JPH0627617B2 - Liquid nitrogen evaporation prevention device in liquid nitrogen storage tank for semiconductor sensor cooling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Industrial Application Field >> The present invention relates to liquid nitrogen evaporation in a low temperature generator for cooling a semiconductor sensor used in a measuring device such as a scanning electron microscope or an X-ray analyzer. Regarding prevention device.

<< Prior Art >> Conventionally, a semiconductor sensor used in a measuring device such as a scanning electron microscope or an X-ray analyzer is mounted on a cold finger extending from a bottom wall of a storage container that stores liquid nitrogen. The semiconductor sensor is kept at a constant temperature by utilizing the vaporization energy of liquid nitrogen.

<Problems to be solved> By the way, since the above-mentioned semiconductor sensor has to maintain the cooling temperature for a long time once cooled, in order to compensate the nitrogen gas scattered by evaporation, liquefied gas is used. The storage container had to be refilled with liquid nitrogen.

However, when the semiconductor sensor is used in a measuring device such as a scanning electron microscope or an X-ray analyzer, the height of the liquefied gas storage container from the floor is regulated because of the irradiation axis. The height from the floor of the liquefied gas replenishment opening that opens at the top of the liquefied gas storage container is, for example, 1.5 m.
It will be opened at a high position. As a result, there is a problem that the liquid nitrogen replenishment work using a Dewar bottle or the like becomes troublesome.

The present invention has been made in view of such a point, by condensing the vaporized gas in the liquefied gas storage container,
An object of the present invention is to provide a liquid nitrogen evaporation preventing device in a liquefied gas storage tank which can prevent consumption of liquid nitrogen and omit liquid nitrogen replenishment work for a long period of time.

<< Means for Solving the Problem >> In order to achieve the above object, the present invention is characterized by having the following configuration, for example, as shown in FIG. 1 and FIG.

That is, the cold finger (7) is continuously fed from the liquefied gas storage tank (4) containing liquid nitrogen,
In a measuring device equipped with a semiconductor sensor (6) on (7), a cryogenic refrigerator (1
The cold head (12) of 1) is arranged so as to face it in a non-contact manner, and this cold head (12) is supported by the mount (3), and the cold end (15) of the cold head (12) is stored as a liquefied gas. A sealing body (16) for thrusting the upper end opening (10) of the liquefied gas storage tank (4) into the tank (4) in a non-contact manner from the upper end opening (10) thereof against the outside air, It is provided over the cold head (12) and the liquefied gas storage tank (4), and the sealing body (16) is configured not to transmit vibration, and the temperature inside the liquefied gas storage tank (4) is measured by a temperature measuring device ( 17) is configured to be detectable, the cryogenic refrigerator (11) is automatically controlled based on the temperature in the liquefied gas storage tank (4) detected by this temperature measurement device (17), and the liquefied gas storage tank ( In 4), the liquid nitrogen was configured to be maintained below the vaporization temperature at atmospheric pressure.

The second aspect of the present invention is characterized in that it is configured as follows.

That is, the cold finger (7) is continuously fed from the liquefied gas storage tank (4) containing liquid nitrogen,
In the measuring device with the semiconductor sensor (6) fixed to (7), arrange the nitrogen gas introduction path (22) so that it communicates with the upper end opening (10) of the liquefied gas storage tank (4). A gas supply control valve (23) is installed in the channel (22), and a cryogenic refrigerator (1) is installed at the upper end opening (10) of the liquefied gas storage tank (4).
The cold head (12) of 1) is arranged so as to face it in a non-contact manner, and this cold head (12) is supported by the mount (3), and the cold end (15) of the cold head (12) is stored as a liquefied gas. A sealing body (16) for thrusting the upper end opening (10) of the liquefied gas storage tank (4) into the tank (4) in a non-contact manner from the upper end opening (10) thereof against the outside air, It is provided over the cold head (12) and the liquefied gas storage tank (4), and this sealing body (16) is constructed so as not to transmit vibration, and the liquid level of liquid nitrogen in the liquefied gas storage tank (4) is It is configured to be detectable by a liquid level meter, and based on the liquid level detection of liquid nitrogen by the liquid level meter, the gas supply control valve (23) is controlled to open and close to introduce nitrogen gas, and a cryogenic refrigerator (11). Automatic operation control,
The phase of the introduced nitrogen gas is changed to liquid nitrogen, and the liquid nitrogen liquid level in the liquefied gas storage tank (4) is raised from a predetermined low level to a predetermined high level to replenish the liquid nitrogen. Configured to do.

