JP3727387B2 - Method for manufacturing crystalline silicon film, device, liquid crystal display device, thin film transistor, and electronic apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The invention disclosed in this specification relates to a method for manufacturing a crystalline silicon semiconductor thin film formed over a substrate having an insulating surface such as a glass substrate.
[0002]
[Prior art]
In recent years, a technique for forming a thin film transistor using a silicon thin film formed on a glass substrate has attracted attention. This thin film transistor is mainly used in an active matrix type liquid crystal electro-optical device and other thin film integrated circuits. In the liquid crystal electro-optical device, liquid crystal is sealed between a pair of glass substrates, and an electric field is applied to the liquid crystal to change the optical characteristics of the liquid crystal and display an image.
[0003]
In particular, an active matrix liquid crystal display device using a thin film transistor is characterized in that a thin film transistor is provided as a switch in each pixel to control charges held in the pixel electrode. An active matrix liquid crystal display device can display a minute image at high speed, and is therefore used for a display of various electronic devices (for example, a portable word processor or a portable computer).
As a thin film transistor used for an active matrix type liquid crystal display device, a thin film transistor using an amorphous silicon thin film (amorphous silicon thin film) is generally used.
[0004]
[Problems to be solved by the invention]
However, in a thin film transistor using an amorphous silicon thin film,
(1) The characteristics are low, and higher quality image display cannot be performed.
(2) A peripheral circuit for driving a thin film transistor arranged in a pixel cannot be configured.
There is a problem.
[0005]
The above problem (2) is that a thin film transistor using an amorphous silicon thin film cannot make a P-channel type thin film transistor practical, so that a CMOS circuit cannot be constructed, and a thin film transistor using an amorphous silicon thin film has a high speed. This can be divided into the problem that the peripheral drive circuit cannot be configured because the operation cannot be performed and a large current cannot flow.
[0006]
As a method for solving these problems, a technique of forming a thin film transistor using a crystalline silicon thin film can be mentioned. Examples of a method for obtaining a crystalline silicon thin film include a method in which heat treatment is performed on an amorphous silicon film and a method in which laser light is irradiated on an amorphous silicon film.
[0007]
The method for crystallizing an amorphous silicon film by heat treatment generally has the following problems. Usually, in order to construct a thin film transistor used for a liquid crystal electro-optical device, it is required to form it on a light-transmitting substrate. Examples of the light-transmitting substrate include a quartz substrate and a glass substrate. However, the quartz substrate is expensive and cannot be used for a liquid crystal electro-optical device in which cost reduction is a major technical problem. Therefore, a glass substrate is generally used, but the glass substrate has a problem that its heat-resistant temperature is low.
[0008]
In general, a Corning 7059 glass substrate is used as a glass substrate used in a liquid crystal electro-optical device. The strain point of this glass substrate is 593 ° C., and when heat treatment is applied at a temperature higher than this temperature, the substrate shrinks or deforms significantly. In recent years, liquid crystal electro-optical devices tend to have a large area, and shrinkage and deformation of the substrate must be suppressed as much as possible.
[0009]
On the other hand, it has been experimentally found that a temperature of 600 ° C. or higher is required to crystallize the amorphous silicon film by heating, and it has been found that the heating time also requires several tens of hours. are doing. Such high-temperature and long-time heating cannot be performed on a large-area glass substrate.
[0010]
A technique for crystallizing an amorphous silicon film by laser light irradiation is also known. However, it is difficult as a real problem to irradiate laser light uniformly over a large area or to irradiate with maintaining a constant irradiation power.
[0011]
An object of the invention disclosed in this specification is to provide a method for manufacturing a semiconductor thin film in which an amorphous silicon film is transformed into a crystalline silicon film by a treatment by heating at a low temperature as much as possible. In particular, it is an object to provide a method for manufacturing a crystalline semiconductor thin film capable of forming a thin film transistor having high performance characteristics.
[0012]
[Means for Solving the Problems]
In order to eliminate the above-described problems, a method for producing a semiconductor thin film according to the present invention includes:
Introducing a metal element into the amorphous silicon film;
Crystallization of the amorphous silicon film to obtain a crystalline silicon film;
Forming a film for diffusing the metal element on the crystalline silicon film;
Diffusing the metal element in a film for diffusing the metal element;
Removing the film in which the metal element is diffused;
It is characterized by having.
[0013]
In the above structure, the amorphous silicon film to be crystallized includes a film formed by a plasma CVD method or a low pressure thermal CVD method on a glass substrate or a glass substrate on which an insulating film is formed.
[0014]
Examples of the metal element include one or more elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au. These metal elements have a catalytic action to promote crystallization of silicon, and nickel (Ni) is particularly effective among these metal elements.
[0015]
Examples of the method for introducing the metal element include a method of forming a layer of these metals or a layer containing a metal on the surface of the amorphous silicon film. Specifically, a method of forming a layer of a metal element or a layer containing a metal element by a CVD method, a sputtering method, or a vapor deposition method, or a method of applying a solution containing a metal element on an amorphous silicon film Can be mentioned.
When CVD, sputtering, or vapor deposition is used, it is difficult to form a very thin uniform film, so metal elements are present non-uniformly on the amorphous silicon film. As a result, there is a problem that metal elements tend to be unevenly distributed during crystal growth.
On the other hand, a method using a solution is very preferable because the concentration of the metal element can be easily controlled and the metal element can be uniformly held in contact with the surface of the amorphous silicon film.
[0016]
In order to crystallize an amorphous silicon film into which a metal element for promoting crystallization of silicon is introduced, heating may be performed at a temperature of 450 ° C. or higher. The upper limit of this heating temperature is limited by the heat resistant temperature of the glass substrate used as the substrate. In the case of a glass substrate, this heat-resistant temperature can be considered as a strain point of glass. As an example of the heat treatment, a temperature of about 550 ° C. is appropriate from the viewpoint of heat resistance and productivity of the glass substrate.
When a material that can withstand a temperature of 1000 ° C. or higher, such as a quartz substrate, is used as the substrate, the heating temperature in this heating can be increased according to the heat resistant temperature. In addition, the higher the heating temperature, the more excellent the crystallinity can be obtained.
