JP2624318B2 - Image sensor and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor serving as an image input unit such as a facsimile and a method of manufacturing the same, and more particularly, to an amorphous silicon photodiode and a polycrystalline silicon on the same insulating substrate. The present invention relates to an image sensor having a thin-film transistor integrated therein, which is simple in process, inexpensive, and capable of high-speed reading, and a method of manufacturing the same.

[Conventional technology]

An image sensor using an amorphous silicon photoelectric conversion element is an important device as an image input unit such as a facsimile. Initially, only an amorphous silicon photodiode was formed on a glass substrate, and a plurality of external drive circuits were mounted.However, the drive circuit was formed with polycrystalline silicon thin film transistors, eliminating the need for an external drive circuit. Sensors are being developed. An image sensor in which an amorphous silicon photodiode and a polycrystalline silicon thin film transistor are integrated does not require an external drive circuit, so the mounting cost is low, and the field effect mobility of the polycrystalline silicon thin film transistor is close to that of a single crystal silicon transistor. , High-speed operation is possible.

FIG. 2 shows an image sensor in which a conventional amorphous silicon photodiode and a polycrystalline silicon thin film transistor are integrated and a method of manufacturing the same, which is described in the Technical Report ED85-30 of the Institute of Electronics, Information and Communication Engineers (1985). FIG. In FIG. 2, 1 is an insulating substrate, 2 is a transparent electrode,
3 is an amorphous silicon film, 4 is a polycrystalline silicon film, 5 is a gate insulating film, 6 is a gate electrode, 7a and 7b are protective films, 8a and 8b are source and drain regions, respectively, 9 is a source and drain electrode. It is.

Next, the manufacturing process of FIG. 2 will be described. First, a polycrystalline silicon film 4 is formed on a substrate 1 by source pressure CVD, and is removed except for a portion to be a transistor (step (a)). Next, after the gate insulating film 5 is formed by thermal oxidation, a polycrystalline silicon film to be the gate electrode 6 is formed, and the source region 8a and the drain region 8b are formed by ion implantation (step (b)). After forming the protective film 7a (step (c)), the source / drain electrodes 9 are formed (step (d)). A polycrystalline silicon thin film transistor is formed by the steps described above. Next, after forming an amorphous silicon film 3 as a photoelectric conversion film by PCVD,
The transparent electrode 2 is formed (step (e)). Unnecessary portions of the amorphous silicon film 3 are removed by etching (step (f)), and a protective film 7b is formed (step (g)), whereby a conventional amorphous silicon photodiode and a polycrystalline silicon thin film transistor are formed. To complete an image sensor that integrates

[Problems to be solved by the invention]

However, an image sensor in which a conventional amorphous silicon photodiode and a polycrystalline silicon thin film transistor are integrated is manufactured by the above-described process. In such a conventional method, the polycrystalline silicon film 4 is not formed. Since the process is performed using source pressure CVD, a high-temperature process of 600 ° C. or more must be performed, and an expensive quartz substrate must be used as the insulating substrate 1. Further, since the formation of the polycrystalline silicon film 4 and the formation of the amorphous silicon film 3 are performed separately, there is a problem that the manufacturing process becomes longer.

The present invention has been made in order to solve the above-described problems, and an image sensor in which an amorphous silicon photodiode and a polycrystalline silicon thin film transistor that can simplify a manufacturing process and can use an inexpensive glass substrate are integrated. And a method for producing the same.

[Means for solving the problem]

The image sensor according to the present invention, on a photosensor substrate in which an optical sensor using an amorphous silicon layer as a photoelectric conversion material is arranged one-dimensionally or two-dimensionally on an insulating substrate, a part of a circuit for driving the photosensor or In an image sensor obtained by integrating thin film transistors using a polycrystalline silicon layer as a whole, a polycrystalline silicon layer formed by laser annealing a desired region of the amorphous silicon layer is used as an active layer of the thin film transistor. is there.

