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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device/circuit having at least partially crystallized semiconductor layer and a manufacturing method thereof. The semiconductor device/circuit manufactured according to the present invention is
formed on any of insulation substrates such as glass substrates and semiconductor substrates such as single crystal silicon substrates. In particular, the present invention relates to a semiconductor device/circuit having a thin film transistor (TFT)
and/or a thin film diode (TFD) (for example, image sensor) manufactured by way of crystallization (activation) through heat annealing.
2. Description of the Prior Art
Thin film semiconductor devices such as TFT and TFD are classified into amorphous devices and crystalline devices depending on the crystalline structures of the semiconductor materials used. Amorphous silicon can be fabricated at a low
temperature and shows excellent mass productivity. However, it is inferior to crystalline silicon in view of physical properties such as field effect mobility or conductivity. So it has been demanded for crystalline semiconductor devices in order to
obtain high speed characteristics. On the other hand, it has been known that amorphous semiconductors are usable, for example, to light sensors since they generally show large change in the photoconductivity. It has been proposed recently a circuit for
driving a light sensor using an amorphous silicon diode or a thin film diode by a thin film transistor using crystalline silicon capable of high speed operation (for example, integrated image sensor circuit).
FIGS. 1A-1E show an example for the steps of fabricating a circuit comprising a combination of an amorphous silicon diode and a crystalline silicon TFT in the prior art. An underlying insulation film 51 is formed on a glass substrate 50, over
which an amorphous silicon film is formed and crystallized by applying long time annealing at a temperature higher than 800.degree. C. Then, it is patterned to obtain an island-like silicon region 52. Then, a gate insulation film 53 is formed and,
further, gate electrodes 54N and 54P are formed (refer to FIG. 1A).
Then, an N-type impurity region 55N and a p-type impurity region 55P are formed by using known CMOS fabrication technique. In this impurity introduction step, an impurity element is introduced into a semiconductor layer with a gate electrode as
a mask in a self-aligning manner. After the implantation of impurities, the impurities are activated by laser annealing, heat annealing or like other means (refer to FIG. 1B).
Then, a first interlayer insulator 56 is formed through which contact holes are formed, thereby forming electrode/wiring 57a, 57b, 57c for source and drain of TFT, and an electrode 57d for an amorphous silicon diode (FIG. 1C).
Then, p-, I- (intrinsic) and N-type amorphous silicon films 58P, 58I and 58N are successively laminated, which are then patterned to form a diode junction portion (FIG. 1D).
Finally, a second interlayer insulator 59 is formed through which contact holes are formed thereby forming an electrode 60 of the amorphous silicon diode to complete a circuit (FIG. 1E).
In the prior art method requiring such procedures, it is necessary to form silicon films 52, 58I and the interlayer insulators 56, 59 each by two layers, which requires film formation for long time and, in addition, the N-type layer 58N and the
p-type layer 58P have to be formed. Therefore, it involves a problem that the throughput is reduced. Further, a plasma CVD or vacuum CVD process used for forming such films, takes much dead time for the maintenance of the apparatus and the presence of
such additional step further reduces the throughput.
Furthermore, since crystallization of the silicon film used in the crystalline silicon TFT also requires a temperature higher than 600.degree. C. and needs a time as much as 24 hours or longer for crystallization, many facilities for
crystallization apparatus are required in actual mass production, which results in enormous installation cost.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a technique capable of overcoming the foregoing problems by simultaneously forming a semiconductor layer to form a TFT and a TFD using only a single interlayer insulator, as well as crystallizing
the silicon film at a temperature lower than 600.degree. C. and in such a short period of time as causing no substantial problems.
Another object of the present invention is to provide a method capable of simplifying production processes and saving the number of film-forming steps.
A further object of the present invention is to improve crystallization and activation of amorphous silicon, in particular, in an impurity region of TFT and TFD (source, drain or n-type or p-type region), thereby lowering the resistivity.
A further object of the present invention is to lower the resistivity in an impurity region by annealing at a lower temperature and for a shorter period of time.
