JP6265291B2 - Bonded wafer manufacturing method and bonded wafer - Google Patents

Description

  The present invention relates to a method for manufacturing a bonded wafer and a bonded wafer, and more particularly to a method for manufacturing a bonded wafer capable of suppressing metal contamination by exhibiting higher gettering ability.

In recent years, SOI wafers having an SOI (Silicon on Insulator) structure are attracting attention in the field of highly integrated CMOS devices, high voltage devices, and image sensors. This SOI wafer has a structure in which an insulating film such as silicon oxide (SiO ₂ ) and a single crystal silicon layer used as a device active layer are sequentially formed on a support substrate. When used, the parasitic capacitance generated between the element and the substrate is reduced, so that the device can be increased in speed, increased in breakdown voltage, reduced in power consumption, and the like.

  One of typical methods for manufacturing such an SOI wafer is a bonding method. In this bonding method, an insulating film is formed on at least one of a support substrate wafer and an active layer wafer, and then these wafers are bonded together via an insulating film, and then heat treatment is performed at a high temperature of about 1200 ° C. This is a method for manufacturing an SOI wafer (hereinafter, an SOI wafer manufactured by a bonding method is referred to as a “bonded wafer”).

  The bonded wafer thus obtained has advantages in terms of electrical characteristics and the ability to form a homogeneous silicon layer, while having structural demerits against metal contamination. That is, the diffusion coefficient of many metal impurities is smaller in the silicon oxide film than in silicon. Therefore, when metal impurities enter from the surface side of the active layer wafer, the metal impurities are difficult to pass through the silicon oxide layer, and thus accumulate in the active layer wafer.

  In response to this problem, several techniques for improving the gettering capability of the bonded wafer have been proposed. For example, in Patent Document 1, an ion-implanted damage layer is formed by ion-implanting a neutral element that is electrically inactive in silicon from the surface of either a support substrate wafer or an active layer wafer. Thus, a method for manufacturing a bonded wafer having sufficient gettering capability while suppressing generation of leakage current, deterioration of breakdown voltage of an insulating film, and the like is described.

  Further, in Patent Document 2, a single crystal silicon layer and a gettering layer made of silicon containing at least oxygen among oxygen, carbon, and nitrogen are sequentially formed on the support substrate wafer, and made of single crystal silicon. High gettering is achieved by forming an insulating layer made of a silicon insulating film on the surface of the active layer wafer and bonding the surface of the gettering layer on the wafer for the support substrate and the surface of the insulating layer on the wafer for the active layer together. A method for producing a bonded wafer having the capability is described.

JP2007-318102A JP2010-258083

  However, it has been found that the techniques described in Patent Document 1 and Patent Document 2 still have insufficient gettering ability for metal impurities. That is, the techniques described in Patent Document 1 and Patent Document 2 both inject monomer ions (single ions) into a silicon wafer. However, according to the study by the present inventors, the bonded wafer subjected to the monomer ion implantation has insufficient gettering ability and has a low effect of reducing metal contamination, so that the bonded wafer has higher gettering ability. There was a need to establish a method for producing the above.

  Therefore, an object of the present invention is to provide a bonded wafer capable of suppressing metal contamination by exhibiting higher gettering ability and a method for manufacturing the same.

  According to further studies by the present inventors, it has been found that there are the following advantages compared with the case of injecting monomer ions by irradiating the silicon wafer with cluster ions. That is, when irradiating with cluster ions, even when irradiating at an acceleration voltage equivalent to that of monomer ions, the energy per atom or molecule collides with the silicon wafer with a smaller energy than in the case of monomer ions. The peak concentration of the profile in the depth direction can be made high. As a result, the inventors have found that the gettering ability is improved, and have completed the present invention.

  That is, in the method for producing a bonded wafer according to the present invention, at least the surface of the active layer wafer among the active layer wafer and the support substrate wafer made of silicon single crystal is irradiated with cluster ions and irradiated. A cluster ion irradiation step for forming a modified layer in which the constituent elements of the cluster ions are dissolved in the surface of the substrate, and an insulating film is formed on at least one surface of the wafer for active layer and the wafer for support substrate It comprises an insulating film forming step and a bonding step of bonding the modified layer side surface of the active layer wafer to the support substrate wafer via the insulating film.

  Here, the active layer wafer may be an epitaxial silicon wafer in which a silicon epitaxial layer is formed on the surface of a silicon wafer. In this case, the modified layer is formed on the surface of the silicon epitaxial layer in the cluster ion irradiation step. It is formed.

  The cluster ions preferably contain carbon as a constituent element, and more preferably contain two or more elements containing carbon as a constituent element. The cluster ion may further contain a dopant element, and the dopant element may be one or more elements selected from the group consisting of boron, phosphorus, arsenic, and antimony.

