JPH075129A - Ion scattering surface analysis method and apparatus - Google Patents

Abstract

(57) [Abstract] [Purpose] A method for surface analysis of semiconductor materials, etc. during thin film growth, and in particular, enables observation of the composition and structure of surface atoms and electrons by attaching them to thin film growth equipment and other analysis equipment. The purpose is to [Structure] Pulsed He, Ne, A of 3 keV or less
The low-energy ion particle beam such as r is generated by the magnetic field prism 5
After being deflected in an arc shape by and converged by the objective lens 6, it collides with the observation sample 7. The collision ion particles are inelastically scattered by the atoms of the surface layer, and among them, the ion particles scattered in the direction of 180 degrees are detected. The scattered neutralized particles go straight to the detector 9, and the scattered ion particles are deflected again by the magnetic field prism, accelerated between the grid 17 and the detector 10, and then detected by the detector 10. The outgoing angle of the scattered ion particles from the magnetic field prism can be finely adjusted. [Effect] The device is miniaturized, and it is possible to know the atomic position and concentration, and the chemical bonding state of the sample surface, regardless of the type of surface atoms.

Description

Detailed Description of the Invention

[0001]

[Industrial application] A method for surface analysis of semiconductor materials and the like, which is particularly effective for composition analysis and structure analysis of crystal surfaces.

[0002]

2. Description of the Related Art In connection with the development of semiconductor devices, a technique for controlling the crystal surface structure and the crystal growth process by observing in real time the composition and structure of the surface, which is changing due to crystal growth, is important. ing. For example, Si-UL
In SI, as the device becomes finer, the thinning of the channel and the high impurity concentration of the channel stopper layer are required, but in order to realize this structure, it is necessary to form an abrupt impurity distribution. To this end, there is a need for a technique for observing the positions and concentrations of various elements adsorbed on a Si crystal substrate in real time to suppress the diffusion of atoms accompanying crystal growth and perform atomic layer growth. . The low-energy ion scattering surface analyzer is capable of performing composition analysis and structure analysis at the atomic layer level near the crystal surface by in-situ observation, and has recently been researched and developed as a useful analysis method for the above purpose. Is being promoted.

A conventional low energy ion scattering surface analyzer is shown in FIGS. 2 and 3. In the apparatus shown in FIG. 2, Naoharu Sugiyama et al., Japanese Journal of Applied Physics, 1990, Vol. 29, No. 10, pages L1922 to L1925 (Japanease Journal of Applide Physi
cs Volume 29, No.10 (1992) p.L1922-p.L1
925), and an ion particle source 1 of several keV or less pulsed by a chopping plate 4
The ion particle beam emitted from the
The detector 9 was used to measure the flight time of particles scattered backward by 180 degrees with respect to the incident direction and the number of particles. Since the time-of-flight method is used for energy analysis of scattering particles, the energy spectrum can be measured at one time. Further, by changing the direction of the sample surface with respect to the incident direction with the goniometer 13, it is possible to analyze the structure of several atomic layers on the sample surface. Furthermore, in the apparatus shown in FIG.
As disclosed in Japanese Patent Publication No. 43-43, neutralized particles among particles that are pulsed and deflected by the magnetic field prism 5 into the sample 7 and are scattered backward by 180 degrees, are ionized particles of several keV or less. The method of measuring the flight time and the number of particles by the detector 9, deflecting the ion particles by the magnetic field prism 5 again, and measuring the detection position and the number of particles by the detector 23 having a positional resolution has been proposed. It was
In this method, scattered ion particles and neutralized particles can be separated and simultaneously measured. Since the scattered ionic particles can obtain information on the surface more than the neutralized particles, the surface analysis described above could be performed.

