JP3028823B2 - Charge coupled device and solid-state imaging device using the same - Google Patents

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 number of pixels of a CCD imaging device has been remarkable. A two-dimensional CCD image pickup device generally includes a photodiode array that stores signal charges by photoelectric conversion, and a vertical CCD and a horizontal CCD that read out signal charges of the photodiode array. In these CCD imaging devices
Usually, two layers of transfer electrodes overlapping each other via an interlayer insulating film are used for the CCD. However, with the recent increase in the number of pixels and the miniaturization of each part of the CCD, there has been a problem that a short circuit between the first-layer transfer electrode and the second-layer transfer electrode often occurs. The reason 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 the transfer electrode, so that the quality is not very good, and the thickness of the interlayer insulating film is also scaled. Is gradually becoming thinner.

On the other hand, there is a CCD image pickup apparatus in which a photodiode array is not formed and only a vertical CCD and a horizontal CCD are used. In this case, the vertical CCD unit is used as a photoelectric conversion unit and a transfer unit. In this method, an incident optical image is transmitted through a transfer electrode made of a polycrystalline silicon film to generate signal charges on the substrate surface. However, in this method, the transfer electrode made of a polycrystalline silicon film transmits red light of visible light substantially, but attenuates other light. Particularly, blue light hardly transmits. Therefore, it is difficult to apply this method as it is to a color camera. In order to solve this, it is conceivable to use a transparent electrode such as ITO for the transfer electrode. However, in the case of a transparent conductive film such as ITO, if an attempt is made to realize a transfer electrode having an overlapping structure, there is no suitable interlayer insulating film, and a highly reliable transfer electrode cannot be obtained.

(Problems to be Solved by the Invention) As described above, in the conventional CCD image pickup device having the two-layer transfer electrode structure, a short circuit accident between the first-layer transfer electrode and the second-layer transfer electrode occurs with miniaturization. And there was a problem in reliability. Further, when a transparent conductive film is used as a transfer electrode, there is a problem that it is difficult to form a transfer electrode having a two-layer structure because there is no appropriate interlayer insulating film.

The present invention has been made in view of the above points, and a CCD and a CCD that improve reliability by eliminating a short circuit accident between transfer electrodes.
It is an object to provide an imaging device.

[Constitution of the Invention] (Means for Solving the Problems) A CCD according to the present invention comprises a semiconductor substrate on which a charge transfer channel is formed, and a first insulating film on the charge transfer channel region of the substrate. A plurality of transfer electrodes obtained by patterning a single-layer conductor film formed in an array, and a second insulating film interposed therebetween so as to cover at least a gap between the transfer electrodes on the surface on which the transfer electrodes are formed. Formed
A gap potential control electrode for setting a transfer channel potential of the gap portion between an “H” level potential and an “L” level potential of a transfer channel below the transfer electrode is provided.

(Operation) According to the present invention, since the transfer electrode is formed by patterning a single-layer conductor film, even if the device is miniaturized, a short-circuit accident between the electrodes due to the overlap of the transfer electrode as in the related art can be prevented. The occurrence is effectively prevented. This single-layer transfer electrode structure was used in early CCDs before the technology of double-layer polycrystalline silicon was developed. However, when the transfer electrodes are formed of a single-layer conductor film in this manner, potential barriers and potential pockets are formed in the gaps between the transfer electrodes in the transfer channel, and as they are, charges due to residual signal charges are left. This results in a decrease in transfer efficiency. In this respect, in the present invention, the electric potential of the gap between the transfer electrodes is controlled by the control electrode provided on the transfer electrode, thereby preventing the charge transfer efficiency from being lowered.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing a main structure of a CCD according to an embodiment. An n-type buried channel is formed on the surface of a p-type silicon substrate 1 (the whole may be a p-type substrate or a p-type well formed on an n-type silicon substrate. The same applies to the following embodiments). A plurality of transfer electrodes 4 (4 ₁ , 4 ₂ ,...) Are arranged and formed on the charge transfer channel 2 with a gate insulating film 3 interposed therebetween. Transfer electrode 4
Is a single-layered electrode formed by depositing a polycrystalline silicon film by a CVD method and patterning the same, and arranged with a small gap 7. An interlayer insulating film 5 is further formed on the surface on which the transfer electrode 4 is formed by CVD, and a gap control electrode 6 is formed thereon.

