Plasma processing apparatus and method

[0002] The present invention relates to a plasma processing apparatus and method for supplying high-frequency power to antennaes to generate an electric field, causing the electric field to generate a plasma and using the plasma to process specimens.

[0003] In a plasma processing apparatus which generates plasma in a vacuum processing chamber by supplying a high-frequency current to a coil-shaped antenna to generate an electric field, causing the electric field to generate a plasma, and using the plasma for processing, if the electric field generated by the coil-shaped antenna is strong, byproducts are hardly deposited on the inner wall of the vacuum chamber by the resulting high-density plasma. On the other hand, if the electric field is weak, the density of the resulting plasma is low, and byproducts are easily deposited on the inner wall of the chamber. Such a deposit is not desirable.

[0004] One method of solving this kind of problem has been disclosed in Japanese Non-examined Patent Publication No. 8-316210 (1996). The proposed method comprises the steps of providing a high-frequency antenna which can carry a high frequency current around the outer dielectric wall of a vacuum chamber, providing an electrode which forms a uniform electric field on the inner surface of the dielectric material between this high-frequency antenna and the dielectric member to electrostatically connect the electrode with a plasma, connecting the high-frequency antenna and the electrode in parallel, supplying a small power to the electrode during plasma processing, and supplying a great power to the electrode at a break in the processing to clean the inside of the chamber.

[0005] Further, a plasma processing method has been disclosed in U.S. Pat. No. 5,811,022, which comprises the steps of providing a divided Faraday shield between the vacuum chamber and an induction coil to which a high-frequency power is applied, selecting the divided Faraday shield, and controlling the level of a plasma potential change.

[0006] The method described in the aforementioned Japanese patent employs a method of individually performing wafer processing and a cleaning process for cleaning the inside of the vacuum chamber. However, this method does not consider the throughput. Further, in this processing method, when a current flowing through an electrostatically capacitance-coupled electrode (or electrostatic capacitive coupling antenna) is made greater in a circuit having the high-frequency antenna and the electrode, which are connected in parallel, to prevent byproducts from being deposited on the inner surface of the vacuum chamber during plasma processing, the high-frequency impedances of the high-frequency antenna (inductive) and the electrode (capacitive) may not be matched. This is because the electrostatically capacitance-coupled electrode, which is provided to produce an electrostatic-coupling discharge in the circuit, works as an electric capacitor, and the high-frequency antenna, which is provided to produce an inductive coupling discharge, works as a coil. Consequently, this circuit forms a parallel resonance (which increases the combined impedance infinitely) and prevents impedance matching. Therefore, plasma processing is not available under conditions which may cause a parallel resonance, which restricts the plasma processing conditions.

[0007] Another possible problem of this processing method is that, when a current flowing through an electrostatically capacitance-coupled electrode (or electrostatic capacitive coupling antenna) is made greater to prevent byproducts from being deposited on the inner surface of the vacuum chamber during plasma processing, a great plasma by electrostatic capacitance discharge occurs, which greatly changes the plasma distribution and the uniform wafer processing condition.

[0008] In the method described in the aforementioned U.S. patent, the Faraday shield is capacitively coupled with the induction coil. In other words, when the Faraday shield is assumed to be an electrostatically-coupled electrode, the voltage applied to the electrode may be affected by the precision of re-installation of the induction coil and the electrode after the vacuum chamber is opened to the air, since the circuit for supplying a voltage to the electrode uses a floating capacitance. This floating capacitance must be increased to supply a higher voltage to the electrode. For this purpose, it is required to increase the area of the induction coil and bring the induction coil closer to the electrode. This area expansion means provision of a bigger high-voltage section and the shorter distance between the antenna or coil and the electrode may increase the possibility that abnormal discharges will be generated, which reduces the safety and reliability of the equipment. Therefore, it is not preferable to increase the voltage for the electrode so high in a system using a floating capacitance.

[0009] Meanwhile, a plasma processing apparatus of the magnetic-field plasma type can control the distribution of plasma by varying the magnetic field which is generated by an electromagnet or the like and is fit for uniform wafer processing with less deposition of byproducts. On the other hand, a plasma processing apparatus of the inductive discharge plasma type using no magnetic field has a limited means to control the plasma distribution. For example, this type of plasma processing apparatus controls the distribution of plasma by changing the shape of the vacuum chamber or adjusting the location of the inductive coupling antenna. Further, any change in a process condition may affect the plasma distribution, and a single plasma processing apparatus can perform processing only under a limited condition.

[0010] An object of the present invention is to provide a plasma processing apparatus and method which can easily control the plasma distribution in plasma processing using an inductive coupling antenna.

