Method for recycling a substrate holder

Abstract

A method for recycling a substrate holder adapted to receive a substrate for at least one deposition step of a layer of a material on the substrate also leading to the depositing of a layer of a material on the substrate holder, the method including implanting ion species through a receiving surface of the substrate holder so as to form at least one buried weakened plane delimiting a thin film underneath the receiving surface of the substrate holder, exfoliating the thin film from the substrate holder so as to break up the thin film, and removing a stack including at least one layer of a material deposited on the thin film resulting from the at least one deposition step of the layer of a material on the substrate.

Claims

1. A method for recycling a substrate holder of which one surface, called the receiving surface, is adapted for receiving and handling a substrate designed for at least one deposition step of a layer of a material on said substrate, the deposition step also leading to the deposition of a layer of a material on regions of said substrate holder that are not covered by the substrate during the deposition step, the method comprising the steps of: a) Implanting ion species through the receiving surface of the substrate holder so as to form at least one buried weakened plane delimiting a thin film underneath the receiving surface of the substrate holder; b) Placing the substrate on the receiving surface of the substrate holder, c) Depositing the layer of a material on the substrate and on said substrate holder, and d) Removing the substrate from the receiving surface, e) Exfoliating the thin film from the substrate holder so as to break up the thin film; and f) Removing at least a stack comprising the layer of a material deposited on regions of said substrate holder that are not covered by the substrate during the deposition step.

2. The recycling method according to claim 1, wherein after the implantation step a) the method comprises a step for forming an additional layer on the thin film of the substrate holder and in that the removal step f) comprises a step for peeling off the additional layer.

3. The recycling method according to claim 2, wherein the additional layer is in a polymer material, in particular in a glassy polymer such as BenzoCycloButene (BCB).

4. The recycling method according to claim 1, wherein the removal step c) comprises a step for cleaning the surface of the negative of the substrate holder using a pressurized water jet.

5. The recycling method according to claim 1, wherein the exfoliation e) of the thin film comprises a step for applying an exfoliation heat treatment.

6. The recycling method according to claim 1, wherein the implantation step a) leads to the formation of cavities defining the thin film and in that after the implantation step a) and before the exfoliation step e) the method comprises a heat pre-treatment step adapted to increase the number and size of the cavities.

7. The recycling method according to claim 1, wherein the exfoliation step e) of the thin film comprises a step comprising the deposition of a surface layer on the thin film and on the stack of at least the layer of a material deposited on the thin film.

8. The recycling method according to claim 1, wherein the receiving surface of the substrate holder comprises a main planar region allowing the receiving of a substrate and a peripheral region having an excess thickness of material adapted to hold the substrate in position for the depositing of a layer of a material, and in that the implantation step a) comprises the implanting of ion species through the peripheral region of the receiving surface so that the buried weakened plane delimits the thin film underneath the peripheral region.

9. The recycling method according to claim 1, wherein before the exfoliation step e), the method comprises several successive deposition steps of a layer of at least one material so as to form a stack of several successive layers of at least one material on the thin film.

10. The recycling method according to claim 1, wherein the exfoliation step e) is performed when the thickness of the stack of at least the layer of a material deposited on the thin film is less than 50 micrometers.

11. The recycling method according to claim 1, wherein the substrate holder comprises a silicon wafer 300 mm in diameter and having a peripheral region in the form of a ring of thickness greater than 725 micrometers and of width between 5 mm and 5 cm, the substrate holder being adapted for at least one handling of a silicon substrate having a diameter of 200 mm and for at least the depositing of a layer of a material in titanium dioxide having a thickness of about 1.5 micrometers, step a) comprising the implanting of hydrogen at an energy of between 1 and 300 keV and at a dose of between 1.10.sup.15 and 1.10.sup.17 at/cm.sup.2, the exfoliation step e) comprising the application of heat treatment at a temperature of between 200 C. and 500 C. for a time of between a few minutes to a few hours, and the removal step f) of the stack comprising a step for forming and then a step for peeling off an additional layer in BCB deposited on the thin film.

12. The recycling method according to claim 1, wherein the step of exfoliating the thin film further includes a step comprising the deposition of a surface layer on the thin film and on the sack of at least the layer of a material deposited on the thin film, the material of the surface layer having a different CTE from the CTE of the material of the substrate holder.

