JP2701548B2 - Plasma processing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a plasma processing apparatus for performing dry etching in g the like.

[0002]

2. Description of the Related Art Conventionally, as a method of determining an etching end point of a sample to be etched by a dry etching process, a change in emission intensity of a specific wavelength corresponding to a material to be etched or an etching gas component corresponding to an etching processing time is known. Emission spectroscopy utilizing is widely used. An example of this is disclosed in, for example, JP-A-62-128124.
As disclosed in Japanese Unexamined Patent Publication, a method is used in which the amplification degree of a signal detected by a spectroscope is manually adjusted to an appropriate predetermined value so that a change in emission intensity can be detected between the start and end of etching. There is. However, in recent years, a method of applying a strong magnetic field to improve the etching rate has been used,
In addition, a method of rotating the magnetic field has been proposed in order to ensure the uniformity of the etching rate.

However, according to this method, since the emission intensity fluctuates, it is difficult to determine the end point of the etching stably. For example, as shown in Japanese Patent Application Laid-Open No. 1-2266154, the light emission intensity varies periodically. A method for smoothing a signal by a low-pass filter has been proposed.

[0004]

However, according to such a method, although the variable component can be removed,
Since the actual level that fluctuates is ignored, it does not conform to the actual situation, so that there is a problem that accurate end point determination cannot be performed. In addition, if etching is performed continuously, the quartz glass window of the plasma chamber becomes dirty, and the light reception level obtained through the window will gradually decrease.Therefore, the gain must be manually adjusted and corrected. Also, there is a problem that skill is required to determine the amount.

SUMMARY OF THE INVENTION The present invention solves the above-described problem. In the present invention, even when the state of plasma fluctuates periodically, the end point is determined in accordance with the actual situation. An object of the present invention is to provide an apparatus capable of determining the end point of the plasma processing.

[0006]

SUMMARY OF THE INVENTION In order to solve such a problem, the present invention smoothes an input signal of emission intensity in a plasma which periodically changes by external means and automatically converts the signal. A closed-loop control function is provided so that the gain can be adjusted to the reference level, and this function is executed in a short time in a hardware manner (sampling control).

[0007]

The smoothing means uses a circuit element capable of processing an effective value, and operates only for a certain fixed gate period. The closed loop is controlled by an attenuator, an error amplifier, a V / F converter, a counter, and a D / A converter. With this configuration, the gain is adjusted by the attenuator element, and thereafter, a stable plasma processing end point can be easily determined by a plasma processing detection circuit capable of holding the gain level by a counter.

[0008]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The spectroscope 1 and the photomultiplier tube 2 take out only the required specific wavelength from the light receiving spectrum and convert the light receiving level of this specific wavelength into an electric signal. The effective value calculating means 6 averages the square of the signal amplified to some extent by the amplifier 5 and generates a DC signal proportional to the value obtained by calculating the square root.

The signal converted into an effective value is output through an attenuator 7, and the output signal is compared with a reference level by a level difference determination means 15, and the difference is amplified by an error amplifier 9. The polarity of this error signal is determined by the error polarity determination circuit 1
The output is supplied to the up / down counter 12, and it is determined whether the up / down counter performs up counting or down counting. The absolute value of the error signal is supplied to the voltage-frequency conversion circuit 10 is converted into a pulse corresponding to the magnitude of error here, it is supplied through the gate circuit 11 to the counter 12 (gate circuit 11 The operation will be described later, but it is assumed here that the gate circuit 11 is turned on for easy understanding.)

The result counted by the counter 12 is D /
The signal is output by the A converter 13 as a control signal corresponding to the count result. The control signal controls the attenuation rate of the attenuator 7, and the output of the attenuator 7 automatically matches the reference level so that the error becomes zero. When there is a fluctuation due to the drift, a bias is applied to the input of the amplifier circuit 8 so as to add an offset.

In the method of performing etching by generating plasma using a magnetic field, for example, by using the plasma processing apparatus configured as described above, the input signal (light receiving level) is changed as shown in FIG.
As shown in (a), it changes largely as a whole while changing periodically and small. By outputting the signal that changes as a whole while changing periodically as described above through the effective value calculating means 6, the signal is converted into the effective value of the signal that changes periodically, as shown in FIG. 2 (b). And a signal that does not include vibration can be obtained.

The process is performed, for example, as shown in FIG. 2 (b), at a delay point after a certain time from the plasma discharge. That is, when a certain period of time has elapsed after the occurrence of the plasma discharge, the discharge is in a stable state. Therefore, at this time, a one-shot pulse that continues for a time ΔT is supplied to the gate circuit 11 of FIG. As a result, while the one-shot pulse is continued, the counter 12 counts, and the count result is converted into a DC control signal by the D / A converter and supplied to the attenuator 7, and the attenuation of the attenuator 7 is reduced. adjust. Therefore, when the level before the one-shot pulse is supplied is higher than the reference level, the attenuation is set large so that the output of the attenuator 7 becomes the reference level. Conversely, when the level before the one-shot pulse is supplied is lower than the reference level, the amount of attenuation is set small so that the output of the attenuator 7 becomes equal to the reference level.
Thus, the automatic gain loop operation is performed so that the output of the attenuator 7 becomes equal to the reference level.

Thereafter, even if the gate circuit 11 is closed,
The value of the counter 12 is held, and the value of the counter 12 when the automatic gain loop is adjusted is output to the D / A converter 13, and a control signal corresponding to this is supplied to the attenuator 7, and the automatic gain loop follows. The gain at the time can be maintained.

That is, the attenuation rate of the attenuator 7 is determined when the loop is closed, and this value is maintained even after the loop is opened.

In the above-described embodiment, only the periodically fluctuating input generated by using the magnetic field has been described. However, the present invention can be applied to a case where a periodically fluctuating temperature is kept constant. The present invention can be applied to the case of controlling an object having a similar periodic change.

[0016]

As described above, the present invention has an effect that the end point of the plasma processing can be stably determined in terms of hardware even when the state of the plasma periodically fluctuates or the light receiving level is attenuated. Have.

[Brief description of the drawings]

FIG. 1 is a block diagram according to one embodiment of the present invention.

FIG. 2 is a graph showing plasma emission intensity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Spectroscope 2 Photomultiplier tube 5, 8 Amplifier 6 Effective value calculation means 7 Attenuator 9 Error amplifier 10 Voltage / frequency conversion circuit 11 Gate element 12 Counter 13 D / A converter 14 Polarity discrimination circuit

Claims (1)

(57) [Claims] 1. A method of detecting a specific wavelength from plasma light and
A plasma light specific wavelength detecting means for converting, and a photoelectric conversion output from the plasma light specific wavelength detecting means.
Proportional to the value obtained by averaging the square of the conversion signal and obtaining the square root
Output as an effective value of the photoelectric conversion signal.
Means for calculating the effective value, and varying the gain of the signal output from the effective value calculating means.
Gain varying means, a signal output by the gain varying means, and a desired plasma emission.
Compare with the reference level corresponding to the intensity, and
Level determining means for outputting as a signal, and converting the error signal into a pulse corresponding to the magnitude thereof.
A voltage / frequency conversion circuit, and the number of pulses is increased according to the polarity of the error signal.
Alternatively, a counter that counts down and a control signal corresponding to the result counted by the counter are used.
And a converter for outputting the output signal , wherein the gain changing means changes the gain by the control signal.
The plasma processing apparatus, characterized in that to reduction.