JPH10189988A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fluctuations of element characteristics, while reducing the cost by forming an active layer of silicon crystallized through fusing/ hardening process employing energy beam irradiation and setting the moisture content at a specified level or below. SOLUTION: An underlying silicon oxide 102 is deposited on a glass substrate 101 by sputtering, with the concentration of H2 O being set at 1×10<20> /cm<3> or below. An amorphous silicon (a-Si) 103 is then deposited by low pressure CVD or plasma CVD. It is heat treated at about 450 deg.C, in order to discharge hydrogen in the silicon oxide and the a-Si 103 is crystallized by irradiating a laser beam 107. When an active matrix substrate thus obtained in employed in a liquid crystal display panel, uneven display die to nonuniformity in TFT characteristics can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device using a thin film semiconductor element such as a thin film transistor (hereinafter referred to as TFT) having a crystalline silicon film as an active region and a method for manufacturing the same. In particular, it can be used for active matrix substrates for liquid crystal display devices, general thin film integrated circuits, image sensors, thermal heads with built-in drivers, and three-dimensional ICs.

[0002]

2. Description of the Related Art In recent years, large-sized, high-resolution liquid crystal display devices, monolithic active-matrix liquid crystal display devices in which driver circuits are formed on the same substrate for cost reduction, thin-film integrated circuits, high-speed, high-resolution contact Type image sensor, thermal head with built-in driver, 3D I
In order to realize C or the like, attempts have been made to form a high-performance thin film semiconductor element on an insulating substrate such as glass or on an insulating film. Semiconductor devices used in these devices include:
It is common to use a thin film silicon semiconductor. An amorphous silicon semiconductor (a-
It is roughly classified into two, that is, one made of Si) and one made of a crystalline silicon semiconductor.

[0003] Amorphous silicon semiconductors are most commonly used because they have a low fabrication temperature, can be relatively easily fabricated by a gas phase method, and have high mass productivity. Since the physical properties such as conductivity are inferior to those of a crystalline silicon semiconductor, establishment of a method for manufacturing a semiconductor device made of a crystalline silicon semiconductor has been strongly demanded in order to obtain higher speed characteristics in the future. As the silicon semiconductor having crystallinity, polycrystalline silicon, microcrystalline silicon, amorphous silicon containing a crystal component, and the like are known.

The following three methods are known as methods for obtaining these thin film silicon semiconductors having crystallinity.

(1) A film having crystallinity is directly formed at the time of film formation.

(2) An amorphous semiconductor film is formed in advance,
Crystallinity is imparted by applying heat energy.

(3) An amorphous semiconductor film is formed in advance,
It is made crystalline by irradiating it with an energy beam.

However, in the above method (1), crystallization proceeds at the same time as the film forming step, so that it is difficult to obtain crystalline silicon having a large grain size, and it is necessary to increase the thickness of the silicon film. . However, even if the film is made thicker, basically only a crystal grain size equal to the film thickness can be obtained, and it is theoretically impossible to produce a silicon film having good crystallinity by this method. It is possible. The film forming temperature is 600 ° C.
Since the above is high, there is also a cost problem that an inexpensive glass substrate cannot be used.

The method (2) is used for crystallization of 600
Since heat treatment for several tens of hours is required at a high temperature of not less than ℃, productivity is very poor. In addition, since the solid-phase crystallization phenomenon is used, the crystal grains spread in parallel with the substrate surface by several μm.
However, since the grown crystal grains collide with each other to form a grain boundary, the grain boundary acts as a trap level for carriers, which is a major cause of lowering the mobility of the TFT. ing. Furthermore, each crystal grain exhibits a twin crystal structure, and a large amount of crystal defects called so-called twin crystal defects are present even within one crystal grain.

For this reason, the above method (3) is predominant at present. In the above method (3), the crystallization is carried out by utilizing the melt-solidification process, so that the crystallinity in each crystal grain is very good. In addition, by selecting the wavelength of the irradiation light, only the silicon film to be annealed can be efficiently heated to prevent thermal damage to the underlying glass substrate, and the method of the above (2) can be used. No long-term processing is required. In terms of equipment, high-output excimer laser annealing equipment has been developed, and it is becoming possible to support large-area substrates. A method of manufacturing a semiconductor device using the method (3) has been proposed in Japanese Patent Application Laid-Open No. Hei 4-11722. In this gazette, a base film, a silicon film, and a protective film are laminated and formed, and the silicon film is crystallized by irradiating a laser beam having such an intensity that the upper layer of the silicon film is melted but the lower layer is not melted.

[0011]

Considering the characteristic level currently required for the thin film semiconductor device, the above method (3) is the best method for crystallizing the silicon film. However, melting the silicon film itself even momentarily is a great weak point against impurity contamination. In particular, when a glass substrate is used, alkali metals contained in the glass substrate and impurity contamination such as aluminum, boron, and arsenic pose a problem. For this reason, Japanese Unexamined Patent Publication No.
As described in Japanese Patent No. 11722, particularly when a glass substrate is used, a silicon oxide film is first formed as a base film, a silicon film is formed thereon, and crystallized by laser irradiation.

However, although impurity contamination can be prevented to some extent by these methods, when the silicon film is melted by laser irradiation, the upper layer portion of the silicon oxide (SiO ₂ ) film as a base film which is in contact with the silicon film is It melts at the same time. As a result, especially in the silicon film lower layer region,
Components with a silicon oxide (SiO ₂ ) film as a base film are mixed and a large number of oxygen atoms are taken into the film.

When a semiconductor element is manufactured by using a silicon film containing a large number of oxygen atoms for the active region, several supersaturated oxygen atoms are aggregated to form a cluster, which forms a donor. Since the ionized donor also serves as a scattering center of carriers, it reduces the mobility of the silicon film itself and deteriorates the device characteristics. As described above, the oxygen donor in the silicon film has an adverse effect on the semiconductor element, and therefore should be reduced as much as possible. In the IC manufacturing process using a single-crystal silicon substrate, a thermal donor is decomposed because of a high-temperature treatment step of 1000 ° C. or more such as an oxide film formation step and an impurity diffusion step. However, particularly when a semiconductor device is formed on a glass substrate, the maximum process is about 600 ° C., there is no high temperature process of 1000 ° C. or higher, and the thermal donor remains until the end.

In Japanese Patent Application Laid-Open No. 4-11722, in order to solve the above-mentioned problem, the laser irradiation at the time of crystallization of the silicon film is performed with such an intensity (energy) that the lower layer portion of the silicon film is not melted. In addition, oxygen atoms are prevented from being mixed into the lower underlying SiO ₂ film. However, since the crystallinity of the silicon film also improves with respect to the irradiation energy during crystallization, it is effective when the required device characteristics are low, but it follows the demand for higher performance semiconductor devices. Can not. In that respect, it is not a fundamental solution and has a strong implication as an immediate compromise.

In fact, the inventors of the present invention have disclosed in Japanese Unexamined Patent Publication No. 4-117.
10-20W, as presented by No. 22 publication
Scanning speed of 0.5 to 20c with continuous oscillation argon laser
Irradiation at m / sec to produce a TFT and evaluate it, it was found that a semiconductor element constituting a thin film integrated circuit such as a driver circuit of a liquid crystal display device could not attain a sufficient performance at all. . Therefore, the present inventors have attempted to improve the characteristics of the TFT by performing laser irradiation with energy outside the range described in the above-mentioned publication, that is, higher energy, in order to obtain a semiconductor device with higher performance. At this time, there is no decrease in mobility that is considered to be caused by the oxygen donor as described in the above publication, and as the laser irradiation energy at the time of crystallization of the silicon film is increased, conversely, the mobility is Improved.

However, a new problem has arisen here. Irradiation
Increased energy and improved mobility of semiconductor film
Accordingly, the transistor characteristics of the TFT are shifted to the negative side.
The phenomenon of shifting appeared. This phenomenon is described in JP-A-4-117.
With low energy irradiation as suggested in JP 22
This phenomenon was not seen at all when crystallization was performed.
Energy for crystallizing the silicon film below a certain value.
It only becomes apparent when you raise it. Silicon film at this time
Investigation revealed that the irradiation energy for crystallization was increased.
As the temperature increases, the crystallinity improves.
It was found that the silicon film itself was N-type. TFT
Threshold voltage V _THIs minus
The leak current in the off operation region increases. I
However, the crystallinity of the active region is improved due to the trade-off relationship.
Therefore, the ON characteristics are improved and the current drive capability is increased.
The above contradictory phenomenon was found. Because of this
Additional irradiation energy to improve the crystallinity
The beam output cannot be increased, and the N
Beam irradiation is performed with relatively low energy to prevent mold
I have no choice. Therefore, satisfy the required element characteristics.
Enough high quality crystalline silicon film and high performance
The conductor device could not be realized.

At the same time, the magnitude of the roughness of the silicon film surface at this time also poses a serious problem. That is, the amorphous silicon film has a melting point of 141 due to the energy of strong light.
Heated instantaneously to 4 ° C. or higher, for several tens of nsec. It is cooled to around room temperature and solidified in about a cooling period. At this time, since the solidification rate is too fast, the silicon film is in a supercooled state and solidifies in an instant, and as a result, the crystal grain size is generally very small, about 100 to 200 nm. This phenomenon is particularly remarkable at the three poles where three crystal grains collide. The mountain-shaped swelling caused by the crystal growth is hereinafter referred to as "ridge".

