JP2001358129A - Method and apparatus for plasma processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma processing process which is superior in micro workability and gives few damages to a device. SOLUTION: In the process, an electronic negative gas is introduced to a chamber, and in addition, a positive bias voltage is impressed from a DC pulse power source upon a sample stage, when a prescribed delay time Td elapses, after the plasma generating high-frequency pulse power impressed upon a coil from a high-frequency pulse power source is turned off. Since electron attachment and detachment are apt to occur, after the plasma generating high-frequency pulse power is turned off, the density of electrons is decreased abruptly, and at the same time, anions are abruptly increased. The delay time Td is set, so that Nn/Ne (where Nn and Ne respectively denote the density Nn of anions and density of electrons) may become about 500 or larger.

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 using a high frequency discharge and a plasma processing apparatus.

[0002]

2. Description of the Related Art A plasma generation method using a high-frequency discharge is used in various fields such as a dry etching method for fine processing and a sputtering or plasma CVD method for forming a thin film. There is a strong demand for plasma processing technology to control film quality with high precision or reduce damage accompanying processing.

For example, a dry etching technique applied to microfabrication utilizes a chemical or physical reaction between a gas phase such as radicals (active species) or ions existing in plasma and a solid surface. This is a processing technique for removing unnecessary portions of the sample to be etched. Reactive ion etching (RIE), which is most widely used as a dry etching technique, generates highly reactive radicals or ions in a high-frequency discharge plasma made of a reactive gas, and the generated radicals or ions are etched. This is a technique in which an etching reaction is caused by exposing a sample, and unnecessary portions on the surface of the sample to be etched are removed. Necessary portions on the surface of the sample to be etched, that is, portions not to be removed, are protected by a photoresist pattern usually used as a mask.

[0004] For miniaturization of etching, it is necessary to make the directionality of ions uniform. For this purpose, it is necessary to reduce the scattering of ions in a sheath region which is a boundary between a plasma and a sample to be etched. It is essential. In order to reduce the scattering of ions, it is effective to lower the pressure in the plasma generation chamber to increase the mean free path of the ions.However, when the pressure in the plasma generation chamber is reduced, the radical density decreases. A new problem that the etching rate becomes low occurs.

As a countermeasure, a high-density plasma apparatus such as an inductively-coupled plasma apparatus or a helicon plasma apparatus is being introduced. A high-density plasma device can generate plasma of one to two orders of magnitude higher than a conventional parallel plate RIE device. For this reason,
An etching rate equal to or higher than that of the RIE apparatus can be obtained even under the condition that the pressure of the plasma generation chamber is lower by about one to two digits.

However, the above-mentioned high-density plasma apparatus has the following problems. That is,
(1) Abnormal occurrence of etching shape due to charge-up, (2) Microloading effect, and (3) Deterioration or destruction of gate insulating film. Hereinafter, when a gate electrode is formed by performing plasma etching on a conductive film (for example, a polycrystalline silicon film) deposited on a silicon substrate via an insulating film (for example, a silicon oxide film) using a photoresist pattern as a mask The problem will be described.

(1) First, the occurrence of abnormalities in the etched shape due to charge-up will be described. A typical example of the occurrence of an abnormality in an etching shape due to charge-up is a notch phenomenon in etching of a conductive film. This notch phenomenon means that when a sample to be etched (conductive film) is etched by high-density plasma, the positive ions in the plasma have a large energy toward the sample to be etched, while the electrons in the plasma pass through the sample to be etched. The energy going is small. For this reason, in the isolated pattern region having a large space width, positive ions and electrons are accumulated in a well-balanced manner at the bottom of the sample to be etched (bottom of the space portion). A large amount of electrons are accumulated at the bottom of the sample to be etched (the bottom of the space), while a large amount of electrons are accumulated at the side of the sample to be etched (the side wall of the pattern portion). That is, a charge-up phenomenon occurs in which many electrons adhere to the side walls of the pattern portion.

Therefore, the positive ions which approach the sample to be etched later are attracted to the side wall of the pattern portion, so that a wedge-shaped notch is formed at the bottom of the side wall of the pattern portion (for example, KKChi et al., 1995). DRY PROCES
S SYMPOSIUM Proceedings, p.75, IEEJ). In particular, a notch is significantly formed at the bottom of the inner side wall of the outermost pattern in the dense pattern region.

(2) The localization and non-uniformity of the electric charge also affect the etching rate itself. That is, during etching, the resist mask is positively charged by the injected positive ions, so that in a region of the resist mask where the width of the mask opening is small, the function of preventing the positive ions from entering the mask opening works strongly. For this reason, a so-called microloading effect occurs in a region where the width of the mask opening in the resist mask is smaller, the lower the etching rate. Also, the microloading effect may appear as a difference in the etching angle of the pattern side wall or a difference in the local base selectivity between the isolated pattern region and the dense pattern region.

(3) Further, the imbalance of charge supply is M
There is a possibility that the gate insulating film of the OS transistor may be deteriorated or destroyed. For example, in plasma etching, a large amount of electric charge accumulated in a sample to be etched (conductive film) penetrates the gate insulating film and travels to the silicon substrate. At this time, a large electron current flows through the gate insulating film. The insulation of the film is deteriorated or destroyed. It is known that when the gate insulating film becomes extremely thin, about 10 nm or less, a phenomenon occurs in which the transconductance of the MOS transistor deteriorates, and in extreme cases, the dielectric breakdown of the gate insulating film is caused (for example, ERIGUCHI et al.,
IEICE TRANS. ELECTRON., VOL.E78-C, p.261, IEICE). In particular, the transistor size is reduced to 1
When the thickness is less than μm, the LSI includes a transistor having a so-called antenna structure in which the area of the wiring is three to five digits or more of the area of the transistor. Since the antenna structure functions to increase the penetration of charges in the gate insulating film, it is considered that deterioration or destruction of the gate insulating film due to plasma becomes an increasingly important issue with miniaturization of transistors.

Therefore, as a method for solving the above-mentioned problem of the high-density plasma process, a plasma process using negative ions has been proposed (for example, Y. Horiike et al., 3rd International Conference on Reactive Plasm).
as and 14th Symposium onPlasma Processing
p.515, Japan Society of Applied Physics 1997). According to this proposal, when a sample stage is positively biased in a plasma composed of an electron-negative gas such as chlorine, etching is caused by negative ions. According to the plasma process using such negative ions, it is expected that problems such as deterioration or destruction of the gate insulating film or shape defects such as notches due to charge-up hardly occur.

