Plasma processing apparatus

Abstract: Microwaves supplied from a magnetron (3; 32) through a waveguide (2; 30) are resonated in a cavity resonator (1; 31) to increase their amplitude. The resonated microwaves are emitted into a plasma production chamber (6; 33) through slits (5c, 5c′, 5c″; 43a) and a wall (4, 33a). Then plasma is produced in the plasma production chamber (6; 33) into which plasma processing gas is introduced. The plasma is employed for uniformly processing a substrate (12).

Description: The invention relates to a plasma processing apparatus for processing a substrate according to claim 1. This apparatus is suited for carrying out the respective techniques of CVD, etching, sputtering, ashing, etc. at high speed. Devices using low-temperature plasma roughly includes two categories. One consists of applying a high frequency voltage at about 10 kHz to 30 MHz to one of two parallel plate electrodes in a vacuum to create the plasma (see "HANDOTAI KENKYU" No. 18, pages 121 - 137, 145 - 169). The other introduces microwaves with 2.45 GHz into a vacuum chamber to create the plasma. Conventionally, the device belonging to the former category has been mainly used. On the other hand, the miniaturization of semiconductor devices has caused the problem that the bombardment of ions which is generated in plasma-processing disadvantageously influences the device performance. It has been also required to increase the processing speed in order to improve the processing capability. In order to increase the processing speed, only increasing the density of plasma or the radical concentration of the plasma, which means the concentration of active particles immediately before the ionization, is not sufficient. Specifically, the energy of ions plays an important role in dry etching using plasma and plasma CVD. In the case of dry etching, if the ion energy is too high, the underlying film will be cut or the crystal structure will be badly influenced, thus deteriorating the device performance. On the other hand, if the ion energy is too low, the polymer formed on the etched face will not be sufficiently removed, thus reducing the etching speed; or inversely a passivation film of the polymer will not be formed but the side of the pattern will be etched, thus reducing the dimension accuracy of the pattern. Also in the plasma CVD, the magnitude of ion energy influences the quality of the formed film in such a way that low ion energy leads to coarse film composition while high ion energy leads to dense film composition. Thus, it is indispensable for the future plasma processing to densify the plasma and also properly control the ion energy. Examples of such a plasma processing are the systems of producing plasma using microwaves such as disclosed in JP-A-56-13480 (US-A-4 492 620) and JP-A-56-96841. The EP-A-103 461 shows a plasma deposition apparatus with a plasma formation chamber functioning as a resonator. In the plasma formation chamber gas is introduced to produce a plasma. This apparatus furthermore includes a specimen chamber and a target made of sputtering material interposed between a plasma extraction window and a substrate. Furthermore, the EP-A-103 461 describes a waveguide for transmitting microwaves from a microwave generation source. Since the plasma formation chamber functions as a resonator, the wave length of the microwaves in the resonator deviates when plasma is produced therein and, hence, this state of resonance of the microwaves is not stable when plasma is produced in the resonator. The EP-A-183 561 describes a microwave plasma processing apparatus with a microwave transmission window disposed perpendicular to an electrical field of progressive microwaves transmitted in a waveguide. The microwave transmission window is provided with openings for effectively preventing the breakage of the window without narrowing the plasma area when the window of a weak material such as alumina is subjected to atmospheric pressure. The EP-A-183 561 relates to a basic plasma etching apparatus with no provision for amplifying microwaves and means for homogenizing the plasma for gaining a high quality wafer processing. When plasma is to be produced using microwaves, only the emitting of the microwaves, which is generated by means of a magnetron, into a highly evacuated plasma producing chamber cannot satisfactorily produce plasma. This is because the field strength of the microwaves generated is not so high that the electrons are supplied with a sufficient energy. Thus, in order to sufficiently produce the plasma using microwaves, there have been proposed two techniques: one is to supply the electrons with energy in a cyclotron resonance condition occurring when the cyclotron frequency, which is the orbitral motion frequency when electrons travel in the plane perpendicular to a magnetic field, and the frequency of the microwaves are made equal to each other, and the other is to supply the electrons with an energy corresponding to an electrical field strength which is increased by emitting the microwaves into a cavity resonator to increase the amplitude of the microwaves. The former, which is generally referred to as ECR (Electron Cyclotron Resonance) technique, is disclosed in the above JP-A-56-13480 and US-A-4 492 620. The latter is disclosed in the above JP-A-56-96841. In the case of these techniques, the plasma generated by the microwaves includes the electrons directly supplied with energy from the microwaves so that the voltage across the sheath formed between the plasma and the substrate almost does not vary. Thus, by appropriatly controlling the voltage across the