CN111916327A

CN111916327A - Multi-frequency and multi-stage plasma radio frequency output method and device

Info

Publication number: CN111916327A
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: 2020-11-10
Anticipated expiration: 2039-05-10
Also published as: CN111916327B; TW202044327A; TWI769447B

Abstract

A method of rf power output for plasma etching, comprising: providing a plurality of radio frequency generators, wherein each radio frequency generator outputs radio frequency power with different frequency, the output power of each radio frequency generator is variable, providing a controller, controlling the plurality of radio frequency generators to output the radio frequency power in a continuous pulse period, wherein one pulse period of the continuous pulse comprises three continuous stages, at least one radio frequency generator outputs the radio frequency power in each stage, the three continuous stages are a plasma generation stage, an etching stage and a plasma maintaining stage respectively, and the period length of the pulse period is 50us-0.1 s. The method can realize faster switching speed and carry out radio frequency switching with power in a pulse mode.

Description

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

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 semiconductor wafers so as to obtain semiconductor devices and conductor connections with microscopic sizes. Common plasma etching apparatuses are Capacitive Coupling (CCP) and Inductive Coupling (ICP) etchers, which typically have two rf generators, one of which ionizes a reactant gas introduced into a reaction chamber to generate a plasma, and the other of which controls the energy of ions incident on the wafer surface.

Many plasma processing schemes now use pulsed plasma RF generators instead of continuous plasma RF generators. The pulse plasma RF generator features that in the whole machining period, the RF power source is powered alternately on and off or high and low power RF power source, and the output power is pulse. The on-off duty cycle can 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 chip disappears, electrons accumulated on the surface of the silicon chip and in the etched edge of the deep hole are neutralized with the silicon chip 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 therefore further etching of the deep hole is facilitated in the next opening stage. Moreover, the frequency of the plasma generator can be switched to be suitable for different etching processes in the same pulse.

The existing switchable dual frequency plasma system uses a relay to switch between rf generators with different frequencies, which has two disadvantages: firstly, the switching can not be carried out under the condition of power output or can be carried out only under the condition of low power; secondly, the switching can not be carried out in a pulse power mode, because the switching of the relay is mechanical action, the reaction time is far longer than the pulse period. Therefore, the existing dual frequency plasma switching technology can only be used in the power output occasions with small power and long pulse time (in the order of seconds), and the continuous plasma operation is not easy to maintain.

Disclosure of Invention

In view of the above, in a first aspect, the present invention provides a method for rf power output for plasma etching, the method comprising: providing a plurality of radio frequency generators, wherein each radio frequency generator outputs radio frequency power with different frequencies for outputting to a plasma etcher, the output power of each radio frequency generator is variable, providing a controller, the controller controls the output radio frequency power of the plurality of radio frequency generators to change in a plurality of continuously-performed pulse cycles, each pulse cycle comprises three processing stages, at least one radio frequency generator outputs the radio frequency power in each processing stage, the three processing stages are a plasma generation stage, an etching stage and a plasma maintaining stage which are sequentially performed respectively, the cycle length of the pulse cycle is 50us-0.1s, the plurality of radio frequency generators at least comprise three radio frequency generators which are respectively a high frequency radio frequency generator, a medium frequency radio frequency generator and a low frequency radio frequency generator, and the high frequency radio frequency generator outputs first high frequency radio frequency power to the plasma etcher to generate the first high frequency radio frequency power in the plasma generation stage Generating plasma with sufficient concentration, and outputting second high-frequency radio frequency power to the plasma etcher in the plasma maintaining stage to maintain the plasma.

Optionally, at most two rf generators output rf power simultaneously 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-4 MHz.

Optionally, in the stage of generating plasma, the if rf generator outputs a first if 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 performing high aspect ratio etching.

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

Optionally, the power output by the high frequency RF generator and the medium frequency RF generator is in the range of 50W-10 kW.

Optionally, the low frequency rf generator outputs power in the range of 100W-20 kW.

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 output power of each radio frequency generator is variable, and providing a controller, wherein the controller controls the output radio frequency power of the radio frequency generators to change in a plurality of continuously-performed pulse cycles, each pulse cycle comprises three processing stages, at least one radio frequency generator outputs the radio frequency power in each processing stage, the three processing stages are a plasma generation stage, a primary etching stage and a main etching stage which are sequentially performed, the cycle length of the pulse cycle is 50us-0.1s, the radio frequency generators at least comprise three radio frequency generators, namely a high-frequency radio frequency generator, a medium-frequency radio frequency generator and a low-frequency radio frequency generator, wherein the high-frequency radio frequency generators respectively output first high-frequency radio frequency power, second high-frequency radio frequency power and second high-frequency radio frequency power in the three processing stages, A second high frequency radio frequency power and a third high frequency radio frequency power.

Optionally, in the stage of generating plasma, the if rf generator simultaneously outputs a first if rf power for generating plasma and reactive radicals.

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

Optionally, in the main etching stage, the if rf generator outputs a second if rf power.

