JPH03250765A - Solid-state image sensing element - Google Patents

Abstract

PURPOSE:To contrive to suppress generation of a fine white point at the time of high temperature by a method wherein a semiconductor substrate is constituted of a one conductivity type base region, a first epitaxial layer and a second epitaxial layer and a channel region is formed in this second epitaxial layer. CONSTITUTION:A semiconductor substrate 20 is constituted of a one conductivity type base region 21, a one conductivity type first epitaxial layer 22, which is laminated on this region 21 and has a resistivity of 1OMEGA-cm or lower, and a one conductivity type second epitaxial layer 23, which is laminated on this layer 22 and has a resistivity of a degree identical with that of the region 21. A channel region is formed in this layer 23. Here, a compound material is formed of B being contained in large quantities in the layer 22 and heavy metals, such as Fe, Cu and the like, which are mixed in the Si substrate 20, and the heavy metals are removed to outside of an active region. Thereby, a crystal defect in the active region is decreased and the generation of a fine white point is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a CCD solid-state image sensing device, and particularly to the structure of a substrate for reducing dark current.

(b) Prior Art The Si (silicon) substrate forming the CCD solid-state image pickup device is of P type or N type, and the device structure differs depending on the type of substrate. When a P-type substrate is used, an N-type diffusion region is provided on one surface of the substrate, and this diffusion region is used as an information charge storage and transfer channel. This diffusion region is LO
It is divided by a channel isolation region such as GO9, and an overflow drain is formed in this channel isolation region to receive excess information charges leaking from the diffusion region.

On the other hand, when using an N-type substrate, after forming a P-type diffusion region, a so-called P-Well region, on one surface of the substrate, this P-well region is formed.
An N-type diffusion region that becomes a storage transfer channel is formed in the well region. When using an N-type substrate in this way,
In order to create a vertical overflow drain structure in which excess information charges in the diffusion region are discharged to the N-type substrate side by υ1, an overflow “1-
There is no need to form an F-rain, and it is effective for miniaturization, that is, for increasing pixel density, and future development is expected. However, even CCDs using P-type substrates have higher sensitivity in the infrared region than those using N-type substrates, and are widely used for specific applications such as infrared cameras and high-sensitivity cameras. .

Figure 3 shows a CCD using a P-type substrate.
) is a plan view of the frame transfer type imaging unit, and the same figure (
b) is its X-Y sectional view.

On the main surface of the P-type Si substrate (10), N-type diffusion regions (2) (not shown in the cross-sectional view) separated by the channel separation region (1) are arranged parallel to each other and are embedded. It has a channel structure. Further, on the Si substrate (10), a plurality of transfer electrodes (3) intersect with the diffusion region (2).
, are formed in an array through the membrane <4). This transfer electrode (3
) has a two-layer structure that partially overlaps, and the upper layer has a narrower width above the channel separation region (1). Then, the transfer electrode (3) is provided with a multiphase, for example, 4
Phase transfer lock≠, ~≠4 is applied and the Si substrate (1
Information charges are transferred within 0).

In such a CCD, if there are crystal defects near the surface of the Si substrate (10), the information charges transferred in the Si substrate (10) will be trapped in the crystal defects, reducing the transfer efficiency. An epitaxial layer (12) is completely formed on the surface of the Si substrate (10) to reduce crystal defects. That is, the Si substrate (10) is made of P such as B (boron).
The base region (11) containing type impurities and this base region (
11) P-type epitaxial layer (1
2), and is structured so that a transfer channel is formed in the epitaxial layer (12). This epitaxial layer (12) has an impurity concentration comparable to that of the base region (11), The resistivity is set to about 10 to 20 Ω-■.

In addition, Na adhering to the surface of the Si substrate (10) during the manufacturing process
In order to reduce the influence of alkali metals such as (sodium) on the transfer channel, the Si substrate (10) is
Intrinsic gettering) processing is carried out. This IG process uses supersaturated oxygen present inside the Si substrate (10) to form a segregation region inside the Si substrate (10), and heats the Si substrate (10) to a high temperature to remove oxygen near the surface. After diffusing to the outside of the substrate, the internal oxygen is allowed to precipitate. According to such IG processing, Si substrate (10
) becomes a region free from oxygen precipitation and crystal defects, and a region for trapping impurities is formed inside the Si substrate (10).

