JPH10226893A - Method and equipment for controlling energy of ion made incident on substrate at dry etching - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily change the energy of the ions made incident on a substrate by making the waveform of alternating electric power or high frequency electric power, to be impressed on a substrate electrode, rectangular, making the duty ratio of the rectangular wave variable, and controlling the energy of the ions made incident on the substrate. SOLUTION: A substrate electrode 7, provided inside a vacuum chamber 1, is connected to a rectangular high frequency electric power source 9 for substrate bias. A substrate 10 to be treated is mounted on the substrate electrode 7. ICP (inductively coupled plasma) is used as a plasma generation system, and an electric power of 13.56MHz is impressed from a high frequency electric power source 5 for plasma generation on a high frequency coil 4 for plasma generation to generate plasma. Because the density of the plasma formed by ICP is sufficiently high, plasma density is practically free from fluctuations even if the duty ratio of the rectangular high frequency wave impressed on the substrate electrode 7 is changed and the effective electric power applied to the substrate 10 is changed, and the energy of ions alone is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling the energy of ions incident on a substrate in dry etching for etching a substance on a semiconductor, an electronic component, or another substrate using plasma.

[0002]

2. Description of the Related Art In conventional dry etching, a sine wave is used as an alternating electric field or a high-frequency electric field applied to a substrate. The substrate incident energy of certain ions in the plasma in the prior art is determined by the substrate bias power when the plasma density and the electron temperature are constant. The lower the power, the lower the ion energy, and the higher the power, the higher the energy. Positive ions fly and enter due to the difference between the potential at the place where they were generated and the potential at the destination.
FIG. 7 of the accompanying drawings shows a report example of Coburn et al. (J. Appl. Phys., 43 (1972) 4965) in which the energy distribution of positive ions incident on a wall surface at the ground potential is measured. In this example, since the electrode on which the mass analyzer A is attached is a ground electrode, the positive ions in the plasma enter the mass analyzer with the energy of the difference between the plasma potential and the ground potential. On the other hand, FIG. 8 shows an example measured by an energy analyzer attached to a substrate electrode to which high-frequency power is applied. In this case, the positive ions enter the substrate with the energy of the difference between the plasma potential and the substrate electrode potential. In this example, a sine wave of 13.56 MHZ is applied for 3 OOWs only to the substrate electrode to form plasma. The pressure was 0.4 Pa, and Vdc at this time was about 400 V. A substantially symmetrical energy spectrum distribution is obtained.

In dry etching in the prior art, the exact potential of the substrate electrode is a combined potential of the self-bias potential and the high-frequency potential. The sheath has a potential equal to the difference between the plasma potential and the substrate electrode potential. The ion motion in the sheath is modeled as Child-Langmuir equation J _i = (4/9) · (2q / m _i ) ^1/2 · (ε ₀ V _s ^3/2
/ Ds ² ) and the equation of motion. Assuming that J _i is constant, the sheath thickness ds is determined as a function of the sheath potential for high frequency oscillation. The equation of motion of an ion in a high-frequency electric field is expressed as m (d ² x / dt ² ) = − qE ₀ sin (ωt) when the high-frequency electric field waveform is a sine wave, and combines this expression with the Child-Langmuir expression And the behavior of ions in the sheath can be calculated numerically. FIG. 9 shows the result obtained in such a manner. The high frequency component of the sheath was 400 sin (ωt) [V], and the positive ion species was Ar. The figure shows that the ion energy is 380 to 42 OV and that the plasma reaches the electrode from the sheath end in about 80 Onsec. The ion energy at this time is obtained by tracking ions incident on the sheath that vibrates at a high frequency. As a result, it was found that the energy distribution of ions differs depending on the phase of incidence on the plasma sheath end. That is, the magnitude of the high-frequency perturbation received depends on the phase at which the light enters the sheath, and a difference occurs in the acceleration time, so that the energy of the ions reaching the substrate can be distributed. FIG. 10 is a graph showing how the incident phase of ions is plotted on the horizontal axis and the energy of ions is plotted on the vertical axis, and how the ions incident at each phase are accelerated with time. Immediately before reaching the substrate, ions incident on the sheath at a phase of about 350 ° are accelerated and have large energy, but when reaching the substrate, ions incident on the sheath at a phase of about 250 ° have a large energy. Have. This is determined by the high-frequency electric field that the ions receive through the sheath and reach the substrate. The horizontal axis in FIG. 10 is the incident phase, but also the number of particles that are incident simultaneously. Therefore, when the number of particles having the same energy is counted and displayed on the vertical axis, and the energy is plotted on the horizontal axis, an energy distribution can be obtained. The energy distribution obtained in this manner takes the form of a “bimodal” having peaks on the high energy side and the low energy side as shown in FIG.

