JP2000223065A - Mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small device for analyzing a surface by loading a large sample on a sample stage as it is, by providing a rear-stage reflection electrode on an ion track in order to guide ions ejected from an ion reflector to a detector. SOLUTION: Laser beams going out of a laser beam source 3 are reflected by a mirror 6 having a through hole, and are focused onto a sample 2 by an objective lens 5. Ions generated with irradiation are accelerated by an ion drawing electrode 8, and are guided to this flight-time-type mass spectrometer 1. A polarization electrode 11 is adjusted so as to direct a progressing direction of the ions to an ion reflector (reflectron) 9. The ions reflected by the reflectron 9 are reflected by a rear-stage reflection electrode 40, and focused by an ion lens 41, and are detected by an ion detector 10. Masses are determined by measuring a time required from laser oscillation to arrival at the ion detector 10. By reflecting the ions with the rear-stage reflection electrode 40, the detector 10 can be placed at a position away from a sample container 20, and measurement of a large sample is allowed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for analyzing minute foreign matter and contaminants attached to the surface of a substrate such as a semiconductor product or a liquid crystal display element. The present invention relates to a mass spectrometer capable of directly analyzing a mass spectrometer.

[0002]

2. Description of the Related Art In recent years, with the improvement in the degree of integration of semiconductor products and the like, even minute foreign matters or minute amounts of contaminants have caused defects. In order to improve the yield, it is necessary to analyze the size, composition, and components of these foreign substances and contaminants. As an elemental analysis method for inorganic fine foreign substances, SEM-
Although EDX and the like have been established, methods for analyzing the molecular structure of organic fine foreign substances include a static secondary ion mass spectrometer and a laser mass spectrometer.

An example of the prior art similar to the present invention is disclosed in
-304343 and JP-A-63-146339. These devices are shown in FIGS.
And a microscope-type laser mass spectrometer having the configuration shown in FIG. The laser light emitted from the laser light source 3 is focused and irradiated on the sample 8 by the microscope objective lens 5. By this irradiation, molecules and fragments are desorbed and ionized from the sample 8. The generated ions are accelerated by an electric field generated by the ion electrode 16, are incident on the time-of-flight mass spectrometer tube 1, are reflected by the ion reflector 30, and are incident on the detector 10.

The ion reflector 30 reduces variations in flight time due to a difference in initial velocity of ions emitted from a sample. The energy of the ions accelerated by the electric field is constant regardless of the mass of the ions. Accordingly, ions having a larger mass have lower velocities and a longer time to fly in the time-of-flight mass spectrometer tube 1. From this, the mass of the ions can be determined by measuring the difference between the time when the sample 8 is irradiated with the laser light and the time when the ions enter the detector 10.

In Japanese Patent Application Laid-Open Nos. 9-304343 and 63-146339, ions are reflected by an ion reflector 30 and then travel straight to be incident on an ion detector 34. That is, this ion detector 3
Reference numeral 4 denotes a space provided between the time-of-flight mass spectrometer tube 1 and the sample 8. Providing this space increases the size of the device.

[0006] Therefore, in order to eliminate this interval, the detector may be installed away from the sample chamber. For example, a method called “post-stage acceleration” described in Katsumi Ura “Electron / Ion Beam Optics” (Kyoritsu Shuppan) can be considered. This is a method of attracting ions to the detector 10 by applying a high voltage to the detector 10 as shown in FIG. This method uses a bending angle φ1 of the ion orbit.
Can not be less than 90 °, it is difficult to install the detector 10 away from the sample chamber 20.

[0007]

In recent years, semiconductor wafers have become 12 inches in diameter, and a large sample container is required to analyze foreign substances and contaminants attached to the surface without breaking the diameter. is there. Further, it is necessary to provide a microscope or the like for enlarging and observing the analysis site on the sample. However, in the above-described conventional technology, ions emitted from the ion reflector travel toward the sample, and the ion detector 34 interferes with the sample, the microscope, and the like.