Further, the method for manufacturing an image sensor includes selectively performing laser annealing on an amorphous silicon layer formed on the entire surface of a substrate so as to cover a transparent electrode formed on a photoelectric conversion portion forming region on an insulating substrate to a desired region. Forming a polycrystalline silicon layer,
A thin film transistor having the polycrystalline silicon layer as an active layer is formed, and the source / drain electrodes of the thin film transistor are formed on the entire surface of the substrate except for the upper portion of the gate electrode of the thin film transistor.
And an electrode layer serving as an upper electrode of the photoelectric conversion unit.

[Action]

In the image sensor and the method of manufacturing the same according to the present invention, since the polycrystalline silicon film is formed by using the laser annealing method as described above, the process temperature can be suppressed to 600 ° C. or less, and the use of a cheaper glass substrate is possible. Is possible and cost can be reduced. In addition, since the step of forming the polycrystalline silicon film is omitted and the step of forming the amorphous silicon film is performed simultaneously, the manufacturing process is simplified, and the cost can be further reduced.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing an image sensor and a method of manufacturing the same according to an embodiment of the present invention. In the figure, 1 is an insulating substrate made of glass or the like, 2 is ITO (Indium Tin Oxide)
3 is an amorphous silicon film, 4 is a polycrystalline silicon film, 5 is a gate insulating film, 6 is a gate electrode, 7
a and 7b are protective films, 8a and 8b are source and drain regions, respectively, and 9 is a source and drain electrode.

Next, the manufacturing process will be described with reference to FIGS. First, a transparent electrode 2 made of, for example, ITO is formed on a glass substrate 1 (step (a)), and an amorphous silicon film 3 having a thickness of 0.6 to 2.0 μm to be a photoelectric conversion layer is formed on the entire surface of the substrate. (Step (b)). Then, a laser beam using a XeCl excimer laser as a light source is irradiated only on a portion of the amorphous silicon 3 which will become a transistor, and laser annealing is performed to selectively polycrystallize the amorphous silicon, thereby forming a polycrystalline silicon layer 4. Is formed (step (c)). Next, a gate insulating film 5 and a gate electrode 6 are sequentially formed on a part of the polycrystalline silicon layer 4 (step (d)), and the photoelectric conversion part and the part excluding the source and drain regions on the polycrystalline silicon layer 4 are formed. Next, a protective film 7 also serving as an inter-line insulating film is formed (step (e)). Finally, an amorphous silicon film doped with phosphorus to be the source region 8a and the drain region 8b is formed.
The drain electrode 9 is formed (step (f)). The source / drain electrodes 9 also serve as upper individual electrodes of the photodiode.

Here, as described above, when the amorphous silicon film 3 is laser-annealed to be polycrystalline silicon and the amorphous silicon photodiode and the polycrystalline silicon thin film transistor are integrally formed, the thickness of the amorphous silicon film 3 is It becomes a problem. Amorphous silicon film thickness required for efficient photoelectric conversion is
Although it is 0.6 to 2.0 μm, the amorphous silicon film thickness is desirably 0.3 μm or less when a thin film transistor is manufactured in a staggered structure. Further, when a thin film transistor is manufactured by annealing with a XeCl excimer laser, the thin film transistor cannot be configured in a staggered structure. Therefore, in this embodiment, as described above, the thickness of the amorphous silicon
The thickness of the thin film transistor is set to 0.6 to 2.0 μm, and the thin film transistor has a planar structure. In such a structure, the channel region of the polycrystalline silicon thin film transistor is on the very surface, so that the polycrystalline silicon thin film transistor is sufficiently polycrystallized by XeCl excimer laser annealing. Even if the thickness of the amorphous silicon is made sufficient for photoelectric conversion, the characteristics of the thin film transistor can be improved, so that there is no problem at all.

In the above embodiment, XeCl is used as the oscillating gas of the excimer laser, but the same annealing effect can be obtained by using KrF, KrCl, F ₂ , ArF, and XeF as the oscillating gas. Further, in the above embodiment, an excimer laser is used as a light source for laser annealing, but the present invention is not limited to this, and a laser light source having a wavelength of 400 nm or less may be used as a laser light source.

