JP2001066287A - Measuring apparatus for interface potential - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a measuring apparatus in which a silicon substrate is scanned two-dimensionally by a very thin electron beam, in which high-resolution two-dimensional information at a submicron level can be obtained and in which a high-resolution two-dimensional image is obtained. SOLUTION: In the upper part of the vacuum case 1 of an electron microscope, an ion sensor 2 in which a sensor face 7 responding to ions is formed on the surface of a high-resistance silicon substrate 5 is arranged in such a way that the sensor face 7 is directed upward to the side of the air. An electron- beam irradiation part 3 is installed on the lower side of the silicon substrate 5 inside the vacuum case 1. An electron beam 19 which is generated in the electron-beam irradiation part 3 is irradiated while it is being scanned two- dimensionally on the bottom side of the silicon substrate 5. As a result, a potential in the interface between a solution 9 which is installed so as to come into contact with the sensor face 7, and the sensor face 7 is taken out as an interface potential signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interfacial potential measuring device for measuring a potential distribution at an interface between a solution and a solid (solution / solid interface).

[0002]

BACKGROUND OF THE INVENTION An electron beam or an ion beam generated by the impact ionization effect when an electron beam collides with a gaseous body is:
The use forms are divided into a form using a single beam and a form using a beam scanning in the X and Y directions, such as an electron beam of a cathode ray tube of a television. There are various analysis methods such as electron microscope and SIMS (secondary ion mass spectrometer) based on the radiant energy and beam diameter of the beam by irradiating the sample surface to analyze the interface of the substance.

By the way, the electron beam can be easily reduced to a beam diameter of 0.1 to 1 μm or less by using an appropriate electronic device, and a high spatial resolution can be obtained. The irradiation position of the electron beam can be easily controlled by the action of an electric field and a magnetic field. Furthermore, a potential change on the sample surface can be detected by detecting secondary electrons generated when the measurement object (sample) is irradiated with the electron beam.

[0004] One of the techniques for observing a semiconductor using a scanning electron microscope (SEM) includes, besides using secondary electrons, reflected electrons, and absorbed electrons as signals, an electron electromotive force image (El).
Electromagnetic Force Image or Electron Beam Induced Current Image (Electron Beam)
m Induced Current Image).

[0005] The electron electromotive force image or the EBIC image will be described. When an object is irradiated with an electron beam, some of the incident electrons lose energy inside the sample and become an absorption current. In the process, it interacts with the crystal electrons and causes an avalanche phenomenon. The electron-hole pairs generated by the electron avalanche are drawn into the p region and the n region by the potential gradient of the pn junction.

If the pn junction is short-circuited externally to form a closed circuit, a large current flows and an electromotive force is generated in the portion irradiated with the electron beam. An electromotive force is generated that reaches the quasi-Fermi level of the electron-hole pair near the part. The electromotive force or current is extracted to the outside, and an image created as an amplified SEM video signal is called an electronic electromotive force image or an EBIC image.

FIG. 4 shows a schematic configuration of an apparatus used for observing the EBIC image. In FIG.
an n-junction semiconductor substrate, 42 is a p-region, 43 is an n-region,
44 is a space charge layer between them. A secondary electron detector 45 detects a secondary electron 47 generated when the electron beam 46 accelerated by an acceleration mechanism (not shown) is applied to the p region 42. 48 is a bias power supply for applying a bias voltage to the semiconductor substrate, 49 is a bias resistor,
50 is a capacitor. 51 is a computer having an image processing function, and 52 is a color display. An amplifier 53 amplifies the output of the secondary electron detector 45.

In the observation of the EBIC image by the above-mentioned apparatus, there is a case where no bias voltage is applied, and for example, a slip surface existing in the semiconductor 41 can be obtained up to a detailed structure. The probe current used for EBIC image observation can be on the order (10 ⁻¹¹ A or less) during normal SEM observation, but the acceleration voltage needs to be set appropriately according to the depth of the detection site.

[0009]

Generally, in physical property measurement at a material interface, the beam diameter of the measurement probe light directly determines the measurement target range. The high level and high accuracy of the analysis technique is crucial when the measurement target is a very small area. The probe light is required to have a very small beam diameter from the viewpoint of resolution and the like. When using laser light, the beam diameter should be reduced to 1 μm or less regardless of whether the light is visible light or ultraviolet light. Is extremely difficult, and the wavelength of light itself is limited. Therefore, as a probe light, an ultraviolet laser or an X-ray laser is a limit, but a laser is not yet generally used at present.

