JPH0927399A - Plasma treatment method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the form controllability of fine pattern and improve the reduction of the etching rate in a deep groove/deep hole. SOLUTION: The DC component of the voltage added to a sample 1 is detected, and at least one of the pulse width, pulse period and pulse amplitude of a pulse power source 3' is changed according to the difference signal between the detected signal and a set signal. The output of the pulse power source 3' is applied to the sample 1 via a capacitance element 4, and the DC component of the voltage added to the sample 1 in plasma treatment is controlled to a prescribed value to make the voltage for accelerating electrons or ions constant. Since the voltage for accelerating electrons or ions is controlled constant, the neutralization of charges in a groove bottom/hole bottom by accelerating electron, or the etching rate by accelerating ion can be regularly stably provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing method and apparatus, and more particularly to a plasma processing method and apparatus suitable for processing using a bias applied to a sample.

[0002]

2. Description of the Related Art A conventional example of RF bias is shown in FIG. The sample 1 is placed on the sample table 2, the high frequency power for bias 3 outputs the high frequency shown in FIG. 6, and a sinusoidal voltage is applied via the capacitor 4. The processing gas is exhausted while flowing into the processing chamber 5, and plasma is generated by the high frequency power applied from the high frequency power source 6 for plasma generation via the coil 7 and the insulator 8. Since the amount of electrons supplied from the plasma to the sample is as large as several tens to several hundreds times the amount of positive ions, negative charges are accumulated on the sample 1 side of the capacitor 4. Due to this charge, a negatively shifted voltage appears on the substrate as shown in FIG. This negative voltage accelerates the positive ions, which are the etching species, and makes them vertically incident on the sample 1 to enable vertical etching. However, as the sample pattern becomes finer, various problems described below arise due to the charge-up of positive charges on the bottoms of the grooves and holes.

[0003]

In the substrate bias waveform of FIG. 7, the positive voltage for accelerating the electrons in the positive cycle in which the electrons are incident on the sample is almost 0, so the electrons are hardly accelerated. Incident on the substrate.

When a fine pattern is processed using such a bias application method, local charge-up occurs in the sample. Ions are accelerated and vertically enter the sample to reach the bottom surface of the fine pattern, whereas electrons are not accelerated and areotropically incident on the sample, so that the fine pattern is blocked by the mask and reaches the bottom surface. Not possible (electronic shading phenomenon). Therefore, the side surface of the fine pattern is charged up negatively and the bottom surface is charged up positively.

The charge-up caused by the electron shading causes various problems in plasma etching. One of the most serious problems is local abnormal side etch (notch) in polysilicon processing for gate.
Is the occurrence of.

Further, charge-up due to the electron shading phenomenon occurs also in the processing of metal wiring, and causes damage to the gate oxide film. Positive charges generated on the bottom surface of the fine pattern by electron shading are collected in the floating gate connected to the metal wiring,
Damage such as dielectric breakdown occurs in the gate insulating film between the floating gate and the substrate silicon.

In addition to this, the charge-up due to the electron shading phenomenon is a problem in etching fine holes such as trenches and contact holes, which causes irregular shapes such as sub-trench and bowing. As in the case of etching polysilicon, the side surface of the hole is negatively charged and the bottom surface of the hole is positively charged. Due to this charge-up, the orbits of ions, which are etching species, are bent, and the ions are incident on the side surface of the hole and the end of the hole bottom. For this reason, the side surface of the hole and the end of the bottom surface of the hole are etched, and irregular shapes such as bowing and sub-trench are generated.

The present invention eliminates the electron shading phenomenon and solves various problems caused by the electron shading phenomenon such as notch, charge-up damage, bowing, sub-trench, microloading, and reduction of etching rate in the hole depth direction.

It is an object of the present invention to provide a plasma processing method and apparatus capable of obtaining a desired etching shape by improving the shape controllability of a fine pattern and improving the etching rate reduction in deep grooves / deep holes. is there.

[0010]

According to the present invention, there is provided a sample placing means, a processing chamber containing the sample placing means, a means for supplying gas into the processing chamber, and a means for exhausting the processing chamber. In a plasma processing apparatus equipped with a means for generating plasma in a processing chamber, a means for detecting a DC component of a voltage applied to a sample or a voltage substantially equivalent thereto, and a difference between a signal detected by the detecting means and a setting signal. Depending on the signal, pulse width,
An apparatus provided with a pulsed power source having an electron acceleration function for changing at least one of a pulse period or a pulse amplitude, and means for applying the output of the pulsed power source to a sample via a capacitive element, under reduced pressure. In the plasma processing method of plasmaizing the gas with, and processing the sample placed in the processing chamber using the plasma, the direct current component of the voltage applied to the sample is detected, and by the difference signal between the detected signal and the setting signal, At least one of the pulse width, pulse period, or pulse amplitude of the pulse power supply for electron acceleration is changed, and the output of the pulse power supply is applied to the sample via the capacitive element, and the sample is being plasma-processed. This is achieved by adopting a method of controlling the direct current component of the applied voltage to a predetermined value.

