JP2507992B2 - Ion gun - Google Patents

Description

TECHNICAL FIELD The present invention relates to a Kauffman type ion gun provided with a porous plate at the outlet of an ionization chamber.

The Kaufman type ion gun is used for fine processing of an object to be processed such as a silicon wafer used as a substrate for semiconductor device manufacturing by etching, or for depth analysis in a measuring device such as ESCA. To be

(Prior Art) FIG. 4 shows a conventional Kauffman type ion gun.

2 is an ionization chamber, one of which is an outlet. At the outlet of the ionization chamber, two perforated plates 4 and 6 are provided as a grid insulated from the ionization chamber 2. Inside the ionization chamber 2, a filament 8 for ionization is provided facing the porous plate 4, and the filament 8
Is applied with a negative voltage with respect to the potential of the wall of the ionization chamber 2. The perforated plates 4 and 6 and the filament 8 are normally set to the same potential. The ionization chamber 2 is provided with an inlet 10 for introducing a gas for ionization. Argon gas, for example, is used as the ionization gas, but oxygen or the like is also used in the case of etching.

The two perforated plates 4 and 6 are provided so as to face each other so that their holes overlap each other. An electric field is applied between the two perforated plates 4 and 6 by the power source Vo, and the ions generated in the ionization chamber 2 are accelerated by the electric field between the two perforated plates 4 and 6 to be ionized in the ionization chamber 2.
Taken from.

Reference numeral 12 is a magnet provided so as to surround the side of the ionization chamber 2, and the magnetic force lines of this magnet 12 penetrate through the ionization chamber 2 in the vertical direction in the figure, and the electrons generated from the filament 8 are guided along the magnetic force lines. This is to increase the ionization efficiency by causing the spiral movement and increasing the movement distance of electrons.

A sample chamber 14 is provided at the outlet of the ionization chamber 2.
The sample chamber 14 is provided with a sample 16 which is an object to be processed for etching or analysis, and between the sample 16 and the porous plate 6 at the exit of the ionization chamber 2, the ions emitted from the ionization chamber 2 are Neutralizer 18 for neutralizing charge
Is provided. 20 is an exhaust port connected to an exhaust pump.

In this Kauffman type ion gun, gas is introduced from the gas inlet 10 and ionization is performed in the ionization chamber 2 by the electrons from the filament 8. Ions generated in the ionization chamber 2 are accelerated by the electric field between the two porous plates 4 and 6 to be taken out to the sample chamber 14, the charges are removed by the nutizer 18, and then the sample 16 is irradiated.

(Problems to be Solved by the Invention) As the holes of the two perforated plates 4 and 6 are smaller and provided in larger numbers, the ions passing through those perforated plates 4 and 6 become more uniform, and the current density is increased. Grows larger. Therefore, the diameter of the holes of the perforated plates 4 and 6 is set to about 0.1 to 2 mm.

Two perforated plates with such fine holes 4,6
However, unless the holes are aligned in the order of μm, the extraction efficiency of the ions passing through the perforated plates 4 and 6 becomes very poor. Therefore, the ion extraction efficiency of this type of ion gun is two perforated plates 4, 6
There is a problem that it is not easy to manufacture an ion gun with high ion extraction efficiency because it depends on the hole alignment technology.

Further, since a fixed voltage is applied between the porous plates 4 and 6 and the sample 16, the state of the ion beam with which the sample is irradiated is also fixed. Since the state of the ion beam with which the sample is irradiated is required to be different depending on the use, there is a problem that the use is limited.

It is an object of the present invention to provide a Kaufman type ion gun which is easy to assemble, has a high ion extraction efficiency, and can change the state of the ion beam with which the sample is irradiated, and is versatile.

(Means for Solving Problems) Referring to FIG. 1 showing an embodiment, in the ion gun of the present invention, one porous plate (22) is provided at the exit of the ionization (2) chamber. , The object to be processed (16) is provided outside the ionization chamber (2) on the sample table (24) of which height is variable, facing the porous plate (22), and the porous plate (22) and the object to be processed (16) A power supply (26) for applying an electric field between
The voltage of this power supply (26) is made variable and the perforated plate (22)
The lens action of the can be adjusted, and the distance from the perforated plate (22) to the object to be processed (16) can be adjusted to the sample stage (24).
It is possible to adjust the aperture or the extent of spread of the ion beam by changing the.

