JPH03224226A - Plasma processing and device to be used therefor - Google Patents

Abstract

PURPOSE:To reproduce the state of plasma with good accuracy regardless of a deposited film on the inner wall of a chamber and to improve the reproducibility and accuracy of a processing process to increase a practicability by a method wherein a plasma processing device is provided with a feedback mechanism consisting of an impedance matching circuit and the like. CONSTITUTION:In case a plasma processing device is applied to an ECR plasma etching, a system of the plasma processing device is operated. Hereupon, a plasma impedance is first measured by an impedance matching circuit 14 in a feedback mechanism 50. Then, the measured value is compared with a value, which has been set previously in a feedback parameter setting circuit 19 in the mechanism 50, and only in the case where a difference between both values exceeds predetermined, allowable value the amount of a feedback is calculated by the circuit 19 and the amount is fed back to a change in a prescribed feedback parameter (a microwave power or the like). Thereby a fluctuation in the plasma impedance is inhibited. As a result, the state of plasma is substantially held constant, a plasma processing having a good reproducibility is obtained, the reproducibility and accuracy of a processing process are improved and a practical effect can greatly be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a processing method using a chemical or physical reaction at a gas-solid interface caused by plasma, and an apparatus used therefor.

Astonishing advances in microelectronics centered on conventional technology integrated circuits, together with the sophistication of optoelectronics centered on lasers, are bringing about a major social revolution comparable to the industrial revolution. Since the invention of integrated circuits, the degree of integration of integrated circuits has increased dramatically.
5cale IC, large scale integrated circuit), VLS
I (very large 5cale IC, super L
SI), ULS I (ultra large 5c
Ale IC, ultra-super LSI) are being developed one after another.

With regard to the nine-element structure that has been constructed due to such a large degree of integration (i.e., miniaturization of element dimensions and improvements to the element structure and circuitry) (Table 1). We have reached a stage where further miniaturization cannot be expected, and three-dimensional structures such as structures that utilize trenches formed in the substrate using directional etching, and structures that have multilayered wiring using reflow planarization technology, have reached a stage where further miniaturization cannot be expected. The structure of integrated circuits is also being considered.
In order to increase the degree of integration of integrated circuits, it is also necessary to reduce the dimensions of elements such as front transistors and resistors, as well as the dimensions of wiring patterns, even though it is thought that the physical limit of the element structure will be increased. Yo
At present, fine patterns of 1 μm or less are being put into practical use, and even though they are approaching the limit of about 0.4 μm, which is the limit of light exposure method, it is not possible to draw patterns finer than the wavelength of light with light exposure method, so To obtain fine patterns, it is necessary to use X-rays or electron beams with shorter wavelengths than ζ. Along with lithography, dry etching plays an important role in realizing such fine patterns.

Dry etching method 41 This is a processing method that removes unnecessary portions of a thin film or substrate by using chemical or physical reactions at the gas-solid interface caused by plasma radicans and ions. Dry etching methods include vapor phase etching, plasma etching, sputter etching, and ion beam etching.Sputter etching and ion beam etching may use active ions or radicals, and each method has a particular reactivity. They are also called sputter etching method and reactive ion beam etching method.
There are four of these methods that are suitable for integrated circuit manufacturing process technology.

Reactive sputter etching method (also called reactive ion etching method) When a sample is exposed to reactive ions in plasma generated by high-frequency discharge of an appropriate gas, unnecessary parts of the sample surface are removed by an etching reaction. It is said that the necessary part is common knowledge.
Protected by a photoresist pattern used as a mask.

Figure 8 is a schematic diagram showing a reactive ion etching apparatus as an example of a conventional dry etching apparatus.As shown in this figure, a reactive gas is introduced into a metal chamber 1 (through a gas controller 2) and an exhaust system. An anode (anode) 4 is provided at the top of the chamber 1, and a sample stage 5 serving as a cathode is provided at the bottom. An RF power source 7 is connected via a circuit 6, and a high frequency discharge can be generated between the sample stage 5 and the anode 4.In such a reactive ion etching device, reactive ions in the plasma Ions generated by high-frequency discharge are accelerated within the sheath and impact the sample 8 (ie, plate, the material to be etched) to produce an etching reaction, making it possible to perform a highly directional etching load, so-called anisotropic etching.

