JPH05235354A - Semiconductor device - Google Patents

Abstract

PURPOSE:To enable a transistor to operate under illumination by using a semiconductor layer consisting of a lower layer containing carbon and an upper layer containing nitrogen. CONSTITUTION:A semiconductor device comprises a substrate on which are formed a first conducting layer 2 for a gate electrode, an insulating layer 3 for a gate insulator, a first semiconductor layer 4 for a channel, and second conducting layers 6 for ohmic contact on the first semiconductor layer 4. The first semiconductor layer 4 consists of a lower layer 4a containing carbon and an upper layer 4b containing nitrogen. This improves the photosensitivity of the first semiconductor layer 4, and thus the transistor operation can be stabilized under illumination.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a semiconductor device used for a switching transistor of an active matrix liquid crystal display device and a manufacturing method thereof.

[0002]

2. Description of the Related Art The structure of a conventional semiconductor device is shown in FIG.
The semiconductor device of FIG. 1 is disclosed in Japanese Patent Application No. 3-2756
The semiconductor device disclosed in No. 75. A first conductive layer 2 to be a gate electrode, an insulating layer 3 to be a gate insulating film, and a first semiconductor layer 4 to be a channel layer are provided on a substrate 1, and ohmic contact is provided on the first semiconductor layer 4. A semiconductor device in which a second semiconductor layer 5 serving as a layer and a second conductive layer 6 serving as a source / drain electrode are separately provided, and the first semiconductor layer 4 does not contain a nitrogen element and a carbon element. The lower semiconductor layer 4a and the upper semiconductor layer 4b containing a nitrogen element or a carbon element are formed, and the second semiconductor layer 5 is formed of a microcrystalline semiconductor layer. The first semiconductor layer 4 and the second semiconductor layer 5 are formed of amorphous silicon or the like.

With this structure, when the ohmic contact layer 5 and the source / drain electrodes 6 are divided by etching, the upper semiconductor layer 4 of the first semiconductor layer 4 is divided.
Since b can be used as an etching stopper layer, it is not necessary to form the etching stopper layer in a special step, and the channel width is shortened to achieve high definition.

In such a semiconductor device, (a) a first conductive layer 2 to be a gate electrode is formed on a substrate 1 and patterned, and (b) a gate insulating layer is formed on the first conductive layer 2. An insulating layer 3 to be a film, a lower semiconductor layer 4a containing no nitrogen element and carbon element, a first semiconductor layer 4 composed of an upper semiconductor layer 4b containing nitrogen element or carbon element, and a second semiconductor layer containing a microcrystalline semiconductor layer. Semiconductor layer 5, and source
The second conductive layer 6 to be the drain electrode is sequentially laminated,
(C) The first semiconductor layer 4, the second semiconductor layer 5, and the second conductive layer 6 around the first conductive layer 2 are removed by etching, and (d) the first conductive layer 2 is removed. It is formed by etching away the second semiconductor layer 5 and the second conductive layer 6 in the central portion of.

[0005]

However, in the above-mentioned conventional semiconductor device, the lower semiconductor layer 4 of the first semiconductor layer 4 is formed.
Although the film thickness of a can be made as thin as about 50Å, since i-type amorphous silicon has a good photosensitivity, for example, the film thickness of the lower semiconductor layer 4a is set to 50Å and the upper semiconductor layer 4b is Even if the film thickness is set to about 800 Å, there is a problem that the off current of the transistor rises when irradiated with light.

In addition, the lower semiconductor layer 4a and the upper semiconductor layer 4
As shown in FIG. 2, the barrier ΔE between the lower semiconductor layer 4a and the upper semiconductor layer 4b is increased due to the band gap difference with the upper semiconductor layer 4b.
Occurs, and there is a problem in that the rise in the voltage / current (Vd-Id) characteristics of the transistor deteriorates. That is, a semiconductor layer (for example, the upper semiconductor layer 4b shown in FIG. 1) formed by setting ammonia gas (NH ₃ ) serving as a nitrogen element source to NH ₃ / SiH ₄ = 0.1 and such an ammonia gas are used. Formed without a semiconductor layer (see, for example, FIG.
To the lower semiconductor layer 4a) shown in FIG.
This is because a barrier ΔE of 2 eV is generated. Note that FIG.
Where Ef is the Fermi level, Ec is the conduction band, and E
v represents a valence band, respectively.

[0007]

The semiconductor device according to the first invention is made in view of the above problems, and is characterized in that a gate electrode is formed on a substrate. A conductive layer, an insulating layer to be a gate insulating film, and a first semiconductor layer to be a channel are provided, and a second semiconductor layer to be an ohmic contact layer and a source / drain electrode are provided on the first semiconductor layer. In the semiconductor device provided by dividing the second conductive layer, the first semiconductor layer is formed of a lower semiconductor layer containing a carbon element and an upper semiconductor layer containing a nitrogen element, and preferably ,
The lower semiconductor layer and the upper semiconductor layer have the same band gap. A characteristic of the semiconductor device according to the second invention is that the first conductive layer serving as a gate electrode is formed on the substrate,
An insulating layer to be a gate insulating film and a first semiconductor layer to be a channel are provided, and a second semiconductor layer to be an ohmic contact layer and a second conductive layer to be a source / drain electrode are provided on the first semiconductor layer. In the semiconductor device provided by dividing the layers, the first semiconductor layer is formed by a lower semiconductor layer containing a low concentration of carbon element and an upper semiconductor layer containing a high concentration of carbon element.

[0008]

As described above, the first semiconductor layer serving as a channel is formed of the lower semiconductor layer containing the carbon element and the upper semiconductor layer containing the nitrogen element, or the lower semiconductor layer containing the carbon element at a low concentration. When the upper semiconductor layer containing a high concentration of carbon element is used, the photosensitivity of the first semiconductor layer is lowered, so that the transistor can be stably operated even under light irradiation. Further, as described above, when the band gaps of the lower semiconductor layer and the upper semiconductor layer are matched,
The barrier in the band gap is eliminated, the rise of the voltage / current (Vd-Id) characteristics of the transistor is improved, and a transistor having excellent characteristics can be obtained.

[0009]

EXAMPLES Examples of the first invention will be described below. The structure of the semiconductor device is the same as that of the conventional device shown in FIG. The substrate 1 is composed of a # 7059 substrate or the like. First conductive layer 2
Is formed using chromium (Cr), tantalum (Ta), aluminum (Al), or the like to a thickness of about 1000 Å by a vacuum deposition method or a sputtering method. The insulating layer 3 is composed of a one-layer structure of silicon nitride or a two-layer structure of tantalum oxide and silicon nitride, the silicon nitride layer is formed by plasma CVD method, and the tantalum oxide layer is formed by anodic oxidation method. It is formed. The thickness of this insulating layer 3 is 50
It is about 00Å. Lower semiconductor layer 4 of first semiconductor layer 4
a is, for example, silane gas (SiH ₄ ) and methane gas (C
It is formed to a thickness of about 200Å by a plasma CVD method using H ₄ ). Upper semiconductor layer 4b of the first semiconductor layer 4
Has a thickness of 800 by plasma CVD using silane gas (SiH ₄ ) and ammonia gas (NH ₃ ).
Å It is formed in about. The second semiconductor layer 5 is composed of, for example, an n ⁺ -type microcrystalline semiconductor layer containing phosphine (PH ₃ ) or the like at a high concentration (10 ¹⁸ to 10 ²¹ pieces / cm ³ in terms of phosphorus element), Thickness 100 by plasma CVD method
It is formed to about 0Å. The second conductive layer 6 is formed of aluminum, tantalum, chromium, titanium (Ti), or the like, and is formed to have a thickness of about 1000Å by a vacuum deposition method or a sputtering method.

In FIG. 3, the lower semiconductor layer 4a is formed to a thickness of 200Å without using methane gas or ammonia gas, and the upper semiconductor layer 4b is set so that the flow rate ratio of ammonia gas and silane gas is NH ₃ / SiH ₄ = 0.1. Then 800
The relationship between the gate voltage Vg and the drain current Id of a transistor formed to have a thickness of Å is shown. The drain voltage Vd
Is 15 V, the channel width W and the channel length L of the transistor are
The ratio of W / L = 5.4. As is clear from FIG. 3, this transistor has excellent ON / OFF characteristics. The band gap E of this upper semiconductor layer 4b
_{When opt} was measured, it was 1.9 eV.

In addition, CH ₄ / of methane gas and silane gas
The band gap E _opt of the semiconductor layer formed by changing various SiH ₄ ratios was measured, and as shown in the table below, CH
It was found to be 1.91 eV when ₄ / SiH ₄ = 0.5, which is in agreement with the band gap of the upper semiconductor layer 4b.

CH ₄ / SiH ₄ ratio Bandgap (eV) 0.1 1.88 0.25 1.89 0.5 1.91 0.75 1.93 1.0 1.06 2.0 2.04 ..

That is, when the lower semiconductor layer 4a is formed by setting the flow rate ratio of methane gas and silane gas to 0.5 and the upper layer semiconductor 4b is formed by setting the flow rate ratio of ammonia gas and silane gas to 0.1, the lower layer is formed. A band gap E _opt of the semiconductor layer 4a and the upper semiconductor layer 4b can be made to coincide with each other, and a transistor having excellent ON / OFF characteristics can be obtained.

FIG. 4 shows the photosensitivity of the semiconductor layer formed by changing the flow rate ratio of methane gas and silane gas, and FIG. 5 shows the photosensitivity of the semiconductor layer formed by changing the flow rate ratio of ammonia gas and silane gas. Show. This photosensitivity means that the semiconductor layer (i
The relative photosensitivity when the photosensitivity of the (type amorphous silicon layer) is 1 (10 ⁰ ). The semiconductor layer shown in FIGS. 4 and 5 has a substrate temperature of 240 ° C. and
It is formed by setting the power to 30 W (0.08 W / cm ² ). As is clear from FIG. 4, when the semiconductor layer is formed with the flow ratio of methane gas and silane gas set to 0.1, the photosensitivity of this semiconductor layer is reduced to 1/10, and the flow ratio of methane gas and silane gas is further reduced to 1 When the semiconductor layer is formed by setting to 0.0, the photosensitivity of this semiconductor layer is about 1
/ 700. Incidentally, when the lower semiconductor layer 4a is formed by setting the flow rate ratio of the methane gas and the silane gas to 0.5 as described above, the photosensitivity is 1/25. Further, as apparent from FIG. 5, when the semiconductor layer is formed by setting the flow rate ratio of the ammonia gas and the silane gas to 0.1,
The photosensitivity of this semiconductor layer drops to about 1/350, and when the flow rate ratio is set to 1.0 to form a semiconductor layer, the photosensitivity of this semiconductor layer drops to 1/20000. Therefore, the lower semiconductor layer 4 is formed by using methane gas and silane gas.
By forming a and forming the upper semiconductor layer 4b using ammonia gas and silane gas, a transistor having such a semiconductor layer can operate stably even under light irradiation.

Next, an embodiment of the second invention will be described. The structure of the semiconductor device according to the second invention is the same as that of the semiconductor device shown in FIG. The semiconductor device according to the second invention differs from the semiconductor device according to the first invention in that the first semiconductor layer 4 contains a lower semiconductor layer 4a containing a low concentration of carbon element and a high concentration of a carbon element. It is a point formed by the upper semiconductor layer 4a.

FIG. 6 shows a gate voltage Vg and a drain current of a transistor formed as a first semiconductor layer 4 with a flow rate ratio of methane gas and silane gas of CH ₄ / SiH ₄ = 1.0 and a thickness of 1000 Å. The relationship of Id is shown. The drain voltage Vd is 15V. As is apparent from FIG. 6, even if the channel layer is formed of a single semiconductor layer containing a carbon element, a transistor having favorable ON / OFF characteristics can be obtained. However, in the transistor shown in FIG. Since it is slightly low, a transistor having a large ON current can be obtained by further reducing the flow rate ratio of methane gas and silane gas. On the other hand, as is clear from FIG. 4, the photosensitivity increases when the flow rate ratio between the methane gas and the silane gas is reduced. Therefore, when the lower semiconductor layer 4a of the first semiconductor layer 4 is formed with a small flow ratio of methane gas and silane gas and the upper semiconductor layer 4b is formed with a large flow ratio of methane gas and silane gas, the ON current is increased. Moreover, the transistor has low photosensitivity. That is, the lower semiconductor layer 4a is formed with the flow rate ratio of methane gas and silane gas set to 0.1, and the upper semiconductor layer 4b is formed with the flow rate ratio of methane gas and silane gas set to 1.0.

When the lower semiconductor layer 4a is formed by reducing the flow rate ratio of methane gas, the photosensitivity is increased. Therefore, it is desirable that the lower semiconductor layer 4a be formed as thin as possible, preferably 100 Å or less. .. Further, as described above, when the lower semiconductor layer 4a is formed with a small flow ratio of methane gas and silane gas and the upper semiconductor layer 4b is formed with a large flow ratio of methane gas and silane gas, the band gap E _opt is Lower semiconductor layer 4a
<It becomes the lower semiconductor layer 4b, but ΔE is about 0.04 eV in the combination of the same gas ratios, which can be made considerably lower than the conventional one.

Thus, the lower semiconductor layer 4a is formed of a layer containing a low concentration of carbon element, and the upper semiconductor layer 4 is formed.
Even if b is formed of a layer containing a high concentration of carbon element, the photosensitivity can be further lowered while maintaining the same ON / OFF ratio as the conventional semiconductor device.

[0019]

As described above, according to the semiconductor device of the first invention, the first semiconductor layer to be the channel is formed of the lower semiconductor layer containing the carbon element and the upper semiconductor layer containing the nitrogen element. Therefore, the semiconductor device can be stably operated even under light irradiation, and the band gaps of the lower semiconductor layer and the upper semiconductor layer can be easily matched.
By eliminating the barrier in the bandgap, the voltage / current (Vd-Id) characteristics of the transistor rise better,
A semiconductor device having good characteristics can be obtained.
Further, according to the semiconductor device of the second invention, the first semiconductor layer serving as a channel is formed of a lower semiconductor layer containing a low concentration of carbon element and an upper semiconductor layer containing a high concentration of carbon element. From the ON / same as the conventional semiconductor device
A semiconductor device having a lower photosensitivity while maintaining the OFF ratio can be obtained. Further, in both the first and second inventions, a stopper layer for etching when dividing the source / drain is not required, the manufacturing process is simplified, and the manufacturing yield is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a semiconductor device.

FIG. 2 is a diagram showing a band model of a first semiconductor layer which becomes a channel of a conventional semiconductor device.

FIG. 3 is a VI of a transistor in which an upper semiconductor layer is formed by setting a flow rate ratio of ammonia gas and silane gas to 0.1.
It is a figure which shows a characteristic.

FIG. 4 is a diagram showing the photosensitivity of a semiconductor layer formed by changing the flow rate ratio of methane gas and silane gas.

FIG. 5 is a diagram showing the photosensitivity of a semiconductor layer formed by changing the flow rate ratio of ammonia gas and silane gas.

FIG. 6 is a VI of a transistor in which the first semiconductor layer is formed by setting the flow ratio of methane gas and silane gas to 1.0.
It is a figure which shows a characteristic.

[Explanation of symbols]

1 ... Substrate, 2 ... First conductive layer, 3 ... Insulating layer, 4 ... First semiconductor layer, 4a ... Lower semiconductor layer, 4b ... Upper semiconductor layer, 5 ... second semiconductor layer, 6 ... second conductive layer.

Claims (7)

[Claims] 1. A first conductive layer to be a gate electrode, an insulating layer to be a gate insulating film, and a first semiconductor layer to be a channel are provided on a substrate, and an ohmic contact layer is provided on the first semiconductor layer. In a semiconductor device in which a second semiconductor layer to be a layer and a second conductive layer to be a source / drain electrode are separately provided, the first semiconductor layer contains a lower semiconductor layer containing a carbon element and a nitrogen element. A semiconductor device comprising an upper semiconductor layer. 2. The semiconductor device according to claim 1, wherein the lower semiconductor layer contains up to 40 atom% of carbon element. 3. The semiconductor device according to claim 1, wherein the upper semiconductor layer contains a nitrogen element up to 25 atom%. 4. The band gap of the lower semiconductor layer and the upper semiconductor layer are substantially the same.
The semiconductor device according to. 5. A first conductive layer to be a gate electrode, an insulating layer to be a gate insulating film, and a first semiconductor layer to be a channel are provided on a substrate, and an ohmic contact layer is provided on the first semiconductor layer. In a semiconductor device in which a second semiconductor layer that becomes a second conductive layer and a second conductive layer that becomes a source / drain electrode are provided separately, a lower semiconductor layer containing the first semiconductor layer at a low concentration and a carbon element A semiconductor device, wherein the semiconductor device is formed of an upper semiconductor layer containing a high concentration of. 6. The semiconductor device according to claim 5, wherein the lower semiconductor layer contains up to 20 atomic% of carbon element. 7. The semiconductor device according to claim 5, wherein the upper semiconductor layer contains up to 40 atom% of carbon element.