13. The recycling method according to claim 1, wherein the receiving surface further includes a main planar region allowing the receiving of a substrate and a peripheral region having an excess thickness of material adapted to hold the substrate in position for the depositing of a layer of a material, and the implanting step a) includes the implanting of ion species through the main planar region and through the peripheral region of the receiving surface leading to the formation of a first buried weakened plane underneath the peripheral region, the accumulation of the first buried weakened plane and of the second buried weakened plane delimiting the thin film.

14. The recycling method according to claim 1, wherein the recycling method comprises the repeat at least once of steps b) to d) before performing the exfoliation step e).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other aspects, objectives and advantages of the present invention will become better apparent on reading the following description of one embodiment thereof, given as a non-limiting example and with reference to the appended drawings. Not all the elements in the figures are necessarily drawn to scale for better legibility. The dotted lines symbolize a buried weakened plane. In the remainder of the description and for reasons of simplification, identical, similar or equivalent elements in the different embodiments carry the same reference numbers.

(2) FIGS. 1 to 6 illustrate one embodiment of the method of the invention.

(3) FIG. 7 illustrates a variant of embodiment.

(4) FIGS. 8 to 13 illustrate a variant of the embodiment of the method illustrated in FIGS. 1 to 6.

(5) FIG. 14 illustrates another variant of embodiment of the method of the invention.

(6) FIGS. 15 to 19 illustrate a further variant of embodiment of the method of the invention.

DETAILED DESCRIPTION

(7) FIG. 1 illustrates a substrate holder 1 formed of a silicon wafer having a planar receiving surface 5 with a diameter of 300 mm and resistivity of about 10 ohm.Math.cm. This wafer is particularly adapted for receiving, holding and handling a substrate 2 e.g. a silicon wafer 200 mm in diameter on which a layer of a material 3 is to be deposited.

(8) FIG. 2 illustrates a step a) of the method consisting of implanting ion species in the holder 1, such as hydrogen ions at an energy of between 1 and 300 keV, e.g. 180 keV, and at a dose of between 1.Math.10.sup.16 and 1.Math.10.sup.17 at/cm.sup.2, e.g. 5.Math.10.sup.16 at/cm.sup.2. This implantation at this energy leads to forming a buried weakened plane 4 within the holder 1 substantially parallel to the receiving surface 5 and delimiting a thin film 7.

(9) FIG. 3 illustrates a depositing step at 200 C. to deposit a layer of titanium dioxide TiO.sub.2 on the surface of a substrate 2 held in place on the substrate holder 1. Since the substrate holder 1 has a larger diameter than the substrate 2, the layer 3 of titanium dioxide is also deposited on the holder 1, which initiates the formation of a stack 6 on the holder 1.

(10) FIG. 4 illustrates the substrate holder 1 previously used to perform several successive deposits of a layer 3 of TiO.sub.2 on a substrate 2 (the last substrate on which a layer 3 was deposited having been removed from the holder). The stack 6 of layers of material deposited on the holder 1 therefore results from successive deposits of layers 3 each made on a silicon substrate 2. When the thickness of the stack 6 reaches a threshold value, here about 5 micrometers, an exfoliation step b) of the thin film 7 is carried out as illustrated in FIG. 5. The threshold value of the thickness of the stack 6 beyond which exfoliation is conducted is dependent upon the type of deposited material, on the global heat budget used to form the stack and is determined as from the time at which the depositing of a new layer 3 is perturbed by a variation in the deposition method (variation in capacitive radiofrequency plasmas . . . ) or by detachment of particles from the stack 6.

(11) As illustrated in FIG. 5, the exfoliation step b) leads to breaking-up of the thin film 7 and of the stack 6, the fragments derived from exfoliation remaining on the surface of the negative 8 of the holder 1 or being clustered in different heaps on its surface. The exfoliation step b) can be obtained by applying an exfoliation heat treatment to the substrate holder 1 such as illustrated in FIG. 4. This exfoliation heat treatment conducted at about 500 C. for 2 hours provides the heat budget allowing growth in the number and/or size of the cavities formed by implantation. This causes fracture of the material at the buried weakened plane 4 and exfoliation of the thin film 7 and of the stack 6 by which it is at least partly covered (FIG. 5).

(12) It is to be understood in the present document that the implantation conditions, the heat budget applied and the thickness of the materials above the buried weakened plane 4 are not adapted to detachment of a whole continuous thin film 7 of material, but to obtaining fragmenting of the thin film 7 into several fragments.

