JP6107068B2 - Epitaxial silicon wafer manufacturing method, epitaxial silicon wafer, and solid-state imaging device manufacturing method - Google Patents

Description

  The present invention relates to an epitaxial silicon wafer manufacturing method, an epitaxial silicon wafer, and a solid-state imaging device manufacturing method. In particular, the present invention relates to a method of manufacturing an epitaxial silicon wafer in which metal contamination can be suppressed by exhibiting higher gettering ability and the stacking fault of the epitaxial layer is reduced.

  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 an epitaxial silicon wafer serving as the substrate of the 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 mainly occurs in the manufacturing process of the epitaxial silicon wafer and the manufacturing process (device manufacturing process) of the solid-state imaging device. Metal contamination in the former epitaxial silicon 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 an epitaxial silicon 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 for forming a gettering sink on a silicon wafer, oxygen precipitates (commonly called silicon oxide precipitates, also called BMD: Bulk Micro Defect) or dislocations, which are crystal defects, are formed inside the silicon 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 silicon wafer are generally used.

  Here, there is a technique of forming a gettering site by injecting monomer ions (single ions) into a silicon wafer as one technique for gettering heavy metals. 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 an epitaxial layer is formed on this surface to form an epitaxial silicon 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 (hereinafter referred to as “recovery heat treatment”). ) Is performed with an RTA (Rapid Thermal Annealing) apparatus, thereby shortening the recovery heat treatment step and then forming an epitaxial layer.

  In Patent Document 3, a silicon single crystal substrate having an oxygen concentration of 7 ppma (JEIDA) or more is used, and two sets of carbon ion implantation, crystallinity recovery heat treatment, and epitaxial layer epitaxial growth are performed on the silicon single crystal substrate. A method of manufacturing an epitaxial silicon wafer is described in which two or more carbon ion implantation layers are formed by performing the process more than once, and the oxygen concentration of the outermost surface portion of the epitaxial layer is 5 ppma (JEIDA) or less.

JP-A-6-338507 JP 2008-294245 A JP 2012-59849 A

  By the way, when the oxygen concentration of the silicon wafer is high, large-sized oxygen precipitates (BMD) may be formed in the crystal during the growth process of the single crystal silicon ingot. BMD is useful in that it functions as intrinsic gettering (IG). However, this large BMD does not disappear due to the high-temperature heat treatment during the epitaxial growth process, and causes a stacking fault (SF: Staking Fault) in the epitaxial layer starting from the BMD existing on the surface layer of the silicon wafer. It adversely affects the quality of epitaxial silicon wafers.

  The techniques described in Patent Document 1, Patent Document 2, and Patent Document 3 all implant monomer ions into a silicon wafer before forming an epitaxial layer. However, according to studies by the present inventors, it has been found that an epitaxial silicon wafer into which monomer ions have been implanted has insufficient gettering capability. Intrinsic sink gettering (IG) capability by BMD is insufficient especially when the oxygen concentration of the silicon wafer that is the substrate is low, and monomer ion implantation has insufficient gettering capability as a whole epitaxial silicon wafer, making it more powerful. It was found that gettering ability was required.

  Therefore, in view of the above problems, the present invention has an epitaxial silicon wafer having higher gettering capability and reduced stacking faults in the epitaxial layer, a manufacturing method thereof, and a solid-state imaging device formed from the epitaxial silicon wafer. It aims at providing the manufacturing method of a solid-state image sensor.

  According to the study by the present inventors, it has been found that by irradiating cluster ions on a silicon wafer, there are the following advantages compared to the case of injecting monomer ions. In other words, when cluster ions are irradiated, even if irradiation is performed at an acceleration voltage equivalent to that of monomer ions, the energy per atom or molecule collides with the silicon wafer with a smaller energy than that of monomer ions, so that multiple ions can be applied at a time. The peak concentration of the profile in the depth direction of the irradiated element can be made high, and the peak position can be located closer to the silicon wafer surface. As a result, it was found that the gettering ability of the epitaxial silicon wafer can be sufficiently obtained even if the oxygen concentration of the silicon wafer is low and the gettering ability by intrinsic sink gettering is insufficient. Furthermore, it has been found that the stacking faults of the epitaxial layer can be reduced because the oxygen concentration of the silicon wafer is low.