<< Operation >> In the present invention, in a measuring device in which a cold finger is continuously provided from a liquefied gas storage tank containing liquid nitrogen, and a semiconductor sensor is provided on the cold finger, a cryogenic refrigerator is installed at an upper end opening of the liquefied gas storage tank. The cold head is placed so as to face it in a non-contact manner, and this cold head is supported on a frame, and the cold end of the cold head is projected into the liquefied gas storage tank from the upper end opening in a non-contact manner to store the liquefied gas. A sealing body that seals the upper opening of the tank against the outside air is provided between the cold head and the liquefied gas storage tank, and this sealing body is configured not to transmit vibration, and the temperature inside the liquefied gas storage tank is set. Is configured to be detected by a temperature measuring device, and the cryogenic refrigerator is automatically operated and controlled based on the temperature in the liquefied gas storage tank detected by this temperature measuring device. Since it is configured to maintain the liquid nitrogen below the vaporization temperature at atmospheric pressure in the storage tank, the gas vaporized in the liquefied gas storage tank will be cooled by the cryogenic refrigerator and condensed. Therefore, the liquid nitrogen is not consumed, and the semiconductor sensor can be kept cooling at a constant temperature for a long period of time.

Further, in the second aspect of the present invention, in a measuring device in which a cold finger is continuously taken out from a liquefied gas storage tank containing liquid nitrogen and a semiconductor sensor is fixed to the cold finger, the nitrogen is communicated with the upper end opening of the liquefied gas storage tank. A gas introduction path is arranged, a gas supply control valve is installed in this gas introduction path, and the cold head of the cryogenic refrigerator is placed in a non-contact manner at the upper end opening of the liquefied gas storage tank. This cold head is supported on a gantry, and the cold end of the cold head is projected into the liquefied gas storage tank from its upper end opening in a non-contact manner, and the upper end opening of the liquefied gas storage tank is sealed from the outside air. Is provided over the cold head and the liquefied gas storage tank, and this seal is configured so as not to transmit vibration, and the liquid level of liquid nitrogen in the liquefied gas storage tank is measured by a liquid level gauge. Nitrogen gas is introduced so that the nitrogen gas is introduced by controlling the opening and closing of the gas supply control valve based on the liquid level detection of liquid nitrogen by the liquid level gauge, and the cryogenic refrigerator is automatically operated and controlled. The gas gas is phase-changed to liquid nitrogen, and the liquid nitrogen liquid level in the liquefied gas storage tank is raised from a predetermined low level to a predetermined high level to replenish the liquid nitrogen. Therefore, when the liquid level gauge detects that the liquid level in the liquefied gas storage tank has dropped to a certain level, the gas supply control valve is opened and nitrogen gas is stored in the liquefied gas storage tank in a gaseous state. At the same time as the introduction, the cryogenic refrigerator is operated to condense and liquefy the introduced nitrogen gas. Then, when the liquid level in the liquefied gas storage tank reaches a predetermined level, the gas supply control valve is closed to interrupt the gas supply, and the operation of the cryogenic refrigerator is stopped. Therefore, the liquid nitrogen in the liquefied gas storage tank can always be kept within a certain range, and the semiconductor sensor can be continuously cooled for a long period of time to maintain the semiconductor sensor at a constant temperature. .

