Manufacturing method for epitaxial silicon wafers

Abstract

The present invention provides a method for manufacturing epitaxial silicon wafers that enables the production of epitaxial silicon wafers with a more enhanced passivation effect by fluorine in the silicon epitaxial layer. [Solution] The present invention provides a method for manufacturing an epitaxial silicon wafer, comprising: a first step of irradiating the surface 10A of a silicon wafer 10 with cluster ions 12 containing carbon, hydrogen, and fluorine as constituent elements to form a modified layer 14 in which the constituent elements of the cluster ions 12 are solid-solved in the surface layer of the silicon wafer 10; a second step of forming a silicon epitaxial layer 16 on the modified layer 14 of the silicon wafer 10 to obtain an epitaxial silicon wafer 100; and a third step of heat treatment in which the epitaxial silicon wafer 100 is held at a temperature of 600°C to 1000°C in an inert gas atmosphere.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing epitaxial silicon wafers. [Background technology]

[0002] Epitaxial silicon wafers, which have an epitaxial layer of single-crystal silicon formed on a silicon wafer, are used as device substrates for fabricating various semiconductor devices such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), DRAMs (Dynamic Random Access Memory), power transistors, and BSI (Back Side Illumination) type CISs (CMOS Image Sensors).

[0003] When the epitaxial layer is contaminated with heavy metals, the dark current of the CIS increases, leading to defects called white scratches, which degrades the properties of the semiconductor device. Therefore, to suppress such heavy metal contamination, there is a technique to form gettering sites in the silicon wafer to capture heavy metals. One such method involves implanting ions into the silicon wafer and then forming the epitaxial layer. In this method, the ion-implanted regions function as gettering sites.

[0004] Patent Document 1 describes a method for manufacturing an epitaxial silicon wafer, comprising: a first step of irradiating the surface of a silicon wafer with cluster ions, such as C3H5, whose constituent elements are carbon and hydrogen, to form a modified layer in which the constituent elements of the cluster ions are solid-solved in the surface layer of the silicon wafer; and a second step of forming a silicon epitaxial layer on the modified layer of the silicon wafer. Patent Document 1 shows that the modified layer formed by irradiating with cluster ions whose constituent elements are carbon and hydrogen exhibits higher gettering ability than the ion-implanted region obtained by implanting carbon monomer ions.

[0005] Here, since hydrogen is a lighter element than carbon, when comparing the carbon and hydrogen injected into the reformed layer by cluster ion irradiation, hydrogen diffuses more easily and is more likely to diffuse and desorb from the reformed layer by the heat treatment during the formation of the epitaxial layer. Patent Document 2 describes an improved technique of Patent Document 1 in which, by setting the beam current value to 50 μA or more in the first step of irradiating with hydrogen in the form of cluster ions, it is possible to retain a high concentration of hydrogen in the reformed layer (i.e., directly below the epitaxial layer) even after the formation of the epitaxial layer. The hydrogen remaining in the reformed layer diffuses into the epitaxial layer by the heat treatment during the device formation process in which semiconductor devices are formed in the epitaxial layer, and deactivates (passivates) interface state defects in the epitaxial layer, thereby contributing to the improvement of device characteristics such as the reduction of leakage current. This is called the "hydrogen passivation effect".

[0006] With the increasing three-dimensionality of device structures in recent years, there are concerns that the bonding of chips together will increase the number of interface states, thus requiring enhanced passivation effects. Patent Document 3 describes an improved technique of Patent Document 1 in which, by irradiating the modified layer (i.e., directly beneath the epitaxial layer) with cluster ions using a hydrocarbon compound containing fluorine as an ion source in the first step, it is possible to retain a high concentration of fluorine in the modified layer (i.e., directly beneath the epitaxial layer) even after the formation of the epitaxial layer. The fluorine remaining in the modified layer is expected to exert a passivation effect, similar to hydrogen, and contribute to improving device characteristics. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2012 / 157162 [Patent Document 2] International Publication No. 2016 / 031328 [Patent Document 3] Japanese Patent Publication No. 2022-173926 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0008] However, according to studies by the present inventor, even when fluorine is irradiated in the form of cluster ions as described in Patent Document 3, a high-temperature heat treatment at 1100° C. or higher is performed during formation of the epitaxial layer, so fluorine in the modified layer diffuses outward, and the effect of retaining fluorine in the modified layer after epitaxial growth is limited. It has been found that there is a problem that there is room for improvement in this respect.

