JPH09270233A - Coaxial ecr plasma generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constantly monitor the spectrum of plasma luminescence in a plasma chamber, to confirm the composition and density of plasma, by providing a spectral port and a light leading tube on a coaxial ECR plasma generating device. SOLUTION: A microwave generated by a microwave oscillator is conducted in a coaxial tube cable 17, to be entered into an antenna 7 from a conductor 15. Since a coaxial tube 9 is connected to a chamber 5, the chamber 5 has electric potential same as that of the earth wire of the cable 17. The microwave enters into the plasma chamber 5 by the antenna 7 and the tube 9. A permanent magnet 6 is installed in the periphery of a side wall 44, thereby generating an axial direction magnetic field in the inside of the chamber 5. Gas enters into the chamber 5, and the microwave is transmitted to the antenna 7, to be entered into the chamber 5. A magnetic field is generated in the inside of the plasma chamber by the magnet 6, the gas is converted into plasma by the microwave, and a neutral radical is sprung out from an outlet 14, to be struck to a substrate, thereby forming a thin coat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a plasma generation mechanism that causes a source gas to be resonantly excited by microwaves to generate plasma. Radicals are extracted as a beam from the generated plasma and used for thin film growth. In particular, the present invention relates to a plasma generator capable of irradiating a sample with radicals while spectrally observing plasma emission.

[0002]

2. Description of the Related Art Ishikawa et al. Have proposed a device for generating a high-density plasma by generating a longitudinal magnetic field using a permanent magnet and causing an electron resonance with respect to a microwave introduced by a coil type antenna. Junzo Ishikawa, Yasuhiko Takeiri and Toshinori T
akagi, "Axial magnetic field extraction-type microwa
ve ion source with a permanent magnet ", Rev. Sci.
Instrum. 55 (4), April 1984, p449

FIG. 2 shows a schematic structure. This produces a longitudinal magnetic field in the chamber 21 by the permanent magnet 20. Raw material gas is introduced from the gas inlet 28 into the chamber 21.
Will be introduced. The microwave 30 transmitted through the waveguide 29 is guided to the chamber 21 by the antenna 22. The electrons contained in the gas are vibrated by the microwave. The electron moves cyclotron by the magnetic field and absorbs the microwave resonantly. The electrons excite gas molecules and convert them into plasma. Extraction electrodes 23 and 24 are provided in front of the chamber 21, and ions are accelerated and extracted as an ion beam 31.

The antenna 22 has a shape in which the end of a straight line portion is wound one turn in a lateral coil shape 39. Since it is a coiled antenna, the chamber expands laterally. In order to strengthen the magnetic field generated by the permanent magnet 20, the magnetic extraction electrode 2 is used.
3 and the relay ring 38 made of a ferromagnetic material are used. Since the chamber 21 side and the extraction electrode 23 side have different voltages, they are insulated by the insulator 25. The ferromagnetic relay wheel 38, the insulator 25, and the ferromagnetic lead electrode 24 are welded to each other.

A cooling medium 37 passes through the base flange 36. The intermediate flange 26 is also made of a ferromagnetic material. A magnetic circuit is formed by the permanent magnet 20, the extraction electrodes 23 and 24, and the intermediate flange 26. This is for strengthening the magnetic field lines in the chamber by the permanent magnets. The upper flange 27 is a non-magnetic material. A heater 34 for heating is wound around this. It is stated that an ion beam of a gas such as argon or nitrogen introduced from the gas inlet 28 can be extracted. Gives a small ion source. Japanese Patent Application No. 6-183922 (H6.7.12 application “E
CR ion radical source "JP-A-8-31358)

[0006] This was invented by the present inventor as an ion source and a radical source, with a hint from the device. The antenna which is bent for one turn is passed through the chamber, and microwaves are introduced by the antenna to turn the gas into plasma and to pull out radicals or ions to the outside. Since it is difficult to excite gas only with microwaves, a magnetic field is applied so that electrons resonate with cyclotron. A magnet is provided outside the plasma chamber to generate a vertical magnetic field.

When the frequency of the microwave is 2.45 GHz, when a magnetic field of 875 G is generated by the magnet, the frequency of the spiral motion of the electron matches the microwave frequency, and thus cyclotron resonance occurs. It can efficiently absorb energy from microwaves and excite gas molecules into neutral radicals. ECR because it uses the resonance absorption of microwaves
That.

