JP3910229B2 - Method for producing semiconductor thin film - 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).
[0004]
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.
[0005]
[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) In addition, a peripheral circuit for driving the thin film transistor disposed in the pixel cannot be configured.
There is a problem.
[0006]
The above problem (2) is that a thin film transistor using an amorphous silicon thin film cannot be used in a P-channel type thin film transistor, so that a CMOS circuit cannot be constructed. 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.
[0007]
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.
[0008]
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.
[0009]
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. Yes. 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 solve the above-described problems and improve the characteristics of a crystalline silicon film obtained by utilizing the catalytic action of a metal element.
[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 protective film on the crystalline silicon film;
Forming an amorphous silicon film containing impurities on the protective film;
Diffusing the metal element in the silicon film containing the impurities;
Using the protective film as an etching stopper and removing the silicon film containing the impurities;
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]
In addition, 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 metal element layer or a layer containing a metal element by a CVD method, a sputtering method, or an evaporation method, or a method of applying a solution containing a metal element on an amorphous silicon film Can be mentioned.
[0016]
However, when CVD, sputtering, or vapor deposition is used, it is difficult to form a very thin uniform film, so the metal element is unevenly present 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.
[0017]
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. For example, since the Corning 1737 glass substrate has a strain point of 667 ° C., a heating temperature of about 620 ° C. is appropriate from the viewpoint of the heat resistance and productivity of the glass substrate.
[0018]
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.
[0019]
In the above structure, the step of forming the protective film includes a step of forming a silicon oxide film, a silicon nitride film, or a silicon oxynitride film by plasma CVD or the like. Alternatively, a process of oxidizing the surface of the crystalline silicon film in the air by UV light irradiation or heating can be employed.
[0020]
This protective film functions as an etching stopper, and may be a film that can obtain selectivity in etching with respect to the silicon film. Further, the thickness of the protective film may be several tens to 100 inches. The reason why such a thin film is used is that it is necessary to allow the metal element to move from the crystalline silicon film through the protective film.
[0021]
Further, in the above structure, the amorphous silicon film containing impurities functions as a film for diffusing the metal element, and examples thereof include an amorphous silicon film formed by a general CVD method. be able to. 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.
[0022]
The impurity contained in the amorphous silicon film is at least one element selected from oxygen, carbon, and nitrogen. For example, in the amorphous silicon film, if the impurity concentration is oxygen, 1 × 10 ¹⁹ ~ 1x10 ^{twenty one} Atom cm ^-3 The concentration of carbon or nitrogen is 1 × 10 ¹⁷ ~ 1x10 ²⁰ Atom cm ^-3 It ’s good.
[0023]
This silicon film containing impurities has an effect of gettering a metal element such as nickel because of its amorphous film quality (for example, having many dangling bonds and defects). By adding impurities, the amorphous silicon film has more elements for gettering the metal element. Examples of such elements include impurities, defects due to bonding between Si and impurities, oxygen between silicon bonds, and the like.
[0024]
Making the concentration of the impurity higher than the concentration of the metal element in the crystalline silicon film is effective for trapping more metal elements in the silicon film. Furthermore, it is also effective to make the amorphous silicon film thicker than the crystalline silicon film. This is because the volume ratio with respect to the crystalline silicon film can be increased as the thickness of the silicon film increases. In addition, when an impurity such as oxygen is contained in the amorphous silicon film at a high concentration in this way, it is possible to include many defects when the silicon film is crystallized by heating. As a result, the metal element can be gettered around these defects.
[0025]
Further, as a film for diffusing a metal element, amorphous Si containing impurities as described above _X Ge _1-X A membrane (0 <x <1) can also be used. Amorphous Si _X Ge _1-X For example, silane (SiH _Four ) And germane (GeH) _Four ) And the plasma CVD method may be used.
[0026]
In the above structure, the step of diffusing (absorbing) the metal element into the silicon film containing impurities can be performed by heat treatment. Along with the heating, the metal element is diffused in the silicon film containing the impurity element. In this way, since the metal element in the crystalline silicon film can be effectively sucked out by the silicon film, a crystalline silicon film having a low metal element concentration and good crystallinity can be obtained. .
[0027]
For example, if the silicon film containing impurities and the crystalline silicon film have substantially the same film thickness, the concentration of the metal element in the crystalline silicon film may be reduced to 1/2 or less on average by heating. it can.
[0028]
Note that the above heat treatment step aims at diffusing the metal element to the outside of the crystalline silicon film, and thus the lower limit of the heating temperature is defined as the temperature at which the metal element can diffuse. The higher the heating temperature, the higher the effect of reducing the concentration of the metal element in the crystalline silicon film. Therefore, it is preferable to heat at the highest possible temperature. Therefore, considering that the crystalline silicon film is formed on the substrate, the upper limit of the heating temperature is defined below the strain point of the substrate.
[0029]
The strain point of the substrate is a guideline for setting the heating temperature, and the heating temperature needs to be a temperature at which the deformation and strain of the substrate can be tolerated. For example, as represented by RTP, heating can be performed at a temperature equal to or higher than the strain point of the substrate if the heat treatment is performed for a short time. Furthermore, the temperature and time of the heat treatment also depend on the pattern of the film to be treated, the design rule, and the like. Therefore, after satisfying the above conditions, heat treatment may be performed at 550 ° C. to 1050 ° C. for several minutes to 10 hours.
[0030]
Thus, when the heating temperature is increased as much as possible, the silicon film containing impurities is crystallized due to the catalytic action of the metal element diffused from the crystalline silicon film, and is transformed into the crystalline silicon film. In some cases. In this case as well, even if silicon containing impurities is crystallized as described above, a large number of defects are formed therein, and these act as selective gettering sinks.
[0031]
Since this crystallization process proceeds as the metal element diffuses, crystal growth proceeds from the surface of the crystalline silicon film toward the silicon film containing impurities. Since metal elements such as nickel tend to concentrate at the tip of crystal growth, the concentration of nickel element in the crystalline silicon film can be reduced at the same time as crystal growth proceeds, and at the same time, nickel element segregates. You can erase the area.
