JP4537032B2 - Plasma processing apparatus and plasma processing method - Google Patents

Description

  The present invention relates to a plasma processing apparatus and a plasma processing method for processing the surface of a substrate such as a semiconductor substrate or a liquid crystal substrate, and in particular, plasma suitable for controlling electron density and neutral particle density of plasma by microwave power. The present invention relates to a processing apparatus and a plasma processing method.

  2. Description of the Related Art Conventionally, plasma processing apparatuses that use plasma have been used to create semiconductor devices such as semiconductor microprocessors and semiconductor memories and to perform surface treatment of other workpieces. In recent years, in the production of such a semiconductor device, the processing conditions have to be set in a very narrow range as the substrate element becomes finer. In addition, there is a need to further improve the uniformity within the processing surface. Furthermore, since the substrate has a multilayer structure, it is necessary to etch not only the inorganic insulating film but also the organic insulating film, and it is required that the substrate be processed at the lowest possible temperature so as not to damage the film. In addition, the number of substrates processed per unit time must be increased, and the demand for improvement is severe.

  In response to such needs, the present inventor has published a study of utilizing surface wave mode plasma in order to perform plasma processing at a high density and a low electron temperature (Non-Patent Document 1). This paper describes the research results of generating surface wave mode plasma under a high dielectric window using TM mode microwaves using a horn type circular waveguide. An invention relating to a plasma processing apparatus and a processing method based on this paper has also been published (Patent Document 1). In Patent Document 1, electrical damage to a semiconductor device is avoided by installing a workpiece in a range of 150 mm to 250 mm from a microwave transmission window member that can attenuate the electric field strength of the microwave to 10 V / m or less. However, a method of processing at a stable processing speed has been proposed.

Japan Journal of Applied Physics Vol. 37 (1998) p. L1005-L1007 JP 2001-135620 A

As described above, the plasma processing apparatus using the surface wave can achieve a high density exceeding the cut-off density of microwaves (in the case of 2.45 GHz microwave, the electron density is 7.6 × 10 ¹⁶ / m ³ ). In addition, it has a plasma characteristic of a low electron temperature, and is considered suitable for plasma for processing. However, in Patent Document 1 described above, the relationship between the microwave power and the electron density of the plasma is not mentioned at all, and no examination is made as to whether or not the relationship is a linear relationship indispensable for plasma processing.

  On the one hand, I.I. Ganashev published the paper Japan Journal of Applied Physics Vol. 36 (1997) p. As pointed out in 4704-4710, plasma processing in high density and low temperature can be conventionally performed by using surface wave mode plasma, but mode jump of electron density with increasing microwave power. Occurs, and the behavior of hysteresis is drawn.

  FIG. 10 shows the principle that electron density mode jump and hysteresis occur, and also shows a schematic view of the light emission state when the (4,2) mode of plasma emission changes to the (2,1) mode. The light emission mode appears as a collection of strong light emission portions directly below the dielectric window member through a plurality of slits for introducing microwaves into the chamber. The (4, 2) mode is defined as a collection of four strong emission points in the circumferential semicircle and two in the radial direction. This place where light emission is strong is caused by the fact that the propagating wave resonates on the inner wall of the chamber. The wavelength of the propagating wave varies depending on the electron density, and the electron density has a relationship that varies depending on the microwave power as shown in the graph of FIG. However, since the wavelength of the resonant wave is determined by the chamber diameter, n times the length of the wavelength that can be taken (n is a positive integer) must be equal to the chamber diameter. Therefore, as shown in FIG. 10, the electron density of the plasma does not increase linearly with increasing microwave power, but from the minimum power point in the (4, 2) mode to the next long wavelength. Even though the microwave power is increased to the maximum power point to be transferred, the plasma electron density is almost constant. When the mode jumps to the (2,1) mode having a long wavelength, the electron density is rapidly increased.

  On the other hand, when the microwave power is decreased from the maximum power point in the (2, 1) mode, the electron density is not reduced to the minimum power point, which is the transition point where the wavelength changes, and remains constant, (4, 2) When jumping to mode, the electron density decreases rapidly.

  As described above, since the microwave power and the electron density are not in a linear relationship, there is a problem that it is very difficult to control the electron density of the plasma even if high-speed processing of the semiconductor device can be achieved, and it is not suitable for process processing.

  On the other hand, if the surface wave mode plasma as described above is not used, the relationship between the electron density and the microwave power is almost linear, so that the electron density of the plasma can be easily controlled. However, there is a problem that high-density plasma cannot be obtained and high-speed processing cannot be performed.

