JPH08293464A - Manufacture of semiconductor substrate and semiconductor device - Google Patents

Abstract

PURPOSE: To provide a method of manufacturing a semiconductor substrate and a semiconductor device in which an antireflection film composed of a silicon dioxide film is selectively deposited on the surface of an amorphous silicon film formed on an insulating substrate and after that, the whole surface of the substrate is irradiated with a laser beam to perform annealing processing in the molten crystallization process of a semiconductor film. CONSTITUTION: An antireflection film is selectively deposited in the surface of an amorphous silicon film 12, thereby making it feasible to selectively control the energy power of a laser beam 15 in every substrate region even in the case of radiating the laser beam 15 onto the whole surface of a substrate under same conditions, and a plurality of thin film transistors having a more suitable characteristic for each region on a same substrate can be formed with high accuracy. Further, since the whole surface of a substrate can be processed by the one radiation of an energy ray, a throughput is high and also since the processing can be performed by the irradiation of the low energy power of an energy ray device main body, the burden of the device can be reduced, so that stable process may be always performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate and a method of manufacturing a semiconductor device formed by processing the semiconductor substrate. The present invention relates to a semiconductor substrate and a method for manufacturing a semiconductor device that are preferably implemented in a crystallization process.

[0002]

2. Description of the Related Art As a semiconductor device having a thin film transistor on an insulating substrate such as glass, an active matrix type liquid crystal display device or an image sensor using the thin film transistor as a switching element for each pixel and a peripheral drive circuit for the switching element is known. Etc. are known. Thin film silicon semiconductors are generally used for thin film transistors used in these devices. The thin film silicon semiconductor is roughly classified into two types, that is, an amorphous silicon semiconductor and a crystalline silicon semiconductor.

Amorphous silicon semiconductors are most commonly used because they are low in manufacturing temperature, can be relatively easily manufactured by a vapor phase method, and have high mass productivity. Since it is difficult to reduce the pixel size, it is difficult to increase the aperture ratio of the pixel, and the physical properties such as carrier mobility are inferior to those of a crystalline silicon semiconductor. Therefore, in order to obtain better high-speed characteristics and high aperture ratio, there has been a strong demand for establishment of a method for manufacturing a thin film transistor made of a crystalline silicon semiconductor.

On the other hand, as the crystalline silicon semiconductor, single crystal silicon (c-Si), polycrystalline silicon (p-Si), microcrystalline silicon (μc-Si), amorphous silicon containing a crystalline component, Semi-amorphous silicon having an intermediate state between crystalline and amorphous is known. As a method for obtaining these thin film silicon semiconductors having crystallinity, (1) a film having crystallinity is directly formed at the time of film formation. (2) A semiconductor film is formed and crystallinity is imparted by applying heat energy. (3) A semiconductor film is formed in advance and made crystalline by the energy of laser light. Such methods are known.

Each of the above methods has the following problems.

In the method (1), since crystallization progresses at the same time as the film forming step, it is necessary to thicken the silicon film in order to obtain crystalline silicon. Difficult to do. Therefore, the silicon film contains many grain boundaries, the carrier mobility is limited by the traps at the grain boundary portions, and the current driving capability required for the driving circuit cannot be obtained. Further, since the film forming temperature is as high as 600 ° C. or higher, there is a cost problem that an inexpensive glass substrate cannot be used.

The method (2) has the advantage that it can be applied to a large area, but requires a heat treatment for several tens of hours at a high temperature of 600 ° C. or higher for crystallization. That is, considering the use of an inexpensive glass substrate and the improvement of throughput, which is the number of processes per unit time, it is necessary to simultaneously solve the conflicting problems of lowering the heating temperature and crystallizing in a shorter time.

In the method (3), since the crystallization phenomenon in the melt crystallization process is utilized, the grain boundaries are well processed and a high quality crystalline silicon film is obtained although the grain size is small. Taking the excimer laser used in
There is a problem that the irradiation area of the laser beam is small and the throughput is low, and the stability of the laser is not sufficient to uniformly process the entire surface of the large area substrate.

As a future technology, for example, a high speed thin film transistor which constitutes a peripheral driving circuit of an active matrix type liquid crystal display device and a thin film transistor which constitutes a pixel capable of realizing a high aperture ratio are simultaneously formed on the same substrate. It is desired to do. In such a so-called monolithic substrate, a thin film transistor for a driving circuit needs to have high speed and high carrier mobility, and a thin film transistor for a pixel has a big problem of reducing off current.

