Method for implanting atomic species into a piezoelectric substrate

Abstract

The invention relates to a method for implanting atomic species into a piezoelectric substrate, comprising the steps of I) providing a substrate (100, 200, 300) comprising a piezoelectric portion (112, 210, 310) and an electrically conductive portion (122, 320), III) mounting the substrate (100, 200, 300) with the electrically conductive portion (122, 320) onto a substrate holder (140), and IV) implanting atomic species (170) into the piezoelectric portion (112, 210, 310). Figure 1

Description

Title of the invention: Method for implanting atomic species in a piezoelectric substrate

[0001] The invention relates to a method for implanting atomic species in a piezoelectric substrate, more particularly high-density implantation in bulk piezoelectric substrates.

[0002] The fabrication of piezoelectric-on-insulator (POI) wafers requires the use of an implantation process, particularly a high-density implantation process.

[0003] Ion implantation takes place in an implantation device in which several substrates are subjected to an ion beam. For full-surface implantation, the substrates are mounted on a rotating and / or translating implantation wheel, so that the entire surface passes under the ion beam. Holding means, such as clamps, are used to fix the substrate on the implantation wheel against the rotational forces. Typically, the holding means are fixed metallic holding elements that are also configured to drain electrical charges generated during ion implantation.

[0004] A high-density implantation process results in the accumulation of charges in the piezoelectric substrate being implanted. At the same time, a high temperature gradient is observed in the substrate during implantation, leading to deformation in the form of a bowl and warping of the piezoelectric substrate. As a result, charges and heat cannot be sufficiently dissipated in a metal substrate holder used in the implantation chamber. To overcome this problem, the piezoelectric substrate is placed on an elastomer layer provided on the metal substrate holder. This elastomer layer provides electrical contact between the piezoelectric substrate and the substrate holder. The fixed metal holding members are used to provide electrical contact between the piezoelectric substrate and the substrate holder.The electrical contact obtained is however only a point contact between the piezoelectric substrate and the substrate holder.

[0005] However, a breakdown of the piezoelectric substrate is still observed, which is attributed to a still insufficient charge evacuation.

[0006] Therefore, the dissipation of charges out of a piezoelectric substrate needs to be further improved.

[0007] The object of the invention is achieved by a method of implanting atomic species in a piezoelectric substrate, comprising the steps of a) providing a substrate, comprising a piezoelectric portion and an electrically conductive portion, b) mounting the substrate with the electrically conductive portion on a substrate holder, and c) implanting atomic species into the piezoelectric portion.

[0008] As explained above, the implantation is carried out in the piezoelectric part, and results in an accumulation of charges in the piezoelectric part. The use of an electrically conductive part in the substrate to be implanted, however, results in an improved evacuation of charges from the piezoelectric part because the charges can easily accumulate outside the piezoelectric part, thus reducing the stress and reducing the risk of breakage.

[0009] According to a variant, step b) may comprise providing a layer of elastomer between the substrate holder and the electrically conductive part of the substrate. Thus, the electrically conductive part of the substrate is insulated from the substrate holder.

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

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

[0012] According to a variant of the invention, the piezoelectric substrate and the electrically conductive substrate are chosen such that the difference in thermal expansion coefficients is less than 50*10 6K *, preferably 20*10 6KA. By matching the thermal expansion coefficients, the use of an electrically conductive substrate with thermal expansion parameters that match the thermal expansion parameters of the piezoelectric substrate provides a substrate that will withstand thermal gradients without breaking or exhibiting damage at the interface between the piezoelectric substrate and the electrically conductive substrate.

[0013] According to a variant of the invention, the step of fixing the electrically conductive substrate with the piezoelectric substrate is carried out 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 substrates.

[0014] According to a variant of the invention, the bonding layer may be a bonding layer conductive, especially a metal layer. Again, this results in a more versatile process, with a higher degree of freedom in choosing the electrically conductive substrate. Indeed, the bonding layer can also improve the evacuation of charges from the piezoelectric substrate to the electrically conductive substrate, even when a poorly electrically conductive substrate is used as the electrically conductive substrate.

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

[0016] Providing filled metal cavities in the lower portion of the piezoelectric substrate results in improved conductivity in that portion of the piezoelectric substrate. Thus, charge removal from the piezoelectric substrate is improved because the path to a portion having higher conductivity is reduced.

[0017] According to one variant, the piezoelectric substrate is a solid piezoelectric substrate, in particular a solid piezoelectric wafer. The use of the electrically conductive part makes it possible to implant piezoelectric materials 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 may have a conductivity of 104 S / cm or more. In this context, an electrically conductive part may be made using a metallic or semiconductor material. Preferred materials are, for example, a Si substrate, or a metallic substrate, for example, made of molybdenum, aluminum or tungsten.

