Semiconductor device contact registration structure

An aluminum pattern is formed at the same time as a gate electrode, and anodic oxide films are formed on the surfaces of the aluminum pattern and the gate electrode. After an interlayer insulating film is formed, a contact hole is formed through it. Even if the contact hole is deviated from the intended position, there occurs no failure because of the existence of the aluminum pattern on which the anodic oxide film is formed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the configuration of a contact portion of 
a semiconductor device typified by a thin-film transistor as well as to a 
method of forming it. 
2. Description of the Related Art 
FIGS. 2A to 2E schematically show a conventional, old process used in a 
thin-film transistor manufacturing process, for instance. Specifically, 
this process is to take contact to a semiconductor layer formed on a glass 
substrate or a quartz substrate. 
First, as shown in FIG. 2A, a semiconductor layer 202 is formed on a 
substrate 201 having an insulative surface. The substrate 201 is a quartz 
or glass substrate. The semiconductor layer 202 is an amorphous or 
crystalline silicon film. For example, the semiconductor layer 202 shown 
in FIG. 2A is part of an active layer of a thin-film transistor. 
Next, an insulating film 203 is so formed as to cover the semiconductor 
layer 202. The insulating film 203, called an interlayer insulating film, 
is a silicon oxide film or a silicon nitride film. (FIG. 2B) 
Then, an opening 204 called a contact hole is formed through the insulating 
film 203. (FIG. 2C) 
Finally, a wiring line 205 is formed with such a material a metal or a 
silicide, to complete a contact portion (FIG. 2D) 
However, as the semiconductor layer 202 pattern is miniaturized and is made 
finer, there may occur an erroneous positional relationship between the 
contact hole 204 and the semiconductor layer 202 as shown in FIG. 2E. This 
may result in etching of the substrate 201. Where a silicon oxide film as 
an undercoat film is formed on the substrate 201, it may be etched in a 
similar manner. This may later cause a contact failure, a line 
disconnection, and other failures. 
The above erroneous positional relationship can be caused by a mask 
registration error in forming the contact hole 204, a mask registration 
error in forming the semiconductor layer 202 pattern, and other factors. 
In many cases, these factors occur in combination. 
The state of FIG. 2E may be a cause of a failure in a manufacturing 
process. Although this problem can be solved by increasing the patterning 
accuracy and the accuracy of contact hole formation, these measures can 
cause other undesired effects such as an increase in manufacturing cost 
and reduction in productivity. 
SUMMARY OF THE INVENTION 
An object of the present invention is to solve the above-described 
registration error problem which occurs in forming a contact hole of a 
miniaturized semiconductor device. 
According to a first aspect of the invention, there is provided a 
semiconductor device comprising a semiconductor; an insulating film formed 
on the semiconductor; a plurality of patterns formed on the insulating 
film and made of a material capable of being anodized, at least one of the 
plurality of patterns having a function of determining a position of a 
contact to the semiconductor; and anodic oxide films formed on respective 
surfaces of the plurality of patterns. 
According to a second aspect of the invention, there is provided a 
semiconductor device comprising a semiconductor; an insulating film formed 
on the semiconductor; a plurality of patterns formed on the insulating 
film and made of a material capable of being anodized, at least one of the 
plurality of patterns serving as an electrode and at least one of the 
other patterns having a function of determining a position of a contact to 
the semiconductor; and anodic oxide films formed on respective surfaces of 
the plurality of patterns. 
According to a third aspect of the invention, there is provided a 
manufacturing method of a semiconductor device comprising the steps of 
forming a first insulating film on a semiconductor; forming a thin film on 
the first insulating film with a material capable of being anodized; 
forming an electrode and a pattern for determining a position of a contact 
by patterning the thin film; forming anodic oxide films on respective 
surfaces of the electrode and the pattern; forming a second insulating 
film to cover the electrode and the pattern; and forming a contact hole 
through the first and second insulating films, and forming the contact to 
the semiconductor by utilizing the pattern.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiment 1 
In this embodiment, the present invention is applied to a contact portion 
of a thin-film transistor. 
