JP3368743B2 - Plasma processing apparatus and plasma processing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing apparatus and a processing method, and more particularly to a plasma processing apparatus and a processing method suitable for forming a fine pattern in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art In the technical field of performing etching processing and film forming processing of semiconductors using plasma, plasma is applied to a sample table on which an object to be processed (for example, a semiconductor wafer substrate, hereinafter abbreviated as sample) is placed. USP as a processing apparatus provided with a high frequency power source for accelerating ions in the inside and an electrostatic adsorption film for holding a sample on a sample table by electrostatic adsorption force.
5,320,982 and the like.

In the apparatus described in this specification, plasma is generated by microwaves, the sample is held on the sample stage by electrostatic attraction, and a heat transfer gas is interposed between the sample stage and the temperature of the sample. While performing the control, the sine wave output high frequency power source is used as a bias power source, and the power source is connected to the sample stage to control the ion energy incident on the sample.

Further, in Japanese Laid-Open Patent Publication No. 62-280378, a pulsed ion control bias waveform for stabilizing the electric field strength between the plasma electrode and the electrode is generated and applied to the sample stage so that the ion energy incident on the sample is It is described that the distribution width can be narrowed and the processing dimensional accuracy of etching and the etching rate ratio between the film to be processed and the base material can be increased several times.

Further, in JP-A-6-61182,
It is described that plasma is generated by using electron cyclotron resonance and a pulse bias with a pulse duty width of about 0.1% or more is applied to the sample to prevent the occurrence of notches.

[0006]

Among the above-mentioned prior arts, the pulse bias power supply method described in JP-A-62-280378 and JP-A-6-61182 is an electrostatic discharge between a sample stage electrode and a sample. When applying a pulse bias to a sample using a dielectric layer for adsorption, no study has been made.If it is applied to the electrostatic adsorption method as it is, the ion energy distribution will be generated due to the change in voltage generated across the electrostatic adsorption film. Therefore, there is a drawback that it is not possible to deal with the necessary fine pattern processing while sufficiently controlling the temperature of the sample.

Further, in the conventional sine wave output bias power supply system described in USP 5,320,982,
When the frequency becomes higher, the impedance of the sheath approaches the impedance of the plasma itself or becomes lower than that, so unnecessary plasma is generated by the bias power supply, it is not used effectively for accelerating ions, and the plasma distribution deteriorates and the bias There is a drawback that the controllability of ion energy by the power source is lost.

Further, in plasma processing, it is important to properly control the amount of ions, the amount of radicals, and the species of radicals in order to improve the performance. Conventionally, a gas serving as an ion source or a radical source is used in the processing chamber. In order to generate ions and radicals at the same time by generating a plasma in the processing chamber, the limit of control is becoming clear as the processing of the sample becomes finer.

An object of the present invention is to provide a film for electrostatic attraction.
The sample is applied by applying a pulse bias voltage to the
Suppresses the spread of ion energy distribution during plasma processing
It is to provide a plasma processing apparatus and a plasma processing method capable of controlling the plasma processing.

[0010]

[0011]

[0012]

[0013]

The above object is to provide a vacuum processing chamber.
And a plasma generator that generates plasma in the vacuum processing chamber.
Stage and a sample placed in the vacuum processing chamber for placing the sample to be processed.
Sample stand, electrostatic attraction means for holding the sample on the sample stand, and sample
Connected to the sample table and applying a pulse bias voltage to the sample table.
In a plasma processing apparatus having a loose bias applying means
And the voltage of the electrostatic attraction means is equal to the pulse bias voltage.
Set the pulse bias voltage cycle so that it is 1/2 or less.
The device is set to 0.1 μs to 10 μs and installed in the vacuum processing chamber.
Place the sample to be processed on the sample table and
Holds by adsorption force and generates plasma in the processing chamber
Apply a pulse bias voltage to the sample table together with the sample
In the plasma processing method of plasma processing, electrostatic adsorption
So that the voltage of is less than 1/2 of the pulse bias voltage
Set the pulse bias voltage cycle to 0.1 μs to 10 μs
This is achieved by adopting the method described below.

[0014]

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.
First, FIG. 1 shows a first embodiment in which the present invention is applied to a facing electrode type plasma etching apparatus. In FIG. 1, a processing chamber 10 as a vacuum container is provided with a pair of opposing electrodes composed of an upper electrode 12 and a lower electrode 15. The gap between the parallel plate electrodes 12 and 15 is 10 mm to 40 mm.
It is desirable to set the degree. A high frequency power source 16 for supplying high frequency energy is connected to the upper electrode 12 via a high frequency power source modulation signal source 161. On the lower surface of the upper electrode 12, an upper electrode cover 30 as a plate for removing fluorine and oxygen made of silicon, carbon or SiC
Is provided. Further, a gas introduction chamber 34 having a gas diffusion plate 32 that diffuses the gas into a desired distribution is provided above the upper electrode 12. In the processing chamber 10, the gas required for processing such as etching of the sample is supplied from the gas supply unit 36 through the gas diffusion plate 32 of the gas introduction chamber 34, the upper electrode 12 and the hole 38 provided in the upper electrode cover 30. Supplied. The outer chamber 11 is evacuated by a vacuum pump 18 connected to the outer chamber via a valve 14, and the processing chamber 10 is adjusted to the processing pressure of the sample. A discharge containment ring 37 is provided around the processing chamber 10.

In the present invention, the parallel plate electrodes 12,
It suffices that 15 has a pair of electrodes facing each other, and the parallel plate electrodes 12 and 15 may have a slight concave surface or convex surface in view of requirements such as plasma generation characteristics.

