JPH02109362A - Laminated solid-state image sensing element - Google Patents

Abstract

PURPOSE:To obtain a high-quality photoconductive film and besides to simplify the manufacturing process making a buffer film unnecessary, by making the lower electrodes, which are the picture element electrodes, a specified amorphous silicon photodiode section. CONSTITUTION:This element is provided with a semiconductor substrate 21 in which a signal transfer section is made and a section 30 laminated on this substrate 21 and having an amorphous silicon diode section made from microcrystalline silicon (muC-Si) corresponding to the section of the second layer, metallic electrodes 10, made of Al in the conventional example. This constitution prevents the reaction of these electrodes 30 with a photoconductive film 32 thoroughly, reduces the leakage current when the incident light is cut off, and increases the S/N ratio. Besides, the muC-Si and amorphous Si fit each other very well, and because of this a high-quality film 32 can be obtained. In addition, the manufacturing process can be simplified as the buffer film between the electrodes 30 and the film 33 (a buffer film 11 in the conventional example) is unnecessary.

Description

[Detailed Description of the Invention] [Summary] Regarding a stacked solid-state 1 image element with an improved lower electrode in the amorphous silicon photodiode portion, the lower electrode serving as the pixel electrode in the amorphous silicon photodiode portion A silicon semiconductor substrate that does not react with the amorphous silicon that makes up the conductive film and that does not damage the COD during formation, and a silicon semiconductor substrate in which a signal transfer part is built. The lower electrode, which is laminated thereon and serves as a pixel electrode, is configured to include an amorphous silicon photodiode portion made of microcrystalline silicon.

[Industrial application field]

The present invention relates to a stacked solid-state image sensor in which the lower electrode of an amorphous silicon photodiode portion is improved.

Currently, there is a demand for improved S/N in low illuminance for solid-state image sensors, and the stacked type is no exception.

In order to meet this requirement, the current when the light incidence is turned off must be as small as possible.

[Conventional technology]

FIG. 3 shows a cutaway side view of essential parts for explaining a conventional example.

In the figure, l is a p-type silicon semiconductor substrate, 2 is a MeJI region between p1 type elements, 3 is a storage diode portion, and 4 is a vertical transfer CCD (charge c.

5 is the first layer polycrystalline silicon electrode for driving the COD, 6 is the second layer polycrystalline silicon electrode, and 7 is silicon dioxide (Si0
2), 8 is a first layer metal electrode made of tungsten silicide (WSi), 9 is polyimide or borophosphosilicate glass (borophosphos);
10 is a second layer metal electrode (pixel electrode) made of aluminum (A7), 11 is an i-hydrogenated amorphous silicon carbide (ia-3iC:H) buffer film. , 12 High i type hydrogenated amorphous silicon (ia-5i:H
) photoconductive film, 13 is p-type hydrogenated amorphous silicon carbide (
p-a-3iC:H) buffers 11 and 14 are ITO (
indium-tin-.

xide)i3 bright conductive film is shown, respectively.

This image sensor has the advantage that the light utilization rate is high because the entire light incident surface can be made of a photoconductive film.

[Problem to be solved by the invention]

In the stacked solid-state image sensing device explained with reference to FIG.
Al is used as a material for the second layer metal electrode (pixel electrode) 10 which is the lower electrode of the photodiode portion.

However, A1. is a substance that reacts very easily with silicon, especially amorphous silicon. Therefore, in the image sensor shown in FIG. Although the film 11 is inserted, its thickness can only be about 1,000 (people) at most, so it is not possible to sufficiently suppress the diffusion of A/, and therefore, the incidence of light is turned off. Leakage current also occurs when this happens, making it impossible to obtain a good signal-to-noise ratio.

The most preferable material to deal with these problems is a silicon-based material. In particular, polycrystalline silicon has good compatibility with amorphous silicon, and if the lower electrode is made of polycrystalline silicon, It is known that it is possible to grow a photoconductive film I2 made of high-quality amorphous silicon thereon, and that the leakage current is small when the incidence of light is turned off.

