JPH047535B2 - - Google Patents

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, 3 is an extraction electrode (extractor) that extracts ions emitted from the emitter 2,
Reference numeral 4 denotes a power source for applying an extraction voltage that applies 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. For example, about 500V is used as the voltage generated by the power source 4 for applying the extraction voltage.

5 is an acceleration tube that accelerates the ion beam passing through it in multiple stages;
Reference numeral 6 denotes a voltage divider that applies multistage accelerating voltages to the accelerating tube 5. As the voltage divider 6, for example, a high voltage dividing resistor is used. 7 is a condenser lens that focuses the ion beam, and 8 is a mass separator (mass filter) that separates ions with different masses among the passing ions. The mass separator 8 applies a magnetic field perpendicular to the passing ion beam, and further applies a magnetic field perpendicular to this magnetic field to remove unnecessary ions. That is, by utilizing the property that the trajectory of ions passing through a magnetic field is bent in descending order of mass, an electric field is applied perpendicular to the magnetic field to cause the necessary ions to proceed straight, and unnecessary ions are removed.

9 is an objective lens, 10 is an ion beam X,
A deflector 11 that scans in the Y2 direction is a sample (target) to which the ion beam is finally irradiated. 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 of tap A is the objective lens 9.
The divided voltage of tap B is applied to the condenser lens 7. When the acceleration voltage is 200KV, the voltage applied to the objective lens 9 is, for example,
The voltage applied to the condenser lens 7 is, for example, about 63 KV. Note that the condenser lens 7 and the objective lens 9 are electrostatic lenses that focus the beam by electrolysis. The operation of the device configured as described above will be explained 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 a six-stage acceleration tube 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 is narrowed down to a beam diameter again by an objective lens 9, and then deflected in a predetermined direction by a deflector 10.
Irradiate the target 11. As a result, the surface of the target 11 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 the spacer between the electrodes, along the creeping surface of the insulator, etc.

Vacuum minute discharge occurs between the electrodes.

In the conventional example shown in FIG. 2, the condenser lens 7 and objective lens 9 are supplied with 50 KV and 100 KV, respectively, from the voltage divider 12 as described above. 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 , 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 1 μA, the partial voltage resistance value that provides 100 KV is 500 MΩ, which is 1/2 of 1000 MΩ, so the voltage fluctuation amount is 500 MΩ×1 μA = 500 (V). The error for the rated value of 100KV will be 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.

In order to solve this problem, it would be sufficient to reduce the number of minute discharges, but the current situation is that it is 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, even if a micro discharge occurs and the load current increases, the voltage applied to each electrostatic lens may be prevented from changing. In order to satisfy these conditions, it is necessary to use a voltage divider or a high voltage generating power source with small internal resistance.

The present invention has been made in view of the above points, and its first purpose is to prevent the optimal focusing conditions of the ion beam from deviating even if a minute discharge occurs in the electrostatic lens section. The purpose of this research is to realize a focused ion beam device.

A second object of the present invention is to realize a focused ion beam device that not only does not deviate from the optimal focusing conditions of the ion beam, but also allows a large number of partial pressure points.

(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. In the device, as an accelerating voltage generating circuit, a Cottcroft-Walton circuit is used, in which series circuits of series-connected capacitors are arranged in parallel, and rectifier diodes are cross-connected between each stage of the capacitors in both series circuits. A first diode series circuit whose cathodes are connected in reverse is inserted and connected between the stages of the series circuit of the capacitors at the same position in the Kotscroft-Walton circuit, and a The cross-connected rectifier diodes are replaced with a second diode series circuit connected in series in the forward direction, and the connection points of the diodes constituting the second diode series circuit are connected. It is something.