[0017]
In the above structure, examples of the film for diffusing the metal element include an amorphous silicon film formed by a general CVD method. For example, an amorphous silicon film obtained by the same film formation method as an amorphous silicon film that is a starting film of a crystalline silicon film crystallized by heating can be used.
However, more preferably, the film quality is high so that the defect density is high and the metal element can be easily trapped. This is because the metal element in the crystalline silicon film can be more easily diffused into the silicon film.
In order to obtain an amorphous silicon film having a high defect density, means such as forming a film only with silane without using hydrogen in the plasma CVD method, using a sputtering method, and lowering the film forming temperature in the plasma CVD method are adopted. It can be realized by doing.
[0018]
It is effective to make the amorphous silicon film thicker than the crystalline silicon film. This is because the thicker the amorphous silicon film, the larger the volume ratio with respect to the crystalline silicon film, and the more metal elements can be diffused into the amorphous silicon film. .
[0019]
Further, as a film for diffusing the metal element, a polycrystalline silicon film, an amorphous Si film _X Ge _1-X A membrane (0 <x <1) can also be used. In order to obtain a polycrystalline silicon film, a low pressure CVD method may be employed. In addition, amorphous Si _X Ge _1-X In order to obtain silane (SiH _Four ) And germane (GeH) _Four ) And may be formed by a plasma CVD method.
[0020]
The step of diffusing (absorbing) the metal element into the crystalline silicon film is performed by heat treatment. With heating, the metal element in the crystallized silicon film diffuses into the film that diffuses the metal element, so that the concentration of the metal element in the crystallized silicon film can be lowered.
[0021]
Next, the film in which the metal element is diffused is removed. At this time, if an oxide film is formed in advance on the amorphous silicon film to be crystallized, it can function as an etching stopper, and only the film in which the metal element is diffused can be selectively etched. it can.
[0022]
The configuration of the present invention will be described as a specific example with reference to FIG.
A crystalline silicon film 105 is formed on the glass substrate 101 using nickel which is a metal element that promotes crystallization of silicon. The crystallization method uses heat treatment. Note that a silicon oxide film 102 is formed on the surface of the glass substrate 101 as a base film. (Fig. 1 (B))
[0023]
Next, as shown in FIG. 1C, an oxide film 106 is formed, and an amorphous silicon film 107 is formed as a film for diffusing a metal element, and heat treatment is performed.
This heat treatment is performed at a temperature at which the amorphous silicon film does not crystallize (generally 450 ° C. or lower) and at a temperature at which the amorphous silicon film crystallizes (generally 450 ° C. or higher, preferably 500 ° C. The method can be divided into the above.
[0024]
When heat treatment is performed at a temperature at which crystallization of the amorphous silicon film 107 provided on the crystalline silicon film 105 does not occur, the temperature of the heat treatment is set to 400 to 450 ° C., and the heating time is 5 minutes to What is necessary is just about 10 hours. As a result, the metal element in the crystalline silicon film 105 is gradually diffused (absorbed) into the amorphous silicon film 107. Therefore, when the heat treatment is performed for a long time, the concentration of the metal element in the crystalline silicon film 105 can be gradually reduced.
Then, by removing the amorphous silicon film 107 using the oxide film 106 as an etching stopper, the concentration of the metal element in the crystalline silicon film 105 is compared with the concentration of the metal element in the amorphous silicon film 107. A small crystalline silicon film 108 can be obtained. (Fig. 1 (D)
[0025]
This effect is due to the presence of silicon atoms in the amorphous silicon film 107 in a state of being easily bonded to the metal element (a large amount of unpaired bonds are present in the amorphous state). Further, this effect can be obtained more remarkably when the defect density in the amorphous silicon film 107 is artificially increased.
[0026]
On the other hand, when heat treatment is performed at a temperature at which crystallization of the amorphous silicon film 107 provided on the crystalline silicon film 105 proceeds, diffusion of the metal element occurs when the amorphous silicon film 107 is crystallized. Seems to stop. In addition, when the metal element concentration in the crystalline silicon film 105 and the average value of the metal element concentration in the silicon film 107 (which is crystallized in the heat treatment) for absorbing the metal element are approximately the same. Thus, the diffusion of the metal element apparently stops.
[0027]
However, in the crystalline silicon film 105, it has been found that metal elements are locally concentrated and unevenly distributed. In order to suppress this phenomenon, the method of the present invention is effective. . This is to utilize the phenomenon in which metal elements are concentrated at the tip of crystal growth, and drive the tip of this crystal growth into a silicon film to be removed later, so that it can be used for device fabrication. In the silicon film, a portion in which metal elements are concentrated does not exist.
[0028]
That is, heat treatment is performed at a temperature at which the amorphous silicon film 107 is crystallized, and this film is crystallized. At this time, crystal growth proceeds from the surface of the silicon film 107 in contact with the oxide film 106 to the exposed surface. At the same time as the crystal growth, the portion where the metal element is concentrated moves in the silicon film 107. As a result, the portion where the nickel element is concentrated is driven out of the silicon film 105 and exists in the silicon film 107 (particularly the surface thereof). Then, by removing the silicon film 107 using the oxide film 106 as an etching stopper, a crystalline silicon film 108 without a region in which nickel elements are unevenly distributed can be obtained. (Fig. 1 (D)
[0029]
[Action]
By forming a film for diffusing a metal element such as an amorphous silicon film on the surface of the crystalline silicon film crystallized by the action of a metal that promotes crystallization, and then performing a heat treatment, the metal element The metal element is diffused in the film for diffusing the metal. By doing this, the metal element in the crystalline silicon film can be effectively sucked out by the film for diffusing the metal element, so that the crystalline silicon having a low concentration of the metal element and good crystallinity. A membrane can be obtained.
[0030]
1 can be performed at a temperature that can be withstood by the glass substrate at 550 ° C. or lower, so that, for example, a thin film transistor formed on the glass substrate, such as a liquid crystal electro-optical device, This is extremely useful for the manufacturing process.
