JPS6332357A - Surface evaluating device - Google Patents

Abstract

PURPOSE:To inspect the uniformity of the surface of a substrate nondestructively by controlling the temperature and humidity in a sample chamber and cooling the sample substrate to below its dew point, and varying the relative position between the sample and an illuminator. CONSTITUTION:The sample substrate 11 is fitted on a sample table 12 and a humidity control means 14 and a temperature control means 13 fitted on the sample table 12 are controlled to cool the substrate 11 below the dew point, so that drops of water are condensed over the surface of the substrate 11. The lighting device 15 lights the substrate 11 at an angle within a specific range to observe the surface through a microscope 17. At this time, the position relation where the diffusion intensity of light by the drops of water is large and the nonuniformity of the surface of the substrate 11 can be observed with the best contrast is found and the drops of water on the surface of the substrate 11 are irradiated with light, so that the drops of water diffuse the light in every direction. The intensity and direction of the scattering depend upon the size and shape of water drops, so a hydrophilic and hydrophobic degree difference is observed as a difference in the size and shape of the drops of water to inspect the uniformity of the substrate surface sensitively without any destruction.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention detects the uniformity of the surface condition of a semiconductor substrate on which an organic thin film used for electrical or optical elements is formed. This invention relates to a surface evaluation device for surface evaluation.

(Prior Art) In recent years, development of electrical and optical elements having structures using ultra-thin films has become active. These device structures are constructed by forming one or more angstrom-sized thin films on a substrate. Therefore, the condition of the substrate surface is deeply related to whether a thin film can be formed with uniform thickness and properties. Alternatively, the surface condition of the thin film formed on the substrate is deeply related to whether the next layer can be formed with uniform thickness and properties.

As an example of such ultra-thin films, a method for producing organic thin films using the Langmuir-Prodgett method (LB method) is attracting attention. The LB method spreads organic molecules on the water surface and compresses them by reducing the surface area to form an organic thin film (generally a monolayer).
This is a method of forming and accumulating this on a substrate. In order to uniformly accumulate an organic thin film on a substrate by the LB method, not only the uniformity of the substrate surface becomes a problem, but also the uniformity of each film that is accumulated layer by layer. This is because defects existing in a film tend to form defects in the next film. In addition, defects deteriorate device characteristics.

At present, thin film formation by the LB method is still limited to 1 mm to 0.0 mm.
A macro-level defect with a size of 01fiZ'l is a problem. In other words, manufacturing conditions for precisely transferring a monomolecular film on a water surface onto a substrate, or methods for inspecting the same, have not yet been fully developed.

Methods for inspecting thin films include an optical microscope (TEM) and a scanning electron microscope (SEX). Although TEM is capable of detecting thin films with a thickness of several tens of angstroms, it has the disadvantage that the specimen must be transparent to electron beams and cannot be inspected on an actual substrate. SEM
is a method used to inspect thin films on substrates, but it only detects surface irregularities, and to detect differences in surface conditions, a device equipped with a surface analysis device that uses other electron beams is used. There is a need. Both SEM and TEM are 1 like LB film.
In order to detect disturbances in the structure of a layer whose thickness is only a few tens of angstroms, a magnification of tens of thousands of times or more is required, and it takes a great deal of time to evaluate the entire substrate surface.

In addition, surface evaluation equipment using electron beams is a strong electron beam, so
There is a fear that the structure of organic thin films such as LB films may be destroyed.

In addition, differential interference microscopes and multiple beam interferometers can only observe surface irregularities, but cannot detect changes in composition (edited by the Chemical Society of Japan, New Experimental Chemistry Course, Vol. 18, pp. 30-30). (See page 31).

(Problems to be Solved by the Invention) In order to evaluate the uniformity of the surface of a sample, it is possible to sensitively detect changes in structure or composition within a thickness of several tens of angstroms from the surface, and to evaluate the entire surface of the sample in a short time. There is a need for a surface evaluation device that is capable of non-destructive evaluation.

An object of the present invention is to provide a surface evaluation device that can non-destructively and sensitively inspect the uniformity of a sample surface.

