TW202122646A - Silicon single crystal substrate and silicon epitaxial wafer for solid-state image sensor and solid-state image sensor - Google Patents

Abstract

The present invention is a silicon single crystal substrate for a solid-state image sensor obtained by slicing a silicon single crystal fabricated by a CZ method, where the silicon single crystal substrate is a p-type silicon single crystal substrate whose main dopant is Ga, and the silicon single crystal substrate has a B concentration of 5*1014 atoms/cm3 or less. This provides a silicon single crystal substrate and a silicon epitaxial wafer for a solid-state image sensor that can suppress the residual image characteristics of a solid-state image sensor.

Description

Silicon single crystal substrates and silicon epitaxial wafers for solid-state imaging devices, and solid-state imaging devices

The present invention relates to a silicon single crystal substrate and a silicon epitaxial wafer for a solid-state imaging device, and a solid-state imaging device.

Some people have used solid-state imaging elements in mobile devices such as smartphones. The solid-state imaging element captures the carriers generated by light in the depletion layer region (photodiode) of the PN junction, and converts the optical information into electronic information to obtain images (photoelectric conversion). In recent years, with the increase in the number of images, by placing the cache memory near the photodiode, most images can be obtained in a short time. In addition to high image quality, it can also shoot everything that was difficult to capture in the past. Instant photos. This is because the data can be read from the photodiode in a short time.

The current problem lies in the afterimage characteristics. This is a phenomenon in which the "carriers generated by the photoelectric effect" are captured and released after a certain period of time, which will cause the image to appear to remain behind due to the influence of the carriers. In the case of high-functionality and short-time acquisition of most data, if there is this afterimage, it means that the influence of the previous photographic data will remain. The cause of the afterimage characteristics is a complex of boron and oxygen in the substrate (see Non-Patent Documents 1 and 2 and Patent Documents 1 and 2).

In addition, in recent years, expectations for autonomous driving have increased. Therefore, LiDAR (LiDAR) systems have attracted attention as sensors (eyes). This is a technology that "irradiates infrared rays as a light source and uses a sensor to capture the reflected light to measure the surrounding conditions (distance)." In the past, it was used in fields such as airplanes or mountain surveys. By combining with millimeter wave, high-precision measurement required for automatic operation can be performed. In this LiDAR system, the sensor part uses solid-state imaging elements. Among them, with regard to the meticulous concept of increasing the sensitivity, people have explored methods such as the use of avalanche breakdown of the diode when a photon is incident on a photodiode to double the amount of carrier generation and increase the sensitivity. In this field, if the previous afterimage characteristics are also produced, the accuracy will be reduced (even if there is no light, but there is light. Also, in order to avoid the afterimage, a delay time is set, resulting in a decrease in time resolution, etc.) Possibility. In addition to this automatic operation, solid-state imaging elements are expected to be used in many fields, for example, visual sensors provided in industrial robots, or medical applications such as surgery.

Since the solid-state imaging element including these photodiodes is manufactured using a silicon substrate, it is very important to develop a substrate that can suppress the afterimage characteristics. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] JP 2019-9212 A [Patent Document 2] Japanese Patent Application Publication No. 2019-79834 [Patent Document 3] Japanese Patent No. 3679366 [Non-Patent Literature]

[Non-Patent Document 1] The 77th Academy of Applied Physics Fall Academic Lecture, Collection of Lectures 14p-P6-10 Tsubasa Kanada, Akira Otani "Explanation of the Mechanism of the After-Image Phenomenon of CMOS Image Sensors 1" [Non-Patent Document 2] The 77th Fall Academic Conference of Applied Physics, Lecture Collection 14p-P6-11 Akira Otani, Tsubasa Kanada "Explanation of the mechanism of the afterimage phenomenon of CMOS image sensors 2"

[The problem to be solved by the invention]

The present invention was made in view of the above-mentioned problems, and its object is to provide a silicon single crystal substrate and a silicon epitaxial wafer for a solid-state imaging device that can suppress the residual image characteristics of the solid-state imaging device. [Technical means to solve the problem]

In order to achieve the above object, the present invention provides a silicon single crystal substrate for a solid-state imaging device, which is a silicon single crystal substrate for a solid-state imaging device obtained by slicing a silicon single crystal produced by the CZ method. The substrate is a p-type silicon single crystal substrate whose main dopant is Ga, and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less.

In this way, if a "p-type silicon single crystal substrate obtained by slicing a silicon single crystal produced by the CZ method (Czochralski method)" is used as a silicon single crystal substrate for solid-state imaging devices, and The main dopant system of the p-type silicon single crystal substrate is Ga (gallium) instead of the commonly used B (boron), and the B concentration in the substrate is less than 5×10 ¹⁴ atoms/cm ³ , which can make The B concentration, which is the cause of the after-image characteristic, is reduced, so that the after-image characteristic can be suppressed regardless of the inter-lattice oxygen concentration. In addition, because it is a CZ substrate, it is superior to the FZ (floating zone) substrate in terms of substrate strength, gettering ability, and substrate diameter.

In addition, the so-called "main dopant" refers to the maximum concentration dopant that determines the conductivity type of the silicon single crystal substrate.

In addition, the inter-lattice oxygen concentration in the p-type silicon single crystal substrate is preferably 1 ppma or more and 15 ppma or less.

