JPH11354801A - Manufacture of polycrystalline semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent formation of protrusions on a polycrystalline Si film surface formed by laser-annealing to crystallize amorphous Si, improve the gate dielectric breakdown voltage of a polycrystalline Si TFT and realize a high display quality liquid crystal display element. SOLUTION: An amorphous Si film 14 is cleaned with an ozone-containing solution for forming an oxide film, the oxide film and impurities are cleaned out with HF at the same time until the oxide film and impurities are perfectly removed, where the contact angle of pure water 17 dropped on the amorphous Si film 14 to this film 14 to 60 deg. or more. After the oxide film and impurities are removed completely, the amorphous Si film 14 is laser-annealed to crystallize it, thus obtaining a polycrystalline Si.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a polycrystalline semiconductor which obtains polycrystalline silicon by crystallizing amorphous silicon.

[0002]

2. Description of the Related Art In recent years, as a switching element for a high-definition liquid crystal display element, a polycrystal has been realized because of its low cost, high mobility, and high performance including driving of the liquid crystal display element. Polycrystalline silicon thin film transistor using silicon as a channel layer (hereinafter polycrystalline silicon T
Abbreviated as FT. ) Is being put to practical use. In a liquid crystal display device, since a polycrystalline silicon TFT is formed on an insulating substrate such as non-alkali glass, it is necessary to form the polycrystalline silicon film by a low-temperature process with little damage to the substrate. A laser annealing method for obtaining polycrystalline silicon by irradiating the substrate with a laser beam to crystallize the substrate is employed. It is known that the field effect mobility of a polycrystalline silicon TFT using a polycrystalline silicon film formed by this laser annealing method as a channel is 100 cm ² / Vs or more.

Conventionally, as a laser annealing method, an amorphous silicon film 3 is formed on a glass substrate 1 at a low temperature via an undercoat layer 2 as shown in FIG. Next, as shown in FIG. 5B, dehydrogenation treatment is performed at 500 ° C. for 1 hour so that film ablation does not occur during laser annealing. Next, as shown in FIG. 5C, the natural oxide film 4 formed on the surface of the amorphous silicon film 3 is made of 1% hydrofluoric acid (H
F) Wash and remove for 15 seconds. Next, as shown in FIG. 5D, the amorphous silicon film 3 is crystallized by irradiating a laser beam,
As shown in FIG. 5E, a polycrystalline silicon film 6 was obtained on the glass substrate 1.

[0004]

SUMMARY OF THE INVENTION However, in the prior art,
In the laser annealing method of irradiating the amorphous silicon film with a laser beam to crystallize and form a polycrystalline silicon film, the surface of the formed polycrystalline silicon film is not smooth,
Protrusions of 80 nm or more were formed. For this reason, when a polycrystalline silicon TFT having a coplanar structure on a gate is formed using a conventional polycrystalline silicon film having a projection, when the height of the projection formed on the surface of the polycrystalline silicon is large, the projection portion is formed. Reduces the coverage of the gate insulating film that covers the polycrystalline silicon film with the polycrystalline silicon TFT.
This causes the gate withstand voltage to deteriorate.

A polycrystalline silicon film having a polycrystalline silicon film formed by a conventional laser annealing method as a channel layer.
When FT is applied to a drive circuit portion of a liquid crystal display element and a TFT is manufactured with a gate oxide film thickness of 100 nm, for example,
At a gate voltage of about 30 V, the polycrystalline silicon TFT is broken, which causes image defects such as line defects on the display of the liquid crystal display element, lowers the display quality of the liquid crystal display, and lowers the production yield. Had.

The projections on the surface of the polycrystalline silicon film, which cause deterioration of the gate dielectric breakdown voltage, are crystallized because the process of crystallization of amorphous silicon by laser annealing is instantaneous melting crystallization for several hundred nanoseconds. Occasionally, a crystal grain boundary is generated at a portion where the crystal collision occurs. Then, the projections on the surface of the polycrystalline silicon are formed by XPS (X-ray photoe).
When analyzed by electron spectroscopy, it was found that the amount of the oxygen element was larger than that of the portion having no protrusion. Further, the relationship between the thickness of the oxide film on the surface of the amorphous silicon film and the height of the protrusions formed on the surface of the polycrystalline silicon film after the laser annealing was examined. As shown in FIG. If the height of the protrusion is 6
The native oxide film 4 has a thickness of 10 to 90 nm.
The height of the protrusion when the thickness was about nm was as high as 150 nm.

