JP6030867B2 - Plasma processing equipment - Google Patents

Description

  The present invention relates to a plasma processing apparatus, and more particularly to one using a hollow cathode.

  Conventionally, as a plasma processing apparatus using a hollow cathode, there is one as disclosed in Patent Document 1, for example. In the technique of Patent Document 1, the hollow cathode provided in the processing chamber has a dielectric window for radiating high-frequency power into the processing chamber, and a shower plate is attached to the lower surface of the dielectric window. A plurality of holes are formed in the shower plate, and gas is supplied to the hollow cathode through a gas flow path provided between the shower plate and the dielectric window. Patent Document 1 describes that grooves can be formed instead of a large number of holes, and that holes having a taper shape in the longitudinal section can be used.

JP 2003-68716 A

  The technique of Patent Document 1 attempts to generate a high-density plasma by obtaining an electron confinement effect by hollow cathode discharge, but there is no mention of the relationship between the gas pressure in the processing chamber and the plasma density. .

  An object of the present invention is to provide a plasma processing apparatus capable of increasing the density of plasma in a wide range of gas pressures from a low pressure to a high pressure.

The plasma processing apparatus of one embodiment of the present invention includes a processing chamber. A plasma processing object is disposed inside the processing chamber. An exhaust port for exhausting gas from the inside of the processing chamber and a processing gas supply port for supplying processing gas to the inside of the processing chamber are provided in the processing chamber. A hollow cathode is disposed in the processing chamber. The hollow cathode has at least one groove opened toward the object to be treated. A power supply unit supplies high-frequency power to the hollow cathode. The processing gas supply port is located between the processing object and the hollow cathode. The groove is formed with several kinds of widths in which the groove width is continuous or discontinuous from the opening toward the direction away from the object to be processed. The wide groove portion is formed with high density plasma in a state where the pressure of the processing gas in the processing chamber is low, and the narrow groove portion has a pressure of the processing gas in the processing chamber. High density plasma is formed in a high state.

  In the plasma processing apparatus configured in this way, in the portion where the hollow width of the hollow cathode is wide, electrons are trapped in a state where the pressure of the processing gas in which the mean free path of electrons becomes long and the electrons gain high energy. Since it comes to collide with gas particles, it is possible to increase the density of plasma. Also, in the narrow groove portion, electrons are trapped and the electrons gain high energy and collide with gas particles in a state where the pressure of the processing gas is high, where the mean free path of electrons becomes short. The density can be increased.

  The groove may be formed in a taper shape, or may be formed in a step type having a plurality of steps.

  As described above, in the present invention, since the shape of the groove formed in the hollow cathode is selected as described above, the density of the generated plasma is high regardless of whether the gas pressure is low or high. Can be achieved.

It is a schematic block diagram of the plasma processing apparatus of the 1st Embodiment of this invention. It is the top view and longitudinal cross-sectional view of a hollow cathode used with the plasma processing apparatus of FIG. It is the top view and longitudinal cross-sectional view of the hollow cathode used in the 2nd Embodiment of this invention. It is the top view and longitudinal cross-sectional view of the conventional hollow cathode. It is a figure which shows the relationship between the plasma density and gas pressure in 1st and 2nd embodiment and the conventional plasma processing apparatus. It is a figure which shows the relationship between a mean free path and gas pressure. It is a figure which shows the relationship between electron temperature and gas pressure. FIG. 6 is a partially omitted vertical sectional view of a hollow cathode used in the third to fifth embodiments. It is a figure which shows the relationship between the plasma density and gas pressure in 2nd thru | or 5th embodiment and the conventional plasma processing apparatus. It is the top view and longitudinal cross-sectional view of another example of the hollow cathode used with the plasma processing apparatus of FIG. FIG. 11 is a diagram showing the relationship between plasma density and pressure in the hollow cathode of FIG. 10, the hollow cathode of the second embodiment, and the conventional hollow cathode and flat plate cathode of FIG. FIG. 13 is a diagram showing dimensions of the respective parts of the hollow cathode of FIG. 10, the hollow cathode of the second embodiment, the conventional hollow cathode of FIG. 4 and the flat cathode of FIG. It is a figure which shows the relationship between the plasma density and pressure in a reverse taper type | mold hollow cathode. It is the top view and longitudinal cross-sectional view of a reverse taper type | mold hollow cathode.

