JPH10199699A - Plasma processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce required strength of a magnetic field to form an electromagnetic coil compact by limiting a frequency of microwaves low. SOLUTION: A device comprises a processing container 2 containing a work W to be processed, to which microwaves from a microwave generator 52 are introduced, and a magnetic field is formed to generate electron cyclotron resonance to generate plasma, so a specified treatment is applied to the work W to be processed. In this case, a frequency of above microwaves is set to be within a range between a lower limit frequency as a cutoff frequency decided by an inner diameter L1 in the processing container 2 and an outer limit frequency as the maximum frequency with which standing waves of above microwaves will not be generated on the surface of the work W to be processed. As this frequency, 915MHz may be used, for example. The operation frequency can thus be set small compared to that in conventional devices without reducing a plasma density, thereby a strength of a magnetic field can be set small to achieve compactness of an electromagnetic coil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a plasma processing apparatus for performing a predetermined process on an object to be processed such as a semiconductor wafer.

[0002]

2. Description of the Related Art In recent years, a plasma processing apparatus has been used for processing such as film formation, etching, ashing, and the like in a semiconductor product manufacturing process in accordance with high density and high miniaturization of a semiconductor product. , 0.1 to 10 mTorr
Microwave plasma devices that generate high-density plasma by combining microwaves and a magnetic field from a ring-shaped coil tend to be used because plasma can be stably generated even in a high vacuum state with relatively low pressure. It is in. Conventionally, as a microwave plasma apparatus of this type, for example, a microwave introduction port is provided in a plasma generation chamber having a magnetic field forming means to form an electron cyclotron resonance space, ions are extracted from the plasma generation chamber, and a processing gas in the reaction chamber is extracted from the plasma generation chamber. It is known to perform a film forming process or the like by activating with plasma.

FIG. 3 is a schematic configuration diagram showing such a conventional plasma processing apparatus. A semiconductor wafer W as an object to be processed is placed in a processing chamber 2 formed into a cylindrical shape by, for example, aluminum or the like. A mounting table 4 is provided. The upper portion of the processing vessel 2 is narrowed in a stepped manner, and this portion is configured as a plasma chamber 6 and the lower portion is configured as a reaction chamber 8. Above the plasma chamber 6,
A ceiling lid 10 made of, for example, quartz and hermetically sealing the ceiling of the processing container 2 is provided in an airtight manner, and a microwave introduction window 12 is formed in this portion.

A conical tapered waveguide 14 is connected to the microwave introduction window 12, and a rectangular waveguide 16 is connected to the top of the tapered waveguide 14. The rectangular waveguide 16 has, for example, 2.45 GHz.
A microwave generator 18 for generating the microwave is provided, and the microwave generated here can be introduced into the plasma chamber 6 from the introduction window 12 through the waveguides 16 and 12. ing. A ring-shaped main coil 20 and a sub-coil 22 are disposed outside the plasma chamber 6 of the processing chamber 2 and below the bottom of the processing chamber, respectively. To form a downwardly directed mirror magnetic field. Here, the magnetic field and the microwave are set so as to satisfy the electron cyclotron resonance condition. For a microwave of 2.45 GHz, the magnitude of the magnetic field is approximately 875 gauss.

Accordingly, the plasma gas, eg, argon gas, introduced into the plasma chamber 6 is turned into plasma by electron cyclotron resonance generated by the interaction between the inputted microwave and the magnetic field, and the processing gas supplied below the plasma is For example, a silane gas or oxygen as a film forming gas is activated and reacted to form a film on the wafer surface.

[0006]

By the way, in order to satisfy the electron cyclotron resonance condition, if the potential and mass of the charged particles are determined, the frequency of the microwave and the magnitude of the magnetic field at that time are uniquely determined. However, when the microwave frequency is set to 2.45 GHz as described above,
The main coil 20 and the sub coil 22 which obtain the magnetic field intensity of 875 gauss corresponding thereto are very large,
For example, it becomes a heavy object weighing 100 kg or more, which not only necessitates an increase in cost, but also makes maintenance work difficult and contravenes space saving.

In particular, in the case of a device corresponding to a 12-inch wafer, the diameter of the container is further increased as compared with the case of an 8-inch wafer, so that the coil is further enlarged, for example, to a weight of about 200 kg. Thus, measures to reduce the size of the coil are desired.