[Structure of the invention]

(Means and effects for solving the problems) The present invention provides a sample chamber, sample observation means provided in the sample chamber, temperature control in the sample chamber, (1) cloudiness control in the sample chamber, and (1) cloudiness control in the sample chamber. A sample stage provided and temperature control in the sample chamber (1) This is a surface evaluation device characterized by comprising an illumination device provided in the sample chamber so that the relative position with respect to the sample can be varied.

The present inventors have developed a surface evaluation method, the pseudodrop attachment method, which utilizes the fact that changes in the structure or composition of a substrate surface affect its surface hydrophilicity and hydrophobicity. The water droplet deposition method is as follows. When a substrate is cooled to a temperature below the dew point in a relatively high humidity atmosphere, moisture in the atmosphere condenses on the substrate surface. The size of the water droplets at this time varies depending on the conditions, but is 0.
．． The range is 001mm-Q, 5mm. Furthermore, the difference in hydrophilicity and hydrophobicity of the substrate surface affects the size and shape of this water droplet. When these water droplets are illuminated with light, the water droplets scatter the light in all directions, but the intensity and direction of this scattering depend on the size and shape of the water droplets, so the difference in light scattering is based on the difference in hydrophilicity and hydrophobicity of the substrate surface. In other words, it becomes possible to observe the difference in brightness and darkness of light (see Figure 2).5 This water droplet deposition method can be thought of as measuring the contact angle in a minute area.

Since this method completely detects the properties of the surface, it is possible to detect changes in structure or composition at a depth of several angstroms to several tens of angstroms from the surface.

The surface evaluation device of the present invention can be used when observing the surface condition of a sample using this water droplet adhesion method. Examples of use of the present invention are described below.

The sample is mounted on a sample stage, illuminated at an angle of 45 to 90 degrees relative to the temperature and humidity inside the sample chamber, and observed with a microscope from the opposite direction. The observation direction is in the range of 45 to 90', and a relative position is searched for where the intensity of light scattering by water droplets is large and the non-uniformity of the sample surface can be observed with the best contrast.

If the sample surface has uniform hydrophilicity and hydrophobicity,
The light scattering state of the water droplets is also uniform, and no pattern is observed. However, it is also possible to detect slight structural or compositional changes that affect hydrophilicity or hydrophobicity. Since only water droplets adhere to the sample, if the sample is brought to a temperature above the dew point again, the water droplets will evaporate and the next sample treatment can be carried out as is.

(Example) Example I An example will be shown in which defects in a cumulative film obtained by the LB method were evaluated by a water droplet adhesion method. Since an LB molecule such as stearic acid has a hydrophilic group within one molecule, either the hydrophilic group or the hydrophobic group should be uniformly exposed on the surface of the accumulated film. At this time, a uniform light scattering state is observed in the evaluation using the water droplet adhesion method. However, when the cumulative state of the LB film is deteriorated, the exposure of hydrophilic groups and hydrophobic groups differs depending on how the structure is disturbed, and the hydrophilicity and hydrophobicity of the surface become non-uniform. If this structural disturbance is large enough to be detected with an optical microscope, it can be observed as a difference in the light scattering state using the water droplet deposition method described above.

Cadmium chloride concentration is 2.5×10 mol/i
, a chloroform solution of stearic acid is spread on the water surface at a water temperature of 15 °C, and after waiting for the chloroform to evaporate, it is compressed by reducing the surface area of the water surface with a partition plate, and the surface pressure is maintained at 25 dyne/am. A monomolecular film of stearic acid and stearic acid is formed on the water surface. A silicon substrate that had been previously submerged in water, treated with aqua regia for 10 minutes, and then washed with water, was lifted onto the water surface at a speed of 10 m/min at an angle perpendicular to the water surface, and a monomolecular film of stearic acid was Layers are accumulated. At this time, an aqueous solution is contained between the substrate and the monomolecular film that is being accumulated, which disturbs the structure of the film when it dries.

The substrate on which the organic thin film thus obtained was formed was inspected using a surface evaluation apparatus that is an embodiment of the present invention.