(13) FIG. 6 illustrates a removal step c) to remove the stack 6 which was broken up with the thin film 7.

(14) For this purpose, an additional polymer layer 9 is deposited, for example using a spin coating technique, or by spraying onto the surface of the fragments (still attached to the substrate holder 1), followed by peel-off for example using an adapted grasping and lifting tool to peel off the additional layer 9. The fragments adhere to the additional layer 9 and are therefore easily removed during peel-off. If the additional polymer layer 9 is a BCB film (for example XU35075 by Dow), it is spread by spin coating at between 500 and 1000 rpm at a thickness of the order of 40 micrometers. The resin obtained is polymerized at 250 C. for at least 1 h.

(15) According to one variant illustrated in FIG. 7, the step for forming the additional layer 9 takes place before the exfoliation step b) and the step for removing fragments from the stack and from the polymer is performed by peel-off after exfoliation. In this case, if the polymer is of BCB type, the exfoliation temperature is lowered to 400 C. so as not to damage the polymer and the heating time is extended to 5 h.

(16) The negative 8 of the substrate holder 1 is then freed of exfoliation fragments; its surface has topology close to that of the receiving surface 5 of the initial holder 1. The negative 8 is able again to be used for depositing steps of a layer 3 on a substrate 2. Similarly, it can be recycled after a certain number of deposition steps of a layer 3, under the same conditions as those previously described.

(17) According to one possibility, the surface of the negative 8 of the substrate holder 1 is then cleaned by a pressurized water jet.

(18) According to one non-illustrated alternative, the removal step c) to remove the stack 6 is only obtained by using a pressurized water jet applied to the holder 1 as illustrated in FIG. 5, without previously performing any deposition and peel-off of an additional layer 9.

(19) FIG. 8 illustrates a substrate holder 1 in silicon having a diameter of 300 mm for example whose receiving surface 5 comprises a main planar region 11 and an added peripheral region 12 in the form of a ring of material allowing the receiving and holding in position of a substrate 2 in silicon or germanium having a diameter of 200 mm and thickness of 450 micrometers. In this example, the ring 12 has a thickness of about 720 micrometers and width of between 5 mm and 5 cm.

(20) FIG. 9 illustrates the step for implanting hydrogen ions at an energy of about 190 keV and at a dose of about 7.Math.10.sup.16 at/cm.sup.2 so as to form a first buried weakened plane underneath the main planar region 11 and a second ring-shaped buried weakened plane underneath the ring region 12. As illustrated in FIG. 9, these two weakened planes form a discontinuous thin film 7 which nevertheless extends under the entirety of the receiving surface 5 of the holder 1. If the ring region 12 and the main region 11 are in one same material, e.g. silicon, the depths at which the two weakened planes are formed are identical.

(21) According to one non-illustrated possibility, implantation is conducted solely through the peripheral region 12 comprising the ring so as only to exfoliate a portion of the receiving surface 5 of the substrate holder 1.

(22) FIG. 10 illustrates a deposition step of a layer 3 of SiO.sub.2 (e.g. by PECVD), nickel (e.g. by PVD) or TiO.sub.2 on the substrate 2. Since the substrate holder 1 has a larger diameter than the substrate 2, this deposition also leads to the formation of a layer 3 of material on the holder 1.

(23) FIG. 11 illustrates the stack 6 formed by the succession of layers deposited on the holder 1, resulting from use of the holder 1 for the successive holding of several substrates 2 on which a layer 3 has been deposited.

(24) As illustrated in FIG. 12, once the threshold value of the stack 6 has been exceeded beyond which further depositing of a layer 3 is no longer optimal, e.g. 5 micrometers, heat treatment is applied for about 2 hours at 500 C. so as to cause exfoliation of the thin film 7.

(25) As illustrated in FIG. 13, according to one possible embodiment a removal step performed by peeling off an additional layer 9 formed before the exfoliation step (not illustrated in the Figures) allows the cleaning of the entire surface of the negative 8 of the holder 1. If the additional polymer layer is in BCB for example, the exfoliation temperature is lowered to 400 C. for example.

