JP3541946B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor device having a TFT (thin film transistor) provided on an insulating substrate such as glass and a method for manufacturing the same.
[0002]
[Prior art]
As a semiconductor device having TFTs on an insulating substrate such as glass, an active type liquid crystal display device and an image sensor using these TFTs for driving pixels are known.
[0003]
In general, a thin film silicon semiconductor is used for a TFT used in these devices. Thin-film silicon semiconductors are broadly classified into two types: those made of an amorphous silicon semiconductor (a-Si) and those made of a crystalline silicon semiconductor. Amorphous silicon semiconductors are most commonly used because they have a low manufacturing temperature, can be manufactured relatively easily by a gas phase method, and have high mass productivity. Since it is inferior to a silicon semiconductor having the same, a method for manufacturing a TFT made of a silicon semiconductor having crystallinity has been strongly demanded in order to obtain higher speed characteristics in the future. As the silicon semiconductor having crystallinity, polycrystalline silicon, microcrystalline silicon, amorphous silicon containing a crystal component, semi-amorphous silicon having an intermediate state between crystalline and amorphous, and the like are known. .
[0004]
As a method of obtaining a silicon semiconductor in the form of a thin film having such crystallinity,
(1) A film having crystallinity is directly formed at the time of film formation.
(2) An amorphous semiconductor film is formed and crystallinity is imparted by laser light energy.
(3) An amorphous semiconductor film is formed and crystallinity is imparted by applying thermal energy.
Is known. However, in the method (1), it 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. or higher, so that the method is inexpensive. There was also a cost problem that a glass substrate could not be used. In the method (2), taking an excimer laser, which is currently most commonly used, as an example, there is a problem that the irradiation area of the laser beam is small, so that the throughput is low. The stability of the laser is not enough to uniformly process, and it seems to be a next-generation technology. The method (3) has an advantage of being able to cope with a large area as compared with the methods (1) and (2), but also requires a high heating temperature of 600 ° C. or more, and is inexpensive. 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 is becoming larger, 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 a heating step which is indispensable for semiconductor fabrication lowers the accuracy of mask alignment and the like, and is a serious problem. In particular, in the case of 7059 glass, which is currently most commonly used, the strain point is 593 ° C., and the conventional heating crystallization method causes large deformation. In addition to the problem of temperature, the heating time required for crystallization in the current process is several tens of hours or more, so that it is necessary to further shorten the heating time.
[0005]
[Problems to be solved by the invention]
The present invention provides a means for solving the above problems. More specifically, in a method of manufacturing 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 aim is to provide a process that balances Of course, a crystalline silicon semiconductor manufactured using the process provided by the present invention has physical properties equivalent to or higher than those manufactured by the conventional technology, and can be used for the active layer region of the TFT. It goes without saying that there is something.
[0006]
[Background of the Invention]
The present inventors have conducted the following experiments on the method of forming an amorphous silicon semiconductor film by a CVD method or a sputtering method and crystallizing the film by heating as described in the section of the related art. And discussions.
[0007]
First, as an experimental fact, an amorphous silicon film is formed on a glass substrate, and the mechanism of crystallization of the film by heating is examined. The crystal growth starts from the interface between the glass substrate and amorphous silicon. Above the film thickness, it was recognized that the film proceeded in a columnar shape perpendicular to the substrate surface.
[0008]
The above phenomenon is caused by the fact that a crystal nucleus (a seed serving as a base for crystal growth) exists at the interface between the glass substrate and the amorphous silicon film, and the crystal grows from the nucleus. It is considered to be due to Such crystal nuclei are formed by the presence of a crystalline component of silicon oxide on the surface of a glass substrate such as an impurity metal element or a crystal component on a glass surface (as called crystallized glass). Is considered).
[0009]
Therefore, we thought that it would be possible to lower the crystallization temperature by introducing crystal nuclei more aggressively, and in order to confirm the effect, deposited a small amount of other metal on the substrate, An experiment was conducted in which a thin film made of crystalline silicon was formed and then heated and crystallized. As a result, when some metals were formed on the substrate, a decrease in the crystallization temperature was confirmed, and it was expected that crystal growth using foreign substances as crystal nuclei was occurring. Therefore, the mechanism of a plurality of impurity metals that could be reduced in temperature was investigated in more detail.
[0010]
Crystallization can be considered in two stages: initial nucleation and crystal growth from the nucleus. Here, the initial nucleation rate is observed by measuring the time required for the generation of point-like fine crystals at a constant temperature. The case was also shortened, and the effect of introducing crystal nuclei on lowering the crystallization temperature was confirmed. In addition, unexpectedly, when the growth of crystal grains after nucleation was examined by changing the heating time, after the formation of a certain metal, the amorphous silicon thin film In crystallization, it was observed that the rate of crystal growth after nucleation increased dramatically. This mechanism will be described in detail later.
[0011]
In any case, due to the above two effects, when a thin film made of amorphous silicon is formed on a small amount of a certain kind of metal, and then heated and crystallized, it is difficult to think in the past. It has been found that sufficient crystallinity can be obtained at a temperature of 580 ° C. or less for about 4 hours. Among the impurity metals having such an effect, the effect is most remarkable, and a material selected by us is nickel.
[0012]
One example of the effect of nickel is as follows. Amorphous silicon formed by a plasma CVD method on a substrate (Corning 7059) on which no treatment is performed, that is, a thin film of nickel is not formed. When the thin film made of is crystallized by heating in a nitrogen atmosphere, when the heating temperature was set to 600 ° C., a heating time of 10 hours or more was required. When a thin film made of amorphous silicon on a substrate was used, a similar crystallization state could be obtained by heating for about 4 hours. In this case, the crystallization was determined using Raman spectroscopy. 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 on a thin film of nickel, a lower crystallization temperature and a shorter time for crystallization can be achieved. . Therefore, a more detailed description will be given on the assumption that this process is used for manufacturing a TFT. As will be described in detail later, the nickel thin film is formed not only on the substrate but also on amorphous silicon, and has the same effect. In the following, such a series of treatments will be referred to as “addition of trace amount of nickel”.
