JPH06350065A - Solid-state image pickup device and its manufacture - Google Patents

Abstract

PURPOSE:To improve a converging factor by a lens array and to raise sensitivity by thinning a polycrystalline silicon film at a part having an influence on the shape of a shading film, concerning to a solid-state image sensing device with a lens array. CONSTITUTION:Only at a wiring part (transfer electrode wires 10A and 15A) where the value of resistance becomes an imprortant factor, a polycrystalline silicon film part is thickened by doubling polycrystalline silicon films, and a part having an influence on the shape of a shading film on a charge transfer part (transfer gate electrodes 8-1A and 8-2A) is thinned by leaving only the second one out of the two layers of the polycrystalline silicon films.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device and a method for manufacturing the same.

[0002]

2. Description of the Related Art In a solid-state image pickup device, photoelectric conversion is performed in a photoelectric conversion unit, and accumulated charges are read out to a charge transfer register unit at regular intervals, which are sequentially transferred to an output unit and converted into an electric signal at the output unit. It is a device for outputting to the outside.

FIG. 6 is a plan view of a conventional two-dimensional CCD type solid-state image pickup device, and FIG. 7A is a sectional view taken along line AA of FIG.
(B) is a BB line sectional view of FIG.

This conventional example will be described along with its manufacturing process.

First, the P-type well layer 2 is selectively formed on the surface of the N-type silicon substrate 1. Next, N of the photoelectric conversion unit
The type diffusion layer 3, the N-type buried channel 4 of the charge transfer portion, the P-type diffusion layer 5 of the charge reading portion, and the channel stopper 6 of the element isolation portion are formed by using the lithography technique and the ion implantation technique, respectively.

Next, the surface of the substrate is thermally oxidized to form a first gate insulating film 7, and a 400 nm thick polycrystalline silicon film is deposited on the first gate insulating film 7 by a low pressure CVD method, which is then subjected to a photolithography technique and a dry etching method. Is applied to form the transfer gate electrode 8-1 and the transfer electrode wiring 15.

Next, the first gate insulating film 7 is removed by etching using the transfer gate electrode 8-1 and the transfer gate electrode wiring 15 as a mask, and new thermal oxidation is performed to form a second gate insulating film 9. After that, the polycrystalline silicon film is again 400
Then, the transfer gate electrode 8-2 and the transfer electrode wiring 10 are formed.

Further, after the interlayer insulating film 11 is formed, contact holes (not shown) are opened on the ends of the transfer electrode wirings 10 and 15, and an aluminum film is vapor-deposited by the sputtering method, and N-type diffusion is performed. Metal film wirings (not shown) for supplying transfer pulses are formed on the light shielding film 12 having the opening 17 and the transfer electrode wirings 10 and 15 on the layer 3 respectively.

Finally, a transparent polymer resin is applied by a spin coating method and is thermally cured to form a planarizing layer 13, and then a photosensitive polymer resin is also applied by a spin coating method. The microlenses 14 are formed by patterning using the same, and softening by heat treatment.

[0010]

In the conventional solid-state image pickup device described above, the light-shielding film 12 completely covers the transfer gate electrode and the transfer electrode wiring in order to reduce smear, which is a phenomenon in which light leaks into the charge transfer portion. Is formed in. Since the corresponding transfer gate electrodes of each pixel column are connected in the row direction by the transfer electrode wiring, the transfer pulse is rounded near the center of the chip away from the metal film wiring supplying the transfer pulse to these transfer electrode wirings. The thickness of the polycrystalline silicon film cannot be made very thin in order to prevent the occurrence of electrical characteristics deterioration. For example, light receiving size 1/2 inch, number of pixels 4
In the solid state image pickup device of about 0,000, the layer resistance of the transfer electrode wiring is 40 Ω / □ to prevent the transfer pulse from becoming blunt.
However, a polycrystalline silicon film having a thickness of about 400 nm is required to realize this.

However, the transfer gate electrode 8-2 is N
Since it projects above the mold diffusion layer 3, even if the thickness is about 400 nm, the covering shape becomes poor at the step portion,
Even if a microlens array is used as shown in the cross-sectional view of the conventional solid-state imaging device shown in FIG. 8, the light cannot be completely focused on the light-shielding opening, and a part of the light refracted by the microlens is partially reflected. Since it is reflected or absorbed by the light shielding film 12, there is a problem that the sensitivity is low.

