JP7022982B2 - Exhaust structure for plasma processing room - Google Patents

Description

The present invention relates to an exhaust structure of a plasma processing chamber for performing plasma processing on a thin plate-shaped material to be processed (hereinafter, referred to as a "substrate") such as a wafer.

When plasma treatment such as film formation and etching is performed on the substrate, first, the substrate is set in a closed processing chamber, and the inside is evacuated by discharging gas (air, pretreatment gas, etc.) from the processing chamber. Then, plasma gas is introduced into the processing chamber, the plasma gas is converted into plasma by high frequency power or the like, and the substrate is processed.

There are various methods such as capacitive coupling type and inductively coupled type for power input to convert plasma gas into plasma, but in any case, in order to evenly etch the entire surface of the substrate, it is necessary to perform processing such as etching. The plasma formed in the upper space of the substrate needs to be in a uniform and stable state. Therefore, it is desirable that the treatment chambers near and around the plasma generation space have a uniform shape, and it is not preferable to provide an exhaust port for the vacuum exhaust there. Therefore, conventionally, the exhaust port of the processing chamber for plasma-treating the substrate has been provided so as to be below the surface of the substrate.

On the other hand, in order to improve the efficiency of plasma processing, it is desired to shorten the vacuum exhaust time. Most of the vacuum exhaust time is spent on suction of reaction products and water adhering to the inner wall of the processing chamber, but in order to shorten this, it is necessary to make the cross-sectional area of the exhaust port for vacuum exhaust as large as possible in the processing chamber. It is effective. Therefore, in the conventional device, it is common to provide the exhaust port on the side surface below the board mounting table (board surface) of the processing chamber. However, in this case, if the shape of the exhaust port is a normal circle, it is necessary to secure a depth corresponding to the diameter of the exhaust port below the board mounting table, so this is the opposite of the processing chamber volume. This has led to an increase in exhaust time, which has hindered the shortening of exhaust time.

In order to solve such a problem, in Patent Document 1 (FIG. 2; reprinted in FIG. 6 in the present application), the exhaust port (exhaust hole) 141 is made into a horizontally long rectangle, and the width of the depth is gradually narrowed therein. It discloses a structure in which a joint portion 142 (trapezoidal when viewed from above vertically) is connected to secure a space, and then connected to a vacuum pump by an exhaust pipe 143 provided vertically below.

Japanese Unexamined Patent Publication No. 3-62944

Although the structure of Patent Document 1 can obtain a large opening area in the processing chamber, the gas after leaving the processing chamber can greatly change the angle at the joint portion 42, which causes suction resistance and exhaust gas. Since the length of the exhaust pipe shaft core, which affects the resistance, becomes large, there is a problem that the suction conductance is small.
An object of the present invention to be solved is to provide a structure having a large conductance in a structure for discharging gas inside a plasma processing chamber for applying plasma treatment to a substrate.

The present invention made to solve the above problems is a structure for discharging gas inside a plasma processing chamber for applying plasma treatment to a substrate.
a) A horizontally long exhaust port provided on the side wall of the plasma processing chamber below the surface of the substrate when the substrate is set in the plasma processing chamber.
b) A vacuum pump provided so that the intake port faces the exhaust port,
c) An exhaust structure for a plasma processing chamber, which connects the exhaust port and the intake port, and is provided with a connection portion whose cross section gradually changes from the horizontally elongated shape to the uniform shape from the exhaust port to the intake port. Is.

In the above, "horizontally long" means that the diameter (crossing) in the direction perpendicular to it (horizontal direction) is larger than that in the vertical direction.

A "uniform shape" is a circular or convex polygon that is larger than a quadrangle, and the ratio of the maximum value to the minimum value of the diameter from the center [maximum value / minimum value] is 2 square roots (√2) or less. Say what is. Normally, the intake port of a commercially available vacuum pump is circular, so it is preferable to make it circular, but it may be octagonal or the like for the convenience of manufacturing the connection portion.

Further, "the intake port faces the exhaust port" means that the normal of any point in the plane of the surface constituting the exhaust port passes through the intake port.

