JP7318518B2 - Silicon single crystal substrate and silicon epitaxial wafer for solid-state imaging device, and solid-state imaging device - Google Patents

Description

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.

Solid-state imaging devices are used in mobile devices such as smartphones. A solid-state imaging device obtains an image by converting optical information into electronic information by capturing carriers generated by light in a depletion layer region (photodiode) of a PN junction (photoelectric conversion). In recent years, as the number of pixels has increased, it has become possible to acquire a large number of images in a short period of time by installing cache memory near the photodiodes. It is now possible to take moment-to-moment photographs, which was difficult. This results in reading data from the photodiode in a short time.

The problem at this time is the afterimage characteristic. This is a phenomenon in which carriers generated by the photoelectric effect are trapped and then re-emitted after a certain period of time, so that an image appears to remain under the influence of these carriers. When acquiring a large amount of data in a short time with advanced functions, if there is an afterimage, it means that the influence of the previous captured data remains. It is said that the afterimage characteristic is caused by a complex of boron and oxygen in the substrate (see Non-Patent Documents 1 and 2 and Patent Documents 1 and 2).

In recent years, expectations for automated driving have been increasing, and LiDAR is attracting attention as a sensor (eye) for this purpose. This is a technology that measures the surrounding conditions (distance) by irradiating infrared light as a light source and capturing the reflected light with a sensor. Conventionally, it has been used in fields such as aircraft and mountain range measurement. Combining it with millimeter waves will enable the high-precision measurement required for autonomous driving. In this LiDAR system, a solid-state image sensor is used in the part that serves as a sensor. As a means of increasing sensitivity, methods such as using the avalanche breakdown (avalanche breakdown) of the diode to double the amount of carriers generated when a single photon is incident on the photodiode to increase sensitivity are being investigated. It is In this field as well, when the afterimage characteristic mentioned earlier occurs, the accuracy decreases (detecting the presence of light even when there is no light in the first place). etc.).
Solid-state imaging devices are expected to be used in many fields other than automatic driving, such as visual sensors installed in industrial robots and medical applications such as surgical operations.

Solid-state imaging devices including these photodiodes are manufactured using silicon substrates, so development of substrates capable of suppressing afterimage characteristics is very important.

Japanese Patent Application Laid-Open No. 2019-9212 JP 2019-79834 A Patent No. 3679366

The 77th Japan Society of Applied Physics Autumn Meeting Proceedings 14p-P6-10 Tsubasa Kaneda, Akira Otani The 77th Japan Society of Applied Physics Autumn Meeting Proceedings 14p-P6-11 Akira Otani, Tsubasa Kaneda "Elucidation of the Mechanism of Afterimage Phenomena in CMOS Image Sensors 2"

SUMMARY OF THE INVENTION It is an object of the present invention to provide a silicon single crystal substrate and a silicon epitaxial wafer for a solid-state imaging device capable of suppressing the residual image characteristic of the solid-state imaging device.

To achieve the above object, the present invention provides a silicon single crystal substrate for a solid-state imaging device obtained by slicing a silicon single crystal produced by the CZ method, wherein the silicon single crystal substrate contains Ga as a main dopant. and a B concentration of 5×10 ¹⁴ atoms/cm ³ or less.

As described above, as a silicon single crystal substrate for a solid-state imaging device, the main dopant of a p-type silicon single crystal substrate obtained by slicing a silicon single crystal produced by the CZ (Czochralski) method is generally used. If Ga (gallium) is used in place of B (boron) that is commonly used, and if the concentration of B in the substrate is 5×10 ¹⁴ atoms/cm ³ or less, the concentration of B, which causes image retention, can be lowered. Therefore, the afterimage characteristic can be suppressed regardless of the interstitial oxygen concentration.
Moreover, since it is a CZ substrate, it can be superior to an FZ (floating zone) substrate in terms of substrate strength, gettering ability, substrate diameter size, and the like.

The term "main dopant" means the dopant with the maximum concentration that determines the conductivity type of the silicon single crystal substrate.

Further, it is preferable that the interstitial oxygen concentration in the p-type silicon single crystal substrate is 1 ppma or more and 15 ppma or less.

If it is 15 ppma or less, oxygen becomes the center of generation in the depletion layer even though no light is incident, and electron-hole pairs are generated to generate charges (called white flaws or dark current). Occurrence probability can be reduced. On the other hand, if it is 1 ppma or more, it is possible to more reliably prevent problems such as a decrease in substrate strength and an insufficient gettering ability against heavy metal contamination.

