JPH09115831A - Crystal growth method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce impurities in polysilicon deposited through solid state growth or laser annealing by selectively etching the crystal defect existing in polysilicon deposited through solid state growth by heating amorphous silicon. SOLUTION: An a-Si 2 is deposited on a glass substrate 1 by CVD followed by deposition of Ni. It is then heat treated to diffuse Ni into the a-Si 2 and to deposit p-Si 2a having crystal grains 4 through solid phase growth of a-Si. Since Ni is diffused into a-Si 2a, the solid phase growth temperature lowers but Ni having high diffusion coefficient is accumulated at the grain boundary 5 in p-Si 2a and reacts on Si to form a silicide. Subsequently, Seco etching is performed using an etching liquid. Etching progresses along crystal defect including the grain boundary 5 and Ni accumulated at the grain boundary 5 is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal growth method and a semiconductor device, and more specifically, to a solid phase growth method from amorphous silicon (a-Si) to polysilicon (p-Si) and a polysilicon film thereof. The present invention relates to a semiconductor device manufactured by using.

[0002]

2. Description of the Related Art With an increase in the amount of information, a liquid crystal display (LCD) having a large capacity and capable of displaying characters or images is desired.
For this reason, a non-linear element is added to the picture element so as to equivalently provide a sharp threshold characteristic to a liquid crystal that does not have a sufficient sharpness of the threshold characteristic, thereby increasing the display capacity while maintaining a high display contrast.

A thin film transistor (TFT) is one of such non-linear elements. At present, the application of amorphous silicon (a-Si) film has become the mainstream, but in recent years, in order to improve the response speed, there has been a demand for reduction of resistance and increase of on-current. There is.
Therefore, the use of a semiconductor film made of p-Si, which has better crystallinity than a-Si, has been studied. There are the following three main methods for forming a polysilicon film.

A method of directly growing a polysilicon film on a heated glass substrate by a CVD method (a method of forming a polysilicon film by a CVD method), a-Si film is melted by laser annealing, and crystallized at the time of cooling. To grow a polysilicon film (laser annealing method for forming a polysilicon film), the a-Si film is heat-treated at about 600 ° C. for about 40 hours to be crystallized to grow a polysilicon film. Method (a method for forming a polysilicon film by solid phase growth), a method for forming a polysilicon film by solid phase growth and a method for forming a polysilicon film by laser annealing described above are used in combination, and There is a method of forming a silicon film.

[0005]

SUMMARY OF THE INVENTION However, CVD
In the method of forming a polysilicon film by the method, the heating temperature is high, which adversely affects the glass substrate. In the method of forming a polysilicon film by the laser annealing method and the method of forming a polysilicon film by solid phase growth, when impurities (light element or heavy metal element) are mixed in the a-Si film,
Since the impurities are accumulated in the crystal grain boundaries and the like during heating of solid phase growth and cooling of laser annealing, the electrical characteristics of the TFT formed in the polysilicon film are not improved. For example, it causes an increase in leak current.

Further, as already known, a-Si
By intentionally doping impurities such as Ni into the film, the solid phase growth temperature can be further lowered and the growth rate can be increased. However, in this case, a larger amount of impurities will be accumulated at the grain boundaries and the like. In particular, when a metal that forms silicide is integrated in a crystal grain boundary or the like, the formation of silicide causes a sharp deterioration in the electrical characteristics of the TFT formed in the polysilicon film.

When the solid phase growth and the laser annealing are used together, the impurities accumulated in the crystal grain boundaries due to the heating of the solid phase growth re-dissolve because the crystal temperature rises near the melting point of the crystal during the laser annealing. During cooling, it is frozen in defects and crystal grain boundaries in the polysilicon film. Therefore, a large amount of impurities are contained also in the polysilicon film. The present invention was created in view of the problems of the above-mentioned conventional example, and a crystal growth method and a polysilicon growth method thereof capable of reducing impurities in a polysilicon film formed by solid phase growth or laser annealing. An object is to provide a semiconductor device formed on a film.

[0008]