As the device dimensions are reduced, even though the gate oxide film of a zeta melon transistor is formed thinner and the diffusion layer is formed shallower, the dry etching method (principally) The plasma used is required to have low energy.
However, problems such as this can occur because the charge-up to the gate electric field causes destruction of the gate oxide film, and the impact of high-energy ions on the silicon substrate causes crystal defects and the introduction of impurities. To solve the problem, electron cyclotron resonance (
electron cyclotron resona
An ECR plasma etching method that utilizes the ECR phenomenon has begun to be used.

Problems to be Solved by the Invention However, conventional reactive ion etching (RIE) and ECR plasma etching methods have problems in process reproducibility. This is thought to be because the deposited film on the inner wall of the chamber has a great influence on the etching characteristics since the atmosphere of For example, in ECR plasma etching using IC SFa as the main gas, the etching rate is dependent on the number of processed wafers, which is one of the main causes of process instability.

In the etching method using plasma (!), it is necessary to apply a negative bias voltage to the sample stage in order to accelerate the positive ions generated in the plasma. There is a fixed bias method that uses a power supply, and a self-bias method that uses a negative voltage generated by floating the sample stage using a capacitor.

As an attempt to improve process reproducibility, there is a method in which the negative bias voltage is held at a constant value in the self-bias method. For example, in the reactive ion etching method, the ion energy during etching approximately corresponds to the DC potential Vdc of the sample stage, so the RF power is controlled so that Vdc is constant.

However, the plasma state (such as
It is known that it depends not only on the DC potential Vdc of the sample stage but also on the electron density, ion density, electron temperature, etc. in the plasma. The above methods are rarely used in actual etching methods because these important parameter values cannot be controlled.

Thus, it is the object of the present invention to iL (1,)
To provide a plasma processing method capable of reproducing the plasma state with high precision regardless of the deposited film on the inner wall of the chamber; (2)
) To provide a highly practical plasma processing method that significantly improves processing reproducibility and accuracy; and (3) to provide an apparatus for use in the plasma processing method that has such excellent advantages.

Means for Solving the Problems The plasma processing apparatus of the present invention includes a plasma reaction chamber that generates plasma for processing, a high-frequency power supply that supplies high-frequency power to the plasma reaction chamber via an impedance matching circuit, and a high-frequency power source that supplies high-frequency power to the plasma reaction chamber through an impedance matching circuit. and a feedback mechanism for maintaining the plasma impedance substantially constant, including the impedance matching circuit which also functions as an impedance sensing means.

In some preferred embodiments, the imaginary part of the plasma impedance is substantially preserved.

In one preferred embodiment, the feedback mechanism includes a feedback parameter setting circuit connected to an impedance matching circuit, and the feedback mechanism is configured to set the at least one feedback parameter value to the feedback parameter setting circuit based on information regarding plasma impedance. Direct image feedback is performed based on information about the plasma impedance, or the force set by the feedback mechanism described above.

In a further preferred embodiment, the above feedback is applied to at least one selected from the group consisting of: gas pressure within the plasma reaction chamber, gas flow rate into the plasma reaction chamber, magnetic field, microwave power, and radio frequency power. Information regarding plasma impedance (friend) is the capacitance value of at least one of the capacitors used in the above impedance matching circuit.

The plasma processing method according to the present invention substantially controls the plasma impedance by applying feedback to at least one selected from the group consisting of gas pressure in the plasma reaction chamber, gas flow rate in the plasma reaction chamber, magnetic field, microwave power, and high frequency power. In a preferred embodiment, the imaginary part of the plasma impedance is substantially held constant, and the imaginary part of the plasma impedance is substantially held constant.

