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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor
chips for display, and more particularly to a method of thermally treating
a semiconductor thin film with laser irradiation.
2. Description of Related Art
Liquid crystal display devices which are designed in a large size and with
high minuteness and in which polycrystal silicon thin film transistors are
used as switching elements have been developed with much hope. In order to
mass-produce liquid crystal displays with polycrystal silicon thin film
transistors in a large size and with high minuteness, it is indispensable
to establish a low-temperature process in which low-price glass substrates
are usable. A technique that a laser beam is irradiated onto a
semiconductor thin film of amorphous silicon or the like to form
high-quality polycrystal silicon on a glass substrate having a low melting
point has been greatly expected as a method to perform the low-temperature
process.
FIG. 1 is a schematic diagram showing a previous paper suggested laser beam
irradiation method. A semiconductor chip 101 for display which is a target
to be processed has such a laminating structure that a semiconductor thin
film 103 is formed on a transparent insulating substrate 102. In this
method, a laser beam 105 is irradiated onto a predetermined sectioned area
104 which is provided on the semiconductor thin film 103. In the
conventional method, the output power of the laser beam is limited to a
small level, and thus the maximum area which can be irradiated with
one-shot laser irradiation of laser is limited to a narrow area about 100
.mu.m.sup.2. Accordingly, when a semiconductor thin film 103 having a
large area is required to be processed to satisfy a requirement for a
large-scale picture, the laser beam is irradiated onto the whole
semiconductor thin film while scanning the laser beam 105 or shifting the
laser-irradiation area stepwisely. That is, it has been hitherto
considered important to increase the energy density of the laser beam
rather than to narrow the laser-irradiation area down. With increase of
the energy density, a semiconductor thin film of amorphous silicon or
polycrystal silicon having relatively small grain size is perfectly melted
to increase its grain size. In this method, however, an irradiation time
per chip increases and thus manufacturing throughput is reduced.
Furthermore, the scanning of the irradiation of the laser beam causes
temperature difference to occur locally, and thus causes increase in
variability of crystal grain size. Therefore, wide variations occur in
electrical characteristics of the thin film transistors such as mobility,
a threshold voltage, etc.
The above point will be described in detail with reference to FIG. 2.
In the method as described above, the semiconductor thin film 103 having a
large area is crystallized by irradiating a laser beam onto a small area
while scanning the laser beam as shown in FIG. 2. Accordingly,
non-uniformity of crystallization occurs at an overlap area 106 between a
laser shot and a next laser shot, so that the electrical characteristics
of thin film transistors formed at the overlap area 106 are uneven. For
example, the overlap area 106 is subjected to the laser irradiation
several times, whereas the other areas are subjected to the laser
irradiation only once, so that the heating temperature for the
semiconductor thin film is also locally uneven.
In addition to the method as described above, various laser irradiation
systems have been hitherto proposed. For example, in a method of
manufacturing a semiconductor device as disclosed in Japanese Laid-open
Patent Application No. Sho-60-245124, a laser pulse having wavelength of
150 nm to 350 nm is irradiated at an energy density of 200 to 500
mJ/cm.sup.2 to promote crystallization of a semiconductor thin film. In
this system, an amorphous area and a crystal area coexist on a substrate,
and thin film transistors are integrated over the two areas. Accordingly,
the electrical characteristics of the thin film transistors vary between
both the amorphous area and the crystal area, and thus controllability is
lost.
Furthermore, in a method of manufacturing a semiconductor memory as
disclosed in Japanese Laid-open Patent Application No. Hei-3-273621, a
laser annealing treatment is performed on a memory-cell basis (microarea
in several tens .mu.m order), and non-irradiated areas remain in between
memory cells. Therefore, it is impossible to irradiate a laser beam onto a
large-scale circuit at the same time.
Still furthermore, in a method of manufacturing a liquid crystal display
device as disclosed in Japanese Laid-open Patent Application No.