[0012]

However, generation of a large amount of negative ions occurs in a relatively high pressure region (the above-mentioned Y. Hori
ike et al. report a pressure range of 2 Pa or more), and if the pressure in the plasma generation chamber is lowered to perform finer processing, etching with negative ions cannot be expected. Since the mass of the existing electrons is more than one thousandth smaller than the mass of the negative ions,
Since electrons follow the electric field well, there is also a problem that negative ions cannot be efficiently used in the process.

In view of the foregoing, it is an object of the present invention to provide a plasma processing process that makes full use of the characteristics of negative ions in plasma and has excellent fine workability and less damage to devices.

[0014]

In order to achieve the above object, a first plasma processing method according to the present invention is characterized in that Nn / Ne, which is the value of the ratio between the negative ion density Nn and the electron density Ne, is approximately 500. In the plasma described above, a plasma processing is performed by applying a bias voltage to the sample stage.

According to the first plasma processing method, since the value of the ratio of the negative ion density Nn in the plasma to the electron density Ne in the plasma is approximately 500 or more, the electron density in the plasma is reduced. Since the ratio of the negative ions to the negative charges in the plasma is extremely large and the ratio of the negative ions in the plasma is extremely large, the negative ion current can be effectively extracted, and the negative ions can be effectively irradiated to the sample. In this case, the energy with which the negative ions collide with the sample is proportional to the magnitude of the bias voltage applied to the sample stage. Therefore, by controlling the bias voltage applied to the sample stage, it is necessary to control the plasma processing process. Can be.

In the first plasma processing method, the bias voltage is preferably a positive voltage.

In this case, since only negative ions can be irradiated to the sample, highly selective plasma processing (eg, plasma etching) can be performed at a high processing rate. Since negative ions themselves have a negative charge, even if secondary electrons are generated when they collide with the sample, the surface of the sample is rarely charged to a positive voltage. Usually, when positive ions collide with the sample to generate secondary electrons, the sample surface is charged to a positive potential. Therefore,
When a positive bias voltage is applied to the sample stage in the conventional plasma processing method, a rapid inflow of electrons from the plasma toward the sample surface occurs, and the electrons are accumulated on the sample surface, resulting in charge-up. However, in the first plasma processing method, the problem of charge up hardly occurs because the sample is mainly irradiated with negative ions.

In the first plasma processing method, the bias voltage is preferably a pulse voltage of a positive voltage and a negative voltage.

With this configuration, when a positive bias voltage is applied, negative ions are attracted to the sample surface, while when a negative bias voltage is applied, positive ions are attracted to the sample surface. Since the generated charge is canceled, charge-up can be reduced.

In this case, it is more preferable to include a step of adjusting each pulse width of the positive voltage and the negative voltage of the pulse voltage.

In this way, the balance of the charges accumulated on the surface of the sample can be adjusted, so that the charge-up can be reliably prevented.

In the first plasma processing method, it is preferable that a step of applying a high-frequency power having a frequency of about 0.5 to about twice the ion plasma frequency to the sample stage as a bias voltage is preferable.

In this case, the penetration of the electric field into the plasma increases, and the ion flux flowing into the sample stage increases, so that the rate of the plasma processing increases.

In the first plasma processing method, the plasma is preferably generated from a gas containing hydrogen atoms or hydrogen compounds.

In this case, since the gas containing hydrogen atoms or hydrogen compounds is an electron-negative gas, the ratio of negative ions in the plasma increases, and the value of the ratio of the negative ion density Nn to the electron density Ne is increased. Nn / Ne can be easily set to 500 or more. Further, a gas containing a hydrogen atom or a hydrogen compound has high utility in film formation or etching.

In the first plasma processing method, the plasma is preferably generated from a gas containing a halogen element or a halogen compound.

In this case, since the gas containing a halogen element or a halogen compound is an electron-negative gas, the ratio of negative ions in the plasma increases, so that the value of the ratio of the negative ion density Nn to the electron density Ne is increased. Nn / Ne is 50
It becomes easy to set it to 0 or more. Further, since the halogen element has a high electronegativity, it is highly useful in an LSI process using silicon or aluminum.

In the first plasma processing method, the plasma is preferably generated from a gas containing oxygen atoms or oxygen compounds.

In this case, since the gas containing oxygen atoms or oxygen compounds is an electron-negative gas, the ratio of negative ions in the plasma increases, so that the value of the ratio of the negative ion density Nn to the electron density Ne is increased. Nn / Ne can be easily set to 500 or more. Further, an oxygen atom or an oxygen compound reacts with carbon or hydrogen to generate volatile products such as CO ₂ and H ₂ O, and thus has a high utility value in etching an organic film or an organic-inorganic hybrid film.

[0030] The second plasma processing method according to the present invention comprises:
A step of generating a plasma containing negative ions by a high-frequency power pulse; and a step of applying a bias voltage to a sample stage during a period in which the high-frequency power is off to perform a plasma process mainly using negative ions in the plasma. .

According to the second plasma processing method, the plasma processing mainly using negative ions in the plasma can be performed, so that a highly selective plasma processing (eg, plasma etching) can be performed at a high processing rate. Almost no charge-up problem occurs.

In the second plasma processing method, in the step of performing the plasma processing, the high frequency power is turned off, and the value of the ratio of the negative ion density Nn to the electron density Ne in the plasma, Nn / Ne, is approximately 500. In the state described above, it is preferable to include a step of applying a bias voltage to the sample stage.

With this arrangement, the negative ion current can be effectively extracted, and the sample can be effectively irradiated with negative ions. Therefore, the magnitude of the bias voltage applied to the sample stage can be controlled. Thereby, the process controllability can be improved by controlling the energy at which negative ions collide with the sample.

In the second plasma processing method, the high-frequency power pulse preferably has a duty ratio of less than 50%.

In this case, since the off time of the high frequency power for plasma generation becomes longer, the characteristics of ion-ion plasma (plasma in which the electron density is much smaller than the positive ion density and the negative ion density) are utilized. be able to.

In the second plasma processing method, the step of performing the plasma processing preferably includes a step of applying a bias voltage synchronized with a predetermined time delay with respect to the high frequency power pulse.