[0031]
In order to easily remove the film that diffuses the metal element, it is effective to form an oxide film on the crystalline silicon film. The oxide film is an etchant used for etching a silicon film (for example, hydrazine or ClF). _Three ), It can function as an etching stopper.
[0032]
Further, an amorphous silicon film (second silicon film) is formed on the surface of the crystalline silicon film (first silicon film) crystallized by the action of the metal element, and then heat treatment is performed to form the second layer. By crystallizing the amorphous silicon film, the concentrated portion of the metal element existing in the first silicon film can be driven into the second silicon film, and the metal element is contained in the first silicon film. Can be prevented from being unevenly distributed.
[0033]
【Example】
[Example 1]
In this embodiment, an amorphous silicon film is formed on a glass substrate, a metal film for promoting crystallization of silicon is introduced into the amorphous silicon film, and the amorphous silicon film is then crystallized by heating. Then, an amorphous silicon film is formed on the crystallized silicon film (crystalline silicon film) via an oxide film (silicon oxide film), and subjected to heat treatment again. The present invention relates to a technique for diffusing nickel element from a crystalline silicon film (discharging nickel element into an amorphous silicon film) and, as a result, reducing the nickel element concentration in the crystalline silicon film.
[0034]
FIG. 1 shows a manufacturing process of a crystalline silicon film shown in this embodiment. First, a silicon oxide film 102 is formed as a base film on a Corning 7059 glass substrate 101 (strain point 593 ° C.) to a thickness of 3000 mm. This silicon oxide film 102 is for preventing impurities and alkali ions from diffusing from the glass substrate 101 into a semiconductor thin film to be formed later.
Next, an amorphous silicon film 103 is formed to a thickness of 600 mm by plasma CVD or low pressure thermal CVD.
Then, a nickel acetate solution adjusted to a predetermined nickel concentration is dropped on the amorphous silicon film 103 to form a water film 104. Then, spin coating is performed using the spinner 100 so that the nickel element is held in contact with the surface of the amorphous silicon film 103. (Fig. 1 (A))
[0035]
Next, heat treatment is performed to crystallize the amorphous silicon film 103 to obtain a crystalline silicon film 105. The heating temperature can be 450 ° C. or higher, preferably 500 ° C. or higher. Considering the heat resistance of the glass substrate 101, it is preferable to set the temperature below the strain point of the glass substrate 101. Note that when this heat treatment is performed at a temperature of 500 ° C. or less, the time required for the heat treatment is several tens of hours or more, which is not practical. (Fig. 1 (B))
[0036]
The nickel concentration in the crystalline silicon film 105 is 1 × 10. ¹⁶ Atom cm ^-3 ~ 5x10 ¹⁹ Atom cm ^-3 It is necessary to. Therefore, in the step of FIG. 1A, it is necessary to adjust the nickel concentration in the nickel acetate solution so that the nickel concentration in the obtained crystalline silicon film 105 falls within the above range. The nickel concentration is defined as the minimum value measured using SIMS (secondary ion analysis method).
[0037]
When the crystalline silicon film 105 is obtained, a silicon oxide film 106 is formed on the surface thereof. The thickness of the silicon oxide film 106 may be approximately several tens to 100 mm. The reason why such a thin film is used is that the nickel element in the crystalline silicon film 105 needs to be movable through the silicon oxide film 106. Here, an extremely thin silicon oxide film 106 is formed in the air by irradiation with UV light. Even if the silicon oxide film 106 is a very thin film of a natural oxide film, it has been found that the silicon oxide film 106 has an effect as an etching stopper when the subsequent amorphous silicon film (shown by 107) is etched.
[0038]
Here, the silicon oxide film 106 is formed using a UV oxidation method, but may be formed using a thermal oxidation method. In addition, the silicon oxide film 106 functions as an etching stopper in a later etching process, and may be any film that can obtain selectivity in etching with respect to the crystalline silicon film 105. For example, an extremely thin silicon nitride film can be used instead of the silicon oxide film 106.
[0039]
Next, an amorphous silicon film 107 is formed to a thickness of 600 mm by plasma CVD or low pressure thermal CVD.
[0040]
FIG. 2 shows the concentration distribution in the film thickness direction of the nickel element using SIMS (secondary ion analysis) in this state. FIG. 2 shows the distribution of nickel elements in the depth direction from the surface of the amorphous silicon film 107. As can be seen from FIG. 2, the nickel element in the amorphous silicon film 107 is below the measurement limit (in this case, 1 × 10 ¹⁷ Atom cm ^-3 Is a measurement limit), and the crystalline silicon film 105 has a maximum of 5 × 10 5. ¹⁸ Atom cm ^-3 It can be seen that a certain amount of nickel element is present.
[0041]
Then, heat treatment is performed to diffuse the nickel element in the crystalline silicon film 105 through the oxide film 106 in the amorphous silicon film 107. It can be understood that this step is a step of sucking out nickel element in the crystalline silicon film 105 by the amorphous silicon film 107. (Figure 1 (C))
[0042]
The heating process is performed at a temperature of 400 ° C. to 450 ° C., which is a temperature at which the amorphous silicon film 107 does not crystallize. In this embodiment, heat treatment is performed at a temperature of 450 ° C. for 2 hours. When heat treatment is performed, nickel element in the crystalline silicon film 105 diffuses into the amorphous silicon film 107, and the concentration of nickel element in the crystalline silicon film 105 can be lowered.
[0043]
In general, if the thickness of the amorphous silicon film 107 is set to be equal to or greater than the thickness of the crystalline silicon film 105, the nickel concentration in the crystalline silicon film 105 is reduced to 1/2 or less by performing the heat treatment. It can be.
[0044]
FIG. 3 shows the concentration distribution of the nickel element in the film thickness direction when the heat treatment step shown in FIG. 1C is performed for 2 hours. The data shown in FIG. 3 is based on the same measurement method as the data shown in FIG.
[0045]
As apparent from FIG. 3, nickel is diffused in the amorphous silicon film 107. However, it can be seen that the concentration in the crystalline silicon film 105 is slightly higher. 3 that the nickel element in the crystalline silicon film 105 is sucked into the amorphous silicon film 107 in the heating step shown in FIG.
