JPH03246971A - Charge-coupled device and solid-state image sensing device using same - Google Patents

Abstract

PURPOSE:To enhance reliability by a method wherein a gap-potential control electrode is formed so as to cover a gap between transfer electrodes and a transfer channel potential at the gap part is set between an H-level potential and an L-level potential of transfer channels under the transfer electrodes. CONSTITUTION:A prescribed control potential is impressed on a gap control electrode 6; a prescribed clock voltage is applied to a transfer electrode 4. That is to say, the part under a transfer electrode 43 is set to the H-level phiH by a clock control operation; the part under a transfer electrode 42 is shifted to the L-level phiL. Thereby, signal charges under the electrode 42 are transferred to a potential well under the electrode 43 as shown by shaded lines in the figure. On the other hand, since gaps 7 are small, a gap potential is influenced by potentials of the transfer electrodes at the front and the rear. A gap potential phiG2 at the front in the transfer direction becomes high as compared with a gap potential phiG1 at the rear. In other words, potential barriers of the gap part at the front in the transfer direction become lower than those at the rear. By a change in the potential in the gap parts, the signal charges can be transferred without residues.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Field of Industrial Application) The present invention relates to a charge-coupled device (CCD) and a solid-state imaging device using the same.

(Prior Art) Recently, the increase in the number of pixels in CCD imaging devices has been remarkable. A two-dimensional CCD imaging device is usually composed of a photodiode array that stores signal charges through photoelectric conversion, and a vertical CCD and a horizontal CCD that read out the signal charges of the photodiode array. The CCD in these CCD imaging devices usually uses two layers of transfer electrodes that overlap each other with an interlayer insulating film interposed therebetween. However, with the recent increase in the number of pixels and miniaturization of each part of the CCD, a problem has arisen in that short-circuit accidents between the first layer transfer electrode and the second layer transfer electrode often occur.

The reason for this is that the transfer electrode is usually formed of a polycrystalline silicon film, and the interlayer insulating film is an oxide film obtained by thermally oxidizing this transfer electrode, so the quality is not very good, and the thickness of the interlayer insulating film also scales. This means that it gradually becomes thinner, etc.

On the other hand, some CCD imaging devices are constructed using only vertical CCDs and horizontal CCDs without forming a photodiode array. In this case, the vertical CCD section is used as a photoelectric conversion section and a transfer section. In this method,
The incident optical image is transmitted through a transfer electrode made of a polycrystalline silicon film and generates signal charges on the substrate surface. However, in this method, the transfer electrode made of a polycrystalline silicon film transmits almost all red visible light, but attenuates other light. In particular, almost no blue light passes through. Therefore, it is difficult to apply this method as is to color cameras. To solve this problem, it is conceivable to use a transparent electrode such as ITO for the transfer electrode. However, when trying to realize a transfer electrode with an overlap structure using a transparent conductive film such as ITO, there is no suitable interlayer insulating film, making it impossible to obtain a highly reliable transfer electrode.

(Problem to be solved by the invention) As described above, in CCD imaging devices having a conventional two-layer transfer electrode structure, short-circuit accidents between the first layer transfer electrode and the second layer transfer electrode occur due to miniaturization. There was a problem with reliability. Further, when attempting to use a transparent conductive film for a transfer electrode, there was a problem in that it was difficult to form a two-layer structure transfer electrode because there was no suitable interlayer insulating film.

The present invention has been made in view of the above points, and is a CCD and CCD that eliminates short-circuit accidents between transfer electrodes and improves reliability.
The object of the present invention is to provide a CD imaging device.

[Structure of the Invention (Means for Solving the Problems)] A CCD according to the present invention includes a semiconductor substrate in which a charge transfer channel is formed, and a first insulating film formed on the charge transfer channel region of this substrate. array formed. A plurality of transfer electrodes obtained by patterning a single-layer conductive film were formed with a second insulating film interposed so as to cover at least the gap between the transfer electrodes on the surface where these transfer electrodes were formed.

