JPH0774365A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To enable a TFT provided with necessary characteristics to be selectively formed on a substrate. CONSTITUTION:A TFT of crystalline silicon film and another TFT of amorphous silicon film are selectively formed on a substrate. For instance, in an active matrix type liquid crystal display, a peripheral circuit is formed of crystalline silicon film, and a pixel part is composed of TFTs formed of amorphous silicon film. A crystalline silicon film can be selectively obtained through such a method that metal which selectively accelerates crystallization is introduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device using a TFT (thin film transistor) provided on an insulating substrate such as glass. In particular, the present invention relates to a semiconductor device that can be used for an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art As a semiconductor device having TFTs on an insulating substrate such as glass, active type liquid crystal display devices and image sensors using these TFTs for driving pixels are known.

Thin film silicon semiconductors are generally used for TFTs used in these devices. The thin-film silicon semiconductor is roughly classified into two, that is, an amorphous silicon semiconductor (a-Si) and a crystalline silicon semiconductor. Amorphous silicon semiconductors are the most commonly used because they have a low manufacturing temperature, can be relatively easily manufactured by the vapor phase method, and have high mass productivity. Since it is inferior to the silicon semiconductors it has,
In order to obtain higher speed characteristics in the future, establishment of a method for manufacturing a TFT made of a crystalline silicon semiconductor has been strongly demanded. As the crystalline silicon semiconductor, polycrystalline silicon, microcrystalline silicon, amorphous silicon containing a crystalline component, semi-amorphous silicon having an intermediate state between crystalline and amorphous are known. .

As a method for obtaining these thin film silicon semiconductors having crystallinity, (1) a film having crystallinity is directly formed at the time of film formation. (2) An amorphous semiconductor film is formed and crystallized by the energy of laser light. (3) An amorphous semiconductor film is formed and crystallized by applying heat energy. The method is said to be known. However, in the method (1), it is technically difficult to uniformly form a film having good semiconductor physical properties over the entire surface of the substrate, and since the film forming temperature is as high as 600 ° C. or more, it is inexpensive. There is a cost problem that the glass substrate cannot be used. Also, (2)
In the case of the most commonly used excimer laser, the method of (1) has a problem that throughput is low because the irradiation area of the laser beam is small, and the entire surface of a large area substrate is uniformly processed. The laser is not stable enough, and there is a strong sense that it is a next-generation technology. (3)
The method (1) has an advantage of being able to handle a large area as compared with the methods (1) and (2), but it is still necessary to set the heating temperature to a high temperature of 600 ° C. or higher, and an inexpensive glass substrate is used. Considering this, it is necessary to further lower the heating temperature. In particular, in the case of current liquid crystal display devices, the screen size is increasing, and therefore it is necessary to use a large glass substrate as well. When such a large glass substrate is used, shrinkage or distortion in the heating step, which is indispensable for semiconductor fabrication, lowers the accuracy of mask alignment and the like, which is a serious problem. Particularly, in the case of 7059 glass which is most commonly used at present, the strain point is 593 ° C., and the conventional heat crystallization method causes a large deformation. In addition to the problem of temperature, in the present process, the heating time required for crystallization reaches several tens of hours or more, so it is necessary to further shorten the heating time.

[0005]

SUMMARY OF THE INVENTION The present invention provides means for solving the above problems. More specifically, in a method of manufacturing a thin film of a crystalline silicon semiconductor using a method of crystallizing a thin film of amorphous silicon by heating, the temperature required for crystallization is lowered and the time is shortened. Its purpose is to provide a process that achieves both. Of course, the crystalline silicon semiconductor manufactured by using the process provided by the present invention has physical properties equal to or higher than those manufactured by the conventional technique and can be used for the active layer region of the TFT. It goes without saying that there is.

BACKGROUND OF THE INVENTION The inventors of the present invention form an amorphous silicon semiconductor film by the CVD method or the sputtering method, and crystallize the film by heating, as described in the section of the conventional technique. Regarding the method, the following experiments and consideration were performed.

First, as an experimental fact, when an amorphous silicon film was formed on a glass substrate and the mechanism of crystallizing this film by heating was examined, crystal growth started from the interface between the glass substrate and amorphous silicon. It was confirmed that when the film thickness exceeds a certain level, it progresses in a columnar shape perpendicular to the substrate surface.

According to the above phenomenon, a crystal nucleus (a seed which is a basis of crystal growth) which is a basis of crystal growth exists at the interface between the glass substrate and the amorphous silicon film, and a crystal grows from the nucleus. It is considered that it is due to going. Such crystal nuclei are
It is considered to be a trace amount of impurity metal elements present on the substrate surface or crystal components on the glass surface (so-called crystallized glass is believed to contain silicon oxide crystal components on the glass substrate surface). To be

Therefore, it is thought that the crystallization temperature can be lowered by more positively introducing crystal nuclei, and in order to confirm the effect, a small amount of another metal is formed on the glass substrate, An experiment was conducted to form a thin film of amorphous silicon on the film and then heat crystallization. as a result,
A decrease in the crystallization temperature was confirmed when several metals were formed on the substrate, and it was expected that crystal growth with foreign particles as crystal nuclei occurred. Therefore, the mechanism of a plurality of impurity metals that could be lowered in temperature was investigated in more detail. The plurality of impurity elements are Ni,
Fe, Co, Pd and Pt.

