Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2001-02-16
2003-11-18
Bueker, Richard (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S726000, C209S127100, C209S128000, C209S129000, C209S130000, C096S016000, C073S028020, C073S865500
Reexamination Certificate
active
06648975
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and apparatuses for fabricating quantum dot functional structures, quantum dot functional structures, and optically functioning devices. More particularly, the present invention relates to a method and an apparatus for fabricating a quantum dot functional structure, a quantum dot functional structure, and an optically functioning device, which provide the following outstanding features. The features make it possible to control the diameter of and alleviate the contamination of ultra-fine particles that are expected to provide various functions resulting from the quantum size effects. The features also make it possible to provide an improved efficiency for the optically functioning device fabricated using a quantum dot functional structure, in the transparent medium of which the ultra-fine particles are distributed homogeneously.
2. Description of the Prior Art
To employ semiconductor ultra-fine particles formed of Si families of IV materials for use in an optically functioning device that can emit light in the visible spectrum, it is indispensable to provide spherical ultra-fine particles which are controlled on the order of one nanometer in diameter. Moreover, the laser ablation method is preferably applied to the fabrication of the ultra-fine particles on the order of one nanometer in diameter.
For example,
FIG. 1
is a conceptual view depicting an apparatus, disclosed in Japanese Patent Disclosure No. 9-275075, for applying the laser ablation method to a conventional target material to fabricate ultra-fine particles by deposition.
Referring to
FIG. 1
, a laser light beam is emitted from an excimer laser source
1
and travels through an optical system constituted by a slit
2
, a condenser lens
3
, a mirror
4
, and a laser light inlet window
5
to be guided into a vacuum reaction chamber
6
, where the laser light beam is focused on and thus radiates the surface of a target material
8
placed in a target holder
7
, which is arranged inside the vacuum reaction chamber
6
.
In addition, there is arranged a deposition substrate
9
in a direction normal to the surface of the target material
8
. Substances detached or ejected from the target material
8
by laser ablation are captured or deposited on the deposition substrate
9
.
An explanation will be given below in more detail to a case where semiconductor ultra-fine particles are fabricated with Si being employed as the target material in the apparatus configured as described above.
First, the vacuum reaction chamber
6
is pumped down to an ultra-high vacuum of pressure 1×10
−8
Torr by means of an ultra-high vacuum exhaust system
10
, which is mainly constituted by a turbo-molecular pump, and then the ultra-high vacuum exhaust system
10
is closed.
Subsequently, a helium (He) gas is introduced through a rare-gas guide line
11
into the vacuum reaction chamber
6
. The vacuum reaction chamber
6
is held at a constant pressure (of 1.0 to 20.0 Torr) with the low-pressure rare gas (He), the flow of which is controlled by means of a mass-flow controller
12
and which is differentially exhausted by means of a differential exhaust system
13
mainly consisting of a dry rotary pump. In the He gas atmosphere kept at a pressure of a few Torr, the surface of the target material is radiated with a laser light beam of a high-energy density (e.g., 1.0 J/cm
2
or greater) to cause the substances to be detached or ejected from the target material.
The detached substance gives kinetic energy to the surrounding gas molecules, which are in turn urged to condense and grow in the gas atmosphere into ultra-fine particles of a few to a few tens of nanometers in diameter, the ultra-fine particles being deposited on the deposition substrate
9
.
Originally, since the IV-group semiconductors are an indirect bandgap material, their bandgap transitions cannot be dispensed with phonons. The materials naturally cause much heat to be generated in their recombination, thus providing significantly decreased radiative recombination probability. However, the material shaped in ultra-fine particles having a diameter of a few nanometers causes the wave number selection rule to be relaxed in bandgap transitions and the oscillator strength to be increased. This in turn increases the probability of occurrence of radiative electron-hole pair recombination, thereby making it possible to provide intense light emission.
Here, the wavelength of emitted light (i.e., the energy of emitted photons) is controlled by making use of an increase in absorption edge emission energy (corresponding to bandgap Eg) provided by the quantum confinement effect resulted from a decrease in diameter of ultra-fine particles.
FIG. 2
is an explanatory graph showing the correlation between the diameter of the aforementioned ultra-fine particles and the absorption edge emission energy thereof.
That is, to emit light at a single wavelength, it is indispensable to make the diameter of the ultra-fine particles uniform. If ultra-fine particles of a diameter corresponding to the emission wavelength can be generated and deposited within as narrow a diameter distribution as possible, it is made possible to fabricate an optically functioning device for emitting light of a single color.
As described in the aforementioned prior art, it is required to generate and deposit ultra-fine particles having a particle diameter distribution controlled to provide a single diameter of a few nanometers in order to fabricate an optically functioning device for emitting light at a single wavelength using semiconductor ultra-fine particles.
The prior art makes it possible to control the mean particle diameter by selecting as appropriate the pressure of an atmospheric rare gas or the distance between the target material and the deposition substrate. However, the prior art provides a still broad particle diameter distribution. Thus, it is difficult to obtain semiconductor ultra-fine particles of a uniform diameter distribution having, for example, a geometric standard deviation &sgr;g of 1.2 or less.
That is, this means that more aggressive particle diameter control is required. In addition, nm-sized ultra-fine particles are very sensitive to the contamination of impurities or defects due to their high surface atom ratio (e.g., about 40% at a particle diameter of 5 nm).
That is, it is required to provide a clean and damage-less process as a method for generating and depositing the particles. Moreover, adhering and depositing semiconductor ultra-fine particles directly onto a deposition substrate as in the prior art would tend to result in a thin film of a porous structure formed of a deposit of ultra-fine particles.
Suppose that electrodes are connected to such a porous structure to allow it to function as an optically functioning device. In this case, it may be required to optimize the structure somehow. On the other hand, in order to derive the quantum size effect originally provided for spherical ultra-fine particles to implement a new optical function representative of light emission, further optimized shape and structure may be required such as a structure having particles distributed homogeneously in a stable transparent medium.
In addition, since nm-sized ultra-fine particles have a very sensitive surface as described above, it may become necessary to form a quantum dot functional structure having the particles being homogeneously distributed in a stable transparent medium.
In addition, in order to obtain fine particles having a specified particle diameter, a fine particle classifier may be used for classifying the diameter of fine particles using the mobility which is dependent on the particle diameter. Such a fine particle classifier has been used for performance test of high-performance air filters for collecting and separating sub-micron fine particles with high efficiency, and for generating standard fine particles and measuring the particle diameter upon monitoring of cleaned atmospher
Aya Nobuhiro
Makino Toshiharu
Seto Takafumi
Suzuki Nobuyasu
Yamada Yuka
Browdy and Neimark , P.L.L.C.
Bueker Richard
Matsushita Electric - Industrial Co., Ltd.
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