[0032]
In the present invention, since impurities are contained in the silicon film for diffusing the metal element, the film quality of the two silicon films can be improved through the protective film even if the crystallinity is exhibited by the heat treatment. Can be different.
[0033]
In order to remove the silicon film on the protective film, a wet etching method or a dry etching method may be employed. At this time, since the protective film functions as an etching stopper, the silicon film on the protective film in which the metal element is diffused can be easily and selectively etched.
[0034]
That is, in the present invention, a metal film is formed regardless of whether the silicon film on the protective film is crystallized in the step of diffusing the metal element by forming a protective film serving as an etching stopper on the crystalline silicon film. It is possible to reliably and selectively remove the protective silicon film having a high concentration of elements.
[0035]
Therefore, in the present invention, the heating temperature in the step of diffusing the metal element is such that the concentration of the nickel element in the crystalline silicon film is set to a desired value regardless of whether or not the silicon film containing impurities is crystallized. Any temperature that can be decreased is acceptable.
[0036]
Further, in the above structure, if the atmosphere contains a halogen element in the heating step for diffusing the metal element, the effect of gettering is further improved.
[0037]
As a method for introducing a halogen element, HCl, HF, HBr, Cl ₂ , F ₂ , Br ₂ One or more kinds of gases selected from the above can be used. In general, a hydride of halogen can be used.
[0038]
By heating in an atmosphere containing a halogen element, the halide and nickel react with each other to form a vaporized metal element halide, and thus the action of removing nickel from the crystalline silicon film is further promoted. Also in the crystalline silicon film, the metal element can be brought into an electrically inactive state by forming a halide of the metal element. By introducing a halogen element, the concentration of the metal element can be reduced to 1/10 or less in comparison with the case where no halogen element is introduced in the heat treatment.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of the present invention will be described using 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))
[0040]
Next, as shown in FIG. 1C, the surface of the crystalline silicon film 105 is oxidized to form a silicon oxide film 106. Further, as a film for diffusing a metal element, for example, an amorphous silicon film containing oxygen 107 is deposited.
[0041]
Heat treatment is performed as shown in FIG. The temperature may be about 550 to 1050 ° C., and the heating time may be about 5 minutes to 10 hours. As a result, the metal element in the crystalline silicon film 105 gradually diffuses into the amorphous silicon film 107, and the amorphous silicon film 107 is crystallized. Since the crystallized silicon film 108 contains oxygen as an impurity, a large amount of defects are formed inside, and these defects act as gettering sinks.
[0042]
Then, as shown in FIG. 1E, the silicon oxide film 106 and the amorphous silicon film 107 are sequentially removed, so that the crystallinity compared to the concentration of the metal element in the amorphous silicon film 107 is obtained. A crystalline silicon film 108 having a small concentration of metal element in the silicon film 105 can be obtained.
[0043]
The crystalline semiconductor thin film manufacturing process shown in FIG. 1 can be carried out at a temperature that can be withstood by the glass substrate. Therefore, it is extremely useful for the manufacturing process of a thin film transistor formed on a glass substrate, such as a liquid crystal electro-optic device It will be something.
[0044]
【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) and subjected to heat treatment again, so that the nickel element from the crystalline silicon film is formed in the amorphous silicon film. Is diffused (the nickel element is sucked into the amorphous silicon film), and as a result, the nickel element concentration in the crystalline silicon film is reduced.
[0045]
FIG. 1 shows a manufacturing process of a crystalline silicon film shown in this embodiment. First, as shown in FIG. 1A, a base film 102 is formed on a Corning 1737 glass substrate 101 (strain point 667 ° C.). The base 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.
[0046]
Therefore, in order to obtain this function to the maximum, a silicon nitride film is optimal as the base film 102. However, since the silicon nitride film may be peeled off from the glass substrate 101 due to stress, it is not practical. Absent. Further, although a silicon oxide film can be used as the base film 102, the silicon oxide film has an insufficient barrier effect against impurities. Therefore, in this embodiment, a silicon oxynitride film is formed as the base film 102. In order to form a silicon oxynitride film as the base film 102, a plasma CVD method may be employed. As source gas, silane, O ₂ Gas, N ₂ O gas is used. Or TEOS gas, N ₂ O gas is used.
[0047]
In addition, it is important to make the hardness of the base film 102 as high as possible. According to the durability test of the finally obtained thin film transistor, it has been found that the harder the base film 102, that is, the lower the etching rate, the better the reliability. This suggests that this hardness contributes to the prevention of the intrusion of impurities from the glass substrate 101.
[0048]
Next, an amorphous silicon film 103 is formed to a thickness of 600 mm by plasma CVD or low pressure thermal CVD. This amorphous silicon film 103 is crystallized later. The reason why the low pressure thermal CVD method is employed is that the quality of the obtained crystalline silicon film is excellent. As another film forming method, a plasma CVD method may be employed. Note that it is important that impurities are not mixed in the amorphous silicon film 103 during film formation.
[0049]
The film thickness of the amorphous silicon film 103 is preferably 2000 mm or less. This is because it becomes difficult to remove the metal element in the silicon film when the film thickness is 2000 mm or more. Furthermore, the lower limit of the film thickness of the amorphous silicon film 103 depends on the film formation method and depends on how thin the film can be formed. Therefore, the lower limit of the film thickness is generally about 100 mm, and practically about 200 mm.
[0050]
After the amorphous silicon film 107 is formed, 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 a spinner so that the nickel element is held in contact with the surface of the amorphous silicon film 103. (Fig. 1 (A))
[0051]
In view of residual impurities in the subsequent heating step, nickel nitrate is preferably used instead of the nickel acetate salt solution. This is because the nickel acetate salt solution contains carbon, which is feared to carbonize and remain in the film in the subsequent heating step.
[0052]
Next, as shown in FIG. 1B, heat treatment is performed at a temperature of 450 ° C. to 650 ° C., and the amorphous silicon film 103 is crystallized to obtain a crystalline silicon film 105. In this embodiment, heat treatment is performed at 620 ° C. for 4 hours. This crystal growth proceeds in a disorderly manner in a direction substantially perpendicular to the substrate from the surface of the amorphous silicon film 103 toward the base film 102. Such crystal growth is referred to as vertical growth.
