JP2003124469A - Thin film transistor and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problems that, when a single layer of a silicon nitride film is used as the ground, a level of an interface increases and element characteristics are deteriorated and that, when a ground film is an oxide film formed by a PE-CVD method, the level of the interface also increases, since the film contains many defects and impurities, and the element characteristics are deteriorated. SOLUTION: As to the problem that the levels of the silicon nitride film and the interface of a semiconductor thin film are increased, the surface of the silicon nitride film is oxidized to make the surface portion be a silicon oxy-nitride film. As for the problem due to the defects and impurities of the silicon oxide film formed by the PE-CVD method, the silicon oxide film obtained by oxidizing a silicon thin film is used.

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 more particularly to a polycrystalline silicon thin film transistor (low temperature pol) manufactured by a low temperature process (650 ° C. or lower) suitable for forming a driver for an image display device and its peripheral circuits.
y-Si TFT).

[0002]

2. Description of the Related Art A conventional structure of a thin film transistor for a liquid crystal display (LCD) has a structure in which a silicon nitride film or a silicon oxide film is formed on a insulating substrate by CVD (Chemical).
In general, it is formed by a vapor deposition method and used as a diffusion prevention film that suppresses the diffusion of impurities from the substrate. As the CVD method in this case, the PE-CVD method is generally used in the low temperature poly-Si TFT.

[0003]

The above-mentioned conventional techniques have the following problems. When the base is a silicon nitride film single layer,
Although the diffusion prevention effect is sufficient, there is a problem in that the semiconductor layer of the TFT is in contact with silicon nitride, the level of the interface increases, and the device characteristics deteriorate. Further, when the base film in contact with the semiconductor layer is a silicon oxide film, the oxide film formed by the PE-CVD method contains many defects and impurities, so that the interface level is also large and the device characteristics deteriorate. I will end up. In particular, since the silicon oxide film formed by PE-CVD contains a large amount of carbon, fluorine, OH groups and H ₂ O, it is difficult to control the threshold voltage of the TFT and the characteristics of the TFT are likely to deteriorate. is there.

[0004]

The above problems can be solved by the following means. First, the problem that there are many levels at the interface between the silicon nitride film and the semiconductor thin film can be solved by oxidizing the surface of the silicon nitride film and making the surface portion a silicon oxynitride film. Regarding the problem caused by the defects and impurities of the silicon oxide film formed by the PE-CVD method, the silicon oxide film is not formed by the CVD method but
This can be solved by using a silicon oxide film obtained by oxidizing a silicon thin film. In addition, as a method of oxidation in this case,
It is effective to blow the heated gas to the substrate and perform the oxidation in a short time to suppress the temperature rise of the substrate and perform the oxidation. Alternatively, a method capable of oxidizing at low temperature such as oxygen plasma oxidation may be used.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 shows a sectional view of a CMOS TFT manufactured by applying the present invention. Here, FIG. 1A shows an NMOS transistor portion of a CMOS TFT, and FIG. 1B shows a PMOS transistor portion.

First, as a base film (protective film) on a glass substrate 101, a SiN film 102 and an a-Si film 103 are formed by PE-CVD to 100 nm and 10 n, respectively.
It was formed with a thickness of m. 7 on the surface 103 of the a-Si film
By blowing steam heated at 00 ° C., the silicon oxide film was completely oxidized. The oxidation time at this time is several minutes, and the temperature of the a-Si film 103 rises to 700 ° C., but the temperature of the glass substrate 101 is 600 ° C. or lower, so that the oxidation is possible without deforming the glass. Is.

The gas to be used is not limited to water vapor, but may be O_Two, N
O, N_TwoO or O_TwoAnd hydrogen chloride, O _TwoGas mixture of chlorine
Alternatively, an atmosphere containing a mixed gas thereof may be used.

Then, a-Si is formed by PE-CVD method.
A film of 50 nm is deposited, and p is formed by excimer laser annealing.
As an poly-Si film (corresponding to 106, 107, 108)
It was This film is dry-etched using a resist mask.
100nm gate Si after processed into islands by
O_TwoThe film 104 is formed by PE-CVD and has a thickness of 150 nm.
The gate electrode 105 was formed by the sputtering method. this
In this case, the same method as above was used to obtain 56 nm of poly-S.
After 10 nm oxidation of i surface, gate SiO _TwoMembrane 10
A TFT in which 4 was formed to 90 nm was also manufactured.

