JP2831752B2 - Solid-state imaging device - Google Patents

Description

Description: Object of the Invention (Field of Industrial Application) The present invention relates to a solid-state imaging device, and in particular, to a solid-state imaging device configured by laminating a photoconductor film on a solid-state imaging device chip. Light shielding layer.

(Prior Art) A solid-state imaging device having a structure in which a photoconductor film is stacked on a solid-state imaging device chip (hereinafter, referred to as a stacked solid-state imaging device).
Has an excellent characteristic of high sensitivity and low smear because the opening area of the photosensitive portion can be increased. For this reason, this solid-state imaging device is promising as a camera for various monitoring televisions and high-definition televisions.
At present, an amorphous material film is used as a photoconductive film for this type of solid-state imaging device. For example,
Se-As-Te film, ZnSe-ZnCdTa, a-Si: H film (hydrogenated amorphous silicon film) and the like. Among these materials, the a-Si: H film is becoming a favorite, especially because of its excellent properties and workability, the possibility of forming at a low temperature, and the like.

The schematic sectional structure of this type of stacked solid-state imaging device is the first
As shown in the drawing, when light is incident on the effective imaging pixel region 21, light having energy equal to or larger than the band gap of the photoconductor film 10 generates an electron-hole pair in the photoconductor film 10. The generated electrons and holes move due to the electric field formed by the pixel electrode 9 and the transparent electrode 11, for example, an n-channel.
When a CCD is used for the substrate, electrons are injected as signal charges into the storage diode 4 via the pixel electrode 9 and the pixel electrode wiring 7, and are stored for a certain period of time, then transferred and read by the signal charge transfer unit.

By the way, in general, in a solid-state imaging device, an actual signal output is obtained based on a difference between a signal output at the time of light incidence and an output at the time of darkness. The structure has a completely blocked pixel region (hereinafter referred to as optical black). The optical black is formed by forming a light shielding metal thin film 12 on the surface of a solid-state imaging device (FIG. 1).

In particular, in the stacked solid-state imaging device, since the light shielding layer 12 for forming the optical black 22 is patterned by etching, the transparent electrode 11 thereunder must be resistant to etching. Therefore, the material of the light shielding layer 12 is necessarily restricted in order to ensure the etching selectivity with respect to the transparent electrode. Generally transparent electrode 11
Often, ITO (Indium Tin Oxide) is used,
In this case, a Mo (molybdenum) film is used as the light shielding layer 12 to secure the etching selectivity described above. FIG. 4 is an enlarged schematic diagram showing the vicinity of the light shielding layer (the portion A in FIG. 4) when the Mo light shielding layer is formed by the sputtering method. In this case, to form the light shielding layer, for example, Ar (argon) gas is introduced as an inert gas, and the chamber pressure is set to 1 Pa, and the film is formed by the DC magnetron sputtering method. As shown in FIG. 4, the columnar Mo portion 12-2 and the Mo-free Mo gap portion 12-3.
Is formed. This Mo gap portion has a width of about 200 to 500 °, and thus a sufficient light-shielding effect may not be obtained.

In addition, the Mo gap portion may be widened in a concave portion such as a gap portion of the pixel electrode instead of the flat portion shown in FIG. The same applies to a light shielding layer other than optical black, for example, for separating light between pixels.

On the other hand, since the Mo film originally has a strong tensile stress, the Mo film may peel off from the substrate. In this case,
The Mo film cannot serve as a light shielding layer.

To date, a method has been reported in which the distance between a Mo target and a substrate during sputtering is extremely short and the tensile stress of Mo is reduced by using the nailing effect of Mo (John A. Thornton, DWHoffmann, J. et al. Vac.Sci.Technol. A
3 (1985) p. 576). However, this method has a disadvantage in that the particles (atoms) of Mo collide with the substrate with large energy, and thus cause fatal damage to the photoconductor film of the stacked solid-state imaging device.

(Problems to be Solved by the Invention) As described above, in the conventional multilayer solid-state imaging device,
There is a problem that the film does not provide a sufficient light-shielding effect, and the Mo film used in the optical black part comes off due to the intrinsic tensile stress of Mo and the low adhesion between the Mo film and ITO. was there.

The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a solid-state imaging device having an optical black that has a large light-shielding effect, eliminates peeling of a film of a light-shielding layer, and obtains an accurate dark output.

[Configuration of the invention]

(Means for Solving the Problems) The first aspect of the present invention is characterized in that molybdenum oxide (MoOx) is used as a light shielding layer in a solid-state imaging device. The second feature is that the content of oxygen contained in the molybdenum oxide film is set to 5 atom (at)% or more.