However, in the case of a stacked solid-state image sensor, there is a CCD part 4 below the amorphous silicon photodiode part for transferring charge, and the 'iE electrode/wiring made of Al is used there. ing. Therefore, /l
It is impossible to form polycrystalline silicon that exceeds the melting temperature of .

In the present invention, the lower electrode, which is the pixel electrode in the amorphous silicon photodiode portion, does not react with the amorphous silicon that constitutes the photoconductive film, and moreover, it should be formed so as not to damage the CCD. shall be.

(Means for Solving the Problems) A 41-layer solid-state image sensor according to the present invention includes a silicon semiconductor substrate (for example, a p-type silicon semiconductor substrate 11) in which a signal transfer portion is formed, and a silicon semiconductor substrate (for example, p-type silicon semiconductor substrate 11). A lower electrode (e.g. μC-3i
The T section electrode 20) includes an amorphous silicon photodiode section made of microcrystalline silicon.

[Effect]

By taking the above measures, there is no reaction between the lower electrode and the photoconductive film, the leakage current when the light incidence is turned off is reduced, and the S/N ratio is improved. Also, micro
Crystal silicon and amorphous silicon are very compatible, and therefore a photoconductive film of good quality can be obtained. Furthermore, since there is no need for a buffer film between the lower electrode and the photoconductive film to suppress such reactions, the manufacturing process is simplified.

〔Example〕

FIG. 1 shows a cutaway side view of essential parts for explaining one embodiment of the present invention.

In the figure, 21 is a p-type silicon semiconductor substrate, 22 is a p-type silicon semiconductor substrate, and 22 is a p-type silicon semiconductor substrate.
1 type element isolation region, 23 is a storage diode portion, 24
25 is a first layer polycrystalline silicon electrode for driving the CCD, 26 is a second layer polycrystalline silicon electrode, 27 is a Si02 interlayer insulating film, 28
WS ix first layer metal electrode, 29 polyimide or BPSG flattening film, 30 micro crystal silicon (μC-3i) lower electrode (pixel electrode), 32 1
-a-5i:H photoconductive film, 33 is p-a-5iC:H
The buffer film and 34 each indicate an ITO transparent conductive film.

The difference between this embodiment and the conventional example explained with reference to FIG. This is the point.

Here, μC-3i is a mixture of amorphous silicon and crystalline silicon, and a silicon peak is observed in X-ray diffraction, and it contains hydrogen in the infrared absorption spectrum. Refers to substances that are recognized to exist.

This μC-3i has a temperature range of approximately 200[''C] to 450℃.
A good quality product can be obtained by using a range of about ("C), so even if the growth is performed after forming the CCD part 14 for charge transfer, the heat generated at that time will be transferred to the electrode made of Al.
There is no negative effect on wiring etc.

Next, steps for manufacturing an embodiment of the present invention will be described.

+l) One region 22, a storage diode portion 23, a vertical transfer COD portion 24, etc. are formed on a p-type silicon semiconductor substrate 2 by applying a conventional technique.

(2) Conventional thermal oxidation method, chemical vapor deposition (chemical vapor deposition)
l vapor deposition: CVD)
A first layer polycrystalline silicon electrode 25, a second layer polycrystalline silicon layer 26, and a SiO2 interlayer insulating film 27 are formed by applying a method, photolithography technique, or the like.

(3) By applying ordinary CVD method and photolithography technology, storage diode portion 23 and C00
A first layer metal electrode 28 made of WSiX is formed to connect the signal transfer part made up of the portion 24 and the like. Note that the material for the first layer metal electrode 28 is not limited to WSi or x, and high melting point metal silicides such as molybdenum silicide (MoSi2) or titanium silicide (TiSi2) can be used.

This first metal layer 28 is a p-type silicon semiconductor substrate 2.
Needless to say, it also plays the role of a light shield for the signal transfer portion formed in 1.