After the above steps, with respect to the NMOS transistor portion, the n ⁺ layer 106 and the LDD (lightly do) are implanted by P ion implantation using a resist mask.
A ped drain) layer 107 was formed, and for the PMOS transistor portion, ap ⁺ layer 108 was formed by B ion implantation to manufacture a CMOS transistor.

After the above-mentioned TFT manufacturing process, the interlayer insulating film 109 of SiO ₂ and the Al alloy wiring 11 are formed by the PE-CVD method.
Formed 0. PE-CVD as a passivation film
After forming the SiO ₂ film 111 and the SiN film 112 by the contact hole and forming the contact hole, I
TO (Indium Titanium Oxide)
A film 113 was formed to complete a liquid crystal driving transistor and a circuit CMOS transistor. Then, a liquid crystal process was performed to fabricate a pixel portion of the LCD.

In the case of using a base film obtained by oxidizing a-Si,
In the case of forming a base film only with PE-CVD film,
On the other hand, the on-current of the transistor increases by about 20 to 30%.
It was Also, drain avalanche hot hole deterioration conditions
10% deterioration of TFT on-resistance
Comparing the lifetimes, in the case of the base film of the PE-CVD film, 1
0 ^FourIt is about sec, but when using a thermal oxide film
Is 10⁵It became more than an order of magnitude longer than sec.

Further, when a gate oxide film including a SiO ₂ film formed by oxidizing the poly-Si surface is used,
Extremely reliable TFT with a life of 10 ⁶ sec or more
was gotten. At this time, the poly-Si surface was changed to a SiO ₂ film formed by oxidation, and the poly-Si surface was changed to NH ₃ film.
Even if a SiN film formed by nitriding the SiN film or a SiON film formed by further oxidizing the SiN film is used, the TFT reliability improving effect can be obtained.

Instead of the SiN film formed by the PE-CVD method, a film obtained by nitriding the a-Si film with NH ₃ gas can be used as the base film. In this case Si
A fixed charge in the N film is small, the threshold voltage of the TFT can be easily controlled, and the TFT having good performance and uniform characteristics can be obtained. (Embodiment 2) FIG. 2 shows a sectional view of a CMOS TFT of another embodiment produced by applying the present invention. Here, FIG. 1A shows the NMOS transistor part of the CMOS TFT,
FIG. 3B shows a PMOS transistor section.

First, SiN201 was formed as a base film on the glass substrate 101 by PE-CVD to a thickness of 100 nm. The surface of this SiN film was oxidized by blowing water vapor heated to 700 ° C. to form an oxygen-rich oxynitride film 202 on the surface. At this time, the glass substrate is not deformed as in Example 1, and the gas used may be another oxidizing gas.

After the above steps, an NMOS transistor and a PMOS transistor were manufactured in the same manner as in Example 1. S
When the base film formed by oxidizing iN was used, the on-current of the transistor was increased by about 10 to 20% as compared with the case where the base film was formed only by PE-CVD. Further, when compared with the life of 10% deterioration of the on resistance of the TFT, it is about 10 ⁴ sec in the case of the base film of the PE-CVD film, whereas it is 10 ⁵ sec or more in the case of using the thermal oxide film. It became longer than an order of magnitude. Further, as in the first embodiment, when a part of the poly-Si thermal oxide film is used as the gate oxide film, there is an effect that the life is further extended. (Example 3) FIG. 3 shows TFTs manufactured in Examples 1 and 2.
FIG. 3 shows a configuration diagram of a liquid crystal display device manufactured using. LCD
Is a gate driver circuit 301 and a drain driver circuit 3
02 and an image display unit 303, and the gate driver circuit 301 and the drain driver circuit 302 are CMOs.
It is composed of STFT 304. The image display unit 303 has gate lines 305 and signal lines 306 formed in a matrix.

The above LCD exhibits good performance, especially L
The CD life was 10,000 hours or more for each LCD, and an LCD with a long life was obtained.

