JPH1022490A - Solid-state image pickup device and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the smear of a CCD image pickup device and to prevent a characteristic degradation of an output circuit. SOLUTION: The thicknesses of PSG films 11 provided as transparent insulating protecting films s are made to change in an image region I and in a peripheral circuit region II and a thin film part 11a and a thick film part 11b are formed in the former and in the latter respectively. These forms are obtained by forming a resist mask which covers the peripheral circuit region II on the PSG films of which film thicknesses are firstly formed in equal on a substrate 10 and by making partial dry etching of the PSG films in the image region I via the mask. The angle of incidence of light which may enter regions other than the photodetecting part becomes small in the image region I and the smear is prevented. Charge-up of a gate oxide film of an output transistor caused by charged particles in plasma is not generated in the peripheral circuit region II even if a passivation by a plasma CVD in a latter step is performed, because the PSG film 11 is thick.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device and a method of manufacturing the same, and more particularly, to improving the smear characteristics of a solid-state imaging device using a CCD in an image area and preventing deterioration of characteristics of output transistors in a peripheral circuit area. The present invention relates to an element structure capable of performing the above and a manufacturing method thereof.

[0002]

2. Description of the Related Art Solid-state imaging devices have become widespread as imaging devices capable of realizing small size, light weight, low voltage, low power consumption, and reduction of afterimages in place of conventional imaging tubes. Above all, CCD
Solid-state imaging devices using GaN have remarkable improvements in their performance and integration, and are used in applications such as video cameras, electronic still cameras, videophones, facsimile machines, electronic copiers, image scanners, and ranging systems. .

[0003] CCD image pickup devices are roughly classified into an interline transfer type and a frame transfer type depending on the difference between the photoelectric conversion system and the scanning system. In the interline transfer type, an array of photodiodes as light receiving units and vertical CCD registers are alternately and two-dimensionally arranged, and signal charges generated in the light receiving units are first collectively stored in an adjacent vertical CCD register. Then, the contents of the vertical CCD register are sequentially read out to the horizontal CCD register. On the other hand, in the frame transfer type, a photosensitive section and a storage section, both composed of CCDs, are laid out next to each other, and the signal charges generated in the photosensitive section are first transferred to the storage section, and then the signals of the storage section are transferred. The data is sequentially read out to the horizontal CCD register. In the frame transfer type, the CCD transfer unit is used as it is as a MOS capacitor type light receiving unit.

FIG. 8A shows a planar layout of a general CCD image pickup device. The area where the photodiode array, the vertical CCD register, the photosensitive section, and the storage section are formed is called an image area i, and usually occupies the center of the CCD image sensor chip. Surrounding it are the horizontal CCD register 22 and the output circuit 23 described above.
Is included in the peripheral circuit area ii. The output circuit 23
In this embodiment, a change in potential generated in a floating diffusion layer (not shown) due to electric charges sent from the horizontal CCD register 22 is detected by a transistor formed on the same substrate, and this is amplified by an amplifier 26 and output voltage V _Take out as _OUT .
A MOS transistor 2 for resetting the potential of the floating diffusion layer to a drain potential is provided in a stage preceding the amplifier 26.
4 are connected. The MOS transistor 24 conducts the channel by applying a pulse voltage V _RG to the reset gate electrode, and the diode 25 is provided to prevent V _DD from lowering below the ground potential.

FIG. 1B is a sectional view taken along the line aa of FIG. 1A, and shows a substrate 3 on which all of the above-mentioned circuit elements are formed.
0 shows a state in which a PSG (phosphosilicate glass) film 31 is formed as a transparent insulating protective film on the substrate. PSG film 1
The reason why 2 is frequently used is that a phosphorus gettering effect of harmful ions can be expected. This PSG film is provided under a first-layer Al film and a second-layer Al film (both not shown), and its thickness is generally substantially uniform over the entire surface of the substrate. The first layer Al film is a film for forming an electrode pattern connected to a transfer gate electrode of a horizontal CCD register or a vertical CCD register.
The film is a film for forming a light-shielding pattern for making light incident on a region other than the light receiving section.

