TWI658488B - Plasma processing device - Google Patents

Abstract

The invention provides a plasma processing device. The plasma processing device includes a reaction chamber and upper and lower electrodes in the reaction chamber. A radio frequency power supply is connected through a radio frequency cable and outputs fundamental wave radio frequency power to the lower electrode, so that a generation occurs between the upper and lower electrodes. An electric field is capacitively coupled and a plasma is generated. An electrostatic chuck is arranged above the lower electrode. The electrostatic chuck is used to fix the substrate to be processed. The substrate is processed with the plasma. The bottom of the reaction chamber includes an electrically grounded shield The shield plate surrounds the radio frequency cable, and a ring of dielectric material is disposed between the radio frequency cable and the shield plate.

Description

Plasma processing device

The present invention relates to the technical field of semiconductor processing, and in particular to a plasma processing device, which has a dielectric ring under a plasma reaction chamber to reduce interference of harmonic RF power.

Plasma processing devices are widely used in semiconductor wafer processing processes. As shown in Figure 1, a typical plasma processing device structure is shown. The plasma processing device includes a reaction chamber 30 which can be evacuated. The reaction chamber includes a top cover and a side wall 30a and a bottom wall 30b, and further includes a shield plate 30c extending downward from the bottom wall. The entire reaction chamber is made of metal and grounded. Realize shielding of radio frequency electromagnetic field. The bottom of the reaction chamber includes a pedestal for supporting the wafer to be processed. The pedestal includes a lower electrode 10, and an electrostatic chuck is further disposed above the lower electrode 10, and the wafer to be processed is fixed by the electrostatic chuck. The upper part of the reaction chamber opposite to the pedestal includes an upper electrode 20, and a reaction gas inlet device is further integrated in the upper electrode 20 for uniformly inputting the reaction gas to the wafer below. At least one radio frequency power source is connected to the lower electrode 10 through a matcher and a radio frequency cable. In general, in order to ignite and maintain the plasma concentration, the RF power source 52 is required to input high frequency (greater than 13 MHz) RF power to the lower electrode 10. In order to control the ion energy incident on the upper surface of the substrate, the RF power source 54 is required to input low frequency RF (less than or equal to 2Mhz) Power to the lower electrode 10. Therefore, two types of high-frequency and low-frequency RF power pass through the RF cable at the same time, and finally flow into the lower electrode 10. For the capacitively coupled plasma processing device (CCP) as shown in Figure 1, there is an equivalent capacitor C1 between the upper electrode 20 and the lower electrode 10, and the RF cable itself has a parasitic inductance L0. There is also capacitive coupling between the shield plates 30c, so there is also an equivalent capacitance C2. These capacitance and inductance parameters together determine the output from the matcher. The electric field distribution from the outlet to each electrode of the reaction chamber and each side wall of the reaction chamber, and the frequency characteristics of the entire reaction chamber.

In the conventional technology, the radio frequency output by the radio frequency power supply 52 is generally 30 MHz or 60 Mhz. The following uses 60 MHz as an example to explain the problems of the conventional technology. When 60MHz high-power RF power is sent to the lower electrode in the reaction chamber, because the impedance between the upper and lower electrodes is plasma, the impedance of the plasma will change abruptly with factors such as pressure, plasma concentration, and distribution. Non-linear impedance, so the 60MHz RF power loaded between the upper and lower electrodes will generate a lot of harmonics, of which the second harmonic is the largest harmonic component at 120MHz, and its power accounts for 10-30% of the total RF power in the reaction chamber , The interference on the plasma treatment effect in the reaction chamber is also the largest. The conventional technology cannot effectively remove the interference of these harmonics, so it is difficult to obtain a uniform plasma treatment effect.

Therefore, the industry needs to develop a new device that can realize the smooth flow of the fundamental frequency (2MHz, 60MHz) between the upper and lower electrodes of the plasma processing space, and at the same time, the generated second harmonic should be separated and flowed into the ground.

