TWI416995B - A plasma processing chamber having a switchable bias frequency, and a switchable matching network - Google Patents

Abstract

A plasma processing chamber having a switchable bias frequency superimposed onto plasma source frequency and applied to the cathode. A power source generating multiple RF bias frequencies, via a switch, can be coupled into a match network. The match network couples one of the bias frequencies to the cathode. Another match network applied a source RF power to the cathode. A variable shunt capacitor and a fixed capacitor are connected in parallel to be disposed between ground and input of the switch. Another variable shunt capacitor and a fixed capacitor are also connected together and disposed between ground and the input of the source RF match network.

Description

Plasma processing chamber with switchable bias frequency and switchable matching network

The present invention relates to RF power suppliers and matching networks for plasma processing chambers, and more particularly to RF power sources and matching networks capable of implementing multiple-frequency RF power. .

Plasma processing chambers utilizing dual or multiple RF frequencies are well known in the art. Generally, the dual frequency plasma processing chamber receives a radio frequency bias power (RF bias power) having a frequency lower than about 15 MHz, and the received RF source power has a higher frequency, usually 27 ～. 200MHZ. In this context, RF bias power refers to the RF power used to control the ion energy and its energy distribution. On the other hand, RF source power refers to RF power used to control plasma ion dissociation or plasma density. In some embodiments, the bias frequency at which the etch plasma processing chamber is typically run is, such as 100 KHz, 2 MHz, 2.2 MHz, 13.56 MHz, and the source frequency is such as 13.56 MHz, 27 MHz, 60 MHz, 100 MHz or higher.

Recently, the industry has proposed operating a plasma processing chamber at a bias frequency and two source frequencies. For example, it is proposed to operate a plasma etch chamber at a bias frequency of 2 MHz and two source frequencies of 27 MHz and 60 MH, respectively. In this manner, the dissociation of the various ions can be controlled by the two source RF frequencies described above. Regardless of the configuration, in the prior art, each frequency is provided by an independent RF power source, each independent power source coupled to a separate matching network.

1 is a schematic block diagram of a prior art multiple frequency plasma processing chamber including a biased RF power and two source RF power generators. More specifically, the plasma processing chamber 100 shown in FIG. 1 includes an upper electrode 105, a lower electrode 110, and a plasma 120 generated between the two electrodes. As is well known, the upper electrode 105 is typically embedded in the top cover of the reaction chamber, and the lower electrode 110 is typically embedded in a lower cathode element for placing a semiconductor process component to be processed, such as a semiconductor wafer. As shown in FIG. 1, a biased RF power source 125 provides RF power to plasma processing chamber 100 via matching circuit 140. The frequency of the RF bias is f1, which is typically 2 MHz or 13 MHz (more precisely 13.56 MHz), which is applied to the lower electrode 110. Figure 1 also shows two RF source power sources 130 and 135 operating at frequencies f2 and f3, respectively. For example, f2 can be set to 27 MHz and f3 can be set to 60 MHz. The RF source power sources 130 and 135 provide power to the plasma processing chamber 100 through matching networks 145 and 150, respectively. The RF source power can be applied to the lower electrode 110 or the upper electrode 105. In particular, in all of the figures herein, the output of the matching network is illustrated as a single arrow pointing to the reaction chamber, which is a schematic representation to cover the coupling of any matching network and plasma. Whether through the lower electrode, the electrode on the top cover, or through an inductive coupling coil. For example, the bias power can be coupled through the cathode below, and the source power can be coupled through one of the gas nozzles or an inductor. Conversely, the bias power and source power can also be coupled through the cathode below.

The Summary of the Invention is only intended to provide a basic understanding of some aspects and features of the present invention, and is not intended to limit the scope of the invention or the scope of the invention. The concepts of the present invention are presented in a simplified form as a

A plasma processing chamber provided by a different aspect of the invention has a switchable biasing frequency superimposed on the frequency of the plasma source and applied to the cathode. In accordance with an embodiment of the present invention, a power source capable of generating multiple RF offset frequencies is coupled to a matching network via a switch. The matching network couples one of the bias frequencies to the cathode. Another matching network applies a source RF power to the cathode. A parallel connection of a variable shunt capacitor and a fixed capacitor is provided between the ground and the input of the switch, and a parallel connection of the other variable shunt capacitor and the fixed capacitor is connected to the ground and source RF matching network Between input. A fixed capacitor provides protection for its variable parallel capacitors connected in parallel.