sheath with the high frequency voltage being applied to the electrode on which a substrate is placed, it is possible to provide the plasma with a higher density and control the ion energy properly for a high speed processing. Again, in the plasma processing, the ion energy plays an important role. However, in the prior art the ECR technique disclosed in the above JP-A-56-13480, when a high frequency voltage is applied to the electrode on which the substrate is placed, the high frequency current flows towards the surrounding processing chamber since the ground electrode is not arranged on the side opposite to the above electrode. Thus, the effect of ion energy on the substrate is greater on its periphery and is smaller on its center. Therefore, the entire substrate cannot be processed under a uniform condition. In the prior art technique of using a cavity resonator such as disclosed in the above JP-A-56-96841, the plasma is produced in the cavity resonator so that when the plasma is produced, the wavelength of the microwaves is changed according to the plasma density. Thus, the resonance condition is not satisfied and accordingly the plasma will be unstable. More specifically, since the resonance condition is satisfied before the plasma is produced, the electric field strength of the microwaves becomes greater, thus eventually producing the plasma. However, when the plasma density of the plasma thus produced becomes higher, the wavelength of the microwave will be changed. Thus, the resonance condition will not be satisfied, thereby decreasing the electric field strength. Then, the electrons will be supplied with lower energy and so the plasma density will be decreased. Once the plasma density is decreased, the resonance condition will be satisfied again and the plasma density will be higher. Due to such a phenomenon, it is difficult to produce stabilized plasma using the cavity resonator. Moreover, when the electrode for applying a high frequency voltage is arranged in the cavity resonator in order to control the energy of the ions incident to the substrate from the plasma, reflections of the microwaves or the like will occur so that the plasma formed will furtheron be unstable. The object of the invention is to provide a plasma processing apparatus for processing a substrate which is capable of producing stabilized and high density plasma and is able of providing a uniform energy of ions incident to the substrate over the entire substrate. This object is solved according to the features of claim 1. The dependent claims show advantageous embodiments and further developments of the invention. To attain this object, in accordance with this invention, there is provided a plasma processing apparatus comprising a microwave generation source, a waveguide for supplying the microwaves from the microwave generation source, a cavity resonator at an atmospheric pressure connected with the end of the waveguide to resonate the microwaves, a plasma producing chamber, and a wall with at least one slit provided for relatively uniformly emitting the resonated microwaves into the plasma producing chamber. One gist of this invention is that the waveguide is connected with the cavity resonator and the microwaves are supplied into the plasma producing chamber through the at least one slit provided at the cavity resonator. In such a construction, when the microwaves propagate in the cavity resonator, the microwaves are resonated by the wall in the resonator and the like and also the current corresponding to the electromagnetic field generated flows in the interior surface. If the slit is provided at the boundary between the cavity resonator and the plasma producing chamber so as to traverse the current, charges are accumulated at both ends of the respective slit. Since the amount of the charges accumulated is varied along with the propagation of the microwaves, the electric field at both ends of the slit is also varied. Thus, the microwaves are uniformly emitted from the cavity resonator into the plasma producing chamber. In this way, when the waveguide is conneced with the cavity resonator, the microwaves with an increased amplitude through the resonance in the cavity resonator are emitted into the plasma producing chamber through the slit. The area of the at least one slit is about 1/3 or 1/10 of the sectional area of the resonator. Thus, even if the plasma producing chamber is not formed in a cavity resonator structure unlike the prior art, a high density plasma can be produced. Therefore, the electrode structure according to this invention doesn't have any restriction relative to the cavity resonator. Moreover, since the plasma is not produced in the cavity resonator, the resonance state therein remains unchanged, and so a stabilized plasma can be produced. Further, a cavity resonator connected to ground can be used as an electrode opposite to and in parallel to the electrode on which the substrate is placed, as in the system of parallel plate electrodes, so that the effect of ion energy can be made uniform over the entire substrate. Another gist of this invention is that a slit plate (wall) integral to the cavity resonator is provided, having plural slit-like openings extending towards the plasma producing chamber and gas flow paths extending from a gas supply source to the plasma producing chamber. In such a structure, the gas flow paths are formed among the slit-like openings of the slit plate so as to open towards the plasma producing chamber so that gas can be supplied shower-like into the plasma producing chamber without obstructing the path for introducing the microwaves. Thus, high