Crystallization can be considered by dividing it into two stages: initial nucleation and crystal growth from the nuclei. Here, the initial nucleation rate is observed by measuring the time until point-like fine crystals are generated at a constant temperature. In all cases, the quality of the silicon thin film was shortened, and the effect of introducing crystal nuclei on lowering the crystallization temperature was confirmed.
And, unexpectedly, the growth of crystal grains after nucleation was examined by changing the heating time, and it was found that after depositing a certain metal, the amorphous silicon thin film deposited on it was deposited. In crystallization, it was observed that the rate of crystal growth after nucleation increased dramatically. This mechanism is not clear at present, but it is speculated that some catalytic effect is working.

In any case, due to the above two effects, when a small amount of a certain kind of metal is formed on a glass substrate, a thin film made of amorphous silicon is formed, and then heat crystallization is performed, the conventional method is used. It was found that sufficient crystallinity was obtained at a temperature of 580 ° C. or lower for about 4 hours, which was unexpected. Among the impurity metals having such an effect, the effect is most remarkable, and the material selected by us is nickel.

To give an example of the effect of nickel, there is no treatment, that is, on a substrate on which a very small amount of nickel thin film has not been formed (Corning 70).
59 glass) to be crystallized by heating a thin film of amorphous silicon formed by plasma CVD in a nitrogen atmosphere, when the heating temperature is 600 ° C.,
Although a heating time of 10 hours or more was required, when a thin film made of amorphous silicon on a substrate on which a small amount of nickel thin film was formed was used, the same was true for heating at 580 ° C. for about 4 hours. It was possible to obtain a different crystallization state. In addition, Raman spectroscopy spectrum was utilized for the judgment of crystallization at this time. From this alone, it can be seen that the effect of nickel is very large.

[0013]

[Means for Solving the Problems] As can be seen from the above description,
When a thin film of amorphous silicon is formed after a thin film of nickel is formed, the crystallization temperature can be lowered and the time required for crystallization can be shortened. Therefore, on the premise that this process is used for manufacturing a TFT, a more detailed description will be added. Incidentally, as will be described later in detail, the nickel thin film has the same effect not only on the substrate but also on the amorphous silicon film, and since it was the same in the ion implantation, the present specification In the book, this series of treatments will be referred to as "micro addition of nickel". Further, technically, it is possible to add a small amount of nickel when the amorphous silicon film is formed.

First, a method of adding a small amount of nickel will be described. To add a small amount of nickel, a method of forming a small amount of nickel thin film on a substrate and then forming amorphous silicon
The method of forming amorphous silicon first and then forming a small amount of nickel thin film on top of it also has the same effect of lowering the temperature. The film forming method is spin coating, vapor deposition, or spin coating. It has been proved that any method, a coating method, or a method using plasma can be used, and the film forming method does not matter. However, when forming a small amount of nickel thin film on a substrate, rather than forming a small amount of nickel thin film directly on the 7059 glass substrate, a thin film of silicon oxide (base film) is formed on the substrate. The effect is more remarkable when a very small amount of nickel thin film is formed on it. The possible reason for this is that direct contact between silicon and nickel is important for this low temperature crystallization, and in the case of 7059 glass, components other than silicon impede the contact or reaction between the two. It may be that it is.

Further, as a method of adding a trace amount, it was confirmed that substantially the same effect was obtained by adding nickel by ion implantation, in addition to forming a thin film on or below the amorphous silicon. The amount of nickel is 1 × 10 ¹⁵ ato
It has been confirmed that the addition of the amount of ms / cm ³ or more lowers the temperature. However, at the amount of addition of 5 × 10 ¹⁹ atoms / cm ³ or more, the peak shape of the Raman spectroscopic spectrum is clearly different from that of silicon alone. Since they are different, it is possible to actually use 1 × 10 ¹⁹ atoms / cm ³ to 1 × 10.
It seems to be in the range of ¹⁹ atoms / cm ³ . In this case, when the nickel concentration is 1 × 10 ¹⁵ atoms / cm ³ or less, the action as a catalyst for crystallization is reduced, and when the nickel concentration is 5 × 10 ¹⁹ atoms / cm ³ or more, NiSi is Occurs locally and the semiconductor characteristics are lost. In the crystallized state, the lower the nickel concentration, the more usable as a semiconductor.

