TWI695431B - Plasma etching method - Google Patents

Abstract

The invention discloses a plasma etching method for etching a workpiece to be processed in a reaction chamber. The plasma etching method includes at least one etching step. In each of the etching steps, an upper electrode radio frequency power supply and a lower electrode are adjusted. Steps of phase difference between RF power sources to adjust the angular distribution of plasma. .

Description

Plasma etching method

The invention relates to the technical field of semiconductors, in particular to a plasma etching method.

As the feature size of integrated circuits continues to decrease, the required processing technology is becoming more and more strict. One of the most important requirements is the uniformity of the entire workpiece to be processed, and the uniformity of the entire workpiece to be processed. The better, the higher the product yield and the lower the relative production cost. Inductively coupled plasma etching is currently the main etching method in the field of integrated circuits. Due to the requirement of the reaction chamber for the function of pumping the wafer, the structure of the reaction chamber cannot be completely symmetrical. This asymmetry reduces the uniformity of etching Sex.

The existing inductively coupled plasma equipment is shown in the first figure, in which the upper electrode RF power supply 1 loads power to the outer ring 6 and the inner ring 7 of the inductively coupled coil through the matching device 2 and the current distribution unit 3, and the process gas passes The nozzle 12 installed on the quartz dielectric window 8 enters the reaction chamber 13, and the RF energy on the inductive coupling coil is coupled into the reaction chamber 13 through the dielectric window 8 to generate a plasma 11, acting on the workpiece 9 to be processed, to be processed The workpiece 9 is placed on the electrostatic chuck 10, and the lower electrode RF power source 5 loads the RF energy onto the RF copper column at the bottom of the electrostatic chuck through the matching device 4, thereby providing an RF field, generating RF bias, and forming on the surface of the workpiece to be processed The ion accelerated sheath etches the workpiece 9 to be processed. 14 in the first picture is a phase-locked cable (cable) with a fixed length. The upper electrode RF power supply is often defined as the master power supply and the lower electrode RF power supply is defined For auxiliary power (Slave), the cable (cable) is of fixed length, the common excitation (CEX, Common EXcitation) phase locking angle of the upper and lower electrode RF power is a fixed value, thereby locking the upper electrode RF power 1 and the lower electrode RF power 5 The phase difference of the output RF waveform.

At present, the commonly used method for solving the etching uniformity is to adjust the current proportional distribution unit 3 so that the power loaded on the outer coil 6 and the inner coil 7 is distributed in proportion, so as to achieve the uniformity of the plasma above the workpiece to be processed and further improve the etching rate .

In the process of implementing the present disclosure, the applicant found that the prior art has the following defects:

The above-mentioned method of adjusting the current ratio of the inner and outer rings to improve the etching uniformity is limited by the coil structure and the current ratio adjustment unit. Under some process gases, the adjustment of the current ratio has little contribution to the uniformity, while adjusting the current ratio of the inner and outer rings The radial uniformity of the workpiece to be processed is obvious, and the angular uniformity of the workpiece to be processed is limited.

In view of the above technical problems, the present disclosure provides a plasma etching method to solve the problem of limited adjustment of the angular distribution of the plasma by adjusting the current ratio of the inner and outer rings.

According to an aspect of the present disclosure, there is provided a plasma etching method for etching a workpiece to be processed in a reaction chamber, the plasma etching method includes at least one etching step, and each of the etching steps includes adjustment The step of phase difference between the RF power of the electrode and the RF power of the lower electrode to adjust the angular distribution of the plasma.

In some embodiments of the present disclosure, the step of adjusting the phase difference between the upper electrode RF power supply and the lower electrode RF power supply includes adjusting the phase angle of the output waveform of the upper electrode RF power supply and/or adjusting the lower electrode RF power supply The phase angle of the output waveform.

In some embodiments of the present disclosure, the step of adjusting the phase difference between the upper electrode RF power supply and the lower electrode RF power supply includes periodically changing the phase difference between the first angle and the second angle.

In some embodiments of the present disclosure, the phase difference gradually changes from the first angle to the second angle, or gradually changes from the first angle to the second angle and then gradually changes from the second angle to The first angle.

In some embodiments of the present disclosure, in each change period, the phase difference is discretely changed according to a predetermined step size.