That is, in the method for producing an epitaxial silicon wafer according to the present invention, a silicon wafer having an oxygen concentration of 16 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less is irradiated with cluster ions, The method includes a first step of forming a modified layer in which constituent elements of cluster ions are dissolved, and a second step of forming an epitaxial silicon layer on the modified layer of the silicon wafer.

Here, the oxygen concentration of the silicon wafer is preferably 8 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less.

  In the present invention, after the first step, the second step can be performed by transporting the silicon wafer to an epitaxial growth apparatus without performing a heat treatment for recovering crystallinity on the silicon wafer. However, it is also preferable to perform heat treatment for crystallinity recovery on the silicon wafer after the first step and before the second step.

  Here, the cluster ions preferably include carbon as a constituent element, and more preferably include two or more elements including carbon as a constituent element.

Further, the irradiation conditions of the cluster ions are preferably 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 ¹⁶ atoms / cm ² or less. .

Next, an epitaxial silicon wafer of the present invention includes a silicon wafer, a modified layer formed on the surface of the silicon wafer, in which a predetermined element is dissolved, and an epitaxial layer on the modified layer. The oxygen concentration of the silicon wafer is 16 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less in the region excluding the modified layer, and the predetermined concentration in the modified layer is The half width of the concentration profile of the element is 100 nm or less.

The oxygen concentration of the silicon wafer is preferably 8 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less in the region excluding the modified layer.

  In addition, it is preferable that the peak of the concentration profile in the modified layer is located within a depth of 150 nm or less from the surface of the silicon wafer.

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

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

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

According to the present invention, a silicon wafer having an oxygen concentration of 16 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less is irradiated with cluster ions, and the surface of the silicon wafer is modified with the constituent elements of the cluster ions. Since the quality layer is formed, this modified layer exhibits higher gettering capability, thereby suppressing metal contamination and obtaining an epitaxial silicon wafer with reduced epitaxial defects in the epitaxial layer. In addition, a high-quality solid-state imaging device can be formed from this epitaxial silicon wafer.

It is a model cross section explaining the manufacturing method of epitaxial silicon wafer 100 by one embodiment of the present 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 SIMS measurement in Reference Examples 1 and 2. (A) is the graph which combined the carbon concentration profile of the epitaxial silicon wafer, and the Ni concentration profile after gettering ability evaluation about Example 1 and (B) about the comparative example 2. (A) is the graph which showed the oxygen concentration profile of the epitaxial silicon wafer about Example 4 and the comparative example 6, (B) about Example 5 and the comparative example 7. FIG. 5 is a graph showing thermal donor level density of an epitaxial silicon wafer for Example 3 and Comparative Example 7. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. For convenience of explanation, FIG. 1 exaggerates the thickness of the epitaxial silicon layer 20 relative to the silicon wafer 10, unlike the actual thickness ratio.

(Epitaxial silicon wafer manufacturing method)
A method for manufacturing an epitaxial silicon wafer 100 according to an embodiment of the present invention is shown in FIG. First, the surface 10A of the silicon wafer 10 having an oxygen concentration of 16 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less is irradiated with the cluster ions 16, and the surface 10 A of the silicon wafer 10 is configured with the cluster ions 16. A first step (FIGS. 1A and 1B) for forming a modified layer 18 in which the element is dissolved is performed. Next, a second step (FIG. 1D) for forming an epitaxial silicon layer 20 on the modified layer 18 of the silicon wafer 10 is performed. FIG. 1D is a schematic cross-sectional view of an epitaxial silicon wafer 100 obtained as a result of this manufacturing method. After the first step, the silicon wafer 10 serving as a substrate has a modified layer 18 and a region 19 excluding the modified layer 18.

Here, the oxygen concentration of the silicon wafer 10 used in one embodiment is 16 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less. If the oxygen concentration of the silicon wafer 10 is 16 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less, generation of stacking faults in the epitaxial silicon layer 20 due to BMD can be suppressed. On the other hand, if the oxygen concentration of the silicon wafer 10 is more than 16 × 10 ¹⁷ atoms / cm ³ , the oxygen concentration is too high, so that a large BMD is formed up to the surface layer portion of the silicon wafer 10, resulting in epitaxial silicon In the layer 20, a stacking fault caused by BMD may occur.

