JPH06123744A - High-temperature and high-humidity interatomic-force microscope and observation and quantifying method of chemical reaction - Google Patents

Abstract

PURPOSE:To achieve that a change in the morphology of a surface such as a corrosion phenomenon or the like caused under a high-temperature and high-humidity condition is observed on the spot by a method wherein a probe covered with a noble metal-based thin film and an actuator covered with a fluororesin and a glass-based molding material are used. CONSTITUTION:A probe 1 is covered with a Cr film in 5nm thickness by a sputtering method, and the Cr film is covered additionally with a Pt thin film in 5nm thickness. A probe-driving Z-axis actuator 4 covered with a fluororesin and a glass-based molding material and a sample-scanning X-Y positioner 3 are used. An amplifier 5 which is vacuum-sealed inside a ceramic package and a glass container receives a signal from a probe-displacement measuring system which detects a fluctuation in a force acting between the probe 1 and a sample 2, and it controls the actuator 4 so that the displacement of the probe 1 becomes definite. The probe-displacement measuring system is constituted of a laser semiconductor element 4 and a light-detecting CCD element 7 which have been vacuum-sealed in an antireflective glass container. The whole apparatus is installed inside a glass container 8 whose coefficient of thermal expansion is extremely small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a high temperature and high humidity type atomic force microscope (hereinafter referred to as "high temperature and high humidity type atomic force microscope" which enables in-situ observation of surface morphological changes due to scientific or physical changes such as corrosion phenomenon occurring under high temperature and high humidity. , AFM) and a method of observing and quantifying the chemical reaction thereof.

[0002]

2. Description of the Related Art AFM is a scanning tunneling microscope (hereinafter referred to as
A surface observation means derived from STM)
Similar to M, it is possible to observe the structure at the atomic level by observing the surface morphology on the order of microns. The STM uses the tunnel current flowing between the probe and the sample as the detection probe, and the AFM uses the minute force acting between the probe and the sample as the detection probe. S
The TM requires conductivity for both the probe and the sample.
The feature of the AFM compared with the STM is that the sample does not require conductivity, and is effective as a means for observing the surface structure of a substance having no electrical conductivity such as a dielectric. AFM is Na
noscope II (US Digital Instr.
option of STM manufactured and sold by Ument Inc. and OAFM (trade name of Olympus Optical Co., Ltd.)
Is already on the market. The AFM, which does not require conductivity for the sample to be inspected, is generally considered to be effective for observing the corrosion phenomenon because the corrosion product does not have electrical conductivity.

As described in the field of industrial application, the present invention relates to an AFM capable of in-situ observation of a corrosion phenomenon and the like occurring under high temperature and high humidity. Therefore, to observe the corrosion phenomenon, AFM
The necessity of applying is first explained. The tendency toward lightness, thinness, shortness, and miniaturization is prevailing throughout all industries, and particularly in the field of electronic devices, many thin film devices in which thin films of submicron to subsubmicron, so-called nanometer film thickness are laminated are commercialized. In such thin film devices, the extremely small amount of corrosion phenomenon that has been ignored in the past will determine the function and life of the entire device, and the establishment of technology to observe and quantify the extremely small amount of corrosion phenomenon that progresses on the nanometer scale. Is urgently needed.

Against this background of technological trends, corrosion,
It is a well-known fact that measurement and evaluation technology targeting chemical reactions on the surface such as oxidation and adsorption has been put to practical use.
Focusing on the quantification technology of micro-corrosion, a corrosion evaluation device has recently been proposed that uses a crystal unit as a mass sensor and detects the corrosion phenomenon that progresses on the surface of a thin film provided on the crystal unit in nanogram order. (For example, Japanese Patent Laid-Open No. 3-2
No. 06921). In addition, a thin film sample provided with a fine pattern is exposed to a high temperature and high humidity environment, and the amount of corrosion is quantified from the change in the electrical resistance of the fine pattern sample before and after the exposure (Katsuzumichi Tagami an).
d Hiroshi Hayashida: Corro
sion Rate Activation Ener
gy of Sputtered CoCr Perp
endical Media, IEEE TRAN
SACTIONS ON MAGNETICS, Vol
ume Mag-23, No. 5,1987, pp36
48-3650) has also been proposed.