Next, the crystal morphology in the case of adding a small amount of nickel will be described. As described above, when nickel is not added, nuclei are randomly generated from the crystal nuclei at the substrate interface, etc., and the crystal growth from the nuclei is also random up to a certain film thickness. It is known that columnar crystal growth in which the (110) direction is perpendicular to the substrate is performed, and of course almost uniform crystal growth is observed over the entire thin film. On the other hand, the small amount of nickel added this time had a feature that the crystal growth was different between the nickel-added region and the vicinity thereof. That is, in the nickel-added region, the added nickel or its compound with silicon serves as crystal nuclei, and columnar crystals grow almost perpendicularly to the substrate similarly to the case where nickel is not added. It became clear from the micrograph. Then, crystallization at low temperature was confirmed even in a region in which a small amount of nickel was not added in the vicinity thereof, and in that part, needle-like or columnar crystals were arranged in the (111) direction perpendicular to the substrate and parallel to the substrate. An unusual crystal growth of growing was observed. It is observed that crystal growth in the lateral direction parallel to the substrate grows up to several hundreds of μm in a large region from the region where a small amount of nickel is added, and the growth amount increases in proportion to the increase in time and temperature. I knew that I would do it. As an example, a growth of about 40 μm was observed at 550 ° C. for 4 hours. Moreover, according to the transmission electron microscope photograph, it has been found that all the crystals in the large lateral direction are single crystal-like. The nickel concentration in the trace amount of nickel added portion, the lateral growth portion in the vicinity thereof, and the distant amorphous portion (the low temperature crystallization is not performed in the distant portion, the amorphous portion remains)
When examined by IMS (secondary ion mass spectrometry),
The lateral growth portion was detected by about one digit less than the nickel trace addition portion, and diffusion in the amorphous silicon was observed. In addition, the amorphous portion was observed to be smaller by about one digit. The relationship between this and crystal morphology is not clear at present, but in any case, it is possible to form a silicon thin film having crystallinity of a desired crystal morphology in a desired portion by controlling the amount of nickel added and its position control. is there.

Next, the electrical characteristics of the above-mentioned trace amount nickel addition portion and the lateral growth portion in the vicinity thereof will be described. The electrical characteristics of the portion with a small amount of nickel added are about the same as those of the film with almost no nickel added, that is, the values obtained by crystallization at about 600 ° C. for several tens of hours. When the activation energy was calculated from the property, the addition amount of nickel was 10 ¹⁷ atoms / cm ³ to 10 ¹⁸ a.
When it was set to about toms / cm ^3, no behavior that could be attributed to the nickel level was observed.
(If limited to this fact, the nickel concentration in the film when used as an active layer of a TFT is 10 ¹⁸ atoms / c
It is concluded that there is no hindrance to the operation if m ³ or less)

On the other hand, the lateral growth portion has a conductivity higher than that of the nickel trace addition portion by one digit or more, and has a considerably high value as a crystalline silicon semiconductor. This is considered to be due to the fact that there was little or no grain boundaries existing during the passage of electrons between the electrodes because the current path direction was aligned with the lateral growth direction of the crystal,
It is consistent with the result of the transmission electron micrograph. That is, it is in agreement with the observation fact that needle-like or columnar crystals grow in the direction parallel to the substrate.

Finally, a method of application to a TFT based on the above various characteristics will be described. Where TF
As an application field of T, an active type liquid crystal display device using a TFT for driving a pixel is assumed.

As described above, it is important to suppress the shrinkage of the glass substrate in recent large-screen active type liquid crystal display devices. However, by using the nickel trace amount addition process of the present invention, the strain point of the glass is It is possible to crystallize at a sufficiently low temperature as compared with the above, and it is particularly preferable. According to the present invention, it is possible to easily replace the portion where amorphous silicon is conventionally used with crystalline silicon by adding a small amount of nickel and crystallizing it at about 450 to 550 ° C. for about 4 hours. It is possible. Needless to say, it is necessary to change the design rules and the like accordingly, but it is considered that the existing equipment for both the equipment and the process can suffice, and its merit is great.

Moreover, according to the present invention, the TFT used for the pixel and the TFT forming the driver of the peripheral circuit
It is also possible to separately form and using the crystal forms according to the characteristics, which is particularly advantageous for application to the active liquid crystal display device. A TFT used for a pixel does not require so much mobility, and a smaller off-current is more advantageous than that. Therefore, in the case of using the present invention, a trace amount of nickel is not added to a region which is to be a TFT used for a pixel and is left amorphous.
In the region where the driver of the peripheral circuit is formed, a method of growing a crystalline silicon film by adding a small amount of nickel can be adopted. That is, the TFT formed in the pixel portion does not require such high mobility, and it is necessary to satisfy the problems such as improvement of yield and reduction of off-current for charge retention. In the past, production technology has been accumulated, and it is useful to use a TFT using an amorphous silicon film (amorphous silicon film) whose characteristics can be easily controlled. On the other hand, when considering future applications such as workstations, the TF that configures the peripheral circuits
T requires very high mobility. Therefore, when applying the present invention, a small amount of nickel is added in the vicinity of the TFT forming the driver of the peripheral circuit, and a crystal is grown in one direction (lateral growth) from that, and the crystal growth direction of the channel By aligning with the current path direction (direction in which carriers move), T having a very high mobility can be obtained.
It is effective to make FT.