The device is characterized in that it includes a gap potential control electrode for setting the transfer channel potential of the gap portion between the “H°” level potential and the “L” level potential of the transfer channel below the transfer electrode.

(Function) According to the present invention, since the transfer electrodes are formed by patterning a single-layer conductor film, even if the transfer electrodes are miniaturized, short circuit accidents between the electrodes due to the overlap of the transfer electrodes will occur as in the past. is effectively prevented. This single-layer transfer electrode structure was used in early CCDs before the development of double-layer polycrystalline silicon technology. However, when the transfer electrodes are formed using a single-layer conductor film in this way, potential barriers and potential pockets are formed in the gaps between the transfer electrodes in the transfer channel, and if left as is, electric charges due to signal charges left behind, etc. This results in a decrease in transfer efficiency. In this regard, in the present invention, the potential of the gap between the transfer electrodes is controlled by a control electrode disposed on the transfer electrodes, thereby preventing the charge transfer efficiency from decreasing.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the main structure of a CCD according to an embodiment. A buried channel is formed on the surface of a p-type silicon substrate 1 (the entire p-type substrate may be a p-type substrate, or an n-type silicon substrate with a p-type well formed therein. The same applies to the following embodiments). A type charge transfer channel 2 is formed, and a plurality of transfer electrodes 4 (41, 4□, . . . ) are formed in an array on the charge transfer channel 2 with a gate insulating film 3 interposed therebetween. The transfer electrode 4 is made by depositing a polycrystalline silicon film by CVD method,
This is a single layer electrode arranged with minute gaps 7 obtained by patterning this. An interlayer insulating film 5 is further formed by CVD on the surface on which the transfer electrode 4 is formed, and a gap control electrode 6 is formed thereon.

FIG. 2 shows the state of charge transfer in the CCD of this embodiment.

A predetermined control potential is applied to the gap control electrode 6, and in this state, a predetermined clock voltage is applied to the transfer electrode 4. Actual transfer lock systems include two-phase clock, three-phase clock, four-phase clock, and even single-phase clock, but any of these methods does not matter in this case. Figure 2 (a
), the signal charge under the transfer electrode 42 is transferred to the next transfer electrode 4.
It shows the potential distribution of the transfer channel in the case of downward transfer. That is, by clock control, the lower part of the transfer electrode 43 becomes "H" level φ, and the lower part of the transfer electrode 4□ becomes "H" level φ.
By shifting to the L'' level φ1., the signal charge that was under the transfer electrode 42 is transferred to the potential well under the transfer electrode 4. as shown by diagonal lines in the figure.

Here, the channel potential under the gap 7 has an important meaning. The channel potential of the gap 7 portion is controlled by the gap control electrode 6 as described above, but basically this gap potential φco is the difference between the “H′” level potential φ8 and the “L# level potential φ” of the transfer channel. On the other hand, since gap 7 is small,
The gap potential is influenced by the potentials of the front and rear transfer electrodes (so-called two-dimensional effect). As a result, when focusing on the gaps on both sides of the transfer electrode 4□ from which signal charges are swept out in FIG. 2(a), the gap potential φo2 at the front in the transfer direction becomes higher than the gear potential φold at the rear. In other words,
The potential barrier at the front gap in the transfer direction is lower than that at the rear. Due to such a potential change in the gap portion, all signal charges are transferred without being left behind.

For reference, FIG. 2(b) shows the state of charge transfer when the potential of the gap 7 is not controlled, corresponding to FIG. 2(a). In this case, as shown in the figure, the gap 7 has a deep potential pocket 8 above the "H" level potential.
is formed, and some signal charges are left behind in the transfer. In particular, when the gap 7 is large, for example, greater than the film thickness of the transfer electrode 4, the two-dimensional effect described above is reduced, and the potential pocket 8 is maintained at a constant deep state regardless of the potential of the transfer electrode 4. In this state, unless the gap potential is controlled, the transfer efficiency will be significantly reduced.

Next, an embodiment in which the present invention is more specifically applied to a CCD imaging device will be described.

