JPH07236025A - Close contact image sensor and its production - Google Patents

Abstract

PURPOSE:To keep a gate insulation film flat by stopping the etching accurately at a boarder with the gate insulation film when an amorphous silicon layer formed on the gate insulation film is etched. CONSTITUTION:A chromium layer is depositted on a glass substrate 10 and the layer is subject to patterning to form a chromium electrode 12 and a silicon nitride layer 14 is depositted on the entire face of the electrode 12. Then a silicon oxide layer 16 is depositted on the layer 14 by a thickness of 100A or over and 500A or below by the plasma CVD method. Then an i-type a-Si layer 20 and an n<+> type a-Si layer 22 are sequentially depositted and the layers are subject to patterning by using the RIE method and etching is applied by leaving a part somewhat wider than the width of the chromium electrode 12. In this case, since the silicon oxide layer is on the silicon nitride layer, the etching for the a-Si layer is stopped accurately at the part of the silicon oxide layer to maintain the flatness of the silicon oxide layer after the etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact type image sensor used as a document reading device in a small facsimile, a copying machine or the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art The sensor element of a contact image sensor is
Usually, it is composed of a photoelectric conversion element that converts light into an electric charge and a switching element that takes out the electric charge accumulated in the photoelectric conversion element as a current. 2. Description of the Related Art A contact image sensor including a photodiode as a photoelectric conversion element and a thin film transistor (TFT) as a switching element has been conventionally known (for example, JP-A-3-15797).
No. 0 publication).

FIGS. 5 (a) to 5 (e) show a conventional contact image sensor in which a pin junction photodiode made of amorphous silicon (a-Si) and a TFT made of a-Si are formed on a glass substrate. It is a fragmentary sectional view showing an example of a process.

In this step, first, in FIG.
A chromium layer is deposited and patterned on the glass substrate 60 to form a chromium electrode 62. This will be the gate electrode for the TFT. Next, as shown in FIG. 2B, silicon nitride (SiN) 64, which will be an insulating layer, is deposited on the i-type a-Si layer (i layer) which will be the semiconductor layer of the TFT. 66 and an n ⁺ type a-Si layer (n ⁺ layer) 68 are sequentially deposited. Next, reactive ion etching (R
(IE) method, the i layer 66 and the n ⁺ layer 6 are formed to have a width somewhat wider than that of the chromium electrode 62, as shown in FIG.
8 is patterned.

Then, as shown in FIG. 5 (d), a chrome layer 70 is deposited on the entire surface, and p-type, i-type, n-type a-Si and transparent conductive material are formed on the upper right side of the chrome layer. By depositing a film of ITO 72 and patterning them, a pin junction photodiode 74 is obtained. Thereafter, as shown in FIG. 7E, the chrome layer 70 is patterned to form the source electrode 76 and the drain electrode 78, whereby the TFT 80 is obtained. After depositing a silicon oxide layer 82 to serve as an insulating layer, contact holes 84, 86 and 88 are formed. Further, a metal layer made of aluminum or chromium is deposited on this, and patterned into a predetermined shape to form upper electrodes 90, 92.
To get As a result, the photodiode 74 and the TFT 80
And the upper side of the TFT 80 is shielded by the upper electrode 94.

[0006]

By the way, i-type a-S
i and silicon nitride are similar in property to etching by the RIE method, that is, how they are etched. Therefore, in the step of shifting from FIG. 5B to FIG.
When the i layer 66 and the n ⁺ layer 68 are patterned and etched into a predetermined shape, the silicon nitride layer 64 is etched.
There is a problem that it is difficult to stop accurately at the interface between the and i-layer 66. Also, in the actual etching process, the etching rate is not completely the same depending on the location, and the etching rate is distributed depending on the location, so that the progress of etching may be fast and slow.

Therefore, in FIG. 5C, the silicon nitride layer 64 after the i layer 66 and the n ⁺ layer 68 are etched.
Although the surface of is drawn flat, it is unavoidable that considerable unevenness actually occurs on this surface. Thus, if the surface of the silicon nitride layer 64 after etching has irregularities,
Concavities and convexities are also likely to occur in the portion of the semiconductor layer for the photodiodes 64 deposited on this, and the yield is reduced.

The present invention has been made based on the above circumstances, and the etching is performed accurately at the boundary between the contact type image sensor in which the lower layer is flat after the amorphous layer of the TFT is etched by the RIE method and the lower layer is flat. An object of the present invention is to provide a method for manufacturing a contact-type image sensor that can be stopped.

[0009]

In order to solve the above-mentioned problems, the invention according to claim 1 is a contact image sensor in which a photodiode is used as a photoelectric conversion element and a thin film transistor is used as a switching element to form a sensor element. The gate insulating film is made of silicon nitride and silicon oxide, and the gate insulating film is formed in this order from the gate electrode side to the silicon nitride and silicon oxide.