During the period in which the high-frequency power pulse for plasma generation is off, the electron temperature decreases and electron attachment and dissociation easily occur, so that the number of negative ions increases. By applying a bias voltage, the sample can be effectively irradiated with negative ions.

The third plasma processing method according to the present invention comprises:
The method includes a step of generating plasma containing negative ions by high-frequency power, a step of reducing electron density in the generated plasma, and a step of performing a plasma process using the plasma with reduced electron density.

According to the third plasma processing method, the proportion of negative ions in the plasma increases because the number of positive ions decreases in the plasma in a state where the electron density is reduced. Therefore, when plasma processing is performed using plasma with a reduced electron density, negative ions in the plasma can be mainly used, so that highly selective plasma processing (eg, plasma etching) can be performed at a high processing rate. At the same time, there is almost no charge-up problem.

The plasma processing apparatus according to the present invention includes a plasma generation chamber for generating plasma, a plasma processing chamber for performing plasma processing using the plasma generated in the plasma generation chamber, and a plasma processing chamber between the plasma generation chamber and the plasma processing chamber. And a plasma transport means for transporting the plasma generated in the plasma generation chamber to the plasma processing chamber while reducing the electron density in the plasma.

According to the plasma processing apparatus of the present invention, since the plasma generated in the plasma generation chamber is provided with the plasma transport means for transporting the plasma to the plasma processing chamber while reducing the electron density in the plasma, the electron density is reduced. Plasma processing can be performed using the plasma
Plasma processing using mainly negative ions in plasma can be easily and reliably performed.

[0042] In the plasma processing apparatus of the present invention, the plasma transport means is provided so as to communicate with the plasma generation chamber and the plasma processing chamber, and to surround the vacuum chamber.
It preferably comprises a ring-shaped magnet that generates a substantially parallel static magnetic field inside.

With this configuration, while the plasma generated in the plasma generation chamber is being transported to the plasma processing chamber, the electrons in the plasma are trapped by the ring-shaped magnet, so that the plasma in the plasma transported to the plasma processing chamber is trapped. The electron density is greatly reduced.

In the plasma processing apparatus of the present invention, the plasma transport means includes a vacuum chamber for communicating the plasma generation chamber with the plasma processing chamber, and a plurality of plasma transport means disposed around the vacuum chamber and generating a substantially parallel magnetic field therein. And a Helmholtz coil.

With this configuration, while the plasma generated in the plasma generation chamber is being transported to the plasma processing chamber, the electrons in the plasma are trapped by the Helmholtz coil, so that the electrons in the plasma transported to the plasma processing chamber are trapped. The density is greatly reduced.

In this case, the plurality of Helmholtz coils are
More preferably, a rotating magnetic field is generated by applying currents having different phases.

With this configuration, the plasma generated in the plasma generation chamber is transported to the plasma processing chamber while rotating, so that the plasma in the plasma processing chamber becomes uniform.

The plasma processing apparatus according to the present invention includes a high frequency power pulse circuit for supplying a high frequency power pulse for generating plasma in the plasma processing chamber, and a bias circuit for supplying a bias voltage to a sample stage provided in the plasma processing chamber. And a signal delay circuit for synchronizing the bias voltage with a predetermined time delay with respect to the high-frequency power pulse.

With this configuration, a bias voltage synchronized with a predetermined time delay with respect to the high-frequency power pulse can be applied to the sample stage, so that the sample can be effectively irradiated with negative ions.

[0050]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, a plasma processing method and a plasma processing apparatus according to a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows a schematic overall configuration of a plasma processing apparatus (plasma etching apparatus) according to the first embodiment. In FIG. 1, reference numeral 10 denotes a ground, and inner walls are made of ceramic or Teflon (registered trademark). ) Or a chamber which is covered with an insulator such as quartz and the inside of which is kept in a vacuum. Note that the chamber 10 may have a double structure having an inner chamber made of quartz or the like instead of a structure in which the inner wall is covered with an insulator. The chamber 10 is provided with a well-known gas introducing means for introducing a reactive gas into the chamber 10, but is not shown.

As shown in FIG. 1, a coil 1 is placed on a chamber 10 via a dielectric plate 11 made of ceramic or the like.
2 are provided. One end of the coil 12 is connected to a high frequency pulse power source 14 for plasma generation via an impedance matching circuit 13 and the other end of the coil 12 is grounded. Therefore, when high-frequency pulse power is applied to the coil 12 from the high-frequency pulse power supply 14, the dielectric plate 1
A high-density plasma 15 is generated inside the chamber 10 by an induction electromagnetic field generated through the first electromagnetic field 1.

A metal sample stage 16 whose surface is coated with an insulating material is provided inside the chamber 10, and a photoresist pattern is formed on the surface of the sample stage 16. The sample 17 to be etched is held.

The sample stage 16 is connected to a bias DC pulse power source 18 for applying a bias voltage to the sample stage 16, and the DC pulse power source 18 is connected to the high frequency pulse power source 14 via a signal line 19. Have been. The high-frequency pulse power supply 14 has a built-in signal delay circuit, and a synchronization signal generated by the signal delay circuit is output to a DC pulse power supply 18 via a signal line 19. The DC pulse power supply 18 applies a bias voltage to the sample stage 16 that synchronizes with a high-frequency power pulse applied from the high-frequency pulse power supply 14 to the coil 12 with a predetermined time delay based on a synchronization signal generated by the signal delay circuit. .

FIG. 2 shows changes over time of various parameters in the plasma processing method according to the first embodiment.

After a predetermined delay time Td has elapsed since the high frequency pulse power for plasma generation applied to the coil 12 from the high frequency pulse power supply 14 has been turned off, the DC pulse power supply 18 for bias is turned on. A positive bias voltage is applied from the DC pulse power supply 18 to the sample table 16 with a predetermined pulse width.

Since a reactive gas used for etching, for example, a halogen gas, is an electron negative gas (a gas that generates negative ions when electrons are combined with gas molecules), a high-frequency pulse power for plasma generation is used. In the state after is turned off, that is, in the state of afterglow plasma,
Since there is no electron acceleration source, electrons moving at a high speed diffuse and collide with the wall surface of the chamber 10 to disappear, while electrons moving at a low speed do not diffuse much, so that the electron temperature decreases. When the electron temperature decreases, electron attachment and dissociation (a phenomenon in which electrons attach to the compound and negative ions dissociate from the compound) easily occurs, so that the electron density decreases rapidly and the number of negative ions increases rapidly.

