JP5210905B2 - Plasma processing equipment - Google Patents

Description

  The present invention relates to a plasma processing apparatus, and more particularly to a plasma processing apparatus including a matching device in a high-frequency power supply path.

  In manufacturing a semiconductor, a plasma processing apparatus is used. As the plasma processing apparatus, for example, an electromagnetic wave is radiated through an antenna in a vacuum processing chamber, and plasma is generated in the vacuum processing chamber by interaction with a magnetic field by a magnetic field coil arranged around the vacuum processing chamber. 2. Description of the Related Art Cyclotron Resonance) type etching processing apparatuses are known.

  FIG. 5 is a diagram for explaining an ECR etching apparatus. As shown in FIG. 5, a processing container 37 having a flat antenna 38 made of a conductor such as aluminum or nickel and a dielectric window 32 made of quartz, sapphire or the like capable of transmitting electromagnetic waves is provided on the vacuum container 4. However, it is placed in an airtight manner through a vacuum sealing material 36 such as an O-ring, and forms a processing chamber 35 inside.

  A magnetic field generating coil 31 is provided on the outer periphery of the vacuum vessel 4 so as to surround the processing chamber 35. The antenna 38 has a porous structure for flowing an etching gas. The gas supply device 30 is made of a CFC, C4F6, C4F8, C5F8, CHF3, CH2F2, etc., a CFC, an inert gas such as Ar, N2, or an oxygen-containing gas such as O2, CO, etc. After the flow rate is adjusted by the flow rate adjusting means, it is supplied into the processing chamber 35.

  A vacuum exhaust device 34 is connected to the vacuum vessel 4, and a vacuum exhaust means (not shown) made of TMP and a pressure adjusting means (not shown) made of APC are provided in the vacuum exhaust device 34. Is maintained at a predetermined pressure.

  A high-frequency power source (first high-frequency power source) 20 for plasma generation is connected to the upper portion of the antenna 38 via a matching unit (first matching unit) 21 and a coaxial cable 25. A substrate electrode 1 on which a semiconductor wafer 3 can be placed is provided in the lower part of the vacuum vessel 4. Similarly to the antenna 38, a high frequency power source (second high frequency power source) 6 for ion attraction is connected to the substrate electrode 1 through a matching unit (second matching unit) 7 and a coaxial cable 9. The substrate electrode 1 also has an electrostatic chuck function for electrostatically attracting the semiconductor wafer 3, and the DC power source 2 is connected to the embedded electrostatic chuck electrode 33.

  The operation and problems of the high frequency power source 6 for ion attraction and the matching unit 7 will be described below, but the same applies to the high frequency power source 20 for plasma generation and the matching unit 21.

  The high-frequency power source 6 for ion attraction has an impedance when the substrate electrode 1 is viewed from the high-frequency power source 6, that is, the load impedance XL, and the power source itself so that high-frequency power of a predetermined frequency can be efficiently obtained. It is necessary to match the impedance, that is, the power source impedance XP. For this reason, a matching unit 7 is provided as impedance matching means. However, since the load impedance XL is given by a combination of the impedance of the matching unit 7 itself, the impedance of the substrate electrode 1, the impedance of the plasma 5 for processing the semiconductor wafer generated in the vacuum vessel 4, etc., it is predicted in advance. It is difficult.

Therefore, in the example of FIG. 5, as the matching unit 7, as shown in the drawing, a matching unit including two impedance variable elements 8 a and 8 b and one fixed impedance element 10 for changing the impedance is used. By changing the impedance of the variable elements 8a and 8b, even when the load impedance XL changes, the matching state can be adjusted so that the load impedance XL and the power source impedance XP are always correctly matched.
As described above, in the plasma processing apparatus, with respect to the frequency (basic frequency) of the high-frequency power supplied from the high-frequency power source 6, the matching unit performs impedance matching with the load (plasma) side, so that the reflected wave from the load side is matched. It stops at the vessel and does not return to the high frequency power supply 6. However, the plasma 5 is a non-linear load and generates harmonics. In this case, since the matching unit 7 is not matched to the harmonics, the harmonics received from the load side are passed to the high frequency power source 6. As a result, a standing wave is generated on the transmission line between the matching unit 7 and the high-frequency power source 6 by mixing the traveling wave of the harmonic and the reflected wave. Thus, when a standing wave of harmonics of high frequency power is generated on the transmission line, the generation or distribution characteristics of plasma in the processing container fluctuate indefinitely, which may reduce process reproducibility and reliability. Moreover, there is a possibility that a detection error and a matching error of traveling wave power and reflected wave power may occur.

