JPH08335687A - Method for manufacturing thin film photoelectric conversion device - Google Patents

Abstract

(57) [Summary] [Object] To obtain a manufacturing method for manufacturing a thin film photoelectric conversion device provided with a photoelectric conversion element and an LDD structure thin film transistor having uniform characteristics as a pixel selection switch at low cost. [Structure] A polycrystalline silicon layer 2, a gate insulating film 13, and a gate electrode film 16 are sequentially laminated on an insulating substrate 1, and a photoresist mask 14 is formed on the upper part thereof by photolithography, and a gate electrode is formed by using this. The film 16 is isotropically etched to form the gate electrode 6, the gate insulating film 13 is anisotropically etched to form the gate insulating layer 3, and the gate electrode 6 and the gate insulating layer 3 are used as masks. Polycrystalline silicon layer 2
Introduce impurities into. Further, the base electrode film 20, the semiconductor film 21, and the transparent conductive film 22 are sequentially stacked, and the transparent conductive film 22, the semiconductor film 21, and the base electrode film 20 are etched using the photoresist mask 15 formed by one-time photolithography. As a result, a photoelectric conversion element including the base electrode 10, the semiconductor layer 11 and the transparent electrode 12 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a photoelectric conversion device used in a reading section of a facsimile, a scanner, a digital copying machine, etc., and particularly to a photoelectric conversion element using thin film technology and a photoelectric conversion element generated by the photoelectric conversion element. The present invention relates to a method for manufacturing a thin film photoelectric conversion device having a thin film transistor as a selection switch for transmitting charges to the outside.

[0002]

2. Description of the Related Art With the recent development of information processing technology, inexpensive and high-performance devices and equipment are required. Among facsimiles, which are the main components of a facsimile, a recording part is developed at a low cost and with high performance due to the development of a thermal head or the like in the recording part and the development of an LSI in the communication part. However, on the other hand, the reading section has a complicated optical system, and the cost of the photoelectric conversion device itself is high, which prevents an overall cost reduction. Therefore, there is a need for a technology that enables cost reduction and high performance of the reading unit. As a method for reducing the cost and improving the performance of the reading unit, a structure has been proposed in which the reading target and the photoelectric conversion device are in close contact with each other in order to simplify the optical system. One of such photoelectric conversion devices is a thin film photoelectric conversion in which a thin film technology is used to form a photoelectric conversion element and a thin film transistor as a selection switch for transmitting charges generated in the photoelectric conversion element to the outside on the same substrate. The device is known.

As thin film transistors used in thin film photoelectric conversion devices, those using amorphous silicon, polycrystalline silicon or the like are well known. Since a thin film transistor using polycrystalline silicon has higher mobility than a case using amorphous silicon, a driving circuit of a photoelectric conversion device can be manufactured over one substrate, which leads to downsizing and cost reduction. It is advantageous to
It is also possible to incorporate an external drive circuit on the same substrate. However, the polycrystalline silicon thin film transistor has a problem that it has a large leak current. In particular, in a thin film photoelectric conversion device, since a polycrystalline silicon thin film transistor is used as a selection switch for transmitting charges generated in a photoelectric conversion element to the outside, a high S / N ratio is required. Is serious.

In order to reduce this leak current, a gate offset region having a low concentration of impurities is formed between the channel region and the source region formed in the polycrystalline silicon and between the channel region and the drain region. LDD (Ligh
A thin film transistor having a tly Doped Drain structure has been widely adopted (see Japanese Patent Publication No. 3-38755). Hereinafter, a manufacturing process of the thin film photoelectric conversion device having the n-channel thin film transistor having the conventional LDD structure will be described with reference to process cross-sectional explanatory views of FIGS.

First, a polycrystalline silicon film is formed on an insulating substrate 1, an island-shaped polycrystalline silicon layer 2 is formed by photolithography and etching, and then a gate insulating film 13 made of a silicon oxide film is formed by a CVD method or the like. Form. Further, a gate electrode film 16 made of Ta is formed on top of it (FIG. 4).
(A)). Next, the gate electrode film 16 is formed on the island-shaped gate electrode 6'by photolithography and etching, and P is ion-implanted at a low concentration into the polycrystalline silicon layer 2 using this gate electrode 6'as a mask to form a channel. N on both sides of the area 2a '
A low concentration region 5 of the mold is formed (FIG. 4 (b)). This time,
Since the gate electrode 6 'serves as a mask for ion implantation,
Impurities are not introduced into the channel region 2a 'immediately below the gate electrode 6'.

