JP2024017093A - plasma processing equipment - Google Patents

Abstract

An object of the present invention is to enable uniform etching processing on a substrate to be processed in a plasma processing apparatus. [Solution] A microwave power source that generates microwave power, a waveguide that conveys the microwave power generated by the microwave power source, and a plasma generated by receiving the microwave power conveyed by the waveguide. In the plasma processing apparatus, the waveguide includes a rectangular waveguide connected to the microwave power source side and a circular waveguide connected to the plasma processing chamber side. , a plurality of phase plates made of a dielectric material are inserted into a part of the circular waveguide and are arranged facing each other in a direction perpendicular to the central axis of the circular waveguide. [Selection diagram] Figure 3

Description

The present invention relates to a plasma processing apparatus, and particularly to a plasma processing apparatus that can improve the in-plane uniformity of a wafer.

In recent years, as the degree of integration of semiconductor devices has increased, microfabrication, that is, improved processing accuracy, is required, and at the same time, it is becoming increasingly difficult to improve the uniformity of the etching rate or the uniformity of the CD value (critical dimension) within the wafer surface. became. Furthermore, the materials to be etched have changed from single-layer films to multi-layer films, and multi-step etching in which the etching conditions are changed during the processing of each film or film has come to be frequently used. In this case, since the factors that affect the etching uniformity differ from step to step, it is difficult to obtain etching uniformity and axial symmetry at the time when the etching of each multilayer film is completed.

One of the finer etching techniques in the semiconductor field is dry etching, and among these, dry etching using plasma is often used. Plasma uses collisions of electrons with molecules or atoms of the process gas to excite the process gas molecules or atoms, producing ions and radicals. Plasma processing equipment achieves anisotropic etching using ions and isotropic etching using radicals. As a plasma source, there is an electron cyclotron resonance (ECR). Since ECR can generate high-density plasma, it is used to increase the withstand voltage of DRAM semiconductor devices and to create high-capacity capacitors.

FIG. 7 shows the configuration of a conventional ECR etching apparatus 700. The 2.45 GHz microwave emitted from the magnetron 702 propagates through the isolator 703, the rectangular waveguide 704, and the three-stub tuner 705 in the order of TE10, and the circular-rectangular waveguide converter 706 converts the propagation mode (or mode) is converted to TE11, and the circular rectangular waveguide converter 706 has a diameter of φ90 mm so that the 2.45 GHz microwave can pass through the fundamental TE11 propagation mode.

In order to form microwave radiation with axial symmetry, a dielectric phase plate 708 made of quartz is used to form circularly polarized waves, and by temporally rotating the microwave in the TE11 propagation mode, the microwave The electric field distribution of the wave becomes axially symmetrical and radiates into the cavity 717. In order for the microwave to propagate as a circularly polarized wave in the circular waveguide 707, the dielectric phase plate 708 is placed at an angle of 45 degrees with respect to the polarization plane of the linearly polarized wave in the TE11 configuration. 708 is inserted into the circular waveguide 707. The circularly polarized waves of the microwaves incident on the cavity 717 and the processing chamber 701 are processed through a quartz window 713 and a shower plate 714 at the top of the processing chamber 701 covered by an upper electromagnetic coil 709, a middle electromagnetic coil 710, and a lower electromagnetic coil 711. It is introduced into the chamber 701.

Electron cyclotron motion occurs due to the electric field generated by the microwave and the magnetic field formed perpendicular to the electric field. When the frequency of the microwave is 2.45 GHz, the traveling direction of electrons perpendicular to the magnetic field is bent by the Lorentz force, so that the electrons gradually move in a circular motion. At that time, the magnetic flux density B is determined by the formula fc = eB/2πme (e is the electron charge amount 1.6x10 ^-19 C, me is the electron mass 9.1x10 ^-31 Kg, fc is 2.45 GHz), and if it is 875G, electron cyclotron resonance occurs, increasing the probability of collision between electrons and gas molecules in the processing chamber, making it possible to generate high-density plasma even under low pressure.

The processing chamber 701 is operated by a vacuum pump 718, and the pressure during the etching process is approximately 1 Pa, and a plasma density of 10 ¹¹ cm ^-3 or more can be obtained in this pressure region. Further, since plasma formation and independent ion energy can be controlled by an RF power source 716 applied to the lower electrode 715, precise shape control is possible. Furthermore, in order to improve the in-plane uniformity of the substrate w to be processed, a circularly polarized wave generator 8 made of a dielectric material is used to inject circularly polarized waves into the processing chamber.

