JPS60206064A - Manufacture of solid-state image pickup device - Google Patents

Abstract

PURPOSE:To prevent image-picture defect, deterioration in photosensitivity, after images, and the like by making the crystal grain coarse by heat treatment of an electrode on which a photoconductive film is to be formed. CONSTITUTION:An n<+> type vertical CCD2 and a charge accumulated diode 3 are formed in a p type Si substrate 1 by adjacency. Next, a poly Si electrode 4 serving as a transfer gate electrode is formed on the CCD2. Then, an oxide film 5 is so formed as to bury the electrode 4. An electrode 6 is formed on the film 5 and the diode 3. Then, an oxide film 7 is formed flatly over the whole surface. A flat electrode 8 is formed on the film 7 and the top of the electrode 6. Sweep is performed in the direction of an arrow mark by irradiating the electrode 8 with laser beams. Thereby, the crystals of the electrode 8 grow and the crystal grain becomes coarse. An amorphous Si film 9 with a thickness necessary for photoelectric conversion is formed, and a transparent conductive film 10 is formed thereon. This manufacture enables the increase in size of the crystal grain of the electrode 8, resulting in the prevention of the systematic defect formation of the film 9 ascribing to the crystal grain boundary of the electrode 8.

Description

[Detailed description of the invention] A photoconductor and a charge transfer element or a photoconductor and a solid lightweight,
Advantage 6.6: It is possible to create an imaging device with low power consumption, and it is possible to obtain highly reliable images with little change over time.

However, since it is formed on an 8i wafer as a solid-state imaging device, there are problems in that the usable sensitivity wavelength range is limited mainly to visible wavelengths, and there are also problems in that the effective photosensitive area and signal transfer area of the p-n photodiode that performs photoelectric conversion are Image pickup tubes have an ineffective photosensitive area and are prone to reduced sensitivity and false light such as moiré, and are used in conventional solid-state imaging scanning units, as shown in the diagram above.

That is, on the - face of the P-type silicon substrate (1), there are vertical C0D (21 and
Charge storage diodes (3) of the same (n+ type) are formed adjacent to each other. On this vertical C0D (2), a polysilicon electrode (4) which becomes a transfer gate electrode is formed with a first oxide film (
5) is buried. Also charge storage diode (3)
After the first oxide film (5) including the thermal oxide film is etched to expose the charge storage diode (3), a first electrode (6) made of, for example, aluminum is formed in a predetermined shape. ing. Next, a second oxide film (7) is formed so that the entire surface is almost flat, and then this second oxide film (7) is formed so that the entire surface is almost flat.
The oxide film (7) is etched to expose a part of the first electrode (6). Next, the second oxide film (7) and the first electrode (
6), a second electrode (8) is formed in a predetermined shape on a part of the electrode. Next, a photoconductive film (9) made of amorphous silicon or the like is formed on this second electrode (8) by sputtering or a glow discharge method. Next, it is possible to perform effective photoelectric conversion on the light guide (8) as one pixel, and it is also possible to form a photoconductive film (9) on a device that does not use a photoconductive film (9). However, since the surface unevenness level difference due to the thickness of the polysilicon electrode (4) and the first oxide film (5) is about 2 to 4 μm, the photoconductive film (9) becomes discontinuous due to these level differences. Due to changes in the film quality or abnormal growth of the photoconductive film (9), image defects or, in extreme cases, sensitivity may not be obtained, which tends to result in poor image output.

To prevent peeling, a second oxide film (7
) to eliminate the step difference and create this flat second oxide film (7).
A second electrode (8) is formed on the top by vapor deposition or sputtering.
, and further, a photoconductive film (9) is formed on this electrode (8).

However, even in such a configuration, the second electrode (8
) The photoconductive film (9) formed on the photoconductive film (9) has a problem in that it is susceptible to structural defects, leading to image defects, afterimages, and burn-in. As a result of experiments conducted by the inventors, the orange color was clearly caused by structural defects, particularly the presence of crystal grain boundaries, in the second @ pole (6) on which the conductive film (9) is formed.