In some embodiments of the present disclosure, the predetermined step sizes are all the same.

In some embodiments of the present disclosure, in each change period, the phase difference continuously changes.

In some embodiments of the present disclosure, the phase difference varies linearly and continuously.

In some embodiments of the present disclosure, the change slope of the phase difference is the same.

The present disclosure adopts the CEX phase-locking angle adjustment of the RF power of the upper and lower electrodes during the etching process, which can fully adjust the plasma distribution above the workpiece to be processed, and avoids the adjustment of the angular distribution of the plasma by adjusting the current ratio of the inner and outer rings. The limitation of this is conducive to the uniform distribution of the plasma angle during the etching time, thereby improving the etching uniformity. In the present disclosure, the change cycle and rate of the CEX phase-locking angle can be adjusted, which can compensate for the shortcomings caused by the current proportional adjustment to the greatest extent, and further optimize the etching uniformity.

These and other viewpoints and embodiments will become clear to those of ordinary skill in the related art with reference to the subsequent detailed description and accompanying drawings.

In order to make the purpose, technical solutions and advantages of the present disclosure more clear, the present disclosure will be further described in detail in conjunction with specific embodiments and with reference to the accompanying drawings.

For convenience of description, the above-mentioned electrode RF power source refers to the RF power source of the upper electrode structure, and the lower electrode RF power source refers to the RF power source of the lower electrode structure.

The method adopted in the present disclosure is implemented based on adjusting the phase difference of the output waveform of the RF power supply of the upper and lower electrodes, that is, the CEX phase-locked angle.

The energy of the upper electrode RF power supply structure of the inductively coupled plasma device coupled into the reaction chamber can be divided into capacitive coupling and inductive coupling, of which about 1/3 is capacitive coupling, 2/3 is inductive coupling, and the lower electrode The energy of the RF power source coupling into the reaction chamber is mainly capacitive coupling energy. By adjusting the CEX phase lock angle, the phase difference between the energy of the capacitive coupling of the upper electrode RF power source and the capacitive coupling energy of the lower electrode RF power source can be adjusted. Affect the ion energy and sheath potential above the workpiece to be processed, adjust the angular distribution of the plasma, and then change the etching rate and map distribution of the workpiece to be processed, so the difference in CEX phase lock angle can directly affect the process etching rate (ER, Etch Rate) and graph distribution.

Taking the etching result of the edge circumference of the workpiece to be processed as an example, the point of the workpiece to be processed is 0 degrees at 12 o'clock, and the points that make one rotation clockwise correspond to the measurement positions 0 to 360° in the second figure. The change of the etching rate of the edge circumference of the workpiece to be processed under the CEX phase lock angle. When the CEX phase lock angle changes, the position corresponding to the minimum etching rate shifts with the change of the CEX phase lock angle, which directly affects the etching rate graph distribution. Relative to the position corresponding to the minimum etching rate when the CEX phase locking angle is zero, when the CEX phase locking angle is λ/8, the position corresponding to the minimum etching rate is offset by about 45 degrees, and when the CEX phase locking angle is λ/ At 4 o'clock, the minimum etching rate position is shifted by about 90 degrees. When the CEX phase lock angle is λ/2, the minimum etching rate position is shifted by about 180 degrees. Therefore, when the CEX phase lock angle changes along a wavelength angle, the etching The rate graph rotates correspondingly for one cycle.

The method proposed in the present disclosure is to change the loop of the CEX phase lock angle during the etching process, so that the plasma state during the etching process is constantly changing, and the ion energy and the sheath potential above the workpiece to be processed are continuously changing in cycles to achieve Increased etching uniformity.

