JPH0221662B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a thin film photoelectric conversion element, and particularly to a method for manufacturing a Sanderch-type thin film photoelectric conversion element.

[Prior art]

BACKGROUND ART Recently, as solar cells, image sensors, and the like have become larger in area and longer in length, development of thin film photoelectric conversion elements using photoelectric conversion thin films such as amorphous silicon that can be deposited over large areas has been progressing.

In particular, in the case of an image sensor, by forming a sensor section with the same width as the document, one-to-one imaging becomes possible, the document and the sensor section can be brought into close contact, and a reduction optical system is not required. This makes it possible to easily downsize the document reading section.

In terms of structure, thin film photoelectric conversion elements have two major structures: a sandwich structure in which a photoconductor layer is sandwiched between a first electrode and a second electrode, and a planar structure in which a counter electrode is formed on the photoconductor layer. However, from the viewpoint of increasing the density of the sensor section, a sandwich structure is usually used.

By the way, a photoelectric conversion element with a sandwich structure is composed of, for example, a plurality of chromium electrodes (first electrode) and a transparent indium tin oxide (ITO) electrode (second electrode) formed on a ceramic substrate. It has a structure with an amorphous silicon layer sandwiched therebetween as a photoconductor layer. This amorphous silicon layer is deposited on the chromium electrode by glow discharge decomposition of monosilane gas (SiH ₄ ), etc., but the larger the area to be deposited, the more uniform it is over the entire surface. Forming an amorphous silicon layer is difficult and may be prone to pinholes. This is because, in addition to external causes such as dust in the manufacturing equipment adhering to the substrate surface, there are often internal causes related to the thin film growth mechanism.

Here, let us consider a change in the function of the element caused by the presence of a pinhole in the photoconductor layer in a photoelectric conversion element having a Sand-German trench structure.

First, if we consider the simplest equivalent circuit of a photoelectric conversion element with a Sanderarch structure, it will be as shown in FIG. The series resistance R _s is the sum of the contact resistance of the electrodes and the resistance of the external circuit, and the parallel resistance R _sh is the resistance of the photoconductor layer itself. Here, if there are no pinholes in the photoconductor layer and no shorts occur between the first and second electrodes, the parallel resistance R _sh is infinite (∞).
You can think about it. In Figure 1, I _L is a photocurrent proportional to the intensity of incident light, I _j is the current flowing through the diode, and I _sh
is the leakage current due to shot etc.

Here, if the current flowing through the external circuit is I, then I= _-IL +I _j +I _sh (1) holds true.

FIG. 2 shows a current-voltage characteristic curve (IV curve) for an ideal photoelectric conversion element without pinholes in the photoconductor layer, ie, when parallel resistance R _sh =∞ and R _s =0. Here, I ₁ is a characteristic curve when light is incident, and I ₂ is a characteristic curve when it is dark. Since R _sh = ∞, I _sh 0
When light is incident, the photocurrent −I _L is dominant, and in the dark, the current flowing through the diode I _j
becomes dominant.

Here, in the photoconductor layer, the first electrode and the second electrode
When a pinhole occurs in the area where the electrodes overlap, a short circuit occurs between the first electrode and the second electrode, and the ordinary resistance R _sh decreases significantly. Current in this case −
The voltage characteristic curve is shown in FIG. Here R _s =0
I'll leave it as that. I ₃ is the characteristic curve when light is incident, and I ₄ is the characteristic curve when it is dark.

In this case, for example, in the bias region where the diode current I _j is 0, the relational expression (1) becomes I - I _L + I _sh = - I _L + V/R _sh ...(2), and both in light irradiation and in darkness. As can be seen from the large dependence of the current I on the voltage V, the characteristics are significantly lower than those of the ideal photoelectric conversion element shown in FIG.

That is, in a solar cell, a forward bias region, that is, a V>0 region is used, but the conversion efficiency is lower in the case of a pinhole than in the case of an ideal photoelectric conversion element.

On the other hand, an image sensor uses a bias region, that is, a region where V<0, but the contrast ratio is significantly lower than that of an ideal photoelectric conversion element.

In this way, the occurrence of pinholes in the photoconductor layer of a photoelectric conversion element leads to a decrease in conversion efficiency and open-circuit voltage in solar cells, and a decrease in the ability to read optical images in image sensors. There are fatal defects such as, and a decline in manufacturing yield as an element has become a major problem.

[Purpose of the invention]

The present invention was made in view of the above circumstances, and
Even if a pinhole occurs in a photoconductor layer, the device characteristics are not significantly affected, and the purpose is to prevent a decrease in the manufacturing yield of photoelectric conversion devices.

[Structure of the invention]

In order to achieve the above object, the method for manufacturing a thin film photoelectric conversion element of the present invention includes depositing a photoconductor layer, that is, a photoelectric conversion film, on a first electrode made of a metal film formed on a substrate, and then forming a base layer. This method is characterized by including a step of anodizing the first electrode in the dark, so that even if a pinhole occurs in the photoelectric conversion film, the underlying layer exposed in the film by the pinhole is removed. One electrode is insulated, and short circuit between the second electrode and the first electrode formed on the photoelectric conversion film can be prevented.

〔Example〕

Hereinafter, a method for manufacturing a thin film photoelectric conversion element for an image sensor according to an embodiment of the present invention will be described with reference to the drawings.

First, on an insulating glass substrate 1 commercially available under the trade name Corning 7059#, a tantalum Ta film with a thickness of about 1000 Å was deposited by vapor deposition, and then by photolithography, as shown in Fig. 4. As shown, a tantalum electrode 2 is patterned as an underlying first electrode.

