Patent Publication Number: US-2002007794-A1

Title: Plasma processing apparatus

Description:
[0001] This application claims the benefit of Korean Patent Application No. 2000-30050, filed on Jun. 1, 2000, which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] This invention relates to a plasma processing. More particularly, it relates to a plasma processing apparatus which has a very-high-frequency parallel antenna producing inductively-coupled plasma for treating a large substrate.  
       [0004] 2. Discussion of the Related Art  
       [0005] In a field of manufacturing a semiconductor wafer and a flat panel display, the surface treatment processes such as a dry etching, a chemical vapor deposition and a sputtering use plasma. Recently, in order to achieve lower cost and higher throughput, the semiconductor wafer and the flat panel display tend to be larger in size. The semiconductor wafer particularly tends to have a diameter of greater than 300 mm. As a result, the plasma processing apparatus is changing so as to be suitable for new and different wafer and display panel.  
       [0006] A method of generating the plasma is classified into the diode type, the microwave type and the radio frequency wave type, all of which use a high frequency power. However, they have some problems and limitations.  
       [0007] In accordance with the diode type, minute patterns cannot be achieved during patterning process, because the diode type apparatus has difficulty in controlling a high voltage and needs high-pressure gases.  
       [0008] In accordance with ECR (electron cyclotron resonance) type that is a sort of the microwave type, the plasma density increases even under lower pressure of the gases. However, the uniformity of the plasma density is hardly obtained in a chamber, and this phenomenon become greater whenever the quantity of the plasma is raised.  
       [0009] In accordance with helicon wave type that is relatively a sort of the radio frequency (RF) wave type, often referred to as an inductively coupled plasma type, when generating the small quantity of the plasma, the uniformity of the plasma having a high density can be obtained by way of mutual reactions of the electric field and the magnetic field and by way of exciting the gaseous medium within the chamber. However, when generating the large quantity of the plasma, this helicon type apparatus also has the problem that the density distribution is not uniform. Further, since the conventional plasma processing apparatus uses a radio frequency (RF) electric power, this apparatus has a limitation of lowering an electron temperature of the plasma.  
       [0010] Hereinafter, reference will be made in detail to the conventional inductively coupled plasma processing apparatus, which is illustrated in the accompanying drawings.  
       [0011]FIG. 1 is a schematic diagram illustrating the conventional inductively coupled plasma processing apparatus. As shown, the plasma processing apparatus  10  is widely comprised of a vacuum vessel portion and a high frequency power source portion. The vacuum vessel portion includes a vacuum chamber  11  generating the plasma  12  therein, a gas pipe  8  supplying a process gas, a vacuum pump  20  exhausting residual gases in the vacuum chamber  11 , and an exhaust pipe  18 . The gas pipe  8  is formed in the upper portion of the vacuum chamber  11  and the exhaust pipe  18  is formed in the lower portion of the vacuum chamber  11 . The vacuum pump  20  communicates with the vacuum chamber  11  via the exhaust pipe  18 .  
       [0012] Further, a chuck  14  is usually arranged in the interior bottom of the vacuum chamber  11  and acts as a means for mounting a wafer or substrate  16 . On the top of the vacuum chamber  11 , an insulating plate  6  is arranged in order to place an antenna  4  thereon. Since the insulating plate  6  decreases capacitive coupling between the antenna  4  and the plasma  12  formed in the vacuum chamber  11 , the insulation plate  6  helps the high frequency power to be transferred to the plasma  12  by way of inductive coupling.  
       [0013] Moreover, the high frequency power source portion includes a first high frequency power source  2  that is connected to the antenna  4 , and a second high frequency power source  22  that is connected to the chuck  14 . The first and second high frequency power sources  2  and  22  supply a radio frequency (RF) power having a frequency of less than 20 MHz to the antenna  4  and the chuck  14 , respectively.  
       [0014] It will be described how the plasma processing apparatus  10  generates the plasma.  
       [0015] At first, the vacuum chamber  11  is vacuumized by the vacuum pump  20 . Next, a process gas for the plasma is supplied into the vacuum chamber  11  through the gas pipe  8 , and a predetermined pressure is maintained. The first high frequency power source  2  then supplies the radio frequency (RF) power having a frequency of 13.56 MHz to the antenna  4 . At this time, a changing magnetic field, which is changeable relatively to the time in a direction perpendicular to the plane of the antenna  4 , is generated depending on the supplied RF power. The changing magnetic field induces an electric field under the antenna  4 . The induced electric field is substantially concentric and runs in a circumferential direction. What should be noted is that electrons are accelerated in the circumferential direction by the electric field and collide against the neutral particles within the process gas so as to ionize the gaseous molecules, and thus, to form a plasma such as ion or radical. Meanwhile, the high frequency power applied to the chuck  14  by the second high frequency power source  22  controls the incident ion energy being projected to the wafer or substrate  16 .  