[0005]

The disadvantages of the conventional trace corrosion detection techniques such as the crystal oscillator method and the fine pattern resistance method are
It is summarized in that it does not answer questions such as where on the surface, what kind of condition and how much corrosion has occurred. This question is an important technical issue that must be urgently answered for the reliability of electronic devices in which thinning progresses and corrosion in the early stage is becoming a problem. This problem arises from the fact that the conventional evaluation technique is not a technique that allows in-situ observation of the progress process of a phenomenon under a measurement environment.

Further, in the crystal oscillator method, the measurement time is limited to within 10 hours due to the restriction of the vibration stability of the oscillator, so that it is impossible to evaluate a material having good corrosion resistance and oxidation resistance. It has been pointed out that there is a drawback.

The fine pattern method is limited to a chemical reaction system in which the sample is electrically conductive, the reaction product is non-electrically conductive, and is uniform over the entire surface, and any one of these three conditions must be satisfied. If this is the case, it has the drawback that it cannot be applied.

Since AFM has atomic level resolution and can measure non-conductive substances, it is considered to be one of the extremely effective means for solving this point. However, quantification measurement of corrosion under high temperature and high humidity using AFM has not been done, and in-situ observation is important for further elucidation of corrosion phenomenon. In order to enable in-situ observation, it is necessary to operate the AFM in an environment where the temperature and humidity can be controlled. That is, the in-situ observation apparatus for corrosion by AFM is different from the ordinary AFM in room temperature atmosphere or vacuum.
It is necessary to operate in an extremely harsh operating environment for a measuring device that requires atomic resolution such as high temperature and high humidity. Therefore, there are the following four major technical problems to be overcome.

1) Probe under high temperature and high humidity, scanning probe
Suppress changes and deterioration of the drive system and its circuit system over time.

2) It is possible to prevent the laser semiconductor element and the photo-detecting CCD element, which are the displacement detecting system of the probe, from changing over time or deteriorating.

3) The movement of the observation position and the distortion of the observation image due to the non-uniformity of temperature and the temperature drift are suppressed.

4) The unevenness of the partial pressure of steam and the local dew condensation caused by the uneven temperature and the insufficient supply of steam are suppressed.

The commercially available AFM device described in the section of the prior art does not consider all of the above items 1) to 4), and the AFM image drifts due to the deterioration of the probe and the probe displacement measuring system. However, it becomes impossible to observe the AFM image.

Further, since chemical reactions such as oxidation and corrosion generally accompany volume expansion or contraction, it is said that the surface morphology and surface roughness change on the nanometer scale in the initial stage of the chemical reaction. If changes in the surface roughness, etc., can be accurately measured according to the progress of the chemical reaction that is the object of observation / measurement, it becomes possible to quantify the chemical reaction based on the change in the surface roughness over time, and the chemical reaction progresses. If the process can be observed in-situ under a certain environment, it is possible to provide a completely new in-situ observation method of chemical reaction different from the conventional observation means (XPS and Auger spectroscopy).

However, the conventional surface morphology observation and measurement apparatus, such as a scanning electron microscope and a stylus type surface roughness meter, have insufficient resolution to measure the nanometer level surface morphology change occurring in the initial stage of the chemical reaction. there were.

An object of the present invention is to provide a high temperature and high humidity type atomic force microscope and a method for observing and quantifying chemical reactions, which solves the above problems.

[0017]

Means for Solving the Problems Oxidation and corrosion of the probe surface, especially the tip of the probe under high temperature and high humidity makes it difficult to observe a stable AFM image. Therefore, in the present invention, a conventional AFM probe is coated with a Cr film of 5 nm, and a Cr film is further coated with a noble metal thin film such as Au or Pt to a thickness of 5 nm to oxidize the probe.
Prevented corrosion.

The Z-axis actuator for driving the probe and the XY positioner for scanning the sample were coated with a fluorine resin (film thickness 10 μm) and then further coated with a glass type molding material. As a result, invasion of water vapor was prevented and stable scannability was secured.

The preamplifier, which is the main part of the probe driving circuit system, is sealed in a ceramic package under vacuum, and then gold wires are connected to the terminals, and the glass container is evacuated in the same manner as a vacuum tube. Enclosed. The two-stage vacuum sealing suppressed the invasion of water vapor into the pre-amplification circuit and the excessive temperature rise, and ensured the stable operation of the probe drive circuit. Further, the laser semiconductor element and the photodetection CCD element were vacuum-sealed in a container made of non-reflective glass to prevent deterioration of these elements.

