TWI629919B - Inductively coupled plasma processing device and control method thereof - Google Patents

Abstract

The invention provides an inductively coupled plasma processing device. The inductive coil of the inductively coupled plasma processing device includes a plurality of sub-coils, each of which covers a different area of an insulating material window below; a radio frequency power supply is connected to a plurality of sub-coils through a matching circuit. At the input end, each sub-coil includes the output end electrically connected to the ground. A controller controls the power of the input multiple sub-coils. It is characterized in that the controller controls the multiple sub-coils of the inductor coil to execute multiple processing stages in turn. The input power of at least one sub-coil is higher than the input power of the other sub-coils.

Description

Inductively coupled plasma processing device and control method thereof

The invention provides the technical field of semiconductor processing, and specifically provides a coil driving method suitable for an inductively coupled plasma processing apparatus.

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 100. The bottom of the reaction chamber includes a pedestal for supporting a wafer to be processed. The pedestal includes a lower electrode 122, and a cooling liquid pipe is opened in the lower electrode 122 for heat dissipation of the pedestal. An electrostatic chuck 121 is further included above the lower electrode 122, and the wafer 120 to be processed disposed on the electrostatic chuck is fixed by the electrostatic chuck 121. An edge ring 110 surrounds the electrostatic chuck 121. The top of the reaction chamber opposite the base includes an insulating material window 10. An inductive coil 20 is disposed above the insulating material window 10. The coil 20 is connected to a radio frequency power source through a matching device 30. The RF power is sent to the inductive coil 20 after the impedance is matched by the matcher 30. The electromagnetic field generated by the coil is fed into the reaction chamber below to form and maintain a sufficient concentration of plasma for plasma processing.

With the development of semiconductor technology, the requirements for uniformity and critical dimension (CD) in the wafer process are becoming more and more strict. The unevenness of plasma processing caused by various small factors has become a reality. Obstacles to Plasma Treatment Process Uniformity Requirements. These factors include non-uniform distribution of the RF power input and output ends of the inductor coil, and the geometry of the reaction cavity is not circularly symmetric, and any hardware that has an asymmetrical distribution. its The uniformity of the plasma distribution is the most important factor that affects the uniformity of the plasma treatment effect. Therefore, improving the uniformity of the plasma distribution is the first issue to obtain a better treatment effect.

The improvement of the uniformity of the plasma includes two aspects, one is the concentration difference between the center and the edge area, and the other is that the plasma distribution on a part of the azimuthal in the entire circular processing space is not uniform with other areas. In order to improve the uniformity of the plasma distribution in part of the azimuth angle in the inductively coupled plasma processing device, the conventional technology has proposed many solutions, such as US5975013 or US6288493 to divide the inductor coil into a plurality of independent uniformly distributed on the insulation window 10 Controllable sub-coils, each sub-coil corresponds to a certain azimuth area, and the plasma concentration generated by different coils is controlled by adjusting the power ratio supplied to different sub-coils. Although this method can also correct the plasma distribution non-uniformity in the azimuth to a certain extent, it also has defects: 1. The non-uniform area in the azimuth is very small, for example, when the memory is only non-uniform in the range of 10 degrees, The corresponding optimum needs to set a sub-coil every 10 degrees, so 36 sub-coils are necessary to correct the plasma concentration; 2. Only static correction can be made, and only the current power ratio of each sub-coil can be adjusted to the best after adjustment. Processing process, once the process parameters are changed, the original power output distribution must be adjusted again, so it is not possible to dynamically correct the unevenness of the plasma distribution; 3. There is a gap area between different sub-coils, and it is impossible to adjust the input to different sub-coils. RF power ratio to compensate.

Therefore, the industry needs to find a new coil structure or control method to achieve dynamic plasma concentration unevenness compensation, which can solve the above-mentioned shortcomings that conventional techniques cannot overcome.

The invention discloses an inductively coupled plasma processing device. The inductively coupled plasma processing device includes a reaction chamber. A lower part of the reaction chamber includes a base. For processing the substrate, the top of the reaction chamber includes an insulating material window, and an inductor coil is arranged above the insulating material window. The inductor coil includes a plurality of sub coils, each of which covers a different area of the lower insulating material window; a radio frequency power supply is connected through a matching circuit To the input end of the plurality of sub-coils, each of the sub-coils includes an output end electrically connected to the ground, and a controller controls the power input to the plurality of sub-coils, characterized in that the controller makes the distribution to the plurality of sub-coils The power varies between a plurality of processing stages. In each processing stage, the controller selects at least one sub-coil to form a first sub-coil set, and the other sub-coils in the inductance coil form a second sub-coil set. A power to the first sub-coil set, and a power input to the second sub-coil set at the same time is less than the first power, and the first sub-coil set is different in adjacent or different processing stages, and the complex number of loops Each processing stage makes each sub-coil have the same average input power.

