JP2002033540A - Laser system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a beam delivery system which efficiently delivers laser beam of 200 nm or less. SOLUTION: A system is provided which delivers the laser beam of wavelength 200 nm or less from such laser as F2 laser or ArF laser to another housing, which eventually reaches a work piece, through a sealed enclosure which is air-tightly connected to the laser. The enclosure is exhausted, and then is filled with inert gas so that air, water, hydrocarbon or oxygen within the enclosure is fully discharged. Then, or instead of that, an inert gas flow is set and maintained in the enclosure while the laser is operated. The inert gas is preferred to be of high purity, for example, 99.5% or above, with 99.999% or above especially preferred. Nitrogen or rare gas is preferred. The enclosure is preferred to be sealed off using a transparent window against radiation of 200 nm or below so that no contaminant generated within the enclosure comes into the housing to contaminate the surface in the housing. The enclosure is preferred to be made of steel and/or copper, with the window preferred to be made of CaF2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser,
The present invention relates to a beam delivery system using a discharge-excited fluorine molecular laser emitting at a wavelength of 57 nm. This application is a continuation-in-part of U.S. Pat. No. 6,219,368 B1, which is incorporated herein by reference.

[0002]

2. Description of the Prior Art Molecular fluorine (F ₂ ) lasers operating at a wavelength of about 157 nm are well selected for deep UV / vacuum UV microlithography with sub-0.1 micrometer resolution. Laser radiation of this wavelength is also very useful for micromachining using materials that are normally transparent at commonly available laser wavelengths.

The efficiency of transporting a laser beam of 200 nm or less to a target in an extra cavity is deteriorated by strong absorption in the atmosphere. That is, the laser beam of 200 nm or less of such a laser propagates a predetermined distance along the beam path of the extra cavity between the laser output coupler and the work piece, and the water, oxygen, and carbon atoms located along the beam path. Absorbed by light absorbing species such as hydrogen. For example, the extinction length (1 / e) for the 157nm radiation emitted by the F ₂ laser is 1 millimeter in ambient air.

[0004] High intracavity losses also occur for lasers operating at wavelengths below 200 nm, which are likewise due to characteristic absorption, especially by oxygen and moisture.
It is also due to scattering in the gas and in all optical elements.
Short wavelengths (less than 200 nm), along with absorption, cause high scattering losses due to the wavelength dependence of photons scattered across the cross section.

[0005] 2 emitted by a KrF excimer laser
For conventional lithography systems using 48 nm light, these absorptions and scatterings are less of a problem. Species such as oxygen and moisture in the cavity and atmosphere
It absorbs strongly below 200 nm, especially about 157 nm for the F ₂ laser, but shows negligible absorption at 248 nm. The extinction length in ambient air for 248 nm light is practically 10 meters or more.
The scattering of photons in the gas and the optical element is 248.
At nm, it decreases as compared to the case of shorter wavelengths.
Furthermore, the output beam characteristics are more sensitive to temperature-induced fluctuations in the case of short wavelength lithography such as 157 nm than in the case of long wavelength lithography of 248 nm, and have a greater effect on the fabrication of microstructures. As described above, since the 248 nm light shows small scattering and small absorption, the KrF excimer laser does not cause the same problem as the F ₂ laser.

One possible solution to the problem of absorbing the 157 nm radiation of an F ₂ laser is to seal the beam path with a housing or envelope and purge the beam path with an inert gas. However, this technique typically employs high flow rates to minimize the downtime required to remove absorbing species from the beam envelope. That is, starting with the envelope being filled with ambient air, unacceptably long purge times and high flow rates are required to reduce the partial pressure of the absorbent species to a suitable level. Also, this purging technique needs to be performed with an extremely clean inert gas, for example, an inert gas containing 1 ppm or less of an absorbing substance such as moisture or oxygen. This purity requirement is based on commercially available ultra high purity (UHP)
Satisfaction can be achieved with gas but at the expense of cost. Overall, this purging method is expensive and disadvantageous.

Another solution is to evacuate the beam path. In this case, a much lower pressure vacuum is required and an expensive pump system is required. For example,
Ultrahigh vacuum (U
HV) Pumping equipment and pumping techniques are required.
Such devices and techniques combine an airtight envelope with a high pumping capacity. However, undesirably long initial pumping times are still required. In this evacuation method, the transmission along the beam path envelope, despite evacuation, is due, for example, to "residual" gases, mainly oxygen, water vapor and hydrocarbons, which remain, in particular, adhering to the inner wall of the envelope. Determined by absorption of radiation.

FIG. 1 shows the dependence of the experimentally measured transmission of the 0.5 meter optical path on the residual air pressure. Figure 1
Also shows a theoretical fit curve, which is based on the assumption that the main absorbent species is water vapor with an absorption cross section of about 3 × 10 ⁻¹⁸ cm ² . This assumption is believed to be justified because moisture tends to adhere to the walls of vacuum systems and tends to dominate the residual pressure of such systems.

As is apparent from the figure, 50 millitorr (mTo
At a residual pressure of rr), the light loss is about 1% per 0.5 meter path. At about 100 millitorr, light loss is about 2% per 0.5 meter. At 150 and 200 mTorr, the losses are 3% and 4.5, respectively.
%. In systems such as microlithography steppers, the light beam path can be several meters long, so this loss rate results in an undesirably high total loss.
For example, an average 5 meter beam path is shown in FIG.
99% to 95.5 indicated for a residual pressure of 200 mTorr
% Transmission corresponds to a loss of 10% to 37%.

