JPH0864394A - Plasma processing device - Google Patents

Abstract

PURPOSE: To maintain the periodic fluctuation constant by observing intensity of plasma emission, and modulating each high frequency power source so as to coincide with the period of fluctuation and so as to form the opposite phase. CONSTITUTION: Change with lapse of time of plasma intensity is sensed by a plasma emission receiver 12, and a control device 14 drives a modulator 13 at a frequency as same as the fluctuation frequency of the plasma, and the modulator 13 modulates amplifiers 9a-9c of upper electrodes 7a-7c. This modulation is performed at a cycle as same as the fluctuation of plasma, and the phase is displaced at a cycle as same as form the opposite phase. The power to be given to the electrodes is thereby fluctuated at the same cycle in the opposite direction. Since the power change at the opposite phase is given for a cycle including a constant delay time, plasma emission condition is stabilized. Since the plasma intensity is reflected in the condition, it means that the plasnaa power approaches a constant value. Unevenness of etching is reduced to ±2-3% so as to reduce the temporal unevenness by adjusting the high frequency power to be applied to the upper electrodes 7a-7c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention utilizes plasma to
The present invention relates to an improvement in a plasma processing apparatus in which plasma emission is constant in an apparatus that performs semiconductor etching, CVD (chemical vapor deposition method) and the like.

[0002]

2. Description of the Related Art A plasma processing apparatus is an apparatus having a vacuum chamber, three or more upper electrodes, one lower electrode, and a high frequency power source for each. Applying high-frequency voltages whose phase is equal to each other to the upper electrode to generate a high-frequency electric field that rotates the electric field vector, place a workpiece on the lower electrode, and apply different high-frequency waves to generate self-bias. Then, plasma is brought into contact with the object to be processed to perform etching or thin film formation.

FIG. 1 is a principle block diagram of a plasma processing apparatus. A horizontal lower electrode 2 is provided below the inside of the vacuum chamber 1.
The object 3 to be processed is placed on the lower electrode 2. The lower electrode 2 is insulated from the vacuum chamber 1 by the insulator 4. A high frequency power supply 6 and a matching box 5 are connected to the lower electrode 2. The high frequency power supply generates a high frequency of f2. The matching box 5 is the lower electrode 2
And to match the impedance of the power supply 6. The high frequency of the lower electrode is on the order of several MHz to several tens of MHz.

In this example, three upper electrodes 7a, 7b, 7
There is c. Matching boxes 8a, 8b, 8c and a high-frequency amplifier 9 are provided on the upper electrodes 7a, 7b, 7c, respectively.
a, 9b, 9c and phase shifters 10a, 10b, 10c are connected. These are connected to one oscillator 11. The high frequency oscillated by the oscillator 11 is several tens of MHz to 100 MH.
It is the degree of z. The phase shifter 10 gives a phase change of 360 / n. For example, if there are 3 upper electrodes, 1
It creates a phase difference of 20 degrees. This is amplified by the high frequency amplifiers 9a, 9b and 9c, and passed through the matching boxes 8a, 8b and 8c, respectively, and the upper electrode 7
a, 7b, 7c. For example, if there are three electrodes, sin ωt, sin (ωt + π / 3), sin (ω
A voltage of t + 2π / 3) is applied to each electrode.
These voltages are applied to the electrodes in rotationally symmetric positions to generate a nearly rotating electric field. As a result, the gas introduced into the chamber is excited and converted into plasma.
The upper electrode 7 excites the gas by the electric field in this way,
Generates plasma.

On the other hand, a different high frequency is applied to the lower electrode. This creates an alternating vertical electric field with the chamber. Due to the action of the lower electrode, the gas is excited, self-bias is generated, and the lower electrode becomes a negative voltage. As a result, positive ions are attracted and hit the object to be processed. Etching or thin film formation can be performed depending on the type and pressure of gas.

[0006]

The plasma emits light.
From the observation window (viewport), it can be seen that the plasma is distributed in the chamber. It is considered that the emission intensity is almost proportional to the plasma density. However, sometimes the intensity of plasma emission varies with time. This means that the intensity of plasma is fluctuating. When the plasma intensity fluctuates, the etching distribution becomes uneven in time and space. Even in the case of forming a thin film, the growth rate of the film and the film thickness vary. This is not desirable. It is an object of the present invention to provide a plasma processing apparatus capable of suppressing fluctuations in plasma emission and performing etching and thin film formation with plasma having a constant intensity.

