JP2008166844A - Plasma processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma processing apparatus capable of processing a wide region of a wafer with a diameter of 300 mm or larger, having higher uniformity and higher accuracy. <P>SOLUTION: The plasma processing apparatus is provided with a sample stage 2 which is arranged within a chamber 1 capable of being decompressed and on a top surface of which a semiconductor wafer 3 is placed, a conductive plate 7 with a mostly circular shape arranged parallel to a surface which is placed on the semiconductor wafer 3, located opposite above the sample stage 2 and facing to plasma formed within the chamber 1; a power supply 11 for supplying power for forming the plasma in a space within the chamber 1 between the sample stage 2 connected to the conductive plate 7 and the conductive plate 7; and a supply port supplying a gas containing carbon and fluorine to the space 1. The frequency f1 of the power supplied to the conductive plate 7 is in a range, such that it is higher than 100 MHz and lower than (0.6×C)/(2.0×D) Hz, where C is the speed of a light in vacuum and D is the diameter of the wafer, and the wafer is processed, by setting a distance between the top surface of the sample stage 2 and the conductive plate 7 from 20 to 100 mm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a plasma processing apparatus that performs processing such as etching and ashing on a substrate to be processed, such as a semiconductor wafer, using plasma formed in a decompressed container.

  In the manufacture of semiconductor devices, plasma processing apparatuses are widely used in processes such as film formation and etching. With the miniaturization of devices and the expansion of wafer diameter, the performance required for plasma processing equipment has become increasingly severe. Taking a plasma etching system as an example, improved process performance such as vertical processability (anisotropic etch), high selective processability for mask materials and base materials, etching rate, in-plane uniformity, and stable process for a long time Technology to maintain performance is important.

  Various approaches have been taken to improve process performance. In the old days, a RIE (Reactive Ion Etcher) type plasma source as shown in FIG. 2 has been used for anisotropic etching. However, the RIE apparatus has a common source power source for generating plasma and a bias power source for drawing ions into the wafer, and therefore has a drawback that the plasma density and the ion energy incident on the wafer cannot be controlled independently. Therefore, at present, a plasma source + wafer bias type plasma processing apparatus using a plurality of high-frequency power sources is mainly used.

  Currently, the plasma processing apparatuses mainly used are ICP (Inductively Coupled Plasma), 2 Frequency CCP (Capacitive Coupled Plasma), Microwave ECR (Electron Cyclotron Resonance), UHF (Ultra High Frequency) − It is divided into ECR and the like. Among these, a two-frequency CCP or UHF-ECR type plasma source is used for etching an insulating film such as a silicon oxide film, a silicon nitride film, or a low-k film. Each of these insulating film etching apparatuses has a parallel plate structure. The frequency of the power source for the plasma source is about 13.56 MHz to about 500 MHz, and the frequency of the bias power source is a source of about 400 kHz to 13.56 MHz in order to reduce the influence on the plasma source and efficiently draw ions. A lower frequency is used.

  Also, in these insulating film etching apparatuses, the upper electrode surface is often made of silicon. A CF-based gas is mainly used for etching a silicon oxide film. However, due to multiple dissociation of the CF-based gas by plasma, F radicals that cause a decrease in the resist selectivity and the base nitride film selectivity are inevitably generated. End up. This configuration is intended to cause scavenging of F radicals by reacting silicon of the upper electrode with F radicals in the gas phase.

  On the other hand, techniques related to plasma confinement for maintaining stable process performance for a long time are also important. From the standpoint of stability and contamination, it is very unfavorable that the plasma spreads to a region other than directly above the wafer to be processed, that is, the side wall and the lower periphery of the reaction vessel, and the lower periphery of the electrode. If the side walls and other parts of the reaction vessel are scraped by the plasma spreading to the region other than just above the wafer, heavy metal contamination will occur on the wafer and particles will be generated, both of which significantly reduce the yield. Alternatively, when a gas having a high deposition property is used, the side wall is turned from the scraping side to the deposition side, and the deposit is eventually peeled off to cause foreign matters.

  As a countermeasure against the above-described unnecessary plasma spread, it has been proposed to physically confine plasma using a shield ring or a baffle plate (see, for example, Patent Document 1). Further, a cylindrical confinement mechanism formed by stacking rings has been proposed (see, for example, Patent Document 2). Furthermore, it has been proposed to confine plasma by a magnetic field generated by a permanent magnet (see, for example, Patent Document 3).

Further, as a technique corresponding to such a process at a lower pressure, an electromagnetic wave of 300 MHz to 500 MHz is applied to the upper antenna, a magnetic field of 100 G to 200 G is generated immediately below the antenna by an external coil, and an interaction between the electromagnetic wave and the magnetic field is generated. A technique for generating plasma has been proposed (see, for example, Patent Document 4). In this configuration, an ECR effect that is an interaction between an electromagnetic wave and a magnetic field is used, and plasma can be efficiently generated even at a low pressure of about 0.2 Pa to 4 Pa. In addition, since the frequency in the 300 MHz to 500 MHz band is used, there is an advantage that the electron temperature can be lowered and the multiple dissociation of the CF-based gas can be suppressed. Since this technology has a high plasma generation efficiency at a low pressure, when it is attempted to obtain the same density on the wafer, the source power is required as much as the CCP having a frequency of 27 MHz disclosed in Patent Document 1 and Patent Document 2. Therefore, it was also advantageous for the problem of plasma spreading beyond the wafer.
JP-A-8-335568 JP-A-9-27396 Japanese Patent Laid-Open No. 9-219397 JP 2000-150485 A

  In the technique described in Patent Document 1, an upper electrode is provided on a surface facing a lower electrode on which a wafer is placed, a high frequency of 27.12 MHz is applied to the upper electrode, and a high frequency of 800 kHz is applied to the lower electrode. The apparatus uses a shield ring and a baffle plate as means for confining plasma generated mainly at a high frequency applied to the upper electrode on the wafer.