[0004]

However, the prior art has the following problems. In a uniform magnetic field, charged particles take circular orbits having different radii depending on their energies. Therefore, it is necessary to have a uniform magnetic field in a range that covers all the orbits corresponding to the sample element and having different scattering energies. Therefore, in the method of detecting the energy of ion particles with a detector having a positional resolution, a detector having a size corresponding to that is required. Therefore, the device becomes large-scale,
It was difficult to attach it to a crystal growth device or other analysis device. Furthermore, since the position resolution of the ion particles is performed by measuring the time difference between the electric signals transmitted to both ends of the detector, it is difficult to improve the resolution. In addition, since the distribution of the magnetic field occurs at the boundary of the magnetic field,
The trajectories of scattered ion particles are different from those of the ideal magnetic field distribution. Therefore, it is difficult to accurately specify the position where the ion particles are detected.

[0005]

Therefore, an arc-shaped magnetic field prism for deflecting incident particles is provided with means for accelerating and detecting scattered ion particles by an electric field and further measuring flight time. Further, a mechanism for finely adjusting the direction in which the ion particles are emitted from the magnetic field prism is provided.

[0006]

As a result, the scattered ion particles reach the detector before they are largely resolved by the magnetic field, and the magnetic field prism having the minimum size necessary for deflecting the incident ion particles causes the ion particles to be dispersed. And neutralized particles can be separated and simultaneously detected. Further, by accelerating the ionic particles by the electric field, the ionic particles can be detected before they are separated into a large area, so that the detection unit can be downsized. Furthermore, by increasing the energy of the ion particles and making them enter the detector,
The detection efficiency can be improved, and noise due to electrons can be removed.

By providing a fine adjustment mechanism at the exit of the magnetic field prism for the ion particles, it becomes easy to detect the direction of the scattered ion particles.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
This will be described with reference to FIG. FIG. 1 is a slow ion scattering device showing one embodiment of the present invention. Low-energy ion particles such as He, Ne, and Ar of 3 keV or less emitted from the ion source 1 are pulsed by applying a pulse voltage generated from a pulse generator 3 to a chopping plate 4 according to a signal from a computer 2. To be done. The pulsed ion particle beam is deflected in an arc shape by the magnetic field prism 5, converged by the objective lens 6, and then collides with the observation sample 7. The collision ion particles are inelastically scattered by the atoms of the surface layer, and among them, the ion particles scattered in the direction of 180 degrees are detected. A part of the scattered ion particles becomes a neutralized particle due to the transfer of electric charge with the surface atoms, and goes straight through the chamber 8 to reach the detector 9. The measuring device 11 detects the flight time of the pulsed ion particles reaching the detector 9.

Assuming that the energy T of the reflected particles is m, the mass of the particles is m, and the flying distance from the sample to the detector is d, the time T from the collision with the observation sample 7 to the arrival at the detector is

[0010]

[Equation 1]

[0011] Here, the energy E of the reflective particles
Where Eo is the energy of the incident particle, m is the mass of the ionic particle, and M is the mass of the sample atom, from the relationship of collision of the rigid body model,

[0012]

[Equation 2]

It is obtained by 3 and 4 show the numbers 1 and 2
With helium (He) ion particles and neon (N
e) Results of calculation of flight times of Si atoms and other atoms when ion particles are used as incident ion particles. In this calculation, the flying distance d was set to 1 m. In this measurement, there are two restrictions on the detection limit. One is that surface atoms smaller than the atomic weight of incident ion particles cannot be detected. For example, when Ne ion particles are used, boron (B), carbon (C), and oxygen (O) cannot be detected. The other is due to the time resolution of the measuring device 11. For example, when Si is used as the substrate, the difference between the flight time of Si and the flight time of surface atoms needs to be larger than the minimum detection time difference of the measuring device 11, in other words, the time resolution. Generally, since the time resolution is about 100 nsec, if Ne ion particles are used, arsenic (As), gallium (Ga), aluminum (Al), germanium (G
e), antimony (Sb), etc., and B, C, O, etc. can be detected by using He ion particles.

