JPH0729894A - Porous gas-introducing mechanism - Google Patents

Abstract

PURPOSE:To improve the utilizing efficiency of an etching gas and increase the longitudinal and lateral uniformities of a plasma density in a chamber, by providing just below an upper cover present in the upper part of the chamber a porous plate having a number of fine holes, and by introducing the etching gas into the chamber from the upper cover. CONSTITUTION:In the inside upper part of a chamber 1, an LEP electrode 3 is provided, and in the lower part of the chamber 1, a lower electrode 4 is provided, and further, a wafer 5 is put on the lower electrode 4. A punched plate 12 is provided horizontally in the periphery of the lower electrode 4. Just below an upper cover 2, a porous plate 14 is provided. The material of the porous plate 14 is such an arbitrary one as a metal, ceramic or plastic, and the number of holes, and the diameters and distribution of the holes of the porous plate 14 are arbitrary too, but a uniform gas stream jetted downward from the porous plate 14 is made possible. The etching gas introduced from a gas inlet 13 into a gas accumulating part 15 stays therein once, and a uniform pressure is given to the etching gas. The etching gas is jetted downward through the holes of the porous plate 14, and a plasma is excited by the LEP electrode 3. Since the etching gas is subjected to the action of the LEP electrode 3 almost extensively, the utilizing efficiency of the etching gas is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching gas introduction mechanism in a dry etching apparatus that utilizes a rotating electric field to convert gas into plasma. Advances in photolithography technology and etching technology are indispensable in order to further advance the density of semiconductor integrated circuits.

[0002]

2. Description of the Related Art Dry etching is a method in which a gas is used as a plasma to accelerate the gas, which is then applied to a substrate to remove a semiconductor portion on the substrate which is not covered with a resist by a physical chemical action. It is desirable to etch the portion not covered by the resist as vertically as possible. Wet etching which is used in other fields isotropically proceeds. On the other hand, that the etching progresses only perpendicularly to the resist surface is called anisotropic etching. Dry etching has excellent anisotropy. The properties described above can be expressed by the high anisotropy.

The most widely used etching method at present is reactive ion etching (RIE). The semiconductor is removed by a chemical reaction using a halogen gas as the gas. This uses a parallel plate electrode or the like to apply a high frequency to halogen gas or the like to generate plasma, which etches the semiconductor portion. In order to cut a semiconductor vertically in a fine resist hole, the incident direction of ions must be perpendicular to the substrate surface. For this purpose, the mean free path of the ions may be lengthened to reduce the scattering probability. Therefore, it is necessary to increase the degree of vacuum. However, if the degree of vacuum is increased, high frequency discharge becomes difficult to occur. Then, the etching rate becomes low.

In order to solve this, a magnetron reactive ion etching method and an ECR etching method have been developed. In the magnetron reactive ion etching method, for example, four electromagnets are provided around a conventional parallel plate electrode, and the phase of the exciting current of the electromagnets is changed by 2π / 4 to generate a rotating magnetic field in the chamber. It is intended to raise the ionization efficiency by causing the cyclotron motion of electrons.

In the ECR etching method, for example, a coil is provided outside the chamber to generate a DC magnetic field in the vertical direction.
2.45 GHz microwave is externally introduced into the chamber. Electrons undergo cyclotron motion due to the DC magnetic field, but if the period of the electrons is the same as the period of the microwaves, the electrons resonate and absorb the microwaves. Electrons having kinetic energy collide with gas atoms and molecules to turn them into ions, so that the ionization rate is also improved.

However, in the magnetron reactive ion etching method, the density of the rotating magnetic field is not spatially uniform. Therefore, the plasma density becomes spatially non-uniform. In the ECR etching method, since the magnetic field is also spatially non-uniform, the plasma density becomes spatially non-uniform.

As described above, there is a method of maintaining discharge even in a high vacuum and increasing the ionization rate, but all of them have a drawback that the plasma density becomes non-uniform due to the spatial non-uniformity of the magnetic field. Since the semiconductor part is removed by the action of plasma and radicals, if the plasma is not spatially uniform,
The etching rate will also be spatially non-uniform. If a large-diameter wafer is to be etched, the etching rate within the plane of the wafer becomes non-uniform. Therefore, these methods are not suitable for etching large-diameter wafers.

Therefore, the present inventors have invented a dry etching method using a rotating electric field. JP-A-4-26
No. 8727 and Japanese Patent Laid-Open No. 4-290226. A high frequency voltage having a phase difference of 2π / n is applied to the n electrodes to generate a rotating electric field in the chamber, which causes electrons to rotate around the vertical axis to accelerate and hit gas atoms to form a plasma. To etch.

This is one in which upper and lower parallel plate electrodes and n LEP electrodes are provided in the chamber. The substrate to be etched is placed on the lower parallel plate electrode. The LEP electrodes are provided so as to face each other so as to be rotationally symmetrical. The upper and lower parallel plate electrodes generate an alternating electric field in the vertical direction. The lateral LEP electrodes generate a rotating electric field in the horizontal direction. The high frequency applied to the upper and lower parallel plate electrodes is, for example, 50
MHz, high frequency for horizontal rotating electric field is 300 MHz
Is.

As mentioned above, reactive ion etching utilizes only parallel plate electrodes. Compared to this, the number of LEP electrodes provided on the intermediate side increases. Since the magnetron reactive ion etching method is composed of upper and lower parallel plate electrodes and electromagnets on the side of the middle, it means that the electromagnets are replaced by electrodes.

The inventor named the etching method utilizing such a rotating electric field the LEP method. The entire etching system is called the LEP system, and the laterally symmetrical electrodes are L
We decided to call it an EP electrode. It is not a generic name. It may be called LEP or Lissajous plasma etching apparatus. A Lissajous figure is a locus of two-dimensional motion that combines simple vibrations in mutually perpendicular directions. It has this name because it can be drawn with a machine designed by LISSAJOUS in France.

[0012]

FIG. 1 is a schematic configuration diagram of dry etching targeted by the present invention. Chamber 1
Is a container that can be evacuated. It has a top lid 2 on top. The LEP electrode 3 is provided above the inside of the chamber.
(Or an upper electrode) is provided. This may be 3 or more, but an example using four LEP electrodes 3 is shown here.

A lower electrode 4 is provided below the chamber. The semiconductor wafer 5 is placed on this. This is the subject of etching. A fine pattern of the resist is drawn by applying a resist and photolithography.
The bottom surface of the chamber 1 is closed by a base plate 6. On the side of the chamber 1 is a gas inlet 7 for introducing an etching gas. At the bottom of the chamber 1 is a gas outlet 8 for discharging gas.

High frequencies having different phases are applied to the LEP electrode 3. For this purpose, a high frequency power supply 9 is provided. In the above case, the frequency was 300 MHz, but a high frequency of any frequency can be used. The phase shifter 10 applies a high frequency of 2
Each L by shifting the phase by π / n (n is the number of LEP electrodes)
It is adapted to be applied to the EP electrode 3.

The lower electrode 4 also has a different high-frequency power source 11, which applies a high frequency of, for example, 50 MHz to the lower electrode. Since the lower electrode 4 is overheated, in order to prevent this,
There is a cooling mechanism 16, which circulates cooling water or a coolant to cool the lower electrode.

FIG. 2 is a diagram mainly showing the same gas flow. The gas inlet is in the lower half of the chamber. Sometimes it's one, sometimes two or more. The gas outlet is on the bottom and this is one thing and two things.

A punching plate 12 is horizontally provided at substantially the same height as the wafer 5 of the lower electrode 4. This makes the electric field near the wafer nearly perpendicular to the wafer.
The chamber is at ground potential and the bottom is also at ground potential.

However, since the lower electrode applies a high frequency, it is biased to a negative voltage. The positive ions in the plasma are accelerated by the electric field and thus travel along the lines of electric force.
The lower electrode, which is biased to a negative voltage, has electric lines of force entering the surface almost at right angles. If left as it is, electric force lines enter not only the upper surface of the lower electrode but also the side surface thereof, so that the positive ions hit the side surface of the lower electrode. This is a waste of ions because it does not contribute to etching.

In order to prevent this, the punching plate 12
Is provided at substantially the same height as the upper surface of the lower electrode. The side surface of the chamber, punching plate, and top lid are all at ground potential. The lower electrode 4 has a negative voltage. Positive ions in plasma are more
It is attracted to the upper surface of the lower electrode 4, that is, the wafer surface.
That is, the ions do not hit the side surface of the lower electrode and are not wasted. It may be a conductor plate, but it is a punching plate because it needs to pass gas.

