JP3958244B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND 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 liquid crystal display device.
[0002]
[Prior art]
Known semiconductor devices having TFTs on an insulating substrate such as glass include active liquid crystal display devices and image sensors that use these TFTs to drive pixels.
[0003]
A thin film silicon semiconductor is generally used for TFTs used in these devices. Thin film silicon semiconductors are roughly classified into two types: those made of amorphous silicon semiconductor (a-Si) and those made of crystalline silicon semiconductor. Amorphous silicon semiconductors are most commonly used because they have a low production temperature, can be produced relatively easily by a vapor phase method, and are highly mass-productive. However, physical properties such as conductivity have crystallinity. Since it is inferior to a silicon semiconductor, the establishment of a method for manufacturing a TFT made of a crystalline silicon semiconductor has been strongly demanded in order to obtain higher speed characteristics in the future. As silicon semiconductors having crystallinity, polycrystalline silicon, microcrystalline silicon, amorphous silicon containing crystal components, semi-amorphous silicon having an intermediate state between crystalline and amorphous are known. .
[0004]
As a method of obtaining a thin film silicon semiconductor having these 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.
Is known. However, the method (1) is technically difficult to uniformly form a film having good semiconductor properties over the entire surface of the substrate, and the film forming temperature is as high as 600 ° C. There was a problem of cost that a glass substrate could not be used. In the method (2), the excimer laser, which is currently most commonly used, has a problem that the throughput is low because the irradiation area of the laser beam is small. The laser is not stable enough to treat the material uniformly, and there is a strong sense of the next generation technology. The method (3) has an advantage that it can cope with a large area as compared with the methods (1) and (2), but it is also necessary to set the heating temperature to a high temperature of 600 ° C. or more, which is an inexpensive glass. Considering the use of a substrate, it is necessary to further lower the heating temperature. In particular, in the case of the current liquid crystal display device, the screen has been enlarged, and therefore it is necessary to use a large glass substrate as well. When such a large glass substrate is used, shrinkage and distortion in the heating process that is indispensable for semiconductor fabrication reduce the accuracy of mask alignment and the like, which is a serious problem. In particular, in the case of 7059 glass that is most commonly used at present, the strain point is 593 ° C., and the conventional heat crystallization method causes large deformation. In addition to the temperature problem, in the current process, the heating time required for crystallization is several tens of hours or more, and it is necessary to further shorten the time.
[0005]
[Problems to be solved by the invention]
The present invention provides means for solving the above problems. More specifically, in a method for producing a thin film made of a crystalline silicon semiconductor using a method of crystallizing a thin film made of amorphous silicon by heating, the temperature required for crystallization is lowered and the time is shortened. The purpose is to provide a process that balances the two. Of course, the silicon semiconductor having crystallinity produced using the process provided by the present invention has physical properties equivalent to or better than those produced by the prior art, and can be used for the active layer region of the TFT. It goes without saying that there are. The purpose of this technique is to selectively provide TFTs having necessary characteristics on a substrate.
[0006]
BACKGROUND OF THE INVENTION
The inventors have conducted the following experiment on the method of forming an amorphous silicon semiconductor film by the CVD method or the sputtering method and crystallizing the film by heating, as described in the section of the prior art. And discussed.
[0007]
First, as an experimental fact, when an amorphous silicon film is formed on a glass substrate and the mechanism for crystallizing this film by heating is investigated, crystal growth starts from the interface between the glass substrate and amorphous silicon, Above the film thickness, it was recognized that the film progressed in a columnar shape perpendicular to the substrate surface.
[0008]
In the above phenomenon, there is a crystal nucleus (a seed that becomes the basis of crystal growth) at the interface between the glass substrate and the amorphous silicon film, and the crystal grows from the nucleus. It is considered to be caused by Such crystal nuclei include impurity metal elements that are present in minute amounts on the substrate surface and crystal components on the glass surface (as called crystallized glass, the crystal component of silicon oxide exists on the glass substrate surface) Is considered).
[0009]
Therefore, we thought that it would be possible to lower the crystallization temperature more actively by introducing crystal nuclei, and in order to confirm the effect, deposited a small amount of other metal on the glass substrate, An experiment was conducted in which a thin film made of amorphous silicon was formed, and then heat crystallization was performed. As a result, when several metals were formed on the substrate, a decrease in the crystallization temperature was confirmed, and it was predicted that crystal growth occurred using foreign substances as crystal nuclei. Therefore, the mechanism of the impurity metals that could be reduced in temperature was investigated in more detail. The plurality of impurity elements are nickel (Ni), iron (Fe), cobalt (Co), palladium (Pd), and platinum (Pt).