The invention discloses a plasma processing device. The plasma processing device includes a reaction chamber. The reaction chamber is an air-tight chamber surrounded by side walls and a bottom wall. The reaction chamber includes an upper electrode and a lower electrode. A radio frequency cable is connected and outputs fundamental wave radio frequency power to the lower electrode, so that a capacitive coupling electric field is generated between the upper and lower electrodes and a plasma is generated. An electrostatic chuck is arranged above the lower electrode. The electrostatic chuck is used to fix the substrate to be processed. The plasma treatment of the substrate is characterized in that an electric grounding shielding plate is included below the bottom wall of the reaction chamber, the shielding plate surrounds the radio frequency cable, and a dielectric material ring is arranged between the radio frequency cable and the shielding plate. Changing the RF cable to the shield by setting a dielectric ring The capacitance of the capacitor causes the fundamental RF power output by the RF power source to flow into the reaction cavity, and at the same time, the harmonic RF power generated in the reaction cavity passes through the dielectric material ring and enters the grounded shielding plate.

The dielectric material ring can be moved up and down to adjust the capacitance between the RF cable and the shielding plate. The shielding plate includes a lower end surface, and the upper end of the dielectric material ring is higher than the lower end surface of the shielding plate. The dielectric material ring may include a cavity, and the cavity is filled with a dielectric liquid with an adjustable liquid level. The capacitance value between the RF cable and the shielding plate is adjusted by adjusting the liquid level height.

The relative dielectric constant of the dielectric material of the dielectric material ring is greater than 1.1, and the dielectric constant of the best dielectric material is greater than 1.5. The larger the dielectric constant, the larger the capacitance value and the larger the adjustment range. The dielectric material ring can be made of Teflon or ceramic material.

Further, the dielectric material ring includes a first sub-dielectric material ring and a second sub-dielectric material ring, and the first sub-dielectric material ring can move up and down relative to the second sub-dielectric material ring. Or the dielectric material rings have different thicknesses at different azimuth angles, so that the RF cables have different equivalent capacitances to different azimuth angles, which can further compensate for non-uniformity of RF electric field distribution at the azimuth angles.

10‧‧‧ lower electrode

20‧‧‧up electrode

30a‧‧‧ sidewall

30b‧‧‧ bottom wall

30c‧‧‧Shield

40, 40 ’, 40”, 40a ’, 40b’ ‧‧‧ dielectric rings

FIG. 1 is a schematic diagram of a conventional plasma processing apparatus.

Fig. 2 is a schematic diagram of a plasma processing apparatus of the present invention.

Figure 3 is a schematic diagram of the direction of RF power flow at different frequencies in the plasma processing apparatus of the present invention.

Fig. 4 is a comparison of impedance frequency characteristics between the plasma processing apparatus of the present invention and the conventional technique.

Fig. 5 is a comparison of the etching rates of the plasma processing apparatus of the present invention and the conventional technique at different locations.

Figures 6a and 6b are enlarged views of the second embodiment of the plasma processing apparatus of the present invention within the dotted frame X shown in Figure 2.

Figure 7 is a top view of another embodiment of the dielectric ring of the present invention.

The embodiment of the present invention will be further described below with reference to FIG. 2.