[0007]

SUMMARY OF THE INVENTION The present invention provides a plasma emission receiver for detecting plasma emission intensity, by which the time variation of plasma emission intensity or time variation and spatial variation is measured. Then, a control device is provided to adjust the power of the upper electrode so as to cancel the temporal and spatial fluctuations of the plasma.

In reality, the fluctuation of the plasma emission intensity occurs at a constant frequency f. It is rare to make a completely random fluctuation. There is some periodic condition that causes the plasma emission to fluctuate. Therefore, the photodetector detects this periodic change in plasma, and the control device controls the power of the upper electrode at this period f. With the same period, the controller adjusts the power supplied to the upper electrode so as to cancel the natural plasma fluctuation. That is, the opposite phase modulation is applied to the upper electrode amplifier.

When the fluctuation of the plasma intensity is temporal, or when only the temporal fluctuation is a problem, only one optical receiver for plasma emission is required. Simply a temporal modulation is applied to the amplification circuit of each upper electrode. However, if the spatial variation of the plasma intensity is also a problem, it is necessary to provide a plurality of plasma light emitting and receiving devices. Thereby, the spatial distribution of plasma emission is observed. Alternatively, the spatial distribution is obtained by image processing using a TV camera. When the temporal and spatial variation of plasma emission is determined, the control device adjusts the power to the upper electrode so as to cancel the variation.

[0010]

According to the present invention, the plasma emission is observed, the period and the intensity of the plasma emission are measured, and the high frequency power of the high frequency power source for plasma generation is modulated at a frequency synchronized with the plasma fluctuation frequency. Since the modulation is performed in the opposite phase, the plasma emission can be made constant over time. That is, assuming that the time variation of plasma is represented by BsinΩt, the modulation is performed so that Csin (Ωt + π) (C = B). Ideally, this should cancel the plasma fluctuations. However, in reality, the phase difference may deviate from 180 degrees, and the amplitude C
Is different from the fluctuation amplitude B, so the fluctuation cannot be completely eliminated. However, the fluctuation of the plasma intensity can be reduced as compared with the case where nothing is done.

[0011]

FIG. 2 shows the structure of a plasma processing apparatus according to the present invention. The configuration of the upper electrode and the lower electrode, the power supply, etc. are almost the same as those in FIG. The difference is that the plasma emission light receiver 12 for observing the plasma emission intensity is provided on the side surface of the chamber 1, and a control device for controlling the power of the upper electrode is newly added based on the result.

Although there are overlapping portions, the entire explanation will be given. The vacuum chamber 1 is a space that can be evacuated. It is made entirely of metal and its inner surface is covered by an insulator. A horizontal lower electrode 2 is provided below the inside of the vacuum chamber 1.
There is. A sample (object to be processed) 3 is placed on the lower electrode 2. The lower electrode 2 is connected to the vacuum chamber 1 by the insulator 4.
Is insulated from. The lower electrode 2 has a high frequency power source 6,
Matching box 5 is connected. The high frequency power supply generates a high frequency of f2. The matching box 5 is for impedance matching between the lower electrode 2 and the power supply 6. The high frequency f2 of the lower electrode is about several MHz to several tens of MHz.

Above the vacuum chamber 1, n (n is 3 or more) upper electrodes are provided. In this example, there are three upper electrodes 7a, 7b, 7c. Upper electrodes 7a, 7b, 7c
In the matching boxes 8a, 8b, 8c,
High frequency amplifiers 9a, 9b, 9c, phase shifters 10a, 10
b and 10c are connected. These are one oscillator 1
Connected to 1. High frequency f1 oscillated by oscillator 11
Is on the order of tens of MHz to hundreds of MHz. Phase shifter 1
0 gives a phase change of 360 / n each.

For example, if there are three upper electrodes, a phase difference of 120 degrees is created. This is the high frequency amplifier 9
a, 9b, 9c, and each is passed through the matching boxes 8a, 8b, 8c, and the upper electrodes 7a, 7a
b, 7c. For example, if there are 3 electrodes, s
in ωt, sin (ωt + π / 3), sin (ωt + 2)
A voltage of π / 3) is applied to each electrode. These voltages are applied to the electrodes in rotational symmetry to generate an electric field that rotates about the center of the upper electrode. As a result, the gas introduced into the chamber is excited and converted into plasma. The upper electrode 7 thus excites the gas by the electric field to generate plasma.