If it is less than 15ppma, it can make "even though light is not incident, oxygen will still become the center of production in the depletion layer, and generate electron-hole pairs to cause the phenomenon of charge generation (called white noise, or dark current). "Probability of occurrence" is reduced. On the other hand, if it is 1 ppma or more, it is possible to more reliably prevent "a situation where a decrease in substrate strength or insufficient gettering ability for heavy metal contamination becomes a problem."

In addition, the above-mentioned inter-lattice oxygen concentration value is based on the JEIDA (JEITA) standard. JEIDA is the abbreviation of the Japan Electronics Industry Promotion Association. The JEIDA system shows the use of a defined conversion factor to calculate the inter-lattice oxygen concentration. At present, JEIDA has been renamed JEITA (Electronic Information Technology Industry Association).

Furthermore, the present invention provides a solid-state imaging device including a photodiode portion, a memory portion, and a computing portion. The solid-state imaging device is characterized in that at least the photodiode portion is formed in the solid-state imaging device of the present invention. The silicon single crystal substrate.

The solid-state image sensor includes at least a photodiode part, a memory part, and a computing part. However, since it is the photodiode part that produces the afterimage characteristic, at least the main dopant is Ga and the B concentration is 5×10 ¹⁴ A p-type silicon single crystal substrate of atoms/cm ³ or less is used as a substrate for forming the photodiode, and a solid-state imaging device with suppressed afterimage characteristics can be produced.

Furthermore, the present invention provides a silicon epitaxial wafer for solid-state imaging devices, which is a silicon epitaxial wafer for solid-state imaging devices having a silicon epitaxial layer on the surface of a silicon single crystal substrate, and is characterized in that: the silicon The main dopant of the epitaxial layer system is a p-type epitaxial layer of Ga, and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less.

When using silicon epitaxial wafers to fabricate solid-state imaging devices, since the silicon epitaxial layer (also referred to as the epitaxial layer) that forms the photodiode contains almost no oxygen, even as in the past, the main epitaxial layer The dopant is B, and it should not form a complex of B and oxygen which is the cause of the afterimage characteristics. However, due to the accumulation of the epitaxial layer or the heat treatment in the device manufacturing process, in conventional products, sometimes the oxygen in the silicon single crystal substrate diffuses to the epitaxial layer and causes the afterimage characteristics to occur. However, in the present invention, since the main dopant in the epitaxial layer is Ga and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less, the afterimage characteristic can be suppressed regardless of how oxygen from the substrate diffuses. Furthermore, for example, even if B is contained in a silicon single crystal substrate and the B is diffused into the epitaxial layer, the initial B concentration in the epitaxial layer is extremely low as described above, so the afterimage characteristic can still be suppressed.

In addition, the silicon single crystal substrate can be a p-type silicon single crystal substrate of the main dopant system Ga, and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less.

When the silicon single crystal substrate forming the epitaxial layer contains B and oxygen, depending on their concentration and the heat treatment received by the silicon single crystal substrate, in the past products, sometimes the two elements will diffuse into the epitaxial crystal. Layer and cause the afterimage characteristics to occur. In addition, by setting the main dopant in the silicon single crystal substrate as Ga and setting the B concentration to 5×10 ¹⁴ atoms/cm ³ or less, the afterimage characteristics can be suppressed more reliably.

In addition, the silicon single crystal substrate may be a p ⁺ type silicon single crystal substrate with a main dopant system B and a B concentration of 1×10 ¹⁸ atoms/cm ^{3 or more.}

If it is such a p ⁺ type silicon single crystal substrate, the "getting ability of metal impurities that may be generated by the deposition of the epitaxial layer or the heat treatment of the device manufacturing process" can be further improved. In this case, although there ^{is a concern that B diffuses from the p +} type silicon single crystal substrate to the epitaxial layer, as mentioned above, there is almost no oxygen in the epitaxial layer, so it can be suppressed as a cause of the after-image characteristics The formation of a complex of B and oxygen.

In addition, the silicon single crystal substrate may be a p ^- type silicon single crystal substrate with a main dopant system B and a B concentration of 1×10 ¹⁶ atoms/cm ^{3 or less.}

If it is such a p ^- type silicon single crystal substrate, the "B that diffuses in the epitaxial layer due to the accumulation of the epitaxial layer or the heat treatment in the device manufacturing process" is limited, so the B and B in the epitaxial layer can be suppressed. The formation of oxygen complexes can increase the inter-lattice oxygen concentration of the silicon single crystal substrate to improve the gettering ability and substrate strength.

In addition, the silicon single crystal substrate may be an n-type silicon single crystal substrate.

Since the n-type silicon single crystal substrate contains almost no B, the afterimage characteristic can be suppressed regardless of how the oxygen from the substrate diffuses. The n-type silicon single crystal substrate is also the same as the p ^- type silicon single crystal substrate, which can suppress the formation of a complex of B and oxygen in the epitaxial layer, and can increase the inter-lattice oxygen of the silicon single crystal substrate. Concentration, and improve the gettering ability and substrate strength.

Furthermore, the present invention provides a solid-state imaging device having at least a photodiode portion, a memory portion, and a computing portion, and is characterized in that at least the photodiode portion is formed in the solid-state imaging device of the present invention. The silicon epitaxial layer of the silicon epitaxial wafer used for the device.

