JPH10144606A - Semiconductor thin film and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor thin film with high film quality by a method wherein a thin film which is made of material whose main component is germanium is formed on a polymer substrate and the thin film is crystallized or recrystallized at least partially by a laser beam or an energy beam with a specific energy intensity. SOLUTION: A silicon oxide layer 2 is formed (a) on a polymer substrate 1 which has an undercoating layer on its surface by a sputtering method. At that time, the continuous operating temperature of the substrate 1 is taken into consideration so as to protect the substrate l from damages caused by heat, plasma, etc. An amorphous germanium film 3a is formed (b) on the silicon oxide layer 2 by an ordinary sputtering method and then, in the atmosphere at a room temperature, the amorphous germanium film 3a is crystallized (c) by the application of the laser beam 4 of an XeCl excimer laser, etc., whose energy is not higher than 200mJ/cm<2> to form a germanium layer 3 (d). With this constitution, the influence upon the substrate such as thermal damage can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor thin film and a method for manufacturing the same, and more particularly, to a semiconductor thin film formed on a polymer material substrate and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a thin film transistor used as an active element of a liquid crystal display device is usually formed by forming an amorphous silicon thin film on an insulating substrate. In order to obtain semiconductor characteristics, a method using light, heat, ions, plasma, or the like at a process temperature of 200 ° C. to 1000 ° C. is used. In particular, in recent years, an amorphous silicon thin film is crystallized by laser annealing and used as polycrystalline silicon. The method is starting to be used.

For example, in Japanese Patent Application Laid-Open No. 58-206163, after an amorphous silicon thin film is formed on an insulating substrate, the film is crystallized by laser annealing. The polycrystalline silicon film thus crystallized is
Higher crystallinity and fewer defects than amorphous silicon, a polycrystalline silicon thin film obtained by solid phase growth, or a silicon thin film that is already polycrystalline at the time of film formation. For this reason, when used as an active layer of a transistor, it exhibits extremely excellent performance, enables high-speed driving, and allows not only active elements but also a driving circuit to be manufactured over the same substrate. Further, when such a thin film transistor is applied to an active element of a liquid crystal display, a glass substrate is used because the substrate needs to have a light-transmitting property.

On the other hand, cracking of the substrate due to impact,
In order to cope with reduction in size and weight of the liquid crystal display device, it has been proposed to use a polymer material such as a plastic or a polymer film as a substrate. However, these substrates
Since the heat resistance is not sufficient and it is easily deformed by heat generated in the manufacturing process, it is necessary to keep the forming process temperature extremely low. Therefore, it has been difficult to obtain a semiconductor thin film having excellent properties on a polymer material substrate having low heat resistance by the conventional technology.

On the other hand, in the case where amorphous silicon is crystallized by laser irradiation, the semiconductor layer is melted and the temperature rises, so that the surface temperature of the substrate also rises due to the transmission of the heat. A method of forming a heat diffusion layer as a heat buffer layer between semiconductor layers to enhance the heat dissipation effect (JP-A-4-33327) and a method of forming a thermal barrier layer having low thermal conductivity (JP-A-5-326402) Etc. have been proposed.

However, if it is a semiconductor thin film having a thickness of about 50 to 100 nm used for a normal thin film transistor,
In laser irradiation, some crystallization is observed even with laser light of relatively low energy of about 130 to 200 mJ / cm ² , but in order to sufficiently promote crystallization and obtain a good quality thin film showing excellent semiconductor characteristics 200 mJ / cm ² or more, preferably it is necessary to irradiate a laser having a 250 mJ / cm ² or more high energy. Therefore, the temperature rise of the semiconductor layer also increases, and it is difficult to completely suppress the temperature rise of the substrate even when the above-described thermal diffusion layer or thermal barrier layer is used.
In particular, on a polymer material substrate having a relatively low cost, a wide variety of types, and a continuous usable temperature of 170 ° C. or less, it is not possible to obtain a sufficiently crystallized high-quality semiconductor film without damaging the substrate due to heat. Was.

