JPS6266552A - Focusing ion beam apparatus - Google Patents

Abstract

PURPOSE:To enable safe supply of voltage which gives optimum focusing conditions by connecting a high voltage power source for fine adjustment purpose serially to a Cockcroft-Walton circuit and impressing a voltage on a condenser lens and an objective lens. CONSTITUTION:Cockcroft-Walton circuits of small internal resistance are used in power sources which supply voltages to a condenser lens and an objective lens of a focusing ion beam apparatus. In addition, circuits are so provided as to supply the output of a high frequency power source 30, after rectifying, to high voltage power sources 33, 34 and fed it through variable high voltage generating circuits 37, 38 controlled by respective high frequency oscillators and FV converters 39, 40, so as to obtain high voltages for fine adjustment purpose. High voltages obtained by these circuits are fed to high voltage terminals of the Cockcroft-Walton circuit serially to impress voltages to the objective lens and the condenser lens. Therefore, optimum focusing conditions can be obtained safely by supplying a finely adjusted voltage from a control circuit which is insulated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a focused ion beam device, and more particularly to a focused ion beam device in which a high-voltage power supply circuit that supplies an electrostatic lens for focusing an ion beam is improved. .

(Prior art) A focused ion beam device ionizes atoms, extracts them to form a beam, and irradiates a material with the ion beam to change the shape and properties of the material, or to ionize the secondary particles generated from the material. This is a device that attempts to analyze a substance by measuring the quality m number of ions. FIG. 3 is a diagram showing an example of the electrical configuration of a conventional ion beam device. In the figure,
1 is an accelerating voltage generation circuit that generates high voltage for accelerating the ion beam, 2 is an emitter that emits ions, and 3 is an emitter 2
An extraction electrode 4 extracts ions emitted from the extraction electrode 3, and 4 is a power source for applying an extraction voltage to apply a potential to the extraction electrode 3.

For example, the output voltage of the accelerating voltage generation circuit 1 is 200K.
For example, about 5 KV is used as the supply voltage of one source 4 for applying the extraction voltage. 5 is a multistage acceleration tube that accelerates the ion beam passing through the tube, and 6 is a voltage divider that applies multiple acceleration voltages to the acceleration tube 5. As the voltage divider 6, for example, a high voltage dividing resistor is used. 7 is a condenser lens composed of an electrostatic lens P that focuses the ion beam, and 8 is a quality separator that separates ions having different masses among passing ions. The pawn separator 8 applies a magnetic field to passing ions and an electric field orthogonal to the magnetic field W to remove unnecessary ions. In other words, it takes advantage of the fact that the trajectory of ions passing through a magnetic field is bent more significantly in descending order of mass, and then removes unnecessary ions by applying an electric field perpendicular to the magnetic field to make the necessary ion beams travel straight. It is.

9 is an objective lens also composed of an electrostatic lens; 10
is a deflector that scans the ion beam in the X and Y directions, 11
is the sample that is finally irradiated by the ion beam. 12 is a voltage divider to which the output voltage of the accelerating voltage generation circuit 1 is applied;
Similarly to the voltage divider 6, for example, a voltage dividing resistor for high voltage is used. The voltage divider 12 has taps A and B#i4 as shown in the figure, and the divided voltage of tap A is applied to the objective lens 9, and the divided voltage of tap B is applied to the condenser lens 7.

The operation of the device configured as described above will be explained as follows.

A high-intensity ion beam generated in the emitter 2 and passing through the opening of the extraction electrode 3 is accelerated by six stages of acceleration tubes 5. The high-speed ion beam that has passed through the multi-stage accelerator tube 5 is focused by a condenser lens 7, unnecessary ions are removed by a quality separator 8, and is focused again by an objective lens 9.
A mock sample 11 deflected in a predetermined direction by a deflector 10 is irradiated.

As a result, ion implantation or sputtering with an ion beam is performed on the surface of the sample 11, or secondary ions are ejected.

