JP2004111989A - Manufacturing method of thin film semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a thin film semiconductor device that can effectively eliminate a defective factor such as the occurrence of a natural oxide film, etc. by densifying a semiconductor thin film. <P>SOLUTION: This comprises the steps of forming a semiconductor thin film (an a-Si film) onto a substrate (a glass substrate 1), and emitting laser to the semiconductor thin film to apply laser anneal. The step of applying the laser anneal further includes the steps of irradiating laser in an O<SB>3</SB>gas, and oxidizing the surface of the semiconductor thin film. <P>COPYRIGHT: (C)2004,JPO

Description

<< The present invention relates to a method of manufacturing a thin film semiconductor device.

A polysilicon semiconductor film (p-Si film: polycrystalline silicon film) or an amorphous silicon semiconductor film (a-Si film: amorphous silicon film) as a silicon semiconductor film (semiconductor thin film) is, for example, an active matrix of a liquid crystal device. It is used as a thin film semiconductor constituting a TFT (Thin Film Transistor) on a substrate.

Here, an example of a manufacturing process of a low-temperature p-Si TFT, which is a kind of the above-described TFT, will be briefly described with reference to a process chart shown in FIG.

First, an a-Si film is deposited on a glass substrate 1 by an LPCVD (low pressure CVD) method using a disilane gas or a PECVD (plasma CVD) method using a monosilane gas, and a laser by an excimer laser is applied to the entire surface of the a-Si film. The p-Si film 2 is formed by annealing and crystallizing (step (a) in FIG. 6).

Then, after patterning the p-Si film 2 by etching, a gate insulating film 3 is formed by a CVD method (step (b) in FIG. 6).

Next, after depositing polysilicon, Ta, Cr, Al, or the like at predetermined positions on the gate insulating film 3 to form the gate electrode 4, impurities are implanted by ion doping to form the source / drain regions 2a, 2b. It is formed in a self-aligned manner (step (c) in FIG. 6).

Thereafter, an interlayer insulating film 5 is formed by depositing SiO ₂ or the like by a CVD method, and a contact hole 6 is opened. Then, an ITO film 7 of a pixel electrode and an Al wiring layer 8 serving as a data line are formed. Step (d)).

Next, a passivation film 9 made of SiO ₂ or the like is provided, necessary portions are opened (step (e) in FIG. 6), and the entire manufacturing process of the TFT element substrate is completed.

However, since the surface of the p-Si film 2 formed in the step (a) of FIG. 6 as described above is in an extremely active state by being subjected to laser annealing, it easily oxidizes when it comes into contact with air. As a result, there is a problem that an unnecessary natural oxide film SD1 (see FIG. 3A) is formed.

As shown in FIG. 3A, the natural oxide film SD1 formed on the surface of the p-Si film 2 contains many crystal defects and suboxides (such as Si ^{+ to} Si ³⁺⁾ as unreacted groups. Low oxidation degree silicon) or hydrogen bond. These defect factors have an adverse effect on the interface state between the p-Si film 2 and the gate insulating film 3 and cause a problem that the surface leak current increases or impurity levels are generated to lower the reliability of the TFT. I was

{Circle around (4)} The above-mentioned defect factor has also been a factor that lowers the dielectric breakdown voltage characteristics of the gate insulating film 3.

In particular, as the demand for miniaturization, low voltage, low power consumption, and high reliability of semiconductor devices including the above-described TFTs has increased, the quality of a gate insulating film which affects the characteristics of an element having a MOS structure has been further improved. There has been a demand for thinner films and higher quality, and from such a viewpoint, how to eliminate the above-mentioned defect factors has been an important technical problem.

The present invention has been devised in view of the above problems, and has as its object to densify a silicon semiconductor film and to effectively eliminate defect factors such as generation of a natural oxide film. A method for manufacturing a thin film semiconductor device formed on a substrate that can be formed.

In order to achieve the above object, a method for manufacturing a thin film semiconductor device according to the present invention is a method for manufacturing a thin film semiconductor device in which a semiconductor thin film is formed on a substrate, comprising the steps of: forming a semiconductor thin film on a substrate; Irradiating the semiconductor thin film with a laser to crystallize the semiconductor thin film, and then oxidizing the surface of the crystallized semiconductor thin film, wherein the laser annealing step comprises: during irradiation, the semiconductor thin film by introducing O ₂ gas or water vapor gas after crystallization, O ₃ gas to generate the laser irradiating region of the semiconductor thin film wherein crystallization, with the O ₃ gas The surface of the crystallized semiconductor thin film is oxidized by irradiating the crystallized semiconductor thin film with a laser.

