KR101341132B1 - Epitaxial substrate for back illuminated solid-state imaging device and manufacturing method thereof - Google Patents

Abstract

An object of the present invention is to provide an epitaxial substrate and a method for manufacturing the back-illuminated solid-state image pickup device at a higher production rate.
The epitaxial substrate 100 for back-illumination type solid-state image pickup device of the present invention includes a p-type silicon substrate 1 having carbon, carbon and nitrogen added thereto, and a resistivity of less than 100? Cm, and p on the p-type silicon substrate. A first type epitaxial layer 2 and a p-type or n-type second epitaxial layer 3 on the first epitaxial layer, wherein the first epitaxial layer 2 is formed of a p-type impurity. It is characterized by the peak concentration being 2.7 x 10 ¹⁷ atoms / cm 3 or more and less than 1.1 x 10 ¹⁹ atoms / cm 3.

Description

Epitaxial substrate for back-illumination type solid-state image pickup device and its manufacturing method {EPITAXIAL SUBSTRATE FOR BACK ILLUMINATED SOLID-STATE IMAGING DEVICE AND MANUFACTURING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial substrate for a backside irradiation solid-state image pickup device and a manufacturing method thereof, and more particularly to an epitaxial substrate capable of producing a backside irradiation type solid state image pickup device at a high production rate.

The back-illumination type solid-state image pickup device used in digital video cameras, mobile phones, and the like, can arrange a wiring layer or the like below the sensor unit to directly introduce light from the outside into the sensor to capture clearer images and videos even in dark places. It is widely used in recent years. When manufacturing such a back-illumination type solid-state image sensor, metal may be mixed as an impurity in a semiconductor substrate. The metal mixed in the semiconductor substrate becomes a factor of increasing the dark current of the solid state image pickup device, and causes a defect called a white spot defect.

Incorporation of the metal into the semiconductor substrate mainly occurs in the manufacturing process of the semiconductor epitaxial substrate and the manufacturing process of the solid state imaging device. Metal contamination in the former semiconductor epitaxial substrate manufacturing process is caused by heavy metal particles from the constituent material of the epitaxial growth furnace, or by using chlorine gas as the furnace gas during epitaxial growth. Consideration is given to heavy metal particles resulting from metal corrosion. In recent years, such metal contamination has been improved to some extent by replacing the constituent material of the epitaxial growth furnace with a material having excellent corrosion resistance, but this is not sufficient. On the other hand, in the manufacturing process of the latter solid-state image pickup device, there is a fear that heavy metal contamination of the semiconductor substrate during each treatment such as ion implantation, diffusion, and oxidative heat treatment.

Therefore, conventionally, a gettering sink for trapping metal is formed on a semiconductor epitaxial substrate, or a metal with respect to a semiconductor substrate is formed by using a substrate having a high metal trapping ability (gettering capability) such as a high concentration boron substrate. Pollution has been avoided.

The method of forming a gettering sink on a semiconductor substrate includes an intrinsic gettering (IG) method of forming an oxygen precipitate (commonly known as a silicon oxide precipitate, also referred to as a BMD: Bulk Micro Defect) as a crystal defect in a semiconductor substrate; It is roughly classified by the Extrinsic Gettering (EG) method, which forms a gettering sink on the back surface of the semiconductor substrate.

As an example using the IG method, in forming a device by growing an epitaxial layer on a silicon substrate, by adding carbon and / or nitrogen to the silicon substrate, oxygen precipitates are stably formed in the semiconductor substrate. The method of obtaining a high gettering capability is known (refer patent document 1).

Here, in manufacturing a backside irradiation solid-state imaging device, an epitaxial substrate (see Patent Document 2) in which two epitaxial layers are formed on a p-type silicon substrate can be used. When the first epitaxial layer and the second epitaxial layer are sequentially formed from the silicon substrate, the second epitaxial layer, which is the top epitaxial layer on the surface of the epitaxial substrate, becomes the device layer for manufacturing the device. Here, the first epitaxial layer is a p-type epitaxial layer doped with boron or the like. As a result, the first epitaxial layer has a lower resistivity than the substrate. For this reason, in order to remove a silicon substrate and a 1st epitaxial layer and leave a device layer after a device manufacture, and to make a thin film device, when an etching or polishing etc. is performed from the board | substrate side, a 1st epitaxial layer is an etching stop layer or It functions as a polishing stop layer.

Patent Document 1: Japanese Patent Publication No. 2002-201091 Patent Document 2: Japanese Patent Application Publication H08-241977

The inventors of the present invention have investigated the device characteristics of the back-illuminated solid-state imaging device manufactured in this way, and found that despite the formation of a gettering sink, many devices cannot obtain desired characteristics, resulting in low product yield. As a result, the inventors have carefully examined that the heat treatment in the device manufacturing process led to the recognition that the p-type impurity of the first epitaxial layer was diffused into the device layer (second epitaxial layer). If a large amount of p-type impurities are diffused from the first epitaxial layer into the device layer, an impurity profile (concentration distribution in the thickness direction) different from the desired design is formed in the device layer, so that desired characteristics are not obtained.