[0014]
First, a method of adding a trace amount of nickel will be described. A small amount of nickel can be added by forming a small amount of nickel thin film on a substrate and then forming amorphous silicon on the substrate. The method of forming a film also has the effect of lowering the temperature similarly, and it has been found that the film forming method can be a sputtering method, an evaporation method, a coating method or a spin coating method, and the film forming method does not matter. . However, when a very small amount of nickel thin film is formed on a substrate, rather than forming a very small amount of nickel thin film directly on a 7059 glass substrate, a thin film of silicon oxide is formed on the same substrate and a very small amount of silicon oxide is formed thereon. The effect is more remarkable when a thin nickel thin film is formed. One possible reason for this is that direct contact between silicon and nickel is important for low-temperature crystallization, and in the case of 7059 glass, components other than silicon inhibit contact or reaction between the two. It may be that.
[0015]
As a method of adding a trace amount, almost the same effect was confirmed by adding nickel by ion implantation in addition to forming a thin film in contact with above or below amorphous silicon. For the amount of nickel, 1 × 10^Fifteenatoms / cm³It has been confirmed that the addition of the above amount lowers the temperature, but 1 × 10²¹atoms / cm³At the above addition amount, since the shape of the peak of the Raman spectrum is clearly different from that of the simple substance of silicon, only 1 × 10^Fifteenatoms / cm³~ 5 × 10¹⁹atoms / cm³Seems to be in the range. Considering that the semiconductor material is used for the active layer of the TFT, the amount is 1 × 10^Fifteenatoms / cm³~ 1 × 10¹⁹atoms / cm³It is necessary to keep it low.
[0016]
Next, the features of crystal growth and crystal morphology in the case where a trace amount of nickel is added will be described, and the crystallization mechanism deduced therefrom will be described.
[0017]
As described above, when nickel is not added, nuclei are randomly generated from crystal nuclei at the substrate interface or the like, and crystal growth from the nuclei is also random, depending on the manufacturing method. It is reported that relatively oriented crystals can be obtained. Naturally, almost uniform crystal growth is observed over the entire thin film.
[0018]
First, in order to confirm this mechanism, an analysis by DSC (differential scanning calorimeter) was performed. An amorphous silicon thin film formed on a substrate by plasma CVD was filled in a sample container while remaining on the substrate, and the temperature was raised at a constant rate. Then, a clear exothermic peak was observed at about 700 ° C., and crystallization was observed. This temperature naturally shifts when the heating rate is changed. However, when the temperature is increased at, for example, 10 ° C./min, crystallization starts from 700.9 ° C. Next, three kinds of heating rates were measured, and the activation energy of crystal growth after the initial nucleation was determined by the Ozawa method. Then, a value of about 3.04 eV was obtained. In addition, when the reaction rate equation was determined from the fitting with a theoretical curve, it was found that the reaction was best explained by disorder nucleation and its growth model, and nuclei were generated randomly from crystal nuclei at the substrate interface and the like. The validity of the model of crystal growth from the nucleus was confirmed.
[0019]
Exactly the same measurement as described above was performed on a sample to which a small amount of nickel was added. Then, when the temperature was raised at a rate of 10 ° C./min, crystallization started at 619.9 ° C., and the activation energy for crystal growth obtained from a series of these measurements was approximately 1.87 eV, It has been clarified numerically that the crystal growth is easy. In addition, the reaction rate equation obtained from the fitting with the theoretical curve was close to a one-dimensional interface rate-limiting model, suggesting that the crystal growth had a certain directionality.
[0020]
Next, the results of observation of the crystal morphology of this time with a trace amount of nickel added by TEM (transmission electron microscope) are shown. A characteristic phenomenon found from the results of TEM observation is that crystal growth differs between a region to which nickel is added and a portion in the vicinity thereof. That is, when observing from the cross section of the region to which nickel was added, moire or fringes that appeared to be a lattice image were observed almost perpendicular to the substrate. This is considered to indicate that columnar crystals grow almost perpendicularly to the substrate, similarly to the case where no crystal is formed. Observation from the surface of the region to which nickel was added revealed that the region was not completely uniform as in epitaxy. FIG. 4 shows a TED (transmission electron beam diffraction) pattern indicating this. FIG. 4 shows a pattern obtained by irradiating an electron beam perpendicular to the film surface into a region to which nickel is added. The diameter of the electron beam is several microns, and a large black circle in the center is a pattern from (000). . From FIG. 4, at least about three types of crystals having different angles were observed, and the crystals were not completely formed into rings, so it was found that one crystal grain had a considerable size. In order to further confirm this, the orientation was evaluated using thin film XRD (X-ray diffraction). As a result, a {111} or {110} peak was mainly observed. Here, {hkl} is a symbol indicating a plane including all planes equivalent to the (hkl) plane. This result was compared with the result of thin film XRD of a thin film obtained by crystallizing a thin film having no added nickel of the same thickness. , And it became clear that the addition of nickel increased the orientation.
