Coherent light generators – Particular component circuitry – Optical pumping
Patent
1998-02-26
2000-07-04
Scott, Jr., Leon
Coherent light generators
Particular component circuitry
Optical pumping
372 33, 372 29, H01S 300
Patent
active
060848979
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a laser processing device comprising a laser device which performs a burst operation, and a processing device which subjects a semiconductor, macromolecular material, or inorganic material to a predetermined type of work using the laser light produced from the laser device.
BACKGROUND ART
In reduction projection exposure devices (referred to as "steppers" hereinbelow) which use a laser to carry out the exposure processing of a circuit pattern, the amount of exposure needs to be strictly controlled in order to maintain the resolution of the circuit pattern above a certain level. On the other hand, because the excimer lasers used as light sources for such steppers are what are known as pulse-discharge excitation gas lasers, the pulse energy of every pulse varies, and there is a need to reduce this variation in order to improve the precision with which the amount of exposure is controlled.
Thus, as seen in the literature (Miyachi et al, "Excimer Laser Lithography", Kokusai Laser/Application '91, Seminar L-5, p 36-51), for example, there have been attempts to improve the precision with which the amount of exposure is controlled by means of what is known as multiple-pulse exposure wherein exposure is carried out by continuously oscillating a plurality of pulses. This is to say, this technique attempts to reduce variation in the total amount of exposure by increasing the number of exposure pulses.
Now, in a stepper, exposure and mount movement are repeated alternately. Therefore, the mode of operation of the excimer laser constituting the light source is inevitably a burst mode involving the repetition of an operation in which laser light is continuously oscillated in pulses a predetermined number of times, and then the pulse oscillation is stopped for a predetermined time. In other words, the burst mode involves the alternate repetition of a continuous pulse oscillation time and an oscillation-stopping time.
It should be noted that when "continuous pulse" and "continuous pulse oscillation" are referred to in this specification, they are used with the meaning that pulse discharge is repeatedly carried out and successive pulse laser light can be repeated; and they are used with a different meaning from "continuous oscillation laser" and "CW oscillation" as referred to more generally.
Now, as mentioned above, because excimer lasers are pulse discharge excitation gas lasers, it is difficult to always sustain the oscillation at pulse energy of a constant magnitude. Reasons for this include that the discharge produces density disturbances in the laser gas within the discharge space and causes the subsequent discharge to become non-uniform and unstable, and that such non-uniform discharges and the like produce local temperature increases at the surfaces of the discharge electrodes, and cause degradation of the subsequent discharge and cause the discharge to become non-uniform and unstable.
In particular, this tendency is marked at the start of the abovementioned continuous pulse oscillation period, and a phenomenon known as spiking occurs whereby, as shown by the portion S in FIG. 8(a), relatively high pulse energy is obtained in the initial pulses following the passage of an oscillation-stopping period, but then the discharge degrades and the pulse energy gradually reduces. This is to say, as shown in FIG. 8, even if laser oscillation is undertaken at a predetermined constant discharge voltage corresponding to a constant pulse energy Ps in order to obtain this level of energy, in practice a number of pulses of pulse energy will initially be larger than Ps.
Thus, excimer laser devices operating in burst mode have problems in that the abovementioned variation in the energy of each pulse reduces the precision with which the amount of exposure is controlled, and the phenomenon of spiking also markedly increase such variation and greatly reduces the precision with which the amount of exposure is controlled.
In recent years, moreover, the sensitivity of light-sensitive a
REFERENCES:
patent: 5260961 (1993-11-01), Zhou et al.
patent: 5661744 (1997-08-01), Muraakami et al.
John D. Cuthbert, "Optical/Laser Microlithography V," in the Proceedings of SPIE--The International Society for Optical Engineering, pp. 473-485 and including cover page, copyright page & Table of Contents iii-viii (1992).
Shakushi Tetsuo
Wakabayashi Osamu
Jr. Leon Scott
Komatsu Ltd.
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