JPH10261589A - Semiconductor thin film and thin-film semiconductor device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the mobility of a thin-film-like semiconductor material by applying ultraviolet ray laser beams to an amorphous silicon thin film where the concentration of carbon, nitrogen, and oxygen is equal to or less than a specific value for dissolving, recrystallizing it, and then setting a wavenumber where the Raman shift of a Raman peak is equal to or less than a specific value. SOLUTION: An amorphous silicon covering is formed on a crystal substrate 601 and is etched in a rectangular shape, an amorphous silicon film 602 where the concentration of carbon, nitrogen, and oxygen is equal to or less than 1μ10<19> cm<-3> is obtained and then irradiated with excimer laser beams thus recrystallizing an impurity region. In this case, the Raman peak dependency of an electron mobility is small when the central value of the Raman peak of a silicon covering being subjected to laser annealing treatment is equal to or less than 515 cm<-1> but the electron mobility increases rapidly as the central value of the peak increases when the central value is equal to or more than 515 cm<-1> . More specifically, by setting to a wavenumber where the Raman shift of the Raman peak is equal to or less than 515 cm<-1> , a thin-film semiconductor material with a high mobility can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a semiconductor material containing silicon as a main component. In particular, the present invention aims at improving the characteristics of a silicon semiconductor material in the form of a thin film. By using the semiconductor material according to the present invention, a thin film semiconductor device (such as a thin film transistor) having improved characteristics can be manufactured.

[0002]

2. Description of the Related Art Conventionally, in manufacturing a thin film semiconductor device such as a thin film field effect transistor, an amorphous semiconductor material (a so-called amorphous semiconductor) or a polycrystalline semiconductor material has been used. Hereinafter, the term “amorphous” is used not only to refer to disorder at a purely atomic level but also to a substance having a short-range order of about several nm. More specifically, it means a silicon material having an electron mobility of 10 cm ² / V · s or less or a material having a carrier mobility of 1% or less of an intrinsic carrier mobility of the semiconductor material.
Therefore, a substance which is an aggregate of fine crystals of about 10 nm which is usually called a microcrystal or a semi-amorphous is also referred to as an amorphous.

When an amorphous semiconductor (amorphous silicon, amorphous germanium, or the like) is used, it can be manufactured at a relatively low temperature of 400 ° C. or less. Attention has been paid.

However, since a pure amorphous semiconductor has extremely low carrier mobility (electron mobility or hole mobility), it is rarely used as it is, for example, as a channel forming region of a thin film transistor (TFT). Has been used by irradiating these amorphous semiconductor materials with intense light such as laser light or xenon lamp light and melting and recrystallizing them to transform them into crystalline semiconductor materials, thereby improving their carrier mobility. (In the following text, the method will be referred to as "laser annealing."
It is not necessary to use a laser. Irradiation with strong flash lamp light that provides the same response as laser light irradiation is also included. )

[0005] However, the carrier mobility of a semiconductor material conventionally obtained by the laser annealing method is generally lower than that of a single crystal semiconductor material. For example, in the case of silicon coating is greatest electron mobility that reported is 200cm ² / V · s, which is the electron mobility of the single crystal silicon, 1350 cm ² /
It is only one seventh of V · s. In addition, the characteristics (mainly, mobility) of the semiconductor material obtained by the laser annealing method are poor in reproducibility, and the mobility in the same film has a large variation, so that a large number of elements are formed on the same plane. Since the characteristics of the obtained semiconductor element vary greatly, the yield of the product is significantly reduced.

[0006]

SUMMARY OF THE INVENTION The present invention cannot be put to practical use by the conventional laser annealing method because the mobility is extremely small as compared with a single crystal semiconductor material and the reproducibility thereof is poor. It is an object of the present invention to improve the characteristics of a thin film semiconductor material. That is, a thin film semiconductor material with high mobility is provided, and a method for manufacturing a semiconductor material with high mobility with high reproducibility is provided.

[0007]

Means for Solving the Problems Raman spectroscopy is
This is an effective method for evaluating the crystallinity of a substance, and is also used for the purpose of quantifying the crystallinity of a semiconductor film formed by a laser annealing method. The present inventors obtained these numerical values by focusing on the center value of the Raman peak, the width of the Raman peak, the height of the Raman peak, and the like of the obtained semiconductor film in the study of the laser annealing method. It has been found that it has a very close relationship with the characteristics of the semiconductor thin film to be obtained.

For example, in the case of single crystal silicon, a Raman peak exists at 521 cm ^-1, but the Raman peak of a silicon film subjected to laser annealing tends to move to a shorter wave number (longer wavelength) side. Was observed. Then, it was discovered that there is a strong correlation between the center value of the Raman peak at this time and the carrier mobility of the obtained semiconductor thin film.

FIG. 1 is an example showing this relationship. The center value of the Raman peak (horizontal axis) and the electron mobility of the film (vertical axis) of a film obtained by laser annealing an amorphous silicon film. Shows the relationship. The electron mobility indicates a value obtained by manufacturing a TFT using a silicon film and measuring its CV (capacitance-voltage) characteristic. As is apparent from the figure, the center value of the Raman peak is 515.
There is a large difference in the behavior of electron mobility from cm ^-1 as a boundary. That is, at 515 cm ^-1 or less, the dependence of the electron mobility on the Raman peak is small, but at 515 cm ^-1 or more, the electron mobility rapidly increases with an increase in the center value of the peak.