[0021]
Next, results of observing the crystal morphology near the nickel-added region will be described. First, it was unexpected that crystallization of a region where nickel was not added directly was unexpected. However, a nickel addition portion, a lateral crystal growth portion in the vicinity thereof (hereinafter abbreviated as a lateral growth portion), In a further distant amorphous portion (low temperature crystallization is not performed in a considerably distant portion and the amorphous portion remains), the concentration of nickel was examined by SIMS (secondary ion mass spectrometry). In the sample, a small amount of about one digit was detected from the nickel-added portion, and the amorphous portion was further reduced by about one digit. That is, nickel is diffused over a fairly wide range, and crystallization of a region near the region to which nickel is added is also considered to be an effect of the addition of a small amount of nickel.
[0022]
First, FIG. 5 shows a surface TEM image near the nickel-added region. As is clear from the figure, a characteristic needle-like or columnar crystal having a uniform width is observed in a direction parallel to the substrate. In this lateral growth parallel to the substrate, it has been observed that, from the region where a small amount of nickel is added, the growth is as large as several hundred μm, and the growth amount may increase in proportion to the increase in time and temperature. understood. As an example, a growth of about 20 μm was observed at 550 ° C. for 4 hours. Also, these crystalsGrowth directionThe angle at which they intersectThe angle between the crystal growth directionsIs about 60 degrees in each case, and it has been found that it does not depend on the location. Next, FIGS. 6 and 7 show TED patterns in the above-mentioned region. FIG. 6 shows the tip of the needle crystal, and FIG. 7 shows a region where the needle crystal overlaps to some extent. The pattern is very simple, and a single crystal or at most twin crystals can be seen, and the crystal orientations are very uniform. This pattern agrees very well with [111] incidence. As a result, it was found that the plane parallel to the substrate was (111). Then, the crystal growth direction becomes (111).parallelDirection, the axial direction of the laterally grown crystal isA direction perpendicular to the [111] direction,[-110] DirectionDirection equivalent toIt can be seen that it is. This relationship is briefly shown in FIG. Also,Growth of the laterally growing crystalThe directions have six-fold symmetry with respect to the [111] direction.Perpendicular to the [111] direction and[-110] DirectionDirection equivalent toThis is consistent with the fact that the TED pattern in FIG. 7 is a single crystal like.In addition, "-1" of "[-110]" described in the claims and the specification is shown as a substitute for the symbol in which "-" is described above "1".
[0023]
Based on the above experimental facts, the inventors believe that crystallization proceeds by the following mechanism.
[0024]
First, nucleation occurs. At this time, the activation energy is reduced by adding a small amount of nickel. This is obvious from the fact that crystallization occurs at a lower temperature by adding nickel, and this is because, besides the effect of nickel as a foreign substance, the intermetallic compound composed of nickel and silicon One of them thinks that it may be due to the close lattice constant of crystalline silicon. In addition, since this nucleation occurs almost simultaneously over the entire area to which nickel is added, the crystal growth has a mechanism such that the crystal grows as a plane. In this case, the reaction rate equation becomes a one-dimensional interface rate-determining process, and A substantially vertical columnar crystal is obtained. However, due to the limitation of the film thickness and the influence of stress and the like, the crystal axes do not always have to be completely aligned.
[0025]
However, since the horizontal direction of the substrate is more homogeneous than the vertical direction, columnar or needle-like crystals grow laterally aligned with the nickel-added portion as nuclei, and the direction isPerpendicular to the [111] direction and[-110]Direction equivalent to directionIt becomes. Of course, also in this case, the reaction rate equation is expected to be a one-dimensional interface rate-determining type. Since the activation energy for crystal growth is reduced by the addition of nickel as described above, this lateral growth rate is expected to be very high, which is the case. However,Perpendicular to the [111] direction and[-110] DirectionDirection equivalent toThe reason for the crystal growth at this time has not yet been elucidated.
[0026]
Next, the electric characteristics of the nickel-added portion and the lateral growth portion in the vicinity thereof will be described. Regarding the electrical characteristics of the nickel-added portion, the electrical conductivity is almost the same as that of a film to which almost no nickel is added, that is, a film that has been crystallized at about 600 ° C. for several tens of hours. When the activation energy was determined from the properties, the amount of nickel added was 10 as described above.¹⁷atoms / cm³-10¹⁸atoms / cm³When the degree was set to about the degree, no behavior that might be caused by the nickel level was observed. That is, it is considered from this experimental fact that the above-mentioned concentration can be used as an active layer of a TFT or the like.
[0027]
On the other hand, the laterally-grown portion has a conductivity that is at least one order of magnitude higher than that of the nickel-added portion, and has a considerably high value as a crystalline silicon semiconductor. 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 few or almost no grain boundaries existed during the passage of electrons between the electrodes. Consistent with the results. In other words, it can be considered that the carrier moves along the grain boundaries of the crystals grown in the shape of needles or columns, so that the carrier can easily move.
[0028]
Therefore, the present invention improves the carrier mobility by making the direction substantially along the crystal grain boundaries substantially the same as the direction in which carriers move in a semiconductor device (for example, a TFT). The direction along the crystal grain boundaries is the growth direction of crystal growth in the shape of needles or columns, and this growth direction isPerpendicular to the [111] direction and[-110]Equivalent to directionIs a direction having crystallinity in the axial direction, and this direction is a direction having selectively high conductivity with respect to another direction (for example, a direction perpendicular to crystal growth) as described above. Further, as a practical problem, it is difficult for the crystal growth direction to completely match the carrier flowing direction, and the crystal does not completely grow in a uniform direction over the entire surface. Therefore, as a practical matter, the direction of crystal growth is determined as an average direction. In addition, it can be considered that the direction coincides with the direction in which the carrier flows within a range of about ± 20 °.
[0029]
The crystalline silicon film on the substrate used in the present invention is made of single-crystal silicon.FlowerIs important. That is, it is a crystalline silicon film crystallized into a thin film, and its crystal growth direction isPerpendicular to the [111] direction and[-110]Equivalent to directionAnd is essentially different from single crystal silicon. Therefore, in particular, the crystalline silicon film in the present invention can be called a non-single-crystal silicon film having crystallinity.
