JPH02210882A - Phototransistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve light utilization factor by providing a gap between gate and source electrodes and/or between gate and drain electrodes, at least one of these electrodes being transparent. CONSTITUTION:A phototransistor on a substrate 1 consists of a gate electrode 6, a gate insulating film 3, a semiconductor layer 2, an ohmic contact layer 4, a source electrode 5 and a drain electrode 7. The regions of the semiconductor layer 2 corresponding to the gaps between the source and gate electrodes 5 and 6 and between the drain and gate electrodes 7 and 6 are irradiated with light and photo carriers are generated thereby. Further, light is incident also through the transparent source and drain electrodes 5 and 7 to generate photo carriers. Thus, the phototransistor can be provided on glass. Accordingly, it is possible to obtain the phototransistor with high photosensitivity, while improving the light utilization factor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a phototransistor used in an optical sensor or the like having a switching function and an amplification function, and a method for manufacturing the same.

[Conventional technology]

Conventional phototransistors have a basic structure of bipolar transistors. Follow me.

- The structure is such that light hits the base, and minority carriers are injected into the base using light. Also,
Japanese Patent Application No. 57-220641 discloses the use of an a-8i/metal interface reaction layer as a transparent electrode in the formation of semiconductor devices such as solar cells and photodiodes.

['IAM3 that the invention seeks to solve] By the way, it is difficult to make the conventional bipolar transistors effective in terms of light utilization efficiency, directivity, etc., and it is difficult to develop them into field effect transistors. There were problems such as not being able to do so.

In order to solve this problem, a thin film transistor type phototransistor is proposed in Japanese Patent Application No. 63-244167. Because thin film transistors are structurally field-effect transistors, they have characteristics such as high input impedance and voltage-controlled devices, compared to bipolar transistors.

There are many advantages, and the manufacturing method is relatively simple.

However, the conventional thin-film phototransistor described above has the disadvantage that the source, drain, and gate electrodes are opaque and cover a considerable portion of the phototransistor's channel, resulting in a low light utilization rate. It had

An object of the present invention is to improve the light utilization efficiency in the phototransistor and provide a highly sensitive phototransistor.

[Means to solve the problem]

In order to achieve the above object, the following technical means were used in the present invention.

First, we used thin film transistors to realize voltage-controlled field-effect phototransistors with high input impedance. In addition, in order to simplify the manufacturing method, a Brenna type thin film transistor was used.

In order to obtain even better phototransistor characteristics, a gap was provided between the source electrode and the gate electrode, or between the drain electrode and the gate electrode, or both. In addition, to facilitate the introduction of light and increase the efficiency of light use, the source electrode
At least one of the drain electrode and the gate electrode was a transparent electrode.

Although the use of an opaque substrate is a constraint for an optical sensor, in the present invention, by using a film transistor, it is possible to form a phototransistor on a transparent substrate, that is, glass.

Additionally, hydrogenated amorphous silicon is used as the semiconductor layer to increase sensitivity to light. Hydrogenated amorphous silicon is a thin film that can be deposited by low-temperature processes,
It is a particularly suitable material for making large-area devices.

A film forming method typified by the plasma CVD method is particularly suitable for this purpose, and is suitable for simplifying the production of phototransistors.

[Effect]

A phototransistor formed on a substrate includes a gate electrode, a gate insulating film, a half-soul layer, an ohmic contact layer, a source electrode, and a drain electrode.

The gate electrode operates as a voltage controlled electrode that forms a channel in the semiconductor layer. Basically, no light enters the semiconductor region that overlaps with the gate electrode, so 9
Acts as an electrical switch electrode.

In the semiconductor layer located in the gap between the source electrode and the gate electrode and between the drain electrode and the gate electrode, photocarriers are generated in the region irradiated with light. Further, light also enters through the transparent electrodes of the source electrode and the drain electrode, and photocarriers are generated.

By forming the gate hw electrode, source electrode, and drain electrode in a planar shape, the manufacturing method of the phototransistor is simplified.

〔Example〕

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

First, the manufacturing process is as follows. A-5i (hydrogenated amorphous silicon) layer 2 as a semiconductor layer is formed on the substrate 1 by plasma CVD. Silicon nitride 3 of the gate insulating film is 500 nm thick each.

Deposit to a thickness of 300 nm. After the deposition, the silicon nitride 3 is patterned by photolithography, and an n+ a-Si layer 4 serving as an ohmic contact layer and CrM serving as a gate electrode are deposited thereon by plasma CVD and sputtering, respectively. Film thickness is 30nm each
, 200 nm.

After patterning the Cr film to form the gate electrode 6,
ITO is deposited by sputtering and patterned to form a source electrode 5 and a drain electrode 7. Using these electrodes 5, 6.7 as a mask, n+ 7m4 is removed. This completes the phototransistor, and finally silicon nitride 8 is deposited as a protective film and contact holes are formed to complete the entire process.

In the plasma CVD method, a monosilane SiH4-based gas is introduced into a vacuum container, and RF power is applied to form plasma by glow discharge, thereby depositing decomposed Si and hydrogen on the substrate. . In this case, a-8i (i layer) is formed, but 5iH
If nitrogen or ammonia is introduced together with a, SiN is formed. Furthermore, by introducing phosphine (PHa), a-5i doped with phosphorus, which is an n-type impurity, can be formed. These become a gate insulating film, a protective film, and an ohmic contact layer. Note that a-8i of the i layer and n+ layer
When forming 5iHa, it is also effective to add hydrogen to 5iHa and introduce it into the container.

As shown in FIG. 1, in this embodiment, the source electrode 5
and gate electrode 6. Patterning is performed so that there is a gap between the drain electrode 7 and the gate electrode 6, and the gap interval is 5 μm. Transistor W/L is 500pm/
It is 20 μm. That is, the gate width is 10 μm.

The phototransistor fabricated as described above was biased as shown in FIG. 2, and light was irradiated from the gate electrode 6 side to evaluate its characteristics.

FIG. 3 shows the relationship between drain voltage and drain current during 5 # OOOIt x light irradiation. When the gate electrode potential is set to the same potential as the source electrode potential or to a negative potential, the drain current is kept at a low level, but when the gate potential is biased positively, the drain current has good saturation characteristics as shown in the figure. flows.

FIG. 4 similarly shows the photoelectric dependence of the drain current when the gate voltage is set to a constant value (Vo=10V). Also, in FIG. 5, the same <s, oo.

It shows the relationship between drain current and gate voltage under Qx irradiation. Ratio of drain current in the dark and under light irradiation (
Iphoto/Idark) is 600, which is a satisfactory value.

FIG. 6 shows another embodiment of the invention.

This embodiment is similar to the embodiment shown in FIG. 1, but differs in the transparent electrode and its manufacturing method. After patterning silicon nitride 3, which is a gate insulating film, an a-8i n middle layer 4 is deposited by plasma CVD, and then Cr is deposited by sputter deposition.

At this time, the substrate 1 is heated to 200°C, so that n
An interfacial reaction layer 10 is formed between +asi4 and Cr.

This interfacial reaction layer 10 is a layer that should be called amorphous silicide, and is characterized by being extremely thin (~2 nm). As detailed in the above-mentioned patent application No. 57-220641,
This interfacial layer 10 has high conductivity despite its thinness, and because of its thinness, it transmits light well. Therefore, it is useful as a transparent conductive film.

This interface layer 10 is not limited to Cr, but may also be made of Mo, W, or Ta.

Similar results can be obtained with any metal containing at least one of the following metal groups: Ta, V, Zr, Hf, Ni, and Cu. Further, the substrate may be heated during the deposition of these metals, and it is also possible to form the metals by heat treatment at a temperature of around 200° C. after deposition at room temperature. At this time, the heat treatment atmosphere does not particularly matter; it may be vacuum or nitrogen.

Almost the same results can be obtained even if the test is performed in an atmosphere such as air.

After forming the interface layer 10, the source electrode 5 and the gate electrode 6 are formed.
．． Drain electrode 7 is formed separately.

At this time, the Cr film interfacial reaction layer, n+a-8iJil, is also etched off for separation. Next, Cr is removed, leaving the source electrode 5 and drain electrode 7 partially.

This exposes a region of the interfacial reaction layer 10 closer to the gate electrode. This layer acts as a transparent electrode. In this structure, incident light not only enters the gap between the source electrode and the gate electrode and the gap between the drain electrode 7 and the gate electrode 6 and generates photocarriers, but also enters through the exposed interface layer and enters the semiconductor layer. reach and generate photocarriers. As a result, sufficient carriers are supplied, and a phototransistor with good characteristics can be obtained.

The feature of this embodiment is that the phototransistor can be manufactured by a simple process without using a process-sensitive material such as ITO.

FIG. 7 shows another embodiment of the present invention. After forming a light shielding film 11 of Cr on a glass substrate 1, a silicon nitride film 12 as an insulating film is deposited.

After forming a layer 2 of a-Si and a gate insulating film 3 of silicon nitride on this, buttering is performed.

After depositing the a-8i n+ layer 4 and Cr, Cr is patterned. The gate @w46 and the drain electrode 7 are shaded by the patterned Cr. Next, I'1''O is formed by sputter deposition to form a transparent source electrode 5.Furthermore, using the source electrode 5, gate electrode 6, and drain electrode 7 as a mask, n+a-8i4 is removed by etching. Finally, a protective film 8 is deposited.

As described above, the influence of light from the substrate side can be minimized, and the level of dark current can be made extremely low. FIG. 8 shows another embodiment of the present invention, which is a so-called staggered transistor in which the gate and source and the gate and drain have a semiconductor layer interposed between them, and the gate electrode 6 is made of ITO. source and drain electrodes 5,
7 is made of Cr. Almost the entire surface of the semiconductor layer is irradiated with light, resulting in a phototransistor with good photosensitivity characteristics.

Although the present invention has been described above based on examples, the present invention is not limited to these examples.

That is, the semiconductor layer may be made of amorphous materials such as a-8iC, a-8iGe, etc., or t
It may be a UV group or 1-IV group compound semiconductor.

In addition to silicon nitride, the gate insulating film may be made of oxides such as silicon dioxide, Tazos, AQtos, etc., and a stack of these, ie, SiN/SiOx, Taxes/ Si
N, A11zOs/S i N, etc.
Further, the manufacturing method thereof may be a dry process such as a plasma CVD method or a sputtering method, or a wet process typified by anodization.

Further, the substrate is not limited to a glass substrate, and may be an opaque substrate.

In the embodiment, the case where there is a protrusion between the source electrode and the gate electrode has been described, but a phototransistor having an overlapping portion on either side is also possible.

For example, the gate electrode and the drain electrode may have an overlapping part, and there may be a gap between the source and the gate.Of course, in this case, an insulating film such as silicon nitride must be interposed between the gate and the drain. There is.

〔Effect of the invention〕

According to the present invention, a new thin film transistor type phototransistor can be provided.

In the present invention, by making at least one of the gate, source, and drain electrodes a transparent electrode, the light utilization efficiency can be increased and a phototransistor with high photosensitivity can be obtained.

Furthermore, by using a transparent electrode, it is relatively easy to fabricate a planar phototransistor.

By using a-Si as a semiconductor, it has high photosensitivity, I on / I off ratio and I pho
A phototransistor with a high to /I dark ratio can be provided.

By using an interfacial reaction layer for the transparent electrode, a phototransistor that is easy to manufacture can be provided.

[Brief explanation of the drawing]

1 and 6 to 8 are cross-sectional views of a phototransistor according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of bias application to the transistor, and FIGS. 3 to 5 are the same as those shown in FIG. FIG. 3 is a current-voltage characteristic diagram of a phototransistor according to an example. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Semiconductor layer, 3... Gate insulating film, 4... Ohmic contact, 5... Source electrode, 6... Gate electrode, 7... Drain electrode, 8・
...Protective film, 9...Irradiation light, 10...Interfacial reaction layer,
11... Light shielding film. Vq<v) 2nd γ′ tomari VcL(V)

Claims (1)

[Claims] 1. In a thin film transistor having at least a gate electrode, a source electrode, a drain electrode, a gate insulating film, and a semiconductor layer, an overlapping portion between the gate electrode and the source electrode, between the gate electrode and the drain electrode, or both. 1. A phototransistor characterized in that the electrodes are arranged so that there is no porosity, and at least one of the source electrode, drain electrode, and gate electrode is a transparent electrode. 2. The phototransistor according to claim 1, wherein the gate electrode, source electrode, and drain electrode are formed on the same plane. 3. The phototransistor according to claim 1 or 2, wherein the semiconductor layer is made of hydrogenated amorphous silicon. 4. The phototransistor according to any one of claims 1 to 3, wherein the transparent electrode is ITO (indium tin oxide). 5. The phototransistor according to claim 3, wherein the transparent electrode is an interfacial reaction layer between metal and hydrogenated amorphous silicon. 6. The above metals are Cr, Mo, W, Ti, Ta, V, Zr
6. The phototransistor according to claim 5, wherein the phototransistor is a metal containing at least one selected from the group consisting of , Nb, Hf, Ni, and Cu(7). 7. After forming an interfacial reaction layer by depositing a metal containing at least one of the metal group described in claim 6 on amorphous silicon, removing the metal in a predetermined region to form a source electrode, a drain electrode, and a gate electrode. 7. The method of manufacturing a phototransistor according to claim 3, wherein at least one of the following is manufactured.