[0009] In view of the above problems, an object of the present invention is to provide a method for producing an epitaxial silicon wafer, which can produce an epitaxial silicon wafer in which the passivation effect by fluorine in a silicon epitaxial layer is further enhanced. [[Means for Solving the Problem]]

[0010] In order to solve the above problem, the present inventor has conducted intensive studies and obtained the following findings. That is, it has been found that by performing heat treatment in a specific temperature range of 600°C to 1000°C inclusive in an inert gas atmosphere on an epitaxial silicon wafer obtained by implanting cluster ions containing carbon, hydrogen and fluorine into a silicon wafer and then forming an epitaxial layer, a higher concentration of fluorine can remain in the surface layer (modified layer) of the silicon wafer. Considering that fluorine in the modified layer outdiffuses during high-temperature heat treatment for epitaxial growth, it is generally thought that adding heat treatment after epitaxial growth will further promote the outdiffusion of fluorine; however, performing heat treatment in the specific temperature range surprisingly achieves the effect of increasing the fluorine concentration in the modified layer. This suggests that a considerable amount of fluorine that outdiffused from the modified layer during epitaxial growth actually remains as a solid solution in the bulk portion of the silicon wafer, and is rediffused from the bulk portion and recaptured by the modified layer through the heat treatment after epitaxial growth. Patent Document 3 describes that it is considered that almost no fluorine remains in the silicon wafer due to outdiffusion of fluorine during epitaxial growth. In other words, Patent Document 3 recognizes that fluorine that outdiffused from the modified layer during epitaxial growth desorbs through the surface of the silicon epitaxial layer, and does not provide the finding that fluorine remains in the bulk portion.

[0011] The gist of the present invention, completed based on the above findings, is as follows. [1] A first step of irradiating the surface of a silicon wafer with cluster ions containing carbon, hydrogen and fluorine as constituent elements to form a modified layer in which the constituent elements of the cluster ions are solid-dissolved in a surface layer portion of the silicon wafer; a second step of forming a silicon epitaxial layer on the modified layer of the silicon wafer to obtain an epitaxial silicon wafer; and thereafter, a third step of performing heat treatment that holds the epitaxial silicon wafer at a temperature of 600°C to 1000°C inclusive in an inert gas atmosphere; A method for manufacturing an epitaxial silicon wafer having [a certain characteristic].

[0012] [2] The method for manufacturing an epitaxial silicon wafer according to [1] above, wherein the temperature is 700°C or higher and 900°C or lower.

[0013] [3] The method for manufacturing an epitaxial silicon wafer according to [1] or [2] above, wherein the inert gas atmosphere is a nitrogen atmosphere.

[0014] [4] A method for manufacturing an epitaxial silicon wafer according to any one of the above [1] to [3], wherein the holding time at the temperature is 5 minutes or more.

[0015] [5] The first step involves SIMS analysis of the modified layer after the second step and before the third step, and the peak area of ​​the integrated fluorine concentration profile obtained is 1.0 × 10⁻⁶. 10 atoms / cm 2 A method for manufacturing an epitaxial silicon wafer as described in any one of the above [1] to [4], carried out under the above conditions.

[0016] [6] The method for manufacturing an epitaxial silicon wafer according to any one of the above [1] to [5], wherein the third step is performed under conditions that the peak area, which is the integral value of the fluorine concentration profile obtained by SIMS analysis of the modified layer after the third step, is 1.2 times or more the peak area, which is the integral value of the fluorine concentration profile obtained by SIMS analysis of the modified layer after the second step and before the third step. [Effects of the Invention]

[0017] According to the present invention's method for manufacturing epitaxial silicon wafers, it is possible to manufacture epitaxial silicon wafers in which the passivation effect by fluorine in the silicon epitaxial layer is further enhanced. [Brief explanation of the drawing]

[0018] [Figure 1]This is a schematic cross-sectional view illustrating a method for manufacturing an epitaxial silicon wafer 100 according to one embodiment of the present invention. [Figure 2] This graph shows the concentration profiles of carbon, hydrogen, and fluorine obtained by SIMS after the formation of the epitaxial layer and before heat treatment in the example. [Figure 3] This graph shows the fluorine concentration profile when the heat treatment temperature is set to 800°C in the example. [Figure 4] This graph shows the relationship between heat treatment time and the peak area of ​​the fluorine concentration profile when the heat treatment temperature is set to 700-1100°C in the example. [Modes for carrying out the invention]

[0019] [Method for manufacturing epitaxial silicon wafers] A method for manufacturing an epitaxial silicon wafer 100 according to one embodiment of the present invention will be described below with reference to the drawings. In Figure 1, for the sake of explanation, the thicknesses of the modified layer 14 and the silicon epitaxial layer 16 relative to the silicon wafer 10 are exaggerated, differing from the actual thickness ratio.

