CN112951932B - Silicon single crystal substrate for solid-state imaging device, silicon epitaxial wafer, and solid-state imaging device - Google Patents

Abstract

Technical problems: the invention provides a silicon single crystal substrate and a silicon epitaxial wafer for a solid-state imaging device, which can inhibit the residual image characteristic of the solid-state imaging device. The solution is as follows: a silicon single crystal substrate for a solid-state imaging device, which is obtained by slicing a silicon single crystal produced by a CZ method, characterized in that the silicon single crystal substrate is a p-type silicon single crystal substrate having Ga as a main dopant and has a B concentration of 5X 10 ¹⁴atoms/cm³ or less.

Description

Silicon single crystal substrate and silicon epitaxial wafer for solid-state imaging components, and solid-state imaging components

Technical Field

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

Background technique

Solid-state imaging components have been applied to mobile devices such as smartphones. Solid-state imaging components capture carriers generated by light through the depletion layer region (photodiode) of the PN junction, thereby converting light information into electronic information to obtain images (photoelectric conversion). In recent years, with the increase in the number of pixels, by setting up a cache near the photodiode, multiple images can be obtained in a short time. In addition to high image quality, it is also possible to take photos of every moment that was difficult to capture in the past. This is because data can be read from the photodiode in a short time.

The current problem is the afterimage characteristic. This is a phenomenon in which the carriers generated by the photoelectric effect are captured and released after a certain period of time, so the image remains due to the influence of the carriers. When high functionality is achieved and multiple data are obtained in a short time, if this afterimage exists, it means that the influence of the previous photographic data will remain. As the cause of the afterimage characteristic, it is believed to be a complex of boron and oxygen in the substrate (see non-patent documents 1, 2 and patent documents 1, 2).

In addition, in recent years, expectations for autonomous driving have increased, so LiDAR (laser radar) has attracted attention as a sensor (eye). This is a technology that uses infrared rays as a light source and captures the reflected light through a sensor to measure the surrounding conditions (distance). In the past, it was used in fields such as aircraft or mountain surveying. By combining with millimeter waves, high-precision measurements required for automatic operation can be performed. In this LiDAR system, a solid-state imaging component is used as a sensor. Among them, regarding the elaborate idea of increasing sensitivity, a method is being discussed in which when photons are incident on a photodiode, the avalanche breakdown (sudden collapse) of the diode is used to double the amount of carriers generated to achieve high sensitivity. In this field, if the previous afterimage characteristics are produced, there is a possibility of reduced accuracy (although there is no light, it is perceived. In addition, in order to avoid afterimages, a delay time is set, resulting in a decrease in time resolution, etc.).

Solid-state imaging devices are expected to be used in many fields other than the above-mentioned automatic operation, such as visual sensors provided in industrial robots, and medical applications such as for surgical operations.

Since solid-state imaging devices that include these photodiodes are manufactured using silicon substrates, it is important to develop substrates that can suppress afterimage characteristics.

Prior art literature

Patent Literature

[Patent Document 1] Japanese Patent Application Publication No. 2019-9212

[Patent Document 2] Japanese Patent Application Publication No. 2019-79834

[Patent Document 3] Japanese Patent No. 3679366

Non-patent literature

[Non-patent document 1] 77th Autumn Symposium of the Society of Applied Physics, Proceedings of the Lectures 14p-P6-10 Kaneda Tsubasa and Otani Akira, “Elucidation of the mechanism of the afterimage phenomenon in CMOS image sensors 1”

[Non-patent document 2] 77th Autumn Symposium of the Society of Applied Physics, Proceedings of the Lectures 14p-P6-10 Kaneda Tsubasa and Otani Akira, “Elucidation of the mechanism of the afterimage phenomenon in CMOS image sensors 2”

Summary of the invention

1. Technical issues to be resolved

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a silicon single crystal substrate and a silicon epitaxial wafer for a solid-state imaging element capable of suppressing the afterimage characteristic of the solid-state imaging element.

(II) Technical solution

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

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 a solid-state imaging component, the B concentration that causes the afterimage characteristic can be reduced, and thus the afterimage characteristic can be suppressed regardless of the intercrystalline oxygen concentration. The main dopant of the 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 .

In addition, since it is a CZ substrate, it can be superior to a FZ (floating zone) substrate in terms of substrate strength, impurity gettering ability, substrate diameter size, etc.

The term “main dopant” refers to a dopant with the maximum concentration that determines the conductivity type of a silicon single crystal substrate.