[0010]
Crystallization can be considered in two stages: initial nucleation and crystal growth from the nuclei. Here, the initial nucleation rate is observed by measuring the time until fine crystals are generated in the form of dots at a constant temperature, and this time is an amorphous film formed using the impurity metal as a base. In all cases, the silicon thin film was shortened, and the effect of introducing crystal nuclei on lowering the crystallization temperature was confirmed. Moreover, unexpectedly, when the growth of crystal grains after nucleation was examined by changing the heating time, a certain kind of metal was deposited, and then the amorphous silicon thin film deposited thereon was formed. In crystallization, it was observed that the rate of crystal growth after nucleation increased dramatically. Although this mechanism is not clear at present, it is assumed that some catalytic effect is acting.
[0011]
In any case, due to the above-mentioned two effects, it is not considered in the past when a certain amount of a metal is deposited on a glass substrate, a thin film made of amorphous silicon is formed, and then heated and crystallized. It was found that sufficient crystallinity can be obtained in about 4 hours at a temperature of 580 ° C. or lower. Among the impurity metals having such an effect, the effect is most remarkable, and the material we selected is nickel.
[0012]
As an example of the effect of nickel, an amorphous material formed by plasma CVD on a substrate (Corning 7059 glass) on which no treatment is performed, that is, a nickel thin film is not formed. When a thin film made of silicon is crystallized by heating in a nitrogen atmosphere, if the heating temperature is 600 ° C., a heating time of 10 hours or more is required, but a very small amount of nickel thin film is formed. When a thin film made of amorphous silicon on the substrate was used, a similar crystallization state could be obtained by heating for about 4 hours. The determination of crystallization at this time utilized a Raman spectrum. 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 made of amorphous silicon is formed after forming a thin film of nickel, the crystallization temperature can be lowered and the time required for crystallization can be shortened. . Therefore, a more detailed description will be added on the assumption that this process is used for manufacturing TFTs. As will be described in detail later, the nickel thin film has the same effect even if it is formed on the amorphous silicon film as well as on the substrate (that is, on the lower side of the amorphous silicon film), and ion implantation, Further, since the same applies to the plasma processing, in the present specification, this series of processing will be referred to as “a slight amount of nickel”. Technically, a small amount of nickel can be added during the formation of the amorphous silicon film.
[0014]
First, a method for adding a small amount of nickel will be described. A small amount of nickel can be added by forming a small amount of nickel thin film on the substrate and then forming amorphous silicon. The film forming method also has the effect of lowering the temperature, and the film forming method can be a sputtering method, a vapor deposition method, a spin coating method, a coating method, or a plasma method. It turns out that it doesn't matter. However, when a very small amount of nickel thin film is formed on the substrate, a thin film of silicon oxide (underlying film) is formed on the substrate rather than directly forming a small amount of nickel thin film on the 7059 glass substrate. The effect is more remarkable when a small amount of nickel thin film is formed thereon. A possible reason for this is that the direct contact between silicon and nickel is important for the low-temperature crystallization of this time, and in the case of 7059 glass, components other than silicon inhibit the contact or reaction between the two. It may be mentioned.
[0015]
Further, as a method for adding a small amount of nickel, in addition to forming a thin film in contact with or under amorphous silicon, substantially the same effect was confirmed when nickel was added by ion implantation. For the amount of nickel, 1 x 10 ¹⁵ atoms / cm ^Three Although low temperature has been confirmed with the addition of the above amount, 5 × 10 ¹⁹ atoms / cm ^Three In the above addition amount, the peak shape of the Raman spectrum is clearly different from that of silicon alone. ¹⁵ atoms / cm ^Three ~ 1x10 ¹⁹ atoms / cm ^Three The range is good. Nickel concentration is 5 × 10 ¹⁹ atoms / cm ^Three If it becomes above, NiSi will generate | occur | produce locally and the characteristic as a semiconductor will fall. The nickel concentration is 1 × 10 ¹⁵ atoms / cm ^Three If it is below, the effect of nickel as a catalyst will decrease. In a crystallized state, the lower the nickel concentration, the better.
[0016]
Next, a description will be given of the crystal form when a small amount of nickel is added. As described above, when nickel is not added, nuclei are randomly generated from crystal nuclei such as the substrate interface, and crystal growth from the nuclei is also random up to a certain film thickness. In addition, it is known that columnar crystal growth is performed in which the (110) direction is perpendicular to the substrate, and of course, substantially uniform crystal growth is observed over the entire thin film. On the other hand, the nickel added in a small amount has a feature that the crystal growth is different between the region where nickel is added and the vicinity thereof. In other words, in the region where nickel is added, the added nickel or its compound with silicon becomes a crystal nucleus, and a columnar crystal grows almost perpendicularly to the substrate as in the case where nickel is not added. It became clear from the micrograph. Then, crystallization at low temperatures was confirmed even in the region where nickel in the vicinity thereof was not added in a small amount, and the portion was arranged in the (111) direction perpendicular to the substrate, and needle-like or columnar crystals were parallel to the substrate. A unique crystal growth of growth was observed. The lateral crystal growth parallel to the substrate is observed to grow as large as several hundred μm from a small amount of nickel, and the amount of growth increases in proportion to the increase in time and temperature. I also found out that As an example, a growth of about 40 μm was observed at 550 ° C. for 4 hours. Moreover, according to the transmission electron micrograph, it has been found that all of the large lateral crystals are single crystal-like. Then, the nickel concentration of this small amount of nickel added portion, the laterally grown portion in the vicinity thereof, and the distant amorphous portion (low-temperature crystallization is not performed in a considerably distant portion and the amorphous portion remains) is set to SIMS ( When examined by secondary ion mass spectrometry), the laterally grown portion was detected to be about an order of magnitude less than the portion with a small amount of nickel added, and diffusion in amorphous silicon was observed. In addition, the amorphous portion was observed to be about an order of magnitude less. The relationship between this and the crystal form is not clear at present, but anyway, it is possible to form a silicon thin film having the crystallinity of the desired crystal form in the desired part by controlling the amount of nickel added and its position. is there.
