U.S. patent application number 09/805254 was filed with the patent office on 2001-08-16 for semiconductor device and fabrication met hod thereof.
Invention is credited to Ohnuma, Hideto, Zhang, Hongyong.
Application Number | 20010014517 09/805254 |
Document ID | / |
Family ID | 16535523 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010014517 |
Kind Code |
A1 |
Zhang, Hongyong ; et
al. |
August 16, 2001 |
Semiconductor device and fabrication met hod thereof
Abstract
There is provided a method for eliminating influence of nickel
element from a crystal silicon film obtained by utilizing nickel. A
mask made of a silicon oxide film is formed on an amorphous silicon
film. Then, the nickel element is held selectively on the surface
of the amorphous silicon film by utilizing the mask. Next, a heat
treatment is implemented to grow crystal. This crystal growth
occurs with the diffusion of the nickel element. Next, phosphorus
is doped to a region by using the mask. Then, another heat
treatment is implemented to remove the nickel element from the
pattern under the mask through the course reverse to the previous
course in diffusing the nickel element in growing crystal. Then,
the silicon film is patterned by utilizing the mask again to form a
pattern. Thus, the pattern of the active layer which has high
crystallinity and from which the influence of the nickel element is
removed may be obtained without increasing masks in particular
(i.e. without complicating the process).
Inventors: |
Zhang, Hongyong;
(Atsugi-shi, JP) ; Ohnuma, Hideto; (Atsugi-shi,
JP) |
Correspondence
Address: |
NIXON PEABODY, LLP
8180 GREENSBORO DRIVE
SUITE 800
MCLEAN
VA
22102
US
|
Family ID: |
16535523 |
Appl. No.: |
09/805254 |
Filed: |
March 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09805254 |
Mar 14, 2001 |
|
|
|
09115839 |
Jul 15, 1998 |
|
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|
6204154 |
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Current U.S.
Class: |
438/486 ;
257/E21.413; 257/E29.278 |
Current CPC
Class: |
H01L 29/66757 20130101;
G02F 1/13454 20130101; H01L 29/78621 20130101 |
Class at
Publication: |
438/486 |
International
Class: |
C30B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 16, 1997 |
JP |
9-207177 |
Claims
What is claimed is:
1. A fabrication method of a semiconductor device, comprising steps
of: providing a mask over a part of a semiconductor film comprising
silicon; providing the semiconductor film with a metal promoting
crystallization of silicon using the mask; crystallizing the
semiconductor film provided with the metal; introducing an element
into the semiconductor film using the mask; subjecting the
semiconductor film to heat treatment to getter the metal by the
element; patterning the semiconductor film into at least one
semiconductor island by etching using the mask after the heat
treatment.
2. A fabrication method of a semiconductor device, comprising steps
of: providing a mask over a part of a semiconductor film comprising
silicon; providing the semiconductor film with a metal promoting
crystallization of silicon using the mask; crystallizing the
semiconductor film provided with the metal; introducing an element
into the semiconductor film using the mask; subjecting the
semiconductor film to heat treatment to getter the metal by the
element; patterning the semiconductor film into at least one active
layer by etching using the mask after the heat treatment; and
forming a source region and a drain region in the active layer with
a channel formation region therebetween in the active layer,
wherein a peripheral portion of the mask coincides with a pattern
of the active layer by the patterning.
3. A fabrication method of a semiconductor device, comprising steps
of: providing a mask over a first part of a semiconductor film
comprising silicon; providing the semiconductor film with a metal
promoting crystallization of silicon outside the first part of the
semiconductor film while the first part of the semiconductor film
is provided under the mask; crystallizing the first part of the
semiconductor film provided under the mask while the metal moves
within the first part of the semiconductor film provided under the
mask; introducing an element into a second part of the
semiconductor film provided outside the first part of the
semiconductor film while the first part of the semiconductor film
is provided under the mask; gettering the metal from the first part
of the semiconductor film to the second part of the semiconductor
film by the element; and subsequently patterning the semiconductor
film into at least one semiconductor island by etching the second
part of the semiconductor film using the mask.
4. A fabrication method of a semiconductor device, comprising steps
of: providing a mask over a first part of a semiconductor film
comprising silicon; providing the semiconductor film with a metal
promoting crystallization of silicon outside the first part of the
semiconductor film while the first part of the semiconductor film
is provided under the mask; crystallizing the first part of the
semiconductor film provided under the mask while the metal moves
within the first part of the semiconductor film provided under the
mask; introducing an element into a second part of the
semiconductor film provided outside the first part of the
semiconductor film while the first part of the semiconductor film
is provided under the mask; gettering the metal from the first part
of the semiconductor film to the second part of the semiconductor
film by the element; and subsequently patterning the semiconductor
film into at least one active layer by etching the second part of
the semiconductor film using the mask; and forming a source region
and a drain region in the active layer with a channel formation
region therebetween in the active layer, wherein a peripheral
portion of the mask coincides with a pattern of the active layer by
the patterning.