  The plasma processing apparatus according to the first embodiment of the present invention has a processing chamber 2 as shown in FIG. The processing chamber 2 is made of, for example, metal and has a support base 6 that supports the workpiece 4 inside. A hollow cathode 8 is disposed so as to face the support base 6. Although details of the hollow cathode 8 will be described later, a shield is provided around the hollow cathode 8. The hollow cathode 8 is connected to one end of a high frequency power source, for example, a 13.56 MHz high frequency power source 14 via a power supply unit, for example, a blocking capacitor 10 and a matching unit 12. The other end of the high frequency power source 14 is connected to a reference potential, for example, a ground potential, and the processing chamber 2 is also connected to the ground potential.

  The processing chamber 2 is formed with an exhaust portion 16 for connection to a vacuum pump (not shown) for exhausting the inside. The processing chamber 2 is also formed with a processing gas supply unit 18 connected to an argon gas source (not shown) for supplying a processing gas, for example, an inert gas, specifically, an argon gas. . The exhaust unit 16 and the argon gas supply unit 18 are disposed on the peripheral surface of the processing chamber 2, and the processing gas supply unit 18 is located between the hollow cathode 8 and the support base 6.

  As shown in FIG. 2A, the hollow cathode 8 is formed in a disk shape, for example, and has an annular groove 20 opened on the surface facing the object 4 to be processed. 2B, the groove 20 has a groove bottom in a direction away from the workpiece 4 (downward in FIG. 2B), and the groove width increases from the opening toward the groove bottom. It is a tapered type that gradually becomes smaller. In addition, an example of the dimension of each part of the hollow cathode 8 is shown to Fig.2 (a), (b).

  The plasma processing apparatus according to the second embodiment of the present invention is configured in the same manner as the plasma processing apparatus according to the first embodiment except that the shape of the groove 20a of the hollow cathode 8a is different. The same parts are denoted by the same reference numerals, and description thereof is omitted. As shown in FIGS. 3A and 3B, the groove 20a is of a step type configured in two stages, and the first stage is separated from the workpiece 4 with a constant groove width from the opening. It progresses to the bottom of the first step in the direction. In the second stage, the groove width is smaller than the first stage groove width at the center of the bottom of the first stage, and further to the second stage bottom in a direction away from the workpiece 4 while maintaining the small width. Progressing. An example of the dimension of each part of the hollow cathode 8a is shown in FIGS.

  In the plasma processing in the plasma processing apparatus of the first and second embodiments, the processing chamber 2 is evacuated by a vacuum pump in a state where the workpiece 4 is disposed on the support base 6 to be in a vacuum state. Next, argon gas is supplied into the processing chamber 2 and the high-frequency power source 14 is operated to generate plasma. By introducing this plasma into the processing object 4, the processing object 4 is subjected to plasma processing.

  In the plasma processing apparatus of both embodiments, since the hollow cathodes 8 and 8a are used, high-density plasma can be generated. That is, ions collide with the hollow cathodes 8 and 8a, and electrons are emitted from the hollow cathodes 8 and 8a. Since electrons have a lighter mass and faster moving speed than ions, the hollow cathodes 8 and 8a are negatively charged. Ions are attracted to the negatively charged hollow cathodes 8 and 8a, and an ion sheath region is formed in a region including the grooves 20 and 20a. Electrons emitted from one groove wall of the hollow cathodes 8 and 8a due to ion collision are accelerated in the ion sheath region and move to the groove wall on the opposite side of the hollow cathodes 8 and 8a. Since it is negatively charged, it is reflected by the ion sheath region of the hollow cathode 8, 8a. Electrons are accelerated by the ion sheath while reciprocating in the grooves of the hollow cathodes 8 and 8a, approaching such electrostatic confinement. As a result, high-energy electrons are confined, the ionization probability is increased, and high-density plasma is formed.