[0046]
FIG. 4 shows that after the data shown in FIG. 3 was obtained, the heat treatment was further performed at a temperature of 450 ° C. for 2 hours (the heat treatment was finally applied at a temperature of 450 ° C. for 4 hours). In the state), the nickel concentration distribution.
As apparent from a comparison between FIG. 4 and FIG. 3, it can be seen that the nickel element in the crystalline silicon film 105 is gradually sucked into the amorphous silicon film 107. This is presumably because a large amount of dangling bonds are present in the amorphous silicon film 107, and there are a large number of silicon atoms that are easily bonded to nickel. Further, by applying a long-time heat treatment, the nickel concentration in the crystalline silicon film 105 can be further lowered gradually. Such an action is a remarkable feature that cannot be seen when the amorphous silicon film 107 is crystallized.
[0047]
Then, the amorphous silicon film 107 is removed by etching. Here, as an etchant of the amorphous silicon film 107, hydrazine (N ₂ H ₆ ) Is used. When hydrazine is used as an etchant, the amorphous silicon film 107 has a higher etching rate than the etching rate of the crystalline silicon film 105. In addition, in this embodiment, the silicon oxide film 106 that is not etched with hydrazine (its etching rate is extremely low and can be regarded as not etched when viewed relatively) is used as an etching stopper on the crystalline silicon film 105. Is formed. Therefore, it is possible to selectively remove only the amorphous silicon film 107 that has sucked out nickel. Note that dry etching may be used for etching the amorphous silicon film 107.
[0048]
Next, the silicon oxide film 106 is removed with buffered hydrofluoric acid or hydrofluoric acid to obtain a crystalline silicon film 108 in which the nickel element concentration can be lowered as shown in FIG.
As can be seen from FIG. 4, the concentration of the nickel element in the crystalline silicon film 108 is, for example, 3 × 10. ¹⁸ Atom cm ^-3 It is weak. As can be seen from a comparison with FIG. 2, the concentration of the nickel element can be reduced to 1/2 (averaged to be 1/2 or less) as compared with that before the heat treatment in FIG. Means that.
[0049]
In this embodiment, the amorphous silicon film 107 formed on the crystalline silicon film 105 has the same thickness as that of the crystalline silicon film 105. However, by further increasing the thickness of the amorphous silicon film 107, the concentration of nickel element contained in the finally obtained crystalline silicon film 108 can be further reduced. That is, by making the volume of the amorphous silicon film 107 larger than the volume of the crystalline silicon film 105, more nickel element can be sucked into the amorphous silicon film 107.
[0050]
By adopting the configuration of this embodiment, the nickel concentration in the obtained crystalline silicon film 108 is set to 5 × 10 5. ¹⁸ Atom cm ^-3 It can be as follows.
[0051]
[Example 2]
This embodiment is characterized in that, in the manufacturing process of Embodiment 1 shown in FIG. 1, the heat treatment step shown in FIG. 1C is performed under the condition that the heating temperature is 550 ° C. and the heating time is 4 hours. To do. When the heat treatment step shown in FIG. 1C is performed at 550 ° C. for 4 hours, the amorphous silicon film 107 is crystallized by the action of nickel element diffusing from the crystalline silicon film 105. End up.
[0052]
At this time, crystallization proceeds in a direction from the crystalline silicon film 105 toward the amorphous silicon film 107 through the oxide film 106. As described above, the metal element that promotes the crystallization of silicon tends to concentrate at the tip of crystal growth. Therefore, a region where nickel elements are concentrated is formed on the surface of the crystallized silicon film 107 (which has been transformed into a crystalline silicon film at this stage). As a matter of course, the nickel concentration in the crystalline silicon film 105 is reduced.
[0053]
Further, the unevenly distributed region of nickel element existing on the surface of the crystalline silicon film 105 moves with the tip portion of the crystal growth as the crystallization of the amorphous silicon film 107 proceeds. In other words, this unevenly distributed region of nickel element exists in the silicon film 107 (referred to here as a crystallized state) after the crystallization is completed. Therefore, the unevenly distributed region of nickel element existing on the surface of the crystalline silicon film 105 can be eliminated.
[0054]
When the amorphous silicon film 107 is crystallized in this way, there is a concern whether the crystallized silicon film can be selectively removed. However, since the silicon oxide film 106 functioning as an etching stopper is formed, only the silicon film 107 (crystallized in this case) can be selectively removed. That is, hydrazine and ClF _Three When etching using a gas is performed, the etching rate of the acid film indicated by 106 is extremely small compared to the etching rate of the silicon film 107, so that the etching can be stopped when the etching of the silicon film 107 is completed. it can.
[0055]
When the structure shown in this embodiment is employed, the heating step shown in FIG. 1B and the heating step shown in FIG. 1C can be performed under the same conditions.
[0056]
Example 3
This embodiment shows an example in which a thin film transistor is manufactured using a crystalline silicon film obtained by the manufacturing method described in Embodiment 1 or Embodiment 2. FIG. 5 illustrates a manufacturing process of the thin film transistor described in this embodiment.
A crystalline silicon film 503 is formed over the glass substrate 501 over which the base film 502 is formed, using the method described in Example 1 or Example 2. (Fig. 5 (A))
[0057]
Next, the obtained crystalline silicon film 503 is patterned to form an active layer of a thin film transistor as indicated by 504. Then, a silicon oxide film 505 functioning as a gate insulating film is formed to a thickness of 1000 mm by plasma CVD or low pressure thermal CVD. (Fig. 5 (B))
[0058]
Next, an aluminum film containing scandium is formed to a thickness of 6000 mm and patterned to form a gate electrode 506. Then, an oxide layer 507 is formed in the electrolytic solution by performing anodization using the gate electrode 506 as an anode. The oxide layer 507 has a thickness of 2000 mm. With the thickness of the oxide layer 507, an offset gate region can be formed in a later step.
[0059]
Further, impurity ions are implanted into the active layer 504. Here, phosphorus ions are implanted as impurity ions. In this step, phosphorus ions are implanted in the regions indicated by 508 and 511. The regions indicated by 508 and 511 serve as source / drain regions. An area 509 is an offset gate area. The region 510 is a channel formation region.