5. A fabrication method of an active matrix EL display, comprising
steps of: providing a mask over a part of a semiconductor film
comprising silicon; providing the semiconductor film with a metal
promoting crystallization of silicon using the mask; crystallizing
the semiconductor film provided with the metal; introducing an
element into the semiconductor film using the mask; subjecting the
semiconductor film to heat treatment to getter the metal by the
element; patterning the semiconductor film into at least one
semiconductor island by etching using the mask after the heat
treatment.
6. A fabrication method of an active matrix EL display, comprising
steps of: providing a mask over a part of a semiconductor film
comprising silicon; providing the semiconductor film with a metal
promoting crystallization of silicon using the mask; crystallizing
the semiconductor film provided with the metal; introducing an
element into the semiconductor film using the mask; subjecting the
semiconductor film to heat treatment to getter the metal by the
element; patterning the semiconductor film into at least one active
layer by etching using the mask after the heat treatment; and
forming a source region and a drain region in the active layer with
a channel formation region therebetween in the active layer,
wherein a peripheral portion of the mask coincides with a pattern
of the active layer by the patterning.
7. A fabrication method of an active matrix EL display, comprising
steps of: providing a mask over a first part of a semiconductor
film comprising silicon; providing the semiconductor film with a
metal promoting crystallization of silicon outside the first part
of the semiconductor film while the first part of the semiconductor
film is provided under the mask; crystallizing the first part of
the semiconductor film provided under the mask while the metal
moves within the first part of the semiconductor film provided
under the mask; introducing an element into a second part of the
semiconductor film provided outside the first part of the
semiconductor film while the first part of the semiconductor film
is provided under the mask; gettering the metal from the first part
of the semiconductor film to the second part of the semiconductor
film by the element; and subsequently patterning the semiconductor
film into at least one semiconductor island by etching the second
part of the semiconductor film using the mask.
8. A fabrication method of an active matrix EL display, comprising
steps of: providing a mask over a first part of a semiconductor
film comprising silicon; providing the semiconductor film with a
metal promoting crystallization of silicon outside the first part
of the semiconductor film while the first part of the semiconductor
film is provided under the mask; crystallizing the first part of
the semiconductor film provided under the mask while the metal
moves within the first part of the semiconductor film provided
under the mask; introducing an element into a second part of the
semiconductor film provided outside the first part of the
semiconductor film while the first part of the semiconductor film
is provided under the mask; gettering the metal from the first part
of the semiconductor film to the second part of the semiconductor
film by the element; and subsequently patterning the semiconductor
film into at least one active layer by etching the second part of
the semiconductor film using the mask; and forming a source region
and a drain region in the active layer with a channel formation
region therebetween in the active layer, wherein a peripheral
portion of the mask coincides with a pattern of the active layer by
the patterning.
9. A method according to claim 1 wherein the semiconductor film
comprising silicon comprises SixGe1-x where 0.5<x<1.
10. A method according to claim 2 wherein the semiconductor film
comprising silicon comprises SixGe1-xwhere 0.5<x<1.
11. A method according to claim 3 wherein the semiconductor film
comprising silicon comprises SixGe1-xwhere 0.5<x<1.
12. A method according to claim 4 wherein the semiconductor film
comprising silicon comprises SixGe1-xwhere 0.5<x<1.
13. A method according to claim 5 wherein the semiconductor film
comprising silicon comprises SixGe1-xwhere 0.5<x<1.
14. A method according to claim 6 wherein the semiconductor film
comprising silicon comprises SixGe1-xwhere 0.5<x<1.
15. A method according to claim 7 wherein the semiconductor film
comprising silicon comprises SixGe1-xwhere 0.5<x<l.
16. A method according to claim 8 wherein the semiconductor film
comprising silicon comprises SixGe1-xwhere 0.5<x<1.
17. A method according to claim 1, wherein one or a plurality of
kinds of elements selected among Fe, Co, Ni, Ru, Rh, Pd, Os, Ir,
Pt, Cu, Au, Ge, Pb and In is utilized as the metal promoting the
crystallization of silicon.
18. A method according to claim 1, wherein Ni is utilized as the
metal promoting the crystallization of silicon.
19. A method according to claim 1, wherein an element selected
among P, As and Ab is utilized as the element.
20. A method according to claim 1, wherein P (phosphorus) is
utilized as the element.
21. A method according to claim 1 wherein a device selected from
the group consisting of video camera, portable information
processing terminal, head-mount display, car navigation system,
portable telephone and front type projector is incorporated into
the semiconductor device.
22. A method according to claim 2, wherein one or a plurality of
kinds of elements selected among Fe, Co, Ni, Ru, Rh, Pd, Os, Ir,
Pt, Cu, Au, Ge, Pb and In is utilized as the metal promoting the
crystallization of silicon.
23. A method according to claim 2, wherein Ni is utilized as the
metal promoting the crystallization of silicon.
