CN111916327B

CN111916327B - Multi-frequency multi-stage plasma radio frequency output method and device thereof

Info

Publication number: CN111916327B
Application number: CN201910389487.XA
Authority: CN
Inventors: 叶如彬
Original assignee: Advanced Micro Fabrication Equipment Inc Shanghai
Current assignee: Advanced Micro Fabrication Equipment Inc Shanghai
Priority date: 2019-05-10
Filing date: 2019-05-10
Publication date: 2023-04-28
Anticipated expiration: 2039-05-10
Also published as: CN111916327A; TWI769447B; TW202044327A

Abstract

A method of rf power output for plasma etching, comprising: providing a plurality of radio frequency generators, each radio frequency generator outputting radio frequency power of different frequencies, each radio frequency generator outputting variable power, providing a controller, wherein the controller controls the plurality of radio frequency generators to output radio frequency power during continuous pulses, one pulse period of the continuous pulses comprises three continuous phases, at least one radio frequency generator outputs radio frequency power in each phase, the three continuous phases are respectively a plasma generation phase, an etching phase and a plasma maintenance phase, and the period length of the pulse period is 50us-0.1s. The method can realize faster switching speed and switch the radio frequency with power in a pulse mode.

Description

Multi-frequency multi-stage plasma radio frequency output method and device thereof

Technical Field

The invention relates to a radio frequency pulse output method, a radio frequency source system for executing the method and a plasma etching device comprising the radio frequency source system.

Background

In the existing semiconductor processing, plasma etching equipment is widely adopted to process a semiconductor wafer so as to obtain a semiconductor device and a conductor connection with microscopic dimensions. Common plasma etching apparatus are Capacitively Coupled (CCP) and Inductively Coupled (ICP) etchers, which generally have two rf generators, one for ionizing a reactant gas introduced into a reaction chamber to generate a plasma, and the other for controlling the ion energy incident on the wafer surface.

Many plasma processing schemes now use pulsed plasma rf generators instead of sustained plasma rf generators. The pulse plasma RF generator features that during the whole machining period, the RF power source is not continuously supplied but alternately turned on and off or alternately high power and low power RF power supply, and the output power has pulse waveform. The on-off duty cycle may be adjusted, typically in the range of 10% -90%. The pulse plasma radio frequency has the advantages that in the closing stage, the sheath layer on the surface of the silicon wafer disappears, 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 layer, more electrons can enter the bottom of the deep hole to neutralize ions accumulated at the bottom, and further etching of the deep hole is facilitated in the next opening stage. Also, the frequency of the plasma generator can be switched in the same pulse to be suitable for different etching processes.

The existing switchable dual-frequency plasma system uses a relay to switch between radio frequency generators with different frequencies, and has two disadvantages: firstly, the switching can not be performed under the condition of power output or can be performed only under the condition of low power; and secondly, the switching cannot be performed in the pulse power mode, because the relay switching is a mechanical action, and the response time is far longer than the pulse period. Therefore, existing dual frequency plasma switching techniques can only be used for low power and long pulse time (on the order of seconds) power output applications, and continuous plasma operation is not easily maintained.

Disclosure of Invention

In view of the foregoing, in a first aspect, the present invention proposes a method for rf power output for plasma etching, the method comprising: providing a plurality of radio frequency generators, each radio frequency generator outputting radio frequency power with different frequencies for outputting to one plasma etcher, wherein the power output by each radio frequency generator is variable, providing a controller, and controlling the output radio frequency power of the radio frequency generators to change in a plurality of continuously performed pulse periods, wherein each pulse period comprises three processing stages, at least one radio frequency generator outputs radio frequency power in each processing stage, the three processing stages are respectively a plasma generation stage, an etching stage and a plasma maintenance stage which are sequentially performed, the period length of the pulse period is 50us-0.1s, the radio frequency generators at least comprise three radio frequency generators, namely 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 first high frequency radio frequency power to the plasma etcher in the plasma generation stage so as to generate plasma with sufficient concentration, and outputs second high frequency radio frequency power to the plasma etcher in the plasma maintenance stage so as to maintain plasma.

Optionally, at most two rf generators simultaneously output rf power at each stage.

Optionally, 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.

Optionally, during the plasma generation phase, the intermediate frequency rf generator outputs a first intermediate frequency rf power for generating plasma and reactive radicals.

Optionally, in the etching stage, the intermediate frequency rf generator and the low frequency rf generator output a second intermediate frequency rf power and a first low frequency rf power for high aspect ratio etching.

