TWI769447B - Method and device for multi-frequency and multi-stage plasma radio frequency output - Google Patents

Abstract

A method for outputting radio frequency power for plasma etching, comprising: providing a plurality of radio frequency generators, each radio frequency generator outputting radio frequency power of respective different frequencies, the output power of each radio frequency generator being variable, providing a controller, The controller controls a plurality of radio frequency generators to output radio frequency power during the continuous pulse. One pulse period of the continuous pulse includes three continuous stages. In each stage, at least one radio frequency generator outputs radio frequency power. In the plasma stage, the etching stage and the sustaining plasma stage, the period length of the pulse period is 50us-0.1s. This method can achieve faster switching speed and perform RF frequency switching with power in pulsed mode.

Description

Method and device for multi-frequency and multi-stage plasma radio frequency output

The present invention relates to a radio frequency pulse output method, and more particularly to a radio frequency source system for implementing the method and a plasma etching apparatus including the radio frequency source system.

In existing semiconductor processing, plasma etching equipment is widely used to process semiconductor wafers to obtain micro-sized semiconductor devices and conductor connections. Common plasma etching equipment is capacitively coupled (CCP) and inductively coupled (ICP) etcher. These devices generally have two radio frequency generators, one of which is used to ionize the reactant gas introduced into the reaction chamber to generate electricity. slurry, another RF generator is used to control the ion energy incident on the wafer surface.

Today, many plasma machining processes use pulsed plasma RF generators instead of continuous plasma RF generators. The characteristic of the pulsed plasma RF generator is that during the whole processing period, the RF power supply is not continuously powered, but alternately turns on and off the power supply or alternately performs high-power and low-power RF power supply, and the waveform of its output power is in the form of pulses. The open-close duty cycle can be adjusted, generally within the range of 10%-90%. The advantage of pulsed plasma radio frequency is that in the off stage, the sheath on the surface of the silicon wafer disappears, and the electrons accumulated on the surface of the silicon wafer and in the edge of the etched deep hole are neutralized with the silicon wafer due to the disappearance of the sheath. More electrons can enter the bottom of the deep hole to neutralize the ions accumulated at the bottom, which facilitates further etching of the deep hole in the next turn-on stage. And, in the same pulse, the frequency of the plasma generator can also be switched for different etching processes.

The existing switchable dual-frequency plasma system uses relays to switch between radio frequency generators with different frequencies, which has two disadvantages: one is that the switching cannot be performed under the condition of power output. Or it can only be switched under low power; the second is that it cannot be switched in the pulse power mode, because the relay switching is a mechanical action, and its response time is much longer than the pulse period. Therefore, the existing dual-frequency plasma switching technology can only be used in power output occasions with low power and long pulse time (on the order of seconds), and it is not easy to maintain continuous plasma operation.

In view of the above problems, in a first aspect, the present invention proposes a method for outputting radio frequency power for plasma etching, the method comprising: providing a plurality of radio frequency generators, each radio frequency generator outputting radio frequency power of different frequencies, For output to a plasma etcher, the power output of each radio frequency generator is variable, and a controller is provided, and the controller controls the output radio frequency power of the plurality of radio frequency generators to change in a continuous plurality of pulse cycles, wherein each Each pulse cycle includes three processing stages. In each processing stage, at least one RF generator outputs RF power. The three processing stages are the plasma generation stage, the etching stage, and the maintenance plasma stage, which are performed in sequence. The cycle length is 50us-0.1s, and the plurality of RF generators include at least three RF generators, which are high-frequency RF generators, intermediate-frequency RF generators and low-frequency RF generators, among which the high-frequency RF generators are generating plasma. The stage outputs a first high frequency radio frequency power to the plasma etcher to generate a plasma of sufficient concentration, and a second high frequency radio frequency power is output to the plasma etcher to maintain the plasma in the sustaining plasma stage.

Preferably, at most two RF generators simultaneously output RF power at each stage.

Preferably, the output frequency of the high frequency radio frequency generator is 40MHz-100MHz, the output frequency of the intermediate frequency radio frequency generator is 10MHz-20MHz, and the output frequency of the low frequency radio frequency generator is 200kHz-4MHz.

