TWI505317B - A plasma processing method for a plasma processing apparatus - Google Patents

Description

Plasma processing method for plasma processing device

The present invention relates to a plasma processing method and a plasma processing apparatus, and more particularly to a method of controlling a radio frequency power supply and a radio frequency power supply for supplying radio frequency power to a plasma processing apparatus.

In conventional semiconductor processing, plasma processing equipment is widely used to process semiconductor wafers to obtain microscopic-sized semiconductor devices and conductor connections. Commonly used in plasma equipment are capacitive coupling type (CCP) and inductively coupled (ICP) reaction chambers. These devices generally have two RF power sources, one of which is used to ionize the reaction gas that is introduced into the reaction chamber to generate a plasma. Another RF power source is used to control the ion energy incident on the surface of the wafer.

The plasma processing apparatus shown in Figure 1 includes a reaction chamber 100 that includes a susceptor 22 having a lower electrode therein. Above the lower electrode, there is a fixing device for the wafer 20 to be processed, such as an electrostatic chuck 21, and the wafer 20 is fixed on the upper surface of the electrostatic chuck 21. An edge ring 10 is also included around the electrostatic chuck and wafer. The gas chamber 10 further includes a gas shower head 11 connected to the gas source 110 for uniformly supplying gas into the reaction chamber. The gas showerhead also forms a capacitive coupling as an upper electrode opposite the lower electrode in the susceptor. A first RF power source 31 is electrically coupled to the lower electrode through the matcher 1, and a second RF power source 32 is electrically coupled to the lower electrode through the matcher 2, both of which have a fixed RF frequency. Since the impedance of the plasma varies with parameters such as plasma pressure, radio frequency power, and plasma concentration, it is necessary to continuously adjust the parameters and impedance of the input power to minimize the reflected power. During the plasma processing, both the first and second RF power sources 31, 32 are powered to the lower electrode, and the matchers 1, 2 respectively adjust the impedance parameters through internal movable components to minimize the RF reflected power. It is also possible to adjust the RF power The frequency of source 31 or 32 adjusts the input impedance faster. However, the impedance in the above-described adjustment matchers 1, 2 requires the movement of mechanical components such as mechanically driven variable capacitance or variable inductance to achieve. In addition, when the reflected power is minimized, the mechanical component moves in any direction and then the mechanical component is further moved to a suitable position according to the reflected power value of the feedback, so the process of the matcher impedance or the RF power frequency takes a long time to reach the second level. , such as greater than 1 second.

Nowadays, many plasma processing processes require pulsed plasma processing technology. In some processing periods, the RF power supply is not continuously powered, but is turned on-off alternately or high-power-low-power RF alternates. The output power waveform is pulsed. The type is called pulse plasma processing. The alternate frequency is generally around 500 Hz-500 kHz, and the duty cycle of the turn-on is also adjustable, which can be set as needed within the range of 10%-90%. In this way, each turn-on, turn-off or high-power, low-power switching will cause the impedance in the reaction chamber to change rapidly, and each change time is milliseconds (ms) or even microseconds (μs). The above situation uses matching circuit or RF. Auto Frequency Tuning (AFT) in the power supply cannot meet the requirements of pulse plasma processing because the reaction time is far below the millisecond level.

Therefore, for the above reasons, the industry needs to be able to achieve fast impedance matching in pulse plasma processing using existing hardware or simply adjusting existing hardware conditions.

In view of the deficiencies in the prior art, it is an object of the present invention to provide a plasma processing method that provides a plasma processing apparatus suitable for pulse plasma processing. The present invention provides a plasma processing method for a plasma processing apparatus, the plasma processing apparatus including a reaction chamber including a susceptor, a wafer to be processed fixed on the susceptor, and a plurality of outputs having different RF frequency outputs The RF power source applies an RF electric field to the reaction chamber, and the plurality of RF power sources are pulsed RF power sources. The processing method includes: matching a frequency acquisition phase and a pulse processing phase.

The matching frequency acquisition phase includes: a first matching frequency acquisition step of: adjusting an output of the first pulse RF power source to a first output state, and outputting a second pulse RF power source output to a third output state, so that the reaction chamber has a first impedance, Adjusting the frequency conversion element in the second pulse RF power supply And obtaining a first matching frequency to match the first impedance; and a second matching frequency obtaining step of: adjusting an output of the first pulsed RF power source to a second output state, and outputting a second pulse RF power source output to a fourth output state A second impedance is formed in the reaction chamber to adjust the frequency conversion component in the second pulsed RF power source to obtain a second matching frequency to match the second impedance.

The pulse processing stage includes: a first processing step of: setting the first pulse radio frequency power output to have a first output state, and setting an output of the second pulse radio frequency power source to a third output state and having a first matching frequency; a second processing step: setting the first pulse radio frequency power output to have a second power output state, and setting the output of the second pulse radio frequency power source to a fourth output state and having a second matching frequency characterized by the matching frequency The time of the first or second matching frequency acquisition step in the acquisition phase is less than 100 ms and greater than the time of the first or second processing step in the pulse processing phase.

The time of the first or second processing step in the pulse processing phase is less than 10 ms.

The first output state of the first pulsed RF power source has a first power output, and the second output state has a second power output, wherein the first power output is greater than the second power, wherein the second power output may also be zero.

In the first and second matching frequency acquisition pulse steps, the second pulse RF power output power may be switched between different output powers and may have the same output power in synchronization with the first pulse RF power supply.

The first pulse RF power output frequency is less than the second pulse RF power output frequency. For example, the output frequency of the first pulse RF power source is less than 13 MHz, and the output frequency of the second pulse RF power source is greater than 13 MHz.

Another embodiment of the present invention provides a plasma processing method for a plasma processing apparatus. The plasma processing apparatus includes a reaction chamber including a susceptor on which a wafer to be processed is fixed, and has a different RF frequency output. A plurality of RF power sources apply a radio frequency electric field to the reaction chamber, and a control system controls the plurality of RF power sources, the plurality of RF power sources are pulsed RF power sources, and the processing method includes: the control system sends an incoming matching frequency Obtaining a signal of the phase to the plurality of radio frequency power sources, in the matching frequency acquisition phase, the first radio frequency power source outputs the radio frequency power at the first pulse frequency, so that the output RF power is at the first power and Switching between the second power, the second RF power source adjusts the output frequency synchronized with the first pulse frequency, and obtains first and second matching frequencies corresponding to the first power and the second power output; After obtaining the first and second matching frequencies, the control system sends a signal entering the pulse processing stage to the plurality of RF power sources, and in the pulse processing phase, the first RF power source outputs the RF power at the second pulse frequency, so that The output RF power is switched between a first power and a second power, and the second RF power synchronization is switched between the first and second matching frequencies synchronized with the second pulse frequency; wherein the first pulse frequency is less than the second pulse frequency.

The first pulse frequency is greater than 60 Hz and less than 1000 Hz, and the second pulse frequency is greater than 60 Hz and less than 500 kHz. The second RF power source outputs a constant power in the matching frequency acquisition phase.

The invention can realize the switching of the RF output power and the corresponding matching frequency of the pulse processing stage more quickly, and provide the overall processing speed.

1‧‧‧matcher

2‧‧‧matcher

10‧‧‧Edge ring

11‧‧‧ gas sprinkler

20‧‧‧ wafer

21‧‧‧Electrical chuck

22‧‧‧ pedestal

31‧‧‧First RF power supply

32‧‧‧Second RF power supply

100‧‧‧reaction chamber

110‧‧‧ gas source

S31‧‧‧First matching frequency acquisition step

S32‧‧‧Second matching frequency acquisition step

S41‧‧‧ first processing steps

S42‧‧‧Second processing steps

CW1‧‧‧First impedance state

CW2‧‧‧second impedance state

t1‧‧‧Time required for the first impedance state

t2‧‧‧Time required for the second impedance state

t3‧‧‧Time required for multiple matching frequencies to acquire pulses

1 shows a schematic structural view of the plasma processing apparatus according to the prior art; FIG. 2 shows a schematic diagram of output power and power matching of high frequency and low frequency power supplies according to the prior art; FIG. 3 shows a high frequency and low frequency power supply according to the present invention. Schematic diagram of output power and power matching; FIG. 4 is a schematic diagram showing output power and power matching of high frequency and low frequency power sources according to another embodiment of the present invention.

The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings. One of the first RF power source 31 and the second RF power source 32 described in FIG. 1 is a low frequency RF power source, and one is a high frequency RF power source. The frequency of the high-frequency RF power supply is greater than 13MHz, such as 30MHz, 60MHz, etc., the frequency of the low-frequency RF power supply is less than 13MHz, such as 2MHz, the first RF power supply 31 is the high-frequency RF power supply, and the second RF power supply 32 is the low-frequency RF power supply. The method of the invention is illustrated.

2 is a schematic diagram of prior art high frequency and low frequency power output power and power matching; in plasma processing, the plasma is first ignited, and then some transition steps may be taken to enter the main plasma processing step. This method mimics multiple different resistances In the anti-state, due to the use of the traditional continuous RF generator, the switching speed is very slow, reaching the second level, such as more than 1 second. Using the continuous RF generator at the first output power, as shown in the high-frequency power output curve in Figure 2, after the initial frequency is obtained by the automatic frequency tuning (AFT) function, the matching frequency cannot be directly switched to the next impedance state. Switch to the next power output state preparation, such as the need to prepare the next stage of the boost power. Therefore, the first impedance state (CW1) sustain time (t1) is long enough to reach 1 second or more, and the same second impedance state (CW2) requires as much time (t2). When there are many impedance states, such as high-frequency RF power supply 31 and low-frequency RF power supply 32 respectively having different output powers, and even having a third RF power supply, there are many combinations of different power output states of different RF power sources. If each combined state takes more than 1 second, it takes a lot of time to complete the matching frequency acquisition step before entering the formal pulse plasma processing stage. Therefore, although the prior art can achieve matching for pulsed plasma processing, the processing efficiency needs to be improved.

Compared with the prior art, the present invention uses a pulsed power source such as a low-frequency RF power source 32 to select a matched RF power source, such as a high-frequency RF power source 31. The difference between a pulsed power supply and a conventional continuous power supply is that the pulsed RF power supply includes hardware and software settings that accommodate pulsed power output (fast high and low power output switching). In the different power output switching engineering, the pulsed RF power supply of the present invention can instantaneously realize the switching of the output power, and the prior art requires a time greater than 100 ms to convert from the first output power to the second output power due to the limitation of the hardware. As shown in Figure 2, when CW1 is switched to CW2, although the power output is instantaneously switched, the actual curve is tilted. For example, switching from 1000W to 4000W actually takes more than 2 seconds. Switching between other power values, such as 1000W to 0W, also requires at least a few hundred milliseconds. In addition, when the pulsed power supply is used, the control system that controls the operation of the device in the entire reaction chamber 100 can send the pulsed output power to the pulsed output stage, and the pulsed RF power supply can output the pulsed power according to the command. However, in the prior art, since the conventional continuous RF power supply is used, the control system needs to send a signal for the start and end of each pulse, and the control system needs to perform a certain period of operation and delay before sending the signals to the continuous RF power supply, such as 100-300ms delay. Due to the existence of signal delay, the conventional continuous RF power supply cannot quickly switch the output power or frequency, so both RF power sources of the present invention use a pulsed RF power supply. Pulsed RF power supply included A storage device can store at least two output states, each of which includes a different power output or a frequency output. When a pulsed switch is received from an instruction output state of the control system, the pulsed RF electric field is directly output according to the stored information. Plasma reactor. The use of two or more pulsed RF power sources can reduce the time waste caused by the above power conversion and signal delay, and can realize the switching of the RF output power more quickly.

Before entering the subsequent pulse plasma processing, the matching frequency acquisition phase is first entered. In the matching frequency acquisition phase, the high frequency RF power source (the first RF power source 31) and the low frequency RF power source (the second RF power source 32) can output different levels of power, mimicking the impedance state that occurs during subsequent pulse processing stages. For example, in the pulse processing stage, the output power of the high-frequency RF power source is high, and the output power of the low-frequency RF power source is low, and the same power output state is set correspondingly in the plurality of matching frequency acquisition steps S31 and S32, and then the high-frequency RF power supply is adjusted. The frequency gets the best matching frequency, and finally the matching frequency that can match different states is obtained. Matching of high speed pulse processing states is achieved directly at the high speed switching of the different matching frequencies obtained during the pulse processing phase. For example, when the output power of the low-frequency RF power supply (2MHz) is high power output and low power output respectively, the high-frequency RF power supply (60MHz) is matched to obtain matching frequencies of 59.5MHz and 58.9MHz for the two different stages. Subsequently, in the subsequent pulse processing phase, the high frequency RF power source directly achieves a fast match to the different power output states of the low frequency RF power source (steps S41 and S42 in FIG. 3) using the two matched frequencies obtained. After using the method of the present invention, as shown by the graph of the reflected power of the high frequency power source in Fig. 3, the reflected power can be significantly reduced. When the output power of the low-frequency RF power source is switched according to the pulse frequency, the output power of the high-frequency RF power supply remains basically unchanged, such as maintaining the output power at 1000 W, or the power output change in the two stages before and after is less than 5%, preferably the same. As shown in FIG. 4, the output power of the high-frequency radio frequency power source can also be pulse-switched synchronously with the low-frequency radio frequency power source, and output high-power radio frequency and low-power radio frequency, for example, switching between 1000W and 800W. The output power of the high-frequency RF power supply in FIG. 4 is in the power switching time in steps S31 and S32, and may be synchronized with the power switching time of the low-frequency RF power supply or may have a certain delay. Although the high frequency RF power supply is a pulsed RF power supply that can quickly switch the output state, the present invention requires an analog analog to the impedance state of the subsequent pulse processing stage, so the high frequency RF power supply still maintains an approximate power output. As shown in the high-frequency power reflection power curve of Figure 3, after using the method of the present invention, the high-frequency RF power is maintained at the output power. In the case of 1000W, the reflected powers of the different pulse processing steps S41 and S42 measured at the high-frequency RF power source are 6W and 40W, respectively, which are much smaller than the output power, so the matching effect is good.