Further, the cluster ion irradiation step is preferably performed under the conditions that the acceleration voltage per carbon atom is 50 keV / atom or less, the cluster size is 2 or more, and the carbon dose is 2 × 10 ¹³ atoms / cm ² or more. .

  Furthermore, it is preferable that the cluster irradiation step is performed on both the active layer wafer and the support substrate wafer.

  Furthermore, after the bonding step, heat treatment for strengthening the bond between the active layer wafer and the support substrate wafer can be performed.

  Next, the bonded wafer of the present invention comprises a support substrate wafer made of silicon single crystal, an insulating film formed on the support substrate wafer, and a silicon single crystal formed on the insulating film. In a bonded wafer having an active layer wafer, a modified layer formed by dissolving a predetermined element in the active layer wafer is provided between the insulating film and the active layer wafer. The half width of the concentration profile in the depth direction of the predetermined element is 100 nm or less.

Here, it is preferable that the peak concentration of the predetermined element in the modified layer is 1.0 × 10 ¹⁷ atoms / cm ³ or more.

  The active layer wafer may be an epitaxial silicon wafer in which a silicon epitaxial layer is formed on the surface of a silicon wafer. In this case, the modified layer is located on the surface of the silicon epitaxial layer.

  Furthermore, the predetermined element preferably includes carbon, and more preferably includes two or more elements including carbon. The predetermined element may include a dopant element, and the dopant element may be one or more elements selected from the group consisting of boron, phosphorus, arsenic, and antimony.

  Furthermore, it is preferable to further include a modified layer formed by dissolving the predetermined element in the support substrate wafer between the support substrate wafer and the insulating film.

  According to the present invention, at least the active layer wafer is irradiated with the cluster ions, and the modified layer formed by dissolving the constituent elements of the cluster ions on the surface of the irradiated wafer is formed. By exhibiting the above, a bonded wafer capable of suppressing metal contamination can be manufactured.

It is a model cross section explaining the manufacturing method of the bonded wafer 100 by 1st Embodiment of this invention. It is a model cross section explaining the manufacturing method of the bonded wafer 200 by 2nd Embodiment of this invention. (A) is a schematic diagram explaining the irradiation mechanism in the case of irradiating cluster ions, (B) is a schematic diagram explaining the injection mechanism in the case of injecting monomer ions. It is a graph showing distribution of the carbon concentration with respect to the depth from the surface of the wafer for active layers about this invention example 1 and the comparative example 1. FIG. It is the graph which compared the gettering ability of Ni about this invention example 1 and the comparative example 1. FIG.

  Hereinafter, the present invention will be specifically described with reference to the drawings. In principle, the same components are denoted by the same reference numerals, and description thereof is omitted. The method for manufacturing a bonded wafer according to the first embodiment of the present invention includes, as shown in FIG. 1, at least one of an active layer wafer 11 and a support substrate wafer 12 made of silicon single crystal (FIG. 1A). The surface 11A of the active layer wafer 11 is irradiated with the cluster ions 15 (FIG. 1B), and the modified layer 16 in which the constituent elements of the cluster ions 15 are dissolved is formed on the surface of the irradiated wafer. A cluster ion irradiation step (FIG. 1 (C)), an insulating film forming step for forming an insulating film 17 on at least one surface of the active layer wafer 11 and the support substrate wafer 12 (FIG. 1 (D)), And a bonding step of bonding the surface of the modified layer 16 side of the active layer wafer 11 to the support substrate wafer 12 through the insulating film 17 (FIG. 1E). FIG. 1E is a schematic cross-sectional view of a bonded wafer 100 obtained as a result of this manufacturing method. Hereafter, each process is demonstrated concretely.

  First, an active layer wafer 11 and a support substrate wafer 12 are prepared, and at least the surface 11A of the active layer wafer among these wafers is irradiated with cluster ions 15. As a result, a modified layer 16 in which the constituent elements of the cluster ions 15 are dissolved is formed on the surface 11A of the irradiated wafer. In FIG. 1, only the active layer wafer 11 is irradiated with the cluster ions 15.

  The active layer wafer 11 is a wafer used as a device active layer, and a single crystal silicon wafer made of silicon single crystal is used as the active layer wafer 11. As the single crystal silicon wafer, one obtained by slicing a single crystal silicon ingot grown by the Czochralski method (CZ method) or the floating zone melting method (FZ method) with a wire saw or the like can be used. Also, carbon and / or nitrogen may be added to obtain higher gettering ability. Further, an arbitrary impurity may be added to obtain n-type or p-type.

  As the support substrate wafer 12, similarly to the active layer wafer 11, it is desirable to use a single crystal silicon wafer made of silicon single crystal.

