JP2017183736A - Method for manufacturing semiconductor epitaxial wafer, semiconductor epitaxial wafer, and method for manufacturing solid state image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor epitaxial wafer capable of suppressing metal pollution by exerting higher gettering capability.SOLUTION: A method for manufacturing a semiconductor epitaxial wafer 100 comprises: a first step for forming a first modified layer 18 in which constituent elements of a first cluster ion 16 are solidly solved, on a surface 10A of a semiconductor wafer 10 by irradiating the surface 10A of the semiconductor wafer with the first cluster ion 16; a second step for forming an epitaxial layer 20 on the first modified layer 18; a third step for forming a second modified layer 26 in which constituent elements of a second cluster ion 24 are solidly solved, on a part 20A of a surface of the epitaxial layer 20 by irradiating the part of the surface of the epitaxial layer 20 with the second cluster ion 24.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.

  Therefore, conventionally, a gettering sink for capturing a metal is formed on a semiconductor epitaxial wafer, 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.

  Patent Document 2 describes a method for manufacturing a semiconductor device in which a gettering layer is formed by performing selective ion implantation of a gettering substance on the surface of a region other than a device formation region of a semiconductor wafer.

  Patent Document 3 has a plurality of epitaxial growth layers in an epitaxial growth substrate, and a gettering layer formed by ion implantation between the plurality of epitaxial growth layers. An image sensor formed in the peripheral region is described.

JP-A-6-338507 JP-A-7-26345 JP 2001-177086 A

  The techniques described in Patent Document 1, Patent Document 2 and Patent Document 3 all implant monomer ions (single ions) into a semiconductor wafer or an epitaxial layer 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 the surface of a semiconductor wafer with cluster ions. That is, 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 is smaller than that of monomer ions and collides with the semiconductor wafer. The peak concentration of the profile in the depth direction can be steeply positioned 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. It has also been found that a similar gettering region can be formed by irradiating part of the surface of the epitaxial layer formed on the semiconductor wafer with cluster ions. Based on the above findings, the present inventors have completed the present invention.

  That is, in the method for producing a semiconductor epitaxial wafer according to the present invention, the surface of the semiconductor wafer is irradiated with the first cluster ions, and the constituent elements of the first cluster ions are dissolved on the surface of the semiconductor wafer. A first step of forming a modified layer; a second step of forming an epitaxial layer on the first modified layer of the semiconductor wafer; and irradiating a portion of the surface of the epitaxial layer with second cluster ions; And a third step of forming a second modified layer formed by dissolving the constituent elements of the second cluster ions in part of the surface of the epitaxial layer.

  Here, the semiconductor wafer may be a silicon wafer.

  The semiconductor 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 first modified layer is formed on the surface of the silicon epitaxial layer in the first step. The

  In the present invention, after the first step, the second step can be performed by transferring the semiconductor wafer to an epitaxial growth apparatus without performing a heat treatment for recovering crystallinity on the semiconductor wafer.

  Here, the first and / or second cluster ions preferably contain carbon as a constituent element, and more preferably contain two or more elements containing carbon as a constituent element.

The irradiation conditions of the first cluster ions are as follows: acceleration voltage per carbon atom is 50 keV / atom or less, cluster size is 100 or less, and carbon dose is 5.0 × 10 ¹⁵ atoms / cm ² or less. It is preferable. The irradiation conditions of the second cluster ions are that the acceleration voltage per carbon atom is 50 keV / atom or less, the cluster size is 100 or less, and the carbon dose is 1.0 × 10 ¹⁴ atoms / cm ² or more. preferable.

  The semiconductor epitaxial wafer of the present invention includes a semiconductor wafer, a first modified layer formed on the surface of the semiconductor wafer, in which a predetermined element is dissolved in the semiconductor wafer, and on the first modified layer. An epitaxial layer, and a second modified layer formed on a part of the surface of the epitaxial layer, in which a predetermined element is dissolved in the epitaxial layer, and the first modified layer and the second modified layer. The half width of the concentration profile in the depth direction of the predetermined element in the modified layer is both 100 nm or less.