Incidentally, the value of the interstitial oxygen concentration is based on the JEIDA (JEITA) standard. JEIDA is an abbreviation for the Japan Electronic Industry Development Association, and indicates that the interstitial oxygen concentration is calculated using a conversion factor determined by JEIDA. Currently, JEIDA has been renamed to JEITA (Japan Electronics and Information Technology Industries Association).

Further, the present invention is a solid-state imaging device having a photodiode section, a memory section, and an arithmetic section, wherein at least the photodiode section is formed on the silicon single crystal substrate for the solid-state imaging device of the present invention. Provided is a solid-state imaging device characterized by being a solid-state imaging device.

A solid-state imaging device has at least a photodiode portion, a memory portion, and an arithmetic portion. By using a p-type silicon single crystal substrate containing Ga and having a B concentration of 5×10 ¹⁴ atoms/cm ³ or less, a solid-state imaging device with suppressed afterimage characteristics can be manufactured.

Furthermore, the present invention provides a silicon epitaxial wafer for a solid-state imaging device having a silicon epitaxial layer on the surface of a silicon single crystal substrate, wherein the silicon epitaxial layer is a p-type epitaxial layer containing Ga as a main dopant, and Provided is a silicon epitaxial wafer for a solid-state imaging device, characterized by having a B concentration of 5×10 ¹⁴ atoms/cm ³ or less.

When manufacturing a solid-state imaging device using a silicon epitaxial wafer, the silicon epitaxial layer (simply called an epitaxial layer) in which the photodiode is formed contains almost no oxygen. Even B should not form a complex of B and oxygen that causes afterimage characteristics. However, due to deposition of the epitaxial layer and heat treatment during the device fabrication process, oxygen in the silicon single crystal substrate may diffuse into the epitaxial layer in the conventional product, resulting in afterimage characteristics. 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 characteristics are suppressed regardless of the diffusion of oxygen from the substrate. be able to. Furthermore, even if the silicon single crystal substrate also contains B and the B diffuses into the epitaxial layer, the original B concentration in the epitaxial layer is extremely low as described above, so that the residual image characteristic is still suppressed. can be suppressed.

The silicon single crystal substrate may be a p-type silicon single crystal substrate containing Ga as a main dopant and having a B concentration of 5×10 ¹⁴ atoms/cm ³ or less.

When B and oxygen are contained in the silicon single crystal substrate forming the epitaxial layer, depending on the concentrations of these elements and the heat treatment the silicon single crystal substrate undergoes, both elements diffuse into the epitaxial layer in the conventional product, resulting in afterimage characteristics. It may occur. Therefore, by using Ga as the main dopant in the silicon single crystal substrate and setting the B concentration to 5×10 ¹⁴ atoms/cm ³ or less, the afterimage characteristic can be suppressed more reliably.

Further, the silicon single crystal substrate may be a p ⁺ -type silicon single crystal substrate containing B as a main dopant and having a B concentration of 1×10 ¹⁸ atoms/cm ³ or more.

With such a p ⁺ -type silicon single crystal substrate, it is possible to further enhance the gettering ability of metal impurities and the like that may occur due to the deposition of the epitaxial layer and the heat treatment in the device fabrication process. In this case, B may diffuse from the p ⁺ -type silicon single crystal substrate into the epitaxial layer. can suppress the formation of a complex of

The silicon single crystal substrate may be a p ⁻ -type silicon single crystal substrate containing B as a main dopant and having a B concentration of 1×10 ¹⁶ atoms/cm ³ or less.

With such a p ⁻ -type, the amount of B that diffuses into the epitaxial layer due to the deposition of the epitaxial layer and the heat treatment in the device fabrication process is limited, so the formation of a complex of B and oxygen in the epitaxial layer is suppressed. In addition, by increasing the interstitial oxygen concentration of the silicon single crystal substrate, the gettering ability and substrate strength can be enhanced.

Further, the silicon single crystal substrate can be an n-type silicon single crystal substrate.

Since the n-type silicon single crystal substrate hardly contains B, it is possible to suppress the afterimage property regardless of the diffusion of oxygen from the substrate.
In the case of an n-type silicon single crystal substrate, similarly to the p ⁻ -type silicon single crystal substrate, the formation of a complex of B and oxygen in the epitaxial layer is suppressed and the interstitial oxygen concentration of the silicon single crystal substrate is increased. As a result, gettering ability and substrate strength can be enhanced.

