JP2009212085A - Plasma treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma treatment apparatus further excelling in a plasma ignition property by defining an optimum shape of a top plate according to a material. <P>SOLUTION: This plasma treatment apparatus 11 includes: a treatment vessel 12 having a top opening; a dielectric material 15 which includes ring-shaped recessed groove 16 on a bottom surface thereof, and is disposed to close the top opening of the treatment vessel 12; and an antenna 24 supplying microwaves to the dielectric material 15, and thereby generating plasma on the bottom surface of the dielectric material 15. When assuming the light speed, the frequency of the microwaves, and the relative permittivity of a material constituting the dielectric material 15 as c, f and εr, respectively, the width w of the recessed groove satisfies the expression (1). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

   The present invention relates to a plasma processing apparatus.

  A conventional plasma processing apparatus is disclosed in, for example, Japanese Patent Laid-Open No. 2005-100931 (Patent Document 1). The plasma processing apparatus disclosed in the publication includes a plasma generation chamber that houses a substrate to be processed, an antenna that is driven by microwaves to generate an electromagnetic field, and an opening of the plasma generation chamber that is provided below the antenna. And a taper-like convex part or concave part formed on the lower surface side of the top board.

  The plasma processing apparatus having the above configuration can form an optimum resonance region under any conditions by continuously changing the thickness of the top plate in the radial direction. As a result, it is described that stable plasma can be generated.

Japanese Patent Laid-Open No. 2005-100931

  In addition to quartz, ceramics or the like can be used as the material constituting the top plate having the above configuration. Here, since the microwave resonance region depends on the material of the top plate, it is desirable to define the shape of the top plate according to the material in order to stably generate plasma.

  Accordingly, an object of the present invention is to provide a plasma processing apparatus having more excellent plasma ignitability by defining an optimal shape of the top plate according to the material.

  A plasma processing apparatus according to the present invention includes a processing container having an upper opening, a dielectric having a ring-shaped concave groove on a lower surface thereof and disposed so as to close the upper opening of the processing container, and a microwave in the dielectric. And an antenna for generating plasma on the lower surface of the dielectric. Then, assuming that the speed of light is c, the frequency of the microwave is f, and the relative permittivity of the material constituting the dielectric is εr, the groove width w of the concave groove satisfies Expression (1).

  With the above configuration, the microwave resonates in the width direction of the concave groove to increase the electric field strength on the lower surface of the dielectric. As a result, a plasma processing apparatus excellent in plasma ignitability can be obtained.

  Preferably, when the radius of the dielectric is R, the groove is located outside R / 4 from the center of the dielectric. Thereby, plasma is ignited starting from the outer edge of the dielectric (edge first).

As an embodiment, when the frequency f of the microwave supplied from the antenna is 2.45 × 10 ⁹ (Hz) and the dielectric material is quartz having a relative dielectric constant εr = 3.8, the groove width w of the concave groove Satisfies 33 mm ≦ w ≦ 93 mm.

  Preferably, at least one of the inner peripheral side wall surface and the outer peripheral side wall surface of the concave groove is an inclined surface that is inclined so that the thickness dimension of the dielectric continuously changes. More preferably, the antenna has a plurality of slots penetrating in the thickness direction. The plurality of slots are positioned vertically above the inclined surface. Thereby, the microwave passes through the slot and is radiated to the inclined surface. If the microwave wavelength matches the thickness of the dielectric plate at any position on the inclined surface, the electric field strength on the lower surface of the dielectric increases. As a result, plasma ignitability and ignition stability are improved.

  Preferably, the plurality of slots are inclined at the same angle in the same direction with respect to a straight line connecting the center of the antenna and each slot. Thereby, the E / R distribution is made uniform.

  According to the present invention, by defining the width of the groove by the relative dielectric constant of the dielectric, it is possible to obtain a plasma processing apparatus with more excellent plasma ignitability.