  Here, the semiconductor wafer may be a silicon wafer.

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

  Further, the peak of the concentration profile in the first modified layer is located within a depth of 150 nm or less from the surface of the semiconductor wafer, and the depth from the surface of the epitaxial layer is within a range of 150 nm or less. Preferably, the peak of the concentration profile in the second modified layer is located.

The peak concentration of the concentration profile in the first and / or second modified layer is preferably 1 × 10 ¹⁵ atoms / cm ³ or more.

  Here, the predetermined element preferably includes carbon, and more preferably, the predetermined element includes two or more elements including carbon.

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

  According to the present invention, two modified layers are formed by irradiating the surface of the semiconductor wafer and a part of the surface of the epitaxial layer formed on the semiconductor wafer with cluster ions. By exhibiting higher gettering capability, a semiconductor epitaxial wafer capable of suppressing metal contamination can be obtained, and a high-quality solid-state imaging device can be manufactured from this semiconductor epitaxial wafer.

(A)-(C) are schematic cross sections explaining a part of manufacturing method of the semiconductor epitaxial wafer 100 by one Embodiment of this invention. (A)-(D) are the figures explaining the manufacturing method of the semiconductor epitaxial wafer 100 following FIG.1 (C), the figure on the right side is a wafer surface figure, The figure on the left side is I of the figure on the right side. It is a schematic diagram of -I cross section. (A)-(E) are schematic cross sections 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 the carbon concentration profile obtained by SIMS measurement at the position of the device exclusion region for Example 1. It is a carbon concentration profile obtained by SIMS measurement at the position of the device formation region in Example 1. It is a carbon concentration profile obtained by the SIMS measurement in the position of a device exclusion area | region about the comparative example 1. FIG.

  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 to 3, the thicknesses of the first and second epitaxial layers 14 and 20 are exaggerated with respect to the semiconductor wafer 10, unlike the actual thickness ratio, for convenience of explanation.

(Method of manufacturing semiconductor epitaxial wafer)
A method of manufacturing the semiconductor epitaxial wafer 100 according to the first embodiment of the present invention will be described with reference to FIGS. In this manufacturing method, first, as a first step shown in FIGS. 1A and 1B, the surface 10A of the semiconductor wafer 10 is irradiated with the first cluster ions 16, and the first cluster is applied to the surface 10A of the semiconductor wafer. A first modified layer 18 in which the constituent elements of the ions 16 are dissolved is formed. Next, as a second step shown in FIG. 1C, an epitaxial layer 20 is formed on the first modified layer 18 of the semiconductor wafer 10. Here, the epitaxial layer 20 becomes a device layer for manufacturing a semiconductor element such as a back-illuminated solid-state imaging element.

  Next, the third step shown in FIGS. Here, the surface of the epitaxial layer 20 includes a region 20B (hereinafter referred to as “device formation region”) in which a semiconductor element is manufactured in a later semiconductor manufacturing process and a region 20A (hereinafter referred to as “device exclusion” in which a semiconductor element is not manufactured). Area ”). Examples of the device exclusion region 20A include an edge region (product warranty exclusion region) of about 1 to 5 mm from the outer peripheral edge of the wafer on the surface of the epitaxial layer 20 and a region near the planned scrub line position of the wafer. In the third step, first, as shown in FIG. 2A, a mask 22 is placed in the device formation region 20B. In this state, as shown in FIGS. 2B and 2C, a part of the surface of the epitaxial layer 20 (device exclusion region 20A in this embodiment) is irradiated with the second cluster ions 24 to exclude this device. A second modified layer 26 in which the constituent elements of the second cluster ions 24 are dissolved is formed in the region 20A. As shown in FIG. 2D, the semiconductor epitaxial wafer 100 is obtained by finally removing the mask 22. FIG. 2D 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 impurity may be added to be n-type or p-type. The first embodiment shown in FIGS. 1 and 2 is an example in which a bulk semiconductor wafer 12 having no epitaxial layer on the surface is used as the semiconductor wafer 10.

