JPH01211965A - Manufacture of solid-state image sensing element - Google Patents

Abstract

PURPOSE:To make the depth of a recessed section of a potential well for a charge storage section uniform by implanting impurity ions into a substrate region under a storage-section electrode formed at the charge storage section and making the impurity concentration of said substrate region the same as or higher than that of a substrate region under a transfer gate electrode on the charge transfer section side. CONSTITUTION:Impurity ions are implanted into a substrate region under a storage-section electrode 23 shaped to a charge storage section, the impurity concentration of the substrate region under the storage-section electrode 23 is made the same as or slightly higher than that of a substrate region under a transfer gate electrode 24 on the charge transfer section side, the depth of a recessed section in a potential well is shallowed, and the transfer of carrier is facilitated. Accordingly, all of carriers in the charge storage section 23 are transferred, and are not left, thus equalizing the depth of the recessed section in the potential well for the charge storage section.

Description

[Detailed Description of the Invention] [Summary] Regarding the method for adjusting the impurity concentration in the charge storage part in the manufacturing method of a solid-state image sensor, in order to transfer all the carriers and not to leave them, the concave part of the potential well in the charge storage part is For the purpose of making the depth uniform, in a charge storage part that is provided between a light receiving part and a charge transfer part and has transfer gate electrodes or bias electrodes on both sides, the charge storage part formed in the charge storage part is The method includes a step of implanting impurity ions into the substrate region under the storage section electrode to make the impurity concentration in the substrate region under the storage section electrode equal to or higher than the impurity concentration in the substrate region under the transfer gate electrode on the charge transfer section side. It is characterized by being

[Industrial application field]

The present invention relates to a method of manufacturing a solid-state imaging device, and particularly to a method of adjusting impurity concentration in a charge storage section.

Recently, C
A CD image sensor (solid-state image sensor) has been developed, and there is a demand for further improvement in the performance of the image sensor.

[Problems to be solved by the prior art and the invention] For example, CCD (Charge Coup
(LED Devices) Image sensors usually have three functions: a light receiving section, a charge storage section, and a charge transfer section.The light receiving section (photodiode) converts incident light into carriers (charges).
The charge storage section is a section that stores a certain amount of carriers, and the charge transfer section is a shift register section that sequentially changes and transfers the potentials of the arranged electrodes. FIG. 3 shows a configuration diagram of the line sensor, where 1 is a light receiving section and 2 is a charge storage section.

3 is a charge transfer section, and 4 is an output section.

FIG. 4 shows a cross-sectional view of such a CCD image sensor and a conventional potential diagram. A p-type silicon substrate, 11 a light receiving section (photodiode), and 12 a charge storage section.

13 is a charge transfer section, 21 is an n+ type silicon layer, and 22 is an n
23 is a storage electrode, and 24 is a transfer electrode.

PA, PB, and PC are transfer gate electrodes. Carriers generated in the light receiving section 11 are stored in the charge storage section 12, and when a certain amount is reached, they are transferred to the charge transfer section 13, and the transfer from each section is operated by applying a voltage to the transfer gate electrode. . Note that a plurality of charge transfer units 13 are arranged in a direction perpendicular to the plane of the paper, but only a part of them is shown in the figure. Furthermore, a configuration may be adopted in which a bias electrode for applying a bias is provided instead of the transfer gate electrode.

Fig. 4(b), (C1 is a potential diagram corresponding to the arrangement position in Fig. 4(a), Fig. 4(b) is a potential diagram in a normal state, and Fig. 4(C) is a potential diagram in an operating state. The figure shows.

By the way, when carriers are transferred from the light receiving section 11 to the charge storage section 12, the transfer is from the junction of the photodiode, and there is no problem. However, in order to transfer carriers from the charge storage section 12 to the charge transfer section 13, the potential under the transfer gate electrode PA is not lowered sufficiently. 23
A problem arises in that carriers remain under the surface and are not completely transferred, and moreover, the accumulation part electrode 23, which is provided in large numbers,
There is a drawback that the amount of carrier remaining at the bottom becomes uneven.

That is, although the CCD image sensor is provided with a large number of charge storage sections 12, the depths of the recesses of the potential wells under the electrodes 23 of the large number of charge storage sections vary.
The output becomes uneven, the signal-to-noise ratio deteriorates, and the sensitivity is low.
For example, there is a problem in that the detection ability in dark places is low.

The present invention eliminates such problems and provides a solid-state imaging device that aims to uniformize the depth of the concave portion of the potential well in the charge storage area so that all carriers in the charge storage area are transferred and no carriers remain. This paper proposes a method for manufacturing.

[Means for solving problems]

The purpose of this is to implant impurity ions into the substrate region under the storage electrode formed in the charge storage section, and to change the impurity concentration in the substrate region under the storage electrode to the impurity concentration in the substrate region under the transfer gate electrode on the charge transfer section side. This is achieved by a method for manufacturing a solid-state imaging device that includes a step of increasing the concentration to the same level or to a higher concentration.

[For production]

That is, in the present invention, impurity ions are implanted into the substrate region under the storage electrode of the charge storage section, and the impurity concentration is made equal to or slightly higher than the impurity concentration in the lower region of the transfer gate electrode on the charge transfer section side.

