Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2001-04-19
2004-03-16
Pham, Long (Department: 2814)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S023000, C438S024000, C438S152000, C438S155000, C438S156000, C438S162000, C438S163000, C438S164000
Reexamination Certificate
active
06706544
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light emitting device which has an element with a luminescent material put between electrodes, a manufacturing method thereof, and an electronic appliance using the light emitting device for the display (an indication display or a displaying monitor), particularly to a light emitting device using a luminescent material by which EL (Electro Luminescence) can be obtained (hereinafter referred to as an EL material) and a manufacturing method thereof. The light emitting device according to the present invention includes an organic EL display and an OLED (Organic Light Emitting Diode).
The luminescent material that can be used in the present invention includes all of materials which emit light (phosphorescence and/or fluorescence) through singlet excitation, triplet excitation, or both.
2. Description of the Related Art
Recently, there has been proceeding development of light emitting devices (hereinafter referred to as EL light emitting devices) using self-light emitting elements (hereinafter referred to as EL elements) to which EL phenomenon of luminescent materials is applied. The EL light emitting devices, being display devices using self-light emitting elements, necessitate no back-lighting as in liquid crystal display devices. Furthermore, with their wide viewing angles, the EL light emitting devices attract attention for being used as displays of portable units used outdoors.
There are two types of the EL light emitting device, i.e. an active matrix type and a passive matrix type there has been development of both types actively carried out. At present, the active matrix type EL light emitting device is particularly noted. The active matrix type EL light emitting device is characterized in that a thin film transistor (hereinafter referred to as TFT) is provided for each of pixels of a pixel section to control an amount of current flowing in an EL element.
The advantage of the active matrix type is that a highly fine image can be displayed and an image with larger amount of information can be provided.
However, it makes a manufacturing process complicated to provide the TFT for each of the pixels, and there are caused problems of reduction in yield and increase in manufacturing cost due to a protracted manufacturing term. In particular, many photolithography steps cause remarkable reduction in yield, and reduction in number of photolithography steps was an important subject.
SUMMARY OF THE INVENTION
In view of the above-mentioned problem, it is an object of the present invention to provide an inexpensive light emitting device and a manufacturing method thereof, for which the number of photolithography steps is reduced for improving yield and shortening manufacturing term to reduce manufacturing cost. In addition, it is another object of the present invention to provide an inexpensive electronic appliance for which an inexpensive light emitting device is used as a display.
In order to achieve the above objects, the light emitting device according to the present invention is characterized with a gate electrode comprising a plurality of layers each with a different kind of conductive film, and the conductive films with respectively different thicknesses are provided by making use of their selectivity in etching and are used as masks for adjusting concentrations of impurity regions formed in an active layer. The above reduces the number of photolithography steps in relation to manufacturing the TFT for improving yield of the light emitting device and shortening manufacturing term thereof.
A typical manufacturing process of an n-channel TFT which characterizes the present invention will be explained with reference to
FIGS. 1A through 1E
. In
FIG. 1A
, reference numeral denotes an insulator
100
, which is a substrate provided with an insulating film thereon, an insulating substrate, or an insulating film. On the insulator
100
, there is formed a semiconductor film (typically a silicon film)
101
which becomes an active layer of the TFT. The semiconductor film
101
is covered with an insulating film
102
containing silicon, which film becomes a gate insulating film of the TFT. For the insulating film containing silicon, silicon oxide film, silicon nitride film, silicon oxynitride film, or a laminated film of combination of them can be used.
Next, on the insulating film
102
containing silicon, there is formed a first conductive film
103
and a second conductive film
104
. Here, it is important that the first conductive film
103
and the second conductive film
104
are allowed to have selectivity to each other in etching. Specifically, it can be said that it is important that there is an etching condition under which the second conductive film
104
can be etched with the first conductive film
103
being left.
Typical combination of the first conductive film
103
and the second conductive film
104
are listed as 1) the combination of a tantalum nitride film as the first conductive film and a tungsten film as the second conductive film, 2) the combination of a tungsten film as the first conductive film and an aluminum film as the second conductive film, or 3) the combination of a titanium nitride as the first conductive film and a tungsten film as the second conductive film.
In the above combination of 1), the tungsten film and the tantalum nitride film are etched by a combination of chlorine (Cl
2
) gas and carbon tetrafluoride (CF
4
) gas. By adding oxygen (O
2
) gas to the gasses with the combination an etching rate of the tantalum nitride film is extremely reduced to allow to provide selectivity for the conductive films.
Moreover, in the above combination of 2), with the combination of bromine trichloride (BrCl
3
) gas and chlorine (Cl
2
) gas, an aluminum film is etched and a tungsten film is not. Furthermore, with the combination of chlorine (Cl
2
) gas and carbon tetrafluoride (CF
4
) gas, a tungsten film is eched, but an aluminum film is not. In this way, selectivity can be provided for both of the conductive films.
Next, as shown in
FIG. 1B
, the first conductive film
103
and the second conductive film
104
are etched by using a resist mask
105
to form a gate electrode
106
. Here, a gate electrode obtained by etching the first conductive film is to be referred to as a first gate electrode, and a gate electrode obtained by etching the second conductive film is to be referred to as a second gate electrode. Therefore the gate electrode
106
comprises the first electrode
106
a
and the second gate electrode
106
b.
The gate electrode
106
is preferably formed in a tapered shape with an etching condition. Being tapered is that an edge face of the electrode has an inclined part with an angle between the edge face and the under film which is referred to as a tapered angle. To be formed in the tapered shape is that the electrode is formed in a shape with edges each being inclined with a tapered angle. A trapezoid is included in a tapered shape.
In forming the gate electrode
106
, the gate insulating film
102
is also etched slightly to be a little thinned. The thinning is preferably restrained within 20 to 50 nm although it is differed depending on etching conditions.
In this state, an impurity element (hereinafter referred to as n-type impurity element) is added into the semiconductor film
101
for making the semiconductor an n-type semiconductor. At this time, the gate electrode
106
is used as a mask to add the n-type impurity element to the semiconductor film
101
in being self-aligned. As a specific n-type impurity, an element which belongs to group fifteen in the periodic table (typically phosphorus or arsenic) can be used.
A well-known plasma doping method or an ion implantation method can be used as the method for addition. The impurity element can be added to the semiconductor film in concentrations from 1×10
20
to 1×10
21
atoms/cm
3
. Each of regions
107
and
108
with addition of an n-type impurity element in such concentrations is to be
Fukunaga Takeshi
Inukai Kazutaka
Koyama Jun
Yamazaki Shunpei
Costellia Jeffrey L.
Nixon & Peabody LLP
Pham Long
Semiconductor Energy Laboratory Co,. Ltd.
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