JPH02262369A - Solid image pick-up device and manufacture thereof - Google Patents

Abstract

PURPOSE:To enable the electric connection between a bonding wire and a transparent electrode to be assured as well as enhancing the reliability upon the electric connection by a method wherein a metallic film coming into contact with the end of a photoconductive film and at almost the same level as that of the photoconductive film is formed while a transparent electrode extending from the upper part of the photoconductive film to the upper part of the metallic film is also formed. CONSTITUTION:Within the title solid image pick-up device provided with a semiconductor substrate 1 whereon a signal charge accumulation diode and a signal charge reading-out part are arrayal-formed, a solid image pick-up element chip with a pixel electrode electrically connected to the accumulation diode on the uppermost part thereof, a photoconductive film 3 lamination-formed on the solid image pick-up element chip and a transparent electrode 6 formed on the photoconductive film 3, a bonding pad part impressing outer voltage on the said transparent electrode 6 and a leading-out part thereof comprise of a metallic film, 5 in contact with the end of the said photoconductive film on the pixel region and at almost the same level as that of the photoconductive film 3, the said transparent electrode 6 is formed extending from the photoconductive film 2 to the upper part of the pad leading-out part so that a bonding wire 7 may be connected to the metallic film 5 of the bonding pad part.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention provides a semiconductor substrate in which a signal charge transfer section (solid-state image sensor chip) and a photoelectric conversion section made of a photoconductive film are laminated on a semiconductor substrate. The present invention relates to a stacked solid-state imaging device, and particularly to a solid-state imaging device with an improved means for applying an external voltage to a photoconductive film, and a method for manufacturing the same.

(Prior Art) In recent years, solid-state imaging devices have been developed that use photodiodes as photoelectric conversion units and CCDs as signal charge transfer units. This solid-state image sensor has the advantage of being able to realize a camera that is smaller, lighter, and more reliable than a conventional image pickup tube, and can obtain high-quality images with almost no afterimages. However, solid-state image sensors are mainly formed on Si wafers, and have the drawback that the usable sensitivity wavelength range is limited to the visible wavelength range.Furthermore, the effective photosensitive area of the pn photodiode that performs photoelectric conversion and the ineffective photosensitive area of the signal transfer area are disadvantageous. However, they have drawbacks that image pickup tubes do not have, such as decreased sensitivity and the tendency to generate false signals such as moiré. As a solid-state imaging device that eliminates these drawbacks, there is a stacked solid-state imaging device that uses a conventional solid-state imaging device as a signal charge transfer unit (solid-state imaging device chip) and performs photoelectric conversion with a photoconductive film provided on top of it. Proposed.

FIG. 5 is a cross-sectional view of a pixel portion of a stacked solid-state imaging device that combines a solid-state imaging device chip and a photoconductive film.
A vertical CCD 12 consisting of an n-type buried channel COD is formed on a p-type St substrate and a plate 11. An n+-type storage diode 13 and a p+-type channel stop section 14 for separating each pixel are formed, and a transfer gate is formed on the vertical CCD 12. A poly-Si electrode 15 serving as an electrode is formed. storage diode 1
In the part 3, a contact hole is formed in the oxide film 16 made of a thermal oxide film, a CVD oxide film, etc. so that the n+ part of the storage diode 13 is exposed, and then a first electrode 17 made of, for example, Al1 or MoSi is formed. It is formed into a predetermined shape.

Then, for example, B through a polyimide or melt process.
A surface flattening film 18 made of PSG (boron phosphorus silicate glass) or the like is formed, and a contact hole is formed in this film 18 to expose a part of the first electrode 17. Second electrode (pixel electrode) 19
is formed into a predetermined shape.

On the solid-state image sensor chip thus formed, a photoconductive film 2o of amorphous St or the like is formed by glow discharge or photo-CVD, and then ITO (indium tin oxide film) is formed.
By forming transparent electrodes 21 such as the above, a stacked solid-state imaging device can be obtained.

FIG. 6 shows the overall chip image of the solid-state image sensor in FIG.
This shows how the electrodes are taken out to the outside. Photoconductive film 20
covers the entire effective pixel area of the element, as shown by the dashed line in the figure. Furthermore, ITO is added as an upper electrode on top of that.
A transparent electrode 21 is formed using the above-mentioned method. A large number of first-class bonding pads 22 are arranged outside these. In addition, in this figure, 22a, 22b, 22c at the right end
Only 311 locations are numbered. In addition, illustrations of electrical connections other than the bonding pad 22c are omitted.

