KR20210065043A - Silicon single crystal substrate for solid-state image sensing device, silicon epitaxial wafer and solid-state image sensing device - Google Patents

Abstract

Provided are a silicon single crystal substrate for a solid-state imaging device capable of suppressing the afterimage characteristic of the solid-state imaging device, and a silicon epitaxial wafer. The silicon single crystal substrate for a solid-state imaging device is obtained by slicing a silicon single crystal produced by a CZ method, is a p-type silicon single crystal substrate in which a main dopant is Ga, and has B concentration of 5×1014 atoms/cm^3.

Description

SILICON SINGLE CRYSTAL SUBSTRATE FOR SOLID-STATE IMAGE SENSING DEVICE, SILICON EPITAXIAL WAFER AND SOLID-STATE IMAGE SENSING DEVICE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon single crystal substrate and a silicon epitaxial wafer for a solid-state imaging device, and to a solid-state imaging device.

A solid-state image sensor is used in mobile devices including smartphones. A solid-state image sensor converts optical information into electronic information by capturing carriers generated by light in a depletion layer region (photodiode) of a PN junction to obtain an image (photoelectric conversion). In recent years, with the increase in the number of pixels, by installing a cache memory near a photodiode, it is possible to acquire a large number of images in a short time. it is becoming possible This will read data from the photodiode in a short time.

What becomes a problem at this time is an 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 a large number of data is acquired in a short time with high functionality, if there is this afterimage, it means that the influence of the previous image|photography data remains. It is considered that the cause of the afterimage characteristic is a complex of boron and oxygen in the substrate (see Non-Patent Documents 1 and 2 and Patent Documents 1 and 2).

In addition, recently, expectations for automatic driving are increasing, and LiDAR is attracting attention as a sensor (eye; 目) for this purpose. This is a technique for irradiating infrared light as a light source, capturing reflected light with a sensor, and measuring the surrounding situation (distance), and has been conventionally used in the fields of aircraft and mountain range measurement. It is believed that by combining it with the millimeter wave, the high-precision measurement required for automatic operation becomes possible. In this LiDAR system, a solid-state image sensor is used for the part to be a sensor. Among these, methods for increasing sensitivity by doubling the amount of generated carriers using the avalanche breakdown (avalanche breakdown) of the diode when a photon is incident on one photodiode are considered as an invention to increase the sensitivity. is becoming Even in this field, if an afterimage characteristic occurs a while ago, there is a possibility of a decrease in precision (the presence of light is sensed even when there is no original light. In addition, the temporal resolution is lowered by providing a delay time to avoid the afterimage) have.

The solid-state imaging device is expected to be used in many fields other than the automatic operation described above, such as, for example, a visual sensor installed in an industrial robot, a medical application used in a surgical operation, and the like.

Since the solid-state imaging device including these photodiodes is manufactured using a silicon substrate, it is very important to develop a substrate capable of suppressing the afterimage characteristic.

Japanese Patent Laid-Open No. 2019-9212 Japanese Patent Laid-Open No. 2019-79834 Japanese Patent No. 3679366

77th Applied Physics Society Fall Conference Lecture Preliminary 14p-P6-10　Kaneda Tsubasa, Otani Akira　「Elucidation of the mechanism of afterimage phenomenon in CMOS image sensor 1」 77th Applied Physics Society Fall Conference Lecture Preliminary 14p-P6-11　Akira Otani, Tsubasa Kaneda「Elucidation of the mechanism of afterimage phenomenon in CMOS image sensor 2」

The present invention has been made in view of the above 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 device capable of suppressing the residual image characteristics of the solid-state imaging device.

In order to achieve the above object, the present invention provides a silicon single crystal substrate for a solid-state image pickup device obtained by slicing a silicon single crystal produced by the CZ method, wherein the silicon single crystal substrate is a p-type silicon single crystal substrate in which the main pant is Ga, Further, there is provided a silicon single crystal substrate for a solid-state imaging device, characterized in that the B concentration is 5×10 ¹⁴ atoms/cm ^{3 or less.}

In this way, as a silicon single crystal substrate for a solid-state image sensor, a main p-type silicon single crystal substrate obtained by slicing a silicon single crystal produced by the CZ (Czochralski) method is used instead of the commonly used B (boron). If it is Ga (gallium) and the B concentration in the substrate is 5×10 ¹⁴ atoms/cm ³ or less, the B concentration that causes the afterimage characteristic can be lowered, so that the afterimage characteristic is suppressed regardless of the interstitial oxygen concentration. can do.