       [0016]FIG. 2A is a schematic view showing the structure of an RF power applying apparatus for use in the inductively coupled plasma processing apparatus according to the conventional art. As shown, a coil antenna  4   a  is connected in series with an impedance matching box (I.M.B)  3   a , and then the impedance matching box (I.M.B)  3   a  is connected to the high frequency power source  2   a . In this structure, since each winding (for example, a-b, b-c, c-d or c-e) of the series-connected coil antenna  4   a  is connected in series with other windings of that antenna  4   a , the intensity of an electric current uniformly flows through the series-connected coil antenna  4   a . In the case of this conventional structure, however, it is difficult to control the induced electric field distribution. And the plasma density becomes high in the center of the vacuum chamber, while the plasma density declines near an inner wall of the vacuum chamber. That is because of the ion and/or the electron loss in the inner wall of the vacuum chamber.  
       [0017] Therefore, it is very difficult to maintain the plasma density uniformly in the vacuum chamber. Furthermore, since the windings (for example, a-b, b-c, c-d and d-e of FIG. 2A) are connected in series with each other, a related problem is that a voltage drop is raised by the series-connected coil antenna  4   a , thereby increasing the effect of the conductive coupling to the plasma. Accordingly, the power consumption increases and the plasma uniformity is difficult to be maintained.  
       [0018]FIG. 2B is a view showing an equivalent circuit of FIG. 2A. As shown, the high frequency power from the high frequency power source  2   a  is supplied to each impedance Z 1 , Z 2 , Z 3  or Z 4 . Due to the series connection of the windings (i.e., a-b, b-c, c-d and d-e) of the coil antenna  4   a , the impedance is greater in the series connection than in the parallel connection. Therefore, the insulating plate  6  of FIG. 1 arranged between the antenna  4  and the vacuum chamber  11  is damaged by the plasma.  
       [0019]FIG. 3 is a schematic view showing the structure of an RF power applying apparatus for use in the inductively coupled plasma processing apparatus according to another conventional art. As shown, this apparatus includes first, second and third high frequency power sources  2   b ,  2   c  and  2   d . This RF power supplying apparatus also has first, second and third divided antennas  4   b ,  4   c  and  4   d  that form a loop shape. The first high frequency power source  2   b  is connected with the first antenna division  4   b  through a first impedance matching box  3   b ; the second high frequency power source  2   c  is connected with the second antenna division  4   c  through a second impedance matching box  3   c ; and the third high frequency power source  2   d  is connected with the third antenna division  4   d  through a third impedance matching box  3   d.    
       [0020] The plasma processing apparatus of the antenna division type depicted in FIG. 3 has a technical problem, i.e., the plasma is difficult to be uniformly generated. Namely, the plasma density is high near each antenna division  4   b ,  4   c  and  4   d , but is low in the central core portion of the vacuum chamber  11  of FIG. 1. Thus, the plasma uniformity is difficult to be achieved. Owing to this problem, it is can hardly be used for the large substrate. Further, since this type of apparatus needs an individual power source to each antenna division, the cost becomes higher and the individual impedance matching box is required for efficient use of the power and for impedance matching.  
       [0021] As described above, since the conventional inductively coupled plasma processing apparatus has the series-connected coil antenna that has the high impedance value, the high frequency power source having a frequency of greater than 20 MHz can not be used.  
       SUMMARY OF THE INVENTION  
       [0022] Accordingly, the present invention is directed to an inductively coupled plasma processing apparatus that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
       [0023] To overcome the problems described above, the present invention provides a plasma processing apparatus that treats the large-sized substrate using a uniform density of the plasma.  
       [0024] Another object of the invention is to provide a plasma processing apparatus that can adjust the radical ration in order to decrease the electron temperature of the plasma and to increase the processing selection ratio.  
       [0025] Another object of the present invention is to provide a plasma processing apparatus that can be used in a plasma dry etch process by way of having a large etch selectivity to a layer on the substrate.  
       [0026] Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings.  
