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Claims  |
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What is claimed is:
1. A method of manufacturing a semiconductor device comprising steps of:
introducing catalytic elements into a semiconductor film of low
crystallinity;
applying first heat treatment to said semiconductor film of low
crystallinity to form a crystalline semiconductor film including an
amorphous portion;
applying second heat treatment to said crystalline semiconductor film to
enhance its crystallinity;
irradiating said crystalline semiconductor film of enhanced crystallinity
with a laser light or an intense light;
selectively adding a group XV element to said crystalline semiconductor
film after said irradiating; and
applying third heat treatment to said crystalline semiconductor film of
enhanced crystallinity to have said catalytic elements absorbed in said
region added with group XV elements.
2. A method according to claim 1, wherein the first heat treatment is
performed at a temperature from 450.degree. C. to 650.degree. C.
3. A method according to claim 1, wherein the second heat treatment is
performed at a temperature higher than the first heat treatment.
4. A method according to claim 1, wherein the second heat treatment is
performed at a temperature from 500.degree. C. to 1,100.degree. C.
5. A method according to claim 1, wherein the third heat treatment is
performed at a temperature from 450.degree. C. to 850.degree. C.
6. A method according to claim 1, wherein said semiconductor film of low
crystallinity is an amorphous silicon film formed by a reduced pressure
CVD method.
7. A method according to claim 1, wherein said catalytic elements are one
or plural kinds of elements selected from a group consisting of Ni, Fe,
Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au and Ge.
8. A method according to claim 1, wherein said semiconductor device is an
active matrix type display device.
9. A method according to claim 1, wherein said semiconductor device is an
EL display device.
10. A method according to claim 1, said semiconductor device is an
electronic equipment selected from the group consisting of a video camera,
a digital camera, a rear-type projector, a front-type projector, a
head-mount display, a goggle-type display, a navigation system for
vehicle, a personal computer, and a portable information terminal, a
mobile computer, a cellular phone, and an electronic book.
11. A method according to claim 1, wherein said semiconductor device
comprises a plurality of thin film transistors, and wherein regions of
semiconductor film to which said group XV element is added include at
least one of source and drain regions of said thin film transistors.
12. A method according to claim 1, wherein said group XV element is added
to said semiconductor film by selectively disposing a film containing said
group XV element in contact with portions of said semiconductor film.
13. A method according to claim 1, wherein said first heat treatment is
performed for 4-12 hours.
14. A method according to claim 1, wherein said third heat treatment is
performed for 24 hours.
15. A method of manufacturing a semiconductor device comprising steps of:
introducing catalytic elements into a semiconductor film of low
crystallinity;
applying first heat treatment to said semiconductor film to form a
crystalline semiconductor film;
applying second heat treatment to said crystalline semiconductor film to
enhance its crystallinity after said first heat treatment;
irradiating said crystalline semiconductor film of enhanced crystallinity
with a laser light or an intense light;
adding a group XV element to said crystalline semiconductor film after said
irradiating; and
applying third heat treatment to said crystalline semiconductor film of
enhanced crystallinity to have said catalytic elements absorbed in said
region added with group XV elements.
16. A method according to claim 15, wherein said first heat treatment is
performed for 4-12 hours.
17. A method according to claim 15, wherein said third heat treatment is
performed for 24 hours.
18. A method according to claim 15, wherein said first heat treatment is
performed to diffuse said catalytic element into said semiconductor film.
19. A method according to claim 15, wherein the first heat treatment is
performed at a temperature from 450.degree. C. to 650.degree. C.
20. A method according to claim 15, wherein the second heat treatment is
performed at a temperature higher than the first heat treatment.
21. A method according to claim 15, wherein the second heat treatment is
performed at a temperature from 500.degree. C. to 1,100.degree. C.
22. A method according to claim 15, wherein the third heat treatment is
performed at a temperature from 450.degree. C. to 850.degree. C.
23. A method according to claim 15, wherein said semiconductor film of low
crystallinity is an amorphous silicon film formed by a reduced pressure
CVD method.
24. A method according to claim 15, wherein said catalytic elements are one
or plural kinds of elements selected from a group consisting of Ni, Fe,
Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au and Ge.