As a result, a dense and strong oxide film (eg, SiO ₂ ) is immediately formed on the surface of the semiconductor thin film (eg, a silicon semiconductor film) activated by the laser annealing due to the oxidation reaction with the O ₃ gas. A natural oxide film having a defect factor such as hydrogen or hydrogen bond can be prevented from occurring, and the reliability of the thin film semiconductor device can be improved.

Further, a method of manufacturing a thin film semiconductor device according to another invention of the present application is a method of manufacturing a thin film semiconductor device in which a semiconductor thin film is formed on a substrate, the method comprising: forming a semiconductor thin film on a substrate; A step of irradiating a semiconductor thin film with a laser to perform laser annealing and a step of placing the substrate on which the semiconductor thin film subjected to the laser annealing is formed in an O ₃ gas.

As a result, even if a natural oxide film is generated on the surface of a semiconductor thin film (for example, a silicon semiconductor film) activated after laser annealing, crystal defects, suboxides, or hydrogen in the natural oxide film due to the oxidation reaction with the O ₃ gas. By replacing the bond with an oxygen atom, a defective portion can be repaired and the surface of the semiconductor thin film can be densified.

The semiconductor thin film may be a polysilicon semiconductor film or an amorphous silicon semiconductor film. Thus, the method for densifying a silicon semiconductor film formed on a substrate according to the present invention can be applied to, for example, a low-temperature p-Si TFT manufacturing process or the like to improve TFT characteristics.

The laser annealing can be performed by irradiating an excimer laser having an ultraviolet wavelength region. Accordingly, in the case where the semiconductor thin film is an amorphous silicon semiconductor film, crystallization into a polysilicon semiconductor film can be performed by ultraviolet irradiation of an excimer laser having a large absorption of silicon.

Further, the O ₃ gas can be generated by introducing a steam gas or an O ₂ gas into the irradiation area of the excimer laser, thereby eliminating the need to provide a source of the O ₃ gas, thereby reducing costs. Can be reduced.

Further, the O ₃ gas may be generated by introducing a steam gas or an O ₂ gas into an ultraviolet irradiation area of a separately provided excimer lamp. In this case, it is not necessary to provide an O ₃ gas generation source, and power consumption can be suppressed.

A method for manufacturing a thin film semiconductor device according to the present invention is a method for manufacturing a thin film semiconductor device in which a semiconductor thin film is formed on a substrate, comprising the steps of: forming a semiconductor thin film on a substrate; And performing a laser annealing step. The laser annealing step includes the step of irradiating a laser in O ₃ gas to oxidize the surface of the semiconductor thin film. Since a dense and strong oxide film (SiO ₂ ) is immediately formed on the surface of the semiconductor thin film by an oxidation reaction with O ₃ gas, a natural oxide film having a defect factor such as a suboxide or a hydrogen bond is formed. This has the effect that the occurrence can be prevented beforehand.

Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS.

Here, FIG. 1 is a process chart showing an example of a manufacturing process in the case of manufacturing a low-temperature p-Si TFT, which is a kind of TFT, by the method for manufacturing a thin film semiconductor device according to the present embodiment.

2 and 3 are explanatory views showing states before and after performing the densification processing according to the present embodiment. FIGS. 4 and 5 show cases where the densification processing is performed and cases where the densification processing is not performed. 6 is a graph showing IV characteristics of the TFT of FIG.

In FIG. 1, the same parts as those in FIG. 6 are denoted by the same reference numerals.

In the step (a) of FIG. 1, after forming a base SiO ₂ film 10 on a glass substrate 1 by a thermal oxidation method or a CVD method, an LPCVD method using a disilane gas or a PECVD (plasma) method using a monosilane gas. An a-Si film is deposited by a CVD method, laser annealing is performed by irradiating an excimer laser to the entire surface of the a-Si film, and the a-Si film is crystallized to form a p-Si film 2 (FIG. 2 (a)).

Then, while performing the laser annealing by the excimer laser, an O ₂ gas is introduced into the irradiation region of the excimer laser on the surface of the a-Si film (step (b) in FIG. 1).

In the above step (b), the introduced O ₂ gas is excited by absorbing the ultraviolet light of the excimer laser to generate ozone gas (O ₃ gas). The ozone gas immediately oxidizes the surface of the crystallized p-Si film 2 due to its strong oxidizing power to form a thin SiO ₂ film SD2 having a thickness of, for example, 30 to 100 ° (see FIG. 2B). .

