JPS60157035A - Method for evaluating cleanliness of environment - Google Patents

Abstract

PURPOSE:To detect easily an extremely slight amt. of pollution in environment by allowing a cleaned substrate to stand for prescribed time in the environment to be measured to allow the foreign matter in the environment to stick to the substrate then measuring the contact angle of the substrate surface with a liquid. CONSTITUTION:A clean substrate, for example, a silicon substrate 1 subjected to UV or ozone cleaning is allowed to stand for prescribed time in the place where the environment is desired to be evaluated, i.e., the environment to be measured to allow the contaminant in the environment to stick to the substrate 1. Distilled water is then dropped at, for example, 5 micro-litter to the substrate 1 and the contact angle theta thereof with the substrate 1 is measured by an apparatus for measuring the contact angle. The amt. and quality of the extremely slight amt. of pollution in the environment are thus evaluated from the contact angle theta.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a method for evaluating environmental cleanliness.

In particular, it is used to evaluate the cleanliness of working environments that manufacture electronic components, mainly semiconductors, B-class equipment, pharmaceuticals, etc.

[Technical background of the invention]

Contaminants in the environment are broadly classified into particulates and gases, and several methods have been used to evaluate the amount of pollution for each type.

A typical particulate pollution evaluation method is the suction method. In this method, strong light from a lamp or laser is applied to sample air sucked in by a suction pump, and scattered light from fine particles in the air is measured.

In addition, typical methods for evaluating gaseous contamination include measurement using a detection tube while collecting in an inbinger.

[Problems with background technology]

However, in lean rooms such as those seen in the manufacturing process of semiconductor products, ultra-trace contamination that cannot be detected by the evaluation methods described above may become a problem. In other words, these ultra-trace contaminants adhere to the surface of semiconductor substrates, etc.
It may deteriorate their properties. This is also one of the causes of reduced product yield.

[Purpose of the invention]

An object of the present invention is to easily detect ultra-trace contamination that could not be detected using conventional techniques.

The object of the present invention is to provide a method for evaluating environmental cleanliness.

[Summary of the invention]

This invention measures the cleanliness of the environment by leaving a cleaned substrate in the environment to be measured for a predetermined period of time to allow foreign matter in the environment to adhere to the substrate, and then measuring the contact angle of the surface of the substrate with respect to the liquid. This is an evaluation method that can easily detect ultra-trace contamination that could not be detected using conventional techniques.

[Embodiments of the invention]

The present invention will be explained below using an embodiment (more specifically, drawings). Fig. 1 is a schematic diagram showing a method for evaluating environmental cleanliness according to an embodiment of the present invention. In this embodiment, the environmental cleanliness is evaluated. We were able to roughly determine not only the amount of contamination but also the contaminants.In other words, we prepared a clean substrate 1, for example a silicon substrate (1) that had been cleaned with ultraviolet rays and ozone, and applied liquid ( Drop a small amount of liquid (2).At this time, drop a small amount of liquid (2).
) is preferably one that does not have a strong chemical reaction with the substrate (1) and is not very volatile. Here, distilled water was used, and the amount thereof was 5 microliters. first.

At this time, the contact angle θ of the liquid (2) with respect to the substrate (1) is measured using a contact angle measuring device. Next, this board (1) is placed in the place where you want to evaluate the environment, that is, in the environment to be measured, for a predetermined period of time.
For example, leave it for 60 hours to remove environmental contaminants from the substrate (1).
Attach to. Here again, add distilled water (2) to the substrate (1).
5 microliters of the solution was dropped, and the contact angle θ with the substrate (1) was measured using a contact angle measuring device. At this time, the inventors discovered that the contact angle θ was significantly different before and after leaving the substrate in the environment, and found that this was due to the amount of contamination in the environment in which the substrate (1) was left. To explain in detail, when measured in a clean environment, the contact angle θ of the liquid does not change much before and after leaving the substrate (1) in the environment, but when measured in a contaminated environment, the contact angle θ changes depending on the environment. It was found that the amount increased rapidly after being left alone compared to before being left alone.

The left side of the two-dot chain line in FIG. 2 is a graph showing the measurement results of the amount of environmental pollution according to this example. Three environments with different contamination conditions, such as the presence or absence of one worker, and the type of work, A, B,
The measurement results for C are curves (u) and (
12), (13). From this graph, it was found that the amount of contamination was higher in measurement environments A, B, and C in that order.

As mentioned above, the amount of environmental pollution can be easily measured by the present invention, and the present invention combines the method with a cleaning method using ultraviolet rays and ozone cleaning.

The nature of environmental contaminants can also be easily investigated using examples such as those described below. First, the above-mentioned substrate (1) is left in an environment to be measured for a predetermined period of time, for example, 60 hours.

After leaving it for a while, the surface of the board is cleaned with ultraviolet rays and ozone.

By timing the cleaning rate of substrate surface contamination.

We were able to assess the nature of environmental pollution.

The right side of the two-dot chain line in FIG. 2 shows the measurement results of the properties of environmental pollutants according to this example.

In Figure 2, the curve (2υ, (2ri, (23) is a different environment A,
B and C show the cleaning status of contamination adhered to the surface of the substrate left exposed by ultraviolet rays and ozone cleaning. Judging from the contamination removal rate (corresponding to the slope of the curve in the drawing), environments A and B It was found that the quality of contamination differs between :/C. For example, in environment A where the removal rate is fast, that is, the absolute value of the slope of the graph curve is large, there are contaminants for which ultraviolet rays and ozone cleaning are highly effective.

For example, the environment is contaminated by fluorine chemicals, chlorofluorocarbon gas, etc.1 On the other hand, in environments B and C where the removal rate is slow, that is, the absolute value of the slope of the graph curve is small, ultraviolet rays,
It has been found that the environment is contaminated by contaminants 1, such as organic substances, for which ozone cleaning has little effect.

〔Effect of the invention〕

According to this invention, a particle measuring device using a light scattering method and an inbinger suction method have been developed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating an embodiment of the present invention, and FIG. 2 is a diagram illustrating an example of measuring environmental cleanliness according to the present invention. 1... Semiconductor substrate, 2... Distilled water. 11.21...Measurement results of a board left in environment A. 12,. 22...Measurement results of a board exposed to environmental BK. 13.23...Measurement results of a board left in environment C.

Claims (1)

[Claims] A method for evaluating the cleanliness of an environment, comprising the steps of: leaving a clean substrate in an environment to be measured for a predetermined period of time to cause contaminants in the environment to adhere to the substrate; and measuring a contact angle of the surface of the substrate with respect to a liquid.