density plasma can be uniformly provided to the entire substrate. Moreover, this invention is also characterized in that the slit is formed by a plating technique, that a high frequency power supply is connected between a conductive slit plate with slits and the electrode on which the substrate is placed, and that the application of the high frequency voltage is switched between the slit plate and the electrode. Examples of the invention are described in more detail with reference to the drawings in the following. Fig. 1 is a perspective view of one embodiment of the invention, Fig. 2 is a plan view of one example of a wall provided with slits employed in the embodiment of Fig. 1, Fig. 3 is a plan view of an alternative example of the wall of Fig. 2, Fig. 4 is a plan view of another alternative example of the wall of Fig. 2, Fig. 5 is a perspective view of another embodiment according to the invention, Fig. 6 is a sectional view of the arrangement when this invention is applied to an ashing device, Fig. 7 is a sectional view of the arrangement when this invention is applied to a sputtering device, Fig. 8 is a plan view of a resonator employed in the sputtering device of Fig. 7; Fig. 9 is a sectional view of one embodiment when this invention is applied to an etching device or CVD device, Fig. 10 shows the electric field distribution in the resonance in the E₀₁ mode, Fig. 11 is a perspective view of the plasma processing apparatus according to another embodiment of the invention, Fig. 12 is a plan view of a slit plate (wall) employed in the embodiment of Fig. 11, Fig. 13 is a sectional view along the line XIII-XIII in Fig. 12, Figs. 14 to 16 show sectional views of several examples of a gas blow-out slit, Fig. 17 is a sectional view of the plasma processing apparatus of Fig. 11 in which the slit formed through a plating technique is provided on the side of the cavity resonator, Fig. 18 is a sectional view of the vacuum sealing portion of the slit which is formed by the plating technique and is provided on the plasma producing chamber, Fig. 19 is a sectional view of the slit in Fig. 14 which is formed through the plating technique, Fig. 20 is a plan view of the ceramic plate of Fig. 19, Fig. 21 is a sectional view of the ceramic plate of Fig. 19, Fig. 22 is a sectional view of the plasma processing apparatus according to a further embodiment of the invention and Fig. 23 is a sectional view of a modification of the plasma processing apparatus of Fig. 22. Now referring to Fig. 1, one embodiment of this invention will be explained. In Fig. 1, 1 is a circular cavity resonator in E₀₁ mode to which microwaves are supplied from a magnetron 3 through a waveguide 2. The waveguide 2 is eccentrically attached to one side of the circular cavity resonator 1 so as to provide a desired coupling with the E₀₁ mode. On the other side of the circular cavity resonator 1 a ceramic plate 4 and a wall having at least one slit (slit plate) 5 are attached in this order. The slit plate 5 is connected with a plasma producing chamber 6. The plasma producing chamber 6 is separated from a circular cavity resonator 1 by a plate made of microwave-transmitting material such as ceramics or quartz. The circular cavity resonator 1 is provided with atmospheric pressure in its interior in which microwaves are reflected at the inner wall so as to be resonated. Therefore, the microwaves supplied through the waveguide 2 are resonated in the circular cavity resonator 1 so that they are increased in their amplitude and thereby in their energy. The planar structure of the slit plate 5 is shown by 5c in Fig. 2. As shown, the slit part 5c includes ring-shaped slit openings (referred to as simply slits) in the direction perpendicular to the electrical field in the E₀₁ mode. The resonance in the E₀₁ mode occurs in the electrical field distribution as shown in Fig. 10. Then, the surface current as indicated by broken lines flows on the interior surface of the cavity resonator 1. The surface current on the bottom surface of the cavity resonator 1 flows from its center towards its periphery as shown in Fig. 2, indicated by broken lines. The slit plate 5 is located at the position corresponding to this bottom surface and so the slits 5c are provided in the direction perpendicular to the surface current. The charges due to the surface current are accumulated at both ends of each of these slits 5 so that the electrical field is generated in the slit part 5. This electrical field is varied with the frequency of 2.45 GHz so that the microwaves are emitted from the slits 5c. The length of the slits 5c is set to 60 mm, which corresponds to 1/2 of the wavelength of the microwaves (2.45 GHz) or more, to satisfactorily emit the microwaves. The width of the slits 5c ranges preferably from 5 mm to 15 mm although it varies in accordance with the kind of processing gas. Moreover, in order that the microwaves can be emitted uniformly over the entire periphery of a substrate, many slits 5c are provided so as to occupy about 1/3 to 1/10 of the entire area of the slit plate 5. In the plasma producing chamber 6 there are provided an electrode 7 on which the substrate to be processed is placed, a gas supply tube 9 and a gas exhaust tube 10. The electrode is fixed to the plasma producing chamber 6 by means of an insulator 8 and is connected with a high frequency power supply 11. (The plasma producing chamber 6, the slit plate 5 and the cavity resonator 1, etc. are connected to ground). The gas supply tube 9 is adapted to supply a predetermined amount of plasma processing gas from a gas source (not shown). The gas exhaust tube 10, which