JP3039058B2 - Ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion source for generating an ion beam by using a hydrogen-diluted or helium-diluted hydride gas, and to an ion source capable of extracting required ions from a semiconductor without performing mass spectrometry. About the source.

[0002]

2. Description of the Related Art In doping a semiconductor device with a thin film transistor (TFT) array serving as a driving circuit of a liquid crystal device, polycrystalline silicon, and amorphous silicon, B is used as a target material source gas in an ion source for generating an implanted ion beam. _A hydride gas diluted with 5 to 10% hydrogen such as ₂ H ₆ (diborane) and PH ₃ (silane) is used. In a normal ion source for extracting positive ions, all the ionized elements are extracted, so when the ion source is supplied with hydride gas or PH ₃ gas diluted with hydrogen or helium for stabilization, Are P + (a monovalent positive ion of P; hereinafter, the symbol “+” means a monovalent positive ion), PHx + (x = 1 to
Along with 3), hydrogen ions H + are also extracted.

When a beam extracted from an ion source is implanted into a semiconductor without performing mass spectrometry, hydrogen ions H + are naturally implanted. Hydrogen ions, because of their light mass,
Although it penetrates much deeper than the required impurity ions and only causes defects in unnecessary regions, it is necessary to supply unnecessary energy from a power source for beam transport for ion implantation. Must. For example, 5%
In the case of hydrogen dilution, only 20% to 30% of the required impurity ions of the energy supplied from the power supply are used, and the rest is consumed for accelerating hydrogen ions and generating hydrogen ion beam current. In addition, implantation of hydrogen ions causes heating of the substrate to be implanted and an increase in temperature.

[0004] Such an undesirable situation can be avoided if only the target element or molecular ion can be extracted from the plasma. In this regard, regarding the separation and extraction of charged particles in an ion source, regarding the volume generation type negative ion source that generates a negative ion beam of hydrogen in the field of nuclear fusion, the mass of hydrogen ions and the electron Due to the difference in the radius of gyration between the two due to the difference in mass, some of them trap electrons and generate negative ion beams.
However, this is only the separation of electrons and ions having extremely different masses, and the generation of plasma is also based on arc discharge under thermionic emission of electrons by a filament. The separation of elemental ions generated in the ion source plasma chamber under the supply of gas cannot be considered at all.

[0005]

The principle of the present invention is the same as that of the above-described technique for separating and extracting charged particles in the above-mentioned volume generating type negative ion source. Ion beam using
When generating a plasma, it is possible to suppress the extraction of hydrogen ions or helium ions by applying an appropriate magnetic field to the beam extraction unit according to the mass and kinetic energy of the elements and molecular ions in the plasma. It is an object of the present invention to provide an ion source capable of preventing generation and extraction of impurity ions and extracting only desired ions.

[0006]

According to the present invention, there is provided an ion source using a hydride gas as an ion source gas, wherein a discharge mechanism using high-frequency or microwave power and a discharge mechanism disposed in a plasma chamber near an extraction electrode are provided on an electrode surface. The main feature is that it comprises a plurality of magnets for generating a magnetic field along the same.

The magnetic flux density of the magnetic field between the magnets is in the range of 50 to 500 gauss, and a gas diluted with hydrogen or helium is used as the ion source gas.

[0008]

The hydrogen ions are confined by the magnetic field acting near the extraction electrode, and only the hydride ions are extracted. Since the ion source gas is discharged by high frequency or microwave power to generate plasma, it is possible to prevent the generation of metal impurities from the plasma chamber wall due to the arc discharge observed when using a filament. Only the required ion beam can be extracted. Optimizing the confinement of hydrogen ions by selecting the magnetic flux density of the magnetic field within the range of 50 to 500 Gauss according to the type of hydride gas, the mass of ions in the plasma, and the kinetic energy Can be.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional configuration diagram of an ion source having a high-frequency discharge mechanism.
A hydride gas containing a target element diluted with hydrogen or helium is supplied from a gas inlet 3 formed in the upper chamber wall 2. The drawing electrode system of the ion source shows a three-sheet porous (or multi-slit) electrode system in the figure, and includes a drawing electrode 4, a suppression electrode 5, and a ground electrode 6. These electrodes are attached to the electrode support frames 7, 8 and 9, respectively. The upper chamber wall 2, the electrode support frames 7, 8, 9 are insulating spacers 1 made of ceramic, epoxy resin or the like.
0 and 11 are connected via an insulating tube 12. The extraction electrode 4 and the suppression electrode 5 are connected to the extraction power supply 13 and the suppression power supply 14.
Thus, the ground electrode 6 is biased to a positive potential and a negative potential, respectively.

A frequency typified by 13.56 MHz (other than 27.12 MHz, 40.68 MHz, 108.5
A high-frequency power is supplied from a high-frequency power supply 15 (MHz) to the upper chamber wall 2 serving as a high-frequency electrode and the extraction electrode 4 via a matching circuit 16. In order to generate a magnetic field having a magnetic flux density of 50 to 500 Gauss along the electrode surface in the vicinity of, ie, immediately above, the extraction electrode 4 in the plasma chamber 1, avoid the position of the ion beam extraction hole or slit of the electrode. A plurality of magnets 17 are arranged. The magnet 17 is magnetized so that its side surface has the illustrated polarity.