[0012]

A solid-state image pickup device according to the present invention is a pixel including a photoelectric conversion element array including a plurality of photoelectric conversion elements and a vertical transfer register including a plurality of transfer gate electrodes for each photoelectric conversion element. In a solid-state imaging device having a plurality of columns integrated in parallel and covering a semiconductor chip via an interlayer insulating film and having a light-shielding film having an opening above each photoelectric conversion element, a transfer gate electrode corresponding to each pixel column is provided. The transfer electrode wiring for connecting in the row direction is made of the same material as the transfer gate electrode and is thicker.

According to the method of manufacturing a solid-state image pickup device of the present invention, a gate insulating film is formed in a predetermined region on the surface of a semiconductor substrate, and the gate insulating film is covered with a first conductive film and patterned to form a first conductive film. The step of forming the transfer electrode wiring layer and the step of depositing the second conductive film of the same material as the first conductive film on the entire surface and patterning the second conductive film are laminated on the first transfer electrode wiring layer. A step of forming a second transfer electrode wiring layer that constitutes the transfer electrode wiring and a transfer gate electrode protruding in the column direction from the second transfer electrode wiring layer, and then depositing an interlayer insulating film and opening in a predetermined region And a step of forming a light-shielding film having

[0014]

1 is a plan view showing a CCD type solid-state image pickup device according to an embodiment of the present invention, FIG. 2A is a sectional view taken along the line A--A of FIG. 1, and FIG. It is a BB line sectional view.

A P-type well layer 2 is selectively formed on the surface of the N-type silicon substrate 1. An N-type buried channel 4 is selectively formed on the surface of the P-type well layer 2. N
N-type diffusion layers 3 of the photodiode are arranged in a row in parallel with the buried channel layer 4. Between the N-type diffusion layer 3 and the N-type buried channel 4, a P-type diffusion layer 5 of the charge reading section is provided.
Are formed. Reference numeral 6 is a P ₊ type channel stopper for insulatingly separating the N type diffusion layer 3, the N type buried channel 4 and the like.

One transfer gate electrode 8-1A is provided on the N-type buried channel 4 via the first gate oxide film 7 so as to correspond to each N-type diffusion layer 3, and transfer of each pixel column is performed. The gate electrodes 8-1A are interconnected in the row direction by transfer electrode wirings 15A. The transfer electrode wiring 15A is made of polycrystalline silicon having a thickness of about 400 nm, and the transfer gate electrode 8-
1A is composed of a polycrystalline silicon film having a thickness of about 150 nm. Similarly, on the N-type buried channel 4, there is also a second
The transfer gate electrode 8-2A (a polycrystalline silicon film having a thickness of about 150 nm) is formed on each N-type diffusion layer 3 through the gate oxide film 9 of
One transfer gate electrode 8-2A of each pixel column is formed corresponding to the transfer electrode wiring 10A (thickness of about 400) in the row direction.
nm polycrystalline silicon film). The difference from the conventional example shown in FIG. 6 is that the transfer electrode wiring is thicker than the transfer gate electrode.

Next, the manufacturing method of this embodiment will be described.

First, as shown in FIG. 3A, the P-type well layer 2 is selectively formed on the surface of the N-type silicon substrate 1. Subsequently, as shown in FIG. 3B, the N-type diffusion layer of the photoelectric conversion unit (3 in FIG. 2B), the N-type buried channel 4 of the charge transfer unit, and the P-type diffusion layer of the charge reading unit ( 2) of FIG. 2B and a channel stopper (6 of FIG. 2B) for element isolation are formed.

Next, the surface of the substrate is thermally oxidized to form a first gate oxide film 7 as shown in FIG. 3C, and a polycrystalline silicon film of 250 nm is formed on the first gate oxide film 7 by a low pressure CVD method.
The first transfer electrode wiring layer 15a is formed by depositing and applying the photolithography technique and the wet etching method to form the transfer electrode wiring that connects the transfer gate electrodes 8-1A in the row direction.

Subsequently, by the low pressure CVD method, as shown in FIG.
As shown in FIG.
accumulate. By applying a photolithography technique and a dry etching method to this, as shown in FIG.
The second transfer electrode wiring layer 15b covering the transfer electrode wiring layer 15a and the transfer gate electrode 8-1A protruding in a rectangular shape in the column direction are formed. Next, as shown in FIG. 4B, the first gate oxide film 7 is removed by etching using the transfer electrode wiring 15A having a two-layer film structure and the transfer gate electrode 8-1A as a mask, and new thermal oxidation is performed. After the second gate oxide film 9 is formed by the above, the first polycrystalline silicon electrode (15
A, 8-1A) is formed in the same two steps as in the photoelectric conversion section (3) to the charge transfer section (4).
A second polycrystalline silicon electrode (transfer gate electrode 8-2A and transfer electrode wiring 10A) for reading and transferring signal charges to and from is formed.