The above-mentioned problems are the first invention, which is a step of heating an amorphous silicon film and selectively etching crystal defects existing in a polysilicon film formed by solid phase growth. And a step of forming an amorphous silicon film on a substrate, which is a second invention, and a step of heating the amorphous silicon film to perform solid phase growth of the polysilicon film. And a crystal growth method characterized by including a step of selectively etching crystal defects existing in the polysilicon film, and a step of heating the polysilicon film and performing solid phase growth again, A third aspect of the invention is a step of forming a first amorphous silicon film on a substrate, heating the first amorphous silicon film, Solid phase growth of a silicon film, selective etching of crystal defects present in the first polysilicon film, and formation of a second amorphous silicon film on the first polysilicon film And a step of heating the second amorphous silicon film to perform solid phase growth of the second polysilicon film, which is achieved by a crystal growth method, which is a fourth invention. The polysilicon film or the second amorphous silicon film is heated by laser light irradiation, which is achieved by the crystal growth method according to the second or third invention, which is the fifth invention. After the step of solid-phase growing the silicon film and before the step of selectively etching the crystal defects, the polysilicon film is heated by irradiation with laser light, and the polysilicon film is heated. On the amorphous silicon film, which is achieved by the crystal growth method according to any one of the second to fourth inventions and is a sixth invention, which comprises a step of increasing a crystal grain size of the silicon film. The impurity trapping layer formed below includes a step of moving and trapping impurities by heating in the amorphous silicon film or in a polysilicon film formed by solid-phase growing the amorphous silicon film. A seventh aspect of the present invention, which is achieved by a crystal growth method, characterized in that the impurity trapping layer is removed after the impurities in the amorphous silicon film or the polysilicon film are trapped in the impurity trapping layer. The impurity trapping layer, which is achieved by the crystal growth method according to the sixth aspect of the invention and is the eighth aspect of the invention, has different crystal defects with respect to the polysilicon film. A semiconductor layer having a density, distribution, or size of the above, which is achieved by the crystal growth method according to the sixth or seventh invention, and is the ninth invention, wherein the impurity trapping layer is the poly The impurity trapping layer, which is a tenth invention, is achieved by the crystal growth method according to the sixth or seventh invention, which is a semiconductor layer having different lattice constants with respect to a silicon film. Or a semiconductor layer containing boron, which is achieved by the crystal growth method according to the sixth or seventh invention, and the eleventh invention, heating for moving the impurities, is irradiation with a laser beam. And a crystal growth method according to any one of the sixth to tenth inventions.
The amorphous silicon film before solid phase growth is doped with nickel or copper at a concentration of 1 × 10 ¹⁷ cm ⁻³ or more. It is achieved by the crystal growth method of.

According to the present invention, the amorphous silicon film (a-Si film) is heated to selectively etch crystal defects existing in the polysilicon film (p-Si film) formed by solid phase growth. ing. When impurities (light element or heavy metal element) are mixed in the a-Si film, the impurities are accumulated in crystal defects such as crystal grain boundaries during heating during solid phase growth or cooling during laser annealing. Alternatively, in order to further lower the solid phase growth temperature and improve the growth rate, nickel (Ni) or copper (Cu) having a high concentration (concentration of 1 × 10 ¹⁷ cm ⁻³ or more) is intentionally added in the a-Si film. ), More impurities will be accumulated in crystal defects.

Therefore, by etching the crystal defects by selective etching, impurities are removed from the p-Si film. As a result, the leak current of the transistor or the like formed on the p-Si film can be reduced. Further, by heating or irradiating the polysilicon film again after the crystal defects are etched, the crystal grain size can be further increased to flatten the surface including the concave portion of the etching mark. Alternatively, by coating the a-Si film after etching the crystal defects, it is possible to fill the recesses of the etching marks and flatten the surface.

Further, after the step of solid-phase growing the p-Si film and before the step of selectively etching the crystal defects, the p-Si film is heated by irradiation with laser light to thereby remove the p-Si film. Increase the crystal grain size of the -Si film to increase the p-Si
The crystallinity of the film can be improved. This gives p
It is possible to increase the mobility of carriers such as a transistor formed in the -Si film, reduce the resistance, and increase the on-current.

Further, the impurities in the a-Si film or in the p-Si film formed by solid phase growing the a-Si film are heated in the impurity trapping layer formed on or under the a-Si film. It is moved and captured by. As a result, impurities are removed from the p-Si film. In particular, by removing the impurity trap layer after trapping the impurity in the impurity trap layer, it is possible to prevent the impurity from returning to the p-Si film again even when heat treatment is performed later.

As the impurity trapping layer, a semiconductor layer having different density, distribution or size of crystal defects with respect to the p-Si film, a semiconductor layer having different lattice constants with respect to the p-Si film, or phosphorus or boron is used. A semiconductor layer containing can be used. All of these impurity trap layers are pS
Strain occurs in the interface with the i film or in the impurity trapping layer itself,
It is considered that impurities are captured by this strain.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. (1) First Embodiment of the Present Invention FIG. 1 is a flowchart showing a process sequence of a crystal growth method according to the first embodiment. 2 (a) to (d),
3A and 3B are cross-sectional views showing the crystal growth method according to the first embodiment, and show the case of the flowchart of FIG.