The solid-state imaging device has at least a photodiode part, a memory part, and a computing part. However, since it is the photodiode part that produces the afterimage characteristic, at least the main dopant is Ga, and the B concentration is 5×10 ¹⁴ A p-type epitaxial layer of atoms/cm ³ or less is used as an epitaxial layer for forming the photodiode portion, and a solid-state imaging device with suppressed afterimage characteristics can be produced. [Effects of the invention]

As described above, according to the present invention, it is possible to provide a silicon single crystal substrate for a solid-state imaging device and a solid-state imaging device that can suppress the residual image characteristics of the solid-state imaging device. In addition, it is possible to provide a silicon epitaxial wafer and a solid-state imaging device for a solid-state imaging device that can suppress the residual image characteristics of the solid-state imaging device.

The inventors of the present case have devoted themselves to the research results of "suppression of residual image characteristics of solid-state imaging devices". In particular, they focused on the complex of B and oxygen related to the residual image characteristics. In order to reduce the complex, he considered using Ga instead of B as p Type of main dopant.

In addition, the use of Ga instead of B as an example of the p-type dopant is known to be useful as a silicon single crystal for solar cells (Patent Document 3).

However, solar cells and solid-state imaging devices can be described as different in manufacturing processes and manufacturers, and their technical fields are also different. In addition, the system for solar cells aims to obtain the effect of suppressing light degradation, and the system for solid-state imaging elements aims to obtain the effect of suppressing the afterimage characteristics, and therefore, the intended effect is completely different. Therefore, an example of using a p-type silicon single crystal substrate with Ga as the main dopant as a silicon single crystal substrate for a solid-state imaging device has not existed so far, or even an idea.

In addition, we believe that if the formation of a complex of B and oxygen related to the afterimage characteristics is to be suppressed, the goal of reducing the oxygen concentration is to use FZ substrates (from silicon that is produced by the FZ method and contains almost no oxygen). A silicon single crystal substrate obtained by slicing a single crystal).

However, when the FZ substrate is used as a solid-state imaging element, it has the following disadvantages, so it is almost never used as a solid-state imaging element: (1) Since it contains almost no oxygen, the substrate strength is low, and it cannot be obtained. The gettering ability caused by oxygen precipitates, (2) Since nitrogen is doped in order to increase the strength of the substrate, the resistivity will change due to the production of nitrogen donors and the width of the depletion layer of the photodiode will change. It has an impact on the component characteristics, (3) Compared with the CZ substrate, the diameter is one generation smaller (currently the largest diameter in the mass production level, the CZ substrate is 300mm and the FZ substrate is 200mm) and so on.

As mentioned above, we have found that as long as the main dopant is Ga p-type CZ silicon single crystal substrate, and the B concentration is lower than 5×10 ¹⁴ atoms/cm ³ , there will be a better solid The residual image characteristics of the imaging element or the strength of the substrate, etc., have completed the present invention. In addition, we have found that as long as a silicon epitaxial wafer with the same epitaxial silicon layer as the Ga and B conditions described above, there will be better afterimage characteristics of the solid-state imaging device, thus completing the present invention.

Hereinafter, for an example of the embodiment, the present invention will be described in detail with reference to the drawings, but the present invention is not limited to this embodiment.

The schematic diagram of the silicon single crystal substrate for the solid-state imaging device of the present invention is shown in FIG. 1. As shown in FIG. 1, the silicon single crystal substrate 10 of the present invention is a p-type CZ silicon single crystal substrate whose main dopant is Ga, and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less. First of all, because it is a silicon single crystal substrate produced by the CZ method, for example, compared with the FZ silicon single crystal substrate which contains almost no oxygen, it has "higher substrate strength" and "can obtain the result of oxygen precipitation. "Gettering ability", and "substrate diameter is one generation larger" and other advantages. In addition, the diameter of the substrate is not particularly limited, but, for example, it may be 300 mm or more, and furthermore, it may be 450 mm or more.

In addition, the main dopant, that is, the dopant that determines the conductivity of the substrate, is not B doped in the conventional silicon single crystal substrate for solid-state imaging devices, but Ga. In addition, the B concentration is a low value of ^{5×10 14} atoms/cm ^{3 or less.} _{Therefore, the silicon single crystal substrate of the present invention can suppress the "after-image characteristics due to BO 2} complex" that would be a problem when manufacturing solid-state imaging devices with conventional products whose main dopant is B, and can provide no matter the crystal lattice What's the oxygen concentration, the quality is better than that of the conventional solid-state imaging device in terms of after-image characteristics. The Ga concentration is not particularly limited, and can be appropriately determined according to the desired resistivity and the like. In addition, the lower limit of the B concentration is not particularly limited. Although there is the possibility of unavoidable mixing during single crystal manufacturing, in order to prevent the formation of the above-mentioned BO ₂ complex, it is better to use as little as possible. In addition, as for the dopant, as long as the above conditions are satisfied, other dopants other than Ga and B may be mixed.

In addition, the oxygen concentration of the silicon single crystal substrate 10 may be, for example, 1 ppma or more and 15 ppma or less. If it is less than 15ppma, "even though light is not incident, oxygen will still be the center of production in the depletion layer, and electron-hole pairs will be generated, resulting in the probability of white noise (or dark current) generated by the charge" being reduced. . In addition, if it is 1 ppma or more, it is possible to more reliably prevent "a situation where a decrease in substrate strength or insufficient gettering ability for heavy metal contamination becomes a problem." Moreover, it is preferably 10 ppma or less, and more preferably 5 ppma or less.