In addition, preferably, the interstitial oxygen concentration in the p-type silicon single crystal substrate is 1 ppma to 15 ppma.

If it is 15 ppma or less, the probability of occurrence of a phenomenon (called white spots or dark current) in which oxygen becomes a generation center in the depletion layer even when light is not incident, and generates electron-hole pairs, leading to charge generation, can be reduced. On the other hand, if it is 1 ppma or more, it is possible to more reliably prevent a decrease in substrate strength or insufficient gettering ability against heavy metal contamination from becoming a problem.

The above-mentioned interstitial oxygen concentration value is based on the JEIDA (JEITA) standard. JEIDA is the abbreviation of the Japan Electronics Industry Association, and JEIDA indicates that the interstitial oxygen concentration is calculated using a certain conversion factor. Currently, JEIDA has been renamed JEITA (JEITA).

In addition, the present invention provides a solid-state imaging device having a photodiode portion, a memory portion, and a computing portion, characterized in that at least the photodiode portion is formed on a silicon single crystal substrate used for the solid-state imaging device of the present invention.

A solid-state imaging component includes at least a photodiode portion, a memory portion, and a computing portion. Since it is the photodiode portion that produces the afterimage characteristic, a solid-state imaging component with suppressed afterimage characteristics can be manufactured by using a p-type silicon single crystal substrate whose main dopant is Ga and whose B concentration is less than 5×10 ¹⁴ atoms/cm ³ as a substrate on which at least the photodiode portion is formed.

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

When a solid-state imaging device is made using a silicon epitaxial wafer, since oxygen is almost not contained in the silicon epitaxial layer (also simply referred to as the epitaxial layer) that forms the photodiode, even if the main dopant of the epitaxial layer is B as in the past, a complex of B and oxygen that causes the afterimage characteristic should not be formed. However, due to the accumulation of the epitaxial layer or the heat treatment during the device manufacturing process, in existing products, oxygen in the silicon single crystal substrate sometimes diffuses into the epitaxial layer and causes the afterimage characteristic. However, in the present invention, since the main dopant in the epitaxial layer is Ga and the B concentration is less than 5×10 ¹⁴ atoms/cm ³ , the afterimage characteristic can be suppressed regardless of how the oxygen from the substrate diffuses. In addition, even if B is contained in the silicon single crystal substrate and 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 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.

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

In addition, the silicon single crystal substrate is a p ⁺ -type silicon single crystal substrate in which B is the main dopant and the B concentration is 1×10 ¹⁸ atoms/cm ³ or more.

If it is such a p ⁺ type silicon single crystal substrate, it is possible to further improve the "ability to getter metal impurities that may be generated by the accumulation of the epitaxial layer or the heat treatment in the device manufacturing process". In this case, although B may diffuse from the p ⁺ type silicon single crystal substrate to the epitaxial layer, since the epitaxial layer contains almost no oxygen as mentioned above, it is possible to suppress the formation of a complex between B and oxygen that is the cause of the afterimage characteristic.

In addition, the silicon single crystal substrate is a p ^- type silicon single crystal substrate in which the main dopant is B and the B concentration is 1×10 ¹⁶ atoms/cm ³ or less.

If it is such a p ^- type silicon single crystal substrate, since "B diffused in the epitaxial layer due to the accumulation of the epitaxial layer or the heat treatment in the device manufacturing process" is limited, it is possible to suppress the formation of a complex between B and oxygen in the epitaxial layer, and the doping ability and substrate strength can be improved by increasing the intercrystalline oxygen concentration of the silicon single crystal substrate.

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

Since an n-type silicon single crystal substrate contains almost no B, the afterimage characteristic can be suppressed regardless of the diffusion of oxygen from the substrate.

The situation of n-type silicon single crystal substrate is the same as that of p ^- type silicon single crystal substrate. It is possible to suppress the formation of complexes between B and oxygen in the epitaxial layer, and to improve the doping ability and substrate strength by increasing the intercrystalline oxygen concentration of the silicon single crystal substrate.

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

A solid-state imaging component has at least a photodiode portion, a memory portion, and a computing portion. Since it is the photodiode portion that produces the afterimage characteristic, a solid-state imaging component with suppressed afterimage characteristics can be manufactured by using a p-type silicon single crystal substrate whose main dopant is Ga and whose B concentration is less than 5×10 ¹⁴ atoms/cm ³ as an epitaxial layer on which at least the photodiode portion is formed.

