JPH0690015A - Photodiode and its manufacture - Google Patents

Abstract

PURPOSE:To reduce the etched amount of a bottom electrode when a photoconductive semiconductor layer is dry-etched CONSTITUTION:A photoconductive semiconductor layer 4 and a top electrode 5 are sequentially laminated on a bottom electrode 2 formed on an insulation substrate 1, thus a photodiode PD is formed. On the bottom electrode 2, an etching-resistant film 3 having a stringent etching selectivity against the semiconductor layer 4 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodiode having a lower electrode, a photoconductive semiconductor layer, and an upper electrode, which are sequentially laminated on a surface of an insulating substrate, and a manufacturing method thereof. The photodiode is used in an image sensor (so-called hybrid image sensor) or the like in which the photodiode and a thin film transistor forming a received light amount detection circuit thereof are arranged on the insulating substrate.

[0002]

2. Description of the Related Art Recently, an image sensor of the above type is a C
It has been attracting attention as an image reading device such as a FAX instead of a CD. In addition, the driving circuit unit is also a thin film transistor (TF
T), among others, high performance and low cost can be achieved by integrating with poly-Si TFT (polysilicon thin film transistor). "Development of TFT drive perfect contact type image sensor" (1990, 21st Image Optical Conference) , P11, Itagaki, etc.).

FIG. 6 is a schematic explanatory view of the structure of a conventional image sensor Im, showing a thin film transistor TFT and a photodiode PD formed on an insulating substrate. In FIG. 6, source / drain electrodes 02 made of an amorphous silicon material are formed on an insulating substrate 01. A gate insulating film (SiO2) is formed on the source / drain electrodes 02.
A film) 03 is formed, and a gate electrode (poly-Si) 04 is formed on the gate insulating film 03. The code 0
A thin film transistor TFT is constituted by the elements indicated by 2 to 04. A lower interlayer insulating film (SiO2) 05 is formed on the gate electrode 04, and the lower interlayer insulating film 0 is formed.
A photodiode (sensor portion) PD that detects the amount of received light is formed on the surface 5. The photodiode PD
Is composed of a lower electrode (base electrode) 06, a semiconductor layer (a-Si sensor layer) 07, a transparent electrode (ITO) 08, an upper interlayer insulating film 09, and the like. Thin film transistor TFT
And contact holes B1 and B2 communicating with the respective electrodes 02 and 04 of the TFT are formed in the lower interlayer insulating film 05 and the upper interlayer insulating film 09 separating the photodiode PD. A contact hole B3 communicating with the transparent electrode 08 is formed in the upper interlayer insulating film 09. Each of the contact holes B1, B
The electrodes 02 and 04 of the TFT communicating with 2 and B3 and the transparent electrode 08 of the photodiode PD are connected to the wiring 010 of Al (aluminum). The wiring 010
Is covered with an element protection film (polyimide film) 011. In the image sensor Im shown in FIG. 6, the amount of light received by each photodiode PD is determined by the thin film transistor TFT.
Is detected using.

Regarding the semiconductor layer of the light receiving element (photodiode) of the image sensor Im or the like, in order to obtain the maximum photoelectric conversion efficiency, the absorption coefficient is converted into 5000.
It is known that a film thickness of about -15000 Å (10 −8 meters) is required.
Further, it is necessary to pattern this semiconductor layer by etching in order to isolate elements for each bit, but in the conventional patterning by wet etching (that is, W / E method), etching proceeds isotropically. Therefore, the side etch amount is at least about the thickness of the layer to be etched. FIG. 7 is an explanatory diagram when the semiconductor layer 07 formed on the lower electrode 06 using the resist pattern RP is etched by the W / E method. In the case of the semiconductor layer of the photodiode (light receiving element) PD, that is, the photoconductive semiconductor layer 07, the side etching amount is large because the film thickness is relatively large (see FIG. 7). Further, in wet etching, since etching is performed in a solution, it takes several tens of seconds to wash out the solution when the etching is finished, and it is difficult to control the etching amount. For this reason, the variation in the side etch amount tends to increase. In addition, a photodiode (light receiving element)
Patterning by wet etching has a limit because it is necessary to improve the processing accuracy as the density of PD becomes higher.