In the present invention, due to the above-mentioned configuration, when the plasma shifts from a constant value, it is captured as a change in impedance, and the plasma chamber pressure changes depending on the amount of change in impedance.
Example (Example 1) Figure 1 shows the present invention applied to ECR plasma etching. A plasma processing device is shown. In this figure, reference number 1
0 is a plasma reaction chamber 11 which is a quartz Pelger, 12 is a sample to be etched, and 13 is a sample stage. The sample stage 13 is connected to an RF bias (1
3.56 MHz) is supplied from the RF power supply 15. Microwave power is supplied from the magnetron 16 to the plasma reaction chamber 10, and the electron cyclotron resonance condition is satisfied by this microwave power and the magnetic field generated from the electromagnet 17.

Although the plasma reaction chamber 10 is controlled to a degree of vacuum on the order of 101 to 10-'Pa by an evacuation system 18 including a vacuum pump, the plasma processing apparatus of this embodiment is different from the conventional ECR plasma etching apparatus ( (a) This feedback mechanism 50 also includes the impedance matching circuit 14. By setting a feedback parameter value based on the information regarding the plasma impedance in the plasma reaction chamber 10 taken out from the impedance matching circuit 14 which functions as an impedance detection means, and applying feedback to the magnetron 16 to control its microwave output. , keeping the plasma impedance substantially constant.

Here, the basic principle of the present invention is illustrated in FIGS. 1 and 2A.
This will be explained with reference to the flowchart below. When the system of the plasma processing apparatus starts operating, the plasma impedance is first measured by the impedance detection means 14. Next, the plasma impedance is compared with the value preset in the feedback parameter setting circuit 19. conduct. At this time, only when the difference between the two exceeds a predetermined tolerance value d, the amount of feedback is calculated in the feedback parameter setting circuit 19, and a predetermined feedback parameter (in this example, it is microwave power, - inside the membrane) is calculated. is fed back to changes in (the gas flow in the plasma reaction chamber, the gas pressure in the plasma reaction chamber, the magnetic field or the radio frequency power). In this way, fluctuations in plasma impedance are suppressed, and as a result, the plasma state substantially changes. held constant.

In this embodiment, an arithmetic circuit for calculating the amount of feedback is incorporated in the feedback parameter setting circuit 19, but as shown in FIG. 2B, the difference between the measured value and the set value exceeds the allowable value d. Direct deflection
A feedback mechanism may be used to provide feedback of a fixed amount or an amount proportional to the difference. A brief explanation of plasma impedance measurement.
As shown in FIG. 3A, a bulk plasma 20 containing electrons, ions, and neutral molecules is formed near the surface of the sample 12. The ion sheath 21 has almost no electrons. The positive ions are accelerated by the potential difference applied to the ion sheath 21 and impact the sample 12, causing an etching reaction. This indicates that the ion sheath 21 plays an important role in the etching process.The plasma shown in Figure 3A (can be represented by an equivalent circuit as shown in Figure 3B).About the expression regarding the equivalent circuit of the plasma (
Friend example ζgi J, Ignacio Ulacia F,
other.

Materials Research 5ociet
y Symposia Proceedings, V
ol, 98. pp. 203-208 (1987)
The bulk plasma 20 is represented by a resistor Rb, and the ion sheath 21 is represented by a sheath capacitor Csh and a resistor Rsh connected in parallel. Plasma impedance is reflected in the capacity of the ion sheath (11csh) and is generally capacitive.When the plasma density changes, the thickness Lsh of the ion sheath changes, which is detected as a change in plasma impedance.

In the plasma processing apparatus of this embodiment, the plasma impedance is measured by the impedance matching circuit 14, and the L
Impedance matching is performed in the impedance matching circuit 14 so that maximum power is supplied to the plasma from the RF power source 15. At this time, impedance matching circuit 1
The impedance seen from the output terminal of 4 and the impedance seen from the impedance matching circuit 14 from the plasma side have a complex conjugate relationship with each other.Measurement of plasma impedance (4) This relationship is utilized.

For example, if the impedance matching circuit 14 is composed of two variable capacitors with capacitances C1 and C2 and a coil with inductance L (as shown in Figure 3C), By measuring and tabulating the impedance seen from the plasma side, the plasma impedance can be known from the values of C+ and C2. The dependence of plasma impedance on gas pressure measured by the above method when using a mixed gas with 10%) is shown.