[0060]
After the impurity ion implantation is completed, laser light is irradiated to activate the implanted ions and anneal the damaged source / drain regions 508 and 511 at the time of ion implantation. (Fig. 5 (C))
[0061]
Next, a silicon oxide film 512 is formed as an interlayer insulating film, contact holes are further formed, and a source electrode 513 and a drain electrode 514 are formed using aluminum. Finally, heat treatment is performed in a hydrogen atmosphere at 350 ° C. to complete the thin film transistor. (Fig. 5 (D))
[0062]
Example 4
In this embodiment, nickel, which is a metal element that promotes crystallization of silicon, is selectively introduced to obtain a crystalline silicon film that grows in a direction parallel to the substrate, and at the same time, this crystalline silicon film The present invention relates to a technique for reducing the nickel concentration in the inside.
[0063]
A silicon oxide film having a thickness of 3000 mm is formed as a base film 602 on the glass substrate 601 by a sputtering method. Next, an amorphous silicon film 603 is formed to a thickness of 500 mm by plasma CVD or low pressure thermal CVD.
Next, UV light is irradiated in an oxygen atmosphere to form an extremely thin oxide film (not shown) on the surface of the amorphous silicon film 603. This oxide film is for improving the wettability of the solution in a later solution coating step.
Then, a mask 604 is formed using a resist. A region 605 exposed by the resist mask 604 has a slit shape having a longitudinal direction in a direction perpendicular to the paper surface of FIG.
Next, a nickel acetate solution containing nickel at a predetermined concentration is dropped to form a water film 606. (Fig. 6 (A))
[0064]
Further, spin coating is performed using the spinner 600 so that the nickel element is held in contact with the region 605 on the amorphous silicon film 603 through an oxide film (not shown).
[0065]
Then, the resist mask 604 is removed. Next, heat treatment is performed to crystallize the amorphous silicon film 603. The nickel element diffuses into the amorphous silicon film 603 through the oxide film (not shown) from the state held in contact with the amorphous silicon film 603 via the oxide film (not shown) in the region indicated by 605. As the nickel element diffuses, the amorphous silicon film 603 undergoes crystal growth in a direction parallel to the substrate as indicated by an arrow 607, and a crystalline silicon film 608 is formed.
This crystal growth proceeds in a columnar or needle shape. In the case of the present embodiment, the region indicated by 605 has a slit shape having a longitudinal direction from the front side to the back side of the drawing, so that the crystal growth as indicated by the arrow 607 is substantially along one direction. And proceed. Crystal growth can be performed over several tens of micrometers to 100 micrometers or more. (Fig. 6 (B))
[0066]
After obtaining the crystalline silicon film 608, an oxide film 609 is formed to a thickness of 50 mm by a thermal oxidation method. Further, an amorphous silicon film 610 is formed to a thickness of 1000 mm by plasma CVD or low pressure thermal CVD. (Fig. 6 (C))
[0067]
Then, heat treatment is performed at 450 ° C. for 2 hours to diffuse the nickel element in the crystalline silicon film 608 into the amorphous silicon film 610 through the oxide film 609. Then, the amorphous silicon film 610 is made ClF. _Three Etching with a gas, and the oxide film 609 is removed with buffered hydrofluoric acid. In this manner, a crystalline silicon film 611 with a lowered nickel concentration as shown in FIG. 6D can be obtained. The crystalline silicon film 611 has a feature in which a crystal growth region is formed in a direction parallel to the substrate as indicated by reference numeral 607 and the nickel concentration in the film is low.
[0068]
According to experiments, it has been found that a certain amount of nickel introduced into the region indicated by 605 can increase the distance of crystal growth in a direction parallel to the substrate indicated by 607 (referred to as lateral growth). Yes. However, an increase in the amount of nickel element introduced is not preferable because it causes the nickel concentration in the finally obtained crystalline silicon film 611 to increase. This is because when the nickel concentration in the film increases (according to experiments, 5 × 10 ¹⁹ Atom cm ^-3 If it becomes above, the characteristic as a semiconductor of a silicon film will be impaired, the operation | movement of the thin-film transistor produced will become unstable, or the characteristic deterioration will become serious.
[0069]
However, as shown in the present embodiment, the nickel element is removed after the crystallization is completed to increase the lateral crystal growth distance, and the nickel concentration in the obtained crystalline silicon film 611 ( It is possible to satisfy both demands for reducing the concentration of metal elements) as much as possible.
[0070]
Example 5
In this example, a thin film transistor is configured using the crystalline silicon film obtained in Example 4. FIG. 7 shows a manufacturing process of this example.
A crystalline silicon film is obtained according to the process shown in FIG. This crystalline silicon film has a region where the crystal has grown in a direction parallel to the substrate.
[0071]
As shown in FIG. 7A, the crystalline silicon film is patterned to form a region to be an active layer 703 of the thin film transistor. In FIG. 7A, reference numeral 701 denotes a glass substrate, and reference numeral 702 denotes a silicon oxide film as a base film.
[0072]
Here, it is important that there is no crystal growth start point (region where nickel is introduced) and crystal growth end point in the crystal growth shown in FIG. 6B in the active layer 703. This is because nickel is contained in a high concentration at the start point of crystal growth and the end point of crystal growth.
[0073]
Further, a silicon oxide film 704 functioning as a gate insulating film is formed to a thickness of 1000 mm by plasma CVD. (Fig. 7 (A))
[0074]
Next, a gate electrode 705 is formed by forming a film containing aluminum as a main component and further performing patterning. Using the gate electrode 705 as an anode, the oxide layer 706 is formed by anodizing in an electrolytic solution. In the later step of implanting impurity ions with the thickness of the oxide layer 706, an offset gate region can be formed. (Fig. 7 (B))
[0075]
Phosphorus ions are implanted as impurity ions. In this step, a source region 707 and a drain region 710 are formed. Further, an offset gate region 708 and a channel formation region 709 are formed. After the implantation of impurity ions, the source / drain regions 707 and 710 are activated by irradiating laser light or strong light.
