JPH0134509B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a solid-state imaging device, and particularly to a method for manufacturing a solid-state imaging device configured by combining a charge transfer element and a photoelectric conversion film.

[Technical background of the invention and its problems]

Solid-state image sensors have the advantage of being smaller, lighter, and more reliable cameras than conventional image pickup tubes, and of being able to obtain high-quality images with almost no afterimages.

However, solid-state imaging devices are mainly formed on Si wafers, and have the drawback that the usable sensitivity wavelength range is limited to the visible region, and Pn which performs photoelectric conversion
They have disadvantages not found in image pickup tubes, such as the effective photosensitive area of the photodiode and the ineffective photosensitive area that transfers signal charges, making it difficult to obtain sufficient sensitivity and easily producing false signals such as moiré. As a solid-state imaging device that eliminates these drawbacks, a structure has been proposed in which a conventional solid-state imaging device is used as it is as a scanning section, and a photoconductor film provided thereon performs photoelectric conversion. FIG. 1 is a cross-sectional view of one pixel portion of an interline transfer type solid-state image pickup device that combines such a photoconductor film and a charge transfer device. Using a P-type Si substrate 10, n ⁺
Layer 11 ₁ and the polyester layer disposed on it with an insulating film interposed thereon.
The transfer gate electrodes 12 ₁ and 12 ₂ made of Si constitute a buried channel type vertical readout CCD, and
The n ⁺ layer 11 ₂ constitutes a storage diode that stores signal charges. In the storage diode part of the substrate where the CCD and the storage diode are formed, the first oxide film 13 including the thermal oxide film is etched to expose the n ⁺ layer ₁₁₂ and the first electrode 14 made of Al or the like is etched. Form into a predetermined shape. Thereafter, a second oxide film 15 is further laminated and etched to expose a portion of the first electrode 14 to form a second electrode 16 made of Al or the like. At the top of this amorphous Si
A photoconductor film 17 such as (a-Si) is formed by sputtering or glow discharge decomposition method, and a transparent electrode film 1
8 to obtain a solid-state image sensor having a scanning section and a photoelectric conversion section.

Note that a similar structure in which the first and second electrodes 14 and 16 are made of poly-Si and molybdenum, respectively, is described in JP-A-57-32183.

In such a solid-state image sensor, whereas conventionally only the storage diode functioned effectively as one pixel, the second electrode 16 performs effective photoelectric conversion as one pixel, increasing sensitivity. There are advantages to doing so. In this case, originally the photoconductor film 17 may be formed on the first electrode 14, but
With this, the level difference due to unevenness on the substrate surface is 2 to 4 μm.
Because a certain degree of steep steps are formed in the etched area, the photoconductor film becomes discontinuous due to the steps.
Defects may occur in the image, or in extreme cases, sensitivity may not be obtained, resulting in poor image output. To prevent this,
As shown in the figure, a second oxide film 15 and a second electrode 16 are used to eliminate the step difference while forming a photoconductor film 17 on a surface as smooth as possible. However, even with this configuration, the level difference on the substrate surface cannot be completely eliminated and image defects are likely to occur. Furthermore, the manufacturing process is complicated, and there is a high risk of defects due to pattern misalignment.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing a solid-state imaging device that reduces defects in the photoelectric conversion section by introducing a new electrode configuration for connecting the solid-state scanning section and the photoelectric conversion section. shall be.

[Summary of the invention]

The present invention provides a method for manufacturing a solid-state imaging device in which a photoelectric conversion film is laminated via an insulating film on a semiconductor substrate in which a storage diode and a scanning part are formed in an integrated manner. After depositing an insulating film on the substrate and flattening the surface by applying a resist film to the surface, the entire surface is etched by dry etching, which is set to have the same etching rate for the resist film and the insulating film. The surface of the insulating film is planarized by doing this. Then, a contact hole is formed on each storage diode in the flattened insulating film, and a vertical electrode part that will become a part of the lower electrode is buried in this contact hole, and is connected to each vertical electrode part and connected to the rest of the lower electrode. The method is characterized in that a planar electrode portion is formed, then a photoelectric conversion film is formed thereon, and a transparent conductive film that becomes an upper electrode is further formed.

〔Effect of the invention〕

According to the present invention, it is possible to flatten the surface on which the photoelectric conversion film is provided and effectively prevent the occurrence of image defects. Furthermore, the electrode structure and manufacturing process are simpler than conventional ones, and yields can therefore be improved.