Preferably, in the stage of generating plasma, the intermediate frequency radio frequency generator outputs first intermediate frequency radio frequency power for generating plasma and reactive groups.

Preferably, in the etching stage, the intermediate frequency radio frequency generator and the low frequency radio frequency generator output the second intermediate frequency radio frequency power and the first low frequency radio frequency power for performing high aspect ratio etching.

Preferably, during the sustaining plasma phase, the low frequency RF generator stops outputting RF power to release the charge accumulation of the processed workpiece.

Preferably, the output power range of the high frequency radio frequency generator and the intermediate frequency radio frequency generator is 50W-10kW.

Preferably, the output power of the low frequency radio frequency generator is in the range of 100W-20kW.

The present invention also provides a method for outputting radio frequency power for plasma etching. The method includes: providing a plurality of radio frequency generators, each radio frequency generator outputs radio frequency power of different frequencies to the plasma etching device, and each radio frequency generator outputs radio frequency power of different frequencies to the plasma etching device. The power output of the generator is variable, and a controller is provided, and the controller controls the output radio frequency power of the plurality of radio frequency generators to change in a continuous plurality of pulse cycles, wherein each pulse cycle includes three processing stages, and in each process At least one radio frequency generator in the stages outputs radio frequency power, wherein, the three processing stages are respectively a plasma generation stage, an initial etching stage, and a main etching stage, which are performed in sequence. The generator includes at least three radio frequency generators, which are a high frequency radio frequency generator, an intermediate frequency radio frequency generator and a low frequency radio frequency generator, wherein the high frequency radio frequency generator outputs the first high frequency radio frequency power and the third The second high frequency radio frequency power and the third high frequency radio frequency power.

Preferably, in the stage of generating plasma, the intermediate frequency radio frequency generator simultaneously outputs the first intermediate frequency radio frequency power for generating plasma and reactive groups.

Preferably, in the initial etching stage, the low frequency radio frequency generator outputs the first low frequency radio frequency power.

Preferably, in the main etching stage, the intermediate frequency radio frequency generator outputs the second intermediate frequency radio frequency power.

In a second aspect, the present invention provides a radio frequency source system of a plasma etching device, comprising: a plurality of radio frequency generators for outputting radio frequency power, and each radio frequency generator in the plurality of radio frequency generators outputs power of different frequencies a controller for controlling a plurality of radio frequency generators, so that the plurality of radio frequency generators execute the above method.

In a third aspect, the present invention provides a plasma processing apparatus, comprising a reaction chamber; a base located in the reaction chamber and used to support a substrate to be processed; and a radio frequency source system in the second aspect, used for RF power is supplied to the reaction chamber.

Compared with the prior art of frequency switching through relays, the present invention can achieve faster switching speed, and can perform radio frequency switching with power in a pulse mode. In addition, any stage can be divided into a pulse cycle according to different substrate processing processes. In each stage, the parameters of various RF generators can be flexibly set, such as the number of output RF generators, the power level, etc. Well suited to different processing requirements.

10: Gas shower head

100,W: substrate

101: Through hole

20: External air source

30: reaction chamber

40: Pedestal

50: Processing device

60: Plasma Confinement Device

70: RF Power Supply Unit

701, 702, 703, RF1, RF2, RF3: Radio Frequency Generators

80: Vacuum device

90: Controller

Figure 1 shows a schematic diagram of a CCP processing apparatus using a method according to an embodiment of the present invention.

FIG. 2 shows a schematic diagram of a radio frequency power output of a dual-frequency switchable radio frequency plasma control system in the prior art.

FIG. 3 is a schematic diagram of multi-stage multi-frequency switchable plasma RF power output according to an embodiment of the present invention.

FIG. 4A and FIG. 4B are schematic diagrams of the topography of the sidewall of the through hole during the etching process.

FIG. 5 is a schematic diagram of a multi-stage multi-frequency switchable plasma RF power output according to another embodiment of the present invention.

FIG. 6 is a schematic diagram of the power output of a radio frequency generator with multi-stage pulse power output according to an embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be emphasized that this is only an exemplary illustration, which does not exclude other embodiments utilizing the present invention.

