JP2017175143A - Semiconductor epitaxial wafer manufacturing method, semiconductor epitaxial wafer, and solid-state imaging element manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor epitaxial wafer manufacturing method capable of inhibiting metallic contamination by utilizing higher gettering capability.SOLUTION: A manufacturing method of a semiconductor epitaxial wafer 100 comprises the steps of: forming a first epitaxial layer 12 on a semiconductor wafer 10; forming a second epitaxial layer 14 on the first epitaxial layer 12; and irradiating a semiconductor wafer surface 10A (or a first epitaxial layer surface) with carbon-containing cluster ions to form, on the semiconductor wafer surface 10A (or the first epitaxial layer surface), a modifying layer 18 where carbon is fixed. A peak concentration of a dopant element in the first epitaxial layer 12 is higher than a peak concentration of a dopant element in the second epitaxial layer 14.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a semiconductor epitaxial wafer, a semiconductor epitaxial wafer, and a method for manufacturing a solid-state imaging device. In particular, the present invention relates to a semiconductor epitaxial wafer capable of suppressing metal contamination by exhibiting higher gettering ability and a method for manufacturing the same.

  Metal contamination is a factor that degrades the characteristics of semiconductor devices. For example, in a back-illuminated solid-state imaging device, metal mixed in a semiconductor epitaxial wafer serving as the substrate of this device causes a dark current of the solid-state imaging device to increase and causes a defect called a white defect. The back-illuminated solid-state image sensor has a wiring layer, etc., placed below the sensor part, so that external light can be taken directly into the sensor and clearer images and videos can be taken even in dark places. In recent years, it has been widely used in mobile phones such as digital video cameras and smartphones. Therefore, it is desired to reduce white defect as much as possible.

  Metal contamination in the wafer occurs mainly in the manufacturing process of the semiconductor epitaxial wafer and the manufacturing process (device manufacturing process) of the solid-state imaging device. Metal contamination in the former semiconductor epitaxial wafer manufacturing process is caused by heavy metal particles from the components of the epitaxial growth furnace, or because the chlorine gas is used as the furnace gas during epitaxial growth, the piping material is corroded by metal. The thing by the heavy metal particle to generate | occur | produce is considered. In recent years, these metal contaminations have been improved to some extent by replacing the constituent materials of the epitaxial growth furnace with materials having excellent corrosion resistance, but are not sufficient. On the other hand, in the latter manufacturing process of the solid-state imaging device, there is a concern about heavy metal contamination of the semiconductor substrate during each process such as ion implantation, diffusion and oxidation heat treatment.

  For this reason, conventionally, a gettering sink for capturing metal on a semiconductor epitaxial wafer is formed, or a substrate having a high metal capture capability (gettering capability) such as a high-concentration boron substrate is used. The metal contamination was avoided.

  As a method of forming a gettering sink in a semiconductor wafer, oxygen precipitates (commonly referred to as silicon oxide precipitates, also referred to as BMD: Bulk Micro Defect) and dislocations are formed inside the semiconductor wafer. An intrinsic gettering (IG) method and an extrinsic gettering (EG) method in which a gettering sink is formed on the back surface of a semiconductor wafer are generally used.

  Here, as one method of the heavy metal gettering method, there is a technique of forming a gettering site in a semiconductor wafer by ion implantation. Patent Document 1 describes a manufacturing method in which carbon ions are implanted from one surface of a silicon wafer to form a carbon ion implanted region, and then a silicon epitaxial layer is formed on the surface to form a silicon epitaxial wafer. In this technique, the carbon ion implantation region functions as a gettering site.

  In Patent Document 2, carbon ions are implanted into a silicon wafer to form a carbon implanted layer, and then heat treatment for recovering the crystallinity of the wafer disturbed by the ion implantation is performed with an RTA (Rapid Thermal Annealing) apparatus. A technique for shortening the recovery heat treatment process by performing the process is described.

Furthermore, Patent Document 3 discloses that at least one of boron, carbon, aluminum, arsenic, and antimony is ion-implanted with a dose of 5 × 10 ¹⁴ to 1 × 10 ¹⁶ atoms / cm ² with respect to a silicon single crystal substrate. Then, after cleaning the silicon single crystal substrate subjected to the ion implantation without performing a recovery heat treatment, an epitaxial layer is formed at a temperature of 1100 ° C. or higher using a single wafer epitaxial apparatus. An epitaxial wafer manufacturing method characterized by the above is described.

JP-A-6-338507 JP 2008-294245 A JP 2010-177233 A

  The techniques described in Patent Document 1, Patent Document 2 and Patent Document 3 are all for implanting monomer ions (single ions) into a semiconductor wafer before forming an epitaxial layer. However, according to the study by the present inventors, it has been found that a semiconductor epitaxial wafer subjected to monomer ion implantation has insufficient gettering capability and a stronger gettering capability is required.

  In view of the above problems, the present invention provides a semiconductor epitaxial wafer capable of suppressing metal contamination by exhibiting higher gettering capability, a method for manufacturing the same, and a solid-state imaging device formed from the semiconductor epitaxial wafer. It aims at providing the manufacturing method of a solid-state image sensor.

