JP2002134511A - Method for manufacturing semiconductor substrate and method for manufacturing solid-state image-pickup equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor substrate capable of reducing a defect white blemish of a solid-state image-pickup equip ment and a method for manufacturing the solid-state image-pickup equipment. SOLUTION: The method for manufacturing a semiconductor substrate includes a process for forming a silicon substrate containing nitrogen of 2×1013 atoms/cm3 or more, preferably 2×1014 atoms/cm3 or more, a process for ion- implanting carbon in a dosage of 5×1013 ions/cm2 or more, preferably 1×1015 to 2×1015 irons/cm2 into an one surface of the silicon substrate, and a process for forming an epitaxial layer on the surface of silicon substrate; and the method for manufacturing the solid-state image-pickup equipment includes a process for forming a device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor substrate used for forming a solid-state imaging device. In addition, the present invention relates to a method for manufacturing a solid-state imaging device capable of greatly reducing white defect by improving the gettering ability of an epitaxial substrate.

[0002]

2. Description of the Related Art In general, a semiconductor substrate on which a semiconductor device is formed is a CZ (Czochralski) grown CZ substrate or an MCZ (Magnetic fiber).
An MCZ substrate grown by the ldCzochralski method, an epitaxial substrate having an epitaxial layer formed on the surface of the CZ substrate or the MCZ substrate, and the like are frequently used.

[0003] In particular, for a solid-state imaging device, an epitaxial substrate or an MC is used to reduce image contrast caused by dopant concentration unevenness (Striation).
Z substrates are mainly used. Of the above, the epitaxial substrate can form a low-resistance region under the element formation layer by using a buried region or a low-resistance substrate. Therefore, it is advantageous for low-voltage driving and low power consumption, and its use is expected to expand in the future.

In forming a silicon epitaxial substrate,
As a practical method, chemical vapor deposition (CVD; Chemi
cal Vapor Deposition) method is used. This CVD is performed using SiCl ₄ or SiH
Hydrogen reduction method using Cl ₃ as a source gas, or S
This is performed by a thermal decomposition method using iH ₂ Cl ₂ or SiH ₄ as a source gas.

The reactions using these four main types of source gases are shown below. (Hydrogen reduction method) SiCl ₄ + 2H ₂ → Si + 4HCl (1) SiHCl ₃ + H ₂ → Si + 3HCl (2) (Thermal decomposition method) SiH ₂ Cl ₂ → Si + 2HCl (3) SiH ₄ → Si + 2H ₂ ... (4) Among the above, for a solid-state imaging device, SiHCl ₃ is used as a source gas because the source gas is inexpensive and the growth rate is large and is suitable for forming a thick film epitaxial. Substrates are mainly used.

[0006]

However, when an epitaxial substrate is formed using any of the above source gases, many impurities, particularly metal impurities or heavy metal impurities, are mixed during the formation of the epitaxial layer.
When a solid-state imaging device is formed on a substrate, metal impurities and the like contained in the substrate cause an increase in dark current of the solid-state imaging device, and the solid-state imaging device often generates white defects. Therefore, the characteristics and yield of the solid-state imaging device are reduced.

The source of heavy metal impurities is stainless steel (SUS) in a bell jar of an epitaxial growth apparatus.
System members, source gas piping, and the like can be considered. If the source gas contains a chlorine (Cl) -based gas, the chlorine-based gas is decomposed during epitaxial growth and hydrogen chloride (HCl)
Occurs. It is considered that the HCl corrodes the SUS-based member, so that the metal chloride is taken into the source gas and further into the epitaxial layer. In some cases, HCl gas is intentionally introduced and lightly etched off for the purpose of cleaning the surface of the silicon substrate before the epitaxial layer is formed. However, this HCl also causes corrosion of SUS-based members and the like. It has become.

[0008] Therefore, when a solid-state imaging device is formed using an epitaxial substrate, some gettering technique is required to remove the metal impurities mixed as described above. As a gettering technique, an Intrinsic Getteri is used in which oxygen in a silicon substrate is precipitated only inside the substrate and the oxygen is used as a getter sink.
Extrinsic G in which polysilicon or a high-concentration phosphorus (P) region or the like is formed on the back surface of the substrate and a getter sink is formed by using a strain stress with silicon.
There is the lettering (EG) method and the like. However,
In any case, the ability as a gettering method for the epitaxial substrate was not sufficient, and the white defect caused by the dark current of the solid-state imaging device could not be sufficiently reduced.