(Example) First, prior to describing an example, an apparatus that achieves only the first objective will be described. FIG. 4 is an electrical circuit diagram showing an example of an improved device that achieves only the first objective. The circuit shown in the figure shows a specific configuration of a portion corresponding to the accelerating voltage generation circuit 1 of FIG. 2, and the configuration of FIG. 2 is used as is for the other portions. In the figure, 20
is a well-known Kotscroft-Walton circuit constructed by connecting diodes and capacitors in multiple stages. The Kotscroft-Walton circuit consists of a capacitor C ₁ connected in series across it as shown in the figure.
~Cn (n is an integer, the same applies hereinafter) and between each stage of C ₁ ′ to Cn′, rectifier diodes D ₁ to Dn′, D ₁ to
This is a cross-connection of Dn′ and is used as a high voltage doubler rectifier circuit.

Reference numerals 21 and 22 are high frequency power supplies that generate high frequency high voltages with phases different by 180 degrees. The high frequency power supply 22 is connected to one end of the series circuit of capacitors C ₁ to Cn.
The high frequency power supply 21 is connected to one end of the series circuit of capacitors C ₁ ' to Cn', respectively. D _c1 , D _c1 ′ are diodes that take out the high-pressure rectified output from the third stage column of the Kotscroft-Walton circuit 20; D _c2 ,
Similarly, D _c2 ' is a diode Dck that takes out the high-pressure rectified output from the sixth stage column, and Dck' is a diode that takes out the high-pressure rectified output from the k-th stage (top stage). The high voltage taken out from the top stage of the Kotscroft-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 amplitudes of the high frequency power supplies 21 and 22 so that the output of the Cottcroft-Walton circuit 20 is constant. Cm ₁ ~ Cm ₆ ,
Cm ₁ ′ to Cm ₆ ′ are capacitors C _{1 to} C ₆ , C ₁ ′ to
These are capacitors connected in parallel to C ₆ ' to increase the capacity. The operation of the circuit configured as described above will be explained as follows.

Kotscroft-Walton circuit 20 shown in the figure
When a high frequency high voltage is applied from the high frequency power sources 21 and 22, respectively, the Kotscroft-Walton circuit 20 generates a high voltage at the top stage corresponding to the number of stages. Partial voltages of this high voltage are taken out from the third column and the sixth column, respectively, and directly applied to the condenser lens and the objective lens, respectively. These applied voltages are, for example, 50KV and 100KV as described above.

Now, let's find the internal resistance R ₆ of the voltage divider circuit taken out from the 6th stage of this Kotscroft-Walton circuit 20. Generally, the number of stages of the Kotscroft-Walton circuit 20 as shown in the figure is N, and the high frequency power supply is 2.
When the frequency of 1 and 22 is f and the capacitance of the capacitor is C, the internal resistance R _N is expressed by the following equation.

R _N =1/(f・C)×{(N ³ /+4) −(N ² /2)+(N/2)} ……(1) N=6, f=20KHz, capacitor C ₁ ~Cn ，
If the capacities of C ₁ ′ to Cn ′, Cm ₁ to Cm ₆ , and Cm ₁ ′ to Cm ₆ ′ are all 4000PF, then from the above formula, N=6 and 6
Calculating the voltage dividing resistance R ₆ of the stage, R ₆ = 1/(2 x 10 ⁴ x 8 x 10 ^-9 ) x (6 ³ /4 - 6 ² /2 + 6/2) = 244 (K
Ω) becomes. Therefore, if a minute discharge occurs in the objective lens of the 6th stage, and a discharge current of 1μA flows at its peak, the amount of fluctuation voltage will be 224KΩ x 1μA = 0.244 (V), and the error with respect to the rated value of 100KV is ignored. can. In a focused ion beam device using a liquid metal electrolytic radiation ion source, the half-width of the initial velocity distribution of ions generated from the ion source is usually 10 eV.
The voltage fluctuation caused by the discharge current of about 1 μA that occurs in each electrostatic lens 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 cutoff output of the Kotscroft-Walton circuit 20 is given to the output voltage control circuit 23. The output voltage control circuit 23 compares the input actual output voltage with a reference voltage and performs negative feedback control to control the output amplitudes of the high frequency power supplies 21 and 22 so that the output voltage becomes equal to the reference voltage.