  According to further studies by the present inventors, it has been found that there are the following advantages compared with the case where monomer ions are implanted by irradiating a semiconductor wafer with cluster ions containing carbon. In other words, when irradiating with cluster ions, even if irradiation is performed at an acceleration voltage equivalent to that of monomer ions, the energy per atom or molecule collides with the semiconductor wafer with a smaller energy than in the case of monomer ions. In the concentration profile in the depth direction, the peak concentration can be steeply positioned at a position closer to the surface of the semiconductor wafer, and a plurality of atoms can be irradiated at once, so that a high concentration can be achieved. As a result, it has been found that the gettering ability is improved. In addition, by forming an epitaxial layer with a high dopant concentration immediately below the epitaxial layer on which the device is fabricated, the epitaxial layer functions as a gettering site and contributes to further improvement of gettering capability. Based on the above findings, the present inventors have completed the present invention.

  That is, a method for manufacturing a semiconductor epitaxial wafer according to the present invention includes a step of forming a first epitaxial layer on a semiconductor wafer and a step of forming a second epitaxial layer on the first epitaxial layer. In the manufacturing method, the surface of the semiconductor wafer or the surface of the first epitaxial layer is irradiated with cluster ions containing carbon, and the modified layer in which carbon is dissolved in the surface of the semiconductor wafer or the surface of the first epitaxial layer is formed. And a peak concentration of the dopant element in the first epitaxial layer is higher than a peak concentration of the dopant element in the second epitaxial layer.

Here, the peak concentration of the dopant element in the first epitaxial layer is in the range of 1.0 × 10 ^{18 to} 1.0 × 10 ²⁰ atoms / cm ³ , and the peak concentration of the dopant element in the second epitaxial layer is It is preferable to be in a range of 1.0 × 10 ^{13 to} 1.0 × 10 ¹⁶ atoms / cm ³ .

  The dopant element in the first epitaxial layer is preferably one or more elements selected from the group consisting of boron, phosphorus, arsenic, and antimony.

  In the present invention, it is preferable that the semiconductor wafer is a silicon wafer and the first epitaxial layer and the second epitaxial layer are silicon epitaxial layers.

  Moreover, it is preferable to perform a heat treatment for crystallinity recovery on the semiconductor wafer after forming the next epitaxial layer after the irradiation of the cluster ions.

  Furthermore, it is preferable to irradiate the cluster ions so that the peak of the carbon concentration profile in the modified layer is located within a depth of 150 nm or less from the surface of the semiconductor wafer or the surface of the first epitaxial layer. .

  Next, the semiconductor epitaxial wafer of the present invention is a semiconductor epitaxial wafer having a semiconductor wafer, a first epitaxial layer located on the semiconductor wafer, and a second epitaxial layer located on the first epitaxial layer. And a modified layer formed by solid solution of carbon formed on the surface of the semiconductor wafer or the surface of the first epitaxial layer, and the half-value width of the concentration profile of the carbon in the modified layer is 100 nm. The peak concentration of the dopant element in the first epitaxial layer is higher than the peak concentration of the dopant element in the second epitaxial layer.

Here, the peak concentration of the dopant element in the first epitaxial layer is in the range of 1.0 × 10 ^{18 to} 1.0 × 10 ²⁰ atoms / cm ³ , and the peak concentration of the dopant element in the second epitaxial layer is Is preferably in the range of 1.0 × 10 ^{13 to} 1.0 × 10 ¹⁶ atoms / cm ³ .

  The dopant element in the first epitaxial layer is preferably one or more elements selected from the group consisting of boron, phosphorus, arsenic, and antimony.

  Furthermore, it is preferable that the semiconductor wafer is a silicon wafer, and the first epitaxial layer and the second epitaxial layer are silicon epitaxial layers.

  In the present invention, it is preferable that the peak of the carbon concentration profile in the modified layer is located within a depth of 150 nm or less from the semiconductor wafer surface or the first epitaxial layer surface.

Moreover, it is preferable that the peak concentration of the carbon concentration profile in the modified layer is 1.0 × 10 ¹⁵ atoms / cm ³ or more.

  And the manufacturing method of the solid-state image sensor of this invention forms a solid-state image sensor in the 2nd epitaxial layer of the epitaxial wafer manufactured by the said any one manufacturing method, or the said any one epitaxial wafer, It is characterized by the above-mentioned. And

  According to the method for producing a semiconductor wafer of the present invention, the semiconductor wafer is irradiated with cluster ions, a modified layer composed of the constituent elements of the cluster ions is formed on the surface of the semiconductor wafer, and a device is manufactured. Since the first epitaxial layer having a high dopant concentration is formed immediately below the two epitaxial layers, the modified layer and the first epitaxial layer exhibit higher gettering ability, thereby suppressing metal contamination. A semiconductor epitaxial wafer can be manufactured.

1 is a schematic cross-sectional view illustrating a method for manufacturing a semiconductor epitaxial wafer 100 according to an embodiment of the present invention. It is a model cross section explaining the manufacturing method of the semiconductor epitaxial wafer 200 by other 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 carbon concentration profile obtained by the SIMS measurement in Reference Examples 1 and 2. It is the density | concentration profile of the carbon and dopant element obtained by the SIMS measurement in Experimental example 1, (A) is Example 1-1 of this invention, (B) is Example 1-2 of this invention, (C) is Comparative Example 1-. 1 is shown. It is the density | concentration profile of the carbon obtained by the SIMS measurement in Experimental example 2, and a dopant element, (A) shows this invention example 2-1, (B) shows this invention example 2-2.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In principle, the same components are denoted by the same reference numerals, and description thereof is omitted. 1 and 2 exaggerate the thicknesses of the first and second epitaxial layers 12 and 14 with respect to the semiconductor wafer 10 for convenience of explanation, unlike the actual thickness ratio.