In the present embodiment, it is more preferable to use the silicon wafer 10 having an oxygen concentration of 8 × 10 ¹⁷ atoms / cm ³ or less, and a preferable range is 3 × 10 ¹⁷ atoms / cm ³ to 8 × 10 ¹⁷ atoms / cm ^3. It is. When the oxygen concentration of the silicon wafer 10 is 8 × 10 ¹⁷ atoms / cm ³ or less, oxygen precipitation in the silicon wafer 10 hardly occurs, so that the occurrence of stacking faults due to BMD in the epitaxial layer is almost certainly prevented. be able to. If the oxygen concentration of the silicon wafer 10 is 8 × 10 ¹⁷ atoms / cm ³ or less, the intrinsic gettering (IG) ability by BMD cannot be expected at all. However, in the present invention, cluster ion irradiation described later is performed. Thus, the epitaxial silicon wafer 100 can have a sufficient gettering capability.

The silicon wafer 10 having an oxygen concentration of 16 × 10 ¹⁷ atoms / cm ³ or less is produced by slicing a silicon single crystal ingot obtained by a general CZ method (Czochralski method: Czochralski method) with a wire saw or the like. be able to. The oxygen concentration of a low oxygen single crystal silicon ingot obtained by a general CZ method is 3 × 10 ¹⁷ atoms / cm ³ or more, and a silicon wafer in this concentration range can be produced. The oxygen concentration can be controlled by adjusting the crucible rotation speed, the pressure in the chamber, the Ar gas flow rate, and the like set during the growth of the silicon single crystal ingot. In addition, a silicon wafer having an oxygen concentration of 1 × 10 ¹⁷ atoms / cm ³ or less can be manufactured by an FZ method (floating zone method: floating zone melting method).

  Here, the characteristic process of the present invention is the first process of irradiating the cluster ions shown in FIG. The technical significance of adopting this process will be described together with the effects. The modified layer 18 formed as a result of irradiating the cluster ions 16 is a region where the constituent elements of the cluster ions 16 are locally present as a solid solution in the interstitial positions or substitution positions of crystals on the surface of the silicon wafer. Work 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 (saturated solubility of transition metals) greatly increases when carbon or boron is dissolved to a level equal to or higher than the equilibrium concentration of the silicon single crystal. In other words, 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 cluster ions 16 are irradiated, higher gettering ability can be obtained as compared with the case where monomer ions are implanted, and further, the recovery heat treatment can be omitted. Therefore, it becomes possible to manufacture the epitaxial silicon wafer 100 having higher gettering ability, and the back-illuminated solid-state imaging device manufactured from the epitaxial silicon wafer 100 obtained by this manufacturing method suppresses the generation of white defect as compared with the conventional case. Can be expected.

  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. 2B, 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. .

  Furthermore, the monomer ions are generally implanted at an acceleration voltage of about 150 to 2000 keV. 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. The crystallinity of the epitaxial layer grown on the wafer surface is disturbed. Also, the higher the acceleration voltage, the more the crystallinity is disturbed. Therefore, it is necessary to perform heat treatment (recovery heat treatment) for recovering disordered crystallinity after ion implantation at a high temperature for a long time.

  On the other hand, when irradiating the silicon wafer with cluster ions made of, for example, carbon and boron, as shown in FIG. 2A, when the silicon ion is irradiated onto the silicon wafer, the energy is instantaneously 1350 to 1400. 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 (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 FIG. 4A described later). As a result, it is considered that a higher gettering ability can be obtained than in the case of injecting monomer ions, and a sufficiently high gettering ability can be obtained by one-time cluster ion irradiation. In addition, if it is a form of cluster ion, multiple types of ions can be irradiated to irradiation simultaneously.

  The cluster ions 16 are generally irradiated at an acceleration voltage of about 10 to 100 keV / Cluster. Since the cluster is an aggregate of a plurality of atoms or molecules, it is implanted with a small energy per atom or molecule. Therefore, the damage to the crystal of the silicon wafer is small. Furthermore, due to the difference in the implantation mechanism as described above, the cluster ion irradiation does not disturb the crystallinity of the silicon wafer 10 more than the monomer ion implantation. Therefore, after the first step, the silicon wafer 10 can be transported to the epitaxial growth apparatus and the second step can be performed without performing a recovery heat treatment on the silicon wafer 10 (FIG. 1C).