       [0027] To achieve these and other objects and in accordance with the purpose of the present invention, as embodied and broadly described a plasma processing apparatus having a vacuum chamber for generating plenty of inductively coupled plasmas therein, including: a first very high frequency power source that supplies a very high frequency power having a frequency of 20 to 300 MHz; and a plurality of antenna units parallel-connected each other and applied the very high frequency power by the first very high frequency power source, the antenna units comprising a antenna; wherein the vacuum chamber has a reaction space where the inductively coupled plasmas are generated by the antenna units.  
       [0028] One of the antenna units has at least one variable load that is connected in series. The antenna units having at least one variable load is located in outer part of the antenna. The variable load is a variable capacitor.  
       [0029] A plasma processing apparatus further comprises an impedance matching box that is respectively connected to the very high frequency power source and the antenna. The parallel-connected antenna units maintain a resonance state each other. A plasma processing apparatus further comprises a chuck in the vacuum chamber for mounting a substrate thereon. A plasma processing apparatus further comprises a second very high frequency power source that supplies a very high frequency power having a frequency of 20 to 300 MHz to the chuck.  
       [0030] The preferred embodiment of the present invention further provides a radio frequency (RF) power supplying apparatus, including: a very high frequency power source supplying a very high frequency power having a frequency of 20 to 300 MHz; an impedance matching box connected to the very high frequency power source; and a plurality of antenna units connected in parallel each other; wherein a plurality of the antenna units comprise a antenna; and wherein each antenna unit has at least one variable capacitor and a coil antenna.  
       [0031] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
     [0032] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
     [0033] In the drawings:  
     [0034]FIG. 1 is a schematic diagram illustrating a conventional inductively coupled plasma processing apparatus;  
     [0035]FIG. 2A is a schematic view showing the structure of an RF power applying apparatus used in an inductively coupled plasma processing apparatus according to a conventional art;  
     [0036]FIG. 2B is a view showing an equivalent circuit of FIG. 2A;  
     [0037]FIG. 3 is a schematic view showing the structure of an RF power applying apparatus for use in the inductively coupled plasma processing apparatus according to another conventional art;  
     [0038]FIG. 4 is a schematic diagram illustrating an inductively coupled plasma processing apparatus according to the present invention;  
     [0039]FIG. 5A is a schematic view showing the structure of an RF power applying apparatus for use in the inductively coupled plasma processing apparatus of FIG. 4 according to a first embodiment of the present invention;  
     [0040]FIG. 5B is a view showing an equivalent circuit of FIG. 5A;  
     [0041]FIG. 6A is a schematic view showing the structure of an RF power applying apparatus used in the inductively coupled plasma processing apparatus of FIG. 4 according to a second embodiment of the present invention;  
     [0042]FIG. 6B is a view showing an equivalent circuit of FIG. 6A;  
     [0043]FIG. 7 is a graph showing a relationship between frequency and electron temperature;  
     [0044]FIG. 8A is a graph showing radical characteristics when a radio frequency power having frequency of 13.56 MHz and power of 2 kW is supplied to an antenna of a conventional inductively coupled plasma processing apparatus;  
     [0045]FIG. 8B is a graph showing radical characteristics when a very high frequency power having frequency of 100 MHz and power of 2 kW is supplied to an antenna of the inductively coupled plasma processing apparatus according to the present invention; and  
     [0046]FIG. 9 is a schematic view showing the structure of an RF power applying apparatus for use in the inductively coupled plasma processing apparatus of FIG. 4 according to a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0047] Reference will now be made in detail to embodiments of the present invention, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
     [0048]FIG. 4 is a schematic diagram illustrating an inductively coupled plasma processing apparatus according to the present invention. Although FIG. 4 is similar to FIG. 1, the RF power supplying apparatus has different structure from the conventional art depicted in FIG. 1.  
     [0049] As shown in FIG. 4, the plasma processing apparatus  100  is widely comprised of a vacuum vessel portion and a very high frequency power source portion. The vacuum vessel portion includes a vacuum chamber  110  generating the plasma  112  therein, a gas pipe  108  supplying a process gas, a vacuum pump  120  exhausting residual gases in the vacuum chamber  110 , and an exhaust pipe  118 . The gas pipe  108  is formed in the upper portion of the vacuum chamber  110  and the exhaust pipe  118  is formed in the lower portion of the vacuum chamber  110 . The vacuum pump  120  communicates with the vacuum chamber  110  via the exhaust pipe  118 .  