AFM has a coefficient of thermal expansion of 2 × 10 ^-8 (/ ° C)
And installed in a very small glass container. Diameter 12c
In a cylindrical glass container having a height of 15 cm and a height of 15 cm, there are provided 20 inlets for injecting air whose temperature and humidity are adjusted and 10 outlets for discharging, a total of 20 outlets. The fluctuation of humidity was suppressed. In addition, a small temperature / humidity sensor was installed in the glass container, the fluctuation of temperature and humidity depending on the position in the glass container was measured, and the amount of air sent to the inlet was adjusted so that this fluctuation was minimized. The air inflow amount is automatically adjusted by linking the information from the temperature and humidity sensor with an electromagnetic valve that adjusts the air amount. By making these improvements, AFM
The temperature fluctuation in the environment where the measurement is performed can be suppressed to ± 0.1 ° C. and the humidity fluctuation can be suppressed to within ± 1.0%, and the AFM measurement can be stably performed even under high temperature and high humidity.

In addition, in the method for observing and quantifying a chemical reaction of the present invention, the change in surface morphology or surface roughness of the sample with time is analyzed using a high temperature and high humidity atomic force microscope or an atmosphere controlled atomic force microscope. By measuring on a scale, it enables in-situ observation and quantification of chemical reactions.

[0022]

Since the AFM can measure the surface morphology with a resolution of about 0.1 nm, it is possible to detect extremely minute changes in the surface morphology and surface roughness in the initial stage of the chemical reaction. The high temperature and high humidity type atomic force microscope of the present invention has a temperature of 10
In an environment of 0 ° C or less and relative humidity of 90% or less, an atmosphere-controlled atomic force microscope enables AFM measurement under various gas atmospheres at a temperature of 100 ° C or less. By using these, the reaction process The progress of can be observed on the spot.

The functions of the respective means of the AFM of the present invention and the effects obtained by them will be described in detail in the section of Examples.

[0024]

EXAMPLES Examples of the present invention will be described. FIG. 1 is a block diagram of an embodiment of a high temperature and high humidity type atomic force microscope of the present invention. The high temperature and high humidity type atomic force microscope of the present embodiment operates in a high temperature and high humidity environment where the temperature is 100 ° C. or lower and the relative humidity is 90% or lower, and the temperature fluctuation is ± 0.1 ° C. and the relative humidity fluctuation is ±.
Coefficient of thermal expansion controlled within 1.0% 5 × 10 ^-8 (/ ° C)
It is installed in the following glass container 8. This high temperature and high humidity type atomic force microscope uses a probe 1 coated with a noble metal thin film, a Z axis actuator 4 for driving the probe coated with a fluorine resin and a glass molding material, and an XY positioner 3 for scanning a sample. Using a laser semiconductor device 6 and a photodetection CCD device 7 which are vacuum-sealed in a non-reflective glass container, a probe displacement measurement system is configured, and a ceramic package and a preamplifier for a probe drive circuit vacuum-sealed in a glass container are used. 5 is used.

The probe 1 is a conventional AFM probe in which a Cr film is coated to a thickness of 5 nm by a sputtering method, and a Pt thin film is further coated to a thickness of 5 nm on the Cr film by a sputtering method. C
Oxidation and corrosion of the probe 1 were prevented by coating with r and Pt. The Cr film was provided as an adhesion layer for suppressing peeling of the Pt thin film. The conventional AFM probe is processed from a Si substrate by a dry process, and lacks electrical conductivity. Therefore, the probe 1 and the sample 2 are easily charged with static electricity, and the static electricity causes an unobservable state. There are many. In the probe 1 used in the present invention, the electrical conductivity is ensured by the Pt film, so that it is possible to avoid the above-described state where the observation becomes impossible.

The sample 2 is fixed to an XY positioner 3 which scans the sample. The XY positioner was manufactured by combining piezoelectric elements, and in order to prevent the invasion of water vapor, it was coated with a fluorine resin (film thickness: 10 μm) by an actuator, and then further coated with a glass-based molding material. Four
Is an actuator in the Z-axis direction that drives the probe 1.
The Z-axis actuator 4 of the probe 1 is made of a piezoelectric element similar to that of the XY positioner 3, and is made of a fluorine resin (film thickness: 10
μm) and a glass-based molding material. By covering the XY positioner 3 and the Z-axis actuator 4 with a fluorine resin and a glass-based molding material, it has succeeded in ensuring stable scannability.