  Moreover, as the semiconductor wafer 10, as shown in FIG. 3A, an epitaxial semiconductor wafer in which a semiconductor epitaxial layer (first epitaxial layer) 14 is formed on the surface of the bulk semiconductor wafer 12 can be exemplified. For example, an epitaxial silicon wafer in which a silicon epitaxial layer is formed on the surface of a bulk single crystal silicon wafer. The silicon epitaxial layer can be formed under general conditions by a CVD method. The first 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 of this, in the method of manufacturing the semiconductor epitaxial wafer 200 according to the second embodiment of the present invention, as shown in FIG. 3, the semiconductor wafer having the first epitaxial layer 14 formed on the surface (at least one side) of the bulk semiconductor wafer 12. First surface cluster 10 is irradiated with first cluster ions 16, and a first modified layer made of constituent elements of first cluster ions 16 is applied to surface 10 A of the semiconductor wafer (the surface of first epitaxial layer 14 in this embodiment). And a second step of forming the second epitaxial layer 20 on the first modified layer 18 of the semiconductor wafer 10 (FIG. 3D). And irradiating a part of the surface of the second epitaxial layer (device exclusion region in this embodiment) with the second cluster ions, And having a third step of forming a second reformed layer 26 consisting of constituent elements of the star ions (FIG. 3 (E)), a. The second epitaxial layer 20 becomes a device layer for forming a semiconductor element, and the surface other than the second modified layer 26 becomes a device forming region 20B. Since the steps from FIG. 3D to FIG. 3E are the same as those shown in FIG. FIG. 3E is a schematic cross-sectional view of a semiconductor epitaxial wafer 200 obtained as a result of this manufacturing method.

  Here, the characteristic steps of the present invention are the cluster ion irradiation step on the surface of the semiconductor wafer shown in FIGS. 1 (A) and 3 (B), and FIGS. 2 (B) and 3 (D) to (E). The cluster ion irradiation process to the device exclusion area | region of an epitaxial layer shown in FIG.

  The technical significance of adopting this process will be described together with the effects. The first modified layer 18 formed as a result of the irradiation with the first cluster ions 16 is locally present as the constituent elements of the cluster ions 16 are dissolved in the crystal interstitial positions or substitution positions on the surface of the semiconductor wafer. It is an area and serves as a gettering site Similarly, the second modified layer 26 formed as a result of irradiation with the second cluster ions 24 also functions 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, in the present invention, since the first cluster ions 16 and the second cluster ions 24 are irradiated, 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. 4B, the monomer ions blow off silicon atoms constituting the silicon wafer and are 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 the silicon wafer is irradiated with cluster ions made of, for example, carbon and boron, as shown in FIG. 4A, the first cluster ions 16 are instantaneously 1350 with the energy when the silicon wafer is irradiated. 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. In FIG. 4A, the first cluster ions 16 irradiated to the surface 10A of the semiconductor wafer are illustrated, but the same phenomenon occurs even in the case of the second cluster ions 17 irradiated to the epitaxial layer 20. That is, the “modified layer” in this specification means a layer in which constituent elements of irradiated ions are solid-solved at crystal interstitial positions or substitution positions on the surface of a semiconductor wafer or the surface of an epitaxial layer. The concentration profile of carbon and boron in the depth direction of a silicon epitaxial 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 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). Note that the elements irradiated in the form of cluster ions undergo some thermal diffusion during the formation process of 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 greatly (see FIGS. 5 and 6 described later). As a result, the first and second modified layers 18 and 26 can be formed with the carbon and boron precipitation regions locally and at a high concentration. In addition, since the first modified layer 18 is formed in the vicinity of the surface of the silicon wafer, that is, directly below the epitaxial layer 20, 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.

  In particular, the first modified layer 18 effectively getters heavy metals such as Ni and Cu, while the second modified layer 26 additionally uses slow metals such as Ti and W. Can also be expected to gettering.

  The cluster ion has various clusters depending on the binding mode, and can be generated by a known method as described in, for example, the following documents. 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 first cluster ions 16 and the second cluster ions 24 will be described. In addition, regarding irradiation conditions such as an irradiation element, cluster size, acceleration voltage, and dose described below, the irradiation conditions of the first cluster ions 16 and the irradiation conditions of the second cluster ions 24 are the same or different. Also good.