Optionally, during the sustaining plasma phase, the low frequency rf generator stops outputting rf power to release charge accumulation from the workpiece being processed.

Optionally, the power output by the high-frequency radio frequency generator and the intermediate-frequency radio frequency generator ranges from 50W to 10kW.

Optionally, the power output by the low frequency radio frequency generator ranges from 100W to 20kW.

The invention also provides a method for outputting the radio frequency power for plasma etching, which comprises the following steps: providing a plurality of radio frequency generators, wherein each radio frequency generator outputs radio frequency power with different frequencies to a plasma etching device, the power output by each radio frequency generator is variable, providing a controller, and controlling the output radio frequency power of the plurality of radio frequency generators to change in a plurality of continuously performed pulse periods, wherein each pulse period comprises three processing stages, at least one radio frequency generator outputs radio frequency power in each processing stage, the three processing stages are respectively a plasma generation stage, an initial etching stage and a main etching stage which are sequentially performed, the period length of the pulse period is 50us-0.1s, and the plurality of radio frequency generators at least comprise three radio frequency generators which are respectively 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 respectively outputs first high-frequency radio frequency power, second high-frequency radio frequency power and third high-frequency radio frequency power in the three processing stages.

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

Optionally, during the initial etching stage, the low frequency rf generator outputs a first low frequency rf power.

Optionally, during the main etching stage, the intermediate frequency rf generator outputs a second intermediate frequency rf power.

In a second aspect, the present invention provides a radio frequency source system of a plasma etching apparatus, comprising: a plurality of radio frequency generators for outputting radio frequency power, each of the plurality of radio frequency generators outputting power of a different frequency; and the controller is used for controlling the plurality of radio frequency generators so that the plurality of radio frequency generators execute the method.

In a third aspect, the present invention provides a plasma processing apparatus comprising a reaction chamber; the base is positioned in the reaction cavity and used for supporting a substrate to be processed; and a radio frequency source system as described in the second aspect for providing radio frequency power to the reaction chamber.

Compared with the prior art of frequency switching through a relay, the invention can realize faster switching speed and switch the radio frequency with power in a pulse mode. In addition, any stage can be divided in one pulse period according to different substrate processing technologies, and parameters of various radio frequency generators, such as the number of output radio frequency generators, the power and the like, are flexibly set in each stage so as to better meet different processing technology requirements.

Drawings

Fig. 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 the rf power output of a prior art dual frequency switchable rf plasma control system.

Fig. 3 is a schematic diagram of a multi-stage multi-frequency switchable plasma rf power output in accordance with one embodiment of the invention.

Fig. 4a and 4b are schematic views of the morphology of the sidewall of the via during etching.

Fig. 5 is a schematic diagram of a multi-stage multi-frequency switchable plasma rf power output in accordance with another embodiment of the invention.

Fig. 6 is a schematic diagram of a power output of a radio frequency generator with multi-stage pulsed power output according to one embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings. It is emphasized that this is an example only and does not preclude other embodiments from utilizing the present invention.

Detailed Description

The following describes specific embodiments of the present invention with reference to the drawings.

The invention provides a multi-frequency multi-stage plasma radio frequency pulse output method which can be applied to plasma processing devices, such as a Capacitive Coupling Plasma (CCP) processing device, an Inductive Coupling Plasma (ICP) processing device and the like. Fig. 1 shows a schematic diagram of a CCP processing apparatus using the method of the present invention. The processing device 50 comprises a vacuum reaction chamber 30 surrounded by the outer wall of the reaction chamber, wherein a reaction space is formed inside the reaction chamber for performing plasma etching process treatment; a susceptor 40 is disposed in the vacuum reaction chamber for fixing the substrate W to be processed, and the susceptor 40 is used as a lower electrode of the vacuum reaction chamber. The top in the reaction chamber is provided with a flat gas shower head 10, and the gas shower head 10 is communicated with an external gas source 20 through a pipeline. The gas spray head corresponds to the base in position and is used as an upper electrode of the vacuum reaction cavity. The radio frequency power supply means may comprise a plurality of radio frequency generators, one or more of which may be selectively applied to one of the upper or lower electrodes. As shown in fig. 1, the rf power supply device includes three rf generators 701 to 703, each of which outputs power of a different frequency, and is applied to the lower electrode. For example, the high frequency rf generator 701 ionizes the reactant gases introduced into the reaction chamber to generate a plasma; the intermediate frequency radio frequency generator 702 is applied to the lower electrode, so that a sufficient direct current bias voltage is generated in the sheath layer on the upper surface of the substrate, and charged ions in the plasma are accelerated to bombard the substrate rapidly for etching; the low frequency rf generator 703 outputs low frequency power for etching in cooperation with the intermediate frequency rf generator. A plasma confinement device 60 is disposed around the susceptor 40 for confining the plasma to the plasma region, and a vacuum evacuation device 80 is provided for evacuating unreacted gases and reaction byproduct gases from the reaction chamber 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 apparatus 50 and controls the delivery of reactant gases, maintaining and extinguishing the plasma, supplying cooling gases, and the like.