The invention discloses a plasma processing device with adjustable frequency characteristics. The basic hardware structure in the plasma processing device is the same as the conventional technology shown in FIG. 1, and both include a plasma reaction chamber. During the etching, a reaction gas is provided to the plasma reaction chamber. Corresponding upper and lower electrodes 20 and 10 are provided in the plasma reaction chamber for exciting the reaction gas to generate a plasma, so that the inside of the plasma reaction chamber is filled during the manufacturing process. There is plasma. The main difference is that in the present invention, a dielectric ring 40 is disposed in the space surrounding the RF cable within the shielding plate 30c below the bottom wall 30b. Conventional technology does not have this ring, so the RF cable is surrounded by the atmospheric environment, and the dielectric constant of the atmosphere is close to the vacuum environment, that is, the relative dielectric constant is very close to 1. Therefore, the equivalent capacitance C2 between the radio frequency cable and the shielding plate 30c is a constant, so the entire reaction cavity also has a constant frequency characteristic. Due to the existence of a large number of RF harmonics, the frequency characteristics of the conventional reaction cavity designed to ensure the effective conduction of the fundamental frequency cannot take into account these harmonic powers. Due to the interference of these harmonic powers in the reaction chamber, there is a large non-uniformity in the plasma distribution on the substrate. The dielectric ring 40 in the present invention may be made of a material having a relative dielectric constant greater than 1, such as Teflon, alumina, aluminum nitride, etc., so that the equivalent capacitance can be significantly increased in the space surrounding the RF cable. The value of C2. The dielectric ring 40 may be a cylinder with a through hole in the center, and the central through hole allows the radio frequency cable to pass through the through hole. The dielectric ring 40 can be moved up and down by mechanically driving the component. The dielectric ring 40 has an upper end face a and a lower end face c, and only the dielectric ring above the lower end face (line b in FIG. 2) of the shield plate 30c. Part of the effect on the equivalent capacitance C2, the following part has no effect. Therefore, by driving the dielectric ring 40 to move up and down, the equivalent capacitance C2 can be gradually increased from a minimum initial value to a maximum. The radio frequency cable surrounded by the dielectric ring 40 has a second inductance L2, and the portion on the top not surrounded by the dielectric ring has a first inductance L1. Therefore, the final equivalent circuit of the present invention is as shown in FIG. 3 and includes L2, L1, C1, and variable capacitor C2. Since the C2 capacitance can be adjusted, the equivalent circuit shown in Figure 3 can be adjusted. Frequency characteristics. According to the needs, the fundamental frequencies such as 2MHz and 60MHz can flow smoothly to C1 and return to the ground, and the high-frequency harmonic power is directly guided from C2 to the ground to avoid interference of harmonics on the electric field distribution.

Figure 4 shows the frequency vs. impedance curve, where the frequency characteristic curve 91 is the characteristic curve of the equivalent capacitor C2 when it has an initial value, that is, the dielectric ring 40 is not added in the conventional technology, and the frequency characteristic curve 93 is the capacitor Frequency characteristic curve when C2 has a large value. From Figure 3, it can be seen that for 2MHz and 60MHz radio frequency signals, the impedance of the two before and after the change of C2 is exactly the same. At the same time, the original impedance of the 120MHz harmonic signal is as high as 758.8 ohms. After the capacitance C2 is increased, the impedance becomes 206.6 ohms. . This is only an exemplary increase of C2. In fact, the value of the equivalent capacitance C2 can be further improved by selecting a higher dielectric constant and filling more dielectric materials, that is, the impedance for 120MHz can be further reduced to 100. Below ohm. Therefore, the harmonics generated in the reaction chamber can be smoothly conducted to reduce the interference to the normal fundamental wave, and the plasma processing device can also obtain a uniform plasma distribution. As shown in Fig. 5, the etch rate curve at different positions in the plasma processing device using the dielectric ring of the present invention, where curve 101 is the etch rate curve when C2 is the initial value, and curve 103 is the dielectric ring rising into the shielding plate Curves in interior space. It can be clearly seen that, compared with 101, curve 103 not only significantly improves the uniformity of etching, the fluctuation rate of the etching rate in different regions is smaller, but the overall etching rate is also improved.

In addition to the dielectric ring 40 of the present invention, it may be a single cylindrical body ascending and descending as shown in FIG. 2, or two or more cylindrical bodies located in the inner space of the shielding plate 30 c. As shown in Figs. 6a and 6b, the second embodiment is an enlarged view of the dotted line frame X shown in Fig. 2. It can be seen that the dielectric ring 40 includes two dielectric rings 40a ', 40b' stacked on top of each other. Figure 6a is a state where the two dielectric rings 40a ', 40b' are closely attached together, and Figure 6b is a state where the two dielectric rings are separated from each other. The two dielectric rings 40a 'and 40b' generate different equivalent circuits and different equivalent inductance and capacitance spatial distributions at different positions. For example, the RF cable above the dielectric ring 40a 'in Fig. 6b has an inductance L1, and the dielectric The RF cable part between the loops 40a ', 40b' has inductance L3, the inductance under the dielectric ring 40b 'is L2. In this way, the equivalent capacitance of the RF cable to the shield plate 30c as a whole will change, so the equivalent capacitance can also be adjusted.

The present invention can also adjust the equivalent capacitance between the RF cable and the shield plate 30c through other embodiments. For example, the dielectric ring 40 is a hollow housing made of a dielectric material, and the dielectric coefficient can be filled in the housing. For liquids greater than 1, the amount of dielectric material from the RF cable to the shielding plate can be adjusted by controlling the level of the liquid level, thereby changing the equivalent capacitance C2.