First, an a-Si film 2 having a thickness of about 50 nm is formed on a glass substrate 1 shown in FIG. 2A by a CVD method, and then an aqueous solution of nickel acetate is applied and dried,
A nickel film (Ni film) 3 (not shown) is formed (FIG. 2).
(B)). Then, a heat treatment is performed at a temperature of 550 ° C. for 4 hours to diffuse Ni into the a-Si film 2 and to perform a-
P-Si film 2a having crystal grains 4 obtained by solid phase growth of Si
To form At this time, since Ni is diffused in the a-Si film 2a, the solid phase growth temperature is lowered, but Ni having a large diffusion coefficient is accumulated in the crystal grain boundary 5 in the p-Si film 2a, and Reacts with the formation of silicide. FIG. 2C shows a state after the Ni film 3 is removed. Further, FIG. 2D shows a state after the crystal grain boundaries are removed by etching.

Ni-doped p-Si T grown on solid phase
The EM photograph is shown in FIG. Silicide is in the black part in the center
You can see that it is formed. In addition, FIG.
The secondary ions of Ni are counted by S, and the secondary ions of Ni in the depth direction are counted.
It is the figure converted into concentration distribution. Represented by a linear scale on the horizontal axis
Depth (nm) and the vertical axis represents logarithmic scale p-
Nickel concentration in the Si film 2a (cm^-3). Average
About 1 × 10¹⁹cm ^-3At a concentration of Ni. What
The beam diameter of SIMS is several μm, and Ni is the beam.
Since it is accumulated in crystal defects within the diameter, the measured Ni concentration
The degree is considered to be the average of the amount of Ni present in the beam diameter.
available. Further, FIG. 6 (a) shows a depression on the surface of the p-Si film 2a.
It is a photograph of the crystal surface showing the result of observing the convexity, and the surface is
It is flat.

Next, Secco etching is performed with an etching solution composed of a mixed solution of potassium dichromate, hydrofluoric acid and water.
As a result, as shown in FIG. 2D, etching proceeds along the crystal defects including the crystal grain boundaries 5. At the same time, Ni accumulated in the grain boundaries 5 is also removed. FIG. 6B shows p
-It is a photograph of the crystal surface showing the result of observing the surface irregularities after etching the Si film 2a, and the black portion is removed by etching and is recessed. Further, FIG. 4B is a diagram showing the concentration distribution of Ni in the depth direction. The horizontal axis and the vertical axis are the same as those in FIG. Ni in the p-Si film 2a was significantly reduced, and the average concentration was about 1 × 10 ¹⁸ cm ⁻³ or less.

Then, as shown in FIG. 3A, p-S
A new a-Si film 6 having a thickness of about 200Å is formed on the i film 2a by C
It is formed by the VD method. Next, laser light is irradiated to a-
The p-Si film is solid-phase grown from the Si film 6 and the surface is flattened. As a result, as shown in FIG. 3B, p as an element forming layer is formed on the glass substrate 1 as a whole.
-Si film 7 is formed.

FIG. 4C is a diagram showing the Ni concentration distribution in the depth direction. The horizontal axis and the vertical axis are the same as those in FIG. The Ni in the p-Si film 7 in FIG. 3B is maintained at a concentration of about 1 × 10 ¹⁸ cm ⁻³ or less on average. FIG.
(C) is a photograph of the crystal surface showing the results of observing the irregularities on the surface of the p-Si film 7, and it can be seen that the crystal surface is flat. Furthermore, as a result of Raman scattering measurement, it was confirmed that the quality of the crystal was good.

As described above, according to the first embodiment,
The solid-phase growth temperature and increase the growth rate.
Therefore, a high concentration (concentration: 1 × 10
¹⁷cm ^-3When Ni is doped (above), a larger amount
Impurities will be accumulated in crystal defects such as grain boundaries 4.
However, the crystal defects are etched by selective etching.
As a result, Ni is removed from the p-Si film 2a.

As a result, it is possible to reduce the leakage current of the transistor or the like formed on the p-Si film 7. Further, after etching the crystal defects, the a-Si film 6 is covered,
By performing the laser annealing, the concave portion of the etching mark can be filled and the surface can be planarized. This gives p
-Easily forming elements such as transistors on the Si film 7.

The solid phase growth method shown by the flow chart in FIG. 1 is also possible. That is, without forming the a-Si film 6 after the selective etching of crystal defects, the p-Si film 2a is formed.
May be directly heated by laser annealing or the like. As a result, the crystal grain size of the p-Si film 2a can be further increased and the surface can be flattened. (2) Second Embodiment of the Invention FIG. 7 is a flowchart showing a process sequence of a crystal growth method according to a second embodiment. 8 (a) to 8 (d),
9A and 9B are cross-sectional views showing the crystal growth method according to the second embodiment, and show the case of the flowchart of FIG. The difference from the first embodiment is that after the step of solid-phase growing the p-Si film and before the step of selectively etching crystal defects, the p-Si film is irradiated with p-
That is, the step of heating the Si film to increase the crystal grain size of the p-Si film is included.