[0053]
The lower limit of the heat treatment temperature is preferably 450 ° C. or higher in view of the effect and reproducibility. Moreover, it is preferable that the upper limit shall be below the strain point of the glass substrate to be used. Here, since a Corning 1737 glass substrate having a strain point of 667 ° C. is used, the upper limit is set to 650 ° C. with some allowance.
[0054]
For example, if a quartz substrate is used as the substrate, the heating temperature can be further increased to about 900 ° C. In this case, a crystalline silicon film having higher crystallinity can be obtained. In addition, a crystalline silicon film can be obtained in a shorter time.
[0055]
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. For this reason, it is necessary to adjust the nickel concentration in the nickel acetate solution in the step of FIG. 1A so that the nickel concentration in the obtained crystalline silicon film 105 is in the above range as much as possible. The nickel concentration is defined as the minimum value measured using SIMS (secondary ion analysis method).
[0056]
When the crystalline silicon film 105 is obtained, a silicon oxide film 106 is formed on the surface thereof as shown in FIG. The thickness of the silicon oxide film 106 may be about several tens to 100 inches. 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.
[0057]
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 or a silicon oxynitride film can be used instead of the silicon oxide film 106.
[0058]
Next, an amorphous silicon film 107 containing oxygen as an impurity is formed to a thickness of 600 mm by plasma CVD or low pressure thermal CVD. The amorphous silicon film 107 contains oxygen as an impurity in addition to defects and the like due to the film quality of being amorphous, so that oxygen, SiO _X Therefore, it has a film quality that makes it easy to getter nickel.
[0059]
FIG. 7 shows the result of measuring the concentration distribution of nickel element by SIMS in a state where the amorphous silicon film 107 is formed. As shown in FIG. 7, the concentration of nickel element is 5 × 10 5 at the maximum in the crystalline silicon film 105. ¹⁸ Atom cm ^-3 In the amorphous silicon film 107, the measurement limit (1 × 10 ¹⁷ Atom cm ^-3 )
[0060]
In this embodiment, in order to capture more nickel element in the amorphous silicon film 107, the concentration of oxygen in the amorphous silicon film 107 is considered in consideration of the concentration of nickel element in the crystalline silicon film 105. Concentration is 1x10 ¹⁹ ~ 1x10 ^{twenty one} Atom cm ^-3 To be.
[0061]
After the amorphous silicon film 107 is formed, heat treatment is performed as shown in FIG. As a result, the nickel element in the crystalline silicon film 105 diffuses into the amorphous silicon film 107 through the oxide film 106, so that the concentration of nickel element in the crystalline silicon film 105 can be lowered.
[0062]
Since this step aims at diffusing nickel outside the crystalline silicon film 105, the lower limit of the heating temperature is defined by the temperature at which nickel can diffuse. Moreover, since the above gettering effects can be obtained as the heating temperature is higher, it is preferable to heat at the highest possible temperature. Therefore, the upper limit of the heating temperature is defined below the strain point of the substrate. In an actual process, after satisfying the above conditions, heat treatment may be performed at 550 ° C. to 1050 ° C. Therefore, in this embodiment, in consideration of the heat resistance of the glass substrate, heat treatment is performed at a temperature of 620 ° C. for 2 hours.
[0063]
In this embodiment, since the heating temperature is made as high as possible, the amorphous silicon film 107 is crystallized under the above conditions due to the catalytic action of nickel element diffused from the crystalline silicon film 105. However, the crystalline silicon film 107 is changed to 10 ¹⁹ -10 ^{twenty one} Atom cm ^-3 As described above, since oxygen is contained at a high concentration, many defects are formed in the inside by oxygen elements, and these defects act as gettering sinks. Note that when the amorphous silicon film 107 is heated at a temperature at which it does not crystallize, as described above, unpaired bonds, oxygen, SiO 2 _X These elements have defects due to oxides, and these elements act as gettering sinks.
[0064]
Next, the crystalline silicon film 108 containing nickel element at a high concentration is removed. In this step, wet etching or dry etching can be employed. In this embodiment, the amorphous silicon film 107 is crystallized and transformed into the crystalline silicon film 108. However, in order to selectively remove the crystalline silicon film 108, the crystalline silicon film 105 is preliminarily formed on the crystalline silicon film 105. An oxide film 106 that functions as an etching stopper is formed.
[0065]
Further, 10% of the crystalline silicon film 108 is added. ¹⁹ -10 ^{twenty one} Atom cm ^-3 As described above, since the oxygen is contained in a high concentration, the crystalline silicon film 105 and the crystalline silicon film 108 are different in quality through the silicon oxide film 106.
[0066]
When the crystalline silicon film 108 is removed, an etching solution and etching gas having a high etching selectivity between the silicon film and the oxide film are used. For example, hydrazine (N ₂ H ₆ ) Can be used to remove only the crystalline silicon film 108. As an etching gas, ClF _Three Gas can be used.
[0067]
Next, the silicon oxide film 106 is removed by buffered hydrofluoric acid or hydrofluoric acid to obtain a crystalline silicon film 109 in which the nickel element concentration can be reduced as shown in FIG. Note that as the thickness of the amorphous silicon film 107 for diffusing nickel is increased, the concentration of nickel element in the finally obtained crystalline silicon film 109 can be further reduced. That is, a larger amount of nickel is diffused into the amorphous silicon film 107 or the crystalline silicon film 108 by increasing the volume of the amorphous silicon film 107 than the volume of the crystalline silicon film 109. Can do.
[0068]
In this embodiment, the crystalline silicon film 105 and the amorphous silicon film 107 have substantially the same film thickness. According to the result of measuring the concentration distribution of nickel element in the crystalline silicon film 109 by SIMS, The maximum concentration is 3 × 10 ¹⁸ Atom cm ^-3 Met. That is, after crystallization, the crystal silicon film 105 has a maximum of 5 × 10 5 as shown in FIG. ¹⁸ Atom cm ^-3 Although some nickel is present, the average concentration of nickel element in the crystalline silicon film 105 can be reduced to ½ or less by diffusing the nickel element in the crystalline silicon film 108.
