JP4322350B2 - Plasma processing equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing apparatus for performing plasma processing on a substrate such as a semiconductor substrate.
[0002]
[Prior art]
For example, in a semiconductor device manufacturing process, plasma processing such as etching, sputtering, and CVD (chemical vapor deposition) is frequently used for a semiconductor wafer that is a substrate to be processed.
[0003]
Various plasma processing apparatuses for performing such plasma processing are used, and among them, a capacitively coupled parallel plate plasma processing apparatus is the mainstream.
[0004]
In a capacitively coupled parallel plate plasma processing 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 to provide a gap between the electrodes. A high frequency electric field is formed, plasma of a processing gas is formed by the high frequency electric field, and the semiconductor wafer is subjected to plasma processing.
[0005]
When etching a film on a semiconductor wafer, such as an oxide film, with such a capacitively coupled parallel plate plasma processing apparatus, optimum radical control is possible by forming a medium density plasma with the chamber inside at an intermediate pressure. Thus, an appropriate plasma state can be obtained, and etching with high stability and reproducibility is realized with a high selection ratio.
[0006]
However, in recent years, design rules in USLI have been further miniaturized, and a higher hole shape aspect ratio has been demanded, and conventional conditions for oxide film etching and the like are not necessarily sufficient.
[0007]
Thus, attempts have been made to form high-density plasma while increasing the frequency of the applied high-frequency power and maintaining a good plasma dissociation state. This makes it possible to form an appropriate plasma under a lower pressure condition, and is considered to be able to appropriately cope with further miniaturization of design rules.
[0008]
[Problems to be solved by the invention]
By the way, according to the examination result of the present inventor, when the density of the plasma is increased by increasing the frequency of the high frequency applied in this way, the non-linear characteristic of the plasma appears remarkably, and the reflected wave from the plasma has a harmonic. It has been found that when the electrode diameter is φ250 to φ300, a standing wave is generated on the electrode surface due to such harmonics, and the electric field distribution on the electrode surface becomes non-uniform.
[0009]
If the electric field distribution becomes non-uniform in this way, the plasma density becomes non-uniform, resulting in non-uniform etching rate distribution. Therefore, it is necessary to remove the cause of the non-uniform electric field distribution and make the etching rate distribution uniform. Become.
[0010]
However, in the past, the problems in the case of using such high-density plasma have not always been clearly recognized, and no attempt has been made yet to solve the above-described non-uniform electric field distribution. .
[0011]
The present invention has been made in view of such circumstances, and in plasma processing using high-density plasma that can cope with further miniaturization, the non-uniformity of the electric field distribution on the electrode surface is reduced and the plasma density is made uniform. An object of the present invention is to provide a plasma processing apparatus that can perform the above-described processing.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, the present invention includes a chamber in which a substrate to be processed is accommodated,
First and second electrodes provided to face each other in the chamber;
High frequency applying means for applying a high frequency to the first electrode;
The first electrode is disposed in contact with the end region of the surface facing the second electrode or the peripheral surface of the first electrode, has a ring shape, and generates harmonics of the frequency of the high-frequency applying means. A harmonic absorbing member to absorb,
An exhaust means for maintaining the inside of the chamber at a predetermined reduced pressure state;
A processing gas introduction means for introducing a processing gas into the chamber;
In a state where the substrate to be processed is supported by the first or second electrode, a plasma of a processing gas is formed by forming a high-frequency electric field between the first and second electrodes, and the substrate to be processed is generated by this plasma. A plasma processing apparatus is provided that is subjected to plasma processing.
[0013]
As described above, when the plasma is densified by increasing the frequency of the high frequency applied to the electrode, the harmonics of the reflected wave from the plasma are likely to be generated. When this harmonic wave returns to the high-frequency power source, it is reflected at the boundary between the electrode and the insulator, the feeding position, etc., and a standing wave is generated on the electrode surface. Since the standing wave has a large amplitude at the center of the electrode, the standing wave affects the electric field distribution on the electrode surface and contributes to the plasma near the electrode. Thinning and non-uniform plasma will be generated.
[0014]
In contrast, in the present invention, a high frequency is applied to the first electrode, and the first electrode is in contact with the end region of the surface of the first electrode facing the second electrode or the peripheral surface of the first electrode. Since a harmonic absorbing member that absorbs harmonics of the frequency of the high frequency applying means is disposed, the harmonic reflected from the plasma reaches the high frequency absorbing member before passing through the electrodes and returning to the high frequency power source. Is absorbed. Therefore, generation of standing waves due to harmonics can be effectively prevented, and nonuniformity of the electric field distribution on the electrode surface caused by the standing waves can be reduced and the plasma density can be made uniform.