[0006]

One of the problems unique to the CCD image pickup device is smear. This is because when strong light is incident on a certain place in the image area and signal charges overflowing from the pixels in that place enter the scanning section or light is directly incident on the scanning section, the reproduced image is This is a phenomenon in which bright vertical stripes appear. Here, regarding the direct light incidence on the scanning section, the above-mentioned Al light-shielding pattern performs a certain function of preventing the light. However, when the PSG film is thick, the first layer Al film and the second layer Al film have different functions. Is increased, the light taking-in angle increases, and the taken-in light repeats multiple reflections between these two Al patterns and easily enters the scanning portion.

In order to reduce this smear, P is reduced to such an extent that dark current and white spots are not increased in the image area.
It is effective to reduce the thickness of the SG film. However, when this is actually performed, the transistor 24 of the output circuit 3 is
Characteristics are likely to deteriorate. This deterioration mainly occurs when the surface of the second Al film is further covered with a passivation film. Plasma CV as passivation film
A silicon nitride (SiN) film formed by the method D is usually used. This is because the SiN film has better moisture resistance than the SiOx film, and in particular, the film formed by the plasma CVD method has high reliability due to its dense film quality. However, since there are many charged particles that move at high speed in the plasma, when these charged particles penetrate the thin PSG film and their charges are taken into the gate oxide film, the gate oxide film is damaged or degraded by charge-up. Occurs.

[0008] Further, the above-mentioned problem in the peripheral circuit region is more likely to be more obvious than inconvenience in the image region because the thickness of the PSG film in the peripheral circuit region is consequently smaller than that in the image region. One of the reasons is that it is easy to grow. That is, in recent years, an anti-reflection film such as a TiON film is sometimes provided on the surface of the PSG film in order to suppress the multiple reflection described above. However, since the anti-reflection film has a relatively high specific resistance, the first layer Al When forming a contact between the film and the second-layer Al film, it is desirable that there is no contact. For this reason, in the peripheral circuit region, the anti-reflection film is removed in advance by dry etching, but the underlying PSG film tends to be thinned by the over-etching at this time. Therefore, the PSG film in the peripheral circuit region needs to be thicker than a certain thickness in order to compensate for the film loss due to over-etching.

As described above, the requirements for the optimum thickness of the PSG film are different between the image region and the peripheral circuit region. Accordingly, an object of the present invention is to provide a solid-state imaging device capable of improving smear characteristics and preventing deterioration of characteristics of an output circuit by satisfying both requirements, and a method for manufacturing the same. I do.

[0010]

In order to optimize the thickness of the transparent insulating protective film in both the image area and the peripheral circuit area, the solid-state imaging device of the present invention has a relatively small thickness in the image area. It is intended to achieve the above object by making the film thickness in the peripheral circuit region relatively small and relatively large. To manufacture such a solid-state imaging device, a mask that selectively covers the peripheral circuit region is formed on the transparent insulating protective film, and the transparent insulating protective film is etched through the mask. It is sufficient to remove a part in the thickness direction. Further, if a transparent insulating film for stopping etching capable of ensuring an etching selectivity with respect to this film is provided in a region in the thickness direction of the transparent insulating protective film and at least in a region covering the image region. In addition, the end point of the etching can be easily determined.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the solid-state image pickup device according to the present invention, the transparent insulating protective film is thinned in the image area to the extent that smear can be suppressed, while in the peripheral circuit area, the portion from the plasma to the MOS transistor forming portion is reduced. Since the transparent insulating protective film is thick enough to prevent the incidence of charged particles, it is possible to simultaneously improve the reproduction image quality and prevent the characteristics of the output transistor from deteriorating. Less than,
A preferred embodiment of the present invention will be described with reference to the drawings.

First Embodiment FIG. 1 shows a configuration example of a CCD image pickup device to which the present invention is applied. (A) is a top view, and (b) is a sectional view taken along line AA. This CCD image pickup device 1 is composed of an image area I occupying the center and a peripheral circuit area II surrounding the image area I. Here, the image area I has, for example, an interline transfer type configuration, in which an array of photodiodes and vertical CCD registers are alternately arranged. One peripheral circuit area II has a horizontal CCD register 2
Also, an output circuit 3 is formed. In the output circuit 3, a potential change generated in the floating diffusion layer (not shown) by the electric charge sent from the horizontal CCD register 2 is detected by a transistor formed on the same substrate, and this is amplified by the amplifier 6. To extract the output voltage V _OUT . A MOS transistor 4 for resetting the potential of the floating diffusion layer to a drain potential is connected to a stage preceding the amplifier 6. The MOS transistor 4 conducts its channel by applying a pulse voltage V _RG to the reset gate electrode, and the diode 5 is provided to prevent V _DD from lowering below the ground potential.