The lower electrode 15 for holding the sample 40 has a structure provided with a two-pole type electrostatic chuck 20. That is, the lower electrode 15 includes the outer first lower electrode 15A,
A dielectric layer for electrostatic adsorption (hereinafter, abbreviated as electrostatic adsorption film) is formed on the upper surface of the first and second lower electrodes by the second lower electrode 15B disposed above the inside thereof with the insulator 21 interposed therebetween. 22) is provided. A DC power supply 23 is connected between the first and second lower electrodes via high frequency component cutting coils 24A and 24B, and the second lower electrode 15 is connected.
A DC voltage is applied between both lower electrodes so that the B side becomes positive. This allows the sample 40 to pass through the electrostatic adsorption film 22.
And Coulomb force acting between both lower electrodes
Are adsorbed and held on the lower electrode 15. Electrostatic adsorption film 22
For example, a dielectric material such as aluminum oxide or a mixture of aluminum oxide and titanium oxide can be used. Also, as the power supply 23, several hundreds of volts
Use the DC power source.

A pulse bias power source 17 for supplying a positive pulse bias of 20V to 800V is connected to the lower electrodes 15 (15A, 15B) via blocking capacitors 19A, 19B for cutting DC components. There is.

When the etching process is performed, the sample 40, which is an object to be processed, is placed on the lower electrode 15 of the processing chamber 10 and adsorbed by the electrostatic chuck 20. On the other hand, the gas required for etching the sample 40 is supplied to the processing chamber 10 from the gas supply unit 36 via the gas introduction chamber 34. The outer chamber 11 is evacuated by a vacuum pump 18, and the processing chamber 10 is processed at a sample processing pressure, for example, 5 mTorr to 40 mTorr.
Is exhausted under reduced pressure. Next, from the high frequency power source 16, 20 MHz to 500 MHz, preferably 30 MHz to 200 MHz.
The high frequency power of MHz is output to turn the processing gas in the processing chamber 10 into plasma. On the other hand, the lower electrode 15 has a voltage of 20 V to 800 V and a period of 0.1 μm from the pulse bias power supply 17.
A predetermined pulse bias of s to 10 μs, preferably 0.2 μs to 5 μs is applied to control electrons and ions in plasma to perform a predetermined etching process on the sample 40.

The lower limit of the frequency of the high frequency power source 16 is a frequency at which discharge can be stably maintained at a low pressure, and the upper limit is a frequency at which there is no excessive dissociation of gas.

The etching gas is distributed by the gas diffusion plate 32 to a desired distribution, and then the upper electrode 12 and the upper electrode cover 3 are formed.
It is injected into the processing chamber 10 through the hole 38 opened at 0.

Further, the upper electrode cover 30 is made of carbon, silicon or a material containing these, and fluorine or oxygen components are removed to improve the selectivity with respect to the base such as resist or silicon.

The discharge containment ring 37 localizes the plasma around the sample chamber 40 in the vicinity of the processing chamber 10 to improve the plasma density and to prevent the discharge containment ring 37 from outside the discharge containment ring 37. Minimize unnecessary deposition of deposits on the

As the discharge containment ring 37, it is preferable to use an insulator such as quartz. However, using a semiconductor or conductive material such as carbon, silicon, or SiC,
By connecting to a high frequency power source and causing sputtering by ions, it is possible to reduce deposition of deposits on the ring 37 and also to have an effect of removing fluorine and oxygen.

On the insulator 13 around the sample 40,
When the susceptor cover 39 containing carbon or silicon or these is provided, fluorine and oxygen can be removed, which is useful for improving the selection ratio.

Further, the lower electrode 15 (15A, 15A) is sandwiched by the electric potential of the DC power supply 23 with the electrostatic attraction film 22 of the dielectric material interposed therebetween.
An electrostatic adsorption circuit is formed via B) and the sample 40. In this state, the sample 40 is moved to the lower electrode 15 by electrostatic force.
It is locked and retained by. Sample 4 locked by electrostatic force
A cooling gas such as helium, nitrogen, or argon is supplied to the back surface of 0. The cooling gas fills the concave portion of the lower electrode 15, and the pressure thereof is in the range of several torr to several tens of torr. The electrostatic attraction force is almost zero between the concave portions provided with the gap, and it can be considered that the electrostatic attraction force is generated only in the convex portion of the lower electrode 15.
However, as will be described later, since the voltage can be appropriately set in the DC power supply 23 and the adsorption force that can sufficiently withstand the pressure of the cooling gas can be set, the sample 40 is moved or skipped by the cooling gas. There is nothing to do.

In order to improve the fine workability of the sample, it is preferable to use a higher frequency power source 16 for plasma generation and to stabilize the discharge in the low gas pressure region. In the present invention, the processing pressure of the sample in the processing chamber 10 is 5 mTorr to 40 mTorr. By reducing the gas pressure in the processing chamber 10 to a low pressure of 40 mTorr or less, the collision of ions in the sheath is reduced, so that the directionality of ions is increased during the processing of the sample 40, and vertical fine processing is enabled. . At 5 mTorr or less, in order to obtain the same processing speed, the exhaust device and the high-frequency power source are increased in size, and more than necessary dissociation occurs due to the rise in the electron temperature, which tends to deteriorate the characteristics.

Generally, between the frequency of the power source for plasma generation using parallel plate electrodes and the minimum gas pressure for stable discharge, as shown in FIG. 2, the higher the frequency of the power source, There is a relationship that the minimum gas pressure for stable discharge decreases as the inter-electrode distance increases. In order to avoid the adverse effects of deposits on the surrounding walls and the discharge confinement ring 37, and to effectively function the effect of removing fluorine and oxygen by the upper electrode cover 30, the susceptor cover 39, and the resist in the sample, the maximum gas is used. 2 of mean free path at pressure of 40 mTorr
Corresponding to 5 times or less, it is desirable to set the distance between the electrodes to about 50 mm or less. In addition, the distance between electrodes is 2 to 4 times (4 mm to 8 m) the mean free path at the maximum gas pressure (40 mTorr).
If it is not more than about m), stable discharge becomes difficult.

In the embodiment of the present invention shown in FIG. 1, as the high frequency power source 16 for plasma generation, 20 MHz to 500 MHz,
Since a high frequency power of 30 MHz to 200 MHz is preferably used, stable plasma can be obtained and fine workability can be improved even when the gas pressure in the processing chamber is set to a low pressure of 5 mTorr to 40 mTorr. Further, by using such high frequency power, the dissociation of gas plasma is improved and the selection ratio control during sample processing is improved.