Hereinafter, an example of such a manufacturing method of the silicon single crystal substrate 10 of the present invention will be described in detail. First, referring to FIG. 2 and showing a configuration example of a single crystal pulling device performed by the CZ method.

The single crystal pulling device 20 is composed of "bottom chamber 202 for storing the crucible 201 of molten raw material" and "top chamber 204 for storing and taking out the lifted single crystal (single crystal rod) 203" constitute. In addition, a wire winding mechanism 205 for pulling the single crystal is provided at the top of the top chamber 204, and the wire 206 is lowered or rolled up in accordance with the growth of the single crystal. In addition, at the front end of the wire 206, a seed crystal 207 for pulling the silicon single crystal is mounted on the seed crystal support part 208.

On the other hand, the crucible 201 in the bottom chamber 202 is composed of a quartz crucible 209 on the inside and a graphite crucible 210 on the outside. A heater 211 is arranged around the crucible 201 for adding polysilicon to the crucible. The raw material is melted, and further, the heater is surrounded by a heat insulating material 212. In addition, the inside of the crucible 201 is filled with a silicon melt 216 melted by heating with a heater. In addition, the crucible 201 is supported by a support shaft 213 that can rotate and move up and down. For this purpose, a driving device 214 is installed at the bottom of the bottom chamber 202. In addition, a rectifying cylinder 215 may also be used to rectify the passive gas introduced into the furnace.

Next, a method of manufacturing a silicon single crystal using the above-mentioned device will be explained. First, the polysilicon raw material and the dopant, namely Ga, are placed in the crucible 201 and heated by the heater 211 to melt the raw material. In this aspect, Ga and polysilicon raw materials are placed in a crucible together before melting. However, because of the need for fine concentration adjustment during mass production, it is desirable to produce high-concentration Ga-doped silicon single crystals and then pulverize them into fine particles. The dopant is prepared by the material, and the dopant is inserted after the polysilicon raw material is melted to adjust the concentration to the desired concentration.

Then, after the polysilicon raw materials are all melted, a seed crystal 207 for growing a single crystal rod is installed at the front end of the wire 206 of the winding mechanism 205, and the wire 206 is gently lowered so that the front end of the seed crystal 207 is in contact with the silicon melt liquid. 216 contacts. At this time, the crucible 201 and the seed crystal 207 are rotating in opposite directions, and the inside of the pulling machine is in a decompressed state, and is in a state filled with a passive gas such as argon flowing in from the top of the furnace.

After the temperature around the seed crystal 207 has stabilized, while the seed crystal 207 and the crucible 201 are rotated in opposite directions to each other, the wire 206 is gently wound and the seed crystal 207 is started to be pulled up. In addition, it is implemented to eliminate the necking (necking) of the slip dislocation generated in the seed crystal 207. After the necking is performed to eliminate the thickness and length of the sliding difference row, the diameter is gradually enlarged to produce the cone portion of the single crystal 203, and the diameter is enlarged to the desired diameter. When the diameter of the cone is expanded to a predetermined diameter, it is transformed into a fixed-diameter part (cylindrical part) for making a single crystal rod. At this time, the rotation speed of the crucible, the pick-up speed, the pressure of the passive gas in the chamber, the flow rate, etc., are appropriately adjusted according to the oxygen concentration contained in the grown single crystal. In addition, the crystal diameter is controlled by adjusting the temperature and the pulling speed.

After pulling the single crystal cylindrical part to a predetermined length, this time, after the diameter of the crystal is reduced and the tail is finished, the front end of the tail is separated from the silicon melting liquid surface, and the grown silicon single crystal is rolled up to the top cavity Chamber 204 while waiting for the crystal to cool. After the single crystal rod is cooled to a temperature at which it can be taken out, it is transferred from the pulling machine to the process of processing the crystal into a wafer.

In the processing process, first, the cone part and the tail part are cut, and the periphery of the single crystal rod is cylindrically polished to cut and process the block into an appropriate size. In addition, the single crystal block of the appropriate size is sliced by a slicing machine to form a wafer, and then chamfering, polishing, etc. are performed as needed, and the deformation is further removed by etching to produce a crystal as a substrate. round.

In the above-mentioned example, an example in which only Ga is intentionally doped is given, but the dopant is not limited to this. It is only necessary that Ga doping is used as the main dopant that determines the conductivity type, and the B concentration should be 5×10 ¹⁴ atoms/cm ³ or less. It can be appropriately determined according to the desired resistivity and the like. The resistivity for the solid-state imaging element is preferably in the range of 0.1 to 20 Ωcm, for example.

Fig. 3A shows an example of the solid-state imaging device of the present invention. Here, the "back-illuminated solid-state imaging device" is taken as an example, but the present invention is not limited to this. The solid-state imaging device 30 includes a photodiode unit 303, a memory unit, and a computing unit 304. The solid-state imaging element 30 is formed by forming various elements on the first substrate 301 (the silicon single crystal substrate 10 of the present invention) and the second substrate 302 and bonding them. The first substrate, which forms the photodiode portion 303, is a p-type CZ silicon single crystal substrate with Ga as the main dopant as the silicon single crystal substrate 10 of the present invention, and the B concentration is 5×10 ¹⁴ atoms /cm ³ or less. On the other hand, the second substrate may be, for example, a CZ silicon single crystal substrate. It is not that the main dopant is Ga like the first substrate, but can be appropriately determined.

