TWI554161B - RF matching network and its application of plasma processing chamber - Google Patents

Description

RF matching network and its applied plasma processing chamber

The present invention relates to RF power suppliers and matching networks for plasma processing chambers, and more particularly to RF frequency 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 frequency of 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 frequency used to control ion energy and its energy distribution. On the other hand, RF source power refers to the RF frequency 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.

In the actual working process of the plasma reaction chamber, it is necessary to provide a radio frequency bias power source with different frequencies. For example, sometimes the reaction chamber needs to work at the 2MHz bias frequency and the source frequency of 60MHz at the same time; sometimes the reaction chamber is needed. The room operates at the 13MHz offset frequency and the source frequency of 60MHz. In order to facilitate the selection of the RF offset frequency of different frequencies, in the prior art, a relay is connected at the output of the two RF offset frequencies, and the relay is disconnected. Close the desired RF offset frequency for the selection. However, the relay can only be disconnected from the RF bias supply. The switching selection can only be made, and the RF bias power supply disconnection will affect the plasma energy and its distribution. Therefore, in practice, it is necessary to provide a matching network capable of real-time switching of the RF bias power supply.

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

In order to solve the above problems, the present invention provides a switchable radio frequency matching network for switching two RF bias frequencies to electrodes of a plasma processing chamber without the need to disconnect the RF bias frequency source. The RF matching network includes a resonant circuit, the resonant circuit includes a capacitor, an inductor, and a variable capacitor, and the variable capacitor is adjusted. The resonant circuit can be in a first frequency impedance state and a second Switching between frequency impedance states, in the first frequency impedance state, the resonant circuit is in a high impedance state for the second RF bias frequency, in a low impedance state for the first RF bias frequency; and in the second frequency impedance state, The resonant circuit is in a high impedance state for the first RF bias frequency and a low impedance state for the second RF bias frequency.

The resonant circuit includes a parallel circuit in which a capacitor and an inductor are connected in parallel, and a capacitor and an inductor are respectively connected at two ends of the parallel circuit, and the variable capacitor is coupled between the ground and the RF offset frequency, further A fixed capacitance is coupled between the ground and the RF bias frequency.

The two RF offset frequencies may be provided by a single RF frequency generator or by two RF frequency generators.

The invention also provides a method of operating at two switchable RF offset frequencies a plasma processing chamber comprising: a reaction chamber for generating a plasma in an interior into which it is evacuated; a lower electrode for coupling RF energy to the plasma; and a first RF frequency generator Optionally generating a first RF offset frequency having a first offset frequency below 10 MHz or a second RF having a second offset frequency above the first offset frequency but below 15 MHz a biasing frequency; a first matching network for switchably applying the two RF bias frequencies to electrodes of the plasma processing chamber; and a second RF frequency generator for generating higher a 15 MHz RF source frequency; and a second matching network comprising an input coupled to the second RF frequency generator and an output coupled to the lower electrode.

The first radio frequency matching network includes a resonant circuit, the resonant circuit includes a capacitor, an inductor and a variable capacitor, and the variable capacitor is adjusted. The resonant circuit can be in a first frequency impedance state and a second Switching between frequency impedance states, in the first frequency impedance state, the resonant circuit is in a high impedance state for the second RF bias frequency, in a low impedance state for the first RF bias frequency; and in the second frequency impedance state, The resonant circuit is in a high impedance state for the first RF bias frequency and a low impedance state for the second RF bias frequency.

The plasma processing chamber further includes a second parallel variable capacitor coupled between the ground and the second RF frequency generator.

The first bias frequency is about 2 MHz, the second bias frequency is about 13 MHz, and the frequency of the RF source frequency is any one of 27 MHz, 60 MHz, and 100 MHz.

The plasma processing chamber further comprising a parallel resonant power A path coupled between the output of the second matching network and the lower electrode, the parallel resonant circuit being tuned to have a center frequency of approximately 13 MHz and a bandwidth of 2 MHz.