(Method of manufacturing semiconductor epitaxial wafer)
One embodiment of a method for producing a semiconductor epitaxial wafer of the present invention is shown in FIG. 1, and another embodiment is shown in FIG. As shown in FIGS. 1 and 2, the method for manufacturing a semiconductor epitaxial wafer of the present invention includes a step of forming a first epitaxial layer 12 on a semiconductor wafer 10, and a second epitaxial layer on the first epitaxial layer 12. 14 is formed. Here, the second epitaxial layer 14 becomes a device layer for manufacturing a semiconductor element such as a back-illuminated solid-state imaging element.

  First, the manufacturing method according to the first embodiment will be described with reference to FIG. In the manufacturing method of this embodiment, as shown in FIGS. 1A to 1C, the surface 10A of the semiconductor wafer 10 is irradiated with cluster ions 16 containing carbon, and carbon is applied to the semiconductor wafer surface 10A. The solidified modified layer 18 is formed. Next, the semiconductor wafer 10 is cleaned by a known method such as SC-1 or HF, and the first is formed on the semiconductor wafer 10 (in this embodiment, directly above the modified layer 18) as shown in FIG. Epitaxial layer 12 is formed. Further, as shown in FIG. 1E, a second epitaxial layer 14 is formed on the first epitaxial layer 12. FIG. 1E is a schematic cross-sectional view of a semiconductor epitaxial wafer 100 obtained as a result of this manufacturing method.

  Next, a manufacturing method according to the second embodiment will be described with reference to FIG. In the manufacturing method of this embodiment, first, as shown in FIGS. 2A and 2B, the first epitaxial layer 12 is formed on the semiconductor wafer 10. Next, as shown in FIGS. 2C and 2D, the surface 12A of the first epitaxial layer is irradiated with cluster ions 16 containing carbon, and the carbon is dissolved in the surface 12A of the first epitaxial layer. The modified layer 18 thus formed is formed. Further, after the semiconductor wafer 10 is cleaned by a known method such as SC-1 cleaning or HF cleaning, as shown in FIG. 2 (E), on the first epitaxial layer 12 (in this embodiment, directly above the modified layer 18). 2), the second epitaxial layer 14 is formed. FIG. 2E is a schematic cross-sectional view of a semiconductor epitaxial wafer 200 obtained as a result of this manufacturing method.

  Examples of the semiconductor wafer 10 include a bulk single crystal wafer made of silicon and a compound semiconductor (GaAs, GaN, SiC) and having no epitaxial layer on the surface. Specifically, a bulk single crystal silicon wafer is used. Moreover, the semiconductor wafer 10 can use what sliced the single crystal silicon ingot grown by the Czochralski method (CZ method) and the floating zone melting method (FZ method) with the wire saw etc. Also, carbon and / or nitrogen may be added to obtain higher gettering ability. Further, an arbitrary dopant may be added to obtain n-type or p-type.

  Examples of the first epitaxial layer 12 and the second epitaxial layer 14 include silicon epitaxial layers, which can be formed by a CVD method under general conditions. For example, a source gas such as dichlorosilane or trichlorosilane is introduced into the chamber using hydrogen as a carrier gas, and the growth temperature varies depending on the source gas used, but the semiconductor is formed by CVD at a temperature in the range of about 1000 to 1200 ° C. It can be epitaxially grown on the wafer 10. In this embodiment, n-type or p-type epitaxial layers 12 and 14 are formed by adding an arbitrary dopant.

  Here, one of the characteristic steps of the present invention is a cluster ion irradiation step shown in FIGS. 1B and 2C. The technical significance of adopting this process will be described together with the effects. The modified layer 18 formed as a result of the irradiation of the cluster ions 16 is such that the constituent elements (at least carbon) of the cluster ions 16 are dissolved in the interstitial or substitutional positions of the crystals on the surface of the semiconductor wafer 10 or the first epitaxial layer 12 The region exists locally 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 in the substitution position / interstitial position of the silicon single crystal. It was experimentally confirmed that the solid solubility of heavy metals (saturation solubility of transition metals) greatly increases when carbon or boron is dissolved to an equilibrium concentration or higher of the silicon single crystal. That is, it is considered that the solid solubility of heavy metals is increased by carbon and boron dissolved to an equilibrium concentration or higher, and the capture rate for heavy metals is thereby remarkably increased.

  Here, since the cluster ions 16 are irradiated in the present invention, higher gettering ability can be obtained as compared with the case of injecting monomer ions. Therefore, the back-illuminated solid-state imaging device manufactured from the semiconductor epitaxial wafers 100 and 200 obtained by this manufacturing method can be expected to suppress the occurrence of white defect as compared with the conventional case.

  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 present inventors consider the action of obtaining high gettering ability by irradiating cluster ions 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. .

  On the other hand, when irradiating the silicon wafer with cluster ions made of, for example, carbon and boron, as shown in FIG. 3A, the cluster ions 16 are instantaneously 1350-1400 with the energy when irradiated to the silicon wafer. It becomes a high temperature of about ℃ 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 the present specification means a layer in which constituent elements of ions to be irradiated are dissolved in crystal interstitial positions or substitution positions on the surface of the semiconductor wafer. The concentration profile of carbon and boron in the depth direction of the silicon wafer depends on the acceleration voltage and cluster size of cluster ions, but is sharper than that of monomer ions, and the irradiated carbon and boron exist locally. The thickness of the region to be performed (that is, the modified layer) is approximately 500 nm or less (for example, about 50 to 400 nm). In addition, although the thermal diffusion of the element irradiated in the form of cluster ions is suppressed more than that of the element implanted with monomer ions, some thermal diffusion still occurs in the process of forming the epitaxial layer 20. For this reason, in the concentration profile of carbon and boron after the formation of the epitaxial layer 20, broad diffusion regions are formed on both sides of the peak where these elements exist locally. However, the thickness of the modified layer does not change significantly (see FIGS. 5A and 5B and FIGS. 6A and 6B described later). As a result, the carbon and boron precipitation regions can be locally and highly concentrated. Further, since the modified layer 18 is formed in the vicinity of the surface of the silicon wafer, closer gettering is possible. As a result, it is considered that 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 ion 16 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.