     [0050] Further, a chuck  114  is arranged in the interior bottom of the vacuum chamber  110  and acts as a means for mounting a wafer or substrate  116 . On the top of the vacuum chamber  110 , an insulating plate  106  is arranged in order to place an antenna  104  thereon. Since the insulating plate  106  decreases capacitive coupling between the antenna  104  and the plasma  112  formed in the vacuum chamber  110 , the insulation plate  106  helps the very high frequency power to be transferred to the plasma  112  by way of inductive coupling.  
     [0051] Moreover, the very high frequency power source portion includes a first very high frequency power source  102  that is connected to the antenna  104 , and a second very high frequency power source  122  that is connected to the chuck  114 . The first and second very high frequency power sources  102  and  122  supply a radio frequency (RF) power having a frequency of 20 to 300 MHz to the antenna  104  and chuck  114 , respectively. The advantage of the very high frequency will be explained later, and the explanation of the system of generating the plasma is omitted because it is the same as the conventional art described before.  
     [0052]FIG. 5A is a schematic view showing the structure of an RF power applying apparatus for use in the inductively coupled plasma processing apparatus of FIG. 4 according to a first embodiment of the present invention. As shown, the antenna  114  is comprised of first, second, third and fourth antenna units that are connected in parallel. The first antenna unit includes a coil antenna A-B with a series-connected variable load; the second antenna unit includes a coil antenna C-D with a series-connected variable load; the third antenna unit includes a coil antenna E-F with a series-connected variable load; and the fourth antenna unit includes a coil antenna G-H with a series-connected variable load. Here in FIG. 5, the variable load is indicated as a variable capacitor  105 . An impedance matching box  103  is located between the first very high frequency power source  102  and each antenna unit. The variable load of each antenna unit is, for example, a variable capacitor  105  that maintains a resonance state between the antenna units. The number of the antenna units is changeable depending on the desirable property of the plasma processing apparatus.  
     [0053]FIG. 5B is a view showing an equivalent circuit of FIG. 5A. As shown, the winding of the coil antenna of each antenna unit can be comprised of the single or double winding of wire, and the winding of the coil antenna can be represented by the impedance Z 1 , Z 2 , Z 3  or Z 4  that includes equivalent resistance and equivalent inductance. If the variable capacitors  105  are adjusted to make the imaginary portion of the equivalent impedance of each antenna unit be zero, the resonance state is maintained. Thus, the resonance state results in the equivalent intensity of the electric current flowing each antenna unit, by way of adjusting the variable capacitors  105 . Then, the electric current flowing the antenna units can increase from the above-mentioned process.  
     [0054] Namely, the capacity of the variable capacitor  105  is firstly determined in order to control the energy transmitted to the antenna  104 . Next, the capacity of the capacitor  105  is adjusted in order to maintain the resonance state between the coil antennas. And then, by way of matching the impedance of the antenna  104  to the very high frequency power source  102 , the radio-frequency energy applied from the very high frequency power source  102  is easily transmitted to the plasma in the vacuum chamber. Moreover, the plasma uniformity increases in view of matching the impedance. According to the principles of the present invention, the number of the antenna unit is changeable even if the antenna  104  maintains the resonance state. Since each antenna unit includes the variable load, the current ratio flowing the two antenna units is controlled by way of controlling the variable loads arranged in the two antenna units. Further, the other antenna units are used for inducing the resonance state in the circuit. According to the present invention, the antenna units having the resonance states are arranged in and used for the outer parts of the antenna  104 , and the other antenna units are arranged in and used for the inner parts of the antenna  104 . Therefore, the energy uniformity is readily achieved in all over the antenna  104 .  
     [0055]FIG. 6A is a schematic view showing the structure of an RF power applying apparatus for use in the inductively coupled plasma processing apparatus of FIG. 4 according to a second embodiment of the present invention. And FIG. 6B is a view showing an equivalent circuit of FIG. 6A. As shown, although FIGS. 6A and 6B are respectively similar to the FIGS. 5A and 5B, the variable loads such as the variable capacitors can be omitted in the second embodiment.  
     [0056] According to the preferred embodiments of the present invention described above, since the plasma processing apparatus uses the very-high-frequency parallel antenna producing inductively coupled plasma, the problem of matching the impedance does not occur although the frequency of the applied power to the antenna is enhanced. Therefore, the very high frequency power having a frequency of 20 MHz to 300 MHz can be applied to the antenna, thereby generating the high dense plasma having low electron temperature. Namely, the electron temperature is controllable from 1.5 eV to 2.5 eV, and thus the process gas can be ionized in the optimum condition.  