Furthermore, the present inventors have noticed that this phenomenon is particularly remarkable when using a p-type silicon substrate containing carbon in order to increase the gettering capability, compared to a case of using a p-type silicon substrate without carbon. It was found that the production rate was further lowered. According to this finding, when a p-type silicon substrate without carbon is used, diffusion of p-type impurities from the first epitaxial layer to the device layer can be suppressed, but sufficient gettering capability cannot be obtained.

In view of the above problems, the present invention provides an epitaxial substrate on which a p-type first epitaxial layer is formed on a p-type silicon substrate to which carbon is added, and the second epitaxial layer thereon is a device layer. An object of the present invention is to provide an epitaxial substrate and a method for manufacturing the back-illuminated solid-state image pickup device at a higher product production rate (specifically, 80% or more).

Diffusion of p-type impurities from the first epitaxial layer to the second epitaxial layer serving as the device layer is a phenomenon which directly adversely affects the device characteristics. On the other hand, doping the p-type impurity to the first epitaxial layer is intended to give a function as an etching stop or polishing stop, and carefully removes the p-type impurity concentration in the first epitaxial layer even if the concentration of the p-type impurity is slightly lowered. Etching or polishing), the possibility of removing even the device layer can be reduced. Accordingly, the present inventors set the p-type impurity concentration of the first epitaxial layer to be low in a range in which the first epitaxial layer functions as an etching stop or polishing stop, thereby suppressing the diffusion of the p-type impurity into the device layer. Considering that a higher product production rate can be obtained, the present invention has been completed.

This invention is based on said knowledge and examination, The summary structure is as follows.

(1) p-type silicon substrate having carbon or carbon and nitrogen added and resistivity of less than 100? Cm, a p-type first epitaxial layer on the p-type silicon substrate, and a p-type on the first epitaxial layer or has an n-type second epitaxial layer,

The epitaxial substrate for back-illumination type solid-state image pickup device according to claim 1, wherein the peak concentration of the p-type impurity is 2.7 × 10 ¹⁷ atoms / cm 3 or more and less than 1.1 × 10 ¹⁹ atoms / cm 3.

(2) The epitaxial substrate for back-illumination type solid-state image pickup device according to (1), wherein the first epitaxial layer has a thickness of 4 µm or more and 10 µm or less.

(3) The epitaxial substrate for back-illumination type solid-state image pickup device according to (1) or (2), wherein the second epitaxial layer has a thickness of 4 µm or more and 10 µm or less.

(4) In the said p-type silicon substrate, it is provided with the area | region which has the said carbon or carbon, nitrogen, and the deposit containing oxygen,

The back-illumination type solid-state imaging device according to (1) or (2), wherein the density of the precipitate in the depth-oriented central portion of the p-type silicon substrate in the region is 5 × 10 ⁵ / cm 2 or more and 5 × 10 ⁷ / cm 2 or less. Epitaxial substrate.

(5) The backside irradiation solid according to (1) or (2), wherein the p-type second epitaxial layer has a peak concentration of p-type impurities of 4.4 × 10 ¹³ atoms / cm 3 or more and 2.8 × 10 ¹⁷ atoms / cm 3 or less. An epitaxial substrate for an imaging device.

(6) The backside irradiation solid according to (1) or (2), wherein the n-type second epitaxial layer has a peak concentration of n-type impurities of 1.4 × 10 ¹³ atoms / cm 3 or more and 7.8 × 10 ¹⁶ atoms / cm 3 or less. An epitaxial substrate for an imaging device.

(7) The epitaxial substrate for back-illumination type solid-state image pickup device according to (5), wherein the p-type impurity is boron.

(8) The epitaxial substrate for back-illumination type solid-state image sensor according to (6), wherein the n-type impurity is phosphorus.

(9) The back-illumination solid according to the above (1) or (2), wherein the p-type silicon substrate containing only carbon has an average concentration of carbon of 0.1 × 10 ¹⁶ atoms / cm 3 or more and 20 × 10 ¹⁶ atoms / cm 3 or less. An epitaxial substrate for an imaging device.

(10) In the p-type silicon substrate to which both carbon and nitrogen are added, the average concentration of carbon is 0.1 × 10 ¹⁶ atoms / cm 3 or more and 20 × 10 ¹⁶ atoms / cm 3 or less, and the average concentration of nitrogen is 0.5 × 10 ^13. An epitaxial substrate for back-illumination type solid-state image pickup device according to (1) or (2), wherein atoms / cm 3 or more and 50 × 10 ¹³ atoms / cm 3 or less.

