JPH0748488B2 - Plasma controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a plasma control device that performs an etching process or the like in a semiconductor manufacturing process, and more particularly to a plasma control device suitable for forming a fine pattern.

[Conventional technology]

In a technical field of applying discharge plasma to etching, a plasma processing apparatus equipped with a high-frequency power source for accelerating ions in plasma with respect to an electrode on which an object to be etched (for example, a semiconductor wafer substrate) is mounted, There are plasma processing apparatuses described in JP-A-57-131374, JP-A-56-33839, and JP-A-60-160620 for disposing the etching object between the electrodes.

In these devices, a high-frequency power source is connected between opposing flat plate electrodes to generate plasma, and a high-frequency power source with a different frequency is connected to the electrode on the substrate mounting side to make the ions incident on the substrate. It controls energy.

The two high-frequency power supplies are both configured to supply power to the plasma, and at this time, a filter circuit is provided so that one of the electrodes can be equivalently regarded as the ground potential for each frequency of the power supply. .

In this conventional configuration, in order to stably supply electric power to the plasma, not only the impedance of the plasma but also the total impedance including the filter circuit,
A matching circuit is needed for each power supply frequency.

As described above, in the conventional plasma processing apparatus, since the filter circuit and the matching circuit include the coil and the capacitor,
The frequency band that can be supplied to plasma is limited, and it is difficult to apply a waveform other than a sine wave of a specific frequency.

[Problems to be solved by the invention]

Since the processing accuracy required for etching is about 0.8 μm to 1.3 μm in pattern size, the etching selection ratio between the material to be etched (covering material) and the base material (the etching rate of the coating material and the base material Increasing the ratio),
In addition, it is necessary to perform etching with high dimensional accuracy.

In order to perform such etching, it is necessary to narrow the distribution width of ion energy incident on the object to be etched, to keep the electric field strength between the plasma and the electrode constant, and for this purpose, first, , A special waveform including high-order frequency components such as a rectangular wave and a triangular wave described in the above publication,
It is an essential technical subject to apply the voltage to the electrodes without blunting the waveform.

It is an object of the present invention to provide a plasma processing apparatus capable of applying a special waveform including a high-order frequency component to an electrode without adversely affecting plasma discharge.

[Means for solving problems]

The purpose is to ground the electrode on which the substrate is mounted via a resistor, and to connect one end of the resistor and the substrate mounting electrode to a high frequency power supply (special waveform generation power supply) for controlling the potential of the electrode. In addition, the electrode (power supply side electrode) facing the substrate mounting electrode (ground side electrode) is grounded via the coil, while a high frequency power supply for generating plasma, matching circuit, power supply side electrode, plasma generation This is achieved by providing an electric circuit composed of a space, a ground side electrode, and a bypass capacitor and separating the above two power supply systems.

In other words, a high frequency power supply for generating plasma,
A matching circuit, a power supply side electrode, a plasma generation space, a grounding side electrode, and a bypass filter for passing the power of the high frequency electrode, which is composed of a resistor and a capacitor and is grounded to the resistance of the bypass filter of the plasma generation power system. The power of the high frequency power supply for controlling the potential of the side electrode is superimposed and applied, and a part of the power of the high frequency power supply that passes through the plasma generation space and flows to the power supply side electrode is sent to the ground by the coil. Taking is the solution.

[Action]

In the above configuration, if the output impedance of the special waveform generating power source and the impedance of the resistor are matched, the potential of the ground side electrode can be controlled faithfully to the output waveform of the power source. In addition, sufficient controllability can be provided by using a predetermined resistor having a minimum inductance.

Electric power from the high-frequency power source that contributes to the generation of plasma stably generates plasma by grounding the ground-side electrode through a capacitor that has a sufficiently low impedance at the frequency. Most of the electric power from the special waveform generating power supply flows to the resistor, but part of it flows to the power supply side electrode through the plasma. However, since the amount is as small as 5% or less of the whole, it does not adversely affect the plasma. Further, since it flows to the ground through the coil connected to the power source side electrode, it does not adversely affect the high frequency power source that contributes to plasma generation.

〔Example〕

Hereinafter, some explanation will be given for convenience in determining the circuit constants of the resistors, the coils, and the capacitors, and then the embodiments will be described.

In order to control only the potential of the ground side electrode, it is sufficient to generate a potential difference between the electrode and the ground, without needing to supply all electric power through the plasma.