[0015]
As the harmonic absorbing member, a laminate of harmonic absorbing members having different frequency characteristics can be used. Thereby, harmonics in a wide frequency band can be absorbed. Further, as the harmonic absorbing member, a member having a magnetic resonance loss effect can be used, and examples thereof include those containing ferrite. Furthermore, it is particularly suitable when the frequency of the high frequency applied to the first electrode is 27 MHz or more. That is, when the frequency of the applied high frequency is 27 MHz or more, the plasma density increases, and the influence of the standing wave becomes more remarkable. Furthermore, it is preferable to further have a high frequency applying means for applying a high frequency of 100 kHz to 10 MHz to the second electrode.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view schematically showing a plasma processing apparatus according to an embodiment of the present invention. The plasma processing apparatus 1 is configured as a capacitively coupled parallel plate etching apparatus in which electrode plates are opposed in parallel in the vertical direction, and a plasma forming power source is connected to one of them.
[0017]
This etching processing apparatus 1 has a chamber 2 formed into a cylindrical shape made of aluminum whose surface is anodized (anodized), for example, and this chamber 2 is grounded. A substantially cylindrical susceptor support 4 for placing an object to be processed, for example, a semiconductor wafer (hereinafter referred to as “wafer”) W, is provided at the bottom of the chamber 2 via an insulating plate 3 such as ceramic. Further, a susceptor 5 constituting a lower electrode is provided on the susceptor support 4. A high pass filter (HPF) 6 is connected to the susceptor 5.
[0018]
A refrigerant chamber 7 is provided inside the susceptor support 4, and a refrigerant such as liquid nitrogen is introduced into the refrigerant chamber 7 through a refrigerant introduction pipe 8 and circulated, and the cold heat is 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.
[0019]
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. In the electrostatic chuck 11, an electrode 12 is interposed between insulating materials, and a DC voltage of, for example, 1.5 kV is applied from a DC power source 13 connected to the electrode 12. Electrostatic adsorption.
[0020]
The insulating plate 3, the susceptor support 4, the susceptor 5 and the electrostatic chuck 11 are supplied with a gas for supplying a heat transfer medium, for example, He gas, to the back surface of the wafer W, which is an object to be processed. A passage 14 is formed, and the cold heat of the susceptor 5 is transmitted to the wafer W through the heat transfer medium so that the wafer W is maintained at a predetermined temperature.
[0021]
An annular focus ring 15 is disposed at the upper peripheral edge of the susceptor 5 so as to surround the wafer W placed on the electrostatic chuck 11. The focus ring 15 is made of a conductive material such as silicon, which improves the etching uniformity.
[0022]
An upper electrode 21 is provided above the susceptor 5 so as to face the susceptor 5 in parallel. The upper electrode 21 constitutes a surface facing the susceptor 5 and has an electrode plate 23 having a large number of discharge holes 24, and supports the electrode plate 23, and is made of a conductive material, for example, aluminum whose surface is anodized. It is comprised with the electrode support body 22 of a water cooling structure. An insulating material 25 is provided in a ring shape along the peripheral surface of the upper electrode 21. A ring-shaped harmonic absorbing member 51 is provided from the lower surface end region of the electrode plate 23 to the lower surface of the insulating material 25 so as to be in contact therewith. A ring-shaped insulating material 52 is provided so as to cover the partial region and the lower peripheral surface of the insulating material 25. The upper electrode 21 is supported by the chamber 2 by the insulating material 52. The susceptor 5 and the upper electrode 21 are separated from each other by about 10 to 60 mm, for example.
[0023]
The harmonic absorbing member 51 has a function of absorbing or attenuating harmonics reflected from the plasma from a high-frequency power source 40 to be described later. For example, such a function is realized by utilizing a magnetic resonance loss effect. As a material that absorbs harmonics using such a magnetic resonance loss effect, ferrite can be cited. As the harmonic absorbing member 51, a material containing ferrite can be suitably used. The frequency band to be absorbed can be adjusted by changing the thickness and material of the harmonic absorbing member 51. Moreover, the frequency band which absorbs can be expanded by laminating | stacking what has a different frequency characteristic and comprising the harmonic absorption member 51. FIG. In this way, standing waves can be effectively prevented by absorbing and attenuating harmonics of a desired frequency.
[0024]
A gas inlet 26 is provided in the electrode support 22 in the upper electrode 21, and a gas supply pipe 27 is connected to the gas inlet 26, and a valve 28, A processing gas supply source 30 is connected via the mass flow controller 29. A processing gas for plasma processing, for example, etching is supplied from the processing gas supply source 30.