  The modified layer 18 not only dissolves heavy metals but also captures oxygen, and can suppress oxygen diffusion into the epitaxial silicon layer 20. Here, as one of the factors affecting the device operation of the image sensor (CCD, CIS), there is a change in Vth (Threshold Voltage). When oxygen in the bulk single crystal wafer (silicon wafer) of the epitaxial silicon wafer diffuses into the epitaxial layer, a thermal donor (oxygen donor) is generated, which causes a change in Vth. In this respect, the variation in Vth can be suppressed by the oxygen diffusion suppressing effect of the modified layer 18.

  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 generation method, (1) charged particle beam engineering: Junzo Ishikawa: ISBN978 -4-339-00734-3: Corona, (2) Electron / ion beam engineering: The Institute of Electrical Engineers of Japan: ISBN4-88686-217-9: Ohm, (3) Cluster ion beam foundation and application: 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, irradiation conditions of cluster ions will be described. First, the irradiation element is not particularly limited, and examples thereof include carbon, boron, phosphorus, and arsenic. However, from the viewpoint of obtaining higher gettering ability, the cluster ions preferably contain 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, it is more preferable to include two or more elements including carbon as a constituent element. This is because the types of metals that can be efficiently gettered differ depending on the types of deposited elements, so that two or more types of elements can be dissolved to cope with a wider range of metal contamination. For example, in the case of carbon, nickel can be efficiently gettered, and in the case of boron, copper and iron can be efficiently gettered.

The 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 a small-sized cluster ion beam can be easily formed.

  The compound to be ionized is preferably a compound containing both carbon and a dopant element (boron, phosphorus, arsenic, antimony, etc.). 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 first step of the present embodiment, from the viewpoint of obtaining high gettering capability, the concentration profile of the constituent elements in the modified layer 18 in the depth direction is within a range of 150 nm or less from the surface 10A of the silicon wafer 10. The cluster ions 16 are irradiated so that the peak of 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 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 this embodiment, the carbon dose of the cluster ions 16 is 1 × 10 ¹³ to 1 × 10 ¹⁶ atoms / cm ^2, and more preferably 1 × 10 ^{14 to} 5 × 10 ¹⁵ atoms / cm ² . If it is less than 1 × 10 ¹³ atoms / cm ² , the gettering ability may not be sufficiently obtained, and if it exceeds 1 × 10 ¹⁶ atoms / cm ² , the epitaxial surface may be greatly damaged. It is.

  According to the present invention, as described above, there is no need to perform the recovery heat treatment using a rapid heating / cooling heat treatment device such as RTA or RTO that is separate from the epitaxial device. This is because the crystallinity of the silicon wafer 10 can be sufficiently recovered by a hydrogen baking process prior to epitaxial growth in an epitaxial apparatus for forming the epitaxial silicon layer 20 described below. The general conditions for the hydrogen baking are as follows: the inside of the epitaxial growth apparatus is in a hydrogen atmosphere, the silicon 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 higher and 1200 ° C. or lower at a temperature rising rate, and the temperature is maintained for 30 seconds or longer and 1 minute or shorter. 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, but the crystallinity of the silicon wafer 10 is sufficiently restored by the hydrogen baking under the above conditions. Can be made.

  Of course, recovery heat treatment may be performed after the first step and before the second step by using a heat treatment apparatus separate from the epitaxial apparatus (FIG. 1C). 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, whereas if it exceeds 1200 ° C., it is caused by the heat treatment at high temperature. This is because slip occurs and the heat load on the apparatus increases. Moreover, the heat treatment time is set to 10 seconds or more and 1 hour or less because a recovery effect is difficult to be obtained if the heat treatment time is less than 10 seconds. This is because it becomes larger.

  Such recovery heat treatment can be performed using, for example, a rapid heating / cooling heat treatment apparatus such as RTA or RTO, or a batch heat treatment apparatus (vertical heat treatment apparatus, horizontal heat treatment apparatus). Since the former is a lamp irradiation heating method, it is not suitable for long-time treatment in terms of the device structure, and is suitable for heat treatment within 15 minutes. On the other hand, in the latter, although it takes time to raise the temperature to a predetermined temperature, a large number of wafers can be processed simultaneously. In addition, because of the resistance heating method, long-time heat treatment is possible. An appropriate heat treatment apparatus may be selected in consideration of the irradiation conditions of the cluster ions 16.