[0030]
Finally, a method of applying the present invention to a TFT based on the above various characteristics will be described. Here, as an application field of the TFT, an active matrix liquid crystal display device using the TFT for driving pixels is assumed.
[0031]
As described above, in recent large-screen active matrix type liquid crystal display devices, it is important to suppress shrinkage of the glass substrate. Therefore, crystallization can be performed at a sufficiently low temperature, which is particularly preferable. According to the present invention, it is easy to replace a portion where amorphous silicon is conventionally used with crystalline silicon by adding a trace amount of nickel and crystallizing the same at about 500 to 550 ° C. for about 4 hours. It is possible. Of course, it is necessary to change the design rules and the like accordingly. However, it is considered that the conventional apparatus and process can sufficiently cope with this, and the merits thereof are considered to be great.
[0032]
In addition, according to the present invention, it is possible to separately form a TFT used for a pixel and a TFT forming a driver of a peripheral circuit by using a crystal form according to characteristics, respectively. There are many merits especially for application to A TFT used for a pixel does not require much mobility, and a smaller off-state current is more advantageous. Therefore, when the present invention is used, a small amount of nickel is directly added to a region to be a TFT to be used for a pixel to grow a crystal in a vertical direction, thereby forming a large number of grain boundaries in a channel direction to reduce an off-current. It is possible to lower. On the other hand, the TFT forming the driver of the peripheral circuit needs very high mobility in consideration of application to a workstation in the future. Therefore, when the present invention is applied, a small amount of nickel is added in the vicinity of the TFT forming the driver of the peripheral circuit, a crystal is grown in one direction from the addition, and the crystal growth direction is set to the path direction of the channel current. With the arrangement, a TFT having extremely high mobility can be manufactured.
[0033]
In this manner, a crystalline silicon film can be obtained by selectively performing crystallization in a specific direction. However, if the characteristics of such a crystalline silicon film are to be further improved, a crystallization process can be performed. After that, a laser or a strong light equivalent thereto may be irradiated to crystallize the insufficiently crystallized components remaining at the grain boundaries and the like. In this step, the remaining amorphous component grows with the crystal formed in the previous heating step as a nucleus, and the grain boundaries disappear, so that higher characteristics can be obtained.
[0034]
[Action]
In a semiconductor device using a thin-film semiconductor, the movement of carriers along the crystal grain boundaries is performed by setting the crystal growth direction of a crystalline silicon film that has grown in a needle or column shape in the plane direction of the film as the carrier movement direction. Direction and the carrier can be moved with high mobility.
[0035]
【Example】
[Example 1]
This embodiment is an example of forming a circuit in which a P-channel TFT (referred to as PTFT) using crystalline silicon and an N-channel TFT (referred to as NTFT) using crystalline silicon are combined in a complementary manner on a glass substrate. The configuration of this embodiment can be used for a switching element of a pixel electrode and a peripheral driver circuit of an active type liquid crystal display device, as well as an image sensor and an integrated circuit.
[0036]
FIG. 1 shows a cross-sectional view of a manufacturing process of this embodiment. First, a 2000-nm-thick silicon oxide base film 102 was formed on a substrate (Corning 7059) 101 by a sputtering method. Next, a mask 103 formed of a metal mask, a silicon oxide film, or the like is provided. The mask 103 exposes the base film 102 in a slit shape. When this state is viewed from above, the base film 102 is exposed in a slit shape, and the other portions are masked.
[0037]
After providing the mask 103, a nickel silicide film (chemical formula NiSi) having a thickness of 5 to 200 °, for example, 20 °, is formed by a sputtering method._x, 0.4 ≦ x ≦ 2.5, for example, x = 2.0) is selectively formed in 100 regions. (Fig. 1 (A))
[0038]
Next, an intrinsic (I-type) amorphous silicon film 104 having a thickness of 500 to 1500 Å, for example, 1000 例 え ば is formed by a plasma CVD method. Then, this is annealed at 550 ° C. in a hydrogen reducing atmosphere (preferably, a partial pressure of hydrogen is 0.1 to 1 atm) or at 550 ° C. in an inert atmosphere (atmospheric pressure) for 4 hours to crystallize. . At this time, in the region 100 where the nickel silicide film is selectively formed, crystallization of the crystalline silicon film 104 occurs in a direction perpendicular to the substrate 101. Then, in a region other than the region 100, as indicated by an arrow 105, crystal growth is performed in a lateral direction (a direction parallel to the substrate) from the region 100.
[0039]
As a result of the above steps, the crystalline silicon film 104 can be obtained by crystallizing the amorphous silicon film. Thereafter, a silicon oxide film 106 having a thickness of 1000 ° is 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. I do. Subsequently, aluminum (including 0.1 to 2% of silicon) having a thickness of 6000 to 8000, for example, 6000, is formed by a sputtering method. Note that it is preferable that the step of forming the silicon oxide film 106 and the aluminum film be performed continuously.
[0040]
Then, the silicon film 104 is patterned to form gate electrodes 107 and 109. Further, the surface of the aluminum electrode is anodized to form oxide layers 108 and 110 on the surface. This anodization was performed in an ethylene glycol solution containing tartaric acid at 1 to 5%. The thickness of the obtained oxide layers 108 and 110 was 2000 °. Since the oxides 108 and 110 have a thickness for forming an offset gate region in a later ion doping step, the length of the offset gate region can be determined in the anodic oxidation step.