[0076]
Then, a silicon oxide film 711 serving as an interlayer insulating film is formed to a thickness of 6000 mm by plasma CVD. After forming contact holes in the silicon oxide film 711, a source electrode 712 and a drain electrode 713 are formed. Thus, the thin film transistor is completed. (Fig. 7 (C))
[0077]
Example 6
This embodiment is characterized in that heat treatment is performed again after the crystalline silicon film manufacturing process of Embodiment 1 shown in FIG.
When heat treatment is performed in the step shown in FIG. 1C, nickel (metal element) in the crystalline silicon film 105 is gradually sucked into the amorphous silicon film 107 as shown in FIG. At this time, as shown in FIG. 4, the nickel concentration near the surface of the crystalline silicon film 105 becomes higher than the nickel concentration near the interface of the silicon oxide film 102 under the crystalline silicon film 105. This means that nickel in the crystalline silicon film 105 is segregated on the surface side of the crystalline silicon film 105 as a result of the nickel in the amorphous silicon film 107 being sucked out. ing.
[0078]
Therefore, in the case where a thin film transistor is manufactured using the crystalline silicon film 108 formed on the glass substrate 101 as shown in FIG. 1D, carriers are conducted on the surface of the crystalline silicon film 108. become. It is not preferable that nickel is present in a high concentration in a region where carriers are conducted.
[0079]
Therefore, in this embodiment, after obtaining the state shown in FIG. 1D, heat treatment is performed, and nickel is diffused again into the crystalline silicon film 108. The heat treatment performed here may be a temperature of 400 ° C. or higher because nickel can be diffused. The upper limit is limited by the heat resistance of the glass substrate 101. Therefore, the temperature of the heating performed here may be 400 ° C. or more and not more than the strain point of the glass substrate.
[0080]
Details of this embodiment will be described below with reference to FIG.
The state shown in FIG. 1D is obtained through the manufacturing process as shown in FIG. This state is shown in FIG. FIG. 8A shows a layer 802 (surface side) in which nickel is segregated and nickel is contained in a high concentration, and a layer 801 in which nickel concentration is contained at a lower concentration than the layer side indicated by 802. It is shown. The layers 801 and 802 constitute a crystalline silicon film 108 (see FIG. 1D) formed over the glass substrate 101 with the base film 102 interposed therebetween.
[0081]
In the state shown in FIG. 8A, heat treatment is performed as shown in FIG. Here, heat treatment is performed at 500 ° C. for 2 hours. As a result, the nickel element in the region indicated by 802 diffuses into the region indicated by 801 where nickel is present at a lower concentration. Thus, this region 802 can be made free of nickel segregation. Then, a crystalline silicon film 803 in which the nickel concentration on the surface can be reduced can be obtained. (Fig. 8 (C))
[0082]
Example 7
This example is an example in the case where the structure shown in Example 7 is irradiated with laser light instead of heat treatment in the crystallization step. The steps of this example are shown in FIG.
First, after the process shown in FIG. 1, a layer 802 made of a crystalline silicon film having a high concentration of nickel element on its surface, and a layer 801 made of a crystalline silicon film having a low concentration of nickel element, are shown. Get. (Fig. 9 (A))
[0083]
Next, nickel element is diffused from the layer 802 to the layer 801 by irradiation with laser light. (Fig. 9 (B))
[0084]
Thus, a crystalline silicon film 901 having a state where nickel is uniformly diffused in the film is obtained. (Figure 9 (C))
[0085]
Example 8
This embodiment is characterized in that, in the step shown in Embodiment 1, the amorphous silicon film 107 shown in FIG. 1C is artificially formed with a high defect density.
In the process shown in the first embodiment, as shown in FIG. 2, the crystalline silicon film 105 has an average of 3 × 10 5. ¹⁸ Atom cm ^-3 About nickel element is included. In view of this, the present embodiment is characterized in that the defect density in the amorphous silicon film 107 for removing nickel element is at least equal to or higher than the concentration of nickel element, and its removal capability is enhanced.
[0086]
The defect density in the amorphous silicon film 107 can be estimated by measuring the spin density. In addition, to form defects artificially, sputtering, low-temperature plasma CVD, or hydrogen for neutralizing unpaired bonds is not used, but plasma CVD or vacuum thermal CVD using only silane or disilane. May be used.
[0087]
When the defect density of the amorphous silicon film 107 is increased, the nickel element removal capability can be increased, and the effects shown in FIGS. 3 and 4 can be further increased.
[0088]
Example 9
In this embodiment, a polycrystalline silicon film is used as a film for diffusing nickel element (sucking out nickel element).
[0089]
FIG. 1 shows a manufacturing process of a crystalline silicon film shown in this embodiment. First, a silicon oxide film 102 is formed to a thickness of 3000 mm as a base film on a Corning 7059 glass substrate 101 (strain point 593 ° C.).
Next, an amorphous silicon film 103 is formed to a thickness of 600 mm by plasma CVD or low pressure thermal CVD. Then, a nickel acetate solution adjusted to a predetermined nickel concentration is dropped on the amorphous silicon film 103 and spin coating is performed using the spinner 100 to form the water film 104. As a result, the nickel element is held in contact with the surface of the amorphous silicon film 103. (Fig. 1 (A))
[0090]
Next, heat treatment is performed to crystallize the amorphous silicon film 103 to obtain a crystalline silicon film 105. Here, the heating temperature is 550 ° C., and the heating time is 4 hours (FIG. 1B).
[0091]
When the crystalline silicon film 105 is obtained, a silicon oxide film 106 is formed on the surface thereof to a thickness of about several tens to 100 mm by irradiation with UV light in the air.
Next, a polycrystalline silicon film 107 is formed to a thickness of 600 mm by low pressure thermal CVD. The polycrystalline silicon film 107 does not have to have a film quality required for the active layer of the semiconductor, and is a film having a high defect density. The defect density is preferably higher than the defect density of the crystalline silicon film 105.