A further object of the present invention is to obtain crystalline silicon by low temperature and short time annealing and then using the same to TFT.
A further object of the present invention is to provide a semiconductor circuit in which source, drain of TFT and N-type and p-type regions of TFD are constituted with crystalline silicon, while an active region (channel forming region) of TFT
and an I-layer of TFD is constituted with amorphous silicon, as well as a manufacturing method therefor.
A further object of the present invention is to provide a semiconductor circuit in which the source, drain regions of TFT are constituted with crystalline silicon, while an active region of TFT and TFD are constituted with amorphous silicon, as
well as a manufacturing method thereof.
A further object of the present invention is to provide a semiconductor circuit, in which an active region of a TFT is constituted with crystalline silicon, while an intrinsic region of a TFD is constituted with amorphous silicon, as well as
manufacturing method therefor.
A further object of the present invention is to provide a semiconductor device/circuit in which TFT and/or TFD are formed from one semiconductor film, as well as a manufacturing method thereof.
A further object of the present invention is to provide a method of manufacturing a semiconductor device/circuit capable of attaining a satisfactory light sensitivity.
A further object of the present invention is to provide a method of manufacturing a semiconductor device/circuit capable of crystallizing an active region not introduced with a catalyst element by laterally proceeding crystallization.
A further object of the present invention is to provide a method of manufacturing a semiconductor device/circuit capable of optionally fabricating a crystalline semiconductor region, and an amorphous semiconductor region.
A further object of the present invention is to provide a semiconductor device/circuit containing TFT of extremely high mobility.
The primary feature of the present invention is to add a catalytic element to a selected portion of a semiconductor film for reducing the crystallization temperature in the selected portion and to subject the semiconductor film to a heat
annealing at such a temperature which is enough high to crystallize the impurity added portion but not enough high to crystallize the remaining portion of the semiconductor film, thereby, crystallizing only the selected portion of the semiconductor film.
According to the study of the present inventor, it has been found that one of most major problems of the amorphous silicon TFT is caused by that the conductivity of source, drain regions is remarkably low. It has been found that a satisfactory
operation for driving a TFD is obtainable if the conductivity of the source, drain regions of a TFT is comparable with that of crystalline silicon. It has also been found that the problem in the amorphous silicon TFD is attributable to that the
conductivity of the n-type and p-type regions is low.
The foregoing problems can be solved by proceeding crystallization and activation thereby lowering the resistivity of amorphous silicon, particularly, in impurity regions (source, drain regions or n-type and p-type regions), of TFT and/or TFD.
As a result of the studies conducted by the present inventor, it has been found that crystallization can be promoted by adding a trace amount of a catalyst material to a silicon film in a substantially amorphous state thereby enabling to lower the
crystallization temperature and shorten the crystallization time. In the present invention, the amorphous state and the substantially amorphous state include a so-called amorphous state and an extremely degraded crystalline state if it is present. As
the catalyst element, nickel (Ni), iron (Fe), cobalt (Co) or platinum (Pt) is suitable. Actually, crystallization can be attained by forming a film, particles, cluster or the like containing such a catalyst in the form of elemental metal or a compound
such as silicide in an intimate contact on or below an amorphous silicon film or introducing such a catalyst element into the amorphous silicon film by an ion implantation or like other method and, subsequently, applying heat annealing at an appropriate
temperature, typically, at a temperature below 580.degree. C.
As a matter of fact, there is such a relation that the crystallization time is shorter as the annealing temperature is higher. Further, there is also a relation that the crystallization temperature is lower and the crystallization time is
shorter as the concentration of the catalyst element is greater. According to the study of the present inventor, it has been found that at least one of the elements has to be present at a concentration of higher than 1.times.10.sup.17 cm.sup.-3,
preferably, 5.times.10.sup.18 cm.sup.-3. Also, depending upon the annealing temperature and period, the catalytic element diffuses by 10-20 .mu.m and the crystallization proceeds in a lateral direction.