Japanese Patent Application Laid-Open No. 4-33327 discloses that a very special polymer material substrate having a heat-resistant temperature of 200 ° C. or more, such as polyimide or phenolic resin reinforced with glass, is used to avoid damage to the substrate. A method for forming a high-quality polycrystalline thin film by applying sufficient energy has been disclosed.However, such a high heat-resistant polymer not only significantly increases the substrate cost, but also has a small number of types of materials. The degree of freedom for the selectivity of other properties, such as strength and transparency, is sacrificed. Therefore, it is extremely difficult to select an optimal material according to the application.

As described above, in addition to using silicon, which is the most common and widely applicable semiconductor material, there is a degree of freedom in selecting properties such as transparency and strength. At present, the formation of a high-quality crystallized thin film has not been realized.

[0009]

According to the present invention, a laser beam or an energy beam formed on a polymer material substrate, the main component of which is made of germanium, and having an energy intensity of 200 mJ / cm ² or less is used. A semiconductor thin film that is partially crystallized or recrystallized is provided.

Further, a thin film whose main component is made of germanium is formed on a polymer material substrate, and the thin film is formed to a thickness of 200 mJ.
Provided is a method for manufacturing a semiconductor thin film, which comprises crystallizing or recrystallizing at least a part thereof with a laser beam or an energy beam having an energy intensity of / cm ² or less.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a polymer material substrate on which a semiconductor thin film is formed is not particularly limited as long as it is formed of a polymer material and can be generally used in the field. All substrates can be used. However, the semiconductor thin film formed on this substrate is
It is necessary to have properties such as heat resistance sufficient to perform crystallization or recrystallization sufficiently to exhibit characteristics according to the use. Specifically, a polymer material substrate capable of continuous use at 200 ° C. or higher such as polyimide, polyamide imide, and liquid crystal polyarylate, and a continuous usable temperature of polyester, polycarbonate, polyarylate, polysulfone, polyetherimide, etc. 170
Although a polymer material having a relatively low heat resistance of not more than ℃ is mentioned, a polymer material having a continuous usable temperature of not more than 170 ℃ is preferable. That is, in the case of a polymer material substrate which can be used continuously at 200 ° C. or higher, it is relatively easy to form a high-quality semiconductor thin film thereon, but the material cost is extremely high and the type itself is extremely small. Therefore, it is extremely disadvantageous from the viewpoint of applicability, for example, the room for appropriately selecting other physical properties such as mechanical strength and optical properties becomes extremely narrow. On the other hand, as described later, energy of 200 mJ / cm ² or less Substrates that can withstand high-intensity laser light or energy beams are polymer materials with a continuous usable temperature of 170 ° C or less, and are relatively economical due to relatively low cost. Other physical properties can be selected. Is preferable. The polymer material substrate in the present invention can be used by appropriately selecting the thickness, size, or other physical properties such as mechanical strength and optical properties according to the application. Here, the continuous usable temperature can be considered to be a temperature equal to the lower one of the deflection temperature under load and the UL long-term heat resistance temperature.

The semiconductor thin film formed on the polymer material substrate contains germanium as a main component. The term "main component is made of germanium" means a state in which basic semiconductor characteristics are governed by physical properties inherent to germanium. For example, depending on the application, impurities such as carriers for generating carriers and hydrogen for terminating dangling bonds are reduced by several%. It may be included in the order. Germanium has a melting point of 937 ° C
Which is much lower than silicon at 1410 ° C.
Energy required for crystallization can be extremely reduced as compared with the case where silicon is used. For this reason, it is possible to form a high-quality semiconductor thin film on a polymer material substrate having relatively low heat resistance, thereby increasing the selectivity of the substrate and significantly reducing the substrate cost. Further, by using germanium as the semiconductor thin film, a semiconductor characteristic value inherent to the substance becomes higher than that of silicon. For example, comparing the mobilities of electrons and holes, germanium is superior to each other as described below. As a result, when a thin film transistor or the like is manufactured using this semiconductor thin film, more excellent characteristics are exhibited, and Driving is also possible.

