Ion scattering spectrometer

Abstract: From an ion source and accelerator an ion beam is generated, this ion beam is let go through a circular hole bored in the center of a detector and orifices to irradiate a sample in a sample chamber. The detector detects particles scattered from the sample and arrived at the detector through the orifices. With exhaust units and orifices, the region surrounding the detector is exhausted to be a prescribed degree of vacuum of higher vacuum than the inside of the sample chamber.

Description: The present invention relates to an ion scattering spectrometer in which an accelerated ion beam is bombarded on a sample and particles scattered from the sample are measured to analyze the sample, and in particular to an ion scattering spectrometer that enables to analyze a sample placed in a gas. So far, an ion scattering spectrometer is known in which an accelerated ion beam is bombarded onto a sample and particles scattered from the sample are detected to analyze the structure of the sample. In addition, in such an ion scattering spectroscopy, a time-of-flight analysis method that measures the time-of-flight of the particles to analyze speed (energy) of the particles is known. Such a time-of-flight analysis method carries out energy analysis with the difference of arrival times of the particles scattered simultaneously from the sample. Accordingly, without depending on whether there is an electric charge or not with the particle, the energy analysis can be carried out. The kind of detector being used in the ion scattering spectroscopy differs according to the energy or the like of the particles to be measured. In general, when particles of low energy (approximately several keV) or of medium energy (approximately several hundreds keV) are measured, a microchannel plate (MCP) is employed. Further, when particles of high energy (approximately several MeV) are measured, a semiconductor detector is employed. In the aforementioned ion scattering spectrometer, the scattered ions of low energy or of medium energy can be measured with the microchannel plate (MCP) as a detector. In this case, in order to operate well a detector consisting of this microchannel plate (MCP), the surroundings of the detector is required to be a high vacuum of approximately 10 -7 Torr or less. Further, even when a semiconductor detector capable of being used in a low vacuum (approximately 0.1 Torr) is employed, if a gas being used reacts with the detector, the surroundings of the detector is required to evacuate to a high vacuum. Accordingly, so far, the surroundings of a sample is also made a high vacuum according to this, and measurement of the sample is carried out under a high vacuum. As described above, a conventional ion scattering spectrometer, in particular, an ion scattering spectrometer of low energy or medium energy analysis measures a sample under a high vacuum. A spectrometer in accordance with the preamble of claim 1 is known from US-A-5,447,614. However, if an ion scattering spectroscopy method can be employed in analysis of a sample under a reduced atmospheric pressure (for example, approximately from 10 -2 to 10 -3 Torr) where a certain amount of gas exists, for example, in analysis of a state of a film during vapor-phase deposition or the like, an ion scattering spectrometer can be employed in monitoring a film during film formation. Thus, the range of application of the ion scattering spectrometer can be widened remarkably. An object of the present invention is to provide an ion scattering spectrometer that is capable of analyzing a sample placed in a gas atmosphere such as a gas for film formation. In the present invention, an ion scattering spectrometer is provided as claimed in claim 1. Further preferred embodiments are claimed in dependent claims 2-7. Fig. 1 is a diagram showing schematically an embodiment of the present invention. Fig. 2 is a diagram showing schematically another embodiment of the present invention. In the following, the detail of an ion scattering spectrometer of the present invention will be described with embodiments in which the time-of-flight analysis method is employed in analysis of the speed (energy) of the particles, and with reference to drawings. Here, the time-of flight analysis method analyzes the energy of the particles due to the difference of the flight time of the particles that are scattered simultaneously. Fig. 1 shows a schematic constitution of one embodiment of an ion scattering spectrometer of the present invention. In the figure, reference numeral 1 denotes an ion source and accelerator, reference numeral 2 denotes a detector, reference numerals 3 and 4 denote orifices, reference numeral 5 denotes a sample chamber, reference numeral 6 denotes a sample, reference numeral 7 denotes a gas feeding unit, reference numeral 8 denotes a vacuum gauge, and reference numerals 9 through 12 denote exhaust units. The ion source and accelerator 1 generates prescribed ions at the ion source and accelerates the ions up to a prescribed energy to generate a pulse beam of ions of prescribed energy. The pulse beam of the ions goes past a circular hole 2a bored in the center of the detector 2 to irradiate the sample 6 in the sample chamber 5 through the orifices 4 and 3. Then, the particles scattered from the sample 6 and arrived at the detector 2 through the orifices 3 and 4 are detected by this detector 2. Incidentally, the detector 2 is constituted of a microchannel plate (MCP). In addition, the sample chamber 5 where the sample 6 is placed is fed with a prescribed gas to treat the sample 6 from a gas feeding unit 7, the prescribed gas