JP2002353458A - Thin film semiconductor element and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film semiconductor element of superior reliability and characteristics and its manufacturing method by using a gate insulating film, which prevents deterioration of the reliability of the thin film semiconductor element due to oxide formation of tungsten and deterioration of characteristic due to gate insulating film quality. SOLUTION: The thin film semiconductor element is provided with a silicon semiconductor film 2 having a prescribed form, a first gate insulating film 3 having a prescribed form, a second gate insulating film 4 having a prescribed form, and a gate electrode film 5; the first gate insulating film 3 is a silicon oxide film, where an absolute value of film stress is at most 300 MPa; the second gate insulating film 4 is a silicon oxinitride film; and the gate electrode film 5 is formed of alloy of molybdenum and tungsten.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film semiconductor device used for a semiconductor integrated circuit, a liquid crystal display device, and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art When a polycrystalline silicon thin film transistor is used in an active matrix type liquid crystal display device, a transistor array and peripheral circuits can be integrated. The integration of the peripheral circuit realizes high-definition image display and enables low-cost manufacturing. Since the performance of the polycrystalline silicon thin film transistor is closely related to the driving characteristics of peripheral circuits, higher performance is expected.

Referring to FIG. 3, the structure of a thin film transistor and
A conventional method for producing this will be described. The thin film transistor is provided with a base film 10, a silicon semiconductor film 2, a gate insulating film 3, a gate electrode film 5, a gate wiring film 6, an interlayer insulating film 7, source and drain electrode films 8, 9 on a surface of a substrate 1 such as quartz or glass. Have been. The base film 10 is formed for the purpose of preventing the constituent components of the substrate 1 from diffusing into the polycrystalline silicon semiconductor film 2, but may not be formed depending on the material of the substrate 1 and the method of processing the substrate.

As a material of the gate insulating film 3, silicon oxide or silicon nitride is often used. Film formation is CVD
This is performed using a device. The gate insulating film 3 is formed by heat C
Although VD or plasma CVD is possible, plasma CVD is often used in the process of manufacturing a polycrystalline silicon transistor because it is desirable to lower the process temperature. The gate electrode film 5 has a low resistance in order to prevent delay of a signal, and is formed at a temperature of 500 to 600 ° C. for activating phosphorous and boron impurities implanted by doping.
Must be able to withstand the heat treatment. An alloy of Mo and W has been proposed as a material that achieves both low resistance and heat resistance stability (Japanese Patent Application Laid-Open No. 8-153722).

[0005]

The present inventor evaluated the reliability of a semiconductor thin film element manufactured by using the conventional technique in a high-temperature voltage application test (BT test). The high-temperature voltage application test is a method in which the source and drain of the thin film semiconductor device are grounded at a temperature of 85 to 150 ° C., and a voltage of 30 V is applied to the gate to measure the time variation of the transistor characteristics. Then, in a thin-film semiconductor device using the conventional technique, it has been found that a Vth shift occurs in a high-temperature voltage application test, resulting in insufficient reliability.

In the thin film semiconductor device using the prior art, the reason why the Vth shift becomes large is that moisture contained in the gate insulating film reacts with tungsten in the gate electrode film to generate a tungsten oxide. Conceivable.

On the other hand, by examining the relationship between the film quality of the gate insulating film and various characteristics of the thin-film semiconductor element, it has been found that the sub-threshold characteristic varies depending on the film quality of the gate insulating film.

In order to solve the above-mentioned conventional problems, the present invention uses a gate insulating film structure for preventing the deterioration of the reliability of a thin film semiconductor device due to the formation of tungsten oxide and the deterioration of characteristics due to the quality of the gate insulating film. Accordingly, an object of the present invention is to provide a thin-film semiconductor element having excellent reliability and characteristics and a method for manufacturing the same.

[0009]

In order to achieve the above object, a thin film semiconductor device according to the present invention comprises a silicon semiconductor film on a surface of a transparent insulating substrate, a gate insulating film on the surface, and a gate electrode film on the surface. And a gate wiring film on its surface,
In a thin film semiconductor device comprising an interlayer insulating film covering the gate electrode film, and source and drain electrode films conducting from the silicon semiconductor film to the surface, the gate insulating film has a first gate insulating film and a second gate. An insulating film is formed in this order; the first gate insulating film is a silicon oxide film having an absolute value of a film stress of 300 MPa or less; the second gate insulating film is a silicon oxynitride film; The film is an alloy of molybdenum and tungsten. With the above structure, interfacial stress at the interface between the silicon semiconductor film and the first gate insulating film is reduced, so that the subthreshold characteristics of the thin film semiconductor element are prevented from deteriorating. Due to the presence of nitrogen, the reaction between the moisture contained in the gate insulating film and the tungsten in the gate electrode film is suppressed, the deterioration of the reliability of the thin film semiconductor device is prevented, and a highly reliable thin film semiconductor device is realized. be able to.

