Coherent light generators – Particular resonant cavity – Plural cavities
Patent
1998-01-22
2000-01-11
Lee, John D.
Coherent light generators
Particular resonant cavity
Plural cavities
372 23, 372 68, 21912161, H01S 3082
Patent
active
060144017
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns the control of a laser source with multiple laser units for the energy and spatial optimization of a laser surface treatment.
It finds a general application in laser surface treatment, such as descaling, cleaning, polishing and preparing a surface. More particularly it finds application in the annealing, by excimer laser, of layers of amorphous silicon placed on a substrate.
In general terms, the annealing of amorphous silicon by excimer laser consists of raising the temperature of the layer of amorphous silicon very rapidly to the melting point in order to obtain crystallization in the form of a polysilicon. The melting of the layer of silicon must not for all that disturb the standard glass substrate too significantly.
In practice, the heating effect is due to the optical absorption of the laser beam by a thin film of amorphous silicon, for example over a thickness of less than 30 nm.
Annealing amorphous silicon by excimer laser requires excellent knowledge of the structural characteristics of the sample to be treated, as described at least partly in the patent application entitled "Device and method of controlling laser surface treatment", filed in France by the Applicant, on Aug. 11, 1995, under the number 95 09778, the content of which forms an integral part of the present application for all useful purposes.
First, heating by laser must be effective since it greatly influences the thermal change in the sample, notably with regard to the melting of the layer of silicon, which must be complete, and with regard to the melting of the substrate, which must be avoided.
Secondly, the speed of cooling and solidification of the layer of silicon must be relatively slow since it determines the size of the polysilicon grains present in the layer after annealing, since the large crystals are the most favourable to optimum functioning, for certain microelectronic devices based on silicon.
Applicant has observed that such an optimum treatment, from an energy and spatial point of view, is difficult to obtain using a single laser source.
Applicant therefore, proposes to use a laser source comprising at least two laser units.
However, the control of a laser source with several units, in combination with the laser surface treatment is, in its turn, difficult to implement.
The present invention affords a solution to this problem.
SUMMARY OF THE INVENTION
The object is a device for controlling a laser source comprising at least two laser units and coupling means suitable for coupling the laser beams coming from each unit in order to deliver a resulting laser beam intended for surface treatment.
According to a general definition of the invention, provision is made, in combination with the laser surface treatment, to regulate the characteristics of the laser beams coming from each laser unit in order to obtain a resulting laser beam with a time profile of energy adapted optimally to the said laser surface treatment, and homogenizing means suitable for spatially homogenizing the energy distribution of the resulting laser beam, which makes it possible to adapt in combination the spatial and energy distribution of the resulting laser beam to the chosen surface treatment. The resulting laser beam means a beam consisting of a plurality of initial laser beams.
In practice, in the application consisting of the annealing of amorphous silicon by excimer laser, the time profile of the power of the resulting laser beam comprises a steep rising edge for improving the efficacy of the heating, a substantially flat peak corresponding to a depth of treatment, chosen so as to obtain a complete melting of the layer of amorphous silicon to the said depth, while avoiding the melting of the substrate, and a gentle falling edge for promoting recrystallization.
DESCRIPTION OF THE DRAWINGS
Other characteristics and advantages of the invention will emerge in the light of the following detailed description and the drawings in which:
FIG. 1 schematically a laser source comprising thre
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Godard Bruno
Stehle Marc
Lee John D.
Societe de Production et de Recherches Appliquees
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