[Embodiments of the invention]

FIG. 2 is a sectional view showing one pixel portion of an interline transfer type solid-state image sensor according to an embodiment of the present invention. A P-type Si substrate 20 is used, an n ⁺ layer 21 ₁ is formed thereon, and transfer gate electrodes 22 ₁ and 22 ₂ made of poly-Si are formed on it via a gate oxide film to perform buried channel type vertical readout. The structure is the same as the conventional one in that a CCD is formed and an n ⁺ layer 21 ₂ adjacent to this forms a storage diode. these
The surface of the oxide film 23 on the surface of the substrate on which the CCD and the storage diode are formed is flattened. A contact hole is made on the n ⁺ layer 21 ₂ of this oxide 23,
A vertical electrode portion 24 ₁ is formed by filling this with an electrical material such as metal so that the surface is flat, and a flat electrode portion 24 ₂ is further formed on the oxide film 23 in contact with the vertical electrode portion 24 ₁ . This constitutes a lower electrode 24 corresponding to each pixel. A photoconductor film 25 is laminated thereon, and a transparent conductive film 26 is formed over the entire surface as an upper electrode.

A specific example of the manufacturing process for obtaining this structure will be explained with reference to FIG. 3. Note that parts corresponding to those in FIG. 2 are given the same reference numerals as in FIG. 2. FIG. 3a is formed by the same process as the conventional one. For example, P-type Si
First, n ⁺ layers 21 ₁ and 21 ₂ are formed by diffusion on the electrode 20,
Transfer gate electrodes 22 ₁ and 22 ₂ made of polysilicon are formed thereon via a gate oxide film. This entire surface is covered with a first oxide film 23 ₁ including a thermal oxide film, but there are irregularities. Therefore, next,
As shown in FIG. 2, the second oxide film 23 ₂ is
A resist film 27 is further applied to substantially flatten the surface. Then, the entire surface is etched by reactive ion etching (RIE) under conditions such that the resist film 27 and the second oxide film ₂₃₂ have equal etching rates to obtain the structure shown in FIG. After flattening the surface of the oxide film 23 in this way,
As shown in Figure d, a contact hole is made on the n ⁺ layer 21 ₂ of the storage diode by the RIE method using the resist film 28 as a mask, and a metal film 29 is thinly deposited on the entire surface. This metal film 29 is provided to fill the contact hole with an electrode by electroplating, and is selected from Ni, Cu, Pb, Al, Zn, Ti, Mo, etc. Then, by removing the resist film 28, the metal film 29 is left only inside the contact hole.
As shown in FIG. 2, this contact hole is filled with a vertical electrode portion 24 ₁ by electroplating, and then a flat electrode portion 2 is formed by vapor deposition and patterning of a metal film such as Al.
4 ₂ to form the lower electrode 24.

The electric plating is, for example, nickel plating, and is carried out as follows. First, surface treatment is performed using a double zincate method to improve adhesion.
Next, electroplating is performed using a plating liquid commonly known as a Watto bath.In order to uniformly plate many fine contact holes, the concentration of the Watto bath is diluted to 1/2 of the normal concentration. Stir the liquid thoroughly using a stirring fan. These plating conditions were determined experimentally, and made it possible to uniformly embed nickel into the minute contact holes.

After the lower electrode 24 is formed in this way, as shown in FIG. and complete it.

According to this embodiment, a lower electrode that directly connects the storage diode and the photoconductor film can be formed with a simple structure without having to wrap double electrodes as in the conventional solid-state imaging device shown in FIG. In addition, an improvement in yield can be expected due to the shortening of the process.Furthermore, since the planar electrode portion is formed on the flattened surface, the only unevenness level difference on the surface is the thickness of the planar electrode portion, and there is sufficient thickness for the photoconductor film on the top. Can provide a smooth surface. In the conventional structure, in order to reduce the level difference, for example, the photoconductor film was made thicker than necessary so that the photoconductor film itself also had the role of eliminating the level difference. For this reason, the photoconductor film thickness is, for example, 4 μm, and an electric field is not sufficiently applied to the film, and since light is incident from the transparent conductive film side, signal charges cannot travel sufficiently through the film and disappear. For these reasons, photoelectric sensitivity is often impaired. On the other hand, in this example, the photoconductor film is 2 μm thick.
Or it may be less than this, and high photoelectric sensitivity can be obtained.

