TWI794631B - plasma processor - Google Patents

Abstract

The present invention provides a capacitively coupled plasma processor. A high-frequency radio frequency power supply outputs radio frequency power of a first frequency to a base through a first matcher, and a low-frequency radio frequency power supply outputs radio frequency power of a second frequency through a second matcher. Power to the base, wherein the first frequency is greater than 10MHz, and the second frequency is less than or equal to 300KHz; a controller and a frequency conversion detection part are also connected between the output end of the high frequency radio frequency power supply and the base; wherein the frequency conversion detection part includes a A mixer, the mixer includes a first end receiving an auxiliary frequency signal, a second end receiving a radio frequency power signal reflected by the base, and a third end connected to an input end of a band-pass filter, which filters A signal of a third frequency is output to the controller through the output terminal 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 to control the first matching device or high frequency radio frequency source.

Description

plasma processor

The invention relates to the technical field of semiconductor processing, in particular to a plasma processor, 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 semiconductor wafer processing process requires a large number of plasma processors. These processors will perform plasma etching, chemical vapor deposition and other processes on the substrate to be processed. Fig. 1 shows the structural diagram of a typical plasma processor, the plasma processor includes a reaction chamber 101, the reaction chamber 101 includes a base 10, an electrostatic chuck 21 is arranged above the base, and the electrostatic chuck 21 is fixed to be The substrate 100 is processed. An edge ring 22 is also included surrounding the electrostatic chuck and substrate. The base 10 is connected to a high frequency radio frequency source (HF) through a first matcher 1 , and is connected to a low frequency radio frequency source (LF) through a second matcher 2 . A disk-shaped gas shower head 11 is disposed opposite to the base 10 in the reaction chamber 101 , and the gas shower head 11 communicates with an external gas source 200 through a gas pipe. In the prior art, 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 concentration and ion incidence of plasma P in the plasma processor respectively. The energy of the substrate 100. Wherein each matcher is provided with a filter circuit, such as the parameter setting of the first filter circuit in the first matcher 1 so that only about 60Mhz radio frequency power can pass through, and the radio frequency power of other frequencies such as 1-2MHz, the harmonic frequency of low frequency radio frequency power wave, and the mixing of low frequency and high frequency to produce 58MHz and 62MHz are blocked by the high impedance of the filter.

In applications that require etching ultra-high aspect ratios (greater than 40), such as 3D NAND memory manufacturing processes, ions need to have extremely high incident energy. In order to increase the ion energy without greatly increasing the LF RF power, it is necessary to significantly reduce The frequency of low frequency radio frequency. For example, when the RF frequency of LF is reduced below 300KHz, the frequencies generated by the above mixing are 59.7MHz and 60.3MHz, which are very close to the 60MHz frequency to be detected. At this time, the filter circuit in the matching device cannot filter out the above-mentioned interfering mixing frequency signal. These signals cannot be filtered out, resulting in the inability to accurately detect the magnitude of the high-frequency power reflected to the first matcher 1 , and to accurately control the action of the matcher to perform impedance matching. This has serious consequences: plasma instability, wasted power, overheating of wiring, all of which lead to failure of the plasma treatment process. Even through the special design of the inductance and capacitance in the filter circuit, the filter can filter out 60Mhz and block other mixing frequencies that are only 1/200 different from 60Mhz, but this design requires a large value of inductance and capacitance, resulting in the filter The response of the plasma processor 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, which can still 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 invention provides a plasma processor, comprising: a reaction chamber, the bottom of the reaction chamber includes a base, the base is used to support the substrate to be processed, and the top of the reaction chamber opposite to the base 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, 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 conversion detection part are also connected between the output end of the high frequency radio frequency source and the base; wherein the frequency conversion detection part includes a mixer, and the mixer includes a first end receiving a Auxiliary frequency signal, the second end receives the radio frequency power signal reflected by the base, the third end is connected to the input end of a band-pass filter, and the band-pass filter screens out a signal of a third frequency f3 and passes The output end of the bandpass 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 matching device or the high frequency radio frequency source.

Optionally, the frequency conversion detection part further includes a crystal oscillator, and 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.

Optionally, the first frequency f1 output by the high-frequency radio frequency source can be adjusted within the 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 variable frequency range Δ. The frequency conversion detection part also includes a second crystal oscillator outputting an auxiliary frequency signal, a first end of a second mixer receiving the auxiliary frequency signal, and a second end receiving a first frequency f1 signal output by a high-frequency radio frequency source , the mixed frequency signal output by the second mixer is filtered by a second filter to output the auxiliary frequency signal.

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

Further, the ratio f2/f3 of the second frequency f2 to the third frequency f3 is equal to 30%.

Further, the high-frequency radio frequency source outputs pulsed varying power, so that the output power varies between different power ranges, 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 matching unit, so that the output power of 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, and an extremely low frequency (0.3Mhz) radio frequency power is required for etching with a high aspect ratio, and the high frequency can be effectively separated by using the present invention Mixing signals in RF power for better matching.

