JPS6247167Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a heating device that shields a magnetic field generated by an electric heater.

In an electron microscope, a metal sample placed on an electron beam path is heated and an image of the metal sample depending on the temperature is observed. In addition, in a charged beam processing device such as an electron microscope or an electron beam exposure device, a diaphragm disposed on a beam path is heated to reduce the adhesion of contaminants to the diaphragm. By the way, the heating of the metal sample or diaphragm is generally done by bringing an electric heater configured to pass a current through a metal wire or plate, such as nichrome or tungsten, into contact with the metal sample or diaphragm to be heated. is being carried out. That is, an electric heater is provided near the beam path. Therefore, the magnetic field generated by this electric heater has a magnetic effect on the beam, resulting in the beam position on the sample drifting, especially in electron beam exposure equipment that requires high beam position accuracy. It becomes a big problem. As is well known, there is a method of reducing the influence of external magnetic fields called magnetic shielding. In this method, for example, a device to be protected is surrounded by a ferromagnetic cylinder to prevent magnetic flux lines from entering the hollow part. However, conventionally, such a method has not been used to shield the magnetic field generated by the electric heater for heating the metal sample or diaphragm placed in the charged beam path. Furthermore, because it is structurally impossible to surround the metal sample or aperture that you want to protect with ferromagnetic material, even if you directly surround the heater with ferromagnetic material, the temperature of such a heater would normally have to be raised to nearly 400°C. First, due to the temperature increase, the ferromagnetic material becomes paramagnetic according to the Curieve-Ice law, and it becomes impossible to shield the magnetic field. However, even if the heater is surrounded by a magnetic material with a high Kyrie point, the magnetic permeability of the magnetic material with a high Kyrie point is generally not high enough, and therefore sufficient magnetic field shielding cannot be achieved.

The present invention was developed in view of the above points, and is in contact with a part of the metal body placed in the charged beam path, and also in contact with the area around the electric heater for heating the metal body. A first high magnetic permeability material having a Curie point much higher than the heating temperature of the electric heater surrounded by the metal body does not contact the metal body at all,
Further, by including a second high magnetic permeability material surrounding the first high magnetic permeability material with a space therebetween and having a magnetic permeability far higher than that of the first high magnetic permeability material, the electric heater can be heated. The present invention provides a novel heating device that efficiently suppresses the magnetic influence of the magnetic field generated by the beam on the beam.

FIG. 1 is a schematic diagram of a heating device shown as an embodiment of the present invention, and FIG. 2 is a partially enlarged cross-sectional view of the heating device.

In the figure, numeral 1 represents a beam path of a suitably evacuated lens barrel, and numeral 2 represents a diaphragm having a hole 3 located above the path. 4 is an electric heater, and surrounding the heater is a first heater having a Curie point (about 780 degrees Celsius) that is much higher than the maximum heating temperature of the heater (for example, about 400 degrees Celsius).
Surround with a high magnetic permeability material (eg, pure iron) 5 directly, that is, in contact. The material is surrounded by a second high magnetic permeability material 6 (eg, permalloy) having a magnetic permeability much higher than that of the material with a space therebetween. Note that the first high magnetic permeability material 5 is in contact with the end of the diaphragm 2,
The second high magnetic permeability material 6 is configured so as not to come into contact with the diaphragm at all. 7 is a thermally conductive material (eg, copper) provided so as to directly enclose the second high magnetic permeability material, and has cooling water passages 8 at appropriate locations. Incidentally, the heater 4 is actually, for example, one in the shape of a single heater nichrome wire (electrically insulated with alumina) N reciprocated in a circular shape, as shown in FIG. A small hole (not shown) is made through the first high magnetic permeability material 5, the second high magnetic permeability material 6, and the thermally conductive material 7 from the outside (in the opposite direction of the optical axis) using a The end of the wire is passed through and a current is applied to the nichrome wire from a heating power source K outside the lens barrel.

In such a device, a current is passed from the heating power source K to the electric heater 4, and the electric heater 4 is heated to 400°C.
If the temperature is raised back and forth, the aperture 2 is heated through the first high magnetic permeability material 5. At this time, the magnetic field generated by the electric heater 4 is processed as described below. The first high magnetic permeability material 5 does not have a particularly high magnetic permeability among high magnetic permeability materials, but since it has a high Kyrie point, it has a high magnetic permeability even when the temperature becomes high due to the heat generated by the heater 4. Therefore, some of the magnetic flux lines generated by the heater 4 are concentrated within the first high magnetic permeability material 5, and others leak out of the material. Next, a second high magnetic permeability material 6 is placed around the first high magnetic permeability material with a space therebetween.
Although the Curie point is not very high, the magnetic permeability is extremely high, and since it is not in contact with the heater 4, the first high magnetic permeability material 5, and the diaphragm 2, it has a significantly high magnetic permeability without becoming extremely high temperature. maintain. Therefore, all magnetic flux lines leaking into the space are concentrated within the second high magnetic permeability material and do not leak to the beam path 1 side. still,
Even if there is heat radiation from the first high magnetic permeability material 5,
Since the second high magnetic permeability material 6 is directly wrapped in a thermally conductive material 7 in which cooling water is circulated, it does not reach a high temperature.

According to the present invention, it is possible to efficiently shield the magnetic influence of the magnetic field generated by the electric heater on the beam.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a heating device shown as an embodiment of the present invention, FIG. 2 is a partially enlarged cross-sectional view thereof, and FIG. 3 is a diagram showing an example of an electric heater. 1: Beam path, 2: Diaphragm, 4: Electric heater,
5: first high magnetic permeability material, 6: second high magnetic permeability material,
7: Good thermal conductor material.

Claims (1)

[Scope of utility model registration request] The heating temperature of the electric heater 4 that is in contact with a part of the metal body 2 disposed in the charged beam path 1 and that surrounds the electric heater 4 for heating the metal body 2 so as to be in contact with it. a first high magnetic permeability material 5 having a much higher Curie point; and a first high magnetic permeability material 5 that does not contact the metal body 2 at all and surrounds the first high magnetic permeability material 5 with a space in between. A heating device comprising a second high magnetic permeability material 6 having a much higher magnetic permeability than the magnetic permeability material 5.