  With the conventional technology having such a configuration, it is difficult to cope with a next-generation process that is further miniaturized. That is, in order to cope with miniaturization, a process at a lower pressure is desirable. However, when the frequency of the source power supply is 27.12 MHz, the density sufficient for the process construction at a low pressure of about 0.2 Pa to 4 Pa. It is known that it becomes difficult to generate plasma. In order to increase the plasma density, it is not desirable from the viewpoint of efficiency to input a larger source power, but there is also a problem that an unnecessary plasma density spreading beyond the wafer is also increased.

  In addition, shield rings and baffle plates that have been used in the prior art to prevent unnecessary plasma diffusion and increase the use efficiency of source power also have a sufficient effect under low pressure conditions where the plasma diffusion rate is high. I can't do that. Furthermore, if the surface reaction proceeds such as when such a member is directly exposed to high-density plasma and scraped, foreign matter inappropriate for processing may occur in the processing chamber, or the etching characteristics may change over time. As a result, in order to prevent this, there is a problem that the running cost increases by increasing the frequency of replacement of the above parts.

  Patent Document 2 includes a pair of essentially flat and circular parallel electrodes in a processing chamber, and is configured to apply a high frequency of 27.12 MHz to the upper electrode and a high frequency of 2 MHz to the lower electrode. A configuration is disclosed in which the plasma is confined on the wafer by a cylindrical confinement mechanism formed by stacking rings.

  Even in such a configuration, there is a problem similar to the technique described in Patent Document 1 in processing under a lower pressure condition. Furthermore, if the gaps between the plurality of confinement rings are made very narrow in order to have a sufficient plasma confinement effect, the exhaust conductance is reduced, which makes it impossible to cope with a process with a large gas flow rate. Furthermore, problems due to the reaction between the confinement ring and the plasma also occur in the same manner.

  In such a technique described in Patent Document 1 or Patent Document 2, in processing at a lower pressure, in order to increase the plasma density on the wafer, the power of the power source supplied between the electrodes or between the antenna and the electrodes must be increased. However, there is a problem with respect to the technical requirement to confine the plasma to be diffused in a space of a predetermined size.

  Furthermore, Patent Document 3 discloses a technique for confining plasma by supplying a local magnetic field to a plasma generation space in a processing chamber. In this prior art, permanent magnets are arranged below the stage on which the wafer is placed and on the side wall of the processing chamber. Since the plasma is difficult to diffuse in the direction across the magnetic field, the permanent magnet is arranged so as to generate magnetic field lines perpendicular to the diffusion flux of the plasma.

  However, this conventional technique has a problem that local plasma is generated by a local magnetic field created by a permanent magnet, and the wall surface near the magnet is consumed instead. Furthermore, there has been a problem that the magnetic field produced by the permanent magnet affects the wafer and causes charging damage.

  Further, a technique using UHF-ECR such as the technique described in Patent Document 4 is advantageous for a process having a lower pressure, but when processing a large-diameter wafer, it is compared with other plasma forming methods. There were drawbacks. For example, the half-wave in a vacuum of 450 MHz electromagnetic waves is about 330 mm, and there is a problem that it is difficult to form a plasma with a uniform density in the generations after 300 mm wafer where the half-wavelength of the electromagnetic waves is almost equal to the wafer diameter. It was. For this reason, it has been difficult to accurately process a desired shape in a process such as a stopperless dual damascene, and a wafer having a large diameter cannot be processed with high accuracy under a lower pressure condition.

  An object of the present invention is to provide a plasma processing apparatus capable of processing a wafer having a diameter of 300 mm or more over a wide range more uniformly and with high accuracy. Another object of the present invention is to provide a plasma processing apparatus capable of stably realizing high-precision processing over a long period of time by suppressing plasma diffusion in the processing chamber.

  The above-mentioned purpose is formed in the container, which is arranged in parallel to the surface on which the semiconductor wafer is placed opposite to the upper side of the sample stage, which is placed in a depressurizable container and on which the semiconductor wafer is placed. A substantially circular conductive plate facing the plasma, and a power source connected to the conductive plate and supplying power to form the plasma in a space in the container between the sample stage and the conductive plate And a supply port for supplying a gas containing carbon and fluorine to the space, and the frequency f1 of the power supplied to the conductive plate is 100 MHz <with respect to the velocity C of light in vacuum and the diameter D of the wafer. f1 <(0.6 × C) / (2.0 × D) Hz, and the distance between the upper surface of the sample stage and the conductive plate is between 20 and 100 mm, and the semiconductor wafer To plasma processing equipment More achieved.

  Furthermore, the above object is the above plasma processing apparatus, comprising means for moving the height of the upper surface of the sample table up and down, and the conductive plate is made of silicon and disposed on the semiconductor wafer. The silicon oxide film is processed, and the gas supplied from the supply port is constituted by a plurality of types of gases including carbon and fluorine.