[0007] From the above experimental results, in the conventional laser annealing method, the oxide film on the surface of the amorphous silicon film and the surface adsorbed impurities are not completely removed by washing, and the surface of the amorphous silicon film before laser light irradiation is naturally removed. The presence of even a small amount of an impurity such as an oxide film or carbon (C) or boron (B) causes a protrusion having a height of 80 nm or more on the surface of the crystallized polycrystalline silicon film. It turned out that.

FIG. 5 shows a conventional laser annealing method.
As shown in FIG. 7D, pure water (water droplets) 7 is applied to the surface of the amorphous silicon film 3 as shown in FIG. The surface of the amorphous silicon film 3 and pure water 7 were dropped using a contact angle measuring device.
When the contact angle θ was measured, it was found that the contact angle was 35 ° to 40 °.

On the other hand, when the relationship between the removal state of the oxide film and impurities on the surface of the amorphous silicon film before laser light irradiation and the contact angle with pure water dropped on the surface of the amorphous silicon film was examined, When the contact angle θ between the surface of the amorphous silicon film and the pure water measured by the contact angle measuring device was 60 ° or more, it was found that the oxide film and impurities were completely removed.

From the above, the surface of the amorphous silicon film 3 formed by the above-described conventional laser annealing method, in which the contact angle between the surface of the amorphous silicon film 3 and the pure water 7 is 35 ° to 40 °,
Insufficient cleaning with hydrofluoric acid (HF), insufficient etching of the native oxide film on the surface of the amorphous silicon film, and air such as carbon (C) and boron (B) adsorbed on the surface. It has been clarified that cleaning of impurities in the inside is insufficient, and this causes a protrusion of 80 nm or more on the surface of the polycrystalline silicon film, which eventually deteriorates the gate withstand voltage of the polycrystalline silicon TFT.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is possible to prevent a projection from being formed on the surface of a polycrystalline silicon film during crystallization of the polycrystalline silicon film by laser annealing, thereby deteriorating the gate withstand voltage of the polycrystalline silicon TFT. To provide a high-quality polycrystalline semiconductor manufacturing method capable of obtaining a liquid crystal display element having a good display quality without causing line defects or the like, while improving the manufacturing yield. Aim.

[0012]

According to the present invention, there is provided a method of manufacturing a polycrystalline semiconductor, comprising: irradiating amorphous silicon deposited on a substrate with laser light to crystallize the silicon; Forming an amorphous silicon film on the substrate, oxidizing the surface of the amorphous silicon film to form an oxide film, and dropping pure water onto the surface after removing the oxide film. The contact angle of the pure water to the surface is 60
Performing the step of removing the oxide film so that the temperature of the amorphous silicon film is equal to or higher than the above, and the step of irradiating the amorphous silicon film after the removal of the oxide film with the laser beam to crystallize the amorphous silicon film. It is.

According to another aspect of the present invention, there is provided a method of irradiating a laser beam to amorphous silicon having a contact angle of 60 degrees or more with the surface of pure water when pure water is dropped on the surface. And crystallization.

According to the present invention, the oxide film and the adsorbed impurities on the surface of the amorphous silicon film are sufficiently removed by the above structure, so that the protrusions on the surface of the polycrystalline silicon film caused by the oxide film and the adsorbed impurities are removed. This is intended to prevent the occurrence of the problem and to commercialize a high-quality polycrystalline silicon TFT, improve the display quality of the liquid crystal display element, and further improve the production yield.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment shown in FIGS. FIG. 1 shows a glass substrate 1
FIG. 1 is a schematic cross-sectional view showing a polycrystalline silicon film 12 formed on a substrate 0 via an undercoat layer 11 made of a silicon oxide (SiO ₂ ) film.

Next, a method for manufacturing the polycrystalline silicon film 12 will be described. An undercoat layer 11 is formed on a glass substrate 10 as shown in FIG.
4 is deposited with a thickness of 40-80 nm. Both the undercoat layer 11 and the amorphous silicon film 14 are formed at a film formation temperature of 300 ° C. or lower by using a plasma CVD method. Next, as shown in FIG. 2B, thermal annealing is performed at 450 ° C. for 30 to 60 minutes to desorb hydrogen (H) in the amorphous silicon film 14. At this time, a natural oxide film 15 is formed on the surface of the amorphous silicon film 14.

