JPH0586669B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a solid-state imaging device used in a two-dimensional image sensor, etc., and particularly relates to an optical black area.

[Technical background of the invention]

Figure 1 shows a conventional interline transfer type image sensor 1 using a charge-coupled device (CCD).
An example of the arrangement of the photosensitive pixel section 2, vertical CCD shift register 3, horizontal CCD shift register 4, and output section 5 is shown. Most of the area on the image sensor 1 is a light receiving area (sensor area) 6, and a very small area is an optical black area (hereinafter referred to as OB area) 7 for generating a black level.
As shown by diagonal lines in the figure, the surface of this OB region 7 is covered with an aluminum film to block light input.

Figure 2 shows the OB in the image sensor 1.
A cross-sectional structure of a part of region 7 and a part of sensor region 6 is shown. That is, 21 is, for example, a p-type silicon substrate, 22 is an n ⁺ layer (corresponding to the photosensitive pixel section 2 in FIG. 1) having a conductivity type opposite to that of the substrate 21 and provided on a part of the surface of the substrate; 23 is an n ⁺ layer (corresponding to the vertical CCD shift register 3 in FIG. 1) provided close to the n ⁺ layer 22 on the surface of the substrate, and 24 is a layer from which charges are removed from the n ⁺ layer 22 for the photosensitive pixel portion. An overflow drain part (excess charge discharge part) for discharging this charge (excess charge) when it overflows, 25 an overflow control gate part, 26 a channel stopper part (element isolation part), 27 on the substrate. 28 is a first layer polycrystalline silicon electrode formed in the SiO ₂ film 27, _and 29 is a second layer polycrystalline silicon electrode formed in the SiO ₂ film 27. Polycrystalline silicon electrode 30 is also the SiO ₂ film 27
A first layer for a light shield is formed on the n ⁺ layer 22 for the photosensitive pixel portion except for a portion corresponding to the upper part.
An aluminum film 31 is a protective insulating film formed on the first aluminum film 30 and the SiO ₂ film 27, and 32 is a protective insulating film formed on the protective insulating film 31 in a portion corresponding to the OB region 7. This is a second layer of aluminum film for a light shield.

In the image sensor 1 described above, signal charges generated when light enters the silicon substrate 21 in the sensor region 6 are transferred to the n ⁺ layer 22 for the photosensitive pixel portion.
is accumulated in At that time, if excess charge occurs,
It passes through the overflow control gate section 25 and is discarded into the overflow drain section 26. The charges accumulated in the n ⁺ layer 22 are transferred to the n ⁺ layer 23 for vertical CCD registers, and then transferred horizontally within the vertical CCD register 3 by a transfer clock pulse.
Transferred in four directions to the CCD register. The charges transferred to the horizontal CCD register 4 are transferred in the horizontal direction, converted into voltage by the output section 5, and read out.

In the image sensor 1, an output component (referred to as a dark output component or dark current) is observed at room temperature even if the light input is completely blocked, and this output component increases as the temperature rises. When such a dark output component becomes large, a problem arises in that the dynamic range of the charge readout section (vertical CCD register 3) becomes small.
Therefore, signal processing is performed to subtract the increase in the dark output component due to temperature rise, and the OB area 7 is provided to detect the increase in the dark output component. There is. Therefore, the OB region 7 has the same structure as the sensor region 6 except for the second layer aluminum film 32.

[Problems with background technology]

By the way, when forming the second layer aluminum film 32 by vapor deposition as described above, nitrogen (N ₂ ) was heated at 450°C, for example, in order to recover the damage to the substrate part.
90% hydrogen ( _H2 ) in an atmosphere of 10% for 15 minutes to 30 minutes.
It is necessary to perform annealing for about 1 minute. In this case, H ₂ plays an important role and restores the damage.

Note that if the above-mentioned annealing is performed before patterning the aluminum film 32, the aluminum film 32 cannot be completely etched, so the above-mentioned annealing is performed after the aluminum film 32 is patterned. Furthermore, there is a difference in annealing effect between the OB region 7 where the aluminum film 32 is present on the surface and the sensor region 6 where the aluminum film is not present on the surface. This is because hydroxide (A(OH) ₃ is formed on the surface of the aluminum film 32, and during annealing, the hydroxide on the surface of the aluminum film 32 becomes A ₂ O ₃ (alumina).
This is because it changes to , and releases H ₂ at the same time.
Therefore, the degree of damage recovery of the substrate portion due to annealing differs between the OB region 7 on the surface of which the aluminum film 32 exists and the sensor region 6, and the dark output component of the OB region 7 and the dark output component of the sensor region 6 differ. There will be a difference between the time component and the time component. This poses a problem in canceling out the variation in the dark output component as described above.