As a result, circularly polarized waves are also formed inside the processing chamber, resulting in a more uniform plasma distribution.However, in the design of conventional circular polarizers, reflections from the processing chamber are not taken into account, so When the plasma density in the processing chamber 701 reaches a constant value, reflected waves are generated from the processing chamber 701. Since this reflected wave forms a standing wave with the incident wave, the rotation of the circular waveguide TE11 mode is hindered, and the axial ratio of the circularly polarized wave to be input into the processing chamber 701 is reduced. The axial ratio is defined as the circularity of circularly polarized waves, and 1 is the highest circularity.

Japanese Patent Application Publication No. 6-216073

The plasma processing equipment can be applied to etching processes using chlorine gas, HBr gas, fluorocarbon gas, rare gas, nitrogen gas, oxygen gas, etc., and mixed gases thereof, and applicable materials to be etched include: , organic materials such as BARC, insulating film materials such as SiO2, SiON, SiN, Low-k (low dielectric constant material), High-k (high dielectric constant material), αC (amorphous carbon), poly-Si, Si substrate and metal materials.

As mentioned above, the etching process for multilayer films is performed using a process recipe consisting of multiple steps, but it is well known that the dielectric constant tensor in the plasma processing chamber changes depending on the dissociation and ionization characteristics of each material gas. It is being Therefore, the impedance of the processing chamber changes with each step of the process recipe.

When the impedance of the processing chamber changes, the reflected power to the magnetron increases, and this reflected wave reduces the axial ratio (circularity of electric field rotation) of the circularly polarized wave formed by the dielectric phase plate. Plasma generation within the processing chamber becomes uneven, and the uniformity and axial symmetry of the etching rate on the substrate to be processed deteriorates.

In order to track this dynamically changing impedance, conventionally, as in Patent Document 1, a three-stub tuner is installed in a horn antenna that radiates microwave power into the processing chamber, and the reflected waves from the processing chamber are transmitted to the antenna and dielectric. By reducing the reflected waves from the processing chamber at the horn antenna point to prevent standing waves from forming between the phase plates, the incident microwaves are normally circularly polarized without interfering with the operation of the dielectric phase plate. is converted to

However, since the impedance matching by the three-stub tuner installed on this horn antenna is based on the radiation end of the horn antenna, the impedance of the three-stub tuner itself will fluctuate in order to match with the horn antenna. , the reflection from the three-stub tuner in the horn antenna seen by the circular polarizer equipped with a dielectric phase plate also changes dynamically, resulting in stable circularly polarized waves being radiated into the processing chamber. Needless to say, it is difficult to continue.

Furthermore, the three-stub tuner (hereinafter referred to as the power-side tuner) connected to the magnetron operates to reduce the reflection from the three-stub tuner (hereinafter referred to as the radiation-side tuner) built into the horn antenna. , since it uses the output end of the power source tuner as a reference point, the circular polarizer is still affected by reflection from the radiation tuner, resulting in a lower axial ratio and a failure to obtain a uniform plasma distribution in the processing chamber.

In other words, in the conventional technology, a reflected wave is generated in the waveguide of a microwave plasma processing apparatus by the airtight means (such as a quartz window) of the radiation section or the processing chamber, and the circularly polarized radiation formed by the phase plate reflects this reflected wave. Since the axial ratio decreases due to the effect of

The present invention solves the problems of the prior art described above and provides a plasma processing apparatus that enables uniform etching processing on a substrate to be processed.

In order to solve the above-mentioned problems, the present invention provides a microwave power source that generates microwave power, a waveguide that conveys the microwave power generated by this microwave power source, and a microwave power that is conveyed by the waveguide. In a plasma processing apparatus equipped with a plasma processing chamber that receives microwave power and generates plasma to process a sample, the waveguide is a rectangular waveguide that connects to the side of the microwave power source and a waveguide that connects to the side of the plasma processing chamber. A configuration in which a plurality of phase plates made of a dielectric material are inserted into a part of the circular waveguide to face each other in a direction perpendicular to the central axis of the circular waveguide. And so.