The plurality of sub-coils are evenly distributed above the insulating material window, covering different azimuth areas on the insulating material window. The inductive coil may further include a plurality of sub-coils, each group of sub-coils covering a different window region of insulating material. The sub-coils of each group can be distributed corresponding to different azimuth angles, and can also be distributed internally and externally. By alternately controlling the input power of different groups of sub-coils, the plasma concentration distribution in the reaction chamber can be controlled with greater ability.

In the present invention, a variable capacitor is connected in series to each sub-coil, and the controller changes the power value input to each sub-coil by controlling the capacitance of the series capacitor. The variable capacitor is located between the output end of each sub-coil and the ground or between the output end of the matching circuit and the input end of the sub-coil.

The plurality of processing stages further include an input power of one sub-coil lower than that of other sub-coils, so that the plasma concentration difference produced by different sub-coils is greater, and the lateral diffusion of the plasma is further promoted.

The length of the multiple processing stages is greater than 0.1 seconds and less than 5 seconds to ensure that the plasma is sufficiently diffused between different plasma concentration regions, and to avoid the long-term plasma concentration difference from affecting the uniformity of the plasma processing process below.

10‧‧‧ Insulation window

20‧‧‧coil

30‧‧‧ Matcher

100‧‧‧ reaction chamber

110‧‧‧Edge ring

120‧‧‧ wafer

121‧‧‧ electrostatic chuck

122‧‧‧Lower electrode

201, 202, 203, 204‧‧‧ sub coils

201 ’, 202’, 203 ’, 204’ ‧‧‧ vortex sub-coils

B1, B2, B3, B4‧‧‧ output terminals

C1, C2, C3, C4‧‧‧ Variable Capacitors

T1, T2, T3, T4 ‧‧‧ processing stages

Figure 1 is a schematic diagram of the structure of an inductively coupled plasma processing device.

FIG. 2 is a schematic diagram of an inductor coil and a driving circuit according to the present invention.

FIG. 3 is a schematic diagram of a second embodiment of an inductor coil and a driving circuit according to the present invention.

Fig. 4 is a driving power change diagram of a plurality of sub-coils in the induction coil of the present invention.

FIG. 5 is a driving power change diagram of a plurality of sub-coils in another embodiment of the inductive coil of the present invention.

The specific embodiments of the present invention are further described below with reference to Figures 2 to 4 of the drawings.

The invention discloses an inductively coupled plasma processing device capable of dynamically adjusting the plasma concentration distribution. The plasma processing device includes a plasma reaction chamber 100. When plasma etching is performed, a reaction gas is provided to the plasma reaction chamber 100. A corresponding top inductor coil 20 and a lower electrode 122 are provided in the plasma reaction chamber 100, which are used to excite the reaction gas to generate a plasma and make the process During the process, the plasma reaction chamber 100 is filled with plasma.

A base for placing the wafer 120 is provided at the bottom of the plasma reaction chamber 100. An electrostatic chuck for absorbing the wafer 120 is provided in the base. A heater or a refrigerant may be provided in the electrostatic chuck or the base as required. Temperature control system for flow path.

As shown in Figure 2, the inductive coil 20 of the present invention includes four sub-coils 201-204. These sub-coils 201-204 are evenly distributed on the circumference. The RF electromagnetic field generated by each of the sub-coils 201-204 can affect the plasma below. Plasma concentration in different azimuth regions in the reaction chamber 100. The four sub-coils 201-204 are connected to the matcher 30 through the RF power input A, and the matcher 30 is connected to a RF power source. The output terminals B1-B4 of the four sub-coils 201-204 are connected to the ground through their respective variable capacitors C1-C4. By adjusting the respective variable capacitors C1-C4 of each of the above-mentioned sub-coils 201-204, adjustment of the magnitude of the current on each of the sub-coils 201-204 can be achieved. When the current flowing into the corresponding sub-coil such as 201 is large, the plasma concentration in the area below the corresponding sub-coil 201 will also be large.

