Etching a substrate: processes – Gas phase etching of substrate – With measuring – testing – or inspecting
Reexamination Certificate
1998-12-18
2001-05-15
Dang, Thi (Department: 1763)
Etching a substrate: processes
Gas phase etching of substrate
With measuring, testing, or inspecting
C438S009000
Reexamination Certificate
active
06231774
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing method.
Plasma processing apparatuses constituted by employing various types of plasma sources have been proposed in the area of semiconductor manufacturing apparatuses in the prior art. They include a plasma processing apparatus that is capable of performing plasma processing on an object such as a substrate by forming an electric field between an upper electrode and a lower electrode provided facing opposite each other within a processing chamber and by generating plasma from a processing gas introduced into the processing chamber with the electric field.
The plasma processing apparatuses above also include the so-called magnetic field assist type plasma processing apparatus which is provided with a magnet capable of forming a rotating magnetic field within the processing chamber. By adopting this structure, the electrons within the plasma can be trapped by the magnetic field formed inside the processing chamber so that the number of times they collide with the processing gas particles can be increased, thereby exciting a plasma of high density. In addition, by rotating the magnetic field, a high degree of uniformity in the density of the plasma can be achieved to realize uniformity, high speed plasma processing.
Now, it is crucial in a plasma processing process such as etching that the endpoint of the plasma processing be judged accurately to end the plasma processing with no delay. As a method for detecting the endpoint of plasma processing, a method in which any change in the light spectrum of a specific substance contained within the plasma in the processing chamber is detected, with the endpoint being detected based upon such change, has been proposed in the prior art. This method, which is conceived from the observation that the contents in the plasma change as the etching on the substrate progresses, aims to detect a real-time endpoint of the etching process accurately by monitoring change in the intensity of the light spectrum of a specific substance.
However, in the magnetic field assist type plasma processing apparatus described above, areas with varying degrees of density are formed within the plasma in correspondence to the direction of the magnetic field formed inside the processing chamber. Then, as the magnetic field rotates, the density distribution of the plasma also fluctuates. Consequently, it is necessary to take into consideration fluctuations of the plasma resulting from the rotation of the magnetic field when performing fixed-point observation of the plasma light through, for instance, a detection window provided at a wall of the processing chamber.
Accordingly, Japanese Unexamined Patent Publication No. H04 (1992)-338663, teaches for instance, a technology for achieving accurate endpoint detection by providing a rotary encoder that generates pulses in synchronization with the rotation of the magnet in an etching apparatus, sampling the plasma light in response to the pulses and removing the noise component brought by the rotation cycle of the magnet.
However, in a structure in which the plasma light is sampled in correspondence to the rotation cycle of the magnet, which is determined in hardware as described above, a device such as a rotary encoder must be added to the processing apparatus, resulting in a complicated apparatus configuration, and also in an increase in the initial cost of the apparatus.
In addition, in a structure in which the plasma light is sampled in correspondence to the rotation cycle of the magnet, which is determined in hardware as described above, the sampling cycle varies every time processing is performed. Moreover, in some cases, more efficient processing may be achieved by employing a fixed cycle as a sampling cycle in signal processing software for endpoint detection, and in other cases, a fixed cycle is absolutely required. Thus, there is a problem with the structure described above in that such requirements on the software side cannot be supported with a high degree of flexibility.
SUMMARY OF THE INVENTION
An object of the present invention, which has been completed by addressing the problems of the plasma processing methods in the prior art discussed above, is to provide a new and improved plasma processing method with which the fluctuation cycle of the plasma that fluctuates in each processing, i.e., the rotation cycle of the magnet, can be accurately ascertained through software by sampling the plasma light within the processing chamber over a constant cycle without having to modify the structure of the hardware in the prior art.
Another object of the present invention is to provide a new and improved plasma processing method that is capable of obtaining a more accurate moving average value with relatively little calculation emulating a high sampling quantity without increasing the actual quantity of sampling performed, by creating a pseudo sampling signal having a relatively narrow sampling interval from a sampling signal having relatively wide sampling interval.
In order to achieve the objects described above, in a first aspect of the present invention, a plasma processing method for performing plasma processing on an object placed inside a vacuum chamber by forming an electric field within the vacuum chamber into which a processing gas is introduced and generating plasma that fluctuates over a given fluctuation cycle, which, in order to determine the fluctuation cycle of the plasma, includes:
(a) a step for obtaining sampling data by sampling plasma light of the plasma with a constant sampling cycle;
(b) a step for hypothesizing a plurality of hypothetical fluctuation cycle, calculating a moving average value over each period corresponding to each of the hypothetical fluctuation cycles based upon the sampling data and obtaining a moving average value data for each of the hypothetical fluctuation cycles;
(c) a step for obtaining an approximate expression corresponding to each of the hypothetical fluctuation cycles based upon the moving average value data for each of the hypothetical fluctuation cycles;
(d) a step for ascertaining a quantity of deviation between the moving average value data and the corresponding approximate expression for each of the hypothetical fluctuation cycles at one or two or more time points; and
(e) a step for ascertaining the hypothetical fluctuation cycle having the smallest quantity of deviation among the quantities of deviation to determine the hypothetical fluctuation cycle as the fluctuation cycle of the plasma, is provided.
In addition, in order to ascertain the endpoint of plasma processing based upon the fluctuation cycle of the plasma thus determined;
(f) a step for calculating moving average value data for the period corresponding to the fluctuation cycle of the plasma ascertained in step (e) by using the sampling data; and
(g) a step for determining the endpoint of the plasma processing based upon the moving average value data calculated in step (f) are implemented.
This structure makes it possible to calculate a fluctuation cycle of the plasma that may vary for different processing simply through arithmetic calculation processing in software even when the plasma light is sampled over a constant sampling cycle. Consequently, a fluctuation cycle of plasma can be ascertained with a high degree of accuracy for each processing without having to add a special hardware device.
In addition, in order to achieve the objects described above, in a second aspect of the present invention, in a plasma processing method for performing plasma processing on an object placed inside a reaction chamber by forming an electric field within the reaction chamber into which a processing gas is intoroduced and generating plasma that fluctuates over a given fluctuation cycle,
(a) a step for obtaining sampling data by sampling plasma light of the plasma with a constant sampling period, with said fluctuation cycle not restricted to be an integer multiple of said sampling cycle;
(b) a step for calculating a moving average value
Dang Thi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Tokyo Electron Limited
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