Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Reexamination Certificate
1999-07-21
2002-01-15
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
C315S111510, C315S111410, C156S345420, C324S756010
Reexamination Certificate
active
06339297
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to: a plasma density information measuring method in plasma used in a producing process of a thin film component, a particle beam source or an analysis apparatus; a probe for measuring the plasma density information used for measuring the plasma density information; and a plasma density information measuring apparatus; and more particularly, to a technique for easily measuring the plasma density information over the long term.
(2) Description of the Related Art
In recent years, the use of plasma is increased. In a producing process of a thin film component, using high-frequency plasma generated by high-frequency power (high-frequency electric power) in a range from a RF frequency band of about 10 MHz to a micro frequency band of 2.45 GHz, etching process or CVD (chemical-vapor deposition) are conducted. In such a plasma application technique, it is extremely important for conducting appropriate process to sufficiently grasp the information concerning plasma density which excellently shows the characteristics of generated plasma. In the case of typical plasma comprising monovalent positive ion and electron, the positive ion density and the electron density are substantially equal to each other due to the properties particular to plasma that electrically neutral state is maintained, the electron density is generally called as plasma density.
Conventionally, as a method for measuring the electron density in plasma, there is an electron beam irradiation type plasma vibration probe which was developed relatively recently, in addition to a Langmuir/probe method and a microwave interference measuring method.
The Langmuir/probe method is a method in which a metal probe is directly exposed in plasma in this state, direct current bias voltage, or direct current bias voltage on which high-frequency voltage is superposed is applied to the metal probe, and based on the current value flowing through at that time, electron density is measured.
The microwave interference measuring method is a method in which a chamber for generating plasma is provided with windows which are opposed to each other with plasma positioned therebetween, microwave (e.g., single color laser light) is radiated to the plasma through one of the windows, and the microwave ejected from the other window is detected, and electron density is obtained based on phase contrast between the radiated microwave and ejected microwave.
The electron beam irradiation type plasma vibration method is a method in which a hot filament is placed in a chamber, and based on frequency of plasma oscillations generated when electron beam is irradiated to the plasma from the hot filament, electron density is obtained.
However, when the Langmuir/probe method is used for reactive plasma, there is a problem that the measuring can not be continued for a long time (i.e., life time is short). This is because that stains comprising insulative films are adhered on a measured metal probe within a short time, the current value flowing through the metal probe is varied, and accurate measurement can not be continued soon. In order to remove the stains adhered on the metal probe surface, a method in which negative bias voltage is applied to the metal probe to carry out sputter-removing method using ion, and a method in which the metal probe is allow to glow to evaporate and remove the stains have been attempted, but the effect is poor, and the problem is not solved by these methods.
Further, the microwave interference measuring method has a problem that the measurement can not be conducted easily. This is because a large-scale and expensive apparatus and adjustment of microwave transmission path are necessary, the phase contrast between the radiated microwave and ejected microwave is small and thus, it is difficult to measure precisely. Further, in the case of the microwave interference measuring method, there are drawbacks that only the average density can be obtained, there is no spatial resolution.
Furthermore, in the case of the electron beam irradiation type plasma vibration probe method, in addition to anxiety of plasma atmosphere contamination due to tungsten which is evaporated from the hot filament, there is a problem of anxiety of interruption of measurement caused by break of hot filament. Especially in the case of plasma using oxygen or chlorofluorocarbons gas, the hot filament is easily cut or broken, and it is necessary to frequently exchange the filament, it can not be said that this is practical.
SUMMARY OF THE INVENTION
In view of the above circumstances, it is an object of the present invention to provide a plasma density information measuring method capable of easily measuring the plasma density information over the long term, a probe for measuring the plasma density information, and a plasma density information measuring apparatus.
To achieve the above object, the present invention provides the following structure.
That is, a plasma density information measuring method of the present invention comprises the steps of:
supplying high-frequency power to plasma;
measuring a physical amount indicative of reflection or absorption state of the high-frequency power by plasma load; and
obtaining a frequency at which strong high-frequency power absorption is caused due to plasma density, i.e., a plasma absorption frequency based on the measurement result of the physical amount.
In the case of the plasma density information measuring method of the present invention, the high-frequency power is supplied to plasma, the physical amount indicative of reflection or absorption state of the high-frequency power by plasma load is measured (for example, the reflection amount of the high-frequency power or impedance value of the plasma load is measured). Based on the measured result of the physical amount, plasma absorption frequency at which high-frequency power resonant strong absorption is generated due to plasma density is obtained. If the high-frequency power resonant strong absorption is caused, since the physical amount indicative of reflection or absorption state of high-frequency power by plasma load is largely varied, plasma absorption frequency can easily be obtained. Since the obtained plasma absorption frequency has constant correlation with the plasma density, this is useful plasma density information. In the present invention, high-frequency power, i.e., high-frequency electromagnetic wave is supplied to plasma and thus, even if stains comprising insulative films are adhered to the antenna which supplies high-frequency power, there is little influence, and the plasma absorption frequency can be measured accurately.
In this point, the present invention is superior to the conventional Langmuir probe method. Because in this method, electric current flowing when ion in plasma reaches a surface of a metal probe is detected and therefore, if insulative film is adhered to the metal probe, it is impossible to measure. Further, according to the present invention, since a hot filament is not used unlike the electron beam irradiation type plasma vibration probe method, there is no anxiety of breaking of filament, and it is possible to obtain the plasma density information over the long term.
In the method of the invention, it is preferable that the high-frequency power is supplied to plasma through a division wall. By interposing the dielectric division wall between the plasma side to be measured and the supplying side of the high-frequency power, a foreign object should not enter the plasma from the supplying side of the high-frequency power, and plasma can be maintained clean. Further, in the case of reactive plasma also, the high-frequency power supplying side is not damaged. Furthermore, even if stains such as insulative films are adhered to the surface of the dielectric division wall, there is no change in the measuring system, it is possible to obtain the plasma density information for longer time.
In the present invention, for example, the physical amount indicati
Sugai Hideo
Takasuga Seiichi
Toyoda Naoki
Arent Fox Kintner & Plotkin & Kahn, PLLC
Nissin Inc.
Vu Jimmy T.
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