[0004]

A plasma is generated at a low voltage by alternating power, high frequency power, microwave power, etc.
In an etching apparatus that applies a sinusoidal high-frequency electric field to a substrate electrode, the ion energy distribution and its central energy greatly depend on the ion mass, electron temperature, and the magnitude of the bias potential. In addition, since the energy distribution is determined by the number of alternating electric fields received by the ions, ions having a small mass have a large velocity and reach the substrate within a short period of time, while ions having a large mass have a large width. The width becomes narrow because it flies through the time sheath and reaches the substrate. Similarly, the energy width can be changed by changing the frequency. For the same mass, the higher the frequency, the greater the number of alternating electric fields received during flight, the more averaging occurs and the narrower the energy width. However, when the mass, the electron temperature, and the bias potential of the ions are the same, the energy width can be changed even if the frequency is changed, but the center energy does not change. FIG. 12 shows the calculation results of the ion energy distribution when a high-frequency electric field of 27.12 MHz is applied. It can be seen that the energy width is smaller than when the 13.56 MHz high frequency electric field shown in FIG. 11 is applied. However, the energy at the center does not change.

Accordingly, the present invention provides a method of applying an alternating electric field or a high-frequency electric field to a substrate electrode by changing the duty ratio, which is a period of applying an alternating electric potential or a high-frequency electric potential / one cycle, to easily apply the electric field to the substrate. It is an object of the present invention to provide a method and an apparatus for controlling the energy of ions incident on a substrate in dry etching, in which the energy of incident ions can be changed.

[0006]

When a charged particle flies through an accelerating electric field, the acceleration energy of ions received from the electric field is determined by the magnitude of the electric field in the flight space and the time of flight. The longer you fly in the accelerating electric field, the more energy is given from the electric field. However, since the sheath width is finite, the energy distribution can be made because some of the accelerating energies are obtained or less depending on the time of the electric field acceleration while flying in the alternating electric field. As the frequency increases, the ions fly through a number of alternating electric fields and are averaged. The degree of this averaging determines the energy width. When the frequency is high or heavy particles fly, the ions are subjected to a large number of alternating electric fields, so that the ions are averaged and the energy width is narrowed. Although the above discussion is about the phenomenon when a sine wave is used, the same can be applied when a rectangular wave is used. Therefore, in the present invention, by changing the width of the rectangular wave (duty ratio; alternating potential or high-frequency potential application time / period time) in dry etching using a method of applying a rectangular high-frequency electric field or alternating electric field to the floating electrode substrate. Since the time for applying energy to the ions can be changed, the energy value of the ions can be changed as a result.

[0007]

According to one embodiment of the present invention, a gas mainly composed of a halogen-based gas is introduced into a vacuum, and a plasma is generated at a low pressure by using alternating power, high frequency power, microwave power, or the like. It forms and decomposes the introduced gas, positively utilizes the generated ions of electrons, atoms, molecules, radicals and ions, and applies an alternating electric field or a high-frequency electric field to the substrate electrode in contact with the plasma to remove the substance on the substrate. In dry etching for etching, the energy of substrate incident ions is controlled by changing the waveform of alternating power or high frequency power applied to the substrate electrode to a rectangular wave and varying the duty ratio of the rectangular wave to control the energy of the substrate incident ions. A method is provided.

According to another embodiment of the present invention, a gas mainly composed of a halogen-based gas is introduced into a vacuum, and plasma is formed at a low pressure by using alternating power, high frequency power, microwave power, or the like. A dry process that decomposes the introduced gas and positively utilizes the generated electrons, atoms, molecules, radicals, and ions, and applies an alternating electric field or high-frequency electric field to the substrate electrode in contact with the plasma to etch the substance on the substrate. In the etching, a circuit device for generating alternating power or high-frequency power of a rectangular wave to be applied to the substrate electrode, and a circuit device for controlling a duty ratio of the rectangular wave are configured to control the energy of ions incident on the substrate. Thus, there is provided an energy control device for substrate incident ions.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 schematically shows an example of an inductively coupled etching apparatus in which the present invention is implemented.
Is a vacuum chamber having a cylindrical side wall 2 made of quartz, in which a plasma chamber 3 is formed. A high frequency coil 4 for plasma generation is provided outside the cylindrical side wall 2, and the high frequency coil 4 for plasma generation is connected to a high frequency power supply 5 for plasma generation. A substrate electrode 7 is provided in the vacuum chamber 1 via an insulator 6, and the substrate electrode 7 is connected to a rectangular high-frequency power source 9 for substrate bias via a matching box 8. A substrate 10 to be processed is mounted on the substrate electrode 7 via a substrate holding mechanism 7a.

