JPS61208739A - Focused ion beam device - Google Patents

Abstract

PURPOSE:To minimize voltage fluctuation caused when minute electric discharge occurs in electrostatic lenses by applying electric potentials to the electrostatic lenses directly from columns of an accelerating-voltage-producing circuit consisting of a Cockcroft-Walton circuit. CONSTITUTION:An ion beam from an ion source 2 is accelerated by an accelerator tube 5 and the accelerated ion beam is irradiated upon a sample 11 through a capacitor lens 7 and an objective 9. The power supply of the focused ion beam device of this invention consists of a Cockcroft-Walton circuit 20 consisting of diodes and capacitors connected in multiple stages. In the circuit 20, a high voltage is produced by applying high-frequency voltages from high-frequency power supplies 21 and 22 and voltages are directly applied to the capacitor lens 7 and the objective 9. Since the internal resistance of the voltage- dividing circuit is small, only small voltage fluctuation is caused even when minute electric discharge occurs in the electrostatic lenses. Consequently, it is possible to maintain the beam in an optimally focused state.

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 an electrostatic lens for focusing an ion beam is improved.

(Prior Art) A focused ion beam device is a device that ionizes atoms, extracts them to form a beam, and irradiates a substance with the ion beam to change the shape and properties of the substance. This type of device has recently come to be used as a maskless ion implantation device for semiconductor microfabrication. FIG. 2 is a diagram showing an example of the electrical configuration of a conventional focused 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 that emits ions.
4 is an extraction electrode (extractor) for extracting ions emitted from the emitter 2, and 4 is a power source for applying an extraction voltage to apply a potential to the extraction electrode 3. As the output voltage of the accelerating voltage generating circuit 1, for example, about 200 KV is used. As the voltage generated by the power source 4 for applying the extraction voltage, for example, about 5000V is used.

5 is an acceleration tube that accelerates the ion beam passing through the tube in multiple stages; 6 is a voltage divider that applies multiple acceleration voltages to the acceleration tube 5; The voltage divider 6
For example, a voltage dividing resistor for high voltage resistance is used.

7 is a condenser lens that focuses the ion beam, and 8 is a mass separator (mass filter) that separates ions of different orientations from among the passing ions. The mass separator 8 applies a magnetic field and an electric field perpendicular to the magnetic field to passing ions to remove unnecessary ions. In other words, utilizing the property that the trajectory of ions passing through a magnetic field is bent in descending order of mass, unnecessary ions are removed by applying an LT field perpendicular to the magnetic field to make the necessary ion beams travel straight. It is something.

9 is an objective lens, 10 is a deflector that scans the ion beam in the X and Y directions, and 11 is a sample (target) to which the ion beam is irradiated in an IIA-like manner.

12 is a voltage divider to which the output voltage of the accelerating voltage generating circuit 1 is applied. As the voltage divider 12, for example, a voltage dividing resistor is used like the voltage divider 6. The voltage divider 12 is provided with taps A and B as shown in the figure. The divided voltage to the tap is applied to the objective lens 9, and the divided voltage to the tap B is applied to the condenser lens 7. When the acceleration voltage is 200 KV, the voltage applied to the objective lens 9 is, for example, 100 KV, and the voltage applied to the condenser lens 7 is, for example, about 50 KV. Note that the condenser lens 7 and the objective lens 9 are electrostatic lenses that focus the beam using an electric field. To explain the operation of the device configured in this way,
It is as follows.

A high-intensity ion beam generated from the emitter 2 and passed 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 multistage accelerator tube 5 is narrowed down to a beam diameter by a condenser lens 7, and then unnecessary ions are removed by a mass separator 8. The ion beam that has passed through the mass separator 8 has its beam diameter narrowed down again by an objective lens 9, is deflected in a predetermined direction by a deflector 10, and then irradiates a target 11. As a result, target 1
The surface of 1 is scanned in a predetermined direction, and ions are implanted or sputtered with an ion beam.

FIG. 3 is a diagram showing the trajectory of the ion beam thus formed until it irradiates the target. The numbers in the figure correspond to the numbers of the components in FIG.

(Problems to be Solved by the Invention) By the way, in conventional focused ion beam devices, electrostatic lenses as described above are used as condenser lenses and objective lenses. In the case of an electrostatic lens, it must be vacuum insulated, which causes the following problems.

■Micro discharges occur in spacers between electrodes, along the creeping surface of insulators, etc.

■Vacuum minute discharge occurs between the electrodes.

In the embodiment shown in FIG. 2, the power is supplied to the condenser lens 7 and the objective lens 9 by dividing the voltage as described above! 112
50KV and 100Kv are given respectively. For example, in a focused ion beam device with an accelerating voltage of 200 KV, a high resistance of about 1000 MΩ is used as the voltage divider 12. Therefore, ■.

When there is a minute discharge as explained in (2), a voltage drop occurs due to the resistance due to the discharge current of this minute discharge, and the above-mentioned applied voltages of 50 KV and 100 KV fluctuate, respectively. For example, assume that a minute discharge occurs in the objective lens 9. If the peak value of the discharge current at this time is 1μ8, then 100
The voltage dividing resistance value that provides KV is 50, which is 1/2 of 1000MΩ.
Since it is 0MΩ, the amount of voltage fluctuation is 500MQ×1μA−500(V). The error with respect to the rated value of 100KV is 0°5%. As a result, the ion beam on the sample 11 deviates from the optimal focusing conditions and becomes out of focus.

A similar problem may also occur with the condenser lens 7.

The present invention has been made in view of these points, and
The purpose is to prevent even if a minute discharge occurs in the electrostatic lens part.
The object of the present invention is to realize a focused ion beam device in which the optimum focusing conditions of the ion beam are not deviated from.

(Operating Principle) In order to solve the above-mentioned problems, it is sufficient to reduce the number of minute discharges, but the reality is that it is currently impossible to completely eliminate the number of minute discharges. Therefore, it is necessary to consider countermeasures on the premise that minute discharges will occur. One of the countermeasures is the method described below. That is,
It is sufficient that the voltage applied to each electrostatic lens does not fluctuate even if a micro discharge occurs and the load current increases. In order to satisfy these conditions, it is necessary to use a voltage divider or a high voltage generating power source with a small internal resistance.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, accelerates an ion beam emitted from an ion source, focuses it with an electrostatic lens, and then irradiates the target surface with a focused ion beam. The apparatus is characterized in that the electrostatic lens is supplied with a potential directly from a column of an accelerating voltage generating circuit.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an electrical circuit diagram showing an embodiment of the present invention realized based on the above-described principle. The circuit shown in the figure is
2 shows a specific configuration of the accelerating voltage generation circuit 1 shown in the figure, and the configuration of FIG. 2 is used as is for other parts.

In the figure, 20 is a well-known Cockcroft-Walton circuit constructed by connecting diodes and capacitors in multiple stages. The Cockcroft-Walton circuit consists of capacitors C1 to Cn (n
is an integer, the same applies hereinafter) and rectifier diodes Dl to Dn as shown in the figure between each stage of Cs- to Cn-.

The DI- and [)n- cross-connections are used as a high voltage doubler rectifier circuit.

21 and 22 are high frequency power supplies that generate high frequency high voltages whose phases differ by 180 degrees. The high frequency power supply 22 connects the high frequency power supply 21 to one end of the series circuit of the capacitor Ct-On.
are connected to one end of the series circuit of capacitors C1- to Cn'' respectively. Dcs and Dct- are diodes that take out the high-voltage rectified output from the third column of the Cockcroft-Walton circuit 20, and DO21 and Dc2- are the diodes that take out the high-voltage rectified output from the third column of the Cockcroft-Walton circuit 20. Diode D extracts high-pressure rectified output from the 6th column
ck, D ck- are diodes that take out the high voltage rectified output from the first stage (top stage). The high voltage taken out from the top stage of the Cockcroft-Walton circuit 20 is applied to a multistage accelerator tube (see 5 in FIG. 2), and is further negatively fed back to the output voltage control circuit 23 via a resistor R. The output voltage control circuit 23 controls the output and amplitude of the high frequency power supplies 21 and 22 so that the output of the Cockcroft-Walton circuit 20 is constant. C11-C16, C111-
~c18- are capacitors Ci = Cs, C, respectively
t'' to Co= are capacitors for increasing the capacity, which are respectively connected in parallel.The operation of the circuit configured in this way will be explained as follows.

When a high frequency high voltage is applied from high frequency power sources 21 and 22 to the Cockcroft-Walton circuit 20 shown in the figure, the Cockcroft-Walton circuit 20 generates a high voltage at the top stage corresponding to the number of stages.

The divided voltages of this high voltage are the third column,
The signals are taken out from the sixth column and applied directly to the condenser lens and objective lens, respectively.

These applied voltages are, for example, 50 as described above.
KV, 100KV is taken.

Now, let us find the internal resistance Rs of the voltage dividing circuit taken out from the sixth stage of this Cockcroft-Walton circuit 20. Generally, when the number of stages of the Cockcroft-Walton circuit 20 as shown in the figure is N, and the frequency of the high frequency power source 21°22 is f condenser capacitance IC, the internal paper *Rs is expressed by the following equation.