To prevent these problems, there is a method of increasing the distance between the sample chamber and the time-of-flight mass spectrometer tube 1. However, this causes an increase in the size of the apparatus, and the apparatus cannot be placed in a room with a low ceiling, or the apparatus cannot be installed. The weight is large and maintenance is troublesome.

Therefore, it is conceivable to dispose the detector 10 away from the sample chamber. However, it is difficult to achieve this object by the conventionally used post-acceleration method.

In the conventional mass spectrometer, there is no means for adjusting the trajectory so that ions are incident on the detector.

A first object of the present invention is to provide a small mass spectrometer for analyzing the surface of a large sample.

It is a second object of the present invention to provide a means for adjusting ions to be incident on a detector.

[0013]

According to the present invention, in order to solve the above-mentioned problems, a post-reflection electrode is provided on an ion orbit to guide ions emitted from the ion reflector 30 to the detector. This electrode applies a potential difference between two plates, and the plate on the side through which ions pass is a mesh plate. The trajectory of ions can be adjusted by changing the potential difference.

In addition, the spacing between the nets and the thickness of the net are optimized so as to reduce the reduction in the ion intensity due to the provision of the electrodes. In addition, an ion lens is provided between the latter-stage reflective electrode and the detector in order to facilitate the adjustment of the ion trajectory, so that the ions are focused on the detector.

FIG. 1 shows the configuration of a laser mass spectrometer provided with a rear-stage reflecting electrode 40. As shown in the figure, the detector 10 is set away from the sample chamber 20, and the ion trajectory is drawn toward the detector 10 by the rear-stage reflection electrode 40.

FIG. 2 illustrates the operation of the rear-stage reflection electrode 40. The structure of this electrode was considered by comparing three types of FIGS. 2 (a) to 2 (c). Figure 2 (a) shows the "time of flight mass spectrometer" written by Shigeo Hayakawa (J. Mass Spectroscop).
y. Soc. Jpn., Vol.41, No.3, 1993, pp.121-154), using a sector electric field. In this method, a voltage is applied between two arc-shaped electrodes 39a and 39b, and ions fly on equipotential lines. This method
Since the trajectory of the ions is determined by the shapes of the electrodes 39a and 39b, the trajectory of the ions cannot be easily changed, which does not meet the purpose of the present invention.

FIG. 2 (b) shows a method of drawing a high voltage to the ion detector 10 to generate an electric field E by applying a high voltage to the ion detector 10 and drawing the ions toward the detector 10 by the post-acceleration method described in the prior art. is there. This method uses the bending angle φ of the ion orbit.
1 cannot be set to 90 ° or less, and it is difficult to install the detector 10 away from the sample chamber 20.

FIG. 2 (c) is a diagram showing the principle of the rear reflective electrode used in the present invention. This is two plate-like electrodes 40
When a constant voltage is applied to a and 40b, ions move on a parabolic orbit. Reference numeral 21a denotes the trajectory of the ions from the ion reflector to the subsequent reflection electrode, and reference numerals 21b and 21b 'denote the trajectories of the ions emitted from the rear reflection electrode. The trajectory of the emitted ions depends on the voltage applied to the electrodes.
Translates like b '. The voltage that causes the trajectory of the ions to reach the detector surface can be obtained by the following calculation.

The point where the extension lines of the ion trajectories 21a and 21b intersect is denoted by O, the position where the ions are incident on the latter reflection electrode is A, the position where the ions are emitted from the latter reflection electrode is B, and the vertex of the parabolic trajectory is P. Assuming that the foot of the perpendicular dropped from the points O and P to the electrode 40a is Q, the ion trajectory is symmetric with respect to the straight line OQ. Let the initial velocity of the ions be V0, the angle of incidence on the subsequent reflection electrode be φ1, and the electric field between the electrodes 40a and 40b be E. At the point P, the Z component of the velocity becomes 0, so the time t1 required for the ions M to travel from the point A to the point P is as follows.

[0020]

(Equation 1)

The distance Z0 from the point O to the electrode 40a;
The length X1 of AQ and BQ is

[0022]

(Equation 2)

[0023]

(Equation 3)

## EQU1 ## From Equation 1

[0025]

(Equation 4)

## EQU1 ## This can be rewritten as a relational expression between the initial energy E0 (eV) of the ion M, the voltage E1 between the electrodes, and the electrode interval S as follows.