FIG. 4 is a diagram showing the trajectory of the ion beam thus formed until the sample 11 is irradiated. The numbers in the figure correspond to the numbers of the components in FIG. For example, when the applied voltage is 200 KV, the voltage of the condenser lens 7 is 50 KV, and the voltage of the objective lens 9 is 100 KV.
It is about KV. Since these lenses are of an electrostatic type, they must be vacuum insulated in order to apply the above-mentioned high voltage, which causes the following problems.

■Minute discharge occurs on the spacer between the electrodes, on the creeping surface of the insulating glass, etc.

■Vacuum minute discharge occurs between the electrodes.

In the example shown in FIG.
KV, 100KV voltage is produced. In this focused ion beam device with an accelerating voltage of 200 KV, the voltage divider 12 uses a high resistance value of about 1000 MΩ. Therefore, when there is a microscopic lightning strike as explained in ■■, the condenser lens 7 and the objective lens 9 are fed with electricity from the output terminal of the accelerating voltage generation circuit 1 through the voltage divider 12.
A voltage drop occurs due to the discharge current, and the applied voltage fluctuates. For example, if a minute discharge of 1 μA occurs in the objective lens 9, the partial resistance value of the applied voltage of 100 KV applied to the objective lens 9 is 500 MΩ, which is 1/2 of 100 MΩ, resulting in a voltage fluctuation of 500 MΩ×1 μA = 500 V. This results in an error of 0.5% of the rated value of 100 KV, and the ion beam on the sample 11 deviates from the optimum focusing condition and is out of focus. A similar problem also occurs with the condenser lens 7.

In order to eliminate the above-mentioned drawbacks, it would be sufficient to reduce the number of micro-discharges, but it can be considered that it is impossible to completely eliminate micro-discharges at present. Therefore, it is necessary to prevent the voltage applied to each electrostatic lens from fluctuating even if a minute discharge occurs and the load current increases, and a power supply with low internal resistance must be used. Figure 2 shows the power supply. 2o is a Cottcroft-Walton circuit in which diodes and capacitors are connected in multiple stages. Here, a 12-stage circuit is shown. As shown in the figure, the circuit includes a rectifying diode D! between each stage of capacitors C1-Cl2NC'l-C'12 connected in series at both ends. ~D+2 and D'1 to D'12 are connected to each other, and are used as a high voltage doubler rectifier circuit.

CII~C11° and Cm 11~cm+6 are C1~CG and C'1~c' for reducing the internal resistance of the power supply of the feeder circuit to the objective lens 9 and condenser lens 7.
With a capacitor inserted in parallel to 6, Dc! and Dc′1,
DC2 and DC+ 2 and DC3 and De 13 are diodes that take out voltages to be supplied to the condenser lens 7, objective lens 9, voltage divider 6, and emitter 2, respectively, from the balanced Cockcroft-Walton circuit 20, and P is the objective lens 9.
Q is the output terminal connected to the condenser lens.

21 and 22 are high-frequency, high-voltage power supplies having the same amplitude and 180 degrees of phase difference. A high frequency power source 22 connects a high frequency 'R source 2 to one end of a series circuit of capacitors Cl=Cs2.
1 is connected to one end of a series circuit of capacitors CI 1 to C'12, respectively. The voltage extracted from the top stage of the Kotscroft-Walton circuit 20 is connected to the output voltage control circuit 23 via a resistor R, forming a negative feedback circuit for keeping the output voltage of the Kotscroft-Walton circuit 20 constant. In this circuit 20, the internal resistance of the power supply for the objective lens 9 is 01~C121C'l~C as a 6-stage Kotscroft-Walton circuit 20 (balanced type).
'121 CIlt~CmG, CI'1~C1l'
If s is each 4000PF and the frequency of the high frequency power source 21.22 is 20KH7, then from N- (1/fc) x (N3/4-N''/2+N/2), RG=f1/(2X10' 63
/4-62 /2+6/2>=244 becomes Ω.