(11) a step of forming a p-type first epitaxial layer on a p-type silicon substrate having carbon or carbon and nitrogen added thereto, and having a resistivity of less than 100? Cm; and a p-type on the first epitaxial layer Or a step of forming an n-type second epitaxial layer,

The peak concentration of the p-type impurity in the first epitaxial layer is 2.7 × 10 ¹⁷ atoms / cm 3 or more and less than 1.1 × 10 ¹⁹ atoms / cm 3. Manufacturing method.

(12) The method for producing an epitaxial substrate for a backside irradiation type solid-state image sensor according to (11), wherein the first epitaxial layer has a thickness of 4 µm or more and 10 µm or less.

(13) The backside irradiation type according to (11) or (12), wherein the silicon substrate before the first epitaxial layer forming step has a lattice oxygen concentration of 1 × 10 ¹⁸ atoms / cm 3 or more and 2 × 10 ¹⁸ atoms / cm 3 or less. A method of manufacturing an epitaxial substrate for a solid state image pickup device.

(14) After the step of forming the second epitaxial layer, (11) comprising a heat treatment step for forming a region having a precipitate containing carbon, carbon, nitrogen, and oxygen in the p-type silicon substrate; Or the manufacturing method of the epitaxial board | substrate for back side irradiation type solid-state image sensor as described in (12).

(15) The heat treatment step,

After heating the silicon substrate to a first temperature within the range of 500 to 800 ° C., low temperature heat treatment is performed for 10 to 180 minutes at the first temperature,

Subsequently, (14) comprising heating to a second temperature within a range of 900 to 1150 ° C. at a temperature rising rate of 4 ° C./min or less, and then performing a high temperature heat treatment for 15 to 200 minutes at the second temperature. The manufacturing method of the epitaxial substrate for backside irradiation type solid-state image sensor of description.

According to the present invention, diffusion of the p-type impurity into the device layer can be suppressed by setting the peak concentration of the p-type impurity in the first epitaxial layer to be 2.7 × 10 ¹⁷ atoms / cm 3 or more and less than 1.1 × 10 ¹⁹ atoms / cm 3. Therefore, it is possible to manufacture the back-illumination type solid state image pickup device at a high production rate.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic cross section which shows the epitaxial substrate for backside irradiation type solid-state image sensor which is one Embodiment of this invention.
FIG. 2: is a schematic cross section explaining the manufacturing method of the epitaxial substrate for backside irradiation type solid-state image sensor which is one Embodiment of this invention.
Fig. 3 is a graph showing the distribution of boron concentration with respect to the depth from the epitaxial substrate surface for the epitaxial substrate of the comparative example, (a) shows an epitaxial substrate before heat treatment, and (b) shows an epitaxial substrate after heat treatment. .
4 is a graph showing the thermal history of heat treatment performed on the epitaxial substrate (corresponding to the device manufacturing process) in Comparative Examples and Examples.
FIG. 5 is a graph showing the distribution of carbon concentration to depth from the surface of the epitaxial substrate in Example, where (black square) is an epitaxial substrate before heat treatment, and (white square) is an epitaxial substrate after heat treatment. Indicates.
6 is a graph showing the distribution of carbon concentration to depth from the surface of the epitaxial substrate in a more preferred embodiment, where (black square) is an epitaxial substrate before heat treatment, and (white square) is epitaxial after heat treatment. Represents a tactical substrate.

Hereinafter, the present invention will be described in more detail with reference to the drawings. In addition, the same reference numeral is used for the same component as a principle, and description is abbreviate | omitted.

(Epitaxial substrate for back-illumination solid-state image pickup device)

An epitaxial substrate 100 for a backside illumination solid-state image pickup device according to the present invention includes a p-type silicon substrate 1, a p-type first epitaxial layer 2 on the p-type silicon substrate, and the first epitaxial substrate. The p-type or n-type second epitaxial layer 3 on the tactile layer 2 is provided. In FIG. 1, for convenience of explanation, the thickness is different from the actual thickness ratio, and the thicknesses of the first and second epitaxial layers are exaggerated for the silicon substrate 1.

In order to fully obtain the gettering capability, the p-type silicon substrate 1 has carbon, or carbon and nitrogen added thereto, and the resistivity is less than 100 Ω · cm, preferably 0.008 Ω · cm or more. The p-type impurity of the p-type silicon substrate 1 is preferably boron, and its average concentration is preferably larger than 1.3 × 10 ¹⁴ atoms / cm 3 and 1.1 × 10 ¹⁹ atoms / cm 3 or less.