  In order to avoid such a problem, it is known that the length of the coaxial cable is determined in advance for the harmonic wavelength (Patent Document 1). However, in the technique of Patent Document 1, no consideration is given to the change in the harmonic level for each process condition or due to wear of parts in the processing chamber, and the standing wave of the harmonics generated on the transmission line. The suppression effect is not sufficient.

JP 2004-247401 A

  Here, the relationship between the reflected wave power generated on the transmission line and the length of the coaxial cable (expressed in terms of the wavelength of the fundamental wave) will be described.

  First, the power of the high frequency power source is supplied to the coaxial cable, and the six types of coaxial cables shown in the wavelengths A to F in FIG. 6 are connected to the transmission line between the high frequency power source and the matching unit, and for each connected coaxial cable, The harmonic level (difference with respect to the fundamental wave) for each frequency of the reflected wave power generated on the transmission line was measured.

  FIG. 6 shows the harmonic levels of the fourth harmonic and the fifth harmonic whose output level was high. FIG. 7 shows the VPP voltage generated on the load side at this time (the difference from the normally generated VPP value). Further, FIG. 8 shows the result of measuring the reflected wave power returning to the power source side at this time.

  As shown in the figure, for the coaxial cables of wavelengths C and D, reflected wave power above the fundamental wave was detected. As a result, it can be seen that the VPP voltage also changes, and the reflected wave power increases (VSWR 1.3 or more).

  On the other hand, for coaxial cables of wavelengths A, B, E, and F, the reflected wave power is lower than the fundamental wave, the VPP voltage is equivalent, and the reflected wave power is small (VSWR is 1.3 or less). I understand that. Further, in FIG. 9, the etching rate (ER) in the wafer surface of the coaxial cable having the wavelength D for detecting the reflected wave power above the fundamental wave and the coaxial cable having the wavelength F that is the reflected wave power below the fundamental wave is shown. The measurement results are shown. As shown in FIG. 9, it can be seen that the etching rate is lowered when coaxial cables of wavelengths D and F are used. In other words, it means that the generation of higher harmonics than the fundamental wave on the transmission line of high frequency power affects the process performance.

  In this example, the generation of harmonics on the transmission line was intentionally changed by changing the length of the coaxial cable. As a result, the generation level of the harmonics changes and the generation state of the harmonics on the transmission line changes, and the process performance deteriorates accordingly.

  The present invention has been made in view of such problems, and reduces standing waves due to harmonics from plasma generated on a transmission line that transmits high-frequency power, thereby ensuring process reproducibility and reliability. Is.

  In order to solve the above problems, the present invention employs the following means.

A vacuum processing container provided with a gas supply device for supplying a processing gas; and an antenna that is disposed in the vacuum processing container and generates high-frequency power from a high-frequency power source for plasma generation to the supplied processing gas to generate plasma A sample to be processed, which includes a substrate electrode disposed in the vacuum processing vessel, supplies a high-frequency voltage for ion attraction to the substrate electrode, accelerates ions in the plasma, and is placed on the substrate electrode In a plasma processing apparatus for performing plasma processing on a cable, a cable length adjusting means for variably adjusting the cable length by selecting one of a plurality of cables having different lengths from the high frequency power for ion attraction, the cable length A transmission line connected to the substrate electrode through an adjusted cable and an impedance matching circuit, and a flow on the transmission line A reflected wave detecting means for detecting a reflected wave from the substrate electrode side included in the high frequency power and a control means for controlling the cable length adjusting means, the control means on the transmission line during the plasma processing The length of the cable is adjusted by controlling the cable length adjusting means so as to select one of the plurality of cables such that the magnitude of the harmonic of the reflected wave is equal to or less than that of the fundamental wave.