Next, a photoresist mask 1 covering the upper and side portions of the gate electrode 6'with photolithography.
4'is formed, and P is ion-implanted into the polycrystalline silicon layer 2 from above in a high concentration to form a source region 4a 'and a drain region 4b' which are n-type high concentration regions (FIG. 4).
(C)). At this time, since the gate electrode 6'and the photoresist mask 14 'serve as a mask for ion implantation, the portions of the channel region 2a' and the n-type low concentration region 5 covered by the photoresist mask 14 'remain unchanged. Is the state of. By the above-mentioned two times of ion implantation, the polycrystalline silicon layer 2
Are the channel region 2a ', the source region 4a' and the drain region 4b 'which are n-type high concentration regions, and the gate offset regions 5a' and 5 which are n-type low concentration regions.
b'is formed.

Next, the photoresist mask 14 'is removed, SiO ₂ is deposited on the entire surface by the CVD method, and a hydrogenation process is performed if necessary to improve the transistor characteristics. Next, the base electrode film 2 that constitutes the photoelectric conversion element
0, the semiconductor film 21, and the transparent conductive film 22 are laminated (FIG. 5).
(A)). Next, a photoresist mask (not shown) is formed by photolithography, and the transparent conductive film 22 and the semiconductor film 2 are formed.
1 is separated by etching, a different photoresist mask (not shown) is formed by photolithography, and the base electrode film 20 is separated by etching to form the base electrode 10 'and the semiconductor layer 1
A photoelectric conversion element in which 1'and the transparent electrode 12 'are sequentially laminated is formed (FIG. 5B).

Subsequently, after forming an interlayer insulating film 7 on the entire surface, a contact hole is formed in the interlayer insulating film 7 by photolithography and etching, and an Al film is formed on the contact hole, and then a wiring 8 is formed by photolithography etching. ′ Is formed and the passivation film 9 is formed on these, thereby completing the photoelectric conversion element of the thin film photoelectric conversion device and the thin film transistor of the selection switch at the same time (FIG. 5).
(C)).

[0009]

According to the method of manufacturing a thin film photoelectric conversion device described above, the number of photolithography steps for patterning a photoresist using a mask is seven, and ion implantation for introducing impurities is performed. However, in order to reduce the cost of the reading unit, it is necessary to reduce the number of times. Further, the gate offset regions 5a 'and 5b' which influence the characteristics of the LDD structure polycrystalline silicon thin film transistor are formed by two photolithography processes for producing the gate electrode 6'and the photoresist mask 14 '. Therefore, when the mask alignment is deviated, the lengths of the gate offset regions 5a 'and 5b' vary with respect to the design values, and when used as a selection switch of the photoelectric conversion element, the reading is performed. There is a problem in that non-uniformity of performance occurs.

The present invention has been made in view of the above circumstances, and a thin film photoelectric conversion device including a photoelectric conversion element and a polycrystalline silicon thin film transistor having an LDD structure as a pixel selection switch is manufactured at low cost, and An LDD structure polycrystalline silicon thin film transistor is provided with a manufacturing method for making the characteristics uniform.

[0011]

In order to achieve the above-mentioned object, the invention of claim 1 is characterized by comprising the following steps in a method of manufacturing a thin film photoelectric conversion device. A step of forming a polycrystalline silicon film on an insulating substrate. Forming the polycrystalline silicon film on the polycrystalline silicon layer by photolithography and etching. Forming a gate insulating film on the polycrystalline silicon layer; Forming a gate electrode film on the gate insulating film; Forming a photoresist mask on the gate electrode film by photolithography. Processing the gate electrode film into a gate electrode having a width narrower than that of the photoresist mask by isotropic etching. Process the gate insulating film into a gate insulating layer having the same width as the photoresist mask by anisotropic etching. Impurities are introduced into the polycrystalline silicon layer by using the gate electrode and the gate insulating layer as a mask, and a source region and a drain region in which impurities are introduced at a high concentration and a gate region in which impurities are introduced at a low concentration are introduced. Process of simultaneously forming the offset region. A step of sequentially laminating a base electrode film, a semiconductor film, and a transparent conductive film on all of these. On the drain region (or on the source region) by photolithography
Forming a photoresist mask on. A step of etching the transparent conductive film, the semiconductor film, and the base electrode film using the photoresist mask to form a photoelectric conversion element including the base electrode, the semiconductor layer, and the transparent electrode. A step of forming an interlayer insulating film on all of these. Forming a contact hole in the interlayer insulating film by photolithography etching. The process of forming a conductive film on all of these. A step of forming the conductive film on a wiring by photolithography / etching.