Another consideration is energy stability. It is desirable that the laser energy dose fluctuation and / or the average transfer energy fluctuation be maintained at, for example, 0.5% or less. 0.5% to 1.0% partial pressure of residual oxygen or water vapor
When fluctuating, fluctuations in the absorption of the beam by these species reduce the energy dose stability to below desired or acceptable levels. In the present invention, the first step of reducing the partial pressure of the light-absorbing species along the laser beam path is to reduce the absorptance (%) variation even if the% concentration of these light-absorbing species varies at the same% value It was confirmed that the energy dose stability was increased while decreasing. In this case, a technique for adjusting the beam path of the VUV laser so that the absorption and fluctuation of the absorption of the beam along the beam path is sufficiently low to satisfy the stability standard of the energy dose, for example, <0.5%, is desired. .

As can be seen from the measurements and theoretical fit curves for the beam path evacuation technique described above, for example, to achieve an allowable light loss and allowable light loss variation of less than about 1% per meter path length, the absorbing material The residual pressure of the seed should be reduced to substantially less than about 100 millitorr. Such low pressures can only be obtained by using complex and expensive vacuum equipment and operating this vacuum equipment for an unacceptably long time. Therefore,
This technique results in considerable undesired downtime due to pumping and requires complex and expensive equipment. Laser operating at 200nm or less, in particular a light-absorbing species from the beam path of the F ₂ laser, a need for a method of reducing without requiring excessive downtime or cost.

In the present invention, the light absorbing material species is of the same length along the beam path of the laser beam of 200 nm or less, for example an envelope of the same length that is otherwise substantially free of light absorbing material and / or other contaminant species. It was confirmed that there was a tendency to accumulate more than accumulate along. It has been experimentally observed that this contamination occurs along the beam path from the VUV laser to the imaging system, workpiece or other externally applied process equipment. Such light absorbing material and / or other contaminant species may exit the envelope and contaminate another environment, e.g., the enclosure and contain the imaging system and / or the workpiece containing the workpiece. Is desirable.

[0013]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a laser beam exiting a laser which has a 200 beam path.
It is an object of the present invention to provide a laser system that substantially removes a substance species that strongly absorbs a wavelength of less than nm, such as air, moisture, oxygen, and hydrocarbon.

It is another object of the present invention to flush out contaminants generated along the beam path of the laser beam exiting the laser from the beam path and also to prevent migration from the beam path to an external envelope. Is to provide a system that can propagate to an external envelope.

[0015]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is connected to a laser which emits a laser beam of 200 nm or less, and sends the laser beam to an external housing to finally form a workpiece. A guiding beam delivery system is provided. The system includes an envelope that seals at least a portion of the beam path out of the laser from the atmosphere. The envelope includes a plurality of ports through which an inert gas, preferably 99.5% pure, is flowed into the envelope so that the laser beam is substantially attenuated by light absorbing species present along the video path. And can traverse the envelope without propagation. The envelope may be sealed with a substantially transparent window at an emission wavelength of less than 200 nm and the beam may exit the envelope and enter the outer housing, while contaminants generated within the envelope may be contaminated. Preferably, it cannot escape from and contaminate surfaces within the housing.

According to the present invention, not only is it possible for a 157 nm emission of a molecular fluorine (F ₂ ) laser to propagate a large transmittance along the beam path, but also for 193 nm, 17 nm.
2 nm, 145 nm, it is possible also to ArF, Xe, Kr, Ar and H ₂ lasers operating respectively at 125nm and 121 nm. Advantageously, the absorption rate and the variation of the absorption rate in the envelope are kept at a low level, resulting in greater efficiency, energy stability and energy dose stability. The laser beam of 200 nm or less propagates along the beam path in the envelope and then exits the envelope, preferably to a second envelope, which may include, for example, an optical imaging system of a photolithography system. Because of the input, contaminants generated within the envelope do not exit the envelope due to the presence of the window sealing the envelope.

[0017]

FIG. 2 shows a preferred embodiment of the beam delivery system of the present invention. The invention can be used for any laser, but especially for lasers operating below 200 nm, for example about 193 nm, 172 nm, 1
57 nm, 145 nm, is particularly advantageous with respect to _{ArF, Xe, F 2, Kr} , Ar and H ₂ laser operating at 125nm and 121 nm. In the following preferred embodiments, in particular about 15
An F ₂ laser system operating at 7 nm will be described. Preferably, the optical resonator 1 is mounted on the laser discharge chamber 2 or the tube so that their inclination can be adjusted so that they can be aligned with the optical axis of the resonator 1. Suitable optical and electrical systems are described in U.S. patent application Ser.
Nos. 89 and 09 / 136,353 and U.S. Provisional Application No. 60 / 120,218
Nos., Pp. 147-64, which are hereby incorporated by reference. For example, the F ₂ laser 1
The means for selecting one of the near spontaneous emission lines near 57 nm is part of a suitable optical system.

A pair of main electrodes 3 are connected to an external power supply circuit,
A pulse discharge is generated to excite molecular fluorine in the gas mixture. In addition, UV pre-ionization of the electric discharge can be provided, which can be provided by an array of spark gaps or by another UV radiation source (surface, barrier or other) located near at least one of the main electrodes 3 for the main discharge of the laser. (A corona gas discharge power source). Suitable preionizers are described in US patent application Ser. No. 09 / 247,887, which is also incorporated herein by reference.

A housing or envelope containing the beam path is attached to the output coupling mirror holder 6 of the optical resonator 1, preferably by a vacuum bellows 8, and a conventional O-ring (eg, Vuitton (TM) O-ring), flat packing Alternatively, sealing is performed using another sealing material. This arrangement provides the required degree of freedom for the optical alignment of the output coupling mirror 6, while maintaining a vacuum seal between the output coupler 6 and the beam path envelope 4. Preferably, the residual pressure in the beam path envelope 4 is reduced to less than 200 mTorr, especially 100 mTorr or less.