The present invention focuses on the above problems,
It was created to solve this effectively. An object of the present invention is to provide a plasma processing apparatus in which the required magnetic field strength is reduced by limiting the frequency of microwaves to a low value, and the electromagnetic coil is reduced in size.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention introduces a microwave from a microwave generator into a processing vessel accommodating an object to be processed and forms a magnetic field. In a plasma processing apparatus for generating plasma by generating electron cyclotron resonance and performing predetermined processing on the object to be processed, the frequency of the microwave is increased from a lower limit frequency consisting of a cutoff frequency determined by an inner diameter of the processing container. The maximum frequency at which the standing wave of the microwave does not occur on the surface of the processing object is set within a range of an upper limit frequency.

According to the present invention, as described above, the frequency of the microwave is reduced to a frequency which is higher than the cut-off frequency and which does not generate a standing wave on the surface of the object to be processed. Correspondingly, the strength of the magnetic field that satisfies the electron cyclotron resonance condition can be reduced, and the size of the electromagnetic coil can be reduced. The upper limit frequency of the microwave is 1.5 GHz when the diameter of the object to be processed is 8 inches, and 1.0 GHz when the diameter of the object is 12 inches. Further, the lower limit frequency of the microwave varies depending on the diameter size and the vibration mode of the object to be processed. For example, when the diameter size is 8 inches, when the microwave vibration mode is the TE11 mode, the frequency is 580 MHz and T
In the M01 mode, the frequency is 770 MHz. When the diameter size is 12 inches, the vibration mode is TE11
440 MHz in mode and 5 in TM01 mode.
70 MHz. As such a microwave frequency, for example, an industrial frequency of 915 MHz can be used.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the plasma processing apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. FIG.
Is a sectional view showing an example of a plasma processing apparatus according to the present invention,
FIG. 2 is a diagram showing a relationship between a semiconductor wafer and a standing wave.
The same parts as those shown in FIG. 3 are described with the same reference numerals.

In this embodiment, a case will be described in which an electron cyclotron resonance (ECR) plasma CVD apparatus is taken as an example of a plasma processing apparatus. The plasma processing apparatus 24 has a processing container 2 which is substantially entirely formed of, for example, aluminum into a cylindrical shape. At the bottom of the container, for example, a semiconductor wafer W as an object to be processed is placed. An aluminum mounting table 4 is installed,
An electrostatic chuck 28 made of, for example, a polyimide resin and having a disc-shaped copper foil 26 embedded therein is attached to the upper surface thereof. The copper foil 26 is connected in parallel with a DC power supply 32 via a power supply line 30 and a high frequency power supply for biasing 13.56 MHz, for example, via a matching box 34, and closes the switch 38 to apply a high DC voltage. The wafer W is attracted and held by Coulomb force generated by supplying the wafer W to the electrostatic chuck 26. Further, by applying a bias high frequency to the electrostatic chuck 26, ions are efficiently drawn.

Further, a cooling jacket 39 for cooling the wafer W in order to prevent the wafer W from being excessively heated during the plasma processing and a heater 40 for heating the wafer W when necessary are provided in the mounting table 4. Each is provided and connected to a refrigerant source 42 and a heating source 44, respectively. The upper part of the mounting table 4 in the processing vessel 2 is configured as a reaction chamber 8, and the ceiling is opened. In order to transmit microwaves to this part, a dielectric such as AlN (aluminum nitride) is used. The ceiling lid 10 is airtightly provided via a sealing member 46 such as an O-ring, and constitutes the microwave introduction window 12.

A conical tapered waveguide 48 is connected to the microwave introduction window 12, and a conversion waveguide 49 for converting a vibration mode of the microwave is connected to the tapered waveguide 48. Through a rectangular waveguide 50 having a rectangular cross section
Is connected. Further, the end of the rectangular waveguide 50 is connected to a microwave generator 52 via a matching circuit 51 for performing impedance matching, so that microwaves can be introduced into the plasma chamber 6. .

Here, the frequency of the microwave oscillated by the microwave generator 52 ranges from a lower limit frequency which is a cutoff frequency determined by the inner diameter L1 of the reaction chamber 8 of the processing vessel 2 to a microwave frequency on the surface of the semiconductor wafer W. The frequency is set to any one of the ranges in which a maximum frequency at which a standing wave does not occur is set as an upper limit frequency. The reason for limiting the frequency of the microwave in this way is as follows. When the conditions of the electron cyclotron resonance are satisfied, the frequency of the microwave and the strength of the magnetic field are proportional to each other. When the frequency is increased, the magnetic field must be increased.