  Further, the object is to arrange a sample stage placed in a depressurizable container on which a semiconductor wafer is placed and a surface on which the semiconductor wafer is placed facing the sample stage in parallel with the sample stage. A substantially circular conductive plate facing the plasma formed on the substrate, and supplying electric power to form the plasma in a space in the container between the sample stage and the conductive plate connected to the conductive plate. A first power source, a second power source for supplying power for applying a bias to the semiconductor wafer to an electrode disposed in the sample stage, and a power for applying a bias to the conductive plate A frequency f1 of power supplied to the conductive plate is 100 MHz <f1 <(0.6 × C) with respect to the speed C of light in vacuum and the diameter D of the wafer. /(2.0×D) in the range of Hz A silicon on the semiconductor wafer, comprising a regulator for adjusting a phase difference between each bias formed by the power from the second power source and the power from the third power source to 180 degrees; This is achieved by a plasma processing apparatus for etching an oxide film.

  Furthermore, the object is the plasma processing apparatus, wherein the frequency of power from the second power source is selected from a range between 100 kHz and 20 MHz, preferably between 400 kHz and 13.56 MHz. The frequency of the power from the third power source is achieved by being selected from a range between 100 kHz and 20 MHz, preferably between 400 kHz and 13.56 MHz.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  A first embodiment of a plasma processing apparatus according to the present invention is shown in FIG. FIG. 1 is a longitudinal sectional view showing an outline of a configuration around a processing chamber (vacuum vessel) of the plasma processing apparatus according to the first embodiment of the present invention. A plasma processing apparatus according to the present invention includes a vacuum processing chamber 1, a wafer mounting stage 2, a focus ring 4, a yoke 5, a coil 6, an antenna 7, a gas dispersion plate 8, and a shower plate 9. The gas supply system 10, the first high-frequency power source 11, the first matching device 12, the second high-frequency power source 13, the second matching device 14, the filter circuit 15, and the third high-frequency power source 16. And a third matching unit 17, a temperature adjustment unit 18, a phase adjustment unit 19, an antenna outer peripheral insulating ring 20, a silicon plate support ring 22, and an antenna lid 23. Inside the evacuated vacuum processing chamber 1 having the gas introduction means 10, a wafer mounting stage 2 temperature-controlled by a temperature control device 18 is arranged. Further, a flat antenna 7 made of a substantially circular conductive member substantially parallel to the stage 2 is arranged on the surface facing the stage 2 so as to form a space with a predetermined distance from the stage 2. 7, high-frequency power is applied from the first high-frequency power source 11 via the first matching unit 12, the electromagnetic wave radiated from the antenna 7, and the external coil 6 and the yoke disposed along the outer periphery of the vacuum processing chamber 1. 5, plasma is generated by the interaction with the magnetic field formed in the space between the antenna 7 and the stage 2. Further, by applying a high-frequency bias to the wafer 3 to be processed by the second high-frequency power source 13 and the second matching unit 14 connected to the stage 2, the charged particles formed in the plasma are applied to the surface of the wafer 3. In this way, the plasma processing is performed by causing the excited high energy particles in the plasma to react with the surface of the wafer 3.

  In this embodiment, the frequency f1 of the first high-frequency power source 11 is preferably 100 MHz <f1 <(0.6 × C), where D is the diameter of the wafer to be processed and C is the speed of light in vacuum. ) / (2.0 × D), and more preferably selected from satisfying the relationship of 150 MHz <f1 <(0.5 × C) / (2.0 × D). By using the frequency band, it is possible to generate plasma with high uniformity and efficiency directly above the wafer, and to suppress unnecessary plasma other than directly above the wafer. In this case, processing of a 300 mm wafer was targeted, and the source frequency f1 was set to 200 MHz.

  The frequency of the second high-frequency power source 13 for applying a high-frequency bias to the wafer is preferably 100 kHz so as not to affect the plasma generated by the first high-frequency power and efficiently draw ions into the wafer. To 20 MHz, more preferably 400 kHz to 13.56 MHz. In the present embodiment, a frequency of 4 MHz is used.

  A drooping magnetic field is generated by applying a predetermined current to the two external coils 6. The plasma is generated more efficiently by the interaction between the electromagnetic wave radiated from the antenna 7 into the processing chamber and the magnetic field, that is, the medium density plasma optimum for processing is generated by the output from the lower power source (source power). Can be generated. Furthermore, the shape of the plasma density distribution can be controlled by adjusting the current value flowing through the coil and adjusting the magnetic field strength.

  Since the magnetic field strength for causing ECR resonance at a frequency of 200 MHz is about 70G, the average magnetic field strength in the discharge space is adjusted to approximately 20G to 70G. Further, the magnetic lines of force formed by the yoke 5 and the coil 6 can exert an action of preventing the plasma generated immediately above the wafer from diffusing outside the wafer. Further, the magnetic field intensity used in the plasma processing apparatus according to the present embodiment is reduced as compared with the microwave ECR and the UHF-ECR apparatus. For this reason, the margin for charging damage to the wafer 3 is also greatly improved, and the wafer 3 is stably processed to improve the yield. Furthermore, when using a frequency lower than 200 MHz, the adjustment range of the magnetic field is shifted to the weak magnetic field side.

  Next, the process of determining the frequency range that is a feature of the present invention will be described. Plasma characteristics vary greatly depending on the discharge configuration and discharge frequency. The discharge configuration depends on the etching target and the required process specifications. Therefore, the inventors examined the discharge frequency using UHF-ECR plasma, which is advantageous for lower pressure processes.