FIGS. 1A to 1D show a manufacturing process according to this embodiment, 
i.e., a manufacturing process of a thin-film transistor that is disposed 
in the pixel region of an active matrix liquid crystal display device. In 
the pixel region, the source of the thin-film transistor is connected to 
one of source lines that are arranged in matrix and its drain is connected 
to one of pixel electrodes. 
This embodiment assumes a configuration in which the source line is as 
narrow as less than about 2 .mu.m to increase the aperture ratio of 
pixels, in which case it is difficult to take contact between the source 
region of a thin-film transistor and a source line. 
Although this embodiment describes the manufacturing process of a single 
thin-film transistor, it is an ordinary configuration that more than 
several hundred thousand thin-film transistors are arranged in matrix. 
The manufacturing process will be hereinafter described. First, a silicon 
oxide film or a silicon oxynitride film 102 as an undercoat film is formed 
on a glass or quartz substrate 101 at a thickness of 3,000 to 5,000 .ANG.. 
To form a silicon oxide film, plasma CVD is performed by using material 
gases of silane and oxygen, or by plasma CVD with a TEOS material gas. 
To form a silicon oxynitride film, plasma CVD is performed in which the 
material gases are a combination of silane, oxygen, and ammonia, a 
combination of TEOS and ammonia, a combination of silane, oxygen, and 
N.sub.2 O, or a combination of TEOS and N.sub.2 O. 
The undercoat film 102 has an effect of stabilizing the electrical 
characteristics of an active layer to be later formed thereon as well as a 
function of preventing such impurities as alkali ions from being 
introduced from the glass substrate 101 into the active layer. To attain 
these objects, it is preferred to use a silicon oxynitride film. 
After the formation of the undercoat film 102, an amorphous silicon film 
(not shown) as a starting film to form an active layer is formed by plasma 
CVD or low-pressure thermal CVD. From the viewpoints of film quality and 
electrical characteristics, it is preferred that the amorphous silicon 
film be formed by low-pressure thermal CVD. 
The amorphous silicon film (not shown) is then crystallized into a 
crystalline silicon film (not shown) by heating, laser light illumination, 
a combination thereof, or a combination of infrared light or ultraviolet 
light illumination and one of the above methods. 
An island-like semiconductor layer 103 to later constitute the active layer 
of the thin-film transistor is formed by patterning the crystalline 
silicon film (not shown). 
Thereafter, a 1,000-.ANG.-thick, silicon oxide or silicon oxynitride film 
104, which is to serve as a gate insulating film, is so formed as to cover 
the island-like semiconductor layer 103 in the same manner as the 
undercoat film 102 was formed above. 
Also in this case, from the viewpoints of film quality and electrical 
characteristics, it is preferred that a silicon oxynitride film be formed 
as the gate insulating film 104. 
Next, a 4,000-.ANG.-thick aluminum film (not shown) to constitute a gate 
electrode is formed by sputtering. Scandium is mixed into the aluminum 
film at 0.1 wt % to prevent hillocks and whiskers from occurring due to 
abnormal growth of aluminum in a later heating step or laser light 
illumination step. Hillocks and whiskers, which are generated by a 
phenomenon that aluminum grows to assume a needle or prickle-like shape, 
may cause a problem of short-circuiting between wiring lines. 
The aluminum film (not shown) is then patterned into aluminum patterns 105 
to 107. The pattern 106 is to later constitute a gate electrode. The 
pattern 105/107 will be used to take contact to a source region. 
The pattern 105/107 will not serve as an electrode, but will be used to 
provide a margin for the pattern registration error in forming a contact 
hole. FIG. 1A shows cross-sections of the pattern 105/107 having a 
rectangular or circular shape. Thus, the state of FIG. 1A is obtained. 
Then, anodic oxidation is performed by using the pattern of the aluminum 
patterns 105 to 107 as the anode, whereby anodic oxide films are formed 
thereon. An electrolyte is obtained by neutralizing an ethylene glycol 
solution containing tartaric acid at 3% with aqueous ammonia. Platinum is 
used as the cathode in the electrolyte. 
The temperature of the electrolyte is set at 10.degree. C. The application 
voltage is increased up to 40 V. The thickness of the anodic oxide films 
is set at 600 .ANG.A. 