Further, inside the SiO ₂ film 27, there are parts where the two layers of polycrystalline silicon electrodes 28 and 29 are present and parts where they are not, and the surface of the SiO ₂ film 27 has irregularities. In the OB region 7, the pattern of the first layer aluminum film 30 on the SiO ₂ film 27 is formed in the concave part (for the photosensitive pixel part) on the surface of the SiO ₂ film 27.
(corresponding to the upper part of the n ⁺ layer 22), but is formed on the remaining convex portions. After this,
When the protective insulating film 31 is formed, a step difference of about several μm occurs in the concave portion on its surface. Therefore, when forming the second layer of aluminum film 32 by vapor deposition on the surface of the protective insulating film 31 and etching off the aluminum film on the surface of the sensor region 6,
It becomes difficult to completely etch off the aluminum film on the bottom surface of the concave portion (corresponding to the upper part of the photosensitive pixel portion) on the surface of the protective insulating film 31. If the recesses are not completely etched off and the aluminum film 32' remains, it will cause a serious problem in terms of the photosensitive characteristics of the image sensor 1.
In particular, as the pixel size becomes smaller, the above problem becomes more noticeable.

[Purpose of the invention]

The present invention was made in view of the above circumstances, and
There is no difference in the dark output component between the sensor area and the OB area, and the variations due to temperature in the dark output component in both areas are equal, and the variation in the dark output component due to temperature fluctuations in the sensor area is reduced. The object of the present invention is to provide a solid-state imaging device that enables accurate compensation for the amount of light and prevents etching-off defects in the sensor region of the light-shielding film for determining the OB region.

[Summary of the invention]

That is, in the solid-state imaging device of the present invention, even at high temperatures during annealing, the light-shielding film for determining the OB region is formed in the insulating film on the semiconductor surface by a chemical reaction.
The device is characterized by being provided with a high melting point metal silicide film made of a substance that does not emit H ₂ .

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

Image sensor 1' shown in FIGS. 3 and 4
Compared to the image sensor 1 described above with reference to FIG. 1 and _FIG . For example, 1000 ~
The difference is that a molybdenum silicide (MoSi ₂ ) film 40 with a thickness of about 2000 Å is provided, and the rest is the same, so the same reference numerals will be used and detailed description thereof will be omitted.

In general, in current semiconductor technology, MoSi films are widely used as electrodes for internal wiring, just like polycrystalline silicon, and they have the property of blocking light, and both molybdenum and silicon have hydroxide on their surfaces. Because it does not form, it has the property of not releasing H ₂ through chemical reactions even at high temperatures during annealing.

Therefore, in the image sensor 1' having the above configuration, H ₂ does not diffuse from the MoSi ₂ film 40 to the substrate 21 side during the relatively high temperature treatment in the manufacturing process after the MoSi ₂ film 40 is formed. in this way,
Since the problem of diffusion of H ₂ contained in the second layer aluminum film in the conventional OB region does not occur,
There is no difference between the dark output component of the OB area 7' and the dark output component of the sensor area 6. Then, the variations due to temperature in the dark output component in both regions 7' and 6 become equal, making it possible to accurately compensate for the variation in the dark output component due to temperature fluctuations in the sensor region 6, Image sensor output characteristics are significantly improved under conditions of high ambient temperature.

Furthermore, in the image sensor 1' of the above embodiment, MoSi ₂ is present in the SiO ₂ film 27 in the OB region 7'.
The aluminum film 30 has not yet been formed at the stage of patterning the MoSi ₂ film 40. As a result, the level difference in the concave portion (corresponding to the upper part of the photosensitive pixel portion) on the surface of the SiO ₂ film 27 at the stage of forming the pattern of the MoSi ₂ film 40 is as follows.
This is smaller than the step of the concave portion on the surface of the protective insulating film 31 in the conventional OB region. Therefore, the above
After the MoSi ₂ film 40 is vapor-deposited, the sensor area can be completely etched off.
The MoSi ₂ film does not remain above the photosensitive pixel portion of the sensor region 6, and does not cause defects in the photosensitive characteristics of the image sensor.