On the other hand, a different high frequency f2 is applied to the lower electrode. This creates an alternating vertical electric field with the chamber. Gas is excited by the action of the lower electrode,
Self-bias occurs and the lower electrode becomes a negative voltage. As a result, positive ions are attracted and hit the object to be processed. Etching or thin film formation can be performed depending on the type and pressure of gas.

Further, in the case of the present invention, a view port is provided on the side surface of the chamber (or a view port existing from the beginning is used), and the plasma light emitting / receiving device 12 is provided therein. This may be one photodetector. In this case, the plasma in the region connecting the centers of the upper electrode 7 and the lower electrode 2 can be observed. Plasma emission increases or decreases in proportion to the plasma density. If plasma generation is stable, plasma emission is also stable and its intensity is constant. However, sometimes the plasma emission fluctuates with a certain period Ω. In such a case, the plasma light emitting / receiving device 12 can detect a temporal change in plasma intensity.

The control device 14 thereby drives the modulator 13 at the same frequency as the frequency of the plasma fluctuations. The modulator 13 modulates the amplifier of each upper electrode. This is the same period as the fluctuation of the plasma, but 180 ° out of phase. In other words, it makes the opposite phase. Then, the electric power applied to the electrodes fluctuates in the opposite direction in this cycle. The power of the electrode also changes the power of the plasma. Since the power of the opposite phase is changed including a certain delay time, the plasma emission state is stabilized. Since the light emission state reflects the intensity of the plasma, this means that the power of the plasma has approached a constant value.

There is a delay time for the plasma intensity to follow changes in the power applied to the upper electrode. For this reason, it may be difficult to deal with the fluctuations in the plasma over time. However, in general, plasma fluctuations often occur periodically. In this case, the fluctuation period and phase,
The fluctuation can be compensated by detecting the intensity amplitude. The modulator 13 provides this compensation.

What has been described above is a device for reducing the temporal fluctuation of plasma. In addition to this, if there is a spatial fluctuation, this can also be solved by the present invention. In this case, a plurality of light receivers are provided in order to observe the spatial fluctuation of plasma. Or install a TV camera. As a result, the spatial bias of the plasma between the upper electrodes is known, and different power modulation is applied between the upper electrodes. Then, spatial fluctuations can be resolved.

[0020]

In the conventional apparatus, since the plasma intensity varies with time, the nonuniformity of the etching rate is ± 5%.
Met. When the plasma emission was observed and the high frequency power applied to the upper electrode was adjusted as in the present invention, the nonuniformity of etching was reduced to about ± 2% to ± 3%. The time non-uniformity can be reduced to about half.

Particularly, when a plurality of steps are included and etching conditions are different for each step, a more remarkable effect can be obtained. According to the present invention, the etching strength can be made constant for each step. Although the modulation frequency and phase are different for each step, the plasma emission is actually observed for each step. Therefore, in any case, the power of the upper electrode can be adjusted so as to reduce the fluctuation.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a plasma processing apparatus in which gas is excited by a combination of an upper electrode and a lower electrode to generate plasma, which is used for etching and film formation.

FIG. 2 is a schematic configuration diagram of a plasma processing apparatus of the present invention.

[Explanation of symbols]

 1 Vacuum Chamber 2 Lower Electrode 3 Sample 4 Insulator 5 Matching Box 6 High Frequency Power Supply 7 Upper Electrode 8 Matching Box 9 High Frequency Amplifier 10 Phase Shifter 11 Oscillator 12 Plasma Light Emitting Receiver 13 Modulator 14 Controller

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/205 21/3065

Claims (1)

[Claims] 1. An object to be processed by generating plasma by shifting the phase angle by 2π / n by using n high frequency power sources of 3 or more with different phases at the same frequency for n or more upper electrodes of 3 or more. In a plasma processing apparatus adapted to process plasma by plasma, a light receiving unit for monitoring the emission of plasma, a modulator for modulating each high-frequency power source at a frequency lower than that frequency, and a signal of the light receiving unit are used to determine a predetermined value. And a control device for controlling the modulation level so as to maintain a constant value of.