[0027]

(Equation 5)

Thus, the voltage E1 between the electrodes is obtained as follows.

[0029]

(Equation 6)

X1 is determined as follows from Equation 3.

[0031]

(Equation 7)

As described above, it is possible to adjust the ions to reach the detector only by adjusting the applied voltage from outside the vacuum vessel without moving the electrodes inside the vacuum vessel.

Here, it is necessary that the electrode 40a has a structure in which an ion passage hole is formed at the position where the ions enter and exit, or a mesh plate. In the case of an electrode having an ion passage hole, since the region through which ions pass is limited, it is difficult to adjust the trajectory by changing the voltage described above. Further, the ion beam entering the rear-stage reflection electrode 40 from the ion reflector has a certain degree of spread, and there is a problem that if the hole is made large in order to efficiently pass the ion beam, the lens action becomes large. On the other hand, when the electrode 40a is a mesh plate, the lens action does not increase so much because the meshing lens action cancels each other. Therefore, in the present invention, the plate electrode 40a is formed as a mesh plate.

Further, since the lens function remains even when the mesh plate electrode is used, the emission angle of the ion beam is widened to some extent. Therefore, an ion lens is provided between the rear-stage reflective electrode 40 and the detector 10 so that ions are focused on the detector 10.

By the way, considering the spread of the ion beam, the reflection efficiency at the latter reflecting electrode is also affected by the ratio between the line spacing and the line thickness of the net. If the thickness of the mesh line is w and the spacing between the meshes is M, the rate at which ions pass through the mesh is

[0036]

(Equation 8)

Is as follows. The reason for squaring is that ions pass through the net twice at the time of incidence and at the time of emission. In the present invention, the ratio of passing ions is set to 90% or more. Calculating this,

[0038]

(Equation 9)

## EQU1 ## We decided to use a net that could be mechanically machined within this range.

From the above description, after the rough design of the electrode was performed, the computer simulation of the ion trajectory was performed in order to perform the detailed design in consideration of the effect of the lens action by the mesh plate. The software is MAGNA /
DENBA was used. Since the lens action of the mesh plate increases as the ratio between the electrode interval S and the mesh line interval M increases, the calculation was performed with various values of M / S.

[0041]

(Embodiment 1) FIG. 1 shows an apparatus configuration of Embodiment 1 of the present invention. 1 is a time-of-flight mass spectrometer, 2 is a sample, 3 is a laser light source, 5 is an objective lens, 6 is a mirror with a through hole, 8 is an ion extraction electrode, 9 is an ion reflector, 10 is an ion detector, and 11 is deflection. Electrodes, 20 is a vacuum vessel, 21 is an ion orbit, 40 is a rear reflection electrode, and 41 is an ion lens. FIG. 3 shows details of the rear-stage reflection electrode 40 and the detector 10.

The laser light emitted from the laser light source 3 is reflected by the mirror 6 having a through hole, and is focused on the sample 2 by the objective lens 5. The ions generated by this irradiation are accelerated by the ion extraction electrode 8 and guided to the time-of-flight mass spectrometer 1.
The deflection electrode 11 changes the traveling direction of ions to the ion reflector 9.
It is adjusted to face. Ion reflector 9
Are reflected by the rear-stage reflection electrode 40, converged by the ion lens 41, and detected by the ion detector 10. The time from the laser oscillation until the ions reach the detector 10 is measured, and the mass is determined based on this time.

The length L of the time-of-flight mass spectrometer 1 is 500
mm. Here, as described in the above-mentioned document by Hayakawa, the angle of incidence θ of ions to the ion reflector 9 is described.
When 1 is increased, the mass resolution decreases. Therefore, θ1
Is selected so that the deflection electrode 11 and the rear-stage reflection electrode 40 do not physically interfere with each other.

The detector 10 has a tilt φ0 of 60 with respect to the time-of-flight mass spectrometer 1 so as not to interfere with the sample chamber 20.
°. From now on, the angle φ1 at which the ions are bent by the rear reflective electrode 40 is

[0045]

(Equation 10)

Is as follows. That is, the angle of incidence of the ions on the rear reflective electrode 40 is φ1 / 2, that is, 31.5 °. However, since the above-mentioned θ1 is 3 °, the inclination θ2 of the ion trajectory toward the rear-stage reflection electrode 40 with respect to the vertical line is 3 °, and the electrode is calculated from these and the electrode is φ = 28.5 ° with respect to the horizontal plane. It was installed at an angle.

FIG. 4 is an enlarged view of the rear-stage reflection electrode 40.
4A, 4B, and 4C are an external view of the electrode 40a, an external view of the electrode 40b, and an assembly view of both electrodes, respectively. In FIG. 4C, reference numeral 40c denotes a pillar of the insulator, and reference numeral 40d denotes a stand. The mesh of the electrode 40a was formed by etching, the interval M between the mesh lines was 2 mm, and the thickness w of the mesh line was 30 mm, which was the minimum limit that could be manufactured by etching. From this, the ratio of the thickness of the mesh line to the size of the mesh is 0.015.
From this, the ion passing efficiency was determined as follows as the probability that neither incidence nor reflection would collide with the net.

[0048]

[Equation 11]

From this, the passing efficiency of the ions is 97%, and the reduction of the ionic strength is hardly a problem.

The ion energy E0 was 3.5 kV. In order for the ions to be reflected by the rear-stage reflective electrode, the voltage E1 between the electrodes must be set to a value larger than E0, and a margin for adjustment is necessary for E1 in consideration of adjusting the ion trajectory.

In this embodiment, E1 is set to 4 kV. FIG.
(A) shows the reflection angle from the rear-stage reflection electrode 40 and the electrode interval S
Is 18 mm, that is, the ratio M / S between the mesh line spacings M and S is 1
This is the result calculated for the case of / 9. The horizontal axis indicates the distance from the center of the mesh line to the ion incident position, and the vertical axis indicates the reflection angle. The difference R between the maximum value and the minimum value of the reflection angle is 4.9 °
It became.

Similarly, for various values of M / S, the result of calculating the difference R between the maximum value and the minimum value of the reflection angle is shown in FIG.
(B). From this, the spread angle of the emitted ions is set to 5
° or less, M / S was decided to be 1/9 or less. Further, in consideration of the function as the reflective electrode and the variable applied voltage E1 between the electrodes, the electrode interval S shown in FIG. 2C must be longer than the ion penetration depth Z1. Therefore, the electrode interval S of the present apparatus was set to 9 times the mesh interval, that is, 18 mm. Further, by substituting these values into Equation 7, the distance Z0 from the point O to the electrode 40a is set to 21.
mm.

The spread of the above ions is detected by the detector 1.
In order to converge to one point on zero, an ion lens 41 was provided in front of the detector. In the present embodiment, an Einzel lens as shown in the figure was considered. The voltage of the electrodes 41a and 41c is the same as that of the electrode 40a of the rear reflective electrode, and the voltage of the electrode 41b is the distance between the rear reflective electrode 40 and the principal point of the Einzel lens and the distance between the principal point of the Einzel lens and the detector 10. Were both set to 30 mm. The voltage of the electrodes 41a and 41c is the same as that of the electrode 40a of the rear reflection electrode 40,
The simulation result of the ion trajectory when the voltage of b is 950 V is shown in FIG. This became a trajectory converging on the detector 10. This can eliminate the loss of ionic strength due to the provision of the rear reflective electrode.

As described above, the detector 10 can be placed at a position distant from the sample container 20 as shown in FIG. 1, and a large sample can be measured. Further, the size of the device can be reduced.

(Embodiment 2) FIG. 3B shows an embodiment 2. In the present embodiment, the ion lenses 41a to 41c have a triple cylindrical structure. This is characterized in that the electrode 41a functions as a shield as compared with the first embodiment, so that there is no electric field interference between the ion lens and the outside thereof. The voltage applied to the electrodes 41a and 41c is the same as that of the electrode 40a of the rear reflective electrode, and the simulation result of the ion trajectory when the voltage of the electrode 41b is 0V is shown in the figure. This is Example 1
Similarly, the trajectory converged on the detector 10. This can eliminate the loss of ionic strength due to the provision of the rear reflective electrode.