As in the above example, when a current of 1 .mu.A flows due to a minute discharge, the voltage drop is 1 .mu.AX244KO-0,244V, which can be ignored with respect to the rated value of 100 KV.

In a focused ion beam device using a liquid metal field emission ion source, the half-value width of the initial velocity distribution of ions generated from the ion source is 10 eV, and it is 0.2 to 0.3 V due to the micro discharge of 1μ8 degree in the lens. There is no problem at all with the voltage fluctuation value. In Fig. 2, the accelerating voltage of the condenser lens 7 and objective lens 9 is 200 KV.
In this example, the voltages are 64 KV and 90 KV, respectively, and as mentioned above, the voltages supplied from the Kotscroft-Walton circuit 20 to the condenser lens 7 and the objective lens 9 are 5 KV and 90 KV, respectively.
At 0 KV and 100 KV, the ion beam of FIG. 4 is not focused on the sample 11.

(Problem to be Solved by the Invention) As mentioned above, since the output voltage from the Kotscroft-Walton circuit 20 is extracted from a six-stage circuit, the voltage necessary for the lens to focus the ion beam on the sample 11 is required. cannot be extracted accurately. Therefore, there is a drawback that the focus cannot be set correctly on the sample 11, and mask exposure, ion implantation, etc. cannot be performed accurately. Further, the release of secondary ions is also not sufficient.

The present invention has been made in view of the above points, and its purpose is to adjust the voltage of each lens to a desired voltage by using a Kotscroft-Walton power supply circuit that has a low internal resistance but can only extract voltage in stages. It is an object of the present invention to realize a focused ion beam device that adjusts and supplies ion beams to obtain optimal focusing conditions.

(Means for Solving the Problems) The present invention solves the above-mentioned problems in an accelerating power supply device that can draw out a stepwise high voltage and supplies an accelerating voltage, a condenser lens, and an objective lens voltage.
A high-voltage power supply for fine adjustment controlled by a control unit cut off from high voltage is connected in series to an extraction point close to the lens voltage to be supplied, and is supplied to each lens to optimally focus the ion beam. The present invention is characterized by having a power supply device adapted to obtain the conditions.

(Function) In order to focus the ion beam emitted from the emitter onto the sample, the present invention supplies a desired voltage to the condenser lens and objective lens from a power source in which an adjustment power source is connected in series with the main power source. , the focusing conditions can be optimized.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, reference numeral 30 denotes a high frequency power supply, and its high frequency output is rectified by a rectifier 31 via transformers T2 and T1 to create a DC voltage, which supplies power to the high voltage voltage ff133. The same applies to the circuits of transformer T2, rectifier 32, and high voltage power supply 34. The high voltage power supply 33 has a high frequency oscillator 35. Variable high voltage generation circuit 3
7 and an F/V converter 39. The high frequency oscillator 35 oscillates a high frequency and supplies the high frequency power to the variable high voltage generation circuit 37, and the variable high voltage generation circuit 37 amplifies the input high frequency to a desired amplitude under the control of the output of the F/V converter 39, and then rectifies it. outputs high voltage DC. The output in this case is a high voltage at the corner, which is connected in series to the output point P of the Kotscroft-Walton circuit in Figure 2, and finely adjusted to the objective lens O (Figure 3). supply The high-voltage power supply 34 works in the same way, connecting the positive DC high-voltage output of the variable high-voltage generating circuit 3B in series to the output point Q of the Kotscroft-Walton circuit in FIG. , supplies 64KV in this example. The variable high voltage generation circuit 37 is variable in the range of O to -20KV under the control of the F/V converter 39, and the variable high voltage generation circuit 38 is variable in the range of O to -20KV under the control of the F/V converter 4o.
It is variable within a range of 20KV. 41, 42 are optical fibers, and 43° and 44 are V/F converters. Note that the F/V or V/F converter is a frequency-voltage or voltage-frequency converter. The voltage of the power supply 45 is supplied to the variable resistor VR1, and the result is 1! The output from the terminal is applied to the V/F converter 43, where it is converted into a light pulse having a period corresponding to the output voltage of vRl, and is input to the F/V converter 39 via the optical fiber 41. The three F/V converters convert the input pulse-modulated light into a direct Rffi voltage proportional to its period, and use it as a control voltage for the variable high voltage generation circuit 37.
The output high voltage of No. 7 is varied in the range of 0 to -20KV. Therefore, the voltage supplied to the objective lens 9 can be changed to 100 KV (-0 to -20 KV) depending on the position of the variable resistor VR1. Variable resistor VR2, V/F converter 44.
The circuits of the optical cable 42 and F/V converter 40 work in the same way, and the output high voltage of the variable high voltage generation circuit 38 is adjusted to between O and +20KV.
Vary within the range of. Therefore, depending on the position of the variable resistor VR2, the supply voltage to the condenser lens 7 can be set to 50KV (
+O~20KV). resistor r
l and I'2 are resistors whose one ends are connected to both ends of the output terminals of the high-frequency power source 30, the other ends are connected to each other, and the connection point is grounded to bring the output circuit of the high-frequency power source 30 to a DC ground potential. be. As shown in Fig. 1, resistors r3 and r4 have one end connected to both ends of transformer T2 in the circuit between transformers T1 and T2, and the other ends connected to each other, and a variable voltage generation circuit is connected to the connection point. Connect the high voltage circuit connected directly to the rectifier 32.38 to the rectifier 32. The entire high-voltage power supply 33 is raised from the ground potential to create a high voltage, thereby preventing dielectric breakdown of components and wiring within each circuit.