being a prescribed vapor phase deposition gas in this example. Further, the inside of this sample chamber 5 can be exhausted by an exhaust unit 12 and made an atmosphere of a gas for vapor phase deposition of a prescribed pressure, for example, of approximately 10 -2 Torr. Thereby, a prescribed vapor deposition film can be formed on the sample 6. Further, among exhaust units 9 through 11, the exhaust unit 9 exhausts a region of an ion source and accelerator 1, the exhaust unit 10 a neighboring region of a detector 2, and the exhaust unit 11 a region between an orifice 3 and an orifice 4. The first orifice 3 disposed at a sample 6 side has an aperture of a diameter of 2 mm (conductance: 3.6×10 -4 (m 3 /s)) and the second orifice 4 disposed at a detector 2 side has an aperture of a diameter of 4 mm (conductance: 1.5×10 -3 (m 3 /s)). In addition, the sample 6 is placed 3 mm apart from the aperture of the first orifice 3 and the aperture of the first orifice 3 is placed 50 mm apart from that of the second orifice 4. With such a setting, a region between the first orifice 3 and the second orifice 4 becomes a vacuum of approximately 7.2×10 -5 Torr, and a neighboring region of the detector 2 becomes a vacuum of approximately 2.2×10 -8 Torr. Further, the exhaust units that have exhaust capacity of 0.5 m 3 /s are employed. Now, the aperture of the second orifice 4 is larger in diameter than that of the first orifice 3 so as to secure a solid angle seeing the detector 2 in proceeding direction of the scattered particles. Thereby, almost all of the particles scattered from the sample 6 in the proceeding direction and passed through the orifice 3 can reach the detector 2. An ion scattering spectrometer of the above described constitution of this embodiment employs, for example, a silicon semiconductor wafer as the sample 6. The sample chamber 5, while being exhausted by an exhaust unit 12, is fed with a prescribed vapor deposition gas such as silane (SiH 4 ) from a vapor deposition gas feed unit 7. Thereby, the inside of the sample chamber 5 is made an atmosphere of a vapor deposition gas of a pressure of, for example, approximately 10 -2 Torr to grow a layer of amorphous silicon on a sample 6 in vapor phase. Then, with the exhaust units 9 through 11 the respective regions are exhausted to be the aforementioned degrees of vacuum. Thereafter, a pulse beam of ions generated at the ion source and accelerator 1 (of energy of approximately from several keV to several hundreds keV) is made to go past an aperture 2a disposed at the center of the detector 2 and to irradiate the sample 6 through the second orifice 4 and the first orifice 3. The detector 2 detects particles scattered from the sample 6 and measures time-of-flight of the particles to analyze speed (energy) of the particles. When taking, for example, a Si (100) surface, the number of atoms in one monolayer is, 1 ML = 2/5.431 2 (angstrom 2 ) = 6.8×10 14 (atoms/cm 2 ). On the other hand, one mole (mol) of a gas has a volume of 22.4×10 3 (cm 3 ) under a pressure of 1 atmosphere (atm) and room temperature (20°C), and the number of molecules in one mole (mol) of a gas is 6.02×10 23 . Therefore, under 1 atmosphere, in a unit volume of a gas, there are molecules of 6.02×10 23 (mol -1 )/22.4×10 3 (cm 3 /mol/atm) = 2.68×10 19 (cm -3 · atm -1 ). In the case of the sample 6 being placed 0.3 cm (3 mm) (working distance) apart from the aperture of the first orifice 3, taking this sectional area of the aperture of the orifice 3 as s, in a volume of 0.3 s (cm 3 ) of a pressure of 10 -2 Torr = 1.32 × 10 -5 (atm), there exist molecules of the number of 0.3 s (cm 3 ) × 2.68 × 10 19 (cm -3 · atm -1 ) × 1.32 ×10 -5 (atm) = 1.1 × s × 10 14 . Accordingly, in a unit area, there exist molecules of 1.1 × 10 14 (cm -2 ). This number of molecules is approximately one fifth of one monolayer of Si (100) surface. Therefore, a scattering amount due to the gas is approximately one fifth of the atoms scattered from the surface of the sample 6. Thus, ion scattering spectroscopy of the sample 6 is made possible. Further, by taking the degree of vacuum and the kind of the gas into consideration, a scattering amount due to the gas can be evaluated. By subtracting this amount, a measurement can be carried out further correctly. As described above, an ion scattering spectrometer of this embodiment can analyze a sample placed in a gas, that is, this spectrometer can carry out analysis of state of a film during vapor deposition. Fig. 2 shows another embodiment of the present invention. In this embodiment, compared with the case of Fig. 1, only the first orifice 3 is employed and an exhaust unit 11 for exhausting the region between the orifices is omitted. As shown in the embodiment, when the inside of the sample chamber 5 can be set at a higher vacuum than that necessary for the sample chamber 5, the second orifice and the exhaust unit for exhausting the region between the orifices can be omitted. Incidentally, contrary to the above embodiments, in the present invention, the number of orifice can be increased to 3 or more stages. Further, the ion beam incident on the detector is not restricted only to go through the center of the detector but the detector can be disposed to detect ions of an arbitrary scattering angle. In addition, the present invention is not restricted to the above embodiments and various modifications can be applicable. As described above, according to the present invention, an ion scattering spectrometer that can analyze a sample placed in a gas such as a vapor deposition gas is provided. Thereby, a state of a film during vapor deposition can be analyzed.