Furthermore, since it is a CZ substrate, it can be made superior to a FZ (floating zone) substrate in terms of substrate strength, gettering ability, substrate diameter size, and the like.

On the other hand, the "main dopant" means a dopant with a maximum concentration that determines the conductivity type of a silicon single crystal substrate.

In addition, 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, even though no light is incident, oxygen becomes the center of generation in the depletion layer, and electron hole pairs are generated to generate charges (called a white defect or dark current). 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.

On the other hand, the value of the interstitial oxygen concentration is in accordance with the JEIDA (JEITA) standard. JEIDA is an abbreviation of the Japan Electronics Industry Promotion Association, and indicates that the interstitial oxygen concentration is calculated using the conversion factor determined by JEIDA. Currently, JEIDA is renamed JEITA (Electronic Information Technology Industry Association).

Further, the present invention provides a solid-state image pickup 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 image pickup device of the present invention. provides

The solid-state imaging device has at least a photodiode unit, a memory unit, and an operation unit. Since it is the photodiode unit that generates afterimage characteristics, at least a substrate on which the photodiode unit is formed, wherein the main pant is Ga and the B concentration is 5×10. ^{By using a p-type silicon single crystal substrate of 14} atoms/cm ³ or less, it is possible to manufacture a solid-state imaging device in which the afterimage characteristic is suppressed.

Furthermore, the present invention provides a silicon epitaxial wafer for a solid-state image pickup 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 in which the mainpant is Ga, and further, A silicon epitaxial wafer for a solid-state imaging device is provided, wherein the B concentration is 5×10 ¹⁴ atoms/cm ^{3 or less.}

In the case of manufacturing a solid-state imaging device using a silicon epitaxial wafer, the silicon epitaxial layer (also simply referred to as an epitaxial layer) on which the photodiode is formed contains almost no oxygen. Even with B, the complex of B and oxygen, which causes the afterimage characteristic, will not be formed. However, in conventional products, oxygen in the silicon single crystal substrate diffuses into the epitaxial layer due to deposition of the epitaxial layer or heat treatment during the device manufacturing process, resulting in residual image characteristics in some cases. However, in the present invention, since the main pant in the epitaxial layer is Ga and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less, the afterimage characteristic can be suppressed regardless of diffusion of oxygen from the substrate. Furthermore, even if B is also contained in the silicon single crystal substrate and the B is diffused into the epitaxial layer, the original B concentration in the epitaxial layer is very low as described above, so that the afterimage characteristic can be suppressed.

In addition, the silicon single crystal substrate may be a p-type silicon single crystal substrate in which the main pant is Ga, and the B concentration may be 5×10 ¹⁴ atoms/cm ³ or less.

When the silicon single crystal substrate forming the epitaxial layer contains B and oxygen, depending on their concentration and the heat treatment applied to the silicon single crystal substrate, in conventional products, both elements diffuse into the epitaxial layer, resulting in afterimage characteristics. There are cases. Accordingly, 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 more reliably suppressed.

^{In addition, the silicon single crystal substrate may be 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, it is possible to further increase the gettering ability of metal impurities or the like that may be generated by deposition of an epitaxial layer or heat treatment in a device manufacturing process. In this case, ^{there is a possibility that B may diffuse from the p +} type silicon single crystal substrate to the epitaxial layer, but as described above, since oxygen is hardly contained in the epitaxial layer, the complex of B and oxygen that causes the afterimage characteristic formation can be inhibited.

^{In addition, the silicon single crystal substrate may be 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.

In such a p ⁻ type, B diffused into the epitaxial layer by deposition of the epitaxial layer or heat treatment in the device manufacturing process is limited, so the formation of a complex of B and oxygen in the epitaxial layer is suppressed, and a silicon single crystal By increasing the interstitial oxygen concentration of the substrate, it is possible to increase the gettering ability and the substrate strength.

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

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

In the case of the n-type silicon single crystal substrate, as in the case of 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, so that the gettering ability Alternatively, the strength of the substrate can be increased.

Furthermore, the present invention provides a solid-state imaging device having a photodiode unit, a memory unit, and an arithmetic unit, wherein at least the photodiode unit is formed in the silicon epitaxial layer of the silicon epitaxial wafer for the solid-state imaging device of the present invention. It provides a solid-state imaging device, characterized in that.

