JP3548715B2 - Cracking cell - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a molecular beam cell serving as a molecular beam source in a molecular beam epitaxy apparatus. For example, when evaporating a substance such as As, P, etc., the tetravalent As, P molecule is decomposed into a monomolecular form by evaporation. It relates to a cracking cell that cracks and fires.
[0002]
[Prior art]
In a molecular beam epitaxy (MBE) apparatus, a resistance heating type Knudsen cell (K cell) is generally used as a molecular beam source, and the raw material is vaporized or sublimated for firing. In such a molecular beam source, when the material that evaporates or sublimates is a substance such as As or P, the tetravalent As or P molecule obtained by evaporating or sublimating from the crucible of the K cell is a substrate such as a semiconductor wafer. It is not suitable for film formation and element implantation. For this reason, a cracking cell is used which cracks the molecule such as tetravalent As or P obtained by evaporation or sublimation into a single molecule.
[0003]
FIG. 2 is a schematic sectional view showing an example of the cracking cell. The cracking cell has a K-cell unit 1 and a cracking unit 2.
The K cell unit 1 has a crucible 4 in which a raw material such as As is stored. Around the crucible 4, a heater 5 for heating the raw material a to evaporate or sublime is provided.
[0004]
The crucible 4 is provided with a discharge tube 6 that emits evaporated or sublimated molecules, and has the cracking portion 2 at the upper end thereof. The cracking section 2 is provided with a heater 8 for heating the source molecules in order to thermally decompose molecules passing therethrough and crack molecules such as tetravalent As into monovalent divalent As.
A damper portion 3 is provided at an intermediate portion of the discharge tube 6 extending from the crucible 4 to the cracking portion 2, and the width of the passage of the discharge tube 6 is adjusted by a damper gate 7.
[0005]
In such a cracking cell, when the raw material a such as As stored in the crucible 4 is heated by the heater 5 of the K cell unit 1 to evaporate or sublime, a raw material gas is generated. When the raw material a is As, this gas is a tetravalent As molecule. When the gas reaches the cracking unit 2 through the damper unit 3, the gas is reheated by the heater 8 of the cracking unit 2, thereby being thermally decomposed and released into a vacuum chamber (not shown), such as a semiconductor wafer. 2 (not shown in FIG. 2), and As is deposited on the substrate or injected into the film on the substrate.
[0006]
[Problems to be solved by the invention]
In the above cracking cell, the pressure on the side of the cracking unit 2 on the vacuum chamber side is lower than that on the side of the K cell unit 1 where the raw material a evaporates or sublimates. For this reason, the raw material molecules generated by evaporation or sublimation on the K cell unit 1 side are likely to be re-solidified as the cracking unit 2 side moves. For this reason, there is a disadvantage that the release efficiency of the raw material molecules is low and the yield is low.
[0007]
Further, the conventional cracking cell has a problem that the structure is relatively complicated and large, so that it has a large volume and it is difficult to reduce the size of the device.
The present invention has been made in view of the above-mentioned problems of the conventional cracking cell, and an object of the present invention is to provide a cracking cell that has a high efficiency of releasing raw material molecules, has a simple structure, and can be easily reduced in size.
[0008]
[Means for Solving the Problems]
In the present invention, in order to achieve the above object, a member for heating the raw material a stored in the crucible 11 and a gas molecule for cracking the gas molecules generated by evaporation or sublimation of the raw material a into a single molecule are heated. The members were shared, thereby simplifying the apparatus, and the molecules generated by evaporation or sublimation of the raw material a were immediately cracked and released.
[0009]
That is, the cracking cell according to the present invention covers the crucible 11 for storing the raw material a and the opening of the crucible 11 and is partially embedded in the raw material a stored in the crucible 11, and A heating member 12 provided with an emission port 14 for raw material molecules in a portion to be covered;
[0010]
In this cracking cell, the raw material a is heated by the heating member 12, and the raw material a evaporates or sublimates to generate a gas of the raw material a, that is, raw material molecules. This raw material molecule is, for example, tetravalent in the case of As. Further, these molecules fly to the opening side of the crucible 11 and are heated by the heating member 12 and thermally decomposed when passing through the discharge port 14 of the heating member 12. Thereby, for example, tetravalent As is decomposed into monomolecular divalent As and emitted from the emission port 14.
[0011]