24. A method according to claim 2, wherein an element selected
among P, As and Ab is utilized as the element.
25. A method according to claim 2, wherein P (phosphorus) is
utilized as the element.
26. A method according to claim 2 wherein a device selected from
the group consisting of video camera, portable information
processing terminal, head-mount display, car navigation system,
portable telephone and front type projector is incorporated into
the semiconductor device.
27. A method according to claim 3, wherein one or a plurality of
kinds of elements selected among Fe, Co, Ni, Ru, Rh, Pd, Os, Ir,
Pt, Cu, Au, Ge, Pb and In is utilized as the metal promoting the
crystallization of silicon.
28. A method according to claim 3, wherein Ni is utilized as the
metal promoting the crystallization of silicon.
29. A method according to claim 3, wherein an element selected
among P, As and Ab is utilized as the element.
30. A method according to claim 3, wherein P (phosphorus) is
utilized as the element.
31. A method according to claim 3 wherein a device selected from
the group consisting of video camera, portable information
processing terminal, head-mount display, car navigation system,
portable telephone and front type projector is incorporated into
the semiconductor device.
32. A method according to claim 4, wherein one or a plurality of
kinds of elements selected among Fe, Co, Ni, Ru, Rh, Pd, Os, Ir,
Pt, Cu, Au, Ge, Pb and In is utilized as the metal promoting the
crystallization of silicon.
33. A method according to claim 4, wherein Ni is utilized as the
metal promoting the crystallization of silicon.
34. A method according to claim 4, wherein an element selected
among P, As and Ab is utilized as the element.
35. A method according to claim 4, wherein P (phosphorus) is
utilized as the element.
36. A method according to claim 4 wherein a device selected from
the group consisting of video camera, portable information
processing terminal, head-mount display, car navigation system,
portable telephone and front type projector is incorporated into
the semiconductor device.
37. A method according to claim 5, wherein one or a plurality of
kinds of elements selected among Fe, Co, Ni, Ru, Rh, Pd, Os, Ir,
Pt, Cu, Au, Ge, Pb and In is utilized as the metal promoting the
crystallization of silicon.
38. A method according to claim 5, wherein Ni is utilized as the
metal promoting the crystallization of silicon.
39. A method according to claim 5, wherein an element selected
among P, As and Ab is utilized as the element.
40. A method according to claim 5, wherein P (phosphorus) is
utilized as the element.
41. A method according to claim 5 wherein the active matrix EL
display is provided in a device selected from the group consisting
of video camera, portable information processing terminal,
head-mount display, car navigation system, portable telephone and
front type projector.
42. A method according to claim 6, wherein one or a plurality of
kinds of elements selected among Fe, Co, Ni, Ru, Rh, Pd, Os, Ir,
Pt, Cu, Au, Ge, Pb and In is utilized as the metal promoting the
crystallization of silicon.
43. A method according to claim 6, wherein Ni is utilized as the
metal promoting the crystallization of silicon.
44. A method according to claim 6, wherein an element selected
among P, As and Ab is utilized as the element.
45. A method according to claim 6, wherein P (phosphorus) is
utilized as the element.
46. A method according to claim 6 wherein the active matrix EL
display is provided in a device selected from the group consisting
of video camera, portable information processing terminal,
head-mount display, car navigation system, portable telephone and
front type projector.
47. A method according to claim 7, wherein one or a plurality of
kinds of elements selected among Fe, Co, Ni, Ru, Rh, Pd, Os, Ir,
Pt, Cu, Au, Ge, Pb and In is utilized as the metal promoting the
crystallization of silicon.
48. A method according to claim 7, wherein Ni is utilized as the
metal promoting the crystallization of silicon.
49. A method according to claim 7, wherein an element selected
among P, As and Ab is utilized as the element.
50. A method according to claim 7, wherein P (phosphorus) is
utilized as the element.
51. A method according to claim 7 wherein the active matrix EL
display is provided in a device selected from the group consisting
of video camera, portable information processing terminal,
head-mount display, car navigation system, portable telephone and
front type projector.
52. A method according to claim 8, wherein one or a plurality of
kinds of elements selected among Fe, Co, Ni, Ru, Rh, Pd, Os, Ir,
Pt, Cu, Au, Ge, Pb and In is utilized as the metal promoting the
crystallization of silicon.
53. A method according to claim 8, wherein Ni is utilized as the
metal promoting the crystallization of silicon.
54. A method according to claim 8, wherein an element selected
among P, As and Ab is utilized as the element.
55. A method according to claim 8, wherein P (phosphorus) is
utilized as the element.
56. A method according to claim 8 wherein the active matrix EL
display is provided in a device selected from the group consisting
of video camera, portable information processing terminal,
head-mount display, car navigation system, portable telephone and
front type projector.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention disclosed in the present specification relates
to a thin film transistor using a crystal silicon film and a
fabrication method thereof. The invention also relates to a device
utilizing such a thin film transistor and a fabricating method
thereof.
