Process for separating a plate into individual components

Abstract

Disclosed is a method for separating a plate into multiple individual detached components or cutting the plate into chips. The back end process for a plate includes providing a substrate; attaching the plate to the substrate using a sacrificial layer that is made of materials that in a solid state at ambient temperature and ambient pressure, and having a transformation temperature into one or more gaseous compounds at ambient pressure of between 80° C. and 600° C.; and separating the plate attached on the substrate into a plurality of plate portions; increasing temperature and/or reducing surrounding pressure to transform the sacrificial layer into one or more gaseous compounds.

Claims

1. A process for back end processing of a plate in order to obtain a plurality of individual detached electrical, optical or optoelectronic components, comprising: a) providing a substrate; b) attaching the plate to the substrate by means of a sacrificial layer located between the plate and the substrate, the sacrificial layer being in contact with the plate and with the substrate, the sacrificial layer being made from at least one material that is in a solid state at ambient temperature and ambient pressure, the sacrificial layer having a transformation temperature into one or more gaseous compounds at ambient pressure of between 80° C. and 600° C.; c) separating the plate that is attached to the substrate into a plurality of plate portions that are attached to the substrate, the substrate remaining as a single piece; and d) increasing a temperature and/or reducing a surrounding pressure to a sufficiently high temperature and/or a sufficiently low pressure, respectively, such that the sacrificial layer attached to the plurality of plate portions is transformed into one or more gaseous compounds and the plurality of plate portions remain attached directly to the substrate.

2. The process according to claim 1, wherein the separation step c) includes a step of dicing the plate attached to the substrate by the sacrificial layer.

3. The process according to claim 2, wherein the plate is diced by etching.

4. The process according to claim 3, wherein the etching is plasma etching.

5. The process according to claim 2, wherein the dicing is carried out or induced by means of a laser.

6. The process according to claim 2, wherein the dicing is carried out or induced mechanically.

7. The process according to claim 1, wherein, prior to step b) of attaching the plates to the substrate, grooves are hollowed out on one face of the plate, referred to as a grooved face, said grooves not reaching a face of the plate that is opposite to said grooved face, during the step b), said grooved face is in contact with the sacrificial layer, during the step c) of separating the plate, the plate is thinned via the face opposite said grooved face, at least until the grooves are reached.

8. The process according to claim 1, wherein the sacrificial layer comprises at least 70% by mass of crude polymers.

9. The process according to claim 8, wherein said crude polymers consist of more than 70% by mass of polypropylene carbonate molecules, other polycarbonate molecules and/or polynorbornene molecules.

10. The process according to claim 1, wherein the plate is obtained from a wafer essentially comprising silicon Si, germanium Ge, gallium arsenide GaAs, indium arsenide InAs, indium phosphide InP, gallium phosphide GaP, gallium antimonide GaSb, indium antimonide InSb, silicon carbide SiC, gallium nitride GaN, aluminium nitride AIN, and/or diamond.

11. The process according to claim 1, wherein the sacrificial layer has a transformation temperature to the gaseous state at 100 kPa of between 80° C. and 600° C.

12. The process according to claim 1, wherein the attachment of the plate to the substrate via the sacrificial layer is carried out at a temperature greater than a glass transition temperature of the material or materials of the sacrificial layer.

13. The process according to claim 1, wherein the plate and the substrate have expansion coefficients that are equal or vary by less than 5%.

14. The process of claim 6, wherein the dicing is carried out using a saw blade.

15. The process according to claim 3, wherein the dicing is carried out or induced by means of a laser.

16. The process according to claim 4, wherein the dicing is carried out or induced by means of a laser.

17. The process according to claim 3, wherein the dicing is carried out or induced mechanically.

18. The process according to claim 4, wherein the dicing is carried out or induced mechanically.

19. The process according to claim 2, wherein, prior to step b) of attaching the plates to the substrate, grooves are hollowed out on one face of the plate, referred to as a grooved face, said grooves not reaching a face of the plate that is opposite to said grooved face, during the step b), said grooved face is in contact with the sacrificial layer, during the step c) of separating the plate, the plate is thinned via the face opposite said grooved face, at least until the grooves are reached.

20. The process according to claim 1, wherein the sacrificial layer has a transformation temperature to the gaseous state at 100 kPa of between 230° C. and 350° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood with reference to the figures, which illustrate non-limiting embodiments given by way of example.

(2) FIGS. 1 to 6 are sectional and very schematic views, illustrating an example of the process according to an embodiment of the invention.

(3) FIGS. 7 to 11 are sectional and very schematic views, illustrating an example of the process according to another embodiment of the invention.

(4) FIG. 12 is a flow chart of process steps in accordance with a non-limiting embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) Identical reference signs are used from one figure to another in order to designate identical or similar elements.

(6) With reference to FIG. 1 and the flow chart of FIG. 12, a rigid substrate 2 is provided, for example a sapphire substrate.

(7) This substrate 2 is covered with a sacrificial layer 3.

(8) This sacrificial layer is composed of more than 99% by mass of polymer molecules, for example polypropylene carbonate molecules.

(9) This polymer material 3 can, for example, be applied on the substrate by the same usual methods of application of a photosensitive resin.

