CN108257840B

CN108257840B - Plasma processing device

Info

Publication number: CN108257840B
Application number: CN201611246787.5A
Authority: CN
Inventors: 梁洁; 涂乐义; 叶如彬
Original assignee: Advanced Micro Fabrication Equipment Inc Shanghai
Current assignee: Advanced Micro Fabrication Equipment Inc Shanghai
Priority date: 2016-12-29
Filing date: 2016-12-29
Publication date: 2021-03-30
Anticipated expiration: 2036-12-29
Also published as: TW201841197A; CN108257840A; TWI658488B

Abstract

The invention provides a plasma processing device, which comprises a reaction cavity, an upper electrode and a lower electrode in the reaction cavity, wherein a radio frequency power supply is connected with the lower electrode through a radio frequency cable 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 plasma is generated. The lower part of the bottom wall of the reaction cavity comprises 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 shielding plate.

Description

Plasma processing device

Technical Field

The invention relates to the technical field of semiconductor processing, in particular to a plasma processing device, which is provided with a dielectric ring below a plasma reaction cavity to reduce the interference of harmonic radio frequency power.

Background

A plasma processing apparatus is widely used in a semiconductor wafer processing flow, and a typical configuration of the plasma processing apparatus is shown in fig. 1. The plasma processing device comprises a reaction chamber 30 which can be vacuumized, wherein the reaction chamber comprises a top cover, a side wall 30a, a bottom wall 30b and a shielding plate 30c extending downwards from the bottom wall, and the whole reaction chamber is made of metal and is grounded to shield a radio frequency electromagnetic field. The bottom of the reaction chamber includes a susceptor for supporting a wafer to be processed, and the susceptor includes a lower electrode 10 therein. The lower electrode 10 also includes an electrostatic chuck thereon, by which a wafer to be processed is held. The upper part of the reaction chamber opposite to the base comprises an upper electrode 20, and a reaction gas inlet device is also integrated in the upper electrode 20 and used for uniformly inputting reaction gas to a wafer below. At least one rf power source is connected to the lower electrode 10 through a matcher and an rf cable. Generally, the rf power source 52 is required to input rf power of high frequency (greater than 13MHz) to the lower electrode 10 in order to ignite and maintain plasma concentration, and rf power of low frequency (less than or equal to 2MHz) is required to input to the lower electrode 10 through the rf power source 54 in order to control the ion energy incident to the upper surface of the substrate. So that both high frequency and low frequency rf power can pass through the rf cable and ultimately flow into the lower electrode 10. For the capacitively coupled plasma processing apparatus (CCP) shown in fig. 1, an equivalent capacitance C1 exists between the upper electrode 20 and the lower electrode 10, and the rf cable itself has a parasitic inductance L0, and there is also capacitive coupling between the rf cable and the shielding plate 30C, so there is also an equivalent capacitance C2. The parameters of the capacitor and the inductor jointly determine the electric field distribution from the output end of the matcher to each electrode of the reaction cavity and each side wall of the reaction cavity and the frequency characteristic of the whole reaction cavity.

The rf frequency output by the rf power source 52 in the prior art is typically 30MHz or 60MHz, and the 60MHz is taken as an example to illustrate the problems in the prior art. When 60MHz high power radio frequency power is sent to the lower electrode in the reaction cavity, because the impedance between the upper electrode and the lower electrode is plasma, the impedance of the plasma can be instantly changed along with factors such as air pressure, plasma concentration and distribution change, and the like, and belongs to nonlinear impedance, the 60MHz radio frequency power loaded between the upper electrode and the lower electrode can generate a large amount of harmonic waves, wherein the second harmonic wave, namely 120MHz harmonic wave component, is the largest, the power of the second harmonic wave accounts for 10-30% of the total power of the radio frequency in the reaction cavity, and the interference on the plasma treatment effect in the reaction cavity is the largest. The prior art cannot effectively remove the interference of the harmonics, so that the uniform plasma processing effect is difficult to obtain.