(Embodiment 3) FIG. 3C shows an embodiment 2. In this embodiment, the rear-stage reflecting electrode has the same structure as that of the first embodiment, and the emission angle of ions from the ion reflector is 4.5 °.
Is the case. In this case, the voltage applied between the electrodes is 4
When the voltage is set to kV, no ions are incident on the detector unlike the ion trajectory 21b 'in the figure. Therefore, by setting the voltage to 6 kV, the ion trajectory is made to enter the ion lens as indicated by 21b, and the ion trajectory is bent by the ion lens so that ions enter the detector 10. As described above, in the present invention, by using two plate electrodes as the rear-stage reflection electrode, it is possible to easily adjust the ions to enter the detector.

Example 4 FIG. 6 shows a spectrum obtained by measuring a TiN film on a wafer by this apparatus. From the figure, T
It turned out that the isotope of i and TiN can be measured. Thus, the present apparatus can perform spectrum measurement with the same sensitivity as that of a conventional mass spectrometer.

[0058]

As described above, according to the present invention, by bending the trajectory of the ions incident on the detector, the detector is prevented from interfering with the sample, and the large-diameter sample is placed on the sample stage as it is. , The surface can be observed, and mass spectrometry at that location can be performed. Further, the size of the device can be reduced. Further, it is possible to easily adjust the trajectory of the ions incident on the detector.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a mass spectrometer according to a first embodiment.

FIGS. 2A to 2C are characteristic diagrams showing the principle of a rear reflective electrode.

FIGS. 3A to 3C are enlarged views of a rear-stage reflection electrode.

FIGS. 4A, 4B, and 4C are an enlarged view and a perspective view of a rear reflective electrode.

FIGS. 5A and 5B are characteristic diagrams showing calculation results of a spread angle of ions by a rear-stage reflection electrode. FIGS.

FIG. 6 is a waveform chart showing an example of measuring a TiN film.

FIG. 7 is a configuration diagram of a conventional mass spectrometer.

FIG. 8 is a configuration diagram of a conventional mass spectrometer.

[Explanation of symbols]

1 time-of-flight mass spectrometer, 2 sample, 3 laser light source, 5 objective lens, 6 mirror with through hole, 7 sample base,
8a: an ion extraction electrode; 8b: an electrostatic ion lens;
9 ... Reflectron, 10 ... Ion detector, 13 ... Sample stage scanning mechanism, 14 ... TV camera, 20 ... Vacuum container, 21
... Ion orbit, M1, M2, M3 ... Semi-transparent mirror.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masanori Sakimoto 5-20-1, Josuihoncho, Kodaira-shi, Tokyo F-term in the Semiconductor Division, Hitachi, Ltd. 5C038 FF04 FF07 FF10

Claims (5)

[Claims] 1. A sample container, means for enlarging and observing a sample, means for ionizing an observed part, means for extracting the ions from the sample surface, an ion reflector for reflecting the ions, A mass spectrometer comprising a detector and measuring the mass of ion particles from the flight time of ions reaching the detector from the sample surface, providing two electrodes consisting of a net plate and a flat plate in the inertial flight trajectory of the ions, A mass spectrometer characterized by bending the ion trajectory toward the detector. 2. The mass spectrometer according to claim 1, wherein the thickness of the mesh constituting the mesh plate is not more than 0.03 times the interval between the meshes. 3. The mass spectrometer according to claim 1, wherein an electrode interval S of said parallel plate electrodes and a line interval M of said net satisfy the following relationship. M ≦ 9S 4. The mass spectrometer according to claim 1, wherein an ion lens is provided between said detector and said electrode. 5. The mass spectrometer according to claim 4, wherein said ion lens is fitted with a plurality of cylindrical electrodes of different diameters.
A mass spectrometer characterized in that the outermost electrode shields other electrodes.