As a method of manufacturing a semiconductor film capable of forming thin film transistors having different characteristics on the same substrate, selective melting and crystallization of the semiconductor film is performed on the same substrate by using energy rays such as laser light or electron beam. A method has been proposed. For example, in the first method disclosed in Japanese Patent Application Laid-Open No. 64-45162, the semiconductor film is divided into a plurality of regions in advance so that the portions other than the portion directly irradiated with the laser do not recrystallize, and only the desired regions are formed. There has been proposed a method of irradiating an energy beam to a laser beam and not irradiating the energy beam to other undesired regions. The second method disclosed in Japanese Patent Laid-Open No. 3-292721 proposes a method of forming an energy ray impermeable film in an undesired region and selectively performing melt crystallization treatment.

[0011]

However, the above method has the following problems.

In the first method, laser irradiation is required a plurality of times, the throughput is low, the processing steps are complicated, and it is very difficult to perform accurate alignment. In the second method, the formation of the impermeable film causes a region in the substrate where melt crystallization does not occur. That is, since only an amorphous film and a polycrystalline film can be combined on the same substrate, it is difficult to increase the aperture ratio of the pixel region.

Therefore, in both methods, the throughput of the laser annealing treatment is improved and the characteristics are improved, more specifically, the carrier mobility is improved in the thin film transistor forming the peripheral drive circuit, and the high aperture is formed in the thin film transistor forming the pixel. It is difficult to solve the problems such as realization of the rate and reduction of the leak current at the off time at the same time.

It is an object of the present invention to provide a semiconductor substrate and a method of manufacturing a semiconductor device, which can accurately and economically form thin film transistors having different characteristics on the same substrate.

[0015]

According to a first aspect of the present invention, there is provided a semiconductor substrate and a method for manufacturing a semiconductor device, which are amorphous formed on a substrate having an insulating surface or a substrate whose surface is covered with an insulating film. In the step of irradiating the semiconductor film with energy rays to melt and crystallize the amorphous semiconductor film, antireflection films having different thicknesses are selectively deposited on the surface of the amorphous semiconductor film. To do.

According to a second aspect of the present invention, in the method of manufacturing a semiconductor substrate and a semiconductor device, the energy beam has a wavelength of 400.
The antireflection film is a pulsed light of an ultraviolet laser having a wavelength of nm or less, and the antireflection film is selected as a material that does not absorb the ultraviolet rays.

[0017]

According to the invention of claim 1, it is deposited by chemical vapor deposition (CVD) or sputtering on a substrate having an insulating surface or a substrate whose surface is covered with an insulating film. An antireflection film is selectively provided on the surface of an amorphous semiconductor film such as amorphous silicon. Then laser light,
Alternatively, the entire surface of the substrate is irradiated with a certain constant energy power using an energy beam such as an electron beam.

Since the reflectance of the region where the antireflection film is provided and the region where the antireflection film is not provided on the surface of the amorphous semiconductor film are different from each other, even if irradiation is performed under the same conditions, the antireflection film is not exposed. It is possible to effectively obtain high power.
Therefore, the energy power can be selectively controlled for each region, and a plurality of thin film transistors having different characteristics can be formed in the same substrate with high precision and high throughput.

According to the second aspect of the invention, the energy beam is pulsed light of an ultraviolet laser having a wavelength of 400 nm or less, and the laser beam has an oscillation wavelength of 308 nm, for example.
Then, an excimer laser with an oscillation time of about 50 ns is used. The antireflection film is selected as a material that does not absorb the ultraviolet rays. For example, a silicon dioxide film that does not absorb the ultraviolet rays and has good compatibility with the silicon film in the process is used.

[0020]

EXAMPLE An example of the present invention will be described below with reference to FIGS.

FIG. 1 is a sectional view showing a manufacturing process of TFTs A1 and B1 which are semiconductor devices of an embodiment of the present invention.
FIG. 2 is a plan view of a liquid crystal display device using the TFTs A1 and B1. The process sectional view of FIG. 1 corresponds to the cutting plane L in the plan view of FIG.