In addition to the inductive coil 20 penetrating into the reaction chamber 100 through electric induction, there is also a capacitive coupling phenomenon. The electric field on the coil is coupled into the reaction chamber 100, and the capacitive coupling is not good for plasma processing, so it needs to be minimized as much as possible. . In order to minimize the capacitive coupling of the inductive coil 20, it is necessary to adjust the four variable capacitors C1-C4 to have the optimal initial value Cb. When the value of the variable capacitor C1-C4 is Cb, the borrow on the four sub-coils 201-204 The incident waveform from the input terminal A to the output terminal will be superimposed with the waveform reflected from the variable capacitors C1-C4 to form a standing wave. The voltage amplitude on this standing wave can make the input coil A of the sub-coils 201-204 have the highest voltage V. The output terminals B1-B4 have -V, and the voltage in the middle section of the sub-coils 201-204 is zero. Under such a voltage distribution condition, the downward capacitive coupling of the coil can be minimized, and the voltage distribution on the inductive coil reaches an equilibrium state.

The present invention includes a controller for controlling the variable capacitors to change the capacitance value based on the initial value Cb for a short time so that the current values on the four sub-coils 201-204 are changed in turn. For example, the driving power change diagram of a plurality of sub-coils 201-204 in the inductive coil of the present invention shown in FIG. 4. During the processing stage T1, the capacitance of the coil 201 decreases to Cb- △ C. At this time, the power of the sub-coil 201 will increase. The corresponding lower plasma density will also increase, while the capacitance of the other sub-coils 203-204 will not change, and the plasma concentration will also maintain the initial state. In the processing stage T2, the capacitance of the coil 201 is restored to Cb, and the sub-coil 202 becomes Cb- △ C. At this time, the power of the sub-coil 202 will increase, and the corresponding plasma density will also increase. The capacitances of the coils 203 and 204 remain the same, and the plasma concentration underneath also maintains the initial state. In the subsequent T3 and T4 phases, the power of the sub-coils 203 and 204 is also increased in sequence, while the power of the other coils is maintained at the initial state. In this way, after one cycle of T1-T4, the length of each processing stage is the same. The four areas in the reaction chamber 100 corresponding to the four sub-coils 201-204 generate high plasma concentrations in turn, and the other areas maintain the initial concentration. In this process, The middle and high plasma concentration areas will naturally diffuse to the adjacent areas on both sides of the lower plasma concentration, and the four areas will spread to the surroundings in a time-sharing manner to make the plasma concentration of the entire reaction area below reach equilibrium in long-term operation. In the present invention, the plasma concentration difference between different regions is generated in four regions by quickly adjusting the capacitance, and then the plasma concentration distribution balance is achieved by rotating in a time-sharing manner. Because the existence of the concentration difference promotes the flow in the horizontal direction of the plasma, the more the area with the large concentration difference, the greater the level of horizontal flow formed by the mutual diffusion of the plasma between adjacent areas. For the uneven plasma concentration distribution in the original azimuth, for example, the plasma concentration in one area is smaller than that in the adjacent area. The original concentration difference has an impact on the plasma uniformity, but it is not enough to form a large number of The plasma diffuses horizontally, so this concentration difference is difficult to eliminate. The invention produces a large concentration difference and high power by man-made The input power of the input sub-coil can reach 1.2 or 1.5 times of the input power of the surrounding sub-coils, thereby promoting the horizontal flow of the plasma between different regions, and finally achieving an average plasma concentration distribution.

In order to generate a higher concentration difference, the present invention also proposes another driving power variation method of a plurality of sub-coils 201-204 in the inductor coil. As shown in Figure 5, during the processing stage T1, the capacitance of the coil 201 is reduced to Cb- △ C. At this time, the power of the sub-coil 201 will increase, and the corresponding plasma density will also increase. The capacitance of the coils 202 and 204 does not change. The plasma concentration also maintains the initial state, while the capacitance on the opposite sub-coil 203 becomes Cb + ΔC, and the corresponding regional concentration of the sub-coil 203 will be lower than the initial state. During the processing phase T2, the capacitance C1 of the coil 201 is restored to Cb, and the sub-coil 202 becomes Cb- △ C. At this time, the power of the sub-coil 202 will increase, and the corresponding plasma density will also increase. The capacitance of each sub-coil 203 is not changed, the variable capacitance C4 of the sub-coil 204 is changed to Cb + ΔC, and the corresponding plasma concentration is also reduced. In the subsequent T3 and T4 phases, the power of the sub-coils 203 and 204 is also increased in sequence, while the power of the adjacent sub-coils is maintained at the initial state, and the power of the opposite sub-coil is reduced. In this way, in each processing stage, a greater concentration difference will be generated from the high-concentration area to the low-concentration area, and the corresponding plasma level diffusion effect will be more severe, thereby effectively eliminating the concentration that is too high or too low in some azimuth Area, forming a uniform concentration distribution. In the entire processing process, a plurality of processing stages including loops are included. The power ratio of each processing stage input to each sub-coil 201-204 is shown in Figure 4 or 5. For example, from processing stages T1 to T4, part of the sub-coils are taken turns. The input power is higher than other sub-coils. After going through the various processing stages, the power input to each of the sub-coils 201-204 has the same average value during processing. The average input power of each sub-coil 201-204 refers to the work of each stage of T1-T4. The sum of the rates is divided by the number of processing stages 4. As long as the average power input to each sub-coil 201-204 is the same, the average plasma concentration corresponding to each sub-coil 201-204 can be guaranteed to be the same throughout the processing process.