  Next, another feature of the present invention is that the peak concentration of the dopant element in the first epitaxial layer 12 is made higher than the peak concentration of the dopant element in the second epitaxial layer 14 by adjusting the addition amount of the dopant. Is to set. By forming the first epitaxial layer 12 containing such a high concentration of the dopant element directly under the second epitaxial layer 14 in which the device is manufactured, the first epitaxial layer 12 is also obtained in addition to the modified layer 18. It functions as a ring site and can further improve gettering ability.

Here, the peak concentration of the dopant element in the first epitaxial layer 12 is preferably in the range of 1.0 × 10 ^{18 to} 1.0 × 10 ²⁰ atoms / cm ³ . If it is 1.0 × 10 ¹⁸ atoms / cm ³ or more, a sufficient gettering effect can be obtained, and if it is 1.0 × 10 ²⁰ atoms / cm ³ or less, it is misfit to the second epitaxial layer 14. This is because no metastasis occurs.

In addition, the peak concentration of the dopant element in the second epitaxial layer 14 may be set appropriately as appropriate for manufacturing a semiconductor element such as a solid-state imaging element. For example, 1.0 × 10 ^{13 to} 1.0 × A range of 10 ¹⁶ atoms / cm ³ is preferable.

  The dopant element in the first epitaxial layer 12 and the second epitaxial layer 14 may be boron as a p-type dopant, and one or more selected from the group consisting of phosphorus, arsenic, and antimony as an n-type dopant. Element.

  The combination of conductivity types of the semiconductor wafer 10 / the first epitaxial layer 12 / the second epitaxial layer 14 is not particularly limited, and includes a p / n / p structure, an n / p / n structure, a p / p / p structure, and an n / n. Any of / n structure, n / n / p structure, p / p / n structure, p / n / n structure, and n / p / p structure may be used.

  In the second embodiment shown in FIG. 2, one feature is that the cluster ion irradiation is performed not on the bulk semiconductor wafer 10 but on the first epitaxial layer 12. A bulk semiconductor wafer has an oxygen concentration about two orders of magnitude higher than that of an epitaxial layer. Therefore, in the modified layer formed in the bulk semiconductor wafer, more oxygen is diffused than the modified layer formed in the epitaxial layer, and much oxygen is captured. The trapped oxygen is re-emitted from the capture site during the device process and diffuses into the active region of the device, forming point defects, thus adversely affecting the electrical properties of the device. Therefore, it is an important design condition in the device process to implant ions into an epitaxial layer having a low concentration of dissolved oxygen and to form a gettering layer in the epitaxial layer where the influence of oxygen diffusion can be almost ignored.

  Hereinafter, irradiation conditions of cluster ions will be described. First, if the irradiated element contains at least carbon, the gettering ability of the modified layer 18 can be obtained with certainty. Since the carbon atom at the lattice position has a smaller covalent bond radius than that of the silicon single crystal, a contraction field of the silicon crystal lattice is formed, so that the gettering ability to attract impurities between the lattices is high.

  Other examples of the irradiation element include dopant elements such as boron, phosphorus, arsenic, and antimony. More preferably, the constituent elements of the cluster ions are two or more elements including carbon. This is because the types of metals that can be efficiently gettered differ depending on the types of elements to be dissolved, so that a wider range of metal contamination can be dealt with by dissolving two or more elements in solid solutions. 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.

A compound to be ionized is not particularly limited, and ethane, methane, carbon dioxide (CO ₂ ), or the like can be used as a carbon source compound that can be ionized, and diborane, decaborane ( B ₁₀ H ₁₄ ) or the like can be used. 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 composed of carbon and hydrogen can be generated. As the carbon source compound, it is particularly preferable to use 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. This is because it is easy to control a small-sized cluster ion beam.

  As the compound to be ionized, a compound containing both carbon and the above dopant element is also preferable. This is because if such a compound is irradiated as cluster ions, both carbon and the dopant element can be dissolved in a single irradiation.

  Further, by controlling the acceleration voltage and cluster size of cluster ions, the position of the peak of the concentration profile of the constituent elements in the modified layer 18 can be controlled. In this specification, “cluster size” means the number of atoms or molecules constituting one cluster.

  In the present embodiment, from the viewpoint of obtaining higher gettering capability, the depth from the surface 10A of the semiconductor wafer is within a range of 150 nm or less in the case of FIG. 1, and from the surface 12A of the first epitaxial layer in the case of FIG. The cluster ions 16 are irradiated so that the peak of the carbon concentration profile in the modified layer 18 is located within the range of the depth of 150 nm or less. When the dopant element is also irradiated, the peak position of the concentration profile of the dopant element is preferably the same.