1: first matcher

2: Second matcher

10: Base

11: Gas sprinkler head

21: Electrostatic Chuck

22: Edge ring

30,32: frequency conversion detection part

40: Reflected power signal receiver

100: Substrate

101: reaction chamber

200: external air source

HF: High frequency radio frequency source

LF: Low Frequency RF 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

Fig. 1 is a schematic structural view of a conventional plasma processor; Fig. 2a is a matcher and its control circuit in the plasma processor of the present invention; Fig. 2b is a radio frequency signal processing in a matcher and its control circuit shown in Fig. 2a Schematic diagram of the process; Figure 3a is a matching device and its control circuit of a plasma processor according to another embodiment of the present invention; Figure 3b is a schematic diagram of the radio frequency signal processing process in the matching device and its control circuit in the embodiment shown in Figure 3a .

The specific embodiments of the present invention will be further described below in conjunction with FIG. 2 and FIG. 3 .

As shown in Fig. 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 0.3MHz, and the frequency of the high-frequency radio frequency source HF is 60MHz. Compared with the conventional technology shown in FIG. 1 , the main difference is that the present invention proposes a frequency conversion detection unit 30 suitable for a multi-frequency radio frequency processor with an ultra-low frequency radio frequency power source. The frequency conversion detection part 30 of the present invention includes a crystal oscillator, and the crystal oscillator outputs an auxiliary frequency signal S0 with 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 from the reaction chamber 101 and The auxiliary frequency signal S0 is mixed with the two signals to output a mixed signal S10. As shown in Fig. 2b, the frequency distribution form of each signal S1, signal S0, and signal S10 in the reflection power signal processing process of the present invention is shown. The horizontal axis is the RF frequency, and the vertical axis is the power intensity of different frequencies Each peak represents that a large amount of power in the signal is concentrated at a specific frequency. For example, the reflected power signal S0 has a peak of 59M, indicating that the RF energy of the auxiliary frequency signal S0 is concentrated at 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 signals of the addition and subtraction of the signal S0 and the signal S1. For the convenience of back-end filtering, only the subtracted frequencies are selected: 0.7, 1, and 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 screened out. Although the frequency has been converted, the 1MHz signal S2 can still indirectly reflect the 60MHz amplitude of the signal S1, so by detecting the 1MHz signal strength of the signal S2 , the magnitude of the 60MHz reflected power in the signal S1 can be calculated and deduced. The controller receives the signal S2 and the output power signal of the high-frequency radio frequency source HF to calculate the reflectivity of the 60MHz radio frequency power, and adjusts the variable capacitor in the first matcher 1 to achieve impedance matching according to the reflectivity data.

7倍)所以後端的濾波器在參數固定的情况下無法在如此變動的頻率段訊號S10中有效篩選出有效訊號S2。 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 frequency conversion function. For example, the output frequency of the high-frequency radio frequency source HF can be changed between 58-62MHz. By changing the output frequency of these radio frequency sources, a faster impedance matching speed can be achieved than by adjusting the variable capacitor in the matching circuit. If the fixed auxiliary frequency signal S0 is still used, such as 57 MHz, it will be mixed with the reflected signal S1 to generate a frequency distribution signal S10 of (0.7-1-1.3)~(4.7-5-5.3). Although the frequency difference between different frequencies is 0.3MHz, but because the absolute value of the frequency changes greatly (0.7:4.7

7 times), so the back-end filter cannot effectively filter out the effective signal S2 in such a changing frequency band signal S10 when the parameters are fixed.

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

When the output frequency of the signal S11 is 59MHz, the corresponding mixing signal is 54MHz-59MHz-64MHz, and the corresponding three mixing signal ranges within the frequency range of the signal S11 are 53-57MHz, 58-62MHz, and 63-67MHz. Even though the above three mixing signals all have variable ranges, the three frequency bands do not overlap, so one of the frequency bands can be filtered out with a bandpass filter, for example, the signal with the lowest frequency can be filtered out with a low-pass filter. The frequency segment S11-5MHz is selected as the intermediate frequency signal S14 for output. One end of a second mixer M2 receives the above-mentioned signal S14, and the other end receives the radio frequency signal S12 reflected from the bottom electrode of the base 10 in the reaction chamber 101, wherein the reflected power signal S12 includes (S11-0.3MHz)-S11-( A group of frequency signals of S11+0.3Mhz) are mixed by the second mixer M2 to output a signal S16. The mixed frequency signal includes many mixed frequency signals, including reflected power signal S12, signal S13, signal S14, reflected power signal S12+signal S14. Among them, the signal S12, signal S13, and signal S14 frequency bands all contain the variable frequency signal S11, so after subtracting the two, only the absolute value of the frequency remains, and the formed frequency band is 4.7MHz-5MHz-5.3MHz. The value of the frequency is convenient for subsequent filter parameter design, so 5MHz in the first frequency band is selected as the RF reflection power detection signal S20, the controller receives the signal S20, and after detecting and calculating the strength of the signal S20, the actual RF reflection power can be obtained The specific power level of the signal S12 in the signal S12, and feedback control the first matching unit 1 or the high frequency radio frequency source HF according to the power value. The control signal C1 output by the controller is output to the first matcher 1 for controlling the variable capacitance 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 lower electrode in the susceptor 10 according to the process requirements, reducing the radio frequency power reflection to obtain a stable plasma. The frequency of the signal S0' needs to be greater than or equal to the frequency range of the signal S11. For example, in the above embodiment, 5MHz>62-58=4Mhz, when the frequency 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 mixed signal segments generated after mixing by the first mixer M1 will not have overlapping frequencies, and it can be passed through a fixed low-pass filter The corresponding signal S14 is screened out to prevent signals of other frequency bands from entering subsequent processing circuits through the low-pass filter.

