High-temperature ultrapure water production apparatus and...

Chemistry: electrical and wave energy – Apparatus – Electrolytic

Reexamination Certificate

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C210S900000

Reexamination Certificate

active

06562205

ABSTRACT:

TECHNICAL FIELD
The present invention relates to ultrapure water production apparatus for use in electronics industries including the semiconductor industry, and more particuarly to apparatus for producing high-temperature ultrapure water which is remarkably effective for achieving improvements in rinsing efficiency and drying efficiency in cleaning wafers in the semiconductor fabrication process.
The invention relates also to systems for preparing chemical liquids for use in processes for treating semiconductors or other precision devices, especially for use in cleaning semiconductor wafers, and more particularly to chemical liquid preparation systems for use in preparing and supplying chemical liquids having a high temperature.
The term the “chemical liquid” as used herein includes a cleaning liquid for use in the step of cleaning semiconductor wafers and the step of cleaning other precision devices, and a process liquid for use in inhibiting-a natural oxide film on Si surfaces in the step of treating semiconductors.
BACKGROUND ART
Electronics industries including the semiconductor industry in recent years require water purified to a very high degree. The water to be thus treated is usually industrial water, tap water, well water or the like. Such untreated water contains suspended substances, electrolytes, fine particles, microorganisms, organic matter, dissolved oxygen, etc. in amounts greatly in excess of water quality standard values, so that these impurities must be removed.
FIGS. 3 and 4
show known apparatus for preparing ultrapure water by removing these impurities.
Conventional example 1 shown in
FIG. 3
, i.e., apparatus
71
, comprises a primary pure water system
72
for treating untreated water, and a secondary pure water system
73
for treating the primary pure water obtained
20
. by the primary pure water system
72
to obtain ultrapure water. The primary pure water system
72
comprises a filter
74
, reverse osmosis unit
75
, deaerator
76
and ion exchanger
77
. The secondary pure water system
73
comprises an ultraviolet sterilizer
78
, demineralizer
79
and ultrafiltration (UF) unit
80
. The apparatus
71
removes the ionic component from the feed water by the reverse osmosis unit
75
, ion exchanger
77
and demineralizer
79
until the water has a very low ionic content, giving ultrapure water having a resistivity, for example, of not lower than 18.0 MÙ·cm. However, the apparatus
71
has the problems of being insufficient in its ability to remove nonionic impurities such as silica and organic matter, encountering difficulty in fully removing dissolved oxygen from the product water, necessitating sterilization as held out of operation because the apparatus
71
is operated at room temperature and therefore inevitably permits development and growth of bacteria, and being complex in construction and cumbersome to monitor during operation because the apparatus comprises many treating devices in combination.
On the other hand, the apparatus of conventional example 2 shown in
FIG. 4
is adapted to completely remove nonionic impurities, such as silica and organic colloids, and dissolved oxygen and to produce ultrapure water having a high temperature suitable for achieving improvements in rinsing efficiency and drying efficiency.
The apparatus of conventional example 2 consists mainly of a multi-effect evaporator I for treating primary pure water obtained by a primary pure water system to prepare high-temperature pure water and has an ultrafiltration (UF) unit
2
downstream from the evaporator. The primary pure water system is the same as the one included in the apparatus of conventional example 1. The primary pure water fed to the evaporator I is led into a preheating tube
5
extending vertically through each of effects within the evaporator I and heated with the latent heat of condensation of a portion of water vapor produced in evaporation tubes
7
of each effect. The feed water in the preheating tube
5
within the first effect is heated to a predetermined temperature of about 100° C. by receiving the latent heat of condensation of part of heating steam and enters a water reservoir
13
in the bottom of the first effect. The feed water in the reservoir
13
becomes mixed with the concentrate remaining in the evaporation tubes
7
after releasing water vapor, and a major portion of the mixture is led by a circulating pump
6
to the evaporation tubes
7
arranged at an upper portion of the first effect to flow down the interior of the tubes in the form of a thin film and evaporates at a temperature of about 100° C. by receiving the latent heat of condensation of a major portion of the heating steam from outside the tubes to produce water vapor. The concentrate resulting from production of the water vapor flows down into the reservoir
13
and becomes mixed with feed water as described above. A major portion of the mixture is sent to an upper water chamber
15
by the circulating pump
6
. The remainder of the mixture flows through a communication opening
14
into the water reservoir of the second effect, in which the mixture similarly becomes mixed with the concentrate flowing down the evaporation tubes. A major portion of the resulting mixture is sent to a water chamber in the upper portion of the second effect by a circulating pump.
The water vapor produced in the evaporation tubes in the first effect flows through a demister
16
into a space around evaporation tubes in the second effect. The mist entrained in the water vapor is removed by the demister
16
, remaining only in a very small amount. A major portion of the water vapor condenses on the outer surfaces of the evaporation tubes, and the condensate enters a condensate collector (not shown) in the second effect, while the remaining portion of the water vapor condenses on the outer surface of the preheating tube in the second effect. In the condensate collector, the resulting condensate becomes mixed with the condensate from the evaporation tubes, and the mixture entirely enters a condensate collector in the third effect.
In this way, the above process is repeated in every effect.
The water vapor produced by evaporation in the final effect (nth effect) flows through a demister and condenses on the outer surface of a condensation tube
12
of a condenser
1
, and the condensate enters a water reservoir
11
below the condenser. The whole condensate produced in each effect flows through the condensate collector and similarly enters the water reservoir
11
. The condensate collected in the reservoir
11
is drawn off by an ultrapure water pump
10
and passed through the ultrafiltration unit
2
chiefly intended for the removal of fine particles.
The condensate drawn off by the pump
10
and made free from fine particles by the ultrafiltration membrane
2
is ultrapure water having a high temperature and a resistivity of at least 18.0 MÙ·cm (measured when the pure water of high temperature is cooled to 25° C.; all the resistivities herein referred to are values measured at 25° C.), a value very close to the resistivity of theoretical pure water, and very low in TOC value and in dissolved oxygen concentration. For use in cleaning wafers in the semiconductor fabrication process, it is especially desirable that the high-temperature ultrapure water have a temperature of about 70 to 80° C. when to be effective for achieving remarkably improvements in rinsing efficiency and drying efficiency.
As shown in
FIG. 5
, many chemical liquids are used at high temperatures for cleaning wafers in the semiconductor fabrication process. These chemical liquids are replaced batchwise, such that when used for treating a specified number of wafers, the chemical liquid is drawn off from the cleaning container, followed by supply of a predetermined amount of fresh chemical liquid to the container.
The chemical liquid is conventionally prepared and supplied by such a method that the ultrapure water produced by the apparatus of conventional example 1 and a chemical are supplied in respective specified amounts di

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