  Such a problem also exists when only neutral particles are extracted from the plasma and processed, and if practical use is considered, there is a linear relationship between high-density neutral particles and microwave power. Is required.

  The present invention has been made to solve such problems, and the density of plasma electrons and neutral particles can be increased linearly with respect to microwave power, thereby controlling the process. An object is to provide an easy plasma processing apparatus and a plasma processing method.

  The plasma processing apparatus according to the present invention is characterized by a truncated cone-shaped horn waveguide for propagating microwaves in TM mode, a plasma generation chamber for generating plasma by the microwave energy, and the horn waveguide. A plate-like dielectric window member provided between the tube and the plasma generation chamber, and surface waves generated directly below the dielectric window member in the plasma generation chamber by the microwave in the circumferential direction. The point is to generate a rotating light emission mode by propagating.

  Further, in the present invention, when the microwave passes through the dielectric window member, the maximum amplitude position of the electric field wave constituting this microwave crosses the dielectric window member and transmits the surface wave to the circumference. It is preferable to generate a light emission mode that propagates in the direction and rotates.

  In the present invention, a shower head may be provided below the dielectric window member, and only neutral particles may be taken out below the shower head.

  Further, the plasma processing method according to the present invention is characterized in that a truncated cone-shaped horn waveguide for propagating microwaves in TM mode, a plasma generation chamber for generating plasma by the energy of the microwaves, and the horn type A plasma processing method in a plasma processing apparatus having a planar dielectric window member provided between a waveguide and the plasma generation chamber, wherein the dielectric window member is formed in the plasma generation chamber by the microwave. This is in that a rotating light emission mode is generated by propagating a surface wave generated directly below the surface in the circumferential direction.

  Further, in the present invention, when the microwave passes through the dielectric window member, the maximum amplitude position of the electric field wave constituting this microwave crosses the dielectric window member and transmits the surface wave to the circumference. It is preferable to generate a light emission mode that propagates in the direction and rotates.

  Further, in the present invention, a shower head is provided below the dielectric window member, and only the neutral particles are taken out below the shower head to process the object to be processed installed below the shower head. You may do it.

  According to the present invention, in the plasma processing apparatus and the plasma processing method, the density of plasma electrons and neutral particles is linearly set with respect to the microwave power by causing the microwave to enter the dielectric window member at a predetermined position. Since it can be increased or decreased, it is possible to perform plasma processing in a low temperature region by surface wave plasma while controlling to a desired electron density or neutral particle density.

  Preferred embodiments of a plasma processing apparatus and a plasma processing method according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the structure of a plasma processing apparatus 1A according to the first embodiment of the present invention.

  This plasma processing apparatus 1A includes a plasma generation chamber 2 in which plasma is generated and a frustoconical horn-shaped waveguide 3 that propagates microwaves for generating plasma in the TM mode. A horizontally extending horizontal waveguide 4 is connected to the upstream side of the horn-type waveguide 3, and a microwave oscillator (not shown) is disposed in the horizontal waveguide 4.

  A disk-shaped dielectric window member 5 made of alumina, aluminum nitride, quartz, or the like is provided at a connecting portion between the plasma generation chamber 2 and the horn type waveguide 3. The dielectric window member 5 is supported by a window support member 6 through a sealing material 6a such as an O-ring while maintaining hermeticity.

  The plasma generation chamber 2 is composed of an aluminum chamber or the like. A stage holder 7 for supporting the workpiece W is provided in the plasma generation chamber 2, and the plasma generation chamber 2 is also a processing chamber for the workpiece W. Also serves as. An electric heater 8 for heating the substrate is built in the stage holder 7, and the temperature can be set according to processing. Of course, cooling means may be provided in place of the electric heater 8.

  A gas supply port 61 is provided on the inner wall surface of the window support member 6 in the plasma generation chamber 2 for supplying a reaction gas corresponding to processing into the plasma generation chamber 2. The gas supply port 61 is formed as a circumferential gap in order to uniformly blow out the reaction gas into the plasma generation chamber 2, and the gas introduction pipe 9 is connected to the gap. The shape of the gas supply port 61 is not particularly limited as long as it is uniform. The gas introduction pipe 9 is connected to various gas cylinders (not shown) and is provided with a mass flow controller (not shown) so as to adjust the supply gas amount.

  Further, an exhaust port 10 for exhausting the plasma generation chamber 2 is opened. The exhaust port 10 is connected to a vacuum pump 12 for exhaust via an exhaust pipe 11, and by-products generated after processing, unreacted excited species, and the like are discharged. Further, a valve 13 is provided between the exhaust port 10 and the vacuum pump 12 for keeping the pressure in the plasma generation chamber 2 at a predetermined value.