  By changing the groove shape of the hollow cathodes 8 and 8a in the depth direction like the grooves 20 and 20a, high-density plasma is generated in a wide gas pressure range from low gas pressure to high gas pressure. Can be made.

  In the range where the gas pressure is high, the mean free path is shortened and the electron moving distance is shortened. In the well-type groove 20b shown in FIG. 4, since the groove width is too wide with respect to the mean free path, electrons collide with gas particles before being trapped in the groove, so that high-density plasma can be generated. Can not. However, in the tapered groove 20 shown in FIG. 2B and the step-type groove 20a shown in FIG. Since trapping and electrons gain high energy and collide with gas particles, the plasma density can be increased. Therefore, as described above, generation of high-density plasma can be maintained with a wide range of gas pressures.

  FIGS. 5A to 5C show measurement results of plasma density at various gas pressures in a plasma processing apparatus having a hollow cathode having well-type, tapered-type and step-type grooves. The plasma density was measured using a probe indicated by a broken line in FIG. The position of the probe is measured at a position of 37.5 mm in the radial direction r from the center of the hollow cathode, and the distance z from the opening surface side of the groove of the hollow cathode is 5 mm, 8 mm, and 12 mm. The processing gas is argon gas, and its pressure is 40 to 400 mTorr. The high frequency power is 50W. Each hollow cathode electrode has a diameter of 100 mm and a thickness of 20 mm.

  In the tapered hollow cathode 8 of the first embodiment, the diameter of the outer edge on the opening side of the groove 20 is 85.4 mm, and the groove width of the opening of the groove 20 is 10 mm. Therefore, the diameter of the inner edge on the opening side of the groove 20 is 64.6 mm. The distance from the opening of the groove 20 to the groove bottom of the groove 20, that is, the depth is 10 mm, and the width of the groove bottom is 5 mm.

  In the step-type hollow cathode 8a of the second embodiment, the diameter of the outer edge of the opening of the groove 20a is 80 mm, and the diameter of the inner edge is 70 mm. Therefore, the opening width of the groove 20a is 5 mm. The depth of the groove is constant from the opening to 5 mm, and the second step is formed with a depth of 5 mm from the center of the bottom of the first step, the groove depth being constant and the groove width being 2 mm. Yes.

  In the well-type hollow cathode 8b, as shown in FIGS. 4A and 4B, the diameter of the outer edge of the opening of the groove 20b is 80 mm, and the diameter of the inner edge is 70 mm. Therefore, the opening width of the groove 20b is 5 mm. The depth from the opening to the groove bottom is 10 mm.

  5C, in the case of a well-type hollow cathode, when the gas pressure is increased from 40 mTorr, the plasma density is maximized at 200 mTorr, and when the gas pressure is further increased from 200 mTorr, the plasma density is decreased. . In the case of a tapered hollow cathode, when the gas pressure was increased from 40 mTorr, the plasma density was maximized at 240 mTorr, and when the gas pressure was further increased from 240 mTorr, the plasma density was slightly reduced. In the case of a stepped hollow cathode, when the gas pressure was increased from 40 mTorr, the plasma density reached a maximum at 360 mTorr.

  That is, up to a gas pressure of 200 mTorr, the plasma density of the well-type hollow cathode is the highest, and the plasma density of the step-type hollow cathode is the lowest. When the gas pressure was 200 mTorr or higher, the plasma density of the step-type hollow cathode was the highest, and the plasma density of the well-type hollow cathode electrode was the lowest.

  There is a relationship between the gas pressure and the mean free path as shown in FIG. 6 using the electron temperature as a parameter. The mean free path is long in the range where the gas pressure is low, and the mean free path is short in the range where the gas pressure is high. It has become. Further, it has been measured that there is a relationship as shown in FIG. 7 between the electron temperature and the gas pressure by a well type, a taper type and a step type.