Fig. 2 shows a schematic diagram of the rf power output of a prior art dual frequency switchable rf plasma control system. Four steps are shown, with two frequency outputs in each step, each step being a few seconds to hundreds of seconds long. The radio frequency generator RF1 is continuously operated in each step, but the power is varied. The radio frequency generators RF2 and RF3 are switched in different steps, and the combination of the output power and time of RF2 and RF3 and RF1 can be arbitrarily set. Shown is

RF2 occupying steps

1 and 3, RF3 occupying steps 2 and 4. Since the RF frequency switching in the prior art uses a relay, which can only switch under low power and requires a long time in the order of seconds for switching (e.g., a long power interruption between each step in fig. 2), the plasma control system is not suitable for a pulsed plasma RF generator and a pulsed plasma RF process. In the application of the invention, the pulse frequency of the etching process is 10Hz-20KHz, namely, the pulse duration is 1/20 microsecond-0.1 seconds. In such short pulse durations, switching times on the order of seconds are clearly unsuitable for use in the process of the present invention.

The controller can realize the rapid switching of different radio frequency generators in the radio frequency power supply device without power interruption. The controller may be externally connected to the radio frequency power supply device or may be built in the radio frequency power supply device. Alternatively, each radio frequency generator has a controller built-in. The controller is pre-programmed with parameters to control the different rf generators to output rf power at different stages within successive pulse periods. Such parameters include, but are not limited to: the frequency of the continuous pulses, the number of phases, the duration of each phase, the output power of the rf generator, and the number of rf generators outputting power in one phase. The combination of the different parameters may be varied according to the requirements of the etching process.

In one embodiment, the controller 90 is external to the RF power device 70. The control of the plurality of rf generators by the controller 90 enables the switching frequency to be used in a variety of applications for substrate processing without power interruption, such as in high aspect ratio etching steps for fabricating three-dimensional memories. In the prior art, a source pulsed radio frequency generator (typically a 60MHz high frequency pulsed radio frequency generator) mostly adopts a continuous mode of operation or a pulsed mode of operation. In the continuous mode of operation, the output power of the source pulsed radio frequency generator remains unchanged. In the pulsed mode of operation, the source pulsed radio frequency generator alternately outputs both high and low power or alternately turns the power output on and off during a pulse period. In the invention, one pulse period can be divided into a plurality of stages according to the process requirement, and the source pulse radio frequency generator can be selected to output or not output power at any stage, instead of only performing power adjustment in two stages of one pulse period as in the prior art, the invention has more flexibility and saves the energy consumption of the radio frequency generator.

Fig. 3 illustrates a multi-stage multi-frequency switchable plasma rf power output schematic diagram showing a pulse output method particularly for use in high aspect ratio etching for manufacturing memory according to one embodiment of the invention. A plasma processing arrangement has a pulsed rf generator with three frequencies: high frequency (40-100 MHz) radio frequency generator, intermediate frequency (10-20 MHz) radio frequency generator and low frequency (200 kHz-4 MHz) radio frequency generator. High frequency rf power is typically used to generate a plasma in the chamber, but the presence of high frequency rf power in the chamber during etching can adversely affect the uniformity of the etching. Therefore, the medium-frequency radio frequency power is introduced, so that plasma is kept from being extinguished, and etching uniformity is not greatly influenced. The low-frequency radio frequency power mainly aims 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 of each radio frequency generator may be configured as shown in FIG. 3. In the (1) th stage of each pulse, i.e., the plasma generation stage, a first high frequency power and a first intermediate frequency power are output to dissociate the process gas to generate charged ions and reactive radicals. The output of the first intermediate frequency power is used to assist the first high frequency power to generate the plasma and reactive radicals. In another embodiment, the plasma may also be generated using only the first high frequency power. And (2) outputting the first low-frequency power and the second intermediate-frequency power in the immediate etching stage to generate high bias voltage for high aspect ratio etching. In this phase, the first high-frequency output power is turned off, while the medium-frequency and low-frequency power are used, on the one hand, to maintain the plasma so that it does not extinguish; on the other hand, not outputting high-frequency power can increase the uniformity of etching. Turning off the output of high frequency power at this stage also serves to save power. And (3) a plasma maintaining stage, namely outputting only the second high-frequency power, wherein the second high-frequency power is smaller than the first high-frequency power so as to maintain the plasma and release charge accumulation of the processed workpiece. During the etching process with high aspect ratio, positive charges are accumulated at the bottom of the through hole 101 as the positive particles continuously bombard the substrate 100, and the positive charges with uneven distribution can shift the direction of the positive particles incident downwards in long-distance flight, and further, the etching direction of the etched through hole 101 can also shift, as shown in fig. 4 a. Therefore, in the plasma maintaining stage of this embodiment, only a low-power high-frequency power is output and the intermediate-frequency and low-frequency rf power generators are turned off, so that plasma can be maintained, and charge accumulation at the bottom of the via hole can be released, thereby enabling alignment etching of the via hole, as shown in fig. 4 b.

