JPH0345413Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a gas phase ion source, and more particularly to a gas phase ion source with improved emitter cooling.

(Prior art) A focused ion beam device ionizes atoms,
A device that extracts the ion beam, converts it into a beam, and irradiates the material with the ion beam to change the shape and properties of the material, or to analyze the material by measuring the mass number of secondary ions generated from the material. be. In recent years, this focused ion beam apparatus has come to be used as a means for performing beam writing such as pattern formation on chips formed on a wafer, or as a means for implanting ions into chips.
Ion sources for this type of focused ion beam device include a liquid metal ion source that generates metal ions from liquid metal, and a gas phase ion source that ionizes gas such as He.

FIG. 2 is a diagram showing an example of the configuration of a conventional focused ion beam drawing apparatus. In the figure, 1 is an acceleration voltage generation circuit that generates high voltage for ion beam acceleration;
2 is an ion source that emits ions, 3 is an ion source 2
An extraction electrode 4 extracts ions from the extraction electrode 3, and is a power source for applying an extraction voltage to apply a potential to the extraction electrode 3. The output voltage of the accelerating voltage generating circuit 1 is, for example, about 100 KV, and the supply voltage of the extraction voltage applying power source 4 is, for example, about 5 KV. 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 that focuses the ion beam, and 8 is an E×B (pronounced E-Crosby) mass separator (also called a mass filter) that separates ions with different masses among the passing ions. . The ExB mass separator 8 applies a magnetic field B and an electric field E perpendicular to the magnetic field B to passing ions to remove unnecessary ions.
In other words, by taking advantage of the property that the trajectory of ions passing through a magnetic field is bent significantly in descending order of mass (higher specific charge), an electric field orthogonal to the magnetic field is applied to make the necessary ion beams travel straight. It is to be removed.

Reference numeral 9 designates an objective lens also constructed of an electrostatic lens, 10 a deflector for scanning the ion beam in the X and Y2 directions, and 11 a sample to which the ion beam is finally irradiated. The operation of the device configured as described above will be explained as follows.

A high-intensity ion beam generated in the ion source 2 and passed through the opening of the extraction electrode 3 is accelerated by the multistage acceleration tube 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 an ExB mass separator 8 , refocused by an objective lens 9 , and then transferred to a deflector 1
After being deflected in a predetermined direction at 0, the sample 11 is irradiated. As a result, ion implantation is performed into the sample 11.

Here, when the ion source 2 is a gas phase ion source, cooling of the emitter is performed as follows. As shown in FIG. 3, He gas is sealed and pressurized from a ground potential through an insulating tube 22 into a liquid He dewar (container) 21 placed at an accelerating potential. As a result, liquid He is stored in a reservoir (small container).
The emitter 24 supplied to the reservoir 23 and thermally coupled to the reservoir 23 is cooled to, for example, 20°K or less.

On the other hand, the temperature at the emitter 24 is detected by a thermocouple 25, converted to temperature by a thermometer 26, and displayed. The operator controls the liquid He dewatering unit 2 so that the display on the thermometer 26 reaches a predetermined temperature.
Adjust the He gas pressure in 1. Increasing the gas pressure increases the amount of liquid He supplied to the reservoir 23, increasing the cooling capacity; conversely, decreasing the gas pressure increases the amount of liquid He supplied to the reservoir 23.
The amount of liquid He supplied to 3 is reduced, and the cooling capacity is reduced.

(Problems to be solved by the invention) In the case of the conventional gas phase ion source, as mentioned above, the operator adjusts the He gas pressure in the liquid He dewar while monitoring the temperature of the emitter section. Therefore, if the operator's attention is distracted, the temperature will suddenly drop too much or rise too much, making it difficult to keep the temperature of the emitter section constant. If the temperature is lowered too much, liquid He
It is also uneconomical as it leads to unnecessary consumption.

The present invention was devised in view of these points, and its purpose is to realize a gas phase ion source that can control the temperature of the emitter section at a constant level.

(Means for Solving the Problems) The present invention solves the above problems by detecting the temperature of the emitter in a gas phase ion source that obtains ions by blowing gas onto the cooled emitter. The present invention is characterized by the provision of a control mechanism that controls the flow rate of cooling liquid helium supplied to the emitter so that the temperature reaches a predetermined value.

(Function) In order to keep the temperature of the emitter section constant,
Negative feedback control of He flow rate.

