JPH0448780A - Wiring structure and image sensor - Google Patents

Abstract

PURPOSE:To lower the resistance at a connecting part and to lower an wiring resistance by a method wherein, at a wiring structure and at an image sensor provided with the structure, a high-melting-point metal is laid between an electrode composed mainly of a metal oxide and a wiring connected to the electrode. CONSTITUTION:A barrier metal layer 28 composed of molybdenum(Mo) is laid between a discrete electrode 24 and a signal deriving wiring 27. Instead of molybdenum(Mo), other high-melting-point metals (e.g. Ti, TiN, Ni, Cr, Ta, W) may be used for the barrier metal layer 28. A contact hole 26 is formed in an layer insulating film 25 formed by coating a polyimide; a resist is removed. A molybdenum(Mo) film is formed and patterned; the barrier metal film 28 is formed so as to cover the bottom part of each contact hole 26. Then, an aluminum(Al) film is formed and patterned; the signal deriving wiring 27 connected to each discrete electrode 24 is formed via the barrier metal layer 28. When the barrier metal layer 28 is laid, it is possible to prevent Al from being diffused and to ensure the good electrical connection of the discrete electrode 24 to the signal deriving wiring 27.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a wiring structure of a semiconductor element and an image sensor having the wiring structure, which is used in an image input section of a facsimile machine, an image scanner, or the like.

(Prior Art) An image sensor that reads an image in close contact with a document is composed of a light receiving element array in which a plurality of light receiving elements are arranged in a line, and a drive circuit that drives the light receiving element array. The charges generated in each light receiving element are extracted in time series to a single output line by a switch that sequentially selects each light receiving element.

For example, as shown in FIG. 4, the light-receiving element portion is made of a metal such as chromium on an insulating substrate 21, and has a common electrode 22. Amorphous semiconductor layer 23. Transparent conductive materials based on metal oxides (indium oxide,
It is made of tin (ITO) and is constructed by sequentially stacking individual electrodes 24 formed in a dot-separated manner in the front and back directions of the figure.
Each of the individual electrodes 24 is connected to a signal lead-out wiring 27 through a contact hole 26 formed in an interlayer insulating film 25 made of polyimide.

A bias voltage is applied to the common electrode 22,
When reflected light from the document surface enters from the upper side, a charge corresponding to the photocurrent is generated, and reading is performed from the signal extraction wiring 27.

(Problems to be Solved by the Invention) According to the structure of the light-receiving element described above, when aluminum (AI), which will become the signal lead-out wiring 27, is deposited on the interlayer insulating film 25 by sputtering or the like, metal oxide is removed by aluminum diffusion. Damage may be caused to the interface between the main individual electrode 24 (ITO) and aluminum (AI).

As a result, the ITO/At contact resistance value increases in the contact hole 26, causing disadvantages such as a decrease in the reading output of the image sensor, unevenness of output in each light receiving element, and deterioration of the reading speed, resulting in the performance of the image sensor. There was a problem of lowering the .

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a wiring structure that can ensure a good bonding state between an electrode mainly made of a metal oxide and a wiring connected to this electrode. do.

(Means for Solving the Problems) In order to solve the problems of the above-mentioned conventional example, the invention of claim 1 provides the following:
In the wiring structure, an electrode mainly made of a metal oxide, a barrier layer formed on the electrode and made of a high melting point metal,
It is characterized by having wiring formed on this barrier layer.

Moreover, the invention according to claim 2 is characterized in that the image sensor has the above-mentioned wiring structure.

(Function) According to the present invention, by interposing a high melting point metal between an electrode mainly composed of a metal oxide and a wiring connected to this electrode, the resistance of the connection part is lowered and the wiring resistance is reduced. Can be lowered.

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

FIG. 1 is a sectional view of a light receiving element portion of an image sensor, and parts having the same configuration as those in FIG. 4 are designated by the same reference numerals.