FIG. 1B is a cross-sectional view taken along the line AA of FIG. 1A, and shows a substrate 1 on which all the above-described circuit elements are formed.
0 shows a state in which a PSG (phosphosilicate glass) film 11 is formed as a transparent insulating protective film on the substrate. This PSG
The thickness of the film 11 is not uniform over the entire surface of the substrate, and in the image region I, the thin film portion 11 having an average thickness of about 100 nm
a, In the peripheral circuit region II, the thick film portion 11b has an average film thickness of about 200 nm. The thus configured C of the present invention
In the CD imaging device 1, the smear is reduced by about 10% as compared with the conventional CCD imaging device in which the thickness of the PSG film is 150 nm (same as the thickness portion 11b) over the entire surface of the base. Further, the CCD image pickup device of the present invention finally has a film thickness of about 300 n
m, the surface of which is passivated by the SiN film, and the TDDB of the gate oxide film of the MOS transistor 4 of the output circuit 3.
(Time-dependent dielectric breakdown) The life did not change at all before and after passivation.

Second Embodiment Here, a method of manufacturing the CCD solid-state imaging device described in the first embodiment will be described with reference to FIGS. First, image area I and peripheral circuit area II
On the substrate 10 on which all necessary circuit elements are formed, a PSG film 11 as a transparent insulating protective film is
m was formed. This film is formed, for example, by SiH ₄ /
This was performed by a plasma CVD method using an O ₂ mixed gas.
The state of the base so far is as shown in FIG. On this PSG film 11, normal resist coating, photolithography and development are sequentially performed, and
As shown in FIG. 5, a resist mask 12 (PR) for selectively covering the peripheral circuit region II was formed.

Next, as shown in FIG. 3, about 100 nm was removed from the surface of the PSG film 11 exposed in the opening of the resist mask 12 by anisotropic dry etching. This partial etching was performed by, for example, RIE (Reactive Ion Etching) using SF ₆ / Ar mixed gas. Thereafter, the resist mask 12 is removed by ashing to remove the thin film portion 1 as shown in FIG.
A PSG film 11 having 1a and a thick film portion 11b was obtained.

Third Embodiment Here, in order to easily determine the end point of the RIE described in the second embodiment, a transparent insulating film for stopping etching is provided at an intermediate portion in the thickness direction of the PSG film 11. An example in which a SiN film pattern is interposed will be described with reference to FIGS. The reference numerals in the drawings are partially common to those in FIGS.

FIG. 5 shows a state in which the steps up to resist patterning have been completed, as in FIG. 2 described above.
An SiN film pattern 13 having a thickness of about 50 nm was embedded as a transparent insulating film for stopping etching in the middle of the PSG film 11 in the thickness direction. To obtain this structure, the PSG film 11
Is divided into two times, during which a SiN film is formed and patterned.

That is, first, a thin PSG film was formed on the entire surface of the substrate 10. At this time, the film thickness of the PSG film is a film thickness that is to be finally left in the image area I. Next, a SiN film was laminated on the entire surface of the PSG film, and the SiN film was dry-etched using a resist mask (not shown). This dry etching was carried out under conditions capable of obtaining a high selectivity with respect to the underlying PSG film, for example, using a magnetic field microwave plasma etching apparatus and a CHF ₃ / CH ₂ F ₂ mixed gas. Thereafter, a thin PSG film was formed again. At this time, the thickness of the PSG film was selected such that the total film thickness with the first film thickness became the required film thickness in the peripheral circuit region II.

Next, resist patterning was performed in the same manner as in the second embodiment, and the PSG film exposed in the opening of the resist mask 12 was etched. This selective partial etching was performed under the condition that a high selectivity with respect to the underlying SiN film pattern 13 was obtained. The conditions are, for example, a magnetic field microwave plasma etching apparatus and CH
F ₃ / CH ₂ F ₂ gas mixture using, CH ₂ against CHF ₃ gas as compared to the formation of the aforementioned SiN film pattern 13
This is a condition in which the flow rate ratio of the F ₂ gas is increased to enhance the deposition of the fluorocarbon polymer. In the above-described second embodiment, the etching end point had to be determined based on time control. However, in the third embodiment, the etching rate was lowered when the SiN film pattern 13 was exposed. The determination of the end point has become easier. Thereafter, only the SiN film pattern 13 was selectively etched to obtain a CCD image sensor similar to that shown in FIG.