FIG. 3 is a schematic plan view showing an embodiment of an interline transfer type CCD imaging device. Figure 4 (a) (b) (c
) are a plan view and a sectional view showing the main structure. On a p-type silicon substrate 11, photodiodes 12 formed of an n-type diffusion layer that perform photoelectric conversion and storage are arranged in a two-dimensional array. Alongside this photodiode array, a plurality of vertical transfer CCDs for reading signal charges from each photodiode 12 are formed. 13 or more vertical transfer CCD
n-type buried channel. A horizontal transfer CCD is provided for reading signal charges transferred from the vertical transfer CCD one horizontal column at a time.

14 is an n-type buried channel of the horizontal transfer CCD. A transfer gate 22 is formed between the vertical CCD and the horizontal CCD. On the vertical transfer CCD channel 13, transfer electrodes 15, which are formed by patterning a single-layer polycrystalline silicon film with a gate insulating film 16 in between, are arranged with a minute gap 24 as shown in FIG. Horizontal transfer C
Transfer electrodes 16 are also formed on the OD channel 14 by patterning a single layer polycrystalline silicon film. A p'' type layer 17 serving as a channel stop is formed on the photodiode 12 side of the vertical CCD channel 13. An interlayer insulating film 1 is further formed on the surface where the elements are formed in this way.
Gap control electrodes 19, 20, and 21 are formed of an Al film through the electrodes 8. These control electrodes 19.20.2
1 also serves as a tip shield film. Therefore the vertical CCD
The gap control electrode 19 in the section needs to be formed with a window at least in the photodiode 12 section, and for example, in the example shown in FIG. They form an array. The gap control electrode 20 of the horizontal CCD section is approximately horizontal CC
It completely covers area D.

Control potential V applied to the gap control electrode 19 of the vertical CCD section. 1 and the control potential VG2 applied to the gap control electrode 20 of the horizontal CCD section are set to different values in this embodiment. Specifically, vG2 is set higher than VGI. This is because the clock pulse voltages are different between the vertical CCD and the horizontal CCD. That is, the so-called field shift gate that reads out the signal charge of the photodiode 12 to the vertical CCD channel 13 is common to the transfer gate of the vertical CCD in this embodiment, as is usually done (see FIG. 4). b)).

Therefore, in order to apply a positive voltage to the field shift gate and transfer the signal charge read from the photodiode 12 to the vertical CCD channel 13 without causing it to flow back to the photodiode 12 side, the vertical CCD transfer electrode 15 has, for example, Negative clock pulses varying from -8V to Ov are used. On the other hand, in a horizontal CCD,
Positive clock pulses varying from Ov to 5v are used. On the other hand, the channel potential of the gap portion formed by the gap control electrode needs to be determined in relation to the pulse voltage applied to the transfer electrode, as explained above with reference to FIG. Then, in order to set the gap potential in the vertical CCD and the horizontal CCD to a preferable value between the H" level potential and the "L level potential of the transfer channel as explained in FIG. 2, VGI must be V. It has to be lower than 2.

The operation of the interline transfer CCD imaging device of this embodiment is the same as that of conventionally known devices.

In other words, the signal charge of the photodiode array is read out to the vertical CCD during the vertical blanking period of imaging, and the next field is imaged while being output by the vertical CCD transfer and the horizontal CCD transfer one horizontal column at a time. repeat. In this example, vertical CCD, horizontal CCD
Both CDs are four-phase driven. The specific state of signal charge transfer in these vertical CCDs and horizontal CCDs is explained in Part 5.
This will be explained using Figures (a) and (b).

FIG. 5(a) shows a four-phase clock waveform. Figure 5 (b
) at each time 1.) of the clock waveform. The channel potential distribution under the transfer electrode at −1° is shown.

As shown in the figure, signal charges are transferred along the transfer channel by sequentially repeating "L" and "H" of the clocks φ and φ4 while partially overlapping. As described in the previous embodiment, the barrier or potential pocket that prevents the transfer of signal charges is formed in the transfer channel by the function of the gap control electrode, and the signal charges are transferred without leaving anything behind.