The specific embodiments of the present invention will be described below with reference to the accompanying drawings.

The present invention provides a multi-frequency and multi-stage plasma radio frequency pulse output method, which can be applied to plasma processing devices, such as capacitively coupled plasma (CCP) processing devices, inductively coupled plasma (ICP) processing devices, etc. . Figure 1 shows a schematic diagram of a CCP processing apparatus using the method of the present invention. The processing device 50 includes a vacuum reaction chamber 30 surrounded by the outer wall of the reaction chamber, and a reaction space is formed inside the reaction chamber for plasma etching process treatment; a base 40 is arranged in the vacuum reaction chamber for fixing the substrate to be processed W, the base 40 also serves as the lower electrode of the vacuum reaction chamber. A flat gas shower head 10 is arranged on the top of the reaction chamber, and the gas shower head 10 communicates with an external gas source 20 through a pipeline. The gas shower head corresponds to the position of the base and serves as the upper electrode of the vacuum reaction chamber. The radio frequency power supply device may include a plurality of radio frequency generators, one or more of which may be selectively applied to one of the upper electrode or the lower electrode. As shown in FIG. 1, the radio frequency power supply device includes three radio frequency generators 701-703, which are all applied to the lower electrode, wherein each radio frequency generator outputs power of different frequencies. For example, the high-frequency radio frequency generator 701 ionizes the reaction gas introduced into the reaction chamber to generate plasma; the intermediate frequency radio frequency generator 702 is applied to the lower electrode, so that a sufficient DC bias voltage is generated in the sheath on the upper surface of the substrate to accelerate the electric The charged ions in the slurry rapidly bombard the substrate to perform etching; the low frequency radio frequency generator 703 outputs low frequency power to cooperate with the intermediate frequency radio frequency generator to perform etching. A plasma plasma confinement device 60 is arranged around the base 40 for confining the plasma in the plasma region, and a vacuum device 80 is used for exhausting the plasma in the reaction chamber. The unreacted gas and the reaction by-product gas are used to maintain the vacuum state of the reaction chamber 30 . The controller 90 controls the RF power supply device 70 to complete the etching process. The controller 90 also monitors parameters of the processing device 50 and controls the delivery of reactive gases, maintaining and extinguishing the plasma, supplying cooling gases, and the like.

FIG. 2 shows a schematic diagram of a radio frequency power output of a dual-frequency switchable radio frequency plasma control system in the prior art. The figure shows four steps, with two frequency outputs in each step, each step is from a few seconds to hundreds of seconds long. The RF generator RF1 operates continuously in each step, but the power varies. The radio frequency generators RF2 and RF3 are switched in different steps, and the combination of output power and time of the radio frequency generators RF2, RF3 and RF1 can be arbitrarily set. The figure shows that the radio frequency generator RF2 occupies steps 1 and 3, and the radio frequency generator RF3 occupies steps 2 and 4. Since the RF generator RF frequency switching in the prior art uses relays, it can only be switched at low power and the switching takes a long time on the order of seconds (as shown in Figure 2, there is a relatively long time between each step). long-term power interruption), so the plasma control system is not suitable for pulsed plasma RF generator and pulsed plasma RF process. In the application of the present invention, the pulse frequency of the etching process is 10Hz-20KHz, that is, the pulse duration is 1/20 microsecond-0.1 second. With such a short pulse duration, switching times on the order of seconds are clearly not suitable for the process of the present invention.

The controller can realize fast switching without power interruption of different RF generators in the RF power supply device. The controller may be externally connected to the RF power supply unit, or may be built into the RF power supply unit. Alternatively, a controller may be built into each RF generator individually. The controller is pre-programmed with parameters to control the different RF generators to output RF power at different stages within a continuous pulse cycle. The parameters include, but are not limited to, the frequency of continuous pulses, the number of stages, the duration of each stage, the output power of the RF generator, and the number of RF generators that output power in one stage. The combination of different parameters can be changed according to the requirements of the etching process.