FIG. 8 shows an atomic force microscope (AFM) of the surface state of a crystalline silicon film which was actually crystallized by intense light irradiation.
An image is shown. In FIG. 8, the full scale in the XY direction is 1 μm, and the full scale in the Z direction is 50 nm. When an active region of a semiconductor device such as a MOS transistor is formed with such a crystalline silicon film, an electric field is concentrated on a ridge on the surface of the crystalline silicon film. That is,
This lowers the withstand voltage of the upper insulating film and causes a leak current. Therefore, the reliability of the semiconductor device is significantly reduced, and it is very difficult to obtain a semiconductor device that can be used practically.

Furthermore, as a problem that remains in the crystallization process by irradiation with energy beams, there is a non-uniformity in film quality (crystallinity) of the obtained crystalline silicon film. That is, as a light source,
In general, there is no large-area, high-output device capable of collectively irradiating the silicon film on the substrate, and this is generally achieved by sequentially scanning a small-area beam. Therefore, of course, there is a non-uniformity of crystallinity accompanying the sequential scanning,
This is reflected as it is in the element characteristics, which causes variation in characteristics between elements. At this time, in addition to the characteristic variation between elements due to the original active region crystallinity,
That is, the variation due to the N-type active region is added. As a result, in the TFT, particularly, the threshold voltage V
_TH will not be stable and will vary widely between elements. In an active matrix type liquid crystal display device using this TFT as a pixel switching element, the variation caused by the energy beam sequential scanning for crystallization is emphasized by the N-type active region, so that display (contrast) is performed.
The unevenness appeared as a defect.

Further, in the active matrix substrate for a liquid crystal display device described above, an auxiliary capacitance is generally provided in parallel with the liquid crystal capacitance. When the crystalline silicon film is used as one of the electrodes as the auxiliary capacitance component together with the channel portion of the pixel TFT which switches the pixel electrode, the capacitance deviates from the design value due to the change in the surface area ratio due to the ridge. In addition to the characteristic variations among the TFT elements, it causes display defects such as display unevenness and flicker.

The present invention has been made in view of the above problems, and provides a semiconductor device having high performance, high stability, and high reliability on a substrate having an insulating surface. It is intended for. Also, in a semiconductor device such as an active matrix substrate having a plurality of TFTs on a crystalline silicon film, a simple process that can reduce element characteristics variation when crystallized by the above-described sequential scanning and reduce cost can be achieved. The present invention realizes a semiconductor device having good uniformity.

[0022]

SUMMARY OF THE INVENTION The present invention provides an active matrix liquid crystal display device having a larger size and higher resolution, a driver monolithic type active matrix liquid crystal display device having a driver for driving on the same substrate, and a high speed and high resolution. Instability of device characteristics caused when crystalline silicon crystallized by sequential scanning of energy beam is used for active region to realize contact image sensor with high resolution, thermal head with built-in driver, three-dimensional IC, etc. And to solve the problem of non-uniformity. Specifically, the present invention has the following features.

(1) A semiconductor device in which a thin film semiconductor element having, as an active region, a crystalline silicon film formed in contact with a base film containing silicon oxide as a main component is formed on a substrate. The region is a crystalline silicon film crystallized in a melting and solidifying process by energy beam irradiation, and the underlayer film has a moisture (H ₂ O) concentration of about 1 in the film.
It is characterized by being an insulating film of not more than × 10 ²⁰ / cm ³ .

(2) The concentration of water (H ₂ O) contained in the underlayer film is about 1 × 10 ¹⁹ pieces / cm ³ or less.

(3) A semiconductor device in which a thin film semiconductor element having, as an active region, a crystalline silicon film formed in contact with a base film containing silicon oxide as a main component is formed on a substrate. The region is a crystalline silicon film crystallized in the melting and solidification process by energy beam irradiation, and the underlying film has a SiOH group concentration of about 1 ×.
It is an insulating film having a density of 10 ²¹ / cm ³ or less.

(4) A semiconductor device in which a thin film semiconductor element having, as an active region, a crystalline silicon film formed in contact with a base film containing silicon oxide as a main component is formed on a substrate. The region is a crystalline silicon film crystallized in a melting and solidifying process by energy beam irradiation, and the underlayer film has a moisture (H ₂ O) concentration of about 1 in the film.
× 10 ²⁰ / cm ³ or less, SiO where and contained in the film
The insulating film is characterized in that the concentration of H groups is about 1 × 10 ²¹ pieces / cm ³ or less.

(5) In a semiconductor device having a plurality of thin film transistors formed on a substrate and in contact with a base film containing silicon oxide as a main component, the channel regions of the plurality of thin film transistors are sequentially scanned and irradiated with pulsed laser light. The underlying film made of a crystalline silicon film crystallized by the above, which is formed in a lower layer in contact with the channel region, has a water (H ₂ O) concentration of about 1 × 10 ²⁰ pieces / cm ³ or less. The insulating film and / or the insulating film having a concentration of SiOH groups contained in the film is about 1 × 10 ²¹ / cm ³ or less.

Here, the plurality of thin film transistors are:
In an active matrix substrate having a pixel electrode,
It is suitable to be used for a pixel switching thin film transistor that switches each pixel electrode.

Further, it is preferable that the plurality of thin film transistors are used as thin film transistors forming a driver circuit in a driver monolithic active matrix substrate in which an active matrix and a driver circuit are formed on the same substrate.

(6) A thin film transistor which is formed on a substrate and drives a plurality of pixel electrodes formed in contact with a base film containing silicon oxide as a main component is provided, and each thin film transistor is arranged in parallel with the liquid crystal capacitance of the pixel electrode. In a semiconductor device to which an auxiliary capacitance component is connected, an insulating film having a water (H ₂ O) concentration of about 1 × 10 ²⁰ / cm ³ or less in a film and / or a SiOH group contained in the film. Concentration is about 1 ×
A channel region of the thin film transistor and one electrode of the auxiliary capacitance component connected to the thin film transistor were formed using a crystalline silicon film on a base film formed of an insulating film having a density of 10 ²¹ / cm ³ or less. It is characterized by the following.

(7) Water (H) contained in the film is formed on the substrate.
₂ O) a step of forming an insulating film having a concentration of about 1 × 10 ²⁰ pieces / cm ³ or less, a step of forming a silicon film on the insulating film, and irradiating the silicon film with an energy beam to melt and solidify The method is characterized by including at least a step of crystallizing in the process and a step of using the silicon film as an active region to complete a thin film semiconductor device.

(8) On the substrate, SiOH contained in the film
In the step of forming an insulating film having a base concentration of about 1 × 10 ²¹ pieces / cm ³ or less, forming a silicon film on the insulating film, irradiating the silicon film with an energy beam, and melting and solidifying the same. The method is characterized by including at least a crystallization step and a step of using the silicon film as an active region to complete a thin-film semiconductor device.

(9) The base film is a silicon film formed by a sputtering method at a substrate temperature of 150 ° C. or higher.

(10) The base film is formed of SiH ₄ gas and N ₂
Formed by a plasma CVD method using O gas as a material,
It is a silicon oxide film subjected to a heat treatment at 550 ° C. or more thereafter.

(11) The base film is formed by plasma CVD using an organic silane-based gas such as TEOS and an oxygen gas.
It is a silicon oxide film formed by a method and subjected to a subsequent heat treatment at 550 ° C. or higher.

(12) A step of forming an amorphous silicon film on the base film and crystallizing it in a solid state by heating, and irradiating the crystallized silicon film with an energy beam for melting. And a step of recrystallizing the silicon film by solidifying.

(13) A step of forming an amorphous silicon film on the base film and crystallizing it in a solid state by heating, and irradiating the crystallized silicon film with an energy beam. And a step of recrystallizing the silicon film by melting and solidifying.

In the step of forming an amorphous silicon film on the base film and crystallizing the amorphous silicon film in a solid phase by heating, a catalyst element which promotes the crystallization is introduced. It is characterized in that it is performed later.

(14) In the step of crystallizing the amorphous silicon film in a solid state by heating, the catalyst element which promotes the crystallization is selectively introduced into the amorphous silicon film, and the amorphous silicon film is heated. The treatment is performed by laterally growing crystals from the region into which the catalytic element has been selectively introduced to the peripheral portion thereof, and using the laterally grown regions, the active region of the semiconductor device is used. Is formed.

As the catalyst element, Ni, Co, Pd,
It is preferable to use one or more elements selected from Pt, Cu, Ag, Au, In, Sn, Al, and Sb. In particular, it is preferable to use the Ni element.

It is preferable to use a laser beam having a wavelength of 400 nm or less as an energy beam for crystallizing the silicon film. As the laser light, a wavelength 308
It is preferable to use a XeCl excimer laser beam of nm.

(15) The energy beam applied to the silicon film has an energy density of 250 to 400 m.
It is characterized in that it is a J / cm ² pulsed laser.