This phenomenon clearly indicates that there are two phases. According to our research, 515
At cm ^-1 or less, the film was not melted by laser annealing, and atoms were ordered in a solid phase. At 515 cm ^-1 or more, the film was melted by laser annealing and the liquid phase It is presumed to have solidified through the process.

The center value of the Raman peak did not exceed the Raman peak value of single crystal silicon of 521 cm ^−1, and the maximum value of the obtained electron mobility was about 200 cm ² / V · s. Next, the present inventors have found that in the course of research for improving the mobility, the amounts of oxygen, nitrogen, and carbon contained in the coating greatly affect the mobility. In the structure shown in FIG. 1, the number of nitrogen atoms and oxygen atoms existing in the film was negligibly small, but the number of oxygen atoms was 2 × 10 ^{21 at} the center of the film. cm ^-3 . Therefore, it was investigated how the relationship between the center value of the Raman peak and the electron mobility changes by reducing the number of oxygen atoms contained in the film.

Hereinafter, these oxygen, nitrogen,
The concentration of a different element such as carbon refers to the concentration at the center of the coating. Because the part of the coating near the substrate,
Alternatively, the concentration of these different elements is extremely high in the vicinity of the surface of the coating, but the different elements present in these regions are considered to have little effect on the carrier mobility which is a problem in the present invention. This is because the. The portion with the lowest concentration of cholera heteroelement in the film is the central portion of the film in a normal film, and the central portion of the film is considered to play an important role in semiconductor devices such as field-effect transistors. Because. For the reasons described above, in this specification, when simply referring to the concentration of a different element,
It refers to the concentration at the center of the coating.

This is shown in FIG. As is clear from FIG. 2, the electron mobility was significantly improved by reducing the oxygen concentration in the film. This tendency was the same even when the film contained carbon or nitrogen. The reason is that when the film has a large number of oxygen atoms, when the film is melted and recrystallized by laser annealing, a portion having a small number of oxygen atoms becomes a crystal nucleus and crystal grows. However, the oxygen atoms contained in the film are repelled to the periphery as the crystal grows, and are precipitated at the grain boundaries. Therefore, when viewed through the entire film, the mobility is small due to the barrier generated at the grain boundaries. The theory is that laser annealing causes oxygen atoms or regions with high oxygen atom concentrations (generally considered to have a higher melting point than pure silicon) as crystal nuclei for crystal growth, but the number of oxygen atoms is large. In this case, it has been proposed that crystal nuclei are often generated, so that the size of each crystal becomes small, the mobility becomes small, and the crystallinity is impaired.

In any case, by reducing the oxygen concentration in the coating, extremely large electron mobility could be obtained by laser annealing. For example, by setting the oxygen concentration to 1 × 10 ¹⁹ cm ⁻³ , 1000 c
A large electron mobility of m ² / V · s was obtained. Similar effects could be obtained by reducing the concentration of nitrogen and the concentration of carbon other than the oxygen concentration. further,
A similar tendency was obtained for the hole mobility.

Further, the curve of the position of the Raman peak and the electron mobility showed a bent state as in FIG. 1 regardless of whether the oxygen concentration was high or low. The present inventors presumed that the film on the right side of the dotted line in FIG. 2 was recrystallized after the film was once melted by laser annealing, and named this region a melt-recrystallized region. Large mobility was obtained in this melt-recrystallization region.

The present inventors have further found that a similar tendency is observed in the Raman peak full width at half maximum (FWHM). This is shown in FIG. The horizontal axis in FIG.
The half-width of the Raman peak of the laser-annealed coating is divided by the half-width of single-crystal silicon, and is referred to herein as the half-width ratio (FWHM RATIO). FWHM RA
It is considered that the smaller TIO is, the closer to 1, the structure is closer to single crystal silicon. As is apparent from the figure, when the oxygen concentration is the same, the FWHM RATIO
It was found that the electron mobility was higher as the value was closer to 1. Also, as in the case of the center value of the Raman peak, the electron mobility increases as the oxygen concentration in the film decreases,
A similar tendency was observed for nitrogen and carbon concentrations in addition to oxygen concentration. That is, the smaller the concentration, the higher the electron mobility. Further, a similar tendency was observed for the hole mobility. Also in this case, as in the case of FIG. 2, the left side of the dotted line in FIG. 3 is considered to be a melt-recrystallization region.