  The type of 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 ability, the first and / or second cluster ions preferably include carbon as a constituent element. 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.

  Moreover, as an irradiation element, 2 or more types of elements containing carbon are more preferable. In particular, it is preferable to irradiate one or more dopant elements selected from the group consisting of boron, phosphorus, arsenic and antimony in addition to 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.

  Next, by controlling the acceleration voltage and the cluster size of the first and / or second cluster ions, the concentration profile peaks in the depth direction of the constituent elements in the first modified layer 18 and the second modified layer 26 are controlled. The position can be controlled. In this specification, “cluster size” means the number of atoms or molecules constituting one cluster.

  In the first step of the present embodiment, the depth direction of the constituent elements in the first modified layer 18 is within the range of 150 nm or less from the surface 10A of the semiconductor wafer 10 from the viewpoint of obtaining higher gettering capability. The first cluster ions 16 are irradiated so that the peak of the concentration profile of the second modified layer is within the range of 150 nm or less from the surface 20A of the epitaxial layer 20 in the device exclusion region 20A. The second cluster ions 24 are irradiated so that the peak of the concentration profile of the constituent elements in the depth direction at 26 is located. 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. .

When using C _n H _m (3 ≦ n ≦ 16, 3 ≦ m ≦ 10) as the first and / or second cluster ions as a condition necessary for setting the peak position within the depth range, carbon 1 The acceleration voltage per atom is more than 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 this embodiment, the carbon dose of the first cluster ions 16 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 20 may be seriously damaged. Because there is. In addition, the carbon dose of the second cluster ions 24 is 1 × 10 ¹³ to 1 × 10 ¹⁶ atoms / cm ² , but from the viewpoint of obtaining higher gettering ability, it is 1 × 10 ¹⁴ atoms / cm ² or more. It is preferable to do.

  In the present embodiment, an example in which the second cluster ions 24 are irradiated to the entire device exclusion region 20A is illustrated, but the present invention is not limited to this, and the second cluster ions 24 are irradiated to a part of the device exclusion region 20A. Of course, you may do.

  Note that the second embodiment shown in FIG. 3 is characterized in that the first cluster ions are irradiated not on the bulk semiconductor wafer 12 but on the first epitaxial layer 14. 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.

  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 one embodiment, after the first step, the semiconductor wafer can be transferred to an epitaxial growth apparatus and the second step can be performed without performing a heat treatment for crystallinity recovery on the semiconductor wafer. Semiconductor epitaxial wafers 100 and 200 having high gettering capability can be efficiently manufactured. In other words, it is not necessary to perform the recovery heat treatment using a rapid heating / cooling heat treatment device such as RTA (Rapid Thermal Annealing) or RTO (Rapid Thermal Oxidation) that is separate from the epitaxial device.

  This is because the crystallinity of the semiconductor wafer 10 can be sufficiently recovered by a hydrogen baking process prior to epitaxial growth in an epitaxial apparatus for forming the epitaxial layer 20 described below. 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 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.

  The second epitaxial layer 20 formed on the modified layer 18 includes a silicon epitaxial layer, and can be formed 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. The epitaxial layer 20 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 20 may change due to the out-diffusion of the dopant from the semiconductor wafer 10, and if it exceeds 15 μm, the spectral sensitivity characteristics of the solid-state imaging device are affected. This is because there is a risk of occurrence.

(Semiconductor epitaxial wafer)
Next, semiconductor epitaxial wafers 100 and 200 obtained by the above manufacturing method will be described. The semiconductor epitaxial wafer 100 according to the first embodiment and the semiconductor epitaxial wafer 200 according to the second embodiment are formed on the surface of the semiconductor wafer 10 and the semiconductor wafer 10 as shown in FIGS. 2 (D) and 3 (E). The first modified layer 18 in which a predetermined element is dissolved in the semiconductor wafer 10, the epitaxial layer 20 on the first modified layer 18, and a part of the surface of the epitaxial layer 20 (this embodiment) Then, the second modified layer 26 formed by dissolving a predetermined element in the epitaxial layer 20 is formed in the device exclusion region 20A). Then, characterized in that the half-value width W _A and W _B concentration profile in the depth direction of the predetermined element is both 100nm or less in the first reformed layer 18 and the second reformed layer 26 in any way.