In the (1) th phase of the next pulse period, the first high-frequency power is output again. This is because, in the former stage, only the second high-frequency power of smaller power is output, and the plasma concentration is low at this time, only for maintaining the plasma not extinguished. And in the next pulse period, a plasma of sufficient concentration must be generated again. Thus, stage (1) of the first pulse cycle is used to generate plasma in a chamber without plasma, and stage (1) of the remaining pulse cycle is used to generate plasma of sufficient concentration in a chamber with low concentration plasma. Therefore, the (1) th phase of the pulse cycle is collectively referred to as the plasma generation phase. The controller 90 controls the duration of the three phases, the power output of the three rf generators, and the switching between the rf generators by preset parameters. The switching of the multi-frequency radio frequency pulse can be realized through the configuration of the output power, so that the etching process window is increased, and the high aspect ratio etching is realized more effectively.

Alternatively, the power output by the high frequency RF generator and the intermediate frequency RF generator is in the range of 50W-10kW. The power output by the low frequency radio frequency generator ranges from 100W to 20kW.

Fig. 5 is a schematic diagram of a multi-stage multi-frequency switchable plasma rf power output in accordance with another embodiment of the invention. In another embodiment of the invention, the high frequency RF generator RF1 is a continuous pulse generator, as shown, and the intermediate frequency RF generator RF2 and the low frequency RF generator RF3 are frequency switched. The frequency of each pulse period may be, for example, 10-20kHz. There are three phases within each pulse. The high frequency rf generator outputs rf power at each stage, but with different powers. In the (1) th stage, i.e., the plasma generation stage, RF1 and RF2 output power at respective frequencies, RF1 outputs a first high-frequency radio frequency power, and RF2 outputs a first intermediate-frequency radio frequency power. In stage (2), the initial etch stage, RF1 is turned to output lower power and RF2 is turned off and RF3 is turned on. In stage (3), the main etch stage, RF1 again goes to operate at higher power. At the same time, RF3 is off and RF3 is on. In the primary etching stage, RF1 and RF3 output a second high-frequency radio frequency power and a first low-frequency radio frequency power respectively, and the energy of ions of the plasma is larger at the moment due to the existence of the low-frequency radio frequency power and is used for primary etching. In the main etching stage, 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 larger than the second high-frequency radio frequency power. In this stage, a medium-high frequency rf power is used so that the concentration of the plasma becomes large but the energy is relatively low. Therefore, this embodiment is mainly used for a soft etching (soft etching) process. The controller 90 controls the power change of the three radio frequency generators and the switching between RF2 and RF3 within one pulse time.

The above shows, by way of example only, a combination of the output power and the frequency switching time of three radio frequency generators. The duration of each stage, the power of different radio frequency generators and the switching sequence can be changed according to the actual etching requirement. In general, the controller 90 controls the power output of the radio frequency generator to have the following characteristics:

(1) At most two rf generators have power outputs at any stage in a pulse;

(2) The three frequency generators can be switched in any combination;

(3) The pulse radio frequency generator can be used for three or more stages.

As an example, table 1 lists the power output combinations of a system of three pulsed rf generators, where "ON" represents the power output and "OFF" represents the no power output, with at most two rf generators in each mode.

TABLE 1

As another example, table 2 lists the power output combinations of a system of four pulsed RF generators, where "ON" represents power output and "OFF" represents no power output, with at most two RF generators in each mode.

TABLE 2

FIG. 6 is a schematic diagram of RF generator power output with multi-stage pulsed power output. The pulsed power output, illustrated as 4 phases, the controller 90 controls a single rf generator to output different power at different phases of each pulse. The output power and the duration of each stage can be preset by the controller. The frequency of the pulses may be, for example, 10-20kHz, which may also be set by the controller 90.