Further, the present inventors have found that, among the Raman peaks, the peak intensity attributable to the amorphous component in the film has a close correlation with the electron mobility. FIG. 4 shows the Raman peak (480 cm ⁻¹⁾ due to the amorphous component of the laser-annealed coating.
The intensity Ia of the near-peak is divided by the Raman peak Ic of single-crystal silicon (the peak near 521 cm ^-1 ), and is hereinafter referred to as INTENSITY RATIO. I
Regarding the NENSITY RATIO, if the oxygen concentration in the film is the same, the INTENSITY RATIO
Is small, that is, the less the amorphous component in the film is, the higher the electron mobility is. The smaller the amount of oxygen contained in the film is, the higher the electron mobility is. A similar tendency was observed for nitrogen and carbon concentrations in addition to oxygen concentration. That is, the smaller the concentration, the higher the electron mobility. Further, a similar tendency was observed for the hole mobility. In this case as well, as in FIGS. 2 and 3, the left side of the dotted line in FIG. 4 is considered to be a melt-recrystallization region.

Further, empirically, when the intensity of the Raman peak is large, a large carrier mobility can be obtained.
The intensity of the Raman peak of the film having a small concentration of oxygen, nitrogen and carbon was large.

As described above, it has been clarified that the carrier mobility can be improved by reducing the amounts of oxygen, nitrogen and carbon in the film. In particular, the present inventors set the amount of each of these elements to 5 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less, so that the silicon film has an electron mobility of 1000 cm 3. ² / V ・
It was found that s values could be obtained. The present inventors have found that by further reducing the concentration of these elements, a value closer to the carrier mobility of the single crystal semiconductor can be obtained and the reproducibility thereof can be improved.
Further, by the same method, the hole mobility is set to 30.
A value of 0 to 500 cm ² / V · s could be obtained stably.

However, for example, when the concentration of these elements is set to 1 × 10 ¹⁶ cm ⁻³ or less, the concentration of these elements is extremely small (1 × 10 ¹⁶ cm ⁻³⁾ in an environment with a very high degree of vacuum. Even if laser annealing is performed on the film of the following), it cannot be easily achieved. This is because a small amount of oxygen gas, nitrogen gas, moisture, carbon dioxide, etc. contained in the atmosphere is taken into the film during laser annealing, or these gases adsorbed on the surface of the film are used for laser annealing. It is presumed that this was because it was taken into the film at that time.

In order to avoid these difficulties, a special manufacturing method is required. One method is that the concentrations of oxygen, nitrogen and carbon are very low, for example, 10 ¹⁵ cm ^−3.
A protective film such as silicon oxide, silicon nitride, or silicon carbide is formed to cover the surface of the following amorphous semiconductor film, and then,
By performing laser annealing in a vacuum atmosphere (10 ^-4 torr or less), a semiconductor film with extremely low concentrations of oxygen, nitrogen, and carbon and high mobility can be formed. For example, the concentrations of carbon, nitrogen and oxygen are all 1 × 10 ¹⁵ cm ⁻³ or less, and the electron mobility is 1000 cm ^2.
/ V · s silicon film was obtained.

When forming a protective film of silicon oxide, silicon nitride, silicon carbide, or the like over the surface of the amorphous semiconductor film, the amorphous semiconductor film is formed by a CVD method or a sputtering method in a chamber having one vacuum device. After the formation, a method in which the film is continuously formed without changing the atmosphere in the same chamber, or once in an extremely high vacuum state and then in an atmosphere suitable for film formation is suitable. However, more product yield,
In order to improve reproducibility and reliability, it is desirable to prepare a dedicated chamber for forming each film, and to adopt a method of moving each chamber while keeping the product extremely high vacuum . Selection of these film formation methods is made according to the scale of capital investment. Regardless of which method is adopted, it is important that oxygen, nitrogen, and carbon contained in the underlying amorphous semiconductor film are sufficiently small,
And that no gas is adsorbed at the interface between the amorphous semiconductor and the protective film thereon. For example, even if an extremely pure amorphous semiconductor film is formed, once the film is exposed to the atmosphere and then a silicon nitride film is formed thereon, the carrier of the film obtained by laser annealing the film is obtained. Mobility is generally small,
Also, the probability of obtaining a high mobility is extremely small. This is presumably because the gas is adsorbed on the surface of the amorphous semiconductor film and diffuses into the film during the subsequent laser annealing.

The material of the protective film at this time may be silicon oxide, silicon nitride or silicon carbide, provided that the conditions for transmitting laser light are satisfied, or a chemical formula of SiN _x O _y in which these are mixed. C _z (0 ≦ x ≦ 4/3, 0 ≦
A material including a material represented by y ≦ 2, 0 ≦ z ≦ 1, 0 ≦ 3x + 2y + 4z ≦ 4) may be used. Moreover, the thickness was suitably 50 to 1000 nm.

The present invention provides high carrier mobility by reducing the concentration of oxygen, nitrogen and carbon in an amorphous semiconductor film and reducing the concentration of oxygen, nitrogen and carbon present during laser annealing. The electron mobility or the hole mobility obtained at this time is an average value of the channel formation region of the field-effect transistor formed for the measurement, and the channel formation region is obtained. The mobility in each fine part cannot be determined. However,
As apparent from FIGS. 1 to 4 of the present invention and the description related thereto, the carrier mobility is determined by the position of the Raman peak, the half width of the Raman peak, the intensity of the amorphous component in the Raman peak, and the Raman peak. It has been clarified that parameters can be uniquely determined from the parameters such as the strength of the sample. Therefore, the mobility of a minute area where the mobility cannot be measured directly can be calculated from these information by Raman spectroscopy.
Approximate mobility can be estimated.

