Method for implanting atomic species into piezoelectric substrates

Abstract

The present invention relates to a method for implanting atomic species into a piezoelectric substrate, the method comprising the steps of: I) preparing a substrate (100, 200, 300) having a piezoelectric portion (112, 210, 310) and an electrically conductive portion (122, 320); III) mounting the substrate (100, 200, 300) including the electrically conductive portion (122, 320) on a chuck (140); and IV) implanting atomic species (170) into the piezoelectric portion (112, 210, 310).

Description

[Technical field]

[0001] The present invention relates to a method for implanting atomic species into piezoelectric substrates, and in particular to high density implantation into bulk piezoelectric substrates. [Background technology]

[0002] The fabrication of piezoelectric on insulator (POI) wafers requires the use of implantation processes, particularly high density implantation processes. Summary of the Invention

[0003] The implantation of ions is carried out in an implantation device in which a number of substrates are subjected to an ion beam. For full-surface implantation, the substrates are mounted on an implantation wheel that rotates and / or translates so that the entire surface of the substrate passes under the ion beam. To secure the substrate to the implantation wheel against the rotational forces, a retention means such as a clip is used. Typically, the retention means is a fixed metallic restraint that is further configured to bleed off any charge generated during ion implantation.

[0004] The high density implantation process leads to the accumulation of electric charges in the implanted piezoelectric substrate. At the same time, high temperature gradients are observed in the substrate during implantation, leading to deformations in the form of deflection and warping of the piezoelectric substrate. As a result, the electric charges and heat cannot be dissipated sufficiently in the metallic chuck used in the implantation chamber. To solve this problem, the piezoelectric substrate is placed on an elastomer layer provided on the metallic chuck. This elastomer layer provides thermal contact between the piezoelectric substrate and the chuck. A fixed metallic restraint is used to provide electrical contact between the piezoelectric substrate and the chuck. However, the electrical contact achieved is only a local contact between the piezoelectric substrate and the chuck.

[0005] However, damage to the piezoelectric substrate due to still insufficient drainage of the electric charge is still observed.

[0006] Therefore, there is a need for further improvement in dissipating the charge out of the piezoelectric substrate.

[0007] The object of the present invention is achieved by a method for implanting atomic species into a piezoelectric substrate, the method comprising the steps of: a) providing a substrate having a piezoelectric portion and an electrically conductive portion; b) mounting the substrate including the electrically conductive portion on a chuck; and c) implanting the atomic species into the piezoelectric portion.

[0008] As mentioned above, implantation is performed on the piezoelectric portion, resulting in the accumulation of charge on the piezoelectric portion, however the use of electrically conductive parts in the implanted substrate results in improved drainage of the charge from the piezoelectric portion, since the charge can more easily accumulate on the outside of the piezoelectric portion, reducing stress and reducing the risk of damage.

[0009] According to a variant, step b) may comprise providing an elastomer layer between the chuck and the electrically conductive part of the substrate, the latter thus being insulated from the chuck.

[0010] According to a variant of the invention, step a) may comprise mounting the piezoelectric substrate forming the piezoelectric part to an electrically conductive substrate forming the electrically conductive part of the substrate, for example mounting the two substrates together via molecular adhesion being a reliable mounting process.

[0011] According to a variant of the invention, step a) may further comprise a step of thinning the piezoelectric substrate in order to obtain a piezoelectric layer, in particular with a thickness between 1 μm and 100 μm. Thinning the piezoelectric substrate shortens the length of the path for the charges until they can reach the electrically conductive part. Thus, the accumulation of charges can be reduced even further.

[0012] According to a variant of the invention, the difference in thermal expansion coefficients is 50*10 -6 K -1 Less than 20*10 -6 K -1The piezoelectric and electrically conductive substrates are selected such that the thermal expansion coefficients of the piezoelectric and electrically conductive substrates are less than 0.05 μm. By matching thermal expansion coefficients, the use of an electrically conductive substrate having thermal expansion parameters that match those of the piezoelectric substrate provides a substrate that will withstand thermal gradients without fracturing or exhibiting damage at the interface between the piezoelectric and electrically conductive substrates.