Therefore, as an etching method instead of wet etching, dry etching (Dry etch) is performed.
ing, or D / E method) has been used. FIG. 8 is an explanatory diagram when the semiconductor layer 07 formed on the lower electrode 06 using the resist pattern R is etched by the D / E method. The features of dry etching are that the controllability of etching is higher than that of wet etching and that the processed shape can be controlled. The reason for the high controllability of etching is that dry etching uses gas to perform etching, so that the etching can be instantaneously ended by interrupting the discharge. Further, the reason why the controllability of the processed shape is high is that the processed shape can be changed by the combination of the reaction by the neutral molecules that enter isotropically and the reaction by the ions that enter in the direction of the electric field. Therefore, compared with the above-mentioned wet etching, dry etching has a feature that a side etching amount is small and a processing shape whose processing dimension is faithful to a mask can be obtained.
(For dry etching, Yoshifumi Kawamoto, et al. "MOS
LSI Manufacturing Technology ”, p163, Nikkei McGraw-Hill, 1
There are many documents such as 985)

[Problems to be Solved by the Invention]

However, in dry etching, since accelerated ions are used, there is a tendency that the etching selectivity to the underlying material is lowered due to a physical sputtering phenomenon. For example, when the etching rate of dry etching has a distribution depending on the position in the substrate, the etching is first performed between the time when the etching is first finished at a position in the substrate and the time when the etching is finished at the slowest position. The underlying material is also etched to some extent at the finished position. 9 to 12 show the semiconductor layer 07 on the lower electrode (base material) 06 provided on the insulating substrate 01.
FIG. 6 is a diagram showing an example of an etching process of the semiconductor layer 07 when the etching rate has a distribution depending on the position in the substrate when the film is etched by dry etching. In the examples shown in these figures, when the semiconductor layer 07 is dry-etched, the etching rate at both left and right ends in the figure is higher than that at the central part. As can be seen from FIGS. 9 to 12, when the ratio of the etching rate of the material to be etched (semiconductor layer) 07 to the etching rate of the underlying material (lower electrode) 06 (etching selection ratio) is low, the underlying material (lower electrode) 06 However, there is a problem in that in the worst case, the underlying film is entirely etched depending on the location. As described above, the etching amount of the lower electrode (base material) tends to increase due to the low etching selection ratio, the increase in etching time due to the low etching rate or the increase in film thickness, and the non-uniform etching rate distribution in the substrate. Indicates. It is known that the etching selection ratio can be improved by optimizing the type of etching gas and its composition ratio, but there is a limit depending on the material. In view of the above problems, the present invention provides the following (A1
Subject to the items described in 1). (A11) To reduce the etching amount of the lower electrode (base material) when dry etching the photoconductive semiconductor layer.

[0007]

The present invention devised to solve the above problems will now be described. The elements of the present invention are to facilitate correspondence with the elements of the embodiments described later. , The reference numerals of the elements in the embodiments are enclosed in parentheses. The reason why the present invention is described in association with the reference numerals of the embodiments described later is to facilitate the understanding of the present invention.
It is not intended to limit the scope of the invention to the examples.

In order to solve the above problems, the first aspect of the present application
The photodiode (PD) of the invention is constructed by sequentially stacking a photoconductive semiconductor layer (4) and an upper electrode (5) on a lower electrode (2) formed on the surface of an insulating substrate (1). A photodiode is provided with the following requirement (A1): (A1) An etching resistant thin film (3) having a high etching selection ratio with respect to the semiconductor layer (4) on the upper surface of the lower electrode (2). ) Was formed.

The photodiode (PD) of the second invention of the present application is the photodiode (P) of the first invention.
D) is provided with the following requirement (A2): (A2) The etching resistant thin film (3) is an oxide film of the lower electrode material, a nitride film, or a thin metal film doped with impurities. Be one of the above.