According to one aspect of the invention, a radio frequency matching circuit is provided that is capable of switchably coupling one of two bias frequencies and a source frequency to a cathode. The circuit includes: a switch including an input, a first output, and a second output; a first matching network having an input coupled to the first output of the switch and an output coupled to the cathode, The first matching network is tuned to operate at a first bias frequency below 10 MHz; an input having a second output coupled to the switch and a second matching network coupled to an output of the cathode The second matching network is tuned to operate at a second bias frequency that is higher than the first bias frequency but lower than 15 MHz; and a third having an output coupled to the cathode A matching network is tuned to operate at a source frequency that is higher than the second bias frequency. The circuit further includes: a parallel resonant circuit coupled between the output of the third matching network and the cathode, the parallel resonant circuit can be tuned such that its center frequency and the first The second biasing frequency is the same; a variable shunt capacitor is coupled between ground and the input of the switch; a second variable shunt capacitor coupled between the ground and the input of the third matching network; And a fixed capacitor between the ground and the input of the switch; and/or a second fixed capacitor coupled between the ground and the input of the third matching network.

According to one aspect of the invention, a radio frequency matching circuit is provided that is capable of switchably coupling one of two bias frequencies to a cathode. The circuit includes: a switch including an input, a first output, and a second output; a first matching network having an input coupled to the first output of the switch and an output coupled to the cathode, The first matching network is tuned to operate at a first bias frequency below 10 MHz; an input having a second output coupled to the switch and a second matching network coupled to an output of the cathode The second matching network is tuned to operate at a second bias frequency that is higher than the first bias frequency but lower than 15 MHz; a variable parallel between the ground coupled to the input of the switch a capacitor; and a fixed capacitor coupled between the ground and the input of the switch.

According to another aspect of the present invention, there is provided a plasma processing chamber operating on two convertible RF bias powers, comprising: a reaction chamber for generating a plasma in a vacuum chamber; and one for RF Energy coupled to the cathode of the plasma; a first RF power capable of selectively generating a first bias frequency below 10 MHz or a second bias frequency above the first bias frequency but below 15 MHz a generator comprising: a switch coupled to the first RF power generator, including a first output and a second output; an input having a first output coupled to the switch and an output coupled to the cathode a first matching network, the first matching network being tuned to operate at a first bias frequency; an input having a second output coupled to the switch and a second coupled to an output of the cathode a matching network, the second matching network being tuned to operate at a second bias frequency; a second RF power generator capable of generating a radio frequency source power at a frequency greater than 15 MHz; And, coupled to the input and includes a second RF power generator is coupled to the cathode of said third matching network output. In one embodiment, the first bias frequency is about 2 MHz, the second bias frequency is about 13 MHz, and the source power frequency is one of 27 MHz, 60 MHz, and 100 MHz. The circuit can further include a parallel resonant circuit coupled between the output of the third matching network and the cathode, the parallel resonant circuit being tuned such that its center frequency is approximately 13 MHz, and its frequency bandwidth ( Band) is 2MHz. The circuit can further include a parallel connection between a variable shunt capacitor and a fixed capacitor coupled between ground and the input of the switch. The circuit can further include a parallel connection of a variable shunt capacitor and a fixed capacitor coupled between the ground and the input of the third matching network.

2 shows a block diagram of a multiple frequency plasma processing chamber including two switchable RF bias power sources coupled to a matching network, in accordance with an embodiment of the present invention. In FIG. 2, two RF bias power sources 225 and 255 provide switchable RF bias frequencies f1 and f2 to the reaction chamber 200 via switches 232, which are coupled to matching circuits 240 and 245, respectively. The RF offset frequency f1 is typically 2 MHz or 2.2 MHz, and the RF offset frequency f2 is typically 13 MHz (more accurately 13.56 MHz). Two RF offsets are typically applied to the lower electrode 210. In this manner, the present invention achieves an improved ion energy control. For example, for applications requiring higher bombardment energy, such as front-end etch applications, 2 MHz sources can be utilized, while for applications requiring softer bombardment, such as back-end etch The application can utilize a bias of 13MHz. Figure 2 also shows an RF source power source 235 that operates at frequency f3, for example, 27 MHz, 60 MHz, 100 MHz, and the like. The RF source power source 235 is delivered to the reaction chamber 200 through the matching circuit 250 and applied to the lower electrode 210. The source power is used to control plasma density, ie, plasma ion dissociation.

The structure shown in Figure 2 enables the application of dual frequency (or f1/f3 or f2/f3) of the reaction chamber. For example, f1 may be 400 kHz to 5 MHz; f2 may be 10 MHz to 20 MHz, but is typically lower than 15 MHz; f3 may be 27 MHz to 100 MHz or higher. In a special case, f1 is 2MHz, f2 is 13.56MHz, and f3 is 60MHz. This configuration makes it very easy to run recipes that require switching between low frequency bias power and high frequency bias power during the process.