By the way, the electrostatic adsorption film 22 acts so as to inhibit the action of the pulse bias on the ions. In the present invention, the electrostatic adsorption film 22 is applied with the application of the pulse bias.
One of the features is that the voltage suppressing means is provided in order to suppress the rise of the voltage generated between both ends and to enhance the effect of the pulse bias.

As an example of the voltage suppressing means, the change (V _CM ) of the voltage during one cycle of the bias voltage generated between both ends of the electrostatic adsorption film due to the application of the pulse bias is the magnitude of the pulse bias voltage (V _CM ). _It is preferable to configure it to be 1/2 or less of _p ). Specifically, the electrostatic capacitance of the dielectric is reduced by reducing the thickness of the electrostatic adsorption film made of a dielectric provided on the surface of the lower electrode 15 or by using a material having a large dielectric constant. There is a way to increase.

Alternatively, as another voltage suppressing means,
There is also a method of suppressing the rise of the voltage V _CM by shortening the cycle of the pulse bias voltage. Further, a method of separately providing the electrostatic adsorption circuit and the pulse bias voltage application circuit at different positions, for example, an opposite electrode different from the electrode on which the sample is arranged and held, or a third electrode provided separately is also considered. To be

Next, the relationship between the pulse bias voltage and the change (V _CM ) in the voltage generated across the electrostatic attraction film during one cycle of the pulse bias, which should be brought about by the voltage suppressing means in the present invention, will be described with reference to FIGS. This will be described in detail with reference to FIG.

First, an example of a desirable output waveform used in the pulse bias power supply 17 of the present invention is shown in FIG. In the figure, the pulse amplitude is v _p , the pulse period is T ₀ , and the positive pulse width is T ₁ .

When the waveform of FIG. 3 (A) is applied to the sample via the blocking capacitor and the electrostatic attraction dielectric layer (hereinafter abbreviated as an electrostatic attraction film), plasma is generated by another power source. The potential waveform on the surface of the sample in the steady state in this state is shown in FIG.

However, the direct current component voltage of the waveform: V _DC floating potential of the plasma: V _f The maximum voltage in one cycle of the voltage generated between both ends of the electrostatic adsorption film: V _CM .

In FIG. 3 (B), the portion (I) where the positive voltage is higher than V _f is the portion that mainly draws only the electron current, and the negative portion from V _f is the ionic current. The part where _Vf is drawn is a part where electrons and ions are balanced ( _Vf is usually several V to ten and several V).

Incidentally, in FIG. 3 (A) and the following description,
It is assumed that the capacity of the blocking capacitor and the capacity of the insulator near the sample surface are sufficiently larger than the capacity of the electrostatic adsorption film (hereinafter abbreviated as electrostatic adsorption capacity).

The value of V _CM is expressed by the following equation (Equation 1).

[0051]

[Equation 1]

However, q: ion current density (average value) flowing into the sample during the period (T ₀ −T ₁ ) c: electrostatic adsorption capacity per unit area (average value) i _i : ion current density, ε _r : Relative permittivity of electrostatic adsorption film d: film thickness of electrostatic adsorption film ε ₀ : dielectric constant (constant) in vacuum K: electrode coverage of electrostatic adsorption film (≦ 1) The pulse duty ratio: (T ₁ / T ₀ ) shows a probability distribution of the potential waveform and ion energy of the sample surface when T ₀ is changed while keeping it constant. However, T ₀₁ ,
T ₀₂ : T ₀₃ : T ₀₄ : T ₀₅ = 16: 8: 4: 2: 1.

As shown in (1) of FIG. 4, the pulse period T ₀
Is too large, the potential waveform on the sample surface deviates greatly from the rectangular wave and becomes a triangular wave, and the ion energy has a constant distribution from the lower side to the higher side, which is not preferable.

As shown in (2) to (5) of FIG. 4, as the pulse period T ₀ is reduced, (V _CM / v _p ) becomes a value smaller than 1, and the ion energy distribution also narrows. .

4 and 5, T ₀ = T ₀₁ , TO ₀₂ ,
T ₀₃ , T ₀₄ , and T ₀₅ are (V _CM / v _p ) = 1, 0.63,
It corresponds to 0.31, 0.16, and 0.08.

Next, the pulse off (T ₀ -T ₁ ) period and
FIG. 6 shows the relationship between the maximum voltage V _{CM in} one cycle of the voltage generated across the electrostatic adsorption film.

As the electrostatic adsorption film, a titanium oxide-containing alumina (ε _r = 10) having a thickness of 0.3 mm was used, and the thickness of the electrode was about 50.
% Is coated (K = 0.5), the ion current density i _i
The change in the value of V _CM in the medium density plasma of = 5 mA / cm ² is shown by the thick line (standard condition line) in FIG.

As is apparent from FIG. 6, as the pulse off (T ₀ -T ₁ ) period becomes longer, the voltage V _CM generated across the electrostatic adsorption film becomes a larger value in proportion to it, which is normally used. The applied pulse voltage becomes _vp or more.

[0059] For example, in a plasma etching apparatus, damage, selectivity with the base or the mask, typically the shape or the like, in the gate etch 250Volt ≦ a 50volt ≦ v _p ≦ 200volt oxide film etched by 20volt ≦ v _p ≦ 100volt metal etching Limited to v _p ≤ 800 volt.

When the condition of (V _CM / v _p ) ≦ 0.5 described later is to be satisfied, the upper limit of (T ₀ -T ₁ ) is as follows in the standard state. The gate etch (T ₀ -T ₁₎ ≦ 0.15μs the metal etching (T ₀ -T ₁₎ ≦ 0.35μs oxide film in the etching (T ₀ -T ₁₎ ≦ 1.2μs Incidentally, T ₀ is 0. When the value approaches 1 μs, the impedance of the ion sheath approaches or becomes lower than the impedance of the plasma, so that unnecessary plasma is generated and the bias power supply is not effectively used for accelerating the ions. Therefore, the controllability of the ion energy by the bias power source deteriorates, so T ₀ is 0.1 μm.
s or more, preferably 0.2 μs or more.