According to the present invention, it has become possible to radiate microwaves with a high axial ratio into a processing chamber while reducing the level of reflected waves, and it has become possible to perform uniform etching processing on a substrate to be processed.

1 is a vertical cross-sectional view showing a schematic configuration of a plasma processing apparatus according to Example 1 of the present invention. 1 is a book diagram showing a schematic configuration of a circular polarizer of a plasma processing apparatus according to Example 1 of the present invention. FIG. 1 is a cross-sectional view showing the configuration of a circular polarizer of a plasma processing apparatus according to Example 1 of the present invention. It is a cross-sectional view taken along line xx in FIG. 3. FIG. 2 is a book diagram showing a schematic configuration of a circular polarizer of a plasma processing apparatus according to Example 2 of the present invention. (a) is a cross-sectional view of a rectangular iris of a plasma processing apparatus according to Example 2 of the present invention, and (b) is a YY cross-sectional view in (a). 1 is a vertical cross-sectional view showing a schematic configuration of a conventional plasma processing apparatus.

The present invention provides a plasma processing apparatus that generates plasma using high-frequency power of microwaves and includes a circularly polarized wave generator disposed within a circular waveguide, wherein the circularly polarized wave generator includes a plurality of phase plates arranged opposite to each other. and an actuator for controlling the amount of insertion of the phase plate into the circular waveguide based on the electric field strength signal and the reflected wave signal, and two opposing rows for circularly polarizing the incident TE ₁₁ mode microwave wave. A plurality of dielectric phase plates (for example, three quartz plates in one row) arranged in a stepwise manner are mounted on a linear actuator, and the linear actuator is controlled using an electric field strength signal and a reflected wave signal. By adjusting the insertion length of two rows of phase plates facing each other into the circular waveguide, a high axial ratio can be radiated into the processing chamber while reducing the level of reflected waves. It is.

The present invention provides a circular polarizer for improving the uniformity and symmetry of the etching rate of a substrate to be processed, which converts linearly polarized waves in the TE ₁₁ mode into circularly polarized waves in a plasma processing apparatus using microwaves. In order to match the impedance in the processing chamber according to each step of the process recipe, the circular polarizer has multiple pieces arranged facing each other and connected to a direct-acting actuator that converts linearly polarized waves into circularly polarized waves. A three-stub tuner on the magnetron side of the microwave source, which has a dielectric plate and includes four or more electric field sensors on the radiation side of the circular polarizer described above, determines the axial ratio of the circularly polarized wave emitted from the circular polarizer. By feeding back the reflected wave level measured at the radiation end of the linear actuator to the controller of the direct-acting actuator, it is possible to control the insertion length of the aforementioned plural dielectric plates into the transmission line of the circular waveguide. The impedance of the polarizer itself was configured to be variable according to the impedance of the processing chamber that can be depressurized.

Further, in the present invention, in the ECR plasma processing apparatus, an impedance mismatch occurs between the processing chamber and the microwave transmission line depending on the recipe used in the process. When the reflected waves due to impedance mismatch return to the circular polarizer, the rotating electric field of the TE ₁₁ mode formed by the circular polarizer becomes unstable, resulting in the circularly polarized wave output from the circular polarizer. The axial ratio will decrease. The reduced axial ratio is detected by four electric field sensors installed in the circular polarizer, and the two rows of six dielectric plates are guided by the respective linear actuators 32. By adjusting the insertion length into the wave tube section, the axial ratio of the circularly polarized wave output from the circular polarizer is modified.

Furthermore, since the impedance of the processing chamber changes with each step of the process recipe, the axial ratio (rotation) of the circularly polarized waves emitted from the circular polarizer is This solves the problem that the uniformity and axial symmetry of the etching rate on the substrate to be processed deteriorates due to a decrease in the circularity of the electric field, which causes an imbalance in the plasma distribution generated within the processing chamber. In order to achieve this, in a plasma processing apparatus that generates plasma using high-frequency power of microwaves and includes a circularly polarized wave generator disposed within a circular waveguide, the circularly polarized wave generator includes a plurality of phase plates disposed opposite to each other. By providing an actuator that controls the amount of insertion of the phase plate into the circular waveguide based on the electric field strength signal and the reflected wave signal, the impedance of the circular polarizer itself can be made variable, thereby improving the process recipe. By matching the dynamically changing impedance within the plasma processing equipment, it is possible to adjust the axial ratio of the circularly polarized waves emitted into the processing chamber, thereby improving the uniformity and axial symmetry of the etching rate on the substrate being processed. It is designed to improve the

Embodiments of the present invention will be described in detail below based on the drawings. In all the figures for explaining this embodiment, parts having the same functions are given the same reference numerals, and repeated explanations thereof will be omitted in principle.