Moreover, since the operation of the cryogenic refrigerator is controlled by detecting the temperature or the liquid level in the liquefied gas storage tank, the cryogenic refrigerator is not wastefully operated. In addition, the cold head of the cryogenic refrigerator is placed in the upper end opening of the liquefied gas storage tank so that the cold head of the cryogenic refrigerator faces the non-contact state, and this cold head is supported on the mount to support the cold head. A cold end and a liquefied gas storage tank are provided with a sealing body that projects the cold end into the liquefied gas storage tank from its upper end opening in a non-contact manner and seals the upper end opening of the liquefied gas storage tank against the outside air. Since the sealing body is provided over the entire length and is configured not to transmit the vibration, the vibration due to the operation of the refrigerator is not transmitted to the liquefied gas storage tank.

<< Embodiment >> A drawing shows an embodiment of the present invention, FIG. 1 is an enlarged cross-sectional view of a main part, FIG. 2 is a side view of a low temperature generator, and FIG. 3 is a conceptual diagram of a low temperature generator.

This low temperature generator (1) is a liquefied gas storage tank in which a cold finger (7) supporting a semiconductor sensor (6) of a measuring device such as a scanning electron microscope is continuously extended from its bottom wall (5).
(4) and a cryogenic refrigerator (11) arranged above the liquefied gas storage tank (4). The liquefied gas storage tank (4) is formed of a heat insulating container, and stores liquefied gas for refrigerant such as liquid nitrogen therein.

The cryogenic refrigerator (11) is composed of a cold head (12) and a compressor unit (13), and the cold head (12) corresponds to the upper opening (10) of the liquefied gas storage tank (4). State, bottom
A linear guide mechanism is installed at the upper end of the pedestal (3) erected from (2).
It is supported via (8) so that it can move horizontally in the front-back direction (left-right direction in the figure). And the compressor unit (13) and the cold head (12) are two flexible tubes (14).
The cold refrigerant is obtained by adiabatically expanding the gas refrigerant such as helium compressed by the compressor unit (13) in the cold head (12). The cold end (15) of the cold head (12) is the upper end opening (10).
From the liquefied gas storage tank (4) in a non-contact manner so that the gas vaporized in the liquefied gas storage tank (4) is condensed and reliquefied by the cold generated in the cold end (15). Is configured.

Further, a bellows (16) is arranged between the cold head (12) and the liquefied gas storage tank (4) so that vibrations due to the operation of the cryogenic refrigerator (11) are not transmitted to the liquefied gas storage tank (4). I am doing it. The bellows (16) is provided as a sealing body that seals the upper end opening (10) of the liquefied gas storage tank (4) from the outside air. The cryogenic refrigerator (11) is a liquefied gas storage tank (4).
It is configured to be automatically operated based on the internal temperature. That is, the ambient temperature or liquid temperature in the liquefied gas storage tank (4) is detected by a temperature measuring device (17) such as a thermocouple or a steam left thermometer,
This detected temperature signal is input to the compressor unit (13) of the cryogenic refrigerator (11) via the temperature indicator (18), and when the temperature inside the tank reaches a predetermined high temperature value, the cryogenic refrigerator (11) The operation is started and stopped when the temperature reaches a predetermined low temperature value. The reference value for this operation control is, in the case of liquid nitrogen,
For example, the high temperature value is set to 77K and the low temperature value is set to 73K.

In the figure, reference numeral (20) is a safety valve, (21) is a pressure gauge, (22) is a gas introduction passage for replenishing nitrogen gas in the liquefied gas storage tank (4) in a gaseous state, and (23) is this gas introduction. A gas supply control valve installed in the passage (22).

A liquid level gauge is used instead of the temperature measuring device (17) in the above embodiment, and the gas supply control valve (23) is controlled to open and close based on the liquid level detection signal from the liquid level gauge, and cryogenic refrigeration is performed. The operation of the machine (11) may be controlled. In this case, when the liquid level in the liquefied gas storage tank (4) decreases to a predetermined low level, the gas supply control valve (23) is opened to introduce gaseous nitrogen gas into the liquefied gas storage tank (4). At the same time, the cryogenic refrigerator (11) is operated. Then, the introduced nitrogen gas in a gaseous state is condensed and liquefied by the cold generated in the cold end (15) of the cryogenic refrigerator (11). Then, when the liquid level in the liquefied gas storage tank (4) increases to a predetermined high level, the gas supply control valve (23) is closed and the operation of the cryogenic refrigerator (11) is stopped.

