Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1999-09-23
2001-09-18
Utech, Benjamin L. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S710000, C438S712000, C438S713000, C438S714000
Reexamination Certificate
active
06291355
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a fabrication method for a self-aligned contact opening. More particularly, the present invention relates to a method for improving the self aligned effect of the self-aligned contact opening using polysilicon in order to reduce loss of a cap layer above a word line and a spacer on a sidewall of the word line.
2. Description of Related Art
In the deep sub-micron integrated circuit (IC) process, an opening with smaller size is often formed using a self-aligned contact process. Since the self-aligned contact process indirectly increases the process window of the photolithography, the size of the chip is reduced by using the self-aligned contact process.
In the conventional self-aligned contact process, a nitride cap layer is formed on a word line, with a nitride spacer forming on a sidewall of the word line. A silicon oxide layer is then formed to cover the cap layer and the spacer before coating a photoresist layer on the silicon oxide layer. After the photoresist layer is patterned using photolithography, the silicon oxide layer is etched, using a silicon oxide etching recipe with high etching selectivity for silicon oxide to silicon nitride and the photoresist layer serving as an etching mask. During the etching process, the silicon nitride cap layer above the word line and the silicon nitride spacer on the sidewall of the word line may serve as a secondary mask, so that a self-aligned contact opening is formed in the silicon oxide layer. The self-aligned contact opening is then filled with tungsten or polysilicon to form a plug.
However, some oxygen atoms may be released from the silicon oxide layer into the etching environment when the silicon oxide layer is etched using the conventional silicon oxide etching solution. As the amount of oxygen atoms in the etching solution increases, the degree to which the silicon nitride cap layer and the silicon nitride spacer are removed also increases. As a result, the etching selectivity for silicon oxide to silicon nitride is reduced, causing a more serious parasitic capacitance effect between the word line and the plug, thus the transmission rate of the word line and its adjacent plug are also affected. In an even more serious case, a shortcircuit occurs between the plug and its adjacent word line. With the trend to continuously reduce size of the device, the bottom width of the silicon nitride spacer on the sidewall of the word line is also reduced according to the design rule. This makes performance of the self-aligned contact process even more difficult.
SUMMARY OF THE INVENTION
The invention provides a method for improving the etching selectivity for silicon oxide to silicon nitride without changing the conventional silicon oxide etching recipe, so as to form a self-aligned contact opening with better quality.
As embodied and broadly described herein, the invention provides a method for fabricating a self-aligned contact opening. The method involves forming a conductive line on the substrate, wherein the conductive line is covered by a nitride cap layer and a nitride spacer. A gap between the conductive lines is filled with a silicon oxide layer, while the surface of the nitride cap layer is exposed. A polysilicon layer is selectively formed on the exposed nitride cap layer, followed by forming a photoresist layer, which covers a part of the polysilicon layer and the silicon oxide layer. With the photoresist layer serving as a principal etching mask, and the polysilicon layer as a secondary etching mask, an etching process is performed. The silicon oxide etching recipe having high etching selectivity for silicon oxide to nitride is used in the etching process, so that the self-aligned contact is formed in the silicon oxide layer. The photoresist layer is then removed.
According to the preferred embodiment, the nitride spacer is also included as a secondary mask during the etching step if the surface of the silicon oxide layer is approximately level with the surface of the nitride cap layer. However, the polysilicon layer may extend to a corner of the nitride spacer and has a bumper shape if the surface of the silicon oxide layer is lower than the surface of the nitride cap layer.
Furthermore, the invention provides another fabrication method for a self-aligned contact opening, which method involves forming a conducting layer, a nitride insulating layer, and a polysilicon layer in sequence on a substrate. These layers are then patterned to form a conductive line, a nitride cap layer, and a polysilicon protective layer. A nitride spacer is formed on a sidewall, which covers the conductive line, the nitride cap layer, and the polysilicon protective layer, so that the conductive line is covered by the nitride cap layer and the nitride spacer. A silicon oxide layer is formed to cover the polysilicon protective layer and the nitride spacer. The silicon oxide layer is planarized with a photoresist layer formed thereon. With the photoresist layer serving as a principal etching mask, and the polysilicon protective layer as a secondary mask, an etching process is performed. An etching recipe having high etching selectivity for silicon oxide to nitride is used in the etching process, so that a self-aligned contact opening is formed in the silicon oxide layer. The photoresist layer is then removed.
According to the preferred embodiment, the surface, of the silicon oxide layer is higher than or level with the surface of the polysilicon protective layer after the silicon oxide layer is planarized.
In addition, the invention provides another fabrication method for a self-aligned contact opening, which method involves forming a conducting layer, a nitride insulating layer, and a polysilicon layer in sequence on a substrate. These layers are then patterned to form a conductive line, a nitride cap layer, and a polysilicon protective layer. A nitride spacer is formed on a sidewall, which covers the conductive line, the nitride cap layer, and the polysilicon protective layer. A silicon oxide layer is formed to fill a gap between the conductive lines, while the surface of the nitride cap layer and a corner of the nitride spacer are exposed. The exposed nitride spacer is then protected by a polysilicon spacer formed thereon. A photoresist layer is formed to cover the silicon oxide layer, the polysilicon protective layer, and the polysilicon spacer. With the photoresist layer serving as a principal etching mask, and the polysilicon protective layer as a secondary mask, an etching process is performed. An etching recipe having high etching selectivity for silicon oxide to nitride is used in the etching process so as to form a self-aligned contact opening in the silicon oxide layer. The photoresist layer is then removed.
The fabrication method for the self-aligned contact opening described above adopts the conventional silicon oxide etching recipe and polysilicon to reduce or even prevent loss of the nitride cap layer and the nitride spacer around the conductive line. Since the silicon oxide etching recipe has high etching selectivity for silicon oxide to polysilicon, a polysilicon layer may serve as a protective layer in the invention.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 5670404 (1997-09-01), Dai
patent: 5780339 (1998-07-01), Liu et al.
patent: 5879986 (1999-03-01), Sung
patent: 6080620 (2000-06-01), Jeng
Chen Hsi-Chuan
Huang Sen-Huan
Liu Haochieh
Sheu Bor-Ru
Huang Jiawei
J.C. Patents
Utech Benjamin L.
Vinh Lan
Windbond Electronics Corp.
LandOfFree
Method of fabricating a self-aligned contact opening does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of fabricating a self-aligned contact opening, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of fabricating a self-aligned contact opening will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2502069