The second epitaxial layer 3 is a device layer for manufacturing a backside irradiation solid-state image pickup device. The first epitaxial layer 2 is a p-type epitaxial layer and leaves the second epitaxial layer 3 after the device is fabricated, and is formed from the rear surface side (silicon substrate 1 side) of the epitaxial substrate 100. When performing etching or polishing, it serves as an etch stop layer or a polishing stop layer. That is, since the resistivity of the first epitaxial layer 2 is smaller than that of the silicon substrate 1, the removal of the silicon substrate 1 can be detected based on the change in the resistivity. For example, when the silicon substrate 1 is removed by etching, the etching rate of the first epitaxial layer 2 is lower than that of the silicon substrate 1, and the etching rate can be detected. When removing the silicon substrate 1, it can detect by the change of the resistance value at the time of grinding | polishing.

In addition, in this specification, the process of "device manufacture" specifically means from the epitaxial layer growth process in a semiconductor epitaxial substrate formation process to the formation process of a solid-state image sensor.

Here, as a characteristic configuration of the present invention, the first epitaxial layer 2 has a peak concentration of p-type impurity of not less than 2.7 × 10 ¹⁷ atoms / cm 3 and less than 1.1 × 10 ¹⁹ atoms / cm 3. The technical significance of adopting such a configuration will be explained along with the effect. Regardless of whether or not carbon is added to the silicon substrate 1, the p-type impurity of the first epitaxial layer is somewhat diffused by heat treatment according to its diffusion coefficient. However, as previously described, it is found that this phenomenon is particularly remarkable when using a silicon-doped silicon substrate to increase the gettering capability, compared to a p-type silicon substrate without carbon. It became. Although the cause of this phenomenon is not necessarily clear, the inventors of the present invention have found that the addition of carbon increases the density of precipitates in the silicon substrate, and the interstitial silicon generated thereby causes the diffusion rate of the p-type impurity in the first epitaxial layer. It is estimated to increase. Therefore, by setting the peak concentration of the p-type impurity in the first epitaxial layer to be less than 1.1 × 10 ¹⁹ atoms / cm 3, the p-type from the first epitaxial layer to the second epitaxial layer in the heat treatment of the device manufacturing process. The diffusion amount of impurities can be reduced. When the peak concentration of the p-type impurity is less than 2.7 x 10 ¹⁷ atoms / cm 3, the difference in resistivity between the silicon substrate and the first epitaxial layer becomes small, and the difference in etching rate for the purpose of etching stopping is also remarkably confirmed. Since it tends not to be made, it is set to 2.7 * 10 <^17> atoms / cm <3> or more.

In addition, from the viewpoint of both suppressing impurity diffusion and eliminating stop function, the preferred peak concentration of the p-type impurity of the first epitaxial layer is higher than the p-type impurity concentration of the silicon substrate 1, and is 2.7 × 10 ¹⁷ atoms / cm 3. It is larger, More preferably, it is 3.2 * 10 <^17> atoms / cm <3> or more and 1.1 * 10 <^19> atoms / cm <3> or less.

It is preferable that the 1st epitaxial layer 2 is 4 micrometers or more and 10 micrometers or less, It is more preferable that it is more than 5 micrometers and 10 micrometers or less, It is further more preferable that they are 6 micrometers or more and 10 micrometers or less. In the present invention, since the peak concentration of the p-type impurity in the first epitaxial layer is lowered, the phenomenon of lowering the etching rate in the first epitaxial layer is hardly obtained. Without detecting the completion of removal, the probability of starting removal to the second epitaxial layer can be reduced. Moreover, by setting it as 10 micrometers or less, the curvature of the board | substrate by thickening can be suppressed. On the other hand, the warpage of the epitaxial substrate is caused by lattice constant aberration between layers (the interface between the substrate and the first epitaxial layer), and the lattice constant becomes smaller as the p-type impurity concentration is higher. In the present invention, since the peak concentration of the p-type impurity is lowered, the difference in the p-type impurity concentration at the interface between the silicon substrate and the first epitaxial layer, that is, the difference between the lattice constants, becomes smaller. This is in a difficult state to occur.

Furthermore, by setting the thickness of the first epitaxial layer 2 to 4 mu m or more, diffusion of carbon from the silicon substrate 1 to the second epitaxial layer 3 due to the heat treatment during device manufacturing is sufficiently suppressed. You may.

It is preferable that the 2nd epitaxial layer 3 is 4 micrometers or more and 10 micrometers or less. This is because when the thickness is less than 4 µm, the spectral sensitivity of long-wave incident light may decrease. On the other hand, when the thickness exceeds 10 µm, the flatness of the wafer may decrease. On the other hand, if the amount of diffusion of the p-type impurity into the second epitaxial layer is large, the second epitaxial layer is thickened to remove the region near the first epitaxial layer among the second epitaxial layers after device fabrication. A process may be necessary. However, in the present invention, since the amount of diffusion of the p-type impurity into the second epitaxial layer is small, the thickness of the second epitaxial layer can be reduced to 5 µm or less.

