JPH1041311A - Epitaxial silicon board and solid-state image pickup device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epitaxial Si board wherein metal impurities are effectively removed from an Si epitaxial layer and a solid-state image pickup device of less white dot defects. SOLUTION: After carbon 14 is subjected to ion implantation to an Si board 11 at a dose amount of 5×10<13> atomic cm<-2> or more and oxygen 15 is subjected to ion implantation at the dose amount of the carbon 14 or more, an Si epitaxial layer 17 is formed and an epitaxial Si board 18 is manufactured. Compound of the carbon 14 and the oxygen 15 is formed in the Si board 11 and becomes a getter sink, metal impurities are effectively removed from the Si epitaxial layer 17 and a solid-state image sensing device formed in the epitaxial Si board 18 has less white dot defects.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial silicon substrate for forming a semiconductor device such as a solid-state imaging device, a solid-state imaging device, and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a semiconductor substrate for forming a semiconductor device such as a solid-state imaging device, a CZ substrate grown by a CZ method, an MCZ substrate grown by an MCZ method,
Conventionally, an epitaxial substrate having an epitaxial layer formed on a surface of a Z substrate or an MCZ substrate has been used.

[0003] In particular, for a solid-state imaging device, an epitaxial substrate that can use a CVD method with less segregation of added impurities, an epitaxial substrate that can use a CVD method with less segregation of added impurities, and so on, in order to reduce uneven image contrast due to uneven concentration of added impurities. MCZ substrates with few growth stripes are mainly used.

[0004] Among them, CZ substrate and MCZ
A buried region is formed on the surface of the substrate,
By forming a CZ substrate as a low-resistance substrate, an epitaxial substrate capable of forming a low-resistance region under an epitaxial layer as an element formation layer is effective for low-power driving and low power consumption.

A practical method for forming a Si epitaxial layer on an epitaxial Si substrate is C
The VD method is used, and the following four types of source gases are mainly used. Among them, in the hydrogen reduction method, the following two types of source gases are used. SiCl ₄ + 2H ₂ → Si + 4HCl SiHCl ₃ + H ₂ → Si + 3HCl

In the thermal decomposition method, the following two types of source gases are used. SiH ₂ Cl ₂ → Si + 2HCl SiH ₄ → Si + 2H _{2 Among the} above four types of source gases, they are suitable for solid-state imaging devices because they are inexpensive and are suitable for forming epitaxial layers having a high growth rate and a large thickness. For this reason, SiHCl ₃ is most often used.

However, even in the Si epitaxial layer formed using any of the above source gases, a large amount of metal impurities,
In particular, heavy metal impurities were mixed during epitaxial growth. For this reason, it is not possible to sufficiently reduce the white defect caused by the dark current flowing in the solid-state imaging device,
The characteristics and yield of the solid-state imaging device were low.

As a source of heavy metal impurities, a stainless steel member in a bell jar of an epitaxial growth apparatus, a piping for a source gas, and the like can be considered. That is, when chlorine is contained in the source gas, HCl formed by decomposition of the source gas during epitaxial growth corrodes stainless steel members and pipes to form a heavy metal chloride, and this chloride is used as a source gas. Is taken in, and this raw material gas
It is considered that heavy metal impurities are mixed in the i-epitaxial layer.

Therefore, when a solid-state imaging device is formed on an epitaxial Si substrate, it is necessary to perform some gettering treatment in order to remove metal impurities from the Si epitaxial layer which is an element forming layer. For this reason, various gettering methods have been conventionally considered.

That is, oxygen in the Si substrate is precipitated only inside the Si substrate, and an intrinsic gettering method using this as a getter sink, or polycrystalline Si or a high-concentration phosphorus diffusion region or the like is formed on the back surface of the Si substrate. There is an extrinsic gettering method of forming a getter sink using a strain stress with a Si substrate. However, none of the conventional methods has a weak gettering ability and cannot sufficiently reduce white defect caused by a dark current flowing through the solid-state imaging device.

Therefore, 5 × 10 ¹³ atoms cm ^{−2 is applied} to the Si substrate.
After the carbon is ion-implanted at the above dose, a Si epitaxial layer is formed on the surface of the Si substrate, so that the gettering ability is strong and the white defect of the solid-state imaging device is 1/5 or less of the conventional one. Patent Document 6 discloses an epitaxial Si substrate that can be reduced to
No. 23145 has already been proposed by the present applicant.