In one embodiment, the controller 90 is externally connected to the RF power supply device 70 . Controlling the plurality of RF generators to switch frequencies without power interruption by the controller 90 can be used in a variety of substrate processing applications, such as high aspect ratio etch steps for the fabrication of three-dimensional memory. In the prior art, source pulsed radio frequency generators (usually 60MHz high-frequency pulsed radio frequency generators) mostly adopt a continuous working mode or a pulsed working mode. In continuous operation mode, the output power of the source pulsed RF generator remains unchanged. In the pulse operation mode, the source pulse RF generator alternately outputs high and low power or turns on and off the power output alternately within a pulse period. In the present invention, a pulse cycle can be divided into a plurality of stages according to process requirements, and the source pulse RF generator can be selected to output or not output power at any stage, instead of only two stages of a pulse cycle as in the prior art It is more flexible and saves the energy consumption of the RF generator.

Figure 3 shows a schematic diagram of a multi-stage multi-frequency switchable plasma RF power output according to an embodiment of the present invention, and the pulse output method shown in the schematic diagram is particularly used in high aspect ratio etching for manufacturing memory. A plasma processing configuration has three frequency pulsed RF generators: high frequency (40-100MHz) RF generator, intermediate frequency (10-20MHz) RF generator and low frequency (200kHz-4MHz) RF generator. High frequency radio frequency power is usually used to generate plasma in the cavity, but the presence of high frequency radio frequency power in the cavity during etching will adversely affect the uniformity of etching. Therefore, the introduction of intermediate frequency radio frequency power can not only keep the plasma from extinguishing, but also will not have a great impact on the uniformity of etching. The main function of the low-frequency radio frequency power is to generate enough bias voltage on the upper surface of the substrate, so that charged ions bombard the substrate for etching. Thus, in one embodiment, the power output profile of each RF generator may be configured as shown in FIG. 3 . In the (1) stage of each pulse, that is, the stage of generating plasma, the first high-frequency power and the first intermediate-frequency power are output to dissociate the processing gas to generate charged ions and reactive groups. The output of the first intermediate frequency power is used to assist the first high frequency power to generate plasma and reactive groups. In another embodiment, it is also possible to Only the first high frequency power is used to generate the plasma. The (2) stage, that is, the etching stage, outputs the first low frequency power and the second intermediate frequency power, generates a high bias voltage, and performs high aspect ratio etching. In this stage, the first high frequency output power is turned off, and the intermediate frequency and low frequency power are used. On the one hand, the plasma can be maintained so that it does not go out; on the other hand, the uniformity of etching can be increased by not outputting the high frequency power. Turning off the high-frequency power output at this stage can also save power. The (3) stage, namely the maintenance plasma stage, only outputs the second high frequency power, and the second high frequency power is smaller than the first high frequency power to maintain the plasma and release the charge accumulation of the workpiece. During the high aspect ratio etching process, as the positively charged particles continue to bombard the substrate 100, positive charges will accumulate at the bottom of the through holes 101, and these unevenly distributed positive charges will cause the downwardly incident positively charged particles to travel over long distances. The in-flight direction is shifted, and further, the etching direction of the etched through hole 101 is shifted, as shown in FIG. 4A . Therefore, in the plasma sustaining stage of this embodiment, only low-power high-frequency power is output and the intermediate-frequency and low-frequency RF power generators are turned off, which can maintain the plasma and release the charge accumulation at the bottom of the through hole, so as to accurately Directly etch the vias as shown in Figure 4B.

In the (1) stage of the next pulse cycle, the first high frequency power is output again. This is because, in the previous stage, only the second high-frequency power with lower power is output, and the plasma concentration is lower at this time, and it is only used to maintain the plasma from being extinguished. In the next pulse cycle, a plasma of sufficient concentration must be generated again. Therefore, phase (1) of the first pulse cycle is used to generate plasma in the chamber without plasma, and phase (1) of the remaining pulse cycle is used to generate sufficient concentration of plasma in the chamber of low concentration plasma. Therefore, the (1) stage of the pulse cycle is collectively referred to as the plasma generation stage. The controller 90 controls the duration of the three stages, the power output of the three RF generators, and the switching between the RF generators through preset parameters. Through the above configuration of output power, the switching of multi-frequency radio frequency pulses can be realized, so as to increase the etching process window and realize high aspect ratio etching more effectively.