In addition to separating the 5MHz signal and calculating the power intensity of the corresponding signal S11, the bandpass filter in the present invention 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 into the first matcher 1. The first matching unit 1 will comprehensively calculate and control the variable parameters according to the power strengths of the above two reflected signals (for example, when the high-frequency radio frequency is 60 MHz, the mixing signals 59.7 and 60.3 Mhz), so as to minimize the two reflected powers.

Figure 3b is a schematic diagram of the radio frequency signal processing and frequency conversion that occurs during the operation of the first matching device 1, the second matching device 2 and their control circuits shown in Figure 3a. From the 3b figure, it can be seen that the process of multiple frequency mixing-frequency selection-remixing-frequency selection in the frequency conversion detection part 32 of the present invention finally utilizes two-stage frequency mixing and frequency selection, so that in the high-frequency radio frequency Under variable conditions, the frequency signal to be passed can still be screened out by a fixed filter, and the frequency signal reflects the reflected signal S11 of 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, and the pulse frequency can be selected from 10-100KHz. The variable capacitor in the matcher cannot quickly change the capacitance to achieve fast matching. 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), through the 3a figure The frequency conversion detector 32 can still effectively detect the reflected power value of the high-frequency radio frequency power.

The present invention converts 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 high-frequency signals that need to be detected by filters after changing the frequency bands. signal, and then by measuring the filtered high-frequency signal, the value of the high-frequency radio frequency power reflected from the reaction chamber 101 back to the first matching device 1 is finally calculated. By calculating and obtaining the above-mentioned high-frequency power value, the feedback control first matching unit 1 can realize the matching between 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 with the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. Various modifications and alterations to the present invention will become apparent to those skilled in the art upon reading the above disclosure. Therefore, the protection scope of the present invention should be limited by the scope of the appended patent application.

1: first matcher

2: Second matcher

10: base

11: Gas sprinkler head

30: frequency conversion detection part

40: Reflected power signal receiver

101: reaction chamber

S0, S1, S2, S10: signal

M0: Mixer

Claims (9)

A plasma processor, comprising: a reaction chamber, the bottom of the reaction chamber includes a base, the base is used to support a substrate to be processed, and the top of the reaction chamber opposite to the base includes a gas shower head , a high frequency radio frequency source outputs a radio frequency power of a first frequency f1 to the base through a first matcher, and a low frequency radio frequency source outputs a radio frequency power of a second frequency f2 to the base through a second matcher Seat, 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 conversion detection part are also connected between the output end of the high frequency radio frequency source and the base; wherein the frequency conversion detection part includes A mixer, the mixer includes 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 the input end of a band-pass filter, the A signal of a third frequency f3 is screened out by the band-pass filter and output 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 f3 , to control the first matching device or the high frequency radio frequency source; wherein the ratio f2/f3 of the second frequency f2 to the third frequency f3 is equal to 30%. The plasma processor as described in claim 1, wherein the frequency conversion detection part further includes a crystal oscillator, and 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 as described in 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 Δ in the frequency range is a variable frequency 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 variable frequency range Δ. The plasma processor as described in claim 3, wherein the frequency conversion detection part also includes a second crystal oscillator to output the auxiliary frequency signal, a first end of a second mixer receives the auxiliary frequency signal, a second The end receives the first frequency f1 signal output by the high frequency radio frequency source, and the mixed frequency signal output by the second mixer is filtered by a second filter to output the auxiliary frequency signal. The plasma processor as claimed in claim 3, wherein the variable frequency range Δ is greater than 500KHz and less than or equal to 4MHz. The plasma processor as claimed in claim 4, wherein the second filter is a low-pass filter. The plasma processor as claimed in claim 3, wherein the high-frequency radio frequency source outputs pulsed power, so that the output power varies between different power ranges, wherein the pulse frequency is greater than 10Hz and less than 100KHz. The plasma processor as described in claim 1, wherein a control signal output by the controller controls the action of the variable capacitor in the first matching device, so that the output power of the high-frequency radio frequency source is consistent with that of the plasma processor impedance matching. The plasma processor as claimed in claim 8, wherein the plasma processor is used for etching etching holes with an aspect ratio greater than 40.

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