[0013]

[Table 1]

At this time, the thickness of the semiconductor thin film containing germanium as a main component is not particularly limited, and can be appropriately adjusted and used according to the use. Specifically, considering that crystallization or recrystallization can be performed on at least a part thereof, preferably on the whole of the thin film, 1
The thickness is preferably about 0 nm to 1 μm. Specifically, when this semiconductor thin film is used as an active layer of a thin film transistor, the thickness is preferably about 20 nm to 200 nm.

[0015] The semiconductor thin film by laser light or energy beam having a 200 mJ / cm ² or less of energy intensity, but in which at least a portion of which is crystallized or recrystallized, 200 mJ / cm ² or less of Energy intensity is based on the following data. An amorphous thin film of germanium is formed on a substrate to a thickness of 50 nm by a sputtering method, and an excimer laser (XeCl: 308 n) is used.
m) was irradiated for crystallization, and the progress of crystallization due to a change in energy at that time was measured by Raman spectrum. In addition, an amorphous silicon thin film was similarly formed as a target, and the Raman spectrum was measured. FIG. 4 shows the results. In the case of silicon, sufficient crystallization is not performed unless the energy of the irradiation laser exceeds 200 mJ / cm ² , whereas in the case of germanium,
70 mJ / cm ² crystallization from around advances, it was confirmed that substantially fully crystallized at 150 mJ / cm ² is performed.

The relationship between the irradiation laser energy and the substrate surface temperature during crystallization of the amorphous thin film was measured. The result is shown in FIG. In FIG. 5, on a quartz substrate, about 30 nm of amorphous silicon is formed as an amorphous thin film via a silicon oxide thin film of about 200 nm which is most commonly used as a thermal barrier layer, and laser irradiation is performed.
The measured value at 1.5 μs after irradiation is shown. The measurement of the substrate surface temperature utilizes a change in the electric resistance of a platinum thin film formed on the substrate surface (for the measurement method, see, for example, Jpn. J. Appl.
Phys. 28 (1989) L2131). The substrate surface temperature rises rapidly within 1 μs immediately after laser irradiation, and the maximum temperature increases as the thermal barrier layer becomes thinner.
Thereafter, the temperature gradually decreased, and after 1 μs had elapsed, the temperature became almost constant, almost independent of the thickness of the thermal barrier layer. In FIG. 5, the thickness of the thermal barrier layer is 20
Although the value was at 0 nm, even when the film thickness was in the range of 100 nm to 1 μm, only a difference of about ± 10 ° C. occurred. In addition, when laser crystallization of silicon was attempted using various polymer material substrates, substrate damage was clearly observed for substrates whose substrate surface temperature at 1.5 μs after irradiation exceeded the continuous usable temperature of the substrate. However, no damage was confirmed even if the maximum temperature within 1 μs after irradiation slightly exceeded the continuous usable temperature of the substrate. Also, when germanium was used instead of silicon, the change in the substrate surface temperature with respect to the irradiation energy on the polymer material substrate coincided with the result of FIG.
From this, the substrate surface temperature 1.5 μs after irradiation is
It can be considered as a measure of the irradiation energy that can be used for the substrate (in the past, only the maximum temperature was the subject of discussion on the heat resistance of the substrate). Therefore, for example, for a substrate having a continuous usable temperature of 170 ° C. or less, 200 mJ / c
It was confirmed that laser irradiation with an energy of m ² or more was not appropriate.

From the above results, a semiconductor thin film was formed,
When performing crystallization by laser or energy beam irradiation having an energy intensity of 200 mJ / cm ² or less,
It has been confirmed that crystallization can be realized on a polymer substrate having a continuous usable temperature of 170 ° C. or less, and the influence of damage or heat shrinkage on the substrate can be reduced.
At least a part of the semiconductor thin film is crystallized or recrystallized by a laser beam or an energy beam having an energy intensity of 200 mJ / cm ² or less. Further, even when energy of 70 mJ / cm ² or less is used, defects in the semiconductor thin film can be reduced to some extent, and the effect of improving the film quality is obtained, but crystallization of the semiconductor thin film may not be performed sufficiently. Therefore, it is preferable to use energy of 70 mJ / cm ² or more.