When the electron beam probe light is narrowed down by the optical system, the wavelength is shorter than the beam diameter of the laser light. For this reason, in the case of performing scanning by a conventional electron beam, the beam diameter is reduced to the limit of the order of Å in a high vacuum, but the beam scanning apparatus has become extremely expensive.

On the other hand, for example, Japanese Patent Application Laid-Open No. H10-153
As disclosed in Japanese Patent Application Laid-Open No. 575/575, in order to measure the ion concentration in a solution, Si ₃ N
There is an electron beam scanning type two-dimensional concentration measuring device provided with a sensor having a ₄ (or Ta ₂ O ₃ ) / SiO ₂ / Si structure.

However, in the device disclosed in the above publication, since a non-high-purity silicon substrate having a normal specific resistance is used as the sensor substrate, the back surface of the silicon substrate (the surface opposite to the sensor surface) is used. Even if a fine electron beam is irradiated, there is a disadvantage that electrons do not reach the depletion layer and it is difficult to extract a signal reflecting an interface potential on the sensor surface of the silicon substrate surface. In order to eliminate such inconveniences, it is conceivable to make the electron beam irradiated portion of the silicon substrate thinner.However, under special conditions such as providing the silicon substrate so as to separate vacuum and atmospheric pressure, the silicon substrate is Extremely thinning is not preferable from the viewpoint of mechanical strength, and may cause leakage or breakage.

The present invention has been made in consideration of the above-mentioned matters, and an object of the present invention is to provide a new and useful interface potential measuring device using an electron beam similar to a conventional SEM.

[0014]

In order to achieve the above object, an interfacial potential measuring apparatus according to the present invention has a sensor surface responsive to ions formed on the surface of a high-resistance silicon substrate on the upper part of a vacuum case of an electron microscope. The ion sensor part is arranged such that the sensor surface faces the atmosphere side and upwards, an electron beam irradiation part is provided below the silicon substrate in the vacuum case, and the electron beam generated in the electron beam irradiation part is By irradiating the lower surface side of the silicon substrate while scanning it two-dimensionally, the potential at the interface between the solution provided in contact with the sensor surface and the sensor surface is taken out as an interface potential signal. 1).

In the above interface potential measuring device, the lower surface (back surface) of the silicon substrate is irradiated with an extremely fine electron beam so as to be scanned two-dimensionally. Can be obtained.

In the above-mentioned interfacial potential measuring device,
A secondary electron detector is provided on the lower surface side of the silicon substrate, secondary electrons generated when the silicon substrate is irradiated with an electron beam are detected by the secondary electron detector, and based on the output of the secondary electron detector. A secondary electron image may be obtained (claim 2). In such a case, information inside the silicon substrate can be obtained in addition to the two-dimensional information.

In the interface potential measuring device, a semiconductor position detector may be provided on the lower surface of the silicon substrate (claim 3). In such a case, it is possible to reliably detect the incident position of the electron beam. it can.

[0018]

Embodiments of the present invention will be described with reference to the drawings. First, FIG. 1 shows a first embodiment of the present invention.
1 schematically shows a configuration of an interfacial potential measuring device according to the embodiment, which is configured to measure a two-dimensional distribution of an ion concentration (for example, pH) of a solution or the like. That is, in FIG. 1, reference numeral 1 denotes a vacuum case in which the inside is held in a vacuum, and an ion sensor unit 2 is provided on an upper side thereof,
An electron beam irradiation unit 3 is provided on the lower side, and a space (including the electron beam irradiation unit 3) 4 below the ion sensor unit 2 is maintained in an appropriate vacuum state.

The ion sensor section 2 has a SiO ₂ layer 6 as an insulating layer on the upper surface of a silicon substrate 5 having a high purity (that is, a high resistance having a specific resistance of 30 kΩ · cm or more), and Si ₃ N ₄ as a sensor surface. The layer 7 is sequentially formed by a method such as thermal oxidation or CVD. The sensor surface 7 is formed so as to respond to hydrogen ions, and is arranged so as to face the atmosphere and upward. The thicknesses of the silicon substrate 5, the insulating layer 6, and the sensor surface 7 in the ion sensor section 2 are 0.5 to 1 μm, 100 to 1000, respectively.
{, 100-1000}. Reference numeral 8 denotes a cell which faces the sensor surface 7 and is provided so as to surround the sensor surface 7, and is configured to accommodate a liquid sample 9 such as a solution.