Further, in the method for manufacturing a photodiode of the third invention of the present application, the lower electrode (2), the photoconductive semiconductor layer (4) and the upper electrode (5) are sequentially formed on the surface of the insulating substrate (1). In a method of manufacturing a photodiode (PD) configured by stacking, the following requirements (A3),
(A3), characterized by comprising (A4), after forming the lower electrode (2) on the surface of the insulating substrate (1), an etching resistant thin film forming step of forming an etching resistant thin film (3) on the surface (A4) A semiconductor layer dry etching step of forming a photoconductive semiconductor layer 4 on the surface of the insulating substrate 1 on which the etching resistant thin film 3 is formed, and then patterning the semiconductor layer 4 by dry etching.

The method for manufacturing a photodiode according to the fourth invention of the present application is characterized in that, in the method for manufacturing a photodiode according to the third invention, the following requirement (A5) is provided: (A5) In the etching resistant thin film forming step, the surface of the lower electrode (2) formed on the surface of the insulating substrate (1) is exposed to oxygen plasma or nitrogen plasma to form a thin oxide film or a nitride film (3) on the surface of the lower electrode (2). To form.

Further, a method for manufacturing a photodiode according to a fifth invention of the present application is characterized in that, in the method for manufacturing a photodiode according to the third invention, the following requirement (A6) is provided: (A6) Forming a thin oxide film on the surface of the lower electrode (2) by heat treating the surface of the lower electrode (2) formed on the surface of the insulating substrate (1) in the etching resistant thin film forming step.

The method for manufacturing a photodiode of the sixth invention of the present application is characterized in that, in the method for manufacturing a photodiode of the third invention, the following requirement (A7) is provided: (A7) In the etching resistant thin film forming step, the surface of the lower electrode (2) formed on the surface of the insulating substrate (1) is irradiated with ultraviolet rays in an oxygen atmosphere to form a thin oxide film (3) on the surface of the lower electrode (2). thing.

The method for manufacturing a photodiode of the seventh invention of the present application is characterized in that, in the method for manufacturing a photodiode of the third invention, the following requirement (A8) is provided: (A8) Forming a thin metal film (3) doped with impurities on the surface of the lower electrode (2) formed on the surface of the insulating substrate (1) in the etching resistant thin film forming step.

[0015]

Next, the operation of the present invention having the above features will be described. In the photodiode (PD) of the first invention of the present application having the above-mentioned characteristics, the etching resistant thin film (3) having a high etching selection ratio with respect to the semiconductor layer (4) is formed on the upper surface of the lower electrode 2. Therefore, when the photoconductive semiconductor layer (4) formed on the lower electrode (2) on the surface of the insulating substrate (1) is dry-etched, the etching amount of the lower electrode (2) is reduced. Therefore, the malfunction of the photodiode (PD) due to the damage of the lower electrode (2) is reduced.

In the photodiode (PD) of the second invention of the present application and the photodiode (PD) of the first invention having the above-mentioned characteristics, the etching resistant thin film (3) is provided.
Is formed of one of the oxide film of the lower electrode material, the nitride film, or a thin metal film doped with impurities. Such an etching resistant thin film can be easily formed.

In the method for manufacturing a photodiode of the third invention of the present application having the above-mentioned features, the lower electrode (2) is formed on the surface of the insulating substrate (1), and then the etching resistant thin film (3) is formed. An etching resistant thin film (3) is formed on the surface of the lower electrode (2). Then, a photoconductive semiconductor layer (4) is deposited on the surface of the insulating substrate (1) on which the etching resistant thin film (3) is formed. Then, in the semiconductor layer dry etching step, the semiconductor layer (4)
Is patterned by dry etching. In this semiconductor layer dry etching process, the lower electrode (2) under the semiconductor layer (4) that is etched faster is also etched due to variations in the etching rate of the semiconductor layer (4). Since the etching resistant thin film (3) is formed on the surface of (1), a large amount of the lower electrode (2) will not be etched and defects will not occur in the lower electrode (2).