  Since the present invention has the above-described configuration, it is possible to reduce standing waves due to harmonics generated from plasma generated on a transmission line that transmits high-frequency power, and to ensure process reproducibility and reliability.

It is a figure explaining the plasma processing apparatus concerning an embodiment. It is a figure explaining a modification. It is a figure explaining the example which connected the coaxial cable length switching means and the reflected wave detection means (harmonic level) between the high frequency power supply for ion attraction and a matching device, and between the high frequency power supply for plasma generation and a matching device. It is a figure explaining the example which connected the coaxial cable length switching means and the reflected wave detection means (reflected wave electric power) between the high frequency power supply for ion attraction and a matching device, and between the high frequency power supply for plasma generation and a matching device. It is a figure explaining the etching apparatus of an ECR system. It is a figure which shows the harmonic level of a 4th harmonic and a 5th harmonic. It is a figure which shows the VPP voltage (difference with respect to the VPP value which generate | occur | produces normally) generated on the load side. It is a figure which shows the result of having measured the reflected wave power which returns to the high frequency power supply side. It is a figure which shows that the etching rate is falling when the coaxial cable of the length of the wavelengths D and F is used.

  Hereinafter, the best embodiment will be described with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a plasma processing apparatus according to an embodiment of the present invention. In the figure, the same parts as those shown in FIG. In FIG. 1, a substrate electrode 1, a DC power source 2, a vacuum vessel 4 serving as an etching processing chamber, a plasma 5, a semiconductor wafer 3, a gas supply device 30, a magnetic field generating coil 31, a dielectric window 32, an electrostatic chuck electrode 33, The vacuum exhaust device 34, the processing chamber 35, the vacuum sealing material 36, the processing container 37, the antenna 38, the matching unit 21, the coaxial cable 25, the high frequency power supply 20, the two variable impedance elements 8a and 8b, and the fixed impedance element 10 are respectively This is the same as that in the conventional plasma processing apparatus described in FIG.

  The vacuum processing apparatus of the present embodiment shown in FIG. 1 is different from the conventional vacuum processing apparatus shown in FIG. 5 in that a matching unit 7a is provided as an impedance matching unit instead of the matching unit 7 shown in FIG. The point is that, instead of the coaxial cable 9, a plurality (three in the figure) of coaxial cables 9a, 9b, 9c having different lengths are provided. Although the number of cables is three, any number may be used as long as there is no problem in mounting. Moreover, when using a high-frequency power source for high power, a coaxial tube may be used.

  As shown in FIG. 1, the matching unit 7a includes a reflected wave detection means 13, a switching control means 14, and a coaxial cable length switching means 15a for detecting a reflected wave at a harmonic level, and further includes a coaxial cable length switching means. 15b is also provided in the high-frequency power source 6a. The matching unit 7a includes variable impedance elements 8a and 8b and a fixed impedance element 10.

  In FIG. 1, the reflected wave detecting means 13 is connected between coaxial cables 9a, 9b, 9c and the variable impedance element 8a, and the high frequency power supplied from the high frequency power source 6a is reflected by a non-linear plasma load to generate harmonics. The harmonic level of the reflected wave power when returning to the matching circuit body composed of the variable impedance elements 8a and 8b and the fixed impedance element 10 is detected as the reflected wave power including.

  In wafer processing, first, a dummy wafer is used to generate plasma for each process condition to be used, and the reflected wave detection means 13 detects the harmonic level of the reflected wave power. The switching control means 14 includes a CPU, and the coaxial cable length switching means 15a, 15b switches the coaxial cable length so that the harmonic level of the reflected wave power detected by the reflected wave detection means 13 is lower than the fundamental wave level. The optimum coaxial cable length is stored in advance for each process condition.

  The coaxial cable length switching means 15a and 15b are provided in the high frequency power source 6a and the matching unit 7a as described above, and are switched simultaneously. Depending on the length of the coaxial cable to be used, the supplied power input to the matching unit may not be input as set due to cable loss or the like. For this reason, by setting a conversion value so that predetermined power can be obtained in advance for each coaxial cable to be used, and by setting the output value of the high-frequency power supply when power is supplied according to this conversion value, It is desirable that the power at the cable end be constant regardless of which coaxial cable is used.