[0041]
Next, an impurity imparting one conductivity type is added to the active layer region (which constitutes a source / drain and a channel) by an ion doping method. In this doping step, impurities (phosphorus and boron) are implanted using the gate electrode 107 and the surrounding oxide layer 108 and the gate electrode 109 and the surrounding oxide layer 110 as masks. Phosphine (PH) as doping gas₃) And diborane (B₂H₆), The acceleration voltage is 60 to 90 kV, for example, 80 kV in the former case, and 40 to 80 kV, for example, 65 kV in the latter case. Dose amount is 1 × 10^Fifteen~ 8 × 10^Fifteencm^-2, For example, 2 × 10^Fifteencm^-2, Boron 5 × 10^FifteenAnd At the time of doping, each element is selectively doped by covering one region with a photoresist. As a result, N-type impurity regions 114 and 116 and P-type impurity regions 111 and 113 are formed, so that a P-channel TFT (PTFT) region and an N-channel TFT (NTFT) region can be formed. .
[0042]
Thereafter, annealing is performed by laser light irradiation. As the laser light, a KrF excimer laser (wavelength: 248 nm, pulse width: 20 nsec) was used, but another laser may be used. The irradiation condition of the laser light is such that the energy density is 200 to 400 mJ / cm², For example, 250 mJ / cm²Then, 2 to 10 shots, for example, 2 shots are irradiated at one place. 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 is diffused in the previously crystallized region, re-crystallization easily proceeds by this laser light irradiation, and impurities doped with an impurity imparting a P-type are doped. Regions 111 and 113, and impurity regions 114 and 116 doped with an impurity imparting N can be easily activated.
[0043]
Subsequently, a silicon oxide film 118 having a thickness of 6000 ° is formed as an interlayer insulator by a plasma CVD method, a contact hole is formed in the silicon oxide film 118, and a metal material, for example, a multilayer film of titanium nitride and aluminum is used to form a TFT electrode / wiring. 117, 120 and 119 are formed. Finally, annealing was performed at 350 ° C. for 30 minutes in a hydrogen atmosphere at 1 atm to complete a semiconductor circuit having a complementary TFT. (Fig. 1 (D))
[0044]
The circuit shown above has a CMOS structure in which a PTFT and an NTFT are provided in a complementary manner. However, in the above process, two independent TFTs are formed at the same time, and two independent TFTs are simultaneously formed by cutting at the center. Is also possible.
[0045]
FIG. 2 shows an outline of FIG. 1D viewed from above. The reference numerals in FIG. 2 correspond to those in FIG. As shown in FIG. 2, the direction of crystallization is the direction indicated by the arrow, and the crystal is grown in the direction of the source / drain region (the line direction connecting the source region and the drain region). During the operation of the TFT having this configuration, carriers move between the source and the drain along a crystal grown in a needle or column shape. That is, the carriers move along the crystal grain boundaries of needle-like or columnar crystals. Therefore, the resistance received when carriers move can be reduced, and a TFT having high mobility can be obtained.
[0046]
In this embodiment, as a method for introducing Ni, Ni is selectively formed on the base film 102 under the amorphous silicon film 104 as a thin film (it is difficult to observe the film because it is extremely thin). Although a method of performing crystal growth from this portion is adopted, a method of selectively forming a nickel silicide film after forming the amorphous silicon film 104 may be used. That is, crystal growth may be performed from the upper surface of the amorphous silicon film or from the lower surface. Alternatively, a method 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 may be employed. This case has a feature that the concentration of the nickel element can be controlled.
[0047]
[Example 2]
This embodiment is an example in which an N-channel TFT is provided in each pixel as a switching element in an active liquid crystal display device. In the following, one pixel will be described, but a large number (generally several hundred thousand) of other pixels are formed in a similar structure. It goes without saying that a P-channel type may be used instead of an N-channel type. Further, it can be used not only for the pixel portion of the liquid crystal display device but also for a peripheral circuit portion. Further, it can be used for image sensors and other devices. That is, the application is not particularly limited as long as it is used as a thin film transistor.
[0048]
FIG. 3 schematically shows a manufacturing process of this embodiment. In this example, a Corning 7059 glass substrate (1.1 mm thick, 300 × 400 mm) was used as the substrate 201. First, a base film 203 (silicon oxide) is formed to a thickness of 2000 ° by a sputtering method. Thereafter, in order to selectively introduce nickel, a mask 203 is formed using a metal mask, a silicon oxide film, a photoresist, or the like. Then, a nickel silicide film is formed by a sputtering method. The nickel silicide film is formed to a thickness of 5 to 200 °, for example, 20 ° by a sputtering method. This nickel silicide film has the chemical formula NiSi_x, 0.4 ≦ x ≦ 2.5, for example, x = 2.0. Thus, a nickel silicide film is selectively formed in the region 204.
[0049]
Thereafter, an amorphous silicon film 205 is formed to a thickness of 1000 ° by LPCVD or plasma CVD, dehydrogenated at 400 ° C. for 1 hour, and then crystallized by heat annealing. This annealing step was performed at 550 ° C. for 4 hours in a hydrogen reducing atmosphere (preferably, the partial pressure of hydrogen was 0.1 to 1 atm). This heat annealing step may be performed in an inert atmosphere such as nitrogen.
[0050]
In this annealing step, since a nickel silicide film is formed in a part of the region under the amorphous silicon film 205, crystallization occurs from this part. At the time of this crystallization, as shown by the arrow in FIG. 3B, in the portion 204 where the nickel silicide is formed, crystal growth of silicon proceeds in a direction perpendicular to the substrate 201. Similarly, as indicated by arrows, in regions where nickel silicide is not formed (regions other than region 205), crystal growth is performed in a direction parallel to the substrate.