In the above embodiment, a single layer of the amorphous silicon film 3 was shown as the photoelectric conversion film. However, this is a film in which a film of n ⁺ amorphous silicon doped with boron and a film of non-doped amorphous silicon are sequentially laminated. But it is good.

In the above embodiment, ITO is used as the transparent electrode 2. However, this may be one using indium tin oxide or tin oxide.

Further, an n ⁺ amorphous silicon film obtained by doping amorphous silicon with phosphorus was used as the source region 8a and the drain region 8b, but this was formed in the polycrystalline silicon film 4 by ion implantation. Alternatively, the drain region 8b may be formed.

As described above, according to the present embodiment, the amorphous silicon film 3
By using a method of forming the polycrystalline silicon film 4 by laser annealing, the process temperature can be suppressed to 600 ° C. or less, a cheaper glass substrate can be used, and the cost can be reduced. In addition, since the formation of the polycrystalline silicon film 4 is omitted and the formation is performed at the same time as the formation of the amorphous silicon film, the manufacturing process can be greatly reduced and simplified, and the cost can be further reduced. Further, since the structure is such that the polycrystalline silicon film 4 is formed on the amorphous silicon film 3, the lattice matching at the interface is improved compared to the case where the polycrystalline silicon film is formed directly on the glass substrate as in the related art. Excellent transistor characteristics with excellent defect levels can be obtained.

〔The invention's effect〕

As described above, according to the present invention, the amorphous silicon film that is a photoelectric conversion material is laser-annealed to form a polycrystalline silicon film that is an active layer of a thin film transistor that drives an optical sensor. The process temperature for forming the silicon film can be suppressed to 600 ° C. or less, and a cheaper glass substrate can be used, and the cost can be reduced. In addition, since the formation of the polycrystalline silicon film is performed simultaneously with the formation of the amorphous silicon film, the manufacturing process can be simplified and the cost can be reduced. Also,
Since the polycrystalline silicon film is formed on the amorphous silicon film, lattice matching at the interface is improved, and a transistor with few defects and good characteristics can be formed.
There is an effect that an image sensor capable of high-speed reading with high accuracy can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an image sensor in which an amorphous silicon photodiode and a polycrystalline silicon thin film transistor according to an embodiment of the present invention are integrated and a method for manufacturing the same. FIG. 2 is a conventional amorphous silicon photodiode. FIG. 4 is a cross-sectional view showing an image sensor in which a polycrystalline silicon thin film transistor is integrated and a method for manufacturing the same. In the figure, 1 is an insulating substrate, 2 is a transparent electrode, 3 is an amorphous silicon film, 4 is a polycrystalline silicon film, 5 is a gate insulating film, 6 is a gate electrode, 7 is a protective film, and 8a and 8b are sources, respectively. The region and the drain region 9 are source / drain electrodes. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (2)

(57) [Claims] An optical sensor using an amorphous silicon layer as a photoelectric conversion material is arranged on a photosensor substrate having a one-dimensional or two-dimensional arrangement on an insulating substrate, as part or all of a circuit for driving the photosensor. In an image sensor formed by integrating thin film transistors using a polycrystalline silicon layer, a polycrystalline silicon layer formed by laser annealing a desired region of the amorphous silicon layer is used as an active layer of the thin film transistor. Image sensor. 2. An optical sensor using amorphous silicon as a photoelectric conversion material, one or two dimensions of which are arranged on an insulating substrate, on a light sensor substrate as a part or all of a circuit for driving the light sensor. In a method for manufacturing an image sensor in which thin film transistors made of crystalline silicon are integrated, a transparent electrode is formed in a photoelectric conversion portion forming region on an insulating substrate, and then an amorphous silicon layer is formed on the entire surface of the substrate. A polycrystalline silicon layer is formed in a desired region by selectively annealing the amorphous silicon layer with a laser, a thin film transistor having the polycrystalline silicon layer as an active layer is formed, and a substrate excluding an upper portion of a gate electrode of the thin film transistor is formed. An image sensor comprising: a source / drain electrode of the thin film transistor; and an electrode layer serving as an upper electrode of the photoelectric conversion unit, formed on the entire surface. Manufacturing method of sa.