  Next, after the coaxial cable is switched by the coaxial cable length switching means 15a and 15b so as to have the coaxial cable length stored in advance for each process condition, etching is started.

  As described above, according to the present embodiment, standing waves due to harmonics from plasma that change for each process condition on the transmission line for transmitting high-frequency power can be reduced.

  In this embodiment, before processing the product wafer, the length of the coaxial cable is determined in advance using a dummy wafer so that the harmonic level of the reflected wave power is equal to or lower than the fundamental frequency. The harmonic level of the reflected wave power is detected by, for example, when the harmonic level is changed for some reason, the coaxial cable length is switched by the coaxial cable length switching means 15a, 15b. Standing waves due to harmonics from plasma can be reliably reduced.

  In the above example, the case where the coaxial cable length is switched so that the standing wave due to the harmonic from the plasma does not occur on the transmission line by detecting the harmonic level of the reflected wave has been described. May be detected and the coaxial cable length may be switched.

  FIG. 2 is a diagram for explaining a modification. The difference from the plasma processing apparatus shown in FIG. 1 is that the harmonic level is detected as the reflected wave detection means 13 in the example of FIG. In this example, the reflected wave power is detected as the reflected wave detecting means 40.

  In FIG. 2, the reflected wave detecting means 40 detects reflected wave power returning from the load side. The switching control unit 14 includes a CPU, and the coaxial cable length switching units 15a and 15b are set so that the VSWR (standing wave ratio) calculated based on the reflected wave power from the reflected wave detection unit 40 is 1.3 or less. Thus, the coaxial cable length is switched. Thereby, the standing wave by the harmonic from the plasma on a transmission line can be reduced.

  The example in which the cable length switching unit is applied to the matching unit of the high frequency power source for ion attraction of the plasma etching apparatus has been described above, but can be applied to the matching unit of the high frequency power source for plasma generation. In this case, as shown in FIG. 3, the coaxial cable length switching means 15a and 15b, the coaxial cable 9a, between the high frequency power source 6a for ion attraction and the matching unit 7a, and between the high frequency power source 20a for plasma generation and the matching unit 21a, 9b, 9c, switching control means 14, and reflected wave detection means 13 (harmonic level) can be realized. Further, as shown in FIG. 4, coaxial cable length switching means 15a, 15b, coaxial cables 9a, 9b, between the high frequency power source 6a for ion attraction and the matching unit 7a, and between the high frequency power source 20a for plasma generation and the matching unit 21a, 9c, switching control means 14, and reflected wave detection means 40 (reflected wave power) can be realized.

  As described above, according to the present embodiment, by switching the length of the coaxial cable inserted in the transmission line connecting the high-frequency power source to the antenna or the substrate electrode, the harmonics from the plasma cause the above-mentioned transmission line on the transmission line. The reproducibility and reliability of the process can be ensured by suppressing the occurrence of standing waves.

DESCRIPTION OF SYMBOLS 1 Substrate electrode 2 DC power supply 3 Semiconductor wafer 4 Vacuum vessel 5 Plasma 6 High frequency power supply for ion attraction (second high frequency power supply in the prior art)
6a High frequency power supply for ion attraction (second high frequency power supply)
7 Matching device (second matching device in the prior art)
7a Matching device (second matching device)
8a, 8b Variable impedance element 9, 25, 9a, 9b, 9c Coaxial cable 10 Fixed impedance element 13 Reflected wave detection means (harmonic level)
14 switching control means 15a, 15b coaxial cable length switching means 20 high frequency power supply for plasma generation (first high frequency power supply in the prior art)
20a High frequency power source for plasma generation (first high frequency power source)
21 Matching device (first matching device in the prior art)
21a Matching device (first matching device)
DESCRIPTION OF SYMBOLS 30 Gas supply apparatus 31 Coil for magnetic field generation 32 Dielectric window 33 Electrostatic chuck electrode 34 Vacuum exhaust apparatus 35 Processing chamber 36 Vacuum seal material 37 Processing container 38 Antenna 40 Reflected wave detection means (reflected wave power)

Claims (9)