[0019] According to a variant, step b may be carried out in such a way that the electrically conductive part and / or the bonding layer is / are in electrical contact with at least one metal holding element electrically connected to the substrate holder. Due to the electrical connection between the electrically conductive part and / or the bonding layer of the substrate, the charges accumulated in the piezoelectric part can move out of the piezoelectric part, and be discharged by the metal holding element. This discharge of charges reduces the risk of substrate deformation and high stress occurring, and consequently reduces the risk of breakage.

[0020] According to a variant, in step c), a predetermined division zone may be provided in the piezoelectric part and the method may further comprise a step d) of fixing the piezoelectric part of the piezoelectric substrate on a handling substrate, and a step e) of detaching the remainder of the piezoelectric substrate at the predetermined division zone to transfer a layer of the piezoelectric substrate onto the handling substrate. Using this method, piezoelectric-on-insulator (POI) substrates can be produced, which have a reduced number of defects that can occur due to stress during the implantation step.

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

[0022] [Fig.l] schematically illustrates a method of implanting atomic species in a massive piezoelectric substrate according to a first embodiment of the invention.

[0023] [Fig.2] schematically illustrates a method of implanting atomic species in a massive piezoelectric substrate according to a variant of the first embodiment of the invention.

[0024] [Fig. 3] schematically illustrates a method of implanting atomic species in a massive piezoelectric substrate according to a second embodiment of the invention.

[0025] [Fig.l] schematically shows a method of implanting atomic species in a piezoelectric substrate 100 according to the first embodiment of the invention.

[0026] The method comprises a first step I), corresponding to step a) of the inventive method, consisting of providing a piezoelectric substrate 110 and an electrically conductive substrate 120.

[0027] The piezoelectric substrate 110, in this embodiment, is a bulk piezoelectric substrate, for example a bulk piezoelectric wafer with a thickness of between 200 pm and 700 pm. The invention relates to piezoelectric materials such as LiTaO3, LiNbO3, Quartz, BaTiO3, PbtZpTi / JO3, GaPO4, GaAsO4, A1PO4, FePO4, PbTiO3, KNbO3, BiFeO3Pb(Zn1 / 3Nb2 / 3)1 .TpO,, Pb(Mg1 / 3Nb2 / 3)b;n / )3, Pb(Sc1 / 2Nb i / 2)i-xTixO3. In general, the electrical conductivity of piezoelectric substrates 110 is low, on the order of 10 11 S / cm or less.

[0028] The electrically conductive substrate 120 may be a semiconductor substrate, for example a Si substrate, or a metal substrate, for example a molybdenum, aluminum or tungsten substrate. Semiconductor substrates are attractive because they meet production line specifications in terms of metal contamination. Metals have superior conductivity, but must be chosen such that they meet the metal contamination specifications of the manufacturing line.

[0029] The electrically conductive substrate 120 has a conductivity greater than the conductivity of the piezoelectric substrate 110, of the order of 10 4 S / cm or more.

[0030] Furthermore, the material of the electrically conductive substrate 120 is chosen such so that its coefficient of thermal expansion matches that of the piezoelectric substrate 110, as will be explained later. Preferably, the difference in coefficient of thermal expansion is less than 20*10<

[0031] Next, the piezoelectric substrate 110 is attached to the electrically conductive substrate 120 to form a substrate 100, as illustrated by step II). The substrate 100 comprises a piezoelectric portion 112, made by the piezoelectric substrate 110, and an electrically conductive portion 122, made by the electrically conductive substrate 120.

[0032] In this embodiment, the piezoelectric substrate 110 is attached to the electrically conductive substrate 120 using a bonding layer 130.

[0033] The bonding layer 130 may be an electrically conductive layer or a non-conductive layer. For example, the bonding layer 130 may be a metal layer, which would provide a greater degree of freedom when selecting the electrically conductive substrate 120.

[0034] Before attaching the two substrates, the bonding layer 130 may be provided on the piezoelectric substrate 110 or the electrically conductive substrate 120 by a process known in the art. Alternatively, a bonding layer may be provided on each of the substrates 110 and 120. One or more additional layers may be present between the piezoelectric substrate 110 and the electrically conductive substrate 120. For example, a thin SiO2 layer or a trap-rich layer to further improve the electrical and thermal properties.

[0035] In a variant, the step II) of fixing can also be a direct bonding step, where the piezoelectric substrate 110 is fixed directly to the electrically conductive substrate 120, for example via a molecular adhesion bond.

[0036] A heat treatment may follow the fixing step between the piezoelectric substrate 110 and the electrically conductive substrate 120 to strengthen the bond between the two substrates.

[0037] Then, the substrate 100 is mounted on a substrate holder 140 of an atomic species implantation device, as illustrated by step III) corresponding to step b) according to the inventive method.

