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Grooved and refilled with deposited dielectric material
C438S439000, C438S443000
Reexamination Certificate
active
06239001
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for making a semiconductor device, and more particularly to, a method for making a semiconductor device where a device region and an isolation region for electrically isolating between devices are formed on a semiconductor substrate.
BACKGROUND OF THE INVENTION
Semiconductor devices, such as a transistor, wiring and contact, used to compose an integrated circuit have been needed to be finer with an increase in integration density of integrated circuits. Also, a device isolation width for isolating between devices has been needed to be narrower.
LOCOS process has been generally used to isolate between semiconductor devices. In LOCOS process, bird's beak encroachment may occur during field oxidation. Due to the bird's beak encroachment, the dimensions of device isolation width and device width become difficult to control. Under the circumstances, pad oxide film formed under nitride film is thinned to reduce the bird's beak encroachment of the pad oxide film so as to obtain a fine device.
However, finer device isolation becomes difficult to realize since leakage current is increased by a stress applied to a substrate during oxidation due to bird's beak size and thinned pad oxide film.
Poly-buffer LOCOS process, where polysilicon film is inserted between nitride film and pad oxide film, has been proposed to solve this problem. By inserting the polysilicon film, the bird's beak encroachment can be reduced to relieve the stress applied to the substrate.
N. Shimizu et al., “A Poly-Buffer Recessed LOCOS for 256 Mbit DRAM Cells”, IEDM92, pp.279-282, 1992 suggests a poly-buffer recessed LOCOS process, which is a modified poly-buffer LOCOS process, as a device isolation method applicable to 256 Mbit or more DRAM with a device isolation width of around 0.25 &mgr;m.
The polysilicon film used to relieve the stress needs to be removed with the nitride film after the field oxidation so as to form a transistor, diffusion layer etc. Also, the polysilicon film and the pad oxide film formed thereunder need to be further thinned to realize a finer device isolation width. In general, it is known that there occurs a void in the buffer polysilicon film itself while it serves to relieve the stress to the substrate. In particular, the void occurs around the edge of pattern where the bird's beak extends.
Around this void, the pad oxide film located under the polysilicon film may be also etched when the nitride film is removed by etching. In this state, when the polysilicon film is etched, the substrate may be holed since the void occurring portion does not have the pad oxide film or the pad oxide film is thinned. This is because the substrate is of monocrystalline silicon that has little etch selectivity to the polysilicon film.
When the substrate is holed, the leakage current and resistivity are increased, and therefore the characteristics are reduced or dispersed not to meet the device characteristics required. Further, even if it meets the device characteristics, the aesthetic appearance of the active region is thereby deteriorated.
Also, a method of doping nitrogen into polysilicon film so as to prevent the void from occurring in the buffer polysilicon film is proposed in IEDM94. However, when the void is decreased, the function to relieve the stress is reduced. Further, an additional apparatus to dope nitrogen into the polysilicon film is required.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a method for making a semiconductor device where the deterioration of electrical property can be prevented while employing polysilicon buffer LOCOS process to give finer device isolation to the device.
According to the invention, a method for making a semiconductor device where a device region and a device isolation region for electrically isolating between devices are formed on a semiconductor substrate, the device region including a transistor, comprises the steps of:
forming device isolation film by using polysilicon film or amorphous silicon film as a buffer; and
oxidizing the polysilicon film or amorphous film into silicon oxide film and then removing the silicon oxide film after forming the device isolation film.
According to another aspect of the invention, a method for making a semiconductor device where a device region and a device isolation region for electrically isolating between devices are formed on a semiconductor substrate, the device region including a transistor, comprises the steps of:
forming sequentially first oxide film, polysilicon film and silicon nitride film on the semiconductor substrate;
removing completely the silicon nitride film, the polysilicon film and the first oxide film corresponding to where the device isolation region is formed by etching, and removing part of the semiconductor substrate corresponding to where the device isolation region is formed by etching;
field-oxidizing the etched part of the semiconductor substrate to form field oxide film;
removing the silicon nitride film by etching; and
oxidizing the polysilicon film to form second oxide film and then removing the first and second oxide film over the device region.
According to another aspect of the invention, a method for making a semiconductor device where a device region and a device isolation region for electrically isolating between devices are formed on a semiconductor substrate, the device region including a transistor, comprises the steps of:
forming sequentially first oxide film, polysilicon film and silicon nitride film on the semiconductor substrate;
removing completely the silicon nitride film corresponding to where the device isolation region is formed by etching, and removing part of the polysilicon film corresponding to where the device isolation region is formed by etching;
field-oxidizing the etched part of the polysilicon film to form field oxide film;
removing the silicon nitride film by etching; and
oxidizing the polysilicon film to form second oxide film and then removing the first and second oxide film over the device region.
According to another aspect of the invention, a method for making a semiconductor device where a device region and a device isolation region for electrically isolating between devices are formed on a semiconductor substrate, the device region including a transistor, comprises the steps of:
forming sequentially first oxide film, polysilicon film and silicon nitride film on the semiconductor substrate;
removing completely the silicon nitride film, the polysilicon film and the first oxide film corresponding to where the device isolation region is formed by etching and removing part of the semiconductor substrate corresponding to where the device isolation region is formed by etching so as to form a groove on the semiconductor substrate;
oxidizing sidewall of the groove and part of the polysilicon film and then burying the groove with burying oxide film to form field oxide film;
removing the silicon nitride film by etching; and
oxidizing the polysilicon film to form second oxide film and then removing the first and second oxide film over the device region.
In this invention, the polysilicon film or amorphous silicon film is first oxidized into silicon oxide film and thereafter the obtained silicon oxide film is removed, when the polysilicon film or amorphous silicon film on the base silicon substrate is removed. The silicon oxide film has a high etch selectivity to the silicon substrate. Therefore, the base substrate can be formed not roughed by etching. Thus, LOCOS device isolation process can be conducted giving finer device isolation. Also, the dispersion of device can be reduced, thereby enhancing the reliability and production yield.
REFERENCES:
patent: 4506434 (1985-03-01), Ogawa et al.
patent: 4630356 (1986-12-01), Christie et al.
patent: 5358894 (1994-10-01), Fazan et al.
patent: 5360753 (1994-11-01), Park et al.
patent: 5369051 (1994-11-01), Rao et al.
patent: 5506440 (1996-04-01), Wei et al.
patent: 5554256 (1996-09-01), Pruijmboom et al.
Chaudhuri Olik
Coleman Wiliam David
Hutchins, Wheeler & Dittmar
NEC Corporation
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