FIG. 5 shows that the electron mobility is 22 cm ² / V ·
s, 201cm ² / V · s and 980cm ² / V · s
FIG. 4 shows the full width at half maximum (FWHM) of the Raman peak in each part of the channel forming region of the field effect transistor having the channel forming region formed by the laser annealing. In the drawing, the horizontal axis represents the position of the channel formation region. L is the length of the channel formation region and is 100 μm. X represents the coordinates of the channel formation region, X / L = 0 is the interface of the channel formation region with the source region, X / L = 1 is the interface of the channel formation region with the drain region, and X / L = 0.5 represents the center of the channel formation region. As is clear from the figure, the one with an electron mobility of 22 cm ² / V · s is FWHM
And its fluctuation is not large. The fact that the smaller the FWHM is, the closer the crystallinity of the film is to that of a single crystal, and therefore the higher the electron mobility is, as described in FIG. 3 and the related description, and this data situation is not contradictory. However, the small variation (location dependence) of the FWHM depending on the location indicates that the crystallinity of the coating is almost the same regardless of the location. The oxygen concentration of this coating was about 8 × 10 ²⁰ cm ^−3.
It is estimated that they did not melt by laser annealing.

On the other hand, the electron mobility is 201 cm ² / V · s
Had an oxygen concentration of 8 × 10 ²⁰ cm ⁻³ as well. As is clear from the figure, the FWHM generally decreased, but the location dependency of the FWHM was large. And, depending on the place, the electron mobility is 980 cm ² / V ·
The value of FWHM was equal to or smaller than that of s. A small FWHM implies a high electron mobility in that area,
This means that a portion having crystallinity equivalent to that of single crystal silicon is localized in the same film. However, when mass-produced as a device, it is not desirable to use a material whose characteristics greatly differ depending on the location, even if the mobility is large.

In the case of the electron mobility of 980 cm ² / V · s, the oxygen concentration is remarkably smaller than that of the other two by about 1 ×.
It was 10 ¹⁹ cm ^-3 . As is clear from the figure, the FWHM is generally small, and the location dependency of the FWHM is also small. This suggests that the material has a high electron mobility as a whole and is made of a material having the same crystallinity as single-crystal silicon, and is extremely suitable for mass production of devices and the like.

In order to obtain a high carrier mobility, it is necessary to reduce the concentration of different elements in the film and to optimize the laser annealing conditions as described above. The laser annealing conditions include laser oscillation conditions (continuous oscillation or pulse oscillation, repetition frequency, intensity,
Wavelength, coating, etc.) and cannot be said unconditionally. As the laser, an ultraviolet laser such as various excimer lasers or a visible or infrared laser such as a YAG laser can be used, and it is necessary to select a laser depending on the thickness of a film to be laser annealed. That is, in general, silicon or germanium materials have a short absorption length with respect to ultraviolet light, so that laser light does not reach a deep portion, and laser annealing occurs only in a relatively shallow region of the surface. On the other hand, the absorption length of visible light and infrared light is long, and light penetrates relatively deeply into the inside. Therefore, laser annealing occurs even in deep parts. Therefore, by selecting the film thickness and the type of laser, it is possible to perform laser annealing only near the surface of the film. In any case, high carrier mobility was obtained by selecting the wavelength, intensity and the like of the laser so as to go through the process of melting and recrystallization. In order to satisfy the condition of melting, in a long time,
The temperature of the part irradiated with the laser is higher than the melting point of the semiconductor, that is, in the case of silicon, 140 ° C. under the atmospheric pressure.
0 ° C or higher, 100 ° C for germanium under atmospheric pressure
0 degree C or more is required. However, for example, in a very short time of 10 nanoseconds realized by an excimer laser, the melting of the coating film is not observed even if a temperature instantaneously exceeding 2000 ° C. is observed spectroscopically. Sometimes this is not done, and this definition of temperature does not really make much sense.

As an additional matter, after the semiconductor film is laser-annealed, it is placed in a hydrogen atmosphere at 200-600.
Annealing at a temperature of C for 10 minutes to 6 hours was effective for obtaining high carrier mobility with good reproducibility.
This is considered to be because laser annealing causes recrystallization and, at the same time, dangling bonds (tangling bonds) are generated in semiconductor interatomic bonds, which function as a barrier to carriers. If the semiconductor contains a lot of oxygen, nitrogen, carbon, etc., these are thought to fill the dangling bonds,
When the concentration of oxygen, nitrogen, carbon, or the like is extremely low as in the present invention, it is considered that dangling bonds cannot be filled, and thus it is necessary to perform annealing in a hydrogen atmosphere after laser annealing.