In order to reduce the above-mentioned white defect, the applicant of the present invention has already applied carbon of 5 × 1 to one surface of a silicon substrate.
Ion implantation at a dose of at least ¹³ ions / cm ² ,
An application for a method of manufacturing a semiconductor substrate characterized by forming a silicon epitaxial layer on its surface has been filed (see JP-A-6-338507). According to this method,
The white defect of the solid-state imaging device is reduced to 1/5 or less as compared with the epitaxial substrate using the gettering method.

FIG. 9 shows the reduction of the white defect of the solid-state imaging device by the method described in Japanese Patent Application Laid-Open No. 6-338507. It is a standardized number. As shown in FIG. 9, by a carbon ion implantation, even when the dose of carbon is less than ^{5 × 10 13 ions / cm 2} , white defects is reduced, the dose of carbon 5 × 10 ¹³ ion
When it is s / cm ² or more, white defect is significantly reduced. Increasing the carbon dose to 5 × 10 ¹⁴ ions / cm ² further reduces white spot defects.

However, the dose of carbon is 5 × 10 ¹⁵ ions.
If it exceeds s / cm ² , the crystallinity of the mirror surface of the substrate and the silicon epitaxial layer grown thereon will be low. From the above, JP-A-6-338507 discloses that the dose of carbon is 5 × 10 ^{13 to} 5 × 10 ¹⁵ i.
It is stated that the range of ons / cm ² is preferable.

Further, the applicant of the present application has implanted carbon into one surface of a silicon substrate at a dose of 5 × 10 ¹³ ions / cm ² or more and nitrogen with 1 × 10 ¹² ions / cm 2.
^It has been found that the gettering ability is improved by implanting ions at a dose of ² or more and forming a silicon epitaxial layer on the surface thereof (Japanese Patent Laid-Open No. 11-2).
See the epitaxial silicon substrate and the solid-state imaging device described in JP-A-51322 and their manufacturing methods. According to this method, it is possible to further reduce the white defect of the solid-state imaging device to half as compared with the case where only carbon is ion-implanted.

FIG. 10 shows the reduction of white spot defects in a solid-state image pickup device according to the method described in JP-A-11-251322, where the number of white spot defects when carbon and nitrogen ions are not implanted is assumed to be 100. , Standardize the number of white defect,
It is a logarithmic representation. As shown in FIG. 10, by implanting carbon and nitrogen ions, white defect is further reduced as compared with the case where only carbon is implanted.

However, with the increase in the sensitivity of the solid-state imaging device, it is required to further reduce white spot defects, and it is necessary to further improve the above-described conventional method. The present invention has been made in view of the above problems, and accordingly, the present invention provides a method of manufacturing a semiconductor substrate having the ability to more effectively getter metal impurities mixed during the formation of an epitaxial layer. The purpose is to: Another object of the present invention is to provide a method for manufacturing a solid-state imaging device capable of forming a substrate having high gettering ability of metal impurities and reducing white defect caused by dark current.

[0015]

In order to achieve the above object, a method of manufacturing a semiconductor substrate according to the present invention comprises the steps of forming a silicon substrate containing nitrogen and ion-implanting carbon into one surface of the silicon substrate. And forming a silicon epitaxial layer on the surface of the silicon substrate.

In the method for manufacturing a semiconductor substrate according to the present invention, preferably, the nitrogen content in the silicon substrate is approximately 2 × 10 ¹³
atoms / cm ³ or more, more preferably approximately 2 × 1
0 ¹⁴ atoms / cm ³ or more.
In the method of manufacturing a semiconductor substrate according to the present invention, preferably, the dose of the carbon ion implantation is approximately 5 × 10 ¹³ ions / s.
cm ² or more. Further, in the method of manufacturing a semiconductor substrate according to the present invention, preferably, the upper limit of the carbon dose is within a range that does not impair the crystallinity of the silicon substrate and the silicon epitaxial layer formed on the surface of the silicon substrate. It is characterized by being set. In the method of manufacturing a semiconductor substrate according to the present invention, more preferably, the dose of ion-implanting the carbon is approximately 1 × 10 ¹⁵ to 2 ×.
It is in the range of 10 ¹⁵ ions / cm ² .

In the method for manufacturing a semiconductor substrate according to the present invention, preferably, the step of forming the silicon substrate includes a step of forming a silicon substrate by a CZ method from a silicon solution containing nitrogen. In the method of manufacturing a semiconductor substrate according to the present invention, more preferably, the nitrogen is added to the silicon solution in the form of powdered silicon nitride. In the method of manufacturing a semiconductor substrate of the present invention, preferably, the step of ion-implanting the carbon is such that the carbon has a peak concentration at a position deeper than the surface of the silicon substrate.
A step of ion-implanting the carbon. Preferably, the method for manufacturing a semiconductor substrate of the present invention further includes a step of ion-implanting oxygen into the one surface after forming the silicon substrate and before forming the silicon epitaxial layer.