  In the plasma processing apparatus 1A of the present embodiment having the above basic structure, the TM mode microwave propagated through the horizontal waveguide 4 and the horn-type waveguide 3 is a dielectric window member at the maximum amplitude position of the electric field. The height of the horn-type waveguide 3 is adjusted so as to pass through 5, or the inner diameter of the horizontal waveguide 4 is adjusted. In other words, a position corresponding to an integral multiple of λ / 2 of the electric field wavelength constituting the microwave is set so as to be able to cross the dielectric window member 5 and enter. For fine adjustment of the height, a spacer or the like may be held between the horn type waveguide 3 and the plasma generation chamber 2, or a mechanically movable mechanism may be provided to provide a power source. .

  Next, a plasma processing method by the plasma processing apparatus 1A having the above structure will be described. First, a workpiece W such as siliconware is placed on the stage holder 7 in the plasma generation chamber 2, the plasma generation chamber 2 is sealed, the valve 13 is opened, and the vacuum pump 12 evacuates the plasma generation chamber 2. Exhaust. Subsequently, an appropriate amount of processing gas is supplied from the gas supply port 61 according to the processing content while adjusting the mass flow controller. Thereby, the inside of the plasma generation chamber 2 is maintained at a predetermined pressure state.

  Then, the microwave oscillator is operated to generate a microwave having a predetermined intensity, the microwave is propagated along the horizontal waveguide 4 and the horn-type waveguide 3, and is transmitted through the dielectric window member 5 to be plasma. Supply into the generation chamber 2. At this time, the electric field wavelength of the microwave is transmitted while intersecting the dielectric window member 5 at the maximum amplitude position. By the microwave energy supplied in this way, the processing gas is decomposed to be in a plasma state. The plasma generated at this time is a surface wave mode plasma and propagates in the circumferential direction.

  The surface wave mode plasma propagating in the circumferential direction has been proved by a later-described experiment to have a linear relationship with the microwave power whose electron density can be controlled by a micro oscillator. Therefore, in the first embodiment, it is possible to perform the plasma processing of the workpiece W while controlling the electron density to a desired high density by the surface wave mode plasma.

  Next, a second embodiment of the plasma processing apparatus 1B according to the present invention will be described with reference to FIG. Among the configurations of the second embodiment, the same or corresponding components as those of the first embodiment described above are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 2 is a schematic cross-sectional view of a plasma processing apparatus 1B that processes the workpiece W by generating neutral particles. The plasma processing apparatus 1B of the second embodiment is characterized in that a shower head 14 composed of a quartz plate or the like having a plurality of holes is provided between the dielectric window member 5 and the workpiece W. . The plasma generation chamber 2 is separated into a plasma generation portion 21 and a neutral particle processing portion 22 by the shower head 14.

  When surface waves occur, the electron density exceeds the cutoff, and the electric field in the axial direction (direction is downstream) does not propagate, but the electric field in the lateral direction (direction is circumferential) remains and propagates downstream but attenuates. As a result, the decay of charged particles is accelerated. By providing the shower head 14 at a position where the charged particles are sufficiently attenuated, damage of sputtering due to ion bombardment can be suppressed. The position of the shower head 14 varies depending on the pressure and the microwave power, but may be set to 5 to 25 cm from the dielectric window member 5. Of course, the distance is not limited to this, and by using surface wave plasma, there is no generation of plasma in the downstream region, and it is necessary to dispose at a downstream position where the plasma density is small.

  Since the shower head 14 has innumerable small holes, the charged particles in the reaction gas can be removed by passing through these small holes. In the second embodiment, a small hole is formed in one disk and used as the shower head 14, but instead of this, charged particles are removed using a gap between the two disks. You may go. In this case, the upper and lower disks have holes through which gas passes, and the same effect can be obtained unless they overlap each other. If the shower head 14 has a single structure, the gas flow rate is adjusted by the hole diameter.

  As described above, in the second embodiment, neutral particles are generated by the showerhead 14 from the surface wave mode plasma propagating in the circumferential direction, and the density of the neutral particles is linearly related to the microwave power. Therefore, the workpiece W can be processed while controlling the neutral particle density to a desired high density. Accordingly, it is possible to prevent the substrate, the gate insulating film, and the like from being damaged due to charge-up or damage due to charged particles of electrons or ions, and to meet the demand for miniaturization.