  In the high gas pressure range of 200 to 300 mTorr, the well-type electron temperature is 1.7 to 2 eV as apparent from FIG. From the state where the pressure of the argon gas is 200 to 300 mTorr, the mean free path becomes shorter than the groove width of 5 mm as apparent from FIG. 6, so that the electrons collide with the particles before trapping, and the hollow effect is excellent. It is thought that the plasma density was reduced.

  In the case of the taper type, the electron temperature is about 1.2 eV from FIG. 7 in a high gas range. From FIG. 6, the mean free path is longer than the groove width of 5 mm at the taper type groove bottom and the groove width of 10 mm at the opening. It is considered that the hollow effect worked and the plasma density did not decrease. In the low gas range, the plasma density is lower than in the well type, and in the high gas pressure range, the plasma density is lower than in the step type. The taper type gradually increases the groove width in the direction in which electrons are emitted, and This is considered to be because it is easy to diffuse out of the groove.

  In the case of the step type, the plasma density is lower than that of the well type in a low gas pressure range because the depth of the groove width is only 5 mm and the mean free path becomes long at a low gas pressure. This is probably because the hollow effect is not working well. On the other hand, in the high gas pressure range, the electron temperature is 1.2 to 1.5 eV, and the mean free path is shorter than 5 mm from 280 mTorr or more. However, since the electrons can be trapped at the lower 2 mm, the hollow effect is improved. It is thought that the plasma density did not decrease.

  FIGS. 8A to 8C show the vicinity of a groove of a hollow cathode used in the plasma processing apparatuses of the third to fifth embodiments. Other sizes of the hollow cathode are the same as those of the hollow cathodes 8 and 8a of the first and second embodiments. The step-type hollow cathode 8a used in the second embodiment has the highest plasma density in the high gas pressure range, but the plasma density is low in the low gas pressure range. Therefore, the plasma density is low even in the low gas pressure range. The third to fifth embodiments have been improved so as to be higher. In the third embodiment, as shown in FIG. 8A, the opening width of the first stage of the groove 20c is increased to 10 mm. In the fourth embodiment, as shown in FIG. 4B, the groove 20d is formed by expanding the width of the second stage of the groove 20c in the third embodiment from 2 mm to 5 mm. In the groove 20e of the fifth embodiment, a third stage is formed in addition to the second stage of the groove 20d in the fourth embodiment, as shown in FIG. Is 5 mm.

  FIG. 9 shows the relationship between the plasma density and the gas pressure in the plasma processing apparatus using the well type shown in FIG. 4, the step type shown in FIG. 3, and the hollow cathode shown in FIGS. . From now on, in the low gas pressure range of 200 mTorr or less, the plasma density is improved by expanding the diameter of the opening to 10 mm.

  In each of the above embodiments, the hollow of the hollow cathode is formed in a single layer, but it can be formed in a concentric manner in multiple layers. In each of the above embodiments, the argon gas is used as the processing gas. However, the present invention is not limited to this, and other gases may be used.

  Further, as shown in FIGS. 10A and 10B, a hollow cathode 8f having a reverse step type groove 20f can be used. That is, the groove 20f is configured in two stages, but the first stage advances to a predetermined length in the direction away from the workpiece 4 with a constant width from the opening. From the bottom of the step, the groove width is larger than the groove width of the first step, and further proceeds away from the workpiece 4 while maintaining the large width. In this configuration, when the pressure in the groove 20f of the hollow cathode 8f is high, high-density plasma is generated by the hollow effect on the opening side where the groove width is short, while when the pressure in the groove 20f of the hollow cathode 8f is low. The hollow effect is generated on the wide bottom side, and the high-energy electrons generated there promote ionization near the opening side, so that the plasma density can be increased. That is, in the first stage on the opening side where the groove width is narrow, the plasma can be densified when the electron moving distance is short and the gas pressure is high. In the second-stage groove having a long groove width, the area surrounded by the electrodes is wide, so that electrons are easily trapped, the moving distance is long, and the plasma density can be increased even when the gas pressure is low. .