(26) The negative 8 has a main planar region 11 and a ring-shaped peripheral region 12 formed of material similar to regions 11, 12 respectively of the substrate holder 1 before use. As a result, the negative 8 can again be used as substrate holder 1 for further deposits of layers 3 in the same manner as previously described. According to one possibility, not described, once the threshold thickness of the stack 6 of layers has been reached on the negative 8, this negative can again be recycled by repeating the invention.

(27) According to one variant of embodiment illustrated in FIG. 14, a surface layer 13 e.g. in Si is deposited at a thickness of 5 micrometers on the thin film. 7 and on the stack 6 formed by the successively deposited layers before carrying out the exfoliation step b). This surface layer 13 via its thickness contributes towards increasing the thickness of the assembly of materials lying above the buried weakened plane 4 so that exfoliation leads to the formation of fragments of larger size. This subsequently facilitates the removal step c) and finalization of recycling of the negative 8 of the substrate holder 1.

(28) According to another variant of embodiment, a surface layer 13 of silicon dioxide is deposited at 200 C. by PECVD (Plasma Enhanced Chemical Vapor Deposition) at a thickness of 10 micrometers on a stack 6 of layers of TiO.sub.2 having a thickness of 1 micrometer derived from the successive deposits of a layer 3 on the substrate 2. The SiO.sub.2 material does not have the same CTE as Si material which means that when applying the exfoliation heat treatment at 500 C. at step b) of the method, the layer 13 of SiO.sub.2 is subjected to tensile stress contributing towards exfoliation. Since exfoliation is promoted, the length of exfoliation heat treatment can be reduced compared with the treatment applied if there is no stressed layer 13, whilst allowing the exfoliation of large-size fragments. The use of a stressed layer 13 may additionally allow an upstream reduction in the dose of hydrogen ions implanted into the silicon holder 1. The dose can effectively be reduced from 5.Math.10.sup.16 at/cm.sup.2 to 4.Math.10.sup.16 at/cm.sup.2 so that the cycle time is shorter and the recycling method less costly.

(29) According to yet another variant of embodiment a surface layer 13 of amorphous silicon is deposited by PECVD at a temperature of 250 C. and over a thickness of 15 micrometers. Since implantation was previously performed at a dose of 4.Math.10.sup.16 at/cm.sup.2, exfoliation heat treatment at 500 C. for 1 hour allows exfoliation of the stack 6.

(30) FIGS. 15 to 19 illustrate another variant of embodiment of the method. As illustrated in FIG. 15, an implantation step a) to implant helium ions is performed with energy of 190 keV and dose of 6.Math.10.sup.16 at/cm.sup.2 underneath the receiving surface 5 of a substrate holder 1 in silicon.

(31) Then, with reference to FIG. 16, heat pre-treatment is conducted at 900 C. for 2 hours so as to increase the number and size of helium cavities at the buried weakened plane 4 without however causing exfoliation of the thin film 7 of silicon. It is to be understood in the present document that the heat pre-treatment is also adapted so that the heat budget of the subsequent deposition steps of layers 3 does not cause exfoliation.

(32) FIG. 17 illustrates the substrate holder 1 after use and successive deposits of a layer 3 of TiO.sub.2 on a substrate 2, until a threshold thickness of the stack 6 is obtained of about 5 micrometers on the holder 1. It is to be noted that the stack 6 of TiO.sub.2 is placed under compression during the exfoliation heat treatment but the stress generated is not sufficient alone to obtain exfoliation thereof.

(33) FIG. 18 illustrates a deposition step of a surface layer 13 of silicon nitride by PECVD at 400 C. until a thickness of about 10 micrometers is obtained. After return to ambient temperature, the difference in contraction of the silicon of the holder 1 and of the silicon nitride of the surface layer 13, together with the intrinsic stresses of depositing, generates stress within the holder 1. Since a heat pre-treatment was applied, this stress is alone sufficient to cause exfoliation of the thin film 7.

(34) As illustrated in FIG. 19, the negative 8 of the substrate holder 1 recovered after removing the fragments and cleaning has a main planar region 11 and a peripheral region 12 in the form of a ring of material, identical to those of the substrate holder 1 before use.

(35) The present invention therefore proposes a method for recycling a substrate holder 1 that is simple to implement and which can be used irrespective of the type of material and geometry of the holder 1.

(36) Evidently, the invention is not limited to the variants of embodiment described above as examples, but encompasses all technical equivalents and variants of the described means and the combinations thereof.