This makes it possible to getter impurities, particularly metal impurities, mixed in the silicon epitaxial layer more effectively than before. Therefore, when a semiconductor device is formed using a substrate manufactured according to the method for manufacturing a semiconductor substrate of the present invention, dark current and the like due to impurities in the substrate can be reduced.

Further, in order to achieve the above object, a method of manufacturing a solid-state imaging device according to the present invention comprises the steps of: forming a nitrogen-containing silicon substrate; and ion-implanting carbon into one surface of the silicon substrate. Forming a silicon epitaxial layer on the surface of the silicon substrate; and forming an element on the silicon epitaxial layer.

The method for manufacturing a solid-state imaging device according to the present invention is preferably
The nitrogen content in the silicon substrate is approximately 2 × 10
¹³atoms / cm^Three As described above, more preferably, approximately 2 ×
10 ¹⁴atoms / cm^Three Characterized by the above
You. Preferably, the method of manufacturing a solid-state imaging device according to the present invention
The dose for implanting the carbon is approximately 5 × 10¹³io
ns / cm^Two It is characterized by the above. In addition,
The solid-state imaging device manufacturing method according to
The upper limit of the dose is determined by the silicon substrate and the silicon
The silicon epitaxial formed on the surface of the silicon substrate
It is characterized in that it is set within a range that does not impair the crystallinity of the layer
I do. The method for manufacturing a solid-state imaging device according to the present invention is more preferable.
The dose of ion implantation of carbon is approximately 1 × 1
0^Fifteen~ 2 × 10^Fifteenions / cm^Two That the range is
Features.

In the method of manufacturing a solid-state imaging device according to the present invention, preferably, the step of forming the silicon substrate includes a step of forming a silicon substrate by a CZ method from a silicon solution containing nitrogen. . In the method for manufacturing a solid-state imaging device according to the present invention, more preferably, the nitrogen is added to the silicon solution in the form of powdered silicon nitride.

In the method of manufacturing a solid-state imaging device according to the present invention, preferably, the step of ion-implanting the carbon includes removing the carbon so that the carbon has a peak concentration at a position deeper than the surface of the silicon substrate. It is a step of performing ion implantation. Preferably, the method for manufacturing a solid-state imaging device according to the present invention further includes a step of ion-implanting oxygen into the one surface after forming the silicon substrate and before forming the silicon epitaxial layer. .

This makes it possible to getter impurities, particularly metal impurities, mixed in the silicon epitaxial layer more effectively than before. Therefore, dark current caused by impurities in the substrate can be reduced. This makes it possible to reduce white spot defects in the solid-state imaging device and improve the yield of the solid-state imaging device.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the method for manufacturing a semiconductor substrate and the method for manufacturing a solid-state imaging device according to the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a schematic view of a CZ pull-up apparatus 1 used in a method of manufacturing a semiconductor substrate according to the present embodiment. As shown in FIG. 1, a silicon single crystal 3 is formed from a silicon melt 2. By heating the silicon chip and the powder of silicon nitride in the quartz crucible 4, a silicon melt 2 is obtained. The quartz crucible 4 is heated by the graphite heater 6 via the graphite crucible 5. The silicon single crystal 3 is pulled up by the wire 7. The CZ pulling apparatus 1 is provided with an exhaust unit 8, and the inside of the growth furnace is adjusted to an Ar atmosphere and a pressure of several to several tens of Torr.
In addition, the graphite crucible 5 is rotated by the crucible rotation shaft 9 to uniformly heat the silicon melt 2. A heat shield plate 10 is provided outside the graphite heater 6.

Hereinafter, referring to FIGS. 2A to 2D,
A method for manufacturing a semiconductor substrate according to the present embodiment will be described. First,
A nitrogen-containing silicon substrate 1 is obtained from a nitrogen-doped silicon solution 2 using a CZ pulling apparatus 1 shown in FIG.
1 (corresponding to the silicon single crystal 3 in FIG. 1). Here, the silicon substrate 11 is n-doped with phosphorus.
Type silicon, and the specific resistance of the silicon substrate 11 is 8 to 12
Ω · cm. Nitrogen is added by, for example, adding SiN solid, preferably powdered SiN, to the silicon solution. The concentration of the doped nitrogen can be adjusted by the amount of SiN added. The concentration of the doped nitrogen can be measured by an infrared absorption method.