First, an a-Si film 12 having a film thickness of about 50 nm is formed on the glass substrate 11 shown in FIG. 8A by the CVD method, and then an aqueous solution of nickel acetate is applied and dried, which is not shown. A nickel film (Ni film) 13 is formed (FIG. 8B). Then, a heat treatment is performed at a temperature of 550 ° C. for 4 hours to diffuse Ni into the a-Si film 12 and
When solid-phase grown, p-Si film 1 having crystal grains 14a
2a is formed. At this time, N in the a-Si film 12a
Since i is diffused, Ni accumulates at the crystal grain boundary 15a in the p-Si film 12a and further reacts with Si to form a silicide. FIG. 8C shows a state after the Ni film 13 is removed.

FIG. 1 is a TEM photograph of the Ni state shown in FIG. 8 (c).
It is shown in FIG. The left part of the figure shows Ni silicide. Further, FIG. 10A is a diagram showing the concentration distribution of Ni in the depth direction, which is obtained in the same manner as FIGS. 4A to 4C. The horizontal axis represents the depth (nm) expressed in a linear scale, and the vertical axis represents the nickel concentration (c in the p-Si film 12a expressed in a logarithmic scale).
m ^-3 ) is shown. On average, Ni is contained at a concentration of about 1 × 10 ¹⁹ cm ⁻³ . Further, FIG. 12A shows the p-Si film 12
3a is a photograph of a crystal surface showing the result of observing the unevenness of the surface. Although a protrusion was observed in the photograph, the height of the protrusion is about several nm.

Next, as shown in FIG. 8D, p-Si
Laser annealing is applied to the film 12a. As a result, the crystal grains 14a undergo further solid phase growth, and the crystal grains 14b having a large grain size
Becomes Next, as shown in FIG. 9A, Secco etching is performed to selectively etch crystal defects including the crystal grain boundaries 15b. At this time, at the same time, Ni accumulated in the crystal grain boundary 15b is also removed. Further, FIG. 10B is a diagram showing the concentration distribution of Ni in the depth direction. The horizontal axis and the vertical axis are the same as those in FIG. Ni in the p-Si film 12a is decreasing from the side closer to the surface, and is approximately 1 × 10 ¹⁸ to.
It is distributed in 1 × 10 ¹⁹ cm ⁻³ .

Next, as shown in FIG. 9B, laser light is irradiated to further solid-phase grow the p-Si film 12b, and the surface is flattened. Thereby, the glass substrate 1
1 as a whole, a p-Si film 12c as an element forming layer
Is formed. FIG. 10C is a diagram showing the concentration distribution of Ni in the depth direction. The horizontal axis and the vertical axis are the same as those in FIG. Ni in the p-Si film 12c is approximately 1 × 10 ¹⁸ to 1
It is maintained at × 10 ¹⁹ cm ^-3 . FIG. 12B shows p-
It is a photograph of the crystal surface showing the result of observing the irregularities on the surface of the Si film 12c, and it can be seen that the protrusions are flat. Furthermore, as a result of Raman scattering measurement, it was confirmed that the quality of the crystal was good.

When an element such as a transistor is formed on the p-Si film 12c, the protrusion may be removed by polishing (CMD). Since the protrusion is small, it does not hinder the element formation even if it is not removed. Conceivable. As described above, according to the second embodiment, in order to lower the solid phase growth temperature and improve the growth rate, the high concentration (concentration 1 × 10 ¹⁷ cm 2) is deliberately included in the a-Si film 12. ^-3 or more) Ni is doped, a larger amount of impurities are accumulated in the crystal defects 15b such as crystal grain boundaries. However, by etching the crystal defects 15b by selective etching, the p-Si film 12b Ni is removed from the inside. Thereby, p-Si
Leakage current of a transistor or the like formed in the film 12c can be reduced.

Further, after the step of solid-phase growing the p-Si film 12b and before the step of selectively etching the crystal defects, the p-Si film 12a is heated by irradiation of laser light, and the p-Si film 12a is heated. Since the step of increasing the crystal grain size of the -Si film 12a is included, the crystallinity of the p-Si film 12b is further improved. As a result, the mobility of carriers such as a transistor formed in the p-Si film 12c can be increased to reduce the resistance and increase the on-current.

Further, since the crystal defects are etched and laser-annealed for further solid phase growth, the crystal grain size can be further increased and the surface can be flattened. This facilitates formation of elements such as transistors on the p-Si film 17. Note that the solid phase growth method shown by in the flowchart of FIG. 7 is also possible. That is, an a-Si film may be formed after selective etching of crystal defects and heated by laser annealing or the like. Thereby, the surface can be further flattened.