  As the active layer wafer 11, an epitaxial silicon wafer in which a silicon epitaxial layer 14 is formed on the surface of a bulk silicon wafer 13 can be used as shown in FIG. The silicon epitaxial layer 14 can be formed under general conditions by a CVD method. The silicon epitaxial layer 14 preferably has a thickness in the range of 0.1 to 10 μm, and more preferably in the range of 0.2 to 5 μm.

  As an example, the method for manufacturing a bonded wafer 200 according to the second embodiment of the present invention is for an active layer in which a silicon epitaxial layer 14 is formed on the surface (at least one side) of a bulk silicon wafer 13 as shown in FIG. The cluster ions 15 are irradiated to the wafer 11 (FIGS. 2A and 2B), and the constituent elements of the cluster ions 15 are applied to the surface 11A of the active layer wafer 11 (the surface of the silicon epitaxial layer 14 in this embodiment). A cluster ion irradiation step for forming a modified layer 16 formed by solid solution (FIG. 2C), and an insulation for forming an insulating film 17 on at least one surface of the active layer wafer 11 and the support substrate wafer 12 In the film forming step (FIG. 2D), the surface of the active layer wafer 11 on the modified layer 16 side is pasted to the support substrate wafer 12 via the insulating film 17. And having a bonding process combining. FIG. 2E is a schematic cross-sectional view of a bonded wafer 200 obtained as a result of this manufacturing method.

  Here, regarding the cluster ion irradiation process which is a characteristic process of the present invention, the technical significance of adopting this process will be described together with the effects. The modified layer 16 formed as a result of the irradiation of the cluster ions 15 is such that the constituent elements of the cluster ions 15 are interstitial positions of crystals on the surface of the silicon wafer as the active layer wafer 11 (and the support substrate wafer 12) or This is a region that exists locally as a solution at the substitution position, and serves as a gettering site. The reason is presumed as follows. That is, elements such as carbon and boron irradiated in the form of cluster ions are localized at a high density at the substitution positions and interstitial positions of single crystal silicon. It was experimentally confirmed that the solid solubility of heavy metals (saturated solubility of transition metals) greatly increases when carbon, boron, or the like is dissolved to a level higher than the equilibrium concentration of single crystal silicon. That is, it is considered that the solid solubility of heavy metals is increased by carbon, boron, or the like dissolved to an equilibrium concentration or higher, and the capture rate for heavy metals is thereby significantly increased.

  Thus, in the present invention, since the cluster ions 15 are irradiated, higher gettering ability can be obtained as compared with the case of injecting monomer ions. In the present specification, the “cluster ion” means an ionized product in which a plurality of atoms or molecules are aggregated to give a cluster having a lump to give a positive charge or a negative charge. A cluster is a massive group in which a plurality (usually about 2 to 2000) of atoms or molecules are bonded to each other.

  The inventors of the present invention consider an operation that can obtain such an effect as follows.

  For example, when carbon monomer ions are implanted into a silicon wafer, as shown in FIG. 3B, the monomer ions are blown off silicon atoms constituting the silicon wafer and implanted at a predetermined depth in the silicon wafer. The The implantation depth depends on the type of constituent elements of the implanted ions and the acceleration voltage of the ions. In this case, the concentration profile of carbon in the depth direction of the silicon wafer is relatively broad, and the region where the implanted carbon is present is approximately 0.5 to 1 μm. When multiple types of ions are simultaneously irradiated with the same energy, lighter elements are implanted deeper, that is, implanted at different positions according to the mass of each element, so the concentration profile of the implanted elements becomes broader. .

  Further, in the manufacture of bonded SOI wafers, as will be described later, after bonding the active layer wafer 11 and the support substrate wafer 12 via an insulating film, the bond that strengthens the bond between the two wafers. Although a tempering heat treatment can be performed, if the crystallinity of the wafer surfaces to be bonded is disturbed, the bonding strength between the two wafers may be reduced. However, monomer ions are generally implanted at an acceleration voltage of about 150 to 2000 keV, but each ion collides with silicon atoms with its energy, so that the crystallinity of the surface portion of the silicon wafer into which the monomer ions are implanted is disturbed. Also, the higher the acceleration voltage, the more the crystallinity is disturbed. Therefore, a heat treatment (recovery heat treatment) for recovering the disordered crystallinity after ion implantation is required, and the recovery heat treatment needs to be performed at a high temperature for a long time.

  On the other hand, when irradiating a silicon wafer with cluster ions 15 made of, for example, carbon and boron, as shown in FIG. It becomes a high temperature state of about 1400 ° C., and silicon melts. Thereafter, the silicon is rapidly cooled, and carbon and boron are dissolved in the vicinity of the surface in the silicon wafer. That is, the “modified layer” in this specification means a layer in which constituent elements of irradiated ions are solid-solved at interstitial positions or substitution positions of crystals on the silicon wafer surface. The concentration profile of carbon and boron in the depth direction of the silicon wafer depends on the acceleration voltage and cluster size of the cluster ions 15, but becomes sharper than that of monomer ions, and the irradiated carbon and boron are locally localized. The thickness of the existing region (that is, the modified layer) is approximately 500 nm or less (for example, about 50 to 400 nm). As a result, it is considered that the carbon and boron precipitation regions can be locally and highly concentrated, and higher gettering ability can be obtained. In addition, if it is a form of cluster ion, multiple types of ions can be irradiated simultaneously.