That is, there are many structural defects in the photoconductive film (9) grown near the grain boundaries on the second electrode (8), such as dangling bonds and SL in the case of an amorphous silicon film.
There are many bonds such as -H2+ (5i-Hl)n, which not only cause deterioration in abundance but also tend to cause afterimages and burn-in.

[Purpose of the invention]

The present invention is not based on the above-mentioned problems and experimental results. [Summary of the Invention] That is, the present invention is based on a charge storage diode formed on one surface of a semiconductor substrate, and a charge storage diode formed on one surface of the semiconductor substrate adjacent to the charge storage diode. - a scanning circuit embedded in the first insulating layer on the surface; a first electrode formed on the uneven surface having a top on the scanning circuit and a bottom on the connection with the charge storage diode; A second insulating film formed leaving a top portion on the first electrode, a second electrode formed on the second insulating film and the first electrode at the top, and a second electrode formed on the second electrode, The second electrode is characterized by having at least a step of heat-treating the second electrode to coarsen the crystal grains, and the second m-pole is planar. An example is explained in detail in FIG. 2. do. In the figure, the same parts as in FIG. 1 indicate the same parts.

That is, first, as shown in Fig. 2 (,), a P-type silicon substrate (1) is
is a vertical c consisting of an n+ type buried channel COD.
CD (21) and the same n-type charge storage diode (3
) are formed adjacent to each other. Then, the vertical COD with (2)
On top is a polysilicon electrode (4) that will serve as the transfer gate electrode.
will be established. Next, a first oxide film (5) including a thermal oxide film is formed so as to bury this polysilicon electrode (4), and then this 11th oxide film (5) is used to cover the portion of the charge storage diode (3). After selectively etching to expose the first oxide film (5) and the exposed portion of the charge storage diode (3), a first electrode (with a constant shape) is formed by vapor deposition or sputtering of an alloy of aluminum and silicon, for example. 6)
form.

Next, as shown in FIG. 2(b), a first electrode (6) is provided and a second oxide film (
7) is formed to have a thickness approximately twice that of the uneven step of the first electrode (6). Next, use a spinner to apply a photoresist film to a second oxide film (thick on the concave parts and thin on the convex parts, and make the surface as flat as possible). The resist film Q21 and the second oxide film are etched under conditions such that the etching rate is the same to obtain a second oxide film (7) in which the resist film a2 is completely removed. It ends at a point having a distance of about 0.5 μm from the top of the electrode (6).

Next, as shown in FIG. 2(d), MO is placed on the second oxide film (7).
Δ corresponding to the pixel is deposited using photolithography.
(Perform patterning of 0, glue the specified part, 4.o (1
: Only 1 remains.

Next, as shown in FIG. 2(,), the second oxide film (7) is etched by RIE using Mo (13) as a mask to expose a part of the first electrode (6).

Next, as shown in FIG. 2(f), after Mo Q3 is removed by CDE, a first conductive film (8), which will become a second electrode, is formed by vapor deposition, sputtering, or a combination of these and plating methods.

Next, electrochemical or mechanical polishing is performed as shown in Figure 2 (g). Furthermore, by using these in combination, the oxide film (111) for pixel separation is polished until it is exposed, and a smooth second electrode (
8) is formed. This smooth second electrode (8) is surrounded by an oxide film α1) for pixel isolation, and a portion of its lower part is in contact with the first electrode (6).

Next, as shown in FIG. 2(h), the shape required for the second electrode (8) or the shape of a slit is irradiated with laser light and swept in the direction of the arrow. By doing this, the temperature distribution at the solid-liquid interface of the second electrode (8), which moves with the laser beam, is high at the periphery of the first electrode (6) and low at the center.
) crystal growth is performed. The second result obtained in this way
The crystal grain size of the electrode was etched using a selective etching solution and observed under a microscope, and the crystal grain size was 1 μm or more, which was clear compared to the crystal grain size (about 0.1 μm) produced by conventional manufacturing methods. Grain coarsening was observed. In addition, in order to obtain coarse crystal grains by the above-mentioned manufacturing method, the laser output,
It is necessary to add some ingenuity to the shape of the light, the sweep speed trap, etc.