As shown in the third figure, an embodiment of the present disclosure provides a plasma etching method, which is suitable for the following etching process. The etching process includes etching step step1, etching step step2, etching step step3, ... etching step stepN, the etching time of each etching step is T1, T2, T3...TN, and the CEX phase lock angle is changed from 0° to 360° is defined as a change cycle. In this embodiment, multiple change cycles of the CEX phase lock angle are implemented in each etching step. If the number of change cycles of the CEX phase lock angle in the etching step 1 is a, the CEX phase lock angle The rate of change is K1=360a/T1, and the number of change cycles of the CEX phase-locked angle in the etching step step2 is b, then the rate of change of the CEX phase-locked angle in the etching step step2 is K2=360b/T2, and the CEX in the etching step3 The number of change cycles of the phase-locked angle is c, then the change rate of the CEX phase-locked angle of the etching step step3 is K3=360c/T3, the number of change cycles of the CEX phase-locked angle of the etching step stepN is m, The rate of change of the CEX phase-locked angle is KN=360m/TN. When each etching step is performed, the CEX phase-locked angle changes the corresponding set number of change cycles. When each etching step is performed, the CEX phase-locked angle After a period of change, for each point on the workpiece to be processed, the plasma energy and sheath potential above it have changed by one period, and the etching rate of each point in the circumferential direction has experienced a value from the maximum value to the minimum value. Periodic changes. After multiple cycles, the etching rate of each point in the circumferential direction is equivalent to the average level during the etching time, so the angular uniformity of the etching rate is improved.

）的時間間隔來向下電極射頻電源發送指令，在每個時間點下電極射頻電源的CEX角度分別依次設定為0°、1°、……360°、0°、1°、……360°、……的迴圈，直至蝕刻步驟step1結束，結束後將下電極射頻電源CEX角度恢復至0度，繼續進行下一個蝕刻步驟step，蝕刻步驟stepN進行時，同樣通過以KN=360m/TN的速率來進行CEX鎖相角度的週期性變化，即以TN/360/m（

）的時間間隔來向下電極射頻電源發送指令，令下電極射頻電源的CEX角度分別依次設定為0°、1°、……360°、0°、1°、……360°、……的迴圈，直至蝕刻步驟stepN結束，整個蝕刻過程結束時，恢復下電極射頻電源CEX角度至0°。The plasma etching method corresponding to this embodiment is as shown in the fourth figure below. The upper electrode radio frequency power supply is set as the main power supply, and the lower electrode radio frequency voltage is set as the auxiliary power supply. After the etching starts, set the CEX angle of the upper and lower electrode RF power supply to 0°, and keep the CEX angle of the upper electrode RF power supply unchanged during the subsequent etching process, only by changing the phase angle of the output waveform of the lower electrode RF power supply, that is, CEX Angle to achieve the change of the phase difference of the RF power of the upper and lower electrodes. After the start of the etching step step1, the CEX angle changes at a rate of K1=360a/T1 during a change period, that is, during the entire etching time T1, at T1/360/a (

) Time interval to send commands to the lower electrode RF power supply, at each time point the CEX angle of the electrode RF power supply is set to 0°, 1°, ...360°, 0°, 1°, ...360°, ... until the end of the etching step step1, after the end, the CEX angle of the lower electrode RF power supply is restored to 0 degrees, and the next etching step step is continued. When the etching step stepN is carried out, the rate of KN=360m/TN is also adopted. To perform the periodic change of the CEX phase-locked angle, that is, TN/360/m (

) Time interval to send commands to the lower electrode RF power supply, so that the CEX angle of the lower electrode RF power supply is set to 0°, 1°, ...360°, 0°, 1°, ...360°, ... Circle until the stepN of the etching step is completed, and at the end of the entire etching process, the CEX angle of the RF power of the lower electrode is restored to 0°.

In this embodiment, for each change period, the CEX phase-locked angle changes in steps of 1°. The number of change cycles of each etching step is not limited, and can be adjusted according to actual needs and the conditions of the etching results. Those skilled in the art can understand that the number of change cycles is at least once, but generally speaking, for an etching step with a longer etching time, the number of change cycles is correspondingly greater.

As shown in the fifth figure, the plasma etching method of another embodiment of the present disclosure is different from the previous embodiment in that the CEX phase-locked angle is changed from 0° to 360°, and then from 360° to 0° Defined as a cycle of change.

The number of change cycles of the CEX phase-locked angle in the etching step step1 is a, then the change rate is K1=360a/T1*2, and the number of change cycles of the CEX phase-locked angle in the etching step step2 is b, then the CEX of the etching step2 The rate of change of the phase-locked angle is K2=360b/T2*2, and the number of change cycles of the CEX phase-locked angle of the etching step 3 is c, then the rate of change of the CEX phase-locked angle of the etching step 3 is K3=360c/T3* 2. The number of change cycles of the CEX phase locking angle of the stepN in the etching step is m, and the rate of change of the CEX phase locking angle of the stepN in the etching step is KN=360m/TN*2. When each etching step is performed, the CEX phase lock The angles change the number of change cycles set accordingly, thereby improving the overall uniformity.

