Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Amorphous semiconductor material
Reexamination Certificate
2001-08-22
2004-05-18
Everhart, Caridad (Department: 2825)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Amorphous semiconductor material
C257S064000
Reexamination Certificate
active
06737672
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims priority of Japanese Patent Application Nos. 2000-255646 and 2001-202730, filed on Aug. 25, 2000 and Jul. 3, 2001, the contents being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor devices, manufacturing methods of the same, and semiconductor manufacturing apparatus, in particular, for being suitably applied to a so-called system-on panel, in which a pixel region including thin film transistors and a peripheral circuit region including thin film transistors are formed on a non-crystallized (amorphous) substrate such as a non-alkali glass substrate.
2. Description of the Related Art
A TFT (Thin Film Transistor) is formed on a very thin, fine active semiconductor film. The TFT is examined to be mounted on a large-screen liquid crystal panel or the like in consideration of recent demands for an increase in area. In particular, applications to a system-on panel and the like are expected.
On the system-on panel, polycrystalline semiconductor TFTs (especially polysilicon TFTs (p-Si TFTs)) are formed on a non-crystallized substrate such as a non-alkali glass substrate. In this case, as a popular method, an amorphous silicon (a-Si) film is formed as a semiconductor film, and then irradiated with an ultraviolet short-pulse excimer laser to fuse and crystallize only the a-Si film without influencing the glass substrate, thereby obtaining a p-Si film functioning as an active semiconductor film.
Excimer lasers which emit high-output linear beams coping with a large area of the system-on panel have been developed. A p-Si film obtained by excimer laser crystallization is readily influenced by not only the irradiation energy density but also the beam profile, the state of the film surface, or the like. It is difficult to form uniformly a p-Si film large in crystal grain size in a large area. A sample crystallized by an excimer laser was observed with an AFM to find that crystal grains isotropically growing from nuclei produced at random exhibited a shape close to a regular polygonal shape, projections were observed at a crystal grain boundary at which crystal grains collided against each other, and the crystal grain size was less than 1 &mgr;m, as shown in FIG.
37
.
In this manner, when a TFT is fabricated using a p-Si film obtained by crystallization using an excimer laser, a channel region contains many crystal grains. If the crystal grain size is large, and the number of grain boundaries present in the channel is small, the mobility is high. If the crystal grain size at a channel region portion is small, and the number of grain boundaries present in the channel is large, the mobility is low. Thus, the transistor characteristics of the TFT readily vary dependently on the grain size. In addition, the crystal grain boundaries have many defects, and the presence of the grain boundaries in the channel suppresses transistor characteristics. The mobility of the TFT attained by All this technique is about 150 cm
2
/Vs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide semiconductor devices including TFTs in which the transistor characteristics of the TFTs are made uniform at a high level, and the mobility is high particularly in a peripheral circuit region to enable high-speed driving in applications to peripheral circuit-integrated TFT-LCDs, system-on panels, system-on glasses, and the like.
It is another object of the present invention to provide semiconductor devices in which the insufficiency of the output of an energy beam, which outputs energy continuously in relation to time, is compensated so that the throughput in crystallization of semiconductor films is improved, thereby realizing highly efficient TFTs whose mobility is high particularly in a peripheral circuit region to enable high-speed driving.
It is still another object of the present invention to provide manufacturing methods of such semiconductor devices.
It is still another object of the present invention to provide apparatus for manufacturing such semiconductor devices.
According to the first aspect of the present invention, there is provided a method of manufacturing a semiconductor device in which a pixel region having thin film transistors and a peripheral circuit region are formed on a non-crystallized substrate, comprising crystallizing a semiconductor film formed in the peripheral circuit region with an energy beam which outputs energy continuously along a time axis at least for the peripheral circuit region, thereby forming the semiconductor film into active semiconductor films of the respective thin film transistors.
In this case, the energy beam is preferably a CW laser beam, more preferably, a solid state laser beam (DPSS (Diode Pumped Solid State Laser) laser beam).
By crystallizing a semiconductor film with an energy beam which outputs energy continuously along the time axis, the crystal grain size is increased, e.g., the crystalline state of the semiconductor film is formed into a streamlined flow pattern having long crystal grains in the energy beam scan direction. The crystal grain size in this case is 10 to 100 times the size obtained by crystallization using a currently available excimer laser.
In the first aspect, each semiconductor film is preferably patterned into a linear or island shape on the non-crystallized substrate.
The crystallization technique using a CW laser has conventionally been studied in the SOI field, but a glass substrate has been considered not to resist heat. When a glass substrate is irradiated with a laser while an a-Si film is formed as a semiconductor film on the entire surface, the temperature of the glass substrate rises along with the temperature rise of the a-Si film, and damage such as cracks is observed. In the present invention, the semiconductor film is processed into a linear or island shape in advance to prevent the temperature rise of the glass substrate, generation of cracks, and diffusion of impurities into a film. Even in forming the active semiconductor film of a TFT on a non-crystallized substrate such as a glass substrate, an energy beam which outputs energy continuously along the time axis from a CW laser or the like can be used without any problem.
In the first aspect, an energy beam irradiation positioning marker corresponding to each patterned semiconductor film is formed on the non-crystallized substrate.
This marker can suppress an irradiation position shift of the energy beam. Supply of a stable continuous beam enables so-called lateral growth, and a semiconductor film having large-size crystal grains can be reliably formed.
In the first aspect, it is preferable that slits be formed in each semiconductor film patterned on the non-crystallized substrate, or thin-line insulating films be formed on each semiconductor film, and the semiconductor film be irradiated with the energy beam in an almost longitudinal direction of the slits.
In this case, the slits or insulating films (to be simply referred to as slits hereinafter for convenience) block crystal grains and grain boundaries which grow inward from the periphery in crystallization by irradiation of an energy beam. Only crystal grains which grow parallel to the slits are formed between the slits. If the region between the slits is satisfactorily narrow, single crystals are formed in this region. In this manner, the channel region can be selectively changed into a monocrystalline state by forming the slits so as to set a region where large-size crystal grains are to be formed, e.g., the region between the slits as the channel region of a semiconductor element, e.g., thin film transistor.
In the first aspect, it is preferable that an irradiation condition of the energy beam which outputs energy continuously along the time axis be changed between the pixel region and the peripheral circuit region, that a semiconductor film formed in the pixel region be crystallized with an energy beam which outputs energy pulses, and t
Hara Akito
Sasaki Nobuo
Takeuchi Fumiyo
Yoshino Kenichi
Everhart Caridad
Fujitsu Limited
Greer Burns & Crain Ltd
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