Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
2000-12-27
2003-06-24
Carrillo, Sharidan (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S026000, C134S027000, C134S029000, C134S034000, C134S036000, C134S042000, C134S902000
Reexamination Certificate
active
06582524
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a method for washing wafers and an apparatus for washing wafers, more in particular to the method and the apparatus for washing the wafers in which the removing rate of particles deposited onto the wafers is higher than that of a conventional method or apparatus.
(b) Description of the Related Art
In the manufacture of a semiconductor device, a wafer is washed for removing foreign substances, impurities and contaminations upon completion of each of process steps. The wafer is also frequently washed in pretreatment steps such as an initial washing step before processing a silicon substrate, a pre-oxidation washing step before deposition of a silicon oxide film on the silicon substrate, a washing step before ion implantation and a further washing step before deposition of a CVD film
As shown in
FIGS. 1 and 2
, a conventional wafer washing apparatus
10
known as a single vessel-type apparatus includes an inner chamber
12
for washing wafers with a washing solution composed of pure water and a chemical accommodated therein, an outer chamber
14
which surrounds the periphery of the inner chamber
12
and to which the washing solution overflows from the inner chamber
12
, a pure water supplying apparatus (not shown) and a chemical solution supplying apparatus (not shown).
In the wafer washing apparatus
10
, a plurality of wafers “W” disposed on a lifter
16
in an upright posture and separated from one another are transferred into the inner chamber
12
and washed at a time.
The lifter
16
includes a mounting table
16
a
having, for example, a width “W
1
” of 140 mm and a depth “L
1
” of about 180 mm and a gripping plate
16
b
extending upright from the deepest edge of the mounting table
16
a.
The mounting table
16
a
has a central bottom line and is higher toward the both ends of the table. Both the ends are higher than the central bottom line by a height “H
1
” of 30 mm. The mounting table
16
a
includes a plurality of holding trenches
16
c
extending parallel to the gripping plate
16
b
and separated from one another. The wafer “W” is fixed onto the mounting table
16
a
by engaging the bottom of the wafer “W” into the holding trench
16
c.
The inner chamber
12
is rectangular parallelepiped with a top opening having dimensions capable of accommodating the lifter
16
with the plurality of wafers, for example, a width “W
2
” of 220 mm, a depth “L
2
” of 200 mm and a height “H
2
” of 230 mm, and an inner volume thereof is about 10 liters.
The inner chamber
12
further includes pipes
18
A and
18
B having nozzles for ejecting the chemical solution and the pure water at both ends of the width direction of the inner chambers
12
, and a QDR (quick dump rinsing) drain port
20
having a large opening at the bottom thereof for rapidly discharging the chemical solution and the pure water in the inner chambers
12
.
The outer chamber
14
includes sidewalls disposed outer than those of the inner chambers
12
by about 30 mm, designated by “S” in FIG.
1
. The sidewalls of the outer chamber
12
have a height “H
3
” of 230 mm which is lower than the sidewalls of the inner chamber
12
by 0 to 5 mm (&Dgr;h) as shown in FIG.
1
. The outer chamber
14
further includes, at the bottom thereof, a port
22
for discharging the pure water and d the chemical solution overflown from the inner chamber
12
.
Referring to a flow chart of
FIG. 3
in addition to
FIGS. 1 and 2
, the method of washing the wafers by using the conventional wafer washing apparatus
10
will be described.
At first, pure water is supplied to the inner chamber
12
at a rate of 5 liter/min. through the pipes
18
A and
18
B and is allowed to be over-flown from the inner chamber
12
to the outer chamber
14
. While maintaining the overflow of the pure water, the lifter
16
mounting the wafers is dipped into the pure water in the inner chamber
12
(S
1
: wafer dipping step).
Then, pure water is supplied to the inner chamber
12
at a flow rate of 20 liter/min. for 2 minutes through the pipes
18
A and
18
B (S
2
: pure water upward flowing step).
After the supply of the pure water is stopped, the chemical solution including ammonia (NH
4
OH), hydrogen peroxide (H
2
O
2
) and pure water in a volume ratio of 1:1:50 is supplied to the inner chamber
12
at a flow rate of 20.8 liter/min. for 120 seconds through the pipes
18
A and
18
B for washing the wafers (S
3
: chemical solution upward flowing step).
After the supply of the chemical solution is stopped, the so-called dip washing is conducted for about 480 seconds while the wafers disposed on the lifter
16
are dipped in the chemical solution (S
4
: dip washing step).
Only pure water is supplied to the inner chamber
12
at a flow rate of 20 liter/min. for 30 seconds, in view of the fact that the volume of the inner chamber
12
is about 10 liters, through the pipes
18
A and
18
B for replacing the chemical solution in the inner chamber
12
with the pure water (S
5
: pure water replacing step).
Then, QDR is conducted (S
6
: QDR step). In the QDR washing, at first, the QDR drain port
20
is released to discharge the pure water in the inner chamber
12
supplied thereto in the pure water replacing step S
5
. After the QDR drain port
20
is stopped to fill the inner chamber
12
with the pure water, the QDR drain port
20
is released again to discharge the pure water in the inner chamber
12
. The procedures are repeated five or six times.
Then, only pure water is supplied to the inner chamber
12
at a flow rate of 20 liter/min. for 90 seconds through the pipes
18
A and
18
B, and a specific resistance of the pure water in the inner chamber
12
is confirmed to be substantially same as that of the pure water before the supply to the inner chamber
12
, the lifter is lifted to transfer the wafers to a drying chamber not shown (S
7
: finish washing step).
When the wafers are washed in accordance with the above procedures by using the single vessel-type wafer washing apparatus, the removing rate of particles deposited onto the wafer is poor and the washing of the wafers cannot be conducted satisfactorily.
The number of the particles deposited onto the wafer after the washing is high, and the washing is insufficient as a pretreatment or a post-treatment of a process for forming a finer pattern in a semiconductor device.
With the higher miniaturization and the higher integration of the semiconductor device, the miniaturization is more and more demanded together with the higher accuracy. Accordingly, the sufficient washing of the wafers meeting the higher accuracy processing cannot be achieved in the conventional wafer washing method.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a method for washing wafers and an apparatus for washing wafers which can be satisfactorily used as a pretreatment or a post-treatment of processing a semiconductor device by employing a single vessel-type wafer washing apparatus.
Thus, the present invention provides, in a first aspect thereof, a method including the consecutive steps of: dipping a wafer in a washing solution in a washing chamber; replacing the washing solution by a first chemical solution in the washing chamber receiving therein the wafer, the first chemical solution including at least one chemical; dipping the wafer in the first chemical solution after stopping the replacing; and replacing the first chemical solution by a second chemical solution including the at least one chemical and having a concentration lower than a concentration of said first chemical solution.
In accordance with the present invention, the particles floating in the first chemical solution is over-flown from the washing chamber together with the first chemical solution by replacing the first chemical solution with the second chemical solution, thereby discharging the particles from the washing chamber. Even if the particles are re-deposited onto the wafer in the second chemical solution supply step,
Carrillo Sharidan
NEC Electronics Corporation
Scully Scott Murphy & Presser
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