[0013] According to a variant of the invention, the step of attaching the piezoelectric substrate and the electrically conductive substrate is achieved using a bonding layer between the two substrates. The use of a bonding layer provides a wider choice of suitable materials for the electrically conductive substrate and the piezoelectric substrate.

[0014] According to a variant of the invention, the bonding layer can be a conductive bonding layer, in particular a metal layer. This in turn leads to a more versatile process with a higher degree of freedom for selecting an electrically conductive substrate. In fact, even when a low-electrical-conductivity substrate is used as the electrically conductive substrate, the bonding layer can further improve the drainage of the charges from the piezoelectric substrate towards the electrically conductive substrate.

[0015] According to a variant of the invention, the step of providing an electrically conductive portion may comprise providing one or more cavities on the side of the substrate facing the chuck and filling the one or more cavities with a conductive material, in particular a metal.

[0016] Providing filled metallic cavities at the bottom of the piezoelectric substrate results in improved conductivity in this portion of the piezoelectric substrate, thus improving drainage of charge from the piezoelectric substrate as paths to higher conductivity portions are reduced.

[0017] According to a variant, the piezoelectric substrate is a bulk piezoelectric substrate, in particular a bulk piezoelectric wafer. The use of electrically conductive parts makes it possible to inject the piezoelectric material even for thicknesses of the piezoelectric material of more than 20 μm, in particular more than 100 μm.

[0018] According to a variant of the invention, the substrate is -4The conductive layer may have a conductivity of 100 S / cm or more. In this context, the conductive layer may be realized using a metallic or semiconducting material. Preferred materials are, for example, a Si substrate, or a metallic substrate, for example molybdenum, aluminum, or tungsten.

[0019] According to a variant, step b) can be implemented such that the electrically conductive parts and / or the bonding layer are in electrical contact with at least one metallic restraint electrically connected to the chuck. Due to the electrical connection between the electrically conductive parts and / or the bonding layer of the substrate, the electric charges accumulated in the piezoelectric part can be transferred out of the piezoelectric part and can be drained by the metallic restraint. This drainage of the electric charges reduces the risk of substrate deformation and the occurrence of high stresses, thereby reducing the risk of breakage.

[0020] According to a variant, in step c) a predetermined split area may be provided in the piezoelectric portion and the method may further comprise a step d) of mounting the piezoelectric portion of the piezoelectric substrate on a handle substrate and a step e) of removing the remaining part of the piezoelectric substrate in the predetermined split area and transferring a layer of the piezoelectric substrate to the handle substrate. According to this method a piezoelectric on insulator substrate (POI) may be achieved which includes a smaller number of defects which may occur due to stresses during the implantation step.

[0021] The invention may be understood by reference to the following description considered in conjunction with the accompanying drawings in which reference characters identify features of the invention. [Brief description of the drawings]

[0022] [Figure 1] 1A-1D illustrate a schematic diagram of a method for implanting atomic species into a bulk piezoelectric substrate according to a first embodiment of the present invention; [Diagram 2] 5A-5D show schematic diagrams of a method for implanting atomic species into a bulk piezoelectric substrate according to a variant of the first embodiment of the present invention. [Diagram 3] 5A-5D illustrate a schematic diagram of a method for implanting atomic species into a bulk piezoelectric substrate according to a second embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] FIG. 1 illustrates a schematic diagram of a method for implanting atomic species into a piezoelectric substrate 100 according to a first embodiment of the present invention.

[0024] The method comprises a first step I), corresponding to step a) of the method of the present invention, of providing a piezoelectric substrate 110 and an electrically conductive substrate 120 .

[0025] The piezoelectric substrate 110 in this embodiment is a bulk piezoelectric substrate, such as a bulk piezoelectric wafer with a thickness between 200 μm and 700 μm. The present invention relates to a piezoelectric material, such as LiTaO3, LiNbO3, quartz, BaTiO3, Pb(Zr x Ti 1-x )O3, GaPO4, GaAsO4, AlPO4, FePO4, PbTiO3, KNbO3, BiFeO3, Pb(Zn 1 / 3 Nb 2 / 3 ) 1-x Ti x O3, Pb(Mg 1 / 3 Nb 2 / 3 ) 1-x Ti x O3, Pb(Sc 1 / 2 Nb 1 / 2 ) 1-x Ti x Generally, the piezoelectric substrate 110 has a low electrical conductivity of 10 -11 It is on the order of S / cm or less.