[0011]

In the present invention, since the pulse bias voltage is applied to the sample, the electrons are accelerated and can reach the bottom surface of the fine pattern, and the positive charge on the bottom surface is prevented from being charged up to prevent the occurrence of notches and the like. , To control the pulse period, pulse width, pulse amplitude, etc. so that the difference from the set value disappears while detecting the DC component of the voltage applied to the sample, the electron accelerating voltage and ion accelerating voltage are controlled to a predetermined value, and always Stable characteristics can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram showing an electrode portion to which a bias voltage is applied in the plasma processing apparatus of the present invention. The electrode part in this figure is provided, for example, in place of the sample stage part of the conventional apparatus shown in FIG. In this figure, the same symbols as those in FIG. 5 indicate the same members. In this embodiment, instead of the bias high frequency power source 3 of the plasma processing apparatus having the conventional configuration shown in FIG.
The bias pulse power source 3'shown in FIG. The bias pulse power supply 3'periodically outputs a pulse in the positive direction as shown in FIG. When this pulse is applied to the sample 1 via the capacitance component 4, a sample bias voltage as shown in FIG. 2B is applied to the sample 1. Where τw is the pulse width,
T is the pulse period, Vpls is the pulse amplitude, Vp is the plasma potential, and V _DC is the DC component of the voltage applied to the sample 1.

FIG. 2 (c) shows the change in V _DC when the pulse period T is changed while keeping τw and Vpls constant. (Τw /
When T) << 1, V _DC ≈0 volt. In the region of _VDC > -10 volt, the acceleration of ions is insufficient, so that it is difficult to obtain a vertical shape, and the etching rate is low, which is not preferable for practical use.

Further, in the region of _VDC <Vp-Vpls + 5, since the acceleration of electrons is 5 V or less, it is difficult for the electrons to reach the bottom surface of the deep groove or deep hole. Therefore, it is a region in which it is difficult to improve the shape due to electron acceleration and the reduction in the etching rate in the deep groove / hole.

The portion where preferred properties are _{obtained, -10volt> V DC> Vp-} Vpls + 5volt is a part of, V _DC against small changes in such as a pulse period T are as this portion shown in FIG. 2 (c) Changes greatly. Further, there is a drawback that V _DC changes greatly even if the plasma properties change a little. The absolute value of _VDC is proportional to the average energy of ion acceleration, and the average electron acceleration energy during the period when the electron current flows into the sample 1 is Vpls−Vp + _VDC.
Is almost proportional to the above, and when this value is 5 volt or more, the charge neutralizing effect at the bottom of the deep hole or groove appears, and when this value is 10 volt or more, the above effect becomes remarkable.

When the value of Vpls-Vp + _VDC is about 200 Volt or more, the adverse effect such as large abrasion of the resist film becomes remarkable. The value of Vpls−Vp + _VDC is optimized within the range of the above values according to the material of the sample, the pattern, the aspect ratio of the hole, and the like.

Therefore, when V _DC changes, the acceleration energy of ions and electrons changes, so that the etching rate and the effect of neutralizing electrons at the groove / hole bottom change significantly.

In order to improve this, as shown in FIG. 1 (the other parts of the processing chamber are the same as those in FIG. 5), the voltage applied to the sample stage 2 is biased as a V _DC signal through the low pass filter 10. The voltage is fed back to the pulse power supply 3 ', and control is performed so that the DC component of the voltage applied to the sample 1, _VDC, is always constant. By doing so, a constant _VDC is always applied to the sample even if the plasma or the like fluctuates, so that the electron accelerating voltage and the ion accelerating voltage are controlled to predetermined values, and stable processing becomes possible.

When the sample 1 and the sample table 2 are electrically connected to each other, the _VDC applied to the sample 1 can be detected by the method shown in FIG. When an insulator 11 exists between the sample 1 and the sample table 2 (same as in FIG. 5) (for example, a sample table with an electrostatic adsorption function), an electrode 12 that directly contacts the sample 1 is installed, By obtaining a V _DC signal from this signal through a low pass filter, feedback control can be performed as in FIG. In FIG. 3, 11 is an electrostatic attraction insulator, and 13 is an electrostatic attraction DC power supply.

If the back surface of the sample is covered with an insulator, V _DC cannot be measured even by the method shown in FIG. In this case, if a conductor is installed at the portion in contact with the plasma, the conductor and the sample stand are capacitively coupled, and this conductor is connected to a low-pass filter, then V _DC that is approximately equal to that of the sample can be obtained. You can

FIG. 4 shows an example of the bias pulse power source 3'that can be feedback controlled.

The difference between the set value of _VDC (setting signal 1) and the monitor value of _VDC (monitor signal) is amplified by the differential amplifier 3-1 and input to the voltage controlled oscillator 3-2, and the pulse period T To set. Then, a predetermined pulse width τw is generated by the pulse width generator 3-3 according to the instruction of the setting signal 2, and a predetermined pulse amplitude V is generated by the amplifier 3-4 according to the instruction of the setting signal 3.
Amplify to pls and output. By using this bias pulse power supply 3 ', the pulse period T is automatically controlled so that the DC component V _{DC of the} voltage applied to the sample 1 is always equal to the setting. As a parameter for controlling V _DC or the like to be always constant, the pulse width τw or the pulse amplitude Vpls may be controlled in addition to the example of FIG.
However, in order to keep the ion acceleration energy and the electron acceleration energy constant, it is preferable to control the pulse period and pulse width.