FIG. 2 shows a state of charge transfer of the CCD of this embodiment.
A predetermined control potential is applied to the gap control electrode 6, and a predetermined clock voltage is applied to the transfer electrode 4 in this state. The actual transfer clock system includes a two-phase clock system, a three-phase clock system, a four-phase clock system, and a single-phase clock system. In this case, the system does not matter. Figure 2 (a) in the transfer electrodes 4 ₂ below the signal charges next transfer electrodes 4 ₃
Shown below is the potential distribution of the transfer channel when transferred. That is, the transfer electrode is controlled by the clock control.
4 ₃ below "H" level phi _H, and the transfer by the electrodes 4 ₂ below is shifted to "L" level phi _L, FIG signal charge was the transfer electrode 4 ₂ below as indicated by hatching in the transfer electrodes 4 ₃ Transferred to the lower potential well.

Here, the channel potential below the gap 7 has an important meaning. The channel potential of the gap portion 7 is controlled by the gap control electrode 6 as described above. Basically, the gap potential φ _G0 is the “H” level potential φ of the transfer channel.
It is set to be in the middle of the _H and "L" level potential phi _L. On the other hand, since the gap 7 is small, the gap potential is affected by the potential of the front and rear transfer electrodes (a so-called two-dimensional effect). As a result, when attention is focused on both sides of the gap of the transfer electrodes 4 ₂ the signal charge is swept out in the second view (a), the transfer direction in front of the gap potential phi _G2 is higher than the rear of the gap potential phi _G1. In other words, the potential barrier in the gap part in the forward direction in the transfer direction becomes lower than that in the rear part in the transfer direction. Due to such a potential change in the gap, the signal charge is transferred without being left behind.

For reference, FIG. 2 (b) shows a state of charge transfer in the case where the potential control of the gap 7 is not performed, corresponding to FIG. 2 (a). In this case, the portion of the gap 7 as shown "H" level potential φ deeper than _H potential pockets 8
Is formed, and the transfer of the signal charge is left behind. In particular, when the gap 7 is large and is, for example, larger than the thickness of the transfer electrode 4, the above-described two-dimensional effect is reduced, and the potential pocket 8 is kept in a constant deep state regardless of the potential of the transfer electrode 4. In this state, if the gap potential is not controlled, the transfer efficiency will be greatly 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. Fig. 4 (a) (b) (c)
FIG. 2 is a plan view and a cross-sectional view showing the structure of the main part. On a p-type silicon substrate 11, photodiodes 12 are formed two-dimensionally by an n-type diffusion layer for performing photoelectric conversion and accumulation. A plurality of vertical transfer CCDs for reading out the signal charges of each photodiode 12 in parallel with this photodiode array
Are formed. Reference numeral 13 denotes an n-type buried channel of the vertical transfer CCD. A horizontal transfer CCD for reading the signal charges transferred by the vertical transfer CCD one by one horizontal column is provided. Reference numeral 14 denotes 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, a transfer electrode 15 obtained by patterning a single-layer polycrystalline silicon film via a gate insulating film 23 has a small gap 24 as shown in FIG.
Are formed. Horizontal transfer CCD channel 14
Similarly, transfer electrodes 16 formed by patterning a single-layer polycrystalline silicon film are formed in an array. Vertical CCD channel 1
Channel 12 stops on the photodiode 12 side of p
^{A +} type layer 17 is formed. The gap control electrodes 19, 2 are further interposed on the surface on which the element is formed in this manner via an interlayer insulating film 18.
0 and 21 are formed of an Al film. These control electrodes 19,2
Reference numerals 0 and 21 also serve as light shielding films. Therefore vertical CCD
It is necessary that the gap control electrode 19 is formed with a window at least in the portion of the photodiode 12. For example, in the example shown in FIG. It is formed in an array. Horizontal C
The gap control electrode 20 in the CD portion covers almost the entire horizontal CCD area.

