Coherent light generators – Particular active media – Gas
Reexamination Certificate
2000-03-03
2004-11-16
Wong, Don (Department: 2828)
Coherent light generators
Particular active media
Gas
C372S055000, C372S058000, C372S090000
Reexamination Certificate
active
06819699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ArF excimer laser and a scanning type exposure device. And, the invention also relates to an ultraviolet laser device which oscillates pulsed laser by adding a trace quantity of xenon gas to the gas for the ultraviolet laser introduced into a chamber and exciting the gas for the ultraviolet laser by the pulse oscillation in this chamber, and particularly to an ultraviolet laser device which efficiently supplies the xenon gas into the chamber without modifying an existing laser gas supply equipment.
2. Description of the Related Art
It is conventionally known that the ArF excimer laser uses argon (Ar) and fluorine (F
2
) as a laser gas for a light source of the exposure device which performs exposure of semiconductors.
FIG. 7
shows a cross sectional view of the structure of ArF excimer laser
1
according to prior art. The ArF excimer laser
1
of
FIG. 7
has laser chamber
2
in which laser gas is sealed and an electric discharge is caused to oscillate laser light
11
and narrow-banding unit
10
for narrow-banding (precisely controlling a spectrum width and a center wavelength) the laser light
11
oscillated by the laser chamber
2
.
F
2
, Ar and neon (Ne) are enclosed as the laser gas at a predetermined pressure ratio in the laser chamber
2
. Among them, Ne is a buffer gas occupying about 98% or more of the total volume of the laser gas.
The chamber
2
has therein flowing fan
19
which is rotated by motor
20
therein to circulate the laser gas in the chamber
2
so to guide to between discharging electrodes
5
and
5
. And, a high voltage is applied to between the discharging electrodes
5
and
5
from high-voltage power supply
18
to excite the laser gas by the electric discharge so to oscillate the laser light
11
having a wavelength of about 193 nm.
The oscillated laser light
11
is narrow-banded in the narrow-banding unit
10
disposed outside of the back of the laser chamber
2
and entered a step and repeat exposure device
15
(hereinafter called the stepper) to serve as a light source to expose semiconductor chips.
Generally, in the ArF excimer laser
1
of the above type, a high voltage is applied in a pulsed pattern to perform pulse oscillation of the laser light
11
. Concerning the pulse oscillation, output per pulse is determined as pulse output, and an oscillation frequency of the laser light
11
is determined as a pulse frequency.
Excitation of the laser gas by an electric discharge undergoes the following process. Specifically, the buffer gas to which energy was given by the electric discharge collides with the molecules of F
2
and Ar to give energy to F
2
and Ar so to produce ArF excimer molecules. The energy of the ArF excimer molecules is discharged to cause the laser oscillation.
In the KrF excimer laser, helium (He) had been used for the buffer gas before. But, it came to be known that when Ne was used as the buffer gas, efficiency to give energy to the molecule of F
2
and Ar was higher as compared with the use of He, and the pulse output was increased. Therefore, Ne was originally used as the buffer gas in the ArF excimer laser
1
.
FIG. 8
shows an explanatory diagram of the stepper
15
. In
FIG. 8
, the stepper
15
has reticle
38
(mask for exposure) which is an expansion original plate of an IC circuit, wafer stage
43
which has thereon wafer
41
for producing semiconductor chips and is freely movable in X and Y directions in the drawing, lighting lenses
37
for irradiating the laser light
11
to the reticle
38
, and projection lens
39
which gathers the laser light
11
, which has passed through the pattern of the reticle
38
, to irradiate it to the semiconductor chips on the wafer
41
.
The laser light
11
having entered the stepper
15
is shaped by the lighting lenses
37
and irradiated to substantially the entire surface of the reticle
38
. The laser light
11
having passed through the reticle
38
is irradiated to the entire area of one of the semiconductor chips for a fixed number of pulses through the projection lens
39
to perform the exposure of the semiconductor chip by one operation. After completing the exposure of one semiconductor chip, the wafer stage
43
is moved to perform the exposure of the next semiconductor chip.
But, the aforesaid prior art has the following disadvantages.
The number of semiconductor chips that the stepper
15
can expose in each unit time (hereinafter called the stepper capability) increases as the power (product of pulsed output and pulse frequency) of the laser light
11
increases. In other words, time required for irradiating one semiconductor chip is shortened by increasing the pulse output.
However, there is a problem that a current-carrying capacity of the high voltage power supply
18
must be made large to increase the pulse output, resulting in upsizing the ArF excimer laser
1
.
Moreover, it is necessary to increase a flow velocity of the laser gas which flows between the discharging electrodes
5
and
5
to raise the pulse frequency. It is because a trouble is caused in excitation of the laser gas and the pulse output is lowered greatly if the laser gas deteriorated by a pulse discharge is not removed from between the discharging electrodes
5
and
5
before the next pulse discharge.
However, there is also a problem that the ArF excimer laser
1
is upsized because it is necessary to enlarge the flowing fan
19
to increase a flow rate of the laser gas and to enlarge the motor
20
so to raise the number of rotations.
Now, the ultraviolet laser device used for conventional exposure of semiconductors will be described.
Conventionally, a semiconductor exposure device having the ultraviolet laser device, such as an excimer laser device, as a light source repeats exposure and stage movement alternately to make exposure of IC chips on a semiconductor wafer. Therefore, the ultraviolet laser device performs a burst operation to repeat a continuous pulse oscillation operation which continuously causes a pulse oscillation of the laser light for a given number of times and a pause of the oscillation to pause the pulse oscillation for a predetermined duration.
But, when the burst operation is performed, a burst characteristic and a spike characteristic that energy is gradually lowered are caused, and the laser output from the excimer laser device has a change in energy at every burst. As a result, there is a disadvantage that an amount of light exposure is variable.
Therefore, the applicant for the present invention has proposed a technique to improve variations in the amount of light exposure due to the burst characteristic and the spike characteristic by adding a trace quantity of xenon gas to the gas for ultraviolet laser in the chamber in Japanese Patent Application No. 11-23709.
This art is not effective because it is necessary that a xenon gas cylinder for supplying xenon gas into the chamber is separately disposed from a gas cylinder for the ultraviolet laser and the xenon gas is fed into the chamber three passage quite different from a passage for feeding the gas for ultraviolet laser.
Especially, since a site where the excimer laser is set up is provided with only the laser gas supply equipment such as a gas cylinder for the ultraviolet laser inherently required, it is not efficient to modify such equipment only to supply the xenon gas into the chamber.
Accordingly, in order to remedy the burst characteristic and the spike characteristic of the ultraviolet laser device by adding a trace quantity of xenon gas, it is quite significant to efficiently supply the xenon gas into the chamber without modifying the existing laser gas supply equipment.
SUMMARY OF THE INVENTION
The present invention was completed in view of the above-mentioned problems. And, it is a first object of the invention to provide ArF excimer laser capable of raising a pulse frequency without involving the enlargement of the device and an exposure device which has the ArF excimer laser of a high pulse frequency
Enami Tatsuo
Hori Tsukasa
Mizoguchi Hakaru
Takehisa Kiwamu
Terashima Katsutomo
Komatsu Ltd.
Nguyen Dung
Varndell & Varndell PLLC
Wong Don
LandOfFree
Arf excimer laser device, scanning type exposure device and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Arf excimer laser device, scanning type exposure device and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Arf excimer laser device, scanning type exposure device and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3322794