FIG. 7 is a cross-sectional view of the bonding pad 22c in FIG. 6 connected to the transparent electrode 21. A lead electrode 23 that contacts the transparent electrode 21 extends from the bonding pad 22c.

Bonding pad 22c is bonded to bonding wire 25 on field oxide film 24. With this configuration, the externally applied voltage is applied to the bonding wire 25.
．． The electric field reaches the transparent electrode 21 through the bonding pad 22c and the lead electrode 23, and forms in the photoconductive film 20 an electric field sufficient for the travel of photoexcited carriers inside the photoconductive film 20.

However, this conventional structure has the following problems regarding electrical connections. That is, a connection failure between the transparent electrode 21 and the lead electrode 23 occurs, resulting in poor quality. In FIG. 7, the end face of the photoconductive film 20 forms an appropriate angle, so that the transparent electrode 21 and the photoconductive film 20 are smoothly connected. However, in reality, if a photoconductive film 20 with a thickness of about 1 to 3 μm is formed on the entire surface of a chip or wafer and then the unnecessary parts are removed by etching, etc., the end face becomes almost vertical, and in extreme cases, has a shape cut diagonally in the opposite direction to that shown in FIG. −
On the other hand, the transparent electrode 21 usually has a thickness of about several 100 to 1000 λ, which is considerably thinner than the thickness of the photoconductive film 20. Therefore, in the structure shown in FIG. 7, the transparent electrode 21 is connected to the photoconductive film 2.
When the M-step is cut at the step at the end of 0, an M-step break occurs, resulting in an electrical connection failure.

A bonding pad having a structure as shown in FIG. 8 is also used as a structure that does not cause electrical connection failure due to disconnection of the transparent electrode. FIG. 8(a) is a plan view,
The photoconductive film 20 and the transparent electrode 21 are etched using the same mask pattern. As shown in the figure, a central part 26 of the two-layer film 20.21 is removed on the bonding pad 22c by A1 etc., and the lower bonding pad 22c is removed.
Kudzu is exposed. Figure 8(b) shows A-A' in Figure 8(a).
A cross section is shown. Field oxidation Il! A bonding wire 25 is bonded to the exposed portion of the bonding pad 22c formed on the Li 24, but at this time, the bonding wire 25 is also bonded to a part of the transparent electrode 21 on the photoconductive film 20. An external voltage will be applied to the photoconductive film 20.

However, even with this structure, the following drawbacks may occur regarding electrical connections. That is, the bonding wire 25 made of Al1 or the like still has good bondability to the bonding pad 22c made of Ail or the like, and their bonding is sufficient, but the transparent electrode 21 made of ITO or the like is thin and
Bondability with L is weak or almost non-existent. Therefore, the bonding wire 25 and the transparent electrode 21 are electrically coupled through mechanical contact.

Therefore, when stress such as thermal history is applied, the bonding wire 25 may come off from the transparent electrode 21, which often causes problems in terms of reliability.

(Problems to be Solved by the Invention) As described above, in the conventional bonding pad structure for applying a voltage from the outside to the transparent electrode of a stacked solid-state imaging device, there are problems such as breakage of the transparent electrode and poor bondability. This has led to problems such as poor electrical connections and reduced reliability.

The present invention has been made in consideration of the above circumstances, and its purpose is to ensure electrical connection between the bonding wire and the transparent electrode by a new electrode extraction configuration of the bonding pad portion. Another object of the present invention is to provide a stacked solid-state imaging device and a method for manufacturing the same, which can improve the reliability of electrical connections.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to prevent breakage at the portion where the transparent electrode on the photoconductive film is drawn out to the bonding pad portion, and to provide a metal film with good bondability. The purpose is to bond the bonding wire to the wire.

That is, the present invention provides a solid-state image sensor chip in which a signal charge storage diode and a signal charge readout section are arranged and formed on a semiconductor substrate, and a pixel electrode electrically connected to the storage diode is formed on the top, and this solid-state image sensor chip. In a solid-state imaging device comprising a photoconductive film laminated on an element chip and a transparent electrode formed on the photoconductive layer, a bonding pad section for applying an external voltage to the transparent electrode and its lead-out section are provided. The transparent electrode is formed of a metal film that is in contact with an end portion of the photoconductive film on the pixel region and has a surface height that is approximately the same as that of the photoconductive film, and the transparent electrode is extended from above the photoconductive film to above the pad lead-out portion. A bonding wire is connected to the metal film of the bonding pad portion.