The energy beam is an excimer laser beam whose beam shape is the irradiation surface (silicon film surface).
It is preferable that the active regions of a plurality of semiconductor elements are simultaneously crystallized by sequentially scanning in a direction perpendicular to the longitudinal direction of the beam shape.

The operation of the above features will be described below.

When the present inventors examined the resistance value and carrier concentration of the crystalline silicon film melt-crystallized by laser irradiation, it was found that the dependence on the underlying film was large. Upon closer inspection, as shown in FIGS. 6 and 7,
It was found that the resistance value (carrier concentration) of the upper crystalline silicon film changes depending on the moisture (H ₂ O) concentration and the SiOH group concentration in the underlying film. When the carrier type at this time is examined by Hall effect measurement, it is clearly N type, and the cause of generation of this N type carrier is oxygen that is eluted from the base film due to laser light irradiation to the silicon film and diffused in the silicon film. It was found to be a thermal donor by clusters. In other words, the oxygen donor mixed from the silicon oxide film of the base film is not the component oxygen of the silicon oxide film, but H ₂ O released from the film during the laser crystallization of the upper silicon film and the unstable bonding state. It is mainly formed of SiOH groups. Effect of oxygen donors coming from the underlying film is said is also described in JP-A-4-11722 and JP-rather than decrease phenomenon of the mobility of the silicon film itself, shifting the threshold voltage V _TH in the negative direction in the TFT It was found that it had a very bad effect such as increasing the leak current in the off operation region.

In particular, in a semiconductor device such as an active matrix substrate for liquid crystal display having a plurality of TFTs on the substrate, the oxygen donors described above are a major cause of variations in TFT characteristics. That is, the primary cause of the generation of oxygen donors is a crystallization step by melting and solidifying the silicon film. As described above, the problem is the non-uniformity of film quality (crystallinity) of the obtained crystalline silicon film. In particular, the number of oxygen donors incorporated in the silicon film largely depends on the crystallization process, and the oxygen donor concentration becomes relatively high in the local region where higher energy is applied and the crystallization is performed.
In addition to the original characteristic variation between the elements, the variation due to the oxygen donor is added. As a result, in particular, the threshold voltage V _TH largely varies, and in an active matrix type liquid crystal display device using TFTs as pixel switching elements, variations in characteristics between elements due to energy beam sequential scanning for crystallization are emphasized. It was found that display (contrast) unevenness appeared as a defect.

Further, the present inventors have examined and found that the surface roughness of the crystalline silicon film melt-crystallized by the laser irradiation also largely depends on the underlying film. That is, when the silicon film is instantaneously heated to its melting point by laser irradiation, if a large amount of H ₂ O or SiOH groups is present in the silicon oxide film underneath, they pass through the silicon film and become It was found that it bumped into the inside, which further increased the surface roughness of the silicon film.

The outline of the present invention is a thin film semiconductor device having an underlying film containing silicon oxide as a main component and having a crystalline silicon film crystallized in the melting and solidification process by energy beam irradiation as an active region. The undercoat film has a water (H ₂ O) concentration of about 1 × 10 ²⁰ / cm ^3.
Below, or the concentration of SiOH groups contained in the film is about 1
X 10 ²¹ pieces / cm ³ or less. When a semiconductor device such as a TFT is manufactured with such a configuration, the energy density is reduced to 2 in order to improve element characteristics.
When the energy beam output is increased to 50 to 400 mJ / cm ² , the N-type phenomenon of the silicon film in the active region is reduced, and the device characteristics are stable. Therefore, since sufficient energy can be applied to the silicon film to crystallize it, the crystallinity of the active region is greatly improved, and as a result, the current driving capability is dramatically improved to 50 to ²⁰⁰ cm ² / Vs in electric field mobility. it can. On the other hand, in the TFT, the threshold voltage V
It is possible to realize a high-performance, highly-reliable, and highly-stable semiconductor device that has not been compatible with the related art, without causing adverse effects such as a negative shift of _TH and an increase in leakage current during an off operation.

Specifically, the results of the experiments conducted by the present inventors are shown in FIGS. 6 and 7. FIG. 6 shows the specific resistance of the silicon film after laser crystallization with respect to the moisture (H ₂ O) concentration in the base film (silicon oxide film), and the horizontal axis represents H in the base film. _{The 2} O concentration (number / cm ³ ) is shown, and the vertical axis shows the specific resistance of silicon (Ω · cm). FIG. 7 shows the specific resistance of the silicon film after laser crystallization with respect to the concentration of SiOH groups in the underlying film (silicon oxide film). The horizontal axis represents the concentration of SiOH groups in the underlying film (number / cm). ³ ), and the vertical axis shows the specific resistance (Ω · cm) of silicon. The experimental sample is formed by forming a base film on a glass substrate, forming an amorphous silicon film on the base film, and then performing laser irradiation to crystallize the film. The laser light used is X with a wavelength of 308 nm.
The silicon film was irradiated with an eCl excimer laser at an energy density of 330 mJ / cm ² , which was considerably higher than the standard. The concentration of film moisture (H ₂ O) concentration and SiOH groups in the silicon oxide film, which was calculated from FTIR spectra, H ₂
O concentration is around 3400 cm ^-1 , absorption of OH stretching vibration of H ₂ O, and SiOH group concentration is around 3650 cm ^-1.
It was calculated from the absorption of the OH stretching vibration of the H bond. The presence of H ₂ O can be separately confirmed by the absorption due to the bending vibration of H—O—H near 1620 cm ⁻¹ .

From FIG. 6, the specific resistance of the silicon film is greatly reduced when the H ₂ O concentration is about 1 × 10 ²⁰ pieces / cm ³ or more as a boundary value. Even when the value is about 1 × 10 ²⁰ pieces / cm ³ or less, the H ₂ O concentration shows a gradual decrease tendency as the H ₂ O concentration increases, but the H ₂ O concentration becomes about 1 × 10 ²⁰ pieces / cm ³ or more. At that time, the slope changes and the resistivity of the silicon film sharply decreases. Therefore, the H ₂ O concentration of the base film is about 1 × 10
^{When it is 20} pieces / cm ³ or less, the resistance value of the silicon film is almost saturated, and its change is small. This means that the state is close to intrinsic and the carrier concentration in the film is extremely low. As an empirical value, when a TFT is manufactured using a crystalline silicon film as an active region, the specific resistance of the silicon film is approximately 1 × 10 ⁶ Ω · c.
When it is m or more, it exhibits an enhanced type characteristic, and when it is less than m, it is often a depletion type. According to FIG.
_It can be seen that when the ₂ O concentration is 1 × 10 ²⁰ / cm ³ , the specific resistance of the silicon film is approximately 1 × 10 ⁶ Ω · cm.

Further, it can be seen from FIG. 6 that the specific resistance of the silicon film is completely saturated when the H ₂ O concentration of the underlying film is about 1 × 10 ¹⁹
It can be seen that the number is less than the number of pieces / cm ³ . Therefore, it is below this value that the effect of H ₂ O contained in the underlying film is almost completely eliminated as a device characteristic, and the H ₂ O concentration of the underlying silicon oxide film of the silicon film by laser crystallization in the present invention is less than this value. The more optimal value is 1 × 10 ¹⁹ / c
m ³ or less. The lower the H ₂ O concentration, the better, but the realistic lower limit of production is 1 × 10 ¹⁷ /
cm ³ .

Further, it can be seen from FIG. 7 that the concentration of SiOH groups in the underlayer also affects the specific resistance of the silicon film. FIG. 7 shows that the specific resistance of the silicon film and the SiO2
The relationship of the H group concentration is that the SiOH group concentration is about 1 × 10 ^21.
If the value is larger than the number of pieces / cm ³ , a sharp decrease tendency is shown. That is, when the concentration of the SiOH group in the underlayer is about 1 × 10 ²¹ / cm ³ or less, the resistance value of the silicon film is almost saturated and becomes almost intrinsic, and the carrier concentration in the film is extremely low. Become. In order to further bring out the effects of the present invention, it is most effective to simultaneously control the water (H ₂ O) concentration and the SiOH group concentration, and the water (H ₂ O) concentration of the silicon oxide film as the base film is most effective. Is about 1
More preferably, it is not more than × 10 ²⁰ / cm ³ and the concentration of SiOH groups is not more than about 1 × 10 ²¹ / cm ³ .
The lower the SiOH concentration, the better, but the realistic lower limit of production is about 1 × 10 ¹⁸ / cm ³ .

The value of the surface roughness of the silicon film also depends on the concentration of H ₂ O and the concentration of SiOH groups contained in the underlayer film. Specifically, as these densities increase, the surface roughness increases, but the fluctuation region is mainly outside the above-described concentration range according to the present invention. Therefore, by using the underlayer film of the present invention, the surface roughness due to the bulge at a crystal grain boundary called a ridge, which is observed in a conventional laser crystallization process, is reduced. That is, although the ridge is caused by the crystal growth process itself, impurities such as hydrogen in the amorphous silicon film and H ₂ O spouted from the base film are more prominent. . Actually, as a result of measurement with an AMF (atomic force microscope), the average surface roughness Ra was about 6 to 7 nm in the past, but 4 to 5 n in the present invention.
m.

