JP5696206B2 - Plasma processing equipment - Google Patents

Description

  The present invention relates to a plasma processing apparatus for performing surface treatment such as etching of a substrate and thin film formation by plasma, and more particularly to an inductively coupled plasma processing apparatus.

  In the semiconductor device manufacturing field, inductively coupled plasma processing apparatuses are used as etching and CVD apparatuses. In this inductively coupled plasma processing apparatus, an induction coil having several turns is arranged outside a vacuum vessel, and a high frequency current is passed through the induction coil to supply power to the plasma generated in the vacuum vessel. To maintain. In order to supply a sufficient coil current, this induction coil generates a high voltage of a maximum of several KV non-uniformly along the coil and has a non-negligible stray capacitance existing between the induction coil and the plasma. Exists.

  This high voltage and stray capacitance cause the following two problems. One problem is that the high voltage on the coil is electrostatically coupled by stray capacitance that exists between the plasma and causes local damage to the induction window that exists between the coil and the plasma. Another problem is that while the current circulates on the coil, the coil current becomes non-constant due to the presence of the stray capacitance existing on the line, and the circumferential uniformity of the generated plasma is deteriorated. .

The former problem can be solved by installing a Faraday shield between the induction coil and the plasma as disclosed in, for example, Patent Document 1 and Patent Document 2.
In addition, for the latter problem, for example, as disclosed in Non-Patent Document 1, a method for reducing fluctuations in the coil current by installing a coupling capacitor on the terminal end side of the induction coil is well known. It has been. However, the method of introducing this coupling capacitor has the following problems. For one, the coupling capacitor has the effect of alleviating non-uniformity of the circulating current, but cannot be made uniform in a strict sense. Regarding this point, a quantitative explanation will be given later. The second problem is that the optimum value of the capacitor changes depending on the operating conditions (operating plasma density, pressure, operating gas conditions, etc.), but it is difficult to replace the capacitor each time in a mass production apparatus. Alternatively, the use of a variable capacitor as the capacitor leads to an increase in cost of the control device and a complicated operation method. The third problem is that the coupling capacitor needs to have a withstand voltage performance of several tens of KVA, and the geometrical shape is never small. For example, when mounting in a matching box provided on the upper part of the device, The size of the matching box is increased, which causes a mounting problem.

  In particular, the induction coil group is divided into two systems, an inner circumference and an outer circumference, and the respective coil current ratios are variable to adjust the plasma radial uniformity according to operating conditions (Patent Document 2 and Patents). In the case of Document 3, etc.) or a device that stabilizes the inner wall state in the vacuum vessel by adjusting the voltage applied to the Faraday shield and adjusting the degree of electrostatic coupling with the plasma (Patent Document 2 and Patent Document) In the case of 4), the second and third problems are remarkable.

US Pat. No. 5,534,231 and drawings US Pat. No. 6,756,737 and drawings U.S. Pat. No. 5,777,289 and drawings US Pat. No. 5,817,534 and drawing

MarkJ. Kushner, "Athree-dimensional model for inductively coupled plasma etching reactors: Azimuthal symmetry, coil properties, and comparison to experiments" J. Appl. Phys. 80, 1337

Therefore, if there is non-uniformity in the coil current due to circulation, the uniformity in the circumferential direction of the generated plasma will be reduced unless measures are taken against it. It is desired to improve the nonuniformity of the generated plasma in the circumferential direction by compensating the nonuniformity of the current.
An object of the present invention is to provide a plasma processing apparatus that compensates for a coil current that changes as the coil circulates and improves the uniformity of the generated plasma in the circumferential direction.

  Generally, the plasma density is determined by the plasma current generated by induction, and the induced plasma current is determined by the magnitude of the mutual inductance between the coil and the plasma, together with the current value of the coil itself. When there is a ring-shaped passive conductor in the vicinity of the coil, in addition to the mutual inductance between the coil and plasma, a mutual inductance between the ring conductor and plasma and a mutual inductance between the ring conductor and coil are generated. Affects size. This indicates that these mutual inductances can be a factor controlling the magnitude of the plasma current. In other words, if the coil current has non-uniformity associated with the turn, the mutual inductance may be changed according to the angle with the turn so as to compensate for the non-uniformity. In the present invention, the specific method and the confirmation result of the effect are disclosed.