25. A method according to claim 15, wherein said semiconductor device is an
active matrix type display device.
26. A method according to claim 15, wherein said semiconductor device is an
EL display device.
27. A method according to claim 15, said semiconductor device is an
electronic equipment selected from the group consisting of a video camera,
a digital camera, a rear-type projector, a front-type projector, a
head-mount display, a goggle-type display, a navigation system for
vehicle, a personal computer, and a portable information terminal, a
mobile computer, a cellular phone, and an electronic book.
28. A method according to claim 15, wherein said semiconductor device has a
plurality of thin film transistors, and wherein regions of semiconductor
film to which are added said group XV element are include at least one of
source and drain regions of said thin film transistors.
29. A method according to claim 15, wherein said group XV element is add to
said semiconductor film by selectively disposing a film containing said
group XV element in contact with portions of said semiconductor film.
30. A method of manufacturing a semiconductor device comprising steps of:
introducing catalytic elements into a semiconductor film of low
crystallinity;
applying first heat treatment to said semiconductor film to form a
crystalline semiconductor film including an amorphous portion;
applying second heat treatment to said crystalline semiconductor film to
enhance its crystallinity;
irradiating said crystalline semiconductor film of enhanced crystallinity
with a laser light or an intense light;
adding a group XV element to said crystalline semiconductor film after said
irradiating; and
applying third heat treatment to said crystalline semiconductor film of
enhanced crystallinity to have said catalytic elements absorbed in said
region added with group XV elements.
31. A method according to claim 30, wherein said first heat treatment is
performed for 4-12 hours.
32. A method according to claim 30, wherein said third heat treatment is
performed for 24 hours.
33. A method according to claim 30, wherein the first heat treatment is
performed at a temperature from 450.degree. C. to 650.degree. C.
34. A method according to claim 30, wherein the second heat treatment is
performed at a temperature higher than the first heat treatment.
35. A method according to claim 30, wherein the second heat treatment is
performed at a temperature from 500.degree. C. to 1,100.degree. C.
36. A method according to claim 30, wherein the third heat treatment is
performed at a temperature from 450.degree. C. to 850.degree. C.
37. A method according to claim 30, wherein said semiconductor film of low
crystallinity is an amorphous silicon film formed by a reduced pressure
CVD method.
38. A method according to claim 30, wherein said catalytic elements are one
or plural kinds of elements selected from a group consisting of Ni, Fe,
Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au and Ge.
39. A method according to claim 30, wherein said semiconductor device is an
active matrix type display device.
40. A method according to claim 30, wherein said semiconductor device is an
EL display device.
41. A method according to claim 30, said semiconductor device is an
electronic equipment selected from the group consisting of a video camera,
a digital camera, a rear-type projector, a front-type projector, a
head-mount display, a goggle-type display, a navigation system for
vehicle, a personal computer, and a portable information terminal, a
mobile computer, a cellular phone, and an electronic book.
42. A method according to claim 30, wherein said semiconductor device has a
plurality of thin film transistors, and wherein regions of semiconductor
film to which are added said group XV element are include at least one of
source and drain regions of said thin film transistors.
43. A method according to claim 30, wherein said group XV element is add to
said semiconductor film by selectively disposing a film containing said
group XV element in contact with portions of said semiconductor film.
44. A method of manufacturing a semiconductor device comprising steps of:
introducing catalytic elements into a semiconductor film of low
crystallinity;
applying first heat treatment to said semiconductor film to form a
crystalline semiconductor film;
applying second heat treatment to said crystalline semiconductor film to
enhance its crystallinity;
irradiating said crystalline semiconductor film of enhanced crystallinity
with a laser light or an intense light;
selectively adding a group XV element to said crystalline semiconductor
film after said irradiating; and
applying third heat treatment to said crystalline semiconductor film of
enhanced crystallinity to have said catalytic elements absorbed in said
region added with group XV elements.
45. A method according to claim 44, wherein said first heat treatment is
performed for 4-12 hours.
46. A method according to claim 44, wherein said third heat treatment is
performed for 24 hours.