In this embodiment, a barrier metal layer 28 made of molybdenum (MO) is provided between the individual electrode 24 and the signal lead-out wiring 27.
is interposed. This barrier metal layer 28 is made of other high melting point metals (such as Ti, Ti, etc.) instead of molybdenum (MO).
TiN, Ni, Cr.

Ta, W) may also be used.

The barrier metal layer 28 is formed as follows.

That is, a band-shaped common electrode 22 made of metal such as chromium is formed on an insulating substrate 21. Amorphous semiconductor (a-5i),
Individual electrodes 24 and an amorphous semiconductor layer 23 made of a transparent conductive member (indium tin oxide (ITO)) and formed in a dot-separated manner in the front and back directions of the figure are successively formed,
Form a plurality of photodiodes. Then, polyimide is applied to the entire surface to form an interlayer insulating film 25, a resist is further applied and exposed to form a resist pattern, a contact hole 26 is formed in the interlayer insulating film 25 by an etching process, and the resist is removed. do.

Next, bombardment is applied to the entire surface of the insulating substrate 21 using N2 plasma. This is due to insufficient etching during etching by photolithography after depositing the polyimide interlayer insulating film 25, and non-uniform film thickness when coating the polyimide. This is to remove the polyimide residue generated during the process. Since bombardment using N and plasma is an inert gas, compared to O and plasma, bombardment does not affect the underlying surface due to oxidation, etc.
It is possible to prevent an increase in contact resistance without adversely affecting the surface of the TO (TO). Here, instead of N, Ar
An inert gas such as may also be used.

Next, a molybdenum (MO) film is deposited and patterned to form a barrier metal layer 28 so as to cover the bottom of each contact hole 26. Next, a film of aluminum (AI) is deposited and patterned to form signal lead-out wiring 27 connected to each individual electrode 24 via the barrier metal layer 28.

According to the above embodiment: 1. By interposing the barrier metal layer 28, it is possible to prevent AI diffusion and ensure good electrical connection between the individual electrodes 24 and the signal extraction wiring 27.

Further, in the above embodiments, the photodiode may have a pin structure other than a Schottky one.

In addition, other amorphous materials (a-SiC
, a-5iGe), etc. may also be used.

Further, the present invention can also be applied to semiconductor devices other than light-receiving devices (for example, switching devices).

Next, an example will be described in which the wiring structure as described above is applied to an image sensor formed by arranging a plurality of light receiving elements in a line in which a photodiode and a blocking diode are connected in series with opposite polarities.

Conventionally, this type of image sensor is shown in FIGS. 5 and 6, for example.
As shown in the figure, the photodiode P on the reading circuit side
D and the blocking diode BD on the driving circuit side are connected in series so that the polarities are opposite to each other to form one light receiving element, and a plurality of light receiving elements are arranged in a line shape on the insulating substrate 1 in the front and back directions of the figure. Composed of side by side. Each diode of this image sensor has a photoelectric conversion layer 3a, 3b sandwiched between a lower electrode 2 and an upper electrode 4, and one electrode of at least one diode is a transparent electrode (in FIG. 5, the lower electrode 2a of the photodiode, the In FIG. 6, it is formed by the entire lower electrode 2).

The equivalent circuit of the image sensor configured as described above is shown in FIG. 7, and charges are read out in the following manner.

That is, the photodiode FD is scanned by the shift register SR and signals are sequentially applied, and the photodiode PD is biased in the reverse direction.

Then, during one scan cycle, the photodiode PD is irradiated with light, and a charge corresponding to the amount of the irradiated light is discharged. Then, a reset signal (read pulse) is sequentially applied by the shift register SR, and each photodiode PD is recharged with a charge corresponding to the discharge amount, and at this time, the current flowing through the loading resistor R causes the output terminal T
The potential generated at out is read out as a signal (
JP-A-58-56363, JP-A-61-242068
(See Japanese Patent Publication No. 62-59469).

The reading speed of the image sensor is limited by two factors: the switching characteristics of the blocking diode BD, and a time constant determined by the photodiode capacitance, wiring resistance, and loading resistance.