[0012]

According to the present invention, a thin film photoelectric conversion device having a photoelectric conversion element and a polycrystalline silicon thin film transistor having an LDD structure as a switch for selecting the photoelectric conversion element is manufactured by five photolithography steps and one impurity introduction step. Therefore, the cost can be reduced. Also, L
Since the length of the gate offset region that influences the characteristics of the DD-structure polycrystalline silicon thin film transistor can be formed uniformly, the characteristics of the switch corresponding to each photoelectric conversion element in the thin film photoelectric conversion device become uniform, and the reading can be performed. The performance can be made uniform.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method of manufacturing a thin film photoelectric conversion device according to the present invention will be described below with reference to the cross sectional explanatory views of FIGS. First, on the insulating substrate 1,
For example, a-S is formed by LPCVD (Low Pressure Chemical Vapor Deposition) method.
i is deposited to a thickness of about 100 nm, and then a-Si is converted to polycrystalline silicon by irradiating, for example, an excimer laser, and the polycrystalline silicon layer 2 is formed in an island shape by photolithography and etching. Next, a gate oxide film 13 is formed by depositing a silicon oxide film to a thickness of about 100 nm by, for example, ECR plasma CVD method, and further Ta is formed by, for example, a sputtering method.
Is deposited to a thickness of about 500 nm to form the gate electrode film 16.
Next, a photoresist mask 14 is formed by photolithography on the portion where the channel region is to be formed (FIG. 1).
(A)).

Next, using the photoresist mask 14 as a mask, the gate electrode film 16 is isotropically etched by the CDE (chemical dry etching) method using CF ₄ and O ₂ gas, for example, and the width of the gate electrode film 16 is made wider than that of the photoresist mask 14. Forming a narrow gate electrode 6 (FIG. 1B). continue,
Using the same photoresist mask 14 as a mask, the gate insulating film 13 is anisotropically etched by, for example, RIE (reactive ion etching) method using CHF ₃ and O ₂ gas.
Gate insulating layer 3 having the same width as that of the gate electrode 6 but wider than the gate electrode 6.
Are formed (FIG. 1C). Here, the gate electrode 6 and the gate insulating layer 3 are the same photoresist mask 1
Since it is formed by etching using No. 4, it is formed symmetrically.

Next, after removing the photoresist mask 14, impurity ions such as P are added to the polycrystalline silicon layer 2 from above by the non-mass separation type ion doping method using the gate electrode 6 and the gate insulating layer 3 as a mask from above. To introduce. At this time, in the polycrystalline silicon layer 2, no impurity ions are introduced into the channel region 2a masked by the gate electrode 6, and only the gate insulating layer 3 is masked by one impurity introduction step. Regions become gate offset regions 5a and 5b in which impurities are introduced at a low concentration, and regions without a mask are formed in source regions 4a and drain regions 4b in which impurity ions are introduced at a high concentration (FIG. 2).
(A)). Here, since the gate electrode 6 and the gate insulating layer 3 are formed symmetrically, the gate offset region 5
The lengths of a and 5b are equal.

Next, for example, a base electrode film 20 made of Ti is deposited to a thickness of about 100 nm by a sputtering method, a semiconductor film 21 made of amorphous Si is further deposited to a thickness of about 1 μm by a plasma CVD method, and further ITO is formed by a sputtering method.
The transparent conductive film 22 made of is deposited to a thickness of about 60 nm. Then, by photolithography, a photoresist mask 15 for forming a photoelectric conversion element is formed so as to cover a part of the drain region 4b.
Are formed (FIG. 2B). Next, using this photoresist mask 15, the transparent conductive film 22 is etched by wet etching, the semiconductor film 21 is further etched by RIE, and the base electrode film 20 is further wet-etched to form the base electrode 10 and the semiconductor. A photoelectric conversion element in which the layer 11 and the transparent electrode 12 are sequentially laminated is formed, and the photoresist mask 15 is peeled off (FIG. 2C).

Next, for example, a silicon oxide film is deposited to a thickness of about 1 μm by a plasma CVD method to form an interlayer insulating film 7, and then a contact hole is formed by photolithography, for example, a sputtering method to a thickness of about 1 μm. An Al-Cu film is deposited and patterned by photolithography and etching to form the wiring 8. Furthermore, for example, plasma CV
A thin film photoelectric conversion device is completed by forming a passivation film 9 by depositing a silicon oxide film of about 1 μm by the D method (FIG. 3).

In the method of manufacturing a thin film photoelectric conversion device described above, the thin film photoelectric conversion device can be manufactured by performing the photolithography step 5 times and the impurity introduction once, so that the number of steps can be reduced as compared with the conventional manufacturing method. The cost can be reduced. Further, after the gate electrode 6 and the gate insulating layer 3 are formed by etching using the same photoresist mask 14, impurity ions are introduced from above by using the gate electrode 6 and the gate insulating layer 3 as a mask. Therefore, since the gate offset regions 5a and 5b of the low concentration impurity regions can be formed in a self-aligned manner, the variation in the length of the gate offset regions 5a and 5b can be reduced, which is caused by the photoelectric conversion element. It is possible to make the performance of the charge switch uniform.