On the other hand, since most of the catalyst materials described above is not preferred for an electrical characteristics of silicon, it is desirable that the concentration is as low as possible. According to the study of the present inventor,
it is desired that the concentration of the catalyst material does not exceed 2.times.10.sup.20 cm.sup.-3, preferably, 1.times.10.sup.20 cm.sup.-3 in total in order to attain sufficient reliability and characteristic, particularly, when it is utilized as
an active region. It has been found on the other hand that there is no substantial problem in the source or drain region if the catalyst is present relatively in a large amount. Particularly, it has been found that the concentration of the catalyst
element contained in the active region (channel-forming region) of TFT is desirably smaller by more than one digit as that in the source, drain regions in the first feature of the present invention. In the same way, it is also desired in TFD that the
concentration of the catalyst element contained in the intrinsic region (I-layer) is lower by more than one digit than that in the impurity region (n-type or p-type region).
Further, it should be noted that the amorphous state can be maintained without proceeding crystallization at all in such a region that the catalyst material is not present. For instance, crystallization of amorphous silicon not having such a
catalyst material, usually starts at a temperature higher than 600.degree. C. but it does not proceed at all at a temperature lower than 580.degree. C. However, since hydrogen necessary for neutralizing dangling bonds in amorphous silicon is
dissociated, in an atmosphere at a temperature higher than 300.degree. C., it is desirable that annealing is applied in a hydrogen atmosphere in order to attain a satisfactory light sensitivity.
Further, such a catalyst element has an effect of crystallizing a peripheral area by diffusion during annealing. For instance, when annealing is applied at 550.degree. C. for four hours, the catalyst element diffuses to the periphery as far as
by 10-20 .mu.m to cause crystallization therein. Accordingly, if the width of the gate electrode of TFT is less than 20 .mu.m, preferably, less than 10 .mu.m, crystallization proceeds laterally, and an active region (channel-forming region) not
introduced with the catalyst element can also be crystallized by introducing the catalyst element into the source, drain regions before or after introduction of the n-type or p-type impurities and then applying annealing. Further, in this method, the
concentration of the catalyst element in the active region is generally low as compared with the concentration of the catalyst element in the source, drain regions. The lateral crystallization depends on the temperature and the time of annealing and the
concentration of the catalyst element. Accordingly, the crystalline silicon region and the amorphous silicon region can be prepared optionally by optimizing them.
For instance, when two kinds of TFT gate electrodes having, respectively, 5 .mu.m and the 30 .mu.m width are provided, it is possible to prepare a crystalline silicon TFT from the 5 .mu.m width electrode, while an amorphous silicon TFT from the
30 .mu.m width electrode.
Taking notice on the effect of the catalyst element and by utilizing the same, the present inventor has succeeded in lowering the resistivity in the impurity region by low temperature and short time annealing thereby obtaining crystalline silicon
and using it for TFT.
In the first feature of the present invention, only the impurity region is crystallized and activated by taking an advantageous feature of the crystallization due to the catalyst material while the active region of TFT and the intrinsic region of
TFD are left as they are in the amorphous state, thereby improving the function of the device. The present inventor has made a further study and has found a method capable of simplifying the process, that is, saving the number of film-forming steps as
other object described above. The outline of the method is shown below.
(1) Formation of an amorphous semiconductor (silicon) film
(2) Formation of an insulation film (gate insulation film)
(3) Formation of a TFT gate electrode and a mask material for a TFD
(4) Introduction of doping impurity (for example by ion implantation or ion doping method)
(4') Formation of catalyst element-containing material on a semiconductor (silicon) film
(5) Activation of doped impurity (possible at a temperature lower than 600.degree. C. and within 8 hours)
(6) Formation of an interlayer insulator
(7) Formation of source and drain electrodes of TFT, or alternatively,
(1) Formation of an amorphous semiconductor (silicon) film
(2) Formation of an insulation film (gate insulation film)
(3) Formation of a TFT gate electrode and a mask material for a TFD
(4) Introduction of doping impurity (for example, by ion implantation or ion doping method)
(4') Introduction of catalyst element (for example by ion implantation or ion doping method)
(5) Activation of doped impurity (possible at a temperature lower than 600.degree. C. and within 8 hours)
(6) Formation of an interlayer insulator
(7) Formation of source and drain electrodes of TFT.