In the apparatus shown in FIG. 1, ICP (Inductively Coupled Plasma) is used as a plasma generation method, and 13.56 MHz power is applied from a plasma generation high-frequency power supply 5 to a plasma generation high-frequency coil 4 to generate plasma. generate. Since the plasma formed by the ICP has a sufficiently high density, the plasma density hardly changes even if the effective power applied to the substrate 10 is changed by changing the duty ratio of the rectangular high frequency applied to the substrate electrode 7. Only the energy of the ions changes. Therefore, the energy of ions can be controlled by supplying rectangular high frequency power to the substrate electrode 7 and changing the duty ratio of the rectangular high frequency.

FIG. 2 shows a block diagram of an entire circuit for generating rectangular high-frequency power.
Denotes an oscillation adjustment unit, 12 denotes a basic oscillation unit, 13 denotes a comparison unit, and 14 denotes a mixing unit. These units constitute an oscillation unit. In addition, 15 is a waveform shaping section, 16 is a preamplifier, 17 is a post-amplifier, 18 is a power detector, 19 is a commercial AC power supply, 20 is an AC / DC rectifier, and 21 is a variable voltage automatically. DC power supply unit that can be set, 22 is a power setting unit for maintaining a predetermined power,
They are connected as shown. FIG. 2 shows signal waveforms in each block. Since the signal waveform includes a capacitive reactance and an inductive inductance in the process of amplification and the coupling of the high-frequency output power amplified to a predetermined power to the non-linear load, the over-short resonance at the rise and the under-fall at the fall are included. Although it is inevitable that a shoot resonance occurs, the resonance level and the period can be stabilized by keeping the transition time of the rise and fall of the signal constant. In addition, as for the reproducibility of the target etching process, if the resonance level is sufficiently small and the period is stable as compared with the predetermined required power, no serious problem occurs. A power detection unit 18 is provided at a high frequency output as a means for maintaining a predetermined power, and a detection signal of the power detection unit 18 is compared with a voltage of the power setting unit 22 to automatically change the voltage. By controlling the voltage supplied to the amplifier 17, a closed loop is formed.

FIG. 3 shows a block diagram of a duty ratio variable section and an example of an amplifier section circuit. Parts corresponding to the components shown in FIG. 2 are denoted by the same reference numerals, and 24 is a reference voltage generator. In the circuit device shown in FIG. 3, in the present invention, it is necessary to change the duty ratio of the oscillating frequency. Therefore, in addition to the basic oscillating unit 12, the oscillating unit generates a stable voltage by the reference voltage generating unit 23 and oscillates the voltage. One cycle (oscillation frequency) of charging / discharging is determined by controlling the adjusting unit 11. Similarly, by controlling the reference voltage as a threshold voltage, the comparison unit 13 and the mixing unit are controlled.
The duty ratio is determined by 14 combinations. Since the signal waveform created here is distorted compared to the shape of the target waveform, it is shaped into the target waveform by the waveform shaping unit 15. Since the signal level at this stage is a TTL level, the signal is amplified by the preamplifier 16, sent to the final amplifier 17, and radiated to a predetermined required power. The high-frequency output whose power has been increased to the predetermined power is transformer-coupled, and the power is sent to the load.

By the way, if only a rectangular wave having a constant frequency is to be generated, the odd-number multiple wave may be simply amplified, but the duty ratio cannot be changed. By using the circuit devices of the systems shown in FIGS. 2 and 3, a rectangular wave whose duty ratio Rd can be varied can be generated even at 13.56 MHz. However, since it is a rectangular wave, the fundamental frequency component
(For example, 13.56 MHZ), the frequency spectrum component other than 13.56 MHZ is included, so that matching with plasma as a load cannot be sufficiently obtained. Therefore, the waveform is not a regular rectangle but a broken waveform. However, even if the waveform is distorted, the other components are sufficiently smaller than the fundamental frequency component, so that there is no major problem in energy control.