Therefore, in a gate etcher or the like in which v _p can be kept low, the dielectric constant of the material of the electrostatic adsorption film is 1
High as 0 to 100 (eg Ta ₂ O ₃ ε _r = 2
5) or a thin film thickness without lowering the dielectric strength, for example, 10 μm to 400 μm, preferably 10 μm to 10 μm
It is necessary to set it to 0 μm.

In FIG. 6, the electrostatic capacity c per unit area is
V _CM when increased by 2.5 times, 5 times and 10 times respectively
The value of is also shown. Even if the electrostatic adsorption film is improved, at present it is considered that the improvement of the capacitance c by several times is the limit, and V _CM ≦ 3
Assuming that 00 volt and c ≦ 10c ₀ , 0.1 μs ≦ (T ₀ −
T ₁ ) ≦ 10 μs.

The portion effective for plasma treatment by the acceleration of ions is the portion (T ₀ -T ₁ ), and the pulse duty (T ₁ / T ₀ ) is preferably as small as possible.

FIG. 7 shows the plasma processing efficiency estimated by taking (V _DC / v _p ) in consideration of the time average. (T
_It is preferable to decrease ₁ / T ₀ ) and increase (V _DC / v _p ).

As the efficiency of the plasma treatment, 0.5 ≦ (V _DC
/ V _p ), the condition (V _CM / v _p ) ≦ 0.5, which will be described later.
, The pulse duty is (T ₁ / T ₀ ) ≦ 0.
It will be about 4.

The smaller the pulse duty (T ₁ / T ₀ ) is, the more effective it is to control the ion energy. However, if it is made smaller than necessary, the pulse width T ₁ becomes a small value of about 0.05 μs, which is several tens of MHz. Therefore, it becomes difficult to separate it from the high frequency component for plasma generation, which will be described later. As shown in FIG. 7, 0 ≦ (T ₁ /
When (T ₀ ) ≦ 0.05, the decrease of (V _DC / v _p ) is slight, and when (T ₁ / T ₀ ) is 0.05 or more, no particular problem occurs.

Here, as an example of gate etching, FIG. 8 shows etching rates ESi and ESiO between silicon and an underlying chloride film when chlorine gas of 10 mT is turned into plasma.
₂ shows the ion energy dependence of ₂ . The etching rate ESi of silicon has a constant value at low ion energy. When the ion energy is about 10 V or higher, ESi also increases as the ion energy increases. On the other hand, the etching rate ESiO ₂ of the underlying oxide film is 0 when the ion energy is about 20 V or less, and when it exceeds about 20 V, ESiO ₂ increases with the ion energy.

As a result, when the ion energy is about 20 V or less, there is a region where the selection ratio ESi / ESiO ₂ to the base is ∞. In the ion energy of more than about 20V, the selection ratio ESi / ESiO ₂ with the base decreases rapidly with increasing ion energy.

FIG. 9 shows an oxide film (Si
As an example of etching (O ₂ , BPSG, HISO, etc.), an etching rate ESiO ₂ and ES of an oxide film and silicon when C 4 F 8 gas 10 mT is turned into plasma
It shows the ion energy distribution of i.

The etching rate ESiO ₂ of the oxide film is
It has a negative value at low ion energy and causes a depot.
The ESiO ₂ rapidly rises to a positive value when the ion energy is around 400 V, and thereafter gradually increases. On the other hand, the etching rate ESi of the underlying silicon is
At a place where the ion energy is higher than that of O ₂ , (-) (etching) changes to (+) (etching) and gradually increases.

As a result, in the vicinity of the change of ESiO ₂ from (−) to (+), the selection ratio ESiO ₂ / ESi with the base is
∞, and above that, ESiO ₂ / ESi drops rapidly with increasing ion energy.

8 and 9, the values of ESi and ESiO ₂ and ESi / ESi are applied to the actual process.
The ion energy is adjusted to an appropriate value by adjusting the bias power source in consideration of the magnitudes of O ₂ and ESiO ₂ / ESi.

Further, until the just etching (etching until the underlying film appears), the magnitude of the etching rate is given priority, and after the just etching, the ion energy is changed before and after the just etching by giving priority to the magnitude of the selection ratio. If so, better characteristics can be obtained.

The characteristics shown in FIGS. 8 and 9 are characteristics when the ion energy distribution is limited to a narrow portion. When the energy distribution of ions is wide, each etching rate is a time average value thereof, so that it cannot be set to an optimum value and the selection ratio is significantly lowered.

According to the experiment, if (V _DC / v _p ) is about 0.3 or less, the spread of ion energy is ± 15%.
It was below the level, and a high selection ratio was obtained with the characteristics shown in FIGS. Further, if (V _DC / v _p ) ≦ 0.5, the selection ratio and the like were improved as compared with the conventional sinusoidal bias method.

As described above, as a voltage suppressing means for suppressing the voltage change (V _CM ) during one cycle of the pulse voltage generated between both ends of the electrostatic adsorption film, V _CM is the magnitude of the pulse bias voltage v.
It is preferable that the thickness be less than or equal to 1/2 of _p . Specifically, the thickness of the electrostatic chuck film 22 of the dielectric provided on the surface of the lower electrode 15 is reduced, or the dielectric is The capacitance of the dielectric can be increased by using a material having a high ratio. Alternatively, the period of the pulse bias voltage is 0.
1 μs to 10 μs, preferably 0.2 μs to 5 μs (repetition frequency: corresponding to 0.2 MHz to 5 MHz), and the pulse duty (T ₁ / T ₀ ) is set to 0.05 ≦ (T ₁ /
T ₀ ) ≦ = 0.4 is set to suppress the voltage change across the electrostatic adsorption film.