The laser beam or energy beam is A
UV excimer laser such as rF, KrF, XeCl, etc.
An excimer lamp, an Ar laser having the same wavelength as these, or various energy beams such as an electron beam and an ion beam may be used, or irradiation may be performed as a pulsed laser. In the present invention, the semiconductor thin film is
It may be formed on a polymer material substrate via a thermal barrier layer. This thermal barrier layer functions so as not to damage the substrate by heat when the semiconductor thin film is crystallized or recrystallized, and for example, has a thermal conductivity of silicon oxide, silicon nitride, aluminum oxide, etc. It is preferable to use a relatively small insulating film. As the thickness of the thermal barrier layer increases, the thermal barrier effect increases, but when the thermal barrier layer is thick, defects such as cracks are likely to occur or productivity may be reduced. It is preferable to make the layer as thin as not to appear. Specifically, the laser type, energy,
The thickness can be appropriately adjusted according to the type of the polymer material substrate, the thickness of the semiconductor thin film formed thereon, and the like.
And about 300 nm or less. These thermal barrier layers, for example, sputtering, vapor deposition,
It can be formed using a technique such as a CVD method or an ion plating method. At this time, care must be taken so that the process temperature does not rise above the continuous usable temperature of the substrate. In addition, it is necessary to pay sufficient attention to damage to the substrate due to plasma or the like.

In the production method of the present invention, as a method of forming a crystallized or recrystallized thin film in which the main component is made of germanium on the polymer material substrate, first, the main component is made of germanium on the polymer material substrate described above. And forming a thin film. The germanium thin film at this time, for example,
Using a method such as a sputtering method, an evaporation method, a CVD method, or an ion plating method, an amorphous material, a single crystal, a polycrystal, or a part thereof is formed to be amorphous, a single crystal, a polycrystal, or the like. be able to. During the film formation, as in the case of forming the above-described thermal barrier layer, it is necessary to prevent the temperature of the substrate from being raised to a temperature higher than the continuous usable temperature. You also need to be careful.

Next, 20 μm is applied to the formed germanium thin film.
A laser beam or an energy beam having an energy intensity of 0 mJ / cm ² or less is irradiated to crystallize or recrystallize at least a part, preferably the whole. In the case of crystallization or the like, it is necessary not to raise the substrate temperature to a temperature at which the substrate can be used continuously. For this reason, a thermal barrier layer may be formed on the substrate as described above,
Irradiation with laser light or the like may be performed in a state where the temperature is raised in advance so that the substrate is not damaged by heat or in a state where the substrate is placed in a vacuum. Examples of the semiconductor thin film and the method of manufacturing the same according to the present invention will be described below.

Example 1 First, as shown in FIG. 1A, a silicon oxide layer was formed as a thermal barrier layer on a 0.5 mm thick polycarbonate substrate 1 provided with an undercoat layer (not shown) on the surface. 2 was formed to a thickness of 300 nm by a normal sputtering method. Since the continuous usable temperature of the substrate 1 was 150 ° C.,
Care was taken not to damage the substrate 1 by heat, plasma, or the like.

Next, as shown in FIG. 1B, an amorphous germanium 3a, which is a semiconductor material, was formed on the silicon oxide layer 2 to a film thickness of 50 nm by a usual sputtering method. At this stage, fogging, warpage, undulation, and the like were not particularly observed on the substrate 1. Subsequently, as shown in FIG. 1C, the amorphous germanium 3a was crystallized by laser irradiation 4 to form a germanium layer 3 as shown in FIG. 1D. As a laser, a XeCl excimer laser (wavelength: 308 nm) was used, and irradiation was performed with a pulse having a half width of 30 ns and energy of 180 mJ / cm ² . Substrate 1
Was irradiated at room temperature in the atmosphere without raising the temperature in advance. No fogging, warpage, undulation, etc. were observed on the substrate 1 after the irradiation, and no damage was observed. No abnormalities such as crack generation and ablation were observed in the germanium layer 3.

[0023] As a comparative example, if instead of the irradiation with energy of 180 mJ / cm ^2, except that was irradiated at an energy of 300 mJ / cm ² is obtained by forming the germanium layer in the same manner as described above, the substrate Was clearly damaged. FIG. 2 shows a Raman spectrum of the germanium layer 3 obtained in the above example in comparison with single-crystal germanium and amorphous germanium. At this time, an argon laser was used as a light source, wavelength: 514.5 nm, output: 150
W was set, and measurement was performed for 60 seconds. According to FIG. 2, the germanium layer (b) obtained in the above example has a slight shift as compared with the single crystal germanium layer (c) due to the occurrence of stress in the layer.
A clear peak appears near 0 cm ^−1, which indicates that the crystal is very high quality. On the other hand, in the case of amorphous germanium (a) not subjected to laser irradiation, no such peak was observed.

Further, apart from the above embodiment, a sample irradiated with lasers having different energy values was prepared in the same manner as in the above embodiment, and the Raman spectrum was measured.
No peaks were observed in samples below m ² , as in non-irradiated samples. This is in good agreement with the result using the quartz substrate shown in FIG.

Example 2 First, a silicon oxide layer was formed as a thermal barrier layer on a 0.3 mm thick polysulfone substrate having an undercoat layer (not shown) on the surface in the same manner as in Example 1 by a normal EB evaporation method. To form a film with a thickness of 100 nm. Since the continuous usable temperature of this substrate was 150 ° C., care was taken to prevent the substrate from being damaged by heat, plasma or the like.

Next, amorphous germanium, which is a semiconductor material, is formed on the silicon oxide layer by ordinary plasma CVD.
The film was formed to a thickness of 30 nm by using the method. At this time, the substrate temperature was kept at 120 ° C., and care was taken not to cause damage due to plasma or the like. Reaction pressure is 20Pa, RF power is 10mW / c
and m ^2, GeH ₄ as the reaction gas: using 50 sccm: 10 sccm, H ₂ as diluent gas. At this stage, no fogging, warpage, undulation or the like was observed on the substrate.

Subsequently, the amorphous germanium was crystallized by laser irradiation to form a germanium layer. The laser is a KrF excimer laser (wavelength: 248
Multi-irradiation was performed while moving a pulse having a half width of 20 ns and an irradiation area of 1 mm × 20 nm in steps of 0.1 mm. The energy applied at this time was 150 mJ / cm ² per pulse. The substrate was irradiated at room temperature in the air without raising the temperature in advance. No fogging, warpage, undulation, etc. were observed on the irradiated substrate, and no damage was observed. No abnormalities such as crack generation and ablation were observed in the germanium layer.

The Raman spectrum of the germanium layer obtained in the above example was measured in the same manner as in Example 1.
A peak similar to that shown in FIG. 2B was observed, and it was confirmed that the crystal had a very good quality.

Embodiment 3 First, as shown in FIG. 3A, similarly to the embodiment 1, the undercoat layer (not shown) having a thickness of 0.1
Amorphous germanium 12a, which is a semiconductor material, was formed on a 5 mm polyetherimide substrate 11 to a thickness of 100 nm by using the same plasma CVD method as in Example 2. Since the continuous usable temperature of the substrate 11 was 170 ° C., care was taken to prevent the substrate 11 from being damaged by plasma, heat or the like. At this stage, fogging, warpage, undulation, etc. were not particularly observed on the substrate 11.

Next, the amorphous germanium 12a was crystallized by irradiation with a laser 13 to form a germanium layer 12. The laser 13 was a KrF excimer laser (wavelength: 248 nm), and was irradiated with a pulse having a half width of 20 ns and energy of 120 mJ / cm ² . Substrate 11
Was irradiated at room temperature in the air without raising the temperature in advance. No fogging, warpage, undulation, etc. were observed on the substrate 11 after the irradiation, and no damage was observed. No abnormalities such as crack generation and ablation were observed in the germanium layer 12.

The Raman spectrum of the germanium layer obtained in the above example was measured in the same manner as in Example 1.
A peak similar to that shown in FIG. 2B was observed, and it was confirmed that the crystal had a very good quality.