Here, the manufacturing process of the interline transfer type CCD image sensor of the above embodiment will be briefly described. First, for example, a p-type silicon substrate 21 is coated with a silicon oxide film (SiO ₂ film) 27 having a thickness of, for example, about 1000 Å by thermal oxidation. Next, a resist pattern is formed on this oxide film by photolithography, and using this as a mask, an n ⁺ layer 22 for photosensitive pixels, an n ⁺ layer 23 for a buried channel, which will become a vertical CCD register, are placed at predetermined positions on the surface of the substrate 21. An n ⁺⁺ layer 24 for an overflow drain portion, an overflow control gate portion 25, and a p ⁺ region 26 for a channel stopper portion are formed. Next, a first layer of polycrystalline silicon electrode 28 is formed at a predetermined position on the oxide film 27, and an interlayer silicon oxide film 27 is further formed on the entire upper surface by CVD (chemical vapor deposition). Next, a second layer of polycrystalline silicon electrode 29 is formed at a predetermined position on this oxide film 27, and an interlayer silicon oxide film 27 is further formed on the entire upper surface by the CVD method. Next, on this oxide film 27
A MoSi ₂ film 40 is deposited, and the MoSi ₂ film outside the OB region is etched off by CDE (chemical dry etching) or the like. At this time, no MoSi ₂ film remains above the photosensitive pixel portion of the sensor region 6. Furthermore, a silicon oxide film 27 is formed on the entire upper surface by CVD. Next, an aluminum film 30 is vapor-deposited on this oxide film 27, a portion corresponding to the upper part of the photosensitive pixel portion is etched off to provide an opening window, and a protective insulating film 31 made of, for example, phosphosilicate glass (PSG) is formed over the entire upper surface. form a membrane, 450
°C, 15 min to 30 min in an atmosphere of 90% _N2 and 10% _H2
Anneal for a minute.

Note that, like a polycrystalline silicon film, the MoSi ₂ film 40 can withstand relatively high temperature processing, so it can be deposited even during the manufacturing process as described above.

In addition, instead of the MoSi ₂ film, it may be made of another material (such as titanium silicide) that satisfies the same required properties, that is, has light blocking properties and does not release H ₂ due to chemical reaction during heat treatment in the solid-state imaging device manufacturing process. A light shielding film may also be used.

〔Effect of the invention〕

As described above, according to the present invention, the sensor area and
Since there is no difference in the dark output component between the OB area and the OB area, it is possible to accurately compensate for the variation in the dark output component due to temperature fluctuations in the sensor area. Defects can be prevented and a solid-state imaging device with good characteristics can be realized.

[Brief explanation of drawings]

Figure 1 is a front view schematically showing the arrangement of each element of a conventional image sensor, and Figure 2 is A--A in Figure 1.
3 is a front view schematically showing the arrangement of elements in an embodiment of the solid-state imaging device according to the present invention, and FIG.
FIG. 3 is a cross-sectional view showing a portion along line A'. 1'... Image sensor, 2... Photosensitive pixel section,
3... Vertical CCD shift register, 6... Sensor area, 7'... Optical black area, 21
...Semiconductor substrate, 22...N ⁺ layer for photosensitive pixel section,
23...N ⁺ layer for vertical CCD register, 24...Overflow drain section, 27...Insulating film, 30
...Aluminum film, 40...MoSi ₂ film.

Claims (1)

[Scope of Claims] 1. A semiconductor substrate, a plurality of photosensitive pixel sections each provided on the surface of the semiconductor substrate and accumulating signal charges generated by incident light; A charge readout section that is provided in close proximity and reads out signal charges from the adjacent photosensitive pixel section; a drain section that discharges excess charge from the photosensitive pixel section; a first light-shielding film formed except for the upper portion, and light input to some of the plurality of light-sensitive pixel parts is blocked by the second light-shielding film to generate a dark output component. In a solid-state imaging device, the remaining photosensitive pixel portions are allocated to a sensor area for light reception, and the remaining photosensitive pixel portions are allocated to a sensor area for light reception.
The light-shielding film is made of high-melting point metal silicide that does not release hydrogen ions even at relatively high temperatures, and the second light-shielding film is made of a high-melting-point metal silicide that does not release hydrogen ions even at relatively high temperatures. A solid-state imaging device, wherein the solid-state imaging device is formed between the first light-shielding film and the semiconductor substrate. 2. The solid-state imaging device according to claim 1, wherein the second light shielding film is made of one of molybdenum silicide and titanium silicide. 3. Claim 1, wherein the second light-shielding film has a thickness of 1000 to 2000 [Å].
The solid-state imaging device described in .