Thus SiO ₂ film SD2 which is oxidized with ozone gas does not contaminated impurities as shown in FIG. 2 (b), also to become less extremely dense film crystal defects, naturally including the defective factor Occurrence of oxide film SD1 (see FIG. 3A) on the surface of p-Si film 2 can be prevented.

Note that, instead of the O ₂ gas, a steam gas (H ₂ O) may be introduced into the irradiation region of the excimer laser to generate the ozone gas.

Next, after patterning by etching on the p-Si film 2 on which the SiO ₂ film SD2 has been formed, a gate insulating film 3 is formed by a CVD method (step (c) in FIG. 1).

At this time, since the dense SiO ₂ film SD2 is formed on the p-Si film 2, the interface state between the p-Si film 2 and the gate insulating film 3 becomes good, and the electrical characteristics of the gate insulating film 3 Can be improved.

That is, there is an advantage that the dielectric strength voltage can be improved and the reliability can be improved.

(4) Accordingly, it is possible to meet the demand for a thinner and higher quality gate insulating film 3.

Subsequently, after depositing polysilicon, Ta, Cr, Al, or the like at predetermined positions on the gate insulating film 3 to form the gate electrode 4, impurities are implanted by ion doping to form the source / drain regions 2a, 2b. It is formed in a self-aligned manner (step (d) in FIG. 1).

Thereafter, an interlayer insulating film 5 is formed by depositing SiO ₂ or the like by the CVD method, and a contact hole 6 is opened. Then, an ITO film 7 of a pixel electrode and an Al wiring layer 8 serving as a data line are formed. Step (e)).

Next, a passivation film 9 made of SiO ₂ or the like is provided, necessary portions are opened (step (f) in FIG. 1), and the manufacturing process of the low-temperature p-Si TFT element substrate is completed.
The low-temperature p-Si TFT device manufactured by performing the densification treatment of the SiO ₂ film SD2 with the ozone gas in the step (b) was measured to confirm the IV characteristics. The measurement results as shown in the graph were obtained.

In FIG. 4, solid lines a, b, and c show the case where the drain-source voltages (Vds) are set to 0.1 V, 4 V, and 8 V in the initial state, respectively, and the dashed lines a ', b', and c 'show that the voltage stress is applied. In this state, Vds is set to 0.1 V, 4 V, and 8 V, respectively.

In this graph, if the respective changes in the initial state and the state in which the voltage stress is applied are compared, it can be seen that the displacement is relatively small, and the low temperature produced by performing the densification processing of the SiO ₂ film SD2 is obtained. It can be confirmed that the p-Si TFT element has excellent IV characteristics.

For comparison, FIG. 5 shows a case where a low-temperature p-Si TFT element manufactured without performing the densification treatment (step (b)) according to the present invention was subjected to the same measurement to confirm the IV characteristics. Is shown in the graph.

Comparing the graphs of FIG. 5 and FIG. 4, the densification process (step (b)) in this embodiment is effective for improving the IV characteristics and the reliability of the low-temperature p-Si TFT device. You can see that.

In the present embodiment, the densification process using ozone gas is performed in parallel with or immediately after the laser annealing with the excimer laser in the step (b) to prevent the natural oxide film SD1 from being generated. However, the densification treatment according to the present invention is not limited to this, and after the above-mentioned step (a), that is, after forming the p-Si film 2 by laser annealing, the densification treatment is performed by touching air. Therefore, the present invention can be applied to a case where a native oxide film SD1 is generated on the surface of the p-Si film 2.

In this case, in the step (b), the native oxide film SD1 on the surface of the p-Si film 2 is irradiated with an excimer laser with an output lower than the energy required for crystallization of the a-Si film. ₂ Gas or steam gas is introduced.

As a result, the highly reactive oxygen atoms of the ozone gas generated from the O ₂ gas or the steam gas are converted into sub-oxides (Si ⁺ ) as crystal defects and unreacted groups in the native oxide film SD1 (FIG. 3A). By replacing the silicon oxide with a low oxidation degree such as Si ³⁺ ) or a hydrogen bond, the defective portion can be repaired to form a densified SiO ₂ film SD2 (FIG. 3B).

Then, the densified SiO ₂ film SD2 can contribute to the improvement of the reliability of the TFT element and the like similarly to the effect of the above-described embodiment.

Further, in the above embodiment, the case where the ozone gas for the densification treatment is generated by introducing and exciting an O ₂ gas or a steam gas into an irradiation region of an excimer laser used for laser annealing has been described. However, the present invention is not limited to this. For example, an excimer lamp may be provided separately from the excimer laser, and O ₂ gas or water vapor gas may be introduced into the ultraviolet irradiation region to generate ozone gas.