[0011] Another object of the present invention is to provide a plasma processing apparatus and a method thereof which can suppress deposition of byproducts on the inner wall of the vacuum chamber during plasma processing of a specimen using an inductive coupling antenna.

[0012] The aforesaid first problem can be accomplished by using an apparatus comprising an inductive coupling antenna for a wall enclosing a plasma generating area, an electrostatic capacitive coupling antenna at least for a surface which is not equipped with said inductive coupling antenna, which is electrically connected in series with the electrostatic capacitive coupling antenna, and a means for controlling the ratio of high-frequency currents flowing through said electrostatic capacitive coupling antenna and said inductive coupling antenna by controlling the ratio of high-frequency currents flowing through the inductive coupling antenna and the electrostatic capacitive coupling antenna, which are electrically connected in series, generating a plasma in the vacuum chamber with the electric field using said inductive coupling antenna and the electrostatic capacitive coupling antenna, and using said plasma to process a specimen.

[0013] The aforesaid second problem can be accomplished by using an apparatus comprising an inductive coupling antenna for a wall enclosing a plasma generating area, an electrostatic capacitive coupling antenna for a surface which is not equipped with said inductive coupling antenna, which is electrically connected in series with the electrostatic capacitive coupling antenna, and by generating an electric field using the inductive coupling antenna and the electrostatic capacitive coupling antenna, which are electrically connected in series, adding an electric field produced by the inductive coupling antenna to an area which has a very weak electric field, generating a plasma in the vacuum chamber by these electric fields, and using said plasma to process a specimen.

[0014] The plasma processing apparatus of the present invention can control the ratio of high-frequency currents flowing through inductive coupling and electrostatic capacitive coupling antennaes which are electrically connected in series to adjust the magnitudes of electric fields produced by said antennaes. The present invention has an effect of enabling production of an optimum plasma in the vacuum chamber and suppressing deposition of byproducts on the inner wall of the vacuum chamber during plasma processing of wafers by inductive coupling antennaes.

[0015] FIG. 1 is a sectional view of a plasma processing apparatus which represents a first preferred embodiment of the present invention.

[0016] FIG. 2 is a perspective view of the discharging circuit of the plasma processing apparatus of FIG. 1.

[0017] FIG. 3 is an equivalent circuit diagram of the discharging circuit of FIG. 2.

[0018] FIG. 4 is a diagram of another embodiment of the equivalent circuit of FIG. 3.

[0019] FIG. 5 is a sectional view of a plasma processing apparatus which represents a second preferred embodiment of the present invention.

[0020] FIG. 6 is a perspective view of the discharging circuit of the plasma processing apparatus of FIG. 5.

[0021] FIG. 7 is an equivalent circuit diagram of the discharging circuit of FIG. 6.

[0022] FIG. 8 is a diagram of another embodiment of the equivalent circuit of FIG. 6.

[0023] FIG. 9 is a sectional view of a plasma processing apparatus which represents a third preferred embodiment of the present invention.

[0024] FIG. 10 is a perspective view of the discharging circuit of the plasma processing apparatus of FIG. 9.

[0025] FIG. 11 is a perspective view of the discharging circuit for an experimental plasma processing apparatus using the concept of the third embodiment of the present invention.

[0026] FIG. 12 is a graph which shows the result of an experiment using the apparatus of FIG. 11.

[0027] FIG. 13 is a graph which shows the result of an experiment using the apparatus of FIG. 11.

[0028] FIG. 14 is a graph which shows the result of an experiment using the apparatus of FIG. 11.

[0029] FIG. 15 is a perspective view of a plasma processing apparatus which represents a fourth preferred embodiment of the present invention.

[0030] FIG. 16 is an equivalent circuit diagram of the discharging circuit of FIG. 15.

[0031] FIG. 17 is a perspective view of a plasma processing apparatus which represents a fifth preferred embodiment of the present invention.

[0032] FIG. 18 is an equivalent circuit diagram of the discharging circuit of FIG. 17.

[0033] FIG. 19 is a sectional view of a plasma processing apparatus which represents a sixth preferred embodiment of the present invention.

[0034] FIG. 20 is a sectional view of a plasma processing apparatus which represents another embodiment of the present invention.

[0035] FIG. 21 is a sectional view of a plasma processing apparatus which represents another embodiment of the present invention.

[0036] FIG. 22 is a sectional view of a plasma processing apparatus which represents another embodiment of the present invention.

[0037] FIG. 23 is a sectional view of a plasma processing apparatus which represents another embodiment of the present invention.

[0038] FIG. 24 is a flow diagram which shows an example of a semiconductor processing flow in accordance with the present invention.

[0039] A first embodiment of the present invention will be described in detail with reference to FIG. 1 through FIG. 3.