In this embodiment, the silicon substrate 11
Nitrogen concentration is 2 × 10 ¹³ atoms / cm ³ or 2
The silicon substrate 11 was manufactured to have a density of × 10 ¹⁴ atoms / cm ³ . Then, as shown in FIG. 2A, the silicon substrate 11 doped with nitrogen is processed into a wafer by a processing method similar to that of a normal silicon substrate containing no nitrogen.

Next, as shown in FIG. 2B, after the silicon substrate 11 is subjected to RCA cleaning (washing with an NH ₄ OH / H ₂ O ₂ aqueous solution and then washing with an HCl / H ₂ O ₂ aqueous solution). ,
By performing dry oxidation at 1000 ° C., a 20-nm-thick thermal oxide film 13 is formed on the surface 12 of the silicon substrate. Carbon 14 is accelerated from the mirror surface 12 of the silicon substrate 11 through the thermal oxide film 13 at an acceleration energy of 160 keV.
Ions are implanted under the conditions of a dose of 1 × 10 ¹⁵ ions / cm ² . At this time, the projected range of carbon is about 0.35μ.
m, and the peak concentration of carbon is about 5 × 10 ¹⁸ atoms
/ Cm ³ .

Subsequently, annealing at 1000 ° C. for 10 minutes is performed in a nitrogen atmosphere. As a result, as shown in FIG. 2C, a carbon / nitrogen mixed region 15 having a peak concentration at a position deeper than the mirror surface 12 of the silicon substrate 11 is formed. After that, the thermal oxide film 13 is removed using a solution containing hydrofluoric acid (HF).

Next, as shown in FIG. 2D, an 8 μm thick silicon epitaxial layer 16 is formed on the mirror surface 12 of the silicon substrate 11. The formation of the silicon epitaxial layer 16 is performed at about 1100 ° C. using SiHCl ₃ as a source gas. The silicon epitaxial layer 16 is an n-type silicon layer doped with phosphorus, and has a specific resistance of 40 to 50 Ω · cm.

Through the above steps, an epitaxial substrate 17 having high gettering ability is formed. The reason why the position of the peak concentration in the carbon / nitrogen mixed region 15 is made deeper than the surface is to prevent the crystallinity of the n-type epitaxial layer 16 from deteriorating. Annealing in a nitrogen atmosphere after the ion implantation is performed for the purpose of restoring the crystallinity near the mirror surface 12 which has been made amorphous by the ion implantation and accelerating the interaction between carbon and nitrogen.
It is not always necessary depending on the conditions of ion implantation. Although SiHCl ₃ is used as a source gas for forming the n-type silicon epitaxial layer 16, a gas such as SiCl ₄ , SiH ₂ Cl ₂ , or SiH ₄ described above can be used as a source gas.

(Embodiment 2) FIG.
3 is a cross-sectional view of a solid-state imaging device manufactured using the epitaxial substrate 17 of FIG. The solid-state imaging device shown in FIG. 3 has a p-well 18 in the surface layer of the n-type epitaxial layer 16 of the epitaxial substrate 17 of the first embodiment. An n-type impurity diffusion region 19, an n-type transfer channel region 20, and a p-type channel stopper region 21 are formed in the p-well 18. The n-type transfer channel region 20 forms a vertical transfer register 22. On the n-type impurity diffusion region 19, a p-type region (positive charge storage region) 23 where positive charges are stored is formed. A p-type impurity diffusion region 24 is formed immediately below the n-type transfer channel region 20.

A light receiving portion (photoelectric conversion portion) 25 is constituted by a photodiode PD formed by a pn junction j between the n-type impurity diffusion region 19 and the p well 18. A plurality of transfer electrodes 28 made of first and second polycrystalline silicon are formed on the transfer channel region 20, the channel stopper region 21, and the read gate portion 26 via a gate insulating film (ONO film) 27. However, the transfer electrode 28 is not formed on the light receiving section 25. Further, the Al light shielding film 3 is formed so as to cover each vertical transfer register 22 with an interlayer insulating film 29 interposed therebetween.
0 is formed.

The solid-state imaging device having the above-described configuration is the same as that of the first embodiment.
Are formed on an epitaxial substrate 17 formed according to the method for manufacturing a semiconductor substrate shown in FIG. This gives n
Metal impurities mixed during the formation of the type epitaxial layer 16 are effectively gettered, and white defects of the solid-state imaging device due to dark current are reduced.

(Embodiment 3) Next, the background to the present invention and reduction of white defect in the solid-state imaging device according to Embodiment 2 will be described. As described above, white defects are reduced by implanting carbon ions into one surface of the silicon substrate and forming a silicon epitaxial layer on the surface (see JP-A-6-338507).
The gettering effect due to the reduction of the white defect or the ion implantation of carbon depends on the dose of carbon.