  FIG. 11 shows the relationship between the gas pressure and the plasma density when the reverse step type, flat plate, well type and step type hollow cathodes shown in FIG. 12 are used. As shown in FIG. 12A, the hollow cathodes have the same diameter and the same thickness, for example, a diameter of 100 mm and a thickness of 20 mm. In the groove formed by each hollow cathode, the largest diameter portion is 85 mm, the next largest diameter portion is 80 mm, the next largest diameter portion is 70 mm, and the smallest diameter portion is 65 mm. When a two-step groove is formed, the depth of the first step on the opening side is 5 mm, and the depth of the second step is 10 mm from the opening. In the reverse step type shown in FIG. 5C, the first-stage groove width is 5 mm, the first-stage groove depth is 5 mm, the depth from the second-stage opening is 10 mm, and the groove bottom width is 10 mm. It is. In the flat plate type shown in FIG. 4D, no groove is formed. In the well type shown in FIG. 5E, only one-stage groove is formed, the groove width and the groove bottom width are 5 mm, and the depth is 10 mm. In the step type shown in FIG. 5 (f), the first-stage groove width is 10 mm, the first-stage groove depth is 5 mm, the depth from the second-stage opening is 10 mm, and the groove bottom width is 5 mm. is there.

  In FIG. 11, the input high-frequency power is 50 W, the probe is arranged at z where the distance from the opening surface to the groove is 12 mm at r which is 37.5 mm in the radial direction from the center of the hollow cathode, and the plasma density Is measuring. From the figure, at high pressure, for example, less than 320 mTorr, the plasma density was highest when the reverse-step groove was used.

  FIG. 13 shows the relationship between the gas pressure and the plasma density when the inversely tapered hollow cathode shown in FIGS. 14A and 14B is used. As shown in FIG. 14B, the inversely tapered hollow cathode has a diameter of, for example, 100 mm and a thickness of 20 mm. In the groove formed by the hollow cathode, the largest diameter portion is 85 mm, the next largest diameter portion is 80 mm, the next largest diameter portion is 70 mm, the smallest diameter portion is 65 mm, and the width of the groove bottom is 10 mm. The width of the opening is 5 mm and the depth is 5 mm.

In FIG. 13, the input high-frequency power is 50 W, the probe is arranged at z where the distance from the opening surface to the groove is 12 mm, 15 mm, and 20 mm at r which is 37.5 mm in the radial direction from the center of the hollow cathode Then, the plasma density is measured. From the figure, when a reverse taper electrode is used, the plasma density increases in proportion to the pressure from 40 to 240 mTorr, and the density exceeds 10 ¹¹ cm ⁻³ .

2 Processing chamber 4 Processing object 8 8a Hollow cathode 14 High frequency power supply 16 Exhaust part 18 Gas supply part 20 20a Groove

Claims (3)

A processing chamber having a plasma processing object disposed therein and having an exhaust port for exhausting gas from the inside and a processing gas supply port for supplying a processing gas to the inside;
A hollow cathode disposed in the processing chamber and having at least one groove opened toward the object to be processed;
A power supply unit for supplying high-frequency power to the hollow cathode;
And the processing gas supply port is located between the processing object and the hollow cathode, and the groove has different widths in several steps from the opening toward the direction away from the processing object. The portion having a wide groove width is formed so that high-density plasma can be formed in a state where the pressure of the processing gas in the processing chamber is low, and the portion having a narrow groove width is the processing gas. The plasma processing apparatus is designed so that a high-density plasma can be formed with a high pressure in the processing chamber.   The plasma processing apparatus according to claim 1, wherein the groove is formed in a tapered shape.   The plasma processing apparatus according to claim 1, wherein the groove has a plurality of stages.

Images