JPH063720B2 - Focused ion beam device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a focused ion beam apparatus, and more specifically, chromatic aberration and lens off-axis aberration do not increase even when the acceleration voltage is changed, and the irradiation position of the beam. The present invention also relates to a focused ion beam device that does not change.

(Prior Art) A focused ion beam device ionizes an atom, extracts it as a beam, and irradiates a substance with this ion beam to change the shape or property of the substance, or to generate secondary ions from the substance. It is an apparatus that attempts to analyze the substance by measuring the mass number. FIG. 6 is a diagram showing an electrical configuration example of a conventional ion beam apparatus. In the figure, 1
Is an accelerating voltage generating circuit for generating a high voltage for ion beam acceleration, 2 is an emitter for emitting ions, 3 is an extraction electrode for generating ions from the emitter 2, 4 is the extraction electrode 3
It is a power source for applying a drawing voltage that applies a potential to the. The output voltage of the accelerating voltage generating circuit 1 is, for example, about 200 KV, and the supply voltage of the extraction voltage applying power source 4 is, for example, about 5 KV. Reference numeral 5 is a multistage accelerating tube for accelerating the ion beam passing through the inside thereof, and 6 is a voltage divider for applying multistage accelerating voltage to the accelerating tube 5. As the voltage divider 6, for example, a high voltage resistance voltage dividing resistor is used.
Reference numeral 7 is a condenser lens composed of an electrostatic lens for focusing an ion beam, and 8 is a mass separator for separating ions having different masses from passing ions. The mass separator 8
Is to remove unwanted ions by applying a magnetic field and electrolysis orthogonal to the magnetic field to the passing ions. That is, the ions that pass through the magnetic field utilize the property that the orbits are bent in order from the one with the smallest mass, and further, an electric field that is orthogonal to the magnetic field is given so as to make the necessary ion beam go straight, and unnecessary ions are removed. Is. 9 is an objective lens which is also composed of an electrostatic lens, 10 is an ion beam X,
A deflector that scans in the Y2 direction, and 11 is a sample that is finally irradiated with an ion beam. Reference numeral 22 is a voltage divider to which the output voltage of the accelerating voltage generating circuit 1 is applied. Like the voltage divider 6, for example, a voltage dividing resistor for high voltage is used. The voltage divider 22 is provided with taps A and B as shown in the figure. The divided voltage of the tap A is applied to the objective lens 9 and the divided voltage of the tap B is applied to the condenser lens 7. The operation of the apparatus thus configured will be described below.

The high-intensity ion beam generated in the emitter 2 and passing through the opening of the extraction electrode 3 is accelerated by the six-stage acceleration tube 5. The high-speed ion beam that has passed through the multistage accelerating tube 5 is focused by the condenser lens 7, and then the mass separator 8
Unwanted ions are removed by, and the sample (irradiation object) 11 is irradiated after being focused again by the objective lens 9 and deflected in a predetermined direction by the deflector 10. As a result, ion implantation is performed on the surface of the sample 11.

FIG. 7 is a diagram showing a trajectory until the sample 11 is irradiated with the ion beam thus formed. The numbers in the figure correspond to the numbers of the constituent elements in FIG. For example, when the acceleration voltage is 200 KV, the voltage applied to the condenser lens 7 is 50 KV and the voltage applied to the objective lens 9 is 100 KV.
It is about K.

As described above, the focused ion beam apparatus performs ion implantation on a sample, but the implantation depth is not uniform depending on the material or the necessity thereof, and therefore the implantation depth needs to be changed. The implantation depth is controlled by changing the acceleration voltage. On the other hand, from the viewpoint of the necessity of making the implantation amount constant and accurate drawing, it is necessary to make the diameter of the ion beam on the sample 11 (referred to as the probe diameter) as small as possible. For that purpose, it is particularly necessary to make the amount of chromatic aberration small. is there. Electrostatic lenses are generally used in focused ion beam devices,
It is necessary to increase the lens strength in order to reduce the above-mentioned color-emission amount. If the lens strength is set too strong, the focusing distance of the ion beam will be shortened and the operating distance will be shortened. After the lens 13 like the deflector 10
The method of placing the lens is not possible, and the two-stage deflectors 12a and 12b placed in front of the lens 13 as shown in FIG. The chromatic aberration amount Δw _c is expressed by the following equation.

Δw _c = (C _c × α) × Δw / V (1) However, C _c : Chromatic aberration coefficient α: Beam divergence angle V: Acceleration voltage ΔV: Energy width of emitted ions As described above, the implantation depth When the accelerating voltage is changed for the control of (1), the chromatic aberration amount changes as shown in the formula (1), and particularly when the accelerating voltage is lowered and used, the chromatic aberration amount increases and the beam cannot be focused. In order to solve this, the following electrostatic lens is used. FIG. 3 shows a lens having a five-electrode structure. The electrodes are L ₁ , L ₂ , L from the emitter side.
₃ , L ₄ and L ₅ , L ₁ and L ₅ are grounded, and L ₃
Switch 2 variable voltage Vi, the _{L 2} to Vi / 2, _{L 4} in
The power supply of 50 kV and 25 kV which is switched by 1 is connected. In the objective lens 13 having this configuration, the acceleration voltage V
When, for example, is changed to 200, 100, 50KV,
Since the Vi is changed and the switch 21 is switched, the potential distribution in the objective lens 13 becomes as shown in FIG. Therefore, the position of the main surface of the lens advances toward the sample 11 as the acceleration voltage decreases. By the way, the chromatic aberration coefficient C _c is a constant determined by the electric field and the position of the object point, and the smaller the distance between the principal surface position of the lens and the focal point, the smaller the chromatic aberration coefficient. Therefore, in the above-mentioned apparatus in which the principal surface position moves toward the sample side as the acceleration voltage decreases, the increase in the chromatic aberration amount due to the decrease in the acceleration voltage V is due to the decrease in Cc, as is clear from the equation (1). The chromatic aberration amount Δw _c does not change, which is offset by the decrease in the chromatic aberration amount.

(Problems to be Solved by the Invention) As described above, the lens strength is increased in order to reduce the chromatic aberration of the lens.
The use of a single lens element causes the following problems. In FIG. 5, the objective lens 13 when the acceleration voltage V = 200 kV
When the main surface position of the ₁₃ 1, V = the main Me position of the objective lens 13 when the 100 kV ₁₃ 2, V = a it 13 ₃ when the 50 kV, deflected by the deflector 12 when V = 200 kV the main surface position of the ion beam objective lens 13 ₁
Pass through the center of. When V = 100 kV, the objective lens 13
The main surface position of the objective lens 1 moves to 13 ₂ , but the ion beam passes through the center of the lens 13 ₁ , so the objective lens 1
Inn on the beam entering the 3 because it has shifted the center in the lens principal plane position 13 _2, the image forming point is moved to the central axis side of the sample 11 by the lens action. V = the lens principal plane position of the objective lens 13 when the 50kV in-turned beam is turned 13 ₃ passes through the lens 13 _1, forming on the sample 11 become further displaced the center position of the lens The image moves further toward the central axis. Therefore, lens off-axis aberration occurs, and at the same time, the probe position moves on the sample 11.

The present invention has been made in view of the above problems, and an object thereof is to realize a focused ion beam apparatus in which the probe position of the sample 11 king of the ion beam does not change even if the main surface position of the lens shifts due to a change in acceleration voltage. It is to be.

(Means for Solving Problems) The present invention for solving the problems described above provides an electrode of an objective lens having a plurality of electrodes when the acceleration voltage of the ion beam with which the irradiation target is irradiated is lowered. By changing the voltage applied to the object to move the lens main surface position with respect to the object to be irradiated toward the object to be irradiated, and having a means for suppressing an increase in the amount of chromatic aberration, and providing a two-stage deflector in front of the means. In a focused ion beam device in which the irradiation position of an ion beam on an object to be irradiated is controlled to a predetermined position by deflection by the two-stage deflector, regardless of movement of the main surface position, It is characterized in that it comprises means for switching the deflection gain of the two-stage deflector based on the information indicating the acceleration voltage so that the ion beam is deflected with the center as a deflection fulcrum.

(Function) Focused ions that suppress the increase in the amount of chromatic aberration by changing the voltage applied to the constituent electrodes of the objective lens and moving the lens main surface position when the acceleration voltage is changed to change the ion implantation depth. In the beam device, a direct-current deflection voltage is applied to the deflector in accordance with the amount of movement of the main surface position of the lens to allow the ion beam to pass through the center of each main surface position of the lens and keep the probe position on the sample constant.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 14 is a scanning signal generator, 1a and 15b are multipliers, 1
6 is a deflection gain memory, 17 is an acceleration power source, and 18a, 18
b is an amplifier. Scanning signals are generated in the deflectors 12a and 12b via multipliers 15a and 15b, DA converters 19a and 19b, and amplifiers 18a and 18b, respectively.
Given by. Reference numeral 20 denotes a CPU, and a signal designating an acceleration voltage V is sent from the CPU 20 to the acceleration power supply 17 and the deflector 12 corresponding to the designated acceleration voltage V is supplied.
The address designation signal for reading the deflection gain data Ga and Gb of a and 12b from the deflection gain memory 16 is CP.
It is adapted to be sent to the deflection gain memory 16 from U20. The output acceleration voltage of the acceleration power supply 17 is 200
By setting kV, 100 kV, and 50 kV, the principal surface position of the objective lens changes to 13 ₁ , 13 ₂ , and 13 ₃ . Now, when the V = 200 kV sends a control signal from the CPU20 to the acceleration power supply 17, the deflection gain main surface position of the objective lens is made to 13 _1, this time CPU20 is corresponding to V = 200 kV from deflection gain memory 16 Data G
In order to read a ₁ and Gb ₁ , the scanning signals X and Y from the scanning signal generator 14 are multiplied by Ga ₁ and Gb ₁ in the multipliers 15a and 15b, respectively, and then DA converters 19a and 19b.
Sent to. Therefore, the ion beam deflector 12a so as to pass through the center of the main surface position 13 ₁ of the objective lens Egai the trajectory is deflected by 12b. When the acceleration voltage from the acceleration power source 17 and V = 100 kV, the main surface position of the objective lens becomes 13 _2, deflection gain data G in this case CPU20 is corresponding from deflecting gain memory 16
for reading a _2, Gb _2, so as to pass through the center of the objective lens principal plane position 13 ₂ Egaki the ion beam trajectories, deflectors 12a, is deflected by 12b. Accelerating voltage is V =
Similarly, when the voltage becomes 5 kV, the deflection gains of the deflectors 12a and 12b are changed based on the data read from the deflection gain memory 16 so that the locus of the ion beam becomes. As described above, when the acceleration voltage changes, the position of the main surface of the objective lens 13 changes.
Since the deflection gains of 2a and 12b can be changed, the ion beam always passes through the center of the lens main surface position. Therefore, the off-axis aberration of the lens does not occur, and the position of the probe on the sample 11 does not change. The above deflection gain correction amount is unique to each device, and in these focused ion beam devices, it is considered that all control will be performed by the CPU in the future. Therefore, the deflection gain amount is written in the memory for each device. You can put it in a complicated way.

The example given here is just an example, and for example, the method of applying a voltage to a lens having five lenses is not limited to this, and any method can be used. Further, in the above-described embodiments, the present invention is applied to the device including the objective lens having the five-electrode structure, but the present invention can be similarly applied to the device including the objective lens having the three-electrode structure. Furthermore, in the above-described embodiment, the deflection gain is switched by the digital multiplier, but the deflection gain may be switched by an analog circuit, or the deflection gain may be switched by software.

(Effect of the Invention) As described in detail above, according to the present invention, in the objective lens in which the lens principal surface position is changed so that the amount of chromatic aberration does not increase even if the acceleration voltage is changed, the lens principal surface position changes. Even if the ion beam passes through the center of each principal surface position, no extra-rail aberration occurs, and the position of the probe on the sample surface does not move.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram regarding the lens strength and the position of a deflector, FIG. 3 is a configuration diagram of an objective lens having five lenses, and FIG. 4 is an accelerating voltage and an objective. FIG. 5 is a relationship diagram of the potential distribution of the lens, FIG. 5 is a relationship diagram of the acceleration voltage and the trajectory of the ion beam, FIG. 6 is a schematic configuration diagram of a conventional focused ion beam device, and FIG. 7 is a diagram showing the trajectory of the ion beam. is there. 2 ... Emitter 3 ... Extraction electrode 5 ... Accelerator tube 7 Condenser lens 8 ... Mass separator 9 ... Objective lens 10, 12a, 12b ... Deflector 13 ... Objective lens 13 ₁ , 13 ₂ , 13 ₃ ... Objective lens main surface position 14 ... Scan signal generator 15a, 15b ... Multiplier 16 ... Deflection gain memory 17 ... Acceleration power supply 18a, 18 ... Amplifier 19a, 19b ... DA converter 20 ... CPU

Claims (1)

[Claims] 1. When the acceleration voltage of an ion beam with which an object to be irradiated is lowered, the voltage applied to the electrodes of an objective lens having a plurality of electrodes is changed so that the position of the lens main surface relative to the object to be irradiated is changed. A means for suppressing an increase in the amount of chromatic aberration by moving the ion beam toward the irradiation object is provided, and a two-stage deflector is provided in front of the means, and the ion beam to the irradiation object is deflected by the two-stage deflector. In a focused ion beam device in which the irradiation position is controlled to a predetermined position, the acceleration voltage is expressed so that the ion beam is always deflected with the center of the principal surface as a deflection fulcrum regardless of the movement of the principal surface position. A focused ion beam device comprising means for switching the deflection gain of the two-stage deflector based on information.