The control potential V _G2 applied to control potential V _G1 and the horizontal CCD of the gap control electrode 20 provided on the gap control electrode 19 of the vertical CCD portion in this embodiment is set to a different value. Specifically, V _G2 is set higher than V _G1. This is because the clock pulse voltage differs between the vertical CCD and the horizontal CCD. That is, the so-called field shift gate for reading out the signal charges 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 performed (FIG. 4 ( b)). Therefore, in order to transfer a signal charge read out from the photodiode 12 to the vertical CCD channel 13 by applying a positive voltage to the field shift gate without flowing back to the photodiode 12 side, the vertical CCD transfer electrode 15, for example, A negative clock pulse varying from -8V to 0V is used. On the other hand, in a horizontal CCD, a positive clock pulse that changes in a range from 0 V to 5 V is used. On the other hand, the channel potential of the gap portion by the gap control electrode needs to be determined in relation to the pulse voltage applied to the transfer electrode, as described above with reference to FIG. Then, each of the vertical CCD and the horizontal CCD, to set in the middle of the preferred value of "H" level potential "L" level potential of the transfer channel gap potentials as described in FIG. 2, V _G1 is It must be lower than V _G2 .

The operation of the interline transfer CCD image pickup device of this embodiment is not different from that of a conventionally known device. That is, the signal charges of the photodiode array are read out to the vertical CCD during the vertical blanking period of the imaging, and this is transferred to the vertical CCD and the horizontal CCD.
The operation of imaging the next field while outputting the data by horizontal line transfer by the CCD is repeated. In this embodiment, both the vertical CCD and the horizontal CCD are driven in four phases. The specific signal charge transfer in the vertical CCD and the horizontal CCD will be described with reference to FIGS. 5 (a) and 5 (b).

FIG. 5A shows a four-phase clock waveform. Figure 5 (b) shows the channel potential distribution under the transfer electrodes at each time t ₁ ~t ₅ of the clock waveform. As shown in the figure, the clocks φ _{1 to} φ ₄ partially “L”,
By repeating “H”, signal charges are transferred along the transfer channel. By the action of the gap control electrode, as described in the previous embodiment, no barrier or potential pocket is formed in the transfer channel that hinders the transfer of signal charges, and signal charges are transferred without being left behind.

6 (a) to 6 (g) are cross-sectional views showing specific manufacturing steps for the vertical CCD section. p-type silicon substrate 11
After forming an element isolation region, 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 ((b)). Thereafter, a polycrystalline silicon film 50 is deposited by a CVD method ((c)), a photoresist 31 is formed in a pattern, and the polycrystalline silicon film 50 is selectively etched using the photoresist 31 as a mask, thereby forming a plurality of transfer electrodes. 15 is formed separately ((e)). Then photoresist
The interlayer insulating film 18 is deposited by the CVD method by stripping 31 ((f)), and a metal film such as Al is formed thereon and patterned to form the gap control electrode 19 (g)).

The same applies to the manufacturing process of the horizontal CCD section. As is apparent from FIG. 3, only one polycrystalline silicon film is required for the entire CCD imaging device, and the manufacturing process is simple.

FIGS. 7A to 7E show another example of the manufacturing process of the vertical CCD section. forming a gate oxide film 23 on the p-type silicon substrate 11, after forming an n-type buried channel 13 by ion implantation, depositing a polycrystalline silicon film 50 ₁ by CVD ((a)). Up to this point, it is the same as the previous embodiment. Then a photoresist pattern 32, the polycrystalline silicon film 50 ₁ is selectively etched by using the transfer electrodes 15 ₁
Is formed ((b)). Transfer electrodes 15 ₁ at this stage not all, has every other. Gap between the transfer electrodes 15 ₁ thus is an transfer electrode length. Then the transfer electrodes 15 _first surface to form an oxide film 33 ((c)), then C
Multi crystalline silicon film 50 ₂ of the second layer by VD method, the surface is deposited to be approximately flat ((d)). And performing entire polycrystalline silicon film etching, the gap to the transfer electrodes 15 _{and second} transfer electrodes 15 ₁ previously formed to buried ((e)).

