Method for drying a semiconductor wafer

Details Method for drying a semiconductor wafer Method for drying a semiconductor wafer

2000-02-18

2001-09-18

Wilson, Pamela (Department: 3749)

Drying and gas or vapor contact with solids

Process

Gas or vapor contact with treated material

C034S343000, C034S404000, C034S408000, C034S410000, C034S417000, C034S449000, C034S470000

Reexamination Certificate

active

06289605

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of drying a semiconductor wafer, and more particularly, to a method for removing a residual solution, which comprises dissolved oxygen, from the semiconductor wafer.
2. Description of the Prior Art
During semiconductor fabrication processes, some metal ion, particle and organic compound may remain on the surface of the wafer. Native oxides may also form on the semiconductor wafer after cleaning, deposition, etching and conveying processes, degrading the quality of the semiconductor product. One or more cleaning processes are consequently employed to ensure the surface cleanliness of the semiconductor wafer.
In general, there are two types of cleaning processes: wet and dry. The wet cleaning process is wildly employed. After a wet cleaning process, a drying process is performed on the semiconductor wafer to remove any residual water as quickly as possible. The drying process is used to prevent water mark, and their associated defects, from forming on the wafer. Water mark occur when dissolved oxygen (DO) in the water reacts with the bare silicon on the surface of the semiconductor wafer.
Methods for drying semiconductor wafers according to the prior art include spin drying, IPA vapor drying and Marangoni drying, etc. Each of these drying methods has shortcomings. In order to improve the yield of the semiconductor manufacturing process, and also to avoid environmental pollution from chemical solutions used in some drying processes, a fast and effective drying process must be developed that does not use chemical solutions.
Please refer to FIG.
1
.
FIG. 1
is a cross-sectional diagram of spin drying a semiconductor wafer
10
according to the prior art. The surface of the semiconductor wafer
10
comprises many metal-oxide-semiconductor (MOS) transistors
14
, trenches
16
and contact holes
18
. Droplets
11
remain in the trenches
16
and contact holes
18
of the semiconductor wafer
10
. Spin drying uses centrifugal force to remove the droplets
11
from the surface of the semiconductor wafer
10
. The wafer
10
is spun at high speeds and at room temperature to quickly dry its surface. About six minutes per batch of wafers are required for the drying process. In
FIG. 1
, the arrow
17
indicates the direction of rotation of the semiconductor wafer
10
spinning around an axis of rotation
15
. The arrows
19
indicate the centrifugal force during the spinning process.
In general, the wafer rotational speed must be at least 3500 rpm (revolutions per minute) to ensure a complete removal of the droplets
11
from the surface of the semiconductor wafer
10
. However, excessive rotational speeds can lead to damage to the electric devices on the semiconductor wafer
10
. The speed of rotation is therefore usually set to 3000 rpm when spin drying according to prior art. Because the rotational speed is insufficient, water marks form on the semiconductor wafer
10
. Furthermore, dissolved oxygen in the water marks can cause additional defects on the semiconductor wafer
10
.
When using the prior art spin drying method to dry the semiconductor wafer
10
, the centrifugal drying effect is reduced due to the surface structure of the semiconductor wafer
10
. This structure comprises many trenches and walls, which are a consequence of the many devices on the surface. The droplets
11
are trapped within the trenches
16
and contact holes
18
, and so are difficult to remove by the centrifugal force
19
of the spin drying method. Another problem with spin drying is the issue of static charge. During the high-speed spinning of the semiconductor wafer
10
, it accumulates static charge. This charge attracts particles in the air, thereby reducing the surface cleanliness of the semiconductor wafer
10
.
Please refer to FIG.
2
.
FIG. 2
is a schematic diagram of a prior art IPA vapor drying process of the semiconductor wafer
10
. In
FIG. 2
, the arrows
21
indicate the vertical direction of an upwardly flowing IPA (isopropyl alcohol) vapor. This IPA vapor drying process uses a heater
32
to evaporate an IPA solution
12
, thereby forming the IPA vapor. Next, the semiconductor wafer
10
is placed inside the heated vapor of the IPA solution
12
, and condensed IPA replaces the water adhering to the surface. Finally, the water and the condensed IPA are together taken away through a collector
36
and a pipe
38
, completing the drying of the semiconductor wafer
10
. About 10 min/batch is required for the IPA vapor drying process.
However, the droplets
11
in the trenches
16
and contact holes
18
are not easily replaced by condensed IPA
12
. The IPA process does, however, avoid charge accumulation. It also requires the use of a great deal of IPA solution, which can lead to a lot of environmental pollution.
Please refer to FIG.
3
.
FIG. 3
is a side view of a prior art Marangoni drying process of a semiconductor wafer
20
. The Marangoni drying method involves slowly removing the semiconductor wafer
20
vertically from a washing tank (not shown), at a suitable speed and at room temperature, then using a nitride gas
23
and an IPA vapor
21
to blow dry the semiconductor wafer
20
. When the semiconductor wafer
20
is exiting from the surface
24
, a bent region is formed between the semiconductor wafer
20
and a meniscus
22
between gas and liquid, into which the IPA vapor
21
dissolves. This reduces the surface tension of the water, preventing the semiconductor wafer
20
from dripping water. The advantage of the Marangoni drying method is that it uses less IPA solution. But it is still difficult to replace the droplets of water in trenches and contact holes with condensed IPA.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present invention to provide a drying method for removing a residual solution comprising dissolved oxygen from a semiconductor wafer so as to avoid water marks on a semiconductor wafer, and to avoid the use of chemical solutions so as to prevent environmental pollution.
In a preferred embodiment, the present invention provides a method for drying a semiconductor wafer to remove a residual solution from the semiconductor wafer, the residual solution comprising dissolved oxygen, the method comprising:
placing the semiconductor wafer into a chamber, then lowering the air pressure of the chamber to draw out the oxygen from the water drop on wafer and to maintain evaporation of the residual solution from the semiconductor wafer;
injecting an inert gas into the chamber to exchange the dissolved oxygen in the residual solution with the inert gas; and
heating the semiconductor wafer to accelerate evaporation of the residual solution from the semiconductor wafer.
It is an advantage of the present invention that the drying method replaces the dissolved oxygen without the use of any chemical solutions, and dries the wafer in a vacuum. Thus, the drying method according to the present invention avoids the static charge issue, prevents the formation of water marks, and eliminates pollution from chemical drying solutions.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.


REFERENCES:
patent: 4841645 (1989-06-01), Bettcher et al.
patent: 5212877 (1993-05-01), Onur et al.
patent: 5315766 (1994-05-01), Roberson et al.
patent: 5351415 (1994-10-01), Brooks et al.
patent: 5351419 (1994-10-01), Franka et al.
patent: 5443540 (1995-08-01), Kamikawa
patent: 5551165 (1996-09-01), Turner et al.
patent: 5571337 (1996-11-01), Mohindra et al.
patent: 5634978 (1997-06-01), Mohindra et al.
patent: 5772784 (1998-06-01), Mohindra et al.
patent: 5815947 (1998-10-01), Brooks et al.
patent: 5855077 (1999-01-01), Nam et al.
patent: 5878760 (1999-03-01), Mohindra et al.
patent: 5891256 (1999-04-01), Mohindra et al.
patent: 5932027 (1999-08-01), Mohindra et al.
patent: 5940

Affiliated with

Also associated with

Rating

Method for drying a semiconductor wafer 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 for drying a semiconductor wafer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for drying a semiconductor wafer will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2517444