[0012]

However, even with this epitaxial Si substrate already proposed by the present applicant,
It is considered that the gettering ability is not always sufficiently strong, and it will be difficult to sufficiently reduce the white defect in a high-sensitivity solid-state imaging device in the future. Therefore, there is a need for an epitaxial Si substrate having a stronger gettering ability and a method of manufacturing the same.

[0013]

An epitaxial silicon substrate according to the present invention comprises: a silicon substrate containing carbon having a peak concentration of 1 × 10 ¹⁸ atom cm ^-3 or more and oxygen having a peak concentration of not less than this carbon; And a silicon epitaxial layer laminated on the surface of the silicon substrate.

In the epitaxial silicon substrate according to the present invention, it is preferable that the depth at which the carbon has the peak concentration is equal to the depth at which the oxygen has the peak concentration.

In the solid-state imaging device according to the present invention, the silicon epitaxial layer of the epitaxial silicon substrate is formed as an element forming layer.

A method of manufacturing an epitaxial silicon substrate according to the present invention comprises the steps of: ion-implanting carbon into a silicon substrate at a dose of 5 × 10 ¹³ atoms cm ⁻² or more; A step of implanting ions into the substrate; and a step of forming a silicon epitaxial layer on the surface of the silicon substrate after the ion implantation of the carbon and the oxygen.

In the method of manufacturing an epitaxial silicon substrate according to the present invention, it is preferable that the ion implantation is performed at an acceleration energy at which the projected range of carbon and the projected range of oxygen are equal to each other.

In the method of manufacturing an epitaxial silicon substrate according to the invention of the present application, the ion implantation is performed at an acceleration energy for positioning a depth at which the carbon has a peak concentration and a depth at which the oxygen has a peak concentration in the silicon substrate. Is preferred.

The method of manufacturing an epitaxial silicon substrate according to the present invention comprises the steps of: epitaxial growth at an epitaxial growth temperature;
It is preferable that the silicon epitaxial layer is formed by sequentially repeating cooling to a temperature of 2 or less a plurality of times.

In the method of manufacturing a solid-state imaging device according to the present invention, the epitaxial silicon substrate is manufactured, and a solid-state imaging device is formed using the silicon epitaxial layer of the epitaxial silicon substrate as an element formation layer.

In the epitaxial silicon substrate and the solid-state imaging device according to the invention of the present application, a compound of carbon and oxygen is formed in the silicon substrate, and this compound serves as a getter sink and has an extremely strong gettering ability. it is conceivable that. Therefore, metal impurities are effectively removed from the silicon epitaxial layer.

If the depth at which carbon has a peak concentration is equal to the depth at which oxygen has a peak concentration, the compound of carbon and oxygen is effectively formed in the silicon substrate, and Metal impurities are more effectively removed from the silicon epitaxial layer.

In the method of manufacturing an epitaxial silicon substrate according to the present invention, since carbon and oxygen are ion-implanted into the silicon substrate, even a supersaturated concentration of carbon and oxygen can be introduced into the silicon substrate. It is believed that a compound of carbon and oxygen can be formed in a silicon substrate.

Therefore, when a silicon epitaxial layer is formed on the surface of the silicon substrate after ion implantation, metal impurities mixed into the silicon epitaxial layer can be strongly gettered, and the silicon epitaxial layer can be removed from the silicon epitaxial layer. Metal impurities can be effectively removed.

Further, if ion implantation is performed at an acceleration energy at which the projected range of carbon and the projected range of oxygen are equal to each other, the depth at which carbon has a peak concentration and the depth at which oxygen has a peak concentration are mutually different. As a result, the compound of carbon and oxygen can be effectively formed in the silicon substrate, and metal impurities can be more effectively removed from the silicon epitaxial layer.

Further, if the ion implantation is performed at an acceleration energy at which the depth at which carbon has a peak concentration and the depth at which oxygen has a peak concentration are located not in the surface of the silicon substrate but in the silicon substrate, the crystallinity at the surface of the silicon substrate can be improved. Since the silicon epitaxial layer can be formed on this surface in a state where the deterioration of the silicon epitaxial layer is small, the deterioration of the crystallinity of the silicon epitaxial layer can be reduced.