The preamplifier 5 of the probe driving circuit system receives a signal from the probe displacement measuring system for detecting the fluctuation of the force acting between the probe and the sample, and the force, that is, the displacement of the probe becomes constant. Thus, it plays a major role of finally applying an electric signal for controlling the Z-axis actuator 4 to the Z-axis actuator 4. The electric circuit part of the preamplifier was vacuum-sealed in a ceramic package, gold wires were connected to the terminals, and further vacuum-sealed in a glass container in the same manner as a vacuum tube. The two-stage vacuum sealing suppressed the invasion of water vapor into the pre-amplification circuit and the excessive temperature rise, and ensured the stable operation of the probe drive circuit.

The displacement measuring system of the probe 1 is composed of a laser semiconductor element 6 and a photodetection CCD element 7. The probe 1 has a shape generally called a cantilever, and has a structure that bends in the Z-axis direction when a force acting between the probe and the sample is changed. The deflection amount of the probe system is detected by the displacement measuring system, and the Z-axis actuator 4 is controlled so that the deflection amount becomes constant.
Drive. Therefore, it can be said that the stability and accuracy of displacement measurement determine the stability and accuracy of AFM observation. Therefore, the laser semiconductor element 6 and the light detection CCD element 7
By vacuum sealing in a container made of non-reflective glass, the functional deterioration of these elements was prevented and the stability of measurement was secured.

The thermal expansion coefficient of the entire AFM apparatus is 2 × 10.
^It was installed in a glass container 8 having a very small size of ^-8 (/ ° C). By installing the entire device in a container having a small thermal expansion coefficient, local distortion of the device system due to temperature fluctuation was suppressed, and so-called temperature drift such as movement of the AFM observation position was prevented. In a cylindrical glass container having an AFM diameter of 12 cm and a height of 15 cm, an inlet 9 for sending air whose temperature and humidity are adjusted, and 10 outlets 10 each, for a total of two.
By providing 0 pieces, fluctuations in temperature and humidity depending on the position in the container were suppressed. Air whose temperature and relative humidity have been adjusted is sent to the inlet 9 through a temperature / humidity controller 11. The dew condensation state was prevented as follows. At the start of the test, dry air whose temperature is adjusted to the test temperature and a relative humidity of about 5% is fed into the glass container in which the AFM device is placed, and the inside of the glass container is heated to the test temperature. After confirming that the inside of the container has reached the test temperature by the small temperature / humidity sensor 12, the humidity of the inflowing air is increased to a predetermined humidity over about 30 minutes. By this method, the local condensation phenomenon in the glass container 8 could be completely suppressed. Further, six small temperature / humidity sensors 12 are installed near the probe, measure temperature and humidity fluctuations near the probe, and send air to the ten inlets 9 so as to minimize the fluctuations. The amount was adjusted. The air inflow amount is controlled by the information from the temperature / humidity sensor 12 by controlling the open / closed state of the electromagnetic valve 13 for adjusting the air amount installed between the temperature / humidity controller 11 and the inlet 9. Adjusted automatically. By taking these measures, the temperature fluctuation in the environment where AFM measurement is performed is ±
It became possible to suppress the fluctuation of humidity at 0.1 ° C. within ± 1.0%, and to enable stable AFM measurement even under high temperature and high humidity.

The control measurement system centered on the personal computer 14 was used to drive the probe, scan the sample, input temperature and humidity information from the temperature and humidity sensor, control the electromagnetic valve, measure the AFM image, and perform image processing. Further, reference numeral 15 is an air cylinder for blowing air.

Next, examples of the method for observing and quantifying chemical reactions of the present invention will be described.

FIG. 2 shows an example of in-situ observation of the progress of corrosion of a soda lime silica glass thin film using a high temperature and high humidity type AFM at a temperature of 80 ° C. and a relative humidity of 80%. Figure 2
(A) is the surface state before exposure to high temperature and high humidity (average roughness: 0.24 nm), and FIG. 2 (B) is (80 ° C., 80% R
H) surface condition after 10 hours exposure (average roughness:
0.74 nm). Corrosion phenomenon that progresses in the surface layer of soda lime silica glass (sodium in soda lime silica glass reacts with water vapor and carbon dioxide to form hydrated sodium carbonate) can be clearly observed as a change in surface roughness. Recognize. FIG. 3 shows the measurement results obtained by quantifying the corrosion process of the soda lime silica glass shown in FIG. 2 as the change over time in surface roughness (average roughness) with exposure time. The surface roughness increases linearly in the initial stage of the reaction and then becomes saturated. By defining the slope of the linear region as the corrosion rate, the corrosion rate of the soda lime silica glass thin film under each temperature and humidity condition can be obtained.
Table 1 shows the corrosion rate of the soda lime silica glass thin film in the exposure test in which the relative humidity is constant at 80% and the temperature is changed at 60 to 90 ° C.