N −1/(f−C) X ((NS /4) −(N2 /2)+ (N/2
>) N-6, f -20KHz, :) Ndensa Ct
〜Cn *C1−〜cn −, Qm l 〜cm
Assuming that the capacitances of s + Cs t - to C1B- are all 4000PF, the 6-stage voltage dividing resistor Rs is calculated from the above formula as N-6, and Rs = 1/ (2x 10' X8X 10-'f
) X(63/4-62/2+6/2> =244 <KΩ). Therefore, if a minute tIl electric current is generated in the objective lens of the 6th stage, and a discharge current of 1μΔ flows at the peak, the amount of fluctuation voltage will be 244KQxlμA-0,244(V), which is 100
The error with respect to the rated value of KV is negligible. 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 usually 1 oev, and the voltage fluctuation due to the discharge current of about 1 μA generated in each electrostatic lens is , it is about 0.2 to 0.3 V at most and is not a problem at all.

A resistor R shown in the figure functions as a feedback resistor for feeding back the output voltage to an output voltage control circuit (not shown) for keeping the output voltage constant.

That is, the highest stage output of the Cockcroft-Walton circuit 20 is given to the output voltage control circuit 23. Output voltage control circuit 2
3 compares the inputted actual output voltage with a reference voltage and sets the high frequency power supply 2 so that the output voltage is equal to the reference voltage.
9) which controls the output amplitude of 1.22)! Performs Siri control.

Capacitors Cm1 to cm g connected in parallel to both ends of capacitors C4 to C6 and Cl- to C6-, respectively;
Cl1l r - to CI1+8- is for increasing the value of the capacitance C in equation (1) and reducing the value of the internal resistance RN of the voltage dividing circuit as a whole. Capacitor C1-C6
If the capacitances of CI- and CI- to Ce- are made large in advance, it is not necessarily necessary to provide such a capacitor for parallel connection.

In this way, the high voltage output applied to the multistage accelerator tube is controlled to be constant, but the output voltage of the power supply section to the condenser lens and the objective lens is not controlled by negative feedback. However, as mentioned above, the internal resistance of the Cockcroft-Walton circuit is as low as 20 to 300 Ω, and even with a minute discharge of about 10μ8, the amount of voltage fluctuation is about 2 to 3V.
In an ion beam device that accelerates and focuses ions with an acceleration distribution on the order of eV, this has almost no effect on the focusing effect.

In the above explanation, the case where a Cockcroft-Walton circuit is used as an accelerating voltage generation circuit is taken as an example.
The present invention does not necessarily have to be limited to this. It is a circuit that itself generates high voltage, and the divided voltage extracted from the column can be directly supplied to each electrostatic lens, and the internal resistance of the voltage dividing circuit can be suppressed to about several tens of ohms. If there is, it can be anything.

(Effects of the Invention) As explained in detail above, according to the present invention, power is supplied directly from the column of the accelerating voltage generation circuit to the electrostatic lens, and
By keeping the internal resistance of this voltage dividing circuit low, voltage fluctuations can be reduced even if a minute discharge occurs in the electrostatic lens. Therefore, it is possible to realize a focused ion beam device in which the optimum focusing conditions of the ion beam are always maintained.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of the configuration of a conventional device, and FIG. 3 is a diagram showing the trajectory of an ion beam. 1... Accelerating voltage generation circuit 2... Emitter 3...
Extraction electrode 4...Power supply 5...Acceleration tube
6.12... Voltage divider 7... Condenser lens 8... Mass separator 9... Objective lens 1
0... Deflector 11... Sample 20... Cockcroft-Walton circuit 21.22.
...High frequency power supply 23...Output voltage control circuit Patent applicant: JEOL Co., Ltd. Representative: Patent attorney: Fujiji Ijima, one person: T3 Shunji
q −11jLSa,, + −−z / /
-IJ / Day MIIJPH3; Extraction power fE
9; Objective syn 5; Acceleration tube
10:lll direction device. 7; Condenser lens 111 samples

Claims (2)

[Claims] (1) Accelerate the ion beam emitted from the ion source,
A focused ion beam device that irradiates a target surface after focusing with an electrostatic lens, characterized in that the focused ion beam device is configured such that a potential is directly supplied to the electrostatic lens from a column of an accelerating voltage generation circuit. Beam device. (2) The focused ion beam device according to claim 1, wherein a Cockcroft-Walton circuit is used as the accelerating voltage generating circuit.