The anodic oxide films serve as electrically insulative films covering the 
surfaces of the respective aluminum patterns, as well as have a function 
of suppressing occurrence of hillocks and whiskers as mentioned above. 
Anodic oxide films 108 to 110 are formed by the above step. Thus, the state 
of FIG. 1B is obtained. 
In this state, impurity ions are implanted to form source and drain 
regions. In this embodiment, to form an n-channel thin-film transistor, P 
(phosphorus) ions are implanted by plasma doping. As a result, a source 
region 11, a channel region 12, and a drain region 13 are formed in a 
self-aligned manner. 
Where the anodic oxide film 110 is thick (more than 1,000 .ANG.), offset 
regions corresponding to such a thickness are formed in the active layer. 
This technique is disclosed in Japanese Unexamined Patent Publication Nos. 
Hei. 4-360580 and Hei. 5-166837. 
Subsequently, a silicon oxide film, a silicon nitride film, or a silicon 
oxynitride film is formed as an interlayer insulating film 113 by plasma 
CVD. 
A contact hole 114 is formed through the insulating film 113 and subsequent 
a source line 115 is formed. Even if a certain registration error occurs 
in forming the contact hole 114 for the source region 11, the existence of 
the aluminum pattern 105/107 on which the anodic oxide film 108/109 is 
formed prevents the occurrence of a state as shown in FIG. 2E. This is 
because the width of the pattern 105/107 provides an additional margin in 
forming the contact hole 114. 
In the configuration shown in FIG. 1D, the source line 115 to contact the 
source region 11 of the thin-film transistor is so disposed that the 
source region 11 exists right under it. That is, the source line 115 
overlaps with the active layer (source region 11) of the thin-film 
transistor, and the source line 115 and the source region 11 are brought 
into contact with each other at the overlapping portion. 
While this configuration is advantageous in being capable of increasing the 
aperture ratio, it is disadvantageous in that a registration error of the 
contact hole 114 likely occurs in a case where the source line 115 is 
narrow. 
However, the above registration error problem can be solved by forming the 
pattern 105/107 covered with the anodic oxide film adjacent to the contact 
hole opening area as in this embodiment. 
Naturally the problem of FIG. 2E arises if the pattern registration error 
exceeds the margin that is assured by the pattern 105/107. 
After the formation of the contact hole 114 for the source region 11, the 
source line 115 is formed which is composed of a titanium film, an 
aluminum film, and a titanium film. This wiring line structure is 
effective in thinning down a wiring line because it can reduce the 
resistance. 
After the formation of the source line 115, a second interlayer insulating 
film 116 is formed which is a silicon oxide film or a silicon nitride 
film. Alternatively, a resin material such as acrylic or polyimide may be 
used. The use of a resin material is very advantageous because its surface 
can be planarized. 
After the formation of the second interlayer insulating film 116, a contact 
hole reaching the drain region 13 and an ITO pixel electrode 117 are 
formed. The formation of the contact hole need not be performed at high 
positioning accuracy. 
Where the active layer of the thin-film transistor is miniaturized and the 
positioning accuracy of the contact hole for the drain region 13 is 
required to be increased, it is necessary to secure an increased margin by 
forming an aluminum pattern as in the case of the source region 11. 
Thus, a thin-film transistor is completed as shown in FIG. 1D. In this 
thin-film transistor, by virtue of the existence of the aluminum pattern 
105/107 which increases the positioning margin, the problem of FIG. 2E can 
be prevented from occurring in forming the contact hole for the source 
region 11. 
As a result, it can be prevented that the yield and the reliability are 
reduced by contact failures. 
Embodiment 2 
This embodiment relates to a thin-film transistor which is configured 
differently than in the first embodiment, though it is also disposed in 
the pixel region of an active matrix liquid crystal display device. 
FIGS. 3A to 3C outlines a thin-film transistor according to this 
embodiment. FIG. 3A is a top view and FIGS. 3B and 3C are sectional views 
taken along lines B-B' and C-C' in FIG. 3A, respectively. 
In FIGS. 3A to 3C, reference numerals 301 and 302 denote wiring lines 
called a source line and a gate line, respectively. The source lines 301 
and the gate lines 302 are arranged in matrix and thin-film transistors 
are disposed at their intersections. 