[0020] A method for manufacturing an epitaxial silicon wafer 100 according to one embodiment of the present invention, as shown in Figure 1, comprises: a first step (Figure 1, steps A, B) of irradiating the surface 10A of a silicon wafer 10 with cluster ions 12 containing carbon, hydrogen, and fluorine as constituent elements to form a modified layer 14 in which the constituent elements of the cluster ions 12 are solid-solved in the surface layer of the silicon wafer 10; a second step (Figure 1, steps B, C) of forming a silicon epitaxial layer 16 on the modified layer 14 of the silicon wafer 10 to obtain an epitaxial silicon wafer 100; and a third step (Figure 1, steps C, D) of performing a heat treatment on the epitaxial silicon wafer 100, holding it at a temperature of 600°C to 1000°C in an inert gas atmosphere. The silicon epitaxial layer 16 becomes a device layer for manufacturing semiconductor devices such as BSI-type CIS.

[0021] (1st step) Examples of silicon wafers 10 include bulk single-crystal silicon wafers that do not have an epitaxial layer on the surface 10A that is to be irradiated. Such single-crystal silicon wafers can be obtained by slicing single-crystal silicon ingots grown by the Czochralski method (CZ method) or the floating zone melting method (FZ method) with a wire saw or the like. In addition, carbon and / or nitrogen may be added to the silicon wafer 10 to obtain higher gettering ability. Furthermore, an arbitrary dopant may be added to the silicon wafer 10 at a predetermined concentration to make it n-type or p-type.

[0022] Alternatively, as the silicon wafer 10, an epitaxial silicon wafer may be used, in which a silicon epitaxial layer is formed on the surface of a bulk single-crystal silicon wafer. In this case, the surface of the silicon epitaxial layer becomes the surface 10A of the silicon wafer 10 as the surface to be irradiated. The silicon epitaxial layer can be formed by CVD under general conditions. The silicon epitaxial layer preferably has a thickness in the range of 0.1 to 20 μm, and more preferably in the range of 0.2 to 10 μm.

[0023] As previously described, in the first step (Figure 1, steps A and B), the surface 10A of the silicon wafer 10 is irradiated with cluster ions 12 containing carbon, hydrogen, and fluorine as constituent elements. In this specification, "cluster ions" are obtained by an electron bombardment method, in which electrons collide with gaseous molecules to dissociate the bonds of the gaseous molecules, creating atomic aggregates of various numbers of atoms, causing fragmentation, ionizing these atomic aggregates, and then performing mass separation of the ionized atomic aggregates of various numbers of atoms to extract an ionized atomic aggregate of a specific mass number. In other words, "cluster ions" in this specification are ionized by giving a positive or negative charge to a cluster, which is a mass formed by the aggregation of multiple atoms, and are clearly distinguished from monatomic ions such as carbon ions and monomolecular ions such as carbon monoxide ions. The number of constituent atoms in a cluster ion is usually around 5 to 100. As a cluster ion implantation device using this principle, for example, CLARIS® manufactured by Nissin Ion Equipment Co., Ltd. can be used.

[0024] When a silicon wafer 10 is irradiated with cluster ions 12 containing carbon, hydrogen, and fluorine, the irradiation energy instantly raises the silicon to a high temperature of approximately 1350-1400°C, causing it to melt. Subsequently, the silicon is rapidly cooled, and carbon, hydrogen, and fluorine form solid solutions near the surface of the silicon wafer. In other words, the "modified layer" as used herein refers to a layer in which at least one of the constituent elements of the irradiated cluster ions—carbon, hydrogen, and fluorine—is solid-solved at an interstitial or substitutional position in the crystal of the silicon wafer surface. The modified layer is identified as a region in the SIMS concentration profile of carbon, hydrogen, and fluorine in the depth direction of the silicon wafer where the concentration of at least one element is detected to be higher than the background. After the implantation of cluster ions and before the formation of the epitaxial layer, the modified layer generally extends to the surface of the silicon wafer, down to 1 μm from the surface. In the stage after epitaxial layer formation, carbon diffuses somewhat from the surface to the interior of the silicon wafer, so the surface layer of the silicon wafer (the interface between the epitaxial layer and the silicon wafer) about 2 to 4 μm becomes the modified layer.