In the case of such a solid-state imaging element 30, since the photodiode portion 303 produces the after-image characteristics, the p-type CZ silicon single crystal substrate with Ga as the main dopant is used at least in the first substrate 301, and B The concentration is 5×10 ¹⁴ atoms/cm ³ or less, and it becomes a solid-state imaging element capable of suppressing afterimage characteristics.

Moreover, an example of such a manufacturing method of the solid-state imaging element 30 is shown in FIG. 3B. First, the first substrate 301 and the second substrate 302, which are the substrates of the present invention, are prepared. For these substrates, in addition to forming gate oxide films 305 and the like to form various elements (photodiode portion 303 (light-receiving element), memory portion, and arithmetic portion 304), STI (element separation) 306 and wiring 307 are also formed. , Interlayer insulating film 308 and so on. After that, the first substrate 301 and the second substrate 302 on which various elements are formed are bonded together to produce a solid-state imaging element 30.

In addition, the following description is different from the "solid-state imaging device using a silicon epitaxial wafer capable of suppressing residual image characteristics" in the "state of the solid-state imaging device using the above-mentioned silicon single crystal substrate". First, a schematic diagram of the epitaxial silicon wafer used for the solid-state imaging device of the present invention is shown in FIG. 7. As shown in FIG. 7, the silicon epitaxial wafer 70 of the present invention is on the surface of the silicon single crystal substrate 702, and has a p-type silicon ^{epitaxy whose main dopant is Ga and the B concentration is below 5×10 14} atoms/cm ³晶层701. In the case of such a silicon epitaxial wafer 70, since the original B concentration in the silicon epitaxial layer 701 is extremely low, it also contains almost no oxygen. Therefore, even if oxygen or B diffuses from the silicon single crystal substrate 702, the difference between oxygen and B The formation of the complex is suppressed, and the afterimage characteristic can be suppressed. In addition, the silicon single crystal substrate 702 itself (for example, main dopants, etc.) is not limited and can be appropriately determined. The following is an example of the silicon single crystal substrate 702.

The silicon single crystal substrate 702 may be, for example, a p-type silicon single crystal substrate with a ^{main dopant system Ga and a B concentration of 5×10 14} atoms/cm ^{3 or less.} If it is such a p-type silicon single crystal substrate, it is possible to more reliably suppress the occurrence of "diffusion of B and oxygen into the silicon epitaxial layer 701 due to the heat treatment accepted by the silicon single crystal substrate".

In addition, the silicon single crystal substrate 702 may be, for example, a p ⁺ type silicon single crystal substrate with a ^{main dopant system B and a B concentration of 1×10 18} atoms/cm ^{3 or more.} If it is such a p ⁺ type silicon single crystal substrate, the "gettering ability of metal impurities that may be generated by the deposition of the silicon epitaxial layer 701 or the heat treatment in the device manufacturing process" can be further improved. In this case, although there ^{is a concern that B diffuses from the p +} type silicon single crystal substrate to the epitaxial layer, since there is almost no oxygen in the epitaxial layer, it is possible to suppress the "B and oxygen" which is the cause of the afterimage characteristics. The formation of the complex". The upper limit of the B concentration is not particularly limited, but the higher the better, for example, it may be the solid solution limit of B for silicon single crystal. At this time, the ^{inter-lattice oxygen concentration of the p +} type silicon single crystal substrate is not limited, but in order to more reliably prevent oxygen from ^{diffusing from the p +} type silicon single crystal substrate to the epitaxial layer, it is preferable to remove the inter-lattice oxygen The concentration is set at 20 ppma or less, more preferably at 15 ppma or less.

In addition, the silicon single crystal substrate 702 may be, for example, a p ^- type silicon single crystal substrate with a ^{main dopant system B and a B concentration of 1×10 16} atoms/cm ^{3 or less.} If it is such a p ^- type silicon single crystal substrate, since the "B that diffuses into the epitaxial layer due to the deposition of the epitaxial layer or the heat treatment in the device manufacturing process" is limited, it can more reliably suppress the epitaxial layer The formation of a complex of B and oxygen can improve the gettering ability and the strength of the substrate by increasing the oxygen concentration between the crystal lattices of the silicon single crystal substrate. The lower limit of the B concentration is not particularly limited, and the lower the concentration, the more the formation of the complex of B and oxygen can be suppressed.

In addition, the silicon single crystal substrate 702 may be, for example, an n-type silicon single crystal substrate. If an n-type single crystal silicon substrate, since almost no B, and therefore the p ^- -type silicon single crystal substrate in the same manner, can more reliably inhibit the formation of oxygen complex of B in the epitaxial layer, and may by By increasing the inter-lattice oxygen concentration of the silicon single crystal substrate, the gettering ability and substrate strength are improved.