In the method of manufacturing a photodiode of the fourth invention of the present application having the above-mentioned characteristics, the surface of the lower electrode (2) formed on the surface of the insulating substrate (1) is exposed to oxygen plasma or nitrogen plasma. Since the thin oxide film or the nitride film is formed on the surface of the electrode (2), the etching resistant thin film (3) can be easily formed on the surface of the lower electrode (2).

In the method for manufacturing a photodiode of the fifth invention of the present application having the above-mentioned characteristics, the lower electrode (2) formed on the surface of the insulating substrate (1) is heat-treated in an oxygen atmosphere to form the lower portion of the lower electrode. Since the thin oxide film is formed on the surface of the electrode (2), the etching resistant thin film (3) can be easily formed on the surface of the lower electrode (2).

In the method for manufacturing a photodiode of the sixth invention of the present application having the above-mentioned characteristics, the surface of the lower electrode (2) formed on the surface of the insulating substrate (1) is irradiated with ultraviolet rays in an oxygen atmosphere. Since the thin oxide film (3) is formed on the surface of the lower electrode (2), the etching resistant thin film (3) can be easily formed on the surface of the lower electrode (2).

The method for manufacturing a photodiode of the seventh invention of the present application having the above-mentioned characteristics is a thin metal film (3) in which impurities are doped on the surface of the lower electrode (2) formed on the surface of the insulating substrate (1). To form. The thin metal film (etching-resistant thin film) (3) doped with such impurities can react with the lower electrode material before the completion of the lower electrode film forming step when forming the lower electrode (2) by the thin film technique. It can be easily formed by supplying various gases.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the photodiode PD of the present invention. Such a photodiode PD is used as a sensor substrate (glass substrate) 1 as a part of an image sensor.
Formed on. On the upper surface of the glass substrate 1, the lower electrode 2 as a base layer is about 2000 angstroms (2000 ×
10 −8th meter). In this embodiment, the case where Ti is used as the material of the lower electrode 2 will be described. An etching resistant thin film 3 and a photoconductive semiconductor layer 4 are sequentially formed on the upper surface of the lower electrode 2.
The etching resistant thin film 3 is formed of a material having a lower etching rate than the etching rate of the lower electrode 2 that is etched during the etching process of the semiconductor layer 4. Therefore, by forming the etching resistant thin film 3, the ratio of the etching rate of the material to be etched (semiconductor layer 4) to the etching rate of the base material (etching selection ratio) becomes high.

A photoconductive semiconductor layer 4 is deposited on the upper surface of the lower electrode 2 through the etching resistant thin film 3. As the semiconductor layer 4 of this embodiment, a-Si: H is adopted. A transparent indium tin oxide (ITO) layer serving as the upper electrode 5 is deposited on the upper surface of the semiconductor layer 4.
An interlayer insulating film 6 having a contact hole 6a is formed on the upper surface of the upper electrode 5. As the interlayer insulating film 6, for example, polyimide is used. The lead wiring 7 is formed on the upper surface of the interlayer insulating film 6. The lead wire 7 is
The interlayer insulating film 6 is connected to the surface of the upper electrode 5 through the contact hole 6a.

The lower electrode 2, the etching resistant thin film 3, the semiconductor layer 4, the upper electrode 5, which are formed on the glass substrate 1,
From the interlayer insulating film 6 and the lead-out wiring 7, the photodiode P
D is configured. An image sensor (not shown) is formed by forming a large number of the photodiode PD and a conventional thin film transistor (not shown) on an insulating substrate.