However, the present invention should not be construed as being limited to the contents described in the embodiments shown below. Those skilled in the art will readily understand that the specific configuration can be changed without departing from the spirit or spirit of the present invention.

A first embodiment of the present invention will be described using FIGS. 1 to 4.
FIG. 1 shows a plasma processing apparatus 100 according to this embodiment. In the plasma processing apparatus 100, the 2.45 GHz microwave output from the magnetron 2 passes through the isolator 3, the rectangular waveguide 4, the three-stub tuner 5, and the circular-rectangular waveguide converter 6, and then enters the circular guide of the transmission line. The light enters the wave tube 7, passes through the circular polarizer 30, is radiated to the cavity 17, and generates plasma inside the processing chamber 1.

The function of the circular rectangular waveguide converter 6 is to convert the microwave in the TE ₁₀ propagation mode that has been generated in the magnetron 2 and propagated through the rectangular waveguide 4 into a TE ₁₁ mode suitable for propagation through the circular waveguide 7. Since it can be converted into a propagation mode, the microwave incident on the circular waveguide 7 of the transmission line propagates as a TE ₁₁ mode. The TE ₁₁ mode at this time becomes a linearly polarized wave, but when it further passes through the circular polarizer 30, a circularly polarized wave is formed by the two rows of dielectric plates inside the circular polarizer 30 (see Figure 2). Ru.

As shown in FIG. 2, two rows of dielectric plates 33 to 35 provided in the circular polarizer 30 are inserted into the circular waveguide section 36 in a stepped manner. As a result, the impedance changes gradually with respect to the incident wave, so that reflection to the circular rectangular waveguide converter 6 can be reduced. The two rows of dielectric plates installed in the circular polarizer 30 may be made of, for example, quartz or 99.9% pure alumina.

The microwave in the TE ₁₁ mode incident on the circular polarizer 30 passes through the circular polarizer 30 and is converted into a circularly polarized wave in the TE ₁₁ mode. , and radiates microwave power into the processing chamber 1. At the same time, a magnetic field intensity surface of 875 Gauss is formed by the electromagnetic coils 9 to 11, causing electron cyclotron resonance in the processing chamber 1, and plasma is formed in the supplied material gas G.

By placing the substrate w to be processed on the electrode 15 connected to the RF power source 16, a time-varying electric field is formed, so that the electric field formed on the electrode surface by the ion particles inside the plasma formed above is By colliding with the substrate w to be processed, the thin film on the substrate w to be processed is etched.

However, because the tensor permittivity inside the processing chamber 1 changes due to the distribution of plasma formed within the processing chamber 1, that is, the impedance inside the processing chamber 1 changes, causing an impedance mismatch. When an impedance mismatch occurs, a reflected wave is generated and returns to the circular polarizer 30.

FIG. 2 shows a cross section of a circular polarizer 30 equipped with a total of six dielectric plates 33 to 35 in two rows of three. Since the initial insertion amount of the three sets of dielectric plates 33 to 35 and the angles formed with the plane of polarization are assumed to be non-reflective, the axial ratio (axial symmetry) of circularly polarized waves will deteriorate if reflected waves occur. .

In the configuration shown in FIG. 2, the four electric field sensors 42 (three of which are shown in FIG. 2) provided in the circular polarizer 30 are used to detect the electric meter intensity at each position and to distribute the electric field. By determining , the axial ratio of the circularly polarized wave in the circular polarizer 30 is detected.

The control unit 41 feeds back the electric field distribution information corresponding to the detected axial ratio, and the control unit 41 calculates the stroke amount (displacement amount) of the three sets of linear actuators 32 corresponding to the three sets of dielectric plates 33 to 35. By individually adjusting the insertion length of the dielectric plates 33 to 35 into the circular waveguide section 36, the axial ratio of the circularly polarized waves output from the circular polarizer 30 can be adjusted. .