[0040] FIG. 1 is a sectional view of a plasma processing apparatus which represents the first preferred embodiment of the present invention. The vacuum chamber 2 consists of a discharging section 2amade of an insulating material (or non-conductive material such as silica or ceramic) forming a plasma generating space in the section and a processing section 2bequipped with an electrode 5 on which a specimen to be processed, such as a wafer 13, is placed. The processing section 2bis grounded and the electrode 5 is insulated from the processing section 2bby a proper insulating material. A coil-like inductive coupling antenna 1 is wound around the discharging section 2a. Above the discharging section 2athere is placed a disk-shaped electrostatic capacitive coupling antenna 8 which couples with plasma 6 electrostatically. The inductive coupling antenna 1 and the electrostatic capacitive coupling antenna 8 are connected in series with a primary high-frequency power source 10 via an impedance matching box 3. A load 17, having a variable impedance, is grounded in parallel with the electrostatic capacitive coupling antenna 8. A processing gas is supplied from a gas supplying unit 4 into the vacuum chamber 2. The atmosphere in the vacuum chamber 2 is evacuated to provide a predetermined gas pressure by a vacuum unit 7. A secondary high-frequency power source 12 is connected to the electrode 5.

[0041] In this plasma processing apparatus, a process gas supplied from the gas supplying unit 4 into the vacuum chamber is highly ionized (into plasma) by electric fields generated by the inductive coupling antenna 1 and the electrostatic capacitive coupling antenna 8. The ionized (or plasma) gas is exhausted later by the vacuum unit 7. A high-frequency power in a HF band (e.g. 13.56 MHz, 27.12 MHz, and 40.68 MHz) or in a higher frequency band, such as a VHF band, is supplied to the inductive coupling antenna 1 and the electrostatic capacitive coupling antenna 8 to produce electric fields for plasma. To suppress an unwanted power reflection, the impedance matching box 3 is provided to match the impedances of the antennaes with the output impedance of the primary high-frequency power source 10. For this purpose, the impedance matching box 3 uses two general inverted-L-type variable capacitors having variable electrostatic capacitances. The wafer 13 to be processed is placed on the electrode 5. The secondary high-frequency power source 12 supplies a biasing voltage to the electrode 5 to attract ions in plasma 6 towards the wafer 13.

[0042] FIG. 2 is a perspective view of the plasma processing apparatus of FIG. 1 to show the discharging circuit. In this discharging circuit, the high-frequency current from the primary high-frequency power source 10 flows through the matching box 3, the inductive coupling antenna 1, and the electrostatic capacitive coupling antenna 8 in that order. The current coming from the electrostatic capacitive coupling antenna flows to the ground via the plasma. The load 17 having a variable impedance is grounded in parallel with the electrostatic capacitive coupling antenna 8. The load 17 having a series connection of a variable capacitor and a fixed inductor can reduce the impedance to 0 by resonating in series.

[0043] FIG. 3 shows a circuit equivalent to the discharging circuit of FIG. 2. This circuit has the inductive coupling antenna 1 as load 9 and the electrostatic capacitive coupling antenna 8 as load 11.

[0044] When the impedance of the load 17 is 0, the voltage across the load 11 is 0 and, consequently, a current flowing through the electrostatic capacitive coupling antenna 8 becomes 0, which suppresses the electrostatic capacitive coupling discharge. In other words, plasma is generated only by the inductive coupling discharge. As the impedance of the load 17 increases, the current flowing through the load 11 increases. Consequently, the ratio of plasma generated by the electrostatic capacitive coupling discharge becomes greater.

[0045] In this case, the impedance of the load 11 must be varied in the matching range of the impedance matching box. The following conditions must be satisfied to match impedances.

[0046] One of the matching conditions will be explained by way of example. Let's assume that the loads 9, 11, and 17, respectively, have reactances YL, YC, and YV (in that order). The reactance YL is greater than 0 as it is inductive and the reactance YC is less than 0 as it is capacitive. However, since the loads 11 and 17 are connected in parallel, if the reactance YC is equal to the negative value of the reactance YV, while the reactance YV is positive, this circuit causes a parallel resonance, which drastically increases the combined impedance and prevents impedance matching. As a result, plasma cannot be produced. To enable impedance matching, it is necessary to vary the load 11 while the reactance YV is negative.

[0047] Another matching condition will be explained as another example. Let's assume that the reactance of the combined impedance of the loads 11 and 17, which are connected in series, is YG. The reactance YG is negative (less than 0) when both reactances YV and YC are negative. However, when the reactance YG is greater than YL, the reactance of the load of the whole circuit to be matched becomes negative. As a result, the inverted-L-type matching box may be disabled. In this case, impedance matching is enabled when an inductor is connected in series with the load 9. Although the use of a n-type matching box is also effective, the matching box has a complicated structure.