In FIG. 1, reference numerals 10 and 11 denote counter electrodes and reference electrodes provided in contact with the liquid sample 9 and are connected to a stabilizing bias circuit 16 of a potentiostat 14 described later. Reference numeral 12 denotes an ohmic electrode provided on the silicon substrate 5 for extracting a current signal.
A current-voltage converter 17 and an operational amplifier circuit 18 described later
Is connected to the stabilizing bias circuit 16 through the gate.

In FIG. 1, reference numeral 13 denotes a control box for controlling the ion sensor section 2, which is a potentiometer for applying an appropriate bias voltage to the silicon substrate 5 and extracting a signal obtained at that time as a current signal. It comprises a stat 14 and an interface board 15 for transmitting and receiving signals to and from the potentiostat 14. The potentiostat 14 is a current-voltage converter 1 that converts a current signal extracted from the stabilizing bias circuit 16 and the ohmic electrode 12 formed on the silicon substrate 5 into a voltage signal.
7 and an operational amplifier circuit 18 to which a signal from the current-voltage converter 17 is input.

The electron beam irradiator 3 irradiates the silicon substrate 5 with a sufficiently thin electron beam 19 from its lower surface while scanning it two-dimensionally. The filament 20, the Wehnelt cylinder 21, the anode 22, a condenser lens 23, a deflecting coil 24, an objective lens 25, etc., and have exactly the same configuration as that for electron beam irradiation in a normal SEM. 26 is a scanning power supply unit, and 27 is a variable magnification resistor.

Reference numeral 28 denotes a computer as a control / arithmetic unit having an image processing function. The computer 28 exchanges signals with the control box 13 to control the electron beam irradiating unit 3 and perform various controls and arithmetic operations. Reference numeral 29 denotes a display device such as a color display. Although not shown, the computer 28 includes an input device such as a keyboard and a mouse, and a memory device.

The case where the pH of a solution is measured using the above-structured interfacial potential measuring device will be described. A solution 9 is put into a cell 8 as a sample. Thereby, the sensor surface 7
Is in contact with the solution 9. Then, the counter electrode 10 and the reference electrode 1
Immerse 1 in solution 9.

In the above state, a DC voltage from the potentiostat 14 is applied between the comparison electrode 11 and the ohmic electrode 12 so that a depletion layer is generated on the silicon substrate 5, and a predetermined bias is applied to the silicon substrate 5. Apply voltage.
In this state, an alternating electron current is generated in the silicon substrate 5 by intermittently irradiating the silicon substrate 5 with the electron beam 19 from the electron beam irradiation unit 3. This electron beam 19
Is performed based on a control signal from the computer 28. The current is the pH of the solution 9 in contact with the sensor surface 7 at the point facing the irradiation point of the silicon substrate 5.
The pH value at this portion can be known by measuring the value,
The two-dimensional distribution of H is displayed on the screen of the display device 29.

As described above, in the interface potential measuring device having the above-described structure, the high-purity silicon substrate 5 having the sensor surface 7 formed on the upper surface thereof is two-dimensionally moved by the electron beam 19 emitted from the electron beam irradiation unit 31. Since irradiation is performed, a high-resolution two-dimensional image can be obtained.

FIG. 2 shows an interfacial potential measuring device according to a second embodiment of the present invention. In this embodiment, a secondary electron detector 30 is provided on the lower surface side of the silicon substrate 5.
Is configured to detect secondary electrons 31 generated when the silicon substrate 5 is irradiated with the electron beam 19, and to input the output to the computer 28. 31 and is displayed on the screen of the display device 29 of the computer 28 in a superimposed manner.

In FIG. 2, reference numeral 32 denotes an amplifier for amplifying the output of the secondary electron detector 30. Also, 3
Reference numerals 3 and 34 denote color CRTs. One color CRT 33 is provided with a camera 35 and the other color CRT 3 is provided.
4 is for visual observation.