Capacitors Cm ₁ to Cm ₆ are connected in parallel to both ends of capacitors C ₁ to C 6 and C _{1 ′} to C ₆ ^′ , respectively.
Cm ₁ ′ to Cm ⁶ ′ are for increasing the value of capacitance C in equation (1) and reducing the value of internal resistance R _N of the voltage dividing circuit as a whole. Capacitors C ₁ to _{C 6} and
If the capacitances of C ₁ ′ to C ₆ ′ are increased in advance, it is not necessary to provide such parallel connection capacitors.

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 Kotscroft-Walton circuit is 200KΩ~
It is low at 300KΩ, and even with a fairly large micro discharge of about 10μA, the fluctuation voltage is about 2 to 3V, so 10eV
In an ion beam device that accelerates and focuses ions with a certain degree of acceleration distribution, this has almost no effect on the focusing effect.

As explained in detail above, the improved device shown in FIG. Power cannot be supplied from the voltage dividing point shown in . For example, in the above example, the voltage applied to the condenser lens was 50V, and the voltage applied to the objective lens was 100V, which were values that were well separated. Here, the voltage applied to the condenser lens is 63KV,
If the voltage applied to the objective lens is set to a value of 90 KV, which is in a poor range, it cannot be produced using the improved device shown in Figure 4. Therefore, as shown in Figure 5, variable power supplies E ₁ and E ₂ are connected in series with the voltage taken out from the previous voltage dividing point as shown in the figure, and the outputs of these variable power supplies are adjusted to create a three-stage system. 50KV and 100KV taken out from the 6th and 6th stages are respectively 63KV,
It is possible to make it 90KV. In this case, variable power supply E ₁ produces +13KV and variable power supply E ₂ produces -
It produces 10KV. Installing such a variable power supply complicates the configuration and increases the power supply.
Since it is necessary to float E ₁ and E ₂ and connect them in series, it is necessary to take proper insulation measures, which results in an expensive product. Also, variable power supplies E ₁ , E ₂
There is also a certain limit to the variable range of , and the variable range cannot be expanded that much. In order to avoid such problems, it may be possible to increase the number of stages in the Kotscroft-Walton circuit, but in reality it is not possible to increase the number of voltage dividing points that much. Therefore, it is impossible to finely set the desired divided voltage.

FIG. 1 is an electrical circuit diagram showing one embodiment of the present invention. The embodiment shown in the figure is an improved version of the Kotscroft-Walton circuit 20 shown in FIG.
Other circuit parts not shown in the figure are omitted because they are the same as the configuration diagram of FIG. 5. The circuit shown in the figure replaces the diode D ₃ in Figure 5 with two diodes D ₃₁ and D ₃₁ ', and replaces the diode D ₂ ' with
Two diodes D ₄₂ and D ₄₂ ' are used instead, and the intersection point P ₁ of the series circuit of these diodes is commonly connected. The circumstances during this time are diode D ₄₁ ,
The same applies to D ₄₁ ′, D ₄₂ , and D ₄₂ ′, and P ₃ is the intersection of these diode series circuits. Note that P ₂ is a conventional voltage dividing point (power feeding point). That is, in the circuit of the present invention, only the upper and lower rectifier diode circuits near the voltage dividing point are configured in a bridge shape using four diodes.