This allows the ion beam to be extracted by applying a voltage to the extraction electrode. Neutral radicals can be extracted by setting the electrode voltage to 0 and applying a differential pressure. It is called an ion radical source because it can selectively emit both ion beams and radicals. It can be used for two purposes.

[0009]

An ion source for generating a plasma by a microwave and extracting it as an ion beam to the outside is disclosed. Can be used as both an ion source and a radical source. In any case, it is used alone. The present invention is instead concerned with a radical source that can be used in place of a molecular beam cell in a molecular beam epitaxial growth apparatus (MBE). The object of the present invention relates to a novel component suitable for an MBE apparatus, and a molecular beam epitaxial growth method will be described first.

The MBE apparatus is an apparatus for forming a thin film by irradiating a heated substrate with a molecular beam of a raw material in an ultrahigh vacuum to cause a gas phase reaction. A K cell or a molecular beam cell is used to make the raw material a molecular beam. The crucible of PBN, the heater, the reflector, the support, the thermocouple, etc., and the support is fixed to the ultra-high vacuum flange. Such is a molecular beam cell. This is to evaporate what is solid at room temperature to form a molecular beam by heating. In many cases, the heat-evaporation can make the molecular beam sufficiently reactive.

However, in the case of a certain limited material, it may be impossible to form a thin film by simply using a molecular beam because of its poor reactivity. For example, in the case of nitrogen gas, it is a gas from the beginning and is a stable gas. The reaction does not occur even with molecular beams. In such a case, it is better to use radical rays instead of molecular beams. However, the above-mentioned is not suitable to be attached to a molecular beam epitaxial growth apparatus. The width is too large and the length is insufficient. Since the coil antenna is used and a short cylindrical permanent magnet is used, the width is large and short. The present invention provides for the first time a plasma generation mechanism that can be suitably used as a radical source (radical cell) instead of a molecular beam cell in an MBE apparatus.

[0012]

A plasma generator according to the present invention comprises an ultra-high vacuum flange which can be fixed to a cell mounting flange of an MBE device, and a coaxial tube which is provided at a right angle to the flange at an eccentric position of the ultra-high vacuum flange. A plasma chamber that is provided eccentrically at the tip of the coaxial tube to excite gas to turn it into plasma and release radicals from the outlet, a cylindrical insulator inserted inside the coaxial tube, and a tip inserted into the insulator Is exposed to the plasma chamber, a gas pipe that penetrates the ultra-high vacuum flange to introduce gas into the plasma chamber, and a gas pipe that penetrates the ultra-high vacuum flange to the plasma chamber and allows the plasma inside the plasma chamber to be exposed to the outside. The light guide tube for spectroscopic observation from the inside and the external atmospheric pressure and internal vacuum that are inside the coaxial tube and transmit the microwave given from the outside to the antenna For introducing a current, a cooling pipe that penetrates the ultra-high vacuum flange and is provided around the coaxial tube for passing a medium for cooling the coaxial tube, and an axial magnetic field is provided around the plasma chamber inside the plasma chamber. It is characterized by comprising a permanent magnet that is generated.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An ultra high vacuum flange is fixed to a molecular beam cell mounting flange of a molecular beam epitaxial growth apparatus. When gas is introduced into the plasma chamber from the outside and microwaves are introduced into the plasma chamber from the antenna, the gas is excited by the microwaves. Gas excitation efficiency increases when microwave resonance is absorbed by a permanent magnet. The plasma chamber is supported on the ultra-high vacuum flange by a coaxial tube. Both the gas tubes, the cooling tubes and the spectral light guides are supported by ultra-high vacuum flanges. Further, since the plasma and the flange are separated from each other by the coaxial tube and the insulator, the length becomes longer in the direction perpendicular to the flange. It becomes a vertically long shape similar to a molecular beam cell and can be attached to the port of the molecular beam cell as it is.

Further, since the light guide tube for observing the plasma emission inside the plasma chamber is provided, the emission can be dispersed to observe the state of plasma in-situ. Plasma is an assembly of ions, neutral active species, electrons, neutral molecules, and the like.
Those in the excited state generate light and fall to the ground state.
The spectroscopic analysis of the light reveals what kind of excited state ions and radicals exist. This controls the microwave power. Spectroscopic analysis of such plasma is completely new in the molecular beam epitaxial growth method.