[0069]
Although the amorphous silicon film 107 contains oxygen as an impurity, the same effect can be obtained by containing carbon or nitrogen instead of oxygen. In the amorphous silicon film 107, for example, the concentration of carbon or nitrogen is 1 × 10. ¹⁷ ~ 1x10 ²⁰ Atom cm ^-3 It ’s good. Moreover, you may make it contain not only one type of element but several elements in oxygen, carbon, and nitrogen.
[0070]
In this embodiment, in the step of diffusing nickel shown in FIG. 1D, the amorphous silicon film 107 is heated at a temperature at which it crystallizes. However, the amorphous silicon film 107 is crystallized. Regardless of whether or not the temperature is such that the concentration of nickel element in the crystalline silicon film 105 can be reduced to a desired value.
[0071]
[Example 2]
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.
[0072]
As shown in FIG. 2A, a silicon oxynitride film is formed as a base film 202 to a thickness of 3000 mm on a glass substrate (Corning 1737) 201 by a sputtering method. Next, an amorphous silicon film 203 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 203. This oxide film is for improving the wettability of the solution in a later solution coating step.
[0073]
Then, a silicon oxide film is formed to a thickness of 1500 mm, and a mask 204 having a slit-like opening 205 having a longitudinal direction in a direction perpendicular to the paper surface is formed. The width of the opening 205 is suitably 20 μm or more. The length in the longitudinal direction may be arbitrarily determined.
[0074]
Next, a nickel acetate solution containing nickel at a predetermined concentration is dropped to form a water film 206. Next, spin coating is performed using a spinner so that the nickel element is held in contact with the amorphous silicon film 203 exposed in the opening 205 through an oxide film (not shown).
[0075]
Next, as shown in FIG. 2B, the amorphous silicon film 203 is crystallized by applying heat treatment for 4 hours. In the amorphous silicon film 203, nickel element diffuses into the amorphous silicon film 203 from the region exposed at the opening 205 through an oxide film (not shown). As the nickel element diffuses, in the amorphous silicon film 203, crystal growth proceeds in a direction parallel to the substrate as indicated by an arrow 207, and a crystalline silicon film 208 is formed.
[0076]
This crystal growth proceeds in a columnar or needle shape. In this embodiment, since the region that is the starting point of crystallization is slit-shaped by the opening 205, crystal growth proceeds parallel to the substrate in substantially one direction as indicated by an arrow 207. . This crystal growth parallel to the substrate is referred to herein as lateral growth or lateral growth. This lateral growth can be performed over several tens of μm to 100 μm or more.
[0077]
In the amorphous silicon film 203, in the region exposed by the opening portion 205, the crystal growth is the vertical growth as described above. Therefore, the crystalline silicon film 208 includes a laterally grown region, a vertically grown region, and an amorphous region where crystallization has not progressed.
[0078]
Since catalytic elements such as nickel tend to concentrate at the tip of crystal growth, in the crystalline silicon film 208, at the end of lateral growth, that is, at the interface between the lateral growth region and the amorphous region, and at the vertical growth region. Has a high nickel element concentration. Accordingly, the concentration of nickel element in the lateral growth region is lower than that in the vertical growth region, and further, compared with the vertically grown crystalline silicon film 105 of Example 1, the concentration of nickel element is lower. Yes.
[0079]
When the crystalline silicon film 208 is obtained, after removing the mask 204 made of the silicon oxide film, a silicon oxide film 209 is formed on the surface of the crystalline silicon film 208 by several tens to hundreds of inches as shown in FIG. The film is formed to a thickness of about a degree by a thermal oxidation method. Alternatively, the silicon oxide film 209 may be formed by a UV oxidation method. In addition, the silicon oxide film 209 functions as an etching stopper in a later etching process, and may be any film as long as selectivity can be obtained during etching with respect to the silicon film. For example, an extremely thin silicon nitride film or a silicon oxynitride film can be used instead of the silicon oxide film 209.
[0080]
Next, an amorphous silicon film 210 containing oxygen as an impurity is formed to a thickness of 600 mm by plasma CVD or low pressure thermal CVD.
[0081]
After the amorphous silicon film 210 is formed, heat treatment is performed as shown in FIG. Since this step is intended to diffuse nickel element outside the crystalline silicon film 208, the lower limit of the heating temperature is defined by the temperature at which nickel can diffuse. On the other hand, the upper limit of the heating temperature is defined below the strain point of the substrate, and in the actual process, the heat treatment may be performed at 550 ° C. to 1050 ° C. after satisfying the above conditions. The higher the heating temperature, the higher the gettering as described above. In this example, similarly to Example 1, in consideration of the heat resistance of the glass substrate, heat treatment is performed at a temperature of 620 ° C. for 2 hours. .
[0082]
In this embodiment, since the heat treatment is performed at 620 ° C., as the nickel element diffuses into the amorphous silicon film 210, the amorphous silicon film 210 is crystallized to form the crystalline silicon film 211. Although transformed, the crystalline silicon film 211 has 10 ¹⁹ -10 ^{twenty one} Atom cm ^-3 As described above, oxygen is present at a high concentration, and a large number of defects are formed by this oxygen. Therefore, since these defects act as a Kettering sink, the nickel element diffuses into the amorphous silicon film 210 through the silicon oxide film 209, and the concentration of the nickel element in the crystalline silicon film 208 is lowered. be able to.
[0083]
Next, the crystalline silicon film 211 containing nickel element at a high concentration is removed. In this process, wet etching or dry etching is employed. At this time, an etching gas having a high etching selectivity between the silicon film and the oxide film is used so that the silicon oxide film 209 on the surface of the crystalline silicon film 208 functions as an etching stopper. For example, hydrazine (N ₂ H ₆ ) Can be used to remove only the crystalline silicon film 211. As an etching gas, ClF _Three Gas can also be used.
[0084]
Next, after removing the crystalline silicon film 211, the silicon oxide film 209 is removed with buffer hydrofluoric acid or hydrofluoric acid to obtain a crystalline silicon film in which the nickel element concentration can be lowered. This crystalline silicon film is formed to form island regions 212. This island-shaped region 212 is configured only by the lateral growth region so that it does not include the lateral growth terminal portion where the nickel is present in a high concentration, the vertical growth region, or an amorphous region having different electrical characteristics. To.