That is, according to the present invention, in a semiconductor device in which a large number of thin film transistors (generally called TFTs) are formed on a substrate such as a glass substrate, a region in which a silicon semiconductor film is selectively crystallized and a region in which the silicon semiconductor film remains amorphous. It is an idea of the invention to provide a TFT and selectively form a TFT satisfying required characteristics on the substrate. Further, by making the crystal growth direction parallel to the substrate, the carrier movement direction in the TFT is the same as the crystal growth direction, and a TFT having higher mobility is selectively provided. Although the basic description of the present invention is finished, the specific configuration of the present invention will be described below.

[First Invention] The first invention is described in claim 1. In the first aspect of the present invention, a TFT having high mobility is selectively obtained by making the moving direction of carriers at the time of operation of a thin film transistor (hereinafter referred to as TFT) substantially coincide with the crystal growth direction, and in other regions. By selectively providing a thin film transistor (hereinafter referred to as TFT) using an amorphous silicon film,
A TFT using a crystalline silicon film and a TFT using an amorphous silicon film are selectively obtained in required regions.

As described above, the crystal growth direction can be freely selected from the direction perpendicular to the substrate and the direction parallel to the substrate by adding a small amount of nickel. By selecting the direction in which the TFT is formed (the direction connecting the source and the drain) and the position, the relationship between the direction of carrier flow and the direction of crystal growth during the operation of the TFT can be selected. The direction of carrier flow here means, for example, when an insulated gate field effect semiconductor device is used as a TFT, the direction of carrier flow is the direction connecting the source and drain.

[Second Invention] The second invention is the invention described in claim 2. This second invention uses the first invention for an active matrix type liquid crystal display device. For example, the configuration shown in FIG. 1 can be cited as a typical specific example thereof. In addition, by using a crystalline silicon film that is crystal-grown in a direction parallel to the substrate surface,
A TFT having high mobility can be obtained.

[Third Invention] A third invention is the invention described in claim 3, and relates to a manufacturing process for carrying out the first invention. The present invention utilizes a technique of selectively forming a crystallization region by adding a small amount of nickel.

[Fourth Invention] A fourth invention is the invention described in claim 4. According to the present invention, a TFT using a crystalline silicon film is formed in a peripheral circuit portion of a liquid crystal display device, and the crystalline silicon film forming the TFT is TF.
It is characterized in that the crystal is grown in a direction substantially the same as the moving direction of carriers in T. At the same time, the TFT which constitutes the pixel portion of the liquid crystal display device is constituted by using an amorphous silicon film. Selective formation of the crystalline silicon film and the amorphous silicon film on the same substrate is realized by selectively adding nickel. That is, since the temperature required for crystallization can be set to 550 ° C. or lower in the region where a small amount of nickel is added,
5 in the area where a small amount of nickel was not added
It is possible to leave an amorphous region that does not crystallize at 50 ° C. (it seems to crystallize after several hundred hours or more, but does not crystallize at 550 ° C. for several hours).

In the above invention, it is typically useful to use nickel as a trace metal element for promoting crystallization, but similar effects can be obtained by using cobalt,
Even iron or platinum can be obtained. In the above invention, the type of substrate is not particularly limited, but the usefulness of being able to obtain a crystalline silicon film at a low temperature of 600 ° C. or lower (compared to the conventional one) is a glass substrate, particularly a large area. It becomes remarkable when a glass substrate is used.

In this way, it is possible to selectively crystallize and obtain a crystalline silicon film. However, if the characteristics of such a crystalline silicon film are further improved, after the crystallization step, By irradiating a laser or strong light equivalent thereto, the insufficiently crystallized component remaining in the grain boundaries or the like may be crystallized. Of course, in this step, it is important to prevent such intense light from irradiating the region where the TFT using the amorphous silicon film is to be formed. This is because such strong light crystallizes the amorphous silicon.

[0030]

By selectively introducing a metal element that promotes crystallization, it is possible to selectively form a TFT having required characteristics in a required region.

[0031]

EXAMPLES Example 1 FIG. 1 shows an outline of the example.
FIG. 1 is a top view of a liquid crystal display device, showing pixel portions arranged in a matrix and peripheral circuit portions. In this embodiment, a TFT for driving a pixel and a T forming a peripheral circuit are provided on an insulating substrate (eg, a glass substrate).
It is an example of forming FT. In this embodiment, the peripheral circuit is a circuit having a CMOS structure in which PTFT and NTFT using a crystalline silicon film (referred to as a crystalline silicon film) grown laterally are provided in a complementary type, and a pixel portion is provided. The TFT formed on the substrate is an N-channel type T using an amorphous silicon film.
An example of FT (NTFT) will be described.

In the following, FIG. 2 shows a manufacturing process of a circuit in which the NTFT and the PTFT which compose the peripheral circuit are made complementary, and FIG. 4 shows the manufacturing of the NTFT formed in the pixel. About the process. Further, both steps are performed on the same substrate, and common steps are performed simultaneously. That is, (A) to FIG.
(D) and (A) to (D) of FIG. 4 correspond to each other, and the step of FIG. 2A and the step of FIG. The process and the process of FIG. 4B proceed at the same time.