The envelope 4 has a purging gas inlet 10 and a gas outlet 12 and means for controlling a gas flow rate.
For example, an adjustable needle valve 14 is provided. A pair of entrances 10
/ If only outlet 12 is used, inlet 10 and outlet 1
2 are preferably spaced apart and located at both ends of the envelope 4. The long beam delivery system preferably includes several pairs of gas inlets 10 and outlets 12. Inlet 10 and outlet 12
Is preferably positioned within the envelope to provide a homogeneous medium along the beam path. In this way, any section of the beam delivery system is sufficiently purged with low purge gas consumption. Even with short beam delivery systems, several gas inlets 10 and outlets 12 can be provided, for example, if the clear aperture in the beam delivery system is blocked by a built-in optic or mount.
For example, the beam path can be divided by one or more optical windows.

A suitable vacuum level is provided by a simple and inexpensive (eg, 50 millitorr) one-stage or two-stage mechanical rotor or rotary piston pump or roughing pump (not shown) via pump port 16 to envelope 4. Can be achieved. Pump port 16 need not be a separate connection to envelope 4. For example, the vacuum source is at inlet 10
Alternatively, it can be connected to the envelope 4 using the outlet 12,
When flowing an inert gas, this connection can be sealed off from the pump, for example by a T-valve or similar element.

Preferably, a 0.5 mbar four stage diaphragm pump is used. An oil vapor trap between the pump and the beam path envelope, such as a cryogenic trap or
A Micromaze (TM) filter can be used. A relatively inexpensive three-stage diaphragm pump that does not use oil can also be used. Alternatively, more elaborate pumps such as oil diffusion pumps, cryogenic pumps or turbomolecular pumps can be used. The preferred "air tightness" of the beam path envelope 4 is equivalent to a leak rate of 1 Torr or less per minute. The purging gas is preferably ultra-high purity (UHP) helium, argon or neon, but other inert gases of the UHP grade (eg nitrogen) can also be used.

The laser system of the present invention, particularly 157 nm
A preferred procedure for preparing the beam path envelope 4 for an F ₂ laser emitting at will be described below. Note that the preferred laser system includes a processor that controls and coordinates the various components. The procedure of the present invention for adjusting the beam path can be manual or processor controlled.
If a processor is used, enter the gauge and gas flow meter readings. The processor opens and closes the pump port 16 and the purging gas inlet 10 and outlet 12 and the valve 14.
An output signal is generated to control the flow control.

The preferred method is to first close gas inlet 10 and outlet 12. Next, the pump port 16 is opened, and the envelope 4 is pumped to the envelope 4 by, for example, a 50 mTorr vacuum pump.
Exhaust until indicated to be 0-200 mTorr or less. In a preferred embodiment, the envelope 4 is evacuated to about 0.5 Torr using a three or four stage diaphragm pump.
Next, the pump port 16 is closed, the inlet 10 is opened, and the envelope 4 is filled with the inert gas flowing from the inlet 10 until the inside of the envelope 4 becomes approximately atmospheric pressure or higher. Next, the inlet 10 is closed again, the pump port 16 is opened, and the evacuation process is repeated. Following the evacuation of the envelope 4, these steps of filling the envelope 4 with an inert gas are preferably repeated several times.

After these several gas flushing cycles, the pump port 6 is closed and both the gas inlet 10 and the gas outlet 12 are open. A flow rate selected by the control of the flow control valve 14, preferably a gas flow of about 0.1 liter / min, is set and maintained in the envelope 4. At this time, the pressure is maintained at approximately atmospheric pressure, preferably slightly higher.
At this time, the beam path envelope is ready for laser operation.

FIG. 3 shows the transmittance of a 157 nm beam from an F ₂ laser along a 0.5 meter long optical path using helium and nitrogen as flushing gases. The transmittance increases with the number of flushings as shown, but asymptotically reaches its maximum in only eight flushing cycles. As is clear from the figure, in the case of helium, a transmittance close to 99% can be achieved by eight flushings. The results with nitrogen were not as good as helium. However, the nitrogen used in the experiment was 3 ppm
However, UHP helium is purer and only has a specified moisture level of 1 ppm or less, which can be considered a cause of the difference in performance.

The present invention teaches that the use of the envelope 4 evacuation and inert gas filling cycle can greatly reduce the preparation time and also minimize the inert gas consumption. Things. After the end of these flushing cycles, a flow rate of 0.1 l / min is sufficient to maintain a high transmission for a considerable period of time. The entire preparation cycle advantageously takes only a few minutes. In addition, relatively inexpensive pumps and low cost sealing devices can be used.

In the present invention, contaminants are generated within the envelope, and these contaminants are generated by the VU traversing the interior of the envelope.
On a workpiece being processed or exposed using a V laser beam,
Or make sure that it can flow over the optical device, and other features of the invention are based on this recognition. Contaminant generation rates have been determined to be related to the operation of the laser, for example, by the interaction of the VUV beam or stray light therefrom with components within the envelope or the envelope itself. In addition, the present invention has determined that these contaminants can typically flow out of the opening at the end of the envelope (see FIG. 2).

In the present invention, as shown in FIG.
A VUV beam 22 is provided inside the envelope 4 by providing a light window 18.
Workpiece 20 facing or other processing equipment or beam forming equipment
Device, eg, sealed from an optical imaging system. window
18 is transparent to VUV light and the window is CaF_Twoso
It is preferable to make it, but BaF_Two, BaF, LiF, Sr
F _Two, LiF_Two, MgF_Two, Quartz and fluorine-doped quartz
Such as material or almost transparent to light of about 157 nm
Can be made of other materials known to those skilled in the art as
Wear. This window may be provided with an anti-reflection film. Follow
Is the VUV beam an envelope that protects the beam from attenuation?
But the contaminants generated in the envelope can escape.
These contaminants can be removed from the work piece 20 or other
Deterioration of the physical or optical device is prevented.