In the p-type silicon substrate 1, a region 4 having a precipitate containing carbon or carbon and nitrogen and oxygen is provided, and the center portion in the depth direction of the p-type silicon substrate 1 of the precipitate region 4 is provided. It is preferable that the density of the precipitate in is 5 * 10 <^5> / cm <2> or more and 5 * 10 <^7> / cm <2> or less. If the density of the precipitate is less than 5 × 10 ⁵ / cm 2, there is a fear that the gettering ability is insufficient, while even if the density of the precipitate exceeds 5 × 10 ⁷ / cm 2, epi defects due to excessive precipitation may occur. This is because there is concern. In addition, such a precipitate can be formed by the heat processing process mentioned later. That is, the said precipitate density is a thing after a heat processing process. Moreover, it is preferable to make the size of a precipitate into the range of 10 nm-300 nm. In addition, the said precipitate was measured by etching an epitaxial substrate about 2 micrometers by light etching, and observing an etching surface with an optical microscope. In this specification, when carbon is added to the silicon substrate 1, a "precipitate" means a carbon, oxygen-type precipitate, when carbon and nitrogen are added, and carbon and nitrogen-type precipitates.

In order to ensure sufficient depletion layer in the photodiode, the p-type second epitaxial layer 3 preferably has a peak concentration of p-type impurities of 4.4 × 10 ¹³ atoms / cm 3 or more and 2.8 × 10 ¹⁷ atoms / cm 3 or less. Do.

In order to ensure sufficient depletion layer in the photodiode, the n-type second epitaxial layer 3 preferably has a peak concentration of n-type impurities of 1.4 × 10 ¹³ atoms / cm 3 or more and 7.8 × 10 ¹⁶ atoms / cm 3 or less. Do.

Examples of the p-type impurity of the first epitaxial layer and / or the second epitaxial layer include boron, aluminum, and the like. In particular, it is preferable to use boron in terms of gettering heavy metals having a positive charge in the crystal and ensuring etching stoppage.

Examples of the n-type impurity of the second epitaxial layer include phosphorus, arsenic, and the like. In particular, it is preferable to use phosphorus from the viewpoint of the ease of circuit design in a CMOS process.

In the case of the p-type silicon substrate 1 containing only carbon, the average concentration of carbon is preferably 0.1 × 10 ¹⁶ atoms / cm 3 or more and 20 × 10 ¹⁶ atoms / cm 3 or less. If the carbon concentration is less than 0.1 x 10 ¹⁶ atoms / cm 3, the precipitate cannot be formed sufficiently. On the other hand, if the carbon concentration is more than 20 x 10 ¹⁶ atoms / cm 3, the size of the precipitate becomes small and exhibits gettering capability. This is because there is a risk that the necessary distortion may not be obtained.

In the case of the p-type silicon substrate 1 to which both carbon and nitrogen are added, the average concentration of carbon is similarly 0.1 × 10 ¹⁶ atoms / cm 3 or more and 20 × 10 ¹⁶ atoms / cm 3 or less, and the average concentration of nitrogen is 0.5 × to 10 ¹³ atoms / ㎤ more than 50 × 10 ¹³ atoms / ㎤ or less. If nitrogen is added to the silicon substrate, the effect of increasing the precipitate size can be obtained. If the nitrogen concentration is less than 0.5 × 10 ¹³ atoms / cm 3, the effect of increasing the precipitate size may not be obtained. If the nitrogen concentration exceeds 50 × 10 ¹³ atoms / cm 3, the precipitate size becomes too large, This is because there is a fear that the defects are stretched in the epitaxial layer.

(Method of manufacturing epitaxial substrate for backside illuminated solid state image pickup device)

FIG. 2: is a schematic cross section explaining the manufacturing method of the epitaxial board | substrate 100 for backside irradiation type solid-state image sensor which is one Embodiment of this invention. In the method for producing the epitaxial substrate 100, a p-type silicon substrate 1 having carbon or carbon and nitrogen added thereto and a resistivity of less than 100 Ω · cm is prepared (FIG. 2 (a)), and on the surface thereof. to form the p-type first epitaxial layer 2 (FIG. 2B), and the p-type or n-type second epitaxial layer 3 on the first epitaxial layer 2. It has a process (FIG. 2 (c)) to form. And the p-type impurity to a 2nd epitaxial layer by making the peak concentration of p-type impurity in the 1st epitaxial layer 2 into 2.7 * 10 <^17> atoms / cm <3> or more and less than 1.1 * 10 <^19> atoms / cm <3>. Diffusion can be suppressed, and the back-illumination solid-state image pickup device can be manufactured at a high production rate. As described above, the first epitaxial layer 2 preferably has a thickness of 4 µm or more and 10 µm or less.