When C _n H _m (3 ≦ n ≦ 16, 3 ≦ m ≦ 10) is used as a cluster ion as a necessary condition for setting the peak position within the depth range, the acceleration voltage per carbon atom is , 0 keV / atom and 50 keV / atom or less, preferably 40 keV / atom or less. The cluster size is 2 to 100, preferably 60 or less, more preferably 50 or less.

  For adjusting the acceleration voltage, two methods of (1) electrostatic acceleration and (2) high frequency acceleration are generally used. 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.

Moreover, the dose amount of cluster ions can be adjusted by controlling the ion irradiation time. In the present embodiment, the dose amount of carbon is 1 × 10 ¹³ to 1 × 10 ¹⁶ atoms / cm ² , preferably 5 × 10 ¹⁵ atoms / cm ² or less. If it is less than 1 × 10 ¹³ atoms / cm ² , the gettering ability may not be sufficiently obtained. If it exceeds 1 × 10 ¹⁶ atoms / cm ² , the surface of the epitaxial layer may be seriously damaged. Because there is.

  In the present embodiment, it is preferable that the semiconductor wafer 10 is subjected to a heat treatment for crystallinity recovery after the cluster ion irradiation and before the next epitaxial layer is formed.

  Here, the monomer ions are generally implanted at an acceleration voltage of about 150 to 2000 keV. However, since each ion collides with a silicon atom with its energy, the crystallinity of the surface portion of the silicon wafer into which the monomer ions are implanted is disturbed. Thereafter, the crystallinity of the epitaxial layer grown on the wafer surface is disturbed. On the other hand, cluster ions are generally irradiated with an acceleration voltage of about 10 to 100 keV / Cluster. However, since a cluster is an aggregate of a plurality of atoms or molecules, it must be implanted with a small energy per atom or molecule. Damage to the crystal of the semiconductor wafer is small. Therefore, in the case of cluster ion irradiation, the conditions for the recovery heat treatment can be made relatively gentle. That is, it is not necessary to perform the recovery heat treatment using a rapid heating / cooling heat treatment device or the like separate from the epitaxial device, such as RTA (Rapid Thermal Annealing) or RTO (Rapid Thermal Oxidation).

  This is because the crystallinity of the semiconductor wafer 10 can be sufficiently recovered by a hydrogen baking process performed prior to epitaxial growth in the epitaxial apparatus. The general conditions for the hydrogen baking process are that the inside of the epitaxial growth apparatus is in a hydrogen atmosphere, the semiconductor wafer 10 is placed in the furnace at a furnace temperature of 600 ° C. or higher and 900 ° C. or lower, and 1 ° C./second or higher and 15 ° C./second or lower. The temperature is raised to a temperature range of 1100 ° C. or more and 1200 ° C. or less at a temperature raising rate, and the temperature is maintained for 30 seconds or more and 1 minute or less. This hydrogen baking process is originally intended to remove the natural oxide film formed on the wafer surface by the cleaning process before the epitaxial layer growth. However, the crystallinity of the semiconductor wafer 10 is sufficiently recovered by the hydrogen baking under the above conditions. Can be made.

  Of course, after the first step and before the second step, the recovery heat treatment may be performed using a heat treatment device separate from the epitaxial device. This recovery heat treatment is preferably performed under conditions of 900 ° C. or more and 1200 ° C. or less and 10 seconds or more and 1 hour or less. This recovery heat treatment may be performed at 900 ° C. to 1200 ° C. for 10 seconds to 1 hour. 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.

  This recovery heat treatment is 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) before the semiconductor wafer 10 is transferred into the epitaxial growth apparatus. be able to. 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 16.

(Semiconductor epitaxial wafer)
Next, semiconductor epitaxial wafers 100 and 200 obtained by the above manufacturing method will be described with reference to FIGS. 1 (E) and 2 (E). Semiconductor epitaxial wafers 100 and 200 both have a semiconductor wafer 10, a first epitaxial layer 12 located on the semiconductor wafer 10, and a second epitaxial layer 14 located on the first epitaxial layer 12. The semiconductor epitaxial wafer 100 according to the first embodiment is formed on the surface 10A of the semiconductor wafer, and the semiconductor epitaxial wafer 200 according to the second embodiment is formed on the surface 12A of the first epitaxial layer. It further has a modified layer 18. In any case, the half-value width W of the carbon concentration profile in the modified layer 18 is 100 nm or less.

  That is, according to the manufacturing method of the present invention, compared to the monomer ion implantation, the precipitation region of the elements constituting the cluster ions can be locally and highly concentrated, and as a result, the half width W is 100 nm or less. It became possible to do. The lower limit can be set to 10 nm. Note that the “concentration profile” in this specification means a concentration distribution in the depth direction measured by secondary ion mass spectrometry (SIMS: Secondary Ion Mass Spectrometry). In addition, the “half-value width of the carbon concentration profile” means that when the thickness of the epitaxial layer on the modified layer exceeds 1 μm, the epitaxial layer is thinned to 1 μm in consideration of measurement accuracy. The half-value width when the carbon concentration profile is measured by SIMS.

  Further, since the peak concentration of the dopant element in the first epitaxial layer 12 is higher than the peak concentration of the dopant element in the second epitaxial layer 14, as described above, in addition to the modified layer 18, the first epitaxial layer 12 also functions as a gettering site, and further improvement in gettering capability can be achieved.

  As described above, according to the semiconductor epitaxial wafers 100 and 200 of the present embodiment, metal contamination can be further suppressed by exhibiting higher gettering ability than the conventional one.

