JPH0227432B2 - IONKAKIKO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ionization mechanism that can be used to generate cluster ion beams used, for example, in vapor deposition or crystal growth.

Conventional technology For example, when forming an insulating film or a semiconductor film, instead of ionizing and implanting atomic or molecular particles, a cluster (massive atomic group) in which many atoms are loosely bonded to each other is placed in front of an evaporation source. The electrons are ionized by the bombardment of electrons from the electron emitting filament in the accelerating electrode assembly, forming cluster ions that generate tens of thousands of particles without being affected by space charges.
A so-called Crandion ion source, which can implant a low-speed, large-capacity ion beam of eV or less, is advantageously used.

A triode type is conventionally known as such a cluster ion source, and in such a triode type, thermoelectrons generated from a filament in an ionization part are extracted from a vapor flow to be ionized generated from an evaporation source, etc. Although the vapor flow is ionized by accelerating and colliding, the ionization efficiency cannot be said to be sufficient. Therefore, in order to sufficiently increase the ionization efficiency, high frequencies or electromagnetic fields are generally applied.
Or it is configured in multiple stages. Therefore, the configuration of the ionization section is necessarily complicated.

However, in this type of ionization mechanism, it is necessary to increase the conversion of neutral clusters into the number G of singly charged ions.

In other words, the relationship G=Ne・Ng・Q・Ve (cm ^-3 /sec) (1) holds true, where Ne is the electron density (cm
^-3 ), Ng is the neutral molecular density (cm ^-3 ), Q is the monovalent ionization collision cross section (cm ^-2 ), and Ve is the electron velocity (cm /
sec).

Therefore, in order to increase G, as can be seen from the above equation (1), increase the deposition rate, increase the electron density in the orbit of the neutral beam in the ionization chamber and make it uniform, and collide the clusters. It is necessary to increase the cross-sectional area and the ionization acceleration voltage.

Further, the ionization efficiency R is expressed by the following formula.

R=Ng・Q・ν _i τ=aP(Ve−Vi) (2) Here, P is neutral gas pressure, Q: ionization cross section, Vi
is the ionization voltage, ν _i is the ionization frequency, a is the curve slope, τ
is the time that the electron exists in the ion generation chamber, and Ve is the electron energy.

Then, it is expressed as ν _i τ=γ=R/Ng・Q (3) <γ>=1/Ng∫ ^∞ _p ν _i τf(v)dV ³ (4) where γ is normalized by the atomic density. <γ> is the average value of γ for all electrons in the ion generation chamber, f(v) is the electron velocity distribution function, and dV ³ is the unit area in the total velocity space.

By the way, if the ionization efficiency is increased, the ionization efficiency will be increased. Therefore, from equations (2) to (4), in order to increase R, there is pressure dependence, and the collision space between the clusters and electrons in the ionization chamber is made appropriately large.
And it is necessary to increase the average electron density in that space.

Based on this theoretical background, the present inventor previously proposed in Japanese Patent Application No. 59-204081 that in order to improve the ionization efficiency without complicating the structure as in the past, the filaments were arranged non-opposingly, and on the outside thereof. We proposed an ionization mechanism in which a ring-shaped repeller is maintained at the same potential (negative) as the filament.

Problems to be Solved by the Invention It has been confirmed that the ionization mechanism proposed earlier has better ionization efficiency than the conventional structure in which filaments are arranged opposite each other, but the absolute value of the ion current is small in the high vacuum region. Become.

Therefore, the purpose of the present invention is to improve the ionization mechanism proposed earlier to increase the probability of collision of thermionic electrons with neutral molecules (grastar in this example) and obtain a large ion current with less ionization energy. There is a particular thing.

Means for Solving the Problems In order to achieve the above objects, the ionization mechanism according to the present invention includes a substantially identical ionization mechanism that passes through each filament near the outside of a grid provided surrounding the vapor flow from the evaporation source. An inwardly convex repeller plate is provided at a position facing each filament or a plurality of repeller plates facing each filament on the circumference, so that thermoelectrons collide extensively and repeatedly with the neutral beam penetrating the central region of the ionization section. It is characterized by the fact that

In the ionization mechanism according to the present invention configured as described above, the inwardly convex repeller plate disposed opposite to each filament reflects the thermoelectrons generated by the filament in various directions, and then reflects the thermoelectrons generated by the filament in various directions. Reflects the reflected thermoelectrons repeatedly. In this way, the thermoelectrons collide extensively and repeatedly with the neutral beam penetrating the central region of the ionization chamber. As a result, the ion current region entering the substrate can be circular and wide, and the energy density can be increased. Note that the number orientation and shape of the filament and the inwardly convex repeller plate can be arbitrarily selected. For example, a plurality of convex portions may be provided on the inside, and the shape of the convex portions may be arbitrarily designed.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

Figures 1 and 2 schematically show a cluster ion source implementing the present invention, and 1 is an evaporation source (crucible).
Heating coils 2 are arranged around it. Further, a reflector and cooling device assembly designated by reference numeral 3 is provided outside the evaporation source 1 and the heating coil 2.

An ionization section 4 is provided in front of the ejection nozzle 1a of the evaporation source 1, and as shown in the figure, the ionization section 4 surrounds the path of the cluster from the evaporation source 1 and includes an ionization electron extraction grid 5 and an ionization electron emission filament. 6, a repeller 7 disposed on the dorsal side of each filament 6, and an inwardly convex repeller plate 8 positioned opposite to each filament 6 on a circumference substantially passing through each filament 6. ing. An accelerating electrode 9 is arranged in front of this ionization section 4, and a processing (vapor deposition)
A substrate holder 11 is shown on which a substrate 10 to be processed is mounted.