(3) Third and Fourth Embodiments of the Present Invention FIGS. 13A to 13D are sectional views showing a crystal growth method according to the third embodiment. The difference from the first and second embodiments is that an impurity trapping layer is provided. First, as shown in FIG. 13A, a silicon oxide film 22 having a film thickness of about 200 nm is formed on a glass substrate 21. Further, after forming an a-Si film having a film thickness of about 20 nm, for example, a-Si is formed in two steps of energy of 220 mJ and 330 mJ.
The Si film is irradiated with laser light and annealed to obtain a crystal grain size of about 1
A 0 nm p-Si film (impurity trapping layer) 23 is formed.
The temperature of the laser light is about 1410 ° C., but the required laser light energy differs depending on the laser irradiation device.

Then, as shown in FIG. 13B, p-
An a-Si film 24 having a thickness of about 50 nm and Ni are formed on the Si film 23.
After forming the film 25 in order, as shown in FIG. 13C, heat treatment is performed at a temperature of 550 ° C. for 4 hours to form a-Si.
Ni is diffused in the film 24 and the p-Si film 24a is grown in solid phase. Next, as shown in FIG.
After removing the i film 25, laser annealing is applied to further grow the solid phase and increase the crystal grain size.
As a result, the p-Si film 24b as an element forming layer is created. At this time, Ni moves due to heating and p-S
It is captured by the i film 23.

FIG. 14A shows the result of investigation of the concentration distribution of Ni in the p-Si film (impurity trapping layer) 23 and the p-Si film 24b. The horizontal axis represents the depth (nm) represented on a linear scale, and the vertical axis represents the Ni concentration (cm ⁻³ ) represented on a logarithmic scale. For comparison, the same experiment was performed on a sample having no p-Si film (impurity trapping layer) 23, and the concentration distribution of Ni in the p-Si film 24b was investigated. The investigation result is shown in FIG.

According to the investigation result, a large amount of Ni is contained in p-Si.
It is trapped in the film (impurity trapping layer) 23, and the Ni concentration in the p-Si film 24b is reduced accordingly. The effect is remarkable as compared with the comparative example. Furthermore, as a result of Raman scattering measurement, it was confirmed that the quality of the crystal was good. As described above, according to the third mode, the p-Si film 24 (impurity trapping layer) 23 formed under the a-Si film 24 is formed by solid phase growth of the a-Si film 24. N in the Si film 24a
i is moved by heating and captured. This allows
Ni is removed from the p-Si film 24a. This allows
It is possible to reduce the leak current of the transistor or the like formed on the p-Si film 24b.

After the solid phase growth of the p-Si film 24a, the p-Si film 24a is heated by the irradiation of laser light, so that the crystal grain size of the p-Si film 24b is increased.
The crystallinity of the p-Si film 24b can be improved.
As a result, the mobility of carriers such as a transistor formed on the p-Si film 24b can be increased, the resistance can be reduced, and the on-current can be increased.

In the above, p is used as the impurity trapping layer.
Although the p-Si film 23 having different density, distribution or size of crystal defects is used for the -Si film 24a or 24b, as a fourth mode, as shown in FIG.
It is also possible to use a semiconductor layer having a different lattice constant for the i film 24a or 24b, for example, the SiGe film 26.

Also in this case, the Ni concentration distribution in the p-Si film 24b is as shown in FIG. 16 (a), as in the third embodiment. That is, Ni is captured in the SiGe film 26,
The Ni concentration in the p-Si film 24b can be reduced. Note that FIG. 16B shows an experimental result for a sample that does not have the SiGe film 26. (4) Fifth Embodiment of the Present Invention FIGS. 17A to 17D are sectional views showing a crystal growth method according to the fifth embodiment. The difference from the third and fourth embodiments is that a p-Si film 29 containing phosphorus is formed as an impurity trapping layer on the p-Si film 28 containing Ni that has been solid-phase grown. .

First, as shown in FIG. 17A, a silicon oxide film 22 is formed on a glass substrate 21. continue,
Similarly to the above, the a-Si film is doped with Ni (impurity) and solid-phase grown to form the p-Si film 28. The Ni concentration distribution in the p-Si film 28 at this time is shown in FIG.
Shown in Then, as shown in FIG. 17B, p-Si
P containing phosphorus at a concentration of about 1 × 10 ²⁰ cm on the membrane 28
The -Si film (impurity trapping layer) 29 is formed by the CVD method.

