JPS5923445A - Ion mass separator - Google Patents

Abstract

PURPOSE:To obtain a compact ion mass separator for an ion injection device with excellent chromatic aberration by controlling the strength of an axisymmetric magnetic lens, converging only the desired ion beam on the electrode of a pinhole, and selectively passing through it. CONSTITUTION:A mixed ion beam 10 consisting of a number of elements is emitted from the emitter chip 2 of a field emission type ion beam generation section 1 and is guided into an ion mass separator 4 through a diaphragm 3. A separated ion is converged by an ion beam convergence system 7 and a selective ion beam 11 is guided into the specified position of a semiconductor crystal substrate 9 by an ion beam deflection system 8. The separator 4 consists of an annular axisymmetric magnetic lens 5 and a pinhole electrode 6. The mixed ion beam between the diaphragm 3 and the electrode 6 is sequentially converged with an ion with small mass by a magnetic field and an ion with large mass is converged at a farer position than a field lens. As a result, a separation with excellent chromatic aberration can be performed by controlling the field strength of the lens 5, concentrating only the desired ion, and passing it through the electrode 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an ion implantation system for use in a Marcos fresse ion implantation device that emits a plurality of mixed ions from a field emission type ion beam generator and selectively implants only predetermined ions directly into a semiconductor crystal substrate. The present invention relates to an ion mass separator that can be suitably used for separation.

The Winn filter type separator is known as a conventional ion mass separator and has an excellent resolution of 1, but since the optical system is not axially symmetrical, the ion beam acceleration of the above-mentioned ion implantation device using an axially symmetrical optical system is difficult. When incorporated into a focusing system, aberrations occur and complex operations are required to adjust the optical axis. Furthermore, the device is large and the orbit is fundamentally unstable, making it unreliable for long-term use. As described above, the Winfilter type ion mass separator has excellent resolution, but there are problems in incorporating it into an ion implanter.

An object of the present invention is to provide an ion mass separator that can be suitably incorporated into the above-mentioned maskless ion implantation device and has an axially symmetrical optical system that can separate ions and has a small, double-line structure. This will be explained below with reference to the embodiments shown below.

-3- Figure 1 shows an embodiment in which the ion mass separator according to the present invention is incorporated into the optical system of a maskless ion implanter that can form a submicron finely focused ion beam on a crystal substrate. The tip of the emitter tip of the emission-type ion beam generator l is equipped with a radiation surface with a diameter of 1 μm or less. A mixed ion beam 10 is emitted and guided to an ion mass separator through an aperture 3 located on the optical axis in front of the emitting surface. I will explain the ion mass separator l in detail, but this mass separator selectively separates and emits only the ions to be injected from the mixed ions of multiple elements.
The selected ion beam // focused on the order of submicrons by the ion beam focusing system 7 and focused by the ion beam deflection system g is guided to a predetermined position on the semiconductor crystal substrate t to draw a pattern.

The ion mass separator according to the present invention, which is provided on the front optical axis of the ion beam generating section, has an annular axisymmetric magnetic lens S.
and pinhole electrodes 6. The annular magnetic lens has the property of focusing a beam of charged particles with an axially symmetrical magnetic field, and the focal point varies in proportion to the mass M/l (M is the ion mass number and C is the charge of the ion). Using various methods, a predetermined ion beam is selectively separated from the mixed ion beam of multiple elements emitted from the tip λ' of the emitter chip.

To explain more specifically, the ion mass separator slot aperture 3
As shown in FIG. 2, the magnetic field strength and potential between the magnetic lens and the pinhole electrode 6 are strong at the center of the magnetic lens, and the potential is constant. The strength of the magnetic field changes depending on the current applied to the lens. Therefore, □The mixed ion beam emitted from the tip of the electrode tip flows between the aperture 3 and the pinhole electrode 6 at a constant velocity, but the ions with smaller mass are focused by the magnetic field in order, and the ions with larger mass are farther away than the magnetic field lens. converged at the position. Therefore, the strength of the magnetic field of the magnetic lens S is controlled so that only the ions to be implanted into the crystal substrate are focused on the pinhole position of the pinhole electrode base.
- By doing this, only the desired ions can be concentrated and pass through the pinhole. The strength of the magnetic field of the magnetic lens used at this time needs to be several thousand Gauss or more.

Now, as shown in Fig. 3, the distance from the tip of the emitter tip to the center of the magnetic lens is α, the distance from the center of the magnetic lens to the pinhole electrode 6 is I, and the diameter of the pinhole is d. , the focal point of the magnetic lens kf, the spread angle of the ion beam as θ, and the spread radius of the ion beam in the magnetic lens as rL.

The strength of the magnetic lens is k, and the mass of the ion is η (=M/,)
Then, the ion current 1f passing through the pinhole with respect to the total emitted ion current I is expressed by the following equation, and the closer the value is to lK, the thicker the ion current passing through the pinhole.

6- (When -=α, however, b〈bl or h〉 in Fig. 3
Area of h:) In the above equation, in order to set the value to 1, the beam and 1r should be made equal. Here, k is a parameter indicating the strength of the magnetic lens as described above, and is calculated according to FIG.

1 kt=f=sηvo// Bz(Z)d"Tona'
), O ie, η=svo/f BZ(Z)dZ te4l.