FIG. 2 shows an NTFT and a PT which form a peripheral circuit.
FIG. 4 shows a manufacturing process of a circuit in which the FT and the FT are configured to be complementary.
A manufacturing process of an NTFT provided in a pixel is shown in FIG. First,
A 2000 Å-thick silicon oxide base film 1 formed on a glass substrate (Corning 7059) 101 by a sputtering method.
02 was formed. Next, only in the peripheral circuit portion, that is, in FIG. 2, a mask 103 formed of a metal mask or a silicon oxide film is provided. Note that nickel introduced in a later step easily diffuses into the silicon oxide film, so that when the silicon oxide film is used as the mask 103, a thickness of 1000 Å or more is required. The mask 103 exposes the base film 102 in a slit shape. That is, when this state is viewed from above, the underlying film 102 is exposed in a slit shape and the other portions are masked. Similarly, a mask 103 is provided on the entire surface of the pixel portion shown in FIG.

After the mask 103 is provided, a nickel silicide film (chemical formula NiSi _x , 0.4 ≦ x ≦ 2.
5, for example, x = 2.0) is formed. As a result, the nickel silicide film is formed on the area 100 and the area 204 (FIG. 4) which is the entire pixel area. After that, by removing the mask 103, the nickel silicide film is selectively formed in the region 100.
That is, the trace amount of nickel was selectively added to the region 100.

Next, the mask 103 was removed, and an intrinsic (I-type) amorphous silicon film (amorphous silicon film) 104 having a thickness of 500 to 1500 Å, for example, 1000 Å was deposited by the plasma CVD method. Then, this was annealed at 550 ° C. for 4 hours in a hydrogen reducing atmosphere (preferably, the partial pressure of hydrogen is 0.1 to 1 atm) to crystallize. The annealing temperature can be selected in the range of 450 ° C. to 700 ° C., but if the annealing temperature is low, the annealing time will be long, and if it is high, it will be the same as the conventional method. Moreover, this annealing may be performed in an inert atmosphere (for example, a nitrogen atmosphere) or in the air.

At this time, in the region 100 where the nickel silicide film is selectively formed, the silicon film 104 is crystallized in the direction perpendicular to the substrate 101. And area 1
In the peripheral area of 00, as shown by arrow 105, area 1
From 00, crystal growth is performed in the lateral direction (direction parallel to the substrate). Then, in the pixel portion (shown in FIG. 4) where the mask 103 is provided on the entire surface, the amorphous silicon film remains. This is because the amorphous silicon film is not crystallized by annealing at 550 ° C. for about 4 hours. In this example, the crystal growth distance in the direction parallel to the substrate indicated by the arrow 105 is about 40 μm.

As a result of the above steps, the amorphous silicon film in the peripheral circuit portion shown in FIG. 2 could be crystallized. here,
In the peripheral circuit portion, crystal growth is carried out in the lateral direction (direction parallel to the substrate 101) as shown in FIG.
The amorphous silicon film is left as it is in the pixel portion.

Then, element isolation was performed, and the unnecessary portion of the silicon film 104 was removed to form an element region. In this process, if the length of the active layer of the TFT (the portion where the source / drain regions and the channel formation region are formed) is set to 40 μm or less, the source / drain and channel regions are crystallized in a direction parallel to the substrate. It can be composed of a silicon film. Further, if at least the channel formation region is made of a crystalline silicon film, the length of the active layer can be further increased.

After that, a thickness of 1 is obtained by the sputtering method.
A 000Å silicon oxide film 106 was formed as a gate insulating film. For sputtering, silicon oxide was used as a target, and the substrate temperature during sputtering was 200 to 400.
C., eg 350.degree. C., the sputtering atmosphere is oxygen and argon, argon / oxygen = 0 to 0.5, eg 0.1.
Below. Then, by the sputtering method,
A film of aluminum (containing 0.1 to 2% of silicon) having a thickness of 6000 to 8000Å, for example, 6000Å was formed.
It is desirable that the steps of forming the silicon oxide film 106 and the aluminum film are continuously performed.

Then, the aluminum film was patterned to form the gate electrodes 107 and 109. It goes without saying that these steps are simultaneously performed in FIG. 2 (C) and FIG. 4 (C).

Further, the surface of the aluminum electrode was anodized to form oxide layers 108 and 110 on the surface. This anodic oxidation was performed in an ethylene glycol solution containing 1-5% tartaric acid. Obtained oxide layer 10
The thickness of 8,110 was 2000Å.

Since the oxides 108 and 110 have a thickness to form an offset gate region in the subsequent ion doping process (ion implantation process of a doping material), the length of the offset gate region is anodized. It can be decided by the process.

Next, the gate electrode 107 and the oxide layer 10 around it are formed in the silicon region by ion doping.
8. Impurities (phosphorus and boron) were implanted using the gate electrode 109 and the oxide layer 110 around it as a mask. Phosphine (PH ₃ ) and diborane (B ₂ H ₆ ) were used as the doping gas, and the acceleration voltage was 60 in the former case.
~ 90 kV, for example 80 kV, in the latter case 40-8
It was set to 0 kV, for example, 65 kV. The dose is 1 × 10 ¹⁵
~ 8 × 10 ¹⁵ cm ^-2 , for example, phosphorus is 2 × 10 ¹⁵ cm ^-2 ,
Boron was 5 × 10 ¹⁵ . At the time of doping, each element was selectively doped by covering a region where doping is unnecessary with a photoresist. As a result, N-type impurity regions 114 and 116 and P-type impurity regions 111 and 113 are formed, and P-channel TFTs are formed.
(PTFT) area and N-channel TFT (NTFT)
It was possible to form the area with. At the same time, as shown in FIG. 4, an N-channel TFT could be formed.