FIGS. 6(a) to 6(g) are cross-sectional views showing specific manufacturing steps for the vertical CCD section. p-type silicon substrate 1
After forming an element isolation region 1, a gate oxide film 23 is formed by thermal oxidation (a)), and then an n-type buried transfer channel 13 is formed by ion implantation of phosphorus ((a)).
b)). Thereafter, a polycrystalline silicon film is deposited by the CVD method (c)), a photoresist 31 is patterned, and the polycrystalline silicon film is selectively etched using the photoresist 31 as a mask, thereby separating the plurality of transfer electrodes 15. Forming Be)). Thereafter, the photoresist 31 is peeled off and an interlayer insulating film 18 is deposited by CVD (f)), and metal films such as A and Q are formed thereon and patterned to form the gap control electrode 19 (g).
).

The manufacturing process for the horizontal CCD section is also similar. As is clear from FIG. 3, the entire CCD imaging device requires only one layer of polycrystalline silicon film, and the manufacturing process is simple.

FIGS. 7(a) to 7(e) show another example of the manufacturing process of the vertical CCD section. After forming a gate oxide film 23 on a p-type silicon substrate 11 and forming an n-type buried channel 13 by ion implantation, a polycrystalline silicon film is deposited by CVD (
(a)). The process up to this point is the same as the previous embodiment. Thereafter, a photoresist pattern 32 is formed, and the polycrystalline silicon film is selectively etched using this pattern to form a transfer electrode 151.
((b)). At this stage, the number of transfer electrodes 15 is not all, but every other one. Therefore, the gap between the transfer electrodes 151 is one transfer electrode. After that, an oxide film 33 is formed on the surface of the transfer electrode 151 (C))
Then, a second layer of polycrystalline silicon film is formed using the CVD method.
It is deposited so that the surface is almost flat ((d)). Then, etching is performed on the entire surface of the polycrystalline silicon film to form a transfer electrode 152 embedded in the gap between the previously formed transfer electrodes 15 ((e)).

This method uses a two-layer polycrystalline silicon film or
Unlike the conventional method, the first and second layers are not selectively etched to form a transfer electrode with an overlapping structure. That is, the second layer is etched over the entire surface to form a transfer electrode 15□ in a self-aligned state between the transfer electrodes 15, and as a result, a single layer of polycrystalline silicon film is patterned as in the previous embodiment. It is possible to obtain transfer electrodes arranged with minute gaps in the same way as in the case where the transfer electrodes are formed.

Incidentally, in the present invention, the transfer channel potential in the gap between the transfer electrodes is influenced by the size of the gap and the thickness of the transfer electrode. From this point of view, there are several aspects to the structure of this part.

FIG. 8 shows a case where the gap 24 between the transfer electrodes 15 is relatively large. In this case, the influence of the transfer electrode 15, that is, the two-dimensional effect, on the transfer channel potential at the gap portion is small.

Therefore, in order to control the gap potential, it is preferable that the bottom surface A of the gap 24 of the gap potential control electrode 19 be located below the top surface B of the transfer electrode 14, as shown in the figure.

Conversely, FIG. 9 shows a case where the gap 24 between the transfer electrodes 15 is small. In this case, the potential of the gap part is the transfer electrode 1
5, the gap potential control electrode 1
The bottom surface A of the transfer electrode 9 may be located above the top surface of the transfer electrode 15. As microfabrication technology advances, the gap 24 becomes, for example, 0.5.
When the value is very small, such as .mu.m or less, no special gap potential control is required, and sufficient charge transfer efficiency can be obtained without the formation of potential pockets.

FIG. 10 shows a case where the transfer electrode 15 is processed into a tapered shape. In this case, the gap determined by the bottom surface of the transfer electrode 15 is small, but the bottom surface A of the gap potential control electrode 19
can be positioned below the upper surface B of the transfer electrode 15.

In the embodiment of the CCD imaging device, both the vertical CCD and the horizontal CCD have a structure in which the gap potential control electrode is provided with a single layer transfer electrode, but the present invention is also effective even if the conventional structure is applied to either one.