Next, as shown in FIG. 17C, laser annealing is applied to heat the p-Si film 28.
Ni in the p-Si film 2 is moved into the p-Si film 29.
And the crystal grain size of the p-Si film 28a is grown large. Next, as shown in FIG. 17D, the p-Si film 29 is removed, and the formation of the element formation layer is completed. The Ni concentration distribution in the p-Si film 28a at this time is shown in FIG. That is, Ni is reduced from the surface of the p-Si film 28a. Furthermore, as a result of Raman scattering measurement, it was confirmed that the quality of the crystal was good.

According to the fifth mode, the p-Si film 28 is formed.
After the p-Si film (impurity trapping layer) 29 is formed thereon, Ni in the p-Si film 28a is moved into the p-Si film 29 by heating and trapped in the p-Si film 29. −
Ni in the Si film 28a can be reduced. As a result, when a transistor or the like is formed on the p-Si film 28a, the leak current of the transistor can be reduced and the performance can be improved.

Further, by removing Ni from the p-Si film 29 and then removing the p-Si film 29, it is possible to prevent Ni from returning again to the p-Si film 28a even when a heat treatment is applied later. Can be prevented. Further, after the solid phase growth, laser annealing is further performed to further perform the solid phase growth to increase the crystal grain size. Therefore, the mobility of carriers in the p-Si film 28a is increased to increase the p-Si film. The performance of the transistor formed in 28a can be improved.

As the impurity trapping layer 29, very small crystalline p-Si or a semiconductor having a different lattice constant, for example, SiGe may be used. (5) Sixth Embodiment of the Present Invention FIGS. 19A to 19E are sectional views showing a crystal growth method according to the sixth embodiment. The difference from the fifth embodiment is that a plurality of p-Ss that become element formation regions are formed by partially etching the solid-phase-grown p-Si film 30 containing Ni.
After air isolation to the i film 30a, p-S containing phosphorus as an impurity trapping layer between the p-Si films 30a.
That is, the i film 32 is embedded and Ni is captured therein.

First, as shown in FIG. 19A, a silicon oxide film 22 is formed on a glass substrate 21. continue,
Similarly to the above, the a-Si film is doped with Ni (impurity) and solid-phase grown to form the p-Si film 30. The Ni concentration distribution in the p-Si film 30 at this time is shown in FIG.
Shown in Then, as shown in FIG. 19B, p-Si
After forming a resist mask 31 in a region on the film 30 where an element formation layer is to be formed, the p-Si film 30 is selectively etched and removed by the resist mask 31. As a result, the element forming layer 30a remains on the silicon oxide film 22.

Next, as shown in FIG. 19C, the resist mask 31 is left as it is, and the concentration is about 1 × 10 ²⁰ from the top.
cm-thick phosphorus-containing p-Si film (impurity trapping layer) 3
2 is formed by the CVD method. A p-Si film 32 is embedded between the element forming layers 30a. Next, the resist mask 31 is removed, and the element formation layer 3 is lifted off.
The p-Si film 32 buried between 0a is left.

Next, as shown in FIG. 19D, laser light is irradiated from the surface of the element forming layer 30a and the p-Si film 32 to heat the Ni-p-Si film 30a. While being moved into the Si film 32 and captured by the p-Si film 32, the crystal grain size of the p-Si film 30b is grown large. Next, as shown in FIG. 19E, when the p-Si film 32 is removed by utilizing the difference in etching rate,
The formation of the element forming layer 30b is completed. P-S at this time
The Ni concentration distribution in the i film 30b is shown in FIG. That is, the Ni concentration in the p-Si film 30b decreases, and
It became ¹⁷ cm ^-3 . Furthermore, as a result of Raman scattering measurement, it was confirmed that the quality of the crystal was good.

According to the sixth embodiment, after air isolation is performed on the plurality of p-Si films 30a which will be the element forming regions, p-Si containing phosphorus as an impurity trapping layer is provided between the p-Si films 30a. Since the film 32 is embedded and Ni is captured therein, Ni in the p-Si film 30b can be reduced. Thus, when a transistor or the like is formed on the p-Si film 30b, the leak current of the transistor can be reduced and the performance can be improved.

Further, by removing Ni from the p-Si film 32 and then removing the p-Si film 32, Ni is prevented from returning to the p-Si film 30b again even when a heat treatment is applied later. Can be prevented. Further, after the solid phase growth, laser annealing is further performed to further perform the solid phase growth to increase the crystal grain size. Therefore, the mobility of carriers in the p-Si film 30b is increased to increase the p-Si film. The performance of the transistor formed in 30b can be improved.

As the impurity trapping layer 32, very small crystalline p-Si or a semiconductor having a different lattice constant, for example, SiGe may be used. (6) Seventh Embodiment of the Present Invention FIGS. 21A to 21D are sectional views showing a crystal growth method according to the seventh embodiment. The feature of the seventh mode is that the impurity trapping layers are formed above and below the p-Si film 34 to be the element forming layer. In the seventh embodiment, the SiGe film 33 is formed below the p-Si film 34, and the p-Si film 35 containing phosphorus is formed on the p-Si film 34.

