Chemistry: analytical and immunological testing – Measurement of electrical or magnetic property or thermal... – Of a liquid
Reexamination Certificate
2001-03-15
2004-03-16
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Measurement of electrical or magnetic property or thermal...
Of a liquid
C436S052000, C436S179000, C422S062000, C422S082050, C422S105000
Reexamination Certificate
active
06706533
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for detecting the concentration of a desired substance in a solution as well as a diluting preparation apparatus for diluting and preparing a solid and a high concentration agent to a predetermined concentration.
2. Description of the Prior Art
Detection of the concentration of a specific substance in a solution is universally required in almost all industrial fields. Particularly, in industrial fields associated with semiconductors and liquid crystals, the ingredients and concentration of a solution must be frequently more strictly controlled and managed compared with those in other fields.
In fabrication steps for semiconductors for example, an alkali developing solution for use in development of a positive photoresist is a deciding factor to improve the resolution, dimensional accuracy, and stability, etc., of the photoresist, so that it is necessary to strictly control the ingredients and concentration of the solution while adjusting the positive photoresist used.
For a diluted hydrofluoric acid (an aqueous solution of hydrofluoric acid) for use in etching a silicon oxide film, etc., it is needed to accurately control the rate of etching or the amount of etching corresponding to the thickness of the silicon oxide film, etc. In order to achieve such a requirement it is needed to strictly control the concentration of the diluted hydrofluoric acid.
Japanese patents No. 2090366 (JP, 6-7910,B), No. 2751849 (cf. JP, 8-62852,A), No. 2670211(cf. JP, 6-29207,A; corresponding to U.S. Pat. No. 5,843,602) disclose a dilution apparatus for a developing stock solution equipped with control means for such concentration.
Hereupon, although agents for which strict concentration control is required are shipped to makers using such agents after makers supplying such agents dilute and adjust the concentrations of the agents to desired concentrations, recently there are increased cases in which the makers using such agents dilute and adjust high concentration agents to desired concentration ones.
These dilution apparatuses are classified to continuous ones disclosed in Japanese patents No. 2090366(JP, 6-7910, B) and No. 2751849, and to a batch one disclosed in Japanese Patent No. 2670211.
It is known that the electrical conductivity of a solution is varied depending upon the concentration and temperature of the solution. It is further known that in a wide temperature range and in a wide concentration range a relationship between concentration and electrical conductivity at a predetermined temperature and a relationship between electrical conductivity and temperature at a predetermined concentration do not satisfy a linear equation.
For this, in prior art measurements, it is assumed that after there are set temperature upon the measurement and concentration to be desired in the vicinity of the setting temperature and concentration the electrical conductivity is varied in terms of a linear equation of the concentration and it is further assumed that a change rate of the electrical conductivity upon the temperature being varied is unchanged without depending upon the concentration, and in the vicinity of the setting temperature and concentration, the concentration is estimated by measuring the electrical conductivity and the temperature.
Since the temperature of a solution is typically different from the setting temperature, the measurement for the solution is performed under the conditions where the temperature of the solution is kept at the setting temperature by passing the solution through a temperature controller.
In the continuous dilution apparatus, as disclosed in Japanese patents No. 2090366 (JP, 6-7910, B) and No. 2751849, there are set desired concentration and temperature, and the concentration of an agent is measured at all times while continuously supplying the agent or water, and the amount of supply of the agent or water is adjusted for dilution in response to the variations of the concentration.
Since the adjustment is performed in succession, it is desirable that the concentration measurement for agents is performed in real time, but the measurement of the concentration is retarded by the time that the solution passes through a temperature controller, so that excess and deficiency of an agent or water are likely to happen and hence greater concentration variations are likely to occur for a fluid taken out from a stirring tank into a storage tank.
The batch method is a method as disclosed in the Japanese Patent No. 2670211 wherein there is repeated an operation, where after an agent is diluted with water, the concentration of a diluted solution is measured to calculate the necessary amount of the agent and water and add them into a stirring tank until a solution that has a purposed concentration is obtained. Since in the present system, supply of the agent or water is not performed anew until the concentration is estimated, there can be taken at need the time for which the solution passes through the temperature controller, so that the concentration measurement is achieved more accurately than that of the continuous system. However, the batch system suffers from a difficulty that preparing time is prolonged because there is increased the time needed for the solution to pass through the temperature controller.
Further, the prior art measurement with a conductivity meter suffers from another difficulty that numerical values are inaccurate. Provided variations of the numerical values are large, the allowable concentration of an agent to be prepared must be more narrowed corresponding to those variations than that instructed by a user.
Makers using agents who require convenient concentration control desire that the aforementioned difficulties are solved as quickly as possible.
Although for accurately preparing an agent to a desired concentration it is essential to accurately detect the concentration of the agent, there is a relationship expressed by a linear equation in a predetermined temperature range and at a predetermined temperature both defined by the agent between the concentration of the agent and the electrical conductivity of the solution, so that it is conventionally general that for an electrical conductivity meter used for the control of the concentration there is grasped a relationship between the electrical conductivity of the solution at a predetermined temperature and the concentration of an agent and a relationship between the electrical conductivity of the solution at a certain temperature and the temperature, and that the concentration of the agent is calculated upon measuring the electrical conductivity of the solution, based upon a measured value.
More specifically, there is estimated by an experiment a linear equation Dt=a′C+b′ (Dt indicates an electrical conductivity, C concentration, and a′ and b′ indicate constants.) representative of a relationship between the electrical conductivity of a solution and the concentration of an agent at a certain temperature (setting temperature t). Then, it is assumed that the electrical conductivity becomes higher by d every time the measurement temperature of the electrical conductivity becomes higher by 1 degree than the setting temperature t, and the d is estimated by the experiment. Accordingly, provided the electrical conductivity when the temperature of a solution is T is DT, the electrical conductivity Dt of the solution at the setting temperature t is represented by a formula Dt=Dt−d(T−t). In contrast, since Dt=a′C+b′, DT−d(T−t)=a′C+b′, and solving the equation with respect to C, C=(DT−d(T−t)−b′)/a′. Even when the measurement temperature of the electrical conductivity is shifted from the setting temperature t, temperature compensation is achieved using the foregoing last equation, and hence the concentration is calculated from the electrical conductivity.
Iwao Tomoaki
Nomura Akio
Gordon Brian R
Hochberg D. Peter
Kanto Kagaku Kabushiki Kaisha
Mellino Sean
Vieyra Katherine R.
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