(III) Beneficial effects

As described above, according to the present invention, a silicon single crystal substrate for a solid-state imaging component and a solid-state imaging component capable of suppressing the afterimage characteristic of the solid-state imaging component can be provided. In addition, a silicon epitaxial wafer for a solid-state imaging component and a solid-state imaging component capable of suppressing the afterimage characteristic of the solid-state imaging component can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of a silicon single crystal substrate for a solid-state imaging element of the present invention.

FIG. 2 is a schematic diagram showing an example of a single crystal pulling apparatus based on the CZ method.

FIG. 3A is a schematic diagram showing an example of a solid-state imaging device according to the present invention.

FIG. 3B is a schematic diagram showing an example of a method for manufacturing a solid-state imaging device according to the present invention.

FIG. 4 is a diagram showing a configuration of an example of an afterimage characteristic evaluation device.

FIG. 5 is a diagram showing an example of a measurement procedure of a method for evaluating a semiconductor wafer.

FIG. 6 is a graph showing the evaluation results of afterimage characteristics of Example 1 and Comparative Example 1. FIG.

FIG. 7 is a schematic diagram showing an example of a silicon epitaxial wafer for a solid-state imaging device according to the present invention.

Description of Reference Numerals

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: metal wire; 207: seed crystal; 208: seed crystal support; 209: quartz crucible; 210: graphite crucible; 211: heater; 212: heat insulation material; 213: support shaft; 214: driving device; 215: rectifier cylinder; 216: silicon melt; 30: solid-state imaging component; 301: first substrate; 30 2: second substrate; 303: photodiode unit; 304: memory unit and computing unit; 305: gate oxide film; 306: STI (component separation unit); 307: wiring; 308: interlayer insulating film; 40: afterimage characteristic evaluation device; 401: PN junction; 402: substrate; 403: lighting unit; 404: optical fiber; 405: illuminance meter; 406: Kelvin probe; 407: current measuring device (SMU); 70: silicon epitaxial wafer; 701: p-type silicon epitaxial layer; 702: silicon single crystal substrate.

Detailed ways

The inventors of this case have conducted intensive research on suppressing the afterimage characteristics of solid-state imaging devices, and have particularly focused on the complex of B and oxygen related to the afterimage characteristics. In order to reduce the complex, they conceived of using Ga instead of B as the main p-type dopant.

In addition, as an example of using Ga instead of B as a p-type dopant, a silicon single crystal used for a solar cell is known (Patent Document 3).

However, solar cells and solid-state imaging devices have different manufacturing processes and manufacturers, and the technical fields are also different.

In addition, the purpose of using it for solar cells is to obtain the effect of suppressing light degradation, while the purpose of using it for solid-state image sensors is to obtain the effect of suppressing afterimage characteristics. Therefore, the intended effects are completely different.

Therefore, there has been no example or even no idea of using a p-type silicon single crystal substrate with Ga as a main dopant as a silicon single crystal substrate for a solid-state imaging device so far.

In addition, if it is desired to suppress the formation of a complex between B and oxygen related to the afterimage characteristic, it is considered that an FZ substrate (a silicon single crystal substrate obtained by slicing a silicon single crystal produced by the FZ method and containing almost no oxygen) is used with the goal of reducing the oxygen concentration.

However, FZ substrates are rarely used for solid-state imaging components because of the following disadvantages: (1) Since they contain almost no oxygen, the substrate strength is low and the doping ability generated by oxygen precipitates cannot be obtained; (2) Since nitrogen is doped to increase the substrate strength, the resistivity changes due to the generation of nitrogen donors and the width of the depletion layer in the photodiode part changes, which affects the component characteristics; (3) Compared with CZ substrates, the diameter is one generation smaller (the current maximum diameter at the mass production level is 300 mm for CZ substrates and 200 mm for FZ substrates).

As described above, it was found that as long as the p-type CZ silicon single crystal substrate whose main dopant is Ga and the B concentration is a low value of 5×10 ¹⁴ atoms/cm ³ or less, the afterimage characteristics and substrate strength of the solid-state imaging device are good, thereby completing the present invention. In addition, it was found that as long as the silicon epitaxial wafer has a silicon epitaxial layer with the same Ga and B conditions as described above, the afterimage characteristics of the solid-state imaging device are good, thereby completing the present invention.

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

A schematic diagram of a silicon single crystal substrate for a solid-state imaging device in the present invention is shown in Fig. 1. As shown in Fig. 1, a silicon single crystal substrate 10 of the present invention is a p-type CZ silicon single crystal substrate whose main dopant is Ga and whose B concentration is 5×10 ¹⁴ atoms/cm ³ or less.