In the second feature of the present invention, only the impurity region of TFT is crystallized and activated by taking an advantageous feature of the crystallization due to the catalyst material while TFD is left as it is in the amorphous state
thereby improving the function of the device. The present inventor has made a further study and has found a method capable of simplifying the process, that is, saving the number of film-forming steps as other object described above. The outline of the
method is shown below.
(1) Formation of an amorphous semiconductor (silicon) film
(2) Formation of an insulation film (gate insulation film)
(3) Formation of a TFT gate electrode and a mask material for a TFD
(4) Introduction of doping impurity (for example, by ion implantation or ion doping method)
(4') Formation of catalyst element-containing material on the semiconductor (silicon) film in the TFT region
(5) Activation of doped impurity (possible at a temperature lower than 600.degree. C. and within 8 hours)
(6) Formation of an interlayer insulator
(7) Formation of source and drain electrodes of TFT, or, alternatively,
(1) Formation of an amorphous semiconductor (silicon) film
(2) Formation of an insulation film (gate insulation film)
(3) Formation of a TFT gate electrode and a mask material for a TFD
(4) Introduction of doping impurity (for example, by ion implantation or ion doping method)
(4') Introduction of catalyst element into the semiconductor (silicon) film in the TFT region (for example, by ion implantation or ion doping method)
(5) Activation of doped impurity (possible at a temperature lower than 600.degree. C. and within 8 hours)
(6) Formation of an interlayer insulator
(7) Formation of source and drain electrodes of TFT.
In the third feature of the present invention, only the TFT is crystallized and activated by taking an advantageous feature of crystallization due to the catalyst material while TFD is left as it is in the amorphous state thereby improving the
function of the device. The present inventor has made a further study and found a method capable of simplifying the process, that is, saving the number of film-forming steps as other object described above. The outline of the method is shown below.
(1) Formation of an amorphous semiconductor (silicon) film
(1' Formation of a catalyst element-containing material on or in contact with a semiconductor (silicon) film in the TFT region
(2) Formation of an insulation film (gate insulation film)
(3) Formation of a TFT gate electrode and a mask material for a TFD
(4) Introduction of doping impurity (for example, by ion implantation or ion doping method)
(5) Activation of doped impurity (possible at a temperature lower than 600.degree. C. and within 8 hours)
(6) Formation of an interlayer insulator
(7) Formation of source and drain electrodes of TFT or, alternatively,
(1) Formation of an amorphous semiconductor (silicon) film
(1') Introduction of a catalyst element into the semiconductor (silicon) film in the TFT region (for example, by ion implantation or ion doping method)
(2) Formation of an insulation film (gate insulation film)
(3) Formation of a TFT gate electrode and a mask material for a TFD
(4) Introduction of doping impurity ( for example, by ion implantation or ion doping method)
(5) Activation of doped impurity (possible at a temperature lower than 600.degree. C. and within 8 hours)
(6) Formation of an interlayer insulator
(7) Formation of source and drain electrodes of TFT.
In the fourth feature of the present invention, the present inventor has found a method capable of simplifying the process, that is, saving the number of film-forming steps as the object described above by crystallizing and activating the
impurity regions and the active region of TFT and the intrinsic region of TFD at a temperature lower than that in the prior art. The outline is shown below.