In the first embodiment, the delay time Td
Is set to a time at which the value of the ratio of the negative ion density Nn to the electron density Ne, Nn / Ne, becomes approximately 500 or more. The reason for this will be described later. Note that the delay time T
d varies depending on the type of gas or the pressure of the chamber 10, but is usually 50 μsec to 1 msec.

In a state where the value of the ratio of the negative ion density Nn to the electron density Ne, ie, Nn / Ne is approximately 500 or more,
Since the electron density Ne in the plasma is sufficiently small and the ratio of the negative ions to the negative charge in the plasma is extremely large, when the DC pulse power supply 18 applies a positive voltage to the sample stage 16, the electron flows into the sample stage 16. The electron current is small enough. Thus, the negative ion current is effectively extracted, and the negative ions irradiate the sample 17 to be etched.
At this time, the energy with which the negative ions collide with the sample 17 to be etched is proportional to the magnitude of the bias voltage applied from the DC pulse power supply 18 to the sample stage 16, so that the process controllability is improved.

Hereinafter, the delay time Td is defined as the negative ion density Nn.
Nn / Ne, which is the value of the ratio between the electron density Ne and the
The reason for setting the time to be 0 or more will be described.

The drift current in the plasma is expressed as follows. That is, electron current Je Je = q × Ne × μe × E (1) positive ion current Jp Jp = q × Np × μp × E (2) negative ion current Jn Jn = q × Nn × μn × E (3) where q is an electron charge, Ne is an electron density, Np is a positive ion density, Nn is a negative ion density, and μe is an electron mobility. , Μp is the mobility of positive ions, μn is the mobility of negative ions, and E is the electric field in the plasma.

Incidentally, the electron mobility μe is about several hundred times the mobility of the positive ion and the mobility of the negative ion μn, and the mobility of the positive ion and the mobility of the negative ion are μp.
This value is much larger than n. In addition, the mobility μp of the positive ions and the mobility μn of the negative ions are in the same order, although the difference is about several times. Therefore, when the same amount of electrons as the positive ions are present, most of the current is carried by the electrons.

However, if the amount of electrons decreases and the electron current becomes sufficiently smaller than the sum of the positive ion current and the negative ion current, the effect of the electrons can be neglected. That is, when the relational expression of Nn / Ne≫μe / 2 μn (4) holds, the effect of electrons can be ignored.
Note that the relational expression (4) is derived from the above expressions (1), (2) and (3), and μp = μn and Np = Ne + Nn.

In the relational expression (4), it is assumed that μe / μn is substantially 100 and (Nn / Ne) is (μe
/ 2 μn), the effect of electrons can be neglected. If Nn / Ne, which is the value of the ratio of the negative ion density Nn to the electron density Ne, is almost 500 or more, the effect of electrons can be neglected. Become like The plasma in which the electron density Ne is much smaller than the positive ion density Np and the negative ion density Nn is called an ion-ion plasma.

It is preferable that the duty ratio of the high frequency power pulse for generating plasma is less than 50%. The reason is that when the duty ratio of the high-frequency power pulse for plasma generation becomes 50% or more, the on-time of the high-frequency power for plasma generation becomes longer, and the time during which the sample stage is exposed to the plasma in the on state becomes longer. In other words, the result of the plasma processing is mainly governed by the plasma in the ON state. In order to take advantage of the characteristics of the ion-ion plasma as in the present embodiment, it is preferable that the duty ratio is less than 50% and the ratio of the plasma processing is increased during the period when the high-frequency power is off.

The results of an experiment in which a phosphorus-doped polysilicon film deposited on a silicon oxide film is etched under the following conditions will be described below.

As the reactive gas (etching gas),
50 ml of chlorine gas are introduced per minute under standard conditions, and 5 ml of oxygen gas are introduced per minute under standard conditions.
The pressure in the chamber was set at 0.5 Pa to 2 Pa. Further, 13.5 is supplied from the high frequency pulse power supply 14 to the coil 12.
A high-frequency power having a frequency of 6 MHz was applied with a pulse width of 20 μsec and a time average power of 1000 W, and a positive voltage was applied from the DC pulse power supply 18 to the sample table 16 while changing the voltage value with a pulse width of 400 μsec. .
The repetition frequency of the high-frequency power and the positive voltage pulse was set to 1 kHz, and the delay time T was set to 500 μsec.

As a result of the experiment, the magnitude of the bias voltage was set to 50
When the voltage was changed from V to 150 V, the etching rate was about 200 nm / min, and the selectivity to the silicon oxide film changed from about 200 to about 10. still,
The etched shape was anisotropic.

Further, when a gate electrode made of a phosphorus-doped polysilicon film is formed on a gate insulating film made of a silicon oxide film having a thickness of 3 nm, breakdown of the insulating film due to charge-up, notch and abnormal shape, etc. Was not seen.

By the way, according to the first embodiment, the reason why the charge-up is reduced is considered to be that the contribution of negative ions in the plasma is large. When high-energy positive ions and negative ions are incident on the sample to be etched, in addition to the charge of the incident ions being accumulated on the surface of the sample to be etched, the charge is released from the surface of the sample to be etched with the incidence of ions. The effect of secondary electrons cannot be ignored. When positive ions are incident, secondary electron emission proceeds to increase the accumulation of positive charge, but when negative ions are incident, secondary electron emission seems to cancel the accumulation of negative charge. Work on. For this reason, the charge-up phenomenon is suppressed.

In the first embodiment, a reactive gas consisting of chlorine gas and oxygen gas is used. However, any reactive gas that can easily generate negative ions (electron negative gas) is used. For example, a gas containing a hydrogen atom or a hydrogen compound, a gas containing a halogen element or a halogen compound, a gas containing an oxygen atom or a oxygen compound, or the like can be used.

(Second Embodiment) Hereinafter, a plasma processing method according to a second embodiment of the present invention will be described with reference to FIG.

The second embodiment differs from the first embodiment only in the method of applying a bias DC voltage pulse. Therefore, in the following description, the bias D
Only the method of applying the C voltage pulse will be described.