As shown in FIG. 9, when the dose of carbon is 5 ×
When the density is lower than 10 ¹³ ions / cm ^{2, the} white defect is reduced as compared with the case where carbon is not ion-implanted, but the white defect is not significantly reduced. 5 × carbon dose
In the case of 10 ¹⁴ ions / cm ² , the white defect is further reduced as compared with the case where the dose of carbon is 5 × 10 ¹³ ions / cm ² .

However, if the dose of carbon is a fixed amount, for example, 5
If it exceeds × 10 ¹⁵ ions / cm ² , the crystallinity of the mirror surface of the substrate decreases, and the crystallinity of the silicon epitaxial layer grown on the mirror surface also decreases. From the above, JP-A-6-338507 describes that the dose of carbon is preferably in the range of 5 × 10 ^{13 to} 5 × 10 ¹⁵ ions / cm ² .

As a result of investigating the gettering mechanism in the semiconductor substrate described in JP-A-6-338507, the getter sink was assumed to be a compound of carbon and oxygen (see JP-A-10-41311). JP 6
In the semiconductor substrate described in JP-A-338507, C
Supersaturated interstitial oxygen existing in the Z substrate in advance serves as a source of oxygen. On the other hand, in the case of an epitaxial silicon substrate described in JP-A-10-41311, oxygen is intentionally ion-implanted to promote formation of a getter sink.

Then, the applicant of the present invention focused on nitrogen as an element for accelerating the precipitation of oxygen, and by ion-implanting nitrogen in addition to carbon, the white defect was further reduced as shown in FIG. (Japanese Patent Laid-Open No. Hei 11
251322). Also, when nitrogen is ion-implanted, nitrogen is not ion-implanted (Japanese Unexamined Patent Publication No.
It has been confirmed by the present applicant that the degree of the white defect depends on the dose of carbon as in the case of US Pat. No. 3,338,507. This time, it is clear that more effects can be obtained by using a silicon substrate doped with nitrogen in advance and implanting carbon ions on one surface of the silicon substrate compared to the case where carbon and nitrogen are ion-implanted into the silicon substrate. did.

The possible mechanism of the getter sink being a compound of carbon and oxygen, and nitrogen accelerating the deposition of oxygen, and the results of various experiments, were obtained for a silicon substrate not doped with nitrogen. The preferred dose of carbon is considered to be applicable to the case of nitrogen-doped silicon substrates.

FIG. 4 shows the result of further detailed examination of a suitable dose of carbon. FIG. 4 shows the carbon dose dependency of the white defect when a silicon substrate not doped with nitrogen is used. 9 and 4 differ in the standard of standardization because the types of solid-state imaging devices formed on the substrate are not the same. FIG. 4 shows that the carbon dose amount is 2 × 10 ¹⁵ ions.
The number of white defects at each dose is shown as a relative ratio, with the number of white defects at / cm ² being 1. Under each condition, two wafers were tested, and the respective results were plotted.

As shown in FIG. 4, the carbon dose was 5 × 1
When the carbon dose is increased from 0 ¹⁴ ions / cm ² , the white defect is reduced most when the carbon dose is 1 × 10 ¹⁵ to 2 × 10 ¹⁵ ions / cm ² . When the carbon dose is further increased, the crystallinity of the silicon epitaxial layer grown on the mirror surface of the substrate and the layer above the mirror surface is affected, and the white defect slightly increases.

Next, FIG. 5 shows the nitrogen content dependency and the carbon dose dependency of the white defect when carbon is ion-implanted into a silicon substrate which has been doped with nitrogen in advance. FIG. 5 shows that both the carbon dose and the nitrogen content are 0.
Is standardized with the defect at the time of 100 being taken as 100. Two wafers were tested under the other three conditions, and the results were plotted.

As shown in FIG.
1 x 10 carbon ^Fifteenions / cm^Two 
Was implanted at a dose of. In the upper layer, FIG.
Epitaxy with specific resistance of 40-50Ωcm as shown in
The epitaxial layer was grown to produce an epitaxial substrate. Epi
The formation of the taxi layer is performed at 1110 ° C.
And SiHCl_Three Was used. Such an epitaxial
The solid-state imaging device shown in FIG.
evaluated.