(Embodiment) FIG. 1 shows an embodiment of the present invention. The same parts as those in FIG. 4 are designated by the same symbols.

The number of perforated plates 22 provided at the outlet of the ionization chamber 2 as a grid that is insulated from the ionization chamber 2 is one.
The electric potentials of the porous plate 22 and the filament 8 of the ionization chamber 2 are the same.

In the sample chamber 14, a sample 16 which is an object to be processed is placed on a sample table 24 whose height is variable. The potential of the sample 16 is the ground potential, and the voltage V is applied between the porous plate 22 and the sample 16 by the power source 26. The voltage V of the power supply 26 is variable. 28
Is an ammeter for measuring the current flowing through the sample 16 by ion irradiation.

The distance L between the porous plate 22 and the sample 16 is about 1 cm, and this distance L is the conventional porous plate 6 shown in FIG.
Is smaller than the distance between the sample 16 and the sample 16. Further, no nutrizer is provided between the porous plate 22 and the sample 16.

Like the conventional porous plates 4 and 6, the porous plate 22 has holes with a diameter of about 0.1 to 2 mm.

The voltage V applied between the porous plate 22 and the sample 16 is
This is the ion extraction voltage for extracting ions from the ionization chamber 2 and accelerating and irradiating the sample 16.

In the present embodiment, the spread of the ion beam with which the sample 16 is irradiated can be adjusted by the degree of plasma seepage in the porous plate 22. The extent of the plasma exudation can be adjusted by the ion extraction voltage V, the distance L between the porous plate 22 and the sample 16, and the like.

In this embodiment, the state of the ion sheath when extracting the ions from the plasma in the ionization chamber 2 is shown in FIGS. 2 and 3.

FIG. 2 shows a state in which the ion sheath is concave at the hole portion of the porous plate 22. Such a state of the ion sheath occurs when the plasma density in the ionization chamber 2 is low or when the voltage V is high due to ion extraction.

When ions are extracted from the state as shown in FIG. 2 to the sample 16, the ion beam is focused and the sample 16 is irradiated.

FIG. 3 shows a state in which the ion sheath 30 is extruded from the hole of the porous plate 22 and has a convex shape. Such a state occurs when the plasma density in the ionization chamber 2 is high or when the ion extraction voltage V is low.

When ions are extracted from the state shown in FIG. 3 and irradiated onto the sample 16, the sample 16 is irradiated with the ion beam spread. Irradiation with the ion beam spread in this way is convenient when performing ion etching.

Further, by changing the distance L between the porous plate 22 and the sample 16, the degree to which the ion beam is narrowed or spread can be adjusted.

In this way, the porous plate 22 can be made to have a lens action by the ion extraction voltage V, the distance L, or the plasma density between the porous plate 22 and the sample 16.

(Effect of the Invention) In the Kauffman type ion gun of the present invention, the number of perforated plates provided at the exit of the ionization chamber is one. for that reason,
2 perforated plates like the conventional Kaufman type ion gun
Compared to the one using one, the alignment of the holes between the perforated plates becomes unnecessary. As a result, it becomes possible to easily assemble an ion gun having a high extraction efficiency of the ion beam.

Further, a power source for applying an electric field is provided between the porous plate and the sample, the voltage of this power source is made variable to adjust the lens action of the porous plate, and further, the distance between the porous plate and the sample is made variable. Therefore, the state of the ion beam for irradiating the sample can be adjusted according to the application, such as irradiating the sample with the ion beam squeezed or irradiating the sample with the ion beam expanded. .

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of the present invention, FIGS. 2 and 3 are views for explaining the lens action of the porous plate in the same embodiment, and FIG. 4 is a conventional Kauffman type ion gun. It is a schematic sectional drawing showing. 2 ... Ionization chamber, 16 ... Sample to be processed, 22 ...
… Perforated plate, 26 …… Power supply for ion extraction voltage.

Claims (1)

(57) [Claims] 1. A single perforated plate is provided at the exit of the ionization chamber, an object to be processed is provided outside the ionization chamber on the sample table of variable height facing the perforated plate, and the perforated plate and the object to be treated are provided. A power supply for applying an electric field is provided between the processed objects, and the voltage of this power supply is made variable so that the lens action of the porous plate can be adjusted, and the distance from the porous plate to the processed object is changed by the sample table. An ion gun characterized by being able to adjust the degree of aperture or spread of the ion beam.