[0030]

【Example】

Example 1 A TFT having a planar structure was manufactured, and its electrical characteristics were evaluated. FIG. 6 shows a manufacturing method. First, an amorphous silicon film having a thickness of about 100 nm was formed by a normal RF sputtering method. The substrate was quartz 601, the substrate temperature was 150 ° C., the atmosphere was substantially 100% argon, and the pressure was 0.5 Pascal (pa). Hydrogen and other gases were not intentionally added to argon. The concentration of argon was 99.99% or more. Input power is 200
At W, the RF frequency was 13.56 MHz. Then, this amorphous silicon film is formed into a 100 μm × 500
The amorphous silicon film 602 was obtained by etching in a rectangular shape of μm.

It was confirmed by secondary ion mass spectroscopy (SIMS) that the concentrations of oxygen, nitrogen and carbon in this coating were all 10 ¹⁹ cm ^-3 or less.

Next, this film is placed in a vacuum vessel at a pressure of 10 ^-5 torr, and an excimer laser beam (KrF laser, wavelength 248) is passed through a quartz window provided in the vacuum vessel.
nm, pulse width 10 ns, irradiation energy 200 m
J, an irradiation pulse number of 50 shots) to perform laser annealing.

Further, a gate insulating film 603 having a thickness of about 100 nm was formed thereon by a sputtering method in an oxygen atmosphere. The substrate temperature at this time is 150 ° C., and RF (1
(3.56 MHz) input power was 400 W. The atmosphere was substantially oxygen and no other gas was intentionally added. The concentration of oxygen was 99.9% or more. The pressure is 0.
It was 5 pa.

Thereafter, an aluminum film (thickness: 200 n)
m) was formed by a known vacuum deposition method, and unnecessary portions were removed by a known dry etching method to form a gate electrode 604. The width of the gate electrode was 100 μm. At this time, the photoresist 605 used for the dry etching was left on the gate electrode.

Then, boron ions were implanted at a dose of 10 ¹⁴ cm ^-2 into portions other than the gate electrode by ion implantation. Under the gate electrode, the gate electrode and the photoresist on the gate electrode serve as a mask, so that boso ions are not implanted. By this step, impurity regions, that is, a source region 606 and a drain region 607 were formed in the silicon film. This is shown in FIG.

Further, the entire substrate is placed in a vacuum vessel, and
Excimer laser light (KrF laser, wavelength 248 nm, pulse width 10 nanoseconds, irradiation energy 100 mJ, irradiation pulse number 50 shots) was irradiated at a pressure of 0 ^-5 torr to perform laser annealing. By this step, the impurity region which was ion-implanted and became amorphous was recrystallized.

Next, thermal annealing was performed in a hydrogen atmosphere. Place the substrate in a chamber that can be evacuated,
Once exhausted by a turbo-molecular pump to 10 ^-6 torr and maintained in this state for 30 minutes, hydrogen gas with a purity of 99.99% or more is introduced into the chamber to 100 torr and the substrate is annealed at 300 ° C. for 60 minutes. did. Here, once evacuated, the gas adsorbed on the film
This is for removing water and the like. It has been empirically known that if thermal annealing is performed with these remaining, high mobility cannot be obtained with good reproducibility.

Finally, holes were made in the silicon oxide film (thickness: 100 nm) existing on the source region and the drain region, and aluminum electrodes 608 and 609 were formed in these regions. Through the above steps, a field effect transistor was formed.

As a result of measuring the CV characteristics of this field effect transistor, the electron mobility of the channel formation region was 98%.
0 cm ² / V · s. Further, the threshold voltage (threshold voltage) was 4.9V. The concentration of oxygen, nitrogen, and carbon in the channel formation region of this field-effect transistor was measured by SIMS and found to be 1 × 10 ¹⁹ cm ⁻³ or less.

Example 2 A TFT having a planar structure was manufactured and its electrical characteristics were evaluated. First, an amorphous silicon film having a thickness of about 100 nm and containing phosphorus at a concentration of 3 × 10 ¹⁷ cm ⁻³ was formed by a normal RF sputtering method. With this film thickness, the entire film is annealed by KrF laser light (248 nm) used for the subsequent laser annealing. The substrate was quartz, the substrate temperature was 150 ° C., the atmosphere was substantially 100% argon, and the pressure was 0.5 Pascal (pa). Hydrogen and other gases were not intentionally added to argon. Argon concentration is 99.99%
That was all. Input power is 200W, RF frequency is 1
It was 3.56 MHz. After that, this amorphous silicon film was etched into a rectangle of 100 μm × 500 μm.

It was confirmed by secondary ion mass spectroscopy (SIMS) that the concentrations of oxygen, nitrogen and carbon in this film were all 10 ¹⁹ cm ^-3 or less.

Further, a gate insulating film having a thickness of about 100 nm was formed thereon by a sputtering method in an oxygen atmosphere. At this time, the substrate temperature was 150 ° C. and RF (13.5
6 MHz) input power was 400 W. The atmosphere was substantially oxygen and no other gas was intentionally added. The concentration of oxygen was 99.9% or more. The pressure was 0.5 pa.

Thereafter, an aluminum film (thickness: 200 n)
m) was formed by a known vacuum evaporation method, and unnecessary portions were removed by a known dry etching method to form a gate electrode. The width of the gate electrode was 100 μm.
At this time, the photoresist used for the dry etching was left on the gate electrode.