In the above element, it is preferable that the concentration of nitrogen contained in the second gate insulating film is higher than the concentration of oxygen contained in the gate electrode film. More preferably, the second concentration is higher than the concentration of oxygen contained in the gate electrode film.
2. The concentration of nitrogen contained in the gate insulating film is 100 to 7
It is preferable that the range is as high as 00 atomic%. With the above configuration, it is possible to more effectively prevent a decrease in the reliability of the thin film semiconductor element.

In the above device, the first gate insulating film is formed by plasma CVD using tetraethoxysilane as a source gas, and the second gate insulating film is formed by sputtering using krypton and nitrogen as a discharge gas. It is preferred that

Next, a method of manufacturing a thin-film semiconductor device according to the present invention comprises the steps of: providing a silicon semiconductor film on a surface of a transparent insulating substrate; a gate insulating film on the surface; a gate electrode film on the surface; And a method of manufacturing a thin film semiconductor device comprising: an interlayer insulating film covering the gate electrode film; and a source and drain electrode film conducting from the silicon semiconductor film to the surface, wherein the first gate insulating film is used as the gate insulating film. And a second gate insulating film are formed in this order,
The first gate insulating film is formed by plasma CVD using tetraethoxysilane as a source gas, the second gate insulating film is formed by sputtering using krypton and nitrogen as a discharge gas, and the gate electrode film is formed by: An alloy film of molybdenum and tungsten is formed by sputtering using argon as a discharge gas.

In the above-mentioned manufacturing method, if the first gate insulating film is formed by plasma CVD using tetraethoxysilane as a source gas, the control range of the film stress is wide, and the first gate insulating film can be formed at a low pressure of 300 MPa or less. It is easy to adjust to the stress, and deterioration of the subthreshold characteristic of the thin film semiconductor element is effectively prevented. In addition, forming the second gate insulating film by sputtering using krypton and nitrogen as a discharge gas means that krypton has a larger atomic radius than argon which is usually used as a discharge gas, and is implanted into the film at the time of film formation. It has the characteristic that it is less likely to occur, leaving only nitrogen in the second insulating film, and preventing krypton from being implanted into the second insulating film and the first insulating film and causing defects in the insulating film. It has the effect of preventing the reaction between water contained in the gate insulating film and tungsten in the gate electrode film more effectively, and improves the reliability of the thin film semiconductor element. As a result, a thin film semiconductor device having excellent initial characteristics and high reliability can be realized.

[0014]

Next, a specific example of the present invention will be described.

(Embodiment) The structure of a thin film semiconductor device according to the present invention will be described with reference to FIG.

In this embodiment, a 1737 glass substrate manufactured by Corning Incorporated was used as the transparent insulating substrate 1. In this embodiment, a film obtained by polycrystallizing amorphous silicon (a-Si) using an excimer laser is used as the polycrystalline silicon semiconductor film 2.

In the present embodiment, the first gate insulating film 3 has a discharge power of 400 W and a tetraethoxysilane flow rate of 200 S in order to control the film stress to 300 MPa or less.
CCM, oxygen flow rate 3000 SCCM, substrate temperature 30
0 ° C. In the above, "SCCM" means "standard cc"
/ min ", which is a unit of flow rate at atmospheric pressure (1.013 hPa) and room temperature.

In the present embodiment, the second gate insulating film 4 is formed by mixing krypton with nitrogen (krypton: nitrogen = 1).
00: 1 to 5) As a discharge gas, a film was formed using silicon oxide as a target. Here, as shown in FIG. 2, the concentration of nitrogen contained in the second gate insulating film is preferably higher than the concentration of oxygen contained in the gate electrode film. In this embodiment mode, the concentration of nitrogen contained in the second gate insulating film is set to be about 200 ppm. In FIG.
The black circles indicate the results of the high-temperature and high-pressure application test (BT test). Further, the “BT shift amount” on the vertical axis in FIG.
4 shows a transistor characteristic shift amount in a BT test.