The solid-state imaging device has at least a photodiode unit, a memory unit, and an operation unit. Since it is the photodiode unit that generates afterimage characteristics, at least the photodiode unit is formed as an epitaxial layer, wherein the main pant is Ga, and the B concentration is 5. By using the p-type epitaxial layer of x10 ¹⁴ atoms/cm ³ or less, it is possible to manufacture a solid-state imaging device in which the afterimage characteristic is suppressed.

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 the afterimage characteristic of the solid-state imaging device.

1 is a schematic diagram showing an example of a silicon single crystal substrate for a solid-state image pickup device of the present invention.
2 is a schematic diagram showing an example of a single crystal pulling apparatus according to the CZ method.
3A is a schematic diagram showing an example of the solid-state image pickup device of the present invention.
3B is a schematic diagram showing an example of a method for manufacturing a solid-state image pickup device of the present invention.
4 is a block diagram showing an example of an afterimage characteristic evaluation device.
5 is a diagram showing an example of a measurement sequence of a method for evaluating a semiconductor substrate.
6 is a graph showing the results of afterimage characteristic evaluation of Example 1 and Comparative Example 1. Referring to FIG.
7 is a schematic diagram showing an example of a silicon epitaxial wafer for a solid-state image pickup device of the present invention.

As a result of intensive studies on suppressing the afterimage characteristic of a solid-state image sensor, the present invention focuses on the complex of B and oxygen, which is considered to be related to the afterimage characteristic, and, in order to reduce this, as a p-type main pant. Instead of B, the idea was to use Ga.

On the other hand, it is known that an example in which Ga is used instead of B as a p-type dopant is used as a silicon single crystal for solar cells (Patent Document 3).

However, solar cells and solid-state imaging devices are different in manufacturing processes and manufacturers, and thus technical fields are different.

In addition, in the case of solar cells, the purpose is to obtain an effect of suppressing photodegradation, whereas in the case of a solid-state image sensor, since the purpose is to obtain an effect of suppressing the afterimage characteristic, it is completely different in terms of the intended effect. Do.

Therefore, there have been no examples so far in which a p-type silicon single crystal substrate in which Ga is a main pant is used as a silicon single crystal substrate for a solid-state image sensor, and there has been no such idea.

In addition, if the formation of a complex of B and oxygen, which is considered to be related to the afterimage characteristic, is suppressed, it aims to reduce the oxygen concentration, and is made from a FZ substrate (a silicon single crystal produced by the FZ method and containing little oxygen). It is conceivable to use a silicon single crystal substrate obtained by slicing).

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 is obtained by oxygen precipitates, 2) nitrogen is doped to increase the substrate strength. , the fact that the resistivity changes due to the generation of nitrogen donors and the width of the depletion layer of the photodiode part changes and affects the device characteristics, 3) the diameter is one generation smaller than the CZ substrate (the current maximum diameter at the mass production level is , CZ substrate is 300 mm, FZ substrate is 200 mm), etc., so there are few cases in which the FZ substrate is used for a solid-state image pickup device.

From the above, it has been found that if the main substrate is a p-type CZ silicon single crystal substrate with Ga, and the B concentration is as low as 5×10 ¹⁴ atoms/cm ³ or less, the solid-state image sensor has good afterimage characteristics and substrate strength. Thus, the present invention was completed. In addition, it was discovered that a silicon epitaxial wafer having the same silicon epitaxial layer for Ga and B has good residual image characteristics of a solid-state image pickup device, thereby completing the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, although this invention is demonstrated in detail, referring drawings as an example of embodiment, this invention is not limited to this.

1 is a schematic diagram of a silicon single crystal substrate for a solid-state imaging device in 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 in which the main pant is Ga, and the 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, for example, the substrate strength is higher than that of an FZ silicon single crystal substrate containing almost no oxygen, the gettering ability by oxygen precipitates can be obtained, and the substrate diameter There are advantages such as this first-generation big point. On the other hand, the diameter of the substrate is not particularly limited, but may be, for example, 300 mm or more, and further, 450 mm or more.

Note that the main dopant, that is, the dopant that determines the conductivity type of the substrate, is Ga, not B, which is doped in the conventional silicon single crystal substrate for a solid-state image pickup device. In addition, the B concentration is a low value of ^{5×10 14} atoms/cm ^{3 or less.} _{For this reason, it is possible to suppress the residual image characteristics caused by the BO 2} complex, which has been a problem when the solid-state imaging device is manufactured in the case of the conventional product of the master pant B, regardless of the interstitial oxygen concentration, regarding the residual image characteristics, A silicon single-crystal substrate capable of providing a solid-state imaging device of superior quality than that of the prior art.