  In the second step of this embodiment, the epitaxial silicon layer 20 formed on the modified layer 18 can be formed under general conditions. For example, hydrogen is used as a carrier gas and a source gas such as dichlorosilane or trichlorosilane is introduced into the chamber, and the growth temperature varies depending on the source gas used, but it is approximately 1000 to 1200 ° C. by the CVD method. It can be epitaxially grown on the silicon wafer 10. The epitaxial silicon 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 epitaxial silicon layer 20 may change due to the out-diffusion of dopant from the silicon wafer 10, and if it exceeds 15 μm, the spectral sensitivity characteristics of the solid-state imaging device are affected. This is because it may occur. The epitaxial silicon layer 20 becomes a device layer for manufacturing a back-illuminated solid-state imaging device.

(Epitaxial silicon wafer)
Next, the epitaxial silicon wafer 100 obtained by the above manufacturing method will be described. As shown in FIG. 1D, an epitaxial silicon wafer 100 according to an embodiment is formed by dissolving a predetermined element in the silicon wafer 10 and the silicon wafer 10 formed on the surface 10A of the silicon wafer 10. A modified layer 18 and an epitaxial silicon layer 20 on the modified layer 18 are included. The oxygen concentration of the silicon wafer 10 is 16 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less in the region 19 excluding the modified layer 18 and the depth direction of the predetermined element in the modified layer 18 The half-value width W of the density profile is 100 nm or less.

  That is, according to the manufacturing method of the present invention, the precipitation region of the elements constituting the cluster ions can be locally and highly concentrated as compared with the monomer ion implantation. Became possible. 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 depth direction of the predetermined element in the modified layer” is a state in which the epitaxial layer is thinned to 1 μm when the thickness of the epitaxial layer exceeds 1 μm in consideration of measurement accuracy. Thus, the half width when the concentration profile of the predetermined element is measured by SIMS is used.

Further, according to the manufacturing method of the present invention, in the region 19 excluding the modified layer 18, the oxygen concentration of the silicon wafer 10 is as low as 16 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less. Nevertheless, the modified layer 18 can have sufficient gettering capability. In addition, since the oxygen concentration in the region 19 excluding the modified layer 18 is low, stacking faults in the epitaxial layer can be reduced.

  As described above, in the epitaxial silicon wafer 100, the modified layer 18 captures oxygen in addition to capturing heavy metals, and thus forms a peak of oxygen concentration in the modified layer 18. Therefore, the oxygen concentration is extremely different between the modified layer 18 and the region 19 excluding the modified layer 18. Therefore, when the oxygen concentration in the silicon wafer 10 of the epitaxial silicon wafer 100 is indicated, the upper limit value of the oxygen concentration in the region 19 excluding the modified layer 18 is used. This modified layer 18 suppresses the diffusion of oxygen into the epitaxial silicon layer 20, so that the oxygen concentration in the epitaxial silicon layer 20 can be lowered, and therefore the formation of thermal donors can be reduced. For this reason, the fluctuation | variation of Vth of the solid-state image sensor by this epitaxial silicon wafer 100 can be suppressed.

Further, if the oxygen concentration in the region 19 of the silicon wafer 10 excluding the modified layer 18 is 8 × 10 ¹⁷ atoms / cm ³ or less, it is possible to almost certainly prevent the occurrence of stacking faults due to BMD in the epitaxial layer. As described above.

  The predetermined element is not particularly limited as long as it is an element other than silicon, but as described above, it is preferable to use carbon or two or more elements containing carbon.

From the viewpoint of obtaining a higher gettering capability, the epitaxial silicon wafer 100 preferably has a concentration profile peak in the modified layer 18 within a depth of 150 nm or less from the surface of the silicon wafer 10. Further, the peak concentration of the concentration profile is preferably 1 × 10 ¹⁵ to 1 × 10 ²² atoms / cm ³ , and more preferably in the range of 1 × 10 ¹⁷ to 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.

  According to the epitaxial silicon wafer 100 of the present embodiment, metal gettering can be further suppressed and stacking faults of the epitaxial layer can be reduced by exhibiting higher gettering ability than conventional ones.

(Method for manufacturing solid-state imaging device)
The method for manufacturing a solid-state imaging device according to an embodiment of the present invention provides a solid-state imaging on the epitaxial silicon wafer manufactured by the above-described manufacturing method or the epitaxial silicon layer 20 positioned on the surface of the epitaxial silicon wafer, that is, the epitaxial silicon wafer 100. An element is formed. The solid-state imaging device obtained by this manufacturing method can reduce the influence of heavy metal contamination that occurs during each process of the manufacturing process, and can sufficiently suppress the occurrence of white scratch defects. In addition, this solid-state imaging device can reduce stacking faults in the epitaxial layer. Furthermore, since this solid-state imaging device suppresses oxygen diffusion in the epitaxial silicon layer 20, it is also possible to suppress changes in Vth.

