JPS6220663B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method of introducing a mixed gas of an inert gas and an oxygen gas into the vicinity of the specimen, and generating a glow discharge in the vicinity of the specimen. The present invention relates to electron microscopes and similar devices configured to remove contaminants such as organic substances or organic gas molecules attached to members.

[Prior Art] It is generally believed that sample contamination in an electron microscope or the like occurs when organic gas molecules in residual gas near the sample are solidified by electron beam irradiation and deposited on the sample surface. In order to prevent such sample contamination, conventionally, devices have been widely used in which cooling bodies are installed above and below a sample tube to adsorb organic gas molecules near the sample.

However, such a device does not stop the source of organic gas molecules, but only adsorbs organic gas molecules near the cooling body.
It is impossible to prevent organic gas molecules emitted from the upper magnetic pole of the objective lens closest to the sample or from the surface of the sample tube from adhering to the sample and thereby contaminating the sample.

Therefore, in order to solve these problems, an electrode is installed between the upper and lower magnetic poles of the objective lens, an inert gas is introduced near each magnetic pole, and an alternating current voltage is applied between the electrode and each magnetic pole. It is possible to remove contaminants such as organic gas molecules adhering to the upper magnetic pole of the objective lens, the surface of the sample cylinder, etc. by applying this voltage to generate a glow discharge.

[Problems to be solved by the invention] However, the cooling body and the aperture plate of the objective lens are installed between the upper magnetic pole and the lower magnetic pole of the objective lens, and a new glow discharge Inserting an electrode is not very preferable because it increases the distance between the upper magnetic pole and the lower magnetic pole, which leads to a decrease in resolution.

The present invention has been made in view of these points, and provides an electron microscope and similar devices that can effectively remove the contaminants without widening the distance between the upper and lower magnetic poles of the objective lens. The purpose is to

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a sample contamination prevention cooling body inserted between the upper and lower magnetic poles of an objective lens, such that the upper and lower magnetic poles and other surrounding members are at ground potential. means for electrically insulating from the objective lens, means for introducing an inert gas or a mixed gas of an inert gas and oxygen gas between the upper and lower magnetic poles of the objective lens, and providing a potential difference for glow discharge between the cooling body and the ground potential. power supply,
and means for selecting whether the cooling body is connected to a power source or grounded.

Hereinafter, embodiments of the present invention will be explained in detail based on the drawings.

[Embodiment] FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, in which numeral 1 is an objective lens, and an upper magnetic pole 2 and a lower magnetic pole 3
It is composed of a magnetic pole piece, a yoke 5, and a magnetic excitation coil 6, which are integrated by a spacer 4 made of a non-magnetic material.

Reference numeral 7 denotes a sample chamber provided above this objective lens, in which a sample stage 8 is movably placed, and a sample cylinder 9 holding a sample (not shown) is located on the optical axis of this sample stage. is removably inserted.

Reference numerals 10 and 11 denote cooling bodies for preventing sample contamination placed above and below the sample tube 9. Holes 12a and 12b through which electron beams can pass are formed in the optical axis portion, and these cooling bodies are used for the sample chamber and the yoke, respectively. It penetrates the side wall and is fixed to the cooling tank 13. A refrigerant 14, for example, liquid nitrogen, is introduced into this cooling tank to cool the cooling bodies 10 and 11, thereby adsorbing organic gas molecules near the sample. The cooling tank 13 is held in an outer tank 16 via heat insulators (also serving as electrical insulation) 15a and 15b, and this outer tank is fixed to the side wall of the sample chamber 1 via flanges 17a and 17b. There is. As a result, both the cooling bodies (cooling baths) are electrically insulated from the sample chamber.

18 is an AC power source for discharging (a DC power source may be used)
One end is grounded, and the other end is connected to the cooling tank 13 via a changeover switch S.