  The cluster ions 15 are generally irradiated at an acceleration voltage of about 10 to 100 keV / Cluster. Since the cluster is an aggregate of a plurality of atoms or molecules, the energy per atom or molecule is reduced. The damage to the crystal of the silicon wafer is small. For this reason, when the cluster ions are irradiated, the recovery heat treatment for recovering the damage on the silicon wafer surface can be omitted. Depending on the cluster size and dose used, it may be desirable to perform a recovery heat treatment, but even if a recovery heat treatment is required, it can be recovered by an extremely short heat treatment.

  When performing the recovery heat treatment, specifically, it may be performed at 900 ° C. or more and 1200 ° C. or less for 10 seconds or more and 1 hour or less. Here, the reason why the heat treatment temperature is set to 900 ° C. or more and 1200 ° C. or less is that if the temperature is less than 900 ° C., it is difficult to obtain the crystallinity recovery effect. This is because slip occurs and the heat load on the apparatus increases. Moreover, the heat treatment time is set to 10 seconds or more and 1 hour or less because a recovery effect is difficult to be obtained if the heat treatment time is less than 10 seconds. This is because it becomes larger.

  Such recovery heat treatment can be performed using, for example, a rapid heating / cooling heat treatment apparatus such as RTA or RTO, or a batch heat treatment apparatus (vertical heat treatment apparatus, horizontal heat treatment apparatus). Since the former is a lamp irradiation heating method, it is not suitable for long-time treatment in terms of the device structure, and is suitable for heat treatment within 15 minutes. On the other hand, in the latter, although it takes time to raise the temperature to a predetermined temperature, a large number of wafers can be processed simultaneously. In addition, because of the resistance heating method, long-time heat treatment is possible. An appropriate heat treatment apparatus may be selected in consideration of the irradiation conditions of the cluster ions 15.

  The cluster ion 15 has various clusters depending on the binding mode, and can be generated by a known method as described in the following document, for example. As a method for generating a gas cluster beam, (1) JP-A-9-41138, (2) JP-A-4-354865, and as an ion beam generating method, (1) charged particle beam engineering: Junzo Ishikawa: ISBN978 -4-339-00734-3: Corona, (2) Electron and ion beam engineering: The Institute of Electrical Engineers of Japan: ISBN4-88686-217-9: Ohm, (3) Cluster ion beam basics and applications: ISBN4-526-05765 -7: Nikkan Kogyo Shimbun. In general, a Nielsen ion source or a Kaufman ion source is used to generate positively charged cluster ions, and a large current negative ion source using a volume generation method is used to generate negatively charged cluster ions. It is done.

  Hereinafter, the irradiation conditions of the cluster ions 15 will be described. First, the element to be irradiated is not particularly limited, and examples thereof include carbon, boron, phosphorus, and arsenic. However, from the viewpoint of obtaining higher gettering capability, it is preferable that the cluster ions 15 include carbon as a constituent element. Since the carbon atom at the lattice position has a smaller covalent bond radius than that of single crystal silicon, a contraction field of the silicon crystal lattice is formed, so that the gettering ability to attract impurities between the lattices is high.

  Moreover, it is more preferable to include two or more elements including carbon as a constituent element. This is because the types of metals that can be efficiently gettered differ depending on the types of deposited elements, so that two or more types of elements can be dissolved to cope with a wider range of metal contamination. For example, in the case of carbon, nickel can be efficiently gettered, and in the case of boron, copper and iron can be efficiently gettered.

  Furthermore, in addition to carbon or two or more elements containing carbon as a constituent element, a dopant element can be further included. As this dopant element, one or more elements selected from the group consisting of boron, phosphorus, arsenic and antimony can be used.

The compounds to be ionized are not particularly limited, but enumeration of compounds suitable for ionization includes carbon sources such as ethane, methane, propane, dibenzyl (C ₁₄ H ₁₄ ), carbon dioxide (CO ₂ ), and boron sources. Examples thereof include diborane and decaborane (B ₁₀ H ₁₄ ). For example, when a gas obtained by mixing dibenzyl and decaborane is used as a material gas, a hydrogen compound cluster in which carbon, boron and hydrogen are aggregated can be generated. If cyclohexane (C ₆ H ₁₂ ) is used as a material gas, cluster ions 15 made of carbon and hydrogen can be generated. As the carbon source compound, in particular, a cluster C _n H _m (3 ≦ n ≦ 16, 3 ≦ m ≦ 10) formed from pyrene (C ₁₆ H ₁₀ ), dibenzyl (C ₁₄ H ₁₄ ) or the like is used. Is preferred. This is because it is easy to form a small-sized cluster ion beam.