Next, a manufacturing method of one embodiment of the photodiode PD having the above-mentioned structure will be described. 2-5,
FIG. 3 is an explanatory view of the manufacturing process of the photodiode PD shown in FIG. 1 and a sectional view of relevant parts. First, the glass substrate 1
Ti, which is the material of the lower electrode 2, is deposited on the upper surface of the substrate by DC sputtering to about 2000 angstroms (2000 × 1).
0-8th meter) (see FIG. 2). Next, the Ti surface of the lower electrode 2 is exposed to 02 plasma or N2 plasma to form a thin oxide film or thin vaginalizing film (the above-mentioned etching resistant thin film having a low etching rate) 3 (see FIG. 3). The conditions for forming the etching resistant thin film 3 are as follows: oxygen or nitrogen gas flow rate 5 to 200 sccm, pressure 0.01 to.
1 Torr, RF power-0.1 to 10 mW / square mm
(That is, square millimeters).

As a method of forming the etching resistant thin film 3, instead of the above method, the following (A21) to (A2)
It is possible to adopt the method of 3). (A21) A method of forming a thin oxide film or thin vaginalized film by heating the Ti surface of the lower electrode 2 to 100 to 300 ° C. in an atmosphere containing oxygen or nitrogen. (A22) The Ti surface of the lower electrode 2 is irradiated with ultraviolet rays at an intensity of 0.1 to 10 mW / square mm for 1 to 300 minutes in an atmosphere containing oxygen or nitrogen to form a thin oxide film or a thin vaginalized film. Method. (A23) After forming a Ti layer to a predetermined thickness, further T
When i is sputtered, an oxygen gas, a nitrogen gas, or a gas capable of reacting with Ti is supplied to the chamber in an amount of 1 to 200 sccm.
A method of depositing a very thin Ti layer mixed as an impurity on the Ti layer. In this method, a thin oxide film, a thin vaginalization film, or a thin Ti layer having a different composition is used as the Ti of the lower electrode 2.
The etching resistant thin film 3 is formed on the upper surface or the surface layer of the layer.

Next, on the etching resistant thin film 3,
Non-doped a-Si: H (i layer) or p-type, n-type a-Si: H laminated a-Si: H by p-CVD
(Pin layer or pi layer, in layer) 5000-150
The semiconductor layer 4 is formed by depositing 00 angstrom, and the indium tin oxide (ITO) film that is the transparent conductive film, that is, the upper electrode 5 is deposited by DC magnetron sputtering to about 500 angstrom (see FIG. 4).

Further, a resist pattern 8 is formed on the upper electrode 5 by photolithography, as shown in FIG. Then, the upper electrode (ITO) 5 is first etched with a hydrochloric acid aqueous solution. Further, the semiconductor layer 4 is etched by the D / E (dry etching) method using the same resist pattern RP. The conditions at this time are as follows: F-based gas such as SF6 and CF4 and Cl-F-based gas such as C2 ClF5, Cl-based gas such as Cl2 and CCl4, He, Ne, Ar, H2, N2, O2 and CH4. , C2
Using gas such as H6 and NH3, each gas flow rate 1
Etching is performed at .about.500 sccm, pressure of 0.01 to 1 Torr, and RF power of 0.1 to 10 mW / square mm. At this time, since the layer having a low etching rate, that is, the etching resistant thin film 3 is already formed at the interface between the semiconductor layer 4 and the lower electrode 2, the selection ratio is substantially high, and the lower electrode (Ti) 2 The amount of film loss is minimized. That is, the etching amount of the lower electrode 2 is minimized.

Then, the resist pattern 8 is peeled off,
By forming the interlayer insulating film 6 and the Al lead-out wiring 7 shown in FIG. 1, the photodiode PD (light receiving element) shown in FIG. 1 can be formed. In the above-described embodiment, the etching resistant thin film 3 is formed of the oxide film, the vaginated film, and the impurity film using the same material Ti as that of the lower electrode 2, so that it is easy to manufacture. Further, a plasma method, a heating method, an ultraviolet ray irradiation method, or an impurity injection method can be adopted as the manufacturing method.

Although the embodiments of the photodiode and the method of manufacturing the same according to the present invention have been described in detail above, the present invention is not limited to the above embodiments, and deviates from the invention described in the claims. It is possible to make various design changes without doing so. For example, the lead wiring 10 is made of Al.
Instead of using only one, it is also possible to have a bilayer of Al / Mo.