The present invention also provides a method for manufacturing the solid-state imaging device, comprising:
A photoconductive film is laminated on a solid-state image sensor chip in which a signal charge storage diode and a signal charge readout section are arranged and formed on a semiconductor substrate, and a pixel electrode electrically connected to the storage diode is formed on the top. , a resist is formed on this photoconductive film so as to cover the pixel area, and then the photoconductive film is selectively etched using this resist as a mask,
Next, a metal film is formed on the resist and the image sensor chip, and then the metal film on the resist is removed by removing the resist, and then a transparent electrode that partially extends to the metal film is formed on the photoconductive film. In this method, a bonding wire is then connected onto the metal film.

(Function) According to the present invention, by forming a metal film in contact with the end portion of the photoconductive film, the transparent electrode can be taken out to the bonding pad lead-out portion with almost no step difference. It is possible to prevent step breakage. Further, the bonding wire can be bonded to a metal film with good bondability. Therefore, it is possible to ensure the electrical connection between the bonding pad and the transparent electrode and to improve the reliability of the electrical connection.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a sectional view showing the structure of a bonding pad portion of a stacked solid-state imaging device according to a first embodiment of the present invention. Although not shown in the figure, the configuration of the solid-state image sensor chip is the same as that shown in FIG. 5 above.

A photoconductive film 3 made of amorphous Si or the like is formed on a part of a field oxide film 2 formed around a chip of a semiconductor substrate 1 so as to be continuous with a photosensitive region (pixel region). On the field oxide film 2 that is not covered with the photoconductive film 3, a metal film 5 such as Al1 is formed to have the same thickness as the photoconductive film 3. Further, the transparent electrode 6 is formed on the photoconductive film 3 and is formed so as to partially extend onto the metal film 5. A bonding wire 7 is connected to a portion of the metal film 5 that is not covered with the transparent electrode 6.

FIG. 2 is a sectional view showing the manufacturing process of the bonding pad portion for the transparent electrode of the solid-state imaging device.

First, as shown in the second ffl(a), a solid-state sensor chip (not shown) is formed on a semiconductor substrate 1 in the same way as in the conventional method, and a photoconductive film 3 made of amorphous Si or the like is laminated thereon. In order to leave this photoconductive film 3 covering the photosensitive region (pixel region) and a portion of the field oxide film 2 around the chip, a resist 4 having a predetermined pattern is formed using a normal photolithography process. After that, as shown in Figure 2(b),
Using the resist 4 as a mask, unnecessary photoconductive film 3 around the chip is removed by etching. Next, as shown in FIG. 2C, a metal film 5 having good bondability, such as AfI, is formed on the oxide film 2 and the resist 4 by vapor deposition to a thickness substantially equal to that of the photoconductive film 3. Next, as shown in FIG. 2(d), the resist 4 is melted.
The upper metal film 5 is removed. That is, by the lift-off method,
A metal film 5 having the same thickness as the protective film 3 is formed at the end of the photoconductive film 3.

Next, as shown in FIG. 2(e), a transparent electrode 6 made of ITO or the like is deposited on the entire surface, and then this transparent electrode 5 is patterned into a predetermined pattern. In this patterning, the transparent electrode 6 overlaps the metal film 5 at the chip periphery and is electrically connected to the metal film 5 at the bonding pad area.
be exposed. Further, the metal film 5 is also etched away except for necessary portions such as the bonding pad portion to the transparent electrode 6 and the pad lead-out portion.

Finally, the structure shown in FIG. 1 is obtained by bonding the bonding wire 7 to the bonding pad portion 2/1 of the metal film 5, etc. Due to this bonding, an externally applied voltage is supplied to the transparent electrode 6 via the bonding wire 7 and the metal film 5.

According to the bonding pad drawer structure of this embodiment,
The bonding wire 7 is a metal film 5 with good bondability.
The transparent electrode 6 is formed from above the photoconductive film 3 to extend over a bonding pad lead-out portion made of a metal film 5 having approximately the same thickness as the photoconductive film 3, and is in sufficient contact with this metal film 5. Therefore, the transparent electrode 6 is not broken in this lead-out portion.