  Furthermore, by controlling the acceleration voltage and the cluster size of the cluster ions 15, the peak position of the concentration profile of the constituent elements in the modified layer 16 can be controlled. By irradiation with the cluster ions 15, the concentration peak position can be positioned closer to the active layer wafer surface 11 </ b> A (position far from the surface of the bonded wafer 100) than the monomer ion implantation.

  That is, in the manufacture of bonded SOI wafers, it is required to provide a thick film SOI wafer having a thick active layer wafer or a thin film SOI wafer having a thin active layer wafer. For this reason, for example, when manufacturing a thin film SOI wafer of 1 μm or less, the concentration profile of the implanted element in the depth direction becomes broad in the implantation of monomer ions, and therefore, in the active layer region used as the device fabrication region. Carbon may be diffused, and in this case, the electrical characteristics of the device are deteriorated. In cluster ion irradiation, the concentration profile in the depth direction has a concentration peak locally at an extremely shallow surface position (position closer to the insulating film side), so carbon diffusion into the active layer region used as the device fabrication region Can be eliminated, and the active region can be expanded in the depth direction. In the present specification, the “cluster size” means the number of atoms or molecules constituting one cluster.

In the cluster ion irradiation process of the present invention, from the viewpoint of obtaining higher gettering ability, the peak concentration of the constituent elements of the cluster ions 15 in the modified layer 16 is 1.0 × 10 ¹⁷ atoms / cm ³ or more. The cluster ions 15 are preferably irradiated, and more preferably 1.0 × 10 ¹⁸ atoms / cm ³ or more and 1.0 × 10 ²² atoms / cm ³ or less. In this specification, the “concentration profile in the depth direction of the constituent element” means not a total but a profile of each single element when the constituent element includes two or more elements. .

As a condition necessary for setting the peak concentration of the constituent elements in the above range, in the cluster ion irradiation process, the acceleration voltage of the cluster ion 15 is set to 0 keV / atom and 50 keV / atom or less, and under a condition of 40 keV / atom or less. It is preferable to carry out with. The cluster size is 2 or more, preferably 50 or less. Furthermore, the dose amount of carbon is 2 × 10 ¹³ atoms / cm ² or more, preferably 1 × 10 ¹⁷ atoms / cm ² or less.

  Here, two methods of (1) electrostatic acceleration and (2) high-frequency acceleration are generally used for adjusting the acceleration voltage. As the former method, there is a method in which a plurality of electrodes are arranged at equal intervals and an equal voltage is applied between them to create an equal acceleration electric field in the axial direction. As the latter method, there is a linear linac method in which ions are accelerated using a high frequency while running linearly. The cluster size can be adjusted by adjusting the gas pressure of the gas ejected from the nozzle, the pressure of the vacuum vessel, the voltage applied to the filament during ionization, and the like. The cluster size can be obtained by obtaining a cluster number distribution by mass spectrometry using a quadrupole high-frequency electric field or time-of-flight mass spectrometry and taking an average value of the number of clusters. Furthermore, the dose of carbon can be adjusted by controlling the ion irradiation time.

  As described above, after the cluster ion irradiation step, the insulating layer forming step or the bonding step can be performed without performing the recovery heat treatment on the active layer wafer 11, but after the cluster ion irradiation step, The recovery heat treatment may be performed using a rapid heating / cooling heat treatment apparatus or a batch type heat treatment apparatus. In that case, as described above, the irradiation with the cluster ions 15 in the present invention does not disturb the crystallinity of the silicon wafer as compared with the conventional implantation of monomer ions. Sex can be fully recovered.

  In this way, the modified layer 16 in which the constituent elements of the cluster ions 15 are dissolved can be formed on the surface of the wafer irradiated with the cluster ions 15.

Next, an insulating film forming step for forming an insulating film 17 on at least one surface of the active layer wafer 11 and the support substrate wafer 12 is performed (FIG. 1D). Here, as the insulating film, a silicon oxide (SiO ₂ ) film, a nitride film, or the like can be used. For example, when an SiO ₂ film is used, it can be performed by well-known thermal oxidation. In FIG. 1, the insulating film 17 is formed only on the support substrate wafer 12, but an oxide film may be formed on the active layer wafer 11 on which the modified layer 16 is formed, or both the wafers may be formed. It can also be formed.

  Here, the thickness of the insulating film 17 to be formed may be set in the range of 0.01 μm or more and 30 μm or less, and the thickness of the insulating film 17 adjusts the temperature and processing time of the heat treatment, the atmospheric gas flow rate, and the like. Can be adjusted.