This embodiment will be described in accordance with the manufacturing process of FIG. 1. First, in FIG. 1A, the surface of an insulating substrate 10 made of quartz, glass or the like is cleaned, and then a silicon dioxide film is used as a base coat film 11 for a sputtering apparatus. With a thickness of 30
It is in a state of being deposited to about 0 nm. The required film thickness of this base coat film varies depending on the surface condition of the substrate, and can be omitted if the substrate is sufficiently flat and has a sufficiently low ion concentration that adversely affects semiconductor characteristics such as sodium ions. If the surface condition is severely scratched or uneven, it is necessary to deposit thicker than the above film thickness.

FIG. 1B shows a state in which the amorphous silicon film 12 is deposited on the base coat film 11 by a chemical vapor deposition method or a sputtering method to a thickness of about 50 nm. FIG. 1C shows the amorphous silicon film 1 after that.
2, a transparent anti-reflection film that does not absorb ultraviolet rays,
For example, it is a state in which the silicon dioxide film 13 is deposited by a sputtering method or the like.

The thickness of the silicon dioxide film 13 is as shown in FIG.
Can be calculated based on FIG. 3 shows the relationship between the film thickness of the antireflection film and the reflectance with respect to the laser wavelength of 308 nm. As the antireflection film, the silicon dioxide film 13 is used.
Is used. In this embodiment, the film thickness of the silicon dioxide film 13 is set to 50 nm, which has the lowest reflectance with respect to the XeCl laser having a wavelength of 308 nm. When the effective energy power is calculated based on the reflectance shown in FIG. 3, there is a maximum difference of 40% between the region where the antireflection film is provided and the region where the antireflection film is not provided.

FIG. 1D shows a state in which an antireflection film is selectively formed by photolithography in a high speed thin film transistor region which constitutes a peripheral drive circuit.
The region 14 where the antireflection film is selectively deposited corresponds to the opening portion 26 shown by hatching in the plan view of the photomask 27 for the antireflection film shown in FIG. Next, when the entire surface of the substrate is irradiated with the laser beam 15, amorphous silicon is melted and crystallized, and a crystalline silicon film is obtained by crystal growth.

In this embodiment, the oscillation wavelength of the laser is 3
08 nm, setting irradiation energy density is 200 mJ / cm ²
The oscillation time (pulse width) was about 50 ns, and the oscillation frequency was 300 Hz, but the conditions differ depending on the state (film quality, film thickness, structure) of the film irradiated with laser.

FIG. 1E shows a state in which the antireflection film is removed by using an etchant for SiO ₂ such as a hydrofluoric acid solution after the laser treatment is completed. This indicates that crystalline silicon having different laser energy powers has been obtained. In the present embodiment, since the processing is performed at the set irradiation energy density of 200 mJ / cm ² , the region 16 (the region forming the peripheral drive circuit) 16 covered with the antireflection film has an effective energy power of 280.
Area around mJ / cm ² and not covered with other antireflection film (area forming internal pixels) 17
Is an effective energy power of 200 mJ / cm ² .

Next, the semiconductor substrate 2 produced by the above method
3 in the peripheral drive circuit area 24 and the internal pixel area 25,
For example, by the following manufacturing method, TFTA1, B1
Is configured. Only the TFT region of the crystalline silicon film is left by the etching process, and the gate insulating film 18 is laminated thereon by the sputtering method. Subsequently, the gate electrode 19 is formed and impurities are implanted. Furthermore, when an insulating film 20 made of SiO ₂ is laminated, an opening is provided by etching, and a source electrode 21 and a drain electrode 22 are formed, as shown in FIG.
1 and B1 are completed respectively.

As described above, in the melt crystallization process of the semiconductor film for thin film transistors, the silicon dioxide film 13, which is an antireflection film, is formed on the surface of the amorphous silicon film 12 formed on the insulating substrate 10 in the peripheral driving circuit. By selectively depositing in the region 24 and then irradiating the entire surface of the substrate with the XeCl laser beam 15 under the same conditions, the peripheral drive circuit region 24 is provided with high-speed TFTs (A1, A2 in FIG. 2) having high carrier mobility. ) Can be formed, and at the same time, a TFT (FIG.
B1, B2, B3, B4) can be formed. That is, by processing the entire surface of the substrate with a single laser irradiation, it is possible to form a plurality of thin film transistors having characteristics more suitable for each region on the same substrate with high precision and high throughput. Since the annealing treatment can be performed by irradiation with low energy power, stable treatment can be always performed, the gas life is extended, and the burden on the apparatus can be reduced.

