JPH0855973A - Method of manufacturing solid-state image sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] To manufacture a solid-state image sensor with few white defects and dark current without changing the characteristics. [Structure] Before forming a gate electrode of a charge transfer portion, 1
The epitaxial substrate is subjected to heat treatment at a temperature of 000 ° C. or higher. As a result, the metal in the element active region of the epitaxial substrate is reduced despite a small change in the crystal grain size of the semiconductor layer forming the gate electrode of the charge transfer portion and a small redistribution of impurities forming the diffusion region. The amount of impurities is reduced and the minute defects disappear.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a solid-state image pickup device for forming a solid-state image pickup device on an epitaxial substrate.

[0002]

2. Description of the Related Art Since an element active layer having a resistivity different from that of an underlying substrate can be formed on an epitaxial substrate, a solid-state image pickup element is also formed on the epitaxial substrate from the viewpoint of increasing the degree of freedom in element design. In many cases.
Most of the epitaxial layers of the epitaxial substrate are formed by the CVD method.

[0003]

However, the solid-state image pickup device formed on the epitaxial substrate has many white defects and dark current. It is considered that the causes of these are metal impurities mixed from the CVD apparatus and the raw material gas during the formation of the epitaxial layer, and minute defects in the epitaxial layer.

Therefore, as a countermeasure against these, C
Conventionally, cleaning of VD equipment, piping, raw material gas, etc. and strengthening of gettering for an epitaxial substrate have been performed. However, even with these measures, the white defect and the dark current of the solid-state image sensor cannot be sufficiently improved.

[0005]

According to a first aspect of the present invention, there is provided a method of manufacturing a solid-state image pickup device, wherein a solid-state image pickup device is formed on an epitaxial substrate 12 before forming a gate electrode 23 of a charge transfer portion. In addition, heat treatment at a temperature of 1000 ° C. or higher is applied to the epitaxial substrate 12.

A method of manufacturing a solid-state image sensor according to a second aspect is the method of manufacturing a solid-state image sensor according to the first aspect, characterized in that the heat treatment is performed for 5 hours or more.

The method for manufacturing a solid-state image sensor according to a third aspect is the method for manufacturing a solid-state image sensor according to the first aspect, characterized in that the temperature is 1100 ° C. or higher.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a solid-state image sensor according to the first aspect, wherein the heat treatment is performed in an N ₂ atmosphere.

[0009]

In the method of manufacturing a solid-state image pickup device according to the present invention, in the epitaxial layer 11, the interface between the epitaxial layer 11 and the underlying substrate and the metal impurities in the underlying substrate are redistributed by heat treatment, and the element active region The amount of metal impurities is reduced. In addition, minute defects in the epitaxial layer 11 and at the interface between the epitaxial layer 11 and the underlying substrate disappear by heat treatment.

On the other hand, since the heat treatment on the epitaxial substrate 12 is performed before the gate electrode 23 of the charge transfer portion is formed, the crystal grain size change of the semiconductor layer forming the gate electrode 23 and the diffusion region are formed. There is little redistribution of impurities.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention applied to the manufacture of a CCD image pickup device will be described below with reference to FIGS. In this embodiment, N-type Si manufactured by the CZ method and having a diameter of 4 inches, a plane orientation of <100>, and a resistivity of about 10 Ωcm.
First, the substrate is prepared. Then, by a reduction reaction type CVD method using SiHCl ₃ + H ₂ gas, as shown in FIG.
As shown in, the N-type epitaxial layer 11 having a resistivity of about 10 to 20 Ωcm and a thickness of 10 μm is formed on the Si substrate to form the Si epitaxial substrate 12.

After that, a SiO ₂ film (not shown) having a thickness of 100 nm is formed on the surface of the epitaxial layer 11, and a heat treatment at a temperature of 1100 ° C. in an N ₂ atmosphere is performed for 10 hours. The SiO ₂ film is for preventing the surface of the epitaxial layer 11 from being roughened during this heat treatment, and is therefore removed after the heat treatment.

Next, as shown in FIG. 2B, a P-type well region 13 is formed in the epitaxial layer 11, and a SiO ₂ film 14 is formed on the surface of the P-type well region 13. Then, N-type and P-type impurities are selectively ion-implanted into the P-type well region 13 to form an N-type diffusion region 15 for the vertical register, and the P ⁺ -type well region 1 below the N-type diffusion region 15.
6, and P ⁺ type diffusion region 17 as a channel stopper
Are formed respectively.

