JPH03210470A - Material surface inspection method and device - Google Patents

Abstract

PURPOSE:To measure a local corrosion state in the atmosphere by a method wherein an object to be measured is scanned while the distance between a reference electrode and the object to be measured is kept constant and the work function of a minute part is measured and the local state change of the object to be measured is known from the measuring result. CONSTITUTION:A reference electrode 1 is mounted to a piezoelectric element 8 movable in three directions X, Y, Z in order not only to measure a work function but also to finely adjust the position of the electrode 1 by vibrating the electrode 1. In order to prevent the generation of stray electric capacity between an object 2 to be measured and the reference electrode 1, the reference electrode 1 is adjusted by an X-Y-Z axis stage 3 so that the distance between the measuring surface of the reference electrode 1 and the object 2 to be measured becomes 1/5 of the diameter of the measuring surface of the cylindrical reference electrode 1 or less to perform measurement. By this method, the surface state of the object 2 to be measured opposed to the measuring surface of the reference electrode 1 can be accurately grasped. By this constitution, the deterioration generating position and deterioration state of a material locally deteriorated in the atmosphere by corrosion can be measured.

Description

[Detailed description of the invention] [Industrial application field] The present invention detects material deterioration due to atmospheric corrosion, etc.

This invention relates to a method for detecting local state changes on the surface of a material due to adsorbed substances, etc., and a measuring device therefor.

[Conventional technology]

Electronic products use various metals and semiconductors for signal transmission and recording.

Since these products are used in various environments, corrosion occurs due to the action of moisture contained in the atmosphere, corrosive gases such as sow, dust, and fine particles such as NaCl2. Most of the metals and semiconductors used in these products are thin films, so even the slightest amount of localized corrosion can cause product defects. Therefore, in order to maintain and manage the reliability of electronic products, it is necessary to establish a technique for evaluating the corrosion of materials used in these products in the atmosphere. Furthermore, since corrosion in the atmosphere often originates from locally adsorbed substances or condensed water on the material surface, we will establish evaluation technology for locally adsorbed substances or condensed water on the material surface. It is necessary.

Techniques for monitoring the overall atmospheric corrosion rate of metal materials include, for example, as described in Japanese Unexamined Patent Publication No. 63-83659, metal plates are laminated with an insulator interposed therebetween, and the corrosion resistance of electrodes is measured. A method of determining the corrosion rate of metal by electrochemically measuring the corrosion current flowing between electrodes is known. In addition, techniques for monitoring local corrosion of metal materials include, for example, as described in Japanese Patent Application Laid-open No. 60-233540, in which a method is used to maintain a constant distance from the metal surface in the perpendicular direction to the metal surface in an aqueous solution. , the electrode is connected to the X-Y along with the Z-axis positioning sensor.
- A known method is to attach it to a Z-axis stage, scan in the X-Y directions, measure the potential difference, convert the obtained potential difference into current density, and determine the corrosion rate.

[Problem to be solved by the invention]

The conventional method described above has the following problems.

That is, techniques for measuring the overall corrosion rate of metal materials in the atmosphere and techniques for measuring the local potential and corrosion rate in an aqueous solution are known, but the local corrosion state in the atmosphere is well known. It was difficult to measure the violet.

As described above, the conventional method has a vlA problem in that there is no method for evaluating local corrosion of materials in the atmosphere, which is the environment in which electronic products and the like are actually used.

One object of the present invention is to provide a method for measuring the location and state of deterioration in a material that has locally deteriorated due to corrosion or the like in the atmosphere.

Another object of the present invention is to provide a method for measuring the location and state of local state changes due to adsorbed substances, condensed water, etc. on the surface of a material.

Still another object of the present invention is to provide a measuring device that measures local state changes on the surface of a material.

[Means to solve the problem]

The above purpose is to first use a cylindrical microelectrode with a smooth measurement surface as a reference electrode for measuring minute parts, and to use that reference electrode to measure the distance between the reference electrode and the object to be measured. It scans the object to be measured while keeping it constant and measures the work function of a minute part.

This is achieved by knowing the local state changes of the object to be measured from the results.

[Effect]

The work function is the energy required to extract one electron from a solid containing N electrons and transport it to an infinite distance.

This work function φ is $ = −(Es−Ex−i)=(δE/a
N)t=-fi...(1) This is equivalent to the chemical potential μ, which serves as a guideline for the progress of a chemical reaction, with the equal sign changed.