[0025] Elements irradiated in the form of cluster ions behave differently depending on the element, but some thermal diffusion occurs during the formation process of the silicon epitaxial layer 16, as described later. However, carbon is an element that does not diffuse easily. Therefore, when carbon is included in the constituent elements of the cluster ions, carbon can be dissolved locally and at a high concentration in the modified layer 14. It is thought that this localized solid-solution region of carbon becomes a powerful gettering site, thereby obtaining high gettering ability.

[0026] On the other hand, hydrogen and fluorine injected into the modified layer 14 are easily diffused during the formation process of the silicon epitaxial layer 16. This embodiment aims to enhance the passivation effect of fluorine by leaving a higher concentration of fluorine in the modified layer 14 after epitaxial growth.

[0027] Irradiation conditions for cluster ions 12 include ion species, cluster size, dose, acceleration voltage, and beam current value.

[0028] The constituent elements of cluster ion 12 are not particularly limited as long as they include carbon, hydrogen, and fluorine, but as an example, they consist of carbon, hydrogen, and fluorine. It is also preferable that the constituent elements of cluster ion 12 include elements other than carbon, hydrogen, and fluorine. In particular, it is preferable that the constituent elements of cluster ion 12 include, in addition to carbon, hydrogen, and fluorine, one or more elements selected from the group consisting of boron, phosphorus, arsenic, and antimony. Since the types of metals that can be efficiently gettered differ depending on the type of element that is dissolved in the solid solution, a wider range of metal contamination can be addressed by dissolving multiple elements in the solid solution. For example, in the case of carbon, nickel (Ni) can be efficiently gettered, and in the case of boron, copper (Cu) and iron (Fe) can be efficiently gettered.

[0029] Gaseous molecules that serve as raw materials for cluster ions include hydrocarbon compounds containing fluorine as a constituent element. Examples include fluoromethane (CH3F), trifluoromethane (CHF3), difluoromethane (CH2F2), tetrafluoroethane (C2H5F), 1,3-difluoropropane (C3H6F2), and 1,4-difluoropentane (C4H8F2).

[0030] Examples of ionic species that can be generated and extracted from the above-mentioned gaseous molecules include CH2F with a mass number of 33 and C2H4F with a mass number of 47.

[0031] The cluster size can be appropriately set between 2 and 100, preferably 60 or fewer, and more preferably 50 or fewer. In this specification, "cluster size" refers to the number of atoms constituting one cluster. The cluster size can be adjusted by adjusting the pressure of the gas ejected from the nozzle, the pressure of the vacuum chamber, the voltage applied to the filament during ionization, etc. The cluster size can be determined by obtaining the cluster number distribution by quadrupole high-frequency field mass spectrometry or time-of-flight mass spectrometry and taking the average value of the cluster number.

[0032] The dose of cluster ions can be adjusted by controlling the ion irradiation time. The dose of each element constituting the cluster ion is determined by the cluster ion species (cluster size) and the cluster ion dose (ions / cm²). 2 ) is determined by the following. Therefore, the dose of cluster ions should be set appropriately according to the cluster ion species so that the dose of each element reaches the desired value.

[0033] From the viewpoint of injecting a high concentration of fluorine into the modified layer 14 and retaining a high concentration of fluorine in the modified layer 14 even after the formation of the epitaxial layer, the dose of fluorine is preferably 5 × 10⁻¹⁰. 12 atoms / cm 2 That is all, more 2 × 10 13 atoms / cm2 or more. On the other hand, the dose amount of fluorine is preferably 1×10 16 atoms / cm 2 or less.

[0034] In particular, in the first step (cluster ion irradiation), the peak area, which is the integrated value of a fluorine concentration profile obtained by SIMS analysis of the modified layer 14 after the second step (epitaxial growth) and before the third step (heat treatment), is 1.0×10 10 atoms / cm 2 It is preferable to carry out the process under conditions equal to or higher than the above. Although the upper limit of the peak area is not particularly limited, in the present embodiment, the peak area is approximately 3.0×10 10 atoms / cm 2 or less.