  The experimental apparatus used for the examination is shown in FIG. In this experimental apparatus, a stage 2 for placing a wafer is provided in a depressurizable reaction vessel 1 through which a desired gas can flow, and a substantially circular antenna is disposed substantially parallel to the stage so as to face the space. The antenna 7 is configured to be able to supply power by connecting a high frequency power source 11 for forming plasma. Plasma is generated in the space between the stage 2 and the antenna 7 by the interaction between the electromagnetic wave radiated from the antenna 7 by the electric power and the magnetic field formed by the external coil 6 disposed on the outer periphery of the reaction vessel 1. Further, a wafer having a diameter of about 300 mm is transferred onto a stage by a transfer system (not shown), and a high frequency bias is applied to the wafer by a high frequency power supply 13 connected to the stage, so that an actual etching process can be performed. Furthermore, the CCD camera 31 can observe and record light emitted from unnecessary plasma that spreads from the view port 30 at the bottom of the processing chamber to the bottom of the processing chamber. In examining the frequency, four types of power sources of 450 MHz, 200 MHz, 68 MHz, and 40 MHz were used.

First, FIG. 4 shows the radial distribution of the silicon oxide film etching rate when using a C ₄ F ₈ / Ar / O ₂ mixed gas system at each frequency. The experimental conditions were common to all frequencies, and the source power, bias power, antenna-wafer distance, and processing pressure were 800 W, 1000 W, 30 mm, and 2.0 Pa, respectively. In addition, a magnetic field was not applied to examine only the influence of frequency. Since there is no interaction with the magnetic field, the plasma is generated only by the high frequency electric field. In addition, since the distance between the antenna and the wafer is reduced, the etching rate distribution is considered to directly reflect the electric field intensity distribution directly under the antenna.

  In FIG. 4, in the result of 450 MHz, there is a minimum value of the etching rate around φ150 mm to φ200 mm, which indicates that the electric field strength is weak in this portion. This is because the plasma excited at a frequency of about 450 MHz does not become capacitively coupled plasma even if the reactor itself has a parallel plate structure, and behaves like surface wave plasma (SWP). That is, electromagnetic waves propagate through the sheath existing between the plasma and the antenna, and the standing wave pattern formed immediately below the antenna determines the electric field strength distribution.

  Moreover, since the plasma can be regarded as a dielectric, the wavelength of the electromagnetic wave propagating through the sheath is shortened. In the etching result of 450 MHz, the distance from node to node is about 150 mm to 200 mm, and the wavelength shortening ratio κ is 0.45 to 0.6 (45% to 60%). This value does not change so much in the target pressure range, frequency range, and density range.

  In the UHF-ECR plasma processing apparatus using 450 MHz, processing is actually performed by applying a magnetic field. As an effect of the magnetic field, not only the efficiency of plasma generation can be increased, but also the etching rate distribution can be controlled. For example, if the etching rate without a magnetic field has a simple medium-high distribution, the coil current may be adjusted so that the interaction between the electromagnetic wave and the magnetic field becomes stronger at the outer periphery of the antenna.

  However, as in the result shown in FIG. 4, when a standing wave node is seen in the wafer to be processed, control by the magnetic field becomes difficult. In other words, the frequency at which no standing wave node exists in the wafer range is the upper limit for maintaining good plasma distribution controllability and processing uniformity. That is, a relationship of κλ / 2> D should be established between the half-wave κλ / 2 of the standing wave formed under the antenna and the wafer diameter D. Substituting the wavelength shortening ratio value κ = 0.6 obtained from the experimental results into this inequality and solving for the frequency f, f <(0.6 × C) / (2 × D), which solves the problem. The upper limit of the source frequency suitable for the above is determined. Here, C indicates the speed of light in a vacuum. The above relational expression is f <300 MHz when the diameter of the wafer is 300 mm. However, at a frequency satisfying this condition, there is no minimum value reflecting the standing wave section in the etching rate distribution. It will be clear from the results of FIG.

  From the above discussion, it can be seen that for processing large-diameter wafers of 300 mm or more, lowering the source frequency than 450 MHz is advantageous in terms of distribution controllability and uniformity, but conversely when lowering the frequency, There was concern about the deterioration of plasma generation efficiency and the increase of unnecessary plasma spreading beyond the wafer. Then, the process of setting a preferable lower limit of the source frequency will be described next.

  In order to investigate how the plasma density directly above the wafer changes with respect to the frequency, the Peak-to-Peak value (W-Vpp) of the voltage applied to the wafer when the bias power is fixed at 1000 W was measured. Since the bias power is constant, the value of W-Vpp decreases as the plasma density directly above the wafer increases.

  FIG. 5 shows the output dependency of the W-Vpp source high-frequency power source at each frequency. As can be seen from FIG. 5, W-Vpp is not so different at 450 MHz and 200 MHz, but at 68 MHz, W-Vpp is at least twice as large as 450 MHz. In other words, it can be said that the plasma density on the wafer is considerably low at a frequency around 68 MHz, compared with 450 MHz.

  Furthermore, when the absolute value of the inclination with respect to the source power of W-Vpp is seen in FIG. 5, 450 MHz and 200 MHz are around 0.4, whereas 68 MHz is 0.28. This means that at 68 MHz, even if the source power is increased, the plasma density just above the wafer is difficult to increase. It also means that the source power that does not contribute to increasing the plasma density directly above the wafer is also consumed by the plasma that spreads to parts other than directly above the wafer.

