JPS5812477A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To improve the characteristics of a solid-state image pickup element grealy by forming a channel stopper area without extending it to the edge of an oxidized film for element separation. CONSTITUTION:On a substrate 1, a nitrate film 10 is formed and etched away at a part 10a, and the film 10 is masked for ion implantation. Further, a part 10b of the film 10 is etched away and while an oxidized film 6 for element separation is formed, implanted impurities are diffused to form a P area 9a. Consequently, the high-density P area 9a is limited to the part under said film 6 and never extends to the edge of the film. Consequently, the MOS system reduces random noises and the CCD system reduces a dark current, improving the characteristics of a solid-state image pickup element greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device that can reduce random noise and dark current.

As a solid-state image sensor, J)
Moat) A transistor method in which the transistors are sequentially turned on and off and the charge stored in the photodiode is read out as a signal by this switching action;
The CCD method, in which charges are sequentially transferred, is widely known.

Among these, the Mo1) transistor method has the following problems. That is, a problem with the M08 type solid-state image element is random noise, which is observed as flickering on the digital noise screen. One of the causes of this random noise is a component generated from inside the sensor. This will be explained using FIG.

Figure 1 is a cross-sectional view of one pixel of a conventional solid-state image sensor.
1 is a p-type substrate, 29 i-diffusion layers, 4 is a gate, an oxide film,
5 is a gate electrode, 6 is an oxide film for element isolation (LOCO8 oxide film), T is an interlayer insulating film, * is a vertical signal line, and 9 is a P region as a channel stopper. Here, if the current component of random noise is one, it is known that there is a relationship of 11 (KC ma...@(1)). However, Cv is the vertical signal @SO capacitance.Cv is the capacitance between the vertical signal line 8 and the n-type substrate 1 via the oxide film, and the Op-n junction capacitance component between the l-diffusion layer 2 and the l-type substrate 1 where -direct signal- is in contact. In Cv O, the p-1 junction capacitance component is larger, and by reducing the p-1 junction capacitance component, random noise is reduced and a clean peak is created. It is possible to change the image quality.

However, in implementing the above-mentioned measures according to the prior art, there are the following problems. I have a Fi@ degree. However, the method of reducing the junction capacitance component other than thinning the substrate concentration is to reduce the electrical substrate 1.
The resistivity of the photoresist is a cause of the deterioration of the OAM quality such as loud noises and blueing, and the P effect is weak.

The 11+diffusion layer 2 with which the vertical signal ports come in contact has an 8-layer structure with an oxide film for element isolation. Below the oxide film 6 for element isolation, there are rounded ions that increase the element isolation O effect. A higher*zop region 9 than the implantation K is formed. The method for forming this p@ region 9 will be explained with reference to FIG.

FIG. 2(a) shows the nitride film 10 formed on the L-shaped substrate 1 in good condition. No. 29) is nitride film 100
The state is shown after a portion of 10 m has been etched away. Tuna figure 2 (
c) shows a state in which ions were implanted using the nitride film 10 as a mask. FIG. 2(d) shows a state in which a P region 8 is formed by ion implantation and diffusion of impurities at the same time as the element isolation oxide film 6 is formed. Therefore, as shown in FIG.
At the same time as the high-concentration P region enters, the J [surroundings] come into contact with the high-concentration P region mouth.

In a simple model, the p-n junction capacitance can be expressed as the following equation.

Here, mu is the junction area and q is the amount of electron charge.

#1 is the dielectric constant of si, ri is the permittivity of vacuum, N is the impurity concentration in the P region, ND is the impurity concentration in the n region, and V
is the reverse bias voltage applied to the p-m junction.

φ is the diffusion potential. Since N11l is normally formed at a much higher concentration than N, C is approximately proportional to the square root of N.