[Table 1] By arranging the corrosion rates shown in Table 1 based on the Arrhenius reaction rate equation, the activation energy for corrosion of the soda-lime silica glass thin film can be calculated. The Arrhenius equation is V = A × exp (−E / kT). However, V: reaction rate, A: reaction rate constant,
E: reaction activation energy, K: Boltzmann constant,
T: Absolute temperature. Substituting the corrosion rates in Table 1 into the Arrhenius equation and finding E by the method of least squares, the relative humidity is 8
The corrosion activation energy of the soda lime silica glass thin film at 0% is estimated to be 0.95 eV.

80% relative humidity measured by the same method
Activation energy of pure Co at 0.76e
V, that of pure Fe was 0.60 eV. In addition, it is possible to quantify the in-situ observation or reaction amount of the chemical reaction that proceeds in the atmosphere by introducing other reactive gas such as corrosiveness instead of humidity, that is, water vapor.

[0034]

As described above, the high temperature and high humidity type AFM of the present invention
As a result, it becomes possible to perform in-situ observation by AFM on the surface exposed to a high temperature and high humidity environment, which has been difficult at all in the past, and it is possible to provide an observation device which gives a lot of information on the surface reaction.

Further, the measurement results shown in the examples of the method for observing and quantifying the chemical reaction of the present invention are difficult to measure by the conventional corrosion evaluation method, and in particular, the reaction occurring in the temperature range of 100 ° C. or lower. It has been considered almost impossible to measure activation energy by the conventional method. By applying a high temperature and high humidity type atomic force microscope, this measurement method makes it possible to perform the highly sensitive measurement at a high temperature at a remarkably superior accuracy as compared with the conventional method, and to directly measure the reaction process. Field observation and quantification were successful.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a high temperature and high humidity type atomic force microscope according to the present invention.

FIG. 2 is a photograph showing in-situ observation results showing the progress of corrosion of soda lime silica glass according to the present invention.

FIG. 3 is a view showing a change with time of surface roughness showing a corrosion progressing process of soda lime silica glass according to the present invention.

[Explanation of symbols]

 1 probe 2 sample 3 XY positioner 4 Z-axis actuator 5 preamplifier 6 laser semiconductor element 7 photodetection CCD element 8 glass container 9 inflow port 10 outflow port 11 temperature / humidity controller 12 small temperature / humidity sensor 13 electromagnetic valve 14 personal computer 15 Air cylinder

[Procedure amendment]

[Submission date] September 29, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

Claims (7)

[Claims] 1. A high-temperature and high-humidity atomic force microscope, which is configured to operate in a high-temperature and high-humidity environment having a temperature of 100 ° C. or lower and a relative humidity of 90% or lower. 2. A temperature fluctuation of ± 0.1 ° C. and a relative humidity fluctuation of ± 0.1 ° C.
Thermal expansion coefficient controlled within 1.0% 5 × 10 ⁻⁸ (/
The high temperature and high humidity atomic force microscope according to claim 1, wherein the high temperature and high humidity atomic force microscope is installed in a glass or metal container having a temperature of ℃) or less. 3. The high temperature and high humidity atomic force microscope according to claim 2, further comprising a probe covered with a noble metal thin film. 4. A probe driving Z-axis actuator coated with a fluorine resin and a glass-based molding material, and a sample scanning X-axis.
The high temperature and high humidity atomic force microscope according to claim 3, further comprising a Y positioner. 5. A high temperature and high humidity type atomic force according to claim 4, wherein the displacement measuring system of the probe is constituted by a laser semiconductor element vacuum-sealed in a non-reflective glass container and a CCD element for light detection. microscope. 6. The high temperature and high humidity atomic force microscope according to claim 5, further comprising a ceramic package and a preamplifier for a probe driving circuit vacuum-sealed in a glass container. 7. Observation and quantification of a chemical reaction characterized by measuring the surface morphology or surface roughness of a sample over time using a high temperature and high humidity atomic force microscope or an atmosphere controlled atomic force microscope. Method.