[0035] From the viewpoint of improving gettering capability, the dose amount of carbon is preferably 1×10 13 atoms / cm 2 or more, more preferably 5×10 13 atoms / cm 2 or more. On the other hand, from the viewpoint of reducing the possibility that a large number of defects are formed on the surface of the silicon epitaxial layer 16 due to damage applied to the surface 10A of the silicon wafer 10, the dose amount of carbon is preferably 1×10 16 atoms / cm 2 or less.

[0036] From the viewpoint of implanting high-concentration hydrogen into the modified layer 14 and allowing high-concentration hydrogen to remain in the modified layer 14 even after the epitaxial layer is formed, the dose amount of hydrogen is preferably 1×10 13 atoms / cm 2 or more, more preferably 5×10 13 atoms / cm 2 or more. On the other hand, the dose amount of hydrogen is preferably 2×1016 atoms / cm 2 The following applies:

[0037] The acceleration voltage of cluster ions, along with the cluster size, affects the peak position of the depth-direction concentration profile of the constituent elements in the reformed layer. In this embodiment, the acceleration voltage of cluster ions can be greater than 0 keV / Cluster and less than 200 keV / Cluster, preferably 100 keV / Cluster or less, and more preferably 80 keV / Cluster or less. Two methods are generally used to adjust the acceleration voltage: (1) electrostatic acceleration and (2) radio frequency acceleration. The former method involves arranging multiple electrodes at equal intervals and applying an equal voltage between them to create an axially uniformly accelerating electric field. The latter method is the linear linac method, which accelerates ions using radio frequency while they are driven in a straight line.

[0038] The beam current value for cluster ions is not particularly limited, but is preferably 50 μA or more, more preferably 100 μA or more, and even more preferably 300 μA or more, because it makes it easier for hydrogen and fluorine to remain in high concentrations in the modified layer 14 even after the formation of the subsequent silicon epitaxial layer 16. On the other hand, if the beam current value is too high, there is a risk of excessive generation of defects in the silicon epitaxial layer 16, so it is preferable to keep the beam current value at 5000 μA or less. The beam current value for cluster ions can be adjusted, for example, by changing the decomposition conditions of the raw material gas in the ion source.

[0039] (2nd process) In the second step (Steps B and C in Figure 1), which is performed after the first step described above, a silicon epitaxial layer 16 is formed on the modified layer 14 of the silicon wafer 10 to obtain an epitaxial silicon wafer 100.

[0040] The silicon epitaxial layer 16 can be formed under general conditions. For example, by using hydrogen as a carrier gas and introducing a source gas such as dichlorosilane or trichlorosilane into the chamber, the silicon epitaxial layer 16 can be epitaxially grown on the modified layer 14 of the silicon wafer 10 by CVD at a temperature generally in the range of 1000 to 1200°C, although the growth temperature will vary depending on the source gas used. The thickness of the silicon epitaxial layer 16 is preferably in the range of 1 to 15 μm. If the thickness is less than 1 μm, the resistivity of the effective region of the silicon epitaxial layer 16 used as the device fabrication region may change due to outward diffusion of dopants from the silicon wafer 10, and if the thickness exceeds 15 μm, it may affect the spectral sensitivity characteristics of the CIS.

[0041] Furthermore, after the first step and prior to the second step, the silicon wafer 10 may be subjected to a recovery heat treatment to restore its crystallinity. In this case, the recovery heat treatment can be performed by holding the silicon wafer 10 at a temperature of 900°C to 1100°C for 10 to 60 minutes in an atmosphere such as nitrogen gas or argon gas. Alternatively, the recovery heat treatment can be performed using a rapid heating and cooling device separate from the epitaxial apparatus, such as an RTA (Rapid Thermal Annealing) or RTO (Rapid Thermal Oxidation).

[0042] (3rd step) In the third step (Figure 1, steps C and D), performed after the second step described above, the epitaxial silicon wafer 100 is subjected to a heat treatment in which it is held at a temperature of 600°C to 1000°C (heat treatment temperature) under an inert gas atmosphere. This allows a higher concentration of fluorine to remain in the surface layer (modified layer 14) of the silicon wafer 10. Although this does not limit the present invention, the inventors believe that this effect is achieved as follows: During epitaxial growth in the second step, a large amount of fluorine diffuses outward from the modified layer 14, but the amount of fluorine that desorbs from the silicon wafer 10 is limited, and the large amount of fluorine that diffuses outward remains dissolved in the bulk portion of the silicon wafer 10. Therefore, it is thought that the fluorine remaining in the bulk portion diffuses again and is recaptured in the modified layer 14 by the heat treatment in the third step.