The ion source gas is discharged from the gas inlet 3 with high frequency power supplied between the upper chamber wall 2 and the extraction electrode 4 to generate plasma. Unlike the case of arc discharge due to the use of a filament when plasma is generated, no discharge occurs between the plasma chamber and the inner wall, so that generation of metal impurities from the inner wall surface can be prevented. Since the ion source gas is a hydride diluted with hydrogen or helium, the ion species that is decomposed and ionized by the discharge is a hydrogen ion or a helium ion, or a heavy atom or a molecular ion due to the hydride. For example, when silane PH ₃ gas is used for semiconductors, P + and P + are used as heavy atoms and molecular ions together with H +.
Hx + (x = 1, 2, 3) is generated.

The ions extracted by the extraction electrode system are
It is affected by the magnetic field of the magnet 17. Extraction electrode
The radius of rotation of the ion by the magnetic field just above 3 is the Larmor radius
r, r^Two= 2ME / (qB)^Two  Can be estimated. Where M is the mass of the ion,
q is the electric charge, and generally, the transport of ions in the plasma.
If the kinetic energy E is estimated to be at most 100 eV, the magnetic flux density
Degree B = 100 Gauss, whereas for H + r
= 14.5 mm, r = 80 mm for P +,
As shown in the figure, only H + ion is magnetic field (thin solid line is magnetic field line
), P + ions, and
Gives priority to the heavier ion PHx + (x = 1, 2, 3)
Can be taken out. So we already mentioned
As described above, the ion source is driven by a discharge mechanism using high-frequency power.
Since the generation of metal impurity ions is suppressed,
The ion beam extracted from the source is PHx + (x = 0 to
3) It can be clean and low in impurities
You.

By selecting the magnetic flux density of the magnetic field by the magnet 17 in the range of 50 to 500 gauss according to the type of hydride gas, and thus the mass of the ions to be extracted and the kinetic energy of the ions in the plasma,
The confinement of hydrogen ions and the extraction of desired ions can be optimized.

FIGS. 3 and 4 are cross-sectional views showing a structure for supporting and cooling the magnet 17. FIG. 3 is 9
FIG. 4 is a diagram viewed from a direction different by 0 degrees, and FIG.
It is sectional drawing in a line. The rectangular parallelepiped magnet 17 is housed in a rectangular pipe 18, and the pipe is sealed at the end with a closing plate 19 to form an airtight structure. Square pipe 18 is mounted and held on the stepped portion ₇₁ of the electrode support frame 7 which lead-out electrode 4 is attached. A refrigerant passage 20 is provided in one side of the pipe 18.
A coolant such as cooling water flows through the coolant passage 21, the pipe 22, the manifold 23, and the pipe 24 formed in the flange portion of the electrode support frame 7, and the plasma in a high temperature state is formed. Excessive temperature rise of the magnet 17 arranged in the chamber 1 is prevented.

In the above embodiment, the high frequency discharge type ion source has been described. However, the present invention can be applied to a microwave discharge type ion source, for example, an electron cyclotron resonance (ECR) type ion source. In an ECR ion source, a magnetic field is indispensable for plasma generation. However, even in a high-frequency discharge ion source, plasma generation involves not only an alternating electric field due to high frequency but also plasma generation. It is desirable to apply a magnetic field for stabilization and high density. The coolant passage 19 for cooling the magnet 17 is shown as being formed in one side of the rectangular pipe 18 for housing the magnet, but the coolant pipe (pipe) is fixed to the magnet housing pipe by brazing or the like. You may make it attach.

[0016]

Since the present invention is constructed as described above, unnecessary hydrogen ions can be effectively confined by the magnetic field acting near the extraction electrode, and plasma is generated by high frequency or discharge by microwave power. , The generation of metal impurities from the plasma chamber wall is prevented, and the extraction of hydrogen ions from the ion source is suppressed.
Only required ion beams can be extracted without performing mass spectrometry. Since the extraction of hydrogen ions and metal impurity ions is suppressed or prevented, the ion beam transport energy can be reduced, so that the power supply capacity related thereto can be reduced and unnecessary ions for the substrate to be processed can be reduced. Is not injected, the heat generation and temperature rise can be reduced.

By selecting the magnetic flux density of the magnetic field by the magnet 17 in the range of 50 to 500 Gauss according to the kind of the hydride gas, that is, the mass of the ions to be extracted, and the kinetic energy of the ions in the plasma, the hydrogen ions Can be optimized.

[Brief description of the drawings]

FIG. 1 is a sectional configuration diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of confinement of hydrogen ions.

FIG. 3 is a sectional view of a magnet supporting and cooling unit.

FIG. 4 is a cross-sectional view taken along line AA of FIG.

[Explanation of symbols]

 1 Plasma chamber 2 Upper chamber wall 3 Gas inlet 4 Extraction electrode 5 Suppression electrode 6 Ground electrode 7 Electrode support frame 15 High frequency power supply 17 Magnet 18 Rectangular pipe 19 Closure plate 20 Refrigerant passage

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01J 27/00-27/26 H01J 37/08 H01J 37/05

Claims (3)

(57) [Claims] 1. An ion source using a hydride gas as an ion source gas, comprising: a discharge mechanism using high frequency or microwave power; and a plurality of discharge mechanisms arranged in a plasma chamber near an extraction electrode to generate a magnetic field along an electrode surface. An ion source, comprising: a magnet; 2. The ion source according to claim 1, wherein the magnetic flux density of the magnetic field between the respective magnets is in a range of 50 to 500 Gauss. 3. The ion source according to claim 1, wherein the ion source gas is diluted with hydrogen or helium.