Claims: An ion scattering spectrometer in which an ion beam generated at an ion source (1) is adapted to be accelerated by an accelerator to irradiate a sample (6) placed in a sample chamber (5), and particles scattered from the sample (6) are adapted to be analysed by a time-of-flight analysis method, comprising: a gas introducing means (7) for introducing a prescribed gas into the sample chamber (5) for treating the sample (6); a first exhausting means (12) for exhausting the sample chamber (5) to create in the sample chamber (5) an atmosphere of the prescribed gas of prescribed reduced pressure; a detector (2) disposed at a prescribed position in a region between the ion source (1) and the sample (6) for detecting particles scattered from the sample (6) for the analysis by the time-of-flight analysis method, said detector (2) having a circular hole (2a) in the center thereof; a second exhausting means (10) for exhausting the region including the detector (2) to create in this region an atmosphere of a prescribed reduced pressure which is lower than the prescribed reduced pressure of the atmosphere in the sample chamber (5) ; characterized in the presence of at least one orifice (3,4) disposed between the sample chamber (5) and the detector (2) to separate the region including the detector (2) from the sample chamber (5), said orifice (3,4) having an aperture for passing the ion beam toward the sample (6) and the particles scattered from the irradiated sample (6) toward the detector (2). The ion scattering spectrometer as set forth in claim 1, wherein said at least one orifice disposed between the sample chamber (5) and the detector (2) comprises a first orifice (3) disposed at the sample chamber side and a second orifice (4) disposed at the detector side. The ion scattering spectrometer as set forth in claim 2, further comprising: a third exhaust means (11) for exhausting a region between the first orifice (3) and the second orifice (4). The ion scattering spectrometer as set forth in any one of the preceding claims, wherein the detector(2) is disposed at such a distance apart from the sample (6) that the particles scattered from the sample (6) can be distinguished by their respective times of flight. The ion scattering spectrometer as set forth in any one of the preceding claims, wherein the gas introducing means (7) is constituted to introduce a prescribed vapor deposition gas into the sample chamber (5) and to form a prescribed film on the sample (6). The ion scattering spectrometer as set forth in any one of the preceding claims, wherein the center hole (2a) of the detector (2), the aperture of the at least one orifice (3,4) and the sample (6) are aligned such that the ion beam irradiated from the ion source (1) toward the sample (6) and the particles scattered from the irradiated sample (6) have the same axis. The ion scattering spectrometer as set forth in any one of the preceding claims, wherein said second exhausting means (10) is adapted to exhaust the region including the detector (2) to create in this region an atmosphere of a reduced pressure of approximately 1.33x10 -8 kPa (1x10 -7 Torr) or less and said first exhausting means (12) is adapted to exhaust the sample chamber (5) to create in the sample chamber (5) an atmosphere of reduced pressure of about 1.33 Pa (1x10 -2 Torr).

Inventors: AONO MASAKAZU, KOBAYASHI TAKANE, AONO, MASAKAZU, KOBAYASHI, TAKANE, Aono, Masakazu, (Riken), Kobayashi, Takane, (Riken)
Applicants: RIKAGAKU KENKYUSHO, THE INSTITUTE OF PHYSICAL & CHEMICAL RESEARCH
Application year: 1999
Main classification: H01J49
IPC codes: H01J37, H01J49, G01Q60