Further, if the silicon epitaxial layer is formed in a plurality of times, the thermal history is added a plurality of times, so that crystal defects formed in the silicon substrate by carbon and oxygen ion implantation are grown, Metal impurities mixed in the epitaxial layer can be gettered more strongly, and the metal impurities can be more effectively removed from the silicon epitaxial layer.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the first and second embodiments of the present invention will be described.
Embodiments will be described. Prior to the description of these embodiments, first, the principle of the present invention will be described with reference to FIGS.

FIG. 2 shows that the oxygen concentration is 1
300 keV for a Si substrate of × 10 ¹⁸ atoms cm ^-3 or less
Ion implantation of only carbon at an acceleration energy of 5 and a dose of 5 × 10 ¹⁴ atoms cm ^-2 ,
An n-type Si epitaxial layer having a thickness of 10 μm and a resistivity of 40 to 50 Ωm is formed on the surface of the Si substrate by a CVD method at a temperature of 1150 ° C. using Cl ₃ as a source gas. Shows the result of analyzing by the SIMS method.

As is apparent from FIG. 2, despite the fact that the oxygen concentration of the Si substrate is 1 × 10 ¹⁸ atom cm ⁻³ or less,
Oxygen has the same peak concentration and distribution as carbon in the portion where carbon is ion-implanted. From this, in the portion where carbon was ion-implanted, carbon and oxygen do not exist independently, but a compound of carbon and oxygen is formed,
In the invention described in Japanese Patent Application No. 6-23145 by the applicant of the present application, it is considered that this compound is a getter sink.

Therefore, if a compound of carbon and oxygen is positively formed by simultaneously ion-implanting not only carbon but also oxygen, it is considered that a stronger gettering ability can be obtained. FIG. 3 shows that an epitaxial Si substrate similar to that described above is manufactured except that the thickness of the Si epitaxial layer is 12 μm, and a CCD solid-state imaging device is formed by the method shown in FIGS. The results of the evaluation are shown.

As is apparent from FIG. 3, when the dose of oxygen is equal to or more than the dose of carbon, the white defect is reduced to less than half as compared with the case where oxygen is not ion-implanted.
Therefore, in order to effectively form a compound of carbon and oxygen and obtain a strong gettering ability, the peak concentration of oxygen must be equal to or higher than the peak concentration of carbon, and the projection range after ion implantation with oxygen and carbon. It is desirable to make the distance, that is, the position of the peak density equal to each other.

When carbon is ion-implanted at a dose of 5 × 10 ¹³ atoms cm ⁻² or more as in the invention of the above-mentioned Japanese Patent Application No. 6-23145, the peak concentration of carbon becomes 1 ×.
It is about 10 ¹⁸ atoms cm ^-3 or more. Further, since a compound of carbon and oxygen may be formed, any of these may be implanted first.

FIG. 1 shows a first embodiment which is an epitaxial Si substrate and a method of manufacturing the same. In the first embodiment, as shown in FIG. 1A, a Si substrate 11 made of a Si crystal grown by the CZ method is prepared. This Si substrate 11 has a mirror surface 12 on one surface, is doped with phosphorus, is n-type, and has a resistivity of 8 to 12 Ω.
cm.

Then, the Si substrate 11 is first washed with an aqueous NH ₄ OH / H ₂ O ₂ solution, and further washed with HCl / H ₂ O _2.
The RCA cleaning is performed by cleaning with an O ₂ aqueous solution. next,
By performing dry oxidation at a temperature of 1000 ° C., an SiO ₂ film 13 having a thickness of 20 nm is formed on the mirror surface 12 as shown in FIG.

Thereafter, an acceleration energy of 300 keV and 5 × 1 are applied from the mirror surface 12 through the SiO ₂ film 13.
Ion implantation of carbon 14 at a dose of 0 ¹⁴ atoms cm ^-2 ,
Subsequently, acceleration energy of 240 keV and 5 × 10
Oxygen 15 is ion-implanted at a dose of ¹⁴ atom cm ^-2 .
At this time, the projected range distances of carbon 14 and oxygen 15 are both about 0.6 μm, and the peak concentrations are both 5 × 10 ^18.
Atomic cm- ³ .

Next, annealing is performed at 1000 ° C. for 10 minutes in a nitrogen atmosphere. As a result, as shown in FIG. 1C, a carbon and oxygen implantation region 16 having a peak concentration at a position deeper than the mirror surface 12 of the Si substrate 11 is formed. Thereafter, the SiO ₂ film 13 is removed with a liquid containing an HF solution.