）的時間間隔來向下電極射頻電源發送指令，令下電極射頻電源的CEX角度分別依次設定為0°、1°、……360°、359°、358°、……0°、……的迴圈，直至蝕刻步驟step1結束，結束後將下電極射頻電源CEX角度恢復至0度，繼續進行下一個蝕刻步驟step，蝕刻步驟stepN進行時，同樣通過以KN=360m/TN*2的速率來進行CEX鎖相角度的週期性變化，即以TN/360/m/2（

）的時間間隔來向下電極射頻電源發送指令，令下電極射頻電源的CEX角度分別依次設定為0°、1°、……360°、359°、358°、……0°、……的迴圈，直至蝕刻步驟stepN結束，整個蝕刻過程結束時，恢復下電極射頻電源CEX角度至0°。The plasma etching method corresponding to this embodiment is shown in the sixth figure. After the etching starts, the CEX angle of the upper and lower electrode RF power supplies is set to 0°, and the CEX angle of the upper electrode RF power supply is maintained during the subsequent etching process. Only by changing the CEX angle of the RF power of the lower electrode, the phase difference of the RF power of the upper and lower electrodes can be changed. After the etching step step1 starts, the periodic change of the CEX phase-locked angle is performed at a rate of K1=360a/T1*2, that is, at T1/360/a/2 (

) Time interval to send commands to the lower electrode RF power supply, so that the CEX angle of the lower electrode RF power supply is set to 0°, 1°, …360°, 359°, 358°, …0°,… Circle until the end of the etching step step1, after which the CEX angle of the lower electrode RF power supply is restored to 0 degrees, and the next etching step step is continued. When the etching step stepN is carried out, the same is carried out at a rate of KN=360m/TN*2 The periodic change of CEX phase-locked angle, that is, TN/360/m/2 (

) Time interval to send commands to the lower electrode RF power supply, so that the CEX angle of the lower electrode RF power supply is set to 0°, 1°, …360°, 359°, 358°, …0°,… Circle until the stepN of the etching step is completed, and at the end of the entire etching process, the CEX angle of the RF power of the lower electrode is restored to 0°.

）的時間間隔來向下電極射頻電源發送指令，令下電極射頻電源的CEX角度分別依次設定為0°、q°、2×q°、……360°、0°、q°、2×q°、……360°、……的迴圈（此時，q為360的約數，也即360為q的整數倍），直至蝕刻步驟step1結束，結束後將下電極射頻電源CEX角度恢復至0度，繼續進行下一個蝕刻步驟step，蝕刻步驟stepN進行時，同樣通過以KN=360m/TN的速率來進行CEX角度的週期性變化，即以TN/360/m*q（

）的時間間隔來向下電極射頻電源發送指令，令下電極射頻電源的CEX角度分別依次設定為0°、q°、2×q°……360°、0°、q°、2×q°……360°、……的迴圈（此時，q為360的約數，也即360為q的整數倍），直至蝕刻步驟stepN結束，整個蝕刻過程結束時，恢復下電極射頻電源CEX角度至0°。也就是說，對於該實施例，在蝕刻過程中CEX的變化不受限於按1°的步長進行，可以根據時間間隔按任意角度值q增加，q例如可以為5°、10°等。The plasma etching method of yet another embodiment of the present disclosure, as shown in the seventh figure, differs from the above embodiment in that this embodiment is not limited to changes in steps of 1°. After the etching step step1 starts, the periodic change of the CEX phase-locked angle is performed at a rate of K1=360a/T1, that is, at T1/360/a*q (

) Time interval to send commands to the lower electrode RF power supply, so that the CEX angle of the lower electrode RF power supply is set to 0°, q°, 2×q°, …360°, 0°, q°, 2×q°, respectively , ... 360°, ... (at this time, q is a divisor of 360, that is, 360 is an integer multiple of q), until the end of the etching step step1, after the end, the lower electrode RF power CEX angle is restored to 0 degrees , Continue to the next etching step step, when the etching step stepN is carried out, the periodic change of the CEX angle is also carried out at the rate of KN=360m/TN, that is, TN/360/m*q (