The present invention is particularly effective for a semiconductor device having a plurality of TFTs. That is, in a plurality of TFTs in which a channel region is formed by a crystalline silicon film crystallized by pulsed laser beam sequential scanning irradiation, as described above, crystallinity variations due to pulsed laser beam sequential scanning irradiation are caused. However, in addition to this, variations due to oxygen donors mixed in the silicon film from the base film are added. Therefore, when the present invention is applied to a semiconductor device having a plurality of TFTs, the moisture (H ₂ O) contained in the underlying film below the channel region is contained in the film.
High performance and reliability by using an insulating film with a concentration of about 1 × 10 ²⁰ / cm ³ or less, or a concentration of SiOH groups contained in the film of about 1 × 10 ²¹ / cm ³ or less It is possible to obtain not only a high TFT, but also a large variation in characteristics between TFT elements.

Furthermore, as an application device of the present invention,
This is effective for a semiconductor device in which an extremely large number of TFTs of 10,000 or more are arranged in a matrix, particularly an active matrix substrate for a liquid crystal display. The active matrix substrate for liquid crystal display is composed of pixel switching TFTs connected to each pixel electrode, and if the characteristics of the TFTs vary, display unevenness (contrast unevenness) is caused.
The human eye is very severe, and a subtle difference in TFT characteristics appears as a voltage change of each pixel electrode, which is identified as display unevenness. Therefore, a very high level of uniformity of TFT characteristics between elements is required. The present invention
It is very effective for a plurality of TFT elements requiring such high uniformity, and greatly reduces the striped contrast unevenness caused by the sequential scanning irradiation of the pulse laser light, which has been conventionally seen in the liquid crystal display device. Therefore, a high display quality liquid crystal display device can be realized.

In addition to the pixel TFTs for switching the pixel electrodes arranged in a matrix, the pixel TFTs
In a driver monolithic active matrix semiconductor device having a driver circuit for driving a pixel on the same substrate, in addition to the pixel TFT, a plurality of TFTs constituting the driver circuit have very high characteristic uniformity especially in a shift register circuit and the like. Is required. If the characteristics of these TFTs vary, the drive waveforms for each line will differ, and in this case also, uneven stripe display will appear on the screen. As described above, the human eye is very severe and has the ability to discriminate subtle display unevenness. However, by applying the present invention to these TFTs, even a plurality of TFTs constituting a driver circuit can be used as a substrate. Excellent property uniformity is obtained throughout. As a result, the characteristics of the driver circuit for driving the pixel TFT are stabilized, and defects such as display unevenness due to variations in the driver circuit characteristics in the liquid crystal display device can be reduced.

In the present invention, in addition to the effect of suppressing the N-type phenomenon of the silicon film and improving the uniformity of device characteristics, the effect of reducing the surface roughness of the silicon film due to the laser crystallization as described above is obtained. is there. In an active matrix substrate for liquid crystal display, one electrode of an auxiliary capacitance (Cs) connected in parallel with a liquid crystal capacitance formed by a pixel electrode is formed in the same layer as an active region of a pixel TFT, and a gate insulating film forms a capacitance. A method of forming is used. That is, in order to mitigate the voltage drop phenomenon in the pixel electrode portion that occurs when the gate pulse signal is turned off, the auxiliary capacitance (Cs) is provided in parallel with the liquid crystal capacitance.
The variation in the capacitance value of s) within the screen causes the surface unevenness such as flicker on the screen. When one electrode of the auxiliary capacitance (Cs) is manufactured using a crystalline silicon film obtained by conventional strong light irradiation, the absolute value of the surface roughness due to the ridge is large, and the capacitance value of the auxiliary capacitance (Cs) is large. It was difficult to obtain a liquid crystal display device having variations and good display quality. On the other hand, when the present invention is used, the surface roughness of the silicon film is reduced, so that the variation in the capacitance value of the auxiliary capacitance (Cs) can be suppressed, and a high display quality liquid crystal display without display unevenness can be obtained. The device is obtained.

Various methods can be considered for producing a silicon oxide film which satisfies the conditions of the present invention. Considering the active matrix substrate for a liquid crystal display device, which is a particular object of the present invention, the following three methods can be considered. The method is the best. As a first method, a substrate temperature of 150 ° C. or higher and 300
There is a method in which the film is formed by a sputtering method at a temperature of not more than ° C. In this case, if the temperature is lower than 150 ° C., the quality of the silicon oxide film is not good, and the H ₂ O content in the film becomes large. If the temperature is higher than 300 ° C., Si with oxygen deficiency increases, and the fixed charge density in the film may increase. A second method is a method in which SiH ₄ gas and N ₂ O gas are used as materials and is formed by a plasma CVD method, and then heat treatment is performed at 550 ° C. or more and 600 ° C. or less. Here, at 550 ° C. or lower, H ₂ O in the film,
SiOH groups are not sufficiently released, and when glass is used as the substrate at 600 ° C. or higher, the glass substrate may be softened. A third method is a method in which an organic silane-based gas such as TEOS and an oxygen gas are used as materials and formed by a plasma CVD method, and then heat treatment is performed at 550 ° C. or higher and 600 ° C. or lower. At 550 ° C. or lower, similarly, H ₂ O and SiOH groups existing in the film are not sufficiently released outside the film, and at 600 ° C. or higher, the glass substrate may be softened.

It is particularly desirable to make it by any of the above three methods. According to these methods, the conditions of the silicon oxide film as the base film in the present invention can be sufficiently satisfied, the mass productivity is high, and the silicon oxide film can be uniformly formed on a large substrate.

The present invention aims at achieving high performance of a semiconductor device and at the same time achieving high reliability, stability, and uniformity between elements. However, in order to further enhance the effect, first, a non-film is formed on a base film according to the present invention. A more effective method is to recrystallize this silicon film by forming a crystalline silicon film, heating it to crystallize it in a solid state, and then irradiating it with an energy beam to melt and solidify it. A crystalline silicon film obtained by solid-phase crystallization of an amorphous silicon film by heat treatment has poor crystallinity and is unsuitable as a TFT channel region as it is,
Since the uniformity is good, it is effective in that a seed crystal is prepared during the melt-solidification crystallization. Next, when the crystalline silicon film is irradiated with an energy beam, the crystalline silicon film is recrystallized with a certain amount of crystal information left, and good uniformity due to solid-phase crystallization is reflected. Further, since the amorphous silicon film is recrystallized from the seed crystal, the individual crystal grain size can be made larger than that in the case where the amorphous silicon film is crystallized by direct energy beam irradiation, and the performance of the semiconductor device is improved. You can do it.

The solid phase crystallization step is desirably performed after introducing a catalytic element for promoting crystallization into the amorphous silicon film. According to this method, the heating temperature can be lowered, the processing time can be shortened, and the crystallinity can be improved. Specifically, by introducing a trace amount of a metal element such as nickel or palladium onto the surface of the amorphous silicon film and then heating, the crystallization is completed at 550 ° C. for about 4 hours. In contrast, heat treatment at 600 ° C. or more for several tens of hours is required for ordinary solid-phase crystallization without using a catalyst element. In addition, the crystalline silicon film crystallized by the catalytic element has a twin structure in one grain of the crystalline silicon film crystallized by the usual solid phase growth method, whereas It is composed of a columnar crystal network, and the inside of each columnar crystal is almost in a single crystal state.

The crystalline silicon film crystallized by this catalytic element is very compatible with the recrystallization step by energy beam irradiation. In the recrystallization process by energy beam irradiation, the initial crystallinity is reflected to some extent, and in the crystalline silicon film by the usual solid phase crystallization, the twin crystal structure is reflected and the crystalline silicon film has many crystal defects. . On the other hand, in the case of a solid-phase crystallized silicon film using a catalytic element, the columnar crystals are combined by recrystallization by irradiation with an energy beam, and a crystalline silicon film having very good crystallinity over a wide range is obtained. Can be

Further, by selectively introducing the catalytic element into a part of the amorphous silicon film and heating it, only the region where the catalytic element is selectively introduced is crystallized, and then the lateral region is introduced from the introduced region. Crystal growth can be performed in a direction (direction parallel to the substrate). Inside this lateral crystal growth region, columnar crystals whose growth directions are almost aligned in one direction are crowded, and the crystallinity is lower than that of the region where the catalytic element is directly introduced and crystal nuclei are generated randomly. It is a good area. Therefore, by using the crystalline silicon film in the lateral crystal growth region as an active region of a semiconductor element such as a channel region of a TFT, the performance of a semiconductor device can be further improved.

The types of catalyst elements that can be used in the present invention include Ni, Co, Pd, Pt, Cu, Ag, Au and I.
n, Sn, Al, and Sb can be used. Among them, the most remarkable effect can be obtained particularly when Ni is used. The reason for this has not been fully understood, but we are considering the following model. The catalyst element does not act alone, but acts on crystal growth by bonding to the silicon film to form silicide. This is a model in which the crystal structure at that time acts like a kind of template during crystallization of the amorphous silicon film to promote crystallization of the amorphous silicon film. Ni forms silicide of _two Si and NiSi2. NiSi ₂ exhibits a fluorite-type crystal structure, which is very similar to the diamond structure of single crystal silicon. Moreover, NiSi ₂ has a lattice constant of 5.406 °, which is very close to the lattice constant of 5.430 ° in the crystalline silicon diamond structure. Therefore, NiSi ₂ is the best as a template for crystallizing the amorphous silicon film, and Ni is most preferably used as the catalyst element in the present invention.