  Here, when the insulating film 17 is formed on the surface of the active layer wafer 11, in this case, the insulating film 17 is formed in the modified layer 16 on the surface on the modified layer 16 side.

  Subsequently, a bonding step is performed in which the surface of the modified layer 16 side of the active layer wafer 11 is bonded to the support substrate wafer 12 via the insulating film 17 (FIG. 1E). Thereby, the bonded wafer of this invention can be manufactured. This bonding step can be performed using any known wafer bonding apparatus.

  The insulating film forming step can be performed before the cluster ion implantation step. However, in this case, the insulating film forming step is limited to a wafer that is not irradiated with the cluster ions 15. That is, when the insulating film forming step is performed before the cluster ion implantation step, it is performed on the support substrate wafer 12.

  Thus, bonded wafers 100 and 200 that can further suppress metal contamination can be obtained by exhibiting higher gettering ability than conventional ones.

  The cluster ion irradiation process is performed only on the surface 11A of the active layer wafer 11 in FIGS. 1 and 2, but in addition to the surface 11A, the cluster ion irradiation process is performed on the surface 12A of the support substrate wafer 12. Also good. At that time, the constituent elements of the cluster ions 15 can be the same as or changed from the case where the surface 11A of the active layer wafer 11 is irradiated. Due to the irradiation to the support substrate wafer 12, a modified layer (not shown) is formed between the support substrate wafer 12 and the insulating film 17 and the constituent elements of the cluster ions 15 are dissolved in the support substrate wafer 12. ) Can be further provided. Thereby, the gettering ability can be further improved.

  Further, after the bonding step, as shown in FIG. 1 (F) and FIG. 2 (F), a bonding strengthening heat treatment step is performed, and the bonding surface between the active layer wafer 11 and the support substrate wafer 12 is bonded. Can strengthen the bond. This bond strengthening heat treatment step can be performed under conditions of, for example, 800 ° C. or more and 1200 ° C. or less, 10 minutes or more and 6 hours or less in an oxidizing gas or inert gas atmosphere. Can be strengthened.

  Further, as shown in FIGS. 1G and 2G, a thinning process for reducing the thickness of the active layer wafer 11 can be performed. Thereby, a bonded wafer having an active layer having a desired thickness can be obtained. For this thinning step, for example, a well-known surface grinding and mirror polishing method can be suitably used. Further, the thinning process may be performed using another thinning technique such as a well-known smart cut method.

  Next, the bonded wafers 100 and 200 obtained by the above manufacturing method will be described. The bonded wafer 100 according to the first embodiment and the bonded wafer 200 according to the second embodiment include, as shown in FIGS. 1E and 2E, a support substrate wafer 12 made of a silicon single crystal, In a bonded wafer having an insulating film 17 formed on a support substrate wafer 12 and an active layer wafer 11 made of silicon single crystal formed on the insulating film 17, the insulating film 17 and the active layer A modified layer 16 in which a predetermined element is dissolved in the active layer wafer 11 is provided between the wafer 11 and the half-value width of the concentration profile in the depth direction of the predetermined element in the modified layer 16 is 100 nm or less. It is characterized by being. That is, according to the method for manufacturing a bonded wafer of the present invention, compared to monomer ion implantation, the precipitation region of elements constituting cluster ions can be locally and highly concentrated. It became possible to set it to 100 nm or less.

  The “concentration profile in the depth direction” in this specification means a concentration distribution in the depth direction measured by secondary ion mass spectrometry (SIMS). The “half-value width of the concentration profile in the depth direction of the predetermined element” is measured from the irradiation surface of the cluster ions after removing the support substrate and the BOX layer (insulating film) in consideration of measurement accuracy. As a result.

  The position of the concentration peak in the concentration profile is located near the wafer surface, for example, 150 nm from the wafer surface. Therefore, compared with the case of monomer ion implantation, it can suppress that carbon mixes in the active layer area | region used with a device. Moreover, the use area | region of an active layer can be expanded in the depth direction.

  The predetermined element is not particularly limited as long as it is an element other than silicon. However, as described above, carbon or two or more elements containing carbon are preferable. The predetermined element can further contain a dopant element. As the dopant element, one or more elements selected from the group consisting of boron, phosphorus, arsenic, and antimony can be used.

From the viewpoint of obtaining higher gettering capability, the bonded wafers 100 and 200 both preferably have a peak concentration in the concentration profile of 1 × 10 ¹⁷ atoms / cm ³ or more, and 1.0 × 10 ¹⁸ atoms / cm ^3. More preferably, it is cm ³ or more and 1.0 × 10 ²² atoms / cm ³ or less, and more preferably 1.0 × 10 ¹⁸ atoms / cm ³ or more and 1.0 × 10 ²¹ atoms / cm ³ or less.

  Moreover, the depth direction thickness of the modified layer 16 can be in the range of approximately 30 to 400 nm.