As shown in FIG. 5, when carbon is ion-implanted into a nitrogen-doped silicon substrate at the time of forming the substrate, when carbon is ion-implanted into a silicon substrate not doped with nitrogen with the same doping amount. In comparison, white defect is reduced to about 1/4 or less. Therefore, according to the method for manufacturing a semiconductor substrate of the present invention, the dose of carbon is within a suitable range (5 × 10 ^{13 to} 5 × 10 ¹⁵ ions / cm ² , see JP-A-6-338507). 1 × 10 ¹⁵
It can be seen that a semiconductor substrate with higher gettering than before can be obtained when the density is up to 2 × 10 ¹⁵ ions / cm ² (see FIG. 4).

Although not shown, the method of manufacturing a semiconductor substrate according to the present invention is more effective in reducing white defects than the method of ion-implanting carbon and nitrogen described in Japanese Patent Application Laid-Open No. H11-251322. There is a double effect, which is effective for increasing the sensitivity of the solid-state imaging device.

From the evaluation results shown in FIG. 5, the concentration of nitrogen previously doped into the silicon substrate is 2 × 10 ¹³ atoms.
s / cm ³ or more, preferably 2 × 1
0 ¹⁴ atoms / cm ³ or more. The upper limit of the nitrogen concentration needs to be a concentration at which the crystallinity of the silicon substrate and the silicon epitaxial layer formed on the surface of the silicon substrate are not impaired.

Although not shown, as in the present embodiment, even when a silicon substrate doped with nitrogen in advance is used, or when nitrogen is not doped (Japanese Patent Laid-Open No. 6-338507).
And Japanese Patent Application Publication No.
Similarly to Japanese Patent Application Laid-Open No. 251322), when the dose of carbon is increased, the number of white defects is further reduced. However, the upper limit of the dose of carbon is appropriately set within a range where the crystallinity of the silicon substrate and the silicon epitaxial layer formed on the surface thereof is not impaired.

(Embodiment 4) A method of manufacturing the solid-state imaging device according to Embodiment 2 shown in FIG. 3 will be described below with reference to FIGS. First, as shown in FIG. 6A, n containing nitrogen at a concentration of 2 × 10 ¹³ atoms / cm ^3.
A mold silicon substrate 11 is formed. This silicon substrate 1
No. 1 has a main surface 12 having a (100) plane and a specific resistance of 10Ω.
· The substrate is 8 cm in diameter, which is cm. As in the first embodiment, carbon is applied to the surface of the silicon substrate 11 at 1 × 10 ¹⁵ io.
Ion implantation is performed at a dose of ns / cm ² , and then annealing is performed to form a carbon / nitrogen mixed region 15. The carbon / nitrogen mixed region 15 serves as a getter sink.

Next, as shown in FIG. 6B, an n-type silicon epitaxial layer 16 having a thickness of 8 μm is formed on one main surface of the silicon substrate 1. The epitaxial layer 16 is formed at 1110 ° C. using SiHCl ₃ as a source gas. Next, as shown in FIG. 7C, a p-well 18 is formed on the surface of the n-type silicon epitaxial layer 16. p
The well 18 is formed by, for example, implanting boron ions.

Next, as shown in FIG. 7D, the surface of the n-type epitaxial layer 16 in which the p-well 18 has been formed is
A gate insulating film 27 is formed. The gate insulating film 27 is a laminated film (ONO film) of a silicon oxide film / silicon nitride film / silicon oxide film. Further, n-type and p-type impurities are selectively ion-implanted into the p-well 18 to form an n-type transfer channel region 20 constituting the vertical transfer register 22 and a p-type impurity.
A channel stopper region 21 and a p-type impurity diffusion region 24 are formed.

Next, as shown in FIG. 8E, a plurality of transfer electrodes 28 are formed on the gate insulating film 27. The transfer electrode 28 is formed by forming the first and second polycrystalline silicon layers, for example, by CV.
It is formed by stacking by D and then performing etching. Using the transfer electrode 28 as a mask, the O
The NO film (gate insulating film) 27 is removed, and a gate insulating film 27a made of a silicon oxide film is formed on the light receiving portion 25 again.

Next, as shown in FIG.
5, an n-type impurity is ion-implanted into the n-type impurity diffusion region 1.
9 is formed. P-type impurities are ion-implanted in the upper layer to form a positive charge storage region 23. Thereafter, as shown in FIG. 3, an interlayer insulating film 29 made of, for example, a silicon oxide film is formed on the transfer electrode 28 and the light receiving portion 25. Light receiving unit 2
By forming the Al light-shielding film 30 on the interlayer insulating film 29 except for 5, the solid-state imaging device shown in FIG. 3 is obtained.