This figure shows that due to changes in gas pressure, the electron density, ion density, and electron temperature in the plasma change, and the plasma impedance changes accordingly.From the values of capacitances C1 and C2, It is possible to know the plasma impedance in real time.Capacitance C1
By applying feedback to the microwave output of the magnetron 16 via the calculation circuit of the feedback parameter setting circuit 19 based on the values of C and C2, the plasma impedance can be kept constant. Since the values of This will be explained with reference to FIGS. 5A and B. Let, capacitances C1 and C2 when matched in the impedance matching circuit, Real part of plasma impedance (Figure 5A
) and the imaginary part (Figure 5B) These graphs are obtained from discrete values, and no smoothing processing is performed. The impedance setting value of is converted to the value of capacitance C1 and Ce, respectively, and is 42
pF and 183 pF (indicated by a black circle in the figure), and it is assumed that when the microwave power is changed, the plasma impedance changes as shown by the broken line in the figure. When the amount of microwave absorption increases and the plasma density decreases due to film deposition, the plasma impedance L changes along the broken line. Therefore, by changing the microwave power cf so that the plasma impedance returns to the initial setting value, the plasma state can be maintained approximately constant. In this case, return either the real part or the imaginary part of the plasma impedance to its original value (the other value also returns to almost its original value).

− In order to completely reproduce the plasma state (
Friend: It is necessary to return both the real and imaginary parts of the plasma impedance to their original settings.

If the plasma state can be kept almost constant in either the real part or the imaginary part, as in the case above,
It is preferable to perform correction using the imaginary part.

This is because the imaginary part is thought to reflect the properties of the ion sheath, which is closely related to plasma reactions.

For the purpose of improving the reproducibility of the plasma state, it is not necessarily necessary to determine the value of plasma impedance. In this example, it was possible to use the capacitances C1 and C2 of the variable capacitors. Figure 1 is a graph showing the relationship between the number of wafers processed and the etching rate when reactive ion etching is performed using CaC1aFi gas and SFe gas. A deposited film adheres to the inner wall of the quartz Pelger, and this film absorbs microwaves, which changes the energy supplied to the plasma, resulting in changes in plasma density, etc. Therefore, when using conventional etching equipment, As shown by curve (b) in Figure 6, as the number of wafers processed increases, the etching rate decreases.For example, when 25 wafers are processed, the etching rate may drop to nearly 70% of the initial etching rate. In the actual production line, it was necessary to perform chamber cleaning every 10 sheets as shown in curve (C) in Figure 6. In contrast, in this example, etching was performed as shown in curve (a) in Figure 6. The rate was almost independent of the number of wafers processed. This is because by using the plasma processing apparatus of this example, the plasma density etc. can be kept substantially constant without depending on the deposited film on the inner wall of the quartz Pelger. Although this shows that stable etching characteristics have been obtained, this example illustrates the case where changes in plasma impedance are corrected by microwave output. Similar results were obtained (Example 2). Figure 7 shows the present invention using RIE (reactive ion etching).
This figure shows the plasma processing equipment applied to. In this diagram,
Reference number 30 indicates a plasma reaction chamber 31 for the sample I to be etched.
EI, 32 is the sample stage.
3.56 MHz) is supplied from the RF power supply 34.

Plasma reaction chamber 30 (exhaust system 3 including vacuum pump)
5, the degree of vacuum is controlled to be on the order of 101 to 10" Pa.

The plasma processing apparatus of this embodiment differs from the conventional RIE apparatus (mainly in that it is equipped with a feedback mechanism 51 having a feedback parameter setting circuit 36 connected to an impedance matching circuit 33). It also includes an impedance matching circuit 33 and a feedback parameter setting circuit 36 &
y) Plasma reaction chamber 3 taken out from impedance matching circuit 33 functioning as impedance detection means
Setting the feedback parameter value based on information regarding the plasma impedance within 0, by applying feedback to the RF power supply 34 or the exhaust system 35 to control the RF specific output or the degree of vacuum, the plasma impedance can be substantially adjusted. In this example, when the plasma state was actually controlled using this method, etching could be performed with extremely high reproducibility. As the number of etched sheets increases, gas is released from the deposited film attached to the inner wall of the plasma reaction chamber and the plasma state changes, causing the etching characteristics to change.In contrast, in this example, the etching characteristics were By using the plasma processing apparatus of this embodiment, the plasma density is kept substantially constant and is extremely stable, without depending on the film deposited on the inner wall of the plasma reaction chamber. This shows that excellent etching characteristics were obtained.