First, since it is a silicon single crystal substrate produced by the CZ method, it has advantages such as higher substrate strength, ability to obtain gettering ability generated by oxygen precipitates, and a larger substrate diameter than, for example, a FZ silicon single crystal substrate that contains almost no oxygen. In addition, the substrate diameter is not particularly limited, but can be, for example, 300 mm or more, and can also be 450 mm or more.

In addition, the main dopant, i.e., the dopant that determines the conductivity type of the substrate, is not B doped in the silicon single crystal substrate for the existing solid-state imaging device, but Ga. In addition, the B concentration is a low value of 5×10 ¹⁴ atoms/cm ³ or less. Therefore, the present invention can provide such a silicon single crystal substrate that can suppress the "afterimage characteristics caused by BO ₂ complex" that becomes a problem when manufacturing a solid-state imaging device in the existing products where the main dopant is B, and has a better quality than the existing solid-state imaging device in terms of afterimage characteristics regardless of the interstitial oxygen concentration.

The Ga concentration is not particularly limited and can be appropriately determined according to desired resistivity and the like.

The lower limit of the B concentration is not particularly limited. Although it may be unavoidable to mix in during single crystal production, it is preferably as low as possible to prevent the generation of the BO ₂ complex.

In addition, regarding dopants, as long as the above-mentioned conditions are satisfied, other dopants besides Ga and B may be mixed.

The oxygen concentration of the silicon single crystal substrate 10 can be set to, for example, 1 ppma or more and 15 ppma or less.

When the concentration is 15 ppma or less, the probability of occurrence of white spots (or dark current) in which oxygen becomes a generation center in the depletion layer even when light is not incident and generates electron-hole pairs to generate electric charges can be reduced.

In addition, when it is 1 ppma or more, it is possible to more reliably prevent a decrease in substrate strength or insufficient gettering ability against heavy metal contamination from becoming a problem.

In addition, it is preferably 10 ppma or less, and more preferably 5 ppma or less.

An example of a method for producing the silicon single crystal substrate 10 of the present invention will be described in detail below. First, an example of a configuration of a single crystal pulling apparatus based on the CZ method will be shown with reference to FIG.

The single crystal pulling device 20 is composed of a bottom chamber 202 and a top chamber 204. The bottom chamber 202 accommodates a crucible 201 for melting raw materials, and the top chamber 204 accommodates and takes out the pulled single crystal (single crystal rod) 203. In addition, a winding mechanism 205 for pulling the single crystal is provided at the top of the top chamber 204, which lowers or winds up a metal wire 206 according to the growth of the single crystal. In addition, at the front end of the metal wire 206, a seed crystal 207 for pulling a silicon single crystal is installed on a seed crystal support 208.

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

Next, a method for manufacturing a silicon single crystal using the above-mentioned apparatus is described. First, a polycrystalline silicon raw material and a dopant, i.e., Ga, are placed in a crucible 201, and the raw materials are melted by heating with a heater 211. In this embodiment, Ga and the polycrystalline silicon raw material are placed in the crucible together before melting, but because a fine concentration adjustment is required in mass production, it is desired to produce a high-concentration Ga-doped silicon single crystal, and then finely crush it to produce a dopant, and then put it in after the polycrystalline silicon raw material is melted to adjust it to the desired concentration.

Next, after all the polysilicon raw materials are melted, a seed crystal 207 for growing a single crystal rod is installed at the front end of the metal wire 206 of the winding mechanism 205, and the metal wire 206 is gently lowered so that the front end of the seed crystal 207 contacts the silicon melt 216. At this time, the crucible 201 and the seed crystal 207 rotate in opposite directions to each other, and the interior of the puller is in a decompressed state and is filled with an inert gas such as argon flowing in from the top of the furnace.

After the temperature around the seed crystal 207 is stabilized, the metal wire 206 is gently wound and the seed crystal 207 is pulled up while the seed crystal 207 and the crucible 201 are rotated in opposite directions. In addition, necking is performed to eliminate the slip dislocation generated in the seed crystal 207. After necking is performed until the thickness and length of the slip dislocation are eliminated, the diameter is gradually expanded to produce the conical part of the single crystal 203, and the diameter is expanded to the desired diameter. When the cone diameter is expanded to the specified diameter, it is transferred to the sizing part (cylindrical part) for producing the single crystal rod. At this time, the rotation speed of the crucible, the pulling speed, the inert gas pressure in the chamber, the flow rate, etc. are appropriately adjusted according to the oxygen concentration contained in the growing single crystal. In addition, the crystal diameter is controlled by adjusting the temperature and the pulling speed.