Further, as shown in FIG. 2, the interlayer insulating film 1
1 is formed, a contact hole (not shown) is opened on the end portions of the transfer electrode wirings 10A and 15A, and an aluminum film or the like is deposited to a thickness of 350 nm by a sputtering method, followed by photolithography and dry etching. By applying it, metal film wirings (not shown) for supplying transfer pulses are formed to the light shielding film 12 and the transfer electrode wirings 10A and 15A, respectively.

Finally, a transparent polymer resin is applied by a spin coating method and thermally cured to form a flattening layer 13, and a photosensitive polymer resin is also applied by a spin coating method, and a photolithography technique is used. Patterning and heat treatment to soften the micro lens 14
By forming the, the solid-state imaging device of the present invention is obtained.

Even if the transfer electrode wirings 10A and 15A are thickened to prevent the transfer pulse from being blunted, the thickness of the transfer gate electrode 8-2A protruding onto the N-type diffusion layer 3 can be reduced, so that the light shielding film 12 is formed. The step difference in the vicinity of the opening 17 becomes small, and as shown in FIG. 5, it is possible to prevent the light focused by the microlens 14 from hitting the end portion of the light shielding film 12 and being reflected. That is, the converging angle θ ₁ can be made larger than θ ₂ in the conventional example.

[0024]

As described above, according to the present invention, since the thickness of the transfer gate electrode can be made smaller than that of the transfer electrode wiring, it is possible to prevent the transfer pulse from blunting and increase the amount of light collected. This has the effect of further improving the sensitivity of the solid-state imaging device.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention.

2 is a sectional view taken along the line AA of FIG. 1 (FIG. 2A) and B.
It is a B-line sectional view (FIG.2 (b)).

FIG. 3 (a) for explaining the manufacturing method of the above-described embodiment.
5A to 5D are process sectional views divided into FIGS.

4A to 4C are cross-sectional views in order of the processes, illustrated in FIGS. 4A and 4B for explaining the process subsequent to the process corresponding to FIG.

FIG. 5 is a schematic diagram for explaining the improvement of the amount of collected light according to the above-described embodiment.

FIG. 6 is a plan view showing a conventional example.

7 is a sectional view taken along line AA of FIG. 6 (FIG. 7A) and B.
FIG. 9 is a cross-sectional view taken along line B (FIG. 7B).

FIG. 8 is a schematic diagram for explaining problems of the conventional example.

[Explanation of symbols]

1 N-type silicon substrate 2 P-type well layer 3 N-type diffusion layer 4 N-type buried channel 5 P-type diffusion layer 6 Channel stopper 7 First gate oxide film 8-1, 8-1A First polycrystalline silicon electrode (Transfer gate electrode) 8-2, 8-2A Second polycrystalline silicon electrode (transfer gate electrode) 9 Second gate oxide film 10, 10A Transfer electrode wiring 11 Interlayer insulating film 12 Light shielding film 13 Flattening layer 14 Micro Lens 15, 15A Transfer electrode wiring 16 Polycrystalline silicon film 17 Opening

Claims (2)

[Claims] 1. A semiconductor chip having a plurality of photoelectric conversion element rows formed of a plurality of photoelectric conversion elements and a pixel row formed of a vertical transfer register provided with a plurality of transfer gate electrodes for each photoelectric conversion element arranged in parallel and integrated. In a solid-state imaging device having a light-shielding film that is covered with an insulating film and has an opening above each photoelectric conversion element, transfer electrode wirings that connect corresponding transfer gate electrodes of each pixel column in a row direction are transferred. A solid-state imaging device, which is made of the same material as the gate electrode and is thicker. 2. A step of forming a gate insulating film in a predetermined region of a surface of a semiconductor substrate, covering the gate insulating film with a first conductive film, and patterning to form a first transfer electrode wiring layer, By depositing and patterning a second conductive film of the same material as the first conductive film on the entire surface, the first conductive film is formed.
Forming the second transfer electrode wiring layer and the transfer gate electrode which are stacked on the transfer electrode wiring layer to form the transfer electrode wiring together and the transfer gate electrode projecting in the column direction from the second transfer electrode wiring layer; A step of depositing an insulating film and forming a light-shielding film having an opening in a predetermined region.