) Time interval to send commands to the lower electrode RF power supply, so that the CEX angle of the lower electrode RF power supply is set to 0°, q°, 2×q°……360°, 0°, q°, 2×q°… …360°,… loop (at this time, q is a divisor of 360, that is, 360 is an integer multiple of q) until the end of the etching step stepN, at the end of the entire etching process, the lower electrode RF power CEX angle is restored to 0 °. That is to say, for this embodiment, the change of CEX during the etching process is not limited to steps of 1°, and may be increased at any angle value q according to the time interval, and q may be 5°, 10°, etc., for example.

The plasma etching method of yet another embodiment of the present disclosure is different from the above embodiment in that in each change cycle, the CEX phase-locked angle is continuously changed, and the CEX phase-locked angle is continuously changed from the first angle to the first Two angles, or continuous change from the first angle to the second angle, and then the continuous change from the second angle to the first angle is defined as a change period.

During the etching process, there are etching step1, etching step2, etching step3, ... etching stepstepN, the etching time of each etching step is T1, T2, T3...TN, for any of the etching steps Change cycle, in each change cycle, the CEX phase-locked angle changes from the first angle to the second angle, or from the first angle to the second angle, and then from the second angle to the first angle, in the same etching step The slope of the CEX phase-locked angle change for each change period can be different. For any change period, the CEX phase-locked angle changes continuously from a first angle to a second angle at a changing slope, or continuously changes from a first angle to a second angle at a changing slope, and then changes from a second angle at a changing slope Continuous change to the first angle, that is, the change of the CEX phase lock angle during the etching process can also be extended to continuously change at a certain slope, that is, linear continuous change.

In this embodiment, the change slope of the CEX phase-locked angle of each change period of the same etching step may also be the same. In this case, the change slope of the CEX angle of each etching step may be the same or different. The first angle is preferably 0°, and the second angle is preferably 360° to improve etching uniformity.

The plasma etching method of another embodiment of the present disclosure is different from the above embodiment in that the upper electrode radio frequency power supply is set as the auxiliary power supply and the lower electrode radio frequency power supply is set as the main power supply. In this embodiment, after the etching starts, the CEX angle of the lower electrode RF power supply is set to 0°, and the CEX angle of the lower electrode RF power supply remains unchanged during the subsequent etching process, which is only achieved by changing the CEX angle of the upper electrode RF power supply Changes in the phase difference of the RF power of the upper and lower electrodes.

The plasma etching method of another embodiment of the present disclosure is different from the above embodiment in that the radio frequency power of the upper electrode and the radio frequency of the lower electrode are not divided into main and auxiliary in this embodiment, and the upper and lower electrodes can be set simultaneously after the etching starts The CEX angle of the RF power supply is 0°. In the subsequent etching process, the CEX angle of the upper electrode RF power supply and the CEX angle of the lower electrode RF power supply are simultaneously changed to realize the change of the phase difference of the upper and lower electrode RF power supplies.

So far, this embodiment has been described in detail with reference to the drawings. Based on the above description, those skilled in the art should have a clear understanding of the plasma control method of the present disclosure.

The present disclosure is not only applicable to inductively coupled plasma equipment, but also to capacitively coupled plasma equipment, microwave plasma equipment, and ECR plasma equipment.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present disclosure in detail. It should be understood that the above are only specific embodiments of the present disclosure and are not intended to limit the present disclosure. Within the spirit and principle of this disclosure, any modifications, equivalent replacements, improvements, etc., should be included within the scope of protection of this disclosure.

It should also be noted that the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "back", "left", "right", etc., are only the directions referring to the drawings, not Used to limit the scope of protection of this disclosure. Throughout the drawings, the same elements are denoted by the same or similar reference signs. When it may cause confusion to the understanding of the present disclosure, the conventional structure or configuration will be omitted.

Unless well-known as contrary, the numerical parameters in this specification and the appended claims are approximate and can be changed according to the desired characteristics obtained through the disclosure. Specifically, all numbers used in the specification and claims to indicate the content of the composition, reaction conditions, etc., should be understood as modified by the word "about" in all cases. In general, the meaning of the expression refers to including a specific amount of ±10% change in some embodiments, ±5% change in some embodiments, ±1% change in some embodiments, and in some implementations In the case of ±0.5% change.