Next, as shown in FIG.
Amorphous silicon film 1 with a solution containing ozone (O ₃ )
4 is washed for 23 seconds, and the surface of the amorphous silicon film 14 is oxidized in a range of 0.5 nm to 1.5 nm in thickness to form an oxide film 1.
6 is formed. Incidentally, impurities such as carbon (C) and boron (B) are taken into the oxide film 16 by the oxidation using the solution containing ozone (O ₃ ).

Next, as shown in FIG. 2 (d), the oxide film 16 and impurities such as carbon (C) and boron (B) taken in the oxide film 16 are hydrofluoric acid water (HF) having a concentration of 1%. Wash and remove with. As shown in FIG. 3, cleaning and removal with hydrofluoric acid water (HF) is performed when the contact angle θ between the surface of the amorphous silicon film 14 and the pure water 17 by a contact angle measuring device (not shown) is 60 ° or more. Until it becomes true. FIG. 4 shows the relationship between the cleaning time with hydrofluoric acid water (HF) and the contact angle of pure water on the amorphous silicon film surface measured by a contact angle measuring device. To set the contact angle θ to 60 ° or more, the cleaning time with hydrofluoric acid (HF) needs to be 120 seconds or more.

Next, as shown in FIG. 2E, the amorphous silicon film 14 having a contact angle θ of pure water of 60 ° or more is
As shown in FIG. 2F, the glass substrate 1 is crystallized by laser annealing with a laser beam from a XeCl laser device.
0 through an undercoat layer 11 and a polycrystalline silicon film 1
Form 2 Irradiation energy by laser light is 270
３340 mJ / cm ² . As a result, a polycrystalline silicon film 12 having an average crystal grain size range of 0.3 to 0.8 μm was obtained. When the surface of the polycrystalline silicon film 12 was examined, the height of the surface protrusion was suppressed to 50 nm or less.

A polycrystalline silicon TFT having a gate oxide film thickness of 100 nm and having a coplanar structure on a gate was formed by using the polycrystalline silicon film 12 thus formed as a channel layer. It was confirmed that. At the time of cleaning and removing the oxide film 16 shown in FIG. 2D, a polycrystalline silicon film formed by performing a cleaning time of 120 seconds or less and then laser annealing is used as a channel layer, and a coplanar type having a gate placed thereon is used. When a polycrystalline silicon TFT having a structure was formed and its gate dielectric breakdown voltage was examined, some TFTs were broken at a gate voltage of less than 50 V, and deterioration of the gate dielectric breakdown voltage was observed.

With this configuration, the amorphous silicon film 1
As a pretreatment for laser annealing of No. 4, the contact angle θ of pure water is 6
0 ° or more so that the oxide film 16 and impurities such as carbon (C) and boron (B) are completely removed.
By cleaning and removing the oxide film and impurities on the surface of the amorphous silicon film 14, the height of the protrusion on the surface of the polycrystalline silicon film obtained by crystallization by laser annealing is reduced to 50 nm.
It can be suppressed below. Therefore, by using such a polycrystalline silicon film for the channel layer, it is possible to obtain a good polycrystalline silicon TFT having a high gate withstand voltage and, consequently, a liquid crystal display element having a high display quality without causing line defects due to dielectric breakdown. Also, the production yield is improved.

In this embodiment, an oxide film 16 is formed on the surface of the amorphous silicon film 14 with a solution containing ozone (O ₃ ) before removing the oxide film. Incorporates impurities such as carbon (C) and boron (B), 1%
By cleaning and removing the oxide film 16 with hydrofluoric acid water (HF), impurities such as carbon (C) and boron (B) can be removed together with the oxide film 16 and impurities on the surface of the amorphous silicon film 14 can be completely removed. Become.

The present invention is not limited to the above embodiment, but may be modified without departing from the spirit of the invention. For example, the thickness of an amorphous silicon film or the thickness of an oxide film on the surface thereof may be changed. Although the thickness is not limited, if the oxide film thickness is set to 0.5 nm or less, it becomes thinner than one element, so that impurities cannot be sufficiently removed.
% Of hydrofluoric acid (HF), it takes too much time to clean and remove the oxide film.
m is desirable. In addition, the magnitude of the irradiation energy of the laser light is also arbitrary.