Thus, in principle, the slow ion scattering method can detect a wide range of atomic species from light elements to heavy elements existing on the outermost surface of the substrate. However, it has been difficult to detect the neutralized particles in the case of an element lighter than the substrate element. This is because when measuring the flight time dependence of neutralized particles scattered by the substrate atoms, the particles that penetrate inside the substrate are detected by the effect of being detected later than when they are scattered by the surface atoms. Pull the hem in the direction of longer time,
This is due to the overlap with the signal scattered by the lighter elements.
For example, Si on a GaAs substrate and B on a Si substrate are examples. On the other hand, scattered ion particles are M.Aono
Nuclear Instruments and Methods by Physics Research, 1989, Volume 37/3
8, p. 264 to p. 269 (Nuclear Instrument and Methods i
n Physics Research, Volume B37 / 38 (1989) p.264-p.2
As disclosed in (69), it is known that only signals from a few atomic layers on the outermost surface of the substrate are revealed. Therefore, in the embodiment of FIG. 1, detection is performed by utilizing the fact that the ion particles scattered 180 degrees without being neutralized among the incident ion particles are deflected in the direction opposite to the incident direction by the magnetic field prism. Only the ion particles can be detected by the container 10. That is, the scattered ion particles are deflected by the magnetic field prism 5 in the opposite direction across the vertical plane of the incident ion particles and the substrate and reach the detector 10. Therefore, the neutralized particles can be detected by the detector 9 and the ion particles can be detected by the detector 10 independently. As a result, the signals of several atomic layers on the outermost surface of the substrate can be detected independently.

Further, the ion particles deflected by the magnetic field are
The deflection radius of curvature differs depending on the type of atoms on the sample that has collided. The deflection radius R of the ion particle is expressed by the magnetic flux density B
If 0 and elementary charge are e,

[0016]

[Equation 3]

And is proportional to the square root of the product of atomic weight and energy. Therefore, the spatial position differs depending on the atoms on the surface.

Therefore, in the present invention, in order to reduce the size of the scattered ion particle detecting device, the ion particles are accelerated by an electric field and detected while the deflection angle due to the magnetic field is small. . A grid 17 is provided where the ion particles are deflected by the magnetic field and can be separated from the neutral particles, and a voltage of −2 kV is applied between the grid 17 and the detector 10. The ion particles deflected by the magnetic field pass through the grid 17 and then are accelerated by the electric field to reach the detector 10. Since the flight distance of the ion particles during this period is small, it does not affect the overall flight time of the ion particles. Further, by using this method, it is possible to remove the electrons that cause noise when detecting the ion particles.

In practical application of the present invention, it is important to adjust incident ions, scattered neutral particles, and scattered ions. Since scattered neutral particles and scattered ions are affected by an error in assembling the device and a deviation in the ion trajectory, it is necessary to provide the device with a function so that the two detectors 9 and 10 can detect them simultaneously. 6 and 7 show an embodiment of the present invention having an adjusting mechanism. FIG. 6 shows a structure in which an adjusting mechanism 18 for the shape of a pole piece of a magnet is provided in a portion where scattered ions bent by the magnetic field prism 5 are emitted from the magnetic field. The adjusting mechanism 18 has a structure in which the contour of the outer peripheral portion of the magnetic field can be changed by rotating the pole piece and the magnetic material. Therefore, it is possible to independently adjust the scattered ions when the adjustment up to the scattering neutral particles is completed. Since the trajectories of scattered ions are extremely sensitive to the contour shape of the magnetic field prism, they are useful as an adjusting method when the detector 10 is irradiated with scattered ions due to the deviation of the trajectories. FIG. 7 is an example of another adjustment method. This is to adjust the orbit of scattered ions by moving the magnet itself relative to the ion orbit instead of adding the position adjusting mechanism 22 to the magnet. However, in this case, since the magnet is moved, the adjustment performed in the irradiation of the sample 7 with the incident ions and the detection of the reflected neutral particles by the detector 9 is disturbed. Therefore,
In the embodiment, a diameter of 1 m is provided after the magnetic field prism so that the position of incident ions after exiting from the magnetic field prism 5 does not change.
An ion detector 19 is installed through the pinhole 20 of m, and a drive signal is applied to the position adjusting mechanism 22 so that the time counter 21 always detects the detected ion signal of this ion detector. The adjustment is completed when the detection signal of the scattered ions is obtained from the scattered ion detector 10 in the detection circuit 21. If the above procedure is automated, simpler adjustment can be performed.