[0085]
In the lateral growth region, the concentration of nickel element is relatively lower than that in other regions in crystallization, but in this embodiment, the concentration is further lowered by the gettering step shown in FIG. The nickel concentration of the island-like region 212 made only of the lateral growth region is 10 ¹⁷ Atom cm ^-3 It becomes possible to make order. In addition, a thin film transistor using such an island region 212 has higher mobility than the thin film transistor using the vertically grown crystalline silicon film 109 of the first embodiment.
[0086]
In the step shown in FIG. 2C, oxygen is contained in the amorphous silicon film 210 as an impurity. However, the same effect can be obtained by adding carbon or nitrogen instead of oxygen. Can be obtained. In the amorphous silicon film 210, for example, the concentration of carbon or nitrogen is 1 × 10. ¹⁷ ~ 1x10 ²⁰ Atom cm ^-3 It ’s good. Moreover, you may make it contain not only one type of element but several elements in oxygen, carbon, and nitrogen.
[0087]
In this embodiment, in the step of diffusing nickel shown in FIG. 2D, the amorphous silicon film 210 is heated at a temperature at which it crystallizes. However, the amorphous silicon film 210 is crystallized. Regardless of whether or not the temperature is such that the concentration of the nickel element in the crystalline silicon film 208 can be reduced to a desired value.
[0088]
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. 3 shows a manufacturing process of the thin film transistor described in this embodiment. First, a crystalline silicon film 303 is formed on the glass substrate 301 on which the base film 302 is formed, using the method described in Example 1 or Example 2. (Fig. 3 (A))
[0089]
Next, the obtained crystalline silicon film 303 is patterned to form an active layer of a thin film transistor as indicated by 304. In the second embodiment, the island region 212 corresponds to the active layer 304.
[0090]
Next, a silicon oxide film 305 functioning as a gate insulating film is formed to a thickness of 1000 mm by plasma CVD or low pressure thermal CVD. (Fig. 3 (B))
[0091]
Next, an aluminum film containing scandium is formed to a thickness of 6000 mm and patterned to form a gate electrode indicated by 306. Then, an oxide layer 307 is formed in the electrolytic solution by performing anodization using the gate electrode 306 as an anode. The thickness of the oxide layer 307 is 2000 mm. With the thickness of the oxide layer 307, an offset gate region can be formed in a later step.
[0092]
Further, impurity ions are implanted into the active layer 304. Here, phosphorus ions are implanted as impurity ions. In this step, phosphorus ions are implanted in the regions indicated by 308 and 311. The regions indicated by 308 and 311 are the source / drain regions. An area 309 is an offset gate area. The region 310 is a channel formation region.
[0093]
After the impurity ion implantation is completed, laser light is irradiated to activate the implanted ions and anneal the source / drain regions 308 and 311 damaged during the ion implantation. (Figure 3 (C))
[0094]
Next, a silicon oxide film 312 is formed as an interlayer insulating film, contact holes are further formed, and a source electrode 313 and a drain electrode 314 are formed using aluminum. Finally, heat treatment is performed in a hydrogen atmosphere at 350 ° C. to complete the thin film transistor. (Fig. 3 (D))
Example 4
This embodiment is characterized in that heat treatment is performed again after the crystalline silicon film manufacturing process of Embodiment 1 shown in FIG. That is, the characteristics of the vertically grown crystalline silicon film are improved.
[0095]
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. At this time, 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 is segregated on the surface side of the crystalline silicon film 105 as a result of the nickel in the crystalline silicon film 105 being sucked out of the amorphous silicon film 107. ing.
[0096]
Therefore, when a thin film transistor is manufactured using the crystalline silicon film 109 formed over the glass substrate 101 as shown in FIG. 1D, carriers are conducted on the surface of the crystalline silicon film 109. become. It is not preferable that nickel is present in a high concentration in a region where carriers are conducted.
[0097]
Therefore, in this embodiment, after obtaining the state shown in FIG. 1D, heat treatment is performed to diffuse nickel into the crystalline silicon film 109 again. 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.
[0098]
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. 4A shows a layer 402 (surface side) in which nickel is segregated and nickel is contained at a high concentration, and a layer 401 in which nickel concentration is contained at a lower concentration than the layer side indicated by 402. It is shown. The layers 401 and 402 constitute a crystalline silicon film 109 (see FIG. 1D) formed over the glass substrate 101 with the base film 102 interposed therebetween.
[0099]
In the state shown in FIG. 4A, 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 402 diffuses into the region indicated by 401 where nickel is present at a lower concentration. Thus, this region 402 can be in a state without nickel segregation. Then, a crystalline silicon film 403 in which the nickel concentration on the surface can be reduced can be obtained. (Fig. 4 (C))
[0100]
Example 5
This example is an example in the case where the structure shown in Example 4 is irradiated with laser light instead of heat treatment in the crystallization step. The steps of this example are shown in FIG.
[0101]
First, after the process shown in FIG. 1, a layer made of a crystalline silicon film having a high concentration of nickel element on its surface, indicated by 402, and a layer 401 made of a crystalline silicon film having a low concentration of nickel element, Get. (Fig. 5 (A))
[0102]
Next, nickel element is diffused from the layer 402 to the layer 401 by irradiation with laser light. (Fig. 5 (B))
[0103]
Thereby, a crystalline silicon film 500 having a state where nickel is uniformly diffused in the film is obtained. (Fig. 5 (C))
[0104]
Example 6
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. A manufacturing process of the crystalline silicon film shown in this embodiment will be described with reference to FIG.
[0105]
As shown in FIG. 1A, a silicon oxynitride film is formed as a base film 102 to a thickness of 3000 mm on a Corning 1737 glass substrate 101 (strain point 667 ° 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.
[0106]
Next, as shown in FIG. 1B, heat treatment is performed to crystallize the amorphous silicon film 103 to form a crystalline silicon film 105. Here, heat treatment is performed at 620 ° C. for 4 hours.
[0107]
As shown in FIG. 1C, 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 about several tens to 100 inches. 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.
[0108]
As a method for forming the silicon oxide film 106, a UV oxidation method or a thermal oxidation method may be employed. 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 or a silicon oxynitride film can be used instead of the silicon oxide film 106.