Preferably, the output power range of the high frequency radio frequency generator and the intermediate frequency radio frequency generator is 50W-10kW. The output power range of the low frequency RF generator is 100W-20kW.

FIG. 5 is a schematic diagram of a multi-stage multi-frequency switchable plasma RF power output according to another embodiment of the present invention. In another embodiment of the present invention, as shown in the figure, the high frequency radio frequency generator RF1 is a continuous pulse generator, and frequency switching is performed between the intermediate frequency radio frequency generator RF2 and the low frequency radio frequency generator RF3. The frequency of each pulse period may be, for example, 10-20 kHz. There are three phases within each pulse. High-frequency RF generators output RF power at each stage, but the power varies. In stage (1), the plasma generation stage, the radio frequency generators RF1 and RF2 output power at their respective frequencies, the radio frequency generator RF1 outputs the first high frequency radio frequency power, and the radio frequency generator RF2 outputs the first intermediate frequency radio frequency power . In the (2) stage, that is, the initial etching stage, the radio frequency generator RF1 is turned to output lower power, the radio frequency generator RF2 is turned off, and the radio frequency generator RF3 is turned on to work. In stage (3), the main etch stage, the radio frequency generator RF1 is again turned to operate at a higher power. At the same time, the radio frequency generator RF3 is turned off, and the radio frequency generator RF2 is turned on to work. In the initial etching stage, the radio frequency generators RF1 and RF3 respectively output the second high frequency radio frequency power and the first low frequency radio frequency power. Due to the existence of the low frequency radio frequency power, the energy of the plasma ions is larger at this time, which is used for preliminary etching. In the main etching stage, the radio frequency generators RF1 and RF2 respectively output a third high frequency radio frequency power and a second intermediate frequency radio frequency power, wherein the third high frequency radio frequency power is greater than the second high frequency radio frequency power. In this stage, the RF power of the medium and high frequency is used, so that the concentration of the plasma becomes high but the energy is relatively low. Therefore, this embodiment is mainly used for the process of soft etching. The controller 90 controls the power changes of the above three RF generators within one pulse time and the switching between the RF generators RF2 and RF3.

The combination of output power and frequency switching time of the three RF generators is shown above as an example only. The duration of each stage, the power of different RF generators, and the priority of switching The latter order can be changed according to actual etching needs. Typically, the controller 90 controls the power output of the RF generators to have the following characteristics: (1) at most two RF generators have power output at any one stage in a pulse; (2) switching of the three frequency generators can Arbitrary combination; (3) Pulsed RF generator that can be used for three or more stages.

As an example, Table 1 lists the power output combinations of the system composed of three pulsed RF generators, where "ON" represents power output, "OFF" represents no power output, and there are at most two in each mode The RF generator performs power output.

As another example, Table 2 lists the power output combinations of the system composed of four pulsed RF generators, where "ON" represents power output, "OFF" represents no power output, and there are at most two power outputs in each mode. A radio frequency generator for power output.

FIG. 6 is a schematic diagram of the power output of an RF generator with multi-stage pulse power output. 4 stages of pulsed power output are shown, and the controller 90 controls a single RF generator to output different powers at different stages of each pulse. Wherein, the output power size and length of each stage can be preset by the controller. The frequency of the pulses can be, for example, 10-20 kHz, which can also be set by the controller 90 .

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be construed as limiting the present invention. Various modifications and substitutions to the present invention will become apparent to those of ordinary skill in the art to which the invention pertains after reading the foregoing content. Therefore, the protection scope of the present invention should be defined by the appended claims.