Further, the present invention is a solid-state imaging device having a photodiode section, a memory section, and an arithmetic section, wherein at least the photodiode section is the silicon epitaxial wafer of the silicon epitaxial wafer for the solid-state imaging device of the present invention. Provided is a solid-state imaging device characterized by being formed in layers.

A solid-state imaging device has at least a photodiode portion, a memory portion, and a calculation portion. is Ga and the p-type epitaxial layer having a B concentration of 5×10 ¹⁴ atoms/cm ³ or less can be used to manufacture a solid-state imaging device with suppressed afterimage characteristics.

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 capable of suppressing the afterimage characteristic of the solid-state imaging device. Further, it is possible to provide a silicon epitaxial wafer for a solid-state imaging device and a solid-state imaging device capable of suppressing afterimage characteristics of the solid-state imaging device.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows an example of the silicon single crystal substrate for solid-state image sensors of this invention. It is a schematic diagram which shows an example of the single-crystal pulling apparatus by CZ method. 1 is a schematic diagram showing an example of a solid-state imaging device of the present invention; FIG. It is the schematic which shows an example of the manufacturing method of the solid-state image sensor of this invention. It is a block diagram which shows an example of an afterimage characteristic evaluation apparatus. It is a figure which shows an example of the measurement sequence of the evaluation method of a semiconductor substrate. 4 is a graph showing the results of afterimage characteristic evaluation of Example 1 and Comparative Example 1. FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows an example of the silicon epitaxial wafer for solid-state imaging devices of this invention.

As a result of intensive studies by the inventors of the present invention on suppressing the afterimage characteristics of solid-state imaging devices, in particular, attention was paid to the complex of B and oxygen, which is said to be related to the afterimage characteristics. , the idea of using Ga instead of B as the p-type main dopant.

An example of using Ga instead of B as a p-type dopant is known to be used as a silicon single crystal for solar cells (Patent Document 3).

However, it can be said that the solar cell and the solid-state imaging device are different in manufacturing process and manufacturer, and are in different technical fields.
In addition, while the object for solar cells is to obtain the effect of suppressing photodegradation, the object for solid-state imaging devices is to obtain the effect of suppressing afterimage characteristics. But they are completely different.
Therefore, there has been no actual 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, and there has been no concept of it.

In order to suppress the formation of a complex of B and oxygen, which is said to be related to the afterimage property, an FZ substrate (fabricated by the FZ method and containing almost oxygen) is used with the aim of reducing the oxygen concentration. It is conceivable to use a silicon single crystal substrate obtained by slicing from a silicon single crystal that does not have a crystal structure.

However, when an FZ substrate is used for a solid-state imaging device, 1) the substrate strength is low because it contains almost no oxygen, and the gettering ability due to oxygen precipitates cannot be obtained, and 2) the substrate strength is increased. 3) The diameter is one generation smaller than that of the CZ substrate ( The current maximum diameter at the mass production level is 300 mm for CZ substrates and 200 mm for FZ substrates).

From the above, if the main dopant is Ga p-type CZ silicon single crystal substrate and the B concentration is as low as 5×10 ¹⁴ atoms/cm ³ or less, the afterimage characteristics, substrate strength, etc. of the solid-state imaging device are improved. I found a good thing and completed the present invention. In addition, the inventors have found that a silicon epitaxial wafer having similar silicon epitaxial layers for Ga and B provides good afterimage characteristics of a solid-state imaging device, and completed the present invention.

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

FIG. 1 shows a schematic diagram of a silicon single crystal substrate for a solid-state imaging device according to the present invention. As shown in FIG. 1, the silicon single crystal substrate 10 of the present invention is a p-type CZ silicon single crystal substrate containing Ga as a main dopant and having a B concentration of 5×10 ¹⁴ atoms/cm ³ or less.
First, since it is a silicon single crystal substrate manufactured by the CZ method, it has a higher substrate strength than, for example, an FZ silicon single crystal substrate containing almost no oxygen, a gettering ability due to oxygen precipitates can be obtained, and the substrate There are advantages such as one generation larger diameter. The diameter of the substrate is not particularly limited, but can be, for example, 300 mm or more, and further 450 mm or more.