Hei-5-66422, for crystallization of a semiconductor thin film, a one
(single) shot of laser pulse is irradiated onto each of areas on which a
horizontal scanning circuit and a vertical scanning circuit respectively
will be formed. In this case, it is necessary to make crystallized areas
continuous, and thus the crystal particle size is dispersed at a linking
boundary between the laser-irradiated areas.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of manufacturing
semiconductor chips for display in which semiconductor thin films having a
large size can be mass-produced to have uniform particle size with
shortening a heat-treatment time.
In order to attain the above object, a method of manufacturing
semiconductor chips for display comprises a step of forming a
semiconductor thin film on an insulating substrate, a step of processing
the semiconductor thin film to form an integrated thin film transistors in
a sectioned area for one chip and a step of forming pixel electrodes in
the sectioned area to form a picture (frame), wherein the processing step
contains a step of irradiating a laser pulse to the sectioned area by a
single shot exposure to perform a batch heat-treatment on the
semiconductor thin layer for one chip. At the laser-irradiation step, the
semiconductor thin film is crystallized with the batch heat-treatment, or
the semiconductor thin film is doped with impurities and then the
impurities are activated with the batch heat-treatment. If necessary, the
laser-irradiation step as described above may be performed after the
semiconductor thin film is doped with the impurities, whereby the
crystallization of the semiconductor thin film and the activation of the
impurities are performed at the same time.
In the laser-irradiation step, a one-shot laser pulse may be successively
irradiated onto each of plural sectioned areas which are beforehand
provided on an insulating substrate. In this case, a one-shot laser pulse
is irradiated onto an individual sectioned area except for a separation
band which is provided between neighboring sectioned areas. When the
individual sectioned area is rectangular, a laser pulse having a
rectangular section which conforms to the shape of the sectioned area may
be irradiated by one shot.
As a condition for laser irradiation, a one-shot laser pulse may be
irradiated for a pulse time which is set to 40 nanoseconds or more. In
this case, the batch heat-treatment can be performed to control
crystallization of the semiconductor thin film in a state where the
temperature of the insulating substrate is increased to the room
temperature or more, or decreased to the room temperature or less.
Furthermore, if the semiconductor thin film is beforehand formed at a
thickness which is smaller than the absorption depth of the laser pulse,
the crystallization or activation can be perfectly performed.
If necessary, a one-shot laser pulse may be irradiated through a microlens
array to selectively concentrate the laser pulse on a portion of the
semiconductor thin film, which corresponds to the element area of an
individual thin film transistor. Furthermore, the one-shot laser pulse
irradiation may be performed while controlling the cross-section intensity
distribution of the laser pulse so that the irradiation energy density
increases from the central portion of a sectioned area toward the
peripheral portion thereof.
Furthermore, if necessary, the laser pulse may be irradiated in an oblique
direction onto the insulating substrate. Specifically, at this oblique
laser irradiation step, the laser pulse is irradiated within an incident
angle range of 30.degree. to 60.degree. to the normal direction of the
insulating substrate. For example, the oblique laser irradiation step is
used to crystallize a semiconductor thin film formed of amorphous silicon
with the batch heat-treatment. In this case, the batch heat-treatment is
performed while the insulating substrate is kept in a temperature range of
550.degree. C. to 650.degree. C., thereby promoting crystallization of
amorphous silicon.
According to the present invention, a one-shot laser pulse is irradiated
onto a sectioned area to perform the batch heat-treatment on a
semiconductor thin film for one chip. With this operation, the processing
time for the laser irradiation step can be shortened, and the
mass-production can be performed. The laser irradiation step is used to
promote crystallization of the semiconductor thin film with the batch
heat-treatment. The batch heat-treatment provides crystals having
excellent uniformity, so that the process condition can be stabilized and
uniformity in electric characteristics of the thin film transistors can be
kept. The laser irradiation step as described above is effectively usable
not only for the crystallization of a semiconductor thin film, but also
for the activation of impurities which is performed with a batch
heat-treatment after a semiconductor thin film is doped with the
impurities. When the laser pulse is irradiated onto the semiconductor thin
film, its energy is absorbed on only the surface of the semiconductor thin
film, and then heat is thermally conducted into the inner portion of the
semiconductor thin film, so that the inner portion of the semiconductor
thin film is melted to be recrystallized or annealed to increase the
crystal grain size. Furthermore, the impurities doped into the
semiconductor thin film are activated. As described above, the laser pulse
irradiation enables crystallization of the semiconductor thin film, the
activation of the impurities, etc. at a low temperature without increasing
the temperature of the substrate.