Then, boron ions were implanted into the region other than the gate electrode at 10 ¹⁴ cm ^-2 by ion implantation. Under the gate electrode, the gate electrode and the photoresist on the gate electrode serve as a mask, so that boso ions are not implanted. By this step, impurity regions, that is, a source region and a drain region, were formed in the silicon film.

Further, the whole substrate is placed in a vacuum vessel,
Excimer laser light (KrF laser, wavelength 248 nm, pulse width 10 nanoseconds, irradiation energy 100 mJ, irradiation pulse number 50 shots) was irradiated from the back surface of the substrate at a pressure of ^-5 torr to perform laser annealing. By this step, the amorphous silicon film was crystallized. In this method, unlike in the first embodiment, crystallization of the source or drain region and the channel formation region is performed simultaneously. Therefore, in the method of Example 1, while many defects occurred at the interface between the source or drain region and the channel formation region, an interface with few defects and continuous crystallinity was obtained.

Next, thermal annealing was performed in a hydrogen atmosphere. Place the substrate in a chamber that can be evacuated,
Once evacuated to 10 ⁻⁶ torr with a turbo-molecular pump, it was further heated to 100 ° C. Change this state to 30
And then supply hydrogen gas with a purity of 99.99% or more.
Until the substrate reaches 300 torr.
Annealed at a degree C for 60 minutes. Here, the reason why the evacuation is performed once is to remove gas, moisture, and the like adsorbed on the film. It has been empirically known that if thermal annealing is performed with these remaining, high mobility cannot be obtained with good reproducibility.

Finally, holes were made in the silicon oxide film (thickness: 100 nm) existing on the source region and the drain region, and aluminum electrodes were formed in these regions. Through the above steps, a field effect transistor was formed.

As a result of measuring the CV characteristics of this field effect transistor, the electron mobility of the channel formation region was 99%.
0 cm ² / V · s. Further, the threshold voltage (threshold voltage) was 3.9V. It is considered that the reason why the threshold voltage was improved (decreased) as compared with Example 1 is that the impurity region and the channel forming region were simultaneously and uniformly crystallized by performing laser annealing from the back surface. Also, turn on / off the gate voltage
Then, the ratio of the drain current was 5 × 10 ⁶ .

The concentration of oxygen, nitrogen and carbon in the channel formation region of this field effect transistor was measured by SIMS and found to be 1 × 10 ¹⁹ cm ⁻³ or less. When the channel formation region was measured by Raman spectroscopy, the center value of the Raman peak was 520 c
m ^-1 , the half width of the Raman peak is 4.5 cm ^-1 ,
The presence of silicon which was once melted and then recrystallized was confirmed.

Example 3 A TFT having a planar structure was manufactured, and its electrical characteristics were evaluated. First, using a film forming apparatus having two chambers, an amorphous silicon film having a thickness of about 100 nm and a silicon nitride film having a thickness of 10 nm on the amorphous silicon film were formed on a quartz substrate coated with a silicon nitride film having a thickness of 10 nm. Formed continuously. The amorphous silicon film was formed by a normal sputtering method, and the silicon nitride film was formed by a glow discharge plasma CVD method.

First, the substrate was set in the first preliminary chamber, and the preliminary chamber was heated to 200 ° C., evacuated, and maintained at a pressure of 10 ⁻⁶ torr or less for 1 hour. Next, the first chamber, which is always kept at 10 ^-4 torr or less except for the time of film formation, is evacuated to 10 ^-6 torr so that no outside air enters, and the substrate is moved from the preliminary chamber to the first chamber. the substrate was set in a chamber, while maintaining the substrate and the target to 200 ° C, evacuated, the pressure in the chamber 1 in the following state 10 ^-6 torr
Hold for hours. Then, an argon gas was introduced into the chamber, RF plasma was generated, and a sputter film was formed. As a sputtering target, a silicon target having a purity of 99.9999% or more is used, and contains 1 ppm of phosphorus. The substrate temperature during film formation was 150 ° C., the atmosphere was substantially 100% argon, and the pressure was 5 × 10 ⁻² t.
orr. Hydrogen and other gases were not intentionally added to argon. The concentration of argon is 99.99999
% Or more. The input power was 200 W and the RF frequency was 13.56 MHz.

After the film formation, the RF discharge was stopped, and the first chamber was evacuated to 10 ^-6 torr. Next, the second spare chamber, which is always kept at 10 ^-5 torr or less and is provided between the first chamber and the second chamber, is set to 1
The substrate was evacuated to 0 ^-6 torr and the substrate was transferred from the first chamber to the second preliminary chamber. Further, except for the time of film formation, the second chamber which is kept at 10 ^-4 torr or less and is controlled so that no outside air enters, is evacuated to 10 ^-6 torr, and the substrate is moved from the second preliminary chamber. The substrate is set in the second chamber, and the substrate and the target are set to 200
While maintaining the temperature at C, the chamber was evacuated, and the chamber pressure was maintained at 10 ^-6 torr or less for 1 hour.