The results achieved by this feature of the present invention, in which a window is provided at the end of the beam path of a molecular fluorine VUV laser system, are described in detail below based on experimental results. VUV
Experiments have shown that the presence of the beam results in an increased level of contamination in the envelope. For example, when using a copper envelope, the O ₂ contamination level was 0.5 ppm when the laser was off and 0.8 ppm when the laser was on, with the other conditions being the same. When two consecutive days operating a laser in the case of stainless steel envelope, O ₂ contamination level indicates 0.4～0.5Ppm, fell to 0.25~0.3ppm when the laser is switched off. Then when the laser is switched back on, the O ₂ level will be 0.4
Increased to 5-0.55 ppm.

Thus, particularly during operation of the laser, the windows of the present invention allow impurities to exit the envelope 4 and cause the workpiece 2 outside the envelope.
It is advantageous to prevent zero or other processing equipment from deteriorating. O _2, H ₂ O of the workpiece 20, or other processing devices such as optical imaging device in the air himself by his envelope (not shown), from contaminants such as hydrocarbons and dust Can be protected. This external envelope (not shown) for the work piece can be a clean room or a small housing. External envelope (not shown)
The window 18 can be hermetically connected to the envelope 4 at the window 18 so that the window 18 seals the envelope 4 from an external envelope (not shown). In this way, the envelope 4 and the external envelope (not shown) are optically and mechanically coupled, but there is no fluid passage between the two envelopes. Advantageously, the window 18 prevents contaminants generated in the VUV laser envelope 4 from entering the external envelope (not shown) for the imaging system and / or workpiece.

A very clean gas is flowed near the window 18 to prevent the contaminated gas from approaching the window and depositing a film that absorbs VUV light and attenuates the beam.
8 itself can be kept clean. The technique disclosed in U.S. Pat. No. 4,534,034, which uses an electrostatic settling device to clean the gas before it flows into the window of the laser tube, uses the technique disclosed in US Pat.
8 can be used to maintain cleanliness. In addition, a set of baffles and / or sedimentation separators can be located near the window 18 to trap contaminants and keep them away from the windows 18.

In the present invention, although the method of pumping and purging the inside of the envelope with the inert gas as described above is performed, the generated contaminants deteriorate the atmosphere in the envelope. It has been found that the VUV beam may be attenuated. Further, the present invention has determined that the degree of contamination generated within the envelope depends on the material from which the envelope is made. Further, certain pressures within the envelope can affect the performance of the system. Finally, the particular purge gas used may increase or decrease the performance or advantages of the envelope according to the invention. The present invention not only recognizes these features as potentially affecting the system, but also provides an advantageous beam envelope in accordance with this recognition and the preferred embodiment, as described below.

Experiments were performed according to features recognized as affecting the molecular fluorine laser system and beam path envelope 4 (see above). The present invention provides an improved system based on the results generated in experiments performed on this recognition.

FIG. 5 schematically shows the experimental apparatus used.
Figure 5 is an alternative feature of the embodiment shown in FIG. 4 also shows, including an envelope which is hermetically connected to the F ₂ laser. The envelope 24 has an inlet 26 and an outlet 28 for flowing inert gas into the envelope, and has vacuum bellows at both ends of the envelope 24 to facilitate connection to the laser and the photodetector P. The inlet 26 has a regulating valve V for regulating the flow rate of the purge gas. The envelope 24 may be connected to the outlet via either the inlet 26 or the outlet 28 or via an additional port (not shown), where an additional valve may be provided. The outlet is the water content monitoring system 30
And an O ₂ monitor system 32.

A suitable system for the process includes the window 18 described with reference to FIG. 4 and includes an imaging system instead of a photodetector and an applied process such as a work piece or only a work piece, where the imaging system and the work piece only. Typically, the work piece is located in a housing that is hermetically connected to envelope 24, similar to the photodetector shown in FIG. 5 that is hermetically connected to envelope 24.

Prototype SXUV photodiode and Pt
A long-term exposure test was performed using a photodetector P including a Si photodiode. In this way, the output energy of the VUV beam is precisely measured, and the material such as the material of the envelope itself or the material of the purging gas source and the parameters inside the envelope, for example, the pressure, are changed to change the energy. The effect on the output energy. In addition to monitoring the output energy of the VUV beam, H ₂ O
The monitor 30 and the O ₂ monitor 32 were used to continuously monitor the O ₂ and water vapor contents in the purged exposure box 24. The purge gas used was argon and nitrogen. The flow rate was varied between 10 and 300 l / h. The laser power was varied between 0 and 10W. Further, the material composition of the envelope 24 was changed (using copper, stainless steel, and PTFE hose).

Some preferred devices for experimenting with increasing or decreasing the O ₂ and H ₂ O vapor densities in the envelope 24 under given conditions include: O ₂ detection system (32): Model DF153-10 from Delta F
0; Moisture analyzer (30): 1C-C1 Dew Tr from Edge Tech
ace; both analytical systems 30 and 32 are both MIT Lincoln Lab
And works well within the detection range of 0.1-100 ppm for each contaminant being measured.