47. A method according to claim 44, wherein said first heat treatment is
performed to diffuse said catalytic element into said semiconductor film.
48. A method according to claim 44, wherein the first heat treatment is
performed at a temperature from 450.degree. C. to 650.degree. C.
49. A method according to claim 44, wherein the second heat treatment is
performed at a temperature higher than the first heat treatment.
50. A method according to claim 44, wherein the second heat treatment is
performed at a temperature from 500.degree. C. to 1,100.degree. C.
51. A method according to claim 44, wherein the third heat treatment is
performed at a temperature from 450.degree. C. to 850.degree. C.
52. A method according to claim 44, wherein said semiconductor film of low
crystallinity is an amorphous silicon film formed by a reduced pressure
CVD method.
53. A method according to claim 44, wherein said catalytic elements are one
or plural kinds of elements selected from a group consisting of Ni, Fe,
Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au and Ge.
54. A method according to claim 44, wherein said semiconductor device is an
active matrix type display device.
55. A method according to claim 44, wherein said semiconductor device is an
EL display device.
56. A method according to claim 44, said semiconductor device is an
electronic equipment selected from the group consisting of a video camera,
a digital camera, a rear-type projector, a front-type projector, a
head-mount display, a goggle-type display, a navigation system for
vehicle, a personal computer, and a portable information terminal, a
mobile computer, a cellular phone, and an electronic book.
57. A method according to claim 44, wherein said semiconductor device has a
plurality of thin film transistors, and wherein regions of semiconductor
film to which are added said group XV element are include at least one of
source and drain regions of said thin film transistors.
58. A method according to claim 44, wherein said group XV element is add to
said semiconductor film by selectively disposing a film containing said
group XV element in contact with portions of said semiconductor film. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor
device with the use of a crystalline semiconductor thin film. The category
of a semiconductor device according to the present invention includes not
only devices such as a thin film transistor and a MOS transistor but also
an electronic equipment that has a semiconductor circuit consisted of
these insulated-gate type semiconductor devices and an electronic
equipment such as a personal computer or a digital camera which is
provided with an electro-optical display device comprising an active
matrix substrate (typically, a liquid crystal display device).
2. Description of the Related Art
A thin film transistor (TFT) is known at present as a semiconductor device
using a semiconductor film. The TFT is utilized in various kinds of
integrated circuits, especially for a switching device of a matrix circuit
in an active matrix type liquid crystal display device. Further,
accompanying recent progress in increasing mobility of the TFT, it has
become popular to utilize the TFT as a device of a driver circuit for
driving the matrix circuit. In order to utilize the TFT for the driver
circuit, a semiconductor layer is necessarily a crystalline silicon film
in which the mobility is higher than in the amorphous silicon film. This
crystalline silicon film is called polycrystalline silicon, polysilicon,
microcrystalline silicon, or the like.
A conventionally known method of forming a polycrystalline silicon film
includes a method in which a polycrystalline silicon film is directly
formed, and a method in which an amorphous silicon film is formed by a CVD
method and is subjected to heat treatment at 600 to 1100.degree. C. for 20
to 48 hours to crystallize the amorphous silicon. A polycrystalline
silicon film formed by the latter method has larger crystal grains and
gives more excellent characteristics to a semiconductor device
manufactured from the film.
When a crystalline silicon film is formed on a glass substrate through the
latter method, the upper limitation of about 600.degree. C. is put on the
process temperature for crystallization, thereby taking a lot of time in
crystallizing step. The temperature of 600.degree. C. is close to the
lowest temperature for crystallizing silicon, and the temperature equal to
or less than 500.degree. C. cannot afford to crystallize silicon in a
sufficiently short time period that is paying in terms of industrial
production.
To shorten the crystallization period, the use of a quartz substrate having
high distortion point and rising a crystallizing temperature to about
1,000.degree. C. are appropriate. However, a quartz substrate is very
expensive as compared to a glass substrate, making it difficult to
increase the area of the substrate. For instance, Corning 7059 glass that
is widely used in active type liquid crystal display device has a glass
distortion point of 593.degree. C., and hence the glass substrate suffers
shrinkage and deformation when heated at 600.degree. C. or more for
several hours. The crystallizing process is therefore required to be
lowered in temperature and shortened in time period so that a glass
substrate such as Corning 7059 glass can be utilized.