Next, as shown in FIG. 5, an amorphous hydrogenated silicon layer 3 as a photoelectric conversion film is deposited to a thickness of about 1 μm by glow discharge decomposition of monosilane gas (SiH ₄ ).

After that, using the tantalum electrode as an anode, the eighth
Anodic oxidation is performed in the dark using an anodizing apparatus as shown in the figure.

This anodizing device consists of a cathode 32 made of a platinum PT plate immersed in an electrolyte tank 31, and an anode 33.
A 5% ammonium tartrate aqueous solution is used as the electrolyte. As shown in FIG. 8, in the electrolyte tank 31 of this anodizing device,
The glass substrate 1 after forming the amorphous hydrogenated silicon layer is immersed, the tantalum electrode 2 is connected to the anode 33, and a formation voltage of 50 V is applied until the entire thickness of the tantalum electrode 2 is oxidized. At this time, care must be taken so that the portion of the tantalum electrode designed to be exposed from the amorphous silicon layer is above the liquid level.

As a result, the exposed portion of the tantalum electrode 2 due to the pinhole 4 generated during the deposition process of the amorphous hydrogenated silicon layer and its surroundings are oxidized, and as shown in FIG.
A Ta ₂ O ₅ coating 5 is formed.

Furthermore, after thorough cleaning, an indium tin oxide (ITO) electrode 6 as a second electrode was formed by reactive sputtering using a mixed gas of argon and oxygen _O2 , as shown in FIG. Film thickness
Deposit to a thickness of 700 Å.

In this way, the pinhole generation site in the photoelectric conversion film and the first electrode around it become an insulating film, so that the second electrode enters into the pinhole and the first electrode
Even when the electrode surface is reached, no shot occurs between the first electrode and the second electrode, making it possible to form a highly reliable image sensor.

In addition, in the anodic oxidation process, it is necessary to prevent the electrolyte from coming into contact with the first electrode exposed from the photoelectric conversion film, that is, the lead part of the first electrode. In addition to exposing the area on the surface, it is important to apply a method such as coating this area with a resist and then anodizing it.

In addition to the ammonium tartrate aqueous solution used in the example, the electrolyte used for anodization is
One must use something that does not dissolve the resulting coating, such as an aqueous ammonium borate solution.

Further, in the embodiment, the entire thickness of the first electrode was anodized, but it is not necessarily necessary to form an oxide film entirely, and only the vicinity of the surface may be formed as an oxide film. In any case, it is sufficient that the first electrode in contact with the pinhole part turns into a metal oxide and becomes an insulator, so that even if the second electrode is deposited thereon, a short circuit will not occur.

Furthermore, in addition to the tantalum used in the examples, the material of the first electrode as the base is aluminum, Al,
Any material may be used as long as an oxide film can be easily formed by anodic oxidation, such as titanium Ti, zirconium Zr, niobium Nb, and hafnium Hf.

In addition, the insulating photoelectric conversion film is not limited to the amorphous silicon hydride used in the examples, but may also include amorphous silicon germanium hydride, chalcogenide glasses such as Cerei Se-Telluride Te, cadmium sulfide Cds-CdTe telluride, etc. Needless to say, it is also fine. Incidentally, since these films exhibit conductivity when irradiated with light, it is important to carry out the anodization step in the dark in any case.

〔Effect of the invention〕

As described above, according to the method for manufacturing a thin film photoelectric conversion element of the present invention, after depositing a photoconductive photoelectric conversion film on the first electrode made of a metal film formed on a substrate, By anodizing the first electrode in the dark and turning the exposed part of the first electrode caused by pinholes in the photoelectric conversion thin film into an insulating oxide film, a film is then deposited on the photoelectric conversion film. Even if the second electrode enters the pinhole and reaches the first electrode surface, a short circuit will not occur between the first and second electrodes, resulting in a highly reliable thin film photoelectric conversion element. It becomes possible to form. Furthermore, since only the exposed portion of the first electrode in the photoelectric conversion thin film can be selectively oxidized, it is possible to minimize the reduction in the sensor area.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the equivalent circuit of a normal Sand-Deutsch photoelectric conversion element, FIG. 2 is a diagram showing the current-voltage characteristic curve of an ideal photoelectric conversion element, and FIG. 3 is a diagram showing the current-voltage characteristic curve of an ideal photoelectric conversion element.
FIGS. 4 to 7 are diagrams showing current-voltage characteristic curves of a photoelectric conversion element when a pinhole is generated in a portion where a first electrode and a second electrode overlap in a photoelectric conversion layer. FIG. 8 is a diagram showing an anodizing treatment apparatus used in the manufacturing process of a photoelectric conversion element according to an embodiment of the present invention. 1...Glass substrate, 2...Tantalum electrode, 3...
... Amorphous hydrogenated silicon layer, 4 ... Pinhole, 5 ... Tantalum oxide film, 6 ... Indium tin oxide electrode, 31 ... Electrolyte tank, 32 ... Cathode, 33 ... Anode, I ₁ , I ₃ ...I-V during light irradiation
Characteristic curves, I ₂ , I ₄ ... I-V characteristic curves in the dark.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a thin film photoelectric conversion element with a sandwich structure in which a photoconductive photoelectric conversion thin film is sandwiched between first and second electrodes, comprising: a first electrode made of a metal film on a substrate; a step of depositing a photoelectric conversion thin film on the upper layer of the first electrode, and anodic oxidation of the first electrode in the dark to eliminate pinholes in the photoelectric conversion thin film. Thin film photoelectric conversion characterized by comprising: an anodizing step of insulating the exposed portion of the first electrode caused by the above, and a second electrode forming step of forming a second electrode on the upper layer of the photoelectric conversion thin film. Method of manufacturing elements.