JP2603285B2 - Method for manufacturing photoconductive image sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a photoconductive image sensor using a photoconductor that generates a photocurrent by light irradiation as a light receiving element.

[Conventional technology]

A photoconductive image sensor is widely used as a one-dimensional or two-dimensional image input device such as a facsimile or an image scanner, and a light-receiving unit that detects the presence or absence or intensity of light and a reading device that reads a signal detected by the light-receiving unit. And a circuit. Here, the light receiving section is composed of a large number of light receiving elements made of photoconductors arranged in a line, and the reading circuit is composed of a switching transistor and a driving transistor for sequentially selecting each light receiving element and reading a signal. The conditions required for these elements are that, for the photoconductor, the photosensitivity is high in order to increase the sensitivity of the sensor, and for the transistor, the switching speed is high in order to increase the reading speed, that is, the operating speed, and That is, a large output current can be obtained. Therefore, a material that generates a large photocurrent is required as a photoconductor material, while a material having high carrier mobility is required as a transistor material.

As described above, in a photoconductive image sensor, two types of elements having different functions, that is, a photoconductor and a transistor, are used, and the requirements for each element material are completely different. In conventional photoconductive image sensors, it is difficult to form a CdS-CdSe
Means to increase the sensitivity by using a silicon-based, Se-Te-As-based or amorphous silicon film, while increasing the speed by using crystalline silicon or polycrystalline silicon film with high carrier mobility as a transistor material. Has been taken.

[Problems to be solved by the invention]

However, as described above, in the photoconductive image sensor of the prior art, in order to achieve both high sensitivity and high speed, two photoconductors and transistors are used.
It is necessary to form each type of element with a different material, which not only complicates the structure of the image sensor, but also repeatedly performs film formation and processing steps for each element when forming each element. Therefore, there are disadvantages such as an extremely large number of steps, a high defect rate, and a high manufacturing cost.

An object of the present invention is to provide a method of manufacturing a photoconductive image sensor that can be formed with a small number of steps and that can obtain a high-speed and high-sensitivity photoconductive image sensor.

[Means for solving the problem]

In order to achieve the above object, in the present invention, a transistor formed using a crystalline silicon film or a polycrystalline silicon film formed on a substrate and a photoconductor formed of an amorphous silicon film are integrated. In the method of manufacturing a photoconductive image sensor, after forming the crystalline silicon film or the polycrystalline silicon film, the crystalline silicon film or the polycrystalline silicon film serving as the photoconductor is ion-implanted to form an amorphous state. Thus, the above amorphous silicon film is obtained.

In this case, at the time of the above-described ion implantation, the ion to be implanted is one selected from silicon, germanium, argon, neon or silane, or a combination thereof.

In the formation of the amorphous silicon film, hydrogen ions or fluorine ions are doped.

In this case, the above-described doping of hydrogen ions or fluorine ions is performed by ion implantation or plasma irradiation.

[Action]

Since a crystalline silicon film or a polycrystalline silicon film has high carrier mobility, a high-speed transistor can be obtained by forming a transistor using the film.

Although a crystalline silicon film or a polycrystalline silicon film is low in photosensitivity even when used as a photoconductor as it is, the present inventors have found that amorphous silicon generates a large photocurrent and that silicon crystal becomes amorphous by ion implantation. Paying attention to the phenomenon of becoming amorphous, silicon ions or the like were implanted into a crystalline silicon film or a polycrystalline silicon film, and the film was made amorphous to form a photoconductor.

That is, after the formation of the crystalline silicon film or the polycrystalline silicon film, in the intermediate stage of the transistor formation, only the part of the crystalline silicon film or the polycrystalline silicon film which becomes a photoconductor is implanted with silicon ions or the like to make it amorphous. By adopting a technique of continuing transistor formation, a photoconductor having a large photocurrent and a high-speed transistor can be formed from a crystalline silicon film or a polycrystalline silicon film deposited at the same time.

With the above structure, the film formation and photo-etching steps can be completed only once, respectively. Therefore, separately from the transistor formation step, film formation for photoconductor formation, photo-etching, etc. The structure and the manufacturing process can be greatly simplified as compared with the conventional photoconductive image sensor manufacturing method requiring a process.

〔Example〕

Hereinafter, a method for manufacturing a photoconductive image sensor according to the present invention will be described with reference to examples.

Embodiment 1 FIG. 1 is a schematic sectional view showing the structure of a photoconductive image sensor manufactured by the first embodiment of the method of manufacturing a photoconductive image sensor according to the present invention, wherein 1 is a transistor region, and 2 is a light source. The transistor region 1 includes a gate electrode 3, a gate insulating film 4, an active layer 5, a source / drain 6, an interlayer film 7, a through hole 8, and an aluminum wiring 9, and the photoconductor region 2 It shows that the photoconductor 10 and the photoconductor electrode 11 are included. In this embodiment, a thin film transistor (TFT) having a so-called staggered structure in which the gate electrode 3 is below the active layer 5 is employed as the transistor. The photoconductor 10 is made of an amorphous film formed by patterning the polycrystalline silicon film used for the active layer 5 of the transistor and then implanting silicon ions.