[0048] As explained above, it is possible to change the ratio of a high-frequency current which flows through the inductive coupling antenna 1 and the electrostatic capacitive coupling antenna 8 by changing the impedance of the load 17. This can change the magnitude of an electric field produced by the respective antennaes. In other words, it is possible to change the plasma density produced by respective electric fields according to the location of each antenna and thus control the distribution of plasma in the discharging section 2a.

[0049] Namely, the inductive coupling antenna 1 produces stronger plasma in the outer areas 15aand the electrostatic capacitive coupling antenna 8 produces a stronger plasma in the center area 15b, as seen in FIG. 1. Therefore, the density of the plasma in the center can be controlled by regulating the current flowing through the electrostatic capacitive coupling antenna 8. This enables adequate control of the plasma distribution and uniform wafer processing.

[0050] Further, the electron temperature of the plasma produced by electrostatic capacitive coupling discharge is apt to be higher than that of plasma produced by the inductive coupling discharge. Accordingly, by regulating the ratio of the current flowing through the electrostatic capacitive coupling antenna 8, it is possible to control the ratio of electrostatic capacitive coupling discharge relative to the inductive coupling discharge. Namely, it is possible to control the electron temperature of the plasma and the ionization of the process gas and select optimum processing conditions (e.g. fit for metal etching, gate etching, insulator etching, magnetic head etching, and so on).

[0051] The inductive coupling antenna 1 produces a stronger electric field in the area 15anear the inductive coupling antenna. Therefore, when the inductive coupling antenna 1 produces a plasma, more byproducts are deposited on the ceiling of the discharging section 2athan on the side walls of the discharging section 2ain the vacuum chamber 2. To suppress deposition of byproducts, a disk-like electrostatic capacitive coupling antenna 8, which electrostatically couples with the plasma, is provided over the ceiling of the discharging section to 2aproduce a strong electric field in the area 15bnear the ceiling. This suppresses or prevents deposition of byproducts on the ceiling of the discharging section 2a.

[0052] As described above, in accordance with the first embodiment of the present invention, a strong electric field produced by the electrostatic capacitive coupling antenna can be formed in an area where the electric field produced by the inductive coupling antenna is weak by providing an inductive coupling antenna around the discharging section and an electrostatic capacitive coupling antenna over a surface of the discharging section where the inductive coupling antenna is not located, electrically connecting the inductive coupling antenna and the electrostatic capacitive coupling antenna in series, and supplying high-frequency power to the antennaes. This embodiment has an effect of suppressing the deposition of byproducts on the inner wall of the vacuum chamber even while wafer processing by plasma is in progress.

[0053] Further, by regulating the ratio of currents flowing through the inductive coupling antenna and the electrostatic capacitive coupling antenna, the density of the plasma in the central processing area can be controlled, which enables optimum control of the plasma distribution and uniform wafer processing.

[0054] Similarly, the ratio of the electrostatic capacitive coupling discharge to the inductive coupling discharge can be controlled by regulating the ratio of currents flowing through the inductive coupling antenna and the electrostatic capacitive coupling antenna, for example, by controlling the current which flows through the electrostatic capacitive coupling antenna. This enables control of the electron temperature of the plasma and the ionization of the process gas.

[0055] Although the first embodiment of the present invention employs a method of controlling the current which flows through the electrostatic capacitive coupling antenna using a load 17 as one of the methods of regulating the ratio of currents flowing through the inductive coupling antenna and the electrostatic capacitive coupling antenna, it is also effective to connect the load 17 in parallel with the inductive coupling antenna 1. FIG. 4 shows the equivalent circuit thereof. When the impedance of the load 17 is 0, the high-frequency current flowing through the load 9 of the inductive coupling antenna 1 becomes 0. This current becomes greater as the impedance of the load 17 becomes greater. As explained above, this circuit can control the current which passes through the inductive coupling antenna 1.

[0056] A second embodiment of the present invention will be described in detail below with reference to FIG. 5 through FIG. 8. FIG. 6 is a perspective view of the discharging circuit. Symbols in FIG. 5 and FIG. 6 identify the same members as those in FIG. 1 and FIG. 2. Their explanation is omitted here. FIG. 5 and FIG. 6 are different from FIG. 1 and FIG. 2 in that this embodiment has two upper and lower inductive coupling antennas 1aand 1bwhich are connected in parallel and that a variable capacitor 16 is connected in series with the inductive coupling antenna 1a.