O Ion beam currents rI l ``t I ''81 rIf of five different masses are simultaneously emitted from the tip of the emitter tip, and a current is supplied to the magnetic lens so that the ion beam r converges at the pinhole position. If controlled, as shown in Fig. 3, the ion beam rI with the highest mass will converge at the position h, and the ion beam τb-7- with the smaller mass will point beyond the pinhole. It converges. The ion beam r4, which has a smaller mass than τ, is parallel to the optical axis and does not converge. Furthermore, the convergence point of the ion beam r, which has the smallest mass, is located in front of the magnetic lens. Therefore, assuming that the ion distribution is uniform, the ion beam rI r ”8
+r4+''!l is mixed into the ion beam r2 and passes through the pinhole at a ratio of the area of the ion beam irradiating the pinhole electrode to the diameter of the pinhole.

Next, FIG. 4 shows the relationship between the mass parameter (η/α in 2) and the ion current transmittance (If/L) calculated based on the above-mentioned formula and the mass separation characteristics shown in FIG. The actual parameters used to create this diagram are the distance α from the tip of the emitter tip to the center of the magnetic field lens, and the distance I from the center of the magnetic field lens to the pinhole electrode, both of which are 30 meters, and the spread angle of the ion beam θk is 10 m. rad
and the pore diameters are 10 pm, 50 pm, 100
The case where a pm pinhole electrode is used is shown.

For example, when an AtLBe liquid metal ion current is emitted from the ion beam generating section, Au-B.

Metal ions are Au, + ion/, A, L ox ion, Be +
ion, Be+ ion, and if it is located at point 1 where the transmittance of B,+ ion is maximum, that is, if it is selectively transmitted through the pinhole electrode of B# ion, 8g+ ion will be 2 of B- ion. Act
Since the + ion has about 80 times the mass, the positional relationship of each ion is as shown in the figure (the Au+ ion is not shown). The transmittance of the pinhole electrode for Be+ ion current is approximately □, and the hole diameter is further increased to 10 pm.
It turns out that it is approximately □. In the case of AtL, it can be seen that it is a sieve even if the pore diameter is 100 μm.

Moreover, the same is true for the case of AtL B% gold alloy, and S-
When the ion is 1, the mass of the Be+ ion is 2, and S
Since the mass of AtL pregnant ion/ is about 7 times that of i+, the positional relationship is as shown in the figure, and it can be seen that the case where a pinhole electrode with a hole diameter of 50 μm is used is 9-1. In reality, it is also necessary to consider the ratio of the number of atoms of each ion emitted from the eutectic alloy ion source, but in the above case Sj+.

Si+, ku+ or Bg", B, +, At
1. There is no problem because + has approximately the same number of atoms.

In this way, using the graph in Figure 4, if you know the mass and number of atoms of the other ion beams in the mixed ion beam, which correspond to the ion beam to be transmitted, you can position them on the respective graphs to obtain the desired transmittance. The key is to easily judge how many pinhole electrodes should be used to achieve this. Furthermore, if the ion separator is connected to two or three stages so that the ion beam passes through the pinhole electrode multiple times, the selective transmittance of the ion beam can be dramatically improved.

In the above explanation, an example has been described in which only the desired ion current is transmitted through the pinhole electrode by controlling the strength of the magnetic field with the potential between the diaphragm and the pinhole electrode being constant.
An electrostatic lens effect produced by changing the potential between the aperture and the pinhole 1O-tffi may be used in combination with a magnetic field effect.

In a focused ion beam implanter, aberrations occurring at the exit of the ion mass 1IIi device pose a problem. Of these, chromatic aberration has a large effect, but the ionic eyelid component according to this invention
The ion mass separator is more than an order of magnitude better in terms of chromatic aberration than the conventional filter/filter type ion mass separator, is axially symmetrical, and is small, so it has good consistency even when incorporated into a maskless ion implanter. It is effective in controlling the quality of a eutectic mold liquid metal source, does not cause any problem in forming a fine ion beam, and can also remove neutral ions that may be affected by KM such as ion implantation.

[Brief explanation of the drawing]

741 is an explanatory diagram showing the ion mass separator according to the present invention incorporated into the maskless ion implanter 1, and FIG. Fig. 3 is an explanatory diagram of the principle of the ion quality separator of the present invention, and Fig. 4 is a diagram showing the mass parameters and ion 'f11' of the ion mass separator of the present invention.
Graph showing the relationship between flow permeability. In the figure, l is an ion beam generation part, 2 is an emitter chip,
3 is the aperture, G is the ion mass separator, C is the magnetic V lens, 6
indicates a pin/hole peak, and ji indicates a crystal substrate.

Claims (1)

[Scope of Claim] An ion implantation apparatus in which a mixed ion beam is emitted from a field emission type ion beam generator, focused by an ion beam focusing system, and selectively implanted directly into a semiconductor crystal substrate. An ion mass separator consisting of an axially symmetrical magnetic lens and a pinhole electrode is installed on the optical axis between the ion beam generator and the ion beam focusing system, and the strength of the magnetic lens is controlled to produce only the desired ion beam. An ion mass separator characterized by focusing on a pinhole of a pinhole electrode and selectively passing one ion.