Further, if a standing wave of microwaves is generated on the wafer surface, an electric field distribution is generated on the wafer surface, so that uniformity of processing cannot be maintained. If the frequency of the microwave is smaller than the cutoff frequency determined by the inner diameter of the processing container, the microwave cannot be introduced into the processing container 2 and power cannot be supplied. The frequency of the microwave is determined as described above in consideration of these conflicting characteristics. The upper limit frequency of the microwave is 1.5 GHz when the wafer size is 8 inches, and is 1.0 GHz when the wafer size is 12 inches. The lower limit frequency of the microwave varies depending on the wafer size and the vibration mode of the microwave. For example, when the wafer size is 8 inches, the frequency is 580 MHz when the microwave vibration mode is the TE11 mode, and when the microwave mode is the TM01 mode. 770M
Hz. When the vibration mode is TE11 mode when the wafer size is 12 inches, 440 MH
z and 570 MHz in the TM01 mode.
Accordingly, the operating frequency is significantly lower than the conventionally used 2.45 GHz.

In the present embodiment, an industrial frequency of 915 MHz that satisfies the above both wafer sizes is used as the microwave frequency. Also, the inner diameter L of the processing vessel 2
1 is generally about 10 cm larger than the wafer size. For example, when the wafer size is 8 inches, the inner diameter L
1 is set to about 300 mm, and in the case of 12 inches, it is set to about 400 mm. A ring-shaped main electromagnetic coil 54 is provided on the side of the processing container 2 that partitions the reaction chamber 8 so as to surround the processing container 2, and a sub-magnetic coil 56 similarly formed in a ring shape is provided below the container bottom. Is formed, and a downward mirror magnetic field M1 is formed in the reaction chamber 8 to effectively confine ions, and the magnetic field M1 and the inputted microwaves generate electron cyclotron resonance to generate plasma. It has become.

A plasma gas introduction nozzle 58 is provided on a side wall that partitions the reaction chamber 8.
8, an Ar gas source 62, an oxygen gas source 64, and an NF ₃ gas source 66 as a cleaning gas are connected to a gas passage 60, for example, and open / close valves 68A and 68, respectively.
B, 68C and mass flow controllers 70A, 70B,
The flow rate is controlled by 70C. Further, a processing gas introduction nozzle 7 is provided on a wall that partitions the reaction chamber 8.
The nozzle 72 has a gas passage 74.
, A processing gas, for example, a silane source 76 is connected. The flow rate of this gas is controlled by an on-off valve 68D and a mass flow controller 70D opened in the middle of the gas passage 74. An exhaust port 78 connected to a vacuum pump (not shown) for evacuating the inside of the processing container 2 is provided on a side wall of the processing container 2, and a gate valve 8 is provided.
0, the load lock chamber 82 is connected.

Next, the operation of the embodiment constructed as described above will be described. First, an unprocessed semiconductor wafer W is loaded from the load lock chamber 82 into the processing chamber 2, placed on the mounting table 4, and suction-held by the Coulomb force of the electrostatic chuck 28. After the inside of the processing container 2 is sealed, vacuum is drawn. When a predetermined degree of vacuum is reached, an Ar gas, an O ₂ gas, and a raw material gas, for example, silane gas, are supplied from the respective gas sources into the processing container 2. While maintaining a predetermined process pressure, for example, about 1 mTorr. At the same time, the microwave generated from the microwave generator 52 is propagated to the rectangular waveguide 50 and converted into a predetermined vibration mode by the conversion waveguide 49. Further, the microwave after the mode conversion is The light propagates through the tapered waveguide 48 and is introduced into the plasma chamber 6 from the microwave introduction window 12. Further, the main electromagnetic coil 54 and the sub-magnetic coil 56 are driven to form a mirror magnetic field M <b> 1 directed downward in the processing chamber 2.

Interaction between the mirror magnetic field M1 and the introduced microwaves causes electron cyclotron resonance, and the ions generated by the plasmaization of the argon gas in the reaction chamber 8 are confined along the downward magnetic field M1. The oxygen and silane gas are activated and reacted by the plasma energy, and a film of SiO ₂ is formed while performing sputtering on the wafer surface. At this time,
A bias high frequency power supply 3 is applied to the copper foil 26 of the electrostatic chuck 28.
6, a bias voltage is applied to attract the ions to the wafer surface in a satisfactory manner.