RIE (Reactive Ion Etching)
In the above, a plasma spectroscopic analysis is performed to detect the end point of etching. For example, when the glass is etched to reach the underlying Si, the plasma spectrum changes there, so that the end point can be known. Therefore, etching is stopped. This is the case when the spectrum changes depending on the substance emitted from the object. There is no other example of spectroscopic analysis of plasma. In other words, there is no example of plasma spectroscopic analysis in the molecular beam epitaxial growth method. In the molecular beam epitaxial growth method, it is usual to fly the molecular beam, and there is no room for plasma to intervene. However, when radicals are generated from plasma as in the present invention, it is necessary to monitor the state of plasma and generate radicals in an optimum state.

Therefore, the light guide tube is inserted into the plasma chamber from the outside, and the light is directly extracted to the outside. This is just an empty-core tube. However, a light guide (optical fiber, quartz glass rod) can be used instead of the tube. One of the features of the present invention is real-time spectroscopic observation of plasma.

Furthermore, the eccentricity of the coaxial tube with respect to the plasma chamber,
Eccentricity of the coaxial tube with respect to the flange is also important. The one that penetrates the flange and connects to the plasma chamber,
A coaxial pipe, a light guide pipe, a gas pipe, and two cooling pipes. A coaxial tube mechanically supports the plasma chamber. Moreover, the antenna penetrates the center of the coaxial tube. The central axis of the plasma chamber is p, the central axis of the coaxial tube is q, and the central axis of the ultrahigh vacuum flange is r. If the antenna should be in the center of the plasma chamber, then the coaxial tube center q and the plasma chamber center p must be equal.

That is, q = p. It will be further considered that the center p of the plasma chamber and the center of the flange r should be aligned. That is, one would request p = r. Since such a plasma generation device has never existed, an example cannot be given, but it should be understood that r = q = p. This is because the coaxial tube mechanically supports the plasma chamber.

However, in that case, the gas pipe and the light guide pipe must be provided through the wall of the plasma chamber, and if the coaxial pipe is at the center and the gas pipe and the light guide pipe are at the ends, The rear wall of the plasma chamber must be wide. If the rear wall of the plasma chamber is wide, the mounting port must be wide. Therefore, the ultra high vacuum flange becomes wider. If the coaxial pipe is placed at the center, the outer diameter of the flange cannot be reduced to 114 mm or less.

MBE devices with mounting ports to which flanges with an outer diameter of 114 mm or more can be fixed are not exclusive, but special. Normal MBE
The attachment port of the molecular beam cell of the device can only attach an ultra high vacuum flange with a diameter of 70 mm. The size of the flange is standardized in stages, and in Japan it is 114
Just below mm is 70 mm. Of course, it is possible to make an intermediate size port, but it will be a custom-made product.

If the light guide tube is omitted, the center of the coaxial tube is 7
It could be mounted on a 0 mm outer diameter flange. However, without a light guide tube, plasma cannot be spectrally analyzed. Somehow I want to monitor the plasma directly and optically.

Therefore, in the present invention, the coaxial tube is separated from the center of the plasma chamber and the center of the flange. The coaxial tube center q deviates from the flange center r. It is also deviated from the center p of the plasma chamber. That is, q ≠ r and q ≠ p. The relationship between p and r may be p = r or p ≠ r. By arranging the light guide tube and the gas tube on one of the rear walls of the plasma chamber and the coaxial tube on the other side,
The rear wall of the plasma chamber can be narrowed. Therefore, the entire size including the permanent magnet can be made smaller, and the ultra high vacuum flange can be made smaller. This makes the outer diameter of the flange 70m
m.

[0023]

EXAMPLE A plasma generator according to an example of the present invention will be described with reference to FIG. The mounting flange (ultra high vacuum flange) 1 is a disk-shaped plate to be fixed to the port of the molecular beam cell of the molecular beam epitaxial growth apparatus (MBE).
The diameter is 70 mm (ICF70). The coaxial tube 9 is fixed at a position other than the center r of the flange 1 at a right angle. The plasma chamber 5 is provided at the eccentric position at the tip of the coaxial tube 9. It is important that the position of the coaxial tube is eccentric with respect to the flange 1 and the plasma chamber 5. The center q of the coaxial tube and the center p of the plasma chamber are eccentric by d. As mentioned earlier,
q ≠ r and r ≠ p. It may be p ≠ r or p =
It may be r.