Although this method uses a two-layer polycrystalline silicon film, it does not form a transfer electrode having an overlapping structure by selectively etching the second layer as in the related art. That self-in-aligned state to form the transfer electrodes 15 _2, resulting in the previous examples as well as more of the polycrystalline silicon film pattern between the transfer electrodes 15 ₁ by the second layer is entirely etched Transfer electrodes arranged with a small gap can be obtained in the same manner as when they are formed.

Incidentally, in the present invention, the transfer channel potential in the gap between the transfer electrodes is affected by the size of the gap and the thickness of the transfer electrode. From such a viewpoint, the structure of this portion has several modes.

FIG. 8 shows a case where the gap 24 between the transfer electrodes 15 is relatively large. In this case, the transfer channel potential in the gap has little effect of the transfer electrode 15, that is, the two-dimensional effect. Therefore, in order to control the gap potential, the bottom surface A of the gap potential control electrode 19 at the gap 24 as shown in FIG.
Preferably, it is located below the upper surface B of the transfer electrode 14.

FIG. 9 shows a case where the gap 24 between the transfer electrodes 15 is small. In this case, since the potential of the gap portion is greatly affected by the transfer electrode 15, the bottom surface A of the gap potential control electrode 19 may be located above the upper surface of the transfer electrode 15. If fine processing technology advances and the gap 24 can be reduced to a very small value of, for example, 0.5 μm or less, no special gap potential control is required, and sufficient charge transfer efficiency is obtained in a state where potential pockets and the like are not formed. Also becomes possible.

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 located below the top surface B of the transfer electrode 15.

Note that in the embodiment of the CCD imaging device, the vertical CCD and the horizontal CC
Both D have a structure in which a gap potential control electrode is provided as a single-layer transfer electrode, but the present invention is effective even if a 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 a CCD cross-sectional structure of the main part. Parts corresponding to those in FIG. 1 are denoted by the same reference numerals as in FIG. 1, and detailed description is omitted. In this embodiment, the transfer electrode 9 is
Is formed by patterning a single-layer transparent conductive film. The surface of the substrate on which the transfer electrodes 9 are formed is covered with a CVD insulating film 5, on which a gap control electrode 6 is patterned. The gap control electrode 6 is patterned so as to cover only the gap 7 between the transfer electrodes 9.
This is because it is assumed that each transfer electrode 9 is used as it is as a photoelectric conversion unit having blue sensitivity.

FIG. 12 shows a frame transfer type CC using the structure of FIG.
It is a schematic plan view of D imaging device. A plurality of vertical CCD channels 41 and horizontal CCD channels 42 are formed as shown by broken lines, and a vertical CCD transfer electrode 43 and a horizontal CCD transfer electrode 44 are formed by patterning a layer of a transparent conductive film such as ITO on these channels. It is formed. In the gap portion of the transfer electrode 43 of the vertical CCD and the gap portion of the transfer electrode 44 of the horizontal CCD, only the drawing portion is shown in a simplified manner, but as shown in FIG. 11, gap control is performed in a state where only the gap portion is covered. Electrodes 45 and 46 are provided. In the vertical CCD, the upper half is actually used as a light receiving unit 47 that performs photoelectric conversion, and the lower half is a storage unit that stores one frame of photoelectrically converted signal charges.
48. Therefore, it is only that of the light receiving section 47 that the transfer electrode needs to be transparent, and the remaining transfer electrode may be formed of, for example, a polycrystalline silicon film. However, in this embodiment, as described above, all the transfer electrodes are transparent electrodes. For this reason, although not shown in the drawing, it is necessary to cover the CCD section other than the light receiving section 47 with a light shielding film. The embodiment shows a case of two-phase driving.
Therefore, it is actually necessary to impart asymmetry to the potential well under each transfer electrode. Although detailed description is omitted, for example, ion implantation or the like is partially performed under each transfer electrode to form the storage section and the barrier section. Form.

According to this embodiment also, by providing the gap control electrode with the transfer electrode having a single-layer electrode structure, as in the previous embodiment, the problem of the reduction in reliability when using the overlap electrode structure is solved, and the method is also high. Transfer efficiency is obtained
You can get a CCD. In addition, in the case of a transparent electrode, since there is no good interlayer insulating film, it is difficult to configure a CCD imaging device having a blue sensitivity with an overlapping electrode structure. A device is obtained.