  From the viewpoint of obtaining a higher gettering capability, the depth from the surface 10A of the semiconductor wafer is 150 nm or less in the case of FIG. 1, and the depth from the surface 12A of the first epitaxial layer is 150 nm in the case of FIG. The peak of the carbon concentration profile in the modified layer 18 is preferably located within the following range. When the dopant element is also irradiated, the peak position of the concentration profile of the dopant element is preferably the same.

Further, the peak concentration of the carbon concentration profile is preferably 1 × 10 ¹⁵ atoms / cm ³ or more, more preferably in the range of 1 × 10 ¹⁷ to 1 × 10 ²² atoms / cm ³ , and 1 × 10 ¹⁹ to More preferably within the range of 1 × 10 ²¹ atoms / cm ³ .

  Moreover, the depth direction thickness of the modified layer 18 can be in the range of approximately 30 to 400 nm.

  The first epitaxial layer 12 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. The second epitaxial layer 14 preferably has a thickness in the range of 1 to 15 μm. If the thickness is less than 1 μm, the resistivity of the second epitaxial layer 14 may change due to the out-diffusion of dopant from the semiconductor wafer 10. If the thickness exceeds 15 μm, the spectral sensitivity characteristics of the solid-state imaging device are affected. This is because there is a risk of occurrence.

(Method for manufacturing solid-state imaging device)
In the method for manufacturing a solid-state imaging device according to the embodiment of the present invention, the solid-state imaging device is formed on the second epitaxial layer 14 of the epitaxial wafer manufactured by the above-described manufacturing method or the above-described epitaxial wafer, that is, the semiconductor epitaxial wafers 100 and 200. It is characterized by doing. The solid-state imaging device obtained by this manufacturing method can sufficiently suppress the occurrence of white defect as compared with the conventional case.

(Reference experiment example)
First, the following experiment was conducted to clarify the difference between cluster ion irradiation and monomer ion implantation.

(Reference Example 1)
An n-type silicon wafer (diameter: 300 mm, thickness: 725 μm, dopant: phosphorus, dopant concentration: 5 × 10 ¹⁴ atoms / cm ³ ) obtained from a CZ single crystal silicon ingot was prepared. Next, a C ₅ H ₅ cluster is generated from dibenzyl (C ₁₄ H ₁₄ ) using a cluster ion generator (manufactured by Nissin Ion Instruments Co., Ltd., model number: CLARIS), and a dose of 9.0 × 10 ¹³ Clusters is generated. The silicon wafer was irradiated under the conditions of / cm ² (carbon dose amount 4.5 × 10 ¹⁴ atoms / cm ² ) and an acceleration voltage of 14.8 keV / atom per carbon atom.

(Reference Example 2)
For the same silicon wafer as in Reference Example 1, instead of cluster ion irradiation, carbon monoxide (CO ₂ ) was used as a material gas to generate carbon monomer ions, and a dose amount of 9.0 × 10 ¹³ atoms / cm ² , The silicon wafer was irradiated under the condition of an acceleration voltage of 300 keV / atom.

<SIMS measurement results>
The samples prepared in Reference Examples 1 and 2 were subjected to SIMS measurement, and the carbon concentration profile shown in FIG. 4 was obtained. Note that the depth of the horizontal axis is zero on the surface of the silicon wafer. As is clear from FIG. 4, the carbon concentration profile is sharp in Reference Example 1 where cluster ion irradiation is performed, but the carbon concentration profile is broad in Reference Example 2 where monomer ions are implanted. Further, in Reference Example 1 compared to Reference Example 2, the peak concentration of the carbon concentration profile is high, and the peak position is located closer to the semiconductor wafer surface. From this, it is presumed that the tendency of the carbon concentration profile is the same after the formation of the epitaxial layer.

(Experimental example 1)
(Invention Example 1-1)
An n-type silicon wafer (diameter: 300 mm, thickness: 725 μm, dopant: phosphorus, dopant concentration: 5 × 10 ¹⁴ atoms / cm ³ ) obtained from a CZ single crystal silicon ingot was prepared. Next, a C ₅ H ₅ cluster is generated from dibenzyl (C ₁₄ H ₁₄ ) using a cluster ion generator (manufactured by Nissin Ion Instruments Co., Ltd., model number: CLARIS), and a dose of 9.0 × 10 ¹³ Clusters is generated. The silicon wafer was irradiated under the conditions of / cm ² (carbon dose amount 4.5 × 10 ¹⁴ atoms / cm ² ) and an acceleration voltage of 14.8 keV / atom per carbon atom. Then, after cleaning the silicon wafer with HF, the silicon wafer is transferred into a single wafer epitaxial growth apparatus (Applied Materials Co., Ltd.) and subjected to a hydrogen baking process at a temperature of 1200 ° C. for 30 seconds in the apparatus, and then a carrier of hydrogen. A first silicon epitaxial layer (thickness: 2 μm, dopant: boron, dopant concentration: 3 × 10 ¹⁸ atoms / cm ³ ) is epitaxially grown on a silicon wafer by CVD at 1150 ° C. using a gas, trichlorosilane as a source gas, Subsequently, a second silicon epitaxial layer (thickness: 4 μm, dopant: phosphorus, dopant concentration: 5 × 10 ¹⁴ atoms / cm ³ ) was epitaxially grown to obtain a silicon epitaxial wafer according to the present invention. As the dopant gas, diborane gas (B ₂ H ₆ ) was used in the case of boron doping, and phosphine (PH ₃ ) was used in the case of phosphorus doping.