  The exemplary embodiments of the present invention have been described above, but the present invention is not limited to these embodiments.

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

(Reference Example 1)
N-type silicon wafer (diameter: 300 mm, thickness: 725 μm, crystal orientation: <100>, dopant: phosphorus, dopant obtained from CZ single crystal silicon ingot and having an oxygen concentration of 6.5 × 10 ¹⁷ atoms / cm ³ Concentration: 4 × 10 ¹⁴ atoms / cm ³ ) was prepared. Next, the cluster ion of C ₅ H ₅ produced from dibenzyl (C ₁₄ H ₁₄ ) using a cluster ion generator (manufactured by Nissin Ion Equipment Co., Ltd., model number: CLARIS) is dosed 9.0 × 10 ^13. The silicon wafer was irradiated under conditions of Clusters / cm ² (carbon dose of 4.5 × 10 ¹⁴ atoms / cm ² ) and 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 monomer ions are generated using CO ₂ as a material gas, a dose amount of 9.0 × 10 ¹³ atoms / cm ² , an acceleration voltage of 300 keV / The silicon wafer was irradiated under the same conditions as in Reference Example 1 except that the atom conditions were used.

  About the sample produced by the said reference examples 1 and 2, it measured by SIMS and obtained the carbon concentration profile shown in FIG. Note that the depth of the horizontal axis is zero on the surface of the silicon wafer. As is clear from FIG. 3, 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, the peak concentration of the carbon concentration profile is higher than that in Reference Example 2, and the peak position is located closer to the silicon wafer surface. From this, it is presumed that the tendency of the carbon concentration profile remains the same after the formation of the epitaxial layer.

Example 1
N-type silicon wafer (diameter: 300 mm, thickness: 725 μm, crystal orientation: <100>, dopant: phosphorus, dopant obtained from CZ single crystal silicon ingot and having an oxygen concentration of 6.5 × 10 ¹⁷ atoms / cm ³ Concentration: 4 × 10 ¹⁴ atoms / cm ³ ) was prepared. Next, the silicon wafer was irradiated under the conditions described in Table 1 using a cluster ion generator (manufactured by Nissin Ion Equipment Co., Ltd., model number: CLARIS). Then, after the silicon wafer is subjected to HF cleaning treatment, it is transferred into a single wafer epitaxial growth apparatus (Applied Materials) and subjected to hydrogen baking treatment at a temperature of 1120 ° C. for 30 seconds in the apparatus, followed by hydrogen carrier A silicon epitaxial layer (thickness: 8 μm, dopant type: phosphorus, dopant concentration: 1 × 10 ¹⁵ ) on a silicon wafer by a CVD method at 1150 ° C. using a gas, trichlorosilane as a source gas, and phosphine (PH ₃ ) as a dopant gas atoms / cm ³ ) was epitaxially grown to produce an epitaxial silicon wafer according to the present invention.

(Examples 2 and 3)
An epitaxial silicon wafer according to the present invention was produced under the same conditions as in Example 1 except that the oxygen concentration of the silicon wafer was changed as shown in Table 1.

Example 4
An epitaxial silicon wafer according to the present invention was fabricated under the same conditions as in Example 1 except that the dose was changed to 9.0 × 10 ¹⁴ Clusters / cm ² .

(Example 5)
An epitaxial silicon wafer according to the present invention was fabricated under the same conditions as in Example 3 except that the dose was changed to 9.0 × 10 ¹⁴ Clusters / cm ² .

(Comparative Example 1)
An epitaxial silicon wafer according to a comparative example was produced under the same conditions as in Example 1 except that the oxygen concentration of the silicon wafer was changed as shown in Table 1.

(Comparative Examples 2 to 5)
Comparative example with the same conditions as in Example 1 except that the oxygen concentration of the silicon wafer is changed as shown in Table 1, and carbon monomer ions are implanted under the conditions shown in Table 1 instead of the cluster ion irradiation. The silicon epitaxial silicon wafer concerning this was produced.