  In order to achieve the above object, a plasma processing apparatus according to the present invention comprises a vacuum processing chamber for generating plasma inside, means for introducing a gas into the vacuum processing chamber, and a mounting for mounting a sample in the vacuum processing chamber. An insulating induction window that forms an upper part of the vacuum processing chamber and covers the plasma generation space above the mounting base, and generates plasma in the plasma generation space inside the vacuum processing chamber that is disposed outside the induction window. A coil-shaped induction antenna, a high-frequency power supply for supplying current to the induction antenna, and a matching box, and a conductor disposed near the induction antenna and along the induction antenna The mutual inductance at the circumferential position between the conductor and the antenna and between the conductor and the plasma is controlled.

In this plasma processing apparatus, the conductor disposed along the induction antenna is a ring-shaped conductor substantially concentric with the induction antenna, and between the ring-shaped conductor and the induction antenna and between the ring-shaped conductor and the plasma. It is preferable that the mutual inductance has such a shape that is gradually increased according to the circumference of the ring-shaped conductor.
In the plasma processing apparatus using a ring conductor as a conductor, a Faraday shield is provided between the induction window and the induction coil (induction antenna) so that the voltage can be adjusted through the matching box. Can do. The ring-shaped conductor is in electrical contact with the Faraday shield, and is disposed on the outermost periphery of the plurality of induction coils (induction antennas). The radius of the inner periphery of the ring is in accordance with the circulation of the ring. The ring-shaped conductor is in electrical contact with the Faraday shield and is arranged on the innermost circumference of the plurality of induction coils, and the radius of the outer circumference of the ring is the circumference of the ring. It can be assumed that the shape is recurring according to.
That is, a ring-shaped conductor is installed in the vicinity of the induction coil, and the ring-shaped conductor can have a different radius from the center of the device and a cross-sectional shape of the ring conductor for each coil turning angle.

  In this plasma processing apparatus, the dielectric window can have a flat plate shape. A plasma processing apparatus can be configured by arranging a planar induction coil on a flat induction window.

  According to this plasma processing apparatus, there is a conductor disposed in the vicinity of the induction antenna and along the induction antenna, and the mutual inductance between the conductor and the induction antenna and between the conductor and the plasma in the circumferential position is reduced. Since it is controlled, it is possible to compensate for the coil current that changes as the coil circulates, and to improve the uniformity of the generated plasma in the circumferential direction.

FIG. 1 is a cross-sectional view of the plasma processing apparatus of the present invention. FIG. 2 is a diagram showing a first embodiment of the present invention. FIG. 3 is a diagram showing a current distribution on the induction coil in the prior art. FIG. 4 is an equivalent circuit diagram modeling an induction coil and a plasma circuit in the prior art. FIG. 5 is a diagram showing the distribution of plasma current in the prior art. FIG. 6 is an analysis of the state of plasma diffusion in a vacuum vessel according to the prior art. FIG. 7 is a diagram showing the actual measurement result of the plasma density on the wafer, the actual measurement result of the SiO ₂ etching rate, and the calculation result of the plasma density on the wafer in the prior art. FIG. 8 is a diagram showing a distribution of coil current when an optimum coupling capacitor is inserted at the induction coil termination in the prior art. FIG. 9 is a diagram showing a coil current distribution, a plasma current distribution, and a current distribution on the conductor ring when the ring-shaped conductor of the present invention is inserted. FIG. 10 is an equivalent circuit diagram modeling the ring-shaped conductor, induction coil and plasma circuit of the present invention. FIG. 11 is a diagram showing another embodiment of the ring-shaped conductor of the present invention. FIG. 12 is a diagram showing another embodiment of the ring-shaped conductor according to the present invention. FIG. 13 is a diagram showing an apparatus configuration of the second embodiment of the present invention. FIG. 14 is a diagram showing a coil current distribution and a plasma current distribution when the ring-shaped conductor of the present invention is not used in the second embodiment. FIG. 15 is a diagram showing a coil current distribution and a plasma current distribution when the ring-shaped conductor 8a of the present invention is used in the second embodiment. FIG. 16 is a diagram showing a coil current distribution and a plasma current distribution when the ring-shaped conductor 8b of the present invention is used in the second embodiment.