It is a figure which shows the plasma processing apparatus which concerns on one Embodiment of this invention. It is sectional drawing of the dielectric material shown in FIG. FIG. 2 is a plan view in which the dielectric shown in FIG. 1 and a slot antenna are superimposed. It is a figure which shows the electric field strength of the dielectric material shown in FIG. It is a figure which shows the electric field strength when a groove width is 71 mm. It is a figure which shows the electric field strength when a groove width is 61 mm. It is a figure which shows the electric field strength at the time of setting a groove width to 56 mm. It is a figure which shows the electric field strength when a groove width is 51 mm. It is a figure which shows the electric field strength when a groove width is 46 mm. It is a figure which shows the electric field strength when a groove width is 41 mm. It is a figure which shows the electric field strength when a groove width is 36 mm. 6 is a cross-sectional view of a dielectric as Comparative Example 1. FIG. 10 is a cross-sectional view of a dielectric as Comparative Example 2. FIG. It is sectional drawing of the dielectric material as the comparative example 3. FIG. 3 is a diagram showing an electron number distribution of Example 1. 6 is a graph showing an electron number distribution of Comparative Example 1. FIG. 6 is a graph showing an electron number distribution of Comparative Example 2. FIG. 10 is a diagram showing an electron number distribution of Comparative Example 3. FIG. It is a figure which shows E / R distribution of Example 1. FIG. It is a figure which shows E / R distribution of the comparative example 1. FIG. It is a figure which shows E / R distribution of the comparative example 2. It is a figure which shows E / R distribution of the comparative example 3. It is sectional drawing of the dielectric material as the comparative example 4. FIG. 10 is a plan view in which a dielectric and a slot antenna as Comparative Example 4 are superimposed. FIG. 10 is a plan view in which a slot antenna as a comparative example 5 and a dielectric are superimposed. It is a figure which shows E / R distribution of Example 1. FIG. It is a figure which shows E / R distribution of the comparative example 5.

  A plasma processing apparatus 11 according to an embodiment of the present invention will be described with reference to FIGS. 1 is a diagram showing the plasma processing apparatus 11, FIG. 2 is a sectional view of the dielectric 15, and FIG. 3 is a plan view in which the dielectric 15 and the slot antenna 24 are overlapped. First, referring to FIG. 1, the plasma processing apparatus 11 mainly includes a processing container 12 and a dielectric 15 that constitute a plasma processing space S, a microwave supply device 18, and an exhaust device 26.

The processing container 12 is a bottomed cylindrical body having an upper opening, and includes a susceptor 13 as a holding table for holding the semiconductor wafer W therein, and a gas introduction unit 14 for introducing a processing gas. The susceptor 13 is connected to an AC power source 13a that manages the surface temperature of the semiconductor wafer W and generates a high-frequency signal for bias. The processing gas introduction unit 14 is provided on the side wall surface of the processing container 12 and supplies processing gas from a processing gas supply source (not shown) to the processing space S. As the processing gas, argon gas, C ₄ F ₈ gas or the like is properly used depending on the processing content.

  The dielectric 15 is a disk-shaped member made of quartz, and is disposed so as to close the upper opening of the processing container 12. Further, a sealing material 12 a for sealing the processing space S is provided on the contact surface between the processing container 12 and the dielectric 15.

  Next, the configuration of the dielectric 15 will be described in detail with reference to FIG. A ring-shaped concave groove 16 and a skirt 17 that protects the processing vessel 12 from plasma are provided on the lower surface of the dielectric 15.

  The side wall surfaces 16a and 16b of the concave groove 16 are inclined surfaces that are inclined so that the thickness dimension of the dielectric 15 continuously changes. In this embodiment, the inner peripheral side wall surface 16a and the outer peripheral side wall surface 16b are each a conical surface (conical side wall surface), that is, a cross-sectional shape is a straight line. (Inclined part 34c of FIG. 23) may be sufficient.

  Further, if a region R / 4 (R is a radius of the dielectric 15) from the center of the dielectric 15 is defined as a central region, and an outside of the central region is defined as an end region, the concave groove 16 is defined as an end of the dielectric 15. It is arranged in the partial area. That is, the inner diameter of the groove 16 is larger than R / 4.

  In this embodiment, the diameter of the dielectric 15 is 458 mm, the inner diameter of the concave groove 16 is 190 mm, the outer diameter of the concave groove 16 is 381 mm, the groove width w (width of the bottom wall) of the concave groove 16 is 66 mm, and the center The thickness of the dielectric 15 in the partial region is 30 mm, the thickness of the dielectric 15 in the bottom wall of the concave groove 16 is 15 mm, the angle formed by the lower surface of the central region and the inner peripheral side wall surface 16a is 45 °, and the central region The angle formed between the lower surface of the outer peripheral wall 16b and the outer peripheral side wall surface 16b is 60 °.