While the present invention has been described in detail through the foregoing description of the preferred embodiment, it should be understood that the foregoing description is not to be considered as limiting the invention. Many modifications and substitutions of the present invention will become apparent to those of ordinary skill in the art upon reading the foregoing. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

1. A method for rf power output for plasma etching, the method comprising:

providing a plurality of RF generators, each RF generator outputting RF power of a different frequency to the plasma etching apparatus, each RF generator outputting variable power,

providing a controller controlling the output radio frequency power of the plurality of radio frequency generators to vary over a plurality of consecutively conducted pulse periods, wherein each pulse period comprises three processing stages, at least one radio frequency generator outputting radio frequency power in each processing stage,

wherein the three treatment stages are respectively a plasma generation stage, an etching stage and a plasma maintenance stage which are sequentially carried out, the period length of the pulse period is 50us-0.1s,

the plurality of radio frequency generators at least comprise three radio frequency generators, namely a high frequency radio frequency generator, an intermediate frequency radio frequency generator and a low frequency radio frequency generator, wherein the power ranges output by the high frequency radio frequency generator and the intermediate frequency radio frequency generator are 50W-10kW, the power ranges output by the low frequency radio frequency generator are 100W-20kW, 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, wherein

The high-frequency radio frequency generator is started in the stage of generating plasma so as to output first high-frequency radio frequency power to the plasma etcher to generate plasma with sufficient concentration;

in the etching stage, the low-frequency radio frequency generator is started, and at least one of the high-frequency radio frequency generator and the high-frequency radio frequency generator is started;

the high-frequency radio frequency generator is started to output second high-frequency radio frequency power to the plasma etcher to maintain plasma in the plasma maintaining stage, and the low-frequency radio frequency generator is in a closed state.

2. The method of claim 1, wherein at most two rf generators simultaneously output rf power at each stage.

3. The method of claim 1, wherein the intermediate frequency rf generator outputs a first intermediate frequency rf power for generating plasma and reactive radicals during the generating plasma phase.

4. The method of claim 1, wherein during the etching phase, the intermediate frequency rf generator and the low frequency rf generator output a second intermediate frequency rf power and a first low frequency rf power for high aspect ratio etching.

5. The method of claim 4, wherein the low frequency rf generator stops outputting rf power to release charge accumulation from the workpiece during the plasma sustaining phase.

6. A method for rf power output for plasma etching, the method comprising:

wherein the three processing stages are respectively a plasma generation stage, an initial etching stage and a main etching stage which are sequentially carried out, the period length of the pulse period is 50us-0.1s,

the plurality of radio frequency generators at least comprise three radio frequency generators, namely a high-frequency radio frequency generator, an intermediate-frequency radio frequency generator and a low-frequency radio frequency generator, wherein the high-frequency generator outputs a first high-frequency radio frequency power, a second high-frequency radio frequency power and a third high-frequency radio frequency power in the three processing stages respectively; the power ranges of the high-frequency radio frequency generator and the intermediate-frequency radio frequency generator are 50W-10kW, the power ranges of the low-frequency radio frequency generator are 100W-20kW, 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;

at least one of the high-frequency radio frequency generator and the intermediate-frequency radio frequency generator is started in the stage of generating plasma;

in the primary etching stage, the low-frequency radio frequency generator is started;

in the main etching stage, the low-frequency radio frequency generator is turned off, and at least one of the high-frequency radio frequency generator and the intermediate-frequency radio frequency generator is turned on.

7. The method of claim 6, wherein the intermediate frequency rf generator outputs a first intermediate frequency rf power for generating plasma and reactive radicals simultaneously during the plasma generation phase.

8. The method of claim 6, wherein the low frequency rf generator outputs a first low frequency rf power during the initial etching stage.

9. The method of claim 8, wherein the intermediate frequency rf generator outputs a second intermediate frequency rf power during a main etch phase.

10. A radio frequency source system for a plasma etching apparatus, comprising:

a plurality of radio frequency generators for outputting radio frequency power, each of the plurality of radio frequency generators outputting power of a different frequency;

a controller for controlling the plurality of radio frequency generators such that the plurality of radio frequency generators perform the method of any one of claims 1 to 9.

11. A plasma processing apparatus, comprising:

a reaction chamber;

the base is positioned in the reaction cavity and used for supporting a substrate to be processed; and

the rf source system of claim 10, configured to provide rf power to the reaction chamber.