In the silicon substrate 1 before the first epitaxial layer forming step (FIG. 2), the oxygen concentration between lattice is preferably 1 × 10 ¹⁸ atoms / cm 3 or more and 2 × 10 ¹⁸ atoms / cm 3 or less. If the interstitial oxygen concentration is less than 1 × 10 ¹⁸ atoms / cm 3, the precipitate that functions as a gettering sink cannot be formed sufficiently. On the other hand, if the interstitial oxygen concentration exceeds 2 × 10 ¹⁸ atoms / cm 3, the precipitates This is because the size per unit increases, and the potential for the dislocation to escape to the epitaxial layer increases.

After the step of forming the second epitaxial layer 3 (Fig. 2 (c)), a heat treatment for forming a region having carbon, carbon, nitrogen and precipitates containing oxygen in the p-type silicon substrate 1 It is preferable to carry out the process (Fig. 2 (d)). A sufficient gettering capability can be obtained from the beginning of the device process by performing a heat treatment to form a precipitate region after the epitaxial substrate manufacturing process and before the device manufacturing process, instead of forming the oxygen precipitate by the heat treatment during device manufacturing. have.

In the heat treatment step (FIG. 2 (d)), the silicon substrate 1 is heated to a first temperature within a range of 500 to 800 ° C., and then a low temperature heat treatment is performed for 10 to 180 minutes at the first temperature. , Heating to a second temperature within the range of 900 to 1150 ° C. at a temperature rising rate of 4 ° C./min or less, and then performing a high temperature heat treatment for 15 to 200 minutes at the second temperature. By performing this two-step heat treatment, precipitates can be precipitated to form the precipitate region 4 in the silicon substrate 1. As the precipitate, for example, there may be mentioned SiO _2, SiOC or the like.

1 and 2 show examples of typical embodiments, and the present invention is not limited to these embodiments.

(How to measure)

Below, the measuring method of the numerical value prescribed | regulated by this invention is collectively demonstrated.

Peak concentration or average concentration of carbon or nitrogen: Measure the concentration distribution in the depth direction by SIMS (Secondary Ion Mass Spectrometer), and the maximum concentration in the target depth section is called "peak concentration", and the average concentration in the target depth section It is called "average concentration."

Peak concentration of p-type or n-type impurity: Similarly obtained by SIMS measurement.

Membrane Thickness: FT-IR

Precipitate Density: The epitaxial substrate is etched by light etching about 2 占 퐉 and measured by observing the etching surface with an optical microscope.

Oxygen concentration between lattice: FT-IR (ASTM F121-1979)

Lattice-substituted carbon concentration: FT-IR (ASTM F123-1981)

Oxygen concentration in high boron concentration silicon: SIMS

Carbon concentration in high boron concentration silicon: SIMS

(Example)

(Comparative Example 1)

P-type silicon substrate with carbon (thickness: 775 µm, carbon concentration (average concentration): 5.0 × 10 ¹⁶ atoms / cm 3, boron concentration: 1.34 × 10 ¹⁵ atoms / cm 3, resistivity: 10Ω · cm, interstitial oxygen concentration: 1.5) P-type first epitaxial layer (thickness: 1 mu m, boron concentration (peak concentration): 4.5 x 10 ¹⁹ atoms / cm3, resistivity: 2.5 m? Cm) on the x10 ¹⁸ atoms / cm3) by MOCVD method And an n-type second epitaxial layer (thickness: 5.5 µm, phosphorus concentration (peak concentration): 8.6x10 ¹³ atoms / cm 3, resistivity: 50 Ω · cm) were epitaxially grown in this order. Thereafter, by performing a heat treatment (heating the p-type silicon substrate to 650 ° C., holding at this temperature for 60 minutes, then heating to 1000 ° C. at 3 ° C./min, and maintaining this temperature for 120 minutes), A precipitate region (precipitate density: 2 × 10 ⁶ / cm 2) was formed to obtain an epitaxial substrate for a back-illumination solid-state image pickup device according to a comparative example.

The distribution of the boron concentration with respect to the depth from the surface of the epitaxial substrate is shown in Fig. 3 (a). The measurement was performed by SIMS. 5.5 μm thickness from 0 μm to 5.5 μm (left dashed line) is the second epitaxial layer, and 1 μm thickness from 5.5 μm to 6.5 μm (right dashed line) is the first epitaxial layer and is deeper than 6.5 μm Is a silicon substrate. It can be seen from FIG. 3A that boron is hardly distributed in the second epitaxial layer in the epitaxial substrate before the heat treatment. As shown in A, the maximum concentration (peak concentration) of boron in a 1st epitaxial layer was 4.5 * 10 <^19> atoms / cm <3>.