[0024]

As described above, according to the present invention, the oxide film and the impurities on the amorphous silicon surface before the laser annealing are completely washed and removed, so that the polycrystalline crystallized by the laser light irradiation. The height of the projections formed on the silicon surface can be kept low. Therefore, the polycrystalline silicon T formed using the polycrystalline silicon thus formed is used.
It is possible to suppress the deterioration of the gate insulation withstand voltage of the FT, and it is possible to manufacture a liquid crystal display element with high display quality, and it is possible to prevent a reduction in manufacturing yield.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a polycrystalline silicon film formed on a glass substrate according to an embodiment of the present invention.

FIGS. 2A and 2B show a process of manufacturing polycrystalline silicon according to an embodiment of the present invention. FIG.
(B) when hydrogen (H) is desorbed from the surface of the amorphous silicon film, (c) when an oxide film is formed on the surface of the amorphous silicon film, (d) when cleaning and removing the oxide film, (e) is a schematic explanatory view showing the time of laser beam irradiation, and (f) is a schematic explanatory view showing the time of crystallization of the polycrystalline silicon film.

FIG. 3 is a schematic explanatory diagram showing a contact angle between a surface of an amorphous silicon film and pure water according to the embodiment of the present invention.

FIG. 4 is a graph showing a relationship between a cleaning time with hydrofluoric acid (HF) and a contact angle of pure water in the embodiment of the present invention.

FIG. 5 shows a conventional polycrystalline silicon manufacturing process (a).
(B) when hydrogen (H) is desorbed from the surface of the amorphous silicon film, (c) when cleaning and removing the oxide film, and (d) when irradiating the laser beam. FIG. 4E is a schematic explanatory view showing the time of crystallization of the polycrystalline silicon film.

FIG. 6 is a graph showing the relationship between the oxide film thickness on the surface of an amorphous silicon film of conventional polycrystalline silicon and the height of a protrusion formed on the surface of the polycrystalline silicon after laser annealing.

FIG. 7 is a schematic explanatory view showing a contact angle between a conventional amorphous silicon film surface and pure water.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Glass substrate 11 ... Undercoat layer 12 ... Polycrystalline silicon film 14 ... Amorphous silicon film 16 ... Oxide film 17 ... Pure water

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshito Kawahisa 1-9-2 Harara-cho, Fukaya-shi, Saitama Pref. Inside the Toshiba Fukaya Electronics Factory (72) Inventor Hiroshi Mitsuhashi 1-chome, Harara-cho, Fukaya-shi, Saitama No. 9-2 Toshiba Fukaya Electronics Factory (72) Inventor Takashi Fujimura 1-9-2 Hara-cho, Fukaya-shi, Saitama Prefecture Toshiba Fukaya Electronics Factory

Claims (5)

[Claims] 1. A method for manufacturing a polycrystalline semiconductor in which amorphous silicon deposited on a substrate is crystallized by irradiating a laser beam to the amorphous silicon, wherein: a step of forming an amorphous silicon film on the substrate; Oxidizing a surface of the amorphous silicon film to form an oxide film, and oxidizing the pure water so that a contact angle of the pure water with the surface when the pure water is dropped on the surface after the oxide film is removed is 60 degrees or more. A polycrystalline semiconductor comprising: a step of removing a film; and a step of irradiating the amorphous silicon film after the removal of the oxide film with the laser beam to crystallize the amorphous silicon film. Manufacturing method. 2. The method according to claim 1, wherein the step of forming the oxide film is performed using a solution containing ozone. 3. The method for manufacturing a polycrystalline semiconductor according to claim 1, wherein the step of removing the oxide film is performed using an etching solution containing hydrofluoric acid. 4. The oxide film has a thickness of 0.5 nm to 1.5 n.
4. The method for producing a polycrystalline semiconductor according to claim 1, wherein m is m. 5. A method for producing a polycrystalline semiconductor, comprising irradiating a laser beam to amorphous silicon having a contact angle of 60 ° or more with the pure water when the pure water is dropped on the surface to crystallize the amorphous silicon.