Electric heating – Metal heating – By arc
Reexamination Certificate
1997-05-30
2003-12-02
Wilczewski, Mary (Department: 2822)
Electric heating
Metal heating
By arc
C219S121750, C219S121820, C219S121850, C219S121860, C438S166000, C438S487000, C438S795000, C438S908000, C422S245100, C422S250100
Reexamination Certificate
active
06657154
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor manufacturing apparatus for manufacturing a thin film transistor device formed on a glass substrate of a large area and a manufacturing method for the thin film transistor. The present invention particularly relates to a laser crystallization semiconductor thin film formation apparatus using an ultraviolet pulse laser and a manufacturing method for a polycrystalline semiconductor thin film transistor.
2. Description of the Related Art
Heretofore, a transistor having a MOS (metal-oxide film-semiconductor) structure has been widely used for such as a large scale integrated circuit (LSI). Particularly, in silicon LSI manufacturing processes, since there is a thermal oxide step employing a high temperature process of about 1000° C. for formation of a MOS structure on a silicon wafer, it is easy to produce a clean oxide film-silicon interface.
On the other hand, in manufacturing processes for formation of a so called high temperature polysilicon thin film transistor to be applied to liquid crystal light valves, after an a(amorphous)-Si thin film on a quartz substrate is crystallized by a solid phase growth, patterning and acid-cleaning are conducted for a silicon layer, and an oxide film formation at a high temperature of about 1000° C. are conducted. Since a native oxide film formed at the time of the acid-cleaning is removed during heating, an oxide film is formed on a clean surface of the silicon layer.
However, in a low temperature polysilicon TFT process which is conducted at a temperature below 400° C. using excimer laser annealing, since such a high temperature process can not be employed, means for removing the native oxide film on the silicon surface formed after the acid-cleaning is required. For this reason, a method to sequentially conduct formation of a silicon film, laser irradiation, patterning and cleaning of the silicon film, and formation of a gate insulating film are said to be general, and a cleaning step after patterning plays an important role in,stability and reproducibility of manufacturing processes.
For a way to solve such problems, M. Sekiya et al. has proposed the apparatus composed of an insulating film formation chamber, a laser irradiation chamber, and a hydrogenation chamber, all capable of transporting a substrate in vacuum, in IEEE ELECTRON DEVICE LETTERS, Vol. 15, No. 2, 1994 page 69. In this apparatus, after an amorphous silicon film formed on a glass substrate is crystallized by a laser, hydrogenation and formation of a gate insulating film are conducted sequentially in the same apparatus.
However, according to a manufacturing method using this apparatus, although the silicon surface after crystallization using the laser is kept clean, removal of a native oxide film produced before crystallization by the laser is insufficient. In other words, the native oxide film itself or impurity metal atoms contained in the native oxide film induces variations in the laser crystallization step whereby reproducibility of the process is deteriorated. Moreover, in a case where a subsequent step such as laser crystallization or formation of a thin film is performed after the silicon thin film previously formed is once exposed to the air, cleaning with cleaning liquid such as ammonia/hydrogen peroxide/pure water, hydrochloric acid/hydrogen peroxide/pure water, sulfuric acid/hydrogen peroxide, hydrofluoric acid/pure water or cleaning with heated liquid prepared by heating them must be conducted prior to a next step. The amount of these acid-alkaline type cleaning liquids to be used increases in accordance with an increase in a size of the glass substrate, resulting in an increase in a cleaning liquid cost and waste liquid cost.
On the other hand, the excimer laser annealing apparatus has required a wider setting area than before in accordance with an enlargement of a size of the glass substrate. Particularly, in the laser irradiation chamber, a size of the substrate is larger than an irradiation area, covered by one irradiation of the laser beam. As shown in
FIG. 1
, while horizontally moving the glass substrate
409
set in the vacuum container constituting the ELA (Excimer Laser Annealing) module
407
, the entire surface of the substrate will be crystallized by laser irradiation. In case of such method, when the glass substrate
409
is moved only in one direction on the plane, the setting area of the vacuum container must be two times as large as a size of the glass substrate, and when the glass substrate
409
is moved in two directions on the plane, both directions being perpendicular to each other, the setting area of the vacuum container must be four times as large as the size of the glass substrate. Specifically, laser beam emitted from the excimer laser
401
travels along the optical path
402
, and it passes through the A to C. optical apparatuses
404
,
405
, and
410
and the mirrors
403
a
to
403
e
, the optical apparatuses serving to shape the laser beam to the desired beam. After the laser beam is shaped to the desired beam, it reaches the surface of the glass substrate
409
through the window
406
. The glass substrate
409
is fixed to the substrate holder
411
on the stage which is capable of moving in x- and y-directions on the plane. The glass substrate
409
undergoes laser irradiation on its desired region. In this case, the setting area of the vacuum container must be four times as large as a size of the glass substrate. More specifically, if a substrate has a length dimension, then the vacuum chamber has a dimension which is more than twice the substrate length. However, enlargement of the setting area is not desirable because of an increase in cost of clean room equipment. When a process room equipped with a plurality of functions is arranged in a limited setting area, the space of the laser irradiation room limits the space of a process room equipped with other functions.
Moreover, while keeping the semiconductor surface (interface) clean, although a wet cleaning step for the above-described substrate is omitted, when an irradiation step is conducted, there has been the following problem. Specifically, as disclosed in Japanese Patent Application Laid Open No. 5-211167, when laser irradiation is required for a certain region, (1) a system to previously form a marker for positioning and (2) a system to form an integrated circuit fitting to a region where the laser irradiation was conducted are needed.
In case of the system (
1
), after a certain thin film is formed, resist patterning using photolithography (PR) and thin film etching are conducted, and a marker is formed. Thereafter, cleaning is performed using the acid-alkaline cleaning liquid described above. Subsequently, a silicon thin film is formed, and laser irradiation fitting to the marker position is conducted, whereby a crystallized silicon thin film can be produced. Alternatively, as shown in
FIGS. 2A
to
2
E, the silicon thin film
502
is first formed on the entire surface of the glass substrate
501
(FIG.
2
A). The resist
506
is coated on the silicon thin film
502
(FIG.
2
B). The resist
506
undergoes patterning using a photolithography technique, whereby the resist
507
for developing is formed (FIG.
2
C). Thereafter, the mark portion
504
is formed by dry etching (FIGS.
2
D and
2
E).
On the other hand, in case of the system (
2
), a means for detecting the laser crystallization position using a certain method is required, and it is difficult to obtain a level positioning precision required by a stepper and the like. Also according to the system (
1
), an increase in cost due to an additional PR step and an additional cleaning step is incurred. In a case where a marker is formed directly on a silicon film, the surface of the silicon undergoes the PR step, so that cleaning with a precision is needed. A more simplified marker formation means is required.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide a multifunction sem
Kaneko Setsuo
Tanabe Hiroshi
NEC Corporation
Wilczewski Mary
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