Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-02-17
2001-10-30
Evans, F. L. (Department: 2877)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C356S338000
Reexamination Certificate
active
06310356
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fluid fine particle measuring system and more particularly to a particle measuring system capable of measuring the fine particles contained in a cleaning liquid used for cleaning a silicone wafer in the process of producing semiconductors.
2. Description of Related Art
During the production of semiconductors, a substantial amount of cleaning fluid is required and it is necessary to monitor the purity of the cleaning fluid by measuring the number of fine particles that can be accumulated as a result of the cleaning action. Generally, a predetermined number of fine particles is set and if the cleaning fluid exceeds that number it cannot be used in the process of making semiconductors.
Thus, it is important to insure a precise technique of measuring the fine particles contained in the cleaning fluid. The prior art has used a technique wherein a portion of the cleaning fluid is introduced as sample fluid into a flow-type measuring cell, and a laser beam from a laser light source is emitted into the fluid as an incident light, and the resulting scattered light that can be generated from the fine particles that are suspended in the sample fluid is then measured by a photodetector so that both the size and number of fine particles in the sample fluid are measured.
The cleaning fluid that is frequently utilized in cleaning silicone wafers is a chemical solution which is prepared by mixing ammonia water, hydrogen peroxide water and pure water in a suitable ratio. An alternative cleaning fluid can be prepared by mixing hydrochloric acid, hydrogen peroxide water and pure water in a suitable ratio. Both of these examples of cleaning fluids are prone to froth when used for a cleaning purpose and bubbles are then easily produced in the cleaning fluid and can be introduced into the flow channel of the measuring cell. The presence of bubbles within the sample fluid supplied to the measuring cell can be misdetected as fine particles and thus an error can appear in the measured results resulting in an excessive wastage in the cleaning fluid or an interruption in the process of producing semiconductors.
One technique for eliminating bubbles produced in a sample fluid, in a flow channel of a measuring cell, has been suggested in the Japanese Patent Application Laid-Open No. 61-181939 (1986). In this submerged fine particle measuring system an electronic cooler, for cooling the sample fluid by 10° C.-15° C. cooler than the temperature at the time of the measuring cycle, is provided in combination with a deaerator for reducing the normal pressure, so as to thereby eliminate any bubbles that are provided in the flow channel. The electronic cooler and the deaerator are provided on an upper stream side of the measuring cell. A problem exists, however, in that the pressure may not eliminate larger bubbles contained in the sample fluid and thus there is a possibility that a growth of bubbles can be encouraged in the measuring cell.
In addition, the submerged fine particle measuring system disclosed in the 61-181939 reference requires an active deaerator to provide a reduced pressure to eliminate the bubbles through the use of a vacuum pump. Thus, the cost of such a deaerator system becomes a factor and an increase in space is required adjacent the gas stick.
The semiconductor industry is still attempting to minimize the amount of space that is used for semiconductor tools while increasing the efficiency of monitoring the status of a cleaning fluid.
SUMMARY OF THE INVENTION
The present invention provides a compact structure for a submerged fine particle measuring system wherein bubbles that are produced in the sample fluid can be eliminated at a relatively low cost while maintaining high accuracy.
The present invention utilizes a submerged fine particle measuring system where light is emitted into a measuring cell containing sample fluid flowing through the measuring cell. The scattered light generated from fine particles contained in the sample fluid is detected by an optical detector and a number of fine particles can be counted based on the output of the optical detector.
A cooling unit for cooling the sample fluid so as to dissolve bubbles that may be mixed in the sample fluid is provided, along with a deaerator for separating and eliminating the bubbles in the sample fluid on the upstream side of the measuring cell. The deaerator is passive and is connected with an exhaust line which can be connected to the return line from the sample cell, so that a bubble discharge opening provided in the upper portion of the deaerator is connected through the return line to the lower stream side of the measuring cell.
In the submerged fine particle measuring system of the present invention the solubility of bubbles in the sampling fluid is increased by the cooling unit, so that bubbles cannot be recognized visually and are dissolved within the sample fluid. Additionally, bubbles which may grow downstream of the cooling unit are appropriately separated by the aerator tank, with the gas bubbles drawn off and discharged into a downstream side of the sampling cell, so that the cleaning fluid with the bubbles are discharge or are reintroduced into a storage tank.
REFERENCES:
patent: 4779451 (1988-10-01), Ezawa et al.
patent: 61181939 (1986-08-01), None
patent: 8145856 (1996-06-01), None
Suzuki Riichiro
Yuhara Yoshihito
Evans F. L.
Horiba Ltd.
Price and Gess
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