JPH08273585A - Secondary ion mass spectrometer - Google Patents

Abstract

PURPOSE: To lower the temperature of a sample to establish a steady state in a short time by installing a means for cooling a secondary ion drawing electrode provided opposite to a sample holder within a vacuum vessel. CONSTITUTION: An ion generating part consists mainly of a sample holder 2 in which a sample 1 installed in a vacuum vessel is held, a heat conducting part 4 and a refrigerant introducing part 3, for cooling the holder 2, and a secondary ion drawing electrode 5 provided opposite to the holder 2. Further, a refrigerant introducing part 6 is provided in contact with the electrode 5 with the heat conducting part 7 therebetween. Refrigerants 8A, 8B such as liquefied nitrogen are introduced into the refrigerant introducing parts 3, 6, so that not only the holder 2 but also the electrode 5 are cooled to low temperatures. Therefore, the radiated heat flowing into the sample 1 and the holder 2 is greatly reduced by cooling of the electrode 5, the elevated temperature of the sample 1 becomes much lower than in conventional cases, and the time required to reach a steady state is also reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary ion mass spectrometer, and more particularly to a secondary ion mass spectrometer equipped with a sample cooling mechanism.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view showing the structure of an ion generating part of a conventional secondary ion mass spectrometer for cooling a sample. The sample 1 is mounted on the sample holder 2, and in order to cool the sample 1, a coolant, for example, liquefied nitrogen is introduced into the coolant introduction part 3 and is cooled via the heat conduction part 4. The heat conducting section also has a function of holding the sample holder 2 when the sample holder 2 is conveyed from the preliminary exhaust chamber by the conveying mechanism without breaking the vacuum.

After cooling the sample 1 by introducing a cooling medium, the sample 1 is irradiated with primary ions 10 and the secondary ions 11 generated at that time are collected by the extraction electrode 5 and introduced into the mass spectrometer. Then, the required secondary ions are separated and mass spectrometry is performed.

[0004]

In the above-mentioned conventional secondary ion mass spectrometer, the sample 1 is cooled by radiating heat to the low temperature portion on the back surface side of the sample holder 2. The heat flowing into the sample 1 and the sample holder 2 is heat radiation from a device component facing the front surface of the sample 1, for example, the extraction electrode 5, and is mainly transferred to the refrigerant introduction part 3 which is a low temperature part by heat conduction. It Here, the temperature difference between the sample 1 and the coolant introduction part 3 when the temperature of the sample 1 reaches a constant temperature after a sufficient time has elapsed from the introduction of the coolant is proportional to the thermal resistance during that period and the amount of heat that flows in.

The thermal resistance includes the contact thermal resistance between the sample holder 2 made of Cu or Al, which has good thermal conductivity, and the thermal conductive portion 4, but the contact thermal resistance in vacuum is higher than that in the atmosphere. The impact will increase. Therefore, as shown in FIG. 4, there is a problem that the temperature difference between the sample 1 and the refrigerant introduction part is large, and the time until the temperature becomes constant becomes long, so that a sufficient cooling effect cannot be obtained.

Further, when the sample holder 2 is not sufficiently held by the heat conducting portion 4, there is a problem that the time until the sample temperature reaches the steady state and the temperature at which the sample temperature reaches the temperature vary.

An object of the present invention is to provide a secondary ion mass spectrometer capable of lowering the temperature of a sample in a short time to bring it to a steady state.

[0008]

A secondary ion mass spectrometer according to the present invention comprises a sample holder installed in a vacuum chamber for holding a sample, and a primary holder which is provided so as to face the sample holder and irradiates the sample. It is characterized in that it includes an extraction electrode for extracting secondary ions generated by ions and a cooling means for cooling the extraction electrode.

[0009]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the structure of an ion generating part according to an embodiment of the present invention.

In FIG. 1, the ion generating part of the secondary ion mass spectrometer is installed in a vacuum chamber (not shown) and the sample 1
A sample holder 2 that holds the sample holder 2; an extraction electrode 5 that is provided so as to face the sample holder 2 for efficiently extracting secondary ions 11 generated by the primary ions 10 with which the sample 1 is irradiated; And the sample holder 2 which is in contact with the extraction electrode 5 via the heat conducting portion 7
It is mainly composed of a heat conducting portion 4 and a coolant introducing portion 3 for cooling. In the secondary ion mass spectrometer, the extraction electrode 5 is set to the sample 1 in order to improve the efficiency of secondary ion collection.
It is installed close to the front of the. Therefore, the solid angle expected by the sample holder 2 is a value close to 2π.

According to the present embodiment thus constructed,
By introducing the refrigerants 8A and 8B made of liquefied nitrogen into the refrigerant introducing portions 3 and 6, not only the conventional sample holder 2 but also the extraction electrode 5 can be cooled to -120 ° C.

Here, it is known that the thermal energy radiated from an object having an absolute temperature T [K] is proportional to the fourth power of T. Since the temperature of the extraction electrode 5 at the time of cooling becomes −120 ° C., the thermal energy radiated from the extraction electrode 5 is reduced to 1/10 or less of the conventional room temperature. Therefore, by cooling the extraction electrode 5, the radiant heat flowing into the sample 1 and the sample holder 2 is significantly reduced.

FIG. 2 shows the temperature changes of the sample 1 and the refrigerant introducing part 3 after the introduction of liquefied nitrogen into the refrigerant introducing parts 3 and 6 simultaneously started in this embodiment. As shown in FIG. 2, the temperature difference between the sample 1 and the refrigerant introduction part 3 was ⅕ or less of the conventional temperature, and the reached temperature of the sample temperature was −160 ° C., which is 70 degrees lower than the conventional temperature. Further, the time required for the temperature of Sample 1 to reach a steady state could be reduced to about 1/2. Further, although cooling is started after the sample holder is transported, it is possible to reduce the variation for each cooling.

As a result, secondary ion mass spectrometry can be stably performed even in a sample made of an element having a high vapor pressure such as a 2-4 group compound semiconductor or a sample which is easily broken by heat during irradiation of primary ions. Becomes

Although liquefied nitrogen is used as the refrigerant in this embodiment, it goes without saying that other refrigerants may be used.

[0016]

As described above, according to the present invention, the temperature of the sample can be lowered to a steady state in a short time by providing the means for cooling the extraction electrode provided facing the sample holder. There is an effect that secondary ion mass spectrometry can be stably performed even on a sample that is easily broken by heat.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing the time dependence of sample temperature in Examples.

FIG. 3 is a block diagram of a conventional secondary ion mass spectrometer.

FIG. 4 is a diagram showing time dependence of sample temperature of a conventional secondary ion mass spectrometer.

[Explanation of symbols]

 1 sample 2 sample holder 3 refrigerant introduction part 4 heat conduction part 5 extraction electrode 6 refrigerant introduction part 7 heat conduction part 8, 8A, 8B refrigerant

Claims (1)

[Claims] 1. A sample holder installed in a vacuum chamber for holding a sample, and an extraction electrode provided opposite to the sample holder for extracting secondary ions generated by primary ions with which the sample is irradiated. A secondary ion mass spectrometer, comprising: a cooling unit for cooling the extraction electrode.