[0017]
Next, the electrical characteristics of the nickel slight 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 a film with almost no nickel added, that is, the value obtained by crystallization at about 600 ° C. for several tens of hours, and the temperature dependence of the conductivity. When the activation energy was determined from the properties, the amount of nickel added was 10 ¹⁷ atoms / cm ^Three -10 ¹⁸ atoms / cm ^Three In the case of the degree, the behavior that seems to be attributed to the level of nickel was not observed. (If limited to this fact, the nickel concentration in the film when used for the active layer of TFT is 10 ¹⁸ atoms / cm ^Three It can be said that it is desirable to be less than or equal to)
[0018]
On the other hand, the laterally grown portion has a conductivity higher by one digit or more than that of the portion with a small amount of nickel added, and has a considerably high value as a silicon semiconductor having crystallinity. This is thought to be due to the fact that the current path direction coincided with the lateral growth direction of the crystal, so that there were few or almost no grain boundaries existing while electrons (carriers) passed between the electrodes. It is consistent with the micrograph results. That is, it is in agreement with the observation fact that acicular or columnar crystals grow in a direction parallel to the substrate.
[0019]
Finally, a method applied to the TFT will be described based on the various characteristics described above. Here, as an application field of the TFT, an active liquid crystal display device using the TFT for driving the pixel is assumed.
[0020]
As described above, in recent large-screen active liquid crystal display devices, it is important to suppress the shrinkage of the glass substrate, but by using the nickel micro-addition process of the present invention, compared with the strain point of glass. Therefore, crystallization is possible at a sufficiently low temperature, which is particularly preferable. According to the present invention, the portion where amorphous silicon has been used conventionally can be easily replaced with a crystalline silicon film by adding a small amount of nickel and thermally annealing at about 450 to 550 ° C. for about 4 hours. Is possible. Of course, it is necessary to change the design rules and the like accordingly, but it is considered that the apparatus and the process can be sufficiently handled by conventional ones, and the merit is great.
[0021]
In addition, if the present invention is used, it is possible to separately produce TFTs used for pixels and TFTs that form drivers for peripheral circuits by using crystal forms corresponding to the respective characteristics, and an active matrix liquid crystal display device There are many merits especially in application to. In an active matrix liquid crystal display device, a TFT used for a pixel does not require so much mobility, and a smaller off-state current is more advantageous than that. Therefore, in the case of using the present invention, the crystal is grown in the vertical direction (relative to the substrate surface) by directly adding a small amount of nickel to the region to be the TFT used for the pixel. A large number of grain boundaries can be formed in the direction connecting the drain regions to reduce the off-current. On the other hand, the TFT forming the peripheral circuit driver is required to have a very high mobility when considering application to a workstation in the future. 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 then a crystal is grown in one direction (lateral direction, that is, a direction parallel to the substrate surface), By aligning the crystal growth direction with the channel current path direction (the direction in which carriers move, that is, the direction connecting the source region and the drain region), a TFT having very high mobility can be manufactured.
[0022]
That is, according to the present invention, in a semiconductor device in which a large number of thin film transistors (commonly referred to as TFTs) are formed on a substrate such as a glass substrate, the crystal growth direction of a crystalline silicon semiconductor film constituting a specific TFT is selectively controlled. The idea of the invention is to selectively form TFTs satisfying the required characteristics on the substrate. This is the end of the basic description of the present invention. A specific configuration of the present invention will be described below.
[0023]
In the present invention, for example, in an active matrix type liquid crystal display device having a peripheral circuit portion and a pixel portion as shown in FIG. 1, TFTs (thin film transistors) provided in the pixel portion are grown in a direction perpendicular to the substrate surface. The TFT is formed of a crystalline silicon film, and the TFT formed in the peripheral circuit portion is formed of a crystalline silicon film that is crystal-grown in a direction parallel to the substrate. In the pixel portion, by using a crystalline silicon film crystal-grown in a direction perpendicular to the substrate, the carrier moving between the source and the drain can cross the grain boundary, and the TFT having a small off-current Can be obtained. On the other hand, in the peripheral circuit portion, a source / drain is formed in a direction parallel to the crystal growth direction to obtain a TFT having a high mobility, that is, a high on-current. During the operation of the TFT, carriers flow between the source and the drain, so forming the source / drain in the crystal growth direction reduces the possibility that the carriers cross the grain boundary and reduces the resistance received by the carriers. be able to.