[0031]

The present invention described above has the following effects (A31). (A31) Since the etching resistant thin film having a high etching selection ratio to the semiconductor layer is formed on the upper surface of the lower electrode, the photoconductive semiconductor layer formed on the lower electrode on the surface of the insulating substrate is dry-etched. At this time, even if the etching rate of the semiconductor layer varies, the etching amount of the lower electrode decreases. Therefore, the malfunction of the photodiode due to the damage of the lower electrode is reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a photodiode according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a manufacturing process of the embodiment, which is a cross-sectional view.

FIG. 3 is an explanatory diagram of a process after the process of FIG.

FIG. 4 is an explanatory diagram of a process after the process of FIG.

FIG. 5 is an explanatory diagram of a process after the process of FIG.

FIG. 6 is a schematic explanatory diagram of a configuration of a conventional image sensor Im.

FIG. 7 is an explanatory diagram of a side etching amount at the time of wet etching.

FIG. 8 is an explanatory diagram of an etching state during dry etching, which is a cross-sectional view.

FIG. 9 is an explanatory diagram of an etching state, which is a cross-sectional view.

10 is an explanatory diagram of an etching state after FIG. 9 and is a sectional view.

FIG. 11 is an explanatory view of an etching state after FIG. 10 and is a sectional view.

FIG. 12 is an explanatory view of the etching state after FIG. 11 and is a sectional view.

[Explanation of symbols]

PD ... Photodiode, 1 ... Insulating substrate Glass substrate, 2 ... Lower electrode, 3 ... Etching resistant thin film, 4 ... Semiconductor layer, 5 ... Upper electrode, 6 ... Interlayer insulating film , 7 ... Lead wiring.

Claims (7)

[Claims] 1. A photodiode comprising a photoconductive semiconductor layer and an upper electrode sequentially stacked on a lower electrode formed on the surface of an insulating substrate, wherein:
1. A photodiode characterized by comprising 1), (A1) An etching resistant thin film having a high etching selection ratio with respect to the semiconductor layer is formed on the upper surface of the lower electrode. 2. The photodiode according to claim 1, wherein the following requirements (A2) are satisfied: (A2) The etching resistant thin film contains an oxide film, a nitride film, or impurities of the lower electrode material. One of the doped thin metal films. 3. A method of manufacturing a photodiode comprising a lower electrode, a photoconductive semiconductor layer and an upper electrode, which are sequentially laminated on the surface of an insulating substrate.
3) and (A4) are provided, a method of manufacturing a photodiode, (A3) An etching resistant thin film forming step of forming an etching resistant thin film on the surface after forming a lower electrode on the surface of the insulating substrate, (A4) A semiconductor layer dry etching step of depositing a photoconductive semiconductor layer on the surface of the insulating substrate on which the etching resistant thin film is formed, and then patterning the semiconductor layer by dry etching. 4. The method for manufacturing a photodiode according to claim 3, wherein the following requirement (A5) is satisfied: (A5) In the etching resistant thin film forming step, a lower electrode formed on the surface of the insulating substrate. Exposing the surface to oxygen plasma or nitrogen plasma to form a thin oxide film or a nitride film on the lower electrode surface. 5. The method for manufacturing a photodiode according to claim 3, characterized in that the following requirement (A6) is satisfied: (A6) In the etching resistant thin film forming step, a lower electrode formed on the surface of the insulating substrate. Forming a thin oxide film on the surface of the lower electrode by heat treating the surface in an oxygen atmosphere. 6. The method for manufacturing a photodiode according to claim 3, further comprising the following requirement (A7): (A7) The lower electrode formed on the surface of the insulating substrate in the etching resistant thin film forming step. Forming a thin oxide film on the surface of the lower electrode by irradiating the surface with ultraviolet light in an oxygen atmosphere. 7. The method for manufacturing a photodiode according to claim 3, wherein the following requirement (A8) is satisfied: (A8) In the etching resistant thin film forming step, the lower electrode formed on the surface of the insulating substrate. To form a thin metal film doped with impurities on the surface.