Next, an embodiment in which the present invention is applied to a CCD using a transparent transfer electrode will be described.

FIG. 11 shows the CCD cross-sectional structure of the main part.

Portions corresponding to those in FIG. 1 are designated by the same reference numerals as in FIG. 1, and detailed description thereof will be omitted. In this embodiment, the transfer electrode 9 is formed by patterning a single layer transparent conductive film such as ITO. CVD is applied to the substrate surface on which the transfer electrode 9 is formed.
It is covered with an insulating film 5, on which a gap control electrode 6 is patterned. The gap control electrode 6 is patterned to cover only the gap 7 between the transfer electrodes 9. This is because it is assumed that each transfer electrode 9 portion is used as it is as a photoelectric conversion section having blue sensitivity.

FIG. 12 is a schematic plan view of a frame transfer type CCD imaging device using the structure shown in FIG. 11. Multiple vertical CCs
A D channel 41 and a horizontal CCD channel 42 are formed as shown by broken lines, and a vertical CCD transfer electrode 43 and a horizontal CCD transfer electrode 44 are formed on these channels by patterning a single layer of transparent conductive film such as ITO. Vertical C
In the gap part of the transfer electrode 43 of the CD and the gap part of the transfer electrode 44 of the horizontal CCD, only the lead part is shown for simplification in the figure, but as shown in FIG. 45 and 46 are provided. In reality, the upper half of the vertical CCD is used as a light receiving section 47 that performs photoelectric conversion, and the lower half serves as an accumulation section 48 that accumulates signal charges corresponding to one frame of photoelectric conversion. Therefore, the only transfer electrode that needs to be transparent is the light receiving part 47, and the remaining transfer electrodes may be formed of, for example, a polycrystalline silicon film.

However, in this embodiment, all the transfer electrodes are transparent electrodes as described above.

For this reason, although not shown in the figure, it is necessary to cover the CCD section other than the light receiving section 47 with a light shielding film. Further, in the embodiment, a case of two-phase drive is shown. Therefore, in reality, it is necessary to give asymmetry to the potential wells under each transfer electrode, and although detailed explanation will be omitted, for example, ion implantation may be performed partially under each transfer electrode to separate the storage part and the barrier part. Form.

In this embodiment as well, the transfer electrode has a single-layer electrode structure and a gap control electrode is provided, thereby solving the problem of reduced reliability when using an overlap electrode structure and achieving high transfer. C that provides efficiency
You can get a CD. In addition, in the case of transparent electrodes, there is no good interlayer insulating film, so it is difficult to construct a CCD imaging device with blue sensitivity using an overlapping electrode structure. is obtained.

The present invention is not limited to the above embodiments.

For example, in the embodiment of the CCD imaging device, a case is shown in which only one horizontal CCD is provided, but the present invention can be similarly applied to a structure in which a plurality of horizontal CCDs are provided. In addition, although an n-type buried channel was explained in the embodiment, the present invention can also be applied to a surface channel type, and furthermore, a p-channel type C
It can also be applied to CDs. Furthermore, it goes without saying that the CCD structure of the present invention can be used not only in imaging devices but also in various applications such as shift registers, memories, delay elements, and the like.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain a CCD and a CCD imaging device with improved reliability as a single layer transfer electrode structure without causing a decrease in charge transfer efficiency. .

