Fluid handling – Processes – With control of flow by a condition or characteristic of a...
Reexamination Certificate
2000-06-15
2001-07-31
Buiz, Michael Powell (Department: 3753)
Fluid handling
Processes
With control of flow by a condition or characteristic of a...
C137S014000, C137S081100, C137S487500, C137S454000, C137S255000
Reexamination Certificate
active
06267131
ABSTRACT:
TECHNICAL FIELD
The present invention relates to method of controlling pressure in a chamber accommodating a stepper exposure apparatus, a laser measurement apparatus or the like, and to an apparatus for the same, and an exposure apparatus.
BACKGROUND ART
Exposure apparatus, laser measurement apparatus or the like are accommodated in a chamber formed for example in a clean room, and the position of an X-Y stage thereof is accurately measured with a laser interferometer.
With this measurement using a laser interferometer, since the laser wavelength changes due to changes in temperature or humidity, the temperature and humidity inside the chamber is controlled by an air conditioner.
However, if air disturbances occur along the interferometer beam optical path, the refractive index of the air in the optical path changes, or the laser wavelength changes so that consequently there is a drop in measurement accuracy.
For example, in the case where the temperature, pressure and humidity along the optical path respectively change as &Dgr;T (° C.), &Dgr;P (hPa), &Dgr;H (%), then the relative change amount &Dgr;&lgr;/&lgr; of the laser wavelength &lgr; can be approximately expressed by the following equation:
&Dgr;&lgr;/&lgr;=(0.93&Dgr;
T
+0.27&Dgr;
P
−0.0098&Dgr;
H
)×10
−6
At this time, the measurement error for a measurement length L is according to the following equation:
&Dgr;
L=L×
(&Dgr;&lgr;/&lgr;)
For example for a measurement length L=50 mm, in order to permit a measurement error &Dgr;L <1 nm (10
−9
m), the following must apply:
&Dgr;T<0.022° C.
&Dgr;P<0.074 hPa
&Dgr;H<2.01%
(here only one parameter has been calculated, with other parameters fixed for convenience) With present state chambers the following specifications are met:
Temperature accuracy ripple value=0.02° C. or less
Humidity accuracy ripple value=0.4° C. or less Hence for the temperature and humidity, these are within tolerance.
However, control of pressure inside the chamber is not at present performed.
Atmospheric pressure is the weight of air per unit area. In the normal range of 800~1100 hPa, this continuously changes with the meteorological situation. Normally, with the chamber, the sealing is high, however if there is a gap of pin hole order, the chamber interior and the outside air side are effectively connected pressure wise. Therefore the inside-chamber pressure immediately fluctuates with fluctuations in the external atmospheric pressure. In particular, it is known that for example on windy days, fast fluctuations with periods of several seconds are seen (short period fluctuations), so that the maximum amplitude inside the chamber is as much as 0.4 hPa.
Normally, with long period fluctuations in external atmospheric pressure, these can be corrected by the measuring system software. However, with short period fluctuations in external atmospheric pressure, there is a problem that these cannot be fully corrected.
Furthermore, it has also been considered to control the inside-chamber pressure to an absolute pressure (constant pressure value) irrespective of fluctuations in external atmospheric pressure. In this case however, if the set absolute inside-chamber pressure is 1000 hPa (1 atm.), then for the chamber, a pressure resistant container where the volume does not change even for fluctuations of ±100 hPa (1020 kg/m
2
) is required. At present such a chamber does not exist. That is to say, the plate thickness of the chamber wall must be a plate thickness such as for a submarine.
It is therefore an object of the present invention to address the above problems by providing a method and apparatus for controlling the pressure in a chamber which, when the pressure inside a chamber in which laser measurement is being conducted follows long period fluctuations in external atmospheric pressure, can suppress any following of short period fluctuations in external atmospheric pressure contained in the long period fluctuations in external atmospheric pressure.
DISCLOSURE OF THE INVENTION
To meet the above objectives, a first aspect of the present invention is a method of controlling pressure in a chamber, wherein the pressure in a chamber in which measurement such as laser measurement is conducted is maintained at a set pressure with respect to fluctuations in external atmospheric pressure, comprising the steps of: detecting the external atmospheric pressure; obtaining a long-term flat pressure value with respect to short time fluctuations of the detected external atmospheric pressure; creating a set inside-chamber pressure by adding a predetermined pressure to the obtained pressure value; and detecting the inside-chamber pressure while introducing external atmospheric so that the inside-chamber pressure reaches the set pressure.
A second aspect of the present invention, is a method of controlling pressure in a chamber, wherein the air in a chamber in which measurement such as laser measurement is conducted is circulated with an external air adjuster to maintain the inside-chamber pressure at a set pressure with respect to fluctuations in external atmospheric pressure, involving: detecting the external atmospheric pressure, obtaining a long-term flat pressure value with respect to short time fluctuations of the detected external atmospheric pressure, creating a set inside-chamber pressure by adding a predetermined pressure to the obtained pressure value, and detecting inside-chamber pressure while introducing external air to the external air adjuster so that the inside-chamber pressure reaches the set pressure.
A third aspect of the present invention, is a method of controlling pressure in a chamber according to the second aspect, wherein the external air adjuster comprises; a fan, a damper for adjusting air circulation amount, and an external air introducing valve connected to the fan inlet side, and an opening of the external air introducing valve is adjusted based on a difference between the created set inside-chamber pressure and the detected inside-chamber pressure, to control an external air introduction amount.
A fourth aspect of the present invention, is a method of controlling pressure in a chamber according to any one of the first through third aspects, wherein the control of the external air introduction amount is controlled at a sufficiently high speed with respect to a period of the short time fluctuations of the external atmospheric pressure.
A fifth aspect of the present invention, is an apparatus for controlling pressure in a chamber, wherein the air in a chamber in which measurement such as laser measurement is conducted is circulated with an external air adjuster, and external air is introduced by the external air adjuster to maintain the inside-chamber pressure higher than the external atmospheric pressure, and the apparatus comprises: an external atmospheric pressure sensor that detects external atmospheric pressure; an internal pressure sensor for detecting inside-chamber pressure; and an inside-chamber pressure control device which obtains a long-term flat pressure value with respect to short time fluctuations of the external atmospheric pressure detected by the external atmospheric pressure sensor, creates a set inside-chamber pressure by adding a predetermined pressure to the obtained pressure value, and controls the external air introduction amount with the external air adjuster according to a difference between the inside-chamber pressure detected by the internal pressure sensor and the set inside-chamber pressure.
A sixth aspect of the present invention, is an apparatus for controlling pressure in a chamber according to the fifth aspect, where an air circulation system, that supplies air discharged from inside the chamber back to the chamber, is connected to a chamber in which measurement such as laser measurement is conducted, and the external air adjuster comprises; a fan; a damper for adjusting air circulation amount; and a flow rate control valve connected to the fan inlet side for introducing externa
Kato Katsuhiro
Masada Mutsuo
Nakata Masao
Ogawa Makoto
Okubo Yukiharu
Buiz Michael Powell
Krishnamurthy Ramesh
Nikon Corporation
Oliff & Berridg,e PLC
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