JPH10172496A - Environment controlled scanning type electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable observation of a water-containing sample as is by providing a liquid circulation pipe for holding the inside of a sample chamber at a constant temperature on a sample chamber interior wall and keeping it in a low vacuum of about saturated steam pressure at that temperature. SOLUTION: A liquid circulation pipe 7 is laid on an interior wall of a sample chamber 6, one end thereof is coupled with a water supply port 8a of a constant temperature water circulation device 8, and the other end thereof is coupled to a water drain port 8b of the constant temp. water circulation device 8. This constant temp. water circulation device 8 performs heat exchange for keeping water entered from the water drain port 8b at a constant temperature, and water temperature- controlled from the water supply port 8a to the liquid circulation pipe 7 is supplied. The liquid circulation pipe employs a materiel such as stainless steal that is hardly rusted and easily machined. When a water-containing sample is observed in steam, the sample is first set to a sample holder, the inside of a sample chamber 6 is vacuum- evacuated, and the steam pressure in the sample chamber 6 is set. The constant temp. water circulation device 8 is moved, and a temperature of the water to be supplied to the liquid circulation pipe 7 is set to a temperature corresponding to a saturated steam pressure curve, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to maintaining a sample chamber of an environment-controlled scanning electron microscope at a constant temperature.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for observing various substances under various environments and at high magnification. Environmentally controlled scanning electron microscope (Environmental Scanning Ele)
The ctronMicroscope (hereinafter, referred to as ESEM) is an observation device that satisfies this requirement. The ESEM can create various environments by changing the type of gas introduced into the sample chamber.

[0003] In particular, when a biological sample is observed in a water-containing state, the sample is often placed in a saturated steam pressure atmosphere and microscopically observed in a "water-containing state". The ESEM employs a gas amplification system capable of detecting secondary electrons even under a low vacuum of 2700 Pa (20 Torr), which is a saturated water vapor pressure at normal temperature. This gas amplification method repeats the process of increasing the number of electrons while secondary electrons generated from the sample collide with gas molecules and ionize the gas molecules under a water vapor pressure of, for example, 2700 Pa (20 Torr). It is a method to produce. The amplified electrons are finally captured by the electrodes of the secondary electron detector to which a positive voltage of several hundred V is applied, and output as image signals.

[0004]

When a sample containing water (hereinafter referred to as a water-containing sample) is observed by ESEM,
It is generally desirable to maintain the sample chamber of the ESEM at the saturated vapor pressure of water. However, the temperature inside the sample chamber may not be kept constant depending on the external environment such as the installation location of the ESEM or the state of the sample itself. As shown in the saturated vapor pressure curve of water in FIG. 2, the saturated vapor pressure of water differs depending on the temperature. When the temperature is low, the saturated vapor pressure is low, and when the temperature is high, the saturated vapor pressure is high. For example, 20 ℃
The saturated water vapor pressure is 2330 Pa (17 Torr), but at 30 ° C
It is about double to 4230Pa (32Torr). Saturated steam pressure at 22 ° C
When observing a water-containing sample at 2700 Pa (20 Torr), dew condensation occurs when the temperature in the sample chamber falls below 22 ° C.
If it is higher than that, the water content of the water-containing sample evaporates. In particular, if the water content of the water-containing sample evaporates due to a rise in temperature, the properties of the sample may change and hinder the intended observation.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus capable of observing a water-containing sample as it is by controlling the temperature in a sample chamber and maintaining the vacuum at a low level equivalent to the saturated steam pressure at that temperature. I do.

[0006]

According to a first aspect of the present invention, there is provided an electron gun chamber for accommodating an electron gun for generating a primary electron beam and a sample held in a low-vacuum gas atmosphere. An environment-controlled scanning electron microscope including a sample holder and a sample chamber for storing a secondary electron detector for detecting secondary electrons, wherein an inner wall of the sample chamber is used to hold the sample chamber at a constant temperature. Environmentally controlled scanning electron microscope characterized by providing a liquid circulation pipe ".