A vacuum processing container equipped with a gas supply device for supplying a processing gas;
An antenna that is arranged in the vacuum processing vessel and generates plasma by supplying high-frequency power from a high-frequency power source for plasma generation to the supplied processing gas;
A substrate electrode disposed in the vacuum processing vessel;
In a plasma processing apparatus for supplying a high frequency voltage for ion attraction to the substrate electrode, accelerating ions in the plasma and performing plasma processing on a sample to be processed placed on the substrate electrode,
A cable length adjusting means for variably adjusting the cable length by selecting one of a plurality of cables having different lengths from the high-frequency power for ion attraction, a cable having the adjusted cable length, and an impedance matching circuit. A transmission line connected to the substrate electrode via,
A reflected wave detecting means for detecting a reflected wave from the substrate electrode side included in the high frequency power flowing on the transmission line, and a control means for controlling the cable length adjusting means,
The control means adjusts the cable length so as to select one of the plurality of cables such that the magnitude of the harmonic of the reflected wave on the transmission line during the plasma processing is equal to or less than that of the fundamental wave. A plasma processing apparatus, wherein the length of the cable is adjusted by controlling the means. The plasma processing apparatus according to claim 1,
The control means controls the cable length adjusting means based on a result detected by the reflected wave detecting means during plasma processing of another sample performed under the processing conditions before the plasma processing of the sample to be processed. Then, the plasma processing of the sample to be processed is performed by adjusting the length of the cable. A vacuum processing container equipped with a gas supply device for supplying a processing gas;
An antenna that is arranged in the vacuum processing vessel and generates plasma by supplying high-frequency power from a high-frequency power source for plasma generation to the supplied processing gas;
A substrate electrode disposed in the vacuum processing vessel;
In a plasma processing apparatus for supplying a high frequency voltage for ion attraction to the substrate electrode, accelerating ions in the plasma and performing plasma processing on a sample to be processed placed on the substrate electrode,
A cable length adjusting means for variably adjusting a cable length by selecting one of a plurality of cables having different lengths from the high frequency power for plasma generation, a cable having the adjusted cable length, and an impedance matching circuit. A transmission line connected to the antenna via,
A reflected wave detecting means for detecting a reflected wave from the antenna side included in the high frequency power flowing on the transmission line and a control means for controlling the cable length adjusting means;
The control means adjusts the cable length so as to select one of the plurality of cables such that the magnitude of the harmonic of the reflected wave on the transmission line during the plasma processing is equal to or less than that of the fundamental wave. A plasma processing apparatus, wherein the length of the cable is adjusted by controlling the means. The plasma processing apparatus according to claim 3, wherein
The control means controls the cable length adjusting means based on a result detected by the reflected wave detecting means during plasma processing of another sample performed under the processing conditions before the plasma processing of the sample to be processed. Then, the plasma processing of the sample to be processed is performed by adjusting the length of the cable. In the plasma processing apparatus according to claim 1 or 3,
The cable includes a plurality of coaxial cables having different lengths, and the control unit includes the cable length adjusting unit so that the magnitude of the harmonic wave of the reflected wave detected by the reflected wave detecting unit is a predetermined value or less. A plasma processing apparatus that controls and selects any one of the cables having different lengths. The plasma processing apparatus according to claim 1,
The plasma processing is characterized in that the power supplied to the substrate electrode is kept constant by adjusting the output of the high frequency power supply for ion attraction according to the length of the cable adjusted by the cable length adjusting means. apparatus. The plasma processing apparatus according to claim 3, wherein
A plasma processing apparatus characterized in that the power supplied to the antenna is kept constant by adjusting the output of the plasma forming high-frequency power source according to the length of the cable adjusted by the cable length adjusting means. . The plasma processing apparatus according to claim 6, wherein
A plasma processing apparatus, wherein an output value of a high frequency power supply for ion attraction when power is supplied to each of cables having different lengths adjusted by a cable length adjusting means is set in advance. The plasma processing apparatus according to claim 7, wherein
A plasma processing apparatus, wherein an output value of a high frequency power source for plasma generation when power is supplied to each cable having a different length adjusted by a cable length adjusting means is set in advance.

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