[0057] The plasma processing apparatus of this embodiment can control the plasma distribution by regulating the magnitudes of high-frequency currents which pass through the upper and lower inductive coupling antennaes. How the plasma distribution is controlled will be explained.

[0058] For this explanation, it is assumed that the upper and lower inductive coupling antennas 1aand 1bproduce strong electric fields respectively in areas 25aand 25b, and that the inductive coupling antenna 8 produces a strong electric field in the area 25c. Plasma is generated in these strong electric fields. The discharging section of the vacuum chamber 2 is tapered towards the top. In this embodiment, the area 25ahas a smaller diameter than the area 25b. Consequently, plasma produced by the inductive coupling antenna 1ais the strongest in the center and plasma produced by the inductive coupling antenna 1bis the strongest in the outer periphery. Therefore, the distribution of plasma can be controlled by regulating the ratio of currents flowing through the inductive coupling antennas 1aand 1b.

[0059] A method of regulating the ratio of currents flowing through the inductive coupling antennas 1aand 1bwill be explained with reference to FIG. 7, which shows the equivalent circuit of the discharging circuit of FIG. 6. This circuit represents the inductive coupling antenna 1aas load 9aand the inductive coupling antenna 1bas load 9b. Let's assume that the combined impedance of the load 9aand the variable capacitor 16 is Za and the impedance of the load 9bis Zb. The magnitudes of high-frequency current flowing through the loads 9aand 9bare respectively proportional to 1/Za and 1/Zb. Although the inductive coupling antenna 1ahas a positive reactance, the current can be controlled by changing the impedance Za from a positive value to 0 using the variable capacitor 16 having a negative reactance.

[0060] If the reactance Za becomes negative, impedance matching may be disabled as the reactance Zb is positive. To enable impedance matching, it is recommended to keep the reactance Za positive. Therefore, the circuit of FIG. 7 is able to increase the current flowing through the load 9a.

[0061] In wafer processing by the aforesaid processing method and apparatus, when the high-frequency current for the electrostatic capacitive coupling antenna 8 is made greater and the ratio of currents for the inductive coupling antennaes 1aand 1bis made constant, plasma in the area 25cbecomes greater and the current flowing through the inductive coupling antennaes 1aand 1bgo lower relatively. As a result, less plasma is generated in areas 25aand 25b. Consequently, the plasma becomes highest in density in the center and the wafer processing speed is also highest in the center.

[0062] The plasma distribution and wafer processing speed can be made uniform by reducing the current for the inductive coupling antenna 1a, increasing the current for inductive coupling antenna 1b, and thus producing more plasma in the bigger area 25band less plasma in the smaller area 25a.

[0063] As aforesaid, in addition to the effect described in the first embodiment, the second embodiment also has an effect of finely controlling the distribution of plasma in the discharging section because the plasma processing apparatus of the second embodiment has two inductive coupling antennas of different sizes to which variable quantities of high-frequency power are supplied to produce inductive coupling discharges of different magnitudes.

[0064] Further, as this embodiment can respectively control high-frequency currents which flow through two inductive coupling antennaes 1aand 1band the electrostatic capacitive coupling antenna 8, this embodiment can cause the antennaes to produce strong electric fields in areas 25a, 25b, and 25cto produce the optimum plasma status, which can finely suppress deposition of byproducts on the walls of the vacuum chamber while plasma processing is in progress.

[0065] To reduce the current for the load 9ain the second embodiment, the variable capacitor 16 in the circuit of FIG. 7 must be connected in series with the load 9b(instead of connecting it in series with the load 9a).

[0066] As another circuit to reduce the current flowing through the load 9a, an inductor 19 can be connected in series with the variable capacitor 16, as shown in the equivalent circuit of FIG. 8. In this circuit, the reactances of loads 9aand 9bare positive, while the reactance of the combined impedance of the variable capacitor 16 and the inductor 19 are positive. With this, impedance matching can be carried out without causing any parallel resonance.

[0067] A third embodiment of the present invention will be described in detail with reference to FIG. 9 and FIG. 10. FIG. 9 shows a sectional view of the plasma processing apparatus in accordance with the present invention and FIG. 10 is a perspective view of the discharging circuit. Symbols in FIG. 9 and FIG. 10 denote the same members as those in FIG. 5 and FIG. 6. Their explanation is omitted here. FIG. 9 and FIG. 10 are different from FIG. 5 and FIG. 6 in that the electrostatic capacitive coupling antenna 8aof this embodiment covers the whole discharging section 2aof the vacuum chamber 2.