Alternatively, an ozone gas generation source may be separately provided, and the ozone gas may be directly introduced to perform the densification treatment.

As described above, the method for manufacturing a thin-film semiconductor device according to the present invention is a method for manufacturing a thin-film semiconductor device in which a semiconductor thin film is formed on a substrate, comprising the steps of: forming a semiconductor thin film on a substrate; Irradiating the semiconductor thin film with a laser to perform laser annealing, wherein the laser annealing includes a step of irradiating the laser in an O ₃ gas to oxidize the surface of the semiconductor thin film. Therefore, a dense and strong oxide film (SiO ₂ ) is immediately formed on the surface of the semiconductor thin film activated by the laser annealing by the oxidation reaction with the O ₃ gas, so that a defect factor such as a suboxide or a hydrogen bond is generated. There is an effect that a situation in which a natural oxide film is generated can be prevented beforehand.

Further, a method of manufacturing a thin film semiconductor device according to another invention of the present application is a method of manufacturing a thin film semiconductor device in which a semiconductor thin film is formed on a substrate, the method comprising: forming a semiconductor thin film on a substrate; The step of irradiating the semiconductor thin film with a laser to perform laser annealing, and the step of arranging the substrate on which the semiconductor thin film subjected to the laser annealing is formed in O ₃ gas, enables the silicon semiconductor to be activated after the laser annealing. Even if a native oxide film is formed on the surface of the film, the silicon semiconductor film is repaired by replacing the crystal defects, suboxides, or hydrogen bonds in the native oxide film with oxygen atoms by an oxidation reaction with O ₃ gas, thereby repairing the defective portion. There is an effect that the surface can be densified.

FIG. 4 is a process chart showing an example of a manufacturing process when a low-temperature p-Si TFT is manufactured by applying the method of manufacturing a thin-film semiconductor device according to the present invention. It is explanatory drawing which shows the state of the silicon semiconductor film before and after performing the densification process of the manufacturing method of the thin film semiconductor device which concerns on this invention. It is another explanatory view showing the state of the silicon semiconductor film before and after performing the densification processing of the manufacturing method of the thin film semiconductor device according to the present invention. 6 is a graph showing IV characteristics of a TFT when a densification process is performed in the method for manufacturing a thin film semiconductor device according to the present invention. 5 is a graph showing IV characteristics of a TFT when a densification process in the method for manufacturing a thin film semiconductor device according to the present invention is not performed. FIG. 4 is a process chart showing an example of a conventional low-temperature p-Si TFT manufacturing process.

Explanation of reference numerals

REFERENCE SIGNS LIST 1 glass substrate 2 p-Si film 2 a source region 2 b drain region 3 gate insulating film 4 gate electrode 5 interlayer insulating film 6 contact hole 7 ITO film 8 Al wiring layer 9 passivation film 10 underlying SiO ₂ film SD1 natural oxide film SD2 SiO ₂ film

Claims (6)

A method for manufacturing a thin film semiconductor device in which a semiconductor thin film is formed on a substrate,
Forming a semiconductor thin film on the substrate;
Irradiating the semiconductor thin film with a laser, crystallizing the semiconductor thin film, and then oxidizing the surface of the crystallized semiconductor thin film, comprising:
In the laser annealing step, during the laser irradiation, O ₂ gas or water vapor gas is introduced after crystallization of the semiconductor thin film, and O ₃ gas is applied to a laser irradiation area of the crystallized semiconductor thin film. A method for manufacturing a thin film semiconductor device, comprising: irradiating a laser beam on the crystallized semiconductor thin film in the O ₃ gas to oxidize a surface of the crystallized semiconductor thin film. 4. The method according to claim 1, wherein the semiconductor thin film is a polysilicon semiconductor film. The method of manufacturing a thin film semiconductor device according to claim 1, wherein the semiconductor thin film before the laser annealing is an amorphous silicon semiconductor film. 4. The method according to claim 1, wherein the laser annealing is performed by irradiating an excimer laser having an ultraviolet wavelength region. 5. 5. The method according to claim 4, wherein the O ₃ gas is generated by introducing a steam gas or an O ₂ gas into an irradiation area of the excimer laser. 6. The thin film semiconductor device according to claim 1, wherein the O ₃ gas is generated by introducing a water vapor gas or an O ₂ gas into an ultraviolet irradiation region of an excimer lamp separately provided. Production method.

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