The Ga concentration is not particularly limited and can be appropriately determined depending on a desired resistivity or the like.

In addition, the lower limit of B concentration is not specifically limited. There is a possibility of unavoidable incorporation during the production of single crystals, but in _{order to prevent the generation of the BO 2} complex, the smaller the number, the more preferable.

On the other hand, as for the dopant, the above conditions may be satisfied, and other dopants other than Ga and B may be mixed.

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

If it is 15 ppma or less, even though no light is incident, oxygen becomes a center of generation in the depletion layer and electron hole pairs are generated, thereby reducing the probability of occurrence of a white defect (or dark current) in which an electric charge is generated.

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

On the other hand, it is more preferable to set it as 10 ppma or less, and 5 ppma or less is still more preferable.

An example of the manufacturing method of the silicon single crystal substrate 10 of this invention is demonstrated in detail below. First, a configuration example of a single crystal pulling apparatus according to the CZ method is shown with reference to FIG. 2 .

The single crystal pulling apparatus 20 includes a bottom chamber 202 for accommodating a crucible 201 for melting a raw material, and a top chamber 204 for accommodating and taking out the pulled single crystal (single crystal rod) 203 . And a wire winding mechanism 205 for pulling up a single crystal is provided on the top of the top chamber 204, and the wire 206 is wound up or rolled up according to the growth of the single crystal. A seed crystal 207 is attached to a longitudinal holder 208 at the tip of the wire 206 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. A heater 211 is disposed, and the heater is surrounded by a heat insulating material 212 . And the inside of the crucible 201 is filled with the melted silicon melt 216 by heating with a heater. And, the crucible 201 is supported by a support shaft 213 capable of rotating and moving vertically, and a driving device 214 for this is attached to the lower portion of the bottom chamber 202 . In addition, a rectifying tube 215 for rectifying the inert gas introduced into the furnace may be used.

Next, a method for producing a silicon single crystal using the above apparatus will be described. First, a polycrystalline silicon raw material and Ga as a dope are put in a crucible 201 and heated with a heater 211 to melt the raw material. In this form, Ga is put into the crucible together with the polycrystalline silicon raw material before melting, but since precise concentration control is required in mass production, a high concentration Ga-doped silicon single crystal is produced, and a dope is produced by crushing it, After melting the polycrystalline silicon raw material, it is preferable to adjust it to the desired concentration and then add it.

Next, when all of the polycrystalline silicon raw material is 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 quietly wound down. The tip of 207 is brought into contact with the silicone melt 216 . At this time, the crucible 201 and the seed crystal 207 rotate in opposite directions to each other, and the inside of the pulling machine is in a state of being filled with an inert gas such as argon, which is flowed from the upper part of the furnace in a reduced pressure state.

When the temperature around the seed crystal 207 is stabilized, the wire 206 is quietly wound while rotating the seed crystal 207 and the crucible 201 in opposite directions to start pulling the seed crystal 207 . Then, necking is performed to eliminate slip dislocations generated in the seed crystal 207 . When necking is performed to the thickness and length at which the slip dislocation disappears, the diameter is gradually enlarged to produce a cone portion of the single crystal 203, and the diameter is enlarged to the desired diameter. When the cone diameter is widened to a predetermined diameter, the process shifts to production of a fixed diameter portion (straight body portion) of 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 single crystal to be grown. Further, the crystal diameter is controlled by adjusting the temperature and the pulling rate.

When the single crystal straight body is pulled up to a predetermined length, this time, the crystal diameter is reduced to produce a tail, the tip of the tail is cut off from the silicon melt surface, and the grown silicon single crystal is wound up to the top chamber 204, and the crystal is cooled. waiting to be When the single-crystal rod is cooled to a temperature at which it can be taken out, it is taken out from the pulling machine, and the process proceeds to processing the crystal into a wafer.

In the machining step, first, the cone and the tail are cut and the periphery of the single crystal rod is cylindrically ground, and then cut into blocks of an appropriate size. Then, the single crystal block made into an appropriate size is sliced with a slicer to form a wafer, then chamfered, lapping, etc. are performed as necessary, and further processing deformation is removed by etching to form a substrate. fabricate the wafer.