The technique of crystallizing with excimer laser is one of the techniques
which enable the process to be lowered in temperature and shortened in
time period. An excimer laser light can give, barely putting a substrate
under a thermal effect, the semiconductor film an energy comparable to the
energy by a thermal annealing of around 1,000.degree. C. in a short
period, and can form a semiconductor film of high crystallinity. However,
the excimer laser has nonuniform energy distribution on the irradiated
surface, with the result that the crystallinity of the obtained
crystalline semiconductor film is varied and device characteristics are
also varied between TFTs.
Then, the present inventors have disclosed a technique with which the
crystallizing temperature is lowered while using a heat treatment in
Japanese Patent Application Laid-Open Nos. Hei 6-232059, Hei 7-321339 and
others. In the technique of the publications above, a minute quantity of
catalytic elements are introduced into an amorphous silicon film to which
a heat treatment is subsequently applied to obtain a crystallized silicon
film. Used as the elements for promoting the crystallization are elements
selected from Ni, Fe, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au and Ge, which are
invasive elements with respect to silicon.
At the crystallization in the publications above, a heat treatment causes
the catalytic elements to be diffused in the amorphous silicon film to
advance crystallization of the amorphous silicon film. The employment of
the crystallizing technique in the publications above thus makes it
possible to form crystalline silicon with a heat treatment of 450 to
600.degree. C. for 4 to 12 hours, which allows the use of a glass
substrate.
The crystallization in the publications above, however, has a problem that
the catalytic elements are remained in the crystalline silicon film.
Remaining catalytic elements impair semiconductor characteristics of the
silicon film and damage the stability and the reliability of a device
fabricated from the film.
To eliminate this problem, the present applicant has investigated methods
of removing (gettering) the catalytic elements from a crystalline silicon
film. One of those methods (referred to as the first method) is a heat
treatment in an atmosphere containing a halogen element such as chlorine.
In this method, the catalytic elements in the film are gasified as
halogenate.
Another method (referred to as the second method) among those is a heat
treatment subsequent to selective addition of phosphorus into the
crystalline silicon film. With the heat treatment, the catalytic elements
are diffused into a phosphorus added region and are captured in this
region.
However, the first method requires to set the heat treatment temperature to
800.degree. C. or more so that the gettering effect is obtained, and
cannot use a glass substrate. On the other hand, the second method has a
drawback that the treatment takes ten and several hours, though the heat
temperature may be set to 600.degree. C. or less.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above, and therefore an
object of the present invention is to provide a method of efficiently
conducting a removing step of catalytic elements when using the technique
of removing the catalytic elements in the second method described above.
Another object of the present invention is to make it possible to form on a
glass substrate a semiconductor device of high performance with a process
temperature of 600.degree. C. or less.
Removing the catalytic elements takes time for the possible reason that,
upon completion of crystallization, most catalytic elements in the
crystalline silicon film are present in a bonded state with silicon, not
in their atomistic form. To remove the catalytic elements from the
crystalline silicon film, this bond is necessarily cut. When nickel is
used as the catalytic elements for instance, they are considered to be
present as nickel silicide.
For the purpose of confirming this, a silicon film crystallized by the use
of nickel is etched for about 30 seconds with FPM (an etchant prepared by
mixing 50% HF and 50% H.sub.2 O.sub.2 at a ratio of 1 to 1). The FPM is
capable of removing nickel silicide in a short period of time, and the
presence of the nickel silicide can be confirmed by observing whether or
not a hole is formed by etching.
On the crystallized silicon film, holes are found to be irregularly formed
by the FPM treatment. Though will be explained later, this means that
nickel is locally present in the crystallized region and is bonded with
silicon to form silicide in this nickel-localized portion.
Then, the present invention adopts as the principal construction a process
in which bond between catalytic elements and semiconductor is cut by
irradiating a crystallized semiconductor film with a laser light or
infrared light to diffuse the catalytic elements in their atomistic form.
This construction makes the catalytic elements easy to diffuse in a
semiconductor film, for which the removing step of the catalytic elements
is expected to be lowered in temperature and shortened in time.