That is, the present invention provides a solid-state imaging device in which an array of signal charge storage diodes and an array of signal charge readout units are respectively formed on a semiconductor substrate, and a pixel electrode electrically connected to the signal charge storage diode is formed at the top. In a solid-state imaging device including an element chip and a photoconductor film laminated on the chip, a light shielding layer using molybdenum oxide is formed on the photoconductor film.

(Function) According to the present invention, by using an amorphous molybdenum oxide film as a material of the light shielding layer, it is possible to suppress generation of minute gaps in the light shielding layer. In this case, it is possible to obtain an accurate dark output without light leakage due to the minute gap. Further, in the light shielding layer for pixel separation using the molybdenum oxide film, similar to optical black, there is no light leakage due to the minute gap, sufficient pixel separation is possible, and smear caused by light leakage into the silicon substrate is achieved. Can also be reduced.

Further, as described above, a special effect of preventing the light shielding layer from peeling off from the transparent electrode by oxidizing the Mo film can be expected. That is, the oxygen in the molybdenum oxide film reduces the intrinsic tensile stress of Mo (see FIG. 3), and the adhesion between the film and the ITO is improved, so that the film can be prevented from peeling. Further, damage to the photoconductor film can be almost eliminated. Optical black using the light shielding layer does not peel off the film, so that an accurate dark output can be obtained.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1, 2, and 3. FIG.

FIG. 1 is a sectional view showing a schematic structure of a stacked solid-state imaging device according to an embodiment of the present invention. An interline transfer CCD (IT-CCD) is used for a signal charge reading section.

First, ap ⁺ layer (element isolation region) 2, an n ⁺ layer (vertical CCD channel) 3, and an n ⁺⁺ layer (storage diode) 4 are formed on the surface layer of the p-type silicon semiconductor substrate 1. Further, transfer gate electrodes 5-1 and 5-2 of the vertical CCD are formed of, for example, polycrystalline silicon on the substrate 1 via a gate insulating film made of, for example, SiO ₂ . Next, Si which becomes the first insulating layer 6 is formed thereon.
After O ₂ or the like is deposited by the CVD method, a contact hole for electrical connection between the pixel electrode wiring 7 and the storage diode 4 is formed in the insulating layer 6. For example, a polycide wiring is used as the pixel electrode wiring 7. That is, it is a laminated wiring composed of a polycrystalline silicon layer and a molybdenum silicide layer thereon.
After the pixel electrode wiring 7 electrically connected to the storage diode 4 is formed, a second insulating layer 8 made of, for example, a BPSG or PSG film is formed by a CVD method for the purpose of planarizing the surface shape. 8, a pixel contact hole is formed. The second insulating layer 8 may be made of polyimide or SiO ₂ as long as it can be easily planarized.

Next, after a pixel electrode 9 having a thickness of about 1000 to 3000 ° is formed, a photoconductor film 10 having a thickness of, for example, 2
A hydrogenated amorphous silicon film having a thickness of about μm is formed by a plasma CVD method, and ITO, for example, is formed as a transparent electrode 11 having a thickness of about 300 to 500 ° by a sputtering method. As the pixel electrode 9, for example, Ti is used.

Finally, in order to form the optical black 22, a MoOx film to be the light shielding layer 12 is formed by a reactive sputtering method in a mixed atmosphere of an inert gas and an oxidizing gas, and is patterned to form the structure shown in FIG. Is obtained. At this time, the light shielding layer 13 for pixel separation is also formed at the same time. The thickness of the light shielding layer 12 is about 600 to 10,000 °.

Conditions for forming the molybdenum oxide film include, for example,
There are the following conditions: As an oxidizing gas, the pressure in the chamber into which O ₂ was introduced was set to 0.01 Pa, and further, as an inert gas,
After introducing Ar and setting the pressure in the chamber to 1 Pa, M
o When 400 V is applied to the target and DC magnetron sputtering is performed with a sputtering current of 2 A, Mo atoms in the chamber react with O ₂ in the atmosphere, and a molybdenum oxide film is formed on the semiconductor substrate. The oxygen content can be adjusted to any value by appropriately changing the above conditions.

As another method for introducing oxygen during sputtering, there is a method in which oxygen and an inert gas Ar are mixed in advance and then introduced into a chamber. In this method, Ar and oxygen can be mixed well, so that oxygen enters the Mo thin film uniformly. In addition, if sputtering is performed while oxygen is directly blown onto the Mo target, the oxygen concentration near the target is higher than elsewhere, so a molybdenum oxide film with a high oxygen concentration can be made, reducing wasteful consumption of oxygen. I do.