After the plasma is ignited, the control system of the present invention transmits a signal entering the matching frequency acquisition phase to the first pulse RF power source 31 and the second pulse RF power source 32, and the second pulse RF power source 32 outputs the RF power that changes at the first pulse frequency. The output power of the first pulse RF power source 31 is substantially unchanged, and the output frequency thereof is adjusted by adjusting the internal frequency conversion original. Finally, the first RF power source 31 obtains a plurality of matching frequencies that match different output states of the second RF power source 32. After obtaining a plurality of matching frequencies, the control system sends a signal entering the pulse processing stage to the first pulse RF power source 31 and the second pulse RF power source 32, and the second pulse RF power source 32 outputs the pulse type RF electric field to the plasma at the second pulse frequency. Processing chamber processing wafer 20, the output frequency of the first pulsed RF power source 31 is synchronized between the obtained matching frequencies at a second pulse frequency, wherein the second pulse frequency of the pulse processing phase is greater than that in the matching frequency acquisition phase First pulse frequency. In the prior art, the control system separately sends a control command in the first matching frequency acquisition step (S31 in FIG. 3) and the second matching frequency acquisition step (S32 in FIG. 3) and even more matching frequency acquisition steps to make the RF power supply According to the instruction, the pulsed electric field is outputted to the reaction chamber, and the pulse change of each output power needs to be sent by the control system once, which increases the complexity of the control system, and causes more time waste due to the delay in the command transmission process. In the invention, since the pulse type RF power source is itself, the control system only needs to send a signal once, and the pulsed RF power source can automatically complete the output of multiple pulses, while the other pulsed RF power source completes the acquisition of the matching frequency, and multiple pulses The sum of time (t3) is also only milliseconds, which greatly saves time.

The present invention includes a plurality of matching frequency acquisition steps in the matching frequency acquisition step. As shown in FIG. 3, each matching frequency acquisition step, such as S31 and S32, has a short time and is pulse-shaped, and the frequency can be 60 Hz-1000 Hz, even if The sum t3 of the times used to match the frequency acquisition pulses is also much smaller than the time (t1+t2) of the plurality of matching frequency acquisition steps in the prior art, wherein the length of each of the pulse steps S31, S32 may be 100 us-100 ms, which is optimal. For 1ms-10ms, only 1/100~1/1000 of the time required in the prior art, even if a large number of pulses are needed to match, the time required is short and does not affect the overall processing efficiency.

In the subsequent formal pulse plasma processing stage, the low frequency RF power is switched between high and low output power at a pulse frequency (60 Hz-500 KHz), wherein the high output power is greater than the low input. 2 times the power output. The low output power can also be zero, that is, pulsed plasma processing can be in the alternation of plasma ignition and extinction. When the output power of the low frequency RF power source 32 is switched, the output power of the high frequency RF power source is also set according to the processing requirements, wherein the output frequency of the high frequency RF power source 31 is between the obtained at least two matching frequencies. Switch.