Experimental apparatus: Exposure box 24 was set at 50 mbar
The outside air having the following estimated overpressure was purged at a flow rate of V = 90 liters / hour. In the present invention, this 0
Experiments have confirmed that a range of overpressure of ５０50 mbar is the pressure range for optimal results. Three additional energy monitors and six energy detectors were illuminated at 1 kHz during long term operation. Beam fluence to the optical system is F = 10 mJ / c depending on the specific position of the optical system and the detector
m ² , and the beam fluence to the detector was 10 μJ / cm ² . The laser was operated in energy = constant mode, and the power was checked with multiple energy monitors (readings) and LM100E coherent power meter. The laser power was changed by changing the repetition rate of the laser.

Background information: Jenoptik LOS at 157 nm
(Table 1) summarizes the absorption cross-sections of various pollutants in
reference). Other references refer to these over a wide wavelength range.
The absorption of molecules is shown (see FIG. 6). O_Two, Water vapor and N_Twoof
Absorption coefficient is 140cm each^-1, 64cm ^-1, <0.00
02cm^-1It is. VUV or ArF laser according to the invention
For various stages of a lithography system, including
General contamination levels are below 1 ppm and below 100 ppm
Cover the area between the top (cleanest optical area and
Related to open-ended wafer stage). Grade 7.0, especially
N of grade 9.0 purity_TwoPurge gas is preferred, but etc.
N of class 5.0 purity_TwoGas depends on other system conditions
Enough.

Effect of N ₂ Purge Gas Delivery: As a result of the first consideration based on the realization of the present invention that the manufacturing material of the envelope influences the level of contamination in the envelope, as a material of the envelope 4 PTFE tubing proved undesirable. A brief summary is as follows.

The contamination level of O ₂ was (a) 0.3 ppm for stainless steel tubing (in the case of VUV laser beam turn-off); (b) 0.5 at the output of the exposure box for purged copper tubing.
ppm (in the case of VUV laser beam turn-off);
ppm (in the case of VUV laser beam turn-on); (d) 3.5 ppm at the output of the exposure box for the purged PTFE tube (in the case of VUV laser beam turn-on); (e) Additional 4m MFA gas delivery When the hose was inserted (other conditions were the same) 〜8 ppm (for VUV laser beam turn-on);

From these experimental results, the preferred housing 24 is made of stainless steel or copper and is made of PTFE.
And MFA hose materials are clearly not preferred. The level of contamination and the resulting attenuation of the VUV beam when using a PTFE hose is significantly higher than when using a stainless steel or copper housing. While low contamination levels comparable to those achieved with copper or stainless steel using other materials such as glass can be achieved, glass is subject to other conditions such as handling practicality in these systems. Is not preferred.

These experimental results quantitatively confirm another recognition of the present invention that the contamination level is higher when the VUV laser beam is turned on than when it is turned off. In the present invention, the H ₂ O vapor / moisture contamination level is determined by different settings of tubing or housing material, laser operating conditions,
That is, it was confirmed by an experiment that the VUV beam was hardly influenced by turning on or off.

Repeated experiments have yielded interesting observations on the time constant of the change in the contamination level after opening the exposure box, in connection with the following representative operation.

O ₂ H ₂ O Exposure box closed, 1 pump flash w / N 2 cycle, start 1.2 ppm 2.0 ppm laser on, O ₂ contamination increase, after 30 minutes; 2.0 ppm 1.9 ppm laser continuous operation, eg after 2.5 hours; 1.3 ppm 1.6ppm Laser on continuously, after a long time, eg 15 hours; 0.5ppm 0.8ppm, then eg 2 days later; 0.4-0.5ppm 0.8-0.9ppm When the laser is switched off but the exposure chamber is kept purged (W / o blocking), the O ₂ contamination level drops rapidly to about 0.25-0.30 ppm. When the laser is switched on again after a pause, the O ₂ contamination level again rises to about 0.45-0.55 ppm.
This pattern is shown by the experimental results shown in FIGS.

In addition, another interesting observation was obtained that flushing the exposure box with normal air or pure N ₂ to normal pressure showed a decrease in O ₂ levels. O ₂
The reduction in contamination occurs with two different time constants from the 1 ppm level, as shown by the experimental results shown in FIGS. 9 and 10 (1 ppm = full scale of plotter and v = 3 cm).
/ h). Therefore, in the case of pure N ₂ flushing, FIG.
A constant low O ₂ level is again achieved after about 4.3 × 10 ⁶ laser pulses or shots, as shown in FIG. If the box was flushed with ambient air,
A constant low O ₂ level is achieved after 25 × 10 ⁶ laser pulses, as shown in FIG.

FIGS. 11 and 12 show overlapping plots of O ₂ concentration and laser power as a function of time in the purged beam path of the preferred embodiment. 11 and 12 show how the O ₂ concentration depends on the laser power.

The beam path enclosure of Figure 11 was purged with 99.999% pure N ₂ gas, or "grade 5" N ₂ gas. The lowest O ₂ concentration was observed when the laser was turned off (A).
The O ₂ concentration increases as the laser power increases from 0.2 ppm when the laser is turned off to 0.5 ppm when the laser is at full power (10 W).

The present invention has recognized that O ₂ is generated by the decomposition of residual H ₂ O in an incomplete N ₂ gas purge. Therefore, a high-purity inert gas is preferable. Inert gas may be an inert gas or other gas that does not absorb the VUV _{radiation, N 2, He, Ne,} Kr or Ar is preferred.
The inert gas preferably has a purity of 99.5% or more. Higher purity, for example at least 99.9% or more purity N ₂ gas is more preferable. The “5 grade” purity used in the experiments, ie, 99.999% nitrogen gas, is one example. Furthermore, it can be advantageous to use to reduce the O ₂ concentration of the "7 grade", i.e. Pajibimu passage outside the envelope of the preferred embodiment 99.99999% pure N ₂ gas.
A higher purity inert purge gas, such as 9 grade, ie 99.9999999%, results in a lower O ₂ concentration in the envelope. These purities can also be used for other inert gases such as He, Ne, Kr or Ar.