A capacitance line 303 is to provide an auxiliary, capacitance. Existing in 
the same plane as the gate line 302, the capacitance line 303 is formed at 
the same time as the gate line 302 is formed by patterning. 
Reference numeral 304 denotes a peripheral portion or an ITO pixel 
electrode 305. In this embodiment, the peripheral portion 304 of the pixel 
electrode 305 overlaps with the source line 301 and the capacitance line 
303. 
This configuration eliminates the need of covering the peripheral portion 
of the pixel electrode with a black matrix, thereby providing a maximized 
aperture ratio. 
Reference numeral 306 denotes a peripheral portion of an adjacent pixel 
electrode 307, and 308 denotes a peripheral portion of another adjacent 
pixel electrode. 
An active layer 309 of a thin-film transistor is made of a crystalline 
silicon film. The thin-film transistor of this embodiment crosses the gate 
line at three locations, and therefore has three channel forming regions. 
This structure is equivalent to a series connection of three thin-film 
transistors. 
MOS capacitors are formed at two regions where the active layer 309 crosses 
the capacitance line 303. Reference numeral 313 denotes a portion for 
increasing the capacitance. 
Reference numerals 311 and 312 denote contact holes. 
In FIG. 3B, reference numeral 314 denotes a glass or quartz substrate. From 
the viewpoint of heat resistance, it is preferred to use a quartz 
substrate. On the other hand, to decrease the cost or provide a large-area 
substrate, a glass substrate is preferred. 
Although it is not apparent from FIGS. 3A to 3C, a silicon oxide film or a 
silicon oxynitride film as an undercoat film is formed on the substrate 
314. The undercoat film has an effect of preventing impurities from 
diffusing from the substrate 314. 
A gate insulating film 315 is made of a silicon oxide film. From the 
viewpoint of electrical stability, it is preferred to use a silicon 
oxynitride film rather than a silicon oxide film. A silicon oxynitride 
film can be formed by plasma CVD by using a mixed gas of oxygen, silane, 
and N.sub.2 O or a mixed gas of TEOS and N.sub.2 O. 
Reference numeral 316 denotes an aluminum film containing scandium at 0.18 
wt %. A dense anodic oxide film 317 is formed on the aluminum film 316 by 
anodic oxidation, which is performed in an electrolyte with the aluminum 
film 316 used as the anode. The electrolyte is obtained by neutralizing an 
ethylene glycol solution containing tartaric acid at 3% with ammonia. 
The dense anodic oxide film 317 is highly insulative, and is very hard to 
etch. This embodiment later uses the anodic oxide film 317 in forming 
contact portions 318 and 319, taking advantage of its high etching 
resistance. 
Reference numeral 320 denotes an interlayer insulating film made of a 
silicon oxide film, a silicon nitride film, or a silicon oxynitride film. 
The source line 301 is formed on the interlayer insulating film 320. A 
second interlayer insulating film 321 made of a resin material is so 
formed as to cover the interlayer insulating film 320. Being made of a 
resin material, the surface of the second interlayer insulating film 321 
can be planarized. 
An ITO electrode 305 constituting a pixel electrode is formed on the second 
interlayer insulating film 321 made of a resin material. The ITO electrode 
305 contacts the drain region of the active layer 309 at the portion 318. 
In the contact portion 318, since the contact hole 312 is surrounded by the 
aluminum film 316 and the anodic oxide film 317 formed thereon, there 
occurs no such problem as overetching to the underlying member even if the 
contact hole 312 is formed at a position that is somewhat deviated from 
the intended position. 
That is, since the dense anodic oxide film 317 that is highly resistant to 
various kinds of etching exists except where the contact hole 312 for the 
active layer 309 is to be formed, etching does not proceed past the anodic 
oxide film 317 even if the contact hole forming position is somewhat 
deviated; the underlying member can be prevented from being bored unlike 
the case of FIG. 2E (indicated by numeral 206). 
This is very advantageous in the configuration of FIGS. 3A to 3C which 
makes full use of fine patterns, where a registration error in forming a 
contact hole would otherwise directly lead to a failure. 
