Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1998-11-30
2001-12-11
Kunemund, Robert (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S710000, C438S712000, C438S714000, C438S715000
Reexamination Certificate
active
06329293
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor manufacturing process, and more particularly to a method for cleaning a polymer that is produced in an etching process.
BACKGROUND OF THE INVENTION
In the semiconductor manufacturing process, a deep trench has been widely used in devices, such as when manufacturing a capacitor of a dynamic random access memory (DRAM) unit.
FIG. 1
includes steps of manufacturing the deep trenches applied to a capacitor of a DRAM unit. In FIG.
1
(
a
), a dielectric layer
11
is formed on a silicon substrate
10
and is usually made of silicon dioxide/silicon nitride/silicon dioxide or just silicon dioxide. This dielectric layer is used as a hard mask for a subsequent etching process. The dielectric layer
11
is patterned by a photolithography and an etching process. In FIG.
1
(
b
), a photoresist layer
12
is formed on the dielectric layer
11
and a pattern is defined on photoresist layer
12
by a photolithography process. A window of hard mask
13
on the dielectric layer
11
is formed by a dry anisotropic etching process, then the pattern is transferred to the silicon substrate
10
after removing the photoresist layer
12
as shown in FIG.
1
(
c
). Thereafter, the part of the silicon substrate
10
which is not covered by the hard mask is etched by another dry etching process to obtain a deep trench as shown in FIGS.
1
(
d
) and
1
(
e
).
However, an oxide-rich-polymer
14
will remain at the sidewalls and the bottom of the trenches during the dry etching process. In order to remove this polymer, a wet etching process is commonly used. A buffer oxide etcher (BOE) containing a mixture of hydrofluoric acid and ammonium fluoride is used as an etching agent for the wet etching process. However, the polymer deposition may be changed due to the poor quality of the BOE buffer, the changed chamber condition of the dry etching process, the performance of the spin dryer in the wet etching machine, or a reduced size of the deep trench, resulting in that the BOE solution can not enter the bottom of the deep trench easily. Therefore, the polymer in the bottom of the deep trench can not be removed completely by the wet etching process.
After cleaning the deep trench, another dielectric layer is formed on the silicon substrate and then the trenches are filled with polysilicon or &agr;-silicon, as shown in FIG.
2
. If the polymer in the trench is not removed completely, it will influence the quality of the dielectric layer so that the capacitance of the cell will be reduced or a current leakage will occur. Furthermore, the polysilicon or &agr;-silicon will not fill the trench very well resulting in an occurrence of a void or a seam on the sidewall, poor quality of DRAM, or even a decreased yield of DRAM.
Because the size of the semiconductor device will be minimized, the hole size of the trench of a capacitor in a DRAM unit becomes smaller, the ratio of hole size (0.35 &mgr;m) to depth (7 &mgr;m) is
1
:
20
generally, and it becomes harder to clean the polymer in such a small hole of the trench by a wet etching process. For the above reasons, it is desirable to develop a method to improve the defects of the prior art. It is attempted by the applicant to develop such a process.
SUMMARY OF THE INVENTION
A major object of the present invention is to provide a method for cleaning a polymer formed in a trench of a semiconductor.
The process for removing a polymer formed in a trench according to the present invention includes the steps of introducing a gas into the trench for reacting with the polymer to form a volatile substance and removing the polymer remaining in the trench.
In accordance with the present invention, the deep trench is produced by steps as follows. First, providing a silicon substrate, then forming a dielectric layer on the silicon substrate to serve as a hard mask, and forming a photoresist layer on the dielectric layer. Etching a portion of the photoresist layer to expose a portion of the hard mask and removing the exposed hard mask to expose a corresponding portion of the silicon substrate. Finally, removing the photoresist layer remaining on said dielectric layer and removing the exposed portion of the silicon substrate to form the trench. The exposed portion of the silicon substrate is removed by a dry anisotropic etching process.
The gas for cleaning the polymer is a gaseous hydrofluoric acid and is applied to the trench to react with the polymer for 15 seconds at room temperature and 1 atm. The remaining polymer is removed by a wet etching process using a buffer oxide etcher (BOE) as an etching agent which containing hydrofluoric acid and ammonium fluoride.
In the prior art, the method for cleaning the polymer is just a wet etching process. The buffer oxide etcher (BOE) of the wet etching can not enter or be removed from the trench easily so that it becomes more difficult to completely remove the polymer at the bottom of the deep trench. In the present invention, a gaseous hydrofluoric acid is applied to the trench to clean the polymer and then a wet etching process is performed to remove the remaining polymer in the trench. Because the gas can enter the small hole of the deep trench easily, this method can solve the problem encountered in the prior art, and can effectively improve the quality of a DRAM and increase the yield of the product.
The present invention will be illustrated in details with reference to the accompany drawings, in which:
REFERENCES:
patent: 4343677 (1982-08-01), Kinsbron et al.
patent: 5348619 (1994-09-01), Bohannon et al.
patent: 5688410 (1997-11-01), Kajitani et al.
patent: 5744402 (1998-04-01), Fukazawa et al.
patent: 5759921 (1998-06-01), Rostoker
patent: 5908735 (1999-06-01), Kim et al.
patent: 5933759 (1999-08-01), Nguyen et al.
Tien Yu-Chung
Tsai Song-Ping
Greer Burns & Crain Ltd
Kunemund Robert
Vinh Lan
Winbond Electronics Corp.
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