As mentioned above, the h diffusion layer 2 comes into contact with the low #kf type 1 substrate 1 and the high concentration P region 8 (channel stopper), but the 0 capacitance (per unit area) is due to the high f01' region 3. The OII contact part is larger. In terms of area, the contact area with the low concentration A-type substrate 1 is large, but in order to increase the degree of integration, m+
If you make a small party with two diffusion layers, will the surrounding high # degree be? The area of contact with the region 9 cannot be ignored either, and this area becomes part of the p-4 combined capacity. Therefore, as described above, it is not possible to reduce the capacitance of the vertical signal lines simply by making the substrate thinner.

The following KCCD method has the following problems. In other words, even a CCD type solid-state wrist device can be used as a channel stopper or! An element isolation oxide film process is sometimes used to improve sensitivity. In this case, the high #I which becomes the channel stopper
! A dark current is generated due to the P region of the IIL, resulting in deterioration of image quality.

This modification has been made to solve the above-mentioned problems, and is aimed at eliminating the random noise of the MOB type sensor and reducing the dark current of the CCD type solid-state optical element. be.

3al is a cross-sectional view of the element at each step for manufacturing the solid-state imaging cord according to the present invention.

Figure 3 shows a state in which a nitride film 10 is formed on a type 1 substrate 1. No. 39) shows that a portion 10m of the nitride film 10 has been etched away and is in good condition. Figure 3 (
.) shows a state in which ion implantation is performed using the nitride film 10 as a mask. Figure 3-) shows the nitride film 10
This shows the state in which the portion 10k of is further removed by etching.

Diagram 3 (・) shows the same result when the element isolation oxide film 6 is formed.
This figure shows the state in which P region 9a is formed by implanting impurities and diffusing them.

Does the above process require high concentration? Region (a) is limited to only the portion below the element isolation oxide film 6, and can be prevented from extending to its edges. In this way, the conventional process is
) The solid-state imaging probe of the present invention can be made by simply adding the steps (). Etching Co., Ltd. of Knight 2 Knight Film 02t,
A mask may be used, or over-etching of the goods may be performed.
Nifts, quantity□eh.

There is also a method.

FIG. 4 is a cross-sectional view of one pixel of an embodiment of the solid-state image sensor of the present invention manufactured in this manner.
The same parts as in the figures are given the same reference numerals. Contact between the n diffusion layer 2 and the highly doped P region 1m serving as a channel stopper can be avoided. As a result, the capacitance of the -direct signal line 8 is reduced, resulting in a reduction in second-order noise, and in the case of the CCD method, dark current is reduced. By reducing the capacitance, the circuit speed can be increased. Furthermore, by using a mask, the design range can be expanded by changing the capacitance + diffusion layer O capacitance depending on the circuit part.

It is a sectional view of another embodiment of the tuna fish. 11 is an n-type substrate;
12 FiP wells, 13 n+ forming photodiode
A diffusion layer, 14 an oxide film for element isolation, and 15 a P region of a channel stopper. Sensitivity is improved because photocarriers generated under the element isolation oxide film can be used as effective carriers without recombining or color mixing.

Note that the present invention can be applied to either two-dimensional or -dimensional solid-state imaging devices.

As described above, according to the present invention, random noise can be reduced in the M08 method, dark current can be reduced in the CCD method, and the contrast characteristics of the solid-state image sensor can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a conventional solid-state image sensor, 2wJ is a cross-sectional view of the device in each manufacturing process, FIG. 3 is a cross-sectional view of the solid-state image sensor of the present invention in each manufacturing process, and FIG. 4 is a cross-sectional view of the solid-state image sensor of the present invention. FIG. 5 is a cross-sectional view of one embodiment of the solid-state imaging device, and FIG. 5 is a cross-sectional view of another embodiment. 1aeesp type substrate, 2,3e***111+diffusion layer,
4...Gate oxide film, S.e.. Gate electrode, 6.
...Oxide film for element isolation, T...Interlayer insulating film, 8-
...Vertical signal line, sl...P area. Figure 1 Maro 1, Shin 4 Figure #l5II! J1

Claims (1)

[Claims] In a solid-state imaging device, a channel stopper region of a second conductivity type is formed on a semiconductor substrate of a first conductivity type, and an oxide film for element isolation is formed on the channel stopper region. A solid-state imaging device characterized by being formed so as to extend to the edge of the film.