[0043] The heat treatment atmosphere should be an inert gas atmosphere that does not contain oxidizing or reducing gases. This is because an atmosphere containing oxidizing gases such as oxygen can cause unwanted oxide films to form on the surface, and an atmosphere containing reducing gases such as hydrogen can cause surface roughness. Examples of inert gases include nitrogen and argon, but a nitrogen atmosphere is particularly preferred.

[0044] If the heat treatment temperature is less than 600°C, the effect of recapturing fluorine in the modified layer 14 cannot be sufficiently obtained, and the passivation effect by fluorine in the silicon epitaxial layer cannot be enhanced. For this reason, the heat treatment temperature should be 600°C or higher, preferably 700°C or higher, more preferably 750°C or higher, and even more preferably 800°C or higher.

[0045] If the heat treatment temperature exceeds 1000°C, the amount of fluorine diffusing outward from the modified layer 14 exceeds the amount of fluorine recaptured in the modified layer 14, thus reducing the passivation effect of fluorine in the silicon epitaxial layer. Therefore, the heat treatment temperature should be 1000°C or lower, preferably 900°C or lower, and more preferably 850°C or lower.

[0046] The holding time at the heat treatment temperature (hereinafter also referred to as "heat treatment time") depends on the heat treatment temperature, but from the viewpoint of obtaining sufficient effect in recapturing fluorine in the modified layer 14, it is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 15 minutes or more. Furthermore, if the holding time at the heat treatment temperature is too long, the effect of recapturing fluorine in the modified layer 14 may become saturated or productivity may be impaired, so the holding time is preferably 300 minutes or less, more preferably 240 minutes or less, and even more preferably 120 minutes or less.

[0047] The heat treatment can be performed by removing the epitaxial silicon wafer 100 from the epitaxial growth apparatus and then placing the epitaxial silicon wafer 100 into a separate heat treatment furnace. The heat treatment furnace is not particularly limited, and for example, a rapid heating and cooling heat treatment device such as an RTA or a resistance heating type heat treatment furnace can be used. Specifically, the heat treatment furnace is heated to the heat treatment temperature under an inert gas atmosphere, and then the epitaxial silicon wafer 100 is placed into the heat treatment furnace and held for a predetermined heat treatment time. After that, the epitaxial silicon wafer 100 is removed from the heat treatment furnace.

[0048] The third step, heat treatment, involves analyzing the modified layer 14 after the third step using SIMS to obtain the fluorine concentration profile, which is the peak area (F). A ) is the integral value of the fluorine concentration profile obtained by SIMS analysis of the modified layer 14 after the second step and before the third step, which is the peak area (F B It is preferable to carry out the procedure under conditions where the result is 1.2 times or more of F. A / F B When the ratio becomes 1.2 or higher, the passivation effect of fluorine in the silicon epitaxial layer can be further enhanced. A / F B It is preferably 1.4 or higher. A / F B Since a larger value is preferable, there is no particular upper limit, but in this embodiment it is generally 8.5 or less.

[0049] The manufacturing method of this embodiment described above makes it possible to manufacture epitaxial silicon wafers with a more enhanced passivation effect by fluorine in the silicon epitaxial layer. Furthermore, if the heat treatment of this embodiment is not performed and a large amount of fluorine that diffused outward from the modified layer 14 during epitaxial growth remains dissolved in the bulk portion of the silicon wafer 10, fluorine can easily reach the interface during oxide film formation in the device formation process, raising concerns about inhibition of oxide film growth. This embodiment is preferable in that it eliminates such concerns.

[0050] The semiconductor device formed on the silicon epitaxial layer 16 is not particularly limited and can include, for example, MOSFETs, DRAMs, power transistors, and BSI-type CISs. [Examples]

[0051] [Fabrication of epitaxial silicon wafers] A p-type silicon wafer (diameter: 300 mm, thickness: 775 μm, dopant type: boron, resistivity: 10 Ω·cm) was prepared from a CZ single-crystal silicon ingot. Next, using a cluster ion generator (manufactured by Nisshin Ion Equipment Co., Ltd., CLARIS®), 1,3-difluoropropane (C3H6F2) was ionized as a source gas to generate and extract CH2F cluster ions with a mass number of 33. These were then irradiated onto the surface of the silicon wafer under irradiation conditions of an acceleration voltage of 80 keV / Cluster and a beam current of 100 μA. The dose of cluster ions was 5.0 × 10⁻¹⁶. 14 ions / cm 2 That is, the amount of carbon is 5.0 × 10⁻⁶. 14 atoms / cm 2 Therefore, the hydrogen dose is 1.0 × 10⁻⁶. 15 atoms / cm 2 The fluorine dose is 5.0 × 10⁻⁶. 14 atoms / cm 2 That is the case.