That is, according to the manufacturing method of the present invention, as compared to the monomer ion implantation, since the deposition area of the elements constituting the cluster ions can be localized with high concentration, the half width W _A of the first reforming layer and it became possible to both the 100nm or less half width W _B of the second modified layer. The lower limit can be set to 10 nm. Note that 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: Secondary Ion Mass Spectrometry). In addition, the “half-value width of the concentration profile in the first modified layer” is determined by SIMS in a state where the epitaxial layer is thinned to 1 μm when the thickness of the epitaxial layer is more than 1 μm in consideration of measurement accuracy. The half width when the density profile is measured.

  The predetermined element is not particularly limited as long as it is an element other than the main material of the semiconductor wafer (silicon in the case of a silicon wafer), but it is preferable to use carbon or two or more elements containing carbon as described above. It is.

From the viewpoint of obtaining higher gettering capability, the peak of the concentration profile in the first modified layer 18 is within the range where the depth from the surface 10A of the semiconductor wafer 10 is 150 nm or less in both of the semiconductor epitaxial wafers 100 and 200. It is preferable that the peak of the concentration profile in the second modified layer 26 is located within a range where the depth from the surface 20A of the epitaxial layer 20 is 150 nm or less. Further, the peak concentration of the concentration profile in the first modified layer 18 and / or the second modified layer 26 is preferably 1 × 10 ¹⁵ atoms / cm ³ or more, and preferably 1 × 10 ¹⁷ to 1 × 10 ²² atoms. / Cm ³ is more preferable, and 1 × 10 ¹⁹ to 1 × 10 ²¹ atoms / cm ³ is more preferable.

  In addition, the thickness in the depth direction of the first modified layer 18 and the second modified layer 26 can be approximately in the range of 30 to 400 nm.

  According to the semiconductor epitaxial wafers 100 and 200 of the present embodiment, metal contamination can be further suppressed by exhibiting higher gettering capability than the conventional one.

(Method for manufacturing solid-state imaging device)
The solid-state imaging device manufacturing method according to the embodiment of the present invention includes a solid-state imaging device on the epitaxial wafer manufactured by the above-described manufacturing method or the epitaxial layer 20 positioned on the surface of the above-described epitaxial wafer, that is, the semiconductor epitaxial wafer 100 or 200. It is characterized by forming. The solid-state imaging device obtained by this manufacturing method can sufficiently suppress the occurrence of white defect as compared with the conventional case.

Example 1
An n-type silicon wafer (diameter: 300 mm, thickness: 725 μm, dopant: phosphorus, dopant concentration: 5.0 × 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 ) as the first cluster ion using a cluster ion generator (manufactured by Nissin Ion Equipment Co., Ltd., model number: CLARIS), and the dose is 9 The surface of the silicon wafer was irradiated under the conditions of 0.0 × 10 ¹³ Clusters / cm ² (carbon dose amount 4.5 × 10 ¹⁴ atoms / cm ² ) and acceleration voltage per carbon atom of 14.8 keV / atom, A first modified layer was formed. After that, the silicon wafer is transferred into a single wafer epitaxial growth apparatus (Applied Materials Co., Ltd.), subjected to a hydrogen baking process at a temperature of 1120 ° C. for 30 seconds, and then hydrogen as a carrier gas and trichlorosilane as a source. A silicon epitaxial layer (thickness: 8 μm, dopant: phosphorus, dopant concentration: 1.5 × 10 ¹⁴ atoms / cm ³ ) was epitaxially grown on the first modified layer of the silicon wafer by CVD at 1150 ° C. as a gas. . Next, a photoresist film was formed, and a mask was placed over the epitaxial layer so as to have the arrangement shown in the surface view of FIG. The exposed portion of the epitaxial layer at this time is a region virtually set as a device exclusion region. And the 2nd cluster ion was irradiated to the exposed part of the epitaxial layer on the same irradiation conditions as 1st cluster ion, and the 2nd modified layer was formed. Finally, the mask was removed using a stripping solution to obtain a silicon epitaxial wafer according to the present invention.

(Example 2)
Except that the dose amount of the first and second cluster ions was 6.0 × 10 ¹³ Clusters / cm ² (carbon dose amount 3.0 × 10 ¹⁴ atoms / cm ² ), the same procedure as in Example 1 was performed. A silicon epitaxial wafer according to the invention was manufactured.

(Example 3)
A silicon epitaxial wafer according to the present invention was manufactured in the same manner as in Example 1 except that the material gas of the first and second cluster ions was changed to cyclohexane (C ₆ H ₁₂ ) to adjust the cluster to C ₃ H ₃ . .

Example 4
The same procedure as in Example 3 was performed except that the dose amount of the first and second cluster ions was 6.0 × 10 ¹³ Clusters / cm ² (carbon dose amount 3.0 × 10 ¹⁴ atoms / cm ² ). A silicon epitaxial wafer according to the invention was manufactured.

(Comparative Example 1)
In place of irradiation with the first and second cluster ions, carbon monomer ions are generated using CO ₂ as a material gas. 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 except that it was injected into the surface of the silicon wafer and the exposed portion of the epitaxial layer.

(Comparative Example 2)
A silicon epitaxial wafer according to a comparative example was manufactured in the same manner as in the comparative example 1 except that the dose amount of carbon monomer ions was set to 6.0 × 10 ¹³ atoms / cm ² .

<Evaluation method and evaluation results>
Each sample produced in the above Examples and Comparative Examples was evaluated. The evaluation method is shown below.

(1) SIMS measurement About each produced sample, the SIMS measurement was performed in the position of a device exclusion area | region. As a representative example, the carbon concentration profile of Example 1 is shown in FIG. 5, and the carbon concentration profile of Comparative Example 1 is shown in FIG. The depth of the horizontal axis is zero on the surface of the epitaxial layer. Table 1 shows the half-value width, peak position (peak depth from the surface of the epitaxial layer), and peak concentration of the carbon concentration profile corresponding to the second modified layer obtained here. Furthermore, about each produced sample, after thinning the epitaxial layer to 1 micrometer, SIMS measurement was performed. Table 1 shows the half-value width, peak position (peak depth from the silicon wafer surface excluding the epitaxial layer), and peak concentration corresponding to the first modified layer obtained at this time. In addition, about Example 1, since the SIMS measurement was performed also in the position of a device formation area, the carbon concentration profile is shown in FIG.

(2) Evaluation of gettering ability The surface of the 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. for 30 minutes. The heat treatment was performed. 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 ○: 7.5 × 10 ¹¹ atoms / cm ² or more and less than 1.0 × 10 ¹² atoms / cm ² Δ: less than 7.5 × 10 ¹¹ atoms / cm ²

<Consideration of evaluation results>
First, in Example 1, only the peak corresponding to the first modified layer immediately below the epitaxial layer was detected in the device formation region as shown in FIG. 6, but in the device exclusion region, as shown in FIG. In addition to the peak corresponding to the first modified layer, a peak corresponding to the second modified layer on the top surface of the epitaxial layer was also detected. Then, comparing FIG. 5 of Example 1 and FIG. 7 of Comparative Example 1, the first and second modified carbons were dissolved in a local and higher concentration by cluster ion irradiation than in the case of monomer ion implantation. It can be seen that the quality layer was formed.