In the above exhaust structure, since the exhaust port of the plasma processing chamber and the intake port of the vacuum pump face each other, when exhausting the plasma processing chamber, the gas discharged from the exhaust port has bending resistance (gas flow is a molecular flow) at the connection portion. In the case of, it is less likely to receive resistance due to collision with the inner wall (high conductance). In addition, the length of the exhaust pipe shaft core can be reduced. Therefore, the exhaust of the plasma processing chamber can be performed at a higher speed (in a shorter time) than in the conventional case. In addition, the vacuum exhaust before the plasma treatment promotes the suction of reaction products and moisture adhering to the inner wall, the ultimate vacuum degree is improved, and the gas suction during the plasma treatment can be efficiently sucked. , The adhesion of reaction products and moisture to the wall surface is also reduced.

It is desirable that the area of the cross section of the connection portion does not decrease from the exhaust port to the intake port.
By doing so, the cross-sectional area of the flow path from the exhaust port of the plasma processing chamber to the suction port of the vacuum pump does not decrease, so that suction resistance is generated due to the decrease of the cross-sectional area of the flow path. The conductance can be further increased without any problem .

More preferably, the intake port of the vacuum pump should face the exhaust port directly in front of it. That is, it is desirable that the center line of the exhaust port and the center line of the intake port coincide with each other. As a result, the length of the exhaust pipe shaft can be minimized.

In the plasma processing chamber provided with the exhaust structure according to the present invention, when the plasma processing chamber is exhausted, the exhaust port of the plasma processing chamber and the intake port of the vacuum pump face each other, so that the sucked gas resists bending at the connection portion. (When the gas flow is a molecular flow, it is less susceptible to resistance due to collision with the inner wall) (high conductance). Therefore, in the vacuum exhaust before plasma treatment, the ultimate vacuum degree is improved by promoting the suction of reaction products and water adhering to the inner wall of the treatment chamber, and the exhaust is faster (in a shorter time) than before. )It can be carried out. Further, even in the gas suction during the plasma treatment, the suction can be efficiently performed, and the adhesion of reaction products and water to the wall surface is reduced. This makes it possible to improve the accuracy of plasma processing such as etching.

The schematic diagram which shows the whole structure of the plasma processing apparatus which is one Embodiment of this invention. A side view (a) and a plan view (b) of a connection portion connecting the exhaust port of the plasma processing device and the vacuum pump. The end view (a) on the exhaust port side (processing chamber) and the end view (b) on the intake port side (vacuum pump) of the connection portion. Side view (a), plan view (b) and end view (c) of the (vacuum pump) intake port side of another example of the connection. Side view (a), plan view (b) and end view (c) of the (vacuum pump) intake port side of still another example of the connection. A perspective view of a conventional exhaust structure (reprinted with FIG. 2 of Patent Document 1).

Hereinafter, the plasma processing apparatus according to the present invention will be described with reference to the accompanying drawings. The following embodiments are examples that embody the present invention and do not limit the technical scope of the present invention.

FIG. 1 is a schematic configuration diagram of a plasma processing apparatus 10 that employs an exhaust structure for a plasma processing chamber according to the present invention. The plasma processing apparatus 10 of the present embodiment is an inductively coupled reactive ion plasma processing apparatus (ICP-RIE), and a dielectric window 13 is provided above the housing 12 surrounding the processing chamber 11 and directly above the housing 12. Is provided with a high frequency coil 14. At the lower part of the processing chamber 11, a planar lower electrode 15 on which the substrate to be processed is placed is arranged. A mechanism (not shown) for cooling the substrate mounted on the lower electrode 15 is provided in the lower electrode 15. A load lock chamber 16 for exchanging a substrate between the processing chamber 11 and the outside is connected to the processing chamber 11.

The housing 12 is provided with a gas introduction port 17 for introducing plasma gas or the like into the processing chamber 11 and an exhaust port 18 for exhausting the inside of the processing chamber 11. The exhaust port 18 is provided on the side wall of the housing below the upper surface of the lower electrode 15, and the opening thereof is a horizontally long rectangle. A connection portion 19 is fixed to the exhaust port 18, and is connected to the vacuum pump 20 which is a turbo pump via the connection portion 19. The vacuum pump 20 is not limited to the turbo pump, and an appropriate vacuum pump 20 is selected according to the required exhaust performance. Further, if necessary, a pressure adjusting valve such as a control gate valve may be provided between the connecting portion 19 and the vacuum pump 20.

The connection portion 19 is a member that connects the exhaust port 18 and the vacuum pump 20, and as shown in FIGS. 2A and 2B, a horizontally long rectangular opening 21a that matches the exhaust port 18 is provided on the exhaust port 18 side. The first flange 21 has (FIG. 3 (a)), and the second flange 22 has an octagonal opening 22a (FIG. 3 (b)) on the vacuum pump 20 side, which has an octagonal opening 22a that substantially matches the circular intake port of the vacuum pump 20. ), Each is provided. The internal cross section of the transition portion 23 constituting between the flanges 21 and 22 is continuously changed in order to connect the different shapes of the openings 21a and 22a. That is, the cross-sectional shape is rectangular at the end of the transition portion 23 on the first flange 21 side, and octagonal at the end on the second flange 22 side. Here, the center line of the opening 21a of the first flange 21 (normal line of the opening 21a passing through the center of the opening 21a) and the center line of the opening 22a of the second flange 22 (normal line of the opening 22a passing through the center of the opening 22a). Is set to match.

In the plasma processing apparatus of the present embodiment, since the exhaust port 18 is installed at the position as described above, the distance between the plasma and the inner wall is symmetrical with respect to the center of the lower electrode. That is, it does not significantly affect the state of the plasma (on the substrate). Further, even if exhaust is performed by the vacuum pump 20 during plasma processing in the processing chamber 11, the gas on the substrate surface is higher than that in the case where the exhaust port is at the same height as the substrate mounting table (board surface). Since the flow is less biased, the substrate surface can be treated uniformly.

Further, since the connecting portion 19 is configured as described above, the molecules of the gas (air, plasma gas, etc.) inside the processing chamber 11 collide with the pipe wall or the like between the exhaust port 18 and the vacuum pump 20. Is low and the exhaust resistance is low (that is, the conductance is high). Therefore, when the inside of the processing chamber 11 is evacuated, it is possible to evacuate in a shorter time than before. Further, during the plasma processing, the state of the plasma in the processing chamber 11 is less likely to be disturbed, and the plasma processing can be performed more evenly than before.

Here, the length of the connecting portion 19 will be examined.
It is generally known that the flow of gas flowing through a tube includes a viscous flow and a molecular flow. If the mean free path of the gas is λ and the diameter of the pipe is D, the ratio K (= λ / D. This is called the Knudsen number) is smaller than 0.01, which is a viscous flow and larger than 1. The case is the molecular flow. That is, in the viscous flow, the collision between the gas molecules flowing in the tube is the main resistance factor, and in the molecular flow, the collision between the gas molecule and the tube wall is the main resistance factor. Whether the flow becomes a viscous flow or a molecular flow depends on the pressure p of the gas and the tube diameter D. For example, in the case of air at room temperature (27 ° C), the viscous flow occurs when p · D> 68 (p is Pa, D is m unit), and the molecular flow becomes p · D <0.68. The intermediate region between the two is called the intermediate flow. Specifically, for example, if the pipe diameter D is 10 cm, the viscous flow occurs when the air pressure p is higher than about 10 Pa (10 ^-1 Torr), and it is lower than about 10 ^-1 Pa (10 ^-3 Torr). In some cases, it becomes a molecular flow. Therefore, when the atmospheric pressure processing chamber is evacuated to a pressure lower than 10 ^-1 Pa (10 ^-3 Torr), the air flow in the tube changes from a viscous flow to a molecular flow. It is important to increase the conductance (reduce the resistance) in the suction path because the suction rate is much lower in the molecular flow than in the viscous flow.

In the case of air at 27 ° C (average molecular weight M = 29), the conductance cv (m ³ / s) of a cylindrical tube with a diameter of D and a length of L states that the flow in the tube is viscous.
cv = (π ・ D ⁴・ p) / ( 128・ η ・ L) = 1356 ・ D ⁴・ p / L
(Η is a viscous resistance). On the other hand, if the flow in the tube is a molecular flow, the conductance cp (m ³ / s) will be
cp = co ・ (4 ・ D) / (3 ・ L) = √ ((R ・ T) / (2 ・ π ・ M)) ・ ((π / 4) ・ D ² ) ・ (4 ・ D) / (3 ・ L) = 121 ・ D ³ / L
(Co is the conductance of the orifice of area A). As in this equation, conductance does not depend on pressure in molecular flow.

On the other hand, in the case of the piping as shown in FIG. 2 of Patent Document 1 (FIG. 5 of the present application), the opening (orifice) of the connection portion between the joint portion 42 and the exhaust pipe 43 is a controlling factor of conductance, but the opening. If is a circle of diameter D, this conductance c2 is
c2 = A ・ √ (R ・ T / ( 2 ・ π ・ M )) = 91 ・ D ²
Will be.
According to this, assuming that the diameter of the opening (that is, the diameter of the exhaust pipe 43) D is 10 cm (0.1 m) in the pipe of FIG. 5, the length L of the straight pipe having the same conductance is about 7.5 m. Will be. Therefore, when pipes of the same diameter are used, by adopting an exhaust structure as in the present invention and setting the length of the connecting portion to about several tens of centimeters or less, it is possible to obtain greater conductance than before, especially in the molecular flow region. Will be able to.

In the above embodiment, the opening 22a (of the second flange 22) on the intake port side (of the vacuum pump 20) of the connection portion 19 has an octagonal shape inscribed in the circular intake port of the vacuum pump 20. As shown in 4, it may be an octagon (32a) circumscribing it. In the former case, the opening area at the outlet of the transition portion 23 of the connecting portion 19 is smaller than the opening area of the intake port of the vacuum pump 20, but the gas receives collision resistance when entering the intake port of the vacuum pump 20. There is a merit that there is no. On the other hand, in the latter case, since all the cross sections of the transition portion 33 are larger than the intake port of the vacuum pump (indicated by the dotted line 34), there is no resistance due to the decrease in the cross-sectional area, and a large conductance is ensured. Can be done. The opening of the second flange 32 is a circular shape having the same shape as the suction port of the vacuum pump, and the second flange 32 is used to smoothly change the shape from the octagonal shape to the circular shape of the intake port 34 of the vacuum pump immediately before the second flange 32. By providing a transition portion (not shown), the collision resistance can be reduced and the conductance can be further increased.

If cost is acceptable, it is desirable that the opening itself on the intake port side (of the vacuum pump 20) of the connection be circular to fit the intake port of the vacuum pump 20. FIG. 5 shows an example of a connection portion 39 having a circular opening 42a on the intake port side (of the vacuum pump 20). Although some skill is required to smoothly process the cross section from the rectangular shape to the circular shape at the transition portion 43 from the first flange 41 on the exhaust port side to the second flange 42 on the intake port side, the gas flow is more frequent during use. It becomes smooth and a large conductance can be obtained.

10 ... Plasma processing device 11 ... Processing chamber 12 ... Housing 13 ... Dielectric window 14 ... High frequency coil 15 ... Lower electrode 16 ... Load lock chamber 17 ... Gas inlet 18 ... Exhaust ports 19, 29, 39 ... Connections 20 ... Vacuum pumps 21, 31, 41 ... 1st flange 21a ... Openings 22, 32, 42 ... Second flanges 22a, 32a, 42a ... Openings 23, 33, 43 ... Transition portions

Claims (5)

It is a structure for discharging the gas inside the plasma processing chamber for applying plasma treatment to the substrate.
a) A horizontally long exhaust port provided on the side wall of the plasma processing chamber below the surface of the substrate when the substrate is set in the plasma processing chamber.
b) A vacuum pump provided so that the intake port faces the exhaust port,
c) It is provided with a connecting portion that connects the exhaust port and the intake port and gradually changes the cross section from the horizontally long shape to the uniform shape from the exhaust port to the intake port .
An exhaust structure for a plasma processing chamber, characterized in that the cross-sectional area of the connection portion does not decrease from the exhaust port to the intake port . The exhaust structure for a plasma processing chamber according to claim 1 , wherein the cross section of the connection portion on the intake port side is polygonal. The exhaust structure for a plasma processing chamber according to claim 1 , wherein the cross section of the connection portion on the intake port side is circular. The exhaust structure for a plasma processing chamber according to any one of claims 1 to 3 , wherein the center line of the exhaust port and the center line of the intake port coincide with each other. The connection portion used in the exhaust structure for the plasma processing chamber according to any one of claims 1 to 4 .

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