After that, annealing was carried out by irradiation with laser light to activate the ion-implanted impurities. The laser light is a KrF excimer laser (wavelength 24
Although 8 nm and a pulse width of 20 nsec) were used, other lasers may be used. The irradiation condition of the laser light is such that the energy density is 200 to 400 mJ / cm ² , for example 250.
Irradiation was performed at mJ / cm ² for 2 to 10 shots, for example, 2 shots. It is useful to heat the substrate to about 200 to 450 ° C. during the irradiation with the laser light. In this laser annealing step, since nickel has diffused into the previously crystallized region, recrystallization easily proceeds by the irradiation of this laser light, and the impurities doped with the impurity imparting P-type are doped. Areas 111 and 11
3. Furthermore, the impurity regions 114 and 116 doped with the impurity imparting N-type could be easily activated.

Then, in the peripheral circuit portion, as shown in FIG. 2, a silicon oxide film 118 having a thickness of 6000Å is formed as an interlayer insulator by the plasma CVD method, and a contact hole is formed in the silicon oxide film 118 to form a metal material. , For example, the electrode of the TFT by the multilayer film of titanium nitride and aluminum
The wirings 117, 120 and 119 were formed. Further, in the pixel portion, as shown in FIG. 4, an interlayer insulator 211 was formed of silicon oxide, and after forming contact holes, metal wirings 213 and 214, and an ITO electrode 212 to be a pixel electrode were formed. Finally, in a hydrogen atmosphere at 1 atm, 350 ° C, 3
Annealing was performed for 0 minutes to complete the TFT circuit or TFT. (FIG. 2 (D), FIG. 4 (D))

The circuit shown in FIG. 2 has a CMOS structure in which a PTFT and an NTFT are provided in a complementary type. In the above process, two TFTs are formed at the same time and cut at the center to form two independent TFTs. It is also possible to fabricate them at the same time.

In order to show the positional relationship between the area where nickel is selectively introduced and the TFT in the structure shown in FIG. 2, FIG. 3 shows an outline of FIG. 2 (D) seen from above. In FIG. 3, a trace amount of nickel is selectively added to a region indicated by 100, and thermal annealing causes crystal growth in the lateral direction (the lateral direction of the paper). Then, source / drain regions 111 and 113 and a channel formation region 112 are formed as PTFT in the direction in which the crystal growth is performed. Similarly, the source / drain regions 114
116, the channel forming region 115 is formed as an NTFT.

In the above structure, since the carrier flow direction and the crystal growth direction are aligned with each other, the operation of the TFT can be improved without crossing the grain boundaries when the carriers move. For example, the mobility of the PTFT manufactured in the step shown in FIG. 2 is 120 to 150 cm.
² / Vs, which is the mobility of a conventional PTFT of 50 to 6
It has been confirmed that it can be improved from 0 cm ² / Vs. Also, regarding NTFT, 150 to 180 cm ²
A mobility of / Vs is obtained, which is 80 to 100c of the conventional one.
A high value is obtained as compared with m ² / Vs.

Incidentally, the conventional TFT mentioned here means that an amorphous silicon film formed on a glass substrate is 600
This is a TFT using a crystalline silicon film crystallized by thermal annealing for 24 hours.

Further, in FIG. 3, a gate insulating film and a channel forming region are provided below the gate electrode. As can be seen from FIG. 3, by further lengthening the nickel trace addition region (in FIG. 2, it extends vertically),
A plurality of TFTs can be formed at the same time.

In this embodiment, as a method of introducing nickel, nickel is selectively thin on the upper surface of the base film 102 below the amorphous silicon film 104 (because it is extremely thin, it is difficult to observe it as a film). ), And crystal growth is performed from this portion. However, a method of selectively adding a trace amount of nickel after forming the amorphous silicon film 104 may be used. That is, crystal growth may be performed from the upper surface side or the lower surface side of the amorphous silicon film. Alternatively, a method of forming an amorphous silicon film in advance and then selectively implanting nickel ions into the amorphous silicon film 104 by using an ion doping method may be adopted. in this case,
It has a feature that the concentration of nickel element can be controlled.

When manufacturing a TFT, the crystal growth direction is not merely parallel to the carrier flow, but
It is also possible to control the characteristics of the TFT by setting the angle between the carrier flow direction and the crystal growth direction at an arbitrary angle.