[0020]

As described above, according to the present invention,
In the low-speed ion scattering method, the magnetic field prism unit and ion particle detection unit can be downsized, and scattered neutralized particles and scattered ion particles can be separated and measured, so it is necessary to attach them to a crystal growth device or other analysis device for analysis. Is possible.

Further, in ion particle detection, energy resolution can be improved and noise can be reduced.

[Brief description of drawings]

FIG. 1 is a front view of an ion scattering surface analyzer showing one embodiment of the present invention.

FIG. 2 is a front view of a conventional ion scattering surface analyzer.

FIG. 3 is an explanatory diagram of a conventional ion scattering surface analyzer.

FIG. 4 is an explanatory diagram of a calculation result of a flight time of He ions.

FIG. 5 is an explanatory diagram of a calculation result of flight time for Ne ions.

FIG. 6 is a view of a first embodiment of the present invention including a mechanism for adjusting scattered ion trajectories.
It is explanatory drawing which shows an Example.

FIG. 7 is a view of a first embodiment of the present invention including a mechanism for adjusting scattered ion trajectories.
It is explanatory drawing which shows an Example.

[Explanation of symbols]

1 ... Ion particle source, 2 ... Control computer, 3 ... Pulse generator, 4 ... Chopping plate, 5 ... Magnetic field prism, 6 ... Lens, 7 ... Sample, 8 ... Vacuum chamber,
9 ... Detector, 10 ... Detector, 11 ... Lens, 12 ... Gate valve, 13 ... Sample stage, 14 ... Analytical chamber, 15 ... Linear movement mechanism, 16 ... Electric field prism, 17 ... Grid, 18 ...
Magnetic field adjusting jig, 19 ... Ion detector, 20 ... Pinhole, 21 ... Time counter, 22 ... Position adjusting mechanism, 23 ... Detector, 24 ... Wave height analyzer.

Claims (7)

[Claims] 1. A pulsed, low-energy ion particle of several keV is made to collide with a sample surface and scattered backward with respect to the incident direction, and the ion particle and the neutralized particle from the sample are In an ion scattering surface analyzer characterized by separating and detecting by a magnetic field, as the detector of scattered ion particles from the sample, the scattered ion particles added with an acceleration means for accelerating the scattered ion particles from the sample Ion scattering surface analysis device characterized by being a detector of. 2. The ion scattering surface analyzer according to claim 1, wherein an electric field is used as an accelerating means for accelerating the scattered ion particles from the sample. 3. The ion scattering surface analyzer according to claim 1, wherein an energy analysis is performed by having a system for measuring the flight times of scattered ion particles and neutralized particles. Scattering surface analyzer. 4. The ion-scattering surface analyzer according to claim 1, wherein a fine adjustment mechanism of an exit angle is provided at an exit of the scattered ion particles from the magnetic field prism. 5. The ion scattering surface analyzer according to claim 1, further comprising a position adjusting mechanism for the magnet for the magnetic field prism,
An ion scattering surface analysis device characterized in that the orbits of scattered ions are adjusted by adjusting the position of a magnet. 6. The ion scattering surface analyzer according to claim 1, wherein the detector for the scattered ions is arranged such that the closer the scattered ions are to the direction perpendicular to the sample, the smaller the flight distance from the sample. An ion scattering surface analyzer characterized by the above. 7. A pulsed low-energy ion particle of several keV is made to collide with the sample surface and scattered backward with respect to the incident direction, and the ion particle and the neutralized particle from the sample are An ion scattering surface analysis method characterized by separating and detecting by a magnetic field, wherein the sample surface is analyzed from the ion particles deflected and accelerated with respect to the ion particles from the sample.