Etching a substrate: processes – Gas phase etching of substrate – With measuring – testing – or inspecting
Reexamination Certificate
2000-02-18
2002-04-02
Alanko, Anita (Department: 1746)
Etching a substrate: processes
Gas phase etching of substrate
With measuring, testing, or inspecting
C216S067000, C427S008000, C438S714000
Reexamination Certificate
active
06365060
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for controlling a plasma processing apparatus and more specifically, it relates to a method for controlling the application of high frequency power in a parallel plates plasma processing apparatus.
DESCRIPTION OF THE RELATED ART
So-called parallel plates plasma processing apparatuses achieved by providing an upper electrode (a first electrode) and a lower electrode (a second electrode) with a target object (substrate) mounted thereupon facing each other within a processing chamber constituted of an air-tight processing container have been proposed in the prior art. In a typical parallel plates plasma processing apparatus, a glow discharge is caused between the two electrodes by applying high frequency power for plasma generation to the upper electrode to generate plasma from the processing gas supplied to the processing chamber. By applying high frequency power for biasing to the lower electrode, ions in the plasma are drawn to the target object placed on the lower electrode to perform a specific type of plasma processing such as etching.
During the actual processing, first, a high frequency power of steady-state power, for instance, 27 MHz, for plasma generation is applied to the upper electrode at a time point t
1
, as indicated in FIG.
5
(
a
), to generate plasma inside the processing chamber. Next, as FIG.
5
(
a
) illustrates, after a specific length of time has elapsed and the plasma density inside the processing chamber has stabilized, i.e., at a time point t
2
, a high frequency power of steady-state power, for instance, 800 kHz, for biasing which is lower than the frequency of the high frequency power for plasma generation, is applied to the lower electrode so that the ions in the plasma are controlled to be drawn into the target object placed on the lower electrode.
Now, if high frequency power is applied between the two electrodes in the parallel plates plasma processing apparatus structured as described above, the impedance between the two electrodes is high until plasma is generated and an electrical current starts to flow between the electrodes, which results in a high voltage momentarily generated between the two electrodes.
However, since the frequency of the high frequency power for plasma generation is high, the impedance of the capacitor constituted by the two electrodes is not considered to be excessively high. As a result, the high voltage occurring between the two electrodes due to the application of the high frequency power for plasma generation is not high enough to present a significant problem.
In the case of the high frequency power for biasing whose frequency is relatively low, applied after plasma is generated inside the processing chamber and the impedance between the two electrodes becomes reduced, it is assumed in the prior art that it generates no high voltage such as that described above.
However, through observation made by the inventors of the present invention it has become clear that during actual processing, even when the high frequency power at a relatively low frequency for biasing is applied, a high voltage is generated between the two electrodes to result in, for instance, an abnormal discharge occurring at insulated portions inside the processing chamber.
Now, an explanation is given on the mechanism of such an abnormal discharge in reference to FIG.
5
(
b
). First, when the high frequency power for plasma generation is applied to the upper electrode at the time point t
1
, the voltage rises abruptly at the moment of application. However, since the frequency of the high frequency power for plasma generation is high, the process and the apparatus are not adversely affected to the extent to which an abnormal discharge results.
Next, at the time point t
2
, at which it is assumed that the plasma inside the processing chamber has stabilized, the high frequency power for biasing is applied to the lower electrode. The application of the high frequency power for biasing destabilizes the plasma generation system that has been thus far stable. This temporarily reduces the plasma density to result in an increase in the impedance between the two electrodes. As a result, as indicated in FIG.
5
(
b
), a high voltage is temporarily generated. When this happens, the peak of the voltage of high frequency power for plasma generation applied to the upper electrode is not high enough to affect the process or the apparatus as mentioned earlier. In contrast, the high voltage caused by the high frequency power for biasing applied to the lower electrode causes an abrupt increase in the voltage near the lower electrode which may cause an abnormal discharge inside the processing chamber to adversely affect the process and the apparatus to a considerable degree.
In addition, the high voltage occurring when the high frequency power for biasing is applied to the lower electrode causes a misalignment of the matching point of a matching device connected to the upper electrode. Also, because the matching device engages in a servo operation to correct such misalignment of the matching point, a delay occurs until the plasma inside the processing chamber becomes stabilized again.
Accordingly, a first object of the present invention, which has been completed by addressing the problems of the method for controlling a plasma processing apparatus in the prior art discussed above, is to provide a new and improved method for controlling a plasma processing apparatus that makes it possible to minimize the extent of the adverse effect on the process and the apparatus caused by the high voltage occurring when high frequency power for biasing is applied.
In addition, another object of the present invention is to provide a new and improved method for controlling a plasma processing apparatus that makes it possible to prevent an abnormal discharge which would occur when high frequency power for biasing is applied and to minimize the misalignment of the matching point for the upper electrode which would occur at the same time.
SUMMARY OF THE INVENTION
In order to achieve the objects described above, the present invention provides a method for controlling a plasma processing apparatus having a first electrode and a second electrode facing each other within the processing chamber and generates plasma inside the processing chamber by applying high frequency power for plasma generation having a first frequency to the first electrode via a first matching device and by applying high frequency power for biasing having a second frequency lower than the first frequency to the second electrode via a second matching device to perform a specific type of plasma processing on a target object placed on the second electrode.
In a first aspect of the present invention, the method for controlling the plasma processing apparatus described above comprises a step in which a high frequency power of steady-state power is applied to the first electrode and a high frequency power at a level at which, at least, the high frequency power for biasing can be matched, is applied to the second electrode and a step in which after the high frequency power for biasing has been substantially matched, the high frequency power applied to the second electrode is raised to the steady-state power level.
In this structure, first, plasma is generated inside the processing chamber by applying the high frequency power for plasma generation to the first electrode. In addition, high frequency power for biasing is applied to the second electrode. However, since the high frequency power applied to the second electrode is at a low level that allows the high frequency power for biasing to be substantially matched, its overshoot voltage is not high enough to cause an abnormal discharge even though it is in a low frequency range.
According to the knowledge of the inventors of the present invention, the matching point does not become greatly misaligned even if the power that is being applied changes once the plasma generation system has achieved a matched state, an
Nagaseki Kazuya
Yamazaki Hiroki
Alanko Anita
Finnegan Henderson Farabow Garrett & Dunner
Tokyo Electron Limited
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