Next, a method of manufacturing such an epitaxial silicon wafer of the present invention will be described. First, the silicon single crystal substrate 702 can be obtained by, for example, manufacturing, slicing, chamfering, etc. using the single crystal pulling device 20 of the CZ method as shown in FIG. 2. In addition, in the case of intentional doping of B, it is sufficient to melt the B dopant with the raw material at a desired concentration during single crystal pulling. In addition, a silicon epitaxial layer 701 is stacked on the manufactured silicon single crystal substrate 702. In this case, the epitaxial device used is not particularly limited, and for example, the same device as the conventional one can be used. A silicon single crystal substrate 702 is placed on a susceptor in the furnace, and the furnace is heated, while trichlorosilane is used as carrier gas and raw material gas to flow in the furnace, and for Ga doping, for example, salt is also included. Gallium gas flows together. With this, it is possible to stack an epitaxial layer 701 whose main dopant is Ga p-type, and even if B is unavoidably mixed, the concentration can be suppressed to 5×10 ¹⁴ atoms/cm ³ or less (the lower the better) ”, and the silicon epitaxial wafer 70 of the present invention can be manufactured. In addition, the method of Ga doping is not limited to the above-mentioned method, and can be appropriately determined according to the desired concentration and the like.

Next, a solid-state imaging device using such a silicon epitaxial wafer will be described, but the present invention is not limited to this. It is the same as the solid-state imaging device 30 using the silicon single crystal substrate of FIG. 3A, and is a solid-state imaging device having a photodiode portion, a memory portion, and a computing portion. However, in the example of FIG. 3A, the first substrate 301 forming the photodiode portion 303 is the silicon single crystal substrate 10 of the present invention, but here is replaced by the aforementioned silicon epitaxial wafer 70. The silicon epitaxial layer forming the photodiode part, at least the main dopant in the silicon epitaxial layer is Ga, and the B concentration is below 5×10 ¹⁴ atoms/cm ³ , the quality of the system is better than that in terms of the residual image characteristics Conventional solid-state imaging element. [Example]

Hereinafter, examples and comparative examples are shown to explain the present invention more specifically, but the present invention is not limited to these.

(Example 1) A CZ silicon single crystal was lifted using the device of FIG. 2 and sliced to produce a p-type silicon single crystal substrate for the solid-state imaging device of the present invention whose main dopant was Ga. At the time of production, the specific parameters are as follows. In addition, although Ga is intentionally doped, B is unavoidable. Diameter 300mm, crystal orientation <100>, oxygen concentration: 3.4-10.5ppma, resistivity 5Ωcm, Ga concentration: 3×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (by SIMS Below the lower limit of measurement).

(Comparative Example 1) A p-type silicon single crystal substrate for a conventional solid-state imaging device with B as the main dopant was produced. At the time of production, the specific parameters are as follows. Otherwise, it was produced in the same manner as in Example 1. Diameter 300mm, crystal orientation <100>, oxygen concentration: 3.4 to 10.5ppma, resistivity 10Ωcm, B concentration: 1×10 ¹⁵ atoms/cm ³

The substrates of Example 1 and Comparative Example 1 were used to form PN junctions, and the oxygen concentration dependence of residual image characteristics was compared at the substrate level (evaluated by the "leakage current ratio before and after light irradiation" after annealing at 450°C for 75 hours). The evaluation device and method will be detailed below.

In order to explain the specific evaluation method, an example of the residual image characteristic evaluation device 40 is shown in FIG. 4. The evaluation device is composed of "a device (illumination) 403 for irradiating light to a semiconductor substrate 402 with a PN junction structure 401", an "optical fiber 404", and "a device (illumination meter) 405 with a light quantity measuring light", and Kelvin probe (Kelvin Probe) 406 current measuring device (SMU) 407" constitutes. In addition, after setting the substrate and irradiating the surface of the semiconductor substrate 402 with light of a predetermined illuminance for a predetermined time (the light irradiation step), perform the "after turning off the light irradiation, and measuring the amount of carrier generation after the light irradiation" step.

Here, a white light LED is used for light irradiation. Also, the amount of light at the time of measurement was 500 lux. In addition, the light irradiation time is 10 seconds.

Next, the amount of carriers generated by the PN junction thus formed was measured. The specific timing diagram of light irradiation and measurement is shown in Figure 5. FIG. 5 is a diagram showing an example of the measurement sequence of the evaluation method of the semiconductor substrate.

The amount of carriers generated by light irradiation is affected by the type of semiconductor substrate 402 or the light elements contained in the semiconductor substrate 402, especially carbon elements. Therefore, in order to avoid the initial difference in the amount of carriers generated by light irradiation, which will affect the afterimage characteristics, as shown in Figure 5, the amount of carrier generation (the amount of carriers during light irradiation is measured at one time while the light is irradiated). Child production). In this way, the difference in the amount of initially generated carriers can be taken into consideration, and the semiconductor substrate can be evaluated.

In addition, the measurement time of the carrier generation amount after the light irradiation after the light irradiation was turned off was set to 1 second. In addition, in FIG. 5, the reason why the measurement was once stopped before the measurement of the carrier generation amount after the light irradiation is turned off is to more reliably avoid the noise when the light is turned off.

In addition, the ratio of the current value of the probe is measured by the carrier measurement when the light irradiation is turned on/off to evaluate the afterimage characteristics. For example, the current value after the light irradiation is turned off is higher, which indicates that the carriers are trapped accordingly, and it can be inferred that the afterimage characteristics will be poor.