Example 2 This example is shown in FIGS. 5 and 6. 1000-500 thickness on glass substrate 501
After forming a silicon oxide film 502 of 0 Å, for example, 2000 Å, an amorphous silicon film having a thickness of 300 to 1500 Å, for example, 500 Å was formed by a plasma CVD method. Furthermore, on that, 500-1500Å, for example, 500Å
The silicon oxide film 504 of 1 is formed. It is desirable that these film formations be performed continuously. Then, the silicon oxide film 504
Window 50 for selectively etching and introducing nickel
Opened six. The window 506 was formed in the area where the TFT of the peripheral drive circuit is formed, and was not formed in the pixel portion. Then, the nickel salt film 50 is formed by spin coating.
5 was formed. Explaining this method, first, nickel acetate or nickel nitrate is diluted with water or ethanol to obtain 25 to 200 ppm, for example,
The concentration was 100 ppm.

On the other hand, the substrate was immersed in hydrogen peroxide solution or a mixed solution of hydrogen peroxide solution and ammonia to form an extremely thin silicon oxide film on the exposed portion of the amorphous silicon film (the area of the window 506). . This is to improve the interfacial affinity between the nickel solution prepared as described above and the amorphous silicon film.

The substrate thus treated was placed in a spinner, gently rotated, and 1-10 ml, for example, 2 ml of a nickel solution was dropped on the substrate to spread the solution on the entire surface of the substrate. This state was held for 1 to 10 minutes, for example, 5 minutes. After that, the rotation speed of the substrate was increased and spin drying was performed. This operation may be repeated a plurality of times.
Thus, the thin film 505 of nickel salt was formed.
(Figure 5 (A))

Then, in a heating furnace, 520 to 580
The heat treatment was performed at 4 ° C. for 4 to 12 hours, for example, at 550 ° C. for 8 hours. The atmosphere was nitrogen. As a result, first, nickel diffused into the region immediately below the window 506, and crystallization started from this region. The crystallization region is indicated by the arrow 5.
As shown in 08, it spread around it. on the other hand,
The region far away from the window 506 remained amorphous silicon 509. (Fig. 5 (B))

Then, in the air or oxygen atmosphere, KrF excimer laser light (wavelength 248 nm) or XeCl excimer laser light (wavelength 308 nm) was irradiated for 1 to 20 shots, for example, 5 shots to further improve the crystallinity. Energy density is 200-35
The substrate temperature was set to 0 mJ / cm ² and 200 to 400 ° C.
At this time, the pixel portion was covered with a metal mask 510 so that the laser light was not irradiated. Alternatively,
The beam shape of the laser light is processed into a linear shape and other shapes,
The laser light may be prevented from entering the pixel portion.
(Fig. 5 (C))

Then, the silicon film 503 is etched,
A TFT area of the peripheral circuit and a TFT area of the pixel portion were formed. The former is a crystalline silicon film and the latter is an amorphous silicon film. And the thickness is 1000-1500Å on the whole surface,
For example, a 1200 Å silicon oxide film 511 was formed, and gate electrode portions 512, 513 and 514 were formed from aluminum and its anodic oxide film as in the case of the first embodiment. The gate electrode portion 512 is formed of 51 of the PTFT of the peripheral circuit.
Reference numeral 3 is a gate electrode of the same NTFT, and reference numeral 514 is a gate electrode of a pixel portion TFT.

Then, using these gate electrode portions as masks, N-type and P-type impurities were implanted into the silicon film by the ion doping method as in the first embodiment. As a result,
The source 515 of the peripheral circuit, the channel 516,
Drain 517, source 520 of NTFT of peripheral circuit,
Channel 519, drain 518, NTFT of pixel portion
Source 521, channel 522, and drain 523 were formed. After that, laser irradiation was performed on the entire surface in the same manner as in Example 1 to activate the doped impurities. (Fig. 6 (A))

Thereafter, as an interlayer insulator, a thickness of 3000 to
A silicon oxide film 524 of 8000 Å, for example 5000 Å, was formed. Furthermore, the thickness is 5 by the sputtering method.
An ITO film having a thickness of 00 to 1000 Å, for example, 800 Å was formed, and this was patterned and etched to form a pixel electrode 525. After this, contact holes are formed in the source / drain of the TFT and titanium nitride (thickness 100
0 Å) and aluminum (thickness 5000 Å) two-layer film is deposited, and this is patterned and etched to form electrodes and
Wirings 526 to 530 were formed. In this way, it was possible to form the peripheral circuit with crystalline silicon and the pixel portion with amorphous silicon. (Fig. 6 (B))

In this embodiment, laser irradiation is performed as shown in FIG. In this step, the amorphous component remaining between the silicon crystals grown like needles is also crystallized, and this crystallization is performed by using the needle-like crystals as nuclei to thicken the needle-like crystals. This expands the region in which the current flows and allows a larger drain current to flow.

