Measuring and testing – Fluid pressure gauge – Combined
Reexamination Certificate
1999-11-26
2001-09-18
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Combined
Reexamination Certificate
active
06289737
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vacuum pressure control system for use in a semiconductor manufacturing apparatus or line.
2. Description of Related Art
In a CVD system in a semiconductor manufacturing apparatus or line, for instance, material gas which consists of elements which constitute a thin film material is supplied on wafers placed in a reaction chamber, while the inside of the reaction chamber is maintained under decompression, or vacuum. For example, in a CVD system shown in
FIG. 14
, the material gas is supplied on the wafers placed in the reaction chamber
111
which is a vacuum vessel through an inlet port
111
thereof. Simultaneously, the gas in the reaction chamber
110
is exhausted through an outlet port
112
of the reaction chamber
111
by suction of a vacuum pump
113
. Thus, the inside of the reaction chamber
110
is maintained under vacuum.
At this time, it is necessary to maintain the vacuum pressure in there action chamber
110
constant. However, the constant value varies over a wide range of pressure from atmospheric pressure or a low vacuum near atmospheric pressure to a high vacuum according to various conditions. Then, in Japanese Patent No. 2,677,536, applicant of the present invention has disclosed a vacuum pressure control system capable of providing a constant vacuum over a wide range from a low vacuum near atmospheric pressure to a high vacuum.
FIG. 14
shows an example of the vacuum pressure control system. In such the vacuum pressure control system, the vacuum pressure in the reaction chamber
110
is measured by vacuum pressure sensors
114
and
115
. In response to a difference between the measured pressure value and a desired vacuum pressure value given from the exterior, the control system controls the opening degree of a vacuum proportional opening and closing valve
116
provided with a poppet valve configuration.
The control system changes the conductance of an exhaust system from the reaction chamber
110
to the vacuum pump
113
in accordance with the opening degree of the opening and closing valve
116
, and executes feedback-control on the vacuum pressure in the reaction chamber
110
.
Thus, the control of the opening degree of the vacuum proportional valve
116
makes it possible to widely and surely change the conductance of the exhaust system. Accordingly, the vacuum pressure in the reaction chamber
110
can be maintained constant at a desired vacuum pressure value over a wide range from atmospheric pressure or a low vacuum near atmospheric pressure to a high vacuum.
In the conventional vacuum pressure control system, as mentioned above, the vacuum pressure sensors
114
and
115
measure the vacuum pressure in the reaction chamber
110
, and the opening of the valve
116
is controlled in response to the difference between the measured vacuum pressure value and the desired vacuum pressure value, thereby changing the conductance of the exhaust system. However, the control system can not control the speed at which the vacuum pressure value in the reaction chamber
110
approaches the desired value (referred to as “vacuum pressure changing speed” hereinafter).
In the field of recent semiconductor manufacturing apparatus or line, it is required to prevent particles from flying up in the reaction chamber
110
in order to more improve the quality of a thin film formed on the wafer in the reaction chamber
110
.
For that, when evacuation of the reaction chamber
110
is conducted so that the vacuum pressure value in the reaction chamber
110
which is under atmospheric pressure or a low vacuum near the atmospheric pressure reaches a desired value, the process of exhausting gas from the chamber
110
must be slowly conducted. However, the conventional vacuum pressure control system could not control the progress of exhausting gas from the chamber
110
and could not meet the above requirement.
The conventional vacuum pressure control system is therefore configured such that a bypass valve
117
having a fixed orifice is disposed in parallel to the vacuum proportional opening and closing valve
116
, as shown in FIG.
14
. In order to control the vacuum pressure in the chamber
110
to the desired vacuum pressure value, the bypass valve
117
is opened while the valve
116
is closed to reduce the vacuum pressure changing speed in the reaction chamber
110
so that the conductance of the exhaust system becomes a predetermined value.
The vacuum pressure changing speed which is reduced in the bypass valve
117
is dependent on only the conductance of the exhaust system when the velocity of gas flow (simply referred to as “gas velocity” hereinafter) which passes through the fixed orifice of the bypass valve
117
is in a sound speed region. On the other hand, the gas velocity shifts to a subsonic speed region when the vacuum pressure in the reaction chamber
110
is reduced to an absolute vacuum in proportion to the exhausted volume of gas therefrom. In this manner, when the gas velocity changes from sound speed to subsonic speed, the vacuum pressure changing speed in the reaction chamber
110
slows down in an inverse function.
When the vacuum pump
113
is actuated to start the exhaust of gas from the reaction chamber
110
, of which the inside pressure is initially atmospheric pressure, the vacuum pressure changing speed in the reaction chamber
110
will quicken at a stroke if the fixed orifice of the bypass valve
117
which determines the conductance of the exhaust system is larger than necessary. This is not desirable at all from the viewpoint of preventing the particles from flying up in the reaction chamber
110
.
Although a small fixed orifice which determines the conductance of the exhaust system is desirable from the viewpoint of preventing particles from flying up in the reaction chamber
110
, it requires a considerable long time until the vacuum pressure in the reaction chamber
110
is regulated to the desired vacuum pressure, resulting in a problem that batch processing time in the chamber
110
is prolonged.
Such the problem would be resolved by using a plurality of bypass valves and needle valves in addition to the above mentioned bypass valve
117
, all of which are disposed in parallel to the proportional valve
116
. However, this configuration goes against the trend in recent years to reduce the size and cost of semiconductor manufacturing apparatus.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a vacuum pressure control system capable of preventing particles from flying up in a vacuum vessel by controlling the opening degree of a vacuum proportional opening and closing valve to change the vacuum pressure in the vacuum vessel to a desired vacuum at a predetermined vacuum pressure changing speed commanded from the exterior or determined and stored in advance in a controller to proceed slowly the process of exhausting gas from the vacuum vessel, thereby reducing the gas velocity in the vacuum vessel, and simultaneously, capable of shortening the time required for controlling the vacuum pressure in the vacuum vessel to the desired vacuum.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, according to the first aspect of the present invention, there is provided a vacuum pressure control system including a vacuum pressure proportional opening and closing valve which is disposed on a pipe connecting a vacuum vessel to a vacuum pump and changes its opening degree to regulate vacuum pressure in the vacuum vessel, and a vacuum pressure sensor for measuring the vacuum pressure in the
Kagohashi Hiroshi
Kouketsu Masayuki
Watanabe Masayuki
CKD Corporation
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Oen William
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