Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-06-28
2003-02-18
Ball, Michael W. (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S233000, C156S234000, C156S272800, C156S345420, C219S121600, C427S597000
Reexamination Certificate
active
06521068
ABSTRACT:
The invention relates to a method of detaching a segment disposed on a carrier from a material layer extending in a layer plane and having a specific layer thickness, by means of a laser pulse passing through the carrier.
A method of this type known from DE 196 40 594 provides for the layer disposed directly on the carrier being destroyed as such by the effect of light and detachment of the segment therefore occurring as a result of the destruction.
The destruction of part of the material layer or of a layer specially provided for the purpose application takes place with a relatively long time scale of the order of nanoseconds with the result that in the end the entire layer is heated up and also that the segment is detached with an insufficiently precise boundary surface.
The so-called LIFT processes work in a similar fashion, producing even large quantities of molten material, which give rise to material contamination around the region to be detached and are especially undesirable in microtechnology.
The objective of the invention is therefore to detach segments from a material layer with as little thermal stress and as few thermal side effects as possible.
In a method of the type described in the introduction, this objective is achieved according to the invention in that the laser pulse within a partial layer volume of the segment—the said partial layer volume butting against the carrier, lying in the plane of the layer within an extent of the beam cross-section of the laser pulse and extending transversely to the layer plane via a part of the layer thickness—produces superheated matter in a state of thermodynamic non-equilibrium and of a density similar to the solid state and in that a cohesive, solid partial layer remains in the segment on the side of the partial layer volume opposite to the carrier, the said partial layer being urged away from the carrier by the superheated matter.
The advantage of the solution according to the invention is observable in that, as a result of the specially produced superheated matter in a state of thermodynamic non-equilibrium, instead of the conventional evaporation process of the material, a so-called explosive evaporation now occurs, which on the one hand produces a very high pressure consequently causing marked acceleration during detachment of the cohesive, solid partial layer which, for example, permits precise detachment of the segment from the layer and which on the other hand, on account of the short time duration, avoids thermal stressing of the cohesive, solid partial layer forming the segment. The result of this is that, with the method according to the invention, on the one hand large forces of acceleration are available for the cohesive, solid partial layer, the acceleration forces furthermore being combined with the fact that, on account of the explosive evaporation, the cohesive, solid partial layer undergoes far less thermal stress than with the known method, with the result that here the adverse thermal secondary effects are substantially eliminated.
In particular in the solution according to the invention, a highly excited non-thermodynamic state is achieved with ultra-short laser pulses, in which arrangement the electron temperature may far exceed that of the phonones. The stored energy is transferred from the electrons to the phonone system with a characteristic material-dependent time, for example of the order of magnitude between 50 femtoseconds and 2 picoseconds, in a volume which is determined by the extent of the partial layer volume in the plane of the layer and the extent of the partial layer volume transversely to it, due to the thermal penetration depth of the electrons which, for example at a pulse duration of 100 femtoseconds, is of the order of magnitude of 50 nm. Thus the phonone system can be heated extremely rapidly to a zone above the critical temperature without a conventional evaporation process taking place.
In particular, the high pressure briefly arising due to the explosive evaporation brings about the already described greater acceleration of the cohesive, solid partial layer, which is also responsible for the fact that the thermal stressing of the material is less in the cohesive, solid partial layer.
In an embodiment of the method according to the invention, superheated matter is preferably in the state of thermodynamic non-equilibrium at a temperature above the critical temperature.
Advantageously, the superheated matter according to the invention is producible only with laser pulses, the pulse duration of which is less than 100 picoseconds and the pulse duration of which is so short that it impossible to establish a thermodynamic equilibrium.
In the solution according to the invention, it is especially advantageous if, at least at the beginning, the material of the material layer is present in the superheated matter substantially unchanged and the matter thus simply possesses more energy than before the action of the laser pulse but does not itself change for example chemically.
In the method according to the invention, it is furthermore advantageous if the superheated matter from material of the material layer expands substantially stoichiometrically during detachment of the segment, i.e. that the material composition does not change during expansion of the superheated matter and thus no contaminants occur due to degrading material, with the result that in particular the arising cohesive, solid partial layer, which is detached from the carrier, is not contaminated with constituents resulting from degradation of the superheated matter and thus from non-stoichiometric expansion.
In an embodiment according to the invention, it is furthermore advantageous if the storage of energy in the superheated matter takes place in the electron system only until thermal losses occur.
As regards the description of the method according to the invention, so far it has merely been assumed that at least one laser pulse is necessary. It is especially advantageous if detachment of the segment is performed with a single laser pulse.
Especially great accelerations of the cohesive, solid partial layer can then be achieved if the cohesive, solid partial layer is accelerated away from the carrier by hydrodynamic expansion of the superheated matter in the partial layer volume. An extremely precise tearing of the cohesive, solid partial layer from the surrounding layer is hereby achievable, especially when the segment is still connected with the surrounding layer.
In a large number of applications it is sufficient to detach, i.e. for example to lift off, from the carrier only the cohesive, solid partial layer as a segment from the layer.
However, it is especially advantageous if the cohesive, solid partial layer is accelerated in the direction of a substrate. Here in particular the solution according to the invention lends itself as especially suitable since, by comparison with the state of the art, it is capable of exposing the cohesive, solid partial layer to large forces of acceleration and thus of moving it on to a substrate with great precision.
In this solution it is especially advantageous if the cohesive, solid partial layer is fixed on the substrate, it being possible for this purpose to prepare the substrate for receiving the cohesive, solid partial layer in such a way that adhesion contributes to the fixing.
However, it is especially advantageous if the energy of impact of the cohesive, solid partial layer on the substrate leads to adequate fixing on the latter. Here too, in particular the solution according to the invention can be used highly advantageously since, on account of the large forces of acceleration, it is predestined for fixing the cohesive, solid partial layer on the substrate by means of its impact energy.
The fixing takes place for example in the form of a so-called “cold bonding” of the cohesive, solid partial layer with the substrate.
In this arrangement the substrate is advantageously positioned at a distance from the carrier at which impact-determined fixing of the cohesive, solid partial
Baehnisch Ralf
Huettner Bernd
Menschig Arnd
Ball Michael W.
Haran John T.
Menschig Arnd
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