Embodiments of a plasma processing apparatus according to the present invention will be described below with reference to the drawings.
The first embodiment is an example of the inductively coupled etching apparatus disclosed in Patent Document 2, and this inductive coupling etching apparatus will be taken as an example to describe the prevention of non-uniformity of coil circulation current.

FIG. 1 shows a cross-sectional view of a plasma processing apparatus according to the present invention. The vacuum vessel 2 has a discharge window 2a made of an insulating material (for example, non-conductive material such as Al ₂ O ₃ ceramic) that forms a plasma generating portion and a sample 12 that is an object to be processed. And a processing section 2b on which the electrode 5 is disposed. A coiled inductively coupled antenna 1 is disposed outside the discharge window 2a. The inductive coupling antenna 1 is divided into two systems of an inner peripheral coil 1a and an outer peripheral coil 1b each having two turns, and the energization current can be controlled for each system by controlling a variable capacitor VC4 inside the matching box 3 described later. It is like that. Further, a frustoconical Faraday shield 8 that is capacitively coupled to the plasma 6 is provided outside the discharge window 2a. The inductively coupled antenna 1 and the Faraday shield 8 are connected in series to a first high frequency power supply 10 via a matching unit (matching box) 3. In parallel with the Faraday shield 8, circuits (VC3, L3) having variable impedances are grounded to the ground so that the voltage applied to the Faraday shield 8 can be controlled.

  While the processing gas is supplied from the gas supply device 4 into the vacuum vessel 2, it is evacuated to a predetermined pressure by the exhaust device 7. A processing gas is supplied from the gas supply device 4 into the vacuum vessel 2, and the processing gas is turned into plasma by the action of an electric field generated by the inductively coupled antenna 1 and the Faraday shield 8. A second high frequency power supply 11 is connected to the electrode 5. In addition, by supplying high frequency power in the HF band such as 13.56 MHz, 27.12 MHz, and 2 MHz generated by the first high frequency power supply 10 to the inductively coupled antenna 1 and the Faraday shield 8, an electric field for generating plasma is generated. However, in order to suppress the reflection of power, the matching unit (matching box) 3 is used to match the impedance of the inductively coupled antenna 1 with the output impedance of the first high-frequency power source 10. The matching unit (matching box) 3 uses a variable capacitor 9a, 9b, which is generally called an inverted L type, and whose capacitance can be varied. In addition, a bias voltage is applied to the electrode 5 by the second high-frequency power source 11 in order to draw ions present in the plasma 6 onto the sample 12.

  The Faraday shield 8 is made of a metal conductor having a vertically striped slit, and is arranged so as to overlap the ceramic vacuum vessel 2. The voltage to the Faraday shield 8 can be adjusted by a variable capacitor represented by VC3 in FIG. The Faraday shield 8 has a function of preventing local damage of the ceramic discharge window 2a due to local electrostatic coupling to plasma caused by the non-uniform high voltage of the inner and outer coils 1a and 1b, and a positively controlled size. By providing the plasma with uniform electrostatic coupling, it has a function of maintaining the plasma inner wall in an optimum state.