[0003] 2. Description of Related Art
[0004] Hitherto, there has been known a thin film transistor
(hereinafter referred to as TFT) using an amorphous silicon film.
It is mainly used for constructing an active matrix circuit of an
active matrix liquid crystal display.
[0005] However, the TFT using the amorphous silicon film has had a
drawback that its operation speed is slow and that a P-channel type
TFT cannot be put into practical use. Then, due to such problems,
it was unable to fabricate an active matrix liquid crystal display
to which a peripheral driving circuit is integrated or to construct
various integrated circuits using the TFT.
[0006] As a solution of this problem, there has been known a scheme
of using a crystal silicon film. The crystal silicon film may be
fabricated by heating or by irradiating laser light.
[0007] However, the heating method has had a problem that a glass
substrate cannot be used because it requires a high temperature
process of 900.degree. C. or more. Considering that the main field
of application of the TFT is a liquid crystal display, it is a
preferential subject to be able to use the glass substrate as the
substrate.
[0008] Meanwhile, although the method of irradiating laser light
can realize a process through which no thermal damage is given to
the substrate, it is not satisfactory in terms of the crystal
uniformity and reproducibility and of the degree of
crystallization.
[0009] As one of solutions of such problems, there has been a
method of promoting the crystallization by using a predetermined
metal element, i.e. the inventive method which the present
applicants have proposed. According to this method, a crystal
silicon film is obtained by introducing metal element typified by
nickel to the amorphous silicon film and by implementing a heat
treatment. This method allows the crystal silicon film having good
crystallinity to be obtained while implementing the heat treatment
below about 600.degree. C. which permits to use the glass
substrate.
[0010] However, because the nickel element remains within the
crystal silicon film, the characteristic of the TFT fabricated by
using the crystal silicon film is influenced adversely. In
concrete, it causes problems that the characteristic changes as
time elapses, thus degrading the reliability.
[0011] Accordingly, it is an object of the invention disclosed in
the present specification to provide a technology for suppressing
the metal element from adversely influencing the characteristic of
the TFT fabricated by using the crystal silicon film obtained by
utilizing the metal element which promotes the crystallization of
silicon.
SUMMARY OF THE INVENTION
[0012] One of the invention disclosed in the present specification
features a semiconductor device comprising an active layer having a
crystal structure in which crystal growth has proceeded from the
whole periphery and a semiconductor device utilizing a
semiconductor element having such structure.
[0013] The structure as described above may be obtained by growing
crystal by diffusing nickel 105 from a periphery 201 of a pattern
which turns out to be an active layer as shown in FIG. 1 and by
causing phosphorus doped to a region 108 outside of the pattern to
getter nickel element as shown in FIG. 2.
[0014] The crystal structure continues in the direction 105 in FIG.
1 and in the direction 110 in FIG. 2 and a crystal boundary extends
along that direction. It may be confirmed by observing through an
optical microscope or by TEM (transmission type electronic
microscope).
[0015] Another scheme of the invention pertains to a fabrication
method of a semiconductor device, comprising steps of diffusing
metal element promoting crystallization of silicon from the whole
periphery of a predetermined region of an amorphous silicon film
within the region to grow crystal and of removing the metal element
out of the region by following the course reverse to the diffusing
course.
[0016] This scheme features the steps of growing crystal by
diffusing nickel element from the periphery as shown in FIG. 1B-1
and of moving (removing) the nickel element to the periphery as
shown in FIG. 2A-1.
[0017] The diffusion of the nickel element plays an important role
in the crystallization. However, it is not desirable for the nickel
element to remain within the crystal silicon film thus obtained.
Then, it becomes important how to remove the nickel element
effectively.
[0018] The course for removing the nickel element to the periphery
of the pattern as shown in FIG. 2A-1 is reverse to the course of
diffusing the nickel element during the crystallization. Because
this course has become a course for moving the nickel element once,
its energy level is minimized as a course for moving nickel. That
is, it has become a course where the hindrance is least for moving
nickel. It is irrelevant to the moving direction of nickel.
[0019] Accordingly, the nickel element moves following the most
effective course for removing the nickel element as shown in FIG.
2A-1.
[0020] Another scheme of the invention pertains to a fabrication
method of a semiconductor device, comprising steps of forming a
mask on an amorphous silicon film; selectively doping metal element
which promotes crystallization of silicon to the amorphous silicon
film by utilizing the mask; implementing a heat treatment to grow
crystal from the region where the metal element has been introduced
to the lower part of the mask in the amorphous silicon film;
selectively introducing an element in the XV group to the silicon
film by using the mask; implementing a heat treatment to move the
metal element to the region where the element in the XV group has
been doped; and removing the region where the element in the XV
group has been doped.