[0026] The electrically conductive substrate 120 can be a semiconductor substrate, such as a Si substrate, or a metal substrate, such as a molybdenum, aluminum, or tungsten substrate. Semiconductor substrates are interesting because they meet manufacturing line specifications in terms of metal contamination. Metals have a higher conductivity, but the metal needs to be selected to meet the metal contamination specifications of the manufacturing line.

[0027] The electrically conductive substrate 120 has a higher conductivity than the piezoelectric substrate 110 and is -4 It is on the order of S / cm or more.

[0028] Furthermore, the material of the electrically conductive substrate 120 is selected so that its thermal expansion coefficient matches that of the piezoelectric substrate 110, as described below. The difference in thermal expansion coefficient is 20*10 -6 K -1 It is preferable that it is less than 1000 .mu.m.

[0029] Next, as shown in step II), the piezoelectric substrate 110 is attached to an electrically conductive substrate 120 to form the substrate 100. The substrate 100 comprises a piezoelectric portion 112 realized by the piezoelectric substrate 110 and an electrically conductive portion 122 realized by the electrically conductive substrate 120.

[0030] In this embodiment, a piezoelectric substrate 110 is attached to an electrically conductive substrate 120 using a bonding layer 130 .

[0031] The bonding layer 130 can be an electrically conductive or non-conductive layer. For example, the bonding layer 130 can be a metal layer, which provides more freedom when selecting an electrically conductive substrate 120.

[0032] Before attaching the two substrates, a bonding layer 130 may be provided on the piezoelectric substrate 110 or on the electrically conductive substrate 120 by processes known in the art. In a variant, a bonding layer may be provided on each of the substrates 110 and 120. There may be one or more further layers between the piezoelectric substrate 110 and the electrically conductive substrate 120, such as a thin SiO2 layer or a trap rich layer to further improve electrical and thermal properties.

[0033] In the alternative, the mounting step II) may also be a direct bonding step, where the piezoelectric substrate 110 is directly attached to the electrically conductive substrate 120, for example via molecular adhesive bonding.

[0034] A temperature treatment may be performed after the attachment step between the piezoelectric substrate 110 and the electrically conductive substrate 120 to strengthen the bond between the two substrates.

[0035] The substrate 100 is then mounted on the chuck 140 of an atomic species implanter as shown in step III), which corresponds to step b) according to the method of the present invention.

[0036] Substrate 100 is mounted to chuck 140 via its major surface 124, which is the free surface of an electrically conductive substrate 120. Surface 124 is the free major surface of the electrically conductive substrate opposite the surface on which mounting is performed.

[0037] As shown, the substrate 100 is not directly mounted on the chuck 140, but on an elastomer layer 150 previously provided on the surface 142 of the chuck 140. The elastomer layer 150 is for example a silicone matrix, for example PDMS (polydimethylsiloxane), with a thickness of 50 μm to 500 μm. The elastomer layer 150 is used to compensate for deformations of the substrate 100, for example bending and warping during the subsequent implantation steps. As mentioned above, the elastomer layer 150 also provides a thermal contact between the substrate 100 and the metallic chuck 140 to allow heat dissipation.

[0038] The chuck 140 further comprises one or more metal restraints 160 for holding the substrate 100 in place as the chuck 140 rotates with an implantation wheel (not shown).

[0039] After the placement of the substrate 100 on the elastomer layer 150, ions 170 are implanted into the substrate 100 as shown in step IV), which corresponds to step c) of the method of the present invention. Typical atomic species are hydrogen or a noble gas, for example helium. Ion implantation is used to achieve a mechanically weakened layer 172 inside the piezoelectric part 112. This mechanically weakened layer 172 can serve as a predefined split area in a subsequent layer transfer step to obtain a so-called piezoelectric on insulator or POI substrate.

[0040] The ions 170 are implanted using a high density implantation process using an ion beam current on the order of 1 mA to 25 mA.