[0068] For this explanation, it is assumed that the upper and lower inductive coupling antennas 1aand 1bproduce strong electric fields respectively in areas 25aand 25band that the electrostatic capacitive coupling antenna 8aproduces a strong electric field in the area 25d. Plasma is generated in these strong electric fields. Since the electrostatic capacitive coupling antenna 8ais provided to cover the whole discharging section 2aof the vacuum chamber 2, the area 25dcomprises an area adjoining the whole inner wall of the discharging section 2aof the vacuum chamber 2. The electrostatic capacitive coupling discharge in this area can suppress the deposition of byproducts on the whole inner wall of the discharging section 2aor clean this area. The portion of the electrostatic capacitive coupling antenna 8aprovided between the inductive coupling antennas 1aand 1bprevents an electrostatic capacitive coupling electric field produced by the inductive coupling antennas and plasma from propagating into the discharging section 2aand thus prevents the inner walls of the discharging section 2afrom being eroded away. Namely, it works as a Faraday shield.

[0069] FIG. 10 is a perspective view of the discharging circuit of the plasma processing apparatus of FIG. 9. The electrostatic capacitive coupling antenna 8ahas slits 14 which intersect the inductive coupling antennas 1aand 1bat right angles so that the electric fields produced by the inductive coupling antennas 1aand 1bmay pass into the discharging section 2a. The angle of intersection need not be a right angle so long as the slits do not block the electric fields produced by the inductive coupling antennas 1aand 1b.

[0070] As aforesaid, in addition to the effects described in the first and second embodiments, the third embodiment also has an effect of suppressing or preventing the deposition of byproducts on the whole inner wall of the discharging section 2abecause the electrostatic capacitive coupling antenna 8ais provided to cover the whole discharging section 2a.

[0071] The result of an experiment which uses the concept of the third embodiment of the present invention to produce plasma will be explained with reference to FIG. 11, which shows a discharging circuit used for the experiment. This discharging circuit contains a 1.2 μH inductor in the matching box for easier impedance matching. This circuit also has a 200 pF capacitor connected to the electrostatic capacitive coupling antenna 8ato suppress a current flowing through the electrostatic capacitive coupling antenna. The inductive coupling antenna 1ahas two turns and the inductive coupling antenna 1bhas one turn. Currents for the two inductive coupling antennas 1aand 1band the electrostatic capacitive coupling antenna 8aare each controlled by a load comprising a variable capacitor (16aand 16b) and a fixed inductor.

[0072] FIG. 12 shows a change of the ratio of a current flowing through the inductive coupling antenna 1ato a current flowing through the inductive coupling antenna 1bas the electrostatic capacitance of the variable capacitor 16achanges. As seen from this drawing, it is apparent that the ratio of currents flowing through the antennas 1aand 1bcan be controlled by the variable capacitor 16a. In this circuit, a series connection of the variable capacitor 16aand a 0.9 μH inductor is connected to the end of the antenna 1b. When the variable capacitor 16ais controlled to make the combined impedance of the variable capacitor 16a, the 0.9 μH inductor, and the antenna 1bhave a value of 0, the high-frequency current flows through the antenna 1bonly and the current ratio is 0. If the impedance is greater than 0, the currents flowing through the antennas 1aand 1bhave an identical phase and the current ratio is positive. On the other hand, if the impedance is smaller than 0, the currents flowing through the antennas 1aand 1bhave different phases and the current ratio is negative.

[0073] FIG. 13 shows the uniformity in the density of plasma ion saturated current on the electrode 5 when the current ratio is varied. A positive uniformity means that the plasma density is high in the center and a negative uniformity means that the plasma density is high in the periphery. By controlling the current ratio, the plasma ion saturated current density can be controlled to be even in the whole area (from center to periphery). The experimental equipment shown in FIG. 11 can control the uniformity of the plasma ion saturated current density by 50%.

[0074] FIG. 14 shows the amplitude (peak-to-peak) of a voltage which is generated in the electrostatic capacitive coupling antenna 8awhen the electrostatic capacitance of the variable capacitor 16bis varied. As can be seen, the use of a discharging circuit comprising a series connection of an inductive antenna and an electrostatic capacitive coupling antenna can control the voltage on the electrostatic capacitive coupling antenna 8ain a wider range than the conventional circuit using the floating capacitance (0 to a maximum of about 1000 V).

[0075] Although the third embodiment of the present invention uses two inductive coupling antennas, the plasma processing apparatus can have three or more inductive coupling antennas to control the plasma distribution with a higher precision.