For ordinary plasma, 0.01 μs <τw <10 μs, preferably 0.03 μs <τw <0.5 μs 1/10 ³ <(τw / T) <1/10, preferably 3/10 ³ < (Τw / T) <5/10 ² Vp + 15 volt <Vpls −10 volt <V _DC <Vp−Vpls + 5 volt Vp≈10 to 20 volt In this embodiment, the case where plasma is generated by the inductively coupled high frequency shown in FIG. 1 will be described. However, the present invention can be commonly applied to, for example, microwave plasma, plasma by a high frequency + DC magnetic field, ECR plasma, etc., regardless of the plasma generation method.

The output waveform of the bias pulse power supply 3'is not limited to the waveform shown in FIG. 2 (a). Even in the case where the alternating current is superposed, the amplitude of the alternating current is changed, the case where a plurality of pulses are used, etc., the surface potential of the sample becomes higher than the plasma potential (Vp) by 5 V or more during one cycle of the electron acceleration period. The present invention can be similarly applied as long as the total sum (τw) and the period (T) thereof satisfy the above conditions.

As described above, according to this embodiment, the sample is provided with the pulse bias power source for accelerating the electron of 5 V or more, and the DC component _{VDC of the} voltage applied to the sample is within the range of −10 volt <V _DC <Vp−Vpls + 5volt. In addition, since feedback control is performed so as to be constant, it is possible to neutralize the charge-up of positive charges on the bottom surface of the fine pattern, prevent the occurrence of notches, microloading, and lowering of the etching rate in deep grooves / holes, and the electron acceleration voltage. The ion accelerating voltage is controlled to a predetermined value, and stable characteristics can always be obtained even if the plasma characteristics fluctuate slightly. As a result, the voltage for accelerating electrons and ions is constant, so that the neutralization of charges at the groove bottom / hole bottom by accelerated electrons and the etching rate by accelerated ions can always be obtained stably.

[0026]

According to the present invention, since the direct current component _{VDC of the} voltage applied to the sample can be made constant and the charge-up of positive charges on the bottom surface of the fine pattern can be neutralized, the shape controllability of the fine pattern and the deep groove / There is an effect that the reduction of the etching rate in the deep hole can be improved and a desired etching shape can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an electrode unit used in a plasma processing apparatus of the present invention.

FIG. 2 is a diagram showing an output waveform of a bias pulse power source of the apparatus of FIG. 1, a bias voltage waveform applied to a sample, and its characteristics.

FIG. 3 is a configuration diagram showing another embodiment of an electrode unit used in the plasma processing apparatus of the present invention.

4 is a configuration diagram showing an example of a bias pulse power source of the apparatus of FIG.

FIG. 5 is a diagram showing a conventional plasma processing apparatus.

FIG. 6 is a diagram showing an output waveform of the bias high frequency power source in FIG.

7 is a diagram showing a bias voltage waveform applied to the sample in FIG.

[Explanation of symbols]

1 ... sample, 2 ... sample stage, 3 ... high frequency power supply for bias,
3 '... Bias pulse power supply, 4 ... Capacitance element, 5 ... Processing chamber, 6 ... Plasma generating high frequency power supply, 7 ... Coil, 8 ...
Insulator, 10 ... Low-pass filter, 11 ... Insulator, 12
... electrode, 13 ... DC power supply for electrostatic attraction.

Claims (4)

[Claims] 1. A plasma processing method for converting a gas into plasma under a reduced pressure and processing a sample placed in a processing chamber using the plasma, wherein a direct current component of a voltage applied to the sample is detected, and the detected signal and At least one of the pulse width, pulse period, or pulse amplitude of the pulse power supply for electron acceleration is changed according to the difference signal from the setting signal, and the output of the pulse power supply is applied to the sample via the capacitive element. A plasma processing method, wherein the direct current component of the voltage applied to the sample during plasma processing is controlled to a predetermined value. 2. The plasma processing method according to claim 1, wherein the value of (pulse width / pulse period) is 0.1 or less. 3. The pulse width or pulse of a pulse power source for electron acceleration according to claim 1, wherein the direct current component of the voltage applied to the sample is detected, and the difference signal between the detected signal and the setting signal is used. A plasma processing method in which the cycle is changed. 4. A sample placing means, a processing chamber containing the sample placing means, a means for supplying a gas into the processing chamber, a means for exhausting the processing chamber, and a plasma in the processing chamber. In the plasma processing apparatus including means for generating, a means for detecting a DC component of the voltage applied to the sample or a voltage substantially equivalent thereto, and a difference signal between the signal detected by the detecting means and the setting signal. A pulsed power supply having an electron acceleration function for changing at least one of pulse width, pulse period or pulse amplitude, and means for applying the output of the pulsed power supply to a sample via a capacitive element. A plasma processing apparatus characterized by the above.