JPH04199878A - Solid state image sensing device - Google Patents

Abstract

PURPOSE:To enable subminiaturization of isolation region and attain higher sensibility by combining a P' isolation region with a surface P<+> region. CONSTITUTION:A shallow impurity region 6 having conductivity which differs from a photoelectric conversion device 1 existing on the upper layer of the photoelectric conversion device 1 is used as an isolation region of the photoelectric conversion device 1. More specifically, N type impurities, which are the impurities of the photoelectric conversion device 1 are ion-implanted into a P type silicon substrate 7, thereby forming an N type impurity implantation region where a device isolation between the photoelectric conversion devices 1 is produced with a shallow P<+> layer 6. As a result, it is possible to reduce an isolation width smaller than a critical value of photolithography. This construction makes it possible to obtain a solid state image sensing device where higher sensibility performance is free of any restrictions imposed by a fine processing technology.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state imaging device, and particularly to a solid-state imaging device with improved light utilization efficiency.

[Conventional technology]

An example of a conventional one-dimensional solid-state imaging device is shown in FIG. Fourth
Figure (al indicates its planar structure; in the figure, 1 is a photoelectric conversion region formed by an N-type conductive impurity layer, 2 is a charge transfer channel, and 3 is a P-type conductive impurity layer). 4 is a transfer gate for reading charge from the photoelectric conversion region 1 to the charge transfer element, and 5 is a transfer gate electrode for charge transfer.
b) shows a cross-sectional view of the part indicated by B-B' in Fig. 4(a), and in the figure, 6 is a P+ region formed shallowly on the surface, and 7 is a P-type silicon substrate. .

The signal charge photoelectrically converted by the photoelectric conversion element in the photoelectric conversion region 1 is accumulated in the photoelectric conversion element for a certain period of time, and then read out to the charge transfer channel 2 through the transfer gate 4, and a voltage is applied to the transfer gate electrode 5. The data is sequentially transferred and read externally. The P+ region 6 is formed to embed the N- region of the photoelectric conversion region in the semiconductor substrate 7 for the purpose of reducing dark current.
This prevents the depletion layer in region 1 from reaching the surface.

FIG. 5 shows a conventional method for manufacturing a solid-state imaging device. 10 is a P-type silicon substrate; 11 is a photoresist pattern that serves as a mask for impurity implantation for forming the photoelectric conversion region 12; and 14 is a photoresist pattern that serves as a mask for impurity implantation for forming the isolation region 15.

Next, the manufacturing method will be explained.

First, a photoresist 11 is patterned in a region separating photoelectric conversion elements on a P-type silicon substrate 10 having an impurity concentration of about I x 10"Cm-3 (see FIG. 5).
a)) Using this photoresist 11 as a mask, N-type impurity ions are implanted (FIG. 5(b)).

Next, the photoresist 11 is removed, the implanted N-type impurity is driven by thermal diffusion, and the impurity concentration is increased to 10
A photoelectric conversion region 12 of 17cm-3 to 5×1017an-3 is formed (FIG. 5(C)).

Furthermore, a resist pattern 14 is provided to expose the part that will become the isolation region (FIG. 5(d)), and P-type impurity ions are implanted to form the isolation region, so that the impurity concentration is 5X.
A high-concentration P-type head region 15 of 10" an-3 to I x 1018 cm-3 is formed (FIG. 5(e)). This separation width is limited by the resist blank width Wi determined by the limit of photolithography. That will happen.

Finally, ions are implanted over the entire surface to form a shallow P+ region 13 on the substrate surface.
form.

[Problem to be solved by the invention]

However, the conventional solid-state imaging device is configured as described above, and the photoelectric conversion elements are separated by the separation region 3, so that the light incident on the separation region 3 cannot be effectively utilized. However, in the past, in order to maximize the use of light as an effective image, the separation region between photoelectric conversion elements was made as small as the limit of microfabrication, or the width (indicated by Wi in the figure) was made at the limit of microfabrication technology. was restricted.

Further, as the density of photoelectric conversion elements increases, the ratio of the isolation region 3 to the photoelectric conversion region 1 is increasing, and how to make the isolation region 3 small has become an important issue. In particular, recent linear image sensors
Due to the high integration density (approximately 0.00 pixels and chip size of approximately 8 cm) and the progress toward larger chips, currently only photolithography equipment with a minimum resolution of approximately 3 microns can be used for microfabrication of separation regions.