Reference numeral 19 denotes a gas cylinder containing a mixed gas of an inert gas and a small amount of oxygen gas (inert gas alone may also be used), and this gas cylinder is connected to the inside of the magnetic pole piece via a pipe 20 penetrating the side wall of the yoke 5. ing. The pipe is provided with a variable leak valve 21 for adjusting the flow rate of the mixed gas.

Now, with the objective lens and the sample chamber evacuated, the variable leak valve 21 is opened and the mixed gas is introduced into the magnetic pole piece and the sample chamber to reduce the pressure near the sample to 1×10 ^-1 to 10 ^-3 Create a gas atmosphere around Torr. In this state, when the switch S is switched to the position shown by the dotted line, an AC voltage of about 1 KV is applied from the AC power supply 18 to the cooling bodies 10 and 11 via the cooling tank 13, so that both of these cooling bodies and the earth potential are applied. The maintained upper magnetic pole 2, lower magnetic pole 3, spacer 4, yoke upper cover 5a, sample chamber 7,
Glow discharge is forcibly generated between the sample stage 8 and the sample cylinder 9. This discharge ionizes the mixed gas into ions, and these ions move between the two cooling bodies, the upper magnetic pole, the lower magnetic pole, the spacer, the yoke upper cover, the sample chamber, the sample stage, and the sample cylinder according to the cycle of the AC power supply. Because of the alternating impact, contaminants such as organic substances and organic gas molecules adhering to these members are spattered. In addition, some of the contaminants adhering to the members are oxidized and gasified by high-temperature heating due to ion bombardment, making them more likely to be spattered. The thus gasified and sputtered contaminants are exhausted via an exhaust pipe (not shown). By performing such an operation for about 5 minutes, the contaminants adhering to each member can be completely removed (cleaned).

In this case, when observing a sample such as a metal, the surface of the sample can be cleaned by attaching the sample to the sample tube in advance, and when the sample is to be destroyed by electrical discharge, such as a living organism, only the sample tube is attached.
The sample may be attached after cleaning is completed.
Further, the cleaning speed can be arbitrarily controlled by the pressure near the sample depending on the amount of mixed gas introduced, the amount of oxygen gas introduced, the AC voltage, and the operating time.

After the cleaning is completed, switch the changeover switch S to the position shown by the solid line, and
0 and 11 are kept at ground potential, and the variable leak valve 21 is closed. Thereafter, the inside of the sample chamber etc. is evacuated to a predetermined degree of vacuum, a coolant 14 is introduced into the cooling tank 13, and an electron beam is generated from an electron gun (not shown) to observe a microscopic image.

In the above description, the present invention was applied to an electron microscope, but it goes without saying that it can be similarly applied to a scanning electron microscope, an X-ray microanalyzer, and the like.

[Effects of the Invention] As described above, in the present invention, since the cooling body for preventing sample contamination is used as the glow discharge electrode, it is necessary to insert a new glow discharge electrode between the upper and lower magnetic poles of the objective lens. disappears. Therefore, contaminants near the sample can be removed without deteriorating the resolution due to the widening of the gap between the upper and lower magnetic poles. In addition, organic gas molecules adhering to the surface of the cooling body can be removed by glow discharge, resulting in activation and increasing adsorption efficiency. This has great practical effects, such as eliminating the need to take out the organic gas molecules and remove them from the cooling body.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing one embodiment of the present invention. 1 : Objective lens, 7: Sample chamber, 8: Sample stage, 9: Sample cylinder, 10, 11: Cooling body, 13: Cooling tank, 18: AC power supply, 19: Gas cylinder.

Claims (1)

[Claims] 1. Means for electrically insulating a sample contamination prevention cooling body inserted between the upper and lower magnetic poles of the objective lens from the upper and lower magnetic poles and other surrounding members that are at ground potential, and an inert gas or Selecting a means for introducing a mixed gas of an inert gas and an oxygen gas, a power source for providing a potential difference for glow discharge between the cooling body and a ground potential, and whether the cooling body is connected to a power source or grounded. Electron microscopes and similar devices characterized in that they are equipped with means for.