[0038] The substrate 100 is mounted on the substrate holder 140 via its main surface 124, which is the free surface of the electrically conductive substrate 120. The surface 124 is the main free surface of the electrically conductive substrate opposite the surface where attachment has occurred.

[0039] As illustrated, the substrate 100 is not mounted directly on the substrate holder 140 but on an elastomer layer 150 previously provided on the surface 142 of the substrate holder 140. The elastomer layer 150 is for example a silicone matrix such as PDMS (polydimethylsiloxane) and has a thickness of between between 50 pm and 500 pm. The elastomer layer 150 is used to compensate for deformations of the substrate 100, such as cupping and warping, during the subsequent implantation step. As described above, the elastomer layer 150 further provides thermal contact between the substrate 100 and the metal substrate holder 140 to enable heat dissipation.

[0040] The substrate holder 140 further comprises one or more metal holding members 160 for holding the substrate 100 in place when the substrate holder 140 rotates with the implantation wheel (not shown).

[0041] Following the positioning of the substrate 100 on the elastomer layer 150, ions 170 are implanted into the substrate 100 as illustrated in step IV) corresponding to step c) of the inventive method. Typical atomic species are hydrogen or a noble gas, such as helium. Ion implantation is used to provide a mechanically weakened layer 172 within the piezoelectric portion 112. This mechanically weakened layer 172 may serve as a predetermined division zone in a subsequent layer transfer process to obtain a so-called piezoelectric-on-insulator substrate or POI substrate.

[0042] The ions 170 are implanted using a high density implantation process with ion beam currents in the range of 1 mA to 25 mA.

[0043] Since the ions 170 are implanted into the piezoelectric portion 112 of the substrate 100, and since the piezoelectric portion 112 has low conductivity, the piezoelectric portion 112 of the substrate 100 would have suffered from such a charge accumulation during the ion implantation process as described above compared 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, these charges can be displaced out of the piezoelectric portion 112, which reduces the risk of substrate deformation and high stress occurring, and consequently reduces the risk of breakage.

[0044] In addition, matching the coefficients of thermal expansion 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.

[0045] The electrically conductive portion 122 and / or the bonding layer 130 is / are in electrical contact 162 with one or more metal holding elements 162. Thus, once the electrical charges 180 have entered the electrically conductive portion 122 and / or the bonding layer 130, the charges 180 are discharged via the one or more metal holding elements 160 and the substrate holder 140, which is grounded.

[0046] Preferably, the substrate holder 140 and the one or more metal holding elements 160 are made of the same metal material, in particular aluminum.

[0047] Thus, by using the substrate 100 according to the invention, the inventive implantation process provides improved charge removal compared to the implantation process of the prior art.

[0048] [Fig. 2] illustrates a variant of the first embodiment. In this embodiment, steps I) and II) are identical to the first embodiment, and will therefore not be described again, but reference will be made to their description above. After step II) of fixing the piezoelectric substrate 110 and the electrically conductive part 120, an additional process step II_2) of thinning the piezoelectric part 110 of the substrate 100 is carried out to obtain a modified substrate 200.

[0049] This thinning step may be performed using a mechanical process or a chemical etching process such as those known in the art and suitable for piezoelectric substrates. The thinning step may be accompanied by additional process steps, such as polishing after the thinning step to improve the quality of the surface 212 of the thinned piezoelectric portion 210.

[0050] The thinned piezoelectric portion 210 is thinned to between about 100 pm to 1 pm relative to the bulk material.

[0051] Steps III) and IV) are then carried out in the same manner as described above, except that a modified substrate 200 with the thinned piezoelectric portion 210 is used instead of the substrate 100. Reference is therefore made to the description of steps III) and IV) above with respect to [Fig.l].

[0052] The implanted ions 170 form a predetermined division zone 172 and charges 180 are discharged via the bonding layer 130 and / or the electrically conductive portion 122.

[0053] The thinning of the piezoelectric substrate 110 further improves the evacuation of charges 180 from the piezoelectric portion 210.

[0054] According to a second embodiment, as shown in [Fig. 3], the substrate 300 is produced without fixing a piezoelectric substrate on an electrically conductive substrate. In this embodiment, only a piezoelectric substrate 310 is provided, see step I) in [Fig. 3]. The piezoelectric substrate 310 has the same properties as the piezoelectric substrate 110 described above.

[0055] Next, during step II_1), one or more cavities 312 are formed in a 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 an array, and may all be the same size.

[0056] Next, as illustrated 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, to form the electrically conductive portion 320. The deposition process can be / is carried out such that a conductive layer 318 is made on the surface 314 to interconnect the conductive material 316. The portion of the substrate 300, comprising the conductive material 316 inside the cavities 316 and the layer 318 forms the electrically conductive portion 320 according to the invention.