The details of the manufacturing procedure will be described below with reference to FIG.
First, (a) shows a state in which Cr, NiCr, Mo or the like is deposited on an insulating substrate 25 and then a gate electrode 3 is formed by photoetching, and (b) shows a gate insulating layer made of SiN, SiO ₂ or the like on the entire surface of the sample. After the film 4 is formed, a polycrystalline silicon film 27 is deposited by a low pressure CVD method, (c) is a state in which the pattern of the TFT active layer 5 and the photoconductor 10 are simultaneously formed by photoetching, and (d) is a state. Then, 5 × 10 ¹⁵ / c from the top of the resist pattern 24 in which only the photoconductor pattern portion was opened.
m ² silicon ions are implanted to amorphize the portion of the polycrystalline silicon film that will be the photoconductor, (e) is (d)
(F) shows the TFT source /
The state in which the drain 6 and the photoconductor electrode 11 are simultaneously formed of a phosphorus-doped polycrystalline silicon film, and the figure (g) shows the state in which the interlayer film 7, the through hole 8 and the aluminum wiring 9 are formed to complete the product. It is.

The manufacturing process of the photoconductive image sensor in this embodiment is a process in which a silicon ion implantation process is simply added to the manufacturing process of a known staggered TFT, and a conventional process of manufacturing a TFT and a photoconductor separately. It is greatly simplified as compared with. Further, in the photoconductive image sensor of the present invention, since polycrystalline silicon is used as a transistor material, a high-speed reading circuit can be formed. Furthermore, since polycrystalline silicon is made amorphous and used as a photoconductor, photosensitivity is higher than when polycrystalline silicon is used as a photoconductor as it is. For example, the current increase rate due to light irradiation of 1000 lx with respect to dark current is at most several percent in the photoconductor using polycrystalline silicon, but reaches several tens percent in the photoconductor of the present embodiment.
Therefore, a high-sensitivity, high-speed optical image sensor can be realized. In addition, since the polycrystalline silicon film can be easily deposited on a large-area substrate, there is an advantage that a large-area image sensor can be realized.

Embodiment 2 FIG. 3 is a schematic sectional view showing the structure of a photoconductive image sensor manufactured according to a second embodiment of the method of manufacturing a photoconductive image sensor of the present invention, where 12 is a sapphire substrate,
13 is a transistor region, 14 is a photoconductor region, and the transistor region 13 is a gate electrode 15, a gate insulating film.
16, the active layer 17, the source / drain 18, the interlayer layer 19, the through hole 20, and the aluminum wiring 21, and the photoconductor region 14 includes the photoconductor 22 and the photoconductor electrode 23. In this embodiment, a coplanar TFT formed using a single-crystal silicon film formed on a sapphire substrate 12 is used as a transistor for high-speed operation. Also, the photoconductor is
Silicon ions are implanted into the single crystal silicon film to make it amorphous, and hydrogen ions are doped into the amorphous silicon film for the purpose of increasing the photocurrent by compensating for defects in the amorphous silicon film. It consists of a film that has been made.

The details of the manufacturing procedure will be described below with reference to FIG.
First, (a) shows a state in which a single-crystal silicon film is formed on a sapphire substrate 12, (b) shows a state in which a pattern of a photoconductor 22 and an active layer 17 of a TFT are simultaneously formed on the sample by photoetching, 3C shows a state in which the gate insulating film 16 is formed by using the thermal oxidation method, and FIG.
A state in which a gate electrode 15 is formed of phosphorus-doped polycrystalline silicon or a metal such as Mo on the top, and FIG.
And state of forming simultaneously a source / drain electrode 18 of the TFT by ion implantation, (f) is amorphous by injecting ⁵ × 10 5 / cm ² of silicon ions into the single-crystal silicon film in a portion where the photoconductor (G) shows a state in which an interlayer film 19, a through hole 20, and an aluminum wiring 21 are formed, and a heat treatment at 300 ° C. is performed to form a finished product. It is. In addition, the implantation amount of hydrogen ions in the above (f) is 1 × 10 ¹⁵ to 1 × 10 5
It is desirable to be in the range of ¹⁷ / cm ² .

As shown in the above procedure, as the manufacturing process, the TFT and the photoconductor can be simultaneously formed only by adding a silicon ion and hydrogen ion implantation process to the known coplanar TFT manufacturing process. The image sensor manufacturing process can be greatly simplified.

Further, since the TFT is formed using single crystal silicon, the reading speed can be increased by one digit or more compared to the case where polycrystalline silicon is used.

Further, the hydrogen ion-doped amorphized silicon film used as a photoconductor has excellent photosensitivity due to a defect compensation effect of hydrogen ions.
The current increase rate at the time of light irradiation of 00lx is several tens% in the photoconductor without hydrogen ion doping, whereas it is about 50 times in the hydrogen ion doped amorphized silicon film in this embodiment. The results are shown. This rate of increase is comparable to that of an amorphous silicon film formed by a plasma CVD method known as a high-sensitivity photoconductor material.