An advantage of the present invention is that by using the radio frequency matching network of the present invention, only the size of the variable capacitor can be adjusted to realize instantaneous switching of the RF matching network in two impedance states, thereby ensuring that the two RF offset frequencies are The instantaneous switching of the RF bias frequency source can also be realized under the premise of not breaking the plasma frequency to meet the needs of the plasma processing chamber.

The drawings, which are included in the specification, are exemplary embodiments of the invention The drawings are intended to illustrate the main features of the described embodiments. The figures are not intended to describe each feature of the actual embodiments and the relative dimensions of the depicted elements, which are not drawn to scale.

1 shows a block diagram of a plasma processing chamber having a thermally switched bias frequency, including a switchable two RF bias coupled to a matching network, in accordance with an embodiment of the present invention. Set the frequency source. In FIG. 1, two RF bias frequency sources 125 and 155 provide a switchable RF bias frequency to the reaction chamber 100 via a matching network 140, having RF bias frequencies f1 and f2, 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 bias frequencies are typically applied to the lower electrode 110. 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, 2MHz RF bias frequency can be utilized, while for applications requiring softer bombardment, such as back-end etching (back -end etch) application, available 13 The RF offset frequency of MHz. Figure 1 also shows an RF frequency source 135 that operates at frequency f3, for example, 27 MHz, 60 MHz, 100 MHz, and the like. The RF source frequency source 135 transmits the RF source frequency to the reaction chamber 100 through the matching network 150 and is applied to the lower electrode 110 such that an alternating electric field is generated between the lower electrode 110 and the upper electrode 105, and the alternating electric field is ionized. The introduced reaction gas forms a plasma 120. The RF source frequency is used to control plasma density, ie, plasma ion dissociation.

The structure shown in Figure 1 enables the application of dual frequency (f1/f3 or f2/f3) of the reaction chamber. For example, the frequency f1 may be 400 kHz to 5 MHz; the frequency f2 may be 10 MHz to 20 MHz, but is usually lower than 15 MHz; and the frequency f3 may be 27 MHz to 100 MHz or higher. In the present embodiment, the frequency f1 is 2 MHz, the frequency f2 is 13.56 MHz, and the frequency f3 is 60 MHz. The structure described in this embodiment makes it very easy to operate between the low frequency offset frequency and the high frequency offset frequency in the technical process.

Fig. 2 exemplarily shows an RF matching network in which two of the three available frequencies are switchably applied to the lower electrode 110 of a plasma processing chamber. A radio frequency source having a high frequency f3 is coupled to the lower electrode 110 via a matching circuit 250 and a parallel resonant circuit 230, and two RF bias frequencies having lower frequencies f1 and f2 are coupled to the matching network 240. The RF matching network 240 includes a resonant circuit 220. The resonant circuit 220 includes a parallel resonant circuit in which a capacitor and an inductor are connected in parallel. A capacitor 202 and an inductor 201 are respectively connected to the two ends of the parallel resonant circuit 220. A variable capacitor 205 is coupled between the 202 and the RF bias frequencies of the RF frequencies f1 and f2 to adjust the variable capacitor 205. The resonant circuit can switch between the first frequency impedance state and the second frequency impedance state. a frequency impedance state, the resonant circuit has a high RF bias frequency for the RF frequency f2 The impedance state, the RF bias frequency of the RF frequency f1 is in a low impedance state, that is, the RF bias frequency of the frequency f1 and the RF source frequency of the frequency f3 are coupled to the lower electrode 110; in the second frequency impedance state, the resonant circuit pair The radio frequency offset frequency of the radio frequency f1 is in a high impedance state, and the radio frequency offset frequency of the radio frequency f2 is in a low impedance state, that is, the radio frequency offset frequency of the frequency f2 and the radio frequency source frequency of the frequency f3 are coupled to the lower electrode 110. By adjusting the variable capacitor 205, the RF frequencies f1 and f2 can be instantly switched when the RF bias frequency source is not disconnected.