According to the method of manufacturing a solid-state imaging device of the present embodiment, carbon is ion-implanted into a silicon substrate doped with nitrogen in advance to form a carbon / nitrogen mixed region serving as a getter sink. Thereby, the metal impurities mixed into the epitaxial layer 16 are effectively gettered, and the dark current of the solid-state imaging device can be reduced.
Thereby, it becomes possible to further reduce the white defect of the solid-state imaging device as compared with the related art.

In the present embodiment, only gettering using carbon is performed, but other gettering methods such as IG, polycrystalline silicon gettering, and ring gettering are combined with the carbon gettering. Thus, it has been confirmed that white scratch defects can be further reduced. Further, an oxygen ion implantation step described in Japanese Patent Application Laid-Open No. 10-41311 can be added to the manufacturing method of the present embodiment.

Embodiments of the method for manufacturing a semiconductor substrate and the method for manufacturing a solid-state imaging device according to the present invention are not limited to the above description. For example, in the above embodiment, an n-type impurity diffusion region is formed on the surface of a p-well formed on an n-type silicon epitaxial substrate, and a photodiode is formed by a pn junction between the p-well and the n-type impurity diffusion region. However, the present invention can be applied to a solid-state imaging device having a photodiode of another configuration.

Specifically, the present invention can be applied to a case where an n-type impurity diffusion region is formed in a p-type silicon epitaxial substrate to manufacture a photodiode. Further, the present invention can be applied to a solid-state imaging device having an in-layer lens (on-chip lens). Alternatively, a CCD (char
The present invention can be applied to the manufacture of a solid-state imaging device other than the Ge coupled device, such as an amplification-type solid-state imaging device or a CMOS-type solid-state imaging device, so that dark current can be effectively reduced. In addition, various changes can be made without departing from the spirit of the present invention.

[0057]

According to the method for manufacturing a semiconductor substrate of the present invention, it is possible to manufacture an epitaxial substrate having extremely high gettering ability. Further, according to the method for manufacturing a solid-state imaging device of the present invention, by improving the gettering ability of the substrate and reducing the dark current caused by impurities, the white defect of the solid-state imaging device is reduced and the yield is improved. Can be done.

[Brief description of the drawings]

FIG. 1 is a schematic view of a CZ pull-up device used in a method for manufacturing a semiconductor substrate according to a first embodiment of the present invention.

FIGS. 2A to 2D are cross-sectional views illustrating manufacturing steps of a method for manufacturing a semiconductor substrate according to Embodiment 1 of the present invention.

FIG. 3 is a cross-sectional view of a solid-state imaging device manufactured by a method for manufacturing a solid-state imaging device according to a second embodiment of the present invention;

FIG. 4 is a diagram illustrating a carbon dose dependency of a white defect in the solid-state imaging device according to the third embodiment of the present invention.

FIG. 5 relates to a third embodiment of the present invention, and a second embodiment;
FIG. 4 is a diagram showing white defect when the nitrogen content and the carbon dose are changed in the solid-state imaging device shown in FIG.

6 (a) and 6 (b) show Embodiment 4 of the present invention.
FIG. 6 is a view illustrating a manufacturing process of a method for manufacturing the solid-state imaging device according to the first embodiment.

FIGS. 7 (c) and (d) show Embodiment 4 of the present invention.
FIG. 6 is a view illustrating a manufacturing process of a method for manufacturing the solid-state imaging device according to the first embodiment.

8 (e) and (f) show Embodiment 4 of the present invention.
FIG. 6 is a view illustrating a manufacturing process of a method for manufacturing the solid-state imaging device according to the first embodiment.

FIG. 9 is a diagram illustrating the dependence of white defect on carbon dose in a conventional solid-state imaging device.

FIG. 10 is a diagram showing the dependency of white defect on ion implantation conditions in a conventional solid-state imaging device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... CZ pulling apparatus, 2 ... Silicon liquid, 3 ... Silicon single crystal, 4 ... Quartz crucible, 5 ... Graphite crucible, 6 ... Graphite heater, 7 ... Wire, 8 ... Exhaust part, 9 ... Crucible rotating shaft, 10 ... Heat shielding plate, 11: silicon substrate, 12: silicon substrate surface, 13: thermal oxide film, 14: carbon, 15: carbon / nitrogen mixed region, 16: n-type epitaxial layer, 17
... Epitaxial substrate, 18 ... P well, 19 ... N-type impurity diffusion region, 20 ... Transfer channel region, 21 ... Channel stopper region, 22 ... Vertical transfer register, 23 ... Positive charge accumulation region, 24 ... P-type impurity diffusion region, 25: light receiving section, 26: read gate section, 27, 27a: gate insulating film, 28: transfer electrode, 29: interlayer insulating film, 30: light shielding film.