[0109]
Next, Si in an amorphous state is formed by plasma CVD. _X Ge _1-X A film 107 is formed to a thickness of 600 mm. Note that amorphous Si _X Ge _1-X In the film 107, the concentration of oxygen is, for example, 1 × 10. ¹⁹ ~ 1x10 ^{twenty one} Atom cm ^-3 To be. Si _X Ge _1-X The film 107 contains oxygen as an impurity in addition to defects and the like due to the film quality of being amorphous, so that oxygen, SiO, _X Therefore, it has a film quality that makes it easy to getter nickel.
[0110]
Next, as shown in FIG. 1D, by performing heat treatment, Si in an amorphous state is obtained. _X Ge _1-X The nickel element in the crystalline silicon film 105 is diffused into the film 107 through the silicon oxide film 106.
[0111]
The lower limit of this heating temperature is defined by the temperature at which nickel can diffuse, and the upper limit is defined by the strain point of the substrate. For example, the heat treatment may be performed at a temperature of 600 to 1050 ° C. In this embodiment, Corning 1737 having a strain point of 667 ° C. is used as the glass substrate 101, so that the heating temperature is 620 ° C. and the heating time is 4 hours. By the heat treatment, the nickel element in the crystalline silicon film 105 is changed to Si. _X Ge _1-X The concentration of nickel element in the crystalline silicon film 105 can be lowered by diffusing into the film 107.
[0112]
In this process, Si _X Ge _1-X Since heating is performed at a temperature at which the film 107 crystallizes, Si _X Ge _1-X Film 107 is crystalline Si _X Ge _1-X The film 108 is transformed. However, crystalline Si _X Ge _1-X Since the film 108 contains oxygen at a high concentration, a large number of defects are formed inside the film 108 due to the oxygen. Therefore, since these defects function as gettering sinks, the concentration of nickel element in the crystalline silicon film 105 can be reduced.
[0113]
Then, as shown in FIG. _X Ge _1-X The film 108 and the silicon oxide film 109 are sequentially removed by etching. Si _X Ge _1-X To etch the film 108, Si _X Ge _1-X An etching solution or etching gas having a high etching selectivity between the film 108 and the silicon oxide film 106 is used. As a result, Si that sucked out nickel _X Ge _1-X Only the membrane 108 can be selectively removed.
[0114]
Through the above etching process, a crystalline silicon film 109 in which the nickel element content concentration can be lowered as shown in FIG. For example, the crystalline silicon film 105 and Si _X Ge _1-X If the thickness of the film 107 is approximately the same, the nickel concentration in the crystalline silicon film 109 can be reduced to ½ or less on average through the gettering step of this embodiment.
[0115]
Example 7
In this embodiment, when the metal element is diffused outside the crystalline silicon film, heat treatment is performed in a halogen atmosphere. This embodiment will be described with reference to FIG.
[0116]
As shown in FIG. 6A, a base film 602 is formed on a Corning 1737 glass substrate 601 (strain point 667 ° C.). This base film 602 is for preventing impurities and alkali ions from diffusing from the glass substrate 601 into a semiconductor thin film to be formed later.
[0117]
In this embodiment, a silicon oxynitride film is formed as the base film 602. In order to form a silicon oxynitride film as the base film 602, a plasma CVD method may be employed. As source gas, silane, O ₂ Gas, N ₂ O gas is used. Or TEOS gas, N ₂ O gas is used.
[0118]
Next, an amorphous silicon film 603 is formed to a thickness of 600 mm by plasma CVD or low pressure thermal CVD. This amorphous silicon film 603 is crystallized later. The reason why the low pressure thermal CVD method is employed is that the quality of the obtained crystalline silicon film is excellent. As another film forming method, a plasma CVD method may be employed. Note that it is important that impurities are not mixed in the amorphous silicon film 603 during film formation.
[0119]
Then, a nickel acetate solution adjusted to a predetermined nickel concentration is dropped on the amorphous silicon film 603 to form a water film 604. Then, spin coating is performed using a spinner or the like so that the nickel element is held in contact with the surface of the amorphous silicon film 603.
[0120]
Next, as shown in FIG. 6B, heat treatment is performed at a temperature of 450 ° C. to 650 ° C. in a reducing atmosphere to crystallize the amorphous silicon film 603 to obtain a crystalline silicon film 605. In this embodiment, heat treatment is performed at 620 ° C. for 4 hours.
[0121]
As shown in FIG. 6C, after the crystalline silicon film 605 is obtained, a silicon oxide film 606 is formed to a thickness of 10 to 100 mm by a thermal oxidation method, and then by a plasma CVD method or a low pressure thermal CVD method. Then, an amorphous silicon film 607 containing oxygen as an impurity is formed to a thickness of 600 mm. The concentration of oxygen in the amorphous silicon film 607 is 1 × 10. ¹⁹ ~ 1x10 ^{twenty one} Atom cm ^-3 To be. For this reason, since the amorphous silicon film 607 contains oxygen as an impurity in addition to defects, etc., due to the film quality of amorphous as an element for gettering nickel, oxygen, SiO _X There are defects due to oxides, oxygen between silicon bonds, and the like.
[0122]
Next, in order to remove the nickel element intentionally mixed in the initial stage for crystallization from the crystalline silicon film 605, heat treatment is performed in an atmosphere containing a halogen element. In this embodiment, heat treatment is performed in an atmosphere containing HCl in an amount of 0.5% to 10% (volume%), for example, 5%.
[0123]
In addition, since this heat treatment step aims at diffusing nickel to the outside of the crystalline silicon film 105, the lower limit of the heating temperature is defined by a temperature at which nickel can diffuse. Moreover, since the above gettering effects can be obtained as the heating temperature is higher, it is preferable to heat at the highest possible temperature. Therefore, the upper limit of the heating temperature is defined below the strain point of the substrate. In an actual process, after satisfying the above conditions, heat treatment may be performed at 550 ° C. to 1050 ° C. In this embodiment, in consideration of the heat resistance of the glass substrate, heat treatment is performed at a temperature of 620 ° C. for 2 hours.