[0041] Since ions 170 are implanted into the piezoelectric portion 112 of the substrate 100 and since the piezoelectric portion 112 has a low conductivity, the piezoelectric portion 112 of the substrate 100 is subject to the accumulation of charges during the ion implantation process as described above in relation to the prior art. Due to the presence of the electrically conductive portion 122 and / or the bonding layer 130 of the substrate 100 according to the invention, those charges can be transferred out of the piezoelectric portion 112, which reduces the risk of substrate deformation and the generation of large stresses and therefore the risk of breakage.

[0042] Additionally, matching the thermal expansion coefficient of the piezoelectric portion 112 relative to the electrically conductive portion 122 reduces stress within the substrate and reduces or even prevents the occurrence of cracks or defects within the substrate 100, particularly at the interface between the electrically conductive portion 122 and the piezoelectric portion 112.

[0043] The electrically conductive portion 122 and / or the bonding layer 130 are in electrical contact 162 with one or more metallic restraints 162. Thus, after an electric charge 180 enters the electrically conductive portion 122 and / or the bonding layer 130, the electric charge 180 is drained through the one or more metallic restraints 160 and the grounded chuck 140.

[0044] The chuck 140 and the metal restraint(s) 160 are preferably made from the same metallic material, particularly aluminum.

[0045] Thus, using a substrate 100 according to the present invention, the implantation process of the present invention provides improved drainage of charge compared to conventional implantation processes.

[0046] 2 shows a variant of the first embodiment. In this embodiment, steps I) and II) are not described again since they are the same as in the first embodiment, please refer to their above description. After step II) of mounting the piezoelectric substrate 110 and the electrically conductive part 120, a further process step II_2) of thinning the piezoelectric part 110 of the substrate 100 is realized to obtain a modified substrate 200.

[0047] This thinning step can be achieved, for example, using mechanical processes or chemical etching processes known in the art and adapted to the piezoelectric substrate, and can be accompanied by further process steps, for example polishing after the thinning step, to improve the quality of the surface 212 of the thinned piezoelectric portion 210.

[0048] The thinned piezoelectric portion 210 is approximately 100 μm to 1 μm thinner than the bulk material.

[0049] Steps III) and IV) are then achieved in the same manner as described above, except that the modified substrate 200 including the thinned piezoelectric portion 210 is used instead of the substrate 100. See therefore the description of steps III) and IV) above in relation to FIG.

[0050] The implanted ions 170 effect the predetermined slitting area 172 and allow charge 180 to be evacuated through the bonding layer 130 and / or the electrically conductive portion 122 .

[0051] The thinning of the piezoelectric substrate 110 further improves the drainage of the charge 180 out of the piezoelectric portion 210 .

[0052] According to a second embodiment, as shown in Fig. 3, a substrate 300 is realized without mounting a piezoelectric substrate on an electrically conductive substrate. In this embodiment, only a piezoelectric substrate 310 is provided, see step I) in Fig. 3. This piezoelectric substrate 310 has the same properties as the piezoelectric substrate 110 described above.

[0053] Subsequently, during step II_1), one or more cavities 312 are realized in one main surface 314 of the piezoelectric substrate 310, using patterning and etching steps known in the art. According to one example, the cavities 312 may form a regular pattern or matrix and may all be of the same size.

[0054] Next, as indicated by step II_2), the cavities 312 are filled with a conductive material 316, in particular a metal, using a deposition process known in the art, in order to form an electrical conductor 320. A deposition process can / is performed such that a conductive layer 318 is realized on the surface 314 in order to interconnect the conductive materials 316. The part of the substrate 300 comprising the conductive material 316 and the layer 318 inside the cavities 316 forms the electrical conductor 320 according to the invention.

[0055] The subsequent step III) of placement on the injector wheel and step IV) of implanting ions 170 are achieved as in the first embodiment using the same chuck 140 with the elastomeric layer 150 and the metallic restraint 160, so their description will not be repeated again and reference should be made to the description of figures 1 and 2.

[0056] In this embodiment, charge is collected through a matrix of filled cavities 312 and drainage of charge 380 is achieved from the piezoelectric portion 310 to the electrically conductive portion 320 through a layer 318 in contact 162 with the metallic restraint 160.

