JP2000323460A - Plasma etching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma etching device which is capable of more finely etching a work by the use of a plasma of high density and making an electric field distribution more uniform on the surface of an electrode so as to make the plasma uniform in density and the etching rate distribution uniform. SOLUTION: A first and a second electrode, 21 and 5, are arranged confronting each other in a chamber 2 where a target substrate W is housed, the substrate W is supported on the second electrode 5, a power of high frequency of above 27 MHz is applied to the first electrode 21 from a high-frequency power supply 40, a DC voltage is applied to the first electrode 21 from a DC power supply 43, by which a high-frequency electric field is formed between the first and second electrode to produce processing gas plasma, and the substrate W is subjected to plasma etching by the use of the above gas plasma.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a plasma etching apparatus for performing a plasma etching process on a substrate such as a semiconductor substrate.

[0002]

2. Description of the Related Art For example, in a semiconductor device manufacturing process, a plasma etching process is employed to form a circuit on a semiconductor wafer which is a substrate to be processed.
Various apparatuses are used as apparatuses for performing the plasma etching process, and among them, a capacitively coupled parallel plate plasma etching apparatus is mainly used.

In a capacitively coupled parallel plate plasma etching apparatus, a pair of parallel plate electrodes (upper and lower electrodes) are arranged in a chamber, a processing gas is introduced into the chamber, and a high frequency is applied to one of the electrodes. A high-frequency electric field is formed between the electrodes, and a plasma of a processing gas is formed by the high-frequency electric field to perform a plasma etching process on the semiconductor wafer.

When a film on a semiconductor wafer, for example, an oxide film, is etched by such a capacitively coupled parallel plate plasma etching apparatus, the pressure inside the chamber is set to a medium pressure, and a medium density plasma is formed. Control is possible, whereby an appropriate plasma state can be obtained, and etching with high selectivity, high stability and high reproducibility is realized.

However, in recent years, the design rule in the USLI has been increasingly miniaturized, and a hole shape having a higher aspect ratio has been demanded. In the etching of an oxide film or the like, the conventional conditions are not always sufficient. It is getting.

Therefore, attempts have been made to increase the frequency of the high-frequency power to be applied to form high-density plasma while maintaining a good plasma dissociation state. Accordingly, it is considered that an appropriate plasma can be formed under lower pressure conditions, so that it is possible to appropriately cope with further miniaturization of design rules.

[0007]

According to the results of the study by the present inventors, when the density of the plasma is increased in this way, the non-linear characteristics of the plasma appear remarkably, and the harmonics of the reflected wave from the plasma are reduced. Increase, electrode diameter is φ250 ~ φ3
In the case of 00, it was found that such a harmonic generated a standing wave on the electrode surface, and the electric field distribution on the electrode surface became non-uniform.

When the electric field distribution becomes non-uniform as described above, the plasma density becomes non-uniform, and as a result, the etching rate distribution becomes non-uniform. Therefore, it is necessary to eliminate the cause of the non-uniform electric field distribution and make the etching rate distribution uniform. Is required.

However, conventionally, the problem in the case of using such a high-density plasma has not always been clearly recognized, and attempts to eliminate the above-mentioned non-uniform electric field distribution have not been sufficiently made. Not done.

The present invention has been made in view of the above circumstances, and in plasma etching processing using high-density plasma capable of coping with further miniaturization, the non-uniformity of the electric field distribution on the electrode surface is reduced to reduce the plasma density. It is an object of the present invention to provide a plasma etching apparatus which can make the etching rate uniform and the etching rate distribution is uniform.

[0011]

According to the present invention, there is provided a chamber for accommodating a substrate to be processed,
First and second electrodes provided so as to face each other in a chamber, high-frequency applying means for applying a high-frequency having a frequency of 27 MHz or more to the first electrode, and applying a DC voltage to the first electrode DC voltage applying means, exhaust means for maintaining the inside of the chamber at a predetermined reduced pressure, and processing gas introducing means for introducing a processing gas into the chamber, wherein the substrate to be processed is placed on the second electrode. A plasma etching process for forming a plasma of a processing gas by forming a high-frequency electric field between the first and second electrodes in the supported state, and performing a plasma etching process on the substrate to be processed by the plasma; Provide equipment.