[0051]
Thus, a semiconductor film 205 made of crystalline silicon can be obtained. Next, the semiconductor film 205 is patterned to form an island-shaped semiconductor region (TFT active layer). Further, a gate insulating film (thickness: 70 to 120 nm, typically 100 nm) 206 of silicon oxide is formed by a plasma CVD method in an oxygen atmosphere using tetraethoxysilane (TEOS) as a raw material. The substrate temperature is set to 400 ° C. or lower, preferably 200 to 350 ° C. in order to prevent shrinkage and warpage of the glass.
[0052]
Next, a gate electrode 207 is formed by forming a known film containing silicon as a main component by a CVD method and performing patterning. After that, phosphorus is implanted as an N-type impurity by an ion doping method, and the source region 208, the channel formation region 209, and the drain region 210 are formed in a self-aligned manner. By irradiating a KrF laser beam, the crystallinity of the silicon film having deteriorated crystallinity due to ion doping is improved. At this time, the energy density of the laser beam is 250 to 300 mJ / cm.²And By this laser irradiation, the sheet resistance of the source / drain of this TFT is 300 to 800 Ω / cm.²It becomes.
[0053]
After that, an interlayer insulator 211 is formed using silicon oxide, and a pixel electrode 212 is formed using ITO. Then, a contact hole is formed, and electrodes 213 and 214 are formed of a chromium / aluminum multilayer film in the source / drain region of the TFT. One of the electrodes 213 is also connected to the ITO 121. Finally, annealing in hydrogen at 200 to 300 ° C. for 2 hours completes the hydrogenation of silicon. Thus, the TFT is completed. This process is performed simultaneously in many other pixel regions.
[0054]
In the TFT manufactured in this embodiment, a crystalline silicon film grown in the direction in which carriers flow is used as an active layer constituting a source region, a channel formation region, and a drain region. Since the carriers do not cross, that is, the carriers move along the crystal grain boundaries of the needle-like or columnar crystals, a TFT having a high carrier mobility can be obtained. The TFT manufactured in this embodiment is of an N-channel type, and has a mobility of 90 to 130 (cm).²/ Vs). A conventional N-channel TFT using a crystalline silicon film obtained by crystallization by thermal annealing at 600 ° C. for 48 hours moves from 80 to 100 (cm).²/ Vs), which is a significant improvement in properties.
[0055]
In addition, a P-channel TFT is manufactured by the same manufacturing method as the above process, and its mobility is measured.²/ Vs). This also moves to 30 to 60 (cm) in the conventional P-channel TFT using a crystalline silicon film obtained by crystallization by thermal annealing at 600 ° C. for 48 hours.²/ Vs), which is a significant improvement in characteristics.
[0056]
[Example 3]
This embodiment is an example in which the source / drain is provided in a direction substantially perpendicular to the crystal growth direction in the TFT shown in the second embodiment. That is, in this example, the moving direction is perpendicular to the crystal growth direction, and the carrier moves so as to cross the crystal grain boundaries of acicular or columnar crystals. With such a configuration, the resistance between the source and the drain can be increased. This is because carriers have to move across the crystal grain boundaries of crystals grown in a needle or column shape. In order to realize the configuration of the present embodiment, in the configuration of the second embodiment, it is only necessary to set the direction in which the TFT is provided.
[0057]
[Example 4]
In the present embodiment, in the configuration shown in the second embodiment, the direction in which the TFT is provided (here, defined by the line connecting the source / drain regions; that is, the direction of the TFT is determined by the direction in which carriers flow) is crystalline. The gist is to select the characteristics of the TFT by setting the silicon film at an arbitrary angle with respect to the crystal growth direction with respect to the substrate surface.
[0058]
As described above, when carriers move in the crystal growth direction, the carriers move along the crystal grain boundaries, so that the mobility can be improved. On the other hand, when moving carriers in a direction perpendicular to the crystal growth direction, the carriers have to cross many grain boundaries, so that the carrier mobility decreases.
[0059]
Therefore, by setting the angle between the two states, that is, the angle between the crystal growth direction and the direction in which the carrier moves, in the range of 0 to 90 °, the mobility of the carrier can be controlled. From another viewpoint, the resistance between the source / drain regions can be controlled by setting the angle between the crystal growth direction and the direction in which carriers move. Of course, this configuration can also be used for the configuration shown in the first embodiment. In this case, the slit-shaped nickel trace addition region 100 shown in FIG. 2 rotates in the range of 0 to 90 °, and the angle between the crystal growth direction indicated by the arrow 105 and the line connecting the source / drain regions is 0 to 90 °. ° range. When the angle is close to 0 °, the mobility is large and the electrical resistance between the source and the drain is small. When this angle is close to 90 °, a structure with high mobility and low resistance between source / drain can be obtained.
[0060]
Embodiment 5 FIG. 5 shows this embodiment. After a silicon oxide film 302 having a thickness of 1000 to 5000 Å, for example, 2000 Å was formed on a glass substrate 301, an amorphous silicon film 303 having a thickness of 300 to 1500 Å, for example, 500 Å was formed by a plasma CVD method. Further, a silicon oxide film 304 of 500 to 1500 °, for example, 500 ° was formed thereon. It is desirable that these films be formed continuously. Then, the silicon oxide film 304 was selectively etched to open a window 305 for introducing nickel. The window 305 is formed so as to avoid a portion to be a channel of the TFT. Then, a nickel salt film 307 was formed by a spin coating method. Describing 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.
[0061]
On the other hand, the substrate was immersed in a hydrogen peroxide solution or a mixed solution of a 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 305). This is for improving the interface affinity between the nickel solution prepared as described above and the amorphous silicon film.