10: Gas shower head

W: substrate

20: External air source

30: reaction chamber

40: Pedestal

50: Processing device

60: Plasma Confinement Device

70: RF Power Supply Unit

701, 702, 703: Radio Frequency Generators

80: Vacuum device

90: Controller

Claims (10)

A method of radio frequency power output for plasma etching, the method comprising: providing a plurality of radio frequency generators, each of the plurality of radio frequency generators outputs radio frequency power of respective different frequencies to a plasma etching device, the plurality of radio frequency generators The power of each output of the radio frequency generators is variable, and a controller is provided that controls the output radio frequency power of the plurality of radio frequency generators to vary in a continuous plurality of pulse periods, wherein each pulse period of the plurality of pulse periods is varied. One includes three processing stages, and at least one RF generator outputs RF power in each processing stage, wherein the three processing stages are a plasma generation stage, an etching stage, and a maintenance plasma stage, which are performed in sequence. , the cycle length of each of the plurality of pulse cycles is 50us-0.1s, and the plurality of radio frequency generators include at least three radio frequency generators, which are a high frequency radio frequency generator, an intermediate frequency radio frequency generator and a low frequency radio frequency generator. A radio frequency generator, wherein the high frequency radio frequency generator outputs a first high frequency radio frequency power to a plasma etcher to generate a plasma of sufficient concentration in the plasma generation stage, and outputs a second high frequency in the maintenance plasma stage high frequency radio frequency power to the plasma etcher to maintain plasma; wherein, in the etching stage, the intermediate frequency radio frequency generator and the low frequency radio frequency generator output a second intermediate frequency radio frequency power and a first low frequency radio frequency power respectively, For performing high aspect ratio etching; wherein, in the sustaining plasma stage, the low frequency radio frequency generator stops outputting radio frequency power to release the charge accumulation of the processed workpiece. The method of claim 1, wherein at each stage at most two radio frequency products are The generator simultaneously outputs RF power. The method of claim 1, wherein the output frequency of the high frequency radio frequency generator is 40MHz-100MHz, the output frequency of the intermediate frequency radio frequency generator is 10MHz-20MHz, and the output frequency of the low frequency radio frequency generator is 200kHz-4MHz . The method of claim 1, wherein in the plasma generation stage, the intermediate frequency radio frequency generator outputs a first intermediate frequency radio frequency power for generating plasma and reactive groups. The method of claim 1, wherein the output power of the high frequency radio frequency generator and the intermediate frequency radio frequency generator ranges from 50W to 10kW. The method of claim 1, wherein the output power of the low frequency radio frequency generator ranges from 100W to 20kW. A method of radio frequency power output for plasma etching, the method comprising: providing a plurality of radio frequency generators, each of the plurality of radio frequency generators outputs radio frequency power of respective different frequencies to a plasma etching device, the plurality of radio frequency generators The power of each output of the radio frequency generators is variable, and a controller is provided that controls the output radio frequency power of the plurality of radio frequency generators to vary in a continuous plurality of pulse periods, wherein each pulse period of the plurality of pulse periods is varied. One includes three processing stages, and at least one RF generator outputs RF power in each processing stage, wherein the three processing stages are a plasma generation stage, a preliminary etching stage, and a main etching stage, which are performed in sequence. , the period length of each of the plurality of pulse periods is 50us-0.1s, The plurality of radio frequency generators include at least three radio frequency generators, which are a high frequency radio frequency generator, an intermediate frequency radio frequency generator and a low frequency radio frequency generator, wherein the high frequency radio frequency generators are respectively in the three processing stages outputting a first high frequency radio frequency power, a second high frequency radio frequency power and a third high frequency radio frequency power; wherein, in the initial etching stage, the low frequency radio frequency generator outputs a first low frequency radio frequency power; wherein, in the initial etching stage, the low frequency radio frequency generator outputs a first low frequency radio frequency power; In the main etching stage, the intermediate frequency radio frequency generator outputs a second intermediate frequency radio frequency power. The method of claim 7, wherein in the plasma generation stage, the intermediate frequency radio frequency generator simultaneously outputs a first intermediate frequency radio frequency power for generating plasma and reactive groups. A radio frequency source system of a plasma etching device, comprising: a plurality of radio frequency generators for outputting radio frequency power, each radio frequency generator in the plurality of radio frequency generators outputs power of different frequencies; a controller for controlling The plurality of radio frequency generators enable the plurality of radio frequency generators to perform the method described in any one of items 1 to 8 of the patent application scope. A plasma processing apparatus, comprising: a reaction chamber; a base located in the reaction chamber and used to support a substrate to be processed; to the reaction chamber Provides RF power.

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