Therefore, the electrical connection between the bonding wire 7 and the transparent electrode 6 can be ensured, and reliability can be improved.

FIG. 3 is a cross-sectional view showing the main structure of a second embodiment of the present invention. Note that the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

This embodiment differs from the previously described embodiments in that at the connection portion of the metal film 5, which is the bonding pad lead-out portion between the photoconductive film 3 and the transparent electrode 6, a second layer is further placed on the transparent electrode 6.
The reason is that the metal film 8 is formed.

That is, in this embodiment, the steps up to the step shown in FIG. 2(e) are performed in the same manner as in the previous embodiment. Next, a second metal film 8, for example Al, Ti, Cr, Mo.

A film of Mo5t, W, etc. is formed to cover at least the end of the photoconductive film 3 and the end of the transparent electrode 6 on the bonding pad lead-out side. Then, as in the previous embodiment, A is applied to the bonding pad portion of the first metal film 5.
A bonding wire 7 such as fi is bonded.

Here, when using a metal film with good bondability as the second metal film 8, as shown in FIG. It's okay.

Separately from this, the second metal film 8 is formed on the electrode 6 before patterning the transparent electrode 6, and after processing and forming the metal film 8 into a desired shape, the second metal film 8 is formed on the transparent electrode 6 before patterning. The electrode 6 can also be formed into a predetermined shape. In this case, the second metal film 8 will be formed at least inside the transparent electrode 6 pattern.

In addition, in order to maintain white balance, solid-state imaging devices usually provide a light shield area called an optical black part in a part of the pixel area in order to remove dark current components from output signal components containing dark current. Here, a method of detecting the dark current level is used. This light shield region is generally formed of a metal film in many cases.

Therefore, it is also possible to form this optical black portion using the second metal film 8 of this embodiment.

In this embodiment, the second metal film 8 may be formed by selectively etching the entire surface, or may be formed by direct patterning using a vapor deposition mask as the case may be.

In the former case, a high selection ratio is required because the underlying transparent electrode 6 is not lost during overetching, but according to experiments by the present inventors, the thickness of the ITO electrode of 350 people was 0.2 μm. It has been confirmed that selective etching of the Ti film can be carried out effectively without causing thinning of the ITO electrode by etching using, for example, a photoresist as a mask. For example, 92 g of EDTA (ethylenediaminetetraacetic acid).

Before use, mix a mixture of 70 d of ammonia water (Jail, 4000 d of water) with H2O2 at a ratio of 2:1 to 300:1.
A selectivity ratio of . In the case of MO, selective etching can be performed using the same etching solution. In the case of Cr, a mixed solution of ceric ammonium nitrate, perchloric acid, and water may be used. AI can also be used if desired. Also, CF
If a CDE (chemical dry etching) method with 4:O□=1:2 is used, Mo, W, and MoSi can be etched with a high selectivity to ITO.

According to the bonding pad structure of this embodiment, the bonding wire 7 is connected to the metal film 5 or the metal film 8 with good bondability, and the transparent electrode 6 is extended from above the photoconductive film 3 to a thickness that is approximately equal to the metal film 5 or 8. The metal film 8 is formed so as to straddle the bonding pad lead-out portion made of the metal film 5, and further covers the top thereof with a metal film 8.

Therefore, the lead wire of the transparent electrode 6 is not disconnected at the pad lead-out portion, and the same effect as in the previous embodiment can be obtained.

Note that the present invention is not limited to the embodiments described above. In the examples, an example of an interline transfer type CCD was shown as a scanning section of a photoconductive film stacked solid-state image sensor, but it is of course applicable to MOS types and CPD types having storage diodes. be. In addition, although oxide films such as 5i02 are mainly illustrated as insulating films,
It may be a St, N4 film or a composite film thereof. Furthermore, although we have described the example of amorphous Si as the material for the photoelectric conversion section,
Not limited to this, Sb2S3,5e-As-Te, and CdSe are used as photoelectric conversion materials for image pickup tubes.

It is clear that CdZnTe can be used, and I nSb
Infrared photoelectric materials such as Pb5nTe and CdHgTe can also be used. Moreover, it goes without saying that the present invention can be applied not only to photoconductive films but also to photovoltaic films.