  Next, FIG. 6 shows the frequency dependence of the light emission intensity of the plasma spreading to the outer periphery of the cylindrical portion of the substantially cylindrical stage or to the lower side. The emission intensity was recorded by a CCD camera and a VTR that can be manually controlled for gain, and digitized by image processing. The experimental conditions are set to a pressure of 2.0 Pa, a source power of 1200 W, and a bias power of 1000 W. From FIG. 6, it can be seen that when the frequency is lowered from 450 MHz to 200 MHz, the light emission intensity from the plasma at the outer periphery of the stage or below is slightly increased. Furthermore, it can be seen that the emission intensity increases dramatically at frequencies of about 100 MHz or less (68 MHz, 40 MHz). This is considered to be because the plasma generation mechanism changes depending on the frequency. This is because the plasma is maintained like surface wave plasma at 450 MHz and 200 MHz, whereas it is capacitively coupled plasma at 68 MHz and 40 MHz.

  In surface wave plasma, plasma is generated and maintained by an electric field generated by electromagnetic waves propagating through the sheath under the antenna, while in capacitively coupled plasma, plasma is maintained by statistical heating (Stochastic Heating) due to vibration of the sheath between the electrodes. is doing. Furthermore, since the plasma potential also oscillates greatly in time at frequencies of about 68 MHz and 40 MHz compared with 450 MHz and 200 MHz, the sheath generated between the plasma that spreads on the outer periphery or below the stage and the processing chamber inner wall. It is thought that plasma generation is also performed by. Therefore, as seen in the source power dependence of W-Vpp in FIG. 5, the input source power is not effectively used to increase the density of plasma directly above the wafer.

  At present, the inventors have not grasped the theory that defines the frequency at which the surface wave plasma is transferred to the capacitively coupled plasma when the frequency is lowered from several hundred MHz. However, from the experimental facts, it is considered that there is a boundary at about 100 MHz. This will be apparent from the description of the experimental results from FIG. 4 to FIG.

  From the above, the lower limit of the source frequency that solves the above-described problem is 100 MHz, and by setting f> 100 MHz, the input power can be used efficiently, and the plasma spreading outside the wafer directly can be suppressed. It is possible to suppress the generation of foreign matter caused by scraping of the reactor inner wall or deposits, and it is possible to perform stable treatment for a long time.

  Furthermore, in the above example, the frequency of the high-frequency power source having a configuration based on the UHF-ECR plasma processing apparatus has been studied. However, the data used in the examination is basically the data in the absence of a magnetic field. The presence or absence does not affect the effectiveness of the present embodiment. Further, the plasma treatment is applicable not only to etching but also to other plasma treatment apparatuses.

FIG. 7 shows an example of the etching result when the flat sample of the silicon oxide film is etched by the plasma processing apparatus according to this embodiment in the C ₄ F ₈ / Ar / O ₂ mixed gas system. The effectiveness of the present embodiment can be understood from the fact that the etching rate distribution can be controlled to be 15% convex, 5% flat, and 10% concave by changing the average magnetic field strength. Furthermore, by changing the ratio of the current flowing through each of the two coils and adjusting not only the average magnetic field strength but also the magnetic field line shape, it is possible not only to realize a further super-uniform rate distribution, but also silicon nitride films and various Needless to say, various processes for low-k films can be widely handled.

  More specifically, the plasma generated by the electromagnetic wave in the frequency band has an electron temperature lower than that of microwave ECR plasma or inductively coupled plasma, and has an effect of preventing excessive dissociation of the processing gas. CF gas, which is mainly used for etching insulating films such as silicon oxide films, causes multiple dissociation in plasma with high electron temperature, thereby reducing the selectivity with resist as mask material and underlying silicon nitride film A large amount of F radicals are generated. The plasma source according to the present embodiment has a low electron temperature, can generate a medium density plasma by appropriately adjusting the source power, and realizes a dissociation state suitable for high selectivity processing. I can do it.

  In addition, since stable plasma can be generated at a lower pressure than a capacitively coupled plasma source using the 27 MHz or 60 MHz band, vertical processing corresponding to further device miniaturization becomes possible.

  In the present embodiment, the stage on which the wafer is placed can move up and down, and the distance from the lower surface of the antenna to the wafer to be processed can be adjusted. As described above, multiple dissociation and excessive dissociation of CF-based gas lower the selection ratio, but multiple dissociation can also be suppressed by keeping the antenna surface-wafer distance optimal. This is because the degree of dissociation of the processing gas is affected not only by the electron temperature and electron density but also by the gas residence time. By shortening the gas residence time, that is, by reducing the distance between the antenna surface and the wafer and reducing the volume of the plasma region, multiple dissociation is suppressed, and highly selective processing is possible.

  Further, reducing the antenna surface-wafer distance increases the proportion of the surface in contact with the plasma.

The dissociated species that contributes most to the etching of the silicon oxide film is CF ₂ , but it is known that CF ₂ is generated not only by reaction in the gas phase but also by dissociated species conversion at the surface. That is, C _x F _y, which is a low-order dissociation species of the CF-based gas, adheres to the surface of the antenna or the wafer, and ions from plasma enter the CF ₂ to generate CF ₂ . Therefore, increasing the ratio of the surface in contact with the plasma increases CF _2, can increase the etching rate of the silicon oxide film, and improves the selectivity with respect to the resist.