As shown in FIG. 3, the DC bias voltage is
The high-frequency power pulse for plasma generation is turned off.
After a predetermined delay time Td elapses, the DC pulse
A positive bias voltage and a negative
The bias voltage is applied alternately. Also, the positive bias voltage
The voltage value of the voltage is Vb p and the pulse width is Wb p and negative
Of the bias voltage of Vb n and the pulse width is Wb
n.

According to the second embodiment, the positive bias voltage
When pressure is applied, negative ions are
7 while a negative bias voltage is applied
Sometimes positive ions are drawn into the sample 17 to be etched.
Therefore, electric charges accumulated on the surface of the sample 17 to be etched
Can be reduced, reducing charge-up.
it can. In this case, the voltage value Vb of the positive bias voltage p and
And pulse width Wb p and the voltage value Vb of the negative bias voltage
n and pulse width Wb By optimizing n
Page-up can be minimized.

Hereinafter, a description will be given of the results of an experiment performed on the phosphorus-doped polysilicon film deposited on the silicon oxide film while changing only the bias conditions as compared with the first embodiment.

The positive bias voltage has a voltage value Vb p to 15
0 V and pulse width Wb p is set to 200 μsec, and the negative bias voltage is set to the voltage value Vb. n to 100V
And the pulse width Wb n was set to 150 μsec. The repetition frequency of the high-frequency power pulse for plasma generation is set to 1 kHz, and the delay time Td is set to 5 for both the positive bias voltage and the negative bias voltage.
It was set to 00 μsec.

As a result of the experiment, the etching rate was about 200
nm / min, and the selectivity to the silicon oxide film was about 100, all of which were good. In addition, the etching shape was anisotropic.

Further, when a gate electrode made of a phosphorus-doped polysilicon film was formed on a gate insulating film made of a silicon oxide film having a thickness of 2.6 nm, insulation film destruction, notch and shape caused by charge-up occurred. No abnormalities were found.

(Third Embodiment) Hereinafter, a plasma processing method according to a third embodiment of the present invention will be described with reference to FIG.

The third embodiment is different from the first embodiment only in the method of applying a bias DC voltage pulse. Therefore, in the following description, the bias D
Only the method of applying the C voltage pulse will be described.

As shown in FIG. 4, the DC bias voltage is set to a value after a predetermined delay time Td has elapsed since the high-frequency power pulse for plasma generation was turned off and the high-frequency power pulse was off. A positive bias voltage and a negative bias voltage are applied to the sample table 16 from the DC pulse power supply 18, respectively.

According to the third embodiment, similarly to the second embodiment, when a positive bias voltage is applied, negative ions are drawn into the sample 17 to be etched, while when a negative bias voltage is applied, positive ions are drawn. Since ions are drawn into the sample 17 to be etched, the sample 17
Since the charge accumulated on the surface of the substrate is canceled, charge-up can be reduced.

(Fourth Embodiment) Hereinafter, a plasma processing method according to a fourth embodiment of the present invention will be described with reference to FIG.

The fourth embodiment differs from the first embodiment only in the method of applying a bias DC voltage pulse. Therefore, in the following description, the bias D
Only the method of applying the C voltage pulse will be described.

As shown in FIG. 5, the DC bias voltage is applied to the sample table 16 from the DC pulse power supply 18 after a predetermined delay time Td has elapsed since the high frequency power pulse for plasma generation was turned off. , Positive bias voltage,
A positive bias voltage and a negative bias voltage are repeatedly applied. That is, two positive bias voltages and one negative bias voltage are applied in three cycles in which the high-frequency power pulse is off.

According to the fourth embodiment, similarly to the second embodiment, when a positive bias voltage is applied, negative ions are drawn into the sample 17 to be etched, while when a negative bias voltage is applied, positive ions are drawn. Since ions are drawn into the sample 17 to be etched, the sample 17
Since the charge accumulated on the surface of the substrate is canceled, charge-up can be reduced. In this case, by optimizing the number of times of the positive bias voltage and the number of times of the negative bias voltage, it is possible to minimize the charge-up without changing the voltage values and pulse widths of the positive bias voltage and the negative bias voltage. Can be.

(Fifth Embodiment) Hereinafter, a plasma processing method and a plasma processing apparatus according to a fifth embodiment of the present invention will be described with reference to FIGS. 6, 7A, 7B and 8. explain.

FIG. 6 shows a schematic overall configuration of a plasma processing apparatus (plasma etching apparatus) according to the fifth embodiment. In FIG. 6, reference numeral 20 denotes a grounding, and the inner wall is made of ceramic, Teflon, quartz or the like. Is a chamber that is covered with an insulating material and the inside is kept in a vacuum.
Note that the chamber 20 may have a double structure having an inner chamber made of quartz or the like instead of the structure in which the inner wall is covered with an insulator. The chamber 20 is provided with a well-known gas introducing means for introducing a reactive gas into the chamber 20, but is not shown.

As shown in FIG. 6, the chamber 20 includes a plasma generation chamber 20a for generating plasma, a plasma processing chamber 20b for performing plasma processing using the plasma generated in the plasma generation chamber 20a, and a plasma generation chamber 20a.
a between the plasma processing chamber 20a and the plasma processing chamber 20b.
and a plasma transport chamber 20c for transporting the plasma to the chamber b.

A coil 21 is provided outside the plasma generation chamber 20 a of the chamber 20, and one end of the coil 21 is connected to a first high frequency power supply 23 for plasma generation via an impedance matching circuit 22. And the other end of the coil 21 is grounded. Therefore, when high-frequency power is applied to the coil 21 from the first high-frequency power supply 23, high-density plasma is generated in the plasma generation chamber 20a by the induction electromagnetic field.

A metal sample stage 24 whose surface is coated with an insulating material is provided inside the plasma processing chamber 20b of the chamber 20, and a photoresist pattern is formed on the surface of the sample stage 24. The sample to be etched 25 on which is formed is held.