The dielectric ring in the present invention may be cylindrical or asymmetrical. In addition, as shown in FIG. 7, the top view of the dielectric ring 40 "is notched on one side, so that the overall equivalent capacitance C2 will be smaller than the cylindrical dielectric ring, and the path of RF power flow is not uniform. More harmonic RF power will flow through the thicker part of the dielectric ring 40 "in the figure, and less harmonic RF power. It will flow through the thinner part of the dielectric ring, which is the right side in the figure. Therefore, this structure can supplement the unevenness of the electric field distribution in different positions in the upper plasma reaction chamber to a certain extent, and finally obtain a uniform treatment effect. In the multiple embodiments described in detail above, a ring of dielectric material needs to be provided between the RF cable and the grounded shield plate 30c, so that the equivalent capacitance C2 is sufficiently large, so that the RF power at the fundamental frequency can enter the reaction cavity. Most of the harmonic RF power (greater than 50%) generated in the reaction chamber can flow through the path of the RF cable-dielectric ring-shield plate quickly. The volume, position, and dielectric material selection between the RF cable and the shielding plate occupied by the dielectric ring can be selected according to the specific parameters of the actual reaction cavity, as long as it has a high relative dielectric constant (greater than 1.1, the best dielectric ring greater than 1.5), and the thickness of the dielectric ring material layer is greater than or equal to 30% of the distance from the RF cable to the shield plate, can form a sufficient dielectric layer, so that the equivalent capacitance C2 is sufficient It plays the role of diversion harmonic power.

Although the content of the present invention has been described in detail through the above-mentioned preferred embodiments, it should be recognized that the above description should not be considered as limiting the present invention. Read by those with ordinary knowledge in the field After reading the foregoing, various modifications and alternatives to the present invention will be apparent. Therefore, the protection scope of the present invention should be defined by the scope of the attached patent application.

Claims (9)

A plasma processing device includes a reaction chamber. The reaction chamber is an air-tight chamber surrounded by a top cover, a side wall and a bottom wall. The reaction chamber includes an upper electrode and a lower electrode, and an RF power source passes through A radio frequency cable connects and outputs fundamental wave radio frequency power to the lower electrode, so that a capacitive coupling electric field is generated between the upper electrode and the lower electrode and a plasma is generated. An electrostatic chuck is disposed above the lower electrode, and the electrostatic chuck It is used to fix the substrate to be processed, and the plasma is used to process the substrate. It is characterized in that the bottom of the reaction chamber includes an electrically grounded shielding plate, the shielding plate surrounds the radio frequency cable, and a dielectric material ring is arranged. Between the radio frequency cable and the shield plate, the dielectric material ring includes a first sub-dielectric material ring and a second sub-dielectric material ring, and the first sub-dielectric material ring is opposite to the second sub-dielectric material ring. Moving up and down. The plasma processing apparatus according to item 1 of the scope of patent application, wherein the ring of dielectric material moves up and down. The plasma processing apparatus according to item 2 of the scope of patent application, wherein the shielding plate includes a lower end surface, and an upper end of the dielectric material ring is higher than a lower end surface of the shielding plate. The plasma processing device according to item 1 of the scope of patent application, wherein the dielectric material ring includes a cavity, and the cavity is filled with a dielectric liquid with an adjustable liquid level. The plasma processing device according to item 1 of the scope of the patent application, wherein the relative permittivity of the dielectric material of the dielectric material ring is greater than 1.1. The plasma processing apparatus according to item 5 of the scope of patent application, wherein the dielectric constant of the dielectric material of the dielectric material ring is greater than 1.5. The plasma processing device according to item 6 of the patent application scope, wherein the dielectric material ring is made of Teflon or ceramic material. The plasma processing device according to item 1 of the scope of patent application, wherein the dielectric material rings have different thicknesses at different azimuth angles, so that the RF cable has different equivalent capacitances to different azimuth angles. The plasma processing device according to item 1 of the patent application scope, wherein the dielectric material ring allows the fundamental RF power output by the RF power source to flow into the reaction chamber, and the harmonic RF power generated in the reaction chamber passes through the dielectric material The ring enters the grounded shield.