The charged particles converted into plasma are attracted to the wafer side while performing a circular motion by absorbing a microwave resonating with a cyclotron frequency. In this embodiment, the frequency of the microwave is set to the processing vessel 2. Is set to a predetermined frequency within a range from a lower limit frequency, which is a cutoff frequency determined by the inner diameter L1, to an upper limit frequency having a maximum frequency at which a standing wave does not occur on the wafer surface. Such a frequency is 2.45 GHz which is the microwave frequency of the conventional device.
It can be set to a frequency considerably lower than z, for example, an industrial frequency of 915 MHz, and hardly reduces the plasma density. Here, the frequency 2.4
The magnetic field strength that satisfies the electron cyclotron condition for 5 GHz (wavelength 122 mm) is about 875 gauss, whereas the magnetic field strength that satisfies the electron cyclotron condition for frequency 915 MHz (wavelength 329 mm) is 326.
Since it is about 8 gauss and the magnetic field strength can be greatly reduced, the size of the main electromagnetic coil 54 and the sub electromagnetic coil 56 can be reduced accordingly.

Here, the lower limit frequency and the upper limit frequency will be described in detail. Here, the cut-off frequency determined by the inner diameter L1 of the processing container 2 is set as the lower limit frequency. However, in general, in order to efficiently absorb microwaves and generate plasma, the microwaves are propagated to a deep portion in the processing container 2. Therefore, it is necessary to introduce the main electromagnetic coil 54 to the horizontal level 84 where the lower end is located. This horizontal level 84
Is referred to as an ECR surface, and the microwave propagating through the tapered waveguide 48 penetrates the ceiling lid 10 made of AlN, is introduced into the processing vessel 2, and further propagates through the processing vessel 2 to a deep portion. Ideally, it should be absorbed almost completely by the ECR surface 84. Therefore, the processing vessel 2 that defines the part of the reaction chamber 8 must function as a waveguide. Therefore, in order for the microwave to propagate through this part without being attenuated, the frequency of the microwave must be cut off. Must be larger than

The cutoff frequency depends on the inner diameter of the circular waveguide, that is, the inner diameter L1 of the processing container 8 and the vibration mode of the microwave because the processing vessel 2 functions as a circular waveguide. The frequency fc is expressed as shown in Equation 1 below. fc = 1 / λ = 1 / (A · a) (1) where λc is a cutoff wavelength, A is a waveguide constant that varies depending on the vibration mode, and a is the inner diameter of the waveguide. Then, a = L1 / 2. The waveguide constant is described in Appendix 5 (Section 247) of [Microwave Circuit] published by Nikkan Kogyo Shimbun on February 28, 1969.
It is described as. According to this Appendix 5, the waveguide constant is 3.413 when the microwave oscillation mode is the TE11 mode, and 2.61 when the microwave oscillation mode is the TM01 mode.
3.

Now, the inner diameter L1 of the processing container for processing a wafer having a diameter of 8 inches (approximately 20 cm) is set to be 10 times smaller than the wafer diameter.
Assuming that it is set to be larger by about 0 mm, the inner diameter L1 is 0.3 m. The cut-off frequency fc at this time is approximately 580 MHz when the vibration mode of the introduced microwave is the TE11 mode, and approximately 77 MHz when the vibration mode of the introduced microwave is the TM01 mode.
0MH, which are the lower limit frequencies. Further, assuming that the inner diameter L1 of the processing container for processing a wafer having a diameter of 12 inches (approximately 30 cm) is set to be about 100 mm larger than the wafer diameter, the inner diameter L1 is 0.4 m. The cutoff frequency fc at this time is approximately 440 MHz when the introduced microwave vibration mode is the TE11 mode, and approximately 570 MHz when the introduced microwave vibration mode is the TM01 mode.
These are the lower limit frequencies.

Here, the case where the inner diameter L1 of the processing container is larger than the diameter of the wafer by about 100 mm as an allowance has been described as an example.
It can be smaller or larger than mm, and the lower limit frequency will change accordingly. As is apparent from Equation 1, the lower limit frequency increases as the margin length decreases, and the lower limit frequency decreases as the margin length increases.