Furthermore, in the embodiment shown in FIG. 4, since the bonding wire is connected on the second metal film, it is also possible to use an insulating film instead of the first metal film. However, when forming by the lift-off method, it is not desirable to form the film by CVD or the like, which has good step coverage, and it is preferable to use a metal film that can be easily formed by vapor deposition or the like.

In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As described in detail above, according to the present invention, in the electrode for applying an external voltage to the transparent electrode of a stacked solid-state imaging device consisting of a solid-state imaging device chip and a photoconductive film, the transparent electrode is placed on the photoconductive film. Since it is formed across the bonding pad lead-out part made of a metal film with approximately the same thickness as this, there is no disconnection due to breakage, etc., and the electrical connection from the bonding wire to the transparent electrode is ensured. It is possible,
Moreover, reliability of electrical connection can be improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the structure of a bonding pad portion of a stacked solid-state imaging device according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view showing the manufacturing process of the above embodiment, and FIG. FIG. 4 is a cross-sectional view showing the main part structure of the second embodiment of the present invention, FIG. 5 is a cross-sectional view showing the main part structure of the third embodiment of the present invention, and FIG. 6 is a plan view showing the overall structure of a stacked solid-state imaging device, and FIGS. 7 and 8 are views showing the structure of a bonding pad portion of a conventional device. 1.11... Semiconductor substrate, 2... Field oxide film, 3... Photoconductive film, 4... Resist, 5... First metal film, 6... Transparent electrode, 7. ...Bonding wire, 8...Second metal film, 12...Vertical CCD. 13...Storage diode, 14...Channel stop section, 15...Poly 5ift! pole, 17...first electrode, 19...second electrode (pixel electrode)

Claims (5)

[Claims] (1) A solid-state image sensor chip in which a signal charge storage diode and a signal charge readout section are arranged and formed on a semiconductor substrate, and a pixel electrode electrically connected to the storage diode is formed on the top, and this solid-state image sensor chip. In a solid-state imaging device including a photoconductive film laminated thereon and a transparent electrode formed on the photoconductive film, a bonding pad section for applying an external voltage to the transparent electrode and its lead-out section are connected to a pixel. The transparent electrode is formed of a metal film that is in contact with the end portion of the photoconductive film on the region and has a surface height that is approximately the same as that of the photoconductive film, and the transparent electrode is formed to extend from above the photoconductive film to above the pad lead-out portion. A solid-state imaging device characterized in that a bonding wire is connected to a metal film of a bonding pad portion. (2) A solid-state image sensor chip in which a signal charge storage diode and a signal charge readout section are arranged and formed on a semiconductor substrate, and a pixel electrode electrically connected to the storage diode is formed on the top, and this solid-state image sensor chip. In a solid-state imaging device including a photoconductive film laminated thereon and a transparent electrode formed on the photoconductive film, a bonding pad section for applying an external voltage to the transparent electrode and its lead-out section are connected to a pixel. The first metal film is in contact with the end of the photoconductive film on the region and has a surface height substantially the same as that of the photoconductive film, and the transparent electrode extends from above the photoconductive film to above the pad lead-out portion. A second layer is formed on top of the photoconductive film section and a second pad extension section.
1. A solid-state imaging device, comprising: a first metal film formed thereon, and a bonding wire connected to the first metal film of a bonding pad portion. (3) The solid-state imaging device according to claim 2, wherein the second metal film is formed to include a bonding pad portion, and a bonding wire is connected to the second metal film of the bonding pad portion. . (4) The solid state according to claim 2 or 3, wherein the second metal film is formed at the same time as a light shielding metal film for blocking light from entering the image sensor chip. Imaging device. (5) A photoconductive film is laminated on a solid-state image sensor chip in which a signal charge storage diode and a signal charge readout section are arranged and formed on a semiconductor substrate, and a pixel electrode electrically connected to the storage diode is formed on the top. a step of forming a resist on the photoconductive film so as to cover the pixel region; a step of selectively etching the photoconductive film using the resist as a mask; a step of forming a film; a step of removing the metal film on the resist by removing the resist; a step of forming a transparent electrode partially extending to the metal film on the photoconductive film; A method for manufacturing a solid-state imaging device, comprising the step of connecting a bonding wire thereon.