Then, ammonia gas and disilane gas (Si ₂ H ₆ ) diluted with hydrogen and having a purity of 99.9999% or more diluted with hydrogen were introduced into the second chamber at a ratio of 3: 2.
The total pressure was set to 10 ^-1 torr. Then, an RF current was introduced into the chamber, plasma was generated, and a silicon nitride film was formed. The input power (13.56 MHz) is 2
00W.

After completion of the film formation, the RF discharge was stopped, and the second chamber was evacuated to 10 ^-6 torr. Then the second
A third side of the chamber with a quartz window
Was evacuated to 10 ⁻⁶ torr, and the substrate was transferred from the second chamber to the third preliminary chamber. Then, an excimer laser beam (KrF) is passed through the window of the third preliminary room.
Laser irradiation was performed at a wavelength of 248 nm, a pulse width of 10 nanoseconds, an irradiation energy of 100 mJ, and an irradiation pulse number of 50 shots. Thus, the amorphous silicon film was crystallized.

As described above, the method of continuously performing laser annealing without substantially breaking the vacuum state from the film-forming state involves a method of forming a protective film on an amorphous semiconductor film as shown in this embodiment. Even in the case where the protective film was formed, or in the case where the protective film was not formed as in Examples 1 and 2, there was a remarkable effect in terms of improving the yield. It is considered that the reason is that dust and the like are prevented from adhering to the coating, moisture and gas are absorbed, and scratches are prevented.

When film formation and laser annealing are performed continuously as described above, a film formation chamber and a preparatory chamber are provided as in the present embodiment, and a window is provided in the preparatory chamber to perform laser annealing. A method and a method in which a window is provided in the film formation chamber and laser annealing is performed after the film formation is completed in the film formation chamber can be considered, but the latter method always etches the film adhering to the window because the window becomes cloudy due to film formation. The former is not necessary. Therefore, the former method can be said to be superior in consideration of mass productivity and maintainability.

After the laser annealing in the third preparatory chamber was completed, dry nitrogen gas was introduced into the third preparatory chamber, the atmospheric pressure was reached, and the substrate was taken out. Then, after removing the silicon nitride film by a known dry etching method, the silicon film was etched into a rectangle of 100 μm × 500 μm.

The fact that the oxygen, nitrogen and carbon concentrations of this film are all 10 ¹⁶ cm ⁻³ or less means that another film produced in the same process was subjected to secondary ion mass spectrometry (SIMS).
Was confirmed by analysis.

Further, a gate insulating film having a thickness of about 100 nm was formed thereon by a sputtering method in an oxygen atmosphere. At this time, the substrate temperature was 150 ° C. and RF (13.5
6 MHz) input power was 400 W. The sputtering target was silicon oxide having a purity of 99.9999% or more. The atmosphere was substantially oxygen and no other gas was intentionally added. The concentration of oxygen was 99.999% or more. The pressure was 5 × 10 ^-2 torr.

Thereafter, an aluminum film (thickness: 200 n)
m) was formed by a known vacuum evaporation method, and unnecessary portions were removed by a known dry etching method to form a gate electrode. The width of the gate electrode was 100 μm.
At this time, the photoresist used for the dry etching was left on the gate electrode.

Then, boron ions were implanted into the portion other than the gate electrode at 10 ¹⁴ cm ^-2 by ion implantation. Under the gate electrode, the gate electrode and the photoresist on the gate electrode serve as a mask, so that boso ions are not implanted. By this step, impurity regions, that is, a source region and a drain region, were formed in the silicon film.

Further, the entire substrate is placed in a vacuum vessel,
Excimer laser light (KrF laser, wavelength 248 nm, pulse width 10 nanoseconds, irradiation energy 50 mJ, irradiation pulse number 50 shots) was irradiated from the back surface of the substrate at a pressure of ^-5 torr to perform laser annealing.
By this step, the amorphous silicon film in the impurity region which was made amorphous by the ion implantation step was crystallized.

This method is the same as that of the first embodiment in that two-stage laser annealing is performed. However, by performing the second laser annealing from the back surface of the substrate, the continuous formation of the impurity region and the channel formation region is performed. For connection purposes. In particular, the first laser annealing aims at obtaining a film having a high carrier mobility by a melting-recrystallization process, while the second laser annealing suppresses the output of the laser and fines crystals without melting. An object is to promote visual ordering and reduce resistance of an impurity region. Then, by suppressing the output of the laser, the crystalline region having high mobility (mainly the channel forming region) formed by the first laser annealing is hardly changed. Further, as seen in Example 2, at the interface between the source or drain region and the channel formation region, defects can be reduced and an interface with continuous crystallinity can be obtained.

Unlike the method of Example 2, the reason for performing the first laser annealing for the purpose of forming the channel formation region is that when the laser annealing is performed with an ultraviolet laser, the laser irradiation surface is annealed. This is because there is a high possibility that the phenomenon will not occur in a deep part or a state with high mobility cannot be obtained, which may lower the yield of products. Irradiation from the surface of the film is desired because irradiation of the laser beam from the back surface does not cause high mobility in a region close to the gate electrode, which is fatal to the field-effect transistor. Therefore, in order to improve the yield of the product, in this embodiment, the laser is first irradiated from the front surface of the amorphous silicon film, and then the laser is also irradiated from the back surface of the substrate, so that the continuous formation of the channel forming region and the impurity region is performed. The method of obtaining a joint was adopted.