In Examples 1 and 2 above, the case of dry etching was explained, but it can also be applied to film deposition techniques such as chemical vapor deposition (CVD). Can be applied.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a plasma process with good reproducibility can be obtained regardless of the condition of the surrounding wall of the chamber, and process reproducibility and high precision are realized, which has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the plasma processing apparatus of the present invention. FIG. 2 (A) and (B) are flowcharts for explaining two different procedures of the plasma processing method of the present invention. (A) is a schematic diagram showing the state of plasma used in dry etching. Figure 3 (B) is an equivalent circuit diagram of the plasma shown in Figure 3. Figure 3 (C) is a circuit diagram showing an example of an impedance matching circuit. Figure 4 shows the plasma impedance measurement results. Figure 5 (A and Figure 6 shows the relationship between the number of wafers processed and the etching rate when the plasma processing equipment shown in Figure 1 and the conventional etching equipment are used for reactive ion etching. Fig. 7 shows another embodiment of the plasma processing apparatus of the present invention. Fig. 8 is a schematic diagram showing a conventional reactive ion etching apparatus. 10, 30... Plasma reaction i 13,32...
...Sample stage, 14, 33...Impedance matching circuit Ii & 15.34...RF power #16...Magnetron, 18.35...Exhaust chestnut 19.36...
・Feedback parameter setting times 50゜51...
・Feedback mechanism.

Claims (10)

[Claims] (1) A plasma reaction chamber that generates plasma for processing, a high-frequency power supply that supplies high-frequency power to the plasma reaction chamber via an impedance matching circuit, and a plasma impedance within the plasma reaction chamber that is maintained substantially constant. A plasma processing apparatus comprising: a feedback mechanism for detecting impedance; the feedback mechanism includes the impedance matching circuit that also functions as an impedance detection means. (2) The plasma processing apparatus according to claim 1, wherein the imaginary part of the plasma impedance is substantially maintained. (3) The feedback mechanism includes a feedback parameter setting circuit connected to an impedance matching circuit, and based on information regarding plasma impedance,
The plasma processing apparatus according to claim 1, wherein at least one feedback parameter value is set in the feedback parameter setting circuit. (4) The feedback parameters include gas pressure in the plasma reaction chamber, gas flow rate in the plasma reaction chamber, magnetic field,
The plasma processing apparatus according to claim 3, wherein the plasma processing apparatus is selected from the group consisting of microwave power and high frequency power. (5) The plasma processing apparatus according to claim 3, wherein the information regarding plasma impedance is a capacitance value of at least one of the capacitors used in the impedance matching circuit. (6) The plasma processing apparatus according to claim 1, wherein the feedback mechanism directly provides feedback based on information regarding plasma impedance. (7) The feedback is applied to at least one selected from the group consisting of gas pressure within the plasma reaction chamber, gas flow rate into the plasma reaction chamber, magnetic field, microwave power, and radio frequency power. Plasma processing equipment. (8) The plasma processing apparatus according to claim 6, wherein the information regarding plasma impedance is a capacitance value of at least one of the capacitors used in the impedance matching circuit. (9) By applying feedback to at least one selected from the group consisting of gas pressure in the plasma reaction chamber, gas flow rate into the plasma reaction chamber, magnetic field, microwave power, and high frequency power, the plasma impedance can be substantially adjusted. A plasma processing method that includes etching or depositing a film using a plasma while maintaining the plasma constant. (10) The plasma processing method according to claim 9, wherein the imaginary part of the plasma impedance is substantially maintained.