Furthermore, this work function also changes when a substance is physically adsorbed onto the solid surface, so by measuring the work function, it is possible to know the state of chemical and physical changes on the solid surface.

When considering a system in which an aqueous solution of M" ΔG=ΔGNaP+ΔG501v ten knee-(-qC□/
, )=O...(2) It is expressed as follows. Here, ΔG'' is the free energy change due to vaporization of M, ΔG50IV is the free energy change due to solvation of M ions, ■ is the ionization potential, q is the electric charge, and El
/ is the electromotive force of M/M+half cell, i.e. -(-q E
sh ) is the free energy change due to the transition from the electrostatic potential just outside the free surface of the solution to the Fermi level of M. In addition, the electromotive force of the half cell is expressed by the electrostatic potential difference V between the surface of M in contact with the water film and the solution and the work function φ, as follows: 61 μ = ■ − φ (3), so (2) and ( From the formula 3), the electromotive force of the half cell is 6t/, =V-m= -(AG"'-1aG"1v+
IJ/q...(4)

When the object to be measured M and the reference electrode R are connected and the Fermi levels of M and R are equal, VM-φ-=VR-φR φA: VMR+φR (5). Here, VOR (: VM - VR) is the contact potential difference between the object to be measured and the reference electrode. If the work function φR of the reference electrode in air is known, the work function φH of the object to be measured can be determined by measuring the contact potential difference VMR.

One of the methods for measuring work function is the Kelvin method. This is because when the measurement surface of the object to be measured faces parallel to the measurement surface of the reference electrode and connects the two with a conductive wire, a contact potential difference is created between the two, and a capacitor made up of the two conductor surfaces is charged. is induced. When an external voltage VEX is applied between the object to be measured and the reference electrode, an induced charge Q
is given by the following equation.

Q:C(VMR-V+:x)=C((φx-$R)/
(1-VEX) (6) If the external voltage VEX is adjusted to find a point where the charge Q becomes zero, then vEx=vMR. From this measurement result and the work function φR of the reference electrode determined in advance, the work function φR of the object to be measured can be determined using equation (5).

〔Example〕

The present invention will be explained below using examples.

FIG. 1 is a block diagram of the apparatus of the present invention. The cylindrical reference electrode 1 has a smooth measurement surface and is attached to one end of a reference electrode pedestal 9. The reference electrode is preferably made of, for example, Au, whose work function value is not easily affected by changes in temperature, humidity, or atmospheric gas composition. And this reference electrode is
It is attached to a piezoelectric element 8 movable in two directions, x, y, and z, in order to vibrate the electrode and measure the work function, and to finely adjust the electrode position.

Next, the arrangement of the object to be measured and the reference electrode, and the measurement method will be described.

In order to prevent stray capacitance from occurring between the object to be measured and the reference electrode, the distance between the measurement surface of the reference electrode and the object to be measured is
Measurement is performed by adjusting the reference electrode using the x-y-z axis stage 3 so that the diameter of the cylindrical reference electrode is within 115 mm of the diameter of the measurement surface. This makes it possible to accurately grasp the state of the surface of the object to be measured facing the reference electrode measurement surface. The reference electrode arranged in this manner is vibrated by the oscillator 6, and the distance between the reference electrode and the object to be measured is periodically changed, thereby periodically changing the capacitance of the capacitor constituted by the reference electrode and the sample 2. Needless to say, when vibrating the reference electrode, the reference electrode must not come into contact with the sample. This causes a time variation in charge, i = d Q/ d t =
A current i expressed by (VMs-Vpx)dc/dt-(7) is caused to flow through the circuit. This current is amplified by a preamplifier 4 and phase-detected by a lock-in amplifier 5 to obtain a DC voltage proportional to the amplitude of the AC voltage. If this output is integrated by the integrator 7 and returned to the reference electrode, VMR-V
Feedback automatically operates so that Ex=O, and the DC output voltage VEX of the lock-in amplifier at this time is recorded. The opposite sign of this VEX is VMR. From the measured contact potential difference VMR1 and the work function φR of the reference electrode measured in advance, the work function φ of the object to be measured is determined from equation (5). Then, a computer-controlled x-y-
The work function distribution on the sample surface is measured by scanning the electrode in the X-Y direction using a z-axis stage and a piezoelectric element. Since the measured work function value reflects the state of the sample surface, differences in work function depending on the position may indicate material deterioration, defects, corrosion, or
The position and state of adsorbed substances, etc. can be clarified.