<< Effect >> In the present invention, in a measuring device in which a cold finger is continuously provided from a liquefied gas storage tank containing liquid nitrogen, and a semiconductor sensor is provided on the cold finger, a cold cryocooler is provided at an upper end opening of the liquefied gas storage tank. The head is placed in a non-contact manner, and this cold head is supported on a stand, and the cold end of the cold head is projected into the liquefied gas storage tank from the top opening of the liquefied gas storage tank in a non-contact manner. A sealing body that seals the upper end opening of the liquefied gas against the outside air is provided between the cold head and the liquefied gas storage tank, and this sealing body is configured so as not to transmit vibration, and the temperature inside the liquefied gas storage tank is controlled. The temperature measuring device is configured to be able to detect, and the cryogenic refrigerator is automatically operated based on the temperature in the liquefied gas storage tank detected by this temperature measuring device to store the liquefied gas. Since the liquid nitrogen is configured to be kept below the vaporization temperature at atmospheric pressure in the storage tank, the liquid temperature of liquid nitrogen is kept below the vaporization temperature ( 77 K ) at atmospheric pressure in the liquefied gas storage tank. It is possible to prevent the liquid nitrogen from evaporating and escaping into the atmosphere by maintaining it, preventing the consumption of the liquid nitrogen in the liquefied gas storage tank, and reducing the work of replenishing the liquid nitrogen. It is possible to keep the semiconductor sensor at a constant temperature by continuing to cool the semiconductor sensor for a long period of time.

On the other hand, in the second invention, in a measuring device in which a cold finger is continuously extended from a liquefied gas storage tank containing liquid nitrogen, and a semiconductor sensor is fixed to the cold finger, the nitrogen gas is communicated with the upper end opening of the liquefied gas storage tank. A gas supply control valve is installed in this gas introduction path, and the cold head of the cryogenic refrigerator is placed in a non-contact manner at the upper end opening of the liquefied gas storage tank. The cold head is supported on a frame, the cold end of the cold head is projected into the liquefied gas storage tank from its upper end opening in a non-contact manner, and a sealing body that seals the upper end opening of the liquefied gas storage tank against the outside air is provided. Provided over the cold head and the liquefied gas storage tank, the sealed body is constructed so as not to transmit vibration, and the liquid level of liquid nitrogen in the liquefied gas storage tank is detected by a liquid level gauge. Introduce nitrogen by introducing the nitrogen gas by controlling the opening and closing of the gas supply control valve based on the liquid level detection of liquid nitrogen by a liquid level gauge, and automatically controlling the cryogenic refrigerator. The gas gas is phase-changed to liquid nitrogen, and the liquid nitrogen liquid level in the liquefied gas storage tank is raised from a predetermined low level to a predetermined high level to replenish the liquid nitrogen. Therefore, when the liquid level in the liquefied gas storage tank drops to a certain level, nitrogen gas in the gaseous state is introduced into the liquefied gas storage tank and at the same time the cryogenic refrigerator is operated to condense and liquefy the introduced nitrogen gas. Therefore, the liquid nitrogen in the liquefied gas storage tank can always be kept within a certain range. This makes it possible to automate the refilling work of liquid nitrogen and reduce the burden on the operator.
By cooling the semiconductor sensor of the measuring device continuously for a long period of time, the semiconductor sensor can be maintained at a constant temperature.

Moreover, since the operation of the cryogenic refrigerator is controlled by detecting the temperature or the liquid level in the liquefied gas storage tank, the cryogenic refrigerator can be prevented from being uselessly operated.