The present invention also provides a chamber for accommodating a substrate to be processed, first and second electrodes provided in the chamber so as to face each other, and 27 MH
a first high-frequency application unit that applies a high frequency having a frequency equal to or higher than z, a second high-frequency application unit that applies a high frequency that is lower than the frequency of the first high-frequency application unit to the first electrode, An exhaust unit that maintains the inside of the chamber at a predetermined reduced pressure state; and a processing gas introduction unit that introduces a processing gas into the chamber, wherein the second electrode supports the substrate to be processed, A plasma etching apparatus is characterized in that plasma of a processing gas is formed by forming a high-frequency electric field between the first and second electrodes, and a plasma etching process is performed on a substrate to be processed by the plasma.

The frequency of the second high-frequency applying means is 2 to
Preferably, it is 10 MHz. In any of the plasma etching apparatuses described above, it is preferable that the plasma etching apparatus further includes a high frequency applying unit that applies a high frequency of 100 kHz to 10 MHz to the second electrode.

As described above, since the harmonics from the plasma form a standing wave in the plane of the upper electrode (first electrode), the electric field distribution on the surface of the upper electrode becomes non-uniform. Therefore, the plasma sheath of the upper electrode becomes thinner at the center of the electrode, and the self-bias voltage on the electrode surface becomes non-uniform. In other words, since the standing wave has a large amplitude at the center of the electrode, the standing wave affects the electric field distribution of the upper electrode and contributes to the plasma near the upper electrode. Thinner than At this time, when the frequency applied to the upper electrode is relatively low, that is, 27 MHz
If it is less than 3, the self-bias voltage (V _dc ) is large and the plasma sheath is thick, so that the standing wave has little effect on the plasma uniformity. In addition, since the wavelength of the high frequency is large and the wavelength of the harmonic is also large, a standing wave which affects the plasma processing is not easily generated.

However, when the frequency of the high frequency applied to the upper electrode increases to 27 MHz or more, the self-bias voltage (V _dc ) on the electrode surface also decreases, and as a result, the overall thickness of the plasma sheath decreases, and As the plasma sheath at the center of the electrode becomes thinner due to the non-uniformity of the self-bias voltage (V _dc ) due to the waves, the rate of change in the plasma sheath thickness increases, and the uniformity of the plasma deteriorates.

On the other hand, in the present invention, a high frequency having a frequency of 27 MHz or more is applied to the first electrode and a DC voltage is further applied to the first electrode. As the voltage (V _dc ) increases, the thickness of the plasma sheath increases, and the degree of non-uniformity of the plasma sheath due to non-uniformity of the self-bias voltage (V _dc ) can be reduced. Therefore, the plasma density can be made uniform, and the etching rate distribution can be made uniform.

Further, in another aspect of the present invention, the first aspect
A high frequency having a frequency of 27 MHz or more is applied to the first electrode from the first high frequency applying means, and a high frequency having a frequency lower than the frequency of the first high frequency applying means is applied to the first electrode from the second high frequency applying means. I do. The self-bias voltage due to the high frequency applied from the second high frequency applying means is higher than the self-bias voltage due to the high frequency applied from the first high frequency applying means. An extremely large self-bias voltage (V _dc ) can be obtained as compared with the case of only the high frequency applied from the means, the plasma sheath becomes thick, and the plasma sheath becomes uneven due to the non-uniformity of the self-bias voltage (V _dc ) due to the standing wave. The degree of non-uniformity can be reduced. Therefore, the plasma density can be made uniform, and the etching rate distribution can be made uniform.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view schematically showing an etching apparatus according to the first embodiment of the present invention. This etching apparatus 1 is configured as a capacitive parallel plate etching apparatus in which electrode plates are vertically opposed to each other and one side is connected to a power supply for plasma formation.