The surface evaluation device of this embodiment has a sample chamber 16 that is equipped with an air purifier and can control humidity and temperature, and a sample stage 12 that has a function to quickly raise and lower the temperature. Observing the illumination device 15 that illuminates the sample stage 12,
It is equipped with a telescopic microscope 17 with a magnification of 2 to 20 times as large as a recording device, and an attached photographic device. Further, the relative positions of the substrate 11 on the sample stage 12, the illumination device 15, and the microscope 17 of this surface evaluation device can be varied. The sample stage 12 is provided with a sample temperature control means 13 consisting of a cooling system equipped with a small electronic cooler and a temperature measurement system using a thermocouple. The temperature and humidity control means 14 includes a fully hermetic compressor with an output of 100 W, a 300 W heater, an ultrasonic humidifier, a plate fin cooler thermistor as a dehumidifier, a proportional control system using an electronic temperature controller, and a wet bulb type humidity sensor. It consists of an electronic humidity control system. Humidity is maintained at an appropriate level of 50-90%. It is desirable to use ultrapure water as makeup water to prevent contamination of the substrate.

The substrate is mounted on the sample stage 12, and the temperature and humidity in the sample chamber are set to predetermined values. When the substrate is cooled to a temperature 5° C. lower than the dew point determined by the temperature and humidity inside the sample chamber, water droplets condense all over the substrate surface.

The illumination device 15 illuminates the substrate surface at an angle of 45 to 900 degrees, and the substrate is observed with a microscope 17 from the opposite direction. The observation direction is in the range of 45 to 900 degrees, and a relative position is searched for where the intensity of light scattering by water droplets is large and where the non-uniformity of the substrate can be observed with the best contrast.

FIG. 3 shows a photograph of a silicon substrate on which one monolayer of stearic acid was deposited using the water droplet adhesion method using this surface evaluation apparatus. Disturbances in the monolayer structure with a thickness of 25 angstroms could be recorded with clear contrast. The semi-circular pattern running horizontally on the board in the photo is exactly the same as the meniscus on the water surface that is created when the board is lifted out of the water, and the photographic movement of being pulled up and down. Further accumulation on the visible phosphor molecule accumulation film always worsened the accumulation, and eventually accumulation became impossible.

Example 2 When a silicon substrate is treated with 5-hydrofluoric acid for 1 minute, the natural oxide film of silicon is removed and a pure silicon single crystal surface is exposed. This surface is a hydrophobic surface with a contact angle to water of approximately 90'. However, after treatment with hydrofluoric acid, an oxidized layer is immediately formed when exposed to air under water. The thickness of this natural oxidation layer ranges from several angstroms to several tens of angstroms, as shown in the photograph, which was evaluated using a water droplet method using a highly sophisticated surface evaluation device.

The in-plane distribution of an oxide film with a thickness of about 10 angstroms could be detected. Traces of water flow can be observed during washing.

This reveals that a natural oxide film of silicon is instantly formed by washing with water.

Other Examples A transparent front panel may be provided in place of the microscope as the sample observation means.

〔Effect of the invention〕

According to the present invention, a surface evaluation device is capable of sensitively detecting changes in structure or composition with a thickness of several tens of angstroms or less from the surface, and is capable of non-destructive evaluation of sample surface uniformity, allowing evaluation over the entire sample surface in a short time. can be provided.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the principle of the water droplet adhesion method, and FIGS. 3 and 4 are diagrams showing the structure of the crystal of the base. 1... Hydrophilic substrate 2... Hydrophobic thin film 3... Water droplet 4... Illumination light 5... Scattered light 1.1... Substrate 12... Sample stage 13... Sample temperature Control means 14...Temperature and humidity control means 15...Illuminance device 16...Sample chamber 17...Microscope 18...Guide wire 19...Rotation stage Fig. 1

Claims (2)

[Claims] (1) A sample chamber, a sample observation means provided in the sample chamber,
A temperature control means in the sample chamber, a temperature control means in the sample chamber, a sample stand provided in the sample chamber, a sample temperature control means provided in the sample stand, and a temperature control means in the sample chamber so that the relative position with respect to the sample can be varied. 1. A surface evaluation device characterized by comprising an illumination device provided in the surface evaluation device. (2) The surface evaluation apparatus according to claim 1, characterized in that a microscope is provided as the sample observation means.