[0057] Then, a step III) of positioning on an implantation device wheel and the state IV) of implantation of ions 170 are carried out as in the first embodiment using the same substrate holder 140 with the elastomer layer 150 and the metal holding element 160. Their description will therefore not be repeated, but reference is made to the description of figures 1 and 2.

[0058] In this embodiment, the charges are collected via the filled cavity matrix 312 and the discharge of the charges 380 is carried out via the layer 318, which is in contact 162 with the metal retaining element 160, from the piezoelectric portion 310 to the electrically conductive portion 320.

[0059] Due to the improved conductivity of the substrate 300 including the cavities 312 filled with conductive material 316, thereby forming the electrically conductive portion 320 of the substrate 300, charges can be discharged from the piezoelectric portion 310 through the electrically conductive portion 320 to the grounded substrate holder 340.

[0060] The inventive piezoelectric substrate 100, 200 or 300 may be used as a donor substrate in a subsequent layer transfer process for transferring a thin layer of the piezoelectric material onto a handling substrate to thereby form a piezoelectric-on-insulator substrate. In such a process, the inventive piezoelectric substrate 100, 200 or 300 is attached with the surface of the piezoelectric portion 110, 210 or 310, for example by bonding, to a handling substrate, for example a silicon wafer with or without an additional layer on the surface at which bonding takes place. Transfer of the piezoelectric layer then occurs at the mechanically weakened layer 172 within the piezoelectric portion 110, 210, 310 by applying a thermal or mechanical load.

[0061] Several embodiments of the invention have been described. Nevertheless, it should be understood that various modifications and improvements may be made without departing from the scope of the appended claims.

Claims

Claims

1. A method of implanting atomic species into a piezoelectric substrate, comprising the steps of: a) providing a substrate (100, 200, 300) comprising a piezoelectric portion (112, 210, 310) and an electrically conductive portion (122, 320), then b) mounting the substrate (100, 200, 300) with the electrically conductive portion (122, 320) on a substrate holder (140), and then c) implanting atomic species (170) into the piezoelectric portion (112, 210, 310) of the substrate (100, 200, 300).

2. The method of claim 1, wherein step b) comprises providing an elastomer layer (150) between the substrate holder (140) and the electrically conductive portion (122, 320) of the substrate (100, 200, 300).

3. The method of claim 1 or 2, wherein step a) comprises attaching a piezoelectric substrate (110) forming the piezoelectric portion (112, 210) to an electrically conductive substrate (120) forming the electrically conductive portion (122) of the substrate (100, 200).

4. The method of claim 3, wherein step a) further comprises thinning the piezoelectric substrate (110) to obtain a piezoelectric layer (210), in particular with a thickness between 1 pm and 100 pm.

5. A method according to any one of claims 3 or 4, wherein the piezoelectric substrate (110, 310) and the electrically conductive substrate (120) are chosen such that the difference in thermal expansion coefficients is less than 50*10 6K ', preferably less than 20*10 6K*.

6. The method of any one of claims 3 to 5, wherein the step of bonding the electrically conductive substrate (120) with the piezoelectric substrate (110) is performed using a bonding layer (130) between the piezoelectric substrate (110) and the electrically conductive substrate (120).

7. The method of claim 6, wherein the bonding layer (130) is a conductive bonding layer, in particular a metal layer.

8. The method of claim 1, wherein the step of providing the electrically conductive portion (320) comprises providing one or more cavities (312) in the side (314) of the substrate (300) facing the substrate holder (140) and filling one or more cavities (312) with a conductive material (316), in particular a metal.

9. A method according to any one of claims 1 to 8, wherein the piezoelectric substrate (110, 310) is a solid piezoelectric substrate, in particular a solid piezoelectric wafer, preferably with a thickness greater than 20 pm, even more particularly with a thickness greater than 100 pm.

10. The method of any one of claims 1 to 9, wherein the substrate (100, 200, 300) has a conductivity of 104S / cm or more.

11. A method according to any one of claims 1 to 10, wherein step b) of mounting the substrate (100, 200, 300) on the substrate holder (140) is carried out in such a way that the electrically conductive part (122, 320) and / or the bonding layer (130) is / are in electrical contact (162) with at least one metal holding element (160) electrically connected to the substrate holder (140).

12. A method according to any one of claims 1 to 11, wherein during step c), a predetermined division area (172) is provided in the piezoelectric portion (112, 210, 310), and further comprising a step d) of attaching the piezoelectric portion (112, 210, 310) of the piezoelectric substrate (110, 210, 310) to a handling substrate and a step e) of detaching from the remainder of the piezoelectric substrate (110, 210, 310) at the predetermined division area (172) to transfer a layer of the piezoelectric substrate (110, 210, 310) onto the handling substrate.

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