The present invention developed to attain the above-described object is
characterized by having as its main construction a process comprising:
an introducing step of introducing catalytic elements into a semiconductor
film of low crystallinity;
a first heat treatment step of applying heat treatment to the semiconductor
film of low crystallinity;
a second heat treatment step of applying heat treatment to the
semiconductor film that has been subjected to the first heat treatment;
a catalyst-removing (gettering) step of applying heat treatment to the
semiconductor film that has passed through the second heat treatment to
remove the catalytic elements in the film; and
a light annealing step of irradiating with a laser light or an intense
light the semiconductor film that has passed through the second heat
treatment, the step being put somewhere between the second heat treatment
step and the catalyst-removing step.
In the introducing step above, the semiconductor film of low crystallinity
is either a noncrystalline semiconductor film that does not assume
crystallinity or a semiconductor thin film having crystallinity but almost
no crystal grain of 100 nm order or higher. To be concrete, the
semiconductor film of low crystallinity refers to an amorphous
semiconductor film and a microcrystalline semiconductor film. The
microcrystalline semiconductor film is a semiconductor film in which an
amorphous forms a mixed phase together with a microcrystal containing
crystal grains as large as several to several tens nm.
More specifically, the semiconductor film of low crystallinity includes an
amorphous silicon film, a microcrystalline silicon film, an amorphous
germanium film, a microcrystalline germanium film and an amorphous
Si.sub.1 Ge.sub.1-x (0<.times.<1), and those semiconductor films are
formed through a chemical vapor phase method such as a plasma CVD method
or a reduced pressure CVD method.
The catalytic elements are elements that have a function of promoting
crystallization of semiconductor, in particular, silicon, and usable
element are one or plural kinds of elements selected from Ni, Fe, Co, Ru,
Rh, Pd, Os, Ir, Pt, Cu, Au and Ge which are metal elements invasive with
respect to silicon.
The catalytic elements above may be introduced by adding the catalytic
elements into the semiconductor film of low crystallinity, or by forming a
film containing the catalytic elements so as to come in contact with the
upper or lower surface of the semiconductor film of low crystallinity.
In the former method, a semiconductor film of low crystallinity is formed
and then the catalytic elements are added into the semiconductor film of
low crystallinity through an ion implantation method, a plasma doping
method or the like.
In the latter method, the film containing the catalytic elements may be
formed through, for example, deposition utilizing a CVD method, a
sputtering method, etc., or through coating with a solution containing the
catalytic elements by the use of a spinner. Formation of the film
containing the catalytic elements may be performed either before or after
formation of the semiconductor film of low crystallinity. If the
semiconductor film of low crystallinity is formed first, the film
containing the catalytic elements is formed in close contact with the
upper surface of the semiconductor film and, when that formation order is
reversed, the film containing the catalytic elements is formed in close
contact with the lower surface of the semiconductor film. In the present
invention, the term "be in close contact" refers to, not restricted to a
case where the semiconductor film is literally in close contact with the
catalytic-element film, a case where an oxide film or a natural oxide film
with a thickness of about 10 nm is sandwiched between those films as long
as the catalytic elements can be diffused in the semiconductor film.
When Ni is used as a catalytic element in the introducing step, for
instance, it is appropriate to form an Ni film or an Ni silicide film
through the deposition.
Alternatively, when the coating is employed, a usable solution may be a
solution having a solute of nickel salt such as nickel bromide, nickel
acetate, nickel oxalate, nickel carbonate, nickel chloride, nickel iodide,
nickel nitrate and nickel sulfate, and a solvent consisted of water,
alcohol, acid and ammonia, or may be a solution having a solute of the
nickel element and a solvent selected from a group consisting of benzene,
toluene, xylene, carbon tetrachloride, chloroform and ether. Nickel does
not need to be dissolved completely, an emulsion-like material in which
nickel is dispersed through a medium may also be used.