Here, the theoretical value w ₀ of the groove width (bottom wall width) of the concave groove 16 is expressed by a formula (c) where the speed of light is c, the frequency of the microwave is f, and the relative dielectric constant of the material constituting the dielectric is εr. 2).

In this embodiment, the speed of light c = 2.99979458 × 10 ¹¹ (mm / s), the frequency f of the microwave f = 2.45 × 10 ⁹ (sec−1), and the relative dielectric constant of quartz constituting the dielectric 15. Since εr = 3.8, w ₀ ≈63 mm.

Further, since a margin of ± 50% of the theoretical value w ₀ is allowed for the actual groove width w, the groove is within a range satisfying the formula (1), in this embodiment, within a range of 33 mm ≦ w ≦ 93 mm. The width w can be set.

  In the above-described embodiment, an example in which quartz is adopted as the material constituting the dielectric 15 has been shown. However, the present invention is not limited to this, for example, ceramics such as AlN (relative dielectric constant 9.5 to 9.6). ) May be adopted. In this case, the groove width w of the concave groove 16 is 20 mm ≦ w ≦ 60 mm.

  The microwave supply device 18 is a device that supplies microwaves to the dielectric 15 in order to generate plasma on the lower surface of the dielectric 15, and is a microwave generation source 19 that generates microwaves of a predetermined frequency f, The load matching unit 20, the coaxial waveguide 21, the slow wave plate 22, the antenna cover 23 covering the slow wave plate 22, and the slot antenna 24 are configured.

  The coaxial waveguide 21 includes an inner conductor 21a and an outer tube 21b that covers the inner conductor 21a. The inner conductor 21a has one end connected to the microwave generation source 19 via the load matching unit 20 and the other end connected to the slot antenna 24. The inner conductor 21a receives the microwave generated by the microwave generation source 19. This is supplied to the slot antenna 24. In addition, the shape of the other end portion (on the slot antenna 24 side) of the inner conductor 21 a is a conical shape that spreads toward the slot antenna 24, and microwaves can be efficiently propagated to the slot antenna 24.

  The slot antenna 24 is a thin copper plate plated with a conductive material, for example, Ag, Au or the like, and is disposed on the upper surface of the dielectric 15. The slot antenna 24 is provided with a plurality of slots 25 having a long hole shape penetrating in the thickness direction. Microwaves generated by the microwave generation source 19 are radiated to the dielectric 15 through the slots 25.

  Referring to FIG. 3, when dielectric 15 and slot antenna 24 are overlapped, at least a part of slot 25 is positioned vertically above inner peripheral side wall surface 16a and outer peripheral side wall surface 16b, which are inclined surfaces. . In this embodiment, the slot 25 includes a first slot group 25a positioned vertically above the central region, a second slot group 25b positioned vertically above the inner peripheral side wall surface 16a, and the bottom wall of the groove 16. Are divided into a third slot group 25c positioned vertically above and a fourth slot group 25d positioned vertically above the outer peripheral side wall surface 16b.

The slot 25 is a slot (first and third slot groups 25 a, 25 a) inclined at the same angle θ _{1 in} one direction (clockwise direction) with respect to a straight line connecting the center of the slot antenna 24 and each slot 25. and 25c), such as the other direction (counterclockwise direction) is inclined by the same angle theta ₂ slots (second and fourth slot group 25b, 25d) Toga径direction are arranged alternately (this The arrangement form is called “radial line slot”).

  The exhaust device 26 is a device for discharging the processing gas in the processing space S to the outside, and the processing gas is discharged from the processing space S through the exhaust pipe 27 connected to the processing container 12 and the exhaust pipe 27. And a vacuum pump 28 for discharging.

  Next, the operation of the plasma processing apparatus 11 having the above configuration will be described.

  First, the semiconductor wafer W is placed on the susceptor 13. During the plasma processing, the surface temperature of the semiconductor wafer W is controlled by the susceptor 13 and a bias high frequency is applied to the semiconductor wafer W from the AC power supply 13a.