According to this embodiment, since there are fewer steps as described above, noise called white scratches and unevenness on the substrate is reduced, and high-quality images can be output.

Furthermore, the process of forming the vertical electrode portion of the storage diode can be performed simultaneously with the process of forming other contact holes in the device chip and the process of wiring the electrodes, and in this respect as well, the process can be shortened.

Next, another manufacturing process for obtaining a structure similar to that of the above embodiment will be explained using FIGS. 4a to 4h. Figure 2,
Portions corresponding to those in FIG. 3 are given the same reference numerals. The steps in FIGS. 4a to 4c are the same as those in FIGS. 3a to 3c. In this embodiment, a planar electrode portion 2 is first placed on the surface of the planarized oxide film 23 as shown in FIG. 4d.
4 Form ₂ first. Thereafter, as shown in FIG. 5E, a contact hole is formed on the n ⁺ layer 21 ₂ by the RIE method using the resist film 30 as a mask. Then, as shown in FIG. 5F, a metal film is deposited sufficiently thickly to form a vertical electrode portion 24 ₁ filling the contact hole. After this, the resist film 30 is peeled off and
The unnecessary metal film is lifted off as shown in FIG. 2, and a photoconductor film 25 and then a transparent conductive film 26 are formed thereon as shown in FIG.

It is clear that this embodiment also provides the same effects as the previous embodiment.

In each of the above embodiments, the second oxide film was layered on the first oxide film to smooth the surface, but the first oxide film may be made sufficiently thick to achieve this level of planarization. In addition, the method for forming the vertical electrode portion is not limited to the above embodiments, and electroless plating method or ion plating method may be used, and if the contact hole is large, it may be filled with solder or CVD. .

In addition, as a method for surface flattening, for example, a PSG film is deposited and heat-treated at about 1100℃ in _N2 gas.
It is also possible to use a method of melting the PSG film.

Furthermore, in the above embodiments, an interline transfer type CCD with an embedded channel type vertical readout CCD was used as the signal charge scanning section, but a MOS type or
The present invention can also be applied to those having a CPD type scanning section. Furthermore, although an example has been described in which an oxide film such as SiO ₂ is used as the insulating film, it is also possible to use a Si ₃ N ₄ film or a composite film thereof. It is clear that in addition to a-Si, Sb ₂ S ₃ , Se-As-Te, CdSe, CdZnTe, etc. can be used as the photoconductive film, and it is also possible to use a film that generates the electromotive force instead of a photoconductive film. It's okay. In addition to Ni and Al, the lower electrode materials include Au, Ag,
Metals such as Pt, Al-Si, In, Sn or poly-Si
It is clear that these can be used in appropriate combinations.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one pixel portion of a conventional solid-state image sensor, FIG. 2 is a cross-sectional view showing one pixel portion of a solid-state image sensor according to an embodiment of the present invention, and FIGS. Figures illustrating process examples, FIGS. 4a to 4h are views showing other manufacturing process examples. 20...P-type Si substrate, 21 ₁ ...n ⁺ layer (embedded channel section), 21 ₂ ...n ⁺ layer (storage diode section), 2
2 ₁ , 22 ₂ ...transfer gate electrode, 23, 23 ₁ , 2
3 ₂ ... Oxide film, 24 ₁ ... Vertical electrode section, 24 ₂ ... Planar electrode section, 24 ... Lower electrode, 25 ... Photoconductor film, 2
6...Transparent conductive film.

Claims (1)

[Claims] 1. A step of forming a plurality of signal charge storage diodes and a scanning section for reading out the signal charges on a semiconductor substrate, and a step of depositing an insulating film on the substrate on which the storage diodes and the scanning section are formed. After applying a resist film on the insulating film to planarize the surface, the entire surface of the insulating film is etched by dry etching under conditions where the etching rate is equal for the resist film and the insulating film. A step of forming a contact hole on each of the storage diodes in the insulating film and embedding a vertical electrode portion that will become a part of a lower electrode in the contact hole; forming a planar electrode portion connected to the vertical electrode portion and serving as the remainder of the lower electrode; forming a photoelectric conversion film over the entire surface of the substrate on which the lower electrode is formed; and forming an upper electrode on the photoelectric conversion film. 1. A method for manufacturing a solid-state imaging device, comprising: a step of forming a transparent conductive film.