According to the laser irradiation step of the present invention, the
one-shot laser pulse irradiation is performed for a pulse time which is
set to 40 nanoseconds or more. By setting a one-shot irradiation time of
the laser pulse to a sufficient one, the semiconductor thin film can be
melted and crystallized by only one-shot laser pulse, so that it is
expected to improve the uniformity of the crystal grain size and the
throughput. Furthermore, in the laser irradiation step, the semiconductor
thin film can be subjected to the batch heat-treatment in the state where
the insulating substrate is beforehand increased to the room temperature
or more or decreased to the room temperature or less. Therefore, a cooling
speed of the semiconductor thin film which is once melted by the laser
irradiation can be controlled, so that the crystal grain size, the
activation degree of the impurities, etc. can be adjusted to the optimum
values. Furthermore, by forming the semiconductor thin film at a thickness
which is smaller than the absorption depth of the laser pulse, the
semiconductor thin film can be perfectly melted, and it can be promoted to
obtain crystals having a large particle size.
According to another aspect of the present invention, the one-shot
radiation of the laser pulse is performed through the microlens array to
selectively concentrate the laser pulse on a portion of the semiconductor
thin film which is to be an element area of an individual thin film
transistor. Accordingly, the energy contained in the one-shot laser pulse
can be efficiently used.
According to another aspect of the present invention, the one-shot laser
pulse irradiation is performed while the cross-sectional intensity
distribution of the laser pulse is controlled so that the irradiation
energy density increases from the central portion of the sectioned area to
the peripheral portion thereof. In a laser anneal treatment for a
relative-large area, thermal diffusion occurs from the peripheral portion
of an irradiated area, so that the cooling speed of the peripheral portion
is higher than that of the central portion. In order to compensate for
this (i.e., the difference in cooling speed between the central and
peripheral portions), the cross-sectional intensity distribution of the
laser pulse is beforehand set so as to be increased toward the peripheral
portion to thereby make the cooling speed uniform over the sectioned area.
According to another aspect of the present invention, the oblique laser
irradiation step of irradiating the laser pulse onto the insulating
substrate in an oblique direction is adopted. For example, by irradiating
the laser pulse within an incident angle range of 30.degree. to 60.degree.
to the normal direction of the insulating substrate, the batch
heat-treatment can be performed on a broader area than a vertical laser
irradiation step. That is, when the oblique laser irradiation is
performed, the irradiation area is larger than the cross section of the
laser pulse, and thus a broader area can be subjected to the batch
heat-treatment with a one-shot laser pulse. However, the irradiation
energy density per unit area is smaller in the oblique laser irradiation
than that in the vertical laser irradiation. In order to compensate for
this, the oblique laser irradiation may be performed in a state where the
insulating substrate is kept at a high temperature. For example, when a
semiconductor thin film of amorphous silicon is crystallized, the oblique
laser irradiation is preferably performed in a state where the insulating
substrate is heated within a temperature range of 550.degree. C. to
650.degree. C. If the laser pulse is irradiated within an incident angle
of 60.degree. to the normal direction, the irradiation area would be
increased to be twice as large as that in the vertical laser irradiation.,
however, the energy density would be reduced to half.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing a laser irradiation process;
FIG. 2 is another schematic diagram showing the laser irradiation process;
FIG. 3 is a schematic diagram showing an embodiment of a method of
manufacturing a semiconductor chip for display
FIG. 4 is a cross-sectional view showing an example of the construction of
a thin film transistor contained in a semiconductor chip for display which
is manufactured according to the present invention;
FIG. 5 is a cross-sectional view showing another example of the
construction of a thin film transistor;
FIG. 6 is a plan view showing a multi-chip wafer which is subjected to a
laser irradiation process of the present invention;
FIGS. 7A to 7O are diagrams showing a series of processes for the method of