[0092]
Next, by performing heat treatment, the nickel element in the crystalline silicon film 105 is diffused through the oxide film 106 in the amorphous silicon film 107. (Figure 1 (C))
[0093]
At this time, the lower limit of the heating temperature is defined as a temperature at which nickel can diffuse, and is 400 ° C. or higher. The upper limit is defined as the strain temperature of the glass substrate 101. By this heat treatment, the nickel element in the crystalline silicon film 105 diffuses into the polycrystalline silicon film 107, and the concentration of nickel element in the crystalline silicon film 105 can be lowered.
[0094]
In general, if the thickness of the polycrystalline silicon film 107 is set to be equal to or greater than the thickness of the crystalline silicon film 105, the nickel concentration in the crystalline silicon film 105 is reduced to ½ or less by performing the heat treatment. can do.
[0095]
Then, the amorphous silicon film 107 is removed by etching. Hydrazine (N ₂ H ₆ Or ClF _Three Gas may be used. On the other hand, since the etching rate of silicon oxide is extremely low, the silicon oxide film 106 functions as an etching stopper, so that only the polycrystalline silicon film 107 that has sucked out nickel can be selectively removed.
Next, the silicon oxide film 106 is removed with buffered hydrofluoric acid or hydrofluoric acid to obtain a crystalline silicon film 108 in which the nickel element concentration can be lowered. (Figure 1 (D))
[0096]
Example 10
In this example, the amorphous Si film is formed on the film in which nickel element is diffused (nickel element is sucked out). _X Ge _1-X A film (0 <x <1) is used. FIG. 1 shows a manufacturing process of a crystalline silicon film shown in this embodiment.
[0097]
A silicon oxide film 102 is formed as a base film on a Corning 7059 glass substrate 101 (strain point 593 ° C.) to a thickness of 3000 mm.
Next, an amorphous silicon film 103 is formed to a thickness of 600 mm by plasma CVD or low pressure thermal CVD. Then, a nickel acetate solution adjusted to a predetermined nickel concentration is dropped on the amorphous silicon film 103 and spin coating is performed using the spinner 100 to form the water film 104. As a result, the nickel element is held in contact with the surface of the amorphous silicon film 103. (Fig. 1 (A))
[0098]
Next, heat treatment is performed to crystallize the amorphous silicon film 103 to form a crystalline silicon film 105. Here, the heating temperature is 550 ° C., and the heating time is 4 hours (FIG. 1B).
[0099]
When the crystalline silicon film 105 is obtained, a silicon oxide film 106 is formed on the surface thereof to a thickness of about several tens to 100 mm by irradiation with UV light in the air.
Next, silane (SiH _Four ) And germane (GeH) _Four Si) in an amorphous state by plasma CVD method _X Ge _1-X A film 107 is formed to a thickness of 600 mm. Amorphous Si _X Ge _1-X In order to make the film 107 a film having a high defect density, the substrate temperature at the time of film formation may be lowered or the source gas may not be diluted with hydrogen.
[0100]
Next, by performing heat treatment, amorphous Si _X Ge _1-X The nickel element in the crystalline silicon film 105 is diffused into the film 107 through the oxide film 106. (Figure 1 (C))
[0101]
The lower limit of the heating temperature is defined as the temperature at which nickel can diffuse, and is 400 ° C. or higher. The upper limit is defined by the strain temperature of the glass substrate 101. By the heat treatment, the nickel element in the crystalline silicon film 105 is in an amorphous state. _X Ge _1-X The concentration of nickel element in the crystalline silicon film 105 can be lowered by diffusing into the film 107.
[0102]
And Si _X Ge _1-X The film 107 is removed by etching. At this time, Si _X Ge _1-X An etching solution and an etching gas having a high etching selectivity between the film 107 and the silicon oxide film 106 are used so that the silicon oxide film 106 functions as an etching stopper. As a result, Si that sucked out nickel _X Ge _1-X Only the film 107 can be selectively removed.
[0103]
Next, the silicon oxide film 106 is removed with buffered hydrofluoric acid or hydrofluoric acid to obtain a crystalline silicon film 108 in which the nickel element concentration can be lowered as shown in FIG.
[0104]
【The invention's effect】
By the action of the metal element, a crystalline silicon film can be formed at a lower temperature than the conventional case of about 550 ° C. or lower. Therefore, a crystalline silicon film can be formed on the glass substrate.
[0105]
Further, by diffusing the metal element in the silicon film crystallized by the action of the metal element into the amorphous silicon film, a crystalline silicon film having a low concentration of the metal element can be obtained. Therefore, using the crystalline silicon film, a device free from the adverse effects of metal elements, such as a thin film transistor, can be obtained.
[0106]
Further, since the portion where the metal element is unevenly distributed in the silicon film crystallized by the action of the metal element is removed, a crystalline silicon film without the portion where the metal element is unevenly distributed can be obtained. As a result, a semiconductor element free from the influence of metal elements can be obtained.
[Brief description of the drawings]
FIGS. 1A to 1C are diagrams illustrating a manufacturing process of a crystalline silicon film. FIGS.
FIG. 2 is a diagram showing a concentration distribution of nickel element.
FIG. 3 is a diagram showing a concentration distribution of nickel element.
FIG. 4 is a diagram showing a concentration distribution of nickel element.
FIGS. 5A and 5B illustrate a manufacturing process of a thin film transistor. FIGS.
6A and 6B are diagrams illustrating a manufacturing process of a crystalline silicon film.
FIGS. 7A to 7C illustrate a manufacturing process of a thin film transistor. FIGS.
FIGS. 8A to 8C are diagrams illustrating a manufacturing process of a crystalline silicon film. FIGS.
FIGS. 9A and 9B are diagrams illustrating a manufacturing process of a crystalline silicon film. FIGS.