Moreover, the main dopant, ie, the dopant that determines the conductivity type of the substrate, is Ga instead of B that is doped in the conventional silicon single crystal substrate for solid-state imaging devices. Moreover, the B concentration is as low as 5×10 ¹⁴ atoms/cm ³ or less. For this reason, it is possible to suppress the afterimage characteristics due to the _BO2 complex, which has been a problem when manufacturing solid-state imaging devices with conventional products in which the main dopant is B, and the afterimage characteristics can be suppressed regardless of the interstitial oxygen concentration. , a silicon single-crystal substrate that can provide a solid-state imaging device with better quality than the conventional one.
The Ga concentration is not particularly limited, and can be appropriately determined according to the desired resistivity and the like.
Also, the lower limit of the B concentration is not particularly limited. Although there is a possibility of unavoidable contamination during the production of the single crystal, the smaller the amount, the better, in order to prevent the above-mentioned _BO2 complex from occurring.
Note that the dopant only needs to satisfy the above conditions, and other dopants besides Ga and B may be mixed.

Moreover, the oxygen concentration of the silicon single crystal substrate 10 can be, for example, 1 ppma or more and 15 ppma or less.
If it is 15 ppma or less, the probability of occurrence of white defects (or dark current) in which oxygen becomes the center of generation in the depletion layer and electron-hole pairs are generated to generate charges even though no light is incident is reduced. can do.
Moreover, if it is 1 ppma or more, it is possible to more reliably prevent problems such as a decrease in substrate strength and an insufficient gettering ability against heavy metal contamination.
It should be noted that it is more preferably 10 ppma or less, and even more preferably 5 ppma or less.

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

A single crystal pulling apparatus 20 is composed of a bottom chamber 202 containing a crucible 201 for melting a raw material, and a top chamber 204 containing and taking out a pulled single crystal (single crystal rod) 203 . A wire winding mechanism 205 for pulling up the single crystal is provided in the upper part of the top chamber 204, and the wire 206 is wound up and down according to the growth of the single crystal. At the tip of this wire 206, a seed crystal 207 is attached to a seed holder 208 for pulling up a silicon single crystal.

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. is placed, and the heater is surrounded by a heat insulating material 212 . The crucible 201 is filled with silicon melt 216 melted by heating with a heater. The crucible 201 is supported by a support shaft 213 that can rotate and move up and down, and a driving device 214 therefor is attached to the bottom of the bottom chamber 202 . Alternatively, a straightening tube 215 for straightening the inert gas introduced into the furnace may be used.

Next, a method for manufacturing a silicon single crystal using the above apparatus will be described. First, a polycrystalline silicon raw material and Ga as a dopant are placed in the crucible 201 and heated by the heater 211 to melt the raw material. In the present embodiment, Ga was placed in the crucible together with the polycrystalline silicon raw material before melting. It is preferable to prepare a dopant by crushing it, melt the polycrystalline silicon raw material, adjust the dopant to a desired concentration, and then add it.

Next, when the polycrystalline silicon raw material is completely melted, a seed crystal 207 for growing a single crystal rod is attached to the tip of the wire 206 of the wire winding mechanism 205, and the wire 206 is gently wound down to remove the tip of the seed crystal 207. is brought into contact with the silicon melt 216 . At this time, the crucible 201 and the seed crystal 207 are rotating in opposite directions to each other, and the inside of the pulling machine is in a decompressed state and filled with an inert gas such as argon flowed from the upper part of the furnace. .

When the temperature around the seed crystal 207 is stabilized, the seed crystal 207 and the crucible 201 are rotated in opposite directions, and the wire 206 is gently wound up to start pulling up the seed crystal 207 . Then, necking is performed to eliminate slip dislocations occurring in the seed crystal 207 . When necking is performed to a thickness and length at which the slip dislocation disappears, the diameter is gradually increased to form a cone portion of the single crystal 203, and the diameter is increased to a desired diameter. When the cone diameter has expanded to a predetermined diameter, the production of the constant diameter portion (straight body portion) of the single crystal rod is started. 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 single crystal to be grown. Also, the crystal diameter is controlled by adjusting the temperature and pull rate.

After pulling up the straight body portion of the single crystal by a predetermined length, the diameter of the crystal is reduced to form a tail portion. , wait for the crystals to cool. When the single crystal ingot is cooled to a temperature at which it can be taken out, it is taken out from the pulling machine and the crystal is processed into wafers.