Next, the upper limit frequency will be described. FIG.
When a standing wave 86 of one wavelength is generated on the surface of the wafer W as shown in (1), a large potential distribution is generated on the surface of the wafer W, which increases the non-uniformity of the plasma processing and increases the uniformity of the film thickness. The property is deteriorated. Therefore, the frequency of the microwave must be such that a standing wave of one wavelength does not stand on the wafer surface. Such a frequency is 1.5 GHz when the wafer size is 8 inches, and is 12 GHz. In the case of inches, the frequency is 1.0 GHz, which is the upper limit frequency for each wafer size. Therefore, as described above, the microwave frequency is set to 915 MHz.
If z is set, both sizes of wafers can be accommodated.

Further, the frequency of the microwave is 915 MHz.
If the diameter of the processing container 2 is set to
For 1, the lower limit is about 25 cm when the vibration mode is the TM01 mode. As described above, since the microwave frequency can be set considerably lower than the conventionally used 2.45 GHz, the magnetic field strength for satisfying the ECR resonance condition can be reduced correspondingly as described above. And the electromagnetic coils 54 and 56 can be reduced in size. The microwave frequency may be any frequency within the range of the upper and lower frequencies as long as the sealing is sufficiently performed, and is not limited to the above-mentioned industrial frequency of 915 MHz, but may be reduced within the above-described range. The smaller the value, the smaller the magnetic field strength, which can contribute to the miniaturization of the coil.

In the above embodiment, the case where silane is used as a film forming gas has been described. However, the present invention is not limited to this, and another film forming gas such as disilane may be used. Further, the present invention can be applied not only to a mirror magnetic field but also to a cusp magnetic field. In this embodiment,
Although an ECR type plasma CVD apparatus has been described as an example, the present invention is not limited to this, and can be applied to a plasma ashing apparatus, a plasma etching apparatus, and the like. be able to.

[0029]

As described above, according to the plasma processing apparatus of the present invention, the following excellent operational effects can be exhibited. When performing plasma processing on an object to be processed using electron cyclotron resonance, the frequency of the microwave is set to be smaller than that of the conventional apparatus and set within a predetermined range. Therefore, the size of the electromagnetic coil can be reduced, and the electromagnetic coil can be reduced in size and space.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a plasma processing apparatus according to the present invention.

FIG. 2 is a diagram illustrating a relationship between a semiconductor wafer and a standing wave.

FIG. 3 is a cross-sectional view illustrating an example of a conventional plasma processing apparatus.

[Explanation of symbols]

 Reference Signs List 2 processing container 4 mounting table 6 plasma chamber 8 reaction chamber 10 ceiling lid 12 microwave introduction window 24 plasma generator 28 electrostatic chuck 48 tapered waveguide 49 conversion waveguide 50 rectangular waveguide 52 microwave generator 54 main Electromagnetic coil 56 Sub-magnetic coil 62 Ar gas source 76 Silane gas source 84 ECR surface 86 Standing wave W Semiconductor wafer (workpiece)

Claims (4)

[Claims] 1. A microwave is introduced from a microwave generator into a processing vessel containing an object to be processed, and a magnetic field is formed to generate electron cyclotron resonance to generate plasma. In a plasma processing apparatus that performs a predetermined process, the frequency of the microwave is set to a maximum frequency at which a standing wave of the microwave is not generated on the surface of the processing target from a lower limit frequency including a cutoff frequency determined by an inner diameter of the processing container. A plasma processing apparatus characterized in that the upper limit frequency is set within a range. 2. The method according to claim 1, wherein the upper limit frequency is 1.5 GHz when the diameter of the object is 8 inches, and 1.0 GHz when the diameter of the object is 12 inches. The plasma processing apparatus according to claim 1, wherein: 3. The lower limit frequency of the microwave is 580 MHz when the diameter of the object is 8 inches and the vibration mode is the TE11 mode, and is 770 MHz when the vibration mode is the TM01 mode. Is 4 inches when the diameter size is 12 inches and the vibration mode is TE11 mode.
570M when the vibration mode is TM01 at 40MHz
3. The plasma processing apparatus according to claim 1, wherein the frequency is Hz. 4. The frequency of the microwave, when the diameter of the object to be processed is 8 inches and 12 inches,
2. The plasma processing apparatus according to claim 1, wherein the frequency is 915 MHz.