That is, to explain with reference to one bit of the image sensor shown in FIG. 8, as described above, the photodiode P
When the capacitance Cp of D is recharged with a charge corresponding to the amount of discharge, the blocking diode BD acts as a switching element when the photodiode PD is scanned, so the V-1 characteristic of the blocking diode BD is shown in Fig. 9. A characteristic that rises rapidly as shown by the solid line is desirable.

Furthermore, when the photodiode PD is recharged with a charge corresponding to the amount of discharge, as shown in FIG. 10, if the capacitance Cp of the photodiode PD, the resistance RO of the blocking diode BD, and the wiring resistance Rs are , the photodiode PD is recharged depending on the time constant Cp X (R+Rg+Rs). Therefore, the time constant Cp
It is preferable that X (R+RD +R5) be smaller.

However, according to the image sensor disclosed in JP-A No. 58-56363, a high melting point metal with high specific resistance or a transparent electrode is used for the diode, or a transparent electrode of Nesa film and an A
Some products have a structure in which the contact resistance increases at the connection part with the wiring formed in the H, and the wiring resistance increases.
The drawback was that the reading speed was slow.

Also, JP-A No. 61-242068 and JP-A No. 62-5
The image sensor shown in No. 9469 (Figs. 5 and 6)
According to the figure), since the connection wiring 9 or the wiring 7a, 7b is formed directly on the upper electrodes 4a, 4b of each diode or on each diode, damage to the diode occurs when the connection wiring 9 and wiring 7 are formed. Moreover, when AI is used as the wiring material, the AI diffuses, deteriorating the switching characteristics of the diode and slowing down the reading speed. Furthermore, in this structure, in addition to the capacitance formed by the pair of electrodes of each diode, a capacitance is formed in the portion where the insulating layer 5 is sandwiched between the wiring portion and the lower electrode 2 of the diode, which has the disadvantage of slowing down the reading speed. there were.

In order to eliminate these drawbacks, an embodiment in which the above-mentioned wiring structure is applied to a series-connected photodiode and blocking diode image sensor will be described with reference to FIG.

This light receiving element includes an insulating substrate 1 made of glass or the like, lower electrodes 2a, 2b made of metal such as chromium (C''),
a-3i; photoelectric conversion layers 3a, 3b such as H; upper electrodes 4a, 4 made of a transparent material such as indium tin oxide;
b. A photodiode PD on the reading circuit side and a blocking diode BD on the drive circuit side, which are formed by sequentially laminating and patterning an insulating layer 5 such as polyimide on the insulating substrate 1, and these photodiodes PD and blocking diode BD. Covering insulating layer 5 and this insulating layer 5
contact holes 6a, 6b formed in the contact holes 6a, 6b, and a lead wiring 7a connected to the upper electrodes 4a, 4b of the photodiode FD and blocking diode BD via the barrier metal layers 8a, 8b through the contact holes 6a, 6b; 7b. A light receiving area A is formed above the photodiode PD so that light is irradiated from above, and the upper part of the blocking diode BD is shielded from light by being covered with the lead wiring 7b.

Barrier metal layers 8a and 8b are lead wiring 7a.

It is formed in the same pattern shape as 7b, and is made of a high melting point metal (for example, Ti, TiN, Ni, Cr, Ta, M.

W) or an alloy thereof.

The contact portion (contact hole 6
b) is formed in a portion other than on the lower electrode 2b.

In other words, the structure is such that the lower electrode 2b does not exist below the contact portion of the blocking diode BD.

Further, the lower electrode 2a of the photodiode PD is formed to have the same size as the area of the light receiving area.

That is, the configuration is such that the lower electrode 2a does not exist below the portion where the upper electrode 4a of the photodiode PD and the lead wire 7a are connected.

Next, the manufacturing process of the above-mentioned light receiving element is shown in Fig.
This will be explained with reference to a) to (e).

A metal such as chromium (Cr), titanium (Ti), tantalum (Ta), etc. is deposited on the insulating substrate 1 by vapor deposition or sputtering.
Deposit a film to a thickness of about 8.