A gas tube 3 and a light guide tube 2 are provided in parallel with the coaxial tube 9 in a space on the rear wall 42 of the plasma chamber 5 where the coaxial tube 9 is not present. In both cases, the inside of the plasma chamber 5 is connected to the outside of the flange 1. The gas pipe 3 connects a gas cylinder at an external gas port 13. The source gas enters the plasma chamber 5 from the gas cylinder through the gas port 13, the gas pipe 3 and the gas inlet 47.

The light guide tube 2 is a hollow pipe, and connects the opening 46 of the plasma chamber 5 and the spectroscopic port 12 outside the flange. It can also be replaced by a transparent quartz rod. This is for spectroscopic analysis of the emission state of plasma. Not only the presence / absence of plasma (that is, turning on / off), but also the concentration of ions and the type and concentration of radicals are known. There has never been a spectroscopic analysis of ECR plasma in the molecular beam epitaxial growth method. The present invention can monitor the state of plasma in-situ and always irradiate the substrate with radicals in an optimum state.

An insulator 10 is filled inside the coaxial tube, and a linear antenna 7 is inserted through the center of the insulator 10. The insulator 10 insulates the antenna 7 and the coaxial tube 9 from each other.
There is no function to maintain the vacuum. It is the current introducing terminal 8 that holds the vacuum. This is the conductor 1 at the center of the disk-shaped insulator.
It has a structure that 5 penetrates. The conductor 15 has an axial hole in the front and rear. The antenna side of the current introduction terminal 8 is evacuated,
The other side is atmospheric pressure. Externally, the core wire 18 of the coaxial cable 17 is inserted into the hole. On the vacuum side, the pin 16 at the rear end of the antenna 7 is inserted into the hole. These front and rear holes do not communicate with each other. This is because the vacuum must be maintained here.

The microwave generated by the microwave oscillator propagates through the coaxial tube cable 17. The ground wire of the cable 17 is connected to the coaxial tube 9. The microwave enters the antenna 7 from the conductor 15. The coaxial tube 9 is a chamber 5 (plasma chamber)
The chamber is at the same potential as the ground wire of the cable. Microwaves enter the plasma chamber by the antenna and coaxial tube.

The outlet 1 is provided at the center of the front wall 43 of the plasma chamber 5.
4 opens. A cylindrical permanent magnet 6 is provided around the side wall 44.
Is installed. It is magnetized in the axial direction and produces a magnetic field in the axial direction inside the plasma chamber 5. The outer diameter of the permanent magnet 6 is 35 mm or less.

The gas is gas port 13, gas pipe 3, inlet 4
Enter the plasma chamber via 7. The microwave enters the plasma chamber through the coaxial tube cable, the coaxial tube and the antenna. A magnetic field of 875 G is generated inside the plasma chamber by the permanent magnet 6. The microwave is resonantly absorbed and the gas is converted into plasma. Since there is a pressure difference between the inside and the outside, neutral radicals fly out as radical lines from the outlet 14. This hits a substrate (not shown) to form a thin film.

Many materials can be handled by molecular beam cells (K-cells). The radical source can handle nitrogen, argon, oxygen, etc. Argon is not used for thin film formation, and oxygen can be incorporated into the thin film in a different form.
It is nitrogen that absolutely needs a radical source. It is possible to accurately know the state of nitrogen radicals by plasma spectroscopic analysis. N radicals and N ₂ radicals are produced, but their emission spectra are different. Spectral analysis reveals which radicals are present and in what concentration. That is, the composition concentration of plasma can be known. In the case of one type of gas, the type of such radicals can be distinguished.

Further, when a plurality of gases are introduced, it is possible to know which gas is a radical due to the difference in color. Argon emits blue light, nitrogen emits magenta, and oxygen emits white light. The composition can be known by spectroscopy.

Heat is generated by exciting the gas into the plasma. Cooling water 40 is passed through the cooling pipe 4 to cool the neck of the coaxial pipe 9. The cooling water pipe 4 is wound around the neck in a coil 19 shape. Although it is desirable to wind it around the plasma chamber 5 directly from the viewpoint of cooling efficiency, it cannot be done because of the permanent magnet 6. The reason is that if it is wound around the outer circumference of the permanent magnet, the diameter will increase too much to attach it to a small flange.

