Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Amorphous semiconductor material
Reexamination Certificate
1998-09-04
2002-03-12
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Amorphous semiconductor material
C257S072000
Reexamination Certificate
active
06355940
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention relates to a semiconductor device and a method for manufacturing a semiconductor device, particularly a display included a built-in driver circuit which is integrated a thin film transistor (TFT) as a switching element for a display area and also configuring a driver circuit on the panel end, and used for an active matrix display device such as a liquid crystal display (LCD) and an electroluminescent (EL) display.
b) Description of the Related Art
Due to their advantages in terms of compactness, thinness and reduced power consumption, LCDs have come into widespread practical use in the fields of OA equipment and AV equipment in recent years. In particular, an active matrix type LCD with a TFT arranged on each pixel as a switching element for controlling rewriting timing of pixel data can display moving pictures on a large display with high resolution and is used for various types of TVs and as monitors for personal computers and the like.
An EL display device having organic EL as an optical member was also developed to remedy viewing angle-dependent problems of LCDs. TFTs are also used as switching elements to drive each EL element.
A TFT is a field effect transistor (FET), which is obtained by forming a metal layer and a semiconductor layer into a predetermined shape on an insulating substrate. In the active matrix type LCD, the TFT is connected to each capacitor, which is formed between a pair of substrates with liquid crystal sandwiched therebetween to drive the liquid crystal.
Specifically, instead of amorphous silicon (a-Si) which has been used a lot as the semiconductor layer, LCD using polycrystalline silicon (p-Si) was developed. Annealing with laser light is also used for forming or growing p-Si grains. Generally, p-Si has higher mobility than a-Si, a TFT is downsized, and a high aperture ratio and high resolution can be achieved. Since a gate self-align structure can be adopted, a TFT can be made fine, and parasitic capacitance can be decreased. Thus, the TFT can be made fast. An electrical complementary connection structure of n-ch TFT and P-ch TFT, namely CMOS (complementary metal oxide semiconductor), can also be formed, and a high-speed driving circuit can be configured. Therefore, integral formation of the driving circuit in the periphery of the pixel area on the same substrate allows reduction in the manufacturing cost and reduction in size of the LCD module.
Methods for forming a p-Si film on the insulating substrate include annealing for crystallization of a-Si prepared at a low temperature and a solid phase crystallization in a high temperature state, both requiring processing at a high temperature of 600° C. or more. Therefore, an inexpensive non-alkali glass substrate cannot be used as the insulating substrate because of its inferior heat resistance, and an expensive quartz glass substrate is required, resulting in high costs. Meanwhile, there is developed a method enabling the use of a non-alkali glass substrate as the insulating substrate. This method employs laser annealing to polycrystallize silicon with a substrate at a relatively low temperature of 600° C. or below. Such a process having a processing temperature of 600° C. or below throughout the whole process of the TFT substrate production is called a low-temperature process, which is essential for mass-production of low-cost LCDS.
FIG. 1
is a plan view showing relationships between a subject substrate
1
to be processed and irradiating and scanning directions of the excimer laser in the excimer laser annealing (ELA) effected by irradiating laser light. The subject substrate
1
is an ordinary non-alkali glass substrate, which has a-Si formed on its surface. The substrate
1
is a mother glass substrate having six active matrix substrates
5
for constituting an LCD. The individual active matrix substrate
5
comprises a display area
2
having pixels arranged in a matrix at the center, and a gate driver
43
and a drain driver
44
which are formed around the display area
2
. In the display area
2
, a pixel electrode which is one of the electrodes of a pixel capacitor for driving the liquid crystal is to be arranged in a matrix, and p-Si TFTs which are prepared by polycrystallizing by ELA are connected to them. The gate driver
43
is mainly formed of a shift resister, while the drain driver
44
is mainly formed of a shift resister and a sampling circuit. These drivers
43
,
44
are formed of TFT arrays such as CMOS using the p-Si film prepared by polycrystallization by ELA.
A pulse laser is used for ELA, and each pulse laser beam being irradiated has its edge indicated as C having, e.g., a line width of 0.5 to 1.0 mm and a line length of 80 to 150 mm, in FIG.
1
. The line beam is moved on the subject substrate
1
while overlapping as predetermined, so that the laser light is fully irradiated to process a large area of the substrate
1
, thereby polycrystallizing a-Si.
FIG. 2
shows TFTs formed on the subject substrate
1
, and particularly a plan configuration of an inverter portion used at respective parts in the drivers
43
,
44
.
FIG. 3
is a sectional view taken along line B—B of
FIG. 2. A
gate electrode
51
connected to an input of the inverter is formed on a transparent substrate
50
of a non-alkali glass substrate or the like, and a gate insulating film
52
is formed to cover the gate electrode
51
.
A p-Si film
53
, which is formed by ELA, is formed on the gate insulating film
52
like islands to lie across over the gate electrode
51
in N-ch and P-ch areas. The part of the p-Si film
53
just above the gate electrode
51
is a non-doped channel area CH. On the N-ch side, an LD (lightly doped) area LD doped with a low concentration of N-type impurities is formed on both sides of the channel area CH, and a source area NS and a drain area ND, which are doped with a high concentration of N-type impurities, are formed next to the LD areas LD. On the P-ch side, the non-doped channel area CH has on both its sides a source area PS and a drain area PD which are doped with a high concentration of P-type impurities.
An implantation stopper
54
used to form the source and drain areas PS, PD remains on the channel area CH. An interlayer insulating film
55
is formed to cover the p-Si film
53
and the implantation stopper
54
. A source electrode
56
and a drain electrode
57
are formed on the interlayer insulating film
55
and connected to the source areas NS, PS and the drain areas ND, PD of the p-Si film
53
through contact holes CT formed in the interlayer insulating film
55
. The drain electrode
57
is connected to an output of the inverter, the source electrode
56
on the N-ch side to a low voltage source, and the source electrode
56
on the P-ch side to a high voltage source.
An insulating film
58
having a planarization is formed to fully cover the electrodes. A TFT used as the switching element on the display area
2
is generally an N-ch type and has the same structure as the left sides of FIG.
2
and
FIG. 3. A
pixel electrode (not shown) for driving the liquid crystal is formed on the planarizating insulating film
58
and connected to the source electrode
56
through the contact holes formed in the planarizating insulating film
58
.
FIG. 2
shows particularly the inverter portion of the drivers
43
,
44
. Such an element related to the logical operation is determined at the time of designing to have a W/L value so to decide performance characteristics. Accordingly, the TFT of N-ch and P-ch shown in
FIG. 2
has the island layer of the p-Si film
53
and the gate electrode
51
which are formed to have a width and the like so to fulfill a designed channel width W and a designed channel length L. A single channel area CH having such a value is formed for the individual element.
The p-Si film formed by the excimer laser annealing (ELA) has a disadvantage that a grain size does not become large enough, and a linear area poor in crystallinity is produced in sides of a linear pulse laser beam
Kihara Katsuya
Koga Masayuki
Crane Sara
Hogan & Hartson L.L.P.
Sanyo Electric Co,. Ltd.
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