The plasma etching apparatus 1 has a cylindrical chamber 2 made of aluminum whose surface is anodized (anodized), for example, and the chamber 2 is grounded. A substantially columnar susceptor support 4 for mounting an object to be processed, for example, a semiconductor wafer (hereinafter, referred to as “wafer”) W, is provided on the bottom of the chamber 2 via an insulating plate 3 made of ceramic or the like.
And a susceptor 5 constituting a lower electrode is provided on the susceptor support 4.
The susceptor 5 is connected to a high-pass filter (HPF) 6 for passing a high frequency of 60 MHz described later.

A refrigerant chamber 7 is provided inside the susceptor support 4. In the refrigerant chamber 7, a refrigerant such as liquid nitrogen is introduced and circulated through a refrigerant introduction pipe 8. Cold heat is transferred to the wafer W via the susceptor 5, whereby the processing surface of the wafer W is controlled to a desired temperature.

The susceptor 5 is formed in a disc shape having a convex upper center portion, and an electrostatic chuck 11 having substantially the same shape as the wafer W is provided thereon. The electrostatic chuck 11 has an electrode 12 interposed between insulating materials. When a DC voltage of, for example, 1.5 kV is applied from a DC power supply 13 connected to the electrode 12, the electrostatic chuck 11 holds the wafer W by, for example, Coulomb force. Adsorb electrostatically.

The insulating plate 3, the susceptor support 4, the susceptor 5, and the electrostatic chuck 11
A heat transfer medium, for example, H
A gas passage 14 for supplying e-gas or the like is formed, and the cool heat of the susceptor 5 is transmitted to the wafer W via the heat transfer medium, so that the wafer W is maintained at a predetermined temperature.

An annular focus ring 15 is arranged on the peripheral edge of the upper end of the susceptor 5 so as to surround the wafer W mounted on the electrostatic chuck 11. The focus ring 15 is made of a conductive material such as silicon, so that the uniformity of etching is improved.

An upper electrode 21 is provided above the susceptor 5 so as to face the susceptor 5 in parallel. The upper electrode 21 is connected to the chamber 2 via an insulating material 25.
And an electrode plate 23 having a surface facing the susceptor 5 and having a large number of discharge holes 24, and a conductive material that supports the electrode plate 23, such as aluminum whose surface is anodized. And an electrode support 22 having a water cooling structure. The susceptor 5 serving as the lower electrode and the upper electrode 21 are, for example, 10 to 60 mm in length.
It is about a distance apart.

The electrode support 22 of the upper electrode 21
Is provided with a gas inlet 26, and a gas supply pipe 27 is connected to the gas inlet 26. The gas supply pipe 27 is further connected to a processing gas via a valve 28 and a mass flow controller 29. A source 30 is connected. A processing gas for etching is supplied from a processing gas supply source 30.

[0026] As the processing gas, it is possible to employ any of various conventionally used, for example, fluorocarbon gas (C x _{F y)} and hydrofluorocarbon gases (C _p
H q _{F r)} a halogen element such as can be suitably used a gas containing a. In addition, rare gases such as Ar and He and N
₂ may be added.

An exhaust pipe 31 is connected to the bottom of the chamber 2, and an exhaust device 35 is connected to the exhaust pipe 31. The exhaust device 35 is provided with a vacuum pump such as a turbo-molecular pump, so that the inside of the chamber 2 can be evacuated to a predetermined reduced-pressure atmosphere, for example, a predetermined pressure of 1 Pa or less. Further, a gate valve 32 is provided on a side wall of the chamber 2, and the wafer W is transferred to and from an adjacent load lock chamber (not shown) with the gate valve 32 opened. ing.

A high frequency power supply 40 for plasma formation is connected to the upper electrode 21 via a matching unit 41. The high-frequency power supply 40 has a high frequency of 27 MHz or more. By applying such a high frequency, a high-density plasma can be formed in a preferable dissociated state in the chamber 2 under low-pressure conditions. Is possible. In this example, the high frequency power supply 40
Hz. Further, a DC power supply 43 for increasing the self-bias voltage (V _dc ) of the upper electrode 21 is connected to the upper electrode 21 via a low-pass filter (LPF) 44 that passes only DC. Further, since a capacitor (not shown) is provided in series in the matching unit 41, the high-frequency power supply 40 and the DC power supply 43 do not collide with each other.