     [0057]FIG. 7 is a graph showing a relationship between frequency and electron temperature. As shown, while the frequency of the applied power to the plasma becomes larger, the electron temperature of the plasma is getting lowered. Namely, the electron temperature (eV) is in inverse portion to the frequency (MHz). Therefore, since the plasma processing apparatus according to the present invention adopts the very-high-frequency parallel antenna producing inductively coupled plasma, to match impedance is easy although the applied power to the plasma has a frequency of 20 MHz to 300 MHz. Moreover, the very high frequency power is easily transmitted to the plasma, and thus the electron temperature is declined.  
     [0058]FIG. 8A is a graph showing radical characteristics when a radio frequency power having frequency of 13.56 MHz and power of 2 kW is supplied to an antenna of a conventional inductively coupled plasma processing apparatus. As shown, the degree of forming CF x  radical is researched about the mixed gas of C 4 F 8  and Ar while the pressure of the vacuum chamber is maintained at 2 mTorr. The research shows that the electron temperature of the plasma is about 3 eV.  
     [0059]FIG. 8B is a graph showing radical characteristics when a very high frequency power having frequency of 100 MHz and power of 2 kW is supplied to an antenna of the inductively coupled plasma processing apparatus according to the present invention. Compared to the graph of FIG. 8A, the electron temperature of the plasma is 2 eV when the pressure of the vacuum chamber is maintained at 2 mTorr.  
     [0060] Referring to the FIGS. 8A and 8B, the radical is plentifully generated when the very high frequency power having a frequency of 100 MHz is applied to the antenna, due to the low electron temperature of the plasma. Further, according to the embodiments, since the plasma processing apparatus has the very-high-frequency parallel antenna producing inductively coupled plasma, the CF x /F ratio can be adjusted to have the high radical density of CF 2 , CF 3  and the like after the very high frequency power for generating the plasma is supplied. Further, the CF x /F ratio can also be adjusted to have the low density of fluorine radical after the very high frequency power for generating the plasma is supplied.  
     [0061] Further, according to the plasma processing apparatus having the very high frequency power for generating the inductively coupled plasma, when the parallel antenna is used for the antenna units, the resonance capacitor disposed in the outer parts of the antenna controls the intensity of the current flowing the antenna. Thus, the uniform plasma density can be achieved.  
     [0062] In other words, when the inductively coupled plasma processing apparatus uses the parallel-connected antenna, compared to the conventional series-connected antenna, the following advantages can be achieved.  
     [0063] First, since the impedance of the antenna is low, it is easy to match the impedance.  
     [0064] Second, since the high electric current flows the antenna, the high dense plasma can easily be achieved.  
     [0065] Third, since the voltage applied to the antenna is lower, the damage of the insulating plate caused by the capacitive electric field can be minimized.  
     [0066] Fourth, the radical is plentifully generated due to the low impedance applied to the parallel antenna and due to the easy impedance matching, although the very high frequency power is induced.  
     [0067]FIG. 9 is a schematic view showing the structure of an RF power applying apparatus for use in the inductively coupled plasma processing apparatus of FIG. 4 according to a third embodiment of the present invention. As shown, the antenna  104  is comprised of first, second, third and fourth antenna units that are connected in parallel. Namely, the antenna  104  includes these antenna units. FIG. 9 is similar to FIG. 5A, but each antenna unit does not include the variable capacitor. An impedance matching box  103  is located between the first very high frequency power source  102  and the antenna  104 . The number of the antenna units is changeable depending on the desirable property of the plasma processing apparatus. In this embodiment, the very high frequency power from the first very high frequency power source  102  is applied to the parallel-connected antenna  104 .  
     [0068] Moreover, the very high frequency power having a frequency of 20 MHz to 300 MHz can be applied to the chuck (see reference element  114  of FIG. 4). When this very high frequency power is applied to the chuck, the ion energy is readily controlled and then the process gas largely ionized. Thus, plenty of radicals are generated.  
     [0069] The aforementioned preferred embodiments are particularly useful when the plasma processing apparatus is used in a plasma dry etch process. This is due to the fact that the CF x /F ratio can be adjusted to have the low density of fluorine radical. And also, it is possible to have the high radical density of CF 2 , CF 3  and the like when the dry etch process is conducted using CF x . Therefore, the proper radical ratio, which is relative to increase selection ratio, enhances the dry etch process excellently.  
     [0070] It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.