The secondary electron information includes: (1) Measurement of carrier diffusion distance (2) Position of pn junction (3) Measurement of space charge layer width (4) Observation of defect in diffusion pn junction (5) MOS channel Observation of the formation process (6) Measurement of the surface degraded layer, etc., makes it possible to grasp the internal information in the depletion layer of the silicon substrate 5, so that it is possible to analyze the noise component when the interface information is continued, and to correct the interface information. Can be used.

By the way, one of the semiconductor detectors is a position detector (Position Sensit) utilizing the fact that the output current is different depending on the incident point of the incident electrons.
live Device). FIG. 3 shows an example in which this position detector is provided on the lower surface side of the silicon substrate 5.
That is, in FIG.
A semiconductor position detector for detecting a beam position is provided on the lower surface of the semiconductor device, and one of the semiconductor position detectors 36 is configured to also function as an ohmic electrode. In the interface potential measuring device configured for this purpose, the incident position of the electron beam 19 incident on the silicon substrate 5 can be reliably grasped.

Although the vacuum case 1 is not shown in FIGS. 2 and 3, it goes without saying that the vacuum case 1 is provided similarly to the case shown in FIG.

The present invention is not limited to the above embodiment, but can be implemented in various modifications.
For example, the sensor surface 7 may be formed of Ta ₂ O ₃ , and the sensor surface 7 may be modified with an appropriate responsive substance so as to respond to other ions such as Na and Ca. You may.

The counter electrode 10 and the reference electrode 11 may be made flush with the sensor surface 7 so as to eliminate the influence of the positions of the counter electrode 10 and the reference electrode 11 (position dependence). That is, the counter electrode 10 is formed by shaving the Si ₃ N ₄ layer serving as the sensor surface to a predetermined depth by etching or the like, sputtering platinum on the cut portion, and having the same height as the other portions of the Si ₃ N ₄ layer 7. The reference electrode 11 is formed by shaving the Si ₃ N ₄ layer 7 to a predetermined depth by etching or the like, sputtering platinum on the shaved portion, electrodepositing silver thereon, and further chlorinating. By performing silver treatment, the Si ₃ N ₄ layer 7 is formed to have the same height as other portions.

The semiconductor position detectors 36 and 37 for beam position detection may be provided in the interface potential measuring device shown in FIG.

[0035]

According to the interface potential measuring apparatus of the present invention, since the silicon substrate is two-dimensionally scanned by an extremely thin electron beam, it is possible to obtain high-resolution submicron-level two-dimensional information. A two-dimensional image with high resolution can be obtained.

According to the second aspect of the present invention,
In addition to the two-dimensional information, information inside the silicon substrate can also be obtained, and the two-dimensional information can be appropriately corrected.

Further, according to the third aspect of the present invention, the incident position of the electron beam can be reliably detected.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of an interface potential measuring device according to a first embodiment.

FIG. 2 is a diagram schematically illustrating a configuration of an interface potential measuring device according to a second embodiment.

FIG. 3 is a diagram schematically showing a configuration of an interface potential measuring device according to a third embodiment.

FIG. 4 is a diagram for explaining a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum case, 2 ... Ion sensor part, 3 ... Electron beam irradiation part, 5 ... Silicon substrate, 7 ... Sensor surface, 9 ... Solution, 19
... Electron beam, 30 ... Secondary electron detector, 31 ... Secondary electron, 3
6, 37 ... Semiconductor position detector.

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Claims (3)

[Claims] 1. An ion sensor unit having a sensor surface responsive to ions formed on the surface of a high-purity silicon substrate is disposed on the upper part of a vacuum case of an electron microscope such that the sensor surface faces the atmosphere and upward. An electron beam irradiator is provided below the silicon substrate in the vacuum case, and the lower surface side of the silicon substrate is irradiated with an electron beam generated by the electron beam irradiator while scanning the lower surface of the silicon substrate two-dimensionally. An interfacial potential measuring device wherein an electric potential at an interface between a solution provided in contact with the surface and the sensor surface is taken out as an interfacial potential signal. 2. A secondary electron detector is provided on a lower surface side of a silicon substrate, and secondary electrons generated when the silicon substrate is irradiated with an electron beam are detected by the secondary electron detector. 2. The interfacial potential measuring device according to claim 1, wherein a secondary electron image is obtained based on an output of the container. 3. The interface potential measuring device according to claim 1, wherein a semiconductor position detector is provided on a lower surface of the silicon substrate.