The beam path envelope of FIG. 12 was purged with N ₂ gas at a flow rate of about 150 liters / hour and 300 liters / hour. This figure shows that the O ₂ concentration decreases with increasing N ₂ flow rate. The laser is operated in the constant energy mode, and the laser power is set to a repetition rate of 100.
Hz to 1000 Hz. O ₂ concentrations were observed to decrease with decreasing laser power.

FIGS. 13-15 confirm the recognition of the present invention that the gas flow rate, the inert gas used and the laser power affect the concentration of oxygen in the envelope 24. FIG. FIG. 13 is a graph plotting the O ₂ concentration versus the purge flow rate when the laser is on and off for the argon purge gas and the nitrogen purge gas. The results of the experiment show that both gases, whether the laser is on or off,
Oxygen concentration decreases rapidly with flow up to about 150 l / h and gradually decreases from 150 l / h to 300 l / h. Nitrogen gas produced a lower oxygen concentration than argon purge gas under the same laser operating conditions. The oxygen concentration was greatly reduced when the laser was turned off compared to when the laser was turned on.

FIG. 14 shows that the flow rate of the nitrogen purge gas is 90 l /
The dependence of the oxygen concentration in the envelope 24 on the laser power when changing to h, 150 l / h and 270 l / h is shown. High oxygen concentrations were observed at low flow rates. Oxygen concentration increased with laser power at each flow rate, but at lower flow rates oxygen concentration increased more rapidly with laser power. For example, at 270 l / h, the oxygen concentration hardly increases for a laser power of 0-10 W and remains at about 0.2 ppm, but at 90 l / h, the oxygen concentration becomes 0 ppm.
From about 0.4 ppm to about 1.10 for -10 W laser power.
Increased to 0 ppm.

FIG. 15 shows the generated O ₂ concentration versus the nitrogen purge flow rate when the laser is operating at about 5.4 W.
Oxygen concentration from about 0.6 ppm at 50 l / h to 300 l / h
Is observed to decrease almost asymptotically to 0.005 ppm at which the plot shows V within the envelope.
An estimated concentration of oxygen generated by the UV laser beam is present, not a comprehensive O ₂ concentration.

In short, in the purging envelope 4 described above in which the purging gas is N2 of 5.0 grade, O ₂ and H
Contamination levels of 1 ppm or less for both ₂ O can be achieved. No tendency to approach the zero light level or the laser off level was observed with the laser operating for several days. VUV radiation itself appears to increase the O ₂ content in the exit of the envelope. The reasons may be for one or more of the following reasons. (A) decomposition of residual H ₂ O in the N ₂ purge gas; (b) gas generation from the mirror and / or beam splitter surface or from the wall of the envelope 4 (this gas also has a lower O ₂ content). Decrease as well as asymptotic decrease);

As described above and as shown in FIGS. 7 and 8, an increase in the level of O ₂ contamination is observed when the laser radiation is on as compared to when the laser is off.

Therefore, it is advantageous to provide the above-mentioned window 18 shown in FIG. 4 to separate the envelope 4 of the molecular fluorine laser from the purge volume and / or the workpiece of the external processing device to which the VUV beam is supplied. . Otherwise, V in envelope 4
Contaminants generated by the UV beam can contaminate the purge volume or workpiece of the external device to undesired or unacceptable levels.

Further, as a result of the experiment, when the PTFE hose is used for the envelope 4 composed of the laser purge gas line, the O ₂ contamination level is higher than when stainless steel and / or copper are used as the material of the envelope. Was found to occur. Accordingly, the envelope of the present invention advantageously uses stainless steel and / or copper as the envelope material.

The invention is also applicable to envelopes for beam paths of other radiation below 200 nm, such as radiation affected by absorption in O ₂ and H ₂ O. As an example, a 193 nm output emission of an ArF excimer laser is a frequency doubled output of a solid state laser or a dye laser.
That is, the variation of O ₂ is 193 nm beam path, and the other 200
The present invention is not limited to a fluorine molecular laser,
Advantageously, it also applies to lasers or other lasers operating below 200 nm.

The above description does not limit the scope of the present invention, and many suitable modifications are possible. The scope of the invention includes, in addition to the components recited in the claims, structural and functional equivalents to these components.

For example, US Pat. No. 6,005,
Nos. 880 and 09 / 317,695, 09 / 317,69
No. 5, No. 09 / 317,695, No. 09 / 317,695, No. 09/31
No. 7,695, No. 09 / 317,695, No. 09 / 317,695, No. 0
No. 9 / 317,695, No. 09 / 317,695, No. 09 / 317,695,
No. 09 / 317,695, No. 09 / 317,695, No. 09 / 317,695
No. 09 / 317,695 and 09 / 317,695 can be implemented in combination with the components described herein.

[Brief description of the drawings]

FIG. 1 is a graph showing the dependence of the transmittance of a 157 nm beam propagating along a 0.5 m exhaust beam path on residual air pressure.

FIG. 2: F ₂ laser or 20 operating at about 157 nm
Fig. 3 illustrates a first embodiment of a beam delivery system for other lasers, such as an ArF laser operating below 0 nm, which includes an envelope providing a beam path purged with an inert gas. .

FIG. 3 0.5 purged with helium or nitrogen gas
FIG. 7 is a graph showing the dependence of the transmittance of a 157 nm beam propagating along the m beam path on the number of flashes in the beam path.

FIG. 4. F ₂ laser or 20 operating at about 157 nm
Fig. 3 shows a preferred embodiment of a beam delivery system for other lasers, such as ArF lasers operating below 0 nm, wherein the system includes an envelope sealed with a transparent window providing a beam path purged with an inert gas. It has a vessel.