Next, the epitaxial substrate was subjected to heat treatment under conditions corresponding to the heat treatment in the device fabrication process (heat treatment condition is the heat-time profile shown in FIG. 4), and then measurement as shown in FIG. 3 was performed. The results are shown in FIG. 3 (b). As shown in B, the maximum concentration (peak concentration) of boron in the first epitaxial layer decreases to 3.4x10 ¹⁹ atoms / cm 3 before the heat treatment, so that boron is diffused in the second epitaxial layer and the substrate. It can be seen. In the comparative example 1, while the distribution area of boron was 2.12 micrometers before heat processing (FIG. 3 (a)), it spread | diffused to 3.84 micrometers after heat processing (FIG. 3 (b)). That is, the diffusion amount was 1.72 mu m. In addition, the decrease in maximum concentration (AB) due to diffusion was 1.1 × 10 ¹⁹ atoms / cm 3.

(Examples 1-1 to 1-5)

Experiments similar to those of Comparative Example 1 were carried out on the epitaxial substrate for back-illumination type solid-state imaging device shown in Table 1 having the maximum concentration (peak concentration) of boron in the p-type first epitaxial layer as the scope of the present invention. In addition, carbon concentration and nitrogen concentration of Table 1 mean "average concentration", and boron concentration and phosphorus concentration mean "peak concentration."

Silicon substrate p-type first epi layer 2nd epi layer Carbon concentration Nitrogen concentration Film thickness Boron concentration Challenge type Boron or phosphorus concentration atoms / cm ³ atoms / cm ³ μm atoms / cm ³ atoms / cm ³ Comparative Example 1 5.0 × 10 ¹⁶ - One 4.5 × 1 0 ¹⁹ n 8.6 × 10 ¹³ Example 1-1 5.0 × 10 ¹⁶ - 5 9.0 × 10 ¹⁸ p 2.7 × 10 ¹³ Examples 1-2 5.0 × 10 ¹⁶ - 5 9.0 × 10 ¹⁸ n 8.6 × 10 ¹³ Example 1-3 5.0 × 10 ¹⁶ 1.0 × 10 ¹⁴ 5 9.0 × 10 ¹⁸ n 8.6 × 10 ¹³ Example 1-4 5.0 × 10 ¹⁶ - 5 6.0 × 10 ¹⁸ n 8.6 × 10 ¹³ Examples 1-5 5.0 × 10 ¹⁶ - 4 5.0 × 10 ¹⁸ n 8.6 × 10 ¹³

In addition, the numerical value about board | substrates other than what is shown in Table 1 is the same as that of the comparative example 1.

For these substrates, similarly to Comparative Example 1, the decrease in the diffusion amount and the maximum concentration of boron due to the heat treatment was calculated, and the results are shown in Table 2 together with Comparative Example 1.

Diffusion Maximum concentration decrease μ m atoms / cm ³ Comparative Example 1 1.72 1.1 × 10 ¹⁹ Example 1-1 1.28 3.4 × 10 ¹⁸ Examples 1-2 1.27 3.2 × 10 ¹⁸ Example 1-3 1.28 3.3 × 10 ¹⁸ Example 1-4 1.10 1.7 × 10 ¹⁸ Examples 1-5 1.07 1.6 × 10 ¹⁸

As described above, it can be seen that in Examples 1-1 to 1-5, the diffusion of boron into the second epitaxial layer is suppressed more than in Comparative Example 1.

(Example 2-1)

In the substrate of Example 1-5, the distribution of the carbon concentration with respect to the depth from the epitaxial substrate surface is shown in FIG. After the heat treatment, it can be seen that carbon near the surface of the silicon substrate is slightly diffused to the region near the first epitaxial layer of the second epitaxial layer.

(Example 2-2)

The same experiment as in Example 2-1 was conducted except that the thickness of the first epitaxial layer in the substrate of Example 1-5 was changed from 4 µm to 6 µm. The distribution of carbon concentration versus depth from the epitaxial substrate surface is shown in FIG. 6. 5.5 μm thickness from 0 μm to 5.5 μm (left dashed line) is the second epitaxial layer, and 6 μm thickness from 5.5 μm to 11.5 μm (right dashed line) is the first epitaxial layer and is deeper than 11.5 μm Is a silicon substrate. It is understood that carbon is diffused in the first epitaxial layer, but since the layer is thickened, it is not diffused in the second epitaxial layer serving as the device layer. For this reason, Example 2-2 is a more preferable example, since both the diffusion of boron and the diffusion of carbon can be suppressed with respect to a 2nd epitaxial layer.

According to the present invention, diffusion of the p-type impurity into the device layer can be suppressed by setting the peak concentration of the p-type impurity in the first epitaxial layer to be 2.7 × 10 ¹⁷ atoms / cm 3 or more and less than 1.1 × 10 ¹⁹ atoms / cm 3. Therefore, it is possible to manufacture the back-illumination type solid state image pickup device at a high production rate.