As the insulating film 17, a silicon oxide (SiO ₂ ) film, a nitride film, or the like can be used. 1 and 2, the insulating film 17 is provided only on the support substrate wafer 12. However, the insulating film 17 may be provided on the active layer wafer 11 on which the modified layer 16 is formed. Alternatively, it can be provided on both wafers.

  Thus, according to the semiconductor epitaxial wafers 100 and 200 of the present invention, it is possible to further suppress metal contamination by exhibiting a higher gettering capability than conventional.

  A modified layer (not shown) formed by dissolving a predetermined element in the support substrate wafer 12 may be further provided between the support substrate wafer 12 and the insulating film 17. Thereby, the gettering ability can be further improved.

(Invention Examples 1-3)
As an active layer wafer and a support substrate wafer, an n-type silicon wafer (diameter: 300 mm, thickness: 775 μm, dopant type: phosphorus, dopant concentration: 5.5) collected from a single crystal silicon ingot obtained by the CZ method. 0 × 10 ¹⁴ atoms / cm ³ ) was prepared. Next, a cluster ion generator (manufactured by Nissin Ion Instruments Co., Ltd., model number: CLARIS) was used to generate C ₅ H ₅ clusters as cluster ions, and a dose amount of 1.0 × 10 ¹⁵ Clusters / cm ² (carbon dose) Amount 5.0 × 10 ¹⁵ atoms / cm ² : Invention Example 1), 6.0 × 10 ¹⁴ Clusters / cm ² (carbon dose amount 3.0 × 10 ¹⁵ atoms / cm ² : Invention Example 2), 4.0 × 10 ¹⁴ Clusters / cm ² (carbon dose 2.0 × 10 ¹⁵ atoms / cm ² : Example 3 of the present invention), active layer under the condition of an acceleration voltage of 14.80 keV / atom per carbon atom The surface of the wafer was irradiated. Subsequently, an insulating film having a thickness of 10 nm was formed on the surface of the support substrate wafer, and then the surface of the active layer wafer on the modified layer 16 side was bonded to the support substrate wafer via the insulating film 17. Thereafter, the bonded wafer is transported into a vertical heat treatment apparatus under a hydrogen and oxygen mixed gas atmosphere, and the temperature inside the apparatus is raised to 800 ° C. and held for 2 hours, and then heated to 1200 ° C. to 1 A bond-strengthening heat treatment was applied to maintain the time. Then, after grinding the active layer wafer from the surface side to reduce the thickness of the active layer wafer, the surface was mirror-polished to produce a bonded wafer having an active layer thickness of 3 μm.

(Comparative Examples 1-3)
Instead of the cluster ion irradiation process, carbon monomer ions are generated using CO ₂ as a material gas, and the dose amount is 1.0 × 10 ¹⁵ atoms / cm ² (Comparative Example 1), 6.0 × 10 ¹⁴ atoms / cm. ² (Comparative Example 2), 4.0 × 10 ¹⁴ atoms / cm ² (Comparative Example 3), except that the monomer ion implantation process was performed under the conditions of an acceleration voltage of 80 keV / atom, the same as Example 1 of the present invention, The bonded wafers of Comparative Examples 1 to 3 were manufactured.

  Each sample produced in the above invention examples and comparative examples was evaluated. The evaluation method is shown below.

(1) SIMS measurement First, in order to clarify the difference in carbon distribution immediately after cluster ion irradiation and immediately after monomer ion implantation, the present invention example 1 and comparative example 1 are used for an active layer after cluster ion implantation. SIMS measurement was performed on the wafer. The obtained carbon concentration profile is shown in FIG. 4 for reference. Here, the depth of the horizontal axis in FIG. 4 is zero on the surface of the active layer wafer.

  Next, SIMS measurement was performed on the bonded wafers of Invention Example 1 and Comparative Example 1. The obtained carbon concentration profiles are shown in FIGS. 5 (A) and 5 (B), respectively. The depth of the horizontal axis in FIG. 5 is zero on the wafer side surface for the active layer of the bonded wafer.

  Table 1 shows the full width at half maximum of the carbon concentration profile when SIMS measurement is performed after removing the support substrate and the BOX layer (insulating film) for each sample produced in each of the present invention examples and comparative examples. As described above, the half width shown in Table 1 is the half width when SIMS measurement is performed after the support substrate and the BOX layer are removed. Therefore, the half width shown in Table 1 and FIGS. ) Half width. Table 1 also shows the peak concentration value of the concentration when SIMS measurement is performed after thinning.