Alternatively, a method may be employed in which nickel as a simple
substance or a nickel compound is dispersed in a solution for forming an
oxide film to form an oxide film containing nickel. The OCD (Ohka
Diffusion Source) that is a product of Tokyo Ohka Kogyo, Inc., may be used
as such a solution. With the employment of this OCD solution, a silicon
oxide film is readily formed by coating with the solution a surface where
the film is to be formed and then by baking it at about 200.degree. C. The
same may be applied to the case where other catalytic elements are used.
In respect of how to introduce the catalytic elements, coating has
advantages, over the doping or the film formation of Ni by a sputtering
method. The coating is easiest in adjustment of concentration of the
catalytic elements in the semiconductor film of low crystallinity, and
simplifies the process.
The first heat treatment step mentioned above is a step provided for
diffusing the catalytic elements in the semiconductor film of low
crystallinity. When the heat treatment is applied to the semiconductor
film of low crystallinity to which the catalytic elements have been
introduced, the catalytic elements immediately invade the inside of the
semiconductor film to be diffused. The catalytic elements then exert,
while being diffused, catalytic action on molecular chains in an amorphous
state to crystallize the semiconductor film of low crystallinity.
This catalytic action is disclosed by the present applicant in Japanese
Patent Application Laid-Open Nos. Hei 06-244103, Hei 06-244104 and others.
Since the catalytic element is of an invasive atom with respect to
silicon, silicon that is in contact with the catalytic element is bonded
to the catalytic element to form silicide. It has been found that silicide
then reacts with the silicon bond in an amorphous state to progress the
crystallization. This is because the distance between the atoms of the
catalytic element and of silicon has a very close value to that of the
distance between atoms in single crystal silicon. The distance between
Ni--Si has the closest value to that of the distance between single
crystal Si--Si, and is shorter by about 0.6% of the latter.
When schematizing the reaction for crystallizing an amorphous silicon film
with the use of nickel as a catalytic element, it will be expressed by the
following reaction formula:
Si[a]-Ni
(silicide)+Si[b]-Si[c](amorphous).fwdarw.Si[a]-Si[b](crystalline)+Ni
-Si[c](silicide)
In the reaction formula above, the indicators [a], [b] and [c] indicate
positions of Si atoms.
The reaction formula shows that distance between Si[a] and Si[b] is almost
equal to the distance in a single crystal because an Ni atom in silicide
is substituted by an Si[b] atom of silicon in an amorphous portion. It
also shows that Ni causes crystals to grow while being diffused in the
semiconductor film of low crystallinity. Further shown by the formula is
that, upon completion of the crystallizing reaction, Ni is locally present
at the termination of the diffusion (or at the front of the crystal
growth) in a bonded state with Si. In other words, Ni in a form of
silicide expressed as NiSi.sub.x is irregularly distributed in the film
after crystallization. The presence of this silicide may be confirmed as
holes by applying the FPM treatment to the film after crystallization, as
mentioned above.
Incidentally, it has been found that the energy for promoting this
crystallization reaction is appropriately given through heating in a
heating furnace at a temperature of 450.degree. C. or more. The upper
limitation of the heating temperature is set to 650.degree. C. This is set
in consideration for preventing crystallization of the amorphous
semiconductor film from being progressed at a portion where the film does
not react with the catalytic elements. If the film is crystallized at the
portion where it does not react with the catalytic elements, the catalytic
elements cannot be diffused in that portion, so that crystal grains cannot
be increased in size and variation takes place in the grain size thereof.
The second heat treatment above has an object of enhancing and improving
the crystallinity of the crystalline semiconductor film that has been
crystallized by the catalytic elements.
The crystalline semiconductor film formed by the first heat treatment has
defects in crystal grains and an amorphous portion remained. Therefore in
the present invention, a heat treatment is again performed to crystallize
the amorphous portion and to eliminate the defects in crystal grains. This
time, the heat temperature is set higher than in the first heat treatment,
specifically to 500 to 1,100.degree. C., and preferably 600 to
1,100.degree. C. It is needless to say that, upon practicing the process,
the upper limitation of the temperature is determined depending on the
heat resistance temperature of a substrate.