FIG. 4 shows the energy distribution when the duty ratio is 0.93, FIG. 5 shows the energy distribution when the duty ratio is 0.46, and FIG. 6 shows the energy distribution when the duty ratio is 0.16. As described above, by changing the duty ratio Rd in the system in which the rectangular high-frequency electric field is applied to the substrate electrode 7, the energy of ions incident on the substrate 10 can be easily changed.

In the illustrated embodiment, the case where the rectangular high frequency used for the substrate bias is 13.56 MHz has been described. However, the region where the matching can be easily performed is rather in the low frequency band. In addition, considering the use of a region as narrow as possible as the energy width, it is considered that 1 to 10 MHz is preferable. However, the present invention is not limited to this region. Even if the energy width is somewhat wide, the energy value at the center can be changed, so that it can be used at around 500 kHz.

[0016]

As described above, in the present invention, the waveform of the alternating power or the high frequency power applied to the substrate electrode is a rectangular wave, and the duty ratio of the rectangular wave is varied to control the energy of the ions incident on the substrate. With such a configuration, the energy of ions incident on the high-frequency power application substrate can be made variable, and the substrate material can be processed with ion energy desired for the material. Therefore, the present invention is considered to make a great contribution to the reactive ion etching process used particularly for processing semiconductors and electronic parts.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an inductively coupled etching apparatus embodying the present invention.

FIG. 2 is a block diagram showing a circuit device for generating a rectangular high frequency in the present invention.

FIG. 3 is a block circuit diagram illustrating an example of a circuit device that generates a rectangular high frequency according to the present invention.

FIG. 4 is a graph showing a calculation example of an energy distribution when the duty ratio is 0.93.

FIG. 5 is a graph showing a calculation example of an energy distribution when the duty ratio is 0.46.

FIG. 6 is a graph showing a calculation example of an energy distribution when the duty ratio is 0.16.

FIG. 7 is a schematic diagram showing a conventional example of a mass analyzer having an ion energy analyzer connected to a ground potential unit.

FIG. 8 is a graph showing a measurement example of positive ions (Ar ⁺ ) incident on a substrate electrode in a conventional apparatus.

FIG. 9 is a graph showing a calculation example of the behavior of ions in a sheath by the equation of motion.

FIG. 10 is a graph showing the energy incident phase dependence of ions incident on a sheath.

FIG. 11 is a graph showing a calculation example of ion energy distribution in a conventional apparatus.

FIG. 12 is a graph showing another calculation example of the energy distribution of ions in the conventional device.

[Explanation of symbols]

 1: vacuum chamber 2: cylindrical side wall 3: plasma chamber 4: high frequency coil for plasma generation 5: high frequency power supply for plasma generation 6: insulator 7: substrate electrode 8: matching box 9: rectangular high frequency power supply for substrate bias 10: substrate 11: Oscillation adjustment section 12: Oscillation section 13: Comparison section 14: Mixing section 15: Waveform shaping section 16: Preamplification section 17: Post-amplification section 18: Power detection section 19: Commercial AC power supply 20: AC / DC conversion section 22: DC power supply 23: Power setting 24: Reference voltage generator

Claims (2)

[Claims] 1. A gas mainly containing a halogen-based gas is introduced into a vacuum, and a plasma is formed at a low pressure by using alternating power, high frequency power, microwave power, or the like, and the introduced gas is decomposed.
In dry etching in which the alternating electrons or high-frequency electric fields are applied to the substrate electrode in contact with the plasma to etch substances on the substrate, the generated electrons, atoms, molecules, radicals, and ions among the generated ions are positively used. A method for controlling the energy of substrate incident ions, wherein the waveform of the alternating power or high frequency power to be applied is a rectangular wave, and the energy of the substrate incident ions is controlled by varying the duty ratio of the rectangular wave. 2. A gas mainly composed of a halogen-based gas is introduced into a vacuum, and plasma is formed at a low pressure by alternating power, high frequency power, microwave power, or the like, and the introduced gas is decomposed.
In dry etching in which the alternating electrons or high-frequency electric fields are applied to the substrate electrode in contact with the plasma to etch substances on the substrate, the generated electrons, atoms, molecules, radicals, and ions among the generated ions are positively used. It has a circuit device for generating alternating power or high-frequency power of a rectangular wave to be applied, and a circuit device for controlling a duty ratio of the rectangular wave, and is configured to control the energy of substrate incident ions. Energy control device for substrate incident ions.