Alternatively, by combining the film thickness of the electrostatic attraction film of the dielectric and some of the dielectric constant of the dielectric and the period of the pulse bias voltage, the voltage V _CM generated across the electrostatic attraction film is obtained. May satisfy the condition of (V _CM / v _p ) ≦ 0.5 described above.

Next, an example in which the vacuum processing chamber of FIG. 1 is used for etching an oxide film (eg, SiO2, SiN, BPSG) will be described.

As the gas 19, C ₄ F 8: 1 to 5%,
Ar: 90 to 95%, O ₂ : 0 to 5%, or C ₄ F
8: 1~5%, Ar: 70~90 %, O 2: 0~5%,
The composition of CO: 10 to 20% is used. As the high frequency power source 16 for plasma generation, a higher frequency than the conventional one, for example, 40 MHz is used, and 10 mTorr to 30 m
Measures the stabilization of discharge in the low gas pressure region of Torr.

If the dissociation proceeds more than necessary due to the high frequency of the plasma source high frequency power source 16, the output of the high frequency power source 16 is controlled to be turned on / off or level modulated by the high frequency power source modulation signal source 161. About 5 to 50 μs as the ON (or high level during level modulation) time,
1 for off time (or low level during level modulation)
0 to 100 μs and a cycle of about 20 μs to 150 μs are used, whereby unnecessary dissociation can be prevented.

The modulation cycle of the high frequency power source for plasma source is usually longer than the cycle of pulse bias. Therefore, the modulation ratio of the high-frequency power source for plasma source is set to an integral multiple of the period of the pulse bias, and the phase between the two is optimized to improve the selection ratio.

On the other hand, the ion energy is controlled by accelerating and vertically injecting the ions in the plasma into the sample by applying the pulse bias voltage. As the pulse bias power supply 17, for example, pulse cycle: T = 0.
By using a power source of 65 μs, pulse width: T ₁ = 0.15 μs, and pulse amplitude: Vp = 600 V, the ion energy distribution width becomes ± 15% or less, and
As a result, it is possible to perform plasma treatment with a good selection characteristic of 20 to 50 with respect to SiN and SiN.

Next, another embodiment of the present invention will be described with reference to FIG. This embodiment has a configuration similar to that of the parallel plate electrode type plasma etching apparatus shown in FIG. 1, but the lower electrode 15 holding the sample 40 is provided with a unipolar electrostatic chuck 20. ing. That is, the lower electrode 1
5, a dielectric layer 22 for electrostatic attraction is provided on the upper surface of the electrode 5, and the positive electrode of a DC power supply 23 is connected to the lower electrode 15 via a coil 24 for cutting high frequency components. Also, 2
A pulse bias power supply 17 that supplies a positive pulse bias of 0 V to 800 V is connected via a blocking capacitor 19.

The sample 40 to be processed is placed on the lower electrode 15 and the electrostatic chuck 20, that is, the DC charge 23 supplies the positive charge and the negative charge supplied from the plasma to the electrostatic adsorption film 22. It is adsorbed by the Coulomb force generated between both ends.

The operation of this apparatus is the same as that of the parallel plate electrode type plasma etching apparatus shown in FIG. 1. When performing the etching process, the sample 40 to be processed is placed on the sample table 15 and the electrostatic force is applied. The pressure of the processing chamber 10 is reduced to 5 mTorr to 40 mTorr by introducing the processing gas from the gas supply system 36 into the processing chamber 10 at a predetermined flow rate while evacuating the chamber with the vacuum pump 18. Evacuate under reduced pressure. Next, the high frequency power supply 16 is turned on and a high frequency voltage of 20 MHz to 500 MHz, preferably 30 MHz to 100 MHz is applied between the parallel plate electrodes 12 and 15 to generate plasma. On the other hand, 20 V to 800 V from the pulse bias power supply 17 to the lower electrode 15 with a period of 0.1 μs
A positive pulse bias voltage of 10 μs to 10 μs, preferably 0.2 μs to 5 μs is applied to control the plasma in the processing chamber 10 to etch the sample 40.

By applying such a pulse bias voltage, ions in the plasma or ions and electrons are accelerated and vertically incident on the sample, thereby performing highly accurate shape control or selection ratio control. The characteristics required for the pulse bias power supply 17 and the electrostatic adsorption film 22 are the same as those in the embodiment of FIG.

In the embodiments of the present invention described above, there is a possibility that interference may occur between the output of the pulse bias power supply and the output of the plasma generating power supply. So,
I will talk about this measure.

First, in an ideal rectangular pulse having a pulse width: T ₁ and a pulse period: T ₀ and an infinite rise / fall speed, as shown in FIG. 11, f ≦ 3f ₀ (f ₀ = (1
/ T ₁ )) frequency range includes about 70 to 80% of electric power. The waveform actually applied has a finite rise / fall rate, so the power convergence is further improved, and f ≦ 3.
The frequency range of f ₀ can include about 90% or more of electric power.

In order to uniformly apply a pulse bias having a high frequency component of 3f ₀ to the sample surface, a counter electrode substantially parallel to the sample is provided, and 3f ₀ obtained by the following equation 2 is obtained. Therefore, it is desirable to ground the frequency component in the range of f ≦ 3f ₀ .

[0090]

[Equation 2]

FIG. 12 shows an embodiment of the parallel plate electrode plasma etching apparatus shown in FIG. 1 in which measures against interference between the pulse bias power source output and the plasma generating power source output are taken. In this parallel plate electrode plasma etching apparatus, a high frequency power supply 16 for plasma generation is connected to the upper electrode 12 facing the sample 40. In order to bring the upper electrode 12 to the ground level of the pulse bias, the frequency f ₁ of the high frequency power source 16 for plasma generation is set to be larger than the above 3f ₀ , and the impedance in the vicinity of f ≦ f ₁ is large, so that the other frequencies are Then, the band eliminator 141 having a low impedance is connected between the upper electrode 12 and the contact level.