In the actual example of a solid-state imaging device, it also generates charges by "electron-hole pairs generated by light incident when the shutter is opened", and constructs an image by introducing the charges, but after closing the shutter It is very important to release electron holes quickly. If the release is too slow, it will act as an afterimage, which will affect the next frame.

(Evaluation results of Example 1 and Comparative Example 1) The evaluation results are shown in FIG. 6. In the case of Comparative Example 1 (the main doping is B), it is found that at any oxygen concentration [Oi], compared with Example 1 (the main doping is Ga), the current ratio before and after light irradiation will be larger, and the residual image The characteristics are poor. Specifically, the current ratio before and after light irradiation was 2.7 to 5.2 in Comparative Example 1, and 1.2 to 1.6 in Example 1. If the annealing is performed at 450°C for 75 hours, the current value will change in Comparative Example 1 of B-doped crystals with _{BO 2} defects, but the formation _{of BO 2 is suppressed in Example 1 of Ga-doped crystals.} Changes in current value (changes in residual image characteristics) are suppressed. In addition, in Comparative Example 1, it was found that the current ratio increased as the oxygen concentration increased, and the afterimage characteristics tended to deteriorate as the oxygen concentration increased. On the other hand, in the case of Example 1, even if the oxygen concentration is increased, the current ratio before and after light irradiation is almost fixed at a low value (a value close to 1), and it can be judged that the afterimage characteristics are good.

(Example 2) A CZ silicon single crystal was lifted using the apparatus of FIG. 2 and sliced to produce a p-type silicon single crystal substrate for the solid-state imaging device of the present invention whose main dopant was Ga. At the time of production, the specific parameters are as follows. In addition to Ga, B is also intentionally doped with a small amount to make it. Diameter 300mm, crystal orientation <100>, oxygen concentration: 5ppma, resistivity 4Ωcm, Ga concentration: 3×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹⁴ atoms/cm ³ and the same as in Example 1. Method to evaluate the afterimage characteristics.

(Evaluation result of Example 2) The current ratio before and after the light irradiation is about 1.6, and it can be judged that the afterimage characteristic is good.

(Example 3) In order to fabricate the silicon epitaxial wafer for the solid-state imaging device of the present invention, first, the CZ silicon single crystal was pulled up using the device shown in FIG. 2, and then sliced to produce a p-type dopant with Ga as the main dopant. A silicon single crystal substrate, and on this substrate, a p-type epitaxial layer whose main dopant is Ga is formed. At the time of production, the specific parameters are as follows. (Silicon single crystal substrate) Diameter 300mm, crystal orientation <100>, oxygen concentration: 15ppma, resistivity 4Ωcm, Ga concentration: 3×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (by Below the lower limit measured by SIMS) (Silicon epitaxial layer) Film thickness of epitaxial layer: 5μm, resistivity 10Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (less than the lower limit value measured by SIMS) In addition, the afterimage characteristics were evaluated in the same manner as in Example 1.

(Evaluation result of Example 3) The current ratio before and after the light irradiation is about 1.8, and it can be judged that the afterimage characteristics are good.

(Comparative Example 2) Except that B (concentration of B in the epitaxial layer: 1×10 ¹⁵ atoms/cm ³ ) was used instead of Ga as the dopant of the silicon epitaxial layer, it was produced under the same conditions as in Example 3 The silicon epitaxial wafer was crystallized, and the afterimage characteristics were evaluated in the same manner as in Example 1.

(Evaluation result of Comparative Example 2) The current ratio before and after light irradiation was about 8.2, which was larger than Example 3, and it was judged that the residual image characteristics were poor.

(Embodiment 4) In order to fabricate the silicon epitaxial wafer for the solid-state imaging device of the present invention, first, the CZ silicon single crystal is pulled up using the device shown in FIG. 2, and then sliced to produce p ^{+ whose main dopant is B} Type silicon single crystal substrate, and on this substrate, a p-type epitaxial layer whose main dopant is Ga is formed. At the time of production, the specific parameters are as follows. (Si single crystal substrate) diameter 300mm, crystal orientation <100>, oxygen concentration: 10ppma, resistivity 0.01Ωcm, B concentration: 8.5×10 ¹⁸ atoms/cm ³ (silicon epitaxial layer) epitaxial layer film thickness: 5μm, Resistivity 10Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (less than the lower limit measured by SIMS) Also, in the same manner as in Example 1 Perform an evaluation of the afterimage characteristics.

(Evaluation result of Example 4) The current ratio before and after light irradiation was about 2.1, and it was judged that the afterimage characteristics were good.

(Example 5) In order to produce solid-state imaging device of the present invention with the silicon epitaxial wafer, first, the device of FIG 2 CZ silicon single crystal pulling, slice together to prepare a main dopant is B, p ^- Type silicon single crystal substrate, and on this substrate, a p-type epitaxial layer whose main dopant is Ga is formed. At the time of production, the specific parameters are as follows. (Si single crystal substrate) Diameter 300mm, crystal orientation <100>, oxygen concentration: 15ppma, resistivity 10Ωcm, B concentration: 1×10 ¹⁵ atoms/cm ³ (silicon epitaxial layer) epitaxial layer film thickness: 5μm, resistance Rate 10Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (less than the lower limit measured by SIMS) Also, proceed in the same way as in Example 1. Evaluation of afterimage characteristics.

(Evaluation result of Example 5) The current ratio before and after the light irradiation is about 2.2, and it can be judged that the afterimage characteristic is good.

(Embodiment 6) In order to fabricate the silicon epitaxial wafer for the solid-state imaging device of the present invention, first, the CZ silicon single crystal was lifted using the device of FIG. 2 and then sliced to produce a p-type dopant with Ga as the main dopant. A silicon single crystal substrate, and on this substrate, a p-type epitaxial layer whose main dopant is Ga is formed. At the time of production, the specific parameters are as follows. In addition, in addition to Ga, the epitaxial layer is fabricated by deliberately doping with a small amount of B. (Silicon single crystal substrate) Diameter 300mm, crystal orientation <100>, oxygen concentration: 15ppma, resistivity 4Ωcm, Ga concentration: 3×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (by Below the lower limit measured by SIMS) (Silicon epitaxial layer) Film thickness of epitaxial layer: 5μm, resistivity 8Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹⁴ atoms/cm ³ Also, the evaluation of the residual image characteristics was performed in the same manner as in Example 1.

(Evaluation result of Example 6) The current ratio before and after light irradiation was about 2.3, and it was judged that the afterimage characteristics were good.

In addition, the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, as long as they have substantially the same constitution as the technical idea described in the patent application scope of the present invention, and can exert the same functions and effects, any aspects are included in the technical scope of the present invention.

10: p-type silicon single crystal substrate 20: Single crystal pulling device 201: Crucible 202: bottom chamber 203: Single crystal 204: top chamber 205: winding mechanism 206: Line 207: Seed 208: Seed Support Department 209: Quartz Crucible 210: Graphite crucible 211: heater 212: heat insulation material 213: Support shaft 214: Drive 215: rectifier tube 216: Silicon melt 30: solid-state image sensor 301: first substrate 302: second substrate 303: Light Diode 304: memory unit and computing unit 305: gate oxide film 306: STI (component separation) 307: Wiring 308: Interlayer insulating film 40: Afterimage characteristic evaluation device 401: PN splicing 402: Substrate 403: Lighting 404: Optical fiber 405: Illuminance meter 406: Kevin Probe 407: Current Measuring Unit (SMU) 70: Silicon epitaxial wafer 701: p-type silicon epitaxial layer 702: silicon single crystal substrate

FIG. 1 is a schematic diagram showing an example of a silicon single crystal substrate for a solid-state imaging device of the present invention. FIG. 2 is a schematic diagram showing an example of a single crystal pulling device performed by the CZ method. Fig. 3A is a schematic diagram showing an example of the solid-state imaging device of the present invention. FIG. 3B is a schematic diagram showing an example of the method of manufacturing the solid-state imaging device of the present invention. Fig. 4 is a configuration diagram showing an example of an afterimage characteristic evaluation device. FIG. 5 is a diagram showing an example of the measurement sequence of the evaluation method of the semiconductor substrate. FIG. 6 is a graph showing the evaluation results of the residual image characteristics of Example 1 and Comparative Example 1. FIG. FIG. 7 is a schematic diagram showing an example of the epitaxial silicon wafer for the solid-state imaging device of the present invention.

10: p-type silicon single crystal substrate

Claims (9)

A silicon single crystal substrate for a solid-state imaging element is a silicon single crystal substrate for a solid-state imaging element obtained by slicing a silicon single crystal produced by the Czochralski method (Czochralski method). The crystal substrate is a p-type silicon single crystal substrate whose main dopant is Ga, and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less. The silicon single crystal substrate for a solid-state imaging device according to claim 1, wherein: The inter-lattice oxygen concentration in the p-type silicon single crystal substrate is 1 ppma or more and 15 ppma or less. A solid-state imaging element includes a light diode part, a memory part and a computing part; At least the photodiode portion is formed on the silicon single crystal substrate for the solid-state imaging device described in claim 1 or 2. A silicon epitaxial wafer for solid-state imaging devices, which is a silicon epitaxial wafer for solid-state imaging devices with a silicon epitaxial layer on the surface of a silicon single crystal substrate, the main dopant of which is Ga The p-type epitaxial layer has a B concentration of 5×10 ¹⁴ atoms/cm ³ or less. The silicon epitaxial wafer for a solid-state imaging device according to claim 4, wherein the silicon single crystal substrate is a p-type silicon single crystal substrate whose main dopant is Ga, and the B concentration is 5×10 ¹⁴ atoms/ cm ³ or less. The silicon epitaxial wafer for a solid-state imaging device according to claim 4, wherein the main dopant of the silicon single crystal substrate is a p ⁺ type with a ^{B concentration of 1×10 18} atoms/cm ^{3 or more} Silicon single crystal substrate. The silicon epitaxial wafer for a solid-state imaging device according to claim 4, wherein the main dopant of the silicon single crystal substrate is a p ^- type with a ^{B concentration of 1×10 16} atoms/cm ^{3 or less} Silicon single crystal substrate. The silicon epitaxial wafer for solid-state imaging devices as described in claim 4, wherein: The silicon single crystal substrate is an n-type silicon single crystal substrate. A solid-state imaging element includes a light diode part, a memory part and a computing part; At least the photodiode portion is formed on the epitaxial silicon layer of the epitaxial silicon wafer for the solid-state imaging device according to any one of claims 4 to 8.

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