Furthermore, the cold head of the cryogenic refrigerator is exposed to the liquefied gas storage tank in a non-contact manner, the cold end of the cold head is rushed into the liquefied gas storage tank in a non-contact manner, and the cold head and the liquefaction are liquefied. Since the sealed body provided over the gas storage tank was configured not to transmit vibration, the vibration caused by the operation of the cold head of the cryogenic refrigerator was Can be prevented from being transmitted to the liquefied gas storage tank, whereby it is possible to prevent the semiconductor sensor from becoming unmeasurable due to transmission of operating vibration of the cold head.

[Brief description of drawings]

The drawings show an embodiment of the present invention. FIG. 1 is an enlarged cross-sectional view of a main part, FIG. 2 is a side view of a low temperature generator, and FIG. 3 is a conceptual view of the low temperature generator. 1 ... Low temperature generator, 3 ... Stand, 4 ... Liquefied gas storage tank, 6 ... Semiconductor sensor, 7 ... Cold finger, 10 ... (4) upper end opening, 11 ... Cryogenic refrigerator , 12
...... (11) cold head, 15 …… (12) cold end, 16 …… bellows (sealed body), 17 …… temperature measuring device,
22 …… Gas introduction path, 23 …… Gas supply control valve.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-64-18086 (JP, A) JP-A-59-134479 (JP, A) JP-A-61-268972 (JP, A) Actual development Sho-56- 137085 (JP, U)

Claims (2)

[Claims] 1. A measuring device in which a cold finger (7) is continuously extended from a liquefied gas storage tank (4) containing liquid nitrogen, and a semiconductor sensor (6) is provided on the cold finger (7). Install the cryogenic refrigerator (1
The cold head (12) of 1) is arranged so as to face it in a non-contact manner, and this cold head (12) is supported by the mount (3), and the cold end (15) of the cold head (12) is stored as a liquefied gas. A sealing body (16) for thrusting the upper end opening (10) of the liquefied gas storage tank (4) into the tank (4) in a non-contact manner from the upper end opening (10) thereof against the outside air, It is provided over the cold head (12) and the liquefied gas storage tank (4), and the sealing body (16) is configured not to transmit vibration, and the temperature inside the liquefied gas storage tank (4) is measured by a temperature measuring device ( 17) is configured to be detectable, the cryogenic refrigerator (11) is automatically controlled based on the temperature in the liquefied gas storage tank (4) detected by this temperature measurement device (17), and the liquefied gas storage tank ( 4) The liquid nitrogen is prevented from evaporating in the storage tank of the liquid nitrogen for cooling the semiconductor sensor, characterized in that the liquid nitrogen is kept below the vaporization temperature at atmospheric pressure. Location. 2. A measuring device in which a cold finger (7) is continuously extended from a liquefied gas storage tank (4) containing liquid nitrogen, and a semiconductor sensor (6) is fixed to the cold finger (7). A nitrogen gas introduction path (22) is placed in communication with the upper end opening (10) of (4), and a gas supply control valve (23) is provided in this gas introduction path (22) to provide a liquefied gas storage tank. Extreme temperature refrigerator (11) at the upper opening (10) of (4)
The cold head (12) of the cold head (12) is placed in a non-contact manner, the cold head (12) is supported on the mount (3), and the cold end (15) of the cold head (12) is stored in the liquefied gas storage tank ( The cold head is provided with a sealing body (16) that projects into the interior of the liquefied gas storage tank (4) from the outside air by causing it to protrude into the interior from the top opening (10) in a non-contact manner. (12) and the liquefied gas storage tank (4), and the sealing body (16) is configured not to transmit vibration, and the liquid level of liquid nitrogen in the liquefied gas storage tank (4) is set to the liquid level. The gas supply control valve (23) is controlled to open and close based on the liquid level detection of liquid nitrogen by the liquid level meter to introduce nitrogen gas and the cryogenic refrigerator (11) is automatically operated. Operation control,
The introduced nitrogen gas gas is phase-changed to liquid nitrogen, and the liquid nitrogen liquid level in the liquefied gas storage tank (4) is raised from a predetermined low level to a predetermined high level to replenish the liquid nitrogen. A device for preventing evaporation of liquefied gas in a storage tank of liquid nitrogen for cooling a semiconductor sensor, which is configured to perform.