Also in the contact portion 319 of the source line 301 and the source 
region of the active layer 309 (see FIG. 3C), an aluminum film 322/323 
covered with an anodic oxide film 324 is formed adjacent to the contact 
hole forming area. 
In FIG. 3C, reference numerals 322 and 323 denote cross-sections of the 
aluminum film that is so formed as to surround the contact hole. 
In the contact portion 319 shown in FIG. 3C, by virtue of the structure 
that the area where the contact hole 311 is to be formed is surrounded by 
the aluminum film 322/323 covered with the anodic oxide film 324, there 
can be prevented a failure as shown in FIG. 2E even at the occurrence of a 
registration error in forming the contact hole 311. 
As described above, according to the configuration of FIGS. 3A to 3C, the 
contact hole for each of the source and drain regions of the thin-film 
transistor can be defined in a self-aligned manner by utilizing the 
aluminum film covered with the anodic oxide film. This prevents the 
occurrence of a failure as shown in FIG. 2E. 
The configuration of this embodiment is a very effective technique in 
advancing the miniaturization. 
Embodiment 3 
In the embodiment of FIGS. 1A to 1D, the aluminum pattern (whose 
cross-sections are indicated by numerals 105 and 107 in FIG. 1D) has a 
circular shape, or a rectangular shape or some other proper polygonal 
shape. With such a shape, there is unavoidably formed, between the channel 
forming region and the contact area of the source region (or drain 
region), a high-resistivity region where no impurity ions are implanted. 
Therefore, if it is intended to increase the width of the pattern 105/107 
to obtain a larger process margin, the existence of the high-resistivity 
region adversely affects the characteristics of the thin-film transistor. 
This embodiment is intended to solve the above problem, that is, to secure 
a sufficient process margin in forming a contact hole without adversely 
affecting the characteristics of a thin-film transistor. 
FIGS. 4A to 4E and 5A to 5D outline a manufacturing process according to 
this embodiment. First, as shown in FIG. 4A, a 3,000-.ANG.-thick silicon 
oxide or silicon oxynitride film 402 as an undercoat film is formed on a 
glass substrate 401 by plasma CVD. 
Further, an amorphous silicon film (not shown) is formed by plasma CVD or 
low-pressure thermal CVD, and then crystallized into a crystalline silicon 
film (not shown) by heating or laser light illumination. 
The crystalline silicon film (not shown) is then patterned into an 
island-like region 403 which is to serve as the active layer of a 
thin-film transistor. 
After the formation of the island-like region 403, a 1,000-.ANG.-thick 
silicon oxide region 404 to serve as a gate insulating film is formed by 
plasma CVD so as to cover the island-like region 403. Thus, the state of 
FIG. 4A is obtained. 
Subsequently, an aluminum film 405 to later constitute a gate electrode is 
formed. The aluminum film 405 will also be used in forming contact holes 
for source and drain regions. 
It is noted that other materials capable of being anodized can be used 
instead of aluminum. In particular, where a high-temperature (more than 
800.degree. C.) process is employed with the use of a quartz substrate, it 
is preferred to use a material such as tantalum which is heat resistant 
and capable of being anodized. 
Then, an anodic oxide film (not shown) as thin as 140 .ANG. is formed on 
the surface of the aluminum film 405 by using, as an electrolyte, an 
ethylene glycol solution containing tartaric acid at 3%. In the 
electrolyte, the aluminum film 405 and platinum are used as the anode and 
the cathode, respectively. 
The thickness of the resulting anodic oxide film can be made 140 .ANG. by 
increasing the application voltage up to 10 V. 
Being dense, the anodic oxide film (not shown) has a function of increasing 
the adhesiveness of a resist film that will be used in patterning the 
aluminum film 405. Thus, the state of FIG. 4B is obtained. 
After resist masks 41 to 43 are formed, the aluminum film 405 is patterned 
to form regions 406 to 408. The region 407 will constitute a gate 
electrode while the regions 406 and 408 will secure process margins in 
forming contact holes for source and drain regions. 
After the formation of the regions 406 to 408, porous anodic oxide films 
409 to 411 are formed by using, as an electrolyte, a 3%-aqueous solution 
of oxalic acid. The porous anodic oxide films 409 and 411 are formed by 
anodic oxidation by applying voltages to the aluminum regions 406 and 408 
through wirings 50 as shown in FIGS. 6(A) and 6(B). 