Conventionally, since the high frequency power is entirely supplied to the plasma, impedance matching is performed between the plasma and the high frequency power supply. Now, let the plasma impedance be a + jb
(A is a resistance component and b is a reactance component),
The imaginary component jb is usually 1 / jωC, jω depending on the capacitive and inductive properties.
For example, L is a quantity depending on the frequency f (ω = 2πf). At this time, if the power source impedance is a-jb, the reactance component is canceled and the maximum power is supplied to the plasma without loss. This is a general impedance matching, which is a well-known principle (for example, "Glow Discharge P" by Brian Chapman).
roces-ses) (1980) ").

On the other hand, since the impedance of plasma, which is a load, changes depending on the type of gas used, pressure, supplied power, etc.,
It is difficult to match the impedance of the power supply to the fluctuating load each time, and a matching circuit composed of a coil and a capacitor is inserted to match the impedance Z ₀ (output impedance, Z ₀ = r + jo) peculiar to the power supply. Therefore, in order to enable application to a wide frequency component waveform, the combined reactance component of the reactance component of the load impedance and the reactance components of the coils and capacitors in the matching circuit on the way is sufficiently smaller than the resistance component. It is necessary to.

Therefore, as described above, if the impedance of the load when the electrode to be applied is foreseen from the high frequency power supply (special waveform generation power supply) side that generates a potential at the ground side electrode does not include the reactance component, , The problem can be solved. The output impedance of a normal power supply is about 50Ω in resistance component, while the impedance of plasma is several hundred to several thousand Ω in resistance component and several thousand in reactance component (reactance component at the frequency of the above special waveform generating power supply). Ω
Therefore, if a resistor having a value smaller than the impedance of plasma is connected to the electrode, the potential of the electrode can be controlled without being affected by the fluctuation of the impedance of plasma. Moreover, if the resistance value of the resistor is made equal to the output impedance of the power supply, electric power can be supplied without a matching circuit.

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

In FIG. 1, 1 is an object to be etched (eg, a semiconductor wafer), 2 and 3 are electrodes facing each other, 4 is a high frequency f _H
(Eg 13.56MHz) high frequency power supply, 5 is matching circuit for high frequency power supply 4, 6 is low frequency f _L (eg fundamental frequency
100 KHz) high frequency power source, 7 is a resistor for equalizing the output impedance (for example, 50Ω) of the high frequency power source 6, 8 is a capacitor, 9 is plasma, and 10 is a coil. The high frequency power supply 6 is composed of a signal generator 6a and a power amplifier 6b. The capacitor 8 connected to the electrode 3 has, for example, a capacitance value of 3000 pF, and its impedance is 3.9 Ω for the high frequency f _H 13.56 MHz as shown in FIG. It is as small as 1/10 of the resistance value of the connected resistor 7 (point A in Fig. 3), and is 530 Ω for the above low frequency f _L 100 KHz, which is more than 10 times the resistance value. . (Point B in FIG. 3).

The coil 10 connected to the electrode 2 has, for example, an inductance of 3 μH, and its impedance is
It becomes 255 Ω for the above high frequency f _H 13.56 MHz (point C in FIG. 3), but is only 1.9 Ω for the above low frequency f _L 100 KHz (point D in FIG. 3).

FIG. 2A is a diagram showing the above-mentioned configuration of the main part by an equivalent circuit.

Next, the operation of this embodiment will be described in detail with reference to FIGS.

In FIG. 1, the inside of the processing chamber is ventilated by a vacuum pump (not shown), a reactive gas (for example, carbon tetrachloride, CFC gas, etc.) is introduced from a gas container (not shown), and a predetermined pressure (for example, from 1 Pa) by a pressure control device (not shown). Number + Pa). The capacitor 8 connected to the electrode 3 has a low impedance as described above with respect to the frequency f _H of the high frequency power supply 4, and the coil 10 connected to the electrode 2 has a low impedance with respect to the frequency f _H of the high frequency power supply 4. Has a high impedance as described above.

When high-frequency power is applied to the electrode 2 from the high-frequency power source 4, a current flows as shown by the arrow in FIG. 2 (b) due to the magnitude relationship of the impedance on the f _H = 13.56 MHz line in FIG. Plasma 9 is generated in the substrate 1 to etch the object to be etched 1.

At this time, the load viewed from the high frequency current 4 side is the plasma 9
It can be considered as a combined load of the capacitor 8 and the capacitor 8. By adjusting the circuit constant of the matching circuit 5, the combined impedance can be matched with the output impedance of the high frequency power source 4 in exactly the same manner as in the conventional case. Maintains a stable discharge. For the configuration and operation of the matching circuit and impedance matching, see JP-A-59-73900.
It is a known technique as described in JP-A-59-130098 and the above-mentioned "Glow Discharge Processes".