(c) Problems to be Solved by the Invention Incidentally, in recent video cameras, which are becoming smaller in size, an extremely large number of circuit elements are mounted in a high density inside the housing of the device. Rising temperatures have become a problem. In particular, CCDs have problems such as an increase in dark current and generation of noise when the ambient temperature increases. One type of such noise is minute white spots that occur mainly at high temperatures. Such white spots are cc
It is difficult to eliminate this by devising a driving method for D or by correcting the video signal at the signal processing stage, and countermeasures for the CCD itself are desired.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a CCD solid-state image sensor that can suppress the occurrence of minute white spots at high temperatures.

(d) Means for solving the problems The present invention has been made to solve the above problems,
In a CCD solid-state imaging device, a channel region defined by a channel separation region is formed on one principal surface of a semiconductor substrate, and a plurality of transfer electrodes are arranged and formed on this channel region.
The first feature is that the semiconductor substrate has a base region of -conductivity type and a resistivity of 1Ω-
a first epitaxial layer of one conductivity type having a resistivity of m or less; a first epitaxial layer of one conductivity type laminated on the first epitaxial layer and having a resistivity comparable to that of the base region; The channel region is formed within this second epitaxial layer.

A second feature is that the semiconductor substrate is -
A base region of a conductivity type, a diffusion layer having a resistivity of 1 Ω-m or less by implanting impurities of one conductivity type into one surface of the base region, and a diffusion layer laminated on this diffusion layer and having a resistance similar to that of the base region. an epitaxial layer having a
The channel region is formed within this epitaxial layer.

The third feature is that the semiconductor substrate is
Consisting of a base region of one conductivity type having a resistivity of 1 Ω-m or less, and an epitaxial layer of one conductivity type laminated on the base region and having a resistivity higher than that of the base region,
The channel region is formed within this epitaxial layer.

According to the present invention, impurities such as heavy metals that generate crystal defects that cause minute white spots form a complex with impurities contained in large amounts to reduce resistivity. The composite is segregated within the semiconductor substrate.

Therefore, heavy metals such as iron and copper contained in the active region are completely removed, crystal defects are reduced, and the generation of minute white spots is suppressed.

(f) Example Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of main parts of the solid-state image sensing device of the present invention, and FIG.
The same parts as the figure are shown. In this figure, the electrode structure is the same as in Fig. 3, and the same parts are given the same reference numerals, and the channel stop region and the N-type diffusion region forming the buried channel structure are also the same as in Fig. 3. They have the same configuration.

A feature of the present invention is that a P+ type epitaxial layer (22) is formed between a P type base region (21) and an epitaxial layer (23) of a Si substrate (20). That is, the base region (21) containing P-type impurities
Upper<7=After laminating an epitaxial layer (22) containing a high concentration of P-type impurities such as B from this base region (21), an epitaxial layer (23) in which a transfer channel can be formed is formed again. The epitaxial J'1i (22) on the base region (21) is
〉 and epitaxial layer where transfer channels are formed (
23), the concentration of P-type impurities is about one order of magnitude higher, and the resistivity is set to 1 Ω-m or less.

The resistivity of the base region (2I) and the epitaxial layer (23) is about 10 to 20 Ω-σ, which is the same as in FIG.

Furthermore, in the Si substrate (20), a large amount of B contained in the epitaxial layer (22) is absorbed by the Si substrate (20).
A complex is formed with heavy metals such as Fe and Cu mixed in the active region, and the heavy metals are removed outside the active region. Therefore, crystal defects in the active region are reduced, and the occurrence of fine white spots is suppressed. Therefore, the higher the concentration of B in the epitaxial layer (21), that is, the lower the resistivity of the epitaxial layer (21), the greater the effect of suppressing the generation of minute peaks.