(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. Components that are the same as those in FIG. 3 are designated by the same reference numerals. The liquid He dewar 21 is placed on a dewar mounting insulating stand 31, and the dewar mounting insulating stand 31 is supported by a support 33 via an insulator 32. 34 is an automatic temperature controller which receives a reference voltage Es corresponding to the set temperature at one input and an emitter temperature detection signal detected by the thermocouple 25 at the other input; 35 receives the output of the automatic temperature controller 34; This is a pressure control actuator that controls the pressure of He gas supplied from the He gas cylinder 36. Note that as the automatic temperature controller 34, for example, a PID controller is used.

He gas controlled to a predetermined pressure is released from the pressure control actuator 35 and supplied into the liquid He dewar 21 via the insulating tube 22 . Here, convert He gas into liquid
The reason why an insulating tube is used for the tube that supplies the He dewar 21 is that the He gas cylinder 36 is at ground potential, and the liquid He dewar 21 is connected to the emitter 24.
This is because it is placed at an accelerating potential in the same way as . liquid
Liquid He in the He dewar 21 is supplied to the dewar 23 via the tube 37. The operation of the device configured as described above will be explained as follows.

First, the reference voltage Es is set to a voltage value corresponding to the target temperature for cooling the emitter 24 (for example, 20° C.K). As the set value, a value corresponding to the thermoelectromotive force at 20K of the emitter temperature detection thermocouple 25 is used. It is assumed that the emitter 24 is cooled to a certain temperature by the liquid He supplied to the reservoir 23. The temperature signal of the emitter 24 section detected by the thermocouple 25 is sent to the automatic temperature controller 34.
Enter one input (-) of The automatic temperature controller 34 compares the input temperature signal with the reference voltage Es, and outputs a control signal according to the difference (deviation) between the two voltages to the pressure control actuator 35.
to be applied.

The pressure control actuator 35 is
He gas supplied from the He gas cylinder 36 is pressurized to a predetermined pressure according to the control signal, and the insulating tube 2
2 to the liquid He dewar 21. As a result, the gas pressure inside the dewar 21 increases or decreases, causing the liquid He supplied from the tube 37 to the reservoir 23.
control the amount of Specifically, when the temperature of the emitter 24 has not fallen to the set temperature, the pressure control actuator 35 increases the He gas pressure to increase the amount of liquid He flowing through the tube 37.
On the other hand, if the temperature of the emitter 24 falls too much below the set temperature, the pressure control actuator 35 reduces the He gas pressure to reduce the amount of liquid He flowing through the tube 37.

As a result of such negative feedback control, the temperature of the emitter 24 is automatically controlled to the set temperature. According to the present invention, manual operations by the operator are not required, so there is no inconvenience such as unnecessary discharge of an amount of liquid He. Once in a steady state, the emitter 24 can be maintained at the set temperature at all times unless a large disturbance occurs.

In the above embodiment, if there is a possibility that the emitter temperature will rise when the amount of liquid He gas supplied from the pressure control actuator 35 through the insulating tube 22 suddenly decreases, the electric power output from the automatic temperature controller 34 DC to signal
Just add a signal. In addition, raising the He gas pressure unnecessarily and injecting liquid He is expensive liquid He.
To avoid this, a voltage limiting element such as a Zener diode may be attached to the electrical signal output to clip the output signal below the Zener voltage.

(Effects of the invention) As described above in detail, according to the invention, the temperature of the emitter section can be automatically controlled to always be constant by controlling the flow rate of liquid He.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a conventional configuration of a focused ion beam device, and FIG. 3 is a diagram showing an example of the conventional configuration of an emitter cooling section. DESCRIPTION OF SYMBOLS 1... Accelerating voltage generation circuit, 2... Ion source, 3... Extracting electrode, 4... Voltage application power supply, 5... Multi-stage acceleration tube, 6... Voltage divider, 7... Condenser lens, 8... Mass separator, 9... Objective lens , 10...deflector, 11
...sample, 21...dewar, 22...insulation tube,
23... Reservoir, 24... Emitter, 25... Thermocouple, 26... Thermometer, 31... Dewar mounting insulating stand,
32... Insulator, 33... Support, 34... Automatic temperature controller, 35... Actuator for pressure controller, 36... He gas cylinder, 37... Tube.

Claims (1)

[Scope of utility model registration request] In a gas phase ion source that obtains ions by blowing gas onto a cooled emitter, the emitter temperature is detected and the flow rate of cooling liquid helium supplied to the emitter is adjusted so that the detected temperature becomes a predetermined value. A gas phase ion source characterized by being equipped with a control mechanism.