On the other hand, a bandpass filter 142 having a low impedance near f = f ₁ and a high impedance at other frequencies is installed between the sample stage 15 and the ground level. With such a configuration, the pulse bias power supply 1
The interference between the output of No. 7 and the output of the plasma generating power supply 16 can be suppressed to a level without a problem, and a good bias can be applied to the sample 40.

FIG. 13 shows an example in which the present invention is applied to a plasma etching apparatus of an inductively coupled discharge method and a non-magnetic field type among external energy supply discharge methods. 52
Is a flat coil, 54 is a flat coil with 10 MHz to 250 MHz
It is a high frequency power supply for applying a high frequency voltage of z. Compared with the parallel plate type shown in FIG. 10, the inductively coupled discharge method enables stable plasma generation at a low frequency and low pressure.
On the contrary, since the dissociation easily proceeds, as shown in FIG. 1, the output of the high frequency power source 1 is changed to the high frequency power source modulation signal source 161.
Can be modulated, and unnecessary dissociation can be prevented. The processing chamber 10 serving as a vacuum container includes a sample table 15 on which the sample 40 is placed on the electrostatic adsorption film 22.

When performing the etching process, the sample 40 to be processed is placed on the sample table 15 and held by electrostatic force.
While the processing gas is introduced into the processing chamber 10 from a gas supply system (not shown) at a predetermined flow rate, the pressure in the processing chamber 10 is set to 5 mTorr to 40 m by evacuating by the vacuum pump.
Evacuate to Torr. Next, set the high frequency power source 54 to 13.5
A high frequency voltage of 6 MHz is applied to generate plasma in the processing chamber 10. The sample 40 is etched using this plasma. On the other hand, during etching, the lower electrode 15
Period is 0.1 μs to 10 μs, preferably 0.2 μs to 5 μs
The pulse bias voltage of is applied. The range of the amplitude of the pulse bias voltage varies depending on the film type, as described in the embodiment of FIG. By applying the pulse bias voltage, ions in the plasma are accelerated and vertically incident on the sample, thereby performing highly accurate shape control or selection ratio control. As a result, even if the resist mask pattern of the sample is extremely fine, highly accurate etching processing can be performed.

FIG. 14 shows a schematic diagram of the inductively coupled discharge type non-magnetic field type plasma etching apparatus shown in FIG.
A Faraday shield plate 53 having a gap 55 and a thin shield plate protection insulating plate 54 of 0.5 mm to 5 mm are installed on the processing chamber side 10 of the induction electric high frequency output, and the Faraday shield plate 53 is grounded. By installing the Faraday shield plate 53, the capacitance component between the coil and the plasma is reduced, and the energy of the ions hitting the quartz plate under the coil 52 in FIG. 13 and the shield plate insulating plate 54 in FIG. 14 can be reduced. It is possible to reduce damage to the quartz plate and the insulating plate and prevent foreign matter from entering the plasma.

Further, since the Faraday shield plate 53 also serves as the ground electrode of the pulse bias power supply 17, the pulse bias can be applied uniformly between the sample 40 and the Faraday shield plate 53. In the example of FIG. 14,
No parallel plate type upper electrode or a filter installed on the sample table 15 is required.

FIG. 15 is a vertical sectional front view of a part of an apparatus in which the present invention is applied to a microwave plasma processing apparatus. The lower electrode 15 as the sample table 15 on which the sample 40 is placed on the electrostatic adsorption film 22 has a pulse bias power supply 1
7 and the DC power supply 13 are connected. Reference numeral 41 is a magnetron as a microwave oscillation source, 42 is a microwave waveguide, and 43 is a quartz plate for vacuum-sealing the processing chamber 10 and supplying microwaves to the processing chamber 10. 47
Is a first solenoid coil for supplying a magnetic field, and 48 is a second solenoid coil for supplying a magnetic field. A processing gas supply system 49 supplies a processing gas for performing processing such as etching and film formation into the processing chamber 10. In addition, the processing chamber 10
Is evacuated by a vacuum pump (not shown). The characteristics required for the pulse bias power supply 17 and the electrostatic chuck 20 are the same as those in the embodiment of FIG.

When performing the etching process, the sample 40 to be processed is placed on the sample table 15 and held by electrostatic force.
The pressure of the processing chamber 10 is reduced to 5 mTorr to 40 mTorr by evacuating the processing chamber 10 from the gas supply system 49 to the processing chamber 10 at a predetermined flow rate while evacuating the processing chamber 10 by vacuum. Next, the magnetron 41 and the first and second solenoid coils 47 and 48 are turned on, and the microwave generated in the magnetron 41 is fed from the waveguide 42 to the processing chamber 10.
To generate plasma. The sample 40 is etched using this plasma. On the other hand, during etching, the lower electrode 15 has a period of 0.1 μs to 10 μs.
A pulse bias voltage of 0.2 μs to 5 μs is preferably applied.

By applying such a pulse bias voltage, ions in the plasma are accelerated and vertically incident on the sample, thereby performing highly precise shape control or selection ratio control. As a result, even if the resist mask pattern of the sample is extremely fine, a highly accurate etching process corresponding to the mask pattern can be performed by vertical incidence.

In the plasma etching apparatus of the present invention shown in FIG. 1 and subsequent figures, the DC voltage of the electrostatic adsorption circuit and the pulse voltage of the pulse bias power supply circuit are superposed and generated,
The circuits can be configured in common. Further, the electrostatic attraction circuit and the pulse bias power supply circuit may be separately provided on different electrodes so that the pulse bias does not affect the electrostatic attraction.

Instead of the electrostatic attraction circuit in the embodiment of the parallel plate plasma etching apparatus shown in FIG. 1, other attraction means such as vacuum attraction means can be used as shown in FIG. First, set the pressure in the processing chamber to 5 mTorr to 4
Evacuate to 0 mTorr. Next, a high frequency voltage is applied to the high frequency power source to generate plasma in the processing chamber 10. The sample 40 is etched using this plasma. On the other hand,
During etching, the lower electrode 15 has a period of 0.1 μs
A pulse bias voltage of 10 μs to preferably 0.2 μs to 5 μs is applied. By applying such a pulse bias voltage, ions in the plasma are accelerated and vertically incident on the sample, thereby performing highly accurate shape control or selection ratio control.

In this case, as the characteristic of the voltage supplied from the pulse bias power supply circuit, it is not necessary to consider the influence of the electrostatic attraction circuit, and the voltage characteristic suitable for highly accurate shape control or selection ratio control is provided. It should be done. As a result, even if the mask pattern of the sample is extremely fine,
It is possible to perform highly accurate etching processing corresponding to the mask pattern.

Next, a plasma etching apparatus capable of independently controlling ions and radicals according to another embodiment of the present invention shown in FIG. 17 will be described. In plasma processing, it is important to properly control the amount of ions, the amount of radicals, and the radical species for improving the performance. Conventionally, a gas serving as an ion source or a radical source is caused to flow into the processing chamber, plasma is generated in the processing chamber, and ions and radicals are simultaneously generated. However, as the processing of the sample becomes finer, its limit is becoming apparent.

The embodiment of FIG. 17 is intended to improve this conventional defect and to enable ultrafine plasma processing. In addition to the parallel plate plasma etching apparatus shown in FIG. A gas supply source 60 and a plasma generation chamber 62 for generating radicals are provided.

The features of this embodiment are as follows. The radical source gas supplied from the radical source gas supply source 60 is turned into plasma in the radical generating plasma generation chamber 62, and a desired amount of desired radicals is generated in advance. Then, this radical is caused to flow into the processing chamber 10. On the other hand, the ion source gas is caused to flow into the processing chamber 10 from the ion source gas supply source 36.

A high frequency is output from the plasma generation power source 16 to generate plasma having a low electron temperature (5 eV or less, preferably 3 eV or less) in the processing chamber 10 to generate ions. It should be noted that although the introduced radicals are partially dissociated by the plasma generated in the processing chamber 10, by suppressing the electron temperature of the generated plasma to a low value of about 5 eV or less, re-dissociation of the introduced radicals can be prevented. It can be suppressed to a small value.

By providing a plasma generation source for radical generation that generates radicals separately from the plasma generation source of the processing chamber 10 that mainly generates ions, it is possible to independently control ions and radicals to a desired quality and amount. Therefore, good performance can be obtained even in ultrafine plasma processing.

The plasma generation chamber 62 for generating radicals
Is a processing chamber 1 that mainly generates ions in the processing chamber 10.
It may be provided separately from the zero plasma generation source.

Next, FIG. 18 shows another embodiment of the present invention in which ions and radicals are independently controlled. In FIG. 18, a fluorocarbon gas such as CHF3, CH2F2, C4F8, or CF4 is mixed with a gas containing C and H (C2H4, CH3OH, etc.) if necessary, and the portion A in FIG. It is placed in the plasma generating chamber 62 for generating radicals.

In the plasma generating chamber 62 for generating radicals,
The output of the RF power source 63 of several MHz or several tens of MHz is applied to the coil 65, and several 100 mTorr to several 10 T
Plasma is generated with a gas pressure of orr, and mainly CF2 radicals are generated. CF3 and F generated at the same time are reduced by the H component.

The plasma generation chamber 62 for generating radicals
Since it is difficult to drastically reduce the components such as CF and O, the unnecessary component removing chamber 65 is provided after this. here,
Carbon and materials containing Si (carbon, Si, SiC
Etc.) is installed to reduce unnecessary components or convert them to another gas with less adverse effects. Unnecessary component removal chamber 65
Is connected to a valve 71 to supply a gas composition containing CF2 as a main component.

Between the valve 70 and the valve 71,
Many deposits such as deposits accumulate, so cleaning and replacement are required in a relatively short period of time. Therefore, in order to facilitate opening to the atmosphere and replacement, and for shortening the vacuum rise time at the time of restart, the exhaust device 74 is connected via the valve 72. The exhaust device 74 may also be used as an exhaust device for the processing chamber 10.

An ion source gas (a rare gas such as argon gas or xenon gas) B is connected to the outlet of the valve 71 and supplied to the processing chamber via the valve 73.

The processing chamber 10 is maintained at a pressure of 5-40 mT,
By the modulated high frequency power source 16 of 20MHz or more,
A high density low electron temperature plasma of 10 10 to 11 11 / cm 3 is generated at 5 eV, preferably 3 eV or less, while avoiding dissociation of CF 2 which requires dissociation energy of 8 eV or more, while ionizing the gas for ion source. To proceed. As a result, on the surface of the sample 40, the following reaction, which is assisted by the injection of ions accelerated by the bias power supply 17 at several 100 V, mainly progresses.

SiO2 + 2CF2 → SiF4 ↑ + 2CO ↑ Since Si and SiN, which are the base materials, are not etched by CF2, the oxide film can be etched with a high selectivity.

The increase in F due to partial dissociation of CF2 is reduced by the upper electrode cover 30 made of silicon, carbon, SiC or the like.

As described above, by adjusting the radical source gas A and the ion source gas B, the processing chamber 10
The ratio of ions and radicals in the interior can be controlled almost independently, and the reaction on the surface of the sample 40 can be controlled to a desired one.
It became easier to do. In addition, unnecessary depot components and the like are removed in the unnecessary component removal chamber 65 and are not brought into the processing chamber 10 as much as possible, so that the depot in the processing chamber 10 is significantly reduced and the processing chamber 10 is exposed to the atmosphere. The frequency of cleaning that is open to the public was also greatly reduced.

Next, FIG. 19 shows another embodiment in which ions and radicals are independently controlled. Hexafluoropropylene oxide (CF3CFOCF2, hereinafter abbreviated as HFPO) from A via the valve 70 and the heating pipe portion 66.
Through the unnecessary component removing chamber 65 and the valve 71, mixed with the ion source gas B, and sent to the processing chamber 10. In the heating pipe section 66, HFPO is heated to 800 ° C. to 1000 ° C. and CF2 is generated by the following thermal decomposition.

CF3CFOCF2 → CF2 + CF3CFO CF3CFO is a relatively stable substance and is difficult to decompose, but since it partially decomposes to generate unnecessary O and F, the heating pipe portion 6
After 6, the unnecessary component removing chamber 65 is provided to remove unnecessary components,
Alternatively, it is converted into a substance that does not have an adverse effect. Some C
F3CFOCF2 flows into the processing chamber 10 without being decomposed, but it does not cause a problem because it is not dissociated by plasma having a low electron temperature of 5 eV or less.

The method of using the valve 72 and the exhaust device 74 and the reaction in the processing chamber 10 are the same as in the case of FIG.

The plasma processing apparatus of the present invention provided with the electrostatic adsorption circuit and the pulse bias voltage application circuit is limited to the above-mentioned etching processing by making changes such as introducing the CVD gas instead of the etching gas. Instead, it can be applied to a plasma processing apparatus such as a CVD apparatus.

[0122]

According to the present invention, a film for electrostatic attraction is provided.
Apply a pulse bias voltage to the sample holder
Spreading of ion energy distribution during plasma processing
Can be suppressed .

[0123]

[0124]

[0125]

[0126]

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a parallel plate electrode type plasma etching apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a frequency of a power supply for plasma generation and a stable discharge minimum gas pressure.

FIG. 3 is a diagram showing an example of a desirable output waveform used in the pulse bias power supply of the present invention.

FIG. 4 is a diagram showing a probability distribution of an ion energy and a potential waveform on a sample surface when T ₀ is changed while keeping a pulse duty ratio (T ₁ / T ₀ ) constant.

FIG. 5 is a diagram showing a potential distribution on a sample surface and a probability distribution of ion energy when T ₀ is changed while keeping a pulse duty ratio constant.

FIG. 6 is a diagram showing the relationship between the pulse off (T ₀ -T ₁ ) period and the maximum voltage V _CM during one cycle of the voltage generated across the electrostatic adsorption film.

FIG. 7 is a diagram showing a relationship between a pulse duty ratio and (V _DC / v _p ).

FIG. 8 is a diagram showing ion energy dependence of etching rates ESi and ESiO ₂ of silicon and a chloride film when chlorine gas of 5 mT is turned into plasma.

FIG. 9: CF4 gas 5 mT as an example of etching an oxide film
FIG. 3 is a diagram showing an ion energy distribution of an etching rate ESiO ₂ between an oxide film and silicon and ESi when plasma is generated.

FIG. 10 is a vertical cross-sectional view of a parallel plate electrode type plasma etching apparatus according to another embodiment of the present invention.

FIG. 11 is a diagram showing a relationship between a frequency of a pulse bias power supply and accumulated power.

FIG. 12 is a vertical cross-sectional view of another embodiment in which the parallel plate electrode plasma etching apparatus shown in FIG. 1 is improved.

FIG. 13 is a vertical cross-sectional view of an example in which the present invention is applied to a plasma etching apparatus of an inductively coupled discharge method and a non-magnetic field type among external energy supply discharge methods.

FIG. 14 is a vertical sectional view of a plasma etching apparatus according to another embodiment of the present invention.

FIG. 15 is a vertical cross-sectional front view of a part of an apparatus in which the present invention is applied to a microwave plasma processing apparatus.

FIG. 16 is a vertical sectional view of a parallel plate plasma etching apparatus according to another embodiment of the present invention.

FIG. 17 is a vertical cross-sectional view of a parallel plate electrode plasma etching apparatus capable of independently controlling ions and radicals according to another embodiment of the present invention.

FIG. 18 is a vertical cross-sectional view of a parallel plate electrode plasma etching apparatus capable of independently controlling ions and radicals according to another embodiment of the present invention.

FIG. 19 is a partial detailed view of a parallel plate electrode plasma etching apparatus capable of independently controlling ions and radicals according to another embodiment of the present invention.

[Explanation of symbols]

10 ... Processing chamber, 12 ... Upper electrode, 15 ... Lower electrode, 16
... high frequency power supply, 17 ... pulse bias power supply, 20 ... electrostatic chuck, 22 ... electrostatic attraction film, 23 ... DC power supply, 40 ...
sample.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toru Otsubo, Toru Otsubo 502 Jinrachi-cho, Tsuchiura-shi, Ibaraki Machinery Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-5-275521 (JP, A) JP-A-6- 252097 (JP, A) JP 3-179733 (JP, A) JP 7-74145 (JP, A) JP 5-304115 (JP, A) JP 7-263412 (JP, A) JP-A-6-61182 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/3065 C23C 16/509 C23F 4/00 H01L 21/68

Claims (2)

(57) [Claims] 1. A vacuum processing chamber, a plasma generating means for generating plasma in the vacuum processing chamber, a sample table provided in the vacuum processing chamber for placing a sample to be processed, and the sample table holding the sample. In a plasma processing apparatus having electrostatic attraction means and pulse bias application means connected to the sample stage and applying a pulse bias voltage to the sample stage, the voltage of the electrostatic attraction means is 1 of the pulse bias voltage.
The period of the pulse bias voltage is set to be equal to or less than / 2.
The pulse bias voltage is set to 0.2 μs to 10 μs.
Duty ratio is 40% or less and pulse width is 0.05
A plasma processing apparatus having a length of μs or more . 2. A sample to be processed is placed on a sample table provided in a vacuum processing chamber, the sample to be processed is held by electrostatic attraction, plasma is generated in the processing chamber, and a pulse bias is applied to the sample table. In the plasma processing method of applying a voltage to perform plasma processing on the sample, the electrostatic attraction voltage is 1/2 of the pulse bias voltage.
The period of the pulse bias voltage is set to be as follows .
2 μs to 10 μs, and the pulse bias voltage
Set the duty ratio to 40% or less and set the pulse width to 0.0.
A plasma processing method, characterized in that the processing time is 5 μs or more .