The susceptor 5 serving as the lower electrode is connected to a high-frequency power supply 50 for attracting ions, and a matching unit 51 is interposed in the power supply line. The second high-frequency power supply 50 has a frequency in the range of 100 kHz to 10 MHz, and by applying a frequency in such a range, an appropriate frequency can be obtained without damaging the wafer W to be processed. It can give an ionic effect.
In this example, a frequency of 2 MHz is used.

Next, the processing operation in the plasma etching apparatus 1 configured as described above will be described. First, after the gate valve 32 is opened, the wafer W to be processed is carried into the chamber 2 from a load lock chamber (not shown) and is placed on the electrostatic chuck 11.
The wafer W is electrostatically attracted onto the electrostatic chuck 11 by applying a DC voltage from the high-voltage DC power supply 13. Next, the gate valve 32 is closed, and the inside of the chamber 2 is evacuated to a predetermined degree of vacuum by the exhaust device 35.

Thereafter, the valve 28 is opened and the processing gas is supplied from the processing gas supply source 30 to the mass flow controller 2.
9, while the flow rate is adjusted, the processing gas supply pipe 2
7. The gas is introduced into the upper electrode 21 through the gas introduction port 26, and is further uniformly discharged through the discharge hole 24 of the electrode plate 23 to the wafer W as shown by an arrow in FIG.
The pressure in the chamber 2 is maintained at a predetermined value.

Then, after that, the high frequency power supplies 40 to 27
MHz or higher, for example, 60 MHz,
Is applied to As a result, a high-frequency electric field is generated between the upper electrode 21 and the susceptor 5 as the lower electrode, and the processing gas is dissociated into plasma, and the wafer W is subjected to an etching process by the plasma.

On the other hand, from the high frequency power supply 50, 100 kHz
A high frequency of z to 10 MHz, for example, 2 MHz is applied to the susceptor 5 serving as a lower electrode. Thereby, the ions in the plasma are attracted to the susceptor 5 side, and the anisotropy of the etching is enhanced by the ion assist.

As described above, by setting the frequency of the high frequency applied to the upper electrode 21 to 27 MHz or more, the plasma density can be increased. The generation of the standing wave causes an uneven electric field on the lower surface of the electrode plate 23.

That is, when only the high-frequency power supply 40 is used, the harmonics from the plasma form a standing wave on the surface of the upper electrode 21, and the electric field distribution on the surface of the upper electrode becomes uneven. The frequency of the high frequency applied to the upper electrode is 27 MHz
When the voltage becomes higher than the above, the self-bias voltage (V
_dc ) is also reduced, and as a result, as shown in FIG. 2A, the entire thickness of the plasma sheath S of the upper electrode 21 is reduced. As the plasma sheath at the center of the electrode becomes thinner, the rate of change in the plasma sheath thickness increases and the self-bias voltage on the electrode surface becomes non-uniform.
As a result, the uniformity of the plasma deteriorates.

On the other hand, as described above, the upper electrode 21
By applying a high frequency of a frequency higher than 27 MHz from the high frequency power supply 40 and applying a DC voltage from the DC power supply 43, as shown in FIG. (V _dc ) increases, and its contribution S ₁ forms a thicker plasma sheath S ′, and the degree of non-uniformity of the self-bias voltage (V _dc ) and non-uniformity of the plasma sheath can be reduced. . Therefore, the plasma density can be made uniform, and the etching rate distribution can be made uniform.

For example, from the high frequency power supply 40 to the electrode 21,
When a high-frequency power of 60 MHz and 1 kW is applied, V _dc = about -100 V, and if the variation of V _dc is about ± 10 V, the ratio of the variation becomes considerably large as ± 10%, and the uniformity of the plasma is increased. Is less effective.

However, from the DC power supply 43, for example, -40
When 0 V is applied, the entire _{Vdc is-} (100 + 40
0) V ± 10 V, and the variation ratio of _Vdc is ± 2
%, And the uniformity of _Vdc is improved. As a result, the uniformity of the plasma is also improved.