In the present embodiment, the RF frequency f1/f2 is provided by a separate RF frequency generator to enable immediate switching operation at frequency f1 or f2.

The resonant circuit 220 includes a parallel circuit in which a capacitor ranging from 100 pF to 200 pF and an inductor ranging from 10 uH to 20 uH are connected in parallel. The parallel resonant circuit 220 is respectively connected with a capacitor ranging from 100 pF to 300 pF and a range of An inductance of 1uH-3uH coupled between ground and the RF bias frequency.

The parallel resonant circuit 230 is used to prevent energy from entering a source frequency source of 60 MHz from a bias frequency source of 13.56 MHz. That is, when the matching network 240 is coupled to a 2 MHz bias frequency source, the bias frequency is thirty times lower than the frequency of the 60 MHz plasma source frequency source, so it cannot skip the matching circuit 234. However, when the matching network 240 is coupled to the 13.56 MHz bias frequency, the bias frequency is closer to the frequency f3 of the plasma source frequency source, possibly skipping the matching circuit 234. Accordingly, the present invention provides a parallel resonant circuit 230 that is formed by a capacitor and an inductor connected in parallel. In the present embodiment, when f1 = 2 MHz, f2 = 13.56 MHz, and f3 = 60 MHz, the center frequency of the parallel resonant circuit 230 is 13 MHz, and its variable or bandwidth is Δf = 2 MHz. This prevents the bias frequency of the bias frequency 13.56MHz from leaking into Source frequency source for frequency f3. The resonant circuit is a short circuit of 60 MHz.

In FIG. 2, the parallel variable capacitor 215 operates in conjunction with the matching circuit 234 at a frequency f3. In the present embodiment, the variable capacitors 205 and 215 are implemented using variable vacuum capacitors. Moreover, in the present embodiment, a specific protection mode can be employed to protect the parallel variable capacitor. A fixed capacitor 206 is coupled in parallel to the parallel variable capacitor 205. The fixed capacitor 206 protects the shunt variable capacitor 205 such that it is not affected by high RF currents when set to a low capacitance value. At the same time, the fixed capacitor 210 is coupled in parallel to the parallel variable capacitor 215. The fixed capacitor 210 protects the shunt variable capacitor 215 such that it is not affected by high RF currents when set to a low capacitance value. In the present embodiment, the parallel variable capacitor 205 can vary between approximately 30 pF and 1500 pF, and the fixed capacitor 206 is set to approximately 100 pF. Similarly, in the present embodiment, the parallel variable capacitor 215 can vary between approximately 10 pF and 150 pF, and the fixed capacitor 210 is set at approximately 120 pF.

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 present invention should be apparent to those skilled in the art from this disclosure. Easy to see. 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 specific embodiments are to be considered as illustrative only, and the scope and spirit of the invention are defined by the scope of the patent.

100‧‧‧reaction chamber

105‧‧‧Upper electrode

110‧‧‧ lower electrode

120‧‧‧ Plasma

125‧‧‧RF bias frequency source

135‧‧‧RF source frequency source

140‧‧‧matching network

150‧‧‧matching network

155‧‧‧RF bias frequency source

201‧‧‧Inductance

202‧‧‧ Capacitance

205‧‧‧Variable Capacitance

206‧‧‧Fixed capacitor

210‧‧‧Fixed capacitor

215‧‧‧Variable Capacitance

220‧‧‧Resonance circuit

230‧‧‧Resonance circuit

234‧‧‧Matching circuit

240‧‧‧matching network

250‧‧‧Matching circuit

F1‧‧‧ frequency

F2‧‧‧ frequency

F3‧‧‧ frequency

1 is a schematic diagram of a structure having a thermally switched bias frequency plasma processing chamber in accordance with one embodiment of the present invention.