(4) A flattening film 29 made of BPSG is formed by applying the CCD method. Note that BPSG may be replaced with polyimide, in which case a spin coating method or the like is applied.

f5) A lower part made of μC-8i having a thickness of, for example, about 1.000 C to 4000 C, preferably 2000 C, is formed by applying conventional plasma CVD and photolithography techniques. electrode 30
form.

To form the μC-5i film, 10 [cc] of monosilane (S r H4), 500 (cc) of hydrogen (H2), and 50 [cc] of phosphine (PH3) were added to a normal plasma CVD apparatus.
i H4 as I [%], and the temperature was 200 ['C) to 450 ('C), preferably 300 [''C), and the pressure was 0.2 [Torr] to 1.9 ( Torr], preferably 1.0 [Torr]
, and was grown at an output of 100 (W). According to these conditions, the growth rate is 70 [people/min], and the specific resistance of the obtained μC-5i film is 5 to 8×1O−3 (Ω·
cm).

(6) By also applying the plasma CVD method,
1-a-5r:H having a thickness of, for example, about 1 [μm]
A photoconductive film 32 and a p-a having a thickness of, for example, about 100 [people] to 3001 [people], preferably 150 [people].
-S i C: H buffer film 33 is formed.

(7) By applying the magnetron sputtering method, the thickness can be reduced, for example, from 1,000 to 2,000 [people].
A transparent conductive film 34 of approximately +500 C is formed.

Figure 2 is a diagram for explaining the characteristics of one embodiment of the present invention shown in Figure 1 in comparison with those of the conventional example, with the horizontal axis representing the applied bias voltage and the vertical axis representing the leakage current density. are taken respectively.

In the figure, the solid line shows the characteristic line of an embodiment of the present invention using μC-3i, and the broken line shows the characteristic line of the conventional example using Ae.

As is clear from the figure, in one embodiment of the present invention, 5 [v
] When applying a reverse bias voltage, the leakage current is about 1.5 orders of magnitude lower.

〔Effect of the invention〕

In the stacked solid-state image sensor according to the present invention, a silicon semiconductor substrate in which a signal transfer portion is built, and a lower electrode layered on the silicon semiconductor substrate and serving as a pixel electrode are made of micro-crystal silicon. and an amorphous silicon photodiode portion.

By employing the above configuration, there is no reaction between the lower electrode and the photoconductive film, the leakage current when the circle incidence is turned off is reduced, and the S/N ratio is improved. Also, micro
Crystal silicon and amorphous silicon are very compatible, and therefore a photoconductive film of good quality can be obtained. Furthermore, since there is no need for a buffer number between the lower electrode and the photoconductive film to suppress such reactions, the manufacturing process is simplified.

[Brief explanation of the drawing]

Fig. 1 is a cutaway side view of essential parts for explaining an embodiment of the present invention, and Fig. 2 is a line diagram for explaining the characteristics of the embodiment of the present invention shown in Fig. 1 in comparison with those of a conventional example. 3 and 3 each show a cutaway side view of a main part for explaining a conventional example. In the figure, 21 is a p-type silicon semiconductor substrate, 22 is a p-type silicon semiconductor substrate, and 22 is a p-type silicon semiconductor substrate.
The + type element bone separation region 23 is a storage diode portion, 24
25 is the first layer polycrystalline silicon electrode for driving the CCD, 26 is the second layer polycrystalline silicon electrode, 27 is the 5i02 interlayer insulating film, and 28 is the WSjX first layer. Metal electrode, 29 is polyimide or B
PSG flattening film, 30 is micro crystal silicon (μC-3i) lower electrode (pixel electrode), 32 is 1-a
-5i:) (Photoconductive film, 33 indicates p-a-3iC: H buffer 1 model, and 34 indicates ITO transparent conductive film. Patent applicant: Fujitsu Ltd. Representative Patent Attorney Shoji Aiya

Claims (1)

[Claims] A silicon semiconductor substrate in which a signal transfer portion is built, and an amorphous silicon photodiode portion laminated on the silicon semiconductor substrate and whose lower electrode, which is a pixel electrode, is made of micro-crystal silicon. A stacked solid-state image sensor comprising: