JPH0864393A - Plasma processing device - Google Patents

Abstract

PURPOSE: To provide the processing with high homogeneity by measuring impedance, power, current for each upper electrode so as to obtain the space deflection of plasma, and changing supplying power and phase angle. CONSTITUTION: Impedance Z, the current I flowed to the plasma, and the effective power P are measured so as to monitor a change of condition of upper electrodes 5a-5c, and the high frequency power P and the phase difference Φare controlled. In the upper electrodes 5a-5c, a phase-shifter 8 makes a phase difference at 120 degree, and this phase difference is amplified by amplifiers 7a-7c, and given to the electrodes 5a-5c through matching boxes 6a-6c. The output impedance Za-Zc of the box 6 is monitored, and the flowed current ia-ic is monitored by current transformers 12a-12c. Powers Pa-Pc of the electrodes 5a-5c are thereby obtained. The effective power is obtained by multiplying the impedance Z by the square of the current, and the spatial turbulence of plasma is obtained. Electrical potential and phase angle are controlled for the fine adjustment, and the processing with high homogeneity can be performed.

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 device that performs semiconductor etching, CVD (chemical vapor deposition method), or the like so as to suppress spatial bias of plasma.

[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.
There is. An insulator 3 is provided below the lower electrode 2 and is insulated from the vacuum chamber 1. A sample (object to be processed) 4 is placed on the lower electrode 2. A high frequency power supply 11 and a matching box 10 are connected to the lower electrode 2. The high frequency power supply 11 generates a high frequency of f2. The matching box 10 is provided for impedance matching between the lower electrode 2 and the power supply 11. 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 5a, 5b, 5
There is c. Matching boxes 6a, 6b, 6c and a high frequency amplifier 7 are provided on the upper electrodes 5a, 5b, 5c, respectively.
a, 7b, 7c and phase shifters 8a, 8b, 8c are connected. These are connected to one oscillator 9. The high frequency f1 oscillated by the oscillator 9 is on the order of several tens of MHz to 100 MHz. The phase shifter 8 gives a phase change of 360 / n. For example, if there are three upper electrodes 5, a phase difference of 120 degrees is created. This is amplified by the high frequency amplifiers 7a, 7b and 7c, and passed through the matching boxes 6a, 6b and 6c respectively to the upper electrodes 5a and 5a.
It is given to b and 5c.

For example, if there are three electrodes, sin ωt,
The voltages of sin (ωt + π / 3) and sin (ωt + 2π / 3) are applied to the respective electrodes. These voltages are
An almost rotating electric field is generated by being applied to the electrodes in the rotationally symmetrical position. As a result, the gas introduced into the chamber is excited and converted into plasma. The set of upper electrodes 5 is excited by the alternating electric field rotating the gas in this way to generate plasma.

On the other hand, a different high frequency f2 is applied to the lower electrode 2. This creates an alternating vertical electric field with the chamber. The gas is also excited by the action of the lower electrode. Moreover, self-bias is generated by the action of the lower electrode, and the lower electrode becomes a negative voltage. As a result, positive ions are attracted and hit the object to be processed (sample 4). Etching or thin film formation can be performed depending on the type and pressure of gas.

[0007]

High frequency power having a preset phase difference and amplitude is supplied to three or more upper electrodes. This is sufficient when the effective impedance of the top electrode is equal and constant. A strong rotating electric field is generated at the center of the upper electrode by a well-balanced electric power. However, the effective impedance of the top electrode varies from time to time. Then, even if a voltage with the same amplitude is applied, the power actually input to the upper electrode changes. Since it deviates from the impedance matching condition, reflection between the electrode and the cable increases. This is a spatial power input variation. However, in addition to this, there may be temporal variations in the input of electric power. Then, the plasma density varies spatially and temporally.