[0021] As the metal element promoting the crystallization of
silicon in the present invention, one or a plurality of kinds of
elements selected among Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au,
Ge, Pb and In may be utilized. The better effect and the high
reproducibility may be obtained when Ni is used in particular.
[0022] An element selected among P, As and Ab is utilized as the
element of the XV group. The better effect may be obtained when P
(phosphorus) is used in particular.
[0023] In concrete, a mask 103 made of a silicon oxide film is
formed on an amorphous silicon film 102 at first as shown in FIG.
1A. Then, nickel element is held selectively on the surface of the
amorphous silicon film 102 by utilizing the mask 103. This process
corresponds to the introduction of nickel element.
[0024] While there are sputtering, CVD, plasma treatment, ion
implantation and the like as methods for introducing nickel
element, the method of using a solution is simplest.
[0025] Next, a heat treatment is implemented to grow crystal as
indicated by arrows (105) in FIG. 1B-1. This crystal growth occurs
with the diffusion of nickel element.
[0026] Next, phosphorus is introduced as shown in FIG. 1C by means
of plasma doping or ion implantation. Phosphorus is doped to a
region 108 by using the mask 103 in this step.
[0027] Then, another heat treatment is implemented to remove the
nickel element from the pattern under the mask 103 by following the
course as indicated by arrows 110 reverse to the previous course of
diffusing the nickel element in growing the crystal as shown in
FIG. 2A-1.
[0028] Then, the nickel element is removed by gettering nickel to
the region where phosphorus has been doped.
[0029] Then, the silicon film is patterned by utilizing the mask
103 again to form a pattern 111.
[0030] Thus, the pattern of the active layer which has high
crystallinity and from which the influence of the nickel element
has been removed may be obtained without increasing masks in
particular (i.e. without complicating the process).
[0031] The specific nature of the invention, as well as other
objects, uses and advantages thereof, will clearly appear from the
following description and from the accompanying drawings in which
like numerals refer to like parts.
BRIEF DESCRIPTION OF DRAWINGS
[0032] FIGS. 1A through 1C are diagrammatic views showing steps for
fabricating a TFT;
[0033] FIGS. 2A through 2D are diagrammatic views showing steps for
fabricating the TFT;
[0034] FIG. 3A through 3C are diagrammatic views showing steps for
fabricating the TFT;
[0035] FIG. 4 is a perspective view showing an outline of an
integrated circuit utilizing the TFT; and
[0036] FIGS. 5A through 5F are schematic views of equipments
utilizing the TFT.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0037] First Embodiment
[0038] FIGS. 1A through 1C show steps for fabricating a
semiconductor device according to the present embodiment. At first,
an amorphous silicon film 102 is formed on a glass substrate 101 in
thickness of 50 nm by means of reduced pressure thermal CVD.
[0039] Although plasma CVD may be used as a method for forming the
amorphous silicon film, it is preferable, when the later
crystallization step is considered, to adopt the reduced pressure
thermal CVD which allows a content of hydrogen to be reduced.
[0040] Corning 1737 glass substrate whose distortion point is
667.degree. C. is used as the glass substrate in the present
embodiment
[0041] Although the case of forming the amorphous silicon film
directly on the surface of the glass substrate is exemplified in
the present embodiment, a silicon oxide film, a silicon oxide
nitride film or a silicon nitride film may be formed as an
underlying film on the surface of the glass substrate depending on
the surface condition thereof or on types and concentration of
impurity contained therein.
[0042] After forming the amorphous silicon film 102, a mask 103
made of a silicon oxide film having a thickness of 150 nm is
formed. A silicon nitride film, a silicon oxide nitride film and
the like may be also used as the material of the mask 103. The
material of the mask 103 must be what can sustain a heat treatment
implemented later.
[0043] Next, a nickel acetate solution which has been prepared so
as to have predetermined nickel concentration is applied to obtain
a state in which nickel element is held in contact with the surface
of the specimen as indicated by the reference numeral (104). The
nickel acetate solution which has been prepared to have
concentration of 10 ppm in terms of weight is used in the present
embodiment. Thus, the state shown in FIG. 1A is obtained.
[0044] As another method for introducing nickel, there is a method
of forming a film containing nickel by means of sputtering or CVD.
Further, a method by means of electric discharge using an electrode
containing nickel or ion implantation may be used.
[0045] Next, a heat treatment is implemented for eight hours at
590.degree. C. within nitrogen atmosphere. This heat treatment is
implemented by using a heating furnace equipped with a resistance
heating heater. It is noted that the heat treatment may be
implemented by irradiating infrared rays.
[0046] The nickel element diffuses in the direction of arrows 105
and thereby crystallization proceeds in this step. That is, the
diffusion of nickel and the crystallization proceed in the
direction of the arrows 105. This heat treatment may be implemented
within a range from 500.degree. C. to a distortion point of the
glass substrate.
[0047] FIG. 1B is a section view showing this state of crystal
growth. FIG. 1B-1 is a plan view showing this state seen from the
above.