At this step, an excimer laser light may be irradiated instead of the heat
treatment. However, the excimer laser has inevitable variation in
irradiation energy as mentioned above, involving a fear that the
crystallization of the amorphous portion varies. Particularly, under this
state where every film has different distribution of the amorphous
portion, there is a fear that variations take place not only in
characteristics between devices in one semiconductor device but also in
characteristics between semiconductor devices.
For that reason, it is desirable to apply without fail a heat treatment
after the crystallizing step and before irradiation with an excimer laser
light so that the amorphous portion is crystallized and the defects are
reduced. Accordingly, it is important to use a heat treatment to improve
the crystallinity when excimer laser is used at the subsequent light
annealing step.
Known as a heating method equivalent to the heat treatment in a heating
furnace is the RTA method in which infrared light that peaks at the
wavelength of 0.6 to 4 .mu.m, preferably 0.8 to 1.4 .mu.m is irradiated
for several tens to several hundreds seconds. A semiconductor film that
has high absorption coefficient with respect to infrared light is heated
up to 800 to 1,100.degree. C. in a short period of time by irradiation
with infrared light. However, in the RTA method, irradiation takes longer
time than irradiation with excimer laser so that a substrate readily
absorbs the heat, and hence attention should be given to occurrence of
deflection when using a glass substrate.
One of the objects of the present invention is to remove (getter) the
catalytic elements that are locally present in the crystallized
semiconductor film. In the present invention, a group XV element is used
for gettering of the catalytic elements. Here, the group XV element
includes P, As, N, Sb and Bi. The element having the highest gettering
ability is P and the second highest is Sb.
Enumerated as a removing method of the catalytic elements according to the
present invention are a method in which a group XV element is selectively
added in the crystalline semiconductor film to form a region (film)
containing the group XV element, and a heat treatment is applied thereto
to have the catalytic elements absorbed in the region containing the group
XV element, and a method in which a film containing a group XV element is
formed so as to come in contact with the crystalline semiconductor film
and is subjected to a heat treatment so that the semiconductor film
contains the group XV element.
In the former method, the region containing a group XV element may be
formed in the crystalline semiconductor film through as in introduction of
the catalytic elements to the semiconductor film of low crystallinity, a
vapor phase method such as a plasma doping method and an ion implantation
method.
In the latter method, the film containing a group XV element may be a
silicon film or a silicon oxide film that is made to contain a group XV
element, which is formed through deposition utilizing a CVD method or a
sputtering method, or through coating. A microcrystalline silicon film
containing P for forming NI junction, a PSG film and the like typically
exemplify the film.
The concentration of a group XV element in the region added with a Group XV
element or in the film containing a group XV element is ten times the
concentration of the catalytic elements remained in the semiconductor
film. In the crystallizing method of the present invention, the catalytic
elements are remained in 10.sup.18 to 10.sup.20 atoms/cm.sup.3 order, and
the concentration of a group XV element is therefore set to
1.times.10.sup.19 to 1.times.10.sup.21 atoms/cm.sup.3.
A heat treatment is conducted to remove (to have gettered) the catalytic
elements. With the heat treatment, the catalytic elements are diffused in
the region added with a group XV element or in the film containing a group
XV element, and are bonded there with the group XV element to be
inactivated. Thus, this catalyst-removing step may be regarded as a step
of having the catalytic elements absorbed (gettered) in the region added
with a group XV element or into the film containing a group XV element.
It has been proved that, when a croup XIII element is added as well as a
group XV element, the region or film in which the catalytic elements are
absorbed can obtain higher removing effect than in the case where merely a
group XV element is added. When the group XIII element is additionally
used, the concentration of a group XIII element is 1.3 to 2 times as high
as the concentration of a group XV element. The group XIII element
includes B, Al, Ga, In and Ti.
Through the catalyst-removing step of the present invention, it is possible
to obtain a crystalline semiconductor region where the concentration of
the catalytic elements is reduced down to 5.times.10.sup.17 atoms/cm.sup.3
or less (preferably, 2.times.10.sup.17 atoms/cm.sup.3 or less).
Under the present circumstance in which the lower limit of detection by the
SIMS (secondary ion mass spectroscopy) is about 2.times.10.sup.17
atoms/cm.sup.3, a concentration lower than that cannot be measured.