According to the invention, the coaxial tube 9 is eccentric so that it can be mounted on a small flange (70 mm diameter). A through hole 48 of the coaxial tube is formed at an eccentric position in the ultra-high vacuum flange (mounting flange) 1. A coaxial tube mounting portion 49 is provided eccentrically on the rear wall 42 of the plasma chamber 5. This is because the gas pipe 3 and the light guide pipe 2 are also passed through. The coaxial tube, the gas tube 3, and the light guide tube 2 are distributed to the rear wall 4
By attaching the back wall 42, the area of the rear wall 42 has been successfully reduced. Therefore, the plasma chamber 5 and the permanent magnet 6 can be made small. As a result, the ultra high vacuum flange 1 is also 7
The diameter can be as small as 0 mm. Therefore, the radical source of the present invention can be attached to the molecular beam cell port of a conventional molecular beam epitaxy apparatus.

[0034]

【The invention's effect】

(1) Since the spectroscopic port and the light guide tube are provided, it is possible to always monitor the spectrum of plasma emission in the plasma chamber and to know the composition and concentration of plasma. It is possible to directly investigate whether or not the desired radical is generated.

(2) Since the antenna is made linear and the plasma chamber is made small and the plasma chamber is supported by the coaxial tube, the antenna becomes vertically long and the structure is suitable as a component of the molecular beam epitaxy apparatus.

(3) Since the coaxial tube is eccentric with respect to the flange and the plasma chamber, the rear wall of the plasma chamber can be narrowed despite the addition of the light guide tube for spectroscopic analysis. Therefore, the flange can be made smaller. Most molecular beam cell ports of existing molecular beam epitaxy devices have a diameter of 70 mm.
They can also be attached to them.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a plasma chamber according to an embodiment of the present invention.

[Fig. 2] J. Ishikawa, Y. Takeiri and T. Takagi, "Axial
magnetic field extracton-type microwave ion source
with a permanent magnet ", Rev. Sci. Instrum. 55 (4),
Cross section of the ion source proposed in April 1984, p449 (1984).

[Explanation of symbols]

 1 Mounting Flange (Ultra High Vacuum Flange) 2 Light Guide Tube 3 Gas Tube 4 Cooling Water Tube 5 Plasma Chamber 6 Permanent Magnet 7 Antenna 8 Current Introducing Terminal 9 Coaxial Tube 10 Insulator 11 Eccentric Distance 12 Spectroscopic Port 13 Gas Port 14 Plasma Chamber Outlet 15 Conductor 16 pin 17 Coaxial cable 18 Core wire 19 Coil 20 Permanent magnet 22 Antenna 23 Extraction electrode 24 Extraction electrode 26 Intermediate flange 27 Upper flange 28 Gas inlet 29 Waveguide 40 Cooling water 42 Rear wall 43 Front wall 44 Side wall 46 Opening 47 Gas inlet 48 Coaxial tube through hole 49 Coaxial tube mounting part r Center line of flange q Center line of coaxial tube q Center line of plasma chamber

Claims (1)

[Claims] 1. An ultra-high vacuum flange that can be fixed to a cell mounting flange of an MBE device, a coaxial tube that is provided at a right angle to the flange at an eccentric position of the ultra-high vacuum flange, and a gas that is eccentrically provided at the tip of the coaxial tube to excite gas A plasma chamber that turns the plasma into plasma and emits radicals from the outlet, a cylindrical insulator that is inserted into the coaxial tube, and a linear antenna that is inserted into the insulator and has its tip exposed to the plasma chamber, Coaxial with a gas tube that penetrates the ultra-high vacuum flange to introduce gas into the plasma chamber, and a light guide tube that penetrates the ultra-high vacuum flange to the plasma chamber and allows spectroscopic observation of the plasma inside the plasma chamber from the outside. It penetrates through the ultra-high vacuum flange and the current introducing terminal inside the tube that blocks the external atmospheric pressure and the internal vacuum and transmits the microwave given from the outside to the antenna. It is characterized in that it comprises a cooling pipe which is provided around the coaxial pipe and through which a medium for cooling the coaxial pipe is passed, and a permanent magnet which is provided around the plasma chamber and generates an axial magnetic field inside the plasma chamber. Coaxial ECR plasma generator.