Next, when high frequency power is applied to the electrode 3 from the high frequency power supply 6, the capacitor 8 and the plasma 9 connected to the electrode 3 are connected.
Is the high-frequency power source 6 as shown on the f _L = 100KHz line in Fig. 3.
Since the impedance becomes high with respect to the frequency f _L , the current from the high frequency power source 6 flows through the resistor 7 and a potential is generated at both ends of the resistor 7. In this case, as shown by the arrow in FIG. 2 (c), part of the electric power flows into the electrode 2 through the plasma 9. Since this amount is 5% or less of the whole, the plasma 9 should be affected. There is no. Also, the electric power flowing into this plasma is the coil connected between the electrode 2 and the ground.
Since 10 has a low impedance with respect to the frequency f _L = 100 KHz as shown by point D in FIG. 3, it does not affect the high frequency power source 4 through the coil 10 to the ground. Therefore, it suffices to consider only the resistor 7 as the load of the high frequency power supply 6, and if the resistance value of the resistor 7 is made equal to the output impedance of the high frequency power supply 6 (for example, 50Ω), the high frequency
There is no need for a matching circuit for the low frequency f _L corresponding to the matching circuit 5 for f _H. That is, with respect to the frequency f _L , by selecting the resistance value of the resistor 7, it is possible to always maintain the impedance matching state regardless of the frequency of the applied power.

As described above, in the present embodiment, the matching circuit which was conventionally indispensable between the high frequency power source 6 and the load (plasma) is unnecessary, and the electrode 3 is equivalent to the ground electrode for the high frequency power of the frequency f _H. Therefore, it is only necessary to provide the capacitor 8 connected to the electrode 3 and the coil 10 connected to the electrode 2 so that the electrode 2 is equivalently an earth electrode for the high frequency power of the frequency f _L.

Now, the output from the high frequency power supply 6 is, for example, FIG. 4 (a).
Basic frequency 100KHz, duty 50% (T ₁ = 5μ
sec) rectangular wave (the rectangular wave contains the highest frequency component), the waveform becomes as shown in FIG. 4 (b) due to the influence of the 3000 pF capacitor 8 of this embodiment. At this time, the time constant T ₂ is T ₂ = CR = 3000pF × 50Ω = 0.15μsec, and the distortion factor (= T ₂ / T ₁ ) of the waveform is only 3%, which is a problem as an applied waveform for controlling ions. There is no. By the way, in the conventional configuration, the waveform is as shown in Fig. 4 (c) due to the coil inductance in the matching circuit connected to the electrode 3, the time constant is T ₃ = 1.2 μsec, and the distortion rate is 24%. , Rectangular wave or triangular wave could not be applied.

In the above embodiment, the frequency f _H of the high frequency power source 4 for generating plasma is 13.56 MHz, and the high frequency power source 6 provided on the substrate mounting side.
Frequency f _L is basic frequency 100KHz, duty is 50% rectangular wave, capacitor 8 capacity is 3000pF, coil 10 inductance value is 3μH, power source 6 output impedance is 50Ω.
However, the frequency of each power supply is not limited to this, and if there are two high frequency power supplies in which the frequencies f _L and f _H are different by two digits or more, an appropriate capacitor capacity and coil inductance value are used. It is needless to say that the output impedance and the plasma impedance can be obtained and configured as shown in FIG.

Although the embodiments in which the present invention is applied to dry etching have been described above, it is clear that the present invention can be applied to not only etching but also deposition using plasma and polymerization.

As an application of the present invention, for example, the high frequency power source 6 is composed of a signal generator 6a and a power amplifier 6b, and the signal generator 6a makes the electric field strength between the plasma and the electrode constant.
If a potential waveform for controlling ions (hereinafter referred to as an ion control waveform) described in Japanese Patent Publication No. 2003-242242 is generated and this waveform is applied to the electrode on which the substrate is placed, the distribution width of the ion energy incident on the substrate can be narrowed. It is possible to increase the processing dimensional accuracy of etching and the etching rate ratio between the object to be etched and the base material by several times.

The details will be described with reference to the drawings.

FIGS. 5 (a), (b), and (c) show negative potentials for attracting ions when a waveform 30 for controlling ions is applied from the high-frequency power source 6 to the electrode 3 on which the object to be etched 1 is placed. It is the figure which showed the mode of change of the surface potential 33,34,35 of the to-be-etched object 1 when it is -40, -80, -120V. The horizontal axis represents time and the vertical axis represents potential.