[0024]
In this way, a crystalline silicon film can be obtained by selectively performing crystallization in a direction perpendicular to or parallel to the substrate surface, but the characteristics of such a crystalline silicon film are further improved. If this is the case, after the crystallization step, an insufficiently crystallized component remaining at the grain boundary or the like may be crystallized by irradiating a laser or intense light equivalent thereto. In this step, the characteristics can be improved in the same manner for a silicon film grown in a direction perpendicular to the substrate surface or a silicon film grown in a parallel direction.
[0025]
The present invention is a semiconductor device in which a number of thin film transistors using a crystalline silicon film are provided on a substrate, wherein a part of the number of thin film transistors is more than a crystalline silicon film crystal-grown in a direction parallel to the substrate surface. Thus, another part of the thin film transistor is characterized in that it is made of a crystalline silicon film crystal-grown in a direction perpendicular to the substrate surface.
The present invention is a semiconductor device in which a large number of thin film transistors using a crystalline silicon film are provided on a substrate, and a part of the thin film transistors is provided in a peripheral circuit portion of an active matrix liquid crystal display device, Another part of the plurality of thin film transistors is provided in a pixel portion of an active matrix liquid crystal display device, and the thin film transistor provided in the peripheral circuit portion is a crystalline silicon crystal grown in a direction parallel to the substrate surface. One feature is that the thin film transistor formed of a film and provided in the pixel portion is formed of a crystalline silicon film crystal-grown in a direction perpendicular to the substrate surface.
The present invention also includes a step of forming a substantially amorphous silicon film on a substrate, a step of selectively introducing a metal element that promotes crystallization before or after the step, Crystallizing a crystalline silicon film, and in a region where the metal element is selectively introduced, crystal growth is performed in a direction substantially perpendicular to the substrate surface, and the metal element is selected. One feature of the peripheral region of the introduced region is that crystal growth is performed in a direction substantially parallel to the substrate surface.
The present invention also includes a step of forming a substantially amorphous silicon film on a substrate, a step of selectively introducing a metal element that promotes crystallization before or after the step, Crystallizing the crystalline silicon film, and in the crystallization step, in the region where the metal element is selectively introduced, crystal growth is performed in a direction substantially perpendicular to the substrate surface. In the crystallization step, in the peripheral region of the region where the metal element is selectively introduced, crystal growth is performed in a direction substantially parallel to the substrate surface, and in a direction substantially perpendicular to the substrate surface. By forming a thin film transistor with a crystalline silicon film in a region where crystal growth has been performed, the carrier movement direction in the thin film transistor is made substantially perpendicular to the crystal growth direction of the crystalline silicon film, and the substrate surface A thin film transistor is formed of a crystalline silicon film in a region where crystal growth is performed in a direction substantially parallel to the carrier, whereby the carrier movement direction in the thin film transistor is approximately parallel to the crystal growth direction of the crystalline silicon film. This is a feature.
Further, the present invention is characterized in that at least one material selected from Ni, Co, Pd, and Pt is used as the metal element.
Further, the present invention is characterized in that, after the step of crystallizing the silicon film by heating, the region to which the metal element is added and the periphery thereof are selectively irradiated with a laser or intense light equivalent thereto.
Further, the present invention is characterized in that the addition of a metal element that promotes crystallization is performed by applying or spin-coating a substance containing the metal element.
[Action]
By selecting the crystal growth direction of the crystalline silicon film, a TFT having the required characteristics can be selectively formed.
[0026]
【Example】
Example 1 FIG. 1 shows an outline of an example. FIG. 1 is a top view of a liquid crystal display device, and shows a pixel portion provided in a matrix and a peripheral circuit portion. In this embodiment, a TFT for driving a pixel and a TFT constituting a peripheral circuit are formed on an insulating substrate (for example, a glass substrate). In this embodiment, a circuit having a CMOS structure in which PTFT and NTFT using a crystalline silicon film (called a crystalline silicon film) obtained by lateral growth of a peripheral circuit is provided in a complementary manner, and a pixel portion An example of an N-channel TFT (NTFT) using crystalline silicon grown in the vertical direction will be described.
[0027]
In the following, FIG. 2 shows a manufacturing process of a circuit in which NTFT and PTFT constituting a peripheral circuit are configured in a complementary manner, and FIG. 4 shows a manufacturing process of NTFT formed in a pixel. is there. Both processes are performed on the same substrate, and common processes are performed simultaneously. That is, (A) to (D) in FIG. 2 and (A) to (D) in FIG. 4 correspond to each other, and the process in FIG. 2 (A) and the process in FIG. The process of FIG. 2B and the process of FIG. 4B proceed at the same time.