[0025]
Various conventionally used gases can be employed as the processing gas, for example, a gas containing a halogen element such as a fluorocarbon gas (C _x F _y ) or a hydrofluorocarbon gas (C _p H _q F _r ). Can be suitably used. In addition, a rare gas such as Ar or He or N ₂ may be added.
[0026]
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 includes a vacuum pump such as a turbo molecular pump, and is configured 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 the side wall of the chamber 2, and the wafer W is transported between adjacent load lock chambers (not shown) with the gate valve 32 opened. ing.
[0027]
A first high frequency power supply 40 is connected to the upper electrode 21 via a matching device 41, and power supply at that time is performed by a power supply rod 33 connected to the center of the upper surface of the upper electrode 21. Further, a low pass filter (LPF) 42 is connected to the upper electrode 21. The first high-frequency power source 40 has a frequency of 27 MHz or higher. By applying such a high frequency, it is possible to form a high-density plasma in a preferable dissociated state in the chamber 2, Plasma processing under conditions is possible. In this example, a high frequency power supply 40 of 60 MHz is used.
[0028]
A second high frequency power supply 50 is connected to the susceptor 5 as the lower electrode, 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. By applying a frequency in such a range, the second high-frequency power supply 50 is appropriate without damaging the wafer W that is the object to be processed. An ionic effect can be imparted. In this example, a 2 MHz one is used.
[0029]
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 that is an object to be processed is loaded into the chamber 2 from a load lock chamber (not shown) and placed on the electrostatic chuck 11. The wafer W is electrostatically adsorbed on 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.
[0030]
Thereafter, the valve 28 is opened, and the processing gas from the processing gas supply source 30 is introduced into the upper electrode 21 through the processing gas supply pipe 27 and the gas inlet 26 while its flow rate is adjusted by the mass flow controller 29. Further, as shown by an arrow in FIG. 1 through the discharge hole 24 of the electrode plate 23, the wafer W is uniformly discharged, and the pressure in the chamber 2 is maintained at a predetermined value.
[0031]
Thereafter, a high frequency of 27 MHz or higher, for example, 60 MHz, is applied to the upper electrode 21 from the high frequency power supply 40. As a result, a high-frequency electric field is generated between the upper electrode 21 and the susceptor 5 as the lower electrode, the processing gas is dissociated into plasma, and the wafer W is etched by this plasma.
[0032]
On the other hand, a high frequency of 100 kHz to 10 MHz, for example, 2 MHz is applied from the high frequency power supply 50 to the susceptor 5 that is the lower electrode. Thereby, ions in the plasma are drawn to the susceptor 5 side, and the anisotropy of etching is enhanced by ion assist.
[0033]
Thus, the plasma density can be increased by setting the frequency of the high frequency applied to the upper electrode 21 to 27 MHz or more. However, with this alone, the standing wave is generated on the lower surface of the electrode plate 23 by the harmonics of the reflected wave from the plasma. Is generated, the non-uniformity of the electric field on the lower surface of the electrode plate 23 occurs.
[0034]
That is, when a high frequency of 27 MHz or higher is used, a harmonic of n times the applied frequency is likely to be generated in the plasma, and when this harmonic returns from the upper electrode 21 to the high frequency power source, as shown in FIG. Standing waves are reflected between the portions indicated by A and B at the boundary between 21 and the insulating material 25, the portion indicated by C as the power feeding position, and the like and the position indicated by D as the center of the upper electrode 21. Is generated. If this standing wave wavelength is ¼ times the harmonic wavelength λ, that is, λ / 4, the plasma density increases near the center of the upper electrode 21, causing non-uniform plasma to be generated. It becomes. For example, when a high-frequency power supply 40 having a frequency of 60 MHz is used and the wavelength is 5 m and the distance between A and D is about 0.14 m, the ninth harmonic is easily generated between A and D in the calculation. Become. Considering the wavelength shortening rate proportional to the 1/2 power of the dielectric constant of the high-frequency path material, harmonics of the third to sixth orders are likely to be generated. However, when the distance between A and D is about 0.07 m, it is considered that the same problem occurs even at a high frequency of 13.56 MHz.
[0035]
On the other hand, by providing the ring-shaped harmonic absorbing member 51 from the lower end region of the electrode plate 23 to the lower surface of the insulating material 25 as described above so as to be in contact with them, the harmonics returning to the high frequency power source 40 are obtained. It is possible to effectively prevent the formation of a standing wave that absorbs the wave and causes such plasma non-uniformity. In addition, since the harmonic absorption effect can be improved by making the harmonic absorption member 51 into a ring shape in this way, the shape is not limited to the ring shape. Further, the same effect can be obtained even if the harmonic absorbing member 51 is provided on the peripheral surface of the upper electrode 21 as shown in FIG.