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the basic structure of a CCD according to an embodiment of the present invention, FIGS. 2(a) and 2(b) are diagrams for explaining the charge transfer operation, and FIG. 4(a), 4(b), and 4(c) are plan views showing the main structure of FIG. 3, and their x-x' and y-y' Cross-sectional view, Figure 5 (
a) (b) is a diagram for explaining the operation of the CCD imaging device in FIG. 3; FIGS. 6(a) to (g) are sectional views showing the manufacturing process of the vertical CCD section in FIG. 3; Figures (a) to (e) are cross-sectional views showing other manufacturing process examples, Figures 8 to 10 are enlarged views showing specific examples of the relationship between transfer electrodes and gap control electrodes, and Figure 11 is transparent. CC of other embodiments of the invention using electrodes
12 is a sectional view showing D. FIG. 12 is a plan view showing an embodiment of a frame transfer type CCD imaging device using transparent electrodes. DESCRIPTION OF SYMBOLS 1... P-type silicon substrate, 2... N-type buried transfer channel, 3... Gate insulating film, 4... Transfer electrode, 5
...Interlayer insulating film, 6...Gap control electrode, 7...
・Gap, 11...p-type silicon substrate, 12...
Photodiode, 13...Vertical CCD channel, 1
4...Horizontal CCD channel, 15.16...Transfer electrode, 17...Channel stop, 18...Interlayer insulating film, 19.20.21...Gap control electrode, 22.
... Transfer gate, 23... Gate insulating film, 24...
gap.

Claims (6)

[Claims] (1) A semiconductor substrate in which a charge transfer channel is formed, and a plurality of conductor films obtained by patterning a single-layer conductor film arranged and formed on the charge transfer channel region of this substrate with a first insulating film interposed therebetween. A transfer electrode is formed through a second insulating film so as to cover at least the gap between the transfer electrodes on the surface where these transfer electrodes are formed, and the transfer channel potential of the gap is set below the transfer electrode. A charge-coupled device comprising: a gap potential control electrode for setting between an "H" level potential and an "L" level potential of a transfer channel. (2) The transfer channel potential at the gap on both sides of one transfer electrode changes depending on the clock voltage applied to the adjacent transfer electrode, and when the signal charge under that transfer electrode is transferred, 2. The charge-coupled device according to claim 1, wherein the potential barrier of the transfer channel in the gap portion is smaller than the potential barrier of the transfer channel in the rear gap portion. (3) The charge coupled device according to claim 1, wherein the transfer electrode is a transparent electrode. (4) a semiconductor substrate; a two-dimensional array of photodiodes that photoelectrically converts and accumulates an incident optical image formed on the substrate; and the photodiodes arranged on the substrate along the array of the photodiodes. A plurality of vertical transfer charge-coupled devices that transfer and read signal charges from diodes; and a horizontal transfer device that reads and outputs the signal charges transferred from the vertical transfer charge-coupled devices formed on the substrate one horizontal column at a time. In a solid-state imaging device having a charge-coupled device, at least one of the vertical transfer charge-coupled device and the horizontal transfer charge-coupled device is arranged and formed on a charge transfer channel region formed on the substrate via a first insulating film. A plurality of transfer electrodes obtained by patterning a single-layer conductor film, and a second insulating film formed so as to cover at least the gap between the transfer electrodes on the surface where these transfer electrodes are formed. a gap potential control electrode for setting the transfer channel potential of the gap portion between the "H" level potential and the "L" level potential of the transfer channel below the transfer electrode; Characteristic solid-state imaging device. (5) The solid-state imaging device according to claim 4, wherein the gap control electrode of the vertical transfer charge-coupled device section and the gap control electrode of the horizontal transfer charge-coupled device section are provided separately, and different control potentials are applied to these. (6) a semiconductor substrate; a plurality of vertical transfer charge-coupled devices formed on the substrate for photoelectrically converting an incident optical image and accumulating and transferring the obtained signal charge; In a solid-state imaging device having a horizontal transfer charge-coupled device that reads out and outputs signal charges transferred from the vertical transfer charge-coupled device one horizontal column at a time, at least the vertical transfer charge-coupled device includes a charge formed on the substrate. A plurality of transfer electrodes obtained by patterning a single-layer transparent conductive film arranged and formed on the transfer channel region with a first insulating film interposed therebetween, and at least between the transfer electrodes on the surface where these transfer electrodes are formed. A transfer channel potential of the gap portion formed via a second insulating film so as to cover the gap portion of the transfer electrode is set between the “H” level potential and the “L” level potential of the transfer channel under the transfer electrode. A solid-state imaging device comprising: a gap potential control electrode for controlling a gap potential;