  Next, the processing gas is supplied from the gas introduction unit 14 into the processing space S, and excess processing gas is discharged by the exhaust device 26. As a result, the processing space S can be set at a predetermined pressure.

  When a microwave is generated by the microwave generation source 19 and the microwave is supplied to the dielectric 15 via the load matching unit 20, the coaxial waveguide 21, the slow wave plate 22, and the slot antenna 24, the dielectric An electric field is generated on the lower surface of 15. As a result, the processing gas in the processing space S is ionized and turned into plasma, and a predetermined plasma processing, such as etching processing, ashing processing, and film forming processing, is performed on the semiconductor wafer W by selecting the type of processing gas. Various plasma treatments such as can be performed.

  Next, with reference to FIGS. 4-11, the change of the electric field strength at the time of changing the groove width w of the ditch | groove 16 is demonstrated. FIG. 4 is a diagram showing the electric field strength when the embodiment shown in FIG. 2, that is, the groove width w = 66 mm. 5 to 11, the groove width is 71 mm (FIG. 5), 61 mm (FIG. 6), 56 mm (FIG. 7), 51 mm (FIG. 8), 46 mm (FIG. 9), 41 mm (FIG. 10), 36 mm (FIG. 11). FIG. 4 to 11 are brighter (the color is lighter) as the electric field strength is stronger, and darker (the color is darker) as it is weaker.

  With reference to FIGS. 4 to 11, the electric field strength of a predetermined value or more was confirmed in all the dielectrics 15. Further, it was confirmed that the electric field strength of the dielectric 15 having a groove width of 66 mm (FIG. 4) was the highest, and the electric field strength was decreased as the groove width of the concave groove 16 was increased or decreased.

  That is, by defining the groove width w within the range of the formula (1), in this embodiment within the range of 33 mm ≦ w ≦ 93 mm, the microwave resonates in the width direction of the concave groove 16, and the dielectric 15 Increase the electric field strength on the bottom surface. As a result, plasma ignitability necessary for the treatment can be ensured.

  In particular, in the dielectric 15 having a groove width of 66 mm (FIG. 4), a groove width of 71 mm (FIG. 5), and a groove width of 61 mm (FIG. 6), there may be a portion where the electric field strength is particularly high at a predetermined interval. confirmed. That is, even when the processing space S is set to a low pressure (for example, 50 mT or less) by defining the groove width w within a range of ± 5 mm (± 7.5%) with the dielectric 15 having a groove width of 66 mm as a reference. The plasma ignitability of the plasma processing apparatus 11 is greatly improved.

  On the other hand, in the dielectric 15 having a groove width of 56 mm or less, the electric field strength was not so high even at the position of the groove 16. When these dielectrics 15 are used, it is considered that the plasma is sufficiently ignited if the inside of the processing space S is set to a high pressure (for example, 100 mT or more), but it is considered that the plasma ignitability is lowered in a low pressure environment.

  From the viewpoint of resonating microwaves, the groove width w can be made larger than 71 mm, but the upper limit value of the groove width w is also limited by the diameter of the dielectric 15. That is, if the groove width w is too large with respect to the diameter of the dielectric 15, there is a possibility that the strength of the dielectric 15 is reduced.

  In all cases (FIGS. 4 to 11), it was confirmed that the electric field strength was high at the position of the concave groove 16, and the electric field strength was decreased as the distance from the concave groove 16 was increased. That is, the plasma ignition start point can be controlled by the position of the concave groove 16. Specifically, if the concave groove 16 is disposed in the central region of the dielectric 15, the plasma is ignited starting from the central region (center first). On the other hand, if the recess 16 is disposed in the end region of the dielectric 15, the plasma is ignited starting from the end region (edge first).

  Next, with reference to FIG. 2 and FIGS. 12-22, the change of the uniformity of the plasma when the position and magnitude | size of the ditch | groove 16 are changed is demonstrated. 2 and 12 to 14 are diagrams illustrating the shape of the dielectric (Comparative Examples 1 to 3), and FIGS. 15 to 18 are diagrams illustrating the distribution of the number of electrons Ne when each dielectric is used. 19 to 22 are diagrams showing the distribution of the etching rate (E / R) when each dielectric is used.

