JPS6193534A - Ion source - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an ion source.

BACKGROUND OF THE INVENTION Ion sources are known in which the gaseous material from which ions are to be generated is excited into a fully ionized or plasma state by means of a high-frequency alternating electromagnetic field. Then 1
Desired ions are extracted from the ion source by an electric field generated by one or more extraction electrodes.

SUMMARY OF THE INVENTION However, such known ion sources primarily generate beams of molecular ions and are therefore used, for example, to provide insulating regions in semiconductor substrates used in the manufacture of large scale integrated circuits. For some purposes, these molecular ions are harmful, such as forming or forming regions where such circuits require a particular type of electrical conductivity.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high frequency plasma ion source that primarily generates atomic ions.

According to the invention, there is provided a chamber capable of being evacuated, means for introducing into said chamber in gaseous form a material for forming ions, and said gaseous medium being capable of exciting said gaseous medium into a plasma state. means for applying an alternating electromagnetic field to the plasma; means for applying an electric field to extract ions from the plasma; means for maintaining the walls of the chamber at a high temperature; An ion source is provided comprising means for applying a magnetic field.

The energy required to heat the walls of the chamber may be derived from the plasma or may be provided from an external energy source.

By allowing the walls of the chamber to reach temperatures in the region of 600°C and by applying a magnetic field to the plasma, the temperature of the electrons therein is raised to a value that prevents the molecules of the plasma material from dissociating and recombining. can be done. Thus, the ion source primarily generates atomic ions. Unwanted molecular ions can be removed by a magnetic analyzer.

Preferably, the ion source includes an extraction electrode with a plurality of parallel slits to generate a plurality of parallel individual beams.

The invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: FIG.

To explain the embodiment in FIG. 1, the ion source has a diameter of about 700 nn.
The chamber 1 has a wall 2 made of crystal. This wall 2 has a first port 3 through which the chamber 3 can be evacuated;
There is a second port 4 that allows volatile or gaseous materials to be introduced into the chamber 1 for forming ions.

Surrounding the chamber 1 is a coil 5, which can be energized with current from a high frequency power source 6 of known type, as will be described in more detail below. The frequency and power of this high frequency power source 6 are such that the material introduced into the chamber 1 is fully excited into the plasma state. A second power source 7 is also connected to the coil 5, and this power source is
A stationary solenoidal magnetic field 8 is generated in the region of the main part of the wall 2 of the chamber 1 . Two coils 9 and 10 are each provided to isolate the power source 7 from the high frequency current of the coil 5. Arranged within the chamber 1 is a quartz plate 11, the function of which is to prevent electrons from impinging on those parts of the wall 2 of the chamber 1 which the solenoidal magnetic field 8 does not reach.

Metal plate 12 also defines an exit hole for the ions generated by the ion source.

Also works as an extraction electrode.

In use, the walls 2 of the chamber 1 are heated to a temperature of several hundred degrees Celsius by the impingement of components of the plasma within the chamber 1. The operating temperature of the walls 2 of the chamber 1 is not critical, but takes an optimum value based on the material of the plasma in the chamber 1. For example, if the gaseous material is oxygen at a pressure of about 0.7 mTorr, a wall temperature of about 600° C. is suitable. If necessary,
External heating or cooling means may also be provided. A cooling coil 13 is shown in the accompanying drawings.

In a plasma, most of the tendency for electrons and ions to recombine occurs in their surroundings.

Also, in these low temperature regions, neutral atoms recombine to form molecules. The hot walls 2 of the chamber 1 and the magnetic field 8 control both the temperature distribution of the electrons in the plasma and the ion flux to the walls 2 of the chamber 1. As a result, the number of atomic ions produced by the ion source of the present invention is significantly increased compared to the output from conventional plasma ion emission sources.

FIG. 2 shows a second embodiment of the invention in which the magnetic field 8 is generated by a number of magnets 21 in multipolar form.

This ion source operates in the same manner as in the first embodiment described above and will not be described in further detail. Common parts of both embodiments are designated with the same reference numerals.

If the ion source is to be used to generate ions of a material that is normally in a solid or liquid state, the boat 4 can be connected to a furnace capable of vaporizing this material.

Referring to FIG. 3, an ion beam generator according to the invention has a vacuum chamber 30, which has two ports 32 and 33 to enable it to be evacuated.
One end of the vacuum chamber 30 is fixed to the base plate 25,
This base plate has a central hole 26 that allows the ion beam 27 to enter the vacuum chamber 1 .