In the present invention, it is desirable to use an excimer laser beam having a wavelength of 400 nm or less as an energy beam for crystallizing a silicon film. Wavelength is 40
When the thickness is 0 nm or less, the silicon film has a large absorption coefficient for the wavelength range, so that the energy can be efficiently given to the silicon film, a good crystalline silicon film can be obtained, and the lower glass substrate, etc. The thermal damage to is relatively small. Among them, XeCl excimer laser light has a high oscillation output and high stability, so that its beam size can be expanded to some extent, and is most suitable as a means for annealing a silicon film on a large-area substrate.
The laser light used in the present invention has an energy density of 2
It is desirable to use a pulse laser having a high energy of 50 to 400 mJ / cm ² .

Further, the excimer laser beam is designed so that its beam shape becomes long on the irradiation surface, and is sequentially scanned in a direction perpendicular to the long direction of the beam shape. It is desirable to simultaneously crystallize the active regions of a plurality of semiconductor elements. Because in scanning irradiation, the uniformity in the direction perpendicular to the scanning direction is relatively good, so by expanding the beam size in that direction, it becomes possible to perform more uniform processing on large substrates, etc. This is because the processing efficiency of the process also increases.

[0067]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) A first embodiment using the present invention will be described. In this example, the steps of manufacturing an active matrix substrate for a liquid crystal display device over a glass substrate using the present invention will be described. In this active matrix substrate, an N-type TFT is formed as an element for switching each pixel.

FIG. 1 is a cross-sectional view showing a process for fabricating an arbitrary TFT on the active matrix substrate of this embodiment. The fabricating process proceeds sequentially in the order of (A) → (E). Actually, in an active matrix substrate, hundreds of thousands of TFTs are arranged on the substrate and are formed in a simultaneous process. I do. FIG. 1E shows a completed view of the pixel TFT 121 on the active matrix substrate manufactured in this embodiment. Actually, a plurality of pixel TFTs are simultaneously formed on the substrate in the same process as the pixel TFT 121.

First, as shown in FIG. 1A, a glass substrate 101 having a thickness of 30 is formed by, for example, a sputtering method.
A base film 102 of about 0 nm made of silicon oxide is formed. The sputtering conditions for forming the silicon oxide film were as follows: a quartz target was used and the substrate was heated to 200 ° C. in an Ar / O ₂ mixed gas. At this time, the H ₂ O concentration in the silicon oxide film was 5 × 10 ¹⁸
The number of particles / cm ^{3 is} approximately, and the concentration of SiOH groups is 2 × 10.
It was about ¹⁹ pieces / cm ³ .

Next, an amorphous silicon (a-Si) film 103 having a thickness of 20 to 100 nm, for example, 30 nm is formed by the low pressure CVD method or the plasma CVD method. When the a-Si film 103 is formed by the plasma CVD method, a large amount of hydrogen is contained in the film, which causes film peeling during the subsequent laser irradiation. It is necessary to perform a heat treatment for several hours to release hydrogen in the film.

Thereafter, as shown in FIG. 1B, laser light 107 is irradiated to crystallize the a-Si film 103.
As the laser light at this time, a XeCl excimer laser (wavelength 308 nm, pulse width 40 nsec) was used. The irradiation conditions of the laser beam 107 are as follows.
Energy density of 250 to 400 mJ / cm ² , for example, 320 mJ /
cm ² . The laser light 107 was molded by a homogenizer so that the beam size on the surface of the substrate was a long rectangular shape with a size of 150 mm × 1 mm, and was sequentially scanned in the direction perpendicular to the long side direction. At this time, the overlap amount of the beam accompanying the sequential scanning is set to 90%, so that any one point of the a-Si film 103 is irradiated with the laser beam ten times. By this step, the a-Si film 103 is heated to a temperature equal to or higher than its melting point, melted and solidified, and becomes a crystalline silicon film 103a having good crystallinity. The specific resistance of the crystalline silicon film 103a measured at this time was about 5 × 10 ⁶ Ω · cm.

Next, by removing unnecessary portions of the crystalline silicon film 103a, isolation between elements is performed as shown in FIG. 1C, and the active region (source region,
An island-shaped crystalline silicon film 108 constituting the drain region and the channel region) is formed.

Subsequently, as shown in FIG. 1D, a silicon oxide film having a thickness of 20 to 150 nm, here 100 nm, is covered with a gate insulating film so as to cover the island-shaped crystalline silicon film 108 serving as an active region. The film is formed as 109. Here, TEOS (Tetra E) is used to form the silicon oxide film.
(Ortho Silicate) and oxygen together with oxygen at a substrate temperature of 150 to 600 ° C., preferably 300 to 450 ° C., by RF plasma CVD.
Deposited. Alternatively, the substrate temperature is 350 to 600 ° C., preferably 400 to 550, using TEOS as a raw material together with ozone gas by a low pressure CVD method or a normal pressure CVD method.
C. may be formed.

Subsequently, by the sputtering method,
An aluminum film having a thickness of 300 to 600 nm, for example, 400 nm is formed. Then, the gate electrode 110 is formed by patterning the aluminum film. Further, the surface of the aluminum electrode is anodized to form an oxide layer 111 on the surface. This state corresponds to FIG. The anodization is performed in an ethylene glycol solution containing tartaric acid at 1 to 5%, and the voltage is first increased to 220 V at a constant current, and the state is maintained for 1 hour to complete the process. The thickness of the obtained oxide layer 111 is 200 nm. In addition,
Since the oxide layer 111 has a thickness for forming an offset gate region in a later ion doping process, the length of the offset gate region can be determined in the anodic oxidation process.

Next, an impurity (phosphorus) is implanted into the active region by ion doping using the gate electrode 110 and the oxide layer 111 around it as a mask. Phosphine (PH ₃ ) is used as the doping gas, the acceleration voltage is 60 to 90 kV, for example, 80 kV, and the dose is 1 × 10 4
^{It is set to 15} to 8 × 10 ¹⁵ cm ^-2 , for example, 2 × 10 ¹⁵ cm ^-2 . By this step, the region into which the impurity is implanted will be T
A source region 114 and a drain region 115 of the FT,
A region which is masked by the gate electrode 110 and the oxide layer 111 around the gate electrode 110 and is not implanted with impurities will later become a channel region 113 of the TFT.

Thereafter, as shown in FIG. 1D, annealing is performed by irradiation with a laser beam 112 to activate the ion-implanted impurities and, at the same time, to remove the portions whose crystallinity has deteriorated in the above-described impurity introducing step. Improves crystallinity. At this time, a XeCl excimer laser (wavelength 308 nm, pulse width 40 nsec) was used as a laser, and irradiation was performed at an energy density of 150 to 400 mJ / cm ² , preferably 200 to 250 mJ / cm ² . The sheet resistance of the source region 114 and the drain region 115 into which the N-type impurities (phosphorus) thus formed are injected is 2
It was 00 to 800 Ω / □.

Then, as shown in FIG.
A silicon oxide film of about 00 nm is formed as the interlayer insulating film 116. When this silicon oxide film is formed from TEOS as a raw material by a plasma CVD method with oxygen and oxygen, or a low pressure CVD method with ozone or a normal pressure CVD method, a good interlayer insulating film excellent in step coverage is obtained. Can be

Next, a contact hole is formed in the interlayer insulating film 116, and a source electrode 117 and a pixel electrode 120 are formed. The source electrode 117 is formed of a metal material, for example, a two-layer film of titanium nitride and aluminum. The titanium nitride film is provided as a barrier film for the purpose of preventing aluminum from diffusing into the semiconductor layer. Pixel electrode 12
0 is formed of a transparent conductive film such as ITO.

Finally, in a hydrogen atmosphere of 1 atm, 35
Annealing is performed at 0 ° C. for about 1 hour to complete the N-type pixel TFT 121 shown in FIG. The annealing process supplies hydrogen atoms to the interface between the active region of the pixel TFT 121 and the gate insulating film, and has the effect of reducing dangling bonds that degrade TFT characteristics. In addition, the pixel TF
For the purpose of protecting T121, a necessary portion may be covered with a silicon nitride film formed by a plasma CVD method using SiH ₄ and NH ₃ as source gases.

Each TF produced according to the above embodiment
T is a field effect mobility of 50 to 70 in the panel.
Good characteristics such as cm ² / Vs and a threshold voltage of ^{2 to} 2.5 V were exhibited. In particular, the variation in the threshold voltage of the TFTs within the panel showed a very good uniformity of about 0.5 V in terms of the maximum and minimum differences. As a result, a liquid crystal display panel was manufactured using the active matrix substrate manufactured in this example, and the entire display was performed. As a result, display unevenness caused by non-uniformity of TFT characteristics was greatly reduced, and high display quality was obtained. A liquid crystal display device was realized.