  First, Example 1 is a dielectric 15 shown in FIG. The dielectric 31 (FIG. 12) as the comparative example 1 has an inner circumferential groove 31a located in the central area and an outer circumferential groove 31b located in the end area. The dielectric 32 (FIG. 13) as the comparative example 2 is provided with a concave groove 32 a having a narrower groove width than the concave groove 16, which is biased outward (the outer diameter coincides with the concave groove 16). The dielectric 33 (FIG. 14) as the comparative example 3 is provided with a concave groove 33 a having a narrower groove width than the concave groove 16 inward (the inner diameter coincides with the concave groove 16).

  In addition, the inner peripheral groove | channel in the comparative example 1 is not the object of the groove | channel in this invention.

  Referring to FIGS. 15 to 18, in all dielectrics, the number of electrons Ne tends to increase in the central region and decrease toward the end region. In particular, in Comparative Example 1, it was confirmed that the difference in the number of electrons Ne was large between the central region and the end region (FIG. 16). Therefore, it is desirable to provide the concave groove only in the end region, not in the central region of the dielectric.

  In Comparative Example 3, it was confirmed that the number of electrons Ne was uniform inside (± 100 mm) of the concave groove 33a, but the number of electrons Ne suddenly decreased outside the groove (FIG. 18). On the other hand, in Example 1 and Comparative Example 2, the number of electrons Ne was uniform up to the outer diameter position (± 190 mm) of the concave grooves 16 and 32a. Therefore, it is desirable to arrange the concave groove on the outer side of the dielectric.

  Furthermore, it was confirmed that the number of electrons Ne in the central region is the largest in Example 1 (FIG. 15). Specifically, the electron number Ne in the central region of Comparative Example 2 is approximately 60% of that in Example 1 (FIGS. 15 and 17), and the electron number Ne in the central region of Comparative Example 3 is approximately 70% of that in Example 1. (FIGS. 15 and 18). Therefore, it is desirable that the groove width of the concave groove is larger than a certain extent (61 mm or more according to FIGS. 4 to 11).

  Next, with reference to FIGS. 19 to 22, it was confirmed that the E / R was the most uniform (FIG. 19) in Example 1 and the most nonuniform (FIG. 20) in Comparative Example 1. Further, when the groove is arranged from the central region (Comparative Examples 1 and 3), the E / R of the central region is higher than that of the end region (FIGS. 20 and 22), and the concave groove is arranged from the end region ( Comparative Example 2) confirmed the tendency that the E / R in the end region was higher than that in the central region (FIG. 21).

  Next, changes in plasma ignitability with respect to the positional relationship between the slot 25 and the inclined surfaces 16a and 16b will be described with reference to FIGS. 23 is a diagram showing a dielectric 34 as Comparative Example 4, FIG. 24 is a plan view in which the dielectric 34 and the slot antenna 24 are overlapped, and Tables 1 and 2 are the microwave output and the processing space S. It is a table | surface which shows the plasma ignitability at the time of changing the pressure of.

  Referring to FIG. 23, in the dielectric 34 as the comparative example 4, the thickness of the central region 34a on the lower surface is relatively thin, and the thickness of the end region 34b is relatively thick. Further, an inclined portion 34c whose thickness changes continuously is provided between the central region 34a and the end region 34b. Next, referring to FIG. 24, all the slots 25 are arranged inside the inclined portion 34c, that is, in the flat central region 34a.

  Table 1 shows Example 1 (FIG. 2) based on a combination of microwave output (500 W, 1000 W, 1500 W, 2000 W, 2200 W, 3000 W) and pressure in the processing space S (5 mT, 20 mT, 30 mT, 50 mT, 100 mT). 3) The results of confirming the plasma ignitability of 3). Table 2 shows the results of conducting the same experiment as described above for Comparative Example 4 (FIGS. 23 and 24). In the table, ◯ indicates that the ignitability is good, △ indicates that it is ignited but is not stable, x indicates that it is not ignited, and − indicates that the test is not performed under the conditions. .