Positioned in the path of the ion beam 27 is an electromagnet assembly 28 . The electromagnet assembly 28 includes a first magnetic field 29' oriented out of the plane of the drawings;
The electromagnet assembly 28 has a core 31 in the form of one complete loop, which forms two pairs of pole pieces 34 and 35. Suitably connected pairs of coils 14 and 15 are wound around pairs of pole pieces 34 and 35, respectively.Pairs of pole pieces 35 support multiple water-cooled plates 16; These plates are arranged to cut off those components of the ion beam 27 that have mass-to-charge ratios that differ from the mass-to-charge ratio of the singly ionized monovalent species that are intended to be formed by the magnetic analyzer. The pair of pieces 35 also support the structure 17 defining the exit slit 18.

Plate 16 and structure 17 are cooled with water. Mounted in the vacuum chamber 30 opposite the incoming ion beam 27 is a beam dump 19 that absorbs the energy of the ion beam 27 in the absence of the magnetic field generated by the electromagnet assembly 28. It is constructed to cut and absorb even the slightest amount of water.

Ion beam 27 is generated by auxiliary assembly 20 attached to vacuum chamber 30. This assembly 20 is
A high frequency plasma ion source 21 as described in connection with FIGS. 1 and 2 is provided. This plasma ion source 21
Associated with them are three grid holders and extraction electrodes 22 between which a series of parallel rectangular cross-section beamlets are defined to form an ion beam 27 . The long axes of these beamlets are aligned parallel to the magnetic fields 29' and 29''.

In use, the magnetic field 29' diverges the beam 27 to the right as shown and separates the component ions of different mass-to-charge ratios in the conventional manner.

Ions with widely different mass-to-charge ratios strike the plate 16 and are absorbed by it. Mass − centered around the desired value
Ions with a relatively small dispersion of charge ratio are
is deflected in the opposite direction by the magnetic field 29'' and focused onto the structure 17. The slit 18 allows only ions with the exact desired mass-to-charge ratio to pass through, and the desired ion species.

The beam 23 can be emitted as a rapidly diverging beam 23 with a certain rectangular cross section. All other ions are cut off even by the water cooled structure 17.

The emerging ion beam 23 may exhibit some type of residual structure resulting from the beamlets.

In such cases, if the effect is determined to be undesirable, this effect can be reduced or eliminated by a number of methods, such as the following.

a) Modulating the energy of the input beam 27.

b) Modulating the magnetic fields 29'' and 20''. or C) magnetic field 2
d) electrostatically sweep the ion beam while passing through a field-free region between 9' and 29''; or d) cause a controlled divergence of at least one of the beamlets forming the ion beam 27;

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one embodiment of the invention; FIG. 2 is a schematic diagram showing a second embodiment of the invention; and FIG. 3 is a schematic diagram showing an ion beam generator according to the invention. It is a schematic diagram. 1... Room 2... Wall 3... First port 4... Second port 5... Coil 6... High frequency power supply 7... Second power supply
8...Solenoid magnetic field 9.1o...Coil procedure correction writing method) 1. Display of case Patent Application No. 163788 of 1985 2, Title of invention ion source 3, Person making amendment Relationship to case Applicant 4, Agent

Claims (7)

[Claims] (1) a chamber capable of being evacuated; means for introducing into said chamber in gaseous form a material for forming ions; an ion source comprising means for applying a field and means for applying an electric field to extract ions from the plasma; means for maintaining the walls of said chamber at a high temperature; and a solenoid magnetic field or radius applied to the plasma within said chamber. An ion source comprising means for applying a directional multipolar magnetic field. (2) The means for applying an electric field to extract ions from the chamber comprises an electrode having a plurality of parallel slits formed therein to form a plurality of elongated parallel beamlets. The ion source according to paragraph (1). (3) The means for maintaining the walls of the chamber at a high temperature is set forth in claim (1) or (2), wherein the means for maintaining the walls of the chamber at a temperature of about several hundred degrees Celsius is provided. ion source. (4) An ion source according to claims (1) to (3), which is combined with a magnetic analyzer adapted to select only ions having a predetermined mass-to-charge ratio. (5) The magnetic analyzer includes means for generating two non-parallel magnetic fields, the beamlets of ions are configured to sequentially pass the beam orthogonally thereto, and the first magnetic field is configured to generate two non-parallel magnetic fields. The second magnetic field is operative to select ions with a mass-to-charge ratio of , and the second magnetic field is operative to focus these selected ions to a focal point to form a single divergent ion beam. The ion source according to item (4). (6) An ion source substantially as described with reference to FIGS. 1 and 2. (7) An ion source associated with a magnetic analyzer substantially as described with reference to FIG.