(2) Evaluation of gettering ability The surface of the bonded wafer of each sample prepared in the present invention example and the comparative example was intentionally formed with a Ni contamination liquid (1.0 × 10 ¹² / cm ² ) using a spin coat contamination method. Subsequently, a heat treatment was performed at 900 ° C. for 30 minutes. Thereafter, SIMS measurement was performed. As a representative of the measurement results, the Ni concentration profiles for Invention Example 1 and Comparative Example 1 are shown together with the carbon concentration profiles (FIGS. 5A and 5B). Table 1 shows the results of evaluation of gettering ability for other examples of the present invention and comparative examples. The evaluation criteria were classified as follows according to the peak concentration value of the Ni concentration profile.
A: 3.0 × 10 ¹⁷ atoms / cm ³ or more ○: 2.0 × 10 ¹⁷ atoms / cm ³ or more and less than 3.0 × 10 ¹⁷ atoms / cm ³ Δ: Less than 2.0 × 10 ¹⁷ atoms / cm ³

  First, the present invention example 1 and the comparative example 1 which are different only in that monomer ion implantation is performed instead of cluster ion irradiation will be compared. As shown in FIG. 4, when comparing the carbon concentration profiles of the active layer wafer before the bonding step, which is an intermediate product immediately after the cluster ion irradiation and immediately after the monomer ion implantation, the carbon concentration in the case of cluster ion irradiation. The profile is sharp and the carbon concentration profile is broad in the case of monomer ion implantation. From this, it is estimated that the tendency of the carbon concentration profile is the same even after the bonding step. Actually, as can be seen from the carbon concentration profile (FIGS. 5A and 5B) of the bonded wafer, a modified layer having a local concentration and higher concentration than the monomer ion implantation is formed by the cluster ion irradiation. Yes. Further, when the present invention example 1 and the comparative example 1 are compared from the Ni concentration profiles shown in FIGS. 5A and 5B, the present invention example 1 has a large amount of the modified layer formed by cluster ion irradiation. It can be seen that Ni is captured and exhibits high gettering ability.

  Moreover, as shown in Table 1, all of the inventive examples 1 to 3 irradiated with cluster ions have a full width at half maximum of 100 nm or less, and all have sufficient gettering ability. On the other hand, Comparative Examples 1 to 3 in which monomer ions were implanted all had a half-value width of more than 100 nm, and the gettering ability was insufficient. As described above, Invention Examples 1 to 3 irradiated with cluster ions have higher gettering ability because the half width of the carbon concentration profile is smaller than Comparative Examples 1 to 3 in which monomer ions are implanted. It can be said that

  According to the present invention, metal contamination can be suppressed by exhibiting a higher gettering capability, which is useful in the semiconductor wafer manufacturing industry.

11 Wafer for Active Layer 11A Surface of Wafer for Active Layer 12 Wafer for Support Substrate 12A Surface of Wafer for Support Substrate 13 Bulk Silicon Wafer 14 Silicon Epitaxial Layer 15 Cluster Ion 16 Modified Layer 17 Insulating Film 100, 200 Bonded Wafer

Claims (8)

Of the active layer wafer and support substrate wafer made of silicon single crystal, at least the surface of the active layer wafer is irradiated with cluster ions, and the constituent elements of the cluster ions are dissolved in the irradiated wafer surface. A cluster ion irradiation step for forming a modified layer formed by:
An insulating film forming step of forming an insulating film on at least one surface of the active layer wafer and the support substrate wafer;
A bonding step of bonding the modified layer side surface of the active layer wafer to the support substrate wafer via the insulating film;
And a bonded wafer having a half-value width of a concentration profile in the depth direction of the constituent element in the modified layer after the bonding step is 100 nm or less.   2. The active layer wafer is an epitaxial silicon wafer in which a silicon epitaxial layer is formed on a surface of a silicon wafer, and the modified layer is formed on a surface of the silicon epitaxial layer in the cluster ion irradiation step. The manufacturing method of the bonded wafer of description.   The manufacturing method of the bonded wafer of Claim 1 or 2 with which the said cluster ion contains carbon as a structural element.   The manufacturing method of the bonded wafer of Claim 3 in which the said cluster ion contains 2 or more types of elements containing carbon as a structural element.   The method for producing a bonded wafer according to claim 3 or 4, wherein the cluster ions further contain a dopant element, and the dopant element is one or more elements selected from the group consisting of boron, phosphorus, arsenic, and antimony. . The cluster ion irradiation process, the acceleration voltage per one carbon atom is 50 keV / the atom or less, cluster size two or more claims 1 to 5, the dose of carbon carried by the 2 × ¹⁰ 13 atoms / cm ² or more conditions The manufacturing method of the bonded wafer as described in any one of these.   The manufacturing method of the bonded wafer as described in any one of Claims 1-6 which performs the said cluster irradiation process to both the said wafer for active layers, and the said wafer for support substrates.   The manufacturing method of the bonded wafer as described in any one of Claims 1-7 which performs the heat processing for strengthening the coupling | bonding of the said wafer for active layers, and the said wafer for support substrates after the said bonding process.

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