(Second Embodiment) A second embodiment using the present invention will be described. In this embodiment, steps of manufacturing an active matrix substrate for a liquid crystal display device on a glass substrate using the present invention will be described. In this active matrix substrate, an N-type TFT is formed as an element for switching each pixel electrode, and an auxiliary capacitance (Cs) is provided in parallel with the liquid crystal capacitance of the pixel electrode on the drain region side thereof.

FIG. 2 is a plan view showing the structure of an arbitrary pixel portion in the active matrix substrate described in this embodiment. FIG. 3 shows a TFT cut along the line AA ′ in FIG.
FIG. 4 is a cross-sectional view showing a manufacturing process of (A), and the manufacturing process sequentially proceeds in the order of (A) → (E). 2 and 3
(E) is a completed view of the pixel TFT and the auxiliary capacitance (Cs) part manufactured in the present example, and the switching N
A pixel TFT 221 and a storage capacitor (Cs) 224.

First, as shown in FIG. 3A, a 300 nm-thick
A base film 202 made of silicon oxide is formed. The film forming conditions at this time are as follows: TEOS is used as a material gas.
(Tetra Ethoxy Ortho Silica
te) was used as a raw material, and was decomposed and deposited by an RF plasma method at a substrate temperature of 300 to 400 ° C. under a reduced pressure atmosphere of about 1 Torr together with oxygen. After that, the substrate was annealed at a substrate temperature of 500 to 600 ° C., for example, 600 ° C. for several hours in an inert gas atmosphere. In the heat treatment step,
The water (H ₂ O) contained in the film is released, and at the same time, the bond of the SiOH group is broken, and the OH component is released outside the film. As a result, the water content (H
₂ O) The concentration of about 4 × 10 ²⁰ / cm ³ and the concentration of SiOH groups were about 3 × 10 ²¹ / cm ³ , whereas the H ₂ O concentration of the silicon oxide film after the heat treatment was 2 × 10 ¹⁹ pieces / c
m ³ , and the concentration of SiOH groups is 4 × 10 ²⁰ / c
m ³ .

Then, a low pressure CVD method or a plasma CVD method is performed on the underlying film 202 of the silicon oxide film.
Intrinsic (I-type) amorphous silicon film (a-S) having a thickness of 40 nm
An i film 203 is formed. When the a-Si film 203 is formed by the plasma CVD method, a large amount of hydrogen is contained in the film, which causes film peeling during the subsequent laser irradiation. It is necessary to perform a heat treatment for several hours to release hydrogen in the film.

Then, as shown in FIG. 3A, laser light 207 is irradiated to crystallize the a-Si film 203.
At this time, a XeCl excimer laser (wavelength 308 nm, pulse width 40 nsec) was used as the laser light. The irradiation conditions of the laser beam 207 are as follows.
It is heated to 00 to 500 ° C., for example, 400 ° C., and has an energy density of 200 to 350 mJ / cm ² , for example, 330 mJ /
cm ² . The laser light 207 is sequentially scanned on the substrate surface, and an arbitrary point on the a-Si film 203 is
The scanning pitch was set so that laser irradiation was performed 10 times each. By this step, the a-Si film 203 is heated to its melting point or higher, melted and solidified to become the crystalline silicon film 203a having good crystallinity. Here, the average surface roughness Ra of the surface of the crystalline silicon film 203a measured by an atomic force microscope (AFM) was about 4 to 5 nm.

Next, unnecessary portions of the crystalline silicon film 203a are removed to perform element isolation as shown in FIG. 3 (B), and thereafter, an active region (source region,
Drain region, channel region) and auxiliary capacitance (Cs)
Forming an island-shaped crystalline silicon film 208 which constitutes the lower electrode of FIG. When the state at this time is viewed from above the substrate, an island-shaped crystalline silicon film 208 is formed as shown in FIG.

Next, as shown in FIG. 3C, a photoresist is applied onto the island-shaped crystalline silicon film 208 to be an active region, and is exposed and developed to form a mask 204. That is, the mask 204 covers only a portion which will be a channel region of the TFT later. Then, impurities (phosphorus) are implanted by ion doping using the photoresist mask 204 as a mask.
Phosphine (PH ₃ ) is used as the doping gas, the acceleration voltage is 5 to 30 kV, for example, 15 kV, and the dose amount is 1 × 10 ¹⁵ to 8 × 10 ¹⁵ cm ⁻² , for example, 2 × 10.
¹⁵ cm ^-2 . By this step, the region into which the impurities are injected becomes the source region 214 of the pixel TFT 221 later, and the drain region 215 of the pixel TFT 221 and the lower electrode of the auxiliary capacitance (Cs) 224 are formed. The region which is masked by the photoresist mask 204 and into which impurities are not implanted will later become the channel region 213 of the TFT 221 as described above.

Next, as shown in FIG. 3D, the photoresist mask 204 is removed, and the island-shaped crystalline silicon film 208 is covered with a thickness of 20 to 150 nm, in this case 1
A 00 nm silicon oxide film is formed as the gate insulating film 209. Here, TEOS is used for forming the silicon oxide film.
(Tetra Ethoxy Ortho Silic
ate) as a raw material, and a substrate temperature of 150 to 6 together with oxygen.
It was decomposed and deposited by RF plasma CVD at 00 ° C, preferably 300 to 400 ° C. After the film formation, the gate insulating film 20
In order to improve the bulk property of 9 itself and the interface property of the crystalline silicon film / gate insulating film, annealing was performed at 400 to 600 ° C. for several hours in an inert gas atmosphere. At the same time, the annealing treatment activates the impurities doped in the source region 214 and the drain region 215, and lowers the resistance of the source region 214 and the drain region 215. As a result, the sheet resistance thereof is 800 to 1000.
Became Ω / □.

Subsequently, by the sputtering method,
Aluminum is deposited to a thickness of 300 to 500 nm, for example 400 nm. Then, the aluminum film is patterned to form a gate electrode 210a and a storage capacitor (Cs) 224.
Of the upper electrode 210b is formed. Here, the gate electrode 21
2a, as viewed in plan, as shown in FIG. 2, forms the n-th gate bus line, and the upper electrode 210b of the storage capacitor (Cs) part forms the (n + 1) th gate bus line. I have.

Then, as shown in FIG. 3E, a silicon oxide film having a thickness of about 500 nm is formed as an interlayer insulating film 216. When this silicon oxide film is formed from TEOS as a raw material by a plasma CVD method with oxygen and oxygen, or a low pressure CVD method with ozone or a normal pressure CVD method, a good interlayer insulating film excellent in step coverage is obtained. To be

Next, contact holes are formed in the interlayer insulating film 216 to form the source electrode 217 and the pixel electrode 220. The source electrode 217 is formed of a metal material, for example, a two-layer film of titanium nitride and aluminum. The titanium nitride film is provided as a barrier film for preventing aluminum from diffusing into the semiconductor layer. Pixel electrode 22
0 is formed of a transparent conductive film such as ITO. When the state at this time is viewed from above the substrate, as shown in FIG. 2, the source electrode 217 constitutes a source bus line for transmitting a video signal to the TFT 221, and the pixel electrode 22 is provided between each bus line.
0 is arranged.

Finally, in a hydrogen atmosphere of 1 atm.
Annealing is performed at 0 ° C. for about 1 hour to complete the pixel TFT 221 shown in FIG. The annealing treatment has the effect of supplying hydrogen atoms to the interface between the active region of the pixel TFT 221 and the gate insulating film to reduce dangling bonds that deteriorate the TFT characteristics. Furthermore, the pixel TFT 22
For the purpose of protecting No. 1, the silicon nitride film formed by the plasma CVD method using SiH ₄ and NH ₃ as source gases may be covered only at a necessary portion.

Each TF manufactured according to the above embodiment
T is a field effect mobility of 70 to 90 in the panel.
Good characteristics of cm ² / Vs and a threshold voltage of ^{2 to} 2.5 V were shown. In addition, each pixel TFT 221 has a very good uniformity with a variation in TFT threshold voltage of about 0.5 V in the panel, and also has a lower electrode of its channel region 213 and its auxiliary capacitance (Cs) 224. In the above, both of the surface average roughness Ra are suppressed to about 4 to 5 nm,
There is almost no leakage current through the gate insulating film 209, and the non-uniformity of each capacitance can be suppressed to be small. As a result, a liquid crystal display panel was manufactured using the active matrix substrate manufactured in this example, and the entire display was performed. As a result, display unevenness caused by non-uniformity of TFT characteristics was greatly reduced, and high display quality was obtained. A liquid crystal display device was realized.

(Embodiment 3) A third embodiment using the present invention will be described. In this embodiment, an N-channel type TFT and a P-channel type TFT which form a peripheral driving circuit of an active matrix type liquid crystal display device and a general thin film integrated circuit.
A process of manufacturing a CMOS circuit having a complementary structure on a glass substrate will be described.

FIG. 4 is a plan view showing the outline of the manufacturing process of the TFT described in this embodiment. FIG. 5 is a cross-sectional view of FIG.
It is a sectional view taken along the line B ′, and the steps sequentially proceed in the order of (A) → (F). FIG. 5F shows a completed view of the CMOS circuit according to the present embodiment, which is an N-type TFT.
322 and a P-type TFT 323.

