Laser surface treatment device and method

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65392, 65441, 65 2912, 65 2918, 65 332, 65117, 356369, 2191216, 21912161, 21912162, 21912185, C03B 27012, C03B 524, C03B 526, C03B 3701, C03B 37018

Patent

active

060734647

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to laser surface treatment, and the monitoring thereof.
It finds particular application in the annealing of amorphous silicon samples by excimer laser.


BACKGROUND OF THE INVENTION

In general terms, the purpose of applying a laser beam to a surface is to modify the surface, its structure and its physical state.
In practice, the mechanism involves a partial fusion of the surface, in the case of the crystallization of amorphous silicon.
The Applicant identified a problem of providing a device and a method for monitoring, in real time, on site, both rapidly and nondestructively, a laser surface treatment in which there are at least two generally similar surface fields to be treated, of given depth, to each of which there is to be applied, on one or more occasions, a laser beam treatment, with characteristics chosen so as to change the physical state of each surface field.
The present invention affords a solution to this problem.


SUMMARY OF THE INVENTION

According to a general definition of the invention, the method is characterized by the fact that it effects at least one ellipsometry measurement before at least one of the applications of the laser beam treatment to the second surface field, in at least one area of the first surface field, in order to obtain a characterization of the first surface field, the application of the laser beams and the ellipsometry measurement being performed under generally similar working conditions, which makes it possible to monitor in real time, on site, nondestructively and rapidly, the change in physical field state of each surface field by means of said characterization.
According to one embodiment of the invention, the ellipsometry measurement is spectroscopic.
According to another embodiment of the invention, the ellipsometry measurement is performed at one or several wavelengths.
The optical analysis known as "spectroscopic ellipsometry" normally used in the field of research and development, is known. This type of analysis allows the characterization of a single layer or multilayer stack in a relatively wide range of thicknesses.
It is theoretically possible to use such an optical analysis for monitoring the change in physical state of a surface obtained by laser treatment. However, among other factors, the complexity, the cost of such an analysis, the time required and the size of both the laser and the ellipsometer, is such that persons skilled in the art have not until the present thought of using it in this application, for industrial purposes.
The Applicant observed that it is possible to arrange the analysis field of the ellipsometer to substantially cover (in depth, but at a point) the three-dimensional surface field (often referred to hereinafter as the "surface", in order to simplify) affected by the impact of the laser beam. This opens numerous possibilities for monitoring the laser treatment of different layers of a given surface. In addition, it was observed that this analysis and the laser treatment can be implemented under generally similar working conditions by metrology and/or optical means which are relatively simple and inexpensive, and which facilitate obtaining a reduced bulk, helping to reduce the costs of implementing the method and device of the invention.
In addition, the Applicant observed that the interval of time between two applications of a high-power laser beam makes it possible to effect at least one ellipsometry measurement between laser applications.
The Applicant also observed that physico-chemical characterization by ellipsometry not only allows monitoring, carried out before and/or after the laser treatment, but also allows for the optimization of at least some of the parameters of the laser treatment.
According to the invention, this optimization of the laser treatment takes place according to a predetermined law dependant at least partly on the physico-chemical characterization, before, during or after each step of the laser treatment.
In practice, one of the parameters of t

REFERENCES:
patent: 4962065 (1990-10-01), Brown et al.
patent: 5313044 (1994-05-01), Massoud et al.
patent: 5798837 (1998-08-01), Aspnes et al.
patent: 5858819 (1999-01-01), Miyasaka
patent: 5864393 (1999-01-01), Maris

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