  The ring-shaped conductors 8a and 8b having a specific shape used in the plasma processing apparatus according to the present invention are installed at the locations shown in FIG. That is, the ring-shaped conductor 8a compensates for non-uniformity caused by the circulation of the coil current flowing through the inner induction coil 1a out of the two-system induction coils, and the inner side of the induction coil 1a (frustum-shaped Faraday shield). 8 installed at the bottom of the floor). The ring-shaped conductor 8b compensates for the non-uniformity caused by the circulation of the coil current flowing through the outer periphery induction coil 1b, and is installed at the bottom of the truncated cone outside the induction coil 1b.

  An example of the ring shape of the ring-shaped conductors 8a and 8b is shown in FIG. 2A is a view showing a first embodiment of a ring-shaped conductor used in the plasma processing apparatus shown in FIG. 1, and FIG. 2B is an outer side of the ring-shaped conductor shown in FIG. It is a figure shown about a ring-shaped conductor. Although the ring mechanism will be described later, when a coupling capacitor is not inserted at the end of the coil, the coil current (and hence the plasma current) is generally weak at the power supply end (inlet side) to which the power is connected, and the end (exit) The coil current gradually increases (and therefore the plasma current also increases). In the example shown in FIG. 1, the inner coil 1a corresponds to such a coil. Thus, the ring-shaped conductor 8a for compensating the inner coil has a uniform thickness, but conversely, in the vicinity of the outlet of the inner peripheral coil 1a, the conductor has a smaller radial width in the vicinity of the inlet of the inner peripheral coil 1a. Although the inner radius is not changed, the radial width is increased by increasing the conductor outer radius. By doing so, the mutual inductance between the ring-shaped conductor 8a and the plasma and the inner coil 1a is reduced at the circumferential position (feed end) where the radial width of the ring-shaped conductor 8a is small, and the induced plasma current is increased. Direction. Conversely, at the circumferential position (termination) where the radial width of the ring-shaped conductor 8a is large, the mutual inductance between the plasma coil 1a and the ring-shaped conductor 8a increases, and as a result, the current flows in the ring-shaped conductor 8a. Tends to be smaller. Therefore, it is possible to compensate for the non-uniformity of the plasma current that accompanies the circulation of the original coil current.

  On the other hand, the outer ring-shaped conductor 8b is uniform in thickness, but the outer radius of the conductor is not changed near the entrance of the outer coil 1b, but the radial width of the conductor is increased by reducing the inner radius of the conductor. Conversely, the outer radius of the conductor does not change in the vicinity of the outlet of the outer coil 1b, but the radial width is narrowed by increasing the inner radius. By doing so, the mutual inductance between the ring-shaped conductor 8b and the plasma and the coil 1b is increased at the circumferential position (feeding end) where the radial width of the ring-shaped conductor 8b is large, and the current is eroded by the ring-shaped conductor 8b. The induced plasma current becomes smaller. Conversely, at the circumferential position (termination) where the radial width of the ring-shaped conductor 8b is small, the mutual inductance between the plasma coil 1b and the ring-shaped conductor 8b decreases, and the plasma current tends to increase. Therefore, it is possible to compensate for the non-uniformity of the plasma current that accompanies the circulation of the original coil current.

  Hereinafter, the ring-shaped conductor used in the plasma processing apparatus according to the present invention will be described more quantitatively, and the results of simulations and experiments for verifying the validity of the function will be described.

  First, the non-uniformity of the coil current, the non-uniformity of the plasma current resulting from the non-uniformity of the plasma current, and the non-uniformity of the etching result in the current prior art will be described using simulation and experimental data. Here, as a prior art, in FIG. 1 or FIG. 2, it defines as a thing when there is no conductor ring 8a, 8b, or when a ring with a constant inner radius and outer radius exists in the circumferential direction.