First, as shown in FIG. 21A, a silicon oxide film 22 is formed on a glass substrate 21. continue,
After a SiGe film (impurity trapping layer) 33 having a film thickness of about 20 nm and an a-Si film having a film thickness of about 50 nm are formed in order, the a-Si film is doped with Ni (impurity) in the same manner as described above to form a solid phase. Then, the p-Si film 34 is grown. The Ni concentration distribution in the p-Si film 34 at this time is shown in FIG.

Then, as shown in FIG. 21B, p-
A p-Si film (impurity trapping layer) 35 containing phosphorus at a concentration of about 1 × 10 ²⁰ cm is formed on the Si film 34 by the CVD method. Next, as shown in FIG. 21C, laser annealing is applied and heating is performed to move Ni in the p-Si film 34 into the SiGe film 33 and the p-Si film 35, and thereby the SiGe film 33. The crystal grain size of the p-Si film 34a is increased while being captured inside and in the p-Si film 35.

Then, as shown in FIG. 21D, p-
When the Si film 35 is removed, the formation of the element forming layer 34a is completed. The Ni concentration distribution in the p-Si film 34a at this time is shown in FIG. That is, Ni of the p-Si film 34a
The concentration was reduced to 1 × 10 ¹⁷ cm ⁻³ or less. Furthermore,
As a result of Raman scattering measurement, it was confirmed that the crystal quality was also good.

According to the seventh embodiment, since the impurity trapping layers 33 and 35 are formed above and below the p-Si film 34 serving as the element forming layer, the Ni content in the p-Si film 34a should be reduced. You can Thus, when a transistor or the like is formed on the p-Si film 34a, the leak current of the transistor can be reduced and the performance can be improved. In addition, after capturing Ni in the p-Si film 35, the p-Si film 3 is removed.
By removing 3, even if heat treatment is added later,
The amount of Ni returning to the p-Si film 34a again can be reduced.

Further, after the solid phase growth, laser annealing is further applied to carry out further solid phase growth to increase the crystal grain size, so that the mobility of carriers in the p-Si film 34a is increased and p is increased. The performance of the transistor formed on the -Si film 34a can be improved. Further, as the impurity trapping layers 33 and 35, very small crystalline p-Si or a semiconductor having a different lattice constant, for example, SiGe may be used.

In the above embodiment, Ni is intentionally introduced into the a-Si film, but it is also effective when impurities (light elements or metal elements) are present in the a-Si film from the beginning. . Moreover, the method of removing impurities in the crystal growth method of the present invention is applied to a solid-phase grown p-Si film.
It can also be applied to a p-Si film grown by the VD method.

[0054]

As described above, according to the present invention, crystals existing in a polysilicon film (p-Si film) formed by heating an amorphous silicon film (a-Si film) and solid-phase growing it. Defects are selectively etched. When impurities (light element or heavy metal element) are present in the a-Si film, the impurities are accumulated in the crystal grain boundaries or the like during heating during solid phase growth or during cooling during laser annealing. Therefore, by etching the crystal defects by the selective etching, the impurities are removed from the p-Si film, whereby the leak current of the transistor or the like formed in the p-Si film can be reduced.

After etching the crystal defects, p-
By heating the Si film, it is possible to further increase the crystal grain size and flatten the concave portion of the etching mark. Alternatively, by coating the a-Si film after etching the crystal defects, the recesses of the etching marks can be filled and the surface can be flattened. This facilitates the formation of the element on the element forming layer.

Further, after the step of solid-phase growing the p-Si film, the crystal grain size of the p-Si film is increased by heating the p-Si film by irradiating the laser beam, and p-S
The crystallinity of the i film can be improved. This allows
It is possible to increase the mobility of carriers such as a transistor formed in the p-Si film to reduce the resistance, increase the on-current, and improve the response speed.

Further, the impurities in the a-Si film or in the p-Si film formed by solid-phase growing the a-Si film are heated in the impurity trapping layer formed above or below the a-Si film. The impurities are removed from the p-Si film because they are moved and captured by. As a result, the leak current of the transistor or the like formed on the p-Si film can be reduced. In particular, by removing the impurity trapping layer after trapping the impurities in the impurity trapping layer, p
It is possible to prevent impurities from returning to the -Si film again.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a process sequence of a crystal growth method according to a first embodiment of the present invention.

FIG. 2 is a sectional view (No. 1) showing the crystal growth method according to the first embodiment of the present invention.

FIG. 3 is a sectional view (No. 2) showing the crystal growth method according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a Ni concentration distribution in an element formation layer in the crystal growth method according to the first embodiment of the present invention.