The reason for this is that the transfer gate electrode is formed in the first step, and then the storage electrode is formed in the second step via the insulating film, so during the heat treatment (such as heat treatment for forming the insulating film) in between, , impurities diffuse outward from the substrate region of the storage portion electrode formation portion where the surface is exposed (this is referred to as impurity pile-down). However, since the substrate region under one transfer gate electrode is shielded by the electrode, outward diffusion of impurities is small.

Therefore, the concentration of the substrate region where the storage electrode is formed is lower than that of the substrate region under the transfer gate electrode. In the present invention, impurities are added to the substrate region under the storage electrode, and the concentration is rather higher than that of the substrate region under the transfer gate electrode, so that the depth of the recess of the potential well is made shallow.
This makes it easier to transfer carriers.

〔Example〕

Hereinafter, implementation results will be explained in detail with reference to the drawings.

FIGS. 1A to 1D show cross-sectional views in the order of steps of a method for manufacturing a CCD image sensor according to the present invention.

FIG. 1 (see al; First, a field insulating film 25 is formed on a p-type silicon substrate 10, and an n-type 993
After forming seven layers 22 (this silicon layer 22 may be formed in a later step), transfer gate electrodes PA, PR, and PC are provided via a gate insulating film. This gate electrode is made of conductive polycrystalline silicon and is made of chemical vapor deposition (C
It is deposited using the VD method and patterned using a photo process. Furthermore, as another method, the gate electrode may be formed by a lift-off method.

Refer to FIG. 1(b); Next, after covering the part of the charge storage part other than the part where the storage part electrode is to be formed with a resist film mask 26, boron (B) ions are applied to the part where the storage part electrode is to be formed at a dose of 10.
The injection is performed with an energy output of about 10 ctA and an energy output of several tens of KeV.

FIG. 1 (see C1; next, after thermal oxidation is performed to form an insulating film 27 on the surfaces of the transfer gate electrodes PA, PB, and PC, a second conductive polycrystalline silicon film is deposited by the CVD method, and then photo-coated. Patterning in the process,
Accumulator electrode 23. Transfer electrodes 24 are formed.

Although not shown, since the transfer electrodes are alternately overlapped, there is also an electrode portion that is formed for the first time at the same time as the transfer gate electrode.

See FIG. 1+d); Next, after covering the area other than the light-receiving part with a resist film mask 2B, arsenic (As) or p+ type impurity ions are implanted and heat-treated to form the n+ type silicon layer 21.
Define.

If impurities are added under the storage electrode 23 in this way, the impurity concentration in the substrate region under the transfer gate electrode PA will be 10/cn! (substrate resistance of about 10Ω), whereas the substrate area under the storage electrode of the charge storage section is 10I
ゞ/cfl! It can be formed with a slightly high impurity concentration, and since it is added before forming the storage electrode, there is less evaporation, and the impurity concentration in the substrate region under many storage electrodes can be made uniform. .

FIG. 2 shows a cross-sectional view and a potential diagram of the CCD image sensor according to the present invention, FIG. 2(a) is a cross-sectional view, and FIG. The symbols in the figure are the same as in FIG. 4 above. Second
The potential diagram shown in Figure (b) shows that when the transfer gate electrode PA is operated, all the carriers under the storage electrode 23 are transferred to the transfer electrode without remaining; The substrate region becomes high in impurity concentration, the bottom of the potential well under the storage electrode 23 rises, and during operation, the potential under the transfer gate electrode PA falls below the bottom of the potential well under the storage electrode 23. This is because it will happen.

〔Effect of the invention〕

As is clear from the above description, according to the method for manufacturing a solid-state image sensor according to the present invention, the impurities in the substrate region under the storage electrode are added and made uniform, and the output is made uniform.
This has the effect of improving the ratio and increasing the detection ability in the dark.

[Brief explanation of the drawing]

Figures 1 (a) to (d) are cross-sectional views in the order of steps of the method for manufacturing a CCD image sensor according to the present invention, Figure 2 is a cross-sectional view and potential diagram of the CCD image sensor according to the present invention, and Figure 3 is a line FIG. 4 shows a cross-sectional view of a CCD image sensor and a conventional button length diagram. In the figure, 10 is a p-type silicon substrate, 11 is a light receiving part (photodiode), 12 is a charge storage part, 13 is a charge transfer part, 21 is an n+ type silicon layer, 22 is an n-type silicon layer, 23 is a storage part electrode , 24 is a transfer electrode, 25 is a field insulating film, 27 is an insulating film, 26, 28 are resist film masks, PA, PB, PC are transfer gate electrodes. Afile+;lfr rhyme (2) and non-1 teleseal mFigure 4-1, 0-J

Claims (1)

[Claims] In a charge storage section provided between a light receiving section and a charge transfer section and having transfer gate electrodes or bias electrodes on both sides, impurity ions are implanted into a substrate region under the storage section electrode provided in the charge storage section. , a solid-state imaging device comprising the step of making the impurity concentration of the substrate region under the storage section electrode equal to or higher than the impurity concentration of the substrate region below the transfer gate electrode on the charge transfer section side. Production method.