  FIG. 3 shows the coil current obtained along the coil. 3A is for the inner coil 1a, and FIG. 3B is for the outer coil 1b. The vertical axis in the figure represents the coil current normalized by the average value of the coil current. Of L0 and L1 to L9 on the horizontal axis, L0 and L9 respectively represent a feed line (feed end) and a vertical shaft portion (end) of the return line of the coil. L1, L2 to L8 are obtained by tracing the respective 90 ° arcs when the coil is divided into 8 (every 90 °, 2 turns) in order from the power feeding side. These coil currents are calculated from an equivalent circuit shown in FIG. 4 described later. The calculation conditions at this time were such that the combined impedance of VC3 + L3 shown in FIG. That is, it is an operating condition in which the Faraday shield 8 is grounded. Further, VC4 for adjusting the ratio of the current flowing through the coils 1a and 1b was set to 100 pF. This corresponds to [current of the inner peripheral coil 1a] / [current of the outer peripheral coil 1b] = 1/2.

  From the description of FIG. 3 showing the calculation results, it can be seen that the coil current value of the inner peripheral coil 1a increases as it goes around, while the coil current value of the outer coil 1b decreases as it goes around. In the example taken up in the present embodiment, the inner peripheral coil 1a has no capacitors at the feeding end and the terminal end, and the outer peripheral coil 1b has an inner / outer coil current ratio adjusted to ensure radial uniformity. A variable capacitor VC4 is attached to the end. For this reason, the increasing / decreasing tendency of the coil current is opposite to each other in FIGS. The reason why this phenomenon occurs will be described below.

An equivalent circuit between the coils 1a and 1b, the plasma, and the Faraday shield 8 is expressed as shown in FIG. Here, FIG. 4 corresponds to the outer peripheral coil 1b (or the inner peripheral coil 1a). However, in the case of the inner peripheral coil 1a, VC4 = ∞ (short circuit), and in the case of the outer peripheral coil 1b, VC4 = 100 pF. L0 and L9 are the inductances of the longitudinal shaft portions of the power feeding line and the return line of the coil, and L1, L2,..., L8 are the self of each 90 ° arc when the coil is divided into 8 (every 90 °, 2 turns). Represents inductance. C1 to C9 represent stray capacitances between the coils 1a and 1b and the Faraday shield 8. Note that this stray capacitance is substantially the same in the following description because there is a stray capacitance between the coils 1a and 1b and the plasma even in a device without the Faraday shield 8. Lp1 and Lp2 represent self-inductances of the induction current ring flowing in the plasma, and are divided every quarter. The two-turn coil and the one-turn plasma current are inductively coupled. For example, the plasma Lp1 and the coils L1 and L5 are coupled through mutual inductances M1p1 and M5p1.
The expression of the self-inductance L, the mutual inductance M, and the stray capacitance C used in the circuit calculation is
L = μ ₀ R _a (Log (8R _a / a) −2)
M = μ ₀ (R _a R _b ) ^0.5 * [(2 / k−k) K (k) −2 / kE (k)]
k = [4R _a R _b / ((R _a + R _b ) ² + d ² )] ^0.5
d = ((R _a −R _b ) ² + (Z _a −Z _b ) ² ) ^0.5
C = 2πε ₀ εL / ln (2h / a)
Was used. here,
μ ₀ : Vacuum permeability,
R _{a / b} : main radius of the coil a / b,
a: small radius of coil a,
Z _{a / b} : height direction position of coil a / b,
K (k), E (k): first kind, second kind perfect elliptic integral,
ε ₀ : vacuum dielectric constant,
ε: dielectric constant,
L: coil circumference,
h: Distance between coil and Faraday shield or distance between coil and plasma (when no Faraday shield is provided).

Moreover, specific dimensions used as an apparatus, with respect to the inner circumference coil _{1a, a = 3.2mm, R a} / b = 71mm, 86mm, Z a / b = 80mm, 68mm, with respect to the outer circumference coil 1b is _{R a / B} = 137 mm, 153 mm, Z _{a / b} = 27 mm, 15 mm, for plasma, a = 20 mm, R _a = 60 mm (FIG. 2-6a) and 125 mm (FIG. 26b), Z _a = 55 mm (FIG. 2-6a) , And 0 mm (FIG. 26b). Further, h = 12.5 mm, L = 2πR _a , and ε = 1.