The etching gas is a reactive gas such as Cl ₂ . The LEP does not have a counter electrode (ground electrode) unlike the conventional RIE, and does not require the chamber to be made of quartz unlike the ECR, and therefore has a high degree of freedom in designing the gas blowing holes. However, when the etching gas is blown from the gas inlet 7 on the side surface of the chamber and the outlet is at the lower side, only a part of the gas goes upward and is excited into plasma by the high frequency electric field generated by the LEP electrode. Due to the resistance of the punching plate 12, the gas does not directly escape from the inlet to the outlet. However, since the inlet and the outlet are close to each other, a large amount of gas is discharged without being used, resulting in poor gas utilization efficiency.

The other is the non-uniform plasma density.
This has two non-uniformities. Since the gas is introduced from the side of the chamber, the gas before being excited by the plasma stays below the center of the chamber, and by the action of the LEP electrode,
There is a drawback that the active plasma containing radicals, ions and electrons stays above the chamber. This further reduces the gas utilization efficiency.

The other is the non-uniformity of the plasma in the horizontal plane. Since the plasma density is not uniform in the horizontal plane,
The etching rate in the plane of the wafer is different. Then, it becomes difficult to manufacture a large number of equivalent integrated circuit devices from one wafer.

It is an object of the present invention to solve the above problems, to improve the utilization efficiency of etching gas, and to provide a gas introduction mechanism which enhances the uniformity of plasma density in the chamber in the vertical and horizontal directions. .

[0024]

The dry etching apparatus of the present invention comprises a perforated plate having a large number of fine holes just below the upper lid in the upper part of the chamber, and a gas inlet provided in a part of the upper lid to etch from the upper lid. Introduce gas. A wide horizontal space is created which is surrounded by the upper lid, the perforated plate and the side wall of the chamber.
Since the resistance when passing through the perforated plate is large, the etching gas once reaches an equilibrium state in this space.

That is, the pressure in this gas reservoir becomes constant. Then, the gas is discharged downward from the fine holes that are uniform or distributed, and is uniformly blown into the chamber. The material of the perforated plate, the size of the holes, and the number of holes are arbitrary, but the distribution of the holes greatly affects the etching uniformity. The holes need to be opened on the entire top cover. Also, the gas outlet is provided at or near the bottom of the chamber.

[0026]

The gas is not introduced from the side of the chamber as in the conventional case, but is introduced from above. Since the outlet is at the bottom, all etching gas passes between the LEP electrodes. All gases are excited by the plasma. All gases come to contribute to the etching. Therefore, the gas utilization efficiency is significantly enhanced.

Since the fine holes in the perforated plate increase the flow path resistance of the gas and balance the pressure in the gas reservoir, the velocity of the gas blown out from the hole is constant. Therefore, the gas can be blown from the top to the bottom with a uniform density in the horizontal plane of the chamber. Gas is made into plasma by applying high-frequency waves having different phases to the LEP electrode. Since the velocity of the gas is uniform in the horizontal plane, the density of plasma becomes uniform in the space surrounded by the LEP electrode. Therefore, the uniformity of plasma is increased. Therefore, the etching rate on the wafer surface becomes uniform, and good etching can be performed.

[0028]

FIG. 3 is a schematic configuration diagram of a dry etching apparatus according to an embodiment of the present invention. The chamber 1 is a cylindrical or polygonal space. Upper lid 2 on top, base plate 6 on bottom
There is a closed space. Above the inside of the chamber 1, four LEP electrodes 3 are provided at rotationally symmetrical positions. A lower electrode 4 is provided below the chamber. This places the wafer 5. Punching plate 1
2 is provided horizontally around the lower electrode 4. It will be at ground potential as well as the chamber. The base plate 6 has a gas outlet 8.

There is a gas inlet 13 at a suitable location on the top lid 2. This may be one or more. There is a perforated plate 14 just below the upper lid 2. This is a plate in which many fine holes are formed. The material is arbitrary such as metal, ceramic and plastic. The number of holes, the diameter of the holes, and the distribution of the holes are arbitrary, but it is sufficient that a substantially uniform gas flow can be blown downward. If the hole diameter is large,
Make sure there are no holes directly under the gas inlet 13.

If the hole diameter is small, it does not matter if there is a hole directly below the gas inlet 13. Since the holes of the perforated plate are minute, the flat space surrounded by the upper lid 2, the perforated plate 14, and the side periphery of the chamber is a semi-closed space. This will be referred to as the gas reservoir 15 here.

The etching gas entering the gas reservoir 15 through the gas inlet 13 once stays at the same pressure. Since the lower part of the chamber 1 has a lower pressure, the gas blows downward through the fine holes of the perforated plate. This is excited into plasma by the LEP electrode 3. Inside the plasma, there are positive ions, electrons and radicals, which collide with the surface of the wafer and etch it. In order to increase the etching anisotropy, it is necessary to increase the degree of vacuum in the chamber. This is because the mean free path of ions and radicals is lengthened. The gas can be turned into plasma by the action of the LEP electrode even in high vacuum.

