Radiant energy – Inspection of solids or liquids by charged particles – Including a radioactive source
Reexamination Certificate
2001-07-26
2003-10-07
Berman, Jack (Department: 2853)
Radiant energy
Inspection of solids or liquids by charged particles
Including a radioactive source
C250S309000
Reexamination Certificate
active
06630666
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of this invention relates to devices for analyzing solids and more particularly to a device for analyzing a solid which uses positrons and the transmitting of those positrons onto the solid that is to be analyzed to result in the obtaining of information about the solid.
2. Description of the Related Art
A positron is an elementary particle with a mass equal to that of an electron and a positive charge equal in magnitude to the negative charge of an electron. The positron is thus the anti-particle of the electron. The positron has the same spin and statistics as the electron. A positron, is, in itself, stable but cannot exist indefinitely in the presence of matter, for it will ultimately collide with an electron. The positron and the electron will be annihilated as a result of the collision, and photons (gamma rays) will be created.
When a positron is injected into a solid substance, the positron will annihilate an electron and release gamma rays. These gamma rays are easily detected and can be used to measure properties of the solid material. Particles which can be released from the solid can also be used to measure properties of the solid material. These phenomena are the basis of a wide variety of techniques that can be used as tools for materials and surface analysis and can provide information that is not available from any other technique. Implementation of these techniques requires high quality positron beams. Currently, these techniques are being used at university laboratories, where the required positron beam systems are constructed by the users. However, such systems have the potential to be employed for industrial applications, such as quality control on integrated circuit production lines. It is this need that the current inventor is seeking to address by designing the subject matter of the present invention.
An important application of positron beams is a wide variety of techniques that have been developed for the analysis of solids and surfaces. Each of these techniques has its own characteristic positron beam requirements. Some employ steady state beams while others require pulsed beams. Several will provide usable data with relatively large diameter beams that are typical of radioactive positron source diameters (several millimeters) while other are applicable only using microbeams (less than ten microns in diameter).
In addition to surface analysis techniques, positrons can also be used to analyze properties of solids below the surface of the solid. This unique feature of positron based techniques arises because it is possible to measure the annihilation gamma rays from high energy positrons, which can easily penetrate to the surface of the solid. By varying the energy of the incident positron over a range of a few kilo-electron volts to greater than one hundred kilo-electron volts, positrons can be implanted to varying depths, thus permitting depth profiling of the properties of the solid. The information is contained either in the lifetime of the positrons or in the shape of the gamma ray line, which is Doppler-broadened by the momentum of the annihilated electrons and thus provides information about the chemical environment of the annihilation site.
The following is a list of some of the current applications for positron beams:
1. Positron Remission Spectroscopy (PRS)—This technique is based on the phenomenon that positrons implanted near the surface of a solid can thermalize, that is come to the same temperature as the surface of the solid, and be reemitted. The energy of the reemitted positrons can be analyzed to yield information that is not available with conventional scanning electron microscopy. This PRS technique has the ability to distinguish non-uniform film thickness, varying crystal orientation, differences in concentrations of microscopic voids in the crystal structure, concentrations of adsorbed molecules and contaminant layers.
2. Positron Annihilation Induced Auger Electron Spectroscopy (PAES)—This technique is analogous to Electron Induced Auger Electron Spectroscopy (AES), except that the core hole, which leads to the ejection of the Auger electron, is created by positron annihilation rather than electron impact. For this technique, positrons are injected at low energy into the surface to be analyzed. The ejected electrons are analyzed in the usual way using an electron energy spectrometer, but the measurement is substantially simplified because of the absence of background high-energy secondary electrons.
3. Reemitted Positron Energy Loss Spectroscopy (REPELS)—In this process, low energy monoenergetic positrons bombard the surface to be studied, and those that are reflected are energy analyzed. Energy is lost by transfer to vibrational modes and electronic state transitions of the surface and surface absorbed molecules. By measuring the magnitude of the energy lost, information can be obtained about the chemical composition of the surface of the solid and of surface absorbed molecules.
4. Low-energy Positron Diffraction (LEPD)—For this technique, a crystalline sample is bombarded with low energy (0-300 electron volts) monoenergetic positrons. Because of the low energy, there is relatively little penetration into the solid, and some of the positrons are reflected producing spots on a phosphor screen. This information can be used to determine the crystal structure of a clean substrate or to analyze an adsorbed layer.
5. Positron Induced Ion Desorption Spectroscopy (PIIDS)—This relatively new technique uses positrons to eject ions from the surface of the solid and measures the time required for the ions to reach a detector. Hence, the mass of the ions can be determined. The rate at which the ions are ejected from the surface of the solid is much greater when positrons are used rather than photons.
6. Positron Annihilation Lifetime Spectroscopy (PALS)—Positrons injected into a surface can accumulate in microscopic voids of the solid where such will eventually annihilate an electron of the solid. For high energy positrons obtained directly from the radioisotope of sodium, sodium-
22
, the lifetime can be measured by recording the time delay between the 1.2 million electron volt gamma rays that are emitted by the sodium nucleus simultaneously with the positron and the 511 kilo-electron volt annihilation gamma rays. This technique has been extensively applied to the study of bulk properties of solids. One of the most important current applications of lifetime spectroscopy is the analysis of microvoids in semiconductors and polymers. This technique is the most sensitive one available for studying voids in solids and can provide information about both the size and concentration of the voids. The technique has been applied to characterizing the properties of semiconductors, such as ion-implanted silicon, to study, for example, stress voiding and electromigration. One of the most important current areas of research is the study of the properties of polymers. Positron lifetime spectroscopy is capable of measuring the size and distribution of voids, which determine properties such as strength of the solid, gas permeability of the solid and aging characteristics of the solid. Another important topic is the development of insulators with low dielectric constant for use in microelectronic fabrication. Such insulators are essential for increasing microprocessor speeds and the positron technique described can be used to measure the properties of these insulators.
7. Variable Energy Positron Lifetime Spectroscopy (VEPLS)—The power of the PALS technique can be substantially enhanced by implementing it using a positron beam source of constant energy rather than a radioactive source which has a range of energies. By varying the beam energy, positrons can be implanted to varying depths so that a depth profile of void size and concentration can be obtained. Furthermore, if the beam diameter is small, it can be scanned across the surface of the solid so that three dimensional information can be obta
Berman Jack
Dudding Alfred
Munro Jack C.
LandOfFree
Positron trap beam source for positron microbeam production does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Positron trap beam source for positron microbeam production, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Positron trap beam source for positron microbeam production will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3155691