FIG. 5 is a crystal thin film photograph showing a surface state of the p-Si film in the crystal growth method according to the first embodiment of the present invention.

FIG. 6 is a crystal thin film photograph showing a surface state of a p-Si film in the crystal growth method according to the first embodiment of the present invention.

FIG. 7 is a flowchart showing a process sequence of a crystal growth method according to a second embodiment of the present invention.

FIG. 8 is a sectional view (No. 1) showing the crystal growth method according to the second embodiment of the present invention.

FIG. 9 is a cross-sectional view (No. 2) showing the crystal growth method according to the second embodiment of the present invention.

FIG. 10 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a second embodiment of the present invention.

FIG. 11 is a crystal thin film photograph showing a surface state of a p-Si film in the crystal growth method according to the second embodiment of the present invention.

FIG. 12 is a crystal thin film photograph showing a surface state of a p-Si film in the crystal growth method according to the second embodiment of the present invention.

FIG. 13 is a cross-sectional view showing the crystal growth method according to the third embodiment of the present invention.

FIG. 14 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a third embodiment of the present invention.

FIG. 15 is a sectional view showing a crystal growth method according to a fourth embodiment of the present invention.

FIG. 16 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a fourth embodiment of the present invention.

FIG. 17 is a cross-sectional view showing the crystal growth method according to the fifth embodiment of the present invention.

FIG. 18 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a fifth embodiment of the present invention.

FIG. 19 is a sectional view showing a crystal growth method according to a sixth embodiment of the present invention.

FIG. 20 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a sixth embodiment of the present invention.

FIG. 21 is a sectional view showing a crystal growth method according to a seventh embodiment of the present invention.

FIG. 22 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a seventh embodiment of the present invention.

[Explanation of symbols]

1,11,21 glass substrate, 2,6,12,24 a-Si film, 2a, 12a, 12b, 24a, 24b, 28,30,
30a, 34 p-Si film, 3, 13, 25 Ni film, 4, 14a, 14b crystal grain, 5, 15a, 15b crystal grain boundary, 7, 12c, 28a, 30b, 34a p-Si film (element forming layer ), 22 silicon oxide film, 23 p-Si film (impurity trapping layer), 26,33 SiGe film (impurity trapping layer), 29,32,35 p-Si film containing phosphorus (impurity trapping layer), 31 resist mask.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01L 21/336

Claims (12)

[Claims] 1. A crystal growth method comprising a step of heating an amorphous silicon film to selectively etch crystal defects existing in a polysilicon film formed by solid phase growth. 2. A step of forming an amorphous silicon film on a substrate, a step of heating the amorphous silicon film to cause solid phase growth of the polysilicon film, and selectively selecting crystal defects existing in the polysilicon film. A crystal growth method comprising: an etching step; and a step of heating the polysilicon film to perform solid phase growth. 3. A step of forming a first amorphous silicon film on a substrate; a step of heating the first amorphous silicon film to solid-phase grow the first polysilicon film; A step of selectively etching crystal defects existing in the silicon film; a step of forming a second amorphous silicon film on the first polysilicon film; and a step of heating the second amorphous silicon film, And a step of solid-phase growing the second polysilicon film. 4. The crystal growth method according to claim 2, wherein heating of the polysilicon film or the second amorphous silicon film is performed by irradiation of laser light. 5. The polysilicon film is heated by irradiation with laser light after the step of solid-phase growing the polysilicon film and before the step of selectively etching the crystal defects. The crystal growth method according to claim 2, further comprising a step of increasing a crystal grain size of the film. 6. The impurities in the amorphous silicon film or in a polysilicon film formed by solid phase growing the amorphous silicon film are moved by heating to an impurity trapping layer formed on or under the amorphous silicon film. A method for growing a crystal, which comprises a step of capturing the crystal. 7. The crystal growth method according to claim 6, wherein after the impurities in the amorphous silicon film or the polysilicon film are captured by the impurity trapping layer, the impurity trapping layer is removed. . 8. The crystal according to claim 6, wherein the impurity trapping layer is a semiconductor layer having different density, distribution or size of crystal defects with respect to the polysilicon film. How to grow. 9. The crystal growth method according to claim 6, wherein the impurity trapping layer is a semiconductor layer having a different lattice constant with respect to the polysilicon film. 10. The crystal growth method according to claim 6, wherein the impurity trapping layer is a semiconductor layer containing either phosphorus or boron. 11. The crystal growth method according to claim 6, wherein the heating for moving the impurities is performed by irradiation with a laser beam. 12. The amorphous silicon film before the solid phase growth is doped with nickel or copper at a concentration of 1 × 10 ¹⁷ cm ⁻³ or more, according to any one of claims 1 to 11. Crystal growth method.