manufacturing a semiconductor chip for display according to the present
invention;
FIGS. 8A to 8D are diagrams showing a series of processes for another
embodiment of the semiconductor chip manufacturing method according to the
present invention;
FIG. 9 is a schematic diagram showing a laser irradiation process which is
performed in the process shown in FIG. 7D;
FIGS. 10A to 10C are schematic diagrams showing a series of processes for
another embodiment of the semiconductor chip manufacturing method
according to the present invention;
FIGS. 11A to 11C are schematic diagrams showing a series of processes for
another embodiment of the semiconductor chip manufacturing method
according to the present invention;
FIGS. 12A and 12B are schematic diagrams showing a series of processes for
another embodiment of the semiconductor chip manufacturing method
according to the present invention;
FIG. 13 is a graph showing electrical characteristics of thin film
transistors which are formed by the present invention and the conventional
method;
FIG. 14 is a schematic diagram showing a laser beam irradiation method
using a microlens array;
FIG. 15 is a cross-sectional view showing the microlens array to explain
the function of the microlens array;
FIG. 16 is a schematic diagram showing a surface state of a semiconductor
thin film which was subjected to laser irradiation through the microlens
array;
FIG. 17 is a schematic diagram showing an improved example of the laser
irradiation process according to the present invention; and
FIG. 18 is a graph showing the cross-sectional intensity distribution of a
laser pulse shown in FIG. 17.
FIG. 19 is a schematic diagram showing an improved example (oblique laser
irradiation method) of the conventional laser irradiation process;
FIG. 20 is a cross-sectional view showing the oblique laser irradiation
method shown in FIG. 3;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments according to the present invention will be described
hereunder with reference to the accompanying drawings.
FIG. 3 is a schematic diagram showing a basic process for a method of
manufacturing a semiconductor chip for display (e.g., display panel). In
the semiconductor chip manufacturing method, a film forming process is
first performed to form a semiconductor thin film 2 on a transparent
insulating substrate 1 which is formed of glass material having relatively
low melting point (below 600.degree. C., for example). The semiconductor
thin film 2 is formed of amorphous or polycrystal having relatively small
grain size before processed, for example, it is formed of amorphous
silicon or polycrystal silicon. The semiconductor thin film 2 is subjected
to a series of processes containing a heat treatment process to form
integrated thin film transistors on a sectioned area 3 for one chip. In
this embodiment, the sectioned area 3 contains a matrix array (containing
thin film transistors and electrodes for pixels) 4, a horizontal scanning
circuit 5 and a vertical scanning circuit 6. Integrated thin film
transistors are formed on each of the above elements. Finally, pixel
electrodes for one panel are formed on the matrix array 4 to complete a
semiconductor chip 7 for a display panel.
According to the present invention, the series of processes as described
above contain a laser irradiation process of irradiating a laser pulse 8
on the sectioned area 3 by a one shot exposure to perform the batch
heat-treatment on the semiconductor thin film 2 for one chip. The laser
irradiation process is used to crystallize the semiconductor thin film 2
by the batch heat-treatment. For example, when the semiconductor thin film
2 is formed of amorphous silicon in its precursive state (i.e., before it
is processed), the semiconductor thin film 2 is temporarily melted by the
batch heat-treatment, and then crystallized to obtain polycrystal silicon
having relatively large grain size. On the other hand, when the
semiconductor thin film 2 is formed of polycrystal having a relatively
small grain size in its precursive state, the semiconductor thin film 2 is
temporarily melted by the batch heat-treatment, and then crystallized to
obtain polycrystal silicon having a relatively large grain size. The laser
irradiation process is not limited to crystallization, and it may be
applied to a case where the semiconductor thin film 2 is doped with
impurities and then the impurities are activated by the batch
heat-treatment. Furthermore, the crystallization of the semiconductor thin
film 2 and the activation of the impurities can be simultaneously
performed by the batch heat-treatment.
