Semiconductor device manufacturing: process – Making passive device – Stacked capacitor
Reexamination Certificate
2001-06-14
2003-01-28
Whitehead, Jr., Carl (Department: 2822)
Semiconductor device manufacturing: process
Making passive device
Stacked capacitor
C257S303000
Reexamination Certificate
active
06511891
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a semiconductor structure. More particularly, the present invention relates to the lower electrode structure of a capacitor that can withstand the flushing force produced by a cleaning agent.
2. Description of Related Art
Capacitor is the data storage section of a dynamic random access memory (DRAM). Data value of each memory cell is recorded as the amount of charges carried by the capacitor. Due to the miniaturization of memory cells, each cell is very small. To increase the capacitance of a capacitor and to reduce data errors and the number of memory refreshes, height of the lower electrode is frequently raised to increase the effective surface area of a capacitor.
FIG. 1
is a schematic cross-sectional view of the lower electrode of a conventional capacitor. To fabricate a conventional capacitor, a plurality of metal-oxide-semiconductor MOS transistors is formed over a substrate
100
. Each MOS transistor includes a gate electrode
102
above the substrate
100
, spacers
104
on the sidewalls of the gate electrode
102
and source/drain regions
106
in the substrate
100
on each side of the gate electrode
102
. A dielectric layer
108
is formed over the substrate
100
covering the MOS transistor. A bit line
110
is formed in the dielectric layer
108
. The bit line
110
is electrically connected to one of the source/drain terminals
106
. Another dielectric layer
112
is formed over the substrate
100
covering the bit line
110
. A plurality of lower electrodes
114
that pass through the dielectric layers
108
and
112
is formed with each lower electrode
114
electrically connected to a source/drain terminal
106
.
FIG. 2
is a top view showing a plurality of conventional capacitor lower electrodes on a substrate. As shown in
FIG. 2
, a conventional lower electrode
114
has a rectangular shape. Before carrying out other processing treatment such as the growth of hemispherical silicon grains over the electrode for increasing effective surface area or the deposition of a capacitor dielectric layer, RCA cleaning solution is used to clean the surface. The RCA solution contains de-ionized water, sulfuric acid (H
2
SO
4
) and hydrogen peroxide (H
2
O
2
). The cleaning process includes repeated flushing of the lower electrodes
114
with de-ionized water, sulfuric acid solution and hydrogen peroxide solution.
However, as size of each memory cell is reduced, height of the capacitor lower electrode
114
must increase correspondingly to compensate for the shrinkage in surface area so that sufficient charge storage capacity is still present. Yet, the increase in height makes the lower electrode
114
more vulnerable to tearing when RCA solution is used to clean the surface.
FIG. 3
is a top view showing the array of capacitor lower electrodes-after flushing with a cleaning solution. As shown in
FIG. 3
, a few of the lower electrodes
114
are flushed away from their original positions into new positions
114
a
. Due to the flushing damages, production yield of the process is lowered.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a method of forming the lower electrode of a capacitor capable of withstanding the flushing force produced by a cleaning agent. A lower electrode having a rectangular profile when viewed from the top is provided. The lower electrode is bounded by a pair of ends and a pair of sides. The ends and the sides are linked together. The ends have a wedge shape. The sides have edges that cave in towards the center, thereby forming a recess region between the sides. A flushing operation is carried out using a cleaning solution. The cleaning solution flows from one end of the electrode to the other end along the sides.
This invention also provides an alternative method of forming the lower electrode of a capacitor capable of withstanding the flushing force produced by a cleaning agent. The lower electrode is a rectangular prism and has an hourglass shape when viewed from the top. The two sides of the lower electrode are edges that cave in towards the center. A recess region is defined between the two sides. A flushing operation is carried out using a cleaning solution. The cleaning solution flows from one end of the lower electrode to the other along the two sides of the lower electrode.
The step of flushing the lower electrodes can be carried out before other processing treatment such as the growth of hemispherical silicon grains over the electrode for increasing effective surface area or the deposition of a capacitor dielectric layer. The cleaning process includes repeated flushing of the lower electrodes with solutions such as de-ionized water, sulfuric acid solution and hydrogen peroxide solution.
The capacitor lower electrode structure of this invention has an hourglass profile and hence a more streamline body. According to fluid dynamics, resistant towards fluid motion is smaller. Consequently, the cleaning solution rushing past the lower electrode will cause less shearing and hence will result in the least damage. Furthermore, surface area of the lower electrode is also more than a conventional lower electrode, thereby increasing capacitance of the capacitor.
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: 6184078 (2001-02-01), Yoon et al.
patent: 40-3025971 (1991-02-01), None
patent: 2000-021613 (1998-06-01), None
Lin Benjamin Szu-Min
Sun Nathna
Wang Chuan-Fu
Jr. Carl Whitehead
Perkins Pamela E
United Microelectronics Corp.
Wu Charles C. H.
Wu & Cheung, LLP
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