[0052] Next, the silicon wafer after cluster ion irradiation was transported into a single-wafer epitaxial growth apparatus (manufactured by Applied Materials, Inc.), where it underwent a hydrogen bake treatment at 1120°C for 30 seconds. Then, using hydrogen as the carrier gas and trichlorosilane as the source gas, a silicon epitaxial layer (thickness: 5 μm, dopant type: phosphorus, resistivity: 10 Ω·cm) was epitaxially grown on the surface of the silicon wafer on the side where the modified layer was formed, by CVD at 1120°C, thereby obtaining an epitaxial silicon wafer.

[0053] Next, an isothermal treatment was performed on the epitaxial silicon wafer in a 100% nitrogen atmosphere, where it was held at a predetermined heat treatment temperature for a predetermined heat treatment time. Specifically, the horizontal heat treatment furnace was heated to the heat treatment temperature in a nitrogen atmosphere, and then the epitaxial silicon wafer was placed in the horizontal heat treatment furnace and held for the predetermined heat treatment time. After that, the epitaxial silicon wafer was removed from the horizontal heat treatment furnace. The heat treatment temperatures were set to five conditions: 700°C (inventive example), 800°C (inventive example), 900°C (inventive example), 1000°C (inventive example), and 1100°C (comparative example), and the heat treatment times were set to four conditions: 15 minutes, 30 minutes, 120 minutes, and 240 minutes.

[0054] [SIMS analysis] After the formation of the epitaxial layer and before heat treatment, the concentration profiles of carbon, hydrogen, and fluorine in the depth direction from the surface of the silicon epitaxial layer were measured by SIMS, and the obtained concentration profiles are shown in Figure 2. The carbon concentration profile was higher than the background in the range of approximately 3.5 to 7.0 μm from the surface of the silicon epitaxial layer. The hydrogen and fluorine concentration profiles were higher than the background in the range of approximately 4.8 to 5.2 μm from the surface of the silicon epitaxial layer. Therefore, the thickness of the epitaxial layer formed on the silicon wafer was approximately 4.8 μm, and the range of approximately 4.8 to 7.0 μm from the surface of the silicon epitaxial layer was identified as the modified layer formed in the surface layer of the silicon wafer. From this graph, the peak area, which is the integral value of the fluorine concentration profile, was calculated to be 3.0 × 10⁻⁶.10 atoms / cm 2 That was the case.

[0055] Furthermore, after heat treatment under 20 conditions (5 heat treatment temperatures × 4 heat treatment times), the fluorine concentration profile in the depth direction from the surface of the silicon epitaxial layer was measured by SIMS. As a representative example, the fluorine concentration profile when the heat treatment temperature was 800°C is shown in Figure 3. The peak area was also calculated from the fluorine concentration profiles obtained under each condition, and the relationship between heat treatment time and peak area at each heat treatment temperature is shown in Figure 4. The plot for 0 minutes of heat treatment time in Figure 4 represents the peak area obtained from the fluorine concentration profile before heat treatment shown in Figure 2.

[0056] As is clear from Figure 4, when the heat treatment temperature is 700°C and 800°C, the peak area of ​​fluorine increases with increasing heat treatment time, which means that the amount of fluorine captured in the modified layer increases. This fact suggests that when the heat treatment temperature is 700°C and 800°C, fluorine that diffused from the modified layer (injection region), which is the surface layer of the silicon wafer, to the bulk portion during epitaxial growth is diffused and recaptured in the modified layer by the heat treatment.