Resistor r5. r6 also has a similar function.

As described above, according to the present invention, finely adjusted voltages are applied to the condenser lens and the objective lens, and the optimum focusing conditions can be set in the groove layer so that the ion beam is correctly focused on the sample.

Note that the above is just an example; for example, V/[conversion is not limited to light, it may also be an electrical pulse,
It is also possible to control directly with DC voltage. The reason for using optical transmission is to prevent danger since the high-voltage power supply is at a high voltage as a whole, so electrical control as described above is also possible if care is taken to prevent danger. Also high frequency power supply,
There is no difference between a high frequency oscillator and a low frequency oscillator.

(Effects of the Invention) As described above in detail, according to the present invention, it is possible to finely adjust and apply the voltage that provides the optimum focusing conditions to the condenser lens and the objective lens.

Its adjustment can be remotely controlled by a completely electrically isolated control circuit to prevent high voltage hazards.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a diagram of a high voltage power supply device consisting of a Cottcroft-Walton circuit, Fig. 3 is a diagram showing a conventional focused ion beam device, and Fig. 4 is a diagram of an ion beam device. It is a figure showing the locus of a beam. 1... Accelerating voltage generation circuit 2... Emitter 3...
Extraction electrode 5...Acceleration tube 7...Condenser lens 9...Objective lens 11...Sample
12... Voltage divider 20... Kotscroft-Walton circuit 30... High frequency electricity 111) t 31,3
2... Rectifier 33.34... High voltage power supply 35.36... High frequency oscillator 37.38... Variable high voltage generation circuit 39.40... F/V converter 41.42... Optical fiber 43 .44...V/F converter 45...Power supply patent applicant JEOL Co., Ltd. Representative Patent attorney Fujijima Ijima (1 person) Figure 3 6, +2; Voltage divider 11; Sample 2
Father No. 4 Figure 11 2; Emitter 31 Drawer 1 Slot 51 Liao tube 71 Condenser lens 88 Mass distribution 6 9; Objective lens] 0,4 direction device ++; m

Claims (1)

[Claims] In an accelerating power supply device that can draw out a high voltage in stages and supplies accelerating voltage, condenser lens, and objective lens voltage, a control section that is isolated from the high voltage is placed at a drawing point close to the lens voltage to be supplied. A focused ion beam device comprising: a power supply device that connects a high voltage power supply for fine adjustment controlled in series and supplies it to each of the lenses to obtain optimal ion beam focusing conditions.