Since the plasma processing apparatus performs etching and CVD by collision of plasma with the sample,
The temporal and spatial fluctuations of plasma strongly affect the etching performance. Since the etching rate changes spatially and temporally, the etching rate changes in the plane of the sample. Then, the etching thickness becomes uneven. Since etching is used as a means for fine processing, even slight etching non-uniformity causes variations in device performance.

It is an object of the present invention to eliminate uneven etching and uneven film formation due to changes in the state of the upper electrode. It is another object of the present invention to provide an apparatus capable of performing stable plasma processing temporally and spatially at all times, by following a particularly rapid state change.

[0010]

The present invention constantly measures the impedance Z of all the upper electrodes, the current i flowing into the plasma, and the effective power P given to the plasma in order to monitor the state change of the upper electrodes. . Then, based on this result, the parameters of the phase shifter and the amplifier are changed. The control signal provided to the phase shifter adjusts the phase difference Φ of the power of the adjacent upper electrodes. The signal supplied to the amplifier adjusts the power P for each electrode by changing the amplification factor. The monitoring targets are Z, i, and P. Control target is P, Φ
Is.

In a normal control system, the monitored object and the controlled object are the same physical quantity. Also in the present invention, the electric power P is monitored for each upper electrode and controlled so as to have an appropriate value. The high frequency power P is an observation target and a control target. However, the phase difference Φ between adjacent electrodes is a control target, but is not a monitoring target. This should be noted.

However, even though the power P is both a monitoring target and a control target, the situation is not as simple as in a normal control system. The power that can be controlled is the incident power W. However, in reality, a part of the power is reflected when the power progresses from the electrode to the plasma. This is due to the change in impedance. What effectively enters the plasma is the effective power obtained by subtracting the reflected power U from the incident power W (W−U). This can be calculated by Zi ^2/2. Therefore, the monitored power and the controlled power are actually different.

[0013]

According to the present invention, each upper electrode observes the supplied high frequency power P, the flowing current i, and the impedance Z, and controls the power P and the phase difference Φ applied to each electrode. As a result, the spatial fluctuation of the plasma density can be suppressed at all times. The control variables are P and Φ. The observation targets are P, i, and Z. However, the power P is calculated by multiplying the square of the current by the impedance. The power as a control variable can be changed by adjusting the amplification factor of the amplifier.

For example, assume that there are three upper electrodes. If there is spatial nonuniformity in the plasma generated by this, the current flowing into the plasma and impedance fluctuations will occur. Or it becomes fluctuation of electric power. Instead of directly observing the spatial fluctuation of the plasma density, the P of the electrode,
The state of plasma can be known by monitoring i and Z.
On the contrary, the spatial fluctuation of the plasma density can be corrected by the power and phase difference applied to the upper electrode.

When the spatial fluctuation is persistent, the plasma density can be averaged by such means. This is clear. Instead,
What if the spatial fluctuations also change in time? Also in this case, the present invention can suppress spatial fluctuations. The objects to be monitored are P, i, and Z, and the measurement does not take time. The control variables are also P and Φ, which can be changed immediately. Since the response of the observation system and the control system is quick, it is possible to correct this even if it is a fast plasma fluctuation.

[0016]

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 means for measuring the power applied to the electrodes, the output impedance and the current are provided.
Based on these measurement results, there is a mechanism to adjust the power and phase of each upper electrode. 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. Vacuum chamber 1
A horizontal lower electrode 2 is located below the inside of the. Lower electrode 2
Is insulated from the vacuum chamber 1 by the insulator 3. A sample (object to be processed) 4 is placed on the lower electrode 2.

The lower electrode 2 has a matching box 1
0, the high frequency power supply 11 is connected. High frequency power supply is f
Generates two high frequencies. The matching box 10 is provided for impedance matching between the lower electrode 2 and the power supply 11. The high frequency f2 of the lower electrode is several MHz to several tens of MHz
Is the degree of. Above the vacuum chamber 1, n (n is 3 or more) upper electrodes are provided. In this example, there are three upper electrodes 5. These are designated as 5a, 5b, and 5c. Upper electrode 5
In the matching boxes 6a, 6b, 6c,
High frequency amplifiers 7a, 7b, 7c, phase shifters 8a, 8b, 8
c is connected. These are connected to one oscillator 9. The high frequency f1 oscillated by the oscillator 9 is several tens MH
It is on the order of z to 100 MHz. Phase shifters 8a, 8b,
8c gives a phase change Φ of 360 / n.