Introducing an etching gas from above, LEP
Since the electrode is in the middle of the gas flow path, almost all the etching gas is subjected to the action of the LEP electrode to be in the plasma state. It is not discharged from the chamber as it is. Moreover, since the gas has a uniform flow from the top to the bottom, the gas does not stay separately from the top and the bottom. Use efficiency of etching gas is high. Further, since the holes are uniformly formed in the plane of the perforated plate, the density of the gas flow from the top to the bottom is constant. Since the gas utilization efficiency is high and the density of the gas flow is uniform, the gas consumption can be saved. As described above, the LEP has a high degree of freedom in the design of the gas blowing holes due to its structure and is not restricted by RIE and ECR. Therefore, the above structure can ensure high etching uniformity. .

[0033]

According to the present invention, it is possible to prevent the disadvantage that a part of the gas is exhausted as it is, and the utilization efficiency of the etching gas is improved. Since the same plasma is formed, a smaller amount of gas is required. For this reason,
Running costs can be reduced. Further, it becomes possible to make the gas treatment device smaller.

Since the plasma density is spatially uniform, the etching rate on the wafer surface is uniform. For this reason, many integrated circuit devices of constant quality can be manufactured from one wafer. When manufacturing a large number of integrated circuit devices on a large-diameter wafer, it is extremely important that the etching rate is the same in the plane.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a dry etching apparatus using a rotating electric field.

FIG. 2 is a view showing gas inflow / outflow paths in a conventional device.

FIG. 3 is a diagram for explaining gas passage in the device of the present invention.

[Explanation of symbols]

 1 Chamber 2 Upper Lid 3 LEP Electrode 4 Lower Electrode 5 Wafer 6 Base Plate 7 Gas Inlet 8 Gas Outlet 9 High Frequency Power Supply 10 Phase Shifter 11 High Frequency Power Supply 12 Punching Plate 13 Gas Inlet 14 Perforated Plate 15 Gas Reservoir 16 Cooling Mechanism

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tokuhiko Tamaki, 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Mitsuhiro Oguni, 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Ichiro Nakayama 1006 Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor, Masafumi Kubota 1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Noboru Nomura 1006 Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A cylindrical chamber, an upper lid that closes the upper part of the chamber, a base plate that closes the lower end of the chamber, and three or more sheets provided above the inside of the chamber facing each other at rotationally symmetrical positions. A LEP electrode, a high frequency power source for applying a high frequency voltage with a phase shift to the LEP electrode, a lower electrode provided below the chamber on which a semiconductor wafer to be etched is to be placed, and a high frequency power source for applying a high frequency to the lower electrode. A dry etching apparatus utilizing a rotating electric field including a gas inlet provided on the upper lid for introducing an etching gas into the chamber, and a gas provided on or near the bottom surface of the chamber for discharging the gas from the chamber. Provide a perforated plate just below the upper lid in the outlet and the chamber,
The etching gas introduced from the gas inlet once stays in the gas reservoir between the perforated plate and the upper lid and then passes through the hole of the perforated plate to the side of the LEP electrode, where it becomes plasma. Characteristic porous gas introduction mechanism. 2. A cylindrical chamber, an upper lid that closes the upper part of the chamber, a base plate that closes the lower end of the chamber, and n LEPs provided inside the chamber and facing each other at rotationally symmetrical positions. 2 for the electrode (n ≧ 3) and LEP electrode
Rotation including a high-frequency power source for applying a high-frequency voltage whose phase is shifted by π / n, a lower electrode provided below the chamber on which a semiconductor wafer to be etched is to be placed, and a high-frequency power source for applying a high frequency to the lower electrode A dry etching apparatus utilizing an electric field, which is provided at a gas inlet provided on an upper lid for introducing an etching gas of Cl ₂ into the chamber and at a bottom surface of the chamber or in the vicinity thereof for discharging gas from the chamber. A perforated plate is provided immediately below the upper lid in the chamber and inside the chamber, and the etching gas introduced from the gas inlet temporarily stays in the gas reservoir between the perforated plate and the upper lid and then passes through the hole in the perforated plate to form the LEP electrode. The porous gas introduction mechanism is characterized in that the gas passes through the side of the chamber and becomes a plasma here.