FIG. 5 also shows another embodiment in which the experimental apparatus and the detector P are replaced with an optical imaging system of a photolithography system and / or an outer housing containing the workpiece.

FIG. 6 shows spectral absorption data for a selected absorber species.

FIG. 7 illustrates the effect of switching off a laser on the level of O ₂ along a purged beam path according to a preferred embodiment.

FIG. 8 illustrates the effect of laser switchback on on the level of O ₂ along a purged beam path according to a preferred embodiment.

FIG. 9 shows the rate at which the inert gas purge beam path returns to a low contamination level after flushing the beam path with N ₂ .

FIG. 10 shows the rate at which the inert gas purge beam path returns to a low contamination level after flushing the beam path with ambient air.

[11] overlap plotting O ₂ concentration and laser power of purged beam passage as a function of time, O ₂
5 is an example of a graph showing how the concentration depends on the laser power.

[12] overlap plotting O ₂ concentration and laser power of purged beam passage as a function of time, O ₂
5 is another example of a graph showing how the concentration depends on the laser power.

FIG. 13 is a graph plotting the O ₂ concentration versus the purge flow rate when the laser is on and off for the argon purge gas and the nitrogen purge gas.

FIG. 14b at various nitrogen purge gas flow rates
6 is a graph showing the dependence of the oxygen concentration in the envelope on laser power.

FIG. 15 is a graph showing the dependence of the generated oxygen concentration in the envelope of FIG. 4b on the nitrogen purge flow rate when the laser is on.

[Explanation of symbols]

Reference Signs List 1 resonator 2 laser discharge chamber 3 electrode 4 housing or envelope 6 output coupling mirror 8 vacuum bellow 10 gas inlet 12 gas outlet 14 needle valve 16 pump port 18 VUV transparent window 20 work piece 22 VUV beam 24 envelope 26 entrance 28 Outlet 30 Moisture monitor system 32 0 ₂ Monitor system P Photodetector

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[Procedure amendment]

[Submission date] July 9, 2001 (2001.7.9)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 2

FIG. 3

FIG. 4

FIG. 5

FIG. 6

FIG. 7

FIG. 9

FIG. 11

FIG.

FIG. 8

FIG. 10

FIG.

FIG. 14

FIG. 13

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Klaus Fogler, Germany 37085 Göttingen lee Hittenwalder Straße 13 (72) Inventor Frank Foss, Germany 37581 Bad Gandersheim im Auf dem Mühlenstige 3 (72) Inventor Reinel Petzel Germany 37127 Dransfeld Bouldererberg 18 F-term (reference) 5F071 AA06 EE08 FF07 FF09 JJ03 JJ08

Claims (39)