For example, if there are three upper electrodes, the phase shifter 8 creates a phase difference of 120 degrees. This is amplified by the high frequency amplifiers 7a, 7b and 7c, and each is given to the upper electrodes 5a, 5b and 5c through the matching boxes 6a, 6b and 6c. For example, if there are three electrodes, Asin (ωt + Φ ₁ ) and Bsin (ωt +
The voltages of Φ ₂ ) and Csin (ωt + Φ ₃ ) are applied to the respective electrodes.

These voltages are applied to the electrodes in rotationally symmetrical positions. This produces an electric field that rotates about the center of the upper electrode. Moreover, since a voltage is applied to the plasma, a current determined by the impedance of the plasma flows from the electrode to the plasma. As a result, the gas introduced into the chamber is excited and converted into plasma. The upper electrode 5 thus excites the gas by the alternating 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. By 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.

The present invention further includes means for adjusting the phases Φ ₁ , Φ ₂ , Φ ₃ for the phase shifter 8. This is Figure 3
Can be performed by the MPU 13. Means for adjusting the amplification factor of the amplifier 7 is also provided. These are Asin (ωt + Φ ₁ ), Bsi applied to the upper electrode from the power source.
This means controlling the phases Φ ₁ , Φ ₂ , Φ ₃ and the amplitudes A, B, C of voltage signals such as n (ωt + Φ ₂ ) and Csin (ωt + Φ ₃ ). Since the square of the amplitude is proportional to the power, if the amplitude is specified, the power will be adjusted. However, since the effective impedance of the plasma changes, the voltage amplitude of the amplifier does not uniquely determine the power flowing into the plasma.

The present invention further provides an observation system. this is,
Output impedance Za, Z of the matching box 6
b and Zc are monitored. This is the plasma impedance. The current ia, i flowing into the plasma
b and ic are monitored by the current transformers 12a, 12b and 12c. This is provided between the matching box 6 and the individual upper electrodes 5. Further, a device for directly requesting electric power is provided. Thereby, the power Pa, Pb, Pc of each upper electrode is obtained.

In this way, the impedance Z, the current i and the power P are measured for each upper electrode. After that, the effective power is obtained by multiplying the impedance by the square of the current. The effective power reveals the spatial turbulence of the plasma. FIG. 3 shows a control system. This represents the action of MPU13. The absolute value of the impedance is used, and the absolute value of the current is also used in the calculation. Furthermore, here, a comparison of these parameters is made.

The difference between impedances Za, Zb, and Zc is obtained by a differential amplifier. This result is further compared with a certain value by the comparator.
When it is equal to or higher than a certain value, the H level is output. If it is below a certain value, the L level is output. This is P of MPU
Input to _A , P _A and P _A. Current ia, ib, ic
, Their difference is determined by a differential amplifier. This result is further compared with a constant value by a comparator. If the value is equal to or greater than a certain value, the value is H. This is MP
It is input to P _B , P _B , and P _B of U.

These results are 1 or 0. If the difference in impedance or the difference in current is within the range, the current situation is not changed. Adjustments are made only if these differences are greater than a certain value. Further, the MPU calculates the impedance and the square of the current. n ² is a multiplier that calculates the square of the input. XY is a multiplier. These differences are determined by calculating the power at each electrode. These differences are also checked to see if they are above a certain value. These results are the P _{C of} MUP,
Input to P _C and P _C.