(1) Formation of an amorphous semiconductor (silicon) film
(1') Introduction of a catalyst element (for example, by ion implantation or ion doping method) (catalyst element-containing material in the form of a film may be provided on a silicon film)
(2) Formation of an insulation film (gate insulation film)
(3) Formation of a TFT gate electrode and a mask material for a TFD
(4) Introduction of doping impurity (for example, by ion implantation or ion doping method)
(5) Activation of doped impurity (possible at a temperature lower than 600.degree. C. and within 8 hours)
(6) Formation of an interlayer insulator
(7) Formation of source and drain electrodes of TFT or, alternatively,
(1) Formation of an amorphous semiconductor (silicon) film
(2) Formation of an insulation film (gate insulation film)
(3) Formation of a TFT gate electrode and a TFD mask material
(4) Introduction of doping impurity (for example, by ion implantation or ion doping method)
(4') Introduction of a catalyst element (for example, by ion implantation or ion doping method) (catalyst element-containing material in the form of a film may be provided on a silicon film)
(5) Activation of doped impurity (possible at a temperature lower than 600.degree. C. and within 8 hours)
(6) Formation of an interlayer insulator
(7) Formation of source and drain electrodes of TFT.
In the steps described above, the sequence for the steps of introducing the doping impurity and the catalyst element conducted one after the other (steps (4) and (4') in the first and the second features and the steps (4) and (4') in the latter
alternative steps in the fourth feature) can be reversed. For strictly controlling the concentration of the catalyst element, the ion implantation or like other means is desirable for the step of introducing the catalyst element. Since the catalyst
element is present, the annealing temperature lower than 600.degree. C., typically, lower than 550.degree. C. is sufficient for crystallization and activation, as well as the annealing time within 8 hours, typically, within 4 hours is sufficient. In
particular, in a case where the catalyst element is distributed homogeneously by the ion implantation or ion doping method, crystallization proceeded extremely readily.
In the present invention, if a gate electrode is present on an active region or a mask material is present on an intrinsic region, the catalyst element is not brought into intimate contact with or implanted into the active region directly in the
step for introducing the catalyst element (such as step (4') in the first and the second features of the invention). Accordingly, characteristics of the active region and the intrinsic region are not deteriorated.
Further, if annealing is applied under appropriate conditions for temperature and time, crystallization proceeds from the source, drain regions and the active region also becomes crystalline silicon. As a result, TFT of extremely high mobility
can be obtained.
Referring briefly to the structure of TFD in the present invention, the TFD in the prior art has a laminate structure, whereas the present invention has a feature of a planar structure. In the present invention, the active region of TFT and the
intrinsic region of TFD start from an identical amorphous silicon film. However, since the catalyst element is not introduced in the TFD region, the region is not crystallized by the subsequent annealing step. This is attained since the annealing
temperature in the present invention can be lowered by more than 50.degree. C. than that in the prior art. Therefore, although two layers of silicon films have to be formed in the prior art, it is suffice to form a single silicon film layer in the
present invention. Then, the n-type layer and the p-type layer necessary so far can be obtained by forming them simultaneously in a planar structure upon doping impurities in TFT. That is, the n-type region of TFD is formed upon implantation of n-type
impurities to TFT, while the p-type region of TFD is formed upon implantation of p-type impurities to TFT. As a result, the interlayer insulator can also be a single layer.
Such a planar TFD has a novel feature not obtainable in the prior art. In a case of using a conventional TFD (having a shape as shown in FIG. 1), for example, as a light sensor, the direction of an electric field generated at the inside of the
semiconductor is vertical to a light irradiation plane, so that the light irradiation intensity is not uniform in the direction of the electric field and it has been impossible to efficiently generate electrons and holes and take out them externally. In
addition, short-circuit may be caused sometimes to TFD due to pinholes through the layers. In the present invention, since the direction of the electric field generated in TFD is in parallel with the light irradiation plane, the light intensity is
constant in the direction of the electric field to improve photoelectric conversion efficiency and, in addition, suppress occurrence of short-circuit.
In the present invention, a thin amorphous silicon film with a thickness of less than 1,000.ANG., which is not crystallized by usual heat annealing, is also crystallized due to the effect of the catalyst element. It has been required that the
thickness of the crystalline silicon film is less than 1,000.ANG., preferably, less than 500.ANG. with a view point of avoiding pinholes or insulation failure in the gate insulation film and disconnection of the gate electrode at stepped portions of
TFT. This can not be attained so far by the method other than laser crystallization but this can be attained in accordance with the present invention by heat annealing even at a low temperature. This is naturally attributable to further improvement of
the yield. In addition, in a case of utilizing TFD as a light sensor, S/N ratio and photoelectric conversion efficiency can be improved by using a thin semiconductor film.