After the single crystal cylindrical part is pulled to a predetermined length, the diameter of the crystal is reduced and the tail is made, the front end of the tail is separated from the silicon melt surface, and the grown silicon single crystal is rolled up to the top chamber 204 to wait for the crystal to cool. After the single crystal rod is cooled to a temperature at which it can be taken out, it is taken out from the puller and transferred to the step of processing the crystal into a wafer.

In the processing steps, first, the cone and the tail are cut off, and the periphery of the single crystal rod is cylindrically ground to cut into blocks of appropriate size. In addition, after the single crystal block of appropriate size is sliced into wafers by a slicer, chamfering and polishing are performed as needed, and further etching is performed to remove processing deformation to produce a wafer as a substrate.

In the above example, only Ga is intentionally doped, but the dopant is not limited to this. It is sufficient as long as Ga is doped as a main dopant that determines the conductivity type and the B concentration is set to 5×10 ¹⁴ atoms/cm ³ or less.

It can be appropriately determined according to desired resistivity and the like.

The resistivity of the solid-state image sensor is preferably within a range of 0.1 to 20 Ωcm, for example.

Fig. 3A shows an example of a solid-state imaging device according to the present invention. Here, a 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 device 30 is formed by forming various components on a first substrate 301 (silicon single crystal substrate 10 of the present invention) and a second substrate 302 and bonding them together.

The first substrate, ie, the substrate on which the photodiode portion 303 is formed, is a p-type CZ silicon single crystal substrate whose main dopant is Ga, like the silicon single crystal substrate 10 of the present invention, and whose 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, and its main dopant may not be Ga like the first substrate, and the dopant can be appropriately determined.

In such a solid-state imaging element 30, since it is the photodiode portion 303 that generates the afterimage characteristic, at least the first substrate 301 uses a p-type CZ silicon single crystal substrate whose main dopant is Ga and whose B concentration is less than 5×10 ¹⁴ atoms/cm ³ , thereby achieving a solid-state imaging element with suppressed afterimage characteristics.

In addition, an example of a method for manufacturing the solid-state imaging element 30 is shown in FIG. 3B .

First, the first substrate 301 and the second substrate 302 which are substrates of the present invention are prepared.

For these substrates, in addition to forming a gate oxide film 305 and the like to form various components (photodiode section 303 (light receiving component), memory section and computing section 304), STI (component isolation section) 306, wiring 307, interlayer insulating film 308, etc. are also formed.

Afterwards, the first substrate 301 and the second substrate 302 on which various components are formed are bonded together to manufacture the solid-state imaging component 30 .

In addition, a solid-state imaging device using a silicon epitaxial wafer capable of suppressing afterimage characteristics, which is different from the embodiment of the solid-state imaging device using the silicon single crystal substrate described above, will be described below.

First, a schematic diagram of a silicon epitaxial wafer for a solid-state imaging device in the present invention is shown in FIG7. As shown in FIG7, the silicon epitaxial wafer 70 of the present invention has a p-type silicon epitaxial layer 701 whose main dopant is Ga and whose B concentration is 5×10 ¹⁴ atoms/cm ³ or less on the surface of a silicon single crystal substrate 702. In such a silicon epitaxial wafer 70, since the original B concentration in the silicon epitaxial layer 701 is extremely low and almost no oxygen is contained, even if oxygen or B diffuses from the silicon single crystal substrate 702, it is possible to suppress the formation of a complex between oxygen and B, thereby suppressing the afterimage characteristic.

In addition, the silicon single crystal substrate 702 itself (for example, main dopant, etc.) is not limited and can be appropriately determined. Examples of the silicon single crystal substrate 702 are given below.

The silicon single crystal substrate 702 may be, for example, a p-type silicon single crystal substrate whose main dopant is Ga and whose B concentration is 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 afterimage characteristics caused by diffusion of B and oxygen into the silicon epitaxial layer 701 due to the heat treatment of the silicon single crystal substrate.

In addition, the silicon single crystal substrate 702 can be, for example, a p ⁺ type silicon single crystal substrate whose main dopant is B and whose B concentration is greater than 1×10 ¹⁸ atoms/cm ^3. If it is such a p ⁺ type silicon single crystal substrate, it can further improve the ability to absorb impurities such as metal impurities that may be generated by the accumulation of the silicon epitaxial layer 701 and the heat treatment during the manufacturing process. In this case, although B may diffuse from the p ⁺ type silicon single crystal substrate to the epitaxial layer, since the epitaxial layer contains almost no oxygen, the formation of a complex between B and oxygen that is the cause of the afterimage characteristic can be suppressed. The upper limit of the B concentration is not particularly limited, but the higher the better. For example, it can be the solid solubility limit of B in the silicon single crystal.

At this time, the intercrystalline 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, the intercrystalline oxygen concentration is preferably set to 20 ppma or less, and more preferably set to 15 ppma or less.

In addition, the silicon single crystal substrate 702 may be, for example, a p ^- type silicon single crystal substrate in which the main dopant is B and the B concentration is 1×10 ¹⁶ atoms/cm ³ or less. If it is such a p ^- type silicon single crystal substrate, since "B diffused in the epitaxial layer due to the deposition of the epitaxial layer or the heat treatment in the device manufacturing process" is limited, it is possible to suppress the formation of a complex between B and oxygen in the epitaxial layer, and it is possible to improve the gettering ability and substrate strength by increasing the intercrystalline oxygen concentration of the silicon single crystal substrate. There is no particular lower limit on the B concentration, and the lower the concentration, the more it is possible to suppress the formation of a complex between B and oxygen.

In addition, the silicon single crystal substrate 702 may be, for example, an n-type silicon single crystal substrate. If it is an n-type silicon single crystal substrate, it contains almost no B, so as with a p ^- type silicon single crystal substrate, it is possible to more reliably suppress the formation of a complex between B and oxygen in the epitaxial layer, and it is possible to increase the intercrystalline oxygen concentration of the silicon single crystal substrate, thereby improving the gettering ability and substrate strength.

Next, a method for manufacturing the silicon epitaxial wafer of the present invention described above will be described.

First, the silicon single crystal substrate 702 can be manufactured, for example, using the single crystal pulling apparatus 20 of the CZ method as shown in FIG2 , and obtained by slicing, chamfering, etc. In addition, when B is intentionally doped, when the single crystal is pulled, the B dopant can be melted together with the raw material at the desired concentration.

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 existing one can be used. The silicon single crystal substrate 702 is arranged on a susceptor in a furnace, the furnace is heated, and trichlorosilane or the like is made to flow in the furnace as a carrier gas or a raw material gas, and for Ga doping, for example, a gas containing gallium chloride is also made to flow. In this way, "an epitaxial layer 701 whose main dopant is p-type Ga and whose concentration can be suppressed to below 5×10 ¹⁴ atoms/cm ³ (the lower the better) even if B is inevitably mixed in" can be stacked, thereby manufacturing the silicon epitaxial wafer 70 of the present invention.

In addition, the Ga doping method is not limited to the above method, and can be appropriately determined according to the desired concentration and the like.

Next, a solid-state imaging device using the above-mentioned silicon epitaxial wafer will be described, but the present invention is not limited thereto.

The solid-state imaging device 30 using the silicon single crystal substrate of FIG3A is the same as the solid-state imaging device 30 having a photodiode unit, a memory unit, and a computing unit. However, in the example of FIG3A , the first substrate 301 having the photodiode unit 303 formed thereon is the silicon single crystal substrate 10 of the present invention, but is replaced here with the silicon epitaxial wafer 70 described above.

In the silicon epitaxial layer in which the photodiode portion is formed, at least the main dopant in the silicon epitaxial layer is Ga, and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less, and the quality of the solid-state imaging element is superior to that of the related art in terms of afterimage characteristics.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Example 1)

The CZ silicon single crystal is pulled up using the apparatus of FIG2 and sliced to produce a p-type silicon single crystal substrate for the solid-state imaging device of the present invention, the main dopant of which is Ga. During the production, the specific parameters are as follows. In addition, although Ga is intentionally doped, it is inevitable that B is mixed in.

Diameter 300 mm, crystal orientation <100>, oxygen concentration: 3.4-10.5 ppma, resistivity 5 Ωcm, Ga concentration: 3×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (below the lower limit value measured by SIMS).

(Comparative Example 1)

A p-type silicon single crystal substrate for a conventional solid-state imaging device was produced, the main dopant of which was B. The specific parameters during production were as follows. Other than that, the production was carried out in the same manner as in Example 1.

Diameter: 300 mm, crystal orientation: <100>, oxygen concentration: 3.4-10.5 ppma, resistivity: 10 Ωcm, 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 dependency of the afterimage 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 apparatus and method are described in detail below.

In order to explain a specific evaluation method, an example of an afterimage characteristic evaluation device 40 is shown in FIG4. The evaluation device is composed of a device (illumination unit) 403 for irradiating light to a semiconductor substrate 402 having a PN junction structure 401, an optical fiber 404, a device (illuminance meter) 405 for measuring the light amount, and a current measuring device (SMU) 407 having a Kelvin probe 406. In addition, a substrate is set, and after irradiating the surface of the semiconductor substrate 402 with light of a predetermined illuminance for a predetermined time (a step of irradiating light), a step of turning off the light irradiation and measuring the amount of carriers generated after the light irradiation is performed.

Here, a white light LED was used for light irradiation, and the light intensity during measurement was 500 lux and the light irradiation time was 10 seconds.

Next, the amount of carriers generated by the PN junction formed as described above is measured. A specific timing diagram of light irradiation and measurement is shown in Fig. 5. Fig. 5 is a diagram showing an example of the measurement sequence of the semiconductor substrate evaluation method.

The amount of carriers generated by light irradiation is affected by the type of semiconductor substrate 402 or the light elements, particularly carbon, contained in the semiconductor substrate 402. Therefore, in order to prevent the difference in the amount of carriers generated initially by light irradiation from affecting the afterimage characteristics, the amount of carriers generated is measured once while light irradiation is performed (the amount of carriers generated during light irradiation), as shown in FIG5 . In this way, the semiconductor substrate is evaluated in consideration of the difference in the amount of carriers generated initially.

In addition, the measurement time of the carrier generation amount after light irradiation after light irradiation was set to 1 second.

In addition, in FIG. 5 , the measurement is stopped once before measuring the amount of carrier generation after the light irradiation is turned off. This is because the noise generated when the light irradiation is turned off can be avoided more reliably.

In addition, the afterimage characteristic is evaluated based on the ratio of the current value of the carrier measurement probe when the light irradiation is turned on/off. For example, a higher current value after the light irradiation is turned off indicates that the carriers are trapped, and it can be estimated that the afterimage characteristic is poor.

In the case of an actual solid-state imaging component, charges are generated by electron/hole pairs generated by incident light when the shutter is opened, and an image is constructed by introducing this charge. However, after closing the shutter, it is important to release the electron/hole pairs quickly. If the release is slow, it will become an afterimage and affect the next frame.

(Evaluation results of Example 1 and Comparative Example 1)

The evaluation results are shown in FIG6 . In the case of Comparative Example 1 (mainly doped with B), it was found that the current before and after light irradiation was relatively large compared with Example 1 (mainly doped with Ga) at any oxygen concentration [Oi], and the afterimage characteristic was poor. Specifically, the current ratio before and after light irradiation was 2.7 to 5.2 for Comparative Example 1, while it was 1.2 to 1.6 for Example 1. If annealing is performed at 450°C for 75 hours, the current value changes in Comparative Example 1 in which B-doped crystals produce BO ₂ defects, but BO ₂ formation is suppressed in Example 1 in which Ga-doped crystals are formed, so the change in current value (change in afterimage characteristic) is suppressed. In addition, it can be seen that in Comparative Example 1, the current ratio increases as the oxygen concentration increases, and there is a tendency for the afterimage characteristic to deteriorate as the oxygen concentration increases.

On the other hand, in the case of Example 1, even if the oxygen concentration increases, 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 characteristic is good.

(Example 2)

The CZ silicon single crystal is pulled and sliced using the apparatus of FIG. 2 to produce a p-type silicon single crystal substrate for the solid-state imaging device of the present invention, the main dopant of which is Ga. The specific parameters during production are as follows. In addition, in addition to Ga, a trace amount of B is intentionally doped for production.

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

In addition, in the same manner as in Example 1, the afterimage characteristics were evaluated.

(Evaluation results of Example 2)

The current ratio before and after light irradiation was about 1.6, and it was judged that the afterimage characteristic was good.

(Example 3)

In order to manufacture the silicon epitaxial wafer for the solid-state imaging component of the present invention, first, a CZ silicon single crystal is pulled up using the apparatus shown in FIG2 , and sliced to manufacture a p-type silicon single crystal substrate with Ga as the main dopant, and a p-type epitaxial layer with Ga as the main dopant is formed on the substrate. During the manufacture, 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 (below the lower limit value measured by SIMS)

(Silicon epitaxial layer)

Epitaxial layer thickness: 5μm, resistivity 10Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (below the lower limit value measured by SIMS)

In addition, in the same manner as in Example 1, the afterimage characteristics were evaluated.

(Evaluation results of Example 3)

The current ratio before and after light irradiation was about 1.8, and it was judged that the afterimage characteristic was good.