However, it is assumed that the catalytic elements may be reduced at least
to 1.times.10.sup.14 to 1.times.10.sup.15 atoms/cm.sup.3 by performing the
removing step shown in this specification.
In the present invention, in order to lower the temperature and shorten the
time in the catalyst-removing step, the crystalline semiconductor film is
irradiated with a laser light or an intense light prior to this heat
treatment. By this irradiation with light (light annealing), the film
shifts to a state where the catalytic elements that are locally present in
the crystalline semiconductor film are easily diffused.
As described above, the catalytic elements that are distributed in the
semiconductor film in a bonded state with semiconductor molecules, for
example, in a form of NiSi.sub.x, are returned to its atomistic state when
the Ni--Si bond is cut by light annealing energy, or enter into a state
where remained catalytic elements is easy to diffuse in the crystalline
semiconductor film when Ni--Si bond energy is reduced by light annealing
energy.
The light annealing of the present invention may decrease energy required
to diffuse the catalytic elements, so that the catalytic elements are
diffused by heating at 500.degree. C. or more and also the treatment time
is shortened. Further, an effect may be expected in reduction of an area
of the region or film in which the catalytic elements are absorbed,
leading to enlargement of a portion where a device may be formed. The
upper limitation of the heating temperature in the catalyst-removing step
is about 850.degree. C., a temperature at which the group XV element in
the region or film in which the catalytic elements are absorbed does not
move.
In the light annealing step, it is appropriate that the semiconductor film
is irradiated with light confining to a portion to be a semiconductor
layer that constitutes a semiconductor device. The portion should include
at least a region where a depletion layer of this semiconductor layer is
formed (a channel formation region).
For a light source used in the light annealing, excimer laser having a
wavelength of 400 nm or less may be employed. A usable excimer laser may
be, for example, KrF excimer laser (248 nm in wavelength), XeCl excimer
laser (308 nm in wavelength), XeF excimer laser (351 nm, 353 nm in
wavelength), and ArF excimer laser (193 nm in wavelength). Also, XeF
excimer laser (483 nm in wavelength) can be used. An ultraviolet lamp may
be used. Alternatively, an infrared lamp such as a xenon lamp and an arc
lamp may be used. Also may be used an excimer laser light of pulse
oscillation type.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIGS. 1A to 1G are views showing a manufacturing process according to
Embodiment 1;
FIGS. 2A to 2F are sectional views showing a manufacturing process
according to Embodiment 2;
FIGS. 3A to 3D are sectional views showing a manufacturing process
according to Embodiment 3;
FIG. 4 is a plan view showing a CMOS circuit of Example 1;
FIGS. 5A to 5F are sectional views showing a manufacturing process of TFTs;
FIGS. 6A to 6D are sectional views showing the manufacturing process of
TFTs;
FIGS. 7A to 7E are sectional views showing a manufacturing process of TFTs
according to Example 2;
FIGS. 8A to 8D are sectional views showing the manufacturing process of
TFTs;
FIG. 9 is a perspective view of an active matrix substrate of Example 3;
FIGS. 10A and 10B are top views showing a pixel matrix circuit and a CMOS
circuit, respectively;
FIG. 11 is a sectional view of an active matrix substrate;
FIGS. 12A and 12B are perspective views each showing appearance of a liquid
crystal display device of Example 4;
FIGS. 13A to 13F are structural views showing electronic equipments in
Example 6; and
FIGS. 14A to 14D are structural views showing electronic equipments in
Example 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Description will be made of Embodiments of the present invention with
reference to FIGS. 1A to 3D.
Embodiment 1
This embodiment will be described with reference to FIGS. 1A to 1G.
As shown in FIG. 1A, a substrate 10 is prepared and an under film 11 is
formed on the surface thereof. A substrate that may be used as the
substrate 10 includes: insulating substrates such as a glass substrate, a
quartz substrate and a ceramic substrate; a single crystal silicon
substrate; and further, conductive substrates such as a stainless
substrate, a Cu substrate and a substrate made of a metal material having
high melting point, e.g., Ta, W, Mo, Ti, Cr, or made of an alloy of those
bases (for example, a nitrogen based alloy).
The base film 11 has | | |