Next, thermal annealing was performed in a hydrogen atmosphere. Place the substrate in a chamber that can be evacuated,
Once evacuated to 10 ⁻⁶ torr with a turbo-molecular pump, it was further heated to 100 ° C. Change this state to 30
And then supply hydrogen gas with a purity of 99.99% or more.
Until the substrate reaches 300 torr.
Annealed at a degree C for 60 minutes. Here, the reason why the evacuation is performed once is to remove gas, moisture, and the like adsorbed on the film. It has been empirically known that if thermal annealing is performed with these remaining, high mobility cannot be obtained with good reproducibility.

Finally, holes were made in the silicon oxide film (thickness: 100 nm) existing on the source and drain regions, and aluminum electrodes were formed in these regions. Through the above steps, a field effect transistor was formed.

As a result of producing 100 field effect transistors and measuring their CV characteristics, the electron mobility in the channel forming region was 995 cm ² / V · s on average. Further, the average of the threshold voltage (threshold voltage) was 4.2V. The average of the ratio of the drain current was 8 × 10 ⁶ . The reference value of the electron mobility is 80
When 0 cm ² / V · s, the reference value of the threshold voltage was 5.0 V, and the reference value of the drain current ratio was 1 × 10 ⁶ , the pass / fail of 100 field effect transistors was examined. passed it.

The concentration of oxygen, nitrogen, and carbon in the channel formation region of these field-effect transistors
As a result of measurement by MS, all of the passed field-effect transistors were 1 × 10 ¹⁶ cm ⁻³ or less.

[0069]

According to the present invention, it has been clarified that a film semiconductor having high reproducibility and high mobility can be obtained. In the present invention, laser annealing of a semiconductor film formed on an insulating substrate such as quartz is mainly described. However, the substrate is made of a single crystal semiconductor such as a single crystal silicon substrate used in a monolithic IC or the like. You may. Further, although the embodiment has been described with reference to the silicon coating, the present invention is applied to a germanium coating, a silicon-germanium alloy coating, and other intrinsic semiconductor materials or compound semiconductor materials. be able to. As mentioned earlier, a method called laser annealing was used as a method of improving the mobility of the amorphous film, but this expression also includes a method in which laser is not used, such as flash lamp annealing. That is, the present invention relates to a method for improving the crystallinity of a semiconductor material using strong optical energy.

[Brief description of the drawings]

FIG. 1 shows the relationship between the center value of the Raman peak (RAMAN SHIFT, horizontal axis) and the electron mobility (vertical axis) of a silicon film annealed by laser. The concentration of oxygen in the coating is 2
× 10 ²¹ cm ^-3 .

FIG. 2: Raman peak median (RAMAN SHIF) of laser annealed silicon coatings with various oxygen concentrations
T, horizontal axis) and electron mobility (vertical axis).

FIG. 3 shows the ratio (FWHM RATIO, abscissa) of the ratio of the half-width of the Raman peak of a laser-annealed silicon film having various oxygen concentrations to the half-width of the Raman peak of single-crystal silicon and the electron mobility (vertical axis). Show the relationship.

FIG. 4 shows the intensity of the amorphous component of the Raman peak of the laser-annealed silicon coating with various oxygen concentrations (48
0 cm ^-1 peak) single crystal silicon component intensity (521c
The relationship between the ratio (Ia / Ic, horizontal axis) to the electron mobility (vertical axis) with respect to the peak at m- ¹ ) is shown.

FIG. 5 shows the location dependence of the FWHM of the Raman peak in the channel formation region of a certain field effect transistor. Vertical axis: FWHM, horizontal axis: X / L (L: channel length)

FIG. 6 illustrates an example of a method for manufacturing a field-effect transistor.

[Explanation of symbols]

 601: substrate 602: semiconductor film 603: insulator film 604: gate electrode 605: photoresist 606: source region 607: drain region 608: source electrode 609 ..Drain electrodes

Claims (4)

[Claims] An amorphous silicon thin film having carbon, nitrogen and oxygen concentrations of 1 × 10 ¹⁹ cm ⁻³ or less is irradiated with an ultraviolet laser beam, melted, and then recrystallized.
A semiconductor thin film obtained by reducing the Raman peak Raman shift to a wave number of 515 cm ^-1 or less. 2. The concentration of each of carbon, nitrogen and oxygen is 1 × 10 ¹⁹ cm ⁻³ or less and the electron mobility is 10 cm.
It is obtained by irradiating a silicon thin film of ² / V · s or less with an ultraviolet laser beam, melting and recrystallizing the silicon thin film, and reducing the Raman peak Raman shift to a wave number of 515 cm ⁻¹ or less. Semiconductor thin film. 3. The semiconductor thin film according to claim 1, wherein the ultraviolet laser beam is an excimer laser. 4. A thin film semiconductor device using the semiconductor thin film according to claim 1 in a semiconductor region.