A second high-frequency power source 26 for applying a bias voltage to the sample stage 24 is connected to the sample stage 24, and the second high-frequency power source 26 is connected to the sample stage 24 via a signal line 27. 1 high-frequency power supply 23.
The first high-frequency power supply 23 has a built-in signal delay circuit, and a synchronization signal generated by the signal delay circuit can be output to the second high-frequency power supply 26 via a signal line 27. The second high-frequency power supply 26 samples a high-frequency power pulse synchronized with a high-frequency power pulse applied from the first high-frequency power supply 23 to the coil 21 with a predetermined time delay based on a synchronization signal generated by the signal delay circuit. It can be applied to the platform 24. The high-frequency power is continuously applied from the first high-frequency power supply 23 to the coil 21 and the second high-frequency power is
When high-frequency power is continuously applied from the high-frequency power supply 26 to the sample table 24, the first high-frequency power supply 23 does not output a synchronization signal to the second high-frequency power supply 26.

A ring-shaped magnet 28A (see FIG. 7 (a)) for generating a substantially parallel static magnetic field B is provided inside the plasma transport chamber 20c of the chamber 20 outside. In this way, the plasma generation chamber 2
Since the ring-shaped magnet 28A is provided during the transportation of the plasma generated at 0a to the plasma processing chamber 20b, the electrons in the plasma cross the static magnetic field formed by the ring-shaped magnet 28A due to the Lorentz force. And stays in the inner region of the ring-shaped magnet 28A. Therefore, the plasma 29 in the plasma processing chamber 20b is an ion-ion plasma including only positive ions and negative ions.

The plasma generated in the plasma generation chamber 20a by the plasma transport chamber 20c whose inside is maintained in a vacuum state and the ring-shaped magnet 28A provided outside the plasma transport chamber 20c as described above. Plasma processing chamber 2 while reducing electron density in plasma
0b is provided.

The plasma transport means includes a plasma transport chamber 20c whose interior is maintained in a vacuum state, and a plurality of Helmholtz coils 28B provided outside the plasma transport chamber 20c and forming a substantially parallel magnetic field therein. (FIG. 7
(See (b)).

In this case, as shown in FIG. 7B, a plurality of Helmholtz coils 28B are arranged concentrically, and currents having phases different from each other are applied to the plurality of Helmholtz coils 28B.
When a rotating magnetic field is formed inside the plasma processing chamber, the plasma is transported while rotating, so that the uniformity of the plasma in the plasma processing chamber 20c is improved.

FIG. 8 shows the lapse of time of the high frequency power for plasma generation and the high frequency power for bias in the plasma processing method according to the fifth embodiment. The frequency of the high frequency power for plasma generation is 13.56 MHz. High-frequency power is continuously applied, and high-frequency power having a frequency of 3 MHz is continuously applied as bias high-frequency power.

In the fifth embodiment, the plasma generated in the plasma generation chamber 20a is transferred between the plasma generation chamber 20a and the plasma processing chamber 20b while reducing the electron density in the plasma. Since the plasma transport means for transport is provided, almost no electrons reach the plasma processing chamber 20b, so that the plasma in the plasma processing chamber 20b has the property of ion-ion plasma.

It is preferable that the frequency of the bias high-frequency power applied to the sample stage 24 be set within a range of about 0.5 to about 2 times the ion plasma frequency.

The ion plasma frequency fpi is given by fpi = (q
² · n / ε ₀ · M) ^1/2 / (2π). Where q is unit charge, n is plasma density, and ε
₀ is the vacuum permittivity and M is the mass of the ion.
The ion plasma frequency fpi of Ar ions is about 3 MHz when the plasma density is 10 ¹⁰ cm ⁻³ .

The reason for setting the frequency of the bias high-frequency power within a range of approximately 0.5 to approximately 2 times the ion plasma frequency is as follows. That is, when the frequency of the high frequency power for bias is lower than approximately 0.5 times the frequency of the ion plasma, the ions follow the electric field. If the frequency of the bias high frequency power is higher than approximately twice the ion plasma frequency, the ions cannot follow the electric field,
Again, only the ions of the flux determined by the same diffusion as in the case where no bias is applied are irradiated to the sample stage 24. On the other hand, when the frequency of the high frequency power for bias is set within a range of approximately 0.5 to approximately 2 times the frequency of the ion plasma, the penetration of the electric field into the plasma increases.
The ion flux flowing into the sample stage 24 increases, thereby increasing the plasma processing rate.

Hereinafter, a description will be given of experimental results obtained by etching a phosphorus-doped polysilicon film deposited on a silicon oxide film under the following conditions.

As the reactive gas (etching gas),
HBr gas was introduced at 50 ml per minute under standard conditions, and oxygen gas was introduced at 5 ml per minute under standard conditions, and the pressure in the chamber was set at 3 Pa. Also, the first
The high frequency power for plasma generation of 500 W was applied from the high frequency power supply 23 to the coil 21, and the high frequency power for bias having a voltage amplitude of 100 V _pp was applied to the sample stage 24 from the second high frequency power supply 26.

As a result of the experiment, the etching rate was about 250
nm / min, and the selectivity to the silicon oxide film was about 150 or more. In addition, the etching shape was anisotropic.

When a gate electrode made of a phosphorus-doped polysilicon film was formed on a gate insulating film made of a silicon oxide film having a thickness of 2.6 nm, the insulating film was broken, notched, and shaped due to charge-up. No abnormalities were found.

The HBr gas is composed of H which easily generates negative ions and Br which is a halogen element. Since the oxygen gas is also a gas which easily generates negative ions, the reactive gas containing HBr gas and oxygen gas is used. Gases tend to produce negative ions.

(Sixth Embodiment) Hereinafter, a plasma processing method according to a sixth embodiment of the present invention will be described with reference to FIG.

The sixth embodiment differs from the fifth embodiment only in the method of applying the high-frequency power for plasma generation and for bias, and therefore the following description will be made in the following description.
Only the method of applying high frequency power for plasma generation and bias will be described.

FIG. 9 shows the lapse of time of the high frequency power for plasma generation and the high frequency power for bias in the plasma processing method according to the sixth embodiment. The frequency of the high frequency power for plasma generation is 13.56 MHz. The high-frequency power pulse has a pulse width of 20 μsec and 500 W
And a high-frequency power pulse having a frequency of 3 MHz is continuously applied with a pulse width of 400 μsec and a voltage amplitude of 200 V _pp . The repetition frequency of the high frequency power for plasma generation is 1 kHz, and the delay time Td is 50 kHz.
It was set to 0 μsec.

Hereinafter, a description will be given of experimental results obtained by etching a phosphorus-doped polysilicon film deposited on a silicon oxide film under the following conditions. The type and flow rate of the reactive gas are the same as in the fifth embodiment, and the conditions for applying the high frequency power for plasma generation and the high frequency power for bias are as described above.