In contrast, the output of the high frequency RF power source 31 is pulsed between high and low output power, and the low frequency RF power source 32 is frequency switched. Matching different impedance states is another embodiment of the inventive concept. Simultaneous pulse switching between two RF power sources can also be applied to the method of the present invention. First, a plurality of matching frequencies are used to acquire a pulse to simulate a subsequent impedance state, and a corresponding matching pulse is obtained, and the obtained matching is directly used in the subsequent pulse processing stage. Frequency to quickly match different impedances. The method of the present invention can also be applied when a third or more pulse signals are included, except that more matching frequency acquisition steps need to be set to match more different impedance states.

The specific embodiments of the present invention have been described above. It is to be understood that the invention is not limited to the specific embodiments described above, and various modifications and changes may be made by those skilled in the art without departing from the scope of the invention.

S31‧‧‧First matching frequency acquisition step

S32‧‧‧Second matching frequency acquisition step

S41‧‧‧ first processing steps

S42‧‧‧Second processing steps

T3‧‧‧sum of multiple pulse times

Claims (10)

A plasma processing method for a plasma processing apparatus, the plasma processing apparatus comprising a reaction chamber including a susceptor, a susceptor fixed wafer to be processed, and a plurality of RF power sources having different RF frequency outputs for applying RF An electric field is introduced into the reaction chamber, the plurality of radio frequency power sources are pulsed radio frequency power sources, and the processing method includes: matching a frequency acquisition phase and a pulse processing phase; and the matching frequency acquisition phase includes: a first matching frequency acquisition step: adjusting The output of the first pulse RF power source is the first output state, and the output of the second pulse RF power source is the third output state, so that the first impedance is in the reaction cavity, and the frequency conversion component in the second pulse RF power source is adjusted to obtain the first matching frequency. To match the first impedance; a second matching frequency acquisition step of: adjusting an output of the first pulsed RF power source to a second output state, and outputting a second pulse RF power source output to a fourth output state to have a second impedance in the reaction cavity Adjusting the frequency conversion component in the second pulse RF power source to obtain a second matching frequency to match The second impedance; the pulse processing stage includes: a first processing step: setting the first pulsed RF power output to have a first output state, and setting the second pulse RF power output to a third output state and having a a matching frequency; a second processing step: setting the first pulsed RF power output to have a second output state, and setting the second pulsed RF power output to a fourth output state and having a second matching frequency, characterized by The time of the first or second matching frequency acquisition step in the matching frequency acquisition phase is less than 100 ms and greater than the time of the first or second processing step in the pulse processing phase. The method of claim 1, wherein the time of the first or second processing step in the pulse processing phase is less than 10 ms. The method of claim 1, wherein the first output state of the first pulsed RF power source has a first power output and the second output state has a second power output, wherein the first power output is greater than the second power output. The method of claim 3, wherein the second power output is zero. The method of claim 1, wherein in the first and second matching frequency acquisition pulses, the output power in the third output state is greater than or equal to the output power in the fourth output state. The method of claim 1, wherein the first pulsed RF power output frequency is less than the second Pulsed RF power output frequency. The method of claim 6, wherein the first pulsed RF power output frequency is less than 13 MHz and the second pulsed RF power output frequency is greater than 13 MHz. A plasma processing method for a plasma processing apparatus, the plasma processing apparatus comprising a reaction chamber, a reaction chamber including a base, a wafer to be processed fixed on the base, and a plurality of RF power sources having different RF frequency outputs are applied to the RF electric field to Within the reaction chamber, a control system controls the plurality of radio frequency power sources, the plurality of radio frequency power sources are pulsed radio frequency power sources, and the processing method includes: the control system sends a signal to enter the matching frequency acquisition stage to the plurality of The RF power supply, in the matching frequency acquisition phase, the first RF power source outputs the RF power at the first pulse frequency, so that the output RF power is switched between the first power and the second power, and the second RF power is at the first pulse frequency. Synchronizing the output frequency to obtain first and second matching frequencies corresponding to the first power and the second power output; after obtaining the first and second matching frequencies, the control system sends a signal to enter a pulse processing stage to The plurality of radio frequency power sources, in the pulse processing stage, the first radio frequency power source outputs the second pulse frequency Power, the output RF power is switched between a first power and a second power, and the second RF power synchronization is switched between the first and second matching frequencies in synchronization with the second pulse frequency; wherein the first pulse frequency is less than the first Two pulse frequencies. The method of claim 8, wherein the first pulse frequency is greater than 60 Hz and less than 1000 Hz, and the second pulse frequency is greater than 60 Hz and less than 500 kHz. The method of claim 8, wherein the second RF power source outputs a constant power in the matching frequency acquisition phase.