Example 3 In this example, as in the case of Example 2, a TFT and a photoconductor were formed using a single crystal silicon film formed on a sapphire substrate, except that the photoconductor of Example 2 was formed. In this example, ionized silane is implanted (5 × 10 ¹⁵ / cm ² ) instead of amorphization by silicon ion implantation and defect compensation by hydrogen ion implantation. Since silane is a molecule in which one silicon atom and four hydrogen atoms are bonded, it is possible to simultaneously perform amorphization and hydrogen doping by implanting ionized silane. In the present embodiment, the manufacturing procedure and the element structure were the same as those of the embodiment 2 except for the ion implantation step.

Also in the case of the present embodiment, since a single crystal silicon film is used for TFT formation, high-speed operation of the TFT is possible.

In addition, a highly sensitive photoconductor can be formed by doping the photoconductor with hydrogen.
For example, the current increase rate by light irradiation of 1000 lx with respect to the dark current shows a value of at most several% in the case of the single crystal silicon film, whereas the result of this embodiment is about 50 times.

Further, according to the procedure of the present embodiment, since the amorphous silicon film and the hydrogen doping can be completed by one ion implantation, the process is further simplified without lowering the sensitivity. be able to.

Although three embodiments have been described above, it goes without saying that various changes and modifications can be made without departing from the spirit of the present invention. For example, in the first and second embodiments, an example is shown in which a silicon film which is made amorphous by implantation of silicon ions is used as a photoconductor, but instead of silicon ions, ions of a group IV element such as germanium are used. Alternatively, a silicon film which is made amorphous by implantation of ions of a rare gas such as argon or neon can be used. Further, in the second embodiment, an example is shown in which hydrogen doping for defect compensation is performed by implanting hydrogen ions, but doping by irradiation with hydrogen plasma is also possible. Also, the fact that doping with fluorine or both hydrogen and fluorine ions in place of hydrogen has a defect compensation effect is an example of an amorphous silicon film formed by plasma CVD widely used in solar cells and the like. It is clear from such points of view. Note that, in the above-described embodiment, an example in which a staggered type and a coplanar type TFT are used as a transistor has been described. However, it is apparent from the manufacturing procedure shown in the example that the present invention can be implemented regardless of the type of the TFT. .

〔The invention's effect〕

As described above, in the method for manufacturing a photoconductive image sensor according to the present invention, a transistor is formed using a crystalline silicon film or a polycrystalline silicon film formed on a substrate, and a crystal formed on the substrate is formed. A photoconductive image sensor in which a photoconductor is formed by using a silicon film or a silicon film in which a polycrystalline silicon film is made amorphous is solved, thereby solving the problems of the prior art and reducing the number of processes. A high-speed and high-sensitivity photoconductive image sensor can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a photoconductive image sensor manufactured according to a first embodiment of the method of manufacturing a photoconductive image sensor according to the present invention, and FIG. 2 is a manufacturing procedure of the first embodiment. FIG. 3 is a schematic sectional view showing the structure of a photoconductive image sensor manufactured by the second embodiment of the method of manufacturing a photoconductive image sensor according to the present invention;
FIG. 4 is a schematic sectional view showing a manufacturing procedure of the second embodiment. 1, 13 ... transistor region 2, 14 ... photoconductor region, 3, 15 ... gate electrode 4, 16 ... gate insulating film, 5, 17 ... active layer 6, 18 ... source / drain 7, 19 ... interlayer film, 8, 20 ... through hole 9, 21 ... aluminum wiring, 10, 22 ... photoconductor 11, 23 ... photoconductor electrode, 12 ... sapphire substrate 24 ... resist, 25 …… Insulating substrate 26 …… Single crystal silicon film, 27 …… Polycrystalline silicon film

Continuation of front page (72) Inventor Tadaaki Masumori 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-60-62155 (JP, A)

Claims (4)

(57) [Claims] 1. A photoconductive image sensor formed by integrating a transistor formed using a crystalline silicon film or a polycrystalline silicon film formed on a substrate and a photoconductor formed of an amorphous silicon film. In the method, after forming the crystalline silicon film or the polycrystalline silicon film, the crystalline silicon film or the polycrystalline silicon film portion serving as the photoconductor is ion-implanted to form an amorphous silicon film. A method for manufacturing a photoconductive image sensor, comprising obtaining a film. 2. The photoconductive image sensor according to claim 1, wherein the ions to be implanted are one selected from silicon, germanium, argon, neon or silane, or a combination thereof. Production method. 3. The method according to claim 1, wherein said amorphous silicon film is formed by doping hydrogen ions or fluorine ions. 4. A method for manufacturing a photoconductive image sensor according to claim 3, wherein said doping of hydrogen ions or fluorine ions is performed by ion implantation or plasma irradiation.