The circular polarizer 30, as shown in FIG. , the display of the electric field sensor 42 is omitted). In order to maintain the axial ratio (axial symmetry) of the propagation mode of the TE ₁₁ mode output from the circular polarizer 30, a circular waveguide section 36 is sandwiched between rotary joints 31 placed above and below the circular polarizer 30. A total of six dielectric plates 33 to 35, three in each row, are inserted in two stair-shaped rows. These two rows of stepped dielectric plates 33 to 35 are arranged to face each other.

The insertion lengths of the dielectric plates 33, 34, and 35 into the circular waveguide section 36 are L1, L2, and L3, and their heights are H1, H2, and H3, respectively. The thickness of the dielectric plates 33 to 35 is approximately 1/8λ. λ is one wavelength. When the frequency of the magnetron is 2.45 GHz, the wavelength of the microwave propagating within the circular waveguide section 36 having a diameter of 90 mm is approximately 203 mm.

These two rows of dielectric plates 33 to 35 are each mounted on a direct-acting actuator 32 that is controlled by a control section 41 based on the electric field intensity distribution measured by four electric field sensors 42, and are connected to a circular waveguide section 36. The insertion lengths L1, L2, and L3 of are adjusted.

When the axial ratio of circularly polarized waves is high, the maximum and minimum electric field levels read by the four electric field sensors 42 are close to each other, but when the axial ratio of circularly polarized waves decreases, the four electric field sensors 42 Utilizing the characteristic that the difference between the maximum value and the minimum value of the electric field level read by By adjusting the stroke (displacement amount) of the dielectric plates 33 to 35, the amount of insertion into the circular waveguide section 36 is adjusted.

Furthermore, as shown in FIG. 4 as a cross section taken along line XX in FIG. The a row 37a is installed at a position of 45 degrees from the plane of polarization. The stepped dielectric plate b row 37b is installed at a position of −135 degrees from the plane of polarization. The stepped dielectric plate A row 37a is driven by a linear actuator 32a, and the stepped dielectric plate B row 37b is driven by a linear actuator 32b. The plane of polarization mentioned here is defined as a plane determined by the traveling direction of the linearly polarized wave of the TE ₁₁ mode propagating within the circular waveguide section 36 and the direction of its electric field.

As described above, in this embodiment, the control unit 41 controls the linear actuator 32 based on the electric field intensity distribution measured by the four electric field sensors 42, and the two rows 6 mounted on the circular polarizer 30 A configuration in which the axial ratio of the circularly polarized waves output from the circular polarizer 30 can be controlled by adjusting the length of insertion of the dielectric plates 33, 34, and 35 into the respective circular waveguide sections 36. And so.

As a result, according to this embodiment, it is possible to adjust the axial ratio of the circularly polarized waves output from the circular polarizer 30 to be maximum, and it is possible to reduce the level of reflected waves while increasing the axial ratio of the circularly polarized waves output from the circular polarizer 30. It has become possible to radiate microwaves of a certain ratio into the processing chamber, and it has become possible to perform uniform etching processing on the substrate to be processed.

A second embodiment of the present invention will be described using FIGS. 5 and 6.
In the configuration of the plasma processing apparatus 100 shown in FIG. 1 described in Example 1, the reflected wave from the processing chamber 1 enters the circular polarizer 30 as a linearly polarized wave in the TE ₁₁ mode, so it is a lossless wave. In this case, a normal microwave transmission line becomes symmetrical, and the reflected wave also enters the circular rectangular waveguide converter 6 as a circularly polarized wave by the circular polarizer 30.

Since the circularly polarized wave is an electric field that rotates over time, it enters the three-stub tuner 5 as a TE ₁₀ mode at a certain timing, so the reflected wave power seen from the three-stub tuner 5 is large, and The output of the propagating TE ₁₀ mode microwave becomes unstable.

In the second embodiment, in order to solve the above-mentioned problem, a rectangular iris 43 is provided in the circular rectangular waveguide converter 6, as shown in FIG. A front cross-sectional view of the rectangular iris 43 is shown in FIG. 6(a), and a Y-Y cross-sectional view thereof is shown in FIG. 6(b). The optimal length L ₀ of the rectangular iris 43 in this embodiment is approximately 1/2λg (2.45GHz, when the microwave mode is TE ₁₀ , λg = 148mm), the short direction A of the opening 44 = 47mm, The longitudinal direction B is 64 mm. Furthermore, the lateral direction A of the opening 44 of the square iris 43 is parallel to the polarization plane of the microwave propagating from the circular and rectangular waveguide converter 6.