  However, if the distance between the antenna surface and the wafer is too small, another problem such as deterioration in processing uniformity occurs. In this embodiment, in view of the above, the distance between the antenna surface and the wafer is set to 20 mm to 100 mm. In this embodiment, the vertically movable electrode structure is adopted, but the vertically moving mechanism may be omitted. In this case, the process control range is slightly narrowed, but it goes without saying that the cost can be reduced.

In addition, if the material of the antenna surface in contact with the plasma is devised, further improvement of the selection ratio can be expected. In the present embodiment, a substantially circular silicon plate is used as the material of the antenna surface. The silicon plate 9 has hundreds of fine holes having a diameter of about 0.3 mm to 0.8 mm. Furthermore, between the silicon plate and the antenna body 7, there is installed a gas dispersion plate 8 having about several hundred fine holes having a diameter of about 0.3 mm to 1.5 mm. A processing gas buffer chamber is provided between the gas dispersion plate 8 and the antenna 7, and the processing gas supplied from the gas supply system 10 is uniformly introduced into the processing chamber via the dispersion plate 8 and the silicon plate 9. The In the present embodiment, when etching a silicon oxide film or the like, a CF gas such as C ₄ F ₈ , C ₅ F ₈ , C ₄ F ₆ , or C ₃ F ₆ is used as a processing gas. A mixture of _two or more gases, a rare gas typified by Ar, and O ₂ is used. Further, for a process that requires a higher selection ratio, CO gas is added to the gas system.

  The advantage of using the antenna surface as silicon is that F radicals in the gas phase that lower the selectivity when the silicon oxide film is etched can be removed by reaction with silicon. Furthermore, in the present embodiment, a third high frequency power supply 16 is connected to the antenna 7 via a filter unit 15 and a third matching unit 17. By applying an antenna bias using the third high-frequency power supply 16, the above-described reaction for removing F radicals on the antenna surface can be controlled independently of the plasma density. Therefore, it is possible to easily control the size and shape of a fine pattern.

  Although the antenna surface material is silicon in this embodiment mode, other materials such as silicon carbide, glassy carbon, quartz, anodized aluminum, polyimide, or the like may be used depending on an object to be etched. Absent. The diameter Da of the antenna surface that is in direct contact with the plasma is preferably 0.8D <Da <1.2D with respect to the wafer diameter D from the viewpoint of uniformity of the surface reaction.

  The frequency of the third high frequency power supply 16 for antenna bias is preferably between 100 kHz and 20 MHz, more preferably between 400 kHz and 13.56 MHz so as not to affect the plasma generated by the first high frequency power. Selected. The filter unit 15 is configured to prevent the first high-frequency power from flowing into the third high-frequency power supply and the third high-frequency power from flowing into the first high-frequency power supply.

  Further, in order to control the density distribution of the active species in the gas phase, a substantially annular focus ring 4 is disposed on the outer periphery of the stage 2 so as to surround the wafer 3. In the present embodiment, the focus ring 4 is made of silicon. In this embodiment, the average density of F radicals in the gas phase can be controlled by applying an antenna bias or making the antenna surface-wafer distance variable. 4, the density distribution of F radicals in the wafer surface can be controlled in detail.

  The F radicals generated by the multiple dissociation of the processing gas are also consumed by the resist on the wafer surface. If a member that consumes F radicals is not installed in the region outside the wafer, the F radical density will be higher at the outer periphery of the wafer than at the center of the wafer, but the focus ring 4 has the effect of suppressing this. have. Further, by branching and applying the wafer bias power to the focus ring 4, the effect of suppressing the F radical density at the outer periphery can be enhanced.

  In the present embodiment, the focus ring 4 is made of silicon, but other materials such as silicon carbide, glassy carbon, quartz, anodized aluminum, polyimide, etc. may be used depending on the object to be etched. I do not care. Although not shown, it is possible to control the distribution of the active species in the gas phase by using two lines of processing gas jets.

  In this embodiment, one purpose of using 200 MHz as the frequency of the first high-frequency power supply is to suppress unnecessary plasma other than directly above the wafer, but the antenna bias frequency and the wafer bias frequency are completely set. And using the phase adjusting unit 19 and setting the phase difference between the antenna bias and the wafer bias to approximately 180 ° can further enhance the effect of suppressing unnecessary plasma.

  The plasma potential of the plasma generated by the first high-frequency power varies with time due to the influence of the wafer bias and the antenna bias. By setting the phase of the wafer bias and the antenna bias to 180 °, it is possible to suppress the time-averaged plasma potential to be low, thereby suppressing unnecessary plasma. Furthermore, the energy of ions incident on the processing chamber wall and the stage side wall from unnecessary plasma can be reduced, and wall scraping can be suppressed. This suppresses the generation of foreign matter due to wall shaving, and contributes to the improvement of yield and the operation rate of the apparatus. Further, the side wall of the processing chamber and the antenna body 7 are temperature-controlled by a temperature control unit (not shown), so that stable process performance can be maintained for a long time.

  By using the plasma processing apparatus according to the embodiment of the present invention whose configuration has been described above, a wide range of 300 mm wafer or more is uniform with a high selectivity and a high speed under a low pressure condition suitable for fine processing. Processing can be performed with low power consumption. Further, by suppressing unnecessary plasma in portions other than directly above the wafer, foreign substances that cause a decrease in yield can be reduced, and the above-described advanced process performance can be realized stably over a long period of time. Furthermore, suppression of unnecessary plasma contributes to reducing the running cost of the apparatus.

  Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, in addition to the first embodiment, the configuration is conscious of cost and footprint. Since the basic configuration is the same as that of the first embodiment, the description of the overlapping parts is omitted.

  In the second embodiment of the present invention, in addition to the yoke 5 and the coil 6 which are the first means for forming a magnetic field in the discharge space, a substantially annular second magnetic field forming means 21 is provided above the antenna. It is characterized by having. The second magnetic field forming means 21 is, for example, a permanent magnet made of a material such as ferrite, samarium-cobalt, or neodymium-iron-boron. By using this, detailed magnetic field control in the discharge space is performed at low cost. It becomes possible.

  In the first embodiment, only the yoke 5 and the coil 6 are used as the magnetic field forming means, but when performing detailed magnetic field control, two systems of the coil 6 are installed, and different currents are supplied from different DC power sources to each. The magnetic field strength and the magnetic field line shape were controlled by flowing. If the coil 6 is one system, only the magnetic field intensity can be controlled, and the control range becomes narrow. On the other hand, if the number of coils and the number of DC power supplies associated therewith are increased, the manufacturing and operating costs of the device increase, and consequently the cost of the semiconductor device manufactured by the plasma processing apparatus also increases.

  In the second embodiment, by introducing the second magnetic field forming means 21 described above, the magnetic field strength and the magnetic force line shape can be changed simultaneously with only one coil and one DC power source. The magnetic field formed in the discharge space is formed by superimposing the magnetic field by the second magnetic field forming unit 21 whose magnetic field strength and line shape are fixed and the magnetic field by the first magnetic field forming unit 6 whose magnetic field strength can be changed by current. Because it becomes.

  The shape of the permanent magnet used for the second magnetic field forming means 21 may be substantially annular per se, but considering the cost, a combination of substantially annular magnets divided into a plurality of parts, Furthermore, it is desirable to substitute a plurality of rectangular or cylindrical permanent magnets arranged in a substantially annular shape.

  In the UHF-ECR apparatus, which is a conventional technique, a large triple stub tuner is used as the first matching unit 12 for matching the plasma load with the first high-frequency power source 11 (for example, frequency 450 MHz) for the plasma source. It was. According to the present embodiment, since a frequency of about 200 MHz is used for the source power source, for example, a smaller matching device can be used. These are, for example, a cavity type matching device or a matching device using a vacuum capacitor. Furthermore, since the power supply itself is also reduced in size, the power supply for the source can be arranged at the upper part of the processing chamber, more specifically, at the upper part of the yoke 5.

  In the second embodiment shown in FIG. 8, a source power source (first high frequency power source) 11, an antenna bias matching unit (third matching unit) 17, and a source matching unit are provided on the yoke 5. And units 12 and 15 that also serve as filters. By taking such an arrangement, the footprint of the entire apparatus including the power supply unit can be reduced. Furthermore, since the distance from the source power source to the plasma load can be minimized, the loss in the high-frequency transmission path can be minimized.

  Further, in the second embodiment, the antenna body 7 and the antenna outer peripheral insulating ring 20 are configured to be vacuum sealed. Compared with the first embodiment in which the entire antenna is introduced into a vacuum atmosphere and vacuum-sealed by the antenna lid 23, the structure can be simplified and the number of parts can be reduced, which is advantageous in terms of cost. Become. In addition, compared to the first embodiment in which the propagation path of electromagnetic waves between the first matching unit and the plasma load is almost in a vacuum atmosphere, the part that supplies refrigerant and gas to the antenna is in the atmosphere. The risk of abnormal discharge at the relevant location can be reduced and the device reliability is improved.

  Next, a third embodiment of the present invention will be described with reference to FIG. In the present embodiment, since the basic configuration is the same as that of the first embodiment, differences from the first embodiment will be described. The plasma processing apparatus according to this embodiment has a first high frequency power supply 11 and a second high frequency power supply 13.

  First, as compared with the first embodiment, the means for forming a magnetic field in the discharge space, that is, the yoke 5, the coil 6 and the DC power supply (not shown) in FIG. With this configuration, the cost of manufacturing or operating the apparatus is greatly reduced. On the other hand, the frequency of the first high-frequency power source 11 in the third embodiment has a lower frequency than the first embodiment because the degree of freedom in which the density and intensity of the plasma can be adjusted by applying a magnetic field is reduced. It is desirable to use a frequency of about 100 MHz to 180 MHz.

  Further, the third embodiment does not include a third high-frequency power source for precisely controlling the active species in the gas phase and a third matching unit. Thereby, although the controllability of the active species in the gas phase is lowered, the production / operation cost of the apparatus is further reduced. Although not shown in FIG. 9, it is possible to adjust the density of active species in the gas phase and the distribution thereof by using two processing gas jets.

  As described above, the third embodiment can provide a plasma processing apparatus that can be manufactured and operated at a lower cost.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. A description of the same parts as those of the embodiments described so far will be omitted.

  In the fourth embodiment, a first high-frequency power source 11 is connected to a stage 2 on which a wafer is placed via a filter unit 15 and a matching unit 12, and the wafer stage itself has an antenna for generating plasma. Also serves as. In addition, the yoke 5, the coil 6, the third high-frequency power source 16, and the third matching unit 17 for forming a magnetic field in the discharge space shown in FIG. As the frequency of the first high-frequency power source in this example, it is desirable to use a frequency slightly lower than that of the first embodiment, that is, a frequency of about 100 MHz to 180 MHz because controllability by a magnetic field cannot be expected.