In this cracking cell, the raw material a evaporates or sublimates in the crucible 11 and, when the raw material molecules are generated, is immediately thermally decomposed at the firing port 14, so that the generated raw material molecules are not re-solidified, and the raw material molecules are efficiently removed. Molecules can be cracked and fired. In addition, since only one heat source is required, the structure is simple and the size can be easily reduced.
[0012]
The heating member 12 is an indirect heating element heated by another heating means . By doing so , the heating member 12 can be reduced in size and can be efficiently arranged at the opening of the crucible 11, and the cracking cell can be further reduced in size. As a means for heating the heating member 12, a means for causing electrons emitted from the electron gun 17 to collide with the heating member 12 and heat the heating member 12 by electron impact is used.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described specifically and in detail with reference to the drawings.
FIG. 1 is a schematic vertical sectional view showing a cracking cell according to an embodiment of the present invention.
[0014]
A vessel-shaped crucible 11 made of a chemically stable material is installed in a cylindrical shield 16, and the raw material a is stored in the crucible 11.
The crucible 11 has an upper surface opened, and a heating member 12 is covered on the upper surface. The heating member 12 is made of a high-melting-point material such as Mo, and is provided with a flange-shaped lid 13 that covers the upper opening of the crucible 11, protruding downward from the center of the lid 13, and housed in the crucible 11. And a raw material heating section 15 embedded in the raw material a. Further, the cover 13 is provided with a discharge port 14 having a hole of an appropriate size. This heating member 12 is grounded.
[0015]
An electron gun 17 is provided toward the lid 13 of the heating member 12. The electron gun 17 includes a filament 18 for emitting thermoelectrons, and a Wehnelt 19 for converging the thermoelectrons emitted from the filament 18. A heating power supply 20 and an acceleration power supply 21 are connected to the filament 18 and Wehnelt 19, respectively.
[0016]
Such a cracking cell is installed in a vacuum chamber (not shown). In this vacuum chamber, the raw material molecules are opposed to the lid 13 of the heating member 12 covering the opening of the crucible 11. Is mounted on the substrate 22 such as a semiconductor wafer.
[0017]
In this state, electrons e- are emitted from the electron gun 17 and the electrons collide with the lid 13 of the heating member 12, and the heating member 12 is heated by the electron impact. Then, the raw material a in the crucible 11 is heated by the raw material heating unit 15 of the heating member 12, and the raw material evaporates or sublimates and is vaporized. For example, As has a sublimation point of 616 ° C., but sublimates at about 300 ° C. lower in vacuum. As vaporized by this sublimation is tetravalent.
[0018]
The gas of the raw material a generated as described above, that is, the raw material molecules, rises in the crucible 11 and is emitted toward the substrate 22 through the emission opening 14 formed in the lid 13 of the heating member 12. The raw material molecules are reheated by the heating member 12 and thermally decomposed when passing through the discharge port 14 opened in the lid 13 of the heating member 12. As a result, the raw material molecules are cracked, and, for example, in the case of the above-mentioned As, it is emitted as monomolecular divalent As. Then, this divalent As is incident on the film formation surface of the substrate 22, and is formed or injected on the film formation surface.
[0019]
In the above embodiment, the heating member 12 is an indirect heating element heated by the electron gun 17, but the heating member 12 itself may generate heat. Further, even when the heating member 12 is an indirect heating element, the heating means is not necessarily limited to the electron impact method, and means such as resistance heating and high-frequency heating may be employed.
[0020]
【The invention's effect】
As described above, in the cracking cell according to the present invention, the raw material a evaporates or sublimes in the crucible 11 and is immediately decomposed at the firing port 14 as soon as the molecule is generated. In addition, it is possible to efficiently launch cracked molecules. In addition, since only one heat source is required, the structure is simple and the size can be easily reduced.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal side view showing a cracking cell according to an embodiment of the present invention.
FIG. 2 is a schematic vertical sectional side view showing a conventional example of a cracking cell.
[Explanation of symbols]
11 crucible 12 heating member 14 launch port 17 electron gun a raw material

Claims (1)

A cracking cell for evaporating or sublimating the raw material (a) and cracking and firing the gas molecules of the raw material (a), the crucible (11) containing the raw material a, and the opening of the crucible (11) And a heating member (a part of which is embedded in the raw material (a) accommodated in the crucible (11), and which has a discharge opening (14) for raw material molecules at a portion covering the opening of the crucible (11)). 12) and an electron gun (17) as an indirect heating element for heating the heating member (12) by electron impact .

Images