Next, a second embodiment of the present invention will be described. FIG. 3 is a sectional view schematically showing a plasma etching apparatus according to a second embodiment of the present invention. As in the first embodiment, this plasma etching apparatus 1 'is also configured as a capacitive parallel plate etching apparatus in which electrode plates are vertically opposed to each other and one side is connected to a power supply for plasma formation. 1 are basically denoted by the same reference numerals, and description thereof is omitted.

In the present embodiment, unlike the first embodiment, two high-frequency power supplies are connected to the upper electrode 21. That is, the first high-frequency power supply 6 for forming plasma through the high-pass filter (HPF) 62 and the matching unit 61.
0, and a low-pass filter 65 and a matching unit 6
4, a second high frequency power supply 63 is connected.

The first high-frequency power supply 60 has a high frequency of 27 MHz or more. By applying such a high frequency, a high-density plasma in a preferable dissociated state can be formed in the chamber 2. Thus, plasma processing under low pressure conditions becomes possible. In this example, a 60 MHz power supply is used as the first high frequency power supply 60.

The second high frequency power supply 63 has a lower frequency than the frequency of the first high frequency power supply 60,
The frequency is 10 MHz, and in this example, a frequency of 2 MHz is used. Since the second high frequency power supply 63 has a lower frequency than the first high frequency power supply 60, the upper electrode 21
_Has a function of increasing the self-bias voltage (V _dc ).

A high-pass filter (HPF) 62
Is for cutting frequencies below the frequency of the second high frequency power supply 63, and is a low-pass filter (LPF).
Numeral 65 is for cutting frequencies higher than the frequency of the first high frequency power supply 60.

In the plasma etching apparatus 1 'configured as described above, an etching process is basically performed similarly to the plasma etching apparatus 1 according to the first embodiment. In this case, as in the first embodiment, the upper electrode 2
The plasma density can be increased by setting the frequency of the high frequency applied to 1 to 27 MHz or more. However, only this is because the standing wave is generated on the lower surface of the electrode plate 23 by the harmonic of the reflected wave from the plasma. , Electrode plate 2
3 Non-uniformity of the electric field on the lower surface occurs.

Therefore, in this embodiment, instead of applying a DC voltage from a DC power supply, a high frequency having a frequency lower than that of the first high frequency power supply 60 is applied from the second high frequency power supply 63 to the upper electrode 21. Since the self-bias voltage due to the high frequency applied from the second high-frequency power supply 63 is higher than the self-bias voltage due to the high frequency applied from the first high-frequency power supply 60, the first and second high-frequency power supplies 60, 63
Is superimposed, a very high self-bias voltage (V _dc ) can be obtained as compared with a case where a high frequency is applied only from the first high-frequency power supply 60, and the contribution of the self-bias voltage (V _dc ) results in (b) of FIG. As in case (2), a thicker plasma sheath is formed and the self-bias voltage (V _dc ) is increased.
And the degree of non-uniformity of the plasma sheath can be reduced. Therefore, the plasma density can be made uniform, and the etching rate distribution can be made uniform.

For example, the first high-frequency power supply 60
1, when 60 MHz and 1 kW of high frequency power are applied, V _dc = about −100 V. If the variation of V _dc is about ± 10 V, the rate of variation is ± 10 V.
%, And the plasma uniformity is reduced.

However, the second high frequency power supply 63
When a high frequency power of, for example, 2 MHz and 500 W is superimposed on 1, V _dc by the second high frequency power supply 63 becomes −
It becomes about 400V, and the whole _{Vdc is-} (100 + 40
0) V ± _10V, and _the percentage of variation of _{V d c} is ± 2
%, And the uniformity of _Vdc is improved. As a result, the uniformity of the plasma is also improved.

The present invention is not limited to the above embodiment, but can be variously modified. For example, in the above embodiment, a high frequency is applied to the upper and lower electrodes, but a high frequency may be applied only to the upper electrode. Also, a case has been described in which a semiconductor wafer is used as a substrate to be processed and an oxide film on the wafer is etched. However, the present invention is not limited to this, and may be applied to other etching such as an insulating film other than an oxide film or polysilicon. Can be. Further, the substrate to be processed is not limited to the wafer, and may be another substrate such as a liquid crystal display (LCD) substrate.

