Method for forming bottle trench

Details Method for forming bottle trench Method for forming bottle trench

2003-03-03

2004-11-09

Zarneke, David A. (Department: 2829)

Semiconductor device manufacturing: process

Chemical etching

Combined with coating step

Reexamination Certificate

active

06815356

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming a bottle trench, and more particularly to a method for forming a bottle trench using an etching stop layer.
2. Description of the Prior Art
Generally, capacitors in presently extensively used dynamic random access memory (DRAM) include two electrode plates with an insulating material therebetween. The charge storage capacity of the capacitor depends on the insulating material thickness, the surface area of the electrode plates, and the electrical properties of the insulating material. In recent years, the semiconductor design has a trend toward decreased device size in order to obtain higher density. Therefore, the substrate area of the memory cell must be decreased in order for the integrated circuits to accommodate a large number of memory cells. Also, the electrode plate of the memory cell capacitor must have adequate surface area in order to store sufficient charge.
However, with reduction in size, the trench storage node capacitance in the DRAM decreases accordingly. Therefore, there is a need to increase the storage capacitance in order to maintain sufficient memory operation.
Presently, one popular method of increasing the storage capacitance of DRAM forms a bottle shaped capacitor. This increases the width of the trench bottom for increased surface area.
FIGS. 1A
to
1
H are cross-sections illustrating the conventional process flow of forming a bottle trench. First, referring to
FIG. 1A
, a pad structure
16
including a pad nitride layer
14
and a pad oxide layer
12
is formed on a silicon substrate
10
. Then, the pad structure
16
is used as an etching mask to etch the silicon substrate
10
by dry etching, forming a trench
18
.
Subsequently, referring to
FIG. 1B
, a pad oxide layer
20
, an etching stop layer
22
, and a polysilicon layer
24
are successively formed in the trench
18
. Then, an oxide layer
26
is formed by thermal oxidation. Then, a mask layer
28
, for example, a photoresist layer, is deposited. The etching stop layer
22
can generally be a nitride layer.
Subsequently, referring to
FIG. 1C
, the mask layer
28
at the upper portion of the trench
18
is removed.
Subsequently, referring to
FIG. 1D
, the oxide layer
26
uncovered by the mask layer
28
at the upper portion of the trench
18
is removed.
Subsequently, referring to
FIG. 1E
, the remaining mask layer
28
is removed.
Subsequently, referring to
FIG. 1F
, the upper portion of the polysilicon layer
24
is nitrided to form a nitride layer
30
.
Subsequently, referring to
FIG. 1G
, the oxide layer
26
and the polysilicon layer
24
uncovered by the nitride layer
30
at the bottom portion of the trench
18
are removed by wet etching. Next, the nitride layer
30
and the nitride layer
22
at the bottom portion of the trench
18
are removed by wet etching using phosphoric acid.
Finally, referring to
FIG. 1H
, the residual polysilicon layer
24
at the upper portion of the trench
18
is removed. The pad oxide layer
20
at the bottom portion of the trench
18
is removed by wet etching using the etching stop layer
22
as a mask.
However, the above conventional process uses complicated stacked sacrificial layers. Also, the process is very complicated, and the process time is long, proving detrimental to mass production.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-mentioned problems and provide a method for forming a bottle trench. The benefit of the present invention resides in that TEOS (tetra-ethyl-ortho-silicate) is used as a sacrificial etching stop layer in the bottle trench formation. The TEOS layer can be easily removed with hydrofluoric acid solution.
To achieve the above object, the present inventive method for forming a bottle trench in a substrate having a pad structure and a trench includes the following steps. First, a first insulating layer is formed in the trench, and then a portion of the first insulating layer is removed to a certain depth of the trench. Next, a second insulating layer is formed in the trench, and portions of the second insulating layer on the pad structure and the sidewalls of the trench are removed. Next, an etching stop layer is formed in the trench, and a bottom portion of the etching stop layer is removed. Finally, the etching stop layer is used as a mask to remove the remaining second insulating layer and the first insulating layer.


REFERENCES:
patent: 6391706 (2002-05-01), Wu et al.

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