Therefore, there is a need to develop a new device that can not only realize smooth flow of fundamental frequency (2MHz, 60MHz) to the plasma processing space between the upper and lower electrodes, but also separate the generated second harmonic and flow it to the ground.

Disclosure of Invention

The invention discloses a plasma processing device, which comprises a reaction cavity, wherein the reaction cavity is an airtight cavity formed by surrounding a side wall and a bottom wall, the reaction cavity comprises an upper electrode and a lower electrode, a radio frequency power supply is connected with the lower electrode through a radio frequency cable 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 plasma is generated, an electrostatic chuck is arranged above the lower electrode and used for fixing a substrate to be processed and processing the substrate by using the plasma, and the plasma processing device is characterized in that the lower part of the bottom wall of the reaction cavity comprises 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 shielding plate. The capacitance value between the radio frequency cable and the shielding plate is changed by arranging the dielectric ring, so that fundamental radio frequency power output by the radio frequency power supply flows into the reaction cavity, and meanwhile, harmonic radio frequency power generated in the reaction cavity penetrates through the dielectric ring to enter the grounded shielding plate.

Wherein the ring of dielectric material is movable up and down to adjust the capacitance between the radio frequency cable and the shield plate. The shield plate includes a lower end surface, and an upper end of the dielectric material ring is higher than the lower end surface of the shield plate. The dielectric material ring can comprise a cavity, the cavity is filled with dielectric liquid with adjustable liquid level height, and the capacitance value between the radio frequency cable and the shielding plate is adjusted by adjusting the liquid level height.

The relative dielectric constant of the dielectric material ring is larger than 1.1, the dielectric constant of the optimal dielectric material is larger than 1.5, the larger the dielectric constant is, the larger the capacitance value can be greatly changed, and the adjusting amplitude is larger. The dielectric material ring may optionally be made of teflon or a ceramic material.

Further, the dielectric material ring comprises 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 radio frequency cable has different equivalent capacitances at different azimuth angles, thereby further compensating the radio frequency electric field distribution nonuniformity at the azimuth angles.

Drawings

FIG. 1 is a schematic view of a prior art plasma processing apparatus;

FIG. 2 is a schematic view of a plasma processing apparatus according to the present invention;

FIG. 3 is a schematic diagram of the flow direction of RF power with different frequencies in the plasma processing apparatus according to the present invention;

FIG. 4 is a comparison of the impedance frequency characteristics of the plasma processing apparatus of the present invention with those of the prior art;

FIG. 5 is a comparison of etch rates at different locations for the plasma processing apparatus of the present invention and the prior art;

FIGS. 6a and 6b illustrate a second embodiment of the plasma processing apparatus according to the present invention;

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

Detailed Description

The following describes the present invention 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 prior art shown in figure 1, and the plasma processing device comprises a plasma reaction cavity, reaction gas is provided for the plasma reaction cavity when plasma etching is carried out, and a corresponding upper electrode 20 and a corresponding lower electrode 10 are arranged in the plasma reaction cavity and are used for exciting the reaction gas to generate plasma, so that the plasma (plasma) is filled in the plasma reaction cavity in the process. The main difference is that the present invention provides a ring 40 of dielectric material within the lower shield 30c of the bottom wall 30b and in the space surrounding the radio frequency cable. The prior art does not have the ring, so that the periphery of the radio frequency cable is an atmospheric environment, and the dielectric constant of the atmospheric environment is close to that of a vacuum environment, namely the relative dielectric constant is very close to 1. The equivalent capacitance C2 from the rf cable to the shield 30C is constant and thus the entire reaction chamber has a constant frequency characteristic. Due to the existence of a large number of radio frequency harmonics, the frequency characteristics of the existing reaction cavity designed for ensuring effective conduction of fundamental frequency cannot be considered for leading away the harmonic power. There is a large non-uniformity in the plasma distribution over the substrate due to the interference of these harmonic powers within the reaction chamber. The dielectric ring 40 of 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 placement in the space surrounding the rf cable can significantly increase the value of the equivalent capacitance C2. The dielectric ring 40 may be a cylindrical body with a central through hole that allows the rf cable to pass through the through hole. The dielectric ring 40 can be moved up and down by means of a mechanical drive, wherein the dielectric ring 40 has an upper end face a and a lower end face C, wherein only the part of the dielectric ring above the lower end face (line b in fig. 2) of the shielding plate 30C has an influence on the equivalent capacitance C2, the lower part having no influence. The equivalent capacitance C2 can be gradually increased from the minimum initial value to the maximum by driving the dielectric ring 40 up and down. The rf cable surrounded by the dielectric ring 40 has a second inductance L2, and the portion not surrounded by the dielectric ring has a first inductance L1. The final equivalent circuit of the present invention is shown in fig. 3, and includes L2, L1, C1 and variable capacitor C2. Since the capacitance value of C2 can be adjusted, the frequency characteristic of the equivalent circuit shown in fig. 3 can be adjusted. According to the requirement, the fundamental frequency of 2MHz, 60MHz and the like can smoothly flow to the C1 and return to the ground terminal, and the harmonic power of high frequency is directly led to the ground terminal from the C2, so that the interference of the harmonic to the electric field distribution is avoided.