In order to solve the above problems, the invention of claim 2 is characterized in that, in the invention of claim 1, the thickness of the silicon oxide is 100 angstroms or more and 500 angstroms or less. is there.

In order to solve the above-mentioned problems, a third aspect of the present invention is a first step of forming a gate electrode on a substrate in a method of manufacturing a contact image sensor using a thin film transistor as a switching element of a sensor element. A second step of forming a silicon nitride layer on the gate electrode, a third step of forming a silicon oxide layer on the silicon nitride layer, and an amorphous silicon layer on the silicon oxide layer. A fourth step of forming, a fifth step of patterning the amorphous silicon layer into a predetermined shape and etching up to the silicon oxide layer,
A sixth step of forming a metal layer on the intermediate product obtained by the fifth step and patterning the metal layer into a predetermined shape, and an amorphous silicon layer to be a photodiode on the patterned metal layer. A seventh step of forming and patterning it into a predetermined shape, and an eighth step of forming an insulating film on the intermediate product obtained in the seventh step and patterning it into a predetermined shape, A ninth step of forming a wiring layer on the intermediate product obtained in the eighth step.

In order to solve the above-mentioned problems, in the invention according to claim 4, in the invention according to claim 3, the thickness of the silicon oxide layer is formed to 100 angstroms or more and 500 angstroms or less in the third step. It is characterized by doing.

[0013]

According to the invention described in claim 1, the gate insulating film of the thin film transistor is made of silicon nitride and silicon oxide, and the gate insulating film is formed in this order from the gate electrode side to the silicon nitride and silicon oxide. Forming an amorphous silicon layer, which will be the active layer of the thin film transistor, on the gate insulating film by RI.
When etching with a predetermined pattern using the E method,
Due to the different etching characteristics of amorphous silicon and silicon oxide, the progress of this etching stops exactly when it reaches the silicon oxide portion. As a result, the surface of the silicon oxide after etching can be kept flat.

According to a second aspect of the present invention, by the above configuration,
By setting the silicon oxide layer to 100 angstroms or more, it is possible to effectively stop the etching of the amorphous semiconductor layer by the RIE method, and
By setting the thickness to 500 angstroms or less, it is possible to prevent deterioration of the interface characteristics due to electronegativity.

According to a third aspect of the present invention, by the above configuration,
By providing the third step of forming the silicon oxide layer on the silicon nitride layer, in the subsequent fifth step, the etching of the amorphous silicon layer by the RIE method is accurately stopped at the silicon oxide layer. It is possible to flatten the silicon oxide surface after etching.

According to a fourth aspect of the present invention, according to the above configuration,
In the third step, the thickness of the silicon oxide layer is set to 100.
When the thickness is not less than angstrom, it is possible to effectively stop the etching of the amorphous semiconductor layer by the RIE method in the fifth step, and
By setting the thickness to 0 angstrom or less, it is possible to prevent the deterioration of the interface characteristics due to the electronegativity after the completion of the thin film transistor.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2 are partial cross-sectional views sequentially showing a manufacturing process of a photodiode which is a photoelectric conversion element and a thin film transistor (TFT) which is a switching element of a contact image sensor which is an embodiment of the present invention,
3 and 4 are plan views illustrating a manufacturing process corresponding to FIGS. 1 and 2. 1 (a) to 1 (f) and FIG.
(G)-(j) has shown the cross section along the dashed-dotted line of Fig.3 (a).

In FIG. 1A, first, the glass substrate 1
A chrome layer is deposited on the O.sub.0 layer and patterned to form a chrome electrode 12. FIG. 3A is a plan view showing this state. Here, the dotted line portion in FIG. 3A indicates a region where a lower electrode of a photodiode described later is formed. After the chromium electrode 12 is formed, a silicon nitride layer 14 serving as an insulating film is deposited on the entire surface of the chromium electrode 12, as shown in FIG. In addition, on the glass substrate 10, various circuit portions forming the contact image sensor are collectively formed.

By the way, in the conventional process shown in FIG.
Immediately on the silicon nitride layer 14, i-type and n ⁺ -type a-Si layers to be semiconductor layers of the TFT were deposited. In contrast,
In this embodiment, as shown in FIG. 1C, a silicon oxide layer 16 is deposited on the silicon nitride layer 14 by plasma CVD before depositing the a-Si layer. At this time, the thickness of the silicon oxide layer 16 is set to 100 angstroms or more and 500 angstroms or less for the reason described below. Note that the silicon oxide deposited by plasma CVD may contain both SiO ₂ and SiO ₂ .
In the present embodiment, either one can achieve the intended purpose. Therefore, in this specification, the term "silicon oxide" is used to include SiO ₂ or SiO ₂ or both.