An excimer laser beam source may be used to emit the laser pulse 8. Since
the excimer laser beam is a strong pulse ultraviolet ray, it is absorbed
on the surface layer of the semiconductor thin film 2 of silicon or the
like to increase the temperature of the surface layer, however, it does
not heat the insulating substrate 1. As a precursive film to be formed on
the insulating substrate 1 may be selected a plasma CVD silicon film or
the like which can be formed at a low temperature. For example, when a
plasma CVD silicon film is formed at a thickness of 30 nm on a transparent
insulating substrate 1 of glass material, the melting threshold energy
when an XeCl excimer laser beam is irradiated is about 130 mJ/cm.sup.2.
Energy of about 220 mJ/cm.sup.2 is required to melt the whole film, and it
takes about 70 ns from the time when it is melted until the time when it
is solidified.
The insulating substrate 1 is generally formed of a large-size wafer from
which many semiconductor chips 7 for display are taken out. That is,
plural sectioned areas 3 are set on the insulating substrate 1 in advance,
and the laser pulse 8 is successively irradiated onto each sectioned area
by a single shot exposure in the laser irradiation process. In this case,
the laser pulse 8 is irradiated onto each sectioned area 3 by one shot
except for a separation band which is provided between neighboring
sectioned areas 3. In this embodiment, each sectioned area 3 has a
rectangular shape, and thus the laser pulse 8 having a rectangular section
10 which conforms to the shape of the sectioned area 3 is irradiated by
one shot.
As an irradiation condition, the one-shot irradiation of the laser pulse 8
is performed for a pulse time which is set to 40 nanoseconds or more, for
example. At this time, the batch heat-treatment is performed in a state
where the insulating substrate 1 is increased to the room temperature or
more or decreased to the room temperature or less, thereby controlling the
crystallization of the semiconductor thin film 2. Furthermore, the
semiconductor thin film 2 is formed at a thickness which is smaller than
the absorption depth of the laser pulse 8, thereby enabling the
semiconductor thin film 2 to be perfectly melted.
If necessary, the one-shot irradiation of the laser pulse 8 may be
performed through a microlens array to selectively concentrate the
irradiation of the laser pulse on a portion of the semiconductor thin film
2 which is an element area for each thin film transistor, whereby the
laser energy can be efficiently used. Furthermore, the cross-sectional
intensity distribution of the laser pulse 8 may be controlled for the
one-shot irradiation so that the irradiation energy density increases from
the central portion of each sectioned area 3 toward the peripheral portion
thereof, whereby the temperature gradient of heat radiation through the
insulating substrate 1 is made uniform. Still furthermore, the laser pulse
8 is irradiated from the vertical direction onto the insulating substrate
1 in FIG. 3, however, it may be irradiated from an oblique direction to
the insulating substrate 1 to perform the heat treatment. With this
irradiation, the sectioned area 3 can be set to a value which is larger
than the cross-sectional area 10 of the laser pulse 8.
As described above, the present invention is characterized in that the
large-area semiconductor chip 7 for display is annealed at a time. In this
embodiment, the laser pulse 8 is irradiated over the semiconductor thin
film 2 formed of amorphous silicon or polycrystal silicon having
relatively minute grain size at a time. Each sectioned area 3 serves as an
irradiation area, and each separation band 9 serves as a non-irradiation
area. The sectioned area 3 serving as the laser irradiation area is
provided with a matrix array 4, a horizontal scanning circuit 5 and a
vertical scanning circuit 6. Any of these elements contains thin film
transistors. In the semiconductor chip 7 for display as described above,
the total number of thin film transistors exceeds 100 kbits, and the
diagonal dimension of the sectioned area 3 is above 14 mm. The maximum
diagonal dimension extends to about 3 inches. The excimer laser beam of
300 nm to 350 nm in wavelength is irradiated to the sectioned area 3, and
the energy density thereof is set to about 200 mJ/cm.sup.2 to 400
mJ/cm.sup.2. No thin film transistor is formed at the separation band 9
serving as the non-irradiation area and it is used as a scribe area for
the semiconductor chip 7 for display. As a result, the laser irradiation
area and the laser non-irradiation area coexist on the semiconductor chip
7 for display.
FIG. 4 is a cross-sectional view showing an example of integrated thin film
transistors (TFT) which are formed on the semiconductor chip 7 for display
shown in FIG. 3. In this embodiment, a planar type thin film transistor is
formed. As shown in FIG. 4, a semiconductor thin film 12 constituting an
element area of TFT is formed on the transparent insulating substrate 11.