is connected with a vacuum evacuation pump, is adapted to control the pressure in the plasma producing chamber in the range of 1,3·10² to 1,3·10⁻¹ Pa. In operation, the magnetron 3 is operated to oscillate the microwaves which are supplied to the circular cavity resonator 1 through the waveguide 2. The energy of the microwaves with the amplitude increased in the cavity resonator 1 is emitted into the plasma producing chamber 6 through the slits 5c. Since the amplitude of the microwaves emitted into the plasma producing chamber 6 has been increased in the cavity resonator 1, plasma is produced in the plasma production chamber 6 even if the plasma producing chamber 6 has not a cavity resonator structure. Explanation will be given for the case where the device according to one embodiment of this invention is applied to etching. First, etching gas is supplied from the gas supply tube 9 into the plasma producing chamber 6. With the plasma producing chamber 6 evacuated to a prescribed pressure via the gas exhaust tube 10, the plasma due to the microwaves is produced between the slit plate 5 and the electrode 7. (Since the microwaves directly act on the electrons in the plasma, the potential difference between the plasma and the electrode 7 is in the level of 20 to 30V.) With the wafer (substrate 12) to be processed being placed on the electrode 7, a high frequency voltage is applied to the electrode 7 from the high frequency power supply 11. Since the electrode 7 and the slit plate 5 connected to ground are arranged in parallel to each other, a high frequency current uniformly flows between the electrode 7 and the slit plate 5 connected to ground. Thus, the electrical field occurring between the electrode 7 and the plasma becomes uniform. Accordingly, with the high frequency voltage applied, the ions of etching gas are controlled so as to be incident to the waver with the uniform energy over the entire wafer surface. The ions in the etching gas and/or the radicals of the etching gas excited in the plasma act on the film to be processed on the wafer. By this way, the etching proceeds. Since the energy of the incident ions during the etching is uniform, the etching can be carried out uniformly over the entire wafer. Explanation will be given for the case where the device according to the one embodiment of this invention is applied to plasma CVD. SiH₄ and mixed gas of N₂ and N₂O are supplied from the gas supply tube 9. N₂O and SiH₄ are decomposed by the produced plasma to create SiO, which is formed on the wafer as a film. The film quality is controlled by the incidence of the ions from the plasma. Since the incidence energy of the ions can be made uniform, the film can be formed uniformly on the entire wafer. Although in this embodiment, the resonance mode in the circular cavity resonator 1 was the E₀₁ mode, any other suitable mode can be used. However, the emission efficiency is higher when the slits are in the direction perpendicular to the current flowing in the cavity resonator surface. Thus, the slit plate preferably has the structure as shown in Fig. 3 in the case of the H₀₁ mode and the structure as shown in Fig. 4, in the case of the H₁₁ mode. (Refer to "Microwave Technique" by H. Abe, Tokyo Univ. pp. 71-74, 105-108, 143-145). As described above, in accordance with this embodiment of the invention, the effect of ion energy indispensable to the plasma processing can be made uniform and also stabilized plasma can be produced. Meanwhile, in the embodiment of Fig. 1, the microwaves are only emitted into the plasma producing chamber. Therefore, when the density of the produced plasma exceeds 10¹¹cm⁻³, the microwaves are reflected and the plasma density cannot be further enhanced. Thus, if the plasma density is higher than 10¹¹cm⁻³, a magnetic field 15 which is in parallel to the emitting direction of the microwaves is provided by coils 13 and 14 as shown in Fig. 5. In this embodiment, since the amplitude of the microwaves is increased in the cavity resonator 1, the state of electron cyclotron resonance is not required, but the magnetic field strength in accordance with the required plasma density can be selected. Moreover, since the amplitude of the microwaves can be made greater than the prior art resonance system, stabilized plasma discharge can be produced in the region evacuated to a higher degree. An embodiment in which this invention is applied to an ashing processing will be explained with reference to Fig. 6. Only different matters from the embodiment of Fig. 1 will be explained since the parts indicated by the same reference numerals in Figs. 1 and 6 perform the same operations. A mesh plate 20 is located in the interior of the plasma producing (processing) chamber 6 and a wafer (substrate 12) is placed on a table 7 which is also provided in the plasma producing chamber 6. Oxygen gas is supplied from the gas supply tube 9. The magnetron 3 is operated to supply microwaves thereby to produce plasma between the slit plate 5 and the mesh plate 20. Since the mesh plate 20 is dimensioned so as not to transmit the microwaves, the plasma is confined between the mesh plate 20 and the slit plate 5. The oxygen gas which has been placed in the radical state due to the plasma is supplied onto the wafer through the mesh plate 20. The oxygen radicals ashing-process applies the resist film on the wafer. In the embodiments mentioned above, a combination of a circular cavity resonator and a slit plate has been employed, but this invention is not limited to it. Another embodiment in which this invention is applied to a sputtering device will be explained with reference to Fig. 