(Invention Example 1-2)
A silicon epitaxial wafer according to the present invention was produced in the same manner as in Invention Example 1-1 except that the silicon wafer / first epitaxial layer / second epitaxial layer was changed as follows.
Silicon wafer: p-type silicon wafer (dopant: boron, dopant concentration: 1 × 10 ¹⁵ atoms / cm ³ )
First epitaxial layer: dopant type: phosphorus, dopant concentration: 3 × 10 ¹⁸ atoms / cm ³
Second epitaxial layer: dopant type: boron, dopant concentration: 1 × 10 ¹⁵ atoms / cm ³

(Comparative Example 1-1)
Instead of cluster irradiation, carbon monoxide (CO ₂ ) is used as a material gas to generate carbon monomer ions, and a silicon wafer is formed under the conditions of a dose amount of 9.0 × 10 ¹³ atoms / cm ² and an acceleration voltage of 300 keV / atom. A silicon epitaxial wafer of a comparative example was produced in the same manner as in Example 1-1 of the present invention except that the first epitaxial layer was not formed after implantation.

<Evaluation method and evaluation results>
(1) SIMS measurement SIMS measurement was performed on each of the produced samples, and carbon and dopant concentration profiles shown in FIGS. 5A, 5B, and 5C were obtained. The depth of the horizontal axis is zero on the surface of the second epitaxial layer. For each sample produced, SIMS measurement was performed after the epitaxial layer was thinned to 1 μm. Table 1 shows the half width, peak concentration, and peak position (peak depth from the silicon wafer surface excluding the epitaxial layer) of the carbon concentration profile obtained at this time.

(2) Evaluation of gettering ability The surface of the second epitaxial layer of each prepared sample was intentionally contaminated with Ni contamination liquid (1.0 × 10 ¹³ / cm ² ) using a spin coat contamination method, and subsequently, 900 ° C., A 30 minute heat treatment was applied. Thereafter, SIMS measurement was performed. Ni capture amounts (integrated values of SIMS profiles) were classified as follows and used as evaluation criteria. The evaluation results are shown in Table 1.
A: 1.0 × 10 ¹² atoms / cm ² or more ○: 5.0 × 10 ¹¹ atoms / cm ² or more and less than 1.0 × 10 ¹² atoms / cm ² Δ: 5.0 × 10 ¹¹ atoms / cm ^{2 or} less

<Consideration of evaluation results>
In the present invention example 1-1, a high concentration region of boron is confirmed as shown in FIG. 5A, and in the present invention example 1-2, a high concentration region of phosphorus is confirmed as shown in FIG. 5B. It was done. 5A and 5B, the carbon concentration profile is sharp, whereas in FIG. 5C, the carbon concentration profile is broad. Further, as is clear from the SIMS measurement results in Table 1, it can be seen that a modified layer in which carbon is solid-dissolved locally and at a higher concentration than monomer ion implantation can be formed by cluster ion irradiation. Due to such a high dopant concentration region and a modified layer of carbon, as shown in Table 1, the inventive example was able to obtain a higher gettering ability than the comparative example.

(Experimental example 2)
(Example 2-1)
An n-type silicon wafer (diameter: 300 mm, thickness: 725 μm, dopant: phosphorus, dopant concentration: 5 × 10 ¹⁴ atoms / cm ³ ) obtained from a CZ single crystal silicon ingot was prepared. Next, after cleaning the silicon wafer with HF, the silicon wafer is transferred into a single wafer epitaxial growth apparatus (Applied Materials Co., Ltd.) and subjected to a hydrogen baking process at a temperature of 1200 ° C. for 30 seconds in the apparatus. A first silicon epitaxial layer (thickness: 2 μm, dopant: boron, dopant concentration: 3 × 10 ¹⁸ atoms / cm ³ ) is epitaxially grown on the silicon wafer by CVD at 1150 ° C. using carrier gas, trichlorosilane as a source gas. It was. Next, a C ₅ H ₅ cluster is generated from dibenzyl (C ₁₄ H ₁₄ ) using a cluster ion generator (manufactured by Nissin Ion Instruments Co., Ltd., model number: CLARIS), and a dose of 9.0 × 10 ¹³ Clusters is generated. The silicon wafer was irradiated under the conditions of / cm ² (carbon dose amount 4.5 × 10 ¹⁴ atoms / cm ² ) and an acceleration voltage of 14.8 keV / atom per carbon atom. Thereafter, the silicon wafer is transferred again into the single-wafer epitaxial growth apparatus, and the second silicon epitaxial layer (thickness: 4 μm, dopant: phosphorus, dopant concentration: 5 × 10 ¹⁴ atoms / cm ³ ) is epitaxially grown, and according to the present invention. A silicon epitaxial wafer was obtained. As the dopant gas, diborane gas (B ₂ H ₆ ) was used in the case of boron doping, and phosphine (PH ₃ ) was used in the case of phosphorus doping.

(Invention Example 2-2)
A silicon epitaxial wafer according to the present invention was produced in the same manner as in Invention Example 2-1, except that the silicon wafer / first epitaxial layer / second epitaxial layer was changed as follows.
Silicon wafer: p-type silicon wafer (dopant: boron, dopant concentration: 1 × 10 ¹⁵ atoms / cm ³ )
First epitaxial layer: dopant type: phosphorus, dopant concentration: 3 × 10 ¹⁸ atoms / cm ³
Second epitaxial layer: dopant type: boron, dopant concentration: 1 × 10 ¹⁵ atoms / cm ³

<Evaluation method and evaluation results>
Each sample prepared was evaluated in the same manner as in Experimental Example 1. FIG. 6A shows the carbon and dopant concentration profiles of Example 2-1 of the present invention and FIG. 6B of Example 2-2 of the present invention. Table 2 shows the results of SIMS measurement and gettering ability evaluation after the epitaxial layer was thinned to 1 μm. In Table 2, the peak position of the carbon concentration profile means the peak depth from the surface of the first epitaxial layer excluding the second epitaxial layer.

