TW202125563A - Plasma processing system and method for operating plasma processing system - Google Patents

Abstract

The invention provides a capacitively coupled plasma processor, and the processor is characterized in that a high-frequency radio frequency power supply outputs radio frequency power of a first frequency to a base through a first matcher, a low-frequency radio frequency power supply outputs radio frequency power of a second frequency to the base through a second matcher, the first frequency is greater than 10MHz, and the second frequency is less than or equal to 300KHz; a controller and a variable-frequency detection part are also connected between the output end of the high-frequency radio-frequency power supply and the base; the frequency conversion detection part comprises a frequency mixer, the frequency mixer comprises a first end for receiving an auxiliary frequency signal, a second end for receiving a radio frequency power signal reflected by the base, and a third end connected to an input end of a band-pass filter; the band-pass filter screens out a signal of a third frequency and outputs the signal to the controller through the output end of the band-pass filter, and the controller calculates the radio frequency power value reflected by the base according to the signal of the third frequency so as to control the first matcher or the high-frequency radio frequency power supply.

Description

Plasma processor and operation method of plasma processor

The present invention relates to the technical field of semiconductor processing, in particular to a plasma processor, and in particular to a design and control method of a radio frequency supply system in the plasma processor.

Semiconductor wafers are increasingly widely used in various electronic devices. The processing of semiconductor wafers requires a large number of plasma processors. These processors perform processes such as plasma etching and chemical vapor deposition on the substrate to be processed. Figure 1 shows the structure of a typical plasma processor. The plasma processor includes a reaction chamber 101. The reaction chamber 101 includes a susceptor 10. An electrostatic chuck 21 is provided above the susceptor. The substrate 100 is processed. Surrounding the electrostatic chuck and the substrate also includes an edge ring 22. The base 10 is connected to a high-frequency radio frequency source (HF) through the first matcher 1, and at the same time is connected to a low-frequency radio frequency source (LF) through the second matcher 2. A disc-shaped gas shower head 11 is disposed in the reaction chamber 101 opposite to the susceptor 10, and the gas shower head 11 communicates with an external gas source 200 through a gas pipe. In the conventional technology, the frequency of the high-frequency radio frequency source generally needs to be greater than 13MHz (such as 60MHz), and the frequency of the low-frequency radio frequency source is generally 1-2MHz. The power of the two is used to control the plasma P concentration and ion incidence in the plasma processor. The energy of the substrate 100. Each matcher is provided with a filter circuit. For example, the parameter setting of the first filter circuit in the first matcher 1 allows only the radio frequency power of about 60Mhz to pass, and the radio frequency power of other frequencies such as 1-2MHz, low frequency radio frequency power harmonics The wave, as well as the mixing of low frequency and high frequency, produces 58MHz and 62MHz, which are all blocked by the high impedance of the filter.

In applications where ultra-high aspect ratio (greater than 40) is required for etching, such as 3D NAND memory manufacturing process, ions are required to have extremely high incident energy. In order to increase the ion energy without greatly increasing the LF radio frequency power, it needs to be greatly reduced The frequency of the low frequency radio frequency. For example, when the radio frequency of LF is lowered below 300KHz, the frequencies generated by the above mixing are 59.7MHz and 60.3MHz, which are very close to the 60MHz frequency that needs to be detected. At this time, the filter circuit in the matcher cannot filter out the above-mentioned interfering mixing frequency signal. The inability to filter these signals results in the inability to accurately detect the magnitude of the high-frequency power reflected to the first matcher 1, and therefore the inability to accurately control the action of the matcher to perform impedance matching. This will bring a series of serious consequences: plasma instability, power waste, and circuit overheating, which will cause the plasma treatment process to fail. Even though the inductance and capacitance in the filter circuit are specially designed, the filter can filter out 60Mhz while blocking other mixing frequencies that are only 1/200 from 60Mhz, but this design requires extremely large inductance and capacitance, resulting in a filter The response is too slow to keep up with the rapidly changing impedance state in the plasma processor, and the final matcher still cannot achieve effective impedance matching.

Therefore, the industry needs to develop a new matching circuit that can effectively detect the reflected power of high-frequency RF power when using ultra-low frequency bias RF power, and can also achieve fast impedance matching.