In the processing step, first, the cone portion and the tail portion are cut, the periphery of the single crystal rod is cylindrically ground, and the rod is cut into blocks of appropriate size. Then, after slicing this appropriately sized single crystal block with a slicer into wafers, chamfering, lapping, etc. are performed as necessary, and processing distortion is removed by etching to produce wafers that will serve as substrates. .

In the above example, only Ga was intentionally doped, but the dopant is not limited to this. Ga may be doped 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 solid-state imaging devices 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, 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 has a photodiode section 303 , a memory section, and an arithmetic section 304 . The solid-state imaging device 30 is obtained by forming various elements on each of 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, that is, the side 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 It is 5×10 ¹⁴ atoms/cm ³ or less.
On the other hand, the second substrate can be, for example, a CZ silicon single crystal substrate. The main dopant does not have to be Ga as in the first substrate, and can be determined as appropriate.

In such a solid-state imaging device 30, since it is the photodiode part 303 that the afterimage characteristic occurs, at least the first substrate 301 is a p-type CZ silicon single crystal substrate whose main dopant is Ga, and , and a B concentration of 5×10 ¹⁴ atoms/cm ³ or less, a solid-state imaging device with suppressed afterimage characteristics is obtained.

An example of a method for manufacturing such a solid-state imaging device 30 is shown in FIG. 3B.
First, a first substrate 301 and a second substrate 302, which are substrates of the present invention, are prepared.
A gate oxide film 305 or the like is formed on these substrates to form various elements (a photodiode portion 303 (light receiving element), a memory portion and an arithmetic portion 304), as well as an STI (element isolation) 306, wiring 307, An interlayer insulating film 308 and the like are formed.
After that, the first substrate 301 and the second substrate 302 on which various elements are formed are pasted together to fabricate the solid-state imaging device 30 .

A solid-state imaging device using a silicon epitaxial wafer capable of suppressing afterimage characteristics, which is different from the solid-state imaging device using the silicon single crystal substrate, will be described below.
First, FIG. 7 shows a schematic diagram of a silicon epitaxial wafer for a solid-state imaging device according to the present invention. As shown in FIG. 7, a silicon epitaxial wafer 70 of the present invention has a p-type silicon epitaxial wafer 702 having a main dopant of Ga and a B concentration of 5×10 ¹⁴ atoms/cm ³ or less on the surface of a silicon single crystal substrate 702 . of silicon epitaxial layer 701 . With such a structure, since the original B concentration in the silicon epitaxial layer 701 is extremely low and oxygen is hardly contained, even if oxygen and B diffuse from the silicon single crystal substrate 702, oxygen and B is suppressed, and the afterimage property can be suppressed.
Also, the silicon single crystal substrate 702 itself (for example, the main dopant, etc.) is not limited and can be determined as appropriate. An example of the silicon single crystal substrate 702 is given below.

The silicon single crystal substrate 702 can 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. With such a p-type silicon single crystal substrate, it is possible to more reliably suppress the occurrence of afterimage characteristics due to the diffusion of B and oxygen into the silicon epitaxial layer 701 due to the heat treatment of the silicon single crystal substrate. can.

Also, the silicon single crystal substrate 702 can be, for example, 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. With such a p ⁺ -type silicon single crystal substrate, the ability to getter metal impurities and the like that may occur due to the deposition of the silicon epitaxial layer 701 and heat treatment in the device fabrication process can be further enhanced. In this case, there is a risk that B will diffuse from the p ⁺ -type silicon single crystal substrate into the epitaxial layer. formation can be suppressed.
At this time, the interstitial oxygen concentration of the p ⁺ -type silicon single crystal substrate is not limited, but in order to more reliably prevent the diffusion of oxygen from the p ⁺ -type silicon single crystal substrate to the epitaxial layer, the interstitial oxygen concentration is set to 20 ppma. It is preferably 15 ppma or less, more preferably 15 ppma or less.

Further, the silicon single crystal substrate 702 can 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. With such a p ⁻ -type silicon single crystal substrate, the amount of B diffusing into the epitaxial layer due to the deposition of the epitaxial layer and the heat treatment in the device fabrication process is limited. By more reliably suppressing the formation of , and increasing the interstitial oxygen concentration of the silicon single crystal substrate, the gettering ability and the substrate strength can be enhanced.