[0032]

According to the present invention, since germanium is used as a main component of the semiconductor thin film, a semiconductor characteristic value unique to a substance, for example, mobility of electrons and holes, which is better than when silicon is used, is obtained. Can be various elements,
For example, excellent characteristics can be exhibited when used for an element such as a thin film transistor, a photovoltaic device, or a sensor. Further, the energy required for sufficient crystallization or recrystallization can be significantly reduced to 200 mJ / cm ² or less as compared with the case where silicon is used. This can reduce the effects on the substrate such as thermal damage,
It is not necessary to use a special polymer material whose continuous use temperature is higher than 170 ° C., and a polymer material substrate which is inexpensive and easily available can be used, so that the selectivity of the substrate is expanded. In addition, to reduce the energy required for sufficient crystallization or recrystallization, to form a thermal barrier layer or the like with a special material to suppress heat conduction,
To avoid the problems of productivity reduction and production cost increase by adopting a method of forming a thermal barrier layer extremely thick, such as forming a thin thermal barrier layer directly on a substrate or silicon oxide. With a very simple method, damage to the substrate can be almost completely suppressed.

In addition, the use of germanium provides sufficient energy for crystallization or recrystallization, so that a semiconductor thin film having extremely good film quality can be obtained. Further, according to the method of the present invention, by irradiating a laser beam or an energy beam with an energy of 200 mJ / cm ² or less to germanium formed on the substrate, the continuously usable temperature is 170 ° C. or less even on a substrate. The crystallization or recrystallization can be sufficiently promoted, and a high-quality semiconductor thin film can be formed very easily, the selectivity of the substrate is widened, and the cost and applicability are very advantageous. Therefore, an unprecedented use of the semiconductor thin film can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional manufacturing process diagram of a main part showing an embodiment of a method for manufacturing a semiconductor thin film of the present invention.

FIG. 2 is a diagram showing Raman spectra of the semiconductor thin film of the present invention and another semiconductor.

FIG. 3 is a schematic cross-sectional manufacturing process diagram of a main part showing another embodiment of the method for manufacturing a semiconductor thin film of the present invention.

FIG. 4 is a diagram showing a difference in progress of crystallization due to energy between germanium and silicon according to a Raman spectrum.

FIG. 5 is a diagram showing a relationship between laser irradiation energy to silicon and substrate surface temperature.

[Explanation of symbols]

 Reference Signs List 1, 11 Polymeric material substrate 2 Silicon oxide layer (thermal barrier layer) 3, 12 Germanium layer (crystallized semiconductor thin film) 3a, 12a Amorphous germanium 4, 13 Laser light or energy beam

Claims (8)

[Claims] 1. A laser beam or an energy beam formed on a polymer material substrate, the main component of which is made of germanium, and having an energy intensity of 200 mJ / cm ² or less, at least a part of which is crystallized or recrystallized. A semiconductor thin film characterized in that: 2. The polymer material substrate has a continuous usable temperature of 1.
2. The semiconductor thin film according to claim 1, which is a polymer material substrate at a temperature of 70 ° C. or lower. 3. The semiconductor thin film according to claim 1, wherein the semiconductor thin film is formed on a polymer material substrate via a thermal barrier layer. 4. A laser beam or an energy beam,
4. The semiconductor thin film according to claim 1, which has an energy intensity of 0 mJ / cm ² or more. 5. A thin film whose main component is made of germanium is formed on a polymer material substrate, and the thin film is formed to a thickness of 200 mJ / cm ^2.
A method for producing a semiconductor thin film, comprising crystallizing or recrystallizing at least a portion of the semiconductor thin film with a laser beam or an energy beam having the following energy intensity. 6. The polymer material substrate has a continuous usable temperature of 1.
6. The method for producing a semiconductor thin film according to claim 5, wherein the substrate is a polymer material substrate at 70 ° C. or lower. 7. The method according to claim 5, wherein, after forming the thermal barrier layer on the polymer material substrate, a thin film whose main component is made of germanium is formed on the thermal barrier layer. 8. A laser beam or an energy beam,
The method of any of claims 5-7 having 0 mJ / cm ² or more energy intensity.