(Comparative Example 6)
An epitaxial silicon wafer according to a comparative example was produced under the same conditions as in Example 1 except that no cluster ion irradiation was performed.

(Comparative Example 7)
An epitaxial silicon wafer according to a comparative example was produced under the same conditions as in Example 3 except that the cluster ion irradiation was not performed.

(1) SIMS measurement (carbon)
As a representative example, SIMS measurement was performed on each sample produced in Example 1 and Comparative Example 2, and carbon concentration profiles shown in FIGS. 4A and 4B were obtained. The depth of the horizontal axis is zero on the surface of the epitaxial layer. Furthermore, about each sample produced in Examples 1-3 and Comparative Examples 1-5, after thinning an epitaxial layer to 1 micrometer, SIMS measurement was performed. Table 1 shows the half-value 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 epitaxial silicon wafer of each sample produced in Examples 1 to 3 and Comparative Examples 1 to 5 was subjected to spin coating contamination with Ni contamination liquid (1.0 × 10 ¹² / cm ² ). Was deliberately contaminated with a heat treatment, followed by heat treatment at 900 ° C. for 30 minutes. Thereafter, SIMS measurement was performed. As representative examples, the Ni concentration profiles for Example 1 and Comparative Example 2 are shown together with the carbon concentration profiles (FIGS. 4A and 4B). Table 1 shows the results of gettering ability evaluation for other examples and comparative examples. The peak concentrations of the Ni concentration profile were classified as follows and used as evaluation criteria.
◎: 1 × 10 ¹⁷ atoms / cm ³ or more ○: 7.5 × 10 ¹⁶ atoms / cm ³ or more to less than 1 × 10 ¹⁷ atoms / cm ³ Δ: less than 7.5 × 10 ¹⁶ atoms / cm ³

(3) Stacking fault evaluation About each sample produced in Examples 1-3 and Comparative Examples 1-5, the generation | occurrence | production situation of the stacking fault resulting from BMD observed by an epitaxial layer was investigated. First, the surface of the epitaxial layer is observed in a DWO mode (Dark Field Wide Oblique mode: dark field / wide / oblique incidence mode) using a surface defect inspection apparatus (manufactured by KLA-Tencor: Surfscan SP-2). Next, an LPD (Light Point Defect) site detected by the surface defect inspection apparatus is observed and evaluated using a scanning electron microscope (SEM) to determine whether it is a stacking fault (SF). Do. After SEM observation, an evaluation sample for cross-sectional observation including a stacking fault site is created by focused ion beam (FIB) processing, and this evaluation sample is observed and evaluated using a transmission electron microscope (TEM). Then, it was confirmed whether there was a stacking fault caused by BMD. The observation results of stacking faults were classified as follows and used as evaluation criteria. The evaluation results are shown in Table 1.
○: 10 pieces / wafer or less △: 10 pieces / wafer over

(4) SIMS measurement (oxygen)
SIMS measurement was performed on each of the samples prepared in Examples 4 and 5 and Comparative Examples 6 and 7, and oxygen concentration profiles shown in FIGS. 5A and 5B were obtained. The depth of the horizontal axis is zero on the surface of the epitaxial layer.

(5) Investigation of Thermal Donor Generation Amount For each sample produced in Example 3 and Comparative Example 7, the amount of thermal donor generated in the epitaxial layer was investigated. In this evaluation, the sample epitaxial silicon wafer was subjected to a heat treatment at 450 ° C. for 4 hours in the air atmosphere, and then the thermal donor level density near the center of the epitaxial layer was measured by transient capacitance spectroscopy (DLTS: Deep Level Transient). Spectroscopy). Note that DLTS measurement is based on the temperature dependence of the capacitance change obtained when a Schottky diode is formed on the surface of the bulk crystal and a reverse bias pulse is applied to the diode. This is a method for measuring the type and concentration of heavy metals. Specifically, the carrier is trapped at a deep level by weakening the reverse bias applied to the Schottky diode, and then the depletion layer is widened by strengthening the reverse bias, whereby the carriers emitted from the deep level are increased. This is an evaluation method for measuring by observing the transient response. The result of the thermal donor generation amount is shown in FIG. The depth of the horizontal axis is zero on the surface of the epitaxial layer.