[0048] In FIG. 1B-1, part 107 is the part where edge portions of
the grown crystal collide. A crystal boundary is formed in this
part. A peripheral portion 201 of the mask 103 shown in FIG. 1B-1
coincides with a pattern of an active layer which is to be formed
later.
[0049] After finishing the crystallization, P (phosphorus) is doped
by means of plasma doping or ion implantation.
[0050] The plasma doping is a method which involves no mass
separation and which draws out dopant ions by electric field
directly from atmosphere of plasma of material gas and accelerates
and implants them.
[0051] The ion implantation is a method of selecting ions drawn out
of the atmosphere of plasma of the material gas by means of mass
separating using magnetic field and of accelerating and implanting
them.
[0052] Phosphorus is doped to regions 108 under the dose condition
that average concentration thereof is higher than the concentration
of nickel existing within the film (FIG. 1C).
[0053] Next, a heat treatment is implemented at 620.degree. C. for
two hours within nitrogen atmosphere. The temperature of the heat
treatment is selected from a range from 450.degree. C. to
750.degree. C. (generally, the upper limit thereof is decided by
the distortion point of the glass substrate). The higher the
temperature, the better the effect obtained is as a matter of
course. It is noted that this heat treatment may be implemented by
irradiating infrared rays.
[0054] In this step, the nickel element moves in along the course
indicated by the arrows 110 shown in FIGS. 2A and 2A-1, because the
phosphorus doped to the region 108 couples with nickel and they are
fixed there. Nickel actively moves across a distance of several
tens .mu.m or more in the heat treatment at 620.degree. C.
Meanwhile, phosphorus barely moves (it is necessary to heat up to
800.degree. C. or more for phosphorus to move).
[0055] Phosphorus couples with nickel in various ways and the
coupling state is very stable. Accordingly, the nickel element
which has moved within the film and coupled with phosphorus will
not move from there (the region 108). As a result, a state as if
nickel has moved to the region 108 and has been fixed there is
obtained.
[0056] The moving course 110 of the nickel element within the
crystal silicon film 106 is the course reverse to the previous
moving course of the nickel element during the crystallization.
[0057] Because the moving course of the nickel element in the steps
in FIGS. 2A and 2A-1 is the course where the nickel element has
moved once before, it is in the state in which the nickel element
can readily move (there is less hindrance for nickel to move).
[0058] It is supported by the fact that when an experiment is
carried out by differentiating the moving course of nickel during
the crystallization from the moving course of nickel in the nickel
removing stage, it is observed that the move of nickel in the
latter moving stage is clearly hampered.
[0059] Because the mask 103 decides the pattern of the active layer
of the TFT to be formed later, its size is the same with that of
the active layer of the TFT.
[0060] Accordingly, the moving course of the nickel element in the
step shown in FIGS. 2A and 2A-1 is several .mu.m at most.
[0061] According to fundamental experiments, it has been found that
the greater the ratio between an area of the region where
phosphorus has been doped and an area from which nickel is removed,
the higher the nickel removing effect is and the shorter the moving
course of nickel, the higher the nickel removing effect is.
[0062] Accordingly, the area of the region which is masked by the
mask 104 is preferable to be small.
[0063] Thus, the present embodiment has the structure suitable for
removing nickel in terms of the subjects of the moving course of
nickel and of the moving distance thereof. This is advantageous
also when the sub-micronization of devices proceeds from now
on.
[0064] When the step shown in FIGS. 2A and 2(A-1) ends, the nickel
element concentrates in the region 108. That is, the concentration
of the nickel element within the region which is defined by an
outer periphery 201 reduces and the concentration of nickel in the
region 108 around that region increases.
[0065] Next, the exposed region of the silicon film 106 is removed
by using the mask 103. This step is a step of forming the active
layer pattern 111 of the TFT from the silicon film 106.
[0066] Thus, the state shown in FIG. 2B is obtained. Next, the mask
103 made of the silicon oxide film is removed. Then, a silicon
oxide film 100 is formed in a thickness of 100 nm as a gate
insulating film by means of plasma CVD as shown in FIG. 2C.
[0067] Further, an aluminum film not shown is formed in a thickness
of 400 nm by means of sputtering. Then, a resist mask 112 is formed
on the aluminum film. Next, the aluminum film not shown is
patterned by using the resist mask 112 to form an aluminum pattern
113 as shown in FIG. 2C.
[0068] Next, anodic oxidation is implemented by setting the pattern
113 as an anode while leaving the resist mask 112. Here, an anodic
oxide film 114 is formed in a thickness of 500 nm. Because the
resist mask 112 exists in this step, the anodic oxide film 114
grows selectively on the side face of the aluminum pattern 113.
[0069] This step for growing the anodic oxide film is implemented
by using 3 vol. % of oxalic acid aqueous solution as an electrolyte
and by setting the aluminum pattern as the anode and platinum as
the cathode. The anodic oxide film formed in this step is porous
(FIG. 2D).