In a second aspect, the present invention provides an rf 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 at a different frequency; a controller for controlling the plurality of radio frequency generators so that the plurality of radio frequency generators perform the above 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 the rf source system of the second aspect, for providing rf power to the reaction chamber.

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

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

Fig. 3 is a multi-stage multi-frequency switchable plasma rf power output schematic according to one embodiment of the present invention.

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

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 an rf 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 merely an example and does not preclude additional embodiments of the present invention from being utilized.

Detailed Description

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

The invention provides a method for outputting multi-frequency and multi-stage plasma radio frequency pulses, which can be applied to plasma processing devices, such as a capacitive coupling type plasma (CCP) processing device, an inductive coupling type 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 cavity 30 enclosed by the outer wall of the reaction cavity, wherein a reaction space is formed inside the reaction cavity for carrying out plasma etching process treatment; a base 40 is arranged in the vacuum reaction cavity and used for fixing a substrate W to be processed, and the base 40 is simultaneously used as a lower electrode of the vacuum reaction cavity. The top in the reaction chamber is provided with a flat gas spray header 10, and the gas spray header 10 is communicated with an external gas source 20 through a pipeline. The gas spray head corresponds to the base and is used as an upper electrode of the vacuum reaction cavity. The rf power supply means may comprise a plurality of rf 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 701-703 each outputting power of a different frequency, and each applied to the lower electrode. For example, the high frequency rf 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 sufficient direct current bias voltage is generated in a sheath layer on the upper surface of the substrate, and charged ions in the plasma are accelerated to quickly bombard the substrate for etching; the low frequency rf generator 703 outputs low frequency power to cooperate with the if rf generator for etching. A plasma confinement device 60 is disposed around the susceptor 40 for confining the plasma within the plasma, and a vacuum pumping device 80 is provided for evacuating the unreacted gas and the reaction by-product gas 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 device 50 and controls delivery of reactant gases, maintenance and extinguishing of the plasma, supply of cooling gases, and the like.

Fig. 2 shows a rf power output schematic 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 several seconds to several hundred seconds in duration. The radio frequency generator RF1 continues to operate at each step, but with varying power. The RF generators RF2 and RF3 are switched in different steps, and the combinations of the output power and time of RF2 and RF3 and RF1 can be arbitrarily set. Shown are

steps

1 and 3 occupied by RF2 and steps 2 and 4 occupied by RF 3. Since prior art RF frequency switching utilizes relays that can only be switched at low power and require long times on the order of seconds for switching (e.g., long power interruptions between each step in fig. 2), the plasma control system is not suitable for use with pulsed plasma RF generators and pulsed plasma RF processes. In the application of the invention, the pulse frequency of the etching process is 10Hz-20KHz, namely the pulse duration is 1/20 microseconds-0.1 second. In such short pulse durations, switching times on the order of seconds are clearly not suitable for use in the process of the present invention.

The controller can realize the fast switching without power interruption of different radio frequency generators in the radio frequency power supply device. The controller may be externally connected to the rf power supply device or may be built into the rf power supply device. Or each radio frequency generator is internally provided with a controller. 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 successive pulses, the number of stages, the duration of each stage, the output power of the RF generator, and the number of RF generators in a stage. The combination of different parameters can be changed 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 multiple rf generators by controller 90 to switch frequencies without power interruption can be used in a variety of applications in substrate processing, such as in high aspect ratio etching steps to fabricate three-dimensional memories. In the prior art, the source pulse radio frequency generator (usually 60MHz high frequency pulse radio frequency generator) mostly adopts a continuous operation mode or a pulse operation mode. In the continuous operation mode, the output power of the source pulse radio frequency generator is kept constant. In the pulse working mode, the source pulse radio frequency generator alternately outputs high and low power or alternately turns on and off the power output in one pulse period. In the invention, one pulse period can be divided into a plurality of stages according to the process requirements, the source pulse radio frequency generator can be selected to output or not output power at any stage, and the power regulation can be carried out only in two stages of one pulse period as in the prior art, so that the method has more flexibility and saves the energy consumption of the radio frequency generator.