The subsequent steps are the same as those in the prior art, and are shown in FIG.
As shown in (d), the i-type a-S that becomes the semiconductor layer of the TFT
An i layer (i layer) 20 and an n ⁺ type a-Si layer (n ⁺ layer) 22 are sequentially deposited. Then, the i layer 20 and the n ⁺ layer 22 are patterned by using a reactive ion etching (RIE) method so that only a portion somewhat wider than the chromium electrode 12 is formed as shown in FIG. leave. This is shown in a plan view in FIG. 3 (b).

In the conventional process, since the lower layer of the i layer is a silicon nitride layer immediately and the etching characteristics of the i-type a-Si and the silicon nitride are similar, when the i layer and the n ⁺ layer are etched, It was difficult to stop etching accurately at the interface with the silicon nitride layer. However, in this embodiment, since the silicon oxide layer 16 is provided in advance on the silicon nitride layer 14 as described above, when the i layer and the n ⁺ layer are etched by the RIE method, the etching progresses. It can be stopped reliably when 16 is reached.

The interface characteristics between a-Si and silicon oxide are considered to be inferior to those between a-Si and silicon nitride. This is due to electronegativity. While electrons are attracted toward a-Si at the interface between a-Si and silicon nitride, electrons are attracted toward the silicon oxide at the interface between a-Si and silicon oxide. Therefore, the current in the active layer of the TFT is reduced. However, according to the experiments conducted by the present inventor, it has been found that such a problem does not occur if the thickness of the silicon oxide layer 16 is suppressed to about 500 Å as described above. The reason why the thickness of the silicon oxide layer 16 is 100 angstroms or more is that the effect of stopping the etching cannot be effectively exhibited if the thickness is less than 100 angstroms.

Thus, the silicon nitride layer 14 and the i layer 2 are
Since the silicon oxide layer is provided between the n ⁺ layer 22 and
And, it becomes possible to reliably stop the etching of the i layer 20 at the silicon oxide portion, and as a result, it is possible to maintain the flatness of the surface of the silicon oxide after etching,
There is no unevenness on the surface of the silicon nitride layer as in the conventional case. Therefore, the p-layer, i-layer, and n-layer of the photodiode, which will be formed on this layer in a later step, can be deposited flat and well, so that the product yield is improved.

After the etching process by the RIE method is completed, as shown in FIG. 1 (f), a chromium layer 24 is deposited on the entire surface. Then, as shown in FIG. 2G, p-type, i-type, and n-type amorphous silicon and ITO 26 which is a transparent conductive film are sequentially deposited on the upper right side of the chromium layer 24, and these are patterned. , P
An in-junction photodiode 28 is obtained. Figure 3 (c)
Is a plan view showing this state. Further, as shown in FIGS. 2H and 3D, the chromium layer 24 is patterned to form the source electrode 30 and the drain electrode 32 for the TFT 34, and the lower electrode 33 for the photodiode 28. To form.

Then, after depositing a silicon oxide layer 40 to be an insulating layer on this, as shown in FIGS. 2 (i) and 4 (e), patterning is performed to form a contact hole 42,
44 and 46 are formed. Furthermore, FIG. 2 (j) and FIG.
As shown in (f), a metal layer made of aluminum or chromium is deposited on this and patterned into a predetermined shape to obtain an upper electrode 48. The upper electrode connects the photodiode 28 and the TFT 34, and the TFT 3
The upper side of 4 is shielded by the upper electrode 50. Further, the electrode wiring 52 for the lower electrode of the photodiode 28 is also formed. The electrode wiring 52 is connected to an output circuit (not shown) including an amplifier, an integrator and the like via a matrix connection section.

Although only two sets of TFTs and photodiodes are shown in FIGS. 3 and 4, in the case of a contact type image sensor for A4 size with a sensor density of 8 elements / mm, 1728 sets of similar TFTs are actually used. And the photodiode is lateral,
That is, they are arranged in the main scanning direction. When the output circuit has 32 channels, these are divided into 54 blocks each having 32 sets, and the corresponding sets included in each block are matrix-connected so as to be connected to a common output circuit. On the other hand, the gate electrode 12 is connected in block units to an input circuit (not shown) provided in each block. When an input pulse is supplied from the input circuit to the gate of one block, all the TFTs in that block are turned on, and the charges corresponding to the image signal accumulated in the corresponding photodiode are read out and sent to the output circuit. By performing this operation for all blocks, an image signal for one line can be obtained.

The present invention is not limited to the above embodiments, but various modifications can be made within the scope of the invention.