The semiconductor thin film 12 is formed of silicon which is crystallized
by the one-shot irradiation of the laser pulse as described above. A gate
electrode G which is formed of alloy of aluminum and silicon or the like
is patterned through a gate insulating film 13 on the semiconductor thin
film 12. Both portions of the semiconductor thin film 12 at both sides of
the gate electrode G are doped with n-type impurities of high
concentration to form a source region S and a drain region D of the TFT. A
channel region Ch is also provided between the source region S and the
drain region D. The impurities which are doped at a high concentration by
an ion implantation method or the like are activated by the one-shot
irradiation of the laser pulse. The TFT thus constructed is covered with a
first layer insulating film 14 formed of PSG or the like. A wiring 15
formed of metal aluminum or the like is formed on the first layer
insulating film 14 by a patterning treatment, and it is conducted to the
source region S and the drain region D through contact holes. With respect
to the thin film transistors formed on the matrix array 4 shown in FIG. 3,
in place of the wiring 15, a pixel electrode is connected to the drain
region D. The wiring 15 is further covered with a second layer insulting
film 16 formed of PSG or the like, and a passivation film 17 formed of
P-SiN or the like is formed on the second layer insulating film 16.
FIG. 5 is a cross-sectional view showing another example of the thin film
transistor formed on the semiconductor chip for display shown in FIG. 3.
The TFT of this embodiment is of a reverse-staggered type, and a gate
electrode G formed of alloy of aluminum and silicon or the like is formed
on a transparent insulating substrate 21 by the patterning treatment.
Furthermore, a semiconductor thin film 23 is formed on the gate electrode
G through a gate insulating film 22. The semiconductor thin film 23 is
formed of silicon or the like which is crystallized by the one-shot
irradiation of the laser pulse as described above. A wiring 25 formed of
aluminum or the like is formed at both sides of the gate electrode G on
the semiconductor thin film 23 through an impurity-diffusion layer 24. The
TFT thus constructed is covered with a passivation film 26 formed of P-SiN
or the like.
The following Table 1 shows a concrete irradiation condition for the laser
irradiation method of the present invention, and an irradiation condition
for the previously suggested irradiation method is also shown in the table
for comparison.
TABLE 1
__________________________________________________________________________
COMPARATIVE METHOD
PRESENT INVENTION
__________________________________________________________________________
CRYSTAL GRAIN SIZE
20 nm - 150 nm
100 nm-150 nm
LASER TREATMENT
25 .times. (150 nsec +
150 nsec
TIME 100 msec) = 2.5 sec
(IRRADIATION TIME +
LASER IRRADIATION AT
SINGLE LASER
SCANNING TIME)
25 TIMES IRRADIATION
LASER IRRADIATION
1 cm .times. 1 cm
5 cm .times. 5 cm
__________________________________________________________________________
In an example of the Table 1, the one-shot irradiation of the laser beam
was performed on a section area of 5 cm.times.5 cm. At this time, the
energy density was set to 200 mJ/cm.sup.2 to 450 mJ/cm.sup.2. In the
comparative method, the laser pulse irradiation on a sectioned area of 5
cm.times.5 cm must be divided into 25 laser pulse irradiation shots. That
is, the laser irradiation area per laser pulse shot is limited to an area
of 1 cm.times.1 cm, and thus the one-shot laser pulse irradiation must be
performed totally 25 times to irradiate the whole sectioned area of 5
cm.times.5 cm. The laser processing time per one chip is equal to the sum
of an irradiation time and a scanning time. In the present invention, the
scanning time is equal to zero because the one-shot irradiation is
adopted, and thus the laser processing time is equal to 150 nsec. On the
other hand, in the prior art, the irradiation time per one-shot is equal
to 150 nsec, and the scanning time is equal to 100 msec. Therefore, when
the laser irradiation is carried out 25 times, the total processing time
is equal to 2.5 seconds. Accordingly, the throughput is more remarkably
improved in the present invention than in the prior art. The grain size of
the semiconductor thin film which was processed according to the method of
the present invention was equal to 100 nm to 150 nm. The grain size was
measured with a transmission-type electron microscope (TEM). The grain
size of the semiconductor thin film which was processed according to the
comparative method was equal to 20 nm to 150 nm. As is apparent from this
result, the variations of the grain size could be reduced by the one-shot
irradiation of the laser pulse.