[0017]

As described above, according to the present invention, a TFT having a good interface between a base and a semiconductor thin film can be manufactured, a TFT having good initial characteristics and high reliability can be obtained, and an LCD having a long life can be obtained.
Is obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view for explaining a TFT manufacturing process of one embodiment of the present invention.

FIG. 2 is a cross-sectional view for explaining a TFT manufacturing process according to another embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of an LCD.

[Explanation of symbols]

101 ... Glass substrate, 102, 201 ... SiN film, 10
3 ... SiO ₂ film obtained by oxidizing a-Si, 104 ... Gate oxide film, 105 ... Gate electrode, 106 ... N ⁺ layer 107 ... LDD layer, 108 ... P ⁺ layer, 109 ... Inter-layer Si
O ₂ film, 110 ... Al alloy wiring, 111 ... Passivation SiO ₂ film, 112 ... Passivation SiN film,
113 ... ITO electrode, 202 ... Silicon oxynitride film.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takuo Kaito             Hitachi, Ltd. 3300 Hayano, Mobara-shi, Chiba             Factory Display Group (72) Inventor Naohiro Kamo             Hitachi, Ltd. 3300 Hayano, Mobara-shi, Chiba             Factory Display Group (72) Osamu Okura             Hitachi, Ltd. 3300 Hayano, Mobara-shi, Chiba             Factory Display Group F term (reference) 5F058 BC02 BC11 BF62 BF63 BF72                       BJ01                 5F110 AA14 BB02 BB04 CC02 DD02                       DD13 DD14 DD15 DD17 EE44                       FF02 FF03 FF04 FF07 FF23                       FF26 FF30 GG02 GG13 GG25                       GG45 HJ01 HJ13 HL06 HL07                       HM15 NN03 NN23 NN24 NN35                       PP03

Claims (7)

[Claims] 1. A thin film transistor formed on an insulating substrate having a heat resistance of 650 ° C. or lower, wherein the thin film transistor comprises at least a semiconductor thin film, a gate insulating film, and a gate electrode, and a thin film transistor is provided between the thin film transistor and the insulating substrate. A thin film transistor characterized in that at least one insulating substrate protective film is formed, and the insulating substrate protective film in contact with the semiconductor thin film of the thin film transistor is a silicon oxide film obtained by oxidizing a silicon thin film. 2. The oxidation according to claim 1 is performed in an atmosphere containing at least one gas selected from oxygen, water vapor, ozone, plasma oxygen, N ₂ O, NO, hydrogen chloride and chlorine. Method for manufacturing thin film transistor. 3. The thin film transistor according to claim 1, wherein at least a part of the silicon oxide film in contact with the semiconductor thin film is in contact with a silicon film in a layer different from the semiconductor thin film forming the thin film transistor. . 4. A thin film transistor formed on an insulating substrate having a heat resistance of 650 ° C. or less, the thin film transistor including at least a semiconductor thin film, a gate insulating film, and a gate electrode, and a thin film transistor between the thin film transistor and the insulating substrate. At least one layer of the insulating substrate protective film is formed, and the insulating substrate protective film in contact with the semiconductor thin film of the thin film transistor is a silicon oxide film, and carbon, fluorine, hydrogen in at least a part of the region of the silicon oxide film. The element concentration of any of the above is 1 × 10 ¹⁹ / cm ³ or less, preferably 1 × 10
A thin film transistor having a density of ¹⁸ / cm ³ or less. 5. A thin film transistor formed on an insulating substrate having a heat resistance of 650 ° C. or lower, the thin film transistor including at least a semiconductor thin film, a gate insulating film, and a gate electrode, and a thin film transistor between the thin film transistor and the insulating substrate. At least one layer of the insulating substrate protective film is formed, and the insulating substrate protective film includes a silicon oxynitride film, and the silicon oxynitride film is
A thin film transistor, which is a silicon oxynitride film formed by oxidizing a surface after forming a silicon nitride film. 6. Fabrication of a thin film transistor, characterized in that the oxidation of the silicon thin film and the silicon nitride film according to claim 1 or 5 is performed by a method of heating an oxidizing gas and spraying it on the silicon film and the silicon nitride film. Method. 7. The thin film transistor according to claim 1, wherein at least a part of the gate insulating film is
A thin film transistor comprising an oxide film obtained by oxidizing a semiconductor thin film forming a thin film transistor.