An excimer laser Overview
1. Definitions
Excimer is a compound in excited state into molecules in the ground state atoms dissociation association complex is unstable, the laser transition occurs in the bound state to the exclusion of the laser base state belonging Bound - free transition.
Excimer laser from the term "excited dimer", is a high-voltage pumped gas laser is a pulsed gas laser wavelength in the ultraviolet range. Gas is an inert gas such as argon and krypton inert gas such as chlorine or fluorine. When electrically energized, the gas mixture in a short time to an active state and polyethylene emit ultraviolet laser light, there XeF, KeF, ArF, XeCl, KrCl, ArCl and the like.
Having a pulse energy, high peak power, and the wavelength characteristics in the ultraviolet region.
2. Typical parameters excimer laser
3. History of development
(1) history of the development
1960 proposed excimer bound - free electrons generated gain ideas;
1970 Bosov using electron beam excitation intensity obtained liquid xenon excimer laser, the output wavelength of 172 nm;
In 1974, the United States Kansan State University reported the rare gas halide strong fluorescence radiation in the ultraviolet range.
After excitation mode: pure electron beam expander, self-sustaining discharge, the discharge preionization
(2) Development of excimer laser:
the Lambda Physik Company UV pre electrical configuration shown in Figure 1, a repetition frequency of 500Hz, the average power of about 750w
progress of a pneumatic transfer molecule laser life:
low-temperature cycle produce halide gas purification technology removed HF and other impurities in the molecule, a halogen gas injection to take supplementary technical loss during discharge, increasing the life of the inflator.
(3) Trend - High energy, high power, high repetition rate (high average power)
lithography applications, the quartz lens to reduce chromatic aberration generated on the resolution, the line widths required excimer 0.005-0.003nm within
to avoid excessive peak power, the need to develop a long pulse excimer laser, using the pre-pulse technology.
High voltage, high power pulsed power technology is the key, but it is still in the development stage.
4. Applications
Excimer laser for precision machining, the current in the main industrial applications: preparing a semiconductor chip, an integrated circuit (integrated circuits) and refractive surgery treatment of ocular (eye surgery), also for the manufacture of high-brightness LEDs.
(1) in an excimer laser projection lithography, doping, chemical vapor deposition, etching or the like induced super fine processing of semiconductor dwell
Laser Projection Lithography : to improve the resolution DRAM (Dynamic then memory) requirements 0.35μm or less, the easiest way is to use a shorter wavelength of deep ultraviolet light. And excimer laser having a high output power in the deep ultraviolet light, the exposure time is very short, while the spatial coherence of a laser may be implemented partially coherent illumination, so that the contrast of the projected image, and a scene effective resolution are improved. Patent especially high energy and facilitate focusing, dynamic graphical depiction.
Induced doping : forming ultra-shallow junctions using a short wavelength excimer laser, a narrow pulse, the characteristics of high energy, the doping period, the instantaneous rear surface of the semiconductor melt, and rapid crystallization, smaller crystal structure damage; local heating of the substrate, and can reduce defects induced auto-doping effect, low temperature processing characteristics; solid solubility limit ultra-doping, the doping concentration of the material from the solid solution.
Laser induced deposition : turn on laser photon energy to break chemical bonds directly to most source gas molecules, to produce the desired free radicals, the film deposition can be performed at or near room temperature conditions, is absorbed on a metal, dielectric laser induced deposition of the semiconductor film.
Laser-induced etching : a halogen radical generated by the decomposition of the light, is achieved by chemical etching processes etching of the substrate surface, etching the semiconductor has been achieved, metal, and polymer dielectric film. Due to the narrow high-energy pulse, generated locally very high temperatures, decomposition of the gas not only increases the concentration of free radicals, a halogen atom and exacerbated the rate of chemical reaction with the substrate, can achieve high etch rate.
The excimer laser processing characteristics
The different operating systems, the wavelength of the excimer laser in 192nm (ArF) to 351nm (XeF) range, corresponding to the photon energy 4-6eV, a variety of chemical bonds of organic molecules sufficient to break. An ultraviolet laser beam and the material acts microfabrication and cold working characteristics.
(1) excimer laser by laser-induced chemical removal process for each material shopping, avoiding the thermal effect of infrared laser faculty, having a "cold" processing characteristics
(2) the shortest wavelength excimer laser, having a higher resolution in the process, submicron structures can be formed, and means for processing micron pores having fine processing characteristics.
6. rationale
NLO - stimulated Raman scattering gain coefficient depends only on the intensity of the pump light, to improve the beam quality of the excimer
7. excimer laser major manufacturers
West Germany's Lambda Physik
American Questek
Canada Lumonics
8. research
(1) Analog excimer laser energy distribution
FIG spot energy distribution observed approximately Gaussian energy distribution of the spot in the X direction, as an irregular energy distribution in the Y direction obtained by analyzing the distribution model of laser energy space molecule:
（2）
two,