The present invention provides a plasma processor, including: a reaction chamber, the bottom of the reaction chamber includes a pedestal, the pedestal is used to support a substrate to be processed, and the top of the reaction chamber opposite to the pedestal includes a gas shower head , A high-frequency radio frequency source outputs the radio frequency power of the first frequency f1 to the base through a first matcher, and a low frequency radio frequency source outputs the radio frequency power of the second frequency f2 to the base through a second matcher. Seat, where the first frequency f1 is greater than 10MHz, and the second frequency f2 is less than or equal to 300KHz;

A controller and a frequency-frequency detection unit are also connected between the output end of the high-frequency radio frequency source and the base; wherein the frequency-frequency detection unit includes a mixer, and the mixer includes a first end that receives a Auxiliary frequency signal, the second end receives the radio frequency power signal reflected by the base, and the third end is connected to the input end of a band pass filter. The band pass filter filters out a signal with a third frequency f3 and uses The output end of the band-pass filter is output to the controller, and the controller calculates the value of the radio frequency power reflected by the base according to the signal of the third frequency f3 to control the first matcher or the high frequency radio frequency source.

Optionally, the variable frequency detection unit further includes a crystal oscillator that outputs the auxiliary frequency signal, and the auxiliary frequency is the difference between the first frequency f1 and the third frequency f3.

Optionally, the first frequency f1 output by the high-frequency radio frequency source may be adjustable within a frequency range of (f1-Δ/2)~(f1+Δ/2), and Δ in the frequency range is the frequency conversion range The auxiliary frequency is the difference between the first frequency value f1 and the third frequency f3, wherein the third frequency f3 is greater than or equal to the frequency conversion frequency range Δ. The frequency detection unit also includes a second crystal oscillator that outputs a signal of a third frequency f3, a first end of a second mixer receives the signal of the third frequency f3, and a second end receives the signal output by a high-frequency radio frequency source. The first frequency f1 signal, and the mixing signal output by the second mixer is filtered by a second filter to output the auxiliary frequency signal.

The frequency conversion range Δ of the first frequency f1 is greater than 500K and less than 4MHz. Further, the second filter is a low-pass filter.

Further, the ratio f3/f2 of the third frequency to f3 to the second frequency f2 is less than 60 times.

Further, the high-frequency radio frequency source outputs pulse-likely varying power, so that the output power varies between different power amplitudes, wherein the pulse frequency is greater than 10 Hz and less than 100 KHz.

Wherein, the control signal output by the controller controls the action of the variable capacitor in the first matcher, so that the power output by the high-frequency radio frequency source matches the impedance in the plasma processor.

The plasma processor of the present invention is suitable for etching etching holes with an aspect ratio greater than 40. Extremely low frequency (0.3Mhz) radio frequency power is required for high aspect ratio etching. The high frequency power can be effectively separated after adopting the present invention. The mixing signal in the RF power achieves a better match.

The specific embodiments of the present invention will be further described below with reference to Figures 2 and 3.

