JP2001210267A - Particle detector and mass spectrograph using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize analysis of particles covering broad mass ranges from a light atomic to heavy particle cluster and amicron, at a high detection efficiency, at a high resolving power and at a high SIN(signal to noise) ratio. SOLUTION: The ion to be measured inside the particle detector is first decelerated due to the retarding field caused by the decelerating electrode and then accelerated due to the accelerating field caused by the accelerating electrode to reach the detection point for particle detection. The ion which lost the required energy due to the charge having the homopolarity with the ion for measurement, is all reflected due to the retarding field and cannot reach the detection point. The charge ion having a code opposite to the ion for measurement is accelerated due to the retarding field but cannot reach the detection point due to the reflection caused by the accelerating field. The detection efficiency can be raised to only the extent of the energy brought by the accelerating field. The particle detector can be used for a mass spectrograph analyzing the mass and charge condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a mass spectrometer for analyzing atoms, molecules, clusters, ultrafine particles, etc.
The present invention relates to a particle detector and a mass analyzer that realize high detection efficiency, high mass resolution and a high S / N ratio in a wide mass range.

FIG. 2 shows a mass spectrometer. 1 is a particle detector for detecting the arrived particles, 11 is a particle introduction vacuum vessel, 12 is a vacuum vessel, 13 is an accelerating electrode, 14 is a ground grid electrode, 15 is a lens, and 16 is a reflector (Re).
17, a laser pulse generator, 17a a laser pulse, and 18 a particle to be measured.

[0003] If the particles 18 introduced into the mass spectrometer from point A in the figure are neutral particles, the laser pulse 1 at point B
7a, the ionized particles are accelerated by an electric field applied between the accelerating electrode 13 and the ground grid electrode 14 and given a predetermined energy E ₀ , and the ionized particles fly toward the point C, and are reflected by the reflector 16. It reflects and reaches the particle detector at point D. By measuring the time of flight of the particles from the moment of ionization to the detector, the mass can be determined.

[0004] figure introduced particles to the mass analyzer from the point A, if an ion, predetermined energy E ₀ being accelerated by a pulse electric field applied between the acceleration electrode 13 and the ground grid electrode 14 Given, it flies towards point C, is reflected by reflector 16 and reaches the particle detector at point D. The mass of the particles can be determined by measuring the time of flight of the particles from the moment of application of the pulsed electric field to the detector.

However, contact with the vacuum vessel wall during flight toward point C, grounding grid electrode 14 and reflector 1
Due to scattering when passing through the mesh electrode used in 6, for example, particles having a predetermined energy loss are generated, and some of these particles reach the particle detector at point D. These particles resulted in reduced mass resolution and reduced SNR.

In the particle detector at point D, secondary electrons generated when the arriving particles collide with the entire surface of the detector are amplified,
This is extracted as a detection signal. The higher the energy that the particle has when it collides with the detector, the more secondary electrons are generated, so that the detection efficiency is improved. For this purpose, in the conventional method, an accelerating electric field for additionally accelerating (post-acceleration) particles arriving near the detector and causing the particles to collide with the detector is arranged on the entire surface of the detector.

FIG. 3 shows a conventional particle detector. The operation of the conventional particle detector will be described with reference to FIG. 2
Represents a ground grid electrode, 3 represents a detecting unit, and 4 represents an accelerating electrode for additionally accelerating particles input to the detecting unit 3.
The potential of the grid electrode 2 at the forefront of the particle detector is usually set to the ground potential, but may be set to a predetermined potential as needed. When measured as in FIG. 3 is a positive ion particles, the negative voltage -V ₁ is applied to generate the accelerating electric field in the accelerating electrode 4.

[0008]

In the figure, ,, and indicate the ion particles that have arrived at the particle detector. The ion particles have an energy E of an acceleration energy E ₀ and a charge of +
The measured particle is Ze, ion particles are energy E acceleration energy E ₀ below, the particles are charge + Ze, ion particles, electric charge represents the particles -ze.
An ion particle is an ion particle that is not a measurement target.
In the particle detector of FIG. 3, not only the ion particles to be measured but also all the ion particles having the same sign as the measurement target are drawn into the detection unit 3 by the acceleration electric field of the acceleration electrode 4.
Since the detection is performed, not only the resolution of the particle detector is lowered, but also noise is caused and the SN ratio is lowered.

When examining the characteristics of particles used in the process of manufacturing semiconductor thin films, the characteristics of particles in atmospheric analysis, biopolymer analysis, medical treatment, etc., one or more atomic species (isotope atoms, Clusters composed of many kinds of atoms) (aggregates of several to thousands of atoms) and ultrafine particles (aggregates of thousands to tens of thousands of atoms) are measured. Accurate mass resolution is required in a wide mass range up to 10,000 atoms, but there is no particle detector or mass analyzer having such a wide mass range and precise mass resolution.