In the present invention, the input high-power sub-coil may also be a sub-coil set composed of two sub-coils. For example, it may be 201 and 202 in the T1 processing stage, 202 and 203 in the T2 processing stage, and then 203 and 204. The other sub-coils in the inductance coil form a second sub-coil set, and the power input to the second sub-coil set is lower than the power input to the first sub-coil set. The selection of the first sub-coil set can also be repeated in non-adjacent processing stages. For example, the entire processing process is divided into eight processing stages, T1-T8. Each processing stage selects the input high-power sub-coils in turn as: 201-202-201-203-202-204-203-204, such a power distribution method can also achieve the purpose of the present invention, because the average power on all four sub-coils 201-204 is still the same throughout the entire process, and There is sufficient input power difference between different sub-coils in each processing stage.

In the present invention, the time length of T1 / T2 / T3 / T4 can be set as required, but it cannot be selected too short. If the time is too short, the diffusion of plasma from high concentration to low concentration is not obvious, and it should not be too long if it is too long. The plasma unevenness phenomenon will accumulate in local areas and affect the uniformity of the process, depending on the duration of the current processing process. If the execution time of the current process is more than 30 seconds, the duration of T1 can be selected from 3 seconds to 5 seconds. If the execution time of the current process is only 10 seconds, the optimal maximum duration of T1 should not exceed 1 second to ensure the above. The loops of T1-T4 are executed at least one loop cycle, and it is better to perform more than two loop cycles. So the best time is between 0.1-5 seconds, and the best is 0.2-1 seconds.

As shown in Fig. 3, the second embodiment of the coil structure of the present invention is basically the same as the embodiment shown in Fig. 2 except that the coil structure extends from the inside to the outside of a plurality of vortex sub-coils 201'-204 '.

In addition to the coil structure of the four independent control regions shown in Figs. 2 and 3, the present invention may also have fewer regions such as two or three, or more regions such as six or eight regions, correspondingly. Ground, by controlling the value of the series capacitance of each of the sub-coils 201-204 around Cb, more levels of concentration difference can be obtained, and stronger plasma horizontal diffusion can be obtained in the same processing stage.

According to the principle of the present invention, the power input to each of the sub-coils 201-204 can also be controlled by variable capacitors C1-C4 connected between the input terminal A (or the output end of the matching circuit) and each of the sub-coils 201-204. Realize, at this time, the variable capacitance between the output terminals B1-B4 and ground can be maintained at Cb, and frequent changes are not required. The purpose of the present invention can be achieved by directly regulating the variable capacitance at the input terminal.

In the present invention, the lower the minimum power flowing through each sub-coil 201-204, the lower the plasma concentration of the corresponding area, and the easier it is to form a larger concentration difference with the high-concentration area next to it, but the minimum power is still greater than one Limits to ensure that the plasma in the corresponding area can be effectively electro-ignited and maintained, otherwise instability such as plasma extinguishment may occur. This limitation is related to the pressure required for the plasma processing process, the type of gas, and the specific structural parameters of the reaction chamber 100.

In addition to the inductive coil structure of the present invention, as shown in Figs. 2 and 3, they are composed of identical sub-coils 201-204, and may also be composed of different types of coils. For example, there may be two sets of inductive coils. Located on the periphery of the insulation window, the coil structure is shown in Figure 2 The four sub-coils 201-204 evenly surround the periphery. The second group of coils is located in the center area of the insulation window. The sub-coil structure extends outward from the center as shown in Figure 3. In this way, the inductive coil group formed by combining multiple sets of coils in different regions can also use the method of the present invention to alternately increase the plasma concentration in a local area to achieve the purpose of improving the uniformity of the plasma concentration.