  In Example 1, it was confirmed that the plasma ignitability was good in all combinations of the microwave output and the pressure in the processing space S (Table 1). On the other hand, in Comparative Example 4, although the plasma ignitability improved as the microwave output increased and the pressure in the processing space S increased, it was confirmed that the plasma ignitability as a whole was low (Table 2).

  Therefore, from the viewpoint of plasma ignitability, it is desirable to provide the slot 25 vertically on the inclined surface, that is, the inner peripheral side wall surface 16a and the outer peripheral side wall surface. If the microwave wavelength matches the thickness of the dielectric plate at any position on the inclined surface, the electric field strength on the lower surface of the dielectric increases. As a result, plasma ignitability and ignition stability are improved. This is particularly advantageous when the microwave output is small and the pressure in the processing space S is low.

  Next, the relationship between the arrangement of the slots 25 and the E / R will be described with reference to FIGS. 3 and 25 to 27. 25 is a plan view in which the slot antenna 35 and the dielectric 15 as Comparative Example 5 are overlapped, and FIGS. 26 and 27 are diagrams showing the E / R distributions of Example 1 and Comparative Example 5. FIG.

  First, referring to FIG. 25, the slot antenna 35 as the comparative example 5 omits the first slot group 25a and the third slot group 25c shown in FIG. That is, all the slots 36 provided in the slot antenna 35 are positioned on the inclined surface, that is, vertically above either the inner peripheral side wall surface 16a or the outer peripheral side wall surface 16b. Further, all the slots 36 are inclined at the same angle in the same direction with respect to the straight line connecting the center of the slot antenna 35 and each slot 36 (this arrangement form is called “parallel slot”).

  Referring to FIGS. 26 and 27, it was confirmed that E / R was slightly more uniform in Comparative Example 5. Therefore, from the viewpoint of E / R uniformity, it is desirable to provide the slot only vertically above the inclined surface.

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment shown in figure. Various modifications and variations can be made to the illustrated embodiment within the same range or equivalent range as the present invention.

  The present invention is advantageously used in a plasma processing apparatus.

  DESCRIPTION OF SYMBOLS 11 Plasma processing apparatus, 12 Processing container, 12a Seal material, 13 Susceptor, 13a AC power supply, 14 Gas introduction part, 15, 31, 32, 33, 34 Dielectric, 16, 31a, 31b, 32a, 33a Concave groove, 16a , 16b Side wall surface, 17 skirt, 18 microwave supply device, 19 microwave generation source, 20 load matching device, 21 coaxial waveguide, 21a inner conductor, 21b outer tube, 22 slow wave plate, 23 antenna cover, 24, 35 slot antenna, 25, 36 slot, 25a, 25b, 25c, 25d slot group, 26 exhaust device, 27 exhaust pipe, 28 vacuum pump, 34a central region, 34b end region, 34c inclined portion.

Claims (6)

A processing vessel having an upper opening;
A dielectric having a ring-shaped concave groove on a lower surface and arranged to close an upper opening of the processing vessel;
An antenna for supplying microwaves to the dielectric and generating plasma on the lower surface of the dielectric;
The plasma processing apparatus, wherein the groove width w of the groove satisfies Equation (1) where c is the speed of light, f is the frequency of the microwave, and εr is the relative permittivity of the material constituting the dielectric.
If the radius of the dielectric is R,
The plasma processing apparatus according to claim 1, wherein the concave groove is located outside R / 4 from a center of the dielectric. When the microwave frequency supplied from the antenna is f = 2.45 × 10 ⁹ (Hz) and the dielectric material is quartz having a relative dielectric constant εr = 3.8, the groove width w of the concave groove is The plasma processing apparatus according to claim 1, wherein 33 mm ≦ w ≦ 93 mm is satisfied.   4. The device according to claim 1, wherein at least one of the inner peripheral side wall surface and the outer peripheral side wall surface of the concave groove is an inclined surface that is inclined so that a thickness dimension of the dielectric continuously changes. The plasma processing apparatus according to 1. The antenna has a plurality of slots penetrating in the thickness direction,
The plasma processing apparatus according to claim 4, wherein the plurality of slots are positioned vertically above the inclined surface. The plasma processing apparatus according to claim 5, wherein the plurality of slots are inclined at the same angle in the same direction with respect to a straight line connecting the center of the antenna and each slot.