5 (a), (b), and (c) are all the embodiments shown in FIG. 1, the C ₂ ClF ₅ flow rate is 30 sccm, the pressure is 8 Pa, and the power of the high frequency power source 4 for generating plasma is 250 W (about 1 W). / cm ² ). As shown in FIG.
Basic frequency 100K shown above (b) and (c)
An ion control waveform 30 of Hz is output from the high frequency power source 6 and applied.

This waveform draws positively charged ions in the plasma by linearly lowering the portion 31 toward the negative side, and then raises it to the positive side at the portion 32, causing electrons with negative charges to flow in, and Shaped to neutralize charge.

At this time, the partial drawing voltage for drawing in the ions is (a),
When changing to −40V, −80V, −120V as shown in (b) and (c), the surface potential becomes to the upper right as shown in 33, 34, and 35, respectively. State), flat (state where the charge due to the inflowing ions is canceled at the portion 31 of the ion control waveform and the potential becomes constant), right downward (charge due to the inflowing ion is given at the portion 31 of the ion control waveform) It becomes a smaller state). That is,
In the state of (b), the amount of inflowing ions and the amount of supplied electrons due to the control waveform compete with each other, and the charge on the substrate surface becomes constant. Ions are accelerated by an electric field determined by this constant charge. Therefore, the ion energy incident on the substrate becomes constant, and it becomes possible to perform etching with a high processing dimension accuracy and a high selection ratio with the underlying film.

〔The invention's effect〕

As described above, according to the present invention, it is possible to generate a high-frequency potential in the electrode on which the substrate is placed without performing a matching circuit and to apply a voltage having a waveform of a wide frequency component when performing the plasma processing. It will be possible. In addition, since the electrode facing the substrate mounting voltage is grounded via the coil, the voltage of the special waveform applied to the substrate mounting electrode does not adversely affect the high frequency power source for generating plasma and stabilizes the plasma. Can be generated.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of an apparatus showing an embodiment of the present invention, FIG. 2 (a) is a diagram showing an equivalent circuit of the main part of FIG. 1, and FIG. 2 (b) is a high frequency power system. Figure showing the road, Figure 2 (c)
Is a diagram showing a low-frequency power system path, FIG. 3 is a diagram for explaining the relationship between frequency and impedance, and FIG. 4 (a).
Shows a rectangular wave formed to be applied to the substrate mounting electrode, and FIG. 4 (b) shows a potential waveform when applied to the substrate mounting electrode via a 3000 pF capacitor. c) is a diagram showing the potential waveform of the substrate mounting electrode when the waveform of (a) is applied through a conventional circuit, and FIG. 5 is a diagram when a waveform 30 for controlling ions is applied to the substrate mounting electrode. It is a figure which shows the change of electric potential waveform 33-35, (a), (b),
(C) is a figure which shows each relationship when a negative potential is -40, -80, -120V, respectively. 1 ... Etching object, 2, 3 ... Electrode, 4 ... High frequency power source, 5 ... Matching circuit, 6 ... High frequency power source, 7 ... Resistor, 8 ... Capacitor, 9 ... Plasma, 10 ... …coil.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kazuhiro Ohara, Kazuhiro Ohara, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Pref., Institute of Industrial Science and Technology, Hitachi, Ltd. (56) References JP 60-126832 (JP, A) Kai 61-63021 (JP, A) JP 54-40079 (JP, A)

Claims (2)

[Claims] 1. A power supply for generating plasma between electrodes arranged in a vacuum chamber, a matching circuit for efficiently propagating output power from the power supply to the plasma, and a matching circuit connected to the matching circuit. Connected to the matching circuit, one end of which is connected to the electrode connected to the matching circuit, and the other end of which is grounded, an electrode on which a substrate to be exposed to plasma and processed is placed, and an electrode on which the substrate is placed. A capacitor for grounding the output power from the power supply, a second power supply for outputting power at a frequency lower than the frequency of the power supply for generating the plasma, and a resistance component of the output impedance of the second power supply. Which is a pure resistor having one end connected to the second power source and the electrode on which the substrate is mounted and the other end grounded. 2. The plasma control device according to claim 1, wherein the power supply for generating the plasma has a frequency of 13.56 MHz.
Plasma control apparatus, wherein the second power source is a high frequency power source capable of waveform shaping with a fundamental frequency of 100 KHz.