1: silicon substrate
2: first epitaxial layer
3: second epitaxial layer (device layer)
4: precipitate area
100: epitaxial substrate for backside-illumination solid-state image pickup device

Claims (15)

A p-type silicon substrate having carbon or carbon and nitrogen added thereto, and having a resistivity of less than 100 Ω · cm;
A p-type first epitaxial layer on the p-type silicon substrate,
Having a p-type or n-type second epitaxial layer on the first epitaxial layer,
The first epitaxial layer has a peak concentration of p-type impurity of 2.7 × 10 ¹⁷ atoms / cm 3 or more and less than 1.1 × 10 ¹⁹ atoms / cm 3,
In the said p-type silicon substrate, the area | region which has the said carbon or carbon, nitrogen, and the deposit containing oxygen is provided,
An epitaxial substrate for a back-illumination type solid-state image pickup device having a density of precipitates at a central portion in a depth direction of the p-type silicon substrate in the region of 5 × 10 ⁵ / cm 2 or more and 5 × 10 ⁷ / cm 2 or less. The method of claim 1,
The epitaxial substrate for back-illumination type solid-state image pickup device of which said 1st epitaxial layer is 4 micrometers-10 micrometers in thickness. 3. The method according to claim 1 or 2,
The epitaxial substrate for back-illumination type solid-state image pickup device of which said 2nd epitaxial layer is 4 micrometers-10 micrometers in thickness. delete 3. The method according to claim 1 or 2,
The p-type second epitaxial layer is an epitaxial substrate for back-illumination solid-state image pickup device having a peak concentration of p-type impurity of 4.4 × 10 ¹³ atoms / cm 3 or more and 2.8 × 10 ¹⁷ atoms / cm 3 or less. 3. The method according to claim 1 or 2,
The n-type second epitaxial layer is an epitaxial substrate for a backside irradiation solid-state image pickup device having a peak concentration of n-type impurities of 1.4 × 10 ¹³ atoms / cm 3 or more and 7.8 × 10 ¹⁶ atoms / cm 3 or less. 6. The method of claim 5,
An epitaxial substrate for a back-illumination solid-state image pickup device wherein the p-type impurity is boron. The method according to claim 6,
An epitaxial substrate for back-illumination type solid-state image pickup device wherein the n-type impurity is phosphorus. 3. The method according to claim 1 or 2,
The p-type silicon substrate in which only carbon is added has an average concentration of carbon of 0.1 × 10 ¹⁶ atoms / cm 3 or more and 20 × 10 ¹⁶ atoms / cm 3 or less. 3. The method according to claim 1 or 2,
In the p-type silicon substrate to which both carbon and nitrogen are added, the average concentration of carbon is 0.1 × 10 ¹⁶ atoms / cm 3 or more and 20 × 10 ¹⁶ atoms / cm 3 or less, and the average concentration of nitrogen is 0.5 × 10 ¹³ atoms / cm 3. An epitaxial substrate for a backside-illumination type solid-state image sensor that is 50 x 10 ¹³ atoms / cm 3 or more. Forming a p-type first epitaxial layer on a p-type silicon substrate having carbon or carbon and nitrogen added thereto, and having a resistivity of less than 100 Ω · cm;
And forming a p-type or n-type second epitaxial layer on the first epitaxial layer,
The peak concentration of the p-type impurity in the first epitaxial layer is set to be 2.7 × 10 ¹⁷ atoms / cm 3 or more and less than 1.1 × 10 ¹⁹ atoms / cm 3,
A back-illumination type solid-state image pickup device having a heat treatment step for forming a region having said carbon, carbon, nitrogen, and precipitates containing oxygen in said p-type silicon substrate after said step of forming said second epitaxial layer Method for producing an epitaxial substrate for use. 12. The method of claim 11,
The first epitaxial layer has a thickness of 4 µm or more and 10 µm or less. 13. The method according to claim 11 or 12,
The silicon substrate before the first epitaxial layer forming step has a lattice oxygen concentration of 1 × 10 ¹⁸ atoms / cm 3 or more and 2 × 10 ¹⁸ atoms / cm 3 or less. delete 12. The method of claim 11,
The heat treatment step,
After the silicon substrate is heated to a first temperature within the range of 500 to 800 ° C., low temperature heat treatment is performed for 10 to 180 minutes at the first temperature,
Subsequently, after heating to the 2nd temperature within the range of 900-1150 degreeC by the temperature increase rate of 4 degrees-C / min or less, performing the high temperature heat processing for 15 to 200 minutes at the said 2nd temperature, A method of manufacturing an epitaxial substrate for an imaging device.

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