(Consideration of evaluation results)
4 (A) and 4 (B), the modified layer in which carbon is locally dissolved at a high concentration is formed in Example 1 by cluster ion irradiation as compared with Comparative Example 2 in which monomer ion implantation is performed. You can see that And as shown in Table 1, in Examples 1-3, since the half-value width of the carbon concentration profile is 100 nm or less, gettering ability superior to Comparative Examples 2-5 with respect to Ni It can be seen that Further, in the epitaxial silicon wafers of Examples 1 to 3, since the oxygen concentration of the silicon wafer is 16 × 10 ¹⁷ atoms / cm ³ or less, none of the stacking faults caused by BMD occurs. In Comparative Example 1, sufficient gettering ability was obtained by cluster ion irradiation, but because the oxygen concentration of the silicon wafer was too high, stacking faults due to BMD were observed.

  5A and 5B show that the modified layer formed by cluster ion irradiation captures oxygen and suppresses diffusion of oxygen into the epitaxial layer. Furthermore, FIG. 6 shows that irradiation with cluster ions reduces the level density of the thermal donor near the center of the epitaxial layer. From these results, it can be seen that the modified layer formed by irradiation with cluster ions can suppress oxygen diffusion into the epitaxial layer.

  According to the present invention, it is possible to obtain an epitaxial silicon wafer in which metal contamination can be suppressed and the stacking faults of the epitaxial layer are reduced by exhibiting higher gettering capability. A high-quality solid-state imaging device can be formed from the wafer.

DESCRIPTION OF SYMBOLS 10 Silicon wafer 10A Silicon wafer surface 16 Cluster ion 18 Modified layer 19 Area | region except a modified layer 20 Epitaxial silicon layer 100 Epitaxial silicon wafer

Claims (14)

A modification in which cluster ions are irradiated onto a silicon wafer having an oxygen concentration of 16 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less, and the constituent elements of the cluster ions are dissolved on the surface of the silicon wafer. A first step of forming a layer;
A second step of forming an epitaxial silicon layer on the modified layer of the silicon wafer;
A method for producing an epitaxial silicon wafer, comprising: 2. The method for producing an epitaxial silicon wafer according to claim 1, wherein the silicon wafer has an oxygen concentration of 8 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less.   3. The epitaxial according to claim 1, wherein, after the first step, the second step is performed by transferring the silicon wafer to an epitaxial growth apparatus without performing a heat treatment for recovering crystallinity on the silicon wafer. Silicon wafer manufacturing method.   The method for producing an epitaxial silicon wafer according to claim 1, wherein after the first step and before the second step, the silicon wafer is subjected to a heat treatment for crystallinity recovery.   The manufacturing method of the epitaxial silicon wafer of any one of Claims 1-4 in which the said cluster ion contains carbon as a structural element.   The manufacturing method of the epitaxial silicon wafer of Claim 5 in which the said cluster ion contains 2 or more types of elements containing carbon as a structural element. The irradiation conditions of the cluster ions are an acceleration voltage of 50 keV / atom or less per carbon atom, a cluster size of 100 or less, and a carbon dose of 1.0 × 10 ¹³ atoms / cm ² or more. The manufacturing method of the epitaxial silicon wafer of description. A silicon wafer, a modified layer formed on the surface of the silicon wafer, in which a predetermined element is dissolved in the silicon wafer, and an epitaxial silicon layer on the modified layer,
The oxygen concentration of the silicon wafer is 16 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less in the region excluding the modified layer,
An epitaxial silicon wafer, wherein a half-value width of a concentration profile of the predetermined element in the modified layer is 100 nm or less. The epitaxial silicon wafer according to claim 8, wherein an oxygen concentration of the silicon wafer is 8 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less in a region excluding the modified layer.   The epitaxial silicon wafer according to claim 8 or 9, wherein a peak of the concentration profile in the modified layer is located within a depth of 150 nm or less from the surface of the silicon wafer. The epitaxial silicon wafer according to claim 8, wherein a peak concentration of the concentration profile in the modified layer is 1.0 × 10 ¹⁵ atoms / cm ³ or more.   The epitaxial silicon wafer according to claim 8, wherein the predetermined element includes carbon.   The epitaxial silicon wafer according to claim 12, wherein the predetermined element includes two or more elements including carbon.   In the epitaxial silicon layer located in the surface of the epitaxial silicon wafer manufactured by the manufacturing method of any one of Claims 1-7, or the epitaxial silicon wafer of any one of Claims 8-13, A method for manufacturing a solid-state imaging device, comprising forming a solid-state imaging device.

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