The microwave reflected from the processing chamber 1 passes through the circular polarizer 30 and becomes a circularly polarized wave, but when passing through the opening 44 of the square iris 43, the propagation mode that can be transmitted is TE ₁₀ , that is, in the lateral direction. Only the electric field vector of can be propagated. Therefore, the power transmission of the circularly polarized wave reflected from the processing chamber 1 (assuming that the circularly polarized wave is formed by the circular polarizer 30) is limited to the _TE10 mode in the transverse direction, and passes through the square iris 43. Since the reflected wave power has already been attenuated when the reflected wave power reaches the three-stub tuner 5, the reflected power measuring means of the three-stub tuner 5 shows that the reflected power is small. Further, as with the rectangular iris 43, a rectangular or cross-shaped structure or a plurality of slots may be used as long as the function of blocking part of the circularly polarized power of the reflected wave can be realized.

According to this embodiment, microwaves with a high axial ratio can be stably radiated into the processing chamber while the level of reflected waves is reduced, and uniform etching processing can be performed on the substrate to be processed. It's now possible.

Above, the invention made by the present inventor has been specifically explained based on Examples, but it goes without saying that the present invention is not limited to the Examples and can be modified in various ways without departing from the gist thereof. stomach. For example, the embodiments described above are described in detail to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to having all the configurations described. Further, it is possible to add, delete, or replace a part of the configuration of each embodiment with other configurations.

1 Processing chamber 2 Magnetron 3 Isolator 4 Rectangular waveguide 5 Three-stub tuner 6 Circular-rectangular waveguide converter 7 Circular waveguides 9, 10, 11 Electromagnetic coil 12 Yoke 13 Quartz window 14 Shower plate 15 Electrode 16 RF power source 17 Cavity 18 Vacuum pump 30 Circular polarizer 31 Rotary joints 32, 32a, 32b Direct-act actuators 33, 34, 35 Dielectric plate 36 Circular waveguide section 37a Dielectric plate A row 37b Dielectric plate B row 41 Control section 42 Electric field sensor 43 Square iris 44 Opening 100, 700 Plasma processing device

Claims (5)

a microwave power source that generates microwave power;
a waveguide that transports the microwave power generated by the microwave power source;
A plasma processing apparatus comprising: a plasma processing chamber that receives the microwave power carried by the waveguide and generates plasma to process a sample;
The waveguide includes a rectangular waveguide connected to the microwave power source side and a circular waveguide connected to the plasma processing chamber side, and the circular waveguide is provided in a part of the circular waveguide. A plasma processing apparatus characterized in that a plurality of phase plates made of a dielectric material are inserted facing each other in a direction perpendicular to the central axis of the plasma processing apparatus. 2. The plasma processing apparatus according to claim 1,
The plasma processing apparatus is characterized in that the plurality of phase plates are formed by stacking a plurality of phase plates having different distances from the central axis of the circular waveguide. 3. The plasma processing apparatus according to claim 2,
The plasma processing apparatus further comprises a linear actuator that adjusts the amount of movement of the plurality of stacked phase plates in a direction perpendicular to the central axis of the circular waveguide. 4. The plasma processing apparatus according to claim 3,
The circular waveguide includes a plurality of electric field sensors for detecting the electric field strength of the microwave power inside the circular waveguide on a side closer to the plasma processing chamber than the plurality of phase plates, The amount of inflow and outflow of the plurality of phase plates in a direction perpendicular to the central axis of the circular waveguide is controlled in accordance with information on the electric field strength of the microwave power detected by an electric field sensor. A plasma processing device characterized by adjustment using an actuator. The plasma processing apparatus according to claim 1,
The waveguide further includes a circular rectangular waveguide converter connecting a rectangular waveguide connected to the microwave power source side and a circular waveguide connected to the plasma processing chamber side, and the circular rectangular waveguide A plasma processing apparatus characterized in that a part of a waveguide converter includes a rectangular iris having a rectangular opening.

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