Then, using SiHCl ₃ gas, 11
At a temperature of about 50 ° C., a Si epitaxial layer 17 doped with phosphorus and of n ⁻ type and having a resistivity of 40 to 50 Ωcm is grown on the mirror surface 12 to a thickness of 12 μm. An epitaxial Si substrate 18 in the form is completed.

The reason why the position of the peak concentration of carbon 14 and oxygen 15 in the carbon and oxygen implantation region 16 is made deeper than the mirror surface 12 is that the position of the peak concentration is the mirror surface 12. Degrades the crystallinity of the Si and grows on the mirror surface 12
This is because the crystallinity of the epitaxial layer 17 also deteriorates.

The annealing in the nitrogen atmosphere after the ion implantation of carbon 14 and oxygen 15 is performed because the Si epitaxial layer 17 is grown on the mirror surface 12 later. This is to restore the crystallinity in the vicinity of No. 12.

FIGS. 4 to 6 show a second embodiment which is a CCD solid-state imaging device and a method of manufacturing the same. Also in the second embodiment, as shown in FIGS. 4A and 4B, steps similar to those of the first embodiment shown in FIG. 1 are executed until the epitaxial Si substrate 18 is completed.

However, in the second embodiment, as shown in FIG. 4C, n ^- type Si
A p-type well region 21 is formed in the epitaxial layer 17, and an SiO ₂ film 22 is formed on the surface of the well region 21. Then, n-type and p-type impurities are selectively ion-implanted into the well region 21 to form an n-type transfer channel region 23, a p ⁺ -type channel stopper region 24, and a p ⁺ -type well region 25, respectively. Form.

Next, as shown in FIG. 5 (a), Si ₃ N ₄
The film 26 and the SiO ₂ film 27 are sequentially formed on the entire surface of the SiO ₂ film 22, and the SiO ₂ film 27 and the Si ₃ N ₄ film 26 in the portion where the light receiving section (photoelectric conversion section) is to be formed are selectively formed. To form SiO ₂ films 22 and 27 and Si ₃ N ₄ film 2
6, a gate insulating film 28 is formed. Thereafter, a transfer electrode is formed on the gate insulating film 28 by using the polycrystalline Si film 31.

Next, as shown in FIG.
Using the film 31 as a mask, an n-type impurity is ion-implanted to
⁺ -Type impurity diffusion region 32 is formed of, as shown in FIG. 6 (a), a polycrystalline Si film 31 by ion-implanting a p-type impurity as a mask p ⁺⁺ -type impurity diffusion region 33 formed I do. Then, as shown in FIG. 6B, an interlayer insulating film 34 is formed, and an Al film 35 as a light shielding film is changed to a polycrystalline Si film 31.
Formed on the upper layer.

In the CCD solid-state imaging device manufactured as described above, the pn region between the impurity diffusion region 32 and the well region 21 is
The photodiode formed by the junction and the impurity diffusion region 33 serving as a positive charge storage region constitute a light receiving unit 36. Also, a polycrystalline Si film 31 serving as a transfer electrode
And a part of the well region 21 constitute a read gate unit 37, and a part of the polycrystalline Si film 31 which is a transfer electrode and the transfer channel region 23 constitute a vertical transfer register 38. .

In the first and second embodiments described above,
Although the Si epitaxial layer 17 is formed on the surface of the epitaxial Si substrate 18 at one time, the epitaxial growth at the epitaxial growth temperature and the cooling to a temperature equal to or lower than の of the epitaxial growth temperature are sequentially repeated plural times. 17 may be formed.

In the above-described second embodiment, the p-type well region 21 is formed in the n-type epitaxial Si substrate 18, but these conductivity types may be opposite to each other. Further, in the above-described second embodiment, the CCD solid-state imaging device is formed on the epitaxial Si substrate 18 manufactured in the first embodiment. Can be formed.

[0048]

In the epitaxial silicon substrate according to the present invention, since metal impurities are effectively removed from the silicon epitaxial layer, a semiconductor device having excellent characteristics is formed at a high yield by using the silicon epitaxial layer as an element forming layer. can do.

If the depth at which carbon has a peak concentration is equal to the depth at which oxygen has a peak concentration, metal impurities are more effectively removed from the silicon epitaxial layer. By using the epitaxial layer as an element forming layer, a semiconductor device having more excellent characteristics can be formed with a higher yield.

In the solid-state imaging device according to the present invention, since the metal impurities are effectively removed from the silicon epitaxial layer as the element forming layer, the white defect is small and the yield is high.