  The coils 1a and 1b and the Faraday shield 8 constitute a transmission line of series L and parallel C. Generally, when the terminal is short-circuited, the current increases toward the terminal, and the terminal is opened (or the capacitor terminal). In some cases, it is known that the current decreases towards the end. (For example, said nonpatent literature 1). 3A and 3B correspond to this principle. The distribution of the coil current shown in FIG. 3 is obtained by solving the circuit shown in FIG. 4 with respect to the coil current.

  FIG. 5 shows the distribution of the plasma current in the circumferential direction obtained by the circuit shown in FIG. 4 when the coil current has the above-described non-uniformity. It can be seen that non-uniformity appears in the plasma current according to the non-uniformity of the coil current, and the circumferential non-uniformity is about 5% in the range.

  The plasma is generated in the immediate vicinity of the coil of the vacuum container 2, diffuses in the container 2, and reaches the surface of the electrode 5 that is a sample stage. In the diffusion / arrival process, the nonuniformity of the plasma generation distribution is alleviated to some extent, but the circumferential nonuniformity remains on the sample surface. FIG. 6 shows the state obtained by calculation, and the diffusion equation ∇ · D∇N = S concerning the plasma density N is obtained in the vacuum vessel 2 by the three-dimensional finite element method. Here, S is the plasma generation distribution, and it is assumed that the generation distribution is proportional to the square of the plasma current shown in FIG. 5, and the regions immediately below the coils (6a, 6b... Not shown "). It is shown that the plasma diffuses in the downstream direction from the generation part and reaches the sample surface. As a result, the non-uniformity of the plasma density on the sample surface is 5% in this case, and the etching rate is non-uniform. Affects. In the example of FIG. 6, the average current of the inner peripheral coil 1a is calculated under operating conditions that are twice the average current of the outer peripheral coil 1b. In this case, the plasma density distribution on the wafer is the same as that of the outer peripheral coil 1b. The distribution mainly reflects the non-uniformity in the circumferential direction. The distribution is such that the density is higher on the left half surface and lower on the right half surface than the feeding end.

FIG. 7 shows the results of measuring the plasma density by installing a multi-probe on the sample surface, and the results of etching the SiO ₂ thin film as the material to be etched with Cl ₂ / BCl ₃ gas. It is shown side by side with the calculation result shown in FIG. The three non-uniform directions are almost the same, and it can be seen that the non-uniformity of the lower coil current affects the etching performance.

In addition, it shows about the case where the optimum value capacitor is inserted into the terminal end shown in the publicly known example in this apparatus system. In the case of this embodiment, the input inductance viewed from the feeding end of the outer peripheral coil is L = 1.1 μH, so the value of the optimum insertion capacitor is C = 2 / ω ² / L = 200 pF in capacitance value. . (Ω is an angular frequency, 2π * 13.56 MHz). As shown in FIG. 8, the coil current in this case has the same current value at the input end and termination, and the non-uniformity along the coil is largely alleviated. Uniformity cannot be completely controlled. As in this embodiment, in the case of an induction coil that forms a set with two turns, an averaging effect for two turns can be added and the plasma current can be made uniform to some extent. In the case of adopting a coil configuration such as a parallel connection of one-turn coils, the extreme value of the middle part of the coil remains even if a termination capacitor is used.

  Next, a case where a variable shape ring conductor is mounted in the plasma processing apparatus according to the present invention will be described. In this case, in the case of FIG. 2 of the present embodiment, since the outer peripheral coil has a strong influence on the plasma density non-uniformity on the wafer, the behavior of the outer peripheral coil will be mainly described.