[0070] Next, the resist mask 112 is removed and anodic oxidation is
implemented again. In this step, an ethylene glycol solution
containing 3 vol. % of tartaric acid and neutralized by aqueous
ammonia is used as an electrolyte.
[0071] In this step, because the electrolyte infiltrates to the
porous anodic oxide film 114, an anodic oxide film 115 in the state
as shown in FIG. 2D is formed. The anodic oxide film 115 formed in
this step has a dense film quality. The thickness of the dense
anodic oxide film 115 is 70 nm.
[0072] Here, the aluminum pattern which is left without being
anodized becomes a gate electrode 116 as shown in FIG. 2D.
[0073] Next, the exposed silicon oxide film 100 is removed by means
of dry etching having vertical anisotropy. Thus, the state as shown
in FIG. 3A is obtained. Here, the silicon oxide film left functions
as a gate insulating film 117.
[0074] Next, phosphorus is doped by means of plasma doping or ion
implantation to regions 118 and 120. These regions will be called
high concentrate impurity regions for convenience. It is noted that
no phosphorus is doped to a region 119 (FIG. 3A). This doping step
is implemented under the condition of forming normal source and
drain regions.
[0075] Next, the porous anodic oxide film 114 is removed
selectively to obtain the state shown in FIG. 3B.
[0076] Then, phosphorus is doped again. Here, the doping is
implemented while lowering the dose more than that of the doping in
the previous step in FIG. 3A by one digit.
[0077] In this step, phosphorus is doped to regions 121 and 123.
These regions will be called as low concentrate impurity regions
because the doping is implemented with the lower dose as compared
to the regions 118 and 120 (FIG. 3B).
[0078] Among the low concentrate impurity regions, the drain side
region 123 functions as an LDD (light doped drain).
[0079] Then, the region 122 is defined as a channel region. It is
noted that although a high resistant region called an offset region
is formed by the thickness of the anodic oxide film 115 adjacent to
the channel region 122, its existence is neglected in the present
embodiment because the thickness of the anodic oxide film 115 is as
thin as 70 nm.
[0080] After finishing the doping, laser light is irradiated to
anneal the damage of the doped region and to activate the dopant.
This step may be implemented by irradiating strong light.
[0081] Next, a silicon nitride film 124 is formed in a thickness of
250 nm as an interlayer insulating film by means of plasma CVD.
Further, an acrylic resin film 125 is formed by means of spin
coating. The acrylic resin film is formed so as to have a thickness
of 700 nm at the thinnest part. It is noted that the reason why the
resin film is that the surface thereof may be flattened.
[0082] Next, contact holes are created to form a source electrode
126 and a drain electrode 127. Thus, an N-channel type TFT is
completed as shown in FIG. 3C.
[0083] While the N-channel type TFT has been exemplified above, a
P-channel type TFT may be fabricated by doping boron, instead of
phosphorus, in the steps in FIGS. 3A and 3B.
[0084] Second Embodiment
[0085] A case of fabricating an inverted-stagger type TFT will be
shown in the present embodiment. In this case, an amorphous silicon
film is formed after creating a gate electrode. Then,
crystallization is implemented and nickel is removed.
[0086] The material of the gate electrode must have resistance to
the later heat treatment in case of the present embodiment
[0087] Third Embodiment
[0088] Various devices utilizing the TFT will be exemplified in the
present embodiment. FIG. 4 shows one example of a microprocessor of
a semiconductor circuit utilizing the TFTs and an enlarged view
thereof showing a complementary TFT of an N-type TFT and a P-type
TFT.
[0089] An insulating film 502 is formed on a ceramic substrate 501
to isolate the substrate from the device. Then, formed thereon are
I/O ports 503 through 505, a CPU 506, a cache memory 507, a cache
address array 508, a multiplier 509, a circuit 510 containing a
real-time clock, a serial interface, a timer and the like, a clock
control circuit 511, a cache controller 512 and a bus controller
513.
[0090] The thin film transistor disclosed in the present
specification may be applied to various flat panel displays and to
information processing terminals, video camera and the like
equipped with the flat panel display. These devices will be named
generically as semiconductor devices in the present
specification.
[0091] The concrete structure of various devices will be shown
below. FIGS. 5A through 5F show various semiconductor devices.
These semiconductor devices use the TFT at least partially.
[0092] FIG. 5A shows a portable information processing terminal.
The information processing terminal is equipped with an active
matrix liquid crystal display or an active matrix EL display and a
camera section 2002 for taking in information from the outside. It
is also equipped with an integrated circuit 2006 inside. An image
receiving section 2003 and a control switch 2004 are disposed in
the camera section 2002.
[0093] It is considered that the information process terminals will
be lightened and thinned more and more in order to improve the
portability thereof. In such structure, it is preferable to
integrate a peripheral driving circuit, an operation circuit and a
memory circuit further on a substrate on which the active matrix
display 2005 is formed.