[0062]
The substrate thus treated was placed on a spinner, gently rotated, 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 rotation speed of the substrate. This operation may be repeated a plurality of times. Thus, a thin film 307 of nickel salt was formed. (FIG. 9A)
[0063]
Then, silicon ions were implanted by an ion implantation method. At this time, except for the window 305, that is, in a region covered with the silicon oxide film 304, the largest amount of silicon ions is implanted into the interface between the underlying silicon oxide film 302 and the amorphous silicon film 303. It was done as follows. At this time, in the region of the window 305, since the silicon oxide film 304 does not exist, silicon ions are implanted deeper.
[0064]
Thereafter, in a heating furnace, heat treatment was performed 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 into a region immediately below the window 305, and crystallization started from this region. Then, the crystallization region extended around the periphery as shown by an arrow 308. (FIG. 9 (B))
[0065]
Thereafter, in the air or oxygen atmosphere, KrF excimer laser light (wavelength 248 nm) or XeCl excimer laser light (wavelength 308 nm) was irradiated with 1 to 20 shots, for example, 5 shots to further improve the crystallinity. Energy density is 200-350mJ / cm²The substrate temperature was 200 to 400 ° C. (FIG. 9 (C))
[0066]
Thereafter, the silicon film 303 was etched to form a TFT region. Then, a silicon oxide film 309 having a thickness of 1000 to 1500 Å, for example, 1200 に is formed on the entire surface. Gate electrode portions were formed by the oxide films 312 and 314.
[0067]
Then, using these gate electrode portions as masks, N-type and P-type impurities were implanted into the silicon film by an ion doping method as in Example 1. As a result, a source 315, a channel 316, and a drain 317 of the PTFT, and a source 320, a channel 319, and a drain 318 of the NTFT of the peripheral circuit 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. 9 (D))
[0068]
After that, a silicon oxide film 321 having a thickness of 3000 to 8000 Å, for example, 5000 と し て is formed as an interlayer insulator. Thereafter, contact holes are formed in the source / drain of the TFT, and a two-layer film of titanium nitride (thickness 1000) and aluminum (thickness 5000) is deposited by a sputtering method, and is patterned and etched. Thus, electrodes / wirings 322 to 324 were formed. In this way, an inverter circuit composed of PTFT and NTFT could be formed from crystalline silicon grown in the lateral direction. (FIG. 9E)
[0069]
In this embodiment, as in the first embodiment, the crystallization direction 508 is the same as the direction in which the carriers of the TFT flow (that is, the source-drain direction). Therefore, also in this embodiment, the drain current of the TFT increases, which is convenient for high-speed operation. In addition, 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 the crystallization is performed with the needle crystal as a nucleus so as to make the needle crystal thicker. This expands the region through which current flows, and allows a larger drain current to flow.
[0070]
This is shown in FIG. FIG. 10 shows the result of thinning the crystallized silicon film and observing it with a transmission electron microscope (TEM). FIG. 10A shows the vicinity of the tip of the crystallized region of the silicon film crystallized by the 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. 10A)
[0071]
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 in FIG. 10A is crystallized, but since this crystallization occurs randomly, electric characteristics are not so good. Noteworthy is the crystalline state of the region between the needle-like crystals observed near the center, which seems to be originally amorphous. Here, a thick crystal region is formed so as to grow from a needle crystal. (FIG. 10 (B))
[0072]
FIG. 10 shows the crystal growth tip region having a relatively large number of amorphous regions for simplicity, but the same applies to the vicinity of the root or center of the crystal growth. As described above, by laser irradiation, the amorphous portion can be reduced and the needle crystal can be made thicker, and the characteristics of the TFT can be further improved.
[0073]
【The invention's effect】
When a non-single-crystal silicon semiconductor film having crystallinity provided on a substrate and grown in a direction parallel to the surface of the substrate and having crystallinity is used for the TFT, crystal growth is performed in the direction of the flow of carriers moving in the TFT. By adjusting the direction, the carrier can move along (in parallel with) the crystal grain boundary of the crystal grown in a needle or column shape, and a TFT having high mobility can be obtained. .
[Brief description of the drawings]
FIG. 1 shows a manufacturing process of an example.
FIG. 2 shows an outline of an embodiment.
FIG. 3 shows an outline of an embodiment.
FIG. 4 shows an electron diffraction image.
FIG. 5 is a photograph showing a crystal structure of a silicon film.
FIG. 6 shows an electron diffraction image.
FIG. 7 shows an electron beam diffraction image.
FIG. 8 is a schematic diagram showing a crystal orientation.
FIG. 9 shows a manufacturing process of an example.
FIG. 10 shows a crystal structure of an example.