Figure 3 exemplarily shows a matching circuit in which two of the three available frequencies are switchably applied to the cathode of a plasma processing chamber on. A high frequency f3 is coupled to the cathode via a matching circuit 334 and a parallel resonant circuit 330, and two lower frequencies f1 and f2 are coupled to the switch 332, which switchably causes f1 or f2 to pass through the matching circuit 320 or 322 is coupled to the cathode. In the present embodiment, the RF frequency f1/f2 is provided by a separate RF power generator to enable switchable operation at frequency f1 or f2. Each of the matching circuits is composed of a capacitor and an inductor connected in series. In one embodiment, the matching circuit 320 includes a capacitor of 200 to 500 pF and an inductor of approximately 20 to 50 mH; the matching circuit 322 includes a capacitor of 50 to 200 pF and an inductor of approximately 0.5 to 5 mH; the matching circuit 334 includes A capacitor of approximately 25 pF and an inductor of approximately 0.2-0.3 mH.

The parallel resonant circuit 330 is used to prevent energy from entering the 60 MHz source from the 13.56 MHz power source. That is, when switch 332 is coupled to a 2 MHz bias source, the bias frequency is thirty times lower than the 60 MHz plasma source frequency, so it cannot skip matching circuit 334. However, when the switch 332 is coupled to a 13.56 MHz bias power, the bias frequency is closer to the plasma source frequency f3, possibly skipping the matching circuit 334. Accordingly, the present invention provides a parallel resonant circuit formed by a capacitor and an inductor connected in parallel. In the present embodiment, when f1 = 2MHZ, f2 = 13.56 MHz, and f3 = 60 MHz, the center frequency of the parallel resonant circuit 330 is 13 MHz, and its variable or bandwidth is Δf = 2 MHz. This prevents the bias frequency 13.56 from leaking into the source power source f3. The resonant circuit is a short circuit of 60 MHz.

In the embodiment shown in Figure 3, a variable shunt capacitor 305 is coupled to Switch 332 is preceded, such that it is common to matching circuits 320 and 322 (regardless of which of matching circuits 320 and 322 is coupled to switch 332). Another variable shunt capacitor 315 operates in conjunction with matching circuit 334 for frequency f3. In the present embodiment, two variable parallel capacitors are implemented using variable vacuum capacitors. Also, in the present embodiment, a specific protection test can be employed to protect the variable parallel capacitor described above. A fixed capacitor 300 is coupled in parallel to the variable parallel capacitor 305. The fixed capacitor 300 protects the variable shunt capacitor 305 from being affected by high RF currents when set to a low capacitance value. Conversely, the fixed capacitor 310 is coupled in parallel to the variable shunt capacitor 315. The fixed capacitor 310 protects the variable shunt capacitor 315 from being affected by high RF currents when set to a low capacitance value. In the present embodiment, the variable parallel capacitor 305 can vary between approximately 30 pF and 1500 pF, and the fixed capacitor 300 is set to approximately 100 pF. Similarly, in the present embodiment, the variable shunt capacitor 315 can vary between approximately 10 pF and 150 pF, and the fixed capacitor 310 is set at approximately 120 pF.

Any of the above embodiments can be used to operate a plasma processing chamber to provide a process including a first cycle operating at a first bias frequency and a second cycle operating at a second bias frequency. For example, the reaction chamber can be operated at a low bias frequency, for example, set to approximately 2 MHz during the main etch step; however, to achieve a "soft landing" during the end of the etch, the system can be switched Operates at a higher frequency offset, for example, approximately 13 MHz.

Finally, it should be understood that the processes and techniques described above are not inherently related to any particular device, but should be applied to any suitable combination of components. Further, various types of general purpose devices can be applied in accordance with the teachings herein. It is also advantageous to manufacture a dedicated device to carry out the method steps described herein. The present invention has been described with reference to the specific embodiments, which are intended to be illustrative and not limiting. Those skilled in the art will appreciate that different combinations of hardware, software, and firmware are suitable for use in practicing the present invention. For example, the software can be executed in a variety of programs or scripting languages, such as assembly, C/C++, PERL, SHELL, PHP, JAVA, and the like.

The present invention has been described with reference to the preferred embodiments, and all aspects thereof are intended to be illustrative and not restrictive. In addition, other embodiments of the invention will be apparent to those skilled in the <RTIgt; Different aspects and/or elements of the described embodiments may be used alone or in any combination in the plasma processing chamber field. The above-described embodiments are to be considered as illustrative only, and the scope and spirit of the invention are defined by the claims.