Also, the silicon single crystal substrate 702 can be, for example, an n-type silicon single crystal substrate. Since an n-type silicon single crystal substrate contains little B, the formation of a complex of B and oxygen in the epitaxial layer can be more reliably suppressed in the same manner as the p ⁻ -type silicon single crystal substrate, and By increasing the interstitial oxygen concentration of the silicon single crystal substrate, the gettering ability and the substrate strength can be enhanced.

A method for manufacturing such a silicon epitaxial wafer of the present invention will be described.
First, the silicon single crystal substrate 702 can be manufactured by using, for example, the single crystal pulling apparatus 20 of the CZ method as shown in FIG. In the case of intentionally doping B, the desired concentration of the B dopant may be melted together with the raw material when the single crystal is pulled.
Then, a silicon epitaxial layer 701 is laminated on the manufactured silicon single crystal substrate 702 . In this case, the epitaxial device to be used is not particularly limited, and, for example, the same one as conventional can be used. A silicon single crystal substrate 702 is placed on a susceptor in a furnace, the inside of the furnace is heated, and trichlorosilane or the like is flowed into the furnace as a carrier gas and a raw material gas. flow together. As a result, the epitaxial layer 701 whose main dopant is Ga p-type and whose concentration is suppressed to 5×10 ¹⁴ atoms/cm ³ or less (the lower the better) even if B is inevitably mixed is laminated. It is possible to manufacture the silicon epitaxial wafer 70 of the present invention.
Note that the Ga doping method is not limited to the above, 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.
Like the solid-state imaging device 30 using the silicon single crystal substrate of FIG. 3A described above, this solid-state imaging device has a photodiode section, a memory section, and an arithmetic section. However, in the example of FIG. 3A, the first substrate 301 on which the photodiode portion 303 is formed is the silicon single crystal substrate 10 of the present invention, but here it is replaced with the silicon epitaxial wafer 70 described above.
In the silicon epitaxial layer in which the photodiode part 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 afterimage characteristics are superior to those of the conventional art. It becomes a solid-state imaging device with excellent quality.

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these.

(Example 1)
Using the apparatus shown in FIG. 2, a CZ silicon single crystal was pulled and sliced to produce a p-type silicon single crystal substrate for a solid-state imaging device of the present invention having Ga as the main dopant. Specific parameters for the fabrication are as follows. Although Ga was intentionally doped, it is believed that B was unavoidably mixed.
Diameter 300 mm, crystal orientation <100>, oxygen concentration: 3.4 to 10.5 ppma, resistivity 5 Ωcm, Ga concentration: 3×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (SIMS lower limit value or less)

(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. Specific parameters for the fabrication are as follows. Other than that, it was produced in the same manner as in Example 1.
Diameter 300 mm, crystal orientation <100>, oxygen concentration: 3.4 to 10.5 ppma, resistivity 10 Ωcm, B concentration: 1×10 ¹⁵ atoms/cm ³

A PN junction was formed using the substrates of Example 1 and Comparative Example 1, and the oxygen concentration dependence of afterimage characteristics was compared at the substrate level ("leakage current ratio before and after light irradiation" after annealing at 450°C for 75 hours). ). The evaluation device and method will be described in detail below.

In order to describe a specific evaluation method, FIG. 4 shows an example of an afterimage characteristic evaluation device 40. As shown in FIG. The evaluation apparatus comprises a device (illumination) 403 for irradiating a semiconductor substrate 402 having a PN junction structure 401 with light, an optical fiber 404 and a device (illuminometer) 405 for measuring the amount of light, and a Kelvin probe 406. It consists of a measurement unit (SMU) 407 . Then, after the substrate is placed and the surface of the semiconductor substrate 402 is irradiated with light of a predetermined illuminance for a predetermined time (the step of light irradiation), the amount of generated carriers after the light irradiation is measured after the light irradiation is turned off. perform the process of

Here, a white light LED was used for light irradiation. Also, the amount of light at the time of measurement was set to 500 lux. Moreover, the light irradiation time was set to 10 seconds.

The amount of carriers generated in the PN junction thus formed is measured. FIG. 5 shows a conceptual diagram of specific light irradiation and measurement timings. FIG. 5 is a diagram showing an example of a measurement sequence of a semiconductor substrate evaluation method.

The amount of carriers generated by light irradiation is affected by the type of semiconductor substrate 402 and light elements, especially carbon, contained in the semiconductor substrate 402 . Therefore, in order to prevent the difference in the amount of carriers originally generated by light irradiation from affecting the afterimage characteristics, as shown in FIG. ) was measured. In this way, semiconductor substrates were evaluated in consideration of the difference in the amount of carriers originally generated.