As described above, in conventional solid-state imaging devices, the minimum value of the separation width is limited by the limitations of photolithography for forming separation regions.

This invention was made to solve the above-mentioned problems, and it is possible to form a separation area smaller than the limit of microfabrication technology. The purpose of this invention is to obtain a solid-state imaging device that does not

[Means to solve the problem]

The solid-state imaging device according to the present invention uses, as a separation region between photoelectric conversion elements, a shallow impurity region having a conductivity different from that of the photoelectric conversion elements in the upper layer of the photoelectric conversion elements.

Further, in the solid-state imaging device according to the present invention, the photoelectric conversion element is included in the first impurity region with the same conductivity as that of the first impurity region and at a higher concentration than the first impurity region. It is formed from the second impurity region.

Further, in the solid-state imaging device according to the present invention, an impurity region is provided between the photoelectric conversion elements so as to cover the separation region of the photoelectric conversion elements, and has the same conductivity as the semiconductor substrate and has a higher concentration than the substrate.

[Effect]

The solid-state imaging device of the present invention can form a separation region that is smaller than the limit of miniaturization in photolithographic microfabrication technology,
Effective use of incident light can be achieved and high sensitivity can be achieved.

Furthermore, by creating an impurity distribution within the photoelectric conversion element or by increasing the concentration of the substrate in the region covering the separation area between the photoelectric conversion elements, it is possible to obtain a separation area that is below the limit of miniaturization and achieve high sensitivity. , sufficient isolation withstand voltage between photoelectric conversion elements can be ensured.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a solid-state imaging device according to an embodiment of the present invention, and FIG. 1(a) is a plan view thereof, and FIG.
) is a cross-sectional view of a portion indicated by AA' in FIG. In the figure, 6 is a shallowly formed P+ region. For other parts, the same reference numerals as shown in FIG. 4 indicate the same parts.

In such a configuration, the isolation width between the photoelectric conversion elements 1 can be made smaller than the limit value of photolithography by creating the isolation between the photoelectric conversion elements 1 using the shallow P+ layer 6.

Hereinafter, in order to explain this in detail, a method for manufacturing the solid-state imaging device according to this embodiment will be described using FIG. 2.

In the figure, the same reference numerals as in FIG. 5 according to the conventional example indicate the same parts.

First, as shown in FIG. 2(a), I
A photoresist pattern 11 corresponding to an isolation region of a photoelectric conversion element is formed on a P-type silicon substrate IO having an impurity concentration of about 3. At this time, the dimensions of the resist are determined to make the opening area of the photoelectric conversion element as large as possible.
- Set the limit value W of photolithography for boat fishing.

Subsequently, as this photoresist mask 11, an N-type impurity, which is an impurity for a photoelectric conversion element, is implanted into the silicon substrate by ion implantation to form an N-type impurity implanted region 12 (FIG. 2(b)).

After that, the resist 11 is removed, and the implanted N-type impurity is driven by thermal diffusion to reduce the impurity concentration to I x 101.
An N-type impurity region of 7 cm-' to 5 X I O"am-' is formed. At this time, the impurity is diffused not only in the depth direction but also in the lateral direction, resulting in an effective photoelectric conversion element 1.
The width of the separation region between 21 and 21 is Wl, which is narrower than the limit value W of photolithography (FIG. 2(C)). Usually, the lateral diffusion distance is about 0.7 times the depth diffusion distance. When the diffusion distance is long, it is necessary to determine the resist pattern width W in advance by considering the lateral diffusion distance.

Next, a shallow P+ region 13 is formed on the surface by ion implantation (FIG. 2(d)).

In the manner described above, the solid-state imaging device of this embodiment is completed.

Therefore, in the solid-state imaging device according to this embodiment, the width W' of the separation region between the photoelectric conversion elements 1 can be formed to be less than the limit W of the microfabrication technology of photolithography.

Here, when actually using the solid-state imaging device of the above embodiment, there is no problem in applying a low bias voltage to the photoelectric conversion element l to operate the element.
When applying a high bias voltage to the photoelectric conversion element, a problem arises regarding the isolation breakdown voltage of the photoelectric conversion element. The following two measures can be taken to address this problem.

First of all, create an impurity distribution in the photoelectric conversion element l region,
It is possible to increase the pressure resistance.