Since the plurality of areas of the present invention dynamically adjust the input power of each sub-coil, a high-concentration area in a local area is generated to spread plasma to the surroundings, so it can be adapted to any plasma processing process and can also modify the plasma concentration on any azimuth. It is uneven, has wide adaptability, and has a simple structure, so it has obvious technical advantages over conventional technologies.

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. Various modifications and substitutions of the present invention will become apparent to those skilled in the art to which the present invention pertains after reading the foregoing. Therefore, the protection scope of the present invention should be defined by the scope of the attached patent application.

Claims (11)

An inductively coupled plasma processing device includes an inductive coupled plasma processing device including: a reaction chamber, a lower part of the reaction chamber includes a base, a substrate to be processed is disposed on the base, and a top of the reaction chamber includes an insulating material window, the An inductive coil is provided above the insulating material window, and the inductive coil includes a plurality of sub-coils, each of which covers a different area of the insulating material window below; at least one radio frequency power supply is connected to the input end of the plurality of sub-coils through a matching circuit, Each of the sub-coils further includes an output terminal electrically connected to the ground, and a controller controls the power input to the plurality of sub-coils, wherein the controller causes the power allocated to the plurality of sub-coils to be changed between a plurality of processing stages. In each of the processing stages, the controller selects at least one sub-coil to form a first sub-coil set, and the other sub-coils in the inductance coil form a second sub-coil set, and inputs the first power to the first sub-coil set, while The power input to the second sub-coil set is less than the first power. During adjacent processing stages, the first sub-coil set is not , A plurality of processing stages carried out such that each loop of the sub-coils have the same average input power. The inductively-coupled plasma processing device according to item 1 of the scope of the patent application, wherein the plurality of sub-coils are evenly distributed above the insulating material window, covering different azimuth areas on the insulating material window. The inductively coupled plasma processing device according to item 1 of the scope of the patent application, wherein the inductive coil includes a plurality of sub-coils, each of which covers a different window region of the insulating material. The inductively-coupled plasma processing device according to item 3 of the scope of patent application, wherein the first group of sub-coils in the plurality of sub-coils is located in a central region of the insulating material window, and the second group of sub-coils is located in a peripheral region of the insulating material window . The inductively coupled plasma processing device described in the first item of the patent application scope, wherein a variable capacitor is connected in series to each of the sub-coils, and the controller changes the input to each of the sub-coils by the capacitance of the series capacitor. Power value. The inductively coupled plasma processing device according to item 5 of the scope of the patent application, wherein the variable capacitor is located between the output end of each of the sub-coils and ground or between the output end of the matching circuit and the input end of the sub-coil. The inductively coupled plasma processing device according to item 1 of the scope of patent application, wherein in the plurality of processing stages, the controller inputs the second power to at least one sub-coil, and simultaneously inputs the third power to at least one sub-coil, the The third power is less than the second power and the second power is less than the first power. The inductively coupled plasma processing device described in item 1 of the scope of patent application, wherein the duration of each processing stage is greater than 0.1 seconds and less than 5 seconds. A control method for an inductively coupled plasma processing apparatus includes an inductive coupled plasma processing apparatus including: a reaction chamber, a lower part of the reaction chamber includes a base, a substrate to be processed is disposed on the base, and the top of the reaction chamber includes insulation Material window, an inductance coil is arranged above the insulation material window, the inductance coil includes a plurality of sub-coils, each of which covers a different area of the insulation material window below; the RF power is connected to the input of the plurality of sub-coils through a matching circuit Terminal, each of the sub-coils includes an output terminal electrically connected to the ground, and a controller controls the power input to the plurality of sub-coils, and the control method includes: controlling the input power of the plurality of sub-coils such that The power varies between a plurality of processing stages. In each of the processing stages, the controller selects at least one sub-coil to form a first sub-coil set, and the other sub-coils in the inductance coil form a second sub-coil set. The first power to the first sub-coil set, and the power input to the second sub-coil set is less than the first power, In the adjacent processing stage, the first sub-coil set is different. The multiple processing stages performed in the loop make each of the sub-coils have the same average input power, and the duration of each processing stage is greater than 0.1 seconds and less than 5 seconds. . According to the control method of the inductively coupled plasma processing device described in item 9 of the scope of the patent application, in one processing stage, the input power of a second sub-coil set is smaller than the input power of other sub-coil sets. The control method of the inductively coupled plasma processing device according to item 10 of the scope of the patent application, wherein the second sub-coil set whose input power is smaller than other sub-coil sets is located at the sub-input whose power is greater than other sub-coil sets. The coil set is on the opposite side.