Although the present invention has been described based on the three embodiments, the present invention is not limited to these embodiments. For example, the CCD solid-state imaging device may be a frame transfer type or a frame interline transfer type combining a frame transfer type and an interline transfer type, as long as the CCD includes an image area. Further, the transparent insulating protective film and the transparent insulating film for stopping etching are not limited to the PSG film and the SiN film, and a film capable of performing the same function as these may be appropriately selected and used. In addition, details such as a film thickness and etching conditions can be appropriately changed and selected.

[0021]

As is apparent from the above description, according to the present invention, the smear characteristic is improved by satisfying both the requirements for the optimum thickness of the PSG film different from each other in the image region and the peripheral circuit region. In addition, it is possible to prevent the characteristics of the output circuit from deteriorating. Therefore, the present invention greatly contributes to higher performance and higher reliability of the CCD image pickup device.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing a configuration example of a CCD image pickup device according to the present invention, wherein FIG. 1A is a top view and FIG. 1B is a cross-sectional view taken along line AA.

FIG. 2 is a schematic cross-sectional view showing a state where resist patterning has been performed on a PSG film in an example of the method for manufacturing a CCD image pickup device of the present invention.

3 is a schematic cross-sectional view showing a state where a part of the PSG film in the thickness direction of FIG. 2 is partially etched in an image region.

FIG. 4 is a schematic cross-sectional view showing a state where the resist mask of FIG. 3 is removed.

FIG. 5 shows another example of the method for manufacturing a CCD image pickup device according to the present invention, in which a PSG having a SiN film pattern interposed in the middle thereof.
FIG. 4 is a schematic cross-sectional view showing a state where resist patterning has been performed on the film.

FIG. 6 shows that the PSG film of FIG.
FIG. 4 is a schematic cross-sectional view showing a state where selective and partial etching is performed until an N film pattern is exposed.

FIG. 7 is a schematic cross-sectional view showing a state where the resist mask of FIG. 6 is removed.

8A and 8B are diagrams showing a configuration example of a conventional CCD image pickup device, wherein FIG. 8A is a top view, and FIG. 8B is a cross-sectional view taken along line aa.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... CCD imaging device 2 ... Horizontal CCD register 3 ... Output circuit 4 ... MOS transistor 10 ... Substrate 11 ...
PSG film 11a Thin film part 11b Thick film part I Image area II Peripheral circuit area

Claims (7)

[Claims] 1. A solid-state imaging device having an image area including a CCD on a semiconductor substrate and a peripheral circuit area formed adjacent to the image area for outputting signal charges generated in the image area. A solid-state imaging device in which the thickness of a transparent insulating protective film formed on the entire surface of the base is relatively small in the image region and relatively large in the peripheral circuit region. 2. The solid-state imaging device according to claim 1, wherein said transparent insulating protective film is made of phosphosilicate glass. 3. A first step of forming an image area including a CCD and a peripheral circuit area for detecting signal charges generated in the image area adjacent to each other on a semiconductor substrate, A method for manufacturing a solid-state imaging device, comprising: a second step of forming a transparent insulating protective film; and a third step of selectively reducing the thickness of the transparent insulating protective film in the image area. 4. In the third step, an etching mask for selectively covering the peripheral circuit region is formed on the transparent insulating protective film, and the transparent insulating protective film is etched through the etching mask. 4. The method for manufacturing a solid-state imaging device according to claim 3, wherein a part of the film in the thickness direction is removed by performing. 5. The method according to claim 6, wherein a phosphosilicate glass film is formed as the transparent insulating protective film. 6. A transparent film for stopping etching capable of securing an etching selectivity with respect to the transparent insulating protective film, at least in a region in the thickness direction of the transparent insulating protective film and covering at least the image area. 4. An insulating film is provided.
A method for manufacturing the solid-state imaging device according to the above. 7. The method according to claim 6, wherein a phosphosilicate glass film is formed as the transparent insulating protective film, and a silicon nitride film is formed as the transparent insulating film for stopping the etching.