[Claims] 1. VUV emitting at a wavelength below 200 nm
A laser system including a laser for generating a VUV laser beam and delivering it to a work piece, wherein the discharge system is filled with a laser active medium and is coupled to a power supply circuit, and generates a pulse discharge to excite the laser active medium. A plurality of electrodes; a resonator containing the discharge chamber and generating the VUV laser beam having a wavelength of 200 nm or less; and a hermetically connected to the laser and sealing at least a portion of a beam path exiting the laser from outside air. And an envelope having a plurality of ports, wherein the envelope is evacuated by the plurality of ports, an inert gas is flown into the envelope after the evacuation, and a laser beam is passed along the beam path. The beam energy propagates such that it can reach the workpiece with little attenuation by the light absorbing species present along the beam path. An enclosure for closing, a window for sealing the envelope, wherein the window is substantially transparent at the emission wavelength of 200 nm or less, and can emit a beam from the envelope, but contaminants generated in the envelope are A window that prevents the enclosure from exiting the enclosure and contaminating surfaces outside the enclosure. 2. A laser delivery system coupled to a laser that emits a laser beam at 200 nm or less and delivering the laser beam to an outer housing that ultimately leads to a workpiece, wherein the laser delivery system is air-tightly coupled to the laser. An envelope that seals at least a portion of the outgoing beam path from the outside air; evacuation of the envelope, flowing an inert gas into the envelope after evacuation, and directing a laser beam along the beam path;
A plurality of ports that allow the energy of the beam to traverse the envelope with little attenuation by light absorbing species present along the beam path; and a window that seals the envelope, Substantially transparent at the following emission wavelengths, the beam can exit the envelope and enter the housing, but contaminants generated within the envelope exit the envelope and contaminate surfaces within the housing: A laser delivery system comprising: 3. A discharge chamber filled with a laser active medium, a plurality of electrodes coupled to a power supply circuit to generate a pulsed discharge, and surrounding the discharge chamber and generating a laser beam at a wavelength of about 200 nm or less. A cavity and a beam path for the laser beam exiting the resonator of the laser system are sealed from the outside air and an inert gas is flowed into the beam path so that the energy of the beam is reduced along the beam path. Sealing means for propagating with little attenuation by the light absorbing species present along the beam path; and the beam allowing the light to exit the sealing means and enter the outer housing, while the contaminants are sealed to the sealing means. Means for preventing flow from the housing to the outer housing. 4. VUV emitting at a wavelength below 200 nm
A laser system including a laser for generating a VUV laser beam and delivering it to a work piece, wherein the discharge system is filled with a laser active medium and is coupled to a power supply circuit, and generates a pulse discharge to excite the laser active medium. A plurality of electrodes; a resonator containing the discharge chamber and generating the VUV laser beam having a wavelength of 200 nm or less; and a hermetically connected to the laser and sealing at least a portion of a beam path exiting the laser from outside air. An envelope having a plurality of ports, wherein the plurality of ports allow an inert gas having a purity of 99.5% or more to flow into the envelope to cause a laser beam to flow along the beam path. The energy of the beam is propagated so that it can reach the workpiece with little attenuation by light absorbing species present along the beam path. A laser system, comprising: an envelope. 5. The method of claim 1, further comprising a window sealing the envelope.
The window is substantially transparent at the emission wavelength below 200 nm and can emit a beam from the envelope, but contaminants generated within the envelope exit the envelope and contaminate surfaces outside the envelope. 5. The system according to claim 4, wherein the system is prevented. 6. A laser delivery system coupled to a VUV laser that emits a laser beam at 200 nm or less and delivering the laser beam to an outer housing that ultimately leads to a workpiece, wherein the laser is airtightly coupled to the laser. An envelope that seals at least a portion of the beam path exiting from the atmosphere from outside air; and flowing an inert gas having a purity of 99.5% or more into the envelope to direct a laser beam along the beam path along the beam path. A beam delivery system comprising: a plurality of ports that allow energy to traverse the envelope with little attenuation by light absorbing species present along the beam path. 7. The apparatus further comprises a window for sealing the envelope.
The window is substantially transparent at the emission wavelength of less than 200 nm, and the beam may exit the envelope and enter the housing, but contaminants generated within the envelope exit the envelope and remain within the housing. 7. The system of claim 6, wherein the system prevents contamination of the surface. 8. A discharge chamber filled with a laser active medium, a plurality of electrodes coupled to a power supply circuit to generate a pulse discharge, and surrounding the discharge chamber, generating a laser beam at a wavelength of about 200 nm or less. A cavity and a beam path for a laser beam exiting the resonator of the laser system, which is sealed from the outside air, and an inert gas having a purity of 99.5% or more flows into the beam path, and the laser beam is passed through the beam path. And a sealing means for transmitting energy of the beam along the beam path with little attenuation by light absorbing species present along the beam path. 9. The system further comprising means for allowing the beam to exit the sealing means and enter the outer housing, but for preventing contaminants from flowing from the sealing means to the outer housing. 9. The system according to claim 8, wherein 10. The system according to claim 1, wherein the inert gas is at least 99.9%. 11. The system of claim 10, wherein said inert gas is selected from a group of gases including nitrogen, argon, neon, krypton and helium. 12. The system according to claim 10, wherein said inert gas comprises nitrogen. 13. The system of claim 10, wherein said inert gas comprises argon. 14. The purity of the inert gas is 99.999.
%, Or more than one percent.
A system according to any one of the preceding claims. 15. The system of claim 14, wherein said inert gas is selected from a group of gases including nitrogen, argon, neon, krypton, and helium. 16. The system according to claim 14, wherein said inert gas comprises nitrogen. 17. The system according to claim 14, wherein said inert gas comprises argon. 18. The inert gas has a purity of 99.999.
9. A system according to any of claims 1-4, 6 or 8, characterized in that it is at least 99%. 19. The system of claim 18, wherein said inert gas is selected from a group of gases including nitrogen, argon, neon, krypton, and helium. 20. The system according to claim 18, wherein said inert gas comprises nitrogen. 21. The system of claim 18, wherein said inert gas comprises argon. 22. An overpressure of less than 50 mbar is maintained in said sealing means.
The described system. 23. The system according to claim 3, wherein said sealing means is made of one or more materials selected from the group consisting of stainless steel and copper. 24. The system according to claim 3, wherein said sealing means contains 0.5 ppm or less of O ₂ . 25. The device according to claim 25, wherein the blocking means is CaF _2, LiF ₂ ,
The system according to claim 3, wherein the system is made of a material selected from the group consisting of rF ₂ , MbF ₂ , LiF, BaF, quartz, and fluorine-added quartz. 26. A system according to claim 3, wherein said blocking means comprises CaF ₂ . 27. The method according to claim 1, wherein said laser beam is supplied by an F ₂ laser.
19. The system according to any of 0, 14 or 18. 28. The method according to claim 1, wherein said laser beam is supplied by an ArF laser.
19. The system according to any of 10, 14, or 18. 29. The method according to claim 4, wherein the inert gas flows at a flow rate of 150 liters / hour or more.
19. The system according to any of 8, 10, 14 or 18. 30. The plurality of ports include a port for evacuating the envelope prior to flowing the inert gas into the envelope, wherein the inert gas is less than approximately 0.2 liters / minute. 1-2, characterized by flowing at a flow rate of
19. The system according to any of 6, 10, 14 or 18. 31. The system of claim 30, wherein said envelope is maintained at an overpressure of about 50 mbar or less. 32. The sealing means includes means for evacuating the sealing means before flowing the inert gas through the sealing means, wherein the inert gas is flowed at a flow rate of about 0.2 l / min or less. The system according to claim 3 or 8, wherein 33. The system according to claim 32, wherein an overpressure of about 50 mbar or less is maintained in said sealing means. 34. The system according to claim 1, wherein the envelope is made of one or more materials selected from the group consisting of stainless steel and copper. . 35. The system according to claim 1, wherein the envelope contains less than 0.5 ppm O ₂ . 36. The window is made of CaF _2, LiF ₂ , Sr.
7. A method according to claim 1, wherein the material is selected from the group consisting of F ₂ , MbF ₂ , LiF, BaF, quartz and fluorine-added quartz. System. 37. The system according to claim 1, wherein the window is made of CaF ₂ . 38. The system according to claim 1, wherein the window is located between the envelope and an outer housing of an optical imaging device of a photolithography system. . 39. The system according to claim 3, wherein the blocking means is disposed between the sealing means and an outer housing of an optical imaging device of a photolithography system.