In the method of manufacturing an epitaxial silicon substrate according to the present invention, metal impurities can be effectively removed from the silicon epitaxial layer, so that a semiconductor device having excellent characteristics can be obtained by using the silicon epitaxial layer as an element forming layer. Can be manufactured.

If ion implantation is performed at an acceleration energy at which the projected range of carbon and the projected range of oxygen are equal to each other, metal impurities can be more effectively removed from the silicon epitaxial layer. By using the silicon epitaxial layer as an element formation layer, it is possible to manufacture an epitaxial silicon substrate capable of forming a semiconductor device having more excellent characteristics at a higher yield.

Further, if ion implantation is performed at an acceleration energy at which the depth at which carbon has a peak concentration and the depth at which oxygen has a peak concentration are located not in the surface of the silicon substrate but in the silicon substrate, the crystallinity of the silicon epitaxial layer can be improved. Since deterioration can be reduced, it is possible to manufacture an epitaxial silicon substrate capable of forming a semiconductor device having more excellent characteristics at a higher yield by using the silicon epitaxial layer as an element forming layer.

Further, if the silicon epitaxial layer is formed in a plurality of times, metal impurities can be more effectively removed from the silicon epitaxial layer, so that the silicon epitaxial layer can be used as an element forming layer to obtain more excellent characteristics. An epitaxial silicon substrate capable of forming a semiconductor device with a higher yield can be manufactured.

According to the method of manufacturing a solid-state imaging device according to the present invention, metal impurities can be effectively removed from a silicon epitaxial layer as an element forming layer, so that a solid-state imaging device with few white defects can be manufactured at a high yield. be able to.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a manufacturing method according to a first embodiment of the present invention in the order of steps.

FIG. 2 is a graph showing the relationship between the depth of an epitaxial Si substrate and the concentrations of carbon and oxygen and illustrating the principle of the present invention.

FIG. 3 is a graph showing the relationship between ion implantation conditions and the number of white defect defects and illustrating the principle of the present invention.

FIG. 4 is a side sectional view sequentially showing an initial step of a manufacturing method according to a second embodiment of the present invention.

FIG. 5 is a side sectional view sequentially showing a middle step of a manufacturing method in a second embodiment.

FIG. 6 is a side sectional view sequentially showing final steps of a manufacturing method according to a second embodiment.

[Explanation of symbols]

11 Si substrate 14 Carbon
15 Oxygen 17 Si epitaxial layer 18 Epitaxial Si substrate

Claims (8)

[Claims] 1. A silicon substrate containing carbon having a peak concentration of 1 × 10 ¹⁸ atoms cm ⁻³ or more and oxygen having a peak concentration of not less than carbon, and a silicon epitaxial layer laminated on the surface of the silicon substrate. And an epitaxial silicon substrate comprising: 2. The epitaxial silicon substrate according to claim 1, wherein a depth at which the carbon has the peak concentration is equal to a depth at which the oxygen has the peak concentration. 3. A solid-state imaging device, wherein the silicon epitaxial layer of the epitaxial silicon substrate according to claim 1 is formed as an element formation layer. 4. A step of ion-implanting carbon into the silicon substrate at a dose of 5 × 10 ¹³ atoms cm ⁻² or more; a step of ion-implanting oxygen into the silicon substrate at a dose of not less than the carbon; Forming a silicon epitaxial layer on the surface of the silicon substrate after the ion implantation of oxygen. 5. The method of manufacturing an epitaxial silicon substrate according to claim 4, wherein said ion implantation is performed at an acceleration energy at which a projected range of said carbon and a projected range of said oxygen are equal to each other. 6. The epitaxial growth method according to claim 4, wherein said ion implantation is performed at an acceleration energy for positioning a depth at which said carbon has a peak concentration and a depth at which said oxygen has a peak concentration in said silicon substrate. A method for manufacturing a silicon substrate. 7. The silicon epitaxial layer according to claim 4, wherein the silicon epitaxial layer is formed by sequentially repeating a plurality of times of epitaxial growth at an epitaxial growth temperature and cooling to a temperature equal to or lower than 1/2 of the epitaxial growth temperature. A method for manufacturing an epitaxial silicon substrate. 8. A method for manufacturing a solid-state imaging device, comprising: manufacturing an epitaxial silicon substrate by the method according to claim 4; and forming the solid-state imaging device using the silicon epitaxial layer of the epitaxial silicon substrate as an element formation layer. Method.