In addition, in this embodiment, P is placed on the base region (21).
Although the case where a type 1 epitaxial layer 22) is laminated is illustrated, by implanting and diffusing P type impurities such as B into the base region (21), a high concentration of P+ is created near the surface of the base region (21). After forming the type diffusion layer, the epitaxial layer (23) in which the transfer channel is formed may be laminated. In this case, the P+ type diffusion layer is layered with the P+ type epitaxial layer (23).
It works in the same way as 2).

FIG. 2 is a sectional view showing another embodiment of the invention. This figure also shows the same parts as FIG. 3.

Here, the Si substrate (30) consists of a base region (31) containing a high concentration of P-type impurities and an epitaxial layer (32) having a lower concentration of P-type impurities than the base region (31),
Transfer electrodes (3) are arranged and formed on this epitaxial layer (32). That is, the Si substrate (30) is completely formed by laminating an epitaxial region (32) having a resistivity of about 10 to 20 Ω-σ on a base region (31) having a resistivity of 1 Ω-mark or less. Therefore, the base area (31
) itself is the P+ type epitaxial region (22) in Figure 1.
It acts in the same way as heavy metals are removed. Therefore, even in such a Si substrate (<31), heavy metals in the epitaxial layer (32) (7) serving as the active region are eliminated, crystal defects are reduced, and the generation of minute peaks is suppressed.

In this embodiment, frame transfer type C
Although the illustration is about a CD solid-state image sensor, regardless of the CCD method, even in an interline type etc., if the above-mentioned Si substrate (20), (30) is adopted, the generation of fine white spots can be suppressed. I can figure it out.

(G) Effects of the Invention According to the present invention, the crystal defects in the active region are reduced, so the generation of minute white spots is suppressed. Therefore, it is possible to obtain a stable and good video signal even when the ambient temperature becomes high.
It is possible to provide a CCD solid-state image sensor that is effective for high-density mounting of circuit elements due to miniaturization of video cameras.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the solid-state image sensor of the present invention;
FIG. 2 is a sectional view showing another embodiment, and FIG. 3 is a plan view and a sectional view showing a conventional solid-state image sensor. Diagram 1 ・Soisai1shi → Shimaki Boukengen. 2. Boarding Q @ 竺20: Si :lEach Zuguchii zzj:He°1-Suto1riV Ho: ':i＄昭へ"-Su卆I菆" 2 工r"7体ち- Reno 3 o 2 S4 2 ff 31, be-mata life 32; 1 pin 7 yard eyebrow diagram (a)

Claims (3)

[Claims] (1) In a CCD solid-state imaging device in which a channel region defined by a channel separation region is formed on one principal surface of a semiconductor substrate, and a plurality of transfer electrodes are arranged and formed on this channel region, the semiconductor substrate has the following features: a base region of one conductivity type; a first epitaxial layer of one conductivity type laminated on the base region and having a resistivity of 1 Ω-cm or less; and a first epitaxial layer laminated on the first epitaxial layer and having the same resistivity as the base region. a second epitaxial layer of one conductivity type having a certain resistivity, and the channel region is formed in the second epitaxial layer. (2) In a CCD solid-state imaging device in which a channel region defined by a channel separation region is formed on one main surface of a semiconductor substrate, and a plurality of transfer electrodes are arranged and formed on this channel region, the semiconductor substrate has the following features: A base region of one conductivity type, and an impurity of one conductivity type implanted into one surface of this base region.
It consists of a diffusion layer having a resistivity of Ω-cm or less, and an epitaxial layer of one conductivity type laminated on the diffusion layer and having a resistivity comparable to that of the base region, and the channel region is formed in the epitaxial layer. A solid-state imaging device characterized in that: is formed. (3) In a CCD solid-state imaging device in which a channel region defined by a channel separation region is formed on one main surface of a semiconductor substrate, and a plurality of transfer electrodes are arranged and formed on this channel region, the semiconductor substrate has the following features: It consists of a base region of one conductivity type having a resistivity of 1 Ω-cm or less, and an epitaxial layer of one conductivity type laminated on this base region and having a resistivity higher than that of the base region, and the channel is formed in this epitaxial layer. A solid-state imaging device characterized in that a region is formed.