Figure 3 illustrates a multi-stage multi-frequency switchable plasma rf power output schematic showing a pulsed output method particularly useful in high aspect ratio etching for memory fabrication, in accordance with one embodiment of the present invention. A plasma processing arrangement has a pulsed rf generator with three frequencies: a high frequency (40-100MHz) RF generator, a medium frequency (10-20MHz) RF generator, and a low frequency (200kHz-4MHz) RF generator. High frequency rf power is commonly used to generate plasma in the chamber, but the presence of rf power in the chamber during etching can adversely affect the uniformity of the etch. Therefore, the medium-frequency radio frequency power is introduced, so that the plasma can be kept not to be extinguished, and the etching uniformity cannot be greatly influenced. The low frequency RF power is mainly used to generate sufficient bias voltage on the upper surface of the substrate so as to make the charged ions bombard the substrate for etching. Thus, in one embodiment, the power output of each RF generator may be configured as shown in FIG. 3. In the (1) th stage of each pulse, i.e., the plasma generation stage, the first high frequency power and the first intermediate frequency power are output to dissociate the process gas to generate charged ions and reactive radicals. The first intermediate frequency power is output to assist the first high frequency power to generate plasma and reactive radicals. In another embodiment, the plasma may be generated using only the first high frequency power. And (2) a stage (i.e. an immediate etching stage) for outputting a first low-frequency power and a second medium-frequency power to generate a high bias voltage and performing high aspect ratio etching. In this phase, the first high-frequency output power is switched off, while with the medium-frequency and low-frequency power, on the one hand, the plasma is sustained 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, which only outputs 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 the charge accumulation of the processed workpiece. During the etching process with high aspect ratio, as the positive particles continuously bombard the substrate 100, positive charges are accumulated at the bottom of the through hole 101, and these non-uniform positive charges will shift the direction of the downward incident positive particles in the long-distance flight, and further, the etching direction of the etched through hole 101 will also shift, as shown in fig. 4 a. Therefore, in the plasma sustaining stage of this embodiment, only a small power of high frequency power is output and the middle and low frequency rf power generators are turned off, so that the plasma can be sustained and the charge accumulation at the bottom of the via hole can be released, thereby collimating and etching the via hole, as shown in fig. 4 b.

In the (1) th stage of the next pulse period, the first high-frequency power is output again. This is because, in the previous stage, only the second high-frequency power of a smaller power is output, and the plasma concentration at this time is low, and it is only for maintaining the plasma without extinguishing. And in the next pulse cycle, a plasma of sufficient concentration must be generated again. Thus, the (1) th phase of the first pulse cycle is used to generate plasma in the chamber without plasma, and the (1) th phase of the remaining pulse cycles is used to generate plasma of sufficient concentration in the chamber with low concentration of plasma. Therefore, phase (1) 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 via preset parameters. The switching of multi-frequency radio frequency pulses can be realized through the configuration of the output power, so that the etching process window is enlarged, and the high aspect ratio etching is more effectively realized.

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

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

The combination of output power and frequency switching time of three radio frequency generators is shown above by way of example only. The duration of each stage, the power of different RF 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 RF generator to have the following characteristics:

(1) at most two RF generators have power output at any stage in a pulse;

(2) the switching of the three frequency generators can be combined at will;

(3) can be used for the pulse radio frequency generator with 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 power output and "OFF" represents no power output, and only two rf generators are powered 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 only a maximum of two rf generators per mode.

TABLE 2

Fig. 6 is a schematic diagram of the power output of an rf generator with multi-stage pulsed power output. Illustrated as a 4-phase pulse power output, the controller 90 controls a single rf generator to output different powers at different phases of each pulse. The output power and 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 with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.

Claims

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

providing a plurality of radio frequency generators, wherein each radio frequency generator outputs radio frequency power with different frequency to the plasma etching device, the output power of each radio frequency generator is variable,

providing a controller that controls the output radio frequency power of the plurality of radio frequency generators to vary over a plurality of consecutively occurring pulse cycles, wherein each pulse cycle comprises three processing phases, in each of which at least one radio frequency generator outputs radio frequency power,

wherein, the three treatment stages are respectively a plasma generation stage, an etching stage and a plasma maintaining 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, a medium-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 a plasma generation stage to generate plasma with sufficient concentration, and outputs second high-frequency radio frequency power to the plasma etcher in a plasma maintaining stage to maintain the plasma.

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

3. The method of claim 1, wherein the high frequency rf generator has an output frequency of 40MHz to 100MHz, the intermediate frequency rf generator has an output frequency of 10MHz to 20MHz, and the low frequency rf generator has an output frequency of 200kHz to 4 MHz.

4. The method of claim 1, wherein the if rf generator outputs a first if rf power for generating the plasma and the reactive species during the plasma generating stage.

5. The method of claim 1, wherein during the etching phase, the if rf generator and the lf rf generator output a second if rf power and a first lf rf power for performing high aspect ratio etching.

6. The method of claim 5, wherein during the sustaining plasma phase, the low frequency RF generator stops outputting RF power to discharge charge buildup from the processed workpiece.

7. The method of claim 1, wherein the high frequency rf generator and the intermediate frequency rf generator output power in the range of 50W to 10 kW.

8. The method of claim 1, wherein the low frequency rf generator outputs a power in the range of 100W-20 kW.

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

wherein, the three treatment stages are respectively a plasma generation stage, a primary 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, a medium-frequency radio frequency generator and a low-frequency radio frequency generator, wherein the high-frequency radio frequency generator respectively 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.

10. The method of claim 9, wherein the if rf generator simultaneously outputs a first if rf power for generating plasma and reactive radicals during the plasma generating phase.

11. The method of claim 9, wherein the low frequency rf generator outputs a first low frequency rf power during an initial etch phase.

12. The method of claim 11, wherein the if rf generator outputs a second if rf power during the main etch phase.

13. An rf 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 at a different frequency;

a controller for controlling the plurality of radio frequency generators such that they perform the method of any one of claims 1 to 12.

14. 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 13, configured to provide rf power to the reaction chamber.