First, as shown in FIG. 5A, a glass substrate 301 having a thickness of 300 nm is formed by a plasma CVD method.
A base film 302 made of silicon oxide is formed. The film formation conditions at this time are as follows: silane (S
iH ₄ ) and N ₂ O, and a reduced pressure atmosphere of 0.5 to 1.5 Torr, for example, 0.8 Torr, and a substrate temperature of 3
It was decomposed and deposited by RF plasma at 00 to 350 ° C. Thereafter, the substrate temperature is set to 500 in an inert gas atmosphere.
Annealing treatment was performed at ˜600 ° C., for example, 580 ° C. for several hours. Strictly speaking, the film thus obtained has some components of SiOH. In the heat treatment step, H ₂ O contained in the film is released and Si
The bond of the OH group is also broken and the OH component is released to the outside of the film. As a result, the H ₂ O concentration of the obtained silicon oxide film was 1 × 1
0 to about ¹⁹ / cm ^3, the concentration of SiOH groups, 1 × 10
It became about ²⁰ pieces / cm ³ . Then, a thickness of 20 to 100 nm, for example 50, is formed on the base film 302 made of a silicon oxide film by a low pressure CVD method or a plasma CVD method.
nm intrinsic (I-type) amorphous silicon film (a-Si film) 3
03 is formed.

Next, a photosensitive resin (photoresist) is applied on the a-Si film 303, and is exposed and developed to form a mask 3
04. Due to the through holes in the photoresist mask 304, a-Si
The membrane 303 is exposed. That is, when the state of FIG. 5A is viewed from above, the a-Si film 30 is formed in the region 300 as shown in FIG.
3 is exposed, and the other portion is masked by the photoresist.

Next, as shown in FIG.
1 Nickel is deposited as a catalyst element 305 on the surface by thin film deposition. In this embodiment, the thickness of the catalyst element 305 made of nickel is controlled to be about 1 to 2 nm by increasing the distance between the deposition source and the substrate to be larger than usual and reducing the deposition rate. The surface density of nickel on the glass substrate 301 due to the catalytic element 305 at this time was actually measured and found to be about 1 × 10 ¹³ atoms / cm ² . Then, by removing the photoresist mask 304, the catalyst element 3 made of nickel on the mask 304 is removed.
05 is lifted off, and the a-Si film 303 in the region 300 is removed.
In this case, a small amount of the catalytic element 305 such as nickel was selectively added. Then, this is annealed in an inert atmosphere, for example, at a heating temperature of 550 ° C. for 16 hours to be crystallized.

At this time, in the region 300, a-Si
The a-Si film 303 is crystallized in the direction perpendicular to the glass substrate 301 using nickel added to the surface of the film 303 as a nucleus, and a crystalline silicon film 303b is formed. In the peripheral region of the region 300, crystal growth is performed in the lateral direction (direction parallel to the substrate) from the region 300 as indicated by an arrow 306 in FIGS. 4 and 5B, and the crystal growth is performed in the lateral direction. The formed crystalline silicon film 303c is formed. The remaining silicon film region remains as the amorphous silicon film region 303d. The concentration of nickel in the laterally grown crystalline silicon film 303c is 5 × 10 ^16.
It was about atoms / cm ³ . In the crystal growth, the crystal growth distance in the direction parallel to the substrate indicated by arrow 306 was about 80 μm.

Then, as shown in FIG. 5C, laser light 307 is irradiated to recrystallize the silicon film. As the laser light at this time, a XeCl excimer laser (wavelength 308 nm, pulse width 40 nsec) was used.
The irradiation condition of the laser beam 307 is such that the substrate is set to 200 at the time of irradiation.
To 500 ° C., then heated for example to 400 ° C., the energy density 250~400mJ / cm ^2, for example, 350 mJ / cm ²
And The laser beam 307 was sequentially scanned on the substrate surface, and the scanning pitch was set such that an arbitrary point on the silicon film 303 was irradiated with laser 10 times. By this step, the crystalline silicon regions 303b and 303c are heated to a temperature equal to or higher than their melting points, melted and solidified to recombine a part of them as seed crystals, and the crystalline silicon films 303b ′ and It becomes 303c '. Further, the a-Si region 303d is crystallized to become the crystalline silicon film 303a.

Thereafter, as shown in FIG. 5D, the crystalline silicon film 303c 'is formed into an island-shaped crystalline silicon film constituting an active region (a source region, a drain region, and a channel region) of a later TFT. 308n and 308p,
The other crystalline silicon film is removed by etching to separate the elements.

Next, the island-shaped crystalline silicon films 308n, 3n
08p to a thickness of 20 to 150 nm, here 1
A 00 nm silicon oxide film is formed as the gate insulating film 309. Here, TEOS is used for forming the silicon oxide film.
(Tetra Ethoxy Ortho Silica
te) as a raw material, and a substrate temperature of 150 to 60 together with oxygen.
RF plasma C at 0 ° C., preferably 300-400 ° C.
Decomposed and deposited by VD method. After the film formation, the gate insulating film 309 is formed.
Own bulk properties and island-like crystalline silicon film 308
In order to improve the interface characteristics of the gate insulating film 309, annealing was performed at 500 to 600 ° C. for several hours in an inert gas atmosphere.

Next, as shown in FIG. 5E, a thickness of 400 to 800 nm, for example, 50
A 0 nm aluminum (including 0.1 to 2% silicon) film is formed, and the aluminum film is patterned to form gate electrodes 310n and 310p.

Next, by ion doping, impurities (phosphorus and boron) are implanted into the island-shaped crystalline silicon films 308n and 308p to be the active regions by using the gate electrodes 310n and 310p as masks. Phosphine (PH ₃ ) and diborane (B) are used as doping gases.
₂ H ₆ ), in the former case, the acceleration voltage is 60 to 90 k.
V, for example 80 kV, 40 kV to 80 k in the latter case
V, for example, 65 kV, and the dose amount is 1 × 10 ¹⁵ to 8 ×
10 ¹⁵ cm ^-2 , for example, phosphorus is 2 × 10 ¹⁵ cm ^-2 and boron is 5 × 10 ¹⁵ cm ^-2 . By this step, regions which are masked by the gate electrodes 310n and 310p and into which impurities are not implanted are later formed in the channel regions 313n and 313p of the TFT.
Becomes At the time of doping, each element is selectively doped by covering a region where doping is unnecessary with a photoresist. As a result, the source region 314n and the drain region 315 in which N-type impurities are implanted are formed.
A source region 314p and a drain region 315p into which n-type and P-type impurities are implanted are formed, so that an N-type TFT 322 and a P-type TFT 323 can be formed as shown in FIGS. This state is seen from above the substrate as shown in FIG. 4, in which the island-shaped crystalline silicon films 308n and 308p forming the active region are
The crystal growth direction indicated by arrow 306 is arranged so that the carrier movement direction (source → drain direction) is parallel. By adopting such an arrangement, a TFT having higher mobility can be obtained.

Thereafter, as shown in FIG. 5E, annealing is performed by irradiation with a laser beam 312 to activate the ion-implanted impurities. As the laser light, Xe
Cl excimer laser (wavelength 308 nm, pulse width 40
nsec), and the laser beam was irradiated at an energy density of 250 mJ / cm ² for four shots per location.

Subsequently, as shown in FIG.
The silicon oxide film of 00 nm is used as the interlayer insulating film 316, and T
Formed by a plasma CVD method using EOS as a raw material,
A contact hole is formed in this, and the TFT is made of a metal material, for example, a bilayer film of titanium nitride and aluminum.
The source electrode / wiring 317, the source / drain electrode / wiring 318, and the drain electrode / wiring 319 are formed. Finally, annealing is performed at 350 ° C. for about one hour in a hydrogen atmosphere at 1 atm, so that the N-type TFT 322 and the P-type TFT 3
23 is completed.

The CMO fabricated according to the above embodiment
In the S structure circuit, the field effect mobility of each TFT is 150 to ²⁰⁰ cm ² / Vs for the N-type TFT, and the P-type T
The FT has a high value of 100 to 130 cm ² / Vs, and the threshold voltage is 1.5 to ² V for the N-type TFT and -2 to -2.
It shows a very good characteristic of 5V. Furthermore, there is almost no characteristic deterioration due to repeated measurement, and a highly reliable CMOS
A structural circuit was obtained.

Although the third embodiment according to the present invention has been specifically described above, the present invention is not limited to the above-mentioned embodiments, and various modifications based on the technical idea of the present invention are possible. is there.

For example, in addition to the method of forming the underlayer of the silicon oxide film described in the above embodiment, in the sputtering method, reactive sputtering performed in an oxygen atmosphere using single crystal silicon as a target is also possible. Thermal CV
It may be formed by the method D, and may be subjected to a necessary heat treatment after the film formation.

When the a-Si film is crystallized, X
Although an eCl excimer laser was used, the same effect can be obtained when crystallized by various other strong light irradiation, and a KrF excimer laser having a wavelength of 248 nm or,
The same applies to a continuous oscillation Ar laser having a wavelength of 488 nm.