According to the present invention, it is possible to save the number of processing steps for fabricating a semiconductor device/circuit having, for example, crystalline silicon TFT and amorphous silicon TFD and improving the productivity.
Further, in the present invention, throughput can be improved also by crystallizing silicon, for example, at a temperature as low as 500 .degree. C. and at a processing time as short as four hours. In addition, in a case of adopting a process at a
temperature higher than 600.degree. C. in the prior art, there has been a problem of causing shrinkage or warp in a glass substrate which leads to the reduction of the yield, whereas such problems can be overcome altogether by utilizing the present
invention.
This means that a substrate of a large area can be processed at a time. That is, unit cost can be reduced remarkably by cutting out a number of integrated circuits, etc. from a single substrate by processing a substrate of a large area. Thus,
the present invention is of an industrial advantage.
These and other novel features and advantages of the present invention are described in or will become apparent from the following detailed description of preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiments will be described with reference to the drawings, wherein like elements have been denoted throughout the figures with like reference numerals, and wherein:
FIGS. 1A-1E are cross sectional views illustrating an example of fabrication steps in the prior art;
FIGS. 2A-2F are cross sectional views illustrating fabrication steps in Example 1 of the first feature of the present invention;
FIGS. 3A-3F are cross sectional views illustrating fabrication steps in Example 2 of the first feature of the present invention;
FIGS. 4A-4E are cross sectional views illustrating fabrication steps in Example 3 of the second feature of the present invention;
FIGS. 5A-5F are cross sectional views illustrating fabrication steps in Example 4 of the second feature of the present invention;
FIGS. 6A-6E are cross sectional views illustrating fabrication steps in Example 5 of the third feature of the present invention;
FIGS. 7A-7F are cross sectional views illustrating fabrication steps in Example 6 of the third feature of the present invention;
FIGS. 8A-8F are cross sectional views illustrating fabrication steps in Example 7 of the fourth feature of the present invention;
FIG. 9A is a cross sectional view of a TFD obtained in the previous example;
FIG. 9B is a band diagram of the TFD;
FIG. 9C is a cross sectional view illustrating a modified embodiment of the TFD; and
FIGS. 10A-10F are cross sectional views illustrating fabrication steps in Example 8 of the fourth feature of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Description will be made more specifically to the present invention by way of examples.
EXAMPLE 1
FIGS. 2A-F illustrate cross sectional views for fabrication steps in Example 1 of the first feature according to the present invention. At first, an underlying film 11 made of silicon oxide was formed to a thickness of 2,000.ANG. by a
sputtering method on a substrate (Corning (Trademark) 7059) 10. Further, an intrinsic (I) amorphous silicon film was deposited to a thickness of 500 to 1,500.ANG., for example, 1,500.ANG. by a plasma CVD process. Then, the thus obtained amorphous
silicon film was patterned by photolithography to form an island-like silicon regions 14a (for TFT) and 14b (for TFD). Further, a silicon oxide film 15 was deposited to a thickness of 1,000.ANG. as a gate insulation film by a sputtering method.
Sputtering was applied using silicon oxide as a target, at a substrate temperature of 200.degree. to 400.degree. C., for example, at 250.degree. C. in a sputtering atmosphere of oxygen and argon at an argon/oxygen ratio of 0 to 0.5, for example, less
than 0.1. Successively, a silicon film (containing 0.1 to 2% phosphorus) was deposited to a thickness of 6,000 to 8,000.ANG., for example, 6,000.ANG. by a vacuum CVD process. The steps of forming the silicon oxide and the silicon film are desirably
conducted continuously. Then, the silicon film was patterned to form gate electrodes 16a and 16b for TFT and a mask material 16c for TFD (FIG. 2A).