With respect to electric power, similar differential amplification and processing by a comparator circuit are performed. The result of this is MPU
Input to 13 P _D , P _D , and P _D. The MUP 13 sends a signal for changing the amplification factor to the high frequency amplifier 7 based on the results of these measurements. If this alone is not balanced between the electrodes, further to the phase shifter 8, and sends the signal f _a, f _b, f _c for changing the phase. By these means, the plasma generated by the upper electrode has centrosymmetric homogeneity. For example, control is performed as follows.

(1) Consider the case where P _D = 000. This means that the powers applied to the three electrodes all match (within some tolerance). (1-1) Further, assume that P _A = 000. This means that the impedances are also equal. In this case, the direction of control is determined by the content of P _B.

When P _B = 100 (only the current i _a differs from the other currents) the phase Φ ₁ is adjusted. When P _B = 110 (only the current i _b is different from other currents)
Adjust the phase Φ ₂ . When P _B = 010 (only the current i _c differs from other currents)
Adjust the phase Φ ₃ .

(1-2) When P _A is other than 000. This means that the three electrodes have different impedances. In this case, the effective power cannot be evaluated only by the current. The imbalance is evaluated using the effective power which is Zi ² .

The phase Φ1 is adjusted when P _C = 100 (only A differs from other effective powers). When P _C = 110 (only B is different from other effective power) Adjust the phase Φ2. Adjust phase Φ3 when P _C = 010 (only C differs from other effective power).

The above operation should restore the uniformity of the plasma with respect to the center of the upper electrode. However, if the balance cannot be improved by these operations, the power is changed so that P _D is not = 000.

(2) Adjust P _D ≠ 000 P _D = 101 Φ ₁ . Adjust P _D = 110 Φ ₂ Adjust P _D = 011 Φ ₃ .

As described above, the state of plasma is obtained, and the electric power applied to the electrodes or the mutual phase difference is changed to always generate a well-balanced plasma.

[0033]

In the conventional apparatus, when there is a temporal change in plasma intensity, the plasma is visually observed from the viewport and the fluctuation of the plasma is reduced by manually changing the power ratio between the electrodes. Was there. However, even if the plasma is viewed from a narrow viewport, its fluctuation is not clearly understood, and manual adjustment takes time, and it cannot follow the temporal fluctuation. In the present invention, the electric power sent to the electrodes, the current flowing in the plasma, and the impedance are measured for each electrode, the distribution and the power of the plasma are actually obtained, and the state of the plasma is changed based on this. Since the state of the plasma can be actually known, accurate control can be performed.

Since not only the power but also the phase angle is controlled, delicate adjustment is possible. Since the state monitoring circuit and the control circuit are both configured to have a high speed, it is possible to quickly respond to fluctuations in plasma that are fast in time and suppress fluctuations.

[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 provided with a mechanism for monitoring state variables and a mechanism for controlling plasma.

FIG. 3 is a schematic configuration diagram showing how state variables are taken into an MPU (microprocessor) and control variables are output.

[Explanation of symbols]

 1 Vacuum Chamber 2 Lower Electrode 3 Insulator 4 Sample 5 Upper Electrode 6 Matching Box 7 High Frequency Amplifier 8 Phase Shifter 9 High Frequency Oscillator 10 Matching Box 11 High Frequency Power Supply 12 Current Transformer 13 MPU

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 21/3065 21/31 C

Claims (1)

[Claims] 1. A vacuum chamber capable of being evacuated, a lower electrode provided below the inside of the vacuum chamber, and three or more n upper electrodes provided above the inside of the vacuum chamber. A sample is placed on top, high-frequency power is applied to the lower electrode, and voltages are applied to the upper electrode with the same frequency but different phase angles of 2π / n to generate plasma and treat the object to be processed with the plasma. In such a plasma processing apparatus, the impedance of the plasma seen from each upper electrode, the current flowing into the plasma from each upper electrode, the power applied to each upper electrode is monitored, and the spatial fluctuation of the plasma is determined from these values. A plasma processing apparatus characterized in that a phase difference between the upper electrodes and an electric power applied to the upper electrodes are adjusted.