Furthermore, the word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "a" or "one" before an element does not exclude the presence of multiple such elements.

The ordinal numbers used in the specification and claims, such as "first", "second", "third", etc., are used to modify the corresponding elements, which is not intended to imply that the elements have any ordinal numbers, nor It does not represent the order of a certain element and another element, or the order of manufacturing methods. The use of these ordinal numbers is only used to make a certain element with a certain name can be clearly distinguished from another element with the same name.

Similarly, it should be understood that in order to streamline the disclosure and help understand one or more of the various disclosed aspects, in the above description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together into a single embodiment , Figures, or their descriptions. However, the disclosed method should not be interpreted as reflecting the intention that the claimed disclosure requires more features than those explicitly recited in each claim. Rather, as reflected in the following claims, the disclosed aspects lie in less than all features of a single disclosed embodiment. Therefore, the claims that follow the specific implementation are hereby expressly incorporated into the specific implementation, where each claim itself serves as a separate embodiment of the present disclosure.

1‧‧‧ Upper electrode RF power supply 2,4‧‧‧ Matching device 3‧‧‧Current distribution unit 5‧‧‧Lower electrode RF power supply 6‧‧‧Outer coil of inductive coupling coil 7‧‧‧Inner coupling coil Circle 8‧‧‧Quartz dielectric window 9‧‧‧Workpiece to be processed 10‧‧‧Electrostatic chuck 11‧‧‧Plasma 12‧‧‧‧Nozzle 13‧‧‧Reaction chamber 14‧‧‧Phase-locked cable

The invention can be further understood with reference to the following drawings and description. Non-limiting and non-exhaustive examples are described with reference to the following drawings. The components in the drawings do not have to be actual sizes; the emphasis is on explaining the structure and principles. The first figure is a schematic structural view of an existing inductively coupled plasma device. The second figure is a schematic diagram of the influence of different CEX phase-locking angles on the etching rate at different positions on the edge of the workpiece to be processed according to the present disclosure. The third figure is a schematic diagram of the etching process and the corresponding CEX angle setting according to an embodiment of the present disclosure. The fourth figure is a flowchart of the plasma etching method according to the embodiment shown in the third figure of the present disclosure. FIG. 5 is a schematic diagram of an etching process and corresponding CEX angle setting according to another embodiment of the present disclosure. FIG. 6 is a flow chart of the plasma etching method according to the embodiment shown in FIG. 5 of the present disclosure. FIG. 7 is a flowchart of a plasma etching method according to another embodiment of the present disclosure.

Claims (9)

A plasma etching method is used to etch a workpiece to be processed in a reaction chamber. The plasma etching method includes at least one etching step, and each of the etching steps includes adjusting the upper electrode radio frequency power supply and the lower electrode radio frequency power supply The step of adjusting the phase difference between the phases to adjust the angular distribution of the plasma, wherein the step of adjusting the phase difference between the RF power of the upper electrode and the RF power of the lower electrode includes making the phase difference at a first angle and The second angle changes periodically. The plasma etching method as described in the first patent application, wherein the step of adjusting the phase difference between the upper electrode RF power supply and the lower electrode RF power supply includes adjusting the phase angle of the output waveform of the upper electrode RF power supply and /Or adjust the phase angle of the output waveform of the lower electrode RF power supply. The plasma etching method as described in the first patent application scope, wherein the phase difference gradually changes from the first angle to the second angle in each change period, or gradually changes from the first angle to the second angle Gradually change from the second angle to the first angle. The plasma etching method as described in claim 3, wherein in each change period, the phase difference is discretely changed according to a predetermined step. The plasma etching method as described in claim 4 of the patent application, wherein the predetermined steps are all the same. The plasma etching method as described in claim 3, wherein the phase difference continuously changes in each change period. The plasma etching method as described in claim 6 of the patent application, wherein the phase difference changes linearly and continuously. The plasma etching method as described in claim 7 of the patent application, wherein the change slope of the phase difference is the same. The plasma etching method as described in claim 3, wherein the first angle is zero degrees and the second angle is 360 degrees.

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