  Next, in the plasma processing apparatus 1A of the first embodiment described above, the change in the electron density of the plasma with respect to the microwave power when the surface wave plasma propagating in the circumferential direction is generated immediately below the dielectric window member 5 is shown. It was measured.

  In the first embodiment, oxygen is used as a plasma generating gas, the pressure in the plasma generating chamber 2 is maintained at 133 Pa and 399 Pa, and a microwave of TM01 mode is supplied from the horn waveguide 3 to form a dielectric made of alumina. Oxygen plasma was generated directly under the window member 5. The microwave condition was a frequency of 2.45 GHz, and the power was changed at 0.6 to 1.5 kW. The oxygen gas flow rate was 2 slm. On the other hand, in order to measure the electron density, the apparatus structure is changed to a bottom member with a gauge port 15 as shown in FIG. 3, and a Langmuir probe 16 is connected to the gauge port 15 at the tip of the dielectric window member 5. The electron density was measured by mounting the sensor so that the position was 1 cm from the lower surface.

The result is shown in FIG. As is clear from this result, the electron density increases almost linearly with increasing microwave power. As a result, it is understood that the linearity condition necessary for the plasma processing process is satisfied. The electron density does not exceed the microwave cutoff density of 7.6 × 10 ¹⁶ / m ³ because the measurement position is spaced 1 cm from the lower surface of the dielectric window member 5. Yes, the cut-off density can be exceeded by bringing the measurement point closer to directly below the dielectric window member 5.

  Next, in order to confirm whether the relationship between the microwave power and the electron density is due to surface wave mode plasma, the form of light emission was observed. For this observation, the bottom member of the apparatus shown in FIG. 3 was replaced with a bottom member with a viewport (not shown) and observed through this. The state of plasma emission obtained by this observation is shown in FIG.

  FIG. 5A shows light emission when the microwave power is 1.0 kW, FIG. 5B shows light emission when the microwave power is 0.85 kW, and FIG. 5C shows the light emission when the microwave power is 0.86 kW. Light emission, (d) is light emission when the microwave power is 1.27 kW. Thus, in (a) and (b), clearly ring-shaped light emission was observed, and in (c) and (d), the appearance of strong light emission was observed in synchronization with the surface waves. (C) is a (4, 1) mode surface wave, and (d) is a (2, 1) mode surface wave. In consideration of the light emission of (c) and (d), the electron density measurement port is used to clarify this because it does not rotate in the circumferential direction and appears to be stationary. Then, the electric field intensity corresponding to the emission intensity was measured. The measurement conditions are a microwave power of 0.81 kW and a pressure of 133 Pa. The measurement position was selected to be close to the center of the ring-like light emission (not the center of the ring).

  As a result, as shown in FIG. 6, a wave propagating in the circumferential direction, which is considered to be caused by the surface wave, was measured. When the rotation frequency of this wave is calculated, it is about 22 MHz. From this, it can be seen that the ring-like light emission is formed by the rotation of the light emission corresponding to the wave peak propagating by the surface wave. As described above, the (4, 1) mode surface wave and the (2, 1) mode surface wave have a length that is an integral multiple of the wavelength and the length in the circumferential direction. It appears as a strong position, not at rest.

  When the rotation frequency was measured at the electron density measurement point based on this result, the result was obtained that the number of rotations increased with the increase of the microwave power, similar to the electron density. This is a result of solving the problem that the wavelength of the propagating surface wave changes in the same manner as the electric power changes, and the propagating wavelength is not restricted by the inner diameter of the plasma generation chamber 2.

  Next, Example 2 will be described. In Example 2, the same experiment as in Example 1 was performed by changing the processing gas from oxygen to nitrogen. The result is shown in FIG. It can be seen that when the pressure is 133 Pa, the electron density increases linearly with increasing microwave power.

  In Example 3, similarly, the experiment was performed by setting the processing gas to hydrogen and the pressure to 133 Pa. The result is shown in FIG. It can be seen that also in the case of hydrogen, the electron density increases almost linearly with increasing microwave power.

  Next, a similar experiment was performed for the second embodiment. In Example 4, it was examined whether the relationship between the hydrogen atom concentration as a reactive species and the microwave power was linear. The hydrogen atom concentration was measured by an actinometry method in which luminescence was observed with a monochromator from an observation port (not shown). Argon was used as a small amount of comparative gas added in the actinometry method. The hydrogen gas flow rate is 2 slm, and the argon gas flow rate is 60 sccm. FIG. 9 shows the result. As a result, it was confirmed that the concentration of hydrogen atoms also increased linearly as the microwave power increased. Although not shown in the figure, linearity was similarly confirmed for nitrogen atoms and oxygen atoms.

  According to each of the above embodiments, since the electron density and neutral particle density of the plasma linearly increase / decrease with respect to the increase / decrease of the microwave power, it is easy to obtain the optimum plasma density for the plasma processing, and the desired density It can also be easily set. Therefore, it is possible to perform low-temperature processing using high-density surface wave mode plasma and meet various strict requirements in substrate surface processing.

  The plasma processing apparatus and the plasma processing method according to the present invention are not limited to the above-described embodiments, and can be changed as appropriate. For example, when performing CVD, a gas supply system for CVD (Chemical Vapor Deposition) may be added to the shower head 14. In addition, the present embodiment has various applications such as ashing of an organic resist, etching of an organic insulating film or inorganic insulating film on the surface of the workpiece W, etching of the conductive film, and removal of unnecessary materials by cleaning the surface of the workpiece W. Is possible.

1 is a schematic cross-sectional view showing a first embodiment of a plasma processing apparatus according to the present invention. It is typical sectional drawing which shows 2nd Embodiment of the plasma processing apparatus which concerns on this invention. It is typical sectional drawing of the experimental apparatus used for Example 1 in this embodiment. 4 is a graph showing the relationship between microwave power and electron density in the oxygen gas of Example 1. In Example 1, it is the photograph which shows the luminous body of the plasma of the surface wave mode observed from the viewport, each condition is pressure 133Pa, Microwave power (a) is 1.0 kW, (b) Is 0.85 kW, (c) is 0.86 kW, and (d) is 1.27 kW. In Example 1, it is a figure which shows the waveform of the wave which propagates in the circumferential direction measured in the light emission position of ring-shaped light emission. It is a graph which shows the relationship between the microwave power in the nitrogen gas of Example 2, and an electron density. It is a graph which shows the relationship between the electron density in the hydrogen gas of Example 3, and microwave power. 10 is a graph showing the relationship between the hydrogen atom concentration and the microwave power in the hydrogen gas of Example 4. It is a figure which shows the relationship between the microwave electric power in the conventional plasma processing apparatus, and the electron density of the plasma of a surface wave mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1A, 1B Plasma processing apparatus 2 Plasma generation chamber 3 Horn type waveguide 4 Horizontal waveguide 5 Dielectric window member 6 Window support member 6a Sealing material 7 Stage holder 8 Electric heater 9 Gas introduction pipe 10 Exhaust port 11 Exhaust pipe 12 Vacuum pump 13 Valve 14 Shower head 15 Gauge port 16 Langmuir probe 21 Plasma generating part 22 Neutral particle processing part 61 Gas supply port W Workpiece

Claims (4)

A frustoconical horn-shaped waveguide that propagates microwaves in TM mode;
A plasma generation chamber for generating plasma by the energy of the microwave;
A flat dielectric window member provided between the horn-type waveguide and the plasma generation chamber ;
A height adjusting means for adjusting the height of the horn waveguide ,
A standing wave is formed in the horn type waveguide and in the plasma generation chamber, and the height of the horn type waveguide is adjusted by the height adjusting means, whereby the microwave is applied to the dielectric window member. when transmitting, the combined maximum amplitude position of the electric field of the standing wave at the position of the dielectric window member, to propagate surface waves generated directly below the dielectric window member of the plasma generation chamber in the circumferential direction A plasma processing apparatus that generates a rotating light emission mode.   2. The plasma processing apparatus according to claim 1, wherein a shower head is provided below the dielectric window member, and neutral particles are generated below the shower head. A frustoconical horn-shaped waveguide for propagating microwaves in TM mode, a plasma generation chamber for generating plasma by the energy of the microwave, and provided between the horn-shaped waveguide and the plasma generation chamber A plasma processing method in a plasma processing apparatus having a flat dielectric window member formed and a height adjusting means for adjusting the height of the horn-shaped waveguide ,
A standing wave is formed in the horn-type waveguide and in the plasma generation chamber, and the height is adjusted by the height adjusting means, whereby the microwave is applied to the dielectric window member. when transmitting, the combined maximum amplitude position of the electric field of the standing wave at the position of the dielectric window member, to propagate surface waves generated directly below the dielectric window member of the plasma generation chamber in the circumferential direction A plasma processing method characterized by generating a rotating light emission mode.   4. A shower head is provided below the dielectric window member according to claim 3, and neutral particles are generated below the shower head to process an object to be processed installed below the shower head. A plasma processing method characterized by the above.