7. A processing chamber (plasma producing chamber 33) made of ceramics or quartz is adapted to control the pressure therein in the range of 1,3·10⁻² to 1,3 Pa by means of a gas supply tube and a gas exhaust tube. A target 34 and a wafer table 36 are placed in the processing chamber. The target 34 is connected with a high frequency power supply 35 and the wafer table 36 is connected to ground. A shield chamber 40 and a square-ring shape resonator 31 are provided on the exterior of the processing chamber. The square-ring shape resonator 31 is provided by forming a square waveguide in a ring-shape with the route length of the ring being an integer times 1/2 of the wavelength in the waveguide. The ring-shaped waveguide is provided with a terminating wall so as to preventing the phase of the resonating microwaves from being shifted. The planar structure of the ring-shaped resonator 31 is shown in Fig. 8. The resonator 31 is supplied with microwaves from a magnetron 32 through a waveguide 30. The shield chamber 40 (Fig. 7) is in its exterior provided with coils 37 and 38 so as to generate a cusped magnetic field 42, which is more concretely disclosed in US-A-76 905 and EP-A-85110155. The shield chamber 40 is made of stainless steel which does not outwardly transmit microwaves but transmit the magnetic field. The ring-shaped resonator 31 is, in its interior, provided with a slit means 43 in which a slit 43a is formed in the entire periphery. When microwaves are supplied into the ring-shaped resonator, the amplitude of the microwaves is increased in the resonator and the microwaves with the increased amplitude are emitted into the processing chamber through the slit 43a. When the pressure in the processing chamber into which argon gas has been introduced is maintained at 1,3·10⁻¹ Pa, the plasma confined in the cusped magnetic field 42 is produced between the target 34 and the wafer table 36. Next, with the high frequency voltage applied to the target 40 from the high frequency power supply 35, ions of argon gas are directed to the target, thus sputtering the target material so as to form a film on the wafer (substrate 39). In this embodiment also, as in the embodiment of Fig. 5, the microwaves with the increased amplitude permit stabilized plasma to be produced under the condition of high degree vacuum, thus improving the film quality. The system using such a combination of the ring-shaped resonator and the slit can also be applied to etching and plasma CVD as well as to sputtering. Thus, an embodiment in which this combination is applied to etching will be explained with reference to Fig. 9. Since the basic construction thereof is the same as the sputtering device of Fig. 7, only the difference therefrom will be explained. A lower electrode 46 and an upper electrode 45 are located in the processing chamber (plasma producing chamber 33). The lower electrode 46, fixed to the processing chamber through the insulator 41, is so adapted that a high frequency voltage is applied thereto from the high frequency power supply 47. The upper electrode 45 is connected to ground. In operation, etching gas is introduced into the processing chamber and the pressure therein is maintained at 1,3 Pa. In this state, microwaves are supplied into the ring-shaped resonator 31. Then, the microwaves are amplified in their amplitude and emitted into the processing chamber through the slit 43a. Thus, the plasma due to the microwaves is produced between the upper electrode 45 and the lower electrode 46 in the processing chamber. In this state, when the high frequency voltage is applied to the lower electrode 46, a high frequency current flows uniformly between the parallel plate electrodes and also the ions of the etching gas incident to the wafer are accelerated by the uniform potential difference across the sheath, thus providing uniform etch-processing property to the entire wafer surface. As shown in Figs. 7 to 9, the processing chamber is entirely made of ceramics or quartz. However, it is not necessary to do so, but it may be constituted so that electrodes 34 and 36, or 45 and 46 are isolated from the shield chamber 40 and a part 33a (separating member) through which microwaves are introduced isolates the processing chamber from the ring-shaped resonator 31. As described above, in accordance with this embodiment, for producing plasma using microwaves in the plasma producing chamber, another electrode can be located oppositely to the one electrode on which the wafer is placed. This enables uniform plasma processing to the wafer. Moreover, since the plasma producing chamber needs not to be made in a cavity resonator structure, the electrodes and the plasma producing chamber don't have any limitation to their structure. Further, in accordance with this invention, stabilized plasma can be produced using microwaves. In accordance with this invention, the plasma producing device doesn't have any limitation to its structure in relation to the cavity resonator. Then, the cavity resonator, connected to ground, can be employed as an opposite electrode in parallel to the electrode on which an object to be processed is placed. Thus, since the energy of the microwaves can be propagated through the slit attached to the opposite electrode, the effect of the ions and/or radicals created by the energy can be uniformly given to the object. Further, the plasma processing can be carried out with an optimum ion energy in a high speed process, some miniature patterns of a semiconductor wafer can be made with high accuracy in a high speed process and with less damage; and a uniform film can be formed in a high speed