As shown in Figure 2a, the matcher and its control circuit in the plasma processor of the present invention, the frequency of the low frequency radio frequency source LF in the present invention is 0.3 MHz, and the frequency of the high frequency radio frequency source HF is 60 MHz. Compared with the conventional technology shown in Fig. 1, the main difference is that the present invention proposes a variable frequency detection unit 30 suitable for a multi-frequency radio frequency processor with an ultra-low frequency radio frequency power source. The frequency detection unit 30 of the present invention includes a crystal oscillator, and the crystal oscillator outputs an auxiliary frequency signal S0 having a fixed frequency, such as 59 MHz. One end of a mixer M0 receives the above-mentioned signal S0, and the other end uses a reflected power signal receiver 40 to separate the reflected power signal S1 from the plasma processor. The mixer M0 receives the reflected power signal S1 and S1 from the reaction chamber 101. The auxiliary frequency signal S0 is mixed with the two signals to output the mixed signal S10. As shown in Figure 2b, the frequency distribution of each signal S1, signal S0, and signal S10 during the processing of the reflected power signal of the present invention. The horizontal axis is the radio frequency, and the vertical axis is the power intensity of different frequencies. Each spike represents a large amount of power in the signal concentrated at a specific frequency at the frequency. For example, the reflected power signal S0 has a peak of 59M, indicating the auxiliary frequency signal The radio frequency energy of S0 is concentrated around 59Mhz. The reflected radio frequency signal S1 includes not only the 60 MHz signal output by the high frequency radio frequency source HF, but also the interference signals 59.7 MHz and 60.3 MHz generated after mixing with 0.3 MHz in the base 10. The output signal S10 after mixing by the mixer M0 includes the frequency signal of the addition and subtraction of the signal S0 and the signal S1. In order to facilitate the back-end filtering, only the subtracted frequencies of the two are taken: 0.7, 1, 1.3 MHz. Although the difference between these three frequencies is still only 0.3MHz, because the overall frequency value is greatly reduced, the ratio of the difference between the middle 1MHz and the interference frequencies on both sides becomes 30%. By setting a simple filter, the 1MHz signal can be filtered out. Although the frequency is changed, the 1MHz signal S2 can still indirectly reflect the amplitude of the 60MHz signal in the signal S1, so by detecting the intensity of the 1MHz signal in the signal S2 , Can calculate and derive the magnitude of 60MHz reflected power in signal S1. The controller receives the aforementioned signal S2 and the output power signal of the high-frequency radio frequency source HF to calculate the reflectivity of the 60 MHz radio frequency power, and adjusts the variable capacitor in the first matcher 1 to achieve impedance matching according to the reflectivity data.

The first matcher 1, the second matcher 2 and the control circuit shown in Figure 2a above can effectively match the power source with a fixed radio frequency, but it is really difficult to match the radio frequency power source with the frequency conversion function. For example, the output frequency of the high-frequency radio frequency source HF can be changed between 58-62MHz, and the output frequency of these radio frequency sources can be changed to achieve a faster impedance matching speed than the adjustment of the variable capacitor in the matching circuit. If the fixed auxiliary frequency signal S0 is still used, such as 57MHz, it will be mixed with the reflected signal S1 to produce a frequency distribution signal S10 of (0.7-1-1.3) ~ (4.7-5-5.3). Although the frequency difference between the different frequencies is 0.3MHz, the absolute value of the frequency varies greatly (0.7:4.7≈7 times), so the filter at the back end cannot be at such a variable frequency when the parameters are fixed. The effective signal S2 is effectively filtered out of the segment signal S10.

In order to solve the application problem of frequency conversion applications, the present invention proposes the matching device and its controller of the second embodiment as shown in Figure 3a. In the present invention, another frequency-frequency detection unit 32 is proposed. The frequency-frequency detection unit 32 includes a crystal oscillator which outputs an auxiliary radio frequency signal S0', wherein the frequency of the signal S0' can be selected to be 5 MHz. The frequency of the output signal S11 of the high-frequency radio frequency source HF is adjustable in the range of 58-62MHz. The first mixer M1 receives the signal S0' and the signal S11, and generates the first mixing signal (S11-5MHz)-S11-(S11+5MHz). The frequency of the signal S11 is variable, so these three mixing signals The specific frequency is also variable, when it can be variable frequency.