Next, annealing was performed to remove thermal distortion caused by laser beam radiation.
When the thick amorphous silicon II (9) is produced using the grosmetically-produced method, the crystal grains of the second electrode (8) on which the amorphous silicon film (9) is formed can be made extremely coarse compared to the conventional production method. As a result, the second electrode (
8) Structural defects in amorphous silicon caused by grain boundaries, such as dangling bonds, 8iH2 and (8t
H2) The formation of defects such as n-bonds can be prevented as much as possible, the uniformity of each pixel is improved, good photoelectric conversion characteristics are obtained, and afterimages, burn-in, etc. are significantly improved.
Good image characteristics can be obtained.

In the embodiment described above, an amorphous silicon film (9
) was deposited to a thickness of 3 μm, but the effect on the formation of structural defects in the amorphous silicon film (9) at the crystal grain boundaries of the substrate becomes larger as the thickness of the amorphous silicon film (9) becomes thinner.
In the case of a film thickness of about 1 μm, the effect was particularly significant.

Furthermore, although aluminum was used as the second w and the pole (8) in the above-mentioned embodiments, it is not limited to this, and conductive metals such as Mo + Ti + Cr are also applicable), and furthermore, Al- By using an alloy with a low eutectic point such as 8i, a coarse grain electrode can be easily obtained. It is also useful to use an amorphous silicon film formed by CVD or sputtering.

In addition, in the above embodiment, laser light was used as a heating method for the second electrode (8), but the same effect can be obtained by using an electron beam, and low melting point metals such as eutectic alloys can also be heated. In this case, heating the entire substrate can have a similar effect.

Furthermore, in the embodiments described above, amorphous silicon was used as the photoconductive film, but the invention is not limited to this, and Sb283, which is used as a photoelectric conversion material for image pickup tubes,
Se-As-Te, CdSe, CdZnT
It is clear that InSb, etc. can also be used.
InSb.

Infrared photovoltaic materials such as Pb Sn Te and Cd Hg He can also be used.

Although an example of an interline transfer type CCD has been shown as the scanning unit, it is not limited to this, and a frame transfer type COD, MO8 type CID, BBD, or a combination thereof may be used. In addition to the oxide film, the insulating film also includes SiN, a film, an oxide film, and SiN4. There is no need to explain that a composite layer of JFA is also suitable.

I can do that.

FIG. 3 is a cross-sectional view showing an embodiment in the order of steps.

IP type Si substrate 2... Vertical CCD 3... Charge storage diode 4 ・ Bo'JSi city 4 pole 5 ・
- First oxide film 6-... First electrode 7... Second oxide film 8 - Second electrode (first conductive film) 9... Photoconductive film 10... Transparent conductive film as third electrode ( second conductive film)
11... Electrode isolation oxide film 12... Resist film 13
... Mo mask agent Patent attorney Inoue-Rikitsutsu, 1 Figure

Claims (1)

[Claims] (1) A charge storage diode formed on one surface of a semiconductor substrate, a scanning circuit embedded in one surface of the semiconductor substrate adjacent to the charge storage diode and a first insulating film on the negative surface of the semiconductor substrate, and this scanning circuit. A first electrode formed on an uneven surface having a top portion thereon and a bottom portion connecting to the charge storage diode, and a second insulating film formed on the first electrode with the top portion remaining. a second electrode formed on the second insulating film and the first electrode on the top;
a photoconductive film formed on the second electrode; a step of photoconducting the photoconductive film to coarsen crystal grains; a step of forming the photoconductive film on the second electrode; 2. The method of manufacturing a solid-state imaging device according to claim 1, wherein the two electrodes are formed in a planar shape.