[0028]
FIG. 2 shows a manufacturing process of a circuit in which NTFT and PTFT constituting a peripheral circuit are made complementary, and FIG. 4 shows a manufacturing process of NTFT provided in a pixel. First, a silicon oxide base film 102 having a thickness of 2000 mm was formed on a glass substrate (Corning 7059) 101 by a sputtering method. 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. The mask 103 exposes the base film 102 in a slit shape (indicated by 100). When this state is viewed from the top, the base film 102 is exposed in a slit shape, and the other portions are masked.
[0029]
After the mask 103 is provided, a nickel silicide film (chemical formula NiSi) having a thickness of 5 to 200 mm, for example, 20 mm, is formed by sputtering. _x , 0.4 ≦ x ≦ 2.5, for example, x = 2.0). As a result, the nickel silicide film is formed on the portion of the region 100 and the portion of the region 204 (showing the entire surface of the base film 102 in FIG. 4) which is the entire pixel portion. Thereafter, by removing the mask 103, a nickel silicide film is selectively formed in the region 100 in FIG. That is, a small amount of nickel is selectively added to the region 100.
[0030]
Next, an intrinsic (I-type) amorphous silicon film (amorphous silicon film) 104 having a thickness of 500 to 1500 mm, for example, 1000 mm, was formed by plasma CVD. Then, it was crystallized by annealing at 550 ° C. for 4 hours in a hydrogen reducing atmosphere (preferably the partial pressure of hydrogen is 0.1 to 1 atm) or in an inert atmosphere (atmospheric pressure). The annealing temperature can be 450 ° C. or higher, but if it is high, it becomes the same as the conventional method. Therefore, it can be said that 450 to 550 degreeC is a preferable annealing temperature.
[0031]
At this time, the crystallization of the silicon film 104 occurs in a direction perpendicular to the substrate 101 in 100 regions where the nickel silicide film is selectively formed. Then, in the peripheral region of the region 100, as indicated by an arrow 105, crystal growth is performed from the region 100 in the lateral direction (direction parallel to the substrate). Then, in the pixel portion (shown in FIG. 4) where the nickel silicide film is formed on the entire surface, the entire silicon film 104 is crystal-grown in the direction perpendicular to the substrate 101 as indicated by 215. During the crystal growth, the distance of crystal growth in the direction parallel to the substrate indicated by the arrow 105 is about 40 μm.
[0032]
As a result of the above process, the amorphous silicon film was crystallized to obtain the crystalline silicon film 104. Here, in the peripheral circuit portion, crystal growth in the lateral direction (direction parallel to the substrate 101) is performed as shown in FIG. 2, and in the pixel portion, as shown in FIG. The crystal growth in a direction perpendicular to the direction is performed.
[0033]
Then, element isolation was performed, the unnecessary portion of the crystalline silicon film 104 was removed, and an element region was formed. In this process, if the length of the active layer (the portion where the source / drain region and the channel formation region are formed) of the TFT is set to 40 μm or less, the source / drain and the channel region in the peripheral circuit portion in the direction parallel to the substrate It can be composed of a crystalline silicon film having grown crystals. If at least the channel formation region is formed of a crystalline silicon film, the length of the active layer can be further increased.
[0034]
Thereafter, a silicon oxide film 106 having a thickness of 1000 mm was formed as a gate insulating film by a sputtering method. For sputtering, silicon oxide is used as a target, the substrate temperature during sputtering is 200 to 400 ° C., for example 350 ° C., the sputtering atmosphere is oxygen and argon, and argon / oxygen = 0 to 0.5, for example 0.1 or less. did. Subsequently, aluminum (containing 0.1 to 2% silicon) having a thickness of 6000 to 8000 mm, for example, 6000 mm was formed by sputtering. Note that it is desirable that the silicon oxide film 106 and the aluminum film are formed continuously.
[0035]
Then, gate electrodes 107 and 109 were formed by patterning the aluminum film. Needless to say, these steps are performed simultaneously in FIGS. 2C and 4C.
[0036]
Further, the surface of the aluminum electrode was anodized to form oxide layers 108 and 110 on the surface. This anodization was performed in an ethylene glycol solution containing 1 to 5% tartaric acid. The thickness of the obtained oxide layers 108 and 110 was 2000 mm. Note that the oxides 108 and 110 have a thickness for forming an offset gate region in a later ion doping step (an ion implantation step of a doping material imparting a conductivity type). It can be determined in the anodizing process.
[0037]
Next, impurities (phosphorus and boron) were implanted into the active region by ion doping using the gate electrode 107 and its surrounding oxide layer 108 and the gate electrode 109 and its surrounding oxide layer 110 as a mask. As doping gas, phosphine (PH _Three ) And diborane (B ₂ H ₆ In the former case, the acceleration voltage was 60 to 90 kV, for example 80 kV, and in the latter case, the acceleration voltage was 40 to 80 kV, for example 65 kV. The dose amount is 1 × 10 ¹⁵ ~ 8x10 ¹⁵ cm ^-2 For example, 2 × 10 phosphorus ¹⁵ cm ^-2 Boron 5 × 10 ¹⁵ It was. In 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 a P-channel TFT (PTFT) and an N-channel TFT (NTFT) are formed as shown in FIG. I was able to. At the same time, as shown in FIG. 4, an N-channel TFT could be formed.
[0038]
Thereafter, annealing was performed by laser light irradiation to activate the implanted ions. As the laser light, a KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) was used, but other lasers may be used. The laser light irradiation condition is an energy density of 200 to 400 mJ / cm. ² For example, 250 mJ / cm ² And 2 to 10 shots, for example, 2 shots, were irradiated at one place. It is useful to heat the substrate to about 200 to 450 ° C. during the laser light irradiation. In this laser annealing step, since nickel has diffused in the previously crystallized region, recrystallization easily proceeds by this laser light irradiation, and an impurity doped with an impurity imparting P-type The regions 111 and 113 as well as the impurity regions 114 and 116 doped with an impurity imparting N-type could be easily activated.
[0039]
Subsequently, in the peripheral circuit portion, as shown in FIG. 2, a silicon oxide film 118 having a thickness of 6000 mm is formed as an interlayer insulator by a plasma CVD method, a contact hole is formed therein, and a metal material, for example, TFT electrodes / wirings 117, 120, and 119 were formed of a multilayer film of titanium nitride and aluminum. Further, in the pixel portion, as shown in FIG. 4, an interlayer insulator 211 is formed of silicon oxide, and after forming contact holes, an ITO electrode 212 and metal wirings 213 and 214 to be pixel electrodes are formed. Finally, annealing was performed at 350 ° C. for 30 minutes in a hydrogen atmosphere of 1 atm to complete a TFT circuit or TFT. (Fig. 2 (D), Fig. 4 (D))
[0040]
The circuit shown in FIG. 2 has a CMOS structure in which PTFT and NTFT are provided in a complementary manner. In the above process, two independent TFTs are simultaneously produced by simultaneously producing two TFTs and cutting them at the center. It is also possible.
[0041]
In order to show the positional relationship between the region in which nickel is selectively introduced and the TFT in the structure shown in FIG. 2, FIG. 3 shows an outline of FIG. In FIG. 3, a small amount of nickel is selectively added to a region indicated by 100, and crystal growth is performed in the lateral direction (left and right direction on the paper) by thermal annealing. In the region where the lateral crystal growth is performed, the source / drain regions 111 and 113 and the channel formation region 112 are formed as PTFTs. Similarly, source / drain regions 114 and 116 and a channel formation region 115 are formed as NTFTs.
[0042]
In the structure as described above, since the carrier flow direction and the crystal growth direction are aligned, the operation of the TFT can be improved without crossing the grain boundary when the carrier moves. For example, the mobility of PTFT produced in the process shown in FIG. ² / Vs and the mobility of conventional PTFT is 50-60cm ² It has been confirmed that it can be improved from / Vs. Also for NTFT, 150-180cm ² / Vs mobility is obtained, 80-80cm ² A high value is obtained as compared with / Vs.
[0043]
In FIG. 3, a gate insulating film and a channel formation region are provided under the gate electrodes (107 and 109). As can be seen from FIG. 3, a plurality of TFTs can be formed at the same time by further extending the nickel minute addition region (in FIG. 2, extending vertically).
[0044]
On the other hand, in the NTFT shown in FIG. 4 formed in the pixel portion, the direction of carriers flowing (moving) between the source / drain, that is, between 114 and 116, and the direction of crystal growth indicated by 215 are perpendicular. Therefore, when the carrier moves, the crystal grain boundary must be crossed, and the mobility is 30 to 80 cm. ² / Vs and the characteristics similar to or lower than those of the conventional NTFT. However, when the characteristics of the NTFT shown in FIG. 4 were examined, it was confirmed that the off-current was smaller than that of the NTFT shown in FIG. This is an important characteristic for use for driving the pixel electrode, and is a significant TFT as a TFT for driving the pixel electrode. The conventional TFT here is a TFT using a crystalline silicon film obtained by crystallizing an amorphous silicon film formed on a glass substrate by thermal annealing at 600 degrees for 24 hours. .
[0045]
In this embodiment, as a method for introducing Ni, Ni is selectively formed as a thin film (it is very thin and difficult to observe as a film) on the surface of the base film 102 under the amorphous silicon film 104. Then, a method of crystal growth from this portion was adopted. However, a method of selectively adding a small amount of nickel to the upper surface after the amorphous silicon film 104 is formed may be used. That is, crystal growth may be performed from the upper surface side of the amorphous silicon film or from the lower surface side. Alternatively, a method may be employed in which an amorphous silicon film is formed in advance, and nickel ions are selectively implanted into the amorphous silicon film 104 using an ion doping method. In this case, the concentration of the nickel element can be controlled. Further, a small amount of nickel may be added by plasma treatment instead of forming a nickel thin film.
[0046]
Also, when fabricating a TFT, the crystal growth direction is not simply perpendicular or parallel to the carrier flow, but the angle between the carrier flow direction and the crystal growth direction is set at an arbitrary angle, so that the TFT The characteristics can also be controlled.
[0047]
Example 2 FIGS. 5 and 6 show this example. After a silicon oxide film 502 having a thickness of 1000 to 5000 mm, for example, 2000 mm, was formed on the glass substrate 501, an amorphous silicon film having a thickness of 300 to 1500 mm, for example, 500 mm was formed by a plasma CVD method. Further, a silicon oxide film 504 having a thickness of 500 to 1500, for example, 500, was formed thereon. These film formations are desirably performed continuously. Then, the silicon oxide film 504 was selectively etched, and a window 506 for introducing nickel was opened in a region for forming a TFT of the peripheral drive circuit. At the same time, the silicon oxide film 504 is removed in the pixel region.
[0048]
Then, a nickel salt film 505 was formed by spin coating. To explain this method, first, nickel acetate or nickel nitrate was diluted with water or ethanol to a concentration of 25 to 200 ppm, for example, 100 ppm.
[0049]
On the other hand, the substrate was immersed in a 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 region of the window 506 and the pixel region). . This is to improve the interface affinity between the nickel solution prepared as described above and the amorphous silicon film.
[0050]
A substrate subjected to such treatment was placed on a spinner and rotated gently, and 1 to 10 ml, for example, 2 ml of a nickel solution was dropped on the substrate to spread the solution over the entire surface of the substrate. This state was maintained for 1 to 10 minutes, for example, 5 minutes. Thereafter, spin drying was performed by increasing the number of rotations of the substrate. This operation may be repeated a plurality of times. In this way, a thin film 505 of nickel salt was formed. (Fig. 5 (A))
[0051]
Thereafter, heat treatment was performed in a heating furnace at 520 to 580 ° C. for 4 to 12 hours, for example, at 550 ° C. for 8 hours. The atmosphere was nitrogen. As a result, first, nickel diffused immediately below the window 506 and in the region of the pixel region, and crystallization started from this region. The direction of crystallization was perpendicular to the substrate. And the crystallization area | region extended to the circumference | surroundings. The direction of crystallization at this time was parallel to the substrate. As a result, three regions having different properties were formed. The first is a region 507 or a pixel region 510 immediately below the window 506 where crystallization has progressed perpendicular to the substrate. The second is a region 508 around the above regions 507 and 510, where crystallization progresses horizontally with respect to the substrate. On the other hand, the region 509 far from the window 506 remained amorphous silicon. (Fig. 5 (B))
[0052]
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 200-350mJ / cm ² The substrate temperature was 200 to 400 ° C. (Fig. 5 (C))
[0053]
Thereafter, the silicon film 503 was etched to form a TFT region in the peripheral circuit and a TFT region in the pixel portion. At this time, the region 508 is designed to come to the channel region of the TFT of the peripheral circuit. Then, a silicon oxide film 511 having a thickness of 1000 to 1500 mm, for example, 1200 mm was formed, and gate electrode portions 512, 513, and 514 were formed of aluminum and its anodic oxide film in the same manner as in the first embodiment. The gate electrode portion 512 is the PTFT of the peripheral circuit, 513 is the same NTFT, and 514 is the gate electrode of the pixel portion TFT.
[0054]
Then, using these gate electrode portions as masks, N-type and P-type impurities were implanted into the silicon film by ion doping as in Example 1. As a result, the PTFT source 515, channel 516, and drain 517 of the peripheral circuit, the NTFT source 520, channel 519, and drain 518 of the peripheral circuit, and the NTFT source 521, channel 522, and drain 523 of the pixel portion were formed. Thereafter, laser irradiation was performed on the entire surface in the same manner as in Example 1 to activate the doped impurities. (Fig. 6 (A))
[0055]
Thereafter, a silicon oxide film 524 having a thickness of 3000 to 8000 mm, for example, 5000 mm was formed as an interlayer insulator. Further, an ITO film having a thickness of 500 to 1000 mm, for example, 800 mm, was formed by a sputtering method, and this was patterned and etched to form a pixel electrode 525. Thereafter, contact holes are formed in the source / drain of the TFT, a two-layer film of titanium nitride (thickness 1000 mm) and aluminum (thickness 5000 mm) is deposited, this is patterned and etched, and the electrode / wiring 526 is formed. ~ 530 was formed. In this manner, the peripheral circuit can be formed with crystalline silicon, and the pixel portion can be formed with amorphous silicon. (Fig. 6 (B))
[0056]
In this embodiment, laser irradiation is performed as shown in FIG. In this step, the amorphous component remaining between the silicon crystals grown in a needle shape is crystallized, and this crystallization is performed with the needle crystal as a nucleus and the needle crystal becoming thicker. This widens the current flow region, and allows a larger drain current to flow.
[0057]
This is shown in FIG. FIG. 7 shows a crystallized silicon film which is thinned and observed with a transmission electron microscope (TEM). FIG. 7A shows the vicinity of the tip of the crystallized region of the silicon film crystallized by lateral growth, and needle-like crystals are observed. Further, it can be seen that there are many non-crystallized amorphous regions between the crystals. (Fig. 7 (A))
[0058]
When this is irradiated with a laser under the conditions of this embodiment, the result is as shown in FIG. By this step, the amorphous region which occupies most of the area of FIG. 7A is crystallized, but since this crystallization occurs randomly, the electrical characteristics are not so good. Of note is the crystalline state of the region that appears to be originally amorphous between the needle-like crystals observed near the center. Here, a thick crystal region is formed so as to crystallize and grow from a needle crystal. (Fig. 7 (B))
[0059]
In FIG. 7, for the sake of clarity, the tip region of crystal growth with a relatively large number of amorphous regions was observed, but the same is true near the root and center of crystal growth. In this manner, the amorphous portion can be reduced and the acicular crystal can be thickened by laser irradiation, and the characteristics of the TFT can be further improved.
[0060]
【The invention's effect】
In an active matrix type liquid crystal display device, a TFT in a peripheral circuit portion is composed of a crystalline silicon film crystal-grown in a direction parallel to a carrier flow, and a TFT in a pixel portion is perpendicular to the carrier flow. By using the crystalline silicon film configured as described above, the peripheral circuit portion can be configured to perform high-speed operation, and the pixel portion is provided with a TFT having a small off-current value required for charge retention And was able to.
[Brief description of the drawings]
FIG. 1 shows an outline of an embodiment.
FIG. 2 shows a manufacturing process of the example.
FIG. 3 shows an outline of an example.
FIG. 4 shows a manufacturing process of the example.
FIG. 5 shows a manufacturing process of the example.
FIG. 6 shows a manufacturing process of the 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 regions
112 channel formation region
113 Drain / source region
114 Source / drain region
115 channel formation region
116 Drain / source region
117 electrode
118 Interlayer insulator
119 electrode
120 electrodes
211 Interlayer insulator
213 electrode
214 electrodes
212 ITO (pixel electrode)
215 Crystal growth direction

Claims (6)

A semiconductor device comprising a thin film transistor for a pixel having a crystalline silicon film provided above a substrate and a thin film transistor for a peripheral circuit ,
The crystalline silicon film of the pixel thin film transistor is a columnar crystal in which the (110) direction is arranged in a direction perpendicular to the substrate ,
Crystalline silicon film of the thin film transistor for the peripheral circuit, a semiconductor device characterized by comprising at crystals grown in a direction parallel to the substrate surface. A semiconductor device comprising a thin film transistor for a pixel having a crystalline silicon film provided above a substrate and a thin film transistor for a peripheral circuit ,
The crystalline silicon film of the thin film transistor for the pixel had a thickness of 30 to 150 nm, made of a (110) direction of the columnar arranged in a direction perpendicular to the substrate crystal,
Crystalline silicon film of the thin film transistor of the peripheral circuit, a semiconductor device characterized by comprising at crystals grown in a direction parallel to the substrate surface. Forming an amorphous silicon film over the substrate;
Adding nickel to the amorphous silicon film;
Heating the amorphous silicon film to which the nickel has been added;
A crystalline silicon film having a first region having columnar crystals whose (110) direction is arranged in a direction perpendicular to the substrate and a second region having crystals grown in a direction parallel to the substrate surface is formed. And
A manufacturing method of a semiconductor device , wherein a thin film transistor for a pixel is formed in the first region, and a thin film transistor for a peripheral circuit is formed in the second region . Forming an amorphous silicon film over the substrate;
Adding nickel to the amorphous silicon film;
Heating the amorphous silicon film to which the nickel has been added;
A crystalline silicon film having a first region having columnar crystals whose (110) direction is arranged in a direction perpendicular to the substrate and a second region having crystals grown in a direction parallel to the substrate surface is formed. And
Irradiating the crystalline silicon film with laser light ,
A manufacturing method of a semiconductor device , wherein a thin film transistor for a pixel is formed in the first region, and a thin film transistor for a peripheral circuit is formed in the second region .   5. The method for manufacturing a semiconductor device according to claim 4, wherein the laser light is KrF excimer laser light or XeCl excimer laser light.   6. The method for manufacturing a semiconductor device according to claim 3, wherein the heating temperature is 450 ° C. to 550 ° C. 6.

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