process. Now referring to Figs. 11 to 16, another embodiment of the invention will be explained. In these drawings, components 1 to 4, 6 to 8, 10 and 11 are the same as those shown in Fig. 1, in their structure and function, but a slit plate 5' and a gas supply tube 9' are different from the corresponding components in Fig. 1. More specifically, as shown in Figs. 12 and 13, the slit plate 5' is, among the plural slits 5c, provided with a continuous concentrical groove 5d and a great number of pores 5e which open from the groove 5d into the plasma producing chamber 6. Thus, as can be seen from Figs. 11, 12 and 13, if the slit plate 5' and the ceramic plate 4 are stacked in intimate contact to each other, gas flow paths communicating the gas supply tube 9' with the plasma producing chamber 6 are formed between the slit plate 5' and the ceramic plate 4 by means of the groove 5d and the pores 5e. These gas flow paths serve to jet the gas from the gas supply tube 9' in a shower-like manner towards the substrate placed on the electrode 7 in the plasma producing chamber 6. The gas exhaust tube 10, connected with a vacuum evacuation pump (not shown), is adapted to control the pressure in the plasma production chamber 6 at 1,3·10² to 1,3·10⁻¹ Pa. Explanation will be given for the cases where this embodiment of the invention is applied to etching and plasma CVD. First, the magnetron 3 is operated to oscillate microwaves which are supplied into the cavity resonator 1 through the waveguide 2. The microwaves are increased in their amplitude in the cavity resonator 1 and the microwaves are emitted into the plasma producing chamber 6 through the slits 5c. Since the amplitude of the microwaves has been increased in the cavity resonator 1, plasma is produced and maintained in the plasma producing chamber 6 even if the chamber is not made in a cavity resonator structure. In this state, etching is carried out as follows. First, etching gas is supplied from the gas supply tube 9' into the plasma producing chamber 6. With the plasma producing chamber evacuated to a prescribed pressure from the gas exhaust tube 10, the plasma due to the microwaves is produced between the slit plate 5' and the electrode 7. (Since the microwaves directly act on the electrons in the plasma, the potential difference between the plasma and the electrode 7 is in the level of 20 to 30V.) Thereafter, with the wafer to be processed being placed on the electrode 7, a high frequency voltage is applied to the electrode 7 from the high frequency power supply 11. Since the electrode 7 and the slit plate 5' connected to ground are arranged in parallel to each other, a high frequency current uniformly flows between the electrode 7 and the slit plate 5' connected to ground. Thus, the electrical field occurring between the electrode 7 and the plasma becomes uniform. Accordingly, with the high frequency voltage applied, the ions of etching gas are controlled so as to be incident to the wafer with the uniform energy over the entire wafer surface. The ions in the etching gas and/or the radicals of the etching gas excited in the plasma act on the film to be processed on the wafer (substrate 12). In this way the etching proceeds. Since the energy of the incident ions during the etching and also the gas flow are uniform, the etching can be carried out uniformly over the entire wafer. Plasma CVD is carried out as follows. SiH₄ and mixed gas of N₂ and N₂O are supplied from the gas supply tube 9'. N₂O and SiH₄ are decomposed by the produced plasma to create SiO, which is formed on the wafer as a film. The film quality is controlled by the incidence of the ions from the plasma. Since the incidence energy of the ions can be made uniform, the film can be formed uniformly on the entire wafer surface. Incidentally, the slits in the slit plate 5' may be formed as shown in Figs. 2, 3 and 4 in accordance with the resonance modes of E₀₁, H₀₁ and H₁₁, respectively. Alternative examples of the gas flow paths in the embodiment of Figs. 11 to 13 will be explained with reference to Figs. 14 to 16. In the examples shown in Figs. 14 and 15, a slit plate 5'' is sandwitched between the ceramic plate 4' and a gas jet plate 5f. The gas jet plate 5f is made of alumina ceramic, quartz, etc. which can transmit microwaves. In Fig. 14, a groove 5d' and pores 5e' which form gas flow paths are formed in the gas jet plate 5f while in Fig. 15, the groove 5d' and the pores 5e' are individually in the slit plate 5'' and the gas jet plate 5f. In Fig. 16 in which the gas jet plate 5f is not used, in order to facilitate the emission of microwaves, the slit plate 5''' is provided with tapered slits 5c''. Incidentally, the ceramic plate 4' is not limited to ceramic but can be made of any material which can transmit microwaves. In accordance with this embodiment of the invention, for producing plasma using microwaves in the plasma producing chamber, another electrode can be located oppositely to the one electrode on which the wafer is placed, and the gas can he uniformly directed to the wafer in a shower-like manner. This enables uniform plasma processing to the wafer. Moreover, since the plasma producing chamber needs not to be made in a cavity resonator structure, the electrodes and the plasma producing chamber don't have any limitation to their structure. Further, since the energy of the resonated microwaves can be propagated through the slits 5c' and 5c'' and the gas can be uniformly directed to the wafer, the effect of the ions and/or radicals created by the energy of microwave can be uniformly given to the object to be processed. Moreover, since the effect