[Explanation of symbols]
101 glass substrate
102 Underlayer (silicon oxide film)
103 mask
104 silicon film
105 Direction of crystallization
106 Gate insulating film
107 Gate electrode
108 Anodized layer
109 Gate electrode
110 Anodized layer
111 source / drain region
112 Channel formation area
113 Drain / source region
114 Source / drain region
115 Channel formation area
116 Drain / source region
117 electrodes
118 Interlayer insulator
120 electrodes
119 electrodes
201 glass substrate
202 Base film (silicon oxide film)
203 mask
204 Nickel trace addition area
205 silicon film
206 Gate insulating film
207 Gate electrode
208 Source / drain regions
209 Channel formation area
210 Drain / source region
211 Interlayer insulator
213 electrode
214 electrodes
212 ITO (pixel electrode)

Claims (13)

A semiconductor device using a crystalline silicon semiconductor film provided on a substrate,
The silicon semiconductor film is crystal-grown in a direction parallel to the substrate surface from a region to which nickel is added ,
The plane of the crystal in the silicon semiconductor film parallel to the substrate surface is a (111) plane,
Growth direction of the crystal, [111] to have a 6-fold symmetry with respect to the direction is vertical and [-110] direction equivalent to the direction [111] direction,
Wherein a carrier in the growth direction and the semiconductor device of the crystal and the direction of movement is consistent with the range of ± 20 °. A semiconductor device using a crystalline silicon semiconductor film provided on a substrate,
The silicon semiconductor film has a crystal grain boundary along a direction parallel to the substrate surface from a region to which nickel is added ,
The plane of the crystal in the silicon semiconductor film parallel to the substrate surface is a (111) plane,
Growth direction of the crystal, [111] to have a 6-fold symmetry with respect to the direction is vertical and [-110] direction equivalent to the direction [111] direction,
A semiconductor device, wherein a direction along the crystal grain boundary and a direction in which carriers move in the semiconductor device coincide within a range of ± 20 °. A semiconductor device using a crystalline silicon semiconductor film provided on a substrate,
The silicon semiconductor film is crystal-grown in a direction parallel to the substrate surface from a region to which nickel is added ,
The plane of the crystal in the silicon semiconductor film parallel to the substrate surface is a (111) plane,
Growth direction of the crystal, [111] to have a 6-fold symmetry with respect to the direction is vertical and [-110] direction equivalent to the direction [111] direction,
The growth direction of the crystal has high conductivity with respect to other directions,
Wherein a carrier in the growth direction and the semiconductor device of the crystal and the direction of movement is consistent with the range of ± 20 °. A semiconductor device including a thin film transistor using a crystalline silicon semiconductor film provided over a substrate,
The silicon semiconductor film is crystal-grown in a direction parallel to the substrate surface from a region to which nickel is added ,
The plane of the crystal in the silicon semiconductor film parallel to the substrate surface is a (111) plane,
Growth direction of the crystal, [111] to have a 6-fold symmetry with respect to the direction is vertical and [-110] direction equivalent to the direction [111] direction,
The semiconductor device characterized by the direction of movement of the carriers in the channel of the growth direction and the thin film Toranjita of the crystal is consistent with the range of ± 20 °. A semiconductor device including a thin film transistor using a crystalline silicon semiconductor film provided over a substrate,
The silicon semiconductor film has a source region, a drain region, and a channel formation region,
The silicon semiconductor film is crystal-grown from a region to which nickel is added,
The crystal growth direction in the channel formation region is a direction perpendicular to the [111] direction and equivalent to the [−110] direction;
A semiconductor device, wherein the growth direction and the direction in which carriers move in the channel formation region coincide with each other within a range of ± 20 °. A semiconductor device including a thin film transistor using a crystalline silicon semiconductor film provided over a substrate,
The silicon semiconductor film has a source region, a drain region, and a channel formation region,
The silicon semiconductor film is crystal-grown from a region to which nickel is added,
The crystal growth direction in the channel formation region is a direction perpendicular to the [111] direction and equivalent to the [−110] direction;
The direction of movement of the carriers in the channel forming region and the growth direction of the crystals was consistent with the range of ± 20 °,
The semiconductor device, wherein the silicon semiconductor film has a needle-like or columnar crystal in the channel formation region. A semiconductor device including a thin film transistor using a crystalline silicon semiconductor film provided over a substrate,
The silicon semiconductor film has a source region, a drain region, and a channel formation region,
The silicon semiconductor film is crystal-grown from a region to which nickel is added,
The crystal growth direction in the channel formation region is a direction perpendicular to the [111] direction and equivalent to the [−110] direction;
The direction in which the crystal grows and the direction in which carriers move in the channel formation region match within a range of ± 20 °,
The semiconductor device, wherein the silicon semiconductor film is laser-crystallized after a crystallization step by heating. Forming an amorphous silicon film on a substrate having an insulating surface,
Adding nickel to a part of the amorphous silicon film,
Heating the amorphous silicon film to form crystal grains in the amorphous silicon film in a region to which the nickel is added, and grow the crystal in a direction parallel to the substrate surface with the crystal grains as nuclei; A method for manufacturing a semiconductor device for forming a conductive silicon film, comprising:
A plane parallel to the substrate surface of the crystal in the crystalline silicon film is a (111) plane,
The crystal growth direction is a direction perpendicular to the [111] direction and equivalent to the [-110] direction,
A method for manufacturing a semiconductor device, comprising: matching a growth direction of the crystal with a moving direction of carriers in the semiconductor device. Forming an amorphous silicon film on a substrate having an insulating surface,
Adding nickel to a part of the amorphous silicon film,
Heating the amorphous silicon film to form crystal grains in the amorphous silicon film in a region to which the nickel is added, and grow the crystal in a direction parallel to the substrate surface with the crystal grains as nuclei; Forming a conductive silicon film,
A method for manufacturing a semiconductor device in which the crystalline silicon film is irradiated with a laser beam,
A plane parallel to the substrate surface of the crystal in the crystalline silicon film is a (111) plane,
The crystal growth direction is a direction perpendicular to the [111] direction and equivalent to the [-110] direction,
A method for manufacturing a semiconductor device, comprising: matching a growth direction of the crystal with a moving direction of carriers in the semiconductor device. 10. The method for manufacturing a semiconductor device according to claim 8, wherein a slit-shaped mask is formed on the amorphous silicon film, and the nickel is added. 11. The method for manufacturing a semiconductor device according to claim 8, wherein the concentration of the nickel is 1 × 10 ¹⁵ atoms / cm ³ to 1 × 10 ¹⁹ atoms / cm ³ . The method for manufacturing a semiconductor device according to claim 8, wherein a temperature of the heating is 500 to 550 ° C. 13. 13. The method for manufacturing a semiconductor device according to claim 8, wherein the crystal has a needle shape or a column shape.

Images