FIG. 6 schematically shows a multi-chip wafer to which the laser
irradiation method of the present invention is applied. In this
embodiment, the laser pulse is successively irradiated by one shot onto
each of plural sectioned areas 32 which are beforehand provided on a
transparent insulating substrate (wafer) of 5 inches in diameter, thereby
obtaining totally nine semiconductor chips for display. In the present
invention, the one-shot irradiation of the laser pulse is carried out on
each sectioned area 32 except for a separation band 33 which are provided
between the neighboring sectioned areas 32. As shown in FIG. 6 the size of
each sectioned area is set to a in lateral length and b in longitudinal
length. The size of the separation band is set to b in longitudinal width
and d in lateral width. In this embodiment, a is set to be larger than b,
and c is set to be larger than d. The longitudinal and lateral separation
bands are used as scribe lines at a subsequent process.
Next, the method of manufacturing semiconductor chips for display according
to this embodiment will be described in more detail with reference to
FIGS. 7A to 7O.
First, a transparent insulating substrate 41 is provided in a process of
FIG. 7A. Subsequently, an amorphous silicon film 42 is formed on the
transparent insulating substrate 41 by LPCVD method in a process of FIG.
7B. Thereafter, a resist 43 is patterned on the amorphous silicon film 42
upon the shape of a gate electrode in a process of FIG. 7C, and then
n-type impurities are doped through the resist by an ion implantation
method to form a source region S and a drain region D in a process of FIG.
7D.
Subsequently, a nonreflective coating 44 is formed on the amorphous silicon
film 42 in a process of FIG. 7E. The nonreflective coating is formed of
SiO.sub.2, SiN, SiON or the like. In a next process of FIG. 7F, the
one-shot irradiation of the laser pulse is conducted to crystallize the
amorphous silicon film 42 and activate the impurities doped in the source
region S and the drain region D. At this time, the nonreflective coating
44 has an effect of improving the absorption efficiency of the irradiation
energy of the laser pulse. After the laser irradiation process of FIG. 7F,
the used nonreflective coating is removed by an etching treatment in a
process of FIG. 7G so that only the crystallized silicon film 42 remains.
Subsequently, in a process of FIG. 7H, a patterning is conducted with a
photoresist, and an undesired portion of the silicon film 42 is removed by
a dry etching treatment. Thereafter, a SiO.sub.2 film is formed by a
pressure-reduced CVD to form a gate insulating film 45.
Subsequently, a metal film 46 formed of alloy of aluminum and silicon is
formed in a process of FIG. 7I, and then the metal film is patterned in a
desired shape to form a gate electrode 47 in a process of FIG. 7J. This
patterning is performed with phosphoric acid by a wet etching treatment.
Thereafter, a first layer insulating film 48 of PSG is formed by a CVD
method in a process of FIG. 7K, and then contact holes are formed in the
first layer insulating film 48 and the gate insulating film 45 by the wet
etching treatment in a process of FIG. 7L.
Subsequently, a metal aluminum film is formed by the patterning in a
process of FIG. 7M, and then patterned in a desired shape to form wirings
49 which intercommunicate with the source region S and the drain region D.
Thereafter, a second layer insulating film 50 of PSG is formed by the CVD
method in a process of FIG. 7N, and then a P-SiN film 51 is formed by a
plasma CVD method in a process of FIG. 7O. Thereafter, hydrogen is
introduced into the silicon film 42 through the first layer insulating
film 48 and the second layer insulting film 50 using the P-SiN film 51 as
a cap film. Through the series of processes as described above, a planar
type thin film transistor (TFT) is completed.
Next, another embodiment of the method of manufacturing semiconductor chips
for display according to the present invention will be described in more
detail with reference to FIGS. 8A to 8C.
First, a transparent insulating substrate 61 is provided n a process of
FIG. 8A. The t | | |