Next, as shown in FIG. 2C, Si ₃ N _{4 is used.}
The film 21 and the SiO ₂ film 22 are sequentially laminated on the entire surface of the SiO ₂ film 14, and the part of the SiO ₂ film 2 to be a light receiving portion later is formed.
2 and the Si ₃ N ₄ film 21 are selectively etched. The SiO ₂ film 14 and the Si ₃ N ₄ film 21 thus formed
And the three-layer film of the SiO ₂ film 22 constitutes a gate insulating film. After that, the polycrystalline Si layer 23 as a transfer electrode is replaced with Si.
It is formed on the O ₂ film 22.

Next, as shown in FIG. 3A, polycrystalline Si
Using the layer 23 as a mask, the depth of the P-type well region 13 is 0.4.
Phos is ion-implanted at a position of about μm and heat treatment is performed in an N ₂ atmosphere to form the N-type diffusion region 24. P between the N-type diffusion region 24 and the P-type well region 13
The light receiving portion 25 is formed by a photodiode having an N junction.

Next, as shown in FIG. 3B, polycrystalline Si
B is ion-implanted into the surface of the light receiving portion 25 using the layer 23 as a mask, and heat treatment is performed in an N ₂ atmosphere to form a P ⁺⁺ type diffusion region 26 as a positive charge storage region. Then, as shown in FIG. 3C, an inter-layer insulating film such as the PSG film 27 is formed on the entire surface, an Al film 28 as a light-shielding film is formed, and a surface protective film (not shown) is further formed. And this C
Complete the CD image sensor.

In the above embodiment, the process of FIG.
Heat treatment at a temperature of 100 ° C. was performed for 10 hours,
FIG. 1 shows the number of white defects in the CCD image pickup device when the heat treatment time was 5 hours and when the heat treatment temperatures were 1000 ° C. and 950 ° C., in addition to the present embodiment.

As is apparent from FIG. 1, at a temperature of 1100 ° C., the number of white defects is reduced by 40% or more by the heat treatment for 5 hours or more. Although heat treatment at a temperature of 1000 ° C. is effective, a temperature of 1100 ° C. or higher is preferable.
Further, for example, when heat treatment is performed in an Ar atmosphere, voids may be formed in an incomplete portion of the SiO ₂ film formed before this heat treatment. Therefore, it is desirable to perform this heat treatment in an N ₂ atmosphere. .

Although the N-type epitaxial layer 11 is formed on the N-type Si substrate in the above-mentioned embodiments, white-scratch defects are generated by the above-mentioned heat treatment in the CCD image pickup device of any combination of conductivity types. The effect of reducing can be obtained.

[0020]

According to the method of manufacturing a solid-state image sensor according to the present invention, there is little change in the crystal grain size of the semiconductor layer forming the gate electrode of the charge transfer portion and redistribution of impurities forming the diffusion region. Nevertheless, since the amount of metal impurities in the element active region of the epitaxial substrate is reduced and the microdefects disappear, it is possible to manufacture a solid-state imaging element with few white defects and dark current without changing the characteristics. .

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between heat treatment temperature and heat treatment time and the number of white defects in a CCD image pickup device.

FIG. 2 is a side sectional view showing the first half of one embodiment of the present invention in process order.

FIG. 3 is a side sectional view showing the latter half of one embodiment in process order.

[Explanation of symbols]

 11 Epitaxial Layer 12 Si Epitaxial Substrate 23 Polycrystalline Si Layer

Claims (4)

[Claims] 1. A method of manufacturing a solid-state imaging device, comprising forming a solid-state imaging device on an epitaxial substrate, wherein heat treatment at a temperature of 1000 ° C. or higher is applied to the epitaxial substrate before forming a gate electrode of a charge transfer portion. And a method for manufacturing a solid-state image sensor. 2. The method for manufacturing a solid-state image pickup device according to claim 1, wherein the heat treatment is performed for 5 hours or more. 3. The method for manufacturing a solid-state image pickup device according to claim 1, wherein the temperature is 1100 ° C. or higher. 4. The method for manufacturing a solid-state image pickup device according to claim 1, wherein the heat treatment is performed in an N ₂ atmosphere.