This state is shown in FIG. FIG. 7 shows a thinned crystallized silicon film observed by a transmission electron microscope (TEM). FIG. 7A is a view of the vicinity of the tip of the crystallization region of the silicon film crystallized by lateral growth, and needle-like crystals are observed. Further, it can be seen that many non-crystallized amorphous regions exist between the crystals. (Figure 7 (A))

When this is irradiated with laser under the conditions of this embodiment, it becomes as shown in FIG. By this process, FIG.
The amorphous region, which occupies most of the area of (A), crystallizes, but this crystallization occurs randomly, and the electrical characteristics are not so good. What should be noted is the crystalline state of the region that was originally amorphous between the needle-like crystals observed near the center. Here, a thick crystal region is formed so as to grow by crystallization from a needle crystal. (Fig. 7
(B))

In FIG. 7, for the sake of clarity,
Although the tip region of crystal growth with many amorphous regions was observed, the same is true near the root and center of crystal growth. As described above, by laser irradiation, the amorphous portion can be reduced and the needle crystal can be thickened, and the characteristics of the TFT can be further improved.

[0065]

[Effect] In an active matrix type liquid crystal display device, the TFT in the peripheral circuit portion is formed of a crystalline silicon film which is crystal-grown in a direction parallel to the flow of carriers, and the TFT in the pixel portion is formed of an amorphous silicon film. With this configuration, the peripheral circuit portion can be configured to perform high-speed operation, and the pixel portion can be provided with a switching element having a small off current value required for holding charges. .

[Brief description of drawings]

FIG. 1 shows an outline of an example.

FIG. 2 shows a manufacturing process of an example.

FIG. 3 shows an outline of an example.

FIG. 4 shows a manufacturing process of an example.

FIG. 5 shows a manufacturing process of an example.

FIG. 6 shows a manufacturing process of an example.

FIG. 7 shows a crystal structure of an example.

[Explanation of symbols]

 101 glass substrate 102 base film (silicon oxide film) 103 mask 100 nickel trace addition region 105 crystal growth direction 107 gate electrode 108 anodized layer 109 gate electrode 110 anodized layer 111 source / drain region 112 channel formation region 113 drain / source region 114 Source / Drain Region 115 Channel Forming Region 116 Drain / Source Region 117 Electrode 118 Interlayer Insulator 119 Electrode 120 Electrode 211 Interlayer Insulator 213 Electrode 214 Electrode 212 ITO (Pixel Electrode)

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[Procedure amendment]

[Submission date] August 25, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 7

[Correction method] Change

[Correction content]

[Figure 7]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location G02F 1/136 500 H01L 21/20 8122-4M (72) Inventor Shoji Miyanaga 398 Hase, Atsugi, Kanagawa Prefecture Banchi Co., Ltd. Semiconducting Energy Laboratory

Claims (8)

[Claims] 1. A semiconductor device having a plurality of thin film transistors using a silicon film provided on a substrate, wherein a part of the plurality of thin film transistors uses a crystalline silicon film crystal-grown substantially parallel to a substrate surface. A semiconductor device, wherein the other part of the large number of thin film transistors is formed using an amorphous silicon semiconductor film. 2. A semiconductor device having a plurality of thin film transistors using a silicon film provided on a substrate, wherein a part of the plurality of thin film transistors is provided in a peripheral circuit part of an active matrix type liquid crystal display device. The other part of the thin film transistor is provided in the pixel portion of the active matrix type liquid crystal display device, and the thin film transistor provided in the peripheral circuit portion is composed of a crystalline silicon film crystal-grown in a direction parallel to the substrate surface. The semiconductor device, wherein the thin film transistor provided in the pixel portion is formed of an amorphous silicon film. 3. A process of forming a substantially amorphous silicon film on a substrate, a process of selectively introducing a metal element that promotes crystallization before or after the process, and a process of heating the non-crystalline silicon film. A step of crystallizing the crystalline silicon film, wherein crystal growth is performed in a direction substantially parallel to a substrate surface in the vicinity of the region where the metal element is selectively introduced, A method for manufacturing a semiconductor device, characterized in that a region not selectively introduced into is left as an amorphous silicon film. 4. A method of manufacturing a semiconductor device used for an active matrix type liquid crystal display device having a pixel portion and a peripheral circuit portion, the method comprising forming a substantially amorphous silicon film on a substrate, Before or after the step, a step of selectively introducing a metal element that promotes crystallization into a peripheral circuit portion, and a step of heating the amorphous silicon film in the peripheral portion of the region to which the metal element is added by heating, A step of growing crystals in a direction substantially parallel to the substrate surface; and a step of leaving a region where the metal element has not been introduced in the step as an amorphous silicon film, By forming a thin film transistor in a region where crystal growth is performed substantially in parallel with each other, the moving direction of carriers in the thin film transistor in the region is substantially parallel to the crystal growth direction of the crystalline silicon film. And forming a thin film transistor in the region left as the amorphous silicon film. 5. The method for manufacturing a semiconductor device according to claim 3, wherein nickel is used as the metal element. 6. The method of manufacturing a semiconductor device according to claim 3, wherein the heating temperature is 450 ° C. to 550 ° C. 7. The method according to claim 3 or 4, wherein after the step of crystallizing the silicon film by heating, the region to which the metal element is added and its periphery are selectively irradiated with a laser or strong light equivalent thereto. A method for manufacturing a semiconductor device, comprising: 8. The semiconductor device according to claim 3 or 4, wherein the addition of the metal element that promotes crystallization is performed by coating or spin coating a substance containing the metal element. Manufacturing method.