[0057] When the heat treatment temperature was 900°C, similar to the cases of 700°C and 800°C, the peak area of ​​fluorine increased compared to the case without heat treatment at all heat treatment times, indicating that the amount of fluorine captured in the modified layer could be increased. However, when the heat treatment temperature was 900°C, the peak area of ​​fluorine tended to increase depending on the heat treatment time up to 30 minutes, but the peak area of ​​fluorine tended to decrease in the range of heat treatment times from 120 minutes onward. This suggests that when the heat treatment time is short, the phenomenon of fluorine being recaptured in the modified layer by heat treatment is dominant, whereas when the heat treatment time is long, fluorine from the bulk portion diffuses and is recaptured in the modified layer, and after the bulk portion is depleted of fluorine, fluorine diffuses outward from the modified layer and either returns to the bulk portion or desorbs through the surface of the silicon epitaxial layer.

[0058] When the heat treatment temperature was 1000°C, a heat treatment time of 15 minutes resulted in an increase in the fluorine peak area compared to the case without heat treatment, indicating an increase in the amount of fluorine captured in the modified layer. However, in the range of heat treatment times from 30 minutes onward, the fluorine peak area tended to decrease, and was even lower than the case without heat treatment. This suggests that, at a heat treatment temperature of 1000°C, fluorine recapture and outward diffusion compete, similar to the case at a heat treatment temperature of 900°C, but outward diffusion of fluorine is more dominant than at a heat treatment temperature of 900°C.

[0059] When the heat treatment temperature was 1100°C, the peak area of ​​fluorine decreased as the heat treatment time increased, meaning that the amount of fluorine trapped in the modified layer could not be increased. This fact suggests that, at a heat treatment temperature of 1100°C, outward diffusion of fluorine dissolved in the modified layer is dominant. [Industrial applicability]

[0060] According to the present invention's method for manufacturing epitaxial silicon wafers, it is possible to manufacture epitaxial silicon wafers in which the passivation effect by fluorine in the silicon epitaxial layer is further enhanced.

[0061] Epitaxial silicon wafers are an essential component of semiconductor devices, supporting our daily lives. In particular, CIS (Cylindrical Insulation) is a core component of camera functions in digital cameras and smartphones, and is an indispensable technology for acquiring images and videos. This invention makes it possible to manufacture high-quality epitaxial silicon wafers and provide high-quality, high-precision images. In the medical field, it improves the quality and efficiency of medical care, and contributes to sustainable activities such as improving the health and well-being of society as a whole (Sustainable Development Goal (SDG) 3: "Ensure healthy lives and promote well-being for all at all ages"), and improving social safety and security through the advancement of surveillance and security systems, such as crime prevention and disaster countermeasures (Sustainable Development Goal (SDG) 11: "Make cities inclusive, safe, resilient and sustainable"). [Explanation of Symbols]

[0062] 100 Epitaxial Silicon Wafers 10 silicon wafers 10A Surface of silicon wafer 12 Cluster Ions 14 Modified layer 16 Silicone epitaxial layer

Claims

1. A first step involves irradiating the surface of a silicon wafer with cluster ions containing carbon, hydrogen, and fluorine as constituent elements to form a modified layer on the surface of the silicon wafer in which the constituent elements of the cluster ions are solid-dissolved. A second step is to form a silicon epitaxial layer on the modified layer of the silicon wafer to obtain an epitaxial silicon wafer, Subsequently, a third step is to perform a heat treatment on the epitaxial silicon wafer, holding it at a temperature of 600°C to 1000°C in an inert gas atmosphere. A method for manufacturing an epitaxial silicon wafer having [a certain characteristic].

2. The method for manufacturing an epitaxial silicon wafer according to claim 1, wherein the temperature is 700°C or higher and 900°C or lower.

3. The method for manufacturing an epitaxial silicon wafer according to claim 1 or 2, wherein the inert gas atmosphere is a nitrogen atmosphere.

4. A method for manufacturing an epitaxial silicon wafer according to claim 1 or 2, wherein the holding time at the aforementioned temperature is 5 minutes or more.

5. The first step involves performing SIMS analysis on the modified layer after the second step and before the third step, and the integrated peak area of ​​the fluorine concentration profile obtained is 1.0 × 10⁻⁶. １０ atoms / cm ２ A method for manufacturing an epitaxial silicon wafer according to claim 1 or 2, carried out under the above conditions.

6. The method for manufacturing an epitaxial silicon wafer according to claim 1 or 2, wherein the third step is performed under conditions that the peak area, which is the integral value of the fluorine concentration profile obtained by SIMS analysis of the modified layer after the third step, is 1.2 times or more the peak area, which is the integral value of the fluorine concentration profile obtained by SIMS analysis of the modified layer after the second step and before the third step.

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