FIG. 2 is an enlarged schematic view of a portion A of the light shielding layer 12 in FIG. According to the present invention, since the light shielding layer 12-1 is amorphous, a minute gap unlike the case of columnar crystal Mo does not occur in the light shielding layer 12-1. Therefore, in the optical black 22, an accurate dark output can be obtained, and if the light shielding layer of the MoOx film is formed on the transparent electrode above the pixel gap, the optical gap 22 is caused by the generation of the minute gap. As a result, pixel separation failure between adjacent pixels (for example, color mixing in a single-chip color device) is prevented, and smear can be reduced because there is no light leakage to the semiconductor substrate 1 for the same reason.

According to the present invention, since oxygen is present in the Mo film,
The Mo lattice expands, causing compressive stress. This realizes a low-stress Mo oxide film by canceling the original tensile stress of Mo. As a result, the Mo film serving as the shielding layer can be prevented from peeling off. Third relation between stress and oxygen content of Mo thin film
Shown in the figure. It can be seen that this effect becomes remarkable when the oxygen content is 5 at% or more.

Although the photoconductor film 10 is made of amorphous silicon and has a large compressive stress, it is easy to peel off from the pixel electrode thereunder, but the molybdenum oxide film 12 formed on the photoconductor film 10
Thanks to, that worry is gone.

Although the SiO ₂ film is used as the gate insulating film described above, it is also possible to use, for example, a Si ₃ N ₄ / SiO ₂ film using a nitride. Although the pixel electrode wiring uses polycide, it is not limited to this, and a material with low light transmission such as metal silicide can be selected.

In the present embodiment, the IT-CCD
However, for example, an XY address type MOS, a line address type CPD, a charge sweeping element CSD, BBD, or any other device capable of reading signals can be applied to the present invention.

Although an a-Si: H film was used as the photoconductor film,
SiC: H, a-SiGe: H, a-SiN: H, a-SiSn: H, and mixtures of these, such as Se-As-Te and ZnSe-ZnCdTe, are effective in the present invention.

Further, in the embodiment, the CCD is described as an N channel, but the present invention can be applied to a P channel CCD.

In addition, various modifications can be made without departing from the scope of the present invention.

〔The invention's effect〕

As described above in detail, according to the present invention, complete light shielding can be performed without forming a minute gap in the light shielding layer, and since there is no peeling of the film, accurate light shielding can be performed. You can get the output. Furthermore, the light-shielding layer for pixel separation has remarkable effects, such as preventing pixel separation failure between adjacent pixels and greatly reducing smear.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a schematic structure of a solid-state imaging and oxidizing apparatus according to an embodiment of the present invention, FIG. 2 is a cross-sectional view showing an enlarged portion A in FIG. 1, and FIG. FIG. 4 is a characteristic diagram showing the relationship between stress and oxygen content, and FIG. 4 is an enlarged sectional view of the same portion as FIG. 2 in the conventional example. 1 ... P-type silicon semiconductor substrate, 2 ... P ⁺ layer (element isolation region), 3 ... n ⁺ layer (vertical CCD channel), 4 ... n ⁺⁺ layer (storage diode), 5-1-5 -2: gate electrode for vertical CCD transfer, 6: first insulating layer, 7: pixel electrode wiring, 8
... A second insulating layer, 9 a pixel electrode, 10 a photoconductor film,
11 ... Transparent electrode, 12,12-1,12-2 ... Light shielding layer, 12-
3 ... minute gap in light shielding layer, 13 ... light shielding layer for pixel separation, 21 ... effective imaging pixel area, 22 ... optical black.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akihiko Furukawa 1 Koko Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside of Toshiba Research Institute (72) Inventor Ryohei Miyakawa 1 Kokko-Toshiba-cho, Kochi-ku, Kawasaki-shi, Kanagawa Prefecture Inside Toshiba Research Institute

Claims (2)

(57) [Claims] 1. A solid-state imaging device in which an array of signal charge storage diodes and an array of signal charge readout units are respectively formed on a semiconductor substrate, and a pixel electrode electrically connected to the signal charge storage diode is formed on an uppermost portion. An element chip,
A solid-state imaging device comprising a photoconductive film laminated on the chip, wherein a molybdenum oxide film is used as a light shielding layer on the photoconductive film. 2. The solid-state imaging device according to claim 1, wherein the molybdenum oxide film has an oxygen content of 5 atomic% or more.