The growth distance of the anodic oxide films 409 to 411 can be set up to 
several micrometers. It can be set at 6,000 .ANG. by increasing the 
application voltage up to 8 V. 
The porous anodic oxide film 410 is formed on the side face of the gate 
electrode 407, and will be used in forming low-concentration impurity 
regions (including a region usually called a LDD region). 
In the above step of forming the porous anodic oxide films 409 to 411, the 
anodic oxidation proceeds only on the side faces of the patterns 406 to 
408 because of the existence of the resist masks 41 to 43. 
Once the state of FIG. 4C is obtained, the resist masks 41 to 43 are 
removed. 
Next, anodic oxidation is again performed under the above-mentioned 
conditions for forming a dense anodic oxide film. In this step, anodic 
oxide films 412 to 414 are formed because an electrolyte enters into the 
inside of the porous anodic oxide films 409 to 411. Thus, the state of 
FIG. 4D is obtained. The dense anodic oxide films 412 and 414 are formed 
by anodic oxidation by applying voltages to the aluminum regions 406 and 
408 through the wirings 50 as shown in FIGS. 6(A) and 6(B). Subsequently, 
the wirings 50 are removed from the aluminum regions 406 and 408. 
Thereafter, the exposed portions of the silicon oxide film 404 are removed 
by etching to obtain residual silicon oxide films 415 to 417. The film 416 
will serve as a gate insulating film. 
Next, as shown in FIG. 5A, the porous anodic oxide films 409 to 411 are 
removed selectively. 
FIG. 6A is a top view showing this state. FIG. 5A is a sectional view taken 
along line A-A' in FIG. 6A. 
As shown in FIG. 6A, each area (indicated by circles in FIG. 6A) where a 
contact hole for the active layer 403 is to be formed is surrounded, i.e., 
protected by the aluminum film on which the dense anodic oxide film is 
formed. 
Subsequently, impurity ions are implanted. In this embodiment, to form an 
n-channel thin-film transistor, P ions are implanted by plasma doping. 
In this step, no impurity ions are implanted into regions 418, 423, and 427 
because the aluminum patterns 406 to 408 above the active layer 403 serve 
as masks. Among those regions, the region 423 becomes a channel forming 
region. 
Since impurity ions are directly implanted into regions 420 and 425, they 
become high-concentration impurity regions, i.e., source and drain 
regions, respectively. 
Impurity ions (P ions) are implanted at a lower concentration in regions 
419, 421, 424, and 426 than in the regions 420 and 425 because of the 
residual silicon oxide films 415 to 417 existing above. 
Among the low-concentration impurity regions 419, 421, 424, and 426, the 
regions 421 and 424 are adjacent to the channel forming region 423. In 
particular, the region 424 has a function of reducing the electric field 
strength between the channel forming region 423 and the drain region 425, 
thereby improving the off-current characteristic of the thin-film 
transistor. 
The region 424 is generally called a LDD (lightly doped drain) region. 
Thus, the state of FIG. 5A is obtained. 
After the implantation of impurity ions, laser light or strong light 
illumination is performed to anneal the regions where impurity ions have 
been implanted. Where a quartz substrate is used, the annealing may be 
performed by heating. 
Next, as shown in FIG. 5B, a silicon oxide film, a silicon nitride film, or 
a silicon oxynitride film is formed as an interlayer insulating film 428. 
Contact holes 429 and 430 are then formed. Even if the contact hole forming 
position is deviated from the intended position so that the contact hole 
encompasses an area not covered with the active layer 403, the underlying 
member can be prevented from being bored because the peripheral portion of 
the active layer 403 is protected by the aluminum film 406 or 408 as shown 
in FIG. 6B. 
Once the state of FIG. 5B is obtained, impurity ions, i.e., P ions are 
implanted again. This is to prevent a contact failure from being caused by 
the existence of the low-concentration impurity regions 419 and 426 having 
a relatively high resistivity. 
The regions where impurity ions have been implanted are activated by again 
performing laser light or strong light illumination. The resistivity of 
the contact regions of the active layer can be reduced in this manner. 