The deposited metal is patterned by photolithography to form lower electrodes 2a of the photodiode PD and blocking diode BD.

2b is formed. The lower electrode 2a is sized to have the same area as the light-receiving area of the photodiode PD, and the lower electrode 2b is made as small as possible to function as a capacitor except for the electrode size that provides enough forward current to drive the sensor. It is configured to reduce the capacity and time constant.

Next, a photoelectric conversion film 3' (a-5i and n-type or p-type doped a-St) is deposited over the entire surface by P-CVD. The photoelectric conversion 13' is pinl pi(i
p), in (ni), or i type, and the p layer is diborane (B,
The i-layer is made by doping 1% of silane (SiH,) gas, and the i-layer is made of phosphine (SiH,) gas in 100% silane (SiH,) gas.
It is manufactured by doping 1% of PHs) gas. The film deposition temperature is 200 to 250°C, and the film thickness is 100 OA or less for the p layer and n layer, and 0.5 OA for the i layer.
~2 μm.

After forming the photoelectric conversion film 3', indium tin oxide (
ITO) 4' is deposited on the entire surface using a sputtering method to a thickness of about 80 OA.

Photoelectric conversion film 3' and indium tin oxide (ITo) 4
' The photoelectric conversion layers 3a, 3b and the upper electrode 4a are formed by patterning by photolithography.

4b and has a sandwich structure photodiode F.
D and a blocking diode BD are formed. For the photoelectric conversion film and indium tin oxide (Natsu To), after forming a resist, first indium tin oxide (ITO) was mixed with a mixed acid (HCl:HNO,:H2O-1:
0. g: g) Wet etching with a solution, followed by dry etching of the photoelectric conversion film in an atmosphere of gases such as CF, SF, . . . C, CIF, etc. alone or in combination.

Next, polyimide (Hitachi Chemical's PIX-1400 or PIX-8803, Toshi's Photonice, etc.) is applied to a film thickness of about 1 μm, and contact holes 6a, 6 are formed at desired locations.
form b. The contact holes 6a and 6b are formed at the lower electrode 2. for both the photodiode PD and the blocking diode BD. Photoelectric conversion layer 3. It is fabricated on a portion of the upper electrode 4 other than the sandwich structure. This prevents diode deterioration (leakage) from affecting the diode portion even if the wiring material metal diffuses into the transparent electrode 4 made of ITO by sputtering or vapor deposition during wiring layer deposition, which will be described later. This is to prevent the current from increasing. Further, in the above embodiment, the photoelectric conversion layer 3a,
The doped layer 3b (not shown) is the photoelectric conversion layer 3a, 3
Although it was formed in the same pattern as the a-5i layer of b, if the doped layer (p layer or n layer) on the metal electrodes 2a, 2b side of the photoelectric conversion layers 3a, 3b is formed only on the metal electrodes 2a, 2b, Furthermore, deterioration of the diode can be prevented and the capacitance can be reduced.

Next, barrier metals (Cr, Ta, Ti) are used as wiring materials.
, TiN, Ni, Mo, or an alloy thereof) to a thickness of about 500 A by sputtering or vapor deposition. The barrier metal is made of ITO, which becomes the upper electrode 4, and wiring material (AI).
) is provided to lower the contact resistance with the

After depositing the barrier metal film, a wiring material (AI) is deposited by sputtering or vapor deposition, and a resist pattern (not shown) is formed using a single mask by photolithography.
Al) is etched with phosphoric acid, and the barrier metal is further etched to form lead wirings 7a, 7b and barrier metal layers 8a, 8b. At this time, if the barrier metal is made of molybdenum (MO), the same etching solution as that for the wiring material (AI) can be used, which simplifies the process.

In this embodiment, the blocking diode BD has a structure in which its upper part is shielded from light, but the blocking diode may have the function of a photodiode without shielding its upper part from light. That is, if the diode on the drive circuit side has the function of a blocking diode, one or both of the two diodes may have the function of a photodiode.