  The feature of this embodiment is that the upper antenna 7 can be omitted by making the wafer stage itself also serve as an antenna. In this configuration, a grounded gas introduction system is arranged on the surface facing the wafer instead of the antenna. Therefore, the structure on the wafer facing surface is greatly simplified, and further cost reduction is possible. The grounded gas introduction system includes a ground electrode 24, a gas dispersion panel 8, and a silicon plate 9. The ground electrode 24 and the gas dispersion panel 8 may be formed integrally with the processing chamber lid. Even in this embodiment, there is a drawback that the processing window becomes narrow, but by performing fine tuning for a specific process, a processing apparatus can be provided at lower cost.

  According to the embodiment as described above, in a plasma processing apparatus for processing, using plasma, a semiconductor substrate to be processed that is disposed inside a processing chamber that is a vacuum vessel, a low pressure suitable for microfabrication is provided. Under conditions, a wafer having a diameter of about 300 mm or more can be processed with good uniformity over a wide range. Further, high selection ratio or high speed processing can be performed with low power consumption. Furthermore, it is possible to suppress the diffusion of the plasma and suppress the generation of foreign matter in the processing container, and to realize high performance stably over a long period of time.

Sectional drawing which shows 1st embodiment of the plasma processing apparatus by this invention. The schematic diagram which shows the conventional plasma processing apparatus. Sectional drawing which shows the experimental apparatus used for examination of a source frequency. The figure which shows the etching rate distribution at the time of changing a source frequency. The figure which shows the source power dependence of the wafer bias voltage at the time of changing a source frequency. The figure which shows the source frequency dependence of the emitted light intensity from the unnecessary plasma of parts other than just above a wafer. The magnetic field strength dependence of the etching rate distribution when the plasma processing apparatus according to the present invention is used. Sectional drawing which shows 2nd embodiment of the plasma processing apparatus by this invention. Sectional drawing which shows 3rd embodiment of the plasma processing apparatus by this invention. Sectional drawing which shows 4th embodiment of the plasma processing apparatus by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vacuum processing chamber, 2 ... Wafer mounting stage, 3 ... Wafer, 4 ... Focus ring, 5 ... Yoke, 6 ... Coil, 7 ... Antenna, 8 ... Gas dispersion plate, 9 ... Shower plate, 10 ... Gas supply 11 ... first high frequency power source, 12 ... first matching device, 13 ... second high frequency power source, 14 ... second matching device, 15 ... filter circuit, 16 ... third high frequency power source, 17 ... first Three matching units, 18 ... temperature adjustment unit, 19 ... phase adjustment unit, 20 ... antenna outer peripheral insulating ring, 21 ... second magnetic field forming means, 22 ... silicon plate support ring, 23 ... antenna lid, 24 ... ground electrode , 30 ... viewport, 31 ... CCD camera.

Claims (7)

A sample stage placed in a depressurized container and on which a semiconductor wafer is placed, and a plasma formed in the container placed in parallel with the surface on which the semiconductor wafer is placed facing above the sample stage. A substantially circular conductive plate facing, a power source connected to the conductive plate and supplying power to form the plasma in a space in the container between the sample stage and the conductive plate, and the space And a supply port for supplying a gas containing carbon and fluorine,
The frequency f1 of the power supplied to the conductive plate is in the range of 100 MHz <f1 <(0.6 × C) / (2.0 × D) Hz with respect to the speed C of light in vacuum and the diameter D of the wafer. Because
A plasma processing apparatus for processing the semiconductor wafer by setting a distance between an upper surface of the sample stage and the conductive plate between 20 and 100 mm.   The plasma processing apparatus according to claim 1, further comprising means for moving a height of an upper surface of the sample table up and down.   3. The plasma processing apparatus according to claim 1, wherein the conductive plate is made of silicon and processes a silicon oxide film disposed on the semiconductor wafer.   4. The plasma processing apparatus according to claim 1, wherein the gas supplied from the supply port includes a plurality of types of gases including carbon and fluorine. 5. A sample stage placed in a depressurizable container on which a semiconductor wafer is placed, and a plasma formed in the container placed in parallel with the surface on which the semiconductor wafer is placed facing above the sample stage. A substantially circular conductive plate facing the substrate, and a first power source connected to the conductive plate and supplying power to form the plasma in the space between the sample stage and the conductive plate in the container. A second power source for supplying power for applying a bias to the semiconductor wafer to an electrode disposed in the sample stage; and a third power source for supplying power for applying a bias to the conductive plate And comprising
The frequency f1 of the power supplied to the conductive plate is in the range of 100 MHz <f1 <(0.6 × C) / (2.0 × D) Hz with respect to the speed C of light in vacuum and the diameter D of the wafer. Because
A silicon oxide film on the semiconductor wafer is provided with a regulator for adjusting the phase difference between the biases formed by the power from the second power source and the power from the third power source to 180 degrees. Plasma processing equipment for etching.   6. The plasma processing apparatus according to claim 5, wherein the frequency of the power from the second power source is selected from a range between 100 kHz and 20 MHz, preferably between 400 kHz and 13.56 MHz.   7. The plasma processing apparatus according to claim 5, wherein the frequency of power from the third power source is selected from a range between 100 kHz and 20 MHz, preferably between 400 kHz and 13.56 MHz. apparatus.

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