The gate electrode film 5 has a thickness of about 3 in this embodiment.
A 00 nm molybdenum-tungsten alloy film was formed by sputtering using argon as a discharge gas. In this embodiment, the interlayer insulating film 7 has a thickness of 400 nm by plasma CVD using a mixed gas of tetraethoxysilane and oxygen.
m of SiO ₂ films were produced. The gate wiring film 6 is made of Ti and A
100 nm thick by sputtering
m, the source electrode 8 and the drain electrode 9 are each formed by sputtering a two-layer film of Ti and Al to a thickness of 600 n.
m.

In this embodiment, a 400 nm thick SiO ₂ film is formed by plasma CVD using a mixed gas of tetraethoxysilane (TEOS) and O ₂ in this embodiment.

As a thin film semiconductor device, an n ⁺ doping layer, a p ⁺ doping layer,
Although a protective film made of a SiNx film is formed on the surface, it is not shown in the figure.

As described above, the first gate insulating film is
The low-stress silicon oxide film of not more than MPa, and the second gate insulating film is a silicon oxynitride film having a nitrogen concentration higher than the oxygen concentration contained in the gate electrode film, whereby the polycrystalline silicon semiconductor film and the first gate are formed. Deterioration of subthreshold characteristics of a thin film semiconductor device due to interface stress with an insulating film is prevented, and semiconductor thin film device caused by an oxidation reaction of tungsten (W) at an interface between a second gate insulating film and a gate electrode film The effect of preventing a decrease in the reliability of the semiconductor device is obtained, and a thin film semiconductor device having excellent characteristics and high reliability can be realized.

[0023]

As described above, according to the present invention, it is possible to prevent the sub-threshold characteristic of the thin film semiconductor element from deteriorating due to the interface stress between the silicon semiconductor film and the first gate insulating film, The two effects of preventing a decrease in the reliability of the semiconductor thin film element caused by the oxidation reaction of tungsten (W) at the interface between the insulating film and the gate electrode film are obtained, and the thin film has excellent overall characteristics and high reliability. A semiconductor element can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a structure according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a nitrogen concentration in a second gate insulating film and a BT shift amount in one embodiment according to the present invention;

FIG. 3 is a sectional view showing the structure of a conventional thin film semiconductor device.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 silicon semiconductor film 3 first gate insulating film 4 second gate insulating film 5 gate electrode film 6 gate wiring film 7 interlayer insulating film 8 source electrode 9 drain electrode 10 base film

Continued on the front page F-term (reference) 4M104 AA09 BB16 CC05 DD37 EE03 EE14 GG20 HH20 5F058 BD01 BD04 BD15 BF07 BF14 BF15 BF27 BJ01 5F110 AA14 BB01 CC02 DD02 DD13 EE06 EE38 EE44 FF02 FF04 FF28 NN NN23 NN24 NN35 PP03

Claims (4)

[Claims] 1. A silicon semiconductor film on a surface of a transparent insulating substrate, a gate insulating film on the surface, a gate electrode film on the surface, a gate wiring film on the surface, and an interlayer insulating film covering the gate electrode film And a thin-film semiconductor device comprising a source and drain electrode film conducting from the silicon semiconductor film to the surface, wherein the gate insulating film is formed with a first gate insulating film and a second gate insulating film in this order, The first gate insulating film is a silicon oxide film having an absolute value of a film stress of 300 MPa or less, the second gate insulating film is a silicon oxynitride film, and the gate electrode film is an alloy of molybdenum and tungsten. A thin film semiconductor device characterized by the above-mentioned. 2. The thin film semiconductor device according to claim 1, wherein the concentration of nitrogen contained in said second gate insulating film is higher than the concentration of oxygen contained in said gate electrode film. 3. The first gate insulating film is formed by plasma CVD using tetraethoxysilane as a source gas,
3. The thin-film semiconductor device according to claim 1, wherein the second gate insulating film is formed by sputtering using krypton and nitrogen as a discharge gas. 4. A silicon semiconductor film on a surface of a transparent insulating substrate, a gate insulating film on the surface, a gate electrode film on the surface, a gate wiring film on the surface, and an interlayer insulating film covering the gate electrode film And a method of manufacturing a thin-film semiconductor device having a source and drain electrode film conducting from the silicon semiconductor film to the surface, wherein a first gate insulating film and a second gate insulating film are arranged in this order as the gate insulating film. The first gate insulating film is formed by plasma CVD using tetraethoxysilane as a source gas, and the second gate insulating film is formed by sputtering using krypton and nitrogen as a discharge gas. The method for manufacturing a thin film semiconductor device, wherein the electrode film is formed by sputtering an alloy film of molybdenum and tungsten using argon as a discharge gas.