[0028]

As described above, according to the first aspect of the invention, since the silicon oxide layer is provided on the silicon nitride layer, when the amorphous silicon layer deposited thereon is etched by the RIE method. In addition, since the progress of etching can be accurately stopped at the silicon nitride portion, it is possible to prevent excessive etching to the layer below it and also to keep the surface of the silicon oxide layer after etching flat. Therefore, it becomes easy to form the photodiode on the photodiode, and it is possible to provide the contact image sensor in which the yield in the manufacturing process is improved.

According to the second aspect of the present invention, by setting the thickness of the silicon oxide layer to 100 angstroms or more, the etching can be effectively stopped, and by setting it to 500 angstroms or less, the amorphous It is possible to provide a contact-type image sensor capable of preventing deterioration of interface characteristics due to electronegativity between a silicon layer and a silicon oxide layer.

According to the third aspect of the invention, since the step of forming the silicon oxide layer on the silicon nitride layer is provided, the amorphous silicon layer deposited on the silicon oxide layer is converted into R.
In the step of etching by the IE method or the like, the progress of etching can be accurately stopped at the silicon nitride portion, so that it is possible to prevent excessive etching down to the layer below the surface and the surface of the silicon oxide layer after etching. Since it can be kept flat, it is easy to form a photodiode on it, and it is possible to provide a method for manufacturing a contact image sensor in which the yield is improved.

According to the fourth aspect of the present invention, by setting the thickness of the silicon oxide layer to 100 angstroms or more, the etching can be effectively stopped, and by setting it to 500 angstroms or less, the amorphous It is possible to provide a method for manufacturing a contact-type image sensor capable of preventing deterioration of interface characteristics due to electronegativity between a silicon layer and a silicon oxide layer.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a series of manufacturing steps of a contact image sensor using a thin film transistor as a switching element and a photodiode as a photoelectric conversion element.

FIG. 2 is a partial cross-sectional view showing the manufacturing process of the contact image sensor, following FIG. 1;

FIG. 3 is a partial plan view showing a series of manufacturing steps of the contact image sensor drawn corresponding to FIGS. 1 and 2.

FIG. 4 is a partial plan view showing a series of manufacturing steps of the contact image sensor drawn in correspondence with FIGS. 1 and 2, following FIG. 3;

FIG. 5 is a partial cross-sectional view showing a series of manufacturing steps of a conventional contact image sensor.

[Explanation of symbols]

10, 60 Glass substrate 12, 62 Chrome electrode 14, 64 Silicon nitride layer 16 Silicon oxide 20, 66 i-type amorphous silicon layer 22, 68 n ⁺ -type amorphous silicon layer 28, 74 Photodiode 30, 76 Source electrode 32, 78 Drain electrode 33 lower electrode 34, 80 thin film transistor (TFT) 40, 82 silicon oxide layer 48, 50, 90, 94 upper electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Mitsuru Sakamoto 5-10-1, Fuchinobe, Sagamihara-shi, Kanagawa Inside the Electronics Research Laboratory, Nippon Steel Corporation (72) Seiji Takayama 5--10, Fuchinobe, Sagamihara, Kanagawa No. 1 Nippon Steel Corporation Electronics Research Laboratory

Claims (4)

[Claims] 1. A contact type image sensor in which a photodiode is used as a photoelectric conversion element and a thin film transistor is used as a switching element to form a sensor element, wherein a gate insulating film of the thin film transistor is made of silicon nitride and silicon oxide, and the gate insulating film is provided on a gate electrode side. To the silicon nitride and the silicon oxide in this order. 2. The contact image sensor according to claim 1, wherein the thickness of the silicon oxide is 100 angstroms or more and 500 angstroms or less. 3. A method of manufacturing a contact image sensor using a thin film transistor as a switching element of a sensor element, comprising: a first step of forming a gate electrode on a substrate; and a step of forming a silicon nitride layer on the gate electrode. The second step,
A third step of forming a silicon oxide layer on the silicon nitride layer, a fourth step of forming an amorphous silicon layer on the silicon oxide layer, and patterning the amorphous silicon layer into a predetermined shape. A fifth step of etching to the silicon oxide layer, a sixth step of forming a metal layer on the intermediate product obtained by the fifth step and patterning it into a predetermined shape, A seventh step of forming an amorphous silicon layer to be a photodiode on the patterned metal layer and patterning it into a predetermined shape, and forming an insulating film on the intermediate product obtained in the seventh step. And an eighth step of patterning this into a predetermined shape, and a ninth step of forming a wiring layer on the intermediate product obtained in the eighth step. Method for producing a contact type image sensor according to claim. 4. A silicon oxide layer is formed in the third step.
The method for manufacturing a contact image sensor according to claim 3, wherein the contact image sensor is formed to have a thickness of not less than 00 Å and not more than 500 Å.