(Comparative Example 2)

A silicon epitaxial wafer was prepared under the same conditions as in Example 3, and the afterimage characteristics were evaluated in the same manner as in Example 1, except that B (B concentration in the epitaxial layer: 1×10 ¹⁵ atoms/cm ³ ) was used instead of Ga as the dopant of the silicon epitaxial layer.

(Evaluation results of Comparative Example 2)

The current ratio before and after light irradiation was about 8.2, which was larger than that in Example 3, and it was determined that the afterimage characteristic was poor.

(Example 4)

In order to manufacture the silicon epitaxial wafer for the solid-state imaging device of the present invention, first, a CZ silicon single crystal is pulled up using the apparatus shown in FIG. 2, and sliced to manufacture a p ⁺ type silicon single crystal substrate whose main dopant is B, and a p type epitaxial layer whose main dopant is Ga is formed on the substrate. During the manufacture, the specific parameters are as follows.

(Silicon 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 thickness: 5μm, resistivity 10Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (below the lower limit value measured by SIMS)

In addition, in the same manner as in Example 1, the afterimage characteristics were evaluated.

(Evaluation results of Example 4)

The current ratio before and after light irradiation was about 2.1, and it was judged that the afterimage characteristic was good.

(Example 5)

In order to manufacture the silicon epitaxial wafer for the solid-state imaging device of the present invention, first, a CZ silicon single crystal is pulled up using the apparatus shown in FIG. 2, and sliced to manufacture a p ^- type silicon single crystal substrate whose main dopant is B, and a p-type epitaxial layer whose main dopant is Ga is formed on the substrate. During the manufacture, the specific parameters are as follows.

(Silicon 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 thickness: 5μm, resistivity 10Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (below the lower limit value measured by SIMS)

In addition, in the same manner as in Example 1, the afterimage characteristics were evaluated.

(Evaluation results of Example 5)

The current ratio before and after light irradiation was about 2.2, and it was judged that the afterimage characteristic was good.

(Example 6)

In order to manufacture the silicon epitaxial wafer for the solid-state imaging component of the present invention, first, a CZ silicon single crystal is pulled up using the apparatus of FIG. 2, sliced to manufacture a p-type silicon single crystal substrate with Ga as the main dopant, and a p-type epitaxial layer with Ga as the main dopant is formed on the substrate. During the manufacture, the specific parameters are as follows. In addition, in addition to Ga, a trace amount of B is intentionally doped in the epitaxial layer for manufacture.

(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 (below the lower limit value measured by SIMS)

(Silicon epitaxial layer)

Epitaxial layer thickness: 5μm, resistivity 8Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹⁴ atoms/cm ³

In addition, in the same manner as in Example 1, the afterimage characteristics were evaluated.

(Evaluation results of Example 6)

The current ratio before and after light irradiation was about 2.3, and it was judged that the afterimage characteristic was good.

The present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are examples, and any scheme having substantially the same structure and producing the same function and effect as the technical concept described in the claims of the present invention is included in the technical scope of the present invention.

Claims (6)

1. A silicon epitaxial wafer for a solid-state imaging device, comprising a silicon epitaxial layer on a surface of a silicon single crystal substrate, characterized in that: The silicon epitaxial layer is a p-type epitaxial layer whose main dopant is Ga, and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less. 2. The silicon epitaxial wafer for a solid-state imaging device according to claim 1, characterized in that: The silicon single crystal substrate is a p-type silicon single crystal substrate whose main dopant is Ga, and whose B concentration is 5×10 ¹⁴ atoms/cm ³ or less. 3. The silicon epitaxial wafer for a solid-state imaging device according to claim 1, wherein: The silicon single crystal substrate is a p ⁺ -type silicon single crystal substrate in which the main dopant is B and the B concentration is 1×10 ¹⁸ atoms/cm ³ or more. 4. The silicon epitaxial wafer for a solid-state imaging device according to claim 1, wherein: The silicon single crystal substrate is a p ^- type silicon single crystal substrate whose main dopant is B and whose B concentration is 1×10 ¹⁶ atoms/cm ³ or less. 5. The silicon epitaxial wafer for a solid-state imaging device according to claim 1, wherein: The silicon single crystal substrate is an n-type silicon single crystal substrate. 6. A solid-state imaging component, comprising a photodiode unit, a memory unit and a computing unit, characterized in that: At least the photodiode portion is formed in the silicon epitaxial layer of the silicon epitaxial wafer for a solid-state imaging device according to any one of claims 1 to 5.