With this configuration, there are two more voltage dividing points (power feeding points) above and below the conventional voltage dividing point P ₂ (points P ₁ and P ₃ ).
can be created. If power is supplied to the condenser lens from point P ₁ , the supply voltage V ₁ is V ₁ = 50 (KV) - 8.3 (KV) = 41.7 (KV) If power is supplied from point P ₂ , the supply voltage V ₂
is 50KV, and the supply voltage V ₃ when power is supplied from point P ₃ is V ₃ = 50 (KV) − 8.3 (KV) = 58.3 (KV). can be selected. According to the present invention, since three types of divided voltages can be drawn from one stage of the Kotscroft-Walton circuit, a variable power supply
The variable range of _E1 can also be narrowed, making the configuration easier. For example, if the power supply voltage of the condenser lens is 63V as mentioned above, when the voltage is taken from point _P3 , the voltage borne by variable power supply _E1 is 63 (KV) - 58.3 (KV) = 4.7 (KV ), which reduces the burden. As described above, according to the present invention, the variable range of the variable power source _E1 may be narrow, so
Circuit configuration becomes easier. The same situation applies to the power supply circuit for the objective lens. Note that if the power supply voltages at these voltage dividing points match the voltage applied to the electrostatic lens, the variable power supplies E ₁ and E ₂ are unnecessary.

(Effects of the Invention) As explained in detail above, in the present invention, as an accelerating voltage generation circuit, a series circuit of series-connected capacitors is arranged in parallel, and a rectifier diode is installed between each stage of the capacitors of both series circuits. A cross-connected Kotscroft-Walton circuit is used, and a first diode series circuit connected in reverse so that the cathodes face each other is inserted between stages at the same position in the series circuit of the first capacitor in the Kotscroft-Walton circuit. and replacing the cross-connected rectifier diodes near the first diode series circuit with a second diode series circuit connected in series in the forward direction, and forming the second diode series circuit. Since the connection points of the diodes that constitute the first and second diode series circuits are connected,
By supplying power directly to the electrostatic lens without going through a resistor, the internal resistance of the voltage divider circuit can be kept low, and even if a minute discharge occurs in the electrostatic lens, voltage fluctuations can be reduced. Therefore, it is possible to realize a focused ion beam device in which the optimum focusing conditions of the ion beam are always maintained. Moreover, according to the present invention, a plurality of voltage dividing points can be created from one stage, so even if a variable power source is connected, the variable range can be narrow, and the configuration can be simplified.

[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, FIG. 3 is a diagram showing the trajectory of an ion beam, and FIGS. 4 and 5 are diagrams showing improved examples of the conventional device. 1... Accelerating voltage generation circuit, 2... Emitter, 3
...extraction electrode, 4...electrode, 5...acceleration tube,
6, 12... Voltage divider, 7... Condenser lens,
8... Mass separator, 9... Objective lens, 10...
Deflector, 11... Sample, 20... Cottcroft-Walton circuit, 21, 22... High frequency power supply,
23... Output voltage control circuit, C ₁ ~ Cn, C ₁ ′ ~ Cn′,
Cm ₁ ~ Cm ₆ , Cm ₁ ′ ~ Cm ₆ ′...Capacitor, D ₁ ~
Dn, D ₁ ′ ~ Dn ′, D _c1 〜 Dck, D _c1 ′ ~ Dck′, D ₃₁ ,
D ₃₂ , D ₃₁ ′, D ₃₂ ′, D ₄₁ , D ₄₂ , D ₄₁ ′, D ₄₂ ′...Diode, E ₁ , E ₂ ... Variable power supply.

Claims (1)

[Claims] 1. In a focused ion beam device that accelerates an ion beam emitted from an ion source, focuses it with an electrostatic lens, and then irradiates the target surface, a series circuit of series-connected capacitors is connected in parallel as an accelerating voltage generation circuit. A Kotscroft-Walton circuit is used in which a rectifier diode is cross-connected between each stage of the capacitors in both series circuits, and a cathode is connected between stages at the same position in the series circuit of the capacitors in the Kotscroft-Walton circuit. A first diode series circuit connected in reverse so that the diode series circuits face each other is inserted and connected, and the rectifier diodes cross-connected near the first diode series circuit are connected to a second diode series circuit connected in the forward direction.
A focused ion beam device characterized in that the second diode series circuit is replaced with a diode series circuit, and connection points of the diodes constituting the second diode series circuit are connected.