That is, the breakdown voltage between the photoelectric conversion elements 1 decreases as the depletion layers spread out from the photoelectric conversion elements 1 and come into contact with each other.

Therefore, in order to improve the breakdown voltage between elements, it is sufficient to limit the spread of the depletion layer. The third measure against this is
It is conceivable to double the impurity profile of the photoelectric conversion element, as shown in Figure (a). That is, the interval W
The distance W around the heavily concentrated N-type region 8 formed by
It has a structure in which it is covered with a thinly-concentrated N-type impurity region 9 formed by '. However, it is assumed that W">Wl. In this way, by doubling the impurity profile of the photoelectric conversion element 1 and making the outer concentration thinner, it is possible to suppress the extension of the depletion layer from the photoelectric conversion region 1, Pressure resistance will improve.

A second possibility is to partially increase the substrate concentration to suppress the growth of the depletion layer.

That is, the expansion of the depletion layer of the photoelectric conversion element 1 can be suppressed by increasing the concentration of the silicon substrate 10. An example is shown in FIG. 3(b). When manufacturing this structure, first, a P-type impurity is introduced in advance into a region corresponding to between the photoelectric conversion regions on the surface of a P-type silicon substrate, and the impurity concentration is higher than the substrate concentration or 5×1015a.
Two layers 30 having a thickness of approximately n-3 are formed, and then the steps shown in FIGS. 2(a) to 2(d) are performed. In this way, by forming in advance the two layers 30 with a higher concentration than the substrate in the region corresponding to the separation region between the photoelectric conversion elements 1, the two layers 30
This suppresses the expansion of the depletion layer between the photoelectric conversion elements 1 and improves the breakdown voltage.

Note that element separation in the direction perpendicular to A-A' in FIG. 1 is not particularly limited here, since the dimensions can be determined arbitrarily in a one-dimensional surface solid imaging device.

Furthermore, in the above embodiment, an example using a P-type semiconductor substrate was shown, but an N-type substrate may also be used. In this case, the conductivity type used in the explanation of the above embodiment is changed to the opposite conductivity type. It would be good to read it again.

〔Effect of the invention〕

As described above, according to the present invention, since the surface P+ region serves as the P'' separation region, it is possible to miniaturize the separation region, which could not be achieved with conventional solid-state imaging devices, and achieve high sensitivity. There is an effect.

Furthermore, since the structure is designed to reduce the extension of the depletion layer between photoelectric conversion elements, even when using high bias, sufficient isolation withstand voltage between photoelectric conversion elements can be ensured, making it possible to obtain a highly reliable product. It's effective.

[Brief explanation of the drawing]

1 is a plan view and a cross-sectional structure diagram showing a solid-state imaging device according to an embodiment of the present invention, FIG. 2 is a diagram showing a method for manufacturing the solid-state imaging device of FIG. 1, and FIG. FIG. 4 is a structural diagram showing another embodiment of the imaging device, FIG. 4 is a diagram showing a conventional solid-state imaging device, and FIG. 5 is a diagram showing a manufacturing method of FIG. 4. In the figure, 1 is a photoelectric conversion element, 2 is a charge transfer channel, 3 is a separation region, 4 is a transfer gate, 5 is a transfer gate, and 6. I3 is a P+ region, 7°10 is a P-type silicon substrate, 8 is a thick N-type region, 9 is a thin N-type region, 11 is a photoresist, 12 is an N-type impurity implanted region, 30 is a dark 2
It is a layer. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (3)

[Claims] (1) In a solid-state imaging device having one-dimensionally arranged photoelectric conversion elements and charge readout means, separation between the photoelectric conversion elements is achieved by a shallow impurity having a conductivity different from that of the photoelectric conversion element provided in the upper layer of the photoelectric conversion element. A solid-state imaging device characterized by using layers. (2) The photoelectric conversion element includes a first impurity region, which has the same conductivity as the first impurity region, has a higher concentration than the first impurity region, and is included in the first impurity region. 2. The solid-state imaging device according to claim 1, wherein the solid-state imaging device is formed of a second impurity region formed so as to be formed. (3) An impurity region according to claim 1, which is formed between the photoelectric conversion elements so as to cover the separation region and has the same conductivity as the semiconductor substrate and has a higher concentration than the substrate. Solid-state imaging device.