Then, as shown in FIG. 2B, a photoresist mask 17a was formed and impurities (phosphorus) were implanted into the silicon region by plasma doping using the gate electrode as a mask. Doping was conducted by using phosphine (PH.sub.3 3) as a doping
gas at an acceleration voltage of 60 to 90 kV, for example, 80 kV. The amount of dose was 1.times.10.sup.15 to 8.times.10.sup.15 cm.sup.-2, for example, 2.times.10.sup.15 cm.sup.-2. As a result, an N-type impurity region 18a for TFT and an N-type
impurity region 19n for TFD were formed (FIG. 2B).
Further, as shown in FIG. 2C, nickel ions were implanted by an ion implantation method while leaving the photoresist mask 17a as it was. The amount of dose was 1.times.10.sup.13 to 5.times.10.sup.14 cm.sup.-2, for example, 5.times.10.sup.13
cm.sup.-2. As a result, nickel was implanted at a concentration of about 5.times.10.sup.18 cm.sup.-3 in the amorphous silicon film (FIG. 2C).
Then, as shown in FIG. 2D, a photoresist mask 17b was formed and impurities (boron) were implanted into the silicon region by plasma doping using the gate electrode as a mask. Diborane (B.sub.2 H.sub.6) was used as a doping gas and the
acceleration voltage was 40 to 80 KV, for example, 65 KV. The amount of dose was 1.times.10.sup.15 -8.times.10.sup.15 cm.sup.-2, for example 5.times.10.sup.15 cm.sup.-2. As a result, a P-type impurity region 18b for TFT and a p-type impurity region 19p
for TFD were formed. After boron implantation, nickel was doped by using the photoresist mask 17b like that in FIG. 2C although not shown.
When the doping impurity and nickel were introduced, the impurities were not implanted in a region interposed between the N-type region and the P-type region of TFD and the region became an intrinsic region 19i (FIG. 2D).
Subsequently, impurities were activated by annealing in a reducing hydrogen atmosphere at 0.1 to 1 atm at 500.degree. C. for 4 hours. In this case, since nickel was diffused in the regions 18a, 18b and 19p and 19n to which nickel was previously
implanted, crystallization proceeded easily in these regions by this annealing and the doped impurities were activated. On the other hand, silicon in the active region of TFT and the intrinsic region 19i of TFD were not crystallized since nickel was not
present. After the completion of crystallization, the mask material 16c for TFD was removed (FIG. 2E).
Successively, a silicon oxide film 20 of 6,000.ANG. thickness was formed as an interlayer insulator by plasma CVD, through which contact holes were formed and electrode/wiring 21a, 21b, 21c for TFT and electrode/wiring 21d, 21e for TFD were
formed with a multi-layered film of metal material, for example, titanium or aluminum. Finally, annealing was applied in a hydrogen atmosphere at 1 atm at 350.degree. C. for 30 min. A semiconductor circuit was completed by the steps described above.
After all, the source, drain regions for the TFT of the completed semiconductor circuit were crystalline state and the channel region (active region) for TFT of the same was amorphous state. The P-type and N-type regions for the TFD of the same
were crystalline state and the intrinsic region for TFD of the same was amorphous state.
As apparent from the figures, in these steps, both of the silicon film and the interlayer insulator 20 could be a single layer. As a result, the number of film-forming steps was greatly reduced. Further, when the nickel concentration in the
active region for TFT and the intrinsic region for TFD was measured by secondary ion mass spectroscopy (SIMS), both of them were less than the measuring limit (1.times.10.sup.16 cm.sup.-3). On the other hand, in the impurity regions for TFT and TFD,
nickel at 1.times.10.sup.18 to 5.times.10.sup.18 cm.sup.-3 was detected.