Furthermore, if the energy of the incident particle is the same, the speed of a heavy particle is lower than that of a light particle, so that
The secondary electron emission characteristics of the channel inner wall material that emits secondary electrons by the collision particles provided in the detection unit 3 are deteriorated. For this reason, the sensitivity of the particle detector decreases. In the case of light ions (H +, He +, Ar +), the energy of the incident particles becomes maximum in the detection efficiency of the particle detector in the range of about 10 to 100 keV, whereas the acceleration potential of a commercially available mass analyzer is 1 The particles were not measured at the accelerating potential in the maximum efficiency state of the particle detector in the range of about 10 kV to about 10 kV. For heavy particles, the detection efficiency is maximized with higher energy.

According to the present invention, by preventing ions not to be measured, which are found in the conventional apparatus, from being drawn into the detection section and improving the detection efficiency, a wide range from light atoms to heavy particles such as clusters and ultrafine particles can be obtained. It is intended to realize high detection efficiency, mass resolution and high S / N ratio over a mass range.

[0012]

In order to achieve the above object, according to the present invention, a deceleration electric field having a predetermined intensity is applied immediately before an acceleration electric field so that ion particles which are not to be measured cannot reach a detection unit, Thereafter, a particle detector to which an accelerating electric field is applied and a mass spectrometer used for the particle detector are provided. As a result, particle detectors and mass spectrometers that achieve high mass resolution and a high S / N ratio while maintaining the same high detection efficiency even for clusters and ultrafine particles, which are light to heavy particles, can be made possible. Become.

[0013]

FIG. 1 shows an embodiment of a particle detector according to the present invention. FIG. 1 shows a case where positive ion particles are measured. 5 represents a grid electrode voltage V ₂ is applied for generating a deceleration electric field. In FIG. 1, components denoted by the same reference numerals as those in FIG. 3 represent the same or equivalent components. If positive ion particles entering the grid electrode 2 are to be measured in a state of positive charge + Ze and energy E ₀ , the positive voltage + V ₂ applied to the grid electrode 5 is ZeV
It is set to satisfy _{2 <E 0.} Further, the acceleration electrode 4 disposed in front of the detector 3, the negative voltage -V ₁ is applied.

The ion particles to be measured are first decelerated by the electric field between the grid electrode 2 and the grid electrode 5, and then accelerated by the electric field between the grid electrode 5 and the accelerating electrode 4 in front of the detector. Reaches 3. The energy of the ion particles when reaching the detection unit 3 is E ₀ + Ze
Since the V _1, it can be increased by an amount detection efficiency of energy ZEV _1.

The same charge as the ion particles to be measured +
Ion particles having Ze, but capable of holding only energy below a predetermined energy E ₀ due to scattering or the like in the middle of the flight path, are not only decelerated by the electric field between the grid electrode 2 and the grid electrode 5, Since all of the light is reflected, the light does not reach the detection unit 3 and the ion particles are not measured.

All ion particles having charges opposite to the ion to be measured are accelerated by the electric field between the grid electrode 2 and the accelerating electrode 4. The light is reflected by the electric field and does not reach the detection unit 3. To increase the detection efficiency, V ₁ since as much as possible using a large value, typically, V ₁ is equal to or larger than a predetermined value required to reflect all the ion particles.

The ion particles to be measured are negatively charged particles.
In some cases, the potential V in the above description ₁, V₂Anti-polarity
By setting the rotation, the positive ion
It can be realized with the same effect as on-particle detection.

[Other Embodiments] The particle detector shown in FIG. 1. As a particle detector of a mass spectrometer of a type (time-of-flight type) for analyzing mass and charge by measuring the time of flight of ions; Used as a particle detector for mass spectrometers that analyze mass by passing only ions of a specified mass-to-charge ratio with an electric or magnetic field (electromagnetic, electric, quadrupole, or combined magnetic field and electric field) it can.

[0019]

According to the above method of the present invention, mass resolution is reduced, ion particles and ion particles which cause noise are eliminated, and only ions to be measured are changed from light atoms to heavy particles such as clusters and super particles. High detection efficiency, high mass resolution and high S / N ratio can be measured over a wide mass range up to the fine particles.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of a particle detector according to the present invention.

FIG. 2 is a diagram illustrating a mass analyzer using a particle detector.

FIG. 3 is a diagram illustrating the operation of a conventional particle detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Particle detector 2 Grid electrode 3 Detector 4 Acceleration electrode 5 Grid electrode 13 Acceleration electrode 14 Ground electrode 16 Reflector 17 Laser pulse generator 18 Particle B Position where particles are ionized

Claims (2)

[Claims] 1. A first electrode, a second electrode to which a voltage for generating a decelerating electric field is applied, and a third electrode to which a voltage for generating an accelerating electric field is applied, in order from the incident side of the ion particles. A particle detector in which a detection unit that detects incident ion particles is arranged.
Subsequently, the ion particles are accelerated afterwards and reach the detector, and the ion particles having the same sign as the ion particles to be measured, but not retaining the predetermined energy are reflected by the above-described deceleration electric field, and are detected by the detection unit. Without reaching
A particle detector characterized in that ion particles having charges of opposite sign to the ions to be measured are reflected by the accelerating electric field and do not reach the detection unit. 2. A mass spectrometer using the particle detector according to claim 1.