(10) The polymer can be applied in solution in a solvent, the solvent evaporating rapidly after the application.

(11) The evaporation of the solvent can be terminated by an annealing at a temperature less than the decomposition temperature of the polypropylene carbonate.

(12) A plate 1 is deposited on this polymer material 3, which is firmly attached by applying a mechanical pressure perpendicular to the plate, at a temperature above the glass transition temperature of the sacrificial material.

(13) As illustrated in the figures, this plate can comprise interconnections 7 and a metallisation layer 8 (ground plane).

(14) The material of the solid layer 3, ensures the attachment of the plate 1 to the substrate 2, as illustrated by FIG. 2.

(15) The plate 1 has been obtained from a wafer, for example of GaAs, on which has been deposited, in known manner, elements constituting an integrated semiconductor circuit, such as a barrier layer, a channel layer, drains, sources, etc., which are not shown here.

(16) In this example, the plate 1 is in contact with the sacrificial layer 3 via its backside.

(17) In this example, the plate 1 can, for example, have a thickness of order of 50 μm, and be intended to be used as components which process signals with frequencies of 300 GHz, which require that the thickness is not larger, in order to avoid stray transmission modes inside the chip.

(18) With reference to FIG. 2, which shows the plate attached to the substrate 2 before dicing, it is relatively easy to carry out transport and measurement operations by means of a probe, because the thickness of the substrate 2 compensates for the low thickness of the plate 1 and provides the mechanical strength necessary in order to considerably limit the risk of damage.

(19) These measures can sometimes be accompanied by increases in temperature, under conditions such that the sacrificial layer remains intact, in which case it is judicious to choose a substrate having an expansion coefficient close to that of the plate. In this example, the substrate is a sapphire substrate and the plate is a GaAs plate, but a substrate could be provided that is produced from the same material as that of the wafer from which the plate originates.

(20) With reference to FIG. 3, in order to prepare the dicing step, the photoresist material 4 is deposited so as to define rectilinear openings 5, corresponding to futures dicing.

(21) Conventionally, rectilinear openings are provided extending perpendicularly to the plane of the drawing, such as those 5 visible in the figure, and other rectilinear openings parallel to one another and crossing the rectilinear openings extending perpendicular to the plane of the sheet.

(22) With the methods of dicing by etching or by laser, these openings are not compulsorily rectilinear.

(23) This dicing grid can thus define thousands of future components on a same plate.

(24) A plasma is then applied, so as to etch the plate 1 at the dicing locations 5, as illustrated by FIG. 4. An RIE (“Reactive ion etching”) type etching can be used.

(25) The plate 1 is then diced into a plurality of plate portions 1′ each corresponding to an individual component. In this example, these portions 1′ rest on a same sacrificial layer 3.

(26) By contrast, the substrate is not diced and remains in one piece.

(27) A second plasma, of dioxygen, can then be applied, in order to remove the mask 4 and to hollow out the sacrificial layer at the locations defined by the openings 5, as illustrated by FIG. 5.

(28) The temperature is then increased, for example to 270° C., so that the polymers of the sacrificial layer 3 decompose and evaporate, as illustrated in FIG. 6.

(29) The components 1′ then adhere to the substrate 2 through relatively weak forces (probably Van der Waals forces), thus allowing the assembly to be moved while preserving the positions of the components 1″ on the substrate.

(30) A tool 6 providing a light vacuum suction makes it possible to easily detach the components 1′ from the substrate 2.

(31) In the embodiment of FIGS. 7 to 11, grooves 19 are initially defined, for example on a front side of a thick plate 11.

(32) On this front side, interconnections 17 have already been obtained by processes known from the prior art, which symbolise the presence of an integrated circuit.

(33) These grooves 19 can be hollowed out by processes that are known per se, for example by etching, by laser or by mechanical means.

(34) The locations of the grooves correspond to the edges of the future chips.

(35) These grooves will be hollowed out to a greater depth than the final thickness of the chips.

(36) Then, as illustrated in FIGS. 7 and 8, the plate 11 is attached via its front side on the substrate 12 by means of a sacrificial layer 13.

(37) Holes can then optionally be hollowed out through the substrate 12.

(38) The plate 11 is then thinned to the final thickness of the chips, which has the effect of separating the chips. It is possible, for example, to polish the plate 11 until the grooves 19 are reached.

(39) The plate portions 11′ can then have a thickness of order 50 μm or 100 μm.

(40) After cleaning and optional technological steps such as the hollowing of via-holes through the chips and the metallisation of the backside of the chips (see reference sign 18 in FIG. 10), annealing is performed at the transformation temperature (or above) of the sacrificial layer, in order to detach the chips from the substrate.

(41) As shown in FIG. 11, the sacrificial layer has then disappeared and the chips 11″ adhere lightly to the substrate 12.

(42) In an alternative embodiment that is not shown, it is possible to etch via-holes before the thinning step. It would then be judicious to clean the via-holes once the thinning is performed.

(43) In an alternative embodiment that is not shown, the plate can be grooved on its backside and attached to the substrate by its backside. Once thinned, it is possible to carry out various processes, for example depositing of layers, etchings, etc., and which is all the easier when the substrate is rigid because then the alignments are controlled.