Fig. 3 shows the frequency versus impedance curve, wherein the frequency characteristic curve 91 is the characteristic curve of the equivalent capacitor C2 when the equivalent capacitor C2 has an initial value, i.e. the prior art capacitor C2 has no added dielectric ring 40, and the frequency characteristic curve 93 is the frequency characteristic curve of the capacitor C2 with a larger value. It can be seen from fig. 3 that the impedances of the C2 before and after the change are identical for the radio frequency signals of 2MHz and 60MHz, while the original impedance is as high as 758.8 ohms for the harmonic signal of 120MHz, and the impedance becomes 206.6 ohms after the capacitor C2 is increased. This is also only an exemplary increase in C2, and actually the value of equivalent capacitance C2 can be further increased by selecting a material with a higher dielectric constant, filling more dielectric material, etc., i.e., the impedance for 120MHz can be further reduced to below 100 ohms. Therefore, the harmonic wave generated in the reaction cavity can be smoothly guided away to reduce the interference to the normal fundamental wave, and the plasma processing device can obtain uniform plasma distribution. FIG. 5 is a graph showing the etching rate at different positions in a plasma processing apparatus using the dielectric ring of the present invention, in which the graph 101 is the etching rate at the initial value of C2, and the graph 103 is the etching rate at the time when the dielectric ring rises into the inner space of the shield plate. It is obvious from the above that, compared with 101, the curve 103 not only has significantly improved etching uniformity, small fluctuation range of etching rate in different regions, but also has improved overall etching rate.

The dielectric ring 40 of the present invention may be one cylinder that is raised and lowered as shown in fig. 2, or two or more cylinders may be located in the inner space of the shielding plate 30 c. Referring to fig. 6a and 6b, which are enlarged views of the second embodiment within the dashed box X shown in fig. 2, it can be seen that the dielectric ring 40 comprises two rings 40a 'and 40 b' stacked on top of each other, wherein fig. 6a shows the two dielectric rings 40a 'and 40 b' in a state of being closely attached to each other, and fig. 6b shows the two dielectric rings in a state of being separated from each other. The two dielectric rings 40a 'and 40 b' correspondingly produce different equivalent circuits and different equivalent inductance and capacitance spatial distributions at different positions, for example, the rf cable above 40a 'has an inductance L1 in fig. 6b, the rf cable portion between the dielectric rings 40 a' and 40b 'has an inductance L3, and the inductance below the dielectric ring 40 b' is L2. Thus, the equivalent capacitance of the radio frequency cable to the whole shielding plate 30c is changed, so that the adjustment of the equivalent capacitance can be realized.

The invention can also realize the adjustment of the equivalent capacitance between the radio frequency cable and the shielding plate 30C through other embodiments, for example, the dielectric ring 40 is a hollow shell made of dielectric material, the shell can be filled with liquid with dielectric coefficient larger than 1, the dielectric substance from the radio frequency cable to the shielding plate can be adjusted by controlling the height of the liquid level, thereby changing the equivalent capacitance C2.