  FIG. 9 shows the distribution in the circumferential direction of the coil current, ring current, and plasma current when the ring-shaped conductor 8b is inserted. Compared with FIGS. 3B and 5B without the ring-shaped conductor, the non-uniformity of the coil current itself does not change, but as shown in FIG. 2, the inner radius of the ring-shaped conductor is in the circumferential direction. As a result, the mutual inductance between the plasma, the coil, and the ring-shaped conductor changes, and as a result, the induced magnetic field felt by the plasma becomes uniform, resulting in the plasma as shown in FIG. The current distribution is uniform. As shown in FIG. 9C, a current distributed in the circumferential direction flows in the ring-shaped conductor as a result to compensate for the non-uniformity of the coil current. The surplus current (or insufficient current) for the current that circulates around the ring-shaped conductor flows through the Faraday shield's beam part to satisfy the entire current conservation. This does not affect the induced current.

This result is obtained from an equivalent circuit model when the ring-shaped conductor shown in FIG. 10 is introduced. A ring-shaped conductor circuit indicated by Lf1 to Lf4 is added to the equivalent circuit of FIG. 4, and due to the presence of the ring-shaped conductor, the mutual inductance between the plasma and the coil is, for example, related to the side element Lf1. Mp1f1, M1f1, M5f1, etc. are newly added. As a result of the improved plasma current uniformity, the plasma density uniformity on the wafer surface is improved. Note that the actual radial dimension at each position of the ring conductor having a variable radius is 163, 159, 157, 155 (unit: Lf1, Lf2, Lf3, Lf4 in this order) as shown in the lower right part of FIG. mm). For this dimension, the optimum value was obtained by repeatedly calculating the circuit calculation of FIG.
In this embodiment, since the influence of the current nonuniformity of the inner peripheral coil on the etching uniformity is not great, the calculation details are not presented. Using the ring-shaped conductor 8a shown, the plasma current portion generated by the inner peripheral coil can be made uniform by the same principle.

  In the present embodiment, the ring-shaped conductor having the shape shown in FIG. 3 has been described. For example, the ring-shaped conductor is divided into a main body and an adjustment ring, and the adjustment ring should be designed so that it can be easily replaced. It is also convenient for adjustment according to the actual machine operating conditions and adjustment for machine differences between devices.

  In the present embodiment, the ring-shaped conductor is described as an example of a flat ring whose inner radius or outer radius changes according to the circulation, but the mutual inductance between the side element of the ring, the coil element, and the plasma element is If the shape is variable according to the circulation, the plasma can be made uniform according to the principle of the present invention. For example, the outer ring-shaped conductor 8b may be a simple ring having a constant radius and width as shown in FIG. 11, and may have a shape in which the position in the height direction changes according to the circulation. Further, as shown in FIG. 12, a sheet-like ring-shaped conductor may be arranged along the tapered surface of the tapered discharge window 2a.

  Next, a second embodiment of the present invention will be described. The second embodiment is an embodiment in which a planar induction coil is arranged on a flat plate-shaped induction window made of quartz.

  FIG. 13 shows the overall structure. FIG. 13A is a plan view of the second embodiment, and FIG. 13B is a side sectional view thereof. A two-turn induction coil 1a is arranged on the flat plate induction window 2a. In addition, the compensation ring has a shape like the ring-shaped conductor 8a or 8b. However, in the case of the compensation ring 8b on the outer periphery, it is assumed that it is electrically connected to the conductor cover 13 surrounding the entire coil chamber. In the case of this embodiment, there is no Faraday shield as shown in the first embodiment. In this case, the equivalent circuit shown in FIGS. 4 and 10 can be used as the equivalent circuit, but the stray capacitance (C1 to C9) between the coil and the Faraday shield is the stray capacitance between the coil and the plasma. And change the definition.

  First, FIG. 14 shows the current distribution on the coil and the current distribution on the plasma when there is no compensating ring conductor. In this embodiment, the nonuniformity of the coil current and the plasma current is larger than the coil current (FIG. 3A) and the plasma current distribution diagram 5A shown in the first embodiment. Yes. This is because the stray capacitance between the coil and the plasma is increased because the coil 1a is arranged in close contact with the induction window 2a in the system of FIG. 13 taken up as an example. That is, in the first embodiment, the stray capacitance between the inner peripheral coil and the Faraday shield is about 30 pF, whereas in the second embodiment, the stray capacitance between the coil and the plasma causes the dielectric window 2a to pass through the dielectric window 2a. Due to the sandwiching, it becomes large at about 100 pF.