In the above example, an example of intentionally doping only Ga was given, but the doping agent is not limited thereto. What is necessary is just to dope Ga as a main pant which determines a conductivity type, and to make B concentration 5x10 ¹⁴ atoms/cm ³ or less.

It can be suitably determined according to a desired resistivity etc.

It is preferable that the resistivity for a solid-state image sensor is, for example, in the range of 0.1-20 ohm-cm.

Fig. 3A shows an example of the solid-state image pickup device of the present invention. Here, a back-illuminated solid-state image sensor is exemplified, but the present invention is not limited thereto.

The solid-state imaging device 30 includes a photodiode unit 303 , a memory unit and an arithmetic unit 304 . The solid-state imaging device 30 is formed by forming various elements on each of the first substrate 301 (the silicon single crystal substrate 10 of the present invention) and the second substrate 302 and bonding them together. conjugation).

The first substrate, i.e., the side on which the photodiode portion 303 is formed, is a p-type CZ silicon single crystal substrate in which the main pant is Ga, as in the silicon single crystal substrate 10 of the present invention, and the B concentration is 5 ×10 ¹⁴ atoms/cm ³ or less.

On the other hand, the second substrate can be, for example, a CZ silicon single crystal substrate. Like the first substrate, the main pant may not be Ga, but may be appropriately determined.

In such a solid-state imaging device 30, since it is the photodiode unit 303 that generates an afterimage characteristic, at least the first substrate 301 is a p-type CZ silicon single-crystal substrate in which the main pant is Ga, and also has a B concentration. A solid-state image pickup device in which the afterimage characteristic is suppressed is obtained by using a value of 5×10 ¹⁴ atoms/cm ^{3 or less.}

An example of the manufacturing method of such a solid-state image sensor 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.

On these substrates, in addition to forming a gate oxide film 305 and the like to form various elements (photodiode portion 303 (light receiving element), memory portion and arithmetic portion 304), STI (element isolation) 306 , a wiring 307 , an interlayer insulating film 308 , and the like are formed.

Thereafter, the first substrate 301 and the second substrate 302 on which various elements are formed are pasted together (bonded together) to fabricate the solid-state image sensor 30 .

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

First, Fig. 7 shows a schematic diagram of a silicon epitaxial wafer for a solid-state image pickup device in the present invention. As shown in FIG. 7 , in the silicon epitaxial wafer 70 of the present invention, on the surface of the silicon single crystal substrate 702 , the main dopant is Ga, and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less p It has a silicon epitaxial layer 701 of the same type. In this case, the original concentration of B in the silicon epitaxial layer 701 is very low and hardly contains oxygen, so even if oxygen and B have diffused from the silicon single crystal substrate 702, a complex of oxygen and B is formed. is suppressed, and the afterimage characteristic can be suppressed.

In addition, the silicon single crystal substrate 702 itself (for example, a master pant etc.) is not limited, It can determine suitably. 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 in which the ^{main dopant is Ga and the 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 an afterimage characteristic by diffusion of B and oxygen into the silicon epitaxial layer 701 by the heat treatment applied to the silicon single crystal substrate.

In addition, 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, it is possible to further increase the gettering ability of metal impurities that may be generated by deposition of the silicon epitaxial layer 701 or heat treatment in a device manufacturing process. In this case, ^{there is a possibility that B may diffuse from the p +} type silicon single crystal substrate to the epitaxial layer, but since oxygen is hardly contained in the epitaxial layer, the formation of a complex of B and oxygen that causes afterimage characteristics can be suppressed. can The upper limit of the concentration of B is not particularly limited, the more the concentration is, the better, for example, it can be up to the limit of the solid solution of B in the silicon single crystal.

At this time, the p ⁺ interstitial oxygen concentration of a-type silicon single crystal substrate include, but not limited to, p ⁺ type in order to prevent the diffusion of oxygen in the epitaxial layer more reliably from the silicon single crystal substrate, and the interstitial oxygen concentration to less than 20ppma It is preferable to set it as 15 ppma or less, and it is more preferable to set it as 15 ppma or less.