The present invention is not limited to the above embodiment. For example
In the embodiment of the CCD imaging apparatus, a case where only one horizontal CCD is provided is shown, but the present invention can be similarly applied to a structure in which a plurality of horizontal CCDs are provided. In the embodiment, the n-type buried channel has been described. However, the present invention can be applied to a surface channel type and further to a p-channel type CCD. Further, the CCD structure of the present invention is not limited to an imaging device, and can be used for various applications such as a shift register, a memory, and a delay element.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain a CCD and a CCD image pickup device having improved reliability as a single-layer transfer electrode structure without lowering the charge transfer efficiency. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing a basic structure of a CCD according to an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are views 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 XX 'and YY' of the embodiment applied to a line transfer type CCD image pickup device. 5 (a) and 5 (b) are diagrams for explaining the operation of the CCD image pickup device of FIG. 3, and FIGS. 6 (a) to 6 (g) are manufacturing steps of the vertical CCD section of FIG. 7 (a) to 7 (e) are cross-sectional views showing another example of the manufacturing process, and FIGS. 8 to 10 are enlarged examples of the relationship between the transfer electrode and the gap control electrode. FIG. 11 is a cross-sectional view showing a CCD according to another embodiment of the present invention using a transparent electrode. FIG. 12 is a plan view showing an embodiment of a frame transfer type CCD imaging device using a transparent electrode. 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
... p-type silicon substrate, 12 ... photodiode, 13 ...
… Vertical CCD channel, 14 …… 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)

(57) [Claims] 1. A semiconductor substrate having a charge transfer channel formed thereon, and a single-layer conductive film arranged and formed on the charge transfer channel region of the substrate with a first insulating film interposed therebetween. A plurality of transfer electrodes, and a transfer electrode of the gap formed through a second insulating film so as to cover at least a gap between transfer channel potentials on a surface on which the transfer electrodes are formed. And a gap potential control electrode for setting between a “H” level potential and an “L” level potential of a lower transfer channel. 2. A transfer channel potential in a gap portion on both sides of one transfer electrode changes according to a clock voltage applied to an adjacent transfer electrode, and when a signal charge under the transfer electrode is transferred, the transfer direction is changed. 2. The charge coupled device according to claim 1, wherein a potential barrier of the transfer channel in the front gap portion is smaller than a 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, two-dimensionally arranged photodiodes for photoelectrically converting and accumulating an incident optical image formed on the substrate, and arrayed and formed on the substrate along the array of the photodiodes. A plurality of vertical transfer charge-coupled elements for transferring and reading the signal charges of the photodiode; and reading and outputting the signal charges formed on the substrate and transferred by the vertical transfer charge-coupled elements, one horizontal column at a time. A solid-state imaging device having a horizontal transfer charge-coupled device, wherein at least one of the vertical transfer charge-coupled device and the horizontal transfer charge-coupled device is provided 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 formed in an array, and a gap between at least the transfer electrodes on the surface on which the transfer electrodes are formed. The transfer channel potential of the gap portion formed through the second insulating film so as to cover the transfer portion is set between the “H” level potential and the “L” level potential of the transfer channel below the transfer electrode. And a gap potential control electrode for controlling the solid-state imaging device. 5. The solid-state imaging device according to claim 4, wherein a gap control electrode of the vertical transfer charge-coupled device section and a gap control electrode of the horizontal transfer charge-coupled device section are separately provided, 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 performing photoelectric conversion of an incident optical image and storing and transferring obtained signal charges, and formed on the substrate. A horizontal transfer charge-coupled device that reads out and outputs the signal charges transferred by the vertical transfer charge-coupled device one horizontal row at a time, wherein at least the vertical transfer charge-coupled device is formed on the substrate. A plurality of transfer electrodes formed by patterning a single-layer transparent conductive film arranged and formed on the charge transfer channel region with a first insulating film interposed therebetween, and at least transferring the surface on which the transfer electrodes are formed. The transfer channel potential of the gap formed through the second insulating film so as to cover the gap between the electrodes is changed to the “H” level potential and the “L” level of the transfer channel below the transfer electrode. A solid-state imaging apparatus characterized by being constituted by a gap potential control electrode for setting between the position.