[0049]

As described above, according to the present invention,
Since a high frequency of a frequency higher than 27 MHz is applied to the first electrode and a DC voltage is further applied to the first electrode, the self-bias voltage (V
_dc ) increases, the plasma sheath becomes thicker, and the degree of non-uniformity of the plasma sheath due to non-uniformity of the self-bias voltage (V _dc ) can be reduced. Therefore, the plasma density can be made uniform, and the etching rate distribution can be made uniform.

Further, a high frequency having a frequency higher than 27 MHz is applied to the first electrode from the first high frequency applying means, and the first high frequency is applied to the first electrode from the second high frequency applying means.
When a high frequency having a frequency lower than the frequency of the high frequency applying means is applied, the self-bias voltage due to the high frequency applied from the second high frequency applying means is equal to the self bias voltage due to the high frequency applied from the first high frequency applying means. Since these voltages are higher than the voltage, by superimposing them, it is possible to obtain a self-bias voltage (V _dc ) that is much larger than in the case of only the high frequency applied from the first high frequency applying means, and the plasma sheath becomes thicker. In addition, the degree of non-uniformity of the plasma sheath due to non-uniformity of the self-bias voltage (V _dc ) due to the standing wave can be reduced. Therefore, the plasma density can be made uniform, and the etching rate distribution can be made uniform.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a plasma etching apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining the principle of the present invention.

FIG. 3 is a sectional view showing a plasma etching apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

 Etching apparatus 2; chamber 5; susceptor (second electrode) 6, 62; high-pass filter 21; upper electrode (first electrode) 30; processing gas supply 35; exhaust device 40, 50, 60 , 63; high-frequency power supply 41, 51, 61, 64; matching device 43; DC power supply 44, 65; low-pass filter S, S '; plasma sheath W;

Continued on the front page F term (reference) 4K057 DA02 DA13 DA20 DB06 DD03 DE06 DE07 DE08 DE14 DM01 DM02 DM05 DM06 DM08 DM09 DM16 DM17 DM18 DM19 DM31 DM33 DM37 DM39 DN01 DN02 5F004 AA00 AA01 AA02 AA06 BA04 BA09 BB11 BB28 BB23 BB23 BB23 BC08 BD03 CA06 DA00 DA01 DA02 DA03 DA15 DA16 DA22 DA23 DA25 DB00 DB02 DB03 DB04 DB05 DB06 DB13 DB14

Claims (4)

[Claims] A chamber accommodating a substrate to be processed; first and second electrodes provided in the chamber so as to face each other; and a high frequency having a frequency of 27 MHz or more is applied to the first electrode. High-frequency applying means, direct-current voltage applying means for applying a direct-current voltage to the first electrode, exhaust means for maintaining the inside of the chamber in a predetermined reduced pressure state, and processing gas introducing means for introducing a processing gas into the chamber And forming a plasma of a processing gas by forming a high-frequency electric field between the first and second electrodes in a state where the substrate to be processed is supported by the second electrode. A plasma etching apparatus for performing a plasma etching process on a processing substrate. 2. A chamber for accommodating a substrate to be processed, first and second electrodes provided to face each other in the chamber, and a high frequency having a frequency of 27 MHz or more is applied to the first electrode. A first high-frequency applying unit, a second high-frequency applying unit that applies a high-frequency lower than the frequency of the first high-frequency applying unit to the first electrode, and maintaining the inside of the chamber at a predetermined reduced pressure state. And a processing gas introducing means for introducing a processing gas into the chamber, wherein a high frequency is applied between the first and second electrodes while the substrate to be processed is supported by the second electrode. A plasma etching apparatus, wherein plasma of a processing gas is formed by forming an electric field, and plasma processing is performed on a substrate to be processed by the plasma. 3. The frequency of said second high frequency applying means is 2
3. The plasma etching apparatus according to claim 2, wherein the frequency is 10 MHz to 10 MHz. 4. The frequency of 100 kHz to 10 M is applied to the second electrode.
4. The apparatus according to claim 1, further comprising a high frequency applying means for applying a high frequency of Hz.
Item 6. The plasma etching apparatus according to item 1.