Further, in FIG. 1, a block 12 is a heating power source for heating the evaporation source 1, and a heating coil 2.
It can be connected to, for example, a 13.5V, 430A AC power supply. Block 13 applies ionization acceleration current (Iex) and ionization acceleration voltage (Vex) to grit 5.
For example, Vex = 0.
It can consist of ~2KV, Iex = 500mA DC power supply.
Block 14 is ionized electron emitting filament 6
A power supply that supplies filament current (If) and filament voltage (Vf) to energize Vf = 0 to
It is an AC power supply of 50V, If = 35A. The block 15 is an ion accelerating power source that supplies an ion accelerating voltage (Va) and an ion accelerating current (Ia) to the accelerating electrode 9, and can be composed of a DC power source of 0 to 10 KV and 3 mA.

As shown in FIG. 2, in the illustrated embodiment:
Three filaments 6 are arranged at equal intervals around the grid 5, and a convex repeller plate 8 is arranged on the side between adjacent filaments 6, facing the remaining one filament 6. However, the present invention is not limited to this configuration, and the number of filaments 6 and therefore the number of inwardly convex repeller plates 8 can be selected as appropriate.

The curvature and shape of the inwardly convex repeller plate 8 are designed to reflect the thermoelectrons emitted from each filament 6 in a wide range of directions, thereby increasing the electron density in the space.

Furthermore, it is advantageous to use a filament that does not undergo thermal deformation.

In the operation of the illustrated ionization mechanism constructed in this way, the evaporation source 1 is heated to a desired temperature by energizing the heating coil 2. As a result, the metal in the evaporation source 1 evaporates, and the vapor is ejected from the ejection nozzle 1a to the ionization section 4 maintained at a high vacuum (for example, 1.3×10 ^-3 Pa). Clusters are formed by adiabatic expansion, and the clusters thus formed are emitted from the ionizing electron-emitting filament 6, drawn out by the grid 5, and reflected by the inwardly convex repeller plate 8 to increase the density. is ionized by the hot electrons. The cluster ions thus generated are accelerated by an accelerating electrode, attracted to the substrate 10 kept at a negative potential, and deposited on the substrate 10. In this way, the inwardly convex repeller plate diffuses thermoelectrons over a wide area within the space, thereby increasing the electron density within the space, so a significant improvement in ionization efficiency can be expected.

For example, referring to FIGS. 3 and 4, a comparative example is shown in which a convex repeller plate is provided on the inside (the present invention) and a case where it is not provided. In other words, in FIG. The graph shows the relationship between current and pressure, and the graph is according to the present invention.
The graph shows the case where three filaments are placed 120 degrees apart from each other in a non-opposed arrangement, and the characteristics of the graph are that when six filaments are placed non-opposed in the conventional structure, nearly twice the energy required for ionization is used. It was found that the cases are almost the same.

Figure 4 shows the relationship between ionization acceleration voltage and substrate ion current, the graph shows the case of the present invention, and the graph shows the conventional case in which three filaments are arranged non-opposingly at intervals of 120°. .

5, 6, and 7 show another embodiment of the present invention, in which the embodiment of FIGS. 5 and 6 is applied to a rectangular ion source, 16 is a grid, 17 is a filament,
18 is a back repeller, and 19 is an inwardly convex repeller. FIG. 7 shows a case in which the present invention is applied to a large circular ion source, in which 20 is a grid, 21 is a filament, 22 is a back repeller, and a multi-lobed repeller 23 is placed opposite each filament 21. Each multi-leaf repeller 23 may be constructed integrally or separately.

Effects As explained above, according to the present invention, the inside convex repeller plate is used to cause thermoelectrons to collide with the neutral beam flowing through the center of the ionization chamber over a wide range and repeatedly. Not only can a large ion current be obtained with low ionization energy without requiring a power source to increase ionization efficiency, but also the ion current region entering the substrate can be circular and wide, and the energy density can be increased.

[Brief explanation of drawings]

Fig. 1 shows the configuration of a cluster ion source implementing the present invention, Fig. 2 is a cross-sectional view of the ionization section of the apparatus shown in Fig. 1, and Figs. Graphs showing the characteristics of the ion source of the invention, FIGS. 5, 6, and 7 are schematic diagrams showing other different embodiments of the invention. In the figure, 1: evaporation source, 4: ionization section, 5: grit, 6: filament, 7: repeller, 8: repeller plate convex inward.

Claims (1)

[Claims] 1. An evaporation source that generates a vapor flow to be ionized, and an ionization electron-emitting filament and a grid that are arranged coaxially in front of the evaporation source and ionize the vapor flow from the evaporation source by irradiating the vapor flow with ionization electrons. In an ionization mechanism having an ionization section that surrounds a vapor flow from an evaporation source and passes through each filament disposed near the outside of the grid, the ionization mechanism has a plurality of ionization sections facing each filament on substantially the same circumference passing through each filament, or a plurality of ionization sections facing each filament. An ionization mechanism characterized in that a convex repeller plate is provided on the inside at the position where the thermoelectrons collide repeatedly over a wide range with a neutral beam that penetrates the central region of the ionization section.