  FIG. 15 shows a coil current distribution, a plasma current distribution, and a distribution of current flowing on the outer periphery of the compensating ring conductor when only the inner ring conductor 8a is added among the compensating ring conductors. Although the non-uniformity of the distribution of the coil current itself is not improved as compared with FIG. 14, it can be seen that the plasma current distribution is uniform. It can also be seen that a current distributed in the circumferential direction flows on the outer periphery of the compensating ring-shaped conductor 8a. This is because the compensation ring-shaped conductors 8a having different outer diameters depending on the circumferences are arranged, so that the mutual induction inductance between the compensation ring-shaped conductor, the induction coil, and the plasma at each location changes, As a result, the plasma current is made uniform.

  FIG. 16 shows the coil current distribution, the plasma current distribution, and the distribution of the current flowing in the inner circumference of the compensation conductor ring when only the outer conductor ring 8b is installed among the compensation conductor rings. As in the example of FIG. 15, the non-uniformity of the distribution of the coil current itself is not improved as compared with FIG. 14, but it can be seen that the plasma current distribution is uniform. It can also be seen that a current distributed in the circumferential direction flows on the inner circumference of the compensation conductor ring 8b. Again, the principle similar to that described with reference to FIG. 1, that is, the fact that the mutual inductance changes depending on the location, contributes to uniform plasma current distribution.

  As described above, according to the present invention, the circumferential nonuniformity of the plasma current due to the presence of the stray capacitance of the induction coil can be greatly improved by the compensation conductor ring placed in the vicinity of the coil.

DESCRIPTION OF SYMBOLS 1 Antenna 2 Vacuum container 3 Impedance matching device 4 Gas supply apparatus 5 Electrode 6 Plasma 7 Gas exhaust apparatus 8 Faraday shield 8a Compensation conductor ring 8b Compensation conductor ring 9 Variable capacitor 10 High frequency power supply 11 High frequency power supply 12 Sample 13 Coil chamber cover

Claims (6)

A vacuum processing chamber in which the sample is plasma treated;
A mounting table for mounting the sample;
An insulating guide window that hermetically seals the upper part of the vacuum processing chamber;
A coiled induction antenna disposed outside the induction window and radiating an induction magnetic field;
A high frequency power supply for supplying high frequency power to the induction antenna;
A ring-shaped conductor disposed along the induction antenna,
The plasma processing apparatus, wherein the ring width of the conductor is gradually increased according to the circumference of the induction antenna. The plasma processing apparatus according to claim 1,
When the terminal end of the induction antenna is short-circuited, the ring width of the conductor increases in accordance with the circulation from the feeding end of the induction antenna toward the terminal end of the induction antenna. The plasma processing apparatus according to claim 1,
When the terminal end of the induction antenna is open, the ring width of the conductor is reduced according to the circulation from the feeding end of the induction antenna toward the terminal end of the induction antenna. In the plasma processing apparatus according to any one of claims 1 to 3,
The plasma processing apparatus, wherein the guide window has a flat plate shape. The plasma processing apparatus according to claim 1,
The induction antenna comprises a first induction antenna and a second induction antenna;
The plasma processing apparatus, wherein the conductor is disposed along at least the first induction antenna or the second induction antenna. A vacuum processing chamber in which the sample is plasma treated;
A mounting table for mounting the sample;
An insulating guide window that hermetically seals the upper part of the vacuum processing chamber;
A coiled induction antenna disposed outside the induction window and radiating an induction magnetic field;
A high frequency power supply for supplying high frequency power to the induction antenna;
A ring-shaped conductor disposed along the induction antenna,
The plasma processing apparatus, wherein a shortest distance between the conductor and the induction antenna in a radial direction of the ring-shaped conductor is gradually increased according to the circumference of the induction antenna.