Further, the silicon single crystal substrate 702 may be, for example, a ^{p −} type silicon single crystal substrate in which the ^{main pentrant is B and the B concentration is 1×10 16} atoms/cm ³ or less. With such a p ^- type silicon single crystal substrate, B diffused into the epitaxial layer by deposition of the epitaxial layer or heat treatment in the device manufacturing process is limited, so the formation of a complex of B and oxygen in the epitaxial layer is more reliably suppressed. In addition, by increasing the interstitial oxygen concentration of the silicon single crystal substrate, it is possible to increase the gettering ability and the substrate strength. The lower limit of the concentration of B is not particularly limited, and as it is smaller, the formation of a complex of B and oxygen can be suppressed.

Note that the silicon single crystal substrate 702 can be, for example, an n-type silicon single crystal substrate. Since the n-type silicon single crystal substrate contains almost no B, as in the p ⁻ type silicon single crystal substrate, the formation of a complex of B and oxygen in the epitaxial layer is more reliably suppressed, and the interstitial space of the silicon single crystal substrate is further suppressed. By increasing the oxygen concentration, it is possible to increase the gettering ability and the substrate strength.

A method for manufacturing the silicon epitaxial wafer of the present invention will be described.

First, the silicon single crystal substrate 702 can be obtained by, for example, manufacturing, slicing, chamfering, etc. using a CZ method single crystal pulling apparatus 20 as shown in FIG. 2 . On the other hand, in the case of intentionally doping B, at the time of pulling up a single crystal, the B dope agent may be melted together with the raw material to a desired concentration.

Then, a silicon epitaxial layer 701 is laminated on the manufactured silicon single crystal substrate 702 . In this case, the epitaxial apparatus to be used is not specifically limited, For example, the thing similar to the prior art can be used. A silicon single crystal substrate 702 is placed on a susceptor in the furnace, the inside of the furnace is heated, and trichlorosilane as a carrier gas and raw material gas flows into the furnace, and at the same time, it is used for Ga doping. For example, a gas containing gallium chloride is also allowed to flow. ^{Accordingly, the epitaxial layer 701 is suppressed to a concentration of 5×10 14} atoms/cm ³ or less (the smaller the number is, the better) even if the main pant is Ga p-type, and B is unavoidably mixed. It can be laminated, so that the silicon epitaxial wafer 70 of the present invention can be manufactured.

In addition, the method of Ga doping is not limited to the above, According to a desired density|concentration, etc., it can determine suitably.

Next, a solid-state image pickup device using such a silicon epitaxial wafer will be described, but the present invention is not limited thereto.

Like the solid-state imaging device 30 using the silicon single crystal substrate of FIG. 3A described above, it is a solid-state imaging device having a photodiode unit, a memory unit, and an arithmetic unit. 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 in this case, the silicon epitaxial wafer 70 is replaced with the above-mentioned silicon epitaxial wafer 70 . do.

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 with respect to afterimage characteristics, a solid having superior quality than before. become an imaging device.

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)

Using the apparatus shown in Fig. 2, a CZ silicon single crystal was pulled up and sliced to prepare a p-type silicon single crystal substrate for a solid-state image pickup device of the present invention in which the main pant was Ga. In production, specific parameters are as follows. On the other hand, Ga was intentionally doped, but B is considered to be unavoidably mixed.

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

(Comparative Example 1)

A p-type silicon single-crystal substrate for a conventional solid-state image pickup device having a main principal of B was fabricated. In production, specific parameters are as follows. Other than that, it carried out similarly to Example 1, and produced it.

Diameter 300mm, crystal orientation <100>, oxygen concentration: 3.4~10.5ppma, resistivity 10Ωcm, B concentration: 1×10 ¹⁵ atoms/cm ³

Using the substrates of Example 1 and Comparative Example 1, a PN junction was formed, and the oxygen concentration dependence of the afterimage characteristic was compared at the substrate level (evaluated by "leak current ratio before and after light irradiation" after annealing at 450°C for 75 hours. ). The evaluation apparatus and method will be described in detail below.

In order to demonstrate a specific evaluation method, an example of the afterimage characteristic evaluation apparatus 40 is shown in FIG. This evaluation device includes a device (illumination) 403 for irradiating a semiconductor substrate 402 having a PN junction structure 401, an optical fiber 404, and a device for measuring the amount of light ( illuminometer) 405 and a current meter (SMU) 407 equipped with a Kelvin probe 406 . Then, after installing the substrate, irradiating the surface of the semiconductor substrate 402 with light of a predetermined illuminance for a predetermined time (a step of performing light irradiation), and after turning off the light irradiation, a step of measuring the amount of carriers generated after light irradiation; do

Here, for light irradiation, a white light LED was used. In addition, although it is the light quantity at the time of measurement, it was set as 500 lux. In addition, the time of light irradiation was made into 10 second.