With this example, it is possible to locate local changes in state due to material deterioration, defects, corrosion, adsorbed substances, etc. on the surface of the measured object with a resolution approximately twice the diameter of the measurement surface of the reference electrode used. It is possible to detect the condition and provide an inspection means for maintaining and managing the reliability of the material.

Next, another embodiment will be described in which a method of mechanically vibrating the reference electrode without relying on a piezoelectric element is used as the vibration mechanism of the reference electrode. FIG. 2 is a configuration diagram of a measuring device using a mechanical vibration mechanism. The reference electrode 1 is attached to the tip of a reference electrode pedestal 9 attached to an electrode driver 10, and is driven by a signal from an oscillator 6. By periodically vibrating the reference electrode, the capacitance of the capacitor made up of the reference electrode and the object to be measured changes, causing current to flow through the circuit.

This current is phase-detected by the lock-in amplifier 5, and its output is fed back through the integrator 7, thereby determining the contact potential difference between the reference electrode 5 and the object to be measured, thereby making it possible to measure the work function. The electrode scanning mechanism is similar to the embodiment shown above.
According to this embodiment, which is a method using an X-Y-Z axis stage, it is possible to provide a measuring device that mechanically vibrates a reference electrode and measures a work function in a minute area.

Next, as a method for measuring the contact potential difference, another example will be shown in which the electrostatic potential difference is directly measured. FIG. 3 is a configuration diagram of a measuring device using an electrostatic potentiometer. The reference electrode 1 is attached to one end of the reference electrode pedestal 9. This reference electrode is scanned over a sample 2 placed on an X-Y-Z axis stage 3 controlled by a computer while keeping the distance therebetween constant. The potential difference generated between the reference electrode and the object to be measured is monitored by an electrostatic potentiometer 11, and a voltage is applied from an external power source 12 so that this potential difference becomes zero. The opposite sign of the voltage VEX applied by the external power source when the potential difference becomes zero is the potential difference VMR between the reference electrode and the object to be measured, and thereby the work function of the object to be measured can be measured.

According to this embodiment, the work function can be measured without vibrating the reference electrode, and a simple measuring device can be provided.

〔Effect of the invention〕

According to the present invention, by measuring the local work function of the object to be measured, the diameter of the reference electrode can be estimated using local state changes caused by corrosion, adsorbed substances, dew water, etc. in the atmosphere. Measurements can be made with twice the resolution, making it possible to evaluate local material deterioration in the atmosphere, which was previously impossible to evaluate.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a scanning type popular corrosion detection apparatus according to one embodiment of the present invention, and FIG. 2 is a block diagram of a scanning type atmospheric corrosion detection apparatus according to another embodiment of the present invention. FIG. 3 is a block diagram of a scanning type atmospheric corrosion detection apparatus which is still another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Reference electrode, 2... Sample, 3... x-y-z axis stage, 4... Preamplifier, 5... Lock-in amplifier, 6... Oscillator, 7... Integrator, 8... Piezoelectric element, 9... Reference electrode pedestal, 10... Electrode driver,
11... Electrostatic potentiometer, 12... External power supply. Figure 2

Claims (1)

[Claims] 1. By measuring the work function by scanning a reference electrode while keeping a constant distance from the object to be measured in the direction perpendicular to the surface of the object, A material surface inspection method characterized by determining differences. 2. The location of the object to be measured is determined by scanning the reference electrode in the atmosphere in the direction perpendicular to the surface of the object to be measured while maintaining a constant distance from the object to be measured and measuring the contact potential difference between the object to be measured and the reference electrode. A material surface inspection method characterized by determining differences due to 3. A material surface inspection method for determining differences depending on the location of the object to be measured using the measuring method according to claim 1 or 2. 4. A material surface inspection method for determining differences depending on the location of the object to be measured using the measuring method according to claim 1 or 2. 5. A material surface inspection method for determining differences depending on the location of the object to be measured using the measuring method according to claim 1 or 2. 6. A material surface inspection method for determining differences depending on the location of the object to be measured using the measuring method according to claim 1 or 2. 7. A measuring device for performing the measurement according to claim 1 or claim 2, comprising a reference electrode, a reference electrode driving device, a reference electrode position determining mechanism, and a phase detection device. 8. A measuring device for performing the measurement according to claim 1 or claim 2, comprising a reference electrode, a reference electrode positioning mechanism, and a potential difference measuring device.