[Explanation of symbols]
100, 600 ... Spinner
101, 501, 601, 701 ・ Glass substrate
102, 502, 602, 702. Base film (silicon oxide film)
103, 603... Amorphous silicon film
104, 602 ... Water film
105, 608... Crystalline silicon film
106,609 ・ ・ ・ ・ ・ ・ ・ ・ ・ Oxide film
107, 610... Diffusion film for metal element
108, 611... Crystalline silicon film

Claims (21)

Introducing a metal element for promoting crystallization of silicon into the first amorphous silicon film on the glass substrate;
Heating the first amorphous silicon film to form a crystalline silicon film;
Forming a silicon oxide film on the crystalline silicon film;
Forming a second amorphous silicon film on the silicon oxide film;
Heating the crystalline silicon film and the second amorphous silicon film to move the metal element into the second amorphous silicon film;
Removing the second amorphous silicon film using the silicon oxide film as an etching stopper ;
A method for producing a crystalline silicon film, wherein the silicon oxide film is removed . Introducing a metal element for promoting crystallization of silicon into the first amorphous silicon film on the glass substrate;
Heating the first amorphous silicon film to form a crystalline silicon film;
Forming a silicon oxide film on the crystalline silicon film;
Forming a second amorphous silicon film on the silicon oxide film;
  Heating the crystalline silicon film and the second amorphous silicon film at 450 ° C. or more to move the metal element into the second amorphous silicon film;
Removing the second amorphous silicon film using the silicon oxide film as an etching stopper;
A method for producing a crystalline silicon film, wherein the silicon oxide film is removed. Introducing a metal element for promoting crystallization of silicon into the first amorphous silicon film on the glass substrate;
Heating the first amorphous silicon film to form a crystalline silicon film;
Forming a silicon oxide film on the crystalline silicon film;
Forming a second amorphous silicon film on the silicon oxide film;
The crystalline silicon film and the second amorphous silicon film are heated at a temperature not lower than 450 ° C. and the upper limit of the strain point of the glass substrate, so that the metal element is contained in the second amorphous silicon film. Move to
Removing the second amorphous silicon film using the silicon oxide film as an etching stopper;
A method for producing a crystalline silicon film, wherein the silicon oxide film is removed. Introducing a metal element for promoting crystallization of silicon into the first amorphous silicon film on the glass substrate;
Heating the first amorphous silicon film to form a crystalline silicon film;
Forming a silicon oxide film on the crystalline silicon film;
Forming a second amorphous silicon film on the silicon oxide film;
The crystalline silicon film and the second amorphous silicon film are heated to move the metal element into the second amorphous silicon film, so that the concentration of the metal element in the crystalline silicon film is increased. 5 × 10 ¹⁸ cm ^-3 Below
Removing the second amorphous silicon film using the silicon oxide film as an etching stopper;
A method for producing a crystalline silicon film, wherein the silicon oxide film is removed. Introducing a metal element for promoting crystallization of silicon into the first amorphous silicon film on the glass substrate;
Heating the first amorphous silicon film to form a crystalline silicon film;
Forming a silicon oxide film on the crystalline silicon film;
Forming a second amorphous silicon film on the silicon oxide film;
The crystalline silicon film and the second amorphous silicon film are heated at 450 ° C. or higher to move the metal element into the second amorphous silicon film, and Concentration of metal element is 5 × 10 ¹⁸ cm ^-3 Below
Removing the second amorphous silicon film using the silicon oxide film as an etching stopper;
A method for producing a crystalline silicon film, wherein the silicon oxide film is removed. Introducing a metal element for promoting crystallization of silicon into the first amorphous silicon film on the glass substrate;
Heating the first amorphous silicon film to form a crystalline silicon film;
Forming a silicon oxide film on the crystalline silicon film;
Forming a second amorphous silicon film on the silicon oxide film;
The crystalline silicon film and the second amorphous silicon film are heated at a temperature not lower than 450 ° C. and the upper limit of the strain point of the glass substrate, so that the metal element is contained in the second amorphous silicon film. And the concentration of the metal element in the crystalline silicon film is 5 × 10 ¹⁸ cm ^-3 Below
Removing the second amorphous silicon film using the silicon oxide film as an etching stopper;
A method for producing a crystalline silicon film, wherein the silicon oxide film is removed. 7. The method for manufacturing a crystalline silicon film according to claim 1, wherein the second amorphous silicon film is formed using only silane. 7. The crystalline silicon according to claim 1, wherein each of the first amorphous silicon film and the second amorphous silicon film is an I-type amorphous silicon film. A method for producing a film. In any one of claims 1 to 6, wherein the second amorphous silicon film, a method for manufacturing a crystalline silicon film, which is formed by using a plasma CVD method, a thermal CVD method or a sputtering method . 7. The method for manufacturing a crystalline silicon film according to claim 1, wherein the silicon oxide film on the crystalline silicon film is formed by oxidizing the crystalline silicon film. In any one of claims 1 to 6, a metal element for promoting crystallization of the silicon, Fe, Co, Ni, Pd , Ir, Pt, of the crystalline silicon film, which is a Cu or Au Manufacturing method. In any one of claims 1 to 6, wherein the thickness of the second amorphous silicon film, the crystalline silicon film, wherein a greater thickness than the first amorphous silicon film Manufacturing method. In any one of claims 1 to 6, the defect density of the second amorphous silicon film, the crystalline silicon film being higher than the concentration of the metal element for promoting crystallization of the silicon Manufacturing method. In any one of claims 1 to 6, after the heating of the crystalline silicon film and the second amorphous silicon film, a metal for promoting crystallization of the silicon in the second amorphous silicon film The method for producing a crystalline silicon film, wherein the concentration of the element is higher than the concentration of a metal element that promotes crystallization of the silicon in the crystalline silicon film. In any one of claims 1 to 6, crystalline silicon, which comprises using an amorphous _{Si X Ge 1-X (0} <X <1) in place of the second amorphous silicon film A method for producing a film. Forming a gate insulating film on the crystalline silicon film formed by the manufacturing method according to claim 1;
Forming a gate electrode on the gate insulating film;
Impurity ions are implanted using the gate electrode as a mask to form a source region and a drain region,
Activating the implanted impurity ions;
A method for manufacturing a thin film transistor, comprising forming a source electrode and a drain electrode over the source region and the drain region. Claims 1 to devices, which comprises using a crystalline silicon film formed by the manufacturing method according to any one of 15. A liquid crystal display device using the device according to claim 17 . Claims 1 to TFT, which comprises using a crystalline silicon film formed by the manufacturing method according to any one of 15. 20. A liquid crystal display device using the thin film transistor according to claim 19 . An electronic apparatus using the liquid crystal display device according to claim 18 or 20 .

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