When the output frequency of the signal S11 is 59MHz, the corresponding mixing signal is 54MHz-59MHz-63MHz. Within the frequency range of the signal S11, the corresponding three mixing signal ranges are 53-57MHz, 58-62MHz, and 63-67MHz. Even though the above three mixing signals have variable ranges, the three frequency bands do not overlap, so you can use a band-pass filter to filter out one of the frequency bands. For example, use a low-pass filter to filter the lowest frequency signal The frequency band of S11-5MHz is selected as the intermediate frequency signal S14 and output. A second mixer M2 receives the above-mentioned signal S14 at one end, and the RF signal S12 reflected from the bottom electrode of the base 10 in the reaction chamber 101 at the other end. The reflected power signal S12 includes (S11-0.3MHz)-S11-( S11+0.3Mhz) a set of frequency signals, after being mixed by the second mixer M2, the signal S16 is output. The mixed frequency signal includes many mixed frequency signals, including the first frequency band signal S12, the signal S13, the signal S14, the second frequency band signal S12, and the third frequency band signal S12+signal S14. Since the signal S12, signal S13, and signal S14 frequency bands all contain variable frequency signal S11, only the absolute value of the frequency remains after the two are subtracted, and the resulting frequency band is 4.7MHz-5MHz-5.3MHz, these fixed The value of the frequency is convenient for the subsequent filter parameter design, so the 5MHz in the first frequency band is selected as the RF reflected power detection signal S20. The controller receives the signal S20. After detecting and calculating the strength of the signal S20, the actual RF reflected power can be obtained. A signal with a specific power level in the signal S12, and feedback control of the first matcher 1 or the high-frequency radio frequency source HF according to this power value. The control signal C1 output by the controller is output to the first matcher 1 for controlling the variable capacitor in the first matcher 1, and the control signal C2 output by the controller is output to the high-frequency radio frequency source HF for controlling the high frequency The output frequency or radio frequency power of the radio frequency source HF finally enables the high frequency radio frequency power to be effectively supplied to the bottom electrode in the base 10 according to the process requirements, reducing the reflection of radio frequency power and obtaining a stable plasma. The frequency of the signal S0 needs to be greater than or equal to the frequency variation range of the signal S11. For example, in the above embodiment, 5MHz>62-58=4Mhz. When the frequency variation range of the variable frequency signal S11 is only 2MHz, the frequency of the signal S0 can be 2.5MHz Or 3MHZ, such a signal S0 can ensure that the three mixing signal segments generated after mixing by the first mixer M1 will not have overlapping frequencies, and a fixed low-pass filter can be used to filter out the corresponding The signal S14 prevents signals of other frequency bands from entering the subsequent processing circuit through the low-pass filter.

The band-pass filter of the present invention can not only separate the 5MHz signal and calculate the power intensity of the corresponding signal S11, but also can further detect and calculate the mixing power intensity of 4.7Mhz and 5.3MHz, and use the above mixing power intensity as a parameter. Input to the first matcher 1. The first matcher 1 will comprehensively calculate and control the variable parameters based on the power intensities of the above two reflected signals (for example, when the high-frequency radio frequency is 60MHz, the mixing signals 59.7 and 60.3Mhz), so as to minimize the two reflected powers.

Fig. 3b shows a schematic diagram of the radio frequency signal processing and frequency conversion that occur during the operation of the first matcher 1, the second matcher 2 and its control circuit shown in Fig. 3a. It can be seen from Figure 3b that the process of multiple frequency mixing-frequency selection-remixing-frequency selection in the frequency conversion detector 32 of the present invention is finally used in two stages of mixing and frequency selection, so that the high frequency radio frequency In the case of variable, the frequency signal to be used can still be filtered out by a fixed filter, and the frequency signal reflects the reflected signal S11 of the high frequency radio frequency in the reflected power signal S12. For applications that require pulsed RF power output, the RF power output by the high-frequency RF source HF needs to be quickly switched between high power and low power. The pulse frequency can be selected from 10-100KHz. In this rapid change process, the traditional The variable capacitor in the matching device cannot quickly change the capacitance value to achieve rapid matching, and it is necessary to quickly adjust the frequency of the high-frequency radio frequency source HF to quickly match the impedance in the plasma processor. Therefore, the second embodiment of the present invention can make the signal output by the high-frequency radio frequency source HF change within a frequency conversion range Δ, that is, (f1-Δ/2)~(f1+Δ/2), according to Figure 3a The frequency conversion detector 32 can still effectively detect the reflected power value of the high-frequency radio frequency power.

The present invention transforms the high-frequency signals that cannot be directly separated by filters in the prior art into signals of other frequency bands by means of frequency mixing, and then filters out the high-frequency signals that need to be detected by the filter Then, by measuring the filtered high-frequency signal, the high-frequency radio frequency power value reflected from the reaction cavity 101 back to the first matcher 1 is finally calculated. The above-mentioned high-frequency power value is obtained by calculation, and the feedback control of the first matcher 1 can realize the matching of the high-frequency radio frequency power and the internal impedance of the plasma processor. Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. After those skilled in the art have read the above content, various modifications and substitutions to the present invention will be obvious. Therefore, the scope of protection of the present invention should be limited by the scope of the attached patent application.