[0076] A fourth embodiment of the present invention will be described in detail with reference to FIG. 15 and FIG. 16. FIG. 15 is a perspective view of the plasma processing apparatus. Symbols in FIG. 15 denote the same members as those in FIG. 10. Their explanation is omitted here. FIG. 10 and FIG. 15 are different from each other in that the inductive coupling antennas 1aand 1bare connected differently in the discharging circuit. Namely, in this discharging circuit, the electrostatic capacitive coupling antenna 8ais connected in series with a series connection of the inductive coupling antennas 1aand 1b. To control the current which flows through the electrostatic capacitive coupling antenna 8a, a variable-impedance load 17ais connected in parallel with the electrostatic capacitive coupling antenna 8a. Further, to control the currents which flow through the inductive coupling antennas 1aand 1b, loads 17band 17care connected in series.

[0077] FIG. 16 shows an equivalent circuit of the discharging circuit of the plasma processing apparatus of FIG. 15. This circuit represents the inductive coupling antennas 1aand 1bas load 9aand load 9b, respectively, and the electrostatic capacitive coupling antenna 8aas load 11. In this embodiment, the magnitude of the inductive coupling discharge is controlled by the magnitude of the load 17a. As the impedance of the load 17aincreases, the current flowing through the load 11 increases and, consequently, the plasma produced by electrostatic capacitive coupling discharge becomes greater. Similarly, as the impedance of the load 17bor 17cincreases, the inductive coupling discharge produced by the inductive coupling antenna 1aor 1bbecomes greater. Therefore, the same effects as those of the first through third embodiments can be obtained by controlling the impedances of loads 17a, 17b, and 17c.

[0078] Although the fourth embodiment of the present invention has loads 17a, 17b, and 17c, which are respectively connected in parallel with the inductive coupling antennas 1aand 1band the electrostatic capacitive coupling antenna 8a, one of the loads 17a, 17b, and 17ccan be omitted for the same control effect.

[0079] For impedance matching, it is preferable that the reactance of the load 17ashould be negative to avoid parallel resonance, because the reactance of the impedance of the electrostatic capacitive coupling antenna 8ais negative. Similarly, it is preferable that the reactances of loads 17band 17cshould be positive to avoid parallel resonance, because the reactances of the impedances of the inductive coupling antennas 1aand 1bare positive.

[0080] If the reactance of the load of the discharging circuit to be impedance-matched is negative and the inverted-L-type matching box 3 is disabled, an inductor should be inserted in series between the matching box 3 and the discharging circuit to enable impedance matching.

[0081] A fifth embodiment of the present invention will be described in detail with reference to FIG. 17 and FIG. 18. FIG. 17 is a perspective view of the plasma processing apparatus of the present invention. Symbols in FIG. 17 denote the same members as those in FIG. 15. Their explanation is omitted here. FIG. 17 and FIG. 15 are different from each other in that the inductive coupling antennas are connected differently in the discharging circuit. Namely, in this discharging circuit, the electrostatic capacitive coupling antenna 8ais connected in series with a series connection of the inductive coupling antennas 1aand 1b. To control the current which flows through the electrostatic capacitive coupling antenna 8a, a variable-impedance load 17ais connected in parallel with the electrostatic capacitive coupling antenna 8a. Further, a circuit is provided to ground the connection point of the inductive coupling antennas 1aand 1bvia a variable-impedance load 17b.

[0082] FIG. 18 shows a circuit equivalent to the discharging circuit of FIG. 17. This circuit represents the inductive coupling antenna 1aas load 9a, the inductive coupling antenna 1bas load 9b, and the electrostatic capacitive coupling antenna 8aas load 11. In this embodiment, the magnitude of the inductive coupling discharge is controlled by the magnitude of the load 17a. As the impedance of the load 17aincreases, the current flowing through the load 11 increases. Consequently, the ratio of plasma generated by the electrostatic capacitive coupling discharge becomes greater.

[0083] Further, the load 17bis connected in parallel with a series connection of loads 9band 11. Therefore, the inductive coupling discharge produce by the inductive coupling antenna 1band the electrostatic capacitive coupling discharge produced by the electrostatic capacitive coupling antenna 8acan be controlled by regulating the impedance of the load 17b.

[0084] For impedance matching, it is preferable that the reactance of the load 17ashould be negative to avoid parallel resonance because the reactance of the impedance of the electrostatic capacitive coupling antenna 8ais negative. Similarly, to prevent a parallel resonance with the circuit connected in parallel with the load 17b, it is preferable to make the reactance of the load 17bpositive when the combined reactance of the loads 9b, 11, and 17ais positive or to make the reactance of the load 17bnegative when the combined reactance is negative. If the reactance of the load of the whole discharging circuit to be impedance-matched is negative and the inverted-L-type matching box 3 is disabled, an inductor should be inserted in series with the load 9ato enable impedance matching.

[0085] Therefore, the same effects as those of the first through third embodiments can be obtained.

[0086] A sixth embodiment of the present invention will be described in detail with reference to FIG. 19. FIG. 19 is a sectional view of the plasma processing apparatus of the present invention. The basic concept of this embodiment is the same as that of the first through third embodiments, but the discharging section 20aof the vacuum chamber 20 and the antennas (21 and 28) have different shapes. In this embodiment, the discharging section 20ais cylindrical and the cylindrical electrostatic capacitive coupling antenna 28 wholly covers the cylindrical discharging section 20a. Two inductive coupling antenna coils 21aand 21bare provided on the ceiling of the discharging section 20a.

[0087] In this embodiment, the two inductive coupling antenna coils 21aand 21bproduce strong electric fields in areas 25eand 25fand the electrostatic capacitive coupling antenna 28 produces a strong electric field in area 25g. These strong electric fields produce plasma. Since the cylindrical electrostatic capacitive coupling antenna 28 covers the whole cylindrical discharging section 20a, the electric field in area 25gcovers the inner wall of the discharging section 20a. Therefore, the electrostatic capacitive coupling discharge can prevent the deposition of byproducts on the inner wall of the discharging section 20aor clean deposits from the inner wall.

[0088] Further, the inductive coupling antenna 21aon the ceiling of the discharging section 20ais smaller in diameter than the inductive coupling antenna 21b. Consequently, the plasma produced by the inductive coupling antenna 21ais strongest in the center and the plasma produced by the inductive coupling antenna 21bis strongest in the circumferential area. This embodiment can produce the same effect as that of the other embodiments by using any of their discharging circuits.

[0089] As aforesaid, the plasma processing apparatus in accordance with the present invention controls the ratio of high-frequency currents which flow in the inductive coupling antenna(s) and the electrostatic capacitive coupling antenna. The plasma processing apparatus can also control the ratio of electrostatic capacitive coupling discharge and inductive coupling discharge by changing the impedances of the load 17 and the variable capacitor 16 in the discharging circuit. This can suppress deposition of byproducts on the inner wall of the vacuum chamber during plasma processing. This plasma processing apparatus can also control the distribution of plasma, which enables uniform and various plasma processing, such as etching by plasma.

[0090] The present invention is not limited to the aforesaid first through sixth embodiments. The discharging circuit of the plasma processing apparatus can be built up with a combination of these embodiments. The vacuum chamber need not be divided into two sections (a discharging section and a processing section) and the shape of the discharging section is not limited to those examples provided in the embodiments.

[0091] For example, the vacuum chamber can be shaped as shown in FIG. 20 through FIG. 23. Further, the electrostatic capacitive coupling antenna can be located outside the inductive coupling antenna as shown in FIG. 22, attached to the outer surface of the vacuum chamber, or embedded in the vacuum chamber.

[0092] The reference numerals 20c, 20d, and 20edenote vacuum chambers and at least their parts opposite to the antennas are made of non-conductive material. Reference numeral 21 denotes an inductive coupling antenna. Reference numerals 28a, 28b, 28c, and 28ddenote electrostatic capacitive coupling antennas.

[0093] The present invention is applicable to apparatuses for and methods of using plasma (e.g. etching, CVD, sputtering, etc.) and can process various materials such as semiconductor wafers, liquid crystal display substrates, magnetic heads, etc., to the extent that they can be processed by plasma.

[0094] Further, the present invention can be applied to semiconductor manufacturing processes of the type illustrated in FIG. 24, which shows one semiconductor processing example using the present invention. This process uses one of the plasma processing apparatuses of the aforesaid embodiments.

[0095] In the semiconductor processes, a process recipe is determined to process wafers uniformly (for etching or layer formation) by selecting and controlling the kinds of process (etching) gases, gas pressures in the vacuum chamber, gas flow rates, high-frequency power to be applied to the antennas, etc. To etch aluminum substrates, for example, a chlorine or boron trichloride gas is used. To etch silica substrates, C₄F₈gas is used as a process gas.

[0096] To etch the aforesaid materials by a conventional plasma processing method, different kinds of apparatuses are required because the distribution of plasma varies if the kind of gas or the pressure changes.

[0097] However, the plasma processing apparatus in accordance with the present invention can process two kinds of wafers with a fixed uniform plasma distribution in each process just by adding processes 31a, 31b, and 31cfor controlling high-frequency currents which flow through the inductive coupling antennas to control the plasma distribution and by placing process 30aafter process 31a, process 30bafter process 31b, and process 30cafter process 31c.

[0098] This eliminates the steps required to transfer wafers between one plasma processing apparatus and another, and increases the throughput. Further, as the plasma processing apparatus in accordance with the present invention can perform a plurality of processes, no extra device is required.