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

Then, the afterimage characteristics were evaluated from the ratio of the current values of the carrier measuring probe when light irradiation was turned on and off. For example, a high current value after light irradiation is turned off indicates that the amount of carriers is trapped, and it can be inferred that the afterimage characteristic is poor.

In the example of an actual solid-state imaging device, when the shutter is opened, the electron-hole pairs generated by the incident light generate electric charges, and by capturing these, an image is constructed. It is important that electron-hole pairs are discharged quickly, and if this is slow, it will affect the next frame as an afterimage.

(Evaluation results of Example 1 and Comparative Example 1)
FIG. 6 shows the evaluation results. In the case of Comparative Example 1 (B main doping), the current ratio before and after light irradiation is larger than that of Example 1 (Ga main doping) at any oxygen concentration [Oi], indicating that the afterimage characteristics are inferior. 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. When annealed at 450 °C for 75 hours, the current value changes in _Comparative Example 1 of the B-doped crystal in which _BO2 defects are generated, but the current value change ( afterimage characteristic change) is suppressed. Further, in Comparative Example 1, the current ratio increases as the oxygen concentration increases, indicating that the afterimage characteristics tend 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 substantially constant at a low value (a value close to 1), and it can be judged that the afterimage characteristics are good.

(Example 2)
Using the apparatus shown in FIG. 2, a CZ silicon single crystal was pulled and sliced to produce a p-type silicon single crystal substrate for a solid-state imaging device of the present invention having Ga as the main dopant. Specific parameters for the fabrication are as follows. In addition to Ga, it was manufactured by intentionally doping a small amount of B.
Diameter 300 mm, crystal orientation <100>, oxygen concentration: 5 ppma, resistivity 4 Ωcm, Ga concentration: 3×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹⁴ atoms/cm ³
Then, the afterimage characteristics were evaluated in the same manner as in Example 1.

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

(Example 3)
In order to produce a silicon epitaxial wafer for the solid-state imaging device of the present invention, first, a CZ silicon single crystal was pulled up using the apparatus shown in FIG. A p-type epitaxial layer with Ga as the main dopant was formed on this substrate. Specific parameters for the fabrication are as follows.
(silicon single crystal substrate)
Diameter 300 mm, crystal orientation <100>, oxygen concentration: 15 ppma, resistivity 4 Ωcm, Ga concentration: 3×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (below SIMS lower limit)
(silicon epitaxial layer)
Epitaxial layer thickness: 5 μm, resistivity: 10 Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (below SIMS lower limit)
Then, the afterimage characteristics were evaluated in the same manner as in Example 1.

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

(Comparative example 2)
A silicon epitaxial wafer was produced under the same conditions as in Example 3, except that B was used instead of Ga as a dopant for the silicon epitaxial layer (B concentration in the epitaxial layer: 1×10 ¹⁵ atoms/cm ³ ). The afterimage properties were evaluated in the same manner as in Example 1.

(Evaluation result of Comparative Example 2)
The current ratio before and after light irradiation is about 8.2, which is larger than that of Example 3, indicating that the afterimage characteristic is inferior.

(Example 4)
In order to produce a 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 . Then, a p-type epitaxial layer containing Ga as the main dopant was formed on this substrate. Specific parameters for the fabrication are as follows.
(silicon single crystal substrate)
Diameter 300 mm, crystal orientation <100>, oxygen concentration: 10 ppma, resistivity 0.01 Ωcm, B concentration: 8.5×10 ¹⁸ atoms/cm ³
(silicon epitaxial layer)
Epitaxial layer thickness: 5 μm, resistivity: 10 Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (below SIMS lower limit)
Then, the afterimage characteristics were evaluated in the same manner as in Example 1.

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

(Example 5)
In order to produce a 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. Then, a p-type epitaxial layer containing Ga as the main dopant was formed on this substrate. Specific parameters for the fabrication are as follows.
(silicon single crystal substrate)
Diameter 300 mm, crystal orientation <100>, oxygen concentration: 15 ppma, resistivity 10 Ωcm, B concentration: 1×10 ¹⁵ atoms/cm ³
(silicon epitaxial layer)
Epitaxial layer thickness: 5 μm, resistivity: 10 Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (below SIMS lower limit)
Then, the afterimage characteristics were evaluated in the same manner as in Example 1.