Claims (24)

[Claims] 1. A semiconductor substrate comprising: a step of forming a nitrogen-containing silicon substrate; a step of implanting carbon ions into one surface of the silicon substrate; and a step of forming a silicon epitaxial layer on the surface of the silicon substrate. Manufacturing method. 2. The method according to claim 1, wherein the nitrogen content in said silicon substrate is approximately 2%.
× 10 ¹³ atoms / cm ³ or more in the method for manufacturing a semiconductor substrate according to claim 1, wherein. 3. The silicon substrate has a nitrogen content of about 2
^{3. The} method for manufacturing a semiconductor substrate according to claim 2, wherein the density is at least 10 ¹⁴ atoms / cm ³ . 4. The method of manufacturing a semiconductor substrate according to claim 1, wherein a dose of said ion implantation of carbon is approximately 5 × 10 ¹³ ions / cm ² or more. 5. The semiconductor substrate according to claim 4, wherein the upper limit of the carbon dose is set within a range that does not impair the crystallinity of the silicon substrate and the silicon epitaxial layer formed on the surface of the silicon substrate. Production method. 6. The method of manufacturing a semiconductor substrate according to claim 5, wherein a dose of said ion implantation of carbon is in a range of approximately 1 × 10 ¹⁵ to 2 × 10 ¹⁵ ions / cm ² . 7. The method of manufacturing a semiconductor substrate according to claim 2, wherein a dose of said ion implantation of carbon is approximately 5 × 10 ¹³ ions / cm ² or more. 8. The method of manufacturing a semiconductor substrate according to claim 7, wherein a dose of said ion implantation of carbon is in a range of approximately 1 × 10 ¹⁵ to 2 × 10 ¹⁵ ions / cm ² . 9. The step of forming the silicon substrate includes the step of forming a CZ (Czochralsk) from a silicon solution containing nitrogen.
2. The method for manufacturing a semiconductor substrate according to claim 1, further comprising a step of forming a silicon substrate by the method i). 10. The method according to claim 9, wherein said nitrogen is added to said silicon solution in the form of powdered silicon nitride. 11. The semiconductor substrate according to claim 1, wherein said step of ion-implanting carbon is a step of ion-implanting said carbon such that said carbon has a peak concentration at a position deeper than a surface of said silicon substrate. Manufacturing method. 12. The method according to claim 1, further comprising the step of implanting oxygen into said one surface after forming said silicon substrate and before forming said silicon epitaxial layer. 13. A step of forming a silicon substrate containing nitrogen; a step of ion-implanting carbon into one surface of the silicon substrate; a step of forming a silicon epitaxial layer on the surface of the silicon substrate; Forming an element in a layer. 14. The method according to claim 13, wherein the nitrogen content in said silicon substrate is approximately 2 × 10 ¹³ atoms / cm ³ or more. 15. The method according to claim 14, wherein the nitrogen content in the silicon substrate is approximately 2 × 10 ¹⁴ atoms / cm ³ or more. 16. The method for manufacturing a solid-state imaging device according to claim 13, wherein a dose of said carbon ion implantation is approximately 5 × 10 ¹³ ions / cm ² or more. 17. The solid-state imaging device according to claim 16, wherein the upper limit of the carbon dose is set within a range that does not impair the crystallinity of the silicon substrate and the silicon epitaxial layer formed on the surface of the silicon substrate. Manufacturing method. 18. The method according to claim 17, wherein a dose of the ion implantation of carbon is in a range of approximately 1 × 10 ¹⁵ to 2 × 10 ¹⁵ ions / cm ² . 19. The method for manufacturing a solid-state imaging device according to claim 14, wherein a dose of said carbon ion implantation is approximately 5 × 10 ¹³ ions / cm ² or more. 20. The method according to claim 19, wherein a dose of the ion implantation of carbon is in a range of approximately 1 × 10 ¹⁵ to 2 × 10 ¹⁵ ions / cm ² . 21. The method according to claim 13, wherein the step of forming the silicon substrate includes the step of forming a silicon substrate by a CZ method from a silicon solution containing nitrogen. 22. The method according to claim 21, wherein said nitrogen is added to said silicon solution in the form of powdered silicon nitride. 23. The solid-state imaging device according to claim 13, wherein said step of ion-implanting carbon is a step of ion-implanting said carbon such that said carbon has a peak concentration at a position deeper than a surface of said silicon substrate. Device manufacturing method. 24. The method of manufacturing a solid-state imaging device according to claim 13, further comprising a step of implanting oxygen into said one surface after forming said silicon substrate and before forming said silicon epitaxial layer.