Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Reexamination Certificate
1999-05-19
2002-09-17
Markoff, Alexander (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
C134S001000, C134S902000
Reexamination Certificate
active
06450180
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process and apparatus for treating surfaces with laser light, particularly, though not necessarily, for the removal of foreign materials from substrate surfaces, e.g. removal of photoresist from semiconductor surfaces.
BACKGROUND OF THE INVENTION
In the manufacturing of various products it is necessary to apply a layer of protective material on a surface, which must be removed after a specified manufacturing step has been concluded. An example of such process is the so-called “masking”, where a pattern is created on a surface using a layer of protective material illuminated through a mask, and the surface is then treated with a developer which removes material from the unmasked portions of the surface, therefore leaving a predetermined pattern. The surface is then treated by ion implantation or by etching agents, which introduce the implanted species into the unmasked portions of the surface, or removes material from unmasked portions. Once these processes are completed, the role of the protecting mask ends and it must be removed. The process is conventional and well known in the art, and is described, e.g., in U.S. Pat. No. 5,114,834.
U.S. Pat. No. 5,114,834 describes photoresist removal by ablation, using laser UV radiation, in an oxidizing environment, as described. The ablation process is caused by strong absorption of the laser pulse energy by the photoresist. The process is a localized ejection of the photoresist layer to the ambient gas, associated with a blast wave due to chemical bonds breaking in the photoresist and instant heating. The partly gasified and partly fragmented photoresist is blown upwards away from the surface, and instantly heats the ambient gas. Fast combustion of the ablation products occurs, due to the blast wave and may also be due to the photochemical reaction of the UV laser radiation and the process gases. The main essence of the process is laser ablation with combustion of the ablated photoresist which occurs in a reactive gas flowing through an irradiation zone. The combination of laser radiation and fast combustion provides instantaneous lowering of the ablation threshold of hard parts of the photoresist (side walls). The combusted ablation products are then removed by vacuum suction, or by gas sweeping leaving a completelyclean surface.
Copending patent applications Nos. IL 115931 and IL 119246 (attorney's docket No. 4009) of the same applicant, the contents of which are incorporated herein by reference, describe and claim improved processes for laser removal of foreign materials from surfaces in the presence of reactive gases.
EP-A 0 200 089, corresponding to U.S. Pat. No. 4,670,639, discloses and claims a method for forming narrow metal-free strips in a metallic layer on a plastic sheet, from which capacitors are manufactured, which consists in moving the sheet relative to a plurality of pulse laser beams, arranged parallel to one another in a single plane parallel to the direction of translation of motion of the sheet, to successively generate metal-free areas which are overlapped to form a narrow, completely metal-free strip. The footprint of the laser beam is circular and therefore adjacent two prints overlap to form a wavy edge. The metal-free strips are spaced from one another to leave a metallized area between them. The plastic sheet is then divided into capacitor elements in correspondence to the metal-free strips, which constitute an insulating edge region of the metallization.
While reference is made in this specification to the ablation of photoresist from semiconductor wafers, this will be done for the sake of simplicity, and because it represents a well known and widely approached problem. It should be understood, however, that the invention described hereinafter is by no means limited to the stripping of photoresist from wafers, but it applies, mutatis mutandis, to many other applications, such as stripping and cleaning of photoresist from Flat Panel Displays (FPD) or removal of residues from different objects, such as lenses, semiconductor wafers, or photo-masks.
The laser treatment for the removal of foreign material from surfaces, developed by the art until now, have been found to present certain drawbacks.
One drawback consists in that, as the laser beam sweeps over the surface to be treated, the gases in contact with said surface become depleted of oxidizing components and therefore less effective for the treatment and the depleted gases diffuse beyond the zone which has undergone treatment to the neighboring zones, so that, as the laser beam sweeps over said surface, it encounters increasingly depleted and ineffective gases. Another drawback is that, as a zone of the body being treated is contacted by the laser beam and heated thereby, heat is transferred to some extent to neighboring zones, so that as the laser beam sweeps over the surface to be treated, it encounters zones increasingly heated by conduction, the temperature of which becomes increasingly higher than that required for the treatment. A further drawback is that relatively deep and narrow depressions of the surface to be treated, and particularly their side walls, are not reached by the laser beam as fully as desirable
It is a purpose of this invention to provide an improved process and apparatus for laser removal of foreign materials from surfaces.
It is another purpose of this invention to provide such a process and apparatus which eliminates the drawbacks of the known processes.
It is a further purpose of this invention to provide such a process and apparatus for laser treatment in the presence of reactive gases which permits to maintain an optimal composition of said gases over the treated zones.
It is a still further purpose of this invention to provide such a process and apparatus which avoids overheating of any portions of the treated body.
It is a still further purpose of this invention to provide such a method and apparatus that are based on simple and reliable optical means.
It is a still further purpose of this invention to provide such a method and apparatus that permits fully to treat the depressions of the treated surfaces, and in particular their side walls.
It is a still further purpose of this invention to provide a method and apparatus for the surface treatment of materials by laser pulses wherein which provide essentially stable conditions from pulse to pulse, without residual influence from previous pulses.
Other purposes and advantages of the invention will appear as the description proceeds.
SUMMARY OF THE INVENTION
The method of laser treatment of surfaces according to the invention comprises the steps of:
1) projecting onto the surface to be treated laser pulses defining a beam;
2) causing said beam and said surface to be treated to become relatively displaced in such a way that said beam will intersect at each number of pulses, preferably at each pulse, an area of said surface that is different from and non-adjacent to the area the beam intersected before said displacement; and
4) continuing to cause that the beam and said surface to be treated so to become relatively displaced, until all of said strips have thus been treated by the laser beam.
Preferably, the surface to be treated is ideally divided into a number of strips and said beam and said surface are caused to become relatively displaced in such a way that said beam will intersect at each number of pulses, preferably at each pulse, an area of said surface comprised in a strip that is different from and non-adjacent to the strip in which was comprised the area the beam intersected before said displacement.
The surface to be treated will be called hereinafter “the substrate surface”. The substrate surfaces are generally not plane or smooth, but have projections and/or recesses created e.g. in the masking process or in another process used for imparting to said surface the desired pattern and properties. The expression “ideal surface corresponding to the surface to be treated” or “to the substrate surface”, or, brie
Ghilai Shay
Levinsohn Natalie
Zahavi Dov
Baker & Botts LLP
Markoff Alexander
Oramir Semiconductor Equipment Ltd.
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