As a result of the experiment, the etching rate was about 130
nm / min, and the selectivity to the silicon oxide film was about 150, all of which were good. In addition, the etching shape was anisotropic.

Further, when a gate electrode made of a phosphorus-doped polysilicon film was formed on a gate insulating film made of a silicon oxide film having a thickness of 2.6 nm, insulation film destruction, notch and shape caused by charge-up occurred. No abnormalities were found.

Further, the pattern size dependence of the etching rate, that is, the microloading effect hardly occurs, and the etching rate of a hole having an opening diameter of 0.20 μm is 95% of the etching rate of a hole having an opening diameter of several hundred μm. % Or more.

(Seventh Embodiment) Hereinafter, a plasma processing method and a plasma processing apparatus according to a seventh embodiment of the present invention will be described with reference to FIG.

FIG. 10 shows a schematic overall configuration of a plasma processing apparatus (plasma CVD apparatus) according to the fifth embodiment. In FIG. 10, reference numeral 30 is grounded, and the inner wall is made of ceramic, Teflon, quartz or the like. Is a chamber that is covered with an insulating material and the inside is kept in a vacuum.
Note that the chamber 30 may have a double structure having an inner chamber made of quartz or the like instead of a structure in which the inner wall is covered with an insulator. The chamber 30 is provided with a well-known gas introducing unit for introducing a reactive gas into the chamber 30, but is not shown.

As shown in FIG. 10, the chamber 30
A plasma generation chamber 30a for generating plasma, a plasma processing chamber 30b for performing plasma processing using plasma generated in the plasma generation chamber 30a, and a plasma generation chamber 3
0a and the plasma processing chamber 30b, the plasma generated in the plasma generation chamber 30a is
0b to a plasma transport chamber 30c.

A coil 31 is provided outside the plasma generation chamber 30a of the chamber 30. One end of the coil 31 is connected to a first high-frequency power supply 33 for plasma generation via an impedance matching circuit 32. And the other end of the coil 31 is grounded. Therefore, when high-frequency power is applied to the coil 31 from the first high-frequency power supply 33, high-density plasma is generated in the plasma generation chamber 30a by the induced electromagnetic field.

A metal sample stage 34 whose surface is coated with an insulating material is provided inside the plasma processing chamber 30b of the chamber 30, and an insulating film is formed on the surface of the sample stage 34. Sample 3 to be etched
5 are held.

A second high-frequency power supply 36 for applying a bias voltage to the sample stage 34 is connected to the sample stage 34, and the second high-frequency power source 36 is connected to the second high-frequency power source 36 via a signal line 37. 1 high-frequency power supply 33.
The first high-frequency power supply 33 has a built-in signal delay circuit, and a synchronization signal generated by the signal delay circuit can be output to a second high-frequency power supply 36 via a signal line 37. The second high-frequency power supply 36 samples a high-frequency power pulse synchronized with a high-frequency power pulse applied from the first high-frequency power supply 33 to the coil 31 with a predetermined time delay based on a synchronization signal generated by the signal delay circuit. It can be applied to the platform 34. The high-frequency power is continuously applied from the first high-frequency power supply 33 to the coil 31 and the second high-frequency power is
When high-frequency power is continuously applied from the high-frequency power supply 36 to the sample table 34, the first high-frequency power supply 33 does not output a synchronization signal to the second high-frequency power supply 36.

Outside the plasma transport chamber 30c of the chamber 30, a ring-shaped magnet 38A for generating a substantially parallel static magnetic field B is provided inside. As described above, since the ring-shaped magnet 38A is provided during the transportation of the plasma generated in the plasma generation chamber 30a by the high-frequency discharge to the plasma processing chamber 30b, the plasma 39 in the plasma processing chamber 30b has positive ions and negative ions. An ion-ion plasma consisting of only ions is obtained.

The plasma generated in the plasma generation chamber 30a by the plasma transport chamber 30c whose inside is maintained in a vacuum state and the ring-shaped magnet 38A provided outside the plasma transport chamber 30c as described above. Plasma processing chamber 3 while reducing the electron density in the plasma
0b is provided.
Note that, instead of the ring-shaped magnet 38A, a plurality of Helmholtz coils that form a substantially parallel magnetic field inside may be used.

Hereinafter, the results of an experiment in which a film is deposited on a silicon substrate under the following conditions will be described.

As the reactive gas (film deposition gas), S
200 ml of iH ₄ gas is introduced per minute under standard conditions, and NH ₃ gas is introduced at 50 ml per minute under standard conditions.
The pressure of the chamber was set to 30 Pa, and the temperature of the sample stage 34 was set to 350 ° C. to 450 ° C. When the frequency is 1 from the first high-frequency power supply 33 to the coil 31.
A high frequency power of 3.56 MHz is continuously applied at a power of 500 W, and a high frequency power of a frequency of 2.0 MHz is applied as 100 V _pp as high frequency power for bias.
Was applied continuously at a voltage amplitude of ~ 300 V _pp .

As a result of the experiment, the film deposition rate of the silicon nitride film was about 50 nm / min. After an aluminum film is deposited on the silicon nitride film, the aluminum film and the silicon nitride film are patterned to form a gate electrode on a gate insulating film having a thickness of 2.6 nm. No abnormality such as insulation film breakdown was observed.

[0126]

According to the first plasma processing method, since the electron density in the plasma is sufficiently small and the ratio of the negative ions to the negative charges in the plasma is extremely large, the sample is effectively irradiated with the negative ions. By adjusting the magnitude of the bias voltage applied to the sample stage, the energy of the negative ions colliding with the sample can be controlled to control the plasma processing process.

According to the second or third plasma processing method, plasma processing using mainly negative ions in plasma can be performed, so that highly selective plasma processing can be performed at a high processing rate and charge-up can be performed. The problem described above hardly occurs.

According to the plasma processing apparatus of the present invention,
Since plasma generation means for transporting plasma generated in the plasma generation chamber to the plasma processing chamber while reducing the electron density in the plasma is provided, plasma processing can be performed using plasma with reduced electron density. Therefore, the plasma processing mainly using the negative ions in the plasma can be easily and reliably performed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a plasma processing apparatus (plasma etching apparatus) according to a first embodiment.

