JPH0687409B2 - Method for preventing sample contamination of analyzer using charged particle beam - Google Patents

Description

Detailed Description of the Invention a. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample contamination prevention method in an analyzer using a particle beam such as an electron beam microanalyzer or a scanning electron microscope.

B. 2. Description of the Related Art When an electron beam is applied to a sample with an electron beam microanalyzer for analysis, the sample surface may be contaminated due to adsorption of residual gas in the vacuum container. In particular, when the sample is analyzed at a low temperature, this adsorbed contamination becomes significant and becomes an obstacle to analysis. As a method for reducing such contamination, a method of arranging a so-called cold trap has been used, in which an object having a temperature lower than that of the sample is arranged near the sample and a contaminant is adsorbed to the low-temperature object before the sample. Has been. FIG. 2 shows an example of the cold trap. An annular cold trap C is coaxially arranged with the objective lens L below the objective lens L of the electron optical system, and an arm bar supporting the cold trap is provided outside the vacuum container V. The arm rod is cooled and the cold trap C is cooled by heat conduction.

With the above-described structure, X-rays of the analytical information line emitted from the sample pass through the central hole of the cold trap C and the objective lens L and are incident on the X-ray spectroscope from above the objective lens. Secondary electrons, which are other analysis information lines, are attracted to the secondary electron detector D arranged on the side of the sample S. In detecting the secondary electrons, the cold trap C is located in the path toward the detector D of the secondary electrons, and thus is formed in a small ring shape so as not to interfere with the detection of the secondary electrons.

C. DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The conventional pollution control method using the cold trap described above is limited in shape due to the requirement that it does not interfere with the detection of secondary electrons, has a small surface area, and is cooled by heat conduction from the outside. Since it is difficult to cool it sufficiently, the surface area is insufficient, and the low temperature is insufficient, a sufficient effect of preventing contamination cannot be obtained.

The present invention is intended to provide a method of obtaining a strong anti-contamination effect with a simple structure.

D. Means for Solving the Problems A refrigerant circulating means is provided in the objective lens of the electron optical system, and the objective lens itself is used as a cold trap by forcibly and strongly cooling the yoke of the objective lens by the liquefied gas of the refrigerant.

E. Action The objective lens closely faces the sample, and the sample facing surface has a large area. The pollution prevention ability depends on the adsorption ability of the trap, and the adsorption ability increases as the area increases and the temperature decreases. In the configuration of the present invention, the objective lens itself is a cold trap, so the area is sufficiently larger than that of a conventional cold trap. Also, a cooling medium flow means is provided in the objective lens for direct cooling, so that a sufficiently low temperature can be easily obtained. Moreover, since no separate member is arranged between the sample and the objective lens, there is no interference with secondary electron detection.

F. Embodiment FIG. 1 shows an embodiment of the present invention. The drawing shows only the objective lens of the electron optical system, L is the objective lens, 1 is the yoke, 2 is the excitation winding, and 4 is the magnetic gap provided in the yoke. S is a sample, D is a secondary electron detector, e
Indicates the optical axis of the electron optical system. A copper tube 5 runs along the inner surface of the yoke 1 on the peripheral side and is brazed to the inner surface of the yoke 1. Both ends of the copper tube 5 are pulled out from the peripheral wall of the yoke, and one end of the copper tube 5 is connected to a refrigerant tank N outside the vacuum container V. Liquid nitrogen is put in the refrigerant tank N as a liquefied gas of the refrigerant, and is delivered to the copper pipe 5 via the control valve B in an appropriate amount. The vaporized nitrogen gas is discharged from the other end of the copper tube 5. T is a temperature sensor in contact with the yoke 1, and M is a temperature indicator, and the control valve is manually adjusted so that the temperature display indicates a desired temperature. Of course, this adjustment may be automated. Although liquid nitrogen is directly used as the refrigerant in the above example, since the refrigerant effect is good in the present invention, it is necessary to circulate not the liquid nitrogen itself but the other refrigerant cooled by liquid nitrogen or the like in the copper pipe 5. May be.

G. Effect Since an objective lens (like other lenses) such as an electron beam microanalyzer generates heat by an exciting current, various methods have been conventionally used to suppress the temperature rise.
Therefore, forcibly cooling the objective lens does not hinder the lens function of the objective lens, and the present invention obtains the effect of preventing contamination of the sample and the ordinary effect of cooling the objective lens. One of the features is that the objective lens faces the sample in close proximity and has a large area, so it is an optimal object as a cold trap from the viewpoint of the positional relationship with the sample and interferes with information line detection. High pollution prevention effect.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view of an essential part of an embodiment of the present invention, and FIG. 2 is a vertical sectional side view of a conventional example.

Claims (1)

[Claims] 1. An objective lens for a charged particle beam is provided with a refrigerant circulating means in a yoke thereof, and the refrigerant circulating means is connected to a liquefied gas source for the refrigerant to forcibly and strongly cool the objective lens to obtain the objective. A method for preventing sample contamination of an analyzer using a charged particle beam, characterized in that the lens itself is used as a cold trap.