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

The amount of carriers generated by light irradiation is affected by the type of the semiconductor substrate 402 and the light element contained in the semiconductor substrate 402 , particularly carbon. Therefore, in order to avoid that the difference in the amount of carriers originally generated by light irradiation affects the afterimage characteristic, as shown in Fig. 5, the amount of carriers generated once during light irradiation (the amount of carriers generated during light irradiation) measured. In this way, the semiconductor substrate was 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 after turning off light irradiation was made into 1 second.

In addition, in Fig. 5 , the reason for stopping the measurement once before measuring the amount of generated carriers after turning off light irradiation is to more reliably avoid noise when light irradiation is turned off.

And the afterimage characteristic was evaluated from the ratio of the current value of the carrier measurement probe at the time of light irradiation on-off. For example, a high current value after light irradiation is off indicates that carriers are trapped by that much, and it can be inferred that the afterimage characteristic is bad.

Even in the example of an actual solid-state image sensor, when the shutter is opened, an electric charge is generated by an electron-hole pair generated by incident light, and an image is formed by taking this in. However, after closing the shutter, the electron/hole pair is rapidly generated. It is important that hole pairs are ejected, which, if delayed, is an afterimage, which affects the next frame.

(Evaluation results of Example 1 and Comparative Example 1)

6 shows the evaluation results. It can be seen that, in the case of Comparative Example 1 (B main dope), the current ratio before and after light irradiation is larger than in Example 1 (Ga main dope) at any oxygen concentration [Oi], and the afterimage characteristic is 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 annealing at 450° C. for 75 hours, the current value changes in Comparative Example 1 of the B-doped crystal in which _{BO 2 defects are generated, but in Example 1 of the Ga-doped crystal, BO 2} formation is suppressed, so the current value changes (change in afterimage characteristics) ) is suppressed. Further, in Comparative Example 1, it can be seen that the current ratio increases as the oxygen concentration increases, and the afterimage characteristic tends to deteriorate with the increase in the oxygen concentration.

On the other hand, in the case of Example 1, even when the oxygen concentration is increased, the current ratio before and after light irradiation is almost constant at a low value (a value close to 1), and it can be determined that the afterimage characteristic is good.

(Example 2)

Using the apparatus shown in Fig. 2, a CZ silicon single crystal was pulled up and sliced to prepare a p-type silicon single crystal substrate for a solid-state image pickup device of the present invention having a main pant of Ga. In production, specific parameters are as follows. On the other hand, it was produced by intentionally doping a small amount of B in addition to Ga.

Diameter 300mm, crystal orientation <100>, oxygen concentration: 5ppma, resistivity 4Ωcm, Ga concentration: 3×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹⁴ atoms/cm ³

And it carried out similarly to Example 1, and evaluated the afterimage characteristic.

(Evaluation result of Example 2)

The current ratio before and after light irradiation is about 1.6, and it can be determined that the afterimage characteristic is good.

(Example 3)

In order to manufacture a silicon epitaxial wafer for a solid-state image pickup device of the present invention, first, a CZ silicon single crystal is pulled up using the apparatus shown in FIG. 2 and sliced to prepare a p-type silicon single crystal substrate having a main pant of Ga, On this substrate, a p-type epitaxial layer in which the main dopant is Ga was formed. In production, 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 by SIMS)

(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 the lower limit by SIMS)

And it carried out similarly to Example 1, and evaluated the afterimage characteristic.

(Evaluation result of Example 3)

The current ratio before and after light irradiation is about 1.8, and it can be judged that the afterimage characteristic is 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 ),} It carried out similarly to Example 1, and evaluated the afterimage characteristic.

(Evaluation result of Comparative Example 2)

The current ratio before and after light irradiation is about 8.2, which is large compared to Example 3, and it can be seen that the afterimage characteristic is inferior.

(Example 4)

In order to manufacture a silicon epitaxial wafer for a 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 prepare a p ⁺ type silicon single crystal substrate having a main pant B. , on this substrate, a p-type epitaxial layer in which the main dopant is Ga was formed. In production, 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: 5 μm, resistivity 10 Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (below the lower limit by SIMS)

And it carried out similarly to Example 1, and evaluated the afterimage characteristic.