[0007]

FIG. 1 is a schematic configuration diagram of an ESEM according to an embodiment of the present invention. The electron optical column 1 includes an electron gun 2, a condenser lens 3, a deflection coil 4, and an objective lens 5. The pressure inside the electron optical column 1 is 10 ⁻³ Pa
(10 ⁻⁵ Torr) high vacuum is maintained.

A sample chamber 6 is provided below the electron optical column 1 and houses a sample holder for holding a sample, a secondary electron detector for detecting secondary electrons, and the like. The pressure inside the sample chamber 6 is maintained at a low vacuum filled with water vapor of about 2700 Pa (20 Torr). A pressure limiting orifice (not shown) is provided between the electron optical column 1 and the sample chamber 6.

A liquid circulation pipe 7 extends around the inner wall of the sample chamber 6, and one end thereof is connected to a water supply port 8 of a constant temperature water circulation device 8.
a and the other end is connected to a drain port 8b of the constant temperature water circulation device 8. The constant temperature water circulating device 8 performs heat conversion to bring the water entering from the drain 8b to a constant temperature, and
a, water whose temperature is controlled is supplied to the liquid circulation pipe 7. For the liquid circulation pipe 7, it is necessary to select a material that does not easily rust and is easy to process. In the present embodiment, stainless steel having an inner diameter of 5 mm is used, but aluminum or an aluminum alloy can also be used. In order to attach the liquid circulation pipe 7 to the inner wall of the sample chamber 6, the liquid circulation pipe 7 may be directly attached to the inner wall by, for example, spot welding, or a plurality of short struts may be provided on the inner wall and attached to the struts. In the latter case,
The liquid circulation pipe 7 floats from the inner wall of the sample chamber 6. In any case, a primary electron beam is incident from above the sample chamber 6, and a sample holder (not shown) for holding a sample and a sample stage (not shown) for mounting the sample holder below the sample chamber 6. , The position of the liquid circulation pipe 7 is mainly on the side surface of the inner wall of the sample chamber 6. When observing a water-containing sample in water vapor, the sample is first set in a sample holder, the inside of the sample chamber 6 is evacuated, and the water vapor pressure in the sample chamber 6 is set. Set pressure (degree of vacuum) to 2700Pa (20T
If the temperature is 22 ° C., the saturated vapor pressure can be maintained from the saturated vapor pressure curve of water in FIG.
However, for example, if the temperature in the sample chamber 6 is 30 ° C., the water must be lowered because the water content of the water-containing sample evaporates at this pressure. Then, the constant temperature water circulation device 8 is operated to supply water of 22 ° C. or less to the liquid circulation pipe 7. When the temperature in the sample chamber 6 reaches 22 ° C., observation is started with the temperature of the water supplied to the liquid circulation pipe 7 kept constant at 22 ° C.

[0010]

As described above, the ESEM of the present invention
According to the method, the temperature in the sample chamber can be controlled to match the gas pressure in the sample chamber. Therefore, observation can be performed under a desired environment.

Further, the function of the ESEM of the present invention can be realized only by adding a liquid circulation pipe to the sample chamber of the conventional ESEM and adding a constant temperature water circulation device.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an ESEM according to an embodiment of the present invention.

FIG. 2 is a saturated vapor pressure curve of water.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electron optical column 2 ... Electron gun 3 ... Condenser lens 4 ... Deflection coil 5 ... Objective lens 6 ... .... Sample chamber 7 ... Liquid circulation pipe 8 ... Constant temperature water circulation device

Claims (1)

[Claims] An electron gun chamber for housing an electron gun for generating a primary electron beam, a sample holder for holding a sample in a low vacuum gas atmosphere, and a secondary electron detector for detecting secondary electrons. An environment-controlled scanning electron microscope comprising: a sample chamber to be controlled; and a liquid circulation pipe for maintaining the sample chamber at a constant temperature on an inner wall of the sample chamber. electronic microscope.