In addition to the dielectric ring of the present invention being cylindrical or asymmetrical, 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 is smaller than that of a cylindrical dielectric ring, and the path through which the rf power flows is not uniform, more harmonic rf power flows through the thicker portion of the dielectric ring 40" in the figure, and less harmonic rf power flows through the thinner portion of the dielectric ring, i.e., the right side in the figure. Therefore, the structure can supplement the non-uniformity of the electric field distribution in different directions in the upper plasma reaction cavity to a certain extent, and finally obtain uniform treatment effect. The embodiments described in detail above all require a ring of dielectric material to be placed between the rf cable and the grounded shield 30C, so that the equivalent capacitance C2 is large enough to eventually allow rf power at the fundamental frequency to enter the reaction chamber, and most (greater than 50%) of the harmonic rf power generated in the reaction chamber can quickly flow away through the path of the rf cable-dielectric ring-shield. The volume, position and height between the radio frequency cable and the shielding plate occupied by the dielectric ring and the selection of the dielectric material can be selected according to the specific parameters of the actual reaction cavity, as long as the dielectric ring with higher relative dielectric constant (greater than 1.1, and optimally greater than 1.5) is arranged, and the thickness of the dielectric ring material layer is greater than or equal to 30% of the distance between the radio frequency cable and the shielding plate, enough dielectric layers can be formed, so that the equivalent capacitor C2 can sufficiently play a role in guiding harmonic power.

While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.

Claims

1. A plasma processing device comprises a reaction cavity, the reaction cavity is an airtight cavity surrounded by a top cover, a side wall and a bottom wall, the reaction cavity comprises an upper electrode and a lower electrode, a radio frequency power supply is connected with a radio frequency cable through a matcher and outputs fundamental wave radio frequency power to the lower electrode, a capacitive coupling electric field is generated between the upper electrode and the lower electrode, plasma is generated, an electrostatic chuck is arranged above the lower electrode and used for fixing a substrate to be processed, and the substrate is processed by the plasma,

its characterized in that, reaction chamber diapire below includes the shield panel of an electricity ground connection, the shield panel surrounds radio frequency cable, and a dielectric material ring sets up between radio frequency cable and the shield panel, annular space has between dielectric material ring and the shield panel, the dielectric material ring can reciprocate, makes relative area between dielectric material ring and the shield panel is adjustable, the shield panel includes a terminal surface, the upper end of dielectric material ring is higher than the lower terminal surface of shield panel, just the lower extreme of dielectric material ring is less than the lower terminal surface of shield panel, the shield panel with have the clearance between the matcher, make the dielectric material ring can reciprocate.

2. The plasma processing apparatus of claim 1, wherein the ring of dielectric material comprises a cavity filled with a dielectric fluid having an adjustable fluid level.

3. The plasma processing apparatus of claim 1 wherein the relative permittivity of the dielectric material of the ring of dielectric material is greater than 1.1.

4. The plasma processing apparatus of claim 3, wherein the dielectric material of the ring of dielectric material has a dielectric constant greater than 1.5.

5. The plasma processing apparatus of claim 4, wherein the ring of dielectric material is made of Teflon or a ceramic material.

6. The plasma processing apparatus of claim 1 wherein the ring of dielectric material comprises a first ring of sub-dielectric material and a second ring of sub-dielectric material, the first ring of sub-dielectric material being movable up and down relative to the second ring of sub-dielectric material.

7. The plasma processing apparatus of claim 1 wherein the ring of dielectric material has different thicknesses at different azimuthal angles such that the rf cable has different equivalent capacitances to different azimuthal angles.

8. The plasma processing apparatus of claim 1 wherein the ring of dielectric material is such that fundamental rf power from the rf power supply flows into the reaction chamber while harmonic rf power generated in the reaction chamber passes through the ring of dielectric material into the grounded shield.