(Evaluation result of Example 4)

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

(Example 5)

In order to fabricate a silicon epitaxial wafer for a 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 prepare a p ^- type silicon single crystal substrate having a main pant B. , on this substrate, a p-type epitaxial layer in which the main dopant is Ga was formed. In production, 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: 5 μm, resistivity 10 Ωcm, Ga concentration: 1×10 ¹⁵ atoms/cm ³ , B concentration: 5×10 ¹³ atoms/cm ³ or less (below the lower limit by SIMS)

And it carried out similarly to Example 1, and evaluated the afterimage characteristic.

(Evaluation result of Example 5)

The current ratio before and after light irradiation is about 2.2, and it can be determined that the afterimage characteristic is good.

(Example 6)

In order to manufacture a silicon epitaxial wafer for a 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 prepare a p-type silicon single crystal substrate having a main pant of Ga, On this substrate, a p-type epitaxial layer in which the main dopant is Ga was formed. In production, specific parameters are as follows. On the other hand, the epitaxial layer was prepared by intentionally doping a small amount of B in addition to Ga.

(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 by SIMS)

(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

And it carried out similarly to Example 1, and evaluated the afterimage characteristic.

(Evaluation result of Example 6)

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

In addition, this invention is not limited to the said embodiment. The above-mentioned embodiment is an illustration, and any thing which has substantially the same structure as the technical idea described in the claim of this invention, and shows the same operation and effect is included in the technical scope of this invention.

10… p-type silicon single crystal substrate
20… single crystal pulling device
201… Crucible
202… bottom chamber
203... single crystal
204… top chamber
205… wire winding mechanism
206... wire
207... seed crystal
208… bell holder
209... quartz crucible
210… graphite crucible
211… heater
212... insulator
213... support shaft
214... drive
215... Rectification tube (整流筒)
216... silicone melt
30… solid-state imaging device
301… the first substrate
302... second substrate
303… photodiode part
304… memory and arithmetic
305… gate oxide film
306… STI (Element Isolation)
307... Wiring
308… interlayer insulating film
40… Afterimage characteristic evaluation device
401... PN junction
402... Board
403... light
404... optical fiber
405... light meter
406... Kelvin probe
407... Current Meter (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, comprising:
The silicon single crystal substrate is a p-type silicon single crystal substrate in which the main pant is Ga, and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less. According to claim 1,
A silicon single crystal substrate for a solid-state imaging device, wherein the interstitial oxygen concentration in the p-type silicon single crystal substrate is 1 ppma or more and 15 ppma or less. A solid-state imaging device having a photodiode unit, a memory unit, and an arithmetic unit, comprising:
A solid-state image pickup device, characterized in that at least the photodiode portion is formed on the silicon single crystal substrate for the solid-state image pickup device according to claim 1 or 2. A silicon epitaxial wafer for a solid-state imaging device having a silicon epitaxial layer on a surface of a silicon single crystal substrate, the silicon epitaxial wafer comprising:
The silicon epitaxial wafer for a solid-state imaging device, wherein the silicon epitaxial layer is a p-type epitaxial layer in which the main pant is Ga, and the B concentration is 5×10 ¹⁴ atoms/cm ^{3 or less.} 5. The method of claim 4,
The silicon single crystal substrate is a p-type silicon single crystal substrate in which the main pant is Ga, and the B concentration is 5×10 ¹⁴ atoms/cm ³ or less. 5. The method of claim 4,
The silicon single crystal substrate is a silicon epitaxial wafer for a solid-state image pickup device ^{, wherein the silicon single crystal substrate is a p +} type silicon single crystal substrate having a main dopant of B and a B concentration of 1×10 ¹⁸ atoms/cm ^{3 or more.} 5. The method of claim 4,
The silicon single crystal substrate is a silicon epitaxial wafer for a solid state image pickup device ^{, wherein the silicon single crystal substrate is a p −} type silicon single crystal substrate having a main dopant of B and a B concentration of 1×10 ¹⁶ atoms/cm ³ or less. 5. The method of claim 4,
The silicon epitaxial wafer for a solid-state imaging device, wherein the silicon single crystal substrate is an n-type silicon single crystal substrate. A solid-state imaging device having a photodiode unit, a memory unit, and an arithmetic unit, comprising:
At least the photodiode portion is formed in the silicon epitaxial layer of the silicon epitaxial wafer for a solid-state image pickup device according to any one of claims 4 to 8.

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