[0124]
By heating, nickel diffuses from the crystalline silicon film 605 into the amorphous silicon film 607, and nickel is removed from the crystalline silicon film 605. Further, under the above conditions, the amorphous silicon film 607 is crystallized due to the catalytic action of nickel element diffused from the crystalline silicon film 605. However, since oxygen is contained as an impurity, defects are eliminated. A large number of crystalline silicon films 608 are transformed. This defect acts as a gettering sink, and the nickel element can be removed from the crystalline silicon film 605.
[0125]
Further, in this embodiment, since heat treatment is performed in an oxygen atmosphere containing chlorine (halogen), chlorine and nickel react to form a chloride of impurity metal (nickel) that is easily vaporized. The action of removing nickel from the film 605 is further promoted. For this reason, compared with the case where chlorine is not supplied in the heat treatment as in Example 1, the concentration of the nickel element can be reduced to 1/10 or less of the initial maximum. This effect can be similarly obtained even when other metal elements are used.
[0126]
Further, as the thickness of the amorphous silicon film 607 for diffusing nickel is increased, the concentration of nickel element in the crystalline silicon film 605 can be further reduced. That is, a larger amount of nickel can be diffused into the amorphous silicon film 607 by increasing the volume of the amorphous silicon film 607 compared with the volume of the crystalline silicon film 605.
[0127]
In this embodiment, Cl is selected as the halogen element, and HCl is used as the introduction method. As gases other than HCl, HF, HBr, Cl ₂ , F ₂ , Br ₂ One or a plurality of types selected from can be used. In general, a hydride of halogen can be used.
[0128]
These gases are 0.25-5% if the content (volume content) in the atmosphere is HF, 1-15% if HBr, Cl ₂ 0.25 to 5%, F ₂ If 0.125-2.5%, Br ₂ If it is, it is preferable to set it as 0.5 to 10%. If the concentration is within the above range, a significant effect cannot be obtained. Further, if the concentration is higher than the above range, the halogen etching effect becomes remarkable. .
[0129]
Next, the crystalline silicon film 608 containing nickel element at a high concentration is removed. In this step, wet etching or dry etching can be employed. In this embodiment, since the crystalline silicon film 608 is formed on the crystalline silicon film 605, an etching stopper is previously formed on the crystalline silicon film 605 so that the crystalline silicon film 608 can be selectively removed. A functioning silicon oxide film 606 is formed.
[0130]
Therefore, when the crystalline silicon film 608 is removed, an etching solution or etching gas having a high etching selectivity between the silicon film and the oxide film may be used. For example, hydrazine (N ₂ H ₆ And only the crystalline silicon film 608 can be removed with hydrazine. As an etching gas, ClF _Three Gas can be used.
[0131]
Next, the silicon oxide film 606 is removed with buffered hydrofluoric acid or hydrofluoric acid to obtain a crystalline silicon film 609 in which the nickel element content concentration can be lowered as shown in FIG.
[0132]
Note that since the heat treatment shown in FIG. 6D is performed in an oxygen atmosphere containing HCl, a thermal oxide film may be formed on the surface of the crystalline silicon film 608. In this case, Before the etching of the crystalline silicon film 608, the oxide film on the surface of the crystalline silicon film 608 is first removed by wet etching using buffered hydrofluoric acid or the like, or dry etching.
[0133]
Example 8
In Example 7, in order to remove nickel element intentionally mixed for crystallization from the crystalline silicon film, when performing heat treatment in an atmosphere containing a halogen element, the atmosphere is oxygen and HCl is 1 In this embodiment, an atmosphere containing 1 to 10% HCl in nitrogen is used.
[0134]
Other conditions may be the same as in the seventh embodiment. As a result, compared to the case where chlorine is not supplied in the heat treatment as in Example 1, the nickel element concentration can be reduced to 1/10 or less of the initial maximum. This effect can be similarly obtained even when other metal elements are used.
[0135]
In this embodiment, Cl is selected as the halogen element, and HCl is used as the introduction method. As gases other than HCl, HF, HBr, Cl ₂ , F ₂ , Br ₂ One or a plurality of types selected from can be used. In general, a hydride of halogen can also be used.
[0136]
Example 9
In this example, a quartz substrate is used as the substrate in the method for manufacturing a crystalline silicon film shown in Example 7. Since the quartz substrate can withstand a heating temperature of about 1000, in this embodiment, heating is performed at 950 ° C. for 4 hours in the heat treatment for crystallization shown in FIG. 6B. As a result, a crystalline silicon film having better crystallinity than the crystalline silicon film 605 of Example 7 can be obtained.
[0137]
6D, heat treatment is performed at 950 ° C. for 2 hours in an atmosphere containing 5% HCl in oxygen. Other steps are performed under the same conditions as in Example 7.
[0138]
In the measurement by SIMS, the concentration of nickel element in the crystalline silicon film 605 is on the order of 10 before the gettering step is performed. ¹⁸ Atom cm ^-3 However, in this example, gettering was performed by heating at a high temperature in a halogen atmosphere, so the concentration was reduced to the SIMS measurement limit (1 × 10 ¹⁷ Atom cm ^-3 ) Can be:
[0139]
【The invention's effect】
A crystalline silicon film can be formed at a low temperature by the action of the metal element. Therefore, a crystalline silicon film can be formed on the glass substrate.
[0140]
Further, by diffusing the metal element in the silicon film crystallized by the action of the metal element into the silicon film containing impurities, the concentration of the metal element in the crystalline silicon film can be lowered. Further, since a protective film functioning as an etching stopper is formed on the crystalline silicon film, only this silicon film is selectively used regardless of whether the silicon film in which the metal element is diffused is crystallized. Can be removed. For this reason, a crystalline silicon film having a low concentration of the metal element can be obtained.
[0141]
By using the crystalline silicon film obtained by the present invention, a device free from the adverse effects of metal elements, for example, a thin film transistor can be obtained.
[Brief description of the drawings]
FIG. 1 shows a manufacturing process of a crystalline silicon film of an example.
FIG. 2 is a view showing a manufacturing process of a crystalline silicon film of an example.
FIGS. 3A to 3C illustrate a manufacturing process of a thin film transistor of an example. FIGS.
FIG. 4 is a view showing a manufacturing process of a crystalline silicon film of an example.