Thus, the state of FIG. 5C is obtained. Thereafter, contact wiring 
lines/electrodes 431 and 432 are formed as shown in FIG. 5D, to complete a 
thin-film transistor. 
In this embodiment, by virtue of the existence of the aluminum patterns 406 
and 408 covered with the anodic oxide films that are hard to etch, the 
process margin of the mask registration in forming the contact holes can 
be increased. 
Embodiment 4 
This embodiment corresponds to a case where a contact hole forming position 
is deviated in the thin-film transistor manufacturing process of the third 
embodiment. 
In FIG. 6C, reference numerals 601 to 603 denote a contact hole, an 
electrode, and an aluminum pattern, respectively. The contact hole 601 is 
deviated from the intended position. Even in this case, there can be 
prevented the problem that a portion of the underlying member adjacent to 
the active layer is bored. 
Embodiment 5 
This embodiment is directed to a manufacturing process of a thin-film 
transistor that is configured differently than in the third embodiment. 
FIGS. 7A to 7E and 8A to 8D show a manufacturing process according to this 
embodiment. First, as shown in FIG. 7A, an undercoat film 702 is formed on 
a glass substrate 701 and a crystalline silicon film as an active layer 
703 is formed thereon. Further, a silicon oxide film 704 to serve as a 
gate insulating film is formed. 
After an aluminum film 705 is formed as shown in FIG. 7B, a very thin 
anodic oxide film (not shown) is formed thereon. 
Next, as shown in FIG. 7C, the aluminum film 705 is patterned by using 
resist masks 706 to 708, and then porous anodic oxide films 709 to 711 are 
formed. 
After the resist masks 706 to 708 are removed, dense anodic oxide films 712 
to 714 are formed. Thus, the state of FIG. 7D is obtained. 
In this manner, aluminum patterns 71 to 73 on which the porous anodic oxide 
films 709 to 711 are formed are obtained. The pattern 72 becomes a gate 
electrode. 
Impurity ions are implanted in this state (the active layer 703 is lightly 
doped), to form low-concentration impurity regions 715 and 716 in a 
self-aligned manner. 
After the porous anodic oxide films 709 to 711 are removed, impurity ions 
are implanted again to form a high-concentration impurity region 718 to 
serve as a source region, a region 719 to serve as a channel forming 
region, a high-concentration impurity region 721 to serve as a drain 
region, low-concentration impurity regions 717 and 722, and a 
low-concentration impurity region 720 to serve as a LDD region. 
Subsequently, the regions where impurity ions have been implanted are 
activated by laser light or strong light illumination. Thus, the state of 
FIGS. 7E and 8A is obtained. 
After an interlayer insulating film 723 is formed, contact holes 724 and 
725 are formed. (FIG. 8B) 
Then, impurity ions are again implanted to reduce the resistivity of the 
regions of the active layer which have been exposed by the contact holes 
724 and 725. (FIG. 8C) 
A source electrode 726 and a drain electrode 727 are then formed to 
complete a thin-film transistor. 
Also in this embodiment, even if the contact holes 724 and 725 are deviated 
from their intended positions, the existence of the patterns 71 and 73 
covered with the anodic oxide films prevents the problem of FIG. 2E. 
The top views of FIGS. 6A and 6B similarly apply to this embodiment. The 
porous anodic oxide films 709 and 711 and the dense anodic oxide films 712 
and 714 are formed by the respective anodic oxidation processes by 
applying voltages to the aluminum patterns 71 and 73 through the wirings 
50. After the anodic oxidation processes, the wirings 50 are removed from 
the aluminum patterns 71 and 73. 
Embodiment 6 
This embodiment relates to another example of a pattern registration error 
(see FIG. 9) that is different than shown in FIG. 6B. The wirings 50 as 
shown in FIG. 9 are used in anodic oxidation to form anodic oxide films on 
surfaces of aluminum patterns having a function of determining a position 
of a contact to a semiconductor, e.g. a source and a drain of a 
transistor. 
According to the invention, even where a circuit pattern is miniaturized, 
it can be manufactured with a large process margin, which in turn reduces 
the manufacturing cost, increases the production yield, and improves the 
reliability.