Semiconductor device manufacturing: process – Cleaning of reaction chamber
Reexamination Certificate
1998-04-07
2002-11-12
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Cleaning of reaction chamber
C438S788000, C438S685000
Reexamination Certificate
active
06479410
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a processing method for cleaning an object to be processed after it has been subjected to a film-formation process.
2. Description of Related Art
Aluminum wiring is mainly used as the wiring pattern of an integrated circuit and an SiO
2
or SiOF film is used as an inter-layer insulating film for insulating that wiring. These films are formed by using a plasma apparatus that performs an electron cyclotron resonance (ECR) processing, as shown in
FIG. 6
by way of example.
In
FIG. 6
, microwaves M at, for example, 2.45 GHz are supplied into the interior of a plasma generation chamber
1
A of a vacuum vessel
10
, and also a magnetic field of, for example, 875 Gauss is applied thereto by an electromagnetic coil
12
, so that the mutual interaction (resonance) between the microwaves and the magnetic field causes a plasma to be formed from a plasma gas such as Ar or O
2
and also a film-formation gas such as SiH4 which is introduced into a film-formation chamber
1
B. This forms a film on a semiconductor wafer (hereinafter referred to simply as “wafer”) W that is mounted on a mounting stand
13
(see FIG.
7
A). This mounting stand
13
is provided with a foil electrode
15
and a resistance heater
16
for heating the wafer W to a predetermined temperature, and it is covered by an insulating layer
14
formed of a material such as a polyimide, alumina, or aluminum nitride, and is configured so that the surface thereof acts as an electrostatic chuck.
If the above film-formation step is repeated, a film S will adhere to the periphery of the mounting stand
13
and the inner walls within the film-formation chamber
1
B, as shown in
FIG. 6
, and this film S will crack and generate particles when it reaches a certain thickness. A cleaning process to remove the adhered film S is therefore performed every time a dozen or so wafers W have been processed. The cleaning process for removing an SiO
2
film or the like, is done by sending a fluorine-based gas such as CF
4
or NF
3
as a cleaning gas into the film-formation chamber
1
B, activating the cleaning gas by a plasma, then causing radicals to react with the adhered film to remove it (see FIG.
7
C).
Unfortunately, if the mounting stand
13
is exposed to a plasma, the surface of the electrostatic chuck will be struck by the plasma and will be roughened thereby. This will change the attractive force with respect to the wafer W and the heat conduction within the surface, thus worsening the surface uniformity with which the film thickness is formed on the wafer W. In order to protect the surface of the mounting stand
13
from the plasma, it has been considered to place a dedicated protective wafer CW on the mounting stand
13
as shown in
FIG. 7C
, and perform the cleaning. An alumina (Al
2
O
3
) disk
17
having an aluminum (Al) layer
17
a
formed on the lower surface thereof is used as this protective wafer CW, and this protective wafer CW is held by the electrostatic attraction of the aluminum layer
17
a
onto the mounting stand
13
.
The alumina that is the material of the protective wafer CW is a ceramic. So it is weak with respect to thermal shocks but the protective wafer CW is attracted onto the mounting stand
13
. Therefore, even though the surface temperature is raised abruptly by the plasma, heat escapes towards the mounting stand and thus the thermal shocks can be reduced to a certain extent.
However, there is a tendency towards increasing the processing temperatures during this film-formation process, in order to improve the quality of the film formed thereby, so that the wafer W is heated to approximately 350° C. by the resistance heater
16
and the plasma during the process of forming an SiOF film. The temperature of the surface of the mounting stand
13
at this point is approximately 200° C. In this case, the electrostatic attraction ensures that the thermal shock on the alumina can be reduced to a certain extent, but, even so, the surface temperature of the mounting stand
13
has an upper limit of about 150° C. and thus any temperature above that will cause the alumina to crack from thermal shock. Therefore, to prevent cracking of the protective wafer CW, the cleaning must be performed after the surface temperature of the mounting stand
13
has been reduced to about 150° C., but this means that it takes time before the cleaning can start.
When the cleaning has ended, fluorine from within the cleaning gas is still dispersed within the vacuum vessel in a radical state, or it has adhered to the inner walls thereof. Thus, if the film-formation processing is performed immediately after this cleaning, the fluorine will be incorporated into the processing of the first few wafers W, particularly the very first wafer, which will impair the film quality. In such a case, pre-coating is performed after the cleaning in order to form a pre-coating film on the inner walls of the vacuum vessel
10
and thus fix the fluorine to the inner wall surfaces, as described below. This pre-coating is a film-formation processing that acts as a preliminary step. If the main film-formation processing step is to create an SiO
2
film or the like, the pre-coating film is formed of SiO
2
or SiOF or the like.
To prevent the pre-coating film from forming on the surface of the mounting stand
13
, a protective wafer PW for pre-coating, made of a material such as a silicon wafer, is placed on the surface of the mounting stand
13
(see FIG.
7
D). After the pre-coating has ended, a wafer W for processing is mounted on the mounting stand
13
and once again the formation of an SiO
2
film or the like is performed (see FIG.
7
E).
The pre-coating gas used for this pre-coat is the same as the film-formation gas. So an alumina wafer can be used as the protective wafer PW. Therefore an alumina protective wafer PW is used for the pre-coating. The processing is performed while the temperature of the mounting stand
13
is being raised until it is close to the temperature of the film-formation process.
However, since the pre-coating takes only a short time, the temperature of the mounting stand
13
cannot rise to the temperature required for the film-formation during that time, and thus more time elapses before the film-formation processing can start. If an alumina protective wafer PW is used in this manner, it takes time to adjust the temperature before each of the cleaning processing and the film-formation processing can start, which reduces the throughput.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a processing method that enables cleaning while protecting the mounting surface of the mounting stand for the object to be processed, such as the surface of the electrostatic chuck. In addition to the above object, another object of the present invention is to provide a processing method that enables processing at a high throughput.
The present invention therefore provides a processing method for an object to be processed, comprising the steps of: mounting an object to be processed on a mounting stand provided within a film-formation chamber; performing a film-formation process on the object to be processed by supplying a film-formation gas into the film-formation chamber; mounting a protective plate of aluminum nitride of the same size as the object to be processed on the mounting stand; and then introducing a cleaning gas into the film-formation chamber to form a plasma, thereby cleaning the interior of the film-formation chamber.
After this cleaning process, it is possible to perform a further step of introducing a film-formation gas into the film-formation chamber to perform a pre-coating process, while the protective plate is still mounted on the mounting stand.
REFERENCES:
patent: 5326723 (1994-07-01), Petro et al.
patent: 5456757 (1995-10-01), Aruga et al.
patent: 5620526 (1997-04-01), Watatani et al.
patent: 5705080 (1998-01-01), Leung et al.
patent: 5785796 (1998-07-01), Lee
patent: 5846883 (1998-12-01), Moslehi
Abe Shoichi
Shiota Iku
Niebling John F.
Pompey Ron
Smith , Gambrell & Russell, LLP
Tokyo Electron Limited
LandOfFree
Processing method for object to be processed including a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Processing method for object to be processed including a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Processing method for object to be processed including a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2945585