[0036]
When a ferrite sintered body is used as such a harmonic absorbing member 51, the harmonic can be absorbed and attenuated by the magnetic resonance loss effect as described above. In this case, the frequency band that can be attenuated is shifted depending on the thickness, and when the thickness is halved, the attenuable frequency is about twice. For example, when the thickness is 7 mm (IB-003 manufactured by TDK), a harmonic of 200 to 800 MHz can be attenuated by 20 dB as shown in FIG. Further, when the thickness is 4.5 mm (IB-004 made by TDK), as shown in FIG. 5, the harmonics of 700 MHz to 3 GHz can be attenuated by 20 dB. In addition, it is possible to widen the attenuable frequency band by laminating ferrites having different frequency characteristics. For example, when IB-003 and IB-004 are laminated, harmonics of a wide frequency band of 200 MHz to 3 GHz. Waves can be attenuated.
[0037]
The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in the above embodiment, the case where a high frequency of 27 MHz or higher is applied to the upper electrode has been described, but the present invention is also effective when the frequency is lower than 27 MHz. Moreover, although the high frequency was applied to the upper and lower electrodes, the type which applies a high frequency with a high frequency only to an upper electrode may be sufficient. Furthermore, the present invention can be applied to a device that applies a high frequency high frequency to the lower electrode. In this case, the lower electrode is brought into contact with the end region of the surface facing the upper electrode or the peripheral surface of the lower electrode. A harmonic absorbing member may be disposed. Furthermore, the case where a semiconductor wafer is used as a substrate to be processed and etching is performed has been described. However, the present invention is not limited to this, and another substrate such as a liquid crystal display (LCD) substrate may be used as a processing target. The plasma treatment is not limited to etching, and may be other treatment such as sputtering or CVD.
[0038]
【The invention's effect】
As described above, according to the present invention, a high frequency is applied to the first electrode, and at the end region of the surface of the first electrode facing the second electrode or the peripheral surface of the first electrode. Since the harmonic absorbing member that contacts and absorbs the harmonic of the frequency of the high frequency applying means is arranged, the harmonic reflected from the plasma reaches the high frequency absorbing member before passing through the electrode and returning to the high frequency power source. Harmonics are absorbed. Therefore, generation of standing waves due to harmonics can be effectively prevented, and nonuniformity of the electric field distribution on the electrode surface caused by the standing waves can be reduced and the plasma density can be made uniform.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a plasma etching apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic diagram for explaining a cause of a standing wave formed on a high frequency application electrode.
FIG. 3 is a cross-sectional view showing another example of the arrangement of harmonic absorbing members.
FIG. 4 is a graph showing frequency characteristics of return loss when a ferrite sintered body having a thickness of 7 mm is used as a harmonic absorbing member.
FIG. 5 is a graph showing the frequency characteristics of return loss when a ferrite sintered body having a thickness of 4.5 mm is used as a harmonic absorbing member.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1; Plasma etching apparatus 2; Chamber 5; Susceptor 6; High pass filter 21; Upper electrode 23; Electrode plate 30; Process gas supply source 35; Exhaust apparatus 40, 50; Harmonic absorption member W; semiconductor wafer

Claims (6)

A chamber that accommodates a substrate to be processed;
First and second electrodes provided to face each other in the chamber;
High frequency applying means for applying a high frequency to the first electrode;
Harmonic absorption that is arranged in contact with the end region of the surface of the first electrode facing the second electrode or the peripheral surface of the first electrode and absorbs harmonics of the frequency of the high-frequency applying means. Members,
An exhaust means for maintaining the inside of the chamber at a predetermined reduced pressure state;
A processing gas introduction means for introducing a processing gas into the chamber;
In a state where the substrate to be processed is supported by the first or second electrode, a plasma of a processing gas is formed by forming a high-frequency electric field between the first and second electrodes, and the substrate to be processed is generated by this plasma. A plasma processing apparatus characterized in that plasma processing is performed. The plasma processing apparatus according to claim 1, wherein the harmonic absorbing member is a laminate of harmonic absorbing members having different frequency characteristics. The plasma processing apparatus according to claim 1, wherein the harmonic absorbing member has a magnetic resonance loss effect. The plasma processing apparatus according to claim 3, wherein the harmonic absorbing member includes ferrite. The plasma processing apparatus according to any one of claims 1 to 4, wherein a frequency of a high frequency applied to the first electrode is 27 MHz or more. The plasma processing apparatus according to any one of claims 1 to 5, further comprising a high-frequency applying unit that applies a high frequency of 100 kHz to 10 MHz to the second electrode.

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