In this embodiment, the thickness of the antireflection film is
The difference was 50 nm (a region provided with an antireflection film) and 0 nm (a region not provided with an antireflection film), but it was performed when the film thickness of the antireflection film was three or more different. Alternatively, the film thickness may be changed according to the material of the antireflection film, the characteristics of the thin film transistor to be formed, and the like. Further, although the laser beam 15 is used as the energy beam for irradiation in the melt crystallization step, the same effect can be expected by using an electron beam and an antireflection film made of a material corresponding thereto instead of the laser beam 15.

The semiconductor substrate 23 has a TF of another shape.
It may be used not only for T or TFT but also for other semiconductor devices.

[0032]

As described above, according to the method of manufacturing a semiconductor substrate and a semiconductor device of the present invention, by selectively providing an antireflection film on the surface of the amorphous semiconductor film, each of the semiconductor substrates and the semiconductor device can be formed on the same substrate. It is possible to simultaneously form a thin film transistor having a characteristic more suitable for a region. For example, in an active matrix type liquid crystal display device, an image sensor or the like in which a thin film transistor provided on an insulating substrate such as glass is used for a pixel and its driving circuit, a low leak thin film transistor and peripheral driving circuit for forming a pixel are configured. When a high speed thin film transistor as described above is simultaneously formed on the same substrate, an antireflection film is provided in the peripheral drive circuit region, and then laser irradiation is performed on the entire surface of the substrate with a certain energy power, the antireflection film is formed. A high-speed thin film transistor (for example, polycrystalline silicon) having a high carrier mobility can be formed in the peripheral drive circuit region covered with, and a high opening is formed even in the internal pixel region not covered with the antireflection film. A thin film transistor for obtaining the rate can be formed. Further, since the entire surface of the substrate can be processed with one laser irradiation, throughput can be improved. Furthermore, since the laser device itself can be processed by irradiation with low energy power,
You can always perform stable processing, extend the gas life,
The load on the device can be reduced.

In the method for manufacturing a semiconductor substrate and a semiconductor device according to a second aspect of the present invention, as described above, pulsed light of an ultraviolet laser having a wavelength of 400 nm or less is used as the energy ray irradiated in the melt crystallization step. . Wavelength 400n
An energy ray of m or less has a wavelength matching the absorption coefficient of the semiconductor silicon film, and the semiconductor silicon film can be efficiently heated. Further, the antireflection film is selected as a material which does not absorb the ultraviolet rays, and therefore energy loss in the antireflection film can be eliminated.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of a TFT which is a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a plan view of a liquid crystal display device in which the TFT is used, in which a TFT in a peripheral driving circuit region and an internal pixel region
Is schematically shown.

FIG. 3 is a graph showing the relationship between the film thickness and the reflectance of a silicon dioxide film, which is an antireflection film, with respect to a laser wavelength of 308 nm.

FIG. 4 is a plan view of a photomask for selectively forming an antireflection film.

[Explanation of symbols]

10 Insulating Substrate 11 Base Coat Film 12 Amorphous Silicon Film 13 Silicon Dioxide Film 14 Region with Antireflection Film Formed 15 Laser Light 16 Region Covered with Antireflection Film (Region Comprising Peripheral Driving Circuit) 17 Area Not Covered with Antireflection Film (Area That Comprises Internal Pixel) 18 Gate Insulating Film 19 Gate 20 Insulating Film 21 Source Electrode 22 Drain Electrode 23 Semiconductor Substrate 24 Peripheral Driving Circuit Area 25 Internal Pixel Area 26 Opening Part 27 Photomask A1 TFT (for peripheral drive circuit) A2 TFT (for peripheral drive circuit) B1 TFT (for pixel) B2 TFT (for pixel) B3 TFT (for pixel) B4 TFT (for pixel)

Claims (2)

[Claims] 1. A step of irradiating an energy beam to an amorphous semiconductor film formed on a substrate having an insulating surface or a substrate whose surface is covered with an insulating film to melt-crystallize the amorphous semiconductor film. 2. The method for manufacturing a semiconductor substrate and a semiconductor device, wherein: an antireflection film having a different film thickness is selectively deposited on the surface of the amorphous semiconductor film. 2. The semiconductor substrate according to claim 1, wherein the energy rays are pulsed light of an ultraviolet laser having a wavelength of 400 nm or less, and the antireflection film is selected from a material that does not absorb the ultraviolet rays. Manufacturing method of semiconductor device.