In the third embodiment, the solid-phase crystal growth method employs a method in which a catalytic element is selectively introduced and crystallized, but a method in which the catalytic element is introduced over the entire a-Si film. Is also effective in terms of process simplification. Further, the same effect can be obtained by using a normal solid phase crystal growth method without using a catalytic element. In the third embodiment, as a method of introducing a trace amount of nickel as a catalyst element, a method of forming a nickel thin film on the surface of an a-Si film by a vapor deposition method is employed, but various other methods can be used. . For example, a-
A method of applying an aqueous solution of nickel salt on the surface of the Si film, a method of forming a thin film by a sputtering method or a plating method, a method of directly introducing it by an ion doping method, or the like can be used. Further, as the impurity metal element that promotes crystallization, cobalt, palladium, platinum, copper, silver, gold, indium, tin, aluminum, or antimony can be used in addition to nickel.

Further, as an application of the present invention, in addition to an active matrix type substrate for liquid crystal display, for example, a contact type image sensor, a thermal head with a built-in driver, and a driver built-in type using an organic EL as a light emitting element. An optical writing element, a display element, a three-dimensional IC, etc. can be considered. By using the present invention, high performance such as high speed and high resolution of these elements can be realized. Further, the present invention is not limited to the MOS type transistor described in the above embodiment,
It can be widely applied to all semiconductor processes including a bipolar transistor and an electrostatic induction transistor using a crystalline semiconductor as an element material.

[0113]

By using the present invention, the conventional problems can be solved in general semiconductor devices using a crystalline silicon film crystallized in a melting and solidifying process by energy beam irradiation as an element material, and high performance can be achieved. Further, it is possible to realize a thin film semiconductor device having high reliability and stability, and having excellent property uniformity among a plurality of elements. Particularly in the liquid crystal display device, the characteristics of individual TFTs can be made uniform in the panel, and a high display level liquid crystal display device without display defects due to laser sequential scanning can be obtained. Further, in a TFT that constitutes a thin film integrated circuit, the required high performance and high reliability are satisfied, and particularly, N-type TFT and P-type TFT
With a CMOS circuit having, since it almost as the absolute value of the threshold voltage V _TH, there is no need to perform the control process of the threshold voltage V _TH, such as conventionally required channel doping.

Then, a full driver monolithic active matrix substrate which constitutes an active matrix portion and a peripheral drive circuit portion on the same substrate can be realized by a simple manufacturing process, and the module can be made compact, high performance and low cost. Can be achieved.

[Brief description of the drawings]

FIG. 1 shows a manufacturing process of a first embodiment.

FIG. 2 shows an outline of a second embodiment.

FIG. 3 shows a manufacturing process of a second embodiment.

FIG. 4 shows an outline of a third embodiment.

FIG. 5 shows a manufacturing process of a third embodiment.

FIG. 6 shows the relationship between the H ₂ O concentration in a base film and the resistance of a silicon film.

FIG. 7 shows the relationship between the concentration of SiOH groups in the underlying film and the resistance of the silicon film.

FIG. 8 shows an AFM image of a silicon film surface crystallized by laser irradiation.

[Explanation of symbols]

101, 201, 301 Glass substrate 102, 202, 302 Base film 103, 203, 303 Amorphous silicon (a-
Si) film 204, 304 mask 305 catalytic element 306 arrow 107, 207, 307 laser light 108, 208, 308 active region (island-like crystalline silicon film) 109, 209, 309 gate insulating film 110, 210a 310 gate electrode 210b upper part Electrode 111 Oxide layer 112, 312 Laser light 113, 213, 313 Channel region 114, 214, 314 Source region 115, 215, 315 Drain region 116, 216, 316 Interlayer insulating film 117, 217 Source electrode 317 Source electrode / wiring 318 Source and drain electrodes / wirings 319 Drain electrodes / wirings 120, 220 Pixel electrodes 121, 221 Pixel TFTs 322 N-type TFTs 323 P-type TFTs 224 Storage capacitors (Cs)

Claims (15)

[Claims] 1. A semiconductor device in which a thin film semiconductor element having, as an active region, a crystalline silicon film formed in contact with a base film containing silicon oxide as a main component is formed on a substrate, wherein the active region is formed. Is a crystalline silicon film crystallized in the process of melting and solidifying by energy beam irradiation, and the underlayer film has a water (H ₂ O) concentration of about 1 × 10
A semiconductor device comprising an insulating film having a density of ²⁰ pieces / cm ³ or less. _{2. The} water content (H ₂
2. The semiconductor device according to claim 1, wherein the concentration of O) is further about 1 × 10 ¹⁹ / cm ³ or less. 3. A semiconductor device in which a thin film semiconductor element having a crystalline silicon film in contact with a base film containing silicon oxide as a main component as an active region is formed on a substrate. Is a crystalline silicon film crystallized in the melting and solidification process by energy beam irradiation, and the base film has a SiOH group concentration of about 1 × 10 ^21.
2. A semiconductor device comprising an insulating film having a density of not more than ³ pieces / cm ³ . 4. A semiconductor device in which a thin film semiconductor element having a crystalline silicon film in contact with a base film mainly composed of silicon oxide as an active region is formed on a substrate. Is a crystalline silicon film crystallized in the process of melting and solidifying by energy beam irradiation, and the underlayer film has a water (H ₂ O) concentration of about 1 × 10
A semiconductor device, which is an insulating film having ²⁰ / cm ³ or less and a concentration of SiOH groups contained in the film of about 1 × 10 ²¹ / cm ³ or less. 5. A semiconductor device having a plurality of thin film transistors formed on a substrate and in contact with a base film containing silicon oxide as a main component, wherein channel regions of the plurality of thin film transistors are sequentially scanned and irradiated with pulsed laser light. The underlying film made of a crystallized crystalline silicon film and formed as a lower layer in contact with the channel region has a water (H ₂ O) concentration of about 1 × 10 ²⁰ / cm ³ or less. The concentration of the SiOH group contained in the insulating film and / or the film is about 1 × 10 ²¹ / cm ³
A semiconductor device comprising an insulating film described below. 6. A thin film transistor formed on a substrate and driving a plurality of pixel electrodes formed in contact with a base film containing silicon oxide as a main component, wherein each thin film transistor assists in parallel with a liquid crystal capacitance by the pixel electrode. In a semiconductor device in which capacitive components are connected, the concentration of water (H ₂ O) contained in the film is about 1 × 10 ²⁰ pieces /
cm ³ or less of insulating film and / or Si contained in the film.
A channel region of the thin film transistor and a storage capacitor component connected to the thin film transistor are formed by using a crystalline silicon film on a base film made of an insulating film having an OH group concentration of about 1 × 10 ²¹ / cm ³ or less. A semiconductor device comprising: one of the electrodes. 7. The water content (H) contained in the film on the substrate.
₂ O) a step of forming an insulating film having a concentration of about 1 × 10 ²⁰ / cm ³ or less; a step of forming a silicon film on the insulating film; A method of manufacturing a semiconductor device, comprising at least a step of crystallizing in a process and a step of using a silicon film as an active region to complete a thin film semiconductor device. 8. A step of forming on the substrate an insulating film having a concentration of SiOH groups contained in the film of about 1 × 10 ²¹ pieces / cm ³ or less, and a step of forming a silicon film on the insulating film. A semiconductor device comprising: a step of irradiating the silicon film with an energy beam to crystallize in a melt-solidification process; and a step of using the silicon film as an active region to complete a thin-film semiconductor device. Manufacturing method. 9. The method according to claim 7, wherein the base film is a silicon film formed by a sputtering method at a substrate temperature of 150 ° C. or higher. 10. The base film is a silicon oxide film which is formed by a plasma CVD method using SiH ₄ gas and N ₂ O gas as materials and is then subjected to heat treatment at 550 ° C. or higher. 9. The method of manufacturing a semiconductor device according to claim 7 or 8. 11. A silicon oxide film formed by a plasma CVD method using an organic silane-based gas such as TEOS and an oxygen gas as materials, and then subjected to a heat treatment at 550 ° C. or higher. Said claim 7
Alternatively, the method for manufacturing a semiconductor device according to item 8. 12. A step of forming an amorphous silicon film on the base film and crystallizing the amorphous silicon film in a solid state by heating, and irradiating the crystallized silicon film with an energy beam to solidify it. 9. The step of recrystallizing the silicon film by performing the above process.
A method for manufacturing a semiconductor device as described above. 13. The step of forming an amorphous silicon film on the base film and crystallizing the amorphous silicon film in a solid state by heating the amorphous silicon film, 13. The method of manufacturing a semiconductor device according to claim 12, wherein the method is performed after introducing a promoting catalytic element. 14. The step of crystallizing the amorphous silicon film in a solid state by heating the amorphous silicon film, selectively introducing a catalytic element for promoting the crystallization into the amorphous silicon film, and performing a heat treatment. By performing crystal growth in the lateral direction from the region where the catalytic element is selectively introduced, to the periphery thereof, the active region of the semiconductor device is formed using the region where the crystal is grown in the lateral direction. 14. The method for manufacturing a semiconductor device according to claim 13, wherein the method is formed. 15. The energy beam applied to the silicon film has an energy density of 250 to 400 mJ /.
9. The method for manufacturing a semiconductor device according to claim 7, wherein the pulse laser is a cm ² pulse laser.