FIG. 2 is a diagram showing a time change of various parameters in the plasma processing method according to the first embodiment.

FIG. 3 is a diagram showing a timing of applying a bias DC voltage in a plasma processing method according to a second embodiment.

FIG. 4 is a diagram showing a timing of applying a bias DC voltage in a plasma processing method according to a third embodiment.

FIG. 5 is a diagram showing a timing of applying a bias DC voltage in a plasma processing method according to a fourth embodiment.

FIG. 6 is a schematic sectional view of a plasma processing apparatus (plasma etching apparatus) according to a fifth embodiment.

FIG. 7A is a perspective view of a ring-shaped magnet included in a plasma processing apparatus according to a fifth embodiment,
(B) is a perspective view of a Helmholtz coil included in the plasma processing apparatus according to the fifth embodiment.

FIG. 8 is a diagram showing a time course of high-frequency power for plasma generation and high-frequency power for bias in a plasma processing method according to a fifth embodiment.

FIG. 9 is a diagram showing the timing of applying a bias high-frequency power pulse in the plasma processing method according to the sixth embodiment.

FIG. 10 is a schematic sectional view of a plasma processing apparatus (plasma CVD apparatus) according to a seventh embodiment.

[Explanation of symbols]

 Reference Signs List 10 chamber 11 dielectric plate 12 coil 13 impedance 14 high-frequency pulse power supply 15 plasma 16 sample table 17 sample to be etched 18 DC pulse power supply 19 signal line 20 chamber 20a plasma generation chamber 20b plasma processing chamber 20c plasma transport chamber 21 coil 22 impedance matching circuit Reference Signs List 23 first high frequency power supply 24 sample stage 25 sample to be etched 26 second high frequency power supply 27 signal line 28A ring magnet 28B Helmholtz coil 29 plasma 30 chamber 30a plasma generation chamber 30b plasma processing chamber 320c plasma transport chamber 31 coil 32 impedance matching Circuit 33 First high frequency power supply 34 Sample table 35 Sample to be etched 36 Second high frequency power supply 37 Signal line 38A Ring magnet 39 Plastic Zuma

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G075 AA24 BC02 BC04 BC06 CA14 CA15 CA25 CA47 DA02 DA05 EB01 EB41 EC06 EC10 EE02 FB06 FB12 FC15 4K030 AA06 AA13 BA40 CA04 FA04 JA11 JA17 JA18 KA20 KA30 KA34 KA34 LA15 5A004 A03 BB13 BC08 DA04 DA26 DB02 DB03 5F045 AA08 AB33 AC01 AC11 AC12 AD07 AD08 AE19 AF03 EH03 EH11 EH18 EH20

Claims (18)

[Claims] In a plasma in which Nn / Ne, which is a value of a ratio of a negative ion density Nn to an electron density Ne, is approximately 500 or more, plasma processing is performed by applying a bias voltage to a sample stage. Plasma processing method. 2. The plasma processing method according to claim 1, wherein the bias voltage is a positive voltage. 3. The plasma processing method according to claim 1, wherein the bias voltage is a pulse voltage of a positive voltage and a negative voltage. 4. The plasma processing method according to claim 3, further comprising the step of adjusting each pulse width of the positive voltage and the negative voltage of the pulse voltage. 5. The method according to claim 1, further comprising the step of applying a high-frequency power having a frequency of about 0.5 to about twice the ion plasma frequency to the sample stage as the bias voltage. The plasma processing method as described above. 6. The method according to claim 1, wherein the plasma is generated from a gas containing hydrogen atoms or hydrogen compounds.
4. The plasma processing method according to 1. 7. The plasma processing method according to claim 1, wherein the plasma is generated from a gas containing a halogen element or a halogen compound. 8. The plasma processing apparatus according to claim 1, wherein the plasma is generated from a gas containing oxygen atoms or oxygen compounds.
4. The plasma processing method according to 1. 9. A step of generating plasma containing negative ions by a high-frequency power pulse, and performing a plasma treatment mainly using negative ions in the plasma by applying a bias voltage to a sample stage while the high-frequency power is off. Performing a plasma processing method. 10. The step of performing the plasma processing, wherein the high-frequency power is turned off and the value of the ratio of the negative ion density Nn to the electron density Ne in the plasma is Nn.
10. The plasma processing method according to claim 9, further comprising a step of applying the bias voltage to the sample stage when / Ne is approximately 500 or more. 11. The plasma processing method according to claim 9, wherein a duty ratio of the high frequency power pulse is less than 50%. 12. The plasma processing method according to claim 9, wherein the step of performing the plasma processing includes a step of applying the bias voltage synchronized with the high-frequency power pulse with a delay of a predetermined time. 13. A method comprising: generating a plasma containing negative ions by high-frequency power; reducing an electron density in the generated plasma; and performing a plasma process using the plasma with a reduced electron density. A plasma processing method. 14. A plasma generation chamber for generating plasma, a plasma processing chamber for performing plasma processing using plasma generated in the plasma generation chamber, and a plasma processing chamber provided between the plasma generation chamber and the plasma processing chamber; A plasma processing apparatus, comprising: a plasma transport unit that transports plasma generated in the plasma generation chamber to the plasma processing chamber while reducing electron density in the plasma. 15. The plasma transport means is provided with a vacuum chamber that connects the plasma generation chamber and the plasma processing chamber, and a ring-like shape that is provided to surround the vacuum chamber and generates a substantially parallel static magnetic field therein. The plasma processing apparatus according to claim 14, comprising a magnet. 16. The plasma transport means includes: a vacuum chamber for communicating the plasma generation chamber with the plasma processing chamber; and a plurality of Helmholtz coils arranged around the vacuum chamber and generating a substantially parallel magnetic field therein. 15. The plasma processing apparatus according to claim 14, comprising: 17. The plasma processing apparatus according to claim 16, wherein the plurality of Helmholtz coils generate a rotating magnetic field by applying currents having different phases. 18. A high-frequency power pulse circuit for supplying a high-frequency power pulse for generating plasma in the plasma processing chamber; a bias circuit for supplying a bias voltage to a sample stage provided in the plasma processing chamber; The plasma processing apparatus according to claim 14, further comprising: a signal delay circuit that synchronizes a voltage with a predetermined time delay with respect to the high-frequency power pulse.