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

(Example 6)
In order to produce a silicon epitaxial wafer for the solid-state imaging device of the present invention, first, a CZ silicon single crystal was pulled up using the apparatus shown in FIG. A p-type epitaxial layer with Ga as the main dopant was formed on this substrate. Specific parameters for the fabrication are as follows. The epitaxial layer was manufactured by intentionally doping a small amount of B in addition to Ga.
(silicon single crystal substrate)
Diameter 300 mm, crystal orientation <100>, oxygen concentration: 15 ppma, resistivity 4 Ωcm, Ga concentration: 3×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (below SIMS lower limit)
(silicon epitaxial layer)
Epitaxial layer thickness: 5 μm, resistivity 8 Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹⁴ atoms/cm ³
Then, the afterimage characteristics were evaluated 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 can be judged that the afterimage characteristics are good.

In addition, this invention is not limited to the said embodiment. The above embodiment is an example, and any device that has substantially the same configuration as the technical idea described in the claims of the present invention and produces similar effects is the present invention. It is included in the technical scope of the invention.

10... p-type silicon single crystal substrate,
20... Single crystal pulling apparatus, 201... Crucible, 202... Bottom chamber,
203... Single crystal, 204... Top chamber, 205... Wire winding mechanism,
206... Wire, 207... Seed crystal, 208... Seed holder, 209... Quartz crucible,
210... graphite crucible, 211... heater, 212... heat insulating material, 213... supporting shaft,
214... drive device, 215... rectifier cylinder, 216... silicon melt,
30... solid-state imaging device, 301... first substrate, 302... second substrate,
303... Photodiode section, 304... Memory section and calculation section,
305... Gate oxide film, 306... STI (element isolation), 307... Wiring,
308... Interlayer insulating film,
40... Apparatus for evaluating afterimage characteristics, 401... PN junction, 402... Substrate, 403... Illumination,
404... Optical fiber, 405... Luminometer, 406... Kelvin probe,
407 ... current measuring unit (SMU),
70... Silicon epitaxial wafer, 701... p-type silicon epitaxial layer,
702... Silicon single crystal substrate.

Claims (9)

A silicon single crystal substrate for a solid-state imaging device obtained by slicing a silicon single crystal produced by the CZ method,
The silicon single crystal substrate is a p-type silicon single crystal substrate containing Ga as a main dopant and having a B concentration of 5×10 ¹⁴ atoms/cm ³ or less. substrate. 2. The silicon single crystal substrate for a solid-state imaging device according to claim 1, wherein the interstitial oxygen concentration in said p-type silicon single crystal substrate is 1 ppma or more and 15 ppma or less. A solid-state imaging device having a photodiode section, a memory section, and a calculation section,
3. A solid-state imaging device, wherein at least said photodiode portion is formed on the silicon single crystal substrate for a solid-state imaging device according to claim 1 or 2. A silicon epitaxial wafer for a solid-state imaging device having a silicon epitaxial layer on the surface of a silicon single crystal substrate,
A silicon epitaxial wafer for a solid-state imaging device, wherein the silicon epitaxial layer is a p-type epitaxial layer containing Ga as a main dopant and having a B concentration of 5×10 ¹⁴ atoms/cm ³ or less. 5. The solid-state imaging device according to claim 4, wherein the silicon single crystal substrate is a p-type silicon single crystal substrate containing Ga as a main dopant and having a B concentration of 5×10 ¹⁴ atoms/cm ³ or less. Silicon epitaxial wafer for devices. 5. The solid-state imaging device according to claim 4, wherein the silicon single crystal substrate is a p ⁺ -type silicon single crystal substrate containing B as a main dopant and having a B concentration of 1×10 ¹⁸ atoms/cm ³ or more. silicon epitaxial wafers for 5. The solid-state imaging device according to claim 4, wherein the silicon single crystal substrate is a p ^- type silicon single crystal substrate containing B as a main dopant and having a B concentration of 1×10 ¹⁶ atoms/cm ³ or less. silicon epitaxial wafers for 5. The silicon epitaxial wafer for a solid-state imaging device according to claim 4, wherein said silicon single crystal substrate is an n-type silicon single crystal substrate. A solid-state imaging device having a photodiode section, a memory section, and a calculation section,
A solid-state imaging device, wherein at least the photodiode portion is formed on the silicon epitaxial layer of the silicon epitaxial wafer for a solid-state imaging device according to any one of claims 4 to 8. element.

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