Figure 2 exemplarily shows an RF frequency matching network.

100‧‧‧reaction chamber

105‧‧‧Upper electrode

110‧‧‧ lower electrode

120‧‧‧ Plasma

125‧‧‧RF bias frequency source

135‧‧‧RF source frequency source

140‧‧‧matching network

150‧‧‧matching network

155‧‧‧RF bias frequency source

F1‧‧‧ frequency

F2‧‧‧ frequency

F3‧‧‧ frequency

Claims (9)

An RF matching network is coupled to a first RF offset frequency and a second RF offset frequency for switching the first RF offset frequency and the second RF offset frequency through the RF The matching network is applied to an electrode of a plasma processing chamber, wherein the RF matching network includes a resonant circuit and a variable capacitor, the resonant circuit includes a capacitor and an inductor, and the resonant circuit is the capacitor and a parallel resonant circuit in parallel with the inductor, one end of the resonant circuit is coupled to the first RF offset frequency and the second RF offset frequency, and the other end of the resonant circuit is coupled to the plasma processing chamber An electrode, and the RF matching network is switched between a first frequency impedance state and a second frequency impedance state by adjusting a capacitance of the variable capacitor, wherein the resonant circuit pair is in the first frequency impedance state The second RF bias frequency is in a high impedance state, the first RF bias frequency is in a low impedance state, such that the first RF offset frequency passes through the resonant circuit; A second frequency-impedance state, the resonant circuit of the first RF bias frequency is in a high impedance state, the second RF bias frequency is in a low impedance state, so that the second RF bias frequency by the resonant circuit. The radio frequency matching network of claim 1, wherein the two radio frequency offset frequencies are provided by a single radio frequency generator. The radio frequency matching network of claim 1, wherein the two radio frequency offset frequencies are respectively provided by two radio frequency generators. The radio frequency matching network of claim 1, wherein a capacitor and an inductor are respectively connected to the two ends of the parallel resonant circuit, and the variable Capacitively coupled between ground and the RF bias frequency. The radio frequency matching network according to claim 4, further comprising a fixed capacitor coupled between the ground and the radio frequency offset frequency. A plasma processing chamber operating at two switchable RF offsets, comprising: a reaction chamber for generating a plasma in an interior into which it is evacuated; and a lower electrode for coupling RF energy to The plasma; a first RF frequency generator optionally generating a first RF offset frequency having a first offset frequency of less than 10 MHz or having a higher than the first bias frequency but less than 15 MHz a second RF offset frequency of the second bias frequency; a first matching network for switchingly applying the two RF bias frequencies to the electrodes of the plasma processing chamber, the first matching network The circuit includes a resonant circuit (220) and a variable capacitor (205), the resonant circuit including a parallel resonant circuit connected in parallel by a capacitor and an inductor, the resonant circuit adjusting the capacitance of the variable capacitor Switching between a first frequency impedance state and a second frequency impedance state; a second RF frequency generator that produces a RF source frequency above 15 MHz; and a second matching network, An input coupled to the second RF frequency generator and an output coupled to the lower electrode; wherein, in the first frequency impedance state, the resonant circuit is in a high impedance state for the second RF bias frequency, The first RF offset frequency is low An impedance state; in the second frequency impedance state, the resonant circuit is in a high impedance state for the first RF bias frequency and a low impedance state for the second RF bias frequency. The plasma processing chamber of claim 6, further comprising a second parallel variable capacitor coupled between the ground and the second RF frequency generator. The plasma processing chamber of claim 6, wherein the first bias frequency is about 2 MHz, the second bias frequency is about 13 MHz, and the frequency of the RF source frequency is 27 MHz, 60 MHz, and 100 MHz. One. The plasma processing chamber of claim 6, further comprising a parallel resonant circuit coupled between the output of the second matching network and the lower electrode, the parallel resonant circuit being tuned to have its center The frequency is around 13 MHz and its bandwidth is 2 MHz.