200. . . Reaction chamber

205. . . Upper electrode

210. . . Lower electrode

220. . . plasma

225, 235, 255. . . RF bias power source

232. . . switch

240, 245, 250. . . Matching circuit

F1, f2, f3. . . RF offset frequency

300, 310. . . Fixed capacitor

305. . . Shunt capacitor

315. . . Shunt capacitor

320, 322, 334. . . Matching circuit

330. . . Parallel resonant circuit

332. . . switch

1 is a schematic block diagram of a prior art multiple frequency plasma processing chamber including a biased RF power and two source RF power generators.

2 is a schematic block diagram of a multiple frequency plasma processing chamber including two biased RF powers and a source RF power generator in accordance with a first embodiment of the present invention.

Fig. 3 exemplarily shows an RF power matching circuit.

200. . . Reaction chamber

205. . . Upper electrode

210. . . Lower electrode

220. . . plasma

225, 235, 255. . . RF bias power source

232. . . switch

240, 245, 250. . . Matching circuit

F1, f2, f3. . . RF offset frequency

Claims (11)

An RF matching circuit, the RF matching circuit is switchably coupled to one of two bias frequencies and a source frequency to a cathode, comprising: a switch including an input, a first output, and a second output a first matching circuit comprising an input coupled to the first output of the switch and an output coupled to the cathode, the first matching circuit being tuned to operate at a first bias frequency below 10 MHz a second matching circuit comprising an input coupled to a second output of the switch and an output coupled to the cathode, the second matching circuit being tuned to be at a higher than the first bias frequency but Operating at a second bias frequency below 15 MHz; a third matching circuit comprising an output coupled to the cathode, the third matching circuit being tuned to a source above the second bias frequency Operating at a frequency; and a parallel resonant circuit coupled between the output of the third matching circuit and the cathode, the parallel resonant circuit being tuned to have its center frequency The second biasing frequencies are equal. The radio frequency matching circuit of claim 1, further comprising a variable shunt capacitor coupled between the ground and the input of the switch. The radio frequency matching circuit of claim 2, further comprising a coupling between the ground and the input of the third matching circuit The second variable shunt capacitor. The radio frequency matching circuit of claim 3, further comprising a fixed capacitor coupled between the ground and the input of the switch. The radio frequency matching circuit of claim 4, further comprising a second fixed capacitor coupled between the ground and the input of the third matching circuit. A radio frequency matching circuit, wherein the radio frequency matching circuit is switchably coupled to one of two bias frequencies on a cathode, comprising: a switch including an input, a first output, and a second output; a first match a circuit including an input coupled to a first output of the switch and an output coupled to the cathode, the first matching circuit being tuned to operate at a first bias frequency below 10 MHz; a second a matching circuit comprising an input coupled to a second output of the switch and an output coupled to the cathode, the second matching circuit being tuned to be above a first bias frequency but below 15 MHz Operating at a second bias frequency; a variable shunt capacitor coupled between ground and the input of the switch; and a fixed capacitor coupled between ground and the input of the switch. A plasma processing chamber operating under two switchable RF bias power sources, comprising: a reaction chamber for generating a plasma in an interior where it is evacuated; a cathode for coupling radio frequency energy to the plasma; and a first RF power generator, optionally generating a lower a first offset frequency of 10 MHz or a second bias frequency that is higher than the first bias frequency but lower than 15 MHz; a switch including an input coupled to the first RF power generator, a first An output and a second output; a first matching circuit including an input coupled to the first output of the switch and an output coupled to the cathode, the first matching network being tuned to Operating at a bias frequency; a second matching circuit comprising an input coupled to a second output of the switch and an output coupled to the cathode, the second matching network being tuned to be in the second Operating at a bias frequency; a second RF power generator that produces RF source power above 15 MHz; a third matching circuit including an input coupled to the second RF power generator and coupled to An output of the cathode; and a parallel resonant circuit coupled between the output of the third matching circuit and the cathode, the parallel resonant circuit being tuned to have its center frequency and the second bias The equal frequency is set, wherein the first RF power generator provides the cathode with the first bias frequency and the second bias frequency switchable through the switch. The plasma processing chamber of claim 7, wherein The first bias frequency is about 2 MHz, the second bias frequency is about 13 MHz, and the frequency of the RF source power is any one of 27 MHz, 60 MHz, and 100 MHz. The plasma processing chamber of claim 8, wherein the parallel resonant circuit is tuned to have a center frequency of about 13 MHz and a bandwidth of 2 MHz. The plasma processing chamber of claim 9, further comprising a variable shunt capacitor and a fixed capacitor coupled in parallel between the ground and the input of the switch. The plasma processing chamber of claim 10, further comprising a variable shunt capacitor and a fixed capacitor coupled in parallel between the ground and the input of the third matching circuit.