The method used in the above embodiment is not necessarily limited to this. For example, a plasma CVD method, an ECR-CVD method, a sputtering method, an evaporation method, or the like can be used for depositing a-Si. Further, the polycrystalline silicon film can be formed and used by a method suitable for the material such as a-Si being annealed by an Ar laser, an electron beam, an infrared lamp or the like. The insulating film such as the gate insulating film may be silicon nitride, silicon oxynitride, or the like, and the film forming method is LPCVD method or ECR.
-A method suitable for the material such as a CVD method, a sputtering method, or a vapor deposition method may be used. Further, the gate electrode and the base electrode of the photoelectric conversion element may be made of metal materials such as Ti, W, Cr, Mo, Al, Cu, their alloy materials, and their silicidized materials. Any suitable one may be used. Further, the processing method of the photoelectric conversion element is C
A DE method, an ECR etching method, a helicon wave etching method, or the like may be used.

[0020]

According to the present invention, in the production of a thin film photoelectric conversion device having a photoelectric conversion element and a polycrystalline silicon thin film transistor having an LDD structure as a pixel selection switch, the photolithography and impurity introduction steps are compared with those in the prior art. Can be reduced, and cost can be reduced. Also, L
Since the length of the gate offset region which influences the characteristics of the DD structure polycrystalline silicon thin film transistor can be made uniform, the reading performance of the thin film photoelectric conversion device becomes uniform and the image quality can be made uniform.

[Brief description of drawings]

1A, 1B, and 1C are cross-sectional explanatory views showing main steps of a method of manufacturing a thin film photoelectric conversion device according to the present invention.

2 (a), (b) and (c) are cross-sectional explanatory views showing main steps of a method of manufacturing a thin film photoelectric conversion device according to the present invention.

FIG. 3 is a cross-sectional explanatory view showing main steps of a method of manufacturing a thin film photoelectric conversion device according to the present invention.

4A, 4B, and 4C are cross-sectional explanatory views showing main steps of a conventional method for manufacturing a thin film photoelectric conversion device.

5A, 5B, and 5C are cross-sectional explanatory views showing main steps of a conventional method for manufacturing a thin film photoelectric conversion device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Insulating substrate, 2 ... Polycrystalline silicon layer, 2a ... Channel region, 3 ... Gate insulating layer, 4a ... Source region, 4b ... Drain region, 5a, 5b ... Gate offset region, 6 ... Gate electrode, 7 ... Interlayer insulating film,
8 ... Wiring, 9 ... Passivation film, 10 ... Base electrode, 11 ... Semiconductor layer, 12 ... Transparent electrode, 13 ... Gate
Insulating film, 14, 15 ... Photoresist mask, 1
6 ... Gate electrode film, 20 ... Base electrode film, 21 ... Semiconductor film, 22 ... Transparent conductive film

Claims (1)

[Claims] 1. A step of forming a polycrystalline silicon film on an insulating substrate, a step of forming the polycrystalline silicon film into a polycrystalline silicon layer by photolithography and etching, and a gate insulating film on the polycrystalline silicon layer. A step of forming a gate electrode film on the gate insulating film, a step of forming a photoresist mask on the gate electrode film by photolithography, and an isotropic etching of the gate electrode film. Processing a gate electrode having a width narrower than that of the photoresist mask, processing the gate insulating film into a gate insulating layer having the same width as the photoresist mask by anisotropic etching, and the gate electrode An impurity is introduced into the polycrystalline silicon layer by using the gate insulating layer as a mask, and the impurity is introduced at a high concentration.
A gate region, a drain region, and a gate offset region in which impurities are introduced at a low concentration, and a step of sequentially laminating a base electrode film, a semiconductor film, and a transparent conductive film on top of all of them, and a photolithography process. Forming a photoresist mask on the drain region (or on the source region) by etching the transparent conductive film, the semiconductor film and the base electrode film respectively using the photoresist mask, A step of forming a photoelectric conversion element composed of a base electrode, a semiconductor layer and a transparent electrode, and a step of forming an interlayer insulating film on all of these,
The method further comprises a step of forming contact holes in the interlayer insulating film by photolithography / etching, a step of forming a conductive film on all of these, and a step of forming the conductive film in a wiring by photolithography / etching. A method for manufacturing a thin film photoelectric conversion device, comprising: