JPH08335703A - Thin-film transistor and its manufacture - Google Patents

Abstract

PURPOSE: To provide a transistor which has an excellent mobility by depositing a silicon-made semiconductor active layer and an impurity added silicon-made impurity layer and adding a noble gas element onto a face of the semiconductor active layer which is in contact with the impurity layer. CONSTITUTION: A gate electrode 1 is formed on a glass substrate 10. Then, an insulating film 2 is formed so as to coat the gate electrode 1. Nextly, a first film preparation process is conducted by plasma CVD to form a semiconductor active layer. After the first film preparation process, a plasma treatment is conducted in the same equipment as the first film preparation process was conducted, without exposing the substrate in the air. After the plasma treatment, a second film preparation process is conducted by plasma CVD to form an impurity layer. Finally, a source electrode 7 and a drain electrode 6 are formed and then a passivation film 8 is prepared. Thereby, a thin-film transistor is fabricated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor and its manufacturing method.

[0002]

2. Description of the Related Art Conventionally, a thin film transistor has been manufactured by the method shown in FIG. That is, the substrate 10 such as glass
After forming the gate electrode 1 thereon, an insulating film (for example, a silicon nitride film) 2 is formed so as to cover the gate electrode 1, and then an i layer 3 to be a semiconductor active layer is formed on the insulating film 2 (see FIG. 2). (A)). Next, on the surface of the semiconductor active layer (i layer) 3, an impurity layer (n ⁺ layer) 4 to which impurities have been added is laminated (FIG. 2B).

After forming the impurity layer 4, the semiconductor active layer 3 and the impurity layer 4 are processed into a predetermined shape, then the source electrode 7 and the drain electrode 6 are formed, and finally the passivation film 8 is formed to form a thin film transistor.

By the way, in recent years, the demands on the characteristics of thin film transistors have become strict, and in particular, there has been a demand for thin film transistors having even higher mobility than in the past.

However, the above-mentioned conventional thin film transistor has a limit in its characteristics, and cannot meet the above demand.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thin film transistor having a higher mobility than ever before and a manufacturing method thereof.

[0007]

A thin film transistor for solving the above problems is formed by laminating a semiconductor active layer made of silicon and an impurity layer made of silicon to which impurities are added. A rare gas element is added to the surface in contact with the impurity layer.

Further, in a method of manufacturing a thin film transistor for solving the above-mentioned problems, a first film forming step of forming a semiconductor active layer made of silicon on a surface of a substrate, and the semiconductor active in an atmosphere containing at least a rare gas. The method is characterized by comprising a plasma treatment step of exposing the surface of the layer to plasma and a second film forming step of laminating and forming an impurity layer made of impurity-added silicon on the surface of the semiconductor active layer.

[0009]

The function of the present invention will be described below together with the embodiment of the present invention. Conventionally, the impurity layer (n ⁺ layer) is formed immediately after the semiconductor active layer (i layer) is formed, and the i layer is not subjected to any treatment before the n ⁺ film is formed. Further, no processing was applied to the i layer even before the passivation film was formed.

However, when the present inventor irradiates the surface of the i layer with a rare gas plasma after forming the i layer and then forms the n ⁺ layer, the mobility of the completed thin film transistor is significantly improved as compared with the conventional one. I found a thing. The reason is not clear. However, it was confirmed that a rare gas element exists at the interface between the i layer and the n ⁺ layer when the surface of the i layer is irradiated with a rare gas plasma before the n ⁺ layer is formed and then the n ⁺ layer is formed. Further, the mobility is remarkably improved only when the rare gas element is present at the interface between the i layer and the n ⁺ layer. Therefore, it is considered that this rare gas element causes the mobility improvement. To be

After all, the mobility can be remarkably improved by allowing the rare gas element to exist at the interface between the i layer and the n ⁺ layer. The "interface" here includes a portion having a depth of about 10 nm from the surface of the i layer.

In order to allow the rare gas to exist, it is better to mix H ₂ gas, PH ₃ gas, and F ₂ gas with the rare gas at the interface between the i layer and the n ⁺ layer than when the rare gas is used alone. A rare gas element is likely to be present, which is preferable. The reason is not clear.

The first film forming step, the plasma processing step, and the second film forming step are preferably performed at 350 ° C. or lower. When the temperature is 350 ° C. or lower, the rare gas element is likely to exist at the interface between the i layer and the n ⁺ layer, and the mobility becomes better. The reason for this is unknown. It is more preferable to carry out at 300 ° C or lower.

In particular, since the mobility sharply improves when the content rate of the rare gas element is 0.01 atomic%, the content of the rare gas element is preferably 0.01 atomic% or more. The mobility starts to decrease when the content exceeds 0.5 atom%. Therefore, 0.0
1 atomic% to 0.5 atomic% is preferable (claim 2).

The content of the rare gas element can be increased by, for example, lengthening the irradiation time of plasma, and the rare gas is diluted with another gas (for example, hydrogen gas) and diluted. If plasma is generated by the gas, the content of the rare gas element can be reduced. Therefore, a desired rare gas element content can be obtained by appropriately controlling the dilution ratio of the rare gas and the plasma irradiation time.

As the rare gas, He gas, Ne gas, Ar gas, Xe gas, and Kr gas are appropriately used.

The step of forming the semiconductor active layer (first step)
It is preferable that the film forming step (1) and the step of laminating the impurity layer (second film forming step) are performed by a plasma CVD film forming method (claim 4). When the first film forming step and the second film forming step are performed by the plasma CVD film forming method, both film forming steps can be performed by the same film forming apparatus, and the plasma processing step (the surface of the semiconductor active layer is The step of exposing to plasma can also be performed by changing the introduced gas in the same device. In this way, the first film forming step, the plasma treatment step, and the second film forming step can be performed by the same film forming apparatus by changing only the introduced gas, which means that the layer surface after each step. Since it is possible to perform continuous film formation without exposing the thin film to the atmosphere (claim 5), the surface of each layer is not contaminated by natural oxides, moisture, etc. It can be manufactured.

[0018]

Embodiments of the present invention will be described below. However, it goes without saying that the scope of the present invention is not limited to the following examples.

(Embodiment 1) Embodiment 1 will be described with reference to FIG. In this example, first, the gate electrode 1 was formed on the glass substrate 10. Next, an insulating film (silicon nitride film) 2 was formed with a thickness of 300 nm so as to cover the gate electrode 1.
The substrate temperature was 250 ° C. Next, the first film forming step was performed by the plasma CVD method under the following conditions to form an a-Si (i) layer having a thickness of 100 nm.

Raw material gas: SiH ₄ 100 sccm, H ₂ 400 sccm Gas pressure: 100 Pa Substrate temperature: 250 ° C. RF power: 100 W Base plate: 4 inch square × 16 sheets Electrode: 60 cm square

After the completion of the first film forming step, the plasma treatment step was performed under the following conditions in the same apparatus without exposing the substrate to the atmosphere. Source gas: Ar 600 sccm H ₂ 400 sccm Gas pressure: 70 Pa RF power: 400 W Substrate temperature: 250 ° C. Processing time: 30 minutes

After the plasma processing step was completed, the second film forming step was performed by the plasma CVD method under the following conditions to form an a-Si (n ⁺ ) layer having a thickness of 20 nm. Source gas: SiH ₄ 99 sccm, H ₂ 400 sccm PH ₃ 1 sccm Gas pressure: 100 Pa Base temperature: 250 ° C. RF power: 100 W Finally, after forming the source electrode 7 and the drain electrode 6,
The passivation film 8 was formed to manufacture the thin film transistor shown in FIG.

Measure the mobility of this thin film transistor
As a result, the mobility is 0.6 (cm ²/ Vsec)
It was. Also, i layer and n⁺Noble gas elements at the interface with layers
Content of TREX (total fluorescence X-ray analyzer) and SI
It was 0.7 atomic% when measured by MS.

Comparative Example 1 A thin film transistor was manufactured in the same manner as in Example 1 except that the plasma treatment step in Example 1 was not performed and the mobility was measured. The mobility was 0.3 (cm). ² / Vsec).

The content of the rare gas element at the interface between the i layer and the n ⁺ layer was measured by TREX and SIMS, and it was found to be almost 0 atomic%.

Example 2 In this example, the influence of the content of rare gas element on the mobility was examined. That is, in this example, the content of Ar was changed by changing the ratio of Ar gas and hydrogen gas and controlling the irradiation time of plasma, and the mobility was measured for each. Table 1 shows the results.

[0027]

[Table 1] (*) This is the case of Comparative Example 1 described above. As is clear from Table 1, the improvement of the mobility is more remarkable at the boundary of 0.01 atomic%. Further, even if it exceeds 0.5 atom%, the mobility does not further improve and is saturated.

Example 3 In this example, the plasma treatment process was performed at 200 ° C. to 360 ° C. The other points were the same as in Example 1. The results are shown in Table 2.

[0029]

[Table 2] In this example, as is clear from Table 2, the mobility is 0.4
It was ~ 0.6 (cm ² / Vsec), which was better than Comparative Example 1 but worse than Example 1 in the plasma treatment step at 360 ° C.

Comparative Example 2 In this example, the source gas was (H ₂ 1000 sccm) in the plasma processing step. The other points were the same as in Example 1.

In this example, the Ar content is naturally 0%.
It was Mobility is 0.35 (cm²/ Vsec) and the ratio
Although better than Comparative Example 1, Ar gas or Ar gas
Su and H ₂It is inferior to mixed gas with gas. this is,
Plasma treatment using only hydrogen contributes slightly to improvement in mobility
While Ar gas and H₂Mixed gas with gas
Compared to when used alone,
It also shows that there is a significant mobility improvement.

In the above embodiments, the thin film transistor having the inverted stagger structure has been described as an example, but it goes without saying that the present invention can be applied to a stagger structure, a coplanar structure and an inverted coplanar structure. The thin film transistor of the present invention can be suitably applied to, for example, liquid crystal display devices, solar cells, other electronic elements, and electronic parts.

[0033]

【The invention's effect】

(Claims 1 and 3) The thin film transistor according to claim 1 has a mobility superior to that of the related art. (Claim 2) The thin film transistor according to claim 2 has better mobility than the other cases.

(Claim 3) It is possible to manufacture a thin film transistor having a mobility higher than ever before. (Claims 4 and 5) It is possible to manufacture a thin film transistor having a film without contamination of the interface more easily, and it is possible to manufacture a thin film transistor having further excellent mobility.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a manufacturing process of a thin film transistor according to an example.

FIG. 2 is a conceptual diagram showing a manufacturing process of a thin film transistor according to a conventional example.

[Explanation of symbols]

1 gate electrode, 2 insulating film (silicon nitride film), 3 semiconductor active layer (i layer), 4 impurity layer (n ⁺ layer), 5 rare gas element, 6 drain electrode, 7 source electrode, 8 passivation film, 10 substrate .

Claims (5)

[Claims] 1. A semiconductor active layer made of silicon and an impurity layer made of impurity-added silicon are stacked, and a rare gas element is added to a surface of the semiconductor active layer in contact with the impurity layer. A thin film transistor characterized by being present. 2. The thin film transistor according to claim 1, wherein the content of the rare gas element is 0.01 atom% to 0.5 atom%. 3. A first film forming step of forming a semiconductor active layer made of silicon on a surface of a substrate; a plasma treatment step of exposing the surface of the semiconductor active layer to plasma in an atmosphere containing at least a rare gas; A second film forming step of stacking and forming an impurity layer made of impurity-added silicon on the surface of the semiconductor active layer. 4. The method of manufacturing a thin film transistor according to claim 3, wherein the first film forming step and the second film forming step are performed by a plasma CVD film forming method. 5. The first film forming step, the plasma processing step, and the second film forming step are continuously performed without exposing the substrate to the atmosphere. Alternatively, the method of manufacturing the thin film transistor according to the item 4.