of the ions and/or radicals can be uniformly made, the plasma processing can be carried out with an optimum ion energy and with a high speed process; some miniature patterns of a semiconductor wafer can be made with high accuracy, at high speed process and with less damage; and a uniform film can be formed at a high speed. Some changes or modification in the embodiments of this invention mentioned above will be explained below. As shown in Fig. 17, the slits 5c can be formed by plating the ceramic plate 4 with a gold coating 5''''. The gold coating 5'''' may be deposited on the side of the cavity resonator 1 with respect to the caramic plate (separating member 5). In this case, the pollution of the supplied gas due to the coating material does not occur since the coating 5'''' is not exposed to the gas atmosphere. The ceramic plate in the plasma processing device of Fig. 11 may be vacuum-sealed as shown in Fig. 18. More specifically, an O-ring 13 is sandwitched between the ceramic plate and the plasma production chamber 6 to vacuum-seal the ceramic plate. The ceramic plate is provided with slits formed by the gold coating 5'''' and the O-ring sealed surface of the ceramic plate is also plated with gold. Thus, the O-ring is surrounded by the gold coating 5'''' which is a conductor and the plasma producing chamber 6 and so microwaves don't invade the O-ring. Therefore, the O-ring 13 is not disadvantageously heated by the microwaves. The slits shown in Fig. 14 can be formed by gold coating 5'''' (or an equivalent conductor) on the ceramic plate 4' in such a manner as shown in Figs. 19 to 21. Specifically, as seen from Fig. 20, the lower ceramic plate 5''''' is provided with the continuous gas flow grooves 5d' which are succeeded by the circular gas jet pores 5e' having a diameter of about 1 mm. The gas supplied to the ceramic plate 5''''' is supplied into the plasma producing chamber 6 through the grooves 5d' and the pores 5e'. As seen from Fig. 21 the upper ceramic plate (separating member 4) is, on its lower surface, provided with a slit pattern formed through gold plating (the slits 5c''' are not plated). As shown in Fig. 21, the slit pattern covers the gas flow grooves 5d' of the slit plate 5' so that the microwaves don't invade the groove 5d'. Thus, plasma is not created in the grooves 5d' and the supplied gas is not advantageously decomposed there. Although according to the above modification, the slits have been formed by plating the ceramic plate with a conductor, these slits may be formed by applying the conductor to the ceramic plate or bonding a conductor foil thereto. Further, although gold has been used as the conductor, any other conductive material can be employed. In the case where the slits are formed on the side of the plasma producing chamber with respect to the ceramic plate, the slit plate may be preferably made of noble metal such as gold, silver, platinum, etc. Another embodiment of this invention will be explained with reference to Fig. 22. In Fig. 22, microwaves are supplied from the magnetron 3 to the cavity resonator 1 in the E₀₁ resonance mode through the waveguide 2. The waveguide 2 is provided with a choke flange 51 and an insulator 52 which are inserted on the way of the waveguide. The waveguide is eccentrically attached to the one side of the cavity resonator 1 so as to provide a desired coupling with the E₀₁ mode. On the other side of the cavity resonator 1 attached are in order the ceramic plate and the slit plate 5 having the slits 5c. The slit plate 5 is, in the lower side, connected with the plasma producing chamber 6 by means of an insulator 53. Incidentally, the ceramic plate serves to vacuum-seal the plasma producing chamber 6, so that the cavity resonator 1 may be floated and the high frequency power supply 11 may be connected with the cavity resonator 1. Furthermore leakage of microwaves from the waveguide may be prevented. A further embodiment of this invention will be explained with reference to Fig. 23. As shown in Fig. 23, a slit plate 55 is provided with the slits 5c located oppositely to the substrate 12. The slit plate 55 is, in its periphery, also provided with an inside convex portion 57 and an outside convex portion 59 which are separated from each other by an interval 58. The inside convex portion 57 provides a small gap 56 between its tip and the cavity resonator 1. The small gap 56 and the interval 58 integral therewith constitute a choke flange 51. A ring-shaped insulator 60 is inserted between the tip of the outside convex portion 59 and the cavity resonator 1, so that the cavity resonator 1 may be floated and the high frequency power supply 11 may be connected with the cavity resonator 1. Furthermore, leakage of microwaves from the waveguide may be prevented. The high frequency power supply 11 applies a high frequency voltage to the electrode 7 on which a subtrate is placed and the slit plate 55. The arrangement according to this embodiment can perform the cleaning of the slit plate 55 and the electrode 7 in addition to the plasma processing. More specifically, processing gas of CF₄ is introduced from the gas supply tube 9 into the plasma producing chamber 6. When a high frequency voltage is applied from the high frequency power supply 11 to the slit plate 55 by the switch 61, the energy of the ions from the plasma is increased, thereby cleaning the slit plate 55 at a high speed. Similarly, when the high frequency voltage is applied to the electrode 7, the electrode can be plasma-cleaned. High frequency power supplies may be provided individually for the slit plate 55 and the electrode as shown by dotted lines.

Claims: Plasma processing apparatus for processing a substrate (12, 39) comprising: a microwave generation source (3, 32), a waveguide (2, 30) for supplying the microwaves from the microwave generation source (3, 32), a cavity resonator (1, 31) for resonating the microwaves supplied from the waveguide (2, 30) to increase the amplitude thereof, including a wall (5, 5', 5'', 5''', 5'''', 55, 43) having at least one slit (5c, 5c', 5c'', 43a) disposed in a direction substantially perpendicular to a direction in which a surface current flows on the wall (5, 5', 5'', 5''', 5'''', 55, 43), a separating member (4, 4', 33a), provided on the wall (5, 5', 5'', 5''', 5'''', 55, 43), which can transmit the microwaves, and a plasma producing chamber (6, 33), separated from the cavity resonator (1, 31) by the separating member (4, 4', 33a), in which plasma is produced with introduced processing gas by the microwaves introduced through the at least one slit (5c, 5c', 5c'', 43a) and the separating member (4, 4', 33a), for processing the substrate (12, 39) by the plasma in the plasma producing chamber (6, 33). Apparatus according to claim 1, characterized in that the cavity resonator (1) is formed in the shape of a cylinder (1) and the wall (5, 5', 5'', 5''', 5'''', 55) is provided in form of a slit plate on the bottom surface so as to be one wall with the plasma producing chamber (6). Apparatus according to claim 1, characterized in that the plasma producing chamber (6) is provided with means (13, 14) for generating a magnetic field for increasing the plasma density. Apparatus according to claim 1, characterized in that the plasma producing chamber (6) is provided with a grid plate (20) facing the substrate (12) for shielding the ions in the plasma. Apparatus according to claim 1, characterized in that electrodes (34, 36; 45, 46) are arranged opposite to each other on the upper and lower sides in the plasma producing chamber (33), the cavity resonator is a ring-shaped resonator (31) provided around the plasma producing chamber (33) and the slit (43a) is attached to the inner peripheral wall (43) of the resonator (31). Apparatus according to claim 1, characterized in that the separating member (4, 4', 33a) is made of a ceramic or quartz substrate. Apparatus according to claim 1, characterized in that the wall (5', 5''') is provided with gas supply holes (5d, 5e, 5d'', 5e'') for supplying the processing gas and the gas supply holes (5d, 5e, 5d'', 5e'') are connected with gas supply means (9'). Apparatus according to claim 1, characterized in that the wall (5'''') is formed by plating onto the separating member (4, 4'). Apparatus according to claim 1, characterized in that the wall (5'''') is provided on the side of the cavity resonator (1). Apparatus according to claim 1, characterized in that an electrode (7) on which the substrate (12) is placed is arranged in the plasma producing chamber (6) and a high frequency power supply (11) is connected between the wall (5, 5', 5'', 5''', 5'''', 55) and the electrode (7). Apparatus according to claim 10, characterized in that a switch (61) for switching the high frequency power supply (11) is provided. Apparatus according to claim 5, characterized by means (37, 38) for forming a cusped magnetic field on the electrodes (34, 36, 45, 46). Apparatus according to claim 1, characterized in that a gas jet member (5f) is provided, which can transmit microwaves and is arranged on the side of the plasma producing chamber (6) with respect to the wall (5'') and the separating member (4') and which is provided with gas supply holes (5d', 5e') connected with gas supply means (9') for supplying the processing gas. Apparatus according to claim 1, characterized in that the substrate (12) is processed by the plasma without an additional magnetic field in the plasma producing chamber (6, 33). Apparatus according to claim 14, characterized in that the plasma producing chamber (6, 33) is an etching process chamber.

Inventors: OTSUBO TORU, TAKEUCHI TAKAHIKO, YAMAGUCHI YASUHIRO, OTSUBO, TORU, TAKEUCHI, TAKAHIKO, YAMAGUCHI, YASUHIRO
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1987
Main classification: H01J37
IPC codes: C23C16, H01J37