  As is clear from the SIMS measurement results in Table 1, in Examples 1 to 4, the half-value widths of the carbon concentration profiles in the first modified layer and the second modified layer are both 100 nm or less. Due to the first and second modified layers in which carbon was dissolved in an appropriate and high concentration, a higher gettering ability than Comparative Examples 1 and 2 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 Bulk semiconductor wafer 14 First epitaxial layer 16 First cluster ion 18 First modified layer 20 Second epitaxial layer 20A Device exclusion region 20B Device formation region 22 Mask 24 Second cluster ion 26 Second modified layer

Claims (16)

A first step of irradiating a surface of the semiconductor wafer with first cluster ions to form a first modified layer formed by dissolving the constituent elements of the first cluster ions on the surface of the semiconductor wafer;
A second step of forming an epitaxial layer on the first modified layer of the semiconductor wafer;
Of the surface of the epitaxial layer, the second cluster ions are irradiated only to an edge region of 1 to 5 mm from the outer peripheral edge of the wafer, and only the edge region of the surface of the epitaxial layer is a constituent element of the second cluster ions. A third step of forming a second modified layer formed by solid solution,
A method for producing a semiconductor epitaxial wafer, comprising:   The method for producing a semiconductor epitaxial wafer according to claim 1, wherein the semiconductor wafer is a silicon wafer.   The semiconductor wafer is an epitaxial silicon wafer in which a silicon epitaxial layer is formed on a surface of a silicon wafer, and the first modified layer is formed on a surface of the silicon epitaxial layer in the first step. Manufacturing method of semiconductor epitaxial wafer.   4. The method according to claim 1, wherein after the first step, the semiconductor wafer is transferred to an epitaxial growth apparatus and the second step is performed without performing a heat treatment for recovering crystallinity on the semiconductor wafer. The manufacturing method of the semiconductor epitaxial wafer of description.   The manufacturing method of the semiconductor epitaxial wafer of any one of Claims 1-4 in which the said 1st and / or 2nd cluster ion contains carbon as a structural element.   The method for producing a semiconductor epitaxial wafer according to claim 5, wherein the first and / or second cluster ions include two or more elements including carbon as a constituent element. The irradiation conditions of the first cluster ions are: an acceleration voltage per carbon atom is 50 keV / atom or less, a cluster size is 100 or less, and a carbon dose is 5.0 × 10 ¹⁵ atoms / cm ² or less. A method for producing a semiconductor epitaxial wafer according to 5 or 6. The irradiation conditions of the second cluster ions are an acceleration voltage per carbon atom of 50 keV / atom or less, a cluster size of 100 or less, and a carbon dose of 1.0 × 10 ¹⁴ atoms / cm ² or more. The manufacturing method of the semiconductor epitaxial wafer of any one of 5-7. A semiconductor wafer, a first modified layer formed by dissolving a predetermined element in the semiconductor wafer, an epitaxial layer on the first modified layer, an epitaxial layer formed on the surface of the semiconductor wafer, A second modified layer formed by dissolving a predetermined element in the epitaxial layer formed only in an edge region of 1 to 5 mm from the outer peripheral edge of the wafer,
A semiconductor epitaxial wafer characterized in that the half-value widths of the concentration profiles in the depth direction of the predetermined element in the first modified layer and the second modified layer are both 100 nm or less.   The semiconductor epitaxial wafer according to claim 9, wherein the semiconductor wafer is a silicon wafer.   The semiconductor epitaxial wafer according to claim 9, wherein the semiconductor wafer is an epitaxial silicon wafer in which a silicon epitaxial layer is formed on a surface of a silicon wafer, and the first modified layer is located on a surface of the silicon epitaxial layer.   The peak of the concentration profile in the first modified layer is located within a depth of 150 nm or less from the surface of the semiconductor wafer, and the depth from the surface of the epitaxial layer is within a range of 150 nm or less. The semiconductor epitaxial wafer according to claim 9, wherein a peak of the concentration profile in the second modified layer is located. 13. The semiconductor epitaxial wafer according to claim 9, wherein a peak concentration of the concentration profile in the first and / or second modified layer is 1 × 10 ¹⁵ atoms / cm ³ or more.   The semiconductor epitaxial wafer according to claim 9, wherein the predetermined element includes carbon.   The semiconductor epitaxial wafer according to claim 14, wherein the predetermined element includes two or more elements including carbon.   A solid-state image sensor on an epitaxial layer manufactured on the surface of the epitaxial wafer manufactured by the manufacturing method according to any one of claims 1 to 8 or the epitaxial wafer according to any one of claims 9 to 15. Forming a solid-state imaging device.

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