FIG. 5 is a diagram showing a manufacturing process of a crystalline silicon film of an example.
6A and 6B are diagrams showing a manufacturing process of a crystalline silicon film of an example.
FIG. 7 is a graph showing a nickel concentration distribution of an example.
[Explanation of symbols]
101 ・ ・ ・ ・ ・ ・ ・ ・ ・ Glass substrate
102 ..... Base film (silicon oxide film)
103... Amorphous silicon film
104 ... Water film
105... Crystalline silicon film
106 ..... Silicon oxide film
107... Film for diffusing metal elements
108... Crystalline silicon film

Claims (13)

Forming an amorphous silicon film on the substrate;
Introducing a metal element that promotes crystallization of silicon into the amorphous silicon film;
Crystallizing the amorphous silicon film to form a crystalline silicon film;
Forming a protective film on the crystalline silicon film;
An amorphous silicon film containing oxygen at a concentration of 1 × 10 ¹⁹ to 1 × 10 ²¹ atoms cm ⁻³ is formed on the protective film;
Heating at a temperature below the strain point of the substrate to diffuse the metal element in the silicon film containing oxygen,
A method for producing a semiconductor thin film, wherein the silicon film containing oxygen is removed using the protective film as an etching stopper. Forming an amorphous silicon film on the substrate;
Introducing a metal element that promotes crystallization of silicon into the amorphous silicon film;
Crystallizing the amorphous silicon film to form a crystalline silicon film;
Forming a protective film on the crystalline silicon film;
An amorphous silicon film containing carbon or nitrogen at a concentration of 1 × 10 ¹⁷ to 1 × 10 ²⁰ atoms cm ⁻³ is formed on the protective film;
Heating at a temperature below the strain point of the substrate to diffuse the metal element in the silicon film containing carbon or nitrogen,
A method for producing a semiconductor thin film, wherein the silicon film containing carbon or nitrogen is removed using the protective film as an etching stopper. Forming an amorphous silicon film on the substrate;
Introducing a metal element that promotes crystallization of silicon into the amorphous silicon film;
Crystallizing the amorphous silicon film to form a crystalline silicon film;
Forming a protective film on the crystalline silicon film;
An amorphous silicon film containing oxygen at a concentration of 1 × 10 ¹⁹ to 1 × 10 ²¹ atoms cm ⁻³ is formed on the protective film;
Heating at a temperature below the strain point of the substrate in an atmosphere containing a halogen element to diffuse the metal element in the silicon film containing oxygen,
A method for producing a semiconductor thin film, wherein the silicon film containing oxygen is removed using the protective film as an etching stopper. Forming an amorphous silicon film on the substrate;
Introducing a metal element that promotes crystallization of silicon into the amorphous silicon film;
Crystallizing the amorphous silicon film to form a crystalline silicon film;
Forming a protective film on the crystalline silicon film;
An amorphous silicon film containing carbon or nitrogen at a concentration of 1 × 10 ¹⁷ to 1 × 10 ²⁰ atoms cm ⁻³ is formed on the protective film;
Heating at a temperature below the strain point of the substrate in an atmosphere containing a halogen element to diffuse the metal element into the silicon film containing carbon or nitrogen;
A method for producing a semiconductor thin film, wherein the silicon film containing carbon or nitrogen is removed using the protective film as an etching stopper. Forming an amorphous silicon film on the substrate;
Introducing a metal element that promotes crystallization of silicon into the amorphous silicon film;
Crystallizing the amorphous silicon film to form a crystalline silicon film;
Forming a protective film on the crystalline silicon film;
An amorphous Si _x Ge _1-x film (0 <x <1) containing oxygen at a concentration of 1 × 10 ¹⁹ to 1 × 10 ²¹ atoms cm ⁻³ is formed on the protective film;
Heating at a temperature below the strain point of the substrate to diffuse the metal element in the oxygen-containing Si _x Ge _1-x film;
A method for producing a semiconductor thin film, wherein the Si _x Ge _1-x film containing oxygen is removed using the protective film as an etching stopper. Forming an amorphous silicon film on the substrate;
Introducing a metal element that promotes crystallization of silicon into the amorphous silicon film;
Crystallizing the amorphous silicon film to form a crystalline silicon film;
Forming a protective film on the crystalline silicon film;
An amorphous Si _x Ge _1-x film (0 <x <1) containing carbon or nitrogen at a concentration of 1 × 10 ¹⁷ to 1 × 10 ²⁰ atoms cm ⁻³ is formed on the protective film. ,
Heating at a temperature below the strain point of the substrate to diffuse the metal element into the Si _x Ge _1-x film containing carbon or nitrogen;
A method for producing a semiconductor thin film, wherein the Si _x Ge _1-x film containing carbon or nitrogen is removed using the protective film as an etching stopper. In any one of Claims 1 thru | or 6,
One or more kinds of elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au are used as the metal element. . In any one of Claims 1 thru | or 7,
The method for manufacturing a semiconductor thin film, wherein the protective film is a silicon oxide film, a silicon nitride film, or a silicon oxynitride film. In any one of Claims 1 thru | or 7,
The method of manufacturing a semiconductor thin film, wherein the protective film is formed by oxidizing the surface of the crystalline silicon film. In any one of Claims 1 thru | or 4,
A method for manufacturing a semiconductor thin film, wherein a film thickness of an amorphous silicon film formed on the crystalline silicon film is equal to or greater than a film thickness of the crystalline silicon film. In claim 5 or claim 6,
A method of manufacturing a semiconductor thin film, wherein the amorphous Si _x Ge _1-x film formed on the crystalline silicon film has a thickness equal to or greater than the thickness of the crystalline silicon film. In claim 3 or claim 4,
The atmosphere containing the halogen element is an oxygen atmosphere to which one or plural kinds of gases selected from HCl, HF, HBr, Cl ₂ , F ₂ , and Br ₂ are added. Manufacturing method. In claim 3 or claim 4,
The atmosphere containing the halogen element is a nitrogen atmosphere to which one or plural kinds of gases selected from HCl, HF, HBr, Cl ₂ , F ₂ and Br ₂ are added. Manufacturing method.

Images