[0057] Due to the improved conductivity of the substrate 300 with the cavity 312 filled with conductive material 316, thereby forming an electrically conductive portion 320 of the substrate 300, the charge can be drained from the piezoelectric portion 310 through the electrically conductive portion 320 to the grounded chuck 340.

[0058] The piezoelectric substrate 100, 200 or 300 of the present invention can be used as a donor substrate in a subsequent layer transfer process to form a piezoelectric on an insulator substrate by transferring a thin layer of piezoelectric material to a handle substrate. In such a process, the piezoelectric substrate 100, 200 or 300 of the present invention is attached to a handle substrate, for example a silicon wafer, using the surface of the piezoelectric part 110, 210, 310, for example by bonding, with or without additional layers on the surface to which bonding is performed. Then, the transfer of the piezoelectric layer is performed at the mechanically weakened layer 172 inside the piezoelectric part 110, 210, 310 by applying a thermal or mechanical load.

[0059] A number of embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications and improvements may be made without departing from the scope of the claims that follow.

Claims

1. Step a) of preparing a substrate (100, 200, 300) comprising a piezoelectric part (112, 210, 310) and an electrically conductive part (122, 320); Step b) of mounting the substrate (100, 200, 300) including the electrically conductive part (122, 320) on a chuck (140); Step c) of injecting atomic species (170) into the piezoelectric part (112, 210, 310); A method for injecting atomic species into a piezoelectric substrate, comprising the above steps.

2. The method according to claim 1, wherein step b) includes providing an elastomer layer (150) between the chuck (140) and the electrically conductive part (122, 320) of the substrate (100, 200, 300). The method according to claim 1.

3. The method according to claim 1 or 2, wherein step a) includes mounting a piezoelectric substrate (110) for forming the piezoelectric part (112, 210) on an electrically conductive substrate (120) for forming the electrically conductive part (122) of the substrate (100, 200). The method according to claim 1 or 2.

4. The method according to claim 3, wherein step a) further includes thinning the piezoelectric substrate (110) to obtain a piezoelectric layer (210) having a thickness particularly between 1 μm and 100 μm. The method according to claim 3.

5. The difference in the coefficient of thermal expansion is less than 50*10 －６ K －１ and preferably less than 20*10 －６ K －１ such that the piezoelectric substrate (110, 310) and the electrically conductive substrate (120) are selected. The method according to claim 3.

6. The method according to claim 3, wherein the step of mounting the piezoelectric substrate (110) and the electrically conductive substrate (120) is realized using a bonding layer (130) between the piezoelectric substrate (110) and the electrically conductive substrate (120). The method according to claim 3.

7. The method according to claim 6, wherein the bonding layer (130) is a conductive bonding layer, particularly a metal layer. The method according to claim 6.

8. The method according to claim 1, wherein the step of preparing the electrically conductive part (320) includes providing one or more cavities (312) on a side (314) of the substrate (300) facing the chuck (140), and filling the one or more cavities (312) with a conductive material (316), particularly a metal. The method according to claim 1.

9. The method according to claim 1 or 2, wherein the piezoelectric substrate (110, 310) is preferably a bulk piezoelectric substrate having a thickness greater than 20 μm, more particularly a bulk piezoelectric wafer having a thickness greater than 100 μm. The method according to claim 1 or 2.

10. The substrate (100, 200, 300) has a conductivity of 10 －４ S / cm or more. The method according to claim 1 or 2.

11. Step b) of mounting the substrate (100, 200, 300) on the chuck (140) is realized such that the electrical conduction part (122, 320) and / or the bonding layer (130) is in electrical contact (162) with at least one metallic restraint (160) electrically connected to the chuck (140). The method according to claim 1 or 2.

12. During step c), a predetermined division area (172) is provided to the piezoelectric part (112, 210, 310). The method further includes step d) of attaching the piezoelectric part (112, 210, 310) of the piezoelectric substrate (110, 210, 310) to a handle substrate, and step e) of removing the remaining part of the piezoelectric substrate (110, 210, 310) in the predetermined division area (172) to transfer the layer of the piezoelectric substrate (110, 210, 310) to the handle substrate. The method according to claim 1 or 2.

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