1: The first matcher 2: Second matcher 10: Pedestal 11: Gas sprinkler 21: Electrostatic chuck 22: edge ring 30, 32: Frequency-frequency detector 40: Reflected power signal receiver 100: substrate 101: Reaction Chamber 200: external air source HF: high frequency radio frequency source LF: low frequency radio frequency source M0: mixer M1: first mixer M2: second mixer P: Plasma C1, C2, S0, S0’, S1, S2, S10, S11, S12, S13, S14, S16, S20: signal

Figure 1 is a schematic diagram of the structure of a conventional plasma processor; Figure 2a shows the matching device and its control circuit in the plasma processor of the present invention; Figure 2b is a schematic diagram of the RF signal processing process in the matcher and its control circuit shown in Figure 2a; Figure 3a is a plasma processor matching device and its control circuit according to another embodiment of the present invention; Figure 3b is a schematic diagram of the RF signal processing process in the matching device and its control circuit in the embodiment shown in Figure 3a.

1: The first matcher

2: Second matcher

10: Pedestal

11: Gas sprinkler

30: Frequency detector

40: Reflected power signal receiver

101: Reaction Chamber

S0, S1, S2, S10: signal

M0: mixer

Claims (10)

A plasma processor, including: A reaction chamber, the inner bottom of the reaction chamber includes a pedestal, the pedestal is used to support a substrate to be processed, and the top of the reaction chamber opposite to the pedestal includes a gas shower head, A high frequency radio frequency source outputs a first frequency f1 radio frequency power to the base through a first matcher, and a low frequency radio frequency source outputs a second frequency f2 radio frequency power to the base through a second matcher , Wherein the first frequency f1 is greater than 10MHz, and the second frequency f2 is less than or equal to 300KHz; A controller and a frequency-frequency detector are also connected between the output end of the high-frequency radio frequency source and the base; The frequency detection unit includes a mixer, the mixer includes a first end to receive an auxiliary frequency signal, a second end to receive a radio frequency power signal reflected by the base, and a third end to connect to a band-pass filter The band-pass filter filters out a signal with a third frequency f3 and outputs it to the controller through the output terminal of the band-pass filter. The controller calculates the base based on the signal at the third frequency f3 The radio frequency power value reflected by the base to control the first matcher or the high frequency radio frequency source. The plasma processor according to claim 1, wherein the variable frequency detector further includes a crystal oscillator, the crystal oscillator outputs the auxiliary frequency signal, and the auxiliary frequency is the difference between the first frequency f1 and the third frequency f3 value. The plasma processor according to claim 1, wherein the first frequency f1 output by the high-frequency radio frequency source can be adjusted within a frequency range of (f1-Δ/2)~(f1+Δ/2), the The Δ in the frequency range is a frequency conversion range, and the auxiliary frequency is the difference between the first frequency value f1 and the third frequency f3, wherein the third frequency f3 is greater than or equal to the frequency conversion range Δ. The plasma processor according to claim 3, wherein the frequency detection unit further includes a second crystal oscillator to output the signal of the third frequency f3, and a first end of a second mixer receives the third frequency f3 Signal, a second end receives the first frequency f1 signal output by the high-frequency radio frequency source, and the mixing signal output by the second mixer is filtered by a second filter to output the auxiliary frequency signal. The plasma processor according to claim 3, wherein the frequency conversion range Δ is greater than 500KHz and less than 4MHz. The plasma processor according to claim 4, wherein the second filter is a low-pass filter. The plasma processor according to claim 1, wherein the ratio f3/f2 of the third frequency to f3 to the second frequency f2 is less than 60 times. The plasma processor according to claim 3, wherein the high-frequency radio frequency source outputs pulse-like varying power, so that the output power varies between different power amplitudes, wherein the pulse frequency is greater than 10 Hz and less than 100 KHz. The plasma processor according to claim 1, wherein a control signal output by the controller controls the action of the variable capacitor in the first matcher, so that the power output by the high-frequency radio frequency source and the plasma processor The impedance is matched. The plasma processor according to claim 9, wherein the plasma processor is used to etch etching holes with an aspect ratio greater than 40.

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