  From the above results, in Experimental Example 2 in which the first epitaxial layer was irradiated with cluster ions, the same result as in Experimental Example 1 in which the silicon wafer was irradiated with cluster ions could be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the semiconductor epitaxial wafer which can suppress metal contamination by exhibiting higher gettering capability, its manufacturing method, and the solid-state image sensor which forms a solid-state image sensor from this semiconductor epitaxial wafer A manufacturing method can be provided.

100,200 Semiconductor epitaxial wafer 10 Semiconductor wafer 10A Surface of semiconductor wafer 12 First epitaxial layer 12A Surface of first epitaxial layer 14 Second epitaxial layer 16 Cluster ion 18 Modified layer

Claims (13)

Forming a first epitaxial layer on a semiconductor wafer;
Forming a second epitaxial layer on the first epitaxial layer;
A method of manufacturing a semiconductor epitaxial wafer having
The method further includes the step of irradiating the surface of the semiconductor wafer or the surface of the first epitaxial layer with cluster ions containing carbon to form a modified layer in which carbon is dissolved in the surface of the semiconductor wafer or the first epitaxial layer. And
The peak concentration of the dopant element in the first epitaxial layer is higher than the peak concentration of the dopant element in the second epitaxial layer,
The thickness of the first epitaxial layer is in the range of 0.1 to 10 μm,
A method of manufacturing a semiconductor epitaxial wafer, wherein the thickness of the second epitaxial layer is in the range of 1 to 15 μm. The peak concentration of the dopant element in the first epitaxial layer is in the range of 1.0 × 10 ^{18 to} 1.0 × 10 ²⁰ atoms / cm ³ , and the peak concentration of the dopant element in the second epitaxial layer is 1.0 The method for producing a semiconductor epitaxial wafer according to claim 1, wherein the range is from × 10 ^{13 to} 1.0 × 10 ¹⁶ atoms / cm ³ .   The method for producing a semiconductor epitaxial wafer according to claim 1 or 2, wherein the dopant element in the first epitaxial layer is one or more elements selected from the group consisting of boron, phosphorus, arsenic, and antimony.   The method for producing a semiconductor epitaxial wafer according to any one of claims 1 to 3, wherein the semiconductor wafer is a silicon wafer, and the first epitaxial layer and the second epitaxial layer are silicon epitaxial layers.   The semiconductor epitaxial wafer production according to any one of claims 1 to 4, wherein after the irradiation of the cluster ions and before forming a next epitaxial layer, the semiconductor wafer is subjected to a heat treatment for crystallinity recovery. Method.   The cluster ions are irradiated so that a peak of a carbon concentration profile in the modified layer is located within a depth of 150 nm or less from the surface of the semiconductor wafer or the surface of the first epitaxial layer. The manufacturing method of the semiconductor epitaxial wafer of any one of these. A semiconductor epitaxial wafer having a semiconductor wafer, a first epitaxial layer located on the semiconductor wafer, and a second epitaxial layer located on the first epitaxial layer,
A modified layer formed on the surface of the semiconductor wafer or the surface of the first epitaxial layer, in which carbon is dissolved;
The half value width of the carbon concentration profile in the modified layer is 100 nm or less,
The peak concentration of the dopant element in the first epitaxial layer is higher than the peak concentration of the dopant element in the second epitaxial layer,
The first epitaxial layer has a thickness in the range of 0.1 to 10 μm;
The thickness of the said 2nd epitaxial layer exists in the range of 1-15 micrometers, The semiconductor epitaxial wafer characterized by the above-mentioned. The peak concentration of the dopant element in the first epitaxial layer is in the range of 1.0 × 10 ^{18 to} 1.0 × 10 ²⁰ atoms / cm ³ , and the peak concentration of the dopant element in the second epitaxial layer is 1. The semiconductor epitaxial wafer according to claim 7, which is in a range of 0 × 10 ^{13 to} 1.0 × 10 ¹⁶ atoms / cm ³ .   The semiconductor epitaxial wafer according to claim 7 or 8, wherein the dopant element in the first epitaxial layer is one or more elements selected from the group consisting of boron, phosphorus, arsenic, and antimony.   The semiconductor epitaxial wafer according to any one of claims 7 to 9, wherein the semiconductor wafer is a silicon wafer, and the first epitaxial layer and the second epitaxial layer are silicon epitaxial layers.   The semiconductor according to any one of claims 7 to 10, wherein a peak of a carbon concentration profile in the modified layer is located within a depth of 150 nm or less from the surface of the semiconductor wafer or the surface of the first epitaxial layer. Epitaxial wafer. The semiconductor epitaxial wafer according to claim 7, wherein a peak concentration of a carbon concentration profile in the modified layer is 1.0 × 10 ¹⁵ atoms / cm ³ or more. A solid-state imaging device is formed on the epitaxial wafer manufactured by the manufacturing method according to any one of claims 1 to 6 or the second epitaxial layer of the epitaxial wafer according to any one of claims 7 to 12. A method for manufacturing a solid-state imaging device.

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