Example 2
FIGS. 3A-F illustrate cross sectional views for fabrication steps in Example 2 in the first feature of the present invention. On a substrate (Corning 7059) 30, were formed an underlying film 31 of silicon oxide to a thickness of 2,000.ANG. by
sputtering and, further, an amorphous silicon film by plasma CVD. Then, the amorphous silicon film was patterned to form island-like silicon regions 36a (for TFT) and 36b (for TFD). Further, a silicon oxide film 37 of 1,000.ANG. thickness was formed
as a gate insulation film by plasma CVD using tetraethoxysilane (Si(OC.sub.2 H.sub.5).sub.4, TEOS) and oxygen as the raw material. For the starting material, trichloroethylene (C.sub.2 HCl.sub.3) was used in addition to the gases described above.
Before film formation, oxygen was caused to flow in a chamber at 400 SCCM and a plasma was generated at a substrate temperature of 300.degree. C., total pressure of 5 Pa and an RF power of 150 W and this condition was kept for 10 min. Subsequently, a
silicon oxide film was formed by introducing oxygen at 300 SCCM, TEOS at 15 SCCM and trichloroethylene at 2 SCCM to the chamber. The substrate temperature, the RF power and the total pressure were, respectively, 300.degree. C., 75 W and 5 Pa. After
the completion of the film formation, hydrogen at 100 Torr was introduced into the chamber and hydrogen annealing was applied at 350.degree. C. for 35 min.
Successively, a tantalum film was deposited to a thickness of 6,000 to 8,000.ANG., for example, 6,000.ANG. by sputtering. It is preferred that the film forming steps for the silicon oxide 37 and the tantalum film are conducted continuously.
Instead of tantalum, chromium, molybdenum, tungsten, titanium or the like may also be used so long as it can endure the subsequent thermal annealing step. Then, the tantalum film was patterned to form gate electrodes 38a, 38b for TFT and a mask material
38c for TFD. Further, the surface of the tantalum wiring was anodized to form an oxide layer on the surface. Anodization was conducted in a solution of 1-5% tartaric acid in ethylene glycol. The thickness of the resultant oxide layer was 2,000.ANG.
(FIG. 3A).
Then, impurities (phosphorus) were implanted into the silicon region by plasma doping. Phosphine (PH.sub.3) was used as a doping gas and the acceleration voltage was 60 to 90 kV, for example, 80 kV. The amount of dose was 1.times.10.sup.15
-8.times.10.sup.15 cm.sup.-2, for example, 2.times.10.sup.15 cm.sup.-2. In this way, an N-type impurity region 39 was formed (FIG. 3B).
Successively, nickel ions were implanted by ion implantation. The amount of dose was 1.times.10.sup.13 to 5.times.10.sup.14 cm.sup.-2, for example, 5.times.10.sup.13 cm.sup.-2. As a result nickel was implanted in the amorphous silicon film at a
concentration of about 5.times.10.sup.18 cm.sup.-3 (FIG. 3C). Further, impurities (boron) were implanted again into the silicon region of TFT on the right (P-channel TFT) and the region on the left of TFD (p-type region) by plasma doping while masking
the TFT on the left (N-channel TFT) and the region on the right of TFD (N-type region) with a photoresist 40a. Diborane (B.sub.2 H.sub.6) was used as the doping gas and the acceleration voltage was 50-80 kV, for example, 65 kV. The amount of dose was
1.times.10.sup.15 to 8.times.10.sup.15 cm.sup.-2, for example at 5.times.10.sup.15 cm.sup.-2 which is greater than the amount of phosphorus implanted previously. As a result, an N-type impurity region 41a, a p-type impurity region 41b for TFT and an
N-type region 42n and p-type region 42p for TFD were formed (FIG. 3D.)
Subsequently, the impurities were activated by annealing in a reducing hydrogen atmosphere at 0.1 to 1 atm, at 500.degree. C. for 4 hours. In this case, since nickel was diffused in the regions 41a, 41b and 42p, 42n to which nickel was
implanted previously, crystallization proceeded easily in these regions at such a relatively low temperature. On the other hand, since nickel was not present in the silicon of the active region for TFT and the intrinsic region 42i for TFD, the regions
were not cr | | |