[0094] FIG. 5B shows a head-mounted display comprising an active
matrix liquid crystal display or an EL display 2102 in a main body
2101. It is arranged so that the main body 2101 can be put on the
head.
[0095] FIG. 5C shows a car navigation system. This equipment has a
function of receiving signals from a satellite by an antenna 2204
and of displaying geographical information on an active matrix
liquid crystal display 2202 provided in a main body 2201 based on
the signals.
[0096] An EL type display may be also adopted as the display 2202.
In either case, the display is the active matrix flat panel display
utilizing the TFT. Control switches 2203 are provided on the main
body 2201 so as to be able to manipulate the system in various
ways.
[0097] FIG. 5D shows a portable telephone which comprises, on a
main body 2301 thereof, an active matrix liquid crystal display
2304, a voice output section 2302, a voice input section 2303,
control switches 2305 and an antenna 2306. An equipment in which
the portable information processing terminal as shown in FIG. 5A
and the portable telephone shown in FIG. 5D are combined is also
merchandised in these days.
[0098] FIG. 5E shows a portable video camera comprising, on a main
body 2401 thereof, an active matrix liquid crystal display 2402, a
voice input section 2403, control switches 2404, a battery 2405 and
an image receiving section 2406.
[0099] FIG. 5F shows a front type projector comprising a main body
2501, a light source 2502, a display unit 2503, an optical system
2504 and a screen 2505. The present invention is applicable to the
display unit 2503.
[0100] Although the reflective one has been exemplified as the
liquid crystal display 2503 here, it is also possible to use a
transmission type liquid crystal display by changing the optical
system.
[0101] Fourth Embodiment
[0102] A case of using a film represented by Si.sub.xGe.sub.1-x
(0.5<X<1), instead of the silicon film, in the structure of
the other embodiment will be shown in the present embodiment.
[0103] The present invention allows to use not only simplex of
silicon but also a compound film containing silicon as the main
substance. The film containing silicon as the main substance is
what contains silicon component at least by a half or more.
[0104] For example, the amorphous silicon film 102 may be the film
represented by Si.sub.xGe.sub.1-x (0.5<X<1) embodiment.
[0105] Fifth Embodiment
[0106] A case of introducing phosphorus not by doping but by
forming a silicon film into which phosphorus has been doped in high
concentration in the fabrication step shown in FIG. 1C in the first
embodiment will be shown.
[0107] In this case, the silicon film into which phosphorus has
been doped in high concentration is formed by means of plasma CVD
after ending the crystallization step shown in FIG. 1B.
[0108] Phosphorus is doped by using forming gas in which 98 vol. %
of silane and 2 vol. % of phosphine are mixed for example.
[0109] Then, when a heat treatment is implemented on the silicon
film into which phosphorus has been doped in high concentration
after its formation under the same condition with the first
embodiment, the nickel element moves into the silicon film.
[0110] Although the case of using the silicon film into which
phosphorus has been doped in high concentration has been shown
here, it is also possible to use a PSG film and the like.
[0111] Sixth Embodiment
[0112] The present embodiment pertains to a scheme of side-etching
the side of the active layer pattern 111 after forming the pattern
111 by using the mask 103 as shown in FIG. 2B in the fabrication
steps shown in the first embodiment.
[0113] The pattern 111 becomes the active layer of the TFT in the
scheme shown in the first embodiment. In this case, phosphorus is
doped into the peripheral portion of the pattern 111 which is
adjacent to the region 108 from which nickel has been drawn out.
Therefore, there is a possibility that phosphorus and nickel exist
relatively in high concentration in the peripheral portion of the
pattern 111.
[0114] Then, the side face of the pattern 111 is side-etched after
finishing the patterning shown in FIG. 2B in the present
embodiment. Thereby, the above-mentioned apprehension may be
eliminated and the reliability on the characteristics of the device
may be enhanced further.
[0115] The present embodiment may be implemented by implementing
wet-etching after dry-etching when the method of etching shown in
FIG. 2B is dry-etching. When the method of etching shown in FIG. 2B
is wet-etching, it is arranged so as to advance the wet-etching
further.
[0116] As described above, it is possible to provide the technology
for suppressing the metal element from adversely affecting the
characteristics of the TFT fabricated by using the crystal silicon
film obtained by utilizing the metal element which promotes
crystallization of silicon by using the invention disclosed in the
present specification.
[0117] In particular, the invention disclosed in the present
specification allows to obtain the significant effects of a)
simplifying the processing steps, b) efficiently removing the metal
element and c) accommodating to sub-micron patterns by implementing
the steps of 1) selectively introducing the metal element for
promoting crystallization, 2) selectively doping phosphorus for
removing the metal element and c) forming the active layer pattern
of the TFT by utilizing one mask.
[0118] While the preferred embodiments have been described,
variations thereto will occur to those skilled in the art within
the scope of the present inventive concepts which are delineated by
the following claims.
* * * * *