Furthermore, although the embodiment has been described using a one-line image sensor, a two-dimensional image sensor can be obtained by arranging the light receiving elements two-dimensionally.

Further, in the embodiment, an image sensor having a structure in which light enters from the top has been described, but an image sensor having a structure in which light enters from the bottom may be used, as in the conventional examples shown in FIGS. 5 and 6. In this case, the insulating substrate 1 is formed of a transparent material, and the lower electrode 2a is formed of a transparent material.

2b is a transparent electrode, and as shown in FIG. 6 of the conventional example, a film having the same effect as the light shielding film 10 may be formed below the blocking diode BD.

In addition, as shown in FIG. 11, an integrator S is added to the reading circuit.
When using the photodiode section, the capacitance of the input section can be reduced if the capacitance of the photodiode section is reduced, so the noise generated by the integrator S can be reduced and the S/N ratio can be improved.

According to this embodiment, by interposing a high melting point metal or an alloy thereof between the wiring and the upper electrode, it is possible to lower the resistance of the connection part and lower the wiring resistance.
It is possible to reduce the time constant of sensor signal reading and improve the reading speed.

In addition, since the contact part is formed in a part that does not face the lower electrode, it is possible to prevent deterioration of the diode due to diffusion of the wiring material that occurs when forming the wiring and damage during film formation, and improve the V-I characteristics of the diode. It is possible to improve the reading speed of the sensor.

Further, since unnecessary electrode portions below the wiring can be removed, the capacitance of the diode can be reduced, and the time constant for reading the signal of the sensor can be reduced, thereby improving the reading speed.

(Effects of the Invention) According to the wiring structure of claim 1, by interposing a high melting point metal between the wiring and the electrode, the resistance of the connection part can be lowered and the wiring resistance can be lowered. It is possible to ensure a bond with good characteristics between the electrode and the electrode.

According to the image sensor of claim 2, by lowering the wiring resistance, it is possible to prevent a decrease in the reading output of the image sensor, unevenness of output in each light receiving element, deterioration of the reading speed, etc., and improve the performance of the image sensor. You can improve your performance.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional explanatory diagram of a light-receiving element of an image sensor according to an embodiment of the present invention, and Fig. 2 shows an image sensor in which the present invention is applied to an image sensor consisting of a light-receiving element in which a photodiode and a blocking diode are connected in series with opposite polarities. FIGS. 3(a) to 3(e) are explanatory diagrams of the manufacturing process of the light receiving element of this embodiment, and FIGS. 4 to 6 are cross-sectional views of the light receiving element of the conventional image sensor. 7 is an equivalent circuit diagram of an image sensor, FIG. 8 is an equivalent circuit diagram of a 1-bit light-receiving element, FIG. 9 is a diagram showing VI characteristics of a diode, and FIG. 10 is an equivalent circuit diagram of a 1-bit light-receiving element. Equivalent Circuit Diagram FIG. 11 is an equivalent circuit diagram of an image sensor having an integrator in the reading circuit. 1...Insulating substrates 2a, 2b...Lower electrodes 3a, 3b...Photoelectric conversion layers 4a, 4b...Upper electrode 5... Insulating layers 6a, 6b...Contact holes 7a, 7b...Output wiring 8...Barrier metal layer FD...Photodiode BD...Blocking Diode A...
- Light receiving area 21...Insulating substrate 22...Common electrode 23...Semiconductor layer 24...Individual electrode 25...Interlayer insulating film 26 ... Contact hole 27 ... Signal lead-out wiring 28 ... Barrier metal layer Fig. 1 Fig. 2 BD' ゝ-2 Fig. 3 Fig. 8 Fig. 9 Fig. 5 IGHT Figure 6 Figure 11

Claims (2)

[Claims] (1) A wiring structure including an electrode mainly made of a metal oxide, a barrier layer formed on the electrode and made of a high-melting point metal, and a wiring formed on the barrier layer. (2) An image sensor having the wiring structure according to claim 1.